Performance and capacity fading reason of LiMn_2O_4/graphite batteries after storing at high temperature

Spinel LiMn204 was synthesized by a solid-state method. A 204468-size battery was fabricated and stored at 55℃. The structure and morphology of the LiMn204 cathode were analyzed by X-ray diffraction （XRD） and scanning electron microscopy （SEM） technique. Energy dispersive spectroscopy （EDS） was used to analyze the surface component of the carbon anode. The discharge capacities of LiMn204 stored for 0, 24, 48, and 96 h are 106, 98, 96, and 92 mAh·g^-1, respectively. The cyclic performance is improved after storage. The capacity retentions of LiMn204 stored for 0, 24, 48, and 96 h are 83.8%, 85.8%, 86.9%, and 88.6% after 180 cycles. The intensity of all the LiMn204 diffraction peaks is weakened. Mn is detected from the carbon electrode when the battery is stored for 96 h. Cyclic voltammograms and electrochemical impedance spectroscopy （EIS） were used to examine the surface state of the electrode after storage. The results show that the resistance and polarization of LiMn2O4/electrolyte is increased after storage, which is responsible for the fading of capacity.

Capacity fading of spinel LiMn_2O_4 during cycling at elevated temperature

A normal spinel LiMn_2O_4 as cathode material for lithium-ion cells wascycled galvanostatically (0.2 C) at 55 deg C. To determine the contribution of each voltage plateauto the total capacity fading of the cathode upon repeated cycling, the capacities in each plateauwere separated by differentiation of voltage vs. capacity. The results how that the capacity fadingin the upper voltage plateau is more rapidly than that in the lower during discharging, while incharging process, it fades slower than that in the lower voltage range. The increased capacity shiftand aggravated self-discharge/electrolyte oxidation during discharging contribute to a high fadingrate in the upper step. Capacity shift also takes place during charging process, which againenhancing the fading rate of the lower voltage plateau. An increase in capacity shift, as a resultof an increase in polarization of the cell, plays a major role in determining the fading rate ineach voltage plateau, further reflecting the thickening of the passivation layer on the activeparticles, and the accumulation of electrolyte decomposition. The relative capacity loss formodified spinels is well correlated with the relative increase in the polarization of thehalf-cells, confirming the above causes for capacity fade of this kind of cathode material.

Mechanism of Capacity Fading Caused by Mn(Ⅱ)Deposition on Anodes for Spinel Lithium Manganese Oxide Cell

The capacity fade of spinel lithium manganese oxide in lithium-ion batteries is a bottleneck challenge for the large-scale application.The traditional opinion is that Mn（Ⅱ） ions in the anode are reduced to the metallic manganese that helps for catalyzing electrolyte decomposition.This could poison and damage the solid electrolyte interface（SEI） film,leading to the the capacity fade in Li-ion batteries.We propose a new mechanism that Mn（Ⅱ） deposites at the anode hinders and/or blocks the intercalation/de-intercalation of lithium ions,which leads to the capacity fade in Li-ion batteries.Based on the new mechanism assumption,a kind of new structure with core-shell characteristic is designed to inhabit manganese ion dissolution,thus improving electrochemical cycle performance of the cell.By the way,this mechanism hypothesis is also supported by the results of these experiments.The LiMn2-xTixO4 shell layer enhances cathode resistance to corrosion attack and effectively suppresses dissolution of Mn,then improves battery cycle performance with LiMn_2O_4 cathode,even at high rate and elevated temperature.

Revisiting the capacity-fading mechanism of P2-type sodium layered oxide cathode materials during high-voltage cycling

P2-type sodium layered oxide cathode (Na_(2/3)Ni_(1/3)Mn_(2/3)O_(2)P2-NNMO) has attracted great attention as a promising cathode material for sodium ion batteries because of its high specific capacity. However, this material suffers from a rapid capacity fade during high-voltage cycling. Several mechanisms have been proposed to explain the capacity fade, including intragranular fracture caused by the P2-O2 phase transion, surface structural change, and irreversible lattice oxygen release. Here we systematically investigated the morphological, structural, and chemical changes of P2-NNMO during high-voltage cycling using a variety of characterization techniques. It was found that the lattice distortion and crystal-plane buckling induced by the P2-O2 phase transition slowed down the Na-ion transport in the bulk and hindered the extraction of the Na ions. The sluggish kinetics was the main reason in reducing the accessible capacity while other interfacial degradation mechanisms played minor roles. Our results not only enabled a more complete understanding of the capacity-fading mechanism of P2-NNMO but also revealed the underlying correlations between lattice doping and the moderately improved cycle performance.

Origin of Capacity Fading for Nano-grains Based Electrodes of Li Rechargeable Batteries

1 Results Li1+xV3O8,has been extensively investigated as a positive electrode material for lithium metal polymer batteries and a great deal of interest has been focused on the structural characterization and cyclability of this compound[1-6].From the present work,Li1.1V3O8 nanograins synthesized at low temperature from original two component gel precursor suffer from strong capacity fading on cycling.The latter is characterized by emergence of polarized redox processes at the expense of initial ones.Fro...

Enhanced reversible capacity of Li-S battery cathode based on graphene oxide

Lithium sulfur battery （LSB） offers several advantages such as very high energy density, low-cost, and environmental-friendliness. However, it suffers from serious degradation of its reversible capacity because of the dissolution of reaction intermediates, lithium polysulfides, into the electrolyte. To solve this limitation, there are many studies using graphene-based materials due to their excellent mechanical strength and high conductivity. Compared with graphene, graphene oxide （GO） contains various oxygen functional groups, which enhance the reaction with lithium polysulfides. Here, we investigated the positive effect of using GO mixed with carbon black on the performance of cathode in LSB. We have observed a smaller drop of capacity in GO mixed sulfur cathode. We further demonstrate that the mechanistic origin of reversibility improvement, as confirmed through CV and Raman spectra, can be explained by the stabilization of sulfur in lithium polysulfide intermediates by oxygen functional groups of GO to prevent dissolution. Our findings suggest that the use of graphene oxide-based cathode is a promising route to significantly improve the reversibility of current LSB.

Mechanical behavior analysis of high power commercial lithium-ion batteries

In application,lithium-ion cells undergo expansion during cycling.The mechanical behavior and the impact of external stress on lithium-ion battery are important in vehicle application.In this work,18 Ah high power commercial cell with Li Ni_(0.5)Co_(0.2)Mn_(0.3)O_(2)/graphite electrode were adopted.A commercial compress machine was applied to monitor the mechanical characteristics under different stage of charge(SOC),lifetime and initial external force.The dynamic and steady force was obtained and the results show that the dynamic force increases as the SOC increasing,obviously.During the lifetime with high power driving mode,different external force is shown to have a great impact on the long-term cell performance,with higher stresses result in higher capacity decay rates and faster impedance increases.A proper initial external force(900 N)provides lower impedance increasing.Postmortem analysis of the cells with2000 N initial force suggests a close correlation between electrochemistry and mechanics in which higher initial force leads to higher direct current internal resistance(DCIR)increase rate.In addition,for the cell with higher external force,deformation of the cathode and thicker solid electrolyte interface(SEI)film on the surface of anode and separator are observed.Porosity reduction and closure was also verified after cycles which is an obstacle to the lithium ion transferring.The largest cause of the observed capacity decline was the loss of active lithium through autopsy analysis.In addition,for the cell with higher external force,deformation of the cathode and thicker SEI film on the surface of anode and separator are observed.Porosity reduction and closure was also verified after cycles which is an obstacle to the lithium ion transferring.The largest cause of the observed capacity decline was the loss of active lithium through autopsy analysis.

Mn-based MXene with high lithium-ion storage capacity

3d-transition metal(Fe,Co,Ni,and Mn)-based MXene materials have been predicted to demonstrate exceptional electrochemical performance because of their good electrical conductivity and the presence of metallic atoms with multiple charge states.However,until now,there have been no reports on MXenes based on Fe,Co,Ni,and Mn,due to the lack of 3d-metal-layered precursors.Herein,we successfully synthesized the first 3d-transition metal-based MXenes,Mn_(2)CT_(x) by exfoliating a layered precursor derived from the anti-perovskite bulk Mn3GaC.The as-prepared Mn_(2)CT_(x) MXene nanosheets were employed as anode materials in lithium-ion batteries,which exhibited stable storage capacity of 764.7 mAh·g^(-1) at 0.5 C,placing its storage capacities at an upper-middle level compared with other reported MXene materials as well as other Mn-based anode materials.Overall,this study opens a new avenue for MXene research by synthesizing 3d-transition metal-based MXenes for electrochemical applications.

Influence of Sc^(3+) on LiMn_2O_4 cathode materials at elevated temperature

Sc^3＋-doped lithium manganese oxides were synthesized by solid-state reaction. The influences of doping element on structure, mean valence of manganese, and electrochemical performances were studied by X-ray diffraction （XRD）, galvanostatic charge-discharge and cyclic voltammetric tests, and also electrochemical impedance spectroscopy （EIS）. XRD tests showed that doped lithium manganese oxides were pure spinel structure without other phases. Redox titration and visible spectrophotometry tests indicated that the mean valence of manganese in doped lithium manganese oxides was higher than that of pure one. LiSc0.02Mn1.9804 remained 92.9% of the initial specific discharge capacity after 50th cycle at a constant current of 50 m/g, and the reversibility of LiSc0.02Mn1.98O4 was improved in comparison with pure LiMn2O4 at 50 ℃. EIS indicated that film deposition on spinel particles was suppressed because of Sc^3＋ doping, and the charge transfer between the surface film and spinel particles with increasing temperature for Sc^3＋-doped materials became easier as compared with undoped one.

Li-rich layered oxides:Structure,capacity and voltage fading mechanisms and solving strategies

Lithium rich layered oxides(LLOs)are attractive cathode materials for Li-ion batteries owing to their high capacity(>250 mA h g^(-1))and suitable voltage(∼3.6 V).However,they suffer from serious voltage and capacity fading,which is focused in this review.First,an overview of crystal structure,band structure and electrochemical performances of LLOs is provided.After that,current understanding on oxygen loss,capacity fading and voltage fading is summarized.Finally,five strategies to mitigate capacity and voltage fading are reviewed.It is believed that these understandings can help solve the fading problems of LLOs.

Effects of long-term fast charging on a layered cathode for lithium-ion batteries

Fast charging, which aims to shorten recharge times to 10–15 min, is crucial for electric vehicles(EVs),but battery capacity usually decays rapidly if batteries are charged under such severe conditions.Revealing the failure mechanism is a prerequisite to improving the charging performance of lithium(Li)-ion batteries. Previous studies have focused less on cathode materials while also mostly focusing on their early changes. Thus, the cumulative effect of long-term fast charging on cathode materials has not been fully studied. Here, we study the changes in a layered cathode material during 1000 cycles of 6 C charging based on 1.6 Ah LiCoO_(2)/graphite pouch cells. Postmortem analysis reveals that the surface structure, charge transfer resistance and Li-ion diffusion coefficient of the cathode degenerate during repeated fast charging, causing a large increase in polarization. This polarization-induced poor utilization of the Li inventory is an important reason for the rapid capacity fading of batteries. These findings deepen the understanding of the aging mechanism for cells undergoing fast charging and can be used as benchmarks for the future development of high-capacity, fast-charging layered cathode materials.

水锌离子电池用钒基正极材料的低电流密度稳定性

Vanadium-based cathodes have received widespread attention in the field of aqueous zinc-ion batteries,presenting a promising prospect for stationary energy storage applications.However,the rapid capacity decay at low current densities has hampered their development.In particular,capacity stability at low current densities is a requisite in numerous practical applications,typically encompassing peak load regulation of the electricity grid,household energy storage systems,and uninterrupted power supplies.Despite possessing notably high specific capacities,vanadium-based materials exhibit severe instability at low current densities.Moreover,the issue of stabilizing electrode reactions at these densities for vanadium-based materials has been explored insufficiently in existing research.This review aims to investigate the matter of stability in vanadium-based materials at low current densities by concentrating on the mechanisms of capacity fading and optimization strategies.It proposes a comprehensive approach that includes electrolyte optimization,electrode modulation,and electrochemical operational conditions.Finally,we presented several crucial prospects for advancing the practical development of vanadium-based aqueous zinc-ion batteries.

Modeling and SOC estimation of lithium iron phosphate battery considering capacity loss

Modeling and state of charge(SOC)estimation of Lithium cells are crucial techniques of the lithium battery management system.The modeling is extremely complicated as the operating status of lithium battery is affected by temperature,current,cycle number,discharge depth and other factors.This paper studies the modeling of lithium iron phosphate battery based on the Thevenin’s equivalent circuit and a method to identify the open circuit voltage,resistance and capacitance in the model is proposed.To improve the accuracy of the lithium battery model,a capacity estimation algorithm considering the capacity loss during the battery’s life cycle.In addition,this paper solves the SOC estimation issue of the lithium battery caused by the uncertain noise using the extended Kalman filtering(EKF)algorithm.A simulation model of actual lithium batteries is designed in Matlab/Simulink and the simulation results verify the accuracy of the model under different operating modes.

Surface engineering of Li-and Mn-rich layered oxides for superior Li-ion battery

The Li-and Mn-rich layered oxides(R-LNCM)are considered as promising cathode materials for high-energy density lithium-ion batteries(LIBs).However,the interface side reaction aggravates the voltage and capacity fading between cathode material and electrolyte at high voltage,which severely hinders the practical application of LIB s.Herein,lithium polyacrylate(LiPAA)as the binder and coating agent is applied to suppress the voltage and capacity fading of R-LNCM electrode.The flexible LiPAA layers with high elasticity are capable of impeding cathode cracks on the particle surface via mechanical stress relief.Thus,superior voltage and capacity fading suppression on R-LNCM electrode is finally achieved.As a result,LiPAA-R-LNCM cathode exhibits a remarkable specific capacity of 186 mA·h·g^(-1)with~73%retention at 1℃after 200cycles.Further,the corresponding average discharge potential is maintained to~3.1 V with only~0.4 V falling.

A modeling and experimental study of capacity fade for lithium-ion batteries

Lithium-ion batteries are extensively used in electric vehicles,however,their significant degradation over dis-charge and charge cycles results in severe capacity fade,limiting driving ranges of electric vehicles over time and useful lifetime of batteries.In this study,capacity fade for lithium-ion battery has been investigated through modeling and experiment.A predictive model is developed based on first principles incorporating degradation mechanisms.The mechanisms of degradation considered include solid-electrolyte interface(SEI)growth and ac-tive material loss at both negative and positive electrodes.Battery performance including capacity is measured experimentally under discharge and charge cycling with battery operation temperature controlled.It is shown that battery capacity is reduced over battery discharge/charge cycling at a given battery operation temperature,and the model predicted battery performance,including capacity fade,agrees well with the experimental results.As the number of discharge/charge cycles are increased,battery capacity is reduced significantly;battery ca-pacity fade is increased substantially when battery operation temperature is increased,indicating significantly accelerated aging of the battery at elevated operation temperatures and hence the importance of battery thermal management in the control of battery operation temperature for practical applications such as electric vehicles.Battery capacity fade is mainly caused by SEI film growth at the negative electrode,which is the largest contribut-ing factor to the capacity fade,and the active material isolation at the negative electrode,which is the second largest influencing aging factor.

Electrochemical properties of high-loading sulfur–carbon materials prepared by in situ generation method

A high sulfur content sulfur–carbon composite was synthesized via in situ generation method in aqueous solution.When the sulfur loading is up to 90%,the electrode still exhibits good cycling performance with a reversible capacity of about 623 mAh·g^(-1)after 100 cycles.To further commercialize the Li–S battery,understanding the capacity degradation mechanism is very essential,especially with a high sulfur loading electrode.To achieve this goal,the electrochemical performance of the high sulfur loading electrode was studied,and the structure change of the electrode after cycling was also examined by ex situ scanning electron microscopy(SEM)and other techniques.The result shows that the Li_(2)S_(2)and Li_(2)S inhomogeneous precipitation contributes to the majority capacity fading of the high sulfur loading Li–S cells.

Room-temperature metal-sulfur batteries:What can we learn from lithium-sulfur?

Rechargeable metal-sulfur batteries with the use of low-cost sulfur cathodes and varying choice of metal anodes(Li,Na,K,Ca,Mg,and Al)represent diverse energy storage solutions to satisfy different application requirements.In comparison to the highly-regarded lithium-sulfur batteries,the use of nonlithium-metal anodes in metal-sulfur batteries offers multiple advantages in terms of abundance,cost,and volumetric energy density.Although with the same sulfur cathode,metal-sulfur batteries show considerably differences in the electrochemical reaction pathway and capacity fading mechanism.Herein,we provide an overview of correlations and differences in metal-sulfur batteries,highlighting the knowledge and experience that can be transplanted from lithium-sulfur to other metal-sulfur batteries.We first discuss the historical development and the electrochemical reaction mechanism of various metal-sulfur batteries.This is then followed by an analysis of key challenges of metal-sulfur batteries including polysulfide shutting,cathode passivation,and anode stability.Finally,a short perspective is presented about the possible future development of metal-sulfur batteries.

A Novel Method to Improve the Electrochemical Performance of LiMn_2O_4 Cathode Active Material by CaCO_3 Surface Coating

Spinel LiMn204 was synthesized by glycine-nitrate method and coated with CaCO3 in order to enhance the electrochemical performance at room temperature （25℃） and 55℃. The uncoated and CaCO3-coated LiMn204 materials were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electrochemical tests. XRD and SEM results indicated that CaCO3 particles encapsulated the surface of the LiMn204 without causing any structural change. The charge-discharge tests showed that the specific discharge capacity fade of pristine electrode at 25 and 55℃ were 25.5% and 52%, respectively. However, surface modified cathode shows 7.4% and 29.5% loss compared to initial specific discharge capacity at 70th cycle for 25 and 55~C, respectively. The improvement of electrochemical performance is attributed to suppression of Mn2＋ dissolution into electrolyte via CaCO3 layer.

A Comparative Study of Charging Voltage Curve Analysis and State of Health Estimation of Lithium-ion Batteries in Electric Vehicle

Lithium-ion(Li-ion)cells degrade after repeated cycling and the cell capacity fades while its resistance increases.Degra-dation of Li-ion cells is caused by a variety of physical and chemical mechanisms and it is strongly influenced by factors including the electrode materials used,the working conditions and the battery temperature.At present,charging voltage curve analysis methods are widely used in studies of battery characteristics and the constant current charging voltage curves can be used to analyze battery aging mechanisms and estimate a battery’s state of health(SOH)via methods such as incremental capacity(IC)analysis.In this paper,a method to fit and analyze the charging voltage curve based on a neural network is proposed and is compared to the existing point counting method and the polynomial curve fitting method.The neuron parameters of the trained neural network model are used to analyze the battery capacity relative to the phase change reactions that occur inside the batteries.This method is suitable for different types of batteries and could be used in battery management systems for online battery modeling,analysis and diagnosis.