In-depth investigation of the exothermic reactions between lithiated graphite and electrolyte in lithium-ion battery

Thermal runaway is a critical issue for the large application of lithium-ion batteries.Exothermic reactions between lithiated graphite and electrolyte play a crucial role in the thermal runaway of lithium-ion batteries.However,the role of each component in the electrolyte during the exothermic reactions with lithiated graphite has not been fully understood.In this paper,the exothermic reactions between lithiated graphite and electrolyte of lithium-ion battery are investigated through differential scanning calorimetry(DSC) and evolved gas analysis.The lithiated graphite in the presence of electrolyte exhibit three exothermic peaks during DSC test.The reactions between lithiated graphite and LiPF_(6) and ethylene carbonate are found to be responsible for the first two exothermic peaks,while the third exothermic peak is attributed to the reaction between lithiated graphite and binder.In contrast,diethylene carbonate and ethyl methyl carbonate contribute little to the total heat generation of graphite-electrolyte reactions.The reaction mechanism between lithiated graphite and electrolyte,including the major reaction equations and gas products,are summarized.Finally,DSC tests on samples with various amounts of electrolyte are performed to clarify the quantitative relationship between lithiated graphite and electrolyte during the exothermic reactions.2.5 mg of lithiated graphite (Li_(0.8627)C_(6)) can fully react with around 7.2 mg electrolyte,releasing a heat generation of 2491 J g^(-1).The results presented in this study can provide useful guidance for the safety improvement of lithium-ion batteries.

New Insight on Graphite Anode Degradation Induced by Li-Plating

Graphite is the dominant anode material for lithium-ion batteries;however,it still suffers from Li-plating when charging fast or at low temperature,and Liplating is associated with performance fading and safety concerns.Herein,we clarify the mechanism of lithium evolution from graphite particles by overlithiation cycle test,in-situ XRD,and titration gas chromatography.We observe that the graphite intercalation compounds(GICs,LiC_(12) and LiC_(6)e.g.)gradually become inactive and wrapped by dead lithium or side reaction sediments,while the rate of this degradation will be accelerated as the overpotential of Liplating is decreased after initial Li metal nucleation.This understanding is contradictory to the popular one that the degradation of graphite anode after Li plating is mainly caused by the inferior SEI and dead Li induced hindering of Li-ion intercalation.The isolation of lithiated graphite particles leading to the fast vanishing of Li insertion/deintercalation process in graphite anodes.We further study the insertion/deintercalation vanishing process at low temperature and high rates,respectively.This work provides a insight on graphite anode degradation induced by Li-plating,and the new understanding can be used to guide the design of advanced materials and electrodes to avoid Li-plating and achieve extreme fast while safe charging.

Thermal Runaway Characteristics and Modeling of LiFePO4 Power Battery for Electric Vehicles

LiFePO_(4)(LFP)lithium-ion batteries have gained widespread use in electric vehicles due to their safety and longevity,but thermal runaway(TR)incidents still have been reported.This paper explores the TR characteristics and modeling of LFP batteries at different states of charge(SOC).Adiabatic tests reveal that TR severity increases with SOC,and five stages are identified based on battery temperature evolution.Reaction kinetics parameters of exothermic reactions in each TR stage are extracted,and TR models for LFP batteries are established.The models accurately simulate TR behaviors at different SOCs,and the simulated TR characteristic temperatures also agree well with the experimental results,with errors of TR characteristic temperatures less than 3%.The prediction errors of TR characteristic temperatures under oven test conditions are also less than 1%.The results provide a comprehensive understanding of TR in LFP batteries,which is useful for battery safety design and optimization.

红色小说英译叙事重构对比研究——以《创业史》沙译本和《山乡巨变》班译本为例

关注翻译与政治冲突的叙事建构理论可以评估小说翻译,以发现译者重构译本叙事对社会政治语境的影响。本文借莫娜·贝克的叙事建构理论,对比研究新中国“十七年”间服务于国家叙事对外传播的红色小说《创业史》沙博理译本和《山乡巨变》班以安译本的再叙事。从标示式重构、人物事件再定位和文本素材的选择性采用等三种重构策略在文本层面的操作及其叙事重构效果来看,相较于班译中国文化特色的消弭和改革冲突的弱化,沙译呼应国家叙事对外传播的政治要求,重构且强化了原著的社会主义价值观,塑造蒸蒸日上的国家形象和积极向上的民族形象,国家翻译实践的政治价值和战略意图得以彰显。

Transmission Dynamics of an Outbreak of the COVID-19 Delta Variant B.1.617.2——Guangdong Province,China,May-June 2021

On May 21,2021,a local case of coronavirus disease 2019(COVID-19)was confirmed in a 75-year-old woman(experienced onset of symptoms on May 18)in Liwan District,Guangzhou City,Guangdong Province,China.The number of infections has increased in the following 10 days and led to 5 generations of transmission.

Dendrite-accelerated thermal runaway mechanisms of lithium metal pouch batteries

High-energy-density lithium metal batteries(LMBs)are widely accepted as promising next-generation energy storage systems.However,the safety features of practical LMBs are rarely explored quantitatively.Herein,the thermal runaway behaviors of a 3.26 Ah(343 Wh kg^(−1))Li|LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2)pouch cell in the whole life cycle are quantitatively investigated by extended volume-accelerating rate calorimetry and differential scanning calorimetry.By thermal failure analyses on pristine cell with fresh Li metal,activated cell with once plated dendrites,and 20-cycled cell with large quantities of dendrites and dead Li,dendrite-accelerated thermal runaway mechanisms including reaction sequence and heat release contribution are reached.Suppressing dendrite growth and reducing the reactivity between Li metal anode and electrolyte at high temperature are effective strategies to enhance the safety performance of LMBs.These findings can largely enhance the understanding on the thermal runaway behaviors of Li metal pouch cells in practical working conditions.

Rational design of imine-linked three-dimensional mesoporous covalent organic frameworks with bor topology

Three-dimensional(3D)covalent organic frameworks(COFs)possess great potential applications in various fields.Constructing 3D COFs with large pore sizes is extremely challenging due to the interpenetration and collapse.Herein,we report a series of crystalline imine-linked 3D COFs(3D-bor-COF-1,3D-borCOF-2,3D-bor-COF-3)with mesoporous channels through rationally designing the topology configuration.These 3D-bor-COFs display permanent porosity and Brunauer–Emmett–Teller(BET)surfaces of 3205.5,1752.7,and 2077.3 m2 g−1(SLangmuir=4277.7,2480.3,and 2698.0 m2 g−1),respectively.The pore sizes of 3Dbor-COFs were confirmed by the lattice fringes from high-resolution transmission electron microscopy,as well as structural simulation and nitrogen adsorption isotherm analysis.3D-bor-COFs display large pore sizes(3.8 nm for 3D-borCOF-3),which is among the highest record of 3D COFs.Owing to the unstackedaromatic pore environment and high specific surface area,3D-bor-COFs display excellent adsorption capacity for benzene vapor(1203.9 mg g−1 for 3D-bor-COF-3)under 298 K,which is three times higher than that of the best-reported 2D COF.This work not only provides inspiration for designing 3D mesoporous imineCOFs,but also demonstrates a strategy for constructing aromatics adsorption materials.