Preparation method of flexible negative electrode plate and negative electrode plate

Abstract

The invention belongs to the technical field of lithium battery negative plates, and particularly relates to a preparation method of a flexible negative plate and the negative plate. Comprising the following steps: mixing an active substance, a conductive agent, a thickening agent and a binder to prepare slurry, coating the surface of a current collector with the slurry, and drying to obtain a negative plate; the formula of the slurry also comprises a softening agent; or in the formula of the slurry, the softening agent is not included, but the thickening agent is a flexible thickening agent; the flexibility of the pole piece is improved, powder falling and folding marks of the pole piece in the winding process are avoided, and therefore the service life of the lithium battery is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery negative electrode sheets, and in particular relates to a preparation method of a flexible negative electrode sheet and the negative electrode sheet. Background Art

[0002] Currently, the method for preparing negative electrode sheets for lithium-ion secondary batteries primarily involves mixing active materials, conductive agents, binders, and solvents capable of dissolving the binders into a slurry, which is then coated onto a copper foil current collector. The binders used primarily include styrene-butadiene rubber latex, polyacrylonitrile, polyacrylates, and polystyrene acrylates, and the solvents primarily include deionized water. However, the electrode sheets produced by these methods have point contacts between the active materials within them. When used in flexible lithium-ion secondary batteries, these electrodes are susceptible to shedding between the active materials and the current collector, and between each other, when subjected to certain bending or twisting, resulting in a rapid decrease in capacity. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for preparing a flexible negative electrode sheet and a negative electrode sheet, thereby improving the flexibility of the electrode sheet and preventing the electrode sheet from losing powder and creases during the winding process, thereby increasing the life of the lithium battery.

[0004] The object of the present invention is achieved as follows: A method for preparing a flexible negative electrode sheet, comprising: mixing an active material, a conductive agent, a thickener, and a binder to prepare a slurry, applying the slurry to the surface of a current collector, and drying to obtain a negative electrode sheet; characterized in that:

[0005] The slurry formulation also includes a softener; the thickener in the formulation can be a conventional thickener or a flexible thickener;

[0006] Alternatively, the slurry formulation does not include a softener, but the thickener is a flexible thickener.

[0007] Furthermore, the flexible thickener is one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0008] Preferably, the flexible thickener is sodium carboxymethyl cellulose, which includes conventional sodium carboxymethyl cellulose and modified sodium carboxymethyl cellulose.

[0009] Furthermore, the softener is a dispersant composition, including a main dispersant and an auxiliary dispersant, the main dispersant is 1,3-butanediol, and the auxiliary dispersant is an oligoether substance.

[0010] The oligoether substances include oligoethers and oligoether esters.

[0011] Furthermore, the molecular weight of the oligoether substance is 200 g / mol to 600 g / mol.

[0012] Furthermore, when the slurry is formulated as active material, conductive agent, flexible thickener, and binder, the mass ratio thereof is 92-96:0.5-1.5:1.2-1.8:1.5-2.0;

[0013] When the slurry comprises an active substance, a conductive agent, a thickener, a binder, and a softener, the mass ratio thereof is 92-96: 0.5-1.5: 1.2-1.8: 1.5-2.0: 0.1-0.5.

[0014] The solid content of the slurry is 45-60%, preferably 50-55%.

[0015] Furthermore, the active material is one of artificial graphite, natural graphite, silicon carbon, and silicon oxygen.

[0016] Preferably, the active material is artificial graphite.

[0017] Furthermore, the conductive agent is one of furnace black, conductive carbon black, and graphene.

[0018] Preferably, the conductive agent is conductive carbon black.

[0019] Furthermore, the binder is one of styrene-butadiene rubber, polyacrylic acid, and polyacrylonitrile.

[0020] Preferably, the binder is styrene-butadiene rubber.

[0021] A flexible negative electrode sheet is prepared by the method for preparing a flexible negative electrode sheet.

[0022] The dry film weight of a single side of the active material layer of the flexible negative electrode sheet is 80 to 150 g / cm2.

[0023] Beneficial effects of the present invention: A method for preparing a flexible negative electrode sheet of the present invention, wherein the formula is an active substance, a conductive agent, a thickener, a binder, and a softener, or an active substance, a conductive agent, a flexible thickener, and a binder. The formula is mixed to form a slurry, the slurry is coated on the surface of the current collector, and dried to obtain a negative electrode sheet; a flexible thickener is used to enhance the dispersibility of the negative electrode slurry and reduce agglomeration, and small molecular groups are adsorbed around the hydroxyl groups through hydrogen bonds, so that the thickener side chains are opened and the flexibility of the electrode sheet is enhanced; with the addition of the softener, the softener molecules occupy the space between the binder polymers, reduce the secondary forces (such as hydrogen bonds and van der Waals forces) between the polymer chains, improve the coating cracking and cold-pressed electrode embrittlement caused by polymer shrinkage during the coating and drying process, enhance the flexibility of the electrode sheet, reduce the powder loss and creases of the electrode sheet during the winding process, and thus enhance the life of the lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] This invention has no drawings.

[0025] The technical solution of the present invention is fully and clearly disclosed through text description, and no drawings are needed to assist in the explanation. DETAILED DESCRIPTION

[0026] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0028] It should be noted that all directional indications in the embodiments of the present invention (such as up-down-left-right-front-back...) are only used to explain the relative position relationship - movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly. The connection can be a direct connection or an indirect connection.

[0029] The present invention provides a method for preparing a flexible negative electrode sheet, comprising: mixing an active material, a conductive agent, a thickener, and a binder to prepare a slurry, applying the slurry to the surface of a current collector, and drying to obtain a negative electrode sheet; the method is characterized in that:

[0030] The slurry formulation also includes a softener; the thickener in the formulation can be a conventional thickener or a flexible thickener;

[0031] Alternatively, the slurry formulation does not include a softener, but the thickener is a flexible thickener.

[0032] Furthermore, in one embodiment, the flexible thickener is one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0033] Preferably, the flexible thickener is sodium carboxymethyl cellulose, which includes conventional sodium carboxymethyl cellulose and modified sodium carboxymethyl cellulose.

[0034] The modified sodium carboxymethyl cellulose reduces the rigidity of the material by adding a flexible material. The flexible material is a small molecule compound that is adsorbed around -OH in CMC through intermolecular forces to improve the brittleness of CMC, thereby changing the brittleness of the electrode and improving the toughness.

[0035] Furthermore, in one embodiment, the softener is a dispersant composition including a main dispersant and an auxiliary dispersant, the main dispersant is 1,3-butanediol, and the auxiliary dispersant is an oligoether substance.

[0036] The oligoether substances include oligoethers and oligoether esters.

[0037] The oligoethers include polypropylene glycol diglycidyl ether, polyethylene glycol stearyl ether, polypropylene glycol methyl ether, polyethylene glycol butyl ether, polypropylene glycol butyl ether, polyethylene glycol octyl ether and polyethylene glycol isobutyl ether.

[0038] The oligoether esters include monooleate polyethylene glycol phosphate and glycerol polyoxyethylene ether trioleate.

[0039] Furthermore, in one embodiment, the molecular weight of the oligoether substance is 200 g / mol to 600 g / mol.

[0040] Furthermore, in one embodiment, when the slurry comprises the active material, the conductive agent, the flexible thickener, and the binder, the mass ratio thereof is 92-96: 0.5-1.5: 1.2-1.8: 1.5-2.0;

[0041] When the slurry comprises an active substance, a conductive agent, a thickener, a binder, and a softener, the mass ratio thereof is 92-96: 0.5-1.5: 1.2-1.8: 1.5-2.0: 0.1-0.5.

[0042] The solid content of the slurry is 45-60%, preferably 50-55%.

[0043] The performance comparison of the negative electrode sheets prepared by the above ratios is shown in the following table.

[0044] Table 1 Comparison of performance of negative electrode sheets with different formula ratios

[0045]

[0046] Furthermore, in one embodiment, the active material is one of artificial graphite, natural graphite, silicon carbon, and silicon oxygen.

[0047] Preferably, the active material is artificial graphite; the specific capacity of artificial graphite is about 350 mAh / g, it has high stability, a layered structure suitable for lithium ion insertion / deinsertion, stable cycle performance, mature artificial graphite technology, low cost and good safety.

[0048] Furthermore, in one embodiment, the conductive agent is one of furnace black, conductive carbon black, and graphene.

[0049] Preferably, the conductive agent is conductive carbon black, which has stable conductive properties, high output and low cost.

[0050] Furthermore, in one embodiment, the binder is one of styrene-butadiene rubber, polyacrylic acid, and polyacrylonitrile.

[0051] Preferably, the binder is styrene-butadiene rubber, which has relatively good flexibility. The other two materials are relatively brittle and have poor toughness after forming into films.

[0052] A flexible negative electrode sheet is prepared by the method for preparing a flexible negative electrode sheet.

[0053] The dry film weight of a single side of the active material layer of the flexible negative electrode sheet is 80 to 150 g / cm2.

[0054] In summary, the present invention provides a method for preparing a flexible negative electrode sheet, which has a formula of active material, conductive agent, thickener, binder, and softener, or active material, conductive agent, flexible thickener, and binder. The formula is mixed to form a slurry, and the slurry is coated on the surface of the current collector and dried to obtain a negative electrode sheet. The flexible thickener is used to enhance the dispersibility of the negative electrode slurry and reduce agglomeration. Small molecular groups are adsorbed around hydroxyl groups through hydrogen bonds, which opens the thickener side chains and enhances the flexibility of the electrode sheet. The addition of the softener allows the softener molecules to occupy the space between the binder polymers, reducing the secondary forces (such as hydrogen bonds and van der Waals forces) between the polymer chains, improving the coating cracking caused by polymer shrinkage during the coating and drying process and the embrittlement of the cold-pressed electrode sheet, improving the flexibility of the electrode sheet, and reducing the powder loss and creases of the electrode sheet during the winding process, thereby extending the life of the lithium battery.

[0055] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0056] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for preparing a flexible negative electrode sheet, comprising: The active material, conductive agent, thickener and binder are mixed to form a slurry, the slurry is coated on the surface of the current collector, and dried to obtain a negative electrode sheet; the characteristics are: The slurry formulation also includes a softener; Alternatively, the slurry formulation does not include a softener, but the thickener is a flexible thickener.

2. The method for preparing a flexible negative electrode sheet according to claim 1, wherein: The flexible thickener is one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

3. The method for preparing a flexible negative electrode sheet according to claim 1, wherein: The softener is a dispersant composition, including a main dispersant and an auxiliary dispersant, wherein the main dispersant is 1,3-butanediol and the auxiliary dispersant is an oligoether substance.

4. The method for preparing a flexible negative electrode sheet according to claim 1, wherein: The molecular weight of the oligoether substance is 200 g / mol to 600 g / mol.

5. The method for preparing a flexible negative electrode sheet according to claim 1, wherein: When the slurry comprises active material, conductive agent, flexible thickener and binder, the mass ratio thereof is 92 to 96: 0.5～1.5：1.2～1.8:1.5～2.0； When the slurry comprises active material, conductive agent, thickener, binder and softener, the mass ratio thereof is 92 to 96: 0.5～1.5：1.2～1.8:1.5～2.0：0.1～0.5。 6. The method for preparing a flexible negative electrode sheet according to claim 1, wherein: The active material is one of artificial graphite, natural graphite, silicon carbon and silicon oxygen.

7. The method for preparing a flexible negative electrode sheet according to claim 1, wherein: The conductive agent is one of furnace black, conductive carbon black and graphene.

8. The method for preparing a flexible negative electrode sheet according to claim 1, wherein: The binder is one of styrene-butadiene rubber, polyacrylic acid and polyacrylonitrile.

9. A flexible negative electrode sheet, characterized in that: The flexible negative electrode sheet is prepared by the preparation method of any one of claims 1 to 8.

10. The flexible negative electrode sheet according to claim 9, characterized in that: The dry film weight of the active material layer on a single side of the flexible negative electrode sheet is 80 to 150 g / cm 2 .

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