To obtain further insight into the discharge and charge processes that occurred in LOBs, the morphologies and crystalline characteristics of cathodes at different states were intensively examined. After full discharging, three new peaks located at 32.9°, 35.0° and 58.7° can be clearly observed in the XRD pattern of the Pd/Pd
4S@HCS cathode in Fig. S10d (Supporting information), respectively according to the (100), (101) and (110) planes of Li
2O
2 (PDF#209-0355), and these three peaks disappeared after recharging. This implies that the main discharging product is Li
2O
2, which can be totally decomposed in the charge process. The
in-situ differential electrochemical mass spectrometry (DEMS) was conducted to further investigate the charge product, and the DEMS curve (Fig. S11 in Supporting information) shows that O
2 was main evolved gas during charging, which implies that Li
2O
2 → O
2 conversion is the dominating reaction in the charging process. Nevertheless, there are also little amount of CO
2 generated at the end of charging process, and this is because inevitable by-product could be decomposed at higher charging voltage [
15]. The Raman spectrum of Pd/Pd
4S@HCS cathode at different stages are shown in Fig. S12 (Supporting information). After discharging to 1000 mAh/g, both the main discharging product (Li
2O
2) and intermediate (LiO
2) can be observed in the spectrum (Fig. S12a). The peak at 830 cm
−1 could be associated with the Li
2O
2, the peak at 1123 and 1505 cm
-1 are related to LiO
2-like compound and the strong interaction between LiO
2 and graphitic carbon surface, respectively. [
16] The absence of peaks after recharged suggests the efficient catalytic activity. The SEM images of the Pd/Pd
4S@HCS cathodes at different states are shown in Figs. S10a–c. It is demonstrated that the discharge product Li
2O
2 in the form of toroid shape were imbedded in this cathode after initial discharging, while the discharge product grown in the HCS cathode shows a dense film-like structure in the Fig. S7. After the recharge process, the discharged product cannot be observed in the Pd/Pd
4S@HCS cathode, which means that the Li
2O
2 had totally decomposed account of its fabulous catalytic activity. This result is consistent with the information from XRD patterns. Furthermore, the Pd/Pd
4S@HCS can completely maintain its characteristic morphology with the limited accumulation of by-products, which demonstrate its material durability during cycling. For the HCS, there are amounts of accumulation of by-products after ten cycles, which finally results in the death of cells with HCS cathode. Therefore, it is concluded that the Pd/Pd
4S heterostructure could provide fabulous superior catalytic activities for boosting discharge and charge processes to obtain long cycling life and large specific capacities.