State-of-the-art lithium-ion technology is based upon the shuttling of lithium ions between graphite and layered oxides, a process that limits the amount of Li to <1 per metal site and the volumetric energy density of the cathode to ~3,500 Wh/L.  An alternative to intercalation-based electrodes are the so-called "conversion" electrodes, in which lithium reacts with an unstable host that undergoes significant (reversible) atomic rearrangement on charging and discharging. Of the known metal fluoride conversion electrodes, the best balance of operating voltage, energy density, and cost is CuF₂, which has a theoretical capacity of 466 mAh/g (based on Cu + 2LiF) and a theoretical voltage plateau around 3.5V.

Recently, Wildcat has addressed several challenges currently prevent use of these materials: 1) poor rate capability due to low electronic/ionic conductivity, 2) low energy efficiency, likely from polarization and non-symmetric charge and discharge mechanisms, and 3) limited cycle life caused by sintering of metal nanoparticles and mechanical stress induced by volume expansion.  To overcome these difficulties, Wildcat developed CuF₂-based cathodes with conductive and protective coatings to enable high power and stability. Using Wildcat’s proprietary non-graphitic conductive coating, the cathode exhibits 1^st cycle capacities of >380 mAh/g at a 1C rate.

Wildcat has also investigated alternative compositions that demonstrate improved conductivity and higher voltage.  A second coating is used to prevent copper dissolution and metal agglomeration, leading to a self-discharge rate of 0.2%/day (vs. 2.0%/day for control) and cyclability. To our knowledge, this was the first reported demonstration of rechargeable CuF₂.  Moreover, the CuF₂ material has voltage hysteresis of only 0.1-0.3V, compared with ~0.7-1V for FeF₃ or BiF₃.