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One of the anode materials for lithium batteries-introduction of silicon-based anode materials

wallpapers Tech 2020-08-04
As the anode material with the highest theoretical gram capacity discovered so far, silicon has a broad prospect. A successful application will increase the energy density of the battery by order of magnitude.

The theoretical capacity of silicon is as high as 4200mAh/g, which is more than ten times that of graphite's 372mAh/g. The concept of this number must be clear to everyone. It will be possible to achieve 1,000 kilometers with a single charge.

The voltage platform of silicon is a bit higher than that of graphite. The advantage of this is that lithium is unlikely to be released during charging. In terms of safety performance, it has a significant advantage over graphite. From the perspective of the silicon source, silicon is one of the most abundant elements in the earth's crust. It has a wide range of sources, and it is cheap.

Friends, don't think that we first talked about the current anode material with the highest gram capacity and will not continue to look at the following. This thing is so good, but it is not used on a large scale, and it must have its flaws.

Before talking about defects, let's talk about his charging and discharging mechanism:

The charge and discharge mechanism of silicon is different from that of graphite. Graphite is the intercalation and deintercalation of lithium, while silicon is the alloying reaction.

The biggest flaw of silicon is volume expansion.

During the charging and discharging process, the deintercalation reaction of silicon will be accompanied by a significant volume change (>300%), destroying the material structure and mechanical pulverization, leading to the separation between electrode materials and the electrode material and the current collector. Then the loss of electricity Contact causes the capacity to decay rapidly, and the cycle performance deteriorates. Due to the severe volume effect, the SEI film on the silicon surface is in a dynamic process of destruction and reconstruction, which will cause continuous lithium-ion consumption and further affect cycle performance.

It is precise because of its 300% volume expansion that limits its commercial application at this stage. It is said that the problem's occurrence always accompanies the method to solve the problem. The methods currently studied to explain the expansion of silicon charge and discharge include nano-silicon, porous silicon, and silicon-based composite materials. The synergistic effect between composite materials' various components is used to achieve the purpose of complementary advantages. Among them, silicon and carbon composite materials are an essential research direction, including coated, embedded, and dispersed types.

Nano-silicon, through the preparation of nano-wires, so that all silicon can be utilized, and expansion space is reserved, which can effectively improve the cycle performance. However, this method has a relatively high cost, a complicated process, and a relatively difficult preparation.

Porous silicon also improves cycle performance by reserving silicon expansion space. However, the compaction density is small, the process flow is complicated, and the preparation is difficult.

Silicon/carbon composite materials are mainly carbon-coated, as shown in the figure below. Although the expansion space is reserved, and the cycle performance is improved, the compaction density is small, and the industrialization is difficult.

Trunnano is one of the world's largest manufacturers of lithium battery anode materials. If you are interested, please contact Dr. Leo at brad@ihpa.net.

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