Lithium-ion battery cathode materials have relied on cationic redox reactions until the recent discovery of anionic redox activity in Li-rich layered compounds which enables capacities as high as 300 mAh g⁻¹. In the quest for new high-capacity electrodes with anionic redox, a still unanswered question was remaining regarding the importance of the structural dimensionality. The present manuscript provides an answer. We herein report on a β-Li₂IrO₃ phase which, in spite of having the Ir arranged in a tridimensional (3D) framework instead of the typical two-dimensional (2D) layers seen in other Li-rich oxides, can reversibly exchange 2.5 e⁻ per Ir, the highest value ever reported for any insertion reaction involving d-metals. We show that such a large activity results from joint reversible cationic (Mⁿ⁺) and anionic (O₂)ⁿ⁻ redox processes, the latter being visualized via complementary transmission electron microscopy and neutron diffraction experiments, and confirmed by density functional theory calculations. Moreover, β-Li₂IrO₃ presents a good cycling behaviour while showing neither cationic migration nor shearing of atomic layers as seen in 2D-layered Li-rich materials. Remarkably, the anionic redox process occurs jointly with the oxidation of Ir⁴⁺ at potentials as low as 3.4 V versus Li⁺/Li⁰, as equivalently observed in the layered α-Li₂IrO₃ polymorph. Theoretical calculations elucidate the electrochemical similarities and differences of the 3D versus 2D polymorphs in terms of structural, electronic and mechanical descriptors. Our findings free the structural dimensionality constraint and broaden the possibilities in designing high-energy-density electrodes for the next generation of Li-ion batteries.

锂离子电池阴极材料一直依赖于阳离子氧化还原反应，直到最近在富含锂的层状化合物中发现阴离子氧化还原活性为止，该活性使得容量高达300 mAh g ^-1。在寻求具有阴离子氧化还原作用的新的高容量电极时，关于结构尺寸的重要性仍未得到回答。本手稿提供了答案。本文我们上的β-栗报告₂的IrO ₃相中，尽管具有的IR布置在三维（3D）框架，而不是典型的两维（2D）在其他富锂氧化物可见的层，可以可逆地交换2.5ë ^-每铱，最高值曾报道任何插入反应涉及d-金属。我们表明，这样从关节可逆阳离子（M大活性导致^{Ñ +}）和阴离子（O ₂）^{ñ -}氧化还原过程，后者具有经由互补透射电子显微镜和中子衍射实验可视化，并且通过密度泛函理论计算证实。此外，β-栗₂的IrO ₃的礼物而表示既不阳离子迁移也不如在2D-层状富锂材料看出原子层的剪切良好的循环性能。值得注意的是，阴离子氧化还原过程与Ir ⁴⁺的氧化一起在相对于Li ⁺ / Li ^0的低至3.4 V的电势下发生作为等效在层状α-栗观察到₂的IrO ₃多晶型物。理论计算阐明了3D和2D多晶型在结构，电子和机械描述符方面的电化学相似性和差异。我们的发现释放了结构尺寸上的限制，并拓宽了为下一代锂离子电池设计高能量密度电极的可能性。