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PAN/PVDF nanofiber membranes with core–shell structures were fabricated by electrospinning to improve mechanical and electrochemical properties. [Display omitted] • With the excellent mechanical properties of PAN, the mechanical strength of PAN/PVDF nanofiber separator is increased by 6 times compared with pure PVDF separator; • The PAN/PVDF nanofiber separator takes into account the high electrolyte absorption capacity of PAN and the characteristics of PVDF to promote lithium ion transport, which significantly improves the ionic conductivity, reduces the activation energy during the lithium ion transport process, and improves the battery in high-power charge and discharge performance; • The PAN/PVDF nanofiber separator promotes the uniform transport of lithium ions, thereby inhibiting the formation of lithium dendrites; The ion transport channel constructed by the separator is crucial for the practical performance of Li-ion batteries, including cycling stability and high rate capability under high current. Traditional polyolefin separator is the storage of electrolyte, which guarantees the internal ion transport process. However, its weak interaction with electrolyte and low cationic transport capacity limit the application of lithium ion battery in large current. In this study, a kind of core–shell structured polyacrylonitrile (PAN)/polyvinylidene fluoride (PVDF) nanofiber separator composed of PAN core and PVDF shell was prepared by coaxial electrospinning technique. As a result, the mechanical strength of PAN/PVDF nanofiber separator is increased from 0.6 MPa of PVDF to 3.6 MPa for PAN core. Furthermore, PAN/PVDF nanofiber separator exhibits an improved lithium-ion transference number (0.66), which is resulted from F functional groups of PVDF shell. It is believed that the interactions between the lithium ion and F functional group could construct a fast ion transport channel. The LiCoO 2 /Li half-cells assembled with PAN/PVDF exhibited higher discharge capacity (5C) than those cells using pristine PVDF, PAN separators and polyethylene (PE) separator. It is worth mentioning that the cells with PAN/PVDF separator also have excellent cycle stability. This study provides a new idea about separator-design strategy for high-performance lithium-based battery. [ABSTRACT FROM AUTHOR]

Owing to these phenomena about intercalation and deintercalation lithium-ion, thermal expansion, and external pressure in lithium-ion batteries, the interior separators are often subjected to compression stress. In this study, we have designed a novel model based on the Thiessen Polygon, which is used to describe 3D porous structure of polyethylene (PE) separator. It can simulate the structure evolution of separator during compression. The simulation results show that when the compression stress is up to 60 MPa, the thickness of the separator decreases by nearly 50%, and the porosity decreases from 42.6% to 10%, which severely affects the ionic transmission performance. Additionally, the separator with changed porosity structure under different compression conditions was applied to the electrochemistry-thermal model to simulate the discharge process of the battery. As results, it is found that the discharge capacity is significantly reduced and the temperature is increased due to the structural variation of the separator caused by compression stress. This study develops a novel mechanical model which can be used in the simulation of separator compression process, and involves the simulation of multiple physical fields. And it successfully correlates the mechanical properties of separator with its battery performance. • A novel mechanical model of the PE separator has been developed. • The structure evolution of separator during compression has been simulated. • Compressed separator causes degradation of the battery performance. [ABSTRACT FROM AUTHOR]

In order to solve the shortcomings of the current traditional commercial polyolefin microporous membranes with worse thermostability at high temperature, polyimide (PI) nanofiber membranes prepared by electrospinning are promising separators for lithium ion batteries that operate at high temperatures. This preparation includes the forming process of poly(amic acid) (PAA) fibers membrane and thermal-imidization process. In this study, we design the experiment of thermal-imidization for PAA fibers to improve the mechanical strength and the electrochemical performance of the obtained PI nanofiber membrane. It is found that the degradation phenomenon and the crosslinking function occur after the imidization during the heat treatment. The mechanical strength of PI nanofiber membrane gets improved with new crosslinking system after being heat-treated at 350 °C. LiCoO2/Li cells based on such PI nanofiber membranes exhibit excellent cycle performance (300 cycles) and rate performance (even at high rates of 6 C), better than those employing polyolefin microporous membranes. During the heat treatment of polyamic acid, a thermal imidization process will occur. At the same time, different heat treatment temperatures will lead to differences in the degree of imidization and the structure of the fiber membrane material. It is important to understand the thermal imidization process. The effect of thermal imidization temperature on the performance of the electrospun polyimide lithium ion battery separator is studied. The experimental results show that although the degree of imidization is decreased by the heat treatment at 350 °C, it has better cycle performance (300 circles) and rate performance (even at high rates of 6 C). [ABSTRACT FROM AUTHOR]

It is seen from this figure that the maximum temperature rise of the cell module decreases as the increasing rate of fluid flow. The maximum temperature rise of the cell module is under 40 °C and 36 °C respectively since the flow rate is 0.40 × 10−3 L·s−1 and 1.20 × 10−3 L·s−1, indicating that increasing flow rate increases the cooling capability of the LCP. • A new cooling plate is developed for controlling undesirable cell temperature field. • Inlet and outlet of cooling plate have big impact on cell temperature distribution. • Increasing flow rate decreases cell temperature rise markedly. • Cooling plate channel width has weak impact on cell temperature distribution. • Channel width has great effect on ratio of power consumption of cooling plate. The thermal management for a lithium ion battery cell plays a pivotal role in enhancing the cell performance and reliability for electric vehicles. In this work, a novel serpentine-channel liquid cooling plate with double inlets and outlets is developed for better managing an undesirable temperature distribution of a cell module. With a simplified model for the cell module, numerical analyses are implemented using the software of FloEFD to study effects of flow directions, flow rates and channel widths of the cooling plate on cell temperature distribution under different operating conditions; Likewise, a ratio of power consumption as a non-dimensional number is defined to analyze the hydraulic performance of the developed cooling plate. Results show that locations of the inlet and the outlet as well as flow directions have great impacts on the cell temperature distribution and the ratio of power consumption of the cooling plate. Increasing fluid flow rate substantially decreases the maximum temperature rise of the cell module while it has little effect on the temperature distribution. Moreover, the channel width of the cooling plate has a strong influence on its ratio of power consumption as well as the cell temperature distribution but it has a weak influence on the cell maximum temperature rise. Interestingly, the developed serpentine-channel cooling plate offers one a new method to design a lithium ion battery thermal management system for controlling temperature distribution of a cell module. [ABSTRACT FROM AUTHOR]

It is seen from these two figures that the battery temperature and SOC have a minor effect on its thermal conductivity. Battery thermal conductivity vary with the battery types heavily. • A novel method for determining thermal parameters of lithium ion cells is presented. • Temperature has a linear effect on thermal conductivity and specific heat of cells. • Cell temperature has a higher effect on its specific heat than thermal conductivity. • Cells' thermal conductivity and specific heat vary with the battery types. • The method is more effective to test thermal conductivity and specific heat of cells. Characterizing thermal parameters of a lithium ion battery is a key step to predict the temperature distribution of battery cell modules. In this work, a novel method is developed based on the quasi-steady state heat transfer analysis to determine the thermal conductivity and the specific heat simultaneously. Both prismatic lithium iron phosphate cells and pouch cells with different electrode materials are used in this experimental test. A constant heat flux is applied to the cell surface whereas the heat loss is estimated based upon the temperature drop curve. As such, the quasi-steady state heat transfer can be attained to determine cell thermal parameters. It is observed that cell thermal parameters increase linearly with the increase of the operating temperature. Furthermore, the operating temperature has a more significant influence on the cell specific heat than the thermal conductivity, while the effect of the state of charge has a minimal effect on these two parameters. The current method demonstrates an effective and practical way to determine the thermal conductivity and specific heat of the cell simultaneously. [ABSTRACT FROM AUTHOR]

Graphical abstract It is found that the average heat generation rate of the lithium-ion battery cell has a quadratic relationship with the operating temperatures and operating currents. Tested results of the heat generation rate show a good agreement with results calculated as per widely used Bernardi's heat generation model. Highlights • Reveals a method for testing specific heat and heat generation of a Lithium ion cell. • Increasing temperature linearly increases the specific heat of Lithium ion cell. • Heat generation of Lithium ion cell quadratically increases with increasing current. • Tested results of heat generation via new method and Bernardi model are consistent. Abstract The specific heat and the heat generation rate are the key thermal properties for lithium ion battery cells. Nonetheless, there exists large scattering in data of thermal properties due to factors such as battery temperature nonuniformity during experimental measurement. In this work, a novel calorimetric method for measuring thermal properties of a lithium ion battery cell is proposed by introducing a temperature even out process to minimize the effect of the temperature difference across the battery. Through this method, the specific heat and the heat generation rate can be characterized for the electrochemical batteries. Thermal parameters of a prismatic lithium iron phosphate battery cell are determined for the wide temperature range at varying operating currents. It is found that the specific heat of the lithium ion battery cell has a linear relationship with the operating temperature, whereas the heat generation rate has a quadratic relationship with the operating current. The measured heat generation rate shows a good agreement with calculated results as per Bernardi's heat generation model. This new method allows one to obtain thermal properties of lithium ion battery cells at a lower cost and in a shorter time. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flower-like calcium phosphate coating is successfully formed on the surface of modified PE separator. • The obtained composite separator exhibits stronger affinity to electrolyte and absorbs more liquid electrolyte. • CaP@PE separator possess an improved ionic conductivity (0.52 mS cm−1) and lithium-ion transference number (0.36). • Cell assembled with CaP@PE separator exhibits excellent cycle performance and rate performance. The organic–inorganic composite separator possesses great thermal stability and electrolyte wettability, which is normally prepared via the slurry containing binder. However, this preparation is involved with large amounts of organic solvent that is harmful to health. In this paper, we design a novel method that combines the crosslinking technology and biomimetic mineralization process to prepare a Ca 3 (PO 4) 2 inorganic coating modified polyethylene separator (CaP@PE). The obtained composite separator exhibits stronger affinity to electrolyte, and its porous coating structure can store more liquid electrolyte, thus the ionic conductivity is promoted from 0.27 mS cm−1 to 0.52 mS cm−1 and the lithium-ion transference number is increased from 0.26 to 0.36. Compared with PE separator, CaP@PE separator shows better thermal stability at high temperature. Due to the improved ionic transport performance and reduced charge transfer impedance, LiCoO 2 /Li half-cell employing CaP@PE separator displays superior cycle stability and capacity retention ability after 150 cycles at a current density of 1C. Even at a high rate of 5C (7.5 mA cm−2), the cell with CaP@PE separator still exhibits a discharge capacity of 0.80 mAh. This work provides a promising separator to optimize the electrochemical performance and safety performance in lithium-ion battery. [ABSTRACT FROM AUTHOR]

Thermal characteristics of lithium-ion battery cells are crucial in the thermal design of power battery packs for electric vehicles. In this paper, a calibration calorimetry method of considering the heat loss is proposed to investigate the thermal characteristics of a commercial cylindrical 21700 cell. In the meantime, an existing heat-flux meter method is employed to analyze the present method effectiveness. Furthermore, a cell thermal model by considering the physical specifications and thermal parameters is established to predict the cell's temperature rise during its operation. It is shown that the proposed calibration calorimetry method matches well with the existing heat-flux meter method in determining the cell heat generation rate. The cell heat generation rate increases as the decreasing temperature and the increasing discharge rate, and there exists a quadratic-relationship in them between each other. The established thermal model to predict the cell temperature rise is effective with accuracy of within 3.0 °C. This work is fast and cost-effective in characterizing the thermal characteristics of the commercial cylindrical cells, without resorting to the specialized instruments. • A calibration calorimetry method to analyze cell thermal characteristics is proposed. • The present method is compared with the heat flux meter method. • Cell heat generation is increased at ascending discharge rate and lower temperature. • The established thermal model predicts cell temperature profile is highly feasible. [ABSTRACT FROM AUTHOR]

• Develops a lightweight liquid cooling solution to cool a prismatic hard cased cell. • Effect of fluid flowing on cell thermal distribution is studied numerically. • Dimensionless analysis of cooling performance in cooling plate is performed. • Effectiveness of the lightweight solution was authenticated by an experimental test. The lightweight thermal design is a critical factor that must be taken into consideration during the lithium-ion battery pack manufacturing for electric vehicles. This work develops a lightweight liquid cooling solution to cool a prismatic hard-cased cell from its small lateral surfaces. The effects of fluid flow directions, flow rates, channel dimensions, and cooling mediums on the cell′s thermal distribution were studied. Meanwhile, a dimensionless analysis for the cooling plate performance was imposed. The simulation effectiveness was corroborated through experiments. Simulations show that the lightweight thermal design has a similar cooling effect with the conventional thermal design; crucially, the former can lower the cooling plate weight by 57% compared with the later. Effect of increasing fluid flow rate on minimizing the cell′s temperature rise and difference is positive and negative, respectively. Increasing fluid flow rate and channel width can promote the cooling plate performance. The glycol aqueous solution outperforms the liquid water to weaken the cell′s temperature difference. Experiments authenticating that an excellent effectiveness residing in the current lightweight thermal design to control the cell thermal profile within a desirable level. This work would be valuable for one to design a lightweight cooling system for a battery pack consists of prismatic hard-cased cells. [ABSTRACT FROM AUTHOR]

Purposing to the thermal profile management of typical format 21700 lithium-ion battery cells, this study develops a cellular liquid cooling jacket to meet their requirements. To this end, the effects of fluid flowing, channel dimension, and cooling medium on the cell thermal profile were investigated numerically, and then the simulation effectiveness was authenticated experimentally as per a constructed test bench. Meanwhile, a non-dimensional analysis for the optimum design of cellular cooling jacket was implemented. The results show that the interlaced flow directions can capture a lower temperature standard deviation and a more even thermal distribution. The non-dimensional analysis reveals that the increasing fluid flow rate and channel size can effectively promote the performance of high-efficiency and low-impedance in the designed cellular cooling plate. The glycol aqueous solution to minimize cell's temperature difference and temperature standard deviation is under a stronger capability than that of the liquid water. Experimental verification indicates that the developed cellular cooling jacket is of great control effectiveness to the thermal profile of the cylindrical 21700 cells. A benefit inside this study for the thermal management system designing for the power battery pack of composing with the cylindrical 21700 cells. • A cellular cooling jacket is developed to control thermal profile of a 21700 cell. • Impact of fluid flowing on 21700 cell thermal profiles is studied numerically. • Dimensionless analysis of the cellular cooling jacket performance is conducted. • The effectiveness of battery pack thermal design is verified by a built test bench. • The thermal design is of great effectiveness to control 21700 cell thermal field. [ABSTRACT FROM AUTHOR]

The thermophysical parameters such as thermal conductivity and specific heat play a vital part in the thermal design of the power battery pack composed of cylindrical lithium ion battery cells. This work proposes a quasi steady state method with considering heat loss to measure the thermophysical parameters of two classes of 21700 and 18650 cylindrical cells, respectively. To this end, the theoretical model and the corresponding measurement method were developed in consideration of the heat loss, and the two cells' thermophysical parameters were experimentally determined over a wide operating temperature range of −20–60 °C. The results show that both of the thermal conductivity and the specific heat of the cells increase linearly with the increase of the operating temperature. In comparison, the cell temperature has a greater influence on the specific heat than that of the thermal conductivity. The experimental verification reveals that the measurement error is behind 5.1%. Having a short measurement time within 930s, the present work provides a fast and convenient solution on determining the thermophysical parameters of the cylindrical cells without resorting to the costly instruments. • Proposes a quasi steady state method to measure cylindrical cell thermal parameters. • Cost-effectiveness and fast in current method to derive the cell thermal parameters. • Cell thermal parameters linearly increase as increasing temperature of −20–60 °C. • Experimental verification reveals that the current method is highly feasible. [ABSTRACT FROM AUTHOR]

Thermally induced phase separation (TIPS) is used to prepare polyethylene (PE) micro-porous membrane, consisting of melt blending, fast cooling, stretching and extracting process, which determine the pore-structure of the PE membrane. In this study, we tried to extract PE/liquid paraffin (LP) oil membrane to obtain PE porous membrane by n-hexane (n-PE) and dichloromethane (d-PE). The n-PE membrane would shrink by 10% for extractant volatilizing, less than 15% of the d-PE membrane after the extraction. These PE membranes were applied into symmetrical cells and LiCoO 2 /Li cells. As a result, the LiCoO 2 /Li cell based on n-PE separator exhibited better capacity retention (98%) than d-PE separator (91%) after 80 cycles at a current density of 1C rate for higher ionic conductivity. And the LiCoO 2 /Li cell with d-PE separator had higher capacity at 2C and 3C, it could be attributed to stronger interaction between solvent and wall of d-PE separator with the smaller and curved pore. In addition, the method that electrochemical impedance spectroscopy (EIS) technique carried out with cyclic voltammetry (CV) and charge-discharge curves is successfully applied to monitor the variety of impedance during the cycles, which is helpful to explore the mechanism of capacity attenuation. • The effect of extraction process on electrochemical performance of PE separator was explored. • n-PE membrane exhibited better capacity retention during the cycles, while d-PE membrane had a better C-rate performance. • EIS could be applied to monitor the variety of impedance inside the cell. • The equivalent circuit of EIS results of LiCoO 2 should contain positive region, separator region and negative region. [ABSTRACT FROM AUTHOR]