Study Of Lithium Ion Capacitor With Pre-lithiated Hard Carbon Anode

Their energy density, power density and cycle stability of batteries and capacitorsneed to be improved with the wide application fields of these storage devices.Lithium-ion capacitor has attracted much attention due to its superior power densityand temperature capability than electrochemical capacitor and power density andsecurity than lithium ion batteries. In terms of future industrialization of lithium ioncapacitor, carbonaceous materials seem to be the best alternative because of itscheapness and easy availability. In this paper, the effect of the pre-lithiation capacityof anode, pre-lithiation method and mass ratio of cathode to anode on theelectrochemical performance is evaluated using activated carbon, hard carbon and1M LiPF6/EC+DEC as cathode, anode and electrolyte, respectively.Pre-lithiated hard carbon anode with different pre-lithiation capacity is obtainedby discharging hard carbon/Li half cells and is used as anode for LIC. When thepre-lithiation capacity of anode is less than200mAh/g, the LIC has a low coulombicefficiency and the cathode is highly polarized at high potential region, beyond the safelimit of activated carbon. When the pre-lithiation is large enough, the irreversible ofanode is completely compensated and thus the coulombic efficiency is above100%.The energy density of LIC increases by increasing the pre-lithiation capacity of anode.However, lithium deposites on the anode when the pre-lithiation capacity of anode ismore than400mAh/g. Among various LICs with different pre-lithiation capacity, theLIC with400mAh/g pre-lithiaton capacity (LIC400) has minimum resistance and candeliver a maximum specific energy of76.5Wh/kg and specific power of5.1kW/kg.Meanwhile, LIC400has good cycle durability with energy retention of92.0%after1000cycles.A simple pre-lithiation method can be used for the pre-lithiation of hard carbonanode. The pre-lthiation is achieved by simply short-circuiting hard carbon anode andlithium sources. The capacity of capacitor first increases and then decreases byincreasing the pre-lithiation time and15h is the optimal pre-lithiation time. Thecapacitor with15h pre-lithiation has the maximum specific energy of97.2Wh/kg,45.1Wh/kg even at specific power of5.4kW/kg, minimum resistance and superiorcycle performance with energy retention of91.2%even after1000cycles. The electrochemical performance of LIC can be further enhanced by changingthe mass ratio of cathode to anode. The capacitor with a mass ratio of2.2has the bestperformance. When the current density increases from1.2C to82C, the energydensity of the capacitor decreases from88.7Wh/kg to48.7Wh/kg with energyretention of57.0%. Meanwhile, it has a small charge-transfer resistance of10.4.The capacitor can reach a maximum specific energy of88.7Wh/kg and a powerdensity of12kW/kg.