Amorphous Na_0.7CoO₂–Na_xMO_y (M = N, S, P, B, or C) positive electrode active materials were synthesized by a mechanochemical technique to achieve high capacities and improved cyclabilities owing to their open and random structures. As none of the X-ray diffraction peaks are attributable to the starting materials, it was clear that the reaction between Na_0.7CoO₂ and Na_xMO_y had been successful. The prepared Na_0.76Co_0.8N_0.2O_2.2 (80Na_0.7CoO₂·20NaNO₃ (mol %)) was easily densified by pressing at room temperature, and then applied as a positive electrode in bulk-type all-solid-state sodium cells (Na₁₅Sn₄/Na₃PS₄ glass-ceramic/Na_0.7CoO₂–Na_xMO_y). The cell based on the Na_0.76Co_0.8N_0.2O_2.2 active material without any conductive additives in an ultrathick positive electrode layer (∼50 μm thickness) operated as a secondary battery at 25 °C. The average discharge voltage was 2.9 V, and the initial discharge capacity was 70 mAh g⁻¹ of the positive electrode. This cell exhibited a higher discharge voltage and a larger capacity than cells employing crystalline Na_0.7CoO₂ or milled Na_0.7CoO₂ as the positive electrode. The electrochemical properties of Na_0.7CoO₂ were therefore improved by amorphization with NaNO₃. Furthermore, the cell with the composite electrode containing a conducting additive gave a discharge capacity of 170 mAh g⁻¹ of Na_0.76Co_0.8N_0.2O_2.2, which is the highest reported to date for all-solid-state sodium cells based on oxide positive electrodes. Therefore, the amorphization of layered transition-metal oxides with sodium oxy-acids is an effective way to achieve novel active materials with high capacities.

中文翻译：

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高容量全固态钠电池用氧化钴钠活性材料的非晶化

通过机械化学技术合成了非晶态Na _0.7 CoO ₂ -Na _x MO _y（M = N，S，P，B或C）正极活性材料，由于其开放和无规的结构，可实现高容量和改善的循环性。由于没有X射线衍射峰可归因于原料，因此很明显Na _0.7 CoO ₂和Na _x MO _y之间的反应是成功的。制备的Na _0.76 Co _0.8 N _0.2 O _2.2（80Na _0.7 CoO ₂ ·20NaNO ₃（mol％））易于通过在室温下压制而致密，然后用作块型全固态钠电池（Na ₁₅ Sn ₄ / Na ₃ PS ₄玻璃陶瓷/ Na _0.7 CoO _2）中的正极。–Na _x MO _y）。基于Na _0.76 Co _0.8 N _0.2 O _2.2活性材料的电池，在超厚正极层（厚度约50μm）中，不含任何导电添加剂，可在25°C下用作二次电池。平均放电电压为2.9V，初始放电容量为70mAh g ^-1正极。与使用结晶Na _0.7 CoO ₂或研磨的Na _0.7 CoO ₂作为正极的电池相比，该电池表现出更高的放电电压和更大的容量。因此，通过NaNO ₃的非晶化改善了Na _0.7 CoO ₂的电化学性能。此外，具有包含导电添加剂的复合电极的电池的Na _0.76 Co _0.8 N _0.2 O _2.2的放电容量为170 mAh g ^-1，这是迄今为止基于氧化物正极的全固态钠电池的最高报道。因此，层状过渡金属氧化物用钠氧基酸的非晶化是获得具有高容量的新型活性材料的有效方法。