The dynamic properties of λ-MnO 2 under strain can be different to normal conditions as lithium storage material. Results from firstprinciples calculations show that compressive strain will enhance the electrical conductivity and lithium ion diffusion coefficient simultaneously. We show that 7% compressive strain applied along the (011) direction leads to about two orders of magnitude increase in both the electrical conductivity and Li diffusion coefficient under room temperature. 7% compressive strain applied along the (111) direction will increase the Li diffusion coefficient by five orders of magnitude. These results are important to experimental and industrial preparation and design of λ-MnO 2 materials when interfaces are involved. The physical mechanism behind the strain induced improvement of the dynamic performance is discussed.
A stable interface is vital for the long cycling stability of nickel-rich material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811). As such, the common remedy to improve the stability of nickel-rich layered oxide is to adopt a coating strategy. However, most of the coating materials used in this strategy are often randomly oriented, which may pose challenges toward efficient Li + transportation from the electrolyte to the core material and vice versa. In this work, we demonstrate with the use of a CeO 2 shell with [011] exposed facets as a well-oriented coating material with a shorter straight Li + migration pathway and higher electronic conductivity to further improve the stability and rate performance of the nickel-rich layered oxide. As a result, our CeO 2 [011]-modified LiNi 0.8 Co 0.1 Mn 0.1 O 2 (1.0%-NCM811) showed improved electrochemical performance, especially in terms of rate capability. Cycling stability was also enhanced for tests conducted at room temperature and at an elevated temperature of 55 °C. The higher rate performance by our 1.0%-NCM811 may stem from the open shorter channels available in the [011] facet and the higher electrical conductivity. Based on this work, the orientation of the coating material is crucial as it could affect the rate capability of the core material drastically.
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