Design And Research Of High-energy-density Anode Materials For Rechargeable Batteries

Among stable and sustainable electrochemical energy storage devices,batteries possess unique advantages of good portability,high energy density,long lifetime and zero emission,and other aspects of our life have a wide range of applications,such as portable electronic products,electric tools,automobiles,as well as implantable medical devices.The development of high-performance anode materials for secondary batteries has become one of the tasks in the research and development of high energy density and high safety secondary battery systems.The paper focused on the exploitation of high-capacity anode materials for second batteries?lithium and magnesium battery systems?based on in-situ alloying reactions With the aid of the stable framework of the compound,in this respect,constructing stable alloying in-situ Mn-based,Tin-based,Bi-based anode materials which can exhibit high storage capacity and long cycle life.The cyclic stability of alloying reversible energy storage materials was improved by designing large space network structure,fluorine surface modification and nanostructure.The research content of this thesis mainly includes the following three parts:???the experiments carried out in the lithium battery system are as follows:?1?MnWO₄ nano-materials or MnWO₄-based composites as high-capacity anode material has been demonstrated for reversible Li storage.However,because of the conversion reaction and the alloying reaction during the Li ion insertion/extraction,the experimental capacity of MnWO₄ is far from the theoretical value and dramatically fades after a few cycles.Fluorine?F?doping has been found to be an eff ective way to enhance the surface stability and cycling performance due to the intrinsic stability provided by the F atom.F-doped MnWO₄nano-particles were synthesized by a one-pot hydrothermal reaction.When evaluated as an electrode material for a Li ion battery,the F-doped nano-MnWO₄ delivers a theoretical capacity of 708mAh/g and long cycle life,as demonstrated by more than 85%capacity retention when cycled for 150 cycles.?2?Compared with the commonly used carbonaceous anode materials,Sn-based materials,with higher specific capacities,such as metallic tin?Sn?and tin based oxides?SnO,SnO₂?,have attracted much interest as one of the promising alternatives.However,the practical implementation of Sn-based materials for LIBs suffers from severe capacity loss and short cycle life originating from the great volume changes during lithiation/de-lithiation.The great volume changes lead to strong internal mechanical stresses,and particle cracking during electrochemical cycling.By locating elemental Sn in an open anionic framework,the particle cracking arising from huge volume expansion of Sn-based anode materials during lithiation/de-lithiation is alleviated,and the cycling stability is greatly improved.The Sn-based metal-organic-framework anode material shows superior cyclic stability,with a capacity retention?29?92%?after 200 cycles?and high lithium storage capacity?610mAh/g?.???Rechargeable magnesium battery with high volume energy density and higher safety has become a hot research object of green energy technology,but magnesium battery cathode material is facing more difficult challenges,and it is also crucial to study embedded anode material in magnesium battery system.The anode materials have also been studied in the magnesium battery system:Bismuth-based materials with high theoretical capacity?385mAh/g?are one of the most promising anode materials for magnesium ion batteries.However,these Bi-based materials are limited to fast capacity decay upon cycling because of the large volume changes during the alloying process.Therefore,more Bi-based materials with optimized structures and improved electrochemical performance are still required.A novel Bi-based anode material with a stable alloy reaction is prepared by a solvothermal method.The Mg storage mechanism is elucidated for the first time.Owing to the space confinement of in situ conversion,the anode material shows superior magnesium storage performance,especially the cycling stability?capacity retention?29?96%after 100 cycles?.