Tailoring Co Based Anode Material And Investigation Of Its Performance In Supercapacitor

Supercapacitors（SCs）combine the advantages of lithium ion batteries and conventional capacitors so effectively that they deliver a higher energy density than traditional capacitors and a higher power density than Li-ion batteries.Among numerous electrode active materials,cobalt oxides are regarded as promising material in SCs because of its various valence state,high theoretical capacitance and environmental friendliness.However,the sluggish kinetics and poor conductivity of them result in that fabricating a high performance Co based SCs becomes a chanllenge.In this paper,the history and mechanism of SCs are presented and two stratergies are described to solve the problem.Meanwhile,the process and results are declared in details and the explanation of them is given.The first strategy is to design the morphology of active materials and explore their structure activity relationship.Making bulk cobalt oxides into low dimension would change the mechanism of energy storage,which could lead to the high energy density and poerdensity SCs.In this method,2D Li Co O₂（2D-LCO）which is synthesized by fast composite hydroxide mediated approach could shorten the diffusion path of Li ion,which makes part of diffusion control change into surface control.Thus,2D-LCO not only remains the high energy density advantages,but also improves the power density of devices.Moreover,the asymmetric supercapacitor assembled by 2D-LCO as anode and Fe₂O₃/FeOOH as cathode delivers a high areal energy density of 56.25 m Wh/cm² at1100 m W/cm² with working window of 2.2 V and an excellent cycling stability of 80%at current density of 10 m A/cm² for 2000 cycles.The second strategy is to study the transmission of electron that could reduce the device resistance to improve the performance of SCs.In this method,the contact resistance between N doped carbon cloth and Co₃O₄ is reduced due to the interaction of doped N and Co,which boosts the electrochemical performance significantly.The electrode made by N doped carbon cloth and Co₃O₄ particles shows an ultrahigh specific capacitance of 1,940.13 m F/cm² at 1 m A/cm².An aqueous symmetric supercapacitor（ASSC）based on two electrodes possesses the maximum energy density and power density are 447.42μWh/cm² and 8000μW/cm²,respectively.In practical application,an ASSC could power a digital watch 1 h or a temperature-humidity detector for nearly 2 h,while the charging time is just 250 s.Besides,the ASSC keeps a gratifying capacity retention of 87.7%after 10000 cycles at 40 m A/cm²,which presents an excellent cyclic performance.