Large Lithium-ion Batteries Research Articles

Development of Nasicon-Type Electrolytes Using Combination of Experimental Techniques and Materials Informatics

Introduction Research and development of large lithium-ion batteries is essential for new societal infrastructures such as electric vehicles, aircraft and smart grids. Replacing the liquid electrolyte of conventional lithium-ion batteries with solid electrolytes not only makes them less prone to ignition, but also increases their energy density. Sulfide, chloride and oxide systems are known as solid electrolytes. Sulphide and chloride types have high lithium-ion conductivity but are generally unstable in air. Therefore, there is an urgent need to develop oxide-based solid electrolytes that are stable in air, and the Na superconductor (NASICON) type LiZr2(PO4)3 (LZP) is a candidate oxide-based solid electrolyte for all-solid-state lithium-ion batteries. However, its ionic conductivity is inadequate. We have therefore investigated co-doped LZP (Li1+x+2yCayZr2-ySixP3-xO12), in which Zr is partially replaced by Ca and P by Si. First, a total of 49 compositions were synthesized and their crystal structure, relative density and lithium-ion conductivity were experimentally evaluated [1]. Since lithium-ion conductivity is also affected by microstructural properties such as density, morphology and elemental distribution of the sintered pellets, the conductivity can be improved by controlling process parameters such as heating conditions during the solid-state reaction. Therefore, the material was synthesized in a solid-state reaction under different heating conditions in two stages and the effect of the heating conditions on the microstructural properties of the sintered pellets was investigated [2].Such thorough sample preparation requires considerable time, effort and cost, and consumes a large amount of energy and resources. Therefore, AI-based optimization methods called Bayesian Optimization (BO) have attracted attention. Bayesian optimizations is a method that uses statistical inference to select the next candidate to explore and find the best performing sample with the least number of samples. Using the experimental data obtained in our study, we demonstrated whether the BO algorithm can 'efficiently' find the optimal composition and heating conditions to achieve the highest ionic conductivity of such materials. Experimental Li1+x+2yCayZr2-ySixP3-xO12 was synthesized by a conventional solid-state reaction using two-stage heating. The crystalline phase of the samples was determined by X-ray diffraction (XRD). The micro morphology of the samples was evaluated by scanning electron microscopy. The ionic conductivity of the pellets was measured by AC impedance.BO was performed to evaluate the efficiency of the optimized composition or heating conditions to obtain the highest ionic conductivity of the experimentally evaluated samples. Conductivity at 30 °C was the objective. Results and discussion The Li1.45Ca0.15Zr1.85S0.15P2.75O12 sample heated at 1050°C and 1250°C gave the highest lithium-ion conductivity of 3.3 x 10-5 S/cm at 30°C. Investigation of the sintered samples showed that composition and heating conditions affected the crystalline phase, density, microstructure and elemental distribution. The relationship between ionic conductivity and these observations was so complex that it was difficult to determine the optimum composition and heating conditions intuitively from a few experiments. Figure 1 shows the number of experiments required to find (a) the optimal composition and (b) the optimal heating conditions with 80%, 90% and 100% probability using BO or random search. The results show that using BO can find the optimum composition or optimum sintering conditions in about half the number of trials compared to a random search. Thus, Bayesian optimization has been shown to be effective in finding the optimum composition or process conditions of a material.

Removal of Polyvalent Cations from Aqueous Solutions Prepared By Roasting and Dissolving Spent Lithium-Ion Batteries By Ion-Exchange Membrane Electrodialysis

Background and purposeEfforts to curb CO2 emissions, which cause global warming, are spreading around the world, and countries and regions are attempting to ban new sales of gasoline and diesel vehicles that emit CO2. Therefore, it is expected that the spread of electric vehicles will increase in the future, and that the number of used lithium-ion batteries will increase accordingly. In order to reduce the environmental impact of these battery products, Europe adopted the European Battery Regulation in July 2023, making it mandatory to recycle used batteries. The regulations require recycling of 50% of lithium materials from spent batteries by the end of 2027 and 80% by the end of 2031. In addition, by August 2031, 6% of the materials must be made from recycled lithium. Recycling technology has not yet been established for large lithium-ion batteries, such as those used in cars, because their exteriors are more durable and the risk of ignition is higher than for smaller ones used in mobile phones. Therefore, early establishment of recycling technology is necessary.Lithium is typically recycled by roasting the used lithium-ion batteries, dissolved, and separated through hydrometallurgy. In addition to lithium, polyvalent cations of Cu, Mg, Ca, Mn, Al and so on, which are impurities, are present in high concentrations in the roasted and dissolved solutions of lithium-ion batteries. In hydrometallurgical refining, there is a concern that a high concentration of impurity polyvalent cations may cause a decrease in the recovery rate of lithium. Therefore, it is necessary to reduce the concentration of polyvalent cations in the battery roasting and dissolved solution as much as possible. The purpose of this study was to clarify the possibility of reducing polyvalent cations contained in the roasted and dissolved solution of lithium-ion batteries by electrodialysis using a monovalent permselective cation exchange membrane.Previous research has shown that the monovalent permselective cation exchange membrane used in this study allows small amounts of multivalent ions to permeate. If the solution on the negative electrode side is basic, there is a concern that multivalent ions will precipitate as hydroxides on the surface of the cation exchange membrane and inhibit the permeation of ions. Therefore, in this study, we considered using an acidic solution as the negative electrode solution of the cation exchange membrane. In this study, we use a Ni electrode, which is inexpensive and easy to use industrially. However, the Ni electrode dissolves in acidic solutions. To prevent its dissolution, the electrode was placed in a basic solution separated from the acidic solution by a bipolar membrane.Experimental methodChronoamperometry (CA) was performed using an electrochemical cell with four solution baths separated by two bipolar membranes and a cation exchange membrane. A schematic diagram is shown in Fig.1. The electrode solutions were lithium hydroxide, and the initial solution in the acid solution bath was 1wt% hydrochloric acid. The stock solution tank contained an aqueous solution of roasted and dissolved lithium-ion batteries. The nickel electrode used was a 3 cm × 4 cm nickel mesh (100 mesh, φ 0.10 mm) with a nickel wire (φ 0.30 mm) attached. A voltage of 5 V was applied to CA for 24 hours. Inductively coupled plasma optical emission spectrometer was performed on the solutions in the stock solution and acid solution after the test and the amount of lithium transferred, and the removal rate of polyvalent cations were calculated.ResultsThe ratio of multivalent ions to lithium in the acid solution after the test was decreased compared to the stock solution before the test, indicating that the multivalent ions were successfully reduced. There was a concern that precipitates would form on the surface of the cation exchange membrane, but no precipitate was formed. However, when a voltage was applied for a long time, the cations precipitated on the surface of the bipolar membrane faces the acidic solution, even though the pH of the acid solution after the test was between 1 and 2 where in principle they would not precipitate. In the presentation, we will report on the amount of lithium permeation, the removal rate of polyvalent cations, and the estimated mechanism of precipitation formation.Fig.1 Schematic diagram of ion-exchange membrane electrodialysis.BP: Bipolar membrane, C: Monovalent permselective cation exchange membraneReferences(1) the 91st ECSJ Annual Meeting S11_1_03.(2) the European parliament and the council of the European union. Regulation (EU) 2023/1542 of the European parliament and of the council. 33-34,191 (2023). Figure 1

Direct recycling of anode active material from Li-ion batteries using TiNb2O7 anode

As the demand for large lithium-ion batteries (LIBs) for automotive and other applications rapidly grows, recycling of electrode materials has become essential owing to the large amount of waste material generated by battery manufacturing (e.g., battery scrap) and end-of-life (EOL) batteries. While there have been many studies on recycling of cathode materials, we propose a direct recycling process for anode material using TiNb2O7 (TNO) as the active material, as it offers high capacity and long life. Calcination was introduced to separate the anode active material from the current-collecting foil, and a regeneration method was investigated for TNO anodes from scrap and EOL battery waste. After calcination, the active material can be easily separated from the aluminum current-collecting foil owing to the binder disappearing. The structure of the active material was investigated using X-ray diffraction and scanning electron microscopy. TNO active material recycled from scrap and EOL was found to maintain the structure of virgin material. A cell was fabricated using recycled TNO and cell performance was evaluated. The cell capacity and rate capacity were found to be almost equivalent to those of virgin material. In terms of the carbon footprints of products (CFP), CO2 emissions during the recycling process were compared between recycled material and virgin material, and it was found that CO2 emissions were reduced to 0.7-CO2eq/kg for scrap material and 3.8-CO2eq/kg for EOL waste material, compared with 4.8-CO2eq/kg for virgin material. Thus, the feasibility of low CO2 emissions during TNO anode direct recycling was confirmed in principle. A simple and low CO2 emission recycling loop can thus be constructed by employing a stable TNO active material structure and direct-recycling process with calcination.

Methods for Characterization of Heterogeneous Aging in Large Lithium-Ion Batteries

Lithium-ion batteries have become the predominant storage solution for electrified vehicles and therefore research is moving forward at high speed. The high demand for improvements in extension of the battery life requires effective methods for the detection and understanding of aging phenomena. Recent high energy lithium-ion batteries teardown analyses, performed at KTH [1], have revealed a considerable extent of heterogeneity in the degradation phenomena on multiple levels. These phenomena are expected to strongly affect the rate of ageing of cells, and in turn contribute to an early end-of-life of the system.This presentation will focus on the description of the characterization methods that will be used for future studies on the uneven distribution of cell ageing. Testing has been performed on multiple configurations of silicon – graphite composite electrodes where, given the large volume expansion of the silicon during operation, has additional variables in the degradation mechanisms.Material characterization has been performed in the form of cross section SEM, and NMR, following a methodology developed at KTH to quantify Li-plating in different areas of the jellyroll [2], but extending it to Si. On the other hand, electrochemical measurements have been performed with small lab cells under controlled conditions. In parallel a physics-based model for describing the behaviour of such cells is being developed. The model is currently able to interpret quasi-OCV experimental data and derive the behaviour of each active material involved during these processes.[1] Smith, Alexander J., et al. "Localized lithium plating under mild cycling conditions in high-energy lithium-ion batteries." Journal of Power Sources 573 (2023): 233118.[2] Fang, Yuan, et al. "Quantifying lithium lost to plating and formation of the solid-electrolyte interphase in graphite and commercial battery components." Applied Materials Today 28 (2022): 101527.

Probabilistic lithium-ion battery state-of-health prediction using convolutional neural networks and Gaussian process regression

As the world accelerates its renewable energy transition, lithium-ion batteries are increasingly being used for large scale energy storage. Due to the high cost of production and replacement of large lithium-ion battery packs, accurate estimation of battery state-of-health (SOH) has become important. Accurate estimation is especially important for microgrid and transportation industries where operational batteries will be charged intermittently and incompletely. Incomplete charging scenarios provide models with inconsistent inputs, hence, cause inconsistent output accuracies, which are important to quantify in the context of dispatch controllers and predictive maintenance. In this paper, we present a model that provides a probabilistic prediction of battery SOH from periodic charging events as would be encountered in real world operations. The proposed model combines the feature recognition and many-to-one mapping abilities of the classic convolutional neural network (CNN) with the probabilistic characteristics of Gaussian Process Regression (GPR) models. The combined CNN-GPR model predicts battery SOH to less than 1% mean absolute error using random partial charge segments as input and displays its confidence in the prediction using the variance from the GPR. Additionally, the CNN-GPR is able to predict battery SOH irrespective of battery usage history; this is demonstrated by validation on dynamic data sets where the model achieves a mean absolute error of less than 1% despite only being trained on standardized degradation cycles.

Three-dimensional numerical simulation of the temperature distribution within a large lithium-ion battery

A one-dimensional model of an electrochemical battery does not adequately simulate thermal runaway in a large battery; a three-dimensional model is required. Here, we combine a one-dimensional electrochemical cell with a two-dimensional resistor network to simulate thermal distribution in a lithium-ion battery. Based on electrode current density and the potential distribution, the temperature distribution, as a function of discharge time is predicted using two principal source equations for heat generation: one for the electrochemical reaction and the other for the current collector resistance. The model outputs were in good agreement with the experimental data of Kim et al. [1]. Our results provide an overview of temperature distribution, and also the discharge curves at varying discharge rates. Our findings can be used to optimize the design of large batteries and control their thermal characteristics.

Novel design optimization for passive cooling PCM assisted battery thermal management system in electric vehicles

Recently, the phase change material (PCM) battery thermal management system (BTMS) attracted attention. However, enhancement and optimization for the BTMS are required due to volumetric system design and low thermal conductivity. This study provides a novel design optimization to improve the environmental aspect of the cooling system and reduce its weight. Jute fibers as a planet-system, available, cheap, and weightless material is combined with the PCM battery thermal management based. The thermal behavior of large lithium-ion batteries (LIB) under different load protocols including fast discharge, periodic load, and real drive cycle are investigated. The results with the periodic load profile confirm that the maximum temperature for the cooling strategies of no-cooling, PCM cooling and PCM with jute reaches 39.22 °C, 38.22 °C and 35.09 °C, respectively. Moreover, applying aggressive high constant discharge current leads to further reduction in maximum temperature, where the maximum temperature reaches 47.27 °C, 41.06 °C, and 36.29 °C with the no-cooling, PCM cooling and PCM with jute cooling strategies, respectively. This article represents the first attempt to use a combination of jute and PCM in order to maximize temperature efficiency enhanced. Thus, this research contributes to further design optimization in battery thermal management system simplicity, environmental friendliness, energy and weight saving.

Analysis of Fire Hazards Associated with the Operation of Electric Vehicles in Enclosed Structures

The article discusses the analysis of the possible development of hazards associated with the operation of vehicles equipped with an electric drive using the example of passenger cars. The authors review the problem of the safety of people and property resulting from the occurrence of a fire in an electric passenger car, in the context of fires that have occurred in recent years. Particular attention was paid to the analysis of the state of knowledge concerning the characteristics of the fire progression in an electric car, its heat release rate curve [HRR], total heat release [THR], heat of combustion and factors affecting the fire progression. In this paper, an attempt was made to compare the fire characteristics of an electric car and a passenger car equipped with an internal combustion engine together with an estimation, using CFD simulations, of the impact on the safety of people and property in closed structures such as underground garages or road tunnels. The need for further development of research on electric cars equipped with large lithium-ion batteries in the context of their fire safety is indicated. The authors pay attention to the insufficient amount of data available to understand the fire characteristics of modern electric cars, which would enable the appropriate design of fire safety systems in building structures.

Exploring the economics of large scale lithium ion and lead acid batteries performing frequency response

Provision of ancillary services is one of the key sources of revenue for energy storage. Hence, in order to understand the economic viability of a given technology it is important to assess its potential profitability and performance through provision of such services. Firm Frequency Response (FFR) is a type of ancillary service used for balancing grid frequency; this work uses grid frequency data to determine the real-time usage of lithium ion and lead acid batteries providing FFR. Battery capacity is balanced in real-time using several different proposed strategies; degradation and lifetime are then calculated, along with Net Present Value (NPV) for the different battery types, to ascertain their profitability. Lead acid batteries are found to not be worthwhile investments for this usage. On the other hand, lithium ion batteries are found to be suitable. In particular, battery chemistries providing high power density are economically preferable to those with high energy densities. It is found that the highest NPV (of the order £105) can be achieved when the batteries are used in a way that reduces degradation and increases lifetime; practically, this equates to a high level of capacity balancing in order to maintain battery capacity close to its mid-point, even if this is more costly in the short-term.

The prismatic surface cell cooling coefficient: A novel cell design optimisation tool & thermal parameterization method for a 3D discretised electro-thermal equivalent-circuit model

Thermal management of large format prismatic lithium ion batteries is challenging due to significant heat generation rates, long thermal ‘distances’ from the core to the surfaces and subsequent thermal gradients across the cell. The cell cooling coefficient (CCC) has been previously introduced to quantify how easy or hard it is to thermally manage a cell. Here we introduce its application to prismatic cells with a 90 Ah prismatic lithium iron phosphate cell with aluminium alloy casing. Further, a parameterised and discretised three-dimensional electro-thermal equivalent circuit model is developed in a commercially available software environment. The model is thermally and electrically validated experimentally against data including drive cycle noisy load and constant current CCC square wave load, with particular attention paid to the thermal boundary conditions. A quantitative study of the trade-off between cell energy density and surface CCC, and into casing material selection has been conducted here. The CCC enables comparison between cells, and the model enables a cell manufacturer to optimise the cell design and a systems developer to optimise the pack design. We recommend this is operated together holistically. This paper offers a cost-effective, time-efficient, convenient and quantitative way to achieve better and safer battery designs for multiple applications.

Study of the Test Conditions and Thermostability of an Overcharge Test for Large Capacity Lithium-Ion Batteries

Abstract In this study, a lithium-ion soft-pack battery used in an electric vehicle was taken as the research object. Based on the actual working condition of the traction battery, the regularity of the evolution of the overcharge thermal runaway experiment of the sample was deeply analyzed by taking the charging rate and the ambient temperature as variables. The results showed that the larger the overcharge current was and the higher the ambient temperature was, the lower the overcharge thermal stability of the battery was. Furthermore, based on the concept of the introduction of battery energy during charging, by analyzing the total amount of energy input and the rate of energy input, a unified index was established to measure the change of the battery overcharging stability under different experimental conditions.

(Invited) Experimental Characterization and Modeling of Heat Generation Rates of Lithium-Ion Batteries with NMC/C Chemistries

The operating temperature of a battery strongly affects overall chemical reactions, ion transport, intercalation and deintercalation process and consequently efficiency, cycle life, and safety of battery systems. Therefore, battery thermal management system (BTMS) should be optimally designed to ensure a highly efficient and reliable operation of the battery system, which requires characterization and analysis of heat generated during operations rather than temperature.Characterization of heat generation rates of a battery requires a highly accurate and dynamic calorimeter that is not commercially available. Therefore, we designed a new multifunctional calorimeter for lithium-ion batteries using thermoelectric assemblies (TEA), which enables the measurement of heat generation rate as a function of C rates, state-of-charge (SOC) and temperatures. In addition, the calorimeter also works as a thermostat that is capable of tracking an alternating reference temperature, so that flexibility and accuracy of experiments are ensured. This capability enables to decouple the temperature fluctuation during charging and discharging operations and the measurement of the entropy coefficient.In this paper, the cells used as an example for the experiments are large format pouch type lithium ion batteries with LMO/NMC-Graphite chemistry. The lumped heat generation rate of the cell is measured at different C rates, state-of-charge (SOC) and temperatures. In addition, analysis of the data has shown that both the heat generation rate and the ratio of the total heat generation to the total energy stored or retrieved of the tested cells increase as the current increases or the temperature decreases.Characterization of the heat source terms includes measurement of reversible and irreversible heat sources that can be determined by calorimetric methods. Particularly, the entropy coefficient (dUOC/dT) in the reversible source is the key parameter that determines the amount of the reversible heat generated during operations. Currently, either potentiometric or calorimetric method is used to measure the value of the entropy coefficient, which drawbacks are long measurement time and inaccuracy. Thus, a new method is proposed based on the calorimeter that works as a thermostat in conjunction with an estimation technique. In order to reduce the measurement time, a time-domain background voltage offset correction and a frequency-domain entropy coefficient determination have been newly developed and applied. Comparison between the developed one and the classical methods has shown a drastic reduction of the measurement time and a similar accuracy to the potentiometric method. The proposed method is also used to investigate effects of temperatures and aging on the entropy coefficient. As a result, the reversible heat source term dependent upon the operating conditions such as SOC, temperature and cycle life can be characterized, which are the important factors for design of battery thermal management systems.Moreover, a calorimetric method for the characterization of the reversible and irreversible heat sources is also developed by applying a sinusoidal current excitation to the cell and analyzing the heat generation response in frequency domain. The determined parameters of both heat sources are compared with those measured by hybridized time frequency domain analysis method and EIS analysis, respectively, which shows a good match. Moreover, the calculated reversible and irreversible heat sources terms are compared with the experimental measurement. Results have shown improved performances in the characterization of irreversible and reversible heat with respect to measurement speed and accuracy.Finally, a thermal model that includes irreversible and reversible heat source terms is developed and then incorporated into a reduced-order electrochemical model (ROM). The electrochemical thermal model is validated against the heat generation rate of the cells measured by the developed calorimeter aforementioned. The model is capable of predicting heat generation rates up to 3C from -30°C to 35°C. Based on the validated thermal model, effects of C rates and temperatures on heat sources can be analyzed. The results have shown that the reversible heat is dominant at low C rates, while the irreversible one is dominant at high C rates because the Joule heating, which is the main irreversible heat source, is proportional to the square of the current. Besides, the reversible heat source is dominant at high temperatures, while the irreversible one is dominant at low C rates because battery internal resistance sources such as contact resistance and ionic resistivity rapidly increase at low temperatures.In addition, the lumped model is used to develop a two-dimensional electrochemical thermal model that is validated with temperature images captured by an Infrared thermal camera.Presented experimental characterization of heat generation and the associated theoretical analysis by electrochemical thermal models can provide basics and fundamentals for an optimal design of future battery thermal management systems.

Scale-Up of Physics-Based Models for Predicting Degradation of Large Lithium Ion Batteries

Large lithium-ion batteries (LIBs) demonstrate different performance and lifetime compared to small LIB cells, owing to the size effects generated by the electrical configuration and property imbalance. However, the calculation time for performing life predictions with three-dimensional (3D) cell models is undesirably long. In this paper, a lumped cell model with equivalent resistances (LER cell model) is proposed as a reduced order model of the 3D cell model, which enables accurate and fast life predictions of large LIBs. The developed LER cell model is validated via the comparisons with results of the 3D cell models by simulating a 20-Ah commercial pouch cell (NCM/graphite) and the experimental values. In addition, the LER cell models are applied to different cell types and sizes, such as a 20-Ah cylindrical cell and a 60-Ah pouch cell.

Simulation of voltage imbalance in large lithium-ion battery packs influenced by cell-to-cell variations and balancing systems

Abstract Due to manufacturing tolerances, lithium-ion cells usually suffer from varying capacities, impedances, self-discharge currents and intrinsic aging rates, which are often claimed to be the reason for the voltage imbalance and subsequently deteriorated utilization of the battery pack. However, the true influence of such cell-to-cell variations is still not completely understood. This work presents a lean battery pack modeling approach combined with a holistic Monte Carlo simulation. Using this method, the presented study statistically evaluates how experimentally determined parameters of commercial 18650 nickel-rich/SiC lithium-ion cells influence the voltage drift within a 168s20p battery pack throughout its lifetime. Major degradation mechanisms were represented through the manipulation of the half-cell potentials of the anode and the cathode. A low-DOD cycle profile was used for the aging. Additionally, cell impedance and reversible self-discharge were taken into account. The results obtained in this work reveal that the intrinsic variation of aging rates has the biggest influence on the pack utilization. Furthermore, initial variations of the capacity and impedance of state of the art lithium-ion cells play a rather minor role in the utilization of a battery pack, due to a decrease of the relative variance of cell blocks with cells connected in parallel. Although different self-discharge and aging rates evoked a voltage drift, the utilization of battery packs with and without dissipative balancing remained almost the same, assuming no cells with internal defects were present.

Scandinavian firms to recycle lithium-ion batteries

The Swedish battery start-up Northvolt and Norwegian metal producer Hydro have created a joint venture firm, Hydro Volt, that will build a recycling plant in Fredrikstad, Norway, for lithium-ion batteries from electric vehicles. Due to open in 2021, the plant will have initial capacity to crush and sort over 8,000 metric tons of batteries per year. Aluminum from the batteries will be reused by Hydro, and the remaining so-called black mass will be further processed by Northvolt in Västerås, Sweden. Northvolt is also building a large lithium-ion battery factory in Skellefteå, Sweden. The planned Hydro Volt facility marks a step toward Northvolt’s goal of sourcing 50% of its raw materials from recycled batteries by 2030. The Norwegian Automobile Importers’ Association estimates that electric vehicles will command a 55–60% market share in Norway in 2020, more than in any other country. Lithium-ion batteries from electric cars typically run for 10 years

Actively temperature controlled health-aware fast charging method for lithium-ion battery using nonlinear model predictive control

Previous research has shown that a drastic reduction of charging time compared to constant current constant voltage (CC/CV) charging protocol is possible while suppressing degradation causes by combining constant charging and pulse discharging current. However, effects of temperature variation on side reaction and lithium plating and effects of the frequency of pulse current on lithium stripping have not been considered. In fact, charging currents and operating temperatures dominantly affect the cycle life of battery, where both side reaction and lithium plating are competing. In this paper, reduced order electrochemical life models are developed and validated against experimental data collected at different currents and temperatures and then used to find out optimal temperatures at given charging currents with respect to degradation rates. Thereafter, an optimal charging current at different SOCs has been found using nonlinear model predictive control and then the optimal temperature is determined from the relationship obtained by the models, which reduces side reaction rate and lithium plating rate. In addition, pulse discharging current is added to promote the lithium stripping that recovers ions out of the plated lithium, where the amplitude and frequency of the pulse current are optimized using the models. Finally, the proposed charging method and the 1 C CC/CV charging method were tested in Battery-In-the-Loop using a large format pouch type lithium ion battery to compare each other, where 61% and 39% of charging time is reduced up to 80% and 100% SOC, respectively, while the capacity fade is comparable.

Study on thermal stability of nickel-rich/silicon-graphite large capacity lithium ion battery

The nickel-rich silicon-graphite lithium-ion cells, for example the LiNi0.8Mn0.1Co0.1O2/Silicon-carbon (NMC811/Si@C), have been used in the commercial power batteries to meet the higher capacity requirements now. However, the battery with higher energy is more destructive as thermal runaway occurs. In order to improve the safety of the battery, it is essential to study the thermal stability of this kind of battery. In this work, the differential scanning calorimetry (DSC) and adiabatic rate calorimetry (ARC) have been used to conduct a detail thermal stability analysis for this type of battery of different charge state, the thermal stability mutation of Si@C material has been observed firstly when the SOC is great than 55%. Besides, a reasonable thermal runaway reaction sequence of the battery of NMC811/Si@C is proposed. Moreover, based on the time to maximum reaction rate (TMR), the effective recommendations for the use of NMC811/Si@C lithium ion battery are provided.

Fast and safe charging method suppressing side reaction and lithium deposition reaction in lithium ion battery

Previously published work on fast charging method has demonstrated that the side reaction can be minimized by a properly designed charging protocol, but does not consider effect of lithium plating and stripping. Therefore, a model for side reaction, lithium plating, and stripping is developed and incorporated into a reduced order electrochemical model (ROM) with extended Kalman filter. In addition, effects of negative pulse charging are analyzed and show that negative pulse charging can recover ions from metallic lithium, so the capacity loss is minimized compared with CC charging with the same charging speed. Finally, a new fast charging method is designed by combining negative pulse and different limitations that include anode potential, side reaction rate and cutoff voltage that are estimated from ROM, which is called a fast charging method with negative pulse (FCNP). The proposed method, 2C and 3C CC/CV charging methods are tested in Battery-In-The-Loop using a large format pouch type lithium ion battery. The charging time by FCNP up to 80% SOC is comparable to that by 3C CC/CV at the beginning of life and faster after the middle of life. At the same time, the capacity loss by FCNP is comparable to that by 2C CC/CV.

The Comparison of Thermal Stability and Safety between Fresh and Aging Large Capacity Lithium Ion Battery with Silicon Carbon Anode

Due to the high energy density, lithium ion battery (LIB) plays an important role in electric vehicle (EV). However, the requirement to the energy density keeps increasing. More and more materials are selected to improve the energy density to provide more distance for EV. Silicon, as a famous anode material, provides much higher specific capacity (3579-4200 mAh/g) than graphite (372 mAh/g) does. This research focused on thermal stability and safety of a 30Ah battery with silicon carbon anode. Aging battery would also be compared with the fresh battery after several cycles to different state of health (SOH). The batteries would be analyzed by accelerating rate colorimeter (ARC) to determine the safety. The differential scanning colorimeter (DSC) evaluated the thermal stability of the batteries. The thermal stability of ARC is decided by T1, T2 and T3 which are the self-heating temperature, thermal runaway triggered temperature and the highest temperature, respectively. The scanning electron microscope (SEM) could observe the surface differences with different SOH and various silicon proportion. The research revealed an overall safety assessment of the lithium ion battery with different content of silicon anode under different SOH. Keywords: Lithium ion battery, silicon carbon, thermal runaway, thermal stability Figure 1

Enable Model-Based Diagnostics and Prognostics for Lithium-Ion Batteries

Physicochemical processes in lithium ion batteries occur in intricate geometries over a wide range of time and length scales. As the size of the battery increases, macroscopic design factors in combination with highly dynamic environmental conditions significantly influence the electrical, thermal, electrochemical, and mechanical responses of a battery system. Computer-aided engineering tools are helping to accelerate the design and validation of large format cells and battery pack systems, which heavily replies on costly and time-consuming experimental tests previously. Validated physics-based models are effective in predicting electrochemical performance, thermal and mechanical response of cells and packs under normal and abuse scenarios and provide valuable insights not possible through experimental testing alone for diagnostics and prognostic purpose. NREL pioneered the Multi-Scale Multi-Domain (MSMD) battery model, overcoming challenges in modeling the highly nonlinear multi-scale response of battery systems. The MSMD model provides flexibility and multi-physics expandability through its modularized architecture. The presentation describes present efforts to develop approaches to make the models better suited for engineering diagnostics and prognostic for large lithium-ion battery units by Enhancing computation speed and stability of the pack-level multi-scale model while still resolving nonlinearities of dynamic battery response across scales from particles to packsBlending field simulation with system simulation in a selective fashion to balance speed and accuracy. Applicable techniques include domain decomposition, physics segregation and reduced-order models (ROM) that can integrate into the system modelDeveloping interactive system interface for enhancement of multi-physics integrityIncorporating spatially distributed model to address 3D non-uniform usage and stress factors.