Design And Electrochemical Performance Of Anode Materials For Secondary Ion Batteries

Secondary ion batteries play an important role in our lives.Lithium ion batteries,in particular,make our lives smarter,healthier and cleaner by powering smart phones,wearable devices and electric vehicles.With the continuous development of electronic equipment,the demand for battery performance is increasing.The development of new anode materials for lithium ion batteries provides a way to meet these needs and solve the existing problems of graphite anode,such as low theoretical capacity and poor rate performance.Moreover,potassium ion batteries,are a possible alternative to lithium ion batteries in future application,and the research on anode materials of potassium ion batteries has also attracted the interest of a large number of scientific researchers.In view of the large volume changes,low capacity,and poor conductivity of secondary ion battery anode materials,it is still a big challenge to study anode materials for secondary ion battery with long life,high capacity and excellent rate performance.At present,there are mainly two ways to improve these problems.One of them is structural design,such as composite materials,improving specific surface area and so on.The other is microscopic composition control,such as doping.This paper focuses on these two methods to improve the electrochemical performance of anode materials of potassium ion batteries.The main contents are as follows:(1)A yolk-shell structure of C@TiO₂@Si(CTS)was proposed based on a template method of sol-gel chemistry.The silicon nanoparticles are encapsulated in C/TiO₂ bishells,and there are abundant voids between the silicon core and the C/TiO₂ shell.The yolk shell structure with concentric double shell greatly improves the structural stability of the electrode.Therefore,CTS provides a high specific capacity of 747 mA h g^-1 for lithium storage at a current density of 0.1 A g^-1,which is much better than that(356 mA h g^-1)of C@Si(CS)with only a carbon shell.(2)A free-standing flexible negative electrode,i.e.N-doped carbon nanotube paper(NCTP),was prepared for high-performance potassium storage.The results show that controlling the annealing temperature can effectively improve the nitrogen doping content,carbon defect level and graphitization degree.By comparison of the electrochemical test results,the NCTP annealed at 700 ^? showed a high reversible capacity of 250.1 mA h g^-1at 100 mA g^-1,which showed the most excellent performance,and maintained a high rate capacity of 133 mA h g^-1 at 5 A g^-1.The excellent electrochemical performance comes from the synergistic effect of moderate nitrogen doping,carbon defects and high conductivity of the material.(3)Free-standing electrode of germanium-loaded carbon nanotube arrays(Ge@CNTs)was fabricated by chemical vapor deposition(CVD)and physical vapor deposition(PVD).As an anode material for potassium ion batteries,it exhibits a reversible capacity of 0.1574?A h cm^-2 at 50?A cm^-2 after 100 cycles.The unique structure design of Ge coated CNTs array provides better electrochemical performances compared with Ge and CNTs.