Synthesis And Modification Study Of Ni-Co-Mn Systeme Cathode Materials,Red Phosphorus Anode Materials And Perfluoropolyether-based Electrolytes For Rechargeable Lithium Batteries

Lithium ion battery technologies have been widely used in small electronic devices field since 1990,and has entered a rapid development stage during the past 20 years.The conventional lithium ion batteries are restricted by their theoretical specific capacity and structure stability,making it difficult to meet the goal of sustainable mankind development.Thus,it is imperative to develop and modify electrode materials and electrolytes that provide a high energy density?energy per unit volume?,high specific energy?energy per unit mass?and high safety.In this thesis,the main contents are mainly focused on:1? Firstly,this thesis summarizes the recent process on the cathode/anode materials and various types of electrolytes of rechargeable lithium batteries;presents their representative characteristics and electrochemical performance;and provides the existing challenges and perspectives for rechargeable lithium batteries.2? Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ was prepared using a co-precipitation method and modified with Li₄Ti₅O₁₂.The sample coated with 3 wt.% Li₄Ti₅O₁₂ exhibited the best cyclability and mean coulombic efficiency in the voltage range of 2.0–4.75 V.These improvements are attributed to the effective Li₄Ti₅O₁₂ coating layer,which stabilizes the host structure,protects the electrode surface from electrolyte attack,and prevents the formation of a thick passive film on the electrode surface.The initial irreversible capacity loss was eliminated by blending with 10 wt.% Li₄Ti₅O₁₂,in the larger potential window of1.5–4.75 V.It was confirmed that the irreversible capacity loss decreased with increasing Li₄Ti₅O₁₂ content;this is because Li₄Ti₅O₁₂ offers a larger number of available sites for insertion of extracted lithium.3? Here,a novel designed concept and facile method were firstly used to fabricate?PO₄?3-polyanions doped layered Li Ni_1/3Co_1/3Mn_1/3O₂?LNMC-?PO₄?0.015-O1.94?structure,which could offer more stable high-voltage cycling performance and high rate capability.We attribute this improved performance to the robust Ptet-O covalence,which will stabilize the oxygen close-packed structure during repeated cycling.Moreover,our stepwise pre-cycling treatments could effectively restrain the formation of micro-cracks and non-crystallization defects,and significantly improve cyclic durability with high charge voltage of 4.7V.The LNMC-?PO₄?0.015-O1.94 electrode can still delivers capacity retention of 81% after 200 cycles at a current density of 300 m A/g.The preliminary results reported here manifest that this novel-designed LNMC-?PO₄?0.015-O1.94 material represents an attractive alternative to ultrafast-rate,long-life and high-voltage electrode material for lithium ion batteries.4? An advanced anode material for lithium ion batteries,amorphous red phosphorous/porous carbon microsphere?RP/PCS?,was prepared via a vaporization adsorption method.In the composite,amorphous red phosphorous was mainly loaded into the micropores of the PCS substrate.The RP/PCS delivered a high specific capacity?²500 m Ah/g at current density of 100 m A/g?,excellent cyclability?>1900 m Ah/g at current density of 100 m A/g after 100 cycles?and outstanding rate performance?¹250 m Ah/g at current density of 5 A/g?.The high and stable electrochemical performance of the RP/PCS arised from their unique structure for facilitating rapid mass transport of electrons and Li-ions and accommodating the volume change of RP during cycling.5? We report a multifunctional perfluoropolyether-based liquid polymer electrolyte(dimethyl carbonate terminated-perfluoropolyethers/lithium bis?trifluoromethane sulfonamide salts?PFPE-DMC/Li TFSI??,presenting a unique “anion-solvent” interaction effect.This interaction results in the optimized interfacial chemistry of lithium metal batteries,which could effectively inhibit the corrosion of aluminum current collecors,suppress lithium dendrite growth,and also facilitate the formation of a thin and stable solid electrolyte interphase?SEI?layer on Li anode.Owing to combination of these desirable properties,the electrochemical performances of Li|Li Fe PO₄ batteries using PFPE-DMC/Li TFSI liquid polymer electrolytes are significantly superior to those using traditional carbonate electrolytes even in a wide temperature range.Moreover,PFPE-DMC/Li TFSI electrolytes also possess other eye-catching properties,such as non-flammable,non-volatile,non-hygroscopic,and wide liquid range?-100-200°C?,which further ensure the high safety of the lithium metal batteries and also open a new chapter in the development of electrolyte systems for high energy lithium metal batteries.