Positive pole piece, secondary battery and electric device

Abstract

The embodiment of the invention provides a positive pole piece, a secondary battery and an electric device. The positive pole piece comprises a positive current collector, a positive film layer and a first conductive layer, the positive electrode film layer is positioned on at least one side of the positive electrode current collector, and the surface density of the single-sided positive electrode film layer is 180mg / cm < 2 >-300mg / cm < 2 >; the first conductive layer is located between the positive electrode current collector and the positive electrode film layer, the first conductive layer comprises conductive metal particles, and metal elements in the conductive metal particles comprise one or more of Au, Ag, Al, Ni, Co, Li, Fe, Cu, Al, Ti, Mo, Sn, Sb, In, Zn and Na. The positive pole piece provided by the embodiment of the invention has a relatively good electrolyte infiltration effect under high surface density, and the phenomenon of black spot lithium precipitation can be reduced, so that the battery has relatively high volume energy density and relatively long cycle life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode sheet, a secondary battery and an electric device. BACKGROUND

[0002] The energy density of a battery is one of the core performance indicators of market concern, which directly determines the endurance of an electric device. However, a battery with high energy density is often accompanied by the problem of insufficient cycle life. SUMMARY

[0003] The present application provides a positive electrode sheet, a secondary battery and an electric device, which has good electrolyte wetting effect at high areal density, can reduce the phenomenon of black spot lithium precipitation, so as to make the battery have high volumetric energy density and long cycle life.

[0004] The present application is realized by the following technical solutions: In a first aspect, the present application provides a positive electrode sheet, which comprises a positive current collector, a positive film layer and a first conductive layer. The positive film layer is located on at least one side of the positive current collector, the areal density of the single-sided positive film layer is 180 mg / cm 2 -300 mg / cm 2 The first conductive layer is located between the positive current collector and the positive film layer, and the first conductive layer comprises conductive metal particles, the metal elements in the conductive metal particles include one or more of Au, Ag, Al, Ni, Co, Li, Fe, Cu, Al, Ti, Mo, Sn, Sb, In, Zn and Na.

[0005] In the above technical solution, the areal density of the single-sided positive film layer is controlled in the range of 180 mg / cm 2 -300 mg / cm 2 , which can improve the energy density of the battery. However, within this range of areal density, the electrolyte wetting effect is poor, which easily leads to the phenomenon of black spot lithium precipitation in the positive electrode sheet. To solve this problem, a first conductive layer can be provided between the positive current collector and the positive film layer, and the conductive metal particles therein include the above-mentioned metal elements. These metal elements not only can enhance the affinity to the electrolyte, but also can reduce the interfacial resistance when the electrolyte spreads, thereby improving the wetting effect of the electrolyte on the positive film layer, reducing the phenomenon of black spot lithium precipitation in the positive electrode sheet, and making the battery have high volumetric energy density and long cycle life at the same time.

[0006] In some embodiments of the present application, in the section of the first conductive layer along the thickness direction of the positive electrode sheet, the metal areal density σ of the conductive metal particles is Axdpr, and 0.1 pg / cm 2 ≤σ≤0.3 pg / cm 2 , which can be 0.15 pg / cm2 ≤σ≤0.25μg / cm 2 , wherein A is the volume ratio of the conductive metal particles in the first conductive layer measured by the area ratio of the conductive metal particles in the cross section of the first conductive layer along the positive electrode tab thickness direction, d is the thickness of the first conductive layer, and p is the density of the metal element in the conductive metal particles.

[0007] In the above technical solution, the metal area density of the conductive metal particles is within the above range, which not only helps to improve the energy density of the battery, but also further improves the wetting effect of the electrolyte on the positive electrode film layer, which is beneficial to reduce the phenomenon of lithium precipitation in the black spot of the positive electrode tab, thereby improving the energy density and cycle life of the battery.

[0008] In some embodiments of the present application, the conductive metal particles include first conductive metal particles and second conductive metal particles, and in the cross section of the first conductive layer along the positive electrode tab thickness direction, the particle size of the first conductive metal particles is 3-5 μm, and the particle size of the second conductive metal particles is greater than or equal to 0.5 μm and less than 3 μm.

[0009] In the above technical solution, the particle sizes of the first conductive metal particles and the second conductive metal particles are within the above ranges, respectively, which can be beneficial to the first conductive layer to balance the conductivity and the electrolyte liquid retention performance, thereby improving the kinetic performance and cycle life of the battery.

[0010] In some embodiments of the present application, in the cross section of the first conductive layer along the positive electrode tab thickness direction, the D v50 of the first conductive metal particles is greater than the D v90 of the second conductive metal particles.

[0011] In some embodiments of the present application, the D v50 of the first conductive metal particles is 3.5-4.2 μm; and / or, the D v90 of the second conductive metal particles is 2.5-2.8 μm.

[0012] In the above technical solution, by matching the particle sizes of the first conductive metal particles and the second conductive metal particles, the conductivity of the first conductive layer and the electrolyte liquid retention performance can be further improved, thereby further improving the kinetic performance and cycle life of the battery.

[0013] In some embodiments of the present application, the first conductive layer has a pore structure, and the pore size of the pore structure is 200-400 nm.

[0014] In the above technical solution, the pore size of the pore structure is within the above range, which can further improve the liquid retention capacity of the first conductive layer while improving the wetting effect of the electrolyte on the positive electrode film layer, thereby further improving the cycle life of the battery.

[0015] In some embodiments of the present application, the conductive metal particles include point-shaped conductive metal particles and / or linear conductive metal particles.

[0016] In the above technical solution, the conductive metal particles include the above-mentioned shaped particles, which can help to guide the electrolyte into the first conductive layer and improve the wetting of the electrolyte to the positive film layer, thereby helping to improve the cycle life of the battery.

[0017] In some embodiments of the present application, the first conductive layer further includes conductive carbon particles; optionally, the conductive carbon particles include linear conductive carbon particles.

[0018] In the above technical solution, the arrangement of the conductive carbon particles can further improve the conductivity of the first conductive layer, which is conducive to improving the kinetic performance of the battery.

[0019] In some embodiments of the present application, in the cross section of the first conductive layer along the thickness direction of the positive electrode sheet, the number ratio of the conductive metal particles based on the total number of the conductive metal particles and the conductive carbon particles is 50%-90%.

[0020] In the above technical solution, the number ratio of the conductive metal particles in the above range can help to improve the wetting effect of the electrolyte to the positive film layer, thereby reducing the black spot lithium precipitation phenomenon in the positive electrode sheet, and further improving the cycle life of the battery.

[0021] In some embodiments of the present application, the thickness of the first conductive layer is 2μm-5μm.

[0022] In the above technical solution, the thickness of the first conductive layer in the above range can improve the wetting effect of the electrolyte to the positive film layer while also being conducive to improving the energy density of the battery.

[0023] In some embodiments of the present application, the positive electrode sheet further includes a second conductive layer, the second conductive layer includes carbon nanotubes, and the second conductive layer is located between the first conductive layer and the positive film layer.

[0024] In the above technical solution, the arrangement of the carbon nanotubes in the second conductive layer can help to improve the compaction density of the positive film layer, thereby helping to improve the energy density of the battery.

[0025] In some embodiments of the present application, the thickness of the second conductive layer is 1μm-2.5μm.

[0026] In the above technical solution, the thickness of the second conductive layer in the above range can be conducive to improving the energy density of the battery.

[0027] In some embodiments of the present application, the carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0028] In some embodiments of the present application, the aspect ratio of the single-walled carbon nanotubes is 300-4000, and optionally 1000-2000.

[0029] In the above technical solution, the aspect ratio of the single-walled carbon nanotubes is controlled within the above range, so that the single-walled carbon nanotubes are inserted into the gaps between the active material particles and fill the micropores and gaps of the positive electrode film layer during the compaction process, at the same time, the single-walled carbon nanotubes connect adjacent particles like a "bridge" to reduce the phenomenon of particle slip dislocation, so that the stacking is more regular and compact, and the voids generated by the crushing of the active material particles during the compaction process are also reduced, and the stability of the stacking structure is maintained. Therefore, the compaction density and structural stability of the positive electrode film layer can be improved, thereby further improving the energy density and cycle life of the battery.

[0030] In some embodiments of the present application, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is (2-8):(92-98).

[0031] In the above technical solution, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is within the above range, so that the second conductive layer has good conductivity, and at the same time, the compaction density and structural stability of the positive electrode film layer are improved, and the manufacturing cost of the battery is also reduced.

[0032] In a second aspect, the embodiments of the present application provide a secondary battery, which comprises the positive electrode sheet in any of the embodiments of the first aspect of the present application.

[0033] In a third aspect, the embodiments of the present application provide an electric device, which comprises the secondary battery of the second aspect of the present application.

[0034] The above description is only a summary of the technical solutions of the present application, in order to more clearly understand the technical means of the present application, and to be implemented according to the content of the specification, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0036] Figure 1 The structural schematic diagram of the positive electrode sheet provided by some embodiments of the present application.

[0037] Figure 2A structure schematic diagram of the positive electrode plate is provided for some embodiments of the present application.

[0038] Icon: 10 - positive electrode plate; 100 - positive current collector, 200 - first conductive layer, 300 - positive film layer, 400 - second conductive layer. DETAILED DESCRIPTION

[0039] The embodiments of the present application will be further described in details below with reference to the accompanying drawings and embodiments. The detailed description and the accompanying drawings of the following embodiments are used to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application, i.e., the present application is not limited to the described embodiments.

[0040] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used in the present application are only for the purpose of describing the specific embodiments of the present application, and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0041] The terms "first", "second", etc. in the specification and claims of the present application or in the above description of drawings are used to distinguish different objects, and are not used to describe a specific order or primary and secondary relationship.

[0042] In the present application, the phrase "embodiments" means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present application can be combined with other embodiments.

[0043] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mount", "connect", "connection", "attach" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be direct connection, or indirect connection through intermediate medium; it can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0044] The term "and / or" in the present application is only used to describe the relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent the following three cases: A exists alone, A and B exist together, and B exists alone. In addition, the character " / " in the present application generally represents an "or" relationship between the front and rear associated objects.

[0045] "Multiple" appearing in the present application refers to two or more (including two), and similarly, "multiple groups" refers to two or more groups (including two groups), and "multiple pieces" refers to two or more pieces (including two pieces).

[0046] In the technical path of improving the energy density of the battery, increasing the areal density of the positive electrode film is one of the important directions. However, it should be noted that high areal density will significantly increase the difficulty of electrolyte infiltration. Specifically, the electrolyte usually penetrates from the edge to the central region of the positive electrode film, and as the areal density of the positive electrode film increases, the resistance of this infiltration process increases significantly, making it difficult for the electrolyte to effectively reach the central region of the positive electrode film. This insufficient infiltration can cause some active ions to be deposited on the surface of the positive electrode sheet and form black spots, which ultimately significantly reduces the cycle life of the battery. Therefore, in the high areal density scenario, how to improve the electrolyte infiltration effect of the positive electrode film has become a key technical requirement to improve the cycle life of the battery.

[0047] In view of this, the present application provides a positive electrode sheet, a secondary battery and an electric device, which has a good electrolyte infiltration effect under high areal density, can reduce the phenomenon of lithium deposition of black spots, so as to make the battery have a higher volumetric energy density and a longer cycle life. The embodiments of the present application are described in detail below.

[0048] Positive electrode sheet In a first aspect, the embodiments of the present application provide a positive electrode sheet, which comprises a positive electrode current collector, a positive electrode film and a first conductive layer. The positive electrode film is located on at least one side of the positive electrode current collector, and the areal density of the single-sided positive electrode film is 180 mg / cm 2 -300 mg / cm 2 The first conductive layer is located between the positive electrode current collector and the positive electrode film, and the first conductive layer comprises conductive metal particles, and the metal elements in the conductive metal particles include one or more of Au, Ag, Al, Ni, Co, Li, Fe, Cu, Al, Ti, Mo, Sn, Sb, In, Zn and Na.

[0049] In the positive electrode sheet provided in the embodiments of the present application, the areal density of the single-sided positive electrode film is controlled to be 180 mg / cm 2 -300 mg / cm 2The energy density of the battery can be improved. However, in this area of the areal density, the electrolyte has poor wettability, which can cause black spot lithium precipitation in the positive electrode plate. To solve this problem, a first conductive layer can be provided between the positive electrode current collector and the positive electrode film layer, and the conductive metal particles in the first conductive layer include the metal elements described above. These metal elements not only enhance the affinity for the electrolyte, but also reduce the interfacial resistance when the electrolyte spreads, thereby improving the wettability of the electrolyte to the positive electrode film layer, reducing the black spot lithium precipitation in the positive electrode plate, and enabling the battery to have high volumetric energy density and long cycle life.

[0050] In this application, the areal density of the single-sided positive electrode film layer refers to the mass of the positive electrode active material per unit area of the single-sided positive electrode film layer. The areal density of the single-sided positive electrode film layer can be measured by methods and devices known in the art. For example, discharge the secondary battery to the cut-off voltage, then disassemble the positive electrode plate from the secondary battery, for example, take the single-sided coated positive electrode plate (if it is a double-sided coated plate, first wipe off the positive electrode film layer on one side), punch into a small disc with an area of S1, weigh it, and record it as M1. Then wipe off the positive electrode film layer of the weighed positive electrode plate, weigh the mass of the positive electrode current collector and the first conductive layer, and record it as M0. The areal density of the single-sided positive electrode film layer is (M1-M0) / S1.

[0051] In some examples, the areal density of the single-sided positive electrode film layer can be, but is not limited to, 180 mg / cm 2 , 181 mg / cm 2 , 182 mg / cm 2 , 183 mg / cm 2 , 184 mg / cm 2 , 185 mg / cm 2 , 186 mg / cm 2 , 187 mg / cm 2 , 188 mg / cm 2 , 189 mg / cm 2 , 190 mg / cm 2 , 191 mg / cm 2 , 192 mg / cm 2 , 193 mg / cm 2 , 194 mg / cm 2 , 195 mg / cm 2 , 196 mg / cm 2 , 197 mg / cm 2 , 198 mg / cm 2 , 199 mg / cm 2 , 200 mg / cm 2 , 201 mg / cm 2 , 202 mg / cm2 , 203 mg / cm 2 , 204 mg / cm 2 , 205 mg / cm 2 , 206 mg / cm 2 , 207 mg / cm 2 , 208 mg / cm 2 , 209 mg / cm 2 , 210 mg / cm 2 , 211 mg / cm 2 , 212 mg / cm 2 , 213 mg / cm 2 , 214 mg / cm 2 , 215 mg / cm 2 , 216 mg / cm 2 , 217 mg / cm 2 , 218 mg / cm 2 , 219 mg / cm 2 , 220 mg / cm 2 , 221 mg / cm 2 , 222 mg / cm 2 , 223 mg / cm 2 , 224 mg / cm 2 , 225 mg / cm 2 , 226 mg / cm 2 , 227 mg / cm 2 , 228 mg / cm 2 , 229 mg / cm 2 , 230 mg / cm 2 , 231 mg / cm 2 , 232 mg / cm 2 , 233 mg / cm 2 , 234 mg / cm 2 , 235 mg / cm 2 , 236 mg / cm 2 , 237 mg / cm 2 , 238 mg / cm 2 , 239 mg / cm 2 , 240 mg / cm 2 , 241 mg / cm 2 , 242 mg / cm 2 , 243 mg / cm 2 , 244 mg / cm 2 , 245 mg / cm 2 , 246 mg / cm 2 , 247 mg / cm 2, 248 mg / cm 2 , 249 mg / cm 2 , 250 mg / cm 2 , 251 mg / cm 2 , 252 mg / cm 2 , 253 mg / cm 2 , 254 mg / cm 2 , 255 mg / cm 2 , 256 mg / cm 2 , 257 mg / cm 2 , 258 mg / cm 2 , 259 mg / cm 2 , 260 mg / cm 2 , 261 mg / cm 2 , 262 mg / cm 2 , 263 mg / cm 2 , 264 mg / cm 2 , 265 mg / cm 2 , 266 mg / cm 2 , 267 mg / cm 2 , 268 mg / cm 2 , 269 mg / cm 2 , 270 mg / cm 2 , 271 mg / cm 2 , 272 mg / cm 2 , 273 mg / cm 2 , 274 mg / cm 2 , 275 mg / cm 2 , 276 mg / cm 2 , 277 mg / cm 2 , 278 mg / cm 2 , 279 mg / cm 2 , 280 mg / cm 2 , 281 mg / cm 2 , 282 mg / cm 2 , 283 mg / cm 2 , 284 mg / cm 2 , 285 mg / cm 2 , 286 mg / cm 2 , 287 mg / cm 2 , 288 mg / cm 2 , 289 mg / cm 2 , 290 mg / cm 2 , 291 mg / cm 2 , 292 mg / cm 2 , 293 mg / cm2 , 294 mg / cm 2 , 295 mg / cm 2 , 296 mg / cm 2 , 297 mg / cm 2 , 298 mg / cm 2 , 299 mg / cm 2 , 300 mg / cm 2 , or a numerical range consisting of any two of the aforementioned numerical values.

[0052] In the present application, the cross section of the positive electrode tab can be observed for micro-morphology to observe the boundary between the positive electrode film layer and the first conductive layer in the positive electrode tab and determine the material composition of each layer. The "cross section of the positive electrode tab" refers to a cross section perpendicular to the thickness direction of the positive electrode tab. Further, the cross section of the positive electrode tab can be observed for micro-morphology and combined with composition analysis (such as energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) analysis, etc.) to identify the types of elements to confirm the material composition of the positive electrode film layer and the first conductive layer. Non-limitingly, the cross section of the negative electrode tab can be obtained using instruments or devices including but not limited to a focused electron beam (FIB) electron microscope (non-limiting examples include FEI Scios 2HiVac device, etc.), an ion cross-section polisher (non-limiting examples include IB-09010 CP argon ion cross-section polisher, IB-19500 CP ion cross-section polisher, etc. of Japan JEOL Co., Ltd., etc.), and the cross section of the negative electrode tab can also be obtained using plasma quenching method. The micro-morphology observation method can use instruments or devices including but not limited to scanning electron microscope (SEM) technology, non-limitingly, a high-resolution field emission scanning electron microscope can be used; non-limiting examples of SEM instruments include Sigma 300 scanning electron microscope, Apreo 2 SEM field emission scanning electron microscope, etc. of Germany ZEISS Co., Ltd.

[0053] In some embodiments, in the section of the first conductive layer along the thickness direction of the positive electrode tab, the metal area density σ = A x d x p of the conductive metal particles is 0.1 pg / cm 2 ≤ σ ≤ 0.3 pg / cm 2 , optionally 0.15 pg / cm 2 ≤ σ ≤ 0.25 pg / cm 2 , wherein A is the volume fraction of the conductive metal particles in the first conductive layer with the area fraction of the conductive metal particles measured in the section of the first conductive layer along the thickness direction of the positive electrode tab, d is the thickness of the first conductive layer, and p is the density of the metal element in the conductive metal particles.

[0054] In the above embodiments, the metal area density in the conductive metal particles is within the above range, which not only helps to improve the energy density of the battery, but also further improves the infiltration effect of the electrolyte on the positive electrode film layer, which is beneficial to reduce the phenomenon of lithium precipitation in the positive electrode tab, thereby improving the energy density and cycle life of the battery.

[0055] In this application, the metal area density = metal particle volume ratio x thickness of the first conductive layer x metal element density, wherein it is generally considered that in the cross section CP, the volume ratio ≈ area ratio (when the particles are uniformly dispersed, the two-dimensional cross-sectional area fraction can be approximately replaced by the three-dimensional volume fraction), and the specific test method of the metal area density is as follows: 1. Cross section preparation: discharge the secondary battery to the cut-off voltage, then disassemble the positive electrode tab from the secondary battery, dry the positive electrode tab as a sample, cut the positive electrode tab with an ion beam cutting instrument to form a cross section, take a representative area of the first conductive layer, inlay, polish (avoid particle shedding / deformation), and ensure that the cross section is flat and defect-free.

[0056] 2. CP image acquisition: randomly select 3-5 fields of view (covering the entire cross section) using SEM / optical microscope, and take high-resolution cross section images.

[0057] 3. Parameter measurement: (1) Area ratio: use image analysis software (ImageJ) to outline the metal particle boundary, calculate the total particle area / total area of the field of view, and take the average value of multiple fields of view.

[0058] (2) Thickness of the first conductive layer: measure the vertical distance from the substrate to the top surface on the cross section image, and take the average value of multiple positions (unit: cm, consistent with the density unit).

[0059] (3) Metal element density: refer to the manual (such as Al 2.7 g / cm 3 , Ni 8.9 g / cm 3 , consistent with the actual metal composition of the particles).

[0060] 4. Calculate the metal area density according to the metal area density = metal particle volume fraction x thickness of the first conductive layer x metal element density.

[0061] Please note the following situations: Sampling bias: avoid selecting only local areas, and cover different positions (edge / center) of the base coating.

[0062] Measurement error: when the particle boundary is blurred, use backscattered electron image (SEM-BSE) to enhance the contrast between metal and substrate; measure at least 5 points and take the average value.

[0063] Volume fraction approximation: If the particle agglomeration is serious, it needs to be corrected (such as Scherrer formula) to avoid too large deviation between area fraction and volume fraction.

[0064] In some examples, in the section of the first conductive layer along the positive electrode tab thickness direction, the metal area density of the conductive metal particles can be, but is not limited to, 0.1 μg / cm 2 , 0.11 μg / cm 2 , 0.12 μg / cm 2 , 0.13 μg / cm 2 , 0.14 μg / cm 2 , 0.15 μg / cm 2 , 0.16 μg / cm 2 , 0.17 μg / cm 2 , 0.18 μg / cm 2 , 0.19 μg / cm 2 , 0.20 μg / cm 2 , 0.21 μg / cm 2 , 0.22 μg / cm 2 , 0.23 μg / cm 2 , 0.24 μg / cm 2 , 0.25 μg / cm 2 , 0.26 μg / cm 2 , 0.27 μg / cm 2 , 0.28 μg / cm 2 , 0.29 μg / cm 2 , 0.3 μg / cm 2 , or a numerical range composed of any two of the above values.

[0065] In some embodiments, the conductive metal particles include first conductive metal particles and second conductive metal particles, and in the section of the first conductive layer along the positive electrode tab thickness direction, the particle size of the first conductive metal particles is 3 μm-5 μm, and the particle size of the second conductive metal particles is greater than or equal to 0.5 μm and less than 3 μm.

[0066] In the above embodiments, the particle sizes of the first conductive metal particles and the second conductive metal particles are respectively within the above ranges, which can be beneficial to the first conductive layer to balance the conductivity and the electrolyte retention performance, thereby improving the kinetic performance and cycle life of the battery.

[0067] In this application, the particle size of the conductive metal particles has a meaning known in the art and can be detected using equipment and methods known in the art. For example, after obtaining the positive electrode sheet and drying it, the positive electrode sheet is used as a sample. The positive electrode sheet is cut with an ion beam cutter to form a cross-section. Then, the particle size of the conductive metal particles in the first conductive layer in the cross-section is measured using a scanning electron microscope. The particle size of multiple, such as 50, conductive metal particles is measured, and their average value is calculated as the average particle size.

[0068] In some examples, the particle size of the first conductive metal particle may be, but is not limited to, 3 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5 μm, or a range of any two of the above values.

[0069] In one example, the particle size of the second conductive metal particle may be, but is not limited to, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, or any combination of two of the above values.

[0070] Furthermore, in some embodiments, in the cross-section of the first conductive layer along the thickness direction of the positive electrode sheet, the D of the first conductive metal particles... v50 D greater than the second conductive metal particle v90 .

[0071] In some embodiments, the D of the first conductive metal particle v50 The size is 3.5μm-4.2μm; and / or, the D of the second conductive metal particle is... v90 The thickness ranges from 2.5μm to 2.8μm.

[0072] In the above embodiments, by matching the particle sizes of the first conductive metal particles and the second conductive metal particles, the conductivity of the first conductive layer and the electrolyte retention performance can be further improved, thereby further enhancing the dynamic performance and cycle life of the battery.

[0073] In this application, the volume average particle size D of the first conductive metal particle is... v50 This refers to the particle size value corresponding to a cumulative volume fraction of 50% in the particle size distribution of the first conductive metal particles, and the volume average particle size D of the second conductive metal particles.v90 D90 refers to the particle size value corresponding to the cumulative volume fraction of 90% in the particle size distribution of the second conductive metal particles, which can be detected by using devices and methods known in the art, for example, taking the material to be detected as a sample, and testing the D90 of the first conductive metal particles and the D90 of the second conductive metal particles according to the test standard GB / T 19077-2024 by using a Mastersizer 2000E laser particle size analyzer. v50 v90

[0074] In some embodiments, the first conductive layer has a pore structure, and the pore diameter of the pore structure is 200 nm-400 nm.

[0075] In the above embodiments, the pore diameter of the pore structure is within the above range, which can further improve the liquid retention capacity of the first conductive layer while improving the wettability of the electrolyte to the positive electrode film layer, thereby further improving the cycle life of the battery.

[0076] In the present application, the pore structure refers to a structure having a hole (concave part), for example, the pore diameter can be obtained by observation using a scanning electron microscope (SEM).

[0077] In some examples, the pore diameter of the pore structure can be, but is not limited to, 200 nm, 205 nm, 210 nm, 215 nm, 220 nm, 225 nm, 230 nm, 235 nm, 240 nm, 245 nm, 250 nm, 255 nm, 260 nm, 265 nm, 270 nm, 275 nm, 280 nm, 285 nm, 290 nm, 295 nm, 300 nm, 305 nm, 310 nm, 315 nm, 320 nm, 325 nm, 330 nm, 335 nm, 340 nm, 345 nm, 350 nm, 355 nm, 360 nm, 365 nm, 370 nm, 375 nm, 380 nm, 385 nm, 390 nm, 395 nm, 400 nm, or a numerical range composed of any two of the above values.

[0078] In some embodiments, the conductive metal particles include point-shaped conductive metal particles and / or linear conductive metal particles.

[0079] In the above embodiments, the conductive metal particles include the above-mentioned shape particles, which can help to guide the electrolyte into the first conductive layer and improve the wettability of the electrolyte to the positive electrode film layer, thereby helping to improve the cycle life of the battery.

[0080] In some embodiments, the first conductive layer further includes conductive carbon particles; optionally, the conductive carbon particles include linear conductive carbon particles.

[0081] ​​In the above embodiments, the arrangement of the conductive carbon particles can further improve the conductivity of the first conductive layer, and is conducive to improving the kinetic performance of the battery.

[0082] In the present application, the particle morphology in the first conductive layer can be observed by scanning electron microscopy (SEM). For example, the secondary battery is discharged to the cut-off voltage, and then the positive electrode sheet is disassembled from the secondary battery. The dried positive electrode sheet is used as a sample, and an ion beam cutting instrument is used to cut the positive electrode sheet to form a cross section. A scanning electron microscope of JSM-5610LV type of FEI Company of the United States is used to randomly select 3-5 fields of view (covering the entire cross section), and a high-resolution cross-sectional image is taken. The particle boundary is outlined by using image analysis software (ImageJ), so as to obtain the particle morphology.

[0083] In some embodiments, in the cross section of the first conductive layer along the thickness direction of the positive electrode sheet, the number ratio of the conductive metal particles based on the total number of the conductive metal particles and the conductive carbon particles is 50%-90%.

[0084] In the above embodiments, the number ratio of the conductive metal particles in the above range can be conducive to improving the wetting effect of the electrolyte on the positive electrode film layer, and further reducing the black spot lithium precipitation phenomenon in the positive electrode sheet, thereby further improving the cycle life of the battery.

[0085] In the present application, the number ratio of the conductive metal particles can be obtained by scanning electron microscopy (SEM). For example, the secondary battery is discharged to the cut-off voltage, and then the positive electrode sheet is disassembled from the secondary battery. The dried positive electrode sheet is used as a sample, and an ion beam cutting instrument is used to cut the positive electrode sheet to form a cross section. A scanning electron microscope of JSM-5610LV type of FEI Company of the United States is used to randomly select 3-5 fields of view (covering the entire cross section), and a high-resolution cross-sectional image is taken under the backscattered electron (BSE) mode, wherein the conductive metal particles (high Z) are bright white, and the conductive carbon particles (low Z) are dark gray. The particle boundary is outlined by using image analysis software (ImageJ), and the number of the conductive metal particles and the conductive carbon particles is obtained, so as to calculate the number ratio of the conductive metal particles.

[0086] In some embodiments, the thickness of the first conductive layer is 2 μm-5 μm.

[0087] In the above embodiments, the thickness of the first conductive layer in the above range can improve the wetting effect of the electrolyte on the positive electrode film layer, and also be conducive to improving the energy density of the battery.

[0088] In the present application, the thickness of the first conductive layer can be measured by methods and instruments known in the art. For example, the secondary battery is discharged to the cut-off voltage, and then the positive electrode sheet is disassembled from the secondary battery. After drying, the positive electrode sheet is used as a sample. The positive electrode sheet is cut off by an ion beam cutting instrument to form a cross section. A representative area of the first conductive layer is taken, inlaid, polished (to avoid particle shedding / deformation), and ensured to be flat and defect-free. Using a SEM / optical microscope, 3-5 fields of view (covering the entire cross section) are randomly selected, and high-resolution cross-sectional images are taken. The vertical distance from the substrate to the top surface is measured on the cross-sectional image, and the average is taken from multiple positions.

[0089] In some examples, the thickness of the first conductive layer can be, but is not limited to, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5 μm, or a numerical range composed of any two of the above.

[0090] In some embodiments, the positive electrode sheet further comprises a second conductive layer, the second conductive layer comprises carbon nanotubes, and the second conductive layer is located between the first conductive layer and the positive electrode film layer.

[0091] In the above embodiments, the arrangement of carbon nanotubes in the second conductive layer can be beneficial to improve the compaction density of the positive electrode film layer, thereby being beneficial to improve the energy density of the battery.

[0092] In the present application, carbon nanotubes refer to nanomaterials with several to tens of coaxial hollow cylindrical tubes formed by rolling graphene sheets formed by sp 2 Hybrid bonding. The diameter is usually in the range of several to tens of nanometers, and the length can vary from microns to centimeters, showing a high aspect ratio. According to the number of graphene sheets, it can be divided into: single-walled carbon nanotubes (SWCNTs), few-walled carbon nanotubes (FWCNTs), and multi-walled carbon nanotubes (MWCNTs).

[0093] In some embodiments, the thickness of the second conductive layer is 1 μm-2.5 μm.

[0094] In the above embodiments, the thickness of the second conductive layer is within the above range, which can be conducive to improving the energy density of the battery.

[0095] In some embodiments, the carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0096] In this application, single-walled carbon nanotubes refer to a single cylindrical layer of carbon atoms, and multi-walled carbon nanotubes refer to two or more layers of carbon atoms connected by intermolecular forces, or a single layer of carbon atoms wound around a cylindrical hollow core several times. The type of carbon nanotubes in the electrode plate can be determined by high-power electron microscopy, and the average tube diameter of the carbon nanotubes can be calculated by high-power electron microscopy to distinguish single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0097] In the above embodiments, the carbon nanotubes include the above types, which on the one hand can help improve the compaction density of the positive electrode film layer. On the other hand, single-walled carbon nanotubes have good electronic conductivity and can efficiently transfer electrons, and a small amount of addition can effectively reduce the electronic transmission impedance inside the battery; multi-walled carbon nanotubes have multiple carbon atom layers, and their structure can provide stronger mechanical strength and rigidity, which can provide stronger support during compaction and charging and discharging, reduce the impact of electrode expansion and contraction, reduce the brittle fracture of the electrode, and can improve the cycle life of the battery.

[0098] In some embodiments, the aspect ratio of the single-walled carbon nanotubes is 300-4000, which can be 1000-2000.

[0099] In the above embodiments, the aspect ratio of the single-walled carbon nanotubes is controlled within the above range, which can make the single-walled carbon nanotubes penetrate into the gaps between the active material particles and fill the micropores and gaps in the positive electrode film layer during compaction, while connecting adjacent particles like "bridges" to reduce the phenomenon of particle slip and dislocation, making the accumulation more regular and compact, and also reducing the voids generated by the crushing of active material particles during compaction to maintain the stability of the accumulation structure. Thus, the compaction density and structural stability of the positive electrode film layer can be improved, thereby further improving the energy density and cycle life of the battery.

[0100] In this application, the aspect ratio of the carbon nanotubes refers to the ratio between the length of the carbon nanotubes and their diameter, wherein the length of the carbon nanotubes refers to the value measured along the two ends of the one-dimensional tubular structure. In this application, the carbon nanotubes in the electrode plate can be determined by high-power electron microscopy, and the aspect ratio of the carbon nanotubes can be calculated by high-power electron microscopy.

[0101] In some examples, the aspect ratio of the single-walled carbon nanotubes can be, but is not limited to, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, or a range of values between any two of the aforementioned values.

[0102] In some embodiments, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is (1-8):(92-99).

[0103] In the above embodiments, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is within the above range, which can allow the second conductive layer to have good conductivity and improve the compaction density and structural stability of the positive electrode film layer while reducing the manufacturing cost of the battery.

[0104] In the embodiments of the present application, the positive electrode current collector has two opposite surfaces in the thickness direction of the positive electrode current collector, and the positive electrode active material layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0105] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0106] In some embodiments, when the secondary battery is a lithium ion battery, the positive electrode active material in the positive electrode film layer can include at least one of a lithium-containing phosphate having an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material can also be used. These positive electrode active materials can be used alone or in combination with two or more. Examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1 / 3Co1 / 3Mn1 / 3O2), lithium manganese nickel oxide, lithium manganese nickel cobalt oxide, lithium manganese nickel cobalt magnesium oxide, lithium nickel manganese cobalt aluminum oxide, lithium iron phosphate, lithium titanium oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material can also be used. These positive electrode active materials can be used alone or in combination with two or more.1 / 3 Co 1 / 3 Mn 1 / 3 O2(also can be referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(also can be referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM811), LiNi 0.9 Co 0.05 Mn 0.05 O2(also can be referred to as NCM9), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) and modified compounds thereof. Examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon.

[0107] In some embodiments, when the secondary battery is a sodium ion battery, the positive electrode active material in the positive electrode film layer can include at least one of the following materials: polyanion compounds, sodium transition metal oxides, prussian blue compounds, and modified compounds of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination with two or more.

[0108] wherein the polyanion compound can be Li 1+x Mn 1-y A y P 1-z R zO4; wherein, wherein x is any numerical value in the range of -0.100~0.100, y is any numerical value in the range of 0.001~0.500, z is any numerical value in the range of 0.001~0.100, A includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements of B, S, Si and N.

[0109] As an optional technical manner of the present application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n , wherein A includes one or more elements of Zn, Al, Na, K, Mg, Nb, Mo and W; B includes one or more elements of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge; C includes one or more elements of B, S, Si and N; D includes one or more elements of S, F, Cl and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0110] As an optional technical manner of the present application, the polyanionic compound can be Na 4+x R 3-y P 4-m O 15 / C; wherein 0

[0111] As an optional technical manner of the present application, the polyanionic compound can be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q dwherein A represents an alkali metal element doped to substitute Na, M represents a metal element to substitute V, D represents a doping element to substitute P, Q represents a doping element to substitute F, D includes at least one of Si and S, and Q includes at least one of Cl and O; 3.5≤x≤4.5, 0≤a≤0.15x, 0.8≤y≤1.1, 0≤b≤0.3y, 0≤c≤0.15, 0.8≤z≤1.1, and 0≤d≤0.2z. Optionally, A includes at least one of K and Li; and M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0112] In the sodium transition metal compound, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO2, where M is one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, and V, and 0

[0113] The Prussian blue compound can be a compound having sodium ions, transition metal ions, and cyanide ions (CN - ). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound is, for example, Na a Me b Me' c (CN)6, where Me and Me' are each independently at least one of Mn, Fe, Ni, Co, Cu, and Zn, 0

[0114] In some embodiments, the positive electrode film layer can further optionally include a positive electrode binder. As an example, the positive electrode binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0115] In some embodiments, the positive electrode film layer can further optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] As an example, a structural schematic of the positive electrode tab can be found in FIG. 1. Figure 1The positive electrode tab 10 includes a positive electrode current collector 100, a positive electrode film layer 300, and a first conductive layer 200. The positive electrode film layer 300 is located on at least one side of the positive electrode current collector, and the first conductive layer 200 is located between the positive electrode current collector 100 and the positive electrode film layer 300.

[0117] As another example, a structural schematic diagram of a positive electrode tab can be referred to Figure 2 The positive electrode tab 10 includes a positive electrode current collector 100, a positive electrode film layer 300, a first conductive layer 200, and a second conductive layer 400. The positive electrode film layer 300 is located on at least one side of the positive electrode current collector, the first conductive layer 200 is located between the positive electrode current collector 100 and the positive electrode film layer 300, and the second conductive layer 400 is located between the first conductive layer 200 and the positive electrode film layer 300.

[0118] In some embodiments, the negative electrode tab can be prepared by dispersing conductive metal particles, a positive electrode conductive agent, and a positive electrode binder in NMP solvent in a first ratio to obtain a first conductive layer slurry; coating the first conductive layer slurry on the positive electrode current collector, and after drying, a first conductive layer can be formed on the surface of the positive electrode current collector; Dispersing a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and any other components in a solvent (such as N-methyl pyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the surface of the first conductive layer away from the positive electrode current collector, and after processes such as drying, cold pressing, etc., a positive electrode tab can be obtained.

[0119] Secondary battery In a second aspect, the application provides a secondary battery, which includes the positive electrode tab of any of the embodiments of the first aspect of the application.

[0120] The secondary battery has all the advantages of the positive electrode tab described above, and will not be repeated here.

[0121] The secondary battery provided by the application includes a positive electrode tab and a negative electrode tab. The negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0122] As an example, the negative electrode current collector has two opposite surfaces in the thickness direction of itself, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0123] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0124] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0125] In some embodiments, the negative film layer can further optionally include a negative binder. The negative binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0126] In some embodiments, the negative film layer can further optionally include a negative conductive agent. The negative conductive agent can be selected from at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0127] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0128] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-described components for preparing the negative electrode sheet, such as the negative active material, the negative conductive agent, the negative binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative current collector, and subjecting to drying, cold pressing, and the like to obtain the negative electrode sheet.

[0129] The secondary battery of the present application further includes a separator film, which is disposed between the positive electrode sheet and the negative electrode sheet, and mainly functions to prevent short circuit between the positive and negative electrodes while allowing active ions to pass therethrough. The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be used.

[0130] In some embodiments, the material of the separator film can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited to these. Alternatively, the material of the separator film can include polyethylene and / or polypropylene. The separator film can be a single layer film or a multi-layer composite film. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different. In some embodiments, a ceramic coating or a metal oxide coating can be further provided on the separator film.

[0131] The secondary battery of the present application further includes an electrolyte, which functions to conduct active ions between the positive electrode sheet and the negative electrode sheet. The electrolyte that can be used in the present application can be any known electrolyte in the art.

[0132] In some embodiments, the electrolyte can include an organic solvent, an electrolyte salt, and optionally an additive, and the types of the organic solvent, the lithium salt, and the additive are not particularly limited and can be selected as desired.

[0133] In some embodiments, the secondary battery is a lithium ion battery, and the electrolyte salt can include a lithium salt. As an example, the lithium salt includes, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bis-trifluoromethanesulfonylimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluoro(oxalato)borate), LiBOB (lithium bis(oxalato)borate), LiPO2F2 (lithium difluorophosphate), LiDODFP (lithium difluoro(dioxalato)phosphate), and LiOTFP (lithium tetrafluoro(oxalato)phosphate). The above lithium salt can be used alone or in combination of two or more.

[0134] In some embodiments, the secondary battery is a sodium ion battery, and the electrolyte salt can include a sodium salt. As an example, the sodium salt can be selected from at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0135] In some embodiments, the organic solvent includes, by way of example, at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). The above-mentioned organic solvents can be used alone or in combination of two or more. Alternatively, the above-mentioned organic solvents can be used in combination of two or more.

[0136] In some embodiments, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, and the like.

[0137] By way of example, the additive includes, but is not limited to, at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfate (DTD), propylene sulfate, ethylene sulfite (ES), 1,3-propane sulfone (PS), 1,3-propylene sulfone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl)phosphate (TMSP), tris(trimethylsilyl)borate (TMSB).

[0138] The electrolyte solution can be prepared according to conventional methods in the art. For example, the organic solvent, the electrolyte salt, and the optional additive can be mixed uniformly to obtain the electrolyte solution. The order of adding the materials is not particularly limited, for example, the electrolyte salt and the optional additive can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution; or the electrolyte salt can be added to the organic solvent first, and then the optional additive can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution.

[0139] Electric device In a third aspect, the present application provides a power consuming device, which includes the secondary battery of any of the embodiments of the second aspect.

[0140] According to the present application, since the power consuming device includes the secondary battery of any of the embodiments of the second aspect, the power consuming device has the beneficial effects of the second aspect.

[0141] The power consuming device of the present application is not particularly limited, and can be any power consuming device known in the art. In some embodiments, the power consuming device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a timepiece, a power tool, a flash, a camera, a household large storage battery, a lithium ion capacitor, and the like.

[0142] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application, and should not be construed as limiting the present application. In the embodiments, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0143] Example 1 (1) Preparation of the positive electrode tab The conductive metal particles indium tin oxide (ITO, particle size 2 μm), the conductive carbon particles carbon black SP, and the positive electrode binder polyvinylidene fluoride (PVDF) were dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 80:10:10 to obtain a first conductive layer slurry; the first conductive layer slurry was coated on the surface of a positive electrode current collector aluminum foil with a thickness of 13 μm, dried at 135°C, and a first conductive layer with a single-sided thickness of 2 μm was formed on the surface of the aluminum foil; the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode current collector aluminum foil coated with a first conductive layer on both sides. In the cross section of the first conductive layer along the thickness direction of the positive electrode tab, the metal surface density of the conductive metal particles indium tin oxide (ITO) was 0.1 μg / cm2, and the number ratio of the conductive metal particles to the total number of the conductive metal particles and the conductive carbon particles carbon black SP was 50%. 2 , based on the total number of the conductive metal particles and the conductive carbon particles carbon black SP, the number ratio of the conductive metal particles was 50%.

[0144] The positive electrode active material lithium iron phosphate (LFP), lithium manganate (LMO), positive electrode conductive agent carbon black SP, positive electrode conductive agent carbon nanotube and positive electrode binder polyvinylidene fluoride PVDF are dispersed in N-methyl pyrrolidone NMP solution in a mass ratio of 19:78:0.8:0.7:1.5, fully stirred and mixed, and formulated into a positive electrode slurry with a solid content of 68%. The positive electrode slurry is coated on the surface of the first conductive layer away from the positive electrode current collector aluminum foil, and dried at 120°C to obtain a positive electrode tab with a single-sided positive electrode film layer. Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode tab with a double-sided positive electrode film layer. Then, the positive electrode tab is subjected to cold pressing, cutting and striping to form positive electrode tabs with positive electrode tabs on the opposite sides. Drying under vacuum at 120°C for 10 minutes obtains the positive electrode tab ready for use. The areal density of the single-sided positive electrode film layer is 180 mg / cm 2 , and the thickness of the positive electrode film layer is 95 μm.

[0145] (2) Preparation of negative electrode tab The negative electrode active material artificial graphite, negative electrode binder polyacrylic acid PAA, negative electrode conductive agent carbon black and thickening agent sodium carboxymethyl cellulose (CMC-Na) are dispersed in deionized water in a mass ratio of 96:1.5:1:1.5, fully stirred and mixed, and formulated into a negative electrode slurry with a solid content of 53%. The negative electrode slurry is coated on the surface of the negative electrode current collector copper foil with a thickness of 6 μm, and dried at 100°C to obtain a negative electrode tab with a single-sided negative electrode film layer. Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode tab with a double-sided negative electrode film layer. Drying under vacuum at 100°C for 30 minutes obtains the negative electrode tab ready for use. The areal density of the single-sided negative electrode film layer is 95.6 mg / cm 2 , and the thickness of the single-sided negative electrode film layer is 86 μm.

[0146] (3) Preparation of separator film The separator film substrate is 8 μm thick polyethylene PE.

[0147] (4) Preparation of electrolyte In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP) and propyl propionate (PP) are mixed in a mass ratio of 1:1:1:1:1, and then electrolyte salt LiPF6 is dissolved in the above non-aqueous solvent. After mixing uniformly, an electrolyte is formed, wherein the mass percentage of LiPF6 based on the mass of the electrolyte is 12.5%.

[0148] (5) Assembly of secondary battery The positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a role of separation, and the electrode assembly is obtained by winding. The electrode assembly is placed in an outer packaging aluminum plastic film, water is removed at 80°C, the above electrolyte is injected and packaged, and a secondary battery is obtained after processes such as formation, degassing, and edge cutting.

[0149] Example 2 The difference between this example and Example 1 is that the conductive metal particles are antimony-doped tin oxide (ATO) with a doping ratio of 5%.

[0150] Example 3 The difference between this example and Example 1 is that the conductive metal particles are titanium dioxide (TiO2).

[0151] Example 4 The difference between this example and Example 1 is that the conductive metal particles are lithium polystyrene sulfonate (PSS-Li).

[0152] Example 5 The difference between this example and Example 1 is that the conductive metal particles are zinc oxide (ZnO).

[0153] Example 6 The difference between this example and Example 1 is that the areal density of the single-sided positive electrode film layer is 200 mg / cm 2 .

[0154] Example 7 The difference between this example and Example 1 is that the areal density of the single-sided positive electrode film layer is 240 mg / cm 2 .

[0155] Example 8 The difference between this example and Example 1 is that the areal density of the single-sided positive electrode film layer is 300 mg / cm 2 .

[0156] Example 9 The difference between this example and Example 1 is that in the cross section of the first conductive layer along the thickness direction of the positive electrode sheet, the metal areal density of the conductive metal particles is 0.15 μg / cm 2 .

[0157] Example 10 The difference between this example and Example 1 is that in the cross section of the first conductive layer along the thickness direction of the positive electrode sheet, the metal areal density of the conductive metal particles is 0.2 μg / cm 2 .

[0158] Example 11 The difference between this example and Example 1 is that the metal surface density of the electrically conductive metal particles in the section of the first electrically conductive layer in the thickness direction of the positive electrode sheet is 0.25 μg / cm 2 .

[0159] Example 12 The difference between this example and Example 1 is that the metal surface density of the electrically conductive metal particles in the section of the first electrically conductive layer in the thickness direction of the positive electrode sheet is 0.3 μg / cm 2 .

[0160] Example 13 The difference between this example and Example 1 is that the electrically conductive metal particles contain first electrically conductive metal particles having a particle size dl of 3 μm and second electrically conductive metal particles having a particle size d2 of 0.5 μm, and the number ratio of the first electrically conductive metal particles to the second electrically conductive metal particles is 6:4.

[0161] Example 14 The difference between this example and Example 13 is that the electrically conductive metal particles contain first electrically conductive metal particles having a particle size dl of 2.9 μm and second electrically conductive metal particles having a particle size d2 of 0.4 μm.

[0162] Example 15 The difference between this example and Example 13 is that the electrically conductive metal particles contain first electrically conductive metal particles having a particle size dl of 5 μm and second electrically conductive metal particles having a particle size d2 of 2.8 μm.

[0163] Example 16 The difference between this example and Example 13 is that the electrically conductive metal particles contain first electrically conductive metal particles having a particle size dl of 5.1 μm and second electrically conductive metal particles having a particle size d2 of 3 μm.

[0164] Example 17 The difference between this example and Example 1 is that the number ratio of the electrically conductive metal particles to the electrically conductive carbon particles, based on the total number of the electrically conductive metal particles and the electrically conductive carbon particles, in the section of the first electrically conductive layer in the thickness direction of the positive electrode sheet is 60%.

[0165] Example 18 The difference between this example and Example 1 is that the number ratio of the electrically conductive metal particles to the electrically conductive carbon particles, based on the total number of the electrically conductive metal particles and the electrically conductive carbon particles, in the section of the first electrically conductive layer in the thickness direction of the positive electrode sheet is 80%.

[0166] Example 19 The present embodiment differs from Embodiment 1 in that, in the cross section of the first conductive layer in the thickness direction of the positive electrode sheet, the number ratio of the electrically conductive metal particles to the total number of the electrically conductive metal particles and the electrically conductive carbon particles carbon black SP is 90%.

[0167] Embodiment 20 The present embodiment differs from Embodiment 1 in that, in the cross section of the first conductive layer in the thickness direction of the positive electrode sheet, the number ratio of the electrically conductive metal particles to the total number of the electrically conductive metal particles and the electrically conductive carbon particles carbon black SP is 45%.

[0168] Embodiment 21 The present embodiment differs from Embodiment 1 in that, in the cross section of the first conductive layer in the thickness direction of the positive electrode sheet, the number ratio of the electrically conductive metal particles to the total number of the electrically conductive metal particles and the electrically conductive carbon particles carbon black SP is 92%.

[0169] Embodiment 22 The present embodiment differs from Embodiment 1 in that the thickness of the first conductive layer is 3 pm.

[0170] Embodiment 23 The present embodiment differs from Embodiment 1 in that the thickness of the first conductive layer is 4 pm.

[0171] Embodiment 24 The present embodiment differs from Embodiment 1 in that the thickness of the first conductive layer is 5 pm.

[0172] Embodiment 25 The present embodiment differs from Embodiment 1 in that a second conductive layer having a thickness of 2.5 pm is provided between the first conductive layer and the positive electrode film layer, the second conductive layer includes single-walled carbon nanotubes and a binder polyvinylidene fluoride PVDF, and the mass ratio of the single-walled carbon nanotubes to the binder polyvinylidene fluoride PVDF is 80:20, and the aspect ratio of the single-walled carbon nanotubes is 300.

[0173] Embodiment 26 The present embodiment differs from Embodiment 25 in that the aspect ratio of the single-walled carbon nanotubes is 1000.

[0174] Embodiment 27 The present embodiment differs from Embodiment 25 in that the aspect ratio of the single-walled carbon nanotubes is 2000.

[0175] Embodiment 28 The present embodiment differs from Embodiment 25 in that the aspect ratio of the single-walled carbon nanotubes is 4000.

[0176] Embodiment 29 The difference between this embodiment and embodiment 25 is that the aspect ratio of the single-walled carbon nanotubes is 3000.

[0177] Embodiment 30 The difference between this embodiment and embodiment 25 is that the second conductive layer further comprises multi-walled carbon nanotubes, and the mass ratio of the single-walled carbon nanotubes and the multi-walled carbon nanotubes to the binder polyvinylidene fluoride PVDF is 80:20, the aspect ratio of the multi-walled carbon nanotubes is 200, and the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 2:98.

[0178] Embodiment 31 The difference between this embodiment and embodiment 30 is that the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 4:96.

[0179] Embodiment 32 The difference between this embodiment and embodiment 30 is that the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 6:94.

[0180] Embodiment 33 The difference between this embodiment and embodiment 30 is that the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 8:92.

[0181] Embodiment 34 The difference between this embodiment and embodiment 30 is that the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 10:90.

[0182] Comparative Example 1 The difference between this comparative example and embodiment 1 is that the first conductive layer does not contain conductive metal particles.

[0183] Test Part The secondary batteries prepared in the above embodiments 1-34 and comparative example 1 are measured and tested for performance, and the test results are shown in Tables 1-7, and the specific test methods are as follows: (1) Area density of single-sided positive electrode film layer The secondary battery is discharged at a rate of 1.0C to 2.8V, and the positive electrode sheet is disassembled. The single-sided coated positive electrode sheet (if it is a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first) is cut into a small round piece with an area of S1, weighed, and recorded as M1. Then the positive electrode film layer of the above weighed positive electrode sheet is wiped off, and the mass of the positive electrode current collector and the first conductive layer is weighed and recorded as M0. The area density of the single-sided positive electrode film layer is (M1-M0) / S1.

[0184] (2) Metal elements in conductive metal particles in the first conductive layer Discharge the secondary battery at a rate of 1.0 C to 2.8 V, then disassemble the positive electrode sheet from the secondary battery, and after drying, the positive electrode sheet is used as a sample. The positive electrode sheet is cut off using an ion beam cutting instrument to form a cross section. A representative area of the first conductive layer is taken, inlaid, polished (to avoid particle shedding / deformation), and the cross section is ensured to be flat and defect-free. The cross section is observed for microscopic morphology and combined with energy dispersive spectroscopy (EDS) to identify the types of elements.

[0185] (3) Metal area density Cross section preparation: Discharge the secondary battery at a rate of 1.0 C to 2.8 V, then disassemble the positive electrode sheet from the secondary battery, and after drying, the positive electrode sheet is used as a sample. The positive electrode sheet is cut off using an ion beam cutting instrument to form a cross section. A representative area of the first conductive layer is taken, inlaid, polished (to avoid particle shedding / deformation), and the cross section is ensured to be flat and defect-free.

[0186] CP image acquisition: Use SEM / optical microscope, randomly select 3-5 fields of view (covering the entire cross section), and take high-resolution cross section images.

[0187] Parameter measurement: (a) Area fraction: Use image analysis software (ImageJ) to outline the metal particle boundary, calculate the total particle area / total area of the field of view, and take the average value of multiple fields of view.

[0188] (b) Thickness of the first conductive layer: Measure the vertical distance from the substrate to the top surface on the cross section image, and take the average value of multiple positions (unit: cm, consistent with the density unit).

[0189] (c) Metal element density: Refer to the manual.

[0190] According to the metal area density = metal particle volume fraction x thickness of the first conductive layer x metal element density, the metal area density is calculated.

[0191] (4) Particle size of conductive metal particles Discharge the secondary battery at a rate of 1.0 C to 2.8 V, then disassemble the positive electrode sheet from the secondary battery, and after drying, the positive electrode sheet is used as a sample. The positive electrode sheet is cut off using an ion beam cutting instrument to form a cross section. Then, the particle size of the conductive metal particles in the first conductive layer of the cross section is measured using a scanning electron microscope. The particle sizes of multiple, for example, 50 conductive metal particles are measured, and the average value is calculated as the average particle size of the particles.

[0192] (5) Number ratio of conductive metal particles The secondary battery is discharged at a rate of 1.0 C to 2.8 V, and then the positive electrode sheet is disassembled from the secondary battery. The dried positive electrode sheet is used as a sample, and the positive electrode sheet is cut by an ion beam cutting instrument to form a cross section. A scanning electron microscope of JSM-5610LV type of FEI Company of the United States is used to randomly select 3-5 fields of view (covering the entire cross section), and a high-resolution cross-sectional image is taken under a backscattered electron (BSE) mode, in which the conductive metal particles (high Z) are bright white and the conductive carbon particles (low Z) are dark gray. The particle boundary is outlined by using an image analysis software (ImageJ), and then the number of conductive metal particles and conductive carbon particles is obtained, so that the number ratio of the conductive metal particles is calculated.

[0193] (6) Thickness of the first conductive layer The secondary battery is discharged at a rate of 1.0 C to 2.8 V, and then the positive electrode sheet is disassembled from the secondary battery. The dried positive electrode sheet is used as a sample, and the positive electrode sheet is cut by an ion beam cutting instrument to form a cross section. A scanning electron microscope of JSM-5610LV type of FEI Company of the United States is used to randomly select 3-5 fields of view (covering the entire cross section), and a high-resolution cross-sectional image is taken under a backscattered electron (BSE) mode, in which the conductive metal particles (high Z) are bright white and the conductive carbon particles (low Z) are dark gray. The particle boundary is outlined by using an image analysis software (ImageJ), and then the number of conductive metal particles and conductive carbon particles is obtained, so that the number ratio of the conductive metal particles is calculated.

[0194] (7) Aspect ratio of single-walled carbon nanotubes The secondary battery is discharged at a rate of 1.0 C to 2.8 V, and then the positive electrode sheet is disassembled from the secondary battery. The dried positive electrode sheet is used as a sample, and the positive electrode sheet is cut by an ion beam cutting instrument to form a cross section. A scanning electron microscope of JSM-5610LV type of FEI Company of the United States is used to randomly select 3-5 fields of view (covering the entire cross section), and a high-resolution cross-sectional image is taken under a backscattered electron (BSE) mode, in which the conductive metal particles (high Z) are bright white and the conductive carbon particles (low Z) are dark gray. The particle boundary is outlined by using an image analysis software (ImageJ), and then the number of conductive metal particles and conductive carbon particles is obtained, so that the number ratio of the conductive metal particles is calculated.

[0195] (8) Cycle life The secondary battery is first charged at a rate of 1.0 C to 4.2 V, and then charged at 4.2 V to 0.05 C, and then discharged at a rate of 1.0 C to 2.8 V at 25℃. This process is recorded as one cycle, and the discharge capacity C0 of the first cycle is recorded. The above steps are repeated for 1000 times, and the discharge capacity C1000 of the secondary battery after full charging for 1000 times is recorded. 1000 The cycle capacity retention rate = (discharge capacity of the secondary battery after 1000 cycles C1000 / discharge capacity of the first cycle C0) x 100%. 1000 ​

[0196] (9) Lithium precipitation of the positive electrode tab After 1000 cycles, the battery was charged at a current of 1.0 C to 4.2 V, and then charged at 4.2 V to 0.05 C (full charge, SOC 100%). The electrode assembly was disassembled, and the surface of the positive electrode tab was inspected. If there was a gray area, it was lithium precipitation, and if there was no gray area, it was no lithium precipitation. The degree of lithium precipitation was classified as no lithium precipitation, slight lithium precipitation, moderate lithium precipitation, and severe lithium precipitation. Slight lithium precipitation was less than 0.5% of the total area of the positive electrode tab, moderate lithium precipitation was 0.5-5% of the total area of the positive electrode tab, and severe lithium precipitation was more than 5% of the total area of the positive electrode tab.

[0197] (10) Compaction density of the single-sided positive electrode film layer The secondary battery was discharged at a rate of 1.0 C to 2.8 V, and then the positive electrode tab was disassembled from the secondary battery, for example, a single-sided coated positive electrode tab (if it was a double-sided coated tab, the positive electrode film layer on one side was first wiped off) was cut into a small disc with an area of S1, and its mass and thickness were measured, recorded as M1 and H1. Then the positive electrode film layer of the above weighed positive electrode tab was wiped off, and the total mass and total thickness of the positive electrode current collector and the first conductive layer were measured and recorded as M0 and H0. The compaction density of the single-sided positive electrode film layer was calculated according to the following formula.

[0198] Compaction density of the positive electrode film layer = (M1-M0) /

(H1-H0) x S1

[0199] (10) Energy density At 25°C, the secondary battery was first charged at a rate of 1.0 C to 4.2 V, and then charged at 4.2 V to 0.05 C, and then discharged at a rate of 1.0 C to 2.8 V, and the total discharge energy of the secondary battery was recorded as E0.

[0200] The volume of the secondary battery was obtained as V0.

[0201] The volume energy density of the secondary battery (Wh / L) = discharge energy E0 of the secondary battery / volume V0 of the secondary battery.

[0202] Analysis of test results of each example and comparative example The secondary batteries of each example and comparative example were prepared according to the above method, and the performance parameters were measured, and the results are shown in Tables 1-7 below.

[0203] Table 1 Test results of the positive electrode tab and the secondary battery

[0204] According to Table 1, comparing the test results of Examples 1-8 and Comparative Example 1, it can be seen that when the area density of the single-sided positive electrode film layer is controlled within 180 mg / cm 2 -300 mg / cm 2 and the first conductive layer is provided to include conductive metal particles to reduce the black spot lithium precipitation phenomenon in the positive electrode tab, thereby the secondary battery has a higher volumetric energy density and a longer cycle life.

[0205] Table 2 Test results of positive electrode tabs and secondary batteries

[0206] According to Table 2, comparing the test results of Examples 1, 9-12, it can be seen that when the metal area density is within the range of 0.1 μg / cm 2 -0.3 μg / cm 2 , the secondary battery has a lower degree of lithium precipitation, thereby having a longer cycle life. Further, when the metal area density is within the range of 0.15 μg / cm 2 -0.25 μg / cm 2 , the secondary battery has a longer cycle life.

[0207] Table 3 Test results of positive electrode tabs and secondary batteries

[0208] According to Table 3, comparing the test results of Examples 13-16, it can be seen that when the particle size d1 of the first conductive metal particles is within the range of 3 μm-5 μm, and the particle size d2 of the second conductive metal particles is greater than or equal to 0.5 μm and less than 3 μm, the secondary battery has a lower degree of lithium precipitation, thereby having a longer cycle life.

[0209] Table 4 Test results of positive electrode tabs and secondary batteries

[0210] According to Table 4, comparing the test results of Examples 1, 17-21, it can be seen that when the number of conductive metal particles accounts for 50%-90%, the secondary battery has a longer cycle life. And with the increase of the number of accounts, the cycle life of the secondary battery gradually increases.

[0211] Table 5 Test results of positive electrode tabs and secondary batteries

[0212] According to Table 5, it can be known from the comparison of the test results of Example 1 and Examples 22-24 that when the thickness of the first conductive layer is in the range of 2 μm-5 μm, the secondary battery can have a longer cycle life. And with the increase of the thickness, the cycle life of the secondary battery presents a change trend of first increasing and then decreasing.

[0213] Table 6 Test results of positive electrode sheet and secondary battery

[0214] According to Table 6, it can be known from the comparison of the test results of Examples 25-28 that when the aspect ratio of the single-walled carbon nanotube is in the range of 300-4000, the single-sided positive electrode film layer of the secondary battery can have a higher compaction density, and with the increase of the aspect ratio, the compaction density of the single-sided positive electrode film layer presents a change trend of first increasing and then decreasing. Therefore, when the aspect ratio of the single-walled carbon nanotube is in the range of 1000-3000, the secondary battery can have a higher volumetric energy density.

[0215] Table 7 Test results of positive electrode sheet and secondary battery

[0216] According to Table 7, it can be known from the comparison of the test results of Examples 25-34 that with the addition of the multi-walled carbon nanotube, the compaction density of the single-sided positive electrode film layer can be improved. And when the mass ratio of the single-walled carbon nanotube and the multi-walled carbon nanotube is in the range of (2-8):(92-98), the single-sided positive electrode film layer can have a higher compaction density, and the secondary battery can have a higher volumetric energy density.

[0217] Although the present application has been described with reference to the preferred embodiments, various modifications can be made to it without departing from the scope of the application, and equivalent parts can be substituted therefor. In particular, the technical features mentioned in each of the embodiments can be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode plate, characterized in that, include: Positive current collector; A positive electrode film layer is located on at least one side of the positive electrode current collector, and the areal density of the positive electrode film layer on one side is 180 mg / cm³. 2 -300mg / cm 2 ; as well as, A first conductive layer is located between the positive current collector and the positive electrode film layer. The first conductive layer includes conductive metal particles, and the metal elements in the conductive metal particles include one or more of Au, Ag, Al, Ni, Co, Li, Fe, Cu, Al, Ti, Mo, Sn, Sb, In, Zn and Na.

2. The positive electrode sheet according to claim 1, characterized in that, In a cross-section of the first conductive layer along the thickness direction of the positive electrode sheet, the surface density of the conductive metal particles is σ = A × d × ρ, and 0.1 μg / cm³. 2 ≤σ≤0.3μg / cm 2 The optional value is 0.15 μg / cm. 2 ≤σ≤0.25μg / cm 2 Where A is the area ratio of the conductive metal particles measured in the cross-section along the thickness direction of the positive electrode sheet in the first conductive layer as the volume ratio of the conductive metal particles in the first conductive layer, d is the thickness of the first conductive layer, and ρ is the density of the metal elements in the conductive metal particles.

3. The positive electrode sheet according to claim 1 or 2, characterized in that, The conductive metal particles include a first conductive metal particle and a second conductive metal particle. In the cross-section of the first conductive layer along the thickness direction of the positive electrode sheet, the particle size of the first conductive metal particle is 3μm-5μm, and the particle size of the second conductive metal particle is greater than or equal to 0.5μm and less than 3μm.

4. The positive electrode sheet according to claim 3, characterized in that, In a cross-section of the first conductive layer along the thickness direction of the positive electrode sheet, the D of the first conductive metal particle v50 D greater than the second conductive metal particle v90 .

5. The positive electrode sheet according to claim 4, characterized in that, D of the first conductive metal particle v50 Its thickness ranges from 3.5μm to 4.2μm. And / or, the D of the second conductive metal particle v90 The thickness ranges from 2.5μm to 2.8μm.

6. The positive electrode sheet according to any one of claims 1-5, characterized in that, The first conductive layer has a porous structure with a pore size of 200nm-400nm.

7. The positive electrode sheet according to any one of claims 1-6, characterized in that, The conductive metal particles include dot-shaped conductive metal particles and / or linear conductive metal particles.

8. The positive electrode sheet according to any one of claims 1-7, characterized in that, The first conductive layer also includes conductive carbon particles; Optionally, the conductive carbon particles include linear conductive carbon particles.

9. The positive electrode sheet according to claim 8, characterized in that, In the cross-section of the first conductive layer along the thickness direction of the positive electrode sheet, the proportion of the conductive metal particles is 50%-90% based on the total number of the conductive metal particles and the conductive carbon particles.

10. The positive electrode sheet according to any one of claims 1-9, characterized in that, The thickness of the first conductive layer is 2μm-5μm.

11. The positive electrode sheet according to any one of claims 1-9, characterized in that, The positive electrode further includes a second conductive layer, which comprises carbon nanotubes and is located between the first conductive layer and the positive electrode film.

12. The positive electrode sheet according to claim 11, characterized in that, The thickness of the second conductive layer is 1μm-2.5μm.

13. The positive electrode sheet according to claim 11 or 12, characterized in that, The carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

14. The positive electrode sheet according to claim 13, characterized in that, The aspect ratio of the single-walled carbon nanotube is 300-4000, and can be selected as 1000-2000.

15. The positive electrode sheet according to claim 13, characterized in that, The mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is (2-8):(92-98).

16. A secondary battery, characterized in that, Includes the positive electrode sheet according to any one of claims 1-15.

17. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 16.

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