Preparation And Lithium Storage Properties Of Sunflower Seed Shell-Based Hard Carbon And Its Composites

With the development of science and technology,lithium-ion batteries are widely used in microelectronics,energy storage,and power systems due to their excellent stability,higher cycle life,and lower cost.The large-scale application of lithium-ion batteries stems from their excellent electrochemical performance,which largely depends on lithium-ion battery materials,namely,positive and negative electrode materials.However,the capacity of traditional graphite anode materials(372 m Ah g^-1)has a lower energy density in LIB.Therefore,it is necessary to study advanced harmful electrode materials with high capacity and long cycle performance.Transition metal oxides are considered as the most promising candidate anode materials,such as Mn₃O₄,which has a high theoretical capacity of(937 m Ah g^-1)and a low cost.However,Mn₃O₄ harmful electrode materials have poor conductivity and lithium ion transport efficiency and are prone to volume expansion and capacity loss during charging and discharging.To improve the above problems,we modified the Mn₃O₄ material.In this paper,sunflower seed shell porous carbon was prepared by high-temperature activation of potassium hydroxide using sunflower seed shell as raw material.Mn₃O₄ nanoparticles were embedded into the carbon matrix,and there was a good synergistic effect between the two.At the same time,physical characterization and electrochemical performance tests were conducted on the samples.The research content and results are as follows:（1）The sunflower seed shell and potassium hydroxide were impregnated in a weight ratio of 1:3、1:4 and 1:5,and then subjected to high-temperature activation at 600℃,700℃,and800℃for 1 hour after pre carbonization for 2 hours to obtain porous sunflower seed shell carbon（MSS）with a porous structure.Using a single control variable in two experiments,the effects of activator ratio and activation temperature on the microstructure and electrochemical properties of porous carbon materials were studied.The results show that the specific surface area of porous carbon increases with the increase in the ratio of activating agents.At an activation temperature of 700℃and an impregnation ratio of 1:4,porous carbon materials have the best lithium storage performance,maintaining a specific capacity of 582 m Ah g^-1after 100 cycles at a magnification of 0.2 C.The microstructure and electrochemical properties of carbon materials are closely related to the activation temperature.When the ratio of activating agent is 1:4 and the activation temperature is 700℃,carbon materials have the highest specific surface area(181.163 m² g^-1).（2）Mn₃O₄ nanoparticles were prepared by reacting Mn _SO₄?H₂O as a manganese source with ammonium persulfate.Mn₃O₄ nanoparticles were hydrothermally compounded with MSS and fired at high temperatures to prepare Mn₃O₄/MSS composite materials.The effects of hydrothermal time and the content of Mn₃O₄ on the comprehensive properties of the composite were studied.The results show that when the hydrothermal time is 36 h and the proportion of Mn₃O₄ is 50%,the Mn₃O₄/MSS composite has a stable structure,high specific surface area,and a specific capacity of 1248 m Ah g^-1（100 cycles）at 0.2 C.To verify the excellent performance of Mn₃O₄/MSS composite materials,comparisons were made with porous carbon MSS and pure phase Mn₃O₄ electrodes.The results show that MSS has good cycle stability,and the specific capacity of Mn₃O₄ decreases significantly.The specific capacity of Mn₃O₄/MSS composites is higher than that of pure Mn₃O₄.