Suppression of Na ion intercalation via LATP ceramic electrolyte in Li-Na hybrid ion batteries

The Li-Na hybrid batteries are composed of Li cathode (ex. LiFePO₄) and Na metal anode which can reduce developing cost of cathode materials and material cost for the anode. However, in the Na/LiFePO₄ system, Na intercalation into LiFePO₄ and formation of NaFePO₄ cause instability of the cathode due to the intercalation of large Na-ion, leading to poor cyclability of the hybrid battery. LATP (Li_1+xAl_xTi_2-x(PO₄)₃) ceramic electrolyte can conduct only Li-ion. In this study, LATP is applied for the Na/LiFePO₄ hybrid battery for the first time to prevent Na intercalation into LiFePO₄. Thin PVDF-HFP-based polymer electrolytes are coated on LATP. The coating layer effectively protects LATP from reduction by Na metal anode and reduces the interfacial impedance. After discharging Na/polymer-coated LATP/LiFePO₄ cell, only LiFePO₄ is formed in the cathode, indicating Na-ion flux from Na metal anode is blocked by the LATP layer and the Na intercalation is prevented. As a result, cyclability of the hybrid battery is drastically improved. The discharge capacity at the first and 100th cycle is 145.0 and 149.6 mAh g^-1, respectively with average Coulomb efficiency of 99.7%. The novel hybrid cell using a ceramic electrolyte is a promising configuration for the Li-Na hybrid battery.