Preparation And Electrochemical Characterization Of Anode Materials For Li-ion Batteries Based On Silicon/Aluminum Materials

Lithium ion secondary battery is a new green energy battery, which works by the movement of lithium ions from positive and negative electrodes. The mainly used anode material for current commercial lithium-ion battery is graphite（the theoretical capacity is372 m Ah/g）, which is prone to analyze lihium when the charge and discharge current is large,soa as can not meet the needs of high-performance lithium-ion development. The theoretical capacity of silicon can reach as high as 4200 m Ah/g, which is more than 10 times of graphite anode material. Besides, silicon also has advantages such as suitable potentials for lithium insertion and extraction, low reactivity with the electrolyte and abundant resources, making silicon become the promising next-generation anode material for lithium ion batteries.Unfortunately, there is a huge volume change（80%-400%） during the process of Li alloying and dealloying, which leads to silicon particles crumbing and pulverization and structural collapse, coupled with poor conductive properties of silicon, eventually leading to high irreversible capacity and poor cycle stability of lithium ion battery.Considering of these problems, we used silicon（theoretical capacity is 4200 m Ah/g）as raw material, acid etching method, mechanical milling method, high pressure high temperature method, hydrothermal carbonization method, high temperature carbonization method to prepare and characterization of porous Si/Al, Si/Al/C composite materials. In our work, we used the porous structure, the good mechanical properties of second phase and the differnt platform of silicon and aluminum to reduce the volume change of silicon; used the good conductivity of aluminum and cabon to increase the conductivity of silicon, thus ultimately enhance the electrochemical properties of silicon anode material for lithium-ion battery.The main results of this paper are as follows:1. Carried out the electrochemical properties characterization of silicon. The experimental reaults show that: the discharge capacity of the first cycle of pure silicon is3137 m Ah/g, and remain 86 m Ah/g after 20 cycles at 100 m A/g; Confirming that there is a huge volume change during the process of Li alloying and dealloying eventually leading to high irreversible capacity and poor cycle stability of lithium ion battery.2. Porous alumina material（p-Si/Al） was prepared by using commercial aluminum-silicon alloy Al₇₆Si₂₄ as the raw materials and hydrochloric acid as an etchant.SEM results showed that the p-Si/Al has a rich pore structure, and its capacity can retain 445 m Ah/g after 20 cycles, 325 m Ah/g after 160 cycles at 100 m A/g. Confirming that aluminium can improve the conductivity of silicon anode materials, performing the stability improvment of lithium ion battery..3. Si/Al/C ternary composites were prepared by using the ball milling method with commercial aluminum-silicon alloy Al₇₆Si₂₄ and graphite as raw material. Electrochemical tests show that the discharge capacity of the first cycle of the composite is 1379 m Ah/g, and can retain 453 m Ah/g after 20 cycles and in the subsequent cycles the capacity is basicly no longer decay, leading to 459 m Ah/g after 160 cycles at 100 m A/g. Then, we further development of the preparation process, using a two-step ball milling method to prepare Si-Al/C composite with the materials of silicon powder, aluminum powder and graphite. The capacity of Si-Al/C composite can retian 678 m Ah/g after 100 cycles at 100 m A/g, and has a high capacity retention rate up to 72.3%（Compared with the second cycle）.4. High pressure method was used in the prepration of porous silicon material. we prepared silicon aluminum alloy at 1GPa. Then, we used hydrochloric acid as an etchant to fully etched aluminum element to obtain a porous silicon structure. To further improve the properties of the material, we used hydrothermal carbonization method and high temperature carbonization method to coat a layer of amorphous carbon on the material. Compared to silicon material（3137 m Ah/g in first cycle）, silicon material prepared by high-pressure process can obtain 3938 m Ah/g capacity in the first cycle.In summary, this artical develop the silicon anode material performance from the porous struture design, the second phase introduce, and new technology explore. This work accumulate same basic data for the development of high performance silicon material.