Preparation Of Nonmetallic Atom Doped Carbon Materials For Lithium-O₂ Batteries Electrochemical Performance

Lithium-oxygen battery(Li-O2)has attracted much attention because of its energy density ten times that of lithium-ion battery.However,there are still many problems in the process of conversion into practical application,such as the insoluble insulation of lithium peroxide(Li2O2)generated during battery operation.Li2O2 has stable properties and low reactivity.During the battery cycle,it gradually accumulates on the electrode surface and it’s difficult to decomposed,which leads to the increase of overpotential of the battery,reduced dynamic performance and cycle life of the battery.Therefore,it is important to develop excellent catalysts that can efficiently decompose Li2O2 and improve the electrochemical performance of Li-O2 batteries.In this paper,non-metallic doped carbon materials as the target design of sulfur(S),chlorine(Cl)atoms co-doped porous carbon materials and nitrogen(N),fluorine(F)atoms co-doped three-dimensional network carbon materials as Li-O2 cathode catalyst.Systematically studied Li-O2 cells the effects of catalysts on electrochemical performance,which were provided a green and simple new strategy for the development of high-efficiency catalysts for Li-O2 cells.1.The S,Cl co-doped porous carbon material(CSC)was synthesized by high temperature pyrolysis.The content of S,Cl atoms in the carbon material was adjusted by changing the calcination temperature.When the calcination temperature was 700℃(CSC700)as Li-O2 cathodes,the electrochemical performance of the Li-O2 cell was optimal.When the current density was 250 mA g-1,cut-off capacity of 1000 mAh g-1,can be circular 102 cycles,and the first cycle overpotential as low as 0.91 V.Cut-off potential of 2.2 V,specific discharge capacity about 18000 mAh g-1.Experimental results combine with first principles(DFT)calculations show that doped S,Cl atoms will with carbon atom form C-S bond and C-Cl bond.The C-S bond can be used as the reactive center to enhance the oxygen reduction(ORR)and oxygen precipitation(OER)reactivity,and significantly reduce the reaction overpotential of Li-O2 cell.However,due to the large electronegativity of Cl atom,doping into the carbon material will enhancement of electronegativity of the whole material,which has a strong adsorption effect on the intermediate products,and then plays a regulatory role on the morphology of the discharge products.Experimental results show that with the gradual decrease of Cl atom content,the morphology of the discharge products changes from membrane to circular ring.The Cl,S atom doped carbon material has a certain reactive center and moderate surface adsorption power,and its performance is significantly higher than that of pure carbon material.CSC700 further optimizes the content of S,Cl atoms in the carbon material.CSC700 as a cathode of Li-O2 battery has the best catalytic effect.2.F,N-codoped carbon material(FN-NSC)was synthesized by high temperature pyrolysis.FN-NSC as a self-supported positive electrode was applied to of Li-O2 battery and to explore its electrochemical performance.Experimental results showed that,on the one hand,the introduction of F,N diatoms improves the electron transfer rate,increases the reactive center,and enhances the ORR and OER kinetic performance of the reaction.Which may be due to F and N atoms were introduced into carbon material as the active site,and its electronegativity greater than that of carbon will lead to the increase of e-spin density of adjacent carbon,enhance the adsorption capacity of O2,and improve the performance of ORR and OER.On the other hand,F and N atoms were introduction of carbon material will increased electronegativity of the carbon material,the adsorption capacity of intermediate products changed.Thus regulation discharge morphology discharge product morphology from a single F or N atoms doped circular ring to the diatomic doped thin shell.Thanks to the above advantages,FN-NSC application in Li-O2 battery has lower potential.When the current density is 250 mA g-1,the specific discharge capacity can reach 11383 mAh g-1.When the discharge cut-off capacity is 1000 mAh g-1,continuous operation of 117 cycles.