In Situ Preparation Of Organic Materials For Next Generation Lithium Batteries

With the development of society,the ever-growing demands for energy storage devices have generated a great concern not only over the energy density,but also the safety,cost,and sustainability of lithium batteries.Due to the versatile structure,variable shape and resource sustainability,organic materials become an appealing alternative for improving the sustainable batteries,which usually be chosen as the active material,solid electrolytes and binders.Organic-based lithium batteries have gained increasing interest as one of the next-generation rechargeable batteries with high energy density because of their high theoretical capacity and structure versatility.Moreover,polymer-based solid electrolyte possesses high safety,stable interface with electrodes,processability and flexibility,which is beneficial to large scale application of the solid-state batteries.The main research contents in this thesis are as follows:(1)A binder-free self-supporting organic electrode with excellent redox kinetics is herein demonstrated via in situ polymerization of a uniform thin polyimide(PI)layer on a porous and highly conductive carbonized nanofiber(CNF)framework.The PI active material in the porous PI@CNF film has large physical contact area with both the CNF and the electrolyte thus obtains superior electronic and ionic conduction.As a result,the PI@CNF cathode exhibits a discharge capacity of 170 mAh.g-1 at 1 C(175 mA g-1)and superior cycling stability with 81.3%capacity retention after 1,000 cycles at 1 C.More delightfully,the PI@CNF cathode shows remarkable rate-performance.The specific discharge capacity is 123 mAh g-1 at 100 C discharge rate and the capacity retention was 70.5%compared to the capacity obtained at a 0.5 C discharge rate.Last but not least,a four-electron transfer redox process of the PI polymer was realized for the first time thanks to the excellent redox kinetics of the PI@CNF electrode,showing a discharge capacity exceeding 300 mAh-1 at a current of 175 mA g-1(2)In this work,we design a new strategy to alleviate the issues of solid-state batteries is applied by in-situ polymerization of vinylene carbonate electrolyte(PVC-SPE)between the cathode and the inorganic Li1.5Al0.5Ge1.5(PO4)₃(LAGP)electrolyte.The in-situ polymerization and the intrinsic properties of PVC-SPE construct the ion-conduction network within the porous electrode and the intimate contact of electrolyte-electrode interface.The in-situ PVC-SPE can significantly inhibit the side reaction between lithium anode and LAGP electrolyte,and the potential safety problems caused by lithium dendrite can be effectively avoided.As a result,the in-situ PVC-SPE modified solid-state LiFePO4 batteries show a discharge capacity of 158.8 mAh g-1 and stable cycling performance at 0.2 C rate(94%200 cycles).Besides,the modified solid-state battery shows good rate capability at room temperature.It is anticipated that in situ strategy for addressing interfacial problem and constructing the ion conduction network within the electrode can be a promising choice to fabricate solid batteries.(3)In this work,a polycaprolactone based solid electrolyte(PCL-SPE)was prepared by ring opening of caprolactone initiated by catalyst Al(OTF)₃.The intimate electrolyte-electrode interface contact and the porous electrode ion conduct network was achieved by the process of in situ cationic polymerization.The effects of different amounts of lithium salts and catalysts on the conductivity were studied and the ionic conductivity of PCL-SPE electrolyte was 6.25×10-5 S cm-1 45?.The lithium ion transfer number of PCL-SPE electrolyte was 0.5 and the electrochemical voltage window was as high as 5 V.As a result,the solid LiFePO4 batteries based on in situ PCL-SPE electrolyte delivered a high cycling stability at 45 ? with a capacity retention of 97%after 90 cycles.The solid batteries also shown a high specific capacity of 153 mA h g-1 at 0.1 C with a high coulomb efficiency of nearly 100%.Moreover,thanks to the high stable electrochemical window of PCL-SPE electrolyte,high voltage 4.45 V LiCoO2 solid-state batteries based on PCL-SPE electrolyte also shown a high discharge specific capacity of 162.4 mAh g-1 at 45? and a high cycling stability with a capacity retention of 88.9% after 85 cycles.