Tuning the cathodic-anodic electrochemical transition in lithium iron borate by optimizing synthesis parameters, anionic doping and potential window

Abstract

This report presents a comprehensive investigation into the transformation of a high-capacity LiFeBO3 cathode material to an anode material by fluorine doping. The structural and electrochemical studies of LiFeBO3 are investigated in detail with respect to synthesis temperature, anion doping, and specific potential windows. Lowering the synthesis temperature preserves the monoclinic structure of the material, allowing a higher specific capacity close to 200 mAh g−1 within the potential window of 1.5–4.0 V. However, higher synthesis temperatures leads to the degradation of the monoclinic structure, subsequently reducing the specific capacity to 114 mAh g−1, even though the slurry processing is carried out in an inert atmosphere. The introduction of 10 % fluorine doping induces a complete transformation of the monoclinic structure into a vonsenite-type phase. Surprisingly, the vonsenite-type material exhibits a drastically reduced cathodic capacity of 11 mAh g−1 within the aforementioned potential window. Nevertheless, it displays promising anodic behavior when operated below 2.5 V, demonstrating its potential for application as a conversion-type anode in Li-ion batteries. The crystal structure of the composite material is found to contain LiF and Li–B–O phases, contributing to an extended cycle life compared to undoped carbon-coated Fe3BO5. The cyclability of the anode material is further enhanced by the use of sodium carboxymethyl cellulose (Na-CMC) as a binder and fluoroethylene carbonate (FEC) as an electrolyte additive. Overall, this study furnishes valuable insights into the structural modifications and electrochemical performance of a LiFeBO3 cathode transformed into a fluorine-doped anode material. These findings contribute to the synthesis strategies for novel electrode materials, opening up new avenues for the design and development of advanced Li-ion battery systems with improved performance and longevity.