P2-type Na_0.67Mn_0.6Ni_0.3Ti_0.1O₂ as cathode material for sodium-ion batteries: solid electrolyte versus liquid electrolyte

P2-type Na_0.67Mn_0.6Ni_0.3Ti_0.1O₂ is synthesized via a sol–gel method and its electrochemical performance is investigated as a cathode material for sodium-ion batteries (SIBs) employing both a Na₃Zr₂Si₂PO₁₂ solid electrolyte and an organic liquid electrolyte. In the liquid electrolyte cells, the Na_0.67Mn_0.6Ni_0.3Ti_0.1O₂ cathode exhibits a high discharge capacity of 87.5 mAh g⁻¹, with a capacity retention of 73.2% after 500 cycles at 0.1 C (10 mA g⁻¹), while in the solid electrolyte cells, a higher discharge capacity of 94.5 mAh g⁻¹ at 0.1 C and an improved high-rate capacity of 70.8 mAh g⁻¹ at 2 C are demonstrated. Moreover, stable charge/discharge cycles are observed in the solid electrolyte cells, with a discharge capacity of 75.3 mAh g⁻¹ and a retention of 60.7% over 100 cycles at 1 C. This work highlights the substantial effect of the electrolyte conditions on the performance of layered oxide cathode materials, providing potential strategies to overcome current challenges for high-performance SIBs.