Stability Investigation of Inorganic Li Conductors As Protective Layers for Li-Air Batteries

The development of Li-air battery has received great attention recently. However, using metallic lithium directly as an anode has been challenging due to the high reactivity of Li. Protective coatings with ionic conduction on metallic Li has be proposed to overcome this problem. Inorganic Li ion conductors may be suitable for being used as the protection layer.

NASCION-type LiTi₂(PO₄)₃ and perovsikte-La_0.50Li_0.50TiO₃ are known to be inorganic solid electrolytes with adequate conductivity in a range of 10^-3 S/cm after required modification. However, Li tends to react with La_0.56Li_0.33TiO₃ due to the incorporation of the released electrons with Ti⁺⁴ ions. Simultaneously, Li⁺ ions will migrate into the vacant sites in the cation sublattice. As a result, La_0.50Li_0.50TiO₃ perovsikte becomes a mixed ionic/electronic conductor after reacting with Li. On the other hand, limited reaction was observed on the Li_1+xAl_xTi_2-x(PO₄)₃ electrolyte when the metallic Li was used as the anode.

In order to improve the stability of Li_1+xAl_xTi_2-x (PO₄)₃, a concept of composite electrolyte based on NASCION-type LiTi₂(PO₄)₃ and perovsikte-La_0.50Li_0.50TiO₃ is proposed. With proper mixing and distribution of these two electrolytes, a better stability from the composite electrolyte is expected.

Thus, the objective of this work is (1) to develop a composite electrolyte based on the mixture of Li_1+xAl_xTi_2-x (PO₄)₃, and La_0.50Li_0.50TiO₃, (2) to analyze the interface reaction between two components of composite cathode, (3) to investigate the electrical conduction/stability of composite as a function of volume fraction, grain size, and thickness, (4) to evaluate the feasibility of using composite electrolyte for Li-Air battery. The stability of composite electrolyte will be determined based on the measurement of the induced electronic conductivity and the open circuit voltage after a Li-air cell is assembled.