Microstructure Design And Electrochemical Stability Of Tin-based Anode For Lithium Ion Batteries

With the rapid development of portable electronic products and electric equipments,lithium ion batteries?LIB?are required to meet the ever-growing demand for high energy density,power density and long cycle life.In order to enhance the comprehensive performance of LIB,researches are fastened on designing and developing new anode materials with high performance.Tin-based anode materials have been extensively investigated as candidates for their theoretical capacities about two or three times larger than those of commercial graphite.Unfortunately,the use of tin-based materials is still significantly hindered by large volume change during the lithium ion insertion/desertion process,which renders poor capacity retention and short cycle life.The goal of this paper is to improve the specific capacity,cycle performance and rate performance of Sn by microstructure design of tin-based composite electrodes.Hollow Sn-Cu nanoparticles and Sn-Cu nanotubes with zero and one-dimensional structures were synthesized by using galvanic replacement reaction.The Sn-Cu nanomaterials prepared by this method integrate three important structure features,such as hollow cavity,porous wall and bimetal,et al.These features can buffer stress caused by volume change and provide rapid transmission channel for lithium ions.Based on above structure superiority,these two kinds of hollow Sn-Cu materials exhibit favorable reversible capacity,cycling stability and rate capability.Particularly,Sn-Cu nanotubes delivered a capacity of 437 mA h g^-1 at current density of 0.1 A g^-1even after 200 cycles.We report facile synthesis to prepare three-dimensional porous polyaniline?PANi?hydrogel using ATMP and TPPS as crosslinking agent,respectively.Compared with conventional hydrogel,the ATMP cross-linked PANi hydrogel has a hierarchical porous nanostructure and high surface area(about 37.2 m² g^-1).Furthermore,it displayed excellent specific capacitance of 420 F g^-1 at current density of 0.5 A g^-1,and specific capacitance of 320 F g^-1 even after 2000 cycles at current density of 2 A g^-1.In addition,it can be made into three-dimensional micro-structural device or a fine pattern by using 3D printing or screen printing.A porous composite hydrogel was polymerized in-situ,resulting in a well-connected three-dimensional network consisting of Sn-Cu nanotubes conformally coated by PANi.Overlapped Sn-Cu nanotubes are fixed by PANi hydrogel to form a porous network,which provides fast path for the diffusion of electrons and lithium ions.The combination of Sn-Cu nanotubes and PANi hydrogel is similar to the reinforced concrete structure,which can ensure the integrity and stability of the electrode.As a result,this electrode exhibited a high reversible capacity of 548 mA h g^-1 after 500 cycles at the current density of 0.1 A g^-1.Furthermore,it exhibited a reversible capacity of 378 mA h g^-1 even at a much higher current density of 5 A g^-1.Multilayer Zn-doped SnO₂ nanospheres were successfully synthesized by using Sn/Zn bimetal-organic nanoparticles as precursor.These multilayer spheres are found to be very suitable for solving the critical volume expansion problem and mass transfer property due to its high surface area,small crystal size and hollow structure.Moreover,the covalently interconnected three-dimensional graphene foams encapsulated these multilayer spheres are successfully obtained through self-assembly effect and chemical cross-linking of graphene oxide nanosheets.The graphene network could further greatly improve the cycling stability and rate capability of the Zn-doped SnO₂ spheres electrode due to its flexible buffering matrix and high electric conduction.As a result,the graphene encapsulating multilayer Zn-doped SnO₂ spheres anodes exhibit excellent rate capacity and a high reversible capacity of 446 mA h g^-1even after 1000 cycles at the current density of 1 A g^-1.