About power battery silicon carbon anode materials composite process description

Silicon is given the highest known lithium ion anode materials, can achieve 4200 mah/g, are supposed to be Lithium ion batteries The first choice for anode materials, is widely used but why not? This is due to its limitation crystal structure.

The structure of silicon and graphite layers is different (pictured), the energy storage mechanism is similar to metal materials by alloying and alloying with lithium ion, the charge and discharge electrode reaction can write down the type:

Si + xLi++ xe - > LiXSi

Elemental silicon as the cathode material is The battery Charge and discharge principle as shown in the figure below:

Can be read by the figure in the part of rechargeable lithium ion from the anode material emerge between embedded inside the silicon crystal lattice, caused great expansion (about 300%), to form silicon lithium alloy. When discharging lithium ion from emerge between lattice, and form a great gap. Single use silicon crystal as the cathode material is easy to produce the following questions:

First, in the embedded in the process, silicon crystal there is an obvious changes in the volume, the volume effect is silicon anode materials falls off from the collection of fluid, lead to pole piece Lou foil lead to the phenomenon such as electrochemical corrosion and short circuit, affect the safety and service life of the battery.

Second, silicon carbon for the same main group element, formed in the first charge and discharge will also SEI coated on the surface of silicon, but caused by volume effect of silicon flake situation will cause the repeated damage and reconstruction of SEI, thus increasing the consumption of the lithium ion, ultimately affect the capacity of the battery.

So what's the process in order to complement each other, the silicon can be modified to optimize? The silicon with other material composite processing can play a good effect, including silicon carbon composite material is a kind of study materials.

Carbon materials is currently the most used anode materials and carbon materials can be divided into soft (graphitized carbon), graphite, carbon hard carbon (amorphous carbon) three, its charge and discharge chemical equation can be represented as:

Carbon anode materials has good cycle stability performance and excellent electrical conductivity, and lithium ion and has no obvious influence on the layer spacing, to a certain extent can buffer and meet the volume expansion of silicon, therefore it is often used to composite with silicon.

Often depending on the type of carbon composite material can be divided into two categories: silicon carbon composite material and traditional silicon carbon new composite materials. Including traditional composite material is silicon and graphite, MCMB, carbon black and other composite, new type silicon carbon composite material is silicon and carbon nanotubes, graphene and other new type of carbon nanotube composite.

Silicon carbon anode materials according to the distribution mode is mainly divided into silicon coated type, embedded type and molecular contact type, according to the form is divided into particles and thin films, based on what types of silicon carbide can be divided into binary compound silicon carbon and silicon carbon composite. Below is the different distribution pattern of silicon carbon anode materials:

The preparation of silicon carbide composites with a ball grinding process, high temperature pyrolysis method, chemical vapor phase precipitation, sputtering deposition, deposition method and so on. Prepared by ball milling method of silicon carbon negative reversible capacity can reach 500 ~ 1000 mah/g, ball mill can promote raw materials mixing between the particles and the smaller particle size, the gap between particles is also conducive to the improvement of the performance of the cycle of the battery.

High temperature pyrolysis method is through pyrolysis nano silicon particles and organic precursor or direct pyrolysis of organic silicon precursor method of Si/C composites, silicon carbon composite materials using this method, the g capacity is lower than the high energy ball milling method of Si/C composites, but higher than that of graphite, is about 300 ~ 700 mah/g. This is because the pyrolysis method in the preparation of electrode materials contain a lot of no electrochemical activity substance, decreased capacity of electrode materials.

Preparation of electrode materials, on the other hand, USES the method of pyrolysis of silicon tend to reunite and grew up in the subsequent use more pulverization effect. In addition to methods of CVD, sputtering deposition, has certain difficulty, not commonly used on the production, no longer list.

Silica nanoparticles anode materials is the study of the early, but its expansion volume effect big shortcoming limits its application. Composite was prepared by the silicon carbon composite material for silicon volume expansion reserved space, at the same time, to some extent compensate for the silicon electrical conductivity is bad and the SEI film unstable faults, the manufacturer of batteries widely attention and application.

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