Lithium manganese iron phosphate battery

Abstract

The invention discloses a lithium manganese iron phosphate battery. The battery consists of a positive plate, a negative plate and a diaphragm, the positive plate comprises a positive electrode active material, namely a lithium manganese iron phosphate active material, and the particle size D50 of the positive electrode active material is 1.6-5 microns. The negative plate comprises a negative active material, namely graphite, and the particle size D50 of the negative active material is between 10 microns and 12 microns. The porosity of the diaphragm is set between 40 and 60%. In addition, the difference (delta V) between the stable voltage after the discharge of the battery is finished and the instantaneous voltage at the time of the discharge is finished is within the range of 0.02 to 0.21. The lithium manganese iron phosphate battery shows good structural stability and lithium ion dynamic transmission characteristics in the charging and discharging process, so that the direct-current impedance is reduced, the low-temperature performance is improved, and the lithium manganese iron phosphate battery is suitable for being used as a power battery for high-rate charging and discharging.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, and more specifically to a lithium manganese iron phosphate battery. Background Technology

[0002] New energy vehicles are placing increasingly higher demands on the performance of their power batteries, especially in terms of high-rate charging and discharging, to meet the power requirements during vehicle start-up and acceleration. Low DC internal resistance (DCR) is key to achieving high-rate charging and discharging, directly affecting the power performance and lifespan of lithium-ion batteries.

[0003] Lithium manganese iron phosphate (LMFP) batteries exhibit two voltage plateaus during charge and discharge due to the different charge and discharge voltages of manganese and iron (iron has a lower voltage plateau than manganese). This results in problems with conductivity, impedance, and high-rate charge and discharge capacity, particularly at high rates where capacity loss is severe. Therefore, reducing the DC internal resistance of LMFP batteries has become an urgent task in lithium-ion battery research, requiring collaborative efforts from researchers. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a lithium manganese iron phosphate battery, comprising a positive electrode, a negative electrode, and a separator. The positive electrode comprises a lithium manganese iron phosphate active material with a particle size D50 between 1.6 and 5 micrometers; the negative electrode comprises a graphite active material with a particle size D50 between 10 and 12 micrometers; the separator has a porosity of 40% to 60%; at 25°C, the battery is fully charged with a current of 0.33C and then discharged with the same current to 30% state of charge; the difference between the actual voltage after discharge stabilization and the instantaneous voltage at the end of discharge, ΔV, satisfies a range of 0.02 to 0.21.

[0005] Preferably, the particle size D50 of the positive electrode active material is 1.8 to 5.5 micrometers; the particle size D50 of the negative electrode active material is 10.5 to 11.5 micrometers; the porosity of the separator is 40 to 50%; and ΔV is in the range of 0.02 to 0.1.

[0006] Preferably, the particle size D50 of the lithium manganese iron phosphate active material is 1 to 3 micrometers.

[0007] Preferably, in the lithium manganese iron phosphate active material, the molar ratio of manganese to iron is 0.43 to 2.33.

[0008] Preferably, the OI value of the negative electrode is 8 to 18.

[0009] Preferably, the thickness of the diaphragm is 8 to 18 micrometers.

[0010] Preferably, the positive electrode active material further includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, and lithium nickel manganese oxide.

[0011] Preferably, the mass of lithium manganese iron phosphate active material accounts for 60 to 95% of the total mass of the positive electrode active material.

[0012] Preferably, the areal density of the positive electrode sheet is 350 to 420 g / m³. 2 The compacted density is 2.0 to 2.8 g / cm³. 3 .

[0013] Preferably, the areal density of the negative electrode is 140 to 180 g / m³. 2 The compacted density is 1.4 to 1.7 g / cm³. 3 .

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The lithium manganese iron phosphate battery provided by this invention effectively suppresses ohmic polarization, electrochemical polarization, and concentration polarization during charging and discharging by precisely controlling the particle size of the positive electrode active material, the particle size of the negative electrode active material, the porosity of the separator, and the voltage difference ΔV at the end of charging and discharging. This control strategy helps prevent capacity loss in the lithium manganese iron phosphate battery during high-rate charging and discharging. Therefore, the lithium manganese iron phosphate battery provided by this invention exhibits good structural stability and lithium-ion kinetic transport characteristics during charging and discharging, has low DC impedance, and excellent low-temperature performance, making it very suitable as a power battery for high-rate charging and discharging. Detailed Implementation

[0016] Example 1

[0017] The preparation method of the lithium manganese iron phosphate battery in this embodiment includes the following steps:

[0018] Preparation of S1 negative electrode sheet: The negative electrode active material (artificial graphite), conductive agent CNT, and binder CMC are mixed in a ratio of 92:4:4 and stirred until homogeneous. The mixture is then dispersed in deionized water to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated onto copper foil and dried at 100°C for 12 hours under vacuum to obtain the negative electrode sheet. Next, the negative electrode sheet is cold-pressed at a compaction density of 1.65 to ensure close packing of the particles, thus obtaining the final negative electrode sheet. In this embodiment, the particle size D50 of the negative electrode active material used to prepare the negative electrode slurry is set to 10 micrometers.

[0019] Preparation of S2 positive electrode sheet: The positive electrode active material, conductive agent SP, and binder PVDF are mixed and stirred evenly in a ratio of 94:3:3. The mixture is then dispersed in NMP solvent to form a positive electrode slurry. The positive electrode slurry is coated onto aluminum foil and dried at 85°C for 24 hours under vacuum to obtain the positive electrode sheet. Next, the positive electrode sheet is cold-pressed at a compaction density of 2.5 to ensure close particle packing, ultimately yielding the positive electrode sheet. In this embodiment, the positive electrode active material used to prepare the positive electrode slurry consists of 20% LiMn0.7Fe0.3PO4 and 80% lithium nickel cobalt manganese oxide (NCM), with a particle size D50 set to 1.6 micrometers.

[0020] S3 membrane selection: A polyethylene membrane with a porosity of 45% and a thickness of 14 micrometers was selected as the membrane for the lithium-ion battery.

[0021] S4 Battery Assembly: The previously prepared positive and negative electrode sheets are assembled into a single-electrode pouch cell. After battery assembly, sufficient electrolyte is injected. The electrolyte is an organic solvent solution obtained by dissolving lithium salt (1.2M LiPF6) in a mixture of EC, EMC, and DEC in a 1:1:1 mass ratio.

[0022] S5 Formation: After electrolyte injection, the battery needs to be left to stand at room temperature for 12 hours to allow the electrolyte to fully wet the electrodes. Then, the battery is first charged at a current rate of 0.1C for 5 hours to form the SEI film on the negative electrode and to remove any generated gas. Next, it is charged at a current rate of 0.33C to the predetermined upper limit voltage and maintained at a constant voltage of 0.05C until charging is complete, thus completing the battery formation and charging process in this embodiment.

[0023] Example 2

[0024] The difference from Example 1 is that in S1, the positive electrode active material is composed of 30% LiMn0.7Fe0.3PO4 and 70% lithium nickel cobalt manganese oxide (NCM), with a particle size D50 of 1.8 micrometers. For the negative electrode active material, the particle size D50 is set to 10.5 micrometers.

[0025] Example 3

[0026] The difference from Example 1 is as follows: S1 The positive electrode active material used to prepare the positive electrode slurry consists of 40% LiMn0.7Fe0.3PO4 and 60% lithium nickel cobalt manganese oxide (NCM), with a particle size D50 of 3.9 micrometers; S2 The particle size D50 of the negative electrode active material is set to 11.2 micrometers; S3 The porosity of the selected separator is 50%.

Claims

1. A lithium manganese iron phosphate battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, The positive electrode contains lithium manganese iron phosphate active material with a particle size D50 between 1.6 and 5 micrometers; the negative electrode contains graphite active material with a particle size D50 between 10 and 12 micrometers; the separator has a porosity of 40 to 60%; at 25°C, the battery is fully charged with a current of 0.33C and then discharged with the same current to 30% state of charge; the difference between the actual voltage after the discharge stabilizes and the instantaneous voltage at the end of the discharge, i.e., ΔV, satisfies the range of 0.02 to 0.

21.

2. The lithium manganese iron phosphate battery as described in claim 1, characterized in that, The particle size D50 of the positive electrode active material is 1.8 to 5.5 micrometers; the particle size D50 of the negative electrode active material is 10.5 to 11.5 micrometers; the porosity of the separator is 40 to 50%; and ΔV meets the range of 0.02 to 0.

1.

3. The lithium manganese iron phosphate battery as described in claim 1, characterized in that, The particle size D50 of lithium manganese iron phosphate active material is 1 to 3 micrometers.

4. The lithium manganese iron phosphate battery as described in claim 3, characterized in that, In lithium manganese iron phosphate active materials, the molar ratio of manganese to iron is 0.43 to 2.

33.

5. The lithium manganese iron phosphate battery as described in claim 1, characterized in that, The OI value of the negative electrode is 8 to 18.

6. The lithium manganese iron phosphate battery as described in claim 1, characterized in that, The thickness of the diaphragm is 8 to 18 micrometers.

7. The lithium manganese iron phosphate battery as described in claim 1, characterized in that, The positive electrode active material also includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, and lithium nickel manganese oxide.

8. The lithium manganese iron phosphate battery as described in claim 7, characterized in that, The mass of lithium manganese iron phosphate active material accounts for 60 to 95% of the total mass of positive electrode active material.

9. The lithium manganese iron phosphate battery as described in claim 1, characterized in that, The surface density of the positive electrode is 350 to 420 g / m³. 2 The compacted density is 2.0 to 2.8 g / cm³. 3 .

10. The lithium manganese iron phosphate battery as described in claim 1, characterized in that, The anode sheet density is 140 to 180 g / m³ 2 The compacted density is 1.4 to 1.7 g / cm³. 3 .