Preparation And Optimization Of Oxides As Electrodes For Lithium-ion Batteries

Lithium-ion batteries?LIBs?have been not only extensively applied to consumer electronics and medical equipments,but also have shown great potential for electric vehicles?EVs?thanks to their long cycle life,high energy density and environmental friendliness.However,commercial LIBs still cannot satisfy the demands of many applications such EVs,which require higher energy density,higher power density,safer,and lower price.In this thesis,we have optimized LiNi_1/3Co_1/3Mn_1/3O₂?NCM?as one of most promising cathode materials for next-generation LIBs.In addition,we have developed Co₃O₄/Co@N-doped carbon nanotubes?T-Co₃O₄/Co@NC?as an efficient and highly stable anode material for LIBs.In this thesis,we prepare the carbon-LiNi_1/3Co_1/3Mn_1/3O₂ composite through a simple and cost-effective method at a relatively low temperature via spray drying.Hydrophilic carbon powder obtained by treating commercial Super P powder in nitric acid leads to the well dispersion of carbon powder in LiNi_1/3Co_1/3Mn_1/3O₂ particles,while untreated Super P powder is particularly difficult to be uniformly distributed.The result of X-ray diffraction pattern showing the highly ordered cation mixing of Super P-LiNi_1/3Co_1/3Mn_1/3O₂ after compositing via the proposed approach.The resulted cathode material shows superior rate capability and stability,delivering 115.7 mAh g^-1 even at 1.5 A g^-1,and remains 87.0%after 500 cycles.In contrast,pure LiNi_1/3Co_1/3Mn_1/3O₂ delivers only 57.4 mAh g^-1 at 1.5 A g^-11 and remains 35.2%after 500 cycles,and carbon coated LiNi_1/3Co_1/3Mn_1/3O₂ prepared from the carbonization of sucrose delivers as high as 141.0 mAh g^-1 at 0.1 A g^-1,but only remains 47.5%after 100 cycles.The enhanced rate capability and stability of treated Super P-LiNi_1/3Co_1/3Mn_1/3O₂ is due to the facilitation of electron conduction by introducing homogenously distributed carbon,and thanks to the wellmaintained ordered structure of LiNi_1/3Co_1/3Mn_1/3O₂.Herein,T-Co₃O₄/Co@NC is facilely prepared via the thermal decomposition of Co₃[Co?CN?₆]₂ in N₂ and the oxidation in O₂.T-Co₃O₄/Co@NC exhibits a high degree of graphitization and a large specific surface area,thus promoting the conductivity and providing more active sites.More importantly,the proper existence of metallic Co makes the reaction more reversible and thus leading to the improved cycling stability.Specifically,T-Co₃O₄/Co@NC delivers a high specific capacity of 689.2 mAh g^-1 at 500 mA g^-1 after 400 cycles with the capacity retention rate of 99.5%.In contrast,Co₃O₄/Co@N-doped carbon nanoball?B-Co₃O₄/Co@NC?exhibits a discharge specific capacity of only 247.0 mAh g^-1 after 400 cycles,and the capacity retention rate is as low as 30.1%.Furthermore,T-Co₃O₄/Co@NC also exhibits excellent cycling performance in a full cell,with the coulombic efficiency over 95%and capacity retention rate over 87%after 100 cycles.The improved stability is mainly attributed to the existence of metallic Co which helps to optimize the solid electrolyte interphase film and form carbon nanotubes mediating the volume expansion during discharging.