Electrode thickness matching for achieving high-volumetric-performance lithium-ion capacitors

For lithium-ion capacitors (LICs), the electrode mass balancing and the electrode potential tuning are two techniques that have been widely used to maximize the gravimetric specific capacity and voltage to achieve a maximum gravimetric energy density. However, it is also great important to consider the volumetric performances of energy storage devices for the compact and portable applications. Herein, for achieving high-volumetric-performance LICs, we propose an electrode thickness matching strategy, which is to minimize the thickness of thick cathodes as close to the one of thin anodes as possible via increasing the gravimetric specific capacity and density of cathode materials. It is demonstrated that introducing a highly dense but porous activated carbon/graphene (AC/G) composite rather than the low-density traditional activated carbon as the cathode material, the volumetric energy density of the assembled AC/G//graphite LIC can be increased by 62% to reach a maximum of 98 Wh L-1, which represents one of the highest records for the contemporary LICs. We believe that the thickness matching should be a universal strategy for achieving high volumetric performances and can be applicable to other electrochemical energy storage devices.