Tunnel Formation For Li-ion Transmission And Preparation Of Flexible Electrode Based On Ionic Conductivity Polymers

In the pursuit of the high performances of electrode materials,many strategies have been explored,such as developing new synthesis methods of positive and negative active materials,adjusting the structure of materials,and doping,coating etc.,which greatly improved the energy density,power density and cycle life of the batteries.However,the actual performances of a battery is not only related to the properties of positive and negative materials,but also related to the Li-ion transmission between the cathode and anode during the charge and discharge process.Besides,other parts of batteries' composition and the packaging material also take effect on the performances of batteries.Therefore,the performances will be greatly reduced if all parts of a battery do not match well.In general,Li-ion transmission between solid phases of electrode is a relatively slow step during the process of battery dynamics.It is one of the most important methods to improve the transport rate of Li-ions in solid phase and among the solid phases.In addition,in recent years,with the intelligentization of human life,the electronic devices with flexibility,portability,wearability and weavability have gradually become the focus of researches.Accordingly,such devices demand for the matched flexible power.Now the majority of batteries in the market do not have this capability.To solve these problems,we must make new explorations in flexible electrodes,electrolytes,manufacturing technologies and packaging technology.In all,here we have carried out the construction of Li-ion transmission channel and the preparation of the flexible electrode on the basis of the ionic conductive polymer.? Lithium ion transport channels in electrode materials based on ionic conducting polymers: In the process of electrode preparation,some ionic conductive polymers are introduced to form Li-ion transmission channel to improve the performance of the battery while keeps the bonding between slurry and the electron collector.Firstly,the relative viscosity of the polymers' solution is measured.Then the formation of hydrogen bond is analyzed based on the infrared spectrum and the effects of ionic conductive polymers on the mechanical properties of the electrode is explored.Finally,the types and the amount of the added conductive ionic polymers are determined.On the basis of above experimental results,button cells were assembled with ternary cathode materials as active substance and PAA and PVDF as adhesive,followed by electrochemical tests.The test results indicate that the electrode with ionic conducting polymers not only presents a better rate performance,but also shows a good electrochemical cycling performance.The discharge specific capacity can be recovered after cycles with large charge/discharge current.The main reasons for the improved electrochemical performances of the electrode are the introduction of PAA as forming the tunnel for Li-ion transmission and the interaction through hydrogen bonds.On the one hand,it can increase the bonding degree of the solid powder on the electrode as an adhesive.On the other hand,it promotes the transmission of lithium ion in the solid phase of the electrode,which improves the performances of the battery.? Construction of flexible electrode based on hydrogen bonds for Li-ion batteries: More and more attentions have been paid to the fabrication of flexible batteries and development of new method for flexible electrodes is one of the research hotspots.In this part,the surface oxidation of polypropylene separator was first treated with oxide reagents for the grafting of hydroxyl group and carboxyl group.Ionic conductive polymers,such as PEO and PAA,were added during the preparation of the slurry.In this way,the hydrogen bonds can be formed between the membrane and the interface and among the inside parts of electrode.Therefore,the slurry can be directly coated on the separator surface to form flexible electrodes.Results of electrochemical tests indicate that the as prepared flexible electrode not only has a good cycle performance,but also shows a good rate performance.Besides,the discharge capacity can be recovered after charge/discharge cycles with large currents.Such results can be attributed to:(1)The adopted polymers that forms hydrogen bonds could improve lithium ions transmission and can enhance the lithium ion transport rate inside the solid electrode.(2)The electrolyte can penetrate into the solid electrode through a gap between the particles.The electrolyte cannot penetrate from the side of the current collector to the inside of the solid electrode if use metal current collector.In conclusion,a new method for the preparation of flexible batteries was developed by constructing the hydrogen bonds between the separator surface and inside parts of the electrode.By this method,the scale produce of the flexible electrodes can be achieved,and the electrochemical performances of as prepared flexible electrode are satisfied.