Current collector, positive pole piece and lithium ion battery

Abstract

The invention provides a current collector, a positive pole piece and a lithium ion battery. The current collector comprises a current collector base material; the carbon-coated layer is arranged on the surface of at least one side of the current collector base material along the thickness direction of the current collector base material, and the carbon-coated layer comprises a two-dimensional transition metal boride. According to the current collector, the positive pole piece and the lithium ion battery provided by the invention, the conductivity and the bonding performance of the current collector can be considered, the improvement of the fast charging capability is realized, and the energy density of the lithium ion battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power batteries, in particular to a current collector, a positive electrode sheet and a lithium ion battery. BACKGROUND

[0002] With the deepening of the concept of green energy, in order to improve the energy utilization rate, power and energy storage facilities have developed rapidly in the past decade. As an important single unit for energy storage, lithium ion batteries (LIBs) have received extensive attention. LIBs mainly include positive electrode, negative electrode, electrolyte, separator, and in the positive electrode / negative electrode, active main material, auxiliary material and current collector, etc. Among them, the current collector of the positive electrode is mainly aluminum, titanium, zinc, tin or nickel metal material. As an important component of the electrode sheet, the current collector affects the processing performance, electrical performance and safety performance of the lithium ion battery. SUMMARY

[0003] The present application provides a current collector, a positive electrode sheet and a lithium ion battery, which can balance the conductivity and adhesion of the current collector, improve the adhesion of the positive active layer and the current collector, improve the conductivity of the positive electrode sheet, realize the improvement of the fast charging capacity, and improve the energy density of the lithium ion battery.

[0004] To solve the above technical problems, the present application provides a current collector, comprising:

[0005] a current collector substrate; and

[0006] a carbon coating layer, the carbon coating layer is arranged on at least one side surface of the current collector substrate along the thickness direction thereof, and the carbon coating layer comprises a two-dimensional transition metal boride.

[0007] In an embodiment of the present application, the content of the two-dimensional transition metal boride in the carbon coating layer is 0.5wt%-5wt%.

[0008] In an embodiment of the present application, the two-dimensional transition metal boride comprises at least one of MoB, CrB, TiB, Mo2B, Mn2B2, Nb3B4, Ta3B4 or Cr3B4.

[0009] In an embodiment of the present application, the thickness of the carbon coating layer is 0.5μm-3μm.

[0010] In an embodiment of the present application, the carbon coating layer further comprises a carbon material and a binder, the carbon material comprises at least one of conductive carbon black, graphite, graphene or carbon nanotube, and the binder comprises at least one of polyacrylic acid, butadiene rubber, polyvinyl alcohol, polyacrylamide, methyl cellulose and its salt, alginic acid and its salt.

[0011] In an embodiment of the present application, the content of the carbon material in the carbon coating layer is 30wt%-38wt%, and the content of the binder in the carbon coating layer is 60wt%-65wt%.

[0012] In an embodiment of the present application, the current collector substrate is one or more of aluminum, titanium, zinc, tin, nickel, and alloys thereof, and the thickness of the current collector substrate is 10μm-25μm.

[0013] The present application also provides a positive electrode tab, comprising the current collector and the positive electrode active layer disposed on the carbon coating layer along the thickness direction of the current collector.

[0014] In an embodiment of the present application, the positive electrode active layer comprises a positive electrode active material and a positive electrode binder, the positive electrode active material comprises one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide; the positive electrode binder comprises at least one of polyvinylidene fluoride, polyacrylic acid, and derivatives thereof; and the mass ratio of the positive electrode active material to the positive electrode binder in the positive electrode active layer is (97.1-98.2):(1.0-2.0).

[0015] The present application also provides a lithium ion battery, comprising the positive electrode tab described above.

[0016] In summary, the present application provides a current collector, a positive electrode tab, and a lithium ion battery. By introducing a two-dimensional transition metal boride into the carbon coating layer of the current collector, the conductivity and adhesion performance can be considered due to the characteristics of the two-dimensional transition metal boride, the hydrogen bond between the two-dimensional transition metal boride and the positive electrode binder is easy to form, the adhesion between the positive electrode active layer and the carbon coating layer is improved, and thus the peeling force of the positive electrode tab is improved. At the same time, the conductivity of the positive electrode tab is greatly improved, the electronic transmission impedance is reduced, the polarization resistance of the battery is reduced, the kinetics of the lithium ion battery is improved, the fast charging capability is improved, and the heat generation of the battery is reduced. In addition, the content of the positive electrode active material is increased by reducing the content of the positive electrode binder and the positive electrode conductive agent in the positive electrode active layer, the capacity of the lithium ion battery is improved, and the mass energy density and the volume energy density of the lithium ion battery are improved, thereby improving the competitiveness of the product. DETAILED DESCRIPTION

[0017] The embodiments of the present application are described below by way of specific examples. Those skilled in the art can easily understand other advantages and effects of the present application from the disclosure of the specification. The present application can also be implemented or applied by different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0018] It is to be understood that the application can assume various alternative embodiments, and should not be limited to the examples described herein. Rather, the embodiments are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.

[0019] The technical solutions of the present application are further described in detail below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0020] The present application provides a current collector, comprising a current collector substrate and a carbon coating layer, wherein the carbon coating layer is arranged on at least one side surface of the current collector substrate along the thickness direction thereof, and the carbon coating layer comprises a two-dimensional transition metal boride. The current collector provided by the present application can improve the conductivity of the current collector and improve the adhesion between the current collector and the subsequent active layer.

[0021] In an embodiment of the present application, the current collector substrate is, for example, one or more of aluminum, titanium, zinc, tin, nickel, and alloys of each of them. The thickness of the current collector substrate is 10-25 μm to match different battery systems and meet the manufacturing requirements of lithium ion batteries.

[0022] In an embodiment of the present application, the carbon coating layer is arranged, for example, on one side surface of the current collector substrate along the thickness direction thereof, and is arranged, for example, on both side surfaces of the current collector substrate along the thickness direction thereof. The carbon coating layer comprises, for example, a two-dimensional transition metal boride (MBene), a carbon material, and a binder. In this embodiment, the two-dimensional transition metal boride comprises, for example, at least one of MoB, CrB, TiB, Mo2B, Mn2B2, Nb3B4, Ta3B4, or Cr3B4. The MBene is a two-dimensional boride composed of transition metal and boron atoms, and has a typical two-dimensional layered structure. Due to its own characteristics and the transition metal layer contained therein, the bonding (M-B) between the transition metal and the boron element determines that it has excellent conductivity. The transition metal on the surface is in an unstable state, and attracts anions with strong electronegativity (such as anions of the binder in the carbon coating layer) to combine on the surface, thereby introducing surface modification groups such as -F, -OH groups. The surface modification groups are easy to form hydrogen bonds with other compounds that can form hydrogen bonds, thereby improving the adhesion between the carbon coating layer and the subsequent positive active layer.

[0023] In an embodiment of the present application, the content of the two-dimensional transition metal boride in the carbon coating layer is, for example, 0.5wt%-5wt%. If the content of the two-dimensional transition metal boride is too low, it cannot play a good role and does not play a significant role in improving the adhesion; when the content of the two-dimensional transition metal boride is too high, although it can significantly improve the adhesion, due to the change of the proportion of other components, it will have a side effect on the internal resistance of the battery.

[0024] In an embodiment of the present application, the carbon material includes, for example, at least one of conductive carbon black (Super P), graphite, graphene or carbon nanotubes (CNT), and the binder includes, for example, at least one of polyacrylic acid (PAA), styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyacrylamide (PAM), methyl cellulose and its salt, alginic acid and its salt, etc. The content of the carbon material in the carbon coating layer is, for example, 30wt%-38wt%, and the content of the binder in the carbon coating layer is, for example, 60wt%-65wt%.

[0025] In an embodiment of the present application, the thickness of the carbon coating layer is 0.5μm-3μm. If the thickness of the carbon coating layer is too thin, the carbon coating layer is easy to be discontinuous, cannot form a complete conductive network, leads to the increase of the contact resistance between the current collector and the active material, uneven current conduction, and insufficient bonding force with the active layer, and easy interface peeling in charging and discharging. If the thickness of the carbon coating layer is too thick, it will lead to the decrease of the affinity between the carbon coating layer and the current collector substrate, lead to the delamination of the carbon coating layer-positive active layer test adhesion, thereby the adhesion ability decreases, at the same time, it will increase the proportion of non-active material of the battery, reduce the energy density, and the thick carbon coating layer is easy to be brittle and cracked, and fall off in charging and discharging cycle, cause the rapid increase of the internal resistance of the battery and the capacity attenuation. Therefore, the thickness of the carbon coating layer is controlled to improve the conductive performance and adhesion performance of the current collector, so as to improve the cycle performance of the lithium ion battery.

[0026] In an embodiment of the present application, two-dimensional transition metal boride, carbon material and binder and the like are mixed in a mass ratio, a solvent is added and mixed uniformly to obtain a carbon coating layer slurry, the carbon coating layer slurry is coated on at least one side of the current collector substrate and dried to obtain a current collector. The solvent is, for example, deionized water and the like, and the carbon coating layer slurry is obtained, for example, by stirring and grinding and the like, the stirring speed is, for example, 2000 rpm-4000 rpm, the stirring time is, for example, 15 min-60 min, after stirring, the slurry is sufficiently ground, for example, using a grinder, so that the D50 particle size of the carbon coating layer slurry is, for example, 15 nm-25 nm, the solid content is, for example, 40%-55%, and the viscosity is, for example, 200 mPa.s-230 mPa.s. The D50 particle size refers to the particle size corresponding to the cumulative particle volume of 50% in the particle population of the carbon coating layer slurry. The carbon coating layer slurry is prepared on the current collector substrate by the process flow of gravure coating, baking, electrophoresis and the like, the solvent in the carbon coating layer slurry is removed by baking at, for example, 90°C-110°C, the surface of the carbon coating layer is treated using an electrophoresis machine to maintain the adhesion and corrosion resistance of the carbon coating layer, and a current collector with a carbon coating layer of uniform thickness and density is obtained.

[0027] The present application also provides a positive electrode tab, which comprises a current collector and a positive electrode active layer, the current collector is, for example, selected from the above-mentioned current collectors, and the positive electrode active layer is arranged on the carbon coating layer along the thickness direction of the current collector. The positive electrode active layer comprises, for example, a positive electrode active material and a positive electrode binder and the like. The positive electrode active material comprises, for example, one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide and the like. The positive electrode binder is, for example, selected from at least one of polyvinylidene fluoride (PVDF), polyacrylic acid and its derivatives and the like, wherein the derivatives of polyacrylic acid include, but are not limited to, polyacrylate, polyacrylate, polyacrylate, polyacrylamide, anionic polyacrylamide or polyacrylic acid-polyethylene glycol graft copolymer and the like. The mass ratio of the positive electrode active material and the positive electrode binder in the positive electrode active layer is, for example, (97.1-98.2):(1.0-2.0). Since the MBene introduces a surface modification group on the surface of the carbon coating layer, the surface modification group is easy to form hydrogen bonds with the positive electrode binder, which improves the adhesion of the positive electrode active layer and the carbon coating layer, thereby improving the peel strength of the positive electrode tab, which can reduce the addition amount of the positive electrode binder in the positive electrode active layer, increase the content of the positive electrode active material, improve the capacity of the lithium ion battery, and accordingly improve the mass energy density and volume energy density of the lithium ion battery, and improve the competitiveness of the product.

[0028] In an embodiment of the present application, the positive active layer further comprises a positive conductive agent, for example, selected from one or a combination of two or more in any proportion of conductive carbon black, acetylene black, graphene, carbon nanotube, carbon nanofiber, or porous carbon, and the content of the positive conductive agent in the positive active layer is, for example, 0.5wt%-0.8wt%. Since the MBene in the carbon coating layer has excellent conductivity, it can greatly improve the conductivity of the positive electrode sheet, reduce the electron transmission impedance, and reduce the polarization resistance of the battery, thereby improving the kinetics of the lithium ion battery, achieving the improvement of the fast charging capability and reducing the heat generation of the battery. The improvement of the conductivity of the current collector can reduce the use amount of the positive conductive agent in the positive active layer, increase the content of the positive active material, and improve the energy density of the lithium battery. Therefore, the MBene in the carbon coating layer of the current collector has both conductivity and adhesion, thereby improving the adhesion strength of the positive electrode sheet, optimizing the conductivity of the positive electrode sheet, improving the fast charging capability and reducing the heat generation of the lithium ion battery, and increasing the content of the active material in the positive active layer, thereby improving the energy density of the lithium ion battery.

[0029] In another embodiment of the present application, the positive active layer further comprises a dispersant or the like to improve the uniformity of the positive active layer. The dispersant includes one or a combination of two or more in any proportion of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), styrene-maleic anhydride copolymer (SMA), or acrylic oligomer (AO), and the molecular weight of the dispersant is, for example, 50000-500000. In an embodiment of the present application, the dispersant is, for example, selected from polyvinylpyrrolidone with a molecular weight of 300000, and the content of the dispersant in the positive active layer is, for example, 0.1wt%-0.2wt%.

[0030] In one embodiment of the present invention, the positive electrode active material is selected, for example, from lithium iron phosphate; the positive electrode binder is selected, for example, from polyvinylidene fluoride; and the positive electrode conductive agent is selected, for example, from conductive carbon black. The positive electrode active material, positive electrode conductive agent, and positive electrode binder are mixed, for example, in a mass ratio of 97.6:0.8:1.6. An organic solvent is then added, and the mixture is stirred at 200 rpm-1300 rpm for 40-60 minutes under vacuum to obtain a positive electrode slurry. The viscosity of the positive electrode slurry is, for example, 7600 mPa·s-8000 mPa·s, and the solid content of the positive electrode slurry is, for example, 60%-70%. The organic solvent is, for example, selected from N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated onto the carbon coating layer of the current collector, such as by extrusion coating, with a coating surface density of, for example, 300 mg / 1540.25 mm². 2 -320mg / 1540.25mm 2 The material is then air-dried at room temperature and transferred to an oven for further drying. The positive electrode sheet is obtained through processes such as rolling, edge trimming, cutting, and slitting. In this embodiment, the thickness of the positive electrode active layer on one side is, for example, 75 μm-100 μm. This application does not limit the method of preparing the positive electrode sheet; in other embodiments, the positive electrode sheet can also be obtained by any other method of forming the positive electrode sheet.

[0031] This invention also proposes a lithium-ion battery, comprising a casing and a bare cell disposed within the casing. The bare cell includes a positive electrode, a separator, and a negative electrode. The positive electrode is selected from the aforementioned positive electrode types. The separator is placed between the positive and negative electrodes to prevent short circuits and allow lithium ions to pass through. The positive electrode, separator, and negative electrode are sequentially stacked to ensure that a separator is present between any positive and negative electrode. A multi-layered stack is obtained by winding or folding, and this stack is then inserted into the battery casing as the bare cell. Finally, electrolyte is injected into the casing once or in multiple stages to completely immerse the bare cell in the electrolyte, which then conducts ions between the positive and negative electrodes. In one embodiment of this invention, the lithium-ion battery is, for example, a primary battery or a secondary battery. A secondary battery is, for example, a pouch battery, a hard-shell battery, or a cylindrical battery. This invention does not specifically limit the type of lithium-ion battery. In this embodiment, a pouch battery is used as an example to illustrate the lithium-ion battery.

[0032] In an embodiment of the present application, the negative electrode sheet includes, for example, a negative electrode current collector and a negative electrode active layer coated on at least one side surface of the negative electrode current collector. The negative electrode current collector is selected, for example, from a foil material treated with nickel, titanium, gold, silver, chromium, molybdenum, copper, stainless steel, or carbon. In addition to the foil material, the negative electrode current collector can also be used in any one or a combination of multiple forms such as a film, a mesh, a porous material, a foam, or a non-woven fabric. The thickness of the negative electrode current collector is, for example, 6 μm to 15 μm. In this embodiment, the negative electrode current collector is selected, for example, as a copper foil, and the thickness of the copper foil is, for example, 8 μm.

[0033] In an embodiment of the present application, the negative electrode active layer is provided on either one or both surfaces of the negative electrode current collector, and includes a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and a thickening agent. The negative electrode active material is selected, for example, from graphite or a silicon-containing composite material, including natural graphite, artificial graphite, graphite / silicon oxide composite material, graphite / silicon carbon composite material, graphite / elemental silicon composite material, and the like. The negative electrode binder is selected, for example, from at least one of styrene butadiene rubber, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), carboxylated polyvinyl chloride (CPVC), polyvinyl fluoride (PVF), or polyurethane (PU). The thickening agent is selected, for example, from carboxymethyl cellulose sodium (CMC-Na) or carboxymethyl cellulose lithium (CMC-Li), and the negative electrode conductive agent is selected, for example, from one or a combination of two or more kinds of conductive carbon black, ketjen black, acetylene black, graphene, carbon nanotube, carbon nanofiber, or porous carbon, in any ratio. In an embodiment of the present application, the mass ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode binder, and the thickening agent in the negative electrode active layer is, for example, (91-98.5):(0.5-2):(0.5-5):(0.5-2).

[0034] In an embodiment of the present application, the negative electrode active material is selected, for example, from artificial graphite, the negative electrode conductive agent is selected, for example, from conductive carbon black, the thickening agent is selected, for example, from carboxymethyl cellulose sodium, and the negative electrode binder is selected, for example, from styrene butadiene rubber. The negative electrode active material, the negative electrode conductive agent, the thickening agent, and the negative electrode binder are mixed, for example, in a mass ratio of 97:0.5:0.5:2, deionized water is added, and the mixture is sufficiently stirred and mixed uniformly under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry is coated on a copper foil, then dried at room temperature, transferred to an oven for drying, and subjected to processes such as rolling, edge cutting, sheet cutting, and strip dividing to obtain a negative electrode sheet. The areal density of the negative electrode sheet is, for example, 130 mg / 1540.25 mm2 -150mg / 1540.25mm 2 The thickness of the negative electrode active layer on one side is, for example, 40 μm-70 μm. In other embodiments, the negative electrode sheet can also be obtained by any other method of forming the negative electrode sheet.

[0035] In one embodiment of the present invention, the separator is, for example, a polyethylene (PE) membrane, a polypropylene (PP) membrane, a glass fiber membrane, or a composite membrane, and the thickness of the separator is, for example, 9 μm-15 μm. In another embodiment of the present invention, the separator is, for example, selected as an 8 μm-10 μm polyethylene base membrane, and a 2 μm-4 μm thick nano-alumina coating is coated on at least one side of the base membrane.

[0036] In one embodiment of the present invention, the electrolyte includes, for example, an organic solvent and a lithium salt. The organic solvent is selected from one or more of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC). The lithium salt is selected from, for example, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), or lithium perchlorate (LiClO4). The electrolyte may also include additives, such as those selected from one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (1,3,2-Dioxathiolane 2,2-dioxide (DTD), lithium difluorooxalate borate (LiDFOB), or 1,3-propanesultone (1,3-PS). In this embodiment, in a glove box with an inert gas atmosphere such as argon containing a moisture content and an oxygen content of less than or equal to 0.1 ppm, ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate are mixed, for example, at a mass ratio of 3:5:2. Thoroughly dried LiPF6, VC, and LiDFOB are dissolved in the mixed organic solvent, and after thorough mixing, an electrolyte is obtained, wherein the content of LiPF6 is 12.5 wt%, the content of VC is 3 wt%, and the content of LiDFOB is 0.5 wt%.

[0037] In an embodiment of the present application, the positive electrode sheet, the separator, and the negative electrode sheet are sequentially placed with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and a bare battery cell is obtained by winding. The bare battery cell is loaded into an aluminum plastic film, baked at 80-100°C to remove water, and then injected with the electrolyte into the aluminum plastic film once or in multiple times, sealed, and then subjected to processes of standing, hot and cold pressing, assembly, formation, jigging, and capacity grading to obtain the soft package lithium ion battery.

[0038] The present application will be explained more specifically below by referring to examples, which should not be construed as limiting. Appropriate modifications can be made within the scope consistent with the gist of the present application, which all fall within the technical scope of the present application. Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by conventional methods in the art, and the instruments used in the examples are commercially available.

[0039] Example 1

[0040] Preparation of the current collector: MoB, conductive carbon black, and polyacrylic acid were added into a stirring tank at a mass ratio of 2:34:64, deionized water was added, and stirring was performed at 3000 rpm for 20 min for dispersion, and then a grinding machine was used to sufficiently grind the slurry to obtain a carbon coating layer slurry. The D50 particle size of the carbon coating layer slurry was 20 nm, the solid content was 45.5%, and the viscosity was 215 mPa.s. The carbon coating layer slurry was transferred to a slurry tank, and the aluminum foil was gravure coated and dried to obtain a current collector with a carbon coating layer. The thickness of the aluminum foil was 15 μm, and the carbon coating layer was formed on both sides of the aluminum foil, and the thickness of the single-sided carbon coating layer was 1 μm.

[0041] Preparation of the positive electrode sheet: lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride were mixed at a mass ratio of 97.6:0.8:1.6, and then dry mixed in a stirring tank for 30 min. NMP was added and mixed and stirred at 800 rpm for 60 min to obtain a positive electrode slurry with a viscosity of 7890 mPa.s and a solid content of 65.2%. The obtained positive electrode slurry was coated onto the carbon coating layer of the current collector, and the coating surface density was 303 mg / 1540.25 mm 2 Then, after air drying at room temperature, it was transferred to an oven for drying, and then subjected to processes of rolling, edge cutting, sheet cutting, and striping to obtain the positive electrode sheet. The single-sided thickness of the positive electrode active layer was 80 μm.

[0042] Preparation of the negative electrode sheet: artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber were mixed at a mass ratio of 97:0.5:0.5:2, deionized water was added, and the mixture was sufficiently stirred and mixed uniformly under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry was coated on a copper foil, and the coating surface density was 141 mg / 1540.25 mm 2Then, after being dried at room temperature, the negative electrode active material is transferred to an oven for drying, and then subjected to processes of rolling, trimming, cutting, and slitting to obtain the negative electrode sheet. The single-sided thickness of the negative electrode active layer is 59 pm.

[0043] Preparation of the electrolyte: In an argon atmosphere glove box with water content and oxygen content of 0.1 ppm, ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 3:5:2, and fully dried LiPF6, VC, and LiDFOB are dissolved in the mixed organic solvent to obtain the electrolyte. The content of LiPF6 is 12.5 wt%, the content of VC is 3 wt%, and the content of LiDFOB is 0.5 wt%.

[0044] Selection of the separator: A polypropylene film with a thickness of 12 pm is selected as the separator.

[0045] Preparation of the battery: The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play a role of isolation, and the stack is obtained as a bare cell. Then, the bare cell is placed in an aluminum plastic film, and after water removal at 100°C, the electrolyte is injected and sealed. After standing, hot and cold pressing, assembly, formation, clamping, and capacity distribution, a 100 Ah soft-pack lithium ion battery is obtained.

[0046] Example 2

[0047] In the preparation of the current collector, the mass ratio of MoB, conductive carbon black, and polyacrylic acid is 0.5:35.5:64, and the other steps remain the same as in Example 1.

[0048] Example 3

[0049] In the preparation of the current collector, the mass ratio of MoB, conductive carbon black, and polyacrylic acid is 1:35:64, and the other steps remain the same as in Example 1.

[0050] Example 4

[0051] In the preparation of the current collector, the mass ratio of MoB, conductive carbon black, and polyacrylic acid is 3:33:64, and the other steps remain the same as in Example 1.

[0052] Example 5

[0053] In the preparation of the current collector, the mass ratio of MoB, conductive carbon black, and polyacrylic acid is 4:32:64, and the other steps remain the same as in Example 1.

[0054] Example 6

[0055] In the preparation of the current collector, the mass ratio of MoB, conductive carbon black, and polyacrylic acid is 5:31:64, and the other steps remain the same as in Example 1.

[0056] Example 7

[0057] In the preparation of the positive electrode sheet, the mass ratio of lithium iron phosphate, conductive carbon black and polyvinylidene fluoride is 98:0.8:1.2, and other steps remain unchanged with Example 1.

[0058] Example 8

[0059] In the preparation of the positive electrode sheet, the mass ratio of lithium iron phosphate, conductive carbon black and polyvinylidene fluoride is 98.2:0.8:1.0, and other steps remain unchanged with Example 1.

[0060] Example 9

[0061] In the preparation of the positive electrode sheet, the mass ratio of lithium iron phosphate, conductive carbon black and polyvinylidene fluoride is 97.2:0.8:2.0, and other steps remain unchanged with Example 1.

[0062] Example 10

[0063] In the preparation of the current collector, MoB is replaced by Mo2B, and other steps remain unchanged with Example 1.

[0064] Example 11

[0065] In the preparation of the current collector, MoB is replaced by CrB, and other steps remain unchanged with Example 1.

[0066] Example 12

[0067] In the preparation of the current collector, the mass ratio of MoB, conductive carbon black, polyacrylic acid is 0.3:35.7:64, and other steps remain unchanged with Example 1.

[0068] Example 13

[0069] In the preparation of the current collector, the mass ratio of MoB, conductive carbon black, polyacrylic acid is 6:30:64, and other steps remain unchanged with Example 1.

[0070] Example 14

[0071] In the preparation of the current collector, the thickness of the single-sided carbon coating layer is 0.5 μm, and other steps remain unchanged with Example 1.

[0072] Example 15

[0073] In the preparation of the current collector, the thickness of the single-sided carbon coating layer is 2 μm, and other steps remain unchanged with Example 1.

[0074] Example 16

[0075] In the preparation of the current collector, the thickness of the single-sided carbon coating layer is 3 μm, and other steps remain unchanged with Example 1.

[0076] Example 17

[0077] In the preparation of the current collector, the thickness of the single-sided carbon coating layer is 3.5 μm, and the other steps remain the same as in Example 1.

[0078] Comparative Example 1

[0079] In the preparation of the current collector, no MBene is added, the mass ratio of conductive carbon black and polyacrylic acid is 36:64, and the other steps remain the same as in Example 1.

[0080] Comparative Example 2

[0081] No carbon coating layer is formed on the current collector, and the positive active layer is formed on the aluminum foil, and the other steps remain the same as in Example 1.

[0082] Comparative Example 3

[0083] In the preparation of the current collector, no MBene is added, and carbon nanotubes are added, and the mass ratio of carbon nanotubes, conductive carbon black and polyacrylic acid is 2:34:64, and the other steps remain the same as in Example 1.

[0084] Comparative Example 4

[0085] In the preparation of the current collector, no MBene is added, and the same mass of polyacrylic acid is replaced, i.e. the mass ratio of conductive carbon black and polyacrylic acid is 34:66, and the other steps remain the same as in Example 1.

[0086] In the present application, in Examples 1-17 and Comparative Examples 1-4, positive electrode sheets and lithium ion batteries are prepared using different current collectors, and the performance of the lithium batteries is tested, and the test results are shown in Table 1.

[0087] In an embodiment of the present application, in order to verify whether the performance of the current collector coated with the carbon coating layer meets the requirements, the adhesion test is performed on the current collector. Specifically, in the carbon coating layer area of the current collector, a sample with a width of 20 mm and a length of 120 mm is cut off, the sample is baked at 100°C for 10 minutes, then 3M tape is pasted on the carbon coating layer of the sample, a roller is rolled five times with a pressure of 50N, and then the 3M tape is peeled off. If the tape sticks to the carbon coating layer material, it is judged as unqualified.

[0088] In an embodiment of the present application, in order to verify the improvement of the adhesion of the current collector coated with the carbon coating layer to the positive active layer, the peeling force of the positive electrode sheet is tested. Specifically, a double-sided tape with a length of about 12 cm is adhered to a stainless steel plate along the marking line, and the prepared positive electrode sheet sample is adhered to the other side of the double-sided tape in the marked order. The positive electrode sheet is rolled once under a pressure of 50 N, and then the measured sample is placed on the measuring platform of the peeling force tester and fixed with screws before testing. The average value is displayed by intercepting the relatively stable tensile force data, and the peeling strength = selected average value (mN) / sample width (mm). The test is performed 10 times to obtain the average value.

[0089] In an embodiment of the present application, in order to evaluate the influence of the current collector coated with the carbon coating layer on the conductivity of the positive electrode sheet, a membrane resistance test is performed. Specifically, the positive electrode sheet is cut into a circular sheet with an area of 1540.25 mm 2 by a sheet press, and then placed in the middle of the membrane resistance tester to test the membrane resistance of the positive electrode sheet. The test results are read, and the test is performed 10 times to obtain the average value.

[0090] In an embodiment of the present application, in order to verify the improvement of the current collector added with MBene on the performance of the lithium ion battery, the capacity and direct current resistance (DCR) of the lithium ion battery in different groups are tested. In the capacity test, the battery is first discharged at a constant current of 0.5C to 2.0V, and in this embodiment, 1C is 100A. Then, the battery is charged at a constant current of 0.5C to 3.65V, and then at a constant voltage of 0.05C. The battery is discharged at a constant current of 0.5C to 2.0V, and the discharge capacity is recorded. The average value is calculated from the test results of 25 batteries in each embodiment and the comparative example, and is recorded as the capacity.

[0091] In an embodiment of the present application, the DCR test is performed in a 25°C constant temperature box. The lithium ion battery is placed for 1 h, and then charged at a constant current of 1C to 3.65V, and then charged at a constant voltage until the current is less than or equal to 0.05C. At this time, the state of charge (SOC) of the battery is 100%. The battery is left for 30 min, and then discharged at a constant current of 0.2C for 30 min to adjust the state of charge of the battery to 50%. The battery with a state of charge of 50% is left for another 30 min, and then discharged at a constant current of 0.2C for 30 s, and then discharged at a constant current of 1C for 5 s. The voltage U1 of the last 1 s of the discharge at a constant current of 0.2C, the voltage U2 of the last 1 s of the discharge at a constant current of 1C, the current I1 of the discharge at a constant current of 0.2C, and the current I2 of the discharge at a constant current of 1C are recorded. The DCR of the battery at 25°C, 50% SOC, and 1C constant current discharge for 30 s is calculated as (U2-U1) / (I2-I1).

[0092] In an embodiment of the present application, in order to evaluate the fast charging capability, the positive electrode sheet of the examples and comparative examples is specially prepared into a three-electrode sample battery. Specifically, in a dry environment, lithium sheet is wrapped with copper wire, the copper wire is selected to be copper wire soaked in sulfuric acid (H2SO4) to remove surface impurities, and repeatedly rolled to ensure the adhesion of the lithium sheet and the copper wire, which is used as a reference electrode. Two layers of separators are placed between the positive and negative electrode sheets, and the prepared reference electrode is placed between the two layers of separators. After injection and packaging, a three-electrode battery is prepared for standby. The 0% SOC three-electrode battery is placed in a 25°C constant temperature box for 2h. Then constant current charging is carried out, and when the potential difference between the negative electrode and the reference electrode is less than 0V, the time t1 is recorded and the test is paused. After 30min, constant current charging is carried out at 3C current and 3.65V cutoff, and when the potential difference between the negative electrode and the reference electrode is less than 0V, the time t2 is recorded and the test is paused. After 30min, constant current charging is carried out at 2.5C current and 3.65V cutoff, and when the potential difference between the negative electrode and the reference electrode is less than 0V, the time t3 is recorded and the test is paused. After 30min, constant current charging is carried out at 2C current and 3.65V cutoff, and when the potential difference between the negative electrode and the reference electrode is less than 0V, the time t4 is recorded and the test is paused. After 30min, constant current charging is carried out at 1.5C current and 3.65V cutoff, and when the potential difference between the negative electrode and the reference electrode is less than 0V, the time t5 is recorded and the test is paused. After 30min, constant current charging is carried out at 1C current and 3.65V cutoff, and when the potential difference between the negative electrode and the reference electrode is less than 0V, the time t6 is recorded and the test is paused. After 30min, constant current charging is carried out at 0.5C current and 3.65V cutoff, and when the potential difference between the negative electrode and the reference electrode is less than 0V, the time t7 is recorded and the test is paused. After 30min, constant current charging is carried out at 0.3C current and 3.65V cutoff, and when the potential difference between the negative electrode and the reference electrode is less than 0V, the time t8 is recorded and the test is paused. The total time of t1 to t8 is the fast charging time, and the shorter the time, the stronger the fast charging capability.

[0093] Table 1, performance of the current collector, positive electrode sheet and lithium ion battery in examples 1-17 and comparative examples 1-4

[0094]

[0095] Specifically, the positive electrode sheet prepared by the embodiment of the present application has excellent performance, specifically meets: the current collector adhesion force result is qualified, the positive electrode sheet resistance is ≤0.57Ω, the positive electrode sheet peeling force is ≥7.0N / m, the DCR is ≤0.50mΩ, the capacity is ≥100.0Ah, and the fast charging time is ≤28.0min. Specifically, four or more of the above are embodiments, and six or more of the above are preferred embodiments.

[0096] As shown in Table 1, it can be seen from Comparative Example 1 and Comparative Examples 1-2 that when the carbon coating layer is arranged on the current collector in the positive electrode sheet, the peeling force between the positive electrode active layer and the current collector can be improved, and the resistance of the positive electrode sheet can be effectively reduced, thereby reducing the DCR of the lithium ion battery and improving the fast charging performance of the lithium ion battery. As can be seen from Comparative Example 1 and Comparative Example 1, when MBene is added to the carbon coating layer, the adhesion test of the current collector is qualified, and the peeling force between the positive electrode active layer and the current collector is greatly improved, further reducing the resistance of the positive electrode sheet and the DCR of the lithium ion battery, and the fast charging capacity is obviously improved. As can be seen from Comparative Example 1 and Comparative Examples 3-4, when the carbon nanotube replaces MBene, the conductive capacity can be improved, and when the polyacrylic acid replaces MBene, the adhesion can be improved, but both materials cannot improve the conductive capacity and the adhesion at the same time. Therefore, by adding MBene to the carbon coating layer, the conductive capacity and the adhesion can be improved, thereby improving the adhesion strength of the positive electrode sheet and optimizing the conductive capacity of the positive electrode sheet, and improving the fast charging capacity of the lithium ion battery.

[0097] As shown in Table 1, it can be seen from Comparative Examples 1-6 and 12-13 that as the content of MBene in the carbon coating layer increases, the conductive capacity of the positive electrode sheet is obviously improved, the kinetics of the lithium ion battery is improved to a certain extent, and the peeling force of the positive electrode sheet is obviously improved. However, when the addition amount is less than 0.5wt%, it does not have a good effect; when the addition amount of MBene is greater than 5wt%, the adhesion test and the peeling force test of the positive electrode sheet are improved compared with Example 1, but the improvement effect on the resistance of the positive electrode sheet is poor. Therefore, when the addition amount of MBene is controlled to be 0.5wt%-5wt%, the peeling force of the positive electrode sheet and the comprehensive performance of the lithium ion battery are better.

[0098] As shown in Table 1, it can be seen from Comparative Examples 1, 7-9 and Comparative Example 1 that when MBene is included in the carbon coating layer, the peeling force of the positive electrode sheet is still obviously improved when the content of the positive electrode binder in the positive electrode active layer is reduced, thereby reducing the addition amount of the positive electrode binder in the positive electrode active layer, increasing the addition amount of the positive electrode active material, improving the capacity of the lithium ion battery, and meeting the user's demand. As can be seen from Comparative Examples 1 and 10-11, when different compounds of MBene are selected, they also have good conductive capacity and adhesion improving capacity, but different MBene has different effects on the adhesion and the fast charging performance, which can be selected according to the preparation demand.

[0099] As shown in Table 1, with the increase of the thickness of the carbon coating layer, the peeling force of the positive electrode sheet increases first and then decreases, the resistance of the positive electrode sheet decreases, the DCR of the lithium ion battery decreases, the capacity increases, and the fast charging time is shortened. Therefore, the thickness of the carbon coating layer is controlled to reduce the resistance of the positive electrode sheet, improve the capacity and fast charging time of the battery, and at the same time ensure the adhesion between the carbon coating layer and the positive active layer.

[0100] The application further provides an electronic device comprising at least one lithium ion battery as described above for providing electric energy. The electronic device can be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool, etc. In an embodiment of the application, the vehicle is a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle or an extended range vehicle, etc. The spacecraft includes an airplane, a rocket, a space shuttle and a spacecraft, etc. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy and an electric plane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembling electric tool and a railway electric tool, such as a power drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator and an electric planer, etc. The electronic device comprises the lithium ion battery as described above, and thus has the advantages of the lithium ion battery as described above, which will not be elaborated here.

[0101] In summary, the application provides a current collector, a positive electrode sheet and a lithium ion battery. By introducing a two-dimensional transition metal boride into the carbon coating layer of the current collector, the conductivity and adhesion performance can be considered due to the characteristics of the two-dimensional transition metal boride, the hydrogen bond between the positive electrode binder and the current collector is easy to form, the adhesion between the positive active layer and the carbon coating layer is improved, and thus the peeling force of the positive electrode sheet is improved. At the same time, the conductivity of the positive electrode sheet is greatly improved, the electron transmission impedance is reduced, the polarization resistance of the battery is reduced, the dynamics of the lithium ion battery is improved, the fast charging capability is improved, and the heat generation of the battery is reduced. In addition, the addition amount of the positive electrode binder and the positive electrode conductive agent in the positive active layer is reduced, the content of the positive active material is increased, the capacity of the lithium ion battery is improved, and the mass energy density and the volume energy density of the lithium ion battery are improved, and the competitiveness of the product is improved.

[0102] The above description is merely preferred embodiments of the application and a description of the principles of the technology used, and those skilled in the art should understand that the scope of the application disclosed in the application is not limited to the technical solutions formed by the specific combinations of the technical features described above, and also covers other technical solutions formed by any combination of the above technical features or equivalent features without departing from the inventive concept. For example, the above technical features can be replaced with technical features disclosed in the application (but not limited to) having similar functions to form a technical solution.

[0103] In addition to the technical features described in the specification, the remaining technical features are known to those skilled in the art, and in order to highlight the innovative features of the present application, the remaining technical features will not be described here.

Claims

1. A current collector, characterized in that, include: Current collector substrate; as well as A carbon coating layer is disposed on at least one side surface of the current collector substrate along its thickness direction, the carbon coating layer comprising a two-dimensional transition metal boride.

2. The current collector according to claim 1, characterized in that, The content of the two-dimensional transition metal boride in the carbon coating layer is 0.5wt%-5wt%.

3. The current collector according to claim 1, characterized in that, The two-dimensional transition metal borides include at least one of MoB, CrB, TiB, Mo2B, Mn2B2, Nb3B4, Ta3B4, or Cr3B4.

4. The current collector according to claim 1, characterized in that, The thickness of the carbon coating layer is 0.5μm-3μm.

5. The current collector according to claim 1, characterized in that, The carbon coating layer further includes carbon materials and a binder. The carbon materials include at least one of conductive carbon black, graphite, graphene, or carbon nanotubes. The binder includes at least one of polyacrylic acid, styrene-butadiene rubber, polyvinyl alcohol, polyacrylamide, methylcellulose and its salts, and alginate and its salts.

6. The current collector according to claim 5, characterized in that, The carbon material in the carbon coating layer has a content of 30wt%-38wt%, and the binder in the carbon coating layer has a content of 60wt%-65wt%.

7. The current collector according to claim 1, characterized in that, The current collector substrate is one or more of aluminum, titanium, zinc, tin, nickel and their respective alloys, and the thickness of the current collector substrate is 10μm-25μm.

8. A positive electrode sheet, characterized in that, It includes the current collector as described in any one of claims 1-7 and the positive electrode active layer disposed on the carbon coating layer along the thickness direction of the current collector.

9. The positive electrode sheet according to claim 8, characterized in that, The positive electrode active layer includes a positive electrode active material and a positive electrode binder. The positive electrode active material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide. The positive electrode binder includes at least one of polyvinylidene fluoride, polyacrylic acid, and their derivatives. The mass ratio of the positive electrode active material to the positive electrode binder in the positive electrode active layer is (97.1-98.2):(1.0-2.0).

10. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 8-9.

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