Durable high voltage solid-state sodium batteries with Pseudocapacitive P2 layered oxide cathode

Solid-state sodium batteries (SSBs) have attracted great interests due to their high energy density, good safety and low cost, but their performance including operation voltage, cycling stability and rate capability are far from satisfactory. In this study, a P2-Na0.68Li0.10Ni0.25Mn0.63Ca0.01Ti0.01O2 (NM-L10CT) layered cathode material were successfully fabricated, which possesses a high pseudocapacitance over 92 %, low volume strain of 0.8 %, high Na-ion diffusion coefficient and very good reversibility of anionic redox reaction. Moreover, room temperature solid-state sodium batteries with NM-L10CT and Na3Zr2Si2PO12 (NZSP) solid electrolyte are demonstrated, displaying much improved structural stability and cycling performance compared with that in liquid electrolyte batteries. The NM-L10CT/NZSP/Na SSBs exhibit very excellent electrochemical performance under high cut-off voltage, with high retention rates of 81.2 % after 500 cycles (2.0-4.2 V) and 74.2 % after 300 cycles (2.0-4.3 V), respectively. It has an outstanding rate performance with a high capacity of 115.4 mAh g(-1) at 1 C and 74.5 mAh g(-1) even at 10 C rate. This is due to the significantly reduced interface resistance and improved structural stability in solid state. This work demonstrates the successful application of high voltage layered cathode in SSBs and provides the insightful understanding of such material in liquid electrolyte and solid state battery.