Preparation And Lithium Ion Secondary Battery Performance Study Of Aluminum Hierarchical Nanostrecture

As a new generation energy storage device,lithium-ion secondary battery has long cycle life,high energy density and high power density,which can be widely used in the fields of electronic products,electric vehicles and large-scale energy storage,etc However,the energy density of the commercial lithium-ion secondary battery is limited to the low discharge capacity of cathode and anode materials,which can not meet the increasing demand for the battery with high energy density.The metallic aluminum anode has a theoretical capacity of 993 mAh/g,far exceeding the graphite negative electrode(372 mAh/g),which is expected to greatly increase the energy density of the lithium-ion battery.Meanwhile,aluminum has the advantages of abundant reserves,low cost and good conductivity,making it the most promising anode material for lithium-ion battery.Unfortunately,due to the disadvantage of huge volume change in the process of lithiation/delithiation,the electrode structure is destroyed.In addition,the dense oxide layer on the metallic aluminum surface will impede the rapid transmission of lithium ion and electrons.The construction of specific micro and nano structures has been considered as an effective solution to improve the cycle stability of aluminum based anode.Nevertheless,owing to the high chemical activity and high reduction potential of metal aluminum,the preparation of ordered nanostructures remains a great challenge.Aiming to solve the above issues,in this study,we developed a liquid phase reduction method for the preparation of aluminum hierarchical nanostructures,which can be tuned by a series of reaction parameters such as temperature,types of aluminum salts,solvents and ligands,and the self assembled synthesis of aluminum nanostructures was realized at low temperature.Further,the composite structure with carbon nanotubes was constructed,and the discharge capacity and cycle performance of the composite material as anode material for lithium ion batteries was studied.The main innovations are obtained as follow:1.As revealed by the study of the synthetic reaction kinetics of aluminum nanostructures,we find that:(1)A simple method for preparing non-solvent aluminum hydride is found in ethylene glycol system,and with the increase of reaction temperature,aluminum hydride will gradually decompose to produce aluminum and hydrogen.When the temperature rises to 180?,the pure phased metallic aluminum can be obtained;(2)In the mesitylene system,oxygen can selectively adsorb on the(111)facet of aluminum.With the oxygen-assisted effect,the corolla-like aluminum hierarchical nanostructures with the exposure of Al(111)facet tend to form.For the synthesis with amine ligands,the lone pair of electrons on the nitrogen atom will form a strong adsorption with the electron-deficient aluminum atoms,leading to the isotropic growth of aluminum,namely,nanoparticles;(3)Since aluminum acetacetone(Al(acac)3)has higher reaction threshold than AICl3,the addition of a proper amount of Al(acac)3 to the system may reduce the reactivity.Particularly,with the assistance of oxygen at 140?,the uniform corolla-like aluminum hierarchical nanostructures can be obtained with the molar ratio of AICl3 to Al(acac)3 as 4:1.2.The carbon nanotubes-aluminum nanosheet composite hierarchical nanostructures is prepared by a one-pot method.On one hand,this aluminum hierarchical nanostructures with exposed(111)facets have large specific surface area and strong oxidation resistance;On the other hand,with the introduction of carbon nanotubes,the electrical conductivity of the electode is further improved.Therefore,this unique nanostructure can be used as anode material of lithium-ion secondary battery,and exhibits excellent rate performance and cycle stability.After 500 cycles at a rate of 1 C,the specific capacity can reach 1107 mAh.g-1,and it still has a higher specific capacity under the large rate of 5 C,10 C and 20 C.Finally,according to the first-principle calculations,the calculation results show that this exposed(111)aluminum hierarchical nanostructures has a lower migration energy barrier and a better mechanical performance than the face-centered cubic(fcc)bulk aluminum.Thus,it demonstrates such a remarkable lithium storage performance.