What is a silicon-based aluminum-based alloy material?
1.1 Silicon-based alloy materials
When Si is inserted into lithium, it will form an alloy with high lithium content, Li4.4Si, with a theoretical capacity of 4200mA·h/g, which is the highest theoretical capacity among various alloys currently studied. When the Mg2Si nanoalloy is prepared by vapor deposition method, its first lithium insertion capacity is as high as 1370mA·h/g, but the cycle performance of the electrode material is very poor, and the capacity is less than 200mA·h/g after 10 cycles.
Studies have found that Mg2Si has an inverse fluorite structure. During the process of lithium insertion, lithium is first inserted into the octahedral position in the inverse fluorite structure, then forms an alloy with silicon, and finally forms an alloy with magnesium. There are no inert substances in this material. This is because the electrode material itself undergoes a great volume change when lithium is inserted and extracted, which eventually causes the electrode to collapse.
The nano-NiSi alloy was prepared by high-energy ball milling. The first discharge capacity was 1180mA·h/g, and after 20 cycles, the capacity was over 800mA·h/g. During the process of lithium insertion, silicon and lithium form an alloy, and nickel remains inert to maintain the stability of the structure, so that the cycle performance of NiSi alloy is improved compared with Mg2Si, but the violent agglomeration of nanomaterials limits the further improvement of NiSi cycle performance. Some people use chemical vapor deposition to prepare amorphous silicon films. The maximum discharge capacity reaches 4000mA·h/g, but the capacity drops sharply after 20 cycles. If the discharge termination voltage is increased from 0V to 0.2V, 400mA·h can be maintained. The reversible capacity of /g is stable for 400 cycles.
1.2 Aluminum-based alloy materials
The main forms of aluminum-based alloy materials are Al6Mn, Al4Mn, Al2Cu, AlNi, Fe2Al5 and so on. Although aluminum can form an alloy with high lithium content Al4Li9 with lithium, and its theoretical capacity is 2235mA·h/g, the lithium insertion activity of Al6Mn, Al4Mn, Al2Cu, and AlNi alloys is very low and can almost be considered inert. The mechanism is still not clear.
The nanometer Fe2Al5 material was prepared by ball milling. The first discharge capacity of the sample after 10,000 minutes of ball milling was 485mA·h/g, which was close to its theoretical capacity of 543mA·h/g, but the cycle performance was poor. After 4 cycles, the discharge capacity was 100mA·h/g. .
Through the study of AlSb materials, it can be considered that the main reason for the poor performance of AlSb materials is that its electrical conductivity is too low. By adding Cu, Zn, Sn, etc., its electrical conductivity can be increased, thereby improving its electrochemical performance, such as doping 2 The conductivity of the %Cu Al0.98Cu0.02Sb material is one order of magnitude higher than that of AlSb.