Method for preventing pole piece from being bent and broken

Abstract

The invention provides a method for preventing a pole piece from being bent and fractured, which is characterized in that the amount of powder of the pole piece in a partial bending area is controlled according to a certain rule, and the acting force of the powder in an area with larger curvature on a current collector is reduced, so that the pole piece is prevented from being locally or completely fractured at the bending part; through two items of inspection, the accuracy and the action range of the position of the local thinned area are ensured, the improvement effect of the technology on the bending fracture of the pole piece is exerted to a greater extent, the problem that the thick coated pole piece or the high compacted pole piece is locally or completely fractured at the bending position is solved, and the reliability of the pole piece is improved. And a thick-coated pole piece and a high-compaction pole piece can be effectively prevented from being broken at the bending part.

Description

Technical Field

[0001] The invention relates to the technical field of battery production, and in particular to a method for preventing a pole piece from bending and breaking. Background Art

[0002] Improving the spatial occupancy of active materials is an important way to increase the energy density of batteries. Accordingly, as the coating amount (mass of coating per unit area) and thickness of the active material layer where the active material is located increase, the total amount of powder at the crease of the inner circle of the pole piece during winding increases accordingly, and a large amount of powder is compressed in a very small space, exerting a large extrusion stress on the current collector; when the coating amount and compaction density of the pole piece are increased to a certain value, the extrusion stress of the powder on the crease of the current collector is too large, and the aluminum foil of the inner circle of the wound pole group will be partially or completely broken, resulting in the battery cell being unable to circulate normally, or even unable to be assembled into a battery cell normally. Similarly, under the same coating amount, the rolling density increases, the amount of powder per unit volume increases, and the problem of breakage is also prone to occur during winding.

[0003] At present, one of the ways to solve the problem of brittle fracture of pole piece winding is to improve the flexibility of the pole piece. For example, CN115124638A provides a fluorine-containing polymer that can reduce the crystallinity and melting enthalpy of the binder, thereby improving the flexibility of the pole piece. CN15863643B provides a modified polyurethane softener that can effectively disperse active substances, conductive agents and binders, while reducing the friction between particles and improving the flexibility of the positive pole piece.

[0004] However, adding a softener or changing the molecular structure of the binder to the slurry formula may improve the overall processability of the pole piece, but it may also have a potential impact on the performance of the battery cell. Usually after adding these substances, the electrical properties of the new chemical system need to be re-evaluated, which is bound to increase time and testing costs. And when the thickness of the pole piece is too large, even if a softener and a modified binder are applied, it is difficult to completely solve the problem of pole piece breakage at the bend of the winding core.

[0005] In addition, the current technical means are mainly focused on improving the overall flexibility of the pole piece. In fact, the extrusion stress of the pole piece is relatively high only in some bending areas with larger curvatures. Most areas are under less stress, so most areas do not need to improve flexibility.

[0006] Therefore, how to reduce the extrusion stress of the active material layer with high coating amount and high compaction density on the current collector without changing the formula and prevent the electrode from bending and breaking is a technical problem that needs to be solved urgently at this stage. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for preventing a pole piece from bending and breaking.

[0008] In order to solve the above technical problems, the technical solution of the present invention is:

[0009] A method for preventing a pole piece from bending and breaking, the specific steps are as follows:

[0010] (1) Determine the critical processable coating amount for pole piece winding assembly.

[0011] When the coating amount of the pole piece is CM0 and the rolling density is PD0, the pole group is obtained through the winding assembly process, and after the pole group is disassembled, there is no partial or complete breakage at the fold of the pole piece; when the coating amount of the pole piece is greater than CM0, the rolling density is PD0, the thickness of the active material layer before rolling is T0, and the thickness of the active material layer after rolling is T0′, the pole group is obtained through the winding assembly process, and after the pole group is disassembled, there is a partial or complete breakage at the fold of the pole piece; then CM0 is the critical processable coating amount for winding and assembling the pole piece under the rolling density PD0 condition;

[0012] (2) Confirm the location where the target electrode is partially or completely broken.

[0013] The target electrode has the same formula as the electrode described in step (1), a coating amount of CM1, CM1>CM0, a rolling density of PD0, and an elongation of η. After the winding assembly process, a pole group is obtained. After the pole group is disassembled, it is confirmed that there are n (n is a positive integer) creases of partial or complete breakage of the pole piece, and the distances between the creases and the reference powder line are d1′, d2′, ..., d n ′.

[0014] The pole piece elongation η=(the length L0′ of the active material layer on one side of the pole piece after rolling / the length L0-1 before rolling)·100%.

[0015] (3) For the target pole piece in step (2), a local thinning pretreatment is performed before or after rolling, and the surface of the pole piece facing the core of the wound pole group is the surface where the thinning area is located. The local thinning pretreatment is divided into two methods:

[0016] (a) Local thinning after rolling: distance from the reference powder line d1′, d2′, …, d n The position of ′ is the midline of n thinning areas, the width of each thinning area W = 0.5·π·DI·λ, where Dl is the thickness of the winding structure within the fold number of the thinning area closest to the core, and λ ranges from 1.00 to 5.00; the length of the thinning area is less than or equal to the width of the pole piece, and the depth of the thinning area E = (CM1 / CM0-1)·(T0′-T f ) / 2·ξ, where T f is the thickness of the current collector, and the value range of ξ is 1.00~1.50;

[0017] (b) Local thinning before rolling: distance from the reference powder line d1, d2, ..., d n The position is the midline of n thinning areas, where d1 = d1′ / (1+η), d2 = d2′ / (1+η), …, d n =d n ′ / (1+η), the width of each thinning area W = 0.5·π·DI, where DI is the thickness of the winding structure within the fold number of the thinning area closest to the core, and the value range of λ is 1.00-5.00; the length of the thinning area is less than or equal to the width of the pole piece, and the E of the thinning area is (CM1 / CM0-1)·(T0′-T f ) / 2·ξ, where T f is the thickness of the current collector, and the value range of ξ is 1.00~1.50;

[0018] (4) After the electrode sheet is thinned and pre-treated in step (3), the electrode is further manufactured and wound into an electrode group; the electrode group is disassembled and two inspections and treatments are performed:

[0019] Test 1: Determine whether the winding crease line is within the thinning area. If it is not within the thinning area, perform fine-tuning. Perform test 2 if the requirements of test 1 are met.

[0020] Test 2: Determine whether the pole piece is still partially or completely broken at the bend. If so, make improvements;

[0021] For the problems found in inspections one and two, the objects of fine-tuning and improvement are the pole pieces that have not been pre-treated by thinning;

[0022] (5) According to the parameters finally determined in step (4), thinning pretreatment is performed during the electrode manufacturing process to complete the battery cell manufacturing.

[0023] The "formula" described in the above method for preventing the bending and breaking of the pole piece includes not only the ratio of different raw materials in the coating, but also the current collector. Among them, the raw materials in the coating include but are not limited to battery active materials, conductive agents, adhesives, dispersants, etc.; the current collector includes but is not limited to metal current collectors, metal-polymer composite foils, carbon-coated metal current collectors, lithium iron phosphate coating current collectors, solid electrolyte coating current collectors, etc. "Complete fracture" refers to the appearance of a crack at the crease of the pole piece, or the pole piece is broken at the crease. The target pole piece, that is, the pole piece actually used, is the main research object of this application.

[0024] Preferably, the above method of preventing the pole piece from bending and breaking, and the method of judging whether a local fracture occurs at the crease of the pole piece are: one side of the pole piece is facing the light, if light is seen passing through the crease of the pole piece on the other side of the pole piece, it is considered that a local fracture occurs at the crease.

[0025] Preferably, the above method of preventing the pole piece from bending and breaking may include local thinning by, but is not limited to, laser etching, ion beam etching, and the like.

[0026] Preferably, in the above method for preventing bending and breaking of pole pieces, the fine-tuning process in the first inspection is to move the center line position of the thinning area according to the offset between the winding fold and the thinning area until the winding fold is located within the thinning area.

[0027] Preferably, in the above-mentioned method for preventing the pole piece from bending and breaking, the improved processing method in the second test is to increase ξ and repeat step (3) until there is no local fracture or complete fracture at the bending point of the pole piece; or to perform the thinning pretreatment operation in step (3) at the same position on the two surfaces of the pole piece.

[0028] Preferably, the above-mentioned method for preventing the electrode from bending and breaking, and the improved treatment when the second inspection is unqualified, if "performing the thinning pretreatment operation in step (3) at the same position on both sides of the electrode" is selected, the value of ξ when the local thinning treatment is performed on the surface facing away from the core after the electrode is wound is less than or equal to the value of ξ when the local thinning treatment is performed on the surface facing away from the core after the electrode is wound.

[0029] Beneficial effects:

[0030] The method for preventing the bending and fracture of the pole piece provides a local thinning solution to the problem of bending and cracking of thick-coated electrodes or high-pressure solid electrodes. The amount of powder in the partial bending area of ​​the pole piece is controlled according to certain rules to reduce the force of the powder in the area with larger curvature on the foil, thereby preventing the pole piece from being partially or completely fractured at the bending part. Through two tests, the accuracy and scope of the position of the local thinning area are guaranteed, and the improvement effect of the present technology on the bending and fracture of the pole piece is maximized. The method solves the problem of partial or complete fracture of thick-coated pole pieces or high-pressure solid pole pieces at the bending part, and can effectively prevent the thick-coated pole pieces or high-pressure solid pole pieces from being fractured at the bending part. Specifically:

[0031] (1) The local thinning method is used to prevent the electrode from being partially or completely broken at the bend, and the winding process of thick-coated electrodes or high-pressure compacted electrodes can be realized.

[0032] (2) The area of ​​action of the local thinning treatment is a tiny local area, and most areas of the electrode do not undergo any changes, and the performance of the chemical system remains unchanged.

[0033] (3) It does not involve changes in the formula and does not introduce new substances (softeners and modified binders), thus avoiding the potential impact caused by formula changes and reducing the time and cost consumed in verifying the impact of formula changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is a flow chart of the method for preventing a pole piece from bending and breaking.

[0035] Figure 2 Schematic diagram (side view) of the electrode piece after thinning in Example 1.

[0036] Figure 3 Schematic diagram (top view) of the electrode piece after thinning in Example 1.

[0037] In the figure: 1 is the current collector, 2 is the coating (the coating where the active material is located), and 3 is the groove produced by the thinning pretreatment. DETAILED DESCRIPTION

[0038] The method for preventing the electrode from bending and breaking according to the present invention is described in detail below in conjunction with a blank control group, examples and drawings.

[0039] In the manufacture of soft-pack batteries, in addition to the key technologies involved in this application, the manufacture of soft-pack batteries adopts conventional process technologies and procedures, so the detailed process of the manufacture of soft-pack batteries is omitted.

[0040] In the blank control group and the embodiments, the model of the soft-pack battery is SP515974.

[0041] The blank control group and the embodiment have the same formula of positive and negative electrodes, the same separator, and the same materials such as pole ears and tapes; the formula of positive and negative electrodes in the blank control group and the embodiment are described as follows: the substances and proportions in the positive electrode sheet coating 2 involved in the soft-pack battery are lithium cobalt oxide: conductive agent 1: binder 1 = 98.5%: 0.65%: 0.85%, and the current collector 1 is 9um aluminum foil. The positive electrode with the above formula has the risk of winding fracture under high coating amount and high compaction conditions. The substances and proportions in the negative electrode sheet coating 2 involved in the soft-pack battery are graphite: conductive agent 2: binder 2 = 97.5%: 0.6%: 1.9%, and the current collector 1 is 5um copper foil. The negative electrode with the above formula has no fracture problem in the following embodiments, so the blank control group and the embodiment will no longer describe the state of the negative electrode.

[0042] Blank control group:

[0043] The positive electrode sheet with the above formula has a double-sided coating amount of CM1 = 44.40 mg / cm 2 , rolling density is PD0 = 4.18 g / cm 2 After the electrodes are made using conventional processes (homogenization, coating, rolling, and slitting), the positive electrode, separator, negative electrode, etc. are wound and assembled to obtain an electrode group. After disassembling the electrode group, local fractures appear at the two folds of the electrode sheet near the core of the electrode group.

[0044] The method for judging whether a local fracture occurs at the crease of the pole piece is as follows: one side of the pole piece is facing the light. If light is seen passing through the crease of the pole piece on the other side of the pole piece, it is considered that a local fracture occurs at the crease.

[0045] Example 1

[0046] like Figure 1-3 As shown, the method for preventing the pole piece from bending and breaking comprises the following specific steps:

[0047] (1) The positive electrode sheet with the above formula has a double-sided coating amount of CM0 = 38.02 mg / cm 2 , rolling density is PD0 = 4.18 g / cm 2 When the thickness of the coating before rolling is T0=106um and the thickness of the double-sided coating after rolling is T0′=100um, the positive electrode, the separator, the negative electrode, etc. are wound and assembled to obtain an electrode group. After the electrode group is disassembled, no partial or complete fracture occurs at the fold of the electrode piece;

[0048] When the coating amount of the positive electrode sheet with the above formula increases to 38.52 mg / cm 2 (It differs from CM0 by a coating tolerance), and the rolling density is PD0 = 4.18 g / cm 2 After winding and assembling, the electrode group is obtained. After disassembling the electrode group, one side of the positive electrode plate is facing the light. At the fold on the other side of the electrode plate, it can be seen that the light has penetrated the electrode plate, indicating that the fold has been partially broken. Then CM0 = 38.02 mg / cm 2 The positive electrode sheet with the above formula has a rolling density of PD0 = 4.18g / cm 2 Critical processable coating amount for winding assembly under conditions.

[0049] (2) Confirm the position of the target electrode bending and breaking. The target electrode has the same formula and rolling density as the electrode in step (1), and its double-sided coating amount is CM1 = 44.40 mg / cm 2 , the pole piece elongation is η = 0.9%. After the winding assembly process, the pole group is obtained. After the pole group is disassembled, it is confirmed that there are two folds of local fracture in the pole piece, and the distance between the folds and the reference powder line is d1′ = 51.5mm, d2′ = 105.5mm.

[0050] (3) For the target electrode described in step (2), local thinning pretreatment is performed after rolling. The groove 3 produced by the thinning pretreatment is called the thinning area. The surface of the electrode facing the core of the wound electrode group is the surface where the thinning area is located. The boundary line between the long powder surface of the positive electrode coated with the head end and the empty foil is used as the reference powder line. The position at a distance of d1′=51.5mm and d2′=105.0mm from the reference powder line is used as the midline of the two thinning areas. The width of each thinning area W=0.5·π·Dl·λ=522um, wherein the thickness of the winding structure within the fold number where the thinning area closest to the core of the electrode group is located is Dl=166um, λ=2.0. The length of the thinning area is less than or equal to the width of the electrode, and the depth of the thinning area E=(CM1 / CM0-1)·(T0′-T f ) / 2·ξ=8.0um, where T f =9um, ξ=1.05. In this embodiment, the local thinning is performed by laser etching.

[0051] (4) After the electrode sheet is thinned and pre-treated in step (3), the electrode is manufactured and wound into an electrode group. The electrode group is disassembled and two inspections and treatments are performed:

[0052] Test 1: Determine whether the winding crease line is within the thinning area, and the test is qualified. Then proceed to test 2;

[0053] Test 2: Determine whether the electrode still has partial or complete fracture at the bend. It is found that the first fold still has the problem of light transmission through the crease, indicating that there is partial fracture. Improved treatment method: Increase ξ to 1.2, and perform the partial thinning operation of step (3) on the electrode that has not been pre-treated by thinning. It is found that the electrode with improved parameters is completed. The electrode is made and wound into an electrode group; the electrode group is disassembled. The electrode does not have partial or complete fracture at the bend, and the inspection is qualified.

[0054] (5) According to the parameters finally determined in step (4), thinning pretreatment is performed during the electrode manufacturing process to complete the battery cell manufacturing.

[0055] Example 2

[0056] A method for preventing a pole piece from bending and breaking, the specific steps are as follows:

[0057] Step (1) and step (2) of this embodiment are the same as those of embodiment 1.

[0058] (3) For the target pole piece described in step (2), local thinning treatment is performed before rolling. The surface of the pole piece facing the core of the wound pole group is the surface where the area to be thinned is located. The position at a distance of d1=d1′ / (1+η)=51.0mm and d2=d2′ / (1+η)=104.1mm from the reference powder line is used as the midline of the two thinning areas. The width of each thinning area W=0.5·π·Dl·λ=522um, wherein the thickness of the winding structure within the fold number where the area to be thinned closest to the core of the pole group is located is Dl=166um, λ=2.0. The length of the thinning area is less than or equal to the width of the pole piece, and the depth of the thinning area E=(CM1 / CM0-1)·(T0′-T f ) / 2·ξ=8.0um, where T f =9um,ξ=1.05.

[0059] In this embodiment, the local thinning is performed by laser etching.

[0060] (4) After the electrode sheet is thinned and pre-treated in step (3), the electrode is further manufactured and wound into an electrode group; the electrode group is disassembled and two inspections and treatments are performed:

[0061] Test 1: Determine whether the winding crease line is within the thinning area, which is unqualified; according to the offset between the winding crease and the thinning area, move the center line position of the thinning area in the opposite direction, that is, adjust the values ​​of d1 and d2 in step (3), and according to this parameter, perform the local thinning operation of step (3) on the electrode sheet that has not been pre-treated for thinning; after the parameters are fine-tuned, complete the electrode production and wind it into an electrode group; disassemble the electrode group and determine whether the winding crease line is within the thinning area, which is qualified. Then perform test 2.

[0062] Test 2: Determine whether the electrode piece still has partial or complete fracture at the bend. It is found that the first fold still has the problem of light transmission at the crease, indicating that there is partial fracture; Improved treatment method: Increase ξ to 1.2, and perform the partial thinning operation of step (3) on the electrode piece that has not been pre-treated by thinning. Find the electrode piece with improved parameters, complete the electrode production, and wind it into an electrode group. Disassemble the electrode group. The electrode piece does not have partial or complete fracture at the bend, and the inspection is qualified.

[0063] (5) According to the parameters finally determined in step (4), thinning pretreatment is performed during the electrode manufacturing process to complete the battery cell manufacturing.

[0064] It should be noted that local thinning is performed before rolling, and the centerline position of the thinned area is a calculated value, which may deviate from the actual value. When the number of bending and breaking of the pole piece is large, the probability of failure in the first test is high, and the centerline position of the thinned area is fine-tuned according to the offset. Local thinning is performed after rolling, and the centerline position of the thinned area is the measured data. As long as the measurement is accurate, the result of the first test is usually qualified. Under the premise of achieving the goal of preventing the bending and breaking of the pole piece, while taking into account the position deviation of the winding positive and negative poles, the area of ​​the local thinning area should be as small as possible, that is, the values ​​of λ and ξ should be as small as possible.

[0065] In summary, by comparing the examples and the blank control group, it can be seen that the method of the present invention can improve the manufacturability of the high-density thick-coated electrode without changing the formula. That is, through the method of the present invention, after the high-density thick-coated electrode is wound, the creases will no longer be partially or completely broken, and the subsequent battery cell production can be completed.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention, which are all considered to be within the protection scope of the present invention.

Claims

1. A method for preventing a pole piece from bending and breaking, characterized in that: The specific steps are as follows: (1) Determine the critical processable coating amount for pole piece winding assembly; (2) Confirm the location where the target pole piece is partially or completely broken: (3) For the target pole piece in step (2), a local thinning pretreatment is performed before or after rolling, and the surface of the pole piece facing the core of the wound pole group is the surface where the thinning area is located. The local thinning pretreatment is divided into two methods: (a) Local thinning after rolling: distance from the reference powder line d1′, d2′, …, d n The position of ′ is the midline of n thinning areas, the width of each thinning area W = 0.5·π·DI·λ, where Dl is the thickness of the winding structure within the fold number of the thinning area closest to the core, and λ ranges from 1.00 to 5.00; the length of the thinning area is less than or equal to the width of the pole piece, and the depth of the thinning area E = (CM1 / CM0-1)·(T0′-T f ) / 2·ξ, where T f is the thickness of the current collector, and the value range of ξ is 1.00~1.50; (b) Local thinning before rolling: distance from the reference powder line d1, d2, ..., d n The position is the midline of n thinning areas, where d1 = d1′ / (1+η), d2 = d2′ / (1+η), …, d n =d n ′ / (1+η), the width of each thinning area W = 0.5·π·DI, where DI is the thickness of the winding structure within the fold number of the thinning area closest to the core, and the value range of λ is 1.00-5.00; the length of the thinning area is less than or equal to the width of the pole piece, and the E of the thinning area is (CM1 / CM0-1)·(T0′-T f ) / 2·ξ, where T f is the thickness of the current collector, and the value range of ξ is 1.00~1.50; (4) After the electrode sheet is thinned and pre-treated in step (3), the electrode is further manufactured and wound into an electrode group; the electrode group is disassembled and two inspections and treatments are performed: Test 1: Determine whether the winding crease line is within the thinning area. If it is not within the thinning area, perform fine-tuning. Perform test 2 if the requirements of test 1 are met. Test 2: Determine whether the pole piece is still partially or completely broken at the bend. If so, make improvements; For the problems found in inspections one and two, the objects of fine-tuning and improvement are the pole pieces that have not been pre-treated by thinning; (5) According to the parameters finally determined in step (4), thinning pretreatment is performed during the electrode manufacturing process to complete the battery cell manufacturing.

2. The method for preventing a pole piece from bending and breaking according to claim 1, characterized in that: The specific method for determining the critical processable coating amount of the electrode sheet for winding and assembly in the step (1) is as follows: when the electrode sheet coating amount is CM0, the rolling density is PD0, the thickness of the active material layer before rolling is T0, and the thickness of the active material layer after rolling is T0′, a pole group is obtained through the winding and assembly process, and after the pole group is disassembled, no partial or complete fracture occurs at the fold of the pole sheet; when the electrode sheet coating amount is greater than CM0, and the rolling density is PD0, a pole group is obtained through the winding and assembly process, and after the pole group is disassembled, partial or complete fracture occurs at the fold of the pole sheet; then CM0 is the critical processable coating amount for winding and assembly of the pole sheet under the rolling density PD0.

3. The method for preventing a pole piece from bending and breaking according to claim 1, characterized in that: The specific method for confirming the position where the target electrode piece is partially or completely broken in the step (2) is as follows: the coating amount of the target electrode piece is CM1, CM1>CM0, its rolling density is PD0, and the electrode piece elongation is η; after the winding assembly process, the electrode group is obtained, and after the electrode group is disassembled, it is confirmed that there are n folds where the electrode piece is partially or completely broken, and the distances between the folds and the reference powder line are d1′, d2′, ..., d n ′.

4. The method for preventing a pole piece from bending and breaking according to claim 3, characterized in that: The formula of the target electrode in step (2) is the same as the formula of the electrode in step (1).

5. The method for preventing a pole piece from bending and breaking according to claim 3, characterized in that: The calculation formula of the pole piece elongation in step (1) is: pole piece elongation η=(length L0′ of the active material layer on one side of the pole piece after rolling / length L0-1 before rolling)·100%.

6. The method for preventing a pole piece from bending and breaking according to claim 1, characterized in that: The method for judging whether a local fracture occurs at the crease of the pole piece is as follows: one side of the pole piece is facing the light. If light is seen passing through the crease of the pole piece on the other side of the pole piece, it is considered that a local fracture occurs at the crease.

7. The method for preventing a pole piece from bending and breaking according to claim 1, characterized in that: The local thinning is performed by laser etching or ion beam etching.

8. The method for preventing a pole piece from bending and breaking according to claim 1, characterized in that: The fine-tuning process in the first inspection is to move the center line position of the thinning area according to the offset between the winding fold and the thinning area until the winding fold is located within the thinning area.

9. The method for preventing a pole piece from bending and breaking according to claim 1, characterized in that: The improved processing method in the second test is to increase ξ and repeat step (3) until there is no local fracture or complete fracture at the bending point of the pole piece; or to perform the thinning pretreatment operation in step (3) at the same position on the two surfaces of the pole piece.

10. The method for preventing a pole piece from bending and breaking according to claim 1 or 9, characterized in that: For the improved treatment when the second inspection fails, if "carry out the thinning pretreatment operation in step (3) at the same position on both sides of the pole piece" is selected, the value of ξ when the local thinning treatment is carried out on the surface facing away from the core after the pole piece is wound is less than or equal to the value of ξ when the local thinning treatment is carried out on the surface facing away from the core after the pole piece is wound.

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