Thermal management of lithium‐ion batteries for electric vehicles

Thermal issues associated with electric vehicle battery packs can significantly affect performance and life cycle. Fundamental heat transfer principles and performance characteristics of commercial lithium‐ion battery are used to predict the temperature distributions in a typical battery pack under a range of discharge conditions. Various cooling strategies are implemented to examine the relationship between battery thermal behavior and design parameters. By studying the effect of cooling conditions and pack configuration on battery temperature, information is obtained as to how to maintain operating temperature by designing proper battery configuration and choosing proper cooling systems. It was found that a cooling strategy based on distributed forced convection is an efficient, cost‐effective method which can provide uniform temperature and voltage distributions within the battery pack at various discharge rates. Copyright © 2012 John Wiley & Sons, Ltd.     

Modelling the thermal behaviour of a lithium-ion battery during charge

A method for modelling the thermal behaviour of a lithium-ion battery (LIB) during charge is presented. The effect of charge conditions on the thermal behaviour is examined by means of the finite element method. A comparison of the experimental charge curves with the modelling results validates the two-dimensional modelling of the potential and current density distribution on the electrodes of an LIB as a function of charge time during constant-current charge followed by constant-voltage charge. The heat generation rates as a function of the charge time and the position on the electrodes are calculated to predict the temperature distributions of the LIB based on the modelling results for potential and current density distributions. The temperature distributions obtained from the modelling are in good agreement with the experimental measurements.     

Three-dimensional layered electrochemical-thermal model for a lithium-ion pouch cell

Performance of lithium-ion pouch cell cannot be evaluated only by its external characteristics, such as the surface temperature and potential, as the internal electrochemical and thermal properties of the cell can significantly affect its performance. However, it is difficult to observe the internal thermal and electrochemical characteristics by means of experiment. Within this study a layered three-dimensional electrochemical-thermal coupled model of a lithium-ion pouch cell is proposed, then it is verified by experimental method at several discharge rates. According to this model, the spatial distribution of temperature field and heat generation rate are analyzed at four discharge rates, a fitted surface equation is presented for this battery to roughly predict the heat generation rate according to the discharge rate and depth of discharge. Afterward, several representative electrochemical properties (electric potential, electrolyte concentration, electrode current density, and mass transfer process) are investigated from the spatial perspective, which reveals the transfer process of lithium-ion and current clearly inside the battery. It is also concluded that there exists a gradient both at the plane and thickness of the electrode, and the gradient in the thickness direction is larger than that in the plane. A large gradient in temperature, lithium-ion concentration, electrode potential and current density distribution are located at the connection between tabs and electrodes.     

Numerical modeling and experimental investigation of a prismatic battery subjected to water cooling

In this paper, a numerical model using ANSYS Fluent for a minichannel cold plate is developed for water-cooled LiFePO₄ battery. The temperature and velocity distributions are investigated using experimental and computational approach at different C-rates and boundary conditions (BCs). In this regard, a battery thermal management system (BTMS) with water cooling is designed and developed for a pouch-type LiFePO₄ battery using dual cold plates placed one on top and the other at the bottom of a battery. For these tasks, the battery is discharged at high discharge rates of 3C (60?A) and 4C (80?A) and with various BCs of 5°C, 15°C, and 25°C with water cooling in order to provide quantitative data regarding the thermal behavior of lithium-ion batteries. Computationally, a high-fidelity computational fluid dynamics (CFD) model was also developed for a minichannel cold plate, and the simulated data are then validated with the experimental data for temperature profiles. The present results show that increased discharge rates (between 3C and 4C) and increased operating temperature or bath temperature (between 5°C, 15°C, and 25°C) result in increased temperature at cold plates as experimentally measured. Furthermore, the sensors nearest the electrodes (anode and cathode) measured the higher temperatures than the sensors located at the center of the battery surface.     

PMMA-assisted synthesis of Li1−xNi0.5Mn1.5O4−δ for high-voltage lithium batteries with expanded rate capability at high cycling temperatures

In this work, poly(methyl methacrylate) (PMMA), a non-surfactant polymer was used to synthesize nonstoichiometric Li_0.82Ni_0.52Mn_1.52O_4−δ (0 ≤ δ ≤ 0.25) spinels. The presence of the polymer was found to be beneficial with a view to facilitating the use of the spinel in electrodes for lithium batteries. Thus, PMMA allowed spinel particles of a high crystallinity and uniform size and shape to be obtained, and particle size to be tailored by using an appropriate calcining temperature and time. By controlling these variables, spinels in nanometric, submicrometric and micrometric particle sizes were prepared and characterized by chemical analysis, X-ray diffraction, electron microscopy, thermogravimetry and nitrogen adsorptions measurements. The spinels were obtained as highly crystalline phases with lithium and oxygen deficiency and some cation disorder as revealed by chemical analysis, thermogravimetric and XRD data. Their electrochemical performance in two-electrode cells was tested at room temperature and 50 °C over a wide range of charge/discharge rates (from C/4 to 4C). Cell performance was found to depend on particle size rather than on structural properties. Thus, the spinel best performing at 50 °C was that consisting of submicrometric particles, which delivered a high capacity and exhibited the best capacity retention and rate capability. Particles of submicronic size share the advantages of nanometric particles (viz. the ability to withstand high charge/discharge rates) and micrometric particles (a high capacity and stability at low rates).     

Thermal behavior of small lithium-ion battery during rapid charge and discharge cycles

The secondary batteries for electric vehicles (EV) generate much heat during rapid charge and discharge cycles at current levels exceeding the batteries’ rating, such as when the EV quickly starts consuming battery power or when recovering inertia energy during sudden stops. During these rapid charge and discharge cycles, the cell temperature may increase above allowable limits. We calculated the temperature rise of a small lithium-ion secondary battery during rapid charge and discharge cycles. The heat-source factors were measured again by the methods described in our previous study, because the performance of the battery reported here has been improved, showing lower overpotential resistance. Battery heat capacity was measured by a twin-type heat conduction calorimeter, and determined to be a linear function of temperature. Further, the heat transfer coefficient, measured again precisely by the method described in our previous study, was arranged as a function of cell and ambient temperatures. The temperature calculated by our battery thermal behavior model using these measured data agrees well with the cell temperature measured by thermocouple during rapid charge and discharge cycles. Also, battery radial temperature distributions were calculated to be small, and confirmed experimentally.     

Current density and state of charge inhomogeneities in Li-ion battery cells with LiFePO4 as cathode material due to temperature gradients

Current density distributions and local state of charge (SoC) differences that are caused by temperature gradients inside actively cooled Li-ion battery cells are discussed and quantified. As an example, a cylindrical Li-ion cell with LiFePO₄ as cathode material (LiFePO₄-cell) is analyzed in detail both experimentally and by means of spatial electro-thermal co-simulations. The reason for current density inhomogeneities is found to be the local electrochemical impedance varying with temperature in different regions of the jelly roll. For the investigated cell, high power cycling and the resulting temperature gradient additionally cause SoC-gradients inside the jelly roll. The local SoCs inside one cell diverge firstly because of asymmetric current density distributions during charge and discharge inside the cell and secondly because of the temperature dependence of the local open circuit potential. Even after long relaxation periods, the SoC distribution in cycled LiFePO₄-cells remains inhomogeneous across the jelly roll as a result of hysteresis in the open circuit voltage. The occurring thermal electrical inhomogeneities are expected to influence local aging differences and thus, global cell aging. Additionally the occurrence of inhomogeneous current flow and SoC-development inside non-uniformly cooled battery packs of parallel connected LiFePO₄-cells is measured and discussed.     

A novel experimental study on discharge characteristics of an aluminum‐air battery

In order to explore the discharge characteristics of aluminum‐air battery and find out the best discharge performance of aluminum‐air battery under the optimum working conditions, this paper studies discharge performances of an aluminum‐air battery under various ambient temperature and battery discharge conditions. The relationship between the temperature rise of the battery electrolyte and the discharge current density was studied by an experimental method. Effects of the electrolyte concentration and the ambient temperature on the battery discharge voltage were investigated. In addition, a novel method for calculating the efficiency of the aluminum‐air battery was proposed. Results show that the temperature of the aluminum‐air battery electrolyte gradually increases as its discharge current density increases and the electrolyte temperature rise could reach as high as 10°C after 60 minutes with a constant 35 mA cm^?2 discharge current density. The specific energy and the specific capacity of the aluminum‐air battery first increase and then decrease as the current density increases. When the current density is 25 mA cm^?2, the specific energy has a peak of 3105 Wh kg^?1 for the condition of the chamber temperature 40°C and the electrolyte concentration 2 mol L^?1 (2 M), while the specific capacity has a peak of 2207 Ah kg^?1; furthermore, its efficiencies under various conditions increase first with the current density, reach a peak range of 19.6% to approximately 36% at 25 mA cm^?2, and then decrease. These experimental results could be used as a technical guidance for the optimization in thermal management designs of the aluminum‐air battery under various operating conditions.     

Modeling and validation of temperature changes in a pouch lithium-ion battery at various discharge rates

This paper deals with the thermal modeling of temperature rise in a pouch lithium-ion battery with LiFePO₄ (also known as LFP) cathode material. The developed model represents the main thermal phenomena in the cell in terms of temperature change. The proposed model is validated with the collected experimental data from a module composed of 11 cells. In the conducted experiments, the different charge and discharge rates of 1/2C, 1C, 2C and 2.5C are applied. It is seen that, the increased discharge rates result in increased temperature on the surface of the battery. When the discharge rate is doubled, from 1C to 2C, cell temperatures have risen by 3.5 times. A simplified model for determining the heat generation is developed and validated with the test results.     

Performance characteristics of Ultralife's solid polymer rechargeable batteries

Ultralife Batteries delivered the world's first commercial shipments of solid polymer rechargeable batteries in 1997. The battery consists of a Li_xMn₂O₄⁻ based cathode, graphite anode and proprietary polymeric separator. Energy density of the batteries exceeds 120 W h kg⁻¹ and 200 W h dm⁻³ at the C rate. Pulse capability up to 5 C has been demonstrated. More than 90% of the initial C rate capacity remains after 500 continuous cycles at room temperature. These solid polymer rechargeable batteries also show good low and high temperature performance and have good safety characteristics.     

Thermal modeling of cylindrical lithium ion battery during discharge cycle

Transient and thermo-electric finite element analysis (FEA) of cylindrical lithium ion (Li-ion) battery was presented. The simplified model by adopting a cylindrical coordinate was employed. This model provides the thermal behavior of Li-ion battery during discharge cycle. The mathematical model solves conservation of energy considering heat generations due to both joule heating and entropy change. A LiCoO₂/C battery at various discharge rates was investigated. The temperature profile from simulation had similar tendency with experiment. The temperature profile was decomposed with contributions of each heat sources and was presented at several discharge rates. It was found that the contribution of heat source due to joule heating was significant at a high discharge rate, whereas that due to entropy change was dominant at a low discharge rate. Also the effect of cooling condition and the LiNiCoMnO₂/C battery were analyzed for the purpose of temperature reduction.     

Performance of a liquid cooling-based battery thermal management system with a composite phase change material

This article reports a recent study on a liquid cooling-based battery thermal management system (BTMS) with a composite phase change material (CPCM). Both copper foam and expanded graphite were considered as the structural materials for the CPCM. The thermal behaviour of a lithium-ion battery was experimental investigated first under different charge/discharge rates. A two-dimensional model was then developed to examine the performance of the BTMS. For the copper foam-based CPCM modelling, an enthalpy-porosity approach was applied. The numerical modelling aimed to study the impacts of CPCM types and inlet velocity of heat transfer fluid on both the maximum battery temperature and temperature distribution under different current rates. Dimensional analyses of the results were performed, leading to the establishment of relationships of the Nusselt numbers and dimensionless temperature against the Fourier and Stefan numbers.     

Measurement of interzonal heat and mass transfer by natural convection

Experiments to measure the interzonal heat and mass transfer were carried out in two full size adjoining rooms under two different conditions. Before starting the tests, one of the rooms was heated to an average temperature of 32°C, while the other room was cooled to an average temperature of 19°C. To start the first type of tests, the auxiliary heating and cooling were turned off and the door blocking the opening opened. For the second test, auxiliary cooling was turned off, while the auxiliary heat was left on in the heated room. Visual observations of the flow phenomenon were made. Velocity and temperature profiles of the air-flow through the opening, and air temperatures in the test rooms were measured. The experimental mass and heat flow rates were computed from the velocity and temperature data and compared with the values predicted by the existing algorithms based on the application of the Bernoulli's equation. The agreement between the measured and predicted values is better for a value of discharge coefficient C = 0.45 than it is for C = 0.611 (the theoretical value of C for a sharp edged orifice quoted in the literature).     

High-rate dischargeability enhancement of Ni/MH rechargeable batteries by addition of nanoscale CoO to positive electrodes

Nanoscale cobalt oxide (CoO) particles were synthesized by analysis of CoCO₃ in vacuum. Four groups of sealed Ni/MH batteries with different ratio of nanoscale CoO in the positive electrodes were assembled. The overall characteristics of Ni/MH batteries were investigated at different discharge rates at room temperature. The high-rate discharge performance of the Ni/MH batteries was improved by the addition of nanoscale CoO in positive electrode as compared with the addition of normal CoO. Under high-rate discharge conditions, the batteries with sufficient nanoscale CoO in positive electrodes presented much better cycling stability, higher discharge mean voltage, lower internal resistance and higher high-rate capacity. The addition of 8 wt.% nanoscale CoO was proved a desired amount to modify the battery performance at high discharge rates. Too much nanoscale CoO contributed no effect on the improvement of overall performance of Ni/MH batteries.     

Characterization of a zinc-cerium flow battery

The performance of a divided, parallel-plate zinc-cerium redox flow battery using methanesulfonic acid electrolytes was studied. Eight two and three-dimensional electrodes were tested under both constant current density and constant cell voltage discharge. Carbon felt and the three-dimensional platinised titanium mesh electrodes exhibited superior performance over the 2-dimensional electrodes. The charge and discharge characteristics of the redox flow battery were studied under different operating conditions and Zn/Ce reactant, as well as methansulfonic acid concentration. The cell performance improved at higher operating temperatures and faster electrolyte flow velocities. The number of possible cycles increased at reduced states of charge. During 15 min charge/discharge per cycle experiment, 57 cycles were obtained and the zinc reaction was found to be the limiting process during long term operation.     

Experimental investigation on the essential cause of the degrading performances for an overcharging ternary battery

Ternary power batteries, as the mainstream power sources of electric vehicles, are liable to inducing thermal runaway (TR) with respect to their sensitivity to abusive conditions. Among various abuse conditions, the overcharge of a battery has been considered as the most common and severe case giving rise to thermal safety accidents. In this study, an overcharged battery and a normal battery, both using ternary/graphite electrodes, were investigated and analyzed synergistically through thermal behaviors and electrochemical characteristics. Initially, a series of electrochemical parameters including charge and discharge voltage plateaus, discharged capacity and time at different discharge rates, and internal resistances were carried out. Then, the heat generation behaviors between normal and overcharged batteries were evaluated. Furtherly, the interconnectedness with the electrochemical capacity degradation and heat generation aggravation of the ternary battery after overcharge was analyzed. Besides, the essential causes of the deterioration of electrochemical properties and severe heat behaviors resulting from overcharge were intensively analyzed via microscopic perspectives. In addition, the electrochemical characteristics fading of abused ternary battery triggered by overcharge were investigated, especially under higher temperature (55°C) and ultralow temperature (−20°C) conditions. Therefore, for an overcharged battery, this research not only elaborates the essential causa of the degraded electrochemical and anabatic thermal performance from a materials and thermal science perspective but also provides a foundation for further promoting the safety properties of commercialized power batteries with ternary chemical systems.     

Determination of H2O/H2 system exchange current densities on cycled hydride electrodes from overswitch potential jump at low and high charge/discharge rates

This research paper describes a simplified and quick method for determining the exchange current densities of the H₂O/H₂ system on powder composite electrodes made of hydrogen storage intermetallics.The method is based on the hydrogen storage electrode potential jump upon its galvanostatic overswitching from the cathodic to the anodic direction for low- and high charge/discharge rates. Indeed, research findings indicate that the discharge rate/exchange current density quotient depends either linearly or exponentially on the potential jump for low- and high-charge/discharge rates. This study also defines the applicability ranges for both types of dependencies with the best accuracy for calculating exchange currents (relative experimental error ≤5%) corresponding to potential jumps of up to 0.037 V (discharge rates of up to 0.2C) and 0.08–0.20 V (discharge rates over 0.3C). Furthermore, this study presents other instances of determining exchange currents versus cycling determination for different intermetallics and discusses the effect of the hydride material surface modification and charge/discharge rate conditions on the exchange current density.     

Heat Generation and Thermal Transport in Lithium-Ion Batteries: A Scale-Bridging Perspective

ABSTRACT

Lithium-ion batteries (LIBs) are complex, heterogeneous systems with coupled electrochemical and thermal phenomena that lead to elevated temperatures, which, in turn, limit safety, reliability, and performance. Despite years of research, there are still open questions about the electrochemical-thermal phenomena within battery cells. This article highlights recent advances in thermal characterization and modeling of LIBs with an emphasis on the multi-scale aspect of battery systems: from the microscale electrode components to the macroscale battery packs. Both heat generation and thermal properties (thermal conductivity and specific heat capacity) are impacted by battery capacity, charge/discharge rate, ambient conditions, and the underlying microstructure. Understanding thermal phenomena and designing batteries to prevent thermal runaway requires multiscale efforts from the microstructure of the electrodes to the overall system behavior. Experimental efforts have focused on both property and performance characterization, as well as development of new battery chemistries for improved performance and new designs for improved thermal management. Past numerical modeling work ranges from computationally efficient lumped approaches to high fidelity microstructural finite element models. Ultimately, coupled electrochemical-thermal investigations (both numerical and experimental) are required to further improve the performance and reliability of batteries, and to prevent thermal runaway. This perspective article provides insight into directions to improve these approaches with the goal of informing design of batteries with improved performance, safety, and reliability.     

Experimental analysis on the degradation behavior of overdischarged lithium-ion battery combined with the effect of high-temperature environment

A set of experiments are performed in the present work to investigate the degradation behavior of lithium-ion battery during overdischarge cycling, as well as the influence of a high-temperature environment on the degradation. Among, different discharge cut-off voltages (1.0, 0.5, and 0.2 V) are included. During the overdischarge process, batteries experience a stage where a violent electro-thermal behavior is exhibited, involving sharp decreases in the voltage and current, and a fierce increase in the surface temperature; moreover, several parameters such as the discharge capacity, energy density, and internal resistances are all increased after overdischarge. Besides, a poor rate capacity and serious capacity degradation can also be seen during the overdischarge cycling, which is further reflected by the evolution of battery surface temperature, charge/discharge voltage, and internal resistances. What is more, it is found that battery electro-thermal parameters, eg, temperature rise, degradation rate, and internal resistances, increase exponentially as overdischarge deepens. Finally, a high-temperature environment is verified to deteriorate the degradation of overdischarged battery.