Research On Multi-Interface Characteristic Modulation Method Of Supercapacitor For Low Temperature Environment

In low temperature environments,such as below-40℃,maintaining high energy storage characteristics without attenuation is a key requirement for the practical application of supercapacitors,which widely affects electric vehicles,energy grid systems,and defense weapons and equipment involving low temperature use environments.Although domestic and foreign scholars have carried out a lot of research on low-temperature-resistant supercapacitors,maintaining high capacity and fast charge/discharge capability at ultra-low temperature is still a key problem for supercapacitors.To this end,this thesis has carried out research on the modulation of multi-interface characteristics of supercapacitors for low temperature environments,and systematically explored the low-resistance contact interface modulation of active particles in electrodes,the design of gel electrolytes with low temperature resistance and high conductivity,the fabrication method of three-dimensional current collector with low contact resistance characteristics,and optimized interface construction of graphene microspheres with electrolyte.Finally,the comprehensive power storage capacity of supercapacitors in low temperature environment is significantly improved.The main research contents are as follows:²1)A new rolling film process for mainstream electrode materials has been developed,which realizes the controllable fabrication of high-density and high-conductivity electrode films,and solves the problem of interface modulation of active materials in electrodes.The traditional electrode fabrication methods are slurry coating or dry supershearing.The former has low electrode density,while the latter relies on a complex and expensive supershear system.In this thesis,a new idea of binder fibrillation is used to develop a self-supporting electrode rolling process.The electrode film density reaches 0.617 g cm^-3,and the electrical conductivity reaches 187 S m^-1,which is nearly twice that of the traditional slurry.Coating membrane electrodes,without relying on foreign monopoly super shear system,with large-scale and scalable production capacity.Compared with the advanced commercial electrodes at home and abroad,the self-made electrodes have better electrochemical performance,which lays the foundation for electrode membrane formation for the later exploration of low-temperature energy storage technology.2)The multi-solvent modulation method of the electrolyte is proposed,and the optimal design of the low temperature-resistant organic gel electrolyte is realized,and the problem of low energy density at low temperature is solved.Common low-temperature gel electrolytes are mostly controlled by low-melting solvents in aqueous environments,and the voltage window of aqueous electrolytes is limited,which restricts the energy storage density.In this thesis,the comprehensive modulation of low-temperature ionic conductivity,cycle stability, and melting point of the system is taken as the research idea,and the comprehensive performance of the electrolyte is regulated by a ternary solvent system.The optimally regulated electrolyte exhibits a high conductivity of 2.95 mS cm^-1 at-60℃.The capacitance of the supercapacitor at-60℃maintains more than 98%of the room temperature,and the capacity decays only 3.9%after 10,000 charge/discharge cycles at-40℃.Further utilizing the mechanism of reduced electrochemical activity at low temperature,the voltage window of the gel electrolyte was increased from 3 V at room temperature to 4 V at-60℃through ionic liquid,which more than doubled the stack energy density of the device to 30.8 Wh kg^-1,which is nearly three times higher than the state-of-the-art low-temperature activated carbon supercapacitors reported in the literature.3)A microstructure imprinting control method for the contact state between the current collector and the electrode film is proposed,which reduces the interface contact resistance dozens of times and significantly improves the power density of low-temperature devices.The traditional contact methods are the rolling contact of planar current collectors and the growth contact of three-dimensional current collectors.The former leads to large contact resistance due to limited contact points,while the latter increases the proportion of inactive substances or involves time-consuming and expensive process links,which is lack of engineering practical value.In this thesis,using the idea of molding and forming,a three-dimensional micro-nano hierarchical interface contact method controlled by"roll-to-roll"template imprinting is proposed,and the interface of micro-scale plastic deformation,nano-scale indentation penetration,and micro-nano composite mechanical interlocking is revealed.The contact mechanism clarifies the modulation mechanism of the microstructure on the interface contact resistance and charge transport path,which reduces the contact resistance between the current collector and the electrode film by more than 45times,and further improves the low-temperature energy storage characteristics.The stack at-40℃The power density is increased by more than 50%,reaching 5.5 kW kg^-1,which is close to the performance of Maxwell’s products at room temperature(4～7 kW kg^-1).4)A manufacturing method of graphene microsphere electrode with multistage structure characteristics is proposed,which improves the energy storage interface between graphene electrode and electrolyte,and realizes high-speed energy storage with high energy at low temperature.In view of the problems that graphene is easy to stack,has less effective contact with electrolyte,and restricts the charge storage interface and charge/discharge speed,a graphene microsphere structure with the characteristics of resisting sheet stacking is designed in this thesis.The internal pores are further regulated by thermally exfoliated graphene,which realizes the multistage structure modulation of graphene,increases the energy storage interface between active material and electrolyte ions,and reduces the transmission impedance of ions in the electrode.The specific capacity(193.8 F g^-1)of spherical graphene electrode in ionic liquid is more than three times that of planar laminated graphene electrode.It realizes ultra-high stack energy(41.1 Wh kg^-1)and power density(8.9kW kg^-1)at-60℃,which provides a new solution for expanding the performance limit of low-temperature energy storage devices.