Lithium manganese iron phosphate battery and preparation method thereof
By employing specific material formulations and manufacturing processes, the insulation and low-temperature performance issues of lithium manganese iron phosphate batteries have been resolved, improving the battery's electrochemical cycle performance and low-temperature tolerance, especially its electrochemical performance under low-temperature environments.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-09
- Publication Date
- 2026-04-10
AI Technical Summary
The poor insulation of lithium manganese iron phosphate batteries leads to poor conductivity, affecting cycle performance, and also results in poor low-temperature performance.
The positive electrode is wound in a circular structure, using specific material formulations and manufacturing processes, including the preparation of the positive and negative electrode sheets, the use of a mixed conductive agent of SP and graphene, a mixed binder of PVDF900 and PVDF5130, a binder of graphite and water-based styrene-butadiene rubber, and negative pressure formation treatment at 45-65°C.
It improves the battery's electrochemical cycle performance and low-temperature performance, especially its electrochemical performance, achieving good electrochemical cycle performance and electrochemical performance under low-temperature conditions, especially its electrochemical cycle performance, especially its electrochemical performance, achieving good electrochemical performance, especially its electrochemical performance.
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of lithium batteries, in particular to a lithium manganese iron phosphate battery and a preparation method thereof. BACKGROUND
[0002] Lithium manganese iron phosphate (LMFP) is considered by the industry as an improved version of lithium iron phosphate, and is currently a more feasible solution to improve lithium iron phosphate. This solution introduces manganese elements into lithium iron phosphate and adjusts the atomic ratio of manganese and iron (i.e. manganese-iron ratio) to improve the voltage platform of the material. Lithium manganese iron phosphate (LMFP, chemical formula LiMn 1-x Fe x PO4) is such an upgraded product, where x represents the manganese-iron ratio. It has similar properties to lithium iron phosphate and lithium manganese phosphate, and has better thermal stability, chemical stability and economy compared to ternary materials, and its energy density is also higher than that of lithium iron phosphate.
[0003] Currently, the energy density of widely used lithium iron phosphate cathode materials on the market has reached its limit, and lithium manganese iron phosphate is expected to break through this bottleneck. The highest energy density of lithium iron phosphate battery is 161.27 Wh / kg, and there has been no significant improvement in recent years, so lithium manganese iron phosphate has emerged as the times require. The formula for calculating the energy density of the battery is the product of the battery capacity and the voltage platform divided by the weight. The theoretical specific capacity of lithium iron phosphate battery has approached the limit of 170 mAh / g, so improving the voltage platform is the key to improving the energy density. Lithium manganese iron phosphate has a higher voltage platform than lithium iron phosphate due to the high voltage characteristics of manganese elements, so it is expected to break through the upper limit of the energy density of existing lithium phosphate materials.
[0004] Compared with lithium iron phosphate, lithium manganese iron phosphate has higher voltage and energy density, and better low-temperature performance. Although the theoretical capacity of lithium manganese iron phosphate is the same as that of lithium iron phosphate, the voltage platform of lithium iron phosphate is only 3.4V, while that of lithium manganese iron phosphate can reach 4.1V, which is within the stable electrochemical window of the organic electrolyte system, which makes lithium manganese iron phosphate have higher energy density potential. When the actual capacity of lithium manganese iron phosphate is the same as that of lithium iron phosphate, its energy density can be increased by 15% compared with lithium iron phosphate. In terms of low-temperature performance, the capacity retention rate of lithium manganese iron phosphate at-20℃ is as high as 71%.
[0005] However, lithium manganese iron phosphate is an insulating material, which seriously affects its conductivity and in turn affects its cycle performance. In addition, the platform capacity of manganese elements at low temperature of lithium manganese iron phosphate does not fully play its role, resulting in unsatisfactory low-temperature performance. Therefore, the present application proposes a specific formula and manufacturing process to prepare a lithium manganese iron phosphate battery with long cycle life and super-low temperature performance. SUMMARY
[0006] This invention provides a lithium iron phosphate lithium manganese lithium battery and its preparation method to solve the problems existing in the prior art.
[0007] To achieve the above objectives, the present invention provides a method for preparing a lithium iron phosphate lithium manganese battery, comprising the following steps:
[0008] S1 is used to fabricate the positive and negative electrode plates respectively;
[0009] S2 is stacked in the order of positive electrode, first separator, negative electrode and second separator, and wound to form a battery cell;
[0010] S3 injects electrolyte into the cell and, through formation, sealing and capacity testing, finally produces a lithium iron phosphate manganese lithium battery. The temperature of the formation process is controlled at 45-65℃ and the pressure is maintained at negative pressure.
[0011] Preferably, the pressure during the formation process is controlled between -65 and 90 kPa.
[0012] Preferably, the preparation process of the positive electrode sheet includes mixing lithium manganese iron phosphate, a first conductive agent and a first binder to form a slurry, coating and slitting, wherein the first conductive agent is a mixture of SP and graphene, and the first binder is a mixture of PVDF900 and PVDF5130.
[0013] Preferably, the weight ratio of SP to graphene in the first conductive agent is between 2 and 3:1.
[0014] Preferably, the weight ratio of lithium manganese iron phosphate, the first conductive agent, and the first binder is between 95% and 96% : 1.5% and 2.0% : 2.5% and 3.0%.
[0015] Preferably, the preparation process of the negative electrode sheet includes mixing graphite, a second conductive agent, and a second binder to form a slurry, coating, and slitting, wherein the second conductive agent is SP and the binder is water-based styrene-butadiene rubber.
[0016] Preferably, a thickener is added during the slurry preparation process of the negative electrode sheet, and the preferred thickener is sodium hydroxymethylcarboxylate.
[0017] Preferably, the weight ratio of graphite, thickener, second conductive agent, and second binder is between 96%–96.5% : 1.0%–1.1% : 0.8%–1.0% : 1.5%–1.8%.
[0018] Preferably, the coating density of the positive electrode is 330–350 g / m². 2 The coating surface density of the negative electrode is 155–165 g / m². 2 .
[0019] On the other hand, the present invention provides a lithium iron phosphate lithium manganese battery, which is prepared by the above-described preparation method.
[0020] Compared with the prior art, the present invention has the following beneficial effects:
[0021] By employing the technical solution of this invention, the above-mentioned manufacturing method utilizes a circular winding structure to ensure close contact between the positive and negative electrodes, thereby reducing the resistance to lithium-ion shuttle movement. Furthermore, at a specific higher temperature, a negative pressure formation process ensures that side reactions can proceed fully, thus reducing the excessive gas generated when subsequent side reactions are incomplete, and lowering the risk of battery performance degradation. Based on these methods, the produced lithium iron manganese phosphate battery exhibits excellent electrochemical cycle performance and good low-temperature tolerance. Detailed Implementation
[0022] Example 1
[0023] This embodiment is a cylindrical battery composed of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode consists of a main material, a conductive agent, and a binder, mixed in a weight ratio of 95%, 2.0%, and 2.9%, respectively. The main material is lithium manganese iron phosphate, and the conductive agent is a mixture of SP (Temico) and graphene conductive slurry, with an SP to graphene ratio of approximately 3:1. The binder uses a mixed formulation, mainly composed of PVDF900 and PVDF5130 mixed in a 3:1 weight ratio. The negative electrode consists of a main material, a thickener, a conductive agent, and a binder, with weight ratios of 96.1%, 1.1%, 1.0%, and 1.8%, respectively. The main material is graphite, the thickener is sodium hydroxymethylcarboxylate (CMC), the conductive agent is also SP, and the binder is water-based styrene-butadiene rubber (SBR) (Shanghai Daoying GD1332G). These positive and negative electrode materials are processed through wet pulping, coating, and slitting to ultimately form electrode sheets, with the positive electrode having a coating areal density of 330 g / m³. 2 The coating surface density of the negative electrode is 155 g / m². 2The battery cells are wound into a cylindrical shape using a 9+3 ceramic separator (manufactured by Hebei Jinli New Energy, model 9+3+2) with high air permeability, thus manufacturing a 32700 model cylindrical battery. Flexible leads with tabs are provided at both ends of the cylindrical battery cell, with the positive flexible lead located at the center of the cell and the negative flexible lead located at the side. The positive tab is welded to the positive cover plate, and the negative tab is welded to the negative cover plate. The positive cover plate is welded to the battery casing and remains insulated, while the negative cover plate is directly welded to the negatively charged casing. The positive cover plate has an injection hole and an explosion-proof valve. Both the casing and the cover plate are made of aluminum. After the battery is sealed, electrolyte is injected, followed by 24 hours of high-temperature settling. After the settling process, a high-temperature negative pressure formation treatment is performed at a formation pressure of -70 kPa and a formation temperature of 45°C.
Claims
1. A method for preparing a lithium iron phosphate lithium manganese battery, characterized in that, Includes the following steps: S1 is used to fabricate the positive and negative electrode plates respectively; S2 is stacked in the order of positive electrode, first separator, negative electrode and second separator, and wound to form a battery cell; S3 injects electrolyte into the cell and, through formation, sealing and capacity testing, finally produces a lithium iron phosphate manganese lithium battery. The temperature of the formation process is controlled at 45-65℃ and the pressure is maintained at negative pressure.
2. The method for preparing a lithium iron phosphate / lithium manganese battery according to claim 1, characterized in that, The pressure during the formation process is controlled between -65 and 90 kPa.
3. The method for preparing a lithium iron phosphate / lithium manganese battery according to claim 1, characterized in that, The preparation process of the positive electrode includes mixing lithium manganese iron phosphate, a first conductive agent and a first binder to form a slurry, coating and slitting, wherein the first conductive agent is a mixture of SP and graphene, and the first binder is a mixture of PVDF900 and PVDF5130.
4. The method for preparing a lithium iron phosphate / lithium manganese battery according to claim 1, characterized in that, In the first conductive agent, the weight ratio of SP to graphene is between 2 and 3:
1.
5. The method for preparing a lithium iron phosphate / lithium manganese battery according to claim 1, characterized in that, The weight ratio of lithium manganese iron phosphate, the first conductive agent, and the first binder is between 95% and 96% : 1.5% and 2.0% : 2.5% and 3.0%.
6. The method for preparing a lithium iron phosphate lithium manganese battery according to claim 1, characterized in that, The preparation process of the negative electrode sheet includes mixing graphite, a second conductive agent, and a second binder to form a slurry, coating, and slitting, wherein the second conductive agent is SP and the binder is water-based styrene-butadiene rubber.
7. The method for preparing a lithium iron phosphate lithium manganese battery according to claim 1, characterized in that, A thickener is added during the slurry preparation process of the negative electrode sheet, with sodium hydroxymethylcarboxylate being the preferred thickener.
8. The method for preparing a lithium iron phosphate lithium manganese battery according to claim 1, characterized in that, The weight ratio of graphite, thickener, second conductive agent, and second binder is between 96%–96.5% : 1.0%–1.1% : 0.8%–1.0% : 1.5%–1.8%.
9. The method for preparing a lithium iron phosphate lithium manganese battery according to claim 1, characterized in that, The coating density of the positive electrode is 330-350 g / m2, and the coating surface density of the negative electrode is 155-165 g / m2.
10. A lithium iron phosphate lithium manganese battery, characterized in that, The battery is prepared by the preparation method described in any one of claims 1-9.