Preparation Of Transition Metal Compounds And Research On Electrochemical Performance

With the consumption of traditional fossil fuels and the increasing demand for the environment,efficient,green,economical lithium-ion battery has been successfully applied in production and life.Negative electrode as an important part of lithium-ion battery,which plays a pivotal role in the performance of lithium-ion battery.However,there’re some problems about the commercial graphite such as relatively low reversible specific capacity.Therefore,there is an urgent need to develop such materials with a high specific capacity and long cycle life.The transition metal chalcogenide compounds have become promising anode materials because of their high theoretical specific capacity.However,a single chalcogen compound still has some drawbacks,such as short cycle life,severe bulk expansion,etc.;by the introduction of carbon material or its metal or non-metallic doping is an effective solution.With the properties of the tunable of types and the proportion in layered metal ions,hydrotalcite,layered functional materials,has made rapid development in many areas.Herein,we successfully prepared three kinds of materials for the anode of lithium-ion battery by high temperature pyrolysis hydrotalcite precursors,which have long cycle life and high reversible capacities.The main contents and innovations of the paper are as follows:（1）Preparation of Co6.75Fe2.2.5S8/NSAC,Co6.5Fe2.5Sg/NSAC and the electrochemical research:The precursor of CoFeAl-LDH was first prepared via the method of separate nucleation and crystallization through the equipment of colloid mill,and then by calcination and subsequently by acid etching process of CoFeAl-LDH/AY49 containing both carbon,nitrogen and sulfur with a mass ratio of 1:3,Co6.75Fe2.25S8 embedded within N,S-doped amorphous carbon（Co6.75Fe2.2.5S8/NSAC）nanosheet with a combination of microporous and mesoporous architectures has been obtained.The self-generating N,S co-doped carbon could improve conductivity and cycling stability resulting from a buffering effect.The special architecture would be able to facilitate the mass diffusion and ion transport and accommodate the volume change during the charge-discharge process.The composite indeed exhibits high reversible capacities,long cycling life and excellent rate capability.In addition,a MgCoFe-LDH precursor was prepared by the same method based on the basis of the great flexibility of readily varying cationic type and molar ratio of LDH precursor.The cobalt-iron sulfide with similar structure and different proportions(Co_6.5Fe_2.5S₈/NSAC)was also obtained via the same method,which showed boosted cycle behaviors after test.（2）Preparation of Co_0.75Fe_0.25（S0.2Se0.8）₂ and its electrochemical performance:Firstly,the CoFe-LDH precursor was prepared by nucleation crystallization isolation method.Then the sulfur-doped cobalt iron selenide[Co_0.75Fe_0.25（S0.2Se0.8）₂]was derived from the high temperature roasting of a mixture composed of the precursor,sulfur powder and selenium powder in a mass ratio of 1:1:1 by fully grinding.Electrochemical performance shows that the reversible specific capacity,cycle life and rate capability of sulfur-doped cobalt iron selenide[Co_0.75Fe_0.25（S0.2Se0.8）₂]are far superior to un-doped cobalt-iron selenide Co_0.75Fe_0.25Se2.