Battery Swelling Research Articles

Enhancing performance and longevity of solid-state zinc-iodine batteries with fluorine-rich solid electrolyte interphase

Rechargeable zinc-iodine (ZnI2) batteries have gained popularity within the realm of aqueous batteries due to their inherent advantages, including natural abundance, intrinsic safety, and high theoretical capacity. However, challenges persist in their practical applications, notably battery swelling and vulnerability in aqueous electrolytes, primarily linked to the hydrogen evolution reaction and zinc dendrite growth. To address these challenges, this study presents an innovative approach by designing a solid-state ZnI2 battery featuring a solid perfluoropolyether based polymer electrolyte. The results demonstrate the formation of a solid electrolyte interphase layer on zinc, promoting horizontal zinc growth, mitigating dendrite penetration, and enhancing battery cycle life. Moreover, the solid electrolyte hinders the iodine ion shuttle effect, reducing zinc foil corrosion. Symmetric batteries employing this electrolyte demonstrate excellent cycle performance, maintaining stability for approximately 5000 h at room temperature, while solid-state ZnI2 batteries exhibit over 7000 cycles with a capacity retention exceeding 72.2%. This work offers a promising pathway to achieving reliable energy storage in solid-state ZnI2 batteries and introduces innovative concepts for flexible and wearable zinc batteries.

Designing PVdF-HFP/BTO Piezoelectric Sensor based Sensing System for Detecting Volume Expansion of Battery Cell

Piezoelectric sensor can be used to inform the battery safety by detecting the battery swelling induced pressure. In this study, a piezoelectric sensing material, sensor unit, and sensing system were developed using piezoelectric polymer polyvinylidene fluoride-co-hexafluoropropylene(PVdF-HFP) and piezoelectric ceramic BaTiO<sub>3</sub>(BTO). Free-standing PVdF-HFP/BTO composite nanofiber web was retrieved as the sensing material due to the nanofiber web-based flexibility and the molecular arrangement driven piezoelectric performances. The PVdF-HFP/BTO composite nanofiber web-based sensor was employed in the automatic pressure sensing system, which provides the visual and audible signals once the pressure exceeds a certain limit. Our work demonstrates that the design of new piezoelectric sensing system is a fruitful pathway to sensing the battery malfunctions.

Electrolyte design combining fluoro- with cyano-substitution solvents for anode-free Li metal batteries

Fluoro-substitution solvents have achieved great success in electrolyte engineering for high-energy lithium metal batteries, which, however, is beset by low solvating power, thermal and chemical instability, and possible battery swelling. Instead, we herein introduce cyanogen as the electron-withdrawing group to enhance the oxidative stability of ether solvents, in which cyanogen and ether oxygen form the chelating structure with Li+ not notably undermining the solvating power. Cyano-group strongly bonds with transition metals (TMs) of NCM811 cathode to attenuate the catalytic reactivity of TMs toward bulk electrolytes. Besides, a stable and uniform cathode-electrolyte interphase (CEI) inhibits the violent oxidation decomposition of electrolytes and guarantees the structural integrity of the NCM811 cathode. Also, a N-containing and LiF-rich solid-electrolyte interphase (SEI) in our electrolyte facilitates fast Li+ migration and dense Li deposition. Accordingly, our electrolyte enables a stable cycle of Li metal anode with Coulombic efficiency of 98.4% within 100 cycles. 81.8% capacity of 4.3 V NCM811 cathode remains after 200 cycles. Anode-free pouch cells with a capacity of 125 mAh maintain 76% capacity after 100 cycles, corresponding to an energy density of 397.5 Wh kg-1.

Battery Venting Caused By Fast Charging

Lithium-ion batteries (LIBs) experience high risks of failure during unreasonable fast charging. Various degradation mechanisms inside the LIBs such as lithium (Li) plating, solid electrolyte interphase growth and electrolyte dry-out can undermine the electrochemical performance and induce massive gas generation alongside the operation. As a typical failure behaviour, venting occurs when the internal pressure of battery cell exceeds the safety threshold, releasing the gaseous products as well as depressurizing the cell. Recent studies1–3 of thermal runaway (TR) tests after fast charging have found that accumulated plated Li can react with electrolyte at elevated external temperatures, decreasing both self-heating and onset temperatures of TR. Yet, how fast-charging degradation will affect battery venting behaviours remains unclear.To answer this question, in this study, a series of fast charging experiments under controlled cooling as well as adiabatic TR tests were conducted with 51 Ah LiNi0.6Mn0.2Co0.2O2/graphite prismatic LIBs. The results showed that the prismatic battery underwent severe Li plating with over 30% capacity fade after 10 cycles of 4C charging. In the adiabatic TR tests, the aged batteries after 4C charging exhibited lower self-heating temperature and venting temperature as compared to the fresh batteries, by 51 ℃ and 34.4 ℃ respectively. This can be explained by the additional gas generation from the reaction between plated Li and electrolyte in the fast-charged batteries. Gas analyses of 120 ℃ hot-box tests for the degraded anodes with the electrolyte showed that the vented gas at the early venting stage primarily consisted of carbon dioxide, carbon monoxide and ethylene. The same charging protocols were then conducted in a natural convection thermal chamber with poor heat dissipation, where the temperature rise was much higher than those under forced convection as expected. Excessive cycling operations with off-limit charge rates (5C and 5.6C) were observed to directly cause battery swelling and venting without TR, and the temperature decreasing rates during rest after each charging process tend to slow down and even remain stable during a certain period of time. This indicates that the exothermic reaction between plated Li and electrolyte can be directly triggered by fast charging if heat removal is not effective enough. The findings provide useful insights into battery venting induced by fast charging, which can shed light on battery safety evaluation for fast charging techniques.Acknowledgements:This work is supported by the Faraday Institution BESAFE project (FIRG038), the Imperial College President’s PhD Scholarship Scheme (funded by EPSRC), the National Natural Science Foundation of China (Grant No. 52207241), China National Postdoctoral Program for Innovative Talents (grant no. BX20220171), China Postdoctoral Science Foundation (grant no. 2022M711760), and Shuimu Tsinghua Scholar Program (grant no. 2021SM130).

Direct venting during fast charging of lithium-ion batteries

Lithium-ion batteries pose high risks of failure when subjected to fast charging due to accumulated degradation from side reactions. Venting is a common failure behaviour that results in the release of gases and depressurization. However, the connection between fast-charging degradation and venting characteristics remains unclear. In this study, fast-charging experiments are conducted on LiNi0.6Mn0.2Co0.2O2 (NMC622)/graphite prismatic cells (51 Ah) with controlled cooling, followed by adiabatic thermal runaway tests. The degraded cell, after 4C charging, shows venting at a temperature 34.4 °C lower than a fresh cell. Gas analysis of the degraded anode-electrolyte partially reactive system in hot-box tests reveals that the reaction between plated lithium and electrolyte was a primary contributor to the additional gases. The fast-charging protocols are conducted under natural convection with less heat dissipation, causing battery swelling and venting without thermal runaway when subjected to excessive cycling at off-limit charge rates (5C and 5.6C). The temperature decreasing rates during rest after each charging process slow down or stabilize for a certain period, highlighting the role of exothermic side reactions. This experimentally demonstrates that venting failures can be directly triggered by the exothermic, gas generating reaction during fast charging. These findings inform future designs for safe and rapid battery charging.

Acid- and Gas-Scavenging Electrolyte Additive Improving the Electrochemical Reversibility of Ni-Rich Cathodes in Li-Ion Batteries.

In view of their high theoretical capacities, nickel-rich layered oxides are promising cathode materials for high-energy Li-ion batteries. However, the practical applications of these oxides are hindered by transition metal dissolution, microcracking, and gas/reactive compound formation due to the undesired reactions of residual lithium species. Herein, we show that the interfacial degradation of the LiNi0.9CoxMnyAlzO2 (NCMA, x + y + z = 0.1) cathode and the graphite (Gr) anode of a representative Li-ion battery by HF can be hindered by supplementing the electrolyte with tert-butyldimethylsilyl glycidyl ether (tBS-GE). The silyl ether moiety of tBS-GE scavenges HF and PF5, thus stabilizing the interfacial layers on both electrodes, while the epoxide moiety reacts with CO2 released by the parasitic reaction between HF and Li2CO3 on the NCMA surface to afford cyclic carbonates and thus suppresses battery swelling. NCMA/Gr full cells fabricated by supplementing the baseline electrolyte with 0.1 wt % tBS-GE feature an increased capacity retention of 85.5% and deliver a high discharge capacity of 162.9 mAh/g after 500 cycles at 1 C and 25 °C. Thus, our results reveal that the molecular aspect-based design of electrolyte additives can be efficiently used to eliminate reactive species and gas components from Li-ion batteries and increase their performance.

Influence of swelling on the safety aspects of electric vehicle batteries – Short Review

In transportation sector, electric vehicles (EV) are found to offer more attentions due to its efficiency, pollution free, less maintenance over the conventional fuel-burnt vehicles. In EVs the cost, performance, and safety are all associated to its batteries. Among various types of batteries, lithium-ion battery (LIB) is predominantly used in EVs for its large energy density, long lifespan however safety of LIB is the daunting part. To overcome the catastrophic fault conditions of batteries different safety measures are employed in EVs. One of the accurate and viable methods to predict battery fault is observed to be the battery swelling effect. In the present work, various aspects of swelling effect on battery components for their safety measurements are discussed referring the very recent studies published in the literature. The key aspects of the work include physical and chemical properties; gas formation in battery under fault conditions; protective switch in order to improve and predict LIB safety.

Defective nano-structure regulating C-F bond for lithium/fluorinated carbon batteries with dual high-performance

Lithium/fluorinated carbon (Li/CFx) batteries show significant potential owing to high energy density and long-term storage performance. Restricted to the mutual restriction of F/C ratio and conductivity, the high energy density and power density cannot be achieved simultaneously. Herein, fluorinated honeycomb N-doped graphene (F-HNG) with conductive C-F bond was regulated by structural and heteroatomic defects, which was fabricated by nanoscale etching, NH3 treatment and gas phase fluorination. The unique pore provided smooth channels and storage sites for Li+ migration, while N atom with more electronegativity further regulated the charge distribution of the carbon skeleton. F-HNG delivered dual excellent electrochemical performance of a maximum energy density of 2595.47 Wh kg-1, associated with the unprecedented power density of 73.203 kW kg-1 at an ultrahigh rate of 50 C. Li/F-HNG pouch cell achieved an energy density of 707.52 Wh kg-1 with a mass loading of 10–15 mg cm-2 and reduced the heat release and battery swelling. In-depth density functional theory (DFT) calculations revealed that synergistic effect of porosity and N-doping regulated its C-F bond configuration, thermodynamic parameters, and ion diffusion pathway. This work indicates that nano-defect engineering and heteroatomic doping provide innovative possible directions for the design of CFx cathodes with dual superior performance.

An experimental study on the mechanical characteristics of Li‐ion battery during overcharge‐induced thermal runaway

Lithium batteries are prone to swelling during overcharge, which leads to a huge external force in modules and poses a potential threat to electric vehicles. Therefore, it is extremely important to understand the swelling mechanism of lithium batteries in-depth. In this paper, expansion force evolution during overcharge-induced thermal runaway process for large format lithium-ion battery with Li(Ni0.5Co0.2Mn0.3)O2 cathode is investigated. The rupture of the battery shell due to huge swelling is proved as the trigger of the thermal runaway event. In detail, the expansion force increases dramatically with the state of charge, which can be up to 3400 N. And it is a highly dynamic quantity with four obvious inflection points during overcharge, indicating a strong relationship with failure mechanisms. The inherent failure mechanism behind expansion force is investigated using both in-situ and ex-situ measurement techniques. The results revealing that the early abnormal expansion of the battery is caused by lithium dendrite and lithium plating. The rapid expansion mainly caused by CO, which is produced by incomplete electrolyte oxidation, leads to the rupture of the battery shell and thermal runaway events. This paper aims to unravel the mystery of lithium battery swelling during overcharge and provide valuable guidance to mitigate the overcharge risk induced by battery swelling.

The Formation, Detriment and Solution of Residual Lithium Compounds on Ni-Rich Layered Oxides in Lithium-Ion Batteries

Ni-rich layered transition-metal oxides with high specific capacity and energy density are regarded as one of the most promising cathode materials for next generation lithium-ion batteries. However, the notorious surface impurities and high air sensitivity of Ni-rich layered oxides remain great challenges for its large-scale application. In this respect, surface impurities are mainly derived from excessive Li addition to reduce the Li/Ni mixing degree and to compensate for the Li volatilization during sintering. Owing to the high sensitivity to moisture and CO2 in ambient air, the Ni-rich layered oxides are prone to form residual lithium compounds (e.g. LiOH and Li2CO3) on the surface, subsequently engendering the detrimental subsurface phase transformation. Consequently, Ni-rich layered oxides often have inferior storage and processing performance. More seriously, the residual lithium compounds increase the cell polarization, as well as aggravate battery swelling during long-term cycling. This review focuses on the origin and evolution of residual lithium compounds. Moreover, the negative effects of residual lithium compounds on storage performance, processing performance and electrochemical performance are discussed in detail. Finally, the feasible solutions and future prospects on how to reduce or even eliminate residual lithium compounds are proposed.

Swelling mechanism of 0%SOC lithium iron phosphate battery at high temperature storage

The storage performances of 0% SOC and 100%SOC lithium iron phosphate (LFP) batteries are investigated. 0%SOC batteries exhibit higher swelling rate than 100%SOC batteries. In order to find out the source of battery swelling, cathode and anode electrodes obtained from 0%SOC battery are evaluated separately. By analyzing the results, the anode is identified as the main source of battery swelling. The 0%SOC anodes are then stored with different solvents of electrolyte and gas chromatography is utilized to analyze the main components of the gas products. Moreover, different types of anodes are also investigated. A three-electrode system is designed to study the voltage change during charging and discharging process. The results confirm that the battery swelling is related to the voltage state of the anode. The anode is unstable at high voltage which may cause the decomposition of SEI during storage process. After SEI decomposes, the fresh anode surface will be exposed to the electrolyte, and the new SEI will be formed to generate large amount of gas which can cause the battery swelling. Finally, different SOCs of LFP batteries are investigated. It is found that the swelling rate tends to be stable at 30% SOC.

Tracking Battery Swelling in Uncompressed Li-Ion Cells Via in-Operando X-Ray Radiography and Micro-Tomography

Li-ion battery swelling during cycling is known to be a major cause of battery electrode degradation and can contribute significantly to cell failure [1,2]. The main cause of battery swelling is due to the intercalation of Li into the carbon and LiCoO2 electrodes. This swelling is known to occur anisotropically due to the electric field and Li salt distributions in the electrode [3]. We have used x-ray radiography and µCT to map this swelling, in-operando under charge and discharge conditions, in the layers of an uncompressed Li-ion battery. This study gives insight into the relationship between the battery state of charge and the electrode swelling. The change in swelling due to the electrode geometry is also investigated. Li-ion pouch cells were cycled at 0.5, 1 and 2 C while undergoing x-ray radiography and tomography at the BMIT beamline of the Canadian Light Source. Synchrotron radiography allowed the tracking of the electrode swelling in two dimensions with high temporal (10 s/frame) and spatial resolution (3 µm/pixel). µCT measurements of Li-ion cells were carried out under the same battery cycling conditions and scans were taken at 0, 25, 75 and 100 % state of charge (3 µm/pixel, 225 s/scan). Reconstruction and segmentation of the collected images allowed for the measurement of each electrode volume. From these results it appears that electrode swelling depends on a number of factors, including electrode geometry, charge/discharge rate and battery age. There is also a noticeable degree of irreversibility in the swelling of the electrode, which may be a possible metric for battery degradation. The quantification of the carbon electrode swelling corresponds closely with the theoretical value for lithium intercalation to LiC6, although there is a discrepancy between the swelling value obtained for the LiCoO2 electrode and theory. These results give a valuable insight into the mechanical dynamics of Li-ion batteries under in-operando conditions and will provide validation to, and data for, battery models including stress-strain and degradation models. References Bond, T., Zhou, J., & Cutler, J. (2017). Electrode Stack Geometry Changes during Gas Evolution in Pouch-Cell-Type Lithium Ion Batteries. Journal of The Electrochemical Society, 164(1), A6158–A6162.Chen, C., Wei, Y., Zhao, Z., Zou, Y., & Luo, D. (2019). Investigation of the swelling failure of lithium-ion battery packs at low temperatures using 2D/3D X-ray computed tomography. Electrochimica Acta, 305, 65–71.Zhang, N., & Tang, H. (2012). Dissecting anode swelling in commercial lithium-ion batteries. Journal of Power Sources, 218, 52–55. Figure 1 (a) 2D x-ray radiography of a Li-ion pouch cell and (b) 3D reconstruction of a µCT of a Li-ion pouch cell section. Figure 1

Quantitative Measurements of the Gas Evolution in Li-Ion Batteries Via Oems (Online Electrochemical Mass Spectrometry)

Confronted with the fast-growing marked demand for high energy and power Li-ion batteries in electrical vehicles and hybrid electrical vehicles. Numerous efforts have been applied to develop battery systems with higher charge voltage to achieve higher cell energy. However, a more severe capacity fading is usually observed for the high voltage cell, accompanied with sever battery swelling, which could be attributed to more side reactions. Online electrochemical Mass Spectrometry (OEMS) is an analytical technique that combines electrochemical half-cell experimentation with mass spectrometry. It allows in-situ mass resolved determination of gaseous or volatile electrochemical reactants, reaction intermediates and products in real time. In this work, we will discuss the setup of a laboratory grade OEMS and reported the initial test towards several popular NMC cathode//Graphite lithium ion batteries with different electrolyte choices, and comparison of our results with reported literature will be presented.

Problems and their origins of Ni-rich layered oxide cathode materials

Ni-rich layered oxides, LiNixCoyMnzO2 (NCM) and LiNixCoyAlzO2 (NCA) with x ​+ ​y ​+ ​z ​= ​1 and x ​≥ ​0.8, are regarded to be the best choice for the cathode material of high energy Li-ion batteries due to their combined advantages in capacity, working potential and manufacture cost. However, their application in practical Li-ion batteries is hindered by two essential problems of (1) performance degradation and (2) safety hazard over the whole life of battery. Performance degradation behaves as declines in battery's capacity and working voltage as well as the battery's swelling and impedance growth; Safety hazard arises from thermal runaway under abuse conditions such as overcharging, overheating, and electric shorting. It appears that nearly all problems can be ultimately attributed to the loss of oxygen, especially caused by the oxidation of lattice oxygen in H3 phase where the capacities are contributed by both of the Ni and O redox couples. In this review, the problems and their origins of Ni-rich layered oxides are overviewed, and the solutions attempted to mitigate these problems are outlined.

Infrared Spectroscopic Study of the Thermal Stability of Alkyl Carbonate Electrolytes

Decomposition of ethylene carbonate (EC) in lithium ion batteries leads to battery swelling, off-gassing, and thermal runaway. Ethylene carbonate decomposes electrochemically by reduction at the anode or chemically in the bulk electrolyte at elevated temperature. The formation of a solid electrolyte interface (SEI) on the anode limits electrochemical decomposition so long as the SEI remains intact. While neat ethylene carbonate is thermally stable at temperatures exceeding 150°C, EC-based electrolytes containing lithium hexafluorophosphate (LiPF6) salt are known to chemically react at temperatures as low as 50°C. Decomposition rate has been shown to increase with higher salt content, indicating a salt-catalyzed thermal decomposition mechanism. Trace contaminants, especially moisture, have also been shown to strongly effect electrolyte thermal stability. Thus, small impurities in the manufacture of battery components can have dramatic effect on electrolyte stability and battery aging. Electrolyte decomposition mechanisms have been studied extensively. Differential scanning calorimetry (DSC) and accelerated rate calorimetry (ARC) can identify temperatures of reactions, kinetic parameters, and heat release rates. Decomposition mechanisms and reaction products are also identified indirectly by ex situ electrolyte and off-gas analysis. Despite numerous studies, much remains unknown about decomposition chemistry in lithium ion batteries, especially the role of trace impurities on stability. Further, little is known about electrolyte decomposition mechanisms in batteries, as few operando electrolyte diagnostics exist. In this work, the chemical stability of EC at elevated temperature is studied using infrared spectroscopy. Electrolyte samples are heated on an attenuated total reflection (ATR) spectrometer stage using both liquid samples and in operating half and full cell batteries. Liquid samples were prepared in an argon glove box with varying concentrations of LiPF6 salt, H2O, and in CO2 gas environments (to simulate cathode off-gassing). Accurate temperature readings up to 150°C were made using infrared thermometry. Operando spectroscopic measurements of electrolyte stability in graphite half cells, lithium cobalt oxide (LiCoO2) half cells, and lithium ion full cells were also collected. Reaction rates and activation energies are also reported using time-resolved infrared spectroscopy.

Mechanical Measurements for Early Detection of Thermal Runaway Induced By an Internal Short Circuit

Thermal Runaway is one of the major safety risks in lithium ion batteries. One of the prime reasons for thermal runaway are Internal Short Circuits (ISCs). The ISC phenomenon is very fast and the battery discharges in a matter of seconds, resulting in an explosion which can propagate to other cells, resulting in additional thermal runaway. Hence it is important to understand which sensors can give earliest warning (integrated with voltage measurement) to give a higher confidence level of detecting the imminent evolution of the thermal runaway due to the ISC. Leveraging prior work in [1] where battery swelling was used to improve SOC estimation, we consider the benefits of force measurement along with temperature measurement for detecting the onset of thermal runaway. As it is shown in Figure 1, the measured force increases at the same instance when there is a voltage drop due to the short. The measured force changed earlier than the installed RTD (resistance thermometer) or thermocouple. The mechanical measurement, therefore, can be used in conjunction with electric measurements to generate a robust detection of internal shorts. A 4.5 Ah NCM - Graphite pouch cell with a built-in ISC device was fabricated for the experiment at the University of Michigan Battery Lab. The ISC device used is similar to the one developed by NREL [2]. During the battery fabrication, a hole is cut in the separator, which is then covered by a Phase Change Material (PCM) trigger. The PCM melts when the temperature reaches its melting point at 55oC, thus creating a gap in the separator, allowing the electrodes to contact and triggering the ISC. This pouch cell was inserted in a cell holder shown in Figure 2. A RTD strip with six sensing elements [3] was placed on the cell. A thermocouple was placed between the current collecting tabs (at the position where the venting will occur). There are four load cells (which measure force) attached to the four corners of the cell holder. The instrumented cell fixture was heated in an Accelerating Rate Calorimeter until the ISC is triggered. The temperatures, terminal voltage and load cells were all sampled at 80 Hz during the experiment. The chronology of events shown in Fig.2 suggests that the ISC leads to local heating and gas generation, which results in battery swelling before the elevated temperature can reach to the surface of the cell. The measured voltage exhibits an initial drop (indicated by t=0 in the graph) but subsequently rises again and continued to fluctuate until reaching zero 6.5s later. The force started rising immediately after the initial voltage drop. Even the thin film RTD located on top of the ISC trigger responded slower than the force, at 0.2s after the initial voltage drop. The accumulated pressure inside the cell then caused the pouch to rupture between the electrical contacts (at the weakest part of the pouch cell). The ultimate burst pressure exceeded the measurement range of the sensor, but the timing of the event was observed by the rapid depressurization at 0.55 s. Finally, the thermocouple temperature increased at 0.60s, most likely due to hot gases venting out over the thermocouple placed between the tabs. An ISC event and the eventual rupture can be detected using measured force earlier than using temperature sensors on the surface of the battery. The actual implementation of the mechanical measurement can be achieved with load sensors in the end plates of a battery module [1], or with strain sensors embedded in the module [3].

Looking Deeper into the Galaxy (Note 7)

Li-ion cell designs, component integrity, and manufacturing processes all have critical influence on the safety of Li-ion batteries. Any internal defective features that induce a short circuit, can trigger a thermal runaway: a cascade of reactions, leading to a device fire. As consumer device manufacturers push aggressively for increased battery energy, instances of field failure are increasingly reported. Notably, Samsung made a press release in 2017 following a total product recall of their Galaxy Note 7 mobile phone, confirming speculation that the events were attributable to the battery and its mode of manufacture. Recent incidences of battery swelling on the new iPhone 8 have been reported in the media, and the techniques and lessons reported herein may have future relevance. Here we look deeper into the key components of one of these cells and confirm evidence of cracking of electrode material in tightly folded areas, combined with a delamination of surface coating on the separator, which itself is an unusually thin monolayer. We report microstructural information about the electrodes, battery welding attributes, and thermal mapping of the battery whilst operational. The findings present a deeper insight into the battery’s component microstructures than previously disseminated. This points to the most probable combination of events and highlights the impact of design features, whilst providing structural considerations most likely to have led to the reported incidences relating to this phone.

Infrared Optical Measurements of Thermal Breakdown in Battery Electrolytes

Electrolyte thermal stability is critical for both battery safety and extending battery life. Battery fires are often the result of thermal breakdown of the liquid electrolyte leading to a flammable mixture of volatile products. Even in the absence of fire, electrolyte decomposition leads to battery swelling, harmful precipitates, reduced ion conductivities, and undesirable battery chemistry. Current methods of determining electrolyte stability using ex-situ techniques, such as thermal gravimetric analysis or differential scanning calorimetry, can over predict thermal stability, do not address materials compatibility within batteries, and cannot identify chemical decomposition mechanisms. Infrared optical detection of thermal stability offers an in-situ approach providing: speciation, identification of chemical bonds involved in decomposition, real-time detection, and chemical kinetics. In this work, the thermal stability of the room temperature ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][EtSO4]) is investigated using infrared (IR) spectroscopy. Quantitative IR absorption spectral data are measured for the heated ionic liquid. Spectra have been collected between 25°C and 100°C using a heated optical cell. Multiple samples and cell path lengths were used to determine quantitative values of the absorption coefficient. These results were compared to previous computational models of the ion pair to identify each absorption band with corresponding chemical bonds. The quantitative spectra were then used to measure the rate of thermal decomposition at elevated temperatures revealing the onset of breakdown above 75°C.

Lioh and Li2CO3 Removal By a Dry Process Using Atmospheric Pressure Plasma

LiOH and Li2CO3 are impurities remaining in NCM (Ni, Co, Mn Oxide) cathode powder in its manufacturing. As the sources of battery swelling, they need to be removed to a very low level from the cathode material. The existing technique for removing these impurities is wet washing with such as water. N2 and NF3 mixed gas from a multi layered DBD (Dielectric Barrier Discharge) plasma can remove the LiOH and Li2CO3 in dry environment. We monitored the reaction product gas coming from the conversion reaction by QMS residual gas analyzer. The O2 and CO2 concentration was increased in the conversion reaction of LiOH and Li2CO3 respectively. The addition of little amount of H2 gas into the mixed gas increased the dissociation rate of the NF3 molecule. In that condition, the O2 concentration was decreased in LiOH conversion whereas the CO2 concentration was steeply increased in Li2CO3 conversion. This plasma process could remove up to 80% of impurities of LiOH and Li2CO3 from 622 NCM powder in just one minute.

Rate dependence of swelling in lithium-ion cells

Swelling of a commercial 5 Ah lithium-ion cell with a nickel/manganese/cobalt-oxide cathode is investigated as a function of the charge state and the charge/discharge rate. In combination with sensitive displacement measurements, knowledge of the electrode configuration within this prismatic cell's interior allows macroscopic deformations of the casing to be correlated to electrochemical and mechanical transformations in individual anode/separator/cathode layers. Thermal expansion and interior charge state are both found to cause significant swelling. At low rates, where thermal expansion is negligible, the electrode sandwich dilates by as much as 1.5% as the charge state swings from 0% to 100% because of lithium-ion intercalation. At high rates a comparably large residual swelling was observed at the end of discharge. Thermal expansion caused by joule heating at high discharge rate results in battery swelling. The changes in displacement with respect to capacity at low rate correlate well with the potential changes known to accompany phase transitions in the electrode materials. Although the potential response changes minimally with the C-rate, the extent of swelling varies significantly, suggesting that measurements of swelling may provide a sensitive gauge for characterizing dynamic operating states.