Wound battery

Abstract

The utility model relates to the field of batteries, in particular to a winding type battery. The battery comprises a battery cell, the battery cell comprises a first pole piece, a diaphragm and a second pole piece which are sequentially stacked from outside to inside, and the first pole piece comprises a first current collector and a first active coating located on the surface of the first current collector; the outermost ring of the first pole piece comprises a first straight section, a second straight section and a bent section connected with the first straight section and the second straight section; a safety coating is arranged between the first current collector and the first active coating in the first pole piece on the outer side part of the battery cell, the safety coating is arranged on the first straight section and / or the second straight section, and the length of the safety coating is 2-80% of the length of the first active coating. According to the battery, the deterioration risk of the rate capability and the cycle performance of the battery can be reduced on the premise of ensuring the needling safety and the heavy object impact safety, and the electrochemical performance is considered while the safety performance of the battery cell is improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of batteries, and in particular relates to a wound battery. Background Art

[0002] With the development of science and technology, batteries, as an energy storage device, have the advantages of high energy density and high portability, and have become an indispensable part of our daily life. However, batteries also have certain safety hazards. For example, overcharging, over-discharging, external short circuit, internal short circuit and other problems may lead to safety accidents such as battery fire and explosion. In addition, with the rapid development of battery technology, new materials and structures are constantly emerging, which also brings new challenges to battery application safety.

[0003] During daily use or assembly, when lithium-ion batteries are subjected to mechanical abuse such as impact, drop, and extrusion, they may cause a vicious short circuit inside the battery, such as a short circuit between the positive current collector and the negative electrode membrane, a short circuit between the negative current collector and the positive electrode membrane, a short circuit between the positive electrode membrane and the negative electrode membrane, and a short circuit between the positive current collector and the negative electrode collector, which may cause local hot spots and electrochemical reactions. The superposition effect leads to thermal runaway and fire failure of the battery. Among them, the short circuit between the positive current collector and the negative electrode membrane generates the most heat and is the most dangerous of the four short circuit modes. Current means to improve safety include more stable positive and negative electrode materials, electrolyte additives, safety coatings, etc., but these measures will lose other battery properties, such as cycle capacity attenuation, double charge, double discharge, volume and mass energy density. Therefore, the current technical problem that needs to be solved urgently is to develop a new measure that can not only improve the safety performance of the battery during malicious mechanical abuse, but also avoid affecting the electrochemical performance of the battery. Utility Model Content

[0004] The purpose of the utility model is to overcome the above-mentioned problems existing in the prior art and to provide a new wound battery, which can not only cope with standard safety tests such as needle puncture and heavy object impact, but also reduce the risk of deterioration of battery rate performance and cycle performance, thereby improving the safety performance of the battery cell while taking into account the electrochemical performance.

[0005] In order to achieve the above-mentioned object, the utility model provides a wound battery, the wound battery comprises a battery cell, the battery cell comprises a first pole piece, a separator and a second pole piece stacked in sequence from the outside to the inside, the first pole piece comprises a first current collector and a first active coating located on the surface of the first current collector, the outermost circle of the first pole piece comprises a first straight section, a second straight section and a bent section connecting the first straight section and the second straight section;

[0006] A safety coating is provided between the first current collector and the first active coating in the first pole piece located on the outer part of the battery cell, and the first straight section and / or the second straight section are provided with the safety coating, and the length of the safety coating is 2% to 80% of the length of the first active coating.

[0007] In one embodiment, the safety coating is provided on the bent section of the first pole piece.

[0008] In one embodiment, the safety coating is provided on at least one straight section of the third to sixth circles of the first pole piece along the direction from the outer side of the battery cell to the center of the battery cell.

[0009] In one embodiment, the safety coating extends from an end of the first pole piece away from the center of the battery cell to a point one quarter to three quarters of the length of the first active coating.

[0010] In one embodiment, the first pole piece includes a double-sided area with double sides covered by the first active coating and a single-sided area with one side covered by the first active coating.

[0011] In one embodiment, the safety coating is disposed between the first active coating and the first current collector in the double-sided region.

[0012] In one embodiment, the safety coating is disposed between the first active coating and the first current collector in the single-sided area.

[0013] In one embodiment, the safety coating or ceramic layer is provided on the surface of the first current collector in the single-sided area which is away from the first active coating.

[0014] In one embodiment, the safety coating is located on a surface of the first current collector close to the center of the battery cell.

[0015] In one embodiment, the battery cell further includes a first pole lug located on the first pole piece and a second pole lug located on the second pole piece.

[0016] In one embodiment, a projection of the safety coating in a thickness direction of the battery cell at least partially overlaps with a projection of the first pole tab and / or the second pole tab.

[0017] In one embodiment, in the thickness direction of the first pole piece, projections of the first pole tab and the safety coating do not overlap.

[0018] In one embodiment, the safety coating is provided at a position of the first pole piece corresponding to the second pole lug.

[0019] In one embodiment, a distance from the first pole tab to an end of the safety coating is smaller than a distance from the first pole tab to an end of the first pole sheet located at the center of the battery cell.

[0020] In one embodiment, the length of the safety coating is 30% to 60% of the length of the first active coating.

[0021] In one embodiment, the average thickness of the safety coating is 0.1 μm to 10 μm.

[0022] In one embodiment, the thickness of the first current collector is less than 30 μm.

[0023] In one embodiment, the thickness of the first active coating layer is 20 μm to 100 μm.

[0024] In one embodiment, the ratio of the average thickness of the first active coating to the average thickness of the safety coating is (4-500):1.

[0025] In one embodiment, the thickness of the first current collector decreases or remains unchanged from the inner side of the battery to the outer side of the battery.

[0026] In one embodiment, the thickness of the first active coating decreases or remains unchanged from the inside of the battery to the outside of the battery.

[0027] In one embodiment, the thickness of the safety coating increases or remains constant from the inside of the battery to the outside of the battery.

[0028] In one embodiment, the ratio of the average thickness of the first current collector of the innermost straight section of the battery cell to the average thickness of the first current collector of the outermost straight section of the battery cell is 1:(0.3-1).

[0029] In one embodiment, the ratio of the average thickness of the first active coating layer of the innermost straight section of the battery cell to the average thickness of the first active coating layer of the outermost straight section of the battery cell is 1:(0.3-1).

[0030] In one embodiment, the ratio of the average thickness of the innermost safety coating to the thickness of the outermost safety coating is 1:(1-5).

[0031] In one embodiment, the shape of the safety coating in the cross section of the first pole piece along the thickness direction includes at least one of a rectangle, a triangle and a step shape.

[0032] The utility model adopts the above technical solution to achieve the following beneficial effects:

[0033] (1) The traditional safety coating has a high impedance and there is an electron transmission gap at the interface of the active coating-safety coating-current collector, which increases the ohmic impedance of the battery itself and reduces the rate performance of the battery. The utility model can reduce the loss of the safety coating to the battery rate performance by localizing the safety coating. That is, compared with the traditional safety coating technology, the battery provided by the utility model helps to improve the rate performance of the battery.

[0034] (2) Compared with traditional safety coating technology, the battery provided by the utility model can not only cope with standard safety tests such as needle puncture and heavy object impact, but also reduce the risk of deterioration of battery rate performance and cycle performance while meeting safety standards, which helps to improve the battery's cycle performance and reduce the battery's volume energy density loss, thereby improving the safety performance of the battery cell while taking into account the electrochemical performance.

[0035] The endpoints and any values ​​of the range disclosed in this article are not limited to the precise range or value, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Herein, in the absence of special instructions, data ranges include endpoints. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Shown is a schematic diagram of the battery cell structure of Example 1 of the utility model.

[0037] Figure 2 Shown is a schematic diagram of the battery cell structure of Example 4 of the utility model.

[0038] Figure 3 Shown is a schematic diagram of the battery cell structure of Example 5 of the utility model.

[0039] Figure 4 Shown is a schematic diagram of the battery cell structure of Example 6 of the utility model.

[0040] Figure 5 Shown is a schematic diagram of the battery cell structure of Example 7 of the utility model.

[0041] Figure 6 Shown is a schematic diagram of the battery cell structure of Example 8 of the utility model.

[0042] Figure 7 Shown is a schematic diagram of the battery cell structure of Example 11 of the utility model.

[0043] Figure 8Shown is a schematic diagram of the battery cell structure of the comparative example 3 of the present utility model.

[0044] Fig. 9 Shown is a schematic diagram of the battery cell structure of the comparative example 4 of the present invention. DETAILED DESCRIPTION

[0045] The specific implementation of the present invention is described in detail below. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0046] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by those skilled in the art to which the present invention relates.

[0047] The utility model provides a wound battery, the wound battery comprises a battery core, the battery core comprises a first pole piece, a separator and a second pole piece stacked in sequence from the outside to the inside, the first pole piece comprises a first current collector and a first active coating located on the surface of the first current collector, the outermost circle of the first pole piece comprises a first straight section, a second straight section and a bent section connecting the first straight section and the second straight section;

[0048] A safety coating is provided between the first current collector and the first active coating in the first pole piece located on the outer part of the battery cell, and the first straight section and / or the second straight section are provided with the safety coating, and the length of the safety coating is 2% to 80% of the length of the first active coating.

[0049] In some embodiments, the first electrode is a positive electrode.

[0050] In one embodiment, the safety coating is provided on the bent section of the first pole piece.

[0051] In one embodiment, the safety coating is provided on at least one straight section of the third to sixth circles of the first pole piece along the direction from the outer side of the battery cell to the center of the battery cell.

[0052] In the present invention, the length (maximum length) of the first active coating is L, the center of the winding core is denoted as 0, and the tail end is denoted as L. The safety coating is distributed at any position of the battery core away from the center and close to the outside, and its distribution is not specifically limited, that is, the safety coating can be continuously covered or intermittently covered within the allowable range. The first active coating of the positive electrode active coating can be located on one side or both sides of the first current collector of the positive electrode current collector. When it is located on both sides, the coating positions on both sides may be inconsistent, and the lengths may also be inconsistent. The specific selection can be made according to needs. The safety coating is located between the first current collector of the positive electrode current collector and the first active coating of the positive electrode active coating.

[0053] In one embodiment, the safety coating extends from the end of the first pole piece away from the center of the battery cell to one quarter to three quarters of the length of the first active coating. That is, the safety coating extends from the end of the first pole piece away from the center of the battery cell to one quarter of the length of the first active coating, which means that the safety coating is distributed in the 3 / 4L to L section in the length direction of the first pole piece, and the safety coating extends from the end of the first pole piece away from the center of the battery cell to three quarters of the length of the first active coating, which means that the safety coating is distributed in the 1 / 4L to L section in the length direction of the first pole piece.

[0054] In one embodiment, the safety coating extends from the end of the first pole piece away from the center of the battery cell to one third to two thirds of the length of the first active coating. That is, the safety coating extends from the end of the first pole piece away from the center of the battery cell to one third of the length of the first active coating, which means that the safety coating is distributed in the 2 / 3L to L section in the length direction of the first pole piece, and the safety coating extends from the end of the first pole piece away from the center of the battery cell to one third of the length of the first active coating, which means that the safety coating is distributed in the 1 / 3L to L section in the length direction of the first pole piece.

[0055] In one embodiment, the safety coating is distributed on the first current collector at a section of 0.25L to L in the length direction of the first pole piece, where L is the length of the first active coating. The safety coating can be distributed continuously or at intervals.

[0056] In one embodiment, the safety coating is distributed on the first current collector at a section of 0.45L to L in the length direction of the first pole piece, where L is the length of the first active coating. The safety coating can be distributed continuously or at intervals.

[0057] The safety coating may be located on one side or both sides of the first current collector. In some embodiments, the safety coating is located on both sides of the first current collector. In one embodiment, the first pole piece includes a double-sided area with double sides covered by the first active coating and a single-sided area with one side covered by the first active coating.

[0058] In one embodiment, the safety coating is disposed between the first active coating and the first current collector in the double-sided region.

[0059] In one embodiment, the safety coating is disposed between the first active coating and the first current collector in the single-sided area.

[0060] In one embodiment, the first current collector of the single-sided area is provided with the safety coating or ceramic layer on the side surface facing away from the first active coating, which can improve the safety performance of the battery. Its length can be 2 to 3 times the width of the battery cell, and its thickness can be 0.1 μm to 20 μm, such as 0.1 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm or 20 μm. The end face of the battery cell has a width and a thickness, wherein the width is greater than the thickness, and the width is measured in its transverse direction.

[0061] The ceramic layer can be a conventional ceramic layer in the art, and the ceramic layer can include inorganic particles. The inorganic particles can be selected from the inorganic particles conventionally used in the art, such as the following substances coated with carbon or not coated with carbon: at least one of aluminum oxide, barium sulfate, silicon dioxide, silicon monoxide, zirconium oxide, magnesium oxide, vanadium oxide, titanium oxide, boehmite, lithium iron manganese phosphate and lithium titanate.

[0062] In one embodiment, the safety coating is located on a surface of the first current collector close to the center of the battery cell.

[0063] The thickness of the first current collector from the inside to the outside of the battery cell may be consistent or inconsistent. In one embodiment, the thickness of the first current collector decreases or remains unchanged from the inside of the battery cell to the outside of the battery cell. It should be understood that "remaining unchanged" does not mean that the size is exactly the same. In actual production, there will be a certain error in thickness, which can be ignored.

[0064] The thickness inconsistency can not only be manifested as a difference in thickness, but also can be equivalently reduced by making holes in the current collector, punching wires, etc., which will not be elaborated here. The principle is that the battery cell deforms under the action of external force to produce an internal short circuit point, and the main failure form of the short circuit point is the contact between the first current collector and the negative electrode active material. Reducing the thickness of the first current collector helps to reduce the probability of it contacting the negative electrode active material, thereby improving the pass rate of the safety test.

[0065] In one embodiment, the thickness of the first current collector is less than 30 μm, such as 8 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm.

[0066] In one embodiment, the ratio of the average thickness of the first current collector of the innermost straight section of the battery cell to the average thickness of the first current collector of the outermost straight section of the battery cell is 1:(0.3-1), for example, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1.

[0067] The thickness of the first active coating layer from the inside to the outside of the battery cell may be consistent or inconsistent. In one embodiment, the thickness of the first active coating layer decreases or remains unchanged from the inside of the battery cell to the outside of the battery cell.

[0068] In one embodiment, the first active coating has a thickness of 20 μm to 100 μm, such as 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm.

[0069] In one embodiment, the ratio of the average thickness of the first active coating of the innermost straight section of the battery cell to the average thickness of the first active coating of the outermost straight section of the battery cell is 1:(0.3-1), such as 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1. For the case of inconsistent thickness, please refer to the description of the first current collector.

[0070] In one embodiment, the ratio of the average thickness of the first active coating to the average thickness of the safety coating is (4-500):1, such as 4:1, 10:1, 20:1, 30:1, 40:1, 50:1, 100:1, 200:1, 300:1, 400:1 or 500:1. If the ratio is greater than 500:1, the safety coating is too thin, and the short-circuit impedance is too low when mechanical damage occurs, which is very easy to catch fire and fail, and cannot play a safety role; if the ratio is less than 4:1, the safety coating is too thick, which reduces the electron transmission speed and seriously affects the rate performance of the battery.

[0071] The thickness distribution of the safety coating may be variable or constant, and may include one thickness, two thicknesses, or a combination of multiple thicknesses. In one embodiment, the thickness of the safety coating is 0.1 μm to 10 μm, such as 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0072] The length of the safety coating is 2% to 80% of the length of the first active coating, such as 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%. In one embodiment, the length of the safety coating is 30% to 60% of the length of the first active coating. When the safety coating coating area is too small, the protection of the weak points of the battery cell that are prone to failure is limited, and safety cannot be guaranteed in the event of mechanical damage; if the coating area is too large, it will occupy a large amount of the volume space of the battery cell, affecting the speed of electron transmission, and the energy density and rate performance of the battery cell cannot be guaranteed.

[0073] The shape of the safety coating is not particularly limited, and may be a coating with a flat and uniform thickness, or a coating with a different thickness and an irregular shape. In one embodiment, the shape of the safety coating on the cross section of the first pole piece along the thickness direction includes at least one of a rectangle, a triangle, and a step shape.

[0074] In one embodiment, the safety coating is consistent with the width of the first current collector in the width direction.

[0075] In one embodiment, the ratio of the average thickness of the innermost safety coating to the thickness of the outermost safety coating is 1:(1-5), such as 1:1, 1:2, 1:3, 1:4 or 1:5. The innermost safety coating and the outermost safety coating are both part of the safety coating.

[0076] In some embodiments, the safety coating includes a first coating and a second coating along the winding direction (direction from the inside of the battery to the outside of the battery), and the thickness of the first coating is less than the thickness of the second coating.

[0077] In some embodiments, the safety coating includes a first coating, a second coating, and a third coating along the winding direction (the direction from the inside of the battery to the outside of the battery), the thickness of the first coating is less than the thickness of the second coating, and the thickness of the second coating is less than the thickness of the third coating.

[0078] In some embodiments, in two adjacent safety coatings of different thicknesses, the thickness ratio of the thinner safety coating to the thicker safety coating is 1:(1.1-3), for example, 1:1.1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8 or 1:3.

[0079] In one example, the safety coating may include inorganic particles, which may be selected from inorganic particles conventionally used in the art, such as the following materials coated with or not coated with carbon: at least one of aluminum oxide, barium sulfate, silicon dioxide, silicon monoxide, zirconium oxide, magnesium oxide, vanadium oxide, titanium oxide, boehmite, lithium iron manganese phosphate and lithium titanate. Its composition is conventional in the art and will not be described in detail here.

[0080] In one embodiment, the thickness of the second current collector is less than 30 μm, such as 4 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm.

[0081] In one embodiment, the second active coating has a thickness of 30 μm to 150 μm, such as 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm or 50 μm.

[0082] In one embodiment, the battery cell further includes a first pole lug located on the first pole piece and a second pole lug located on the second pole piece.

[0083] In one embodiment, the projection of the safety coating in the thickness direction of the battery cell at least partially overlaps with the projection of the first pole lug and / or the second pole lug. In the wound structure, the projection of the safety coating along the thickness direction of the battery cell may cover or completely cover the location of the pole lug. In this case, the projection of the pole lug may at least partially overlap with the projection of the safety coating.

[0084] In one embodiment, in the thickness direction of the first pole piece, the projections of the first pole ear and the safety coating do not overlap. This means that after the first pole piece is unfolded, the projections of the first pole ear and the safety coating do not overlap, that is, the positive pole ear is not formed on the active coating with the safety coating.

[0085] In one embodiment, the safety coating is provided at a position of the first pole piece corresponding to the second pole lug, where the corresponding position refers to a projection position along the thickness direction.

[0086] According to the different local distribution positions of the safety coating on the first pole piece, the lead-out position of the winding structure pole ear can be appropriately adjusted to adjust the internal resistance of the battery to achieve the optimal rate performance of the battery itself. For the wound structure battery cell, the first pole ear and the second pole ear can be placed at the head or in the middle of the pole piece.

[0087] In one embodiment, the distance from the first pole ear to the end of the safety coating is smaller than the distance from the first pole ear to the end of the first pole sheet located at the center of the battery cell. This structure is conducive to achieving the minimum DC internal resistance DCIR of the battery cell, improving the rate, and achieving better rate performance.

[0088] The design of other structures refers to the conventional design in the art, such as the separator is wound 0.5 to 2 turns at the winding start end; the width of the separator 110 is greater than the width of the second electrode; the second active coating can cover the first active coating to prevent the positive electrode active material from being embedded in the structure of the negative electrode active material, thereby preventing lithium precipitation. Other conventional designs are not described here one by one.

[0089] The following will be combined with the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0090] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0091] The present invention is described in detail below in conjunction with specific embodiments, which are used to understand rather than limit the present invention.

[0092] Example 1

[0093] The positive electrode material in the battery prepared in this embodiment is lithium cobalt oxide.

[0094] See also Figure 1 , the battery cell in this embodiment is a winding structure, and the battery cell is mainly formed by winding a positive electrode sheet 104, a negative electrode sheet 107 and a separator 110. Among them, the positive electrode sheet 104 includes a positive electrode collector 101 (indicated by a black continuous line), a positive electrode active coating 102 (gray lines) located on both sides of the positive electrode collector, and a safety coating 103 (red lines) between the positive electrode collector 101 and the positive electrode active coating 102; the negative electrode sheet 107 includes a negative electrode collector 105 and a negative electrode active coating 106 located on the surface of the negative electrode collector. In addition, the winding structure includes a negative electrode ear 109 and a positive electrode ear 108. The area of ​​the positive electrode sheet with a single-sided positive electrode active coating in the length direction (the inner side is coated with a positive electrode active coating), the outer side without an active coating is coated with a ceramic layer (green lines), and the area not coated with a positive electrode active coating is coated with a ceramic layer (green lines) on the outer side, the length is about 2.1 times the width of the battery cell, and the thickness is 10μm.

[0095] The thickness of the positive electrode current collector 101 is 12 μm, and the thickness of the positive electrode active coating 102 is 45 μm. The length of the positive electrode active coating is L, and the safety coating 103 is continuously coated in the 0.5L~L section, that is, the length of the safety coating is 0.5L; the main material of the safety coating 103 is alumina ceramic, the surface coating is flat, and the thickness after rolling is 3 μm. The thickness ratio of the positive electrode active coating 102 and the safety coating 103 is 15:1. The width of the separator 110 is greater than the width of the negative electrode sheet 107. The negative electrode active coating 106 can cover the positive electrode active coating 102 to prevent the positive electrode active material from being embedded in the structure of the negative electrode active material, thereby preventing lithium precipitation. The positive electrode ear 108 and the negative electrode ear 109 are placed at the head of the positive and negative electrode sheets. The separator 110 is wound 0.5 to 2 turns at the starting end of the winding.

[0096] Example 2

[0097] Different from Example 1, the thickness of the positive electrode current collector in the length direction changes, specifically, the thickness of the positive electrode current collector 101 at the 0.5L~L section of the positive electrode active coating 102 (including the portion without the positive electrode active coating thereafter) is reduced from 12μm to 8μm. This structure can reduce the probability of the surface positive electrode current collector touching the negative electrode, further improving safety performance.

[0098] Example 3

[0099] Different from Example 1, the thickness of the positive electrode active coating and the negative electrode active coating varies along the length of the electrode sheet, specifically, the thickness of the active coating at the 0.5LL position of the positive electrode active coating is reduced to 75% of the original. This structure can reduce the probability of the surface positive electrode current collector touching the negative electrode, further improving safety performance.

[0100] Example 4

[0101] The difference from Example 1 is that the length of the safety coating 103 is increased (eg Figure 2 As shown), replacing the area covered by the ceramic layer, this structure can further increase the safety performance of the battery cell.

[0102] Example 5

[0103] The difference from Example 1 is that the length of the safety coating 103 is different. Specifically, the length of the safety coating is 1 / 3L, and the coating position is 2 / 3L-L (such as Figure 3 As shown), this approach can further reduce the volume energy density occupied by the safety coating.

[0104] Example 6

[0105] The difference from Example 1 is that the length of the safety coating 103 is different. Specifically, the length of the safety coating is 2 / 3L, and the coating position is 1 / 3L-L (such as Figure 4 This method can further enhance the safety performance of the battery cell in more difficult mechanical abuse tests.

[0106] Example 7

[0107] Different from Example 1, the safety coating is intermittently coated from the end of the pole piece to the head of the pole piece, the safety coating is only present in the straight area of ​​the winding structure, and the bending area is not coated with the safety coating. The total length of the safety coating remains unchanged (e.g. Figure 5 shown).

[0108] Example 8

[0109] Different from Example 1, the position of the pole ear of the winding structure is changed. In order to achieve the minimum DC internal resistance DCIR (increase rate) of the battery cell, the pole ear is placed closer to the primer to achieve better rate performance (such as Figure 6 shown).

[0110] Example 9

[0111] The difference from Example 1 is that the thickness of the safety coating is different, and the thickness of the safety coating is increased from 3 μm to 5 μm. Increasing the thickness of the primer layer has a better effect on high-risk mechanical abuse.

[0112] Example 10

[0113] The difference from Example 1 is that the thickness of the safety coating is different. The thickness of the safety coating is reduced from 3 μm to 2 μm. For safety tests that are easier to pass, the thickness of the safety coating can be appropriately reduced.

[0114] Embodiment 11

[0115] Different from Example 1, the safety coating has two thicknesses: the thickness of the safety coating at the 0.5L to 0.75L section of the positive electrode active coating is 1 μm, and the thickness of the safety coating at the 0.75L to L section of the positive electrode active coating is 3 μm (e.g. Figure 7 This method further enhances the safety performance of the battery cell. The thicker safety coating protects the weak parts of the battery cell that are prone to failure, while the thinner safety coating protects the parts of the battery cell that are not prone to failure, thereby further ensuring safety.

[0116] Example 12

[0117] Different from Example 1, the safety coating has two thicknesses: the thickness of the safety coating at the 0.5L-0.67L section of the positive electrode active coating is 1 μm, the thickness of the safety coating at the 0.67L-0.83L section of the positive electrode active coating is 2 μm, and the thickness of the safety coating at the 0.83L-L section of the positive electrode active coating is 3 μm. This method further enhances the safety performance of the battery cell. The thicker safety coating protects the weak positions of the battery cell that are prone to failure, and the thinner safety coating protects the positions of the battery cell that are not prone to failure. Safety is further guaranteed. This method can specifically improve the pass rate of certain safety tests.

[0118] Comparative Example 1

[0119] Different from Example 1, no safety coating is provided in the battery.

[0120] Comparative Example 2

[0121] Different from Example 1, a safety coating is provided on the electrode of the battery cell, and the length of the safety coating is the same as the length of the positive electrode active coating.

[0122] Comparative Example 3

[0123] The difference from Example 1 is that the length of the safety coating 103 is different. Specifically, the length of the safety coating is 1 / 3L, and the coating position is 1 / 3L-2 / 3L. At this time, the positive electrode sheet in the outermost flat area of ​​the battery is not provided with a safety coating (such as Figure 8 shown).

[0124] Comparative Example 4

[0125] The difference from Example 1 is that the length of the safety coating 103 is different. Specifically, the length of the safety coating is 1 / 3L, and the coating position is 0-1 / 3L (such as Fig. 9 shown).

[0126] Example 13

[0127] Different from Example 1, the positive electrode material of the battery is lithium iron phosphate, and the thickness of its safety coating is 0.1 μm.

[0128] Comparative Example 5

[0129] Different from Example 1, the positive electrode material of the battery is lithium iron phosphate, and no safety coating is provided in the battery.

[0130] Performance Testing

[0131] The lithium-ion batteries of the embodiment and the comparative example were subjected to the following tests, respectively. The test results are shown in Table 1.

[0132] 1) Heavy object impact test

[0133] Take a fully charged lithium ion battery, place the lithium ion battery on a plane, place a steel column with a diameter of 15.8±0.2mm at the center of the lithium ion battery, with the longitudinal axis of the steel column parallel to the plane, and let a weight of 9.1±0.1kg fall freely from a height of 610±25mm to the steel column above the lithium ion battery. Fifteen lithium ion batteries obtained in the same embodiment or comparative example were tested in parallel, and the heavy object impact pass rate of the lithium ion batteries was calculated.

[0134] After disassembling and observing two groups of batteries with different passing rates in the heavy impact safety test, it was found that there were two main differences in the cross-section. First, the failure location was mainly on the outside of the battery cell, with a fracture fold of about 6 folds; second, the battery with a higher passing rate had fewer fracture layers or basically no fractures, that is, the weak point of the battery failure caused by mechanical abuse was a few layers on the surface of the battery cell (there would be certain differences in the number of layers damaged in batteries of different sizes). And the possibility of fracture in the middle of the battery is small. Therefore, setting the safety coating at the weak position, increasing the short-circuit impedance at the weak point, and protecting the weak point from failure can achieve the same safety effect as if the safety coating existed on the entire positive electrode sheet.

[0135] 2) Acupuncture test

[0136] Take a fully charged lithium-ion battery, place it on the surface of the flat plate, and use a 4mm tungsten steel needle to penetrate the center of the battery at a speed of 200mm / s, hold it for 30 minutes, and then slowly lift it up.

[0137] 3) Constant current and constant voltage charging

[0138] Take a lithium-ion battery and fully charge it at 1C at room temperature, with a charge cut-off voltage of 4.5V and a charge cut-off current of 0.02C. The constant current charge ratio is the ratio of the battery capacity in the constant current charging stage to the total battery capacity.

[0139] Table 1

[0140]

[0141]

[0142] It can be seen from Table 1 that, compared with Comparative Examples 1 and 5, the battery cells with safety coatings in the utility model have a higher mechanical safety test pass rate; compared with Comparative Example 2, the battery cells in the utility model embodiments can ensure similar safety effects while taking into account rate performance when part of the safety coating is omitted, and also have advantages in volume energy density.

[0143] From the constant current injection ratio of Example 1 and Comparative Example 2, it can be found that this structure can improve the rate performance of the battery to a certain extent.

[0144] Comparing Example 1 with Example 2 and Example 3, it can be seen that thinning the thickness of the tail positive electrode current collector and the thickness of the positive and negative electrode active coatings helps to further improve the safety test pass rate, but it will bring certain risks accordingly, such as the increase in internal resistance and charging polarization in Example 2, and the deterioration of rate performance; the thinning of the tail active coating thickness in Example 3 leads to a decrease in battery capacity.

[0145] Comparing Example 1 with Example 4, it can be seen that there is a certain loss in safety when using the safety coating to replace the ceramic layer, and the rate performance is basically unchanged.

[0146] From the comparison between Example 1 and Example 5 and Example 6, it is known that the safety test results will be different when the length of the safety coating is different. After shortening the length of the safety coating, some weak points cannot be protected, and the safety test pass rate is reduced. When the length of the safety coating is too long, the improvement effect of the safety test is not obvious.

[0147] Example 5, Comparative Examples 3 and 4 are all designed with local safety coatings, and the coating lengths are the same, but there are significant differences in safety effects. The location of the safety coating will affect the pass rate of the safety test, and placing the safety coating at the tail is more conducive to improving safety. It can be seen that for similar safety tests such as needle puncture and heavy object impact, placing the safety coating close to the outside can improve the pass rate of the safety test.

[0148] From the comparison between Example 1 and Example 7, it can be seen that compared with continuous coating, the results of the safety test are basically the same when the safety coating is not coated on the bending area of ​​the winding structure, but the rate performance can be improved.

[0149] From the comparison between Example 1 and Example 8, it can be seen that adjusting the position of the tab according to the situation is beneficial to improving the rate performance.

[0150] Compared with Examples 9 to 10, Example 1 reduces the thickness of the safety coating, which will lead to a decrease in the safety test pass rate; increasing the thickness of the safety coating will not significantly improve some safety tests with a relatively high pass rate.

[0151] Compared with Examples 11 to 12, when the safety coating is designed to be stepped in Example 1, the pass rate of the safety test can be maintained without significant change while reducing the thickness of the safety coating, which is also beneficial to improving the rate performance.

[0152] It should be noted that, in this article, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises one..." does not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be noted that the scope of the method and device in the embodiment of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0153] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A wound battery, characterized in that: The wound battery comprises a battery cell, wherein the battery cell comprises a first pole piece, a separator and a second pole piece stacked in sequence from outside to inside, the first pole piece comprises a first current collector and a first active coating on a surface of the first current collector, and the outermost circle of the first pole piece comprises a first straight section, a second straight section and a bent section connecting the first straight section and the second straight section; A safety coating is provided between the first current collector and the first active coating in the first pole piece located on the outer part of the battery cell, and the first straight section and / or the second straight section are provided with the safety coating, and the length of the safety coating is 2% to 80% of the length of the first active coating.

2. The wound battery according to claim 1, characterized in that: The safety coating is provided on the bending section of the first pole piece; and / or The safety coating is provided on at least one straight section of the third to sixth circles of the first pole piece along the direction from the outer side of the battery core to the center of the battery core.

3. The wound battery according to claim 1, characterized in that: The safety coating extends from an end of the first pole piece away from the center of the battery cell to a point between one quarter and three quarters of the length of the first active coating.

4. The wound battery according to claim 1, characterized in that: The first pole piece includes a double-sided area with double sides covered by the first active coating and a single-sided area with one side covered by the first active coating; The safety coating is disposed between the first active coating and the first current collector in the double-sided area; The safety coating is disposed between the first active coating and the first current collector in the single-sided area; The safety coating or the ceramic layer is disposed on the surface of the first current collector in the single-sided area which is away from the first active coating.

5. The wound battery according to claim 1, characterized in that: The safety coating is located on a surface of one side of the first current collector close to the center of the battery core.

6. The wound battery according to claim 1, characterized in that: The battery cell further includes a first pole lug located on the first pole piece and a second pole lug located on the second pole piece; The projection of the safety coating in the thickness direction of the battery cell at least partially overlaps with the projection of the first pole tab and / or the second pole tab.

7. The wound battery according to claim 6, characterized in that: In the thickness direction of the first pole piece, projections of the first pole tab and the safety coating do not overlap.

8. The wound battery according to claim 6, characterized in that: The safety coating is provided at a position of the first pole piece corresponding to the second pole ear.

9. The wound battery according to claim 6, characterized in that: The distance from the first pole tab to the end of the safety coating is smaller than the distance from the first pole tab to the end of the first pole sheet located at the center of the battery cell.

10. The wound battery according to claim 1, characterized in that: The length of the safety coating is 30% to 60% of the length of the first active coating; and / or The average thickness of the safety coating is 0.1 μm to 10 μm; and / or The thickness of the first current collector is less than 30 μm; and / or The thickness of the first active coating is 20 μm to 100 μm; and / or The ratio of the average thickness of the first active coating to the average thickness of the safety coating is (4-500):

1.

11. The wound battery according to any one of claims 1 to 10, characterized in that: The thickness of the first current collector decreases or remains unchanged from the inside of the battery to the outside of the battery; and / or The thickness of the first active coating decreases or remains unchanged from the inside of the battery to the outside of the battery; and / or The thickness of the safety coating increases or remains unchanged from the inside of the battery to the outside of the battery.

12. The wound battery according to any one of claims 1 to 10, characterized in that: The ratio of the average thickness of the first current collector of the innermost straight section of the battery cell to the average thickness of the first current collector of the outermost straight section of the battery cell is 1:(0.3-1); and / or The ratio of the average thickness of the first active coating of the innermost straight section of the battery cell to the average thickness of the first active coating of the outermost straight section of the battery cell is 1:(0.3-1); and / or The ratio of the average thickness of the innermost safety coating to the thickness of the outermost safety coating is 1:(1-5).

13. The wound battery according to any one of claims 1 to 10, characterized in that: The shape of the safety coating in the cross section of the first pole piece along the thickness direction includes at least one of a rectangle, a triangle and a step shape.

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