The excitation energy of each mapping was at the O K-edge at 526 -534 eV and the acquisition time was 9 h. A vacuum suitcase shown in Figure was used to transfer the sample from an N2-filled glovebox to the test chamber. The coin cells used for the RIXS measurement were charged/discharged to the target voltage, then disassembled and the electrodes were washed with DMC before drying and spreading onto Cu tape. All steps were carried out in an argon-filled glovebox. Data were processed using the beamline software, Adler-4.0.