Industrial preparation method of lithium iron phosphate (LFP)

Lithium iron phosphate (LiFePO4) has the advantages of environmental friendliness, low price, and good safety performance. It is considered to be one of the most promising cathode materials for lithium ion battery and has been widely used in electric vehicle power battery in China. This year's particularly hot BYD blade battery is the lithium iron phosphate battery.

The basic production process of lithium iron phosphate mainly includes the production of iron phosphate precursor, wet ball milling, spray drying, and sintering. There are also many studies on the synthesis process of lithium iron phosphate, and how to choose the process method is also a subject.

The synthesis methods of lithium iron phosphate mainly include: solid phase method and liquid phase method. The solid phase method includes: high temperature solid phase reaction method, carbothermal reduction method, microwave synthesis method, mechanical alloying method. And the liquid phase method includes: liquid phase Precipitation method, sol-gel method, hydrothermal synthesis method.

Part Ⅰ

 Comparison of process flow between solid phase method and liquid phase method

1. Solid phase synthesis

LiFePO4 solid phase synthesis process

The solid phase synthesis method is the most commonly used method for preparing electrode materials because of its simple process and easy industrialization.

The carbothermal reduction method is the most common solid-phase method. The carbothermal reduction method uses inexpensive ferric iron to reduce to ferric iron, and at the same time, the pyrolytic carbon is coated on the lithium iron phosphate to enhance the conductivity. It's a double benefit.

2.  Liquid phase synthesis

Lithium iron phosphate liquid phase synthesis process

The biggest feature of the preparation by liquid phase synthesis is the addition of solvent.

Taking the hydrothermal method as an example, using water as a solvent in a sealed pressure vessel, the raw material undergoes a chemical reaction under high-temperature and high-pressure conditions, and the nano-precursor is obtained after filtration, washing, and drying, and finally can be calcined at high temperature. Lithium iron phosphate is obtained.

Summary: From the perspective of process flow alone, the solid-phase method is simple and suitable for large-scale production, but its materials are mixed unevenly and the particle size distribution is wide, resulting in poor product consistency; the advantage of the liquid phase method is of course uniform mixing, The product consistency is good, the quality is relatively better, but the reaction process requires high conditions, the production equipment is more complicated, and it is more difficult to mass produce.

Part Ⅱ

Comparison of raw material cost between solid phase method and liquid phase method

From the above production process comparison, we already know that the solid phase method is simple, and the liquid phase method is more complicated regardless of the equipment or process, so the relative production cost is higher, so who is the raw material cost higher?

Cost breakdown of main raw materials for lithium iron phosphate

From the above table, we can clearly see that the raw material cost of the solid phase method is higher, mainly because the price of anhydrous iron phosphate is high, resulting in the high price of the raw material of the solid phase method.

Neither the solid-phase method nor the liquid-phase method is perfect. There are many areas for improvement, and different companies will choose different methods. The reason may be: the consistency and stability of the lithium iron phosphate product produced by the solid phase method will be better, and it is more suitable for the production of lithium iron phosphate cathode materials; while the solid phase method is simpler and more suitable for lithium iron phosphate anodes material.

1.How to optimize the liquid phase method?

The disadvantage of the liquid phase method is that the process is complicated, and the process can be simplified. The lithium iron phosphate cathode material can be obtained by one-time sintering, and the carbon coating method and metal doping method of the lithium iron phosphate are improved, and the conductivity of the lithium iron phosphate cathode is also improved. Problems such as poor performance and low capacity.

2. How to optimize the solid phase method?

What needs to be improved in the production process of the solid phase method of lithium iron phosphate is to increase production efficiency, reduce preparation costs, and improve the problem of batch instability. Compared with the traditional all-solid-phase preparation method, the particle refining process can be increased and the drying process can be eliminated, which greatly reduces the preparation time. The lithium iron phosphate cathode prepared by it has a reversible capacity greater than 156mAh/g and excellent rate performance. In addition, the problems of poor low temperature performance, poor conductivity, and low capacity of the lithium iron phosphate positive electrode can also be improved.

In summary，for lithium iron phosphate, whether it is a liquid phase method or a solid phase method, there is still room for optimization. The final fight for materials is technology. Whether lithium iron phosphate can sit firmly on the throne of mainstream cathode materials will require companies to increase their process optimization and upgrade to push their performance to a higher level.