Battery cell, battery and electric device

Abstract

The invention relates to a battery monomer, a battery and a power utilization device. The embodiment of the invention provides a battery monomer. The battery monomer comprises a negative pole piece, a first isolating membrane, a second isolating membrane and a positive pole piece, the negative pole piece, the first isolating membrane, the second isolating membrane and the positive pole piece are wound into an electrode assembly along the winding direction, and the electrode assembly comprises an arc-shaped corner region; in the arc-shaped corner area, a gap between the convex surface of the negative pole piece and the concave surface of the positive pole piece is a first gap; a gap between the concave surface of the negative pole piece and the convex surface of the positive pole piece is a second gap; the first isolating membrane is arranged in the first gap; the second isolating membrane is arranged in the second gap; the thickness of the first isolating membrane is greater than that of the second isolating membrane.

Description

Technical Field

[0001] The present application relates to a battery cell, a battery, and an electrical device. Background Art

[0002] As an emerging sustainable energy storage technology, lithium-ion batteries have the characteristics of low cost and environmental friendliness, so their application has been increasingly developed in recent years.

[0003] Therefore, higher requirements are put forward for improving the lithium plating problem in the corner area of ​​lithium-ion batteries. Summary of the invention

[0004] The purpose of the present application is to provide a battery cell, a battery, and an electrical device.

[0005] The embodiment of the present application is implemented as follows:

[0006] In a first aspect, an embodiment of the present application provides a battery cell, including:

[0007] A negative electrode sheet, a first separator, a second separator and a positive electrode sheet;

[0008] The negative electrode sheet, the first separator, the second separator and the positive electrode sheet are wound into an electrode assembly along a winding direction, and the electrode assembly includes an arc-shaped corner area; in the arc-shaped corner area, the gap between the convex surface of the negative electrode sheet and the concave surface of the positive electrode sheet is the first gap; the gap between the concave surface of the negative electrode sheet and the convex surface of the positive electrode sheet is the second gap; the first separator is arranged in the first gap; the second separator is arranged in the second gap;

[0009] The thickness of the first isolation film is greater than the thickness of the second isolation film.

[0010] After the battery has been cycled, the first gap between the convex surface of the negative electrode piece and the concave surface of the positive electrode piece in the corner area is always reduced more than the second gap between the concave surface of the negative electrode piece and the convex surface of the positive electrode piece, which causes lithium deposition to occur first on the convex surface of the negative electrode piece in the corner area. Therefore, the above technical solution can achieve the purpose of increasing the first gap by setting a thicker first isolation film in the first gap between the convex surface of the negative electrode piece and the concave surface of the positive electrode piece in the corner area; and setting a thinner second isolation film in the second gap between the concave surface of the negative electrode piece and the convex surface of the positive electrode piece in the corner area, so as to achieve the purpose of not making the second gap too large. Ultimately, the purpose of improving the lithium deposition problem in the corner area of ​​the battery can be achieved by regulating the first gap and the second gap, and it is beneficial to improve the battery cycle performance.

[0011] In some embodiments, at least one surface of the first isolation film is provided with a first coating; the first coating includes first particles;

[0012] At least one surface of the second isolation film is provided with a second coating; the second coating includes second particles;

[0013] D of the first particle V 50 greater than the D of the second particle V 50.

[0014] In some embodiments, the D of the first particle V 50 is greater than or equal to 15μm.

[0015] In some embodiments, the D of the second particle V 50 is less than or equal to 10μm.

[0016] In some embodiments, the D of the first particle V 50 is 15μm~30μm.

[0017] In some embodiments, the D of the second particle V 50 is 5μm~10μm.

[0018] In some embodiments, the first isolation film has a thickness of 35 μm to 65 μm.

[0019] In some embodiments, the second isolation film has a thickness of 15 μm to 25 μm.

[0020] In some embodiments, the surface density of the first isolation film and the second isolation film is 5 g / m 2 ~10g / m 2 Optionally, the difference between the surface density of the first isolation film and the second isolation film is -1g / m 2 ~1g / m 2 .

[0021] In some embodiments, the first particulate matter includes at least one of organic particulate matter or inorganic particulate matter.

[0022] In some embodiments, the second particulate matter includes at least one of organic particulate matter or inorganic particulate matter.

[0023] In some embodiments, the organic particles include at least one of polyvinylidene fluoride particles, polyimide particles, or polyethylene oxide particles.

[0024] In some embodiments, the inorganic particulate matter includes at least one of alumina particles or boehmite particles.

[0025] In some embodiments, the first isolation film satisfies at least one of the following characteristics:

[0026] (1) The air permeability of the first isolation film is 425 seconds / 100 cc to 430 seconds / 100 cc;

[0027] (2) The porosity of the first isolation membrane is 48% to 50%;

[0028] (3) The liquid absorption rate of the first isolation film is 130% to 135%.

[0029] In some embodiments, the second isolation film satisfies at least one of the following characteristics:

[0030] (1) The air permeability of the second isolation film is 316 seconds / 100cc to 400 seconds / 100cc;

[0031] (2) The porosity of the second isolation film is 30% to 45%;

[0032] (3) The liquid absorption rate of the second isolation film is 110% to 126%.

[0033] In a second aspect, an embodiment of the present application provides a battery, comprising the battery cell provided in the first aspect.

[0034] In a third aspect, an embodiment of the present application provides an electrical device, the electrical device comprising a battery provided by any of the aforementioned implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0037] Figure 2 yes Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0038] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0039] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0040] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0041] Figure 6 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application;

[0042] Figure 7 It is a schematic diagram of an electrode assembly according to one embodiment of the present application.

[0043] icon:

[0044] 101 negative electrode plate; 102 second isolation film; 103 positive electrode plate; 104 first isolation film;

[0045] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0046] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0048] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0049] In the description of the embodiments of the present application, the orientations or positional relationships indicated by the technical terms "inside" and "outside" are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0050] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0051] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0052] In the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the heights, lengths, widths, and other dimensions of the various components in the embodiments of the present application shown in the drawings, as well as the overall heights, lengths, widths, and other dimensions of the integrated device are only exemplary descriptions and should not constitute any limitation to the present application.

[0053] After research, it was found that lithium deposition at the corner of the negative electrode of the wound battery mainly occurs on the convex surface of the corner of the negative electrode. When the gap at the corner was further measured by high-definition CT (computed tomography), it was found that the first gap between the convex surface of the negative electrode and the concave surface of the positive electrode at the corner was smaller than the second gap between the concave surface of the negative electrode and the convex surface of the positive electrode. It can be seen that the first gap is reduced more after the cycle, which will lead to poor electrolyte infiltration on the convex surface of the negative electrode, causing lithium deposition; further research also found that when the second gap between the concave surface of the negative electrode and the convex surface of the positive electrode is too large, lithium deposition will occur on the concave surface of the negative electrode through the corner.

[0054] Based on this, refer to Figure 1 to Figure 7 In a first aspect, the present application provides a battery cell, including:

[0055] The battery cell comprises a negative electrode sheet 101, a first separator 104, a second separator 102 and a positive electrode sheet 103; the negative electrode sheet 101, the first separator 104, the second separator 102 and the positive electrode sheet 103 are wound into an electrode assembly along a winding direction, and the electrode assembly comprises an arc-shaped corner area; in the arc-shaped corner area, the gap between the convex surface of the negative electrode sheet 101 and the concave surface of the positive electrode sheet 103 is a first gap; the gap between the concave surface of the negative electrode sheet 101 and the convex surface of the positive electrode sheet 103 is a second gap; the first separator 104 is arranged in the first gap; the second separator 102 is arranged in the second gap;

[0056] The thickness of the first isolation film 104 is greater than the thickness of the second isolation film 102 .

[0057] After the battery has been cycled, the first gap between the convex surface of the negative electrode sheet and the concave surface of the positive electrode sheet in the corner area is always reduced more than the second gap between the concave surface of the negative electrode sheet and the convex surface of the positive electrode sheet, which causes lithium deposition to occur first on the convex surface of the negative electrode sheet in the corner area. Therefore, the above technical solution can achieve the purpose of increasing the first gap by setting a thicker first isolation film in the first gap between the convex surface of the negative electrode sheet and the concave surface of the positive electrode sheet in the corner area. At the same time, due to the larger particle size of the first particles, it has a certain effect of resisting the expansion of the negative electrode. In addition, the larger gaps between the larger particles can promote the circulation and infiltration of the electrolyte; and a thinner second isolation film is set in the second gap between the concave surface of the negative electrode sheet and the convex surface of the positive electrode sheet in the corner area, so as to achieve the purpose of not making the second gap too large. Finally, the purpose of improving the lithium deposition problem in the corner area of ​​the battery can be achieved by regulating the first gap and the second gap, and it is beneficial to improve the battery cycle performance.

[0058] In some embodiments of the present application, the battery cell includes an electrode assembly and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer; the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer; during the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The first separator is arranged in the first gap between the positive electrode sheet and the negative electrode sheet; the second separator is arranged in the second gap between the positive electrode sheet and the negative electrode sheet, which plays a role in preventing the positive and negative electrodes from short-circuiting, and allows ions to pass through.

[0059] In some embodiments of the present application, the positive electrode sheet 103 , the negative electrode sheet 101 , the first isolation film 104 , and the second isolation film 102 may be formed into the above-mentioned electrode assembly through a winding process.

[0060] Figure 7 A wound electrode assembly is shown. Figure 7 In some embodiments of the present application, the positive electrode sheet 103, the negative electrode sheet 101, the first isolation film 104, and the second isolation film 102 are wound to form an electrode assembly, which can be prepared in the following manner:

[0061] The die-cut first isolation film 104, the second isolation film 102, the negative electrode sheet 101, and the positive electrode sheet 103 are stacked in the order of second isolation film 102, negative electrode sheet 101, first isolation film 104, positive electrode sheet 103, second isolation film 102, negative electrode sheet 101, ... and then wound into an electrode assembly along the direction indicated by arrow C in the figure.

[0062] from Figure 7It can be seen that the first isolation film 104 is disposed between the convex surface of the negative electrode sheet and the concave surface of the positive electrode sheet; the second isolation film 102 is disposed between the concave surface of the negative electrode sheet and the convex surface of the positive electrode sheet.

[0063] The "convex surface" in the above technical solution refers to the outer surface of the arc-shaped corner area of ​​the wound electrode assembly formed by the winding process (for example Figure 7 The convex surface is the surface indicated by arrow A); the “concave surface” refers to the inner surface of the arc-shaped corner area of ​​the wound electrode assembly formed by the winding process (e.g. Figure 7 The convex surface is the surface indicated by arrow B).

[0064] In some embodiments of the present application, the above-mentioned wound electrode assembly, except for the arc-shaped corner area; the remaining area is a straight area. For the straight area, the setting of the isolation film is not limited. Optionally, in some embodiments, the same isolation film as the aforementioned arc-shaped corner area can be selected.

[0065] Further, in some embodiments of the present application, at least one surface of the first isolation film is provided with a first coating; the first coating includes first particles;

[0066] At least one surface of the second isolation film is provided with a second coating; the second coating includes second particles;

[0067] D of the first particle V 50 greater than the D of the second particle V 50.

[0068] The thickness of the isolation membrane can be controlled by the particle size of the particles in the coating. A coating containing particles of larger particle size is coated on the isolation membrane, which can increase the thickness of the isolation membrane. The increase in the thickness of the isolation membrane can increase the length of the electrode sheet when it is wound around. When the battery is under pressure, the increased length will be pressed to the corner, thereby achieving the purpose of creating a gap at the corner. On the other hand, larger particles can more effectively resist the expansion of the negative electrode sheet, thereby increasing the first gap between the convex surface of the negative electrode sheet and the concave surface of the positive electrode sheet in the arc-shaped corner area. Because the gap between larger particles is larger, it can promote the infiltration of electrolyte. The above technical solution is provided by providing at least one surface of the first isolation membrane with a first coating; the first coating includes first particles; at least one surface of the second isolation membrane with a second coating; the second coating includes second particles; the D of the first particles V 50 greater than the D of the second particle V 50; the first gap between the convex surface of the negative electrode sheet and the concave surface of the positive electrode sheet at the corner can be increased; thereby helping to improve the problem of lithium deposition first occurring on the convex surface of the negative electrode sheet at the corner.

[0069] Further, in some embodiments of the present application, D of the first particle V 50 is greater than or equal to 15μm.

[0070] In the above technical solution, D of the first particle V 50 is greater than or equal to 15 μm, which can increase the first gap between the convex surface of the negative electrode plate and the concave surface of the positive electrode plate, which is beneficial to improving lithium deposition in the battery corners.

[0071] For example, in some embodiments of the present application, the D of the first particle is V 50 is 15 μm, 20 μm, 25 μm, 28 μm, 30 μm or a range between any two of the foregoing values.

[0072] Further optionally, in some embodiments of the present application, D of the first particle V 50 is 15 μm to 30 μm. For example, in some embodiments of the present application, D V 50 is 15μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm or the area between any two of the aforementioned values.

[0073] Further, in some embodiments of the present application, the D V 50 is less than 10μm.

[0074] In the above technical solution, D of the second particle V 50 is less than 10μm, and smaller particles are arranged in the second gap between the concave surface of the negative electrode plate and the convex surface of the positive electrode plate, which can improve the lithium deposition on the concave surface of the negative electrode plate; it is beneficial to the battery cycle performance.

[0075] For example, in some embodiments of the present application, the D of the second particle V 50 is 10μm, 9μm, 8μm, 7μm, 6μm, 5μm, 4μm, 3μm, 2μm, 1μm or a range between any two of the foregoing values.

[0076] Further optionally, in some embodiments of the present application, the D V 50 is 5 μm to 10 μm. For example, D V 50 is 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm or a range between any two of the foregoing values.

[0077] The above “D V"50" is a well-known meaning in the art, which indicates the particle size corresponding to when the cumulative volume distribution percentage of the first particulate matter or the second particulate matter reaches 50%, and can be measured by instruments and methods known in the art. For example, it can be measured by a laser particle size analyzer with reference to GB / T 19077-2016. The testing instrument can be the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0078] Furthermore, in some embodiments of the present application, the thickness of the first isolation film is 35 μm to 65 μm.

[0079] In the above technical solution, by setting the thickness of the first isolation membrane to 35μm to 65μm, it is beneficial to ensure the mechanical strength and structural stability of the first isolation membrane, and to ensure that the first gap between the convex surface of the negative electrode plate and the concave surface of the positive electrode plate is within an appropriate range, which is beneficial to improving the problem of lithium deposition in the battery corners.

[0080] Exemplarily, in some embodiments of the present application, the thickness of the first isolation film is 35μm, 36μm, 37μm, 38μm, 39μm, 40μm, 42μm, 45μm, 48μm, 50μm, 52μm, 55μm, 58μm, 60μm, 61μm, 62μm, 63μm, 64μm, 65μm or a range between any two of the aforementioned values.

[0081] Furthermore, in some embodiments of the present application, the thickness of the second isolation film is 15 μm to 25 μm.

[0082] In the above technical solution, by setting the thickness of the second isolation membrane to 15μm to 25μm, it is beneficial to ensure the mechanical strength and structural stability of the second isolation membrane, and to ensure that the second gap between the concave surface of the negative electrode plate and the convex surface of the positive electrode plate is within an appropriate range, which can improve lithium deposition on the concave surface of the negative electrode plate; it is beneficial to the battery cycle performance.

[0083] Illustratively, in some embodiments of the present application, the thickness of the second isolation film is 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm or a range between any two of the aforementioned values.

[0084] Furthermore, in some embodiments of the present application, the surface density of the first isolation film and the second isolation film are both 5g / m 2 ~10g / m 2 .

[0085] In the above technical solution, the surface density of the first isolation film and the second isolation film are both 5g / m 2 ~10g / m2 ; It is beneficial to the battery cycle performance.

[0086] For example, in some embodiments of the present application, the surface density of the first isolation film and the second isolation film can be selected from the following values: 5 g / m 2 5.5g / m 2 , 6g / m 2 , 6.5g / m 2 , 7g / m 2 , 7.5g / m 2 , 8g / m 2 , 8.5g / m 2 , 9g / m 2 , 9.5g / m 2 , 10g / m 2 Or the range between any two of the above values.

[0087] In some optional embodiments of the present application, the difference in surface density between the first coating and the second coating is -1 g / m 2 ~1g / m 2 For example, the difference in surface density between the first coating and the second coating is -1 g / m 2 、-0.8g / m 2 、-0.5g / m 2 、-0.2g / m 2 , 0g / m 2 , 0.1g / m 2 , 0.2g / m 2 , 0.3g / m 2 , 0.5g / m 2 , 0.8g / m 2 , 1g / m 2 Or the range between any two of the above values.

[0088] In the above technical solution, the difference in surface density between the first isolation film and the second isolation film is -1g / m 2 ~1g / m 2, under the premise that the difference between the two is not large, the thickness of the separator can be directly controlled by adjusting the particle size of the particles. The coating of the first separator contains first particles with larger particle size, and the coating of the second separator contains second particles with smaller particle size. During the winding process, the first separator is set between the convex surface of the negative electrode plate and the concave surface of the positive electrode plate. On the one hand, the larger particles can more effectively resist the expansion of the negative electrode plate and prevent the gap between the convex surface of the negative electrode and the concave surface of the positive electrode from decreasing too quickly; on the other hand, the larger inter-particle gaps in the first separator are more, which can promote the full infiltration of the electrolyte and improve the gap between the convex surface of the negative electrode plate and the concave surface of the positive electrode plate as a whole; and the second separator is set between the concave surface of the negative electrode plate and the convex surface of the positive electrode plate to prevent the gap between the positive and negative electrode plates from being too large.

[0089] Furthermore, in some embodiments of the present application, the first particulate matter includes at least one of organic particulate matter or inorganic particulate matter.

[0090] In some embodiments, the second particulate matter includes at least one of organic particulate matter or inorganic particulate matter.

[0091] In the above technical solution, by controlling the first particles and the second particles to include at least one of organic particles or inorganic particles, the thickness of the first isolation film and the second isolation film can be adjusted, which is beneficial to improving lithium deposition in battery corners.

[0092] Exemplarily, in some embodiments of the present application, the first particles and the second particles are both selected from any one of organic particles or inorganic particles; or in some embodiments of the present application, the first particles and the second particles are both selected from a mixture of organic particles and inorganic particles; or in some embodiments of the present application, the first particles are selected from any one of organic particles or inorganic particles; and the second particles are selected from a mixture of organic particles and inorganic particles; or in some embodiments of the present application, the first particles are selected from a mixture of organic particles and inorganic particles; and the second particles are selected from any one of organic particles or inorganic particles.

[0093] Furthermore, in some embodiments of the present application, the above-mentioned organic particles include: at least one of polyvinylidene fluoride particles, polyimide particles or polyethylene oxide particles.

[0094] Exemplarily, in some embodiments of the present application, the above-mentioned organic particles include: any one of polyvinylidene fluoride particles, polyimide particles or polyethylene oxide particles; or in some embodiments of the present application, the above-mentioned organic particles include: a mixture of polyvinylidene fluoride particles, polyimide particles and polyethylene oxide particles; or in some embodiments of the present application, the above-mentioned organic particles include: a mixture of polyvinylidene fluoride particles and polyimide particles; or in some embodiments of the present application, the above-mentioned organic particles include: a mixture of polyimide particles and polyethylene oxide particles.

[0095] Furthermore, in some embodiments of the present application, the inorganic particulate matter includes at least one of aluminum oxide particles or boehmite particles.

[0096] For example, in some embodiments of the present application, the inorganic particulate matter includes: any one of aluminum oxide particles or boehmite particles; or in some embodiments of the present application, the above-mentioned inorganic particulate matter includes: a mixture of aluminum oxide particles and boehmite particles.

[0097] In other optional embodiments, exemplarily, the first particulate matter includes a mixture of polyvinylidene fluoride particles, polyimide particles, polyethylene oxide particles, aluminum oxide particles and boehmite particles; or in some exemplary embodiments of the present invention, the second particulate matter includes a mixture of polyvinylidene fluoride particles, polyimide particles, polyethylene oxide particles, aluminum oxide particles and boehmite particles.

[0098] In some embodiments of the present application, the air permeability of the first isolation membrane is 425 sec / 100cc to 430 sec / 100cc. Exemplarily, the air permeability of the isolation membrane is 425 sec / 100cc, 426 sec / 100cc, 427 sec / 100cc, 428 sec / 100cc, 429 sec / 100cc, 430 sec / 100cc, or a range between any two of the foregoing values.

[0099] In some embodiments of the present application, the porosity of the first isolation membrane is 48% to 50%; illustratively, the porosity of the isolation membrane is 48%, 48.1%, 48.2%, 48.3%, 48.5%, 48.8%, 48.9%, 49%, 49.2%, 49.5%, 50% or a range after any two of the foregoing values.

[0100] In some embodiments of the present application, the liquid absorption rate of the first isolation membrane is 130% to 135%; illustratively, the liquid absorption rate of the isolation membrane is 130%, 131%, 132%, 133%, 134%, 135% or a range between any two of the foregoing values.

[0101] In some embodiments of the present application, the air permeability of the second isolation film is 316 seconds / 100cc to 400 seconds / 100cc. Exemplarily, the air permeability of the isolation film is 316 seconds / 100cc, 317 seconds / 100cc, 320 seconds / 100cc, 330 seconds / 100cc, 350 seconds / 100cc, 380 seconds / 100cc, 390 seconds / 100cc, 400 seconds / 100cc, or a range between any two of the foregoing values.

[0102] In some embodiments of the present application, the porosity of the second isolation membrane is 30% to 45%; illustratively, the porosity of the isolation membrane is 30%, 31%, 32%, 33%, 34%, 35%, 36%, 38%, 40%, 41%, 42%, 43%, 44%, 45% or a range after any two of the foregoing values.

[0103] In some embodiments of the present application, the liquid absorption rate of the second isolation membrane is 110% to 126%; illustratively, the liquid absorption rate of the isolation membrane is 110%, 112%, 115%, 118%, 120%, 122%, 125%, 126% or a range between any two of the foregoing values.

[0104] In some embodiments of the present application, the first isolation film and the second isolation film can be prepared by the following method:

[0105] Prepare a first slurry containing first particles with a larger Dv50, apply the first slurry on at least one surface of the base film to form a first coating; dry; and prepare a first isolation film;

[0106] The second particles containing a smaller Dv50 are made into a second slurry, and the second slurry is coated on at least one surface of the base film to form a second coating; and the second coating is dried to obtain a second isolation film.

[0107] In some embodiments of the present application, the first coating and the second coating mentioned above also contain a binder; optionally, in some embodiments of the present application, illustratively, the binder mentioned above can be selected from at least one of polyacrylate, polyethersulfone, polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, polytetrafluoroethylene, vinyl alcohol or polyurethane.

[0108] In some embodiments of the present application, the material of the base film includes at least one of polypropylene or polyethylene. Exemplarily, the material of the base film is selected from any one of polypropylene or polyethylene; or in some embodiments of the present application, the material of the base film is selected from a mixture of polypropylene and polyethylene.

[0109] In other optional embodiments of the present application, the material of the above-mentioned base film can be selected from at least one of glass fiber, non-woven fabric or polyvinylidene fluoride. The base film can be a single-layer film or a multi-layer composite film, without special restrictions. When the base film is a multi-layer composite film, the materials of each layer can be the same or different, without special restrictions.

[0110] [Positive electrode]

[0111] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0112] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0113] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0114] In some embodiments, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM 811 )、lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc. Examples of olivine-structured lithium-containing phosphates can include but are not limited to lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), composite materials of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of composite materials of lithium manganese iron phosphate and carbon.

[0115] In some embodiments, in order to further improve the energy density of the battery, the positive electrode active material for a lithium-ion battery can include a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and one or more of its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0116] In some embodiments, by way of example, the positive electrode active material for a lithium-ion battery can include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, LiFePO4, and LiMnPO4, and one or more of them.

[0117] In the present application, the modified compound of each positive electrode active material mentioned above may be a compound obtained by doping and / or surface coating the positive electrode active material.

[0118] As an optional technical method of the present application, the polyanionic compound can be Li 1+x Mn 1-y A y P 1-z R z O4; wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from the group consisting of B, S, Si and N.

[0119] As an optional technical method of the present application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n , wherein A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from the group consisting of B, S, Si, and N; D includes one or more elements selected from the group consisting of S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the positive electrode active material is electrically neutral.

[0120] The battery will be accompanied by Li deintercalation and consumption during the charge and discharge process, and the molar content of Li is different when the battery is discharged to different states. In the list of positive electrode materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode material is used in the battery system, and the molar content of Li will change after charge and discharge cycles.

[0121] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0122] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0123] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0125] [Negative electrode]

[0126] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0127] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0128] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0129] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be a negative electrode active material for a battery 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 be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from 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.

[0130] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0131] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0132] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0133] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0134] In other embodiments, the current collector of the negative electrode sheet may generally include a current collector body and a primer layer, and the primer layer may be disposed on at least one side of the current collector body.

[0135] It should be noted that when selecting the positive electrode active material and the negative electrode active material of the present application, it is necessary to satisfy the requirement that when the battery cell is fully charged, the rebound rate of the negative electrode sheet is greater than the rebound rate of the positive electrode sheet.

[0136] For example, in some embodiments of the present application, the rebound rate test method is: first, use a micrometer to measure the thickness of the negative electrode sheet and the positive electrode sheet that are not filled with liquid after winding, which is recorded as t1; then, the normally produced battery is fully charged and disassembled, and after the positive and negative electrode sheets are separated, the thickness of the positive and negative electrode sheets is measured, which is recorded as t2. Rebound rate = (t2-t1) / t1.

[0137] [Electrolytes]

[0138] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0139] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0140] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0141] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl 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 sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0142] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0143] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0144] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0145] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0146] In some embodiments, reference Figure 2 , the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0147] Some embodiments of the present application provide a battery, comprising a battery cell provided by any of the aforementioned embodiments.

[0148] In the above technical solution, the term "battery" may refer to at least one of a battery cell, a battery module or a battery pack.

[0149] For example, in some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0150] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0151] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0152] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0153] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0154] Some embodiments of the present application provide an electrical device, which includes the battery cell provided by any of the aforementioned embodiments, or the electrical device includes the battery provided by any of the aforementioned embodiments.

[0155] The battery cell, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0156] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0157] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the battery, a battery pack or a battery module can be used.

[0158] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery may be used as a power source.

[0159] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0160] Example 1

[0161] A battery cell is provided, which is prepared according to the following steps:

[0162]

Isolation film preparation

[0163] The first particles (polyvinylidene fluoride PVDF particles) with a Dv50 of 15 μm and a binder (polyacrylate) were added to deionized water in a mass ratio of 9:1, and stirred in a high-speed mixer to obtain a uniformly dispersed first coating slurry, referred to as the "first slurry"; similarly, the second particles (polyvinylidene fluoride PVDF particles) with a Dv50 of 10 μm and a binder (polyacrylate) were added to deionized water in a mass ratio of 9:1, and stirred in a high-speed mixer to obtain a uniformly dispersed second coating slurry, referred to as the "second slurry", and the solid matter content in the first slurry and the second slurry was 50 wt.%.

[0164] The first slurry was applied to both surfaces of a 5 μm thick polypropylene base film (PP) by extrusion coating; then placed in a vacuum dryer at 50°C for 12 hours, and then hot-pressed by a calender to prepare a first isolation film; the surface density of the first isolation film was 5 g / m 2 The thickness of the first isolation film is 36.7 μm. The air permeability of the first isolation film is 425 seconds / 100 cc. The porosity of the first isolation film is 50%. The liquid absorption rate of the first isolation film is 135%.

[0165] The second slurry was applied to the two surfaces of a 5 μm thick polypropylene base film (PP) by extrusion coating; then placed in a vacuum dryer at 50°C for 12 hours, and then hot-pressed by a calender to prepare a second isolation film; the surface density of the second isolation film was 5 g / m 2 The thickness of the second isolation film is 26 μm. The air permeability of the second isolation film is 400 seconds / 100 cc. The porosity of the second isolation film is 45%. The liquid absorption rate of the second isolation film is 126%.

[0166]

Negative electrode sheet preparation

[0167] The negative electrode material (graphite), conductive agent (acetylene black), binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 97.3:1.2:0.8:0.7, and deionized water was added as a solvent, and the mixture was stirred and mixed to obtain a negative electrode slurry. The negative electrode slurry was then coated on both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to a compaction density of 1.65 g / cc to obtain a negative electrode sheet.

[0168]

Positive electrode sheet preparation

[0169] The positive electrode material 0.4Li2MnO3·0.6LiNi 0.5 Mn 0.5O2, conductive agent (acetylene black), and binder PVDF (polyvinylidene fluoride) are mixed in a weight ratio of 94:4:2, and solvent N-methylpyrrolidone is added. The mixture is stirred thoroughly to obtain a positive electrode slurry, which is then coated on both surfaces of the positive electrode current collector aluminum foil. The positive electrode sheet is obtained after drying and cold pressing to a compaction density of 1.65 g / cc.

[0170]

Electrolyte preparation

[0171] In an argon atmosphere glove box with a water content of <10ppm, EC (ethylene carbonate), PC (polycarbonate), and DMC (dimethyl carbonate) are mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6 and additives vinylene carbonate (VC), vinyl sulfate (DTD), and propylene sulfite (PS) are added. After stirring evenly, an electrolyte is obtained; wherein the concentration of LiPF6 is 1 mol / L, and the mass percentages of VC, DTD, and PS are 3%, 1%, and 1%, respectively.

[0172]

Battery assembly

[0173] The die-cut first separator, the second separator, the negative electrode sheet, and the positive electrode sheet are wound into an electrode assembly in the order of the second separator, the negative electrode sheet, the first separator, the positive electrode sheet, the second separator, the negative electrode sheet, etc.; the electrode assembly is placed in an outer package and injected with the electrolyte, and then a battery cell is obtained through formation, aging and other processes. The battery cell is as follows Figure 7 As shown, in the arc-shaped corner area, the gap between the convex surface of the negative electrode plate and the concave surface of the positive electrode plate is the first gap; the gap between the concave surface of the negative electrode plate and the convex surface of the positive electrode plate is the second gap; the first isolation membrane is arranged in the first gap; and the second isolation membrane is arranged in the second gap.

[0174] Embodiment 2-6

[0175] The differences from Example 1 are shown in Table 2.

[0176] Comparative Example 1

[0177] The difference from Example 1 is the preparation of the isolation film. The first isolation film and the second isolation film of this comparative example are the same; the details are as follows:

[0178] Polyvinylidene fluoride (PVDF) particles with a Dv50 of 10 μm and a binder (polyacrylate) were added to deionized water at a mass ratio of 9:1, and stirred in a high-speed mixer to obtain a uniformly dispersed slurry; the content of solid matter in the slurry was 50 wt.%.

[0179] The slurry was applied to the two surfaces of a polypropylene base film (PP) with a thickness of 5 μm by extrusion coating; then placed in a vacuum dryer at 50° C. for 12 hours, and then hot-pressed by a calender to prepare a first isolation film and a second isolation film.

[0180] The surface density of the first isolation film and the second isolation film is 5g / m 2 The thickness of the first isolation film and the second isolation film is 25.3 μm. The air permeability of the first isolation film and the second isolation film is 370 seconds / 100 cc. The porosity of the first isolation film and the second isolation film is 40%. The liquid absorption rate of the first isolation film and the second isolation film is 120%. See Table 2 for details.

[0181]

Performance test

[0182] Performance tests of various examples and comparative examples:

[0183] 1. Isolation film performance test

[0184] (1) Air permeability test of isolation film:

[0185] The air permeability of the isolation membrane is tested using a conventional isolation membrane air permeability tester. A isolation membrane sample with a cut-off area of ​​100mm×100mm is taken to ensure that the sample is intact and undamaged. A pressure of 1.21KPa is applied through the isolation membrane air permeability tester in a normal pressure environment. The area through which 100mL of air passes is 6.45cm 2 The time required for the isolation film sample. Three samples of each isolation film of the embodiment or comparative example were tested, and the average value of the three measurement results was taken as the air permeability of the isolation film.

[0186] (2) Porosity test of isolation membrane:

[0187] The porosity of the isolation membrane is tested by weighing method. First, weigh the isolation membrane with volume V and record it as m0. Then, completely immerse the weighed isolation membrane in n-hexadecane reagent for 2 hours. Then, take out the isolation membrane and wipe off the residual reagent on the surface of the isolation membrane with dust-free paper. The isolation membrane is weighed and recorded as m1. The porosity of the isolation membrane is calculated using the following formula:

[0188]

[0189] In the above formula, ε is the porosity, unit: %; "ρ" is the density of n-hexadecane, unit: g / cm 3 .

[0190] (3) Liquid absorption test of isolation film:

[0191] First, weigh the mass of the isolation membrane and record it as m0. Then, completely immerse the weighed isolation membrane in the aforementioned electrolyte for 2 hours. Then, take it out and wipe off the residual electrolyte on the surface of the isolation membrane with dust-free paper. Then weigh it again and record it as m1. Use the following formula to calculate the liquid absorption rate of the isolation membrane:

[0192]

[0193] In the above formula, θ is the liquid absorption rate, unit: %.

[0194] (4) Test of isolation film thickness:

[0195] The thickness of the isolation film is tested using a micrometer, and the micrometer is calibrated using a standard gauge block before each test. During the test, 7 or more random positions are selected for each embodiment or comparative example each time, and after obtaining ≥ 7 readings, the maximum and minimum values ​​are removed and the average value is calculated as the thickness of the isolation film.

[0196] 2. Battery performance test

[0197] (1) Gap test between positive electrode and negative electrode:

[0198] The gap between the positive electrode piece and the negative electrode piece of the battery cell that has come off the production line through the normal process is measured by computer tomography (CT). A CT photo is scanned from top to bottom from the top corners of the positive and negative electrodes of the battery cell. The CT photo at a position of 15 mm from top to bottom is taken, and the distance between the tangent line of the convex surface of the inner layer of the negative electrode piece in the horizontal corner area and the tangent line of the convex surface of the outer layer of the positive electrode piece is measured as the gap between the convex surface of the negative electrode piece and the concave surface of the positive electrode piece; the gaps between the convex surface of all the negative electrode pieces to the concave surface of the positive electrode piece of a battery are measured and the average value is taken as the gap between the convex surface of the negative electrode piece and the concave surface of the positive electrode piece of the battery cell. The distance between the tangent line of the convex surface of the inner positive electrode sheet in the corner area and the tangent line of the convex surface of the outer negative electrode sheet is measured as the gap between the convex surface of the positive electrode sheet and the concave surface of the negative electrode sheet. The gaps between the convex surface of the positive electrode sheet and the concave surface of the negative electrode sheet of all the positive electrode sheets of a single cell are measured and the average value is calculated as the gap between the convex surface of the positive electrode sheet and the concave surface of the negative electrode sheet of the battery cell.

[0199] (2) Battery cell cycle performance test:

[0200] At 25℃, the battery was charged to 4.4V at a constant current of 1C, then charged at a constant voltage of 4.4V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 1C. The first cycle discharge capacity (C d1 ); Repeat the charge and discharge until the 500th cycle, and the discharge capacity after 500 cycles is recorded as C dn .

[0201] Capacity retention rate (%) = discharge specific capacity after 500 cycles (Cdn ) / First week discharge capacity (C d1 ).

[0202] (3) The level of lithium deposition at the interface of the negative electrode corner after 500 cycles of the battery cell. The criteria are shown in Table 1:

[0203] Table 1

[0204]

[0205] After cycling the battery cells of each embodiment or comparative example for 500 cycles, the determination of lithium deposition on the interface at the negative electrode corner is as follows:

[0206] After 500 cycles, the battery cell was charged to 4.4V at a constant current of 1C, and then charged at a constant voltage of 4.4V until the current dropped to 0.05C. The battery cell was then disassembled to determine the lithium deposition at the corner of the negative electrode interface. The lithium deposition at the concave and convex surfaces of the corner area of ​​the negative electrode of each embodiment or comparative example was graded according to the judgment levels in Table 1 above.

[0207] The performance test results of various embodiments and comparative examples are shown in Table 3 and Table 4.

[0208] Table 2 Preparation parameters of isolation film

[0209]

[0210] Table 3 Isolation film properties

[0211]

[0212] Table 4 Battery cell performance

[0213]

[0214] From the data in Table 3 above, we can see that:

[0215] Compared with Comparative Example 1, the air permeability, porosity and liquid absorption of the first isolation membranes of Examples 1-4 are improved, which indicates that particles with larger particle sizes will not have much impact on the pores of the base membrane.

[0216] From the results in Table 3 above, it can be seen that when the coating surface density is 5g / m 2When the Dv50 of PVDF is ≤20μm, the air permeability, porosity and liquid absorption of the isolation membrane increase with the increase of Dv50. This is because too small particles will block the pores on the base membrane due to dense distribution, resulting in a decrease in the air permeability, porosity and liquid absorption of the isolation membrane. As the particle size increases, the probability of blocking the pores on the base membrane decreases, so the air permeability, porosity and liquid absorption of the isolation membrane increase; but when Dv50≥20μm, the air permeability, porosity and liquid absorption of the isolation membrane are basically the same, because too large particles can no longer block the gaps on the base membrane. At the same coating surface density, the thickness of the isolation membrane increases with the increase of particle size.

[0217] Coating surface density is 10g / m 2 The thickness of the isolation film coated by PVDF with a Dv50 of 15 μm is the same as that of PVDF with a Dv50 of 30 μm but a coating surface density of only 5 g / m 2 The thickness of the coated isolation membrane is similar, but the air permeability, porosity and liquid absorption rate of the former are reduced. This is because the coating surface density increases and the particles accumulate more, so the thickness increases, but at the same time it also causes the pores of the base membrane to be blocked, and indicators such as porosity and liquid absorption rate decrease.

[0218] Under the same coating surface density conditions, the thickness, porosity, liquid absorption rate, etc. of the isolation membrane formed by coating PVDF and Al2O3 particles with the same Dv50 are not much different.

[0219] From the data in Table 4 above, we can see that:

[0220] Compared with comparative example 1, the gap between the convex surface of the negative electrode piece and the concave surface of the positive electrode piece in each embodiment is increased, which can effectively improve the lithium deposition condition of the convex surface of the negative electrode piece, and the corresponding cycle performance of the lithium-ion secondary battery is improved.

[0221] Combining the PVDF particle size, isolation film thickness, gap between the convex surface of the negative electrode piece and the concave surface of the positive electrode piece, and lithium plating level at the convex corner of the negative electrode piece in Examples 1 to 3 and Comparative Example 1, under the same isolation film coating surface density conditions, with the increase of PVDF particle size (Dv50), the isolation film thickness gradually increases, causing the gap between the convex surface of the negative electrode piece and the concave surface of the positive electrode piece to increase, but the lithium plating condition at the convex corner of the negative electrode piece first changes from level four to level one as the gap between the convex surface of the negative electrode piece and the concave surface of the positive electrode piece increases from 16.8μm to 32.7μm, and then when the gap further increases to 36.2μm, the lithium plating condition deteriorates and drops to level two. At the same time, the lithium deposition condition at the concave corner of the negative electrode piece also shows the same rule, that is, as the gap between the concave surface of the negative electrode piece and the convex surface of the positive electrode piece increases from 12.4μm to about 17μm, the lithium deposition level increases, but as the gap further increases to 21.3μm, the lithium deposition level decreases. The above shows that:

[0222] (1) Under the same surface density conditions, the increase in particle size (Dv50) can increase the thickness of the separator, thereby increasing the gap between the positive electrode and the negative electrode at the corner. However, only a suitable gap can improve the lithium deposition condition at the corner of the negative electrode.

[0223] (2) When the particle size (Dv50) of the first particles is 15 μm to 30 μm and the thickness of the separator is about 35 μm to 65 μm, so that the gap between the convex surface of the negative electrode sheet and the concave surface of the positive electrode sheet is about 25 μm to 50 μm, the lithium deposition condition at the corner of the convex surface of the negative electrode sheet is improved;

[0224] (3) When the particle size (Dv50) of the second particles is 5 to 10 μm and the thickness of the separator is about 15 to 25 μm, so that the gap between the concave surface of the negative electrode plate and the convex surface of the positive electrode plate is about 10 to 17 μm, the lithium deposition state at the corner of the concave surface of the negative electrode plate is improved;

[0225] (4) When the particle size of the isolation film between the convex surface of the negative electrode piece and the concave surface of the positive electrode piece is 25 μm, and the particle size of the isolation film between the concave surface of the negative electrode piece and the convex surface of the positive electrode piece is 10 μm, the lithium deposition state at the corner of the battery can be improved, thereby improving the cycle performance of the lithium-ion secondary battery.

[0226] From the comparison between Example 3 and Example 4, it can be seen that under the same Al2O3 and PVDF particle size conditions, there is no obvious difference in the thickness of the isolation membrane and the gap between the positive and negative electrode sheets, so that the lithium deposition conditions at the corner of the negative electrode sheet are the same, which shows that inorganic particles or organic particles can play a similar role.

[0227] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

Claims

1. A battery cell, characterized in that: include: A negative electrode sheet, a first separator, a second separator and a positive electrode sheet; the negative electrode sheet, the first separator, the second separator and the positive electrode sheet are wound into an electrode assembly along a winding direction, and the electrode assembly includes an arc-shaped corner area; in the arc-shaped corner area, the gap between the convex surface of the negative electrode sheet and the concave surface of the positive electrode sheet is a first gap; the gap between the concave surface of the negative electrode sheet and the convex surface of the positive electrode sheet is a second gap; the first separator is arranged in the first gap; the second separator is arranged in the second gap; The thickness of the first isolation film is greater than the thickness of the second isolation film.

2. The battery cell according to claim 1, characterized in that: At least one surface of the first isolation film is provided with a first coating; the first coating includes first particles; At least one surface of the second isolation film is provided with a second coating; the second coating includes second particles; The D of the first particle V 50 is greater than the D of the second particle V 50.

3. The battery cell according to claim 2, characterized in that: The D of the first particle V 50 is greater than or equal to 15μm.

4. The battery cell according to any one of claims 2 to 3, characterized in that: The D of the second particle V 50 is less than or equal to 10μm.

5. The battery cell according to any one of claims 2 to 4, characterized in that: The D of the first particle V 50 is 15μm~30μm.

6. The battery cell according to any one of claims 2 to 5, characterized in that: The D of the second particle V 50 is 5μm~10μm.

7. The battery cell according to any one of claims 2 to 6, characterized in that: The thickness of the first isolation film is 35 μm to 65 μm.

8. The battery cell according to any one of claims 2 to 7, characterized in that: The second isolation film has a thickness of 15 μm to 25 μm.

9. The battery cell according to any one of claims 2 to 8, characterized in that: The surface density of the first isolation film and the second isolation film is 5g / m 2 ~10g / m 2 Optionally, the difference in surface density between the first isolation film and the second isolation film is -1g / m 2 ~1g / m 2 .

10. The battery cell according to any one of claims 2 to 9, characterized in that: The first particulate matter includes at least one of organic particulate matter or inorganic particulate matter; and / or The second particulate matter includes at least one of organic particulate matter or inorganic particulate matter.

11. The battery cell according to claim 10, characterized in that: The organic particles include at least one of polyvinylidene fluoride particles, polyimide particles or polyethylene oxide particles.

12. The battery cell according to claim 10, characterized in that: The inorganic particles include at least one of aluminum oxide particles or boehmite particles.

13. The battery cell according to any one of claims 1 to 12, characterized in that: The first isolation film satisfies at least one of the following characteristics: (1) The air permeability of the first isolation film is 425 seconds / 100 cc to 430 seconds / 100 cc; (2) The porosity of the first isolation film is 48% to 50%; (3) The liquid absorption rate of the first isolation film is 130% to 135%.

14. The battery cell according to any one of claims 1 to 12, characterized in that: The second isolation film satisfies at least one of the following characteristics: (1) The air permeability of the second isolation film is 316 seconds / 100cc to 400 seconds / 100cc; (2) The porosity of the second isolation film is 30% to 45%; (3) The liquid absorption rate of the second isolation film is 110% to 126%.

15. A battery, characterized in that: A battery cell comprising the battery cell according to any one of claims 1 to 14.

16. An electrical device, characterized in that: The electrical device comprises the battery according to claim 15.

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