A safety cell electrode structure and a lithium-ion battery

Abstract

The present invention belongs to the technical field of batteries, and particularly relates to a safety electrode structure for a battery cell, comprising a current collector; a safety coating coated on one end of the current collector; an insulating layer coated on the other end of the current collector; wherein, a first thinning area and a second thinning area are respectively provided at opposite ends of the safety coating and the insulating layer in the length direction, and the second thinning area overlaps the first thinning area. By optimizing the coating structure of the electrode, the present invention can improve the safety performance of the battery cell. In addition, the present invention also discloses a lithium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a safe battery cell pole piece structure and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in power fields such as electric vehicles, as well as consumer fields such as mobile phones, watches, tablets, and notebooks because of their advantages such as high specific energy, strong endurance, long cycle life, wide operating range, short charging time, and large current discharge.

[0003] As lithium-ion batteries gradually develop towards fast charging, high energy density and other fields, the safety issues brought by battery cells have gradually become the focus of attention. Lithium-ion battery mechanical abuse safety tests such as needle puncture, unilateral extrusion, and foreign body extrusion are a focus of attention.

[0004] During the needle puncture, unilateral extrusion, and foreign body extrusion tests, lithium-ion batteries will have four total contact short circuits: "positive active material and negative active material", "positive active material and negative current collector", "positive current collector and negative active material", and "positive current collector and negative current collector". Among the four short circuit modes, the short circuit mode that is most likely to cause thermal runaway is the short circuit between the "positive current collector and the negative active material".

[0005] In the existing structure, the ability to improve the safety of the battery cell through the diaphragm and the electrolyte is limited, and there is no obvious effect on improving the safety of mechanical abuse such as needle puncture, unilateral extrusion, and foreign body extrusion. Summary of the invention

[0006] One of the purposes of the present invention is to provide a safe battery cell electrode structure in view of the deficiencies in the prior art, and to improve the safety performance of the battery cell by optimizing the coating structure of the electrode.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A safe battery cell pole piece structure comprises a current collector; a safety coating coated on one end of the current collector; and an insulating layer coated on the other end of the current collector; wherein the safety coating and the insulating layer are respectively provided with a first thinned area and a second thinned area at opposite ends in the length direction, and the second thinned area overlaps the first thinned area.

[0009] Preferably, it also includes an active material layer, which is coated on the surface of the safety coating. A third thinned area is provided at one end of the active material layer close to the insulating layer, and the third thinned area overlaps the second thinned area.

[0010] Preferably, the first thinning area, the second thinning area, and the third thinning area each have two thickness measurement points. The thickness difference between the two thickness measurement points in the first thinning area is 1.5 μm to 4 μm, the thickness difference between the two thickness measurement points in the second thinning area is 1 μm to 2 μm, and the thickness difference between the two thickness measurement points in the third thinning area is -3 μm to 10 μm.

[0011] Preferably, the thickness of the safety coating is less than or equal to the thickness of the insulating layer, and the thickness of the insulating layer is less than or equal to the thickness of the active material layer.

[0012] Preferably, the safety coating includes at least one of a first active material, a conductive agent, a binder, or an inorganic filler. The first active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium nickel cobalt manganate, and lithium titanate. The conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene, and carbon fiber. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, and sodium carboxymethyl cellulose. The inorganic filler includes at least one of alumina, boehmite, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, calcium oxide, zirconium dioxide, and magnesium hydroxide.

[0013] Preferably, the mass ratio of the conductive agent to the first active material is 0.004 to 0.02, the mass ratio of the binder to the first active material is 0.02 to 0.08, and the mass ratio of the conductive agent to the binder is 0.005 to 0.8.

[0014] Preferably, the insulating layer includes at least one of an insulating material and a binder. The insulating material includes at least one of alumina, boehmite, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, calcium oxide, zirconium dioxide, magnesium hydroxide, and a polymer. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, and sodium carboxymethyl cellulose.

[0015] Preferably, the mass ratio of the binder to the insulating material is 0.03 to 0.25.

[0016] Preferably, the active material layer includes at least one of a second active material, a conductive agent, and a binder. The second active material includes at least one of lithium cobaltate, lithium iron phosphate, lithium titanate, and lithium nickel cobalt manganate. The conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene, and carbon fiber. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, and sodium carboxymethyl cellulose.

[0017] A second object of the present invention is to provide a lithium-ion battery including the above-mentioned safety cell electrode structure.

[0018] The beneficial effects of the present invention are as follows: The safety coating and the insulating layer are coated on the surface of the current collector, and the safety coating and the insulating layer are respectively provided with a first thinning area and a second thinning area, that is, the safety coating and the insulating layer are overlapped in a thinning manner, which is conducive to the coating of the coating. Among them, the insulating layer is located at the tail of the electrode sheet, and the insulating layer is thinned, there is no accumulation of materials, and it will not affect the coating of the next process. When the tail of the safety coating is not thinned, there will be accumulation and protrusion at the tail during the coating process. When the insulating layer is coated, the slurry at the protrusion will move to both sides of the protrusion, resulting in the inability to cover the insulating layer at the protrusion, and there is a risk of missing coating of the insulating layer. There is a color difference between the safety coating and the insulating layer, and the color difference at the protrusion affects the induction of the equipment during the coating process of the active material layer, causing positioning difficulties and affecting the size of the active material layer. The safety coating and the insulating layer of the present invention can avoid the above problems through thinning treatment, that is, solve the problem of size induction during the coating process of the safety cell, help improve the preparation efficiency of the cell, and thus improve the yield and production capacity of the cell. Description of the Drawings

[0019] The features, advantages, and technical effects of the exemplary embodiments of the present invention will be described below with reference to the drawings.

[0020] Figure 1 It is a structural schematic diagram of the present invention.

[0021] Among them, the reference numerals are explained as follows:

[0022] 10 - Current collector;

[0023] 1 - Safety coating; 11 - First thinning area;

[0024] 2 - Insulating layer; 21 - Second thinning area;

[0025] 3 - Active material layer; 31 - Third thinning area;

[0026] X - Length direction. Detailed Embodiments

[0027] As used in the specification and claims, certain terms are used to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same component. The specification and claims do not use the difference in names as a way to distinguish components, but rather use the difference in functions of components as the criterion for distinction. As used throughout the specification and claims, "comprising" is an open-ended term and should be interpreted as "comprising but not limited to". "Substantially" means within an acceptable error range, and those skilled in the art can solve technical problems within the preset error range and basically achieve the technical effects.

[0028] In addition, terms such as "first", "second", etc. are used only for descriptive purposes and should not be construed as indicating or implying relative importance.

[0029] In the invention, unless otherwise clearly specified and defined, terms such as "mounted", "connected", "coupled", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] The following is a further detailed description of the present invention in conjunction with the Figure 1 This is not intended to limit the present invention.

[0031] A safety battery electrode structure, comprising a current collector 10; a safety coating 1 coated on one end of the current collector 10; an insulating layer 2 coated on the other end of the current collector 10; wherein, at the opposite ends of the safety coating 1 and the insulating layer 2 in the length direction X, a first thinning zone 11 and a second thinning zone 21 are respectively provided, and the second thinning zone 21 overlaps the first thinning zone 11.

[0032] Since the existing structure has limited ability to improve the safety of the battery cell through the diaphragm and the electrolyte, and has no obvious effect on the improvement of mechanical abuse safety such as needle puncture, unilateral extrusion, and foreign body extrusion, the safety coating 1 and the insulating layer 2 are coated on the surface of the current collector 10, and the safety coating 1 and the insulating layer 2 are respectively provided with a first thinning area 11 and a second thinning area 21, that is, the safety coating 1 and the insulating layer 2 are overlapped by thinning, which is conducive to the coating of the coating, wherein the insulating layer 2 is located at the tail of the pole piece, and the insulating layer 2 is thinned, and there is no accumulation of materials, which will not affect the coating of the next process. If the tail of the safety coating 1 is not thinned, there will be accumulation and bulges at the tail during the coating process. When the insulating layer 2 is coated, the slurry of the insulating layer 2 at the bulge will move to both sides of the bulge, resulting in the inability to cover the insulating layer 2 at the bulge, and there is a risk of leakage of the insulating layer. There is a color difference between the safety coating 1 and the insulating layer 2. The color difference at the bulge affects the induction of the equipment during the coating process of the active material layer 3, causing positioning difficulties and affecting the size of the active material layer 3. The safety coating 1 and the insulating layer 2 of the present invention can avoid the above-mentioned problems through thinning treatment, that is, solve the size induction problem during the coating process of the safety battery cell, which helps to improve the preparation efficiency of the battery cell, thereby improving the battery cell quality rate and production capacity.

[0033] In the safety cell electrode structure according to the present invention, an active material layer 3 is also included. The active material layer 3 is coated on the surface of the safety coating 1. A third thinning area 31 is provided at one end of the active material layer 3 close to the insulating layer 2. The third thinning area 31 overlaps the second thinning area 21. Specifically, the coating order is safety coating 1, insulating layer 2 and active material layer 3. The tail of the active material layer 3 is thinned and contacts the surface of the insulating layer 2. If the active material layer 3 is not thinned, the tail will be raised. When the surface density at the raised part exceeds the upper limit of the surface density, the final finished cell will have a risk of lithium deposition on the negative electrode corresponding to this part. At the same time, the raised part will cause excessive pressure at this part during rolling. The aluminum foil at this part will be subjected to greater stress during rolling, and there is a risk of breaking. The safety coating 1, insulating layer 2 and active material layer 3 of the present invention can avoid the above problems after thinning, which helps to improve the preparation efficiency of the cell, thereby improving the cell quality rate and production capacity.

[0034] In the safety cell electrode structure according to the present invention, the first thinning area 11, the second thinning area 21 and the third thinning area 31 each have two thickness measurement points, the thickness difference between the two thickness measurement points of the first thinning area 11 is 1.5um to 4um, the thickness difference between the two thickness measurement points of the second thinning area 21 is 1um to 2um, and the thickness difference between the two thickness measurement points of the third thinning area 31 is -3um to 10um. For details, see Figure 1As shown, measure the thickness at a position 3 mm from the end of the thinning of the safety coating 1, denoted as a, and the thickness at a position where the safety coating 1 is greater than or equal to 15 mm is A. That is, the two thickness measurement points of the first thinning area 11 are A and a, and there is a relationship between A and a: 1.5 μm ≤ A - a ≤ 4 μm; measure the thickness at a position 3 mm from the end of the thinning of the insulating layer, denoted as b, and the thickness at a position where the insulating layer is greater than or equal to 15 mm is B. That is, the two thickness measurement points of the second thinning area 21 are B and b, and there is a relationship between B and b: 1 μm ≤ B - b ≤ 2 μm; measure the thickness at a position 3 mm from the end of the thinning of the active material layer, denoted as c, and the thickness at a position where the active material layer is greater than or equal to 15 mm is C. That is, the two thickness measurement points of the third thinning area 31 are C and c, and there is a relationship between C and c: -3 μm ≤ C - c ≤ 10 μm.

[0035] In the safety cell electrode structure according to the present invention, the thickness of the safety coating 1 is less than or equal to the thickness of the insulating layer 2, and the thickness of the insulating layer 2 is less than or equal to the thickness of the active material layer 3. However, the present invention is not limited thereto, and the thicknesses of the safety coating 1, the insulating layer 2, and the active material layer 3 can be adjusted according to the actual structure of the battery.

[0036] In the safety cell electrode structure according to the present invention, the safety coating 1 includes one or a combination of first active materials, conductive agents, binders, or inorganic fillers. The first active materials include one or a combination of lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium nickel cobalt manganate, and lithium titanate. The conductive agents include one or a combination of conductive carbon black, carbon nanotubes, graphene, and carbon fibers. The binders include one or a combination of polyvinylidene fluoride, copolymer of vinylidene fluoride - hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salts, and sodium carboxymethyl cellulose. The inorganic fillers include one or a combination of alumina, boehmite, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, calcium oxide, zirconium dioxide, and magnesium hydroxide.

[0037] In the safety cell electrode structure according to the present invention, the mass ratio of the conductive agent to the first active material is 0.004 - 0.02, the mass ratio of the binder to the first active material is 0.02 - 0.08, and the mass ratio of the conductive agent to the binder is 0.005 - 0.8. It can be understood that the following relationships exist for the material mass ratios: 0.004 ≤ conductive agent / first active material ≤ 0.02, 0.02 ≤ binder / first active material ≤ 0.08, 0.005 ≤ conductive agent / binder ≤ 0.8. There is no limitation here.

[0038] In the safety cell electrode structure according to the present invention, the insulating layer 2 comprises one or more combinations of insulating materials and binders. The insulating materials include one or more combinations of alumina, boehmite, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, calcium oxide, zirconium dioxide, magnesium hydroxide and polymer. The binders include one or more combinations of polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose.

[0039] In the safety cell electrode structure according to the present invention, the mass ratio of the binder to the insulating material is 0.03 to 0.25. It can be understood that: the insulating material and the binder satisfy the following relationship 0.03 ≤ binder / insulating material ≤ 0.25, which is not limited here.

[0040] In the safety cell electrode structure according to the present invention, the active material layer 3 comprises one or more combinations of a second active material, a conductive agent and a binder. The second active material includes one or more combinations of lithium cobaltate, lithium iron phosphate, lithium titanate, lithium nickel cobalt manganate. The conductive agent includes one or more combinations of conductive carbon black, carbon nanotubes, graphene, carbon fiber. The binder includes one or more combinations of polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose.

[0041] Lithium ion battery

[0042] The present invention includes the above-mentioned safety cell electrode structure.

[0043] Preparation of safety coating:

[0044] Lithium iron phosphate, conductive carbon, carbon nanotubes, PVDF, ceramics are added to the stirring tank in a preset mass ratio and in a preset order. The viscosity of the slurry after stirring is between 100 and 2000 mPa·s. The slurry after stirring is evenly coated on both sides of the positive current collector 10 by gravure coating. The thickness of the current collector 10 is 9 μm, and the coating surface density is 14 mg / 1540.25 mm^2. At this time, the single-sided thickness of the safety coating 1 is 6 μm, and the tail is thinned to A - a = 3 μm.

[0045] Preparation of insulating layer:

[0046] Boehmite and polypropylene are added to the stirring tank in a preset mass ratio and in a preset order. The viscosity of the slurry after stirring is between 300 and 5000 mPa·s. The slurry after stirring is evenly coated on both sides of the empty aluminum foil at the tail by gravure coating. The coating thickness is 9 μm. At this time, B - b = 2 μm.

[0047] Preparation of the positive electrode sheet:

[0048] Mix lithium cobaltate, conductive carbon black, and the binder polyvinylidene fluoride evenly at a mass ratio of 96:2.5:1.5 to make a lithium-ion battery positive electrode slurry with a preset viscosity. Coat the slurry on the current collector 10 with a safety coating 1. At this time, thin it to C - c = 7 um, and cold press the positive electrode sheet. Then perform trimming, slitting, and strip cutting. After strip cutting, dry it at 110 °C for 4 hours under vacuum conditions, and finally weld the tab to make the lithium-ion battery positive electrode sheet.

[0049] Preparation of the lithium-ion battery:

[0050] Wind the above positive electrode sheet, separator, and negative electrode sheet into an electrode core. The separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode is led out by spot welding with an aluminum tab, and the negative electrode is led out by spot welding with a nickel tab. Then place the electrode core in an aluminum-plastic packaging bag, inject the electrolyte, and go through processes such as encapsulation, formation, and capacity measurement to make the lithium-ion battery.

[0051] It should be noted that: The electrode core can include at least two mutually stacked electrode sheets with opposite polarities. The electrode sheets with opposite polarities respectively form the positive electrode sheet and the negative electrode sheet of the battery. To avoid short circuit between the positive and negative electrode sheets, a separator is provided between every two adjacent electrode sheets, and the electrode sheets with opposite polarities are electrically isolated by the separator.

[0052] The at least two electrode sheets can include a first electrode sheet and a second electrode sheet. The first electrode sheet and the second electrode sheet have opposite polarities and are mutually stacked.

[0053] Specifically, the first electrode sheet can be the positive electrode sheet, and the second electrode sheet can be the negative electrode sheet; or, the first electrode sheet can be the negative electrode sheet, and the second electrode sheet can be the positive electrode sheet, which is not limited here.

[0054] In some examples, the electrode core can be a wound electrode core. Among them, there is one first electrode sheet and one second electrode sheet. The first electrode sheet, separator, and second electrode sheet stacked in sequence are wound around the winding center to form a winding structure.

[0055] In some other examples, the electrode core can be a stacked electrode core. Among them, there are multiple first electrode sheets and multiple second electrode sheets. The multiple first electrode sheets and the multiple second electrode sheets are alternately stacked in the same direction in sequence, and a separator is provided between every two adjacent first electrode sheets and second electrode sheets to electrically insulate the first electrode sheet and the second electrode sheet.

[0056] Based on the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains are also able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions, or variations made by those skilled in the art on the basis of the present invention all fall within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A safety cell electrode structure, characterized in that, it includes: a current collector (10); a safety coating (1), coated on one end of the current collector (10); an insulating layer (2), coated on the other end of the current collector (10); wherein, the safety coating (1) and the insulating layer (2) are respectively provided with a first thinning area (11) and a second thinning area (21) at opposite ends in the length direction of the current collector (10), and the second thinning area (21) overlaps the first thinning area (11); it further includes an active material layer (3), the active material layer (3) is coated on the surface of the safety coating (1), and a third thinning area (31) is provided at one end of the active material layer (3) close to the insulating layer (2), and the third thinning area (31) overlaps the second thinning area (21).

2. A safety cell electrode structure as described in claim 1, characterized in that: both the first thinning area (11), the second thinning area (21) and the third thinning area (31) have two thickness measurement points, the thickness difference between the two thickness measurement points of the first thinning area (11) is 1.5um - 4um, the thickness difference between the two thickness measurement points of the second thinning area (21) is 1um - 2um, and the thickness difference between the two thickness measurement points of the third thinning area (31) is -3um - 10um.

3. A safety cell electrode structure as described in claim 1, characterized in that: the thickness of the safety coating (1) is less than or equal to the thickness of the insulating layer (2), and the thickness of the insulating layer (2) is less than or equal to the thickness of the active material layer (3).

4. A safety cell electrode structure as described in claim 1, characterized in that: the safety coating (1) includes at least one of a first active material, a conductive agent, a binder or an inorganic filler, the first active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium nickel cobalt manganate, lithium titanate, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene, carbon fiber, the binder includes at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride - hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose, and the inorganic filler includes at least one of alumina, boehmite, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, calcium oxide, zirconium dioxide, magnesium hydroxide.

5. A safety cell electrode structure as described in claim 4, characterized in that: the mass ratio of the conductive agent to the first active material is 0.004 - 0.02, the mass ratio of the binder to the first active material is 0.02 - 0.08, and the mass ratio of the conductive agent to the binder is 0.005 - 0.

8.

6. A safety cell electrode structure as described in claim 1, characterized in that: The insulating layer (2) comprises at least one of an insulating material and an adhesive. The insulating material comprises at least one of alumina, boehmite, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, calcium oxide, zirconium dioxide, magnesium hydroxide and a high molecular polymer. The adhesive comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt and sodium carboxymethyl cellulose.

7. A safety cell electrode sheet structure according to claim 6, characterized in that: the mass ratio of the adhesive to the insulating material is 0.03 to 0.

25.

8. A safety cell electrode sheet structure according to claim 1, characterized in that: the active material layer (3) comprises at least one of a second active material, a conductive agent and an adhesive. The second active material comprises at least one of lithium cobaltate, lithium iron phosphate, lithium titanate and lithium nickel cobalt manganate. The conductive agent comprises at least one of conductive carbon black, carbon nanotubes, graphene and carbon fiber. The adhesive comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt and sodium carboxymethyl cellulose.

9. A lithium ion battery, characterized in that: it comprises the safety cell electrode sheet structure according to any one of claims 1 to 8.

Images