Preparation Of Asymmetric Ionogels And Their Applications As Flexible Thermoelectrics Materials

Circular economy is an inevitable choice for sustainable development.In today's energy shortage,the conversion of unused or low-grade waste heat energy into electric energy will produce huge environmental and economic benefits.The high-efficient conversion of low-grade waste heat energy into electrical energy through thermoelectric conversion technology helps to make up for the shortcomings in the field of low-grade waste heat recovery.The key point of the technology is to build thermoelectric materials with high thermoelectric parameters,high efficiency,scalability and low cost.Compared with electronic thermoelectric materials,thermionic materials have a Seebeck coefficient that is several orders of magnitude higher.Ionic liquid materials widely used in ionic thermoelectricity have attracted widespread attention in the thermoelectric conversion of low-grade thermal energy due to their non-volatility,wide electrochemical window,low thermal conductivity and high stability.However,the complicated packaging process and leakage of ionic liquids cannot be ignored,which affects its scalability.The ionogel solves the encapsulation and leakage problems on the premise of maintaining the characteristics of the ionic liquid,and then further broadens the application scenarios and scope.More importantly,the solid ionogel is very beneficial to the manufacture and use of thermoelectric devices.The performance of ionic thermoelectric materials is mainly affected by Seebeck coefficient(?i),electrical conductivity(?i)and thermal conductivity(?).Although researchers have done a lot of research on the development of ion thermoelectric materials with high Seebeck coefficient,high conductivity and low thermal conductivity.The most important ion Seebeck coefficient is directly related to the output voltage,the current research on high Seebeck coefficient ion thermoelectric materials are poor.Therefore,the development of flexible ionic gel materials with excellent Seebeck coefficients is still a challenge.The starting point of this paper is to promote the separation of anion and cation in ionic liquid and increase the difference in the migration rate of anion and cation in the ionic gel.The interaction of the polymer matrix and a cation or anion is used to design ionogels with an asymmetric structure.The second chapter uses the dipole interaction between polymer and cationic ion to increase the positive migration rate for material design.Two different components of poly(vinylidene fluoride-co-hexafluoropropylene)and ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt are selected as the main materials.The migration of cations is restricted by the dipole interaction between the vinylidene fluoride unit and the imidazole cation ion in the polymer.Three kinds of poly(vinylidene fluoride-co-hexafluoropropylene)-based ionogel films prepared by room temperature solvent evaporation method(PVDF-HFP-5545-50wt%IL,PVDF-HFP-9010-50wt%IL,PVDF-HFP-5545-9010-50wt%IL).The influence of the asymmetric structure on the thermoelectric parameters of the ionogels is obtained by measuring the ion Seebeck coefficient,ion conductivity,and thermal conductivity.The feasibility of the positive increase of Seebeck coefficient by the polymer matrix affecting the migration of a single ion through the force has been verified.The third chapter uses the hydrogen bond interaction between polymer and anion to limit anion migration for material design.Two polyacrylates and 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt were selected as the main materials.The hydrogen bond interaction between ethyl acrylate and anion restricts anion,promotes the separation of anion and cation,and reduces the migration of anion.Three kinds of ionic gels are prepared by the solvent replacement method and the direct polymerization method(PEA-IGs?PMMA-IGs?Asymmetrical PEA/PMMA-IGs).The experimental results show that the Seebeck coefficient can reach+25.86 mV K-1 when the PEA matrix of the asymmetric ionogel is at the hot side,and it is 16.11 mV K-1 when the PMMA matrix is at the hot side.Both of them far exceed PMMA ionogels(+4.09 mV K1)and PEA ionogels(+8.06 mV K-1).Polyacrylate-based asymmetric ionogels exhibit diode-like effect,and the Seebeck coefficient can be adjusted by changing the direction of the heat source.The hydrogen bonding between the polymer and the ionic liquid promotes the dissociation of ion pairs and restricts the migration of anions.The Seebeck coefficient has been greatly improved compared to single-layer ionogels.The design idea of an asymmetric structure is of great significance for improving the thermoelectric parameters of polymer ionic liquid-based ionogels.This ionic gel with an adjustable and excellent Seebeck coefficient shows great application potential in flexible electronic products,especially wearable energy supply systems.