Control of Graphene Heteroatoms in a Microball Si@Graphene Composite Anode for High-Energy-Density Lithium-Ion Full Cells

The use of Si and nitrogen-doped graphene to fabricate composite anodes in lithium-ion batteries (LIBs) is attracting intense attention. However, the reported strategies are limited to achieving a cost-effective, scalable, and facile approach. In particular, many reports on Si/N-graphene (N-Gra) anodes cannot achieve a high first discharge capacity while retaining a high Coulombic efficiency (CE). Herein, we report a Si@N-Gra composite with core-shelled microballs of Si NPs and electrochemically exfoliated graphene by NH3 as a nitrogen source. We use H2 and NH3 to control the O and N content and to optimize the anode performance. It is found that N-Gra in the Si@N-Gra composite anode highly improves the electric conductivity and ion mobility. As a result, the microballs structure (Si@N-ECGB) exhibit the highest initial discharge capacity of up to 2604.5 mAh/g with an 85.2% CE. This excellent performance is attributed to efficient lithiation/delithiation that maintains the stability of the Si@N-ECGB. A full cell of Si@N-ECGB||NMC 811 (Ni/Mn/Co = 8:1:1) is demonstrated, from which a high initial capacity (170 mAh/g) and μ84% retention after 100 cycles are achieved. This work provides a potential strategy for achieving high capacity and stability in LIBs.