| With the advancement of society and the development of economy,the energy crisis is becoming more and more prominent.Traditional lithium-ion batteries can no longer meet people’s energy needs.So,it is urgent to develop high specific capacity and high energy density battery systems.Lithium-sulfur batteries(Li-S)have been considered as one of the most promising next energy storage systems due to its high theoretical specific capacity(1675 mAh g-1),abundant storage,and environmentally friendly.However,Li-S batteries have not yet been widely commercialized due to several challenges.For example,the low utilization of the active sulfur,the dissolving of the polysulfides,the bad rate performance,the short cycle performance,the generation of the lithium dendrites,and so on.In this paper,we successfully synthesize the cathode materials of high-performance Li-S batteries by utilizing transition metal selenides’ adsorption and catalytic conversion advantages towards polysulfides.We also analysis the reaction mechanism of transition metal selenides towards polysulfides in depth by using phase characterization and electrochemical performance measurement.The specific contents are as follows.(1)We first etched CoAl-LDH using the sodium hydroxide solution,then selenized the generated Co-PHF at 500℃ under Ar atmosphere.The obtained CoSe2-PHF combined the high catalytic activity of transition metal compound and high electrical conductivity of selenium,which can efficiently accelerate the catalytic conversion of LiPSs,expedite the electron transport,and improve utilization of active sulfur during the charge-discharge process.As a result,with CoSe2-PHF/S-based cathodes,the Li-S batteries exhibited a reversible specific capacity of 955.8 mAh g-1 at 0.1 C and 766.0 mAh g-1 at 0.5 C,along with a relatively small capacity decay rate of 0.070%per cycle within 400 cycles at 1 C.Even at the high rate of 3 C,the specific capacity of 542.9 mAh g-1can be maintained.(2)We synthesized nickel-cobalt bimetal selenides using Ni-Co acetate hydroxide as a precursor.We first prepare Ni0.33Co0.67(CO3)0.5OH precursor by hydrothermal method.Then we selenize the precursor at 500℃ under Ar atmosphere to obtain Ni0.33Co0.67Se2.The study shows that the hollow nanorods in the Ni0.33Co0.67Se2 can effectively host sulfur and mitigate volume expansion.In addition,the synergistic effect of transition metal nickel-cobalt enables the material to effectively adsorb polysulfides and catalyze its conversion,then accelerate the reaction kinetics.Therefore,Ni0.33Co0.67Se2/S composite exhibits excellent electrochemical performance.At the rate of 0.1 C,0.2 C,0.5 C,1 C and 2 C,the reversible discharge capacities of the Ni0.33Co0.67Se2/S electrodes are 945.7 mAh g-1,845.6 mAh g-1,741.0 mAh g-1,650.5 mAh g-1 and 450.8 mAh g-1,respectively.After 400 cycles at the rate of 1 C,the specific capacity can still be maintained at 493.7 mAh g-1 and the coulomb efficiency is close to 100%.The corresponding capacity retention rate is 70.5%,and the capacity decay rate for per cycle is 0.073%.When the surface load of sulfur in the electrode material was 1.2 mg/cm2 and 3.0 mg/cm2,the specific capacities of the batteries remained 668.7 mAh g-1 and 464.4 mAh g-1 after 150 cycles at the rate of 0.5 C,and the corresponding capacity retention rates were 88.3%and 80.2%,respectively. |
