Lithium Storage Properties Of AlCuFe Quasicrystals And AlCuFe Quasicrystal/Graphite Composites Prepared By Mechanical Alloying

Anode materials play an important role in improving the performance of lithium ion batteries.Among them,there are many kinds of negative electrode materials,and aluminum-based negative electrodes have been widely studied in recent years due to their high lithium insertion capacity.However,the large volume expansion has always restricted its further development,and the alloying of aluminum alloy is an important solution.Al-Cu-based iron quasicrystals are solid ordered phases with a special atomic arrangement.Its icosahedral structure contains a large number of tetrahedral gaps and can be used as a good energy storage material.Our previous studies have shown that as-cast AlCuFe quasicrystals can store lithium,but the lithium storage capacity is low.On the one hand,based on the as-cast quasicrystal,it is modified to study the method of increasing its lithium storage capacity.On the other hand,Al-Cu-based iron quasicrystals prepared by a mechanical alloying method.The optimum process conditions of Al-Cu-based iron quasicrystals prepared by mechanical alloying method were studied,and the phase structure changes of AlCuFe alloy during mechanical alloying were studied.The AlCuFe quasicrystal lithium storage performance obtained by mechanical alloying was studied.In this paper,high energy planetary ball milling and vibrating ball milling are used in two different equipments.The Al,Cu and Fe element powders are used for mechanical alloying to prepare Al₆₄Cu_23.5Fe_12.5 quasicrystals.The phase structure changes and structural evolution analysis during mechanical alloying at different rotational speeds and different times were studied.The effects of high temperature annealing on different state samples were investigated.The lithium storage performance of powders with different structures was studied by charge and discharge tests,and the electrochemical properties of the generated quasicrystal samples were further tested to understand the mechanism of lithium deintercalation.It is found that with the increase of ball milling speed and time,the powder sample is transformed from crystalline elemental powder to stableβ-phase Al（Cu,Fe）.At the same time,the ferromagnetism decreases with the structural transformation until it is converted to theβphase,and the ferromagnetism of the sample is stabilized at a fixed value.Further,the particle diameter of the powder particles gradually decreases,and the shape tends to be regular.The planetary balls were ground at 250 rpm for 10 hours and the samples were annealed at 930°C to obtain single phase quasicrystals.The degree of amorphization in the ball milled sample is inversely proportional to the amount of quasicrystalline phase after heat treatment.The lower ball milling speed and shorter ball milling time are beneficial to the quenching of the quasi-crystal phase after annealing and releasing the ball-grinding stress.The results of lithium storage performance test show that in the process of mechanical alloying,the discharge specific capacity increases with the increase of ball milling time,and the capacity tends to be stable after the ball milling is amorphized.The discharge capacity of the Al₆₄Cu_23.5Fe_12.5 quasicrystal obtained by mechanical alloying and subsequent heat treatment was stabilized at 60 mAh/g.It is significantly higher than the capacity of the same component amorphous alloy.The quasicrystal sample showed an oxidation peak at around1.0V,and the reduction peak potential was about 0.25V,indicating that the quasicrystal can store lithium.The EIS test showed that the material exhibited higher charge transport resistance and Warburg impedance for the first cycle.After multiple cycles,the channel for deintercalating lithium is opened and the cycle performance is enhanced.In this paper,graphite-Al-Cu-Fe quasicrystal nanocomposites were synthesized by artificial graphite and as-cast Al-Cu-Fe quasicrystals through two different mechanical alloying equipments:high-energy planetary ball milling and vibrating ball milling.The structural changes and physical properties of the powders were investigated for different equipment,time and speed.The microstructure of the composite and the in situ analysis of amorphous graphite crystallography were performed using HRTEM.The properties of the composite and the deintercalation mechanism of lithium ions were investigated by lithium storage performance test.The results show that the graphite-Al-Cu-Fe quasicrystal nanocomposite was successfully synthesized by planetary ball milling at 550 rpm for 60 h.Too low energy input cannot completely amorphize graphite,and too high will destroy the quasicrystal structure.As the milling time is extended,the two phases are uniformly mixed,the quasicrystalline particles are reduced,and the amorphous graphite forms an annular ring similar to onion.The diameter varies from 4 to 20 nm,and the particles are composed of different numbers of concentric shells to form an uneven coating of aligned crystals.And there are a large number of crystal defects in the composite material.The charge and discharge test showed that the composite had a first discharge specific capacity of 784 mAh/g and stabilized at 465 mAh/g after 20 cycles.Compared with the quasicrystal,60 mAh/g has a significant improvement and good cycle stability.