CN115692730A - Safety pole piece and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a safety pole piece, which comprises: a current collector; a safety coating coated on a surface of the current collector, the safety coating including a first active material, a conductive agent, a binder, and an inorganic filler; the active material layer is coated on the surface of the safety coating and comprises a second active material, a conductive agent and a binder; wherein, the safety coating has a concave structure, and the active material layer is at least partially embedded in the concave structure. According to the invention, by optimizing the pole piece structure, the safety performance of the battery cell can be improved, and the loss of the energy density of the battery can be reduced. In addition, the invention also discloses a preparation method of the safety pole piece.

Description

Safety pole piece and preparation method thereof

Technical Field

The invention belongs to the technical field of batteries, and particularly relates to a safety pole piece and a preparation method thereof.

Background

The lithium ion battery has the advantages of light weight, high specific power, high voltage platform, small self-discharge, long cycle life, small environmental pollution, no memory effect and the like, so that the lithium ion battery is widely applied to the fields of electronic equipment, power automobiles and the like. With the continuous expansion of the application field, people increasingly pay more attention to the safety problem of the battery cell while continuously tightening the requirements on the energy density, the charging time, the rate discharge capability, the discharge temperature rise and the like of the lithium ion battery. Mechanical abuse safety tests of lithium ion batteries, such as needling, unilateral extrusion and foreign matter extrusion, are gradually important targets of attention, wherein a common failure mode is that a positive current collector and a negative active material are in contact with each other to cause thermal runaway.

The existing structure increases the coating thickness of diaphragm ceramics, or carries out coating treatment on a current collector or a pole piece, but the energy density of the lithium ion battery is reduced to a great extent.

Disclosure of Invention

One of the objects of the present invention is: aiming at the defects of the prior art, the safety pole piece is provided, the safety performance of the battery cell can be improved by optimizing the pole piece structure, and the loss of the energy density of the battery can be reduced.

In order to achieve the purpose, the invention adopts the following technical scheme:

a security pole piece comprising: a current collector; a safety coating coated on a surface of the current collector, the safety coating including a first active material, a conductive agent, a binder, and an inorganic filler; the active material layer is coated on the surface of the safety coating and comprises a second active material, a conductive agent and a binder; wherein, the safety coating has a concave structure, and the active material layer is at least partially embedded in the concave structure.

Preferably, the current collector further comprises an insulating layer, the insulating layer is coated on one end surface of the current collector, the insulating layer is adjacent to the safety coating, the active material layer partially covers the insulating layer, and the insulating layer comprises an insulating material and a binder.

Preferably, the depth of the recessed features is less than the thickness of the security coating.

Preferably, the thickness of the insulating layer is smaller than that of the safety coating layer, and the thickness of the safety coating layer is smaller than that of the active material layer.

Preferably, the first active material includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganate, lithium nickel cobalt manganese oxide, and lithium titanate, the conductive agent is at least one of conductive carbon black, carbon nanotube, graphene, and carbon fiber, the binder is at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, and sodium carboxymethylcellulose, the inorganic filler is at least one of alumina, boehmite, silica, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, calcium oxide, zirconium dioxide, and magnesium hydroxide, and the second active material is at least one of lithium cobaltate, lithium iron phosphate, lithium titanate, and lithium nickel cobalt manganese oxide.

Preferably, the recessed structure faces the active material layer so that the active material layer is embedded in the recessed structure.

Preferably, the shape of the concave structure is rectangular, circular, triangular or semicircular.

Preferably, the number of the concave structures is multiple, the concave structures are arranged in an array, the distance between two adjacent concave structures is 1mm-30mm, and the area of each concave structure is 0.01mm ² -30mm ² 。

Preferably, the recessed structure is formed by laser cleaning.

The second objective of the present invention is to provide a method for preparing a safety pole piece, comprising:

adding a first active substance, a conductive agent, a binder and an inorganic filler into a stirring tank according to a preset mass ratio and a preset sequence for stirring, and then coating on a current collector to form a safe coating;

carrying out laser cleaning on the surface of the safety coating to form a concave structure;

and adding the second active substance, the conductive agent and the binder into a stirring tank according to a preset mass ratio and a preset sequence, stirring, and then coating the safety coating to form an active substance layer.

The invention has the advantages that the concave structure is arranged on the safety coating, when the active substance layer is coated, the concave structure can contain part of the active substance layer, namely more second active substances are coated, so that the energy density loss caused by using the safety coating is reduced, meanwhile, the safety coating has the characteristic of lithium ion conduction electronic insulation in the electrolyte, and has good toughness and mechanical strength, the pole piece can be better protected when being pierced or extruded by a foreign object, the short circuit of the battery is avoided, and the safety performance of the battery is improved. According to the invention, by optimizing the pole piece structure, the safety performance of the battery cell can be improved, and the loss of the energy density of the battery can be reduced.

Drawings

Features, advantages and technical effects of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.

Fig. 1 is a schematic structural diagram of embodiment 1 of the present invention.

Fig. 2 is a schematic structural view of example 1 of the present invention before coating an active material layer.

FIG. 3 is a schematic view of a recess structure according to the present invention.

FIG. 4 is a schematic structural view of comparative example 1 in the present invention.

Wherein the reference numerals are as follows:

1, current collector;

2-a security coating; 21-a recessed structure;

3-an insulating layer;

4-active substance layer.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

As used in the specification and in the claims, certain terms are used to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This specification and claims do not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. "substantially" means within an acceptable error range, and a person skilled in the art can solve the technical problem within a certain error range to substantially achieve the technical effect.

Furthermore, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the present invention, unless otherwise explicitly stated or limited, the terms "mounted," "connected," "fixed," and the like are to be construed broadly and may, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

The present invention will be described in further detail with reference to fig. 1 to 4, but the present invention is not limited thereto.

The safety pole piece comprises a current collector 1; the safety coating 2 is coated on the surface of the current collector 1, and the safety coating 2 comprises a first active substance, a conductive agent, a binder and an inorganic filler; an active material layer 4 coated on the surface of the safety coating 2, the active material layer 4 including a second active material, a conductive agent and a binder; the safety coating 2 has a recessed structure 21, and the active material layer 4 is at least partially embedded in the recessed structure 21.

Because the diaphragm pottery of current structure increase coating thickness, or carry out coating treatment to mass flow collector or pole piece, but to a great extent reduced lithium ion battery's energy density, therefore, set up sunk structure 21 on safety coating 2, when coating active substance layer 4, sunk structure 21 can hold partial active substance layer 4, more second active substance of coating promptly, help reducing the energy density loss that uses safety coating 2 to cause, simultaneously, safety coating 2 has the lithium ion and switches on the insulating characteristic of electron in the electrolyte, and has good toughness and mechanical strength, can better protection pole piece when the pole piece receives the foreign object to pierce through or extrude, avoid the battery short circuit, help improving the security performance of battery.

In addition, the safe coating 2 has the advantage of high electrochemical stability among all substances, and does not generate side reaction in electrolyte, thereby further ensuring the use safety of the battery.

In the safety pole piece, the safety pole piece further comprises an insulating layer 3, the insulating layer 3 is coated on one end surface of the current collector 1, the insulating layer 3 is adjacent to the safety coating 2, the active material layer 4 partially covers the insulating layer 3, and the insulating layer 3 comprises an insulating material and a binder. Specifically, the coating order of the safety pole piece is safety coating 2, insulating layer 3 and active material layer 4, and insulating layer 3 is added, so that the contact short circuit between the positive current collector and the negative active material can be avoided.

In the security pole piece according to the invention, the depth of the recessed structures 21 is less than the thickness of the security coating 2. It is understood that the maximum depth of the recessed structures 21 is less than the thickness of the security coating 2.

In the safety pole piece according to the invention, the thickness of the insulating layer 3 is smaller than that of the safety coating 2, and the thickness of the safety coating 2 is smaller than that of the active material layer 4.

In the safety pole piece, the first active material comprises one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium nickel cobalt manganese oxide and lithium titanate, the conductive agent is one or more of conductive carbon black, carbon nano tubes, graphene and carbon fibers, the binder is one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate and sodium carboxymethylcellulose, the inorganic filler is one or more of alumina, boehmite, silica, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, calcium oxide, zirconium dioxide and magnesium hydroxide, and the second active material is one or more of lithium cobaltate, lithium iron phosphate, lithium titanate and lithium nickel cobalt manganese oxide.

In the safety pole piece according to the invention, the recessed structure 21 faces the active material layer 4, so that the active material layer 4 is embedded in the recessed structure 21, and the safety coating 2 and the active material layer 4 are in an embedded structure

In the safety pole piece according to the invention, the shape of the recessed structure 21 is a regular shape such as a rectangle, a circle, a triangle or a semicircle.

In the safety pole piece according to the invention, the number of the concave structures 21 is multiple, the multiple concave structures 21 are arranged in an array, the processing is convenient, the large concave concentration caused by the irregular arrangement of the concave structures 21 can be avoided, the foil is broken due to stress concentration, the distance between two adjacent concave structures 21 is 1mm-30mm, for example, the distance between two adjacent concave structures 21 is 2mm, 4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 18mm, 20mm, 22mm, 24mm, 26mm, 28mm, 30mm, the strength reduction or the breakage of the foil caused by the over-small distance between the concave structures 21 is prevented, meanwhile, the phenomenon that the energy density of the battery is improved due to the over-large distance between the concave structures 21 is avoided, and the area of the concave structures 21 is 0.01mm ² -30mm ² For example, the area of the concave structure 21 is 1mm ² 、2mm ² 、4mm ² 、6mm ² 、8mm ² 、10mm ² 、12mm ² 、14mm ² 、16mm ² 、18mm ² 、20mm ² 、22mm ² 、24mm ² 、26mm ² 、28mm ² 、30mm ² Prevent that the sunk area is too big, lead to the foil to break, prevent simultaneously that the sunk area undersize from influencing active material layer 4 and fill the effect.

In the safety pole piece according to the invention, the recess structures 21 are formed by laser cleaning.

The battery comprises a positive plate, a negative plate and a diaphragm which is arranged between the positive plate and the negative plate at intervals.

The separator may be any of various materials suitable for use in lithium ion battery separators in the art, and for example, may be a combination including, but not limited to, one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fiber, and the like.

The lithium ion battery also comprises electrolyte, and the electrolyte comprises an organic solvent, electrolyte lithium salt and an additive. Wherein the content of the first and second substances,the electrolyte lithium salt may be LiPF used in a high-temperature electrolyte ₆ And/or LiBOB; or LiBF used in low-temperature electrolyte ₄ 、LiBOB、LiPF ₆ At least one of; or LiBF used in anti-overcharge electrolyte ₄ 、LiBOB、LiPF ₆ At least one of LiTFSI; may also be LiClO ₄ 、LiAsF ₆ 、LiCF ₃ SO ₃ 、LiN(CF ₃ SO ₂ ) ₂ At least one of (a). And the organic solvent may be a cyclic carbonate including PC, EC; or chain carbonates, including DFC, DMC, or EMC; and also carboxylic acid esters including MF, MA, EA, MP, etc. And additives include, but are not limited to, film forming additives, conductive additives, flame retardant additives, overcharge prevention additives, control of H in the electrolyte ₂ At least one of additives of O and HF content, additives for improving low temperature performance, and multifunctional additives.

The preparation method of the safety pole piece comprises the following steps:

adding a first active substance, a conductive agent, a binder and an inorganic filler into a stirring tank according to a preset mass ratio and a preset sequence for stirring, and then coating on a current collector 1 to form a safety coating 2;

carrying out laser cleaning on the surface of the safety coating 2 to form a concave structure 21;

adding a second active substance, a conductive agent and a binder into a stirring tank according to a preset mass ratio and a preset sequence for stirring, and then coating the safe coating 2 to form an active substance layer 4;

and rolling, slitting and welding the safety pole pieces, and winding the safety pole pieces, the diaphragm and the negative pole piece to obtain a finished product battery core.

Example 1

1. Adding lithium iron phosphate, conductive carbon, carbon nano tubes, PVDF and ceramics into a stirring tank according to a preset mass ratio and a preset sequence, stirring to obtain slurry of a safe coating 2, and then stirring at a ratio of 15mg/1540.25mm ² The surface density of the positive current collector is coated to form a safety coating 2;

2. after the positive current collector is coated with the safety coating 2, carrying out laser cleaning to form rectangular concave structures 21, wherein the concave structures 21 are distributed in an array mode, and the adjacent distance is 1mm;

3. adding boehmite and polypropylene into a stirring tank according to a preset mass ratio and a preset sequence, stirring to form insulating layer 3 slurry, and then coating the insulating layer 3 slurry on the positive current collector of the existing safety coating 2;

4. adding lithium cobaltate, conductive carbon and a binder into a stirring tank according to a preset mass ratio and a preset sequence, stirring to obtain active substance layer 4 slurry, and coating the active substance layer 4 slurry on the positive current collector to obtain a safety pole piece;

5. and rolling, slitting and welding the safety pole pieces, and winding the safety pole pieces, the diaphragm and the negative pole piece to obtain a finished product battery core.

Example 2

The difference from the first embodiment is that: in the embodiment, after the positive electrode current collector is coated with the safety coating 2, the laser cleaning is performed to form the circular concave structure 21, that is, the concave structure 21 is circular.

The other structures are the same as those of embodiment 1, and are not described herein.

Comparative example 1

1. Adding lithium iron phosphate, conductive carbon, carbon nanotubes, PVDF and ceramics into a stirring tank according to a preset mass ratio and a preset sequence, stirring to obtain slurry of a safety coating 2, and then coating on a positive current collector to form the safety coating 2;

2. adding boehmite and polypropylene into a stirring tank according to a preset mass ratio and a preset sequence, stirring to obtain insulating layer 3 slurry, and then coating the insulating layer 3 slurry on a positive current collector of the existing safety coating 2;

3. adding lithium cobaltate, conductive carbon and a binder into a stirring tank according to a preset mass ratio and a preset sequence, stirring to obtain active substance layer 4 slurry, and coating the active substance layer 4 slurry on the positive current collector to obtain a safety pole piece;

4. and rolling, slitting and welding the safety pole piece, and winding the safety pole piece, the diaphragm and the negative pole piece to obtain a finished product battery cell.

Energy Density and needling test results for cells prepared in Table 1, examples 1-2 and comparative example 1

Examples	Example 1	Example 2	Comparative example 1
				Needle stick test	5/5	5/5	5/5
Energy density boost ratio	3％	2％	0％

From the table above, it can be seen that the improvement ratios of the energy density of the embodiments 1 to 2 are higher than that of the comparative example 1, and the needling test structures of the embodiments 1 to 2 and the comparative example 1 are the same, which indicates that the energy density of the safety pole piece can be improved while the needling safety test passing rate of the safety pole piece is ensured.

Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (10)

1. A safety pole piece, comprising:

a current collector (1);

a safety coating (2) coated on the surface of the current collector (1), wherein the safety coating (2) comprises a first active material, a conductive agent, a binder and an inorganic filler;

the active substance layer (4) is coated on the surface of the safety coating (2), and the active substance layer (4) comprises a second active substance, a conductive agent and a binder;

wherein the security coating (2) has a recess structure (21), the active substance layer (4) being at least partially embedded in the recess structure (21).

2. A security pole piece as claimed in claim 1, wherein: still include insulating layer (3), insulating layer (3) coating in the one end surface of mass flow body (1), insulating layer (3) adjoin to safety coating (2), active material layer (4) partly cover insulating layer (3), insulating layer (3) include insulating material and binder.

3. A security pole piece as claimed in claim 1, wherein: the depth of the recessed structures (21) is smaller than the thickness of the security coating (2).

4. A security pole piece as claimed in claim 2, wherein: the thickness of the insulating layer (3) is smaller than that of the safety coating (2), and the thickness of the safety coating (2) is smaller than that of the active material layer (4).

5. A security pole piece as claimed in claim 1, wherein: the first active material comprises at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganate, lithium nickel cobalt manganese oxide and lithium titanate, the conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene and carbon fibers, the binder is at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate and sodium carboxymethylcellulose, the inorganic filler is at least one of aluminum oxide, boehmite, silicon dioxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, calcium oxide, zirconium dioxide and magnesium hydroxide, and the second active material is at least one of lithium cobaltate, lithium iron phosphate, lithium nickel cobalt oxide and lithium manganese oxide.

6. A security pole piece as claimed in claim 1, wherein: the recessed structure (21) faces the active material layer (4) so that the active material layer (4) is fitted into the recessed structure (21).

7. A security pole piece as claimed in claim 1, wherein: the shape of the concave structure (21) is rectangular, circular, triangular or semicircular.

8. A security pole piece as claimed in claim 1, wherein: the number of the concave structures (21) is multiple, the concave structures (21) are arranged in an array mode, the distance between every two adjacent concave structures (21) is 1mm-30mm, and the area of each concave structure (21) is 0.01mm ² -30mm ² 。

9. A security pole piece as claimed in claim 1, wherein: the recessed structure (21) is formed by laser cleaning.

10. A preparation method of a safety pole piece is characterized by comprising the following steps:

adding a first active substance, a conductive agent, a binder and an inorganic filler into a stirring tank for stirring, and then coating on a current collector (1) to form a safety coating (2);

carrying out laser cleaning on the surface of the safety coating (2) to form a concave structure (21);

and adding the second active material, the conductive agent and the binder into a stirring tank, stirring, and then coating on the safety coating (2) to form an active material layer (4).

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