Nondisassembly Repair of Degraded LiFePO4 Cells via Lithium Restoration from the Solid Electrolyte Interphase

The disposal of degraded batteries will be a severe challenge with the expanding market demand for lithium iron phosphate (LiFePO4 or LFP) batteries. However, due to a lack of economic and technical viability, conventional metal extraction and material regeneration are hindered from practical application. Herein, we propose a nondisassembly repair strategy for degraded cells through a lithium restoration method based on deep discharge, which can elevate the anodic potential to result in the selective oxidative decomposition and thinning of the solid electrolyte interphase (SEI) on the graphite anode. The decomposed SEI acts as a lithium source to compensate for the Li loss and eliminate Li-Fe antisite defects for degraded LFP. Through this design, the repaired pouch cells show improved kinetic characteristics, significant capacity restoration, and an extended lifespan. This proposed repair scheme relying on SEI rejuvenation is of great significance for extending the service life and promoting the secondary use of degraded cells.

Advances in acoustic techniques for evaluating defects and properties in lithium-ion batteries: A review

With the rapid demand for high-performance energy storage systems, lithium-ion batteries (LiBs) have emerged as the predominant technology in various applications. However, ensuring the safety and reliability of these batteries remains a critical challenge. Ultrasound-based detection, as a non-destructive and effective method for monitoring the internal state of LiBs, has gradually emerged as a valuable tool to enhance battery safety, reliability, and performance. This paper provides a review of recent advancements in the field of acoustic detection for LiBs, delving into the fundamental principles and mechanisms governing the propagation of acoustic signals within these batteries. This paper reviews the correlation between these acoustic signals and the operational status of the battery, as well as the association with internal side reactions during abnormal conditions. The strengths and limitations of current ultrasound-based detection methods are emphasized, offering insights to guide researchers, engineers, and industry professionals in advancing the field. The review aims to foster the development of robust ultrasound-based detection solutions for the next generation of energy storage systems.

Side Reactions/Changes in Lithium-Ion Batteries: Mechanisms and Strategies for Creating Safer and Better Batteries

Lithium-ion batteries (LIBs), in which lithium ions function as charge carriers, are considered the most competitive energy storage devices due to their high energy and power density. However, battery materials, especially with high capacity undergo side reactions and changes that result in capacity decay and safety issues. A deep understanding of the reactions that cause changes in the battery's internal components and the mechanisms of those reactions is needed to build safer and better batteries. This review focuses on the processes of battery failures, with voltage and temperature as the underlying factors. Voltage-induced failures result from anode interfacial reactions, current collector corrosion, cathode interfacial reactions, overcharge, and over-discharge, while temperature-induced failure mechanisms include SEI decomposition, separator damage, and interfacial reactions between electrodes and electrolytes. The review also presents protective strategies for controlling these reactions. As a result, the reader is offered a comprehensive overview of the safety features and failure mechanisms of various LIB components.

The Potential Regulation of Working Anode for Long-Term Zero-Volt Storage at 37 °C in Li-Ion Batteries

The advanced lithium-ion batteries that can tolerate zero-volt storage (ZVS) are in high demand for implantable medical devices and spacecraft. However, ZVS can raise the anode potential, leading to Cu current collector dissolution and solid-electrolyte interphase (SEI) degradation, especially at 37 °C. In this contribution, by quantitatively regulating the dosage of Li6CoO4 cathode additives, controllable potential of the working anode under abusive-discharge conditions is demonstrated. The addition of Li6CoO4 keeps zero-crossing potential (ZCP) and the potential of ZVS below 2.0 V (vs Li/Li+) for LiCoO2|mesocarbon microbead cells at 37 °C. The capacity retention ratio (CRR) increases from 69.1% and 35.9% to 98.6% and 90.8% after 10 and 20 days of ZVS, respectively. The Cu dissolution and SEI degradation are effectively suppressed, while the over-lithiated cathode exhibits high reversible capacity after ZVS. The limiting conditions of long-term ZVS are further explored and a corresponding guide map is designed. When quantitatively regulating ZCP and the potential in ZVS, Cu dissolution, SEI degradation, and irreversible conversion of the cathode constitute the limiting conditions. This contribution designs the most reasonable potential range for ZVS protection at 37 °C, and realizes the best CRR record through precise potential regulation for the first time.

Accelerated aging of lithium-ion batteries: bridging battery aging analysis and operational lifetime prediction

The exponential growth of stationary energy storage systems (ESSs) and electric vehicles (EVs) necessitates a more profound understanding of the degradation behavior of lithium-ion batteries (LIBs), with specific emphasis on their lifetime. Accurately forecasting the lifetime of batteries under various working stresses aids in optimizing their operating conditions, prolonging their longevity, and ultimately minimizing the overall cost of the battery life cycle. Accelerated aging, as an efficient and economical method, can output sufficient cycling information in short time, which enables a rapid prediction of the lifetime of LIBs under various working stresses. Nevertheless, the prerequisite for accelerated aging-based battery lifetime prediction is the consistency of aging mechanisms. This review, by comprehensively summarizing the aging mechanisms of various components within LIBs and the battery degradation mechanisms under stress-accelerated conditions, provides a reference for evaluating the consistency of battery aging mechanisms. Furthermore, this paper introduces accelerated aging-based lifetime prediction models and offers constructive suggestions for future research on accelerated lifetime prediction of LIBs.

Lithium Iron Phosphate Enhances the Performance of High-Areal-Capacity Sulfur Composite Cathodes

Lithium iron phosphate (LiFePO₄, "LFP") was investigated as an additive in the cathode of lithium-sulfur (Li-S) batteries. LFP addition boosted the sulfur utilization during Li-S cycling, achieving an initial capacity of 1465 mAh/g_S and a long cycle life (>300 cycles). Polysulfide adsorption experiments showed that LFP attracted polysulfides, and thus, the presence of LFP should alleviate the shuttle effect, a common failure mode. Postmortem characterization found iron phosphides, iron phosphates, and LiF in the electrode, indicating that LFP underwent dynamic reconstruction during Li-S cycling. We suspect that the formation of these species played a role in the observed performance. From the processing standpoint, adding LFP improved slurry rheology, making the preparation of a high-loading electrode more consistent. Benefiting from the high sulfur utilization and the ability to prepare electrodes with high mass loading, the S-LFP hybrid cell showed an excellent areal capacity of 2.65 mAh/cm² and could be stably cycled at 2 mAh/cm² for 250 cycles. Our results demonstrated the LFP addition as a promising strategy for realizing Li-S batteries with high sulfur loading and areal capacity.

Impact of Individual Cell Parameter Difference on the Performance of Series-Parallel Battery Packs

Lithium-ion power batteries are used in groups of series-parallel configurations. There are Ohmic resistance discrepancies, capacity disparities, and polarization differences between individual cells during discharge, preventing a single cell from reaching the lower limit of the terminal voltage simultaneously, resulting in low capacity and energy utilization. The effect of the parameter difference (difference in parameters) of individual cells on the performance of the series-parallel battery pack is simulated and analyzed by grouping cells with different parameters. The findings reveal that when cells are connected in series, the capacity difference is a significant factor impacting the battery pack's energy index, and the capacity difference and Ohmic resistance difference are significant variables affecting the battery pack's power index. When cells are connected in parallel, the difference in Ohmic internal resistance between them causes branch current imbalance, low energy utilization in some individual cells, and a sharp expansion of unbalanced current at the end of discharge, which is prone to overdischarge and shortens battery life. Interestingly, we found that when there is an aging cell in a series-parallel battery pack, the terminal voltage of the single battery module containing the aging single cell will decrease sharply at the end of discharge. Evaluating the change rate of battery module terminal voltage at the end of discharge can be used as a method to evaluate the aging degree of the battery module. The research results provide a reference for connecting batteries to battery packs, particularly the screening of retired power battery packs and the way to reconnect into battery packs.

Effect of High-Rate Cycle Aging and Over-Discharge on NCM811 (LiNi0.8Co0.1Mn0.1O2) Batteries

Inconsistencies in a monomer battery pack can lead to the over-discharge of a single battery. Although deep over-discharge can be avoided by optimizing the battery control system, slight over-discharge still often occurs in the battery pack. The aging behavior of cylindrical NCM811 batteries under high-rate aging and over-discharge was studied. By setting the end-of-discharge of 1 V, the battery capacity rapidly decayed after 130 cycles. Additionally, the temperature sharply increased in the over-discharge stage. The micro short-circuit was found by the discharge voltage curve and impedance spectrum. Batteries with 100%, 79.6% and 50.9% SOH (state of health = Q_now/Q_new × 100%) as a result of high-rate aging and over-discharging were subjected to thermal testing in an adiabatic environment. The battery without high-rate aging and over-discharge did not experience thermal runaway. However, severe thermal runaway occurred in the 79.6% and 50.9% SOH batteries. Regarding the cyclic aging of the 50.9% SOH battery, the fusion temperature of the separator decreased by 22.3 °C, indicating a substantial degradation of the separator and thus reducing battery safety. Moreover, the results of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses revealed that the particles of the positive material were broken and detached, and that large-area cracks and delamination had formed on the negative material. Furthermore, Ni deposition and the uneven deposition of P and F on the negative surface were observed, which increased the risk of short-circuit in the battery. Positive and negative materials were attached on both sides of the separator, which reduced the effective area of ionic transportation.

Improved Zero-Charge Storage Performance of LiCoO2/Mesocarbon Microbead Lithium-Ion Batteries by Li5FeO4 Cathode Additive

Discharging lithium-ion batteries to zero-charge state is one of the most reliable ways to avoid the thermal runaway during their transportation and storage. However, the zero-charge state causes the degradation or even complete failure of lithium-ion batteries. Specialized solutions are required to endow lithium-ion batteries with improved zero-charge storage performance, namely, the ability to tolerate zero-charge state for a long time without unacceptable capacity loss. Here, we report that a Li₅FeO₄ cathode additive can improve the zero-charge storage performance of LiCoO₂/mesocarbon microbead (MCMB) batteries. The irreversible charge capacity of the Li₅FeO₄ additive results in the downregulation of anode and cathode potentials when the battery is at zero-charge state. More importantly, the Li₅FeO₄ additive offers a small discharge plateau below 2.9 V versus Li/Li⁺, which can hold the anode potential at zero-charge battery state (APZBS) in a potential range of 2.4∼2.5 V versus Li/Li⁺ during storage for 10 days. Such a precise control on APZBS not only suppresses the decomposition of the solid electrolyte interface film on the MCMB anode and inhibits the dissolution of the copper current collector occurring at high potentials but also avoids the excessive decrease of the cathode potential at the zero-charge battery state and consequently protects the LiCoO₂ cathode from overlithiation occurring at low potentials. As a result, the Li₅FeO₄ additive with a charge capacity percentage of 23% in the cathode increases the capacity recovery ratio of the LiCoO₂/MCMB battery from 37.6 to 95.5% after being stored at the zero-charge state for 10 days.

Power Batteries Health Monitoring: A Magnetic Imaging Method Based on Magnetoelectric Sensors

With the popularity of electric vehicles, the ever-increasing demand for high-capacity batteries highlights the need for monitoring the health status of batteries. In this article, we proposed a magnetic imaging technique (MIT) to investigate the health status of power batteries nondestructively. This technique is based on a magnetic sensor array, which consists of a 16-channel high-performance magnetoelectric sensor, and the noise equivalent magnetic induction (NEB) of each channel reaches 3–5 pT/Hz1/2@10 Hz. The distribution of the magnetic field is imaged by scanning the magnetic field variation of different positions on the surface. Therefore, the areas of magnetic anomalies are identified by distinguishing different magnetic field abnormal results. and it may be possible to classify the battery failure, so as to put forward suggestions on the use of the battery. This magnetic imaging method expands the application field of this high-performance magnetoelectric sensor and contributes to the battery’s safety monitoring. Meanwhile, it may also act as an important role in other nondestructive testing fields.

A Method for Monitoring State-of-Charge of Lithium-Ion Cells Using Multi-Sine Signal Excitation

In this paper, a method for monitoring SoC of a lithium-ion battery cell through continuous impedance measurement during cell operation is introduced. A multi-sine signal is applied to the cell operating current, and the cell SoH and SoC can be simultaneously monitored via impedance at each frequency. Unlike existing studies in which cell impedance measurement is performed ex situ through EIS equipment, cell state estimation is performed in situ. The measured impedance takes into account cell temperature and cell SoH, enabling accurate SoC estimation. The measurement system configured for the experiment and considerations for the selection of measurement parameters are described, and the accuracy of cell SoC estimation is presented.

Mechanical Failure Mechanism of Silicon-Based Composite Anodes under Overdischarging Conditions Based on Finite Element Analysis

Overdischarge is a severe safety issue that can induce severe mechanical failure of electrode materials in lithium-ion batteries. A considerable volume change of silicon-based composite anodes undoubtedly further aggravates the mechanical failure. However, the mechanical failure mechanism of silicon-based composite anodes under overdischarging conditions still lacks in-depth understanding despite many efforts paid under normal charging conditions. Herein, we have modeled and tracked the mechanical failure evolution of silicon/carbon nanofibers, a typical silicon-based anode, under overdischarging conditions based on the finite element simulation, with derived optimization strategies of optimal Young's modulus and stable microstructure. The severe contact damage between silicon nanoparticles and carbon nanofibers, which causes larger shedding and breakage risks, has been found to contribute to mechanical failure. To improve the electrode stability, an optimal Young's modulus interval ranging from ∼75 to ∼150 GPa is found. Furthermore, increasing the embedding depth of silicon nanoparticles in carbon nanofibers has proven to be an effective strategy for improving electrochemical stability due to the faster lithium salt diffusion and more uniform current density distribution, which was further verified by the experimental capacity retention ratio of carbon-coated silicon and silicon/carbon nanofibers (84 vs 75% after 100 cycles). Our results provide meaningful insights into the mechanical failure of silicon-based composite anodes during overdischarging, giving reasonable guidance for electrode safety designs and performance optimization.

Studies on the deposition of copper in lithium-ion batteries during the deep discharge process

End-of-life lithium-ion batteries represent an important secondary raw material source for nickel, cobalt, manganese and lithium compounds in order to obtain starting materials for the production of new cathode material. Each process step in recycling must be performed in such a way contamination products on the cathode material are avoided or reduced. This paper is dedicated to the first step of each recycling process, the deep discharge of lithium-ion batteries, as a prerequisite for the safe opening and disassembling. If pouch cells with different states of charge are connected in series and deep-discharged together, copper deposition occurs preferably in the cell with the lower charge capacity. The current forced through the cell with a low charge capacity leads, after lithium depletion in the anode and the collapse of the solid-electrolyte-interphase (SEI) to a polarity reversal in which the copper collector of the anode is dissolved and copper is deposited on the cathode surface. Based on measurements of the temperature, voltage drop and copper concentration in the electrolyte at the cell with the originally lower charge capacity, the point of dissolution and incipient deposition of copper could be identified and a model of the processes during deep discharge could be developed.

Identification and characteristic analysis of powder ejected from a lithium ion battery during thermal runaway at elevated temperatures

The thermal runaway of a lithium ion battery under abusive conditions has become an urgent problem in recent years. The thermal runaway generates flammable and toxic gases and ejects a hazardous black solid powder. Although relevant research on gas vented from thermal runaway has been studied in recent works, the composition, hazardous characteristics and formation process of the ejected powder remain unclarified. To investigate the hazardous characteristics of the ejected powder products and further provide insights into the thermal runaway mechanisms of lithium ion battery in terms of the identified components, a series of instrumental tests were performed and analyzed in this work. The results show that the powder ejected from the thermal runaway of a lithium ion battery is composed of carbon, organic chemicals, carbonate, metal, metal oxides and other impurities. Different states of charge of the lithium ion battery, heating modes and environmental atmospheres have certain effects on the formation of the ejected powder. These effects include the production of slightly different components in the ejected powder and changes in the particle sizes. The ejected powder is produced via a complex formation process and is hazardous due to its organic components, metal and metal oxides.

Effects of Overdischarge Rate on Thermal Runaway of NCM811 Li-Ion Batteries

Overdischarge often occurs during the use of battery packs, owing to cell inconsistency in the pack. In this study, the overdischarge behavior of 2.9 Ah cylindrical NCM811 [Li(Ni0.8Co0.1Mn0.1)O2] batteries in an adiabatic environment was investigated. A higher overdischarge rate resulted in a faster temperature increase in the batteries. Moreover, the following temperatures increased: Tu, at which the voltage decreased to 0 V; Ti, at which the current decreased to 0 A; and the maximum temperature during the battery overdischarge (Tm). The following times decreased: tu, when the voltage decreased from 3 to 0 V, and ti, when the current decreased to 0 A. The discharge capacity of the batteries was 3.06–3.14 Ah, and the maximum discharge depth of the batteries was 105.51–108.27%. Additionally, the characteristic overdischarge behavior of the batteries in a high-temperature environment (55 °C) was investigated. At high temperatures, the safety during overdischarging decreased, and the amount of energy released during the overdischarge phase and short-circuiting decreased significantly. Shallow overdischarging did not significantly affect the battery capacity recovery. None of the overdischarging cases caused fires, explosions, or thermal runaway in the batteries. The NCM811 batteries achieved good safety performance under overdischarge conditions: hence, they are valuable references for battery safety research.

Impedance Characterization of an LCO-NMC/Graphite Cell: Ohmic Conduction, SEI Transport and Charge-Transfer Phenomenon

Currently, Li-ion cells are the preferred candidates as energy sources for existing portable applications and for those being developed. Thus, a proper characterization of Li-ion cells is required to optimize their use and their manufacturing process. In this study, the transport phenomena and electrochemical processes taking place in LiCoO2-Li(NiMnCo)O2/graphite (LCO-NMC/graphite) cells are identified from half-cell measurements by means of impedance spectroscopy. The results are calculated from current densities, instead of absolute values, for the future comparison of this data with other cells. In particular, impedance spectra are fitted to simple electrical models composed of an inductive part, serial resistance, and various RQ networks—the parallel combination of a resistor and a constant phase element—depending on the cell. Thus, the evolution of resistances, capacitances, and the characteristic frequencies of the various effects are tracked with the state-of-charge (SoC) at two aging levels. Concretely, two effects are identified at the impedance spectrum; one is clearly caused by the charge transfer at the positive electrode, whereas the other one is presumably caused by the transport of lithium ions across the solid electrolyte interphase (SEI) layer. Moreover, as the cells age, the characteristic frequency of the charge transfer is drastically reduced by a factor of around 70%.

Investigation of a commercial lithium-ion battery under overcharge/over-discharge failure conditions

A lithium-ion battery (LIB) may experience overcharge or over-discharge when it is used in a battery pack because of capacity variation of different batteries in the pack and the difficulty of maintaining identical state of charge (SOC) of every single battery.

Abuse tolerance behavior of layered oxide-based Li-ion battery during overcharge and over-discharge

The main reason for the degradation of slightly overcharged NCM/graphite full cells was found to be the unstable crystal structure of the NCM material at a relatively high delithiation state.