Electrochemical performance of all-solid-state lithium secondary batteries with Li-Ni-Co-Mn oxide positive electrodes

LiNi1/3Co1/3Mn1/3O2 was applied as a promising material to the all-solid-state lithium cells using the 80Li2S.19P2S5.1P2O5 (mol%) solid electrolyte. The cell showed the first discharge capacity of 115 mAh g-1 at the current density of 0.064 mA cm-2 and retained the reversible capacity of 110 mAh g-1 after 10 cycles. The interfacial resistance was observed in the impedance spectrum of the all-solid-state cell charged to 4.4 V (vs. Li) and the transition metal elements were detected on the solid electrolyte in the vicinity of LiNi1/3Co1/3Mn1/3O2 by the TEM observations with EDX analyses. The electrochemical performance was improved by the coating of LiNi1/3Co1/3Mn1/3O2 particles with Li4Ti5O12 film. The interfacial resistance was decreased and the discharge capacity was increased from 63 to 83 mAh g-1 at 1.3 mA cm-2 by the coating. The electrochemical performance of LiNi1/3Co1/3Mn1/3O2 was compared with that of LiCoO2, LiMn2O4 and LiNiO2 in the all-solid-state cells. The rate capability of LiNi1/3Co1/3Mn1/3O2 was lower than that of LiCoO2. However, the reversible capacity of LiNi1/3Co1/3Mn1/3O2 at 0.064 mA cm-2 was larger than that of LiCoO2, LiMn2O4 and LiNiO2.