Study On Novel Solid Electrolytes For Electrochromic Devices

Electrochromism is the phenomenon that when an external voltage is applied to an electrochromic material,the material itself undergoes a redox reaction and can reversibly change its color,spectral transmittance,and reflectivity.Due to the broad application prospects,electrochromic devices assembled from electrochromic materials and electrolytes have been gradually developed,such as electrochromic smart windows,electrochromic reflecting mirrors,and electrochromic display devices.However,the traditional liquid electrolyte has brought many limitations to the application of electrochromic devices,such as easy leakage,difficult packaging and so on.Therefore,the development of an all solid electrolyte for electrochromic devices is the key to solve this problem.PEO-based solid electrolytes are the most widely studied in solid electrolytes.They have the advantages of high chemical stability,strong ability to dissociate lithium salts,and good compatibility with lithium metal.The problem of low ionic conductivity has caused great constraints in the actual application.Based on this,it is proposed to use PEGMA as the matrix of all solid electrolyte,which was prepared by solid-liquid grinding and ultraviolet curing or thermal curing.The electrolyte,WO₃film,and NiO film were assembled into an all solid-state electrochromic device,and the change of transmittance when voltage was applied was tested.The specific research work is as follows:1.Using poly（ethylene glycol）methyl ether methacrylate（PEGMA）,2-hydroxy-2-methylphenylacetone（HMPP）and lithium perchlorate（LiClO₄）as raw materials,through solid-liquid grinding and ultraviolet curing a novel solid electrolyte based on PEGMA was prepared.The electrolyte has extremely high transparency（transmittance in the visible light wavelength range of 400⁸00 nm is about 97%）,and does not interfere with the color change process of the electrochromic device.The electrolyte also has high thermal stability（thermal decomposition temperature of250℃）and high ionic conductivity（2.56×10^-44 S/cm at room temperature）,which can meet the requirements of electrochromic devices.2.Using poly（ethylene glycol）methyl ether methacrylate（PEGMA）,azobisisobutyl cyanide（AIBN）,lithium perchlorate（LiClO₄）and polycarbonate（PC）as raw materials,through solid-liquid grinding and heat curing a novel polymer electrolyte based on PEGMA was prepared.The electrolyte also has a very high transparency（transmittance in the visible light wavelength range of 400⁸00 nm is about 95%）,and will not interfere with the color change process of the electrochromic device.Compared with the above-mentioned electrolyte prepared by ultraviolet curing,the electrolyte also has higher thermal stability（thermal decomposition temperature of300℃）and higher ionic conductivity（at room temperature is 6.12×10^-44 S/cm）,which can meet the requirements of electrochromic devices.3.The WO₃ film and NiO film deposited on FTO glass were prepared by hydrothermal method,and they were assembled with the two above prepared electrolytes to form an all solid-state electrochromic device.The electrochromic device successfully achieved color changes reversibly between transparent（bleached state）and dark blue（colored state）,and the change in transmittance at a wavelength of660 nm reaches 66.97%and 66.63%,which indicates both electrolytes have excellent performance when applied to electrochromic devices.