Energy band modulation of Li2O-rGO core–shell as cathode sacrificial additive enables capacity enhancement of hard carbon anode in Li-ion batteries

Lithium oxides (Li2O) possess a considerable theoretical capacity, rendering them highly promising as cathodic pre-lithiation additives. However, its decomposition voltage exceeds the charging cut-off voltage of most cathode materials, hindering its direct use as a cathode sacrificial additive. Herein, we design a facile and safe method to reduce the decomposition energy of Li2O at room temperature to offset the irreversible capacity loss by using a core-shell structured Li2O-reduced graphene oxide (rGO)-polyethylene glycol (PEG) composite (denoted as Li2O-rGO-PEG). The graphene oxide (GO) was heat-treated to remove oxygen functional groups to synthesize rGO, and then reacted with Li2O to form a Li2O-rGO composite. According to the DFT calculations, the density of states at the Fermi level of Li2O-rGO becomes continuous and features a metallic nature, which significantly improves the electrical conductivity of Li2O and facilitates electron conduction that modify the delithiation potential of Li2O. PEG was used to enhance the cohesive force between rGO and Li2O and to protect Li2O from atmospheric contamination. Moreover, in order to demonstrate the excellent pre-lithiation ability of Li2O-rGO-PEG composite, hard carbon (HC) with low initial coulombic efficiency (ICE) was used as the anode. In the application of LFP (Li2O)/HC full cell, Li2O was decomposed to Li+ to effectively improve the initial charge capacity from 149.7 to 200 mAh/g and discharge capacity from 104.2 to 147.5 mAh/g, which are 33.6 % and 41.6 % higher than those of the pristine LFP/HC full cell, respectively. The cathode pre-lithiation method proposed in this work is simple and environmentally friendly. The successful utilization of Li2O as a pre-lithiation additive effectively addressed the issue of low initial coulombic efficiency of the HC, indicating excellent prospects for practical applications.