Preparation And Properties Of WS₂/C Composites As Anode For Lithium And Sodium Ion Batteries

Lithium-ion batteries and sodium-ion batteries are the most important secondary batteries in the field of energy storage,and have been widely studied and put into use.With the advent of two-dimensional material research,transition metal sulfides（TMDCs）with two-dimensional structure have also become a hot issue.The ionic metals in TMDCs have many valence states and diversity,as a conversion type battery.It has a high theoretical specific capacity when used as an anode for lithium ion and sodium ion batteries in the field of energy storage.Taking tungsten disulfide（WS₂）as an example,its interplanar spacing is 6.18?,about 0.65-0.7 nm,and the crystal planes are connected by van der Waals force.Some characteristics of the intercalated anode material exist in the intercalation of ions,which makes it have great advantages in the field of secondary battery energy storage.However,in the actual energy storage research,it has been found that TMDCs have problems such as poor conductivity and serious volume expansion.To overcome these limitations,carbon-based materials can be added as a composite component to increase electrical conductivity and buffer volume expansion during charging/discharging.In addition to acting as conductive and protective materials,carbon materials can increase the specific capacity and cycle life of lithium-ion and sodium-ion battery applications,effectively extending cycle life.Therefore,this paper mainly studies the synergistic effect of nano-crystallization of WS₂ and carbon materials.The specific work is as follows:1、In the process of hydrothermal preparation of WS2,surfactants were used to control the growth of crystals,and a micron-sized pure 2H crystal form of WS₂（2H-WS2）nanoporous spheres（WS₂ Nano-MS）was prepared.WS₂ Nano-MS has high capacity performance(100mAg^-1:776.6/374.8mAhg^-1;1000mAg^-1:472.3/217.2mAhg^-1)and high cycle retention（81.2/55%;72.8/38.7%）when used as a lithium/sodium ion battery anode.It can be seen that the nanostructured WS₂ has a certain improvement in lithium/sodium storage performance,but has poor performance at high current density and in sodium ion batteries.2、The WS₂ Nano-MS was optimized under the premise of nanocrystallization.Nano-hollow carbon spheres were introduced as the growth carbon substrate of 2H-WS₂,and a nano-sized 2H-WS₂/hollow carbon sphere composite anode material（WS₂ Nano-HMS）was prepared.When used as a lithium/sodium ion battery anode,WS₂ Nano-HMS has higher capacity performance(100mAg^-1:987/575.2mAhg^-1;1000mAg^-1:825.5/379mAhg^-1)and higher cycle retention（81.5/76%;64/49.3%）.It can be seen that the introduction of nano hollow carbon spheres improves the lithium/sodium storage performance of the electrode material,but the irreversible collapse of the hollow carbon sphere at a large current density results in poor cycle stability.3、A nano-sized 2H-WS₂/rGO composite electrode material（WS₂/rGO Nano-HC）was prepared by introducing graphene as the growth carbon substrate of 2H-WS2 under the premise of nanocrystallization.WS₂/rGO Nano-HC has higher capacity performance(100mAg^-1:1097/668.5mAhg^-1;1000mAg^-1:932.8/259mAhg^-1)and higher cycle retention rate（86.7/78.1%;86/73.2%）when used as a lithium/sodium ion battery anode.It can be seen that the introduction of graphene converts the composite electrode material into a two-dimensional structure,which further optimizes the electrochemical performance of the composite electrode.