Transition metal oxide coated diaphragm and preparation method thereof

Abstract

The invention relates to the technical field of preparation of lithium ion battery diaphragms, in particular to a transition metal oxide coated diaphragm for improving the performance of a lithium iron phosphate battery and a preparation method of the transition metal oxide coated diaphragm. The transition metal oxide coated diaphragm comprises a diaphragm substrate and a diaphragm coating coated on the surface of one side of the diaphragm substrate, and the diaphragm coating is a transition metal oxide particle coating. According to the invention, the transition metal oxide particle material is innovatively coated on the surface of the diaphragm, and the coating is further tightly attached to the lithium iron phosphate positive electrode material through the bonding effect of the binder in the coating, so that the contact resistance of the system is reduced. The high-rate discharge performance and the specific discharge capacity of the lithium iron phosphate are improved by regulating and controlling the proportion and the use amount of the transition metal oxide particle material, the binder and the conductive agent in the coating.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery diaphragm preparation, and in particular to a transition metal oxide coated diaphragm and a preparation method thereof. The method is convenient and quick, and can improve the electrochemical performance of lithium iron phosphate batteries and reduce impedance. Background Art

[0002] In the field of power and energy storage batteries, more attention has been paid to the energy density, cycle life and safety of lithium-ion batteries in the past. Lithium iron phosphate has become the most promising lithium-ion battery cathode material due to its long cycle life, low cost, environmental friendliness and high safety performance. However, the lithium iron phosphate material itself has poor ion and electron conductivity, poor high-rate discharge capacity and lacks the ability to charge quickly. The research direction focuses on the lithium iron phosphate material itself, such as improving the ion and electron conductivity by refining the grains of the lithium iron phosphate material, shortening the diffusion path of lithium ions, and modifying it by doping and modification. However, these treatment methods are relatively complicated and it is difficult to achieve comprehensive performance improvement in a short time. As one of the four major components of lithium-ion batteries, the diaphragm is located between the positive and negative electrodes and can play a role in hindering electron transmission and conducting lithium ions. Therefore, the performance of lithium-ion batteries can be affected by simply coating and modifying the diaphragm. Summary of the invention

[0003] The present invention provides a method for preparing a transition metal oxide coated diaphragm, which can improve the electrochemical performance of lithium iron phosphate batteries, and can more quickly achieve the high-rate discharge performance of lithium iron phosphate, improve the discharge specific capacity, and reduce the impedance. The present invention is achieved through the following technical solutions: First, the transition metal oxide coated diaphragm comprises a diaphragm substrate and a diaphragm coating coated on one side of the diaphragm substrate; the diaphragm coating is a transition metal oxide particle coating, and the transition metal oxide particle coating comprises a binder, a conductive agent and transition metal oxide particles.

[0004] The transition metal oxide particle coating is formed by uniformly coating a liquid slurry on a diaphragm substrate and then drying the slurry, and the thickness of the transition metal oxide particle coating is 1-50 μm; The liquid slurry is formed by uniformly mixing transition metal oxide particles, a binder and a conductive agent. The mass ratio of the transition metal oxide particles, the binder and the conductive agent in the liquid slurry is 90:1-9:1-9.

[0005] The particle size D of the transition metal oxide particles 50 The particle size D of the binder is 1 to 30 μm; 50 The particle size D of the conductive agent is 2 to 40 μm; 50 2~40 μm.

[0006] The transition metal oxide particles are any one or more combinations of RuO2, Co3O4, MnO2, CrO, CuO, and FeO; the binder is any one or more combinations of PVDF, PMMA, PAA, SBR, and PVP; the conductive agent is any one or more combinations of Ketjen black, acetylene black, conductive carbon black, carbon nanotubes, and graphene.

[0007] The membrane substrate is any one of a PP / PE / PP composite base film, a PP base film, a PE base film or a ceramic coated membrane; and the thickness of the membrane substrate is 5 to 40 μm.

[0008] When the transition metal oxide coated separator is used to prepare a button battery, the transition metal oxide particle coating faces the positive electrode side of the lithium iron phosphate.

[0009] The transition metal oxide particle coating and the lithium iron phosphate positive electrode plate must be tightly connected.

[0010] Secondly, the preparation method of the transition metal oxide coated diaphragm comprises the following steps: S1, preparing transition metal oxide particle slurry; S2, preparing a mixed slurry of a conductive agent and a binder; S3, preparing a coating liquid slurry, mixing the transition metal oxide particle slurry and the mixed slurry of the conductive agent and the binder to obtain a coating liquid slurry; S4, preparing a coated diaphragm, coating the coating slurry on the surface of the diaphragm substrate, and drying to obtain a transition metal oxide coated diaphragm.

[0011] Furthermore, the coated diaphragm is prepared by coating the coating slurry on the surface of the diaphragm substrate and obtaining the transition metal oxide coated diaphragm after drying, including: on one side of the diaphragm substrate surface, coating the coating slurry on the diaphragm substrate surface by means of a coating roller, and then drying in an oven to obtain the transition metal oxide coated diaphragm.

[0012] The beneficial effects of the present invention are: Compared with the prior art, the advantages of the present invention are: (1) The present invention innovatively proposes coating the surface of the diaphragm with transition metal oxide particles, and further closely bonds the coating to the lithium iron phosphate positive electrode material through the bonding effect of the binder in the coating. The electrochemical performance of the resulting lithium iron phosphate battery is significantly improved.

[0013] (2) The transition metal oxide particle coating of the present invention can improve the performance of the battery simply by adjusting the properties of the transition metal oxide particles in the coating and the ratio and amount of the binder and the conductive agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the structure of the transition metal oxide coated diaphragm of the present invention; Figure 2 Impedance diagrams of button cells prepared with the transition metal oxide coated separator and ordinary separator; Figure 3 Long cycle diagram of button cells prepared with the transition metal oxide coated separator and ordinary separator at a discharge rate of 10 C; In the figure: In the figure: 1-transition metal oxide particle coating, 2-diaphragm matrix, 3-lithium iron carbonate positive electrode. DETAILED DESCRIPTION

[0015] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but the present invention is not limited in any way. Any changes or substitutions made based on the teachings of the present invention belong to the protection scope of the present invention.

[0016] Example 1 Step 1, taking 5 g of FeO powder and mixing it with N-methylpyrrolidone (NMP) to prepare a transition metal oxide particle slurry, wherein the mass ratio of FeO to NMP is 2:10; Step 2: Take 0.06g of acetylene black and 0.06g of PVP and mix them with N-methylpyrrolidone (NMP) to obtain a mixed slurry of a conductive agent and a binder. The mass ratio of acetylene black, SBR and NMP is 1:1:10; Step 3, mixing and stirring the transition metal oxide particle slurry, the conductive agent, and the binder mixed slurry for 20 minutes to obtain a liquid slurry; Step 4: Use a coating roller to evenly coat the liquid slurry on the PE base film. The thickness of the PE base film is 20 μm, and the thickness of the diaphragm coating is 4 μm. After drying the coated diaphragm at 80° C., a transition metal oxide coated diaphragm is obtained.

[0017] Example 2 Step 1, taking 4 g of MnO2 powder and mixing it with N-methylpyrrolidone (NMP) to prepare a transition metal oxide particle slurry, wherein the mass ratio of MnO2 to NMP is 3:10; Step 2: Take 0.05 g of graphene and 0.05 g of SBR and mix them with N-methylpyrrolidone (NMP) to obtain a mixed slurry of a conductive agent and a binder. The mass ratio of graphene, SBR and NMP is 2:2:15; Step 3: Mix and stir the transition metal oxide particle slurry, the conductive agent and the binder slurry for 20 minutes to obtain a liquid slurry.

[0018] Step 4: Use a coating roller to evenly coat the liquid slurry on the PP base film. The thickness of the PP base film is 10 μm, and the thickness of the diaphragm coating is 3 μm. After drying the coated diaphragm at 80° C., a transition metal oxide coated diaphragm is obtained.

[0019] Example 3 Step 1, taking 1 g of CrO powder and mixing it with N-methylpyrrolidone (NMP) to prepare a transition metal oxide particle slurry, wherein the mass ratio of CrO to NMP is 1:4; Step 2: Take 0.08 g of graphene and 0.08 g of PMMA and mix them with N-methylpyrrolidone (NMP) to obtain a mixed slurry of a conductive agent and a binder. The mass ratio of graphene, SBR and NMP is 1:1:8; Step 3: Mix and stir the transition metal oxide particle slurry, the conductive agent and the binder slurry for 20 minutes to obtain a liquid slurry.

[0020] Step 4: Use a coating roller to evenly coat the liquid slurry on the PP / PE / PP base film. The thickness of the PP / PE / PP base film is 20 μm, and the thickness of the diaphragm coating is 5 μm. After drying the coated diaphragm at 80°C, a transition metal oxide coated diaphragm is obtained.

[0021] Example 4 Step 1, taking 1g of CuO powder and mixing it with N-methylpyrrolidone (NMP) to prepare a transition metal oxide particle slurry, wherein the mass ratio of CuO to NMP is 1:3; Step 2: Take 0.11 g of conductive carbon black and 0.11 g of PVDF and mix them with N-methylpyrrolidone (NMP) to obtain a mixed slurry of conductive agent and binder. The mass ratio of conductive carbon black, PVDF and NMP is 1:1:3; Step 3: Mix and stir the transition metal oxide particle slurry, the conductive agent and the binder slurry for 20 minutes to obtain a liquid slurry.

[0022] Step 4: Use a coating roller to evenly coat the liquid slurry on the PP base film. The thickness of the PP base film is 14 μm, and the thickness of the diaphragm coating is 10 μm. After drying the coated diaphragm at 80° C., a transition metal oxide coated diaphragm is obtained.

[0023] The transition metal oxide coated diaphragm prepared in Implementation 1-4 was compared with the ordinary diaphragm, and its charge and discharge performance was tested. The charge and discharge performance was tested by assembling it into button batteries, and it was found that the discharge specific capacity at 10 C could reach more than 120 mAh / g.

Claims

1. A transition metal oxide coated diaphragm, characterized in that: It comprises a diaphragm substrate (2) and a diaphragm coating coated on one side surface of the diaphragm substrate (2); the diaphragm coating is a transition metal oxide particle coating (1).

2. The transition metal oxide coated diaphragm according to claim 1, characterized in that: The transition metal oxide particle coating (1) is formed by uniformly coating a liquid slurry on a diaphragm substrate (2) and then drying it, and the thickness of the transition metal oxide particle coating (1) is 1 to 50 μm; the liquid slurry is formed by uniformly mixing transition metal oxide particles, a binder and a conductive agent, and the mass ratio of the transition metal oxide particles, the binder and the conductive agent in the liquid slurry is 90:1 to 9:1 to 9.

3. The transition metal oxide coated diaphragm according to claim 2, characterized in that: The particle size D of the transition metal oxide particles 50 The particle size D of the binder is 1 to 30 μm; 50 The particle size D of the conductive agent is 2 to 40 μm; 50 2~40 μm.

4. The transition metal oxide coated diaphragm according to claim 1, characterized in that: The transition metal oxide particles are any one or more combinations of RuO2, Co3O4, MnO2, CrO, CuO, and FeO; the binder is any one or more combinations of PVDF, PMMA, PAA, SBR, and PVP; the conductive agent is any one or more combinations of Ketjen black, acetylene black, conductive carbon black, carbon nanotubes, and graphene.

5. The transition metal oxide coated diaphragm according to claim 1, characterized in that: The diaphragm substrate (2) is any one of a PP / PE / PP composite base film, a PP base film, a PE base film or a ceramic coated diaphragm; the thickness of the diaphragm substrate is 5 to 40 μm.

6. The transition metal oxide coated diaphragm according to claim 1, characterized in that: The transition metal oxide particle coating (1) is tightly connected to the lithium iron phosphate positive electrode plate (3).

7. The method for preparing a transition metal oxide coated diaphragm according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: S1, preparing transition metal oxide particle slurry; S2, preparing a mixed slurry of a conductive agent and a binder; S3, preparing a coating liquid slurry, mixing the transition metal oxide particle slurry and the mixed slurry of the conductive agent and the binder to obtain a coating liquid slurry; S4, preparing a coated diaphragm, coating the coating slurry on the surface of the diaphragm substrate, and drying to obtain a transition metal oxide coated diaphragm.

8. The method for preparing a transition metal oxide coated diaphragm according to claim 7, characterized in that: The coated diaphragm is prepared by using NMP as a solvent, and the coating slurry is coated on one side of the surface of the diaphragm substrate by means of a coating roller, and then dried in an oven to obtain a transition metal oxide coated diaphragm.

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