| In the past,researchers mainly studied the energy conversion based on insertion-deinsertion mechanism of simple metal cations(such as Li+,Na+,etc.)in layered materials,but neglected the energy conversion of coordination anions under certain conditions.This is because most of the coordination anions have large ionic radius and relatively high electrochemical stability.Fortunately,the dual-ion batteries have higher voltage output than the conventional lithium-ion batteries,and the electrode materials are generally environmentally friendly and cheap.At present,graphite is still the most ideal cathode active material.However,the anode materials show various defects.For example,when carbon materials are used as the anodes,the cycling life of the battery can’t reach the ideal value;when metal lithium is used as the anode,the cost of battery is high and the safety is not guaranteed.The electrolytes have a large number of coordination anions and simple cations,and the different ions have a great influence on the electrochemical performance of the battery,especially on the working voltage output.However,the dual-ion battery works at a high voltage range,which is bound to have a great impact on electrode materials and electrolyte systems,such as the collapse of electrode materials and the decomposition of electrolytes.Hence,the development of a series of dual-ion battery systems with excellent cycling performance and high safety will become a research hotspot in the battery field.In this paper,we carried out systematic research work aiming to develop novel high-performance dual-ion battery systems,and obtained main achievements and progress are listed as follows:(1)Based on the defects of carbon or lithium anodes,a C/PF6-/Al dual-ion battery system was assembled,where conventional graphite and metal aluminum were used as cathode and anode of the dual-ion battery,respectively,LiPF6-EMC organic solvent with a small amount of AIF3 and VC additive was used as the electrolyte.First,the optimal position of PF6-inserted in the graphite layers was obtained by the theoretical calculations.Moreover,the structure characteristics between the graphite layers will not be destroyed during the insertion process.The results show that the maximum working voltage of the battery is up to 4.5 V,and the stable voltage output is 4.2 V.At the same time,the battery exhibits excellent rate and cycling performance.After 1000 cycles,the discharge capacity of the battery remains around 90 mA h g-1.In addition,with the addition of AlF3 additive,the formed AIF4-also participates in the insertion-deinsertion reaction to some extent,thus improving the energy storage capacity of the battery.More importantly,the addition of AIF3 relieves the corrosion rate of metal A1 anode in the alloying and dealloying process,thus effectively improving the cycling performance of the battery.(2)In order to improve the gas generation of the dual-ion battery systems,a C/Gel electrolyte-PF6-/Al dual-ion battery system was assembled,where graphite and metal A1 were adopted as cathode and anode,respectively.It is found that the gel electrolyte has rich pore structures,which can improve the ionic conductivity of the gel electrolyte.The addition of SiO2 further significantly improves the mechanical strength and interface effect of the gel electrolyte.The results show that the ionic conductivity of the gel electrolyte can reach to 2.39 mS cm-1 and increases with the increase of experimental temperature.After 1000 cycles,the discharge capacity remains 85 mA h g-1 with a retention rate of 71.8%.In addition,the gas generation of the battery can be effectively improved based on the gel electrolyte,thus further improving the safety of the dual-ion battery.(3)It is easy to cause the corrosion of Al during the deposition and decomposition of Li+ on the metal A1 anode.Ni foam composite material was prepared by the hydrothermal and solvent thermal methods as the anode.Through the related tests,it is found that this composite has a large number of clusters of net-work nanochannel structures,and these clusters are evenly and compactly adsorbed on the Ni foam substrate,which can effectively promote the adsorption of the ions by the electrode materials.The results show that the battery has excellent electrochemical performance.After 500 cycles,the discharge capacity remains at 90 mA h g-1 and the coulombic efficiency is up to 98%.The electrochemical corrosion of the composite anode is obviously reduced,although the cycling performance is slightly lower than Al anode.(4)Further,a Si nanosphere@graphene composite anode was prepared using the solvent thermal method,assembling C/PF6-/SiNS@G dual-ion battery.First,the morphology and electrochemical properties of the composite were investigated.After high temperature treatment,Si nanospheres still maintain high crystalline degree,and it is coated perfectly by the layered graphene,which can improve the specific surface area and surface structure of the materials,and further enhance the electrochemical performance of the materials.It is found that the self-discharge rate is only 14%when the battery is charged to 5.0 V,and the stable working voltage output can reach to 4.3 V.In addition,the discharge capacity can remain 100 mA h g-1 at the current density of 100 mA g-1 after 1000 cycles with a retention rate of 83%,and the volume expansion rate of the composite anode is only 48.6%,proving that the composite has outstanding structural and electrochemical stability.Finally,a kind of cathode material for the dual-ion battery with excellent comprehensive performance is obtained. |
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