Design And Synthesis Of Nickel-based Transition Metal Electrode Materials And Their Enhanced Performances For Lithium Ion Batteries

With the fast pace of change in new energy resource technologies,portable electronic devices have become a significant and essential part of people's daily lives where the lithium ion battery(LIB)plays a core role.Nevertheless,the development of LIBs has failed to keep pace with the increasing demands of our life and work,which has led to people reconsidering due to their high cost but low capacity and poor cycling performance at higher rates.Transition metal compounds are widely used in lithium-ion batteries due to their high energy density and environmental friendliness,and nickel-based transition metal compounds are becoming hotter due to their high theoretical specific capacity,low self-discharge rate,and good safety of use when applied in lithium ion battery as electrode materials.For instance,the theoretical specific capacities of ternary cathode materials LiNi1/3CO1/3Mn1/3O2 and NiS2 anode materials are 278 and 870 mAh g-1,respectively.However,due to the appearance of lithium dendrites and the volume expansion of the electrode material during charging and discharging,the cycling stability of the lithium ion battery deteriorates and the poor conductivity directly leads to the unsatisfactory rate performance of the electrode material.Therefore,this article proposes effective methods to improve electrochemical performance for these two kinds of electrode materials,and makes detailed explanations for the results.1.Synthesis of disk-like LiNi1/3Co1/3Mn1/3O2 nanoplates with exposed(001)planes and study on their lithium propertiesThe disk-like LiNi1/3Co1/3Mn1/3O2 nanosheets were synthesized by adding a specific surfactant based on the Pechini method.The results show that the mixture of liquid surfactants plays a key role in the morphology change of the LiNi1/3Co1/3Mn1/3O2 nanosheets.It can not only make the nanoparticles uniformly dispersed,but also can change the size of the nanoparticles,and the most important is that the active planes can be exposed.X-ray diffraction(XRD)was used to analyze the phase composition of nanosheets.FESEM and HRTEM were used to characterize the morphology of the nanosheets.The electrochemical properties of the nanosheets were further explored.As a cathode active material,it displays a high specific capacity of 165 mAh g-1 at 2 C after 200 cycles while its capacity retention ratio is 98.2%.2.Synthesis of durian-like NiS2@rGO nanocomposites and study on their lithium properties durian-like NiS2@rGO nanocomposites was synthesized by a EDTA-2Na assisted hydrothermal method with adding appropriate amount of GO.The results showed that the EDTA-2Na and GO played important roles in the formation of durian-like morphology and the enhancement of the rate performance:EDTA-2Na as a kind of potent chelating agent could bind unstable Ni2+ as stable chelate compound and avoid Ni2+ from being oxidized by GO;the addition of the GO could not only increase the electrical conductivity of the electrode materials during the charge and discharge process,the GO with oxygen functional groups were also able to serve as a substrate for the nucleation of NiS2,and the functional groups between graphene oxides and NiS2 could promote good dispersion for nanomaterials during the nucleation and the growth process.The NiS2@rGO nanocomposites could deliver a reversible discharge capacity around 1053,947,885,798,603 mAh g-1 at the current rates of 100,200.500,1000,2000 mA g-1 and remain stable after 200 cycles when using as anode active materials in lithium ion batteries.