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

Gang Liu; Zixuan Fang; Tingting Feng; Ming Zhang; Mengqiang Wu

doi:10.1016/j.jcis.2024.04.100

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

J Colloid Interface Sci. 2024 Apr 16:667:688-699. doi: 10.1016/j.jcis.2024.04.100. Online ahead of print.

Authors

Gang Liu¹, Zixuan Fang², Tingting Feng¹, Ming Zhang¹, Mengqiang Wu³

Affiliations

¹ School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu 611731, Sichuan, China.
² School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu 611731, Sichuan, China. Electronic address: zixuanfang@uestc.edu.cn.
³ School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu 611731, Sichuan, China; Yangtze Delta Region Institute (HuZhou), University of Electronic Science and Technology of China, Huzhou 313001, Zhejiang, China. Electronic address: mwu@uestc.edu.cn.

PMID: 38670012
DOI: 10.1016/j.jcis.2024.04.100

Abstract

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.

Keywords: Cathode pre-lithiation; Hard carbon; Lithium oxide; Lithium-ion battery; Reduced graphene oxide.