Probing Temperature-Dependent Solidification Dynamics of Commercial, Carbonate-Based Battery Electrolytes Using Micro-Raman Spectroscopy

Safety of lithium batteries is one of the major hurdle for their further development in all the fields of electrical energy storage, especially electric transportation. Commercial lithium batteries use as electrolytes, mixtures of at least one cyclic carbonate, the most common of which is ethylene carbonate (EC) to which various proportions of propylene carbonate (PC) can be optionally added. They are necessary to dissociate the lithium salt used as solute, as they are highly polar (ε > 60). Since such cyclic carbonates are either solid (EC) at room temperature, or highly viscous (PC), co-solvents or thinners are usually added, the most common of which are dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl-methylcarbonate (EMC). The solutes containing in the electrolyte compositions are usually selected from lithium salts with low lattice energy like LiBF4, LiCF3SO3, Li[CF3SO2)2N], LiPF6. In practice, LiPF6 is almost exclusively used because of its high conductivity and beside does not corrodes aluminum, the current collector, at potentials up to 4.5 V vs Li+:Li°.The linear components (DMC, DEC, EMC) acting mainly as a diluent of high-melting EC, are however the least stable component and have low flash points that are serious handicaps for lifetime and safety. It thus makes it a critical requisite to reconsider the choice of the electrolyte, especially trying to get rid of the alkyl carbonate, fragile to reduction (RO-, RCO2 •) [1], and with low flash points (dimethyl carbonate, DMC, Fp = 17 °C). On the other hand, poly ethers are a good alternative, Moreover ethers [2, 3] are also easily biodegradable solvents that are very stable to reduction and anodically withstand up to 3.9 V, suitable for the LiFePO4 electrode but all formerly known representatives solvates Li+ strongly enough to co-intercalate in the graphite negative electrode and exfoliate it. We have put forward a new electrolyte composition comprising a polyether to which a bulky Tert-butyl group is appended (“hindered glyme”), totally preventing co-intercalation while keeping good conductivity. This alkyl carbonate-free electrolyte shows remarkable cycle efficiency of the graphite electrode, not only at RT, but also at 50 and 70°C with lithium bis(fluorosulfonimide) salt. The two-ethylene bridge “hindered glyme” has higher boiling point and a flash point of 80°C, a considerable advantage for safety. Reference: 1. D. Aurbach, B. Markovsky, I. Weissman, E. Levi, Y. Ein-Eli, Electrochim. Acta 1999, 45(1-2), 67-86. 2. D. Aurbach, E. Granot, Electrochim. Acta 1997, 42(4), 697-718. 3. S. Tobishima, H. Morimoto, M. Aoki, Y. Saito, T. Inose, T. Fukumoto, T. Kuryu, Electrochim. Acta 2004, 49(6), 979-978. Figure 1

Performance analysis of liquid-based battery thermal management system for Electric Vehicles during discharge under drive cycles

Novel battery thermal management system for electric vehicles with a loop heat pipe and graphite sheet inserts

The typical structure of energy management system for new electric vehicle was analyzed to summarize the function. The research trend was pointed out based on the analysis of performance characteristics of energy management system for electric vehicle.

In the early stages of developing new standards, there are obstacles in formulating standard technical requirements due to a lack of information about stakeholder needs from different perspectives that may lead to formulated standards not being accepted by consensus. So it is important to know all the needs of stakeholders and seek a mutual agreement for each stakeholder. This study uses FACTS (framework for the analysis, comparison, and testing standards) in the development framework of standardization and testing requirements Battery Management System (BMS) for electric vehicles. There are three stages in the method of FACTS: analysis, comparison, and testing. FACTS approach is used to identify the needs of stakeholders on the technical requirements and provide a framework to define the testing required in the BMS. This approach provides additional information about formalism and structure, so the standards development can be applied to all stakeholders. FACTS approach is only used for the standardization process, especially in the drafting. The results of this study are the framework that can be used in the preparation of BMS standards so that BMS standards in Indonesia could be developed.

Effective thermal management of battery pack is essential for electric vehicle to adapt to different kinds of external environment, achieve desired working efficiency and life cycle of the power batteries. In this paper, a novel thermal management system is designed for battery pack in electric vehicle. Visualized simulation analysis of the thermal management system is carried on under different working conditions by CFD, then the structure parameters will be optimized. According to the conclusion, the thermal management system has been indicated to be effective to ensure an appropriate temperature range and the normal work of the power batteries in electric vehicle.

Liquid electrolytes in Li-ion batteries have been extensively developing to improve ionic conductivity, electrochemical stability, thermal stability, and safety by using various solvents, high concentration electrolytes, electrolyte additives, and lithium imide salts such as lithium bis (trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imde (LiFSI). The electrolytes extensively used in commercial Li-ion batteries are LiPF6 dissolved in some carbonate solvents such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC). Therefore, the optimal temperature range of the Li-ion batteries is a narrow range of 15℃-35 ℃ since Li-ion battery operated in the out of the comfortable temperature range will accelerate to degrade with serious risks of safety problems such a fire and explosion. The carbonate solvents occur the oxidation with CO2 gas generation on high-voltage cathodes such as LiCoO2, LiNi1-x-yCoxMnyO2, and LiNi0.5Mn1.5O4 under high-temperature conditions.In this work, we investigated the electrochemical and physicochemical properties of LiFSI/GBL-based electrolytes and effects of additives into the electrolytes on application to Li-ion batteries using LiNi0.8Co0.1Mn0.1O2 (NCM) cathode and TiNb2O7 (TNO) anode [1]. GBL has attractive properties of a low melting point of -43.6℃, a high boiling point of 204℃, and a high flash point of 98℃. However, Li-salt used for GBL-based electrolytes was not LiPF6 but LiBF4 [2] because LiBF4 is significantly chemical stable in GBL solvent. LiPF6 decomposes GBL, which is caused by HF generation from decomposition of LiPF6. Therefore, we have focused on LiFSI with chemical stability and high conductivity for the GBL-based electrolytes. Furthermore, we investigated the cosolvents for the GBL-based electrolyte for a decrease in the viscosity. Propyl propionate (PP) was used as the cosolvent because it has advantageous properties of only a low viscosity but also a very low melting point of -76℃ and a high boiling point of 122℃ compared to DMC and MEC. This paper reports on ionic conductivity, viscosity, self-diffusion coefficient (D Li) of Li+ ion of LiFSI/GBL-based electrolytes, and the performance of fabricated TNO/NCM pouch cells using the LiFSI/GBL/PP electrolytes with additives.Fig.1(a) and (b) show ionic conductivity of GBL electrolytes and other solvent electrolytes dependent on Li-salt concentration. The conductivity of LiFSI/GBL electrolyte was higher than that of LiTFSI/GBL and LiBF4/GBL electrolyte in all the concentration. A low-concentration LiFSI/GBL (1:10 by mol) electrolyte at a LiFSI molar fraction (XLiFSI) of 0.091exhibited the highest conductivity of 12.3 mS cm-1 at 25℃ compared to LiBF4/GBL, LiTFSI/GBL, and LiFSI-based electrolytes with other solvents of PC, DMC, DEC, and PP. Electrochemical stability of TNO and NCM electrode in the low-concentration LiFSI/GBL at XLiFSI=0.111 electrolyte was investigated by AC-impedance and liner sweep voltammetry (LSV) measurement. Impedance spectra as shown in Fig.2 indicated that a large interface resistance of the TNO electrode in the GBL electrolyte was significantly decreased by adding 2wt% fluoroethylene carbonate (FEC). The anodic dissolution of Al current collector for the NCM cathode in the electrolyte by LSV measurement was effectively suppressed by adding 2wt% lithium difluoro(oxalate)borate (LiDFOB), which overcame the strong corrosion of Al. Adding PP cosolvent into the LiFSI/GBL electrolyte decreased the viscosity and increased D Li in the electrolyte. We fabricated TNO/NCM pouch cells (70 ×100 ×1.2 mm) using LiFSI/GBL/PP and LiFSI/other solvent electrolytes at XLiFSI=0.111 with the additives. Charge-discharge cycling tests were conducted between 1.5 V and 3.0 V. The nominal capacity and voltage at 0.2 C were 900 mAh and 2.25 V, respectively. Fig.3 shows charge-discharge rate cycle performance at -20℃ of the cells with various electrolytes. Low-temperature rate capability of the cells using the LiFSI/GBL/PP electrolytes was superior to that using the DMC, PP, GBL, and PC electrolyte. It was demonstrated that the cells using the LiFSI/GBL/PP (1:2:6) electrolyte maintained high capacity with less gas generation by charge-discharge cycle tests between -20℃ and 45℃ compared to the cell using the LiFSI/DMC electrolyte. Fig.4 shows the amount and composition of each gas generated from the cells after 400 cycles at 45℃. The amount of CO2 generated from the LiFSI/GBL/PP electrolyte was 1/10th smaller than that from the DMC electrolyte, indicating that the LiFSI/GBL/PP electrolyte is electrochemical stable under a high-potential condition of the charged NCM cathode. We propose that low-concentration LiFSI/GBL/PP electrolytes with the additives of FEC and LiDFOB are promising electrolytes with high-rate, low-temperature performance, and good electrochemical stability with less gassing for wide temperature operation in Li-ion batteries.

<title>ABSTRACT</title> <p>Lithium-ion (Li-ion) batteries are increasingly targeted for electrical energy storage due to their exceptional energy and power density. However, Li-ion batteries operating in the hostile military environments are prone to catastrophic thermally induced failures or reduced lifetime if not maintained within narrow operating windows. There is great interest in advanced thermal management to optimize battery pack performance and enhance safety. In this numerical study, we examine the performance and safety benefits afforded by thermal management systems with effective thermal conductivities beyond the limits of traditional conductive cooling. Thermal runaway simulations based on NREL’s multi-scale multi-domain (MSMD) model illuminate how advanced thermal management can improve power density, while mitigating thermal runaway and cell fratricide potential. More efficient cooling increases the margin of safety, allowing end users to extend the pack operating envelope over an interrelated three parameter space encompassing the maximum permissible discharge rate, ambient operating temperature, and/or thermal runaway pack protection thresholds. Enhanced battery cooling will make Li-ion batteries safer for next generation military vehicles.</p>

<div class="section abstract"><div class="htmlview paragraph">In the era of Software Defined Vehicles, the complexity and requirements of automotive systems have increased knowingly. EV Thermal management systems have become more complicated while having multiple functions and control strategies within software frameworks. This shift creates new challenges like increased development efforts and long lead time in creating an efficient thermal management system for Electric Vehicles (EV’s) due to battery charging and discharging cycles. For solving these challenges in the early stages of development makes it even more challenging due to the unavailability of key components such as fully developed ECU hardware, High voltage battery pack and the motor.</div><div class="htmlview paragraph">To address this, a novel framework has been designed that combines virtual simulation with physical emulation at the same time, enabling the testing and validation of thermal control strategies without fully matured system and the ECU hardware. The framework uses the Speedgoat QNX machine as the central controller which hosts the control logics and electro-thermal models developed in Simulink and Simscape. Speedgoat is physically connected to a non-functional vehicle equipped with key thermal components such as a radiator cooling fan, AC compressor, HVAC blower, active grille shutters (AGS), valves etc. The heat load for different conditions is emulated using heater carts and vehicle itself. The entire system is designed to be mobile, allowing it to be placed inside a climatic chamber.</div><div class="htmlview paragraph">By controlling all the components through Speedgoat and offering an interactive calibration interface for real time calibration, this framework bridges the gap between simulation and physical testing. It helps in accelerating controls development, optimizes thermal control strategies, ensures energy efficiency, reliability, and cost effectiveness in system design.</div></div>

A refrigerant-injection heat pump-based efficient integrated thermal management system for electric vehicles approaching the wide temperature range in China

Design and simulation of a lithium-ion battery with a phase change material thermal management system for an electric scooter

Lithium-ion batteries (LIBs) have found widespread application in energy storage due to their high energy density, low self-discharge and low maintenance characteristics. However, the stability and longevity of the batteries under extreme operating conditions is yet to be fully understood. Numerous experimental and simulation studies have been performed to elucidate the effect of temperature, current, depth of discharge, and the number of cycles [1,2,3] on the performance of LIBs. These studies show that the solid-electrolyte interface (SEI) layer and gas formation accelerate at high C-rates due to increased electrolyte decomposition [4,5]. Consequently, the cell's internal resistance increases, resulting in ever-increasing irreversible heat generation inside the cell [6]. This heat generation leads to high internal temperature and a corresponding reduction in cell capacity. The data of cell temperature for a wide range of ambient temperatures and cycling rates is limited because cell performance is typically reported at room temperature. The design of battery packs for electric vehicles(EVs) is also based on test data taken at room conditions. Given that the cell's capacity, specific energy, maximum power output is bound to depend on C-rate and ambient temperature, it is necessary to test and design battery packs based on these parameters.The thermal characteristics of a lithium-ion cell can be predicted using a physics-based thermal model or data-driven methods (DDM) relying on empirical data. Experimental determination of internal cell parameters required in physics-based thermal models is challenging and time-consuming for commercial cells. On the other hand, DDM requires only cell cycling data at specific operating conditions, thereby eliminating the need for internal parameter estimation. This model predicts the experimental input and output data pattern and fits the response surface to estimate the unknown output. In this study, surrogate modelling has been employed to estimate the surface temperature, capacity, energy, and average power of commercial lithium-ion cells for different discharge currents and ambient temperatures. Surrogate modelling, a popular data analysis and reduced-order modelling technique, aims to find a global minimum of a particular objective function using a few objective function evaluations [7]. The surrogate-based model divides experimental data into training and test data sets. The training data set is employed to train the algorithm. After that, the testing data set is used to validate the model's accuracy. Experiments were performed to develop a surrogate model, with the number of experiments decided using the design of experiments[8] for a current range of 0.5C to 3C-rate and ambient temperature range of 0°C to 45°C . The cycling of cells was performed using a high current battery cycler (Arbin), and the ambient temperature was maintained using a thermal chamber (Cincinnati). The surface temperature of commercial 18650 (NMC811) lithium-ion cells was recorded using T-type thermocouples and a National Instruments DAQ module. A polynomial response surface was fitted using surrogate modelling on experimentally obtained data. The response surface shown in figure 1. contains nine data points for the preliminary study, sub-divided into a set of seven training and two testing data. The prediction error sum of squares (PRESS) is currently bounded within 10% due to the limited training data set availability and is expected to be within a band of 1% after adding data from ongoing experiments. The estimation of temperature, capacity, and specific energy can be used to optimize and develop an improved thermal management system for electric vehicles that works under various operating conditions. References Waldmann, T., Wilka, M., Kasper, M., Fleischhammer, M., & Wohlfahrt-Mehrens, M. (2014). Journal of Power Sources, 262, 129-135.Guan, T., Sun, S., Yu, F., Gao, Y., Fan, P., Zuo, P., Du,C., & Yin, G. (2018). Electrochimica Acta, 279, 204-212.Simolka, M., Heger, J. F., Traub, N., Kaess, H., & Friedrich, K. A. (2020). Journal of The Electrochemical Society, 167(11), 110502.Xu, B., Diao, W., Wen, G., Choe, S. Y., Kim, J., & Pecht, M. (2021). Journal of Power Sources, 510, 230390.Rashid, M., & Gupta, A. (2017). Electrochimica Acta, 231, 171-184.Leng, F., Tan, C. M., & Pecht, M. (2015). Scientific reports, 5(1), 1-12.Queipo, N. V., Haftka, R. T., Shyy, W., Goel, T., Vaidyanathan, R., & Tucker, P. K. (2005). Progress in aerospace sciences, 41(1), 1-28.Li, W., Xiao, M., Peng, X., Garg, A., & Gao, L. (2019). Applied Thermal Engineering, 147, 90-100. Figure 1

Multi-objective design optimization of battery thermal management system for electric vehicles

Apart from increasing the battery size of electric vehicles (EVs), another approach to reduce range anxiety and to achieve mass market penetration is to increase the charging power and thus significantly lower charging times. To date, commercial lithium-ion battery (LIB) cells are almost exclusively based on graphite as anode material.[1] Here, owing to the low potential of the graphite electrode during charge, the charging rate must be limited in order to avoid lithium plating, which can thermodynamically occur in regions of the electrode where the potential drops below 0 V vs. Li+/Li. Plated lithium is very reactive, leading to irreversible reactions with the electrolyte and therefore strongly reduces lifetime and safety of a battery.[2] Studying lithium plating in a battery cell is very challenging since post-mortem diagnostics do not reflect the electrode state during operation, since plated lithium will reintercalate into the active graphite material on a timescale of minutes at room temperature.[3] , [4] Hence, non-destructive operando techniques[5] , [6] are necessary to elucidate and follow lithium plating mechanisms in an operating cell.In this study, we present data collected via Neutron Depth Profiling (NDP) during lithium plating induced by fast charging of a graphite electrode at a rate of 2 C. NDP is a lithium-sensitive, non-destructive technique utilizing the neutron capture reaction of 6Li atoms to quantitatively measure the lithium distribution over the thickness of an electrode by probing the energy loss of charged particles formed by the neutron capture reaction.[7] We employ a recently developed operando NDP cell that shows a cycling performance comparable to a commercial cell even at high charging rates, and at the same time allows charged particles to exit the cell through a thin Kapton® window.[8] We were able to resolve the lithium depth distribution changes during the open circuit voltage (OCV) phase after a constant current charge with a time resolution of 2 min. This exceptionally high time resolution was achieved by combining the high cold neutron flux of 2.7×109 ncm-2s-1 at the NIST Center for Neutron Research (Washington D.C., USA) with a 6Li enriched electrolyte and a 6LiFePO4 cathode, which enhances the signal by an additional factor of 12. In order to achieve lithium plating already at a rate of 2 C, the LiPF6 salt concentration in the EC/EMC = 3/7 (w/w) electrolyte was reduced to 0.3 M.Figure 1 shows the NDP signal intensity as a function of the energy of the detected tritium particles, which translates into a depth profile: signals at an energy of ≈2400 keV represent lithium at the interface between the graphite electrode and the Cu current collector, and signals at decreasing energies represent lithium from increasing depth into the graphite electrode, with signals at an energy of ≈800 keV deriving from the graphite anode / separator interface. It is clearly visible that lithium plating starts towards the separator facing side of the graphite anode, caused by the lithium-ion concentration gradient forming over the thickness of the electrode during fast charging (dark blue profile); during the subsequent OCV phase, lithium re-distributes over the anode thickness, whereby this equilibration process is observed to be completed within ≈24 min.[1] C. Pillot, “The Rechargeable Battery Market and Main Trends 2014-2025”, 32nd International Battery Seminar and Exhibit, 3/9/2015, Presentation.[2] J. C. Burns, D. A. Stevens, J. R. Dahn, J. Electrochem. Soc. 2015, 162, A959.[3] Z. Y. Tang, J. J. Xue, C. Y. Liu, X. G. Zhuang, Acta Phys. - Chim. Sin. 2001, 17, 388.[4] M. Park, X. Zhang, M. Chung, G. B. Less, A. M. Sastry, J. Power Sources 2010, 195, 7904.[5] J. Wandt, P. Jakes, J. Granwehr, R. A. Eichel, H. A. Gasteiger, Mater. Today 2018, 21, 231.[6] R. Bhattacharyya, B. Key, H. Chen, A. S. Best, A. F. Hollenkamp, C. P. Grey, Nat. Mater. 2010, 9, 504.[7] M. Trunk, M. Wetjen, L. Werner, R. Gernhäuser, B. Märkisch, Z. Révay, H. A. Gasteiger, R. Gilles, Mater. Charact. 2018, 146, 127.[8] F. Linsenmann et al., A Lithium-Ion Battery Cell Design for Operando Neutron Depth Profiling, to be submitted. Figure 1

Introduction. Lithium-ion batteries (LiB) have been widely used as power sources in many electric/electronic products such as cellular phones, digital cameras, portable computers, etc. Currently, most commercial lithium-ion batteries utilize carbon-based materials as anodic active substance and Cu foils as electric collectors. However, technologies related to LiB have been sophisticated to be close to the theoretical capacitance of carbon-based materials (LiC6: 372 mAh g-1). Considering on the applications in automobile industry for electric vehicles (EVs), it is highly desirable to explore some new anode materials with higher powder density and satisfied lifetime cycles to meet expanding needs for lithium-ion battery industry. To obtain higher gravimetric and volumetric capacity, Sn-based materials have attracted much interest as replacements for the conventional carbonaceous anode materials of Li-ion batteries, because the Sn materials has higher theoretical capacitance (Li4.4Sn: 994 mAh g-1) than that of graphite mentioned above. Pure Sn metal, however, exhibits poor cyclic lifetime due to its mechanical scalability from volume expansion and contraction of the pure Sn metal during lithium insertion and extraction processes. During the charge-discharge cycles, this mechanical scalability will crack and deteriorate the electrode, significantly affecting the mechanical stability and cyclic lifetime of the battery. In this study, we will report porous Sn-TiO2composite films fabricated on Cu sheets, to provide space for the volume change of Sn in the charge-discharge actions as anode materials for Li-ion batteries. Experimental. Various nanoporous Sn-TiO2 composite films were coated on Cu sheets by a hybrid electroplating, i.e., combining electro-deposition with electrophoric deposition, using an EtOH-H2O mixed bath mainly containing SnCl2 and TiCl3.The effects of ratios of Sn2+/Ti3+ and EtOH/H2O, current density, and operating temperature on the formation and electrochemical behaviors of the films were investigated. Moreover, in order to remove water absorbed in the films and improve the adhesion between the films and Cu substrates, the Sn-SnO2-TiO2anodes were heated at 423 – 473 K for 2 – 4 h in air. The morphology, chemical composition, chemical state, and crystalline structure of the electrodeposited films before and after heat treatment were investigated by a field emission scanning electron microscopy (FE-SEM) attached with an energy dispersive X-ray (EDX) analyzer, transmission electron microscopy (TEM) with x-ray energy-dispersive analysis (EDS), and x-ray diffractometer (XRD), and x-ray photoelectron spectroscopy (XPS). Electrochemical charge-discharge performances of the Sn2-TiO2 films electrodeposited on Cu sheets as binder-free anodes were investigated using home-made pouch cells assembled in an Ar-filled glove box. The cathode was utilized with a lithium metal foil, and the electrolyte solution was made of 1M LiPF6 in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) with a volumetric ratio of 1:1:1, respectively. The cells were charged and discharged at 0.1 A g-1 by a battery test system, and the cut-off voltage range was 0.01 – 2.0 V (vs. Li/Li+) at 303 K. Results and Discussion. Figs. 1a-1c show the representative FESEM images of as-deposited porous Sn-TiO2 films on Cu sheets, which were fabricated in plating baths with different ethanol/water ratios. It can be seen that the films composed of nano-flakes or nano-needles, thus making a networked nanoporous structure. The morphologies of the electrodeposited films were depended predominantly on ratios of Sn2+/Ti3+ and EtOH/H2O in electroplating baths, as well as the current density and operating temperatures. After heat treatment at 473 K for 2h (Fig.1d), the Sn nano-crystals grew into nano-sheets with micrometer sizes in across while remaining the nanoporous structure. Moreover, according to EDX and XPS analysis, the electrodeposited films consisted of Sn, SnO2, and a small amount of TiO2in 1–6 at%, irrespective of heat treatment. XRD measurement confirmed that the Sn is polycrystalline with a preferential in Sn (200) facet, which is different from the conventional Sn electrodeposits from a sulfuric-based bath that has a preferential Sn (220) facet. Furthermore, it is found that the Sn-SnO2-TiO2 composite films after heating exhibited good performance in charge-discharge Furthermore, it is found that the Sn-SnO2-TiO2 composite films exhibited a high initial discharge capacity of 1069 mAh g-1 and good cycle-life stability in charge-discharge evaluation, indicating a promising future as binder-free anode material for Li-ion batteries.