Study On High Energy-density And Long-life Secondary Batteries Using Oxygen Group Element-based Energy-storage Materials And Their Enhancement Mechanisms

Depending on the increasing demand of energy,the development of new energy storage technologies has become more and more important to address the energy crisis.Energy-storage materials based on compounds of oxygen group elements have received widespread attention and applied in lithium-based secondary batteries due to their stable nature and outstanding electrochemical performance.However,it is difficult to meet the requirements of long battery life with a single optimization over materials.In addition,the formation of lithium dendrites,resulted from uneven deposition of lithium metal in traditional lithium-ion batteries,not only depletes a large amount of active lithium and electrolyte,but also lead to high safety risks.It is a potentially efficient strategy to construct a lithium/magnesium dual-ion battery by combining the use of magnesium metal instead of lithium as a uniform ion deposition anode and lithium ion as an"ion reservoir"in the electrolyte,which does not tend to grow dendrites and can improve safety and electrochemical performance.In this thesis,a series of high-performance cathode materials for lithium storage or lithium/magnesium dual ion storage are designed and synthesized based on oxygen group elements.Combined with modified electrolytes,the electrochemical reaction mechanism of lithium based single/dual ion batteries are systematically studied,and methods to effectively improve the cycle life and performance of the batteries are demonstrated.The research work are mainly as follows:（1）A lamellar yolk–shell In₂O₃@S@C micro-nano structure with high conductivity and stability was prepared,which was used as the host for loading sulfur for lithium-sulfur battery,achieving high capacity and long cycling life.The yolk-shell structure has been verified by using synchrotron X-ray nanotomography technology.A powerful barrier that effectively inhibits the shuttling of polysulfides has been constructed through combination of chemisorption by core and physical confinement by shell,confining sulfur and polysulfides within a stable framework,enabling continuous kinetic conversion.The constructed lithium-sulfur battery exhibits a high capability over 1000 cycles at 1.0 C with a capacity decay rate as low as 0.038%per cycle.Tests at temperatures of-10°C and 50°C have also shown the wide temperature tolerance of the developed lithium-sulfur batteries.A nondestructive in situ monitoring method of the interfacial reaction resistance in different cycling stages has been studied,which provides a new analysis way for understanding the capacity decay of electrochemical energy-storage systems.（2）Although lithium-sulfur batteries have a high specific capacity,the inherent dendrite growth of lithium metal anode has always been a safety risk.A high-performance Li/Mg dual-ion battery combining the advantages of high safety and fast ionic kinetics was constructed by using a Ni Co₂S₄ cathode with a copper current collector,a dendrite-free magnesium metal anode and dual-salt electrolyte based on a modified all-phenyl complex.X-ray near-edge absorption spectroscopy has demonstrated that in a APC-Li TFSI dual-ion electrolyte with lithium bis（trifluoromethanesulfonyl）imide as lithium additive,the in-situ participation of a copper collector in the reaction improves the reactivity of Ni Co₂S₄ cathode,synergistically enhances the efficient storage and diffusion of lithium/magnesium dual ions,achieving low polarization and fast redox reaction kinetics.Such combination enables a reversible capacity of 204.7 m Ah g^-1 after 2600 cycles at 2.0 A g^-1,and delivers an ultrahigh full electrode-basis energy density of 708 Wh kg^-1 at 0.1 A g^-1.In addition,the dual-ion battery also shows good rate-performance and wide temperature tolerance at-10°C and 50°C.Both the electrochemical tests with limited electrolyte and the pouch cell show a good application potential of the developed dual-ion system.（3）The water-organic hybrid lithium/magnesium dual-ion electrolyte（APC-Li TFSI-4000）was further obtained by modifying and optimizing the aforementioned dual-ion electrolyte.A high-performance lithium/magnesium dual-ion energy storage system was constructed by combining the highly active Co Se₂ cathode using a copper current collector.The introduction of traces of water in the electrolyte completely releases the activity of lithium bis（trifluoromethanesulfonyl）imide,achieving ultra-fast dual-ion reaction kinetics and excellent rate-performance.Such Li/Mg dual-ion battery affords an exceptional long life of 4800 cycles at 5.0 A g^-1.Stable cycles of 7000 and4000 cycles were achieved at-10°C and 60°C respectively.In addition,the pouch cell achieves a stable long cycle of 1500 cycles and reversible charging and discharging at a low temperature of-10°C.The water-organic hybrid electrolyte strategy will inspire new ideas for the development of high-performance Li/Mg dual-ion batteries.（4）Considering the application performance of the above Li/Mg dual-ion batteries,a porous Ni_0.85Se nanosheet has also been prepared as the cathode for Li/Mg dual-ion batteries using lower cost Ni instead of Co.The novel water-organic hybrid electrolyte combined with the catalytic reaction of copper current collector further enhances the cycling stability of the dual-ion battery.This Li/Mg dual-ion battery achieves an extremely long reversible life of 10,000 cycles at 2.0 A g^-1 with a consistently high Coulombic efficiency of close to 100%.The stable long cycling at low temperatures of-10°C also demonstrate the practical potential of this dual-ion battery.In addition,multi-layered pouch cell based on the combination of electrolyte and cathode/anode shows the good value of the Li/Mg dual-ion energy storage systems.The three-dimensional reconstruction and elemental absorption edge imaging of the electrode material by synchrotron X-ray nanotomography technology has further yielded information on the spatial distribution of different elements in the material,providing a new analytical perspective for the study of the structural evolution of the electrode material in the dual-ion energy-storage system.