Preparation And Electrochemical Li/Na-storage Characteristics Of 3D Mesoporous Carbon/Tin Dioxide Composites

At present,the conventional graphite anodes used in commercial lithium-ion batteries（LIBs）have a low theoretical specific capacity of 372 mAh g^-1 and poor rate performance,seriously hindering the development of next-generation LIBs with high energy density and high rate performance.SnO₂ anode,which possesses an outstanding specific capacity of 782 mAh g^-1 in LIB_S,is considered as the potential substitute material for graphite anode due to its suitable execution voltage,environmental benignity,natural abundance,and low price advantages.However,some inherent disadvantages of SnO₂ anode,such as insufficient electrical conductivity,huge volume expansion,and severe agglomeration during cycling,depress its practical applications in LIBs.To overcome the disadvantages of SnO₂anode,in this paper,SnO₂/carbon composites with three-dimensional mesoporous morphology were fabricated,and their electrochemical Li/Na-storage performances were studied.The main works of this paper are as follows:（1）The NMC@SnO₂ composite,in which active SnO₂ nanoparticles were coated by the N-doped mesoporous carbon matrix,was prepared by a facile SiO₂ template method,using glucosamine hydrochloride as carbon source and nitrogen source,and stannous chloride as tin source.It was found that the content of tin dioxide in NMC@SnO₂ significantly affects the morphology and electrochemical properties of the hybrid electrode materials.The active SnO₂ could be strictly coated by carbon matrix in the NMC@SnO₂ composite with 32 wt.%of SnO₂ and exhibits superior electrochemical Li/Na-storage performance.When used as anode material for LIBs,the discharge capacity of NMC@SnO₂ remains at 782.7 mAh g^-1 after 300discharge/charge cycles at 0.5 A g^-1.And a high discharge capacity of 304.3 mAh g^-1is obtained after 300 cycles at a current density of 0.2 A g^-1 in SIBs.（2）To further enhance the electrochemical performance of the 3D SnO₂/C composites,the N-doped mesoporous carbon（NMC）framework was prepared firstly by SiO₂ template method and served as the preformed carbon matrix in the following procedure.Then,the 3D NMC/SnO₂ composite with ultrafine SnO₂ particles（～5 nm）was fabricated via a facile wet-impregnation approach.Finally,the NMC/SnO₂@PPy was fabricated through a vapor-phase polymerization approach.In the NMC/SnO₂@PPy composite,both the inside and outside walls of NMC/SnO₂ were in situ coated by ultrathin polypyrrole（PPy）layers.And the electrochemical experiment results show that the NMC/SnO₂@PPy anode exhibits outstanding electrochemical Li/Na-storage performance.In LIBs,the discharge capacity of 774.9 mAh g^-1 can be achieved after 300 charge/discharge cycles at a current density of 0.5 A g^-1.A high discharge capacity of 591 mAh g^-1 can be maintained after 1000 cycles at a high current density of 1 A g^-1.When tested in SIBs at a current density of 0.2 A g^-1,the NMC/SnO₂@PPy anode shows a reversible capacity of 343.2 mAh g^-1 after 300cycles.