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The fire accidents caused by the thermal runaway of lithium-ion battery has extremely impeded the development of electric vehicles. With the purpose of evaluating the fire hazards of the electric vehicle, a full-scale thermal runaway test of the real lithium-ion battery pack is conducted in this work. The experimental process can be divided into three stages according to the combustion behavior. (1) Thermal runaway of the triggered module was induced and shows transient jet flame; (2) thermal runaway propagated between cells and further resulted in the constant repetition of ignition and re-ignition behavior; (3) the fire extinguish stage, in which the flame was suppressed and released a considerable amount of smoke. It is worth mentioning that it takes 22 s to evolve the triggered thermal runaway event to the worst case that the flame can spread throughout the whole cargo compartment. However, the water cannot directly act on the cells due to the shielding of the pack’s cover in the fire extinguish stage, which greatly limits its cooling effect. The potential flame spread over electric vehicle is observed in this work, which can provide useful guidelines for the safety design of lithium-ion battery system.

The cell-to-cell electrical contact resistance was investigated to estimate the effect of faulty electrical contact point(FECP) on the performance of battery packs. The temperature of the FECP in series circuit rises instantaneously compared to that of other normal points after the start of the current load, but the temperature of the FECP in parallel circuit rises just after the voltage turning point at the end of the charging/discharging process. The voltage difference between the highest voltage and the lowest voltage of the cells at the end of discharge stage increases apparently while the battery pack contains the FECPs, which is a typical feature during the decay of battery packs. In this study, the capacity retention of LiFePO4/C battery at room temperature reaches to 80% after 1260 cycles for a 1p3s pack, 1210 cycles for a 3p3s pack and 1510 cycles for a single cell, in which the average cell-to-cell connector impedance is 0.13 mΩ in the circuit. By contrast, the cyclic charge-discharge stops at 381st cycle for a 1p3s pack with a FECP(0.42 mΩ) in series circuit and at 1097th cycle for a 3p3s pack with a FECP(0.41 mΩ) in parallel circuit.

Conventional polymer binder in a lithium-sulfur (Li-S) battery, poly(vinylidene fluoride) (PVDF), suffers from insufficient ion conductivity, poor polysulfide-trapping ability, weak mechanical property, and requirement of organic solvents, which significantly encumber the industrial application of Li-S battery. Herein, a water-soluble binder with trifunctions, covalently cross-linked quaternary ammonium cationic starch (c-QACS), is developed to confront these issues. Similar to the poly(ethylene oxide) solid electrolytes, the c-QACS binder remarkably improves Li+ ion transfer capacity. The abundant O actives endow the c-QACS binder with admirable lithium polysulfide-trapping capability to retard the shuttle effect. In addition, the formed 3D network effectively maintains the electrode integrity during cycling. Benefiting from the above merits, the sulfur cathode with the c-QACS binder demonstrates a performance improvement of 300 and 150% compared with sulfur cathode with PVDF and bulk QACS binder after 100 cycles at 0.2C.

Silicon-based anode materials are indispensable components in developing high energy density lithium-ion batteries, yet their practical application still faces great challenges, such as large volume change during the lithiation and delithiation process that causes the pulverization of silicon particles, and continuous formation and reformation of the solid electrolyte interfaces (SEI) which results in a low initial coulombic efficiency. As an endeavor to address these problems, in this study, Si/SiO/Li2SiO3@C structures were prepared via a facile method using SiO, pitch powder and Li2CO3/PVA solution followed by annealing treatment. The Si/SiO/Li2SiO3@C composite shows a great improvement in lithium storage where a high discharge capacity of 1645.47 mA h g−1 was delivered with the 1st C.E. of 69.05% at 100 mA g−1. These results indicate that the designed method of integrating prelithiation and carbon coating for SiO and the as-prepared macro scale Si/SiO/Li2SiO3@C structures are practical for implementation in lithium-ion battery technology.

Summary The aprotic lithium-oxygen (Li-O2) battery has attracted worldwide attention because of its ultrahigh theoretical energy density. However, its practical application is critically hindered by cathode passivation, large polarization, and severe parasitic reactions. Here, we demonstrate an originally designed Ru(II) polypyridyl complex (RuPC) though which the reversible expansion of Li2O2 formation and decomposition can be achieved in Li-O2 batteries. Experimental and theoretical results revealed that the RuPC can not only expand the formation of Li2O2 in electrolyte but also suppress the reactivity of LiO2 intermediate during discharge, thus alleviating the cathode passivation and parasitic reactions significantly. In addition, an initial delithiation pathway can be achieved when charging in turn; thus, the Li2O2 products can be decomposed reversibly with a low overpotential. Consequently, the RuPC-catalyzed Li-O2 batteries exhibited a high discharge capacity, a low charge overpotential, and an ultralong cycle life. This work provides an alternative way of designing the soluble organic catalysts for metal-O2 batteries.

SiOx is regarded as a promising anode material for the next-generation lithium-ion batteries (LIBs) because of its high theoretical capacity. In order to relieve the volume variation and enhance the electronic and ionic conductivity, a SiOx@TiO2@N-doped carbon (NC) composite is prepared using biopolymer chitin as carbon precursor. The TiO2 coating layer shields the SiOx in the alkaline chitin solution, enabling the homogeneous and stable dispersion of the SiOx during the synthesis process. After emulsion, freeze-drying, and carbonization, the SiOx@TiO2@NC composite is obtained. The dual-confinement of TiO2 and NC effectively buffers the volume variation of SiOx and enhances the electronic/ionic conductivity. The enhanced structural integrity and conductivity guarantee the superior rate capability and the stable long-term cyclability of the SiOx@TiO2@NC composite. After 650 cycles at 0.5 and 1 A g−1, SiOx@TiO2@NC maintains reversible capacities of 633 and 540 mA h g−1, showing capacity retentions of 92.3% and 96.9%, respectively. After 100 cycles at 0.5 C, the assembled SiOx@TiO2@NC//LiFePO4 full cells can retain a discharge capacity of 121 mA h g−1, maintaining 90% of the third capacity. This work provides a chance for the industrial application of biopolymer chitin in LIBs, and may alleviate the pressure of environmental protection.

MnO/nitrogen-doped graphene (MnO/NG) composite cathode was fabricated by a facile one-pot method as cathode catalyst for non-aqueous lithium oxygen batteries. It exhibited superior electrochemical performance with higher round-trip efficiency and better cyclic stability. It showed a high round-trip efficiency of 84.6% at the current density of 0.05 mA cm−2 with the discharge and charge overpotentials of 0.11 and 0.41 V, respectively. Through scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy, it was confirmed that MnO nanoparticles were homogeneously dispersed on NG surface. The density functional theory calculations demonstrated that the superior electrochemical performance of MnO/NG might be attribute to the exposure of stoichiometric MnO (100) surface, with the ORR and OER overpotential only to be 0.21 and 0.24 V, respectively. The discharging-charging voltage gap is 0.45 V, in good agreement with the experimental value of 0.52 V.

With the popularization of lithium ion battery cells, the battery thermal management system (BTMS) has been paid much attention since it is important in ensuring the safety and performance of lithium ion battery pack. Although the BTMS based on the forced-air convection with the advantage of low-cost, simple, and tight design has been favored by practical applications in electric vehicles and electrochemical energy storage stations, the forced-air convection is always criticized for its low cooling efficiency and low-temperature uniformity. Thus, extensive investigation has been conducted to optimize the BTMS based on the forced-air convection. This paper reviews the developments on the application of forced-air convection into BTMS in terms of preheating and cooling. Firstly, the thermal models for battery cells are introduced from the perspective of the lumped model and electrochemical model. Meanwhile, the methods to simulate the flow field are also presented. The computational fluid dynamics and short-cut methods have been compared in the paper. The main optimization route is summarized which includes optimization of pure forced-air convection, the combination with phase change material(PCM), and integration with heat pipe. For the optimization of the pure forced-air convection, four technical routes are concluded, which are the location of inlets and outlets, flowing tunnel, controlling strategy, and flowing state. As for the hybrid BTMS based on forced-air convection with heat pipe and PCM, some extra structures such as mesh or finned structure are also included for enhancing the heat dissipation. Finally, some perspectives and outlooks on BTMS based on the forced-air convection are put forward for future development.

To improve the electrochemical performance of lithium sulfur batteries, a conductive Lewis base matrix, nitrogen doped graphene (NG), was prepared here through a facile strategy of annealing a polypyrrole/reduced graphene oxide composite. The obtained NG was demonstrated with enriched pyridinic-N doping and was employed as the matrix of sulfur cathode with ultra-high rates, reversible capacity and high coulombic efficiency. The improved performance can be attributed to the high conductivity of the NG and the enhanced adsorption energy of Li 2 S n (n=4-8) on the NG surface. The NG can act not only as an electronic conductive network but also as a Lewis base “catalyst” matrix that promotes the higher Li 2 S n to be further oxidized completely to S 8 as demonstrated in the cyclic voltammetry curve, which can thus significantly improve the sulfur utilization and cyclic stability even at a high sulfur loading of 75% (w/w) in the S@NG composite.

Aprotic lithium-oxygen (Li-O2) battery has attracted worldwide attention because of its ultrahigh theoretical energy density. However, its practical application is critically hindered by cathode passivation, large polarization and severe parasitic reactions. Here, we demonstrated a newly designed ruthenium (II) polypyridyl complex (RuPC) by which an expanded reversibly Li2O2-formation/decomposition could be achieved in lithiumoxygen batteries. Experimental and theoretical results revealed that the RuPC can not only expand the formation of Li2O2 in electrolyte, but also suppress the reactivity of LiO2 intermediate during discharge, thus alleviating the cathode passivation and parasitic reactions significantly. In addition, an initial delithiation pathway can be achieved when charging in turn, thus the Li2O2 products can be decomposed reversibly with a low overpotential. As a result, the RuPC-catalyzed Li-O2 batteries exhibited a high discharge capacity (~9281 mAh g-1), a low charge overpotential (0.54 V) and a ultralong cycle life (371 cycles). This work provides an alternative way of designing the soluble organic catalysts for metal-oxygen batteries.

Three classical iron sources including FePO4·2H2O, FeC2O4·2H2O and Fe2O3 are explored to study the mechanism and kinetics of LiFePO4 synthesis via solid-state reactions. During the initial formation of LiFePO4, the reactivity of FePO4 appears to be higher than that of FeC2O4 because the latter involves two stages including the decomposition of FeC2O4 and then the formation of LiFePO4. Fe2O3 shows the lowest reactivity among the solid-state reactions. Meanwhile, the optimal sintering temperature for FePO4 to form LiFePO4 is lower than those for FeC2O4·2H2O and Fe2O3. A larger primary particle size should be responsible for the lower specific capacity of LiFePO4 synthesized with micro-Fe2O3. The kinetic mechanism for obtaining single-phase LiFePO4 corresponds to the diffusion model, calculated by using Coats–Redfern and Doyle equations in which FeC2O4·2H2O and FePO4·2H2O obey 3-dimensional diffusion (cylinder, GB equation) and Fe2O3 obeys 1-dimensional diffusion.