Lithium ion battery pole piece wrinkle improvement method and system, pole piece and lithium ion battery

Abstract

According to the lithium ion battery pole piece wrinkle improvement method and system, the pole piece and the lithium ion battery, the internal space amount of a roll core or a lamination is quantitatively calculated, the sum of the rebound allowable space amount and the total space amount needed by rebound of the roll core or the lamination is compared, and whether the pole piece has the wrinkle risk or not is judged according to the comparison result; if it is judged that the pole piece has the risk of wrinkling, the allowable rebound space amount between the pole piece and the diaphragm is adjusted through the embossing treatment procedure, so that the allowable rebound space amount in the winding core or the lamination can meet the volume change requirement of the pole piece in the charging and discharging process, and the problem that the pole piece wrinkles due to insufficient space after the pole piece rebounds is effectively solved; therefore, the problem that the roll core is ultra-wide and ultra-thick is solved, and the production yield is improved; and when the method for improving the wrinkles of the lithium ion battery pole piece is used, a glued diaphragm is not needed, so that the production cost of a battery cell is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery manufacturing, and specifically relates to a method and system for improving wrinkles on a lithium ion battery pole piece, a pole piece and a lithium ion battery. Background Art

[0002] At a time when new energy technologies are developing rapidly, lithium-ion batteries have been widely used in the new energy vehicle industry, energy storage industry, portable mobile electronic products and other fields due to their advantages such as high energy density, high output voltage and long cycle life.

[0003] The composition of lithium-ion batteries mainly includes five core parts: positive electrode, separator, negative electrode, organic electrolyte and battery shell. According to the structural characteristics, lithium-ion batteries can be divided into cylindrical, square shell and soft pack batteries; according to the preparation process, they can be divided into winding type and stacked type. The production process of batteries involves many fine processes, such as pulping, coating, rolling, die cutting, winding, welding, injection, formation, capacity division, etc.

[0004] In the production process of lithium-ion batteries, especially in the stages of liquid injection, formation and capacity separation, the interface of the negative electrode sheet is prone to wrinkles. This will not only cause the size of the battery pack to exceed the specified standard, but may also cause lithium metal precipitation in the wrinkled area, thereby damaging the performance of the battery and increasing safety risks.

[0005] The reason is that during the above process, the thickness of the pole piece increases due to the embedding of lithium ions, which eventually changes the stress distribution state between the pole piece and the diaphragm. The changed stress is difficult to be evenly distributed, and stress concentration will occur in local areas. When the stress cannot be released in time and gradually accumulates as the thickness of the pole piece increases, the pole piece in the stress concentration area will be twisted and then develop into wrinkles. At present, the degree of wrinkling of the pole piece is gradually reduced from the inside to the outside. The presence of wrinkles will have a significant impact on battery performance and battery safety. Summary of the invention

[0006] The present invention provides a method and system for improving wrinkles on a lithium ion battery pole piece, a pole piece and a lithium ion battery, so as to improve the wrinkles on the pole piece interface.

[0007] The present invention provides a method for improving wrinkles on a lithium-ion battery pole piece, the method comprising:

[0008] Determine the total amount of space required for pole piece rebound;

[0009] Determine the amount of rebound allowance inside the core or stack;

[0010] Determine whether the pole piece has a wrinkle risk according to the total amount of space required for the rebound and the amount of space allowed for the rebound inside the winding core or the laminate;

[0011] If it is determined that the pole piece has a risk of wrinkling, the pole piece is embossed.

[0012] Furthermore, the total amount of space required for pole piece rebound is determined to include:

[0013] The total amount of space required to determine the pole piece rebound includes:

[0014] The amount of space required for the single-layer positive electrode sheet to rebound is calculated based on the initial thickness of the single-layer positive electrode sheet and the thickness of the single-layer positive electrode sheet when fully charged;

[0015] The amount of space required for the single-layer negative electrode sheet to rebound is calculated based on the initial thickness of the single-layer negative electrode sheet and the thickness of the single-layer negative electrode sheet when fully charged;

[0016] The total amount of space required for the rebound is determined according to the amount of space required for the single-layer positive electrode sheet to rebound and the amount of space required for the single-layer negative electrode sheet to rebound.

[0017] Furthermore, the total amount of space required to determine the pole piece rebound also includes:

[0018] Determine the total amount of space required for the positive electrode sheet to rebound according to the number of layers of the positive electrode sheet between two preset electrode sheet center points after winding or stacking and the amount of space required for the single-layer positive electrode sheet to rebound;

[0019] Determine the total amount of space required for the rebound of the negative electrode sheet according to the number of layers of the negative electrode sheet between the preset center points of the two electrode sheets after winding or stacking and the amount of space required for the rebound of the single-layer negative electrode sheet;

[0020] The total amount of space required for the rebound is the sum of the total amount of space required for the positive electrode sheet to rebound and the total amount of space required for the negative electrode sheet to rebound.

[0021] Further, determining the amount of rebound allowable space inside the core or stack includes:

[0022] The amount of allowable rebound space is obtained by subtracting the thickness of the positive electrode sheet, the negative electrode sheet and the separator between the two preset electrode sheets from the distance between the two preset electrode sheets after winding or stacking.

[0023] Furthermore, the two preset electrode sheets are one of two adjacent negative electrode sheets, two adjacent positive electrode sheets, or an adjacent positive electrode sheet and a negative electrode sheet.

[0024] Furthermore, the preset distance between the two pole pieces is the distance between the center points of the two pole pieces.

[0025] Furthermore, if the amount of space allowed for the rebound is less than the total amount of space required for the rebound, it is determined that there is a risk of wrinkling of the electrode piece, and the electrode piece is embossed.

[0026] Furthermore, if the amount of space allowed for rebound is less than the sum of the total amount of space required for the positive electrode sheet to rebound and the total amount of space required for the negative electrode sheet to rebound, it is determined that there is a risk of wrinkling of the electrode sheet, and the electrode sheet is embossed.

[0027] Furthermore, when the electrode sheet is subjected to embossing treatment, the positive electrode sheet is subjected to embossing treatment first.

[0028] Furthermore, the thickness of the first embossed pattern generated after the positive electrode sheet is embossed is less than or equal to a first set threshold.

[0029] Furthermore, if the thickness of the first embossed pattern generated after embossing the positive electrode sheet is equal to the first set threshold, and the amount of space allowed for rebound is still less than the total amount of space required for rebound, the negative electrode sheet continues to be embossed.

[0030] Furthermore, the first set threshold is 30% of the initial thickness of the positive electrode sheet.

[0031] Furthermore, the thickness of the second embossed pattern generated after the negative electrode sheet is embossed is less than or equal to a second set threshold.

[0032] Furthermore, the second set threshold is 30% of the initial thickness of the negative electrode sheet.

[0033] Furthermore, the embossed pattern includes at least one of a circle, an ellipse and a stripe.

[0034] The present invention also provides a lithium-ion battery pole piece wrinkle improvement system, the system comprising:

[0035] A first determining unit is used to determine the total amount of space required for the pole piece to rebound;

[0036] A second determining unit is used to determine the amount of rebound allowable space inside the winding core or the stack;

[0037] A first judgment unit is used to judge whether the pole piece has a wrinkle risk according to the total amount of space required for the rebound and the amount of space allowed for the rebound inside the winding core or the laminate;

[0038] The pole piece embossing unit is used to perform embossing on the pole piece that has the risk of wrinkling.

[0039] The present invention also provides a pole piece, the surface of which is provided with a plurality of protruding indentations.

[0040] Furthermore, the indentation is at least one of circular, elliptical and strip-shaped.

[0041] Furthermore, the indentation is circular, and the diameter of the indentation is greater than or equal to 0.5 mm and less than or equal to 5 mm.

[0042] Furthermore, the thickness of the indentation is less than or equal to 10% of the thickness of the pole piece.

[0043] Furthermore, the ratio of the area of ​​the region on the pole piece where the indentation is provided to the total area of ​​the pole piece is greater than or equal to 20% and less than or equal to 95%.

[0044] The present invention also provides a lithium ion battery, comprising a diaphragm and the above-mentioned pole piece.

[0045] Compared with the prior art, the present invention has at least the following technical effects:

[0046] The present invention quantitatively calculates the amount of internal space of the winding core or stack, and compares the amount of space allowed for rebound with the sum of the total amount of space required for rebound of the winding core or stack, and determines whether the electrode piece has a risk of wrinkling according to the comparison result. If it is determined that the electrode piece has a risk of wrinkling, the amount of space allowed for rebound between the electrode piece and the diaphragm is adjusted through an embossing process, so that the amount of space allowed for rebound inside the winding core or stack can meet the volume change requirement of the electrode piece during the charging and discharging process, effectively solving the problem of wrinkling of the electrode piece due to insufficient space after the electrode piece rebounds, which in turn causes the winding core to be too wide and too thick, thereby improving the production yield; and when using the above method for improving the wrinkling of lithium-ion battery electrode pieces, there is no need to use a glue-coated diaphragm, thereby reducing the production cost of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A simplified flowchart of a method for improving wrinkles of a lithium-ion battery electrode in Embodiment 1 of the present invention;

[0048] Figure 2 This is a schematic diagram of the structure of a wound pole piece in Embodiment 1 of the present invention;

[0049] Figure 3 The schematic diagram of the structure of the positive and negative electrode sheets before and after embossing in Example 1 of the present invention;

[0050] Figure 4 This is a schematic diagram of the structure of a battery cell produced according to an industrial standard model in Embodiment 5 of the present invention;

[0051] Figure 5 This is a schematic diagram of the structure of a battery cell produced according to the method for improving the wrinkles of a lithium-ion battery electrode sheet disclosed in one embodiment in embodiment five of the present invention. DETAILED DESCRIPTION

[0052] The following is a description of a lithium-ion battery pole piece wrinkle improvement method, system, pole piece and lithium-ion battery of the present invention in conjunction with schematic diagrams, wherein preferred embodiments of the present invention are shown, and it should be understood that those skilled in the art can modify the present invention described herein and still achieve the beneficial effects of the present invention. Therefore, the following description should be understood as being widely known to those skilled in the art and not as a limitation of the present invention.

[0053] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the accompanying drawings are in very simplified form and are not in exact proportions, and are only used to facilitate and clearly assist in illustrating the purpose of the embodiments of the present invention.

[0054] Please refer to Figure 1 This embodiment provides a method for improving wrinkles on a lithium-ion battery electrode, the method comprising:

[0055] S1. Determine the total amount of space required for the pole piece to rebound;

[0056] S2. Determine the amount of space allowed for rebound inside the core or laminate;

[0057] S3. Determine whether the pole piece has a risk of wrinkling according to the total amount of space required for the pole piece to rebound and the amount of space allowed for rebound inside the winding core or the laminate;

[0058] S4. If it is determined that the electrode sheet has a risk of wrinkling, the electrode sheet is embossed.

[0059] The method quantitatively calculates the internal space of the core or stack, and compares the amount of space allowed for rebound with the sum of the total space required for rebound of the core or stack, and judges whether there is a risk of wrinkling of the electrode according to the comparison result. If it is judged that there is a risk of wrinkling of the electrode, the amount of space allowed for rebound between the electrode and the diaphragm is adjusted through an embossing process, so that the amount of space allowed for rebound inside the core or stack can meet the volume change requirement of the electrode during the charging and discharging process, effectively solving the problem of wrinkling of the electrode due to insufficient space after the electrode rebounds, which in turn causes the core to be too wide and too thick, thereby improving the production yield; and when using the above method to improve the wrinkles of lithium-ion battery electrodes, there is no need to use a glue-coated diaphragm, thereby reducing the production cost of the battery cell.

[0060] It is understandable that the assembly order of the pole pieces is generally diaphragm, negative pole piece, diaphragm, positive pole piece, diaphragm, negative pole piece, diaphragm. Based on this assembly order, the number of assembly layers of the pole pieces can be selected according to actual conditions. The pole piece assembly methods include stacking and winding. The winding assembly method is to wind the positive pole piece, diaphragm and negative pole piece together in a certain order to form a cylindrical battery cell; the stacking assembly method is to alternately stack the positive pole piece and the negative pole piece, and bond them together through external pressure and heating to form a battery cell. The method for improving the wrinkles of lithium-ion battery pole pieces disclosed in this embodiment is applicable to both of the above-mentioned two assembly methods and pole pieces with any number of assembly layers.

[0061] Specifically, in step S1, the specific method for determining the total amount of space required for the pole piece to rebound is:

[0062] First, the amount of space required for the single-layer positive electrode sheet to rebound is calculated based on the initial thickness of the single-layer positive electrode sheet and the thickness of the single-layer positive electrode sheet when fully charged; the amount of space required for the single-layer negative electrode sheet to rebound is calculated based on the initial thickness of the single-layer negative electrode sheet and the thickness of the single-layer negative electrode sheet when fully charged.

[0063] Specifically, the amount of space required for the single-layer positive electrode sheet to rebound is: a = W c1 -W c ; where a is the total space required for the single-layer positive electrode to rebound, W c1 is the thickness of the single-layer positive electrode after full charge, W c It is the thickness of the positive electrode sheet before winding.

[0064] The space required for the single-layer negative electrode sheet to rebound is: b = W c1 -W c ; where a is the total space required for the single-layer negative electrode to rebound, W c1 is the thickness of the single-layer negative electrode after full charge, W c It is the thickness of the single-layer negative electrode sheet before winding.

[0065] In a specific embodiment, the initial thickness of the single-layer negative electrode sheet and the single-layer positive electrode sheet, as well as the thickness of the single-layer negative electrode sheet and the single-layer positive electrode sheet when fully charged can be obtained by precision equipment such as an electronic micrometer, a thickness gauge, a microscope or an online thickness measurement system.

[0066] Further, in step S2, after determining the amount of space required for the rebound of a single-layer positive electrode sheet and the amount of space required for the rebound of a single-layer negative electrode sheet, the total amount of space required for the rebound of the positive electrode sheet is determined according to the number of layers of the positive electrode sheet between the two preset electrode sheet center points after winding or stacking and the amount of space required for the rebound of the single-layer positive electrode sheet; and the total amount of space required for the rebound of the negative electrode sheet is determined according to the number of layers of the negative electrode sheet between the two preset electrode sheet center points after winding or stacking and the amount of space required for the rebound of the single-layer negative electrode sheet. Finally, the total amount of space required for the rebound is obtained according to the sum of the total amount of space required for the rebound of the positive electrode sheet and the total amount of space required for the rebound of the negative electrode sheet.

[0067] In this embodiment, the two preset pole pieces can be selected according to actual conditions, and no specific limitation is imposed here. For example, the first pole piece and the last pole piece in the stacked or wound structure can be selected as the two preset pole pieces.

[0068] In a specific embodiment, when the winding core or the stack is stacked from the inside to the outside in sequence with the separator, the negative electrode sheet, the separator, the positive electrode sheet, the separator, the negative electrode sheet and the separator, the center distance between two adjacent negative electrode sheets is measured, and the total amount of space required for the positive electrode sheet to rebound is a, and the total amount of space required for the negative electrode sheet to rebound is b. At this time, the total amount of space required for the rebound is a+b.

[0069] In another specific embodiment, when the winding core is stacked from the inside to the outside in sequence with a separator, a negative electrode sheet, a separator, a positive electrode sheet, a separator, a negative electrode sheet, a separator, a positive electrode sheet, a separator, a negative electrode sheet, and a separator, the center distance between the first layer of negative electrode sheet and the last layer of negative electrode sheet is measured, the total amount of space required for the positive electrode sheet to rebound is 2*a, and the total amount of space required for the negative electrode sheet to rebound is 2*b. At this time, the total amount of space required for rebound is 2*a+2*b.

[0070] In step S2, the amount of allowable rebound space is obtained by subtracting the thickness of the positive electrode sheet, the negative electrode sheet and the separator between the two preset electrode sheets from the distance between the two preset electrode sheets after winding or stacking. Preferably, the amount of allowable rebound space is obtained by subtracting the thickness of the positive electrode sheet, the negative electrode sheet and the separator between the two preset electrode sheets from the distance between the center points of the two preset electrode sheets after winding or stacking.

[0071] In this embodiment, the thickness of the positive electrode sheet and the negative electrode sheet between the two preset center points of the electrode sheets refers to the initial thickness of the positive electrode sheet and the negative electrode sheet.

[0072] In this embodiment, the two preset pole pieces selected in step S2 are the same as the two preset pole pieces selected in step S1.

[0073] In a specific embodiment, please refer to Figure 2, the winding is performed on the winding core in a positive and negative alternating winding manner, and the winding core is sequentially stacked with separator 1, negative electrode sheet 2, separator 1, positive electrode sheet 3, separator 1 and negative electrode sheet 2 from the inside to the outside, and the distance c between the center points of two adjacent negative electrode sheets is obtained. Figure 2 As shown, l1 and l4 are the rebound allowable spaces between the negative electrode sheet 2 and the diaphragm 1, l2 and l3 are the rebound allowable spaces between the positive electrode sheet and the diaphragm 1, and the rebound allowable space y between two adjacent negative electrode sheets is l 1、 l 2、 The sum of l3 and l4. Calculate the rebound allowable space y between two adjacent negative pole pieces: y = c-2W m -W a -W c ; Among them, W m is the thickness of the diaphragm, W a is the thickness of the negative electrode sheet before winding, W c is the thickness of the positive electrode sheet before winding.

[0074] In another specific embodiment, the winding is performed on the winding core in a positive and negative alternating winding manner, and the winding core is sequentially stacked from the inside to the outside with a separator, a negative electrode sheet, a separator, a positive electrode sheet, a separator, a negative electrode sheet, a separator, a positive electrode sheet, a separator, a negative electrode sheet and a separator, and the center distance between the first layer of negative electrode sheet and the last layer of negative electrode sheet is obtained. At this time, the amount of space allowed for rebound is: y = c-4W m -2W a -2W c .

[0075] In another specific embodiment, the winding is performed on the winding core in a positive and negative alternating winding manner, and the winding core is sequentially stacked from the inside to the outside with a separator, a negative electrode sheet, a separator, a positive electrode sheet, a separator, a negative electrode sheet and a separator, and the distance between the center point of the adjacent positive electrode sheet and the center point of the negative electrode sheet is obtained. At this time, the amount of rebound allowable space between the center point of the adjacent positive electrode sheet and the center point of the negative electrode sheet is calculated as: y = cW m -1 / 2*W a -1 / 2*W c .

[0076] In steps S1 and S2, two adjacent negative electrode sheets, two adjacent positive electrode sheets, or adjacent positive electrode sheets and negative electrode sheets are preferably selected as the preset two electrode sheets for calculating the total amount of space required for rebound.

[0077] It is understandable that in a cell structure with multiple layers of pole pieces, the thickness between the positive pole pieces and the thickness between the negative pole pieces are generally set to be the same to ensure that the coating amount, drying degree and compaction degree of each positive pole piece are consistent with each negative pole piece. Therefore, by selecting two adjacent negative pole pieces, two adjacent positive pole pieces, or adjacent positive pole pieces and negative pole pieces as the preset two pole pieces for calculating the total amount of space required for rebound and the amount of space allowed for rebound, the amount of space required for rebound of the remaining pole pieces and the amount of space allowed for rebound between the pole pieces can be determined, and the amount of calculation can be simplified, thereby improving the efficiency of wrinkle risk judgment.

[0078] In a specific embodiment, the winding is performed on the core in a positive and negative alternating winding manner, and the core is stacked from the inside to the outside in sequence, the separator, the negative electrode sheet, the separator, the positive electrode sheet, the separator, the negative electrode sheet, the separator, the positive electrode sheet, the separator, the negative electrode sheet and the separator, and the center distance between two adjacent negative electrode sheets is obtained. At this time, the amount of space allowed for rebound is: y = c-2W m -W a -W c , the amount of space required for rebound is: a+b.

[0079] Furthermore, in steps S1 and S2, a cross-sectional scan is performed on the wound or stacked battery cell to obtain a distance between two preset center points of the pole pieces.

[0080] In a specific embodiment, a CT (Computerized Tomography) device is used to perform a cross-sectional scan on the wound core. Figure 2 , which is a schematic diagram of the structure of the negative electrode under CT scanning.

[0081] In another specific embodiment, a high-precision thickness measuring instrument can be used to directly measure the thickness of the membrane to be wound on the winding core.

[0082] The operation sequence of the above steps S1 and S2 is not specifically limited here, that is, the total amount of space required for the pole piece to rebound can be determined first, or the amount of space allowed for rebound inside the winding core or the stack can be determined first.

[0083] In step S3, the method for determining whether there are wrinkles on the lithium-ion battery electrode comprises the following steps:

[0084] If the amount of space allowed for rebound is greater than or equal to the sum of the total amount of space required for the positive electrode sheet to rebound and the total amount of space required for the negative electrode sheet to rebound, it is judged that the electrode sheet has no risk of wrinkling, and there is no need to emboss the positive electrode sheet and the negative electrode sheet. The core can be directly placed in the battery casing and the subsequent battery assembly process can be carried out.

[0085] If the amount of space allowed for rebound is less than the sum of the total amount of space required for the positive electrode sheet to rebound and the total amount of space required for the negative electrode sheet to rebound, it is determined that there is a risk of wrinkling the electrode sheet, and the electrode sheet is embossed.

[0086] In a specific embodiment, the winding is performed on the core in a positive and negative alternating winding manner. When the core is stacked from the inside to the outside in sequence with the separator, the negative electrode sheet, the separator, the positive electrode sheet, the separator and the negative electrode sheet, the center distance between two adjacent negative electrode sheets is obtained. At this time, the total amount of space required for rebound is a+b, and the amount of space allowed for rebound is: y=c-2W m -W a -W c， If a+b>y=c-2W m -W a -W c， It is judged that the electrode has a risk of wrinkling if a+b≤y=c-2W m -W a -W c， It is determined that there is no risk of wrinkling of the electrode.

[0087] In step S4, when the electrode sheets are embossed, the positive electrode sheets are embossed first.

[0088] The reason for embossing the negative electrode sheet preferentially instead of the positive electrode sheet is that the material of the positive electrode sheet usually includes metal oxides. After these materials are coated on the current collector, the formed positive electrode sheet is usually harder and more rigid than the negative electrode sheet. Therefore, during the embossing process, the positive electrode sheet is less likely to be deformed and damaged.

[0089] During the embossing process, it is necessary to pay attention to controlling the speed and pressure of the roller so that the embossing effect on the surface of the positive and negative electrode sheets is uniform; further, it is also necessary to pay attention to adjusting the thickness of the embossed pattern by adjusting the air pressure applied by the embossing roller on the electrode sheets. It can be understood that the greater the air pressure value, the more obvious the bumps formed by the embossing roller on the positive and negative electrode sheets, and the thicker the embossed pattern.

[0090] In this embodiment, the thickness of the first embossed pattern generated after embossing the positive electrode sheet needs to be less than or equal to the first set threshold value, so as to avoid damage to the positive electrode sheet caused by the embossing operation. Here, the thickness of the first embossed pattern refers to the height of the first embossed pattern protruding from the surface of the positive electrode sheet.

[0091] In a specific embodiment, the first set threshold is 30% of the initial thickness of the positive electrode sheet.

[0092] Furthermore, in the present embodiment, after embossing the positive electrode plate, the total amount of space required for the plate to rebound and the amount of space allowed for rebound are continuously compared; if the total amount of space required for the plate to rebound is less than or equal to the amount of space allowed for rebound, it is determined that the plate has no risk of wrinkles and no further embossing is required; if the total amount of space required for the plate to rebound is greater than the amount of space allowed for rebound, it is determined that the plate still has a risk of wrinkles and the plate continues to be embossed until the total amount of space required for the plate to rebound is less than or equal to the amount of space allowed for rebound, and then the embossing is stopped.

[0093] In particular, if the thickness of the first embossed pattern generated after the embossing treatment of the positive electrode sheet is equal to the first set threshold, and the amount of space allowed for rebound is still less than the sum of the total amount of space required for the positive electrode sheet to rebound and the total amount of space required for the negative electrode sheet to rebound, the negative electrode sheet will continue to be embossed.

[0094] In this embodiment, the thickness of the second embossed pattern generated after the negative electrode sheet is embossed should be less than or equal to the second set threshold value, so as to avoid the embossing operation causing damage to the negative electrode sheet itself. Similarly, here, the thickness of the second embossed pattern refers to the height of the second embossed pattern protruding from the surface of the negative electrode sheet.

[0095] In a specific embodiment, the second set threshold is 30% of the initial thickness of the negative electrode sheet.

[0096] In another specific embodiment, the embossing pattern includes but is not limited to at least one of a circular, elliptical and strip shape. A circular embossing pattern can provide uniform stress distribution, which helps to accommodate the volume expansion of active materials during battery cycling; a strip embossing pattern can provide a directional structure, which helps to align the pole piece during winding or stacking, and can also enhance the mechanical strength of the pole piece; an elliptical embossing pattern can increase the surface area of ​​the pole piece, thereby increasing the contact area with the electrolyte, which helps to improve the ion transmission efficiency of the battery; it is understandable that those skilled in the art can select different depression patterns according to actual conditions.

[0097] In a specific embodiment, embossing can be achieved by an embossing roller 1. Figure 3 The specific embossing process can be: feeding the electrode 5 (negative electrode or positive electrode) between the embossing rollers 4, and completing it through a conveyor belt or other automated equipment, so that the electrode 2 enters the embossing area smoothly and accurately. Please continue to refer to Figure 3 When the pole piece 5 passes through the embossing roller 4, the pattern of the roller will be imprinted on the surface of the pole piece 5 to form a uniformly distributed convex dot structure. The thickness of the pole piece 2 before embossing is l5, the thickness of the pole piece 5 after embossing is l6, and the thickness of the imprinted pattern is l6-l5.

[0098] In step S4, by embossing the surface of the positive electrode sheet and / or the negative electrode sheet, a thick embossed pattern is formed on the surface of the electrode sheet, increasing the space share of the positive electrode sheet and the negative electrode sheet in the thickness direction, thereby increasing the space between the positive electrode sheet and the negative electrode sheet and the diaphragm after winding, so that the internal space of the winding core can meet the volume change requirements of the electrode sheet during the charging and discharging process, effectively solving the problem of the electrode sheet wrinkling due to insufficient space after the electrode sheet rebounds, and then causing the winding core to be too wide and too thick. In addition, in the above steps, by giving priority to embossing the positive electrode sheet and setting the maximum thickness of the embossed pattern, neither the positive electrode sheet nor the negative electrode sheet will be damaged during the embossing process, ensuring the overall performance and reliability of the battery.

[0099] It can be seen that the above-mentioned method of improving the wrinkles of the ion battery electrode can effectively solve the problem of electrode wrinkles caused by insufficient space after the electrode rebounds, which in turn causes the winding core to be too wide and too thick, thereby improving the production yield.

[0100] Embodiment 2

[0101] Based on the same inventive concept, this embodiment discloses a lithium-ion battery pole piece wrinkle improvement system, which is used to implement the lithium-ion battery pole piece wrinkle improvement method disclosed in Example 1, thereby achieving the technical effect disclosed in Example 1.

[0102] Specifically, the lithium-ion battery pole piece wrinkle improvement system includes: a first determination unit, used to determine the total amount of space required for pole piece rebound; a second determination unit, used to determine the amount of space allowed for rebound inside a winding core or a stack; a first judgment unit, used to judge whether the pole piece has a wrinkle risk based on the total amount of space required for rebound and the amount of space allowed for rebound inside the winding core or the stack; and a pole piece embossing unit, used to perform embossing on the pole piece with a wrinkle risk.

[0103] In a specific embodiment, the first determination unit includes at least one of precision equipment such as an electronic micrometer, a thickness gauge, a microscope or an online thickness measurement system; the second determination unit includes precision instruments such as CT scanning equipment, the first judgment unit includes a microcontroller unit and other equipment for calculation and judgment, and the pole piece embossing unit includes an embossing roller for performing an embossing operation. Those skilled in the art can choose to set a plurality of different devices in different units and set specific connection methods between different devices according to actual conditions to achieve improvement of lithium-ion battery pole piece wrinkles.

[0104] Embodiment 3

[0105] Based on the same inventive concept, this embodiment discloses a pole piece. After being treated by the lithium-ion battery pole piece wrinkle improvement method disclosed in Example 1, the wrinkle risk of the pole piece is improved. The pole piece after embossing treatment is assembled into a battery cell, and a plurality of protruding indentations are generated on the surface of the pole piece through hot pressing treatment.

[0106] A possible heat pressing operation sequence is:

[0107] The obtained battery cell is placed in a special hot pressing device, appropriate pressure is applied to the device, and the core is heated to a specific temperature by a heating plate or other heating elements.

[0108] During the hot pressing process, the positive and negative pole sheets with convex embossing effects will gradually return to a flat state or decrease to different thicknesses under the action of pressure. For example, the convex embossing decreases from 30% of the initial thickness of the pole sheet to 10% of the initial thickness of the pole sheet, so that the space between the positive pole sheet and the diaphragm, and the space between the negative pole sheet and the diaphragm created during winding are released or partially released. The space generated after the release can be used for the subsequent rebound of the positive and negative pole sheets, which helps to have more space to accommodate the change in volume of the positive and negative electrode materials during the battery charging and discharging process, thereby reducing the stress of the material and avoiding wrinkles or damage.

[0109] After hot pressing, the thickness and width of the core meet the design standards, forming a strong and uniform overall structure. The core with this structure can be directly placed into the battery case, ready for the subsequent battery assembly process.

[0110] It can be understood that the above-mentioned indentation is the thickness of the convex embossing still existing on the surface of the pole piece after the embossing and hot pressing operations.

[0111] In this embodiment, the indentation is at least one of a circle, an ellipse and a strip, preferably a circle. Those skilled in the art can select different indentation shapes according to actual conditions.

[0112] In a specific embodiment, when the selected indentation is circular, if the diameter range of the indentation is too small, the indentation is sharp and may cause damage to the pole piece; if the diameter range of the indentation is too large, the indentation cannot remain stable and cannot provide support.

[0113] Therefore, when the selected indentation is circular, in order to make the indentation produce a better support effect and not cause damage to the pole piece, the diameter range of the indentation is controlled to be greater than or equal to 0.5 mm and less than or equal to 5 mm, preferably 2.5 mm-3.5 mm.

[0114] In this embodiment, the thickness of the indentation finally obtained on the pole piece is less than or equal to 10% of the thickness of the pole piece. Specifically, the thickness disclosed in the critical value is the thickness obtained after the hot pressing treatment of the embossed pattern with the maximum thickness disclosed in Example 1 (the embossed pattern with a thickness of 30% of the initial thickness of the pole piece). It can be understood that if the thickness of the embossed pattern after the embossing treatment is less than 30% of the initial thickness of the pole piece, then after the hot pressing treatment, the thickness of the indentation finally obtained is less than 10%, for example, 5%.

[0115] It can be understood that if the area of ​​the region with the indentation on the surface of the pole piece is too small, the overall support effect will be reduced, thereby affecting the final improvement effect of the battery pole piece wrinkles; if the area of ​​the region with the indentation on the surface of the pole piece is too large, the pole piece will be damaged.

[0116] Therefore, in this embodiment, in order to make the indentation produce a better supporting effect and not cause damage to the pole piece, the ratio of the area of ​​the region where the indentation is provided on the pole piece to the total area of ​​the pole piece is controlled to be greater than or equal to 20% and less than or equal to 95%, preferably 50%-80%.

[0117] Embodiment 4

[0118] Based on the same inventive concept, this embodiment discloses a lithium-ion battery, including the pole piece and the diaphragm in the third embodiment, wherein the pole piece and the diaphragm are wound or stacked to form a winding core or a stack. The advantages of the pole piece in the third embodiment are also possessed by the lithium-ion battery provided in the fourth embodiment of the present application, which will not be described in detail here.

[0119] It is understandable that the number of assembly layers of the pole pieces and the diaphragms in the above-mentioned winding core or stack can be selected according to actual conditions. Exemplarily, it includes two layers of negative pole pieces, four layers of diaphragms and one layer of positive pole piece, and the assembly order is diaphragm, negative pole piece, diaphragm, positive pole piece, diaphragm, negative pole piece, diaphragm. Different numbers of assembly layers can be selected according to actual use conditions, and the embodiments of the present application do not impose specific restrictions on this.

[0120] Embodiment 5

[0121] This embodiment is a comparative embodiment, and the performance of the lithium-ion battery disclosed in the fourth embodiment is compared with the lithium-ion battery produced under the industrial standard production mode.

[0122] The positive and negative electrodes are obtained by adopting the standard industrial production mode, and the battery is made after winding, hot pressing, tab welding, shelling and liquid injection. The positive electrode is prepared with lithium iron phosphate, conductive agent, dispersant and binder as raw materials, and the active material coating surface density is 0.284g / 1540mm 2 , compacted density is 2.45g / cm 3The negative electrode is prepared with graphite, conductive agent, dispersant and binder as raw materials, and the active material coating surface density is 0.140g / 1540mm 2 , compacted density is 1.52g / cm 3 ; The diaphragm is made of PP

[0123] (Polypropylene) material, base film thickness is 16u, no coating.

[0124] In another specific embodiment, the positive electrode of the lithium ion battery is prepared with lithium iron phosphate, a conductive agent, a dispersant and a binder as raw materials, and the active material coating surface density is 0.292g / 1540mm 2 , compacted density is 2.55g / cm 3 The negative electrode is prepared with graphite, conductive agent, dispersant and binder as raw materials, and the active material coating surface density is 0.145g / 1540mm 2 , compacted density is 1.57g / cm 3 ; The diaphragm is made of PP material, the base film thickness is 12u, and there is no coating.

[0125] The above two lithium-ion battery cells are produced according to the industrial standard mode and the production mode provided in this embodiment, and the cells in the two modes are fully charged and disassembled. Please refer to Figure 4 and Figure 5 , respectively, are schematic diagrams of the negative electrode interface of a normally produced battery cell and a battery cell produced using the method described in the present invention after being fully charged and disassembled. Figure 4 For battery cells produced according to industrial standard models, it can be found that there are serious wrinkles on the surface of the negative and positive pole pieces of the battery cells. The severity of the wrinkles gradually deepens from the outside to the inside, which will lead to accelerated deterioration of the battery cell cycle and aggravation of the battery cell safety issues. Figure 5 For the battery cell produced according to the method for improving the wrinkles of the lithium-ion battery pole piece in this embodiment, the overall interface is good and free of wrinkles, which can greatly improve the long-term electrical performance and safety performance of the battery cell.

[0126] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for improving wrinkles on a lithium-ion battery pole piece, characterized in that: The method comprises: Determine the total amount of space required for pole piece rebound; Determine the amount of rebound allowance inside the core or stack; Determine whether the pole piece has a wrinkle risk according to the total amount of space required for the rebound and the amount of space allowed for the rebound inside the winding core or the laminate; If it is determined that the pole piece has a risk of wrinkling, the pole piece is embossed.

2. The lithium-ion battery pole piece wrinkle improvement method according to claim 1, characterized in that: The total amount of space required to determine the pole piece rebound includes: The amount of space required for the single-layer positive electrode sheet to rebound is calculated based on the initial thickness of the single-layer positive electrode sheet and the thickness of the single-layer positive electrode sheet when fully charged; The amount of space required for the single-layer negative electrode sheet to rebound is calculated based on the initial thickness of the single-layer negative electrode sheet and the thickness of the single-layer negative electrode sheet when fully charged; The total amount of space required for the rebound is determined according to the amount of space required for the single-layer positive electrode sheet to rebound and the amount of space required for the single-layer negative electrode sheet to rebound.

3. The lithium-ion battery pole piece wrinkle improvement method according to claim 2, characterized in that: The total amount of space required to determine pole piece rebound also includes: Determine the total amount of space required for the positive electrode sheet to rebound according to the number of layers of positive electrode sheets preset between two electrode sheets after winding or stacking and the amount of space required for the single-layer positive electrode sheet to rebound; Determine the total amount of space required for the negative electrode sheet to rebound according to the number of layers of the negative electrode sheet between two preset electrode sheets after winding or stacking and the amount of space required for the single-layer negative electrode sheet to rebound; The total amount of space required for the rebound is the sum of the total amount of space required for the positive electrode sheet to rebound and the total amount of space required for the negative electrode sheet to rebound.

4. The lithium-ion battery pole piece wrinkle improvement method according to claim 3, characterized in that: Determining the amount of rebound allowance within a core or stack includes: The amount of allowable rebound space is obtained by subtracting the thickness of the positive electrode sheet, the negative electrode sheet and the separator between the two preset electrode sheets from the distance between the two preset electrode sheets after winding or stacking.

5. The method for improving wrinkles of a lithium-ion battery pole piece according to claim 3 or 4, characterized in that: The two preset electrode sheets are one of two adjacent negative electrode sheets, two adjacent positive electrode sheets, or an adjacent positive electrode sheet and a negative electrode sheet.

6. The lithium-ion battery pole piece wrinkle improvement method according to claim 4, characterized in that: The preset distance between the two pole pieces is the distance between the center points of the two pole pieces.

7. The lithium-ion battery pole piece wrinkle improvement method according to claim 1, characterized in that: If the amount of space allowed for rebound is less than the total amount of space required for rebound, it is determined that there is a risk of wrinkling of the pole piece, and the pole piece is embossed.

8. The lithium-ion battery pole piece wrinkle improvement method according to claim 7, characterized in that: When the electrode sheet is subjected to embossing treatment, the positive electrode sheet is subjected to embossing treatment first.

9. The lithium-ion battery pole piece wrinkle improvement method according to claim 8, characterized in that: The thickness of the first embossed pattern generated after the positive electrode plate is embossed is less than or equal to a first set threshold.

10. The lithium-ion battery pole piece wrinkle improvement method according to claim 9, characterized in that: If the thickness of the first embossed pattern generated after embossing the positive electrode sheet is equal to the first set threshold, and the amount of space allowed for rebound is still less than the total amount of space required for rebound, the negative electrode sheet continues to be embossed.

11. The lithium-ion battery pole piece wrinkle improvement method according to claim 10, characterized in that: The first set threshold is 30% of the initial thickness of the positive electrode sheet.

12. The lithium-ion battery pole piece wrinkle improvement method according to claim 10, characterized in that: The thickness of the second embossed pattern generated after the negative electrode sheet is embossed is less than or equal to the second set threshold.

13. The lithium-ion battery pole piece wrinkle improvement method according to claim 12, characterized in that: The second set threshold is 30% of the initial thickness of the negative electrode sheet.

14. The lithium-ion battery pole piece wrinkle improvement method according to claim 13, characterized in that: The embossing pattern includes at least one of a circle, an ellipse and a stripe.

15. A lithium-ion battery pole piece wrinkle improvement system, characterized in that: The system comprises: A first determining unit is used to determine the total amount of space required for the pole piece to rebound; A second determining unit is used to determine the amount of rebound allowable space inside the winding core or the stack; A first judgment unit is used to judge whether the pole piece has a wrinkle risk according to the total amount of space required for the rebound and the amount of space allowed for the rebound inside the winding core or the laminate; The pole piece embossing unit is used to perform embossing on the pole piece that has the risk of wrinkling.

16. A pole piece, characterized in that: The surface of the pole piece is provided with a plurality of protruding indentations.

17. The pole piece according to claim 16, characterized in that: The indentation is at least one of a circle, an ellipse and a strip.

18. The pole piece according to claim 17, characterized in that: The indentation is circular, and the diameter of the indentation is greater than or equal to 0.5 mm and less than or equal to 5 mm.

19. The pole piece according to claim 16, characterized in that: The thickness of the indentation is less than or equal to 10% of the thickness of the pole piece.

20. The pole piece according to claim 16, characterized in that: The ratio of the area of ​​the region on the pole piece where the indentation is provided to the total area of ​​the pole piece is greater than or equal to 20% and less than or equal to 95%.

21. A lithium ion battery, characterized in that: The invention comprises a diaphragm and a pole piece as claimed in any one of claims 16 to 20.

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