Robust Surface Reconstruction Induced by Subsurface Ni/Li Antisites in Ni-Rich Cathodes

Loss of active materials is a critical problem of layered oxide cathodes for lithium-ion batteries and undermines their long-term electrochemical performance. However, the atomic-scale outward migration mechanism of transition metals and oxygen remains elusive due to a highly localized environment at surface. Here, the robust surface reconstruction of LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) induced by artificially introduced Ni/Li antisites is reported. Using scanning transmission electron microscopy, the outward co-migration process of nickel and oxygen ions is directly revealed at the atomic scale, finally resulting in a stable surface structure. The robust nature of this surface structure originates from the strong linear superexchange interaction between subsurface Ni_Li and surface Ni as supported by first-principles calculations. An idealized subsurface structure with $\frac{1}{3}$ Ni_Li is designed to suppress the outward migration of transition metal and oxygen ions and provide a universal lattice-coherent surface protection strategy for layered lithium transition metal oxide cathodes.     

优先流作用下的胶体-重金属共迁移试验研究

土壤中的重金属污染物大部分源自外界的工、农业排放,地表土层是重金属迁移至地下的必经途径。由于干缩和动植物活动,地表土中存在大孔隙,形成污染物运移的优势通道,在一些情况下,这些通道是重金属穿过包气带向下迁移的唯一途径。针对胶体对重金属具有较大吸附能力且在优先流条件下具有移动性,从而可能加快重金属污染物迁移这一问题,通过等温吸附试验确定了上海表层褐黄色粉质黏土与土壤胶体对重金属镉、铅的吸附特征,制备具有可重复性优先流特征的试验土柱,进行优先流条件下胶体-重金属共迁移土柱淋滤试验,分析得到胶体-重金属共迁移规律。试验结果表明,胶体对重金属的吸附能力明显高于粉质黏土。有胶体情况下,镉出流量是无胶体情况下镉出流量的1.49倍,铅的出流量是无胶体情况下的33.88倍,有胶体情况下土上吸附的重金属和孔隙溶液中的重金属浓度都低于无胶体的情况,更多的重金属随胶体向下迁移,优先流条件下胶体明显加快了重金属的迁移。虽然铅的源浓度和淋滤时间都大于镉,但铅的出流量仅约为镉的1/13,由于易发生吸附,铅在土中的迁移能力较弱。