Research finds new method to improve LR03 alkaline battery SiO material efficiency for the first time

　　As the energy density of lithium-ion batteries continues to increase, traditional graphite materials can no longer meet the design needs of high-specific-energy batteries. Si-based materials have become the most popular with their capacities of up to 4200mAh/g and lithium-embedded platforms that are close to graphite. It is a promising next-generation high-capacity anode material. However, the volume expansion of Si material can reach more than 300% during the alloying process with Li, which leads to the powdering and fragmentation of particles and the destruction of the SEI film, thus seriously affecting lithium ions. Battery cycle life. The emergence of SiOx materials has brought about a turning point in the application of high-capacity Si-based anodes. The volume expansion of SiOx materials during the lithium insertion process is only about 118%, which greatly improves the cycle life of Si-based materials. However, SiO materials are unique The reaction mechanism of Li will generate Li4SiO4 material that has no electrochemical activity during the first process of embedding Li into the material. As a result, the first efficiency of SiOx material is much lower than that of graphite and silicon carbon materials, which has also become a major obstacle to the application of SiOx materials. .

　　In order to solve the problem of low initial efficiency of SiOx materials, various Li replenishment strategies have been developed to try to compensate for the Li consumed in the negative electrode during the first charging process. Yu Zhang (first author) and Dong Yang (corresponding author) of Fudan University , AngangDong (corresponding author) and others reduced the loss of Li during the first embedding process by reacting MgO with SiO2 in SiOx materials to generate MgSiO3, significantly improving the first efficiency of SiO materials.

　　In the experiment, YuZhang first used ball milling to grind and mix SiO, MgO and Si materials to obtain nanoscale particles. The addition of Si particles was mainly to further increase the capacity of the material. In addition, the author also prepared materials without adding Si, and then The ground slurry is granulated and dried using spray drying. The dried particles are calcined in a nitrogen atmosphere to obtain particles of SiO-Mg2SiO4-Si or SiO-MgSiO3-Si. Then, oleic acid is used as the carbon source. The obtained material particles are coated.

　　The picture below is an SEM picture of the SiO material precursor and the sintered material. From picture b below, you can see that the size of the spray-dried SiO mixed precursor particles is in the micron level (1.1-31.7um, D50 is 10.6um). These particles are composed of primary particles with a size at the nanometer level (diameter between 46-260nm, D50 is 112nm). From the figures h and i below, you can see that the subsequent 1100°C sintering and carbon coating treatments do not cause secondary damage to the material. The particle morphology has a great influence. The element distribution analysis of the particles also shows that elements such as Si, Mg and O are evenly distributed inside the material.

　　According to XRD studies, the SiO-MgO-Si mixture begins to generate Mg2SiO4 when heated to above 800°C, but when the temperature further increases to above 1100°C, Mg2SiO4 will be further converted into MgSiO3. The specific surface area of the material after sintering at different temperatures shows that as the temperature increases, the specific surface area of the material will decrease significantly. After carbon coating, the specific surface area of the material will be further reduced, and the specific surface area of the material will be obtained at higher temperatures. The specific surface area of the C-SiO-MgSiO3-Si material is only 1.1m2/g. Such a small specific surface area significantly inhibits the occurrence of side reactions and promotes the improvement of first-time efficiency.

　　Although ordinary SiO has a relatively high material capacity (1800mAh/g), its first efficiency is low (less than 70%), and the C-SiO-Mg2SiO4 material processed at 1000°C has a first efficiency of 75.8%. If we After adding some Si to the material, we can further improve the capacity of the material. C-SiO-Mg2SiO4-Si-800, C-SiO-Mg2SiO4-Si-900, C-SiO- prepared at 800-1200℃ The reversible capacities of Mg2SiO4-Si-1000, C-SiO-MgSiO3-Si-1100 and C-SiO-MgSiO3-Si-1200 materials reach 1825, 1771, 1711, 1608 and 1299mAh/g respectively (as shown in Figure a below, the current Density 150mA/g), the highest first efficiency can reach 78.3% (1100℃), which is much higher than C-SiO and C-SiO-Si materials (less than 70%), which shows that the addition of MgO consumes part of the material SiO2, therefore, effectively suppresses side reactions during the first lithium insertion process and reduces the consumption of active Li. Due to the smaller volume expansion during the lithium insertion process, SiO materials should theoretically have better cycle performance. From Figure d below, we can see that the SiO material after MgO treatment still maintains very good cycle performance. The capacity retention rate of half-cell batteries still reaches over 60% after 100 cycles.

　　Powdering and fragmentation of particles are important reasons for the decline in the life of Si-based materials. Therefore, the author also used SEM to analyze the electrode after 100 cycles (as shown in the figure below). From figures a and b below, it can be seen that regardless of The appearance and cross-section of the particles have almost maintained their original appearance, and no obvious structural damage has been found, which is very beneficial to improving the cycle life of Si-based materials.

　　The principle of MgO improving the first efficiency of SiO material is shown in the figure below. Generally speaking, SiO material is not a strictly stoichiometric material, but is composed of nanocrystalline Si distributed in SiO2. During the first lithium insertion process, Li will interact with it. The SiO2 reaction generates products such as Li4SiO4 and Li2O that have no electrochemical activity, thus resulting in low initial efficiency. If we use MgO to first react with SiO2 to generate Mg2SiO4 and MgSiO3 products, it can effectively suppress the side reactions of Li and improve the performance of SiO materials. The first efficiency, while the reaction products Mg2SiO4 and MgSiO3 have a porous structure, so they can also well absorb the volume expansion of the Si material during the lithium insertion process, thus improving the material cycle performance to a certain extent.

　　SiO material has smaller volume expansion and better cycle performance than SiC material. It is a very promising next-generation high-capacity anode material. However, the limitations of the inherent reaction mechanism make the first efficiency of SiO material far lower. Due to graphite and silicon-carbon materials, it has become a key factor restricting their development. YuZhang et al. reacted with MgO and SiO2 to generate Mg2SiO4 and MgSiO3, which effectively suppressed side reactions during the first embedding process of Li and reduced the consumption of active Li. This greatly improves the first-time efficiency of the material, and the preparation method of the material has the potential for large-scale production. Currently, kilogram-level samples can be produced at the laboratory level, so it has broad application prospects.

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