Heating-temperature-dependent electrochemical-performance-enhanced surface structural evolution during chemical treatment of Li-rich layered material by sodium thiosulfate

Chemical activation of Li-rich layered oxide (LLO) is an effective way to mitigate the intrinsic drawbacks of LLO. Herein, the Li-rich layered material 0.25Li2MnO3·0.75LiMn0.42Ni0.48Co0.1O2, which has a relatively higher Ni content, is treated with a common reducing substance sodium thiosulfate (Na2S2O3) over a wide range of heating temperature (300 °C, 500 °C, 750 °C). The experimental results demonstrate that: (1) Na2S2O3 can successfully pre-activate LLO by extracting Li+ out of the material to form LiNaSO4, (2) the pre-activated material shows a high correlation with the heating temperature of this treatment, that is, with the increase of heating temperature from 300 °C to 750 °C the spinel-to-layered phase transition takes place in the particle surface region. This unusual structural evolution is in fact associated with the enrichment of Ni element in particle surface region, meanwhile leads to a remarkable improvement of each electrochemical performance. Hence, this high temperature surface treatment by Na2S2O3 is anticipated to be an effective strategy to pre-activate the Li-rich layered material so that overcomes its intrinsic drawbacks to some extent. [Display omitted] •A common reducing substance Na2S2O3 is used for treating Li-rich layered material.•The surface structure shows high correlation with heating temperature of treatment.•An unusual spinel-to-layered phase transition takes place in particle surface region.•Electrochemical performances are notably improved after high temperature treatment.