The mechanism of V-modification in Li2CoSiO4 cathode material for Li-ion batteries: A combined first-principles and experimental study

Lithium cobalt silicate Li2CoSiO4 (LCSO) is a unique cathode candidate that has the potential to simultaneously achieve both high energy-density and high safety. However, it was plagued with poor electrochemical performances owing to limited effective modification of its polymorphic and electronic structures. Functional groups modification has long been proven to be effective approaches for enhancing chemical/physical properties that are highly desirable for energy storage systems. Here the multivalent vanadium (V) doping to modify the tetrahedral functional groups in LCSO was proposed. Based on density functional theory calculations and experimental analysis, V prefers to be doped at Si site, which improves both the electronic and ionic conductivities of LCSO. First-principles modeling with Madelung matrix analysis reveals that the V3d-O2p orbital overlaps largely account for the reduction of the electronic energy gap by ∼1.40 eV and the lithium migration energy barrier by ∼0.20 eV Li2CoV0.1Si0.9O4/C shows the highest initial discharge capacity of 220.1 mAh g−1, compared to only 135.0 mAh g−1 for Li2CoSiO4/C. The discharge rate and cycling stability are also improved. Electrochemical impedance spectroscopy indicates that charge transfer resistance and Li diffusion resistance are reduced by 22.8% and 53.2%, respectively, after V-modification. © 2020 Elsevier Ltd