Growth Of Solid Electrolyte Interface Research Articles

Characterization of pristine and aged NMC lithium-ion battery thermal runaway using ARC experiments coupled with optical techniques

Battery thermal runaway (TR) challenges battery applications due to safety considerations, potentially endangering consumers. Understanding the process is crucial to defining first alarm strategies that indicate the risk of TR and designing systems to mitigate this problem. For this reason, the present paper aims to characterise key variables of the venting and thermal runaway processes. Experimental tests were conducted in an accelerating rate calorimeter (ARC) using the heat wait seek (HWS) protocol, which tracks the battery temperature after detecting an exothermic reaction during the seek period. The maximum temperature rise rate and peak temperature that the calorimeter can achieve are 15 °C/min and 300 °C. Two optical accesses in the ARC were modified to use optical techniques such as Schlieren double pass and infrared. The results cover 3 different cell conditions: Pristine cells at state of charge (SOC) 100 %, pristine cells at SOC 50 %, and aged cells at SOC 100 %. For statical purposes, each cell condition was repeated 5 times. The aged battery was cycled to boost solid electrolyte interface growth. The images obtained were post-processed, with a specific methodology for each optical technique, and according to the parameters intended to be obtained. The main result shows that for higher SOC, the exothermic reaction is detected earlier than for SOC 50 %, which was only detected in an advanced TR stage (higher temperature rise rate). Therefore, the battery system capability to detect plays a crucial role in safety. Safety actuation time is reduced by ∼ 40 % for SOC 50 %. However, the energy to manage during this situation is lower (∼42 %), depending on the mass inside the battery, revealing the importance of a good venting cap design. Infrared images have shown higher particle temperatures for higher SOC, about 150 °C higher than the SOC 50 %. The particle velocity, in this case, achieved 30 m/s.

Low‐temperature performance of Na‐ion batteries

AbstractSodium‐ion batteries (NIBs) have become an ideal alternative to lithium‐ion batteries in the field of electrochemical energy storage due to their abundant raw materials and cost‐effectiveness. With the progress of human society, the requirements for energy storage systems in extreme environments, such as deep‐sea exploration, aerospace missions, and tunnel operations, have become more stringent. The comprehensive performance of NIBs at low temperatures (LTs) has also become an important consideration. Under LT conditions, challenges such as increased viscosity of electrolyte, abnormal growth of solid electrolyte interface, and poor contact between collector and electrode materials emerge. The aforementioned issues hinder the diffusion kinetics of sodium ions (Na+) at the electrode/electrolyte interface and cause rapid degradation of battery performance. Consequently, the optimization of electrolyte composition and cathode/anode materials becomes an effective approach to improve LT performance. This review discusses the conduction behavior and limiting factors of Na+ in both solid electrodes and liquid electrolytes at LT. Furthermore, it systematically reviews the recent research progress of LT NIBs from three aspects: cathode materials, anode materials, and electrolyte components. This review aims to provide a valuable reference for developing high‐performance LT NIBs.

The Voltage-Based Implementation of the Tunneling Mechanism in Aging Models for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have become one of the most crucial power sources for electronics and electric vehicles due to high energy density, long cycle life, environmental friendliness, etc. Precise explanation and prediction of the aging behavior of LIBs is quickly becoming a hotspot. A solid electrolyte interface (SEI) growth is regarded as the dominant factor of capacity losses in LIBs. However, the previous SEI growth and aging models were based on energy levels. That means the energy barrier related to the Fermi level of SEI and electrode was used as the input parameter. It is not straightforward to implement, especially for industrial applications. Furthermore, the state-of-charge (SoC) and the energy barrier were usually assumed to be constant during (dis)charging, contradicting common sense and affecting the calculations' accuracy.The present work proposes and experimentally validates an advanced voltage-based aging model. The voltage of the anode electrode is adopted as an input parameter in this model. It is easier to introduce dependence of aging on the voltage/SoC of the electrode with this model. It is found that deep delithiation of the anodes and lower SoC of LIBs will mitigate electron tunneling, lower SEI growth, and reduce calendar aging. Commonly used anode materials, such as graphite, Li4Ti5O12, and blended Si/C, are presented as interesting cases to investigate the effects of different electrode materials on the tunneling current profiles during (dis)charging for the first time. The model is instructive and can predict aging in LIBs with various electrode materials. This model and related analyses are beneficial for further optimizing LIB's electronic and electrode properties and as interesting limiting cases for testing battery modeling software.

Physics-Based State of Health Prediction of Lithium-Ion Battery during Fast Charging

Electrification of the transportation sector and increased use in consumer electronics have driven the increasing demand for lithium-ion batteries (LiBs) (1). Despite their high energy density and long service life, LiBs suffer from capacity degradation due to continuous growth of solid electrolyte interface (SEI) layer and plating of lithium on the anode surface. Graphite, the anode in most LiBs, has a high tendency to catalyze the degradation of the electrolyte consisting of LiPF6 and ethylene carbonate to form an SEI of Li-rich carbonate, phosphate, and fluoride compounds (2, 3). The SEI film grows during service due to the deposition of reaction products and repeated cycles of damage and reformation due to the contraction and expansion associated with volume changes during Li-ion intercalation and deintercalation. Additionally, fast or low-temperature charging of batteries results in lithium plating on the anode surface because the elevated concentration of Li+ on the anode surface results in graphite potential falling below 0V vs. Li+/Li and increased likelihood of Li deposition compared to intercalation (4). Lithium loss due to the side reactions of SEI growth and plating contributes to capacity loss and may increase the likelihood of battery failure. Hence, accurate modeling of the side reactions is required to determine the state of health (SOH) and predict the remaining capacity of LiBs during operation (5).We report an experimentally validated single particle model (SPM) to estimate the influence of SEI growth and Li plating on the capacity changes in Lithium Cobalt Oxide (LCO)/Carbon cells during repeated cycling (6-8). The SPM model idealizes each electrode as a single particle to approximate the cell response. A. Sarkar et al. (5) included the influence of SEI growth, plating, SEI fracture, and temperature in the SPM model to determine the influence of the side reactions on battery performance. The parameters corresponding to side reactions, such as the SEI film growth rate, conductivity of the SEI film, and reversibility of the plating reaction, were determined through comparison of numerical predictions of cell voltage and capacity change with experimental response measured at charging rates of 0.1C and fast charging rate of 2C on PowerStream 35 mAh LCO/C coin cells (Lir2032) as shown in Figure 1. In addition, the coin cells were subjected to charge/discharge experiments at charging rates varying from 0.1C – 5C for 100 cycles. Experimental measurements of the cell capacity changes were compared to model predictions for the different charging rates to validate the modeling assumptions and determine the efficacy of the estimated parameters in describing the cell degradation. The agreement between the model prediction and measured experimental response showed that the single particle model augmented with side reaction mechanisms can describe the cell degradation and is suitable for predicting the remaining capacity and safety of LiBs subjected to a range of charging rates. The model can also predict the accumulation of irreversibly plated lithium on the anode surface during repeated fast charging. The amount of plated lithium determines the severity of dendritic growth, and thus, model predictions of lithium accumulation may be used to estimate the likelihood of battery failure under fast charging conditions. Acknowledgment:This work was supported by the National Science Foundation, Iowa State University, and University of Connecticut.

Effect of Solvent Segregation on the Performance of Lithium-Ion Batteries

The pseudo two-dimensional (P2D) model is one of the most powerful tools in modelling lithium-ion batteries (LIBs) 1, in that it can describe the complex electrochemical and thermal behaviours of LIBs with high fidelity yet maintain relatively high computing efficiency. To achieve that, many assumptions have been made, one of which is the single solvent assumption. However, most electrolytes used in LIBs uses multiple solvents to balance the requirements of conductivity, diffusivity and viscosity 2. Therefore, the single solvent assumption indicates that all solvents move as a single entity.However, previous experimental studies have shown that Li+ preferentially attracts cyclic carbonates (like ethylene carbonate, EC) rather than linear carbonates (such as ethyl-methyl carbonate, EMC) to form ion-solvent clusters 3. During charge/discharge, ion-solvent clusters move between the positive and negative electrodes to constitute ionic current. At the electrolyte-electrolyte interface, Li+ de-solvates from the clusters and intercalates into the electrode, or vice versa. Such process will induce concentration gradients of both solvents and lithium ions; the solvent concentration has been ignored in the P2D model. The simplification means the current P2D model fails to capture two important phenomena: (1) many electrolyte properties - including conductivity, diffusivity, and thermodynamic factors - are sensitive to the solvent concentration 4; (2) the solvent components in the ion-solvent clusters are preferentially consumed by interfacial side reactions such as the growth of solid-electrolyte interface (SEI) 3.To fill this gap, we add an extra governing equation for the solvent concentration (in our case, EC) which allows us to describe an electrolyte with two solvents and one salt. We also include a cross diffusion term to consider the dragging effect between the working solvent (EC) and lithium ions. For the charge conservation equation, we directly use measured liquid junction potential as a function of both solvent and lithium-ion concentration, which avoids possible errors brought by identifying the thermodynamic factors.To elucidate the effect of solvent segregation, we compare the overpotential and concentration profile of Li ion and EC at the end of 3C discharge of the normal DFN (single case) and our revised model (double case). The revised model predicts opposite EC concentration compared with Li+, which has been observed by Wang et al. 5 For a high value of , the dragging effect between Li+ and EC is more significant, inducing high concentration gradients of both species. The EC overpotential can be as high as 10 mV and further affects the rate performance of LIBs. This revised model captures more complicated transport mechanisms in the electrolyte and opens the chance of linking the microscopic understanding on solvation structure to a continuum level model. Reference: (1) Newman, J.; Thomas-Alyea, K. E. Electrochemical Systems; 2004.(2) Xu, K. Electrolytes and interphases in Li-ion batteries and beyond. Chem Rev 2014, 114 (23), 11503-11618. DOI: 10.1021/cr500003w.(3) Xu, K. Solvation Sheath of Li+ in Nonaqueous Electrolytes and Its Implication of Graphite/ Electrolyte Interface Chemistry. J. Phys. Chem. C 2007.(4) Ding, M. S.; Xu, K.; Zhang, S. S.; Amine, K.; Henriksen, G. L.; Jow, T. R. Change of Conductivity with Salt Content, Solvent Composition, and Temperature for Electrolytes of LiPF6 in Ethylene Carbonate-Ethyl Methyl Carbonate. Journal of The Electrochemical Society 2001, 148 (10). DOI: 10.1149/1.1403730.(5) Wang, A. A.; Greenbank, S.; Li, G.; Howey, D. A.; Monroe, C. W. Current-driven solvent segregation in lithium-ion electrolytes. Cell Reports Physical Science 2022, 3 (9). DOI: 10.1016/j.xcrp.2022.101047. Figure 1

Reversible growth of solid electrolyte interface enhances charge capacity in cobalt sulfide-carbon nanotube anodes

The development of high-performance anode materials for lithium-ion batteries is a critical aspect of advancing energy storage technology. This study presents a novel approach to improve the charge capacity of anodes by harnessing the reversible growth of the solid electrolyte interface (SEI). This work focuses on cobalt sulfide (Co9S8) nanoparticles incorporated into a porous carbon nanotube (CNT) structure. Through a two-step pyrolysis process, Co9S8CNT composites, characterized by their conductive and mechanically robust CNT matrix are successfully synthesized. These Co9S8CNT anodes exhibit excellent initial charge capacity (560.5 mAh g−1 at 100 mA g−1) and remarkable stability, with a charge capacity of 633 mAh g−1 after 1000 cycles at 1000 mA g−1, accompanied by a Coulombic efficiency exceeding 99 %. Notably, this investigation reveals that the growth of the SEI plays a pivotal role in enhancing the charge capacity. Through in-situ Raman spectroscopy and other analytical techniques, it is suggested that the reversible reduction of organic solvent molecules within the large polymeric SEI is responsible for the increased charge capacity. This unique phenomenon is characterized by changes in the SEI's composition, driven by the charge and discharge processes. This study is a novel attempt to report a SEI's reversible growth that results in improved charge capacity, contrasting with prior research where SEI growth typically leads to capacity loss. Understanding this stable system provides valuable insights into increasing the cycle life and charge capacity of anodes, not only for transition metal sulfides but also for broader applications in energy storage.

Effects of Cathode Loadings on the Performance of the LiNi0.8Mn0.1Co0.1O2 Cathode in Lithium Batteries

LiNixMnyCozO2 (NMCs, x + y + z = 1) represent one promising cathode material for next-generation lithium-ion batteries (LIBs) and beyond, due to their high specific capacity and low cost.1-3 The current commercialized batteries tend to utilize high loadings of cathode materials and thin Li anodes for producing higher energy densities. However, a systematic study on the effects of cathode loadings is missing. To this end, we recently conducted a comparative study on the effects of different cathode loadings on the performance of LiNi0.8Mn0.1Co0.1O2 (NMC811). The NMC811 loading ranges from 2 – 14 mg/cm2. The resultant Li||NMC811 cells were tested for their capacity retention and sustainable capacity at different C-rates. Our study revealed that the cathode loadings have remarkably affected the cell performance. With increasing NMC811 loadings, the cells are more liable to fade in their capacity, due to a faster growth of solid electrolyte interface (SEI) on NMC811 particles and thereby a more sluggish Li-ion transportation. We also noticed that the Li anode side had remarkable effects on the Li||NMC811 cells. Particularly, we demonstrated that a polymeric surface coating via molecular layer deposition could protect the Li anode from degradation and thereby sustain Li||NMC811 cells for a better performance. Therefore, we concluded that the performance of the Li||NMC811 cells suffers from the issues of both the NMC811cathode and Li anode. It is significant to address their issues simultaneously for high performance.

Probe Growth and Degradation of SEI at Multivalent Battery Systems

Solid Electrolyte Interface (SEI) has not been widely reported for multivalent battery systems. Question such as whether there’s a SEI growth at the interface of the metal anode and the multivalent electrolytes is unclear. How the SEI is formed and its evolution with the electrochemical process is not known. Our lab has spent a great deal of efforts of understanding the role of SEI, its composition and evolution for multivalent electrolyte systems, and this work aims to give an overview of the recent research efforts with the use of the operando electroanalytical methods that reveal the SEI evolution for multivalent battery designs.

Safety Evaluation of Temperature-Dependent Aging Mechanisms of Li-Ion Batteries Using ARC Tests with Multiple Online Sensors

Compared to many other characteristics of Li-ion batteries, the safety behavior is a critical property and should be examined carefully. Especially manufacturers and most studies only focus on the safety of pristine cells. However, the safety behavior can drastically change dependent on the prior aging conditions such as ambient temperature. Especially low temperature aged cells with Li plating show a drastically decreased safety behavior [1]. Moreover, cells aged at higher temperatures with a distinct solid-electrolyte-interface (SEI) layer on the anode show an increased onset of self-heating leading to improved safety [2]. Post-Mortem analysis of aged cells confirmed the two dominating aging mechanisms: Li plating and SEI growth for low and high temperature range, respectively.Heat-wait-seek (HWS) tests under quasi-adiabatic conditions in an accelerated rate calorimeter (ARC) are a well-known method to evaluate the safety behavior of Li-ion batteries and can reveal critical temperatures such as the onset of self-heating. HWS tests on cells aged at different temperatures until different state-of-health (SOH) reveal the trend that a more pronounced aging increases or decreases the onset of self-heating depending on whether SEI growth or Li plating is the dominating aging mechanism.In addition to the temperature measurement, multiple sensors for voltage, resistance, strain, and ultrasonic transmission and reflection were placed on the pouch cell for a better understanding of the ongoing processes while the HWS tests. The benefit of these sensors is that they are cheap, allowing them to be widely implemented. Furthermore, an externally coupled mass spectrometer provides information about the gases produced and released after venting of the cell [3]. By Correlating different sensors signals, critical events on the way to the thermal runaway can be reliably identified or even predict in an early stage.Hence, the HWS tests on Li-ion batteries aged at different temperatures in combination with the multi sensor study provide a comprehensive understanding of the influence of temperature dependent aging state on the safety behavior of Li-ion pouch cells. Acknowledgment We gratefully acknowledge the German Federal Ministry of Education and Research (BMBF) for the financial support of the projects AnaLiBa (03XP0347C) and MiCha (03XP0317C) within the AQua cluster.

Ceramic Fillers for Improved Lithium-Sulfur Batteries

With the decarbonization of transportation, the demand for electric vehicles (EVs) and batteries that can power these EVs has been increasing. Lithium-ion-based batteries are already well-established and are considered the main chemistries to power current EVs. However, limited specific energy (< 300 Wh/kg) prevents these batteries from having high mileage vehicles. Lithium-sulfur batteries are considered the most promising next-generation energy storage system as they high theoretical capacity (~1675 mAhg-1), low cathode materials cost, and cell energy densities that can exceed 700 Wh/kg [1,2]. However, some major drawbacks prevent the Li-S battery system from being applicable in energy devices and hinder its commercialization, that include low power density and rapid capacity degradation during their cycling life. In addition, the lithium metal anode in Li-S batteries bring various issues to the forefront such as continuous solid electrolyte interface growth, dendrite formation, and loss of active lithium and electrolyte. These issues are further exacerbated at high C-rates which increases the possibility of an internal short-circuit and sudden cell failure [3]. In order to promote longer life cycles and prevent sudden cell failure, a thorough understanding of the cell’s electrochemical behavior is crucial for the development of a stable and practical Li-S battery system. The introduction of oxide fillers such TiO2, Al2O3, SiO2, etc. has been previously studied in various lithium-ion systems and has been shown to improve the cell’s lithium-ion transport properties, which in turn improve the performance of Li-S cells [4]. When used as interlayers they can also trap soluble polysulfides diffusing out of the cathode and reduce their crossover to the anode which helps reduce the shuttle effect of said polysulfides.In the present study, the use of a polysulfide immobilizing system to reduce sulfur loss and improve capacity retention has been demonstrated. The galvanostatic charge-discharge cycling study shows that cells retain higher capacity during the course of cycling. The initial capacity for Li-S cells with the filler average 1300+ mAh/g (C/10) while the capacity stabilizes around 1000 mAh/g after 3 cycles (C/5). The capacity retention at C/5 after 75 cycles was approximately 875 mAh/g which represents a rate 0.17% drop per cycle. When compared to control cells, the cells containing no fillers had lower initial capacity that averaged 1050 mAh/g and that rapidly declined to stabilize around 650 mAh/g. However, after this major drop, the cells remained stable no with measurable drop after 75 cycles. The behavior indicates that the cells with fillers delayed the effect of sulfur loss experienced in cells without fillers; however, the slow capacity drop that ensued, indicates that while polysulfide trapping was efficient it was unable to fully prevent it. The effect of fillers on the Coulombic efficiency (CE) also supports the polysulfide “trapping” mechanism and shows the ability of the cell to reduce the shuttle effect that contributes to lower CE values. Further electrochemical studies have been performed to understand the mechanisms of the improvement of the cell.

How Cyclic Aging at Different Temperatures Affects Safety of Li-Ion Pouch Cells

Li-ion battery safety behavior is critical and should be examined carefully. However, safety testing is typically performed only on pristine cells. This neglects the significant effect of aging conditions, such as ambient temperature, on safety behavior. For example, aging at low temperatures results in Li plating and thus drastically reduces safety [1–3]. Cells aged at higher temperatures with a pronounced solid-electrolyte-interface (SEI) layer on the anode show an increased onset of self-heating leading to improved safety [3,4].The temperature dependent cyclic aging behavior of commercial Li-ion pouch cells is evaluated using an Arrhenius plot. Further Post-Mortem analyses of aged cells from both branches of the V-shaped Arrhenius plot confirm two dominant aging mechanisms: Li plating and SEI growth for the low and high temperature ranges, respectively.Heat-wait-seek (HWS) tests under quasi-adiabatic conditions in an accelerated rate calorimeter (ARC) are used to evaluate safety behavior and identify critical temperatures such as the onset of self-heating. Multiple sensors (voltage, resistance, temperature, strain, and ultrasonic transmission) are placed on the pouch cell to provide a better understanding of the processes taking place during HWS tests. These sensors show that some critical events, such as the onset of swelling, venting, or separator melting, are only slightly affected by aging. In contrast, the onset of self-heating depends on the aging mechanism and state of health (SOH) of the cell, as a more pronounced aging has a greater impact on the change in safety. This knowledge can be used, for example, by cell manufacturers to estimate the minimum safety of aged cells based on tests of new cells.

A review of the use of Mxenes as hosts in lithium metal anodes and the anode formation

Severe dendritic growth and volume expansion are easily induced during the cycling process when lithium metal is used as an anode electrode directly. These problems cause the solid electrolyte interface (SEI) layer to break and re-form, which consumes the active lithium metal and electrolyte, thereby reducing the Coulomb efficiency and rapid capacity. Designing a host matrix with rapid mass transfer and enough storage space to promote lithium homogeneous deposition, hence reducing the repeated SEI growth and the formation of dead lithium, is an effective method to address the concerns mentioned above issues. MXenes with two-dimensional layered structures have been regarded as feasible hosts for stabilizing lithium due to their superior electrical conductivity, sizeable interlayer space, abundant lithiophilic surface functional groups, and excellent mechanical properties. In this review, we first summarized the multiple synthesis methods of MXenes, including etching the precursor MAX phase, chemical vapor deposition, UV-induced etching, and mechanochemical et al. Various synthesis methods would induce different surface termination and lamellar structures, affecting lithium metal nucleation and growth behavior. Subsequently, pure MXene, MXene-carbon and MXene-non carbon hybrid compounds applied for lithium metal anode hosts were introduced, focusing on alleviating noticeable volume changes and inhibiting lithium dendrite growth. Finally, some modification strategies and potential research prospects were summarized and prospected.

Operando Analysis of the Gassing and Swelling Behavior of Lithium-ion Pouch Cells during Formation

Improving the energy density of lithium-ion batteries advances the use of novel electrode materials having a high specific capacity, such as nickel-rich cathodes and silicon-containing anodes. These materials exhibit a high level of gas evolution during formation, which poses a safety hazard during operation. Analyzing the gas volume and the gassing duration is thus crucial to assess material properties and determining suitable formation procedures. This paper presents a novel method for evaluating both gassing and swelling simultaneously to determine the operando gas evolution of pouch cells with volume resolutions below 1 μl. Dual 1D dilatometry is performed using a cell expansion bracket which applies a quasi-constant force on the cell, thus providing reproducible formation conditions. The method was validated using the immersion bath measurement method and NCM/graphite pouch cells were compared to high-energy NCA/silicon-graphite pouch cells. Silicon-containing cells exhibited gas evolution higher by a factor of seven over ten successive cycles, thus demonstrating the challenges of high-silicon anodes. The concurrent dilation analysis further revealed a constant thickness increase over the formation, indicating continuous SEI growth and lithium loss. Consequently, the method can be used to select an ideal degassing time and to adjust the formation protocols with respect to gas evolution.

Interfacial-Catalysis-Enabled Layered and Inorganic-Rich SEI on Hard Carbon Anodes in Ester Electrolytes for Sodium-Ion Batteries.

Constructing a homogenous and inorganic-rich solid electrolyte interface (SEI) can efficiently improve the overall sodium-storage performance of hard carbon (HC) anodes. However, the thick and heterogenous SEI derived from conventional ester electrolytes fails to meet the above requirements. Herein, an innovative interfacial catalysis mechanism is proposed to design a favorable SEI in ester electrolytes by reconstructing the surface functionality of HC, of which abundant CO (carbonyl) bonds are accurately and homogenously implanted. The CO (carbonyl) bonds act as active centers that controllably catalyze the preferential reduction of salts and directionally guide SEI growth to form a homogenous, layered, and inorganic-rich SEI. Therefore, excessive solvent decomposition is suppressed, and the interfacial Na+ transfer and structural stability of SEI on HC anodes are greatly promoted, contributing to a comprehensive enhancement in sodium-storage performance. The optimal anodes exhibit an outstanding reversible capacity (379.6 mAh g-1 ), an ultrahigh initial Coulombic efficiency (93.2%), a largely improved rate capability, and an extremely stable cycling performance with a capacity decay rate of 0.0018% for 10 000 cycles at 5 A g-1 . This work provides novel insights into smart regulation of interface chemistry to realize high-performance HC anodes for sodium storage.

Capacity Degradation and Aging Mechanisms Evolution of Lithium-Ion Batteries under Different Operation Conditions

Since lithium-ion batteries are rarely utilized in their full state-of-charge (SOC) range (0–100%); therefore, in practice, understanding the performance degradation with different SOC swing ranges is critical for optimizing battery usage. We modeled battery aging under different depths of discharge (DODs), SOC swing ranges and temperatures by coupling four aging mechanisms, including the solid–electrolyte interface (SEI) layer growth, lithium (li) plating, particle cracking, and loss of active material (LAM) with a P2D model. Additionally, the mechanisms causing accelerated capacity to drop near a battery’s end of life (EOL) were investigated systematically. The results indicated that when the battery operated with a high SOC range, the capacity was more prone to accelerated degradation near the EOL. Among the four degradation mechanisms, li plating was mainly sensitive to the operation temperature and SOC swing ranges, while the SEI growth was mainly sensitive to temperature. Furthermore, there was an inhibitory interaction between li plating and SEI growth, as well as positive feedback between LAM and particle cracking during battery aging. Additionally, we discovered that the extremely low local porosity around the anode separator could cause the ‘knee point’ of capacity degradation.

Quantitative investigation of the cycling behavior and SEI formation of tin through time-resolved microgravimetry

Insufficient understanding on the mechanism of electrode failure restricts the development of sensitive electrode materials such as tin-based alloys. Here-in, a non-destructive and time-resolved in-situ characterization method is proposed for the investigation of the electrode failure. The cycling behavior of tin electrode and the evolution of the Solid-Electrolyte Interface (SEI) were investigated via combining quartz crystal micro-gravimetry (QCM) with cyclic voltammetry (CV). Key findings were further confirmed by ex-situ SEM, TEM and XPS. Remarkably, opposite to the general behavior, SEI thickness grows linearly with the electrode's thickness. This is ascribed to the continuous cracking and oxidization of Sn. However, below a critical thickness (Xo), the SEI growth by cracking (Xsn > Xo) transitions to diffusion-controlled growth (Xsn ≤ Xo). Surprisingly, after serious fracture of Sn, the QCM mass spectrometry reveals, the mass of Li2O also cycled reversibly along with Li insertion. Despite the general belief that the SEI is formed before the lithiation, the inorganic SEI mainly composed of Li2O and Li2CO3 unexpectedly forms in the later cycles during the lithiation. This inorganic part of the SEI plays the most important role of stabilizing the SEI. Preventing its formation, by using an unsuitable voltage window, results in a completely porous non-self-limiting SEI along with a porous electrode.

Accurate prediction of remaining useful life for lithium-ion battery using deep neural networks with memory features

Li-ion batteries degrade with time and usage, caused by factors like the growth of solid electrolyte interface (SEI), lithium plating, and several other irreversible electrochemical reactions. These failure mechanisms exacerbate degradation and reduce the remaining useful life (RUL). This paper highlights the importance of feature engineering and how a careful presentation of the data can capture the hidden trends in the data. It develops a novel framework of deep neural networks with memory features (DNNwMF) to accurately predict the RUL of Li-ion batteries using features of current and previous n cycles. The results demonstrate that introducing memory in this form significantly improves the accuracy of RUL prediction as root mean square error (RMSE) decreases more than twice with memory compared to without memory. The optimal value of n, referred to as nopt, is also determined, which minimizes the prediction error. Moreover, the number of optimization parameters reduces by more than an order of magnitude if an autoencoder is used in conjunction with the proposed framework (DNNwMF). The framework in this paper results in a trade-off between accuracy and computational complexity as the accuracy improves with the encoding dimensions. To validate the generalizability of the developed framework, two different datasets, i) from the National Aeronautics and Space Administration’s Prognostic Center of excellence and ii) from the Center for Advanced Life Cycle Engineering, are used to validate the results.

Experimental Study of the Degradation Characteristics of LiFePO4 and LiNi0.5Co0.2Mn0.3O2 Batteries during Overcharging at Low Temperatures

Battery overcharging can occur due to capacity and internal resistance variations among cells or battery management system failure that both accelerate battery degradation, which is more likely at low temperatures because of the large polarization effect. This study experimentally investigated the battery degradation characteristics during charging of LiFePO4 (LFP)/Graphite batteries at voltages of 3.65–4.8 V and Li(Ni0.5Co0.2Mn0.3)O2 (NCM)/Graphite batteries at 4.2–4.8 V at −10 °C with currents of 0.2–1 C. The results showed that the LFP cell capacities decreased linearly with an increasing number of cycles, while the NCM cell capacities faded in three trends with an increasing number of cycles under different conditions with linear fading, accelerated fading, and decelerated fading. The incremental capacity curves and differential voltage curves showed that the LFP cell degradation was mainly caused by the loss of lithium inventory (LLI), with some effect from the loss of active material (LAM). In the NCM cells, both the LLI and LAM significantly contributed to the degradation. Combined with internal battery morphology observations, the LAM mainly occurred at the anode, and the main side reactions leading to the LLI with lithium plating and solid electrolyte interface growth also occurred at the anode.

Electrochemical modeling, Li plating onsets and performance analysis of thick graphite electrodes considering the solid electrolyte interface formed from the first cycle

Based on a crack dominated solid electrolyte interface (SEI) resistance, an electrochemical model considering the SEI formed from the first cycle is established to investigate the comprehensive influence of electrode thickness, solid volume fraction and C-rate on the performance of thick graphite electrodes. Reasonable agreement is obtained for the simulated and measured charge and discharge profiles of Li/graphite cells including the first cycle. The periodic evolution of SEI film resistance during the cycles can be well interpreted by the mechanism based on the growth of SEI crack. The potential drop over SEI is found to contribute little to the polarization during Li inter- and deintercalation, and the electrode porosity reduction caused by SEI growth has larger effect for thick electrode than traditional thin electrode. The cell voltages, total potential drop of the electrode, state of charge and ratio of SEI capacity to the total capacity at the onsets of Li plating are analyzed. A linear relationship is developed for the Li plating onset voltages with the increasing of electrode thicknesses, solid volume fractions and C-rates. Finally, the performance of Li/graphite cells with electrode thicknesses (δ) ranging from 100 μm to 500 μm, solid volume fractions (εs) ranging from 0.35 to 0.6 and C-rates ranging from 0.05C to 0.5C is simulated and compared. The ionic migration limitation is aggravated by the growth of SEI for electrodes thicker than 300 μm as the solid volume fraction increases. The maximal areal capacity appears around δ = 500 μm and εs = 0.4, with a rate performance of 13.8 mAh cm−2, 13.6 mAh cm−2 and 13.1 mAh cm−2 at 0.1C, 0.2C and 0.5C, respectively.

Toward more realistic microgrid optimization: Experiment and high-efficient model of Li-ion battery degradation under dynamic conditions

Accurate and high-efficient battery life prediction is critical for microgrid optimization and control problems. Extracted from EV (electric vehicle)-PV(photovoltaics)-battery-based microgrid working profiles, five sets of accelerated aging experiments are conducted on LFP (graphite-LiFePO4) cells to reflect the effect of different energy storage capacities on battery degradation. Apart from SEI (solid electrolyte interface) growth and LAM (loss of active materials), lithium plating is likely to occur after prolonged cycling under the DOD (depth of discharge) range of over 80% when there are current pulses of around 1.5C. As for the degradation modelling, to efficiently solve while maintaining prediction accuracy, this work develops a reduced-order semi-empirical model (ROSEM) to compute fastly for control algorithms. The model reveals physical mechanisms and thus can generalize across actual conditions compared with another four semi-empirical models. The proposed ROSEM can precisely predict nonlinear battery degradation with less than 1.6% relative errors, and the computation duration for 500 cycles is less than 5s. The margin of simulation errors can be further narrowed to 0.6% with the correction of ANN (artificial neural network).