Research On Preparation And Lithium Storage Properties Of Mn₃O₄/graphene Composites

As an important energy storage device,lithium-ion batteries play an important role in the mobile information era.With the advent of the era of electric vehicles,higher demands are placed on the performance of lithium-ion batteries.As one of the transition metal oxide?TMO?,the Mn_x O_y has the virtue of high theoretical capacity,environmental friendliness,and low price.However,TMO also have defects such as poor electrical conductivity and volume effect.In order to improve these defects,Mn₃O₄ is selected as the research object in this thesis.The multilayered graphene sheets?MLGS?prepared by simple ultrasound was used as a substrate to synthesize nano-manganese Mn₃O₄/multi-layer graphene composites,which method improved the lithium storage performance of the materials.In addition,Fe and Co ions were doped during the preparation process,and the effects of different doping levels on the lithium storage properties of the composites were discussed.With proper doping,the cycle stability and rate performance of the composites are improved.The specific research content is as follows:?1?Mn₃O₄/MLGS composites were prepared by a hydrothermal method.The nano Mn₃O₄ particles are evenly distributed on the graphene sheets,and the particle size is about10 nm.Compared to pure Mn₃O₄ having good rate capability and cycle,reversible capacity up to 620 mAhg^-1is demonstrated at a high current density of 100 m Ag^-1after 50 cycles;When loops back to 100 mAg^-1from high-rate of 2000 mAg^-1,the capacity retention rate is86%,and there is a high capacity retention rate,which reflects the improvement of the lithium storage capacity of the graphene composite on the Mn₃O₄.?2?Fe-doped Mn₃O₄/MLGS composites were synthesized by adding different amounts of iron ions,and the effects of different iron ion doping on the morphology and lithium storage properties of the composites were studied.As the proportion of iron ions increases,part of the particle size increases and a small amount of agglomeration occurs,and the gap between the particles increases.Electrochemical performance tests show that when the doped iron is 10%,the lithium-storage performance of the composite is superior,and at a current density of 100 mAg^-1,it has a reversible specific capacity of 720 mAhg^-1.At a high magnification current density of 1000 mAg^-1,the reversible specific capacity is 360 mAhg^-1after 10 cycles.Through appropriate iron ion doping,the lithium storage performance of the material is improved.?3?Co-doped Mn₃O₄/MLGS composites were synthesized by adding different amounts of cobalt ions.The effects of different cobalt ion doping on the morphology and lithium storage properties of the composites were studied.With the increase of the proportion of cobalt ions,the size of the Mn₃O₄ nanoparticles decreases,and the amount of loaded oxide on the graphene substrate increases,the distribution is uniform,and the proportion of oxides increases.Electrochemical tests showed that when 15%of cobalt was doped,the lithium storage performance was optimal,cycling and charging and discharging at 100 mAg^-1current density for 50 times,still maintain a reversible specific capacity of 900 mAhg^-1.At2000 mAg^-1high current density,the sample also performed excellently,with a reversible specific capacity of 420 mAhg^-1;it exhibited excellent rate performance.