A method for preparing a high-compaction-density electrode

Abstract

The present invention relates to the technical field of lithium battery electrodes, and discloses a method for preparing a high tap density electrode, comprising the following steps: 1) coating an A1 coating and a B1 coating on both sides of an electrode foil respectively; 2) drying the A1 coating and the B1 coating; 3) coating an A2 coating and a B2 coating on the surfaces of the dried A1 coating and B1 coating; 4) drying the A2 coating and the B2 coating; the coatings on the A side and the B side are arranged in a staggered manner along the extending direction of the electrode foil; 5) rolling the electrode to a designed thickness. By means of two coatings to achieve the designed surface density, the surface density and thickness consistency of the coatings are improved. At the same time, a staggered design is adopted between the coatings on both sides, so that when the electrode is rolled, the coatings on both sides are successively stressed in a stepped manner, effectively alleviating the problem of material dropping caused by excessive compaction density in the coating head area when the electrode with a high tap density under gap coating is rolled. This not only reduces the defective rate of the appearance of the rolled electrode, but also improves the voltage drop consistency of the lithium battery.

Description

Technical Field

[0001] This invention patent relates to the technical field of lithium battery electrodes. Specifically, it relates to a method for preparing a high tap density electrode. Background Art

[0002] The structure of the electrode has an important impact on the electrical performance and safety of lithium-ion batteries. For a non-continuous gap coating electrode structure, whether the equipment is a transfer coating operation or an extrusion coating operation, affected by the rheology and thixotropy of the slurry, the thickness of the coating at the starting coating line position (coating head) is often thicker than that of the middle coating, and the thickness of the coating at the ending coating position (coating tail) is significantly thinner than that of the middle coating.

[0003] In the prior art, when the single-sided and double-sided coatings of the electrode are designed to be aligned, the empty foil area of the electrode first passes through the roll nip of the roll press, and then the double-sided coatings pass through the roll nip. Due to the sudden force on the double-sided coatings, it often leads to excessive compaction density in the coating head area and causes material dropping. After the electrode drops material, it not only affects the winding design margin of the negative electrode covering the positive electrode in the length direction of the electrode, but also there is a risk that the dropped powder falls into the internal battery core, affecting the consistency of the battery voltage drop. In severe cases, it even leads to potential safety hazards of the battery.

[0004] In order to improve the energy density of lithium-ion batteries, the design of electrodes with high tap density is often pursued, which further increases the risk of excessive compaction and coating dropping in the aligned coating head area. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a high tap density electrode, aiming to solve the problem of coating dropping at the coating head during roll pressing under the traditional single-sided and double-sided alignment design of electrode coating in the prior art.

[0006] This invention is implemented as follows. A method for preparing a high tap density electrode includes the following steps:

[0007] 1) Coat A1 coating and B1 coating on both sides of the electrode foil respectively;

[0008] 2) Dry the A1 coating and B1 coating;

[0009] 3) Coat A2 coating on the surface of the dried A1 coating; coat B2 coating on the surface of the dried B1 coating;

[0010] 4) Dry the A2 coating and B2 coating; the A1 coating and A2 coating form the A-side coating of the electrode, and the B1 coating and B2 coating form the B-side coating of the electrode; the A-side coating and the B-side coating are arranged in a staggered manner along the extending direction of the electrode foil;

[0011] 5) Roll the electrode to the designed thickness.

[0012] Optionally, in step 1), the coating head of the A1 coating and the coating tail of the B1 coating are located at the same end of the electrode sheet, and the coating tail of the A1 coating and the coating head of the B1 coating are located at the other end of the electrode sheet.

[0013] Optionally, in step 3), the coating head and the coating tail of the A2 coating are respectively aligned with the coating tail and the coating head of the A1 coating, and the coating head and the coating tail of the B2 coating are respectively aligned with the coating tail and the coating head of the B1 coating.

[0014] Optionally, in the moving direction of the electrode sheet during rolling, the end of the B-side coating is longer than the end of the A-side coating by a misalignment length L.

[0015] Optionally, the misalignment length L ≥ (r(h1 - s) - (h1 - s) 2 / 4) 0.5 , where r is the radius of the rolling rolls of the rolling press, s is the width of the roll gap of the rolling press, and h1 is the designed thickness of the electrode sheet after rolling.

[0016] Optionally, in step 5), when the electrode sheet passes through the roll gap of the rolling press, the bare foil area, the single-sided coating area, and the double-sided coating area of the electrode sheet pass through the roll gap of the rolling press in sequence.

[0017] Optionally, in step 5), the compaction density of the electrode sheet coating after rolling the electrode sheet to the designed thickness is 1.0 - 2.5 g / cm 3 , and the designed thickness h1 of the electrode sheet after rolling is 50 - 200 μm.

[0018] Optionally, when the electrode sheet passes through the roll gap of the rolling press, the B-side coating with the coating tail of the B1 coating enters the roll gap of the rolling press before the A-side coating with the coating head of the A1 coating.

[0019] Optionally, in step 1), the areal densities of the A1 coating and the B1 coating are respectively 10% - 90% of the designed areal densities of the A-side coating and the B-side coating of the electrode sheet.

[0020] Optionally, the electrode sheet is a negative electrode sheet or a positive electrode sheet of a lithium battery.

[0021] Compared with the prior art, a method for preparing a high-compaction-density electrode sheet provided by the present invention achieves the designed areal density through two coatings, improves the areal density and thickness consistency of the coatings, and at the same time adopts a misalignment design between the two-sided coatings, realizing that the coatings on both sides of the electrode sheet are stressed in a stepped manner successively when the electrode sheet is rolled, effectively alleviating the problem of material dropping caused by excessive compaction density in the coating head area when the electrode sheet with a high-compaction-density design by gap coating is rolled. It not only reduces the defective rate of the appearance of the rolled electrode sheet but also improves the voltage drop consistency of the lithium battery. Description of the Drawings

[0022] Figure 1It is a schematic diagram of a method for preparing a high-compaction density electrode sheet provided by the present invention;

[0023] Figure 2 It is a schematic diagram of winding a negative electrode sheet and a positive electrode sheet prepared by a method for preparing a high-compaction density electrode sheet provided by the present invention.

[0024] Explanation of reference numerals:

[0025] 100 - A-side coating, 110 - A1 coating, 120 - A2 coating, 111 - coating head of A1 coating, 112 - coating tail of A1 coating; 200 - B-side coating, 210 - B1 coating, 220 - B2 coating, 211 - coating head of B1 coating, 212 - coating tail of B1 coating; 300 - electrode foil; 410 - upper roller, 420 - lower roller;

[0026] 1 - negative electrode sheet; 2 - positive electrode sheet, 21 - single-sided coating, 22 - double-sided coating. Detailed implementation manners

[0027] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] The implementation of the present invention will be described in detail below with reference to specific embodiments.

[0029] In the drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and cannot be understood as a limitation of this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0030] Refer to Figure 1-2 As shown, it is a preferred embodiment provided by the present invention.

[0031] A method for preparing a high-compaction density electrode sheet includes the following steps:

[0032] 1) Coat A1 coating 110 and B1 coating 210 on both sides of electrode foil 300 respectively;

[0033] 2) Dry A1 coating 110 and B1 coating 210;

[0034] 3) Coat the surface of the dried A1 coating 110 with the A2 coating 120; coat the surface of the dried B1 coating 210 with the B2 coating 220;

[0035] 4) Dry the A2 coating 120 and the B2 coating 220; the A1 coating 110 and the A2 coating 120 form the A-side coating 100 of the electrode sheet, and the B1 coating 210 and the B2 coating 220 form the B-side coating 200 of the electrode sheet; the A-side coating 100 and the B-side coating 200 are arranged in a staggered manner along the extending direction of the electrode sheet foil 300;

[0036] 5) Roll the electrode sheet to the designed thickness.

[0037] A method for preparing a high tap density electrode sheet provided by this embodiment achieves the designed areal density through two coatings, improves the areal density and thickness consistency of the coating surface, and at the same time adopts a staggered design between the two surface coatings, realizing that the coatings on both sides of the electrode sheet are successively stressed in a stepped manner when being rolled, effectively alleviating the problem of material dropping caused by excessive compaction density in the coating head area when the electrode sheet is rolled under the high tap density design of gap coating. This not only reduces the defective rate of the appearance of the rolled electrode sheet but also improves the voltage drop consistency of the lithium battery.

[0038] Specifically, the electrode sheet foil 300 can be copper foil or aluminum foil. The A-side coating 100 and the B-side coating 200 are respectively coated on the upper and lower surfaces of the electrode sheet foil 300, and it can be applied to the positive electrode sheet or the negative electrode sheet of the lithium battery. Usually, the foil of the negative electrode sheet uses copper foil, and the foil of the positive electrode sheet uses aluminum foil.

[0039] For example, the negative electrode material of the lithium battery includes high tap density artificial graphite, conductive agent, binder and other materials (these materials adopt the existing lithium battery negative electrode materials), and the designed compaction density of the negative electrode rolling is 1.8 g / cm 3 , and the negative electrode raw materials are mixed into a uniform slurry with viscosity, solid content, fineness, etc. meeting the technical indicators through a set pulping process, and then the slurry is sprayed onto the upper and lower surfaces of the copper foil in two operations by an extrusion coater.

[0040] The materials of the A-side coating 100 and the B-side coating 200 can be the same, for example, both are negative electrode materials. When preparing the positive electrode sheet structure, the materials of the A-side coating 100 and the B-side coating 200 adopt positive electrode materials.

[0041] Specifically, in step 1), the coating head 111 of the A1 coating and the coating tail 212 of the B1 coating are located at the same end of the electrode sheet, and the coating tail 112 of the A1 coating and the coating head 211 of the B1 coating are located at the other end of the electrode sheet. This indicates that the coating directions of the A1 coating 110 and the B1 coating 210 are opposite. For example, the A1 coating 110 is coated from front to back, while the B1 coating 210 is coated from back to front. The opposite coating directions of the A1 coating 110 and the B1 coating 210 result in better coating uniformity, and the coating head positions of the A1 coating 110 and the B1 coating 210 can be staggered, avoiding the problem of excessive thickness and easy material dropping at the coating head position on the same end of the double-sided coating electrode sheet.

[0042] Specifically, in step 3), the coating head and coating tail of the A2 coating 120 are respectively aligned with the coating tail 112 and coating head of the A1 coating, and the coating head and coating tail of the B2 coating 220 are respectively aligned with the coating tail and coating head of the B1 coating 210.

[0043] The coating direction of the A2 coating 120 is opposite to that of the A1 coating 110, and the coating direction of the B2 coating 220 is opposite to that of the B1 coating 210, thereby better ensuring the thickness uniformity of the A-side coating 100 and the B-side coating 200 and avoiding the problem of material dropping during rolling caused by inconsistent thickness.

[0044] Specifically, in the moving direction of the electrode sheet during rolling (i.e., Figure 1 the moving direction of the electrode sheet in

[0045] The starting coating position is the coating head, and the position at the end of coating is the coating tail. The thickness of the coating at the starting coating line position (coating head) is usually thicker than that of the middle coating, and the thickness of the coating at the end of coating (coating tail) is significantly thinner than that of the middle coating, which is determined by the coating process itself.

[0046] The end of the B-side coating 200 is longer than the end of the A-side coating 100 by a misalignment length L. When the electrode sheet structure is rolled in its moving direction, the empty foil area of the electrode sheet foil 300 first enters the rolling nip of the rolling machine, and then the single-sided coating area (e.g., the B-side coating 200) and the double-sided coating area (both the A-side coating 100 and the B-side coating 200 enter the nip) pass through the rolling nip of the rolling machine in sequence without overlap. The misalignment length of the B-side coating 200 and the A-side coating 100 enables the coatings on both sides to be stressed in a stepped manner successively, effectively alleviating the problem of material dropping during rolling of the electrode sheet under the high compaction density design of gap coating due to excessive compaction density in the coating head area.

[0047] Preferably, the misalignment length L ≥ (r(h1 - s) - (h1 - s) 2 / 4) 0.5 , where the roll radius of the roll press is r, the roll gap width of the roll press is s, and the designed thickness of the electrode sheet after rolling is h1.

[0048] The thickness of the electrode sheet foil 300 is h2. Then, when the lower roll 420 just touches the end position of the B - side coating 200 and the upper roll 410 touches the head position of the A - side coating 100, the misalignment length is the smallest.

[0049] The misalignment length L ≥ (r 2 - (r + (s - h2) / 2 - (h1 - h2) / 2) 2 ) 0.5 = (r(h1 - s) - (h1 - s) 2 / 4) 0.5 ,

[0050] If the misalignment length is too long, it will waste materials. If the misalignment length is too short, the problem of coating material falling off during high - compaction cannot be solved. The misalignment length calculated by the above formula is a more appropriate misalignment length and has been verified in engineering practice, ensuring the yield rate of electrode sheet preparation.

[0051] Optionally, in step 5), the compaction density of the electrode sheet coating corresponding to the designed thickness of the electrode sheet after rolling is 1.0 - 2.5 g / cm 3 , and the designed thickness h1 of the electrode sheet after rolling is 50 - 200 μm.

[0052] Optionally, in step 1), the areal densities of the A1 coating 110 and the B1 coating 210 are 10% - 90% of the designed areal densities of the A - side coating 100 and the B - side coating 200 of the electrode sheet respectively. By coating twice to achieve the designed areal density of the A - side coating 100 or the B - side coating 200, the areal density and thickness consistency of the coating can be better improved.

[0053] In the following specific embodiment: A type 18650 cylindrical lithium - ion battery, the negative electrode includes materials such as artificial graphite with high compaction density, conductive agent, binder, etc. The designed compaction density of the negative electrode after rolling is 1.8 g / cm 3 . The negative electrode raw materials are mixed into a uniform slurry with viscosity, solid content, fineness, etc. meeting the technical indicators through a set pulp - making process, and then the slurry is sprayed onto the copper foil surface by a double - die - head extrusion coater in two coatings. The specific steps are as follows:

[0054] 1) Coat the negative electrode slurry A1 coating 110 and B1 coating 210 on the copper foil surface at the same time with a gap. The two ends of the A1 coating 110 and B1 coating 210 are both designed with dislocation. The coating head 111 and the coating tail of the A1 coating are respectively at the same end of the electrode sheet as the coating tail and the coating head of the B1 coating 210.

[0055] 2) Dry the A1 coating 110 and B1 coating 210.

[0056] 3) Coating the A2 coating 120 and B2 coating 220 on the surface of the A1 coating 110 and B1 coating 210 at the same time for the second time. Among them, the coating tail and coating head of the A2 coating 120 are respectively aligned with the coating head and coating tail of the A1 coating 110, and the coating head and coating tail of the B2 coating 220 respectively overlap with the coating tail and coating head of the B1 coating 210.

[0057] 4) Dry the A2 coating 120 and B2 coating 220.

[0058] 5) After the dried negative electrode sheet passes through the gap between the upper roller 410 and the lower roller 420 of the roller press, it is rolled to the designed thickness of 140 μm.

[0059] Furthermore, in step 3), a two - coating production process is adopted to form the A - side coating 100 or B - side coating 200, which can counteract the problem of poor consistency of coating surface density and thickness caused by the thicker coating head and thinner coating tail. The thickness difference between the coating in the edge area and the coating in the middle area can be controlled within ±2 μm.

[0060] Furthermore, the radius of the roller of the roller press used is r = 400 cm, the width of the roll gap between the upper and lower rollers of the roller press is s = 120 μm, the designed thickness of the electrode sheet after rolling is h1 = 130 μm, and the thickness of the foil is h2 = 9 μm. According to the formula L≥(r 2 -(r+(s - h2) / 2-(h1 - h2) / 2) 2 ) 0.5 Calculation shows that the dislocation length L of the negative electrode coating is ≥6.3 mm.

[0061] Furthermore, referring to Figure 2 , in the winding structure of a cylindrical lithium - ion battery, the coating of the negative electrode sheet 1 should be able to completely cover the coating of the positive electrode sheet 2. At the same time, the coating in the edge area will not fall off during rolling. Then, the dislocation length between the A - side coating and the B - side coating at the inner end of the negative electrode sheet 1 in the inner circle of the winding core is designed to be 8 mm, and the dislocation length between the A - side coating and the B - side coating of the negative electrode sheet 1 in the outer circle of the winding core is designed to be 55 mm.

[0062] Referring to the above method for preparing the high-compaction-density negative electrode sheet, both sides of the positive electrode sheet foil are respectively coated with a single-sided coating 21 and a double-sided coating 22, and the single-sided coating 21 and the double-sided coating 22 are also designed with a dislocation, wherein the end of the double-sided coating 22 extends beyond the end of the single-sided coating 21 by a dislocation length L. According to the winding structure of the positive electrode sheet 2 and the negative electrode sheet 1 designed as above, the coating of the negative electrode sheet 1 can completely cover the coating of the positive electrode sheet 2, and at the same time, the coating in the edge area will not fall off during rolling. In practice, the yield rate of the lithium battery electrode sheet is greatly improved.

[0063] For the negative electrode sheet 1 produced according to the requirements of the above embodiment, the consistency of the coating thickness is significantly improved, and the appearance of the negative electrode sheet 1 after rolling is good, and no abnormal phenomena such as material dropping occur in the edge area of the coating.

[0064] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-compaction-density electrode sheet, characterized in that, It includes the following steps: 1) Coat A1 coating and B1 coating on both sides of the pole piece foil respectively; 2) Dry the A1 coating and B1 coating; 3) Coat A2 coating on the surface of the dried A1 coating; Coat B2 coating on the surface of the dried B1 coating; 4) Dry the A2 coating and B2 coating; The A1 coating and A2 coating form the A-side coating of the pole piece, and the B1 coating and B2 coating form the B-side coating of the pole piece; the A-side coating and the B-side coating are arranged in a staggered manner along the extension direction of the pole piece foil; 5) Roll the pole piece to the designed thickness; The pole piece foil is copper foil or aluminum foil; In step 1), the coating head of the A1 coating and the coating tail of the B1 coating are located at the same end of the pole piece, and the coating tail of the A1 coating and the coating head of the B1 coating are located at the other end of the pole piece; In step 3), the coating head and coating tail of the A2 coating are aligned with the coating tail and coating head of the A1 coating respectively, and the coating head and coating tail of the B2 coating are aligned with the coating tail and coating head of the B1 coating respectively; In the moving direction of the pole piece rolling, the end of the B-side coating is longer than the end of the A-side coating by a misalignment length L; The misalignment length L ≥ (r(h1 - s) - (h1 - s) 2 / 4) 0.5 , where r is the radius of the roll press rolls, s is the roll gap width of the roll press rolls, and h1 is the designed thickness of the pole piece after rolling.

2. The preparation method of a high-compaction-density electrode sheet according to claim 1, wherein, In step 5), when the pole piece passes through the roll slit of the rolling machine, the empty foil area, the single-sided coating area and the double-sided coating area of the pole piece pass through the roll slit of the rolling machine in sequence.

3. The preparation method of a high-compaction-density electrode sheet according to claim 2, characterized in that In step 5), the compaction density of the electrode coating when the electrode is roll-pressed to the designed thickness is 1.0~2.5 g / cm 3 , and the designed thickness h1 after roll-pressing the electrode is 50~200 µm.

4. The preparation method of a high-compaction-density electrode sheet according to claim 2, wherein When the pole piece passes through the roll slit of the rolling machine, the B-side coating with the coating tail of the B1 coating enters the roll slit of the rolling machine before the A-side coating with the coating head of the A1 coating.

5. The preparation method of a high-compaction density electrode sheet according to claim 1, characterized in that, In step 1), the areal densities of the A1 coating and B1 coating are 10%-90% of the designed areal densities of the A-side coating and B-side coating of the pole piece respectively.

6. The preparation method of a high-compaction-density electrode sheet according to claim 1, wherein, The pole piece is the negative electrode piece or the positive electrode piece of a lithium battery.

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