Carbon-composited Materials With Special Structure As Anode Materials For Lithium Ion Battery

As traditional energy,fossil energy such as coal,oil and natural gas have played an allimportant role in global economic development.However,the energy exploitation and usage will cause some environmental problems such as.geological collapse and acid rain.In addition,the reserves of these fossil energy are limited and cannot be regenerated in a short period of time.As the population grows,the demand for energy is also increasing,so it is urgent to find an environment-friendly and recyclable energy?called new energy?.Only by finding a suitable new energy can people better promote economic development without affecting the environment,and promote the society from industrial civilization to ecological civilization.Lithium ion batteries?LIBs?is a new energy that have been invented recently.Compared with the traditional battery,LIBs have the advantages of long cycle life,no memory effect,non-pollution,high energy density and high output voltage.Due to these advantages,LIBs have been widely used in electronic products and transportation.In order to use LIBs for high energy density products,the electrochemical performance of LIBs needs to be further improved.As an important part of LIBs,anode material is also an important object that needs improvement.Graphite is used as the commercial anode material due to its high safety and low cost,but its low theoretical capacity?372mAh/g?limits the electrochemical performance of LIBs.So it is necessary to find some materials with high capacity to replace graphite,such as tin-based materials,transition metal oxides and sulfides.Although these materials own high capacity,they suffer from poor cycling performance due to the volume expansion and poor conductivity.This thesis focus on designing and preparing a caron-composited materials with special structure to improve the electrochemical performances of anode materials?tin-base materials,transition metal oxides and sulfides?by reducing the size of material,preparing special morphology,coating and compositing with carbon.The details are mainly as follows:1.Pomegranate-like porous carbon coated Cu_xSn_y/Sn/SnO₂ submicrospheres as anode materials for lithium ion battery.Tin-based materials such as Cu-Sn alloy,SnO₂ and Sn have attracted much attention due to their higher theoretical specific capacity when they are used as anode materials for LIBs.However,they suffer from poor cycling performance due to the volume expansion and poor conductivity.As carbon-coated and porous structure can buffer volume expansion,improve electrical conductivity and facilitate lithium ion transmission,thus this paper designed and prepared pomegranate-like Cu_xSn_y/Sn/SnO₂/C submicronsphere with nanoparticles,porous structure and carbon coating to improve the electrochemical performance of the material.The Cu_xSn_y/Sn/SnO₂ submicrosphere is prepared by in situ polymerization of the dopamine on the surface of CuSn?OH?₆ submicrosphere and then calcination in H₂/Ar atmosphere.The Cu_xSn_y/Sn/SnO₂ submicrosphere exhibits excellent cycle performance and rate performance when used as anode materials for LIBs.The test results show that the Cu_xSn_y/Sn/SnO₂/C submicrosphere can keep a capacity of 604mAh/g after 150 cycles at the current density of 200 mA/g.Based on the excellent performance of Cu_xSn_y/Sn/SnO₂/C submicrosphere,it is expected to become a promising anode material for LIBs.2.Sandwich-like C@SnO₂/Sn/void@C hollow spheres as anode materials for lithium ion battery.SnO₂ as anode materials for LIBs exhibits poor cycling performance due to the volume expansion during the cycling process.As hollow structure,carbon coating and introduction of Sn can accommodate the volume change under discharge/charge process,shorten the transmission distance of Li ions and increase the specific capacity,sandwich-like C@SnO₂/Sn/void@C hollow spheres?referred as C@SnO₂/Sn/void@C HSs?was designed and prepared in this work.The C@SnO₂/Sn/void@C HSs were facilely prepared by using SnO₂ as self-template,polymerizing the dopamine in the inner and outside surface of SnO₂,and then carbonizaion.The C@SnO₂/Sn/void@C HSs displayed excellent electrochemical performance as anode materials for LIBs,which delivered a high capacity of 786.7 mAh/g at the current density of 0.5 A/g after 60 cycles.In addition,the electrochemical performances of the products that obtained under different calcination temperatures and atmospheres were also studied.The results also showed that the cycle performance and rate performance of C@SnO₂/Sn/void@C HSs were much better.The simple synthesis method for C@SnO₂/Sn/void@C HSs with special structure will provide a promising method for preparing other anode materials for LIBs.3.Hierarchical three-dimensional porous MnO/void/N-doped carbon composites as anode materials for lithium ion battery.Manganese oxide?MnO?has a high theoretical specific capacity when used as LIBs anode materials.However its capacity decays rapidly due to the disadvantages of poor conductivity and volume expansion.The porous and void structure can relief the volume expansion in the lithiation-delithiation process,and the N-doped 3D carbon framework can enhance the conductivity of the composites,provide more channels for Li⁺transportation and sites for Li storage.Therefore,novel three-dimensional?3D?porous composites with void space constructed by one-dimensional MnO nanorods and 3D N-doped carbon framework?marked as 3Dp-MnO/void/NC?were designed and prepared in this study.When 3Dp-MnO/void/NC composites were served as anode materials for LIBs,enhanced cycling performance and rate performance were achieved.The results showed that the 3Dp-MnO/void/NC composites delivered a high capacity of 1000 mAh/g after 150 cycles at 200mA/g.Therefore,the proposed strategy can be extended to synthesize other 3D metal oxide composites with excellent electrochemical performance for LIBs.4.ReS₂@CMK-3 composites with nanosheets-on-channel architecture as anode materials for lithium ion battery.In the preparation of rhenium sulfide?ReS₂?,it agglomerated easily.Furthermore,ReS₂ suffered from poor cycle performance due to its poor conductivity and volume expansion when used as anode material for LIBs.As the CMK-3 can prevent the agglomeration of ReS₂ nanosheets,provide ordered porous structure and enhance the electrical conductivity of the composites,thus we have designed and prepared ReS₂@CMK-3 composites with nanosheets-on-channel structure,which were assembled by thin ReS₂ nanosheets growth on the CMK-3 channel.The ReS₂@CMK-3 composites were prepared by using CMK-3 as a nanoreactor with a facile one-pot hydrothermal method.Owing to the large surface area,ordered mesoporous structure and excellent electronic conductivity,the ReS₂@CMK-3 composites exhibited larger discharge capacity,superior cycling performance and higher rate performance compared with pristine ReS₂ when they were applied as anode materials for LIBs.As a result,the ReS₂@CMK-3 composites delivered a reversible capacity of 620 mAh/g after200 cycles at 0.5 A/g,indicating their potential as promising anode materials for LIBs.5.Fluffy carbon-coated ReS₂ nanoflowers as anode materials for lithium ion battery.Compositing with carbon is a common method to improve the electrochemical performance of ReS₂.But in the previous references,the contact surface between carbon materials and ReS₂ is limited,and ReS₂ has not been better protected.Because carbon-coated structure can increase the contact area and relief the volume expansion,thus carbon-coated ReS₂ nanoflowers?ReS₂/C nanoflowers?with a fluffy structure were designed and synthesized.In the preparation process,the polyethyleneglycol?PEG?is not only used as carbon source but also applied to reduce the particle size.Compared with the pure ReS₂,the obtained ReS₂/C nanoflowers own smaller particle size?²00 nm?,fluffy structure and high contact surface with carbon,which could accommodate the volume change under discharge/charge process,shorten the transmission distance of Li ions and enhance the electrical conductivity.As anode materials for LIBs,ReS₂/C nanoflowers can exhibit a high capacity of 501 mAh/g in the first cycle 215 mA/g and keep a capacity retention of 98%after100 cycles.This structure and easy preparation method can also be applied for the preparation of other transition metal sulfides.