An electrochemical approach to converting alloy scraps to (FeCrNiMnX)3O4 high-entropy oxides for lithium-ion batteries

Alloy scraps containing plenty of Ni, Cr, Mn, and Fe are promising secondary sources, however, it is still difficult to valorize them due to the high corrosion resistance and mechanical strength and the multi-step processes of separation and purification. Herein, we employed an electrochemical oxidation approach to converting alloys scraps to porous transition metal oxides (TMOs) in highly corrosive molten salts. The resultant TMOs are directly used as feedstocks to synthesize quaternary medium-entropy (FeCrNiMn)3O4 and a series of spinel (FeCrNiMnX)3O4 (X = Zn, Ti, Nb, Sb, Bi, W, and Zr) oxides via solid-state reaction. When employed as anodes for Li-ion batteries (LIBs), the reversible capacity the (FeCrNiMnZn)3O4 reaches 636.4 mAh/g at 500 mA g−1 after 250 cycles and the rate capacity reaches 252.4 mAh/g after 2000 cycles at 3 A/g. The good Li-storage performance is thanks to their excellent electronic conductivity and milder volume change. This work provides a facile route for the direct recovery of full components from alloy scraps and gives insights into the design of HEOs with different elements.