The rapid development of lithium-ion batteries(LIBs)is faced with challenge of its safety bottleneck,calling for design and chemistry innovations.Among the proposed strategies,the development of solid-state batteries(...The rapid development of lithium-ion batteries(LIBs)is faced with challenge of its safety bottleneck,calling for design and chemistry innovations.Among the proposed strategies,the development of solid-state batteries(SSBs)seems the most promising solution,but to date no practical SSB has been in large-scale application.Practical safety performance of SSBs is also challenged.In this article,a brief review on LIB safety issue is made and the safety short boards of LIBs are emphasized.A systematic safety design in quasi-SSB chemistry is proposed to conquer the intrinsic safety weak points of LIBs and the effects are accessed based on existing studies.It is believed that a systematic and targeted solution in SSB chemistry design can effectively improve the battery safety,promoting larger-scale application of LIBs.展开更多
Thermal runaway(TR)is a critical issue hindering the large-scale application of lithium-ion batteries(LIBs).Understanding the thermal safety behavior of LIBs at the cell and module level under different state of charg...Thermal runaway(TR)is a critical issue hindering the large-scale application of lithium-ion batteries(LIBs).Understanding the thermal safety behavior of LIBs at the cell and module level under different state of charges(SOCs)has significant implications for reinforcing the thermal safety design of the lithium-ion battery module.This study first investigates the thermal safety boundary(TSB)correspondence at the cells and modules level under the guidance of a newly proposed concept,safe electric quantity boundary(SEQB).A reasonable thermal runaway propagation(TRP)judgment indicator,peak heat transfer power(PHTP),is proposed to predict whether TRP occurs.Moreover,a validated 3D model is used to quantitatively clarify the TSB at different SOCs from the perspective of PHTP,TR trigger temperature,SOC,and the full cycle life.Besides,three different TRP transfer modes are discovered.The interconversion relationship of three different TRP modes is investigated from the perspective of PHTP.This paper explores the TSB of LIBs under different SOCs at both cell and module levels for the first time,which has great significance in guiding the thermal safety design of battery systems.展开更多
The integration of battery energy storage systems(BESS)throughout our energy chain poses concerns regarding safety,especially since batteries have high energy density and numerous BESS failure events have occurred.Wid...The integration of battery energy storage systems(BESS)throughout our energy chain poses concerns regarding safety,especially since batteries have high energy density and numerous BESS failure events have occurred.Wider spread adoption will only increase the prevalence of these failure events unless there is a step change in the management and design of BESS.To understand the causes of failure,the main challenges of BESS safety are summarised.BESS consequences and failure events are discussed,including specific focus on the chain of events causing thermal runaway,and a case study of a BESS explosion in Surprise Arizona is analysed.Based on the technology and past events,a paradigm shift is required to improve BESS safety.In this review,a holistic approach is proposed.This combines currently adopted approaches including battery cell testing,lumped cell mathematical modelling,and calorimetry,alongside additional measures taken to ensure BESS safety including the requirement for computational fluid dynamics and kinetic modelling,assessment of installation level testing of the full BESS system and not simply a single cell battery test,hazard and layers of protection analysis,gas chromatography,and composition testing.The holistic approach proposed in this study aims to address challenges of BESS safety and form the basis of a paradigm shift in the safety management and design of these systems.展开更多
Lithium iron phosphate batteries have been increasingly utilized in recent years because their higher safety performance can improve the increasing trend of recurring thermal runaway accidents.However,the safety perfo...Lithium iron phosphate batteries have been increasingly utilized in recent years because their higher safety performance can improve the increasing trend of recurring thermal runaway accidents.However,the safety performance and mechanism of high-capacity lithium iron phosphate batteries under internal short-circuit challenges remain to be explored.This work analyzes the thermal runaway evolution of high-capacity LiFePO_(4) batteries under different internal heat transfer modes,which are controlled by different penetration modes.Two penetration cases involving complete penetration and incomplete penetration were detected during the test,and two modes were performed incorporating nails that either remained or were removed after penetration to comprehensively reveal the thermal runaway mechanism.A theoretical model of microcircuits and internal heat conduction is also established.The results indicated three thermal runaway evolution processes for high-capacity batteries,which corresponded to the experimental results of thermal equilibrium,single thermal runaway,and two thermal runaway events.The difference in heat distribution in the three phenomena is determined based on the microstructure and material structure near the pinhole.By controlling the heat dissipation conditions,the time interval between two thermal runaway events can be delayed from 558 to 1417 s,accompanied by a decrease in the concentration of in-situ gas production during the second thermal runaway event.展开更多
A composite separator of SiC/PVDF-HFP was synthesized for lithium-ion batteries with high thermal and mechanical stabilities.Benefiting from the nanoscale,high hardness,and melting point of SiC,SiC/PVDFHFP with highly...A composite separator of SiC/PVDF-HFP was synthesized for lithium-ion batteries with high thermal and mechanical stabilities.Benefiting from the nanoscale,high hardness,and melting point of SiC,SiC/PVDFHFP with highly uniform microstructure was obtained.This polarization caused by barrier penetration was significantly restrained.Due to the Si-F bond between SiC and PVDF-HFP,the structural stability has been obviously enhanced,which could suppress the growth of lithium(Li) dendrite.Furthermore,some 3D reticulated Si nanowires are found on the surface of Li anode,which also greatly inhibit Li dendrites and result in irregular flakes of Li metal.Especially,the shrinkage of 6% SiC/PVDF-HFP at 150℃ is only 5%,which is notably lower than those of PVDF-HFP and Celgard2500.The commercial LiFePO_(4) cell assembled with 6% SiC/PVDF-HFP possesses a specific capacity of 157.8 mA h g^(-1) and coulomb efficiency of 98% at 80℃.In addition,the tensile strength and modulus of 6% SiC/PVDF-HFP could reach 14.6 and 562 MPa,respectively.And a small deformation(1000 nm) and strong deformation recovery are obtained under a high additional load(2.3 mN).Compared with PVDF-HFP and Celgard2500,the symmetric Li cell assembled with 6% SiC/PVDF-HFP has not polarized after 900 cycles due to its excellent mechanical stabilities.This strategy provides a feasible solution for the composite separator of high-safety batteries with a high temperature and impact resistance.展开更多
Structurally compact battery packs significantly improve the driving range of electric vehicles.Technologies like Cell-to-Pack increase energy density by 15%-20%.However,the safety implications of multiple tightly-pac...Structurally compact battery packs significantly improve the driving range of electric vehicles.Technologies like Cell-to-Pack increase energy density by 15%-20%.However,the safety implications of multiple tightly-packed battery cells still require in-depth research.This paper studies thermal runaway propagation behavior in a Cell-to-Pack system and assesses propagation speed relative to other systems.The investigation includes temperature response,extent of battery damage,pack structure deformation,chemical analysis of debris,and other considerations.Results suggest three typical patterns for the thermal runaway propagation process:ordered,disordered,and synchronous.The synchronous propagation pattern displayed the most severe damage,indicating energy release is the largest under the synchronous pattern.This study identifies battery deformation patterns,chemical characteristics of debris,and other observed factors that can both be applied to identify the cause of thermal runaway during accident investigations and help promote safer designs of large battery packs used in large-scale electric energy storage systems.展开更多
As the energy density of battery increases rapidly,lithium-ion batteries(LIBs)are facing serious safety issue with thermal runaway,which largely limits the large-scale applications of high-energy-density LIBs.It is ge...As the energy density of battery increases rapidly,lithium-ion batteries(LIBs)are facing serious safety issue with thermal runaway,which largely limits the large-scale applications of high-energy-density LIBs.It is generally agreed that the chemical crosstalk between the cathode and anode leads to thermal runaway of LIBs.Herein,a multifunctional high safety electrolyte is designed with synergistic construction of cathode electrolyte interphase and capture of reactive free radicals to limit the intrinsic pathway of thermal runaway.The cathode electrolyte interphase not only resists the gas attack from the anode but suppresses the parasitic side reactions induced by electrolyte.And the function of free radical capture has the ability of reducing heat release from thermal runaway of battery.The dual strategy improves the intrinsic safety of battery prominently that the triggering temperature of thermal runaway is increased by 24.4℃and the maximum temperature is reduced by 177.7℃.Simultaneously,the thermal runaway propagation in module can be self-quenched.Moreover,the electrolyte design balances the trade-off of electrochemical and safety performance of high-energy batteries.The capacity retention of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)|graphite pouch cell has been significantly increased from 53.85%to 97.05%with higher coulombic efficiency of 99.94%at operating voltage extended up to 4.5 V for 200 cycles.Therefore,this work suggests a feasible strategy to mitigate the safety risk of high-energy-density LIBs without sacrificing electrochemical performances.展开更多
Currently,the effective and clean suppression of lithium-ion battery(LIB)fires remains a challenge.The present work investigates the use of various inhibitor doses(Xin)of dodecafluoro-2-methylpentan-3-one(C_(6) F_(12)...Currently,the effective and clean suppression of lithium-ion battery(LIB)fires remains a challenge.The present work investigates the use of various inhibitor doses(Xin)of dodecafluoro-2-methylpentan-3-one(C_(6) F_(12)O)in 300 Ah LIBs,and systematically examines the thermal and toxic hazards of the extinguished batteries via real scale combustion and gas analysis.The inhibitor is shown to be completely effective.The inhibition mechanism involves a combination of chemical inhibition and physical cooling.While the chemical inhibition effect tends to saturate with increasing Xin,the physical cooling remains effective at higher inhibitor doses.However,extinguishing the battery fire with a high Xin of C_(6)F_(12)O is found to incur serious toxicity problems.These results are expected to provide a guideline for the design of inhibitor doses for the suppression of LIB fires.展开更多
A quantitative relationship between safety issues and dendritic lithium(Li) has been rarely investigated yet. Herein the thermal stability of Li deposits with distinct surface area against non-aqueous electrolyte in p...A quantitative relationship between safety issues and dendritic lithium(Li) has been rarely investigated yet. Herein the thermal stability of Li deposits with distinct surface area against non-aqueous electrolyte in pouch-type Li metal batteries is probed. The thermal runaway temperatures of Li metal batteries obtained by accelerating rate calorimeter are reduced from 211 ℃ for Li foil to 111 ℃ for cycled Li.The initial exothermic temperature is reduced from 194 ℃ for routine Li foil to 142 ℃ for 49.5 m~2g^(-1) dendrite. Li with different specific surface areas can regulate the reaction routes during the temperature range from 50 to 300 ℃. The mass percent of Li foil and highly dendritic Li reacting with ethylene carbonate is higher than that of moderately dendritic Li. This contribution can strengthen the understanding of the thermal runaway mechanism and shed fresh light on the rational design of safe Li metal batteries.展开更多
Thermal runaway caused by overcharging results in catastrophic disasters. The influences of charging rate, ambient temperature and aging on thermal runaway caused by overcharging are studied qualitatively and quantita...Thermal runaway caused by overcharging results in catastrophic disasters. The influences of charging rate, ambient temperature and aging on thermal runaway caused by overcharging are studied qualitatively and quantitatively in this manuscript. The results of overcharging tests indicate that high charging rate and ambient temperature increase thermal runaway risk. Aging in 40 ℃ decreases thermal runaway risk. The risk increase of battery with high overcharging rate and in high ambient temperature is due to fast lithium plating reaction and accelerated SEI decomposition, respectively. The risk decrease of aged battery is due to the occurrence of SEI before overcharging tests. SEI suppresses the side reactions between lithium plating and electrolyte. The results of orthogonal tests indicate that the rank of effect is: discharging rate > ambient temperature > aging. The heat generation is calculated based on the results of overcharging tests. The calculation results indicate that heat generated by side reactions contributes more to the total heat generation. Although thermal runaway does not occur during overcharging with low current, the heat dissipation of the lithium-ion battery is the most and deserves focus. The results are important to the design of battery management system and thermal management system to prevent thermal runaway induced by overcharging in total lifespan of battery.展开更多
Thermal runaway is a critical issue for the large application of lithium-ion batteries.Exothermic reactions between lithiated graphite and electrolyte play a crucial role in the thermal runaway of lithium-ion batterie...Thermal runaway is a critical issue for the large application of lithium-ion batteries.Exothermic reactions between lithiated graphite and electrolyte play a crucial role in the thermal runaway of lithium-ion batteries.However,the role of each component in the electrolyte during the exothermic reactions with lithiated graphite has not been fully understood.In this paper,the exothermic reactions between lithiated graphite and electrolyte of lithium-ion battery are investigated through differential scanning calorimetry(DSC) and evolved gas analysis.The lithiated graphite in the presence of electrolyte exhibit three exothermic peaks during DSC test.The reactions between lithiated graphite and LiPF_(6) and ethylene carbonate are found to be responsible for the first two exothermic peaks,while the third exothermic peak is attributed to the reaction between lithiated graphite and binder.In contrast,diethylene carbonate and ethyl methyl carbonate contribute little to the total heat generation of graphite-electrolyte reactions.The reaction mechanism between lithiated graphite and electrolyte,including the major reaction equations and gas products,are summarized.Finally,DSC tests on samples with various amounts of electrolyte are performed to clarify the quantitative relationship between lithiated graphite and electrolyte during the exothermic reactions.2.5 mg of lithiated graphite (Li_(0.8627)C_(6)) can fully react with around 7.2 mg electrolyte,releasing a heat generation of 2491 J g^(-1).The results presented in this study can provide useful guidance for the safety improvement of lithium-ion batteries.展开更多
With the continuing boost in the demand for energy storage,there is an increasing requirement for batteries to be capable of operation in extreme environmental conditions.Sodium-ion batteries(SIBs) have emerged as a h...With the continuing boost in the demand for energy storage,there is an increasing requirement for batteries to be capable of operation in extreme environmental conditions.Sodium-ion batteries(SIBs) have emerged as a highly promising energy storage solution due to their promising performance over a wide range of temperatures and the abundance of sodium resources in the earth's crust.Compared to lithiumion batteries(LIBs),although sodium ions possess a larger ionic radius,they are more easily desolvated than lithium ions.Fu rthermore,SIBs have a smaller Stokes radius than lithium ions,resulting in improved sodium-ion mobility in the electrolyte.Nevertheless,SIBs demonstrate a significant decrease in performance at low temperatures(LT),which constrains their operation in harsh weather conditions.Despite the increasing interest in SIBs,there is a notable scarcity of research focusing specifically on their mechanism under LT conditions.This review explores recent research that considers the thermal tolerance of SIBs from an inner chemistry process perspective,spanning a wide temperature spectrum(-70 to100℃),particularly at LT conditions.In addition,the enhancement of electrochemical performance in LT SIBs is based on improvements in reaction kinetics and cycling stability achieved through the utilization of effective electrode materials and electrolyte components.Furthermore,the safety concerns associated with SIBs are addressed and effective strategies are proposed for mitigating these issues.Finally,prospects conducted to extend the environmental frontiers of commercial SIBs are discussed mainly from three viewpoints including innovations in materials,development and research of relevant theoretical mechanisms,and intelligent safety management system establishment for larger-scale energy storage SIBs.展开更多
1.Introduction With the superior performance of high energy density,lightweight and long life span,lithium-ion battery(LIB)are perceived as an attractive and reliable power source for modern-used portable electronics,...1.Introduction With the superior performance of high energy density,lightweight and long life span,lithium-ion battery(LIB)are perceived as an attractive and reliable power source for modern-used portable electronics,ecofriendly electric vehicles and power distribution,and thereby a remarkable solution to assuage energy dependence on fossil fuel and environmental concern.Nevertheless,the unexpected Li plating together with the Li dendrites growth on graphite anode surface has been a profound hindrance to the practical application of LIB,of which induces inferior Coulombic efficiency,poor lifespan and safety concern[1].展开更多
NASICON-type Na_(3)V_(2)(PO_(4))_(3) is a promising electrode material for developing advanced sodium-ion batteries.Preparing Na_(3)V_(2)(PO_(4))_(3) with good performance by a cost-effective and large-scale method is...NASICON-type Na_(3)V_(2)(PO_(4))_(3) is a promising electrode material for developing advanced sodium-ion batteries.Preparing Na_(3)V_(2)(PO_(4))_(3) with good performance by a cost-effective and large-scale method is significant for industrial applications.In this work,a porous Na_(3)V_(2)(PO_(4))_(3)/C cathode material with excellent electrochemical performance is successfully prepared by an agar-gel combined with freeze-drying method.The Na_(3)V_(2)(PO_(4))_(3)/C cathode displayed specific capacities of 113.4 mAh·g^(-1),107.0 mAh·g^(-1) and 87.1 mAh·g^(-1) at 0.1 C,1 C and 10 C,respectively.For the first time,the 500-mAh soft-packed symmetrical sodium-ion batteries based on Na_(3)V_(2)(PO_(4))_(3)/C electrodes are successfully fabricated.The 500-mAh symmetrical batteries exhibit outstanding low temperature performance with a capacity retention of 83%at 0℃ owing to the rapid sodium ion migration ability and structural stability of Na_(3)V_(2)(PO_(4))_(3)/C.Moreover,the thermal runaway features are revealed by accelerating rate calorimetry(ARC)test for the first time.Thermal stability and safety of the symmetrical batteries are demonstrated to be better than lithium-ion batteries and some reported sodium-ion batteries.Our work makes it clear that the soft-packed symmetrical sodium ion batteries based on Na_(3)V_(2)(PO_(4))_(3)/C have a prospect of practical application in high safety requirement fields.展开更多
Fluorinated electrolytes possess good antioxidant capacity that provides high compatibility to high-voltage cathode and flame retardance;thus,they are considered as a promising solution for advanced lithium-ion batter...Fluorinated electrolytes possess good antioxidant capacity that provides high compatibility to high-voltage cathode and flame retardance;thus,they are considered as a promising solution for advanced lithium-ion batteries carrying both high-energy density and high safety.Moreover,the fluorinated electrolytes are widely used to form stable electrolyte interphase,due to their chemical reactivity with lithiated graphite or lithium.However,the influence of this reactivity on the thermal safety of batteries is seldom discussed.Herein,we demonstrate that the flame-retardant fluorinated electrolytes help to reduce the flammability,while the lithium-ion batteries with flame-retardant fluorinated electrolytes still undergo thermal runaway and disclose their different thermal runaway pathway from that of battery with conventional electrolyte.The reduction in fluorinated components(e.g.,LiPF 6 and fluoroethylene carbonate(FEC))by fully lithiated graphite accounts for a significant heat release during battery thermal runaway.The 13%of total heat is sufficient to trigger the chain reactions during battery thermal runaway.This study deepens the understanding of the thermal runaway mechanism of lithium-ion batteries employing flame-retardant fluorinated electrolytes,providing guidance on the concept of electrolyte design for safer lithium-ion batteries.展开更多
Safety issue of lithium-ion batteries(LIBs)such as fires and explosions is a significant challenge for their large scale applications.Considering the continuously increased battery energy density and wider large-scale...Safety issue of lithium-ion batteries(LIBs)such as fires and explosions is a significant challenge for their large scale applications.Considering the continuously increased battery energy density and wider large-scale battery pack applications,the possibility of LIBs fire significantly increases.Because of the fast burning and the easy re-ignition characteristics of LIBs,achieving an efficient and prompt LIBs fire suppression is critical for minimizing the fire hazards.Different from conventional fire hazards,the LIBs fire shows complicated and comprehensive characteristics,and an effective and suitable fire-extinguishing agent particularly designed for LIBs is highly desirable.Considerable efforts have been devoted to this topic,to the best of our knowledge,a comprehensive review on this regard is still rare.Moreover,in practice,a guidance for the design and selections of a proper fire-extinguishing agent for LIBs is urgently needed.Herein,the special mechanisms and characteristics for LIBs fire and the corresponding design principles for LIBs fire-extinguishing agent were introduced.It is revealed that a fire-extinguishing agent developed for LIBs fire will most likely need a high heat capacity,high wetting,low viscosity and low electrical conductivity.After a comprehensive comparison of these agents in terms of these performances,water-based fire-extinguishing agents show best.Several typical fire-extinguishing agents such as gaseous agents,dry powders,water-based and aerosol fire-extinguishing agents were then introduced,and their fire extinguishment mechanisms were presented.Finally,their effectiveness in suppressing the fire were summarized.Water-based fire-extinguishing agents possess high cooling capacity and excellent anti-reflash performance for the fire.We believe this review could shed light on developing an efficient fire-extinguishing agent particularly designed for LIBs.展开更多
External short circuit(ESC)of lithium-ion batteries is one of the common and severe electrical failures in electric vehicles.In this study,a novel thermal modelis developed to capture the temperature behavior of batte...External short circuit(ESC)of lithium-ion batteries is one of the common and severe electrical failures in electric vehicles.In this study,a novel thermal modelis developed to capture the temperature behavior of batteries under ESC conditions.Experiments were systematically performed under different battery initial state of charge and ambient temperatures.Based on the experimental results,we employed an extreme learming machine(ELM)-based thermal(ELMT)model to depict battery temperature behavior under ESC,where a lumped-state thermal model was used to replace the activation function of conventional ELMs.To demonstrate the effectiveness of the proposed model,wecompared the ELMT model with a multi-lumped-state thermal(MLT)model parameterized by thegenetic algorithm using the experimental data from various sets of battery cells.It is shown that the ELMT model can achieve higher computa-tional efficiency than the MLT model and better fitting and prediction accuracy,where the average root mean squared error(RMSE)of the fitting is 0.65℃ for the ELMT model and 3.95℃ for the MLT model,and the RMES of the prediction under new data set is 3.97℃ for the ELMT model and 6.11℃ for the MLT model.展开更多
Internal short circuit(ISC)is the major failure problem for the safe application of lithium-ion batteries,especially for the batteries with high energy density.However,how to quantify the hazard aroused by the ISC,and...Internal short circuit(ISC)is the major failure problem for the safe application of lithium-ion batteries,especially for the batteries with high energy density.However,how to quantify the hazard aroused by the ISC,and what kinds of ISC will lead to thermal runaway are still unclear.This paper investigates the thermal-electrical coupled behaviors of ISC,using batteries with Li(Ni_(1/3)CO_(1/3)Mn_(1/3))O_(2) cathode and composite separator.The electrochemical impedance spectroscopy of customized battery that has no LiPF6 salt is utilized to standardize the resistance of ISC.Furthermore,this paper compares the thermal-electrical coupled behaviors of the above four types of ISC at different states-of-charge.There is an area expansion phenomenon for the aluminum-anode type of ISC.The expansion effect of the failure area directly links to the melting and collapse of separator,and plays an important role in further evolution of thermal runaway.This work provides guidance to the development of the ISC models,detection algorithms,and correlated countermeasures.展开更多
By virtue of the crucial effect of the crystal structure and transition metal(TM)redox evolution on the performance of LiNi_(x)Co_(y)Mn_(z)O_(2)(NCM)cathode,systematical investigation is carried out to better understa...By virtue of the crucial effect of the crystal structure and transition metal(TM)redox evolution on the performance of LiNi_(x)Co_(y)Mn_(z)O_(2)(NCM)cathode,systematical investigation is carried out to better understand the charge mechanism upon deep charging.Based on the results of X-ray diffraction and highresolution transmission electron microscope,phase transformations existing on particle surface are promoted by high potential because of the deeper lithium vacancies,accompanied by more substantial structure instability.Soft X-ray absorption spectroscopy indicates that Ni acts as the major contributor to charge compensation while Co displays a remarkable redox activity over the deep charge range.The elevated integrated intensity of pre-edge in O K-edge spectra reveals the extensive amount of holes formed in O 2 p orbitals and the enhanced hybridization of TM 3 d-O 2 p orbitals.Considering the close relationship between thermal behavior and structural evolution,the tendency of phase transitions and O_(2) release upon heating is accelerated by voltage rise,demonstrating the aggravated instability due to deeper Li utilization.Remaining Li contents in NCM are employed to estimate the amount of oxygen released in structural transformation and its detrimental effect on stability declares Li contentdependent characteristics.Furthermore,the extended Li vacancies,higher proportion of Ni4+and stronger orbital hybridization are considered as three factors impeding the thermal stability of the highlydelithiated NCM.展开更多
Based on the synchrotron soft X-ray absorption spectroscopy experiments,the fundamental electronic structures of layered Li NixCoyMnzO_(2)(NCM)are investigated systematically and the data of transitionmetal(TM)L-and O...Based on the synchrotron soft X-ray absorption spectroscopy experiments,the fundamental electronic structures of layered Li NixCoyMnzO_(2)(NCM)are investigated systematically and the data of transitionmetal(TM)L-and O K-edges spectra are collected.Distribution of Ni ions under different oxidation states is evaluated according to linear combination fit.It is found that the ratio of Ni^(4+)expands with the increase of Ni since it dominates in charge compensation during charging,and that the existence of Ni^(3+)is nearly negligible in delithiated NCM.The valence state of Co also strongly depends on Ni content,the perceptible position shift of Co L_(3)-edge absorption peak towards higher energy in Ni-rich material agrees well with the small voltage plateau at around 4.2 V.The stability of Mn is verified as no obvious spectral change with the Mn L-edge is observed.Moreover,as Ni content rises,the O 2p holes near the Femi level increases with higher oxidation state of Ni,indicating the enhanced hybridization of O 2p-TM 3 d.Delithiated NCMs with higher Ni content are prior to lose electron existing in highly hybridized Ni3 dO 2 p bands upon heating,which accounts for the pronounced O_(2)release in phase transitions and the deterioration in thermal stability.These detailed observation of the electronic structure evolution is one of the key ingredients to improving the electrochemical and thermal performance of NCM.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant No.2021YFB2500300)。
文摘The rapid development of lithium-ion batteries(LIBs)is faced with challenge of its safety bottleneck,calling for design and chemistry innovations.Among the proposed strategies,the development of solid-state batteries(SSBs)seems the most promising solution,but to date no practical SSB has been in large-scale application.Practical safety performance of SSBs is also challenged.In this article,a brief review on LIB safety issue is made and the safety short boards of LIBs are emphasized.A systematic safety design in quasi-SSB chemistry is proposed to conquer the intrinsic safety weak points of LIBs and the effects are accessed based on existing studies.It is believed that a systematic and targeted solution in SSB chemistry design can effectively improve the battery safety,promoting larger-scale application of LIBs.
基金supported by the National Natural Science Foundation of China(No.U20A20310 and No.52176199)sponsored by the Program of Shanghai Academic/Technology Research Leader(No.22XD1423800)。
文摘Thermal runaway(TR)is a critical issue hindering the large-scale application of lithium-ion batteries(LIBs).Understanding the thermal safety behavior of LIBs at the cell and module level under different state of charges(SOCs)has significant implications for reinforcing the thermal safety design of the lithium-ion battery module.This study first investigates the thermal safety boundary(TSB)correspondence at the cells and modules level under the guidance of a newly proposed concept,safe electric quantity boundary(SEQB).A reasonable thermal runaway propagation(TRP)judgment indicator,peak heat transfer power(PHTP),is proposed to predict whether TRP occurs.Moreover,a validated 3D model is used to quantitatively clarify the TSB at different SOCs from the perspective of PHTP,TR trigger temperature,SOC,and the full cycle life.Besides,three different TRP transfer modes are discovered.The interconversion relationship of three different TRP modes is investigated from the perspective of PHTP.This paper explores the TSB of LIBs under different SOCs at both cell and module levels for the first time,which has great significance in guiding the thermal safety design of battery systems.
文摘The integration of battery energy storage systems(BESS)throughout our energy chain poses concerns regarding safety,especially since batteries have high energy density and numerous BESS failure events have occurred.Wider spread adoption will only increase the prevalence of these failure events unless there is a step change in the management and design of BESS.To understand the causes of failure,the main challenges of BESS safety are summarised.BESS consequences and failure events are discussed,including specific focus on the chain of events causing thermal runaway,and a case study of a BESS explosion in Surprise Arizona is analysed.Based on the technology and past events,a paradigm shift is required to improve BESS safety.In this review,a holistic approach is proposed.This combines currently adopted approaches including battery cell testing,lumped cell mathematical modelling,and calorimetry,alongside additional measures taken to ensure BESS safety including the requirement for computational fluid dynamics and kinetic modelling,assessment of installation level testing of the full BESS system and not simply a single cell battery test,hazard and layers of protection analysis,gas chromatography,and composition testing.The holistic approach proposed in this study aims to address challenges of BESS safety and form the basis of a paradigm shift in the safety management and design of these systems.
基金supported by the National Key R&D Program of China(2021YFB2402001)the China National Postdoctoral Program for Innovative Talents(BX20220286)+1 种基金the China Postdoctoral Science Foundation(2022T150615)supported by the Youth Innovation Promotion Association CAS(Y201768)。
文摘Lithium iron phosphate batteries have been increasingly utilized in recent years because their higher safety performance can improve the increasing trend of recurring thermal runaway accidents.However,the safety performance and mechanism of high-capacity lithium iron phosphate batteries under internal short-circuit challenges remain to be explored.This work analyzes the thermal runaway evolution of high-capacity LiFePO_(4) batteries under different internal heat transfer modes,which are controlled by different penetration modes.Two penetration cases involving complete penetration and incomplete penetration were detected during the test,and two modes were performed incorporating nails that either remained or were removed after penetration to comprehensively reveal the thermal runaway mechanism.A theoretical model of microcircuits and internal heat conduction is also established.The results indicated three thermal runaway evolution processes for high-capacity batteries,which corresponded to the experimental results of thermal equilibrium,single thermal runaway,and two thermal runaway events.The difference in heat distribution in the three phenomena is determined based on the microstructure and material structure near the pinhole.By controlling the heat dissipation conditions,the time interval between two thermal runaway events can be delayed from 558 to 1417 s,accompanied by a decrease in the concentration of in-situ gas production during the second thermal runaway event.
基金supported by the Natural Science Foundation of Science and Technology Department of Sichuan Province, China (23NSFSC6224)the Higher Education Talent Training Quality and Teaching Reform Project of Sichuan Province, China (JG2021-1098)+3 种基金the Industry-university cooperation collaborative education project of the Ministry of Education, China (221001359095358 and 220604738021813)the Development Research Center of Sichuan Cuisine (CC21Z02)the “Sichuang Fusion” Youth Red Dream Building Project of Chengdu University,China (cxcysc2022001)the Solid-state Fermentation Resource Utilization Key Laboratory of Sichuan Province (2020GTJ002)。
文摘A composite separator of SiC/PVDF-HFP was synthesized for lithium-ion batteries with high thermal and mechanical stabilities.Benefiting from the nanoscale,high hardness,and melting point of SiC,SiC/PVDFHFP with highly uniform microstructure was obtained.This polarization caused by barrier penetration was significantly restrained.Due to the Si-F bond between SiC and PVDF-HFP,the structural stability has been obviously enhanced,which could suppress the growth of lithium(Li) dendrite.Furthermore,some 3D reticulated Si nanowires are found on the surface of Li anode,which also greatly inhibit Li dendrites and result in irregular flakes of Li metal.Especially,the shrinkage of 6% SiC/PVDF-HFP at 150℃ is only 5%,which is notably lower than those of PVDF-HFP and Celgard2500.The commercial LiFePO_(4) cell assembled with 6% SiC/PVDF-HFP possesses a specific capacity of 157.8 mA h g^(-1) and coulomb efficiency of 98% at 80℃.In addition,the tensile strength and modulus of 6% SiC/PVDF-HFP could reach 14.6 and 562 MPa,respectively.And a small deformation(1000 nm) and strong deformation recovery are obtained under a high additional load(2.3 mN).Compared with PVDF-HFP and Celgard2500,the symmetric Li cell assembled with 6% SiC/PVDF-HFP has not polarized after 900 cycles due to its excellent mechanical stabilities.This strategy provides a feasible solution for the composite separator of high-safety batteries with a high temperature and impact resistance.
基金supported by the Natural Science Foundation of Hebei Province (B2021507001)the National Natural Science Foundation of China (52106284, 52076121)+2 种基金the Ministry of Science and Technology (2022YFE0207900)the support of the Science and Technology Project of Langfang (2021011017)the Project to Promote Innovation in Doctoral Research at CPPU (BSKY202302)。
文摘Structurally compact battery packs significantly improve the driving range of electric vehicles.Technologies like Cell-to-Pack increase energy density by 15%-20%.However,the safety implications of multiple tightly-packed battery cells still require in-depth research.This paper studies thermal runaway propagation behavior in a Cell-to-Pack system and assesses propagation speed relative to other systems.The investigation includes temperature response,extent of battery damage,pack structure deformation,chemical analysis of debris,and other considerations.Results suggest three typical patterns for the thermal runaway propagation process:ordered,disordered,and synchronous.The synchronous propagation pattern displayed the most severe damage,indicating energy release is the largest under the synchronous pattern.This study identifies battery deformation patterns,chemical characteristics of debris,and other observed factors that can both be applied to identify the cause of thermal runaway during accident investigations and help promote safer designs of large battery packs used in large-scale electric energy storage systems.
基金supported by the National Key R&D ProgramStrategic Scientific and Technological Innovation Cooperation(2022YFB3803500)the National Key Research and Development Program of China(2019YFA0705700)+1 种基金the National Natural Science Foundation of China(52076121,51904016,and 52004138)the Fundamental Research Funds for the Central Universities。
文摘As the energy density of battery increases rapidly,lithium-ion batteries(LIBs)are facing serious safety issue with thermal runaway,which largely limits the large-scale applications of high-energy-density LIBs.It is generally agreed that the chemical crosstalk between the cathode and anode leads to thermal runaway of LIBs.Herein,a multifunctional high safety electrolyte is designed with synergistic construction of cathode electrolyte interphase and capture of reactive free radicals to limit the intrinsic pathway of thermal runaway.The cathode electrolyte interphase not only resists the gas attack from the anode but suppresses the parasitic side reactions induced by electrolyte.And the function of free radical capture has the ability of reducing heat release from thermal runaway of battery.The dual strategy improves the intrinsic safety of battery prominently that the triggering temperature of thermal runaway is increased by 24.4℃and the maximum temperature is reduced by 177.7℃.Simultaneously,the thermal runaway propagation in module can be self-quenched.Moreover,the electrolyte design balances the trade-off of electrochemical and safety performance of high-energy batteries.The capacity retention of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)|graphite pouch cell has been significantly increased from 53.85%to 97.05%with higher coulombic efficiency of 99.94%at operating voltage extended up to 4.5 V for 200 cycles.Therefore,this work suggests a feasible strategy to mitigate the safety risk of high-energy-density LIBs without sacrificing electrochemical performances.
基金funded by the Science and Technology Project of the State Grid Corporation of China (Exploration study on Fire Extinguishing Technology of Lithium Ion Energy Storage Battery DG71-18-002)。
文摘Currently,the effective and clean suppression of lithium-ion battery(LIB)fires remains a challenge.The present work investigates the use of various inhibitor doses(Xin)of dodecafluoro-2-methylpentan-3-one(C_(6) F_(12)O)in 300 Ah LIBs,and systematically examines the thermal and toxic hazards of the extinguished batteries via real scale combustion and gas analysis.The inhibitor is shown to be completely effective.The inhibition mechanism involves a combination of chemical inhibition and physical cooling.While the chemical inhibition effect tends to saturate with increasing Xin,the physical cooling remains effective at higher inhibitor doses.However,extinguishing the battery fire with a high Xin of C_(6)F_(12)O is found to incur serious toxicity problems.These results are expected to provide a guideline for the design of inhibitor doses for the suppression of LIB fires.
基金supported by the National Key Research and Development Program(2021YFB2500300)the National Natural Science Foundation of China(22179070,22109084,22075029,and U1932220)+1 种基金the China Postdoctoral Science Foundation(2021TQ0161 and 2021M691709)the Beijing Natural Science Foundation(JQ20004)。
文摘A quantitative relationship between safety issues and dendritic lithium(Li) has been rarely investigated yet. Herein the thermal stability of Li deposits with distinct surface area against non-aqueous electrolyte in pouch-type Li metal batteries is probed. The thermal runaway temperatures of Li metal batteries obtained by accelerating rate calorimeter are reduced from 211 ℃ for Li foil to 111 ℃ for cycled Li.The initial exothermic temperature is reduced from 194 ℃ for routine Li foil to 142 ℃ for 49.5 m~2g^(-1) dendrite. Li with different specific surface areas can regulate the reaction routes during the temperature range from 50 to 300 ℃. The mass percent of Li foil and highly dendritic Li reacting with ethylene carbonate is higher than that of moderately dendritic Li. This contribution can strengthen the understanding of the thermal runaway mechanism and shed fresh light on the rational design of safe Li metal batteries.
基金the support given by National Natural Science Foundation of China(51874184)the Key Natural Science Foundation in Jiangsu Province(18KJA620003)Jiangsu Project Plan for Outstanding Talents Team in Six Research Fields(TD-XNYQC-002)。
文摘Thermal runaway caused by overcharging results in catastrophic disasters. The influences of charging rate, ambient temperature and aging on thermal runaway caused by overcharging are studied qualitatively and quantitatively in this manuscript. The results of overcharging tests indicate that high charging rate and ambient temperature increase thermal runaway risk. Aging in 40 ℃ decreases thermal runaway risk. The risk increase of battery with high overcharging rate and in high ambient temperature is due to fast lithium plating reaction and accelerated SEI decomposition, respectively. The risk decrease of aged battery is due to the occurrence of SEI before overcharging tests. SEI suppresses the side reactions between lithium plating and electrolyte. The results of orthogonal tests indicate that the rank of effect is: discharging rate > ambient temperature > aging. The heat generation is calculated based on the results of overcharging tests. The calculation results indicate that heat generated by side reactions contributes more to the total heat generation. Although thermal runaway does not occur during overcharging with low current, the heat dissipation of the lithium-ion battery is the most and deserves focus. The results are important to the design of battery management system and thermal management system to prevent thermal runaway induced by overcharging in total lifespan of battery.
基金supported by the Key-Area Research and Development Program of Guangdong Province (2020B090919004)the Ministry of Science and Technology of China (2019YFE0100200)+3 种基金the National Natural Science Foundation of China (52007099, 51706117, 52076121, 51877138)the Shanghai Science and Technology Development Fund (19QA1406200)the China Postdoctoral Science Foundation (2020M680550)the support from the “Shuimu Tsinghua Scholar Program” from Tsinghua University。
文摘Thermal runaway is a critical issue for the large application of lithium-ion batteries.Exothermic reactions between lithiated graphite and electrolyte play a crucial role in the thermal runaway of lithium-ion batteries.However,the role of each component in the electrolyte during the exothermic reactions with lithiated graphite has not been fully understood.In this paper,the exothermic reactions between lithiated graphite and electrolyte of lithium-ion battery are investigated through differential scanning calorimetry(DSC) and evolved gas analysis.The lithiated graphite in the presence of electrolyte exhibit three exothermic peaks during DSC test.The reactions between lithiated graphite and LiPF_(6) and ethylene carbonate are found to be responsible for the first two exothermic peaks,while the third exothermic peak is attributed to the reaction between lithiated graphite and binder.In contrast,diethylene carbonate and ethyl methyl carbonate contribute little to the total heat generation of graphite-electrolyte reactions.The reaction mechanism between lithiated graphite and electrolyte,including the major reaction equations and gas products,are summarized.Finally,DSC tests on samples with various amounts of electrolyte are performed to clarify the quantitative relationship between lithiated graphite and electrolyte during the exothermic reactions.2.5 mg of lithiated graphite (Li_(0.8627)C_(6)) can fully react with around 7.2 mg electrolyte,releasing a heat generation of 2491 J g^(-1).The results presented in this study can provide useful guidance for the safety improvement of lithium-ion batteries.
基金supported by the Natural Science Foundation of Jiangsu Province(No.BK20220618)the National Natural Science Foundation of China(Nos.22078028 and 21978026)。
文摘With the continuing boost in the demand for energy storage,there is an increasing requirement for batteries to be capable of operation in extreme environmental conditions.Sodium-ion batteries(SIBs) have emerged as a highly promising energy storage solution due to their promising performance over a wide range of temperatures and the abundance of sodium resources in the earth's crust.Compared to lithiumion batteries(LIBs),although sodium ions possess a larger ionic radius,they are more easily desolvated than lithium ions.Fu rthermore,SIBs have a smaller Stokes radius than lithium ions,resulting in improved sodium-ion mobility in the electrolyte.Nevertheless,SIBs demonstrate a significant decrease in performance at low temperatures(LT),which constrains their operation in harsh weather conditions.Despite the increasing interest in SIBs,there is a notable scarcity of research focusing specifically on their mechanism under LT conditions.This review explores recent research that considers the thermal tolerance of SIBs from an inner chemistry process perspective,spanning a wide temperature spectrum(-70 to100℃),particularly at LT conditions.In addition,the enhancement of electrochemical performance in LT SIBs is based on improvements in reaction kinetics and cycling stability achieved through the utilization of effective electrode materials and electrolyte components.Furthermore,the safety concerns associated with SIBs are addressed and effective strategies are proposed for mitigating these issues.Finally,prospects conducted to extend the environmental frontiers of commercial SIBs are discussed mainly from three viewpoints including innovations in materials,development and research of relevant theoretical mechanisms,and intelligent safety management system establishment for larger-scale energy storage SIBs.
基金supported by the National Natural Science Foundation of China (U2033204)the China Postdoctoral Science Foundation (2021M703053)+1 种基金supported by the China National Postdoctoral Program for Innovative Talents(BX20220286)supported by Youth Innovative Promotion Association CAS (Y201768)
文摘1.Introduction With the superior performance of high energy density,lightweight and long life span,lithium-ion battery(LIB)are perceived as an attractive and reliable power source for modern-used portable electronics,ecofriendly electric vehicles and power distribution,and thereby a remarkable solution to assuage energy dependence on fossil fuel and environmental concern.Nevertheless,the unexpected Li plating together with the Li dendrites growth on graphite anode surface has been a profound hindrance to the practical application of LIB,of which induces inferior Coulombic efficiency,poor lifespan and safety concern[1].
基金This work was supported by the National Key Research and Development Program(2016YFB0901505)the Natural Science Foundation of China(22005190,21938005)+1 种基金the Science&Technology Commission of Shanghai Municipality(19DZ1205500)Zhejiang Key Research and Development Program(2020C01128).
文摘NASICON-type Na_(3)V_(2)(PO_(4))_(3) is a promising electrode material for developing advanced sodium-ion batteries.Preparing Na_(3)V_(2)(PO_(4))_(3) with good performance by a cost-effective and large-scale method is significant for industrial applications.In this work,a porous Na_(3)V_(2)(PO_(4))_(3)/C cathode material with excellent electrochemical performance is successfully prepared by an agar-gel combined with freeze-drying method.The Na_(3)V_(2)(PO_(4))_(3)/C cathode displayed specific capacities of 113.4 mAh·g^(-1),107.0 mAh·g^(-1) and 87.1 mAh·g^(-1) at 0.1 C,1 C and 10 C,respectively.For the first time,the 500-mAh soft-packed symmetrical sodium-ion batteries based on Na_(3)V_(2)(PO_(4))_(3)/C electrodes are successfully fabricated.The 500-mAh symmetrical batteries exhibit outstanding low temperature performance with a capacity retention of 83%at 0℃ owing to the rapid sodium ion migration ability and structural stability of Na_(3)V_(2)(PO_(4))_(3)/C.Moreover,the thermal runaway features are revealed by accelerating rate calorimetry(ARC)test for the first time.Thermal stability and safety of the symmetrical batteries are demonstrated to be better than lithium-ion batteries and some reported sodium-ion batteries.Our work makes it clear that the soft-packed symmetrical sodium ion batteries based on Na_(3)V_(2)(PO_(4))_(3)/C have a prospect of practical application in high safety requirement fields.
基金This work is funded by National Natural Science Foundation of China(Grant No.52006115)Ministry of Science and Technology of China(Grant No.2019YFE0100200)+3 种基金National Natural Science Foundation of China(Grant No.52076121)China National Postdoctoral Program for Innovative Talents(Grant No.BX20190162)China Postdoctoral Science Foundation(Grant No.2019M660631)the Tsinghua University Initiative Scientific Research Program(Grant No.2019Z02UTY06).
文摘Fluorinated electrolytes possess good antioxidant capacity that provides high compatibility to high-voltage cathode and flame retardance;thus,they are considered as a promising solution for advanced lithium-ion batteries carrying both high-energy density and high safety.Moreover,the fluorinated electrolytes are widely used to form stable electrolyte interphase,due to their chemical reactivity with lithiated graphite or lithium.However,the influence of this reactivity on the thermal safety of batteries is seldom discussed.Herein,we demonstrate that the flame-retardant fluorinated electrolytes help to reduce the flammability,while the lithium-ion batteries with flame-retardant fluorinated electrolytes still undergo thermal runaway and disclose their different thermal runaway pathway from that of battery with conventional electrolyte.The reduction in fluorinated components(e.g.,LiPF 6 and fluoroethylene carbonate(FEC))by fully lithiated graphite accounts for a significant heat release during battery thermal runaway.The 13%of total heat is sufficient to trigger the chain reactions during battery thermal runaway.This study deepens the understanding of the thermal runaway mechanism of lithium-ion batteries employing flame-retardant fluorinated electrolytes,providing guidance on the concept of electrolyte design for safer lithium-ion batteries.
基金This work was supported by the National Key Research and Development Program of China(grant number 2017YFC0804700)the National Key Research and Development Program(2019YFC0810703)the National Natural Science Foundation of China(grant number 51874041).
文摘Safety issue of lithium-ion batteries(LIBs)such as fires and explosions is a significant challenge for their large scale applications.Considering the continuously increased battery energy density and wider large-scale battery pack applications,the possibility of LIBs fire significantly increases.Because of the fast burning and the easy re-ignition characteristics of LIBs,achieving an efficient and prompt LIBs fire suppression is critical for minimizing the fire hazards.Different from conventional fire hazards,the LIBs fire shows complicated and comprehensive characteristics,and an effective and suitable fire-extinguishing agent particularly designed for LIBs is highly desirable.Considerable efforts have been devoted to this topic,to the best of our knowledge,a comprehensive review on this regard is still rare.Moreover,in practice,a guidance for the design and selections of a proper fire-extinguishing agent for LIBs is urgently needed.Herein,the special mechanisms and characteristics for LIBs fire and the corresponding design principles for LIBs fire-extinguishing agent were introduced.It is revealed that a fire-extinguishing agent developed for LIBs fire will most likely need a high heat capacity,high wetting,low viscosity and low electrical conductivity.After a comprehensive comparison of these agents in terms of these performances,water-based fire-extinguishing agents show best.Several typical fire-extinguishing agents such as gaseous agents,dry powders,water-based and aerosol fire-extinguishing agents were then introduced,and their fire extinguishment mechanisms were presented.Finally,their effectiveness in suppressing the fire were summarized.Water-based fire-extinguishing agents possess high cooling capacity and excellent anti-reflash performance for the fire.We believe this review could shed light on developing an efficient fire-extinguishing agent particularly designed for LIBs.
基金support by the National Key Researchand Development Program of China(2018YFBO104100).
文摘External short circuit(ESC)of lithium-ion batteries is one of the common and severe electrical failures in electric vehicles.In this study,a novel thermal modelis developed to capture the temperature behavior of batteries under ESC conditions.Experiments were systematically performed under different battery initial state of charge and ambient temperatures.Based on the experimental results,we employed an extreme learming machine(ELM)-based thermal(ELMT)model to depict battery temperature behavior under ESC,where a lumped-state thermal model was used to replace the activation function of conventional ELMs.To demonstrate the effectiveness of the proposed model,wecompared the ELMT model with a multi-lumped-state thermal(MLT)model parameterized by thegenetic algorithm using the experimental data from various sets of battery cells.It is shown that the ELMT model can achieve higher computa-tional efficiency than the MLT model and better fitting and prediction accuracy,where the average root mean squared error(RMSE)of the fitting is 0.65℃ for the ELMT model and 3.95℃ for the MLT model,and the RMES of the prediction under new data set is 3.97℃ for the ELMT model and 6.11℃ for the MLT model.
基金supported by the Ministry of Science and Technology of China under the contract No.2019YFE0100200the National Natural Science Foundation of China(grant Nos.51706117,52076121)funded by the Tsinghua Scholarship for Overseas Graduate Studies。
文摘Internal short circuit(ISC)is the major failure problem for the safe application of lithium-ion batteries,especially for the batteries with high energy density.However,how to quantify the hazard aroused by the ISC,and what kinds of ISC will lead to thermal runaway are still unclear.This paper investigates the thermal-electrical coupled behaviors of ISC,using batteries with Li(Ni_(1/3)CO_(1/3)Mn_(1/3))O_(2) cathode and composite separator.The electrochemical impedance spectroscopy of customized battery that has no LiPF6 salt is utilized to standardize the resistance of ISC.Furthermore,this paper compares the thermal-electrical coupled behaviors of the above four types of ISC at different states-of-charge.There is an area expansion phenomenon for the aluminum-anode type of ISC.The expansion effect of the failure area directly links to the melting and collapse of separator,and plays an important role in further evolution of thermal runaway.This work provides guidance to the development of the ISC models,detection algorithms,and correlated countermeasures.
基金supported by the National Natural Science Foundation of China(No.51976209)the Fundamental Research Funds for the Central Universities(No.WK2320000040)+1 种基金the Synchrotron Radiation Joint Fund of University of Science and Technology of Chinasupported by Youth Innovation Promotion Association CAS(No.Y201768)。
文摘By virtue of the crucial effect of the crystal structure and transition metal(TM)redox evolution on the performance of LiNi_(x)Co_(y)Mn_(z)O_(2)(NCM)cathode,systematical investigation is carried out to better understand the charge mechanism upon deep charging.Based on the results of X-ray diffraction and highresolution transmission electron microscope,phase transformations existing on particle surface are promoted by high potential because of the deeper lithium vacancies,accompanied by more substantial structure instability.Soft X-ray absorption spectroscopy indicates that Ni acts as the major contributor to charge compensation while Co displays a remarkable redox activity over the deep charge range.The elevated integrated intensity of pre-edge in O K-edge spectra reveals the extensive amount of holes formed in O 2 p orbitals and the enhanced hybridization of TM 3 d-O 2 p orbitals.Considering the close relationship between thermal behavior and structural evolution,the tendency of phase transitions and O_(2) release upon heating is accelerated by voltage rise,demonstrating the aggravated instability due to deeper Li utilization.Remaining Li contents in NCM are employed to estimate the amount of oxygen released in structural transformation and its detrimental effect on stability declares Li contentdependent characteristics.Furthermore,the extended Li vacancies,higher proportion of Ni4+and stronger orbital hybridization are considered as three factors impeding the thermal stability of the highlydelithiated NCM.
基金supported by the National Natural Science Foundation of China(No.51976209)the Fundamental Research Funds for the Central Universities(No.WK2320000040)supported by the Youth Innovation Promotion Association CAS(No.Y201768)。
文摘Based on the synchrotron soft X-ray absorption spectroscopy experiments,the fundamental electronic structures of layered Li NixCoyMnzO_(2)(NCM)are investigated systematically and the data of transitionmetal(TM)L-and O K-edges spectra are collected.Distribution of Ni ions under different oxidation states is evaluated according to linear combination fit.It is found that the ratio of Ni^(4+)expands with the increase of Ni since it dominates in charge compensation during charging,and that the existence of Ni^(3+)is nearly negligible in delithiated NCM.The valence state of Co also strongly depends on Ni content,the perceptible position shift of Co L_(3)-edge absorption peak towards higher energy in Ni-rich material agrees well with the small voltage plateau at around 4.2 V.The stability of Mn is verified as no obvious spectral change with the Mn L-edge is observed.Moreover,as Ni content rises,the O 2p holes near the Femi level increases with higher oxidation state of Ni,indicating the enhanced hybridization of O 2p-TM 3 d.Delithiated NCMs with higher Ni content are prior to lose electron existing in highly hybridized Ni3 dO 2 p bands upon heating,which accounts for the pronounced O_(2)release in phase transitions and the deterioration in thermal stability.These detailed observation of the electronic structure evolution is one of the key ingredients to improving the electrochemical and thermal performance of NCM.