Lower Interfacial Resistance between a Ta-Doped Li7La3Zr2O12 (LLZTO) Solid Electrolyte and NiCl2 Cathode by a Simple Heat Treatment for a High-Specific Energy Thermal Battery

Large current discharge is restricted because of the poor conductivity between the Ta-doped Li7La3Zr2O12 (LLZTO) solid electrolyte and electrode. The poor conductivity would be caused by the interfacial reaction between LLZTO and the cathode, which is detrimental to the secondary Li ionic or metal battery. In this case, we studied the interfacial reaction between LLZTO and a haloid cathode (NiCl2) for a thermal battery for the first time, and a lower interfacial resistance could be obtained by a simple heat treatment. Owing to the element interdiffusion of Cl- and O2- at a high temperature of 600 °C, the main reaction products are LaOCl, LiCl, and La2Zr2O7. This reaction reduces the interfacial resistance from 3 Ω to 2 Ω. After a pretreatment at 600 °C, the discharge specific energy could reach 1254 Wh kg-1 from 828 Wh kg-1 at 550 °C with a cut-off voltage of 1.8 V. These results suggest that the interfacial reaction could be significant for the battery by adding interfacial contact. It is an effective approach to decrease the interfacial resistance at high temperature for some specific system, such as a haloid cathode-solid electrolyte.