Study On The Electrochemical Performance Of Cr₂O₃-based Nanocomposites As Anode Materials For Lithium-ion Batteries

In recent years,our country has vigorously developed the application of clean energy.Among the many clean energy applications,lithium-ion batteries have rapidly dominated the new energy market due to their environmental protection and low-cost advantages,and have broad development prospects.At present,with the vigorous development of electronic products and electric vehicles,traditional carbon material batteries are increasingly limiting their applications due to their low specific capacity.Therefore,researchers focus their research on new anode materials for improving the energy density of lithium-ion batteries,one of the main directions is transition metal oxides with generally high theoretical specific capacity.Among the transition metals,Co₃O₄,Fe₂O₃,MnO,NiO,etc,all have higher theoretical specific capacities.However,the higher discharge plateaus of these materials result in a narrower battery voltage window,resulting in lower battery energy density.Cr₂O₃has obvious advantages over other transition metal oxides due to its higher theoretical specific capacity（1058 mAh/g）and lower discharge plateau,and is considered as a promising anode material for lithium-ion batteries.However,the traditional Cr₂O₃ material,like other transition metal oxides,undergoes a huge change in volume after charging and discharging cycles,and the internal structure of the material is destroyed.With the increase of the number of cycles,the battery performance will also decrease rapidly.This problem severely limits the application of this material in Li-ion batteries.It has been found that constructing nanocomposites with special morphologies,such as mesoporous and carbon-coated structures,while reducing the degree of particle aggregation,can effectively deal with the above problems.Based on the research,this paper will take the chromium trioxide crystal as the basis of the research object,and carry out the following three aspects of work to prepare the corresponding nanocomposite materials,and to study and improve their electrochemical properties:（1）In the experiment,ammonium chromate（（NH₄）₂CrO₄）was used as the precursor to synthesize the negative electrode material of lithium ion battery.In the reactor,（NH₄）₂CrO₄ reacts with sucrose（carbon source）hydrothermally to form nanocomposite particles with a very stable core-shell structure,and the molar mass ratio of precursor to carbon source is 2:1 and 1:1 two groups of samples,and three groups of samples in total with the bare Cr₂O₃ crystals obtained by calcining the precursor.The experimental results show that the carbon-coated nanocomposite（Cr₂O₃@C）has improved energy density performance and cycling stability for Li-ion batteries compared to bare Cr₂O₃ crystals.And the sample with a molar ratio of 1:1 reached a reversible specific capacity of 542mAh·g^-1 after 300 charge-discharge cycles at a current density of 100 mA·g^-1,showing more superior electrochemical performance.（2）The experiment continued to use ammonium chromate as a precursor to synthesize the negative electrode material of lithium ion battery.The ammonium chromate crystals were first calcined,and then phenolic resin was used as the carbon source.After grinding and drying,annealing was performed.The Cr₂O₃@C nanocomposites with a core-shell structure were divided into three groups of samples according to the amount of phenolic resin.After characterization and electrochemical testing,it was found that when 240 mg of phenolic resin was used,the coating effect was the best and the particle size was more uniform.After 300 charge-discharge cycles at a current density of 100 mA·g^-1,a reversible specific capacity of 541.7 mAh·g^-1 was achieved.（3）Finally,the experiment used chromium nitrate nonahydrate（Cr（NO₃）₃·9H₂O）as the precursor,sucrose as the carbon source,graphene oxide（GO）as the dopant,and urea as the precipitant.G/Cr₂O₃@C（carbon-coated graphene/chromium trioxide composite）was prepared by hydrothermal method and annealing treatment using different experimental sequences.Characterization images show that the wrinkled graphene flakes are doped between the Cr₂O₃@C particles,and the particle size is small,which weakens the aggregation phenomenon.In terms of electrochemical performance,after 100 charge-discharge cycles at a current density of 100 mA·g^-1,a reversible specific capacity of 571.9 mAh·g^-1 was achieved,and the rate performance test reached762.7 mAh·g^-1.The experimental results show that the special structure of Cr₂O₃-based materials can be synthesized by using the appropriate proportion of carbon source and doping material,which can greatly improve the electrochemical performance of Cr₂O₃-based materials as anode materials for lithium ion batteries.