(Digital Presentation) Role of Phosphorus Doping on Silicon Anode Performance in Lithium-Ion Batteries Via Facile Solid-State Synthesis

Lithiated silicon (Li15Si4) has a theoretical specific capacity of 3579 mAh g-1 compared to 372 mAh g-1 for graphite at conventional conditions. However, the large volume fluctuations during (de)lithiation result in irreversible damage to the solid-electrolyte interphase (SEI) and then gradual capacity loss as the electrolyte is reduced to reform the surface passivation layer in each cycle. One approach to mitigate this issue is to develop an artificial SEI layer on the silicon surface to limit strain-induced fracture during cycling. The approach presented herein is unique in that both surface functionalization and homogenous doping of the silicon are simultaneously achieved by introducing a trace amount of phosphorus via facile solid-state synthesis. Increased thermodynamic stability of the Li-P-Si ternaries as evidenced in previous studies has been corroborated herein, showing that the P-doped lithium silicide exhibits a contracted crystal lattice which both reduces the Li+ mobility and suppresses the chemical reaction between lithium silicide and typical organic electrolytes. The effect of P-doping, specifically the doping amount and depth within the silicon particles, on the electrochemical performance in lithium-ion batteries was investigated. In conclusion, the solid-state reaction between red phosphorus and nanoparticulate silicon is a relatively simple and tunable method enabling versatile studies of the interfacial chemistry of silicon electrodes over hundreds of cycles.