Pre-lithiation optimized voltage ranges and MnO2/rGO negative electrodes with oxygen vacancies for enhanced performance of lithium-ion capacitors

Abstract

Lithium-ion capacitors are identified as outstanding hybrid energy storage devices combining the advantages of lithium-ion batteries and supercapacitors. However, the kinetics mismatch between positive and negative electrodes blocks the electrochemical performance. Thus, we design moderate amount of oxygen vacancies in manganese oxide nanosheets/reduced graphene oxide composites (OV-MnO2/rGO) for lithium-ion capacitors. Oxygen vacancies in MnO2 crystal enhance lithium-ion diffusion and electric conductivity to offset kinetics mismatch. OV-MnO2/rGO in half cells delivers good specific capacity of 1052 mAh g − 1 at 0.1 A g − 1 and cyclic performance (87.3% capacity retention after 450 cycles). Asymmetric lithium-ion capacitors were assembled with OV-MnO2/rGO negative electrodes and N-doped carbon nanosheets positive electrodes. The real working voltage ranges of electrodes under different pre-lithiation degrees are further investigated in pouch cells with inbuilt lithium metal electrode. By optimizing voltage ranges of electrodes based on pre-lithiation, the devices yield ultrahigh energy density of 206.2 Wh kg −1 at 250 W kg −1, excellent power density of 25,000 W kg −1 at 41.7 Wh kg −1 and stable cycling performance (79.8% after 10,000 cycles).