Enhanced electrochemical performance of bulk type oxide ceramic lithium batteries enabled by interface modification

Abstract

The interface issue is one of the severe problems in all-solid-state (ASS) batteries, especially for oxide-type batteries with a full ceramic structure. Rigid interfacial contact between electrodes and electrolyte and poor mechanical properties of ceramics limit the choices of applicable materials and fabrication processes for ASS batteries. In this report, a bulk type ASS lithium battery with an initial discharge capacity of 112.7 mA h g⁻¹ is successfully fabricated. A garnet-structured Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZO-Ta) ceramic pellet is used as the solid electrolyte. A slurry of a composite cathode consisting of Li[Ni_0.5Co_0.2Mn_0.3]O₂, In_2(1−x)Sn_2xO₃, Li₃BO₃, and polyvinylidene fluoride was tape-cast on the LLZO-Ta pellet and annealed to improve the interfacial contact among the particles in the composite cathode as well as between the composite cathode and the electrolyte pellet. Without the surface modification of a Li[Ni_0.5Co_0.2Mn_0.3]O₂ active material, an obvious degradation of discharge capacity due to polarization is observed during cycling. When a layer of a Li–Ti–O precursor is coated on the surface of Li[Ni_0.5Co_0.2Mn_0.3]O₂ particles, in situ spinel Li[Ti_0.1Mn_0.9]₂O₄ is formed at the surface after annealing, leading to an enhancement of discharge capacity of the battery and great improvement for cycling stability. This novel method of interface modification reduces the interfacial polarization with an enhanced Li⁺ transfer between the cathode and the electrolyte. Our experimental results reveal that the interface engineering by means of reasonable regulation on the surface constituent of electrode materials can effectively improve the capacity and cycling stability of ASS lithium batteries.