Ni-Composite Microencapsulated Graphite as the Negative Electrode in Lithium-Ion Batteries I. Initial Irreversible Capacity Study

A novel approach for suppressing the solvated lithium intercalation in graphite was developed by microencapsulating graphite with nanosized Ni-composite particles. The Ni-composite graphite showed great improvement in charge-discharge performance, coulomb efficiency, and cycling behavior when used as the negative electrode in a Li-ion cell with propylene carbonate (PC)-based electrolyte. For example, a 10 wt % Ni-composite coating increased the initial charge-discharge coulomb efficiency of SFG75 graphite (75 mm, Timcal America) from 59 to 84% and the reversible capacity by 30-40 mAh/g. The Ni-composite coating consisted of nanosized particles distributed over the surface of the graphite particle, which effectively blocked some of the edge surfaces exposed to the electrolyte. This minimized solvated lithium intercalation at these edge sites, which subsequently minimized the PC reduction within the graphite and the exfoliation of the graphene layers, and also gas evolution. Corresponding improvements in both the charge-discharge performance and safety of the negative electrode in a rechargeable Li-ion cell resulted. © 2000 The Electrochemical Society. S0013-4651(99)08-113-6. All rights reserved.