| In order to reduce the environmental pollution caused by the massive consumption of fossil fuels,green energy production and storage technologies have been vigorously developed in recent years.With the rapid growth of electric vehicles,wearable electronic devices and smartphones,the market demand for electrochemical energy storage is also increasing.At present,graphite as a negative electrode material has been widely used in battery production,but the traditional graphite negative electrode material mainly comes from non-renewable fossil fuels,consumes a lot of energy in the preparation process,and the material has low energy density and poor stability of large current cycle,which cannot meet the requirements of charging and discharging performance of new energy vehicles and intelligent equipment.Biomass carbon material has the advantages of renewable,pollution-free,wide source,etc.,and is expected to replace graphite as the main negative electrode material.The metal oxide Ti O2 material with good cycle stability is used to compound with biological carbon material,which has small volume change and good cycle stability and safety in the process of charge and discharge.In view of the disadvantages of low specific capacity of Ti O2,poor conductivity and easy aggregation,reducing Ti O2 aggregation and improving the conductivity is the research focus in this field.In this paper,wheat straw nanospheres with a wide range of sources were selected as carbon sources,and were prepared by hydrothermal carbonization method as anode materials for lithium-ion batteries.Kirkendall effect was used to prepare nano hollow Ti O2.The prepared carbon materials were combined with nano Ti O2,and the three materials were characterized and tested for electrochemical performance.The electrochemical transformation mechanism and charge-discharge performance of materials were investigated.The main research contents and conclusions are as follows:.（1）wheat straw pellet carbon was obtained by hydrothermal carbonization method.The effects of hydrothermal duration,additives and activation temperature on the morphology and properties of the material during hydrothermal carbonization process were investigated.The results showed that the hydrothermal temperature of 220℃and hydrothermal duration of 12 h had the best pellet formation effect and electrochemical performance.Three additives,ethanol,citric acid and ferric chloride,were added to change the degree of cellulose hydrolysis in the hydrothermal carbonization process.The results showed that when citric acid was used as an additive,it could not only promote the hydrolysis reaction,but also bring abundant functional groups,providing more active sites for Li+.The activation temperature of 700℃can retain more surface functional groups while having larger specific surface area.After electrochemical test,the discharge capacity of wheat straw ball carbon prepared under the best conditions stabilized at 570.7 m Ah g-1 after 100 cycles at 0.5 C rate.（2）Using Ti（SO4）2 titanium source,Kirkendal effect was used to prepare nano hollow Ti O2 and perform hydrothermal composite with wheat straw sphere carbon.The influence of hydrothermal composite duration on the properties of the composite was explored.The results showed that the hydrothermal duration was 24 h,Ti O2 was uniformly coated without large-scale aggregation,the carbon sphere was uniform in size,and the structure of the composite was stable.Excellent electrochemical performance,stable capacity at 530 m Ah g-1 after 100 cycles at 0.5 C current density.In order to test the cycling stability under high current density,the composite was cycled1000 times at a magnifying rate of 5 C,with 520.9 m Ah g-1 remaining.The experimental results show that the biological carbon material as the matrix can improve the conductivity of the composite material,Ti O2 can improve the cyclic stability of the material,and the synergistic effect of the two can improve the lithium storage performance of the composite material. |
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