Cr₂O₃ Carbon Composites Synthesis And Research On Lithium Electrical Properties

As an environmentally friendly renewable energy storage device,Lithium-ion batteries（LIBs）have been widely used in various portable electronic products.In recent years,with the rapid increase of household vehicles and atmospheric pollution LIBs have been used as power batteries in cars.People have higher requirements for energy density,safety performance and service life of LIBs.so researchers have been working hard to improve the performance of LIBs.The performance of LIBs mainly depend on the performance of electrode materials.Therefore,the development of cathode and anode materials is the key to improving the performance of LIBs.The commercial anode material（graphite carbon）has a relatively low specific capacity(372 mA hg^-1).The transition metal oxide has a high reversible capacity,which is about 2 to 5 times that of as much graphitic carbon,and they are cheap and easy to obtain.So they have gradually attracted people’s attention.However,they also have some drawbacks,such as poor conductivity,low reversible capacity and poor cycle stability etc.Therefore,in this paper,we synthesize the composites of C and Cr₂O₃ by using different methods.They contain the advantages of carbon materials and transition metal oxides,Which improve the electrochemical performance of chromium oxide as the anode material of lithium batteries.The specific research works as follows:（1）We used polyvinyl pyrrolidone as carbon source and added graphene to increase the conductivity of material.At the same time,we use the spray drying method to wrap chromium salts in carbon spheres.The innovation is that we used the decomposition characteristics of NH4Cl.When the material was carbonized in tube furnace at 620℃,NH₄Cl would be completely decomposed and then it would form a hollow carbon sphere structure.Finally,we synthesized the hollow core-shell composites（Cr₂O₃@C@G）.We could see its hollow structure after we observed with TEM.In addition,we conducted XRD tests on the materials of before and after calcination.We found that the materials not carbonized contained NH₄Cl,but the carbonized materials did not contain NH₄Cl.This is a good illustration of the role of NH₄Cl in the preparation process.The battery capacity is maintained at 648 mA hg^-1after 120 cycles at a current density of 0.1 Ag^-1.After 600 cycles at a current density of 1 Ag^-1,the battery capacity can still be maintained at 347 mA hg^-1.The outstanding electrochemical performance is mainly due to the special morphology of Cr₂O₃@C@G material.（2）We synthesized the binder-free electrode material Cr₂O₃@C by using electrospinning technology,Cr₂O₃ was well wrapped in the carbon fiber.It not only increases the conductivity of the electrode material,but also restrains the volume effect of Cr₂O₃ during charge and discharge.The results show that Cr₂O₃@C composites have better cycle characteristics and higher specific capacity.After testing,the battery capacity is 590 mA hg^-11 after 150 cycles at 0.1 Ag^-11 current density.We used SEM to observe the electrode material after cycling and found that the fiber still maintains a high degree of integrity which fully explains the reason why Cr₂O₃@C composites can perform long cycles.