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Lithium-ion batteries (LIBs) have been widely used in various electronic devices. It has been realized that the surface/interface structures of electrode materials for LIBs are crucial to the electrochemical performance of those materials. Experimental evidence suggests that coatings made of Calcium Fluoride (CaF2) and Magnesium Fluoride (MgF2) improve LIB performance, but the information about the diffusion rate of Lithium in these materials (CaF2 and MgF2) is not yet known. This important information is needed to ensure that the coating material will not slow down the total reaction occurring in the battery system. We investigate Li diffusion in two coating materials for LIB cathode viz., MgF2 (space group: P42/mnm) and CaF2 (space group: Fm3m) by means of first-principles Density Functional Theory (DFT) calculations coupled with the Climbing Image Nudged Elastic Band (CI-NEB) method. We find that the lowest activation energy at the concentration of Li 4at% was 0.63 eV in CaF2 and 0.37 eV in MgF2. CaF2 has higher activation energy, which may be caused by a larger radius of Ca than Mg. The lower energy barrier indicates a higher diffusivity rate. This finding suggests that MgF2 gives a higher performance than CaF2. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) have been widely used in various electronic devices. It has been realized that the surface/interface structures of electrode materials for LIBs are crucial to the electrochemical performance of those materials. Experimental evidence suggests that coatings made of Calcium Fluoride (CaF2) and Magnesium Fluoride (MgF2) improve LIB performance, but the information about the diffusion rate of Lithium in these materials (CaF2 and MgF2) is not yet known. This important information is needed to ensure that the coating material will not slow down the total reaction occurring in the battery system. We investigate Li diffusion in two coating materials for LIB cathode viz., MgF2 (space group: P42/mnm) and CaF2 (space group: Fm3m) by means of first-principles Density Functional Theory (DFT) calculations coupled with the Climbing Image Nudged Elastic Band (CI-NEB) method. We find that the lowest activation energy at the concentration of Li 4at% was 0.63 eV in CaF2 and 0.37 eV in MgF2. CaF2 has higher activation energy, which may be caused by a larger radius of Ca than Mg. The lower energy barrier indicates a higher diffusivity rate. This finding suggests that MgF2 gives a higher performance than CaF2. [ABSTRACT FROM AUTHOR]