Achieving the High Capacity and High Stability of Li‐Rich Oxide Cathode in Garnet‐Based Solid‐State Battery

Solid‐state batteries (SSBs) based on Li‐rich Mn‐based oxide (LRMO) cathodes attract much attention because of their high energy density as well as high safety. But their development was seriously hindered by the interfacial instability and inferior electrochemical performance. Herein, we design a three‐dimensional foam‐structured GaN−Li composite anode and successfully construct a high‐performance SSB based on Co‐free Li1.2Ni0.2Mn0.6O2 cathode and Li6.5La3Zr1.5Ta0.5O12 (LLZTO) solid electrolyte. The interfacial resistance is considerably reduced to only 1.53 Ω cm2 and the assembled Li symmetric cell is stably cycled more than 10,000 h at 0.1–0.2 mA cm−2. The full battery shows a high initial capacity of 245 mAh g−1 at 0.1 C and does not show any capacity degradation after 200 cycles at 0.2 C (≈100 %). The voltage decay is well suppressed and it is significantly decreased from 2.96 mV/cycle to only 0.66 mV/cycle. The SSB also shows a very high rate capability (≈170 mAh g−1 at 1 C) comparable to a liquid electrolyte‐based battery. Moreover, the oxygen anion redox (OAR) reversibility of LRMO in SSB is much higher than that in liquid electrolyte‐based cells. This study offers a distinct strategy for constructing high‐performance LRMO‐based SSBs and sheds light on the development and application of high‐energy density SSBs. We successfully constructed a high‐performance solid‐state battery based on Li‐rich Li1.2Ni0.2Mn0.6O2 cathode, Li6.5La3Zr1.5Ta0.5O12 solid electrolyte and GaN‐modified Li anode. The assembled Li symmetric cell shows quite low interfacial resistance and great interfacial stability, and the full battery shows a high initial capacity, a high capacity retention, a high rate capability and a significantly mitigated voltage decay demonstrating a great potential in high energy density solid‐state battery.