Investigation on step overcharge to self-heating behavior and mechanism analysis of lithium ion batteries

To obtain intrinsic overcharge boundary and investigate overcharge mechanism,here we propose an innovative method,the step overcharge test,to reduce the thermal crossover and distinguish the overcharge thermal behavior,including 5%state of charge(SOC)with small current overcharge and resting until the temperature equilibrium under adiabatic conditions.The intrinsic thermal response and the self-excitation behaviour are analysed through temperature and voltage changes during the step overcharge period.Experimental results show that the deintercalated state of the cathode is highly correlated to self-heating parasitic reactions.Before reaching the upper limit of Negative/Positive(N/P)ratio,the temperature changes little,the heat generation is significantly induced by the reversible heat(endothermic)and ohmic heat,which could balance each other.Following that the lithium metal is gradually deposited on the surface of the anode and reacts with electrolyte upon overcharge,inducing selfheating side reaction.However,this spontaneous thermal reaction could be“self-extinguished”.When the lithium in cathode is completely deintercalated,the boundary point of overcharge is about 4.7 V(~148%SOC,>40℃),and from this point,the self-heating behaviour could be continuously triggered until thermal runaway(TR)without additional overcharge.The whole static and spontaneous process lasts for 115 h and the side reaction heat is beyond 320,000 J.The continuous self-excitation behavior inside the battery is attributed to the interaction between the highly oxidized cathode and the solvent,which leads to the dissolution of metal ions.The dissolved metal ions destroy the SEI(solid electrolyte interphase)film on the surface of the deposited Li of anode,which induces the thermal reaction between lithium metal and the solvent.The interaction between cathode,the deposited Li of anode,and solvent promotes the temperature of the battery to rise slowly.When the temperature of the battery reaches more than 60℃,the reaction between lithium metal and solvent is accelerated.After the temperature rises rapidly to the melting point of the separator,it triggers the thermal runaway of the battery due to the short circuit of the battery.

Overcharge-to-thermal-runaway behavior and safety assessment of commercial lithium-ion cells with different cathode materials:A comparison study

In this paper,overcharge behaviors and thermal runaway(TR)features of large format lithium-ion(Liion)cells with different cathode materials(LiFePO4(LFP),Li[Ni_(1/3)Co_(1/3)Mn_(1/3)]O_(2)(NCM111),Li[Ni_(0.6)Co_(0.2)Mn_(0.2)]O_(2)(NCM622)and Li[Ni_(0.8)Co_(0.1)Mn_(0.1)]O_(2)(NCM811))were investigated.The results showed that,under the same overcharge condition,the TR of LFP Li-ion cell occurred earlier compared with the NCM Li-ion cells,indicating its poor overcharge tolerance and high TR risk.However,when TR occurred,LFP Li-ion cell exhibited lower maximum temperature and mild TR response.All NCM Liion cells caught fire or exploded during TR,while the LFP Li-ion cell only released a large amount of smoke without fire.According to the overcharge behaviors and TR features,a safety assessment score system was proposed to evaluate the safety of the cells.In short,NCM Li-ion cells have better performance in energy density and overcharge tolerance(or low TR risk),while LFP Li-ion cell showed less severe response to overcharging(or less TR hazards).For NCM Li-ion cells,as the ratio of nickel in cathode material increases,the thermal stability of the cathode materials becomes poorer,and the TR hazards increase.Such a comparison study on large format Li-ion cells with different cathode materials can provide deeper insights into the overcharge behaviors and TR features,and provide guidance for engineers to reasonably choose battery materials in automotive applications.

Evolution of the morphology,structural and thermal stability of LiCoO_(2) during overcharge

The overcharge behaviors of 1000 m Ah LiCoO_(2)/graphite pouch cells are systematically investigated through the analysis of morphology,structural and thermal stability of LiCoO_(2) under different state of charge(SOC)of 120%,150%,174%,190%and 220%.The LiCoO_(2) experiences the phase transition from O3 to H1-3 and then O1 together with the grain breakage and boundary slip as evidenced by XRD and SEM analysis respectively,which results in the pronounced Co dissolution after the SOC of 174%.The impedance analysis of the pouch cells and coin cells demonstrates that the main contribution of impedance increase originates from the LiCoO_(2) electrode.Under the combined effect of structural collapse,Co dissolution,and electrolyte oxidization,the thermal stability of Li CoO_(2) cathode materials reduces with the progressing of overcharge as revealed by differential scanning calorimetry(DSC)results.We hope that this comprehensive understanding can provide meaningful guidance for advancing the overcharge performance of LiCoO_(2)/graphite pouch cells.

Effect of Overcharge on Electrochemical Performance of Sealed-Type Nickel/Metal Hydride Batteries

The effects of overcharge on electrochemical performance of AA size sealed-type nickel/metal hydride（Ni/MH） batteries and its degradation mechanism were investigated. The results indicated that the relationship between the effects of different overcharge currents on the increasing velocity of inner pressure and the degradation velocity of cycle life and discharge voltage remains in almost direct proportion. After overcharge cycles, the positive electrode materials remain the original structure, but there occur some breaks because of the irreversible expand of crystal lattice. And the negative electrode alloy particles have inconspicuous pulverization, but are covered with lots of corrosive products and its main component is rare earth hydroxide or oxide. These are all the main reasons leading to the degradation behavior of the discharge capacity and cycle life of Ni/MH batteries.

Overcharge to Remove Cathode Passivation Layer for Reviving Failed Li–O_(2)Batteries

Prolonging the lifetime of batteries is a long-term pursuit,and it is also one of the prerequisites for the practical application of batteries.However,this endeavor is challenging for high-energy Li–O_(2)batteries due to their poor charge efficiency and cathode passivation-induced by-products accumulation.Here,we demonstrated that overcharging Li–O_(2)batteries could facilitate the decomposition of accumulated residue products and revive the cathode;thus,the battery lifespan could be significantly extended.This long battery lifetime not only made full use of the Li anode but also enabled the battery to recycle in a safer way without the risk of firing and explosion.Furthermore,overcharge could be used in Li–O_(2)batteries with high mass loading,high rate,and large capacity.This overcharge strategy simplified the cathode regenerating procedures and realized system-level efficient use of battery components,thereby prolonging the life of Li–O_(2)batteries to meet the requirements of practical applications.

N-phenylmaleimide as a New Ploymerizable Additive for Overcharge Protection of Lithium-ion Batteries

1 Results In persuit of better safety controls of lithium batteries,much efforts has been focused on the development of the internal and self-actuating overcharge protection additives.We report a novel electropolymerizable electrolyte additive for overcharge protection of lithium batteries. Electrochemical properties and overcharge behavior of NPM as a new polymerizable electrolyte additive for overcharge protection of lithium ion batteries are studied by cyclic voltammetry,charge-discharge measurements...

Insight into the structural evolution and thermal behavior of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) cathode under deep charge

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.

Explosion behavior investigation and safety assessment of large-format lithium-ion pouch cells

Large-format lithium-ion(Li-ion) batteries with high energy density for electric vehicles are prone to thermal runaway(or even explosion) under abusive conditions. In this study, overcharge induced explosion behaviors of large-format Li-ion pouch cells with Li[NiCoMn]Ocathode at different current rates(C-rates)(0.5C, 1C, 2C) were investigated. The explosion characteristics of the cells were elucidated by discussing the evolution of the cell voltage, the surface temperature and the shock wave pressure.Generally, the whole overcharge process could be divided into four stages according to the evolution of several key parameters and the overcharge behaviors;the overcharge C-rate has a great influence on cells’ thermal behaviors. The experimental results showed that the thermal runaway process of Liion cells caused by overcharging consisted of two kinds of explosions, physical explosion and chemical explosion. The existence of observable negative pressure zone in the pressure curves indicated that the Li-ion cells are not a self-supplying oxygen system during the explosion. Further, the explosion dynamics parameters were matched. An explosion TNT-equivalent conversion strategy that depended on the pressure of the shock wave was utilized to evaluate the released energy and its hazards. In addition, with respect to the overcharge of Li-ion pouch cells, a safety assessment method and a safety management method were proposed based on the explosion behaviors. From the perspective of battery safety, this study is of great significance for the safety design of Li-ion cells and can provide guidance for engineers to optimize the safety function of battery packs.

Impact of evolution of cathode electrolyte interface of Li(Ni0.8Co0.1Mn0.1)O2 on electrochemical performance during high voltage cycling process

In this work, the electrochemical performance of LiNi0.8Co0.1Mn0.1O2(NCM811) has been investigated after cycling with various upper cutoff voltages. Noteworthily, electrochemical impedance of NCM811 declined with the increasing cycle number to high voltages. It was found that the decline of charge transfer impedance could be related to the structural and compositional change of cathode electrolyte interphase(CEI) of NCM811 when charging to high voltages, based on the characterization of electrochemical impedance spectroscopy(EIS), X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). The corresponding mechanism has also been proposed in this study. Specifically, due to the increasing roughness of cathode surface, the bottom of CEI film and cubic phase on cathode surface form a transition region mainly at high voltages, leading to the nonobvious boundary. This newly formed transition region at high voltages could promote the Li ion diffusion from electrolyte to cathode, then reducing charge transfer impedance. Additionally, the decrease of Li F on the surface of the cathode could also make a contribution to lower the interface impedance. This study delivers a different evolution of CEI on NCM811, and the impact of CEI evolution on electrochemical performance when charging to a high voltage.

Influences of multi factors on thermal runaway induced by overcharging of lithium-ion battery

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.

Symmetrizing cathode-anode response to speed up charging of nanoporous supercapacitors

Asymmetric behaviors of capacitance and charging dynamics in the cathode and anode are general for nanoporous supercapacitors.Understanding this behavior is essential for the optimal design of supercapacitors.Herein,we perform constant-potential molecular dynamics simulations to reveal asymmetric features of porous supercapacitors and their effects on capacitance and charging dynamics.Our simulations show that,counterintuitively,charging dynamics can be fast in pores providing slow ion diffusion and vice versa.Unlike electrodes with singlesize pores,multi-pore electrodes show overcharging and accelerated co-ion desorption,which can be attributed to the subtle interplay between the dynamics and charging mechanisms.We find that capacitance and charging dynamics correlate with how the ions respond to an applied cell voltage in the cathode and anode.We demonstrate that symmetrizing this response can help boost power density,which may find practical applications in supercapacitor optimization.

Self-actuating protection mechanisms for safer lithium-ion batteries

Safety issue is still a problem nowadays for the large-scale application of lithium-ion batteries(LIBs)in electric vehicles and energy storage stations.The unsafe behaviors of LIBs arise from the thermal run-away,which is intrinsically triggered by the overcharging and overheating.To improve the safety of LIBs,various protection strategies based on self-actuating reaction control mechanisms(SRCMs)have been proposed,including redox shuttle,polymerizable monomer additive,potential-sensitive separator,thermal shutdown separator,positive-temperature-coefficient electrode,thermally polymerizable addi-tive,and reversible thermal phase transition electrolyte.As build-in protection mechanisms,these meth-ods can sensitively detect either the temperature change inside battery or the potential change of the electrode,and spontaneously shut down the electrode reaction at risky conditions,thus preventing the battery from going into thermal runaway.Given their advantages in enhancing the intrinsic safety of LIBs,this paper overviews the research progresses of SRCMs after a brief introduction of thermal runaway mechanism and limitations of conventional thermal runaway mitigating measures.More importantly,the current states and issues,key challenges,and future developing trends of SRCTs are also discussed and outlined from the viewpoint of practical application,aiming at providing insights and guidance for developing more effective SRCMs for LIBs.

Consumer Entry: Impact on Expert's Pricing and Overcharging Behavior

In a credence goods market,a consumer(he)is unaware of his true need,w hich can be either intense or minor.A n expert(she)designs a menu that either charges a u n iform price to both services,termed pooling pricing,or varies charges according to service types,termed differential pricing.Learning the menu offered by the expert and anticipating her behavior in serving consumers,a consumer weighs the expected u tility of service provision against the cost incurred in transportation to decide w hether to visit the expert,termed entry decision.Upon arrival of a consumer,the expert discerns his true need and recommends a service along w ith the associated charge.Under the lia b ility assumption,the expert provides a service to satisfy the consumer's need.However,the consumer is unable to discern the nature of the service actually provided.This can induce the expert w ho adopts differential pricing to recommend intense service to a consumer w ith m inor need,termed overcharging.We investigate the effects of consumers'entry decision on the expert's optim al pricing strategy and the occurrence of overcharging,and study the robustness of the main results to practical features.

Thermodynamics and overcharging problem in extended phase space of charged AdS black holes with cloud of strings and quintessence under charged particle absorption

The thermodynamics and overcharging problem in RN-AdS black holes with a cloud of strings and quintessence are investigated by the absorption of scalar particles and fermions in extended phase space.The cosmological constant is treated as the pressure of the black hole.The parameters related to quintessence and the cloud of strings are treated as thermodynamic variables.We find that the first law of thermodynamics is satisfied and the second law of thermodynamics is indefinite.Furthermore,we find that near-extremal and extremal black holes cannot be overcharged.