Construction And Sodium-storage Performance Of Cation-doped Layered Metal Sulfide Nanosheet Arrays Grown On Carbon Papers

Due to the exhausting fossil energy and the deteriorating environment,it is imperative to develop the inexpensive,efficient and eco-friendly electrical-energy storage?EES?devices.The electrochemical-secondary battery is particularly attractive among multifarious energy storage technologies due to its highly efficient of energy conversion,simple maintenance and flexibility in use.The sodium-ion batteries?NIBs?,as an alternative to lithium-ion batteries?LIBs?,have attracted significant attention as promising candidates in recent years,owing to the high natural abundance of sodium resources,and similar working principles of sodium with lithium.The design of low-cost and high-performance anode materials is one of the key factors to promote its future commercialization.Among certain available candidates,two dimensional?2D?layered metal sulfides have great potential as anode materials to application in NIBs owing to their unique layered structures and high theoretical capacities.However,they usually suffer from low reversible capacity as well as poor rate performance and cycle performance,which seriously limit its progress and application in electrochemical performance.Here,cation doped layered metal sulfides?SnS₂ and MoS₂?nanosheet arrays uniformly grown on the substrate of carbon paper are successfully synthesized via a simple one-step hydrothermal method.The as-prepared samples,when directly used as binder-free anodes for NIBs,exhibit significantly improved the sodium-storage performance.The main research contents and conclusions are as follows:?1?Synthesis and sodium-storage performance of matal ion?Fe,Co and Ni?doped SnS₂ nanosheet arrays vertically grown on carbon paper:Tin tetrachloride is used as a tin source,thioacetamide as a sulfur source,commercial carbon paper as a substrate and a current collector,and a small amount of iron nitrate,cobalt chloride,nickel chloride as doped iron source,cobalt source,nickel source,respectively.Fe,Co,Ni separately doped SnS₂ nanosheets were prepared by one-step solvothermal method and the nanosheets uniformly rivet on the substrate of carbon paper to form a nano-network structure with open channels.By optimizing the amount of doping source,the self-supporting electrodes of CP@Fe6-SnS₂?Fe/?Fe+Sn?=6%?,CP@Co9-SnS₂?Co/?Co+Sn?=9%?,and CP@Ni9-SnS₂?Ni/?Ni+Sn?=9%?with the better performance were obtained.The as-prepared electrode CP@Fe6-SnS₂,CP@Co9-SnS₂and CP@Ni9-SnS₂ represent reversible capacity 434.0 mAh g^-1,428.3 mAh g^-1 and666.3 mAh g^-11 at 100 mA g^-1 after 100 cycles,which is much higher than pure CP@SnS₂ with a reversible capacity of 198.9 mAh g^-1.Furthermore,the rate performance of samples have also been greatly improved.At 1000 mA g^-1,the reversible capacities of CP@Fe6-SnS₂,CP@Co9-SnS₂ and CP@Ni9-SnS₂ are 245.6mAh g^-1,334.9 mAh g^-1 and 436.8 mAh g^-1,respectively.All is better than that of CP@SnS₂(169.9 mAh g^-1).The significantly improved electrochemical performance mainly because that doping will enlarge the interlayer distance of SnS₂?001?crystal plane,which is favorable for the insertion and extraction of Na⁺and creates more buffer space for the host material to undergo volume change during the electrochemical reaction.In addition,doping can generate a large number of defects acted as new active sites for the storage of sodium and cause re-adjustment of the internal electronic structure which improves the conductivity of the material.?2?Synthesis and sodium-storage performance of Fe doped MoS₂ nanosheet arrays vertically grown on carbon paper:Using thiourea,ammonium molybdate and ferric nitrate as sulfur source,molybdenum source and the iron source,respectively,and the commercial carbon paper as the substrate and the current collector,Fe doped MoS₂ nanosheets are highly ordered grown on carbon papers by a simple one-step hydrothermal method.When evaluated as anode electrode for NIBs,as-prepared CP@Fe6-MoS₂?Fe/?Fe+Mo?=6%?self-supporting electrode displays excellent electrochemical performances.CP@MoS₂ and CP@Fe6-MoS₂ display initial reversible capacity of 446 mAh g^-11 and 570.7 mAh g^-1 at 100 mA g^-1.Furthermore,the charge specific capacity can be maintain at 249.1 mAh g^-11 and 609.3 mAh g^-11 after 80cycles.At a high current density of 1000 mA g^-1,CP@MoS₂ and CP@Fe6-MoS₂exhibit reversible capacity of 178 mAh g^-1 and 296.3 mAh g^-1,which compared with the capacity at 100 mA g^-1,retention rates were 39.6%and 51.8%,respectively.Such superb electrical properties may mainly be attributed to the Fe doping which causes a large number of defects in the crystal structure of MoS₂ and improves the conductivity of the material.This work presents an efficient strategy of introducing the foreign cations into the crystalline structure of the host material,which opens the door to new possibility in tuning the intrinsic properties for improving the electrochemical properties of materials.