Yong Hao

Hybridization of lithium-ion batteries and electrochemical capacitors: fabrication and challenges

Conventional electrochemical double-layer capacitors (EDLCs) are well suited as power sources for devices that require large bursts of energy in short time periods. However, when compared to their battery counterparts, EDLCs suffer from low energy densities. The low energy density of EDLCs hinders their applications in devices that require a simultaneous supply of high power and high energy. In order to improve the energy density of EDLCs, the concept of hybridization of lithium-ion batteries (LIBs) and EDLCs has gathered much attention in past years. Such a hybrid is typically referred to as “lithium-ion capacitor” (LIC) or “lithium capacitor” and essentially utilizes a lithium intercalating anode (such as graphite or Li4Ti5O12) and a fast charging-discharging EDLC electrode (such as activated carbon, carbon nanostructures) in a lithium-salt based electrolyte. Although such a system sounds quite ideal in theory, there are major challenges that need to be addressed in order to fully realize the benefits of LIB and EDLC electrodes in conjunction. Most of these challenges stem from the mismatch in capacity of the electrodes and also the charging-discharging times of the electrodes. For instance, the EDLC electrode acts as the limiting factor for the capacity of the system while the LIB electrode limits the power of the system. Here we have fabricated a hybrid capacitor that utilizes a Li4Ti5O12 (LTO) based anode and an activated carbon (AC) composite based cathode. Half-cell testing for both LTO and AC have been shown along with full cell evaluation.