A high areal loading electrode and its preparation method

Abstract

The present invention discloses a high areal loading electrode and a preparation method thereof, belonging to the technical field of battery electrodes. A high areal loading electrode includes a binder, a conductive agent, a cathode material, an additive and a solvent. The mass ratio of the binder, the conductive agent to the cathode material is (1-2):(0.5-1):(94-98); the additive is a three-dimensional highly conductive material, and the mass of the three-dimensional highly conductive material is 0.5%-3% of the mass of the electrode solid material. By using the high areal loading electrode and the preparation method thereof of the present invention, the problems of poor cycle performance and rate performance of the existing high areal loading electrodes can be solved.

Description

Technical Field

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

[0002] With the continuous increase in the demand for the energy density of lithium-ion batteries in fields such as electric vehicles and large-scale energy storage, the development of high areal loading electrodes (areal loading ≥ 6 mAh / cm²) has become a key technical direction for improving battery capacity. Compared with traditional low areal loading electrodes (≤ 3 mAh / cm²), high areal capacity electrodes can not only improve 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 areal loading conditions, the increase in electrode thickness leads to a significant extension of the ion / electron transport path, resulting in problems such as low active material utilization and poor rate performance, which seriously restrict the practical application of high energy density batteries.

[0003] During the coating and drying process of high areal loading electrodes, the binder floats up, resulting in uneven distribution of the carbon-binder phase in the electrode, increasing the tortuosity of the electrode and the ion / electron transport impedance. The uneven distribution of the carbon-binder phase also causes a lack of buffering between the active material particles inside the electrode, resulting in local overpressure during the rolling process of the electrode sheet, causing uneven pore distribution inside the electrode sheet and even rupture of the active material particles. With the increase in the number of cycles, these two factors exacerbate the capacity loss of the battery.

[0004] Methods such as laser pore formation, directional freeze-drying, wood templates, and 3D printing have been applied to improve the cycling performance of high areal loading electrodes, but the essence of these methods is to increase the porosity of the electrodes, which will sacrifice the energy density of the battery, and many methods are difficult to apply in large-scale production processes. Developing high-performance high areal loading electrodes with a standard electrode porosity (25% - 30%) is an important means to improve the energy density of batteries. Summary of the Invention

[0005] The purpose of the present invention is to provide a high areal loading electrode and a preparation method thereof to solve the problems of poor cycling performance and rate performance of existing high areal loading electrodes.

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

[0007] Preferably, the three-dimensional highly conductive material is highly crystalline 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 diameter of 56.201 Å.

[0008] Preferably, the particle size of the three-dimensional highly conductive 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 preparation method of the above high areal loading electrode includes the following steps:

[0012] S1. Mix the binder and the solvent, stir evenly to obtain a clear colloidal solution;

[0013] S2. Add the conductive agent and the positive electrode material to the mixture and stir evenly to obtain an electrode slurry; coat the slurry on a current collector, dry, slice, and roll to obtain a high areal loading electrode

[0014] S3. Pass the three-dimensional highly conductive material through a 100-mesh sieve and add it to the electrode slurry, stir evenly; add a solvent to adjust the viscosity of the electrode slurry to obtain a modified electrode slurry;

[0015] S4. Coat the modified electrode slurry on a current collector, dry, slice, and roll to obtain a high areal loading electrode.

[0016] Preferably, in S3, the viscosity of the modified electrode slurry is 4000 cps - 8000 cps.

[0017] Preferably, in S4, the compaction density of the rolling is 3.2 g / cm 3 -3.4 g / cm 3 .

[0018] Preferably, in S4, the areal loading of the high areal loading electrode is 7 mAh / cm² - 9 mAh / cm².

[0019] The advantages and positive effects of the high areal loading electrode and its preparation method of the present invention are:

[0020] 1. In the present invention, a highly conductive additive with a three-dimensional structure is added 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, making the carbon-binder phase and pore distribution inside the electrode more uniform, enhancing the electrolyte wettability; and providing sufficient buffering during the rolling process, slowing down overpressure, and improving the ion / electron transport performance of the high areal loading electrode. Under the same test conditions, the cycle performance and rate performance of the battery electrode sheet modified by adding the three-dimensional highly conductive additive are significantly improved.

[0021] 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.

[0022] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0023] Figure 1 It is the preparation flow chart of the embodiment of the present invention;

[0024] Figure 2 It is the SEM image of the cross-section of the high areal loading electrode prepared in Example 1 of the present invention and the energy spectrum analysis diagram of C element; (a) overall cross-section, (b) upper half of the cross-section, (c) lower half of the cross-section, (d) is the C element energy spectrum distribution diagram corresponding to (a), (e) is the C element energy spectrum distribution diagram corresponding to (b), (f) is the C element energy spectrum distribution diagram corresponding to (c);

[0025] Figure 3 It is the SEM image of the cross-section of the high areal loading electrode prepared in Comparative Example 1 of the present invention and the energy spectrum analysis diagram of C element; (a) overall cross-section, (b) upper half of the cross-section, (c) lower half of the cross-section, (d) is the C element energy spectrum distribution diagram corresponding to (a), (e) is the C element energy spectrum distribution diagram corresponding to (b), (f) is the C element energy spectrum distribution diagram corresponding to (c);

[0026] Figure 4 It is the focused ion beam scanning electron microscope (FIB-SEM) image of the cross-section of the high areal loading electrode prepared in Example 1 of the present invention; (a) top, (b) middle, (c) bottom;

[0027] Figure 5 It is the focused ion beam scanning electron microscope (FIB-SEM) image of the cross-section of the high areal loading electrode prepared in Comparative Example 1 of the present invention; (a) top, (b) middle, (c) bottom;

[0028] Figure 6 It is the test results of the Coulomb efficiency and discharge specific capacity of slow charge and fast discharge of the soft-pack batteries of Example 1, Example 2 and Comparative Example 1 of the present invention;

[0029] Figure 7 This is the test result of the charging specific capacity during fast charging of the soft-pack batteries in Example 1, Example 2 and Comparative Example 1 of the present invention. Detailed implementation manners

[0030] The following will describe in detail the implementation manners of the present invention with reference to the accompanying drawings.

[0031] A high areal loading electrode includes a binder, a conductive agent, a cathode material, an additive and a solvent. The mass ratio of the binder, the conductive agent to the cathode material is (1 - 2):(0.5 - 1):(94 - 98). The additive is a three-dimensional highly conductive material, and the mass of the three-dimensional highly conductive material is 0.5% - 3% of the mass of the solid electrode material.

[0032] The three-dimensional highly conductive material is a 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 diameter of 56.201 Å.

[0033] The particle size of the three-dimensional highly conductive material is 50 mesh - 100 mesh.

[0034] The binder is polyvinylidene fluoride, the conductive agent is conductive carbon black Super P, and the solvent is N-methylpyrrolidone.

[0035] The cathode material is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0036] As Figure 1 shown. The preparation method of the above high areal loading electrode includes the following steps:

[0037] S1. Slowly stir and mix the binder and the solvent until evenly mixed to obtain a clear gelatinous solution.

[0038] S2. Add the conductive agent and the cathode material into the mixed solution, and stir evenly by means of slow stirring and high-speed homogenization to obtain a uniform electrode slurry.

[0039] S3. Pass the three-dimensional highly conductive material through a 100-mesh sieve and then add it into the electrode slurry, and stir evenly by means of high-speed homogenization.

[0040] Add a solvent to adjust the viscosity of the electrode slurry to obtain a modified electrode slurry.

[0041] The viscosity of the modified electrode slurry is 4000 cps - 8000 cps.

[0042] S4. Coat the modified electrode slurry on a current collector, dry it, then slice and roll it to obtain a high areal loading electrode.

[0043] The current collector uses aluminum foil with a thickness of 10um. The compaction density after rolling is 3.2g / cm 3 - 3.4g / cm 3 .

[0044] The areal loading of the high areal loading electrode is 7mAh / cm² - 9mAh / cm².

[0045] Example 1

[0046] A high areal loading electrode includes a polyvinylidene fluoride binder, conductive carbon black Super P, NCM811 cathode material, high-crystallinity three-dimensional carbon additive, and N-methylpyrrolidone solvent.

[0047] The mass ratio of polyvinylidene fluoride, conductive carbon black Super P to NCM811 is 1.8:0.7:97.

[0048] The mass of the high-crystallinity three-dimensional carbon is 0.5% of the mass of the electrode solid material.

[0049] The areal loading of the high areal loading electrode is 8mAh / cm². The electrode thickness is 150μm.

[0050] Example 2

[0051] A high areal loading electrode includes a polyvinylidene fluoride binder, conductive carbon black Super P, NCM811 cathode material, high-crystallinity three-dimensional carbon additive, and N-methylpyrrolidone solvent. )

[0052] The mass ratio of polyvinylidene fluoride, conductive carbon black Super P to NCM811 is 1.8:0.7:94.5.

[0053] The mass of the high-crystallinity three-dimensional carbon is 3% of the mass of the electrode solid material.

[0054] The areal loading of the high areal loading electrode is 8mAh / cm². The electrode thickness is 150μm.

[0055] Comparative Example 1

[0056] A high areal loading electrode includes a polyvinylidene fluoride binder, conductive carbon black Super P, NCM811 cathode material, and N-methylpyrrolidone solvent.

[0057] The mass ratio of polyvinylidene fluoride, conductive carbon black Super P to NCM811 is 1.8:1.2:97.

[0058] The areal loading of the high areal loading electrode is 8mAh / cm². The electrode thickness is 150μm.

[0059] Energy spectrum analysis of C elements was performed on the cross-sections of the high areal loading electrodes prepared in Example 1 and Comparative Example 1, and the results are as Figure 2 , Figure 3 shown. In Example 1, the distribution of C elements inside the electrode sheet was relatively uniform. In Comparative Example 1, the C elements in the upper part of the electrode sheet were significantly higher than those at the bottom near the current collector, and the distribution of C elements inside the electrode sheet was uneven. This indicates that adding high-crystallinity three-dimensional carbon to the electrode sheet can effectively inhibit the problems of binder floating and uneven distribution of carbon-binder phase during the drying process.

[0060] Focused electron beam scanning electron microscopy was used to observe the cross-sections of the high areal loading electrodes prepared in Example 1 and Comparative Example 1, and the results are as Figure 4 , Figure 5 shown. In Example 1, the pores inside the electrode sheet were uniform and there were few ruptures of the active material particles. In Comparative Example 1, the pore distribution inside the electrode sheet was uneven, with significantly more pores at the top than at the bottom, and a large number of overpressure ruptures occurred in the active material particles on the surface of the electrode sheet and at the bottom near the current collector. This indicates that adding high-crystallinity three-dimensional carbon can alleviate the overpressure problem during the rolling process.

[0061] The electrode sheets in Example 1, Example 2, and Comparative Example 1 were assembled into NCM811||CuLi soft-pack batteries. Slow charge and fast discharge tests were carried out on the soft-pack batteries. Long-term cycling tests were carried out at a rate of constant current-constant voltage charging at 0.1C and constant current-constant voltage discharging at 0.5C, with the voltage range of 3V - 4.3V and the cut-off current of constant voltage charge / discharge being 0.05C. The CuLi composite tape had a copper foil thickness of 6μm and 50μm thick Li foils on both sides, and an ester-based electrolyte was used.

[0062] The test results of Coulomb efficiency and discharge specific capacity for slow charge and fast discharge of the soft-pack batteries in Example 1, Example 2, and Comparative Example 1 are as Figure 6 shown. The soft-pack batteries in Example 1 and Example 2 had higher discharge specific capacity and cycle retention rate compared to the soft-pack battery in Comparative Example 1, and the Coulomb efficiency was more stable. The soft-pack battery in Example 1 had the highest discharge specific capacity and cycle retention rate, and the most stable Coulomb efficiency.

[0063] Fast charge tests were carried out on the NCM811||CuLi soft-pack batteries in Example 1, Example 2, and Comparative Example 1. Constant current charging was carried out at 0.5C, and the cut-off voltage was 4.3V. The CuLi composite tape had a copper foil thickness of 6μm and 50μm thick Li foils on both sides, and an ester-based electrolyte was used.

[0064] The test results of charge specific capacity for fast charge of the soft-pack batteries in Example 1, Example 2, and Comparative Example 1 are as Figure 7 shown. The charge specific capacities of the soft-pack batteries in Example 1 and Example 2 were both higher than that of the soft-pack battery in Comparative Example 1, and Example 1 had the highest charge specific capacity; this indicates that adding three-dimensional highly conductive additives to the electrode material can significantly improve the rate performance of high areal loading electrode sheets.

[0065] In the present invention, a highly conductive additive with a three-dimensional structure is added 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-binder phase and pore distribution inside the electrode more uniform, and enhance the electrolyte wettability. Moreover, it provides sufficient buffering during the rolling process, slows down overpressure, and improves the ion / electron transport performance of the high areal capacity electrode. Under the same test conditions, the cycle performance and rate performance of the battery electrode sheet modified by adding the three-dimensional highly conductive additive are significantly improved.

[0066] Therefore, by using the high areal capacity electrode and its preparation method described in the present invention, the problems of poor cycle performance and rate performance of the existing high areal capacity electrodes can be solved.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high areal loading electrode, characterized in that: It includes a binder, a conductive agent, a cathode material, an additive and a solvent. The mass ratio of the binder, the conductive agent to the cathode material is (1 - 2):(0.5 - 1):(94 - 98); the additive is a three-dimensional highly conductive material, and the mass of the three-dimensional highly conductive material is 0.5% - 3% of the mass of the electrode solid material; The three-dimensional highly 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 diameter of 56.201 Å; The particle size of the three-dimensional highly conductive material is 50 mesh - 100 mesh; The positive electrode material is LiNi 0.8 Co 0.1 Mn 0.1 O2; The areal loading of the high areal loading electrode is 7 mAh / cm² - 9 mAh / cm².

2. The high areal 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.

3. A method for preparing a high areal loading electrode according to any one of claims 1-2, characterized in that, It includes the following steps: S1. Mix the binder and the solvent, and stir evenly to obtain a clear colloidal solution; S2. Add the conductive agent and the cathode material to the mixed solution and stir evenly to obtain an electrode paste; S3. Pass the three-dimensional highly conductive material through a 100-mesh sieve and add it to the electrode paste, and stir evenly; add a solvent to adjust the viscosity of the electrode paste to obtain a modified electrode paste; S4. Coating the modified electrode paste on a current collector, drying, slicing and rolling to obtain a high areal loading electrode.

4. The preparation method of a high areal loading electrode according to claim 3, wherein: In S3, the viscosity of the modified electrode paste is 4000 cps - 8000 cps.

5. The preparation method of a high areal capacity electrode according to claim 3, wherein: In S4, the compaction density of the roll pressing is 3.2 g / cm 3 - 3.4 g / cm 3 .

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