Study On The High-capacity Anode Materials For Energy Storage Batteries

Since the first launch of lithium-ion battery(LIBs)by Sony corporation in 1991,LIBs are becoming the indispensable tools for the human beings and changing our everyday lives.To meet the ever-growing demand for electric vehicles and large-scale energy storage,researchers are chasing for higher energy and power densities than before as well as safety.However,as the commercially used graphite and lithium titanate oxide(Li₄Ti₅O₁₂),they still face the issues of dendrite formation and low specific capacity,respectively.Therefore,exploiting suitable anode materials with safer working voltage,higher reversible capacity and faster kinetic properties is more urgent than before.In addition,similar issues occur in the development of sodium-ion batteries(SIBs),which is characteristics as the abundant resources and low cost.However,the reversible capacity is still low owing to the large ionic radius of Na⁺ions.In view of the above-mentioned problems,this thesis aims to develop high-performance anode materials to satisfy the great demand for high efficiency Li⁺and Na⁺storage.We propose a series of materials design strategies and obtain several kinds of new anode materials.Besides the improved performance,we studied the structure-property relationship of anode materials,beneficial to develop new materials for ionic storage.The main research conclusions are listed as follows:Firstly,a new fast ion conductor Li_0.5La_0.5Ti O₃ anode is successfully synthesized via solid-state reaction.In comparison with commercial Li₄Ti₅O₁₂,Li_0.5La_0.5Ti O₃demonstrates a low working potential and high reversible capacity.In the voltage range of 0.01-3.0 V,Li_0.5La_0.5Ti O₃ delivers a reversible specific capacity of 229 m Ah g^-1.After 150 cycles,a high capacity retention is achieved as 97%.Moreover,beneficial from the inherent fast ion diffusion and pseudocapacitance,the micro-sized Li_0.5La_0.5Ti O₃ exhibits comparable rate performance as nano Li₄Ti₅O₁₂ with specific capacity of 101 m A h g^-1 at 10 C rate.In-situ synchrotron XRD suggests an intercalation mechanism with negligible cell parameters change of 0.068%after once charge-discharge.The first-principles calculations reveal that Li_0.5La_0.5Ti O₃ owns low lithium-ion migration barriers with decreased band gap of 1.3 e V.Secondly,we propose a new strategy to improve the volumetric capacity via constructing the carbon free electrode.By taking advantage of the metallic conductivity of Fe Se,we remove the conductive additives from the electrode complex,and increase the utilization of active material from 70%to 96.7%,the highest value in the sodium-based electrode materials.This strategy also could effectively increase the tap density of t-Fe Se electrode,and thus induce the high volumetric specific capacity up to 1011 m A h cm^-3.Impressively,the carbon-free t-Fe Se electrode delivers a high initial coulombic efficiency of 96%because removing out carbon additive and reducing the content of insulating binder could greatly suppresses the side reaction between the electrode and electrolyte.Then we extend the design strategy to lithium-ion battery system,achieving high volume energy density of 1373 W h L^-1 and power density of 7200 W h L^-1.Thirdly,a new composite compound using metallic Fe Se_0.5S_0.5 and high-capacity S element,to increase the reversible capacity and rate performance.Interestingly,a spontaneous chemical reaction occurs to form a Fe Se_0.5S_0.5@Cu-S heterostructure material.Beneficial from the unique heterostructure,Fe Se_0.5S_0.5@Cu-S delivers a high reversible specific capacity of 964 m A h g^-1 in the voltage range of 3.0-0.3 V at the current density of 200 m A g^-1,which is much higher than other conversion reaction materials.Moreover,the capacity retention of the heterostructure material can reach94.4%after 5000 cycles at a high current density of 10A g^-1.Even,at a high current density of 20A g^-1,the heterostructure could maintain a high capacity of 689 m Ah g^-1.Finally,we expand the above-mentioned strategy of using metallic materials as the anode to enhance ionic storage performance to synthesize metallic Fe Ti₂S₄ material which is self-assembled by nanosheets.In LIBs,Fe Ti₂S₄ anode shows a high reversible capacity of 811 m A h g^-1.After 50^th cycle,there is no capacity loss.At a high current density of 10A g^-1,Fe Ti₂S₄ could also deliver a capacity of 328 m A h g^-1.Then,we employ it as the anode material for SIBs and achieves a high reversible specific capacity475 m A h g^-1 after 2000 cycles.The excellent electrochemical performances could be attributed to the high conductivity of metallic Fe Ti₂S₄.In this thesis,we propose the several effective strategies to enhance the electrochemical performance of anode materials by taking advantage of high electronic conductivity.This methodology opens a new way to design high volumetric energy LIBs and SIBs in future.In addition,our proposed new anode materials demonstrate great potential in the commercial applications.