| Zinc ion batteries are regarded as a promising energy storage system with high safety,high cost effectiveness and environmental friendliness,and are also considered as the most well-developed alternative to lithium ion batteries.As the most widely used electrolyte for zinc ion batteries,aqueous electrolytes have the advantages of environmental protection and safety,but there are still some problems that hinder the development of zinc ion batteries.During the charge/discharge process of aqueous zinc ion batteries,not only the insertion/extraction of Zn2+but also the coinsertion/coextraction of protons（H+）occurs.The excessive and uncontrolled protons coinsertion/coextraction for a long time will affect the lattice of the cathode material,causing distortion of the lattice and eventually the collapse of the cathode material structure,resulting in the degradation of the performance of zinc ion batteries.In this thesis,the problem of structural collapse of cathode material caused by uncontrolled coinsertion/coextraction of protons during charge/discharge is addressed by proposing the use of nitrile to limit the activity of water in order to maintain the stability of cathode material by reasonably controlling the concept of coinsertion/coextraction of protons.Finally,this approach allows zinc ion batteries to achieve excellent cycling stability while maintaining high capacity.The main contents are as follows:（1）Zinc bis（trifluoromethanesulfonyl）imide（Zn（TFSI）2）was used as the zinc salt,and Zn（TFSI）2·x SN·y H2O hydrated salt electrolyte was obtained by adding succinonitrile（SN）and water as ligands.A small amount of protons coinsertion/coextraction can activate the cathode,enhance the capacity and ensure the stability of the cathode,while an excessive amount of protons coinsertion/coextraction can distort the cathode lattice and collapse the structure.Therefore,the cyano（-CN）in SN and H2O form a hydrogen bond to limit the activity of water,and the ratio of SN to H2O is regulated to achieve a reasonable regulation of protons coinsertion/coextraction,so as to select a Zn（TFSI）2·9SN·5H2O electrolyte that can guarantee both high capacity and cycling stability.The initial voltage of protons inserting was found by the differential capacity curve,and the optimum ratio of protons and Zn2+insertion was calculated to be0.53:0.24 during the discharge process.At this point,the amount of protons coinsertion can ensure both a good capacity and excellent cycling stability.（2）Between the larger viscosity of SN and the capacity to be improved,single nitrile:butyronitrile（BN）,hexanenitrile（HN）and multiple nitrile:SN,adiponitrile（ADN）were selected for comparison.The strength of hydrogen bond formed by different nitrile and H2O is different,and the inhibition effect on H2O activity is also different.The ionic conductivity was tested for the electrolytes formulated with these four nitrile types,and the lowest conductivity was measured for the Zn（TFSI）2·9SN·5H2O electrolyte.Although the mononitrile electrolytes Zn（TFSI）2·9BN·5H2O and Zn（TFSI）2·9HN·5H2O possessed high ionic conductivity,the electrochemical windows of these two electrolytes were narrower than those of the dicarbonitrile electrolytes as measured by LSV,and the cycling stability of the mononitrile electrolytes was measured to be poorer than that of the dicarbonitrile electrolytes after cycling tests.The Zn（TFSI）2·9ADN·5H2O electrolyte with the best performance and stability was selected for the long cycle test,and the capacity retention rate of 92.69%was maintained after 1300 cycles at a current density of 1.0 A g-1,and the performance and capacity retention rate remained excellent after replacing the zinc salt.The electrolyte was also tested at high and low temperatures,proving that the electrolyte has good performance and capacity retention at high temperature of 80℃and low temperature of-10℃,which promotes the practical application and development of zinc ion batteries. |
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