Potassium-ion batteries (KIBs) are promising candidates for large-scale energy storage due to the abundance of potassium and its chemical similarity to lithium. Nevertheless, the performances of KIBs are still unsatisfactory for practical applications, mainly hindered by the lack of suitable cathode materials. Herein, combining the strong inductive effect of sulphate and the feasible preparation of Fe²⁺-containing compounds in oxalate system, a compound with novel architecture, K₄Fe₃(C₂O₄)₃(SO₄)₂, has been identified as a low-cost and environmentally friendly cathode for stable potassium-ion storage. Its unique crystal structure possesses an unprecedented two-dimensional framework of triple layers, with 3.379 Å interlayer distance and large intralayer rings in the size of 4.576×6.846 Å. According to first-principles simulations, such a configuration is favorable for reversible K-ion migration with a very low volume change of 6.4%. Synchrotron X-ray absorption spectra and X-ray diffraction characterizations at different charging/discharging states and electrochemical performances based on its half and full cells further verify its excellent reversibility and structural stability. Although its performance needs to be improved via further composition tuning with multi-valent transition metals, doping, structural optimization, etc., this study clearly presents a stable structural model for K-ion cathodes with merits of low cost and environmental friendliness.

钾离子电池（KIB）由于钾的丰度及其与锂的化学相似性，有望成为大规模储能的候选材料。然而，KIB的性能对于实际应用仍然不能令人满意，主要是由于缺乏合适的阴极材料而受到阻碍。在此，结合硫酸盐的强诱导作用和在草酸盐体系中可行地制备含Fe ²⁺的化合物，一种结构新颖的化合物K ₄ Fe ₃（C ₂ O ₄）₃（SO ₄）₂，已被确定为低成本和环保阴极，可稳定地保存钾离子。其独特的晶体结构具有前所未有的三层二维框架，层间距离为3.379Å，且层内大环的尺寸为4.576×6.846Å。根据第一性原理模拟，这种配置有利于可逆的K离子迁移，其体积变化非常小，仅为6.4％。同步加速器的X射线吸收光谱和X射线衍射在不同的充电/放电状态下的表征以及基于半电池和全电池的电化学性能进一步证明了其优异的可逆性和结构稳定性。尽管其性能需要通过 通过使用多价过渡金属进行进一步的成分调整，掺杂，结构优化等，这项研究清楚地提出了一种稳定的K离子阴极结构模型，具有低成本和环境友好的优点。