Engineering crystal facets to enhance their functionalities often require complex processing routes to suppress the growth of surfaces with the lowest thermodynamic energies. Herein, we report a unique method to control the morphologies of β-MnO₂ crystals with different occupancy of {100}/{111} facets through the effect of K⁺ cations. Combining aberration-corrected scanning transmission electron microscopy (STEM), ultramicrotomy, and dynamic functional theory (DFT) simulation, we clarified that the β-MnO₂ crystals were formed through a direct solid-state phase transition process. Increasing the concentration of K⁺ cations in the precursor gradually changed the morphology of β-MnO₂ from bipyramid prism ({100}+{111} facets) to an octahedron structure ({111} facets). The K⁺ cations controlled the morphology of β-MnO₂ by affecting the formation of α-K_0.5Mn₄O₈ intermediate phase and the subsequent phase transition. Utilizing the β-MnO₂ crystals as the cathode for Li-ion batteries showed that highly exposed {111} facets offered β-MnO₂ crystal better rate performance, with ~70% capacity retention when the charge-discharge rate increased from 20 mA/g to 200 mA/g. Our work revealed a new mechanism to tune the morphology of this earth-abundant metal oxide crystal, which could be used to adjust its electrochemical performance for different applications, such as supercapacitors and catalysts for metal-air batteries and fuel cells.

为了提高其功能性而对晶体面进行工程处理通常需要复杂的工艺路线，以抑制具有最低热力学能量的表面的生长。此，我们报告来控制β-MnO的的形貌的独特方法_2个晶体通过K的效果不同占用{100} / {111}面的⁺阳离子。组合像差校正扫描透射电子显微镜（STEM），超薄切片，并动态函数理论（DFT）模拟，我们澄清，β-MnO的₂晶体通过直接固态相变过程形成。增加K的浓度⁺在前体阳离子逐渐改变的形态β-MnO的₂从双锥棱镜（{100} + {111}面）到八面体结构（{111}面）。在K ⁺阳离子控制β-MnO的形态₂通过影响α-K的形成_0.5的Mn ₄ ø ₈中间阶段和随后的相变。利用β-MnO的₂晶体作为阴极为锂离子电池表明，高度暴露的{111}面提供β-MnO的₂充放电速率从20 mA / g增加到200 mA / g时，晶体具有更好的速率性能，容量保持率约为70％。我们的工作揭示了一种调节这种富含地球的金属氧化物晶体形态的新机制，该机制可用于调整其电化学性能以用于不同的应用，例如用于金属-空气电池和燃料电池的超级电容器和催化剂。