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.