Modeling of steady‐state and transient thermal performance of a Li‐ion cell with an axial fluidic channel for cooling

Thermal management of Li‐ion cells is an important technological problem for energy conversion and storage. Effective dissipation of heat generated during the operation of a Li‐ion cell is critical to ensure safety and performance. In this paper, thermal performance of a cylindrical Li‐ion cell with an axial channel for coolant flow is analyzed. Analytical expressions are derived for steady‐state and transient temperature fields in the cell. The analytical models are in excellent agreement with finite‐element simulation results. The dependence of the temperature field on various geometrical and thermal characteristics of the cell is analyzed. It is shown that coolant flow through even a very small diameter axial channel results in significant thermal benefit. The trade‐off between thermal benefit and reduction in cell volume, and hence capacity due to the axial channel, is analyzed. The effect of axial cooling on geometrical design of the cell, and transient thermal performance during a discharge process, is also analyzed. Results presented in this paper are expected to aid in the development of effective cooling techniques for Li‐ion cells based on axial cooling. Copyright © 2014 John Wiley & Sons, Ltd.     

The improved discharge performance of Li/CFx batteries by using multi-walled carbon nanotubes as conductive additive

The discharge performance of Li/CF_x (x = 1) battery is improved by using multi-walled carbon nanotubes (MWCNTs) as an alternative conductive additive. Compared with the battery using acetylene black as conductive additive at the same amount, the Li/CF_x battery using MWCNTs as conductive additive has higher specific capacity and energy density as well as smoother voltage plateau, especially at higher discharge rate. The specific capacity at discharge rate of 1 C is improved by nearly 26% when MWCNTs are employed as conductive additive. Meanwhile, it is also found that the discharge performance is able to be tuned by the amount of MWCNTs and the battery containing more MWCNTs is favorable to be discharged at higher rates. The specific capacity of Li/CF_x battery with 11.09 wt.% MWCNTs is approximately 712 mAh g⁻¹ at the discharge rate of 1 C. It is proposed that the formed three-dimensional networks of MWCNTs in cathode, which enlarges the contact area of interphase and facilitates electrons delivery, accelerates the rates of lithium ion diffusion into the fluorinated layers and electrons transport in cathode at the same time, which improves the discharge performance of Li/CF_x battery subsequently, especially at higher rates.     

Discharge–charge characteristics and performance of Li/FeOOH(an) battery with PAN-based polymer electrolyte

The discharge–charge characteristics and performance of a Li/FeOOH(an) solid polymer battery are investigated. The cell uses a cathode of amorphous FeOOH with aniline derivatives (FeOOH(an)) and a polyacrylonitrile-based solid polymer electrolyte. The ionic conductivity of the electrolyte sample used for electrochemical measurements is 1.6×10⁻³ Ω⁻¹ cm⁻¹ at room temperature. Its anodic stability is above 4.5 V. The diffusion coefficient of Li⁺ ions into the cathode is found to be 2.97×10⁻¹¹ cm² s⁻¹ by a.c. impedance spectroscopy. Variations of impedance parameters and the diffusion coefficient are investigated during the first discharge–charge. From the results of these measurements, it is concluded that the structure of FeOOH(an) is deformed by Li⁺ ion insertion/extraction. The electrochemical redox reaction of FeOOH(an) is investigated by cyclic voltammetry. In the potential range 2.0 to ∼4.0 V, the first discharge–charge is irreversible. Thereafter, reversible cycling processes take place. The initial discharge capacity is ∼130 mA h g⁻¹ at a current density of 0.1 mA cm⁻².     

Thermal simulation of high‐power Li‐ion battery with LiMn1/3Ni1/3Co1/3O2 cathode on cell and module levels

Thermal modeling of temperature rise in high‐power Li‐ion battery cells and modules is presented here. Simulation results are validated by experiments. Results indicate that entropy heat generation plays a significant role in heat generation of Li‐ion battery cells and should be included in simulation as a function of state of charge (SOC). Simulation results utilizing measured overpotential resistance and entropy heat generation provide the best fit when compared to experimental results. Resistance data provided by supplier shows significant difference compared with measured data and should be critically examined for any module design purposes. Copyright © 2013 John Wiley & Sons, Ltd.     

Degradation mechanisms in Li‐ion batteries: a state‐of‐the‐art review

One of the most prominent energy storage technologies which are under continuous development, especially for mobile applications, is the Li‐ion batteries due to their superior gravimetric and volumetric energy density. However, limited cycle life of Li‐ion batteries inhibits their extended use in stationary energy storage applications. To enable wider market penetration of Li‐ion batteries, detailed understanding of the degradation mechanisms is required. A typical Li‐ion battery comprised of an active material, binder, separator, current collector, and electrolyte, and the interaction between these components plays a critical role in successful operation of such batteries. Degradation of Li‐ion batteries can have both chemical and mechanical origins and manifests itself by capacity loss, power fading or both. Mechanical degradation mechanisms are associated with the volume changes and stress generated during repetitive intercalation of Li ions into the active material, whereas chemical degradation mechanisms are associated with the parasitic side reactions such as solid electrolyte interphase formation, electrolyte decomposition/reduction and active material dissolution. In this study, the main degradation mechanisms in Li‐ion batteries are reviewed. Copyright © 2017 John Wiley & Sons, Ltd.     

Electrochemical intercalation of lithium into carbons using a solid polymer electrolyte

A study of the electrochemical performance of carbon materials from different types was carried out on true solid polymer-based poly(ethylene oxide) (PEO) with LiTFSI for application as the negative electrode in lithium ion solid-state batteries (LISSBs) at 60 °C. The reversible and irreversible capacity depend strongly on the crystallinity, the form of carbon and the impurities. A comparison of particle versus fiber was done when we investigated the charge/discharge characteristics with different current densities. The galvanostatic curves show high reversibility of the lithium—carbon in solid polymer electrolyte. The kinetics of electrochemical intercalation of lithium into carbon was studied by impedance spectroscopy especially for evaluating the diffusion coefficient in different origins of carbon. The degree of ionization of lithium was investigated by using solid-state ⁷Li nuclear magnetic resonance spectroscopy when the electrode is fully intercalated or doped down to 0 V. The chemical shift of ⁷Li NMR in lithium intercalation or doping in the carbons was classified in two ranges, 42 ppm and 9 ppm. ⁷Li NMR suggests the carbon with a 42 ppm range is the best choice for LISSBs.     

Fabrication and characteristics of a composite cathode of sulfonated polyaniline and Ramsdellite–MnO2 for a new rechargeable lithium polymer battery

The ionic conductivity of a polyacrylonitrile (PAN)-based solid polymer electrolyte is 1.4×10⁻³ S cm⁻¹, which is sufficient for the electrolyte to be used in a rechargeable lithium polymer battery. The anodic stability of the solid polymer electrolyte is over 4.6 V (vs. Li/Li⁺). A reduced, highly sulfonated form of polyaniline (SPAn) and Ramsdellite–MnO₂ (R-MnO₂) are synthesized and used as a cathodic material for a rechargeable lithium polymer battery. Three kinds of cathodes are prepared from SPAn, R-MnO₂, and a mixture of SPAn and R-MnO₂. The electrochemical properties and diffusion coefficient of lithium ions in each cathode, and the interface between the solid polymer electrolyte and each cathode are investigated by cyclic voltammetry and impedance spectroscopy. The redox processes of the SPAn cathode are two-step reactions. The cathodic and anodic peak currents increase as the cycle number increases. In the redox processes of the R-MnO₂ cathode, the cathodic peak current on the second cycle is 62% of that on the first cycle. The Li/R-MnO₂ battery has a very high initial discharge capacity, but very poor cycleability. For the composite cathode, the cathodic peak current on the second cycle is 72% of that on the first cycle, i.e., higher than that for the R-MnO₂ cathode. The diffusion coefficient of the composite cathode during the discharge process is close to the sum of each variation in the SPAn and R-MnO₂ cathodes. The instability of the R-MnO₂ cathode at x=0.3 and x=0.2 during the charge process is not observed with the composite cathode. The discharge–charge performance of three types of battery are investigated. The initial discharge capacity of the Li/composite cathode battery is 97.0 m Ah g⁻¹. This battery has higher discharge capacity than the Li/SPAn battery (66.8 m Ah g⁻¹), and better cycleability than the Li/R-MnO₂ battery.     

Discharge characteristic of a non-aqueous electrolyte Li/O2 battery

Discharge characteristic of Li/O₂ cells was studied using galvanostatic discharge, polarization, and ac-impedance techniques. Results show that the discharge performance of Li/O₂ cells is determined mainly by the carbon air electrode, instead by the Li anode. A consecutive polarization experiment shows that impedance of the air electrode is progressively increased with polarization cycle number since the surfaces of the air electrode are gradually covered by discharge products, which prevents oxygen from diffusing to the reaction sites of carbon. Based on this observation, we proposed an electrolyte-catalyst “two-phase reaction zone” model for the catalytic reduction of oxygen in carbon air electrode. According to this model, the best case for electrolyte-filling is that the air electrode is completely wetted while still remaining sufficient pores for fast diffusion of gaseous oxygen. It is shown that an electrolyte-flooded cell suffers low specific capacity and poor power performance due to slow diffusion of the dissolved oxygen in liquid electrolyte. Therefore, the status of electrolyte-filling plays an essential role in determining the specific capacity and power capability of a Li/O₂ cell. In addition, we found that at low discharge currents the Li/O₂ cell showed two discharge voltage plateaus. The second voltage plateau is attributed to a continuous discharge of Li₂O₂ into Li₂O, and this discharge shows high polarization due to the electrically isolating property of Li₂O₂.     

基于伪二维电化学-热耦合模型的锂电池热特性研究

锂电池放电过程中的产热受电池内部电化学反应和欧姆效应影响,电池产热由电池化学与动力学决定,而电池动力学依赖于电池运行条件和设计参数。锂电池的六个温度依赖性参数对锂电池的放电过程中的产热速率具有影响,包括固相活性颗粒和电解液中的锂离子扩散系数、反应速率常数、电极开路电压、电解液离子电导率、热力学因子和阳离子迁移数。基于LiFePO_4圆柱形电池建立了伪二维电化学-热耦合模型,研究电池在恒流放电过程中的产热速率,以及正极、隔膜和负极各部分的产热速率和所占比例。结果表明,总产热功率随反应热的波动而变化,其中正极电极层中反应热占比最大,负极电极层中极化产热所占比例高于正极,而隔膜中的产热主要来源自欧姆热。不同对流传热系数条件下,电池的表面温度和内部温度差都不同,因此要合理的采取电池热管理措施。     

Modelling electrode material utilization in the trench model 3D-microbattery by finite element analysis

A mathematical model for ionic transport in 3D-microbattery (3D-MB) using finite element analysis is presented here, based on concentrated solution theory, ionic and atomic diffusion and the Butler-Volmer equation. The model is used to study electrochemical processes taking place in the electrodes and electrolyte of a 3D-MB in the trench architecture, with a 10 μm thick electrolyte layer separating 10 μm thick graphite anode and LiCoO₂ cathode plates. The effect of changing conductivity of the positive electrode and the electrode plate height is also studied. Qualitative and quantitative data describing battery performance in terms of concentration gradient development and discharge curves points out the range for the most favourable electronic conductivity values of the electrodes: the values should not differ by more than order of magnitude. Furthermore, it is shown that also with optimal electrode conductivity values for electrodes, the Li ion diffusion in the electrodes during discharge is limiting the performance of the battery due to inhomogeneous lithiation and delithiation. Changing electrode height can be used to fine tune surface area usage, but has a limited effect on the overall battery performance.     

Physicochemical properties of lithium iron phosphate‐carbon as lithium polymer battery cathodes

Lithium iron phosphate‐carbon (LiFePO₄/multiwalled carbon nanotubes (MWCNTs)) composite cathode materials were prepared by a hydrothermal method. In this study, we used MWCNTs as conductive additive. Poly (vinylidene fluoride‐co‐hexafluoropropylene)‐based solid polymer electrolyte (SPE) was applied. The structural and morphological performance of LiFePO₄/MWCNTs cathode materials was investigated by X‐ray diffraction and scanning electron microscopy/mapping. The electrochemical properties of Li/SPE/LiFePO₄‐MWCNTs coin‐type polymer batteries were analyzed by cyclic voltammetry, ac impedance and galvanostatic charge/discharge tests. Li/SPE/LiFePO₄‐MWCNTs polymer battery with 5 wt % MWCNTs demonstrates the highest discharge capacity and stable cyclability at room temperature. It is indicated that LiFePO₄‐MWCNTs can be used as the cathode materials for lithium polymer batteries. Copyright © 2011 John Wiley & Sons, Ltd.     

Study of multiple interactions in mesoporous composite PEO electrolytes

This paper discusses the FT-infrared (IR) and NMR spectroscopy results of a mesoporous silica (SBA-15) composite poly(ethylene oxide) (PEO) solid lithium polymer electrolyte. The changes in COC, CH, and ClO₄ stretching IR vibrational modes indicated a combination of multiple interactions through Lewis acid–base reactions which interrupt the PEO crystalline structure. Higher salt disassociation by SBA-15 is also apparent from ClO₄ vibrational band mode.NMR studies indicated three types of Li ion environments; the first one is Li ions within the conventional amorphous PEO, the second is Li ions on the surface of mesoporous SBA-15 and the third is Li ions trapped along with PEO in the nano-tubular channels of SBA-15. Annealing leads to interaction of more PEO and lithium ions with the SBA-15 and free ions for conduction, as reflected in the ⁷Li variable temperature (VT)-NMR measurements and variable temperature ion conductivity.     

Plate flat heat pipe and liquid‐cooled coupled multistage heat dissipation system of Li‐ion battery

A thermal management system with the capability of achieving excellent heat dissipation is essential to the development of battery pack for transportation devices. To meet the temperature uniformity requirements of the battery pack, the plate flat heat pipe and liquid‐cooled coupled multistage heat dissipation system had been introduced. In this article, the research status of thermal management systems in battery pack was introduced. And the heat generation and heating power of the Li‐ion cell were studied. Then, the structure model of plate flat heat pipe system was proposed. Finally, the enhanced heat conduction effect of the thermal management system proposed in this article was comprehensively analyzed. Through the analysis of the results, in high discharge rates, the thermal management system proposed in this article could meet the temperature uniformity requirements of battery pack; also, the internal difference would reduce by 30.20%.     

A novel titania nanorods‐filled composite solid electrolyte with improved room temperature performance for solid‐state Li‐ion battery

Solid‐state batteries (SSBs) with room temperature (RT) performances had been one of the most promising technologies for energy storage. To achieve a chemical stable and high ionic conductive solid electrolyte, herein, a titania (TiO₂) (B) nanorods‐filled poly(propylene carbonate) (PPC)‐based organic/inorganic composite solid electrolyte (CSE) was prepared for the first time. It was found that by using TiO₂(B) nanorods, the ionic conductivity of the CSE membrane could be improved to 1.52 × 10^?4 S/cm, the electrochemical stable window was more than 4.6 V, and the tensile strength reaches 27 MPa with a strain less than 6%. The CSE was applied for SSB and showed excellent room temperature electrochemical performances. At 25°C, the LiFePO₄/CSE/Li SSB with 3%TiO₂‐filled CSE had the first cycle specific discharge capacity of 162 mAh/g with a capacity retention of 93% after 100 cycles at 0.3C. While the NCM622/CSE/Li SSB with 3%TiO₂‐filled CSE had the first specific discharge capacity of 165 mAh/g with a capacity retention of 88% after 100 cycles at 0.3C. The enhancement effect of TiO₂(B) nanorods could be ascribed that the rod‐like fillers provide more continuous Li‐ion transport path compared with nano particles, and the surface porosity and composition of TiO₂(B) nanorods could also improve the interfacial contact and Lewis acid‐base reaction sites between polymer and fillers. The TiO₂(B) nanorods‐filled CSE with high chemical stability, potential window, and ionic conductivity was promising to meet the requirements of SSBs.     

A validation study of lithium‐ion cell constant c‐rate discharge simulation with Battery Design Studio®

We compare battery performance simulations from a commercial lithium‐ion battery modeling software package against manufacturer performance specifications and laboratory tests to assess model validity. A set of commercially manufactured spiral wound lithium‐ion cells were electrochemically tested and then disassembled and physically characterized. The Battery Design Studio® (BDS) software was then used to create a mathematical model of each battery, and discharge simulations at constant C‐rates ranging from C/5 to 2C were compared against laboratory tests and manufacturer performance specifications. Results indicate that BDS predictions of total energy delivered under our constant C‐rate battery discharge tests are within 6.5% of laboratory measurements for a full discharge and within 2.8% when a 60% state of charge window is considered. Average discrepancy is substantially lower. In all cases, the discrepancy in simulated vs. manufacturer specifications or laboratory results of energy and capacity delivered was comparable to the discrepancy between manufacturer specifications and laboratory results. Results suggest that BDS can provide sufficient accuracy in discharge performance simulations for many applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of single crystalline electro-conductive Na0.44MnO2 nanowires with high aspect ratio for the fast charge–discharge Li ion battery

We report the fast charge–discharge Li ion battery based on the nanostructural controlled Na_0.44MnO₂ wires with high aspect ratio. The good fast charge–discharge property is observed because the single crystalline Na_0.44MnO₂ nanowires have a high electronic conductivity as electrode active materials of lithium ion battery due to the one-dimensional single crystalline nanowire. Moreover, such nanosize structure could reduce the required lithium diffusion length in the active materials to the several tens of nanometer, also reduce the effective specific current density by high surface area, and increase the stability of cycle performance by the one-dimensional single crystalline structure.     

β‐molybdenum carbide/carbon nanofibers as a shuttle inhibitor for lithium‐sulfur battery with high sulfur loading

We report the synthesis of β‐molybdenum carbide/carbon nanofibers (β‐Mo₂C/CNFs) by electrospinning and annealing process, when exploited as an interlayer in Li‐S batteries, demonstrating significantly improved electrochemical behaviors. The synthesized β‐Mo₂C/CNFs with 3D network structure and high surface area are not only conducive to ion transport and electrolyte penetration but also effectively intercept the shuttle of lithium polysulfide by polar surface interaction. Moreover, the reaction kinetics of the batteries enhanced is due to the presence of β‐Mo₂C, promoting the solid‐state polysulfide conversion reaction in the charge‐discharge process. Compared with the batteries with CNF interlayer and without interlayer, the batteries using a β‐Mo₂C/CNFs interlayer with a sulfur loading of 4.2 mg cm^‐2 delivered excellent electrochemical performance because of a facile redox reaction during cycling. The discharge capacity at the first cycle at 0.7 mA cm^?2 was 1360 mAh g^?1, maintaining a specific capacity of 974 mAh g^?1 after 160 cycles. Furthermore, it showed a high‐rate capacity of 700 mAh g^?1 at 14 mA cm^?2. This work demonstrates the β‐Mo₂C/CNFs as a promising interlayer to exploit Li‐S battery commercialization.     

Effect of electrode physical and chemical properties on lithium‐ion battery performance

The effect of physical and chemical properties on the performance of both positive and negative electrodes is studied for lithium‐ion (Li‐ion) batteries. These properties include the lithium diffusivity in the active electrode material, the electrical conductivity of the electrode, and the reaction rate constant at electrode active sites. The specific energy and power of the cells are determined at various discharge rates for electrodes with different properties. In addition, this study is conducted across various cell design cases. The results reveal that at moderate discharge rates, lithium diffusivity in the active negative‐electrode material has the highest impact on cell performance. The specific energy and power of the cell are improved ~11% by increasing the lithium diffusivity in the active negative‐electrode material by one order of magnitude. Around 4% improvement in the cell performance is achieved by increasing the reaction rate constant at the active sites of either electrodes by one order of magnitude. Copyright © 2013 John Wiley & Sons, Ltd.     

Solid-state diffusion limitations on pulse operation of a lithium ion cell for hybrid electric vehicles

A 1D model based on physical and electrochemical processes of a lithium ion cell is used to describe constant current and hybrid pulse power characterization (HPPC) data from a 6 Ah cell designed for hybrid electric vehicle (HEV) application. An approximate solution method for the diffusion of lithium ions within active material particles is formulated using the finite element method and implemented in the previously developed 1D electrochemical model as an explicit difference equation. Reaction current distribution and redistribution processes occurring during discharge and current interrupt, respectively, are driven by gradients in equilibrium potential that arise due to solid diffusion limitations. The model is extrapolated to predict voltage response at discharge rates up to 40 C where end of discharge is caused by negative electrode active material surface concentrations near depletion. Simple expressions are derived from an analytical solution to describe solid-state diffusion limited current for short duration, high-rate pulses.     

Effects of alkali ion on boosting WO3 photoelectrochemical performance by electrochemical doping

Electrochemical doping is a promising method to modify the photoelectrochemical performance of semiconductors. The published works using H ions as compensated cations have shown increased photocurrents, but theories vary about the causes of the improvement of photoelectrochemical performance. In this paper, we present the effects of cation ion and the key factors of enhancement using alkali sulfates ((Li/Na/K)₂SO₄) as the electrolyte for electrochemical doping. The effective electrode surface area (ECSA) was increased for the WO₃ film after electrochemical doping. The Li-ion, with the smallest radius and thereby the highest potential to insert into the WO₃ cell, results in the Li ion inserted WO₃ with the highest photocurrent in the three electrochemically doped samples. To investigate the possible factors affecting the photoelectrochemical performance, the electrochemically doped samples and a control sample were annealed under inert gas (Ar). The lower photocurrents were observed for the electrochemically doped samples after annealing, confirming that the key factors are the increase of the effective electrode surface area caused by electrochemical doping and ion compensation, rather than the ions themselves and the chemical bonds between alkali ions and W or O.