Preparation And Electrochemical Performances Of Electrode Materials For Lithium-ion And Zinc-ion Batteries

Lithium-ion batteries（LIBs）are the most advanced commercial secondary batteries with the advantages of high energy density,high operating voltage,long cycle life,high power density,low self-discharge,no memory effect,and environmental friendliness.LIBs have been used in communication,electronics,transportation,aerospace and energy storage and other fields.The performances of batteries are mainly determined by electrode materials.In order to further improve the performances of LIBs,broaden their application field,and serve the development of the national economy,people are continuing to increase the research and development of the electrode materials.However,with the rapid expansion of the application scope of LIBs,the increasing usage and shortage of lithium resources,people have to invest in researches and development works on finding alternatives to LIBs to alleviate concerns about the shortage of lithium resources.To this end,the ternary（Li Ni_xCo_yMn_zO₂）cathode materials and Sn S/Mo S₂ anode material have been studied in depth in this dissertation,and the emerging zinc-ion secondary batteries（ZIBs）cathode materials have been preliminary explored.The specific research content as follows:（1）Aiming at the problem that Ni-rich ternary cathode materials with unstable structural during electrode reactions and side reactions at the interface with electrolyte cause serious capacity degradation,this paper adopts the combined modification strategy of surface coating and ion doping to improve the electrochemical performances.This work introduced P source in the co-precipitation process to obtain a polyanion of PO₄^3-doped ternary precursor,and then introduced Ti source in the lithiation process.At last,the PO₄^3--doped and Li₂Ti O₃-coated Li Ni_0.6Co_0.2Mn_0.2O₂ ternary cathode material was prepared after heat treatment.This paper adopted the synergistic solution of surface coating combined with doping in order to improve the interfacial and internal structural stability of the NCM materials.By optimizing the coating and doping amount,the sample P3-NCM-LT1 with 0.03 mol%PO₄^3-doping and 1.0 mol%Li₂Ti O₃ coating exhibits excellent performance and cycling stability.The reversible capacity achieves 157.8 m Ah·g^-1 at a current density of 10 C,and the capacity retention rate is 77.4%after 800 cycles at a cut-off voltage of 4.5 V and a current density of 1C.The results reveal that fast ion conductor Li₂Ti O₃ as coating material can suppress the interfacial side reaction and reduce the ion transferring resistance of the modified layer,while PO₄^3-can stabilize the crystal structure,reduce cation mixing and improve ionic conductivity in the bulk.The synergistic optimization strategy can significantly improve the comprehensive electrochemical performances of the composite cathode material.（2）Due to the problems of solid-solid wetting and complex preparation in non-aqueous environment,it is usually difficult to coat full protective film on the surface of the Ni-rich ternary cathode materials.To solve this problem,in this paper,Mg₃B₂O₆ with light weight,corrosion resistance and high mechanical strength is selected as coating material.Through a redox reaction in non-aqueous solution at room temperature,a Mg₃B₂O₆ modified layer was in-situ synthesized on the surface of the Li Ni_0.8Co_0.1Mn_0.1O₂ secondary particles.Finally,the Mg₃B₂O₆fully coats Li Ni_0.8Co_0.1Mn_0.1O₂ composite cathode material was prepared.The Mg₃B₂O₆ coating film with a thickness of about 10 nm was formed on the surface of the Li Ni_0.8Co_0.1Mn_0.1O₂.The film shows a cross-linked architecture consisted with nanosheets.Under the condition of the optimal coating amount（1%）,the specific discharge capacity of the composite remains160.6 m Ah·g^-1 after 400 cycles at a high cut-off voltage of 4.5 V and a current density of 1 C,and the capacity retention rate is up to 80.3%.The results reveal that the Mg₃B₂O₆ coating layer plays a significant role in promoting the cycling stability of the Li Ni_0.8Co_0.1Mn_0.1O₂.The simple and low-cost surface modification process is easy for industrial production.（3）In view of poor intrinsic conductivity and volume effect in the Li⁺ion de/intercalation process,as well as the common problem of low initial Coulombic efficiency for the metal sulfide anode materials.In this thesis,a 3D Sn S/Mo S₂/C composite anode material with nanosheet structure was constructed by a ball milling assisted salt template method.Under the optimal conditions,the initial Coulombic efficiency of the composite reaches 90.2%,and the average discharge capacity at the current densities of 0.2 and 5 A·g^-1 is 651.8and 238.8 m Ah·g^-1,respectively.The reversible capacity was 726.8 m Ah·g^-1after 100 cycles at 1.0 A·g^-1 and 514.5 m Ah·g^-1 after 500 long cycles at 1.0 A·g^-1,showing excellent cycling stability.This study found that the Sn S and Mo S₂ are encapsulated in the 3D carbon nanosheets in a capsule-like form,and local heterostructures are formed between the two grains.The abundant grain boundary suppress volume change during cycling,which promotes the development of capacity and improves cycling stability.（4）In view of the complex process problem that the organic redox active molecules usually require pre-polymerization as the cathode materials of ZIBs.In this thesis,1,5-naphthalene diamine was used as cathode material and directly fabricated into cathode in form of monomer.The electrode was assembled into the zinc-ion batteries.Electropolymerization is carried out through the initial discharge process to form polymers with conformational isomers.The initial discharge specific capacity is 128.7 m Ah·g^-1.It shows a high reversible capacity at high rate and a good cycle capacity retention rate at a high rate of 5 A·g^-1.The morphology and infrared spectra of the electrode materials before and after polymerization were compared.The results shows that the primary amine groups are involved in the polymerization reaction among 1,5-naphthalene diamine monomers.The electrons deviate from the amine group to generate free radical rearrangement and polymerization to form polymers with conformational isomers.