Enhanced Capacity and Retention in Lithium Iron Orthosilicate Cathode Via Tuning Its Composition By Hydrothermal Synthesis

Abstract

During the past three decades, scientists have designed and tested a range of new materials for application in Li-ion batteries to meet the increasing energy storage demand. Still, the quest for delivering higher energy density while being safer and sustainable remains an ongoing challenge for Li-ion batteries. This work presents our recent efforts on improving an important cathode material, Li2FeSiO4 (LFS), in order to make use of its attractive properties in terms of sustainability and safety. We apply compositional engineering to tune the electronic and crystal structures of LFS and eventually its electrochemical performance. We take advantage of the versatility of hydrothermal synthesis and synthesize various cation-substituted and non-stoichiometric LFS in orthorhombic Pmn21 structure. Partially substituting Co for Fe is found to allow faster phase transformation from pristine Pmn21 to inverse Pmn21 with important positive ramifications in its cycling performance. More interesting, the insertion of Co alters the surface activities of LFS and induces the formation of cathode-electrolyte interphase (CEI) layers with lower resistance and better uniformity that protect the bulk particles from detrimental reactions with the electrolyte. Consequently, the participation of Co helps LFS to have improved capacity retention. To boost the capacity of LFS, we design Fe-rich LFS materials that deliver higher capacity within a reasonable voltage window. By combining DFT calculation with experimental testing, we find that Fe-rich composition LFS shows also promise in facilitating electronic and ionic transport.