Preparation And Properties Of Carbon Quantum Dots Based Single Lithium-ion Polymer Electrolyte

With the development of new energy field,the increasing demand for high power density energy storage equipment is becoming more and more urgent,traditional anode materials used carbon-based gradually fails to meet the energy density of the practical application.Rechargeable lithium metal batteries（LMB）using lithium metal as anode materials have attracted much attention due to their high theoretical specific capacity(3860 m Ah g^-1)and low electrochemical potential（-3.04V vs.SHE）.And it is easy to lead LMB performance loss and safety problems in the charging and discharging pro-cess because the growth of lithium dendrite caused by concentration polarization.Sin-gle lithium ion polymer electrolyte（SLIC-SPE）can effectively solve the above prob-lems.In this thesis,the anions were grafted onto the surface of carbon quantum dots（CQD）.In electrochemical reaction,CQD anions are difficult to move,thus increasing the Li⁺transport number because of the steric hindrance effect between CQD and polymer ma-trix segments at molecular scale.The research content is as follows:Three types of single lithium-ion polymer lithium salts based CQD were designed and synthesized:carboxylic acid based carbon quantum dot lithium salt（COOLiCQD）,polythylbenzene sulfonate carbon quantum dot lithium salt（PLSSCQD）,styrene tri-fluoromethanesulphonylimide carbon quantum dot lithium salt（LiSTFSICQD）.The physicochemical properties of CQDs were analyzed by morphology and structure char-acterization,and it was proved that the CQDs were synthesized.The COOLiCQD was selected as the polymer lithium salt and mixed with polyeth-ylene oxide（PEO）to prepare the SPE membranes.The ionic conductivity of the SPE is 1.60×10^-6 S cm^-1 at room temperature,and the Li⁺transport number is 0.9140 at the optimum ratio.Through the performance test of lithium metal battery,the LMB shows good rate performance and cycle stability.The PLSSCQD was selected as the polymer lithium salt and mixed with PEO to pre-pare the SPE membranes.The ionic conductivity of the SPE is 2.93×10^-6 S cm^-1 at room temperature,and the Li⁺transport number is 0.9446 at the optimum ratio.The cycle test of symmetric lithium battery shows that the SPE can reduce the concentration polari-zation in electrochemical reaction,thus effectively improving the cycle stability and rate performance of the battery.The assembled all-solid-state pouch cell works stably during bending and unfolding.The LiSTFSICQD was selected as the polymer lithium salt and mixed with poly（eth-ylene glycol）diacrylate（PEGDA）to prepare SPE membranes by in-situ polymerization method.The SPE membrane demonstrated a densify and uniform surface,the ionic conductivity of the SPE is 2.13×10^-4 S cm^-1 at room temperature,and the Li⁺transport number is 0.9690 at the optimum ratio.The SPE membrane also showed a high elec-trochemical stability window.The LMB assembled with LiFe PO₄（LFP）and ternary material（NCM811）showed stable cycle and rate performance,proved that the SPE can be used in high-voltage electrode.