Low-cost iron trichloride cathode for all-solid-state lithium-ion batteries

The dominant chemistries of lithium-ion batteries on the market today still rely on flammable organic liquid electrolytes and cathodes containing scarce metals, such as cobalt or nickel, raising safety, cost and environmental concerns. Here we show a FeCl3 cathode that costs as little as 1% of the cost of a LiCoO2 cathode or 2% of a LiFePO4 cathode. Once coupled with a solid halide electrolyte and a lithium-indium (Li-In) alloy anode, it enables all-solid-state lithium-ion batteries without any liquid components. Notably, FeCl3 exhibits two flat voltage plateaux between 3.5 and 3.8 V versus Li+/Li, and the solid cell retains 83% of its initial capacity after 1,000 cycles with an average Coulombic efficiency of 99.95%. Combined neutron diffraction and X-ray absorption spectroscopy characterizations reveal a Li-ion (de)intercalation mechanism together with a Fe2+/Fe3+ redox process. Our work provides a promising avenue for developing sustainable battery technologies with a favourable balance of performance, cost and safety. The authors present a FeCl3 cathode design that enables all-solid-state lithium-ion batteries with a favourable combination of low cost, improved safety and good performance.