Optimization of heat treatment conditions for fabricating pre-lithiated silicon monoxide as an anode material for lithium-ion batteries

Herein, we compared the galvanostat- and thermal-driven electrochemical reactions occurring in lithiated silicon monoxide and found that the kinetics of the initial irreversible formation of certain phases (galvanostat-electrochemical reaction) do not agree with those of the pre-lithiation reaction between silicon monoxide and lithium metal (thermal-driven electrochemical reaction). However, thermal-driven electrochemical reactions occurring at high temperatures yielded phases similar to those formed galvanostatically, thereby reducing the initial irreversibility of cell. The kinetics of pre-lithiation were investigated by heating a silicon monoxide/lithium powder mixture to 600^◦C at heating rates of 9^◦C min^–1 and 14^◦C min^–1. Lithium oxide and lithium metasilicate were formed in both cases, while lithium silicate was formed only when the heating rate was 14^◦C min^–1. The identities of these irreversibly formed products were determined by XRD, DTA and the effect of heating rate was elucidated by electrochemical tests. Pre-lithiated samples heated at rates of 9^◦C min^–1 and 14^◦C min^–1 exhibited initial coulombic efficiencies of 78.83% and 81.72%, respectively. These values are higher than those observed for bare silicon monoxide anodes, thus indicating that heating conditions influence the irreversible formation of the above mentioned phases and affect the irreversible capacity of silicon monoxide.