Sodium-ion batteries (SIBs) for grid-scale applications need active materials that combine a high energy density with sustainability. Given the high theoretical specific capacity 501 mAh g⁻¹, and Earth abundance of disodium rhodizonate (Na₂C₆O₆), it is one of the most promising cathodes for SIBs. However, substantially lower reversible capacities have been obtained compared with the theoretical value and the understanding of this discrepancy has been limited. Here, we reveal that irreversible phase transformation of Na₂C₆O₆ during cycling is the origin of the deteriorating redox activity of Na₂C₆O₆. The active-particle size and electrolyte conditions were identified as key factors to decrease the activation barrier of the phase transformation during desodiation. On the basis of this understanding, we achieved four-sodium storage in a Na₂C₆O₆ electrode with a reversible capacity of 484 mAh g⁻¹, an energy density of 726 Wh kg⁻¹ _cathode, an energy efficiency above 87% and a good cycle retention.

用于电网规模应用的钠离子电池（SIB）需要结合高能量密度和可持续性的活性材料。考虑到高的理论比容量501 mAh g ^-1和地球上丰富的重氮二钠（Na ₂ C ₆ O ₆），它是SIB最有希望的阴极之一。但是，与理论值相比，可逆容量大大降低，对这种差异的理解受到限制。在这里，我们揭示的Na不可逆相变₂ ç ₆ ö ₆循环期间的钠恶化氧化还原活性的起源₂ Ç ₆ Ò₆。活性颗粒尺寸和电解质条件被确定为降低脱氮过程中相变的活化势垒的关键因素。基于这种理解，我们在Na ₂ C ₆ O ₆电极中实现了四钠存储，可逆容量为484 mAh g ^-1，能量密度为726 Wh kg ^-1 _阴极，能量效率超过87％并具有良好的循环保持力。