Controllable Fabrication Of 3d Ternary Transition Metal Chalcogenides And Their Application In Alkali-Ion Batteries

In the modern society,it is almost impossible to get rid of the dependence on the electric energy.With the popularization of portable electronic devices and the promotion of electric vehicles(EVs)in China,it is imperative to develop energy storage systems that meet the demand of environmentally friendliness,efficiency and conveniences.Among so many energy storage systems,lithium-ion batteries(LIBs)have been applied in various energy storage occasions due to their higher energy density and portability.Although the advantages of lithium-ion batteries are extremely prominent,due to the low reserves of lithium elements,their cost is high low for them to meet the large-scale energy storage requirements.Therefore,sodium and potassium,which are the IA group elements with similar properties to lithium,have been developed as sodium/potassium-ion batteries,which can be functioned as a substitute for lithium-ion batteries.In alkali-ion(Li,Na,K)batteries,the anode,as the host material of alkali metal ions,plays a vital role for the overall cycle stability,safety and energy density of the battery.Among them,the transition metal chalcogenides(TMCs)anode materials have so many advantages such as high capacity,low toxicity,simple synthesis method and low cost,and has been widely favored by researchers in recent years.In order to solve the problems of TMCs materials such as low electroconductivity,serious serious volume change during cycles,and poor cycle stability,the main solutions are carbon coating,nanocrystallization,and the synthesizing ternary or even multi-element compounds through alloy engineering to increase absorption sites of alkali-ion,enhanced conductivity and cycle stability.In this paper,through some quick and convenient synthesis methods,several nano-sized ternary transition metal chalcogenide materials with carbon coating have been proposed,and their corresponding performance is investigated for alkali-ion batteries.The main contents for this paper are:1.A new synthetic strategy for carbon-coated high-quanlity FePSe3 nanosheets(termed as FePSe3/C)for was developed.The hybrid nanosheets were combined with van der Waals force and formed typical van der Waals heterostructure.Organic metal compounds ferrocene was employed as both Fe and carbon source to synthesis FePSe3 for the first time.The reaction time was largly shortened to 30 min at least while the original synthesis time takes about 7-10 days.Further investigations showed that the FePSe3 is in rhombohedral phase and the thickness of the nanosheets was measured to be about 15 nm.When functioned as cathode for secondary sodium batteries,FePSe3/C hybrid nanosheets presented satisfactory performance:when the voltage range was set as 0.8-2.2 V,Cs remained 182.7 mA h g-1 after 50 trails at 50 mA g-1;142 mA h g-1 remained at 1000 mA g-1 after 200 cycles.Also,it could also deliver excellent rate performance under different performing conditions ranging from 0.1 and 5 A g-1.2.A solid-state solution of MnS0.5Se0.5 nanocubes in rock-salt phase derivated from the corresponding endmembers of MnS and MnSe has been synthesized,and the MnS0.5Se0.5 nanocubes have been assembled with N-doped graphene to form a new kind of heterostructured nanohybrids(shortened as MnS0.5Se0.5/N-G hybrids),which are very potential for fabrication of metal-ion batteries including LIBs and/or SlBs.Investigations revealed that there had been vacancies generated and active sites increased via a nonequilibrium alloying of MnS and MnSe into the solid-state solution of the MnS0.5Se0.5 nanocubes with segregation and defects achieved in the relative low temperatures.Meanwhile,the introduction of N-doped graphene forming heterojunction interfaces between MnS0.5Se0.5 and N-doped graphene,which efficiently enhanced the electroconductivity and avoided agglomeration of the MnS0.5Se0.5 nanocubes with considerably improved electrochemical properties.As a result,the MnS0.5Se0.5/N-G hybrids delivered superior Li/Na storage capacities with outstanding rate performance as well as satisfactorily lasting stability(1038/457 mA h g-1 at 0.1 A g-1 after 100 cycles).Additionally,the full-cell LIBs of the anodic MnS0.5Se0.5/N-G constructed with cathodic LiFePO4(LFP)further confirmed the promising future for its practical application.3.A new synthetic route to high-quality carbon coated CoNiSe2 nanoparticles(termed as CoNiSe2@C)have been developed.The synthesis process involves the pyrolytic of bis(cyclopentadienyl)nickel,bis(cyclopentadienyl)cobalt and selenium powder at 600?.This simple one-pot synthesis method breaks through the limitations of original synthesis methods with multiple steps and long preparation time of CoNiSe2,besides,through this synthesis method,in-situ carbon coating can be achieved.When functioned as lithium-ion batteries anode,the CoNiSe2@C hybrids present a discharge capacity of 645 mA h g-1 after 100 cycles at 100 mA g-1,which showed almost no capacity decay.In addition,the CoNiSe2@C hybrids showed excellent rate performance and superior long-term stability.The capacity retention of 1 A g-1 after 1200 cycles are as high as 93%.At the same time,we have investigated the ability of the CoNiSe2@C hybrids as a potassium host material:the discharge capacity remained 165 mA h g-1 after 100 cycles at 100 mA g-1.The one-step synthesis method proposed in this chapter is simple and convenient,and the product showed excellent lithium-ion battery performance.It would provide a new synthetic method for other ternary or even multi-element transition metal chalcogenides that are difficult to synthesize.