High-surface-load electrode and preparation method thereof

Abstract

The invention discloses a high-surface-load electrode and a preparation method thereof, and belongs to the technical field of battery electrodes. A high-surface-load electrode comprises a binder, a conductive agent, a positive electrode material, an additive and a solvent, and the mass ratio of the binder to the conductive agent to the positive electrode material is (1-2): (0.5-1): (94-98); the additive is a three-dimensional high-conductivity material, and the mass of the three-dimensional high-conductivity material is 0.5%-3% of the mass of the electrode solid material. By adopting the high-surface-load electrode and the preparation method thereof, the problem that an existing high-surface-load electrode is poor in cycle performance and rate capability can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrodes, and in particular to a high surface loading electrode and a preparation method thereof. Background Art

[0002] As the demand for lithium-ion battery energy density in electric vehicles, large-scale energy storage and other fields continues to increase, the development of high-area-load electrodes (area-load ≥ 6mAh / cm²) has become a key technical direction for improving battery capacity. Compared with traditional low-area-load electrodes (≤ 3mAh / cm²), high-area-capacity electrodes can not only increase the energy density of single cells, but also reduce the use of inactive materials such as metal current collectors and separators, thereby reducing the production cost of batteries. However, under high-area-load conditions, the increase in electrode thickness leads to a significant extension of the ion / electron transmission path, causing problems such as low utilization of active materials and decreased rate performance, which seriously restricts the practical application of high-energy-density batteries.

[0003] During the coating and drying process of high surface load electrodes, the binder will float up, resulting in uneven distribution of carbon glue phase in the electrode, increasing the electrode tortuosity and ion / electron transfer impedance. Uneven distribution of carbon glue phase will also cause a lack of buffer between active material particles inside the electrode, and local overpressure will occur during the rolling process of the pole piece, resulting in uneven distribution of pores inside the pole piece and even rupture of active material particles. As the number of cycles increases, these two factors aggravate the capacity loss of the battery.

[0004] Laser pore formation, directional freeze drying, wood templates, 3D printing and other methods have been used to improve the cycle performance of high-surface-load electrodes, but the essence of these methods is to increase the porosity of the electrode, which will sacrifice the energy density of the battery, and many methods are difficult to apply to large-scale production processes. Developing high-performance high-surface-load electrodes with standard electrode porosity (25%-30%) is an important means to improve battery energy density. Summary of the invention

[0005] The purpose of the present invention is to provide a high surface loading electrode and a preparation method thereof, so as to solve the problem that the existing high surface loading electrode has poor cycle performance and rate performance.

[0006] To achieve the above-mentioned purpose, the present invention provides a high surface loading electrode, comprising a binder, a conductive agent, a positive electrode material, an additive and a solvent, wherein the mass ratio of the binder, the conductive agent and the positive electrode material is (1-2): (0.5-1): (94-98); the additive is a three-dimensional high conductive material, and the mass of the three-dimensional high conductive material is 0.5%-3% of the mass of the electrode solid material.

[0007] Preferably, the three-dimensional high-conductivity material is high-crystallinity three-dimensional carbon, with a conductivity of 40.94 S / cm (test pressure 10 MPa), a specific surface area of ​​190.5924 m² / g, and an average pore size of 56.201 Å.

[0008] Preferably, the particle size of the three-dimensional high-conductivity material is 50 mesh-100 mesh.

[0009] Preferably, the binder is polyvinylidene fluoride (PVDF), the conductive agent is conductive carbon black Super P, and the solvent is N-methylpyrrolidone (NMP).

[0010] Preferably, the positive electrode material is LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811).

[0011] The method for preparing the above-mentioned high surface loading electrode comprises the following steps: S1, mixing the binder and the solvent, stirring evenly to obtain a clear colloidal solution; S2, adding the conductive agent and the positive electrode material to the mixed solution and stirring evenly to obtain an electrode slurry; coating the slurry on the current collector, slicing and rolling after drying to obtain a high surface load electrode S3, adding the three-dimensional high-conductivity material to the electrode slurry after passing through a 100-mesh sieve, and stirring evenly; adding a solvent to adjust the viscosity of the electrode slurry to obtain a modified electrode slurry; S4. Apply the modified electrode slurry on the current collector, slice and roll it after drying to obtain a high surface loading electrode.

[0012] Preferably, in S3, the viscosity of the modified electrode slurry is 4000cps-8000cps.

[0013] Preferably, in S4, the compaction density of the roller pressing is 3.2 g / cm 3 -3.4g / cm 3 .

[0014] Preferably, in S4, the surface loading of the high surface loading electrode is 7 mAh / cm²-9 mAh / cm².

[0015] The advantages and positive effects of the high surface loading electrode and the preparation method thereof of the present invention are: 1. The present invention adds a high conductivity additive with a three-dimensional structure to the electrode material, which can increase the conductivity of the electrode. Its three-dimensional structure can inhibit the floating of the binder during the drying process, make the carbon gel phase and pore distribution inside the electrode more uniform, and enhance the electrolyte wettability; and provide sufficient buffering during the rolling process to reduce overpressure and improve the ion / electron transmission performance of the high surface load electrode. Under the same test conditions, the battery pole piece modified with the three-dimensional high conductivity additive has significantly improved cycle performance and rate performance.

[0016] 2. The electrode preparation method of the present invention is simple and easy to operate, and is easy to realize industrial production; and it will not increase the porosity of the electrode sheet and will not weaken the energy density of the battery.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a preparation flow chart of an embodiment of the present invention; Figure 2 The SEM image of the cross section of the high surface loading electrode prepared in Example 1 of the present invention and the energy spectrum analysis diagram of the C element; (a) the whole cross section, (b) the upper half of the cross section, (c) the lower half of the cross section, (d) is the energy spectrum distribution diagram of the C element corresponding to (a), (e) is the energy spectrum distribution diagram of the C element corresponding to (b), and (f) is the energy spectrum distribution diagram of the C element corresponding to (c); Figure 3 The SEM image of the cross section of the high surface loading electrode prepared in Comparative Example 1 of the present invention and the energy spectrum analysis diagram of the C element; (a) the entire cross section, (b) the upper half of the cross section, (c) the lower half of the cross section, (d) is the energy spectrum distribution diagram of the C element corresponding to (a), (e) is the energy spectrum distribution diagram of the C element corresponding to (b), and (f) is the energy spectrum distribution diagram of the C element corresponding to (c); Figure 4 Focused electron beam scanning electron microscope (FIB-SEM) images of the cross section of the high surface loading electrode prepared in Example 1 of the present invention; (a) top, (b) middle, (c) bottom; Figure 5 Focused electron beam scanning electron microscope (FIB-SEM) images of the cross section of the high surface loading electrode prepared in Comparative Example 1 of the present invention; (a) top, (b) middle, (c) bottom; Figure 6 The coulombic efficiency and discharge specific capacity test results of the soft-pack batteries of Example 1, Example 2 and Comparative Example 1 of the present invention are shown; Figure 7 The fast charging specific capacity test results of the soft-pack batteries of Example 1, Example 2 and Comparative Example 1 of the present invention are shown. DETAILED DESCRIPTION

[0019] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0020] A high surface loading electrode comprises a binder, a conductive agent, a positive electrode material, an additive and a solvent, wherein the mass ratio of the binder, the conductive agent and the positive electrode material is (1-2): (0.5-1): (94-98). The additive is a three-dimensional high-conductivity material, and the mass of the three-dimensional high-conductivity material is 0.5%-3% of the mass of the electrode solid material.

[0021] The three-dimensional high conductive material is highly crystalline three-dimensional carbon with a conductivity of 40.94 S / cm, a specific surface area of ​​190.5924 m² / g, and an average pore size of 56.201 Å.

[0022] The particle size of the three-dimensional high conductive material is 50 mesh to 100 mesh.

[0023] The binder is polyvinylidene fluoride, the conductive agent is conductive carbon black Super P, and the solvent is N-methylpyrrolidone.

[0024] The positive electrode material is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0025] like Figure 1 The method for preparing the above-mentioned high surface loading electrode comprises the following steps: S1. Mix the binder and the solvent at a low speed and stir them evenly to obtain a clear colloidal solution.

[0026] S2. Add the conductive agent and the positive electrode material to the mixed solution, and stir evenly by low-speed stirring and high-speed homogenization to obtain a uniform electrode slurry.

[0027] S3. Pass the three-dimensional high-conductivity material through a 100-mesh sieve and add it into the electrode slurry, and stir it evenly by high-speed homogenization.

[0028] A solvent is added to adjust the viscosity of the electrode slurry to obtain a modified electrode slurry.

[0029] The viscosity of the modified electrode slurry is 4000cps-8000cps.

[0030] S4. Apply the modified electrode slurry on the current collector, slice and roll it after drying to obtain a high surface loading electrode.

[0031] The current collector is made of aluminum foil with a thickness of 10um. The compaction density of the roller is 3.2g / cm 3 -3.4g / cm 3 .

[0032] The surface loading of high surface loading electrodes is 7mAh / cm²-9mAh / cm².

[0033] Example 1 A high surface loading electrode comprises a polyvinylidene fluoride binder, conductive carbon black Super P, NCM811 positive electrode material, a high crystallinity three-dimensional carbon additive and an N-methylpyrrolidone solvent.

[0034] The mass ratio of polyvinylidene fluoride, conductive carbon black Super P and NCM811 is 1.8:0.7:97.

[0035] The mass of high-crystallinity three-dimensional carbon is 0.5% of the mass of the electrode solid material.

[0036] The high-area-load electrode has an areal load of 8 mAh / cm² and an electrode thickness of 150 μm.

[0037] Example 2 A high surface loading electrode, comprising a polyvinylidene fluoride binder, conductive carbon black Super P, NCM811 positive electrode material, a high crystallinity three-dimensional carbon additive and an N-methylpyrrolidone solvent. The mass ratio of polyvinylidene fluoride, conductive carbon black Super P and NCM811 is 1.8:0.7:94.5.

[0038] The mass of high-crystallinity three-dimensional carbon is 3% of the mass of the electrode solid material.

[0039] The high-area-load electrode has an areal load of 8 mAh / cm² and an electrode thickness of 150 μm.

[0040] Comparative Example 1 A high surface loading electrode comprises a polyvinylidene fluoride binder, conductive carbon black Super P, NCM811 positive electrode material and N-methylpyrrolidone solvent.

[0041] The mass ratio of polyvinylidene fluoride, conductive carbon black Super P and NCM811 is 1.8:1.2:97.

[0042] The high-area-load electrode has an areal load of 8 mAh / cm² and an electrode thickness of 150 μm.

[0043] The cross-sections of the high surface loading electrodes prepared in Example 1 and Comparative Example 1 were subjected to energy spectrum analysis of the C element, and the results are as follows: Figure 2 , Figure 3As shown. In Example 1, the C element is distributed evenly inside the pole piece. In Comparative Example 1, the C element on the upper part of the pole piece is significantly higher than that on the bottom near the current collector, and the C element is unevenly distributed inside the pole piece. This shows that adding high-crystallinity three-dimensional carbon to the pole piece can effectively suppress the problems of binder floating and uneven distribution of carbon glue phase that occur during the drying process.

[0044] The cross sections of the high surface loading electrodes prepared in Example 1 and Comparative Example 1 were observed by focused electron beam scanning electron microscopy. Figure 4 , Figure 5 As shown. In Example 1, the internal pores of the pole piece are uniform, and the active material particles are less broken. In Comparative Example 1, the internal pores of the pole piece are unevenly distributed, the top pores are significantly more than the bottom, and a large number of active material particles on the surface of the pole piece and near the bottom of the current collector are broken due to overpressure. This shows that the addition of high-crystallinity three-dimensional carbon can alleviate the overpressure problem during rolling.

[0045] The pole pieces in Example 1, Example 2 and Comparative Example 1 were assembled into NCM811||CuLi soft-pack batteries. The soft-pack batteries were subjected to slow charge and fast discharge tests, and long cycle tests were performed at a rate of 0.1C constant current-constant voltage charging and 0.5C constant current-constant voltage discharge, with a voltage range of 3V-4.3V and a constant voltage charge / discharge cut-off current of 0.05C. The CuLi composite tape specifications have a copper foil thickness of 6μm, a Li foil on both sides of 50μm each, and an ester electrolyte.

[0046] The test results of the slow charge and fast discharge coulombic efficiency and discharge specific capacity of the soft-pack battery of Example 1, Example 2 and Comparative Example 1 are as follows: Figure 6 As shown. The soft-pack batteries in Examples 1 and 2 have higher discharge specific capacity and cycle retention rate than the soft-pack battery in Comparative Example 1, and the coulombic efficiency is more stable. The soft-pack battery in Example 1 has the highest discharge specific capacity and cycle retention rate, and the coulombic efficiency is the most stable.

[0047] The NCM811||CuLi soft-pack batteries of Example 1, Example 2 and Comparative Example 1 were fast-charged, with 0.5C constant current charging, a cut-off voltage of 4.3V, a CuLi composite tape with a copper foil thickness of 6 μm, and Li foils on both sides of 50 μm each, and an ester electrolyte.

[0048] The fast charging specific capacity test results of the soft pack batteries of Example 1, Example 2 and Comparative Example 1 are as follows: Figure 7 The charging capacity of the soft-pack batteries in Examples 1 and 2 is higher than that in Comparative Example 1, and Example 1 has the highest charging capacity, indicating that adding a three-dimensional high-conductivity additive to the electrode material can significantly improve the rate performance of the high-area-load electrode.

[0049] The present invention adds a high conductivity additive with a three-dimensional structure to the electrode material, which can increase the conductivity of the electrode. Its three-dimensional structure can inhibit the floating of the binder during the drying process, make the carbon gel phase and pore distribution inside the electrode more uniform, and enhance the electrolyte wettability; and provide sufficient buffering during the rolling process to reduce overpressure and improve the ion / electron transmission performance of the high surface load electrode. Under the same test conditions, the battery pole piece modified with the three-dimensional high conductivity additive has significantly improved cycle performance and rate performance.

[0050] Therefore, the high surface loading electrode and the preparation method thereof described in the present invention can solve the problems of poor cycle performance and rate performance of existing high surface loading electrodes.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A high surface loading electrode, characterized in that: It includes a binder, a conductive agent, a positive electrode material, an additive and a solvent, wherein the mass ratio of the binder, the conductive agent and the positive electrode material is (1-2): (0.5-1): (94-98); the additive is a three-dimensional high-conductivity material, and the mass of the three-dimensional high-conductivity material is 0.5%-3% of the mass of the electrode solid material.

2. A high surface loading electrode according to claim 1, characterized in that: The three-dimensional high-conductivity material is high-crystallinity three-dimensional carbon with a conductivity of 40.94 S / cm, a specific surface area of ​​190.5924 m² / g, and an average pore diameter of 56.201 Å.

3. A high surface loading electrode according to claim 1, characterized in that: The particle size of the three-dimensional high-conductivity material is 50 meshes to 100 meshes.

4. A high surface loading electrode according to claim 1, characterized in that: The binder is polyvinylidene fluoride, the conductive agent is conductive carbon black Super P, and the solvent is N-methylpyrrolidone.

5. The high surface loading electrode according to claim 1, characterized in that: The positive electrode material is LiNi 0.8 Co 0.1 Mn 0.1 O2.

6. A method for preparing a high surface loading electrode according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, mixing the binder and the solvent, stirring evenly to obtain a clear colloidal solution; S2, adding the conductive agent and the positive electrode material to the mixed solution and stirring evenly to obtain an electrode slurry; S3, adding the three-dimensional high-conductivity material to the electrode slurry after passing through a 100-mesh sieve, and stirring evenly; adding a solvent to adjust the viscosity of the electrode slurry to obtain a modified electrode slurry; S4. Apply the modified electrode slurry on the current collector, slice and roll it after drying to obtain a high surface loading electrode.

7. The method for preparing a high surface loading electrode according to claim 1, characterized in that: In S3, the viscosity of the modified electrode slurry is 4000cps-8000cps.

8. The method for preparing a high surface loading electrode according to claim 1, characterized in that: In S4, the compaction density of the roller pressing is 3.2 g / cm 3 -3.4g / cm 3 .

9. The method for preparing a high surface loading electrode according to claim 1, characterized in that: In the S4, the surface loading of the high surface loading electrode is 7 mAh / cm²-9 mAh / cm².

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