Study On The Electrochemical Property Of Ti-base Lepidocrocite-type Anode Materials For Potassium-ion Storage

With the rapid improvement of consumption level and electronic manufacturing technique,consumer electronic products have become necessary in our everyday lives.Lithium ion batteries have been popularly used as the main power supply for the portable electronic products,including the mobile phone batteries,laptops and digital cameras.And their application has been gradually extended to the electric vehicles.However,it is well known that lithium carbonaceous is rare in the earth curst with uneven distribution that can't satisfy the fast growing demand for renewable energy.Thus,exploration of a new type of energy storage device is more urgent than before.In contrast,potassium is rich in natural resources,which is 600 times larger than lithium reserves,as well as easier to obtain.Furthermore,the working principle of potassium ion secondary battery is identical with lithium ion batteries,which makes the potassium ion battery likely to replace lithium ion battery to become a new generation of energy storage devices.It is well known that electrode materials are the key factor in determining battery performance.Ti-based anode materials have received the widespread attention due to its stable chemical properties,nontoxicity,low cost and high safety.Meanwhile,Ti-based anode materials usually have high working voltage platform which can avoid the formation of lithium dendrites during the charge and discharge process.The voltage platforms of Ti-based material are very stable and both the chemical diffusion coefficient and coulombic efficiency are very high,which makes the Ti-based materials a very promising anode material for Lithium-Ion batteries.But Ti-based anode materials to be used in potassium ion battery still has many obvious disadvantages,such as low coulomb efficiency and bad cycle performance.It is meaningful to design of novel Ti-based anode material for potassium ion storage.In this thesis,we prepared two kinds of Ti-based lepidocrocite-type compounds K_0.8Li_0.27Ti_1.73O₄ and K_0.8Mg_0.4Ti_1.6O₄,together with their potassium storage properties.The main research results are listed as following:Firstly,we prepared pure phase of titanium lepidocrocite structure K0.8Li_0.27Ti1.₇₃O₄ material by a facile solid-state reaction.The introduction of K ions is likely to expand the interlayer spacing,which can accommodate more K ions;on the contrary,replacing Ti ions with Li ions can keep the charge balance.The electrode materials deliver an average capacity of 103.2 mA h g^-1,and good rate performance in the optimal voltage range.Furthermore,we studied the electrochemical reaction mechanism.During the charge and discharge process,the potassium ions abjection from the positive material and move to the negative side then embedded between the layers of anode material,then in the next charge and discharge process,the potassium ion transfer from anode side to cathode materials reversibly.Secondly,we use the simple solid-state reaction to prepare titanium lepidocrocite structure K_0.8Mg_0.4Ti_1.6O₄ material.As magnesium ion have higher diffusion energy barriers than lithium ion,more energy needed for magnesium ions spread from the octahedral side to the interlayer space,we designed and synthesized the new compound with more stable octahedral structure during the electrochemical process,so as to guarantee the material stability during the charge and discharge process and obtained more excellent coulombic efficiency,cycle and rate performance.In this thesis,we focused on Ti-based lepidocrocite-type compounds as the brand-new anode materials of potassium ion batteries,and obtained a better cycle and rate performance by replacing Ti partially with two different elements.At the same time,we discussed the essential reasons that compounds with different elements exhibited different electrochemical performance.In conclusion,our work on Ti-based lepidocrocite structure material provides a reference and new direction for the design and development of new anode materials for potassium ion batteries.