Electrode sheet and battery

Abstract

The application provides an electrode sheet and a battery. The electrode sheet comprises a current collector, a protective layer arranged on the surface of the current collector, and an active material layer arranged on the surface of the protective layer away from the current collector; and the protective layer comprises a metaphosphate. The application can avoid the short circuit phenomenon in the battery, and improve the safety and other performances of the battery.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage devices, specifically to an electrode sheet and a battery. Background Technology

[0002] Batteries are common electrochemical energy storage devices, typically consisting of a positive electrode, a separator, and a negative electrode stacked sequentially. During use, batteries are often subjected to pressure, impacts, and other stressors, leading to mechanical damage and severe internal short circuits. These short circuits can occur between the positive and negative current collectors, the positive and negative electrode coatings, or both. These short circuits cause heat generation (especially the faster heat generation from the contact short circuit between the positive and negative electrode coatings), increasing the risk of thermal runaway and compromising battery safety. Therefore, improving battery safety and other performance aspects is urgently needed. Summary of the Invention

[0003] This invention provides an electrode sheet and a battery that can avoid short circuits inside the battery and improve battery safety and other performance characteristics.

[0004] In one aspect, the present invention provides an electrode sheet comprising a current collector, a protective layer disposed on the surface of the current collector, and an active material layer disposed on the side of the protective layer opposite to the current collector; the protective layer comprises metaphosphate.

[0005] According to one embodiment of the present invention, the chemical formula of the metaphosphate is M(PO3)n, n≥1, and M includes one or more of Li, Al, Fe, Mg, Ti, Ba, Ca, Sr, Y, Nb, K, La, Na, Zn, Nd, and Mn.

[0006] According to one embodiment of the present invention, the particle size Dv50 of the particles in the protective layer is 0.01 μm to 3 μm.

[0007] According to one embodiment of the present invention, the mass percentage of metaphosphate in the protective layer is 82% to 98.5%.

[0008] According to one embodiment of the present invention, the protective layer further includes a first adhesive and a first conductive agent, wherein the mass percentage of the first adhesive is 1% to 10%, and the mass percentage of the first conductive agent is 0.5% to 8%.

[0009] According to one embodiment of the present invention, the protective layer has an uneven structure on the side facing the active material layer.

[0010] According to one embodiment of the present invention, the maximum thickness of the protective layer is H. 1maxThe minimum thickness of the protective layer is H. 1min 20% ≤ (H) 1max -H 1min ) / H 1max ≤80%.

[0011] According to one embodiment of the present invention, the average thickness of the protective layer is 1 μm to 10 μm.

[0012] According to one embodiment of the present invention, the electrode sheet is a positive electrode sheet.

[0013] In another aspect, the present invention provides a battery comprising the above-described electrode sheet.

[0014] In this invention, a protective layer containing metaphosphate is provided between the current collector and the active material layer. This protective layer can prevent short circuits caused by contact between the current collector of the electrode sheet and the current collector or coating of the other polarity electrode sheet, as well as the resulting thermal runaway, thereby improving the safety of the battery. At the same time, it can also reduce the internal resistance and internal resistance growth rate of the electrode sheet and the battery. Even under high temperature conditions, it can still maintain a low internal resistance and internal resistance growth rate, thereby improving the battery's cycle performance and other electrochemical properties. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the electrode sheet structure according to an embodiment of the present invention.

[0016] Explanation of reference numerals in the attached figures: 1: Current collector; 2: Protective layer; 21: First recessed area; 22: First raised area; 3: Active material layer; 31: Second recessed area; 32: Second raised area; 4: Overlapping area; △H, H 1min H 1max H 2min H 2max :thickness. Detailed Implementation

[0017] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] like Figure 1 As shown, an embodiment of the present invention provides an electrode sheet, including a current collector 1, a protective layer 2 disposed on the surface of the current collector 1, and an active material layer 3 disposed on the side of the protective layer 2 facing away from the current collector 1; the protective layer 2 includes metaphosphate.

[0019] A protective layer 2 containing metaphosphate is formed on the surface of the current collector 1. This protects the electrode sheet and prevents short circuits between the positive and negative electrodes (e.g., short circuits caused by mechanical abuse such as punctures, compression, and impacts in lithium-ion batteries). In particular, it prevents the current collector 1 from contacting the coating of the opposite polarity electrode (e.g., preventing the current collector 1 of the positive electrode from contacting the coating of the negative electrode), thus improving battery safety. Simultaneously, metaphosphate is an anionic material, and its polyanionic groups have a strong binding force on oxygen. When oxygen evolution occurs on the electrode sheet (usually more easily under high-temperature conditions), the metaphosphate in the protective layer 2 can bind the oxygen, thereby maintaining the thermal and structural stability of the electrode sheet and improving its safety. Furthermore, metaphosphate has good chemical stability; it does not participate in reactions during battery charging and discharging, exhibiting minimal changes, thus making the electrochemical performance of the electrode sheet and the battery more stable.

[0020] Therefore, by setting a protective layer 2 containing metaphosphate between the current collector 1 and the active material layer 3, it is possible to avoid short circuits between the current collector 1 of the electrode sheet and the current collector 1 or coating of the other polarity electrode sheet (such as short circuits between the positive and negative electrodes caused by mechanical abuse such as puncture, squeezing, and impact), as well as the resulting thermal runaway problems, thereby improving battery safety. At the same time, it can also reduce the internal resistance and internal resistance growth rate of the electrode sheet and the battery. Even under high temperature conditions (such as 45°C), it can still maintain a low internal resistance and internal resistance growth rate, improving the battery's cycle performance and other electrochemical performance and electrochemical performance stability.

[0021] Generally, the chemical formula of the above metaphosphate is M(PO3)n, where n≥1, and PO3... - The valence is -1, and M is a metallic element, which can specifically include one or more metallic elements from Group IA, Group IIA, Group IIIA, Group IIIB, Group IVB, Group VB, Group VIIB, Group VIII, Group II, and the lanthanides in the periodic table.

[0022] In some embodiments, M includes one or more of Li, Na, K, Mg, Ca, Sr, Ba, Al, Y, Ti, Nb, Mn, Fe, Zn, La, and Nd.

[0023] For example, the aforementioned metaphosphate may include one or more of lithium metaphosphate (LiPO3), sodium metaphosphate (NaPO3), potassium metaphosphate (KPO3), magnesium metaphosphate (Mg(PO3)2), calcium metaphosphate (Ca(PO3)2), strontium metaphosphate (Sr(PO3)2), barium metaphosphate (Ba(PO3)2), aluminum metaphosphate (Al(PO3)3), yttrium metaphosphate (Y(PO3)3), titanium metaphosphate, niobium metaphosphate (Nb(PO3)5), manganese metaphosphate, iron metaphosphate (Fe(PO3)3), zinc metaphosphate (Zn(PO3)2), lanthanum metaphosphate (La(PO3)3), and neodymium metaphosphate (Nd(PO3)3).

[0024] Metaphosphate, as a filler for protective layer 2, can improve the stability of protective layer 2 and its protective effect on the electrode sheet, and optimize the electrochemical performance of the electrode sheet. Metaphosphate is the main component of protective layer 2, and its mass percentage in protective layer 2 (i.e., the mass ratio of metaphosphate to protective layer 2) is not less than 50%, further not less than 60%, and even further not less than 70% or 80%.

[0025] According to the inventors' research, the mass percentage of metaphosphate in the above-mentioned protective layer 2 can be specifically 82% to 98.5%, for example, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 98.5% or any combination thereof. This is beneficial for balancing the improvement of the safety and electrochemical performance of the electrode sheet.

[0026] Generally, the protective layer 2 may further include a first binder and a first conductive agent. The mass percentage of the first binder may be 1% to 10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination thereof. The mass percentage of the first conductive agent may be 0.5% to 8%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any combination thereof. By providing a protective layer 2 with such a composition between the current collector 1 and the active material layer 3, it is beneficial to further improve the safety and electrochemical performance of the electrode sheet.

[0027] Further research revealed that the particle size Dv50 of the particles in the aforementioned protective layer 2 can range from 0.01 μm to 3 μm, for example, within the ranges of 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3 μm, or any combination thereof. Dv501 represents the particle size at which the particles in the protective layer 2 reach 50% of the total volumetric particle size distribution, starting from the smallest particle size side. Generally, the smaller the particle size Dv50 in the protective layer 2, the more particles there are under the same protective layer 2 thickness, which is beneficial to improving the protection of the electrode sheet. For example, it is beneficial to isolate and protect the current collector of the electrode sheet, thereby improving the safety performance of the electrode sheet. However, if the particle size Dv50 is too small, it will also affect the internal resistance and other properties of the electrode sheet to a certain extent. For example, if the particle size Dv50 in the protective layer 2 is too small, the specific surface area of ​​the particles in the protective layer 2 will be larger, requiring more conductive agent. Therefore, if the content of the first conductive agent in the protective layer 2 remains unchanged, the particle size Dv50 in the protective layer 2 decreases, its conductivity decreases, and the internal resistance of the electrode sheet increases significantly.

[0028] The particle size Dv50 of the particles in the protective layer 2 is obtained from all the material particles in the protective layer 2 that exist in particulate form. Specifically, the metaphosphate and the first conductive agent in the protective layer 2 exist in particulate form, that is, the particles in the protective layer 2 include metaphosphate particles and first conductive agent particles. In specific implementation, a powder formed by the particles in the protective layer 2 (including metaphosphate particles and conductive particles) can be obtained (that is, the powder simultaneously includes metaphosphate particles and conductive particles), and then the particle size Dv50 of the powder is measured, which is the particle size Dv50 of the particles in the protective layer 2.

[0029] As described above, metaphosphate is the main component of protective layer 2 (e.g., the mass content of metaphosphate in protective layer 2 is not less than 82%). The particles in protective layer 2 are mainly metaphosphate particles, with fewer particles of other materials such as the first conductive agent (the mass content of the first conductive agent does not exceed 8%). That is, when testing the particle size Dv50 of the particles in protective layer 2, the powder formed by the particles in protective layer 2 is mainly composed of metaphosphate particles, with fewer particles of other materials such as the first conductive agent. The measured particle size Dv50 of this powder can be basically equal to the particle size of the metaphosphate. The particle size Dv50, that is, the particle size Dv50 of the particles in the above-mentioned protective layer 2, can be basically equal to the particle size Dv50 of the metaphosphate in the protective layer 2. That is, the particle size Dv50 of the metaphosphate can be 0.01μm to 3μm, for example, 0.01μm, 0.05μm, 0.1μm, 0.2μm, 0.3μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.8μm, 2μm, 2.3μm, 2.5μm, 2.8μm, 3μm or any combination thereof.

[0030] In addition, such as Figure 1 As shown, the protective layer 2 has an uneven structure on the side facing the active material layer 3, that is, the side of the protective layer 2 facing the active material layer 3 is an uneven curved surface, such as a wavy curved surface. The thickness of the protective layer 2 is uneven, which helps to improve the safety of the electrode sheet while further improving its energy density and other performance.

[0031] Specifically, such as Figure 1 As shown, the protective layer 2 has a first recessed area 21 and a first protruding area 22 on the side facing the active material layer 3. The first recessed area 21 is recessed towards the side of the protective layer 2 away from the active material layer 3, and the first protruding area 22 protrudes towards the active material layer 3 relative to the first recessed area 21. There are multiple first recessed areas 21 and first protruding areas 22, and these first recessed areas 21 and first protruding areas 22 are distributed alternately. Specifically, they can be distributed alternately along the length direction of the electrode sheet, that is, there is a first protruding area 22 between two adjacent first recessed areas 21, and there is a first recessed area 21 between adjacent first protruding areas 22, so that the side of the protective layer 2 facing the active material layer 3 forms a wavy curved surface.

[0032] Correspondingly, the active material layer 3 has a textured structure adapted to the protective layer 2, that is, the side of the active material layer 3 facing the protective layer 2 is an uneven curved surface, such as a wavy curved surface, and the thickness of the active material layer 3 is uneven. Figure 1As shown, the side of the active material layer 3 facing the protective layer 2 has a second recessed area 31 and a second protruding area 32. The second recessed area 31 is recessed towards the side of the active material layer 3 away from the protective layer 2, and the second protruding area 32 protrudes towards the protective layer 2 relative to the second recessed area 31. There are multiple second recessed areas 31 and second protruding areas 32, and these second recessed areas 31 and second protruding areas 32 are staggered. Specifically, they can be staggered along the length of the electrode sheet, that is, there is a second protruding area 32 between two adjacent second recessed areas 31, and there is a second recessed area 31 between adjacent second protruding areas 32, so that the two sides of the active material layer 3 facing the active material layer 3 form a wavy curved surface. The second recessed area 31 of the active material layer 3 corresponds one-to-one with the first protruding area 22 of the protective layer 2 and is adapted to each other. The second protruding area 32 of the active material layer 3 corresponds one-to-one with the first recessed area 21 of the protective layer 2 and is adapted to each other.

[0033] Specifically, the electrode sheet includes an area where the protective layer 2 and the active material layer 3 overlap (hereinafter referred to as the overlapping area 4). The overlapping area includes a first protrusion area 22 of the protective layer 2 and a second protrusion area 32 of the active material layer 3. The first protrusion area 22 and the second protrusion area 32 are staggered, that is, there is a second protrusion area 32 between every two adjacent first protrusion areas 22, and there is a first protrusion area 22 between every two adjacent second protrusion areas 32. The thickness ΔH of the overlapping area 4 is equal to the distance in the first direction from the side of the first protrusion area 22 facing the active material layer 3 (which is also the side where the first protrusion area 22 and the second recessed area 31 of the active material layer 3 are connected) to the side of the second protrusion area 32 facing the protective layer 2 (which is also the side where the second protrusion area 32 and the first recessed area 21 of the protective layer 2 are connected).

[0034] Further research revealed that the maximum thickness of protective layer 2 (i.e., the thickness of the thickest part of protective layer 2) is H. 1max The minimum thickness of protective layer 2 (i.e., the thickness of the thinnest part of protective layer 2) is H. 1min The degree of overlap between protective layer 2 and active material layer 3 is Y = (H 1max -H 1min ) / H 1max20% ≤ Y ≤ 80%, where Y is, for example, a range consisting of 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any two of these. In contrast, if the overlap ratio Y is too low, the area between the protective layer 2 and the active material layer 3 is less, resulting in poor interfacial bonding and slightly lower interface stability. After multiple charge-discharge cycles, this leads to a larger interfacial impedance, meaning a significant increase in internal resistance during battery cycling, affecting battery capacity and other performance characteristics. Conversely, if the overlap ratio Y is too high, the active material layer 3 extends into the protective layer 2 to a greater extent, which can affect the functionality of both the protective layer 2 and the active material layer 3. For example, excessive overlap ratio Y can cause the active material layer and the protective layer to be overly compressed, thus affecting their respective functions (e.g., excessive compression of the protective layer by the active material layer affects its protective function, leading to reduced safety). Therefore, controlling the overlap ratio Y within the aforementioned range (20% ≤ Y ≤ 80%) is beneficial for further improving the safety and electrochemical performance of both the electrode sheet and the battery.

[0035] Generally, the thickness of the protective layer 2 corresponding to the multiple first recessed areas 21 is basically the same, and the minimum thickness H of the protective layer 2 is... 1min The thickness is approximately equal to the thickness of the protective layer 2 corresponding to the first recessed area 21; the thickness of the protective layer 2 corresponding to the plurality of first protruding areas 22 is approximately the same, and the maximum thickness H of the protective layer 2 is... 1max It is basically equal to the thickness of the protective layer 2 corresponding to the first protrusion area 22.

[0036] Furthermore, the thickness of the active material layer 3 corresponding to the aforementioned plurality of second recessed regions 31 is basically the same, and the minimum thickness H of the active material layer 3 is... 2min The thickness is approximately equal to the thickness of the active material layer 3 corresponding to the second recessed region 31; the thickness of the active material layer 3 corresponding to the plurality of second protruding regions 32 is approximately the same, and the maximum thickness H of the active material layer 3 is... 2max It is approximately equal to the thickness of the active material layer 3 corresponding to the second protrusion region 32. The minimum thickness H of the active material layer 3 is... 2min Greater than 0.

[0037] Furthermore, the thickness ΔH of the overlapping region 4, and the difference in thickness (H) between the first protruding region 22 and the first recessed region 21. 1max -H 1min The difference in thickness between the second raised area 32 and the second recessed area 31 (H) 2max -H 2min They are basically equal, that is, ΔH = H 1max -H 1min =H 2max -H 2min .

[0038] Specifically, during the preparation of the electrode sheet, it is usually necessary to roll the coating (such as the above-mentioned protective layer 2 and active material layer 3) applied to the surface of the current collector 1 to compact the coating. After rolling, a portion of the protective layer 2 and the active material layer 3 overlap, that is, a portion of the active material layer 3 protrudes towards the protective layer 2 to form a second protrusion area 32, while a portion of the protective layer 2 protrudes towards the active material layer 3 to form a first protrusion area 22, thereby forming an overlapping area 4 where the protective layer 2 and the active material layer 3 overlap.

[0039] In addition, the average thickness H1 of the above-mentioned protective layer 2 can be 1μm to 10μm, for example, a range of 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or any two of these, which is beneficial to improving the safety, electrochemical performance and energy density of the electrode sheet and the battery.

[0040] Generally, the greater the thickness of the protective layer 2, the better the safety of the battery. Considering actual mechanical abuse and other situations, according to the inventor's research, when the thickness of the protective layer 2 is not less than 1μm, the safety performance of the electrode sheet can be significantly improved. When the thickness of the protective layer 2 is not less than 2μm, the safety performance of the electrode sheet can be improved even more significantly, and it can pass more stringent tests such as needle penetration and extrusion. As the thickness of the protective layer 2 increases, the energy density of the electrode sheet is usually reduced to some extent. Currently, the energy density of batteries used in mobile phones or other similar electronic products is usually 650Wh / L to 750Wh / L. Taking a battery with an energy density of 700Wh / L as an example, the aforementioned protective layer 2 is placed between the current collector 1 and the active material layer 3 of the electrode sheet (such as the positive electrode sheet). This can improve the safety and electrochemical performance of the battery. When the average thickness of the protective layer 2 is controlled within 5μm, its energy density is not lower than 680Wh / L (when the average thickness of the protective layer 2 is about 5μm, its energy density is about 680Wh / L). The energy density loss is small and the practicality is strong. When the average thickness of the protective layer 2 is about 10μm, its energy density is about 660Wh / L. When the average thickness of the protective layer 2 is greater than 10μm, its energy density is generally lower than 650Wh / L. The capacity reduction of the battery under the same volume is more obvious. Therefore, taking into account factors such as the safety, energy density and electrochemical performance of the electrode sheet, it is preferable to control the average thickness H1 of the protective layer 2 within the above range (i.e., 1 μm to 10 μm), and more preferably the average thickness H1 of the protective layer 2 is 2 μm to 5 μm.

[0041] The average thickness H1 of the protective layer 2 is approximately equal to the minimum thickness H of the protective layer 2. 1min With maximum thickness H 1max The average value, i.e., H1 = (H 1min+H 1max ) / 2.

[0042] Specifically, the minimum thickness H of the protective layer 2 1min The thickness of the protective layer 2 corresponding to the first recessed area 21 is greater than 0, for example, 0 < H. 1min <10μm, H 1min For example, a range consisting of 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 9.5μm, or any two of them.

[0043] In addition, the maximum thickness H of the protective layer 2 1max (The thickness of the protective layer 2 corresponding to the first protrusion 22) is greater than H. 1min For example, 1≤H 1min ≤10μm, H 1max For example, a range consisting of 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any two of these.

[0044] In practice, the cross-section of the electrode coating can be analyzed using a scanning electron microscope (SEM) to obtain an SEM cross-sectional image showing the electrode coating. This allows for the measurement of the minimum thickness (thickness of the protective layer 2 corresponding to the first recessed area 21) and the maximum thickness (thickness of the protective layer 2 corresponding to the first raised area 22) of a selected region (e.g., within a field of view at a magnification of 1K, within a 10μm length along the current collector 1). In other words, the minimum thickness H of the protective layer 2 can be measured. 1min and maximum thickness H 1max Similarly, the maximum thickness H of the active material layer 3 1max and minimum thickness H 2min It can also be measured in a similar way to protective layer 2, which will not be described in detail here.

[0045] Furthermore, the current collector 1 has two opposing surfaces (i.e., two opposite surfaces). The aforementioned protective layer 2 and active material layer 3 are respectively disposed on at least one surface of the current collector 1. Specifically, the active material layer 3 can be disposed on one surface of the current collector 1, and the other surface of the current collector 1 is an empty foil area (i.e., the other surface of the current collector 1 is not provided with the active material layer 3 or other coatings). In this case, the aforementioned protective layer 2 is disposed between the active material layer 3 and the surface of the current collector 1. Alternatively, the active material layer 3 can be disposed on both the front and back surfaces of the current collector 1. In this case, the protective layer 2 can be disposed on one surface of the current collector 1, or the protective layer 2 can be disposed on both the front and back surfaces of the current collector 1.

[0046] Specifically, the average thickness H1 of the protective layer 2 and the maximum thickness H of the protective layer 2 are... 1max Minimum thickness H of protective layer 21min The maximum thickness H of the active material layer 3 2max Minimum thickness H of active material layer 3 2min Both refer to the thickness on one side. Taking the average thickness H1 of the protective layer 2 as an example, when the protective layer 2 is provided on both the front and back surfaces of the current collector 1, the average thickness H1 of the protective layer 2 refers to the average thickness of the protective layer 2 provided on one surface of the current collector 1 (single-sided thickness), rather than the sum of the average thicknesses of the protective layers 2 provided on both the front and back surfaces of the current collector 1 (double-sided thickness).

[0047] When the protective layer 2 is provided on both the front and back surfaces of the current collector 1, the average thickness H1 of the protective layer 2 on the two surfaces of the current collector 1 can be the same or different, and the maximum thickness H 1max They can be the same or different, minimum thickness H 1min They can be the same or different.

[0048] Specifically, the electrode sheet can be a positive electrode sheet or a negative electrode sheet. Taking the electrode sheet as a positive electrode sheet as an example, by setting the protective layer 2 containing metaphosphate on the surface of the current collector 1 of the positive electrode sheet, the short circuit phenomenon caused by the contact between the positive electrode sheet and the negative electrode current collector 1 or coating of the negative electrode sheet can be avoided, thus avoiding thermal runaway and improving the safety and other performance of the electrode sheet. At the same time, it can also reduce the internal resistance and internal resistance normality of the battery, and improve the electrochemical performance and electrochemical performance stability of the battery.

[0049] When the electrode sheet is a positive electrode sheet, the current collector 1 is a positive electrode current collector, which can be a conventional positive electrode current collector in the art, such as aluminum foil; when the electrode sheet is a negative electrode sheet, the current collector 1 is a negative electrode current collector, which can be a conventional negative electrode current collector in the art, such as copper foil.

[0050] Specifically, the active material layer 3 includes an active material, a second conductive agent, and a second binder. The mass percentage of the active material can be 90% to 99%, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any two of these. The mass percentage of the second conductive agent can be 0% to 5%, for example, 0%, 1%, 2%, 3%, 4%, 5%, or any two of these. The mass percentage of the second binder can be 1% to 5%, for example, 1%, 2%, 3%, 4%, 5%, or any two of these.

[0051] Specifically, when the aforementioned electrode sheet is a positive electrode sheet, the aforementioned active material layer 3 is a positive electrode active material layer, wherein the active material is a positive electrode active material, which may include lithium-containing active materials, such as one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide. In the positive electrode active material layer 3, the mass percentage of the positive electrode active material can be 90% to 98%, the mass percentage of the second conductive agent can be 1% to 5%, and the mass percentage of the second binder can be 1% to 5%.

[0052] When the above-mentioned electrode sheet is a negative electrode sheet, the above-mentioned active material layer 3 is a negative electrode active material layer, wherein the active material is a negative electrode active material, which may include at least one of graphite, mesophase carbon microspheres, soft carbon, hard carbon, silicon material, silicon-oxygen material, silicon-carbon material, and lithium titanate; wherein, the graphite may specifically be artificial graphite and / or natural graphite, etc.

[0053] Furthermore, when the electrode sheet is a negative electrode sheet, the negative electrode active material layer may also include a thickener. In the negative electrode active material layer, the mass percentage of the negative electrode active material may be 90% to 99%, the mass percentage of the second conductive agent may be 0% to 3%, the mass percentage of the second binder may be 1% to 5%, and the mass percentage of the thickener may be 0% to 2%.

[0054] The thickener may include, but is not limited to, sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

[0055] The conductive agents (first conductive agent and second conductive agent) in the above-mentioned protective layer 2 and active material layer 3 may include one or more of conductive carbon black, carbon nanotubes, conductive graphite, graphene, carbon fiber, and metal powder. The first conductive agent and the second conductive agent may be the same or different.

[0056] The adhesives (first adhesive and second adhesive) in the protective layer 2 and the active material layer 3 may include one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber. The first adhesive and the second adhesive may be the same or different.

[0057] In addition, the electrode sheet is provided with tabs, which can be located at the end or middle of the electrode sheet along its length. The tabs can be welded to the current collector 1 or integrally formed with the current collector 1. Tab adhesive is provided on the tabs, which can be attached to the side of the tab away from the current collector 1 and can be located at the welding point between the tab and the current collector 1.

[0058] The aforementioned electrode sheet can be prepared using conventional methods in the art, such as coating. Specifically, this process may include: coating a slurry containing a protective layer 2 material onto the surface of the current collector 1, drying it to form a dry film of the protective layer 2 on the surface of the current collector 1; then coating a slurry containing an active material layer 3 material onto the surface of the dry film of the protective layer 2, drying it, and then performing processes such as rolling to sequentially form the protective layer 2 and the active material layer 3 on the surface of the current collector 1. In specific implementation, parameters such as coating thickness, rolling pressure, and compaction density can be adjusted to make a portion of the protective layer 2 and the active material layer 3 overlap, forming the aforementioned overlapping region 4, and satisfying a preset overlap degree Y. After rolling, conventional slitting equipment in the art, such as a slitting machine, can be used to cut the electrode sheet to form electrode sheets with preset shapes and widths. Then, tabs are welded to preset positions on the electrode sheets, for example, the tabs are welded to the current collector 1 at the end or middle of the electrode sheet, and tab adhesive (protective adhesive paper) is attached to the tabs.

[0059] The battery provided in this embodiment of the invention includes the electrode sheet described above. The battery in this embodiment of the invention has the same advantages as the electrode sheet described above, which will not be repeated here.

[0060] Specifically, the aforementioned battery can be a lithium-ion battery, but is not limited to this.

[0061] Specifically, the battery may include a positive electrode sheet having the aforementioned protective layer 2 (i.e., the electrode sheet is a positive electrode sheet), or a negative electrode sheet having the aforementioned protective layer 2 (i.e., the electrode sheet is a negative electrode sheet), or may simultaneously include a positive electrode sheet having the aforementioned protective layer 2 and a negative electrode sheet having the aforementioned protective layer 2 (i.e., the electrode sheet includes both a positive electrode sheet and a negative electrode sheet). When the electrode sheet is a positive electrode sheet, the battery also includes a negative electrode sheet, which can be a conventional negative electrode sheet in the art (the components and contents of the negative electrode sheet, such as the negative electrode active material, conductive agent, and binder, are described above and will not be repeated here); when the electrode sheet is a negative electrode sheet, the battery also includes a positive electrode sheet, which can also be a conventional positive electrode sheet in the art (the components and contents of the positive electrode sheet, such as the positive electrode active material, conductive agent, and binder, are described above and will not be repeated here).

[0062] In addition, the battery also includes a separator between the positive and negative electrode plates, which is used to separate the positive and negative electrode plates to prevent them from short-circuiting due to contact.

[0063] Specifically, the battery mentioned above includes a cell, which includes the positive electrode, separator, and negative electrode. The cell can be a stacked cell, that is, the positive electrode, separator, and negative electrode are stacked in sequence, or the cell can be a wound cell (or wound core), that is, the positive electrode, separator, and negative electrode are stacked and then wound to form a wound structure.

[0064] In addition, the battery also includes adhesive tape for fixing the battery cells, which is attached to the core, for example, to secure the core.

[0065] In addition, the battery also includes a package for encapsulating the battery cell, which may include, for example, an aluminum-plastic film, and the battery may specifically be a pouch cell.

[0066] The battery of the present invention can be manufactured by conventional methods in the art. For example, a positive electrode, a separator, and a negative electrode are sequentially arranged to form the above-mentioned battery cell (such as a stacked battery cell or a wound battery cell). The encapsulation body (such as an aluminum-plastic film) is formed by stamping or other methods. The battery cell is then encapsulated and baked until the moisture content is within acceptable limits. Electrolyte is then injected into the battery cell. The battery cell is then charged and discharged using a formation device to harden it. Cells with acceptable capacity are sorted out. The battery cell is then resealed to seal the encapsulation body, and the edges of the encapsulation body are folded to reduce the overall size of the battery, thus basically forming the battery. Subsequently, the battery is subjected to an open circuit voltage (OCV) test to measure its self-discharge capacity (K value) in order to screen out batteries with acceptable K values, thereby obtaining the above-mentioned battery.

[0067] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0068] Example 1

[0069] 1. Preparation of positive electrode sheet

[0070] (1) Preparation of slurry

[0071] By weight, 90% Al(PO3)3, 5% PVDF and 5% carbon black are mixed evenly, N-methylpyrrolidone (NMP) is added to it and stirred evenly to obtain a protective layer slurry with a solid content of 40%.

[0072] By weight, 96% lithium cobalt oxide, 1% carbon black, 1% carbon nanotubes and 2% PVDF were mixed, NMP was added and stirred evenly to obtain a positive electrode slurry with a solid content of 70%.

[0073] (2) Coating

[0074] The protective layer slurry is coated on both sides of the aluminum foil and dried to form a dry protective film.

[0075] The positive electrode slurry is then coated onto the protective dry film on both sides of the filter membrane. After drying, it is rolled using a roller press to sequentially form a protective layer and a positive electrode active material layer of a predetermined thickness on both sides of the aluminum foil, thus obtaining the positive electrode precursor. The positive electrode precursor is then slit to a predetermined width using a slitting machine. Finally, positive electrode tabs are welded and tab adhesive is applied to obtain the positive electrode sheet (its structure is as follows). Figure 1 (As shown).

[0076] The average thickness (single-sided thickness) of the positive electrode active material layer is H2 = 45 μm, and the average thickness (single-sided thickness) of the protective layer is H1 = 3 μm.

[0077] 2. Preparation of negative electrode sheet

[0078] By weight, 96% artificial graphite, 1% carbon black, 1.5% styrene-butadiene rubber, and 1.5% sodium carboxymethyl cellulose were mixed, deionized water was added, and the mixture was stirred evenly to obtain a negative electrode slurry with a solid content of 40%.

[0079] The negative electrode slurry is coated onto both sides of the copper foil using an extrusion coating process. After drying and rolling, the negative electrode precursor is obtained. The negative electrode precursor is then cut to a preset width using a slitting machine. Negative electrode tabs are then welded on and attached with tab adhesive to obtain the negative electrode sheet.

[0080] 3. Battery manufacturing

[0081] The positive electrode, separator, and negative electrode are stacked in sequence and then wound to form a core, which is then fixed with adhesive tape. The aluminum-plastic film is punched using a punching die, and then the core is sealed with the punched aluminum-plastic film. After baking, liquid injection, formation, secondary sealing, and edge folding, a wound lithium-ion battery is obtained.

[0082] Following the preparation process of the electrode sheet and battery in Example 1, electrode sheets and batteries of Examples 2 to 33 and Comparative Examples 1 to 2 were prepared respectively. The composition, particle size Dv50, and thickness (average thickness H1, minimum thickness H) of the protective layer in each example and comparative example were specified. 1min Maximum thickness H 1max The parameters such as overlap ratio Y are different, as shown in Table 1. Except for the differences shown in Table 1, the other conditions are the same.

[0083] The test procedure for the overlap degree Y between the protective layer and the active material layer of the positive electrode is as follows: Take the positive electrode, cut it using an ion beam profiler, observe the cross-section of the coating using SEM, and measure the maximum thickness H of the protective layer within a 10 μm range along the length of the positive electrode current collector within a field of view at a magnification of 1K. 1max and minimum thickness H 1min , degree of coincidence Y = (H1max -H 1min ) / H 1max .

[0084] The electrode sheets and lithium-ion batteries of each embodiment and comparative example were subjected to the following performance tests:

[0085] (1) Needle penetration test: The lithium-ion battery is fully charged (charged to 4.48V at 1.5C and cut off at 0.05C), and then placed on the test table of the needle penetration test equipment. A tungsten steel needle with a diameter of 3mm and a needle tip length of 3.62mm is used to penetrate the battery from the middle at a speed of 100mm / s. The battery is considered to have passed the test if it does not catch fire or explode. A total of x0 lithium-ion batteries were tested, and the number of batteries that passed the test was x1. The needle penetration test pass rate = x1 / x0, x0 = 30. The results are shown in Table 2.

[0086] (2) Foreign object compression test: The lithium-ion battery was fully charged (charged to 4.48V at 1.5C, cut off at 0.05C), and then placed on the test table of the compression equipment. An M2*4 screw (screw diameter of 2mm and screw length of 4mm) was placed in the middle of the battery. Then the compression equipment was started and the compression plate was pressed down at a speed of 100mm / s to compress the battery. When the compression pressure of the compression plate reached 13KN, the compression was stopped. The battery was considered to have passed the test if it did not catch fire or explode. A total of y0 lithium-ion batteries were tested, and the number of batteries that passed the test was y1. The compression test pass rate = y1 / y0, y0 = 30. The results are shown in Table 2.

[0087] (3) 45℃ Cyclic Impedance Growth Rate Test: The lithium-ion battery was fully charged (1.5C charging to 4.48V, 0.05C cutoff), and then the internal resistance of the battery was tested at 25±3℃ and recorded as R0; the battery was cycled at 45±3℃ with 1.5C charging / 0.5C discharging. After the 500th charge-discharge cycle (i.e., after 500 cycles), the battery was fully charged, and the internal resistance of the battery was tested at 25±3℃ and recorded as Rn; the internal resistance growth rate m of the battery after 500 cycles at 45℃ was measured as m = (R n -R0) / R0, the results are shown in Table 2.

[0088] (4) Energy density test: Volumetric energy density VED = battery capacity E / battery volume V, battery volume V = battery length × battery width × battery height), the results are shown in Table 2; among them, the test process for battery capacity E is as follows: fully charge the battery (charge to 4.48V at 1.5C, cut off at 0.05C), and then discharge it to 3.0V at a current of 0.2C. The discharge energy is the battery capacity E.

[0089] Table 1. Composition and parameters of the protective layer of the positive electrode in each embodiment and comparative example.

[0090]

[0091] Table 2. Battery performance test results for each embodiment and comparative example.

[0092]

[0093] As can be seen, compared with Comparative Example 1 and Comparative Example 2, Examples 1 to 33, by setting a protective layer containing metaphosphate on the surface of the positive current collector of the positive electrode sheet, can simultaneously improve the safety and energy density of the battery, reduce the internal resistance of the battery and the rate of increase of internal resistance after cycling under high temperature conditions, and improve the electrochemical performance and electrochemical performance stability of the battery. In particular, when the particle size Dv50 in the protective layer is controlled to be 0.01μm to 3μm, the mass percentage of metaphosphate in the protective layer is 82% to 98.5%, the overlap ratio Y between the protective layer and the active material layer satisfies 20% ≤ Y ≤ 80%, and the average thickness H1 of the protective layer is 1μm to 10μm, the improvement effect on battery safety, energy density, and electrochemical performance is even more outstanding. Among them, the needle penetration pass rate of these batteries is as high as 25 / 30 or more, and most of them can reach 30 / 30. The screw extrusion pass rate is as high as 25 / 30 or more, and most of them can reach 30 / 30, demonstrating good safety. At the same time, the energy density of these batteries is as high as 660Wh / L or more, and most of them can reach 680Wh / L or more. After 500 cycles at 45℃, the internal resistance growth rate is as low as 68%, and most of them are as low as 62%, demonstrating good electrochemical performance and electrochemical performance stability.

[0094] Compared to Comparative Example 1, Examples 1 to 33 have a protective layer with metaphosphate as the main component on the surface of the positive electrode current collector, which can significantly improve the safety performance of the battery and reduce energy density loss (the energy density loss rate is mostly less than 2%).

[0095] In Comparative Example 2, the main component of the protective layer is LiFePO4. Compared with Comparative Example 2, the protective layers of Examples 1 to 33 introduce metaphosphates (Al(PO3)3, Y(PO3)3, La(PO3)3, LiPO3, Mg(PO3)2) as the main component. This can significantly reduce the growth rate of the battery's internal resistance while maintaining the battery's high safety and energy density. The reason for this is that Al(PO3)3 is used as the filler in the protective layer, which has higher electrochemical inertness, is more stable during battery cycling, and has a smaller increase in internal resistance.

[0096] As can be seen from Examples 1 and 12-19, if the protective layer is too thin (as in Example 12), the battery safety will be weakened; if the protective layer is too thick (as in Example 19), the battery energy density will be significantly reduced (the energy density loss rate in Example 19 reaches 9%), and the battery internal resistance growth rate will be high. Therefore, controlling the average thickness of the protective layer within a suitable range (e.g., 1 μm to 10 μm) can better balance and improve these battery performance characteristics (as in Examples 1 and 13-18).

[0097] As can be seen from Examples 1 and 20-26, if the overlap ratio Y between the protective layer and the active material layer is too low (as in Examples 20 and 21), the internal resistance of the battery increases significantly. This is because a low overlap ratio results in poor interfacial bonding between the protective layer and the active material layer, leading to a larger increase in internal resistance during battery cycling. Conversely, if the overlap ratio Y is too high (as in Example 26), the active material layer and the protective layer excessively compress each other, especially the active material layer excessively compressing the protective layer, which affects the protective performance of the protective layer and reduces battery safety. Therefore, controlling the overlap ratio Y between the protective layer and the active material layer within a suitable range (e.g., 20% ≤ Y ≤ 80%) can better balance and improve these battery performance characteristics (as in Examples 1 and 16-19).

[0098] As can be seen from Examples 1 and 27 to 29, the particle size Dv50 in the protective layer also affects the performance of the battery. Compared with Example 29, the particle size Dv50 in the protective layer of Examples 1, 27 and 28 is in the range of 0.01μm to 3μm, which can significantly improve the safety performance of the battery while maintaining a high capacity and a low internal resistance growth rate.

[0099] As can be seen from Examples 1 and 30 to 33, the content of components such as metaphosphate in the protective layer also affects the performance of the battery. Compared with Examples 32 and 33, Examples 1, 30 and 31 control the mass percentage content of metaphosphate in the protective layer within the range of 82% to 98.5%, which can significantly improve the safety of the battery and enable the battery to have both a lower internal resistance growth rate and a higher capacity.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrode sheet, characterized by, The device includes a current collector, a protective layer disposed on the surface of the current collector, and an active material layer disposed on the side of the protective layer facing away from the current collector; the protective layer includes metaphosphate, the mass percentage of which is 82%~98.5%; the chemical formula of the metaphosphate is [missing information]. n≥1, M is one of Li, Al, Fe, Mg, Ti, Ba, Ca, Sr, Y, Nb, K, La, Na, Zn, Nd, Mn; The protective layer has a concave-convex structure on the side facing the active material layer, and the active material layer has a concave-convex structure adapted to the protective layer; the protective layer has a first recessed area and a first protruding area on the side facing the active material layer, the first recessed area is recessed towards the side of the protective layer away from the active material layer, and the first protruding area is protruding towards the active material layer, and there are multiple first recessed areas and first protruding areas, which are staggered along the length direction of the electrode sheet. The overlap between the protective layer and the active material layer is Y = (H 1max -H 1min ) / H 1max , 20%≤Y≤80%, where, H 1max H represents the thickness of the thickest part of the protective layer. 1min This refers to the thickness of the thinnest part of the protective layer.

2. The electrode pad of claim 1, wherein The particles in the protective layer have a particle size Dv50 of 0.01 μm to 3 μm, and the particles in the protective layer include metaphosphate particles.

3. The electrode sheet according to claim 1 or 2, characterized by The protective layer further includes a first adhesive and a first conductive agent, wherein the first adhesive has a mass percentage content of 1% to 10%, and the first conductive agent has a mass percentage content of 0.5% to 8%.

4. The electrode pad of claim 1, wherein The average thickness of the protective layer is 1 μm to 10 μm.

5. The electrode pad of claim 1, wherein The electrode sheet is a positive electrode sheet.

6. A battery, characterized by Includes the electrode sheet as described in any one of claims 1-5.

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