Positive pole piece, preparation method thereof and battery cell

Abstract

The invention provides a positive pole piece, a preparation method thereof and a battery cell, the positive pole piece comprises a current collector, and a first film layer and a second film layer which are sequentially arranged on the current collector, the material of the first film layer comprises a lithium-rich manganese-based material, and the material of the second film layer comprises lithium transition metal phosphate. The lithium transition metal phosphate particles and the lithium-rich manganese-based material particles can be directionally arranged through layered arrangement, so that crystal lattice cracks caused by expansion and shrinkage differences of the particles during direct mixing are reduced, and the stability of a conductive network is maintained; the lithium transition metal phosphate is arranged on the second film layer, and the lithium-rich manganese-based material is arranged on the bottom layer, so that the overcharge of the lithium-rich manganese-based material can be effectively relieved, the structural stability of the material is maintained, and the Li2MnO3 phase is ensured to slowly release lithium, thereby stably and permanently supplementing lithium for the phosphate.

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, as well as a battery cell. Background Art

[0002] Lithium transition metal phosphates with olivine structure have the advantages of being non-toxic, pollution-free, highly safe, and low-cost, and are considered to be very promising positive electrode materials for lithium-ion batteries. However, the cyclic capacity decay of lithium transition metal phosphate materials is relatively fast, which seriously hinders their application. To address this problem, one of the current methods to improve it is to directly blend lithium-rich manganese-based materials to make up for the loss of active lithium in lithium transition metal phosphate materials, thereby improving the long-cycle performance of lithium transition metal phosphate systems. However, since lithium transition metal phosphates have poor intrinsic electronic and ion conductivity, they have a high degree of polarization during the charge and discharge process. Direct blending with lithium-rich manganese-based materials can easily lead to overcharging of lithium-rich manganese-based materials, resulting in a large and irreversible phase change of Li2MnO3, a rapid decay of the material structure, and a large loss of active lithium, which is not conducive to long-cycle lithium replenishment. Summary of the invention

[0003] The embodiments of the present invention provide a positive electrode plate and a preparation method thereof, as well as a battery cell, which can improve the technical problems of overcharging and poor stability existing in existing lithium-ion batteries directly mixed with lithium-rich manganese-based materials.

[0004] In a first aspect, an embodiment of the present invention provides a positive electrode plate, comprising a current collector and a first film layer and a second film layer sequentially arranged on the current collector, wherein the material of the first film layer comprises a lithium-rich manganese-based material, and the material of the second film layer comprises a lithium transition metal phosphate.

[0005] In one embodiment, the material of the first film layer further includes lithium manganese oxide; and / or

[0006] The material of the first film layer also includes the lithium transition metal phosphate, and the mass ratio of the lithium transition metal phosphate to the lithium-rich manganese-based material in the first film layer is A:C, wherein 0%<A≤40%, 20%<C<99%.

[0007] In one embodiment, the chemical formula of the lithium transition metal phosphate is LiMn (1-x-y) Fe x M y PO4, wherein M is one or more metal elements, 0.8≥1-xy≥0.2, 0.8≥x≥0.2, y≤0.1; and / or

[0008] The chemical formula of the lithium-rich manganese-based material is Li d Ni a Co b Mn c A(1-a-b-c) O2, wherein A is one or more metal elements, 1.5>d>0, 1≥a≥0, 0.3≥b≥0, 1≥c≥0, 0.1≥1-abc; and / or

[0009] The chemical formula of the lithium manganese oxide is LiMn (2-y) D y O4, wherein D is one or more metal elements, and y≤0.1.

[0010] In one embodiment, the lithium transition metal phosphate is in a granular form, and the ratio of the minimum diameter to the maximum diameter of the Martin diameter of the lithium transition metal phosphate is (0.1-0.6):1; and / or

[0011] The lithium transition metal phosphate is in granular form, and the particle size D50 of the lithium transition metal phosphate is 0.5 μm to 2 μm; and / or

[0012] The lithium-rich manganese-based material is in a granular form, and the ratio of the minimum diameter to the maximum diameter of the Martin diameter of the lithium-rich manganese-based material is 0.2 to 0.8; and / or

[0013] The primary particles D50 of the lithium-rich manganese-based material are 100nm to 800nm, and the secondary particles D50 are 4μm to 9μm.

[0014] In one embodiment, the material of the second film layer further includes a lithium supplement.

[0015] In one embodiment, the material of the first film layer further includes lithium manganese oxide, the lithium transition metal phosphate, a first conductive agent and a first binder, and the mass percentage ratio of the lithium transition metal phosphate, the lithium manganese oxide, the lithium-rich manganese-based material, the first conductive agent and the first binder in the first film layer is A:B:C:D:(1-ABCD), wherein 0%<A≤40%, 0%≤B≤40%, 20%<C<99%, 0%<D≤7%, 0%<1-ABCD≤7%; and / or

[0016] The material of the second film layer also includes a second conductive agent and a second binder. The mass percentage ratio of the lithium transition metal phosphate material, the lithium supplement agent, the second conductive agent and the second binder in the second film layer is X:Y:Z:(1-XYZ), wherein 90%≤X≤98%, 0%<Y≤1%, 0%<Z≤3%, and 0%<1-XYZ≤4%.

[0017] In one embodiment, the mass ratio of the second film layer to the first film layer is (3-18):2; and / or

[0018] The ratio of the sum of the thickness of the first film layer and the thickness of the second film layer to the thickness of the current collector is (10-80):1; and / or

[0019] The surface density of the first film layer is 20 g / m 2 ~120g / m 2 The surface density of the second film layer is 90g / m 2 ~250g / m 2 .

[0020] In a second aspect, an embodiment of the present invention provides a method for preparing a positive electrode sheet, comprising the following steps:

[0021] Providing a current collector and a first film layer slurry, disposing the first film layer slurry on at least one side of the current collector to obtain a first film layer disposed on the current collector, wherein the first film layer slurry includes a lithium-rich manganese-based material;

[0022] A second film layer slurry is provided, and the second film layer slurry is disposed on a side of the first film layer away from the current collector to obtain a positive electrode sheet, wherein the second film layer slurry includes lithium transition metal phosphate.

[0023] In one embodiment, the method for preparing the first film layer slurry comprises the following steps:

[0024] Providing a lithium-rich manganese-based material, lithium manganate, lithium transition metal phosphate, a conductive agent, a binder and a solvent, mixing them to obtain a first film layer slurry; and / or

[0025] The method for preparing the second film layer slurry comprises the following steps:

[0026] A lithium transition metal phosphate, a lithium supplement agent, a conductive agent, a binder and a solvent are provided and mixed to obtain a second film layer slurry.

[0027] In a third aspect, an embodiment of the present invention provides a battery cell, comprising the above-mentioned positive electrode plate, or a positive electrode plate made by the above-mentioned method for making the positive electrode plate.

[0028] In an embodiment of the present invention, the lithium transition metal phosphate and the lithium manganese-rich based material can be arranged in layers through a layered arrangement, thereby reducing the generation of lattice cracks caused by the difference in expansion and contraction between the two during direct mixing, and maintaining the stability of the conductive network; by placing the lithium transition metal phosphate in the second film layer and the lithium manganese-rich based material in the bottom layer, the overcharge of the lithium manganese-rich based material can be effectively alleviated, the structural stability of the lithium manganese-rich based material can be maintained, and the slow release of lithium from the Li2MnO3 phase can be ensured, thereby stably and persistently replenishing lithium for the lithium transition metal phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 This is a scanning electron microscope (SEM) image of a cross section of a positive electrode sheet provided in Example 1 of the present invention (magnified 3000 times);

[0031] Figure 2 This is a scanning electron microscope (SEM) image (magnified 5000 times) of a cross section of a positive electrode sheet provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention. In the present invention, unless otherwise specified, the directional words used, such as "upper" and "lower", generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the drawings; while "inside" and "outside" refer to the outline of the device.

[0033] The technical solution of this application is as follows:

[0034] In a first aspect, an embodiment of the present application provides a positive electrode plate, comprising a current collector and a first film layer and a second film layer sequentially arranged on the current collector, wherein the material of the first film layer comprises a lithium-rich manganese-based material, and the material of the second film layer comprises a lithium transition metal phosphate.

[0035] In the present application, the particles of lithium transition metal phosphate and layered oxide (lithium-rich manganese-based material) are different in size, and the expansion and contraction degrees of the particles are quite different. The particles can be arranged in a directional manner through a layered arrangement, thereby reducing the generation of lattice cracks caused by the expansion and contraction differences between the two during direct mixing, and maintaining the stability of the conductive network; by placing the lithium transition metal phosphate in the second film layer and the lithium-rich manganese-based material in the bottom layer, the overcharge of the lithium-rich manganese-based material can be effectively alleviated, the structural stability of the lithium-rich manganese-based material can be maintained, and the slow release of lithium from the Li2MnO3 phase can be ensured, thereby stably and persistently replenishing lithium for the phosphate.

[0036] In some embodiments, the material of the first film layer further includes lithium manganese oxide.

[0037] In the present application, since lithium transition metal phosphate has poor electronic and ion conductivity, lithium manganate has much better ion conductivity than lithium transition metal phosphate, and lithium manganate is arranged in the first film layer to effectively improve the low temperature performance of lithium transition metal phosphate in the second film layer. At the same time, lithium manganate and lithium transition metal phosphate have different particle sizes, and the expansion and contraction degree of the particles are quite different. The particles can be arranged in a directional manner through layered arrangement, which reduces the generation of lattice cracks caused by the expansion and contraction differences of the particles during direct mixing, and maintains the stability of the conductive network.

[0038] In some embodiments, the material of the first film layer further includes lithium transition metal phosphate, and the mass ratio of the lithium transition metal phosphate to the lithium-rich manganese-based material in the first film layer is A:C, wherein 0%<A≤40%, 20%<C<99%.

[0039] In the present application, the lithium transition metal phosphate in the first film layer may be the same as or different from the lithium transition metal phosphate in the second film layer. The particles of lithium manganate and lithium-rich manganese-based materials are much larger than those of lithium transition metal phosphates, and mixing a small amount of lithium transition metal phosphates can increase the compaction of the pole piece.

[0040] In some embodiments, the lithium transition metal phosphate is in a granular form, and the ratio of the minimum diameter to the maximum diameter of the Martin diameter of the lithium transition metal phosphate is (0.1-0.6):1, for example, it can be 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, etc. Within this range, the size of the particles in the first film layer can be matched, thereby improving the compaction density of the pole piece.

[0041] In some embodiments, the lithium transition metal phosphate is in a granular form, and the particle size D50 of the lithium transition metal phosphate is 0.5-2 μm. Within this range, a combination of large and small particles can be achieved in the first film layer, thereby increasing the compaction density of the electrode.

[0042] In some embodiments, the lithium-rich manganese-based material is in granular form, and the ratio of the minimum diameter to the maximum diameter of the Martin diameter of the lithium-rich manganese-based material is 0.2 to 0.8, for example, it can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8. Within this range, the combination of large and small particles in the first film layer can be achieved, thereby improving the compaction density of the pole piece.

[0043] In some embodiments, the primary particle D50 of the lithium-rich manganese-based material is 100nm to 800nm, for example, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, etc. The secondary particle D50 of the lithium-rich manganese-based material is 4 to 9μm, for example, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, etc. In the present application, the secondary particles are agglomerated by the primary particles. Within this range, the size of the particles in the first film layer can be matched, thereby improving the compaction density of the pole piece.

[0044] In some embodiments, the material of the second film layer further includes a lithium supplement.

[0045] In the present application, the lithium replenisher can make up for the active lithium lost in the formation of the solid electrolyte interphase (SEI film) at the initial stage of the cycle, thereby improving the initial efficiency of the battery and the capacity retention rate of the system.

[0046] In some embodiments, the lithium supplement includes one or more of Li2O and Li2O2.

[0047] In some embodiments, the material of the first film layer also includes a first conductive agent and a first binder, and the mass percentage ratio of the lithium transition metal phosphate, lithium manganese oxide, lithium-rich manganese-based material, the first conductive agent and the first binder in the first film layer is A:B:C:D:(1-ABCD), wherein 0%<A≤40%, 0%≤B≤40%, 20%<C<99%, 0%<D≤7%, and 0%<1-ABCD≤7%.

[0048] In some embodiments, the material of the second film layer also includes a second conductive agent and a second binder, and the mass percentage ratio of the lithium transition metal phosphate material, the lithium supplement agent, the second conductive agent and the second binder in the second film layer is X:Y:Z:(1-XYZ), wherein 90%≤X≤98%, 0%<Y≤1%, 0%<Z≤3%, and 0%<1-XYZ≤4%.

[0049] In the present application, the first conductive agent and the second conductive agent may be the same or different. The first adhesive agent and the second adhesive agent may be the same or different.

[0050] As an example, the conductive agent in the material of the first film layer and the material of the second film layer independently includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0051] As an example, the binder in the material of the first film layer and the material of the second film layer independently includes one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0052] In some embodiments, the mass ratio of the lithium transition metal phosphate material, the lithium supplement agent, the conductive agent, and the binder in the second film layer is 96.8:0.7:1:1.5.

[0053] In some embodiments, the mass ratio of the second film layer to the first film layer is (3-18): 2. As an example, the mass ratio of the second film layer to the first film layer is 3:2, 4:2, 5:2, 6:2, 7:2, 8:2, 9:2, 10:2, 11:2, 12:2, 13:2, 14:2, 15:2, 16:2, 17:2 or 18:2.

[0054] In some embodiments, the mass ratio of the second film layer to the first film layer is 7:3.

[0055] In some embodiments, the ratio of the sum of the thickness of the first film layer and the thickness of the second film layer to the thickness of the current collector is (10-80):1, for example, it can be 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, etc.

[0056] In some embodiments, the ratio of the sum of the thickness of the first film layer and the second film layer to the thickness of the current collector is 25:1.

[0057] In some embodiments, the surface density of the first film layer is 20 g / m 2 ~120g / m 2 , for example, it can be 20g / m 2 , 30g / m 2 , 40g / m 2 , 50g / m 2 , 60g / m 2 , 70g / m 2 , 80g / m 2 , 90g / m 2 , 100g / m 2 , 110g / m 2 , 120g / m 2 The surface density of the second film layer is 90-250 g / m 2 , for example, it can be 90g / m 2 , 110g / m 2 , 130g / m 2 , 150g / m 2, 170g / m 2 , 190g / m 2 , 210g / m 2 , 230g / m 2 , 250g / m 2 wait.

[0058] In some embodiments, the lithium transition metal phosphate has the formula LiMn (1-x-y) Fe x M y PO4, wherein M is one or more metal elements, 0.8≥1-xy≥0.2, 0.8≥x≥0.2, y≤0.1.

[0059] In some embodiments, M includes but is not limited to at least one of Ti, Zr, Al, K, and Mg.

[0060] In some embodiments, the chemical formula of the lithium-rich manganese-based material is Li d Ni a Co b Mn c A (1-a-b-c) O2, wherein A is one or more metal elements, 1.5>d>0, 1≥a≥0, 0.3≥b≥0, 1≥c≥0, 0.1≥1-abc.

[0061] In some embodiments, A includes but is not limited to at least one of Ti, W, Al, K, and Mg.

[0062] In some embodiments, the primary particles of the lithium-rich manganese-based material are in the shape of strips, which can reduce side reactions and improve the kinetic performance of the battery.

[0063] In the present application, the shape of the primary particles can be a regular rectangular parallelepiped or an irregular strip.

[0064] In some embodiments, the chemical formula of lithium manganese oxide is LiMn (2-y) D y O4, wherein D is one or more metal elements, and y≤0.1.

[0065] In some embodiments, D includes but is not limited to at least one of Co, Cr, Ti, Al, and V.

[0066] In some embodiments, particles with a particle size of 0.5 to 2 μm account for 30% to 70% of the first film layer, for example, 30%, 40%, 50%, 60%, 70%, etc.

[0067] In some embodiments, particles with a particle size of 0.1 to 1 μm account for 30% to 70% of the second film layer, for example, 30%, 40%, 50%, 60%, 70%, etc.

[0068] In some embodiments, the open porosity of the positive electrode plate is 15% to 40%, for example, 15%, 20%, 25%, 30%, 35%, 40%, etc., and the open porosity ratio of the second film layer to the first film layer is 0.8 to 1.5, for example, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, etc. Within this range, the porosity of the plate is moderate, so that the plate can have a suitable impedance and low energy density.

[0069] In some embodiments, the specific adhesion of the positive electrode sheet is 0.05 to 40, for example, it can be 0.05, 5, 10, 15, 20, 25, 30, 35, 40, etc. The specific adhesion of the positive electrode sheet = the weight percentage A (%) of the binder in the sheet / the peeling force B (N) of the sheet.

[0070] In some embodiments, the powder resistivity of the positive electrode sheet after powder scraping is ≤300000Ω*cm, for example, it can be 250000Ω*cm, 200000Ω*cm, 150000Ω*cm, 100000Ω*cm, 50000Ω*cm, etc.

[0071] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode sheet, comprising the following steps:

[0072] S1. providing a current collector and a first film layer slurry, disposing the first film layer slurry on at least one side of the current collector to obtain a first film layer disposed on the current collector, wherein the first film layer slurry comprises a lithium-rich manganese-based material;

[0073] S2. Provide a second film layer slurry, and place the second film layer slurry on the side of the first film layer away from the current collector to obtain a positive electrode sheet, wherein the second film layer slurry includes lithium transition metal phosphate.

[0074] In step S1,

[0075] In some embodiments, the material of the first film layer further includes lithium manganese oxide.

[0076] In some embodiments, the material of the first film layer further includes lithium transition metal phosphate.

[0077] In some embodiments, the first film layer slurry further includes a conductive agent and a binder.

[0078] In some embodiments, the method for preparing the first film layer slurry comprises the following steps:

[0079] A lithium-rich manganese-based material, lithium manganate, lithium transition metal phosphate, a conductive agent, a binder and a solvent are provided and mixed to obtain a first film layer slurry.

[0080] In some embodiments, the first film layer slurry is disposed on at least one side of the current collector to obtain a first film layer disposed on the current collector, comprising:

[0081] The first film layer slurry is coated on at least one side of the current collector and dried to obtain the first film layer disposed on the current collector.

[0082] In some embodiments, the drying temperature is 80° C.-140° C., and the drying time is 8 h-24 h.

[0083] In step S2,

[0084] In some embodiments, the material of the second film layer further includes a lithium supplement.

[0085] In some embodiments, the second film layer slurry further includes a conductive agent and a binder.

[0086] In some embodiments, the method for preparing the second film layer slurry comprises the following steps:

[0087] A lithium transition metal phosphate, a lithium supplement agent, a conductive agent, a binder and a solvent are provided and mixed to obtain a second film layer slurry.

[0088] In some embodiments, the second film layer slurry is disposed on the side of the first film layer away from the current collector to obtain a positive electrode sheet, including:

[0089] The second film layer slurry is coated on the side of the first film layer away from the current collector, dried and pressed to obtain a positive electrode sheet.

[0090] In some embodiments, the drying temperature is 80℃-140℃, for example, it can be 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, etc., and the drying time is 8h-24h, for example, it can be 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, etc.

[0091] In the preparation method of the positive electrode plate, the lithium-rich manganese-based material, lithium manganate, lithium transition metal phosphate, conductive agent and binder used in the first film layer and the lithium transition metal phosphate, lithium supplement, conductive agent and binder used in the second film layer are as described above.

[0092] In a third aspect, an embodiment of the present application provides a battery cell comprising the above-mentioned positive electrode plate.

[0093] Example 1

[0094] A method for preparing a positive electrode sheet comprises the following steps:

[0095] (1) Preparation of the first film layer slurry: lithium transition metal phosphate material (the ratio of the minimum diameter to the maximum diameter of Martin diameter is 0.4, the particle size D50 is 1.5 μm, LiMn 0.6 Fe 0.4 PO4), lithium manganate material (LiMn2O4), lithium-rich manganese-based material (chemical formula 0.15Li2MnO3·0.85LiMnO2, the ratio of the minimum diameter to the maximum diameter of Martin diameter is 0.6, the primary particle D50 is 500nm, the secondary particle D50 is 6μm), conductive carbon black (sp) and polyvinylidene fluoride (PVDF) are uniformly dispersed in N-methylpyrrolidone (NMP) solvent to prepare a slurry, wherein the mass ratio of lithium transition metal phosphate material, lithium manganate material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) is 10:21:67:0.8:1.2;

[0096] (2) Preparation of the second film layer slurry: lithium transition metal phosphate material (the ratio of the minimum diameter to the maximum diameter of Martin diameter is 0.4, the particle size D50 is 1.5 μm, LiMn 0.6 Fe 0.4 PO4), Li2O, conductive carbon black (sp), and polyvinylidene fluoride (PVDF) are uniformly dispersed in N-methylpyrrolidone (NMP) to prepare a slurry, wherein the mass ratio of lithium transition metal phosphate material, Li2O, conductive carbon black (sp), and polyvinylidene fluoride (PVDF) is 96.8:0.7:1:1.5;

[0097] (3) taking the bottom layer slurry, evenly coating it on the surface of the aluminum foil, and drying it at 110° C. for 16 h to form the first film layer;

[0098] (4) Take the second film layer slurry (the mass ratio of the lithium transition metal phosphate material, lithium manganate material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) in the second film layer slurry to the lithium transition metal phosphate material, Li2O, conductive carbon black (sp), polyvinylidene fluoride (PVDF) in the first film layer slurry is 7:3), evenly coat it on the surface of the first film layer, dry it at 110°C for 16 hours, and then roll the layered pole pieces to form a positive electrode piece (the ratio of the sum of the thickness of the first film layer and the second film layer to the thickness of the current collector is 45:1, and the surface density of the first film layer is 70g / m 2 The surface density of the second film layer is 170g / m 2 ).

[0099] A method for preparing a battery cell comprises the following steps:

[0100] (1) Preparing the negative electrode sheet: Graphite, conductive agent acetylene black, binder carboxymethyl cellulose (CMC), and SBR (styrene butadiene rubber) are mixed in a mass ratio of 96:1:1.2:1.8, and then deionized water is added as a solvent, and stirred evenly to prepare a slurry;

[0101] (2) The slurry is evenly coated on the surface of the copper foil, and then dried and rolled to form a negative electrode sheet. The drying temperature is 90° C. and the drying time is 10 hours.

[0102] (3) Assembly: The positive electrode sheet, negative electrode sheet and isolation film are wound to obtain a bare cell, the bare cell is placed in an outer packaging shell, and after drying, an electrolyte is injected. After vacuum packaging, standing, forming and shaping steps, a cell is obtained, wherein the electrolyte is prepared by dissolving LiPF6 in an organic solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 1:1:1.

[0103] Example 2

[0104] This embodiment is basically the same as Embodiment 1, except that the first membrane layer slurry in this embodiment does not contain lithium manganese oxide and lithium transition metal phosphate, and the mass ratio of lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) is 98:0.8:1.2.

[0105] Example 3

[0106] This embodiment is basically the same as Embodiment 1, with the only difference being that in this embodiment, the first membrane layer slurry does not contain lithium manganese oxide, and the mass ratio of lithium transition metal phosphate material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) is 10:88:0.8:1.2.

[0107] Example 4

[0108] This embodiment is basically the same as Embodiment 1, except that the first membrane layer slurry in this embodiment does not contain lithium transition metal phosphate, and the mass ratio of lithium manganese oxide material, lithium manganese-rich based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) is 21:77:0.8:1.2.

[0109] Example 5

[0110] This embodiment is basically the same as Embodiment 1, except that the mass ratio of lithium transition metal phosphate material, lithium manganese oxide material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) in the first membrane layer slurry in this embodiment is 37:40:21:0.8:1.2.

[0111] Example 6

[0112] This embodiment is basically the same as Embodiment 1, except that the mass ratio of lithium transition metal phosphate material, lithium manganese oxide material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) in the first membrane layer slurry in this embodiment is 29:2:67:0.8:1.2.

[0113] Example 7

[0114] This embodiment is basically the same as Embodiment 1, except that the mass ratio of lithium transition metal phosphate material, lithium manganese oxide material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) in the first membrane layer slurry in this embodiment is 20:21:57:0.8:1.2.

[0115] Example 8

[0116] This embodiment is basically the same as Embodiment 1, except that the mass ratio of lithium transition metal phosphate material, lithium manganese oxide material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) in the first membrane layer slurry in this embodiment is 2:21:75:0.8:1.2.

[0117] Example 9

[0118] This embodiment is basically the same as Embodiment 1, except that the mass ratio of lithium transition metal phosphate material, Li2O, conductive carbon black (sp), and polyvinylidene fluoride (PVDF) in the second membrane layer slurry in this embodiment is 90:0.7:1:1.5.

[0119] Example 10

[0120] This embodiment is basically the same as Embodiment 1, except that the mass ratio of lithium transition metal phosphate material, Li2O, conductive carbon black (sp), and polyvinylidene fluoride (PVDF) in the second membrane layer slurry in this embodiment is 98:0.7:1:1.5.

[0121] Embodiment 11

[0122] This embodiment is basically the same as Embodiment 1, except that the mass ratio of lithium transition metal phosphate material, Li2O, conductive carbon black (sp), and polyvinylidene fluoride (PVDF) in the second membrane layer slurry in this embodiment is 96.8:0.1:1:1.5.

[0123] Example 12

[0124] This embodiment is basically the same as Embodiment 1, except that, in this embodiment, the mass ratio of lithium transition metal phosphate material, Li2O, conductive carbon black (sp), and polyvinylidene fluoride (PVDF) in the second membrane layer slurry is 96.8:1:1:1.5.

[0125] Example 13

[0126] This embodiment is basically the same as Embodiment 1, with the only difference being that the mass ratio of the lithium transition metal phosphate material, lithium manganate material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) in the second film layer slurry used in this embodiment to the lithium transition metal phosphate material, Li2O, conductive carbon black (sp), polyvinylidene fluoride (PVDF) in the first film layer slurry used is 9:1.

[0127] Embodiment 14

[0128] This embodiment is basically the same as Embodiment 1, with the only difference being that the mass ratio of the lithium transition metal phosphate material, lithium manganate material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) in the second film layer slurry used in this embodiment to the lithium transition metal phosphate material, Li2O, conductive carbon black (sp), polyvinylidene fluoride (PVDF) in the first film layer slurry used is 3:2.

[0129] Embodiment 15

[0130] This comparative example is basically the same as Example 1, with the only difference being that in the first membrane layer slurry in this comparative example, the mass ratio of lithium transition metal phosphate material, lithium manganese oxide material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) is 80:0:20:0.8:1.2.

[0131] Example 16

[0132] This comparative example is basically the same as Example 1, except that the mass ratio of lithium transition metal phosphate material, Li2O, conductive carbon black (sp), and polyvinylidene fluoride (PVDF) in the second membrane layer slurry in this comparative example is 99:0:0.5:0.5.

[0133] Embodiment 17

[0134] This comparative example is basically the same as Example 1, with the only difference being that the mass ratio of the lithium transition metal phosphate material, lithium manganate material, lithium-rich manganese-based material, conductive carbon black (sp) and polyvinylidene fluoride (PVDF) in the second film layer slurry used in this comparative example to the lithium transition metal phosphate material, Li2O, conductive carbon black (sp), polyvinylidene fluoride (PVDF) in the first film layer slurry used is 3:8.

[0135] Comparative Example 1

[0136] This comparative example is basically the same as Example 1, with the only difference being that the coating material of the positive electrode plate in this comparative example does not contain lithium manganese oxide material and lithium-rich manganese-based material, and only contains one layer of coating (i.e., the first film layer slurry and the second film layer slurry are mixed together for coating).

[0137] Comparative Example 2

[0138] This comparative example is basically the same as Example 1, except that the first film layer slurry and the second film layer slurry in this comparative example are mixed together for coating.

[0139] Comparative Example 3

[0140] This comparative example is basically the same as Example 1, except that the positions of the first film layer and the second film layer in this comparative example are exchanged.

[0141] Test example:

[0142] The positive electrode sheets obtained in the embodiments and comparative examples were subjected to a roller peeling force test, the weight percentage of the binder in the sheet was defined as A (%), the size of the sheet peeling force was defined as B (N), the specific adhesion force C of the sheet was defined as C = A / B, and the test results of the specific adhesion force C of the sheet are shown in Table 1.

[0143] The cells obtained in the examples and comparative examples were placed in a 45°C incubator, charged to 4.25V at 1C constant current and constant voltage, and then discharged to 2.5V at 1C. The discharge capacity in the first week was A, and after 1000 cycles, the discharge capacity was B, so the capacity retention rate was B / A*100%, as shown in Table 1.

[0144] Table 1

[0145]

[0146]

[0147] From Table 1, we can see that:

[0148] Compared with Examples 2 to 4, the capacity retention rate of the battery in Example 1 is higher. It can be seen that the capacity retention rate of the battery can be improved by adding lithium manganese oxide and lithium transition metal phosphate to the first film layer.

[0149] Compared with Example 15, the capacity retention rate of the batteries of Example 1 and Examples 5 to 8 is higher. It can be seen that the capacity retention rate of the battery can be adjusted by controlling the mass ratio of the lithium transition metal phosphate, lithium manganese oxide, lithium-rich manganese-based material, the first conductive agent and the first binder in the first film layer.

[0150] Compared with Example 16, the capacity retention rate of the batteries of Example 1 and Examples 9 to 12 is higher. It can be seen that the capacity retention rate of the battery can be adjusted by controlling the mass ratio of the lithium transition metal phosphate material, the lithium supplement agent, the second conductive agent and the second binder in the second film layer.

[0151] Compared with Example 17, the capacity retention rate of the batteries of Example 1, Example 13 and Example 14 is higher. It can be seen that the capacity retention rate of the battery can be adjusted by controlling the mass ratio of the second film layer to the first film layer.

[0152] Compared with Comparative Example 1, the capacity retention rate of the battery in the embodiment is higher. It can be seen that the capacity retention rate of the battery can be improved by controlling the composition of the first film layer and the second film layer and arranging them on the current collector in a layered manner.

[0153] Compared with Comparative Example 2, the capacity retention rate of the battery in the embodiment is higher. It can be seen that the capacity retention rate of the battery can be improved by arranging the first film layer and the second film layer on the current collector in a layered manner.

[0154] Compared with Comparative Example 3, the capacity retention rate of the battery in the embodiment is higher. It can be seen that the capacity retention rate of the battery can be improved by sequentially arranging the first film layer and the second film layer on the current collector in a layered manner.

[0155] The embodiments of the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A positive electrode sheet, characterized in that: The invention comprises a current collector and a first film layer and a second film layer which are sequentially arranged on the current collector. The material of the first film layer comprises a lithium-rich manganese-based material, and the material of the second film layer comprises a lithium transition metal phosphate.

2. The positive electrode sheet according to claim 1, characterized in that: The material of the first film layer further includes lithium manganate; and / or The material of the first film layer also includes the lithium transition metal phosphate, and the mass ratio of the lithium transition metal phosphate to the lithium-rich manganese-based material in the first film layer is A:C, wherein 0%<A≤40%, 20%<C<99%.

3. The positive electrode sheet according to claim 2, characterized in that: The chemical formula of the lithium transition metal phosphate is LiMn (1-x-y) Fe x M y PO4, wherein M is one or more metal elements, 0.8≥1-xy≥0.2, 0.8≥x≥0.2, y≤0.1; and / or The chemical formula of the lithium-rich manganese-based material is Li d Ni a Co b Mn c A (1-a-b-c) O2, wherein A is one or more metal elements, 1.5>d>0, 1≥a≥0, 0.3≥b≥0, 1≥c≥0, 0.1≥1-abc; and / or The chemical formula of the lithium manganate is LiMn (2-y) D y O4, wherein D is one or more metal elements, and y≤0.

1.

4. The positive electrode sheet according to claim 1, characterized in that: The lithium transition metal phosphate is in a granular form, and the ratio of the minimum diameter to the maximum diameter of the Martin diameter of the lithium transition metal phosphate is (0.1-0.6):1; and / or The lithium transition metal phosphate is in granular form, and the particle size D50 of the lithium transition metal phosphate is 0.5 μm to 2 μm; and / or The lithium-rich manganese-based material is in a granular form, and the ratio of the minimum diameter to the maximum diameter of the Martin diameter of the lithium-rich manganese-based material is 0.2 to 0.8; and / or The primary particles D50 of the lithium-rich manganese-based material are 100nm to 800nm, and the secondary particles D50 are 4μm to 9μm.

5. The positive electrode sheet according to claim 1, characterized in that: The material of the second film layer also includes a lithium supplement.

6. The positive electrode sheet according to claim 5, characterized in that: The material of the first film layer also includes lithium manganese oxide, the lithium transition metal phosphate, a first conductive agent and a first binder, and the mass percentage ratio of the lithium transition metal phosphate, the lithium manganese oxide, the lithium-rich manganese-based material, the first conductive agent and the first binder in the first film layer is A:B:C:D:(1-ABCD), wherein 0%<A≤40%, 0%≤B≤40%, 20%<C<99%, 0%<D≤7%, 0%<1-ABCD≤7%; and / or The material of the second film layer also includes a second conductive agent and a second binder. The mass percentage ratio of the lithium transition metal phosphate material, the lithium supplement agent, the second conductive agent and the second binder in the second film layer is X:Y:Z:(1-XYZ), wherein 90%≤X≤98%, 0%<Y≤1%, 0%<Z≤3%, and 0%<1-XYZ≤4%.

7. The positive electrode sheet according to claim 1, characterized in that: The mass ratio of the second film layer to the first film layer is (3-18):2; and / or The ratio of the sum of the thickness of the first film layer and the thickness of the second film layer to the thickness of the current collector is (10-80):1; and / or The surface density of the first film layer is 20 g / m 2 ~120g / m 2 The surface density of the second film layer is 90g / m 2 ~250g / m 2 .

8. A method for preparing a positive electrode sheet, characterized in that: The following steps are involved: Providing a current collector and a first film layer first slurry, disposing the first film layer slurry on at least one side of the current collector, and the first film layer first film layer slurry comprises a lithium-rich manganese-based material; A second film layer second slurry is provided, and the second film layer slurry is disposed on a side of the first film layer away from the current collector to obtain a positive electrode sheet, wherein the second film layer slurry includes lithium transition metal phosphate.

9. The method for preparing a positive electrode sheet according to claim 8, characterized in that: The method for preparing the first film layer slurry comprises the following steps: Mixing the lithium-rich manganese-based material, lithium manganate, lithium transition metal phosphate, a first conductive agent, a first binder and a first solvent to obtain the first film layer slurry; and / or The method for preparing the second film layer slurry comprises the following steps: The lithium transition metal phosphate, the lithium supplement agent, the second conductive agent, the second binder and the second solvent are mixed to obtain a second film layer slurry.

10. A battery cell, characterized in that: The invention comprises a positive electrode sheet as described in any one of claims 1 to 7, or a positive electrode sheet prepared by the method for preparing a positive electrode sheet as described in claim 8 or 9.

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