Manufacture of lithium iron phosphate batteries, production process of lithium iron phosphate

Introduction of lithium iron phosphate

Lithium-ion battery as a high performance secondary green battery, It has the advantages of Gaodianya, high energy density(including volume energy, mass ratio energy), low self-discharge rate, wide operating temperature range, long cycle life, environmental protection, no memory effect, and high current charging and discharging. The improvement of the performance of lithium-ion batteries depends largely on the improvement of electrode materials, especially the positive ones. At present, the most widely studied positive materials are LiCoO2, LiNiO2, and LiMn2O4. However, due to the toxicity of cobalt and limited resources, the difficulty in preparing lithium nickel acid, the poor cyclic properties and high temperature properties of lithium manganese acid, and other factors, they are restricted. Their application and development. Therefore, the development of new high energy and cheap cathode materials is very important for the development of lithium ion batteries.

In 1997, Padhi et al. reported that lithium iron phosphate(LiFePO4) with olivine structure can reversibly inlay lithium, and has the characteristics of high capacity, good cyclic performance, stable electrochemical performance, and low price. It is the preferred generation of green positive materials., Especially as a powerful lithium ion battery material. The discovery of lithium iron phosphate has attracted the attention of many researchers in the field of electrochemistry at home and abroad. In recent years, with the increasing application of lithium batteries, more and more research has been done on LiFePO4.

Structure of lithium iron phosphate

Lithium iron phosphate(LiFePO4) has an olivine structure and is a slightly distorted hexagonal dense accumulation. Its space group is Pmnb type, and the crystalline structure is shown in Figure 2.1.

Detailed production process of lithium iron phosphate

LiFePO4 consists of FeO6 octahedron and PO4 tetrahedron to form a space skeleton. P occupies a tetrahedron position, while Fe and Li are filled in an octahedral gap, where Fe occupies a coangular octahedral position and Li occupies a coplanar octahedral position. A FeO6 octahedron of the lattice is common to two FeO6 octahedrons and one PO4 tetrahedron, while the PO4 tetrahedron is common to one FeO6 octahedron and two LiO6 octahedron. Due to the close arrangement of nearly hexagonal accumulated oxygen atoms, lithium ions can only be deem bedded on a two-dimensional plane, and therefore have a relatively high theoretical density(3.6 g/cm3). In this structure, the voltage of Fe2 + / Fe3 + relative to metallic lithium is 3.4 V, and the theoretical specific capacity of the material is 170 mA · h/g. A strong P-O-M Covalent bond is formed in the material, which greatly stabilizes the crystal structure of the material, resulting in high thermal stability of the material.

Wang et al. made a detailed analysis of the electrochemical properties of LiFePO4. Figure 2.2 is cyclic load voltammetry of LiFePO4, forming two peaks in the C-V diagram, and Li + is removed from the LixFePO4 structure during anode scanning. The oxidation peak is formed at 3.52 V; When Li + is embedded in the LixFePO4 structure when scanned from 4.0 to 3.0, the corresponding reduction peak is formed at 3.32 V; The Redox peak in the C-V curve shows that reversible lithium ion abridging occurs on the LiFePO4 electrode.

Properties of lithium iron phosphate

1) High energy density

Its theoretical specific capacity is 170mAh/g, and the actual specific capacity of the product can exceed 140mAh/g(0.2 C, 25 °C);

2) Security

It is currently the safest lithium ion battery cathode material; Does not contain any heavy metal elements that are harmful to the human body;

3) Long life span

Under 100 % DOD conditions, you can charge and discharge more than 2,000 times; (Reason: The stability of the lithium iron phosphate lattice is good, and the embedding and deactivation of lithium ions have little effect on the lattice, so it has good reversibility. The deficiency is that the electrode ion conductivity is poor, and it is not suitable for large current charging and discharging, and it is blocked in the application. Solution: The electrode surface is coated with conductive materials and doped for electrode modification. ))

The service life of lithium iron phosphate battery is closely related to its service temperature, and it's low or high service temperature has great negative potential in its charging and discharging process and use process. Especially used in electric vehicles in northern China, lithium iron phosphate batteries can not supply electricity normally or their power supply is too low in autumn and winter, and their working environment temperature needs to be adjusted to maintain their performance. At present, it is necessary to consider the space limitation problem to solve the temperature environment of lithium iron phosphate batteries. The more common solution is to use aerogel felt as a thermal insulation layer.

4) Charging performance

Lithium batteries of lithium ferric phosphate positive electrode materials can be charged at a high rate and the battery can be filled within 1 hour as soon as possible.

Detailed production process of lithium iron phosphate

Process of production of lithium iron phosphate

1, iron phosphate drying water removal

(1) Oven drying process: Stainless steel box full of raw materials iron phosphate placed in the oven, adjust the oven temperature 220 ±

20 °C, 6-10 hours dry. Out of the next process to the converter sintering.

(2) The sintering process of the converter: the heating up of the converter and the passing of nitrogen to meet the requirements, the feed(from the baking room of the upper process)

Material), regulating temperature 540 ± 20 °C, sintering 8-12 hours.

2, grinding machine mixing process

During normal production, two grinding machines are put into operation at the same time. The two devices have the same material and operation(one can also run separately during commissioning). The procedures are as follows:

(1) Lithium carbonate grinding: weighing lithium carbonate 13Kg, sucrose 12Kg, pure water 50Kg, mixed grinding 1-2 hours. Pause.

(2) Mixed grinding: Add iron phosphate 50Kg, pure water 25Kg, mixed grinding 1 to 3 hours. Stop, feed into the dispersing machine. Sampling granularity.

(3) Cleaning: weighing 100Kg pure water, 3 to 5 times cleaning grinder, lotion all transferred to the dispersion machine.

3, dispersed machine material dispersion process

(1) Transfer about 500Kg of materials(including materials from the cleaning grinder) mixed with two or two grinders(or one grinder mixed twice) to the dispersing machine, add 100Kg pure water, adjust stirring speed, and fully stir and disperse for 1-2 hours. Wait to pump into the spray drying equipment.

4, spray drying process

(1) Adjust the inlet temperature of the spray drying equipment at 220 ± 20 °C, the outlet temperature at 110 ± 10 °C, and the feed speed at 80 Kg/hr. Then, the feed spray drying begins to give the drying material.

(2) The solid content can be adjusted to 15 % ~ 30 % according to the size of the spray particle.

5, hydraulic press material pack material adjustment hydraulic press pressure of 150 tons and 175 tons, in the mold loaded spray dry materials, holding pressure for a certain period of time, compacted into a block. Load the casserole into the pushboard furnace. At the same time, several groups of bulk samples are placed to compare with the compressed materials.

6, push plate furnace sintering first warming, pass nitrogen, reach atmosphere requirements of 100 ppm or less, push the coffin into the push plate furnace, according to the warming section 300-550 °C, 4-6 hours; Constant temperature section 750 °C 8-10 hours; The cooling section is carried out 6-8 hours.

7, roller pressure Super fine grinding

The materials of the pushboard furnace are input into ultra-fine grinding, the rotation speed is adjusted, and the roller pressure grinding is sent to ultra-fine grinding for grinding. Test granularity per batch.

8, screening, packaging

Screening and packaging of grinding materials. 5Kg, 25Kg two specifications.

9, inspection, storage

Product inspection, label into the library. Including product name, inspector, material batch, date.

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