Preparation Of Polyurethane-based Solid Electrolyte For Electrochromism And Research On Its Whole Device Stability

In recent years,with the rapid development of smart wearable devices,people have put forward higher requirements for the versatility,mechanical flexibility and low energy consumption of related products.Among them,the intelligent and controllable color change is one of the indispensable functions of such products,which can be widely used in portable display,visual inspection,fashion creativity and other fields.As an important branch in the field of intelligent discoloration,electrochromism has attracted widespread attention due to its advantages of low power consumption,fast response speed,and strong controllability.The current research focus has gradually shifted from smart windows and anti-glare Rigid devices such as sight glasses are transferred to foldable,embeddable,and wearable flexible electrochromic devices.With the innovative development of flexible electrochromic materials,flexible electrochromic devices have made great breakthroughs,but a lot of research work is still focused on the use of liquid electrolytes,which have problems such as easy leakage and flammability,and are not suitable for flexible wearable applications.Therefore,a reliable,stable and safe electrolyte for electrochromic needs to be developed urgently.In response to the above problems,this paper uses thermoplastic polyurethane（TPU）as the polymer framework and lithium perchlorate（LiClO₄）as the lithium source,and develops a gel-state electrolyte with high ionic conductivity and a high-safety all-solid electrolyte.The device assembly and performance research investigated the application prospects of electrolytes in the field of electrochromism.The specific contents are as follows:First of all,TPU,LiClO₄ and N,N-dimethylformamide（DMF）are used to realize the preparation of TPU-based gel electrolyte,which solves the problem that liquid electrolyte is not conducive to the application of flexible devices.At the same time,with the help of ionic liquid doping,the ionic conductivity of the electrolyte is significantly improved,and a TPU-based gel electrolyte with high ionic conductivity and mechanical stability is obtained.After doping,the ionic conductivity of the gel electrolyte is increased from 3.8×10^-4 S/cm to 8.5×10^-4 S/cm.The PEDOT:PSS film prepared by the screen printing method is assembled into a size of 10×10 cm² The flexible electrochromic device,the optical contrast of the device can reach 33.1%under the color-changing voltage of-3.3 V.Coloring time is 89.8 s,and fading time is 44.6 s.The coloring efficiency is 256.8 cm²/C,which is better than the current gel electrolyte.The performance of large-area electrochromic devices under the system,but the devices still have problems such as complex preparation process and insufficient stability in extreme special environments.Secondly,in order to solve the problem of insufficient extreme environmental stability of the gel electrolyte for electrochromic,TPU and LiClO₄ were melt blended directly by the casting film method to obtain an all-solid electrolyte film（without any liquid components）,and then with the PEDOT:PSS thin film prepared by the screen printing method were assembled into an all-solid-state flexible electrochromic device with a size of 10×10 cm².The feasibility of applying the all-solid electrolyte to the flexible electrochromic device was studied.The test found that the device has a significant discoloration effect,the optical contrast is 18.2%.Coloring time is 83.2 s,and fading time is 38.3 s.But after 40 cycles,only 7.69%of the optical contrast remains,and the device can hardly change color.In this regard,this article conducts a failure analysis of the device and determines that the problem lies in the structural damage of the indium tin oxide（ITO）conductive layer as the counter electrode of the device during the electrochemical reaction.Finally,in order to solve the problem of insufficient cycle stability of all-solid-state flexible electrochromic devices,a PANI electrochromic layer was sprayed on the surface of the ITO conductive layer of the counter electrode to assemble complementary flexible electrochromic devices.The results show that the device has excellent electrochromic performance,its optical contrast can reach 36.5%（658 nm）,its cycle stability has also been greatly improved,after 500cycles can be maintained at 60%of the original.Coloring time is 80.1 s,and fading time is 36 s.The all-solid-state complementary flexible electrochromic device is simple to prepare,it has good environmental stability,cycle stability and practical application potential.