Electrochemical study of nanometric Si on carbon for lithium ion secondary batteries

Abstract

The electrochemical and thermochemical properties of a silicon–graphite composite anode for lithium ion batteries were evaluated. The electrochemical properties were varied by the condition of pretreatment. The electrochemical pretreatment of constant current (C/10) and constant potential for 24 h showed specific discharge and charge capacities of 941 and 781 mA h g−1 to give a specific irreversible capacity of 161 mA h g−1 and a coulombic efficiency of 83%. The initial cycle as the next cycle of pretreatment showed a specific charge capacity (Li desertion) of 698 mA h g−1 and a coulombic efficiency of 95%. Coulombic efficiency at the fifth cycle was 97% to clear up almost all of the irreversible capacity. During the pretreatment cycle to the fourth cycle, the average specific charge capacity was 683 mA h g−1 and the cumulative irreversible capacity was 264 mA h g−1. Exothermic heat values based on the specific capacity of the discharged (Li insertion) electrode of silicon–graphite composite for the temperature range of 50–300 °C were 2.09 and 2.21 J mA−1h−1 for 0 and 2 h as time of pretreatment in the case of just disassembled wet electrodes and 1.43 and 1.01 J mA−1h−1 for 12 and 24 h as time of pretreatment in the case of dried electrodes, respectively.