Lithium ion secondary battery
By using adhesive tape with high electrolyte wettability in lithium-ion batteries, the problems of adhesive tape preventing lithium ions from passing through and electrolyte accumulation are solved, achieving higher energy density and improved safety performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-07
Smart Images
Figure CN121812697A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, and specifically to a lithium-ion secondary battery. Background Technology
[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and environmental friendliness, have been widely used in mobile phones, laptops, new energy vehicles, and other fields. As market demand continues to expand, higher requirements are being placed on the energy density and safety performance of lithium-ion batteries.
[0003] In existing lithium-ion batteries, protective adhesive tape is typically applied to the coating ends of the positive and negative electrodes or at the electrode tab welding points to ensure battery safety. However, existing adhesive tape prevents lithium ions from passing through, causing the tape-attached area to lose capacity and thus reducing the overall energy density of the lithium-ion battery. To achieve the required energy density, the electrodes usually need to be coated with a longer active coating to compensate for the energy density loss caused by the tape blocking lithium ion passage, which increases material costs to some extent. Furthermore, existing adhesive tape prevents electrolyte flow, causing electrolyte accumulation at the tape interface. This leads to gas bubbling at the interface between the tape and the positive electrode, resulting in tape edge formation and affecting battery safety. Summary of the Invention
[0004] The purpose of this invention is to overcome the aforementioned problems in the prior art and to provide a lithium-ion secondary battery. The lithium-ion secondary battery of this invention (hereinafter referred to as the battery) has high energy density and good safety performance.
[0005] This invention provides a lithium-ion secondary battery, comprising a positive electrode, a separator, and a negative electrode, wherein the positive electrode, the separator, and the negative electrode are wound together to form a core; the positive electrode includes a positive current collector and a positive active coating located on at least one side of the positive current collector; the positive electrode includes adhesive tape, which partially covers the positive active coating at the tail end of the positive electrode and extends to the positive current collector; the adhesive tape includes a substrate layer and a coating applied to at least one side of the substrate layer; the coating includes an adhesive and inorganic particles; the electrolyte wettability of the adhesive tape is greater than or equal to 15 mm / 30 s.
[0006] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: (1) The adhesive paper of the present invention allows lithium ions to shuttle and electrolyte to flow, which can effectively avoid the problem of electrolyte accumulating below the adhesive paper interface, causing bubbles or ridges; (1) The lithium-ion secondary battery of the present invention has high energy density and good safety performance.
[0007] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description
[0008] Figure 1 The diagram shown is a schematic diagram of the positive electrode sheet in an example of the present invention.
[0009] Figure 2 The diagram shown is a schematic diagram of the adhesive tape in an example of the present invention.
[0010] Figure 3 The diagram shown is a structural schematic of the core in an example of the present invention.
[0011] Figure 4 The image shown is a scanning electron microscope (SEM) image of the adhesive tape substrate layer in an example of the present invention.
[0012] Figure 5 The image shown is a photograph of the battery negative electrode in a fully charged state according to an example of the present invention.
[0013] Figure 6 The image shown is a photograph of a pair of proportional battery negative electrode plates in a fully charged state according to the present invention.
[0014] Figure 7 The image shown is an infrared spectrum of the adhesive tape in an example of the present invention.
[0015] Figure 8 The image shown is a SEM image of the adhesive tape coating in an example of the present invention.
[0016] Figure 9 The image shown is a top view of the positive electrode sheet in an example of the present invention. Detailed Implementation
[0017] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.
[0018] This invention provides a lithium-ion secondary battery, comprising a positive electrode, a separator, and a negative electrode, wherein the positive electrode, the separator, and the negative electrode are wound together to form a core. The positive electrode includes a positive current collector and a positive active coating located on at least one surface of the positive current collector.
[0019] In this invention, the positive electrode sheet includes adhesive paper, which partially covers the positive active coating at the tail of the positive electrode sheet and extends to the positive current collector. For example... Figure 1 The figure shows a schematic diagram of the structure of the positive electrode sheet in an embodiment of the present invention. As can be seen from the figure, the positive electrode sheet includes a positive current collector 1 and a positive active coating 2 located on both sides of the positive current collector; the positive electrode sheet includes an adhesive paper 3, which partially covers the positive active coating at the tail of the positive electrode sheet and extends to the positive current collector.
[0020] In this invention, the adhesive tape includes a substrate layer and a coating applied to at least one surface of the substrate layer; the coating includes an adhesive and inorganic particles. For example... Figure 2 The figure shows a schematic diagram of the adhesive tape in an embodiment of the present invention. As can be seen from the figure, the adhesive tape includes a substrate layer 5 and a coating 4 coated on one side surface of the substrate layer.
[0021] In this invention, the electrolyte wetting rate of the adhesive paper is greater than or equal to 15 mm / 30 s (e.g., 15 mm / 30 s, 16 mm / 30 s, 17 mm / 30 s, 18 mm / 30 s, 19 mm / 30 s, 20 mm / 30 s, 25 mm / 30 s, 30 mm / 30 s, 35 mm / 30 s, 40 mm / 30 s or 45 mm / 30 s).
[0022] In one example, the electrolyte wetting rate of the adhesive tape is 15 mm / 30 s to 30 mm / 30 s.
[0023] The adhesive tape of this invention allows lithium ions to shuttle normally. Therefore, in the area of the positive electrode covered by the adhesive tape, lithium ions can still shuttle freely and quickly, allowing the capacity of the positive electrode active coating in the adhesive tape-covered area to be fully utilized, reducing material costs and effectively improving the energy density of the battery. Simultaneously, the adhesive tape also allows electrolyte flow. The better the wettability of the adhesive tape, the better the fluidity of the electrolyte and the lithium-ion conductivity. By controlling the electrolyte wetting speed of the adhesive tape to be greater than or equal to 15mm / 30s, it can be ensured that the electrolyte can quickly and evenly penetrate the adhesive tape. This avoids the problem of electrolyte accumulation or local enrichment at the edges of the adhesive tape when the electrolyte wetting speed is less than 12mm / 30s, which can lead to problems such as adhesive tape bulging, edge formation, or interface separation. This helps improve the interface stability and safety of the battery during long-term cycling, while also ensuring the effective utilization of the capacity in the adhesive tape area, effectively improving the overall energy density of the lithium-ion battery.
[0024] In this invention, the electrolyte wetting rate of the adhesive tape can be tested using conventional methods in the art. For example, the battery is discharged to 0% SOC (e.g., discharged to 2.7V), the adhesive tape is disassembled and dried at 60°C for 2 hours. Then, the adhesive tape is laid flat on a table with the coated side facing up. 20 μL of electrolyte (lithium hexafluorophosphate dissolved in a mixed solution of DMC / DEC / EC in a volume ratio of 1:1:1, wherein the concentration of lithium hexafluorophosphate is 1 mol / L) is dropped onto the coating. After standing for 30 seconds, the length of the electrolyte spreading along the length of the adhesive tape is measured and defined as the electrolyte wetting rate of the adhesive tape.
[0025] In this invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active coating located on at least one side of the surface of the negative electrode current collector; the adhesive tape portion covers the positive electrode active coating for a length L1, and the negative electrode active coating at the tail of the core extends beyond the positive electrode active coating for a length L2 (the tail of the core is the area where the core ends along the winding direction). Figure 3 The figure shows a schematic diagram of the core structure in an embodiment of the present invention. As can be seen from the figure, the length of the adhesive paper covering the positive active coating is L1, and the length of the negative active coating at the tail of the core extending beyond the positive active coating is L2.
[0026] In one instance, 1mm ≤ L1 < 10mm (e.g., 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm).
[0027] In one instance, L2 ≥ 1 / 2L1.
[0028] In one embodiment, L1+L2≥3.5mm (e.g., 3.5mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 18mm or 20mm, etc.).
[0029] When the length of the positive electrode active coating covered by the adhesive tape (L1) and the length of the negative electrode active coating exceeding the positive electrode active coating (L2) satisfy a specific relationship, on the one hand, it can avoid the risk of short circuit caused by direct contact between the positive and negative electrodes due to burrs or positive electrode particles piercing the separator during charging and discharging, thus improving the safety performance of the battery; on the other hand, it can ensure that the negative electrode has sufficient lithium-ion accommodating space at the corresponding position of the positive electrode area covered by the adhesive tape, effectively avoiding the precipitation of lithium dendrites due to the inability of lithium ions to be fully inserted into the negative electrode during charging, which can further reduce the safety risk of internal short circuit caused by lithium dendrites piercing the separator.
[0030] In this invention, the material of the substrate layer includes at least one of polyethylene terephthalate, polyethylene, polypropylene, polyimide, polyvinyl chloride, and a composite material of polyethylene and polypropylene.
[0031] In one example, the porous membrane material comprises polyethylene terephthalate.
[0032] In this invention, the adhesive comprises at least one of polyisobutylene, styrene-isoprene copolymer, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene and styrene-butadiene rubber.
[0033] In one instance, the adhesive comprises polyisobutylene.
[0034] In this invention, the inorganic particles include alumina, boehmite, and lithium lanthanum zirconium oxide (Li7La3Zr2O). 12 (LLZO), Lithium Lanthanum Titanium Oxide Li 3x La (2 / 3-x) / 3 TiO3 (LLTO), Lithium titanium aluminum phosphate (Li) 1+x Al x Ti 2-x At least one of (PO4)3 (LATP), magnesium oxide, titanium oxide, hafnium dioxide, silicon dioxide, tin oxide, cerium dioxide, nickel oxide, zirconium oxide, zinc oxide, calcium oxide, magnesium hydroxide, aluminum hydroxide, barium hydroxide, barium sulfate, calcium silicate, and titanium dioxide.
[0035] In one instance, the inorganic particles comprise aluminum oxide.
[0036] In this invention, the substrate layer includes pores formed by a plurality of intersecting and / or stacked fibers.
[0037] In this invention, the diameter of the fiber is 2μm-10μm (e.g., 2μm, 4μm, 6μm, 8μm or 10μm).
[0038] In this invention, the average particle size of the inorganic particles is 150 nm to 2 μm (e.g., 150 nm, 500 nm, 1 μm, 1.5 μm or 2 μm).
[0039] like Figure 4The image shown is a scanning electron microscope (SEM) image of the adhesive tape substrate layer in an example of the present invention. As can be seen from the image, the substrate layer of the present invention contains several intersecting and / or stacked fibers. These fibers have a suitable diameter, which not only forms a sufficiently dense support structure to ensure the puncture resistance of the adhesive tape during cycling, but also enhances the interfacial adhesion between the coating and the substrate layer, as well as the liquid retention capacity of the adhesive tape. This promotes rapid lithium ion transport and uniform electrolyte flow, further preventing electrolyte accumulation under the adhesive tape and the resulting bulging, thereby further reducing the risk of lithium plating at the negative electrode. If the fiber diameter is too large (e.g., >10 μm), the porosity between the fibers will increase accordingly, the puncture resistance of the substrate layer will decrease significantly, the coating will easily peel off, and the liquid retention capacity of the adhesive tape will become unbalanced, with localized excessively rapid electrolyte flow and insufficient liquid retention, failing to further reduce the risk of lithium plating at the negative electrode. If the fiber diameter is too small (e.g., <2μm), the pores between the fibers will be too narrow, reducing the lithium-ion shuttle efficiency, weakening the electrolyte retention capacity of the adhesive paper, resulting in insufficient electrolyte supply during cycling, affecting cycling stability, and making it difficult to further improve the lithium plating effect on the negative electrode.
[0040] In this invention, the diameter of the fiber can be tested using conventional methods in the art. For example, the battery is discharged to 0% SOC, the adhesive tape is disassembled and removed, and 10 scanning electron microscope (SEM) images are taken at different positions of the adhesive tape under a scanning electron microscope. The diameter of any 80 fibers in each SEM image is measured, the average value is taken, and the average value of the data from the 10 SEM images is calculated to obtain the average diameter of the fiber.
[0041] In this invention, the average particle size of the inorganic particles can be obtained by conventional methods in the art, such as testing the diameter of 100 particles arbitrarily on the surface of the adhesive paper coating under SEM, calculating the average value, measuring 10 times at 10 different locations on the adhesive paper, taking the average value, and recording it as the average particle size of the inorganic particles.
[0042] In this invention, the pore size of the substrate layer is 0.1μm-25μm (e.g., 0.1μm, 0.5μm, 1μm, 5μm, 10μm, 15μm, 20μm or 25μm).
[0043] In one example, the pore size of the substrate layer is 0.5 μm-10 μm.
[0044] The pores in the substrate layer are formed by several intersecting and / or stacked fibers; therefore, the pore size of the substrate layer is affected by the fibers. When the pore size of the substrate layer is within a suitable range, the pores have sufficient accommodating space, allowing some coating material to slowly penetrate into the interior of the substrate layer pores rather than just remaining on the surface. This results in effective embedding with an appropriate amount, improving the adhesion between the substrate layer and the coating, as well as the puncture strength of the adhesive tape, reducing the risk of short circuits in the battery. Simultaneously, it does not disrupt the lithium-ion shuttle channels and electrolyte flow space, and avoids excessive coating penetration due to excessive pore size, preventing pore blockage caused by excessive embedding. Furthermore, it helps improve the electrolyte retention capacity of the adhesive tape, allowing it to absorb more electrolyte and improve lithium-ion transport.
[0045] In this invention, the pore size of the substrate layer can be tested using conventional methods in the art, such as discharging the battery to 0% SOC, disassembling and removing the adhesive tape, immersing it in a benzene solution for 4 hours, removing the adhesive tape and drying it, and then testing the pore size of the adhesive tape with a pore size meter.
[0046] In this invention, the thickness of the substrate layer is 5μm-20μm. By controlling the thickness of the substrate layer to meet the above range, this invention can ensure the mechanical strength of the adhesive tape, further improve the puncture strength and puncture resistance of the adhesive tape, reduce the risk of foreign objects such as burrs and lithium dendrites puncturing the adhesive tape and separator, and further improve the safety performance of the battery.
[0047] In this invention, the coating thickness is 2μm-15μm. A coating thickness within this range helps to further improve the puncture resistance of the adhesive tape and enhance the puncture safety of the battery.
[0048] In this invention, the thickness of the substrate layer and the coating can be tested using conventional methods in the art. For example, the battery is discharged to 0% SOC, the adhesive tape is disassembled and removed, soaked in benzene solution for 4 hours, the adhesive tape is removed and dried, the adhesive tape is laser-cut using an argon ion milling (CP) instrument, and the substrate layer and coating are observed using SEM. At least 10 sites are selected on the substrate layer and coating, the thickness at each site is measured, and the average value is taken.
[0049] In this invention, the area of the negative electrode sheet corresponding to the adhesive paper portion covering the positive electrode active coating is golden yellow when the negative electrode sheet is fully charged. For example... Figure 5 The image shown is a photograph of the battery negative electrode in a fully charged state according to an example of the present invention. Figure 6The image shown is a photograph of a pair of proportional battery negative electrode sheets in a fully charged state. By comparison, it can be seen that the area of the negative electrode sheet covered by the adhesive tape and the positive active coating in the fully charged state is golden yellow. This indicates that the interface between the negative electrode sheet and the positive active coating covered by the adhesive tape in this area is in good contact, and the adhesive tape has not undergone excessive shrinkage, displacement or damage. This can effectively ensure the smooth ion transport channel between the positive and negative electrodes in this area, reduce the interface resistance, promote uniform current distribution, avoid the risk of local lithium plating or internal short circuit, and thus effectively improve the charge and discharge rate performance and safety performance of the battery.
[0050] In this invention, "fully charged state" refers to the state in which the battery completes the electrochemical charging reaction and reaches its energy storage limit at an ambient temperature of 23±2°C, at which point the battery voltage reaches its design limit. In this state, the actual usable capacity of the battery is basically at the designed rated capacity (i.e., 100% SOC).
[0051] In this invention, the bending stiffness of the adhesive tape is ≤15mN. Since the adhesive tape is located at the junction of the positive electrode active coating and the empty foil area (positive electrode current collector) at the tail of the positive electrode sheet, the smaller the bending stiffness of the adhesive tape, the more flexible it is. This avoids the problem of excessive bending stress during bending, which can lead to the adhesive tape developing edges, due to the adhesive tape being too stiff.
[0052] In this invention, the bending stiffness of the adhesive tape can be tested by conventional methods in the art, such as using a stiffness tester according to the national standard GB / T 22364-2018, with a bending angle of 15° and a bending length of 10mm.
[0053] In this invention, the puncture resistance of the adhesive tape is ≥0.8 N / μm. This ensures that the adhesive tape has excellent mechanical properties, preventing sharp foreign objects such as burrs and lithium dendrites from puncturing it. When this adhesive tape is applied to a battery, it can significantly reduce the risk of the separator being punctured, block internal short circuits caused by positive and negative electrode contact, and improve the safety performance of the battery.
[0054] In this invention, the puncture resistance of the adhesive tape can be tested by conventional methods in the art, such as laying the adhesive tape flat in the tensile testing machine fixture and clamping it, puncturing it at a rate of 100 mm / min, recording the maximum load (N) at the moment of penetration, and dividing it by the average thickness (μm) of the adhesive tape to obtain the puncture resistance of the adhesive tape (N / μm).
[0055] In this invention, the thermal shrinkage rate of the adhesive paper in the width direction is ≤2%; the thermal shrinkage rate of the adhesive paper in the length direction is ≤2%. The low thermal shrinkage rate of the adhesive paper of this invention helps to further improve the thermal stability of the adhesive paper and the thermal safety of the battery.
[0056] In one example, the adhesive tape has a heat shrinkage rate of 0.1%-0.8% in the width direction and a heat shrinkage rate of 0.1%-0.8% in the length direction.
[0057] In this invention, the testing methods for the heat shrinkage rate of the adhesive tape in both the width and length directions are the same. One example is taken here: A sample of the adhesive tape is taken, and its original length L0 is tested at room temperature. The sample is then placed in a vacuum drying oven at 120℃±2℃ and heated for 30 minutes. After heating, the length L1 of the heated sample is tested at room temperature. The heat shrinkage rate is calculated using the following formula: In this invention, the slope of the thinned region at the tail end of the positive electrode active coating is k, which extends from the center of the core to the tail end, where k = h / d; h is the thickness of the positive electrode active coating on one side of the positive electrode current collector, in μm, and the range of h is 15μm-150μm; d is the orthogonal projection distance between the starting point and the ending point of the thinned region on the surface of the positive electrode current collector.
[0058] In one instance, k is 0.75-10 (e.g., 0.75, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10).
[0059] In one instance, d is 0 < d ≤ 15 mm (e.g., 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, or 15 mm). For example, when d is 10 mm and h is 50 μm, k is 5.
[0060] When the slope k of the thinned region at the tail of the positive electrode active coating meets a specific range, it can further improve the adhesion between the adhesive paper and the positive electrode active coating interface, prevent the adhesive paper from peeling off or separating from the positive electrode active coating in the later stages of cycling, improve the interface performance between the positive electrode and the adhesive paper, and help improve the lithium ion transport rate between the positive and negative electrodes in the active coating covered by the adhesive paper during cycling, thereby improving the long-cycle performance of the battery.
[0061] In one example, the adhesive comprises polyisobutylene, and the porous membrane material comprises polyethylene terephthalate; the infrared spectrum of the adhesive tape is measured at ~1365 cm⁻¹. -1 It has the first characteristic peak at ~3253 cm⁻¹ -1 It has a second characteristic peak, and the ratio of the peak intensity of the first characteristic peak to the second characteristic peak is Q, where Q ≥ 1.05. For example... Figure 7 The image shows the infrared spectrum of the adhesive tape in an example of the present invention. As can be seen from the image, the infrared spectrum of the adhesive tape is within the range of ~1365 cm⁻¹. -1 It has a first characteristic peak, corresponding to the characteristic peak of polyisobutylene, at ~3253 cm⁻¹.-1 It has a second characteristic peak, which corresponds to the characteristic peak of polyethylene terephthalate. Figure 7 The value of Q is 1.37. The larger the Q value, the higher the content of high-sol adhesive in the adhesive layer, the better the liquid retention capacity of the adhesive paper, the better the fluidity and ion shuttle capacity of the electrolyte, the smaller the swelling of the adhesive paper, and the more effectively the electrolyte can be prevented from accumulating at the adhesive paper interface.
[0062] In this invention, the dyne value of the positive electrode current collector is greater than or equal to 30 dyn, which can further improve the adhesion between the adhesive tape and the current collector, prevent the battery from developing ridges, and prevent gas from accumulating and bubbling at the interface between the adhesive tape and the positive electrode. The higher the dyne value of the positive electrode current collector, the tighter the bond between the adhesive tape and the positive electrode current collector, further preventing the adhesive tape from developing ridges.
[0063] In this invention, based on the total weight of the coating, the mass content of the inorganic particles is 40%-80% (e.g., 40%, 50%, 60%, 70% or 80%), and the mass content of the adhesive is 20%-60% (e.g., 20%, 30%, 40%, 50% or 60%).
[0064] The inventors of this invention have discovered that a specific ratio of the inorganic particles and the binder in the coating enables the adhesive tape to possess both safety properties and excellent adhesive strength. For example... Figure 8 The image shown is an SEM image of the adhesive tape coating in an example of the present invention. As can be seen from the image, the inorganic particles are uniformly distributed in the coating. The inorganic particles are connected and fixed to each other by an adhesive, and are tightly bonded to the substrate layer by the adhesive. The high hardness of the inorganic particles further enhances the puncture strength of the adhesive tape, thereby improving puncture resistance. Simultaneously, the gaps created by the accumulation of appropriately sized inorganic particles form a porous structure, which helps to increase the electrolyte retention capacity of the adhesive tape.
[0065] In this invention, the total weight of the coating is used as a basis. The mass content of the inorganic particles and the binder can be tested by conventional methods in the art. For example, the battery is discharged to 0% SOC (e.g., discharged to 2.7V), the positive electrode is removed, and the adhesive coating is collected as a test sample. The mass of the coating sample is accurately weighed (denoted as m1). Benzene solution is used as the extractant, and extraction is performed at room temperature to completely dissolve the binder. Subsequently, the insoluble inorganic particles are separated by filtration or centrifugation, and the residue is washed, dried to constant weight, and weighed (denoted as m2). The mass of the binder is the difference between the total mass of the sample and the mass of the inorganic particles (i.e., m1-m2). The mass content of the inorganic particles in the coating can be calculated using formula 1: m2 / m1×100%. The mass content of the binder in the coating can be calculated using formula 2: (m1-m2) / m1×100%.
[0066] In this invention, the positive electrode plate further includes a tab groove and a positive electrode tab located in the tab groove.
[0067] like Figure 9 The figure shows a top view of the positive electrode sheet in an embodiment of the present invention. As can be seen from the figure, the adhesive tape covers the tab groove 6 and part of the positive electrode tab 7. Since the adhesive tape can ensure the normal shuttle of lithium ions, the part of the positive electrode active coating covered by the adhesive tape can also normally insert and extract lithium, and there will be no accumulation of lithium ions at the edge of the adhesive tape, which would cause lithium plating in the later stage of cycling. At the same time, it can also improve the energy density of the battery.
[0068] In this invention, along the thickness direction of the positive electrode sheet, the overlapping area of the positive electrode tab and the projection of the positive electrode sheet is S1mm. 2 The overlap area between the adhesive tape and the projection of the positive electrode sheet is S2mm. 2 .
[0069] In one instance, 1 < S2 / S1 ≤ 4.
[0070] The adhesive tape of this application has a certain liquid retention capacity, which can improve the transmission efficiency of lithium ions between the positive electrode tab and the electrolyte and reduce the internal resistance of the battery. However, if there is too much electrolyte, the adhesive tape is prone to loss of adhesion, and side reactions are likely to occur at the interface between the positive electrode tab welding area and the electrolyte. Simply changing the overlapping area S1 of the projection of the positive electrode tab and the positive electrode sheet (i.e., the area of the positive electrode tab welding area) has limited improvement effect. For example, although increasing the welding area of the positive electrode tab can make the current distribution more uniform, reduce the local current density, and reduce local side reactions, an excessively large welding area will lead to uneven welding quality, increase the risk of defects such as pores and cracks, and easily cause stress concentration in the welding area of the positive electrode tab, causing the positive electrode tab to fall off or break. Although reducing the welding area of the positive electrode tab can reduce the contact area between the electrolyte and the welding area of the positive electrode tab to reduce side reactions, it will also increase the internal resistance of the battery.
[0071] The inventors of this invention discovered through research that by adjusting the overlap area S1 of the projection of the positive electrode tab and the positive electrode sheet and the overlap area S2 of the projection of the adhesive paper and the positive electrode sheet to satisfy a specific relationship, excessive side reactions between the electrode tab welding area and the electrolyte can be avoided; this is beneficial for uniform current distribution and reducing excessively high local current density, thereby avoiding aggravated local heating and further improving the safety performance of the battery.
[0072] In this invention, the positive electrode active coating comprises a positive electrode material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode material comprises at least one of the lithium metal transition oxides, such as lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. The positive electrode conductive agent may include conductive agents conventionally used in the art, such as at least one of vapor-grown carbon fiber (VGCF), conductive carbon black, Ketjen black, and acetylene black. The positive electrode binder may include binders conventionally used in the art, such as at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyimide (PI), styrene-butadiene rubber (SBR), polyisobutylene (PIB), and carboxymethyl cellulose (CMC).
[0073] In this invention, based on the total weight of the positive electrode active coating, the content of the positive electrode material can be 80-99.8% by weight, the content of the positive electrode binder can be 0.1-10% by weight, and the content of the positive electrode conductive agent can be 0.1-10% by weight.
[0074] In this invention, the negative electrode active coating comprises a negative electrode material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode material comprises silicon-based materials and carbon-based materials. The silicon-based material comprises at least one of silicon-carbon, silicon-oxygen, elemental silicon, and silicon alloys; the carbon-based material comprises at least one of graphite, hard carbon, soft carbon, and graphene. The negative electrode conductive agent may include conductive agents conventionally used in the art, such as at least one of vapor-grown carbon fiber (VGCF), conductive carbon black, Ketjen black, and acetylene black. The negative electrode binder may include binders conventionally used in the art, such as at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyimide (PI), styrene-butadiene rubber (SBR), lithium acrylate, polyisobutylene (PIB), and carboxymethyl cellulose (CMC).
[0075] In this invention, based on the total weight of the negative electrode active coating, the content of the negative electrode material can be 80-99.8% by weight, the content of the negative electrode binder can be 0.1-10% by weight, and the content of the negative electrode conductive agent can be 0.1-10% by weight.
[0076] In this invention, the electrolyte comprises an organic solvent, a conductive lithium salt, and additives. The organic solvent comprises carbonate solvents and / or carboxylic acid ester solvents. The carbonate solvents may include cyclic carbonate solvents and chain carbonate solvents. The cyclic carbonate solvents may include cyclic carbonates conventionally used in the art, such as at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). The chain carbonate solvents may include chain carbonates conventionally used in the art, such as at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). The carboxylic acid ester solvents may include carboxylic acid esters conventionally used in the art, such as at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB). The electrolyte salt comprises at least one of lithium hexafluorophosphate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethanesulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, or lithium difluorosulfonylimide. The additive comprises at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propenesulfonate lactone, vinyl ethylene carbonate, vinyl sulfate, succinic acid nitrile, glutaronitrile, adiponitrile, heptaonitrile, octanoic acid nitrile, sebaconitrile, 1,3,6-hexanetrionitrile (HTCN), glycerol trionitrile, and 1,2-bis(2-cyanoethoxy)ethane.
[0077] In this invention, the diaphragm can be a conventional choice in the art, for example, the diaphragm includes at least one of polyethylene and polypropylene.
[0078] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.
[0079] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0080] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.
[0081] The following examples illustrate the lithium-ion secondary battery of the present invention.
[0082] Example 1 The battery is prepared according to the following method: (1) Preparation of adhesive paper Polyisobutylene and alumina (average particle size 0.9 μm) were mixed uniformly at a mass ratio of 50:50 and added to toluene solution to obtain a coating slurry. The coating slurry was uniformly coated onto one side of a polyethylene terephthalate substrate layer (substrate layer thickness 10 μm), dried, and then bonded to a release film and wound up to prepare adhesive tape. The electrolyte wetting rate of the adhesive tape was 22 mm / 30 s. The substrate layer included pores formed by several intersecting and / or stacked fibers with a fiber diameter of 4.5 μm, a pore size of 5 μm, a coating thickness of 4.5 μm, a bending stiffness of 8.5 mN, a puncture resistance of 1.5 N / μm, a thermal shrinkage rate of 0.18% in the width direction and 0.17% in the length direction, and a peak intensity ratio Q of 1.37 for the first characteristic peak to the second characteristic peak in the infrared spectrum of the adhesive tape. (2) Preparation of positive electrode sheet Lithium cobalt oxide, PVDF, and conductive carbon black were mixed in a mass ratio of 97:2:1. N-methylpyrrolidone was added, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode active material slurry. The positive electrode active material slurry was uniformly coated on both sides of an 8 μm thick aluminum foil, dried, rolled, slit, and the tab grooves and positive electrode tabs were welded. The adhesive tape prepared in step (1) was then pasted onto the end of the positive electrode active coating and extended to the positive electrode current collector to obtain a positive electrode sheet. The dyn value of the positive electrode current collector was 32 dyn. (3) Preparation of negative electrode sheet Graphite, styrene-butadiene rubber, sodium carboxymethyl cellulose and conductive carbon black were mixed evenly in a mass ratio of 97:1:1.5:0.5. After adding an appropriate amount of deionized water and dispersing evenly, a negative electrode slurry was prepared. The negative electrode slurry was evenly coated onto both sides of a copper foil with a thickness of 6μm. After drying, rolling, cutting and welding of negative electrode tabs, a negative electrode sheet was obtained. (4) Battery preparation The positive electrode sheet, separator (polyethylene film with a thickness of 8 μm) prepared in step (2) and the negative electrode sheet prepared in step (3) are stacked in sequence to ensure that the separator is between the positive and negative electrode sheets to play a role in isolation. Then, the core is obtained by winding. The core is sealed with aluminum-plastic film and baked in a vacuum for 24 hours to remove moisture. Then, the electrolyte (lithium hexafluorophosphate dissolved in a mixed solution of DMC / DEC / EC with a volume ratio of 1:1:1, where the concentration of lithium hexafluorophosphate is 1 mol / L) is injected into the dried bare cell. After vacuum sealing, standing, formation, shaping and sorting, a lithium-ion battery is obtained. Among them, L1 is 2.5 mm, L2 is 1.5 mm, and k is 1.5.
[0083] Examples 2-6 were performed following Example 1, except that the parameters of the adhesive tape were changed, as detailed in Tables 1-1 and 1-2. In Example 2: L1 was 2 mm, L2 was 1.5 mm, k was 5, and the dyn value of the positive current collector was 30 dyn. In Example 3: L1 was 3.4 mm, L2 was 2 mm, k was 8.5, and the dyn value of the positive current collector was 35 dyn.
[0084] Example 7 group This set of embodiments is based on Embodiment 1, except that the length L1 of the adhesive tape covering the positive active coating and the length L2 of the negative active coating extending beyond the positive active coating are changed, as follows: Example 7a, L1 is 2mm, L2 is 1.2mm; Example 7b, L1 is 1.2 mm, L2 is 1 mm; Example 7c, L1 is 4mm, L2 is 1.2mm; In Example 7d, L1 was 5 mm and L2 was 1.5 mm.
[0085] Example 8 group This set of embodiments is based on Embodiment 1, except that the slope k of the thinned region at the tail of the positive electrode active coating and the dyne value of the positive electrode current collector are changed, as follows: Example 8a, k is 0.75; the dyn value of the positive current collector is 40 dyn; Example 8b, k is 10; the dyn value of the positive current collector is 42dyn.
[0086] Unless otherwise stated, the lithium-ion secondary batteries of Examples 1 to 8 all meet the following requirement: the infrared spectrum of the adhesive tape is within ~1365 cm⁻¹. -1 It has the first characteristic peak at ~3253 cm⁻¹ -1 It has a second characteristic peak, and the ratio of the peak intensity of the first characteristic peak to the second characteristic peak is Q≥1.05; the area of the negative electrode sheet covered by the positive active coating on the adhesive paper in the fully charged state is golden yellow.
[0087] Comparative Example 1 This comparative example is based on Example 1, except that the parameters of the adhesive tape are changed, as shown in Table 1.
[0088] Comparative Example 2 This comparative example is based on Example 1, except that conventional adhesive tape (i.e., which does not allow lithium ions and electrolyte to pass through) is used.
[0089] Test case (1) Loop test The batteries prepared in the examples and comparative examples were subjected to cycle tests, and the specific test methods are as follows: S1. Under 25℃ conditions, charge at a constant current of 0.5C to 4.5V, and then charge at a constant voltage to 0.05C to cut off. S2, constant current discharge at 0.5C until cutoff at 3.0V, record the first discharge capacity as the initial capacity Q1; S3. Repeat steps 1-2. The discharge capacity obtained after 600T cycles is taken as the battery capacity Q2. Calculate the capacity retention rate (%) according to the following formula: Capacity retention rate (%) = Q2 / Q1 100%, and record the results in Table 2.
[0090] (2) Energy density test The energy density of the lithium-ion secondary batteries prepared in the examples and comparative examples was tested, and the specific testing methods are as follows: Under 25℃ conditions, the volume of the lithium-ion secondary battery after the second sealing process is recorded as the battery volume. In the sorting process, the lithium-ion battery is fully charged to the charging cutoff voltage of 4.5V using a standard constant current and constant voltage at 0.2C. After resting for 10 minutes, it is discharged to the discharge cutoff voltage of 3.0V using a standard constant current at 0.2C. The energy is recorded as the discharge energy. The ratio of the discharge energy to the battery volume is the energy density, with the unit being Wh / L. The results are recorded in Table 2.
[0091] (3) Interfacial stability test of adhesive tape In a 25℃ environment, the charging time for 10%-80% SOC was controlled at 11 minutes (SOC is the battery's state of charge; a fully charged battery is 100% SOC, and an empty battery is 0% SOC), the charging time for 0-10% SOC was 5 minutes, the charging time for 80-100% SOC was 20 minutes, and the discharging time was 60 minutes. This charge-discharge cycle test was performed on the battery using this charge-discharge cycle. One charge and one discharge are called one cycle. After fully charging, the battery was left to stand for 30 minutes before being discharged. This fast charging cycle test was performed until 50 charge-discharge cycles were completed. On the 51st cycle, the battery was fully charged (100% SOC) using the fast charging cycle. The battery was then removed and disassembled to observe the state of the adhesive tape interface. The criteria for judging the interface phenomenon of the adhesive tape are as follows: 1) "0" indicates a smooth interface without bubbles or ridges; 2) "1" indicates tiny bubbles or slight ridges; 3) "2" indicates large areas of obvious bubbles or severe ridges. The results are recorded in Table 2.
[0092] (4) Battery self-discharge K-value test K is the voltage decay value of the battery per hour, mV / h; the internal resistance of the voltage was tested at different times, and the results were recorded in Table 2 using the formula K=(OCV1-OCV2) / time interval between two tests.
[0093] Table 1-1 Table 1-2 Table 2 As can be seen from Table 2, the adhesive tape of the present invention has better interface stability compared with the comparative example. It can maintain a smooth interface after multiple charge-discharge cycle tests under fast charging conditions, with no bubbles or ridges, or only tiny bubbles and slight ridges. The battery of the present invention has high energy density and excellent cycle performance.
[0094] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A lithium-ion secondary battery, characterized in that, The lithium-ion secondary battery includes a positive electrode, a separator, and a negative electrode, wherein the positive electrode, the separator, and the negative electrode are wound together to form a core; the positive electrode includes a positive current collector and a positive active coating located on at least one side surface of the positive current collector; The positive electrode sheet includes adhesive paper, which partially covers the positive active coating at the tail of the positive electrode sheet and extends to the positive current collector; The adhesive tape includes a substrate layer and a coating applied to at least one surface of the substrate layer; the coating includes an adhesive and inorganic particles; The electrolyte wetting rate of the adhesive tape is greater than or equal to 15 mm / 30 s.
2. The lithium-ion secondary battery according to claim 1, wherein, The negative electrode sheet includes a negative electrode current collector and a negative electrode active coating located on at least one side of the surface of the negative electrode current collector; the adhesive tape portion covers the positive electrode active coating for a length of L1, and the negative electrode active coating at the tail of the core extends beyond the positive electrode active coating for a length of L2; Preferably, 1mm ≤ L1 < 10mm; Preferably, L2 ≥ 1 / 2L1; Preferably: L1+L2≥3.5mm.
3. The lithium-ion secondary battery according to claim 1 or 2, wherein, The material of the substrate layer includes at least one of polyethylene terephthalate, polyethylene, polypropylene, polyimide, polyvinyl chloride, and a composite material of polyethylene and polypropylene; And / or, the adhesive comprises at least one of polyisobutylene, styrene-isoprene copolymer, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene and styrene-butadiene rubber. And / or, the inorganic particles include at least one of alumina, boehmite, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium titanium aluminum phosphate, magnesium oxide, titanium oxide, hafnium dioxide, silicon dioxide, tin oxide, cerium dioxide, nickel oxide, zirconium oxide, zinc oxide, calcium oxide, magnesium hydroxide, aluminum hydroxide, barium hydroxide, barium sulfate, calcium silicate, and titanium dioxide.
4. The lithium-ion secondary battery according to claim 1 or 2, wherein, The substrate layer includes pores formed by a plurality of intersecting and / or stacked fibers, preferably, the diameter of the fibers is 2μm-10μm; And / or, the average particle size of the inorganic particles is 150 nm-2 μm.
5. The lithium-ion secondary battery according to claim 1 or 2, wherein, When the negative electrode sheet is fully charged, the area corresponding to the adhesive paper portion that covers the positive electrode active coating is golden yellow.
6. The lithium-ion secondary battery according to claim 1 or 2, wherein, The pore size of the substrate layer is 0.1μm-25μm; preferably 0.5μm-10μm. And / or, the thickness of the substrate layer is 5μm-20μm; And / or, the thickness of the coating is 2μm-15μm.
7. The lithium-ion secondary battery according to claim 1 or 2, wherein, The bending stiffness of the adhesive tape is less than or equal to 15 mN; And / or, the puncture resistance of the adhesive tape is greater than or equal to 0.8 N / μm; And / or, the heat shrinkage rate of the adhesive tape in the width direction is less than or equal to 2%; And / or, the adhesive tape has a thermal shrinkage rate of less than or equal to 2% in the length direction.
8. The lithium-ion secondary battery according to claim 1 or 2, wherein, Along the direction extending from the center of the core to the tail, the tail of the positive electrode active coating includes a thinned region with a slope of k, where k = h / d; h is the thickness of the positive electrode active coating located on one side of the positive electrode current collector, in μm; d is the orthogonal projection distance between the start point and the end point of the thinned region on the surface of the positive electrode current collector; Preferably, k is 0.75-10; Preferably, 0 < d ≤ 15 mm.
9. The lithium-ion secondary battery according to claim 3, wherein, The adhesive includes polyisobutylene, and the porous membrane material includes polyethylene terephthalate. Preferably, the infrared spectrum of the adhesive tape is within ~1365 cm⁻¹. -1 It has the first characteristic peak at ~3253 cm⁻¹ -1 It has a second characteristic peak, and the ratio of the peak intensity of the first characteristic peak to the second characteristic peak is Q, where Q ≥ 1.05; And / or, the dyn value of the positive current collector is greater than or equal to 30 dyn; And / or, based on the total weight of the coating, the inorganic particles have a mass content of 40%-80%, and the adhesive has a mass content of 20%-60%.
10. The lithium-ion secondary battery according to claim 1 or 2, wherein, The positive electrode plate also includes a tab groove and a positive electrode tab located in the tab groove; Preferably, the adhesive tape covers the tab groove and part of the positive electrode tab.