Preparation And Electrochemical Properities Of Titanium-based Oxide Negative Materials For Sodium Ion Batteries

Economic development seriously relies on energy sources,while the consumption of fossil fuel gives rise to growing resource exhaustion and environmental pollution,which makes people turn their attention to clean and renewable energy sources such as solar energy,tidal energy,wind energy,and so on.However,a stable and reliable energy storage system is needed in ultilizing these renewable energy sources owing to their instability and severe dependence on nature.Electrochemical energy storage system can meet the requirements of practical application,especially,alkali metal?lithium and sodium?ion battery energy storage devices have received massive attention and been widely studied.Lithium-ion batteries are widely applied in communications equipment,electronic products and cars.Sodium-ion batteries are considered to be the most promising low-cost sustainable energy storage technology,especially in the field of large-scale energy storage,due to abundant sodium reserves and low price.Developing low cost and high performance electrode materials is the key to realize the commercialization of SIBs in the future.In this paper,titanium-based materials have been adopted as the subject investigated.A new type of layered Ti-based anode material and a type of Ti-based oxide capable of storaging sodium have been designed and synthesized,and their electrochemical properties were investigated systematically.The main research contents and results are as follows:A new type of layered Ti-based anode material,Na₂Li₂Ti₅O₁₂,has been synthesized via solid-state reaction and ion-exchange method.Compared with the precursor Na₂Li₂Ti₅O₁₂,there is no transformation in the crystal structure.The active site of sodium insertion increases when replacing the interlayer potassium atoms with sodium atoms,and the corresponding theoretical specific capacity increases accordingly.The results show that the ion-exchanged material delivers a high reversible specific capacity and excellent cycling performance with a capacity retention of 82.5%after 330 cycles?excluding the cycles at 200 mA/g for the activation?at the high current density of 400mA/g as anode for sodium-ion batteries.Moreover,it displays a reversible capacity of 60mAh/g at a huge current density of 4 A/g which surpasses all layered Ti-based anode materials reported.Electrodes prepared with different binders deliver different electrochemical properties since different binders have different mechanical binding forces.The elasticity of NaCMC is higher than PVDF and electrode prepared with more elastic NaCMC delivers higher initial coulombic efficiency and better cycling performance than that of PVDF.By means of dynamic analysis based on CV technique,it can be ovserved that there exists intercalation type pseudocapacitive behavior in Na₂Li₂Ti₅O₁₂,which is conducive to the rapid storage of sodium ions and the stability of long-term cycling.Nanocrystalline Ti Nb₂O₇ particles encapsulated in the amorphous region were synthesized by the amorphization treatment of the highly crystalline Ti-based oxide by a simple mechanical ball milling method and the lithium/sodium storage behaviors of crystalline TiNb₂O₇ and amorphous TiNb₂O₇ have been studied.Highly crystalline TiNb₂O₇ exhibits a reversible capacity of²60 mAh/g and favorable cycling performance while ball-milled displays low reversible capacity and sloping plateau in lithium-ion batteries,indicating that ball-milling destroys the lithium intercalation channels and sites.In sodium-ion batteries,ball-milled TiNb₂O₇ shows high reversible capacity while crystalline TiNb₂O₇ is not active in sodium storage,which suggest that ball-milling destroys lithium storage sites but increase sodium storage sites.Dynamic analysis based on CV technique reveals that sodium storage in ball-milled is a kind of capacitive behavior which comes from adsorption on the particle surface and sodium storage in lattice mismatch sites and amorphous area.As anode material for sodium-ion batteries,layered Ti-based materials exhibit high reversible capacity and favorable cycling performance as well as high voltage plateau which ensures the safety of batteries.The facile synthesis methods of the materials make them easy to be industrialized,providing valueable references for future research on sodium-ion batteries anode materials.