锂离子电池快充石墨负极研究与应用

相较于传统燃油汽车,电动汽车缓慢的充电速度始终制约了其进一步推广。为电动汽车实现“加油式”快速充电能够缓解充电桩的使用压力,增加电动汽车的应用场景和市场占有率。因此,亟需开发出具有快速充放电能力的高性能锂离子电池。石墨因其低廉的价格和优异的电化学性能已经在锂离子电池负极领域得到了广泛的商业化应用,然而其较低的嵌锂电位导致在快充过程中出现析锂,损害电化学性能的同时会带来安全隐患。因此,必须对石墨进行改良处理,以适应快充技术的需要。本文系统介绍了近年来石墨负极快充化改良领域的研究进展,从成分设计,形貌调控,结构优化,电解液适配等方面进行了评述,并总结了快充石墨面临的挑战,展望了其发展前景,为推动快充技术的商业化应用提供了借鉴。     

锂离子电池快充石墨负极研究与应用

Driven by the excessive environmental pollution caused by the over-use of non-renewable fossil-derived energy, renewable energy and electrochemical energy storage devices have made great progress in the past decades. Electrochemical energy storage devices, such as lithium-ion batteries, have the advantages of high capacity, long life cycle, and good safety performance; therefore, they have been used in various applications. For example, economical and environment-friendly electric vehicles have recently taken up increasing market share. However, when compared with vehicles propelled using fossil-derived energy, the slow charging speed of electric vehicles has always restricted their further promotion. The realization of rapid charging for electric vehicles can alleviate the high-pressure usage of charging piles as well as increase the application and market share of electric vehicles. Therefore, it is important to develop high-performance lithium-ion batteries with rapid charge and discharge capacities. The fast-charging capacity of lithium-ion batteries is limited by the slow migration of lithium ions in the electrode and the electrode/electrolyte interface. Therefore, the key to developing fast-charging lithium-ion batteries lies in the successful design of suitable electrode materials. Because of its low cost and excellent electrochemical performance, graphite has been widely used to develop the cathode of lithium-ion batteries. However, the migration of lithium ions in graphite is slow, resulting in large polarization during the high-current charge and discharge processes. In addition, the low lithium intercalation potential of graphite leads to lithium precipitation during fast charging, which can decrease the electrochemical performance and cause potential safety hazards. Therefore, graphite must be improved to meet the needs of such fast-charging devices. In this article, we systematically introduce the research progress made in recent years within the scope of rapid-charging improvement of graphite(-based) cathodes and then highlight the modification strategies for graphite with the goal of achieving functional coating, desired morphological and structural design, optimized electrolyte properties, and an improved charging protocol. Additionally, this article evaluates the advantages and disadvantages of the modification strategies as well as their application prospects. The scheme of functional coating for modifying graphite must simplify the process and improve production efficiency to meet the needs of industrial development. Morphology design should ensure satisfactory initial Coulomb efficiency, while the improvement of the electrolyte properties and optimization of the charging protocol need to consider the commercialization costs. Finally, this paper proposes further evaluation of the effects of the modification strategies based on soft-pack or cylindrical batteries to strengthen the commercialization prospect of the modification strategies.      

改性石墨用于锂离子电池负极

石墨可用于锂离子电池负极材料，其改性方面的研究主要有：石墨的还原、氧化、表面包膜以及物理法处理。这些方法可以改变石墨的电子状态及表面结构，能够提高石墨的性能。本文介绍了改性石墨用于锂离子电池负极的研究概况。     

改性球形天然石墨锂离子电池负极材料的研究

将天然鳞片石墨制成球形石墨,在其表面包覆一层纳米非石墨化碳材料制成具有核壳结构的改性球形石墨。实验结果表明:此法显著提高了天然石墨的振实密度、可逆容量(达365mAh·g-1 ),首次库仑效率( >93% )和循环稳定性(循环500次后,容量保持率>80% )。分析并讨论了负极材料的结构及其与电化学性能的关系。     

氯化钠对锂离子电池石墨负极的修饰改性

Numerous carbonaceous materials have been studied as anodes of lithium ion batteries during the past several years[1￣4].Graphite was favored for battery applications because it exhibits a high specific capac- ity, low working potential close to that of l…     

石墨炔在锂/钠离子电池负极中的应用

二维石墨炔优异的物理和化学性质受到了广泛的关注。近几年,与石墨炔相关的理论、合成和应用研究快速发展,并取得显著成果。基于石墨炔独特的制备方式与可控的分子结构,其已经在很多传统的研究领域展现出潜力,也在一些新兴的研究方向上产生重要影响,表明石墨炔的研究正逐渐成为一个非常热门研究领域。而石墨炔在电化学储能方面的研究越来越多,文章概述了石墨炔与电化学储能相关的优异特性,总结了石墨炔的常规制备方法,重点讨论了在低温制备优势下石墨炔家族成员的迅速壮大和相应石墨炔新成员独特结构对电化学储锂和储钠行为的影响。     

嵌锂石墨充电机制的abinitio和DFT理论研究

用ab initio/HFt DFT/B3LYP方法探究了在锂离子二次电池中锂离子在石墨负 电极材料里可逆脱过程。理论计算结果表明，嵌锂石墨LIG充放电机制是锂在石黑 碳层间可闹乱子嵌脱，同时伴随着锂与碳层间发生电荷连续转移和碳层堆积方式改 变的协同过程；计算结果也明确证实，嵌锂石墨嵌入脱出锂离子的过程就是锂离子 二次电池储存与释放能量的过程，提出的嵌锂石墨充放电机制较好地丰富了固体电 解质相界面SEI机理和单电子还原机理。     

硅/石墨复合物用作锂离子电池负极材料

以石墨和纳米硅粉为原料, 利用机械球磨的方法制备了硅/石墨复合物, 用作锂离子电池负极材料. 采用XRD, SEM以及电化学测试等手段对材料进行了结构表征和性能测试. 通过球磨不同质量比的硅和石墨, 并对相应的复合物进行充放电测试, 寻找到了硅和石墨的最佳比例, 其值为1∶9. 实验结果表明, 所得材料既具备高于纯纳米硅的循环性能, 又具有比石墨高的可逆容量.     

嵌锂石墨充电机制的abinitio和DFT理论研究

用ab initio/HFt DFT/B3LYP方法探究了在锂离子二次电池中锂离子在石墨负 电极材料里可逆脱过程。理论计算结果表明，嵌锂石墨LIG充放电机制是锂在石黑 碳层间可闹乱子嵌脱，同时伴随着锂与碳层间发生电荷连续转移和碳层堆积方式改 变的协同过程；计算结果也明确证实，嵌锂石墨嵌入脱出锂离子的过程就是锂离子 二次电池储存与释放能量的过程，提出的嵌锂石墨充放电机制较好地丰富了固体电 解质相界面SEI机理和单电子还原机理。     

含硫添加剂对石墨负极低温性能的研究

锂离子电池的低温性能主要取决于石墨负极,通过添加剂来改善负极的低温性能是研究的焦点之一. 本文比较了3种具有不同含硫官能团的添加剂DTD(ethylene sulfate)、1,3-PS(1,3-propane sultone)和ES(ethylene sulfite)对传统商业化材料人造石墨负极低温性能的影响. DFT（密度泛函理论）计算、扫描伏安法（CV）、扫描电子显微镜（SEM）和电化学测试结果表明,3种含硫添加剂均可在人造石墨负极表面参与成膜,并对其低温性能产生比较大的影响. 其中,DTD对石墨负极低温性能改善最为明显,1,3-PS对石墨负极的低温性能造成不利影响,而ES则没有明显作用. 电化学交流阻抗（EIS）和X射线光电子能谱（XPS）表明,这3种添加剂的不同作用主要在于其所形成的电极界面膜在电化学阻抗方面存在着明显的差异.     

Theoretical Studies on Reaction Mechanisms of HNCS with NH (X3∑)

The reaction mechanisms of HNCS with NH(X3∑) were theoretically investigated. The minimum energy paths (MEP) of the reaction were calculated by using the density functional theory(DFT) at the B3LYP/6-311 G** level. The equilibrium structural parameters, the harmonic vibrational frequencies, the total energies, and the zeropoint energies(ZPE) of all the species were calculated. The single-point energies along the MEP were further refined at the QCISD(T)/6-311 G** level. It was found that the mechanisms of the HNCS NH(X3∑) reaction involve two channels producing the HNC HNS and the N2H2 CS products. Channel 1 plays a dominant role and the HNC HNS are the main products. The reaction is exothermic.     

Theoretical Study on Electronic Gain-and-loss Properties of TEMPO and Its Derivates in Charge/Discharge Processes

Theoretical study on the electronic structures and related properties of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and its cationic lipid derivates in the charge/discharge processes has been carried out using the density functional theory (DFT) at the (U)B3LYP/6-31G(d,p) or 6-31+G(d,p) level. The changes and regularities of geometric and electronic properties of these compounds in the charge/discharge processes were revealed in detail. The compu-tational results show that the substitute group plays a very important role in the electronic structures and related properties of TEMPOs during the charge/discharge processes. It isvery interesting to find that after getting an electron, TEMPO is more stable in singlet state but the lipid is more stable in triplet state. For TEMPO, both the charge and the discharge processes greatly influence the electronic properties of N and O atoms of the radical part. For the cationic lipid, the discharge process mainly influences the pyridinium head and the charge process mainly influences the free radical head. Moreover, the solvent effect plays an important role in some bond lengths and the charge population of the free radical head. In addition, the UV-Vis absorption spectra of TEMPO and the lipid were calculated and simulated using TDDFT at the 6-31G(d,p) or 6-31+G(d,p) level, in satisfying agreement with the experimental ones.     

芴与苯并硒化二唑共聚物的电子结构和光谱性质的理论研究

用密度泛函B3LYP方法对低聚体(DEF-BSeD)n(n=1~4)[其中9,9二乙基芴(DEF)单元与苯并硒化二唑(BSeD)单元的摩尔比分别为1∶1和2∶1]进行全优化, 计算电离能(PI)、电子亲和势(EA)和能隙(ΔH-L), 在基态结构的基础上用TD-DFT和ZINDO方法计算激发能和电子吸收光谱, 并利用外推法得到高聚物的相应性质. 从外推结果看出, 随着聚合物中BSeD比例的增大, 聚合物的最低单激发能呈减小的趋势, 最大电子吸收光谱红移. 用CIS方法优化得到单体的S1激发态结构, 计算结果表明, 激发态的结构更趋近于平面构型.     

硝酰阳离子和二氧化氮分子的弯曲变形研究

采用密度泛函理论的B3LYP方法(6-311＋G*基组)计算了、NO2以及其它与硝化反应机理研究相关的分子、离子和激发态的结构与性质.进而研究了当键角在90～180°之间变化时，这些相关物质能量的变化规律，由此探讨了不同硝化机理发生的可能性，为以后进一步研究不同结构与活性的芳香化合物的硝化反应机理提供依据.     

全氟代金刚烷及其自由基的理论研究

采用密度泛函理论(DFT)方法:BHLYP、B3LYP、BP86、BLYP,在全电子的双ζ基组加极化函数和弥散函数(DZP＋)基组下,计算了全氟代金刚烷(C10F16)及其自由基(C10F15)的总能量、优化几何构型、电子亲和势和谐振频率.在B3LYP水平上所得到的可靠绝热电子亲和势(EAad)分别为: C10F16, 1.06 eV; C10F15, 4.11和 3.03 eV.     

甲醇在Ru(0001)表面吸附的密度泛函研究

采用密度泛函理论(DFT)的B3LYP方法,以原子簇Ru15为模拟表面,对甲醇在理想的Ru(0001)面三种吸附位置(top,fcc,hcp)的吸附模型进行了几何构型优化,能量计算,Mu lliken布局分析以及振动频率计算,结果表明顶位为最有利的吸附位.这些变化与实验观察到的甲醇在过渡金属表面解离的结果相一致.同时通过对吸附过程的分析推测其可能的解离途径.     

同晶置换改性FAU分子筛结构及吸附性能的密度泛函理论研究

采用密度泛函理论(DFT)方法,考察了八面沸石(FAU)型分子筛β笼孔道结构内含氧化合物(甲醇、二甲醚、丙醛)的吸附,并进一步计算研究了Zn,Ca同晶置换改性的作用机理.研究结果表明,β笼孔道结构内,Al原子为甲醇、二甲醚和丙醛的吸附活性位,Si原子无吸附活性.Zn,Ca掺杂的β笼结构内,正2价的Zn和Ca掺杂替换正3价的Al,导致邻近的Si原子位置形成缺电子空穴,增强了甲醇、二甲醚和丙醛的吸附,而杂原子Zn和Ca本身并没有吸附活性.     

乙烯自由基与臭氧反应的DFT计算研究

采用密度泛函B3LYP/6-311G**水平计算研究了O3氧化乙烯基（C2H3）的机理,全参数优化了反应势能面上各驻点的几何构型,用内禀反应坐标（IRC）计算和频率分析方法,对过渡态进行了验证.结果表明，乙烯基（C2H3）与O3之间有很强的反应活性.     

机器学习结合密度泛函理论计算在材料科学中的研究进展

近年来,材料科学研究中密度泛函理论(DFT)计算与机器学习相结合的方法呈现爆炸式增长的趋势。本文综述了DFT及其高通量方法产生的大量计算数据与机器学习相结合的原理和意义,从DFT计算的基本原理出发,重点介绍了机器学习方法的流程、常用的算法及其在催化材料预测热门研究方向中的应用,最后剖析了这个新兴领域目前存在的研究问题、挑战以及未来的发展前景。     

ZnO和ZnS本征点缺陷的理论研究

基于第一性原理和热动力学方法,通过模拟计算分析了不同温度和分压下ZnS和ZnO晶体本征点缺陷的性质.振动熵的计算结果表明,在高温条件下,振动熵对缺陷形成能的贡献不能忽略.对比分析2种晶体本征点缺陷随环境条件变化的规律,结果表明,2种晶体的主导缺陷均为空位型.氧空位(V_O)在ZnO中更易形成,富氧和低温条件有利用于ZnO的p型本征掺杂.而锌空位(V_(Zn))在ZnS中形成能最低,因此ZnS比ZnO更容易形成p型掺杂.研究还发现2种晶体的肖特基缺陷都不稳定,而弗伦克尔缺陷比较稳定.除ZnS反弗伦克尔缺陷外,有价态的缺陷对的形成能均比中性缺陷对的形成能低.