Secondary battery and electric device

Abstract

The invention discloses a secondary battery and an electric device, and belongs to the technical field of batteries. According to the secondary battery provided by the invention, the positive electrode active material layer is arranged on at least one surface of the positive electrode current collector, the positive electrode lithium supplement agent layer is arranged on the surface, far away from the positive electrode current collector, of the positive electrode active material layer, and the proper type of ion trapping agent is selected in the positive electrode lithium supplement agent layer; the positive electrode active material layer and the positive electrode lithium supplement agent layer are well matched with each other, so that the cycle performance and the quick charge performance of the secondary battery can be effectively improved, and meanwhile, the initial internal resistance of the secondary battery can be effectively reduced.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular relates to a secondary battery and an electrical device. Background Art

[0002] The existing positive electrode active materials have the problem of fast charging capability and high temperature cycle life needing to be further improved. Artificially adding lithium supplements can effectively make up for the active lithium consumed by the formation of SEI at the negative electrode and subsequent battery cycles, which is an effective means to improve the cycle life of secondary batteries. In addition, suitable lithium supplement materials can also effectively reduce the DC internal resistance (DCR) of secondary batteries and improve the fast charging capability of secondary batteries. However, the introduction of lithium supplements still has the problem of not significantly improving the cycle life and fast charging capability of secondary batteries, and the reduction in the initial internal resistance of secondary batteries is not significant. Summary of the invention

[0003] The purpose of the present application is to solve the technical problems in the prior art of poor high-temperature cycle performance, high initial internal resistance and poor fast charging performance of secondary batteries when lithium supplement agents are introduced into the positive electrode active materials, and to provide a secondary battery and an electrical device with excellent high-temperature cycle performance, fast charging performance and low initial internal resistance.

[0004] To achieve the above-mentioned object, in a first aspect of the present application, a secondary battery is provided, comprising a positive electrode plate, a negative electrode plate, a separator and an electrolyte, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and a positive electrode lithium replenisher layer disposed on the positive electrode active material layer away from the surface of the positive electrode current collector; the positive electrode lithium replenisher layer comprises a lithium replenisher and an ion capture agent; the positive electrode active material layer comprises a positive electrode active material;

[0005] The ion trapping agent includes a perfluorosulfonic acid group.

[0006] As an embodiment of the present application, the ion capture agent includes at least one of sulfonated polytetrafluoroethylene and perfluorosulfonic acid resin.

[0007] As an embodiment of the present application, the positive electrode lithium supplement layer further includes a first slurry additive, a first conductive agent, and a first binder; the positive electrode active material layer further includes a second slurry additive, a second conductive agent, and a second binder.

[0008] As an embodiment of the present application, the mass of the positive electrode active material accounts for 90 to 98% of the total mass of the positive electrode active material layer.

[0009] As an embodiment of the present application, the mass of the lithium replenisher accounts for 93-99% of the total mass of the positive electrode lithium replenisher layer.

[0010] As an embodiment of the present application, the mass of the ion capture agent accounts for 0.1 to 5% of the total mass of the positive electrode lithium replenisher layer.

[0011] As an embodiment of the present application, the mass of the first slurry additive accounts for 0.1 to 5% of the total mass of the positive electrode lithium supplement.

[0012] As an embodiment of the present application, the thickness ratio m of the positive electrode active material layer to the positive electrode lithium replenisher layer is 10-500.

[0013] As an embodiment of the present application, the mass ratio of the lithium supplement agent to the positive electrode active material is (1.05-50.6):1000.

[0014] As an embodiment of the present application, the first slurry additive and the second slurry additive are each independently selected from at least one of 3,4-dihydroxy-3-cyclobutene-1,2-dione, 1,3,5-benzenetricarboxylic acid, diketosuccinic acid, and oxomalic acid.

[0015] As an embodiment of the present application, the lithium supplement includes at least one of Li2C4O4, Li5FeO4, Li6CoO4, Li2NiO2, Li3N, Li2C3O5, Li2C4O6, 2-cyclopropene-1-one-2,3-dihydroxylithium, and 3,4-dihydroxybenzonitrile dilithium.

[0016] As an embodiment of the present application, the first conductive agent and the second conductive agent are each independently selected from at least one of acetylene black, Ketjen black, CNT, SWCNT, Super P, VGCF, and graphene.

[0017] As an embodiment of the present application, the first binder and the second binder each independently include at least one of polytetrafluoroethylene, polyurethane resin, polyacrylic acid, and styrene-butadiene rubber.

[0018] As an embodiment of the present application, the surfaces of the positive electrode active material and the lithium supplement agent are both provided with a carbon coating layer with a thickness of 1 to 100 nm, and the carbon in the carbon coating layer of the positive electrode active material includes at least one of N-doped carbon and F-doped carbon.

[0019] As an embodiment of the present application, the positive electrode active material includes Li a Mn x Fe y M z PO4, wherein 0.95≤a≤1.05, 0.4≤x≤0.8, 0.2≤y≤0.6, 0<z≤0.08, and M includes at least one of Mg, Ti, V, Co, Mo, and W.

[0020] In a second aspect of the present application, an electrical device is provided, comprising the secondary battery described above.

[0021] Compared with the prior art, the beneficial effects of this application are:

[0022] The secondary battery provided by the present application is provided with a positive electrode active material layer on at least one surface of the positive electrode current collector, and a positive electrode lithium replenisher layer is provided away from the positive electrode current collector surface by the positive electrode active material layer, and a suitable type of ion capture agent is selected in the positive electrode lithium replenisher layer. The positive electrode active material layer and the positive electrode lithium replenisher layer cooperate well with each other, thereby effectively improving the cycle performance and fast charging performance of the secondary battery, and at the same time effectively reducing the initial internal resistance of the secondary battery. DETAILED DESCRIPTION

[0023] In order to better illustrate the purpose, technical solutions and advantages of the present application, the present application will be further described below in conjunction with specific embodiments.

[0024] Unless otherwise specified, the reagents, methods and equipment used in this application are conventional reagents, methods and equipment in the art.

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0026] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0027] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0028] In one embodiment of the present application, the present application provides a secondary battery, including a positive electrode plate, a negative electrode plate, a separator and an electrolyte, wherein the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and a positive electrode lithium replenisher layer disposed on the positive electrode active material layer away from the surface of the positive electrode current collector; the positive electrode lithium replenisher layer includes a lithium replenisher and an ion capture agent; the positive electrode active material layer includes a positive electrode active material;

[0029] The ion trapping agent includes a perfluorosulfonic acid group.

[0030] The secondary battery provided in the present application can effectively improve the high temperature cycle performance and fast charging performance of the secondary battery by adding a suitable type of ion capture agent to the positive electrode lithium replenisher layer, and the positive electrode active material layer and the positive electrode lithium replenisher layer cooperate well with each other, thereby effectively reducing the initial internal resistance of the secondary battery.

[0031] Specifically, the present application adds a substance including a perfluorosulfonic acid group as an ion capture agent to the positive electrode lithium replenisher layer. The substance including a perfluorosulfonic acid group can be stably wrapped on the surface of the lithium replenisher, effectively reducing the pH value of the lithium replenisher material and reducing the influence of free lithium on the positive electrode lithium replenisher layer; at the same time, as an ion capture agent, the substance including a perfluorosulfonic acid group has a strong electronegative fluorine atom, which can effectively adsorb the metal ions dissolved in the positive electrode active material layer, increase the metal ion concentration near the positive electrode active material layer, and thus limit the continuous dissolution of the metal ions; in addition, the substance including a perfluorosulfonic acid group The adsorption of metal ions by the substance can also limit the migration of metal ions to the electrolyte and the negative electrode, thereby reducing the consumption of active lithium and increasing the cycle life of the battery; and the presence of the substance including the perfluorosulfonic acid group can also inhibit the migration of hydrogen ions to the positive electrode, further reducing the corrosion effect of hydrogen ions on the positive electrode active material layer, and improving the stability of the positive electrode active material layer, thereby effectively inhibiting the dissolution of metal elements in the positive electrode active material layer, the transport of hydrogen ions to the positive electrode active material layer, and the migration of metal ions in the battery, thereby effectively improving the high-temperature cycle stability of the secondary battery.

[0032] In one embodiment, the ion capture agent includes at least one of sulfonated polytetrafluoroethylene (Nafion) and perfluorosulfonic acid resin.

[0033] The present application has found that when the ion capture agent is further selected as the above substances, especially sulfonated polytetrafluoroethylene, as a typical solid superacid, it can achieve a more excellent comprehensive effect.

[0034] In one embodiment, the positive electrode lithium supplement layer further includes a first slurry additive, a first conductive agent, and a first binder; the positive electrode active material layer further includes a second slurry additive, a second conductive agent, and a second binder.

[0035] In one embodiment, the mass of the positive electrode active material accounts for 90-98% of the total mass of the positive electrode active material layer.

[0036] It should be noted that the testing and calculation method for the mass percentage of the positive electrode active material to the total mass of the positive electrode active material layer is: using ICP-OES to test the positive electrode active material content, and then dividing the mass of the positive electrode active material by the total mass of the positive electrode active material layer to obtain the corresponding mass percentage.

[0037] Exemplarily, the mass percentage of the positive electrode active material to the total mass of the positive electrode active material layer may be any point value between 90 and 98% or any two point range values, for example, it may be one of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or any two range values.

[0038] The present application study found that, based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode active material will affect the high temperature cycle performance, fast charging performance and initial internal resistance of the battery. When the mass of the positive electrode active material is further selected to account for 90-98% of the total mass of the positive electrode active material layer, the comprehensive performance of the secondary battery obtained is better.

[0039] In one embodiment, the mass of the lithium replenisher accounts for 93-99% of the total mass of the positive electrode lithium replenisher layer.

[0040] It should be noted that the test and calculation method for the mass percentage of the mass of the lithium supplement agent to the total mass of the positive electrode lithium supplement agent layer is: the mass of the lithium supplement agent is tested by ICP-OES, and the mass of the lithium supplement agent is divided by the total mass of all substances in the lithium supplement agent layer (excluding foil) to obtain the corresponding mass percentage.

[0041] In one embodiment, the mass of the lithium supplement agent can be any point value or any two point range values ​​between 93% and 99% of the total mass of the positive electrode lithium supplement agent layer, for example, it can be one of 93%, 94%, 95%, 96%, 97%, 98%, 99% or any two range values.

[0042] In one embodiment, the mass of the lithium supplement agent accounts for 95-98% of the total mass of the positive electrode lithium supplement agent layer, for example, it can be 95%, 95.2%, 95.4%, 95.6%, 95.8%, 96%, 96.2%, 96.4%, 96.6%, 96.8%, 97%, 97.2%, 97.4%, 97.6%, 97.8%, 98%, or any two of the range values.

[0043] The present application has found that when the mass of the lithium supplement agent accounts for 93% to 99% of the total mass of the positive electrode lithium supplement agent layer, especially in the range of 95% to 98%, it can optimize the internal interface of the battery and reduce the initial internal resistance of the battery while avoiding lithium plating and ensuring battery safety; at the same time, the introduction of the lithium supplement agent within the above range can also effectively improve the fast charging performance of the battery; and, due to the introduction of the lithium supplement agent, the active lithium increases, thereby effectively improving the high temperature cycle performance of the battery.

[0044] In one embodiment, the mass of the ion capture agent accounts for 0.1-5% of the total mass of the positive electrode lithium replenisher layer.

[0045] In one embodiment, the mass of the first slurry additive accounts for 0.1-5% of the total mass of the positive electrode lithium supplement.

[0046] It should be noted that, based on the total mass of the positive electrode lithium replenisher layer, the test and calculation method for the mass percentage of the ion capture agent and the first slurry additive is: use ICP-OES and infrared to test the content of the ion capture agent and the first slurry additive, and divide the mass of the ion capture agent and the first slurry additive by the total mass of the positive electrode lithium replenisher layer (excluding foil) to obtain the corresponding mass percentage.

[0047] Exemplarily, the mass percentage of the mass of the ion capture agent to the total mass of the positive electrode lithium replenishing agent layer can be any point value or any two point range values ​​between 0.1 and 5%, for example, it can be 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.6%, 4.8%, 5% or any two range values.

[0048] The present application study found that the addition amount range of the ion capture agent will affect its coating effect on the lithium supplement agent, thereby affecting the amount of free lithium, and further affecting the high-temperature cycle performance, fast charging performance and initial internal resistance of the battery; at the same time, the addition amount range of the ion capture agent will also affect its electronegativity, thereby affecting its dissolution and migration of metal ions, and further affecting the high-temperature cycle performance of the battery; in addition, the addition amount of the ion capture agent will also affect its transport of hydrogen ions to the positive electrode, thereby affecting the stability of the positive electrode active material layer, and further affecting the cycle performance of the battery.

[0049] Exemplarily, the mass percentage of the mass of the first slurry additive to the total mass of the positive electrode lithium supplement agent can be any point value or any two point range values ​​between 0.1 and 5%, for example, it can be 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.6%, 4.8%, 5% or any two range values.

[0050] The present application study found that the mass percentage of the first slurry additive will synergistically affect the lithium supplement agent with the ion capture agent. When the mass percentage of the first slurry additive is within the above range, it can work better with the lithium supplement agent to improve the stability of the positive electrode lithium supplement agent layer, thereby improving the overall performance of the secondary battery.

[0051] In one embodiment, the thickness ratio m of the positive electrode active material layer to the positive electrode lithium replenisher layer is 10-500.

[0052] It should be noted that the testing and calculation method of the thickness ratio m of the positive electrode active material layer and the positive electrode lithium replenisher layer is: take the electrode sheet after rolling and cut it to expose a regular cross-section, and use a scanning electron microscope (SEM) to measure the thickness of the positive electrode active material layer and the positive electrode lithium replenisher layer in the cross-section. The ratio of the thickness of the positive electrode material layer to the thickness of the positive electrode active material layer is m.

[0053] Exemplarily, the thickness ratio m of the positive electrode active material layer to the positive electrode lithium supplement layer can be any point value or any two point range values ​​between 10 and 500, for example, it can be one of 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 500 or any two range values.

[0054] In one embodiment, the thickness ratio m of the positive electrode active material layer to the positive electrode lithium supplement layer is 30 to 80. For example, it can be one of 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80 or any two of the ranges.

[0055] The present application has found that controlling the thickness of the positive electrode active material layer and the positive electrode lithium replenisher layer within an appropriate range can effectively control the mass percentage range of the lithium replenisher in the positive electrode plate, thereby balancing the relationship between the battery's safety and cyclability, fast charging, and initial internal resistance; when the thickness ratio m of the positive electrode active material layer and the positive electrode lithium replenisher layer is selected to be 10 to 500, especially 30 to 80, the comprehensive performance of the secondary battery obtained is better.

[0056] In one embodiment, the mass ratio of the lithium supplement agent to the positive electrode active material is (1.05-50.6):1000.

[0057] It should be noted that the test and calculation method of the mass ratio of the lithium supplement agent to the positive electrode active material is: use ICP-OES to test the content of the lithium supplement agent and the positive electrode active material, and divide the mass of the lithium supplement agent by the mass of the positive electrode active material to obtain the mass ratio of the lithium supplement agent to the positive electrode active material.

[0058] Exemplarily, the mass ratio of the lithium supplement agent to the positive electrode active material may be any point value or any two point range values ​​between (1.05-50.6):1000, for example, it may be one of 1.05:1000, 2:1000, 4:1000, 6:1000, 8:1000, 10:1000, 15:1000, 20:1000, 25:1000, 30:1000, 35:1000, 40:1000, 45:1000, 50:1000, 50.6:1000 or any two range values.

[0059] In one embodiment, the mass ratio of the lithium supplement and the positive electrode active material is (20-30):1000. For example, it can be one or any two of 20:1000, 21:1000, 22:1000, 23:1000, 24:1000, 25:1000, 26:1000, 27:1000, 28:1000, 29:1000, 30:1000.

[0060] The present application study found that the mass ratio of the lithium replenisher to the positive electrode active material in the positive electrode plate is in the range of (1.05-50.6):1000, which can effectively balance the effects of the lithium replenisher and the positive electrode active material, and maximize the lithium replenishment effect of the battery; in particular, the mass ratio of the lithium replenisher to the positive electrode active material is further selected to be (20-30):1000, and the high-temperature cycle performance and fast charging performance of the secondary battery obtained are better, and the initial internal resistance is lower.

[0061] In one embodiment, the first slurry additive and the second slurry additive are independently selected from at least one of 3,4-dihydroxy-3-cyclobutene-1,2-dione, 1,3,5-benzenetricarboxylic acid, diketosuccinic acid, and oxomalic acid.

[0062] The present application study found that selecting the above-mentioned type of substance as the first slurry additive or the second slurry additive can effectively interact with the lithium supplement agent and the positive electrode active material, neutralize the alkalinity of the lithium supplement agent and the positive electrode active material, and improve the stability of the positive electrode sheet, thereby improving the high temperature cycle performance of the secondary battery.

[0063] In one embodiment, the lithium supplement includes at least one of Li2C4O4, Li5FeO4, Li6CoO4, Li2NiO2, Li3N, Li2C3O5, Li2C4O6, 2-cyclopropene-1-one-2,3-dihydroxylithium, and 3,4-dihydroxybenzonitrile dilithium.

[0064] The present application has found that when the above-mentioned type of lithium supplement is selected, its capacity is utilized within a suitable voltage range, which can better match the lithium iron manganese phosphate material, thereby improving the overall performance of the secondary battery. In addition, the above-mentioned type of lithium supplement also has a high irreversible capacity, which can replenish the active lithium consumed by the generated SEI film, and can also provide more active lithium for subsequent cycles, thereby improving the fast charging performance and high temperature cycle performance of the secondary battery.

[0065] In one embodiment, the first conductive agent and the second conductive agent are independently selected from at least one of acetylene black, Ketjen black, CNT, SWCNT, Super P, VGCF, and graphene.

[0066] The research in this application found that by introducing the above-mentioned types of first conductive agent and second conductive agent, a three-dimensional conductive path can be effectively formed in the positive electrode plate, effectively increasing the conductive contact between the positive electrode active material and the lithium supplement agent, improving the electronic conductivity of the positive electrode, reducing the initial internal resistance of the battery, and improving the fast charging performance of the battery.

[0067] In one embodiment, the first binder and the second binder independently include at least one of polytetrafluoroethylene, polyurethane resin, polyacrylic acid, and styrene-butadiene rubber.

[0068] The present application has found that selecting the above-mentioned types of substances as the first binder or the second binder can ensure that the positive electrode sheet has better cohesion and peeling force, thereby improving the overall performance of the secondary battery.

[0069] In one embodiment, the surfaces of the positive electrode active material and the lithium supplement are both provided with a carbon coating layer with a thickness of 1 to 100 nm, and the carbon in the carbon coating layer of the positive electrode active material includes at least one of N-doped carbon and F-doped carbon.

[0070] It should be noted that the test method for the thickness of the carbon coating layer on the surface of the positive electrode active material and the lithium supplement is: using a transmission electron microscope (TEM) to test the thickness of the carbon layer. The test method for the doping element is: using an X-ray photoelectron spectroscopy (XPS) to test the doping element.

[0071] Exemplarily, the thickness of the carbon coating layer on the surface of the positive electrode active material and the lithium supplement agent may be any point value or any two point range values ​​between 1 and 100 nm, for example, it may be one of 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, and 100 nm or any two range values.

[0072] The present application has found that by setting a carbon coating layer within a specific thickness range on the surface of the positive electrode active material and the lithium supplement, and limiting the carbon of the carbon coating layer to include at least one of N-doped carbon or F-doped carbon, the conductivity of the positive electrode active material and the lithium supplement can be significantly improved, and the resistivity of the positive electrode active material and the lithium supplement can be reduced, thereby effectively improving the kinetic performance of the battery, improving the fast charging performance of the battery, and reducing the initial internal resistance of the battery; and the doped atoms in the N-doping and / or F-doping of the introduced carbon coating layer have a certain electronegativity, which can adsorb the dissolved metal ions and limit the migration of the metal ions to the electrolyte and the negative electrode, thereby further improving the high temperature cycle performance of the secondary battery.

[0073] In one embodiment, the thickness of the carbon coating layer on the surface of the positive electrode active material and the lithium supplement agent is 40-60 nm, for example, it can be one or any two of 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, 50 nm, 52 nm, 54 nm, 56 nm, 58 nm, 60 nm.

[0074] The present application has found that when the thickness of the carbon coating layer on the surface of the positive electrode active material and the lithium supplement agent is further selected to be 40 to 60 nm, the comprehensive performance of the secondary battery obtained is better.

[0075] In one embodiment, the positive electrode active material includes Li a Mn x Fe y M z PO4, wherein 0.95≤a≤1.05, 0.4≤x≤0.8, 0.2≤y≤0.6, 0<z≤0.08, and M includes at least one of Mg, Ti, V, Co, Mo, and W.

[0076] The present application has found that when the positive electrode active material is further selected as the above-mentioned type of substance, its conductivity is better and its coordination effect with the lithium supplement is better, thereby being able to improve the overall performance of the secondary battery.

[0077] In one embodiment, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material. The present application has no limitation on the negative electrode active material, and any known negative electrode active material can be used. As an example, the negative electrode active material can be at least one of artificial graphite, natural graphite, silicon-carbon composite material, silicon alone, silicon oxide, and hard carbon.

[0078] In one embodiment, the negative electrode current collector may be made of a material with good electrical conductivity and mechanical strength to perform the functions of conducting electricity and collecting current. In one embodiment, the negative electrode current collector may be made of a metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector is made of copper foil.

[0079] In one embodiment, the electrolyte includes an organic solvent, a lithium salt and an additive. The present application has no limitation on the organic solvent, lithium salt and additive in the electrolyte, and any known organic solvent, lithium salt and additive can be used.

[0080] Exemplarily, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide; and the additive includes at least one of vinylene carbonate (VC), fluoroethylene carbonate, vinyl sulfate, and 1,4-butanesultone.

[0081] In one embodiment, the separator of the secondary battery is disposed between the positive electrode and the negative electrode.

[0082] In one embodiment of the present application, the present application proposes an electrical device, and the electrical device includes the secondary battery described in the present application.

[0083] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0084] Example 1

[0085] The present invention provides a secondary battery, wherein a method for preparing the secondary battery comprises the following steps:

[0086] (1) Preparation of positive electrode sheet

[0087] S1, the positive electrode active material lithium manganese iron phosphate (structural formula LiMn 0.58 Fe 0.4Mg 0.02 PO4), a second conductive agent (Super P), a second binder (polyvinylidene fluoride, PVDF) and a second slurry additive (3,4-dihydroxy-3-cyclobutene-1,2-dione) are mixed in a mass ratio of 96:1:2:1, and after adding solvent N-methylpyrrolidone, they are stirred in a vacuum mixer to obtain a uniform positive electrode active material layer slurry;

[0088] S2, mixing the lithium replenisher (Li5FeO4), the first conductive agent (acetylene black), sulfonated polytetrafluoroethylene, the first binder (styrene-butadiene rubber) and the first slurry additive (3,4-dihydroxy-3-cyclobutene-1,2-dione) in a mass ratio of 95:1:1:1:2, adding solvent N-methylpyrrolidone and stirring in a vacuum mixer, and obtaining a uniform positive electrode lithium replenisher layer slurry after stirring;

[0089] S3, the positive electrode active material layer slurry is evenly coated on the 12μm positive electrode current collector, and after coating, it is dried in an oven at 100°C to obtain a positive electrode active material layer with a thickness of 200μm (double layer); then the positive electrode lithium supplement layer slurry is evenly coated on the positive electrode active material layer, and after coating, it is dried in an oven at 100°C, and then the positive electrode sheet is obtained after rolling, slitting and cutting;

[0090] Wherein, the thickness ratio m of the positive electrode active material layer to the positive electrode lithium supplement layer is 30;

[0091] The mass ratio of lithium supplement agent to positive electrode active material is 20:1000;

[0092] (2) Preparation of negative electrode sheet

[0093] According to artificial graphite: conductive carbon black (Super-P): acrylonitrile multi-polymer (LA133) ： Polyvinyl pyrrolidone (PVP): carboxymethyl cellulose (CMC) = 97:0.5:1.4:0.5:0.6 mass ratio, add the negative electrode active material artificial graphite and conductive carbon black (Super-P) into a stirring tank for thorough mixing, then add a quantitative binder acrylonitrile multipolymer (LA133), dispersant polyvinyl pyrrolidone (PVP), negative electrode thickener carboxymethyl cellulose (CMC), deionized water and continue stirring to obtain a negative electrode slurry with good dispersion, wherein the content of deionized water in the negative electrode slurry is 50%; the stirred negative electrode slurry is coated on the surface of the negative electrode current collector copper foil, and dried at 90°C, then the electrode sheet is rolled to a suitable thickness, and then cut and slit, and after slitting, it is dried at 110°C under vacuum conditions for 5h, and finally the pole ears are welded to make the negative electrode sheet;

[0094] (3) Preparation of electrolyte

[0095] Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent consisting of ethyl methyl carbonate (EMC), propylene carbonate (PC), and dimethyl carbonate (DMC) (mass ratio of 1:1:1) to obtain an electrolyte with a concentration of 1 mol / L;

[0096] (4) Preparation of secondary batteries

[0097] The positive electrode sheet, separator, and negative electrode sheet are wound in sequence so that the separator is located exactly between the positive and negative electrodes to isolate the two electrodes. Then they are wound into bare cells and loaded into aluminum-plastic films. They are baked at 80°C to remove moisture. After the moisture is removed, electrolyte is injected. After sealing, hot and cold pressing, secondary sealing, formation, and capacity division, a secondary battery is obtained.

[0098] Embodiments 2 to 6

[0099] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass ratio of the lithium supplement agent, the first conductive agent, the ion capture agent, the first slurry additive and the first binder in the positive electrode lithium supplement agent layer slurry is adjusted to achieve the parameters in Table 1.

[0100] Embodiments 7 to 10

[0101] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the thickness of the positive electrode lithium replenisher layer is adjusted to achieve the parameters in Table 1.

[0102] Examples 11-12

[0103] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass ratio of the positive electrode active material, the second conductive agent, the second slurry additive and the second binder in the positive electrode active material layer is adjusted to achieve the parameters in Table 1.

[0104] Embodiments 13 to 16

[0105] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that both the positive electrode active material and the lithium supplement agent have a layer of coated carbon with different thicknesses, and the coated carbon is N-doped carbon.

[0106] Embodiment 17

[0107] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the positive electrode active material and the lithium supplement agent are coated with a layer of carbon, and the coated carbon is F-doped carbon.

[0108] Embodiment 18

[0109] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the positive electrode active material is lithium manganate, and the lithium supplement is 2-cyclopropene-1-one-2,3-dihydroxylithium.

[0110] Embodiment 19

[0111] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the first slurry additive is 1,3,5-benzenetricarboxylic acid, and the second slurry additive is oxomalic acid.

[0112] Embodiment 20

[0113] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the first conductive agent is acetylene black, the second conductive agent is graphene, the first binder is polyurethane resin, and the second binder is polyacrylic acid.

[0114] Comparative Example 1

[0115] The comparative example of the present application provides a secondary battery, which is different from Example 1 in that no ion capture agent is added to achieve the parameters in Table 1.

[0116] Comparative Example 2

[0117] The comparative example of the present application provides a secondary battery, which is different from Example 1 in that no lithium supplement is added to achieve the parameters in Table 1.

[0118] In the secondary batteries provided in the embodiments and comparative examples, the mass ratio A1 of the lithium replenisher, the first conductive agent, the ion capture agent, the first slurry additive and the first binder in the positive electrode lithium replenisher layer, the thickness ratio m of the positive electrode active material layer and the positive electrode lithium replenisher layer, the mass ratio A2 of the positive electrode active material, the second conductive agent, the second slurry additive and the second binder in the positive electrode active material layer, the mass ratio q of the lithium replenisher and the positive electrode active material, and the thickness d of the carbon coating layer are as shown in Table 1;

[0119] Table 1

[0120]

[0121]

[0122] The performance tests of the secondary batteries provided in the embodiments and comparative examples are as follows;

[0123] 1. Initial internal resistance (DCR): At a constant temperature of 25°C, fully charge at 1C to 4.25V, then discharge at 1C for 0.5h, and then discharge at 5C for 10s, calculate the DCR value (50% SOC);

[0124] 2. 45℃ Cycle Performance: At a constant temperature of 45℃, the voltage range is 2.5-4.25V, 1C constant current and constant voltage charging (constant voltage to 0.05C) and constant current discharge are used, and the capacity retention rate is recorded after 1500 cycles;

[0125] 3. Fast charging performance: Vref is defined as the potential difference between the negative electrode of the secondary battery and the reference electrode (lithium metal electrode). At a constant temperature of 25°C, 0.33C0 is fully discharged to 2.5V (C0 is the 0.33C constant capacity of the battery); then follow the steps below:

[0126] 1) 1 / 3C0 constant current charge to 10%C0, let stand for 30 minutes;

[0127] 2) 5C0 constant current charging until Vref≤0, then jump to the next step;

[0128] 3) 4C0 constant current charging until Vref≤0, then jump to the next step;

[0129] 4) xC0 is charged at constant current until Vref≤0, then jump to the next step;

[0130] 5) x is 5 / 4 / 3 / 2 / 1 / 0.5 / 0.4 / 0.3 / 0.2 / 0.1 from step 2 (i.e. starting from 5C0, step charging to 0.1C0, and the cutoff condition of each step is that the potential difference Vref between the negative electrode potential and the reference electrode reaches 0V);

[0131] 6) Let stand for 30 minutes;

[0132] 7) Record battery fast charging data and calculate the average charging rate of the battery in the 10%-80% SOC range;

[0133] The results obtained are shown in Table 2;

[0134] Table 2

[0135]

[0136]

[0137] It can be seen from Table 2 that when the technical solution provided by the present application is adopted, the obtained secondary battery has excellent high-temperature cycle performance and fast charging performance, and the initial internal resistance of the obtained secondary battery is low; specifically, the initial internal resistance of the obtained secondary battery is below 46.78 mΩ, the capacity retention rate after 1500 cycles at 45°C is above 70.38%, and the average charge rate of 10-80% SOC is above 1.78C;

[0138] It can be seen from Examples 1 to 20 and Comparative Example 1 that when the ion capture agent is not introduced into the positive electrode lithium supplement layer, the cycle capacity retention rate of the obtained secondary battery is only 70.21%; it can be seen from Examples 1 to 20 and Comparative Example 2 that when there is no lithium supplement, the initial DCR of the obtained secondary battery shows a significant increasing trend, and the cycle performance and rate performance both decrease to a certain extent.

[0139] Finally, it should be noted that the above embodiments are intended to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A secondary battery, characterized in that: It includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte. The positive electrode plate includes a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, and a positive lithium replenisher layer arranged on the positive active material layer away from the surface of the positive current collector; the positive lithium replenisher layer includes a lithium replenisher and an ion capture agent; the positive active material layer includes a positive active material; and the ion capture agent includes a perfluorosulfonic acid group.

2. The secondary battery according to claim 1, characterized in that: The ion capture agent includes at least one of sulfonated polytetrafluoroethylene and perfluorosulfonic acid resin.

3. The secondary battery according to claim 1, characterized in that: The positive electrode lithium supplement layer further includes a first slurry additive, a first conductive agent, and a first binder; the positive electrode active material layer further includes a second slurry additive, a second conductive agent, and a second binder.

4. The secondary battery according to claim 3, characterized in that: Satisfy at least one of the following: a. The mass of the positive electrode active material accounts for 90-98% of the total mass of the positive electrode active material layer; b. The mass of the lithium replenisher accounts for 93-99% of the total mass of the positive electrode lithium replenisher layer; c. The mass of the ion capture agent accounts for 0.1 to 5% of the total mass of the positive electrode lithium replenisher layer; d. The mass of the first slurry additive accounts for 0.1 to 5% of the total mass of the positive electrode lithium supplement.

5. The secondary battery according to claim 1, characterized in that: The thickness ratio m of the positive electrode active material layer to the positive electrode lithium supplement layer is 10-500.

6. The secondary battery according to claim 1, characterized in that: The mass ratio of the lithium supplement agent to the positive electrode active material is (1.05-50.6):1000.

7. The secondary battery according to claim 3, characterized in that: Satisfy at least one of the following: a. The first slurry additive and the second slurry additive are independently selected from at least one of 3,4-dihydroxy-3-cyclobutene-1,2-dione, 1,3,5-benzenetricarboxylic acid, diketosuccinic acid, and oxomalic acid; b. The lithium supplement includes at least one of Li2C4O4, Li5FeO4, Li6CoO4, Li2NiO2, Li3N, Li2C3O5, Li2C4O6, 2-cyclopropene-1-one-2,3-dihydroxylithium, and 3,4-dihydroxybenzonitrile dilithium; c. The first conductive agent and the second conductive agent are independently selected from at least one of acetylene black, Ketjen black, CNT, SWCNT, SuperP, VGCF, and graphene; d. The first binder and the second binder each independently include at least one of polytetrafluoroethylene, polyurethane resin, polyacrylic acid, and styrene-butadiene rubber.

8. The secondary battery according to claim 1, characterized in that: The surfaces of the positive electrode active material and the lithium supplement agent are both provided with a carbon coating layer with a thickness of 1 to 100 nm, and the carbon in the carbon coating layer of the positive electrode active material includes at least one of N-doped carbon and F-doped carbon.

9. The secondary battery according to claim 1, characterized in that: The positive electrode active material includes Li a Mn x Fe y M z PO4, wherein 0.95≤a≤1.05, 0.4≤x≤0.8, 0.2≤y≤0.6, 0<z≤0.08, and M includes at least one of Mg, Ti, V, Co, Mo, and W.

10. An electrical device, characterized in that: The invention comprises a secondary battery as claimed in any one of claims 1 to 9.

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