Positive plate and battery

Abstract

The invention relates to the technical field of batteries, in particular to a positive plate and a battery comprising the positive plate. The positive plate comprises a positive current collector and a positive active layer, the positive active layer comprises a first active layer and a second active layer, the first active layer comprises a first active material which is a primary particle, the second active layer comprises a second active material which is a secondary spherical particle, and the first active layer and the second active layer are arranged along the width direction of the positive plate; the positive current collector comprises a first region and a second region which are connected, the first active layer is located on the surface of the first region, and the second active layer is located on the surface of the first active layer and covers the second region; the ratio of the porosity of the positive active layer to the porosity of the second active layer is (0.58-0.95): 1, and the positive plate meets the following relational expression: H / H is more than or equal to 20 and less than or equal to 700. The matching degree of lithium ion diffusion rates between the upper layer and the lower layer of the positive plate is relatively high, the transmission efficiency of lithium ions can be improved, and the cold start performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a positive electrode and a battery including the positive electrode. Background Technology

[0002] Lithium-ion batteries, with their high energy density, long lifespan, and excellent charge-discharge performance, have become an indispensable energy source for mobile electronic devices, electric vehicles, and energy storage systems. To further optimize battery performance and improve energy density, double-layer coating technology for cathode materials has emerged. However, existing double-layer coating technologies for cathode materials still have some problems in practical applications. For example, in low-temperature environments, the cold-start performance of double-coated cathode sheets is poor, limiting the application of this technology. Summary of the Invention

[0003] Research has found that due to the complex structure of the double-coated positive electrode, there is a significant gradient in the diffusion rate of lithium ions between the two layers. When the battery is in a low-temperature environment, the lithium ion diffusion rate between the upper and lower layers is mismatched, resulting in severe internal polarization of the battery and a significant decrease in lithium ion transport efficiency. This makes it difficult for the double-coating technology to exert its advantages in low-temperature environments.

[0004] To address the issue of mismatched lithium-ion diffusion rates between the upper and lower layers of a double-coated cathode sheet at low temperatures, this invention provides a cathode sheet and a battery incorporating the cathode sheet. The cathode sheet of this invention exhibits a high degree of matching between the upper and lower lithium-ion diffusion rates, which reduces internal polarization of the battery, improves lithium-ion transport efficiency, and enhances the battery's cold-start performance.

[0005] To achieve the above objectives, a first aspect of the present invention provides a positive electrode sheet, wherein the positive electrode sheet includes a positive current collector and a positive active layer located on one or both surfaces of the positive current collector. The positive active layer includes a first active layer and a second active layer. The first active layer includes a first active material, which is a primary particle. The second active layer includes a second active material, which is a secondary spherical particle. Along the width direction of the positive electrode sheet, the positive current collector includes a first region and a second region connected together. The first active layer is located on the surface of the positive current collector in the first region, and the second active layer is located on the surface of the first active layer and covers the second region. The ratio of the porosity of the positive active layer to the porosity of the second active layer is (0.58-0.95):1, and the positive electrode sheet satisfies the following relationship: 20≤H / △H≤700, where H is the width of the positive active layer projected onto the positive current collector in mm, and △H is the width of the second active layer projected onto the positive current collector in the second region in mm.

[0006] A second aspect of the present invention provides a battery, wherein the battery includes the positive electrode sheet described in the first aspect of the present invention.

[0007] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0008] The positive electrode sheet of the present invention, by controlling the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer, enables a high degree of matching between the diffusion rates of lithium ions in the first and second active layers, thereby improving the lithium ion transport efficiency and enhancing the cold-start performance of the battery. Furthermore, the structure of the positive electrode sheet of the present invention is such that a first active layer comprising primary particles is located on the surface of the positive electrode current collector in a first region, and a second active layer comprising secondary spherical particles is located on the surface of the first active layer and covers the second region. The secondary spherical particles provide more transport channels for lithium ions and are less prone to significant volume expansion at high temperatures, thus improving the high-temperature cycle performance of the battery. The second active layer located on the surface of the first active layer... The active layer simultaneously covers the second region, and the second active layer and the first active layer of the first region are adjacent in the width direction of the positive electrode sheet. This effectively protects the first active layer, balances the relationship between primary particles and electrolyte in the first active layer, and avoids excessive contact between primary particles and electrolyte, which would affect the cycle performance of the battery. At the same time, controlling H / ΔH can improve the overall structural stability of the positive electrode sheet, further enhance the protective effect of the second active layer of the second region on the first active layer of the first region, increase the transport rate of lithium ions in the first active layer, and further improve the cold start performance of the battery. This allows the battery to have both high high-temperature performance and good cold start performance. In addition, the positive electrode sheet with the above structure can also reduce the risk of lithium plating.

[0009] Other features and advantages of the present invention will be described in detail in the following detailed description section.

[0010] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0011] Figure 1 The diagram shown is one of the side view structural schematic diagrams of the positive electrode sheet of the present invention.

[0012] Figure 2 The image shown is a second side view of the positive electrode structure of the present invention.

[0013] Figure 3The diagram shown is one of the schematic diagrams illustrating the width of the positive electrode active layer in the positive electrode sheet of the present invention.

[0014] Figure 4 The diagram shown is a second schematic showing the width of the positive electrode active layer in the positive electrode sheet of the present invention.

[0015] Figure 5 The diagram shown is the third schematic diagram of the width of the positive electrode active layer in the positive electrode sheet of the present invention.

[0016] Figure 6 The third side view of the positive electrode sheet of the present invention is shown.

[0017] Figure 7 The fourth schematic diagram of the side view of the positive electrode sheet of the present invention is shown. Detailed Implementation

[0018] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. Unless otherwise specified herein, data ranges include endpoints.

[0019] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0020] A first aspect of the present invention provides a positive electrode sheet, wherein the positive electrode sheet includes a positive current collector and a positive active layer located on one or both surfaces of the positive current collector. The positive active layer includes a first active layer and a second active layer. The first active layer includes a first active material, which is a primary particle. The second active layer includes a second active material, which is a secondary spherical particle. Along the width direction of the positive electrode sheet, the positive current collector includes a first region and a second region connected together. The first active layer is located on the surface of the positive current collector in the first region, and the second active layer is located on the surface of the first active layer and covers the second region. The ratio of the porosity of the positive active layer to the porosity of the second active layer is (0.58-0.95):1 (e.g., 0. The positive electrode sheet has the following ratios: 0.58:1, 0.6:1, 0.53:1, 0.65:1, 0.68:1, 0.7:1, 0.73:1, 0.75:1, 0.78:1, 0.8:1, 0.83:1, 0.85:1, 0.88:1, 0.9:1, 0.93:1, or 0.95:1, and satisfies the following relationship: 20≤H / △H≤700 (e.g., 20, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, or 700), where H is the width of the positive electrode active layer projected onto the positive electrode current collector in mm, and △H is the width of the second active layer in the second region projected onto the positive electrode current collector in mm.

[0021] like Figure 1 , Figure 2 , Figure 6 and Figure 7 As shown, the positive electrode sheet includes a positive current collector and a positive active layer located on one or both surfaces of the positive current collector. The positive active layer includes a first active layer and a second active layer. The first active layer is located on the surface of the positive current collector, and the second active layer is located on the surface of the first active layer away from the positive current collector. Along the width direction of the positive electrode sheet, the positive current collector 11 includes a first region 111 and a second region 112 connected together. The first active layer 21 is located on the surface of the positive current collector in the first region 111, and the second active layer 22 is located on the surface of the first active layer 21 away from the positive current collector and covers the second region 112. The number of second regions can be one or two. When the number of second regions is one, as shown... Figure 1 and Figure 2 As shown, in the width direction of the positive electrode sheet, the second region is located on one side of the first region; when the number of second regions is 2, in the width direction of the positive electrode sheet, the second region is located on both sides of the first region.

[0022] It is understood that the width H of the orthographic projection of the positive electrode active layer onto the positive electrode current collector is the width of the entire positive electrode active layer projected onto the positive electrode current collector, and the width ΔH of the orthographic projection of the second active layer in the second region onto the positive electrode current collector is the width of the orthographic projection of the second active layer located in the second region onto the positive electrode current collector. In this invention, the width is the vertical distance along the width direction of the positive electrode sheet.

[0023] In the positive electrode sheet of the present invention, when the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer is controlled within the above-mentioned range, a high degree of matching can be achieved in the diffusion rates of lithium ions in the first and second active layers, thereby improving the lithium ion transport efficiency, reducing the diffusion resistance of lithium ions at the interlayer interface, improving the migration efficiency of lithium ions in the positive electrode active layer, and improving the low-temperature discharge performance of the battery. When the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer is higher than 0.95:1, the matching degree between the two layers is low. If the porosity of the second active layer is too small or the porosity of the positive electrode active layer is too large, the packing density between the active material particles in the second active layer will be too large, which will easily form a steric hindrance effect on the diffusion of lithium ions, resulting in a longer diffusion path for lithium ions, increasing concentration polarization, and reducing the cold start performance of the battery. When the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer is less than 0.58:1, the matching degree between the two layers is also low. If the porosity of the positive electrode active layer is too small or the porosity of the second active layer is too large, the number of contact points between the active material particles in the first active layer increases, and the internal resistance also increases, which increases the capacity loss of the battery. At the same time, the transport of lithium ions is hindered, which reduces the transport efficiency of lithium ions and reduces the cold start performance of the battery.

[0024] The positive electrode of this invention comprises both primary particles and secondary spherical particles. The secondary spherical particles have a more stable structure and are less prone to significant volume expansion at high temperatures. Furthermore, they provide more transport channels for lithium ions, increasing the lithium ion transport rate and thus improving the battery's high-temperature cycle performance. While the internal path of lithium ions in primary particles is shorter than that in secondary particles, the transport paths within primary particles are fewer, resulting in a lower lithium ion transport rate. This leads to increased polarization and negatively impacts the battery's cold-start performance. To improve the lithium ion transport rate in the first active layer, which includes primary particles, the contact between the first active layer and the electrolyte can be increased. However, due to the larger specific surface area of ​​the primary particles, excessive contact with the electrolyte can lead to excessive side reactions between the primary particles and the electrolyte, which is detrimental to lithium ion transport.

[0025] Therefore, in the positive electrode sheet of the present invention, in the first region, a first active layer comprising primary particles is disposed on the surface of the positive electrode current collector, and a second active layer comprising secondary spherical particles is disposed on the surface of the first active layer. This fully utilizes the advantage of the secondary spherical particles in providing more transport channels for lithium ions, thereby improving the high-temperature cycle performance of the battery. Simultaneously, to avoid excessive contact between the primary particles and the electrolyte and reduce side reactions between the primary particles and the electrolyte, in the second region, a second active layer comprising secondary spherical particles is disposed on the surface of the positive electrode current collector (e.g., ...). Figure 2 As shown in the diagram, a second active layer is disposed on one side of the first active layer, thus connecting the first active layer to the second active layer on the surface of the positive electrode current collector. The second active layer has a larger porosity, which ensures that the first active layer, including primary particles, can maintain appropriate contact with the electrolyte, improving the lithium-ion transport rate in the first active layer. It also prevents excessive contact between the primary particles and the electrolyte, reducing side reactions between the primary particles and the electrolyte, further enhancing the lithium-ion transport rate in the first active layer, improving the battery's cold-start performance, and enabling the battery to possess both high-temperature performance and superior cold-start performance. Furthermore, the positive electrode sheet with the above structure can reduce the risk of lithium plating and prevent lithium plating from occurring.

[0026] Simultaneously, controlling the positive electrode sheet to satisfy the following relationship: 20≤H / △H≤700, can improve the structural stability of the positive electrode sheet, further balance the relationship between the electrolyte and the primary particles in the first active layer, so that the second active layer in the second region can effectively protect the first active layer, avoid excessive contact between the electrolyte and the primary particles, and further improve the high-temperature cycle performance of the battery. When H / ΔH is higher than 700, either ΔH is too small or H is too large. If ΔH is too small, the width of the orthographic projection of the second active layer on the positive current collector in the second region is too small, which cannot effectively protect the first active layer. During battery cycling, the primary particles in the first active layer are in excessive contact with the electrolyte, leading to an increase in side reactions and affecting the transport rate of lithium ions in the first active layer. In addition, the bonding force between the first and second active layers may also be weakened due to ΔH being too small. As a result, during battery cycling, due to the volume expansion and contraction of the positive active material, the positive active layer is prone to delamination or detachment, further shortening the cycle life of the battery. If H is too large, the volume change of the positive electrode sheet is uneven during battery charging and discharging, which easily leads to stress concentration, causing structural damage to the positive active material, resulting in pulverization and detachment of the positive electrode sheet, thus making the cycle performance of the lithium-ion battery worse. When H / ΔH is less than 20, either ΔH is too large or H is too small. If ΔH is too large, the width of the orthographic projection of the second active layer in the second region onto the positive electrode current collector is too large, resulting in a longer transport path for lithium ions in the second active layer in the second region and increased resistance. This increases the internal resistance of the battery and reduces the cold start capability. In addition, it will prevent some of the active materials in the second active layer from forming an effective bond with the active materials in the first active layer, affecting the overall structure and performance of the positive electrode sheet, and thus affecting the capacity of the lithium-ion battery and reducing the energy density. If H is too small, the coating area of ​​the positive electrode active layer is too small, directly leading to a reduction in battery capacity and a further reduction in energy density, failing to realize the advantage of double-layer coating in improving energy density.

[0027] In this invention, the positive electrode active layer can be located on one or both surfaces of the positive electrode current collector. When the positive electrode active layer is located on one surface of the positive electrode current collector, the ratio of the porosity of the positive electrode active layer on that side to the porosity of the second active layer on that side is (0.58-0.95):1, and the positive electrode active layer on that side satisfies the relationship: 20≤H / ΔH≤700. When the positive electrode active layer is located on both surfaces of the positive electrode current collector, in both positive electrode active layers, the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer satisfies (0.58-0.95):1, and both positive electrode active layers on both sides satisfy the relationship: 20≤H / ΔH≤700. It is understood that when the positive electrode active layer is located on both surfaces of the positive electrode current collector, H / ΔH and the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer need to be calculated separately.

[0028] In this invention, the edge line of the positive electrode active layer projected onto the positive electrode current collector can be a straight line (e.g., ...). Figure 3 , Figure 4 It can also be a curve (such as...) Figure 5 When the edge line of the positive electrode active layer projected onto the positive electrode current collector is a straight line and parallel to the edge line of the positive electrode current collector (e.g.) Figure 3 In the width direction of the positive electrode sheet, the distance from any point on the edge line of the orthographic projection of the positive electrode active layer onto the positive electrode current collector to the edge line of the positive electrode current collector is equal. In this case, H is the distance from any point on the edge line of the orthographic projection of the positive electrode active layer onto the positive electrode current collector to the edge line of the positive electrode current collector. When the edge line of the projection of the positive electrode active layer onto the positive electrode current collector is a straight line and not parallel to the edge line of the positive electrode current collector (e.g....), Figure 4 In the width direction of the positive electrode sheet, the distance from any point on the edge line of the orthographic projection of the positive electrode active layer onto the positive electrode current collector to the edge line of the positive electrode current collector is not equal. In this case, H can be taken as the average value. That is, on the edge line of the orthographic projection of the positive electrode active layer onto the positive electrode current collector, with the length of the edge line as the reference, 50 points are selected at equal intervals (i.e., the distance between each point is equal, so that the calculation result is more accurate), the width corresponding to each point is measured, and the average value is taken to obtain H; when the edge line of the projection of the positive electrode active layer onto the positive electrode current collector is a curve (e.g., ... Figure 5 In the width direction of the positive electrode sheet, the distance from any point on the edge line of the orthographic projection of the positive active layer onto the positive current collector to the edge line of the positive current collector is not equal. In this case, H can be obtained by averaging. That is, on the edge line of the orthographic projection of the positive active layer onto the positive current collector, taking the length of the edge line as a reference, 50 points are randomly selected, the width corresponding to each point is measured, and the average value is taken to obtain H. The edge line of the orthographic projection of the second active layer onto the positive current collector in the second region can be a straight line or a curve. Along the width direction of the positive electrode sheet, the measurement of the width ΔH of the orthographic projection of the second active layer onto the positive current collector in the second region can be performed with reference to the measurement of H.

[0029] In this invention, by configuring the structure of the positive electrode sheet and simultaneously controlling the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer, as well as the H / ΔH ratio, a battery can achieve both higher high-temperature performance and better cold-start performance compared to existing technologies. To further improve the effect, one or more of the technical features can be further optimized.

[0030] In one example, the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer is (0.65-0.9):1.

[0031] In one example, the porosity of the positive electrode active layer is 32%-48% (e.g., 32%, 35%, 38%, 40%, 42%, 45%, or 48%). In this invention, the porosity of the positive electrode active layer can be obtained by testing the following method: In the portion of the positive electrode active layer that simultaneously includes a first active layer and a second active layer, six sites are taken at equal intervals along the length of the positive electrode sheet, and the porosity at each of the six sites is measured. The average value is taken as the porosity of the positive electrode active layer. The porosity can be obtained using methods conventional in the art.

[0032] In one example, the porosity of the second active layer is 35%-55% (e.g., 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, or 55%). In this invention, the porosity of the second active layer can be obtained by measuring the porosity of the second active layer in the second region. For example, in the second active layer of the second region (this portion of the second active layer has no first active layer in the thickness direction of the positive electrode sheet), three sites are taken at equal intervals along the length of the positive electrode sheet, and the porosity at each of the three sites is measured. The average value is taken as the porosity of the second active layer. The porosity can be tested using methods conventional in the art.

[0033] According to one specific embodiment, the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer is (0.58-0.95):1, the porosity of the positive electrode active layer is 32%-48%, and the porosity of the second active layer is 35%-55%.

[0034] According to one specific embodiment, the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer is (0.65-0.9):1, the porosity of the positive electrode active layer is 32%-48%, and the porosity of the second active layer is 35%-55%.

[0035] In one example, the width H of the orthographic projection of the positive electrode active layer onto the positive electrode current collector is 30mm-400mm (e.g., 30mm, 50mm, 100mm, 150mm, 200mm, 250mm, 300mm, 350mm, or 400mm). It is understood that when there is a positive electrode active layer on one side of the positive electrode current collector, the width of the orthographic projection of the positive electrode active layer onto the positive electrode current collector is the width of the orthographic projection of the positive electrode active layer on that side (i.e., the side with the positive electrode active layer) onto the positive electrode current collector; when there are positive electrode active layers on both sides of the positive electrode current collector, the width of the orthographic projection of the positive electrode active layers on both sides is the same, and the width of the orthographic projection of the positive electrode active layer onto the positive electrode current collector is the width of the orthographic projection of the positive electrode active layer on either side onto the positive electrode current collector.

[0036] In one example, the width ΔH of the orthographic projection of the second active layer in the second region onto the positive current collector is 0.5mm-3mm (e.g., 0.5mm, 0.8mm, 1mm, 1.3mm, 1.5mm, 1.8mm, 2mm, 2.3mm, 2.5mm, 2.8mm, or 3mm). It is understood that when the second region on one side of the positive current collector has a second active layer, the width of the orthographic projection of the second active layer onto the positive current collector is the width of the orthographic projection of the second active layer on that side of the second region (i.e., the side with the second active layer) onto the positive current collector; when both sides of the second region have positive second active layers, the width of the orthographic projection of the second active layers on both sides onto the positive current collector is the same, and the width of the orthographic projection of the second active layer in the second region onto the positive current collector is the width of the orthographic projection of the second active layer in either side of the second region onto the positive current collector.

[0037] In one instance, the average particle size of the primary particles is smaller than the average particle size of the secondary spherical particles.

[0038] In one example, the average particle size of the primary particles is 0.2 μm to 6 μm (e.g., 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm).

[0039] In one example, the average particle size of the secondary spherical particles is 0.8 μm to 40 μm (e.g., 0.8 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm or 40 μm).

[0040] In this invention, the average particle size of the primary particles can be obtained by the following method: Using a scanning image of the surface of the first active layer obtained by SEM, draw the smallest square or rectangle that completely surrounds one primary particle; that is, draw a square or rectangle whose edge connects to all four sides of the square or rectangle. The length of one side of the square or the length of the long side of the rectangle is the particle size of the primary particle. Within an arbitrarily selected 100μm*100μm area on the surface of the first active layer, measure the particle size of any 100 primary particles, and take their average value as the final measurement value. It should be noted that if 100 primary particles can be observed in the captured image, the average particle size of the primary particles is taken as the average particle size of any 100 primary particles in that image. If no 100 primary particles are observed in the image, take multiple images, and take the average particle size of the total 100 primary particles as the average particle size of the primary particles. The scanning image is obtained by peeling off the second active layer from the positive electrode to expose the first active layer, and then observing the surface of the first active layer using a scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.). The average particle size of the secondary particles can be measured on the scanning image of the surface of the second active layer obtained by SEM using the same method as the average particle size of the primary particles, wherein the scanning image of the surface of the second active layer is obtained using a scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.).

[0041] According to one specific embodiment, the average particle size of the primary particles is 0.2μm-6μm, and the average particle size of the secondary spherical particles is 0.8μm-40μm. The average particle size of the primary particles is smaller than the average particle size of the secondary spherical particles.

[0042] In one example, the composition of the primary particles and the composition of the secondary spherical particles may be the same or different, and each is independently selected from LiMn2O4 and Li4Ti5O4. 12 Li3V2(PO4)3, LiFe (1-x) W x PO4, LiNi x Mn y Co (1-x-y) O2 and LiNi x Co y Al (1-x-y)At least one of O2, wherein 0≤x≤1 (e.g., 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1), 0≤y≤1 (e.g., 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1), x+y≤1, and W includes one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, V and Ti.

[0043] In one example, the primary particles and the secondary spherical particles are composed of lithium iron phosphate (LiFe). (1-x) W x PO4).

[0044] In one example, the positive electrode active layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode active material includes a first active material and a second active material.

[0045] In one example, the surface of the positive electrode active material includes a carbon coating layer with a thickness of 1 nm to 20 nm (e.g., 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 15 nm, or 20 nm). In this invention, the thickness of the carbon coating layer can be obtained by testing 100 positive electrode active materials selected arbitrarily from HRTEM images of the surface of the first active layer and the surface of the second active layer, respectively. The thickness of the carbon coating layer on the surface of each of the 100 positive electrode active materials is measured, and the average value is taken as the thickness of the carbon coating layer.

[0046] In one example, the weight ratio of the positive electrode material in the positive electrode active layer to the weight ratio of the second active material in the second active layer is (0.95-1):1 (e.g., 0.95:1, 0.96:1, 0.97:1, 0.98:1, 0.99:1, or 1:1). Controlling the weight ratio of the positive electrode material in the positive electrode active layer to the weight ratio of the second active material in the second active layer within the above range allows for the control of the porosity of both the positive electrode active layer and the second active layer within appropriate ranges. Furthermore, it can further improve the charge-discharge performance of the battery, reduce battery impedance, and enhance the battery's room-temperature cycle performance and rate performance. When the weight ratio of the positive electrode material in the positive electrode active layer to the weight ratio of the second active material in the second active layer is greater than 1:1, the weight content of the second active material in the second active layer is too small, which will lead to insufficient electrochemical reaction of the electrode during the charging and discharging process, reduced utilization of active materials, and thus affect the room temperature cycle performance of the lithium-ion battery. As the number of cycles increases, the capacity decay of the battery will accelerate significantly. If the weight content of the positive electrode material in the positive electrode active layer is too large, the adhesion between the positive electrode active layer and the positive electrode current collector will be insufficient, the structural stability of the positive electrode sheet will deteriorate during the cycle, and phenomena such as the detachment of the positive electrode active layer will easily occur, affecting the room temperature cycle life of the battery. When the weight ratio of the positive electrode material in the positive electrode active layer to the weight ratio of the second active material in the second active layer is less than 0.95:1, the weight content of the second active material in the second active layer is too high, and the migration resistance of lithium ions in the electrolyte will also increase, affecting the rate performance of the battery. Conversely, if the weight content of the first active material in the first active layer is too low, the adhesion between the first active layer and the positive electrode current collector will be insufficient, affecting the electron transport efficiency and reducing the rate performance of the lithium-ion battery.

[0047] In one example, the weight content of the positive electrode material in the positive electrode active layer is 90%-95% (e.g., 90%, 91%, 92%, 93%, 94% or 95%).

[0048] In one example, the weight content of the second active material in the second active layer is 92%-96% (e.g., 92%, 93%, 94%, 95% or 96%).

[0049] In one example, the first active layer includes a first positive electrode binder and a first positive electrode conductive agent.

[0050] In one example, the second active layer includes a second positive electrode binder and a second positive electrode conductive agent.

[0051] In one example, the positive electrode active layer includes a positive electrode binder and a positive electrode conductive agent.

[0052] In one example, the second positive electrode binder in the second active layer has a weight content of 2%-3.5% (e.g., 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, or 3.5%), and the second positive electrode conductive agent has a weight content of 2%-4.5% (e.g., 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.3%, or 4.5%).

[0053] In one example, the positive electrode binder includes a first positive electrode binder and a second positive electrode binder.

[0054] The first positive electrode binder and the second positive electrode binder may be the same or different, and each independently includes one or more of polyvinylidene fluoride (PVDF), acrylic acid-modified polyvinylidene fluoride, carboxylic acid-modified polyvinylidene fluoride, polyacrylic acid, polyacrylic acid copolymer, polymethyl methacrylate, and polyimide.

[0055] In one example, the positive electrode conductive agent includes the first positive electrode conductive agent and the second positive electrode conductive agent.

[0056] The first positive electrode conductive agent and the second positive electrode conductive agent may be the same or different, and each independently includes one or more of carbon black, carbon nanotubes, carbon fibers, acetylene black, Ketjen black and conductive graphite.

[0057] In one example, the average particle size of the positive electrode conductive agent is 10nm-300nm (e.g., 10nm, 30nm, 50nm, 80nm, 100nm, 130nm, 150nm, 180nm, 200nm, 230nm, 250nm, 280nm, or 300nm). The method for testing the average particle size of the positive electrode conductive agent can refer to the method for testing the average particle size of primary particles.

[0058] In one example, the ratio of the average particle size of the positive electrode conductive agent to the thickness of the carbon coating layer is (4-200):1 (e.g., 4:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 110:1, 120:1, 130:1, 140:1, 150:1, 160:1, 170:1, 180:1, 190:1, or 200:1). Controlling the ratio of the average particle size of the positive electrode conductive agent to the thickness of the carbon coating layer within the above range enables the positive electrode sheet to have a complete conductive network, improves the electron transport rate, reduces the battery impedance, and improves the battery's room temperature cycling and rate performance. When the ratio of the average particle size of the positive electrode conductive agent to the thickness of the carbon coating layer is greater than 200:1, the carbon coating layer is too thin, resulting in insufficient thickness and continuity, making it impossible to form an effective conductive network and leading to significant impedance in the electron transport path. Conversely, if the average particle size of the positive electrode conductive agent is too large, the contact area between the conductive agents is small, resulting in a longer electron transport path and increased impedance, thus increasing the internal resistance of the lithium-ion battery and affecting its room-temperature cycling and rate performance. When the ratio of the average particle size of the positive electrode conductive agent to the thickness of the carbon coating layer is less than 1:1, the carbon coating layer is too thick, occupying too much space and reducing the amount of positive electrode material, thus decreasing the capacity of the lithium-ion battery and affecting its energy density. If the average particle size of the positive electrode conductive agent is too small, poor contact between the conductive agents will occur, further increasing the internal resistance of the lithium-ion battery and reducing its capacity and energy density.

[0059] In one example, the weight content of the positive electrode binder in the positive electrode active layer is 2.5%-4.5% (e.g., 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.3%, or 4.5%), and the weight content of the positive electrode conductive agent is 2.5%-5.5% (e.g., 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8%, 5%, 5.3%, or 5.5%).

[0060] In this invention, the weight contents of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode active layer, as well as the weight contents of the second active material, second positive electrode conductive agent, and second positive electrode binder in the second active layer, can be determined by thermogravimetric analysis (TGA). Specifically, taking the "weight content of the second active material in the second active layer" as an example, TGA is performed on the binder standard sample, the conductive agent standard sample, and the solid under an inert atmosphere, and the weight loss rate of the three is recorded. Then, the positive electrode active layer is peeled off from the positive electrode sheet, and a sample of the second active layer is obtained from the second active layer in the second region. A certain amount of the second active layer is weighed, and TGA is performed under the same conditions as above to obtain the thermogravimetric curve of the second active layer. By comparing it with the thermogravimetric curve of the standard sample, the weight content of the second active material in the second active layer can be obtained. It can be understood that the sampling for measuring the weight contents of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode active layer can be directly taken from the positive electrode active layer peeled off from the positive electrode sheet.

[0061] In one instance, such as Figure 6 and Figure 7 As shown, the positive electrode sheet further includes a ceramic layer 24, the surface of the positive current collector in the third region 113 includes the ceramic layer 24, and the positive active layer is adjacent to the ceramic layer.

[0062] In one example, the second active layer and the ceramic layer are adjacent and have a mixing region, the width of which is 0.1mm-3mm (e.g., 0.1mm, 0.3mm, 0.5mm, 0.8mm, 1mm, 1.3mm, 1.5mm, 1.8mm, 2mm, 2.3mm, 2.5mm, 2.8mm, or 3mm). It is understood that the second active material and ceramic particles coexist in the mixing region. The width of the mixing region can be obtained using SEM, for example, by photographing a mixing region of a certain length, calculating the area of ​​the mixing region using image processing software, and dividing the calculated area by the length of the mixing region to obtain the width of the mixing region.

[0063] In one example, the width of the ceramic layer is 0.5mm-5mm (e.g., 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm or 5mm).

[0064] In one example, the ratio of the width of the ceramic layer to the width of the mixing region is (1-50):1 (e.g., 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, or 50:1). Controlling the ratio of the ceramic layer width to the mixing region within this range ensures that the ceramic layer effectively blocks structural changes in the positive electrode active material and reduces side reactions between it and the electrolyte, thereby improving the battery's room-temperature cycle performance and rate performance. When the ratio of the width of the ceramic layer to the width of the mixing region is greater than 50:1, the excessive width of the ceramic layer hinders the transport of electrons in the positive electrode, exacerbating polarization during charging and discharging. This affects the room-temperature cycle performance of the lithium-ion battery, causing its capacity to decrease more rapidly after multiple charge-discharge cycles. It also reduces the utilization rate of the battery's internal space, impacting the capacity and energy density of the lithium-ion battery. Conversely, if the width of the mixing region is too small, the ceramic layer cannot fully play its role in blocking structural changes and side reactions of the positive electrode active material during charging and discharging, leading to rapid performance degradation of the positive electrode active material and shortening the room-temperature cycle life of the lithium-ion battery. When the ratio of the width of the ceramic layer to the width of the mixing region is less than 1:1, the ceramic layer is too narrow to fully cover the positive electrode active material coating. This will cause changes in the contact environment between some of the positive electrode active material and the electrolyte during the charging and discharging process of the lithium-ion battery, affecting the lithium-ion insertion and extraction process, and thus reducing the energy density and room temperature cycle life of the lithium-ion battery. Since the ceramic layer itself is non-conductive, when it is mixed with the positive electrode active layer, it will hinder the electron transport path in the positive electrode sheet. An excessively large width of the mixing region layer has a more significant hindering effect, affecting the charging and discharging efficiency and power performance of the lithium-ion battery, and affecting the rate performance of the battery.

[0065] In one example, the width of the ceramic layer is (1.5-30):1 with the width of the mixing region.

[0066] According to one specific embodiment, the positive electrode active layer and the ceramic layer are adjacent to each other and have a mixing region, the width of the mixing region is 0.1mm-3mm, the width of the ceramic layer is 0.5mm-5mm, and the width of the ceramic layer and the width of the mixing region are (1-50):1.

[0067] According to one specific embodiment, the positive electrode active layer and the ceramic layer are adjacent to each other and have a mixing region, the width of the mixing region is 0.1mm-3mm, the width of the ceramic layer is 0.5mm-5mm, and the width of the ceramic layer and the width of the mixing region are (1.5-30):1.

[0068] In one example, the ceramic layer comprises ceramic particles and a third binder.

[0069] In one example, the ceramic particles comprise one or more of boehmite, Al2O3, SiO2, and TiO2.

[0070] In one instance, the third adhesive comprises polyvinylidene fluoride.

[0071] In one example, the weight ratio of the ceramic particles to the third binder is (9-1):(1-9) (e.g., 9:1, 8:2, 7:3, 5:5, 4:6, 3.5:6.5, 3:7, 2.5:7.5, 2:8, 1.5:8.5, or 1:9). It is understood that the weight percentage of the ceramic particles in the ceramic layer can be in the range of 90%-10% (e.g., 90%, 80%, 70%, 60%, 50%, 40%, 35%, 30%, 25%, 20%, 15%, or 10%), and the weight percentage of the third binder in the ceramic layer can be in the range of 10%-90% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%). However, it is required that the sum of the weight percentage of the ceramic particles in the ceramic layer and the weight percentage of the third binder in the ceramic layer is 100%.

[0072] In one example, the positive current collector includes a metal layer and a carbon coating layer located on one or both surfaces of the metal layer.

[0073] In one example, the ratio of the thickness of the metal layer to the thickness of the carbon coating layer on one side is (8-35):1 (e.g., 8:1, 10:1, 15:1, 20:1, 30:1, or 35:1). Controlling the ratio of the metal layer thickness to the carbon coating layer thickness within this range ensures improved adhesion between the positive electrode active layer and the positive electrode current collector, while simultaneously enhancing electron transport within the positive electrode sheet, reducing the battery's internal resistance, and improving the battery's room-temperature cycle performance. When the ratio of the thickness of the metal layer to the thickness of the single-sided carbon coating layer is greater than 35:1, the excessive thickness of the metal layer increases the weight of the battery, thereby reducing the energy density of the lithium-ion battery. Simultaneously, as the thickness of the metal layer increases, the electron transport path within the metal layer becomes longer, leading to increased electron transport resistance and thus increasing the internal resistance of the lithium-ion battery. Conversely, if the thickness of the carbon coating layer is too small, it cannot effectively reduce the contact resistance between the metal layer and the positive electrode active layer, increasing the internal resistance of the lithium-ion battery and affecting its room-temperature cycle performance. Furthermore, the carbon coating layer can improve the viscosity strength between the positive electrode active layer and the positive electrode current collector, reducing the shedding of active particles during cycling. A carbon coating layer that is too thin cannot provide sufficient adhesion, causing active particles to easily detach and accelerating the degradation of the lithium-ion battery's cycle performance. When the ratio of the thickness of the metal layer to the thickness of the carbon coating layer on one side is less than 8:1, the metal layer is too thin, making it more prone to corrosion or deformation during battery cycling, which shortens the cycle life of the lithium-ion battery. In addition, the contact area between the metal layer and the positive electrode active layer is reduced due to the thin metal layer, resulting in decreased interface stability and increased contact resistance between the positive electrode active layer and the positive electrode current collector, affecting the battery's room temperature cycling performance. On the other hand, the carbon coating layer is too thick, which causes more side reactions during cycling, accelerates capacity decay, and further affects the cycle life of the lithium-ion battery.

[0074] In one example, the thickness of the metal layer is 6 μm to 20 μm (e.g., 6 μm, 10 μm, 15 μm, or 20 μm).

[0075] In one example, the metal layer is aluminum foil.

[0076] In one example, the thickness of the carbon coating layer on one side is 0.4 μm to 2 μm (e.g., 0.4 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm or 2 μm).

[0077] In one example, the bulk resistivity of the positive electrode is 5 Ω·cm to 40 Ω·cm (e.g., 5 Ω·cm, 10 Ω·cm, 15 Ω·cm, 20 Ω·cm, 25 Ω·cm, 30 Ω·cm, 35 Ω·cm, or 40 Ω·cm). Controlling the bulk resistivity of the positive electrode within this range allows for smoother electron transport, reduces impedance, improves rate performance, and ensures a more uniform charge distribution within the battery, thus improving the battery's room-temperature cycle performance. When the bulk resistivity of the positive electrode is greater than 40 Ω·cm, the excessively high resistivity increases the battery's electronic resistance, hindering electron transport during charging and discharging, and reducing the battery's discharge rate. Conversely, when the bulk resistivity of the positive electrode is less than 5 Ω·cm, the excessively low resistivity causes electron transport to be too rapid, potentially leading to uneven charge distribution within the battery, increasing stress and strain during charging and discharging, thereby accelerating material fatigue and aging in the lithium-ion battery and shortening its cycle life.

[0078] In one example, the bulk resistivity of the positive electrode is 8 Ω·cm - 25 Ω·cm.

[0079] A second aspect of the present invention provides a battery, wherein the battery includes the positive electrode sheet described in the first aspect of the present invention.

[0080] The materials used in the battery, except for the positive electrode, can all be manufactured in accordance with the methods described in this art, achieving both high high-temperature cycle performance and good cold-start performance, while reducing the risk of lithium plating.

[0081] The battery can be a lithium-ion rechargeable battery.

[0082] The battery can be a wound lithium-ion secondary battery or a stacked lithium-ion secondary battery.

[0083] In one example, the battery includes a negative electrode, a separator, and an electrolyte. The negative electrode can be a conventional negative electrode in the art, for example, the negative electrode may include a negative current collector and a negative active layer located on one or both surfaces of the negative electrode.

[0084] The electrolyte can be a conventional electrolyte in the art, for example, the electrolyte includes lithium salt, organic solvent and additives.

[0085] The diaphragm can be a conventional diaphragm in the art.

[0086] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0087] The following examples illustrate the positive electrode sheet and battery of the present invention.

[0088] (1) Positive electrode plate

[0089] The positive electrode current collector consists of a metal layer and a carbon coating layer on both sides of the metal layer. The thickness of the metal layer is 15 μm, the thickness of the single-sided carbon coating layer is 0.9 μm, and the ratio of the thickness of the metal layer to the thickness of the single-sided carbon coating layer is 16.7.

[0090] A first active material (primary lithium iron phosphate particles that do not easily agglomerate into secondary particles, with an average particle size of 2.4 μm), a first positive electrode binder (PVDF), and a first positive electrode conductive agent (conductive carbon black SP) are mixed in N-methylpyrrolidone (NMP) and stirred to form a uniform and stable first slurry. A second active material (secondary spherical lithium iron phosphate particles, with an average particle size of 22.9 μm), a second positive electrode binder (PVDF), and a second positive electrode conductive agent (conductive carbon black SP) are mixed in N-methylpyrrolidone (NMP) at a weight ratio of 92.5:3.5:4 and stirred to form a uniform and stable second slurry. The first slurry is coated onto the surfaces of the first coating areas on both sides of the positive electrode current collector (aluminum foil) in the first region to form a first coating layer. The second slurry is then coated onto the surfaces of the first coating areas on both sides, covering the second region to form a second coating layer. The positive electrode active layer comprises 95% positive electrode material by weight, 2.5% positive electrode binder by weight, and 2.5% positive electrode conductive agent by weight. The carbon coating layer on the surface of the positive electrode active material has a thickness of 2.1 nm, the average particle size of the positive electrode conductive agent is 195.3 nm, and the ratio of the average particle size of the positive electrode conductive agent to the thickness of the coating layer is 93.

[0091] Ceramic particles (alumina) and a third binder (PVDF) are mixed in a weight ratio of 8:2 to form a ceramic coating. This ceramic coating is then applied to both sides of the positive current collector in the third region to form a ceramic layer. After drying and compaction with a roller press, a positive electrode sheet (such as...) is obtained. Figure 1 (As shown).

[0092] The width H of the positive electrode active layer projected onto the positive electrode current collector is 120 mm. The width ΔH of the second active layer projected onto the positive electrode current collector in the second region is 1.9 mm. H / ΔH = 120 / 1.9 ​​= 63.2. The porosity of the second active layer is 48.3%, and the porosity of the positive electrode active layer is 37.8%. The ratio of the porosity of the positive electrode active layer to the porosity of the second active layer is 0.783. The width of the ceramic layer is 2.8 mm, and the width of the mixing region is 0.5 mm. The ratio of the width of the ceramic layer to the width of the mixing region is 5.6.

[0093] (2) Negative electrode sheet

[0094] Graphite material (average particle size 18.8 μm), anode binder (SBR), and anode conductive agent (conductive carbon black) are mixed using water as a solvent. The mixture is stirred to form a uniform and stable anode slurry. This slurry is then uniformly coated on both sides of a copper foil. After drying and compaction using a roller press, the anode sheet is obtained. In the anode active layer, the graphite material accounts for 95% by weight, the anode binder accounts for 3% by weight, and the anode conductive agent accounts for 2% by weight.

[0095] (3) Electrolyte

[0096] The concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L, and the solvent is a mixture of ethylene carbonate, dimethyl carbonate and 1,2-propylene glycol carbonate in a volume ratio of 1:1:1.

[0097] (4) Lithium-ion batteries

[0098] The positive electrode sheet obtained in step (1), the negative electrode sheet obtained in step (2), and the separator (a conventional separator is sufficient) are wound together to form a bare cell. After hot pressing, aluminum tabs and copper-plated nickel tabs are welded together. After the aluminum-plastic film is punched, it is packaged and baked at 95°C in vacuum for 24 hours. Then, the electrolyte obtained in step (3) is injected. After the electrolyte is injected, the battery is formed, sealed, sorted, and tested by OCV to obtain a lithium-ion soft-pack battery.

[0099] Example 2 group

[0100] This set of examples illustrates the effects of a change in the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer.

[0101] Example 2a

[0102] The experiment was carried out in accordance with Example 1, except that the porosity of the positive electrode active layer was 32.1%, the porosity of the second active layer was 54.7%, and the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer was 0.587.

[0103] Example 2b

[0104] The experiment was carried out in accordance with Example 1, except that the porosity of the positive electrode active layer was 44.6%, the porosity of the second active layer was 50.2%, and the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer was 0.888.

[0105] Example 2c

[0106] The experiment was carried out in accordance with Example 1, except that the porosity of the positive electrode active layer was 33.7%, the porosity of the second active layer was 51.4%, and the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer was 0.656.

[0107] Example 2d

[0108] The experiment was carried out in accordance with Example 1, except that the porosity of the positive electrode active layer was 33.2%, the porosity of the second active layer was 35.3%, and the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer was 0.941.

[0109] Example 2e

[0110] The experiment was carried out in accordance with Example 1, except that the porosity of the positive electrode active layer was 47.5%, the porosity of the second active layer was 50.3%, and the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer was 0.944.

[0111] Example 3 Group

[0112] This set of examples illustrates the effects of changes in H / ΔH.

[0113] Example 3a

[0114] The same procedure is followed as in Example 1, except that the width H of the positive active layer projected onto the positive current collector is 30 mm, and the width ΔH of the second active layer projected onto the positive current collector in the second region is 1.5 mm, with H / ΔH = 30 / 1.5 = 20.

[0115] Example 3b

[0116] The same procedure is followed as in Example 1, except that the width H of the positive active layer projected onto the positive current collector is 400 mm, and the width ΔH of the second active layer projected onto the positive current collector in the second region is 1.9 mm, with H / ΔH = 400 / 1.9 ​​= 210.5.

[0117] Example 3c

[0118] The same procedure is followed as in Example 1, except that the width H of the positive active layer projected onto the positive current collector is 278 mm, and the width ΔH of the second active layer projected onto the positive current collector in the second region is 3 mm, with H / ΔH = 278 / 3 = 92.7.

[0119] Example 3d

[0120] The same procedure is followed as in Example 1, except that the width H of the positive active layer projected onto the positive current collector is 350 mm, and the width ΔH of the second active layer projected onto the positive current collector in the second region is 0.5 mm, with H / ΔH = 350 / 0.5 = 700.

[0121] Example 4 group

[0122] This set of embodiments is used to illustrate the effect when the ratio of the weight content of the positive electrode material in the positive electrode active layer to the weight content of the second active material in the second active layer changes.

[0123] Example 4a

[0124] The experiment was carried out in accordance with Example 1, except that the weight content of the positive electrode material in the positive electrode active layer was 90%, the weight content of the second active material in the second active layer was 95.5%, and the ratio of the weight content of the positive electrode material in the positive electrode active layer to the weight content of the second active material in the second active layer was 0.942.

[0125] Example 4b

[0126] The experiment was carried out in accordance with Example 1, except that the weight content of the positive electrode material in the positive electrode active layer was 90%, the weight content of the second active material in the second active layer was 92%, and the ratio of the weight content of the positive electrode material in the positive electrode active layer to the weight content of the second active material in the second active layer was 0.978.

[0127] Example 4c

[0128] The experiment was carried out in accordance with Example 1, except that the weight content of the positive electrode material in the positive electrode active layer was 95%, the weight content of the second active material in the second active layer was 96%, and the ratio of the weight content of the positive electrode material in the positive electrode active layer to the weight content of the second active material in the second active layer was 0.99.

[0129] Example 4d

[0130] The experiment was carried out in accordance with Example 1, except that the weight content of the positive electrode material in the positive electrode active layer was 91.5%, the weight content of the second active material in the second active layer was 96%, and the ratio of the weight content of the positive electrode material in the positive electrode active layer to the weight content of the second active material in the second active layer was 0.953.

[0131] Example 4e

[0132] The experiment was carried out in accordance with Example 1, except that the weight content of the positive electrode material in the positive electrode active layer was 94%, the weight content of the second active material in the second active layer was 93%, and the ratio of the weight content of the positive electrode material in the positive electrode active layer to the weight content of the second active material in the second active layer was 1.011.

[0133] Example 5 group

[0134] This set of examples illustrates the effect of changing the ratio of the average particle size of the positive electrode conductive agent to the thickness of the carbon coating layer.

[0135] Example 5a

[0136] The experiment was carried out in accordance with Example 1, except that the average particle size of the positive electrode conductive agent was 254.8 nm, the thickness of the carbon coating layer was 1.3 nm, and the ratio of the average particle size of the positive electrode conductive agent to the thickness of the carbon coating layer was 196.

[0137] Example 5b

[0138] The experiment was carried out in accordance with Example 1, except that the average particle size of the positive electrode conductive agent was 20 nm, the thickness of the carbon coating layer was 4.8 nm, and the ratio of the average particle size of the positive electrode conductive agent to the thickness of the carbon coating layer was 4.2.

[0139] Example 5c

[0140] The experiment was carried out in accordance with Example 1, except that the average particle size of the positive electrode conductive agent was 298.5 nm, the thickness of the carbon coating layer was 1.3 nm, and the ratio of the average particle size of the positive electrode conductive agent to the thickness of the carbon coating layer was 229.6.

[0141] Example 6 group

[0142] This set of embodiments is used to illustrate the effects that occur when the ratio of the width of the ceramic layer to the width of the mixing region changes.

[0143] Example 6a

[0144] The same procedure is followed as in Example 1, except that the width of the ceramic layer is 1.5 mm, the width of the mixing region is 1 mm, and the ratio of the width of the ceramic layer to the width of the mixing region is 1.5.

[0145] Example 6b

[0146] The same procedure is followed as in Example 1, except that the width of the ceramic layer is 5 mm, the width of the mixing region is 0.1 mm, and the ratio of the width of the ceramic layer to the width of the mixing region is 50.

[0147] Example 6c

[0148] The same procedure was carried out as in Example 1, except that the width of the ceramic layer was 4.5 mm, the width of the mixing region was 2.1 mm, and the ratio of the width of the ceramic layer to the width of the mixing region was 2.14.

[0149] Example 6d

[0150] The same procedure was carried out as in Example 1, except that the width of the ceramic layer was 5 mm, the width of the mixing region was 0.17 mm, and the ratio of the width of the ceramic layer to the width of the mixing region was 29.4.

[0151] Example 6e

[0152] The same procedure was carried out as in Example 1, except that the width of the ceramic layer was 0.5 mm, the width of the mixing region was 0.6 mm, and the ratio of the width of the ceramic layer to the width of the mixing region was 0.8.

[0153] Comparative Example 1

[0154] The experiment was carried out in accordance with Example 1, except that the porosity of the positive electrode active layer was 36.1%, the porosity of the second active layer was 36.8%, and the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer was 0.981.

[0155] Comparative Example 2

[0156] The experiment was carried out in accordance with Example 1, except that the porosity of the positive electrode active layer was 31.4%, the porosity of the second active layer was 54.8%, and the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer was 0.573.

[0157] Comparative Example 3

[0158] The same procedure is followed as in Example 1, except that the width H of the positive active layer projected onto the positive current collector is 400 mm, and the width ΔH of the second active layer projected onto the positive current collector in the second region is 0.56 mm, with H / ΔH = 400 / 0.56 = 714.3.

[0159] Comparative Example 4

[0160] The same procedure is followed as in Example 1, except that the width H of the positive active layer projected onto the positive current collector is 30 mm, and the width ΔH of the second active layer projected onto the positive current collector in the second region is 1.6 mm, with H / ΔH = 30 / 1.6 = 18.8.

[0161] Comparative Example 5

[0162] The procedure is carried out in accordance with Example 1, except that the first active material and the second active material in the first active layer are interchanged, that is, the first active material is a secondary spherical particle and the second active material is a primary particle.

[0163] The lithium-ion batteries prepared in the examples and comparative examples were subjected to the following tests:

[0164] 1. Cold start performance test

[0165] Under (25±2)℃ conditions, discharge at 1C standard constant current until the discharge termination voltage is 2.2V, and let stand for 30 minutes; then charge at 1C standard constant current and constant voltage until the charging limit voltage is 3.65V, with a cutoff current of 0.05C, and let stand for 30 minutes; discharge at 1C standard constant current until the discharge termination voltage is 2.2V to obtain the actual capacity C0 of the cell, and let stand for 30 minutes; charge at 1C standard constant current and constant voltage until the charging limit voltage is 3.65V, with a cutoff current of 0.05C, and discharge with 1C0 for 30 minutes, which is 50% SOC; after standing at (25±2)℃ for 2 hours, place the cell in a -28℃ constant temperature chamber and maintain the constant temperature for 4 hours; test the end voltage value of 3C constant current discharge for 2 seconds, which is the cold start end voltage of the cell, in V.

[0166] 2. Cell discharge rate test

[0167] Under (25±2)℃ conditions, discharge at a 1C standard constant current until the discharge termination voltage is 2.2V, and let stand for 30 minutes; then charge at a 1C standard constant current and constant voltage until the charging limit voltage is 3.65V, with a cutoff current of 0.05C, and let stand for 30 minutes; discharge at a 1C standard constant current until the discharge termination voltage is 2.2V to obtain the actual capacity C0 of the cell, and let stand for 30 minutes; charge at a 1C standard constant current and constant voltage until the charging limit voltage is 3.65V, with a cutoff current of 0.05C, and discharge with 1C0 for 30 minutes, which is 50% SOC; after standing at (25±2)℃ for 2 hours, discharge at a certain rate for 10 seconds until the discharge limit voltage is 2.2V, and this rate is the discharge rate of the cell.

[0168] 3. High-temperature cycle test of battery cells

[0169] Discharge the battery at 55°C using a 3C standard constant current until the discharge termination voltage is 2.2V, and let it rest for 30 minutes. Then charge it using a 3C standard constant current and constant voltage until the charging limit voltage is 3.65V and the cutoff current is 0.05C, and let it rest for 30 minutes. Discharge it using a 3C standard constant current until the discharge termination voltage is 2.2V, and let it rest for 30 minutes. Repeat the above full charge and discharge steps until the capacity decays to 80% and then cuts off. The number of repeats is the cycle number, which is used to evaluate the cycle performance of the battery after aging.

[0170] 4. Cell room temperature cycle test

[0171] Discharge the battery at 25°C using a 3C standard constant current until the discharge termination voltage of 2.2V, and let it rest for 30 minutes. Then charge it using a 3C standard constant current and constant voltage until the charging limit voltage of 3.65V is reached, with a cutoff current of 0.05C, and let it rest for 30 minutes. Discharge it again using a 3C standard constant current until the discharge termination voltage of 2.2V is reached, and let it rest for 30 minutes. Repeat the above full charge and discharge steps until the capacity decays to 80% and then stops. The number of repeats is the cycle number, which is used to evaluate the battery's cycle performance after aging.

[0172] The results are recorded in Table 1.

[0173] Table 1

[0174]

[0175]

[0176] As can be seen from Table 1, by comparing the comparative examples and the embodiments, the battery prepared by the positive electrode sheet in the embodiments has significantly improved high-temperature cycle performance and cold-start performance. This indicates that by setting the structure of the positive electrode sheet and controlling the ratio of the porosity of the positive active layer to the porosity of the second active layer and the H / ΔH ratio, the battery can have both high high-temperature performance and good cold-start performance.

[0177] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active layer located on one or both sides of the positive current collector. The positive active layer includes a first active layer and a second active layer. The first active layer includes a first active material, which is a primary particle. The second active layer includes a second active material, which is a secondary spherical particle. Along the width direction of the positive electrode sheet, the positive current collector includes a first region and a second region connected together. The first active layer is located on the surface of the positive current collector in the first region, and the second active layer is located on the surface of the first active layer away from the positive current collector and covers the second region. The ratio of the porosity of the positive electrode active layer to the porosity of the second active layer is (0.58-0.95):1, and the positive electrode sheet satisfies the following relationship: 20≤H / △H≤700, where H is the width of the positive electrode active layer projected onto the positive electrode current collector in mm, and △H is the width of the second active layer projected onto the positive electrode current collector in the second region in mm.

2. The positive electrode according to claim 1, wherein, The porosity of the positive electrode active layer is 32%-48%; And / or, the porosity of the second active layer is 35%-55%; And / or, the ratio of the porosity of the positive electrode active layer to the porosity of the second active layer is (0.65-0.9):

1.

3. The positive electrode according to claim 1, wherein, The width H of the positive electrode active layer projected onto the positive electrode current collector is 30mm-400mm; And / or, the width ΔH of the second active layer in the second region projected onto the positive current collector is 0.5mm-3mm.

4. The positive electrode sheet according to claim 1, wherein, The average particle size of the primary particles is smaller than the average particle size of the secondary spherical particles. And / or, the average particle size of the primary particles is 0.2 μm-6 μm; And / or, the average particle size of the secondary spherical particles is 0.8 μm-40 μm; And / or, the positive electrode active layer includes a positive electrode active material, the surface of which includes a carbon coating layer, the thickness of which is 1nm-20nm; And / or, the positive electrode active layer includes a positive electrode conductive agent, the average particle size of which is 10nm-300nm; And / or, the composition of the primary particles and the composition of the secondary spherical particles are each independently selected from LiMn2O4 and Li4Ti5O4. 12 Li3V2(PO4)3, LiFe (1-x) W x PO4, LiNi x Mn y Co (1-x-y) O2 and LiNi x Co y Al (1-x-y) At least one of O2, wherein 0≤x≤1, 0≤y≤1, x+y≤1, and W includes one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, V, and Ti.

5. The positive electrode according to claim 4, wherein, The weight ratio of the positive electrode material in the positive electrode active layer to the weight ratio of the second active material in the second active layer is (0.95-1):1; And / or, the weight content of the positive electrode material in the positive electrode active layer is 90%-95%; And / or, the weight content of the second active material in the second active layer is 92%-96%; And / or, the ratio of the average particle size of the positive electrode conductive agent to the thickness of the carbon coating layer is (4-200):

1.

6. The positive electrode according to claim 1, wherein, The positive current collector includes a metal layer and a carbon coating layer located on one or both surfaces of the metal layer, wherein the thickness of the metal layer is in the ratio of (8-35):1 to the thickness of the carbon coating layer on one side. Preferably, the thickness of the metal layer is 6μm-20μm; Preferably, the thickness of the carbon coating layer on one side is 0.4μm-2μm.

7. The positive electrode according to claim 1, wherein, Along the width direction of the positive electrode sheet, the positive electrode current collector further includes a third region, which is connected to the second region. The positive electrode sheet also includes a ceramic layer that covers the third region, and the positive electrode active layer is adjacent to the ceramic layer. And / or, the bulk resistivity of the positive electrode is 5 Ω·cm-40 Ω·cm.

8. The positive electrode according to claim 7, wherein, The second active layer and the ceramic layer have a mixing region, the width of which is 0.1mm-3mm; And / or, the width of the ceramic layer is 0.5mm-5mm.

9. The positive electrode according to claim 8, wherein, The ratio of the width of the ceramic layer to the width of the mixing region is (1.5-50):1, preferably (1.2-30):

1.

10. A battery, characterized in that, The battery comprises the positive electrode sheet according to any one of claims 1-9.

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