Layered transition metal oxides are the most important cathode materials for Li/Na/K ion batteries. Suppressing undesirable phase transformations during charge-discharge processes is a critical and fundamental challenge towards the rational design of high-performance layered oxide cathodes. Here we report a shale-like NaxMnO2 (S-NMO) electrode that is derived from a simple but effective water-mediated strategy. This strategy expands the Na+ layer spacings of P2-type Na0.67MnO2 and transforms the particles into accordion-like morphology. Therefore, the S-NMO electrode exhibits improved Na+ mobility and near-zero-strain property during charge-discharge processes, which leads to outstanding rate capability (100 mAh g−1 at the operation time of 6 min) and cycling stability (>3000 cycles). In addition, the water-mediated strategy is feasible to other layered sodium oxides and the obtained S-NMO electrode has an excellent tolerance to humidity. This work demonstrates that engineering the spacings of alkali-metal layer is an effective strategy to stabilize the structure of layered transition metal oxides.

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Solid electrolyte interface (SEI) is considered as one of the most important factors determining the electrochemical performance of lithium-ion batteries. Here we introduce 31 P nucleus as a probe to detect the formation and composition of SEI on Si anode. Through detecting the phosphorus compound forming on the Si anode by 31 P NMR, a decomposition mechanism of the new addives is proposed.

富锂正极材料 xLi 3 NbO 4 •(1-x)LiMO 2 (M＝Mn, Co; 0＜x＜1)的制备及 电化学性能研究 杨春 a 龚正良 * ,a 赵文高 a 杨勇 * ,a,b (a 厦门大学能源学院 厦门 361005) (b 厦门大学化学化工学院 固体表面物理化学国家重点实验室 厦门 361005) 摘要 采用高温固相法合成了含铌富锂材料 xLi 3 NbO 4 •(1-x)LiMnO 2 (0＜x＜1), 研究了 Li 3 NbO 4 含量对其结构和性能 的影响. X 射线衍射分析结果表明当 x 取值在 0.25～0.67 之间时可得到纯相固溶体材料, 属立方晶系, 为 Fm-3m 空间群. x＝0.25 和 x＝0.43 的材料具有较好的电化学性能, 首次放电容量可达 216 mAh•g-1 , 但是两者都表现出明显的电压衰 退, x＝0.43 的材料由于含有更多的 Li 3 NbO 4 组分, 电压衰减的情况得到了抑制. x＝0.43 材料的非原位 XPS 和 XAFS 研 究表明, 其充电过程分为两个阶段, 4.3 V 以下的阶段发生的电化学过程是脱出 Li ＋ 同时 Mn 3＋ 被氧化到 Mn 4＋ , 4.3 V 以上 的阶段则由 O 2-的氧化来提供电荷补偿. 通过对 x ＝ 0.43 的样品进行钴掺杂, 考察了钴掺杂对 0.43Li 3 NbO 4 • 0.57LiMn 1-y Co y O 2 (y＝0.25, 0.5