Study On Carbon Cathode Materials For Aluminum-ion Batteries

There are two major challenges,energy and environment,facing by human beings in the 21 st Century.Therefore,in order to realize the efficiency and sustainable development in the society,it is required to develop an efficient,clean and renewable energy.Since there are many limitations for the Lithium battery,such as resources scarcity,high cost and safety,it is of great significance to pay attention to the next generation of ultra-high capacity rechargeable aluminum-ion battery cells.Al batteries have some advantages,such as high energy density,a wide range of reserves,low cost and safety.At present,the research of cathode material of Al battery concentrates on the direction of transition metal oxide,sulfide and chloride,and carbon material.Foam was used as the cathode material to produce a cycle and stable aluminum-ion battery structure by using different current collector,anode material,separator and electrolyte.Then take this preparation process,research on artificial graphite film,carbon fiber paper(CFP)and foam.The results show that the artificial graphite film has an excellent discharge capacity in the first time with a bad cycle performance.While for the CFP,the cycle performance is good but the discharge specific capacity is low.The specific discharge capacity increases with the cycle until reach to its limit.The density of foam is too large,resulting in a low discharge specific capacity.Therefore,CFP has the best comprehensive performance.Thus,it is chosen as a positive electrode material for aluminum-ion batteries to modify and to improve the performance of the battery.CFP was made holes by surface treatment.Firstly,the thermal oxidation is used for the treatment.With the increase of temperature,the diameter of the fiber decreases and the specific surface area increases.The area with the existence of structural defects on the surface of the carbon fiber reacted first.With temperatures below 600 ?,thermal oxidation has no significant effect on the carbon fiber.When the temperature is higher than 700 ?,increases on the time can effectively reduce the fiber diameter.The best heat treatment temperature is 700 ?,the treatment time is 120 min.Under this situation,CFP can maintain a more complete structure strength and a larger surface area with a good cycle stability,as well as a larger discharge capacity of 35 m Ah g-1.The next step is to use ammonia gas to do some treatment on the carbon fiber,so that the carbon fiber can be etched along the surface groove,to further deepen the groove and increase the surface defects of the carbon fiber,but the influence on the diameter is small.As for the performance of electrochemical,ammonia treatment can activate the potential discharge capacity of aluminum-ion batteries in advance.The best treatment conditions for ammonia treatment is under a 1100 ? in the ammonia atmosphere,heating 120 min,in order to maintain a more complete structure and mechanical strength.In the meanwhile,it can have a larger surface area with a good cycle stability,and have a larger discharge capacity of 40 m Ah g-1.Thermal oxidation treatment increases the carbon fiber surface by reducing the diameter,while ammonia treatment increases the carbon fiber surface by etching grooves and increasing defects.Therefore,the thermal oxidation of carbon fiber is carried out first,followed by ammonia treatment,so as to further expanding the performance of the positive electrode carbon material.After thermal oxidation at 700 ? for 120 min,CFP treated with ammonia at 1100 ? for 120 min has the highest discharge capacity of about 55 m Ah g-1 at the discharge current density of 100 m A g-1.After cycling 150 times,it remains at 52 m Ah g-1,the charge and discharge ability is excellent.After 700 ? thermal oxidation treatment for 120 min,ammonia treatment at 1100 ? for 90 min and thermal oxidation treatment at 700 ? for 90 min,the maximum discharge specific capacity of CFP at 1100 ? for 120 min with 100 m A g-1 discharge reaches to the highest density at about 45 m Ah g-1.After cycling for 150 times,it remains at 45 m Ah g-1,the cycle performance is excellent.After the last treatment on the activation of CFP by KOH with the concentration of 0.1 mol L-1 KOH,the fiber surface pores appear,the discharge capacity first decreases and then increases,indicating that KOH pore and thermal oxidation and ammonia treatment is not stable enough,and its Decomposition products can improve the discharge capacity of the cathode material.When the heat treatment temperature is greater than 800 ?,it is possible to activate CFP fully.