(Invited) Composition and Interfacial Engineering of Lithium Iron Orthosilicate Cathodes with Superior Intercalation Properties

摘要

The quest for Li-ion batteries (LIBs) delivering higher energy density while being safer and sustainable has intensified recently. This work presents our advances towards improving the intercalation properties of an important cathode material, Li_2FeSiO_4(LFS), in order to take advantage of its attractive properties in terms of sustainability and safety. LFS theoretically has 330 mAh g~(-1) capacity (2 Li~+ per formula unit), however, inherently it exhibits relatively poor Li-ion intercalation kinetics, interfacial reactivity and complex phase transitions resulting in lower than one Li~+ storage and poor capacity retention. In this work, we apply a multi-prong strategy to overcome these obstacles making use of compositional engineering to tune the electronic and crystal structures of LFS in concert withmechanochemical processing and polymer coating to provide a stabilizing interphase. We take advantage of the versatility of hydrothermal synthesis [1a] and mechanochemical activation and synthesize various cation-substituted and non-stoichiometric LFS nanomaterials with annealed orthorhombic Pmn2_1structure. Firstly, mechanochemical annealing leads to activation of Li-ion diffusion (D_(Li)) by one order of magnitude enhancement [2a,b]. Secondly, partial substituting Co for Fe is found to allow faster phase transformation from pristine Pmn2_1 to inverse Pmn2_1 with important positive ramifications in its cycling performance [1b]. Thirdly, we boost the capacity of LFS, bydesigning Fe-rich (and not Li-rich!) LFS materials that deliver higher capacity within a reasonable voltage window [1c]. Lastly, PEDOT coating and near the surface composition alteration allows for stable cycling performance with >1.2 Li capacity [2c].