Structural and electrochemical investigation of lithium ions insertion processes in polyanionic compounds of lithium and transition metals

The paper considers approaches to the synthesis as well as the structural and electrochemical properties of lithium and transition metals polyanionic compounds as promising cathode materials for lithium-ion battery. The characteristics of lithium and transition metals sulfates are considered, among which iron-lithium sulfate and a composite electrode material Li2Fe(SO4)(2)/C based on it was selected for further detailed study. The relationships between the synthesis conditions and the structural and electrochemical characteristics of the material were revealed. Based on the structural data the computational method of the bond valence strengths (BVS) applying the bond valence energy landscape algorithm (BVEL) provided activation energy maps of lithium ion migration in the Li2Fe(SO4)(2) crystal structure. The method of scanning electron microscopy (SEM) made it possible to characterize the morphological state of the material, to determine the particle size distribution, which were then used to determine the geometry of the diffusion space of particles. Applying the electrochemical kinetics investigation methods (CV, GITT, EIS) the parameters of lithium ion transport in the electrodes were determined. The quasi-equilibrium E(c) dependence of the Li2Fe(SO4)(2)/C electrode was obtained, this dependence was simulated using an approach based on the Frumkin intercalation isotherm and the lattice gas model, and the thermodynamic characteristics of the interparticle interaction in the material were obtained. The diffusion coefficient of lithium ions D in the material was estimated using the CV method: 1.6.10(-15) cm(2).s(-1) in the anodic half cycle and 10-(15) cm(2).s(-1) in the cathodic half cycle, respectively. The dependences of D on the lithium ion concentration in the intercalate and electrode potential were obtained using GITT and EIS methods, a comparison of these methods results was performed. (C) 2020 Elsevier B.V. All rights reserved.