Silicon-based anode, the main force of next-generation lithium-ion battery anode materials

From the perspective of the working principle of lithium batteries: during the charging process, lithium ions are separated from the positive electrode material and embedded in the negative electrode material through the electrolyte. At the same time, electrons move from the negative electrode material to the positive electrode material. Since the negative electrode material has more micropores, the lithium ions that reach the negative electrode will be embedded in the micropores. The more lithium ions can be inserted into the negative electrode material, the higher the charging capacity of the battery. During the discharge process, lithium ions are detached from the negative electrode material and intercalated into the positive electrode material through the electrolyte. The more lithium ions in the negative electrode are intercalated into the positive electrode material, the higher the discharge capacity of the battery.

It can be seen that the negative electrode material has a great influence on the energy density, cycle performance, charge-discharge rate and low-temperature discharge performance of lithium-ion batteries.

Lithium battery anode materials are mainly divided into carbon materials and non-carbon materials. Carbon materials include: graphite, graphene, and disordered carbon. At present, graphite-based negative electrode materials are widely used in lithium-ion batteries, such as artificial graphite and natural graphite. Non-carbon materials mainly include: silicon-based negative electrode materials, lithium titanate negative electrode materials, etc. Silicon-based anode materials can be divided into SiO anode materials, silicon-carbon anode materials, and silicon-based alloy anode materials.

From the perspective of gram capacity, silicon-based negative electrodes have an absolute advantage. The theoretical gram capacity of the graphite negative electrode is 372mAh/g, and the theoretical gram capacity of the silicon-based negative electrode can be as high as 4200mAh/g. The capacity of commercial graphite-based anodes is 360-365 mAh/g, which is close to the theoretical upper limit, and silicon-based anodes have become the main force of the next-generation anode materials. Therefore, the application of silicon-based negative electrodes can increase the energy density of power batteries and increase the cruising range of new energy vehicles.

Fast-charging models are coming one after another, and the performance of the silicon-based battery is extremely high. As consumers have higher requirements for the duration of energy replenishment, shortening the duration of energy replenishment is a problem that needs to be solved in the development of new energy vehicles. From the perspective of the supply side, many car companies have launched or will soon launch 800V fast charging models. In order to improve the charging and discharging efficiency of the battery for integrated power equipment, it is necessary to use a high-rate battery. A high-rate battery generally refers to a lithium-ion battery with a continuous discharge capacity ≥ 3C. A lithium-ion battery is a rechargeable high-rate battery that mainly relies on lithium ions to move between the positive and negative electrodes to work. Therefore, anode materials with high rate performance will improve the charge and discharge capabilities of lithium batteries.

Large cylindrical batteries are launched, and the expansion rate tolerance of negative electrode materials is improved. Silicon is inherently less stable than graphite, so its expansion rate is extremely high during charging and discharging. Generally, the volume expansion of carbon-based negative electrodes in the lithium intercalation reaction does not exceed 10%, while that of silicon-based negative electrodes is as high as 300%, which causes side reactions such as SEI film damage and leads to battery capacity attenuation. The main reasons for the increase in demand for silicon-based anode materials driven by large cylindrical batteries are: 1) The volume of cylindrical batteries is larger. The silicon-based negative electrode has a very high expansion rate during the charging and discharging process, and the large cylindrical battery has a large volume, which reserves a certain space for the expansion of silicon and reduces the impact of expansion; 2) large cylindrical battery The surface of the battery is curved. When the silicon-based negative electrode expands, multiple directions can share the expansion pressure, so the expansion tolerance for the silicon-based negative electrode is higher.

In addition, silicon-based anode materials also have the advantages of low lithium intercalation potential, stable discharge platform, and abundant reserves, making them one of the most promising materials to replace graphite anodes.


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