Main components of LiBs cell
Grinding
One option for the synthesis of cathode and anode materials is the so-called solid-state process.
In this process route, the active material is created from the raw materials through a chemical transformation in suitable furnaces. Depending on the raw materials used, a wet grinding stage with dry pre-grinding processes can be required for the raw materials prior to the synthesis.
Therefore, the finer the material, the more evenly mixed, so how finely the material is de-agglomerated is important in order to increase the efficiency of the battery.
Grinding
The impacted stress energy from external is stored by elastic deformation in the particles. If it exceeds a critical value, then it is broken. The external energy into the product is changed to make a new surface.
De-Agglomeration
The primary particles are very fine(under micron). However, it is aggregated by electrostatic force or drying process. De-agglomeration process is dry dispersing process and it doesn’t make a new surface.
Process Solution
In this process, we use machines for the fine grinding of solids of every hardness for any required end fineness.
For the high nickel NCM, the LiOH is better than LiCO3 for the Lithium source because of high chemical reaction. The target size of LiOH is approx. 7 – 8 micron(d50). And in this process, jet milling solution is needed.
After heat treatment, the products are agglomerated and it requires de-agglomeration process. And air Jet mill such as CGS has been normally used.
Jet mills are process equipment by means of a fluid under specific pressure and temperature. And it use a gas or steam in expanding jets. Particles are accelerated and mostly crushed by impact with each other.
For cathode materials (LMO, NMC, LFP…), Anode Materials (LTO, Si-Based Material), ceramic coated separator, wet grinding process is proceeded.
Ionic diffusion constant depends on particle size with diffusion in nano-sized particles being much faster than micro-sized particles or bulk. However, the higher surface area also results in other undesirable effects such as low packing density in the cathode and potential electrode/electrolyte reactions.
For this reason, a narrower particle size distribution is required, and grinding solutions such as Neos, Zeta® can meet the required particle size distribution.
Wet grinding system is solution for Anode materials. Nowadays due to many requirements especially for larger capacity, silicon based anode material has been highly regarded as a next generation anode material. Because silicon has around 10 times higher theoretical specific capacity compare to graphite.
However, silicon shows extremely high volumetric changes during lithiation and de-lithiation result in short cycle number by structural damage this problem must be resolved first to be commercialized.
One of way to solve this problem is to make a silicon graphite nano composite. The raw material of silicon is normally metallurgical grade of silicon but the other type of silicon like as poly silicon which can be found as a byproduct in the process of electrical material. This silicon powder must be ground down to nano range normally below 100 nm to minimize the strain during lithiation and delithiation then dry out and coated with carbon source like a pitch. So it is ground by nanomill like Zeta® RS. And after carbon coating it is ground by dry grinding machine but after dry grinding process, bare silicon which means not coated by carbon source can be exposed, so this process can be repeated 2-3 times.
System Solution
Pumping solutions like NEMO® progressing cavity pumps or PERIPRO peristaltic pumps are the important machines in battery producing lines, that have been used to convey many kinds of glue and battery slurry and so on mediums, as the dosing and metering pumps, mainly application in the battery slurry process and coating procedure.
The axial speed is very small that means low shear rate is applied into the medium, so the results is that the mechanical and chemical characteristics of the medium does not change conserves its viscosity without break any emulsion. When pumping solution is used, pump keep the same volumetric displacement each rotation, the flux volume can be based on the volumetric displacement.
With pumping solution, it is possible to keep linear performance with the rotating speed, the same volumetric displacement each rotation. And, there is no pulsation, continuous uninterrupted flow. For shear sensitive Mediums, low shear factor of all type of pumps, can handly solids particles without damage them, with High solid, high viscosity.
Especially, when producing lithium-ion battery electrode, usually select pumps to dose or meter kinds of slurry for positive pole or negative pole, including solvent series liquid and water series medium.
Analyzing Solution
In the process of making the batteries anode and cathode, the raw material is heat-treated and sintered.
Sintering is the process of heating the mixed raw material and making it into a thermosetting material. For heat treatment and sintering, it is important to understand the thermal properties of the batteries’ raw materials and active materials.
By doing a thermal analysis of active materials, thermal behavior can be identified according to the composition of each active material. For example, when the active materials reacting with active gases such as O2 and H2, the properties of active materials change. To avoid this phenomenon, there is a method of measuring thermal properties with TGA and DSC. The TGA analyzes the changes of mass under the inert gas atmospheres such as N2 and Ar in the Glove box. DSC analyzes the thermal properties of active materials by preventing the active gas reaction by sealing with a high-pressure sample fan. In addition, the gas from thermal analysis can also be analyzed by coupling GC-MS or QMS to the TGA or STA. In addition, DIL or TMA can be utilized to evaluate the sintering of the material.