Synthesis And Electrochemical Performances Of Tin Sulfide (Monosulfide)/Graphene Composites

Rechargeable lithium ion batteries?LIB?have high energy density and are important power sources for electronic devices and electric/hybrid vehicles.At the same time,due to the low cost of sodium resources,sodium ion batteries?SIB?have also received widespread attention.However,the theoretical capacity of commercially available graphite anode materials is relatively limited(372 m Ah g^-1).In particular,when graphite is used as the anode of SIB,the capacity is only 35 m Ah g^-1,which has been unable to meet the requirements of energy density.Recently,metal sulfides?Sn S₂,Sn S?have received more and more attention due to the high theoretical capacity.Graphene also gain the attention due to the highe electrical conductivity,large specific surface area and structural stability.The conductivity of the material can also accommodate the volume expansion of the metal sulfide during charging and discharging,so as to obtain better cycle stability and rate performance.However,due to the large atomic radius of sodium ions,the limited layer spacing and easy stacking characteristics of the layered material Sn S₂,the electrode structure will be unstable and the migration rate of Li⁺/Na⁺will be limited.The initial coulomb efficiency is relatively low.Therefore,in this paper,with the focus on size controlling,adjusting the layer spacing,and improving the initial Coulomb efficiency,separately prepared Sn S₂/graphene composites with size-tunable and interlayer expansion and Sn S tightly wrapped in multilayer graphene composite to reconstruct flake-like graphite structure to improve Li⁺/Na⁺migration speed and initial coulomb efficiency.The specific research contents are as follows:?1?Controlling the particle sizes of electrode materials has long been recognized as an effective way to improve the cycle stability and rate property of both lithium-ion battery?LIB?and sodium-ion battery?SIB?.A simple one-step hydrothermal process for the preparation of composites with size-tunable tin disulfide on reduced graphene oxide?Sn S₂/RGO?is reported.These novel material allow to comprehensively study the effect of particle sizes on electrochemical properties for LIB and SIB anodes.The structure,morphology,phase compositions,and Li⁺/Na⁺storage behaviors of three different Sn S₂/RGO composites obtained at heat-treatment times of 12,24 and 48 hours are characterized systematically.The electrochemical reaction kinetics is demonstrated by differential charge capacity plots and apparent ion diffusion coefficients.Surface capacitive and diffusion-controlled capacitive contributions to lithium/sodium ions storage are also compared.The results show that the small-sized nanoarchitecture can promote both the charge and ions transfer and thus improve the pseudocapacitor contribution.The reversible capacity maintains at 1211 m Ah g^-1for LIB after 200 cycles and 841 m Ah g^-1for SIB after 100 cycles,respectively.?2?Sn S₂materials have attracted broad attention in the field of electrochemical energy storage due to its layered structure with high specific capacity.However,the easy restacking property during charge/discharge cycling would lead to electrode structure instability and serve capacity decrease.We report a simple one-step hydrothermal synthesis of Sn S₂/graphene/Sn S₂?Sn S₂/r GO/Sn S₂?composite with ultrathin Sn S₂nanosheets covalently decorated on both sides of reduced graphene oxide sheets via C?S bonds.Owing to the graphene sandwiched between two Sn S₂sheets,the composite presents an enlarged interlayer spacing of?8.03?for Sn S₂,which could facilitate the insertion/extraction of Li⁺/Na⁺ion with rapid transport kinetics,as well as inhibiting the re-stacking of Sn S₂nanosheets during the charge/discharge cycling.The density functional theory calculation reveals the most stable state of the moderate interlayer spacing for the sandwich-like composite.The diffusion coefficients of Li/Na-ions from both molecular simulation and experimental observation also demonstrate that that this state is the most suitable for fast ions transport.In addition,numerous ultra-tiny Sn S₂nanoparticles anchored on the graphene sheets can generate dominant pseudocapacitive contribution to the composite especially at large current density,guaranteeing its excellent high-rate performance with 844 and 765 m Ah g^-1for Li/Na-ion batteries even at10 A g^?1.No distinct morphology changes occur after 200 cycles,and the Sn S₂nanoparticles still recover to pristine phase without distinct agglomeration,demonstrate that this composite with high rate capabilities and excellent cycle stability.?3?As an anode electrode material for lithium ion batteries,Sn S has a high specific capacity and has received widespread attention,but its practical application is still hindered by low reversibility of conversion reaction and large irreversible capacity caused by solid electrolyte interphase?SEI?.In this paper,Sn S nanoparticles are encapsulated into sulfur-doping graphene bubble film?Sn S@G?by a scalable electrostatic self-assembly of Sn S₂/graphene oxide and hexadecyl trimethyl ammonium bromide,then followed by thermal decomposition of Sn S₂and sulfur-doping in graphene.Due to electrostatic attraction,Sn S nanoparticles are tightly wrapped in multilayer graphene sheets to form a flake-graphite-like structure.Compared with the disorderly stacked Sn S/graphene sheet composite,the closely packed Sn S@G shows much lower specific surface area,smaller irreversible Li⁺consumption and surface film resistance after lithiation.The Sn S@G composite anode exhibits great initial Coulombic efficiency?83.2%?,which is the highest value among the chemical synthesized Sn S anodes.It also presents unprecedented cycling stability(1462 m Ah g^?1after 200 cycles at 0.1 A g^-1and1020 m Ah g^?1after 500 cycles at 1 A g^-1)and superior rate capabilities(750 m Ah g^-1at 5A g^?1)upon Li storage,which demonstrates its excellent electrochemical performance and great potential as a negative electrode material for lithium ion batteries.