Phase Transition And Control Of SnO₂-based Anode Materials In Electrochemical Process

The loss of structure integrity and intrinsic poor conductivity of SnO₂ anode are regarded as the main origination of capacity decay and poor rate capability.In this work,a serious phase separation of???during cycling was confirmed and related with the capacity decaying closely.To address these challenges,We synthesized SnO₂based composites with different nanostructure based on the modification idea of doping,designing special nanostructures and compounding other materials,and studied their electrochemical properties.At the same time,the mechanism of dopants and nanostructures to enhance the electrochemical performance of materials was also studied.An amorphous transparent Nb doped SnO₂ thin film with high conductivity was fabricated.The Nb dopant with a full oxidation state endows SnO₂ with high conductivity of 211.42 S/cm by increasing its carrier concentration to the level of 3.02×10^-20 cm^-3.At a rate of 20 C(about 30 Ag^-1),discharge capacity of Nb doped SnO₂thin film with Nb content of 6 at.%can still remain 658 mAhg^-1 and the discharge capacity of this sample can maintain at 986 mAhg^-1 after 90 cycles when the rate returned back to 0.1 C.During the electrochemical cycling,the strong interplay of Nb dopant with host SnO₂ was verified.Nb with an optimized content of 6 at.%can suppress the allotropy transformation from?-Sn to?-Sn and sustain a capacity of982.7 mAhg^-1 till to 200 cycles.At the same time,Nb doped amorphous SnO₂crystallized into rutile structure,which would help to release stress caused by lithiation and delithiation during electrochemical reaction.The improved cycling performance is closely related with a persistence of Nb⁵⁺valence,which will help to keep high conductivity of the host SnO₂ materials.As a result,Nb doped SnO₂ thin film with Nb content of 6 at.%remained crack-free,with a low electrical impedance within 200 cycles.The SnO₂ nanotubes@Nb doped TiO₂ nanorods composite was fabricated by electrospinning and hydrothermal method.SnO₂ nanotubes have the hollow structure,which is conducive to the full penetration of the electrolyte.The Nb doped TiO₂nanorods uniformly cover the tube surface and act as a solid shell during the cycling,effectively suppressing the volume expansion of the SnO₂ nanotubes and maintaining the stability of the structure,thereby increasing its reversible specific capacity and cycling stability.In addition,the connected nanorods form a good charge transport network.At a rate of 5C,the sample with optimal parameters can maintain a discharge capacity of 644.9 mAhg^-1.