Preparation And Application Of Zn-based Cathode Materials For Lithium-selenium Batteries

Since the advent of lithium batteries in the 1970s,the development of electronic equipment is changing rapidly,and people’s needs for energy storage equipment are increasing.Today,with the traditional development of electrode materials for lithium ion batteries and approaching the limit,new electrode materials must be developed to meet people’s increasingly high energy storage equipment requirements.Lithium selenium（Li-Se）batteries are considered to be promising cathode materials for lithium-ion batteries because of their large theoretical volume-specific capacitance(3260 m Ah cm^-3),a high volume energy density(2530 Wh L^-1),a high electron conductivity(1×10^-3Sm^-1),and a natural abundance and environment-friendly.However,commercialization of the lithium selenium battery has been hampered by volume expansion,poor catalytic reaction dynamics,a low Se utilization rate,and poor cycling stability of the polyselenium shuttling back and forth between the positive and negative electrode.To address the above problems,there is an urgent need to design and develop a selenium cathode material with a large specific surface area and a strong catalytic effect.In this paper,the method of combining theoretical calculation and experimental data from the cathode material of lithium selenium battery constructs the catalytic modified nitrogen doped porous carbon based material as the cathode carrier material of lithium selenium battery to solve the problem of curbing the commercialization of lithium selenium battery.Develop the cathode carrier material of lithium selenium battery with the dual functions of chemical catalysis and physical adsorption.The specific research contents of this paper are as follows:（1）Using the silica ball as a hard template,prepared ZnCo bimetallic nitrogen doping grading porous carbon material,the bimetallic doping graded porous carbon material with honeycomb interconnected porous structure and the high surface area of 560 m2g-1,can adjust the Co salt and Zn salt added ratio of 1:0,0:1,1:10 and 1:1,respectively get Co nanoparticles,ZnCo double atom and both Co nanoparticles and Zn single atom porous carbon-based materials.The experimental results show that ZnCo double single atom material（ZnCo-NC）has the best performance,still having the mass specific capacity of354 m Ah g^-1after 1000 charge and discharge cycles at the current density of 2 C.Through DFT calculations,the change in free energy of ZnCo-NC/Se is found to be smaller than that of the other two samples,which indicates that the ZnCo atoms have a synergistic catalytic effect in the lithium selenium battery electrode reaction,and therefore have more benefits in reducing Se.（2）A carbon-based porous selenium cathode material（ZnS-NC）is prepared with the silica ampoule as the sulfur source and the zinc nitrate hexahydrate as the zinc source.The catalytic effect of the ZnS-NC material has been effectively enhanced compared to the non-sulfated（Zn-NC）materials.A test of the CV at scan rates of 0.1 to0.5 m V s^-1revealed that the relative ratio of the capacitance contributions of ZnS-NC/Se from 0.1 m V^-1to 0.5 m V s^-1increased as the scan sped up,with a greater value than Zn-NC/Se at each scan indicating that ZnS-NC may improve the reaction kinetics of the battery.After 200 cycles of charging and discharging at the 0.5 C current density,it has a mass-specific capacity of 613 m Ah g^-1,which has almost no attenuation compared to the original discharge capacity(620 m Ah g^-1),indicating that ZnS-NC can effectively improve the Se utilization rate and improve the charging and discharging cycle performance of the lithium selenium battery.DFT calculations further confirm that ZnS can indeed reduce the energy barrier of the reaction in the discharge reaction process,catalyzing the conversion of Se₈to Li₂Se direction,as well as improving the reaction dynamics of the selenium cathode in the charging and discharging process.