Cycle-stable Si-based composite anode for lithium-ion batteries enabled by the synergetic combination of mixed lithium phosphates and void-preserving F-doped carbon

Abstract

Silicon-based materials have been considered as the promising anode candidates for next-generation high-energy-density lithium-ion batteries (LIBs). However, their widespread application is unfortunately restricted by severe volume variations during cycling and poor electronic conductivity. To overcome these challenges, we showcase an innovative design of dual core−shell structured Si-based nanocomposites working as anode for LIBs with boosted performance, where the Si nanoparticle core is tightly wrapped by a mixed lithium phosphate (Li3PO4/Li4P2O7) shell and void-preserving F-doped carbon shell (denoted as Si@LPO@void@FC). For such novel structured composite, the inner L3PO4/Li4P2O7 layer acting as artificial solid-electrolyte interphase (SEI) and the outer void-preserving F-doped C can effectively tolerate the volume changes while ensuring the stability of SEI layer, facilitate the Li+ migration and electron transfer, and reinforce the structural stability during cycling. Consequently, the as-fabricated Si@LPO@void@FC anode exhibits a reversible capacity of 569 mAh/g after 500 cycles at 1 A/g, and an exceptional long-term cycling stability with 76% capacity retention over 1000 cycles at 4.0 A/g can be achieved. Additionally, the full cell assembled with Si@LPO@void@FC anode and LiFePO4 cathode also demonstrates a good cycling performance with 117 mAh/g at 1 C for over 150 cycles with 92% capacity retention, suggesting the potentiality for practical application. Furthermore, the mechanisms of the enhanced structural stability of Si@LPO@void@FC anode are carefully elaborated by substantial in situ/ex situ microscopic techniques and electrochemical tests. It is expected that our findings in this work can provide guiding significance for improving the cycling performance of Si-based composite anodes toward high-performance LIBs.