物理化学学报 >> 2021, Vol. 37 >> Issue (11): 2011003.doi: 10.3866/PKU.WHXB202011003

所属专题: 能源与材料化学

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锂离子电池正极材料中的极化子现象理论计算研究进展

叶耀坤, 胡宗祥, 刘佳华, 林伟成, 陈涛文, 郑家新(), 潘锋()   

  • 收稿日期:2020-11-02 录用日期:2020-12-10 发布日期:2020-12-16
  • 通讯作者: 郑家新,潘锋 E-mail:zhengjx@pkusz.edu.cn;panfeng@pkusz.edu.cn
  • 作者简介:郑家新,北京大学深圳研究生院副教授(PI)、研究员。于2008年获得北京大学物理学和数学双学士学位,2013年获得北京大学凝聚态物理博士学位。主要研究方向包括材料计算和模拟方法的开发、通过理论计算方法(如第一性原理、分子动力学等)解决锂电池基础和应用科学问题
    潘锋,1985年获北京大学化学学士学位,1994年获英国Strathclyde大学博士学位。北京大学深圳研究生院新材料学院创院院长、北京大学讲席教授、博导。研究方向为新能源材料基因和结构化学。国家材料基因组重点专项首席科学家第一联系人:

    These authors contributed equally to this work.

  • 基金资助:
    国家重点研发计划(2016YFB0700600);国家自然科学基金(21603007);国家自然科学基金(51672012);广东省重点实验室(2017B0303010130);深圳市科技创新委员会(ZDSYS20170728102618)

Research Progress of Theoretical Studies on Polarons in Cathode Materials of Lithium-Ion Batteries

Yaokun Ye, Zongxiang Hu, Jiahua Liu, Weicheng Lin, Taowen Chen, Jiaxin Zheng(), Feng Pan()   

  • Received:2020-11-02 Accepted:2020-12-10 Published:2020-12-16
  • Contact: Jiaxin Zheng,Feng Pan E-mail:zhengjx@pkusz.edu.cn;panfeng@pkusz.edu.cn
  • About author:Email: panfeng@pkusz.edu.cn (F.P.)
    Email: zhengjx@pkusz.edu.cn (J.Z.)
  • Supported by:
    the National Key R&D Program of China(2016YFB0700600);the National Natural Science Foundation of China(21603007);the National Natural Science Foundation of China(51672012);the Guangdong Key-lab Project(2017B0303010130);the Shenzhen Science and Technology Innovation Committee(ZDSYS20170728102618)

摘要:

作为一种高能量密度储能器件,锂离子电池不仅已经广泛应用于消费电子领域(如笔记本电脑、智能手机),而且也适合用于电动车中的动力电池。正极是锂电池最为重要的组成部分。在正极材料的研究中,当电子在空间上局域分布并与晶格耦合将形成极化子,极化子现象近些年逐渐引起人们更多关注,主要是因为其减弱电子导电性,不利于电子传导,是磷酸铁锂等正极材料电子导电性差的根本原因。极化子是一种晶格畸变束缚电子作整体运动的晶体缺陷。开展极化子现象的相关机理研究,将为设计高导电性正极材料提供理论指导,对锂离子电池电化学性能的进一步提升有着重要意义。基于第一性原理的理论计算方法已成为研究正极材料中极化子的重要研究手段,能够判断体系是否有极化子出现以及分析极化子的出现对正极材料的物理化学性能影响。本文主要从理论计算的角度出发,首先介绍了极化子的基本物理概念,其次结合我们的相关研究综述了极化子的理论计算判别方法、极化子对常见类型正极材料导电性能的影响与调控和当前研究方法的一些理论难题,最后从基础理论和实际应用两个角度对未来正极材料中的极化子研究进行展望。

关键词: 极化子, 锂离子电池, 正极材料, 电子导电性, 第一性原理计算

Abstract:

In addition to their extensive commercial application in electronic devices such as cell phones and laptops, lithium-ion batteries (LIBs) are most suitable to fulfill the energy storage requirements of electric vehicles because of their recognized safety, portability, and high energy density. Cathodes are the most important part of LIBs, and various cathode materials have been widely investigated over the past decades. Polaron formation has been attracting increasing attention in the research of cathode materials, as it limits electron conduction. In particular, polarons are responsible for low electronic conductivity in cathode materials like olivine phosphate. Polaron is a typical crystal defect caused by the integrated motion of lattice distortion and its trapping electrons. Research on the mechanism of polaron formation will provide theoretical guidance for the design of high-electronic-conductivity cathode materials and improvement of the electrochemical performance of LIBs. Theoretical calculation is a direct and important method to study polaron formation in a specific crystal material, because the presence of polarons and their formation mechanisms can be effectively verified through this method. In this article, we first introduce the basic physical concept of polarons and their dynamical model according to the Marcus and Emin-Holstein-Austin-Mott theories. A comparison of the general properties of large and small polarons, summarized in this chapter, reveals that small polaron formation more likely occurs in cathode materials. Moreover, the theoretical characterization, electrical impact, control and challenges of polarons are reviewed. Although a universal necessary and suitable condition for the theoretical characterization of polarons has not yet been found, we still propose three criteria that are proven to be feasible and practical for the theoretical identification of polarons when applied in combination. Experimental characterizations are also introduced briefly for reference, because the comparison with the experiment is suggested to be necessary and mandatory. The electrical impact caused by polarons results in low electronic conductivity, which has been broadly reported in layered, olivine, and spinel cathode materials. Doping can weaken the influence of polarons and, thus, significantly enhance the electronic conductivity, thereby becoming the most prevalent strategy for tuning polarons. Although theoretical calculations have been widely and effectively conducted in the study of polarons, some challenges may still be faced because of the intrinsic shortcomings of the traditional density functional theory, which need to be addressed. Finally, further research on polarons from the perspective of basic theory and practical applications is prospected.

Key words: Polaron, Lithium-ion battery, Cathode materials, Electronic conductivity, First-principle calculations

MSC2000: 

  • O641