Investigation of impedance evolution in Li-ion batteries following lithium plating and online detection methods

<div class="section abstract"><div class="htmlview paragraph">In the realm of low-altitude flight power systems, such as electric vertical take-off and landing (eVTOL), ensuring the safety and optimal performance of batteries is of utmost importance. Lithium (Li) plating, a phenomenon that affects battery performance and safety, has garnered significant attention in recent years.</div><div class="htmlview paragraph">This study investigates the intricate relationship between Li plating and the growth profile of cell thickness in Li-ion batteries. Previous research often overlooked this critical aspect, but our investigation reveals compelling insights. Notably, even during early stage of capacity fade (~ 5%), Li plating persists, leading to a remarkable final cell thickness growth exceeding 20% at an alarming 80% capacity fade.</div><div class="htmlview paragraph">These findings suggest the potential of utilizing cell thickness growth as a novel criterion for qualifying and selecting cells, in addition to the conventional measure of capacity degradation. Monitoring the growth profile of cell thickness can enhance the safety and operational efficiency of lithium-ion batteries in low-altitude flight systems. Furthermore, this study proposes an innovative approach for onboard Li plating detection by considering signals related to cell thickness data. This method reduces computational demands, enhancing detection efficiency—a vital advancement for real-time monitoring in low-altitude flight power systems. Moreover, our research establishes a strong correlation between the occurrence of Li plating and the loss of active material in the negative electrode, shedding light on the underlying mechanisms and emphasizing the need to mitigate this phenomenon.</div><div class="htmlview paragraph">Overall, this study significantly contributes to the existing research focused on improving the safety and efficiency of lithium-ion batteries in low-altitude flight applications. By emphasizing robust detection techniques for Li plating, we pave the way for safer and more efficient power sources in this rapidly evolving field.</div></div>

Lithium plating significantly reduces the lifetime of lithium-ion batteries and may even pose a safety risk in the form of an internal short circuit, leading to catastrophic cell failure. Low temperatures, high charge currents and battery age are known to be contributing factors to increased lithium plating. To reduce or avoid battery ageing induced by lithium plating, a method for lithium plating detection is essential to help understand the favourable conditions under which battery charging is optimised. In this study, we present a concept to design an experiment-based approach to improve lithium plating detection sensitivity using the non-destructive voltage relaxation analysis method. Commercial NCA/graphite cells are employed for this study. Here, the reversible part of the plated lithium providing a unique cell voltage relaxation profile is used as a pseudo-measure to detect the onset of plating. This profile is observed while the cell is at rest as well as under a low C-rate discharge regime immediately after charging. It is found that the CV (Constant Voltage) phase cut-off current value significantly influences plating detection. To address this issue, a procedure to determine the optimal cut-off current in the CV phase of charging is introduced to improve the detection sensitivity. With the proposed method, plating detection chances are improved which will help in understanding the favourable conditions and developing plating control strategies. Furthermore, a correlation between lithium plating and Electrochemical Impedance Spectroscopy (EIS) measurements are utilized to demonstrate the influence of previous ageing conditions on lithium plating.

Lithium plating in a commercial lithium-ion battery – A low-temperature aging study

Adverse lithium plating is a significant side reaction during the fast charging of lithium-ion (Li-ion) batteries when the Li-ion flux exceeds the intercalation or diffusion limits of graphite electrodes. Accurate quantification of lithium plating has always been a tough challenge given the severe defects of online detection methods such as coulombic efficiency and voltage relaxation plateau, making the mathematical correlation between cell-level thermal safety hazards and quantitative lithium plating events still a bottleneck problem. In this study, we apply a three-electrode (3E) Li-ion cell configuration and the accelerating rate calorimeter (ARC) to comprehensively investigate the interplay of unfavorable lithium plating on thermal runaway characteristics of Li-ion batteries. Lithium plating is introduced by cycling 3E Li-ion cells at low temperatures and quantified by analyzing potential-based plating energy, coulombic inefficiency, internal resistance, and voltage relaxation plateau. Surface microscopic characterization is carried out on graphite electrodes to reveal the morphologies and chemical states of lithium deposition. ARC experiments are implemented at full-cell and partial-cell scales to fundamentally understand the effects and contributions of thermally unstable lithium plating to the overall safety performance of Li-ion cell chemistries.

Lithium-ion (Li-ion) batteries play a vital role in our daily lives by powering essentials like smartphones, electric vehicles, and energy storage systems. One of the main factors that lead to accelerated aging of Li-ion batteries is the lithium plating effect. An improved understanding of lithium plating holds the potential to extend lifespan, enhance performance, and reduce cost of lithium-ion batteries. Lithium plating occurs while charging in low temperatures or with high currents, as lithium-ions accumulate on the anode.Lithium plating can be separated into two parts, a reversible and an irreversible part. During relaxation, when the battery sits idle, or while discharging, reversible plating is stripped from the anode. Typically, when plating is stripped, a voltage plateau can be observed. In contrast, irreversible plating consists of lithium deposits that cannot be stripped during discharge, therefore causing a loss of capacity.In this work, we present a novel non-destructive method for determining a cell's threshold plating current using only electrical measurements. The method is validated using commercial 3.2Ah Panasonic NCR18650B cells at varying low temperatures and charging currents. The designed method requires the use of two identical cells, a reference and a test cell. After completely discharging both batteries at room temperature to reach 0% depth of discharge (DOD), the same plating tests at low temperatures are conducted on both cells. Once the cells are fully charged with a constant current of 0.5C, the reference cell experiences relaxation for 10 minutes. Simultaneously, a sine wave current is applied to the test cell, leading to small charging and discharging cycles. During the positive half-wave of the sine, plating occurs and during the negative half-wave reversible plating is stripped again. As plating only occurs, once the threshold plating current is exceeded, the sine amplitude must be greater than this threshold. It is important to note that, the charging current consists of intercalation current and plating current.Intercalation is the insertion of Li-ion into the layered structure of graphite during charging. As charging progresses, the surface concentration of intercalated lithium increases, but simultaneously, the number of vacancies for lithium intercalation at the graphite surface decreases. When the anode potential falls below 0V, thermodynamically allowing lithium plating, the intercalation current decreases and the plating current increases. With continued charging, the plating current continues to increase, while the intercalation current gradually diminishes.We assume that only the part of the sine exceeding this threshold is responsible for the lithium plating, while the portion below this threshold contributes to intercalation. In contrast, the negative half-wave is completely responsible for stripping. After 10 minutes, both cells are discharged with a low current while the remaining reversible plating is stripped. From the voltage and current measurements during discharge, we can compute how much reversible plating was stripped during the sine phase and during the discharge. To determine the plating current, the plated charge amount dQ on the positive sine half-wave is calculated by the difference between the stripped charge amount on the sine negative half-wave and the difference between the stripped charge amount of the reference cell and the test cell (c.f. attached figure). With the known plated charge amount dQ, the sine is integrated to find the threshold plating current.To validate the precision of this method, we subject an additional cell to charging at the same low temperature as the other cells. The charging involved varying currents from 0.04C to 0.4C in 10 steps, with a 1.5-hour interval between each step for the cell to cool down. To determine the threshold plating current, a differential voltage analysis (DVA) was conducted at each step, thus identifying the lowest current where a voltage plateau occurred, as the threshold plating current. Further refinement involves smaller steps to achieve a more accurate plating current. We assume this result is the true threshold plating current. Comparing with our novel method, in the worst case we achieve an error of less than 100mA. To ensure the reliability and reproducibility of this method across varying cells, additional plating tests, involving various cell chemistry types, are planned. Figure 1

Lithium plating detection using differential charging current analysis in lithium-ion batteries

A new on-line method for lithium plating detection in lithium-ion batteries

Lithium Plating Mechanism, Detection, and Mitigation in Lithium-Ion Batteries

Lithium plating detection of lithium-ion batteries based on the improved variance entropy algorithm

Fast charging is a key requirement for customer acceptance of battery electric vehicles. Fast charging of lithium-ion batteries is limited by lithium plating, an undesired side reaction that leads to rapid degradation and poses a potential safety hazard. In order to approach but not exceed the lithium plating current limit during fast charging, a variety of analytical tools have been developed to detect lithium plating. In this publication, we propose a new impedance-based method for the time-resolved detection of lithium plating. The proposed method was demonstrated with an integrated cell monitoring circuit capable of measuring the impedance during cell operation, bringing the feasibility of implementation in an automotive target application within reach. Importantly, the proposed method eliminates the temperature dependence which is an intrinsic problem for impedance-based lithium plating detection in automotive lithium-ion cells, thus making on-board plating detection feasible.

Cycle life is critically important for applications of lithium-ion batteries (LIBs). Numerous models have been proposed in the literature to predict the life time of LIBs (1, 2). Most of these models focused on growth of solid-electrolyte-interphase (SEI), which leads to capacity fade that is proportional to the square root of time, and the aging rate increases with cell temperature by following the Arrhenius law. Several recent experimental studies, however, reported aging behavior that cannot be explained by, at least not solely by, SEI growth. For instance, Waldmann et al. (3) cycled a set of 1.5Ah graphite/NMC cells at different temperatures, and found that the cell at 25oC had the longest life. Plotting cell aging rate with reciprocal temperature, they observed a transition of activation energy from a positive value at T>25oC to a negative value at T<25oC, indicating a transition of dominating aging mechanisms. The main aging mechanism at T>25oC is SEI growth, and at T<25oC is believed to be lithium plating, i.e. deposition of metallic lithium on graphite surfaces. The lithium deposition reaction directly reduces cell capacity by consuming active lithium. In worst-case scenarios, the plated lithium can pierce the separator, induce internal short circuit and cause catastrophic consequences. Research efforts on the effects of lithium plating over cell aging are rather limited in the literature, especially in terms of numerical modeling. In the present study, we present a comprehensive LIB aging model with incorporation of both SEI growth and lithium plating. The model can well capture the recently discovered LIB aging behaviors associated with lithium plating. In addition, the relative contribution to cell aging by SEI growth and by lithium plating can be quantified for cells at different operating conditions with different design parameters. Figure 1 shows the variation of cell capacity with cycle number for a plug-in electric-vehicle (PHEV) LIB with energy density of 170 Wh/kg cycled at 25oC with 1C charge and 2C discharge. At this moderate operating condition it is usually believed that lithium plating is not a concern. However, we found in our experiment that cell capacity dropped abruptly after ~3000 cycles, which is in consistence with the recently reported nonlinear aging behavior by Schuster et al. (4). The model presented in this study well captures this nonlinear behavior, as shown in Fig. 1a, and this abrupt drop in cell capacity is attributed to the rapid rise of lithium plating rate after extended cycling as shown in Fig. 1b. The model is then applied to predict the cycle life of the above PHEV cell at different ambient temperatures, as shown in Fig. 2a. It is found that the cell at 20oC has the longest cycle life. Either increasing or lower the temperature would accelerate cell aging. These results are in accordance with the recent experiment findings by Waldmann et al (3). The effects of electrode thickness on the cycle life are also investigated, as shown in Fig. 2b. These cells are cycled at 25oC with 1C charge and 1C discharge. Even at this moderate operating condition, cells with thicker electrode have much poorer life as shown in Fig. 2b, which is because lithium plating is more prone to occur with the increase of electrode thickness. This result has a profound implication on high-energy, thick-electrode cells for all electric vehicles (EV). Details about the model development, and about the effects of cell design parameters and operating conditions on cell aging due to lithium plating will be given in this presentation. Finally, we shall propose some novel strategies to significantly extend the cycle life and increase fast rechargeability of energy-dense EV batteries.

Lithium plating on the negative electrode of Li-ion batteries remains as a great concern for durability, reliability and safety in operation under low temperatures and fast charging conditions. High-accuracy detection of Li-plating is critically needed for field operations. To detect the lithium plating is to track its multiphysics footprint since lithium plating often is a localized event while the driving force from chemical, electrical, thermal and mechanical origins could vary with time and locality which makes the detection and characterization challenging. Here, we summarize the multiphysical footprints of lithium plating and the corresponding state-of-the-art detection methods. By assessing and comparing these methods, the combination of capacity/voltage differential, R–Q mapping and Arrhenius outlier tracking could be promising and effective for battery diagnosis, prognosis and management. We analyze the origins of quantitative error in sample preparation, overly simplified assumption and dynamic evolution of the plated Li, and recommend the in situ and quantitative chemical analysis method, such as in situ NMR, EPR, X-ray and neutron. In addition, we propose the four conjectures on the capacity plunge, lithium plating, pore clogging, electrolyte drainage and rapid SEI growth, can be aligned and unified to one scenario basically triggered by lithium plating.

The local lithium plating caused by anode crack defect in Li-ion battery

Fast charging technology is widely recognized as a critical factor in bolstering consumer appeal of battery electric vehicles (BEVs). The U.S. Department of Energy (DOE) has set a goal of developing extreme fast charging (XFC) battery technology that can recharge a 200-mile BEV in 10 minutes. A key barrier to XFC of automotive Li-ion batteries is the issue of lithium plating, which drastically deteriorates battery life and even induces hazardous consequences. Fundamentally, lithium plating is affected by the rate capability of ion transport in the electrolyte, intercalation reaction at graphite surface, and solid-state diffusion in graphite particles. Research in the literature, accordingly, has been focusing on improving electrolyte transport properties, enhancing charge transfer kinetics, or utilizing smaller particles. Li-ion battery is well known for its trade-off nature. Improving one property without sacrificing others is always challenging. An alternative approach to suppressing lithium plating is to elevate charge temperature. Indeed, an increase in temperature can boost the rate capability of the above three processes simultaneously. However, an elevated temperature, on the other hand, accelerates the solid-electrolyte-interphase (SEI) growth. Owing to the interplay between lithium plating and SEI growth, it is universally believed that Li-ion batteries have an optimal life at room temperature. [1] In 2018, our group presented a numerical study revealing that the optimal temperature of a Li-ion battery, in contrary to the conventional wisdom, actually increases with an increase of charge rate and/or energy density.[2] Enlightened by this finding, we proposed a heated-charge method [2, 3] to charge a Li-ion cell at an elevated temperature of 40-60oC to enable XFC without Li plating. Very recently, Tesla has applied this concept in its V3 superchargers. Using an ‘On-route Battery Warmup’ strategy, Tesla vehicles are designed to arrive at a fast charging station at a temperature of ~40oC, demonstrating the commercial viability of charging a BEV at an elevated temperature. Nevertheless, a potential issue of Tesla’s on-route warmup strategy is the slow heating speed, making a battery stay at a high temperature for a long period of time and hence incurring excessive SEI-induced degradation. Currently, we are developing an XFC battery based on the heated-charge method. With a novel structure, our battery has >100x faster heating than conventional external heating methods, thereby limiting the duration of heating to a matter of seconds. More profoundly, we will present in this talk that our battery, having an energy density of 210 Wh/kg, could sustain 2,000 cycles of 10-min (6C) charge to 80% state of charge with only 7% capacity loss.

Intelligent lithium plating detection and prediction method for Li-ion batteries based on random forest model