Investigation of Electrochemical Performance and Gas Swelling Behavior on Li₄Ti₅O₁₂/Activated Carbon Lithium-Ion Capacitor with Acetonitrile-Based and Ester-Based Electrolytes

Lithium-ion capacitors (LICs) have gained significant attention due to the combination on the advantages of electric double-layer capacitors (EDLCs) and lithium-ion batteries (LIBs). Herein, the LIC pouch cell was fabricated by an activated carbon (AC) cathode and a Li4Ti5O12 (LTO) anode. Two organic electrolytes (1 mol L−1 LiBF4/acetonitrile (AN) and 1 mol L−1 LiPF6/ ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + dimethyl carbonate (DMC)) were chosen and the gas swelling behavior was studied. Compared with the ester-based LIC, the AN-based LIC displays higher energy density of 13.31 Wh kg−1 at 11.4 W kg−1 and even provides a value of 9.1 Wh kg−1 at 1075 W kg−1. Because of the lower DC Resistance of 0.761 mΩ, the maximum power density of the AN-based LIC reaches 12.5 kW kg−1. The AN-based LIC delivers good stability with an energy retention of 88.3% after 900 cycles. It is discovered that the swelling behavior of AN-based LICs is more serious and the major component is H2. The difference of swelling behavior among the LICs, lithium nickel cobalt manganese oxide (NCM)/LTO LIB and AC/AC EDLC is proposed to be caused by the AC electrode and the interfacial reaction of LTO