Winding type battery cell, battery, battery pack and power utilization device

Abstract

The invention provides a winding type battery cell, a battery, a battery pack and a power utilization device, aiming at weakening a lithium removal reaction of a positive electrode active material layer in a corner region so as to improve the safety of the battery. The winding type battery cell comprises a winding structure formed by winding a positive pole piece, a negative pole piece and an isolating membrane; the isolating membrane is arranged between the positive pole piece and the negative pole; the winding structure comprises a straight area and a corner area connected with the straight area; each positive pole piece comprises a first positive active material layer arranged on the surface of the straight area and a second positive active material layer arranged on the concave surface of the corner area; the conductivity sigma1 of the first positive electrode active material layer and the conductivity sigma2 of the second positive electrode active material layer satisfy 0 < = sigma2 < = 40% * sigma1.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a wound battery cell, a battery, a battery pack and an electrical device. Background Art

[0002] A battery composed of cells formed by winding is called a wound battery. The wound cells can be wound into hard shell cylindrical or square shapes. The advantage of the wound structure battery is that the processing cost is low, and whether it is manual, semi-automatic or fully automatic winding, it is easy to achieve high efficiency and high quality. However, safety accidents caused by lithium deposition in the corners of wound batteries have frequently occurred, which has attracted widespread attention. Summary of the invention

[0003] The present application is made in view of the above-mentioned problems, and its purpose is to provide a wound battery cell, a battery, a battery pack and an electrical device to weaken the delithiation reaction of the positive electrode active material layer in the corner area, thereby improving the battery safety.

[0004] In order to achieve the above objectives, this application provides the following technical solutions.

[0005] The first aspect of the present application provides a wound battery cell, which includes a wound structure formed by winding a positive electrode sheet, a negative electrode sheet and a separator; the separator is arranged between the positive electrode sheet and the negative electrode; the wound structure includes a straight area and a corner area connecting the straight area; each of the positive electrode sheets includes a first positive electrode active material layer arranged on the surface of the straight area and a second positive electrode active material layer arranged on the concave surface of the corner area; the electrical conductivity σ1 of the first positive electrode active material layer and the electrical conductivity σ2 of the second positive electrode active material layer satisfy: 0≤σ2≤40%×σ1.

[0006] Therefore, the present application coats a positive electrode active material with a lower conductivity than that of the straight area on the concave surface of the positive electrode corner area, thereby preventing the positive electrode from forming an effective conductive network on the concave corner surface, reducing the conductivity of the positive electrode on the concave corner surface, increasing the resistance of the positive electrode on the concave corner surface, blocking the electron transmission between the positive electrode current collecting layer and the positive electrode active material, and thus weakening or preventing the delithiation reaction of the positive electrode active material layer in the corner area. The positive electrode active material layer does not deintercalate lithium ions or the number of deintercalated lithium ions is small, which can reduce the probability of lithium plating or avoid the occurrence of lithium plating, thereby improving battery safety.

[0007] In any embodiment, in the innermost winding circle of the winding structure, the gap between the positive electrode sheet in the corner area and the negative electrode sheet adjacent to the inner side is D, and the relationship between σ2 / σ1 and D satisfies the following condition:

[0008] When 0≤D≤100μm,σ2 / σ1≤40%;

[0009] When 100μm<D≤500μm,σ2 / σ1≤30%;

[0010] When 500μm<D≤1000μm,σ2 / σ1≤20%;

[0011] When D>1000μm, σ2 / σ1≤15%.

[0012] As the distance between the positive and negative electrodes at the corner increases, the lithium deposition problem becomes more serious. Therefore, at the winding coils with larger spacing, the conductivity of the corner area is further reduced, and the risk of lithium deposition is lower. Through research, it is found that when the relationship between σ2 / σ1 and D meets the above conditions, the charging window of the corner area is closer to the straight area.

[0013] In any embodiment, in the winding structure, from the innermost winding turn to the outermost winding turn, σ2 of different winding turns increases.

[0014] As the number of winding layers increases, the bending degree of the pole piece is smaller and the lithium plating problem is reduced. Therefore, as the number of winding layers increases, the conductivity σ2 of the corner area can be appropriately increased to take into account higher battery capacity and other performance.

[0015] In any embodiment, the positive electrode plate includes two active materials with different electrical conductivities: a low conductivity active material and a high conductivity active material; the first positive electrode active material layer uses a high conductivity active material; and the second positive electrode active material layer uses a low conductivity active material or a mixture of a low conductivity active material and a high conductivity active material.

[0016] By coating active materials with different conductivity in different areas of the positive electrode, the conductivity can be easily differentiated. At the same time, the conductivity value can be adjusted by mixing low-conductivity active materials with high-conductivity active materials in the corner area. For example, for electrodes that require a higher σ2 value, the proportion of high-conductivity active materials can be increased. For electrodes that require a lower σ2 value, the proportion of low-conductivity active materials can be increased.

[0017] In any embodiment, the second positive electrode active material layer is a mixture of a low conductivity active material and a high conductivity active material, and the second positive electrode active material layer includes: at least one first covering layer covered by the low conductivity active material, and at least one second covering layer covered by the high conductivity active material, the first covering layer and the second covering layer are spliced ​​into the second positive electrode active material layer.

[0018] This splicing structure is easier to implement in terms of technology.

[0019] In any embodiment, the second positive electrode active material layer includes: a plurality of first covering layers and a plurality of second covering layers, and the plurality of first covering layers and the plurality of second covering layers are alternately distributed.

[0020] Alternating stacking can improve the uniformity of conductivity distribution in the corner area.

[0021] In any embodiment, the second positive electrode active material layer includes: a plurality of first covering layers and a second covering layer, and the plurality of first covering layers are distributed at intervals.

[0022] The second covering layer can be distributed continuously, but is only coated on a part of the width of the pole piece, and the first covering layer is coated on the remaining width. The multiple first covering layers are distributed at intervals to improve the uniformity of the conductivity distribution in the corner area.

[0023] A second aspect of the present application provides a battery, comprising the wound battery cell of the first aspect of the present application.

[0024] A third aspect of the present application provides a battery pack comprising the battery of the second aspect of the present application.

[0025] The fourth aspect of the present application provides an electrical device comprising at least one selected from the wound battery cell of the first aspect of the present application, the battery of the second aspect of the present application, or the battery pack of the third aspect of the present application.

[0026] In summary, compared with the prior art, the present invention achieves the following technical effects:

[0027] (1) coating the concave surface of the corner area of ​​the positive electrode sheet with an active material having a lower conductivity than that of the straight area, thereby preventing the positive electrode of the concave corner from forming an effective conductive network, reducing the conductivity of the positive electrode of the concave corner, increasing the resistance of the positive electrode of the concave corner, and further weakening or preventing the delithiation reaction of the positive electrode active material layer in the corner area, thereby improving battery safety;

[0028] (2) In view of the different distances between the positive and negative electrodes caused by cells with different degrees of curvature, the difference between σ2 and σ1 is designed in a differentiated manner, so as to solve the lithium plating problem more specifically and take into account multiple aspects of battery performance such as battery capacity;

[0029] (3) There are various ways to achieve the difference in conductivity between the straight area and the corner area on the same electrode, which can be achieved by alternately coating materials with different conductivity or by intermittently coating low conductivity materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of a wound battery cell according to an embodiment of the present application;

[0031] Figure 2 for Figure 1A magnified schematic diagram of the corner;

[0032] Figure 3 A schematic diagram of a corner of a wound battery cell according to an embodiment of the present application;

[0033] Figure 4 A schematic diagram of a corner of a wound battery cell according to another embodiment of the present application;

[0034] Figure 5 A schematic diagram of a corner of a wound battery cell according to another embodiment of the present application;

[0035] Figure 6 A schematic diagram of a corner of a wound battery cell according to another embodiment of the present application;

[0036] Figure 7 A schematic diagram of a corner of a wound battery cell according to another embodiment of the present application;

[0037] Figure 8 A schematic diagram of a corner of a wound battery cell according to another embodiment of the present application;

[0038] Fig. 9 A schematic diagram of a corner of a wound battery cell according to another embodiment of the present application;

[0039] Fig.10 This is a schematic diagram of a cathode and anode electrode gap test device of the present application;

[0040] Fig.11 Schematic diagram of the gap between the positive and negative electrodes of the corner detected by micro-CT in one embodiment of the present application;

[0041] Fig.12 is a schematic diagram of a battery module according to an embodiment of the present application;

[0042] Fig.13 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0043] Fig.14 yes Fig.13 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0044] Fig.15 is a schematic diagram of an electrical device using a wound battery cell according to an embodiment of the present application as a power source;

[0045] Fig.16 is a comparison diagram of the corner charging windows of Examples 1 to 5 of the present application;

[0046] Fig.17 is a comparison diagram of the corner charging windows of Examples 1 to 3 of the present application;

[0047] Fig.18is a comparison diagram of the corner charging windows of Examples 6 to 8 of the present application;

[0048] Fig.19 It is a comparison diagram of the corner charging windows of Examples 9 to 13 of the present application.

[0049] Description of reference numerals:

[0050] 1-battery pack; 2-upper box; 3-lower box; 4-battery module; 5-battery;

[0051] 11,31,41,51,61,71,81,91 - isolation membrane;

[0052] 12,32,42,52,62,72,82,92-negative electrode;

[0053] 13,33,43,53,63,73,83,93- positive electrode;

[0054] 130-corner area;

[0055] 330,320,430-current collector;

[0056] 331 low conductivity active material layer;

[0057] 431, 531, 631, 731, 831, 931 - first covering layer. DETAILED DESCRIPTION

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

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

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

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

[0062] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0063] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0064] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0065] In a wound battery cell, the concave corners of the positive electrode are squeezed and denser than the straight area material, resulting in too little matching negative electrode material. This makes this area more susceptible to lithium desorption, severe lithium deposition, and reduced safety.

[0066] To this end, the present application proposes a wound battery cell, which includes a winding structure formed by winding a positive electrode sheet, a negative electrode sheet and a separation film; the separation film is arranged between the positive electrode sheet and the negative electrode; the winding structure includes a straight area and a corner area connecting the straight area; each of the positive electrode sheets includes a first positive electrode active material layer arranged on the surface of the straight area and a second positive electrode active material layer arranged on the concave surface of the corner area; the electrical conductivity σ1 of the first positive electrode active material layer and the electrical conductivity σ2 of the second positive electrode active material layer satisfy: 0≤σ2≤40%×σ1.

[0067] The winding structure can be square winding, cylindrical winding, or other regular / irregular winding forms, the corner area refers to the bending area, and the other area is the straight area. The surface of the straight area refers to the inner surface or outer surface (usually the inner and outer surfaces have the same conductivity), and the concave surface of the corner area also refers to the surface close to the winding core. Figure 1 As shown, it is an elliptical winding, including a positive electrode sheet 13, a negative electrode sheet 12 and a separator 11, and the positive electrode sheet 13 includes a corner area 130 and a straight area.

[0068] The wound battery cell is not limited to the material system and can be an alkali metal battery or an alkali ion battery, such as a lithium metal battery, a sodium metal battery, a potassium metal battery, a lithium ion battery, a sodium ion battery, a potassium ion battery, a Na-S battery, etc.

[0069] The conductivity at each location refers to the average conductivity of the active material within a defined area.

[0070] Therefore, the present application coats a positive electrode active material with a lower conductivity than that of the straight area on the concave surface of the positive electrode corner area, thereby preventing the positive electrode from forming an effective conductive network on the concave corner surface, reducing the conductivity of the positive electrode on the concave corner surface, increasing the resistance of the positive electrode on the concave corner surface, blocking the electron transmission between the positive electrode current collecting layer and the positive electrode active material, and thus weakening or preventing the delithiation reaction of the positive electrode active material layer in the corner area. The positive electrode active material layer does not deintercalate lithium ions or the number of deintercalated lithium ions is small, which can reduce the probability of lithium plating or avoid the occurrence of lithium plating, thereby improving battery safety.

[0071] At the same time, simply making the conductivity of the concave surface of the corner area lower than that of the straight area cannot effectively solve the lithium deposition problem. It is also necessary to lower it to a specific level, for example, making σ2 lower than 40% of σ1, so that the corner area can reach a charging window similar to that of the straight area, that is, the lithium deposition problem is effectively improved.

[0072] In addition, except for the concave surface in the corner area, the remaining surfaces of the positive electrode sheet (including the convex surface in the corner area) can be made of active materials with a conductivity of σ1.

[0073] In some embodiments, in the innermost winding circle of the winding structure, the gap between the positive electrode sheet in the corner area and the negative electrode sheet adjacent to the inner side is D, and the relationship between σ2 / σ1 and D satisfies the following condition:

[0074] When 0≤D≤100μm,σ2 / σ1≤40%;

[0075] When 100μm<D≤500μm,σ2 / σ1≤30%;

[0076] When 500μm<D≤1000μm,σ2 / σ1≤20%;

[0077] When D>1000μm, σ2 / σ1≤15%.

[0078] Among them, the innermost side of the wound battery cell is usually the negative electrode sheet. One winding circle refers to a pair of positive and negative electrode units. The "innermost winding circle" refers to the innermost positive and negative electrode sheets, that is, the positive and negative electrode sheets close to the core.

[0079] The gap D is the distance L between the vertex of the concave corner of the positive electrode and the vertex of the convex surface of the negative electrode opposite to it. L minus the thickness of the diaphragm is D, such as Figure 2 It can be detected by micro CT and other equipment, which can be the following process: scan the image through the micro CT unit, lock the winding position of the battery cell, distinguish the main material structure of the battery cell - current collector, positive and negative electrode active materials, separator, pores according to the display difference of the image, use the micro CT measurement function to measure the positive and negative electrode (cathode and cathode) gaps at the concerned position, and mark them on the image to obtain the size of the gap D.

[0080] After experimental verification, it was found that the degree of lithium deposition on the concave corner surface has a certain relationship with the gap between the positive and negative electrodes of the corner. The larger the gap, the more serious the lithium deposition. Therefore, the conductivity of the positive electrode on the concave corner surface needs to be appropriately reduced as the gap increases. When the relationship between σ2 / σ1 and D meets the above conditions, the charging window of the corner area is closer to the straight area. For example, when 0≤D≤100μm, σ2 is preferably kept below 40% of σ1, and can also be below 35%, including but not limited to σ2 / σ1=40%, 38%, 35%, 34%, 33%, 30%, 28%, 25%, 23%, 20%, 18%, 15%, 13%, 10%, 8%, 5%, 3%, 1%, 0.5%, 0.1%, 0.01%, etc. When 100μm<D≤500μm, σ2 / σ1 can be below 30%, or below 25%, or below 22%, etc. When 500μm<D≤1000μm, σ2 / σ1 may be 20% or less, or 15% or less, or 12% or less, etc. When D>1000μm, σ2 / σ1 may be 15% or less, or 13% or less, or 10% or less, or 5% or less, or 1% or less, or 0.1% or less, or 0.01% or less, etc.

[0081] In some embodiments, in the winding structure, from the innermost winding turn to the outermost winding turn, the σ2 of different winding turns increases.

[0082] Generally speaking, as the number of winding layers increases, the bending degree of the pole piece is smaller and the lithium deposition problem is reduced. Therefore, as the number of winding layers increases, the conductivity σ2 of the corner area can be appropriately increased to take into account higher battery capacity and other performance.

[0083] In some embodiments, the positive electrode plate includes two active materials with different electrical conductivities: a low conductivity active material and a high conductivity active material; the first positive electrode active material layer uses a high conductivity active material; and the second positive electrode active material layer uses a low conductivity active material or a mixture of a low conductivity active material and a high conductivity active material.

[0084] Low conductivity active materials also include materials with almost zero conductivity. Low conductivity active materials can be obtained by reducing the content of the conductive agent in the positive electrode slurry formula, or replacing the conductive agent with high conductivity with a conductive agent with low conductivity, or replacing the conductive agent with high conductivity with a non-conductive material.

[0085] By coating active materials of different conductivities in different areas of the positive electrode plate, the conductivity differentiation can be easily achieved. At the same time, the conductivity value can be adjusted in the corner area by mixing low conductivity active materials with high conductivity active materials. For example, for pole pieces that require higher σ2 values, the proportion of high conductivity active materials can be increased. For pole pieces that require lower σ2 values, the proportion of low conductivity active materials can be increased. The mixture of low conductivity active materials and high conductivity active materials can be mixed into a slurry and then coated, or both can be independent slurries and coated on different areas of the corner area separately, such as one coating the bottom layer and the other coating the surface layer, or two staggered coatings. Specifically, it can be as follows Figure 3 As shown, it includes a positive electrode sheet 33 , a negative electrode sheet 32 ​​, and a separator 31 . The current collector 320 of the negative electrode sheet 32 ​​is covered with negative active material, and the concave surface of the current collector 330 of the positive electrode sheet 33 is completely covered with a low conductivity active material layer 331 .

[0086] In some embodiments, the second positive electrode active material layer is a mixture of a low conductivity active material and a high conductivity active material, and the second positive electrode active material layer includes: at least one first covering layer covered with the low conductivity active material, and at least one second covering layer covered with the high conductivity active material, the first covering layer and the second covering layer are spliced ​​into the second positive electrode active material layer.

[0087] This spliced ​​structure is easy to implement in terms of technology. Specifically, in some embodiments, the second positive electrode active material layer includes: a plurality of the first covering layers are spaced apart, such as Figure 4 and 5 shown. Figure 4 It includes a positive electrode sheet 43, a negative electrode sheet 42 and a separator 41. The concave surface of the current collector 430 of the positive electrode sheet 43 has a plurality of first covering layers 431 and a second covering layer, and the plurality of first covering layers 431 are distributed at intervals. Figure 5 It includes a positive electrode sheet 53, a negative electrode sheet 52 and a separator 51, and a plurality of the first covering layers 531 are spaced apart on the concave surface of the positive electrode sheet 53. The second covering layer can be distributed continuously, but is only coated on a part of the width of the electrode sheet, and the first covering layer is coated on the remaining width. The spaced distribution of the plurality of first covering layers can improve the uniformity of the conductivity distribution in the corner area. Alternatively, in some embodiments, the second positive electrode active material layer includes: a plurality of first covering layers and a plurality of second covering layers, and the plurality of the first covering layers and the second covering layers are alternately spliced, such as Figure 6 and 7 shown. Figure 6 It includes a positive electrode sheet 63 , a negative electrode sheet 62 and a separator 61 , and a plurality of the first covering layers 631 and a plurality of the second covering layers are alternately spliced ​​and covered on the concave surface of the positive electrode sheet 63 . Figure 7 It includes a positive electrode sheet 73 , a negative electrode sheet 72 and a separator 71 , and a plurality of the first covering layers 731 and a plurality of the second covering layers are alternately spliced ​​and covered on the concave surface of the positive electrode sheet 73 .

[0088] Alternatively, in some embodiments, Figure 8 As shown, it includes a positive electrode sheet 83, a negative electrode sheet 82 and a separator 81, the second positive electrode active material layer uses a mixture of a low conductivity active material and a high conductivity active material, and the second positive electrode active material layer includes: a first covering layer 831 composed of a low conductivity active material covering the concave surface, and a second covering layer composed of a high conductivity active material covering the first covering layer 831, that is, the first covering layer 831 and the second covering layer are stacked. Alternatively, the order of the first covering layer 931 and the second covering layer is exchanged, as shown in FIG. Fig. 9 As shown, Fig. 9 A positive electrode tab 93 , a negative electrode tab 92 , and a separator 91 are shown.

[0089] In some embodiments, the isolation film or the winding core may be thinned to reduce the gaps at the corners of the positive and negative electrode sheets, thereby reducing the lithium plating problem.

[0090] In addition, the present invention has no particular restrictions on the preparation process of the positive electrode plate, and any process of covering different conductivity materials on the same electrode plate can be used, for example, it can be pre-coating, intermittent coating, transfer coating, etc.

[0091] Among them, pre-coating is to pre-coat the corners of the pole piece with a material of specified conductivity, dry the pole piece, and then normally coat the large surface and / or corners with a material of specified conductivity. Intermittent coating is to intermittently coat the active material of specified conductivity on the large surface and corners. Transfer coating is a process that can achieve a thinner layer of coating material.

[0092] The coating method of the slurry of low conductivity active material on the surface of the corner concave positive electrode can be: continuous coating, segmented / intermittent coating, mixed coating with other materials, layered coating, special design, etc.; it can also be: mixed coating with normal slurry, and / or, layered coating with normal slurry, and / or, segmented coating with normal slurry, and / or, cross coating with normal slurry, etc. The conductive agent content in the corner concave positive electrode active material can be adjusted according to the specific situation.

[0093] In addition, the wound battery cell, battery module, battery pack and electrical device of the present application are described below with appropriate reference to the drawings.

[0094] In one embodiment of the present application, a wound battery cell is provided.

[0095] Generally, a wound battery cell includes a positive electrode sheet, a negative electrode sheet, and a separator. 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 separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0096] [Positive electrode]

[0097] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0098] 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.

[0099] 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.).

[0100] In some embodiments, when the type of wound battery cell is a lithium-ion battery cell, the positive electrode active material may adopt a positive electrode active material for lithium-ion batteries known in the art. As an example, 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. Among them, 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 / 3Co 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 )、LiNi0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure 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 iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0101] In some embodiments, when the wound battery cell is a sodium ion battery cell, the positive electrode active material may be a positive electrode active material for sodium ion batteries known in the art. As an example, the positive electrode active material may be used alone or in combination of two or more. Among them, the positive electrode active material may be selected from sodium iron composite oxide (NaFeO2), sodium cobalt composite oxide (NaCoO2), sodium chromium composite oxide (NaCrO2), sodium manganese composite oxide (NaMnO2), sodium nickel composite oxide (NaNiO2), sodium nickel titanium composite oxide (NaNi 1 / 2 Ti 1 / 2 O2), sodium nickel manganese composite oxide (NaNi 1 / 2 Mn 1 / 2 O2), sodium iron manganese composite oxide (Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2), sodium nickel cobalt manganese composite oxide (NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), sodium iron phosphate (NaFePO4), sodium manganese phosphate (NaMn P O4), sodium cobalt phosphate compounds (NaCoPO4), Prussian blue materials, polyanion materials (phosphates, fluorophosphates, pyrophosphates, sulfates), etc., but the present application is not limited to these materials. The present application can also use other traditionally known materials that can be used as positive electrode active materials for sodium ion batteries.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] [Negative electrode]

[0106] 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, wherein the negative electrode film layer includes a negative electrode active material.

[0107] 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.

[0108] 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.).

[0109] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the 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.

[0110] 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).

[0111] 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.

[0112] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0113] 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.

[0114] [Isolation film]

[0115] The present application has no particular limitation on the type of isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected.

[0116] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0117] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be made into a wound battery cell through a winding process.

[0118] The present application has no particular limitation on the shape of the wound battery cell, which may be square winding, cylindrical winding, or other regular / irregular winding forms.

[0119] In one embodiment of the present application, a battery is provided.

[0120] Typically, a battery includes a wound cell and an electrolyte, which conducts ions between the positive and negative electrodes.

[0121] [Electrolytes]

[0122] 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.

[0123] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] In some embodiments, the battery may include an outer packaging that can be used to encapsulate the wound battery cell and the electrolyte.

[0128] In some embodiments, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed.

[0129] Fig.12 4 is an example of a battery module. Fig.12 In the battery module 4, the multiple batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the multiple batteries 5 can be fixed by fasteners.

[0130] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of batteries 5 are received in the receiving space.

[0131] 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.

[0132] Fig.13 and Fig.14 1 is a battery pack 1 as an example. Fig.13 and Fig.14 The 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.

[0133] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used 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.

[0134] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0135] Fig.15The 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 secondary battery, a battery pack or a battery module can be used.

[0136] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0137] Example

[0138] 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.

[0139] The testing method of the positive and negative electrode gap D in the following embodiments is as follows.

[0140] like Fig.10 The assembly diagram of the equipment and samples is shown in the figure. The battery to be tested is placed on the device table, and the battery is placed at an angle that is convenient for microCT observation. The image is scanned by the micro CT unit, the winding position of the battery cell is locked, and the main material structure of the battery cell - current collector, positive and negative active materials, separator, and pores are distinguished based on the display differences of the image. The cathode and cathode gaps at the concerned positions are measured using the micro CT measurement function, and marked on the image to obtain the size of the cathode and cathode gaps.

[0141] Fig.11 This is an example of measuring the gap between the positive and negative electrodes of the present invention. It is a corner structure image of a wound battery scanned by micro-CT. The structural unit of the battery can be clearly seen through the micro-CT scan image, including cathode current collector aluminum foil, anode current collector copper foil, cathode active material, anode active material, and diaphragm. The distance L and the thickness of the diaphragm are measured by micro-CT. D is obtained by deducting the thickness of the diaphragm from L.

[0142] Examples 1 to 5

[0143] According to the formulas of the Base group, different embodiments and comparative examples shown in Table 1, positive electrode slurries were prepared respectively, and the positive electrode slurries of the embodiments were coated on the current collector at least including the positive electrode position of the corner concave surface, and the normal slurry of the Base group was coated on the other positions of the current collector. After a series of processes, positive electrode sheets were prepared, and the positive electrode sheets of different embodiments were respectively made into wound batteries with the same negative electrode sheets, separators, etc., to obtain wound batteries of different embodiments. Among them, the positive electrode active material, the conductive agent, and the adhesive are NCM, respectively. 811, conductive carbon black, polyvinylidene fluoride. The innermost positive and negative electrode gap D (i.e. excluding the thickness of the separator) in all embodiments and the Base group is 0 um. All positions of the positive electrode current collector of the Base group are coated with a material with normal conductivity (i.e. K).

[0144] The charging windows of the large surface and corners of the 25℃Base group battery samples and the innermost corner charging windows of the battery samples of different embodiments were tested respectively, and the large surface and corner charging windows of the 25℃Base group and the corner charging windows of different embodiments were obtained. For specific data comparison, see Fig.16 and 17 shown.

[0145] Table 1 Base group and Examples 1 to 5 formulation data

[0146]

[0147] Fig.16 and 17 The data proves that reducing the conductivity of the corner position can increase the charging window of the corner, and can even reach or exceed the charging window of the normal large surface position, and the lower the conductivity of the positive electrode on the concave corner, the more significant the effect of improving the lithium deposition at the corner. The data of the embodiment proves that reducing the content of the conductive agent in the positive electrode slurry to reduce the conductivity of the electrode sheet has a significant effect on improving the lithium deposition at the corner.

[0148] Examples 6 to 13

[0149] A wound cell with different positive and negative electrode gaps D in the innermost circle was made, and materials with different conductivity were set at the concave corners for different gaps, as shown in Table 2. The basic materials and assembly methods of the battery were the same as those in Example 1, the conductivity of the active material at the corners was adjusted by the content of the conductive agent, the composition with conductivity K was the same as the Base group, and the active material in the straight area of ​​each embodiment was the same as the Base group.

[0150] Table 2 Winding structures and material properties of Examples 6 to 13

[0151]

[0152] The innermost corner charging windows of battery samples of different embodiments were tested at 25°C. For specific data comparison, see Figure 18-19 And as shown in Table 2.

[0153] Fig.18 and 19 Data proves that: according to the size of the gap between the positive and negative electrodes at the innermost corner, the conductivity of the positive electrode on the concave surface of the inner corner can be reduced accordingly, which can increase the charging window of the corner and even make it close to the charging window of the large surface, thereby reducing the risk of lithium plating at the corner.

[0154] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A wound battery cell, characterized in that: The wound battery cell includes a winding structure formed by winding a positive electrode sheet, a negative electrode sheet and a separation film; the separation film is arranged between the positive electrode sheet and the negative electrode; the winding structure includes a straight area and a corner area connecting the straight area; each of the positive electrode sheets includes a first positive electrode active material layer arranged on the surface of the straight area and a second positive electrode active material layer arranged on the concave surface of the corner area; the electrical conductivity σ1 of the first positive electrode active material layer and the electrical conductivity σ2 of the second positive electrode active material layer satisfy: 0≤σ2≤40%×σ1.

2. The wound battery cell according to claim 1, characterized in that: In the innermost winding circle of the winding structure, the gap between the positive electrode sheet in the corner area and the negative electrode sheet adjacent to the inner side is D, and the relationship between σ2 / σ1 and D satisfies the following conditions: When 0≤D≤100μm,σ2 / σ1≤40%; When 100μm<D≤500μm,σ2 / σ1≤30%; When 500μm<D≤1000μm,σ2 / σ1≤20%; When D>1000μm, σ2 / σ1≤15%.

3. The wound battery cell according to claim 1, characterized in that: In the winding structure, from the innermost winding turn to the outermost winding turn, the σ2 of different winding turns increases.

4. The wound battery cell according to claim 1, characterized in that: The positive electrode plate includes two kinds of active materials with different electrical conductivities: a low-conductivity active material and a high-conductivity active material; the first positive electrode active material layer uses a high-conductivity active material; the second positive electrode active material layer uses a low-conductivity active material or a mixture of a low-conductivity active material and a high-conductivity active material.

5. The wound battery cell according to claim 4, characterized in that: The second positive electrode active material layer is a mixture of a low conductivity active material and a high conductivity active material, and the second positive electrode active material layer includes: at least one first covering layer covered by the low conductivity active material, and at least one second covering layer covered by the high conductivity active material, the first covering layer and the second covering layer are spliced ​​into the second positive electrode active material layer.

6. The wound battery cell according to claim 5, characterized in that: The second positive electrode active material layer includes: a plurality of first covering layers and a plurality of second covering layers, and the plurality of first covering layers and the plurality of second covering layers are alternately distributed.

7. The wound battery cell according to claim 5, characterized in that: The second positive electrode active material layer includes: a plurality of first covering layers and a second covering layer, and the plurality of first covering layers are distributed at intervals.

8. A battery, characterized in that: A wound battery cell comprising any one of claims 1 to 7.

9. A battery pack, characterized in that: Comprising the battery as claimed in claim 8.

10. An electrical device, characterized in that: It comprises at least one of the wound battery cell according to any one of claims 1 to 7, the battery according to claim 8, or the battery pack according to claim 9.

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