Electrode sheet, battery cell and battery

Abstract

An electrode sheet, a battery cell and a battery. The electrode sheet comprises a current collector and a first protective layer, the current collector being provided with an active substance layer, the first protective layer being arranged between the current collector and the active substance layer, and the ratio of the reflected light intensity of the first protective layer to the reflected light intensity of the active material layer being not smaller than 2. When a CCD camera is used to acquire an image of the electrode sheet, real-time and accurate detection of information such as whether there is a first protective layer and position information thereof can be achieved, thus avoiding waste of the active material layer during coating. In addition, the arrangement of the first protective layer also helps to improve the yield of batteries, thereby ensuring the safety performance of batteries.

Description

Electrode sheet, battery cell and battery Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries, and in particular relates to an electrode sheet, a battery core and a battery. Background Art

[0002] Lithium-ion batteries have a high probability of failure when subjected to mechanical abuse (such as needle puncture, extrusion, etc.) or external impact. The reason is that when the battery is subjected to mechanical damage or impact, a relatively serious short circuit will occur inside. In order to reduce the probability of short circuit, those skilled in the art usually apply a protective layer between the current collector and the active material layer to improve the safety performance of the battery. This protective layer is usually a black-gray coating. During the coating process, it is usually necessary to locate the coating area of ​​the protective layer to coat the other side. However, since the reflective ability of the protective layer and the active material layer are both weak and the color distinction is low, it is easy to cause the coating area of ​​the protective layer to be difficult to distinguish, making it difficult for the CCD camera to identify the coating area of ​​the protective layer. When coating the active material layer, it often exceeds the area of ​​the protective layer, resulting in waste of the active material layer and is not conducive to improving the safety performance of the battery. Therefore, how to achieve accurate detection of the position information of the protective layer while ensuring the safety performance of the lithium-ion battery is a technical problem that needs to be solved in this field.

[0003] Summary of the Invention

[0004] The present invention provides an electrode sheet. When a CCD camera is used to acquire an image of the electrode sheet, real-time and accurate detection of information such as the presence and position of a first protective layer can be achieved, thereby avoiding waste of the active material layer during the coating process. Moreover, due to the provision of the first protective layer, the yield rate of the battery is improved, thereby ensuring the safety performance of the battery.

[0005] The present invention also provides a battery cell, which includes the above-mentioned electrode sheet and has the advantages of high safety performance and low cost.

[0006] The present invention also provides a battery, which includes the above-mentioned battery cell and has excellent safety performance, high yield rate and low cost, which is conducive to large-scale production.

[0007] According to a first aspect of the present invention, an electrode sheet is provided, comprising a current collector and a first protective layer; an active material layer is provided on the current collector, wherein the first protective layer is provided between the current collector and the active material layer; and the ratio of the reflected light intensity of the first protective layer to the reflected light intensity of the active material layer is not less than 2.

[0008] The electrode sheet as described above, wherein the ratio of the reflected light intensity of the first protective layer to the reflected light intensity of the active material layer is not less than 3.

[0009] The electrode sheet as described above, wherein the first protective layer comprises conductive particles, and the whiteness of the conductive particles is ≥30.

[0010] The electrode sheet as described above, wherein the conductive particles include at least one of AZO and ATO.

[0011] The electrode sheet as described above, wherein the conductive particles include a core and a conductive coating layer covering at least a portion of the surface of the core, and the conductive coating layer is selected from at least one of AZO and ATO.

[0012] The electrode sheet as described above, wherein the conductive coating layer accounts for 1 to 30% by mass of the conductive particles; and / or,

[0013] The core is selected from at least one of aluminum oxide, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, and boehmite.

[0014] The electrode sheet as described above, wherein the first protective layer comprises 70-98% by mass of conductive particles and 2-30% by mass of an adhesive.

[0015] The electrode sheet as described above, wherein the resistivity of the conductive particles is 1 to 100 Ω·cm.

[0016] The electrode sheet as described above, wherein the resistance of the first protective layer is 1 to 1000 mΩ.

[0017] The electrode sheet as described above, wherein the thickness of the first protective layer is 0.5-5 μm.

[0018] A second aspect of the present invention provides a battery cell comprising the electrode sheet described in the first aspect.

[0019] The battery cell as described above, wherein the battery cell is a laminate structure, a protective unit is provided on the outermost side of the laminate structure, the protective unit is the electrode sheet coated on one side, and the coated side faces the center of the laminate structure, and the uncoated side is provided with a second protective layer.

[0020] The battery cell as described above, wherein the battery cell is a roll core structure, the roll core structure includes a first pole piece and a second pole piece that are stacked and wound, wherein the first pole piece of the outermost layer of the roll core structure is the electrode sheet, the first pole piece of the outermost layer of the roll core structure has the current collector, and the current collector includes a double-sided coating area and a single-sided coating area connected in sequence, the coated surface of the single-sided coating area faces the center of the roll core structure, and the uncoated surface is provided with a second protective layer.

[0021] In the battery cell as described above, the current collector includes a double-sided coating area, a single-sided coating area, and a tail area that are connected in sequence, and a second protective layer extension portion is provided on a side of the tail area away from the center of the core structure.

[0022] A third aspect of the present invention provides a lithium-ion battery comprising the battery cell described in the second aspect.

[0023] The implementation of the present invention has at least the following beneficial effects:

[0024] The electrode sheet provided by the present invention controls the ratio of the reflected light intensity of the first protective layer to the reflected light intensity of the active material layer to be no less than 2. When a camera is used to obtain an image of the electrode sheet, the difference in reflected light intensity is helpful in distinguishing the first protective layer from the active material layer, thereby easily obtaining information such as the presence and position of the first protective layer, solving the problem in the prior art that it is difficult to identify the coating area of ​​the first protective layer and that waste is easily caused when coating the active material layer. In addition, by providing the first protective layer, it is helpful to improve the needle penetration rate, thereby helping to improve the yield rate of the battery and ensuring the safety performance of the battery.

[0025] The battery cell provided by the present invention has the advantages of high safety performance and low cost due to the inclusion of the above-mentioned electrode sheet.

[0026] The battery provided by the present invention, because it includes the above-mentioned battery cell, has excellent safety performance, high yield rate and low cost, which is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a schematic structural diagram of an electrode sheet in one embodiment of the present invention;

[0028] FIG2 is a schematic cross-sectional view of an embodiment of the present invention when the battery cell has a laminated structure;

[0029] FIG3 is a schematic diagram of a cross-sectional structure of an embodiment of the present invention when the battery core has a wound structure;

[0030] FIG4 is a schematic cross-sectional view of another embodiment of the present invention when the battery cell has a wound structure;

[0031] FIG5 is a schematic structural diagram of an electrode sheet in another embodiment of the present invention;

[0032] FIG6 is a schematic diagram of the top view of the positive electrode sheet in Comparative Examples 2-4 of the present invention.

[0033] Explanation of the accompanying reference numerals: 1-current collector; 11-double-sided coating area; 12-single-sided coating area; 13-finishing area; 101-first protective layer; 102-active material layer; 1021-extension area; 10a, 10b-protective monomer; 103-second protective layer; 1031-extension of the second protective layer; 10-first pole piece; 20-second pole piece; 30-diaphragm; 1001-first pole tab; 2001-second pole tab. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0035] It should be noted that the X direction in Figures 1, 2, 5 and 6 refers to the length direction of the electrode sheet, which is also the length direction of the current collector; the Z direction refers to the thickness direction of the electrode sheet, which is also the thickness direction of the current collector; and the Y direction refers to the width direction of the electrode sheet, which is also the width direction of the current collector.

[0036] As shown in Figure 1, the first aspect of the present invention provides an electrode sheet, including a current collector 1, a first protective layer 101, and an active material layer 102; the first protective layer 101 is arranged on at least one functional surface of the current collector 1, and the active material layer 102 is arranged on the surface of the first protective layer 101 away from the current collector 1; the ratio of the reflected light intensity of the first protective layer 101 to the reflected light intensity of the active material layer 102 is not less than 2.

[0037] The present invention does not limit the specific shape and structure of the electrode sheet. For example, the electrode sheet may be in the shape of a conventional rectangular parallelepiped in the art.

[0038] The electrode sheet includes a current collector 1, a first protective layer 101, and an active material layer 102. The current collector 1 has two largest and opposite functional surfaces, namely a first functional surface and a second functional surface. The first protective layer 101 can be provided on one functional surface or on both functional surfaces. The provision of the first protective layer 101 can significantly improve the safety performance of the battery in the event of mechanical abuse. The active material layer 102 is provided on the surface of the first protective layer 101 away from the current collector.

[0039] The ratio of the reflected light intensity of the first protective layer 101 to the reflected light intensity of the active material layer 102 is not less than 2, where the reflected light intensity of the first protective layer 101 and the reflected light intensity of the active material layer 102 refer to the intensities of light reflected from the surfaces of the protective layer 101 and the active material layer 102 under the same light source, which can be measured, and is recorded as the reflected light intensity. When the above relationship is satisfied, the difference in reflected light intensity between the first protective layer 101 and the active material layer 102 is significant.

[0040] The present invention does not limit the preparation process of the above-mentioned electrode sheet. For example, the current collector includes two largest and opposite functional surfaces, which are divided into a first functional surface (A surface) and a second functional surface (B surface). When coating the A surface of the current collector 1, the first protective layer 101 is first coated, and then the first protective layer of the B surface is coated by positioning the position of the first protective layer on the A surface, and then the active material layer of the A surface is coated by positioning the position of the first protective layer on the B surface, and finally the active material layer of the B surface is coated by positioning the position of the first protective layer on the A surface.

[0041] By controlling the ratio of the reflected light intensity of the first protective layer 101 to the reflected light intensity of the active material layer 102, it is helpful to identify the position and size of the first protective layer 101 and the active material layer 102, which is beneficial for accurate positioning during the coating process. When the ratio of the reflected light intensity of the first protective layer 101 to the reflected light intensity of the active material layer 102 is not less than 2, it helps to achieve the consistency of the size of the first protective layer 101 and the active material layer 102 in the length direction and the width direction of the current collector. If the ratio of the reflected light intensity of the first protective layer 101 to the reflected light intensity of the active material layer 102 is less than 2, the reflected light intensities of the two are equivalent, that is, the difference in reflected light intensity is not large, and it is difficult to distinguish between the active material layer 102 and the first protective layer 101, then positioning errors may occur when coating the other surface, which will cause the size of the active material layer 102 in the width direction of the current collector 1 to exceed the size of the first protective layer 101 in the width direction of the current collector 1, resulting in waste of the active material layer 102, and even leading to the inability to complete the coating of the active material layer.

[0042] According to the present invention, when a CCD camera is used to capture an image of the electrode sheet, the presence and position of the first protective layer 101 on the electrode sheet can be accurately detected in real time. This helps avoid waste of the active material layer during the coating process. Furthermore, the provision of the first protective layer helps improve the yield rate of the battery and ensures battery safety. The inventors believe that by controlling the ratio of the reflected light intensity of the first protective layer 101 to the reflected light intensity of the active material layer 102 to be no less than 2, the difference in reflected light intensity between the first protective layer 101 and the active material layer 102 is significant under the same light source. When a camera is used to capture an image of the battery assembly, it is helpful to distinguish the first protective layer 101 from the active material layer 102, and it is easy to obtain information such as the presence and position of the first protective layer 101. When coating another functional surface of the current collector 1, the coating position of the first protective layer 101 can be judged in real time to avoid the coating area of ​​the active material layer 102 on the other functional surface exceeding the range of the first protective layer 101, especially to ensure that the size of the active material layer 102 in the length direction is consistent with the size of the first protective layer 101 in the length direction, and the size of the active material layer 102 in the width direction is consistent with the size of the first protective layer 101 in the width direction. In addition, due to the setting of the first protective layer, it also helps to improve the yield of the battery and ensure the safety performance of the battery.

[0043] The present invention does not limit the specific composition of the first protective layer 101, as long as it can play a protective role and meets the above-mentioned relationship of reflected light intensity. In some embodiments, the first protective layer 101 includes conductive particles.

[0044] By selecting conductive particles of different whiteness, it is possible to control the intensity of the reflected light of the first protective layer 101. In some embodiments, the whiteness of the conductive particles is ≥30. When the whiteness of the conductive particles is less than 30, it is difficult to control the intensity of the reflected light of the first protective layer 101. When the whiteness of the conductive particles is greater than or equal to 30, the intensity of the reflected light of the first protective layer 101 can be effectively controlled. For example, the conductive particles can be at least one of AZO and ATO. In the present invention, the whiteness of the conductive particles refers to a physical quantity that describes the proportion of white light components in the light reflected from the surface of the conductive particles. The higher the whiteness of the conductive particles, the more white light components in the light reflected from its surface, and the whiter the conductive particles appear under light.

[0045] The present invention does not limit the specific structure of the conductive particles. In some embodiments, the conductive particles include at least one of AZO and ATO, that is, the conductive particles can be AZO, ATO or conductive particles formed by a mixture of the two components; in addition, in some embodiments, the conductive particles can also include a core material and a conductive coating layer covering at least part of the surface of the core material, and the conductive coating layer is selected from at least one of AZO and ATO; in this case, at least a part of the conductive coating layer constitutes the outermost layer of the conductive particles, and the conductive coating layer only needs to cover at least a part of the core material. Moreover, the conductive particles of the above two structures can coexist and be mixed to form the above protective layer, for example: a part of the conductive particles are AZO, and a part of the conductive particles are ATO-coated core materials, and so on.

[0046] It's worth noting that in existing technologies, the conductive agent used in the first protective layer is often gray or black, while the active material layer is often black. This difference in reflected light intensity between the two is minimal, making identification difficult. However, the present invention utilizes the core-shell structured conductive particles, which help adjust the whiteness of the conductive particles to ≥30, thereby adjusting the reflected light intensity of the first protective layer.

[0047] Among them, the core material can be an inorganic filler, which makes the core material have the characteristics of high mechanical strength, good stability and good heat resistance. In the case of mechanical damage to the battery, the core material can play a good protective role, reduce the probability of short circuit, and improve the safety performance of the battery.

[0048] In addition, the excellent dispersibility of the inorganic filler itself enables the conductive particles to also have good dispersion performance, which is conducive to ensuring the uniformity of the intensity of the reflected light of the first protective layer.

[0049] ATO refers to antimony-doped tin dioxide, wherein the doping amount of antimony is greater than 0% and less than or equal to 30%; AZO refers to aluminum-doped zinc oxide, wherein the doping amount of aluminum is 1% to 10%.

[0050] The present invention does not limit the specific type of the core material. For example, the core material is selected from at least one of aluminum oxide, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, and boehmite.

[0051] By controlling the mass content of the conductive coating layer in the conductive particles, the reflected light intensity of the first protective layer can be further adjusted. In one embodiment, when the mass content of the conductive coating layer in the conductive particles is 1% to 30% (for example: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%), it can be ensured that the reflected light intensity of the first protective layer satisfies the above relationship, and it can also ensure that the battery has good safety performance. Among them, the mass content of the conductive coating layer in the conductive particles refers to the mass content of the conductive coating layer in all the conductive particles.

[0052] The first protective layer 101 of the present invention further includes an adhesive. The present invention does not limit the specific type of adhesive, as long as it can ensure effective bonding between the first protective layer and the current collector. For example, the adhesive includes one or more of polyvinylidene fluoride (PVDF), acrylic acid-modified PVDF, polyacrylate polymers, polyacrylic acid, polyacrylic salts, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0053] By adjusting the mass content of the conductive particles and the adhesive in the first protective layer 101 , not only can the intensity of the light reflected by the first protective layer 101 be further regulated, but the first protective layer 101 can also be effectively bonded to the current collector. In some embodiments, the first protective layer 101 includes 70% to 98% conductive particles (for example, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%) and 2% to 30% adhesive (for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%) by mass.

[0054] The provision of the first protective layer 101 may also lead to an increase in battery impedance. To avoid the increase in battery impedance, the inventors have found that when the resistance of the first protective layer 101 is 1 mΩ to 1000 mΩ, the battery can still maintain good cycle performance.

[0055] Specifically, the resistance of the first protective layer 101 can be controlled by selecting conductive particles with different resistivities, controlling the content of the conductive particles in the first protective layer, and other factors.

[0056] In some specific embodiments, the resistivity of the conductive particles can be controlled to be 1 Ω·cm to 100 Ω·cm by adjusting factors such as the type of the conductive coating material and the mass content of the conductive coating in the conductive particles.

[0057] The inventors have also discovered that smaller conductive particles facilitate thinner coating of the first protective layer 101 on the positive electrode current collector, and enable a more dense distribution of the conductive particles on the first protective layer, resulting in a lithium-ion battery with both good energy density and safety. In some specific embodiments, the conductive particles of the present invention have an average particle size of 0.05 μm to 0.5 μm.

[0058] As the thickness of the first protective layer 101 increases, the safety performance of the lithium-ion battery can also be improved accordingly, but at the same time it will also lead to a corresponding decrease in the battery's volume energy density. In order to achieve both the safety performance and volume energy density of the lithium-ion battery, the thickness of the first protective layer 101 can be set to 0.5μm~5μm.

[0059] The present invention does not limit the material of the active material layer 102, and the active material layer 102 may be composed of conventional components in the art, including active material, conductive agent, adhesive, etc. The active material, conductive agent, adhesive, etc. may be conventional materials in the art.

[0060] Taking the positive electrode sheet as an example, the positive electrode active material includes lithium-containing transition metal oxides, such as one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese oxide, and lithium-rich manganese-based materials, and the conductive agent includes one or more of carbon black, carbon nanotubes, graphene, and carbon fibers.

[0061] The electrode sheet of the present invention can also be prepared by conventional technical means in the field. Specifically, the raw materials constituting the first protective layer can be uniformly dispersed in a solvent to obtain a first protective layer slurry, and the raw materials constituting the active material layer can be uniformly dispersed in a solvent to obtain an active material layer slurry. The first protective layer slurry is then coated on at least one functional surface of the current collector, and the first protective layer is obtained after drying. The active material layer slurry is then coated on the first protective layer, and dried to obtain the electrode sheet of the present invention.

[0062] The present invention does not specifically limit the coating method, and any coating method such as gravure coating, extrusion coating, spray coating, screen printing, etc. can be used to coat the first protective layer slurry and the active material layer slurry.

[0063] The electrode sheet can be a negative electrode sheet or a positive electrode sheet. For example, when the electrode sheet is a positive electrode sheet, the current collector is aluminum foil, and the material of the active material layer is a ternary material or a positive electrode active material such as lithium iron phosphate; when the electrode sheet is a negative electrode sheet, the current collector is copper foil, and the material of the active material layer is a negative electrode active material such as graphite or silicon-based.

[0064] A second aspect of the present invention provides a battery cell comprising the electrode sheets provided in the first aspect. The electrode sheets include a first electrode sheet and a second electrode sheet of opposite polarity, wherein the first electrode sheet and / or the second electrode sheet may be the electrode sheet structure provided in the first aspect of the present invention. In addition, the battery cell further comprises a separator, which may be a separator conventionally used in the art, such as a PP film or a PE film.

[0065] Specifically, the first electrode sheet, the second electrode sheet, and the separator can form the battery cell. A battery cell refers to the electrochemical cell containing the first and second electrode sheets installed inside a battery. The battery cell is generally not used directly. By installing the battery cell and the protection circuit inside the battery casing, a battery for charging and discharging can be formed. Since the battery cell is the energy storage part of the battery, the quality of the battery cell directly determines the quality of the battery.

[0066] The battery cell can be a wound structure or a laminated structure.

[0067] As shown in Figure 2, when the battery cell has a laminated structure, the laminated structure includes multiple first electrode sheets 10 and multiple second electrode sheets 20. During the processing, the first electrode sheets 10 and the second electrode sheets 20 are alternately stacked in the same direction, and a separator 30 is placed between two adjacent first electrode sheets 10 and second electrode sheets 20, and finally stacked to form a laminated structure. At this time, in some embodiments, the outermost side of the laminated structure is provided with protective cells 10a and 10b. The protective cells 10a and 10b are electrode sheets coated on one side, with the coated side facing the center of the laminated structure, and the uncoated side is provided with a second protective layer 103.

[0068] The electrode sheet of the present invention comprises a current collector, a first protective layer, and an active material layer. When the first protective layer and the active material layer are sequentially applied to only one functional surface of the current collector, it is referred to as a single-sidedly coated electrode sheet. In this case, that functional surface is the coated surface; the other functional surface, lacking the active material layer, is the uncoated surface. A second protective layer 103 is applied to the uncoated surface.

[0069] Specifically, a first protective layer and an active material layer are sequentially coated on one functional surface (coated surface) of the current collector in the protective monomer, and a second protective layer is provided on the other functional surface (uncoated surface), which can protect the laminated structure.

[0070] The material of the second protective layer may be the same as or different from that of the first protective layer of the present invention, and the present invention does not impose any further restrictions thereon.

[0071] When the battery cell is a wound structure, the wound structure includes a first pole piece and a second pole piece. During the winding process, the first pole piece, the diaphragm and the second pole piece are wound in the same direction starting from the winding head end and finally form a wound structure. At this time, as shown in Figure 3, in some embodiments, the battery cell is a rolled core structure, and the rolled core structure includes a first pole piece 10 and a second pole piece 20 that are stacked and wound, wherein the first pole piece 10 of the outermost layer of the rolled core structure is an electrode sheet, and the first pole piece 10 of the outermost layer of the rolled core structure has a current collector, which includes a double-sided coating area and a single-sided coating area connected in sequence, the coated surface of the single-sided coating area faces the center of the rolled core structure, and the uncoated surface is provided with a second protective layer.

[0072] The first current collector is divided into a double-sided coating area and a single-sided coating area based on the arrangement of the active material layer. The double-sided coating area has both functional surfaces of the current collector coated with a first protective layer and an active material layer. The single-sided coating area has one functional surface (referred to as the coated surface) coated with a protective layer and then an active material layer, while the other functional surface (referred to as the uncoated surface) is not coated with an active material layer. In this case, the coated surface of the single-sided coating area faces the center of the core structure, while the uncoated surface is provided with a second protective layer to protect the wound structure.

[0073] The material of the second protective layer may be the same as or different from that of the first protective layer of the present invention, and the present invention does not impose any further restrictions thereon.

[0074] Furthermore, as shown in Figure 5, in some embodiments, the current collector 1 includes a double-sided coating area 11, a single-sided coating area 12, and a tail area 13 connected in sequence, the coated surface of the single-sided coating area 12 faces the center of the core structure, the uncoated surface is provided with a second protective layer 103, and the side of the tail area 13 away from the center of the core structure is provided with a second protective layer extension 1031.

[0075] Among them, no active material layer is set on the two functional surfaces of the tail area 13. At this time, the second protective layer extension part 1031 is only set on the side of the tail area 13 away from the center of the core structure, that is, the part of the second protective layer 103 extending to the tail area.

[0076] When winding, the end of the double-sided coating area away from the single-sided coating area is used as the winding starting end, which is conducive to ensuring that the second protective layer is arranged on the outermost side of the battery cell.

[0077] The second protective layer can be made of the same or different materials as the first protective layer. When the second protective layer and the first protective layer have the same specific composition, this helps improve production efficiency and reduce production costs. Furthermore, when the second protective layer and the first protective layer are made of the same material, the second protective layer and the first protective layer can be applied continuously.

[0078] The battery cell is also provided with a first pole tab 1001 and a second pole tab 2001 , so that when the battery cell is used in a battery, it can be connected to an external circuit through the first pole tab 1001 and the second pole tab 2001 to realize the charging and discharging functions of the battery.

[0079] In some embodiments, the first tab 1001 and the second tab 2001 are located on the same end face of the battery cell, thereby facilitating connection between the battery and an external circuit. It is understood that, in order to avoid short circuits, the first tab 1001 and the second tab 2001 are spaced apart from each other.

[0080] A third aspect of the present invention provides a lithium-ion battery comprising the battery cell of the third aspect and, in addition, an electrolyte. Due to the inclusion of the battery cell, the lithium-ion battery has an excellent yield rate.

[0081] The present invention will be further described below with reference to specific examples and comparative examples.

[0082] Example 1

[0083] 1. Preparation of slurry

[0084] 90 wt% of ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles) and 10 wt% of PVDF are mixed, a certain amount of NMP is added, and the solid content of the slurry is adjusted to 40%, and the mixture is stirred to prepare a first protective layer slurry;

[0085] 90 wt% of ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles) and 10 wt% of PVDF are mixed, a certain amount of NMP is added, and the solid content of the slurry is adjusted to 40%, and the mixture is stirred to prepare a second protective layer slurry;

[0086] 96 wt% lithium cobalt oxide, 1 wt% carbon black, 1 wt% carbon nanotubes, and 2 wt% PVDF were mixed, and a certain amount of NMP was added to adjust the solid content of the slurry to 70%. The mixture was stirred to prepare a positive electrode active material layer slurry.

[0087] 96 wt% of artificial graphite, 1 wt% of carbon black, 1.5 wt% of styrene-butadiene rubber, and 1.5 wt% of sodium carboxymethyl cellulose were mixed, deionized water was added, and the solid content of the slurry was adjusted to 40%. The mixture was stirred to prepare a negative electrode active material layer slurry.

[0088] 2. Preparation of positive electrode

[0089] According to the position shown in Figure 5, the protective layer slurry (the first protective layer slurry is consistent with the second protective layer slurry) is coated on the positive electrode collector to form the first protective layer and the second protective layer, and then the positive electrode active material layer slurry is coated on the first protective layer by an extrusion coater. Specifically, the first protective layer is applied on one functional surface (first side) of the positive electrode collector, and then the first protective layer on the first side is positioned to apply the first protective layer to the other functional surface (second side) of the positive electrode collector, and then the first protective layer on the second side is positioned to apply the positive electrode active material layer on the first side, and then the positive electrode active material layer slurry on the second side is applied by positioning the first protective layer on the first side. Then, the positive electrode sheet is obtained after drying.

[0090] 3. Preparation of negative electrode sheet

[0091] The negative electrode active material layer slurry is coated on the negative electrode current collector through an extrusion coating process, and the negative electrode sheet is obtained after drying.

[0092] 4. Preparation of batteries

[0093] Use a roller press to roll the positive and negative electrode sheets to the designed thickness, and weld the tabs on the positive and negative electrode sheets respectively; place the separator between the positive and negative electrode sheets, wind them, and fix them with adhesive tape to obtain a battery assembly;

[0094] Use a punching die to punch out the aluminum-plastic film, then use the punched aluminum-plastic film to encapsulate the battery components, bake until the moisture content is qualified, and inject electrolyte; use lithium-ion battery formation equipment to charge and discharge to harden the battery components, and sort the capacity of the battery components, and then perform secondary sealing and folding to obtain the battery;

[0095] Perform OCV test on the battery to test the voltage drop K value of the battery per unit time, and select products with qualified K value. The qualified range is K value < 0.1mV / h.

[0096] Example 2

[0097] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0098] The “90 wt % ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)” in Example 1 is replaced by “90 wt % AZO”, and other conditions remain unchanged.

[0099] Example 3

[0100] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0101] Replace the “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)” in Example 1 with “90 wt% AZO-coated aluminum oxide (wherein the mass content of the conductive coating layer AZO accounts for 10% of the mass content of the conductive particles)”, and other conditions remain unchanged.

[0102] Example 4

[0103] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0104] Replace the “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)” in Example 1 with “90 wt% ATO-coated magnesium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)”, and other conditions remain unchanged.

[0105] Example 5

[0106] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0107] Replace the “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)” in Example 1 with “90 wt% ATO-coated boehmite (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)”, and other conditions remain unchanged.

[0108] Example 6

[0109] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0110] Replace the “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)” in Example 1 with “90 wt% ATO-coated silicon oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)”, and other conditions remain unchanged.

[0111] Example 7

[0112] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0113] Replace the “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)” in Example 1 with “90 wt% ATO-coated zinc oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)”, and other conditions remain unchanged.

[0114] Example 8

[0115] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0116] Replace the “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)” in Example 1 with “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 30% of the mass content of the conductive particles)”, and other conditions remain unchanged.

[0117] Example 9

[0118] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0119] Replace the “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)” in Example 1 with “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 20% of the mass content of the conductive particles)”, and other conditions remain unchanged.

[0120] Example 10

[0121] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0122] The “96 wt % lithium cobalt oxide” in Example 1 was replaced with “96 wt % lithium nickel cobalt manganese oxide”, and other conditions remained unchanged.

[0123] Example 11

[0124] The preparation process is basically the same as that of Example 1, except that the adhesive tape used in this example is blue insulating adhesive tape, and other conditions remain unchanged.

[0125] Example 12

[0126] The preparation process is basically the same as that of Example 1, except that the adhesive tape used in this example is brown insulating adhesive tape, and other conditions remain unchanged.

[0127] Example 13

[0128] The preparation process is basically the same as that of Example 1 (slurry preparation, positive electrode sheet preparation, negative electrode sheet preparation), except that it is a laminated structure, specifically including the following steps:

[0129] Preparation of protected monomer:

[0130] The first protective layer slurry is applied to a functional surface (first side) of the positive electrode current collector to form a first protective layer, and then the positive electrode active material layer slurry is applied to the first protective layer through an extrusion coater. Specifically, the positive electrode active material layer slurry is first applied to the first side by positioning the position of the first protective layer. Then, by positioning the position of the positive electrode active material layer slurry on the first side, the other functional surface (second side) of the positive electrode current collector is coated, that is, the second protective layer slurry is applied to the second side to form a second protective layer, and then dried to obtain a protective monomer.

[0131] Battery preparation

[0132] Use a roller press to roll the positive and negative electrode sheets to the designed thickness, and die-cut soft tabs (blank aluminum foil and copper foil) from the positive and negative electrode sheets; place the separator between the positive and negative electrode sheets and stack them to obtain a stacked core structure, wherein protective cells are set at the top and bottom of the stacked core structure;

[0133] Use aluminum tabs to weld the soft tabs of the positive electrode together, and use nickel tabs to weld the soft tabs of the negative electrode together. Secure them with green tape to obtain a battery assembly.

[0134] Use a punching die to punch out the aluminum-plastic film, then use the punched aluminum-plastic film to encapsulate the battery components, bake until the moisture content is qualified, and inject electrolyte; use lithium-ion battery formation equipment to charge and discharge to harden the battery components, and sort the capacity of the battery components, and then perform secondary sealing and folding to obtain the battery;

[0135] Perform OCV test on the battery to determine the K value of the battery and select products with qualified K value.

[0136] Example 14

[0137] The preparation process is basically the same as that of Example 13, except that the components of the first protective layer and the second protective layer are different. The first protective layer slurry is 10wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles), 80wt% titanium oxide, and 10wt% PVDF. The second protective layer slurry is 90wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles), 10wt% PVDF. Other conditions remain unchanged.

[0138] Example 15

[0139] The preparation process is basically the same as that of Example 13, except that the components of the first protective layer and the second protective layer are different. The first protective layer slurry is 90wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 1% of the mass content of the conductive particles) and 10wt% PVDF, and the second protective layer slurry is 90wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles) and 10wt% PVDF. Other conditions remain unchanged.

[0140] Example 16

[0141] The preparation process is basically the same as that of Example 13, except that the components of the first protective layer and the second protective layer are different. The first protective layer slurry is 90wt% AZO-coated aluminum oxide (wherein the mass content of the conductive coating layer AZO accounts for 10% of the mass content of the conductive particles) and 10wt% PVDF, and the second protective layer slurry is 90wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles) and 10wt% PVDF. Other conditions remain unchanged.

[0142] Example 17

[0143] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0144] Replace the “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)” in Example 1 with “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 2% of the mass content of the conductive particles)”, and other conditions remain unchanged.

[0145] Example 18

[0146] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0147] Replace the “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)” in Example 1 with “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 35% of the mass content of the conductive particles)”, and other conditions remain unchanged.

[0148] Example 19

[0149] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0150] Replace the "90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles) and 10 wt% PVDF" in Example 1 with "98 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles) and 2 wt% PVDF", and the other conditions remain unchanged.

[0151] Example 20

[0152] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0153] Replace the "90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles) and 10 wt% PVDF" in Example 1 with "72 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles) and 28 wt% PVDF", and the other conditions remain unchanged.

[0154] Example 21

[0155] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0156] Replace the "90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles) and 10 wt% PVDF" in Example 1 with "65 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles) and 35 wt% PVDF", and the other conditions remain unchanged.

[0157] Example 22

[0158] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0159] The “90 wt % ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10 wt % of the mass content of the conductive particles)” in Example 1 is replaced with “70 wt % AZO, 20 wt % ATO”, and other conditions remain unchanged.

[0160] Example 23

[0161] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0162] Replace the "90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)" in Example 1 with "20 wt% ATO, 70 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer ATO accounts for 10% of the mass content of the conductive particles)", and other conditions remain unchanged.

[0163] Comparative Example 1

[0164] The preparation process is basically the same as that of Example 1, except that in this comparative example, a protective layer is not coated on the positive electrode sheet, and other conditions remain unchanged.

[0165] Comparative Example 2

[0166] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0167] The “90 wt % ATO-coated titanium oxide (wherein the mass content of the conductive coating layer AZO accounts for 10% of the mass content of the conductive particles)” in Example 1 is replaced by “90 wt % lithium iron phosphate”, and other conditions remain unchanged.

[0168] Comparative Example 3

[0169] The preparation process is basically the same as that of Example 1, except that the composition of the first protective layer is different;

[0170] The “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer AZO accounts for 10% of the mass content of the conductive particles) and 10 wt% PVDF” in Example 1 is replaced by “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer AZO accounts for 10% of the mass content of the conductive particles), 5 wt% carbon black, and 5 wt% PVDF”, and other conditions remain unchanged.

[0171] Comparative Example 4

[0172] The preparation process is basically the same as that of Example 1, except that the components of the protective layer are different;

[0173] The “90 wt% ATO-coated TiO2 (wherein the mass content of the conductive coating layer AZO accounts for 10% of the mass content of the conductive particles) and 10 wt% PVDF” in Example 1 are replaced with “90 wt% ATO-coated titanium oxide (wherein the mass content of the conductive coating layer AZO accounts for 50% of the mass content of the conductive particles), 5 wt% carbon black, and 5 wt% PVDF, while other conditions remain unchanged.

[0174] Test example

[0175] 1. Needle Penetration Test: Fully charge the lithium-ion battery and place it on the test bench of the needle penetration test equipment. A tungsten steel needle with a diameter of 3mm and a tip length of 3.62mm is inserted through the center of the battery at a speed of 100mm / s. The battery passes the test if it does not catch fire or explode. The pass rate is calculated by dividing the number of passes by the number of tests. The number of tests is 30.

[0176] 2. Whiteness test: Use a colorimeter to test the powder color of the protective layer conductive particles and the safety layer conductive particles respectively, and take their L value (retain the integer digit) as the whiteness value.

[0177] 3. Reflected light intensity ratio: Use a CCD camera to expose the protective layer and the active material layer and record the reflected light intensity value. The reflected light intensity value of the protective layer / the reflected light intensity value of the active material layer is the reflected light intensity ratio of the protective layer to the active material layer.

[0178] Table 1 compares the reflected light intensity of the first protective layer components, the second protective layer components, the whiteness of the conductive particles, the ratio of the reflected light intensity of the first protective layer to the active material layer (A / B), and the battery puncture pass rate of each embodiment and comparative example.

[0179] Table 1 In Table 1, “ / ” represents no data

[0180] According to Table 1, we can see that:

[0181] 1. By comparing the examples and comparative examples, it can be seen that since comparative example 1 does not contain a protective layer, the needle puncture rate is directly 0, and the battery safety is poor; the examples have a high needle puncture rate by providing a protective layer, which is beneficial to improving the safety performance of the battery.

[0182] 2. Comparing Examples 1-11 and 17-23, it can be seen that controlling the content of each component of the conductive particles in the protective layer is beneficial to adjusting the whiteness of the conductive particles, and further beneficial to adjusting the reflected light intensity of the protective layer.

[0183] 3. Examples 1-11 and 17-23 of the present invention can all achieve normal coating during the coating process, that is, the size of the positive electrode active material layer in the width direction of the positive electrode current collector is ensured to be equal to the size of the first protective layer in the width direction of the positive electrode current collector, and no waste occurs. In comparative examples 2-4, the protective layer contains dark substances with weak reflected light intensity, such as lithium iron phosphate, carbon black, and ATO-coated titanium oxide (ATO accounts for 50wt%), resulting in little difference in reflected light intensity between the protective layer and the active material layer. During the coating process, the size of the positive electrode active material layer in the width direction of the positive electrode current collector of comparative examples 2-4 exceeds the size of the protective layer in the width direction of the positive electrode current collector. This method is needed to achieve the difference between the positive electrode current collector and the positive electrode active material layer to position the coating on the other side, resulting in a positive electrode active material layer with a certain width being directly covered on the positive electrode current collector. The part that exceeds the protective layer (i.e., exceeds area 1021) causes waste of the active material layer on the positive electrode current collector, with a waste rate of about 5%.

[0184] After research, the inventor believes that when the ratio of the reflected light intensity of the first protective layer to the reflected light intensity of the active material layer in the embodiment satisfies the above relationship, it is beneficial to distinguish between the active material layer and the first protective layer, and can realize real-time and accurate detection of information such as the presence and position of the first protective layer, which is beneficial to positioning the coating and improving the accuracy of the coating. In addition, by setting the first protective layer, the needle penetration rate is significantly improved, thereby improving the battery yield, which is beneficial to the safety performance of the battery.

[0185] The above describes in detail the preferred embodiments of the present invention and their experimental verification. It should be understood that numerous modifications and variations based on the concepts of the present invention can be made by those skilled in the art without inventive effort. Therefore, any technical solution that can be derived by those skilled in the art based on the concepts of the present invention through logical analysis, reasoning, or limited experimentation based on the existing technology should be within the scope of protection defined by the claims.

Claims

1. An electrode sheet, characterized in that: It comprises a current collector and a first protective layer; an active material layer is arranged on the current collector, wherein the first protective layer is arranged between the current collector and the active material layer; A ratio of the intensity of reflected light from the first protective layer to the intensity of reflected light from the active material layer is not less than 2.

2. The electrode sheet according to claim 1, characterized in that: A ratio of the intensity of reflected light of the first protective layer to the intensity of reflected light of the active material layer is not less than 3.

3. The electrode sheet according to claim 1 or 2, characterized in that: The first protective layer includes conductive particles, and the whiteness of the conductive particles is ≥30.

4. The electrode sheet according to claim 3, characterized in that: The conductive particles include at least one of AZO and ATO.

5. The electrode sheet according to claim 3 or 4, characterized in that: The conductive particles include a core and a conductive coating layer covering at least a portion of the surface of the core, and the conductive coating layer is selected from at least one of AZO and ATO.

6. The electrode sheet according to claim 5, characterized in that: The mass content of the conductive coating layer in the conductive particles is 1% to 30%.

7. The electrode sheet according to claim 5 or 6, characterized in that: The core is selected from at least one of aluminum oxide, magnesium oxide, titanium oxide, zinc oxide, silicon oxide and boehmite.

8. The electrode sheet according to any one of claims 5 to 7, characterized in that: The ATO is antimony-doped tin dioxide, wherein the doping amount of antimony is greater than 0% and less than or equal to 30%.

9. The electrode sheet according to any one of claims 5 to 8, characterized in that: The AZO is aluminum-doped zinc oxide, wherein the aluminum doping amount is 1% to 10%.

10. The electrode sheet according to any one of claims 1 to 9, characterized in that: The first protective layer comprises 70% to 98% of conductive particles and 2% to 30% of adhesive according to mass content.

11. The electrode sheet according to any one of claims 10, characterized in that: The adhesive includes one or more of polyvinylidene fluoride PVDF, acrylic acid-modified PVDF, polyacrylate polymers, polyacrylic acid, polyacrylic salt, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

12. The electrode sheet according to any one of claims 1 to 11, characterized in that: The resistivity of the conductive particles is 1 Ω·cm to 100 Ω·cm.

13. The electrode sheet according to claim 12, characterized in that: The resistance of the first protective layer is 1 mΩ to 1000 mΩ.

14. The electrode sheet according to any one of claims 1 to 13, characterized in that: The thickness of the first protective layer is 0.5 μm to 5 μm.

15. A battery cell, characterized in that: The electrode sheet comprises the electrode sheet according to any one of claims 1 to 14.

16. The battery cell according to claim 15, characterized in that: The battery core is a laminate structure, the outermost side of the laminate structure is provided with a protective unit, the protective unit is the electrode sheet coated on one side, with the coated side facing the center of the laminate structure, and the uncoated side is provided with a second protective layer.

17. The battery cell according to claim 15, characterized in that: The battery core is a rolled core structure, and the rolled core structure includes a first pole piece and a second pole piece that are stacked and wound, wherein the first pole piece of the outermost layer of the rolled core structure is the electrode sheet, and the first pole piece of the outermost layer of the rolled core structure has the current collector, and the current collector includes a double-sided coated area and a single-sided coated area connected in sequence, the coated surface of the single-sided coated area faces the center of the rolled core structure, and the uncoated surface of the single-sided coated area is provided with a second protective layer.

18. The battery cell according to claim 17, characterized in that: The current collector includes a double-sided coating area, a single-sided coating area, and a tail area which are connected in sequence. A second protective layer extension portion is arranged on a side of the tail area away from the center of the core structure.

19. The battery cell according to claim 17, characterized in that: The material of the first protective layer is the same as that of the second protective layer.

20. A battery, characterized in that: A battery cell comprising any one of claims 15 to 19.

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