Synthesis And Performance Of Electrode Materials For Rechargeable Lithium Batteries

With the development of electric vehicle industry,It is crucial to improve the energy density of aboard power supply.In this thesis,rechargebale lithium batteries?lithium ion batteries and lithium air batteries? are selected as research objects and we aims to explore new and high efficiency cathode catalysts for lithium air batteries and new anode materials with good performance at high current and long cycling lifespan for lithium ion batteries.The specific contents are as follows:?1?A Li-air battery mold capable of completely replacing argon in the air chamber introduced during battery assembly in the glovebox and slowing down the evaporation of electrolyte during battery operation has been successfully developed.It could also be used for accurate online analysis of the generated gas during discharge-charge process of the batteries.Three generally used methods of rolling,coating and spray have been comparatively studied to optimize the cathode process of Li-air batteries.The results revealed that nickel foam is a preferred substrate,compared with carbon paper,for cathode prepared with spray method because of its skeletal porous structure.An intermediate pressing process could improve the performance of the electrode prepared with coating method by establishing a sufficient path for oxygen diffusion.Among the studied processes in this work,spray method along with the nickel foam as substrate is the best approach to fabricate high performance Li-air batteries due to the enhanced oxygen diffusion kinetics.?2?A double perovskite oxide,Sr₂CrMoO_6-? nanoparticles,was successfully synthesized using sol-gel and annealing method with the assistance of citric acid and ethylene diamine tetraacetic acid,it was investigated for the first time as cathode catalyst in non-aqueous Li-air batteries.The Sr₂CrMoO_6-? was found to promote the formation and decomposition of Li₂O₂ resulting in excellent Li-air batteries performance.At 75 mA g^-1,the Sr₂CrMoO_6-? catalyst delivers a discharge capacity of2306 mAh g^-1,the gap between its charge/discharge potentials was 400 mV lower than that of the pure Super P electrode.When the current density was increased to 150mA g^-1,a discharge capacity retention of 85.4% could be achieved by the Sr₂CrMoO_6-? based electrode.At 200 mA g^-1,the capacity of Sr₂CrMoO_6-? based electrode doubles that of the pure Super P electrode.Moreover,superior durability is demonstrated by Sr₂CrMoO_6-? based electrodes at current densities of 75,150 and 200mA g^-1.?3?Nickel sulfide with flower-like?f-NiS? and rod-like nickel sulfide morphologies were synthesized by hydrothermal method with and without the assistance of cetyltrimethyl ammonium bromide,respectively.As representatives of metal sulfides,the as-prepared NiS materials were employed,for the first time,as cathode catalysts for Li-air batteries,and their catalytic performance was electrochemically evaluated.Both NiS catalysts,especially the flower-like one,demonstrate excellent catalytic activities towards the formation and decomposition of Li₂O₂,resulting in improved specific capacity,decreased charge/discharge overpotentials?increased round-trip efficiency?,enhanced high-rate dischargeability and superior cycling performance from that of the pure Super P based electrode.At a current density of 75 mA g^-1,the f-NiS and r-NiS catalysts exhibit reversible capacities of about 6733 and 3794 mAh g^-1,respectively,with round-trip efficiencies of 61.8% and 60%.When the current density is increased to 150 and 200 mA g^-1,f-NiS delieves 5704 and 4533 mAh g^-1,respectively,and 3161 and 2797 mAh g^-1could be achieved by the r-NiS.Moreover,both NiS catalysts based electrodes exhibit quite stable cycling performance,drastically better than the pure Super P cathode.?4?An uniformly dispersed bi-component nanocompotie of transition metal oxide/mixed transition metal oxide,0.29 Mn₂O₃/0.14 NiMn₂O₄(Ni_0.14Mn_0.86O_1.43),with a porous and hollow microspheric structure was successfully synthesized with a facile co-precipitation and annealing method based on the complexation between Ni²⁺ and NH₃.As anode material of Li-ion batteries,the as-prepared Ni_0.14Mn_0.86O_1.43 demonstrate excellent high rate capability and exciting lifespan.At 50 mA g^-1,a reversible capacity achieves at 756 mAh g^-1,and the capacity retention obtains at 95.2%,81.3%,69.7%,65.4%,54.7%,respectively,when the current density is increased to 200,800,1000,1200 and 1600 mA g^-1.After 150 charge-discharge cycles at 800 mAh g^-1,the capacity retains at 408 mAh g^-1,which is about 69.3% of that at a current density of 50 mA g^-1.In summary,the main contents of this work include:a novel Li-air battery mold was developed;cathode process of Li-air batteries was optimised;two efficient cathode catalysts with exciting performance was successfully developed for Li-air batteries;a new non-stoichiometric Ni-Mn oxide with porous and hollow structure was developed as anode material for Li-ion batteries with excellent high-rate discharge ability and prolonged lifespan.