Overcharge Process Research Articles

Design of thermal management system for high-power liquid-cooled charging pile

Abstract High-power ultra-fast charging causes the charging gun to rapidly heat up, posing safety hazards. Therefore, the focus of the research is on thermal management during the overcharge process. To address this, a novel thermal management control system (TMS) for high-power liquid-cooled charging piles has been designed. The liquid circulation channels connect the cables and the charging gun, with coolant flowing through the pipes. A pump delivers the coolant to the charging gun to remove heat. The TMS monitors temperature, pressure, and flow to control the oil pump and fan speeds, maintaining the perforating gun temperature within a preset range and managing the system’s heat. This TMS system enables the liquid-cooled charging cables to carry larger currents, significantly enhancing charging power.

Effects of Li1.3Al0.3Ti1.7(PO4)3 solid-state electrolytes on the safety of hybrid solid–liquid batteries

Hybrid solid–liquid batteries (HSLBs) are emerging as promising solutions to address the safety issues of lithium-ion batteries. However, the effects of solid-state electrolytes (SSEs) on battery safety remain unclear, hindering the large-scale application of HSLBs. This paper presents a comprehensive investigation on the safety performance of HSLBs with different amounts of nano-sized Li1.3Al0.3Ti1.7(PO4)3 (LATP) SSEs in the LiNi0.9Co0.05Mn0.05O2 cathode under thermal, electrical, and mechanical abuse conditions. The HSLBs with LATP SSEs exhibit significantly enhanced tolerance to overcharge, as the battery with 5 wt% LATP does not go into thermal runaway throughout the whole overcharge process. In-depth characterizations reveal that the LATP additives experience electrochemical delithiation during overcharge and generate a protective coating layer on the cathode surface, thus effectively mitigating the cathode structural changes and cathode-electrolyte interfacial reactions. Benefiting from the coating layer, the HSLBs with LATP SSEs also exhibit reduced temperature rise rate and retarded thermal runaway during the accelerating rate calorimetry and oven tests, as well as enhanced rate performance and cycling stability. Finally, the safety, electrochemical performance, and cost of HSLBs and conventional LIBs are comprehensively compared through a radar graph, aiming to provide guidance for the rational design of high–energy density and high-safety batteries.

Hydrogen bond-induced configuration and electron transfer on layered double hydroxide for high-performance sodium-iodine batteries

Sodium-iodine (Na-I2) batteries are appealing electrochemical energy storage devices owing to the low cost and high energy density. However, they are constrained by shuttle effect due to the high solubility of iodine/iodide in electrolyte and the sluggish reaction kinetics of I2 ↔ 2I−. Accordingly, Na-I2 batteries with superficial redox mechanism and superior rate capability almost seem impossible. Herein, a layered double hydroxide (LDH) formulated as Ni2Al(OH)4.2(CO3)1.4·2H2O (NiAl-LDH) and an iodine-decorated LDH (NiAl-LDH-I2) were synthesized. When used as the Na-I2 battery cathode in the NaClO4 electrolyte, NiAl-LDH-I2 exhibits an increasing capacity, accompanied with a transformation from the (de)intercalation to the surface-controlled (pseudo)capacitive behavior. This is ascribed to irreversible reduction reaction of ClO4− → Cl− and the formation of I+-Cl− on the LDH surface over an overcharge process. Density functional theory (DFT) calculations reveal that the adsorbed I2 and I-Cl both exhibit zigzag chain-like configurations, which are not easily intercalated into the interlayer space of NiAl-LDH, but can be anchored on the NiAl-LDH surface via multiple hydrogen bonds. These hydrogen bonds can stabilize I+ to boost the multi-electron redox reaction of 2I− ↔ I2 ↔ 2I+. The adsorbed I2 is activated by the electron transfer and the elongation of I-I bond, then fasten the reaction kinetics of I2 ↔ 2I−. Therefore, NiAl-LDH-I2 shows outstanding rate capability and cycling performance with a large capacity of 310/ 210 mAh/g at 0.3/ 1.5 A/g and excellent capacity retention over 2700 cycles.

Analysis of Structural Changes in Practical Batteries during Overcharging Using Synchrotron X-Ray CT Imaging

Lithium-ion rechargeable batteries are desired for applications such as power sources for electric vehicles, which require increased energy density to extend cruising range. In the cathode, increasing the nickel content makes it possible to increase the energy density, but this is problematic due to a decrease in safety. To solve this problem, it is necessary to clarify the phenomena leading to structural breakdown by operando observation[1]. We have developed a system for operando non-destructive observation of the internal structure of all batteries under transient conditions using 100 keV collimated light of SPring-8 beamline. In this study, the difference in the behavior of LiCoO2 (LCO), LiNi0.6Mn0.2Co0.2O2 (NMC622) and LiNi0.8Mn0.1Co0.1O2 (NMC811) during overcharging was discussed in combination with the measurement of the electronic structure of the cathode active materials from the surface to the bulk.A 40-layer laminated battery (1 Ah) was used, with LCO, NMC622 and NMC811 as the cathodes and natural graphite as the anode. After charging to 100% SOC at 1C (1C=160 mAh/g) rate at room temperature, the overcharge process performed under 3C and/or 6C rate from 100% SOC while measuring voltage and temperature. Overcharge behavior inside the battery was observed simultaneously by operando X-ray CT during overcharge process.During the overcharge test at 6C rate, the maximum temperature of the LCO laminated battery was 390 ℃, while NMC811 laminated battery reached over 600 ℃ (Fig. 1). Point 1 in Fig. 1 is the point where changes in the electrode structure begin to be observed by the operando X-ray CT measurements. The point 1 of NMC811 occurred earlier (203 s) than LCO (542 s). From the O-K XAS result (Fig. 1d), the pre-edge (located at 519 ev) of NMC811 was much higher than LCO and NMC622 when overcharging to 200% SOC, meanwhile the O-Ni bond in NMC is more unstable than O in LCO in the overcharged state. The unstable electronic structure of oxygen on the surface of NMC811 is the starting point for the rapid structural change of the battery during overcharging. Reference s : [1] Donal P. Finegan; Mario Scheel; James. Robinson; Bernhard T.; Marco Di M.; Gareth H. Phys.Chem.Chem.Phys. (2016), 18, 30912. Figure 1

Li-Ion Cell Safety Monitoring Using Mechanical Parameters, Part 3: Battery Behaviour during Abusive Overcharge

The electrochemical and mechanical behaviour of 18,650 Li-ion cells subjected to abusive overcharge has been studied in constant current and constant voltage mode. The results from the cell deformation monitoring via a rectangular rosette strain gauges indicate an over-swelling process starting shortly after the cell voltage increases above 4.2 V. The acoustic ultrasound interrogation measurement and data treatment using clustering and mapping software, carried out in parallel, showed an abnormal evolution of the signals’ power density spectral patterns, suggesting changes in the structure of the cell jellyroll induced by the overcharge reactions. The increase in cell skin temperature due to the overcharge process starts considerably later. The results suggest that the monitoring of the mechanical behaviour of cylindrical-format Li-ion cells can be used for the detection and alerting of early overcharge safety events.

Overcharge to Remove Cathode Passivation Layer for Reviving Failed Li–O 2 Batteries

Overcharge to Remove Cathode Passivation Layer for Reviving Failed Li–O ₂ Batteries

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[Ni0.8Co0.1Mn0.1]O2 cathode 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 Li-ion 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.

Investigation and Suppression of Oxygen Release by LiNi0.8Co0.1Mn0.1O2 Cathode under Overcharge Conditions

AbstractThe safety issue of lithium‐ion batteries is a crucial factor limiting their large‐scale application. Therefore, it is of practical significance to evaluate the impact of their overcharge behavior because of the severe levels of oxygen release of cathode materials during this process. Herein, by combining a variety of in situ techniques of spectroscopy and electron microscopy, this work studies the structural degradation of LiNi0.8Co0.1Mn0.1O2 (NCM811) accompanying the oxygen release in the overcharge process. It is observed that a small amount of O2 evolves from the initial surface at ≈4.7 V. When charging to a higher voltage (≈5.5 V), a large amount of O2 evolves on the newly formed surface due to the occurrence of microcracks. Based on experimental results and theoretical calculations, it is determined that the oxygen release mainly occurs in the near‐surface regions, where the remaining oxygen vacancies accumulate to create voids. To suppress the oxygen release, single‐crystalline NCM811 with integrated structure is introduced and serves as a cathode, which can effectively inhibit morphology destruction and reduce the activation of lattice oxygen in the surface region. These findings provide a theoretical basis and effective strategy for improving the safety performance of Ni‐rich cathode materials in practical applications.

Comprehensive Investigation of a Slight Overcharge on Degradation and Thermal Runaway Behavior of Lithium-Ion Batteries.

Overcharge is a hazardous abuse condition that has dominant influences on cell performance and safety. This work, for the first time, comprehensively investigates the impact of different overcharge degrees on degradation and thermal runaway behavior of lithium-ion batteries. The results indicate that single overcharge has little influence on cell capacity, while it severely degrades thermal stability. Degradation mechanisms are investigated by utilizing the incremental capacity-differential voltage and relaxation voltage analyses. During the slight overcharge process, the conductivity loss and the loss of lithium inventory always occur; the loss of active material starts happening only when the cell is overcharged to a certain degree. Lithium plating is the major cause for the loss of lithium inventory, and an interesting phenomenon that the arrival time of the dV/dt peak decreases linearly with the increase of the overcharge degree is found. The cells with different degrees of overcharge exhibit a similar behavior during adiabatic thermal runaway. Meanwhile, the relationship between sudden voltage drop and thermal runaway is further established. More importantly, the characteristic temperature of thermal runaway, especially the self-heating temperature (T1), decreases severely along with overcharging, which means that a slight overcharge severely decreases the cell thermal stability. Further, post-mortem analysis is conducted to investigate the degradation mechanisms. The mechanism of the side reactions caused by a slight overcharge on the degradation performance and thermal runaway characteristics is revealed.

Thermal safety study of Li‐ion batteries under limited overcharge abuse based on coupled electrochemical‐thermal model

Many fire accidents of electric vehicles were reported that happened during the charging process. In order to investigate the reasons that lead to this problem, this paper studies the thermal safety of Li-ion batteries under limited overcharge abuse. A 3D electrochemical-thermal coupled model is developed for modeling thermal and electrochemical characteristics from normal charge to early overcharge state. This model is validated by experiment at charge rates of 0.5C, 1C, and 2C. The simulation results indicate that irreversible heat contributes most to temperature rise during the normal charge process, but the heat induced by Mn dissolution and Li deposition gradually dominates heat generation in the early overcharge period. Based on this, a threshold selection method for multistage warning of batteries overcharge is proposed. Among them, level 1 should be considered as a critical stage during the early overcharge process due to the deposited lithium starts to react with electrolyte at the end of level 1, where temperature rate increases to 0.5°C min−1 for 1C charge. While the thresholds of levels depend on charge rate and composition of battery. Furthermore, several critical parameters are analyzed to figure out their effects on thermal safety. It is found that the temperature at the end of overcharge is significantly influenced by the change of positive electrode thickness and solid electrolyte interface (SEI) film resistance. The final temperature increases by 17.5°C and 7.9°C, respectively, with positive electrode thickness ranging from 50 to 80 μm and SEI film resistance increasing from 0.002 to 0.03 Ω.

Overcharge and Aging Analytics of Li-Ion Cells

Overcharge presents a serious safety concern for large scale applications of Li-ion batteries. Despite the availability of several studies of aging-induced and overcharge-induced degradation, there still exists a knowledge gap of what would happen if both degradation mechanisms simultaneously occur. In this work, commercial graphite/LCO pouch cells (5 Ah) are continuously cycled at different upper cutoff voltages, 4.2 through 4.8 V, to elucidate the cumulative effect of the overcharge process on the long-term cycling. As the upper cutoff voltage is extended, the cell gains a higher initial capacity but the cycle life diminishes significantly. Cells overcharged beyond 4.5 V experience significant volume expansion and a high rate of capacity fade, as well as a considerable increase in the temperature and internal resistance. Lithium plating and electrolyte decomposition are observed in cells charged beyond 4.5 V, with SEM-EDS verifying their presence. Electrochemical evidence of both degradation modes appears as a voltage undershoot in the discharge curves. A comparative study of various State of Health (SoH) estimation parameters is presented with the introduction of a new dimensionless SoH indicator, ΦR, based on internal resistance measurement. The proposed degradation number is found to be a good indicator of aggravated degradation in Li-ion cells.

Thermal runaway behavior during overcharge for large-format Lithium-ion batteries with different packaging patterns

• Thermal runaway behavior during overcharging is investigated. • The impact of cell packing patterns is revealed. • A specialized test platform is established to conduction experiments. • The thermal runaway behaviors of the tested cells are compared. Lithium-ion batteries are the main energy storage unit for electric vehicles. The prevention of thermal runaway is essential for ensuring safe operation of these batteries. Different cell packaging patterns have an influence on the thermal runaway behavior of lithium-ion batteries during overcharging. In this paper, prismatic and pouch lithium-ion battery cells with the same capacity and chemistries are used to experimentally investigate the internal failure mechanisms and associated external characteristics during overcharging. The entire overcharge process is divided into five stages according to the voltage and temperature curves. The results indicate that the pouch battery cell exhibits better thermal behavior characteristic and overcharge tolerance when compared to the prismatic battery cell in stages I to III. However, the prismatic battery cell has better thermal runaway buffering characteristic, smaller deformation and longer early warning time. This is due to the use of a safety valve which results in subsided damage caused by thermal runaway. Their maximum surface temperature differences increase linearly with the overcharge process, until thermal runaway occurs and rapid rise to the highest temperature point takes place. These results provide an insight into the safety and thermal management design of battery systems.

Overcharge cycling effect on the thermal behavior, structure, and material of lithium-ion batteries

The present study investigates the overcharge cycling effect on thermal behavior, structure, and electrode material of lithium-ion batteries (LIB) with a Lix(Ni0.3Co0.3Mn0.2)O2 cathode. The thermal behavior of LIBs with different overcharged degrees was studied using vent sizing package 2 and differential scanning calorimetry. Changes in the internal composition of the batteries during overcharge were observed using a scanning electron microscope and an inductively coupled plasma optical emission spectrometer. The results indicate that the overcharge process can be divided into four stages. A battery was more likely to trigger thermal runaway during overcharge under adiabatic conditions than in an ambient environment. During overcharge, the surface temperature of a 150% state-of-charge (SOC) battery was approximately 3.0 °C higher than that of a 100% SOC battery. Because of generated gas and lithium deposition during overcharge cycling, the battery thickness increases and coulombic efficiency decreases. The apparent exothermic onset temperature (T0) of a battery with 150% SOC was 87 °C below that of a 100% SOC battery. Cathode material becomes highly reactive when the battery was overcharged to 150% SOC. Here, the released heat was 1026.4 J/g. These results provide feasible support for understanding the overcharge mechanism and battery management system.

Overcharge behaviors and failure mechanism of lithium-ion batteries under different test conditions

Overcharge is one of the most severe safety problems for the large-scale application of lithium-ion batteries, and in-depth understanding of battery overcharge failure mechanism is required to guide the safety design of battery systems. In this paper, the overcharge performance of a commercial pouch lithium-ion battery with Liy(NiCoMn)1/3O2-LiyMn2O4 composite cathode and graphite anode is evaluated under various test conditions, considering the effects of charging current, restraining plate and heat dissipation. Charging current is found to have only minor influences on battery overcharge behaviors, whereas the battery overcharged with pressure relief design (restraining plate and cuts on pouches) and good heat dissipation shows significantly improved overcharge performance and can endure larger amount of overcharge capacity and higher temperature before thermal runaway. Characterizations on cathode and anode materials at different overcharge states are carried out to identify the side reactions inside the battery. The overcharged cathode suffers from electrolyte decomposition, transition metal dissolution and phase transition, but still exhibits no obvious exothermic behaviors before thermal runaway occurs. Severe lithium plating happens on the anode, and would accelerate the overcharge-induced thermal runaway process. Further analysis on the onset temperature of thermal runaway helps to reveal the overcharge-induced thermal runaway mechanism of lithium-ion batteries. The result shows that rupture of the pouch and separator melting are the two key factors for the initiation of thermal runaway during overcharge process.

Investigation of Interfacial Changes on Grain Boundaries of Li(Ni0.5Co0.2Mn0.3)O2 in the Initial Overcharge Process

AbstractThe interfacial changes and Li ions kinetics on grain boundaries of cathode are still not very clear, especially in the initial overcharge process. Herein, interfacial changes and electrochemical kinetics of Li ions on grain boundaries of Li(Ni0.5Co0.2Mn0.3)O2 (NCM523) are investigated in the initial overcharge to 4.9 V. The mechanism of electrochemical process and interfacial changes of NCM523 is proposed in this study. Two triggering potentials are detected: 4.4 V, indicating oxidation of lattice oxygen; 4.7 V, meaning electrochemical oxidation of electrolyte. Combining with in situ electrochemical impedance spectroscopy results and transmission electron microscope characterization, oxidation of lattice oxygen can be related to the formation of rock salt phase, hampering lithium ions migration from one primary particle to another when charging to higher than 4.4 V. When potential rises to 4.7 V, electrolyte begins to be electrochemical oxidized, causing severe capacity degradation due to excessive consumption of lithium ions. All these factors synergistically induce the capacity degradation of NCM523 during the overcharge cycling performance. The upper limiting voltage of NCM523 should be no higher than 4.4 V to prolong its life cycle.

Influence of Current Rate on the Degradation Behavior of Lithium-Ion Battery under Overcharge Condition

In the present work, an experimental study is carried out to investigate the influence of current rate, i.e. cycle rate, charge rate and discharge rate on the degradation behavior of a lithium-ion battery during overcharge process. Several parameters, such as capacity degradation rate, temperature rise, temperature difference and voltage are discussed correspondingly. It is found that battery capacity experiences significant degradation under the abusive condition of overcharge cycle, and the current rate is revealed to affect the degradation rate greatly. Among, the cycle rate is exhibited to have the largest influence on the degradation of overcharged battery, followed by the charge rate and discharge rate. Under the condition of low cycle rate or low charge rate, the capacity degradation behaves much more severely, which is contrary to that of discharge condition where when decreasing the discharge rate, the degradation of battery is restrained. After the overcharge test, a recovery of discharge capacity can be observed as a function of rest time. Finally, the variation of battery internal characterizations, including the anode and separator before and after overcharge cycle are researched respectively.

Overcharge investigation of large format lithium-ion pouch cells with Li(Ni0.6Co0.2Mn0.2)O2 cathode for electric vehicles: Thermal runaway features and safety management method

In this paper, the overcharge-induced thermal runaway features of large format commercial lithium-ion batteries with Li(Ni0.6Co0.2Mn0.2)O2 (NCM622) cathode for electric vehicles under different current rates (C-rates) have been systematically studied at ambient temperature. The overcharge process is characterized as four stages. The temperature rise and the maximum temperature of the battery surface don't increase in proportion to the applied C-rates. However, with the increase of C-rates, the crest voltage of voltage curve rises linearly. When the voltage reaches approximately 5.1 V, a new voltage plateau appears in the cases below 2C. It is not sufficient that the temperature sensor is placed only near the terminal tab for most battery packs of EVs. In addition, the accumulated heat analysis demonstrates that side reactions dominate the temperature rise and contribute to most of the accumulated heat before thermal runaway. To mitigate the impact of overcharge and avoid the thermal runaway risk, a safety management method is proposed. Furthermore, the sharp drop in voltage before thermal runaway also provides a feasible approach to forewarn the users of the impending risk. These results are important for building safer batteries and providing information for the safety monitoring function of the battery management system (BMS).

From the charge conditions and internal short-circuit strategy to analyze and improve the overcharge safety of LiCoO2/graphite batteries

The overcharge safety and behaviors of lithium-ion batteries (LIBs) with LiCoO2 cathode are investigated under a successive constant current (CC) and constant voltage (CV) charge mode. It is indicated that in the case of smaller charge currents, a higher probability for the LIBs passing the overcharging test can be obtained. The batteries can safely pass CC overcharge test at 0.25C to 10 V, and then about 80% batteries can also pass CV overcharge test. Whereas, with increasing the CC currents to 0.33C, 0.5C, and 1C, about 50%, 30%, and 10% batteries can directly pass the overcharge test at the CC step, and then about 20%, 10%, and 0% batteries approach 10 V and subsequent pass CV overcharge test, respectively. Besides the charge current, it is also demonstrated that whether the LiCoO2/graphite batteries are likely to achieve energy balance and pass the overcharge test basically depends on the formation of the internal short-circuit pathways derived from the cobalt and lithium deposition in the separator during the overcharge process. The cobalt deposition will be more uniform when the battery core has shape stability of assembly-structure, which can be used as an effective measure to raise LIBs through the overcharge test. In addition, relative more uniform cobalt dendrites can also be formed if a double layer separator is adopted, which reduces the local short-circuit risk caused by the melting or shrinkage of the separator and correspondingly improves the ratio of LIBs passing through the overcharge test. These risk reduction measures can be used in the battery manufacture to improve the overcharge safety of LIBs.

Overcharge Investigation of Large Format Lithium-Ion Pouch Cells with Li(Ni0.6Co0.2Mn0.2)O2 Cathode for Electric Vehicles: Degradation and Failure Mechanisms

In this paper, overcharge behaviors of a large format lithium-ion battery with Li(Ni0.6Co0.2Mn0.2)O2 cathode for electric vehicles are investigated, and the overcharge-induced degradation and failure mechanisms of the whole overcharge process are studied using both in-situ and ex-situ techniques. The whole overcharge-to-thermal runaway process can be characterized as four stages. In stage I, no obvious capacity fade is observed due to the excessive capacity of both cathode and anode. In stage II, once the state of charge (SoC) exceeds 130%, the decomposition of active materials at elevated potential dominates the capacity decay. Meanwhile, the loss of lithium inventory occurs resulting from lithium plating and other lithium involved side reactions concomitantly with the oxidation of electrolyte. In stage III, when the cell is overcharged up to 145% SoC, the structures of both the cathode and anode collapse and the component of cathode changes. As a result, cell temperature begins to rise more dramatically, which adversely leads to more aggressive side reactions, causing cell failure. In stage IV, the cell ruptures and thermal runaway happens, as a result of internal short circuit. This work provides deeper insights into the degradation and failure mechanisms of lithium-ion battery during the whole overcharge process.

Probing the cooling effectiveness of phase change materials on lithium-ion battery thermal response under overcharge condition

Usage of phase change materials (PCM) can help reduce the safety risk during LIB operation. This work investigates the cooling effectiveness of PCM on lithium ion battery operation under overcharge scenario. Combined with adiabatic overcharge tests at 0.1, 0.2, 0.5, 1, 2 current rates (C-rate), the relationship of cell thermal performance and cooling efficacy with C-rates, thermal contact resistance, amount and melting temperature of PCM are analyzed by lumped model. Results indicate steep decline of cooling effectiveness with C-rate increase. Temperature difference between cell and PCM is stable below 1C, however, abrupt hikes are observed at higher C-rates. Effectiveness increase with PCM thickness is also seen up to a critical thickness of 3 mm beyond which minimal change is observed while thermal contact resistance is found to enlarge the temperature difference between cell and PCM during the melting process causing wide variability in cooling effectiveness magnitude. For similar latent heat and density material, low melting temperature PCM exhibits superior cooling characteristics as compared to its high temperature counterpart. The results contribute to enhanced understanding of the thermal performance of PCM and LIB during overcharge process under varying conditions.