A novel efficient three-stage electrochemical pre-lithiation method for the amorphous carbon negative electrodes of lithium-ion capacitors

Abstract

Electrochemical pre-lithiation stands as a practical and widely adopted technique for precisely controlling the degree of pre-lithiation, but the process is usually time-consuming. Herein, we introduce a novel three-stage electrochemical pre-lithiation method, comprising an initial stage of a high current density, a second stage of a low current density, and an additional stage of constant voltage to ensure the complete formation of solid electrolyte interphase (SEI) on the amorphous carbons: soft carbon (SC) and hard carbon (HC). Lithium-ion capacitors (LICs) are configured with the pre-lithiated SC or HC as the negative electrode and activated carbon as the positive electrode to assess the efficacy and adaptability of this three-stage pre-lithiation approach. Our findings demonstrate that this method can reduce the pre-lithiation time from 1114 to 604 min for SC, and from 1913 to 1080 min for HC, achieving nearly 46 % and 44 % decreases, respectively. Furthermore, the three-stage pre-lithiation method can simultaneously increase reversible Li-ion storage capacity within the same operating potential window, thereby enhancing the electrochemical performance of the LIC cells. Specifically, the LIC cell employing the three-stage pre-lithiated SC exhibits an energy density of 96.5 Wh kg-1 at 0.15 kW kg-1 and 76.5 Wh kg-1 at 5.98 kW kg-1. These cells demonstrate remarkable reversibility, retaining 89.6 % charge capacity after 10,000 cycles. Similarly, the LIC with the three-stage pre-lithiated HC achieves even higher energy densities of 105.3 Wh kg-1 at 0.15 kW kg-1 and 86.42 Wh kg-1 at 5.98 kW kg-1 with a retention of 85.2 % after 5000 cycles. The successful implementation and validation of this three-stage pre-lithiation method pave the way for further development of LICs.