Study On Quasi-solid-state Electrolytes For Lithium-ion Battery

Lithium ion battery as a new generation of"environmentally friendly"energy storage technology,known as"the dominant power in the new century"because of their superior specific energy,long cycle life,high working voltage,etc.With the in-depth application of lithium ion battery in various fields,higher performances are required.As a key component of a battery,electrolyte has a potent influence on its safety,specific energy and even cycling life.However,the reported liquid and solid-state electrolytes for lithium ion batteries still exist some problems.On the one hand,the safety problems of liquid electrolyte block development of the lithium ion battery.Inorganic solid-state electrolyte has obvious advantages in safety,but with high lattice energy and poor processability.Polymer electrolyte show poor ion transport ability and low ionic conductivity at room temperature.In addition,introducing liquid plasticizer in to polymer electrolyte,named gel polymer electrolyte,is an effective way to improve the ion conductivity,but the thermal stability of the organic polymer substrate restricting its development.On the other hand,with the development of flexible electronic equipment,exploitation of flexible electrolyte capable of good compatibility of electrode is a key technology in the development of flexible lithium ion battery.Therefore,it is really need to develop an electrolyte which combine excellent mechanical properties with electrochemical and safety performance.In this paper we present a series of novel ionogel electrolytes,used incombustible inorganic nanomaterial as scaffold to immobilize ionic liquid through in situ method.In-depth study of their structure,composition,physical properties and electrochemical performance,explore the mechanism of ionic conduction and the relationship between scaffold structure and electrochemical performance.We started from the electrodes and the electrolyte materials;optimize the structure of battery to design a new type of high security of solid state lithium ion batteries.This paper is focused on the development of ionogel electrolyte and flexible electrolyte for lithium ion batteries.The main research progresses are as followed:?1?“Liquid-in-Solid”and“Solid-in-Liquid”electrolytes with high rate capacity and long cycling life for lithium-ion batteries.The electrolytes are prepared by a nonaqueous self-assembly sol-gel process,in which ionic liquid electrolyte is immobilized within an inorganic gel.These electrolytes were found to exhibit high ionic conductivity,low electronic conductivity,and good thermal and mechanical stability.The inorganic gels weaken the interaction of anions and cations and thereby improve lithium salt dissociation and enhance transport of Li⁺.Also,the electrolytes are stable:no spontaneous phase separation occurs after one year of storage.In addition,their synthesis and shaping are very easy and cheap and form a new class of solid electrolytes,which offer exciting opportunities for preparation of in situ solid-state lithium-ion batteries.Cells with LiFePO₄cathodes and ionogel electrolyte attained a capacity of 150 mAh g^-1 for more than 300cycles,and even at the 2C rate,the capacity still stayed over 98 mAh g^-1.?2?Self-regulative nanogelator solid electrolyte:a new option to improve the safety of lithium battery.This solid electrolyte is prepared through in-situ synthesis of porous oxide served as the nanogelator to immobilize ionic liquid electrolyte.In order to achieve better understanding of the nanogelator solid electrolytes system,we compare the synthesis and properties of solidified ionic liquid electrolytes within the Ti-nanogelator and Si-nanogelator.This kind of nanogelator with self-regulation ability,can adapt to different kinds of ionic liquids,such as imidazolium,pyrrolidinium,piperidinium,etc,by adjusting the ion transport channels.The electrolyte was optimized by change the content and species of ionic liquid,the highest ionic conductivity reached 2.93×10^-3 S cm^-1 at room temperature.The electrolyte also had good compatibility with LiCo O₂,LiFePO₄,LiNi_1/3Mn_1/3Co_1/3O₂and Lithium-rich cathodes.Among them,Lithium-rich batteries outperform conventional batteries based on liquid electrolyte.Electrolyte has excellent thermal stability;batteries containing this electrolyte can operation at 100°C?3?Organically modified silica-supported ionogels electrolyte for high temperature lithium-ion batteries.A new solid-state ionogel electrolyte was synthesized by a silane coupling agent?SCA?that can spontaneously form porous network to confine ionic liquid?IL?.We found that the epoxy group grafted on silica can promote the ionic dissociation of the lithium salt and ionic liquid,make the ionic conductivity higher than that of pure ionic liquid electrolyte.The ionogel with an optimized molar ratio IL/SCA=0.75exhibits order pore structure,which provides directed pathways for efficient Li⁺transport.Furthermore,the ionogel show excellent thermal stability,wide redox stability windows,can improve the operating temperature of batteries from room temperature to at least 90°C.Li/LiFePO₄ and Li/Li₄Ti₅O₁₂ batteries with this solid-state ionogel electrolyte exhibit high capacities and good cycle performance.Li/Li₄T_i5O₁₂ batteries remain 80 mAh·g^-1 after 580cycles at the current rate of 0.1C at room temperature?4?Flexible electrolyte preparation and its application in lithium ion batteries.A new organic-inorganic compound flexible electrolyte was prepared by introduce polymer PVDF-HFP as the flexible scaffold and in situ generate TiO₂ as rigid scaffold,ionic liquid electrolytes as ionic conduction media is immobilized in those 3D scaffold.The electrolyte was found to exhibit good mechanical strength,flexible,no crack under extrusion deformation and bending deformation,can be designed into various shapes and sizes.Furthermore,the electrolyte also has a high ionic conductivity and wide electrochemical window.Cells with this electrolyte exhibited high capacity and rate performance at room temperature.The flexible electrolyte will replace the traditional organic electrolyte used in flexible lithium ion batteries.