Amorphous titanium oxide passivated lithium titanium phosphate electrode for high stable aqueous lithium ion batteries with oxygen tolerance

- A feasible sol-gel process for amorphous TiO2 coating layer has been applied on LiTi2(PO4)3 anode film.
- The surface protection by the electrically insulated TiO2 layer can suppress the side reactions on anode.
- The electric conductivity of the outermost layer is not necessary.
- The oxygen tolerant stability enhancement by the protection layer is due to the physical encapsulation and ionic conductivity.

Undesirable side reactions at interface usually ruin the electrode stability and lead to serious self-discharge or decrease the coulombic efficiency. An ionic permeable and electronic insulating amorphous TiO2 passivation could be deposited on the carbon encapsulated LiTi2(PO4)3 electrode through sol-gel method, which drastically enhance the aqueous electrode stability and oxygen tolerance in wide potential window by kinetically suppressing the side reactions at new formed interface. Raman depth profile and SEM have confirmed this surface coating, while nanoelectronic conductivity analysis reveal the TiO2 layer is electronically insulate. The capacity retention of the TiO2 passivated carbon encapsulated LiTi2(PO4)3/LiNO3/LiMn2O4 coin cell for 2000 cycles is 66% assembled in ambient air, which is higher than 55% for the one without TiO2 coating. Electrochemical investigation suggests the TiO2 layer is Li+ ionic conductive, which suppressed the surface water reduction or oxygen reduction reaction. As an interestingly result, the cell stability improvement also benefited from the less degradation of the LiMn2O4 counter electrode. This comprehensive understanding of the electrode passivation using an ionic conductive layer can be potentially applied in other electrochemical devices.