Charge-Transfer Reaction at the Lithium Phosphorus Oxynitride Glass Electrolyte/Lithium Manganese Oxide Thin-Film Interface and Its Stability on Cycling

Charge-transfer reaction at a lithium manganese oxide (LiMn2O4) thin-film electrode/lithium phosphorus oxynitride glass electrolyte (LiPON) interface was investigated using all-solid-state thin-film batteries (Li/LiPON/LiMn2O4). X-ray diffraction measurements revealed that the crystal structure of the thin-film LiMn2O4 electrode changed on depositing the LiPON thin-film electrode, but a thermal treatment at 498K for 60min re-formed the original crystal structure. The potential sweep curve of the thermally treated film battery was identical to the cyclic voltammogram of a LiMn2O4 thin-film electrode in a conventional organic electrolyte (1mol dm(-3) LiClO4 dissolved in propylene carbonate). In contrast to a LiPON/LiCoO2 interface, the charge-transfer resistance at the LiPON/LiMn2O4 interface did not decrease sufficiently after the thermal treatment relative to the charge-transfer resistance of the organic electrolyte/LiMn2O4 interface. This indicates that there should be a compatible electrode and LiPON film electrolyte combination to obtain an effective decrease in the charge-transfer resistance. Charge-discharge tests revealed that the resultant film battery repeated stable charge-transfer reaction on its cycling compared with the organic electrolyte system. Also, this electrochemical stability was maintained at a high temperature (333K), which is probably because the formation of the LiMn2O4/LiPON interface inhibited Mn dissolution from the LiMn2O4 thin-film electrode.