Winding type lithium ion battery and positive plate suitable for lithium ion battery

Abstract

The utility model relates to the field of lithium ion batteries, and discloses a winding type lithium ion battery and a positive plate suitable for the lithium ion battery. The positive plate comprises a current collector, two surfaces of the current collector are respectively coated with a positive active material layer, cracks are uniformly distributed on each positive active material layer, the length of each crack is 3-20mm, and the width of each crack is less than or equal to 0.02 mm. The preparation method is applied to preparation of the winding type lithium ion battery, and is beneficial to improving the volume energy density of the pole piece and improving the capacity of the lithium ion battery.

Description

Technical Field

[0001] The utility model relates to the field of lithium ion battery manufacturing, in particular to a wound lithium ion battery and a positive electrode sheet suitable for the lithium ion battery. Background Art

[0002] With the promotion of environmental protection and green energy, lithium-ion batteries are being used more and more widely, and the demand for large-capacity batteries is becoming more and more widespread. One of the ways to increase the volume energy density of lithium-ion batteries is to increase the coating surface density (g / ㎡) of polar active materials. That is, when the battery thickness is constant, the higher the coating surface density of polar active materials, the fewer the total number of pole pieces, the smaller the thickness of the current collector, the greater the thickness of the polar active materials, and the higher the volume energy density of lithium-ion batteries.

[0003] The preparation process of the electrode in the prior art is as follows: after coating the polar active material, the electrode is dried and then passed through two steel rollers with the same roller diameter. The gap between the two steel rollers is adjusted so that the electrode passes straight between the two steel rollers. Under the pressure of the two steel rollers on the electrode, the density of the polar active material coating on the surface of the electrode increases, and the polar active material coating becomes more compact.

[0004] At present, the double-sided surface density of the positive electrode coating generally reaches about 400g / ㎡~420g / ㎡. The challenge of further improvement is that the greater the surface density, the thicker the pole piece thickness. The thicker the pole piece thickness, the harder the pole piece after rolling, and the more likely the R angle position will cause the pole piece to crack, break, and lose powder when the pole piece is wound. Due to this problem, it is difficult to further increase the pole piece surface density. In the process of conducting research on the present utility model, the inventor found that when the double-sided surface density of the positive electrode pole piece exceeds 400 g / ㎡~420g / ㎡, the pole piece (especially the R angle position of the pole piece) is prone to cracking, breaking, and powdering during the pole piece winding process. This problem hinders the further improvement of the volume energy density of lithium-ion coiled batteries. Summary of the invention

[0005] The technical problem to be solved by the embodiments of the utility model is to provide a wound lithium-ion battery and a positive electrode sheet suitable for lithium-ion batteries, which are applied to the preparation of wound lithium-ion batteries, which is beneficial to improving the volume energy density of the electrode sheet and improving the capacity of the lithium-ion battery.

[0006] The present utility model provides a positive electrode sheet suitable for lithium-ion batteries, including a current collector, on both surfaces of which positive electrode active material layers are coated respectively, and each positive electrode active material layer is evenly distributed with cracks, each of which has a length of 3 to 20 mm and a width of ≤0.02 mm.

[0007] Optionally, the coating area density of the positive electrode active material layer is 500-520 g / ㎡.

[0008] Optionally, the coating surface density of the positive electrode active material layer is 500 g / ㎡.

[0009] Optionally, the coating area density of the positive electrode active material layer is 520 g / ㎡.

[0010] In the second aspect, an embodiment of the utility model provides a wound lithium-ion battery, wherein the wound body of the lithium-ion battery is formed by stacking and winding a negative electrode sheet, a separator, and any of the positive and negative electrode sheets described above, and the innermost layer and the outermost layer of the wound body are both negative electrode sheets.

[0011] As can be seen from the above, after the pole pieces are rolled and compacted, before the pole pieces are stacked and wound to prepare the lithium-ion battery winding body, uniformly distributed tiny cracks are formed on the polar active material layer of the positive pole piece, and the length of each crack is 3~20mm, and the width is ≤0.02mm. The pole piece that is very hard and brittle after rolling and compacting becomes relatively soft, and the polar active material layer is not easy to crack and fall off when the winding is bent sharply, avoiding the undesirable situation of cracking and breaking on the surface of the pole piece in the stacking and winding process. It can be seen that the use of the technical solution of this embodiment is conducive to increasing the coating thickness of the polar active material layer of the pole piece, and is conducive to increasing the coating surface density of the lithium-ion wound battery. It is particularly suitable for positive pole pieces and improves the volume energy density of wound lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of this application, and do not constitute an improper limitation of the present invention.

[0013] Figure 1 A perspective structural diagram of a pole piece softening device provided in an embodiment of the utility model;

[0014] Figure 2 A schematic cross-sectional view of a pole piece provided in an embodiment of the utility model;

[0015] Figure 3 A schematic diagram of the top view structure of a pole piece provided in an embodiment of the utility model.

[0016] 1: bracket; 21: first roller; 22: second roller;

[0017] 3: Transmission mechanism; 4: Auxiliary roller; 51: First transmission film.

[0018] 52: second transmission film; 6: positive electrode current collector; 7: positive electrode active material layer. DETAILED DESCRIPTION

[0019] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The schematic embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0020] Examples of embodiments of the present invention described in detail below are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0021] The embodiments described below with reference to the drawings attached to this specification are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore should not be construed as limiting the present invention.

[0022] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0023] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] Embodiment 1:

[0025] See also Figure 1-3 .

[0026] This embodiment provides a device suitable for use in the preparation process of a pole piece for a lithium-ion rolled battery, which can be used for softening the pole piece.

[0027] The pole piece of the lithium-ion battery includes a current collector and a polar active material layer coated on the surface of the current collector.

[0028] The preparation process of the pole piece is as follows: a coating machine is used to evenly coat the polar active material slurry on the surface of the current collector made of metal foil, generally double-sided coating. After coating, it is conveyed to a drying room for drying to solidify the polar active material layer on the surface of the current collector, and the pole piece is rolled up, and the rolled pole piece is unrolled and conveyed to a roller pressing device to compact the polar active material layer, compact it to a predetermined surface density, and then rolled up for use.

[0029] When preparing lithium-ion batteries, the pole pieces are cut according to the pole piece size required for the current batch of lithium-ion batteries, and are divided into strips to obtain pole pieces of predetermined width and length.

[0030] This embodiment further adds a pole piece softening process after the pole piece slitting process and before the lithium-ion battery winding process, which is particularly suitable for the preparation of positive pole pieces with high coating surface density, so as to overcome the problem that the positive pole pieces with high coating surface density in the prior art have high rigidity and the polar material layer is easily broken and detached during the winding process, resulting in defects.

[0031] This embodiment provides a pole piece softening device, which mainly includes: a bracket 1, a transmission mechanism 3, and at least one group of roller pairs.

[0032] The bracket 1 is the base of the pole piece softening equipment, the transmission mechanism 3 and each roller pair are mounted on the bracket 1, and the transmission mechanism 3 is used to drive the pole piece to move from one end of the transmission mechanism 3 to the other end.

[0033] The structure of each roller pair is as follows: each roller pair includes a roller with a larger roller diameter and at least one roller with a smaller roller diameter. For the convenience of description, the roller with a larger roller diameter is recorded as the first roller 21, and the rollers with smaller roller diameters are all recorded as the second roller 22. The surfaces of the first roller 21 and the second roller 22 are both of high strength rigidity, such as but not limited to steel rollers. A rubber roller sleeve with a certain thickness and good elasticity is tightly sleeved on the surface of the first roller 21, and the rubber roller sleeve has a certain compression resilience.

[0034] The first roller 21 and the second roller 22 in each roller pair can be a one-to-one structure, or a one-to-two or one-to-many structure. When it is a one-to-two or one-to-many structure, each roller pair further includes an auxiliary roller 4, which is directly opposite to the first roller 21 up and down, and two or more second rollers 22 are respectively connected near the edge of the auxiliary roller 4. When used, the auxiliary roller 4 and the first roller 21 rotate synchronously relative to each other. During the rotation of the auxiliary roller 4, each second roller 22 located at the edge of the auxiliary roller 4 is pressed on the surface of the pole piece between the auxiliary roller 4 and the first roller 21 in sequence, so that each second roller 22 is matched with the first roller 21 in sequence to roll and soften the pole piece.

[0035] When the first roller 21 and one of the second rollers 22 act on the two surfaces of the electrode piece, the gap between the rubber roller sleeve outside the first roller 21 and the second roller 22 is smaller than the thickness of the electrode piece, and the second roller 22 acts on the outer surface of the rubber roller sleeve through the pressure of the electrode piece. Under the action of pressure, an elastic concave surface is formed at the position where the rubber roller sleeve contacts the electrode piece. Under the pressure of the first roller 21, the electrode piece is tightly attached to the elastic concave surface of the rubber roller sleeve, that is, the electrode piece is bent along the elastic concave surface, and the degree of bending is the depth of the elastic concave surface of the rubber roller sleeve. The user adjusts the distance between the first roller 21 and the second roller 22 according to the softening parameters of the electrode piece, and selects the thickness of the rubber roller sleeve and the elastic strength.

[0036] In the transmission and formation of the pole piece, a plurality of groups of evenly distributed roller pairs are arranged. The pole piece moved by the transmission mechanism 3 passes between the first roller 21 and the second roller 22 of each roller pair, so that the pole piece passes through each roller pair in sequence. Each roller pair respectively performs even rolling and softening on the surface of the pole piece, so as to form evenly distributed slight cracks in the polar material layer of the pole piece, thereby achieving the softening treatment of the pole piece with high coating density.

[0037] When the pole piece passes through the first roller 21 and the second roller 22 of each roller pair, since the roller diameter of the second roller 22 is smaller than the roller diameter of the first roller 21, the second roller 22 with high strength and rigidity on the outer surface acts on the surface of the pole piece so that the pole piece is closely attached to the surface of the rubber roller sleeve on the outer surface of the first roller 21. Under the action of pressure, the surface of the rubber roller sleeve is elastically concave, and the pole piece is bent and deformed in close contact with the elastic concave surface of the rubber roller sleeve, and the bending deformation of the pole piece is restored as the elastic concave surface is restored. The pole piece passes through each group of roller pairs in sequence, and each part of the pole piece undergoes the above-mentioned micro-bending when passing through each group of roller pairs, and is deformed to a straight state as the elastic concave surface of the rubber roller sleeve is elastically restored. When the pole piece passes through each group of roller pairs, the pole piece is bent in close contact with the elastically deformed rubber roller sleeve and then restored to a straight state. That is, when multiple sets of roller pairs are arranged in sequence during the movement of the pole piece, each part of the pole piece is bent several times against the elastically deformed rubber roller sleeve it passes through and then recovers to be straight, until the pole piece cup is transmitted to the end of the pole piece softening device, and the pole piece is output in a straight shape.

[0038] The inventors discovered during the research of the utility model that, at each location of the pole piece, when the pole piece is bent against the elastically deformed rubber roller sleeve and then restored to straightness against the elastically recovering rubber roller sleeve, uniform microcracks are generated in the polar active material layer on the surface of the pole piece.

[0039] As an illustration of this embodiment, the spacing between the first roller 21 and the second roller 22 of each roller pair can be adjusted, and the thickness and elastic coefficient of the rubber roller sleeve can be selected to control the size of the microcracks formed in the polar active material layer of the electrode sheet. The spacing between each roller pair can be adjusted to control the distribution of the microcracks, such as but not limited to setting the crack width of the cracks formed on the polar material layer to be less than or equal to 0.02 mm, and the length of each crack to be about 3 to 20 mm, which is not limited here.

[0040] As can be seen from the above, after the pole pieces are rolled and compacted, before the pole pieces are stacked and wound to prepare lithium-ion battery winding bodies, the pole pieces are further softened using the pole piece softening equipment of this embodiment, so that each part of the pole piece is bent under the tight pressure of the outer surface of the second roller 22, close to the elastically deformed rubber roller sleeve outside the first roller 21, and is restored to straightness under the tight pressure of the second roller 22, and then separated from the current roller pair, and then enter the next roller pair (if multiple roller pairs are provided), and the pole piece is softened again, and the bending-restoring straightness change is repeated many times, thereby forming evenly distributed tiny cracks on the pole piece, so that the pole piece that is very hard and brittle after rolling and compacting becomes relatively soft, and when the winding is bent significantly, the polar active material layer is not easy to crack and fall off, thereby avoiding the undesirable conditions of cracking and breaking of the pole piece surface in the stacking and winding process. It can be seen that the technical solution of this embodiment is beneficial to increasing the coating thickness of the polar active material layer of the electrode sheet, which is beneficial to increasing the coating surface density of the lithium-ion wound battery, and is particularly suitable for positive electrode sheets, improving the volume energy density of the wound lithium-ion battery.

[0041] As an illustration of this embodiment, this embodiment preferably illustrates that a rubber roller sleeve having a certain elastic deformation thickness is sleeved on the outer surface of the first roller 21 . In practice, the rubber roller sleeve may also be sleeved on the outer surface of the second roller 22 , but is not limited thereto.

[0042] In order to improve the bending effect of the pole piece, it is preferred but not limited to designing the roller diameter R2 of the second roller 22 in each roller pair to be less than or equal to 1 / 2 of the roller diameter R1 of the first roller 21, that is, R2<=1 / 2*R1.

[0043] As an illustration of this embodiment, this embodiment preferably sets a plurality of roller pairs so that the pole piece passes through the softening of at least two roller pairs. When a plurality of roller pairs are set, it is preferred that the arrangement of any two adjacent roller pairs is opposite, that is, one of any two adjacent roller pairs is recorded as the first roller pair and the other is the second roller pair. The first roller 21 of the first roller pair and the second roller 22 of the second roller pair are located on the same side (taking the lower side as an example), and the second roller 22 of the first roller pair and the first roller 21 of the second roller pair are located on the other side (taking the upper side as an example). During the transmission of the pole piece, when the pole piece passes through the first roller pair, the second roller 22 of the first roller pair is pressed against the pole piece from the front side, and the back side of the pole piece is pressed against the surface of the rubber roller sleeve on the outer surface of the first roller 21. The pole piece bends downward with the elastic deformation of the surface of the rubber roller sleeve on the back side and returns to straightness with the recovery of the elastic deformation. The pole piece leaves the first roller pair and enters the second roller pair in sequence. The second roller 22 of the second roller pair is in close contact with the back of the pole piece, and the front of the pole piece is in close contact with the surface of the rubber roller sleeve on the outer surface of the first roller 21. The pole piece bends upward with the elastic deformation of the surface of the rubber roller sleeve on the front side and recovers to be straight with the recovery of the elastic deformation. As can be seen from the above, when the pole piece passes through any two adjacent roller pairs, the bending directions of the pole piece under the action of the roller pairs are opposite, and after each bend, the pole piece recovers to be straight with the elastic recovery of the current rubber roller sleeve, and enters the next roller pair in a straight state. The use of the technical solution of this embodiment is further conducive to improving the softening effect of the pole piece and improving the balance of the cracks in the polar active material layer on each surface of the pole piece.

[0044] For any two adjacent roller pairs, the first roller 21 of one roller pair and the second roller 22 of the other roller pair are located on the same side of the passing pole piece, and the second roller 22 of one roller pair and the first roller 21 of the other roller pair are located on the other side of the passing pole piece.

[0045] As a schematic diagram of this embodiment, the transmission mechanism 3 of this embodiment includes a flexible membrane (referred to as the first transmission membrane 51) that moves under the drive of the transmission wheel. As shown in the figure, the first transmission membrane 51 is annularly sleeved on the transmission wheels at both ends. The first transmission membrane 51 located at the top is used as a thin film to carry the processed pole piece. The pole piece enters the top surface of the first transmission membrane 51 from one end. The first transmission membrane 51 and the pole piece located on its top surface, and the first transmission membrane 51 is also located between the two rollers of each group of roller pairs. With this scheme, the pole piece to be softened is located on the surface of the first transmission membrane 51, and the bottom surface is covered by the first transmission membrane 51. When rolling, the rollers located at the bottom of each group of roller pairs act on the bottom surface of the first transmission membrane 51 respectively, but not directly on the surface of the pole piece. The pole piece is rolled, bent and softened under the coating of the first transmission membrane 51. The use of the scheme is conducive to improving the protection of the polar active material layer and preventing it from falling off.

[0046] As a technical solution of this embodiment, the transmission mechanism 3 of this embodiment also includes: a flexible second transmission film 52, which moves synchronously with the first transmission film 51 face to face under the drive of the transmission wheel, and the second transmission film 52 partially covers the top surface of the pole piece located on the first transmission film 51, so that the pole piece whose upper and lower surfaces are respectively wrapped and covered by the first transmission film 51 and the second transmission film 52 passes through each group of roller pairs in sequence, and each group of roller pairs bends and softens the pole piece. The optimized design of this embodiment is conducive to the comprehensive protection of the two surfaces of the pole piece to prevent the pole powder from falling off.

[0047] As an illustration of this embodiment, one of the transmission wheels connected to the first transmission film 51 is a driving wheel, and the others are driven wheels.

[0048] As an illustration of this embodiment, it is possible but not limited to making the front end of the first transmission membrane 51 located below closer to the front end of the second transmission membrane 52 located above, so that at the front end of the equipment, the upper part of the front end of the first transmission wheel is empty, so as to reserve a certain space for the user to place the pole piece to be processed.

[0049] As an illustration of this embodiment, a receiving device is also provided at the end of the transmission mechanism 3, so that the pole pieces softened by each roller pair come out of the transmission mechanism 3 and fall onto the receiving device for collection of the pole pieces.

[0050] The following is a further description of the use process of the pole piece softening equipment:

[0051] A 14μm aluminum foil is used as the positive electrode current collector 6, the positive electrode active material is lithium cobalt oxide, and the positive electrode solvent is N-methylpyrrolidone (1-Methyl-2-pyrrolidinone, CAS: 872-50-4, chemical formula: C5H9NO, referred to as NMP). The component ratio of the positive electrode active material is: lithium cobalt oxide: conductive agent: binder = 98.2:0.8:1, and the half-cell gram capacity is greater than 190mAh / g.

[0052] 6μm copper foil is used as the negative electrode current collector, the negative electrode active material is artificial graphite, and the negative electrode solvent is deionized water. Negative electrode formula: graphite: conductive agent: binder: thickener = 96.2:0.8:1.2:1.8, half-cell gram capacity> 355mAh / g.

[0053] The membrane used is a wet-process base membrane with a thickness of 16 μm, a porosity of 42±3 (%), and an air permeability of 150±30s / 100mL.

[0054] The conventional wearable battery electrolyte used is LiPF6, and the lithium salt is added with improved wetting additives according to the existing technology.

[0055] The preparation process of lithium-ion batteries is as follows:

[0056] 1) Ingredients: Prepare the ingredients according to the above formula ratio, sieve out the slurry and set aside;

[0057] 2) Coating: Double-sided coating is performed in a continuous scraper coater to obtain the electrode, which is then dried in an oven.

[0058] In this step:

[0059] The positive electrode sheets with high surface density of 500 g / ㎡ and 520 g / ㎡ were prepared as the positive electrode sheets of the experimental group and set aside. The negative electrode sheets with coating surface density of 224 g / ㎡ and 233 g / ㎡ were prepared to match the above high surface density positive electrode sheets and set aside.

[0060] Positive electrode sheets with coating surface densities of 400 g / ㎡ and 420 g / ㎡ were prepared as positive electrode sheets for the control group and set aside. Negative electrode sheets with coating surface densities of 179 g / ㎡ and 188 g / ㎡ were prepared to match the above-mentioned positive electrode sheets for the control group and set aside.

[0061] 3) Compacting: Roll-press the dried positive electrode sheet and negative electrode sheet, specifically using two parallel rollers with smooth surface and high rigidity, with adjustable gap between the two rollers and consistent diameters. When rolling, adjust the spacing between the two rollers (same spacing everywhere) to compact the polar active layer of the electrode sheet to a predetermined compaction density. Further compaction processes can be, but are not limited to, referring to the prior art.

[0062] The compaction density of the positive electrode active material layer 7 is 4.1-4.15 g / dm³, and the compaction density of the negative electrode active material layer is 1.7-1.75 g / dm³.

[0063] 4-1) Sheet making: Use a slitting machine to slit the rolled electrode sheet. The negative electrode sheet is 1.0mm wider than the positive electrode sheet and 40mm longer than the positive electrode sheet.

[0064] 4-2) Softening, before winding and packaging:

[0065] Part of the positive electrode sheets of the experimental group were taken and softened by using a plate softening device to obtain positive electrode sheets of experimental group 1. The spacing between the upper and lower roller groups of the softening device was adjusted so that uniform cracks were formed on the polar active material layer of the positive electrode sheets of the experimental group 1. Under a microscope, the size of each crack formed was approximately: 3 to 20 mm in length and ≤ 0.02 mm in width. The positive electrode sheets of the experimental group 1 after softening had a certain degree of softness.

[0066] Some positive electrode sheets of the experimental group were not softened and were recorded as positive electrode sheets of experimental group 2. Observation under a microscope showed that the surface of the positive electrode sheets of experimental group 2 was uniform and flat, and the electrode sheets had strong rigidity.

[0067] The positive electrode sheet of the control group was not subjected to the softening process of this step. Under the microscope, the surface of the positive electrode sheet of the control group was uniform and flat. Since the coating thickness of the electrode sheet was smaller than that of the positive electrode sheet of the experimental group 2, the rigidity of the electrode sheet was smaller than that of the experimental group 2.

[0068] 5) Winding packaging: Use existing winding equipment and winding technology to make a laminated body, and wind the laminated body to obtain a wound body. In the wound body, the negative electrode sheet has one more layer than the positive electrode sheet, so that the innermost layer and the outermost layer of the wound body are both negative electrode sheets.

[0069] The positive electrode sheet, negative electrode sheet and separator of experimental group 1 were used to obtain the wound battery of experimental group 1 according to the winding process. The electrode sheet in the winding process had good winding performance.

[0070] The positive electrode sheet, negative electrode sheet and separator of experimental group 2 were used to obtain the wound battery of experimental group 2 according to the winding process. During the winding process and the bending process of the electrode sheets, the polar material layer of some electrode sheets had cracks, fractures and other defects at the bending position (also known as R angle), and the winding process could not be applied.

[0071] The positive electrode sheet, negative electrode sheet and separator of the control group were used to obtain the wound battery of the control group according to the winding process. The electrode sheet in the winding process had good winding performance.

[0072] Continue according to the following steps respectively.

[0073] 6) Tab welding: The positive tab is an aluminum tab of 0.1*4*18mm, and the negative tab is a nickel tab of 0.1*4*18mm. Use an ultrasonic welder to weld the tabs to the positive and negative pole handles of the winding body firmly.

[0074] 7) Packaging: Use aluminum plastic film packaging;

[0075] 8) Baking: Baking in a high vacuum oven at 90°C for 12 hours;

[0076] 9) Injection: Inject electrolyte at a rate of 3.8g / Ah;

[0077] 10) Formation: High temperature and pressure formation, temperature is 60℃, pressure is 0.5Mpa;

[0078] 11) Molding: First, vacuum the excess electrolyte and the gas generated by the formation, then cut off the remaining edges and complete the folding molding.

[0079] 12) After the battery is formed, performance testing, verification and comparison are carried out.

[0080] The positive electrode sheet of the experimental group 1 and the positive electrode sheet of the control group were taken to prepare a lithium-ion wound battery with a battery model of P5324037-3.7V, and experimental analysis and comparison were performed. The experimental data are shown in Table 1 below.

[0081] Table 1:

[0082] Material Experimental Group 1 Comparison group Improvement rate Positive electrode capacity mAh / g 144 144 Negative electrode capacity mAh / g 355 355 Aluminum foil thickness μm 14 14 Copper foil thickness μm 6 6 Diaphragm thickness μm 16 16 Aluminum plastic film thickness μm 111 111 Positive electrode double-sided density g / ㎡ 500 400 25.00% Negative electrode double-sided density g / ㎡ 224 179 25.14% Positive electrode sheet rolling thickness μm 0.136 0.112 21.43% Negative electrode sheet rolling thickness μm 0.142 0.114 24.56% Battery thickness 5.4mm 5.28 5.34 -1.12% Nominal capacity 517 509 1.57% Volumetric energy density 384.1 373.9 2.73%

[0083] It can be seen from the above that compared with the positive electrode of the control group, the volume energy density of the battery of the experimental group 1 using the high surface density positive electrode is increased by 2.73%.

[0084] The positive electrode sheet of the experimental group 1 and the positive electrode sheet of the control group were taken to prepare a lithium-ion wound battery with a battery model of P5524037-3.7V, and experimental analysis and comparison were performed. The experimental data are shown in Table 2 below.

[0085] Table 2:

[0086] Material Experimental Group 1 Comparison group Improvement rate Positive electrode capacity mAh / g 144 144 - Negative electrode capacity mAh / g 355 355 Aluminum foil thickness μm 14 14 Copper foil thickness μm 6 6 Diaphragm thickness μm 16 16 Aluminum plastic film thickness μm 111 111 Positive electrode double-sided density g / ㎡ 520 420 23.81% Negative electrode double-sided density g / ㎡ 233 188 23.94% Positive electrode sheet rolling thickness μm 0.141 0.116 21.55% Negative electrode sheet rolling thickness μm 0.147 0.12 22.50% Battery thickness 5.4mm 5.44 5.54 -1.81% Nominal capacity 538 535 0.56% Volumetric energy density 387.9 378.8 2.40%

[0087] It can be seen from the above that compared with the positive electrode sheet of the control group, the volume energy density of the battery of the experimental group 1 using the high surface density positive electrode sheet is increased by 2.4%.

[0088] It can be seen from the above that by adopting the technical solution of this embodiment, during the preparation process of the battery, for the positive electrode sheets with high surface density, the electrode sheet softening equipment of this embodiment is used to soften the electrode sheets before the winding process. This can effectively avoid the problems of high-density positive electrode sheets such as cracking and falling off of the R roll during the winding process due to the excessive thickness of the polar material layer, which is beneficial to improving the energy density of lithium-ion batteries.

[0089] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A positive electrode sheet suitable for lithium-ion batteries, characterized in that: The invention comprises a current collector, on both surfaces of which positive electrode active material layers are coated respectively, and each positive electrode active material layer is evenly distributed with cracks, each of which has a length of 3-20 mm and a width of ≤0.02 mm.

2. The positive electrode sheet for lithium-ion batteries according to claim 1, characterized in that: The coating area density of the positive electrode active material layer is 500-520 g / ㎡.

3. The positive electrode sheet suitable for lithium-ion batteries according to claim 2, characterized in that: The coating area density of the positive electrode active material layer is 500 g / ㎡.

4. The positive electrode sheet suitable for lithium-ion batteries according to claim 2, characterized in that: The coating area density of the positive electrode active material layer is 520 g / ㎡.

5. A wound lithium-ion battery, characterized in that: The wound body of the lithium-ion battery is formed by stacking and winding a negative electrode sheet, a separator, and the positive electrode sheet and the negative electrode sheet according to any one of claims 1 to 4, and the innermost layer and the outermost layer of the wound body are both negative electrode sheets.

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