Preparation And Performance Regulation Of High Specific Capacity Lithium Ion Battery Electrode Materials

With the rapid development of electric vehicles and other energy storage devices,the demand for high specific capacity lithium ion battery electrode materials has been accelerated.Lithium nickel cobalt manganese oxide cathode materials(referred to as ternary material)have become a hot spot of research due to its high energy density and high stability,and have become promising cathode materials for new generation of commercial lithium ion batteries.However,with the increasing nickel content,the ternary materials have disadvantages such as poor rate performance and cycle stability,which cannot meet the demand of high-performance lithium ion batteries.Studies have shown that the electrochemical properties and structural stability of electrode materials are closely related to the composition,microstructure and morphology of the materials.The purpose of this paper is to study the regulation mechanism of multi-metal ion co-precipitation reaction,and combine it with the subsequent calcination treatment to effectively control the particle size,morphology,porosity,crystallinity,specific surface area and metal ion distribution of ternary materials.It aims to design and prepare high-performance lithium-ion battery electrode materials with high energy density,excellent rate and cycle performance,and high safety,through improving lithium ion diffusion rate,structural stability and safety performance of the electrode materials.A novel method based on “non-equilibrium interdiffusion induced by crystallinity difference” was proposed to prepare hollow structural materials.It was successfully applied to synthesis of one-dimensional hollow structure MC2O4·x H2O(M=Ni,Co,Mn,Cu and Fe)precursors.The mechanism of non-equilibrium interdiffusion induced by crystallinity difference was demonstrated by experiments.Specifically,core-shell oxalate precursors were synthesized by sequential co-precipitation.The core part of the core-shell oxalate precursors has poorer crystallinity,while the shell part has better crystallinity,which induces non-equilibrium interface diffusion between different layers.The driving force for the formation of the hollow structure is the crystallinity difference.The non-equilibrium interface diffusion method is general for hollow structure synthesis.This strategy is applicable not only in aqueous systems,but also in water/alcohol systems.Moreover,it can be extended to synthesize hollow structure multi-metal carbonate precursor with carbonate ions as precipitant.The method has mild reaction conditions and versatility,and provides an effective approach for preparing hollow structural materials.Considering that hollow structure materials have unique properties in energy storage,we successfully prepared a variety of one-dimensional tubular structure cathode materials,including Li Ni0.8Co0.1Mn0.1O2,Li Ni0.5Co0.2Mn0.3O2,Li Ni0.6Co0.2Mn0.2O2 and Li Ni0.8Co0.15Al0.05O2,by mixing the hollow structure oxalate precursor with lithium and subsequent calcination.The one-dimensional hollow structure oxalate precursor is advantageous for ion diffusion and transport during calcination due to its thin wall,thereby reducing the cation mixing,which is beneficial to improve the rate performance and cycle performance of the material.The one-dimensional hollow structure cathode material Li Ni0.8Co0.1Mn0.1O2 exhibits excellent rate performance and cycle performance.The first charge-discharge specific capacity was 232.2 and 194.5 m Ah g-1,respectively,and the coulombic efficiency of the first charge and discharge was 83.7%.After 100 cycles at 0.5 C rate,the capacity retention of the Li Ni0.8Co0.1Mn0.1O2 microtube sample reached 87.4%.In addition,the one-dimensional Na0.56Ni0.13Co0.13Mn0.54O2 microtube was also successfully prepared by mixing with sodium and subsequent calcination.The results showed that the prepared one-dimensional hollow structure material exhibits excellent electrochemical performance in both lithium ion battery and sodium ion battery system.In this dissertation,mild sequential co-precipitation and conventional co-precipitation reactions were also designed in a carbonate system to control synthesis of hierarchical urchin-like Ni Co2O4 hollow nanospheres and solid nanospheres,respectively.Ni Co2O4 hollow nanospheres and solid nanospheres were used as anode materials for lithium ion batteries,and their electrochemical properties were tested.The first discharge specific capacity of the as-prepared urchin-like Ni Co2O4 hollow nanospheres was 973.7 m Ah g-1 at 0.1 C rate and the capacity retention after 100 cycles was 95.6% at a discharge rate of 0.5 C.Furthermore,one-dimensional hollow structure Ni Co2O4 was prepared by oxalate sequential co-precipitation in aqueous solution system and used as anode material.The results showed that Ni Co2O4 hollow structure material exhibited better rate and cycling performances than the solid sample due to its larger specific surface area and shorter ion diffusion length.The hollow structure could suppress structural strain and have better cycle performance during charge and discharge.