In this talk, He will present their recent work on Li-ion battery, in particle for the cathode material such as LiFePO4, as an example to illustrate the capability of soft X-ray spectroscopy. By means of elemental- and orbital-sensitive X-ray absorption (XAS) and X-ray emission (XES) spectroscopies, we are able to depict both key unoccupied and occupied states in electrodes. These key energy states play a decisive role in various practical characteristics of electrodes including Li diffusion, phase transformation, and safety issue. In addition, as a composite mesoscale system, the performance of LIB is not only determined by the fundamental physical and chemical properties of the individual components, but also relies on the morphology, assembly, and heterogeneity of functional units in a battery cell. All these processes are interrelated, and evolve over multiple time and length scales during and even after cycling throughout the lifetime of a battery. Therefore, development ofin situ and in operando characterization techniques to capture these responsive, dynamic, and sequential phenomena is stringent and necessary for battery research.