Adsorption energy engineering of nickel oxide hybrid nanosheets for high areal capacity flexible lithium-ion batteries

Enriching electrode materials with definite functions is of great influence but highly challenging towards achieving high areal capacity lithium ion batteries (LIBs). Taking transition metal oxides (TMOs) as a case study, several attempts have been employed to demonstrate the large variations in lithium storage performance of TMOs, but explanation of the adsorption capability is rarely reported. Herein, the Li-ion storage chemistry of NiO nanosheets is successfully enhanced by modulating the position of the p-orbital energy level via engineering with porous N-doped carbon fiber and carbon quantum dots (CDs). The as-prepared monolithic NiO hybrid nanosheets (denoted CF/ECF/NiO/CD) exhibit high reversible areal capacity of 3.97 mA h cm(-2) at 0.25 mA cm(-2), excellent cyclic stability with capacity of 2.91 mA h cm(-2) at 3.0 mA cm(-2), as well as attractive rate capacity of 2.61 mA h cm(-2) at 6.0 mA cm(-2). In situ Raman analyses, XPS, and DFT calculations reveal that performance enhancement is related to the electronic modulations between NiO, porous carbon fiber and CDs that triggers the shift of the pband towards accommodating interfacial electron transfer that helps in promoting the Li storage activity. In addition, an all-flexible lithium ion battery based on CF/ECF/NiO/CD anode is assembled and a volumetric energy density of 619.9 Wh L-1 is achieved (equivalent to an energy density of 201.7 Wh kg(-1)). This work opens an achievable approach for high-areal-capacity LIBs and provides relevant understanding into designing other LIB electrodes and beyond.