Critical Applications of Permanent Magnetic Iron Removers in Cathode Materials and Precursors Production Processes

Here it explains on the impact to cathode materials and precursor production

Permanent magnetic iron removers has the characteristics of strong magnetic force, simple structure, low energy consumption, easy operation and low cost. This article mainly introduces different types of permanent magnetic iron removers and their applications in multi-material precursors. By using integrated permanent magnetic iron removers system throughout multi-component precursor preparation process, it can effectively reduce the magnetic foreign matter in multi-material precursors.

Permanent Magnetic Iron Remover

Magnetic foreign matter in the multiple cathode materials can cause perforation of the diaphragm, resulting in internal short circuits of the battery, leading to self-discharge of the battery, or even fire and explosion, which affects the safety performance of the battery. Therefore, the control of magnetic foreign matter is one of the keys to solving the safety problem of lithium batteries. Currently, the metal foreign matter of multi-materials used in industry needs to be controlled at a level of tens of ppb. The content of magnetic foreign matter has also become an important criterion for measuring the quality of cathode materials and precursor production for lithium-ion batteries.

Magnetic foreign matter in multi-materials mainly comes from raw materials and equipment wear during the production process, and is mainly composed of magnetic metal impurities. Therefore, in order to ensure that the magnetic foreign matter of the multiple cathode materials is at a low level, its raw materials and production process need to be strictly controlled. Multi-material precursor is one of the main raw materials of multi-material. It not only affects the performance quality of multi-material, but also has a great impact on magnetic foreign matter. Therefore, its magnetic foreign matter must be controlled.

Permanent magnetic iron removers has the characteristics of strong magnetic force, simple structure, low energy consumption, easy operation and low cost, widely used in the production of multi-material precursors, this article mainly introduces the types of permanent magnetic iron removers and their applications in precursor production.

1 Types of permanent magnetic iron removal

Permanent magnetic iron remover is a new type of iron remover that has gradually developed and is being applied with the development of rare earth technology in my country. Its working magnetic field strength is generally between 6000 and 12000 GS. The service life can reach more than 10 years. Its working principle is that when the material passes through the permanent magnetic iron remover, the magnetic impurities contained in the material are adsorbed on the surface of the magnetic rod by its magnetic force. Normal materials flow out from the discharge port, thus achieving the purpose of removing magnetic foreign matter. According to its application type in the production of multi-material precursors, it can be divided into pipeline-type iron removers, drawer-type iron removers, rotary-type iron removers, etc.

1.1 Pipeline-type iron remover

The pipeline type iron remover is a built-in iron remover, which is mainly composed of a magnetic bar inserted into the pipeline. The simplest way is to place one or more magnetic bars in the diameter of a section of the pipeline through which the slurry flows. The pipeline is installed horizontally or at a certain angle to the ground (generally <45°). When the material passes through the pipeline, the magnetic foreign matter mixed in the material can be automatically separated. However, this type of iron remover is not convenient to disassemble and clean. Later, after development, its structure has been greatly improved.

The iron remover is replaced by a section of stainless steel pipe. Both sides of the stainless steel pipe are equipped with matching flanges, quick connectors or threaded pipes for connecting with the original pipe. The stainless steel pipe is made of multiple magnetic bars, which can increase the probability of the iron inclusions in the material being attracted by the magnetic bars. It can be customized into round or square shapes according to user requirements. It can be installed horizontally, vertically or at any angle to the ground, which also increases the convenience of cleaning.

Figure 1  Pipeline-type iron remover

This type of iron remover can be widely used in pipelines for transporting raw material solutions of multi-material precursors and reaction slurry. Figure 1 shows the appearance of a commonly used pipeline iron remover. However, during use, it should be noted that the diameter of the pipeline should not be too large and the slurry flow rate should not be too fast, otherwise it will be difficult to ensure the iron removal effect.

1.2 Drawer-type iron remover

The drawer-type iron remover is composed of multiple magnetic bars and a drawer-type channel frame. When the material passes through the frame, the magnetic foreign matter mixed in the material can be automatically separated. When cleaning the drawer-type iron remover, you can directly pull out the frame with the iron removal rod for cleaning. After cleaning, you can directly install it, which makes disassembly and assembly relatively easy.

Generally, there is a guide plate above the channel frame, through which the material can fully contact with the iron removal rod, thus improving the efficiency of iron removal.

This type of iron remover can be used in wet or dry material transportation in the production process of multi-material precursors, and has a good iron removal effect. Figure 2 is the appearance of a drawer-type iron remover.

Figure 2 Drawer-type iron remover

1.3 Rotary-type iron remover

The rotary-type iron remover is composed of multiple magnetic bars, a multi-pole fixed magnetic system and a non-magnetic shell. An independent motor drives the magnetic system to rotate, so that the iron removal operation can be carried out continuously and evenly, realizing the separation of magnetic objects and materials. Since the magnetic system is constantly rotating, the contact area with the material is larger and the iron removal efficiency is higher. This type of iron remover is mainly used for dry material iron removal in the production process of multi-material precursors. Figure 3 is the appearance of a rotary-type iron remover.

Figure 3  Rotary-type iron remover

Application of permanent magnetic iron remover in the production of multi-material precursors

Table 1 is a table of the sources of magnetic foreign matter in multi-material precursors and the types of commonly used iron removers. According to the production process of multi-material precursors. The main introduction points of magnetic foreign matter are raw materials and auxiliary materials, wear or corrosion of process metal equipment. Combined with the form of raw materials in each process and the characteristics of the iron remover, raw material preparation and precursor reaction process. It mainly involves the transportation and transfer of liquid raw materials and slurries. It mainly uses pipeline iron removers for iron removal. After being converted into filter cake or dry powder, drawer-type and rotary-type iron removers are often used for iron removal. At present, various forms of iron removers are used in series or in parallel in actual industrial production. The magnetic foreign matter in general products can reach below 50 ppb.

Table 1  Sources of Magnetic Foreign Matter in multi-materials Precursors and Types of de-ironing separator

NO.	Process	Sources of magnetic foreign bodies	Types of iron removers
1	Raw material preparation	Raw materials and auxiliary materials	Pipeline-type iron remover
2	Precursor reaction	Wear or corrosion of reactor and accessories	Pipeline-type iron remover
3	Filter washing	Wear or corrosion of filter washing equipment	Drawer-type iron remover  or rotary-type iron remover
4	Drying and sieving	Wear or corrosion from drying and sieving	Drawer-type iron remover  or rotary-type iron remover
5	Mixing and packaging	Wear or corrosion of mixing equipment	Drawer-type iron remover  or rotary-type iron remover

Summarize

Permanent magnetic iron removers has the characteristics of strong magnetic force, simple structure, low energy consumption, easy operation and low cost. It is widely used in the current industrial production of multi-material precursors. Use different types of iron removers and combine them in the whole process. It can effectively reduce the level of magnetic foreign matter in multi-material precursors.If the content of magnetic foreign matter is too high, in addition to using a permanent magnetic iron remover, an electromagnetic iron remover is also needed. The combination of the two will have a better effect in removing magnetic foreign matter. In addition, the control of magnetic foreign matter in multi-material precursors requires not only the use of a later demagnetization device, but also efforts to reduce the introduction of magnetic foreign matter. Only through multi-faceted efforts can we truly control the magnetic foreign matter in products and improve the quality of multi-material precursor products.

 2. Metal Isolation Solutions

As the requirements for metal impurities become higher and higher, the ppb values of metal impurities are 1000-500-200-100-50-30-20-10.

As it becomes a consensus that tungsten carbide coating cannot be used on the surface of battery material production line equipment; tungsten carbide and tungsten are both good conductive materials, and because it is non-magnetic and cannot be removed by iron removers, it is classified as the same level as copper and zinc by battery manufacturers and battery material manufacturers for control.

When purchasing new equipment, battery material manufacturers require the equipment manufacturers to "use non-metallic coatings or non-metallic materials to replace all areas that come into contact with the materials."

There are dozens of projects, in the spray drying equipment and flash drying equipment used in iron phosphate and lithium iron phosphate projects, including the use of KNM1000 nano-coating on the inner wall of the supporting pipeline to isolate metal and reduce the introduction of metal impurities into the battery materials. Users in material factories highly appreciate the effect of using Naimer KNM1000 nano ceramic coating in reducing metal impurities. The equipment factories expressed recognition for the construction work, coordination progress, delivery and after-sales service of Naimer KNM1000 nano-ceramic coating, which is urgent for users.