Loss Of Lithium Inventory Research Articles

Mechanistic calendar aging model for lithium-ion batteries

In this work we present a novel mechanistic calendar aging model for a commercial lithium-ion cell with NCA cathode and silicon-graphite anode. The mechanistic calendar aging model is a semi-empirical aging model that is parameterized on component states of health, instead of capacity. Three component states of health are derived from the degradation modes, which are calculated by fitting the electrode potential curves at every check-up measurement. The aging data used for model parameterization spans 672days of storage at 27 different combinations of ambient temperature (Tamb) and state of charge (SOC). To compensate for the influence of the check-up measurements on cell degradation, the aging data is pre-processed in two steps, considering immediate degradation caused by the check-up cycles and accelerated degradation during subsequent storage. The loss of active anode material is negligible during check-up-compensated calendar aging. For loss of lithium inventory and loss of active cathode material, Tafel and Arrhenius terms are successfully used to model Tamb and SOC dependence. The mechanistic calendar aging model predicts the capacity with <1% mean deviation for 7 different storage conditions after 672days without check-ups. The check-up compensation increases predicted lifetime by >150% for exemplary storage at Tamb=60°C and SOC=50%.

Recycling silicon scrap for spherical Si–C composite as high-performance lithium-ion battery anodes

The growth of the semiconductor and solar industry has been exponential in the last two decades due to the computing and energy demands of the world. Silicon (Si) is one of the main constituents for both sectors and, thus, is used in large quantities. As a result, a lot of Si waste is generated mainly by these two industries. For a sustainable world, the circular economy is the key; thus, the waste produced must be upcycled/recycled/reused to complete the circular chain. Herein, we show that an upcycled/recycled Si can be used with carbon as a composite anode material, with high Si content (∼40 wt%) and loading of 3–4 mAh/cm2 for practical use in lithium-ion batteries. The unique spherical jackfruit-like structure of the Si–C composite can minimize the total lithium inventory loss compared to the conventional Si–C composite and pure Si, resulting in superior electrochemical performance. The superior electrochemical performance of Si–C composites enables the cell energy density of ∼325 Wh kg−1 (with NMC cathode) and ∼260 Wh kg−1(with LFP cathode), respectively. The results demonstrate that Si-based industrial waste can be upcycled for high-performance Li-ion battery anodes through a controllable, scalable, and energy-efficient route.

Reviving Inactive Lithium and Stabilizing Lithium Deposition for Improving the Performance of Anode-Free Lithium–Sulfur Batteries

Anode-free lithium–sulfur batteries (AFLSBs) show a surprisingly prolonged cycle life 2-fold higher than anode-free lithium metal batteries. The principal difference is the presence of an intrinsic polysulfide (PS) shuttle between electrodes in AFLSBs. However, the underlying mechanism for the impact of PS redox species on the electrochemical performance of AFLSBs is not clearly understood. Herein, we investigate the role of PS redox species in retrieving inactive lithium for compensating lithium inventory loss using titration gas chromatography, thereby quantifying inactive lithium accumulated after several cycles. Moreover, XPS analysis reveals reduced lithium sulfide (Li2S/Li2S2) species formed through PS redox shuttle refresh inactive solid electrolyte interface (SEI) composition and stabilize the consecutive cycle lithium deposition. Interestingly, synchrotron-based operando transmission X-ray microscopy (TXM) reveals dense and granular electrodeposited lithium morphologies in AFLSBs. Therefore, the interplay between reviving inactive lithium for compensating lithium inventory loss and stabilizing lithium electrodeposition endows high electrochemical performance in AFLSBs.

Comprehensive investigation on the durability and safety performances of lithium-ion batteries under slight mechanical deformation

Mechanical abuse is a general abuse behavior in electric vehicles. To prevent the safety risk from mechanical deformation, it is necessary to understand its failure mechanism and its effects on battery performance. There is a knowledge gap in the influence of slight mechanical deformation on the durability and safety of lithium-ion batteries. This study comprehensively investigates the changes in electrochemical properties, morphology, and thermal stability in commercial ternary/graphite lithium-ion batteries by multiple techniques. Tested cells are indented from 4 mm to 6.8 mm and cycled for 620 cycles. The results of cycle aging exhibit that indentation can improve the cycle performance of tested cells, but the effect turns negative for the cells when the indentation depth exceeds 6.5 mm. The electrochemical impedance spectroscopy measurements exhibit that indentation retarded the increase of impedance of indented cells during the aging process. It could be due to the increase of compact density weakening the degradation in the anode electrode. But the degradation in the cathode electrode is aggravated by mechanical deformation. During the cycle aging of tested cells, the loss of lithium inventory dominates the degradation of indented cells in the first 500 cycles and then follows the loss of active material damage. The apparent morphology of electrodes in deformed and aged cells exhibits that active material particles are compacted in the dented area, and cracks are formed in the fold area. After cycle aging, the compressed area surrounding the dent is covered by a layer of reaction products of electrolyte with lithium at the anode electrode. The adiabatic tests show the thermal stability of indented cells reduces firstly and then increases with the increase of indentation depth, as well as the aged cells.

Physics-based model informed smooth particle filter for remaining useful life prediction of lithium-ion battery

Accurately predicting the remaining useful life (RUL) of lithium-ion batteries is essential for battery management systems (BMS) as rapid capacity declines and failure can impact equipment operation and pose safety hazards. However, battery aging is a complex electrochemical process influenced by various factors such as cycle time, temperature, and loading conditions. To address this, a physics-informed smooth particle filter (SPF) framework for RUL prediction is proposed in this work, which estimates parameters of a single particle model (SPM) of LiBs by extracting three main degradation mechanisms: active material loss in positive and negative electrodes and loss of lithium inventory. Unlike traditional prognostic frameworks, this approach utilizes the SPM to estimate degradation parameters directly from voltage and capacity data, enabling more accurate quantification of degradation mechanisms and prediction of capacity fade trends. The estimated capacity is then used to develop an RUL predictor based on an SPF, which produces more accurate RUL predictions compared to conventional capacity-based methods. The proposed framework achieves a best-case RUL prediction of 2402 cycles at the prediction starting point of 2000 cycles, with a minimum relative error of around 0.089% compared to approximately 0.8% for the traditional framework. Additionally, the proposed framework is demonstrated to be dependable and robust, even when dealing with LiBs data containing Gaussian white noise and dynamic discharging profiles.

Comprehensive analysis of lithium-ion cells and their aging trajectory toward nonlinear aging

More than 30 years after the market introduction of lithium-ion batteries, research still struggles to understand the complex interplay of different aging mechanisms that can lead to a sudden drop in usable capacity. Understanding this nonlinear aging behavior is important to develop optimal strategies regarding the cell design and operation. In this work, we present an extensive analysis of a cycle aging test comprising 62 commercial large-scale pouch-bag type cells in a constant force bracing. The dataset includes eight cells, which exhibit nonlinear aging. Nondestructive methods, such as differential voltage analysis, reveal that the capacity loss is limited by the loss of lithium inventory, which is not homogeneous within the cell . With destructive post-mortem analysis we observe that aging is focused toward the center of the anode. Occurring lithium-plating seems to intensify with aging at high temperatures. Our results point toward a two-step mechanism, where elevated temperatures drive SEI-growth at the electrodes’ center, which, in turn, impair mass transfer kinetics and lead to the deposition of metallic lithium. Ultimately, our work can help to identify the most relevant mechanisms and interactions that provoke nonlinear aging.

The feasibility for natural graphite to replace artificial graphite in organic electrolyte with different film-forming additives

The feasibility for natural graphite (NG) to replace artificial graphite (AG) in organic electrolytes with different additives are investigated. Although the strong film-forming additives contributes to form robust solid electrolyte interphase (SEI) film on graphite particle surface, great differences in gas evolution, lithium inventory loss and other side reactions are observed. Lithium bis(oxalato)borate (LiBOB) and Fluoroethylene carbonate (FEC) are found more effective and the combination shows to be more promising. In the optimized electrolyte, natural graphite anode exhibits excellent long-term cycling capability. After 800 cycles at high temperature, the capacity retention is comparable to that using artificial graphite. The mechanisms for the capacity-fading of the full cells with AG and NG anode are investigated by ICP, SEM and polarization studies. The results shows that NG electrode consumes more active lithium due to the rough surface and larger volume expansion. The rapid capacity-fading in the initial 100 cycles is related to the instability of the SEI film aroused from large volume expansion. The systematic analysis is inspiriting for the development of high performance lithium ion batteries with reduced cost.

Digital twin-long short-term memory (LSTM) neural network based real-time temperature prediction and degradation model analysis for lithium-ion battery

Real-time temperature prediction is essential to circumvent thermal safety issues for lithium-ion batteries (LIB). However, its industrial applications are challenging due to operating temperature, voltage range, capacity degradation, and current rate (C-rate) variations. This study proposes a digital twin (DT) technology and long short-term memory (LSTM) neural network-based method for real-time temperature prediction and degradation pattern analysis. The DT model is established based on lumped thermal equivalent circuits to describe the dynamic thermal behavior of LIB and identify the parameters by calculations. Furthermore, the real-time temperature prediction framework considering voltage, current, and operating temperature is further designed following identifying results, which consists of indicators extraction, correlation analysis, LSTM neural network, and DT model four parts. In addition, the incremental capacity analysis (ICA) method is used to analyze LIB degradation patterns. The experimental results indicate that the primary degradation pattern of the experimental sample is loss of lithium inventory (LLI), and the loss of active material (LAM) appears after 600 cycles. Moreover, the maximum error and root mean square error (RMSE) of the temperature prediction framework is 0.31 °C and 0.17 °C under the constant current (CC) discharging condition, 0.85 °C and 0.47 °C under the dynamic discharging condition, respectively. The results demonstrate that the proposed real-time temperature prediction framework delivers acceptable accuracy for CC discharging and dynamic discharging conditions, which can complete the requirements of practical applications. This study dramatically reduces the response time of temperature prediction and guides optimizing battery thermal management systems (BTMS).

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.

Multilayer Graphene as a Cathode Conductive Additive in Lithium-Ion Pouch Cells: A Correlation of Changes in Electrolyte Uptake and Composition of the Electrode Electrolyte Interface with Enhanced Cycling Stability

The electrochemical performance of the lithium-ion battery is significantly affected by the choice of electrode conductive additives. In this study, a mixed conductive additive with an equal proportion of multilayer-graphene (MLG) and carbon black (CB) is used in LiNi1/3Mn1/3Co1/3O2 (NMC-CB-MLG) electrodes. The electrochemical performance of these electrodes is compared at coin cell and pouch cell formats with that of the LiNi1/3Mn1/3Co1/3O2 (NMC) electrodes prepared with CB alone as a conductive additive (NMC-CB). While CB independently increases rate capability, mixing MLG with CB as a conductive additive enhances cycling stability. The pouch cells fabricated using the NMC-CB-MLG electrode show a superior capacity retention of 80% after 730 cycles at 1C, compared to 65% at 320 cycles of NMC-CB. The differences in the capacity retention of both cells are correlated with the electrolyte uptake and stability of the electrode–electrolyte interface (EEI) due to changes in the chemical composition as investigated using X-ray photoelectron spectroscopy. The main reasons for the capacity fade of NMC-CB are explained by the formed unstable EEI and cathode electrode cracking, which lead to loss of lithium inventory and loss of active materials. This study concludes that MLG mixed with CB can be used as a conductive additive in commercial large-format lithium-ion high energy cells.

Revealing the Impact of High Current Overcharge/Overdischarge on the Thermal Safety of Degraded Li-Ion Batteries

To analyze the impact of two commonly neglected electrical abuse operations (overcharge and overdischarge) on battery degradation and safety, this study thoroughly investigates the high current overcharge/overdischarge effect and degradation on 18650-type Li-ion batteries (LIBs) thermal safety. Based on the temperature-voltage behavior and induced thermal runaway (TR) mechanisms, the overcharge and overdischarge-triggered TR processes are divided into four and three stages. Furthermore, the degradation effect is analyzed by analyzing the incremental capacity-differential voltage curves. During the high current cycling process, lithium inventory decreases significantly. Besides, the active material decreases when the battery degrades to a certain level. Lithium plating is the primary reason for lithium inventory loss; the plated lithium grows with the increment of degraded/overcharged level. Besides, the dissolution and deposition affect the internal short circuit degree, which can be observed from the electrode potential and cell voltage value. Moreover, battery cells undergo different degradation degrees, and different current rates of charging/discharging exhibit similar temperature-rising trends during the adiabatic TR tests. However, with the degradation degree increase, battery capacity fades, TR becomes easier to be triggered by the high current rate, and TR reactions are severe. This study guides early quantitative detection, safer battery cell design, and enhanced thermal safety management.

Comprehensive analysis on aging behavior and safety performance of LiNixCoyMnzO2/graphite batteries after slight over-discharge cycle

Over-discharge is one of the common abuse conditions for lithium-ion batteries (LIBs), while the safety hazard of over-discharged cell is still unclear. In this work, the aging behavior and safety performance of commercial Li(Ni0.5Co0.2Mn0.3)O2/graphite LIBs under 1.5, 1.0, 0.5, and 0.0 V over-discharge cycles are investigated. The cells experience capacity decay and structural damage during over-discharge cycle. Compare to the normal cycled cells, the increased impedance after over-discharge cycle leads to more heat generation during operating, which further accelerates the inconsistency of LIB module. Moreover, the thermal runaway behavior of the over-discharged cell was studied using Extended Volume Accelerating Rate Calorimeter. The kinetics of self-heating reaction is obtained, and the criticality of thermal runaway under different heat dissipation conditions was analyzed based on Semenov model. The thermal stability and maximum safe storage temperature of the LIB were decreased after over-discharge cycle, especially for the cell over-discharged to 0.0 V. Based on the electrochemical impedance spectroscopy, the loss of lithium inventory relate to the growth of solid electrolyte interphase (SEI) film is found to be the primary aging contribution. Moreover, the post-mortem test implied the dissolution of Cu initiated when over-discharged to 0.5–0.0 V.

State estimation and aging mechanism of 2nd life lithium-ion batteries: Non-destructive and postmortem combined analysis

Lithium-ion batteries used in electric vehicles (EVs) are expected to reach end-of-life (EoL) after 10–15 years of operation. Consequently, it is urgent to devise repurposing strategies, which may range from recycling to a 2nd life in stationary energy storage applications. In this paper, aiming the 2nd life repurposing of the batteries, the state estimation and aging mechanisms of retired 32,650-type LiFePO4/graphite batteries were studied. The aging state of batteries was evaluated in terms of their capacity, resistance and self-discharge rate. Test results show that there is no strong correlation between battery capacity decay and resistance increase. To identify and quantify the aging mechanisms of the 2nd life batteries after being cycled at different rates (0.5C, 1C and 2C), non-destructive analyses (incremental capacity/differential voltage curves, modified equivalent circuit model, and electrochemical impedance spectroscopy) are combined with postmortem analysis. The results reveal that the aging of the batteries cycled at 0.5C is primarily due to the loss of active material (LAM), while the loss of lithium inventory (LLI) is rather insignificant. For the batteries cycled at 1C and 2C, in addition to LAM, LLI is also severe, eventually leading to an increase in resistance of the battery, which causes a rapid decline of the battery capacity. The results also indicate the non-destructive methods are reliable to identify ongoing aging mechanisms.

A Post-Mortem Study Case of a Dynamically Aged Commercial NMC Cell

Lithium-ion batteries are currently the pioneers of green transition in the transportation sector. The nickel-manganese-cobalt (NMC) technology, in particular, has the largest market share in electric vehicles (EVs), offering high specific energy, optimized power performance, and lifetime. The aging of different lithium-ion battery technologies has been a major research topic in the last decade, either to study the degradation behavior, identify the associated aging mechanisms, or to develop health prediction models. However, the lab-scale standard test protocols are mostly utilized for aging characterization, which was deemed not useful since batteries are supposed to age dynamically in real life, leading to aging heterogeneity. In this research, a commercial NMC variation (4-4-2) was aged with a pragmatic standard-drive profile to study aging behavior. The characterized measurable parameters were statistically investigated before performing an autopsy on the aged battery. Harvested samples of negative and positive electrodes were analyzed with Scanning Electron Microscopy (SEM) and the localized volumetric percentile of active materials was reported. Loss of lithium inventory was found to be the main aging mechanism linked to 20% faded capacity due to heavy electrolyte loss. Sparsely distributed fluorine from the lithium salt was found in both electrodes as a result of electrolyte decomposition.

Stabilizing the Interphase in Cobalt‐Free, Ultrahigh‐Nickel Cathodes for Lithium‐Ion Batteries

AbstractHigh‐nickel layered oxide cathodes, such as LiNi1‐x‐yMnxCoyO2 (NMC) and LiNi1‐x‐yCoxAlyO2 (NCA), are at the forefront for implementation in high‐energy‐density lithium‐ion batteries. The presence of cobalt in both cathode chemistries, however, largely deters their application due to fiscal and humanitarian issues affiliated with cobalt sourcing. Increasing the Ni content drives down the Co content, but introduces additional structural and electrochemical problems attributed to high‐Ni cathodes. Herein a dually modified cobalt‐free ultrahigh‐nickel cathode 0.02B‐LiNi0.99Mg0.01O2 (NBM) is presented with 1 mol% Mg and 2 mol% B that exhibits a high initial 1C discharge capacity of 210 mA h g−1 with a 20% capacity retention improvement over 500 cycles when benchmarked against LiNiO2 (LNO) in pouch full cell configurations with graphite anode. Postmortem analyses reveal the enhanced performance stems from reduced active lithium inventory loss and localized surface reactivity in the NBM cathode. The stabilized cathode‐electrolyte interphase subsequently reduces transition‐metal dissolution and ensuing chemical crossover to the graphite anode, which prevents further catalyzed parasitic reactions that harmfully passivate the anode surface. Altogether, this study aims to highlight the importance of electrode characterization and analysis from an interphasial viewpoint and to push the ongoing research to stabilize cobalt‐free ultrahigh‐Ni cathodes for industrial feasibility.

SiO-induced thermal instability and interplay between graphite and SiO in graphite/SiO composite anode

Silicon monoxide (SiO), which exhibits better cyclability compared to silicon while delivering higher capacity than that of graphite, is an adequate material for the development of lithium-ion batteries (LIBs) having higher energy densities. However, incorporating silicon-based materials including SiO into stable graphite anode inevitably degrades not only cycle life but also calendar life of LIBs, while little is known about their aging mechanisms. Here, SiO-induced thermal instability of the graphite/SiO composite anode is investigated. We reveal that under thermal exposure, SiO accelerates the loss of lithium inventory and concomitantly facilitates the lithium de-intercalation from graphite. This self-discharge phenomenon, which is weakly observed in the graphite anode without SiO, is the result of preferential parasitic reaction on the SiO interface and spontaneous electron and lithium-ion migration to equilibrate the electron energy imbalance between graphite and SiO. Understanding this underlying electron-level interplay between graphite and SiO in the composite anode will contribute toward improving shelf life of SiO-containing LIBs in actual operating conditions.

Insights on the degradation mechanism for large format prismatic graphite/LiFePO4 battery cycled under elevated temperature

Increasingly, batteries are being exposed to elevated temperatures to promote charging capability and satisfy various requirements. A comprehension of the degradation mechanism under elevated temperature is essential for advanced battery management. Here, commercial 100 Ah prismatic graphite/LiFePO4 batteries cycled under 45 °C are investigated. Less than 500 cycles are reached when capacity fades to 90 % of the nominal value, while more than 1300 cycles are reached under room temperature. Comprehensive post-mortem analysis is conducted to explore the mechanism of accelerated aging for 45 °C cycled batteries. The concentration of electrolyte salt dropping from 13.19 wt% to 12.98 wt% indicates the decomposition of electrolyte which brings about the gas release and battery volume expansion. Loss of electrolyte associated with enhanced evolution of solid electrolyte interface (SEI) film also leads to loss of lithium inventory. Larger LiFePO4 particles tend to fracture and Fe dissolves from them. It is proposed that Fe deposition accelerates the SEI film generation and the deposition blocks the graphite layers and limits lithium intercalation. From time-of-flight secondary ion mass spectroscopy depth profiling results, it is found that cathode electrolyte interphase film thickens moderately while SEI film thickens sharply, causing anode porosity to drop from 46.22 % to 40.11 %.

Physics-Informed Optimal Experiment Design of Calendar Aging Tests and Sensitivity Analysis for SEI Parameters Estimation in Lithium-ion Batteries

This paper focuses on sensitivity analysis and optimal experiment design for calendar aging tests to find SEI (solid-electrolyte interface) degradation parameters. This parameterization facilitates predicting the Li-ion battery end-of-life. To this end, a physics-based model of SEI layer is used to develop a closed form solution for loss of Lithium inventory during calendar aging. This model is shown to match experimental data. Further, the developed model is used to find the sensitivity of LLI (loss of Lithium inventory) to SEI parameters in diffusion-limited and kinetically limited SEI patterns.Through this sensitivity analysis, we show that in the kinetically limited case, performing calendar aging tests at high SOCs gives the most accurate results. For the diffusion limited case, we use optimal experiment design techniques to find the optimal calendar aging SOCs. It is also shown that, these optimal SOC values result in higher accuracy estimations compared to sub-optimal SOCs.

Degradation model of high-nickel positive electrodes: Effects of loss of active material and cyclable lithium on capacity fade

Nickel-rich layered oxides have been widely used as positive electrode materials for high-energy-density lithium-ion batteries, but the underlying mechanisms of their degradation have not been well understood. Here we present a model at the particle level to describe the structural degradation caused by phase transition in terms of loss of active material (LAM), loss of lithium inventory (LLI), and resistance increase. The particle degradation model is then incorporated into a cell-level P2D model to explore the effects of LAM and LLI on capacity fade in cyclic ageing tests. It is predicted that the loss of cyclable lithium (trapped in the degraded shell) leads to a shift in the stoichiometry range of the negative electrode but does not directly contribute to the capacity loss, and that the loss of positive electrode active materials dominates the fade of usable cell capacity in discharge. The available capacity at a given current rate is further decreased by the additional resistance of the degraded shell layer. The change pattern of the state-of-charge curve provides information of more dimensions than the conventional capacity-fade curve, beneficial to the diagnosis of degradation modes. The model has been implemented into PyBaMM and the source codes are openly available in the GitHub repository https://github.com/mzzhuo/PyBaMM/tree/pe_degradation.

Adaptive fast charging control using impedance-based detection of lithium deposition

The recently introduced impedance-based detection method for the retrospective identification of lithium deposition is used in a long-term ageing study. Six lithium-ion cells are fast charged for 250 cycles with two different strategies, (i) constant-current constant-voltage and (ii) detection-based, adaptive charging control in which the current of the following step is controlled by the detection result of the previous step. The adaptive charging control leads intentionally to critical charging currents with minor lithium deposition effects for the majority of cases. Nevertheless, only marginal capacity fade can be observed after the whole long-term experiment, proving that the detection method reacts sensitively and reliably on minor lithium deposition. On the other hand, the adaptive charge control leads to significantly higher currents, thus reduced charging durations. Hence, the method qualifies for both adaptive fast charging control and for the identification of charging rate limits. A differential voltage analysis is performed before and after the long-term study, identifying the loss of lithium inventory, as well as the loss of anode active material as dominant degradation modes. Additionally, a sensitivity analysis with varying detection time and measurement accuracy is carried out to identify minimum measurement requirements and to increase the method’s time- and cost-efficiency.