| As global energy demand increases,there is an urgent need for efficient,safe,and environmentally friendly energy storage technologies.Electrochemical energy storage represented by lithium-ion batteries are the most important energy storage method and are widely used in various fields,including electric vehicles,mobile communications,and energy storage stations.However,traditional electrochemical energy storage using organic solutions poses safety risks due to their flammability and explosiveness.One solution is to use aqueous electrolytes,which are safer and more environmentally friendly.However,their low decomposition voltage results in low energy density,making it difficult to promote their application.Improving the decomposition voltage of aqueous electrolytes and developing those with superior performance are currently hot topics in energy storage research.This paper discusses the mechanism of water-containing electrolytes from a physical perspective.The decomposition of water in electrolytes is primarily a matter of potential energy.The study aims to explore new strategies for increasing the decomposition voltage of aqueous electrolytes and optimizing their properties by focusing on how to increase the reaction potential energy.Part I involves a mechanistic investigation of the surface energy and potential windows of the electrolyte.we investigate the mechanism by which surfactants affect the surface energy of electrolyte solutions,and establish a physical model for the relationship between the surface energy of electrolyte solutions and the potential window.We study the effect of surface energy on the mechanism of electrolyte decomposition at the positive and negative electrodes,and use cationic,and nonionic surfactants to adjust the surface energy of electrolyte solutions.Electrochemical experiments demonstrate a relationship between the decomposition voltage of the solution-water molecule and the surface energy.Surfactants can cause a change in the surface energy of electrolyte solutions,which can increase the decomposition potential by 0.13V.The second part employs hydrogen bonding to enhance the decomposition voltage of the electrolyte by augmenting the bond energy required for water molecule decomposition.An innovative technology route is proposed to achieve low concentration and high voltage by using hydrogen bonding to increase the bond energy of water molecules and thus widen the potential window of the electrolyte.The decrease in surface energy of the electrolyte solution in the previous research only increased the potential energy of water molecules escaping from the electrolyte,but did not increase the bond energy of water molecule decomposition.It was discovered that water in the electrolyte can be divided into free water and bound water,with bound water usually formed by the hydration of cations and water molecules in the electrolyte,and its decomposition potential window is wider than that of free water molecules.Free water molecules in the electrolyte solution are captured by the hydrophilic groups on nonionic surfactant polyethylene glycol through hydrogen bonding,which increases the potential window for water molecule decomposition.This differs from the classic high-concentration salt technology route,where free water is trapped in the water-polyethylene glycol-salt system,and the potential window for electrolyte decomposition is significantly increased to 3V,far exceeding the conventional water decomposition voltage of 1.23 V and conventional electrolyte decomposition voltage.This electrolyte can achieve a 2.3V supercapacitor,which is much higher than the 1.8V of conventional neutral water-based supercapacitors.Part three,mechanisms affecting conductivity,dissolution kinetics including viscosity and ion migration rate.Explore ion transport models in water/oil composite systems.Optimize the performance of high-voltage electrolytes.Reducing or eliminating free water in electrolytes can increase the decomposition voltage of aqueous electrolytes,but it can increase the viscosity of the electrolyte,which is not conducive to ion migration and can lead to decreased conductivity.Conductivity affects the power of electrochemical energy storage devices such as batteries and supercapacitors.We studied the factors affecting electrolyte viscosity and proposed a new strategy to combine water and oil using the properties of polyethylene glycol.The addition of oil helps to reduce the internal friction of the electrolyte and increase the migration rate of hydrated cations in the system,thereby improving the conductivity and power performance of the electrolyte.Combining the advantages of water-based and organic-based systems,it is different from using metal salts that are soluble in both water and oil.We have achieved a new method of water/organic solvent composite electrolyte.The fourth part explores the mechanism of the impact of hydrogen bonding and hydration energy on the decomposition energy of water molecules,and simultaneously explores the mechanism of solid electrolyte interphase(SEI)formation.To further increase the decomposition voltage of the electrolyte,it is crucial to further increase the potential energy of water molecule decomposition by using a solid polyethylene glycol and water,as well as a system of co-melting lithium salts.We achieved a super high lithium-water mole ratio(1:1),and due to the high lithium-water mole ratio,water molecules have a higher decomposition energy under the strong influence of metallic lithium ions.SEI can form on the surface of the lithium titanium oxide electrode in the electrolyte system,further expanding the potential window of electrolyte decomposition.By applying this new electrolyte,a stable 2.5V aqueous lithium titanium oxide soft pack battery was obtained. |
