Lithium ion battery

Abstract

The invention provides a lithium ion battery which is characterized in that a battery cell is formed by winding a positive pole piece, a negative pole piece and a diaphragm spaced between the positive pole piece and the negative pole piece, and the battery cell is provided with a straight area and bending areas positioned at two ends of the straight area; the positive pole piece comprises a positive current collector and a positive active material layer, the positive active material layer is arranged on at least one surface of the positive current collector, and the positive active material layer comprises a non-fluorine adhesive; and a concave region is arranged on the surface of the positive active material layer in the bending region. According to the invention, the surface density of the bending area of the positive pole piece is reduced, the problems of cracks and powder falling in the bending area of the winding core due to the hard and brittle pole piece during winding are improved, the CB value of the position is increased, the porosity of the pole piece at the position is increased, infiltration and absorption of electrolyte are facilitated, the mass transfer resistance of lithium ions is effectively reduced, and the service life of the lithium ion battery is prolonged. The problem of lithium precipitation in a bending area at the later stage of high-temperature circulation is solved, and the electrochemical performance of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a lithium-ion battery. Background Art

[0002] The European Union is introducing a regulation on the use of perfluorinated substances (PFAS), and PVDF is within its control scope. Therefore, it is urgent to develop a new type of binder for use in lithium-ion batteries.

[0003] Common binders that can replace PVDF include non-fluorinated binders such as PAA, PAN, and PI. However, their molecular structures are mainly composed of strongly polar functional groups, and the positive electrode sheets generally show hardness and brittleness, resulting in low compaction, large thickness after winding, and loss of energy density.

[0004] Specifically, when a non-fluorinated binder is applied to a wound battery with a positive electrode sheet having a high areal density (20 mg / cm 2 and above), cracks appear in the bent area of the wound battery core, making the appearance of the battery core abnormal, and further causing serious lithium deposition in the bent area of the battery after high-temperature cycling.

[0005] Therefore, how to find a more suitable positive electrode sheet for lithium-ion batteries to solve the above problems existing in lithium-ion batteries using such binders has become one of the focuses widely concerned by many front-line scientific researchers and R & D enterprises in the field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a lithium-ion battery. The lithium-ion battery provided by the present application introduces a non-fluorinated binder into the positive electrode sheet and sets a concave area in the bent area, which improves the lithium deposition problem in the bent area after high-temperature cycling of lithium ions and is beneficial to improving the energy density.

[0007] In view of this, the present application provides a lithium-ion battery, including a packaging bag, a battery core housed in the packaging bag, and an electrolyte filled in the packaging bag. The battery core is wound by a positive electrode sheet, a negative electrode sheet, and a separator spaced between the positive electrode sheet and the negative electrode sheet. The battery core has a flat area and bent areas at both ends of the flat area;

[0008] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a conductive agent, a toughening agent, and a non-fluorinated binder;

[0009] A concave area is provided on the surface of the positive electrode active material layer in the bent area;

[0010] The width range of the bent area provided with the concave area is 1-10 mm.

[0011] In some specific embodiments, the porosity of the positive electrode active material layer in the bent region of the concave portion area is 23% to 35%.

[0012] In some specific embodiments, the conductive agent is a conductive agent network composed of single-walled carbon nanotubes with an aspect ratio greater than 2000 and multi-walled carbon nanotubes with an aspect ratio greater than 2000.

[0013] In some specific embodiments, the conductive agent includes single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black; the tube length of the multi-walled carbon nanotubes > 30 μm, and the diameter range is 5 to 10 nm, and the tube length of the single-walled carbon nanotubes > 15 μm, and the diameter range is 1 to 3 nm;

[0014] And / or, the mass ratio of the single-walled carbon nanotubes, multi-walled carbon nanotubes, and the carbon black is 1:(3 to 4):(4 to 5).

[0015] In some specific embodiments, the radial dimension a of a single concave portion in the concave portion area is 0.3 to 2 mm; and / or, the depth b of a single concave portion in the concave portion area is 5 to 50 μm; and / or, the number of single concave portions in the concave portion area is greater than or equal to 50.

[0016] In some specific embodiments, the non-fluorine binder includes one or more of PAA, PAN, and PMMA;

[0017] And / or, the weight-average molecular weight of the non-fluorine binder is 1 million to 1.3 million;

[0018] And / or, the particle size of the non-fluorine binder is 50 to 80 μm;

[0019] And / or, the swelling rate of the non-fluorine binder in the electrolyte is 20% to 50%;

[0020] And / or, the dissolution rate of the non-fluorine binder in the electrolyte < 10%.

[0021] In some specific embodiments, the cohesive force between particles in the positive electrode active material layer in the bent region > 30 N / m, and / or, the porosity of the positive electrode active material layer in the straight region is 15% to 20%.

[0022] In some specific embodiments, the positive electrode active material includes one or more of lithium cobaltate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate;

[0023] And / or, the Dv50 particle size of the positive electrode active material is 10 to 20 μm;

[0024] And / or, the specific surface area of the positive electrode active material is 0.1 to 0.5 m 2 / g.

[0025] In some specific embodiments, the toughening agent includes one or more of a small molecule ester toughening agent, a rubber toughening agent, and an ionic liquid;

[0026] and / or, the mass content of the toughening agent in the positive electrode active material layer is 0.1% to 2.0%;

[0027] and / or, the mass content of the conductive agent in the positive electrode active material layer is 1.0% to 2.0%;

[0028] and / or, the mass content of the positive electrode active material in the positive electrode active material layer is 95.6% to 99%;

[0029] and / or, the mass content of the non-fluorine binder in the positive electrode active material layer is 0.5% to 2.0%.

[0030] In some specific embodiments, the elongation rate of the positive electrode tab is 0.8% to 1.3%.

[0031] The present invention provides a lithium-ion battery, including a packaging bag, a battery cell housed in the packaging bag, and an electrolyte filled in the packaging bag. The battery cell is wound by a positive electrode tab, a negative electrode tab, and a separator spaced between the positive electrode tab and the negative electrode tab. Among them, the battery cell has a flat area and bending areas at both ends of the flat area; the positive electrode tab includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a conductive agent, a toughening agent, and a non-fluorine binder; a concave portion area is provided on the surface of the positive electrode active material layer in the bending area; the width range of the bending area provided with the concave portion area is 1 to 10 mm. In the lithium-ion battery provided in this application, a non-fluorine binder is introduced into the positive electrode active material layer of the positive electrode tab. It contains strong polar functional groups such as carboxyl groups and cyano groups, which can improve the adhesion between the positive electrode active material layer and the positive electrode current collector, and improve the safety of the lithium-ion battery; at the same time, the setting of the concave portion area on the surface of the positive electrode active material layer in the bending area improves the porosity and CB value of the bending area, improves the infiltration of the electrolyte, increases the retention amount of the electrolyte in the bending area, and effectively reduces the mass transfer resistance of lithium ions. Thus, the problem of lithium deposition in the bending area in the later stage of high-temperature cycling due to the introduction of the non-fluorine binder is solved; further, the limitation of the width range of the bending area provided with the concave portion area can improve the compaction of the positive electrode tab, reduce the thickness of the battery cell, and improve the energy density of the lithium-ion battery.

[0032] On the other hand, the conductive agent in this application adopts a three-dimensional conductive network with a specific aspect ratio composed of single-walled and multi-walled structures, which can provide a longer electron path for lithium ions, reduce impedance, and improve rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the cell structure of the lithium-ion battery provided by the present invention;

[0034] Figure 2 Schematic diagram of the structure of the positive electrode sheet after unfolding provided by the present invention;

[0035] Figure 3 Schematic diagram of the cell structure of Comparative Example 3 provided by the present invention. Detailed implementation manners

[0036] To further understand the present invention, the preferred implementation manners of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention rather than limiting the claims of the present invention.

[0037] There is no particular limitation on the source of all raw materials of the present invention, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0038] There is no particular limitation on the purity of all raw materials of the present invention. The present invention preferably uses analytical pure or the purity conventional in the field of preparing lithium-ion battery positive electrode sheets.

[0039] In view of the problem of lithium deposition in the bending area due to the introduction of non-fluorine binder in the positive electrode active material layer of the positive electrode sheet in the prior art, the present application provides a lithium-ion battery. By introducing a non-fluorine binder into the positive electrode active material layer of the positive electrode sheet and providing a concave area on the surface of the positive electrode active material layer in the bending area, and at the same time defining the width of the concave area in the bending area, the above-mentioned multiple technical means act synergistically to ensure the stable adhesion between the positive electrode active material layer and the positive electrode current collector while reducing the areal density of the bending area, increasing the porosity of the bending area, improving the problem of lithium deposition in the bending area in the later stage of high-temperature cycling of the lithium-ion battery, and at the same time improving the electrochemical performance of the lithium-ion battery; specifically, the present invention provides a lithium-ion battery, including a packaging bag, a cell accommodated in the packaging bag, and an electrolyte filled in the packaging bag. The cell is wound by a positive electrode sheet, a negative electrode sheet, and a separator spaced between the positive electrode sheet and the negative electrode sheet. The cell has a flat area and bending areas at both ends of the flat area;

[0040] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a conductive agent, a toughening agent, and a non-fluorine binder;

[0041] A concave area is provided on the surface of the positive electrode active material layer in the bending area;

[0042] The width range of the bent area where the concave area is set is 1 to 10 mm.

[0043] The schematic diagram of the battery cell of the lithium-ion battery provided by this application is as Figure 1 shown. The battery cell has a flat area and a bent area. The concave area can be set at any position in the bent area, not limited to Figure 1 the position shown, and can also be a concave area with a specific width set in the radial direction of the bent area; as Figure 1 shown, the width range of the bent area where the concave area is set is 1 to 10 mm. Specifically, the width range of the bent area where the concave area is set is 2 to 6 mm; more specifically, the width range of the bent area where the concave area is set is 3 to 5 mm. In this application, the concave area is not completely distributed in the bent area, and the concave area is only set within the above width range to further improve the compaction density of the positive electrode sheet, reduce the thickness of the battery cell, and increase the volume energy density.

[0044] As Figure 2 shown, Figure 2 it is the schematic diagram of the structure of the positive electrode sheet after unfolding. Among them, both surface A and surface C are positive electrode active material layers. In this invention, the radial dimension a of a single concave in the concave area is 0.3 to 2 mm, specifically 0.5 to 1.5 mm, and more specifically 0.6 to 1.2 mm.

[0045] In this invention, the depth b of a single concave in the concave area is 5 to 50 μm, specifically 15 to 35 μm, and more specifically 20 to 30 μm.

[0046] In this invention, the distance c between two adjacent single concaves in the concave area is 50 to 200 μm, specifically 80 to 150 μm, and more specifically 100 to 120 μm.

[0047] The limitation of the above size parameters a, b, and c of the single concave can further improve the lithium deposition in the bent area and reduce the loss of energy density on the basis of ensuring the high compaction and porosity of the positive electrode sheet.

[0048] In this invention, the number of single concaves in the concave area of the bent area is preferably greater than or equal to 50, more preferably greater than or equal to 80, more preferably greater than or equal to 120, and more preferably greater than or equal to 200.

[0049] In the present invention, the porosity of the positive electrode active material layer in the bent region of the recessed area is 23% to 35%, specifically 25% to 33%, and more specifically 27% to 31%. The setting of the recessed area enables the porosity of the positive electrode active material layer in the bent region to be regulated within the above range, which can increase the residual liquid coefficient by 0.05 to 0.1. As is well known to those skilled in the art, the residual liquid coefficient is specifically the actual capacity of the battery cell / the mass of the electrolyte actually retained in the battery cell.

[0050] In the present invention, a single recess in the recessed area preferably includes a non-through hole; a single recess in the recessed area is preferably prepared by a mechanical behavior of laser drilling; the laser drilling will not damage the positive electrode active material layer around the recessed area, and can maintain the stability of the structure of the recessed area.

[0051] In the present invention, the cohesion of the positive electrode active material layer of the positive electrode plate > 30 N / m, specifically > 32 N / m, and more specifically > 35 N / m. It can be understood that the cohesion of the positive electrode active material layer can be used to measure the bonding degree between the positive electrode active materials in the positive electrode active material layer.

[0052] The test method for the cohesion: Fix one side of the positive electrode active material layer of the positive electrode plate to be tested on a steel plate, attach a tape to the surface of the other side of the positive electrode active material layer, and leave one end of the tape unmounted on the positive electrode plate to be tested; fix the positive electrode plate to be tested on a tensile testing machine, and use the unmounted end of the tape to peel the tape from the surface of the positive electrode active material layer. The peeling force after the tape is peeled from the surface of the positive electrode active material layer is the cohesion of the positive electrode active material layer of the positive electrode plate.

[0053] In the present invention, the weight loss rate of the positive electrode plate before and after the recessed area is provided is preferably 3.0% to 15.0%, more preferably 5.0% to 13.0%, and more preferably 7.0% to 11.0%.

[0054] The porosity of the positive electrode active material layer at the flat region position is 15% to 20%, specifically 16% to 19%, and more specifically 17% to 18%.

[0055] In the present invention, the non-fluorine binder includes one or more of PAA, PAN, and PMMA; specifically, the non-fluorine binder is selected from PAA, PAN, or PMMA; more specifically, the non-fluorine binder is selected from PAN-based multi-component copolymer polymer materials; the molecular structure of the non-fluorine binder is rich in strong polar functional groups, which can form intermolecular forces such as hydrogen bonds in addition to van der Waals forces, improving the bonding strength, so that in the safety test of the battery provided by the present invention, the risk of detachment of the positive electrode paste from the current collector aluminum foil is reduced, and the problems of explosion and fire caused by the short circuit of the anode - aluminum foil are avoided, improving the safety performance.

[0056] In the present invention, the molecular weight of the non-fluorine binder is 1 million to 1.3 million. Specifically, the molecular weight of the non-fluorine binder is 1.05 million to 1.25 million. More specifically, the molecular weight of the non-fluorine binder is 1.1 million to 1.2 million.

[0057] In the present invention, the particle size of the non-fluorine binder is 50 to 80 μm. Specifically, the particle size of the non-fluorine binder is 55 to 75 μm. More specifically, the particle size of the non-fluorine binder is 60 to 70 μm. In this application, the particle size of the non-fluorine binder refers to the particle size of the non-fluorine binder raw material.

[0058] In the present invention, the swelling rate of the non-fluorine binder in the electrolyte is 20% to 50%. Specifically, the swelling rate of the non-fluorine binder in the electrolyte is 25% to 45%. More specifically, the swelling rate of the non-fluorine binder in the electrolyte is 30% to 42%.

[0059] In the present invention, the dissolution rate of the non-fluorine binder in the electrolyte < 10%. Specifically, the dissolution rate of the non-fluorine binder in the electrolyte ≤ 8%. More specifically, the dissolution rate of the non-fluorine binder in the electrolyte ≤ 5%.

[0060] It can be understood that the swelling rate is the absorption capacity of the binder for the electrolyte. A suitable swelling rate can improve the de-lithiation and intercalation capacity on the positive electrode side; the dissolution rate refers to that at a certain temperature, some short branched chains in the binder formed by the polymerization of polymer chain segments will dissolve into the electrolyte. If the dissolution rate is too large, on the one hand, it will damage the structure of the binder in the positive electrode active material layer and reduce the adhesion force; on the other hand, the dissolved short branched chains will affect the physical and chemical properties of the electrolyte, thereby affecting the transmission of lithium ions.

[0061] The swelling rate of the non-fluorine binder in the present invention after being soaked at 80 °C for 72 h is 20% to 50%, and the dissolution rate after being dried at 60 °C for 24 h is within 10%. Therefore, the non-fluorine binder still maintains the integrity of the structure during long cycles, ensuring the stability of the positive electrode structure after long cycles; in addition, the non-fluorine binder in the present invention has a small current density at a voltage of 3 V to 5 V, and the order of magnitude is about 10 -5 or so, ensuring that it can work in a high-voltage system above 4.5 V.

[0062] The above dissolution rate and swelling rate can be obtained through the following test methods: A glue film of a certain size prepared from a non-fluorine binder is completely immersed in an electrolyte solvent and placed in a vacuum oven at 80°C for 72H; the mass change rate of the glue film before and after immersion is calculated as the swelling rate; then the immersed glue film is baked in an oven at 80°C for 48H, and the dissolution rate can be calculated based on the mass of the glue film before immersion and the mass of the glue film after baking. The mass of the glue film before immersion is m0, the mass of the glue film after immersion is m1, and the mass of the glue film after baking is m2; therefore, the swelling rate of the non-fluorine binder = (m1 - m0) / m0, and the dissolution rate = (m2 - m0) / m0. In the above process, the residual electrolyte on the surface of the glue film needs to be wiped off before weighing the immersed glue film; the size of the glue film: length * width * thickness = 10cm * 30cm * 1cm, and the composition of the electrolyte solvent: EC:PC:DEC:PP = 15:10:10:65.

[0063] In addition, the non-fluorine binder in the present application has a low glass transition temperature (T g ), and the T g range is -30°C to 50°C. High molecular polymers with low Tg will maintain excellent toughness at low temperatures, and the degree of freedom of molecular segments is higher. Therefore, the positive electrode plate prepared from the positive electrode active material layer including the non-fluorine binder has a higher tap density, the positive electrode plate is thinner, and the thickness of the next-stage battery cell is smaller, improving the volumetric energy density. The structure of traditional PVDF is an alternating arrangement of CH 2 and CF 2 groups. The molecular structure of the non-fluorine binder in the present invention contains polar functional groups such as carboxyl groups or cyano groups. In addition to forming van der Waals forces, strong forces such as hydrogen bonds can also be formed, which is directly manifested in the improvement of the adhesion of the positive electrode plate.

[0064] The present invention designs the concave area to reduce the areal density of the bending area and increase the porosity at this position; the polar functional groups contained in the non-fluorine binder can provide strong cohesive force between particles, thereby eliminating the abnormality in the bending area of the high-tap-density positive electrode plate and solving the problem of excessive width of the next-stage battery cell; the liquid retention amount is increased, and the lithium deposition in the bending area in the later stage of high-temperature cycling is improved; there is a large cohesive force between the positive electrode active material layers of the positive electrode plate, which can avoid the damage to the structure of the positive electrode active material layer caused by mechanical behaviors such as laser drilling, and at the same time avoid the risk of structural collapse caused by the repeated shrinkage and expansion between particles during cycling.

[0065] The present invention addresses the problems commonly existing in high areal density positive electrode sheets, such as poor toughness and low compaction. During winding, cracks and powder shedding generally occur in the bending area of the positive electrode sheet, resulting in the overall cell being overly wide. By setting a recessed area, the areal density at this location is reduced, avoiding abnormal winding. The recessed area of the positive electrode sheet can increase the porosity of the positive electrode sheet, improve the infiltration of the electrolyte, and increase the liquid retention capacity in the bending area. The present invention improves the occurrence of cracks and powder shedding in the bending area, avoids the overall cell being overly wide, improves the problem of sudden capacity drop due to electrolyte dry-out in the later stage of high-temperature cycling, and can increase the capacity by 50T - 100T.

[0066] In the present invention, the conductive agent is a conductive agent network with an aspect ratio greater than 2000, composed of single-walled carbon nanotubes and multi-walled carbon nanotubes. Specifically, the aspect ratio > 4000, and more specifically, the aspect ratio > 10000. Further, the conductive agent includes single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black. The tube length of the multi-walled carbon nanotubes > 30μm, and the diameter range is 5 - 10nm. The tube length of the single-walled carbon nanotubes > 15μm, and the diameter range is 1 - 3nm. Specifically, the tube length of the multi-walled carbon nanotubes > 35μm, and the diameter range is 6 - 9nm. The tube length of the single-walled carbon nanotubes > 20μm, and the diameter range is 1.5 - 2.5nm. The mass ratio of the single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black is 1:(3 - 4):(4 - 5). Specifically, the mass ratio of the single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black is 1:3:4. Conductive agents with different aspect ratios are intertwined with each other to form a more perfect three-dimensional conductive network structure, greatly shortening the electron conduction path, enhancing the electron conduction ability on the positive electrode side, reducing the impedance of the cell and the polarization during the cycling process, and enhancing the long cycling life. Further, the specific surface area of the single-walled carbon nanotubes is larger than that of the multi-walled carbon nanotubes, and the conductivity is better. However, due to the limitations of the production process, the residual metal impurities in the single-walled carbon nanotubes are more, and the gas generation risk is high. Therefore, by optimizing the ratio of single-walled carbon nanotubes and multi-walled carbon nanotubes, the cycling and storage performance can be balanced.

[0067] In the present invention, the positive electrode active material in the positive electrode active material layer includes one or more of lithium cobaltate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate. Specifically, the positive electrode active material includes lithium cobaltate, lithium nickel cobalt manganate, or lithium nickel cobalt aluminate.

[0068] In the present invention, the Dv50 particle size of the positive electrode active material is preferably 10 - 20μm, more preferably 12 - 18μm, and even more preferably 14 - 16μm. In this application, the Dv50 particle size of the positive electrode active material refers to the Dv50 particle size of the positive electrode active material raw material.

[0069] In the present invention, the specific surface area of the positive electrode active material is preferably 0.1 - 0.5m 2 / g, more preferably 0.15 - 0.45m2 / g, more preferably 0.2 - 0.4 m 2 / g, more preferably 0.25 - 0.35 m 2 / g.

[0070] In the present invention, the toughening agent preferably includes one or more of small molecule ester toughening agents, rubber toughening agents, and ionic liquids, more preferably a small molecule ester toughening agent, a rubber toughening agent, or an ionic liquid. Specifically, the small molecule ester toughening agent is selected from one or more of ethylene - acrylate, polyurethane, and methyl methacrylate; the rubber toughening agent is selected from one or more of hydrogenated nitrile rubber, styrene - butadiene rubber, and carboxy nitrile rubber; the ionic liquid is selected from one or more of 1 - ethylpyridinium bromide, 1 - hexyl - 3 - methylpyridinium bromide, and butylpyridinium bromide.

[0071] In the present invention, the mass content of the toughening agent in the positive electrode active material layer is 0.1% - 2.0%, specifically 0.2% - 1.5%, more specifically 0.4% - 1.0%, and even more specifically 0.6 - 0.8%.

[0072] In the present invention, the mass content of the conductive agent in the positive electrode active material layer is 1.0 - 2.0%, specifically 1.2 - 1.7%, more specifically 1.4 - 1.6%.

[0073] In the present invention, the mass content of the non - fluorine binder in the positive electrode active material layer is 0.5 - 2.0%, specifically 0.8 - 1.7%, more specifically 1.0 - 1.5%, and even more specifically 1.2 - 1.4%; when the mass content of the non - fluorine binder is less than 0.5%, the slurry will settle within 24 hours, the adhesion of the positive electrode plate is less than 5 N / m, and powder falling will affect processing; when the mass content of the non - fluorine binder is higher than 2.0%, the positive electrode plate shows obvious hard brittleness, resulting in low compaction of the electrode plate, while reducing the main material ratio and losing energy density.

[0074] In the present invention, the mass content of the positive electrode active material in the positive electrode active material layer is 95.6% - 99%, specifically 96% - 98.5%, more specifically 96.5% - 98%, and even more specifically 97% - 97.5%.

[0075] In the present invention, the positive electrode active material layer is preferably obtained by coating a positive electrode slurry formed by a positive electrode active material, a conductive agent, a toughening agent, and a non - fluorine binder on a current collector and then rolling.

[0076] In the present invention, the thickness of the positive electrode active material layer can be 4 - 5 mm, or 4.2 - 4.8 mm, or 4.4 - 4.6 mm. The current collector preferably includes aluminum foil.

[0077] In the present invention, the surface tension of the positive electrode paste is 18 to 25 mN / m, specifically 19 to 24 mN / m, more specifically 20 to 23 mN / m, and even more specifically 21 to 22 mN / m.

[0078] In the present invention, the surface roughness of the current collector is 0.2 to 1.5 μm, can be 0.5 to 1.2 μm, and can be 0.7 to 1.0 μm. Specifically, the current collector can be selected from aluminum foils; among them, aluminum foils with too large roughness or overly smooth aluminum foils will result in poor adhesion and uniformity of the positive electrode active material layer.

[0079] In the present invention, the thickness of the current collector is 4 to 12 μm, can be 5 to 11 μm, can be 6 to 10 μm, and can be 7 to 9 μm.

[0080] In the present invention, the surface tension of the current collector is 30 to 40 mN / m, can be 32 to 38 mN / m, and can be 34 to 36 mN / m. In the present invention, the surface tension of the current collector is preferably greater than the surface tension of the positive electrode paste, which is beneficial to the uniform spreading of the paste on the surface of the aluminum foil, making the coating thickness of the positive electrode plate consistent, and greatly avoiding the situation of uneven coating thickness of the electrode plate; in addition, the adhesion between the positive electrode active material layer and the positive electrode current collector is large, which is beneficial to improving the safety performance.

[0081] In the present invention, the positive electrode plate is preferably a high surface density positive electrode plate. Among them, the surface density of the positive electrode plate ≥ 20 mg / cm 2 , specifically ≥ 22 mg / cm 2 , more specifically ≥ 25 mg / cm 2 .

[0082] In the present invention, after rolling, the elongation rate of the positive electrode plate is 0.8% to 1.3%, specifically 0.9% to 1.2%, and more specifically 1.0% to 1.1%. Among them, the elongation rate of the positive electrode plate increases with the increase of the compaction density. Compared with the positive electrode plate prepared by PVDF, the positive electrode plate prepared by the binder of the present invention has an elongation rate 0.1% to 0.2% higher after rolling, making the coating thickness of the positive electrode plate provided by the present invention consistent, and avoiding the problems of water ripples and trailing at the head and tail of the coating; under the condition of ensuring a high compaction density of the positive electrode plate, the increase of the elongation rate of the positive electrode plate has little impact on the thickness and energy density of the next stage.

[0083] In the present invention, the weight loss rate of the positive electrode plate before and after setting the concave portion area is 3.0% to 15.0%, specifically 5.0% to 13.0%, and more specifically 7.0% to 11.0%.

[0084] Before the electrolyte injection of the battery cell provided by the present invention, the swelling range of the positive electrode plate is 1.0% - 5.0%; after the electrolyte injection, the actual residual electrolyte amount of the battery cell can be increased by 5.0% - 20.0%.

[0085] In this application, the specific method for detecting the porosity is as follows: weigh the mass (m) of a positive electrode plate of a certain size with a balance, and the true volume V of the positive electrode plate can be measured by a true density meter. 真 , the theoretical volume (V 理论 ) of the positive electrode plate can be calculated from the length * width * height of the positive electrode plate; the true density ρ1 of the positive electrode plate = m / V 真 , the theoretical density ρ2 of the positive electrode plate = m / V 理论 , and the porosity (P) of the positive electrode plate = 1 - ρ1 / ρ2.

[0086] In this application, the test method for the tube diameters of single-walled carbon nanotubes and multi-walled carbon nanotubes is the test method for the average tube diameter. The test is carried out by using a scanning electron microscope. In the range of 20μm × 20μm, the tube diameters of carbon nanotube bundles are counted. At three different positions of each bundle, the width of the carbon nanotube bundle is measured once, which is recorded as the tube diameter of the carbon nanotube bundle. The average value of the tube diameters of all carbon nanotube bundles in this area is the average tube diameter; the test method for the tube length is the test method for the average length. The test is carried out by using a scanning electron microscope. In the range of 20μm × 20μm, the lengths of carbon nanotube bundles are counted. The average value of the lengths of all carbon nanotube bundles in this area is the average length.

[0087] In this application, the weight-average molecular weight of the non-fluorine binder is tested by gel permeation chromatography (GPC).

[0088] As non-fluorine binders for the positive electrode, PAA, PAN, PMMA, etc. generally have the disadvantages of poor toughness and low compaction. Their disadvantages are more obvious especially in the design system of high compaction, thick electrode sheets, and winding structures. The main disadvantages are manifested in abnormal winding processes, excessive width of the next-stage battery cells, and lithium deposition in the bending area during the later stage of high-temperature cycling. Through controlling the above-mentioned various parameters of the positive electrode sheet and combining with the setting of the concave area in the bending area, the present invention realizes the application of non-fluorine binders in wound-structured battery cells. It can not only make full use of the excellent adhesion and excellent slurry stability of non-fluorine binders, but also solve the defect that the positive electrode sheet using non-fluorine binders is hard and brittle, resulting in low compaction. Especially, problems such as cracks and powder shedding occur in the bending area of the positive electrode sheet during the winding process, leading to lithium deposition in the bending area during the later stage of high-temperature cycling. Specifically, a concave area is set in the bending area on the inner side of the positive electrode sheet before winding. On the one hand, it appropriately reduces the areal density here, which can avoid cracks in the positive electrode sheet during winding. On the other hand, it increases the porosity. A large porosity is beneficial to improving the charge and discharge rate performance of the battery, can increase the liquid retention capacity of the battery cell. A high liquid retention capacity in the bending area of the battery cell can avoid lithium deposition caused by dry electrolyte during the later stage of high-temperature cycling and improve high-temperature cycling. The conductive agent uses single-walled carbon nanotubes and multi-walled carbon nanotubes with multi-scale aspect ratios to interweave and construct a more perfect three-dimensional conductive network, providing a longer electron path, which can reduce impedance and improve rate performance. Therefore, through the synergistic effect of multiple items, the present invention can not only ensure that the positive electrode sheet can achieve high compaction, but also solve the problem of lithium deposition at high temperatures, ensuring the electrochemical performance of lithium-ion batteries.

[0089] The wound non-fluorine positive electrode sheet of the present invention with a specific structure and characteristic parameters is specially designed. Through the synergistic effect of multiple improvements, a positive electrode sheet using a non-fluorine binder is obtained. The present invention further designs the surface roughness of the specific current collector, the thickness of the current collector, the surface tension of the current collector, and controls the amount of binder used. Combined with the setting method of the concave area in the bending area on the inner side of the positive electrode sheet, it appropriately reduces the areal density in the bending area on the inner side of the positive electrode sheet, improves the problems of cracks and powder shedding in the bending area of the winding core due to the hard and brittle electrode sheet during winding, increases the CB value at this position, increases the porosity of the electrode sheet at this position, is beneficial to the infiltration and absorption of the electrolyte, effectively reduces the mass transfer resistance of lithium ions, improves the problem of lithium deposition in the bending area during the later stage of high-temperature cycling, and also reduces the polarization rate during the cycling process and improves the cycle capacity retention rate. The present invention solves the application limitation of non-fluorine binders in wound-structured battery cells with high compaction and thick electrode sheets, and completely replaces PVDF.

[0090] Furthermore, the surface tension of the positive electrode slurry used in the present invention differs from the surface tension of the current collector by 10 - 20 mN / m, with better leveling property during coating, good consistency of the electrode sheet thickness, avoiding the risk of uneven electrode sheet thickness, and having a large adhesion force, thus improving the safety performance.

[0091] In summary, the present invention uses a green and environmentally friendly non-fluorine binder to prepare a cathode electrode sheet with a higher areal density. By combining the setting of a concave area in the bending area of the cathode electrode sheet, and further using single / multi-walled carbon nanotubes with different aspect ratios to construct a perfect conductive network, and further combining the control of the roughness of the current collector and the extension of the electrode sheet, a cathode electrode sheet with an areal density as high as 25 mg / cm 2 is obtained, which is compacted to 4.30 g / cc. After winding, a battery cell with ultra-high energy density is obtained, solving the problem of lithium deposition in the bending area of the battery cell, reducing the impedance of the battery cell, and improving the long cycle life.

[0092] To further illustrate the present invention, the lithium-ion battery provided by the present invention will be described in detail below in conjunction with embodiments. However, it should be understood that these embodiments are implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given only to further illustrate the features and advantages of the present invention, rather than a limitation on the claims of the present invention. The protection scope of the present invention is not limited to the following embodiments.

[0093] Example 1

[0094] 1) Preparation of the cathode slurry of the lithium-ion battery containing a non-fluorine binder

[0095] Prepare the cathode active slurry according to the mass ratio of lithium cobaltate (96.2%), conductive carbon black (SP) (1.0%), single-walled carbon nanotubes (SWCNTs) (0.2%), multi-walled carbon nanotubes (MWCNTs) (0.8%), non-fluorine binder (PAA) 0.8%, and toughening agent (ethylene-acrylate) 1.0%; among them, the Dv50 of lithium cobaltate is 15 μm, the specific surface area is 0.3 m 2 / g, the weight-average molecular weight of the non-fluorine binder is 1.2 million, the particle size is 65 μm, the aspect ratio of the single-walled carbon nanotubes is 2000, and the aspect ratio of the multi-walled carbon nanotubes is 6000; specifically, the following steps are included:

[0096] The non-fluorine binder (PAA) and toughening agent (ethylene-acrylate) are fully dispersed in N-methylpyrrolidone (NMP). The self-rotation is set to 1600 rpm. After stirring for 20 min, conductive carbon black (SP) is added, the self-rotation is set to 3500 rpm, and the stirring time is 30 min. Then single-walled carbon nanotubes and multi-walled carbon nanotubes are added. The self-rotation is set to 1600 rpm. After stirring for 20 min, the vacuum is started, and stirring is carried out for 150 min to ensure that the single-walled carbon nanotubes and multi-walled carbon nanotubes are evenly dispersed. Finally, lithium cobaltate is added, the self-rotation is set to 1600 rpm, and the stirring time is 20 min. The vacuum system needs to be closed at this stage. After 20 min, the vacuum is started again, and stirring is carried out for 4 h to complete the batching and obtain the positive electrode active paste. The temperature during the preparation process of the above positive electrode active paste is maintained at 25 °C. The viscosity range of the paste when discharging is 5000 - 7000 mPa·s, and the surface tension is 20 mN / m. The dissolution rate of the non-fluorine binder PAA is 5%, and the swelling rate is 20%.

[0097] 2) Preparation of the positive electrode plate

[0098] The above positive electrode active paste is coated on the surface of the current collector aluminum foil by spraying. The thickness of the aluminum foil is 9 μm, the surface roughness is 0.6 μm, the surface tension is 35 mN / m, and the coating speed is controlled at 20 m / min.

[0099] The obtained wet film is dried in an oven at three different temperatures to obtain a positive electrode plate with an active material layer on the surface. The temperature of the first stage is controlled at 110 °C, the temperature of the second stage is controlled at 130 °C, and the temperature of the third stage is controlled at 110 °C. The thickness of the active material layer is 150 μm, the cohesive force of the active material layer is 35 N / m, and the elongation rate of the positive electrode plate is 1.1%.

[0100] 3) Laser drilling

[0101] A concave area is set in the inner bending area of the positive electrode plate prepared in step 2). The power of the laser drilling is set to 20 W, the frequency is 10 KHZ, and the speed is 4 m / min to obtain a concave area composed of several single concave parts, and thus a positive electrode plate with a concave area is obtained. The width of the above concave area is 1 mm, the radial dimension a of a single concave part in the concave area is 0.5 mm, the depth b is 5 μm, the adjacent distance c is 120 μm, the number of concave parts per unit width is 50, and the weight loss rate of the positive electrode plate is 3.0%.

[0102] 4) Preparation of the negative electrode paste and negative electrode plate

[0103] Prepare a negative electrode active paste according to the mass ratio of graphite (90.40%), silicon carbide (6.80%), conductive single-walled carbon nanotubes (0.20%), sodium carboxymethyl cellulose (CMC) (1.60%) and binder (SBR) (1.0%);

[0104] The above negative electrode active paste is coated on the surface of the negative electrode current collector (copper foil) by spraying. The thickness of the current collector is 5 μm. After drying, a negative electrode plate is obtained. The areal density of the negative electrode plate is 10.20 mg / cm 2 ;

[0105] 5) The above positive electrode plate and negative electrode plate are successively roll-pressed, slit, and wound to obtain an electric core. Among them, the tap density of the positive electrode plate is 4.30 g / cc, and the areal density is 25.0 mg / cm 2 , and the porosity of the active material layer with a concave portion in the bending area of the positive electrode plate is 28%, and the porosity of the positive electrode active material layer in the straight area is 18%.

[0106] Example 2

[0107] 1) Preparation of a lithium-ion battery positive electrode paste containing a non-fluorine binder

[0108] Prepare a positive electrode active paste according to the mass ratio of lithium cobaltate (96.2%), conductive carbon black (SP) (1.0%), single-walled carbon nanotubes (SWCNTs) (0.2%), multi-walled carbon nanotubes (MWCNTs) (0.8%), non-fluorine binder (PAN) 0.5%, and toughening agent (ethylene-acrylate) 1.3%; among them, the Dv50 of lithium cobaltate is 15 μm, and the specific surface area is 0.3 m 2 / g, the weight-average molecular weight of the non-fluorine binder is 1.2 million, the particle size is 65 μm, the aspect ratio of single-walled carbon nanotubes is 2000, and the aspect ratio of multi-walled carbon nanotubes is 6000; specifically, it includes the following steps:

[0109] The non-fluorine binder (PAN) and toughening agent (ethylene-acrylate) are fully dispersed in N-methylpyrrolidone (NMP). The self-rotation is set to 1600 rpm. After stirring for 20 min, conductive carbon black (SP) is added, the self-rotation is set to 3500 rpm, and the stirring time is 30 min. Then, single-walled carbon nanotubes and multi-walled carbon nanotubes are added. The self-rotation is set to 1600 rpm. After stirring for 20 min, the vacuum is started, and stirring is carried out for 150 min to ensure the uniform dispersion of single-walled carbon nanotubes and multi-walled carbon nanotubes. Finally, lithium cobaltate is added, the self-rotation is set to 1600 rpm, and the stirring time is 20 min. The vacuum system needs to be closed at this stage. After 20 min, the vacuum is started again, and stirring is carried out for 4 h to complete the batching and obtain the positive electrode active paste. The temperature during the preparation process of the above positive electrode active paste is maintained at 25 °C. The viscosity range of the paste when discharging is 5000-7000 mPa·s, and the surface tension is 20 mN / m. The dissolution rate of the non-fluorine binder PAN is 3.5%, and the swelling rate is 23%.

[0110] 2) Preparation of the positive electrode plate

[0111] The above positive electrode active paste is coated on the surface of the current collector aluminum foil by spraying. The thickness of the aluminum foil is 9 μm, the surface roughness is 0.6 μm, the surface tension is 35 mN / m, and the coating speed is controlled at 20 m / min.

[0112] The obtained wet film is dried in an oven at three different temperatures to obtain a positive electrode plate with an active material layer on the surface. The temperature of the first stage is controlled at 110 °C, the temperature of the second stage is controlled at 130 °C, and the temperature of the third stage is controlled at 110 °C. The thickness of the active material layer is 140 μm, the cohesion of the active material layer is 30 N / m, and the elongation rate of the positive electrode plate is 1.3%.

[0113] 3) Laser drilling

[0114] A concave area is set in the inner bending area of the positive electrode plate prepared in step 2). The power of the laser drilling is set to 20 W, the frequency is 10 KHZ, and the speed is 8 m / min to obtain a concave area composed of several single concave parts, thereby obtaining a positive electrode plate provided with a concave area. The width of the above concave area is 3 mm, the radial dimension a of a single concave part in the concave area is 0.3 mm, the depth b is 10 μm, the adjacent distance c is 60 μm, the number of concave parts per unit width is 100, and the weight loss rate of the positive electrode plate is 3.0%.

[0115] 4) Preparation of the negative electrode paste and the negative electrode plate

[0116] Prepare a negative electrode active paste according to the mass ratio of graphite (90.40%), silicon carbide (6.80%), conductive single-walled carbon nanotubes (0.20%), sodium carboxymethyl cellulose (CMC) (1.60%), and binder (SBR) (1.0%);

[0117] Coat the above-mentioned negative electrode active paste on the surface of the negative electrode current collector (copper foil) by spraying. The thickness of the current collector is 5 μm. After drying, a negative electrode sheet is obtained. The areal density of the negative electrode sheet is 10.20 mg / cm 2 ;

[0118] 5) Successively roll, slit, and wind the above-mentioned positive electrode sheet and negative electrode sheet to obtain an electric core. Among them, the tap density of the positive electrode sheet is 4.30 g / cc, and the areal density is 25.0 mg / cm 2 , and the porosity of the active material layer with a concave area in the bending area of the positive electrode sheet is 36%, and the porosity of the positive electrode active material layer in the straight area is 18%.

[0119] Example 3

[0120] 1) Preparation of a lithium-ion battery positive electrode paste containing a non-fluorine binder

[0121] Prepare a positive electrode active paste according to the mass ratio of lithium cobaltate (96.2%), conductive carbon black (SP) (1.0%), single-walled carbon nanotubes (SWCNTs) (0.2%), multi-walled carbon nanotubes (MWCNTs) (0.8%), non-fluorine binder (PMMA) 1.2%, and toughening agent (ethylene-acrylate) 0.6%; among them, the Dv50 of lithium cobaltate is 15 μm, the specific surface area is 0.3 m 2 / g, the weight-average molecular weight of the non-fluorine binder is 1.2 million, the particle size is 65 μm, the aspect ratio of single-walled carbon nanotubes is 2000, and the aspect ratio of multi-walled carbon nanotubes is 6000; specifically, it includes the following steps:

[0122] The non-fluorine binder (PMMA) and toughening agent (ethylene-acrylate) are fully dispersed in N-methylpyrrolidone (NMP). The self-rotation is set to 1600 rpm. After stirring for 20 min, conductive carbon black (SP) is added, the self-rotation is set to 3500 rpm, and the stirring time is 30 min. Then single-walled carbon nanotubes and multi-walled carbon nanotubes are added. The self-rotation is set to 1600 rpm. After stirring for 20 min, the vacuum is started, and stirring is carried out for 150 min to ensure that the single-walled carbon nanotubes and multi-walled carbon nanotubes are evenly dispersed. Finally, lithium cobaltate is added. The self-rotation is set to 1600 rpm, and the stirring time is 20 min. The vacuum system needs to be closed at this stage. After 20 min, the vacuum is started again, and stirring is carried out for 4 h to complete the batching, obtaining the positive electrode active paste. The temperature during the preparation process of the above positive electrode active paste is maintained at 25 °C. The viscosity range of the paste when discharging is 5000-7000 mPa·s, and the surface tension is 20 mN / m. The dissolution rate of the non-fluorine binder PAA is 8.3%, and the swelling rate is 36%.

[0123] 2) Preparation of the positive electrode plate

[0124] The above positive electrode active paste is coated on the surface of the current collector aluminum foil by spraying. The thickness of the aluminum foil is 9 μm, the surface roughness is 0.6 μm, the surface tension is 35 mN / m, and the coating speed is controlled at 20 m / min.

[0125] The obtained wet film is dried in an oven at three different temperatures to obtain a positive electrode plate with an active material layer on the surface. The temperature of the first stage is controlled at 110 °C, the temperature of the second stage is controlled at 130 °C, and the temperature of the third stage is controlled at 110 °C. The thickness of the active material layer is 130 μm, the cohesion of the active material layer is 37 N / m, and the elongation rate of the positive electrode plate is 1%.

[0126] 3) Laser drilling

[0127] A concave area is set in the inner bending area of the positive electrode plate prepared in step 2). The power of the laser drilling is set to 30 W, the frequency is 10 KHZ, and the speed is 8 m / min to obtain a concave area composed of several single concave parts, thereby obtaining a positive electrode plate provided with a concave area. The width of the above concave area is 6 mm, the radial dimension a of a single concave part in the concave area is 1.6 mm, the depth b is 22 μm, the adjacent distance c is 80 μm, the number of concave parts per unit width is 90, and the weight loss rate of the positive electrode plate is 3.0%.

[0128] 4) Preparation of the negative electrode paste and the negative electrode plate

[0129] Prepare a negative electrode active paste according to the mass ratio of graphite (90.40%), silicon carbide (6.80%), conductive single-walled carbon nanotubes (0.20%), sodium carboxymethyl cellulose (CMC) (1.60%), and binder (SBR) (1.0%);

[0130] Coat the above-mentioned negative electrode active paste on the surface of the negative electrode current collector (copper foil) by spraying. The thickness of the current collector is 5 μm. After drying, a negative electrode sheet is obtained. The areal density of the negative electrode sheet is 10.20 mg / cm 2 ;

[0131] 5) Successively roll, slit, and wind the above-mentioned positive electrode sheet and negative electrode sheet to obtain an electric core. Among them, the tap density of the positive electrode sheet is 4.30 g / cc, and the areal density is 25.0 mg / cm 2 , and the porosity of the active material layer with a concave area in the bending area of the positive electrode sheet is 35%, and the porosity of the positive electrode active material layer in the straight area is 18%.

[0132] Example 4

[0133] 1) Preparation of a lithium-ion battery positive electrode paste containing a non-fluorine binder

[0134] Prepare a positive electrode active paste according to the mass ratio of lithium cobaltate (95.5%), conductive carbon black (SP) (1.0%), single-walled carbon nanotubes (SWCNTs) (0.2%), multi-walled carbon nanotubes (MWCNTs) (0.8%), non-fluorine binder (PAA, PAN) 2%, and toughening agent (ethylene-acrylate) 0.5%; among them, the Dv50 of lithium cobaltate is 15 μm, and the specific surface area is 0.3 m 2 / g, the weight-average molecular weight of the non-fluorine binder is 1.2 million, the particle size is 65 μm, the aspect ratio of single-walled carbon nanotubes is 2000, and the aspect ratio of multi-walled carbon nanotubes is 6000; specifically, it includes the following steps:

[0135] Disperse non-fluorine binders (PAA, PAN) and toughening agents (ethylene-acrylate) thoroughly in N-methylpyrrolidone (NMP), set the self-rotation speed to 1600 rpm, after stirring for 20 min, add conductive carbon black (SP), set the self-rotation speed to 3500 rpm, and stir for 30 min; then add single-walled carbon nanotubes and multi-walled carbon nanotubes, set the self-rotation speed to 1600 rpm, after stirring for 20 min, start the vacuum, and stir for 150 min to ensure the uniform dispersion of single-walled carbon nanotubes and multi-walled carbon nanotubes; finally add lithium cobaltate, set the self-rotation speed to 1600 rpm, and stir for 20 min. The vacuum system needs to be closed at this stage. After 20 min, start the vacuum again and stir for 4 h to complete the batching and obtain the positive electrode active paste; the temperature during the preparation process of the above positive electrode active paste is maintained at 25 °C, the viscosity range of the paste when discharged is 5000 - 7000 mPa·s, and the surface tension is 20 mN / m; the dissolution rate of non-fluorine binders PAA and PAN is 6.5%, and the swelling rate is 42%;

[0136] 2) Preparation of the positive electrode plate

[0137] Coat the above positive electrode active paste on the surface of the current collector aluminum foil by spraying. The thickness of the aluminum foil is 9 μm, the surface roughness is 0.6 μm, the surface tension is 35 mN / m, and the coating speed is controlled at 20 m / min;

[0138] Dry the obtained wet film in an oven at three different temperatures to obtain a positive electrode plate with an active material layer on the surface. Among them, the temperature of the first stage is controlled at 110 °C, the temperature of the second stage is controlled at 130 °C, and the temperature of the third stage is controlled at 110 °C; the thickness of the active material layer is 120 μm, the cohesive force of the active material layer is 45 N / m, and the elongation rate of the positive electrode plate is 0.8%;

[0139] 3) Laser drilling

[0140] Set a recessed area in the inner bending area of the positive electrode plate prepared in step 2). Set the power of laser drilling to 40 W, the frequency to 20 KHZ, and the speed to 5 m / min to obtain a recessed area composed of several single recesses, thereby obtaining a positive electrode plate with a recessed area; the width of the above recessed area is 7 mm, the radial dimension a of a single recess in the recessed area is 2 mm, the depth b is 35 μm, the adjacent distance c is 100 μm, the number of recesses per unit width is 60, and the weight loss rate of the positive electrode plate is 3.0%;

[0141] 4) Preparation of the negative electrode paste and the negative electrode plate

[0142] Prepare the negative electrode active paste according to the mass ratio of graphite (90.40%), silicon carbide (6.80%), conductive single-walled carbon nanotubes (0.20%), sodium carboxymethyl cellulose (CMC) (1.60%) and binder (SBR) (1.0%);

[0143] Coat the above negative electrode active paste on the surface of the negative electrode current collector (copper foil) by spraying. The thickness of the current collector is 5 μm. After drying, a negative electrode sheet is obtained, and the areal density of the negative electrode sheet is 10.20 mg / cm 2 ;

[0144] 5) Successively roll, slit and wind the above positive electrode sheet and negative electrode sheet to obtain an electric core. Among them, the tap density of the positive electrode sheet is 4.30 g / cc, and the areal density is 25.0 mg / cm 2 , and the porosity of the active material layer with a concave area in the bending area of the positive electrode sheet is 32%, and the porosity of the positive electrode active material layer in the straight area is 18%.

[0145] Example 5

[0146] 1) Preparation of a lithium-ion battery positive electrode paste containing a non-fluorine binder

[0147] Prepare the positive electrode active paste according to the mass ratio of lithium cobaltate (95.5%), conductive carbon black (SP) (1.0%), single-walled carbon nanotubes (SWCNTs) (0.2%), multi-walled carbon nanotubes (MWCNTs) (0.8%), non-fluorine binder (PAN, PMMA) 1.8%, and toughening agent (ethylene-acrylate) 1.5%; among them, the Dv50 of lithium cobaltate is 15 μm, and the specific surface area is 0.3 m 2 / g, the weight-average molecular weight of the non-fluorine binder is 1.2 million, the particle size is 65 μm, the aspect ratio of single-walled carbon nanotubes is 2000, and the aspect ratio of multi-walled carbon nanotubes is 6000; specifically, it includes the following steps:

[0148] Disperse non-fluorine binders (PAN, PMMA) and toughening agents (ethylene-acrylate) thoroughly in N-methylpyrrolidone (NMP). Set the rotation speed to 1600 rpm, and after stirring for 20 min, add conductive carbon black (SP). Set the rotation speed to 3500 rpm and stir for 30 min. Then add single-walled carbon nanotubes and multi-walled carbon nanotubes. Set the rotation speed to 1600 rpm, stir for 20 min, and then start the vacuum and stir for 150 min to ensure the uniform dispersion of single-walled carbon nanotubes and multi-walled carbon nanotubes. Finally, add lithium cobaltate, set the rotation speed to 1600 rpm, and stir for 20 min. The vacuum system needs to be closed at this stage. After 20 min, start the vacuum again and stir for 4 h to complete the batching and obtain the positive electrode active paste. The temperature during the preparation process of the above positive electrode active paste is maintained at 25 °C. The viscosity range of the paste when discharged is 5000 - 7000 mPa·s, and the surface tension is 20 mN / m. The dissolution rate of non-fluorine binders PAN and PMMA is 2.4%, and the swelling rate is 50%.

[0149] 2) Preparation of the positive electrode plate

[0150] Coat the above positive electrode active paste on the surface of the current collector aluminum foil by spraying. The thickness of the aluminum foil is 9 μm, the surface roughness is 0.6 μm, the surface tension is 35 mN / m, and the coating speed is controlled at 20 m / min.

[0151] Dry the obtained wet film in an oven at three different temperatures to obtain a positive electrode plate with an active material layer on the surface. The temperature of the first stage is controlled at 110 °C, the temperature of the second stage is controlled at 130 °C, and the temperature of the third stage is controlled at 110 °C. The thickness of the active material layer is 100 μm, the cohesive force of the active material layer is 40 N / m, and the elongation rate of the positive electrode plate is 0.9%.

[0152] 3) Laser drilling

[0153] Set a concave area in the inner bending area of the positive electrode plate prepared in step 2). Set the power of laser drilling to 60 W, the frequency to 10 KHZ, and the speed to 3 m / min to obtain a concave area composed of several single concave parts, and thus obtain a positive electrode plate with a concave area set. The width of the above concave area is 10 mm, the radial dimension a of a single concave part in the concave area is 0.8 mm, the depth b is 50 μm, the adjacent distance c is 200 μm, the number of concave parts per unit width is 30, and the weight loss rate of the positive electrode plate is 3.0%.

[0154] 4) Preparation of the negative electrode paste and the negative electrode plate

[0155] Prepare the negative electrode active paste according to the mass ratio of graphite (90.40%), silicon carbide (6.80%), conductive single-walled carbon nanotubes (0.20%), sodium carboxymethyl cellulose (CMC) (1.60%) and binder (SBR) (1.0%);

[0156] Coat the above-mentioned negative electrode active paste on the surface of the negative electrode current collector (copper foil) by spraying. The thickness of the current collector is 5 μm. After drying, a negative electrode sheet is obtained, and the areal density of the negative electrode sheet is 10.20 mg / cm 2 ;

[0157] 5) Successively roll, slit and wind the above-mentioned positive electrode sheet and negative electrode sheet to obtain an electric core. Among them, the tap density of the positive electrode sheet is 4.30 g / cc, and the areal density is 25.0 mg / cm 2 , and the porosity of the active material layer with a concave portion area in the bending area of the positive electrode sheet is 25%, and the porosity of the positive electrode active material layer in the straight area is 18%.

[0158] Example 6

[0159] The preparation method of the electric core is basically the same as that of Example 1, except that: the width of the concave portion area is 1 mm, the number of concave portions per unit width remains unchanged, the aspect ratio of the single-walled carbon nanotubes is 4000, and the aspect ratio of the multi-walled carbon nanotubes is 10000.

[0160] Example 7

[0161] The preparation method of the electric core is basically the same as that of Example 6, except that: the width of the concave portion area is 2 mm.

[0162] Example 8

[0163] The preparation method of the electric core is basically the same as that of Example 6, except that: the width of the concave portion area is 4 mm.

[0164] Example 9

[0165] The preparation method of the electric core is basically the same as that of Example 6, except that: the width of the concave portion area is 6 mm.

[0166] Example 10

[0167] The preparation method of the electric core is basically the same as that of Example 6, except that: the width of the concave portion area is 8 mm.

[0168] Example 11

[0169] The preparation method of the battery cell is basically the same as that of Example 7, except that: in the recessed area, the radial dimension a of a single recess is 0.5 mm, the depth b is 20 μm, the adjacent distance c is 90 μm, the number of recesses per unit width is 75, and the porosity of the active material layer in the recessed area provided in the bent area of the positive electrode tab is 33%.

[0170] Example 12

[0171] The preparation method of the battery cell is basically the same as that of Example 7, except that: in the recessed area, the radial dimension a of a single recess is 1 mm, the depth b is 15 μm, the adjacent distance c is 125 μm, the number of recesses per unit width is 48, and the porosity of the active material layer in the recessed area provided in the bent area of the positive electrode tab is 28%.

[0172] Example 13

[0173] The preparation method of the battery cell is basically the same as that of Example 7, except that: in the recessed area, the radial dimension a of a single recess is 1.2 mm, the depth b is 35 μm, the adjacent distance c is 145 μm, the number of recesses per unit width is 40, and the porosity of the active material layer in the recessed area provided in the bent area of the positive electrode tab is 27%.

[0174] Example 14

[0175] The preparation method of the battery cell is basically the same as that of Example 7, except that: in the recessed area, the radial dimension a of a single recess is 0.4 mm, the depth b is 10 μm, the adjacent distance c is 186 μm, the number of recesses per unit width is 33, and the porosity of the active material layer in the recessed area provided in the bent area of the positive electrode tab is 25%.

[0176] Example 15

[0177] The preparation method of the battery cell is basically the same as that of Example 7, except that: in the recessed area, the radial dimension a of a single recess is 1.7 mm, the depth b is 12 μm, the adjacent distance c is 175 μm, the number of recesses per unit width is 35, and the porosity of the active material layer in the recessed area provided in the bent area of the positive electrode tab is 26%.

[0178] Example 16

[0179] The preparation method of the battery cell is basically the same as that of Example 7, except that: in the recessed area, the radial dimension a of a single recess is 1.8 mm, the depth b is 40 μm, the adjacent distance c is 60 μm, the number of recesses per unit width is 100, and the porosity of the active material layer in the recessed area provided in the bent area of the positive electrode tab is 35%.

[0180] Example 17

[0181] The preparation method of the battery cell is basically the same as that of Example 13, except that: the non-fluorine binder is selected from PAN, and the cohesive force of the positive electrode active material layer is 36 N / m.

[0182] Example 18

[0183] The preparation method of the battery cell is basically the same as that of Example 17, except that the content of the non-fluorine binder is 1.2 wt%, and the cohesive force of the positive electrode active material layer is 37 N / m.

[0184] Example 19

[0185] The preparation method of the battery cell is basically the same as that of Example 18, except that the content of the non-fluorine binder is 0.6 wt%, and the cohesive force of the positive electrode active material layer is 32 N / m.

[0186] Example 20

[0187] The preparation method of the battery cell is basically the same as that of Example 18, except that the content of the non-fluorine binder is 0.5 wt%, and the cohesive force of the positive electrode active material layer is 30 N / m.

[0188] Example 21

[0189] The preparation method of the battery cell is basically the same as that of Example 18, except that the content of the non-fluorine binder is 1.8 wt%, and the cohesive force of the positive electrode active material layer is 40 N / m.

[0190] Example 22

[0191] 1) Preparation of the positive electrode slurry of the lithium-ion battery containing the non-fluorine binder

[0192] Prepare the positive electrode active slurry according to the mass ratio of lithium cobaltate (96.2%), conductive carbon black (SP) (1.0%), single-walled carbon nanotubes (SWCNTs) (0.2%), multi-walled carbon nanotubes (MWCNTs) (0.8%), non-fluorine binder (PAN, PAA) 0.8%, and toughening agent (ethylene-acrylate) 1.0%; among them, the Dv50 of lithium cobaltate is 15 μm, the specific surface area is 0.3 m 2 / g, the weight-average molecular weight of the non-fluorine binder is 1.2 million, the particle size is 65 μm, the aspect ratio of single-walled carbon nanotubes is 2000, and the aspect ratio of multi-walled carbon nanotubes is 4000; specifically, it includes the following steps:

[0193] Disperse non-fluoride binders (PAN, PAA) and toughening agents (ethylene-acrylate) thoroughly in N-methylpyrrolidone (NMP), set the self-rotation to 1600 rpm, after stirring for 20 min, add conductive carbon black (SP), set the self-rotation to 3500 rpm, and stir for 30 min; then add single-walled carbon nanotubes and multi-walled carbon nanotubes, set the self-rotation to 1600 rpm, after stirring for 20 min, start the vacuum, and stir for 150 min to ensure the uniform dispersion of single-walled carbon nanotubes and multi-walled carbon nanotubes; finally add lithium cobaltate, set the self-rotation to 1600 rpm, and stir for 20 min. The vacuum system needs to be closed at this stage. After 20 min, start the vacuum again and stir for 4 h to complete the batching and obtain the positive electrode active paste; the temperature during the preparation process of the above positive electrode active paste is maintained at 25 °C, the viscosity range of the paste when discharging is 5000 - 7000 mPa·s, and the surface tension is 20 mN / m; the dissolution rate of non-fluoride binders PAA and PAN is 5%, and the swelling rate is 20%;

[0194] 2) Preparation of the positive electrode sheet

[0195] Coat the above positive electrode active paste on the surface of the current collector aluminum foil by spraying. The thickness of the aluminum foil is 9 μm, the surface roughness is 0.6 μm, the surface tension is 35 mN / m, and the coating speed is controlled at 20 m / min;

[0196] Dry the obtained wet film in an oven at three different temperatures to obtain a positive electrode sheet with an active material layer on the surface. The temperature of the first stage is controlled at 110 °C, the temperature of the second stage is controlled at 130 °C, and the temperature of the third stage is controlled at 110 °C; the thickness of the active material layer is 135 μm, the cohesive force of the active material layer is 36 N / m, and the elongation rate of the positive electrode sheet is 1.1%;

[0197] 3) Laser drilling

[0198] Set a recessed area in the inner bending area of the positive electrode sheet prepared in step 2). Set the power of laser drilling to 40 W, the frequency to 15 KHZ, and the speed to 5 m / min to obtain a recessed area composed of several single recesses, and thus obtain a positive electrode sheet with a recessed area; the width of the above recessed area is 3 mm, the radial dimension a of a single recess in the recessed area is 1 mm, the depth b is 28 μm, the adjacent distance c is 90 μm, the number of recesses per unit width is 67, and the weight loss rate of the positive electrode sheet is 3.0%;

[0199] 4) Preparation of the negative electrode paste and the negative electrode sheet

[0200] Prepare the negative electrode active paste according to the mass ratio of graphite (90.40%), silicon carbide (6.80%), conductive single-walled carbon nanotubes (0.20%), sodium carboxymethyl cellulose (CMC) (1.60%) and binder (SBR) (1.0%);

[0201] Coat the above negative electrode active paste on the surface of the negative electrode current collector (copper foil) by spraying. The thickness of the current collector is 5 μm. After drying, a negative electrode plate is obtained, and the areal density of the negative electrode plate is 10.20 mg / cm 2 ;

[0202] 5) Successively roll, slit and wind the above positive electrode plate and negative electrode plate to obtain an electric core. Among them, the tap density of the positive electrode plate is 4.30 g / cc, and the areal density is 25.0 mg / cm 2 , and the porosity of the active material layer with a concave portion in the bending area of the positive electrode plate is 34%, and the porosity of the positive electrode active material layer in the straight area is 18%.

[0203] Example 23

[0204] The preparation method of the electric core is basically the same as that of Example 22, except that: the aspect ratio of the single-walled carbon nanotubes is 2000, and the aspect ratio of the multi-walled carbon nanotubes is 6000.

[0205] Example 24

[0206] The preparation method of the electric core is basically the same as that of Example 22, except that: the aspect ratio of the single-walled carbon nanotubes is 3000, and the aspect ratio of the multi-walled carbon nanotubes is 8000.

[0207] Example 25

[0208] The preparation method of the electric core is basically the same as that of Example 22, except that: the aspect ratio of the single-walled carbon nanotubes is 3000, and the aspect ratio of the multi-walled carbon nanotubes is 10000.

[0209] Example 26

[0210] The preparation method of the electric core is basically the same as that of Example 22, except that: the aspect ratio of the single-walled carbon nanotubes is 4000, and the aspect ratio of the multi-walled carbon nanotubes is 10000.

[0211] Comparative Example 1

[0212] The preparation method of the electric core is basically the same as that of Example 26, except that: the entire bending area is provided with a concave portion area.

[0213] Comparative Example 2

[0214] The preparation method of the electric core is basically the same as that of Example 26, except that: the width of the concave portion area is 15 mm.

[0215] Comparative Example 3

[0216] The preparation method of the battery cell is basically the same as that of Example 26, except that: the conductive agent only includes single-walled carbon nanotubes.

[0217] Comparative Example 4

[0218] The preparation method of the battery cell is basically the same as that of Example 26, except that: the non-fluorine binder is hydrogenated nitrile rubber; the dissolution rate of the non-fluorine binder is 13.8%, and the swelling rate is 84%; the cohesive force of the active material layer is 25 N / m, and the elongation rate of the positive electrode sheet is 1%.

[0219] Comparative Example 5

[0220] The preparation method of the battery cell is basically the same as that of Example 26, except that: in the concave portion area, the radial dimension a of a single concave portion is 2.5 mm, the depth b is 60 μm, and the adjacent distance c is 250 μm.

[0221] The electrochemical performances of the battery cells prepared in the above examples and comparative examples were detected, and the results are shown in Table 1;

[0222] Table 1 Data table of the electrochemical performances of the battery cells prepared in the examples and comparative examples

[0223]

[0224]

[0225]

[0226] As can be seen from Table 1, in Example 1, although the width of the concave portion area and the content of the non-fluorine binder are within the scope of the present application, the width of the concave portion area is relatively low, and the introduction of a high content of the non-fluorine binder still causes the problem of lithium deposition in the bending area; in Example 2, although the width of the concave portion area and the content of the non-fluorine binder are within the scope of the present application, the content of the non-fluorine binder is still relatively low compared to the range of the width of the concave portion area, and lithium deposition will also occur in the bending area; in Examples 3 to 5, the selection of the width, size, quantity, non-fluorine binder and conductive agent of the concave portion area can keep the energy density, capacity retention rate, liquid retention coefficient and impedance of the lithium-ion battery at a good level, and no lithium deposition problem will occur in the bending area.

[0227] In Example 6, although the width of the concave portion area and the content of the non-fluorine binder are within the scope of the present application, the width of the concave portion area is relatively low, and the introduction of a high content of the non-fluorine binder still causes the problem of lithium deposition in the bending area; in Examples 7 to 9, the preferred width selection of the concave portion area enables the lithium-ion battery to have excellent energy density, capacity retention rate, impedance and residual liquid coefficient, and no lithium deposition will occur in the bending area.

[0228] In Embodiment 11 and Embodiment 12, the preferred ranges of the radial dimension a, depth b of a single recess in the recess region, and the distance c between two adjacent single recesses enable the lithium-ion battery to have excellent energy density, and no lithium deposition occurs in the bending region; in Embodiment 13 and Embodiment 14, too few single recesses in the recess region result in lithium deposition in the bending region.

[0229] In Embodiment 17 and Embodiment 18, the preferred range of the non-fluorine binder content enables the lithium-ion battery to have excellent energy density, and no lithium deposition occurs in the bending region. In Embodiment 19 and Embodiment 20, the content of the non-fluorine binder is relatively low compared to the width of the recess region, resulting in lithium deposition in the bending region.

[0230] In Embodiment 22 to Embodiment 26, the aspect ratio of single-walled carbon nanotubes in the conductive agent is ≥3000, and the aspect ratio of multi-walled carbon nanotubes is ≥10000, enabling the lithium-ion battery to have a lower impedance, and thus enabling the lithium-ion battery to have excellent electrochemical performance.

[0231] In Comparative Example 1, a recess region is provided throughout the bending region, and this setting method greatly reduces the energy density of the lithium-ion battery.

[0232] In Comparative Example 2, the width of the recess region is too large relative to the content of the non-fluorine binder, resulting in lithium deposition in the bending region and affecting the electrochemical performance of the lithium-ion battery.

[0233] In Comparative Example 3, a single type of single-walled carbon nanotube is selected as the conductive agent without forming a three-dimensional conductive network, resulting in an increase in impedance and thus affecting the electrochemical performance of the lithium-ion battery. In Comparative Example 4, hydrogenated nitrile rubber is selected as the non-fluorine binder, resulting in an increase in both its dissolution rate and swelling rate, reducing the adhesiveness of the positive active material layer, and lithium deposition occurs in the bending region, thus affecting the electrochemical performance of the lithium-ion battery.

[0234] In Comparative Example 5, the dimensions a, b, and c of a single recess are too large, greatly reducing the energy density of the lithium-ion battery.

[0235] In this article, specific examples are used to elaborate on the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those of ordinary skill in the art in the technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The protection scope of the present invention patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that have no substantial difference from the literal description of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A lithium-ion battery, comprising a packaging bag, a battery cell contained in the packaging bag, and an electrolyte filled in the packaging bag, wherein the battery cell is wound by a positive electrode sheet, a negative electrode sheet, and a separator spaced between the positive electrode sheet and the negative electrode sheet, characterized in that: The battery cell has a straight area and bending areas located at two ends of the straight area; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is disposed on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material, a conductive agent, a toughening agent and a non-fluorine adhesive; A concave region is provided on the surface of the positive electrode active material layer in the bending region; The width of the bending zone in which the recessed area is arranged is in the range of 1 to 10 mm.

2. The lithium-ion battery according to claim 1, characterized in that The porosity of the positive electrode active material layer in the bending region where the recessed portion is provided is 23-35%.

3. The lithium-ion battery according to claim 1, characterized in that The conductive agent is a conductive agent network composed of single-walled carbon nanotubes with an aspect ratio greater than 2000 and multi-walled carbon nanotubes with an aspect ratio greater than 2000.

4. The lithium-ion battery according to claim 3, characterized in that: The conductive agent includes single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black; the multi-walled carbon nanotubes have a tube length of >30 μm and a tube diameter range of 5 to 10 nm, and the single-walled carbon nanotubes have a tube length of >15 μm and a tube diameter range of 1 to 3 nm; And / or, the mass ratio of the single-walled carbon nanotubes, the multi-walled carbon nanotubes and the carbon black is 1:(3-4):(4-5).

5. The lithium-ion battery according to claim 1, characterized in that: The radial dimension a of a single recess in the recessed area is 0.3 to 2 mm; and / or the depth b of a single recess in the recessed area is 5 to 50 μm; and / or the number of the single recesses in the recessed area is greater than or equal to 50.

6. The lithium-ion battery according to claim 1, characterized in that The non-fluorine adhesive includes one or more of PAA, PAN and PMMA; and / or, the weight average molecular weight of the non-fluorine adhesive is 1 million to 1.3 million; And / or, the particle size of the non-fluorine adhesive is 50 to 80 μm; And / or, the swelling rate of the non-fluorine adhesive in the electrolyte is 20% to 50%; And / or, the dissolution rate of the non-fluorine adhesive in the electrolyte is less than 10%.

7. The lithium-ion battery according to claim 1, characterized in that: The cohesive force between particles in the positive electrode active material layer in the bending area is greater than 30 N / m, and / or the porosity of the positive electrode active material layer in the straight area is 15% to 20%.

8. The lithium ion battery according to any one of claims 1 to 7, characterized in that: The positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; And / or, the Dv50 particle size of the positive electrode active material is 10 to 20 μm; And / or, the specific surface area of ​​the positive electrode active material is 0.1 to 0.5 m 2 / g.

9. The lithium ion battery according to any one of claims 1 to 7, characterized in that: The toughening agent includes one or more of a small molecule ester toughening agent, a rubber toughening agent and an ionic liquid; And / or, the mass content of the toughening agent in the positive electrode active material layer is 0.1% to 2.0%; And / or, the mass content of the conductive agent in the positive electrode active material layer is 1.0% to 2.0%; And / or, the mass content of the positive electrode active material in the positive electrode active material layer is 95.6% to 99%; And / or, the mass content of the non-fluorine binder in the positive electrode active material layer is 0.5% to 2.0%.

10. The lithium ion battery according to any one of claims 1 to 7, characterized in that: The elongation rate of the positive electrode sheet is 0.8% to 1.3%.

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