Electrode plate and lithium ion battery

Abstract

The invention relates to an electrode pole piece and a lithium ion battery in the technical field of lithium batteries, the electrode pole piece comprises a current collector and an active substance layer at least arranged on one side of the current collector, a functional layer is arranged on one side, far away from the current collector, of the active substance layer, the functional layer is of a multi-layer structure, and the functional layer is arranged on the current collector. Each functional layer comprises an inorganic solid electrolyte and a polymer, the functional layer further comprises a conductive agent, and the mass ratio of the conductive agent in each functional layer is gradually reduced in the direction away from the active material layer. According to the invention, the functional layers with a multi-layer structure are arranged, and the mass ratio of the conductive agent in each functional layer is gradually reduced along the direction far away from the active substance layer, so that the electric performance of the battery can be ensured, and meanwhile, direct contact of positive and negative pole pieces can be blocked when the diaphragm is shrunk or punctured, and the like, and a battery cell is prevented from being out of control.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to an electrode plate and a lithium ion battery. Background Art

[0002] With the popularization of new energy vehicles, the market demand for lithium batteries, which are the main components of new energy vehicles, is increasing.

[0003] When a traditional lithium-ion battery is working, the separator between the positive electrode and the negative electrode may shrink or be punctured. Once this happens, the positive electrode and the negative electrode will come into direct contact, which will cause the battery to lose control, affecting battery performance or causing safety problems. Therefore, providing an insulating coating with ion conductivity on the surface of the positive electrode active material layer helps improve battery safety.

[0004] However, the biggest problem with this method of coating the surface of the active material layer of the electrode with an ion conductive and electronic insulating slurry to form a coating is that during the coating process, the electronic insulating slurry will infiltrate into the pores inside the electrode and wrap the active material, resulting in electronic insulation between the active materials and affecting the electrical performance.

[0005] Therefore, there is an urgent need for an electrode plate that can ensure the safety of the battery without affecting its electrical performance. Summary of the invention

[0006] In order to solve the above problems, the present invention discloses an electrode plate and a lithium-ion battery. The technical solution of the present invention is implemented as follows:

[0007] The first aspect of the present invention discloses an electrode plate, the electrode plate comprising a current collector and an active material layer at least arranged on one side of the current collector, the functional layer is a multilayer structure, and each functional layer comprises an inorganic solid electrolyte and a polymer;

[0008] The functional layer further includes a conductive agent, wherein a mass ratio of the conductive agent in each functional layer gradually decreases along a direction away from the active material layer.

[0009] Preferably, the functional layer includes at least two layers, wherein the innermost functional layer close to the active material layer is the first functional layer, and the outermost functional layer away from the active material layer is the second functional layer, and the mass ratio of the conductive agent in the second functional layer does not exceed 0.01%.

[0010] Preferably, the active material layer includes an active material, an active material conductive agent and a binder.

[0011] Preferably, the polymer is a polymer solid electrolyte, and the polymer includes at least one of polyacrylic acid, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride and polymethylethylene carbonate.

[0012] Preferably, the inorganic solid electrolyte includes at least one of a sulfide solid electrolyte, an oxide solid electrolyte, and a halide solid electrolyte.

[0013] Preferably, the mass ratio of the inorganic solid electrolyte, the polymer solid electrolyte and the conductive agent in the first functional layer is (5%-99%): (1%-94%): (0.1%-10%)

[0014] Preferably, the mass ratio of the polymer solid electrolyte in the first functional layer is (50%-90%).

[0015] Among them, the mass proportion of the polymer solid electrolyte is preferably 50%-90%.

[0016] Preferably, the mass ratio of the inorganic solid electrolyte to the polymer solid electrolyte in the second functional layer is (5%-99%): (1%-95%);

[0017] Preferably, the mass ratio of the polymer solid electrolyte in the second functional layer is (1%-10%).

[0018] Preferably, the thickness of each functional layer is 0.5 μm-10 μm;

[0019] Preferably, the thickness of each functional layer is 1 μm to 2 μm.

[0020] Preferably, the functional layer completely covers the active material layer.

[0021] The second aspect of the present invention discloses a lithium-ion battery, the lithium-ion battery comprising the above-mentioned electrode plate;

[0022] The electrode plate includes at least one of a positive electrode plate and a negative electrode plate;

[0023] The lithium-ion battery further includes a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0024] The present invention arranges a functional layer of a multilayer structure outside the active material layer of the electrode pole piece, wherein the content of the conductive agent in the functional layer is arranged in a gradient, wherein the conductive agent content of the inner functional layer close to the active material layer is higher, so that the internal resistance of the battery can be reduced, thereby improving the cycle performance of lithium ions, and further improving the fast charging and high-rate discharge performance of the battery. At the same time, the conductive agent content of the outer functional layer far away from the active material layer is lower, which can ensure the conduction of lithium ions while its electronic conductivity is very low. When the diaphragm shrinks or is punctured, the direct contact between the positive and negative pole pieces is blocked to avoid the battery cell from losing control. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only one embodiment of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] The same parts are denoted by the same reference numerals. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to directions in the drawings, and the words "bottom" and "top", "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0027] Figure 1 Schematic diagram of the structure of the positive electrode plate of the lithium-ion battery in an embodiment of the present invention.

[0028] In the above drawings, the meanings of the symbols of the reference numerals are as follows:

[0029] 1. Second functional layer, 2. First functional layer, 3. Positive electrode active material layer, 4. Current collector. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with 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 of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by technicians in the technical field to which the present invention belongs; the terms used in the specific implementation methods are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" in the specification and claims of the present invention and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0032] In the description of the specific implementation methods of the present invention, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0033] Reference to "embodiments" in the present invention means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present invention may be combined with other embodiments.

[0034] In the description of the embodiments of the present invention, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects before and after are in an "or" relationship.

[0035] Throughout the present invention, numerical values ​​represent approximate measures or limits of ranges to cover minor deviations from given values ​​as well as embodiments with about the values ​​mentioned and embodiments with the exact values ​​mentioned. Except for the working examples provided at the end of the detailed description, all numerical values ​​of parameters (e.g., amounts or conditions) in this specification (including the appended claims) should be understood to be modified by the term "about" in all cases, regardless of whether "about" actually appears before the numerical value. "About" indicates that the stated numerical value allows some minor imprecision (close to the exact value of the value to some extent; approximately or reasonably close to the value; almost). If the imprecision provided by "about" is not otherwise understood in this ordinary sense in the art, "about" as used in the present invention at least indicates the variation that can be produced by the ordinary methods of measuring and using such parameters. For example, "about" may include a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in some aspects, optionally less than or equal to 0.1%.

[0036] Additionally, disclosure of ranges includes disclosure of all values ​​within the entire range and further divided ranges, including endpoints and sub-ranges given for such ranges.

[0037] When traditional lithium-ion batteries are working, the diaphragm between the positive electrode and the negative electrode may shrink or be punctured. Once this happens, the positive electrode and the negative electrode will come into direct contact, causing the battery cell to lose control, affecting battery performance or causing safety problems.

[0038] In order to solve the above problems, the present invention proposes a technical solution, by arranging a functional layer of a multi-layer structure on the outside of the active material layer of the electrode plate, wherein the mass proportion of the conductive agent in each functional layer gradually decreases along the direction away from the active material layer, so that the inorganic solid electrolyte and the polymer solid electrolyte in the outer functional layer can ensure lithium ion conduction, and at the same time, its electronic conductivity is very low, which can block the direct contact between the positive and negative plates when the diaphragm shrinks or is punctured, thereby preventing the battery cell from losing control.

[0039] The first aspect of the present invention discloses an electrode plate, which includes a current collector and an active material layer arranged on at least one side of the current collector, wherein the functional layer is a multilayer structure, each of the functional layers includes an inorganic solid electrolyte and a polymer, and the functional layer also includes a conductive agent, wherein the mass ratio of the conductive agent in each functional layer gradually decreases along the direction away from the active material layer.

[0040] In the present application, a multi-layer gradient structured functional layer is used, wherein the content of the conductive agent in the functional layer close to the active material layer is higher, and the content of the conductive agent in the functional layer far from the active material layer is lower. This arrangement, on the one hand, maintains the advantage of the functional layer in improving battery safety, and on the other hand, avoids the negative impact of the penetration of electronic insulating slurry into the functional layer during the molding process on the electrode and the internal resistance of the entire battery.

[0041] In some embodiments, the functional layer includes at least two layers, wherein the innermost functional layer close to the active material layer is the first functional layer, and the outermost functional layer away from the active material layer is the second functional layer, and the mass ratio of the conductive agent in the second functional layer does not exceed 0.01%.

[0042] The present application includes at least two functional layers. The conductive agent in the outermost second functional layer is of relatively low quality, preferably contains no conductive agent, which can ensure the lithium ion conduction therein. At the same time, its electronic conductivity is very low, which can block the direct contact between the positive and negative electrodes when the diaphragm shrinks or is punctured, thereby avoiding the loss of control of the battery cell.

[0043] In the present application, the functional layer can be only two layers, or multiple layers, such as three layers, four layers, five layers, etc. The above is only an example and not a limitation. When it is set as multiple layers, it only needs to ensure that the innermost layer is the first functional layer, the outermost layer is the second functional layer, and the mass ratio of the conductive agent in the second functional layer does not exceed 0.01%, and no other restrictions are imposed.

[0044] In specific applications, the conductive agent is selected from one or more of carbon black, carbon nanotubes, carbon fibers, graphene, and metal particles. The above are only examples and not limitations.

[0045] The at least one mentioned in the present invention refers to a combination of two or more in addition to one.

[0046] In some embodiments, the active material layer includes an active material, an active material conductive agent, and a binder.

[0047] In specific applications, when the active material is a positive electrode active material, any one or a combination of at least two of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium iron phosphate, lithium titanate or lithium-rich manganese-based materials can be selected. The above are all common positive electrode active materials in the field, which are only examples and not limitations.

[0048] In specific applications, when the active material is a negative electrode active material, it can be selected from any one or a combination of at least two of artificial graphite, natural graphite, microcrystalline graphite, soft carbon and hard carbon. The above are common negative electrode active materials in the art, which are only examples and not limitations.

[0049] In specific applications, the active material conductive agent includes any one or a combination of at least two of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers. The above are all common conductive agents in the art, only for illustration, not limitation.

[0050] In specific applications, the binder includes any one or a combination of at least two of polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic plastics, other polyolefins and their copolymers, polysulfone, polyphenylene ether, or carboxymethyl cellulose, preferably polytetrafluoroethylene or polyvinyl chloride. The above are all common binders in the art, only for illustration, not limitation.

[0051] In some embodiments, the polymer is a polymer solid electrolyte, and the polymer includes at least one of polyacrylic acid, polyoxyethylene, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride, and poly(methyl ethylene carbonate).

[0052] The polymer adopted in the present invention is a polymer solid electrolyte, which is different from the gel polymer, reducing the possibility of its infiltration into the pores of the active material layer. At the same time, the polymer solid electrolyte can be used both as an electrolyte and as a binder, so there is no need to add an additional binder, which can further improve the cycle performance of the battery.

[0053] In some embodiments, the inorganic solid electrolyte includes at least one of sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes.

[0054] Using the inorganic solid electrolyte makes up for the problem of poor ionic conductivity of the polymer solid electrolyte itself. Compared with the case of simply using the polymer solid electrolyte, it can better improve the cycle performance of the battery. At the same time, the inorganic solid electrolyte can improve the mechanical strength and thermal stability of the battery, further enhancing the safety of the battery.

[0055] In specific applications, the halide solid electrolyte includes Li2CdC l4 , Li2MgC l4 , Li2Cd I4 , Li2ZnI4, Li3OCl, LiI, Li5ZnI4, Li3OCl 1-x Br x (where 0 < x < 1) of at least one.

[0056] The sulfide solid electrolyte includes Li2S-P2S5, Li2S-P2S5-MS x (where M is Si, Ge, and Sn and 0 ≤ x ≤ 2), Li3.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.3 , Li 9.6 P3S 12 、Li7P3S 11 、Li9P3S9O3、Li 10.35 Si 1.35 P 1.65 S 12 , Li 9.81 Sn 0.81 P 2.19 S 12 , Li 10 (Si 0.5 Ge 0.5 )P2S 12 、Li(Ge 0.5 Sn 0.5 )P2S 12 、Li(Si 0.5 Sn 0.5 )PsS 12 , Li 10 GeP2S 12 (LGPS), Li6PS5X (where X is Cl, Br or I), Li7P2S8I, Li 10.35 Ge 1.35 P 1.65 S 12 , Li 3.25 Ge 0.25 P 0.75 S4, Li 10 SnP2S 12 , Li 10 SiP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 C l0.3 , (1-x) P2S 5-x At least one of Li2S (wherein 0.5≤x≤0.7).

[0057] Oxide solid electrolytes include perovskite type, garnet type, LISICON type, and NASICON type. Among them, the perovskite type solid electrolyte material is preferably lithium lanthanum titanate / lithium lanthanum titanate (Li 0.33 La 0.56 TiO3, LLTO), the garnet-type solid electrolyte material is preferably lithium zirconium oxide / lithium lanthanum zirconate (Li7La3Zr2O 12, LLZO), NASICON type (sodium super ion conductor) solid electrolyte material is preferably lithium aluminum titanium phosphate LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3).

[0058] In the present application, the functional layer has a multi-layer structure, and the inorganic solid electrolyte, polymer solid electrolyte and conductive agent in each functional layer can be of the same type for easy preparation, or different types can be selected and matched according to needs.

[0059] In some embodiments, the mass ratio of the inorganic solid electrolyte, the polymer solid electrolyte and the conductive agent in the first functional layer is (5%-99%): (1%-94%): (0.1%-10%)

[0060] In some preferred embodiments, the mass ratio of the polymer solid electrolyte in the first functional layer is 50%-90%. The mass ratio of the polymer solid electrolyte is controlled within the above range. It can be used as a binder to improve the adhesion between the inorganic solid electrolyte and the conductive agent, help to better construct a conductive network, and thus improve the cycle performance of the battery.

[0061] In some embodiments, the mass ratio of the inorganic solid electrolyte to the polymer solid electrolyte in the second functional layer is (5%-99%): (1%-95%);

[0062] In some preferred embodiments, the mass ratio of the polymer solid electrolyte in the second functional layer is 1%-10%.

[0063] In some embodiments, the thickness of each functional layer is 0.5 μm-10 μm; in specific applications, the thickness of each functional layer can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm. The above values ​​are only examples and are not limiting.

[0064] In some preferred embodiments, the thickness of each functional layer is 1 μm-2 μm. When the thickness of the functional layer is within this range, the battery can have low impedance, good cycle stability and good rate performance.

[0065] In the present application, the thickness of each functional layer can be set to the same thickness, or can be set to different thicknesses according to requirements.

[0066] In some embodiments, the functional layer completely covers the active material layer. The functional layer of the present application completely covers the active material layer, which can prevent the positive and negative electrodes from directly contacting each other when the separator shrinks or is punctured, causing the battery cell to lose control.

[0067] The second aspect of the present invention discloses a lithium-ion battery, which includes the above-mentioned electrode plate; the electrode plate includes at least one of a positive electrode plate and a negative electrode plate; the lithium-ion battery also includes a separator arranged between the positive electrode plate and the negative electrode plate.

[0068] In the present application, one of the positive electrode plates can be the above-mentioned electrode plates, one of the negative electrode plates can be the above-mentioned electrode plates, or both of them can be the above-mentioned electrode plates, and the preparation method of the above-mentioned electrode plates is not limited, and can be prepared by wet coating or dry method.

[0069] The embodiments of the present invention will be described in more detail below through examples and comparative examples. It should be noted that the embodiments of the present invention are not limited to these examples.

[0070] The following examples and comparative examples are all preparation processes of lithium-ion batteries, wherein the comparative examples are control groups of the examples, used to assist in illustrating the effects of the examples.

[0071] It should be noted that, in order to reduce errors, the lithium-ion batteries in all embodiments of the present invention use the positive electrode sheet as the electrode sheet described in this application, and the positive electrode sheet structure is Figure 1 The electrode plate comprises a current collector 4 and a positive electrode active material layer 3 arranged on both sides of the current collector 4, a first functional layer 2 is arranged on the side of the positive electrode active material layer 3 away from the current collector 4, and a second functional layer 1 is arranged on the side of the first functional layer 2 away from the positive electrode active material layer 3.

[0072] Example 1

[0073] 1. Preparation of positive electrode sheet containing composite first functional layer and second functional layer (wet coating):

[0074] 1.1. The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed uniformly in a mass ratio of 95:2:3 to form a positive electrode slurry, and the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, dried at 100°C to form a positive electrode active material layer, and then cold pressed to obtain a positive electrode sheet containing an active material layer;

[0075] 1.2. Dissolve LLZO inorganic solid electrolyte, PVDF polymer solid electrolyte and conductive agent superconducting carbon (Super-P) in an organic solvent N, N-dimethylpyrrolidone at a mass ratio of 85:10:5, mix evenly to form a first functional layer slurry, apply the first functional layer slurry on the surface of the positive electrode active material layer in step 1.1, and dry at 60° C. to obtain a positive electrode sheet containing a first functional layer with a thickness of 5 μm;

[0076] 1.3, rolling the positive electrode sheet containing the first coating obtained in step 1.2;

[0077] 1.4. Dissolve LLZO inorganic solid electrolyte and PVDF polymer solid electrolyte in an organic solvent N,N-dimethylpyrrolidone at a mass ratio of 90:10, mix them evenly to form a second functional layer slurry, apply the second functional layer slurry on the surface of the first functional layer in step 1.3, and dry them at 80° C. to obtain a second functional layer with a thickness of 10 μm, that is, to obtain a positive electrode sheet containing a composite first functional layer and a second functional layer;

[0078] 1.5. The positive electrode sheet containing the composite functional layer obtained in step 1.4 is trimmed, cut into pieces, and divided into strips. After the strips are divided, they are used as positive electrode sheets for lithium-ion batteries.

[0079] 2. Preparation of negative electrode sheet:

[0080] 2.1. The negative electrode active material graphite, the conductive agent superconducting carbon (Super-P), the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene butadiene rubber (SBR) are prepared into a negative electrode slurry at a mass ratio of 96.5:1.0:1.0:1.5, coated on the current collector copper foil and dried at 90°C to form a negative electrode active material layer, and then cold pressed to obtain a negative electrode sheet;

[0081] 2.2. The negative electrode sheet prepared in step 2.1 is trimmed, cut into pieces, and slit into strips to produce negative electrode sheets for lithium-ion batteries.

[0082] 3. Preparation of electrolyte

[0083] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0084] 4. Preparation of batteries

[0085] The positive electrode sheet and the negative electrode sheet prepared above are stacked in order with the separator so that the separator is between the positive and negative electrode sheets to obtain a bare cell. The bare cell is placed in an outer packaging shell, and an electrolyte is injected. After vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0086] Comparative Example 1

[0087] 1. Preparation of positive electrode sheet without functional layer:

[0088] 1.1. The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed uniformly in a mass ratio of 95:2:3 to form a positive electrode slurry, and the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, dried at 100°C to form a positive electrode active material layer, and then cold pressed to obtain a positive electrode sheet containing an active material layer;

[0089] 1.2. The positive electrode sheet containing the active material layer obtained in step 1.1 is trimmed, cut into pieces, and divided into strips. After the strips are divided, they are used as positive electrode sheets for lithium-ion batteries.

[0090] 2. Preparation of negative electrode sheet:

[0091] 2.1. The negative electrode active material graphite, the conductive agent superconducting carbon (Super-P), the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene butadiene rubber (SBR) are prepared into a negative electrode slurry at a mass ratio of 96.5:1.0:1.0:1.5, coated on the current collector copper foil and dried at 90°C to form a negative electrode active material layer, and then cold pressed to obtain a negative electrode sheet;

[0092] 2.2. The process of step 2.1 is performed by trimming, cutting and stripping, and the negative electrode sheets of lithium-ion batteries are made after stripping.

[0093] 3. Preparation of electrolyte

[0094] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0095] 4. Preparation of batteries

[0096] The positive electrode sheet and negative electrode sheet prepared above are stacked in order with the separator so that the separator is between the positive and negative electrode sheets, and then 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, shaping and other processes, a lithium-ion battery is obtained.

[0097] Comparative Example 2

[0098] 1. Preparation of positive electrode sheet containing only the first functional layer:

[0099] 1.1. The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed uniformly in a mass ratio of 95:2:3 to form a positive electrode slurry, and the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, dried at 100°C to form a positive electrode active material layer, and then cold pressed to obtain a positive electrode sheet containing an active material layer;

[0100] 1.2. Dissolve LLZO inorganic solid electrolyte, PVDF polymer solid electrolyte and conductive agent superconducting carbon (Super-P) in an organic solvent N, N-dimethylpyrrolidone at a mass ratio of 70:20:10, mix evenly to form a first functional layer slurry, apply the first functional layer slurry on the surface of the positive electrode active material layer in step 1.1, and dry at 60° C. to obtain a positive electrode sheet containing a first functional layer with a thickness of 5 μm;

[0101] 1.3. The positive electrode sheet containing the first functional layer obtained in step 1.2 is trimmed, cut into pieces, and divided into strips. After the strips are divided, they are used as positive electrode sheets for lithium-ion batteries.

[0102] 2. Preparation of negative electrode sheet:

[0103] 2.1. The negative electrode active material graphite, the conductive agent superconducting carbon (Super-P), the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene butadiene rubber (SBR) are prepared into a negative electrode slurry at a mass ratio of 96.5:1.0:1.0:1.5, coated on the current collector copper foil and dried at 90°C to form a negative electrode active material layer, and then cold pressed to obtain a negative electrode sheet;

[0104] 2.2. The negative electrode sheet prepared in step 2.1 is trimmed, cut into pieces, and slit into strips to produce negative electrode sheets for lithium-ion batteries.

[0105] 3. Preparation of electrolyte

[0106] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0107] 4. Preparation of batteries

[0108] The positive electrode sheet and negative electrode sheet prepared above are stacked in order with the separator so that the separator is between the positive and negative electrode sheets, and then 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, shaping and other processes, a lithium-ion battery is obtained.

[0109] Comparative Example 3

[0110] 1. Preparation of positive electrode sheet containing only the second functional layer:

[0111] 1.1. The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly at a mass ratio of 97:1.5:1.5 to form a positive electrode slurry, and the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, dried at 100°C to form a positive electrode active material layer, and then cold pressed to obtain a positive electrode sheet containing an active material layer;

[0112] 1.2. Dissolve LLZO inorganic solid electrolyte and PVDF polymer solid electrolyte in an organic solvent N,N-dimethylpyrrolidone at a mass ratio of 70:30, mix them evenly to form a second functional layer slurry, apply the second functional layer slurry on the surface of the positive electrode active material layer in step 1.1, and dry them at 80° C. to obtain a positive electrode sheet containing a second functional layer with a thickness of 10 μm;

[0113] 1.3. The positive electrode sheet containing the second functional layer obtained in step 1.2 is trimmed, cut into pieces, and divided into strips. After the strips are divided, they are used as positive electrode sheets for lithium-ion batteries.

[0114] 2. Preparation of negative electrode sheet:

[0115] 2.1. The negative electrode active material graphite, the conductive agent superconducting carbon (Super-P), the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene butadiene rubber (SBR) are prepared into a negative electrode slurry at a mass ratio of 96.5:1.0:1.0:1.5, coated on the current collector copper foil and dried at 90°C to form a negative electrode active material layer, and then cold pressed to obtain a negative electrode sheet;

[0116] 2.2. The negative electrode sheet prepared in step 2.1 is trimmed, cut into pieces, and slit into strips to produce negative electrode sheets for lithium-ion batteries.

[0117] 3. Preparation of electrolyte

[0118] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0119] 4. Preparation of batteries

[0120] The positive electrode sheet and negative electrode sheet prepared above are stacked in order with the separator so that the separator is between the positive and negative electrode sheets, and then 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, shaping and other processes, a lithium-ion battery is obtained.

[0121] In order to further demonstrate the technical effect of the present invention, a total of four groups of samples from Example 1 and Comparative Examples 1-3 were used for comparative experiments, with 20 samples in each group, and the experimental results were averaged. The test method is as follows:

[0122] 1. Acupuncture test:

[0123] ①Fully charge the battery using the standard charging method;

[0124] ② Use A high temperature resistant steel needle (the cone angle of the needle tip is 45° to 60°, the surface of the needle is smooth, free of rust, oxide layer and oil), penetrates the battery cell plate in a direction perpendicular to the battery cell plate at a speed of (25±5) mm / s, and the penetration position is preferably close to the geometric center of the pierced surface, and the steel needle stays in the battery cell;

[0125] ③Observe for 1 hour and record the safety level of the battery cell.

[0126] 2. Internal resistance test: obtained through DCR test, 25℃, 3C discharge for 10 seconds.

[0127] 3. Fast charging test:

[0128] ① At room temperature: discharge at 1C current to the discharge end voltage (2.75V), and let stand for 1h;

[0129] ② Then charge it in the standard charging mode, discharge it at 1C current to the discharge end voltage (2.75V), and let it stand for 1 hour;

[0130] ③ Charge at 2C constant current to the charge end voltage, let stand for 1h; then discharge at 1C to the discharge end voltage (2.75V);

[0131] Charge at 2C constant current and constant voltage to the charge end voltage, then discharge at 1C to the discharge end voltage (2.75V), repeat 10 times, no lithium deposition after fully charged dissection

[0132] standard:

[0133] 4. High rate discharge performance test:

[0134] ①At room temperature: charge with standard charging method, let stand for 0.5h, discharge at 1C and 3C respectively to the end voltage (2.75V);

[0135] ②Standards:

[0136] 5. Cycle performance test: 1C constant current and constant voltage charge to the upper voltage limit, stand for 1 hour, 1C constant current discharge to the lower voltage limit, stand for 1 hour, cycle 500 times, and calculate the discharge capacity retention rate;

[0137] The test results are shown in the following table:

[0138] sheet:

[0139]

[0140]

[0141] According to the above table, a plurality of functional layers are arranged between the pole piece and the diaphragm, wherein the content of the conductive agent gradually decreases from the pole piece to the diaphragm, which can reduce the internal resistance of the battery, improve the cycle performance of the battery, and at the same time ensure the safety performance of the battery.

[0142] It should be pointed out that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An electrode plate, comprising a current collector and an active material layer disposed at least on one side of the current collector, characterized in that: A functional layer is disposed on a side of the active material layer away from the current collector; The functional layer is a multi-layer structure, and each functional layer includes an inorganic solid electrolyte and a polymer; The functional layer further includes a conductive agent, wherein a mass ratio of the conductive agent in each functional layer gradually decreases along a direction away from the active material layer.

2. The electrode plate according to claim 1, characterized in that: The functional layer includes at least two layers, wherein the innermost functional layer close to the active material layer is the first functional layer, and the outermost functional layer away from the active material layer is the second functional layer, and the mass ratio of the conductive agent in the second functional layer does not exceed 0.01%.

3. The electrode plate according to claim 1, characterized in that: The active material layer includes an active material, an active material conductor and a binder.

4. The electrode plate according to claim 1, characterized in that: The polymer is a polymer solid electrolyte, and the polymer includes at least one of polyacrylic acid, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride and polymethylethylene carbonate.

5. The electrode plate according to claim 1, characterized in that: The inorganic solid electrolyte includes at least one of a sulfide solid electrolyte, an oxide solid electrolyte, and a halide solid electrolyte.

6. The electrode plate according to claim 4, characterized in that: The mass ratio of the inorganic solid electrolyte, the polymer solid electrolyte and the conductive agent in the first functional layer is (5%-99%): (1%-94%): (0.1%-10%); Preferably, the mass ratio of the polymer solid electrolyte in the first functional layer is (50%-90%).

7. The electrode plate according to claim 4, characterized in that: The mass ratio of the inorganic solid electrolyte to the polymer solid electrolyte in the second functional layer is (5%-99%): (1%-95%); Preferably, the mass ratio of the polymer solid electrolyte in the second functional layer is (1%-10%).

8. The electrode plate according to claim 1, characterized in that: The thickness of each functional layer is 0.5 μm-10 μm; Preferably, the thickness of each functional layer is 1 μm to 2 μm.

9. The electrode plate according to claim 1, characterized in that: The functional layer completely covers the active material layer.

10. A lithium ion battery, characterized in that: Comprising the electrode plate as described in any one of claims 1 to 9; The electrode plate includes at least one of a positive electrode plate and a negative electrode plate; The lithium-ion battery further includes a separator disposed between the positive electrode sheet and the negative electrode sheet.

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