No abstract

One of the most relevant negative characteristics of high-capacity cathodes for lithium batteries is indeed non-flat voltage-time (V-t) or voltage-capacity (V-C) behaviour during charge-discharge. A clear rationale for this behaviour has not yet been addressed in the literature. Here, by means of density functional theory (DFT) calculations corroborated by basic experimental electrochemical characterization, we investigated both the thermodynamic and the kinetic aspects relevant to voltage variations during charge-discharge of Li 2 FeSiO 4 intended as a model case. A simple physical model allowed us to take into account all the experimental evidence. We suggested that voltage deviations from its theoretical value are due to the formation of undesired delithiated structures caused by concentration gradients. We also related voltage behaviour to relevant quantities such as reaction energies, lithium diffusion coefficients, and particle size, so suggesting some strategies for optimization of materials. Methodology Experimental detailsLi 2 FeSiO 4 /C was synthesized by both nitrate sol-gel and solid state synthesis methods. For the sol-gel method, lithium † Electronic supplementary information (ESI) available: V-C diagrams of discharge measurements of our sample with different rates, and absolute value of slope of charge-discharge diagrams versus square root of the applied rates. See

Transition metal lithium orthosilicates are of interest as cathode materials for lithium batteries. Density functional theory (DFT) calculations were performed to evaluate the structural and electrochemical properties of the different polymorphs of Li 2 MnSiO 4 . Our computational studies predict superior properties for the Pmn2 1 polymorph even after extraction of two Li per formula unit. We state that the shortcomings observed for Li 2 MnSiO 4 as a cathode are caused by two mechanisms. Switching of the magnetic state occurs during the first cycles. The subsequent transition, under delithiated conditions, from the Pmn2 1 or Pmnb polymorphs to the electrochemically weakest P2 1 /n polymorph is the second mechanism that may gradually lead to electrochemical and structural collapse. A comparison with companion data obtained on Li 2 FeSiO 4 is also made.