Positive pole piece and battery

Abstract

In order to solve the problems of battery impedance increase and electrical performance reduction caused by unreasonable structural design of the existing positive pole piece, the invention provides a positive pole piece and a battery, the positive pole piece comprises a current collector, a protective coating and a positive active material layer, the protective coating is arranged on at least one side of the current collector, and the positive active material layer is arranged on the protective coating. The positive active material layer is arranged on one side, deviating from the current collector, of the protective coating; the protective coating comprises a first conductive agent; the positive active material layer comprises a positive active material and a second conductive agent; the mass percentage of the first conductive agent in the protective coating is P1%, and the thickness of the protective coating on one side of the current collector after rolling is t [mu] m; the single-side coating surface density of the positive electrode active material layer is sigma g / m < 2 >, the mass percent of the positive electrode active material in the positive electrode active material layer is P2%, and the mass percent of the second conductive agent in the positive electrode active material layer is P3%; the positive pole piece meets the formula 1, and t is larger than or equal to 0.5 and smaller than 5.9.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a positive electrode sheet. BACKGROUND

[0002] In the related art, in order to improve the safety performance of the battery cell, an overheat protection coating is generally coated between the positive current collector and the positive active material coating to prevent the battery from thermal runaway, but the overheat protection coating causes the increase of the impedance of the battery cell, the loss of the electrical performance or the energy density of the battery.

[0003] Therefore, it is urgent to provide a positive electrode sheet which can improve the energy density and the electrical performance of the battery while meeting the safety performance. SUMMARY

[0004] In view of the problem that the unreasonable structure design of the existing positive electrode sheet leads to the increase of the impedance of the battery and the reduction of the electrical performance, the application provides a positive electrode sheet and a battery.

[0005] The technical scheme adopted by the application to solve the above technical problem is as follows: In a first aspect, the application provides a positive electrode sheet, comprising a current collector, a protection coating and a positive active material layer, the protection coating is arranged on at least one side of the current collector, and the positive active material layer is arranged on the side of the protection coating away from the current collector. The protection coating comprises a first conductive agent, and the positive active material layer comprises a positive active material and a second conductive agent. The mass percentage of the first conductive agent in the protection coating is P1%, and the thickness of the protection coating after rolling on one side of the current collector is t μm. The single-sided coating area density of the positive active material layer is σ g / m 2 The mass percentage of the positive active material in the positive active material layer is P2%, and the mass percentage of the second conductive agent in the positive active material layer is P3%. The positive electrode sheet satisfies formula 1: Wherein, 0.5≤t<5.9.

[0006] Optionally, when 0.5≤t<2.5, the positive electrode sheet satisfies formula 2: .

[0007] Optionally, when 2.5≤t<5.9, the positive electrode sheet satisfies formula 3: .

[0008] Optionally, 0.5≤P1≤6.0, 88≤P2≤99, 0.2≤P3≤3, and 170≤σ≤195.

[0009] Optionally, the protective coating further comprises an inorganic material, and the inorganic material comprises at least one of boehmite, alumina, magnesia, barium titanate, silicon dioxide, and titanium dioxide.

[0010] Optionally, the mass percentage of the inorganic material in the protective coating is 70% to 96%.

[0011] Optionally, the protective coating further comprises a binder, and the binder comprises at least one of polyvinylidene fluoride, polyacrylonitrile copolymer, polyacrylic acid, polyacrylic acid salt, and polyacrylate.

[0012] Optionally, the first conductive agent comprises at least one of conductive carbon black, carbon nanotube, carbon fiber, and graphene. Optionally, the second conductive agent comprises at least one of conductive carbon black, carbon nanotube, carbon fiber, and graphene.

[0013] Optionally, the positive electrode active material comprises at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganate, lithium nickelate, lithium manganese iron phosphate, lithium-rich manganese-based material, lithium vanadium phosphate, lithium titanate, and lithium vanadium phosphate oxide.

[0014] The application further provides a battery comprising the positive electrode sheet according to any one of the above.

[0015] In the application, by limiting the thickness t of the protective coating after rolling on any side of the current collector to be within the range of 0.5 to 5.9 μm, the mass percentage P1 of the first conductive agent in the protective coating, the single-side coating surface density σ of the positive electrode active material layer, the mass percentage P2 of the positive electrode active material in the positive electrode active material layer, and the mass percentage P3 of the second conductive agent in the positive electrode active material layer satisfy the relationship of formula 1, so that the design of the protective coating can meet the safety performance of the battery, while reducing the thickness of the protective coating and the battery impedance as much as possible, reducing the battery polarization, and improving the battery electrical performance and energy density. If the positive electrode sheet is lower than the range shown in formula 1, the thickness of the protective coating is too large or the single-side coating density of the positive electrode active material layer is too small, so that the battery impedance is too large and the battery energy density is reduced. If the positive electrode sheet is higher than the range shown in formula 1, the thickness of the protective layer is too low, so that the protective coating cannot prevent the thermal runaway of the battery, and the safety performance of the battery is reduced. DETAILED DESCRIPTION

[0016] In order to make the technical problems, technical solutions and beneficial effects of the application clearer, the application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0017] An embodiment of the present application provides a positive electrode sheet, comprising a current collector, a protective coating and a positive electrode active material layer, the protective coating is arranged on at least one surface of the current collector, and the positive electrode active material layer is arranged on the side of the protective coating away from the current collector; The protective coating comprises a first conductive agent, and the positive electrode active material layer comprises a positive electrode active material and a second conductive agent. The mass percentage of the first conductive agent in the protective coating is P1%, and the thickness of the protective coating on one side of the current collector after rolling is t μm. The single-side coating area density of the positive electrode active material layer is σ g / m 2 The mass percentage of the positive electrode active material in the positive electrode active material layer is P2%, and the mass percentage of the second conductive agent in the positive electrode active material layer is P3%. The positive electrode sheet satisfies formula 1: Wherein, 0.5≤t<5.9.

[0018] In the present embodiment, by limiting the thickness t of the protective coating on any one side of the current collector after rolling to be within the range of 0.5-5.9 μm, the mass percentage P1 of the first conductive agent in the protective coating, the single-side coating area density σ of the positive electrode active material layer, the mass percentage P2 of the positive electrode active material in the positive electrode active material layer, and the mass percentage P3 of the second conductive agent in the positive electrode active material layer satisfy the relationship of formula 1, so that the design of the protective coating can meet the safety performance of the battery, while the thickness of the protective coating and the battery impedance are reduced as much as possible, the battery polarization is reduced, and the battery electrical performance and energy density are improved. If the positive electrode sheet is lower than the range shown in formula 1, the thickness of the protective coating is too large or the single-side coating area density of the positive electrode active material layer is too small, so that the battery impedance is too large and the battery energy density is reduced. If the positive electrode sheet is higher than the range shown in formula 1, the thickness of the protective layer is too low, so that the protective coating cannot prevent the thermal runaway of the battery, and the safety performance of the battery is reduced.

[0019] Specifically, the thickness of the protective coating on any one side of the current collector after rolling includes but is not limited to 0.5 μm, 1 μm, 1.3 μm, 1.6 μm, 1.9 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3.1 μm, 3.3 μm, 3.6 μm, 3.9 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5.1 μm, 5.4 μm or 5.8 μm.

[0020] In some embodiments, when 0.5≤t<2.5, the positive electrode sheet satisfies formula 2: By limiting the thickness t of the protective coating on either side of the current collector to be in the range of 0.5-2.5 pm after rolling, the positive electrode sheet satisfies the relationship shown in equation 2, so that the protective coating can also satisfy the safety performance of the battery at a thinner thickness, while reducing the battery impedance and improving the energy density of the battery.

[0021] In some embodiments, when 2.5≤t<5.9, the positive electrode sheet satisfies equation 3: By limiting the thickness t of the protective coating on either side of the current collector to be in the range of 2.5-5.9 pm after rolling, the positive electrode sheet satisfies the relationship shown in equation 3, so that the battery has better safety performance, while reducing the battery impedance, improving the energy density and electrical performance of the battery.

[0022] In some embodiments, 0.5≤P1≤6.0, 88≤P2≤99, 0.2≤P3≤3, 170 g / m 2 ≤σ≤195 g / m 2 By limiting the mass percentage P1 of the first conductive agent in the protective coating, the single-sided coating area density σ of the positive electrode active material layer, the mass percentage P2 of the positive electrode active material in the positive electrode active material layer, and the mass percentage P3 of the second conductive agent in the positive electrode active material layer to be in the above ranges, while also satisfying the relationship shown in equation 1, the battery has better safety performance, electrical performance, and higher energy density.

[0023] Specifically, the mass percentage P1% of the first conductive agent in the protective coating includes but is not limited to 0.5%, 0.8%, 1.1%, 1.4%, 1.7%, 2%, 2.3%, 2.6%, 2.9%, 3.2%, 3.5%, 3.8%, 4.1%, 4.4%, 4.7%, 5%, 5.3%, 5.6%, or 6.0%.

[0024] The mass percentage P2% of the positive electrode active material in the positive electrode active material layer includes but is not limited to 88%, 91%, 94%, 97%, or 99%.

[0025] The mass percentage P3% of the second conductive agent in the positive electrode active material layer includes but is not limited to 0.2%, 0.5%, 0.8%, 1.1%, 1.4%, 1.7%, 2%, 2.3%, 2.6%, or 3%.

[0026] The single-sided coating area density of the positive electrode active material layer includes but is not limited to 170 g / m 2 , 173 g / m 2 , 176 g / m 2 , 179 g / m 2 , 182 g / m 2 , 185 g / m 2 , 188 g / m2 , 191 g / m 2 or 195 g / m 2 .

[0027] In some embodiments, the protective coating further comprises an inorganic material, the inorganic material comprising at least one of boehmite, alumina, magnesia, barium titanate, silicon dioxide, titanium dioxide. By selecting the above inorganic material, insulation and heat conduction effects are achieved when internal short circuit occurs, the progress of thermal runaway is delayed, and the risk of battery thermal runaway is reduced.

[0028] In some embodiments, the mass percentage of the inorganic material in the protective coating is 70% to 96%. By limiting the mass percentage of the inorganic material, it is ensured that the protective coating can have good insulation and heat conduction effects, and the risk of battery thermal runaway is reduced. Specifically, the mass percentage of the inorganic material in the protective coating includes but is not limited to 70%, 73%, 76%, 79%, 82%, 85%, 88%, 91%, 94% or 96%.

[0029] In some embodiments, the protective coating further comprises a binder, the binder comprising at least one of polyvinylidene fluoride, polyacrylonitrile copolymer, polyacrylic acid, polyacrylate, polyacrylate. By introducing the binder into the protective coating, the bonding strength between the protective coating and the positive active material layer and the current collector is ensured.

[0030] In some embodiments, the first conductive agent comprises at least one of conductive carbon black, carbon nanotubes, carbon fibers, graphene. By selecting the above first conductive agent, the impedance of the protective coating is reduced, an efficient electron transport network is constructed, battery polarization is reduced, and battery electrical performance is improved.

[0031] In some embodiments, the second conductive agent comprises at least one of conductive carbon black, carbon nanotubes, carbon fibers, graphene. By selecting the above second conductive agent, the impedance of the positive active material layer is reduced, an efficient electron transport network is constructed, battery polarization is reduced, and battery electrical performance is improved.

[0032] In some embodiments, the positive active material comprises at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium nickel cobalt aluminum, lithium nickel cobalt manganate, lithium nickelate, lithium manganese iron phosphate, lithium-rich manganese-based material, lithium vanadium phosphate, lithium titanate, and lithium vanadium phosphate. It can be understood that the positive active material is not particularly limited and can be any known material suitable for use as a positive active material.

[0033] An embodiment of the present application also provides a battery comprising the positive electrode sheet as claimed in any one of the above, to improve the safety performance and electrical performance of the battery.

[0034] In the present application, the kind of the current collector is not particularly limited, which can be any known material suitable for use as a positive electrode current collector. In one embodiment, the current collector comprises at least one or more of aluminum, stainless steel, nickel plating, titanium, tantalum and the like metal materials, and carbon cloth, carbon paper.

[0035] Further, the battery further comprises a negative electrode and an electrolyte. In the present embodiment, the kind of the negative electrode is not limited, which can be any known negative electrode, such as a silicon negative electrode, a graphite negative electrode, a silicon-carbon negative electrode, a silicon-oxygen negative electrode, a lithium negative electrode, a lithium alloy negative electrode, a lithium-free negative electrode, etc. The composition of the electrolyte is not limited, which can be any known electrolyte suitable for use in a lithium battery.

[0036] In a preferred embodiment, the positive electrode current collector is a metal material.

[0037] An embodiment of the present application also provides a power-using device comprising the battery described above.

[0038] For example, the power-using device can include, but is not limited to, a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, and an energy storage system.

[0039] The present application is further illustrated by the following examples.

[0040] Example 1 The present embodiment is used to illustrate the positive electrode tab and the battery disclosed in the present application.

[0041] 1. Preparation of the positive electrode tab: Aluminum oxide, polyvinylidene fluoride and carbon nanotubes with a mass ratio of 92:5:3 were dispersed in N-methylpyrrolidone, and stirred uniformly to prepare a protective coating slurry. The slurry was coated on both sides of a 9 μm aluminum foil, and dried to obtain an aluminum foil with a protective coating. Lithium cobaltate, polyvinylidene fluoride and carbon nanotubes with a mass ratio of 97.4:1.8:0.8 were mixed and dispersed in N-methylpyrrolidone, and stirred uniformly to prepare a positive electrode active material layer slurry. Subsequently, the slurry was coated on the surface of the protective coating away from the aluminum foil, and the coating surface density σ was 182 g / m 2 After drying and rolling, the single-sided thickness t of the protective coating after rolling was 3 μm. The tab was cut to obtain a positive electrode tab with a protective coating and a positive electrode active material layer.

[0042] 2. Preparation of the negative electrode tab: The artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose are prepared into a negative electrode slurry with a mass ratio of 98:1.5:0.5, coated on two surfaces of a copper foil, baked at 95°C, rolled, and cut to obtain a negative electrode sheet.

[0043] 3. Preparation of electrolyte: The vinyl carbonate (EC), propylene carbonate (PC), propyl propionate (EP) and diethyl carbonate (DEC) are mixed and stirred according to a mass ratio of 10:20:40:30 to form a mixed solvent, and then LiPF6, 1,3,6-hexane trinitrile 1%, 1,3-propane sultone 5% and ethylene sulfate 3% are added to the mixed solvent, and the concentration of lithium salt is 1M.

[0044] 4. Preparation of battery: The above positive electrode sheet, negative electrode sheet and separator are wound, packaged with an aluminum plastic film, and then subjected to conventional lithium battery preparation processes such as baking, liquid injection and hot pressing to obtain a battery.

[0045] Example 2 Example 2 is used to illustrate the positive electrode sheet and battery disclosed in the present application, which includes most of the operation steps in Example 1, and the difference lies in the preparation of the positive electrode sheet.

[0046] Silicon dioxide, sodium polyacrylate and conductive carbon black with a mass ratio of 86.2:12:1.8 are dispersed in deionized water, and fully stirred to obtain a protective coating slurry, which is coated on both sides of a 9μm aluminum foil, and dried to obtain an aluminum foil with a protective coating. Lithium cobaltate, polyvinylidene fluoride and carbon nanotubes with a mass ratio of 97:2:1 are mixed and dispersed in N-methyl pyrrolidone, and fully stirred to obtain a positive electrode active material layer slurry, which is then coated on the surface of the protective coating away from the aluminum foil, and the coating surface density σ is 180g / m 2 , dried, and rolled, and the thickness t of the protective coating after rolling is 1.8μm. The sheet is cut to obtain a positive electrode sheet with a protective coating and a positive electrode active material layer.

[0047] Example 3 Example 3 is used to illustrate the positive electrode sheet and battery disclosed in the present application, which includes most of the operation steps in Example 1, and the difference lies in the preparation of the positive electrode sheet.

[0048] Boehmite, polyvinylidene fluoride and conductive carbon black with a mass ratio of 94.9:4:1.1 are dispersed in N-methyl pyrrolidone, and fully stirred to obtain a protective coating slurry, which is coated on both sides of a 9μm aluminum foil, and dried to obtain an aluminum foil with a protective coating. The lithium cobaltate, polyvinylidene fluoride and carbon nanotube with a mass ratio of 98:1:1 were mixed and dispersed in N-methyl pyrrolidone to prepare an anode active material layer slurry, which was then coated on the surface of the protective coating away from the aluminum foil with a coating surface density σ of 175 g / m 2 , dried, rolled, and the thickness t of the single side of the protective coating after rolling was 1.7 μm. The pole piece was slitted to obtain an anode pole piece with a protective coating and an anode active material layer.

[0049] Example 4 Example 4 is used to illustrate the preparation of the anode pole piece of the present disclosure, which includes most of the operation steps in Example 1, and the difference lies in the preparation of the anode pole piece.

[0050] The barium titanate, sodium polyacrylate, carbon nanotube and conductive carbon black with a mass ratio of 87:10:1:2 were dispersed in deionized water, fully stirred and uniformly mixed to prepare a protective coating slurry, which was coated on both sides of the 9 μm aluminum foil, and dried to obtain an aluminum foil with a protective coating; The lithium cobaltate, polyvinylidene fluoride and carbon nanotube with a mass ratio of 97.4:1.7:0.9 were mixed and dispersed in N-methyl pyrrolidone to prepare an anode active material layer slurry, which was then coated on the surface of the protective coating away from the aluminum foil with a coating surface density σ of 187 g / m 2 , dried, rolled, and the thickness t of the single side of the protective coating after rolling was 2.3 μm. The pole piece was slitted to obtain an anode pole piece with a protective coating and an anode active material layer.

[0051] Examples 5-10 Examples 5-10 are used to illustrate the anode pole piece of the present disclosure. They include most of the operation steps in Example 1, and the difference lies in the use of the formulations in Table 1.

[0052] Comparative Example 1 Comparative Example 1 is used to compare the anode pole piece and battery of the present disclosure. It includes most of the operation steps in Example 1, and the difference lies in the preparation of the anode pole piece.

[0053] The lithium cobaltate, polyvinylidene fluoride and carbon nanotube with a mass ratio of 97:2:1 were mixed and dispersed in N-methyl pyrrolidone to prepare an anode active material layer slurry, which was then coated on the surface of the aluminum foil with a coating surface density σ of 180 g / m 2 , dried, rolled and slitted to obtain an anode pole piece with an anode active material layer.

[0054] Comparative Example 2 Comparative Example 2 is used to illustrate the positive electrode sheet and battery disclosed in the present application. It includes most of the operation steps in Example 1, except that the preparation of the positive electrode sheet is different.

[0055] Silicon dioxide, sodium polyacrylate, and carbon nanotubes were mixed in a mass ratio of 87:10:3, and dispersed in deionized water to prepare a protective coating slurry. The slurry was coated on both sides of a 9 μm aluminum foil, and dried to obtain an aluminum foil with a protective coating. Lithium cobaltate, polyvinylidene fluoride, and carbon nanotubes were mixed in a mass ratio of 97.4:1.7:0.9, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material layer slurry. The slurry was then coated on the surface of the protective coating away from the aluminum foil, and the coating surface density σ was 187 g / m 2 . After drying and rolling, the single-sided thickness t of the protective coating was 2.0 μm. The sheet was cut to obtain a positive electrode sheet with a protective coating and a positive electrode active material layer.

[0056] Comparative Example 3 Comparative Example 3 is used to illustrate the positive electrode sheet and battery disclosed in the present application. It includes most of the operation steps in Example 1, except that the preparation of the positive electrode sheet is different.

[0057] Silicon dioxide, sodium polyacrylate, and conductive carbon black were mixed in a mass ratio of 86:10.8:3.2, and dispersed in deionized water to prepare a protective coating slurry. The slurry was coated on both sides of a 9 μm aluminum foil, and dried to obtain an aluminum foil with a protective coating. Lithium cobaltate, polyvinylidene fluoride, and carbon nanotubes were mixed in a mass ratio of 98:1:1, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material layer slurry. The slurry was then coated on the surface of the protective coating away from the aluminum foil, and the coating surface density σ was 180 g / m 2 . After drying and rolling, the single-sided thickness t of the protective coating was 4.3 μm. The sheet was cut to obtain a positive electrode sheet with a protective coating and a positive electrode active material layer.

[0058] Comparative Examples 4-11 Comparative Examples 4-11 are used to illustrate the positive electrode sheet and battery disclosed in the present application. They include most of the operation steps in Example 1, except that the formulations in Table 1 are used.

[0059] Table 1 Performance Test I. The positive electrode sheet and battery obtained by the preparation method in the above examples and comparative examples were subjected to the following performance tests: 1. Heavy impact test method: The batteries prepared in the examples and comparative examples were charged at 25°C at 0.5C constant current to 4.50V, and then charged at constant voltage to a cutoff current of 0.02C. Subsequently, the battery was subjected to a weight impact test, the battery was placed on a plane, a steel column with a diameter of 15.8±0.2mm was placed on the center of the battery, the longitudinal axis of the steel column was parallel to the plane, a weight with a mass of 9.1±0.1kg was allowed to freely fall from a height of 610±25mm onto the steel column above the center of the battery, and the battery was observed for 6 hours after the test was completed. If the battery did not catch fire or explode, the test was passed. Ten batteries were tested for each example, and the weight impact test pass rate was used as an indicator to evaluate safety.

[0060] 2. Center needle puncture test method: The batteries prepared in the examples and comparative examples were charged at 25°C at 0.5C constant current to 4.50V, and then charged at constant voltage to a cutoff current of 0.02C. Subsequently, the battery was transferred to a needle puncture device, and a steel needle with a diameter of 4mm was uniformly penetrated through the center of the lithium ion battery at a speed of 30mm / s at 25°C, and the battery was left for 5min. If the battery did not catch fire or explode, the test was passed. Fifteen batteries were tested for each example, and the center needle puncture pass rate was used as an indicator to evaluate safety.

[0061] 3. Energy density loss test: The batteries prepared in the examples and comparative examples (without aging) were charged at 25°C at 0.5C constant current to 4.50V, and then charged at constant voltage to a cutoff current of 0.02C, left for 5min, and discharged at 0.2C constant current to 3.0V. The discharge energy was recorded. In addition, the thickness of the battery was measured using a PPG battery thickness gauge with a thickness measurement pressure of 650kgf. Thirty-two batteries were tested for each example, and the average value was taken as the battery energy density of the example.

[0062] Note: The unit of battery energy density is Wh / L, the units of battery thickness, length, and width are mm, and the unit of discharge energy is mWh. The battery energy density loss is based on Comparative Example 1, and the energy density loss of Comparative Example 1 is 0%.

[0063] 4. Cycle test method: The batteries prepared in the examples and comparative examples were charged at 25°C, ① at 1C constant current to 50% SOC, and then transferred to 0.65C constant current charging to 4.50V, with a cutoff current of 0.05C; ② discharged at 0.5C constant current to 3.0V; steps ① and ② were cycled 800T, and the cycle capacity retention rate was recorded. Three batteries were tested for each example.

[0064] 5. Battery impedance test: The batteries prepared from the examples and comparative examples were discharged at 25℃ with 0.2C constant current to 3.0V, and then rested for 5min, followed by charging with 0.5C constant current for 1h, resting for 10min, and testing the battery impedance with a battery internal resistance tester, and recording the data. 32 batteries were tested for each example, and the average value was taken as the battery impedance of the example.

[0065] The test results are shown in Table 2.

[0066] Table 2 From the data in Table 2, when the values of t, P1, P2, P3 and σ are within the ranges, the examples satisfying formula 1, formula 2 or satisfying formula 1, formula 3 perform better overall in the battery safety performance, energy density and electrical performance tests. From comparative example 2 and comparative example 3, when the values of t, P1, P2, P3 and σ are within the ranges, lower than 8, the battery cell cycle performance is poor, higher than 21.5, the battery cell safety performance is poor. From the comparison of example 6 and example 9, reducing the value of P1 can improve the safety performance, but will cause the impedance to rise and the cycle performance to decrease. From the comparison of example 4 and comparative example 2, reducing the value of t will cause the safety performance to decrease, while the battery cell energy density increases and the impedance decreases. From the comparison of example 1 and comparative example 11, reducing the value of P3 will cause the cycle performance to be lost. From the comparison of example 5 and comparative example 10, reducing the value of P2 will cause the battery cell energy density to decrease, and in addition, an unreasonable value of P3 will cause the battery cell safety performance to decrease. From example 10 and comparative example 8, a low value of σ will cause the battery cell energy density to be greatly lost. From example 9, a high value of σ will affect the battery cell safety and cycle performance.

[0067] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A positive electrode plate, characterized in that, It includes a current collector, a protective coating, and a positive electrode active material layer, wherein the protective coating is disposed on at least one side of the current collector, and the positive electrode active material layer is disposed on the side of the protective coating opposite to the current collector; The protective coating includes a first conductive agent; the positive electrode active material layer includes a positive electrode active material and a second conductive agent. The mass percentage of the first conductive agent in the protective coating is P1%, and the thickness of the protective coating on the current collector side after rolling is t μm; The surface density of the single-sided coating of the positive electrode active material layer is σ g / m. 2 The mass percentage of the positive electrode active material in the positive electrode active material layer is P2%, and the mass percentage of the second conductive agent in the positive electrode active material layer is P3%. The positive electrode plate satisfies equation 1: , where 0.5≤t<5.

9.

2. The positive electrode sheet according to claim 1, characterized in that, When 0.5 ≤ t < 2.5, the positive electrode plate satisfies equation 2: .

3. The positive electrode sheet according to claim 1, characterized in that, When 2.5 ≤ t < 5.9, the positive electrode plate satisfies equation 3: .

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, 0.5≤P1≤6.0,88≤P2≤99,0.2≤P3≤3,170≤σ≤195。 5. The positive electrode sheet according to claim 1, characterized in that, The protective coating also includes inorganic materials, including at least one of boehmite, alumina, magnesium oxide, barium titanate, silicon dioxide, and titanium dioxide.

6. The positive electrode sheet according to claim 5, characterized in that, The inorganic material in the protective coating accounts for 70% to 96% of the total mass.

7. The positive electrode sheet according to claim 1, characterized in that, The protective coating further includes an adhesive, which includes at least one of polyvinylidene fluoride, polyacrylonitrile copolymer, polyacrylic acid, polyacrylate, and polyacrylate.

8. The positive electrode sheet according to claim 1, characterized in that, The first conductive agent includes at least one of conductive carbon black, carbon nanotubes, carbon fibers, and graphene; And / or, the second conductive agent includes at least one of conductive carbon black, carbon nanotubes, carbon fibers, and graphene.

9. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium nickel oxide, lithium manganese iron phosphate, lithium-rich manganese-based materials, lithium vanadium phosphate, lithium titanate, and lithium vanadium oxide phosphate.

10. A battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1 to 9.

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