Electrochemical Properties of the Mesocarbon Microbeads (MCMBs) in an All-solid-state Electrochemical Cell by use of the Amorphous Solid Electrolyte Li₃PS₄

Abstract

Electrochemical properties of the mesocarbon microbeads (MCMBs) were investigated as anode active materials for an all-solid-state cell in which amorphous Li₃PS₄ (a – Li₃PS₄) was used as solid electrolytes and Li – In alloy was used as a counter electrode. The amount of Li⁺ ions that were inserted into the MCMBs denoted as x in the notation Li_xC₆ (0 < x < 1). X-ray diffraction measurements suggested that Li⁺ ions were inserted into the disordered portions of MCMBs at the initial reaction stage with the composition range of 0 < x < 0.13. After the initial reaction stage, Li⁺ ions were intercalated into the graphite layers of MCMBs in the composition range of 0.13 < x < 0.91. The Li⁺ ions inserted into the disordered portions of MCMBs could not be extracted in the discharge process and then caused the irreversible capacity of the first charge-discharge cycle. On the other hand, Li⁺ ions that were intercalated into the graphite layers can be reversibly deintercalated in the composition range of 0.13 < x < 0.91. The charge-discharge capacity of the MCMBs was gradually decreased with an increase in the cycle number. Raman spectroscopy suggested that the capacity fading during the charge-discharge cycles would be caused by the deterioration of the MCMBs’ crystallinity.