Electrode sheet, electrode assembly, battery cell and manufacturing method therefor, battery, and electrical device

Abstract

An electrode sheet, an electrode assembly, a battery cell and a manufacturing method therefor, a battery, and an electrical device, relating to the technical field of batteries. A protective layer is provided on at least an end surface of the electrode sheet, the protective layer comprises aluminum oxide or silicon oxide, and the minimum resistance R of the protective layer satisfies: R≥25Ω. The protective layer is dense, which is conducive to improving the reliability of the battery cell.

Description

Pole piece, electrode assembly, battery cell and preparation method thereof, battery, and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410269711.2 filed on March 8, 2024, entitled “Pole piece, electrode assembly, battery cell and preparation method thereof, battery, and electrical device,” and the entire contents of that application are incorporated into this application by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a pole piece, an electrode assembly, a battery cell and a preparation method thereof, a battery, and an electrical device. Background Art

[0004] With the increasing severity of environmental pollution, the new energy industry has attracted more and more attention. In the new energy industry, battery technology is an important factor in its development.

[0005] The development of battery technology requires consideration of multiple design factors, such as energy density, cycle life, and reliability. The design of the pole piece in a battery cell is crucial to its reliability. Therefore, how to provide a pole piece to improve the reliability of a battery cell is a pressing technical issue.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a pole piece to improve the reliability of a battery cell.

[0008] In order to achieve the above-mentioned objectives, the present application provides a pole piece, an electrode assembly, a battery cell and a preparation method thereof, a battery, and an electrical device.

[0009] In a first aspect, a pole piece is provided, wherein at least an end surface of the pole piece is provided with a protective layer, the protective layer comprises aluminum oxide or silicon oxide, and the minimum resistance R of the protective layer satisfies: R≥25Ω.

[0010] In the embodiments of the present application, a protective layer is provided on at least the end surface of the electrode. The protective layer comprises aluminum oxide or silicon oxide. This protective layer reduces the risk of short circuits caused by contact between the end surface and electrodes of opposite polarity, thereby improving the reliability of the battery cell. The minimum resistance R of the protective layer is greater than or equal to 25Ω. This ensures that the protective layer maintains a certain resistance at its weakest point, resulting in a denser layer and reducing the risk of short circuits. Therefore, the technical solutions of the embodiments of the present application contribute to improving the reliability of the battery cell.

[0011] In a possible implementation, the protective layer includes silicon oxide, which is easier to prepare than a protective layer made of aluminum oxide, thus reducing the difficulty of preparing the protective layer.

[0012] In one possible implementation, the thickness d1 of the protective layer satisfies the following conditions: 26nm≤d1≤200nm; alternatively, 120nm≤d1≤198nm. When d1 is greater than or equal to 26nm, the protective layer has a relatively suitable thickness, effectively reducing the risk of short circuits. When d1 is less than or equal to 200nm, the protective layer has a relatively low thickness, which can reduce the adverse effects of excessive protective layer thickness on battery cell performance.

[0013] In one possible implementation, the minimum resistance R of the protective layer satisfies the following conditions: 26Ω≤R≤372Ω; alternatively, 220Ω≤R≤372Ω. This provides a protective layer with a suitable resistance, further reducing the risk of short circuits in the battery cells. Furthermore, it reduces the time and temperature required to prepare a protective layer with a relatively high resistance.

[0014] In one possible implementation, the shear strength G of the protective layer satisfies the following conditions: 120 MPa ≤ G ≤ 250 MPa; alternatively, 135 MPa ≤ G ≤ 220 MPa. This reduces the risk of the protective layer falling off the electrode assembly and helps reduce the time and temperature required to prepare a protective layer with greater shear strength.

[0015] In one possible implementation, based on the total mass of all elements at the first position of the pole piece, the mass content A of the Si element satisfies the following: A<0.01wt%, where the first position is 5mm from the end surface. In this way, the first position of the pole piece contains almost no Si element, thereby reducing the adverse effects of Si on the cycling performance of the battery cell, and achieving both high reliability and good cycling performance of the battery cell.

[0016] In one possible implementation, the electrode piece includes a main body and a tab, the tab protruding from the main body along a first direction, and the protective layer is provided on an end surface of the main body along the first direction and at least a portion of the tab. This reduces the risk of short circuits caused by the end surface and the tab overlapping with electrodes of opposite polarity.

[0017] In one possible implementation, the protective layer is provided on the end surface of the main body along a second direction, where the second direction is perpendicular to the first direction and parallel to the surface on which the pole piece is located. Thus, the protective layer is provided on both the end surface of the main body along the first direction and the end surface along the second direction, further reducing the risk of short circuits caused by the pole piece overlapping an electrode of opposite polarity.

[0018] In one possible implementation, the electrode is a positive electrode, which includes a positive electrode active material, which includes a layered transition metal oxide. A battery fabricated using this positive electrode active material has a higher energy density, thereby achieving both high energy density and high reliability.

[0019] In one possible implementation, the layered transition metal oxide includes LiNi 0.8 Co 0.1 Mn 0.1 O2 or LiNi 0.6 Co 0.2 Mn 0.2 The positive electrode active material has a high nickel content and a high gram capacity, which is conducive to preparing a battery with a high energy density.

[0020] In a second aspect, an electrode assembly is provided, comprising the electrode piece in the first aspect and any possible implementation thereof.

[0021] In a third aspect, a battery cell is provided, comprising: the electrode assembly according to the second aspect; and a housing for accommodating the electrode assembly. The battery cell can achieve both high reliability and good cycle performance.

[0022] In a fourth aspect, a method for preparing a battery cell is provided, comprising: placing an electrode assembly in a container; introducing a first reactant and a second reactant into the container to obtain an electrode assembly provided with a protective layer, wherein the temperature difference T0 between the first reactant and the second reactant and the temperature of the container satisfies: T0≤4°C, the first reactant includes a gaseous aluminum compound or a gaseous silicon compound, and the second reactant includes water vapor; taking the electrode assembly provided with the protective layer out of the container and placing it in a shell to obtain the battery cell.

[0023] In an embodiment of the present application, the first reactant and the second reactant react on the exposed metal surface of the electrode assembly, thereby forming a protective layer on the exposed metal surface of the electrode assembly. This reduces the risk of short circuits caused by the exposed metal in the electrode assembly overlapping electrodes of opposite polarity, thereby improving the reliability of the battery cell. The temperature difference between the first reactant and the second reactant and the temperature of the container is less than or equal to 4°C. This reduces the risk of condensation of the first reactant and the second reactant. The first reactant and the second reactant can be deposited and reacted more uniformly on the exposed metal surface, thereby forming a denser protective layer, further reducing the risk of short circuits. The electrode assembly with the protective layer is removed from the container and placed in the housing, thereby facilitating assembly of the battery cell. Furthermore, since the housing is not placed in the container, the protective layer is not formed inside the housing, thereby reducing the adverse effects of the protective layer on the battery cell. Therefore, the battery cell obtained by this technical solution has better overall performance.

[0024] In a possible implementation, the first reactant includes the gaseous silicon compound, the gaseous silicon compound includes gaseous silane, and the general formula of the silane satisfies: R'-Si(OR) n , wherein R' includes an organic or inorganic functional group, R includes an alkyl group, and n is an integer with 2≤n≤4. Thus, a reaction occurs between the gaseous silane and the water vapor, thereby generating silicon oxide on the exposed metal surface.

[0025] In one possible implementation, the introducing the first reactant and the second reactant into the container includes: heating silane to a first temperature T1, and introducing a carrier gas into a storage tank storing the silane to obtain the gaseous silane; heating water to a second temperature T2, and introducing the carrier gas into a storage tank storing the water to obtain the water vapor; and introducing the gaseous silane and the water vapor mixed with the carrier gas into the container to obtain an electrode assembly provided with the protective layer.

[0026] In the above technical solution, by introducing a carrier gas into a storage tank storing silane and water, gaseous silane and water vapor can be obtained at a lower temperature. When the difference between the temperature of the gaseous silane and water vapor and the temperature of the container meets a certain range, the container can have a lower temperature, thereby reducing the risk of the container's temperature being too high and adversely affecting the electrode assembly.

[0027] In a possible implementation, the first temperature T1 satisfies: 60°C ≤ T1 ≤ 100°C; and / or the second temperature T2 satisfies: 60°C ≤ T2 ≤ 100°C; and / or the temperature T3 of the container satisfies: 60°C ≤ T3 ≤ 100°C.

[0028] By setting T1, T2, and T3 to meet the above-mentioned temperatures, it is convenient to convert silane and water into gaseous silane and water vapor, and the temperature of the container can be kept at a lower level.

[0029] In a possible implementation, the first temperature T1, the second temperature T2, and the temperature T3 of the container are the same, so as to further reduce the risk of condensation of gaseous silane and water vapor, thereby facilitating the formation of a denser protective layer.

[0030] In one possible implementation, the flow rate of the gaseous silane is less than or equal to the flow rate of the water vapor, which is beneficial to the reaction between the silane and water molecules and also helps to reduce the waste of silane.

[0031] In a possible implementation, the inlet flow rate Q1 of the gaseous silane satisfies: 0.05 L / min≤Q1≤1 L / min.

[0032] In a possible implementation, the water vapor introduction flow rate Q2 satisfies: 0.1 L / min≤Q2≤2 L / min.

[0033] By setting the flow rate of gaseous silane and water vapor, gaseous silane and water vapor enter the container at a more appropriate rate, which facilitates the reaction of gaseous silane and water vapor on the metal surface and the formation of a protective layer; at the same time, it is also beneficial to reduce the risk of silane penetrating into the exposed metal position of the electrode assembly.

[0034] In a possible implementation, the boiling point of the silane is less than or equal to 200° C. This is conducive to the reaction between the silane and water molecules at a lower temperature in the container.

[0035] In one possible implementation, the silane includes at least one of (H5C2O)3Si-CH2CH2-Si(OC2H5)3, (H5C2O)3Si-(CH2)3-NH-(CH2)3-Si(OC2H5)3, (H5C2O)3Si-(CH2)3-S4-(CH2)3-Si(OC2H5)3, (H5C2O)3Si-(CH2)3-NH-CO-NH2, CHOCHCH2-O-(CH2)3-Si(OCH3)3, or CH3-Si(OCH3)3; the silane uses the above substances to facilitate hydrolysis. Optionally, the silane includes (H5C2O)3Si-CH2CH2-Si(OC2H5)3.

[0036] In one possible implementation, the reaction time t1 of the gaseous silane and the water vapor satisfies: 4h≤t1≤12h. In this way, the protective layer can be formed in a shorter time, reducing the risk of forming a protective layer on the active material layer of the electrode assembly due to excessively long reaction time.

[0037] In one possible implementation, the pressure P within the container satisfies the following: 0.09 MPa ≤ P ≤ 0.11 MPa. This allows the protective layer to be formed at atmospheric pressure, reducing the complexity of the production process. Furthermore, forming the protective layer at atmospheric pressure reduces the risk of silane penetrating into unexposed metal areas of the electrode assembly, thereby mitigating adverse effects on the battery's cycling performance and other electrical properties.

[0038] In one possible implementation, the container is in communication with the external environment, so that a relatively constant pressure can be maintained in the container.

[0039] In one possible implementation, the carrier gas includes at least one of nitrogen, argon, carbon dioxide, and helium. Optionally, the carrier gas includes nitrogen. The carrier gas does not react with silane and water vapor, thereby reducing adverse effects on the reaction of silane and water vapor.

[0040] In one possible implementation, placing the electrode assembly in the container includes connecting the electrode assembly to an end cap assembly, and placing the electrode assembly with the end cap assembly connected thereto in the container. Thus, processing after the electrode assembly and the end cap assembly are connected as a whole facilitates forming a protective layer at the connection between the electrode assembly and the end cap assembly.

[0041] In one possible implementation, placing the electrode assembly connected to the end cap assembly in the container includes: placing multiple electrode assemblies connected to the end cap assembly in a holder, the holder covering the largest surface area of ​​the electrode assembly; and placing the holder loaded with the multiple electrode assemblies in the container. This allows the component formed by the connection of the multiple electrode assemblies and the end cap assembly to be processed within the container, which improves production efficiency. Furthermore, the holder covering the largest surface area of ​​the electrode assembly also helps reduce the risk of silane and other substances entering the interior of the electrode assembly.

[0042] In one possible implementation, the preparation method further includes: before introducing the first reactant and the second reactant into the container, introducing an inert gas into the container to evacuate air from the container. This can reduce the adverse effects of air on the reaction between silane and water vapor.

[0043] In a fifth aspect, a battery is provided, comprising the battery cell of the third aspect, and / or a battery cell obtained according to the preparation method of the fourth aspect and any possible implementation thereof.

[0044] In a sixth aspect, an electrical device is provided, comprising the battery described in the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0046] FIG1 is a schematic structural diagram of a pole piece before cutting the pole lugs according to an embodiment of the present application;

[0047] FIG2 is a schematic structural diagram of a pole piece after cutting the pole lugs according to an embodiment of the present application;

[0048] FIG3 is a cross-sectional view along the AA direction in FIG2 ;

[0049] FIG4 is a cross-sectional view along the BB direction in FIG2 ;

[0050] FIG5 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0051] FIG6 is a schematic diagram of a method for preparing a battery cell according to an embodiment of the present application;

[0052] FIG7 is a schematic diagram of an electrode assembly connected to an end cap assembly according to an embodiment of the present application;

[0053] FIG8 is a schematic diagram of a bracket provided with an electrode assembly;

[0054] FIG9 is a schematic diagram of silane and water vapor deposition according to an embodiment of the present application;

[0055] FIG10 is a schematic diagram of an apparatus for preparing a protective layer according to an embodiment of the present application;

[0056] FIG11 is a schematic diagram of a battery according to an embodiment of the present application;

[0057] FIG12 is a schematic diagram of an electrical device according to an embodiment of the present application. DETAILED DESCRIPTION

[0058] The embodiments of the electrode sheet, electrode assembly, battery cell and its preparation method, battery, and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0059] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0060] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0061] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0062] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0063] The development of battery technology must simultaneously consider multiple design factors, such as energy density, cycle life, discharge capacity, charge and discharge rate, reliability, etc. After cutting, the exposed metal of the pole piece is at risk of short circuiting when it overlaps with an electrode of opposite polarity or other components of the battery cell. In some processing methods, a corresponding protective layer is provided at the exposed metal position of the pole piece to reduce the risk of short circuit and improve the reliability of the battery cell. However, the density of the above protective layer is poor, and there is still a risk of short circuit after the pole piece is overlapped with an electrode of opposite polarity.

[0064] In light of this, the present application provides a pole piece having a protective layer provided on at least the end surface of the pole piece. The protective layer comprises silicon oxide and has a minimum resistance greater than or equal to 25Ω. This provides a denser protective layer, which can reduce the risk of short circuits and improve the reliability of the battery cell.

[0065] [Pole piece]

[0066] Figure 1 is a schematic structural diagram of the pole piece of an embodiment of the present application before the pole lug is cut, Figure 2 is a schematic structural diagram of the pole piece of an embodiment of the present application after the pole lug is cut, Figure 3 is a cross-sectional view along the AA direction in Figure 2, and Figure 4 is a cross-sectional view along the BB direction in Figure 2.

[0067] In one embodiment of the present application, for example, as shown in FIG. 1 to FIG. 4 , a protective layer 35 is provided on at least the end surface of the pole piece 1 , and the protective layer 35 includes silicon oxide or aluminum oxide.

[0068] The end surface of the pole piece 1 may include any one of opposite end surfaces along a first direction (eg, y direction in the figure) of the pole piece 1 and opposite end surfaces along a second direction (eg, x direction in the figure).

[0069] The surfaces of the two opposite ends along the first direction of the pole piece 1 may include a first end surface 3301 a and a second end surface 3301 b .

[0070] The surfaces of the two opposite ends along the second direction of the pole piece 1 may include a third end surface 3302a and a fourth end surface 3302b.

[0071] The end surface of the electrode 1 may be a surface formed by cutting, and after cutting, the metal on the end surface is exposed. For example, as shown in Figures 1 to 3, the end surface of the main body 330 along the first direction may include a first end surface 3301a and a second end surface 3301b. The first end surface 3301a may be a surface formed during the process of cutting the electrode along the cutting line 124 to prepare the electrode ear 331, and the second end surface 3301b may be a surface generated by cutting during the process of striping the electrode 1. Striping may refer to the process of cutting a large electrode into multiple small electrode pieces 1 by cutting.

[0072] As an example, the end surface along the first direction and the end surface along the second direction are both provided with a protective layer 35. In this way, all end surfaces of the pole piece 1 are provided with a protective layer 35, which is beneficial to further reduce the risk of short circuit caused by the pole piece 1 overlapping with an electrode of opposite polarity.

[0073] As another example, as shown in FIG. 1 to FIG. 4 , the end surface of the pole piece 1 along the first direction is provided with a protective layer 35 , and the end surface of the pole piece 1 along the second direction is not provided with a protective layer 35 .

[0074] As another example, the end surface of the pole piece 1 along the first direction close to the pole ear (the first end surface 3301a) is provided with a protective layer 35, and the end surface of the end away from the pole ear (the second end surface 3301b) is not provided with a protective layer 35; and the end surface along the second direction of the pole piece 1 is not provided with a protective layer 35.

[0075] The material of the protective layer 35 can be inorganic. For example, the protective layer 35 includes aluminum oxide or silicon oxide. The inorganic protective layer 35 is not easy to swell when immersed in the electrolyte and is not easy to fall off during the long-term use of the battery cell.

[0076] The minimum resistance R of the protection layer 35 satisfies: R≧25Ω.

[0077] The minimum resistance of the protective layer 35 can be determined by cutting the electrode into multiple parts, testing the resistance of the protective layer of each part (ie, the protective layer at different positions), and taking the minimum value of the multiple resistances measured as the minimum resistance.

[0078] The minimum resistance of the protective layer 35 can reflect the density of the protective layer 35. The greater the minimum resistance of the protective layer 35, the better the deposition effect of the protective layer 35 and the denser the protective layer 35.

[0079] The minimum resistance R of the protection layer 35 may be 100Ω, 200Ω, 500Ω, 1000Ω, or any value within the above range.

[0080] By setting the minimum resistance R of the protective layer 35 to be greater than or equal to 25Ω, the weakest position of the protective layer 35 still has a certain resistance, and the protective layer 35 is denser, which can reduce the risk of short circuit.

[0081] In the embodiment of the present application, a protective layer 35 is provided on at least the end surface of the electrode 1. The protective layer 35 comprises aluminum oxide or silicon oxide. This protective layer 35 reduces the risk of short circuits caused by contact between the end surface and electrodes of opposite polarity, thereby improving the reliability of the battery cell. The minimum resistance R of the protective layer 35 is greater than or equal to 25Ω, making the protective layer 35 denser, reducing the risk of short circuits and improving the reliability of the battery cell.

[0082] In some embodiments, the protective layer 35 includes silicon oxide. The silicon oxide may have the following structure: -Si-O-Si-. Silicon oxide is less likely to swell when immersed in electrolyte and less likely to fall off during long-term use of the battery cell 3.

[0083] A protective layer made of silicon oxide is easier to prepare than a protective layer made of aluminum oxide, which helps reduce the difficulty of preparing the protective layer.

[0084] In some embodiments, the thickness d1 of the protective layer 35 satisfies: 26 nm ≤ d1 ≤ 200 nm. d1 can be 26 nm, 56 nm, 80 nm, 100 nm, 120 nm, 160 nm, 198 nm, 200 nm, or any value within the above range.

[0085] The thickness d1 of the protective layer 35 may be an average thickness of the protective layer 35. For example, the thickness of the protective layer 35 may be measured at multiple locations, and the average of the thicknesses at the multiple locations may be taken as d1. For example, the thickness of the protective layer 35 may be measured at multiple locations on the end surface, and the average of the multiple thicknesses may be calculated to obtain the thickness d1 of the protective layer 35.

[0086] At different locations, for example, at the first end surface 3301 a and the second end surface 3301 b , the protective layer 35 has the same or substantially the same thickness.

[0087] When d1 is greater than or equal to 26 nm, the protective layer 35 has a relatively suitable thickness, which can effectively reduce the risk of short circuit; when d1 is less than or equal to 200 nm, the thickness of the protective layer 35 is relatively small, which can reduce the adverse effects of the excessive thickness of the protective layer 35 on the performance of the battery cell 3.

[0088] In some embodiments, the thickness d1 of the protective layer 35 satisfies: 120 nm ≤ d1 ≤ 198 nm. In this way, the protective layer 35 has a greater thickness, which is beneficial to further improve the resistance of the protective layer 35.

[0089] In some embodiments, the minimum resistance R of the protection layer 35 satisfies: 26Ω≤R≤372Ω.

[0090] The resistance of the protective layer 35 is related to the thickness, density, and uniformity of the protective layer 35. When the thickness of the protective layer 35 is constant, the denser and more uniform the protective layer 35 is, the greater the minimum resistance of the protective layer 35 is.

[0091] By setting the minimum resistance of the protective layer 35 to satisfy the above range, the protective layer 35 can have the greatest possible resistance while having an appropriate thickness.

[0092] In some embodiments, the minimum resistance R of the protection layer 35 satisfies: 220Ω≤R≤372Ω. In this way, the minimum resistance of the protection layer 35 is relatively large, which is conducive to further reducing the risk of short circuit.

[0093] In some embodiments, a ratio R / d2 of the minimum resistance R of the protective layer 35 to the minimum thickness d2 of the protective layer 35 satisfies: R / d2≥2Ω / nm; optionally, 2Ω / nm≤R / d2≤2.4Ω / nm.

[0094] The ratio R / d1 of the resistance R of the protective layer 35 to the thickness d1 of the protective layer 35 may be 2Ω / nm, 2.2Ω / nm, 2.4Ω / nm, or any value within the above range.

[0095] The resistance-to-thickness ratio may be the ratio of the resistance to the thickness of the protective layer at the same position. The resistance-to-thickness ratio may reflect the density of the protective layer 35 . The larger the resistance-to-thickness ratio, the denser the protective layer 35 .

[0096] By setting the ratio of the resistance to the thickness of the protective layer 35 to meet the above range, the protective layer 35 has a higher resistance with a smaller thickness, and the protective layer 35 is denser, which is beneficial to further reduce the short circuit risk of the battery cell.

[0097] In some embodiments, the shear strength G of the protective layer 35 satisfies: 120 MPa≤G≤250 MPa. G can be 120 MPa, 135 MPa, 180 MPa, 200 MPa, 220 MPa, 250 MPa, or any value within the above range.

[0098] The shear strength of the protective layer 35 can reflect the bonding strength between the protective layer 35 and the electrode 1 (e.g., the exposed metal at the first end surface 3301a). The greater the shear strength of the protective layer 35, the stronger the bond between the protective layer 35 and the electrode 1, and the lower the risk of the protective layer 35 falling off the electrode 1. In addition, during the long-term use of the battery cell, the risk of the protective layer 35 swelling due to electrolyte immersion is low, and the protective layer 35 is less likely to fall off, which helps improve the reliability of the battery cell.

[0099] The shear strength of the protective layer 35 is related to the thickness of the protective layer 35. The silicon oxide in the protective layer 35 is connected to the metal of the pole piece 1 through a chemical bond. The thicker the protective layer 35 is, the greater the shear strength of the protective layer 35 is.

[0100] When the shear strength of the protective layer 35 is greater than or equal to 120 MPa, the risk of the protective layer 35 falling off the pole piece 1 is low; when the shear strength of the protective layer 35 is less than or equal to 250 MPa, it is convenient to prepare the protective layer 35, which is beneficial to reduce the time required for preparing the protective layer 35 and the temperature required for preparing the protective layer 35.

[0101] Optionally, 135 MPa≤G≤220 MPa. In this way, the protective layer 35 has a higher shear strength, and is conducive to reducing the time and temperature required for preparing the protective layer 35.

[0102] In some embodiments, based on the total mass of all elements at the first position of the pole piece 1 , the mass content A of the Si element satisfies: A<0.01 wt %, and the first position is 5 mm away from the end surface.

[0103] The first position may be a position in the pole piece 1 that is 5 mm away from the end surface along any direction.

[0104] As an example, the first position is a position along the first direction (y direction in the figure) where the distance between the pole piece 1 and the second end surface 3301b is 5 mm.

[0105] As another example, the first position is a position along the second direction (x direction in the figure) where the distance between the pole piece 1 and the third end surface 3302a is 5 mm.

[0106] The first location of the electrode sheet 1 contains multiple elements of the material that makes up the electrode sheet 1. For example, for a positive electrode sheet, the first location of the positive electrode sheet includes elements of the material that makes up the positive electrode current collector, such as Al; elements of the material that makes up the positive electrode film layer, and Si that may penetrate into the positive electrode film layer. For a negative electrode sheet, the first location of the negative electrode sheet includes elements of the material that makes up the negative electrode current collector, such as Cu; elements of the material that makes up the negative electrode film layer, and Si that may penetrate into the negative electrode film layer.

[0107] During the preparation of the protective layer 35, the raw materials for preparing the protective layer 35, such as silane and water, are deposited and reacted on the electrode 1. The mass content of the Si element can reflect the degree of silane penetration or adhesion to the electrode 1, or can reflect the content of silicon oxide on the electrode 1.

[0108] Silicon oxide or silicon affects the conductivity of the electrode, thereby affecting the electrical performance of the battery cell, such as the capacity retention rate, power, and resistance of the battery cell.

[0109] When the mass content of Si is less than 0.01 wt%, it can be roughly assumed that the first location does not contain silicon oxide or that silane has not penetrated the first location. In this way, the risk of silicon oxide or silane being disposed on the non-exposed metal area of ​​the electrode 1 is low, thereby minimizing the impact on the electrical performance of the battery cell and reducing the impact on the cycle performance of the battery cell.

[0110] In some embodiments, the metal on the end surface is chemically bonded to the silicon oxide in the protection layer 35. Specifically, the metal and the silicon oxide are bonded to each other through a covalent bond.

[0111] As an example, the combination of metal and silicon oxide is represented by: Me-Si-O-Si, where Me represents metal.

[0112] As an example, Me is aluminum. As another example, Me is copper.

[0113] The shear strength of the protective layer 35 is related to the connection between the protective layer 35 and the exposed metal of the pole piece 1. In this embodiment, the bonding force between the protective layer 35 and the end surface 3301 is strong, and the protective layer 35 is not easy to fall off.

[0114] In some embodiments, the pole piece 1 includes a main body 330 and a pole tab 331 , the pole tab 331 protruding from the main body 330 along a first direction, and a protective layer 35 is provided on an end surface 3301 of the main body 330 along the first direction and at least a portion of the pole tab 331 .

[0115] The first direction is the direction in which the tab 331 protrudes from the main body 330 . For example, as shown in FIG. 2 , the first direction is the y direction.

[0116] At least part of the tab 331 is provided with a protective layer 35. It is understandable that the protective layer 35 is provided on part of the tab 331 or on the entire tab 331. At least part of the tab 331 may refer to the exposed metal portion of the tab 331.

[0117] As an example, as shown in Figure 2, the tab 331 may include a first part 3311 and a second part 3312, the first part 3311 is connected to the second part 3312 and the first part 3311 is close to the main body 330 relative to the second part 3312; the main body 330 includes a first area 3302 and a second area 3303 connected, and the second area 3303 is close to the tab 331 relative to the first area 3302; the first part 3311 of the tab 331 and the second area 3303 of the main body 330 are coated with an insulating material, the second part 3312 of the tab 331 is a bare aluminum foil, and the first area 3302 of the main body 330 is coated with an active material; the first part 3311 is not provided with a protective layer 35, and the second part 3312 is provided with a protective layer 35.

[0118] As another example, the entire area of ​​the main body 330 is coated with active material, the entire area of ​​the tab 331 is exposed aluminum foil, and the entire area of ​​the tab 331 is provided with a protective layer 35 .

[0119] In some embodiments, the first position is 5 mm away from the end surface of the main body 330 along the first direction. This position is convenient for reflecting the infiltration of silicon elements, thereby reflecting the changes in the electrical properties of the battery cell to a certain extent.

[0120] In some embodiments, the metal in the tab 331 is chemically bonded to the silicon oxide in the protective layer 35. This reduces the risk of a short circuit caused by the tab 331 being connected to an electrode of opposite polarity.

[0121] In some embodiments, a protective layer 35 is provided on the end surface of the main body 330 along a second direction, and the second direction is perpendicular to the first direction and parallel to the surface where the pole piece 1 is located. For example, the second direction is the x direction in FIG1 .

[0122] In this embodiment, the end surface of the main body 330 along the second direction and the end surface along the first direction are both provided with a protective layer 35, which is beneficial to further reduce the risk of short circuit caused by the pole piece 1 overlapping with the electrode of opposite polarity.

[0123] In some embodiments, the electrode is a positive electrode, and the positive electrode includes a positive active material, and the positive active material includes a layered transition metal oxide. The battery prepared by using the above positive active material has a higher energy density, so that the battery can take into account both a higher energy density and a higher reliability.

[0124] The layered transition metal oxide may include a ternary material, lithium cobaltate, a lithium-rich manganese-based material, etc.

[0125] As an example, the chemical formula of the layered transition metal oxide satisfies: Li x (Ni a Co b Mn c ) 1-d M d O 2-y N1] y , where M includes at least one of Mg, Zr, Al, B, Ta, Mo, W, Nb, Sb, La, N includes at least one of F, S, P, 0.6 ≤ a < 1, 0 < b < 0.4, 0 < c < 0.4, a + b + c = 1, 0 ≤ d < 1, 0.2 ≤ x ≤ 1.2, 0 ≤ y < 2. In the above technical solution, the positive active material satisfying the above chemical formula has a high nickel content, and the positive active material has a high specific capacity.

[0126] a can be 0.6, 0.7, 0.8, 0.9 or any value within the above range, b can be 0.1, 0.2, 0.3 or any value within the above range, c can be 0.1, 0.2, 0.3 or any value within the above range, d can be 0, 0.1, 0.6, 0.6, 0.8 or any value within the above range, x can be 0.2, 0.5, 1, 1.2 or any value within the above range, and y can be 0, 0.5, 1, 1.5, 2 or any value within the above range.

[0127] When d is greater than 0, the layered transition metal oxide includes the M element, and the layered transition metal oxide can have higher stability; when d is 0, the layered transition metal oxide does not include the M element.

[0128] It can be understood that the position of the M ion in the layered transition metal oxide structure can be the position replacing part of the transition metal. For example, when the layered transition metal oxide is a nickel-cobalt-manganese-based ternary material, the M ion can replace part of the manganese position, nickel position or cobalt position.

[0129] When y = 0, the layered transition metal oxide does not include the N element. It can be understood that the position of the N ion in the layered transition metal oxide structure can be the position replacing part of the O.

[0130] The battery is accompanied by Li intercalation and deintercalation and consumption during the charge and discharge process. The molar content of Li varies when the battery is discharged to different states. The above definition of x includes the molar content of Li under different charge and discharge states of the battery (usually the battery voltage is between 2-5V).

[0131] In some embodiments, the layered transition metal oxide comprises LiNi 0.8 Co 0.1 Mn 0.1 O2 or LiNi 0.6 Co 0.2 Mn 0.2 The positive electrode active material has a high gram capacity, which is conducive to preparing a battery with a high energy density.

[0132] The electrode piece 1 can be a positive electrode piece or a negative electrode piece. As an example, both the positive electrode piece and the negative electrode piece have the structure described above for the electrode piece 1.

[0133] [Positive electrode]

[0134] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on the positive electrode current collector.

[0135] The positive electrode current collector may be a metal foil or a composite current collector. For example, the positive electrode current collector may be an aluminum foil.

[0136] The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0137] The positive electrode film layer includes a positive electrode active material. The positive electrode active material can be any positive electrode active material known in the art for use in batteries. For example, the positive electrode active material is lithium iron phosphate, a ternary material, or a lithium-rich manganese-based material.

[0138] The positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0139] The positive electrode film layer may further optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0140] [Negative electrode]

[0141] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector.

[0142] The negative electrode current collector can be a metal foil or a composite current collector. The negative electrode current collector can be copper foil. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0143] The negative electrode film layer includes a negative electrode active material. The negative electrode active material can be a negative electrode active material for batteries that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0144] As an example, the negative electrode active material is a carbon material.

[0145] The negative electrode film layer may further optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0146] [Electrolytes]

[0147] The electrolyte conducts ions between the positive and negative electrodes. The present invention does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0148] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0149] The electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0150] The solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0151] The electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and may also include performance additives that can improve certain battery properties, such as improving battery overcharge performance, improving battery high or low temperature performance, etc.

[0152] [Isolator]

[0153] The separator is used to separate the positive electrode sheet from the negative electrode sheet. The embodiment of the present application has no particular limitation on the type of separator, and any known porous structure separator with good chemical and mechanical stability can be selected.

[0154] The separator can be made of at least one of fiberglass, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. In the case of a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0155] [Electrode assembly]

[0156] An embodiment of the present application provides an electrode assembly, which includes the electrode piece 1 in any of the above embodiments.

[0157] The positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process, wherein the positive electrode sheet and the negative electrode sheet can have the structure described in the electrode sheet 1.

[0158] [Battery Cell]

[0159] FIG4 is a schematic diagram of the structure of a battery cell according to an embodiment of the present application. For example, as shown in FIG4 , a battery cell 3 includes a housing 31 , an end cap assembly 32 and an electrode assembly 33 .

[0160] The housing 31 is used to accommodate the electrode assembly 33. The shape of the housing 31 can be determined based on the shape of the electrode assembly 33. The housing 31 can accommodate one or more electrode assemblies. For example, as shown in FIG4 , the housing 31 accommodates four electrode assemblies 33. The housing 31 can be made of metal, such as copper or aluminum.

[0161] The end cap assembly 32 is used to cover the housing 31 to seal the electrode assembly 33. The end cap assembly 32 is connected to the electrode assembly 33, wherein the end cap assembly 32 can be directly connected to the electrode assembly 33 or indirectly connected to the electrode assembly 33.

[0162] As an example, as shown in FIG4 , the electrode assembly 33 is made by winding a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet.

[0163] The end cap assembly 32 is connected to the electrode assembly 33. As an example, the end cap assembly 32 is welded to the electrode lug 33a of the electrode assembly 33 via a current collecting member 34. The electrode lug 33a of the electrode assembly 33 may be formed by stacking the lugs 331 of multiple electrode sheets 1. The current collecting member 34 may be made of metal, such as copper or aluminum.

[0164] The end cap assembly 32 includes an electrode terminal 322. For example, as shown in FIG4 , the end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal. One current collecting member 34 is used to connect the positive electrode tab to the positive electrode terminal, and the other current collecting member 34 is used to connect the negative electrode tab to the negative electrode terminal.

[0165] In some embodiments, the shape of the battery cell 3 can be cylindrical, square, or any other shape. The battery cell 3 can be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery, a magnesium-ion battery, etc. The battery cell 3 can serve as the smallest structural unit of the battery.

[0166] In some embodiments, the battery cells 3 can be assembled into a battery module. The number of battery cells 3 contained in the battery module can be one or more, and the specific number can be selected according to the application and capacity of the battery module.

[0167] 1 to 5 , the embodiments of the pole piece and the battery cell are described above. The preparation method of the battery cell is described below in conjunction with FIG. 6 . Similar descriptions can be found in the description of the embodiments of the pole piece and the battery cell, which will not be repeated here.

[0168] [Method for preparing battery cells]

[0169] FIG6 is a schematic diagram of a method for preparing a battery cell according to an embodiment of the present application. For example, as shown in FIG6 , the method 200 for preparing a battery cell includes the following steps.

[0170] Step 210: Place the electrode assembly 33 in a container.

[0171] The electrode assembly 33 may be prepared by winding the positive electrode sheet, the separator, and the negative electrode sheet, or by laminating the sheets.

[0172] In step 210, only the electrode assembly 33 can be placed in the container, or the ear portion 33a of the electrode assembly 33 can be welded to the end cover assembly 32 through the current collecting component 34, so that the electrode assembly 33 and the end cover assembly 32 form a component, and then the component is placed in the container.

[0173] The container can be connected to the external environment. For example, the container is connected to the first connecting component, so that gas can be introduced into the container through the first connecting component; for another example, the container can also discharge gas from the container through the second connecting component.

[0174] As an example, the container discharges the gas inside the container through the second connecting component. The second connecting component can be provided with special elements so that the gas inside the container can be discharged to the external environment through the second connecting component, but the gas in the external environment will not enter the container through the second connecting component.

[0175] In step 220, a first reactant and a second reactant are introduced into the container to obtain an electrode assembly provided with a protective layer 35, wherein the temperature difference T0 between the first reactant and the second reactant and the temperature of the container satisfies: T0≤4°C, the first reactant includes a gaseous aluminum compound or a gaseous silicon compound, and the second reactant includes water vapor.

[0176] The gaseous first reactant and the second reactant are easily introduced into the container, thereby facilitating the reaction between the first reactant and the second reactant.

[0177] The temperature of the first reactant and the second reactant is no higher than the temperature of the container by no more than 4°C, or the temperature of the first reactant and the second reactant is less than or equal to the temperature of the container. T0 can be 0°C, 1°C, 2°C, 4°C, or any value within the above ranges.

[0178] As an example, before the first reactant and the second reactant are introduced into the container, the first reactant is stored in a first device and the second reactant is stored in a second device. The first device and the second device are provided with temperature sensors to monitor the temperatures of the first reactant and the second reactant; and a temperature sensor is provided in the container to monitor the temperature inside the container. The difference between the temperatures of the first reactant and the second reactant and the temperature of the container can be calculated based on the temperature value monitored by the temperature sensor.

[0179] When the temperature difference between the first reactant and the second reactant and the temperature inside the container is too large, the risk of condensation of the first reactant and the second reactant (for example, condensation at the inlet of the container or at the baffle at the inlet of the container) increases, thereby reducing the reactants that can react in the container and increasing the risk of the generated protective layer 35 being not uniform or dense enough.

[0180] Gaseous aluminum compounds and gaseous silicon compounds can react with water molecules to form aluminum oxide protective layers and silicon oxide protective layers on the exposed metal surface of the electrode assembly.

[0181] The gaseous aluminum compound may be trimethylaluminum.

[0182] In the embodiment of the present application, T0 is set to satisfy T0≤4°C, the risk of condensation of the first reactant and the second reactant is reduced, the loss of the first reactant and the second reactant can be reduced, and the deposition of the first reactant and the second reactant on the exposed metal surface is more uniform, which is conducive to obtaining a denser protective layer 35.

[0183] After a period of reaction, a protective layer 35 may be formed on the metal surface. In step 220, the protective layer 35 may be formed on the end surface of the electrode piece, the exposed metal surface of the electrode tab 331, the exposed metal surface of the end cap assembly 32, and the exposed metal surface at the connection between the end cap assembly 32 and the electrode assembly 33.

[0184] In step 230 , the electrode assembly 33 provided with the protective layer 35 is taken out from the container and placed into the housing 31 to obtain a battery cell 3 .

[0185] After generating a protective layer 35 having a certain thickness, the container can be cooled, and the electrode assembly 33 provided with the protective layer 35 and connected to the end cover assembly 32 can be taken out, and then the electrode assembly 33 can be placed in the shell 31, and the end cover assembly 32 can be connected to the shell 31 to obtain the battery cell 3.

[0186] In this embodiment, the first and second reactants react on the exposed metal surfaces of the electrode assembly 33, forming a protective layer 35 on the exposed metal surfaces. Protective layer 35 comprises silicon oxide. This reduces the risk of short circuits caused by the exposed metal in the electrode assembly 33 colliding with electrodes of opposite polarity, thereby improving the reliability of the battery cell 3. The temperature difference between the first and second reactants and the temperature of the container is less than or equal to 4°C. This reduces the risk of condensation and loss of the first and second reactants. The first and second reactants are deposited more evenly on the exposed metal surfaces, facilitating the formation of a denser protective layer, further reducing the risk of short circuits. The electrode assembly 33, equipped with protective layer 35, is removed from the container and placed within the housing 31, facilitating assembly of the battery cell 3. Furthermore, since the housing 31 is not placed within the container, the protective layer 35 is not formed within the housing, minimizing the adverse effects of the protective layer 35 on the battery cell. Therefore, the battery cell 3 obtained with this technical solution exhibits superior overall performance.

[0187] In some embodiments, the first reactant includes trimethylaluminum and the second reactant includes water vapor.

[0188] As an example, during the preparation of battery cells, the process can be carried out in a factory with a high level of protection. As another example, a container is placed under vacuum conditions to carry out the reaction between trimethylaluminum and water vapor.

[0189] In some embodiments, the first reactant includes a gaseous silicon compound, the gaseous silicon compound includes gaseous silane, and the general formula of silane satisfies: R'-Si(OR) n , wherein R' includes an organic or inorganic functional group, R includes an alkyl group, and n is an integer and 2≤n≤4.

[0190] n may be 2, 3 or 4; R includes an alkyl group, for example, R may be a methyl group or an ethyl group; R' includes an organic or inorganic functional group, for example, R' may include an amino group or a methyl group. As an example, n is 3.

[0191] In silane, the -(OR) group is a hydrolyzable group, which facilitates the hydrolysis of silane to produce -Si-OH groups. The end surface of the electrode and at least part of the surface of the electrode tab 331 have exposed metal. The -Si-OH groups can combine with the metal and the -Si-OH groups and -Si-OH groups can cross-link on the metal surface to form a protective layer 35. The reaction between silane and water vapor on the metal surface can be roughly divided into the following three steps.

[0192] (1) Silane hydrolysis: -Si-OR + H2O → -Si-OH + ROH;

[0193] (2) Adsorption on metal surface: -Si-OH+Me-OH→Me-O-Si-+H2O, where Me represents metal;

[0194] (3) Cross-linking to form a protective layer: -Si-OH+HO-Si-→-Si-O-Si-+H2O.

[0195] On the one hand, after hydrolysis, silane is adsorbed on the metal surface through the reaction between its -Si-OH group and the Me-OH group on the metal surface. Silane forms Si-O-Me on the metal interface. The covalent bond between Si-O and Me is strong, and the bond between silane and metal is relatively firm. On the other hand, the remaining silane molecules form a protective layer with a three-dimensional network structure on the metal surface through the condensation reaction between the -Si-OH groups.

[0196] Before introducing gaseous silane into the container, the silane may be vaporized outside the container (eg, in an additional storage tank); similarly, before introducing water vapor into the container, the water may be vaporized outside the container.

[0197] By introducing gaseous silane and water vapor into the container, the mixing of silane and water vapor is facilitated, thereby facilitating the reaction.

[0198] In the step of introducing the first reactant and the second reactant into the container, gaseous silane may be introduced first and then water vapor; water vapor may be introduced first and then gaseous silane; or gaseous silane and water vapor may be introduced simultaneously.

[0199] As an example, silane and water vapor are stored in different storage tanks, and valves are provided between the storage tanks and the container. The valve of the storage tank storing silane is first opened to introduce gaseous silane into the container, and then the valve of the storage tank storing water vapor is opened to introduce water vapor into the container.

[0200] Silane has high reliability and the risk of explosion in the container is very low. By adding silane to the container, the reliability of the battery cell preparation method is higher; and the requirements for the conditions in the container are lower, which is conducive to reducing the complexity of the preparation method.

[0201] In addition, the first reactant is gaseous silane, which does not require vacuuming of the container. This can reduce the complexity of the operation and is also beneficial for reducing the risk of silane and the like penetrating or adsorbing into the active material layer of the electrode assembly 33, thereby reducing the adverse effects on the cycle performance of the battery cell 3.

[0202] In some embodiments, gaseous silane and water vapor can be introduced directly into the container, and the temperature in the container can be adjusted to the temperature at which the silane vaporizes to reduce the temperature difference between the gaseous silane and water vapor and the container. For example, a silane with a lower vaporization temperature can be selected.

[0203] In some embodiments, the first reactant and the second reactant are introduced into the container, including: heating silane to a first temperature T1, and introducing a carrier gas into a storage tank storing silane to obtain gaseous silane; heating water to a second temperature T2, and introducing a carrier gas into a storage tank storing water to obtain water vapor; and introducing gaseous silane and water vapor mixed with a carrier gas into the container to obtain an electrode assembly provided with a protective layer.

[0204] Silane is heated to a temperature T1 and a carrier gas is introduced into a storage tank containing the silane to convert the silane into a gaseous state. This is advantageous for converting the silane into a gaseous state at a relatively low temperature.

[0205] The water is heated to a second temperature T2, and a carrier gas is introduced into the storage tank storing the water, so that the water can be converted into water vapor. This is conducive to converting the water into water vapor at a lower temperature.

[0206] Temperature T1 can be lower than or equal to the vaporization temperature of silane. When temperature T1 is lower than the vaporization temperature of silane, the introduction of a carrier gas facilitates vaporization of the silane at a lower temperature. When temperature T1 is equal to the vaporization temperature of silane, the carrier gas facilitates the introduction of the silane into the container. Similarly, temperature T2 can be lower than or equal to the vaporization temperature of water.

[0207] As an example, the temperature T1 is lower than the vaporization temperature of silane, and the temperature T2 is lower than the vaporization temperature of water.

[0208] In the above embodiment, by introducing a carrier gas into a storage tank storing silane and water, gaseous silane and water vapor can be obtained at a lower temperature. When the difference between the temperature of the gaseous silane and water vapor and the temperature of the container satisfies a certain range, the container can have a lower temperature, thereby reducing the risk of the container's excessive temperature adversely affecting the electrode assembly (for example, the isolation membrane in the electrode assembly).

[0209] In some embodiments, the first temperature T1 satisfies: 60°C≤T1≤100°C; and / or, the second temperature T2 satisfies: 60°C≤T2≤100°C; and / or, the temperature T3 of the container satisfies: 60°C≤T3≤100°C.

[0210] T1 can be 60°C, 80°C, 100°C or any value within the above range, T2 can be 60°C, 80°C, 100°C or any value within the above range, and T3 can be 60°C, 80°C, 100°C or any value within the above range.

[0211] The temperature T3 of the container may refer to the temperature inside the container, and the electrode assembly placed in the container may have the same temperature as the container.

[0212] By setting T1, T2, and T3 to meet the above-mentioned temperatures, it is convenient to convert silane and water into gaseous silane and water vapor, and the container can have a lower temperature, thereby reducing the adverse effects of excessive temperature in the container on the isolation membrane in the electrode assembly 33.

[0213] In some embodiments, the first temperature T1, the second temperature T2, and the temperature T3 of the container are the same, which can further reduce the risk of condensation of gaseous silane and water vapor, thereby facilitating the formation of a denser protective layer.

[0214] As an example, the first temperature T1 is 60°C, the second temperature T2 is 60°C, and the temperature T3 of the container is 60°C.

[0215] As an example, after the electrode assembly 33 connected to the end cap assembly 32 is placed in a container, the container is heated to a temperature T3.

[0216] In some embodiments, the flow rate of the gaseous silane is less than or equal to the flow rate of the water vapor, which is beneficial to the reaction between the silane and the water molecules and also helps to reduce the waste of silane.

[0217] For example, when both a carrier gas and water vapor are introduced into a container, the water vapor introduction rate refers to the rate at which the mixed gas of water vapor and carrier gas is introduced into the container. For example, when only water vapor is introduced into the container, the water vapor introduction rate refers to the rate at which the water vapor is introduced into the container.

[0218] In the case where a carrier gas and gaseous silane are introduced into the container simultaneously, the flow rate of the gaseous silane refers to the rate at which the mixed gas of gaseous silane and carrier gas is introduced into the container. In the case where only gaseous silane is introduced into the container, the flow rate of the gaseous silane refers to the rate at which the gaseous silane is introduced into the container.

[0219] In some embodiments, the flow rate Q1 of the gaseous silane satisfies: 0.05 L / min≤Q1≤1 L / min.

[0220] In some embodiments, the water vapor flow rate Q2 satisfies: 0.1 L / min≤Q2≤2 L / min.

[0221] Q1 can be 0.05 L / min, 0.5 L / min, 1 L / min or any value within the above range, and Q2 can be 0.1 L / min, 1 L / min, 2 L / min or any value within the above range.

[0222] By setting Q1 and Q2 to meet the above range, gaseous silane and water vapor enter the container at a more appropriate rate, which facilitates the reaction of gaseous silane and water vapor on the metal surface and the formation of the protective layer 35; at the same time, it is also beneficial to reduce the risk of silane penetrating into the exposed metal position of the electrode assembly.

[0223] In some embodiments, the silane has a boiling point less than or equal to 200°C.

[0224] In this way, silane can be converted into gaseous silane at a temperature of 200°C or below, which is beneficial for saving energy. In addition, the temperature of the container can also be set at a temperature of 200°C or below, which is beneficial for the reaction between silane and water molecules to proceed at a lower temperature.

[0225] In some embodiments, the silane includes at least one of (H5C2O)3Si-CH2CH2-Si(OC2H5)3, (H5C2O)3Si-(CH2)3-NH-(CH2)3-Si(OC2H5)3, (H5C2O)3Si-(CH2)3-S4-(CH2)3-Si(OC2H5)3, (H5C2O)3Si-(CH2)3-NH-CO-NH2, CHOCHCH2-O-(CH2)3-Si(OCH3)3, or CH3-Si(OCH3)3. Using the above-mentioned silane facilitates the hydrolysis of the silane.

[0226] As an example, silane includes (H5C2O)3Si-CH2CH2-Si(OC2H5)3.

[0227] As an example, the silane is CH3-Si(OCH3)3. This helps reduce steric hindrance, facilitates cross-linking between -Si-OH groups, facilitates the formation of the protective layer 35, and helps reduce the temperature or time required to prepare the protective layer 35, thereby helping to reduce the risk of excessive silane penetration into the electrode.

[0228] In some embodiments, the reaction time t1 of the gaseous silane and water vapor satisfies: 4h≤t1≤12h.

[0229] t1 can be 4h, 8h, 10h, 12h or any value within the above range.

[0230] The reaction time t1 may refer to the duration of the passage of gaseous silane and water vapor into the container.

[0231] By setting t1 to meet the above range, a protective layer 35 with a certain thickness can be generated in a shorter time, and the risk of excessive deposition of silane at non-exposed metal locations of the electrode assembly (for example, locations where the active material layer is provided) due to excessive reaction time can be reduced.

[0232] The preparation conditions of the protective layer 35 are related to the thickness, shear strength, and density of the protective layer 35. For example, the time and temperature for preparing the protective layer 35 are low. In a shorter time and at a lower temperature, a protective layer 35 with a suitable thickness and shear strength can be prepared at the exposed metal position of the electrode. Moreover, in a shorter time and at a lower temperature, the risk of silane penetrating into the non-exposed metal position of the electrode is lower, and the probability of the protective layer 35 being formed at the non-exposed metal position is lower, thereby reducing the impact on the electrical performance of the battery cell (such as cycle performance and power). When the temperature difference between the first reactant, the second reactant, and the container is small, the risk of condensation of the first reactant and the second reactant is lower, which is conducive to the first reactant and the second reactant being deposited more and more evenly on the exposed metal surface of the electrode assembly, and is conducive to the preparation of a denser protective layer 35 with a higher minimum resistance. By reasonably setting the reaction time, temperature, and the temperature difference between the first reactant, the second reactant, and the container, it is conducive to preparing a protective layer 35 with a suitable thickness and shear strength, and the battery still has good electrical performance.

[0233] In some embodiments, the pressure P within the container satisfies the following: 0.09 MPa ≤ P ≤ 0.11 MPa. This allows the protective layer 35 to be formed at atmospheric pressure, reducing fabrication complexity. Furthermore, compared to vacuum conditions within the container, this reduces the risk of silane, etc., penetrating into the active material layer of the electrode assembly 33 and other locations.

[0234] In some embodiments, the container is in communication with the external environment. That is, during the reaction of silane and water molecules, the container is in communication with the external environment, so that a relatively stable pressure is maintained in the container.

[0235] In some embodiments, the carrier gas includes at least one of nitrogen, argon, carbon dioxide, and helium; alternatively, the carrier gas includes nitrogen. The carrier gas does not react with silane and water vapor, thereby reducing adverse effects on the reaction of silane and water vapor.

[0236] Figure 7 is a schematic diagram of an electrode assembly connected to an end cap assembly according to one embodiment of the present application, and Figure 8 is a schematic diagram of a bracket equipped with the electrode assembly. In Figure 7, the end cap assembly 32 is located below the electrode assembly 33 (the end cap assembly is not shown in Figure 7), and the tab 331 of the electrode assembly 33 is connected to the end cap assembly 32 via a current collecting member 34.

[0237] In some embodiments, for example, as shown in Figures 7 and 8, step 210 includes: placing multiple electrode assemblies 33 connected to end cap assemblies 32 in a holder 2, with the holder 2 covering the largest surface area of ​​the electrode assemblies 33; and placing the holder 2 loaded with the multiple electrode assemblies 33 in a container. This allows the component formed by the connection of the multiple electrode assemblies 33 and the end cap assemblies 32 to be processed in the container, which helps improve production efficiency. In addition, the holder 2 covering the largest surface area of ​​the electrode assemblies 33 also helps reduce the risk of silane and other substances entering the interior of the electrode assemblies 33.

[0238] FIG9 is a schematic diagram of silane and water vapor deposition according to an embodiment of the present application. As shown in FIG8 and FIG9 , after the gaseous silane and water vapor enter the container, the silane and water vapor can be deposited on the surfaces of the electrode assembly 33 and the end cap assembly 32 along a first direction (the direction in which the tab 331 protrudes from the main body 330), such as the direction indicated by arrows CC in FIG8 and FIG9 . By controlling the conditions of the battery cell preparation method, the risk of silane deposition on non-exposed metal portions of the electrode assembly 33 (e.g., portions where active material is disposed) can be reduced, thereby reducing the adverse effects on the cycling performance of the battery cell.

[0239] In some embodiments, the electrode assembly 33 is not subjected to plasma surface treatment (PLASMA) before step 210. This saves the step of plasma surface treatment, reduces process complexity, and saves costs.

[0240] In some embodiments, step 210 includes connecting the electrode assembly 33 to the end cap assembly 32 and placing the electrode assembly 33 connected to the end cap assembly 32 in a container. Thus, the electrode assembly 33 and the end cap assembly 32 are connected as a whole and then processed, which facilitates the preparation of the protective layer 35 at the connection between the electrode assembly 33 and the end cap assembly 32.

[0241] In some embodiments, the preparation method 200 further includes: before introducing the gaseous silane and water vapor into the container, introducing an inert gas into the container to evacuate the air from the container, thereby reducing the adverse effects of air on the reaction between the silane and water vapor.

[0242] As an example, the inert gas introduced into the container has a relatively high temperature. In this way, the container and the electrode assembly can be quickly heated by the inert gas having a relatively high temperature.

[0243] In some embodiments, the time t3 for introducing the inert gas satisfies the following conditions: 5 min ≤ t3 ≤ 30 min; and / or the inert gas introduction flow rate V2 satisfies the following conditions: 0.1 L / min ≤ V2 ≤ 2 L / min. This allows the air in the container to be discharged more quickly and efficiently.

[0244] The gas introduced can be nitrogen, helium, argon and other gases.

[0245] The time t3 can be 5 min, 10 min, 30 min or any value within the above range, and the flow rate V2 can be 0.1 L / min, 1 L / min, 2 L / min or any value within the above range.

[0246] Figure 10 is a schematic diagram of an apparatus for preparing a protective layer according to an embodiment of the present application. For example, as shown in Figure 10, apparatus 1 may include a container 100, a first storage tank 101, a second storage tank 102, a third storage tank 103, and a fourth storage tank 104. Each of the first storage tank 101, the second storage tank 102, and the third storage tank 103 is provided with a flow rate regulating valve 110 and is in communication with the container 100. The container 100 is used to accommodate the electrode assembly 33 connected to the end cap assembly 32. The first storage tank 101 is used to store silane, the second storage tank 102 is used to store water, the third storage tank 103 is used to store inert gas, and the fourth storage tank 104 is used to store carrier gas.

[0247] During the preparation of the protective layer, the inert gas in the third storage tank 103 can be first introduced into the container 100 to expel the air in the container 100; then, the silane in the first storage tank 101 and the water in the second storage tank 102 are heated, and the carrier gas in the fourth storage tank 104 is introduced into the first storage tank 101 and the second storage tank 102 respectively to obtain gaseous silane and water vapor; then, the gaseous silane and water vapor are introduced into the container 100.

[0248] [Battery]

[0249] The present invention provides a battery comprising the battery cell 3 of the above embodiment. Figure 11 is a schematic diagram of a battery according to an embodiment of the present invention. As shown in Figure 11, the battery 5 may comprise a plurality of battery cells (not shown).

[0250] The battery cells 3 can be directly assembled into the battery 5 , or they can be assembled into battery modules first, and then multiple battery modules can be assembled into the battery 5 .

[0251] [Electrical devices]

[0252] An embodiment of the present application provides an electrical device, comprising the battery described in the above embodiment.

[0253] Figure 12 is a schematic diagram of an electric device according to an embodiment of the present application. As shown in Figure 12, the present application provides an electric device 6, which includes the battery according to the above embodiment.

[0254] Optionally, the electrical device may also be an energy storage device, a lighting device, a spacecraft, etc., and the embodiments of the present application include but are not limited to the above.

[0255] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0256] [Example of a method for producing a battery cell]

[0257] Example 1

[0258] (1) LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black, and binder polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent in a weight ratio of 93:2:5 to form a uniform positive electrode slurry; the positive electrode slurry is coated on a 12μm thick aluminum foil, and after drying, rolling, slitting, die-cutting and other processes, the positive electrode sheet is obtained.

[0259] (2) The negative electrode active material graphite, conductive carbon black, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber latex (SBR) are fully stirred and mixed in an appropriate amount of deionized water at a weight ratio of 96.5:1.0:1.0:1.5 to form a uniform negative electrode slurry; the negative electrode slurry is coated on an 8 μm thick copper foil, and after drying and other processes, a negative electrode sheet is obtained.

[0260] (3) The positive electrode sheet, the separator (9 μm thick PE film), and the negative electrode sheet are stacked in sequence and then wound to obtain an electrode assembly. The electrode assembly itself has an aluminum positive electrode tab and a copper negative electrode tab. The positive and negative electrode tabs are welded to the aluminum positive electrode adapter and the copper negative electrode adapter, respectively. Then, the positive and negative electrode adapters are welded to the positive and negative electrode posts of the end cover assembly, respectively, to obtain a battery component including the electrode assembly and the end cover assembly.

[0261] (4) Place the battery components in a container, heat the container to a temperature T3 of 60°C, and introduce nitrogen as a protective gas into the container at a flow rate of 1 L / min for 2 minutes to exhaust the air in the container.

[0262] (5) Silane (H5C2O)3Si-CH2CH2-Si(OC2H5)3 is heated to a first temperature T1, T1 is 60°C, and nitrogen is introduced into the storage tank storing the silane to obtain gaseous silane; gaseous silane is introduced into the container at a flow rate Q1 of 0.05 L / min.

[0263] (6) The water is heated to a second temperature T2, T2 being 60° C., and nitrogen is introduced into the storage tank containing the water to obtain water vapor; water vapor is introduced into the container at a flow rate Q2 of 0.1 L / min; and the total reaction time t1 is controlled to be 12 h.

[0264] (7) After the reaction time is reached, the introduction of gaseous silane and water vapor is stopped and the container is cooled; thereafter, the components consisting of the electrode assembly and the end cap assembly are removed from the container and welded to the shell to assemble the battery cell.

[0265] In Example 1, T0 is 0°C.

[0266] Example 2-3

[0267] The difference between Example 2-3 and Example 1 is that T0 is 2°C and 4°C.

[0268] Examples 4-5

[0269] The difference between Example 4-5 and Example 1 is that the temperature T1 of the gaseous silane and the temperature T2 of the water vapor are different.

[0270] Examples 6-7

[0271] The difference between Example 6-7 and Example 1 is that the reaction time t1 of gaseous silane and water vapor is different.

[0272] Examples 8-9

[0273] The difference between Example 8-9 and Example 1 is that the flow rate Q1 of the gaseous silane introduced into the container and the flow rate Q2 of the water vapor introduced into the container are different.

[0274] Examples 10-11

[0275] The difference between Example 10-11 and Example 1 is that the types of silane are different.

[0276] Example 12

[0277] The difference between Example 12 and Example 1 is that the first reactant is trimethylaluminum. It should be noted that, in order to further improve the reliability and safety of the method, the container was vacuumed before the reaction, and the flow rates of the first and second reactants into the container were appropriately adjusted. The specific parameters can be found in Table 1.

[0278] When the first reactant is trimethylaluminum, the container may not be vacuumed. In this case, production needs to be carried out in a workshop with a higher level of protection.

[0279] Comparative Example 1

[0280] The difference between Comparative Example 1 and Example 1 is that the temperature difference between the gaseous silane and water vapor and the container is greater than 4°C.

[0281] [Example of battery cell]

[0282] Examples 1-12 of the battery cell can be prepared from Examples 1-12 of the battery cell preparation method, respectively. Comparative Example 1 of the battery cell can be prepared from Comparative Example 1 of the battery cell preparation method.

[0283] Table 1 Parameters of Examples and Comparative Examples of the Preparation Method of Battery Cells

[0284] Table 2 Comparative Examples and Examples of Battery Cells

[0285] Table 3 Experimental results of battery cell examples and comparative examples

[0286] [Test of the thickness of the protective layer]

[0287] The electrode assembly is disassembled, and the thickness of the protective layer at the first end surface 3301a, the second end surface 3301b, and the tab 331 of the positive electrode is observed using a scanning electron microscope (eg, ZEISS sigma 300).

[0288] [Composition of protective layer]

[0289] Energy-dispersive X-ray spectroscopy (EDS) on a ZEISS sigma 300 was used to analyze the surface of the relevant area. The instrument's data revealed the distribution of each element, and thus the mass percentage of Si.

[0290] As an example, a sample is taken in the direction where the active material layer is provided at the second end surface 3301b (for example, as shown in FIG2 , a sample is taken along the y direction at the second end surface 3301b), and an area of ​​10 mm × 10 mm is cut out to obtain a sample. The sample is placed in a testing device for elemental testing, and the quantitative analysis is performed by microbeam analysis energy spectrum method according to GB-T17359-2012. The proportions of C, Ni, Co, Mn, O, and Si elements (when the active material in the electrode is a ternary material) or the proportions of C, Fe, O, and Si (when the active material in the electrode is lithium iron phosphate) can be measured. Among them, to test the Si content at a position 5 mm away from the second end surface 3301b, the ruler in the equipment can be used to locate the point 5 mm away from the second end surface 3301b, and the Si content at this point can be tested.

[0291] It should be noted that, when an insulating layer is provided on the surface of the main body of the electrode piece, it is necessary to avoid the area of ​​the insulating layer during sampling.

[0292] [Shear strength test]

[0293] A tab with a protective layer is used as a test sample. Double-sided tape is used to adhere the sample to a stainless steel plate. The sample's length extends beyond the plate by a certain distance. The tensile testing machine clamps the end of the sample that extends beyond the plate and pulls upward until the sample detaches from the plate. For example, a 15mm-long strip of double-sided tape is used to adhere the sample to the plate. At the end of the test, a 9mm x 9mm area of ​​the sample corresponding to the tape detaches from the plate.

[0294] Shear strength is calculated based on the tensile testing machine's measurement results: Shear strength = shear force / bond area. In the example above, the bond area is 9 mm x 9 mm.

[0295] It should be noted that in the embodiment of the present application, the bonding strength between the protective layer and the electrode assembly is relatively large. Therefore, what is tested is the strength when a specific area of ​​the sample to be tested is detached from the stainless steel plate (that is, the strength when the entire area of ​​9mm×9mm is detached from the stainless steel plate), rather than the strength when any area of ​​the test sample is detached from the stainless steel plate (that is, not the strength when any position within the 15mm length is detached from the stainless steel plate).

[0296] After soaking the electrode assembly in the electrolyte at 60°C for 7 days, the electrode assembly was disassembled and the shear strength of the positive electrode tab with the protective layer was tested again. It should be noted that during the soaking of the electrode assembly in the electrolyte at 60°C, the shear strength was tested every other day. The shear strength obtained on the 7th day showed a gradual trend (i.e., the shear strength did not decrease or decreased slightly after the 7th day). The shear strength on the 7th day reflects the durability of the protective layer.

[0297] [Cycling performance test]

[0298] Battery cells were charged and discharged at 25°C. A single charge and discharge cycle involved the following steps: 1C constant-current charging to 4.25V, followed by constant-voltage charging until the current fell below 0.05C, followed by a 30-minute pause, followed by 1C constant-current discharge to 2.5V, followed by a 30-minute pause.

[0299] After one charge and discharge cycle, the discharge capacity of the battery cell is recorded. This is the first discharge capacity.

[0300] After 500 charge and discharge cycles, the discharge capacity after 500 cycles was recorded. The capacity retention rate after 500 cycles = discharge capacity after 500 cycles / initial discharge capacity.

[0301] [Test of resistance and density of protective layer]

[0302] Use an AC voltmeter to test the resistance of the protective layer. As an example, in the test sample, only the end surface is provided with a protective layer, and the position of the pole ear is specially treated without a protective layer. The test sample is used to test the resistance of the protective layer. Specifically, one end of the pole ear is connected to one end of the AC voltmeter, and the end surface of the main body is connected to the other end of the AC voltmeter through a conductive metal rod. The AC voltmeter and the end surface provided with the protective layer form a loop, so that the resistance of the protective layer can be measured. It should be noted that the resistance of the current collector of the pole piece itself is very small (for example, generally a few milliohms), and the resistance measured by the AC voltmeter can be approximately considered to be the resistance of the protective layer.

[0303] During the resistance test, it can be considered that the resistance of the protective layer at a specific location is being tested. As an example, during the resistance test of the end surface, 30 locations on the end surface are tested for resistance, and the minimum resistance value is recorded as the minimum resistance. Specifically, areas of a certain size can be cut out at 30 locations on the end surface of the electrode, and resistance tests are performed on each of the 30 cutout samples, with the minimum resistance value of the 30 measured resistances being recorded as the minimum resistance.

[0304] Different locations of the electrode assembly with a protective layer were placed in contact with the anode of a fully charged battery, and the probability of fire was recorded. Specifically, the electrode assembly with the protective layer was fabricated into a battery and fully charged to 100% SOC. After full charge, the battery was disassembled and the location with the protective layer was placed in direct contact with the negative electrode active material area, and the probability of fire was recorded. Full charge refers to charging the battery to 100% SOC using a certain current, for example, charging a lithium iron phosphate battery to 3.65V and a ternary material battery to 4.3V.

[0305] As an example, during a fire test, the same battery is tested at 10 different locations, a total of 10 times, and the probability of fire is recorded. After testing one location, if a fire occurs, it can be extinguished with fire extinguishing sand. Then, a fire test can be performed again at a different location.

[0306] The fire test can be understood as a test of the "line" on the end surface or the tab. Compared with using EDS and other means to observe whether the target element (for example, Si element) is present at this location, the fire test is more sensitive and more stringent. In addition, it should be noted that in the actual process, the overlap of aluminum and the fully charged anode, and the subsequent short circuit and fire are a relatively dangerous failure mode. Therefore, by setting a corresponding protective layer, the probability of battery fire can be reduced.

[0307] In the embodiments and comparative examples of the preparation method of the battery monomer, combined with Examples 1-12 and Comparative Example 1, compared with Comparative Example 1, by controlling the temperature difference between the gaseous silane and water vapor and the container is less than or equal to 4°C, the prepared protective layer is denser and the resistance of the protective layer is greater, and the risk of fire, short circuit, etc. occurring after the electrode tab provided with the protective layer is overlapped with the fully charged anode is reduced.

[0308] Combined with the examples 1-12 of the present application, in the battery cells prepared by the preparation method of the embodiments of the present application, the risk of silicon oxide or silicon in silane existing at the non-exposed metal position of the electrode assembly is lower, and the battery cells still have a high capacity retention rate. In addition, the protective layer has approximately the same thickness at different positions. However, due to factors such as the deposition direction of the first reactant and the second reactant, the thickness of the protective layer at the tab position is slightly greater than the thickness of the protective layer at the first end surface position and the second end surface position.

[0309] As shown in Examples 1-11 and Comparative Example 1, the preparation method of the embodiments of the present application is simpler, and an electrode assembly provided with a protective layer can be obtained without vacuuming. As shown in Examples 1 and 12, compared with the use of trimethylaluminum and water vapor for reaction, the use of silane and water vapor for reaction is beneficial to reducing the complexity of preparing battery cells, does not require a higher level of protection, and does not require special treatment of the reaction container. In addition, compared to Example 12, the mass content of the Si element at a position 5 mm from the end face in Examples 1-11 is less than 0.01% (it can be considered that there is no Si element), while the mass content of the Al element in the alumina at a position 5 mm from the end face in Example 12 is about 5%.

[0310] As shown in Examples 1-12, the shear strength of the protective layer is within the range of 120 MPa to 250 MPa. Even after being immersed in electrolyte, the protective layer still maintains a shear strength exceeding 100 MPa. The risk of the protective layer detaching from the electrode sheet is low, and battery cells fabricated using electrode sheets equipped with the protective layer are suitable for use as driving power sources for electric vehicles. Furthermore, the shear strength of the protective layer is within the range of 135 MPa to 220 MPa, indicating a suitable thickness for the protective layer. Furthermore, the protective layer can be produced at relatively low container temperatures.

[0311] As shown in Examples 2-3, reducing the temperature difference between the gaseous silane and water vapor and the container is conducive to preparing a denser, thicker and more resistive protective layer.

[0312] In combination with Examples 1-5, by setting the temperature T3 of the container, the temperature T1 of the gaseous silane, and the temperature T2 of the water vapor within the range of 60°C to 100°C, a protective layer of corresponding thickness can be generated, and the risk of the container temperature being too high and affecting the isolation membrane in the electrode assembly can be reduced.

[0313] As shown in Examples 6-7, the reaction time between silane and water vapor is correlated with the thickness of the protective layer. Setting the reaction time t1 between 4 and 12 hours can produce a protective layer of suitable thickness. Furthermore, setting the reaction time t1 between 4 and 8 hours can produce a protective layer of suitable thickness in a shorter time, thereby reducing the risk of silane and other substances penetrating into the active material.

[0314] As shown in Examples 8-9, by controlling the flow rates of the gaseous silane and water vapor entering the container, the silane and water vapor are fully mixed and reacted.

[0315] As shown in Examples 10-11, the preparation method of the present invention is also applicable to a variety of hydrolyzable silanes. Different silanes have different boiling points. Therefore, at the same temperature, the thickness of the protective layer produced by using different silanes will be slightly different.

[0316] It should be noted that the above embodiments and comparative examples are described using a positive electrode sheet whose current collector is aluminum foil. The embodiments of the present application can also be applied to positive electrode sheets and negative electrode sheets whose current collectors are made of other materials.

[0317] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A pole piece, characterized in that: A protective layer is provided on at least the end surface of the pole piece. The protective layer comprises aluminum oxide or silicon oxide. The minimum resistance R of the protective layer satisfies: R≥25Ω.

2. The pole piece according to claim 1, characterized in that: The protective layer includes silicon oxide.

3. The pole piece according to claim 1 or 2, characterized in that: The thickness d1 of the protective layer satisfies: 26 nm ≤ d1 ≤ 200 nm.

4. The pole piece according to claim 3, characterized in that: The thickness d1 of the protective layer satisfies: 120nm≤d1≤198nm.

5. The pole piece according to any one of claims 1 to 4, characterized in that: The minimum resistance R of the protective layer satisfies: 26Ω≤R≤372Ω.

6. The pole piece according to claim 5, characterized in that: The minimum resistance R of the protective layer satisfies: 220Ω≤R≤372Ω.

7. The pole piece according to any one of claims 1 to 6, characterized in that: The shear strength G of the protective layer satisfies: 120 MPa≤G≤250 MPa.

8. The pole piece according to claim 7, characterized in that: The shear strength G of the protective layer satisfies: 135 MPa≤G≤220 MPa.

9. The pole piece according to any one of claims 2 to 8, characterized in that: Based on the total mass of all elements at the first position of the pole piece, the mass content A of the Si element satisfies: A<0.01wt%, and the first position is a position 5 mm away from the end surface.

10. The pole piece according to any one of claims 1 to 9, characterized in that: The pole piece includes a main body and a pole tab, wherein the pole tab protrudes from the main body along a first direction, and the protective layer is provided on an end surface of the main body along the first direction and at least a portion of the pole tab.

11. The pole piece according to claim 10, characterized in that: The protective layer is provided on the end surface of the main body along a second direction, and the second direction is perpendicular to the first direction and parallel to the surface where the pole piece is located.

12. The pole piece according to any one of claims 1 to 11, characterized in that: The electrode sheet is a positive electrode sheet, and the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a layered transition metal oxide.

13. The pole piece according to claim 12, characterized in that: The layered transition metal oxide includes LiNi 0.8 Co 0.1 Mn 0.1 O2 or LiNi 0.6 Co 0.2 Mn 0.2 At least one of O2.

14. An electrode assembly, characterized in that: include: A pole piece as claimed in any one of claims 1 to 13.

15. A battery cell, characterized in that: include: The electrode assembly according to claim 14; A shell is used to accommodate the electrode assembly.

16. A method for preparing a battery cell, characterized in that: include: placing the electrode assembly in a container; A first reactant and a second reactant are introduced into the container to obtain an electrode assembly provided with a protective layer, wherein a difference T0 between the temperature of the first reactant and the second reactant and the temperature of the container satisfies: T0≤4°C, the first reactant comprises a gaseous aluminum compound or a gaseous silicon compound, and the second reactant comprises water vapor; The electrode assembly provided with the protective layer is taken out from the container and placed into a shell to obtain the battery cell.

17. The preparation method according to claim 16, characterized in that The first reactant includes the gaseous silicon compound, the gaseous silicon compound includes gaseous silane, and the general formula of the silane satisfies: R'-Si(OR) n , wherein R' includes an organic or inorganic functional group, R includes an alkyl group, and n is an integer and 2≤n≤4.

18. The preparation method according to claim 17, characterized in that: The step of introducing the first reactant and the second reactant into the container comprises: Heating silane to a first temperature T1 and introducing a carrier gas into a storage tank storing the silane to obtain the gaseous silane; heating water to a second temperature T2 and introducing the carrier gas into a storage tank storing the water to obtain the water vapor; The gaseous silane mixed with the carrier gas and the water vapor are introduced into the container to obtain an electrode assembly provided with the protective layer.

19. The preparation method according to claim 18, characterized in that The first temperature T1 satisfies: 60°C ≤ T1 ≤ 100°C; and / or, the second temperature T2 satisfies: 60°C ≤ T2 ≤ 100°C; and / or, the temperature T3 of the container satisfies: 60°C ≤ T3 ≤ 100°C.

20. The preparation method according to claim 18 or 19, characterized in that: The first temperature T1, the second temperature T2, and the temperature T3 of the container are the same.

21. The preparation method according to any one of claims 17 to 20, characterized in that: The inlet flow rate of the gaseous silane is less than or equal to the inlet flow rate of the water vapor.

22. The preparation method according to any one of claims 17 to 21, characterized in that The inlet flow rate Q1 of the gaseous silane satisfies: 0.05 L / min≤Q1≤1 L / min.

23. The preparation method according to any one of claims 17 to 22, characterized in that: The water vapor inlet flow rate Q2 satisfies: 0.1 L / min≤Q2≤2 L / min.

24. The preparation method according to any one of claims 17 to 23, characterized in that The boiling point of the silane is less than or equal to 200°C.

25. The preparation method according to any one of claims 17 to 24, characterized in that The silane includes at least one of (H5C2O)3Si-CH2CH2-Si(OC2H5)3, (H5C2O)3Si-(CH2)3-NH-(CH2)3-Si(OC2H5)3, (H5C2O)3Si-(CH2)3-S4-(CH2)3-Si(OC2H5)3, (H5C2O)3Si-(CH2)3-NH-CO-NH2, CH2OCHCH2-O-(CH2)3-Si(OCH3)3 or CH3-Si(OCH3)3.

26. The preparation method according to any one of claims 17 to 25, characterized in that The reaction time t1 of the gaseous silane and the water vapor satisfies: 4h≤t1≤12h.

27. The preparation method according to any one of claims 17 to 26, characterized in that The pressure P in the container satisfies: 0.09 MPa≤P≤0.11 MPa.

28. The preparation method according to any one of claims 17 to 27, characterized in that The container is in communication with the external environment.

29. The preparation method according to any one of claims 18 to 28, characterized in that The carrier gas includes at least one of nitrogen, argon, carbon dioxide or helium.

30. The preparation method according to any one of claims 16 to 29, characterized in that: Placing the electrode assembly in the container comprises: placing a plurality of the electrode assemblies in a bracket, wherein the bracket covers the largest surface of the electrode assembly; The rack loaded with the plurality of electrode assemblies is placed in the container.

31. The preparation method according to any one of claims 16 to 30, characterized in that Placing the electrode assembly in the container comprises: The electrode assembly is connected to an end cap assembly, and the electrode assembly connected with the end cap assembly is placed in the container.

32. The preparation method according to any one of claims 16 to 31, characterized in that The preparation method further comprises: Before the first reactant and the second reactant are introduced into the container, an inert gas is introduced into the container to exhaust the air in the container.

33. A battery, characterized in that: Including the battery cell according to claim 15; and / or, the battery cell obtained by the preparation method according to any one of claims 16-32.

34. An electrical device, characterized in that: Comprising a battery according to claim 33.

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