Effect of the Ammonium Copper Fluoride Precursor on Formation of High-Performance Copper Fluoride Cathode Material for Thermal Battery

Abstract A high-performance copper fluoride cathode material with high operating voltage and discharge specific capacity is very attractive for lithium thermal batteries (LTBs). This study investigated the effect of ammonium copper fluoride precursors on the formation of nanoscale copper fluoride (CuF2) cathode materials. Density functional theory calculations were used to analyze structural changes and energy variations during discharge. Results show that smaller precursor particles facilitate the formation of nanoscale CuF₂ with a tendency for aggregation. The CuF₂-35 material, synthesized at 35°C, exhibits a nanoscale structure with nanopores of 2-10 nm and 25-45 nm (1:6 ratio). When combined with carbon nanotubes (CNTs), CuF₂-35/CNTs demonstrate a discharge specific capacity of 508.6 mAh g-1 (96% of theoretical capacity) and a discharge specific energy of 1363.48 Wh kg-1 at 300 mA g-1 with a 2.0 V cutoff. The discharge process involves an interfacial step followed by two sequential electrochemical reactions: the conversion of Cu²⁺ to Cu⁺ and subsequently Cu⁺ to Cu. These findings highlight CuF2 as an excellent cathode material for LTBs, offering high capacity, energy density, and a well-defined discharge mechanism. The results indicate that copper fluoride is an excellent cathode material for LTBs.