Prismatic Battery Research Articles

Coupled Numerical Approach for Automotive Battery Pack Lifetime Estimates With Thermal Management

This study combined a simple two-dimensional (2D) finite volume model (Kim model), which employs Ohm's law along with charge conservation over the electrodes and Butler–Volmer charge transfer kinetics for prismatic battery cells coupled with the single particle model (SPM) in order to model the thermal state of automotive battery packs. The objective here was to determine the effects of liquid cooling applied to the packs under standard driving cycles. A model developed by Kim provided a means for determining a nonuniform current distribution over the surface of the current collectors. The Kim model is based on the application of Ohm's law over a conducting medium, with empirical source terms representing current flowing into or out of an adjacent electrode layer. Here, a modeling advance is presented where empirical source terms in the Kim model were replaced with ones based on the chemistry and physics occurring inside the battery. As such, fundamental battery function was imparted to the model by integrating the SPM into the 2D finite volume Kim model. The 2D procedure described above was carried out on electrode sheets at different positions inside the cell, and determined thermal generation values that were mapped volumetrically into a heat transfer simulation, which, in turn, updated the electrochemical simulation. Capacity fade kinetics were determined by fitting experimental data to simulated results. With time-temperature profiles produced as described above for different pack cooling levels and varying degrees of cell degradation, a basic SPM simulation was then used with thermal overlays to estimate automotive cell life under various driving scenarios and various cooling levels. With these simulations, scenarios representing different thermal management regimes along with driving behavior were able to show the combined impact on automotive battery pack lifetimes.

Simulation of electrical abuse of high-power lithium-ion batteries

A numerical study is performed to analyze the temperature variation and distribution of high-power prismatic Li-ion batteries in excess duration and high-rate current abuse scenarios. With an adiabatic condition at the bottom of the cuboid battery, the highest temperature point is located at the center of the bottom surface, and the lowest is located at the cathode lead at the beginning and then moves to the corner near the cathode during the charging/discharging processes. The rising rate of battery temperature and maximum temperature difference decrease gradually with time, meanwhile the temperature difference of leads increases at first then decreases. With the same current rate, the heat generation rate and temperature difference of discharging are higher than those of the charging processes.

Thermal Performance of a Liquid Cooling System for a Li-ion Battery Pack

Battery thermal management has been a very active research field in recent years because of its great essentiality for power battery systems. In order to maintain the maximum temperature and local temperature difference in appropriate range, a newly-designed liquid cooling system for lithium-ion battery pack is proposed in this paper. CFD modeling is employed to investigate the heat transfer performance of the liquid cooling system for the lithium-ion battery pack. It shows that the total temperature rise of the whole battery pack decreases with the temperature of cooling liquid and the maximum temperature can be controlled under 40 ℃ for 192 evenly-distributed prismatic batteries.

Transient thermal analysis of a lithium-ion battery pack comparing different cooling solutions for automotive applications

This paper presents a computational modeling approach to characterize the internal temperature distribution within a Li-Ion battery pack. In the mathematical formulation both entropy-based and irreversible-based heat generation have been considered; combined with CFD software in order to simulate the temperature distribution and evolution in a battery pack.A prismatic Li-ion phosphate battery is tested under constant current discharge/charge rates of 1C, 2C, 5C and 8C. Model parameters (in particular, the entropic heat coefficient and the internal resistance) needed for the calibration of the model are determined using experimentation.The model is then used to simulate two different strategies for the thermal control of a battery pack in case of car application: an air-cooling and a liquid-cooling strategy.The simulation has highlighted the pros and cons of the two strategies, allowing a good understanding of the needs during the process of battery pack design and production.

Thermal management of a large prismatic battery pack based on reciprocating flow and active control

This paper reports the thermal management of a prismatic Li-ion battery pack consisting of a total of 18 cells based on reciprocation flow and active control. Both controlled experiments and accompanying analysis are reported to illustrate the effectiveness of reciprocating cooling flow combined with active control for regulating the cell temperature, reducing temperature non-uniformity, and minimizing parasitic power consumption. Experimentally, a platform with a 3 by 6 prismatic battery module was constructed to perform controlled tests on several competing cooling strategies, including unidirectional cooling flow, reciprocating cooling flow with constant period, and the actively controlled reciprocating cooling flow. The surface and core temperatures of the cells were monitored by the thermocouples during the tests. The major observations from these experiments were twofold. First, the reciprocating cooling flow is effective in reducing the maximum temperature rise and the temperature non-uniformity in the battery pack of practical size. Second, the active control of the reciprocating flow can further reduce both the temperature non-uniformity and the cooling power consumption with a minimal increased maximum temperature rise. Thus through the active control of reciprocating cooling flow, the battery pack can reach a more uniform temperature at the minimum parasitic energy consumption.

Compression Experiment and Simulation on Prismatic Lithium-ion Batteries

In order to understand the mechanical characteristics and failure modes of prismatic lithium-ion battery under mechanical loading conditions, flat plate compression and hemispherical punch indentation test were performed on 186570 prismatic LiFePO4 lithium-ion batteries and bare cells (cells without shell casing). Load and displacement of the cells and bare cells were measured in all tests. Additionally, temperature and voltage of the battery cells were also recorded. In flat plate compression condition, the battery shell casing cracked and electrolyte was squeezed from the cells. In hemispherical punch indentation condition, the punch displacements were stopped when a drop in force and voltage of the cell, as well as a rise in temperature indicated an internal short circuit in the cell. From the measured load-displacement data of the bare cell under flat compression condition, the individual compression stress-strain curves were calculated for the bare cells and used to develop a finite element model for the prismatic LiFePO4 battery. The bare cell is modeled as compressible foam material in LS-Dyna. This model can successfully predicted the load displacement relation of the cell under compression condition. On the other hand, this model can closely predict the force and punch displacement corresponding to the onset of short circuit in the cell under hemispherical punch indentation condition. The present tests and simulation can help to understand the deformation shape and internal short circuit mechanism of the prismatic lithium-ion cells under mechanical abuse conditions.

Preliminary Study on the Safety of a Lithium Ion Battery Pack Under Water Immersion

Most battery packs are required to comply with IP67 standard to guarantee waterproof before commercialization. However, passing the IP67 standard cannot 100% guarantee that the battery pack do not leak when immersed in fluid like dirty water or sea water during the whole life cycle, especially under some extremely conditions. It is reported that, in 2012 several Fisker Karma electric vehicles were burned after sea water intrusion caused by Hurricane Sandy. In 2016, two electric buses were burned into fire after overnight water immersion due to a heavy rain in Nanjing, China. Obviously, it can be very dangerous when water seeps through the cover of battery packs and cause electrical short circuit inside the battery. Therefore, it is critical to study on the phenomena on and the mechanism of water immersion upon battery pack. It is known that the whole battery pack is a complex system. And it is hard to monitor all the phenomena and confirm the repeatability of the experiment if the whole battery pack is thrown into water directly during investigation. Moreover, ruining a whole battery pack cost so much. For these reasons, a substitute experiment was proposed. The two special batteries/modules, which at the highest potential or lowest potential, were considered as the most probably dangerous ones in a battery pack(Figure a). The voltage of the whole battery pack was simulated by a high voltage Digatron battery charger. A single cell was connected with the charger in series. When anode of the single cell is connected to the positive electrode of the charger, it represents that the cell is in the highest potential. Meanwhile the negative electrode of charger is connected with a copper sheet to simulate a full circuit of the battery pack, as shown in Figure b1. Similarly, to simulate the single cell being in the lowest potential, cathode of the single cell was connected to the negative electrode of charger, while the positive electrode of charger was connected with an aluminum sheet as shown in Figure b2. During the experiment, only the tested battery and metal sheet were soaked in salt water with a 3.5 wt% concentration of NaCl to simulate the environment of sea water. In addition, experiments with both electrodes of the charger connected with two metal sheets(Figure b3) or two single cells(Figure b4) were also conducted for references. Pouch cells and prismatic cells were used in the study. During the experiment, we found that when a single cell was immersed into water, electric arc can be observed near the poles of the cell. The poles of prismatic cell fused near the area where the electric arc was triggered. A ball of flames appeared obviously and some other small flames can be seen floated on the water surface. After experiment, the special odor of electrolyte can be smelt above the water, indicating that the electrolyte has leaked from the shell of prismatic battery(Figure c). The cell material and separator were found intact after disassembled. The test of the pouch cell showed similar phenomena of the electric arc, however, no obvious flame appeared on the water surface. For further analysis, dummy cells with only empty shells were used. Electrolyte was injected into the empty battery shells, then similar tests as Figure b2 were conducted. The same experimental phenomena for dummy cells were observed, and the electrolyte was considered the main cause for the flame on water. In conclusion, electric arc containing enormous energy will be released due to high voltage when the battery pack is immersed under water. And the arc hazard is only caused by high voltage, with limited relationship with the cell. The electric arc with large amount of energy will make the poles or the battery shell fuse then lead to battery failure, including electrolyte leakage. The leaked electrolyte can be ignited by electric arc which is one of the most dangerous factors in battery pack water immersion. Acknowledgement: This work was supported by Project U1564205 supported by National Natural Science Foundation of China. Figure 1

Controlling the shape change and dendritic growth in Zn negative electrodes for application in Zn/Ni batteries

Abstract Porous zinc electrodes are elaborated, assembled in Zn/Ni 3–4 Ah prismatic batteries and monitored upon charge/discharge cycling (150 cycles at C/3 rate followed by 150 cycles at 1C rate). Migration of zinc within the thickness of the zinc electrodes is revealed by X-Ray radiography, scanning electron microscopy, and X-EDS elemental cartography. Electrodes using either zinc oxide plus calcium hydroxide or directly calcium zincate as active material show similar behavior: neither dendrite formation nor morphological shape changes are observed after 300 charge/discharge cycles. Upon cycling, zinc accumulates at the core of the porous electrode, in the vicinity of the primary current collector and not at the surface, therefore avoiding any risk of dendrite formation. This suggest that the electrode operation is controlled by a core-shell mechanism, with a core of active zinc in the vicinity of the primary current collector, trapped in an electrode shell which is created by the outer portion of the electrode (active material, conductive additives, binder …). However, changing from C/3 to 1C rate after 150 cycles significantly improves the capacity of batteries using calcium zincate; this is correlated to its initial atomic homogeneity associated with higher porosity and an optimal electronic percolation.

Transient electrochemical heat transfer modeling and experimental validation of a large sized LiFePO4/graphite battery

Both measurement and modeling of thermal performance in lithium-ion battery cell are considered crucial as they directly affect the safety. Even though the operation of a lithium-ion battery cell is transient phenomena in most cases, most available thermal models for lithium-ion battery cell predicts only steady-state temperature fields. This paper presents a mathematical model to predict the transient temperature distributions of a large sized 20Ah-LiFePO4 prismatic battery at different C-rates. In this regard, the lithium-ion battery is placed in a vertical position on a stand inside the lab with an ambient air cooling and the battery is discharged under constant current rate of 1C, 2C, 3C, and 4C in order to provide quantitative data regarding thermal behavior of lithium-ion batteries. Additionally, IR images are taken for the same battery cell during discharging. The present model predictions are in very good agreement with the experimental data and also with an IR imaging for temperature profiles. The present results show that the increased C-rates result in increased temperatures on the principle surface of the battery.

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

ABSTRACTIn 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.

Uneven temperature and voltage distributions due to rapid discharge rates and different boundary conditions for series-connected LiFePO4 batteries

This paper presents the surface temperature and voltage distributions on a prismatic lithium-ion battery pack at 1C, 2C, 3C, and 4C discharge rates and 5°C, 15°C, 25°C, and 35°C boundary conditions (BCs) for water cooling and ~22°C for air cooling methods. It provides quantitative data regarding thermal behaviour of lithium-ion batteries for designing thermal management systems and developing reliable thermal models. In this regard, three large LiFePO4 20Ah capacity, prismatic batteries are connected in series with four cold plates used between cells and eighteen thermocouples are placed at distributed locations on the principle surface of all three cells: the first six for the first cell, the second six for the second cell, and the third six for the third cell, and the average and peak surface temperatures as well as voltage distributions are measured and presented in this study. In addition, the simulated heat generation rate, temperature and voltage distributions are validated with an experimental data for the above mentioned C-rates and BCs. The present study shows that increasing discharge rates and BCs results in increase in the maximum and average surface temperatures at the three locations (near the anode, cathode, and mid surface of the body). The highest value of the average surface temperature is obtained for 4C and 35°C BC (36.36°C) and the lowest value is obtained for 1C and 5°C BC (7.22°C) for water cooling method.

Multivalent Zinc Ion, Nickel Ion and Magananese Ion Batteries: Recent Progress and Battery Products

Due to the energy crisis and environmental deterioration, our society seeks the safety, environmentally friendly, and low cost batteries to meet the demand of the “next generation” electric or electrical devices. The state-of-the-art batteries generally utilize univalent ions (i.e. H+ Na+ or Li+) as media for energy storage. More recently, we have firstly proposed a storage mechanism of multivalent ion (Ni2+, Zn2+, Mg2+, Ca2+, Ba2+, or La3+ ions) as a new strategy for energy storage, in which multivalent ions rather than conventional univalent ions are used as medium for energy storage. This is a new strategy providing possibility for invention of new safety and ecofriendly energy devices based on various multivalent ions instead of conventional univalent ions. Since I invented three kinds of rechargeable multivalent ion batteries, named as zinc ion, nickel ion and manganese ion batteries, the researchers around the world have paid much attentions on the multivalent ion batteries. At first, I will summarize the recent progress on these multivalent ion batteries. And the ion storage mechanism of multivalent ions (Ni2+, Zn2+, Mg2+, Ca2+, Ba2+, Sr2+ or La3+ ions) and univalent ions (Li+, Na+ or K+) in specific nanostructure materials will be discussed in detail[1,2]. Subsequently, we firstly introduce the battery produts of multivalent zinc ion batteries. The cylinder and prismatic zinc ion battery products show promising performance. They are totally eco-friendly, low cost and safety. These multivalent ion products exhibit a high energy density up to 110 Wh/Kg, cycle life up to over 500 times at 1C/1C, and fast charge/discharge ability up to 20C/20C over 2000 times. This is the first step to commercialize the multivalent zinc ion, nickel ion and manganese ion batteries. With the future improvement both on the charge storage mechanism and technology, I believe that the multivalent ion batteries are the altinatives to the unsafety lithium batteries. Reference [1] Xu, C., et al, Secondary batteries with multivalent ions for energy storage, Scientific reports, 2015, 1283: 14120; [2] Xu, C., et al, Energetic zinc ion chemistry: the rechargeable zinc ion battery. Angew. Chem. Int. Ed., 2012, 51, 933 Acknowledgements: We thank the financial surppots from NSFC, 973, and Shenzhen Technical Plan Projects.

Characterization and modeling of the thermal mechanics of lithium-ion battery cells

The thermal mechanics of Lithium-ion (Li-ion) batteries is explored with a focus on thermal swelling. Experiments show for the first time that the swelling shape of prismatic battery cells due to temperature variations is significantly different from that due to Li-ion intercalation in unconstrained conditions. In contrast to uniform and orthotropic Li-ion intercalation swelling in a direction perpendicular to electrodes, the nonuniform temperature distribution in the jellyroll and the gaps/voids between electrodes result in distinguishable different swelling shapes. A unique coupled thermal-structural analysis with a simple, but efficient 3-D finite numerical model is proposed to investigate the impact of temperature variations on the thermal behaviors of battery cells. Anisotropic heat conduction and temperature dependency of the coefficient of thermal expansion are taken into account and found to have an impact on temperature distribution and thermal expansion. Experimental validation of the proposed model clearly demonstrates that the coupled thermal-structural analysis with the proposed model can predict accurately the thermal swelling at unconstrained conditions. The solution at pack (constrained) conditions shows that the nonuniform temperature distribution of the jellyroll still plays a critical role for the thermal swelling shape, although the gaps/voids do not occur because of the constraints from spacers in the pack, suggesting that the estimation of core temperature is important. Such an accurate model, able to estimate cell thermal behavior, is beneficial to the design of Li-ion batteries, development of stress or strain sensors, optimum sensor placement, and thermal management of not only single battery cells but also battery packs.

Investigate the lithium Dynamics in Li-Rich Layered Oxide Cathode Material Via Operando Neutron Diffraction

The progressive advancements in communication and transportation has changed human daily life to a great extent. While important advancements in battery technology has come since its first demonstration, the high energy demands needed to electrify the automotive industry have not yet been met with the current technology. One possible cathode material are the Li-rich layered oxide compounds xLi2MnO3.(1-x)LiMO2 (M= Ni, Mn, Co) (0.5=<x=<1.0) that exhibit capacities over 280 mAh g-1. In this class of compounds, lithium ions can reside in both lithium layer and transition metal layer of close packed oxygen framework, typical from O3 type layered oxides like LiCoO2.1-3 Large irreversible capacities are often observed in these materials due to irreversible oxygen loss or side reactions stemming for the electrolyte. It has been also observed using ex-situ NMR that lithium reinsertion back into the transition metal layer is little to none. However, these studies have not revealed the dynamic process of lithium migration for the Li-rich material under operando electrochemical cycling conditions. In order to gain more in-depth insights about the lithium (de-)intercalation mechanisms in Li-rich layered oxides, track particularly the lithium ions in transition metal layer, operando neutron diffraction experiments were designed to quantitatively observe lithium migration in this type of oxides during the electrochemical process. In this study, we use amorphous silicon as an anode for the neutron diffraction battery design in order to avoid any overlap of signal that may be associated with the anode material. We perform operando neutron diffraction to probe lithium and oxygen for a high Li-rich (HLR), Li[Lix/3Ni(3/8-3x/8)Co(1/4-x/4)Mn(3/8+7x/24)O2 (x = 0.6) material, and low Li-rich (LLR), Li[Lix/3Ni(1/3-x/3)Co(1/3-x/3)Mn(1/3+x/3)O2 (x = 0.24) material with varying degrees of the high voltage plateau. In conjunction with the operando neutron diffraction, density functional theory (DFT) calculations were used to explore the incorporation of dilute oxygen vacancy, its affect on the lattice mechanics and oxygen positions. We also observe site-dependent lithium migration taking place during different stage of charging/discharge processes. Furthermore, this work demonstrates the potential of investigating dynamic changes of light elements in large format (10-100 times larger format than the typical operando cells for synchrotron X-ray diffraction) prismatic and cylindrical batteries under realistic cycling condition via operando neutron diffraction method. Acknowledgements UCSD’s efforts are supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231, Subcontract No. 7073923, under the Advanced Battery Materials Research (BMR) Program. The neutron experiments benefited from the SNS user facility, sponsored by the office of Basic Energy Sciences (BES), the Office of Science of the DOE. H.L. acknowledges the financial support from the China Scholarship Council under Award No. 2011631005. Y.C. acknowledge the support from U.S. DOE’s Office of Basic Energy Sciences, Material Science and Engineering Division. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. Reference 1. H. Liu, D. Qian, M. G. Verde, M. Zhang, L. Baggetto, K. An, Y. Chen, K. J. Carroll, D. Lau, M. Chi, G. M. Veith and Y. S. Meng, Acs Appl Mater Inter, 2015, 7, 19189-19200. 2. M. G. Verde, H. D. Liu, K. J. Carroll, L. Baggetto, G. M. Veith and Y. S. Meng, Acs Appl Mater Inter, 2014, 6, 18868-18877. 3. H. D. Liu, C. R. Fell, K. An, L. Cai and Y. S. Meng, J Power Sources, 2013, 240, 772-778.

Modelling Short-Circuit in Large-Format Lithium-Ion Pouch Cells

Internal short-circuit in lithium-ion batteries is a terrible abuse of the system and often leads to thermal runaway. Yet short-circuit conditions are difficult to investigate experimentally. Even the commonly used nail penetration tests hardly show reproductive results. Large-format lithium-ion pouch cells, often employed in electric vehicles, show particular catastrophic effects, due to their high energy density. Electrochemical-thermal coupled models of different scale and dimension were developed to examine various short-circuit scenarios. All are based on the work of Newman et al1,2. To facilitate convergence at high discharge currents a radial mass transport coefficient for solution diffusion is included3. Furthermore, different reduction approaches for the computation of the solid diffusion are adapted4. Simulation results for a simple high current discharge are validated with a surface temperature distribution measurement experiment. Therefore a commercially available 63Ah pouch bag cell with a nickel manganese cobalt oxide cathode is equipped with a matrix of temperature sensors attached to the top surface and discharged at 8 C. The 2D5and 3D model setup allows analyzing the spatial propagation of the short from its first occurrence until the exothermic side reactions initiate. This is particular interesting for large pouch cell or prismatic battery formats, as they show an inhomogeneous current distribution that affects the temperature development. Considering that the cell’s horizontal dimensions are large compared to its vertical dimensions, temperature and current are likely to show greater in plane gradients than cross plane gradients. Therefore it is reasonable to start with a model of a single cell layer, or electrode sandwich, consistent of the negative current collector, the anode, the separator, the cathode and the positive current collector. This reduces the computational effort and provides sufficient results for short-circuit scenarios, where all layers are affected in the same way, for example nail penetration of the complete cell. The model of the entire cell compromises 70 electrode sandwich layers. It allows a more detailed analysis of internal short circuits, like particle induced shorts. Additionally it represents more realistic thermal boundary conditions. Thus potential cooling strategies can be investigated. With models of this scale it is also possible to study the influence of the short location or the number of affected layers on the intensity of the short. All these models are very sensitive to parameter and setup changes and often lack convergence. This, to some extent, explains the poor reproducibility of experiment results. Nevertheless, numerical simulation of internal short circuit in large-format battery cells provides good insight into the mechanisms and processes during the abuse and thus helps to evaluate safer battery operation strategies and cell design options. First results of different nail penetration scenarios show that most of the heat in the beginning results from the ohmic heating in the nail. However, the nail soon turns into a heat sink and most heat is produced in the cell domain further away from the nail due to electrochemical heating. A variation of the penetration depths illustrates that an increase in the number of penetrated layers causes a faster temperature rise in the beginning, but results in a lower overall peak temperature. In any case, irrespective of the number of penetrated layers, thermal runaway is triggered. Different cooling strategies are tested on a half penetrated cell. None of them, not even strong cooling, is able to prevent thermal runaway. References M. Doyle, T. F. Fuller and J. Newman, J. Electrochem. Soc., 140, No. 6 (1993)D. Bernardi, E. Pawlikowski and J. Newman, J. Electrochem. Soc., 132, No. 1 (1985)J. Mao, W. Tiedemann and J. Newman, Journal of Power Sources, 271, 444-454 (2014)O. Iliev, A. Latz, J. Zausch, S. Zhang, Berichte des Frauenhofer ITWM, 214 (2012)N. P Volk, S. Arnold, A. Jossen, Poster SGBM 2014 (2014)

The Ionogel of N-Butyl-N-Methylpyrrolidinum Bis(trifluoromethanesulfonyl) Imide and Polyvinylidenefluoride-Co-Hexafluoropropylene for Flexible Lithium Ion Battery

Rechargeable lithium ion batteries (LIBs) have been applied in portable electronics and electricity powered transportation due to the high energy and power density. Unlike the traditional batteries packed in a cylindrical type, currently, most LIBs used in the consumer electronics (like smart phones and pads) are prismatic batteries. To meet the requirement of the electronics with particular shape such as wearable devices the flexible energy storage devices have been developed. For the safety concern, the solid electrolytes, such as polymer electrolyte, are developed to avoid leakage of liquid electrolyte. Nevertheless, the larger interfacial resistance between the solid electrolyte and electrodes and less flexibility reduced its application. Therefore, the gel-type electrolytes are favored because lithium ion is more easily to transport in gel electrolyte than solid electrolyte. Yet, as reported, certain amount of the organic solvents such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) have been usually used with polymers in the traditional gel electrolytes, causing the suspicion of solvent leakage. In this work, the solvent-free polymer-based ionogel electrolyte (IGE) composed of nonflammable and thermally stable N-butyl-N-methylpyrrolidinum bis(trifluorome­thanesulfonyl) imide (PYR14TFSI) room temperature ionic liquid and polyvinylidenefluoride-co-hexafluoropropylene (P(VdF-HFP)) are prepared by the solution casting method. The thermal and electrochemical properties are determined by the DSC and DMA measurements. The electrical properties are investigated by the linear sweep voltammetry, cyclic voltammetry and impedance spectroscopy. It is found that the as-prepared ionogel electrolytes are flexible self-standing films with wide electrochemical windows. The best conductivity obtained at room temperature is 6.0 × 10−4 S cm−1. The highest capacity of the half-cell (Li/IGE/LiFePO4) achieves 143 mA h g-1 at 0.2C rate. And even after 50 cycles, the capacity retains 135 mA h g-1at 0.2C. This study reveals that the ionogel electrolyte is a promising safe electrolyte for application in the flexible LIBs. Acknowledge: The authors gratefully acknowledge the Ministry of Science and Technology and Chung Yuan Christian University, Taiwan, R. O. C. for supporting this research work.

Operando Lithium Dynamics in the Li-Rich Layered Oxide Cathode Material Via Neutron Diffraction

The progressive advancements in communication and transportation has changed human daily life to a great extent. While important advancements in battery technology has come since its first demonstration, the high energy demands needed to electrify the automotive industry have not yet been met with the current technology. One possible cathode material are the Li-rich layered oxide compounds xLi2MnO3.(1-x)LiMO2 (M= Ni, Mn, Co) (0.5=<x=<1.0) that exhibit capacities over 280 mAh g-1. In this class of compounds, lithium ions reside in both lithium layer and transition metal layer of close packed oxygen framework, typical from O3 type layered oxides like LiCoO2.1 , 2 Large irreversible capacities are often observed in these materials due to irreversible oxygen loss or side reactions stemming for the electrolyte. It has been also observed using ex-situ NMR that lithium reinsertion back into the transition metal layer is little to none. However, these studies have not revealed the dynamic process of lithium migration for the Li-rich material under operandoelectrochemical cycling conditions. Neutron scattering has several distinct advantages for battery studies: 1) The sensitivity of neutron to light elements such as lithium and oxygen are significant in order to determine their position in the crystal structure; 2) Compares to the X-ray, the neutron shows larger scattering contrast between neighboring elements in the periodic table specifically the scattering lengths; and 3) The deep penetration capability of neutron allows simultaneous observation of the cathode and anode.3 However, challenges exist in broadening the application of operando neutron diffraction for Li-ion batteries research. First, limited by the generation reactions of neutrons, the neutron flux is usually several orders of magntitude lower than X-rays. In another words, longer acquisition times as well as larger amounts of samples are required for neutron diffraction experiments. In addition, the existence of hydrogen, which has a large incoherent neutron-scattering cross-section, is detrimental to the signal-to-noise ratio of neutron diffraction pattern. Separators (polyethylene based porous membrane) and poly carbonate based electrolyte solutions contain a considerate amount of hydrogen. These two major reasons pose significant challenges to operando neutron diffraction for lithium ion battery research although it is such a powerful technique for light elements like lithium. In order to gain more in-depth insights about the lithium (de-)intercalation mechanisms in Li-rich layered oxides, track particularly the lithium ions in transition metal layer, operando neutron diffraction experiments were designed to quantitatively observe lithium migration in this type of oxides during the electrochemical process. In this study, we use amorphous silicon as an anode for the neutron diffraction battery design in order to avoid any overlap of signal that may be associated with the anode material. We perform operando neutron diffraction to probe lithium and oxygen for a high Li-rich (HLR), Li[Lix/3Ni(3/8-3x/8)Co(1/4-x/4)Mn(3/8+7x/24)O2 (x = 0.6) material, and low Li-rich (LLR), Li[Lix/3Ni(1/3-x/3)Co(1/3-x/3)Mn(1/3+x/3)O2 (x = 0.24) material with varying degrees of the high voltage plateau. In conjunction with the operando neutron diffraction, density functional theory (DFT) calculations were used to explore the incorporation of dilute oxygen vacancy, its affect on the lattice mechanics and oxygen positions. We also observe site-dependent lithium migration taking place during different stage of charging/discharge processes. Furthermore, this work demonstrates the potential of investigating dynamic changes of light elements in large format (10-100 times larger format than the typical operando cells for synchrotron X-ray diffraction) prismatic and cylindrical batteries under realistic cycling condition via operando neutron diffraction method. Acknowledgements UCSD’s efforts are supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231, Subcontract No. 7073923, under the Advanced Battery Materials Research (BMR) Program. The neutron experiments benefited from the SNS user facility, sponsored by the office of Basic Energy Sciences (BES), the Office of Science of the DOE. H.L. acknowledges the financial support from the China Scholarship Council under Award No. 2011631005. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. Reference 1. H. Liu, D. Qian, M. G. Verde, M. Zhang, L. Baggetto, K. An, Y. Chen, K. J. Carroll, D. Lau, M. Chi, G. M. Veith and Y. S. Meng, Acs Appl Mater Inter, 2015, 7, 19189-19200. 2. M. G. Verde, H. D. Liu, K. J. Carroll, L. Baggetto, G. M. Veith and Y. S. Meng, Acs Appl Mater Inter, 2014, 6, 18868-18877. 3. H. D. Liu, C. R. Fell, K. An, L. Cai and Y. S. Meng, J Power Sources, 2013, 240, 772-778. Figure 1

Development of a Liquid Cooled Battery Module

This paper describes the development of a liquid cooling system of battery module with lithium-ion prismatic metal can battery cells that can be used in hybrid electric vehicles (HEV). Initially, a design concept of a liquid cooled battery module is selected based on the functional requirements associated with maximum battery cell temperature rise, temperature uniformity across the battery module, temperature uniformity within each individual lithium-ion prismatic battery cell, and total pressure loss of the liquid cooling system. A three-dimensional battery module thermal model and an analytical optimization approach are developed for selected design concept of the liquid cooled battery module. Finally, by performing analytical optimization study to examine the effects of geometries of the inlet duct, manifold, and the outlet duct on battery module thermal behavior and total pressure loss of cooling system, the optimal design concept of liquid-cooled battery module is identified to maximize its durability and driving range.

Thermal Management in Hybrid Power Systems Using Cylindrical and Prismatic Battery Cells

Lithium ion (Li-ion) batteries are promising as both alternative and auxiliary power sources in hybrid and electric vehicles. However, the reliable and efficient operation of the Li-ion batteries depends critically on effective thermal management, due to both the high operational thermal loads and the possible range operational conditions. This work therefore studied the issue of thermal management of battery systems under extreme hot conditions. This study combined both experimental testing and high-fidelity computer fluid dynamics (CFD). Due to the difficulty of conducting experiments under extreme conditions, controlled experiments were first conducted so that CFD models could be validated. The validated CFD models were then applied to study various aspects of thermal management issues in battery systems, with an emphasis on comparing the operation of prismatic and cylindrical batteries under extremely hot environments. The results presented include temperature distribution among cells, pump power required, and different geometrical layouts of the cells. These results are expected to provide insights into the design and optimization of battery systems.

Thermal modeling of large prismatic LiFePO4/graphite battery. Coupled thermal and heat generation models for characterization and simulation

This paper deals with the thermal modeling of a large prismatic Li-ion battery (LiFePO4/graphite). A lumped model representing the main thermal phenomena in the cell, in and outside the casing, is hereby proposed. Most of the parameters are determined analytically using physical and geometrical properties. The heat capacity, the internal and the interfacial thermal resistances between the battery and its cooling system are experimentally identified. On the other hand, the heat sources modeling is considered to be one of the most difficult task. In order to overcome this problem, a heat generation model is included. More specifically, the electrical losses are computed thanks to an electrical model which is represented by an equivalent electric circuit. A method is also proposed for parameter determination which is based on a quasi-steady state assumption. It also takes into account the battery heating during characterization which is the temperature variation due to heat generation during current pulses. This temperature variation is estimated thanks to the coupled thermal and heat generation models. The electrical parameters are determined as function of state of charge (SoC), temperature and current. Finally, the proposed coupled models are experimentally validated with a precision of 1 °C.