Positive plate and preparation method thereof, battery and power utilization device

Abstract

The invention relates to the field of batteries, in particular to a positive plate and a preparation method thereof, a battery and an electric device. The positive plate comprises a current collector and an active material layer arranged on at least one side surface of the current collector along the thickness direction; wherein the active substance layer comprises an active substance; the active substance comprises first particles; the first particles have cracks, the average length of the cracks in the first particles is L, the average particle size of the first particles is Dx50, and L and Dx50 meet the condition that L / Dx50 is larger than or equal to 0.1 and smaller than or equal to 0.7. The preparation method of the positive plate comprises the following steps: coating at least one side surface of a current collector along the thickness direction with slurry containing an active substance so as to form an active substance layer on the current collector, thereby obtaining the positive plate. According to the positive plate provided by the invention, the optimal balance of the lithium ion transmission performance and the structural stability of the positive active material is realized, and the comprehensive performance of the lithium ion battery is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a positive electrode sheet and a preparation method thereof, a battery and an electrical device. Background Art

[0002] As a core energy storage device in the new energy field, the energy density and cycle life of lithium-ion batteries are highly dependent on the performance of the positive electrode material. High-nickel lithium nickel cobalt manganese oxide (LiNixCoyMnzO2, x≥0.8) is regarded as the preferred positive electrode material for the next generation of high-energy density batteries due to its high specific capacity (≥200mAh / g) and low cost. However, in order to achieve high volumetric energy density and thus increase the compaction density of the electrode, high-nickel materials are prone to fracture during high compaction due to the hard and brittle nature of the particles, leading to the following problems: Structural degradation: Long cracks randomly generated inside the particles will destroy the integrity of the crystal structure, triggering continuous side reactions between the active material and the electrolyte, resulting in a significant decrease in cycle life; Kinetic limitation: Excessive reduction in porosity under high compaction hinders lithium ion transmission, especially under low temperature (-40℃) or high rate (≥3C) conditions, where polarization intensifies and the discharge capacity drops sharply; Safety risks: Particle breakage exacerbates interface instability, and lattice oxygen release at high temperatures can easily cause thermal runaway. Summary of the Invention

[0003] In view of this, the present invention is committed to providing a positive electrode sheet and a preparation method thereof, a battery and an electrical device to solve the problems of structural collapse of positive electrode materials and insufficient lithium ion diffusion paths in the prior art.

[0004] In order to solve the above technical problems, this application is implemented as follows:

[0005] The present application provides a positive electrode sheet, comprising a current collector and an active material layer provided on at least one surface of the current collector along a thickness direction;

[0006] The active material layer includes an active material;

[0007] The active material includes first particles; the first particles have cracks, the average length of the cracks in the first particles is L, the average particle size of the first particles is Dx50, and the L and the Dx50 satisfy: 0.1≤L / Dx50≤0.7.

[0008] In some embodiments, the number of cracks in the first particle is ≤3.

[0009] In some specific embodiments, the L and the Dx50 satisfy: 0.2≤L / Dx50≤0.6.

[0010] In some specific embodiments, the particle size of 10% of the cumulative volume of the first particles is Dx10, the particle size of 90% of the cumulative volume of the first particles is Dx90, and the Dx10, the Dx90 and the Dx50 satisfy: (Dx90-Dx10) / Dx50≤0.8.

[0011] In some embodiments, the active substance further comprises second particles.

[0012] In some specific embodiments, the average particle size of the second particles is Dy50, and Dy50 and Dx50 satisfy: Dy50<Dx50.

[0013] In some specific embodiments, the Dy50 and Dx50 satisfy: 1.8≤Dx50 / Dy50≤4.

[0014] In some specific embodiments, the Dx50 is 8 μm to 15 μm.

[0015] In some specific embodiments, the Dy50 is 1.2 μm to 4 μm.

[0016] In some specific embodiments, based on the total volume of the active substance, the volume content of the first particles is 50% to 90%.

[0017] In some specific embodiments, based on the total number of particles of the active material, the number of the first particles having cracks is 10% to 50%.

[0018] In some embodiments, the active material comprises a metal oxide.

[0019] In some specific embodiments, the metal in the metal oxide includes at least one of Ni, Co, Mn, and Al.

[0020] In some specific embodiments, the metal in the metal oxide further includes at least one of Zr, Ti, Sr, Mg, Na, Mo, Ca, Ba, La, and Y.

[0021] In some embodiments, the tap density of the active material is 1.5 g / cm 3 ~2.7g / cm 3 .

[0022] In some embodiments, the specific surface area of the active material is 0.3 m 2 / g~1.2m 2 / g.

[0023] In some specific embodiments, the bonding force between the active material layer and the current collector is ≥10 N / m.

[0024] In some specific embodiments, the contact resistance between the active material layer and the current collector is 0.0012Ω / cm 2 ~0.0225Ω / cm 2 .

[0025] In some specific embodiments, the active material layer further includes a conductive agent and a binder.

[0026] In some specific embodiments, the mass ratio of the active material, the conductive agent, and the binder is (80-98):(1-10):(1-10).

[0027] In some specific embodiments, the conductive agent includes at least one of conductive carbon black, acetylene black, graphene, conductive graphite, conductive carbon tubes, and conductive carbon fibers.

[0028] In some embodiments, the binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, or sodium carboxymethyl cellulose.

[0029] In some specific embodiments, the compaction density of the positive electrode sheet is 3.2 g / cm 3 ~3.8g / cm 3 .

[0030] In some specific embodiments, the surface capacity of the positive electrode sheet is 2.55 mAh / cm 2 ~3.55mAh / cm 2 .

[0031] In some specific embodiments, the porosity of the positive electrode sheet is 20% to 35%.

[0032] A second aspect of the present application provides a method for preparing a positive electrode sheet, comprising the following steps:

[0033] (1) applying a slurry of an active material containing first particles onto at least one surface of a current collector in a thickness direction;

[0034] (2) Drying to form an active material layer on the current collector to obtain a positive electrode sheet.

[0035] In some embodiments, the active substance comprises second particles.

[0036] In some specific embodiments, the solid content of the slurry is 60 wt % to 75 wt %.

[0037] In some specific embodiments, the drying temperature is 90° C. to 110° C., and the drying time is 2 h to 4 h.

[0038] In some specific embodiments, after the drying is completed, post-processing is further included; the post-processing includes roller pressing.

[0039] The third aspect of the present application further provides a battery, comprising a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode sheet described above, and / or a positive electrode sheet prepared according to the above preparation method.

[0040] A fourth aspect of the present application further provides an electrical device, which includes the above-mentioned battery.

[0041] Through the above technical solution, the beneficial technical effects of the present invention are:

[0042] In the present application, the positive electrode sheet provided includes a current collector and an active material layer disposed on the surface of the current collector, wherein the active material layer includes an active material comprising a first particle, the first particle has cracks, the average length (L) of the cracks and the average particle size (Dx50) of the first particle satisfy 0.1≤L / Dx50≤0.7, the cracks in the first particle neither cause the positive electrode active material to break, maintain a certain structural integrity of the crystal structure of the positive electrode active material, avoid continuous side reactions between the positive electrode active material and the electrolyte, thereby improving the cyclability of the battery, and at the same time, the crack structure in the first particle can provide an effective channel for lithium ions, improve the lithium ion transmission performance, and improve the battery's rate performance. The optimal balance between the lithium ion transmission performance and structural stability of the positive electrode active material is achieved, significantly improving the overall performance of the lithium ion battery. It avoids the collapse of the particle structure caused by excessive particle breakage (L / Da50>0.7) and prevents the rate performance from decreasing due to insufficient lithium ion diffusion path (L / Da50<0.1).

[0043] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention.

[0045] Figure 1 Shown is a schematic structural diagram of the positive electrode sheet in this application;

[0046] Figure 2 Shown is a cross-sectional polishing-scanning electron microscopy (CP-SEM) image of the positive electrode sheet in Example 3. DETAILED DESCRIPTION

[0047] The present invention discloses a positive electrode sheet and a method for preparing the same, a battery, and an electrical device. Those skilled in the art may refer to the contents of this document and appropriately improve the process parameters to achieve the desired results. It should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0048] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0049] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0050] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0051] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0052] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0053] In lithium-ion batteries, high nickel materials such as lithium nickel cobalt manganese oxide (LiNi x Co y Mn zNickel O2 (x ≥ 0.8) is considered the preferred cathode material for next-generation high-energy-density batteries due to its high specific capacity (≥ 200 mAh / g) and low cost. However, to achieve high volumetric energy density and thus increase the compaction density of the electrode, high-nickel materials are prone to fracture during high-density compaction due to their hard and brittle particle nature. The long, random cracks generated within the particles can destroy the integrity of the crystal structure, triggering continuous side reactions between the active material and the electrolyte, resulting in a significant decrease in cycle life. At the same time, the excessive reduction in porosity under high compaction hinders lithium-ion transport, especially at low temperatures (-40°C) or high-rate conditions (≥ 3C), where polarization is intensified, leading to a sharp drop in discharge capacity. Furthermore, particle breakage exacerbates interfacial instability, and the release of lattice oxygen at high temperatures can easily trigger thermal runaway.

[0054] In view of this, the present application proposes a positive electrode sheet and a preparation method thereof, a battery, and an electrical device, wherein the positive electrode sheet has the characteristics of high capacity and excellent cycle performance. The present application and optional embodiments are described in more detail below.

[0055] [Positive electrode]

[0056] In some embodiments, the present application provides a positive electrode sheet, comprising a current collector and an active material layer disposed on at least one surface of the current collector along a thickness direction;

[0057] The active material layer includes an active material;

[0058] The active material includes first particles; the first particles have cracks, the average length of the cracks in the first particles is L, the average particle size of the first particles is Dx50, and the L and the Dx50 satisfy: 0.1≤L / Dx50≤0.7.

[0059] In the present application, the positive electrode sheet provided includes a current collector and an active material layer arranged on the surface of the current collector, wherein the active material layer includes an active material comprising a first particle, the first particle has cracks, the average length (L) of the cracks and the average particle size (Dx50) of the first particle satisfy 0.1≤L / Dx50≤0.7, the cracks in the first particle will not cause the positive electrode active material to break, maintain a certain structural integrity of the crystal structure of the positive electrode active material, avoid continuous side reactions between the positive electrode active material and the electrolyte, thereby improving the cyclability of the battery, and at the same time, the crack structure in the first particle can provide an effective channel for lithium ions, improve the transmission performance of lithium ions, and thereby improve the rate performance of the battery. If the length of the crack structure is too long, it will cause the structure of the first particle to collapse, the electrolyte to be locally enriched, the side reaction between the positive electrode active material and the electrolyte to intensify, and the cycle performance of the battery to be reduced. If the length of the crack structure is too short, the lithium ion transmission performance cannot be improved.

[0060] Therefore, in this application, by limiting the ratio of the average length (L) of the cracks in the first particles of the active material to the average particle size (Dx50) of the first particles to between 0.1 and 0.7, an optimal balance between the lithium ion transport performance and structural stability of the positive electrode active material is achieved, significantly improving the overall performance of the lithium ion battery. This not only avoids the collapse of the particle structure caused by excessive particle breakage (L / Da50>0.7), but also prevents the reduction of rate performance caused by insufficient lithium ion diffusion path (L / Da50<0.1).

[0061] The positive electrode sheet of the present application is suitable for use in lithium-ion batteries to alleviate problems such as structural collapse and insufficient lithium ion diffusion paths caused by cracking of the positive electrode active material of existing lithium-ion batteries.

[0062] In this application, the term "crack" refers to a crack extending from the surface of the first particle to the interior of the first particle. In this application, the crack structure in the first particle can be formed by applying a slurry containing the active material of the first particle to the surface of the current collector, drying it, and then rolling it to produce a high tap density and fast ion transport.

[0063] In some embodiments, the number of cracks in the first particle is ≤3.

[0064] In the present application, the number of cracks in a first particle refers to the number of cracks in a single first particle. If the number of cracks in a first particle is too many, the first particle will face the risk of breakage.

[0065] In this application, the test method for the average length of cracks is as follows: the pole piece is cut into small discs with a diameter of 0.7 cm. Under CP-SEM 1000x observation, in an area of 50 μm long and 30 μm wide, the number of all particles containing cracks is counted as X, and the length of each crack L1, L2, L3...Lx is measured using software. The average crack length L = (L1+L2+L3...+Lx) / X.

[0066] In some embodiments, L and Dx50 satisfy: 0.2≤L / Dx50≤0.6. As an example, L / Dx50 can be any one of 0.2, 0.3, 0.4, 0.5, and 0.6, or a range of values between any two of them.

[0067] In the present application, by regulating the average length (L) of the cracks and the average particle size (Dx50) of the first particles within the above range, a certain structural integrity of the crystal structure of the positive electrode active material can be maintained, and continuous side reactions between the positive electrode active material and the electrolyte can be avoided, thereby improving the cyclability of the battery. At the same time, the crack structure in the first particles can provide an effective channel for lithium ions, thereby improving the transmission performance of lithium ions and improving the rate performance of the battery.

[0068] In some embodiments, the particle size of 10% of the cumulative volume of the first particles is Dx10, the particle size of 90% of the cumulative volume of the first particles is Dx90, and Dx10, Dx90, and Dx50 satisfy the following: (Dx90-Dx10) / Dx50≤0.8. As an example, (Dx90-Dx10) / Dx50 can be any one of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8, or a range of any two thereof.

[0069] In this application, (Dx90 - Dx10) / Dx50 represents the particle size distribution span of the first particles. By regulating the particle size distribution span of the first particles within the above range, the consistency of the crack ratio in the first particles can be ensured, thereby ensuring that the positive electrode active material has both excellent lithium ion transport performance and structural stability, thereby improving the rate performance and cycling stability of the lithium-ion battery.

[0070] In some embodiments, the active material further comprises second particles.

[0071] In some embodiments, the average particle size of the second particles is Dy50, and Dy50 and Dx50 satisfy: Dy50<Dx50.

[0072] In some embodiments, Dy50 and Dx50 satisfy: 1.8≤Dx50 / Dy50≤4. As an example, Dx50 / Dy50 can be any one of 1.8, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, 3.2, 3.5, 3.8, and 4, or a range of values therebetween.

[0073] like Figure 1 As shown, in the structural diagram of the positive electrode sheet, the second particles are filled in the pores of the first particles. In the present application, by regulating the average particle size of the second particles to be smaller than the average particle size of the first particles, on the one hand, the second particles can be filled in the gaps between the first particles, reducing the porosity of the positive electrode sheet and increasing the load and compaction density of the positive electrode active material; at the same time, the second particles are filled in the gaps of the first particles so that the first particles and the second particles can be closely stacked, which can inhibit excessive rupture of the first particles, make the cracks evenly distributed, have low compaction resistance and high void connectivity, and enhance rate performance. If the average particle size of the second particles is too large, the second particles cannot be filled in the pores of the first particles; if the difference between the average particle size of the second particles and the average particle size of the first particles is too large, the compaction density is too high, causing the particles to break, thereby reducing the cycle performance.

[0074] In some embodiments, Dx50 is 8 μm to 15 μm. As an example, Dx50 can be any one of 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm and 15 μm, or a range of values between any two of them.

[0075] In some embodiments, the Dy50 is 1.2 μm to 4 μm. As an example, Dy50 can be any one of 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.4 μm, 3.5 μm, 5.8 μm, and 4 μm, or a range of any two thereof.

[0076] In this application, the Dx50 test method is as follows: the electrode is cut into small discs with a diameter of 0.7 cm. Under CP-SEM observation at 1000x magnification, the diameter of 100 large particles is measured using software. The average value is taken as the large particle size Dx50. The Dy50 test method is the same as above.

[0077] In this application, the terms "Dx50" and "Dy50" both refer to the volume median particle size Dv50; "Dx90" refers to the particle size of 90% of the cumulative volume of the particles; and "Dx10" refers to the particle size of 10% of the cumulative volume of the particles.

[0078] In the present application, by controlling the average particle size of the first particles and the average particle size of the second particles within the above range, the electrode structure dominated by large particles can increase the compaction density, reduce the proportion of inactive substances (conductive agents, binders), and increase the volume energy density; small particles are embedded in the gaps between large particles, which can inhibit the excessive breakage of the first particles, make the cracks evenly distributed, and the compaction resistance is low and the void connectivity is high, and the rate performance is enhanced. The combination of Dx50 (8-15μm) and Dy50 (1.2-4μm) achieves fine regulation between graded filling (reducing porosity), kinetic optimization (balancing ion / electron transport) and side reaction control. The combination of Dx50 / Dy50≤4 can avoid the risk of small particles, and the lower limit of Dx50 (8μm) ensures structural stability.

[0079] In some embodiments, the volume content of the first particles is 50% to 90% based on the total volume of the active substance. As an example, the volume content of the first particles can be any one of 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, and 90%, or a range therebetween, based on the total volume of the active substance.

[0080] In the present application, by regulating the volume content of the first particles within the above range, the positive electrode sheet can achieve an optimal solution between porosity, conductive network, and side reaction suppression.

[0081] In this application, the test method for the volume content of the first particles is as follows: the electrode is cut into small discs with a diameter of 0.7 cm. Under CP-SEM 1000x observation, the number of first-type particles Y1 and the number of second-type particles Y2 in an area of 50 μm long and 30 μm wide are counted. The volume V1 of the large particle is approximately calculated as V1 = π × (Dx50) 3 / 6, the volume of small particles V2 is approximately calculated as V2 = π × (Dy50) 3 / 6, then the volume ratio of the first type of particles to the total particles is E=(Y1×V1) / (Y1×V1+Y2×V2).

[0082] In some embodiments, based on the total number of particles of the active material, the number of first particles having cracks is 10% to 50%. As an example, based on the total number of particles of the active material, the number of first particles having cracks can be any one of 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50%, or a range therebetween.

[0083] In the present application, by regulating the number of the first particles having cracks within the above range, energy density, fast charging capability and cycle life can be taken into account.

[0084] In some embodiments, the tap density of the active material is 1.5 g / cm 3 ~2.7g / cm 3 As an example, the tap density of the active material may be 1.5 g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 and 2.7 g / cm 3 Any point value in or any range of values between them.

[0085] In some embodiments, the specific surface area of the active material is 0.3 m 2 / g~1.2m 2 As an example, the specific surface area of the active material can be 0.3 m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g、1m 2 / g, 1.1m 2 / g and 1.2m 2 Any point value in / g or any range of values between them.

[0086] In this application, the comprehensive performance of lithium-ion batteries is significantly improved by precisely controlling the ratio of crack length to particle diameter of the positive electrode active material (10-70%) and combining the synergistic optimization of compaction density, porosity, particle volume ratio, and specific surface area parameters.

[0087] In some embodiments, the active material includes, but is not limited to, metal oxides.

[0088] Preferably, the metal in the metal oxide includes, but is not limited to, at least one of Ni, Co, Mn and Al.

[0089] Preferably, the metal in the metal oxide also includes, but is not limited to, at least one of Zr, Ti, Sr, Mg, Na, Mo, Ca, Ba, La and Y.

[0090] Preferably, the active material includes, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide.

[0091] In some embodiments, lithium nickel cobalt manganese oxide can be purchased or prepared using the following preparation method.

[0092] Specifically, the preparation method of lithium nickel cobalt manganese oxide includes the following steps:

[0093] The nickel-cobalt-manganese precursor and the lithium source are mixed, sintered and annealed to obtain lithium nickel-cobalt-manganese oxide;

[0094] Wherein, the nickel-cobalt-manganese precursor includes NiCoMn(OH)2;

[0095] The lithium source includes LiOH;

[0096] Wherein, the sintering is staged sintering, and the conditions for the first sintering in the staged sintering are: a heating rate of 2°C / min to 5°C / min, a temperature of 400°C to 500°C, and a time of 2h to 5h; as an example, the heating rate can be any one of 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min and 5°C / min, or a range between any two of them, the temperature can be any one of 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C and 500°C, or a range between any two of them, and the time can be any one of 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, and 5h, or a range between any two of them;

[0097] Conditions for the second sintering in the staged sintering: a heating rate of 1°C / min to 3°C / min, a temperature of 750°C to 850°C, and a time of 10h to 20h; as an example, the heating rate may be any one of 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, and 3°C / min, or a range between any two of them; the temperature may be any one of 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, and 850°C, or a range between any two of them; and the time may be any one of 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, and 20h, or a range between any two of them;

[0098] Annealing conditions: a cooling rate of 0.5°C / min to 2°C / min, and a temperature of 300°C to 400°C; as an example, the cooling rate can be any one of 0.5°C / min, 1°C / min, 1.5°C / min and 2°C / min, or a range between any two of them, and the temperature can be any one of 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C and 400°C, or a range between any two of them.

[0099] Of course, it is not limited thereto, and other similar active substances may also be used, as long as they do not limit the purpose of this application.

[0100] In some embodiments, the bonding force between the active material layer and the current collector is ≥10 N / m. As an example, the bonding force between the active material layer and the current collector can be any one of 10 N / m, 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, 40 N / m, 45 N / m, and 50 N / m, or a range therebetween.

[0101] In some embodiments, the contact resistance between the active material layer and the current collector is 0.0012Ω / cm 2 ~0.0225Ω / cm 2 As an example, the contact impedance between the material layer and the current collector can be 0.0012Ω / cm 2 , 0.0015Ω / cm 2 , 0.002Ω / cm 2 , 0.003Ω / cm 2 , 0.005Ω / cm 2 , 0.008Ω / cm 2 , 0.01Ω / cm 2 , 0.015Ω / cm 2 , 0.02Ω / cm 2 and 0.0225Ω / cm 2 Any point value in or any range of values between them.

[0102] In this application, the test method of contact impedance is: use a 46-probe electrode resistance test system, input the electrode thickness, collector thickness and volume resistivity of the collector in advance, then place the electrode on the measuring stage, the position of the probe contact is the intersection of the bold scale on the scale plate, drop the handle to the bottom, start the measurement, after the measurement is completed, lift the handle, move the electrode position, and repeat the test 5 times.

[0103] In the present application, by controlling the bonding force and contact impedance between the active material layer and the current collector within the above ranges, it is beneficial to improve the cycle performance and capacity retention rate of the battery.

[0104] In some embodiments, the active material layer further includes a conductive agent and a binder.

[0105] In some embodiments, the mass ratio of the active material, the conductive agent, and the binder is (80-98):(1-10):(1-10). As an example, the mass ratio of the active material, the conductive agent, and the binder can be any one of 80:10:10, 85:5:10, 85:10:5, 90:5:5, 95:2:3, 95:3:2, and 98:1:1, or a range between any two of the above.

[0106] In some embodiments, the conductive agent includes, but is not limited to, at least one of conductive carbon black, acetylene black, graphene, conductive graphite, conductive carbon tubes, and conductive carbon fibers.

[0107] In some embodiments, the binder includes, but is not limited to, at least one of polytetrafluoroethylene, polyvinylidene fluoride, or sodium carboxymethyl cellulose.

[0108] In some embodiments, the compaction density of the positive electrode sheet is 3.2 g / cm 3 ~3.8g / cm 3 As an example, the compaction density of the positive electrode sheet can be 3.2g / cm 3 , 3.3g / cm 3 、3.4g / cm 3 、3.5g / cm 3 、3.6g / cm 3 、3.7g / cm 3 and 3.8g / cm 3 Any point value in or any range of values between them.

[0109] In this application, the test method of the compaction density of the positive electrode sheet is as follows: the positive electrode sheet is cleaned with dimethyl carbonate 2-5 times and placed in an oven for drying to fully remove the dimethyl carbonate; a disc with an area of S cut off from the double-sided coating area on the positive electrode sheet is weighed to obtain the sum of the mass of the foil and the coating m1, and the thickness of the foil and the coating is measured using a spiral micrometer as d1; all the material powder on the surface of the disc is scraped off, the surface of the disc is wiped with N-methylpyrrolidone to fully remove the powder, and it is fully dried, and the disc is weighed again to obtain the foil mass m2, and the thickness of the foil is measured again using a spiral micrometer as d2; the compaction density is calculated as (m1-m2) / [S×(d1-d2)] (unit: g / cm 3 ).

[0110] In the present application, the cracks in the first particles are generated during the compaction process of preparing the positive electrode sheet. By regulating the compaction density of the positive electrode sheet within the above range, and then controlling the length of the cracks in the first particles within a reasonable range, an optimal balance between the lithium ion transport performance and structural stability of the positive electrode active material is achieved, thereby significantly improving the overall performance of the lithium-ion battery.

[0111] In some embodiments, the surface capacity of the positive electrode is 2.55 mAh / cm 2 ~3.55mAh / cm 2 As an example, the surface capacity of the positive electrode sheet can be 2.55 mAh / cm 2 , 2.6mAh / cm 2 , 2.7mAh / cm 2, 2.8mAh / cm 2 , 2.9mAh / cm 2 、3mAh / cm 2 、3.1mAh / cm 2 、3.2mAh / cm 2 、3.3mAh / cm 2 、3.4mAh / cm 2 、3.5mAh / cm 2 and 3.55mAh / cm 2 Any point value in or any range of values between them.

[0112] In this application, the test method of the surface capacity of the positive electrode sheet is as follows: the positive electrode sheet is wiped clean on one side with N-methylpyrrolidone, and then cut into electrodes with an area of K with a cutting machine to make a buckle battery, and then tested and calculated by a Beit battery tester. The test conditions are at 25°C, 0.1C constant current charging to 4.2V, 4.2V constant voltage to 0.01C; then 0.1C constant current discharge to 2.5V to obtain the battery capacity; then the battery capacity is divided by the total area K of the positive electrode sheet coating to obtain the single-sided surface capacity of the electrode sheet, the unit is mAh / cm 2 .

[0113] In some embodiments, the porosity of the positive electrode sheet is 20% to 35%. As an example, the porosity of the positive electrode sheet can be any one of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, and 35%, or a range therebetween.

[0114] In this application, by controlling the surface capacity and porosity of the positive electrode sheet within the above range, combining the ratio of the crack length to the particle diameter of the positive electrode active material, the compaction density, the porosity, the particle volume ratio, and the synergistic optimization of the specific surface area parameters, the comprehensive performance of the lithium-ion battery is significantly improved.

[0115] In some embodiments, the current collector includes, but is not limited to, aluminum foil.

[0116] Of course, it is not limited thereto, and other similar current collectors may also be used as long as they do not limit the purpose of this application.

[0117] In some embodiments, the thickness of the current collector is 10 μm to 16 μm. As an example, the thickness of the current collector can be any one of 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm and 16 μm, or a range between any two of them.

[0118] Therefore, in this application, by limiting the ratio of the average length (L) of the cracks in the first particles of the active material to the average particle size (Dx50) of the first particles to between 0.1 and 0.7, the optimal balance between the lithium ion transport performance and structural stability of the positive electrode active material is achieved. At the same time, combined with the coordinated optimization of the compaction density, porosity, particle volume ratio, and specific surface area parameters, the overall performance of the lithium ion battery is significantly improved. It not only avoids the collapse of the particle structure caused by excessive particle breakage (L / Da50>0.7), but also prevents the decline in rate performance caused by insufficient lithium ion diffusion path (L / Da50<0.1).

[0119] [Preparation method of positive electrode sheet]

[0120] A second aspect of the present application provides a method for preparing a positive electrode sheet, comprising the following steps:

[0121] (1) applying a slurry of an active material containing first particles onto at least one surface of a current collector in a thickness direction;

[0122] (2) Drying to form an active material layer on the current collector to obtain a positive electrode sheet.

[0123] In this application, the preparation method of the positive electrode material provided mainly includes applying a slurry containing a first particle active material to the surface of a current collector to form an active material layer, thereby obtaining a positive electrode sheet. The first particles have a crack structure, and the ratio of the average length (L) of the cracks in the first particles to the average particle size (Dx50) of the first particles is between 0.1 and 0.7, achieving an optimal balance between the lithium ion transport performance and structural stability of the positive electrode active material, significantly improving the overall performance of the lithium-ion battery. This preparation method is simple in process, easy to operate, highly feasible, and easy to industrialize.

[0124] It should be understood that all the features and advantages described above for the “positive electrode sheet” are also applicable to the “method for preparing the positive electrode material” and will not be described in detail here.

[0125] In some embodiments, the active substance comprises second particles.

[0126] In some embodiments, in some specific implementations, the slurry further includes a conductive agent, a binder, and a solvent;

[0127] Preferably, the solvent includes, but is not limited to, N-methylpyrrolidone.

[0128] Of course, it is not limited thereto, and other similar solvents may also be used as long as they do not limit the purpose of this application.

[0129] In some embodiments, the solid content of the slurry is 60 wt % to 75 wt %. As an example, the solid content of the slurry can be any one of 60 wt %, 62 wt %, 64 wt %, 65 wt %, 67 wt %, 69 wt %, 70 wt %, 72 wt %, 73 wt %, 74 wt % and 75 wt %, or a range therebetween.

[0130] In some embodiments, the drying temperature is 90° C. to 110° C., and the drying time is 2 hours to 4 hours. As an example, the drying temperature can be any one of 90° C., 92° C., 95° C., 98° C., 100° C., 102° C., 105° C., 108° C., and 110° C., or a range between any two thereof, and the drying time can be any one of 2 hours, 2.5 hours, 3 hours, 3.5 hours, and 4 hours, or a range between any two thereof.

[0131] In some embodiments, after the drying is completed, post-processing is further included; the post-processing includes roller pressing.

[0132] As an example, a method for preparing a positive electrode sheet includes the following steps:

[0133] The first type of active particles and the second type of active particles are mixed; the mixed active particles, carbon black and polyvinylidene fluoride are respectively added to N-methylpyrrolidone (NMP), mixed and stirred by a homogenizer to obtain a positive electrode slurry with a solid content of 60 to 75%; the positive electrode slurry is applied to at least one surface of a positive electrode current collector, and after drying and rolling, the positive electrode sheet is obtained.

[0134] The third aspect of the present application further provides a battery, comprising a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode sheet described above, and / or a positive electrode sheet prepared according to the above preparation method.

[0135] In some embodiments, the battery further comprises a negative electrode sheet, an electrolyte, and a separator. That is, the battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator.

[0136] In the embodiments of the present application, in the battery, there is no limitation on the specific materials and structures of the negative electrode sheet, isolation membrane, and electrolyte. Components and structures that are well known in the art and can be used for secondary batteries can be selected as long as the purpose of the present application can be achieved.

[0137] Preferably, the electrolyte contains 1% to 5% by mass of vinylene carbonate and 0.5% to 2% by mass of vinyl sulfate additive, and the viscosity of the electrolyte is ≤3.5 mPa·s (25° C.).

[0138] Preferably, the negative electrode is made of a silicon-carbon composite material with a specific capacity of 450 mAh / g to 600 mAh / g, and the positive and negative electrode capacity ratio N / P is 1.05 to 1.15.

[0139] The battery mentioned in the embodiments of this application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application may be a battery cell, or the battery may include a battery module (or battery module) or a battery pack.

[0140] In some embodiments, a battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. The electrode assembly can be a wound structure or a stacked structure, which is not limited in the present embodiment.

[0141] In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module.

[0142] In some embodiments, the battery may be a battery pack, which may include a case and battery cells, wherein the battery cells or battery modules are housed in the case.

[0143] It should be understood that multiple battery cells can be assembled into a battery module or a battery pack. The number of battery cells contained in a battery module or a battery pack can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module or battery pack.

[0144] A fourth aspect of the present application further provides an electrical device, which includes the above-mentioned battery.

[0145] In some embodiments, the electrical device includes at least one of an electric vehicle, a drone, or an energy storage system.

[0146] The present invention is further described in detail below by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0147] Example 1

[0148] The preparation of the positive electrode sheet includes the following steps:

[0149] (1) A first particle of lithium nickel cobalt manganese aluminum (NCMA) having an average particle size Dx50 of 10.2 μm and a second particle of lithium nickel cobalt manganese aluminum (NCMA) having an average particle size Dy50 of 3.2 μm are mixed to obtain an active material; in the active material, the volume content of the first particle is 80%, the particle size of 10% of the cumulative volume of the first particles is Dx10, the particle size of 90% of the cumulative volume of the first particles is Dx90, Dx10, Dx90 and Dx50 satisfy: (Dx90-Dx10) / Dx50=0.4; the tap density of the active material is 2.5 g / cm 3 The specific surface area of the active material is 0.54m 2 / g;

[0150] (2) dispersing the active material, conductive carbon black (a conductive agent), and polyvinylidene fluoride (a binder) in N-methylpyrrolidone at a mass ratio of 97:1.5:1.5 to obtain a slurry with a solid content of 65 wt%;

[0151] (3) The slurry was coated on one side of a 15 μm thick current collector aluminum foil in the thickness direction, dried at 100 ° C for 2 h, and then rolled to form an active material layer on the current collector to obtain a compaction density of 3.5 g / cm 3 positive electrode sheet; wherein, in the active material, the average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, satisfying: L / Dx50 is 35%, and based on the total number of particles of the active material, the number content of the first particles with cracks is 30%.

[0152] Example 2

[0153] The preparation of the positive electrode sheet is different from that of Example 1 in that:

[0154] The compaction density of the positive electrode is 3.2g / cm 3 The average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, which satisfies: L / Dx50 is 28%, and based on the total number of particles of the active substance, the number content of the first particles with cracks is 25%.

[0155] The rest are the same as in Example 1.

[0156] Example 3

[0157] The preparation of the positive electrode sheet is different from that of Example 1 in that:

[0158] The compaction density of the pole piece is 3.7g / cm 3 The average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, which satisfies: L / Dx50 is 48%, and based on the total number of particles of the active substance, the number content of the first particles with cracks is 45%.

[0159] The rest are the same as in Example 1.

[0160] Example 4

[0161] The preparation of the positive electrode sheet is different from that of Example 1 in that:

[0162] In the active substance, the volume content of the first particles is 50%, the average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, which satisfies: L / Dx50 is 18%, and based on the total number of particles of the active substance, the number content of the first particles with cracks is 12%.

[0163] The rest are the same as in Example 1.

[0164] Example 5

[0165] The preparation of the positive electrode sheet is different from that of Example 1 in that:

[0166] In the active substance, the volume content of the first particles is 70%, the average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, which satisfies: L / Dx50 is 40%, and based on the total number of particles of the active substance, the number content of the first particles with cracks is 35%.

[0167] The rest are the same as in Example 1.

[0168] Example 6

[0169] The preparation of the positive electrode sheet is different from that of Example 1 in that:

[0170] In the active substance, the volume content of the first particles is 90%, the average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, which satisfies: L / Dx50 is 55%, and based on the total number of particles of the active substance, the number content of the first particles with cracks is 50%.

[0171] The rest are the same as in Example 1.

[0172] Example 7

[0173] The preparation of the positive electrode sheet is different from that of Example 1 in that:

[0174] The average particle size Dx50 of the first particles is 12.7 μm, the average particle size Dy50 of the second particles is 5.6 μm, the average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, which satisfies: L / Dx50 is 25%. Based on the total number of particles of the active substance, the number content of the first particles with cracks is 20%.

[0175] The rest are the same as in Example 1.

[0176] Example 8

[0177] The preparation of the positive electrode sheet is different from that of Example 1 in that:

[0178] The average particle size Dx50 of the first particles is 12.7 μm, the average particle size Dy50 of the second particles is 3.2 μm, the average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, which satisfies: L / Dx50 is 45%. Based on the total number of particles of the active substance, the number content of the first particles with cracks is 40%.

[0179] The rest are the same as in Example 1.

[0180] Example 9

[0181] The preparation of the positive electrode sheet is different from that of Example 1 in that:

[0182] The average particle size Dx50 of the first particles is 10.2 μm, the average particle size Dy50 of the second particles is 5.6 μm, the average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, which satisfies: L / Dx50 is 15%, and based on the total number of particles of the active substance, the number content of the first particles with cracks is 10%.

[0183] The rest are the same as in Example 1.

[0184] Comparative Example 1

[0185] The preparation of the positive electrode sheet is different from that of Example 1 in that:

[0186] The compaction density of the positive electrode is 3.9g / cm 3 The average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, which satisfies: L / Dx50 is 68%, and based on the total number of particles of the active substance, the number content of the first particles with cracks is 65%.

[0187] The rest are the same as in Example 1.

[0188] Comparative Example 2

[0189] The preparation of the positive electrode sheet is different from that of Example 1 in that:

[0190] The compaction density of the positive electrode is 3.0g / cm 3 The average length of the cracks in the first particles is L and the average particle size of the first particles is Dx50, which satisfies: L / Dx50 is 8%, and based on the total number of particles of the active substance, the number content of the first particles with cracks is 5%.

[0191] The rest are the same as in Example 1.

[0192] Battery preparation and performance testing

[0193] 1. Battery preparation:

[0194] (1) The electrolyte contains 5% by mass of vinylene carbonate and 2% by mass of vinyl sulfate as an additive, and the solvent of the electrolyte is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (the volume ratio of EC, DMC, and EMC is 1:1:1); and the viscosity of the electrolyte is ≤3.5 mPa·s at 25°C;

[0195] (2) The negative electrode is made of silicon-carbon composite material with a specific capacity of 600 mAh / g;

[0196] (3) The positive electrode sheets prepared in the above-mentioned embodiment and comparative example were assembled with the electrolyte and the negative electrode sheet respectively to obtain a battery; wherein the capacity ratio N / P of the positive and negative electrodes was 1.05.

[0197] 2. Performance Testing

[0198] (1) Rate performance test: The voltage window is 2.5-4.2V. Place the battery in a 25℃ constant temperature box for more than 4 hours and test it according to the following steps:

[0199] 1) Discharge the battery at a constant current of 0.1C to a cutoff of 2.5V and let it stand for 10 minutes;

[0200] 2) Charge the battery at a constant current of 0.1C to a cutoff of 4.2V, and at a constant voltage of 0.01C to a cutoff, and let it rest for 10 minutes;

[0201] 3) Discharge the battery at a constant current of 0.1C to a cutoff of 2.5V, and let it rest for 10 minutes. Read the capacity at this point and record it as the first discharge capacity C0;

[0202] 4) Charge the battery at a constant current of 0.1C to 4.2V, and at a constant voltage of 0.01C, and let it rest for 10 minutes.

[0203] 5) Discharge the battery at a constant current of 0.5C to a cutoff of 2.5V and let it stand for 10 minutes;

[0204] 6) Charge the battery at a constant current of 0.1C to 4.2V, and at a constant voltage of 0.01C, and let it rest for 10 minutes.

[0205] 7) Discharge the battery at a constant current of 1C to a cutoff of 2.5V and let it stand for 10 minutes;

[0206] 8) Charge the battery at a constant current of 0.1C to 4.2V, and at a constant voltage of 0.01C, and let it rest for 10 minutes.

[0207] 9) Discharge the battery at a constant current of 2C to a cutoff of 2.5V and let it stand for 10 minutes;

[0208] 10) Charge the battery at a constant current of 0.1C to 4.2V, and at a constant voltage of 0.01C, and let it rest for 10 minutes.

[0209] 11) Discharge the battery at a constant current of 3C to a cutoff of 2.5V and let it stand for 10 minutes;

[0210] 12) Charge the battery at a constant current of 0.1C to 4.2V, and at a constant voltage of 0.01C, and let it rest for 10 minutes.

[0211] 13) Discharge the battery at a constant current of 4C to a cutoff of 2.5V and let it stand for 10 minutes;

[0212] 14) Charge the battery at a constant current of 0.1C to 4.2V, and at a constant voltage of 0.01C, and let it rest for 10 minutes.

[0213] 15) Discharge the battery at 5C constant current to 2.5V cutoff, and let it stand for 10 minutes;

[0214] 16) Charge the battery at a constant current of 0.1C to 4.2V, and at a constant voltage of 0.01C, and let it rest for 10 minutes.

[0215] 17) Discharge the battery at 6C constant current to 2.5V cutoff, and let it stand for 10 minutes;

[0216] 18) Charge the battery at a constant current of 0.1C to 4.2V, and at a constant voltage of 0.01C, and let it rest for 10 minutes.

[0217] 19) Discharge the battery at 8C constant current to 2.5V cutoff, and let it stand for 10 minutes;

[0218] 20) The rate performance of the battery, that is, the capacity retention rate, is obtained by the ratio of each rate discharge to the first discharge capacity.

[0219] (2) Cycling performance test: The voltage window is 2.5-4.2V. Place the battery in a 25℃ constant temperature box for more than 4 hours and test it according to the following steps:

[0220] 1) Discharge the battery at a constant current of 0.1C to a cutoff of 2.5V and let it stand for 5 minutes;

[0221] 2) Charge the battery at a constant current of 0.2C to a cutoff of 4.2V, and at a constant voltage of 0.05C to a cutoff, and let it rest for 5 minutes;

[0222] 3) Discharge the battery at a constant current of 0.2C to a cutoff of 2.5V, and let it rest for 5 minutes. Read the capacity at this point and record it as the first discharge capacity C0;

[0223] 4) Charge the battery at a constant current of 1.0C to 4.2V, and charge at a constant voltage of 0.05C to cut off, and let it rest for 5 minutes;

[0224] 5) Discharge the battery at a constant current of 2.0C to a cutoff of 2.5V and let it stand for 5 minutes;

[0225] 6) Repeat steps (4) and (5) 600 times;

[0226] 7) The cycle performance of the battery, i.e., the capacity retention rate, is obtained by calculating the ratio of the 600th discharge capacity to the first discharge capacity in steps (4) and (5).

[0227] (3) 130℃ hot box test: Take a battery and place it in a 25℃ constant temperature box for more than 4 hours. Then test it according to the following steps:

[0228] 1) Discharge the battery at a constant current of 0.1C to a cutoff of 2.5V and let it stand for 5 minutes;

[0229] 2) Charge the battery at a constant current of 0.2C to a cutoff of 4.2V, and at a constant voltage of 0.05C to a cutoff, and let it rest for 5 minutes;

[0230] 3) Place the battery in an incubator and set the heating rate to 5K / min. Raise the temperature to 130°C and hold for 1 hour. Then stop heating and allow the battery to cool to below 30°C.

[0231] 4) The battery is considered passed if it does not catch fire or emit smoke, otherwise it is considered failed. At least 5 batteries must be tested. If all pass, it is considered passed. If only one fails, it is considered failed.

[0232] 5) After the test is completed, if the battery does not leak, catch fire, or explode, it is considered to have passed. The above test results are shown in Table 1.

[0233] The parameters of the positive electrode sheets in the embodiment and the comparative example are compared in Table 2.

[0234] Table 1

[0235]

[0236] Table 2

[0237]

[0238] As shown in Tables 1 and 2, the relationship between the crack ratio (L / Dx50) and the compaction density (P) is as follows: the compaction density of the positive electrode sheets in Examples 1 to 3 increases from 3.2 g / cm 3 Increased to 3.7g / cm 3 The compacted density of the positive electrode in Example 2 is 3.2 g / cm 3 The low compaction density leads to loose contact between particles, a crack ratio of 28%, and limited 8C performance (72%); the compaction density of the positive electrode in Example 1 is 3.5g / cm 3 , moderate compaction density (3.5g / cm 3 ) balance ion transport and structural stability, the crack ratio is 35%, and the performance is optimal; the compaction density of the positive electrode in Example 3 is 3.2g / cm 3 , the excessively high compaction density caused particle breakage, the crack ratio was 48% (close to the safety upper limit), and the cycle retention rate dropped to 80%.

[0239] The influence of the volume content of the first particle on the performance: in Example 4, small particles account for 50%, the particles are loosely stacked, the crack ratio is only 18%, the lithium ion diffusion is hindered, and the 8C retention rate is 65%; in Example 5, the volume ratio is optimized (large particles 70% + small particles 30%), the crack ratio is 40%, the porosity is moderate (about 20%), and the 8C retention rate is 82%; in Example 6, large particles account for 90%, stress concentration causes a crack ratio of 55% (exceeding the safety threshold), and the hot box test caught fire.

[0240] Optimization window of particle size ratio (Dx50 / Dy50): Dx50 / Dy50=2.2:1 in Example 7: small particle size difference, sufficient filling of small particles, crack ratio of 25%, but the compaction density is fixed at 3.5g / cm 3 When the porosity is slightly lower, the 8C retention rate is 75%; in Example 8, Dx50 / Dy50=4:1: the particle size difference increases, large particles are more susceptible to compression and fracture, the crack ratio is 45%, and the 8C retention rate drops to 70%; in Example 9, Dx50 / Dy50=1.8:1: the particle size is close to uniform, and effective grading cannot be formed, the crack ratio is only 15%, the lithium ion transmission path is insufficient, and the 8C retention rate is 62%.

[0241] Comparative Example Failure Analysis: The compaction density of the positive electrode in Comparative Example 1 is 3.9g / cm 3 , high pressure compaction (>3.8g / cm 3 ) resulted in particle breakage, cracking ratio of 68%, structural collapse and thermal runaway (fire); the compaction density of the positive electrode sheet in Comparative Example 2 was 3.0 g / cm 3 , insufficient compaction (<3.2g / cm 3) results in loose contact between particles, the crack ratio is only 8%, and the diffusion of lithium ions is seriously hindered.

[0242] The CP-SEM image of the positive electrode sheet prepared in Example 1 is as follows: Figure 2 As shown. Figure 2 It can be seen that the first particles are broken, the number of particles with cracks accounts for 30%, and the crack ratio L / Dx50 is 35%.

[0243] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet includes a current collector and an active material layer provided on at least one surface of the current collector in the thickness direction; The active material layer includes an active material; The active material includes first particles; the first particles have cracks, the average length of the cracks in the first particles is L, the average particle size of the first particles is Dx50, and the L and the Dx50 satisfy: 0.1≤L / Dx50≤0.

7.

2. The positive electrode sheet according to claim 1, characterized in that The active substance meets at least one of the following technical features (1) to (3): (1) The number of cracks in the first particle is ≤3; (2) L and Dx50 satisfy: 0.2≤L / Dx50≤0.6; (3) The particle size of 10% of the cumulative volume of the first particles is Dx10, and the particle size of 90% of the cumulative volume of the first particles is Dx90. The Dx10, the Dx90 and the Dx50 satisfy: (Dx90-Dx10) / Dx50≤0.

8.

3. The positive electrode sheet according to claim 1, characterized in that The active substance meets at least one of the following technical features (1) to (3): (1) The active material further includes second particles; The average particle size of the second particles is Dy50, and Dy50 and Dx50 satisfy: Dy50<Dx50; The Dy50 and Dx50 satisfy: 1.8≤Dx50 / Dy50≤4; The Dx50 is 8 μm to 15 μm; The Dy50 is 1.2 μm to 4 μm; (2) Based on the total volume of the active substance, the volume content of the first particles is 50% to 90%; (3) Based on the total number of particles of the active material, the number content of the first particles having cracks is 10% to 50%.

4. The positive electrode sheet according to claim 1, characterized in that The active substance meets at least one of the following technical features (1) to (5): (1) The active material includes a metal oxide; The metal in the metal oxide includes at least one of Ni, Co, Mn and Al; the metal in the metal oxide also includes at least one of Zr, Ti, Sr, Mg, Na, Mo, Ca, Ba, La and Y; (2) The tap density of the active material is 1.5 g / cm 3 ~2.7g / cm 3 ; (3) The specific surface area of the active material is 0.3 m 2 / g~1.2m 2 / g; (4) The bonding force between the active material layer and the current collector is ≥10 N / m; (5) The contact resistance between the active material layer and the current collector is 0.0012Ω / cm 2 ~0.0225Ω / cm 2 .

5. The positive electrode sheet according to claim 1, characterized in that: The active material layer also includes a conductive agent and a binder; The mass ratio of the active material, the conductive agent and the binder is (80-98): (1-10): (1-10); The conductive agent includes at least one of conductive carbon black, acetylene black, graphene, conductive graphite, conductive carbon tube and conductive carbon fiber; The binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride or sodium carboxymethyl cellulose.

6. The positive electrode sheet according to claim 1, characterized in that The compaction density of the positive electrode sheet is 3.2 g / cm 3 ~3.8g / cm 3 ; And / or, the surface capacity of the positive electrode is 2.55 mAh / cm 2 ~3.55mAh / cm 2 ; And / or, the porosity of the positive electrode sheet is 20% to 35%.

7. The method for preparing a positive electrode sheet according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) applying a slurry of an active material containing first particles onto at least one surface of a current collector in a thickness direction; (2) Drying to form an active material layer on the current collector to obtain a positive electrode sheet.

8. The method for preparing a positive electrode sheet according to claim 7, wherein: The method for preparing the positive electrode sheet satisfies at least one of the following technical features (1) to (4): (1) The active substance includes second particles; (2) The solid content of the slurry is 60 wt% to 75 wt%; (3) The drying temperature is 90° C. to 110° C., and the drying time is 2 h to 4 h; (4) After the drying is completed, post-processing is also included; the post-processing includes roller pressing.

9. A battery comprising a positive electrode, characterized in that: The positive electrode sheet includes the positive electrode sheet according to any one of claims 1 to 6, and / or the positive electrode sheet prepared by the preparation method according to any one of claims 7 to 8.

10. An electrical device, characterized in that: The electric device includes the battery according to claim 9.

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