The success of K-ion battery technology will rely on the development of robust cathode materials that can incorporate and shuttle large amounts of K reversibly. Recent experimental work has demonstrated the viability of layered KCrO₂ as a cathode material for K-ion batteries; however, some fundamental details of structural phase transitions and K ordering during cycling remain unknown. We report on a first-principles thermodynamic investigation of layered K_xCrO₂ (0 ≤ x ≤ 1) in the O3 and P3 host structures. We predict that P3 is preferred at intermediate x, with the stable K orderings belonging to staircases of phases that contain antiphase boundaries between ordered regions. Varying densities of these boundaries allow for smooth changes in composition. At high x, we predict the stability of “M” phases containing a mixture of octahedral and prismatic K coordination within each layer, which is accommodated by undulations of the oxide host. Our calculated voltage curve and analysis of structural evolution indicate that the predicted phase stability, including the formation of the M phases, is mostly compatible with experimental observations.

中文翻译：

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K离子电池层状K _x CrO ₂的有序化和结构转变

钾离子电池技术的成功将依赖于坚固的阴极材料的开发，该材料可以可逆地掺入和穿梭大量的钾。最近的实验工作证明了层状KCrO ₂作为K离子电池正极材料的可行性。然而，在循环过程中结构相变和K有序性的一些基本细节仍然未知。我们分层K的第一性原理热力学调查报告_X的CrO ₂（0≤ X在O3和P3主体结构≤1）。我们预测在中间x时P3是首选，其中稳定的K阶属于相的阶梯，这些阶的阶之间包含反相边界。这些边界的变化密度允许组成的平滑变化。在高x处，我们预测每一层中包含八面体和棱柱形K配位混合物的“ M”相的稳定性，该稳定性由氧化物主体的起伏提供。我们计算的电压曲线和结构演化分析表明，预测的相稳定性（包括M相的形成）与实验观察结果基本相符。