New Calcium-ion Battery And Key Electrode Materials

As the most mature electrochemical energy storage technology,lithium ion battery has been widely used in many fields.However,with the increasing energy demand,the development of lithium-ion batteries will be under the pressure of the limited capacity and high cost in the future,searching for new electrochemical energy storage devices have become research emphasis.Attributed to substantial deposits and higher theoretical volume energy density,calcium ion batteries have attracted more and more attention.However,the development of calcium ion batteries is still relatively slow.There are two main challenges:develop new electrolyte components that allow calcium metal to deposit efficiently at room temperature,and develop high performance electrode materials to build high energy density calcium ion battery systems.In this paper,in terms of material design,we focus on facilitating the transport of calcium ions by taking advantage of 3D channel structure of NASICON-type materials,so as to obtain high performance electrode materials;In terms of battery system construction,we studied the transport behavior of calcium ions in organic electrolyte system and aqueous electrolyte system respectively.The concentrated electrolyte was used to broaden the stable voltage window of aqueous electrolyte,which provides a possibility for the development of high energy density aqueous calcium ion battery system.Specific research contents are as follows:First,from the perspective of improving dynamic performance,we chosed the NASICON type electrode materials with high ionic conductivity in order to promote kinetic property of calcium ions,taking advantage of its three-dimensional channel characteristics to improve the kinetic performance of calcium ions.Ca_0.5Ti₂（PO₄）₃@C microspheres were synthesized by electrostatic spinning,and the electrochemical performance was tested as anode in the organic calcium ion battery.The material has excellent performance and good cycle stability in Ca（PF₆）₂ electrolyte system.Under the large current density of 2 A g^-1,the material shows the charging capacity of 45 mAh g^-1.When the current density changes back to 0.02 A g^-1,the charging capacity can be restored to the original 90 mAh g^-1.In addition,the specific capacity of the material remained stable at 70 mAh g^-1 after 1500 cycles.Second,we used the concentrated Ca（TFSI）₂ aqueous electrolyte to widen electrolyte voltage window.As the concentration increased from 1 m to 5 m,the voltage widow raised from 2.22 V to 2.65 V.With the average working voltage increasing in the aqueous battery,more electrode materials will be applied in the widened voltage window to so as to build an aqueous calcium ion battery system with high energy density.We also chosed Prussian blue analogue CuHCF as the positive electrode and organic material PTCDA as the negative electrode to assemble the full battery.The full battery demonstrated a power density of 191 W kg^-1 and a coulomb efficiency of 98%in the 5 m electrolyte,which proved that material still exhibits good cycle reversibility and excellent rate performance under the electrolyte system.In general,based on the research on the material design and system of calcium ion battery,we have prepared the electrode materials with the rapid transfer ability of calcium ions,and widened the voltage window of calcium ion batteries in aqueous system,making it possible for more high-performance electrode materials to applied.These results provide useful experimental basis for the construction of high energy density calcium ion battery system in the future.