The space-group change and surface degradation of spinel-type LiNi_0.5Mn_1.5O₄ upon the Li extraction reaction at 4.9 V were investigated using single-crystal samples. The stoichiometric LiNi_0.5Mn_1.5O₄ single crystals having an octahedral shape with 0.07 × 0.07 × 0.07 mm³ of the maximum size were synthesized via a self-flux method utilizing high-temperature molten chlorides, i.e., MnCl₂ and NiCl₂, at 750 °C. Single-crystal X-ray diffraction (XRD) structure analysis of LiNi_0.5Mn_1.5O₄ revealed the cubic P4₃32 space group, cell parameter of a = 8.1723(2) Å, and preferred occupation of the Ni atoms in two types of octahedral sites with occupancy values of 77.4% and 7.5% for the 4b and 12d sites, respectively. Moreover, electrochemical lithium extraction experiments were carried out using single-crystal LiNi_0.5Mn_1.5O₄ samples, and fully delithiated single-crystal samples were successfully obtained following charging at 4.9 V. Single-crystal XRD analysis of delithiated Ni_0.5Mn_1.5O₄ revealed the structural change from the P4₃32 space group to Fd3̅m, together with the cell parameter change to a = 8.0095(5) Å. The valence changes of the Ni atoms from +2 to +4 resulted in the apparent atomic disordering of Mn and Ni in the Ni_0.5Mn_1.5O₄ structure. Surface morphology changes of the single crystals were observed following charging at 4.9 V, suggesting the micrometer scale degradation originated from the lattice volume change upon the Li extraction reaction.

中文翻译：

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尖晶石型LiNi _0.5 Mn _1.5 O _4的单晶电化学提取锂的结构变化和形貌表面降解

使用单晶样品研究了在4.9V下Li萃取反应时尖晶石型LiNi _0.5 Mn _1.5 O ₄的空间群变化和表面降解。化学计量的LiNi _0.5锰_1.5 ø ₄具有0.07×0.07×0.07毫米的八面体形状的单晶³的最大尺寸的物通过利用高温的熔融氯化物自助熔剂法，即的MnCl合成₂和的NiCl ₂，在750℃。LiNi _0.5 Mn _1.5 O ₄的单晶X射线衍射（XRD）结构分析显示立方P 4₃ 32空间群，单元参数a = 8.1723（2）Å，并且优先选择两种类型的八面体位点中的Ni原子，其4b和12 d位点的占有率分别为77.4％和7.5％。此外，使用单晶LiNi _0.5 Mn _1.5 O ₄样品进行了电化学锂萃取实验，并在4.9 V充电后成功获得了完全脱锂的单晶样品。脱锂的Ni _0.5 Mn _1.5 O ₄的单晶XRD分析揭示了从P 4 ₃ 32空间群到FD 3米，连同小区参数变化到一个= 8.0095（5）。Ni原子从+2到+4的价态变化导致Ni _0.5 Mn _1.5 O ₄结构中Mn和Ni的表观原子无序。在4.9 V充电后观察到单晶的表面形态变化，这表明微米级的降解是由于Li萃取反应时晶格体积的变化引起的。