Preparation Of Transition Metal Sulfides And Improvement Of Lithium/Sodium Storage

Transition metal sulfides（TMSs）are considered one of the most promising negative electrode materials for lithium-ion batteries（LIBs）and sodium ion batteries（SIBs）due to their high theoretical capacity,good thermal stability,and low price.However,the poor conductivity and large volume expansion in the energy storage reaction of TMSs themselves always result in the rapid capacity decline,which seriously hinders their commercial applications.Based on the above issues,this paper aims at improving the electrochemical performance of TMSs materials through designing nanoporous structures,introducing conductive carbon materials,and preparing high entropy materials to alleviate the volume changes during the energy storage process of TMSs and improve the imperfect conductivity of the materials.Nitrogen doped carbon coated three-dimensional nanoporous TMSs were prepared through dealloying,chemical vapor deposition and sulfurization processes,as well as carbonization treatment.As negative electrode materials for LIBs and SIBs,the performances of the carbon coated TMSs were greatly enhanced than that of bare TMSs.The specific research content of this article is as follows:1.Preparation and lithium/sodium storage performance of nitrogen doped carbon coated three-dimensional nanoporous nickel cobalt iron aluminum sulfide（NiCoFeAlS_x@N-C）A homogeneous Ni₉Co_0.5Fe_0.5Al₉₀ multielement alloy precursor was designed and prepared,and then nitrogen doped carbon coated three-dimensional nanoporous nickel cobalt iron aluminum sulfide（NiCoFeAlS_x@N-C）was prepared through simple dealloying,chemical vapor deposition vulcanization process,and carbonization treatment.Benefiting from the carbon coating,which can effectively alleviate volume expansion during cycling and further improve the conductivity of the material,NiCoFeAlS_x@N-C material exhibits significantly better discharge specific capacity than NiCoFeAlS_x material both in lithium and sodium storage processes.Especially as a negative electrode material for LIBs,the NiCoFeAlS_x@N-C electrode still has a reversible specific capacity of up to 954.1 mAh g^-1 after 220 cycles at 200m A g^-1,which is much higher than the corresponding specific capacity(250.2 mAh g^-1)of NiCoFeAlS_x.When used as a negative electrode material for sodium storage,the NiCoFeAlS_x@N-C displayed discharge specific capacity of 199.2 mAh g^-1 after 150 cycles at500 mA g^-1,which is still significantly higher than the corresponding specific capacity(38.9m Ah g^-1)of NiCoFeAlS_x.The experimental results indicate that carbon coating has successfully improved the lithium/sodium storage performance of NiCoFeAlS_x materials,which can provide ideas for improving the performance of other TMSs.2.Preparation and lithium/sodium storage performance of nitrogen doped carbon coated three-dimensional nanoporous nickel cobalt iron vanadium aluminum high entropy sulfide（NiCoFeVAl S_x@N-C）This work attempts to adjust the element content of materials in order to achieve high entropy structure,therefore,we design and prepare Ni₃Co₃Fe₃VAl₉₀ multi-element alloy precursor with uniform composition.Furthermore,using a similar synthesis method from the previous work,nitrogen doped carbon coated three-dimensional nanoporous nickel cobalt iron vanadium aluminum high entropy sulfide（NiCoFeVAl S_x@N-C）was prepared as a negative electrode material for LIBs and SIBs.Compared with NiCoFeVAl S_x,it exhibits superior performance both in lithium and sodium storage.For example,NiCoFeVAl S_x@N-C material holds a discharge specific capacity of up to 839.1 mAh g^-1 after 50 cycles at 200 mA g^-1 as the negative electrode for LIBs,which is much higher than the corresponding specific capacity(635.1 mAh g^-1)of NiCoFeVAl S_x.When the material is used as the negative electrode material for SIBs,the specific capacity of the NiCoFeVAl S_x@N-C material remains around 131.1 mAh g^-1 after 150 cycles at 500 mA g^-1,which is significantly higher than the corresponding specific capacity(26.7 mAh g^-1)of NiCoFeVAl S_x.The performance of NiCoFeVAl S_x has been greatly optimized,which possibly benefits by the alleviated the volume expansion and the reduced charge transfer impedance during the repeated insertion and removal of Li⁺/Na⁺.In addition,the electrochemical performance of NiCoFeVAl S_x as the anode material of LIBs is more ideal than that of NiCoFeAlS_x in the previous work,which may be attributed to the better structural stability of high entropy sulfide.3.Preparation and lithium storage performance of nitrogen doped carbon coated three-dimensional nanoporous nickel cobalt iron vanadium manganese sulfide（NiCoFeVMn S_x@N-C）The previous work improved the cycling performance of the material through high entropy structuring and regulating the proportion of nickel,cobalt,and iron components.Due to the high theoretical capacity of iron based sulfides,this work attempts to increase the iron content of material.A homogeneous Ni_0.3Co_0.4Fe₆V_3.3Mn₉₀ multi-element alloy precursor was designed and prepared,and nitrogen doped carbon coated three-dimensional nanoporous nickel cobalt iron vanadium manganese sulfide（NiCoFeVMn S_x@N-C）was further synthesized as a negative electrode material for LIBs.It may be attributed to the fact that the carbon shells can effectively adapt to structural changes caused by volume expansion and improve material conductivity.After 130 cycles at 500 mA g^-1,it exhibited a high reversible specific capacity of 778.9 mAh g^-1,which is far superior to the discharge specific capacity(459.9 mAh g^-1)obtained by NiCoFeVMn S_x under the same conditions.The electrochemical performance of the NiCoFeVMn S_x@N-C material is effectively improved than that of bare sulfide.