The Study Of Cathode Material-organic Sulfide Of Lithium Ion Battery With High Energy

Lithium secondary batteries are the future of chemical power sources on account of their properties such as high specific energy, portable, high working voltage, etc. Since lithium possesses supreme high specific energy (3860Ah/g) and low potential (-3.036V,vs.H+/H2), the increasing of battery's specific energy depends on the performance of positive active materials in large. Lithium metal oxides(LiCoO2,LiNiO2,LiMn2O4, etc) used extensively at present can't increase battery's specific energy more while organic sulfides can do. Organic sulfides are to be oxidised to form polymers containing s-s bonds as charging , and polymers will be reduced to their low molecular monomer as discharging. However, the speed of organic sulfides' reoxide reaction is very slow at the temperature ranging from -100C to 500C. But it would be enhanced very much if organic sulfides were mixed with conductive polymer-polyaniline(PAn). Poly-o-toluidine(POT) is selected as the electro-catalyst of 2,5-dimercaptan-1,3,4-thiadiazole(DMcT) because the solubility of POT in organic solvents is much higher than that of PAn. Therefore, DMcT can contact with POT at molecular level. It suggests that the oxidative reaction order is 2 and the reduced reaction order is 1 by testing its electrode kinetics. The electrochemical behaviors of DMcT on the different current collectors are studied in this paper by means of testing their cyclic voltammogram properties. It shows that copper be more suitable for the current collector than other metals such as Pt, Al, Ni. With the increasing of POT content in DMcT/POT composite which uses copper as substrate the conductivity of cathode is promoted but its reversibility goes to bad. Accordingly the reversibility of the composite electrode is best when the weight ratio of DMcT/POT equals to 1. We have made test batteries which constructed by DMcT/POT composite cathode, metal lithium anode and different electrolytes. The exporting capacity of which charged to 4.75V is larger than that of which charged to 4.25V and 4.50V by 38.5% and 24.1% respectively. Although battery's working voltage plateau decreases with increasing of discharging current density, the exporting capacity of the battery has little changes. It shows that the charge-discharge performance of the battery, which is fabricated by casting the polymer electrolytes on the surface of the cathode directly then impregnating the composite electrode in liquid electrolytes for seconds, is much better than that of other batteries. The best battery,s charge-discharge current density is as high as 0.33 mA/cm2, and its specific energy accesses to 110Ah/kg. Moreover its capacity remains 80% of initial capacity even after 20 cycles. Its charging-discharging efficiency can get up to 85%. However its noumenal resistance and electrochemical polarization resistance is higher than that of nonaqueous lithium ion batteries by two orders of magnitude.