A Hybrid Li₄Ti₅O₁₂/Activated-carbon Anode Prepared By In Situ Copolymerization And CO₂ Post-activation For High Power Li-ion Capacitors

A new type of energy storage devices,the so-called Li-ion capacitors(LICs),possessed higher energy density than electric double layer capacitor(EDLC)and higher power density than lithium ion batteries(LIBs),have been an ideal storage device for electric vehicle.Lithium titanate(LTO)is one of the best choose of the anode materials for the LICs because of its many advantages such as stable structure,small volumetric change in the process of Li-ion insertion/de-insertion,good cycle performance and safety.However,its low electronic and Li-ion conductivity diminished the energy storage ability at a certain extent,leading to a poor rate capacity performance.Therefore,a lot of work is devoted to solving this problem so that it can be applied at high rate now.This issue have innovated the composite process of LTO based on the in situ copolymerization and reaction activation method.The LTO-AC composite materials with large specific surface area,high porosity and controllable structure were prepared and then characterized,conclusions are as follows:As compared to the pure LTO,the rate and cycle performance of LTO-AC are promoted effectively.When the content of active carbon was 54% in the composite materials,the materials display the best rate capability.Though the specific capacity of the first discharge was 99.6 mAh/g at 1C,it can still delivered a discharge capacity of 68.5 mAh/g at 40 C,the capacity retention is about 32% higher than pure LTO.Moreover,the half cell can remain more than 96% capacity of initial value after 300 cycles at 5C.In this paper,by using commercial activated carbon YEC-8b and LTO-AC as the positive and negative,respectively,the optimum mass ratio of positive and negative of LTO-AC-1//AC,LTO-AC-2//AC and LTO-AC-3//AC capacitors are 3.5,2.5,2.0 respectively.In which,the LTO-AC-3//AC capacitor has better rate and cycle performance.It can deliver a energy density of 45 Wh/kg at the current density of 0.1 A/g(1.5-2.8V),and even at a high current density of 4 A/g,the energy density can still remain 38 Wh/kg,the corresponding power density is as high as 7.5 kW/kg,while capacitors of LTO//AC,LTO-AC-1//AC,LTO-AC-2//AC are only 30.5,27.3,25 Wh/kg,respectively.Furthermore,the capacity retention of LTO-AC-3 //AC was up to 90.84% at 0.5 A/g after 2000 cycles.