Vertical sand mill plays a vital role in the preparation of silicon-carbon anode materials, especially in achieving nanometerization, uniform dispersion and close compounding of silicon particles with the carbon matrix. The following are its specific applications and key functions:

Core applications and functions

1. Nanonization of silicon particles:

       Problem: Pure silicon as an anode material will undergo huge volume expansion (about 300%) during the charge and discharge process, resulting in particle powdering, repeated rupture and regeneration of the SEI film, destruction of the conductive network, and ultimately rapid battery capacity attenuation.

        Solution: Grinding silicon particles to nanometer size (usually targeting below 100nm, or even to tens of nanometers) is one of the most effective strategies to mitigate the volume expansion effect. Nano-silicon particles have a higher specific surface area, shorter lithium ion diffusion paths, and can better withstand the stress caused by volume changes.

Function of vertical sand mill: Vertical sand mill efficiently crushes and refines micron-sized or even larger-sized silicon powder (or silicon source precursor) to the required nanometer level through the strong collision, shearing and friction of grinding beads (such as zirconia beads, alumina beads, etc.) at high speeds. This is one of the mainstream methods for industrial production of nanosilica powder.

2. Uniform dispersion and composite of silicon and carbon materials:

        Problem: Silicon nanoparticles are easy to agglomerate and need to be evenly dispersed in a conductive carbon matrix (such as graphite, hard carbon, soft carbon, graphene, carbon nanotubes, etc.) to form an effective conductive network and buffer its volume expansion.

        Solution: When preparing silicon-carbon composites, it is usually necessary to wet grind and mix silicon powder, carbon source (such as graphite, asphalt, polymer, etc.) or carbon precursor with other additives (such as conductive agent, binder precursor).

Functions of the vertical sand mill:

Powerful dispersion: The vertical sand mill can not only crush silicon particles, but also powerfully break up the agglomerates of silicon particles and the agglomerates of carbon materials (such as the agglomeration of graphene and CNT).

Uniform mixing: In the grinding chamber, the materials are vigorously stirred and circulated to ensure that silicon particles, carbon materials and other components are uniformly mixed at the molecular/nano level.

                                                                                                                                                                                                                            The strong mechanical force during the grinding process can sometimes promote the formation of closer physical contact and even certain chemical bonding between silicon particles and carbon materials (especially carbon with active surfaces), which is conducive to subsequent heat treatment to form a more stable composite structure (such as silicon being coated with a carbon layer).

3. Control particle morphology and particle size distribution:

        The role of vertical sand mill: By accurately controlling grinding parameters (such as grinding bead size, filling rate, rotor speed, grinding time, slurry solid content, flow rate, etc.), the morphology (tending to be spherical or quasi-spherical) and particle size distribution (PDI) of the final silicon particles can be controlled to a certain extent. Narrow particle size distribution is critical for electrode slurry stability, coating uniformity and battery performance consistency.

4. Promote surface modification:

       Question: Nano-silicon has high surface activity and is prone to oxidation or side reactions with the electrolyte.

       Solution: Sometimes surface modifiers (such as carbon-containing small molecules, surfactants, polymer monomers, etc.) are added during the grinding process.

       Function of vertical sand mill: The fresh silicon surface and high-intensity mechanical energy produced by grinding help the adsorption, reaction or coating of the modifier on the surface of silicon particles, achieving in-situ surface modification, improving the lyophilicity and dispersion stability of silicon, and possibly inhibiting side reactions.

5. Advantages and Challenges

Advantages:

It can produce nano-silica powder and silicon-carbon composite slurry on a large scale and continuously.

It has high grinding efficiency and can effectively achieve nanometerization and uniform dispersion.

The process is relatively mature and the equipment options are wide.

Challenges:

Contamination control: Impurities introduced by media and lining wear are the main challenges, requiring continuous optimization of materials and processes.

Energy consumption: Achieving nanoscale grinding requires high energy input.

Process optimization is complex: Involves multiple interacting parameters and requires a large number of experimental optimizations to obtain the best performance.

Risks of over-grinding: Improper control can easily lead to particles that are too small and have many defects.

Cost: High-quality grinding beads and wear-resistant linings are more expensive.

Vertical sand mill is the core equipment in the industrial preparation of silicon carbon anode materials, especially nano silicon carbon composite materials. It is mainly used to realize the nanometerization of silicon particles and the efficient and uniform dispersion and compounding of components such as silicon and carbon materials. By precisely controlling the grinding media, process parameters (rotation speed, time, temperature, etc.) and slurry state, the vertical sand mill can produce silicon carbon anode materials that meet the needs of high-performance lithium-ion batteries. However, impurity contamination caused by grinding media wear is a key challenge restricting its application, which requires continuous improvement through the selection of high-performance wear-resistant materials and optimization of processes. With the continuous development of silicon carbon anode technology, the sanding process will continue to be optimized and play a greater role in improving material performance and reducing costs.