Lithium manganese iron phosphate positive electrode material and preparation method thereof

Abstract

The invention relates to a new energy battery technology, and provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof. The material is prepared through a two-step centrifugal spraying and sintering process, lithium, manganese, iron and phosphorus of the material are matched according to LiMnXFe1-XPO4, and X is more than 0.2 and less than 1. According to a battery prepared from the material, the 0.1 C discharge capacity exceeds 157.3 mAh / g, the charge capacity reaches 160.6 mAh / g, and the charge-discharge efficiency reaches up to 97.9%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a lithium manganese iron phosphate positive electrode material and a preparation method thereof. BACKGROUND

[0002] In recent years, with the rapid development of new energy vehicles, the demand for power batteries is also increasing. The power battery industry has become a new industry that countries around the world are competing to develop, especially lithium-ion power batteries. The performance of lithium-ion batteries depends on the positive and negative electrode materials. If the specific capacity of the positive electrode material can be improved by 50%, the power density of the battery can be increased by 28%. At present, the low specific capacity of the positive electrode material limits the development of lithium-ion batteries. Therefore, researching and improving the specific capacity of the positive electrode material of lithium-ion batteries is of great practical significance to promote the technological progress and performance improvement of lithium-ion batteries.

[0003] Lithium iron phosphate batteries have become the preferred type of lithium-ion power batteries due to their excellent safety, long cycle life, and abundant raw material resources. Using lithium iron phosphate battery positive electrode materials can significantly improve the capacity, cycle stability, safety, and rate performance of lithium-ion batteries. Compared with lithium cobaltate and ternary materials, the cycle performance is improved by more than 20%, the raw material cost is reduced by more than 70%, and the safety is better than lithium cobaltate and ternary materials. Lithium iron phosphate battery positive electrode material is the most commonly used positive electrode material for large-scale power lithium batteries worldwide. However, lithium iron phosphate batteries also face the problems of short cycle life and insufficient thermal stability.

[0004] In recent years, lithium manganese iron phosphate positive electrode materials have emerged in the battery industry and received widespread attention. This material combines the excellent properties of lithium manganese phosphate and lithium iron phosphate, with higher operating voltage, lower self-discharge rate, and excellent cycle stability, while also inheriting the high safety of lithium iron phosphate. In addition, manganese is a non-rare metal with abundant reserves, easy to obtain, and relatively low cost, making the raw material cost of lithium manganese iron phosphate positive electrode material relatively low.

[0005] Therefore, it is necessary to develop a lithium manganese iron phosphate battery positive electrode material. SUMMARY

[0006] To solve the above problems, the application provides a lithium manganese iron phosphate battery positive electrode material and a preparation method thereof. The positive electrode material can be prepared by adjusting the ratio of manganese and iron and by a secondary sintering method to obtain a lithium manganese iron phosphate battery positive electrode material with high carbon content, good cycle performance, and good low-temperature performance. In order to achieve the above purpose, the following technical solutions are adopted:

[0007] This invention provides a method for preparing lithium manganese iron phosphate cathode material. First, basic raw materials are mixed and subjected to initial centrifugal spraying, followed by initial sintering and crushing to prepare a precursor. Then, the precursor is mixed with a carbon source and subjected to a second centrifugal spraying, followed by a second sintering and crushing, ultimately obtaining the lithium manganese iron phosphate cathode material. The raw materials include lithium, manganese, iron, phosphorus source, and water as the medium, in the order of LiMn... X Fe 1-X The PO4 ratio is used for preparation, with an X value between 0.2 and 1.

[0008] Preferably, the initial mixture of the lithium manganese iron phosphate cathode material has a solid content of 10%-30% and a particle size of D50 of less than 1.8 μm.

[0009] Preferably, the preparation of the cathode material further includes adding Ti to obtain a Ti-doped lithium manganese iron phosphate cathode material.

[0010] Preferably, the initial sintering temperature during the preparation process is controlled between 825℃ and 835℃, and the second sintering temperature is between 785℃ and 795℃.

[0011] Preferably, the molar ratio of Li, Mn, Fe and P in the initial raw materials is between (1.04-1.08):(0.56-0.64):(0.36-0.44):(1.01-1.09).

[0012] Preferably, the initial raw materials also include PEG-800.

[0013] Preferably, the lithium source can be lithium carbonate, the iron source can be iron oxide, the phosphorus source can be ammonium phosphate, the carbon source can be starch, and the manganese source can be manganese carbonate.

[0014] Preferably, the furnace pressure during the first and second sintering is maintained at 20Pa-50Pa.

[0015] Preferably, the inlet air temperature for the first spray drying is 200℃-280℃, and the outlet air temperature is 90℃-120℃; the inlet air temperature for the second spray drying is 100℃-200℃, and the outlet air temperature is 65℃-90℃.

[0016] On the other hand, the present invention provides a lithium manganese iron phosphate cathode material prepared by the above-described method for preparing lithium manganese iron phosphate cathode material.

[0017] The beneficial effects of this invention are as follows:

[0018] 1. The lithium manganese iron phosphate cathode material developed in this invention has a carbon content that can be controlled between 1.75% and 2.25%, and a tap density that can reach 0.85 g / cm³. 3 The compacted density can reach 2.37 g / cm³. 3The specific surface area can be reduced to 13.95 m². 2 With a resistivity of 9.1 Ω·cm, it exhibits excellent overall performance.

[0019] 2. The coin cell battery prepared using the lithium manganese iron phosphate cathode material of the present invention has a discharge capacity of over 157.3 mAh / g at a 0.1C rate, a charging capacity of up to 160.6 mAh / g, and a charge-discharge efficiency of up to 97.9%. Detailed Implementation

[0020] Example 1

[0021] 3000L of water was added to reactor S1. 238kg of lithium carbonate was added and stirred for 0.5h. Then 202kg of iron oxide was added and stirred for 2h. Next, 738kg of ammonium dihydrogen phosphate was added and stirred for 0.5h. 3800L of water was then added, followed by 438kg of manganese carbonate and stirred for 2h. Finally, PEG-800, titanium dioxide, and glucose were added and stirred for 0.5h. The mixture was then passed through a sand mill containing 130kg of zirconia balls for ball milling for 0.5h. The mixture was then re-milled. The material is returned to the reactor and recycled to a ball mill. It is then transferred to a sand mill containing 230 kg of zirconia balls for ball milling, with the final ball milling particle size controlled. The stirring frequency is set to 23 Hz and the mill speed is set to 679 rpm. The solid content of the material obtained from ball milling is 15% (of which, the Li:Mn:Fe:P ratio in the lithium, manganese, iron, and phosphorus sources is 1:0.6:0.4:1), the D50 particle size is 1.64 μm, the viscosity is 1366 mPa·s, and the pH is 6.71.

[0022] After the S2 reaction, the material obtained from the ball mill was fed into an atomizing tower for the first spray drying. The inlet air temperature was set to 240℃, the outlet air temperature to 110℃, the atomizer frequency to 35Hz, the atomization flow rate to 0.6m³ / h, the bag temperature to 92.4℃, the atomizer cooling temperature to 65℃, the tower negative pressure to -0.4Pa, the supply air frequency to 32Hz, the induced air frequency to 44Hz, the precursor weight to 1352kg, the potting mix weight to 4.84kg, the atomizer cooling oil level to 0MPa / h, the atomizing disc orifice diameter to 4mm, and the number of atomizing disc orifices to 4. The tap density was TD 0.72g / cm³. 3 The Mn content is 16.41%, the Fe content is 11.66%, and the P content is 16.37%.

[0023] S3 feeds the material after the first spray drying into the kiln nitrogen generator for the first sintering. The kiln temperature is set to 830℃, and the nitrogen flow rate is set to 240m³ / h. 3 / h, nitrogen and oxygen content is 5ppm, furnace pressure is set to 34Pa;

[0024] S4 uses a pulverizer to pulverize the material after the first sintering. The feeding screw frequency is set to 50Hz, the pulverizing frequency is set to 25Hz, the pulverizing current is set to 35A, the grading frequency is set to 35Hz, the induced draft frequency is set to 50Hz, and the crushing weight is 953kg. The pulverized material is tested and found to have a Li content of 4.41%, a Mn content of 18.90%, a Fe content of 13.79%, and a P content of 19.97%.

[0025] S5: 953 kg of pulverized material was mixed with glucose and added to 1800 L of water. The reaction was carried out in a reaction vessel and sand mill. The stirring motor frequency was set to 23 Hz, the mill speed to 1000 rpm, and the fine grinding vessel speed to 1200 rpm. The particle size of the resulting material was measured as D. 50 : 0.39μm, D 90 1.74 μm, solid content 46.6%, pH 8.2;

[0026] After the S6 reaction, the reaction solution was sent to an atomizing tower for a second spray drying. The inlet air temperature was set to 200℃, the outlet air temperature to 70℃, the atomizer frequency to 35Hz, the atomization flow rate to 0.82m³ / h, the bag filter temperature to 66℃, the atomizer cooling temperature to 55℃, the tower negative pressure to -220Pa, the supply air frequency to 29Hz, the induced air frequency to 34Hz, the precursor weight to 1025kg, the potting mix weight to 6.34kg, the atomizer cooling oil level to 0MPa / h, the atomizing disc orifice diameter to 4mm, and the number of atomizing disc orifices to 4. After the second spray drying, the material tested showed a C content of 4.65%, a Mn content of 16.03%, an Fe content of 14.11%, a P content of 17.82%, and a tap density (TD) of 1.50g / cm³. 3 ;

[0027] S7 feeds the spray-dried mixture into the kiln nitrogen generator for a second sintering process. The kiln temperature is set to 790℃, and the nitrogen flow rate is set to 240m³ / h. 3 / h, nitrogen and oxygen content set to 5ppm, furnace pressure set to 34Pa; the material obtained from the second sintering was tested and found to have a C content of 1.83% and a S content of 0.02%;

[0028] S8 uses a pulverizer to pulverize the mixture after the second sintering. The feeding screw frequency is set to 50Hz, the pulverizing frequency is set to 48Hz, the pulverizing current is set to 48A-52A, the grading frequency is set to 38Hz, and the induced draft frequency is set to 43Hz. After pulverization, lithium manganese iron phosphate cathode material is obtained, with a weight of 958kg.

[0029] Example 2

[0030] The first sintering temperature in step S3 of Example 1 is set to 825°C, and the second sintering temperature in step S7 is set to 785°C. Other operations and steps are the same as in Example 1.

[0031] Example 3

[0032] The first sintering temperature in step S3 of Example 1 is set to 835°C, and the second sintering temperature in step S7 is set to 795°C. Other operations and steps are the same as in Example 1.

Claims

1. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that, First, the basic raw materials are mixed and subjected to an initial centrifugal spraying, followed by an initial sintering and crushing to prepare a precursor. Then, the precursor is mixed with a carbon source and subjected to a second centrifugal spraying, followed by a second sintering and crushing, ultimately yielding lithium manganese iron phosphate cathode material. The raw materials include lithium, manganese, iron, phosphorus source, and water as the dielectric, according to the LiMn... X Fe 1-X The PO4 ratio is used for preparation, with an X value between 0.2 and 1.

2. The method for preparing lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The initial mixture of this lithium manganese iron phosphate cathode material has a solid content of 10%-30% and a particle size of D50 of less than 1.8 μm.

3. The method for preparing lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The preparation of this cathode material also includes adding Ti to obtain Ti-doped lithium manganese iron phosphate cathode material.

4. The method for preparing the lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The initial sintering temperature during the preparation process is controlled between 825℃ and 835℃, and the second sintering temperature is between 785℃ and 795℃.

5. The method for preparing the lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The molar ratio of Li, Mn, Fe and P in the initial raw materials is between (1.04-1.08): (0.56-0.64): (0.36-0.44): (1.01-1.09).

6. The method for preparing lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The initial raw materials also include PEG-800.

7. The method for preparing the lithium iron phosphate cathode material as described in claim 1, characterized in that, Lithium sources can be lithium carbonate, iron oxide, phosphorus sources can be ammonium phosphate, carbon sources can be starch, and manganese sources can be manganese carbonate.

8. The method for preparing lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The furnace pressure for both the first and second sintering was maintained between 20 Pa and 50 Pa.

9. The method for preparing the lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The inlet air temperature for the first spray drying is 200℃-280℃, and the outlet air temperature is 90℃-120℃; the inlet air temperature for the second spray drying is 100℃-200℃, and the outlet air temperature is 65℃-90℃.

10. The lithium manganese iron phosphate cathode material prepared by the method for preparing lithium manganese iron phosphate cathode material according to any one of claims 1-9.