Positive pole piece, preparation method of positive pole piece, electrode assembly, battery and power utilization device

Abstract

The invention discloses a positive pole piece, a preparation method of the positive pole piece, an electrode assembly, a battery and a power utilization device. The positive pole piece comprises a positive current collector, a positive active layer is arranged on at least one surface of the positive current collector, the positive active layer comprises a plurality of preset bending areas arranged at intervals in the length direction, and an ion insulation layer is arranged on the surface, away from the positive current collector, of at least one preset bending area of the positive active layer. The ion insulation layer is arranged on the surface of the at least one preset bending area of the positive electrode active layer in the positive electrode plate, so that after the positive electrode plate is used for winding and assembling an electrode assembly, the ion insulation layer is just located in the winding bending area of the electrode assembly, and the electrode assembly is not damaged due to the ion insulation effect of the ion insulation layer. And ion transmission can be well blocked in the bending area of the winding type electrode assembly, so that the risk of lithium precipitation in the bending area can be well reduced, and the cycle performance and the service life of the battery are improved.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a positive electrode plate and a preparation method thereof, an electrode assembly, a battery, and an electrical device. Background Art

[0002] In recent years, new energy vehicles have developed rapidly. The battery drive system is the main factor affecting the performance and cost of new energy vehicles. Secondary batteries have become the preferred power battery solution in the current new energy vehicle battery drive system due to their high energy density, low memory effect and high operating voltage.

[0003] The electrode assembly of a secondary battery generally consists of a positive electrode sheet, a separator, and a negative electrode sheet. For wound electrode assemblies, the gap between the positive and negative electrode sheets at the bend of the winding core is large, which can easily lead to a longer ion migration path at the bend. This can also lead to insufficient lithium insertion capacity in the negative electrode, resulting in a higher risk of lithium plating. Summary of the Invention

[0004] In view of the above problems, the present application provides a positive electrode plate and its preparation method, an electrode assembly, a battery and an electrical device, aiming to solve the technical problem of how to reduce the risk of lithium plating in the electrode.

[0005] In a first aspect, an embodiment of the present application provides a positive electrode plate, comprising a positive electrode current collector, wherein a positive electrode active layer is provided on at least one surface of the positive electrode current collector, the positive electrode active layer comprises a plurality of predetermined bending regions spaced apart along the length direction, and an ion insulating layer is provided on a surface of at least one of the predetermined bending regions of the positive electrode active layer away from the positive electrode current collector.

[0006] By arranging an ion insulating layer on the surface of at least a predetermined bending area of ​​the positive electrode active layer in the positive electrode sheet, after the positive electrode sheet is used to be wound and assembled into an electrode assembly, the ion insulating layer is located exactly in the bending area where the electrode assembly is wound. The ion insulating effect of the ion insulating layer can effectively block ion transmission in the bending area of ​​the wound electrode assembly, thereby effectively reducing the risk of lithium deposition in the bending area, thereby improving the cycle performance and service life of the battery.

[0007] In some embodiments, the ionic conductivity of the ion insulating layer is less than or equal to 1×10 -6 S / cm; and / or,

[0008] The material of the ion insulating layer includes high molecular polymer.

[0009] Ionic conductivity is less than or equal to 1×10 -6S / cm ion insulating layer can play a good ion insulating effect during the charge and discharge process. The high molecular polymer has very low ion conductivity and is therefore well suited to be used as a material for forming the ion insulating layer.

[0010] In some embodiments, the high molecular weight polymer includes at least one of an acrylic copolymer and a vinyl aromatic hydrocarbon polymer.

[0011] The above-mentioned high molecular polymer is not only easy to prepare but also has stable performance, and the ion insulating layer formed can stably achieve the ion insulating effect.

[0012] In some embodiments, the acrylic acid ester copolymer includes a copolymer of methacrylic acid and methyl methacrylate; or

[0013] The vinyl aromatic hydrocarbon polymer includes a polymer of at least one monomer selected from the group consisting of styrene, distyrene, tristyrene, methylstyrene, ethylstyrene, propylstyrene, butylstyrene, halogenated styrene, nitrostyrene, styrylamine, styrene propene and styrene butene.

[0014] The high molecular weight polymer formed by the above monomers can achieve a good ion insulation effect.

[0015] In some embodiments, the width of the ion insulating layer is 0.2 mm to 0.3 mm wider than the coating width of the positive electrode active layer; and / or,

[0016] The thickness of the ion insulating layer is 3 μm to 30 μm.

[0017] By providing an ion insulating layer that is wider than the coating width of the positive electrode active layer, ion transmission in the predetermined bending region of the positive electrode active layer can be more comprehensively blocked. The ion insulating layer of the aforementioned thickness can effectively block ion transmission.

[0018] In some embodiments, the positive electrode sheet is in a winding structure along the length direction, and the ion insulating layer is provided on the surface of each predetermined bending area away from the positive electrode current collector, and each ion insulating layer is located on the concave surface of the bending area of ​​the winding structure.

[0019] For the positive electrode sheet with a wound structure used in a wound electrode assembly, since the risk of lithium deposition is higher on the concave surface of the bending area of ​​the wound electrode assembly, the ion insulation layer is arranged on the concave surface of the bending area of ​​the wound structure to more effectively reduce the risk of lithium deposition.

[0020] In a second aspect, an embodiment of the present application provides a method for preparing the above-mentioned positive electrode sheet, comprising:

[0021] preparing the positive electrode active layer on at least one surface of the positive electrode current collector;

[0022] The ion insulating layer is prepared on a surface of the positive electrode active layer away from the positive electrode current collector in at least one predetermined bending region along the length direction.

[0023] After preparing a positive electrode active layer on the positive electrode current collector, an ion insulating layer is prepared on at least one predetermined bending area of ​​the positive electrode active layer along the length direction. After the positive electrode sheet obtained in this way is used to be wound and assembled into an electrode assembly, the ion insulating layer can be precisely positioned in the bending area of ​​the wound electrode assembly. This positive electrode sheet preparation method is not only simple in process, but also the ion insulating effect of the prepared ion insulating layer can effectively block ion transmission in the bending area of ​​the wound electrode assembly, thereby improving the cycle performance and service life of the battery.

[0024] In some embodiments, the steps of preparing the ion insulating layer include:

[0025] preparing a precursor solution containing polymer monomers and initiator;

[0026] During the winding process, the precursor solution is coated on the predetermined bending area to carry out in-situ polymerization reaction to obtain the ion insulating layer.

[0027] The ion insulating layer is realized through the precursor solution coating process, which is not only simple in process, but also controllable in coating amount and formation position of the ion insulating layer. At the same time, the ion insulating layer can be stably synthesized by in-situ polymerization on the predetermined bending area.

[0028] In some embodiments, the polymer monomer includes at least one of an acrylate monomer and a vinyl aromatic hydrocarbon monomer; and / or,

[0029] The initiator includes at least one of azobisisobutyronitrile and dibenzoyl peroxide.

[0030] The polymer monomer is not only easy to obtain, but also the ion insulating layer formed can stably achieve the ion insulating effect. The initiator can well initiate the in-situ polymerization reaction of the polymer monomer.

[0031] In some embodiments, the acrylic acid ester monomer includes a mixed monomer of methacrylic acid and methyl methacrylate; or

[0032] The vinyl aromatic hydrocarbon monomer includes at least one monomer selected from the group consisting of styrene, distyrene, tristyrene, methylstyrene, ethylstyrene, propylstyrene, butylstyrene, halogenated styrene, nitrostyrene, styrylamine, styrene propene and styrene butene.

[0033] The above monomers can be well subjected to in-situ polymerization reaction, and the obtained high molecular polymer can well achieve ion insulation effect.

[0034] In some embodiments, based on the total weight of the precursor solution being 100%, the precursor solution comprises: 99% to 99.98% of polymer monomers and 0.02% to 1% of initiator; and / or,

[0035] The temperature of the in-situ polymerization reaction is 80°C to 120°C.

[0036] The precursor solution of the above formulation can be well coated through the die, and the in-situ polymerization reaction of the polymer monomer can be well achieved under the above temperature conditions.

[0037] In a third aspect, an embodiment of the present application provides an electrode assembly, comprising a positive electrode sheet, a negative electrode sheet, and an isolating member located between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet, the isolating member, and the negative electrode sheet are in a wound structure, and the positive electrode sheet comprises the positive electrode sheet provided in the first aspect of the embodiment of the present application and / or the positive electrode sheet prepared by the preparation method provided in the second aspect of the embodiment of the present application; wherein the ion insulating layer is located in the bending region of the wound structure.

[0038] By using the positive electrode pole piece unique to the embodiment of the present application in an electrode assembly with a winding structure, an ion insulating layer is provided on the surface of at least one bending area of ​​the positive electrode active layer in the positive electrode pole piece. The ion insulating effect of the ion insulating layer can effectively block the ion transmission in the bending area of ​​the wound electrode assembly, thereby effectively reducing the risk of lithium deposition in the bending area, thereby improving the cycle performance and service life of the electrode assembly.

[0039] In some embodiments, the ion insulating layer is located on the concave surface of the bending region of the positive electrode sheet, and the length L of the nth ion insulating layer starting from the starting point of the positive electrode sheet winding is n =π(D0+0.5(n+1)δ1+0.5(n-1)δ2+(2n+4)δ3) / 2, where n is an odd number greater than or equal to 1; or the length L of the n'th ion insulating layer n' =π(D0+0.5n'δ1+0.5n'δ2+(2n'+4)δ3) / 2, where n' is an even number greater than or equal to 2;

[0040] Wherein, D0 is the equivalent diameter of the arc corner of the innermost bending area of ​​the negative electrode sheet, δ1 is the thickness of the negative electrode sheet, δ2 is the thickness of the positive electrode sheet, and δ3 is the thickness of the separator.

[0041] According to the number of bends of the positive electrode sheet when it is wound in sequence, an ion insulating layer of a certain length is set. Specifically, from the inside to the outside of the winding core, the length of each ion insulating layer increases in sequence according to the formula. In this way, each ion insulating layer can well cover the bending area surface corresponding to the winding structure, thereby more effectively reducing the risk of lithium plating.

[0042] In some embodiments, D0 is 0.01 mm to 0.6 mm, δ1 is 0.08 mm to 0.26 mm, δ2 is 0.097 mm to 0.2 mm, and δ3 is 0.006 mm to 0.016 mm; and / or,

[0043] Along the length direction of the positive electrode sheet, the distance between two adjacent ion insulating layers is equal to the circumference of the winding needle of the positive electrode sheet.

[0044] The parameters corresponding to D0, δ1, δ2, and δ3 are easy to achieve, and the resulting electrode assembly can improve volumetric energy density. The spacing between adjacent ionic insulating layers along the length of the positive electrode sheet does not change with the number of wound positive electrode sheets, remaining consistent with the circumference of the winding needle. This makes it easy to control the spacing during the winding process and allows the ionic insulating layers to be precisely positioned within the bends of the wound structure.

[0045] In a fourth aspect, an embodiment of the present application provides a battery, comprising the electrode assembly provided in the third aspect of the embodiment of the present application.

[0046] Based on the low risk of lithium plating in the electrode assembly of the embodiment of the present application, the battery of the embodiment of the present application has good cycle performance and service life.

[0047] In a fifth aspect, an embodiment of the present application provides an electrical device, comprising the battery provided in the fourth aspect of the present application.

[0048] By adopting the battery provided in the fourth aspect of the embodiment of the present application, such an electrical device has good charge and discharge cycle performance and can work better.

[0049] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0051] Figure 1 This is a schematic structural diagram of the positive electrode sheet according to an embodiment of the present application;

[0052] Figure 2 This is a schematic structural diagram of an electrode assembly according to an embodiment of the present application;

[0053] Figure 3 This is a schematic diagram of a battery cell structure of an embodiment of a secondary battery of the present application;

[0054] Figure 4 for Figure 3 A schematic diagram of an exploded view of a battery cell of a secondary battery shown;

[0055] Figure 5 This is a schematic structural diagram of an embodiment of a battery module of the present application;

[0056] Figure 6 This is a schematic structural diagram of an embodiment of a battery pack of the present application;

[0057] Figure 7 for Figure 6 Schematic diagram of the exploded structure of the battery pack shown;

[0058] Figure 8 Schematic diagram of an embodiment of an electrical device including the secondary battery of an embodiment of the present application as a power source.

[0059] Description of reference numerals:

[0060] 110-positive electrode current collector; 111-positive electrode active layer; 112-ion insulating layer;

[0061] A-predetermined bending area; B-predetermined straight area;

[0062] 11-positive electrode sheet; 12-negative electrode sheet, 13-separator;

[0063] A'-bending area; B'-straight area;

[0064] 20 - battery cell; 21 - housing; 22 - top cover assembly; 23 - electrode assembly; 30 - battery module; 40 - battery pack; 41 - upper case; 42 - lower case. DETAILED DESCRIPTION

[0065] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0066] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art 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" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0067] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0068] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0069] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0070] In the description of the embodiments of this application, the term "plurality" refers to two or more (including two). Similarly, "multiple groups" refers to two or more (including two groups), and "multiple sheets" refers to two or more (including two sheets). "At least one" refers to more than one (including one, two, three, etc.).

[0071] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to 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.

[0072] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0073] With the increasing depletion of traditional energy resources, the development of new energy storage devices is gaining increasing attention. Secondary batteries, in particular, have attracted considerable attention due to their high energy density, high theoretical capacity, excellent cycle stability, and environmentally friendly properties. Secondary batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, but are also widely used in a variety of fields, including electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles. As the application areas of secondary batteries as power batteries continue to expand, their market demand is also growing, and the requirements for battery performance, such as cycle performance, are becoming increasingly stringent.

[0074] The electrode assembly of a secondary battery generally consists of a positive electrode sheet, a separator, and a negative electrode sheet. A wound electrode assembly is formed by stacking and winding the positive electrode sheet, separator, and negative electrode sheet. Currently, conventional wound lithium-ion battery electrode assemblies typically consist of a positive electrode sheet with a positive active layer uniformly coated on the current collector surface, a separator, and a negative electrode sheet, which are assembled using the winding needle of a winding machine.

[0075] The winding core of the wound electrode assembly will form an arc-shaped corner. The gap between the positive electrode sheet and the negative electrode sheet at the bending position of the arc-shaped corner is large, which easily leads to a longer ion migration path at the bending point. At the same time, the inner corner is often accompanied by insufficient CB (that is, the ratio of the mass of negative electrode active material per unit area to the mass of positive electrode active material per unit area), resulting in insufficient lithium insertion capacity of the negative electrode, and ultimately resulting in a higher risk of lithium plating in the bending area of ​​the wound electrode assembly.

[0076] Based on the above considerations, in order to accurately and effectively prevent lithium deposition at the corners of the wound electrode assembly, an ion insulating layer is provided on at least one predetermined bending area of ​​the positive electrode active layer along the length direction on the positive electrode current collector. After such a positive electrode sheet is used to be wound and assembled into an electrode assembly, the ion insulating layer on the outer surface of the positive electrode active layer can be accurately positioned in the bending area where the electrode assembly is wound. Moreover, the ion insulating effect of the ion insulating layer can well block the ion transmission in the bending area of ​​the wound electrode assembly. Therefore, the embodiment of the present application utilizes a new mechanism for preventing lithium deposition, combined with the position of the ion insulating layer, to accurately and effectively prevent lithium deposition at the corners of the wound electrode assembly, thereby improving the cycle performance and service life of the battery. Therefore, the following technical solution is proposed.

[0077] Positive electrode sheet and preparation method thereof

[0078] In a first aspect, the present invention provides a positive electrode sheet, such as Figure 1 As shown, the positive electrode plate includes: (1) a positive electrode current collector 110, which is used to collect the current generated by the positive electrode plate. (2) a positive electrode active layer 111, which is a film layer containing positive electrode active material and can realize the insertion and extraction of active metal ions. The positive electrode active layer 111 is provided on at least one surface of the positive electrode current collector 110. In other words, the positive electrode active layer 111 can be provided on one surface of the positive electrode current collector 110, or on two opposite surfaces of the positive electrode current collector 110. The positive electrode active layer 111 includes a plurality of predetermined bending regions A spaced apart along the length direction; and two adjacent predetermined bending regions A are connected by a predetermined straight region B. (3) An ion insulating layer 112 has the effect of blocking ion transmission; the ion insulating layer 112 is located on the surface of the positive electrode active layer 111 in the predetermined bending area A, and can be located on the surface of the positive electrode active layer 111 in one predetermined bending area A, or on the surface of the positive electrode active layer 111 in multiple predetermined bending areas A, that is, the ion insulating layer 112 is provided on the surface of at least one predetermined bending area A away from the positive electrode current collector 110.

[0079] It should be noted that the embodiment of the present application divides the positive electrode active layer 111 into a plurality of predetermined bending areas A spaced apart along the length direction. These areas are predefined based on the position of the positive electrode active layer 111 in the wound electrode assembly after winding. Along the length direction of the positive electrode sheet, the two ends of the predetermined straight area B are connected to the adjacent predetermined bending areas A, and the adjacent predetermined bending areas A have opposite predetermined bending directions, that is, the actual bending directions after winding are opposite. Figure 2 As shown, the positive electrode active layer 111 corresponds to the bending area A' of the electrode assembly after being wound along the predetermined bending area A in the length direction, and corresponds to the straight area B' of the electrode assembly after being wound along the predetermined straight area B in the length direction. The straight area B' connects the adjacent bending areas A', and the bending directions of the adjacent bending areas A' are opposite.

[0080] Since the positive electrode active layer 111 includes multiple predetermined bending regions A separated by multiple predetermined straight regions B along its length, multiple ion insulating layers 111, i.e., multiple ion insulating units having an ion insulating effect, can be provided. Each ion insulating layer 111 is provided on a single predetermined bending region A. As needed, an ion insulating layer 111 is provided on the surface of at least one predetermined bending region A away from the positive electrode current collector 110.

[0081] The positive electrode plate of the embodiment of the present application can be configured for use in a wound electrode assembly. When the electrode assembly is subsequently wound and assembled, the ion insulating layer 112 can be precisely positioned on the outer surface of the predetermined bending area A of the positive electrode active layer 111 in the bending area A' of the wound electrode assembly after winding. In addition, the ion insulating effect of the ion insulating layer 112 can effectively block the ion transmission in the bending area A' of the wound electrode assembly. Therefore, lithium deposition at the corners of the bending area of ​​the wound electrode assembly can be accurately and effectively prevented, thereby improving the cycle performance and service life of the battery.

[0082] In some embodiments, the ion insulating layer 112 refers to a unit layer having a function of blocking ion transport, mainly referring to blocking the transport of active metal ions. Specifically, the ion conductivity of the ion insulating layer 112 is less than or equal to 1×10 -6 S / cm; Ionic conductivity is a measure of the tendency of a substance to conduct ions. The intrinsic ionic conductivity of the ionic insulating layer of the embodiment of the present application is ≤1×10 -6 S / cm, which can play a good ion insulation effect during the charge and discharge process of the electrode assembly, thereby effectively blocking the ion transmission of the positive electrode sheet in the bending area of ​​the electrode assembly, thereby avoiding lithium deposition at the corners of the bending area of ​​the electrode assembly.

[0083] Specifically, ionic conductivity testing can be performed using conventional testing methods. For example, in the present embodiment, the testing method includes: using 19 mm diameter stainless steel sheets as electrodes on both sides, using the ion insulating layer to be tested as a separator, and taking LiPF6 electrolyte to assemble a symmetrical button cell. The AC impedance R of the symmetrical button cell is then measured using a LAND device, and the ionic conductivity is calculated according to the following formula:

[0084] Ionic conductivity = thickness of the ion insulating layer to be measured / (electrode area S × symmetrical button cell impedance R).

[0085] In some embodiments, the material of the ion insulating layer 112 includes a polymer. The polymer has very low ionic conductivity and can therefore be well used as a material for forming the ion insulating layer. The ionic conductivity of the ion insulating layer composed of the polymer is less than or equal to 1×10 -6 S / cm.

[0086] In some embodiments, the polymer of the ion insulating layer 112 includes at least one of an acrylic copolymer and a vinyl aromatic polymer. The polymer is not only easy to prepare but also has stable performance. The formed ion insulating layer 112 can stably achieve an ion insulating effect.

[0087] In some embodiments, the acrylic ester copolymer includes a copolymer of methacrylic acid and methyl methacrylate. The acrylic ester copolymer formed from these monomers can achieve excellent ion insulation. Specifically, the methyl methacrylate content of the mixed monomers is 2-40% by weight. The acrylic ester copolymer prepared from the mixed monomers of methyl methacrylate and methacrylic acid can achieve excellent ion insulation.

[0088] Alternatively, the vinyl aromatic hydrocarbon polymer includes a polymer of at least one of styrene, styrene distilbenes, tristyrene distilbenes, methylstyrene, ethylstyrene, propylstyrene, butylstyrene, halogenated styrenes, nitrostyrene, styrylamine, styrene propene, and styrene butene. The vinyl aromatic hydrocarbon polymer formed from the above-mentioned styrene and its derivative monomers can achieve excellent ion insulation effects.

[0089] In some embodiments, the width of the ion insulating layer 112 is 0.2 mm to 0.3 mm wider than the coating width of the positive electrode active layer 111. The coating width of the positive electrode active layer 111 refers to the effective width of the positive electrode active layer 111 along the width direction of the positive electrode sheet after the positive electrode sheet is formed. It is the width actually visible in the electrode assembly. The width of the ion insulating layer 112 is the width along the width direction of the positive electrode sheet. Specifically, both ends of the ion insulating layer 112 along the width direction of the positive electrode sheet extend by 0.2 mm to 0.3 mm from both ends of the coating width of the positive electrode active layer 111. By providing an ion insulating layer 112 that is wider than the coating width of the positive electrode active layer 111, ion transmission in the predetermined bending region of the positive electrode active layer can be more comprehensively blocked. The coating width of the positive electrode active layer 111 can be set according to specific circumstances. For example, the effective coating width can be designed to be 40 mm to 300 mm.

[0090] In some embodiments, the thickness of the ion insulating layer 112 is 3 μm to 30 μm. For example, the thickness may be 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 20 μm, 25 μm, 28 μm, 30 μm, etc. Ion insulating layer 112 of such thickness can effectively block ion transport while having little impact on the volumetric energy density of the battery.

[0091] In some embodiments, the width of the ion insulating layer 112 is 0.2 mm to 0.3 mm wider than the coating width of the positive electrode active layer 111 at both ends, and the thickness of the ion insulating layer 112 is 3 μm to 30 μm, which can more effectively block ion transmission. The length of a single ion insulating layer 112 and the spacing between two adjacent ion insulating layers 112 can be adjusted based on the specific position and thickness of the positive electrode sheet in the wound electrode assembly, and the thickness of the negative electrode sheet and separator.

[0092] In some embodiments, the positive electrode sheet is in a winding structure along the length direction, and an ion insulating layer 112 is provided on the surface of each predetermined bending area A away from the positive electrode current collector, and each ion insulating layer 112 is located on the concave surface of the bending area of ​​the winding structure.

[0093] The risk of lithium plating is higher on the concave surface of the bending area of ​​the wound structure. For the positive electrode sheet with a wound structure used in a wound electrode assembly, an ion insulating layer is provided on the concave surface of each bending area, which can more effectively reduce the risk of lithium plating.

[0094] In some embodiments, the positive electrode current collector 110 has two opposite surfaces in its thickness direction, and the positive electrode active layer 111 is disposed on either or both of the two opposite surfaces of the positive electrode current collector 110 .

[0095] As an example, the positive electrode current collector 110 may be a metal foil or a composite current collector. For example, as the metal foil, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, nickel, titanium, silver-surface-treated aluminum or stainless steel, etc. may be used. The composite current collector may include a polymer material base layer and a metal 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 material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0096] As an example, the positive electrode active layer 111 includes a positive electrode active material, and the positive electrode active material may include at least one of the following materials: lithium-containing phosphate, lithium transition metal oxide and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active layers may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium-containing phosphates may include but are not limited to at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon. 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 NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc.

[0097] In some embodiments, the positive electrode active layer 111 may further include a conductive agent and a binder, wherein the mass proportion of the positive electrode active material may be 95% to 100%, that is, the conductive agent and the binder may be added or not. Specifically, the mass ratio of the positive electrode active material, the conductive agent and the binder may be (95 to 99): (0.5 to 2.5): (0.5 to 2.5). 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. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0098] In the second aspect, the present invention provides a method for preparing the above-mentioned positive electrode sheet, combining Figure 1 and Figure 2 , the preparation method of the positive electrode sheet includes:

[0099] S01: preparing a positive electrode active layer 111 on at least one surface of a positive electrode current collector 110;

[0100] S02: preparing an ion insulating layer 112 on a surface of the positive electrode active layer 111 that is away from the positive electrode current collector and at least one predetermined bending region A along the length direction.

[0101] In the embodiment of the present application, the ion insulating layer 112 is prepared after the positive electrode active layer 111 is prepared. Since the ion insulating layer 112 is on the outer surface of the positive electrode active layer 111, the preparation of the ion insulating layer 112 can accurately cover the target position and can be accurately positioned in the actual bending area of ​​the positive electrode sheet when the electrode assembly is assembled in the winding process. Specifically, after the positive electrode active layer 111 is prepared on the positive electrode current collector 110, the ion insulating layer 112 is prepared on at least one predetermined bending area A along the length direction of the positive electrode active layer 111. After the positive electrode sheet obtained in this way is used for winding and assembling into an electrode assembly, the ion insulating layer 112 can be accurately positioned in the bending area of ​​the electrode assembly. This method of preparing the positive electrode sheet is not only simple in process, but also can effectively block the ion transmission in the bending area of ​​the wound electrode assembly through the ion insulating effect of the prepared ion insulating layer 112, thereby improving the cycle performance and service life of the battery.

[0102] In some embodiments, the step of preparing the positive electrode active layer 111 includes: preparing a positive electrode slurry containing a positive electrode active material, and then coating and drying the positive electrode slurry to obtain the positive electrode active layer.

[0103] In some embodiments, the steps of preparing the ion insulating layer 112 include:

[0104] S021: Prepare a precursor solution containing polymer monomers and initiator;

[0105] S022: During the winding process, the precursor solution is coated on the predetermined bending area A to perform an in-situ polymerization reaction to obtain the ion insulating layer 112.

[0106] The synthesis of the ion insulating layer 112 is achieved through a coating process of a precursor solution containing polymer monomers and initiators. Not only is the process simple, but the coating amount and the formation position of the ion insulating layer 112 are controllable. At the same time, by performing in-situ polymerization on the predetermined bending area A, the ion insulating layer 112 can be synthesized very stably.

[0107] Specifically, during the winding process of the positive electrode sheet into a battery cell, after accurately identifying the actual corner position of the positive electrode sheet, the precursor solution is coated on the inner surface of the corner of the predetermined bending area A of the positive electrode sheet, where the ion insulating layer 112 needs to be set, by die coating, and then in situ polymerization is achieved; for example, the sheet passes through a high-temperature section to complete pre-polymerization, and finally the complete polymerization of the polymer monomer is achieved through a tunnel furnace or hot pressing process.

[0108] It should be noted that if the ion insulating layer is provided between the positive electrode current collector and the positive electrode active layer, the preparation of the ion insulating layer must be carried out in the coating process (i.e., the ion insulating layer is first coated and prepared, and then the positive electrode active layer is coated). In this way, the position of the ion insulating layer is easy to deviate from the bending zone during winding, and the degree of deviation is greater as it goes to the outer circle. Due to inaccurate positioning, the lithium deposition phenomenon cannot be effectively overcome. However, the ion insulating layer of the present application is provided on the surface of the bending zone of the positive electrode active layer away from the positive electrode current collector. This can accurately and effectively prevent lithium deposition at the corners of the bending zone of the wound electrode assembly, thereby improving the cycle performance and service life of the battery.

[0109] In some embodiments, the polymer monomer includes at least one of an acrylate monomer and a vinyl aromatic hydrocarbon monomer; the above polymer monomer is easily available on the market, and the synthesized high molecular polymer has stable performance, and the obtained ion insulating layer can stably achieve an ion insulating effect.

[0110] In some embodiments, the initiator includes at least one of azobisisobutyronitrile and dibenzoyl peroxide. The above initiator can well initiate the in situ polymerization reaction of the polymer monomer.

[0111] Specifically, the polymer monomer includes at least one of an acrylic acid ester monomer and a vinyl aromatic hydrocarbon monomer, and the hair dryer includes at least one of azobisisobutyronitrile and dibenzoyl peroxide.

[0112] In some embodiments, the acrylate monomer includes a mixed monomer of methacrylic acid and methyl methacrylate, with methyl methacrylate and methacrylic acid being copolymerized and pre-stirred or ultrasonically dispersed. The vinyl aromatic hydrocarbon monomer includes styrene and its para- or meta-substituted derivatives, such as dimers of styrene and styrene, tristyrene, methylstyrene (such as 4-methylstyrene), ethylstyrene (such as α-methylstyrene), propylstyrene, butylstyrene (such as 4-tert-butylstyrene), halogenated styrene (such as 4-halogenated styrene), nitrostyrene (such as 3-nitrostyrene, 4-nitrostyrene), styrylamine (such as 4-styrylamine), styrene propene and styrene butene (such as 4-phenyl-1-butene). The above monomers are self-polymerized and the product molecular weight consistency is good.

[0113] The above monomers can be well subjected to in-situ polymerization reaction, and the obtained high molecular polymer can well achieve ion insulation effect.

[0114] In some embodiments, based on the total weight of the precursor solution being 100%, the precursor solution comprises: 99% to 99.98% of polymer monomers and 0.02% to 1% of initiator; the precursor solution with the above formulation can be well coated through the die.

[0115] In some embodiments, the temperature of the in-situ polymerization reaction is 80% to 120°C. The above-mentioned ion insulating precursor can be easily synthesized by thermally induced in-situ polymerization. In order to realize the above-mentioned in-situ polymerization reaction, components used in the winding equipment are used: including a set of coating dies and a pair of heating plates. During the winding process, a precursor solution containing the above-mentioned polymer monomer and initiator is coated on a predetermined bending area of ​​the positive electrode active layer by die coating, and then the pole piece passes through a high-temperature section (80°C to 120°C) to complete pre-polymerization, and finally the polymer monomer is completely polymerized when the core passes through a tunnel furnace (60°C to 90°C) or hot pressing (75°C to 110°C).

[0116] By constructing an ion insulating layer 112 in situ on the inner surface of the positive electrode sheet in the bending area of ​​the winding core by simple heating and polymerization, the ion insulating properties of the ion insulating layer 112 are utilized to block the ion transmission at the corners, thereby effectively improving the risk of lithium plating at the corners of the winding core of the electrode assembly in the early stage of the cycle and during long cycles.

[0117] Specifically, by controlling the coating amount of the precursor solution (e.g. 0.13 g / m 2 ~0.5g / m 2), thereby constructing the in-situ polymerized ion insulating layer 112, the thickness of which can be controlled within a range of 3 μm to 30 μm. The above coating amount is the single-sided coating weight, which is the unit area weight of the precursor solution applied to a single surface of the positive electrode active layer 111 after drying. After the positive electrode sheet is prepared, the positive electrode sheet product is subsequently prepared by conventional electrode sheet preparation methods such as cold pressing and die-cutting. It is then assembled with the negative electrode sheet and separator into a wound electrode assembly to prepare a battery.

[0118] The ion insulating layer 112 is prepared during the winding process of the electrode assembly. Considering the certain fluctuations in the thickness of the incoming electrode sheets during the production process, the winding parameters are adjusted promptly before the start of the winding process based on the actual thickness of the positive and negative electrode sheets to ensure that the sheet misalignment is within the control specifications. At the same time, the actual corner position of each layer of sheet is identified in real time, thereby calibrating the starting position of the ion insulating layer coating.

[0119] Electrode assembly

[0120] In a third aspect, the present invention provides an electrode assembly, such as Figure 3 As shown, it includes a positive electrode sheet 11, a negative electrode sheet 12 and an isolation member 13 located between the positive electrode sheet 11 and the negative electrode sheet 12. The positive electrode sheet 11, the isolation member 13 and the negative electrode sheet 12 are in a wound structure. The positive electrode sheet 11 includes the positive electrode sheet provided by the first aspect of the above-mentioned embodiment of the present application and / or the positive electrode sheet prepared by the preparation method provided by the second aspect of the above-mentioned embodiment of the present application; wherein the ion insulating layer 112 is located in the bending area A' of the winding structure.

[0121] By using the positive electrode sheet unique to the embodiment of the present application in an electrode assembly with a winding structure, an ion insulating layer is provided on the surface of at least one bending area of ​​the positive electrode active layer wound by the positive electrode sheet. The ion insulating effect of the ion insulating layer can effectively block the ion transmission in the bending area of ​​the wound electrode assembly, thereby effectively reducing the risk of lithium deposition in the bending area, thereby improving the cycle performance and service life of the electrode assembly.

[0122] In some embodiments, the ion insulating layer 112 is located on the concave surface of the bending region of the positive electrode sheet 11 of the electrode assembly. The length L of the nth ion insulating layer 112 from the starting point of the positive electrode sheet 11 is n =π(D0+0.5(n+1)δ1+0.5(n-1)δ2+(2n+4)δ3) / 2, where n is an odd number greater than or equal to 1; or the length L of the n'th ion insulating layer 112 n'=π(D0+0.5n'δ1+0.5n'δ2+(2n'+4)δ3) / 2, n' is an even number greater than or equal to 2; wherein D0 is the equivalent diameter of the arc corner of the innermost bending area of ​​the negative electrode sheet, δ1 is the thickness of the negative electrode sheet, δ2 is the thickness of the positive electrode sheet, and δ3 is the thickness of the separator.

[0123] Specifically, the ion insulating layer 112 is provided on the concave surface of each bending area of ​​the positive electrode sheet 11, and the length is set according to the above formula; for example, counting from the core of the positive electrode sheet 11, the length L1 of the first ion insulating layer 112 is L1 = π(D0 + 0.5(1+1)δ1 + (2+4)δ3) / 2, the length L2 of the second ion insulating layer 112 is L2 = π(D0 + 0.5×2δ1 + 0.5×2'δ2 + (2×2+4)δ3) / 2, the length L3 of the third ion insulating layer 112 is L3 = π(D0 + 0.5(3+1)δ1 + 0.5×2δ2 + (2×3+4)δ3) / 2, and the length L4 of the fourth ion insulating layer 112 is L4 = π(D0 + 0.5×4δ1 + 0.5×4'δ2 + (2×4+4)δ3) / 2; and so on according to the above formula.

[0124] According to the number of times the positive electrode sheet 11 is bent from the starting point of the winding core, an ion insulating layer 112 of a certain length is set. Specifically, from the inside to the outside of the winding core, the length of each ion insulating layer 112 increases successively according to the formula. In this way, each ion insulating layer 112 can well cover the bending area corresponding to the winding structure, thereby more effectively reducing the risk of lithium plating.

[0125] In some embodiments, the equivalent diameter D0 of the arc-shaped corner of the innermost bending area of ​​the negative electrode sheet, the winding thickness δ1 of the negative electrode sheet, the winding thickness δ2 of the positive electrode sheet, and the thickness δ3 of the isolation member after hot pressing and shaping can be selected according to the actual size requirements of the electrode assembly; for example, D0 can be 0.01mm~0.6mm, δ1 can be 0.08mm~0.26mm, δ2 can be 0.097mm~0.2mm, and δ3 can be 0.006mm~0.016mm; the parameters corresponding to the above D0, δ1, δ2, and δ3 are easy to achieve, and the formation of an electrode assembly can improve the volume energy density.

[0126] In some embodiments, the spacing between two adjacent ion insulating layers 112 along the length of the positive electrode sheet 11 is equal to the circumference of the winding needle of the positive electrode sheet 11. The spacing between two adjacent ion insulating layers 112 refers to the distance between adjacent ends of two adjacent ion insulating layers 112 along the length of the positive electrode sheet 11, for example, the distance between the end of the first ion insulating layer 112 and the beginning of the second ion insulating layer 112 along the length of the positive electrode sheet 11.

[0127] The spacing between adjacent ion insulating layers 112 along the length direction of the positive electrode sheet 11 does not change with the increase in the number of layers of the wound positive electrode sheet 11, and always remains consistent with the circumference of the winding needle. This makes it easy to control the spacing through the winding process, and at the same time allows the ion insulating layer 112 to be accurately positioned in the bending area A' of the winding structure.

[0128] The electrode assembly of the embodiment of the present application can be prepared by stacking and winding the positive electrode sheet 11, the separator 13 and the negative electrode sheet 12, and the preparation of the ion insulating layer 112 on the positive electrode sheet 11 can be achieved during the winding process of the electrode assembly. During the winding process of the positive electrode sheet 11, after accurately identifying the actual corner position of the positive electrode sheet 11, the polymerization precursor solution is coated on the concave surface of each corner of the positive active layer 111 of the positive electrode sheet 11 by die coating, and then the positive electrode sheet 11 passes through the high-temperature section to complete the pre-polymerization of the ion insulating layer 112, and finally the complete polymerization of the polymer monomer is achieved during the winding core passing through the tunnel furnace or hot pressing process. The in-situ polymerized ion insulating layer 112 formed has good ion insulating ability, which can effectively block the ion transmission between the concave side of the positive electrode sheet 11 and the convex side of the negative electrode sheet 12 at the corner of the bending area of ​​the electrode assembly winding core, thereby avoiding lithium deposition at the corner of the bending area of ​​the electrode assembly.

[0129] In some embodiments, the negative electrode sheet 12 includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode active material is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0130] The negative electrode current collector can be a metal foil, a metal foam, or a composite current collector. For example, as the metal foil, aluminum or stainless steel treated with silver, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, nickel, or titanium can be used. The metal foam can be nickel foam, copper foam, aluminum foam, alloy foam, or carbon foam. The composite current collector can include a polymer material base layer and a metal layer. The composite current collector can 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, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0131] In some embodiments, the material of the positive electrode current collector may be aluminum foil, and the material of the negative electrode current collector may be copper foil.

[0132] The negative electrode active layer contains a negative electrode active material. As an example, the negative electrode active material can adopt the negative electrode active material for battery cells 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 can 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 can 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 battery negative electrode active materials can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0133] The negative electrode active layer may also optionally 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). The negative electrode active layer may also optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the negative electrode active layer may also optionally include other additives, such as dispersants, thickeners (e.g., sodium carboxymethyl cellulose), and the like.

[0134] In some embodiments, the separator 13 can be a separate component located between the positive and negative electrodes, or it can be attached to the surface of the positive and negative electrodes. The separator 13 includes an isolation membrane. The present application has no particular restrictions on the type of isolation membrane, and any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be selected. As an example, the main material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics. The isolation membrane can be a single-layer film or a multi-layer composite film, without special restrictions. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without special restrictions.

[0135] In some embodiments, the separator 13 may be a solid electrolyte layer. The solid electrolyte is disposed between the positive electrode sheet 11 and the negative electrode sheet 12 and serves to transmit ions and isolate the positive and negative electrodes.

[0136] Battery

[0137] In a fourth aspect, an embodiment of the present application provides a battery, comprising the electrode assembly provided in the third aspect of the embodiment of the present application.

[0138] The battery provided in the embodiment of the present application uses an electrode assembly unique to the embodiment of the present application. Based on the characteristic of the electrode assembly having a low risk of lithium plating, the battery in the embodiment of the present application has excellent cycle performance and service life.

[0139] Specifically, the battery can be a secondary battery, including a wound electrode assembly, specifically including a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet is the positive electrode sheet provided in the first aspect of the embodiment of the present application and / or the positive electrode sheet prepared by the preparation method provided in the second aspect of the embodiment of the present application. The positive electrode sheet, separator, and negative electrode sheet are stacked and wound to form the electrode assembly.

[0140] In some embodiments, the secondary battery comprises a lithium-ion battery. During the battery's charge and discharge processes, active lithium ions are intercalated and released between the positive and negative electrodes. The electrolyte acts as an ion conductor between the positive and negative electrodes. A separator is positioned between the positive and negative electrodes, primarily to prevent short circuits between the positive and negative electrodes while allowing lithium ions to pass through.

[0141] Electrode assemblies, used in lithium-ion batteries, consist of a wound positive electrode sheet, a negative electrode sheet, and a separator. They also include a casing and mechanical components. The lithium-ion insulation effect of the insulating ion layer, which is in situ polymerized inside the corners of the positive electrode sheet's bend, effectively reduces the risk of lithium deposition at the corners of the winding core, thereby reducing battery life degradation and safety risks.

[0142] In some embodiments, the battery includes an electrolyte that 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 needs. For example, the electrolyte can be liquid, gel, or solid.

[0143] In some embodiments, the separator is a separator, and the electrolyte is an electrolyte. The electrolyte includes an electrolyte salt and a solvent. If the secondary battery is a lithium-ion battery, 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.

[0144] In some embodiments, the solvent in the electrolyte can be selected from 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 sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0145] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include 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, and additives that improve battery high or low temperature performance.

[0146] In some embodiments, the secondary battery of the present application may include any one of a battery cell, a battery module, and a battery pack.

[0147] The battery cell refers to a battery housing and an electrode assembly encapsulated in the battery housing. The shape of the battery cell is not particularly limited and can be cylindrical, square or any other shape. Figure 3 The battery cell 20 shown has a square structure.

[0148] In some embodiments, as Figure 4 As shown, the outer packaging of the battery cell 20 may include a shell 21 and a top cover assembly 22. The shell 21 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 21 has an opening connected to the receiving cavity, and the top cover assembly 22 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the isolation membrane and the negative electrode sheet contained in the secondary battery of the embodiment of the present application can be formed into an electrode assembly 23 through a winding process. The electrode assembly 23 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 23. The number of electrode assemblies 23 contained in the battery cell 20 can be one or more, which can be adjusted according to actual needs.

[0149] The preparation method of the battery cell 20 is well known. In some embodiments, the positive electrode sheet, separator, and negative electrode sheet can be assembled with an electrolyte to form the battery cell 20. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound to form an electrode assembly 23. The electrode assembly 23 is then placed in an outer package, dried, and then injected with electrolyte. The battery cell 20 is then vacuum packaged, allowed to stand, formed, and shaped.

[0150] A battery module is assembled from the battery cells 20 , that is, it may contain a plurality of battery cells 20 , and the specific number can be adjusted according to the application and capacity of the battery module.

[0151] In some embodiments, Figure 5 FIG3 is a schematic diagram of an exemplary battery module 30. In the battery module 30, multiple battery cells 20 may be arranged sequentially along the length of the battery module 30. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 20 may be secured together using fasteners.

[0152] Optionally, the battery module 30 may further include a housing having an accommodation space, and the plurality of battery cells 20 may be accommodated in the accommodation space.

[0153] A battery pack is assembled from the battery cells 20 described above, and may contain multiple battery cells 20, wherein multiple battery cells 20 may be assembled into the battery module 30 described above. The specific number of battery cells 20 or battery modules 30 contained in a battery pack may be adjusted according to the application and capacity of the battery pack.

[0154] As in the embodiment, Figure 6 and Figure 7 Figure 4 is a schematic diagram of an example battery pack 40. The battery pack 40 may include a battery box and multiple battery modules 30 disposed within the battery box. The battery box comprises an upper case 41 and a lower case 42. The upper case 41 covers the lower case 42 and forms an enclosed space for accommodating the battery modules 30. The multiple battery modules 30 may be arranged in any manner within the battery box.

[0155] Electrical devices

[0156] In a fifth aspect, embodiments of the present application further provide an electrical device comprising the battery provided in the fourth aspect of the present application. The battery can serve as both a power source and an energy storage unit for the electrical device. The electrical device of embodiments of the present application exhibits excellent cycle performance and operates efficiently.

[0157] Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc. The electrical devices may use secondary batteries, battery modules, or battery packs based on their usage requirements.

[0158] Figure 8 The diagram is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0159] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0160] Example

[0161] 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.

[0162] 1. Positive Electrode Sheet and Electrode Assembly Examples

[0163] Example A1

[0164] A positive electrode sheet includes a positive electrode current collector, and positive electrode active layers are provided on both surfaces of the positive electrode current collector. The positive electrode active layer on one surface of the positive electrode current collector includes a plurality of predetermined bending regions spaced apart along the length direction, and an ion insulating layer is provided on the surface of each predetermined bending region away from the positive electrode current collector. After the positive electrode sheet is wound, the predetermined bending regions correspond to the bending regions of the electrode assembly, and adjacent predetermined bending regions have opposite predetermined bending directions. After winding, the actual bending directions in the electrode assembly are opposite. Among them, the positive electrode collector is aluminum foil, the positive electrode active layer contains LiFePO4, and the positive electrode sheet is prepared by dissolving LiFePO4, conductive agent acetylene black, and binder polyvinylidene fluoride (PVLF) in a solvent N-methylpyrrolidone (NMP) in a weight ratio of 97:2:1. After fully stirring and mixing, the positive electrode slurry is evenly coated on the positive electrode collector, and then dried, cold pressed, and cut. The thickness of the ion insulating layer is 15μm, and the width of the ion insulating coating is 0.3mm wider than the coating width of the positive electrode active layer at both ends. The material includes acrylic copolymers, which are obtained by in-situ polymerization on the positive electrode active layer.

[0165] An electrode assembly comprises the aforementioned positive electrode sheet, a separator, and a negative electrode sheet wound together. The separator is a porous polypropylene separator. The negative electrode sheet is prepared by dissolving artificial graphite, carbon black as a conductive agent, styrene-butadiene rubber (SBR) as a binder, and sodium carboxymethyl cellulose (CMC) as a thickener in a solvent in a weight ratio of 97.2:0.8:0.8:1.2, and then mixing them uniformly to form a negative electrode slurry. The negative electrode slurry is evenly coated on a negative electrode current collector copper foil, dried, cold pressed, and slit.

[0166] Length of the ion insulating layer on the positive electrode sheet: the length L of the nth ion insulating layer starting from the winding starting point of the positive electrode sheet n=π(D0+0.5(n+1)δ1+0.5(n-1)δ2+(2n+4)δ3) / 2, where n is an odd number greater than or equal to 1; the length of the n'th ion insulating layer L n' =π(D0 + 0.5n'δ1 + 0.5n'δ2 + (2n' + 4)δ3) / 2, where n' is an even number greater than or equal to 2. The maximum value of n is 27, and the maximum value of n' is 28. D0 is the equivalent diameter of the arc corner of the innermost bend of the negative electrode sheet, specifically 160 μm. δ1 is the thickness of the negative electrode sheet, specifically 133 μm. δ2 is the thickness of the positive electrode sheet, specifically 176 μm. δ3 is the thickness of the separator, specifically 11 μm. The spacing between two adjacent ion insulating layers, i.e., the circumference of the winding needle used for winding, is 340 mm.

[0167] Preparation of electrode assembly: The positive electrode sheet, separator and negative electrode sheet without ion insulating layer are wound, and during the winding process, the precursor solution (including: 21.25g methyl methacrylate, 3.75g methacrylic acid, and 0.125g dibenzoyl peroxide initiator) is coated on the inner side of each predetermined bending area of ​​the positive active layer of the positive electrode sheet by die coating. The wound electrode sheet is then passed through a high temperature section (80°C) to complete pre-polymerization, and finally a positive electrode sheet with an ion insulating layer in situ polymerized on the surface and an electrode assembly formed by winding the electrode sheet are prepared during hot pressing (95°C).

[0168] Example A2

[0169] A positive electrode plate and an electrode assembly, which differ from Example A1 in that the acrylic copolymer of the ion insulating layer material is replaced by a trifluorostyrene polymer.

[0170] Preparation of electrode assembly: The positive electrode sheet, separator and negative electrode sheet without ion insulating layer are wound, and the precursor solution (including 15g trifluorostyrene and 0.03g azobisisobutyronitrile initiator) is coated on the inner side of each predetermined bending area of ​​the positive active layer of the positive electrode sheet (towards the winding needle side) by die coating during the winding process. The wound electrode sheet is then passed through a high-temperature section (100°C) to complete pre-polymerization, and finally a positive electrode sheet with an ion insulating layer in situ polymerized on the surface and an electrode assembly formed by winding the electrode sheet are prepared during hot pressing (90°C).

[0171] Example A3

[0172] A positive electrode plate and an electrode assembly, which differ from Example A1 in that the acrylic copolymer of the ion insulating layer material is replaced by a styrene polymer.

[0173] Example A4

[0174] A positive electrode sheet and an electrode assembly, which differ from Example A1 in that the thickness of the ion insulating layer is 10 μm.

[0175] Example A5

[0176] A positive electrode sheet and an electrode assembly, which differ from Example A1 in that the thickness of the ion insulating layer is 2 μm.

[0177] Example A6

[0178] A positive electrode sheet and an electrode assembly, which differ from Example A1 in that: the maximum value of n is 29, the maximum value of n' is 30, δ1=121 μm, δ2=165 μm, and δ3=10 μm.

[0179] Example A7

[0180] A positive electrode sheet and an electrode assembly, which differ from Example A1 in that: the positive electrode sheet has no ion insulating layer in the 1st to 5th predetermined bending areas from the starting point of winding (corresponding to the 1st to 5th bending areas after winding).

[0181] Example A8

[0182] A positive electrode sheet and an electrode assembly, which differ from Example A1 in that the positive electrode sheet has no ion insulating layer in the 10th to 14th predetermined bending areas from the starting point of winding (corresponding to the 10th to 14th bending areas after winding).

[0183] Comparative Example A1

[0184] A positive electrode plate and an electrode assembly, which differ from Example A1 in that: there is no ion insulation layer.

[0185] 2. Secondary Battery Cell Example

[0186] Example B1 to Example B8 and Comparative Example B1 to Comparative Example B2;

[0187] Embodiments B1 to B8 and Comparative Examples B1 to B2 each provide a secondary battery cell, each comprising an electrode assembly formed by winding a positive electrode sheet, a separator, and a negative electrode sheet, and also comprising an electrolyte. The electrode assemblies used in the secondary battery cells of Embodiments B1 to B8 and Comparative Examples B1 to B2 correspond to the electrode assemblies provided in Embodiments A1 to A8 and Comparative Examples A1 to A2, respectively. For example, the electrode assembly in Embodiment A1 serves as the electrode assembly of the secondary battery cell of Embodiment B1, the electrode assembly in Embodiment A2 serves as the electrode assembly of the secondary battery cell of Embodiment B2, and so on. The electrode assembly in Comparative Example A2 serves as the electrode assembly of the secondary battery cell of Comparative Example B2.

[0188] Preparation of electrolyte:

[0189] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3 / 7, 12.5% ​​LiPF6 lithium salt was added and dissolved in the organic solvent, and stirred to obtain an electrolyte.

[0190]

Battery assembly

[0191] Secondary battery cell assembly: The negative electrode sheet, separator, and positive electrode sheet are stacked in sequence through a winding process to form an electrode assembly, which is then packaged, injected with electrolyte, formed, and sorted to form a cylindrical lithium-ion secondary battery, which is a secondary battery cell.

[0192] Performance Testing

[0193] The secondary battery cells were tested.

[0194] Ten secondary battery cells prepared in each of the examples and comparative examples were taken for lithium deposition testing. The testing process is as follows:

[0195] At 25°C, the battery was charged at a constant current of 1.5C to 3.65V and then the constant voltage was cut off to 0.05C. The battery was then discharged at a rate of 0.33C to 2.5V. The charge and discharge process was cycled 50 times, 100 times, 300 times, and 500 times respectively. The battery was disassembled and the lithium deposition conditions at the corners of the interface bending zone were recorded. The results are shown in Table 1 below.

[0196] Table 1

[0197]

[0198] Note: The above definition of lithium deposition degree (for the corner area of ​​the bending zone, the area of ​​the lithium deposition zone is observed with the naked eye): (1) Severe lithium deposition: the area of ​​the lithium deposition zone is ≥ 30% of the area of ​​the corner bending zone; (2) Moderate lithium deposition: 30% of the area of ​​the corner bending zone > the area of ​​the lithium deposition zone ≥ 10% of the area of ​​the corner bending zone; (3) Slight lithium deposition: 10% of the area of ​​the corner bending zone > the area of ​​the lithium deposition zone; (4) No lithium deposition: no lithium deposition zone is visible to the naked eye. (5) The mth bending zone refers to the mth bending zone counted from the inner circle of the winding core after the positive electrode sheet is wound; for example, the 1st to 3rd bending zones are the 1st to 3rd bending zones after the positive electrode sheet is wound starting from the inner circle.

[0199] The data of the examples and comparative examples in Table 1 show that the lithium plating phenomenon can be reduced by providing an ion insulating layer on the surface of the positive electrode current collector away from the bend area of ​​the positive electrode active layer. Comparative Example B1 does not have an ion insulating layer, so lithium plating occurs after the battery is cycled for 50, 100, 300, and 500 times, and the lithium plating becomes more serious as the number of cycles increases. Examples B1, B2, B3, B4, and B6 can all achieve no lithium plating by selecting parameters such as the material type, thickness, and length of the ion insulating layer. Example B5 does not have lithium plating even when the battery is cycled for a small number of charge and discharge cycles because the ion insulating layer is thin. Although some bend areas have slight lithium plating after 500 cycles, it does not affect the overall improvement effect of the battery. Example B7 does not have an ion insulating layer in the 1st to 5th bend areas, so after the battery is cycled for charge and discharge, lithium plating occurs in the bend area without the ion insulating layer, but no lithium plating occurs in other bend areas with the ion insulating layer. Similarly, in Example B7, since there is no ion insulating layer in the 10th to 14th bending regions, as the number of battery charge and discharge cycles increases, lithium deposition occurs in the bending regions without the ion insulating layer, but there is no lithium deposition in other bending regions with the ion insulating layer.

[0200] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A positive electrode plate, characterized in that: The invention comprises a positive electrode current collector, wherein a positive electrode active layer is provided on at least one surface of the positive electrode current collector, the positive electrode active layer comprises a plurality of predetermined bending regions spaced apart along the length direction, and an ion insulating layer is provided on a surface of at least one of the predetermined bending regions of the positive electrode active layer away from the positive electrode current collector.

2. The positive electrode sheet according to claim 1, wherein: The ionic conductivity of the ion insulating layer is less than or equal to 1×10 -6 S / cm; and / or, The material of the ion insulating layer includes high molecular polymer.

3. The positive electrode sheet according to claim 2, wherein: The high molecular polymer includes at least one of an acrylic ester copolymer and a vinyl aromatic hydrocarbon polymer.

4. The positive electrode sheet according to claim 3, wherein: The acrylic acid ester copolymer includes a copolymer of methacrylic acid and methyl methacrylate; or The vinyl aromatic hydrocarbon polymer includes a polymer of at least one monomer selected from the group consisting of styrene, distyrene, tristyrene, methylstyrene, ethylstyrene, propylstyrene, butylstyrene, halogenated styrene, nitrostyrene, styrylamine, styrene propene and styrene butene.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The width of the ion insulating layer is 0.2 mm to 0.3 mm wider than the coating width of the positive electrode active layer; and / or, The thickness of the ion insulating layer is 3 μm to 30 μm.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The positive electrode sheet is in a winding structure along the length direction, and each of the ion insulating layers is located on a concave surface of a bending region of the winding structure.

7. A method for preparing a positive electrode sheet according to any one of claims 1 to 6, characterized in that: include: preparing the positive electrode active layer on at least one surface of the positive electrode current collector; The ion insulating layer is prepared on a surface of the positive electrode active layer away from the positive electrode current collector in at least one predetermined bending region along the length direction.

8. The preparation method according to claim 7, wherein The steps of preparing the ion insulating layer include: preparing a precursor solution containing polymer monomers and initiator; During the winding process, the precursor solution is coated on the predetermined bending area to carry out in-situ polymerization reaction to obtain the ion insulating layer.

9. The preparation method according to claim 8, wherein The polymer monomer includes at least one of an acrylic acid ester monomer and a vinyl aromatic hydrocarbon monomer; and / or, The initiator includes at least one of azobisisobutyronitrile and dibenzoyl peroxide.

10. The preparation method according to claim 9, characterized in that The acrylic acid ester monomer includes a mixed monomer of methacrylic acid and methyl methacrylate; or The vinyl aromatic hydrocarbon monomer includes at least one monomer selected from the group consisting of styrene, distyrene, tristyrene, methylstyrene, ethylstyrene, propylstyrene, butylstyrene, halogenated styrene, nitrostyrene, styrylamine, styrene propene and styrene butene.

11. The preparation method according to any one of claims 8 to 10, characterized in that: Based on the total weight of the precursor solution being 100%, the precursor solution comprises: 99% to 99.98% of polymer monomers and 0.02% to 1% of initiator; and / or, The temperature of the in-situ polymerization reaction is 80°C to 120°C.

12. An electrode assembly, characterized in that: It includes a positive electrode sheet, a negative electrode sheet and an isolating member located between the positive electrode and the negative electrode sheet, the positive electrode sheet, the isolating member and the negative electrode sheet are in a wound structure, the positive electrode sheet includes the positive electrode sheet according to any one of claims 1 to 6 and / or the positive electrode sheet prepared by the preparation method according to any one of claims 7 to 11; wherein the ion insulating layer is located in the bending area of ​​the wound structure.

13. The electrode assembly according to claim 12, wherein: The ion insulating layer is located on the concave surface of the bending area of ​​the positive electrode sheet, and the length L of the nth ion insulating layer starting from the starting point of the positive electrode sheet winding is n =π(D0+0.5(n+1)δ1+0.5(n-1)δ2+(2n+4)δ3) / 2, where n is an odd number greater than or equal to 1; or the length L of the n'th ion insulating layer n' =π(D0+0.5n'δ1+0.5n'δ2+(2n'+4)δ3) / 2, where n' is an even number greater than or equal to 2; Wherein, D0 is the equivalent diameter of the arc corner of the innermost bending area of ​​the negative electrode sheet, δ1 is the thickness of the negative electrode sheet, δ2 is the thickness of the positive electrode sheet, and δ3 is the thickness of the separator.

14. The electrode assembly according to claim 13, wherein D0 is 0.01 mm to 0.6 mm, δ1 is 0.08 mm to 0.26 mm, δ2 is 0.097 mm to 0.2 mm, and δ3 is 0.006 mm to 0.016 mm; and / or, Along the length direction of the positive electrode sheet, the distance between two adjacent ion insulating layers is equal to the circumference of the winding needle of the positive electrode sheet.

15. A battery, characterized in that: Comprising the electrode assembly according to any one of claims 12 to 14.

16. An electrical device, characterized in that: Comprising the battery of claim 15.

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