Preparation Of High-performance Transition Metal Chalcogenide Cathode Materials And Research On Aluminum Storage Performance

In recent years,new rechargeable battery technology has drawn widespread attention in energy storage field in consideration of the rapid increasing market requirement for the electrical vehicles and personal electronics.Among current well-studied energy storage devices,the rechargeable battery systems,for instance,the commercialized lithium-ion battery,still face severe challenges including high cost,safety problems and so on.However,due to its inherent safety,non-toxicity and high abundance?the most abundant metal elements in the earth's crust?,aluminum provides the possibility for the future large-scale application of aluminum ion batteries.In addition,as a trivalent charge carrier,aluminum possesses ultra-high theoretical specific gravimetric and volumetric capacities?about four times of lithium?,which makes aluminum one of the ideal elements for rechargeable batteries.Although great efforts have been made to apply aluminum to electrochemical energy storage devices since 1800,the development of aluminum ion batteries is still hindered by many problems,such as electrode material disintegration,the formation of passive oxide film,insufficient cycle life and so on.However,through unremitting efforts,Dai et al.have made breakthroughs in the research of aluminum ion batteries.They proposed a new aluminum ion battery based on ionic liquid electrolyte and three-dimensional graphite foam positive electrode.This aluminum ion battery effectively avoids the hydrogenation of the electrode and the rapid decay of capacity.Recently,a few feasible cathode materials,such as three-dimensional porous graphene,FeS₂,CoSe₂,SnS₂ and V₂O₅,with reasonable electrochemical performances in aluminum ion batteries have been proved.Unfortunately,to some extent,these materials still fail in outputting high energy density,excellent rate performance and long-term cycle stability.Therefore,the development of new cathode materials with excellent electrochemical performance and in-depth study of the electrochemical mechanism is urgently needed for targeting advanced aluminum-ion batteries.In this paper,the microstructure,phase information and electrochemical properties of the synthesized multi-level structured FeS₂@C,N-MoSe₂@C and WS₂ star-shaped microsheet cathode materials were studied in depth by a variety of ex-situ testing methods and first-principles calculations to study its electrochemical reaction mechanism.The main contents are as follows:?1?The novel nanoflake-assembled multi-layer structured Fe S₂@C hybrids were synthesized by a solvothermal method coupled with the sulfidation strategy.We can see that the as-prepared the Fe S₂@C exhibits prefer electrochemical performances.A high capacity of 212 and 95 mAh g^-1 can be achieved at the current density of 0.1 A g^-1 and 10 A g^-1.After 1000 cycles at a current density of1 A g^-1,the discharge specific capacity can be stabilized at?120 mAh g^-1 with the Coulomb efficiency of?100%.The novel carbon coated multi-layer architecture can effectively improve electrode conductivity and increase active materials/electrolyte interface area,accelerate the metal-ions/electrons transport,thereby offering an enhanced electrochemical performances.?2?A uniform N-MoSe₂@C composite cathode material was synthesized via an ion complexation-induced method followed by further selenization-within-nanospheres strategy and applied to aluminum ion batteries for the first time.The synthesized N-MoSe₂@C showed excellent aluminum storage performances with good rate capabilities and long-term cycling stability.The initial specific discharge capacity is?140 mAh g^-1 even at a high current density of 1 A g^-1 and maintain a high reversible specific capacity of 190 mAh g^-1 after 5000 cycles with a Coulomb efficiency of?100%.The superior electrochemical performances can be ascribed to the following characteristics:the small size and uniform distribution of MoSe₂ nanoparticles in the carbon matrix that provided short diffusion path for both electrons and ions;nitrogen doping further improves the conductivity of the carbon matrix,which greatly improves the transport efficiency of carriers in it;as a porous structure,the pores inside the composite material can effectively adapt to the volume expansion caused by the carriers embedded in the MoSe₂ layers.In addition,ex-situ XPS characterizations and DFT calculations confirmed that the electrochemical energy storage mechanism of the MoSe₂//Al battery is:reversible intercalation/deintercalation of Al³⁺ions between MoSe₂ layers at cathode,and reversible conversion between AlCl₄^-ions and Al₂Cl₇^-polyanions along with the anode.?3?We developed a facile ion complexation and followed by further vulcanization-within-nanosheet strategy to synthesize the novel star-shaped WS₂ microsheet assembly and applied then into aluminum-ion batteries.With the method of theory guides practice,the Al reactivity mechanism towards WS₂-based cathode was explored.Firstly,the DFT calculations revealed that the energy storage involved the intercalation of AlCl₄^-into WS₂ layers.Subsequently,we further confirmed the DFT calculation conjecture through ex-situ XRD and XPS tests,that is,during the charging and discharging process,the AlCl₄^-polyanion intercalation between the WS₂ layer and partial S₂^-oxidation reaction occurred in cathode.When assembled into a soft aluminum-ion battery,the as-synthesized WS₂ microsheet assemblies cathodes deliver impressive electrochemical characteristics(for example,119 mAh g^-1 remained after 500 cycles at 1 A g^-1).Furthermore,low and high temperature electrochemical performances of aluminum-ion batteries were explored,showing high capacity retentions in a wide temperature range of-20?70?.