Preparation of high-performance copper fluoride cathode material for thermal batteries: effect of heat treatment temperature of precursor ammonium copper fluoride

A copper fluoride with small size and high purity is very important to present its ability as a cathode material for lithium thermal batteries (LTBs). In this paper, we investigate the effect of the heat treatment temperature of the precursor ammonium copper fluoride on the preparation of a high-performance copper fluoride cathode. The color of CuF₂ gradually changes from white to dark brown as the heat treatment temperature of the ammonium copper fluoride precursor is increased due to the change in dimensions and morphology. The CuF₂-250 prepared at the heat treatment temperature of 250 ℃ has a small D50 particle size of 1.838 µm (agglomeration of particles from 50 to 100 nm), high purity, large BET surface area of 16.3649 m²/g, and excellent working properties. Its operating voltage reached as high as 3.5 V in the initial activation stage at a discharge current density of 500 mA/g, which is attributed to the better conductivity caused by its small size favorable shortened Li⁺ diffusion path, and its specific capacity and discharge time at the cut-off voltage of 1.5 V were 498 mAh/g close to 94% of the theoretical specific capacity (528 mAh/g) and ultralong 3585 s, respectively. This study provides a guideline for the development of high-performance cathode materials for LTBs.