Electrode sheet, electrode assembly, battery cell and preparation method therefor, battery, and electric device

Abstract

An electrode sheet, an electrode assembly, a battery cell and a preparation method therefor, a battery, and an electric device, relating to the technical field of batteries. A protective layer is provided on at least the surface of an end portion of the electrode sheet, and the protective layer comprises silicon oxide; and on the basis of the total mass of all elements of a first position of the electrode sheet, the mass content A of an Si element satisfies: A is less than 0.01 wt%, and the first position is a position 5 mm distant from the surface of the end portion.

Description

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

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent document claims priority to and the benefit of Chinese patent application No. 202410269745.1, filed on March 8, 2024, entitled "Pole Sheet, Electrode Assembly, Battery Cell, Method for Making Same, Battery, and Electric Device." The entire contents of the aforementioned patent application are incorporated by reference into this patent document. 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 the reliability and cycle performance of the battery cell. Therefore, how to provide a pole piece that improves the reliability and cycle performance of the battery cell is a technical problem that needs to be solved urgently.

[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 and cycle performance 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 the end surface of the pole piece is provided with a protective layer, and the protective layer includes silicon oxide; 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 5mm away from the end surface.

[0010] In an embodiment of the present application, a protective layer is provided on at least the end surface of the pole piece, and the protective layer includes silicon oxide. In this way, the provision of the protective layer can reduce the risk of short circuit caused by the end surface overlapping with the electrode of opposite polarity, which is beneficial to improving the reliability of the battery cell. Based on the total mass of all elements in the first position of the pole piece, the mass content A of the Si element satisfies: A<0.01wt%. In this way, the first position of the pole piece contains almost no Si element, thereby reducing the adverse effect of the Si element on the cycle performance of the battery cell. Therefore, the technical solution of the embodiment of the present application is conducive to improving the reliability and cycle performance of the battery cell.

[0011] In a possible implementation, based on the total mass of all elements at the second position of the pole piece, the mass content B of the Si element satisfies: B≤0.05wt%, and the second position is 3 mm away from the end surface.

[0012] In a possible implementation, based on the total mass of all elements at the third position of the pole piece, the mass content C of the Si element satisfies: C≤1.2wt%, and the third position is a position 0.5 mm away from the end surface.

[0013] In the above technical solution, as the distance from the end surface decreases, the Si content gradually increases. In the above technical solution, the Si content at the second and third positions still has a small value, which can reduce the impact on the cycle performance of the battery cell.

[0014] In one possible implementation, based on the total mass of all elements on the end surface of the electrode piece, the mass content D of the Si element satisfies the following: 8wt%≤D≤35wt%; alternatively, 15wt%≤D≤30wt%. In this way, the end surface has a certain mass content of Si and a certain amount of silicon oxide, thereby reducing the risk of short circuits caused by the end surface of the electrode piece overlapping an electrode of opposite polarity.

[0015] In a possible implementation, the thickness d1 of the protective layer satisfies: 20 nm ≤ d1 ≤ 200 nm. In this way, the protective layer can have a certain shear strength while reducing other adverse effects caused by excessive thickness of the protective layer.

[0016] In one possible implementation, the thickness d1 of the protective layer satisfies the following conditions: 80 nm ≤ d1 ≤ 170 nm. When d1 is greater than or equal to 80 nm, the protective layer has a relatively suitable thickness, which can reduce the risk of short circuits. When d1 is less than or equal to 170 nm, the protective layer has a relatively small thickness, which can reduce the adverse effects of excessive protective layer thickness on the performance of the battery cell.

[0017] In one possible implementation, the shear strength G of the protective layer satisfies the following conditions: 70 MPa ≤ G ≤ 200 MPa. This ensures a strong bond between the protective layer and the electrode sheet, reducing the risk of the protective layer detaching from the electrode sheet and helping to reduce the time and temperature required to prepare the protective layer. Alternatively, 100 MPa ≤ G ≤ 150 MPa. This ensures a relatively suitable bond between the protective layer and the electrode sheet while also minimizing the adverse effects on the electrical performance of the battery cell caused by preparing a protective layer with higher shear strength.

[0018] 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.

[0019] 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.

[0020] In a possible implementation, the electrode sheet is a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a layered transition metal oxide.

[0021] In the above technical solution, the battery prepared by using the above positive electrode active material has a higher energy density, so that the battery can have both higher energy density and higher reliability.

[0022] 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.

[0023] In a second aspect, an electrode assembly is provided, comprising the electrode piece in the first aspect and any possible implementation thereof.

[0024] 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.

[0025] In a fourth aspect, a method for preparing a battery cell is provided, comprising: placing an electrode assembly in a container; introducing gaseous silane, water vapor, and a pH adjuster into the container to obtain an electrode assembly provided with a protective layer, wherein the protective layer comprises silicon oxide, and the silane has a general formula of: R'-Si(OR) n , wherein R' includes an organic or inorganic functional group, R includes an alkyl group, n is an integer and 2≤n≤4; the electrode assembly provided with the protective layer is taken out from the container and placed in a shell to obtain the battery cell.

[0026] In an embodiment of the present application, gaseous silane and water vapor react on the exposed metal surfaces of the electrode assembly, thereby forming a protective layer on the exposed metal surfaces of the electrode assembly. The protective layer includes silicon oxide. 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. By introducing a pH regulator into the container, the reaction between silane and water molecules can be promoted, which helps to improve the reaction efficiency between silane and water molecules, reduce the time the electrode assembly is placed in the container, and further reduce the adverse effects of Si element penetration into the active material area on the cycle performance of the battery cell. The electrode assembly with the protective layer is removed from the container and placed in the shell, thereby facilitating the assembly of the battery cell. In addition, since the shell is not placed in the container, no protective layer is formed inside the shell, thereby reducing the adverse effects of the protective layer on the battery cell. Therefore, the battery cell obtained by this technical solution has good reliability and cycle performance.

[0027] In one possible implementation, the pH adjuster includes an alkaline gas. The alkaline gas has a low risk of reacting with the positive electrode active material in the electrode assembly, such as residual alkali on the surface of the positive electrode active material, which is beneficial for reducing the adverse effect on the battery capacity.

[0028] In one possible implementation, the alkaline gas includes at least one of ammonia, phosphine, methylamine, dimethylamine, trimethylamine, or ethylamine. The pH adjuster, as an alkaline gas, has suitable alkalinity, which is beneficial to improving the reaction efficiency between silane and water molecules.

[0029] In one possible implementation, the pH adjuster includes acidic gas, which can promote the reaction between silane and water molecules, thereby improving the preparation efficiency of the protective layer.

[0030] In one possible implementation, the acidic gas includes at least one of hydrogen fluoride, hydrogen sulfide, hydrogen chloride, or sulfur dioxide. The acidic gas has suitable acidity, which is conducive to improving the reaction efficiency between silane and water molecules.

[0031] In one possible implementation, the temperature T of the container satisfies the following conditions: 45° C. ≤ T ≤ 120° C. When the temperature T is greater than or equal to 45° C., the temperature difference between the gaseous silane and the container is reduced. When the temperature T is less than or equal to 120° C., the adverse effects of excessive temperature inside the container on the separator of the electrode assembly can be reduced.

[0032] In a possible implementation, 60° C. ≤ T ≤ 100° C. This helps to further reduce the temperature difference between the gaseous silane in the container and facilitates the reaction between the silane and water molecules.

[0033] 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.

[0034] 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, CH2OCHCH2-O-(CH2)3-Si(OCH3)3, (CH3)2-Si(OCH3)2 or CH3-Si(OCH3)3; the silane uses the above substances to facilitate hydrolysis.

[0035] In one possible implementation, the silane includes (CH3)2-Si(OCH3)2, which has a low boiling point, making it easy to convert silane into gaseous silane; at the same time, the silane has low steric hindrance, which is conducive to the formation of silicon oxide.

[0036] In one possible implementation, the flow rate Q1 of the gaseous silane, the flow rate Q2 of the water vapor, and the flow rate Q3 of the pH adjuster satisfy the following relationship: Q2 ≥ Q1 > Q3. This facilitates the reaction between water molecules and silane while also saving silane usage.

[0037] In one possible implementation, the inlet flow rate Q1 of the gaseous silane satisfies: 0.5 L / min ≤ Q1 ≤ 1.5 L / min; and / or, the inlet flow rate Q2 of the water vapor satisfies: 1 L / min ≤ Q2 ≤ 2 L / min; and / or, the inlet flow rate Q3 of the pH adjuster satisfies: 0.1 L / min ≤ Q3 ≤ 1 L / min.

[0038] By setting the flow rates of gaseous silane, water vapor, and pH adjuster, gaseous silane, water vapor, and pH adjuster 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; in addition, it is also beneficial to reduce the risk of silane penetrating into the unexposed metal parts of the electrode assembly.

[0039] In one possible implementation, the reaction time t1 of the gaseous silane and the water vapor satisfies the following conditions: 2h ≤ t1 ≤ 8h; alternatively, 4h ≤ t1 ≤ 6h. This allows for the formation of a protective layer in a shorter time, reducing the risk of the protective layer forming on the active material layer of the electrode assembly due to prolonged reaction time, thereby mitigating adverse effects on the battery's electrical properties, such as cycling performance.

[0040] In one possible implementation, the pressure P within the container satisfies the following conditions: 0.09 MPa ≤ P ≤ 0.11 MPa. This allows the protective layer to be formed at atmospheric pressure, reducing manufacturing complexity and minimizing the risk of silane penetrating into unexposed metal areas of the electrode assembly, thereby reducing the impact on the cycling performance of the battery cells.

[0041] 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.

[0042] In one possible implementation, the preparation method further includes: introducing a carrier gas into a storage tank storing water to obtain the water vapor. In this way, the water vapor can be obtained by the carrier gas, thereby facilitating the introduction of the water vapor into the container.

[0043] In a possible implementation, the carrier gas flow rate Q4 satisfies: 0.9 L / min≤Q4≤2.2 L / min. This facilitates obtaining water vapor.

[0044] In one possible implementation, placing the electrode assemblies in the container includes placing multiple electrode assemblies in a rack, with the rack covering the largest surface area of ​​the electrode assemblies; and placing the rack containing the multiple electrode assemblies in the container. This allows multiple electrode assemblies to be processed in the container, improving production efficiency. Furthermore, the rack covering the largest surface area of ​​the electrode assemblies also reduces the risk of silane and other substances entering the interior of the electrode assemblies.

[0045] In one possible implementation, the preparation method 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. This can reduce the adverse effects of air on the reaction between the silane and water vapor.

[0046] 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.

[0047] 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.

[0048] In a sixth aspect, an electrical device is provided, comprising the battery described in the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] 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.

[0050] FIG1 is a schematic structural diagram of a pole piece before cutting the pole lugs according to an embodiment of the present application;

[0051] FIG2 is a schematic structural diagram of a pole piece after cutting the pole lugs according to an embodiment of the present application;

[0052] FIG3 is a cross-sectional view along the AA direction in FIG2 ;

[0053] FIG4 is a cross-sectional view along the BB direction in FIG2 ;

[0054] FIG5 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0055] FIG6 is a schematic diagram of a method for preparing a battery cell according to an embodiment of the present application;

[0056] FIG7 is a schematic diagram of an electrode assembly connected to an end cap assembly according to an embodiment of the present application;

[0057] FIG8 is a schematic diagram of a bracket provided with an electrode assembly;

[0058] FIG9 is a schematic diagram of silane and water vapor deposition according to an embodiment of the present application;

[0059] FIG10 is a schematic diagram of an apparatus for preparing a protective layer according to an embodiment of the present application;

[0060] FIG11 is a schematic diagram of a battery according to an embodiment of the present application;

[0061] FIG12 is a schematic diagram of an electrical device according to an embodiment of the present application. DETAILED DESCRIPTION

[0062] 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.

[0063] " 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.

[0064] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0065] 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.

[0066] 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.

[0067] The development of battery technology requires simultaneous consideration of multiple design factors, such as energy density, cycle life, discharge capacity, charge and discharge rate, and reliability. After cutting, the exposed metal of the electrode in the battery cell poses a risk of short circuiting due to contact with electrodes of opposite polarity or other components of the battery cell. In some treatment methods, a corresponding protective layer is provided at the exposed metal position of the electrode assembly to reduce the risk of short circuits and improve the reliability of the battery cell. However, the above treatment methods have a limited effect on improving the cycle performance of the battery cell.

[0068] 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 the Si content at a certain distance from the end surface is less than 0.01 wt%. This protective layer can reduce the risk of short circuits, and the Si content at a certain distance from the end surface is very low, thereby reducing the adverse effects of Si on the cycling performance of the battery cell. As a result, the battery cell of the present application has high reliability and cycling performance.

[0069] [Pole piece]

[0070] 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.

[0071] In an embodiment of the present application, for example, as shown in conjunction with 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.

[0072] 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).

[0073] 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 .

[0074] 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.

[0075] 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.

[0076] As an example, the end surface along the first direction and the end surface along the second direction are both provided with the protection layer 35 .

[0077] 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 .

[0078] 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.

[0079] The protective layer 35 includes silicon oxide, wherein the silicon oxide may have the following structure: -Si-O-Si-. The silicon oxide is not likely to swell when immersed in the electrolyte and is not likely to fall off during long-term use of the battery cell 3.

[0080] The protective layer 35 has certain insulating properties, which can reduce the risk of short circuit caused by the end surface overlapping with the electrode with opposite polarity, and is beneficial to improving the reliability of the battery cell.

[0081] 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 a position 5 mm away from the end surface.

[0082] The first position may be a position in the pole piece 1 that is 5 mm away from the end surface along any direction.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] In this embodiment of the present application, a protective layer 35 comprising silicon oxide is provided on at least the end surface of the pole piece 1. This protective layer 35 reduces the risk of short circuits in the battery cell, thereby improving the reliability of the battery cell. At the first position of the pole piece 1, the mass content A of the Si element satisfies the requirement: A < 0.01 wt%. This ensures that the battery cell exhibits high cycling performance. Therefore, the technical solutions of this embodiment of the present application are beneficial for improving the reliability and cycling performance of the battery cell.

[0090] In some embodiments, based on the total mass of all elements at the second position of the pole piece 1 , the mass content B of the Si element satisfies: B≤0.05wt%, and the second position is 3 mm away from the end surface.

[0091] In some embodiments, based on the total mass of all elements at the third position of the pole piece 1 , the mass content C of the Si element satisfies: C≤1.2 wt %, and the third position is 0.5 mm away from the end surface.

[0092] B may be 0.05wt%, 0.02wt%, 0.01wt%, 0wt% or any value within the above range, and C may be 1.2wt%, 1.1wt%, 1wt%, 0.5wt%, 0wt% or any value within the above range.

[0093] The second position may be a position 3 mm away from the end surface of the pole piece 1 in any direction; the third position may be a position 0.5 mm away from the end surface of the pole piece 1 in any direction.

[0094] As an example, the second position is a position that is 3 mm away from the second end surface 3301 b along the first direction, such as the y direction in FIG. 1 .

[0095] As an example, the third position is a position that is 0.5 mm away from the second end surface 3301 b along the first direction, such as the y direction in FIG. 1 .

[0096] In the above technical solution, the Si content gradually increases as the distance from the end surface decreases. In the above technical solution, the Si content at the second and third positions still has a relatively low value, which can reflect that the Si content in the unexposed metal portion of the electrode 1 is relatively low, thereby reducing the impact on the cycle performance of the battery cell.

[0097] In some embodiments, based on the total mass of all elements on the end surface of the pole piece, the mass content D of the Si element satisfies the following: 8 wt% ≤ D ≤ 35 wt%; alternatively, 15 wt% ≤ D ≤ 30 wt%. Thus, the end surface has a certain mass content of Si and a certain amount of silicon oxide, thereby reducing the risk of short circuits caused by the end surface of the pole piece 1 overlapping with an electrode of opposite polarity.

[0098] D can be 8 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, 35 wt% or any value within the above range.

[0099] In some embodiments, the thickness d1 of the protection layer 35 satisfies: 20 nm≤d1≤200 nm.

[0100] The thickness d1 of the protective layer 35 can be 190 nm, 160 nm, 100 nm, 50 nm, 20 nm, or any value within the foregoing range. The thickness d1 of the protective layer 35 can be the average thickness of the protective layer 35. For example, the thickness d1 can be measured at multiple locations on the end surface, and the average of the multiple data points can be used as the thickness at the end surface.

[0101] 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.

[0102] When d1 is greater than or equal to 20 nm, the protective layer 35 has a relatively suitable thickness, which can reduce the risk of short circuit, and the protective layer 35 has a certain shear strength, and the risk of falling off is low; when d1 is less than or equal to 200 nm, the adverse effect of the excessive thickness of the protective layer 35 on the performance of the battery cell 3 can be reduced.

[0103] In some embodiments, the thickness d1 of the protective layer 35 satisfies: 80 nm ≤ d1 ≤ 170 nm. d1 can be 80 nm, 100 nm, 120 nm, 160 nm, 170 nm, or any value within the above range.

[0104] When d1 is greater than or equal to 80 nm, the protective layer 35 has a relatively suitable thickness, which can reduce the risk of short circuit; when d1 is less than or equal to 170 nm, the thickness of the protective layer 35 is relatively small, which can reduce the adverse effects of excessive thickness of the protective layer 35 on the performance of the battery cell 3.

[0105] In some embodiments, the shear strength G of the protective layer 35 satisfies: 70 MPa≤G≤200 MPa.

[0106] G can be 70 MPa, 80 MPa, 85 MPa, 90 MPa, 96 MPa, 100 MPa, 120 MPa, 150 MPa, 170 MPa, 200 MPa, or any value within the above range.

[0107] The shear strength of the protective layer 35 is related to the thickness of the protective layer 35. In the embodiment of the present application, the thicker the protective layer 35 is, the greater the shear strength of the protective layer 35 is.

[0108] The shear strength of the protective layer 35 reflects the bond strength between the protective layer 35 and the electrode 1. 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. Furthermore, during the long-term use of the battery cell 3, the risk of the protective layer 35 swelling due to electrolyte immersion is low, making the protective layer 35 less likely to fall off, thereby improving the reliability of the battery cell 3.

[0109] When the shear strength of the protective layer 35 is greater than or equal to 70 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 200 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.

[0110] The protective layer 35 having the shear strength within the above range is not easily detached from the pole piece 1 , so that the battery cell including the pole piece 1 has a longer service life, and the battery cell can be suitable for electric vehicles.

[0111] The test method for the shear strength of the protective layer 35 can be found in the test method section below.

[0112] In some embodiments, 100 MPa≤G≤150 MPa. G can be 100 MPa, 115 MPa, 130 MPa, 135 MPa, 150 MPa, or any value within the foregoing range.

[0113] In this embodiment, 100 MPa≤G≤150 MPa, the protective layer 35 and the electrode 1 have a relatively suitable bonding strength, and are conducive to reducing the adverse effects on the electrical performance of the battery cell 3 caused by preparing the protective layer 35 with higher shear strength.

[0114] 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.

[0115] As an example, the combination of metal and silicon oxide is represented by: Me-Si-O-Si, where Me represents metal.

[0116] As an example, Me is aluminum. As another example, Me is copper.

[0117] 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.

[0118] 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 .

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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 .

[0123] In some embodiments, the first position is 5 mm from the end surface of the main body 330 along the first direction. For example, the first position is 5 mm from the second end surface 3301b along the first direction. The Si content at the first position can easily reflect the infiltration of silicon elements, and thus can reflect the changes in the electrical performance of the battery cell to a certain extent.

[0124] 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.

[0125] 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 .

[0126] 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.

[0127] In some embodiments, the electrode sheet is a positive electrode sheet, which includes a positive electrode active material, which includes a layered transition metal oxide. Batteries fabricated using this positive electrode active material have a higher energy density, thereby achieving both high energy density and high reliability.

[0128] Layered transition metal oxides may include ternary materials, lithium cobalt oxide, lithium-rich manganese-based materials, and the like.

[0129] As an example, the chemical formula of a layered transition metal oxide includes: Li x (Ni a Co b Mn c ) 1-d M d O 2-y N y , M includes at least one of Mg, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, N includes at least one of F, S, and 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。

[0130] 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.

[0131] When d is greater than 0, the layered transition metal oxide includes the M element, and the layered transition metal oxide may have higher stability; when d is 0, the layered transition metal oxide does not include the M element.

[0132] It is understood that the position of the M ion in the layered transition metal oxide structure can be to replace a portion of the transition metal. For example, in the case where the layered transition metal oxide is a nickel-cobalt-manganese-based ternary material, the M ion can replace a portion of the manganese site, the nickel site, or the cobalt site.

[0133] In the case of y=0, the layered transition metal oxide does not include N. It is understood that the position of N ions in the layered transition metal oxide structure may be a position that replaces a portion of O.

[0134] The battery is accompanied by Li 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 limitation on x includes the molar content of Li in different charge and discharge states of the battery (usually the battery voltage is between 2-5V).

[0135] In the above technical solution, the positive electrode active material satisfying the above chemical formula has a higher nickel content and a higher gram capacity.

[0136] 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.

[0137] 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.

[0138] [Positive electrode]

[0139] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on the positive electrode current collector.

[0140] 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.

[0141] 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.).

[0142] 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.

[0143] 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.

[0144] 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.

[0145] [Negative electrode]

[0146] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector.

[0147] 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.).

[0148] 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.

[0149] As an example, the negative electrode active material is a carbon material.

[0150] The negative electrode film layer may 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.

[0151] [Electrolytes]

[0152] 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.

[0153] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] [Isolator]

[0158] 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.

[0159] 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.

[0160] [Electrode assembly]

[0161] An embodiment of the present application provides an electrode assembly, which includes the electrode piece 1 in any of the above embodiments.

[0162] 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.

[0163] [Battery Cell]

[0164] 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 .

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] [Method for preparing battery cells]

[0174] 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.

[0175] Step 210: Place the electrode assembly 33 in a container.

[0176] Optionally, the electrode assembly 33 includes a main body 330 and a tab 331 , and the tab 331 protrudes from the main body 330 along a first direction.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] Step 220: introducing gaseous silane, water vapor, and a pH adjuster into the container to obtain an electrode assembly provided with a protective layer 35, wherein the protective layer 35 comprises silicon oxide; 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.

[0182] Gaseous silane and water vapor are easily introduced into the container, thereby facilitating the reaction between silane and water molecules.

[0183] The pH adjuster can be a gas, so that after the pH adjuster enters the container, it can promote the reaction between silane and water molecules. By introducing the pH adjuster into the container, the reaction between silane and water molecules can be promoted, which is beneficial to improving the reaction efficiency between silane and water molecules, and further beneficial to reducing the time that the electrode assembly 33 is placed in the container, thereby reducing the risk of silane penetrating into the non-exposed metal parts of the electrode assembly 33 (for example, the area of ​​the electrode where the active material is provided), reducing the risk of silicon oxide being generated at the non-exposed metal parts of the electrode assembly 33, and thus reducing the adverse effects on the cycle performance of the battery cell.

[0184] 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.

[0185] In silane, the -(OR) group is a hydrolyzable group, which facilitates the hydrolysis of silane to produce -Si-OH groups. The end surface 3301 of the main body 330 and at least a portion of the surface of the tab 331 have exposed metal. The -Si-OH groups can bind to 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.

[0186] (1) Silane hydrolysis: -Si-OR + H2O → -Si-OH + ROH;

[0187] (2) Adsorption on metal surface: -Si-OH+Me-OH→Me-O-Si-+H2O, where Me represents metal;

[0188] (3) Cross-linking to form a protective layer: -Si-OH+HO-Si-→-Si-O-Si-+H2O.

[0189] 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 three-dimensional network structure protective layer on the metal surface through the condensation reaction between the -Si-OH groups.

[0190] 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.

[0191] By introducing gaseous silane and water vapor into the container, the mixing of silane and water vapor is facilitated, thereby facilitating the reaction.

[0192] In step 220, gaseous silane may be introduced first, followed by water vapor, and then the pH adjuster; water vapor may be introduced first, followed by gaseous silane, and then the pH adjuster; or gaseous silane, water vapor, and the pH adjuster may be introduced simultaneously.

[0193] As an example, silane, water vapor, and pH adjuster are respectively stored in different storage tanks, and valves are provided between the storage tanks and the containers. 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, and then the valve of the storage tank storing the pH adjuster is opened to introduce the pH adjuster into the container.

[0194] 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 3301 of the main body 330, the exposed metal surface of the 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.

[0195] 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 .

[0196] After the protective layer 35 having a certain thickness is generated, the container can be cooled, and the electrode assembly 33 provided with the protective layer 35 can be taken out. Then, the electrode assembly 33 is placed in the shell 31, and the end cover assembly 32 is connected to the shell 31 to obtain the battery cell 3.

[0197] In the embodiment of the present application, gaseous silane and water vapor react on the exposed metal surfaces of the electrode assembly 33, thereby forming a protective layer 35 on the exposed metal surfaces of the electrode assembly 33. The protective layer 35 comprises silicon oxide. This reduces the risk of short circuits caused by the exposed metal in the electrode assembly 33 interfacing with electrodes of opposite polarity, thereby improving the reliability of the battery cell 3. By introducing a pH adjuster into the container, the reaction between the silane and water molecules is promoted, which helps improve the efficiency of the reaction, reduces the time the electrode assembly must be placed in the container, and reduces the risk of silicon oxide forming on non-exposed metal surfaces of the electrode assembly, thereby reducing the impact on the cycling performance of the battery cell. The electrode assembly 33 with the protective layer 35 is removed from the container and placed into the housing 31, facilitating assembly of the battery cell 3. Furthermore, since the housing 31 is not placed in the container, the protective layer 35 is not formed inside the housing, thereby reducing the adverse effects of the protective layer 35 on the battery cell. Therefore, the battery cell 3 obtained by this technical solution has excellent reliability and cycling performance.

[0198] The preparation method of the battery cell of the embodiment of the present application does not use the vacuum treatment of the container. This can reduce the complexity of the operation and is also beneficial to reduce 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 electrical properties of the battery cell 3 (such as cycle performance, power, resistance).

[0199] Silane has high reliability and the risk of explosion in a sealed 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.

[0200] In some embodiments, the electrode assembly 33 is not subjected to plasma surface treatment (PLASMA) prior to step 210. The addition of a pH adjuster improves the reaction efficiency between silane and water molecules, allowing the protective layer 35 to have a certain thickness and a certain bonding strength between the protective layer 35 and the metal, making it less likely to fall off after being immersed in the electrolyte. Furthermore, eliminating the plasma surface treatment step reduces process complexity and saves costs.

[0201] In some embodiments, the pH adjuster includes an acidic gas or an alkaline gas. Acidic or alkaline gases can promote the hydrolysis of silane, thereby reducing the reaction time between silane and water molecules. Using alkaline gases as pH adjusters allows silane to hydrolyze in an alkaline atmosphere, which helps improve the reaction efficiency between silane and water molecules.

[0202] In some embodiments, the acid gas may include HF, H 2 S, HCl, SO 2 , and the like.

[0203] In some embodiments, the pH regulator includes an alkaline gas. The alkaline gas has little effect on the electrode assembly 33. For example, the alkaline gas does not react with the substance in the electrode piece, which can reduce the impact on the active substance. As a possible example, compared with the acidic gas, the risk of alkaline gas reacting with the residual alkali (such as lithium hydroxide, lithium carbonate) on the surface of the ternary material in the positive electrode piece is smaller, so that the risk of Li inside the ternary material being released to the surface of the ternary material is smaller, the risk of loss of active lithium is smaller, and the impact on the capacity and initial efficiency of the battery is smaller.

[0204] In some embodiments, the alkaline gas may include at least one of ammonia, phosphine, methylamine, dimethylamine, trimethylamine, or ethylamine. The pH adjuster as an alkaline gas has suitable alkalinity, which is beneficial to improving the reaction efficiency between silane and water molecules.

[0205] As an example, methylamine is selected as the alkaline gas.

[0206] In some embodiments, the temperature T of the container satisfies: 45°C≤T≤120°C.

[0207] T may be 45°C, 60°C, 80°C, 100°C, 120°C, or any value within the above range.

[0208] The temperature T of the container may refer to the temperature inside the container. The electrode assembly placed in the container may have the same temperature as the container. As an example, after the electrode assembly 33 connected to the end cap assembly 32 is placed in the container, the container is heated to temperature T.

[0209] The thickness of the protective layer 35 is related to the temperature of the container. The higher the temperature of the container, the more favorable it is for the hydrolysis of silane, and thus the more favorable it is for the formation of a thicker protective layer 35.

[0210] When the temperature T is greater than or equal to 45°C, the temperature difference between the gaseous silane is conducive to reducing the temperature of the container. When T is less than or equal to 120°C, the adverse effects of excessive temperature in the container on the isolation membrane of the electrode assembly can be reduced.

[0211] In some embodiments, 60° C. ≤ T ≤ 100° C. Thus, this temperature range is beneficial for further reducing the temperature difference between the container and the gaseous silane, and further reducing the temperature of the container, thereby reducing the adverse effects of excessive temperature inside the container on the separator of the electrode assembly.

[0212] The gaseous silane, water vapor, pH adjuster, and container may have the same temperature or different temperatures.

[0213] In some embodiments, gaseous silane, water vapor, and a pH adjuster can be introduced directly into the container, and the temperature within the container can be adjusted to a temperature at which the silane vaporizes to reduce the temperature difference between the gaseous silane and water vapor, as well as the temperature of the container. For example, a silane with a lower vaporization temperature can be selected.

[0214] In some embodiments, silane can be heated to a first temperature T1, and a carrier gas is introduced into a storage tank storing silane to obtain gaseous silane; water can be heated to a second temperature T2, and a carrier gas is introduced into a storage tank storing water to obtain water vapor; gaseous silane and water vapor mixed with a carrier gas, and an alkaline gas are introduced into the container to obtain an electrode assembly provided with a protective layer.

[0215] By setting the carrier gas, it is convenient to pass the gaseous silane and water vapor into the container through the carrier gas. It is understandable that the gaseous silane and the carrier gas, the water vapor and the carrier gas are passed into the container together.

[0216] 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.

[0217] In some embodiments, R includes a methyl group. When R is a methyl group, steric hindrance can be reduced, facilitating crosslinking between -Si-OH and -Si-OH, and facilitating the formation of silicon oxide. In addition, when R is a methyl group, silane has a lower boiling point, facilitating the conversion of silane into gaseous silane.

[0218] In some embodiments, the silane has a boiling point less than or equal to 200°C.

[0219] 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.

[0220] 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, CH2OCHCH2-O-(CH2)3-Si(OCH3)3, (CH3)2-Si(OCH3)2 or CH3-Si(OCH3)3; the silane uses the above substances to facilitate hydrolysis.

[0221] In some embodiments, silane includes (CH3)2-Si(OCH3)2, which has a low boiling point, facilitating the conversion of silane into gaseous silane; at the same time, the silane has a low steric hindrance, which is conducive to the formation of silicon oxide, thereby facilitating the preparation of the protective layer 35, and is conducive to reducing the temperature or time required to prepare the protective layer 35, thereby helping to reduce the risk of excessive silane penetration into the electrode.

[0222] In some embodiments, the flow rate Q1 of the gaseous silane, the flow rate Q2 of the water vapor, and the flow rate Q3 of the pH adjuster satisfy the following conditions: Q2 ≥ Q1 > Q3. This facilitates the reaction between the water molecules and the silane and reduces the amount of silane used.

[0223] As an example, the flow rates of gaseous silane and water vapor are the same.

[0224] As another example, the flow rate of water vapor is greater than the flow rate of silane.

[0225] The pH adjuster introduction flow rate Q3 may refer to the speed at which the pH adjuster is introduced into the container.

[0226] When both a carrier gas and water vapor are introduced into the container, the water vapor introduction rate, Q2, refers to the rate at which the mixed gas of water vapor and carrier gas is introduced into the container. When only water vapor is introduced into the container, the water vapor introduction rate, Q2, refers to the rate at which the water vapor is introduced into the container.

[0227] When both a carrier gas and gaseous silane are introduced into the container, the gaseous silane introduction flow rate, Q1, refers to the rate at which the mixture of gaseous silane and carrier gas is introduced into the container. When only gaseous silane is introduced into the container, the gaseous silane introduction flow rate, Q3, refers to the rate at which water vapor is introduced into the container.

[0228] In some embodiments, the inlet flow rate Q1 of the gaseous silane satisfies: 0.5 L / min ≤ Q1 ≤ 1.5 L / min; and / or, the inlet flow rate Q2 of the water vapor satisfies: 1 L / min ≤ Q2 ≤ 2 L / min; and / or, the inlet flow rate Q3 of the pH adjuster satisfies: 0.1 L / min ≤ Q3 ≤ 1 L / min.

[0229] Q1 can be 0.5 L / min, 1 L / min, 1.5 L / min or any value within the above range; Q2 can be 1 L / min, 1.5 L / min, 2 L / min or any value within the above range; Q3 can be 0.1 L / min, 0.5 L / min, 1 L / min or any value within the above range.

[0230] By setting the flow rates of gaseous silane, water vapor, and pH adjuster, gaseous silane, water vapor, and pH adjuster 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.

[0231] In some embodiments, the reaction time t1 of the gaseous silane and water vapor satisfies: 2h≤t1≤8h.

[0232] t1 can be 2h, 4h, 6h, 8h or any value within the above range.

[0233] The reaction time t1 may refer to the duration of the passage of gaseous silane and water vapor into the container.

[0234] 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.

[0235] In some embodiments, 4h≤t1≤6h. In this way, the protective layer 35 with a suitable thickness can be obtained in a shorter time.

[0236] The preparation conditions of the protective layer 35 are related to the thickness and shear strength of the protective layer 35. For example, the time and temperature for preparing the protective layer 35 are relatively low. In a shorter time and at a lower temperature, a protective layer 35 with a relatively 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 generated 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). By reasonably setting the reaction time t1 and temperature T, it is beneficial to prepare a protective layer 35 with a relatively suitable thickness and shear strength, and the battery still has good electrical performance.

[0237] 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.

[0238] 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.

[0239] In some embodiments, the preparation method further comprises: introducing a carrier gas into a storage tank storing water to obtain water vapor. In this way, water vapor can be obtained by the carrier gas, thereby facilitating the introduction of the water vapor into the container.

[0240] As an example, the temperature of silane is increased to convert it into gaseous silane, which is then introduced into a container; a carrier gas is introduced into a storage tank containing water to convert the water into water vapor, which is then introduced into the container; and a pH adjuster gas is introduced into the container.

[0241] In a possible implementation, the carrier gas flow rate Q4 satisfies: 0.9 L / min≤Q4≤2.2 L / min. This facilitates obtaining water vapor.

[0242] The carrier gas flow rate Q4 and the water vapor flow rate Q2 can satisfy 0.9Q2≤Q4≤1.1Q2. This is conducive to introducing an appropriate amount of water vapor into the container and maintaining the pressure balance in the container.

[0243] As an example, Q4 is the same as Q2.

[0244] 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 provided with the electrode assembly. In Figure 7 , the end cap assembly 32 is located below the electrode assembly 33 (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.

[0245] 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.

[0246] 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.

[0247] The battery cell prepared by preparation method 200 has a Si element content measured at a position 5 mm away from the end surface 3301 (for example, the first end surface 3301a and the second end surface 3301b) of the electrode assembly 33 along the CC direction, which is less than 0.01 wt%, and this value is basically close to 0.

[0248] 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.

[0249] 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.

[0250] 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.

[0251] The gas introduced can be nitrogen, helium, argon and other gases.

[0252] 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.

[0253] The time and flow rate of the inert gas can be set according to actual needs, as long as the air in the container can be discharged.

[0254] 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, the third storage tank 103, and the fourth storage tank 104 is provided with a flow control 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 water, the second storage tank 102 is used to store silane, the third storage tank 103 is used to store a pH adjuster, and the fourth storage tank 104 is used to store nitrogen.

[0255] During the preparation of the protective layer, the inert gas nitrogen in the fourth storage tank 104 can be first introduced into the container 100 to expel the air in the container 100; the carrier gas nitrogen in the fourth storage tank 104 can be introduced into the first storage tank 101 to obtain water vapor, and then the mixed gas of water vapor and nitrogen can be introduced into the container 100; the second storage tank 102 can be used to obtain gaseous silane, and the gaseous silane can be introduced into the container 100; the pH adjuster in the third storage tank 103 can be introduced into the container 100.

[0256] In the preparation method of the embodiment of the present application, by reasonably setting the reaction time t1 and the temperature T, it is beneficial to prepare a protective layer 35 with a relatively suitable thickness and shear strength, and the battery still has good electrical performance; by reacting silane and water molecules on the metal surface under normal pressure, it is beneficial to reduce the risk of silane penetrating into the non-exposed metal of the electrode assembly 33, thereby reducing the adverse effects on the electrical performance of the battery; by reasonably setting the flow rate of gaseous silane, water vapor, and pH regulator, it is beneficial to the reaction between silane and water molecules and reduce the risk of silane penetrating into the non-exposed metal position of the electrode assembly; and it is also beneficial to reduce the waste of silane; by introducing the pH regulator into the container, it is beneficial to promote the reaction between silane and water, and it is beneficial to prepare a protective layer 35 of corresponding thickness at a lower temperature and in a shorter time, and the battery has good electrical performance.

[0257] [Battery]

[0258] 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).

[0259] 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 .

[0260] [Electrical devices]

[0261] An embodiment of the present application provides an electrical device, comprising the battery described in the above embodiment.

[0262] 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.

[0263] 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.

[0264] 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.

[0265] [Example of a method for producing a battery cell]

[0266] Example 1

[0267] (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.

[0268] (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.

[0269] (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.

[0270] (4) The battery components are placed in a container, and the temperature of the container is raised to a temperature T of 82°C. Nitrogen is introduced into the container as a protective gas at a flow rate of 0.01 L / min for 30 min to exhaust the air in the container.

[0271] (5) Silane (CH3)2-Si(OCH3)2 is heated to 82°C (this temperature is close to the boiling point of the silane) to obtain gaseous silane; the gaseous silane is introduced into the container at a flow rate of Q1.

[0272] (6) Nitrogen is introduced into the storage tank storing water to obtain water vapor; a mixed gas of water vapor and nitrogen is introduced into the container at a flow rate of Q2, wherein the flow rate Q4 of nitrogen introduced into the storage tank storing water is approximately 0.9 to 1.1Q2.

[0273] (7) A pH regulator, methylamine gas, is introduced into the container at a flow rate of Q3; the total reaction time t1 is controlled at 6 h.

[0274] (8) 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.

[0275] Examples 2-4

[0276] The difference between Example 2-4 and Example 1 is that the types of pH regulators are different.

[0277] Examples 5-8

[0278] The difference between Examples 5-8 and Example 1 is that the temperature T of the container is different.

[0279] Examples 9-11

[0280] The difference between Examples 9-11 and Example 1 is that the flow rates Q of the gaseous silane, water vapor, and pH adjuster introduced into the container are different.

[0281] Examples 12-13

[0282] The difference between Examples 12-13 and Example 1 is that the flow rate of the pH regulator into the container is different.

[0283] Examples 14-16

[0284] The difference between Examples 14-16 and Example 1 is that the reaction times are different.

[0285] Examples 17-18

[0286] The difference between Example 17-18 and Example 1 is that the types of silane are different.

[0287] Comparative Example 1

[0288] The difference between Comparative Example 1 and Example 1 is that no pH adjuster was introduced into the container.

[0289] [Example of battery cell]

[0290] Examples 1-18 of the battery cell can be prepared from Examples 1-18 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.

[0291] Table 1 Parameters of Examples and Comparative Examples of the Preparation Method of Battery Cells

[0292] Table 2 Comparative Examples and Examples of Battery Cells

[0293] Table 3 Experimental results of embodiments and comparative examples

[0294] It should be noted that in Table 2, “ / ” indicates that the corresponding test was not performed. Specifically, Examples 5-6, 9, 12, and 14-15 were not tested for shear strength and Si content on the end surface after electrolyte immersion.

[0295] [Testing of protective layer]

[0296] (1) Test of the thickness of the protective layer

[0297] 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).

[0298] (2) Testing of Si elements in the protective layer at different positions of the electrode assembly

[0299] Energy-dispersive X-ray spectroscopy (EDS) on the ZEISS sigma 300 was used to analyze the surface of the relevant area to determine the Si content. The instrument's data revealed the distribution of each element, and thus the Si mass fraction.

[0300] The electrode assembly was immersed in an electrolyte at 60°C for 7 days, and the Si content on the end surface was measured. The change in Si content before and after immersion in the electrolyte reflects the bonding strength between the protective layer and the electrode current collector.

[0301] As an example, the Si content is tested by the following method. Take a sample in the direction where the active material layer is provided at the second end surface 3301b (for example, as shown in FIG2 , take a sample along the y direction at the second end surface 3301b), and cut out an area of ​​10mm×10mm to obtain a sample. The sample is placed in a testing device for element testing, and the quantitative analysis is performed by referring to the GB-T17359-2012 microbeam analysis energy spectrum method. The proportion of C, Ni, Co, Mn, O, and Si elements (when the active material in the electrode piece adopts a ternary material) or the proportion of C, Fe, O, and Si (when the active material in the electrode piece adopts lithium iron phosphate) can be measured. Among them, to test the Si content at a position 5mm away from the second end surface 3301b, the ruler in the equipment can be used to locate the point 5mm away from the second end surface 3301b, and the Si content at this point can be tested. Similarly, to test the Si content at positions 3 mm and 0.5 mm away from the second end surface 3301b, the ruler in the equipment can be used to locate the points 3 mm and 0.5 mm away from the second end surface 3301b, and the Si content at these points can be tested.

[0302] 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.

[0303] (3) Short-circuit test of batteries with protective layers

[0304] Different positions of the electrode assembly with a protective layer are connected to the anode of a fully charged battery, and the probability of short circuit (or fire) is recorded. Specifically, the electrode assembly with a protective layer is made into a battery and fully charged to 100% SOC; after full charge, the battery is disassembled and the position with the protective layer is directly contacted with the negative electrode active material area to record the short circuit (or fire) situation. Among them, full charge means using a certain current to charge the battery to 100% SOC, for example, a lithium iron phosphate battery is charged to 3.65V, and a ternary material battery is charged to 4.3V.

[0305] [Shear strength test]

[0306] 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.

[0307] 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.

[0308] 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).

[0309] [Battery cell performance test]

[0310] Battery cells were charged and discharged at 25°C. A single charge / 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.

[0311] After one charge and discharge cycle, the discharge capacity of the battery cell is recorded. This is the first discharge capacity.

[0312] 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.

[0313] In the embodiment of the method for preparing a battery cell, in combination with Examples 1-18, the preparation method of the embodiment of the present application is simpler, and an electrode assembly provided with a protective layer can be obtained without vacuuming. In addition, compared with the method of performing vacuuming during the preparation of the protective layer, not performing vacuuming is conducive to reducing the risk of excessive infiltration of silane at the non-exposed metal position of the electrode assembly (the non-exposed metal position of the pole piece). Since silicon oxide or silicon element is not conductive, the deposition of silane or the generation of silicon oxide at the non-exposed metal position will affect the conductive performance, thereby affecting the electrical performance of the battery cell (such as the capacity retention rate). Therefore, the pole piece prepared by the method of the embodiment of the present application has a very low Si element content at a position 5 mm away from the end surface, and the battery cell has a high capacity retention rate.

[0314] As shown in Examples 1-18, the content of Si element tends to gradually increase with the smaller the distance from the end surface, which is related to the direction in which the reactants are introduced into the container during the preparation of the protective layer (combined with the schematic diagrams of Figures 8 and 9 and the description above); and after the electrode assembly is soaked for a certain period of time, the end surface of the electrode is tested again, and a certain amount of Si element is still retained on the end surface, which reflects that the protective layer is not easy to fall off from the electrode.

[0315] As shown in Examples 1-18 and Comparative Example 1, the reaction efficiency of silane and water molecules is improved by adding a pH regulator in the embodiments of the present application, and a protective layer is generated in a shorter time, and the risk of silicon oxide or silicon elements existing in the non-exposed metal positions of the electrode assembly is further reduced.

[0316] In Examples 1-18, there was no short circuit or fire when the pole piece provided with a protective layer was overlapped with the electrode of opposite polarity. Therefore, the provision of the protective layer can reduce the risk of short circuit in the battery cell. Moreover, the capacity retention rate of the battery cells of Examples 1-3 and Examples 5-18 after 500 cycles is about 90%. Therefore, the battery cells of the embodiments of the present application have high reliability and high cycle performance.

[0317] As shown in Examples 1-4, either alkaline or acidic gases can be used as pH adjusters to improve reaction efficiency. As shown in Example 1-3, compared to the acidic gas pH adjuster in Example 4, the battery cells prepared using alkaline gas as the pH adjuster exhibited higher capacity and higher capacity retention. In Examples 1-3, the capacity retention was approximately 90%; in Example 4, the capacity retention was approximately 70.5%.

[0318] As shown in Examples 5-8, increasing the temperature within the container facilitates the hydrolysis of silane, thereby facilitating the formation of a thicker protective layer within the same timeframe. Furthermore, setting the container temperature within the range of 60°C to 100°C or 80°C to 100°C facilitates the formation of a protective layer of appropriate thickness without overheating the container.

[0319] As shown in Examples 9-11, increasing the flow rates of gaseous silane, water vapor, and pH adjuster into the container facilitates obtaining a thicker protective layer within the same timeframe. As shown in Examples 10-11, a water vapor flow rate greater than that of gaseous silane facilitates the reaction and reduces silane waste. As shown in Examples 12-13, setting the pH adjuster flow rate within the range of 0.1 L / min to 1 L / min reduces pH adjuster waste and facilitates the reaction between silane and water molecules.

[0320] In combination with Examples 14-16 and Example 1, a protective layer of corresponding thickness can be generated within 2h to 8h, and the preparation method of the embodiments of the present application has high efficiency; further, in combination with Examples 1, 15 and 16, by setting the reaction time to 4h to 6h, a protective layer of appropriate thickness can be prepared in a shorter time, and has high reaction efficiency.

[0321] As shown in Examples 17-18, the preparation method of the embodiments of the present application is applicable to a variety of silanes; further as shown in Example 1, the use of silanes with a methyl group as the R group is conducive to obtaining a thicker protective layer at a lower temperature.

[0322] 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.

[0323] 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, and the protective layer comprises silicon oxide; 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.

2. The pole piece according to claim 1, characterized in that: Based on the total mass of all elements at the second position of the pole piece, the mass content B of the Si element satisfies: B≤0.05wt%, and the second position is a position 3 mm away from the end surface.

3. The pole piece according to claim 1 or 2, characterized in that: Based on the total mass of all elements at the third position of the pole piece, the mass content C of the Si element satisfies: C≤1.2wt%, and the third position is a position 0.5 mm away from the end surface.

4. The pole piece according to any one of claims 1 to 3, characterized in that: Based on the total mass of all elements on the end surface of the pole piece, the mass content D of the Si element satisfies: 8wt%≤D≤35wt%.

5. The pole piece according to claim 4, characterized in that: 15wt%≤D≤30wt%.

6. The pole piece according to any one of claims 1 to 5, characterized in that: The thickness d1 of the protective layer satisfies: 20 nm ≤ d1 ≤ 200 nm.

7. The pole piece according to claim 6, characterized in that: 80nm≤d1≤170nm.

8. The pole piece according to any one of claims 1 to 7, characterized in that: The shear strength G of the protective layer satisfies: 70 MPa≤G≤200 MPa.

9. The pole piece according to claim 8, characterized in that: 100MPa≤G≤150MPa.

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; Gaseous silane, water vapor, and a pH adjuster are introduced into the container to obtain an electrode assembly provided with a protective layer, wherein the protective layer comprises silicon oxide, and the general formula of the silane satisfies: R'-Si(OR) n , wherein R' comprises an organic or inorganic functional group, R comprises an alkyl group, and n is an integer and 2≤n≤4; 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 pH adjuster includes an alkaline gas.

18. The preparation method according to claim 17, characterized in that: The alkaline gas includes at least one of ammonia, phosphine, methylamine, dimethylamine, trimethylamine or ethylamine.

19. The preparation method according to claim 16, characterized in that The pH adjuster includes an acidic gas.

20. The preparation method according to claim 19, characterized in that The acid gas includes at least one of hydrogen fluoride, hydrogen sulfide, hydrogen chloride or sulfur dioxide.

21. The preparation method according to any one of claims 16 to 20, characterized in that: The temperature T of the container satisfies: 45°C≤T≤120°C.

22. The preparation method according to claim 21, characterized in that The temperature T of the container satisfies: 60°C≤T≤100°C.

23. The preparation method according to any one of claims 16 to 22, characterized in that: The boiling point of the silane is less than or equal to 200°C.

24. The preparation method according to any one of claims 16 to 23, 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, (CH3)2-Si(OCH3)2 or CH3-Si(OCH3)3.

25. The preparation method according to claim 24, characterized in that The silane includes (CH3)2-Si(OCH3)2.

26. The preparation method according to any one of claims 16 to 25, characterized in that The inlet flow rate Q1 of the gaseous silane, the inlet flow rate Q2 of the water vapor, and the inlet flow rate Q3 of the pH adjuster satisfy: Q2≥Q1>Q3.

27. The preparation method according to any one of claims 16 to 26, characterized in that The inlet flow rate Q1 of the gaseous silane satisfies: 0.5 L / min≤Q1≤1.5 L / min; and / or, the inlet flow rate Q2 of the water vapor satisfies: 1 L / min≤Q2≤2 L / min; and / or, the inlet flow rate Q3 of the pH adjuster satisfies: 0.1 L / min≤Q3≤1 L / min.

28. The preparation method according to any one of claims 16 to 27, characterized in that The reaction time t1 of the gaseous silane and the water vapor satisfies: 2h≤t1≤8h.

29. The preparation method according to claim 28, characterized in that 4h≤t1≤6h.

30. The preparation method according to any one of claims 16 to 29, characterized in that: The pressure P in the container satisfies: 0.09 MPa≤P≤0.11 MPa.

31. The preparation method according to any one of claims 16 to 30, characterized in that The container is in communication with the external environment.

32. The preparation method according to any one of claims 16 to 31, characterized in that The preparation method further comprises: A carrier gas is introduced into a storage tank storing water to obtain the water vapor.

33. The preparation method according to claim 32, characterized in that The carrier gas inlet flow rate Q4 satisfies: 0.9 L / min≤Q4≤2.2 L / min.

34. The preparation method according to any one of claims 16 to 33, 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.

35. The preparation method according to any one of claims 16 to 34, characterized in that The preparation method further comprises: Before introducing gaseous silane, water vapor and pH regulator into the container, Inert gas is introduced into the container to evacuate the air in the container.

36. The preparation method according to any one of claims 16 to 35, 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.

37. 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 16-36.

38. An electrical device, characterized in that: Comprising a battery according to claim 37.

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