Sample preparation Single crystal LMNO with disordered arragement of transition metals (Fd 3m) was synthesized by polymer assisted sol-gel method (described previously in Ref. ). Al foil electrodes for the operando measurement were prepared depositing an ink composition of 90 wt % LMNO, 7% conductive carbon, and 3% polyvinylidene fluoride (Solef PVDF 5130/1001, Solvay) binder with a doctor blade. The electrodes were dried for 12 h at 110 °C in vacuum oven and then compressed at a pressure of 10 MPa.