Preparation Of High-performance Hydrogel Electrolyte For Electrochemical Energy Storage

Wearable smart devices have attracted more and more attention due to their light weight and multiformity,and are gradually reaching into various fields of daily life.Traditional supercapacitors and batteries assembled with liquid electrolytes are restricted here because they cannot withstand excessive external deformation and the leakage of toxic and volatile liquid electrolytes,so flexible solid-state electrolytes are particularly a better choice.Compared with traditional liquid electrolytes,flexible electrolytes,especially hydrogel electrolytes,have aroused great interest on account of good processability,modulus suitable for smart devices,extremely high safety,ionic conductivity comparable to liquid electrolytes,and higher dielectric Constants.As one of the core components of flexible batteries&supercapacitors,hydrogel electrolytes are responsible to provide sufficient electrochemical windows and faster ionic conductivity for flexible batteries&supercapacitors,and to support flexible batteries&supercapacitors to avoid damage and short circuit when subjected to external forces.Among the hydrogel electrolytes,polyvinyl alcohol?PVA?is the most studied,but this material shows poor water retention and poor self-healing properties,and cannot achieve stretching and compression,which cannot meet the increasing demand for wearable smart devices.Therefore,a series of novel self-healing polymer materials were prepared as hydrogel electrolytes,such as polyacrylic acid?PAA?,polyacrylamide?PAAm?and zwitterionic polymer?Polyzwitterionic?.However,the hydrogel electrolyte still has shortcomings that are difficult to overcome:1)the contradiction between modulus and dynamic self-healing;2)poor interface between the electrode and the electrolyte;3)poor ionic conductivity;4)The narrow potential window cannot support high-energy batteries or supercapacitors.In this paper,the above problems are effectively solved by changing the functional monomers,configuration and conformation of hydrogel to control the ion transport.Systematic studies are carried out on gel electrolyte modulus,dynamic self-repair,electrochemical window and ionic conductivity,etc.1.In the first part,the high-strength PAA@metal ions system was employed as the research object.The P?AA-co-AAm?/CoCl₂ hydrogel electrolyte with a balance between modulus and dynamic self-healing was obtained by the strategy of changing the coordination form inside the hydrogel,replacing the widely used Fe³⁺by two-coordinated Co²⁺.Using tensile tests and electrochemical characterization,the effect of the monomer ratio?AA to AAm?and Co²⁺content on the hydrogel strength was studied.Furthermore,it was found that the P?AA-co-AAm?/CoCl₂ hydrogel electrolyte maintained the same length and ionic conductance after repeated reciprocating stretching,and could quickly return to its original shape even after stretching more than 10-fold.The supercapacitor compounded with commercial activated carbon exhibits excellent electrochemical performance,namely 134.1 F g^-1high capacitance,superior flexibility,self-healing performance,high rate performance,and high cycle stability.2.In the second part,PAAm and chitosan?CS?were used to construct a hydrophilic SiO₂ inorganic nanocluster-reinforced polymer hydrogel?PACH/SiO₂?,combined with low-concentrated LiTFSI?10M?to construct hydrogel-based WiSE?HiSE?overall the attribute improvement.It was systematically studied among the tensile properties,self-healing properties,water retention properties,and the ratio of water to salt of HiSE.When the water molecules are extremely scarce,the polymer will form a phase separation with high-concentration ions to be a hierarchical structure that facilitates the rapid transport of ions,which has been systematically characterized and explained using DCS,Raman,DFT calculation.Through electrochemical methods,the capacity&capacitance,energy density,flexibility and stability of HiSE-based supercapacitors and lithium ion batteries were studied in details.The specific energy density of the former is 23.54 W h kg^-1,and the latter exhibits a specific energy density of 110.7 W h kg^-1,both of which can maintain high rate performance and long-term stability.3.In the third part,in order to effectively improve the modulus and stability of HiSE,the long-chain hydrophobic PDMS and N-isopropylacrylamide were copolymerized in high viscosity CS solution to prepare PPCE with stable mechanical properties.The introduction of long-chain hydrophobic PDMS segments can not only effectively increase the modulus of the electrolyte,but also further reduce the water content inside the hydrogel without reducing the ionic conductivity,thereby effectively improving the electrochemical window.The electrochemical stability of PPCE at 2.7 V was verified by linear sweep voltammetry and oscillation experiments.As a result,PPCE-based AC supercapacitors exhibit high capacitance(114.1 F g^-1),high stability?capacitance retention of 93.2%after 1000 cycles?,and high rate performance.After being subjected to 1000-cycle bending,the PPCE-based supercapacitor keeps its capacitance unchanged,which provides a new idea forbuilding aqueous high-energy-density wearable smart devices with safety.In summary,this thesis is based on the multidisciplinary interdisciplinary researchof polymer chemistry,polymer physics,electrochemistry and physics.Moreover,itopens a new avenue for developing high-performance hydrogel electrolytes,high-energy flexible supercapacitors and lithium-ion batteries.