Positive pole piece, preparation method and battery

Abstract

The invention provides a positive pole piece. The positive pole piece comprises a positive current collector, safe coating points distributed on the surface of the positive current collector, and a positive active material layer covering the surface of the positive current collector and the safe coating points, the area, covered by the safe coating points, of the surface of the positive current collector is a first area, the safe coating points are discontinuously distributed on the positive current collector to form a conductive gap, the area, exposed out of the conductive gap, of the surface of the positive current collector is a second area, and the conductive gap and the second area are filled with the positive material, so that the positive material is electrically conducted with the positive current collector; the area of the conductive gap accounts for 10%-90% of the area of the positive electrode current collector; according to the invention, the plurality of safe coating points are formed on the surface of the positive current collector, so that the anti-puncture capability and the safety performance of the positive pole piece can be improved; the safe coating points are discontinuously distributed on the positive current collector to form conductive gaps, and the conductive gaps are convenient for ions in the positive active material layer to pass through and are electrically connected with the positive current collector, so that the conductivity of the positive pole piece is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode sheet and a preparation method thereof, and a battery. Background Art The current market is paying more and more attention to the safety performance of batteries, such as needle penetration tests. Figure 1 and Figure 5 As shown, the conventional positive electrode sheet is an aluminum foil directly coated with active material. When the needle puncture test is carried out, the positive and negative electrodes are short-circuited, and the burrs of the aluminum foil pierce the separator and come into direct contact with the negative electrode active material and copper foil, causing a sharp increase in heat generation, resulting in the battery cell catching fire and failing.

[0002] like Figure 2 As shown, the prior art first coats a layer of safety primer on the aluminum foil, and then coats the positive electrode active material on the safety primer. In this way, when the puncture test is performed, the burrs of the aluminum foil are blocked by the safety primer, and there will be no direct contact between the aluminum foil and the negative electrode active material or copper foil, which greatly reduces the heat generation and improves the battery safety performance. However, the problem with the prior art is that the safety primer is costly and inefficient, and the safety primer has poor conductivity, the electrical connection between the aluminum foil and the active material is poor, the internal resistance of the battery is greatly increased, and the dynamic performance is deteriorated.

[0003] Therefore, how to overcome the above-mentioned technical problems and defects becomes a key issue that needs to be solved. Summary of the invention

[0004] In view of the problems of high cost, low efficiency and poor conductivity of existing safety primers, the present invention provides a positive electrode plate and a preparation method and a battery.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows: The first aspect of the present invention provides a positive electrode sheet, comprising a positive electrode current collector, safety coating points distributed on the surface of the positive electrode current collector, and a positive electrode active material layer covering the surface of the positive electrode current collector and the safety coating points; The area on the surface of the positive electrode current collector covered by the safety coating is the first area, the safety coating is discontinuously distributed on the positive electrode current collector to form a conductive gap, the area on the surface of the positive electrode current collector exposed from the conductive gap is the second area, and the positive electrode material is filled in the conductive gap and the second area, so that the positive electrode material is electrically conductive with the positive electrode current collector; The area ratio of the conductive gap to the area ratio of the positive electrode current collector is 10%-90%.

[0006] Optionally, the distance between two adjacent conductive gaps is 10 μm to 200 μm.

[0007] Optionally, the ratio of the maximum area to the minimum area of ​​the safety coating point is (1.5-3):1.

[0008] Optionally, the safety coating includes ceramic material, and the ceramic material includes one or more of aluminum oxide, zirconium oxide, magnesium oxide, silicon oxide, silicon nitride, and boron nitride.

[0009] Optionally, the safety coating point also includes lithium iron phosphate. Taking the total mass of the safety coating point as 100%, the mass percentage of the ceramic material in the safety coating point is 10%-95%; the mass percentage of the lithium iron phosphate in the safety coating point is 0-85%.

[0010] Optionally, the safety coating point also includes a binder and a conductive agent. Taking the total mass of the safety coating point as 100%, the mass percentage of the binder in the safety coating point is 1.5%-4.5%; the mass percentage of the conductive agent in the safety coating point is 0.5%-3.5%.

[0011] A second aspect of the present invention provides a method for preparing a positive electrode sheet, comprising the following preparation process: S1. Spray the safety slurry on the surface of the positive current collector and dry it to form safety coating points, wherein the area on the surface of the positive current collector covered by the safety coating points is the first area; the safety coating points are discontinuously distributed on the positive current collector to form a conductive gap, and the area on the surface of the positive current collector exposed by the conductive gap is the second area; S2. Coating the positive electrode slurry on the conductive gap, the second region and the surface of the safety coating point, and filling the conductive gap and the second region with the positive electrode slurry so that the positive electrode material is electrically conductive with the positive electrode collector, and drying to obtain a positive electrode sheet.

[0012] Optionally, in step S1, the method for preparing the safety slurry includes the following process: S11. The ceramic material is mixed evenly with the NMP solvent to form a safe slurry having a solid content of 29%-31% and a viscosity of 300-1000mPas; or, S12. Mix the ceramic material with lithium iron phosphate, mix them evenly in NMP solvent, and form a safe slurry with a solid content of 29%-31% and a viscosity of 300-1000 mPas.

[0013] Optionally, in step S1, the spraying method is: spraying the safety slurry on the surface of the positive electrode current collector so that the area of ​​the positive electrode current collector surface covered by the safety coating points accounts for 10%-90% of the area of ​​the positive electrode current collector.

[0014] Optionally, in step S1, the process of "spraying the safety slurry on the surface of the positive electrode current collector and drying it to form safety coating spots" is: spraying the safety slurry on one side of the positive electrode current collector and drying it to form safety coating spots; then spraying the safety slurry on the other side of the positive electrode current collector and drying it to form safety coating spots.

[0015] A third aspect of the present invention provides a battery, comprising a negative electrode sheet, a separator, and the positive electrode sheet as described above or the positive electrode sheet prepared by the method for preparing the positive electrode sheet as described above.

[0016] According to the pole piece provided by the present invention, by forming a plurality of safety coating points on the surface of the positive electrode current collector, the puncture resistance and safety performance of the positive electrode pole piece can be improved; the safety coating points are discontinuously distributed on the positive electrode current collector to form a conductive gap, and the conductive gap facilitates the passage of ions in the positive electrode active material layer to achieve electrical connection with the positive electrode current collector, thereby improving the conductive performance of the positive electrode pole piece. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 It is a schematic diagram of the structure of an existing positive electrode sheet without a safety primer layer; Figure 2 It is a schematic diagram of the structure of an existing positive electrode sheet with a safety primer layer; Figure 3 is a schematic structural diagram of a positive electrode sheet provided by an embodiment of the present invention; Figure 4 is a schematic top view of a positive electrode current collector in a positive electrode sheet provided by an embodiment of the present invention; Figure 5 It is a schematic diagram of the needle puncture of the existing positive electrode sheet without a safety primer layer; Figure 6 Schematic diagram of acupuncture of a positive electrode sheet provided by an embodiment of the present invention; The reference numerals in the drawings of the specification are as follows: 1-positive electrode plate; 11-positive electrode current collector; 111-first region; 112-second region; 12-safety coating point; 13-positive electrode active material layer; 14-conductive gap; 2-negative electrode plate; 21-negative electrode current collector; 22-negative electrode active material layer; 3-diaphragm. DETAILED DESCRIPTION

[0019] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] In the description of the present invention, it should be understood that the terms "longitudinal", "radial", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0021] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] like Figure 3-Figure 4 As shown, in one embodiment, the first aspect of the present invention provides a positive electrode sheet 1, including a positive electrode collector 11, safety coating points 12 distributed on the surface of the positive electrode collector 11, and a positive electrode active material layer 13 covering the surface of the positive electrode collector 11 and the safety coating points 12; The area on the surface of the positive electrode current collector 11 covered by the safety coating 12 is the first area 111. The safety coating 12 is discontinuously distributed on the positive electrode current collector 11 to form a conductive gap 14. The area on the surface of the positive electrode current collector 11 exposed from the conductive gap 14 is the second area 112. The positive electrode material is filled in the conductive gap 14 and the second area 112, so that the positive electrode material is electrically conductive with the positive electrode current collector 11. The area ratio of the conductive gap 14 to the area ratio of the positive electrode current collector 11 is 10%-90%.

[0023] Specifically, the area of ​​the conductive gap 14 accounts for the area ratio of the positive electrode current collector 11, which is any point value among 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%, or a range value consisting of any two point values; in a preferred embodiment, the area of ​​the conductive gap 14 accounts for 30%-60% of the area of ​​the positive electrode current collector 11.

[0024] When the area ratio of the conductive gap 14 to the area ratio of the positive electrode current collector 11 is 10%-90%, the battery cell needle puncture pass rate reaches more than 90%, and the internal resistance is reduced by 10-30% compared with the conventional safety primer (conductive gap 14 area ratio <10%), the battery capacity is increased by 0.5%-2%, and the energy density is increased by 0.5%-2%; when the area ratio of the conductive gap 14 to the area ratio of the positive electrode current collector 11 is less than 10%, the battery internal resistance will be too large, affecting the battery capacity and reducing the battery energy density; when the area ratio of the conductive gap 14 to the area ratio of the positive electrode current collector 11 is greater than 90%, the battery cell needle puncture pass rate will be less than 90%.

[0025] The present invention forms a plurality of safety coating points 12 on the surface of the positive electrode current collector 11 , thereby improving the anti-puncture capability and safety performance of the positive electrode plate 1 .

[0026] The safety coating points 12 are discontinuously distributed on the positive current collector 11 to form conductive gaps 14 . The conductive gaps 14 facilitate the passage of ions in the positive active material layer 13 and achieve electrical connection with the positive current collector 11 , thereby improving the conductivity of the positive electrode sheet 1 .

[0027] like Figure 3-Figure 4 As shown, in one embodiment, the distance between two adjacent conductive gaps 14 is 10 μm-200 μm.

[0028] Specifically, the distance between two adjacent conductive gaps 14 is any point value among 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm or 200μm, or a range value consisting of any two point values; in a preferred embodiment, the distance between two adjacent conductive gaps 14 is 50μm~150μm.

[0029] When the distance between two adjacent conductive gaps 14 is 10μm~200μm, the extension of foil burrs generated during needle puncture can be well blocked, and the smaller the distance between the conductive gaps 14, the better the blocking effect; when the distance between two adjacent conductive gaps 14 is less than 10μm, the technical effect is close to that of conventional safety primer, and there is no internal resistance advantage; when the distance between two adjacent conductive gaps 14 is greater than 200μm, the technical effect is close to that of no safety primer, and the needle puncture pass rate cannot be improved.

[0030] like Figure 3-Figure 4 As shown, in one embodiment, the ratio of the maximum area to the minimum area of ​​the safety paint point 12 is (1.5-3):1.

[0031] Specifically, the ratio of the maximum area to the minimum area of ​​the safety paint dots 12 is any point value among 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3:1, or a range value consisting of any two point values; in a preferred embodiment, the ratio of the maximum area to the minimum area of ​​the safety paint dots 12 is (2-2.5):1.

[0032] When the ratio of the maximum area to the minimum area of ​​the safety coating points 12 is (1.5-3):1, that is, the safety coating points 12 are relatively evenly distributed on the positive electrode current collector 11, which can effectively block the extension of the burrs of the positive electrode current collector 11 during needle puncture; when the ratio of the maximum area to the minimum area of ​​the safety coating points 12 is less than 1.5:1, the size of the safety coating points 12 is similar, but the conductive gap 14 increases, and the technical effect is close to that of no safety primer, which will reduce the needle puncture pass rate; when the ratio of the maximum area to the minimum area of ​​the safety coating points 12 is greater than 3:1, the size of the safety coating points 12 is uneven, the conductive gap 14 is small, and the technical effect is close to that of conventional safety primers, without internal resistance advantages.

[0033] like Figure 3-Figure 4 As shown, in one embodiment, the safety coating 12 includes a ceramic material, and the ceramic material includes one or more of aluminum oxide, zirconium oxide, magnesium oxide, silicon oxide, silicon nitride, and boron nitride.

[0034] Specifically, the ceramic material also includes Li 1.5 Al0.5Ti 1.5 (PO 4 ) 3 , Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 , Li 10 G 2 S 12 , Li6.5 La 3 Zr 1.5 Ta 1.5 O 12 , Li 7 La 3 Zr 2 O 12 , Li 5 La 3 Ta 2 O 12 , Li 5 La 3 Nb 2 O 12 One or more of the .

[0035] The ceramic material of the invention has good electrical conductivity and puncture resistance, and has a stable structure and good performance.

[0036] like Figure 3-Figure 4 As shown, in one embodiment, the safety coating point 12 also includes lithium iron phosphate. Taking the total mass of the safety coating point 12 as 100%, the mass percentage of the ceramic material in the safety coating point 12 is 10%-95%; the mass percentage of the lithium iron phosphate in the safety coating point 12 is 0-85%.

[0037] Specifically, the mass percentage of ceramic material in the safety coating point 12 is any point value among 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%, or a range value consisting of any two point values; in a preferred embodiment, the mass percentage of ceramic material in the safety coating point 12 is 50%-80%.

[0038] When the mass percentage of ceramic material in the safety coating point 12 is 10%-95%, the presence of ceramic material can effectively block the extension of the burrs of the positive electrode collector 11 during needle puncture; when the mass percentage of ceramic material in the safety coating point 12 is less than 10%, there is less ceramic material and the needle puncture improvement effect is not good; when the mass percentage of ceramic material in the safety coating point 12 is greater than 95%, there is more ceramic material, the conductivity of the electrode becomes worse, and there is no internal resistance advantage.

[0039] Specifically, the mass percentage of lithium iron phosphate in the safety coating point 12 is any point value among 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%, or a range value consisting of any two point values; in a preferred embodiment, the mass percentage of lithium iron phosphate in the safety coating point 12 is 15%-45%.

[0040] When the mass percentage of lithium iron phosphate in the safety coating point 12 is 0-85%, the presence of lithium iron phosphate can provide additional capacity support for the battery and can also slightly improve the pass rate of needle puncture; when the mass percentage of lithium iron phosphate in the safety coating point 12 is greater than 85%, the amount of ceramic material added will be reduced and the improvement effect of needle puncture will be poor.

[0041] like Figure 3-Figure 4 As shown, in one embodiment, the safety coating point 12 also includes a binder and a conductive agent. Taking the total mass of the safety coating point 12 as 100%, the mass percentage of the binder in the safety coating point 12 is 1.5%-4.5%; the mass percentage of the conductive agent in the safety coating point 12 is 0.5%-3.5%.

[0042] Specifically, the mass percentage of the adhesive in the safety coating point 12 is any point value among 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or 4.5%, or a range value consisting of any two point values; in a preferred embodiment, the mass percentage of the adhesive in the safety coating point 12 is 2-4%.

[0043] Specifically, the binder includes one or more of PVDF, PAA, PAM, SBR, and PMMA.

[0044] Specifically, the mass percentage of the conductive agent in the safety coating point 12 is any point value among 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or 3.5%, or a range value consisting of any two point values; in a preferred embodiment, the mass percentage of the conductive agent in the safety coating point 12 is 1-3%.

[0045] Specifically, the conductive agent includes one or more of carbon nanotubes, conductive carbon black, Ketjen black, acetylene black, carbon fiber, and graphene.

[0046] A second aspect of the present invention provides a method for preparing a positive electrode plate 1, comprising the following preparation process: S1. Spray the safety slurry on the surface of the positive current collector 11, dry it to form a safety coating point 12, and the area on the surface of the positive current collector 11 covered by the safety coating point 12 is the first area 111; the safety coating point 12 is discontinuously distributed on the positive current collector 11 to form a conductive gap 14, and the area on the surface of the positive current collector 11 exposed by the conductive gap 14 is the second area 112; S2. The positive electrode slurry is coated on the conductive gap 14, the second region 112 and the surface of the safety coating point 12. The positive electrode slurry is filled in the conductive gap 14 and the second region 112, so that the positive electrode material is electrically connected with the positive electrode collector 11, and the positive electrode sheet is obtained by drying.

[0047] Specifically, in step S1, the safety slurry is sprayed on the surface of the positive electrode current collector 11 and dried to form the safety coating 12, which can improve the puncture resistance and safety performance of the positive electrode plate 1. The area of ​​the conductive gap 14 accounts for 10%-90% of the area of ​​the positive electrode current collector 11.

[0048] In step S2 , the positive electrode slurry is filled in the conductive gap 14 and the second region 112 , so as to facilitate the passage of ions in the positive electrode active material layer 13 and achieve electrical connection with the positive electrode current collector 11 , thereby improving the conductivity of the positive electrode sheet 1 .

[0049] like Figure 3-Figure 4 As shown, in one embodiment, in step S1, the method for preparing the safety slurry includes the following process: S11. The ceramic material is mixed evenly with the NMP solvent to form a safe slurry having a solid content of 29%-31% and a viscosity of 300-1000mPas; or, S12. Mix the ceramic material with lithium iron phosphate, mix them evenly in NMP solvent, and form a safe slurry with a solid content of 29%-31% and a viscosity of 300-1000 mPas.

[0050] Specifically, in step S11, 90-95% of ceramic material, 1-3% of conductive agent, 4-7% of binder and NMP solvent are mixed evenly to form a safe slurry; Specifically, in step S12, 10-50% of ceramic material, 45-85% of lithium iron phosphate, 1-3% of conductive agent, 4-7% of binder and NMP solvent are mixed evenly to form a safe slurry; Specifically, in step S11 and step S12, the solid content of the safety slurry is any point value of 29%, 29.5%, 30%, 30.5% or 31% or a range value consisting of any two point values; in a preferred embodiment, the solid content of the safety slurry is 15%-45%.

[0051] When the solid content of the safety slurry is 29%-31%, the safety slurry can be coated on the positive electrode current collector 11 more evenly, and the safety coating points 12 are evenly dispersed with good gaps; when the solid content of the safety slurry is less than 29%, the dispersion gaps of the safety coating points 12 will be larger after the safety slurry is coated; when the solid content of the safety slurry is greater than 31%, it will make the safety slurry coating difficult and the dispersion gaps of the safety coating points 12 will be too small.

[0052] Specifically, in step S11 and step S12, the viscosity of the safety slurry is any point value of 300mPas, 400mPas, 500mPas, 600mPas, 700mPas, 800mPas, 900mPas or 1000mPas or a range value consisting of any two point values; in a preferred embodiment, the viscosity of the safety slurry is 600-800mPas.

[0053] When the viscosity of the safety slurry is 300-1000mPas, the safety slurry can be coated on the positive electrode current collector 11 more evenly, the safety coating points 12 are evenly dispersed, and the conductive gap 14 is good; when the viscosity of the safety slurry is less than 300mPas, the safety slurry will be thinner and have greater fluidity, making it difficult for the safety coating points 12 to be evenly dispersed, and the conductive gap 14 will be too large or too small; when the viscosity of the safety slurry is greater than 1000mPas, the safety slurry will be too thick and have less fluidity, making it difficult to coat the positive electrode current collector 11, and the safety coating points 12 cannot be well dispersed, and the conductive gap 14 is too small.

[0054] like Figure 3-Figure 4 As shown, in one embodiment, in step S1, the spraying method is: spray the safety slurry on the surface of the positive electrode collector 11, so that the area of ​​the surface of the positive electrode collector 11 covered by the safety coating point 12 accounts for 10%-90% of the area of ​​the positive electrode collector 11.

[0055] Specifically, the safety slurry can be controlled by the slurry spraying equipment so that the safety slurry is evenly sprayed on the surface of the positive electrode current collector 11. By spraying the surface of the positive electrode current collector 11 1-9 times, the area of ​​the surface of the positive electrode current collector 11 covered by the safety coating points 12 accounts for 10%-90% of the area of ​​the positive electrode current collector 11. This can not only improve the anti-puncture ability and safety performance of the positive electrode plate 1, but also facilitate the ions in the positive active material layer 13 to be electrically connected to the positive electrode current collector 11 through the conductive gap 14, thereby improving the conductivity of the positive electrode plate 1.

[0056] like Figure 3-Figure 4 As shown, in one embodiment, in step S1, the process of "spraying the safety slurry on the surface of the positive electrode current collector 11, and drying to form the safety coating point 12;" is: spraying the safety slurry on one side of the positive electrode current collector 11, and drying to form the safety coating point 12; then spraying the safety slurry on the other side of the positive electrode current collector 11, and drying to form the safety coating point 12.

[0057] Specifically, safety coating dots 12 are formed on both sides of the positive current collector 11, which can not only improve the puncture resistance and safety performance of the positive electrode plate 1, but also facilitate the ions in the positive active material layer 13 to be electrically connected to the positive current collector 11 through the conductive gap 14, thereby improving the conductivity of the positive electrode plate 1.

[0058] like Figure 6 As shown, in one embodiment, the third aspect of the present invention provides a battery, including a negative electrode sheet, a separator 3 and a positive electrode sheet 1 as described above or a positive electrode sheet 1 prepared by the preparation method of the positive electrode sheet 1 as described above.

[0059] In one embodiment, the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder; the positive electrode active material includes lithium iron phosphate (LFP), lithium iron manganese phosphate (LMFP), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel oxide (LNO), ternary materials (NCM, NCA), lithium manganese-rich (LMR), lithium nickel manganese oxide (LNMO), lithium vanadium phosphate (Li 3 V 2 (PO 4 ) 3 ,LiVOPO 4 )

[0060] In some embodiments, the positive electrode conductive agent includes one or more of graphite, superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, carbon nanofibers, metal powders, metal fibers, and polyphenylene derivatives.

[0061] In some embodiments, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0062] In some embodiments, the mass percentage of each component in the positive electrode active material layer is: 96-98 wt % of positive electrode active material, 0.5-2 wt % of conductive agent, and 1.0-2.0 wt % of binder.

[0063] When the mass ratio of the positive electrode active material in the positive electrode active material layer is within the above range, the positive electrode plate 1 can have a higher lithium removal and insertion capacity, and the battery can have a higher capacity.

[0064] The positive electrode current collector 11 is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector 11 includes one or more of copper, nickel, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector 11 is selected from aluminum foil.

[0065] In some embodiments, the negative electrode sheet includes a negative electrode current collector 21 and a negative electrode active material layer coated on one or both sides of the negative electrode current collector 21 , wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a thickener.

[0066] In one embodiment, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes one or more of a graphite negative electrode material, a silicon-oxygen negative electrode material, a silicon-carbon negative electrode material, a silicon negative electrode material, a tin negative electrode material, a tin oxide negative electrode material, a tin alloy negative electrode material (Sn-Fe, Sn-Co, Sn-Cu, etc.), a lithium metal negative electrode material, a lithium alloy negative electrode material (Li-Ag, Li-Al, Li-Sn, Li-Mg, Li-Zn, Li-In, Li-Ga, etc.), and a lithium-free negative electrode material.

[0067] In some embodiments, the negative electrode conductive agent includes one or more of graphite, superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, carbon nanofibers, metal powders, metal fibers, and polyphenylene derivatives.

[0068] In some embodiments, the negative electrode binder includes one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, and polymethacrylic acid.

[0069] In some embodiments, the thickening agent includes one or more of sodium alginate, sodium carboxymethyl cellulose, and carboxymethyl chitosan.

[0070] In some embodiments, the mass percentage of each component in the negative electrode active material layer is: 96%-97% of negative electrode active material, 0.5%-1.5% of conductive agent, 1%-2% of binder and 0.5%-1.5% of thickener.

[0071] The negative electrode current collector 21 is selected from metal materials that can conduct electrons. Preferably, the negative electrode current collector 21 includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector 21 is selected from copper foil.

[0072] The negative electrode sheet 2 can be prepared according to conventional methods in the art. For example, the negative electrode active material layer is usually prepared by coating a negative electrode slurry made of a negative electrode active material, a negative electrode conductive agent, a negative electrode binder and any other components on the negative electrode current collector 21, followed by drying and cold pressing. The solvent can be an aqueous solvent, but is not limited thereto.

[0073] Specifically, the diaphragm 3 can be selected from one or more materials such as polypropylene (PP), polyethylene (PE), PP / PE / PP composite film, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ceramic diaphragm 3, ceramic polyamide (PI), aramid (AF), non-woven fabric, etc.

[0074] In a preferred embodiment, the production of the battery includes the following steps: The positive electrode sheet 1, the separator 3 and the negative electrode sheet 2 are stacked in order, so that the separator 3 is located between the positive and negative electrodes to play an isolating role. The electrode sheet and the separator 3 are placed in the aluminum-plastic film bag formed by punching and forming by stacking. The electrolyte, gel electrolyte or solid electrolyte prepared as above are respectively injected into the baked and dried battery cell. After vacuum packaging, standing, formation and other processes, a battery is obtained.

[0075] The beneficial effects of the present invention are further illustrated below in conjunction with embodiments.

[0076] In order to make the invention purpose, technical scheme and beneficial technical effect of the present invention clearer, the present invention is further described in detail below in conjunction with examples. However, it should be understood that the examples of the present invention are only for explaining the present invention, not for limiting the present invention, and the examples of the present invention are not limited to the examples given in the specification. The specific experimental conditions or operating conditions not specified in the examples are prepared under conventional conditions, or prepared under the conditions recommended by the material supplier.

[0077] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0078] In the following examples, the reagents, materials and instruments used, unless otherwise specified, can be purchased commercially or obtained by synthetic methods known in the art.

[0079] Table 1 Design of safety coating points of Examples 1-7 and Comparative Examples 1-5; Example 1 This embodiment is used to illustrate the positive electrode sheet and battery disclosed in the present invention; it includes the following operating steps: Preparation of safe slurry: The ceramic material and the NMP solvent are mixed evenly to form a safe slurry with a solid content of 30% and a viscosity of 600 mPas; Preparation of positive electrode: The safety slurry is sprayed on one side of the positive electrode current collector surface, dried and solidified to form a 6μm thick safety coating point; and a conductive gap is formed between two adjacent ceramic materials, and the distance of the conductive gap is 10μm; Spray the safety slurry on the other side of the positive electrode current collector, dry and solidify to form the same safety coating point; Lithium cobalt oxide, single-walled carbon nanotubes, conductive carbon black SP and binder PVDF are mixed in a ratio of 97.3:0.5:1.0:1.2 to prepare positive electrode slurry, which is coated on the surface of the above-mentioned safety coating point on a coating machine. After drying, rolling, die-cutting and other processes, a positive electrode sheet that meets the requirements is obtained.

[0080] Preparation of negative electrode sheet: Graphite, CMC additive, conductive carbon black SP and binder SBR are mixed in a ratio of 97:1.1:0.8:1.1 to form a slurry, which is then coated on the negative electrode collector on a coating machine. After drying, rolling, die-cutting and other processes, the negative electrode sheet that meets the requirements is obtained.

[0081] Preparation of electrolyte: LiPF 6 ) was dissolved in a mixed solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (the mass ratio of the three was 1:2:1) to obtain an electrolyte with a concentration of 1 mol / L.

[0082] Preparation of diaphragm: PE porous polymer film is used as the diaphragm substrate; Preparation of the battery: The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, and the separator is placed between the positive and negative electrodes to play an isolating role. Then the stacked electrode sheets and the separator are placed in the aluminum-plastic film bag formed by punching and forming. The non-aqueous electrolyte prepared above is respectively injected into the baked and dried battery cells. After vacuum packaging, standing, formation and other processes, a battery with a capacity of 1Ah is obtained.

[0083] Embodiment 2-8 Examples 2-8 are used to illustrate the positive electrode sheet and battery disclosed in the present invention, including most of the operating steps in Example 1, except that: The components, contents and parameters of the safety layer shown in Table 1 were used.

[0084] Comparative Examples 1-5 Comparative Examples 1-5 are used to illustrate the positive electrode sheet and battery disclosed in the present invention, including most of the operating steps in Example 1, except that: The components, contents and parameters of the safety layer shown in Table 1 were used. Performance Testing The batteries prepared in the above Examples 1 to 8 and Comparative Examples 1 to 5 were subjected to the following performance tests: Needle puncture test: Place a fully charged battery on a puncture table and fix a 3mm diameter nail in the center of the battery cell. Then penetrate the battery cell at a speed of 150mm / s to observe whether the battery cell catches fire.

[0085] Battery internal resistance test: the voltage at the last second of static state is V0, the voltage after 18s discharge is V1, the current during discharge is I, DCR=(V0-V1) / I; The test results are shown in Table 2.

[0086] Table 2 Electrochemical performance of lithium battery It can be seen from Table 2 that, compared with Comparative Example 3, when no safety coating is provided on the surface of the current collector, the puncture pass rate of Examples 1-3 cannot be improved.

[0087] Compared with Comparative Examples 1-2 and Comparative Example 5, Example 2 and Example 4-6 can effectively block the extension of foil burrs generated during needle puncture when the distance between two adjacent conductive gaps is 10μm~200μm. Within this range, the smaller the distance between the conductive gaps, the better the blocking effect; when the distance between two adjacent conductive gaps is less than 10μm, the technical effect is close to that of conventional safety primer, and the internal resistance of the battery is large; when the distance between two adjacent conductive gaps is greater than 200μm, the technical effect is close to that of no safety primer, and the needle puncture pass rate cannot be improved.

[0088] Compared with Comparative Examples 4-5, when the ratio of the maximum area to the minimum area of ​​the safety coating points in Example 5 and Examples 7-8 is (1.5-3):1, that is, the safety coating points are relatively evenly distributed on the positive electrode current collector, the extension of the burrs of the positive electrode current collector during puncture can be effectively blocked; when the ratio of the maximum area to the minimum area of ​​the safety coating points is less than 1.5:1, the size of the safety coating points is similar, but the number of conductive gaps increases, and the technical effect is close to that of no safety primer, which will reduce the puncture pass rate; when the ratio of the maximum area to the minimum area of ​​the safety coating points is greater than 3:1, the size of the safety coating points is uneven, the number of conductive gaps is small, the technical effect is close to that of conventional safety primers, and there is no internal resistance advantage.

[0089] Compared with Comparative Examples 1-3 and Comparative Example 5, when the area of ​​the conductive gap accounts for 10%-90% of the area of ​​the positive electrode collector, the cell needle puncture pass rate reaches more than 90%, and the internal resistance is reduced by 10-30% compared with the conventional safety primer (conductive gap area ratio <10%), the battery capacity is increased by 0.5%-2%, and the energy density is increased by 0.5%-2%; when the area of ​​the conductive gap accounts for less than 10% of the area of ​​the positive electrode collector, the technical effect is close to that of the conventional safety primer, which will cause the battery internal resistance to be too large, affect the battery capacity, and reduce the battery energy density; when the area of ​​the conductive gap accounts for more than 90% of the area of ​​the positive electrode collector, the technical effect is close to that of no safety primer, which will cause the cell needle puncture pass rate to be less than 90%.

[0090] In summary, the electrode sheet provided by the present invention can improve the anti-puncture ability and safety performance of the positive electrode sheet by forming a plurality of safety coating points on the surface of the positive electrode current collector; the safety coating points are discontinuously distributed on the positive electrode current collector to form a conductive gap, and the conductive gap facilitates the passage of ions in the positive electrode active material layer to achieve electrical connection with the positive electrode current collector, thereby improving the conductive performance of the positive electrode sheet.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A positive electrode sheet, characterized in that: It includes a positive electrode current collector, safety coating points distributed on the surface of the positive electrode current collector, and a positive electrode active material layer covering the surface of the positive electrode current collector and the safety coating points; The area on the surface of the positive electrode current collector covered by the safety coating is the first area, the safety coating is discontinuously distributed on the positive electrode current collector to form a conductive gap, the area on the surface of the positive electrode current collector exposed from the conductive gap is the second area, and the positive electrode material is filled in the conductive gap and the second area, so that the positive electrode material is electrically conductive with the positive electrode current collector; The area ratio of the conductive gap to the area ratio of the positive electrode current collector is 10%-90%.

2. The positive electrode sheet according to claim 1, characterized in that: The distance between two adjacent conductive gaps is 10 μm to 200 μm.

3. The positive electrode sheet according to claim 1, characterized in that: The ratio of the maximum area to the minimum area of ​​the safety coating point is (1.5-3):

1.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The safety coating includes ceramic materials, and the ceramic materials include one or more of aluminum oxide, zirconium oxide, magnesium oxide, silicon oxide, silicon nitride, and boron nitride.

5. The positive electrode sheet according to claim 4, characterized in that: The safety coating also includes lithium iron phosphate. Taking the total mass of the safety coating as 100%, the mass percentage of the ceramic material in the safety coating is 10%-95%; the mass percentage of the lithium iron phosphate in the safety coating is 0-85%.

6. The positive electrode sheet according to claim 5, characterized in that: The safety coating point also includes a binder and a conductive agent. Taking the total mass of the safety coating point as 100%, the mass percentage of the binder in the safety coating point is 1.5%-4.5%; the mass percentage of the conductive agent in the safety coating point is 0.5%-3.5%.

7. The method for preparing a positive electrode sheet according to any one of claims 1 to 6, characterized in that: The preparation process includes the following: S1. Spray the safety slurry on the surface of the positive current collector and dry it to form safety coating points, wherein the area on the surface of the positive current collector covered by the safety coating points is the first area; the safety coating points are discontinuously distributed on the positive current collector to form a conductive gap, and the area on the surface of the positive current collector exposed by the conductive gap is the second area; S2. Coating the positive electrode slurry on the conductive gap, the second region and the surface of the safety coating point, and filling the conductive gap and the second region with the positive electrode slurry so that the positive electrode material is electrically conductive with the positive electrode collector, and drying to obtain a positive electrode sheet.

8. The method for preparing a positive electrode sheet according to claim 7, characterized in that: In step S1, the method for preparing the safety slurry includes the following process: S11. The ceramic material is mixed evenly with the NMP solvent to form a safe slurry having a solid content of 29%-31% and a viscosity of 300-1000mPas; or, S12. Mix the ceramic material with lithium iron phosphate, mix them evenly in NMP solvent, and form a safe slurry with a solid content of 29%-31% and a viscosity of 300-1000 mPas.

9. The method for preparing a positive electrode sheet according to claim 7, characterized in that: In step S1, the spraying method is: spraying the safety slurry on the surface of the positive electrode current collector so that the area of ​​the positive electrode current collector surface covered by the safety coating points accounts for 10%-90% of the area of ​​the positive electrode current collector.

10. The method for preparing a positive electrode sheet according to claim 7, characterized in that: In step S1, the process of "spraying the safety slurry on the surface of the positive electrode current collector and drying to form safety coating spots" is: spraying the safety slurry on one side of the positive electrode current collector and drying to form safety coating spots; then spraying the safety slurry on the other side of the positive electrode current collector and drying to form safety coating spots.

11. A battery, characterized in that: The invention comprises a negative electrode sheet, a separator and a positive electrode sheet as claimed in any one of claims 1 to 6 or a positive electrode sheet prepared by the method for preparing a positive electrode sheet as claimed in any one of claims 7 to 10.

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