Antifluorite-type Na5FeO4 as a low-cost, environment-friendly cathode with combined cationic/anionic redox activity for sodium ion batteries: a first-principles investigation抗萤石型Na5FeO4作为低成本,环境友好的阴极,具有用于钠离子电池的阳离子/阴离子氧化还原活性: 第一性原理研究RSC ADVANCESIF4.62022-01-014OAAI