Among the potential cathode candidates for Na-ion batteries (NIBs), Na-based layered transition-metal oxides hold the greatest promise by virtue of their appropriate energy density, environmental benignity, and affordable synthesis. However, the theoretical energy density of most layered oxide cathodes is limited as their charge compensation process relies solely on the cationic redox of transition-metal (TM) ions. To break this shackle, anionic redox has emerged as a lever to improve the energy density of layered oxides. Herein, a systematic overview of the latest progresses on anionic-redox-active layered oxide cathodes is presented, with focus on the mechanism studies of anionic redox reaction. The practical challenges of anion redox in layered oxides are also summarized, and the possible solutions are suggested. In contrast to the Li-ion system, anion redox activity is uncovered for both Na-rich and Na-deficient layered oxides, and their underlying anionic reaction mechanisms exhibit many discrepancies. Moreover, the promise of utilizing sole anionic redox in NIBs with earth-abundant and low-cost elements is also considerable. This overview could provide robust guidance for further development of high-energy layered oxide cathodes with anionic redox activity.

在钠离子电池（NIB）的潜在阴极候选物中，基于钠的层状过渡金属氧化物具有适当的能量密度，环境友好性和可负担的合成能力，因此具有最大的前景。但是，大多数层状氧化物阴极的理论能量密度受到限制，因为它们的电荷补偿过程仅取决于过渡金属（TM）离​​子的阳离子氧化还原。为了打破这种束缚，阴离子氧化还原已成为改善层状氧化物能量密度的一种手段。在此，对阴离子-氧化还原-活性层状氧化阴极的最新进展进行了系统的概述，重点是阴离子氧化还原反应的机理研究。还总结了层状氧化物中阴离子氧化还原的实际挑战，并提出了可能的解决方案。与锂离子系统相反，富钠和缺钠的层状氧化物均未发现阴离子氧化还原活性，并且其潜在的阴离子反应机理表现出许多差异。此外，在富含地球和低成本元素的NIB中使用唯一的阴离子氧化还原的前景也很可观。该概述可以为进一步开发具有阴离子氧化还原活性的高能层状氧化物阴极提供强有力的指导。