Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 6, Issue 4, Pages 3016-3022Publisher
AMER CHEMICAL SOC
DOI: 10.1021/am4056084
Keywords
lithium-ion battery; cobalt sulfide; reduced graphene oxide; in situ TEM; anode
Funding
- Program for New Century Excellent Talents in University of Ministry of Education of China [NCET-11-1081]
- National Science Foundation of China [1203168]
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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.
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