title: In situ transmission electron microscopy observation of electrochemical behavior of CoS(2) in lithium-ion battery.
abstract: Metal sulfides are a type of potential anode materials for lithium-ion batteries (LIBs). However, their electrochemical behaviors and mechanism during the charge and discharge process remain unclear. In the present paper, we use CoS2 as a model material to investigate their electrochemical process using in situ transmission electron microscopy (TEM). Two kinds of reaction behaviors are revealed. The pure CoS2 particles show a side-to-side conversion process, in which large and anisotropic size expansion (47.1%) occurs that results in the formation of cracks and fractures in CoS2 particles. In contrast, the CoS2 particles anchored on reduced graphene oxide (rGO) sheets exhibit a core-shell conversion process involving small and homogeneous size expansion (28.6%) and few fractures, which attributes to the excellent Li(+) conductivity of rGO sheets and accounts for the improved cyclability. Single-crystalline CoS2 particle converts to Co nanocrystals of 1-2 nm embedded within Li2S matrix after the first lithiation. The subsequent electrochemical reaction is a reversible phase conversion between Co/Li2S and CoS2 nanocrystals. Our direct observations provide important mechanistic insight for developing high-performance conversion electrodes for LIBs.
authors.affiliation: Institute of Physical Chemistry, Zhejiang Normal University , Jinhua 321004, China.
authors.forename: Qingmei
authors.initials: Q
authors.lastname: Su
authors.forename: Jian
authors.initials: J
authors.lastname: Xie
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.forename: Yijun
authors.initials: Y
authors.lastname: Zhong
authors.forename: Gaohui
authors.initials: G
authors.lastname: Du
authors.forename: Bingshe
authors.initials: B
authors.lastname: Xu