Lithium ion battery

Abstract

The invention provides a lithium ion battery. The lithium ion battery comprises a battery cell, the battery cell comprises a diaphragm and a pole piece, the group margin of the lithium ion battery is gamma, the unit is%, and the distance between the diaphragm and the pole piece is defined as dgap; wherein gamma and dgap meet the relational expression that dgap / gamma is greater than or equal to 1 mu m and less than or equal to 3 mu m; and gamma is 90%-98%. When the diaphragm structure is designed, parameters such as a specific proportional relation between gamma and dgap are considered, so that accurate control over the diaphragm in the battery manufacturing process is facilitated, the liquid infiltration retention capacity of the battery cell can be effectively improved, the risk that the battery cell enters a shell badly can be avoided, and meanwhile, the production consistency and yield are improved.

Description

Technical Field

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

[0002] Lithium-ion batteries, an essential energy component in electric vehicles, are primarily categorized into prismatic, cylindrical, and pouch-type structures. Cylindrical batteries are widely used due to their high energy density, long lifespan, and stability. However, their unique structural design results in a relatively lean electrolyte, posing challenges to high-rate charge and discharge performance.

[0003] Creating a gap between the separator and the electrode not only buffers the stress caused by the expansion of the positive and negative electrodes but also stores electrolyte, thereby improving the electrolyte wetting defects of cylindrical cells. However, if the gap is too large, the cell will not fit properly into the battery case, while if the gap is too small, the cell's ability to retain electrolyte will be reduced. Summary of the Invention

[0004] The main purpose of the present invention is to provide a lithium-ion battery to solve the problem in the prior art that the unreasonable structural spacing between the diaphragm and the electrode piece leads to poor shell insertion of the cylindrical battery cell or poor liquid retention capacity of the battery cell.

[0005] In order to achieve the above object, according to one aspect of the present invention, a lithium ion battery is provided, including a cell, the cell including a diaphragm and an electrode, the group margin of the lithium ion battery is γ, the unit is %, and the distance between the diaphragm and the electrode is defined as d gap ; Among them, γ and d gap Satisfy the relationship: 1μm≤d gap / γ≤3μm;γ is 90%~98%.

[0006] Furthermore, the above-mentioned diaphragm is a first diaphragm, which includes a base film and a first primer layer stacked at least on the first surface of the base film along the thickness direction of the base film, the first primer layer includes a first organic polymer, and the first organic polymer protrudes from the surface of the first primer layer; the thickness of the base film is d, the thickness of the first primer layer is d1, and the D50 particle size of the first organic polymer is d2; when there is only one first primer layer on the surface of the base film, d gap = d2-d1; when the other surface opposite to the first surface of the base film also has a first primer layer, d gap =2×(d2-d1); d1 and d2 satisfy: 1 <d2 / d1≤3。

[0007] Furthermore, the above-mentioned diaphragm is a second diaphragm, which includes a base film and a second primer layer stacked at least on the first surface of the base film along the thickness direction of the base film, and an organic coating layer stacked on the surface of the second primer layer away from the base film; the thickness of the base film is d, the thickness of the second primer layer is d1, and the thickness of the organic coating layer is d3; when there is only one second primer layer on the surface of the base film, d gap = d3; when the other surface opposite to the first surface of the base film also has a second primer layer, the d gap =2×d3; d1 and d3 satisfy: 0 <d3 / d1≤2。

[0008] Furthermore, the glass transition temperature of the first organic polymer is 80-110° C.; and the particle size of the first organic polymer must satisfy the following relationship: 0<(D99-D10) / D50≤2.5.

[0009] Furthermore, the above d gap 0.5~4.0μm.

[0010] Furthermore, the above d is 5 to 15 μm, and / or the base film is a polyolefin separator, and the base film is a polyethylene separator and / or a polypropylene separator.

[0011] Furthermore, the above-mentioned d1 is 1 to 5 μm, and / or the first primer layer and the second primer layer each independently include inorganic particles and a first binder, and the inorganic particles are selected from any one or more of boehmite, aluminum oxide, magnesium hydroxide, magnesium oxide, titanium dioxide, silicon dioxide, titanium oxide, barium titanate, zinc oxide, nickel oxide, magnesium fluoride, zirconium oxide, cerium oxide and barium sulfate; and / or the first binder is a homopolymer and / or copolymer of an acrylate monomer, and the acrylate monomer is selected from any one or more of an acrylic acid monomer, a hydrocarbon acrylic acid monomer, an acrylate monomer and a hydrocarbon acrylate monomer.

[0012] Furthermore, the coverage of the organic coating on the second primer layer is 10 to 90%.

[0013] Furthermore, the above-mentioned d3 is 0.5 to 4.0 μm, and / or the organic coating includes a second organic polymer and a second binder, and / or the second organic polymer is selected from any one or more of polyvinylidene fluoride, polytetrafluoroethylene and polyhexafluoroethylene; and / or the second binder is a homopolymer and / or copolymer of an acrylate monomer, and the acrylate monomer is selected from any one or more of an acrylic acid monomer, a hydrocarbon acrylic acid monomer, an acrylate monomer and a hydrocarbon acrylate monomer.

[0014] Furthermore, the first organic polymer is a styrene-acrylate polymer; and / or D50 is 2-8 μm.

[0015] Applying the technical solution of the present invention, the present invention takes into account γ and d when designing the diaphragm structure. gap This helps to achieve precise control of the diaphragm during the battery manufacturing process, which can not only effectively improve the liquid retention and infiltration ability of the battery cell, but also avoid the risk of poor battery cell shell entry, and at the same time improve production consistency and yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 A schematic structural diagram of the embedded diaphragm in Example 1 of the present application is shown.

[0018] Figure 2 A schematic structural diagram of the composite diaphragm in Example 2 of the present application is shown.

[0019] The above drawings include the following reference numerals:

[0020] 1. Base film; 2. First primer layer; 3. First organic polymer; 4. Second primer layer; 5. Organic coating layer. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0022] As analyzed in the background technology of this application, there is a problem in the prior art that the structural spacing between the diaphragm and the electrode is unreasonable, resulting in poor shell insertion of the cylindrical battery cell or poor liquid retention capacity of the battery cell. This application provides a lithium-ion battery.

[0023] In a typical embodiment of the present application, a lithium-ion battery is provided, including a cell, the cell including a diaphragm and an electrode, the group margin of the lithium-ion battery is γ, the unit is %, and the distance between the diaphragm and the electrode is defined as d gap ; Among them, γ and d gap Satisfy the relationship: 1μm≤d gap / γ≤3μm;γ is 90%~98%.

[0024] The present invention takes into account γ and d when designing the diaphragm structure. gap This helps to achieve precise control of the diaphragm during the battery manufacturing process, which can not only effectively improve the liquid retention and infiltration ability of the battery cell, but also avoid the risk of poor battery cell shell entry, and at the same time improve production consistency and yield.

[0025] In addition, d gap / γ can be 1μm, 1.04μm, 1.05μm, 2.09μm, 2.11μm, 2.61μm, 2.71μm or 3μm. Of course, the above d gap / γ can be 1μm≤d gap The value of any point within the range of / γ≤3μm will not be repeated here.

[0026] The above-mentioned γ is 90% to 98%, or 95% to 97%. Controlling the group margin within the above range is beneficial to the efficient use of the internal space of the battery cell, which helps to improve the energy density of the battery and meet the strict volume efficiency requirements of high-performance batteries. On the other hand, although the interior of the battery cell is highly compact, it can still ensure sufficient infiltration of the electrolyte, reducing the risk of battery performance degradation due to uneven distribution of the electrolyte. The optimized group margin of 95% to 97% is more conducive to maintaining high energy output. At the same time, it can also leave enough space to buffer the expansion of the battery cell during the cycle, reducing the safety risks caused by excessive compression. In addition, strict group margin control improves the process consistency of battery manufacturing and reduces the battery performance differences caused by fluctuations in shell utilization.

[0027] In some embodiments, the above γ can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97% or 98%. Of course, the above γ can be any point value within 90% to 98%, which will not be repeated here.

[0028] Group margin γ: refers to the group margin in the thickness direction of the battery when the battery cell is in an empty state (empty condition: discharged to 2.5V at 1C at 25°C); it represents the ratio of the actual internal cross-sectional area of the battery cell to the maximum internal cross-sectional area, that is, when the battery cell is cut horizontally, the cross-sectional area of various materials in the wound battery cell is L, the inner diameter area of the battery shell is N, and the group margin is L / N.

[0029] Diaphragm gap value d gap : A diaphragm sample with a cross-section width of about 0.5 cm was prepared using an argon ion polishing instrument. After gold spraying, a focused ion beam scanning electron microscope (SEM) was used to photograph the diaphragm cross-section. The shooting conditions were: voltage 5kV, magnification 10k.

[0030] In one embodiment of the present application, the above-mentioned diaphragm is a first diaphragm, such as Figure 1 As shown, the first diaphragm includes a base film 1 and a first primer layer 2 stacked at least on the first surface of the base film 1 along the thickness direction of the base film 1. The first primer layer 2 includes a first organic polymer 3, and the first organic polymer 3 protrudes from the surface of the first primer layer 2. The thickness of the base film 1 is d, the thickness of the first primer layer is d1, and the D50 particle size of the first organic polymer is d2. When there is only one first primer layer on the surface of the base film, dgap = d2 - d1; When the other surface opposite to the first surface of the base film also has a first bottom coating, d gap = 2×(d2 - d1); d1 and d2 satisfy: 1 < d2 / d1 ≤ 3.

[0031] The above first separator takes into account parameters such as the specific proportional relationship among the thickness (d) of the base film, the thickness (d1) of the first bottom coating, the particle size (d2) of the first organic polymer, γ, and dgap, which helps to achieve precise control of the separator during the battery manufacturing process. Specifically, on the one hand, the first organic polymer can effectively increase the electrolyte retention space between the separator and the electrode sheet, thereby improving the electrolyte infiltration performance under high-rate charge and discharge conditions, which is a key factor for the fast charging ability and cycle life of lithium-ion batteries. On the other hand, the first organic polymer can increase the mechanical strength and thermal stability of the separator, which plays an important role in preventing safety problems such as internal short circuits and thermal runaway in the battery.

[0032] The large-particle-size first organic polymer forms tiny protrusions in the first bottom coating, increasing the distance between the separator and the electrode sheet, promoting the uniform distribution of the electrolyte, and improving the liquid retention capacity. Controlling the ratio of d2 / d1 within the above range helps to balance the energy storage density and cycle life of the battery cell, and提升 the fast charging ability and overall performance of the battery. Specifically, controlling 1 < d2 / d1 ≤ 3 helps to reduce the risk of poor contact between the separator and the electrode sheet caused by an overly large d2 / d1 ratio, or helps to reduce the risk of poor liquid retention effect caused by an overly small d2 / d1 ratio, improving the stability of the internal structure of the battery cell and the efficiency of electrical performance. In addition, limiting the ratio of d2 / d1 within the above range is conducive to achieving precise coating of the separator and uniform distribution of the polymer, improving the controllability of the manufacturing process and the yield rate of the battery.

[0033] In addition, the above d2 / d1 can be 1.2, 1.5, 2, 2.5, or 3. Of course, the above d2 / d1 can be any point value within the range 1 < d2 / d1 ≤ 3, which will not be elaborated here.

[0034] In an embodiment of the present application, the above separator is a second separator. As Figure 2 shown, the second separator includes a base film 1 and at least one second bottom coating 4 laminated on the first surface of the base film 1 along the thickness direction of the base film 1. An organic matter coating 5 is laminated on the surface of the second bottom coating 4 away from the base film 1; the thickness of the base film 1 is d, the thickness of the second bottom coating 4 is d1, and the thickness of the organic matter coating 5 is d3; when there is only one second bottom coating on the surface of the base film, d gap = d3; when the other surface opposite to the first surface of the base film also has a second bottom coating, the d gap = 2×d3; d1 and d3 satisfy: 0 < d3 / d1 ≤ 2.

[0035] The above-mentioned second separator takes into account parameters such as the thickness (d) of the base film, the thickness (d1) of the second bottom coating, the thickness (d3) of the organic coating, and the specific proportional relationship between γ and dgap. This helps to achieve precise control of the separator during the battery manufacturing process. By laminating an organic coating on the second bottom coating, on the one hand, it can effectively increase the electrolyte retention space between the separator and the electrode sheet, thereby improving the electrolyte wetting performance under high-rate charge and discharge conditions, which is a key factor for the fast charging ability and cycle life of lithium-ion batteries. On the other hand, by setting an organic coating on the second bottom coating, the mechanical strength and thermal stability of the separator can be increased, which plays an important role in preventing safety problems such as internal short circuits and thermal runaway in the battery.

[0036] Controlling the ratio of d3 / d1 within the above range enables the organic coating in the composite separator to effectively increase the spacing between the separator and the electrode sheet, improve the retention and distribution of the electrolyte, without affecting the overall assembly of the battery cell. The appropriate d3 / d1 ratio reduces the risk of the separator being too fragile or too rigid, improves the ability of the separator to maintain structural stability during the charge and discharge cycle of the battery, reduces the risk of internal short circuits in the battery cell, and helps to balance the fast charging ability and cycle life of the battery, improving the overall performance of the battery.

[0037] In addition, limiting the ratio of d3 / d1 within the above range makes the manufacturing process easier to control, improves the uniformity of the separator and the production consistency of the battery. The above d3 / d1 can be 0.5, 0.8, 1, 1.2, 1.5, 1.6, 1.7, 1.8 or 2. Of course, the above d3 / d1 can be any point value within the range of 0 < d3 / d1 ≤ 2, which will not be elaborated here.

[0038] At the same time, both the above-mentioned first separator and the second separator can have a gap spacing with a double-sided structure. On the one hand, it enables sufficient electrolyte retention space between the positive and negative electrode sheets and the separator, promoting the uniform distribution of the electrolyte inside the battery cell, especially improving the wetting property of the battery cell under fast charging or high-rate charge and discharge conditions. On the other hand, the symmetric d gap value helps to balance the stress distribution inside the battery cell, reduce the performance degradation caused by uneven expansion during the charging process, thereby improving the cycle stability and energy density of the battery. Therefore, the double-sided coated separator increases the stability of the overall structure of the battery cell, and can better reduce the risk of internal short circuits in the battery cell, especially when the battery is subjected to external impact or extrusion, improving the safety performance of the battery.

[0039] In an embodiment of the present application, the glass transition temperature of the above-mentioned first organic polymer is 80 - 110 °C; the particle size of the first organic polymer needs to satisfy: 0 < (D99 - D10) / D50 ≤ 2.5.

[0040] The first organic polymer, with a glass transition temperature in the range of 80-110°C, exhibits excellent thermal stability and moderate elasticity, effectively resisting temperature changes during the battery's charge and discharge processes while maintaining the separator's mechanical strength and deformation recovery capabilities. Fine particle size control facilitates uniform coating during manufacturing, improving separator consistency and, in turn, enhancing the battery's overall performance and production yield. Specifically, a strictly controlled particle size distribution range of 0 < (D99-D10) / D50 ≤ 2.5 improves the uniformity of the first organic polymer particle distribution, thereby optimizing electrolyte wetting, reducing electrolyte flow resistance, and enhancing the battery's fast-charging performance.

[0041] In addition, the glass transition temperature of the first organic polymer can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C or 110°C. Of course, the glass transition temperature of the first organic polymer can be any point value within the range of 80-110°C, which will not be repeated here.

[0042] The particle size distribution (D99-D10) / D50 of the above-mentioned first organic polymer can be 0.5, 1, 1.2, 1.5, 2 or 2.5. Of course, the particle size distribution (D99-D10) / D50 of the above-mentioned first organic polymer can be any point value within the range of 0<(D99-D10) / D50≤2.5, which will not be repeated here.

[0043] In one embodiment of the present application, the above d gap 0.5~4.0μm.

[0044] d gap On the one hand, within the above range, there is enough space inside the battery cell to store the electrolyte, which promotes the uniform infiltration of the electrolyte and improves the battery's liquid retention capacity and fast charging performance. gap The presence of d relieves the pressure of the expansion of the positive and negative electrode materials on the diaphragm during the charge and discharge process of the battery, maintains the structural stability of the battery cell, and improves the cycle life of the battery. gap The upper limit of d reduces the risk of excessive spacing between the diaphragm and the pole piece, ensures the compactness of the battery cell components, and is conducive to improving the assembly accuracy and energy density of the battery. In addition, the appropriate d gap The range reduces the probability of direct contact between the diaphragm and the electrode, reduces the risk of internal short circuit in the battery, and enhances the safety of the battery.

[0045] It should be noted that through d gap The coordinated control with the group margin can maximize the use of the space inside the battery shell while retaining sufficient electrolyte, achieving dual optimization of high energy density and efficient electrolyte retention.

[0046] The above d gapIt can be 0.5μm, 1μm, 1.5μm, 2.0μm, 2.5μm, 3.0μm, 3.5μm or 4.0μm. Of course, the above d gap It can be any point value within 0.5 to 4.0 μm, and will not be described in detail here.

[0047] In one embodiment of the present application, the above-mentioned d is 5 to 15 μm, or 7 to 12 μm, and / or the base film is a polyolefin membrane, and the base film is a polyethylene membrane and / or a polypropylene membrane.

[0048] The selected base film thickness range gives the diaphragm good mechanical strength and electrolyte permeability, while reducing the dead space inside the battery, which helps to improve the battery's energy density and cycle stability. At the same time, within the above thickness range, the manufacturing of the diaphragm and the assembly process of the battery cell are more controllable, improving production efficiency and battery consistency. Due to its unique melting point and thermal shrinkage properties, polyolefin materials can effectively prevent the diaphragm from shrinking less than the electrode sheet when the battery overheats, reducing the risk of short circuits and enhancing battery safety. The combination of the polyolefin base film and the specific thickness of the base film optimizes the wettability of the diaphragm, improves the uniform distribution of the electrolyte inside the battery cell, and further improves the fast charging capability of the battery cell.

[0049] In addition, the above-mentioned d can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm. Of course, the above-mentioned d can be any point value within 5~15μm, which will not be repeated here.

[0050] In one embodiment of the present application, the above-mentioned d1 is 1 to 5 μm, or 2 to 4 μm, and / or the first primer layer and the second primer layer each independently include inorganic particles and a first binder, and the inorganic particles are selected from any one or more of boehmite, aluminum oxide, magnesium hydroxide, magnesium oxide, titanium dioxide, silicon dioxide, titanium oxide, barium titanate, zinc oxide, nickel oxide, magnesium fluoride, zirconium oxide, cerium oxide and barium sulfate; and / or the first binder is a homopolymer and / or copolymer of an acrylate monomer, and the acrylate monomer is selected from any one or more of an acrylic acid monomer, a hydrocarbon acrylic acid monomer, an acrylate monomer and a hydrocarbon acrylate monomer.

[0051] The addition of inorganic particles improves the thermal stability and mechanical strength of the separator, while the acrylic binder promotes the bonding of the particles to the base film, enhancing the separator's resistance to electrolyte corrosion and electronic insulation properties. The combination of inorganic particles and binder forms an insulating layer under high temperature or short-circuit conditions, effectively preventing direct contact between electrodes and reducing the risk of thermal runaway. The selected d1 thickness range ensures a moderate basecoat thickness that neither hinders electrolyte penetration nor effectively creates a gap, improving electrolyte wettability and distribution within the battery cell.

[0052] In addition, the above d1 can be 1 μm, 2 μm, 3 μm, 4 μm or 5 μm. Of course, the above d1 can be any point value within 1 to 5 μm, which will not be repeated here.

[0053] In one embodiment of the present application, the coverage of the organic coating on the second primer layer is 10-90%, or 30-70%.

[0054] The coverage of the organic coating on the second primer layer refers to the ratio of the organic coating area to the second primer layer area. If the coverage of the organic coating on the second primer layer is too low, there will be fewer contact points between the organic coating and the electrode, and the gap will be easily invalidated. If the coverage of the organic coating on the second primer layer is too high, the coating cost will increase and there will be a risk of organic coating clogging. Controlling the coverage of the organic coating on the second primer layer to 10-90% helps maintain the effectiveness of the gap while minimizing the risk of organic coating clogging.

[0055] In addition, the coverage of the organic coating on the second primer layer can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%. Of course, the coverage of the above-mentioned organic coating on the second primer layer can be any point value within the range of 10 to 90%, which will not be repeated here.

[0056] In one embodiment of the present application, the above-mentioned d3 is 0.5 to 4.0 μm, and / or the organic coating includes a second organic polymer and a second binder, and / or the second organic polymer is selected from any one or more of polyvinylidene fluoride, polytetrafluoroethylene and polyhexafluoroethylene; and / or the second binder is a homopolymer and / or copolymer of an acrylate monomer, and the acrylate monomer is selected from any one or more of an acrylic acid monomer, a hydrocarbon acrylic acid monomer, an acrylate monomer and a hydrocarbon acrylate monomer.

[0057] The specific range of d3 creates the necessary separator spacing, improving electrolyte retention while maintaining the compactness of the battery cell. The presence of the organic coating promotes uniform electrolyte distribution, avoids local electrolyte depletion, and improves the battery's charge and discharge efficiency and cycle performance. The combination of polyvinyl fluoride polymers and acrylic binders imparts excellent chemical stability and mechanical toughness to the coating, enhancing the separator's heat resistance and pressure resistance. Furthermore, the specialized materials and thickness control of the coating simplify the manufacturing process, improve coating consistency, and facilitate the mass production of high-performance lithium-ion batteries.

[0058] In addition, in the process of obtaining the organic coating, the coating method is selected to be any one of spraying, spot coating or intermittent coating.

[0059] In addition, the above-mentioned d3 can be 0.5μm, 1μm, 1.5μm, 2.0μm, 2.5μm, 3.0μm, 3.5μm or 4.0μm. Of course, the above-mentioned d3 can be any point value within 0.5~4.0μm, which will not be repeated here.

[0060] In one embodiment of the present application, the first organic polymer is a styrene-acrylate polymer; and / or D50 is 2 to 8 μm, or 2.5 to 6 μm.

[0061] Styrene-acrylate polymers have good thermal stability and moderate elasticity, with a glass transition temperature ranging from 80 to 110°C. They can effectively withstand temperature fluctuations during the battery's charge and discharge processes while maintaining the separator's mechanical strength and deformation recovery. Fine particle size control facilitates uniform coating during manufacturing, improving separator consistency and, in turn, enhancing the battery's overall performance and production yield. Specifically, selecting a D50 particle size of 2 to 8 μm facilitates improved uniformity in the distribution of the first organic polymer particles, thereby optimizing electrolyte wetting, reducing electrolyte flow resistance, and improving the battery's fast-charging performance.

[0062] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0063] Example 1

[0064] 1) Inorganic boehmite particles (average particle size of 0.8 μm), a binder (an acrylate homopolymer (average particle size of 0.3 μm), and a first organic polymer 3 (styrene-acrylate polymer, D50 particle size d2 = 4 μm) were mixed and stirred in a mass ratio of 90:5:5 at a stirring speed of 1500 rpm for 90 min to obtain a mixture slurry; wherein the particle size of the organic polymer styrene-acrylate polymer satisfies the following: (D99-D10) / D50 = 2.

[0065] 2) The mixture slurry is coated on one surface of the base film 1 (polyethylene diaphragm, thickness d is 9 μm) in the thickness direction, and dried in an oven at 45°C for 0.5 h to obtain a diaphragm. A first primer layer 2 is formed on the surface of the diaphragm, with a thickness d1 = 3 μm, to obtain an embedded diaphragm, the structural diagram of which is shown in FIG. Figure 1 As shown, the first primer layer is embedded with an organic polymer styrene-acrylate polymer.

[0066] The NCM811 positive electrode, embedded separator, and graphite negative electrode are stacked in order, then wound to obtain an electrode assembly and placed in an outer package. After welding the tabs, the coil core is placed in a steel shell. After vacuum packaging, liquid injection, standing at room temperature for 24 hours, formation (0.02C constant current charging to 3.75V, then 0.1C constant current charging to 4.3V), shaping, and capacity testing, a cylindrical lithium-ion battery is obtained. Its group margin is γ, which is 95.8%, and the spacing d between the embedded separator and the electrode piece is d. gap =d2-d1=1μm, d2 / d1=1.33, d gap / γ is 1.04μm.

[0067] Example 2

[0068] 1) Inorganic boehmite particles (average particle size of 0.8 μm) and a binder (an acrylate homopolymer (average particle size of 0.3 μm)) were mixed and stirred in a mass ratio of 95:5 at a stirring speed of 1500 rpm for 90 minutes to obtain a mixture slurry; wherein:

[0069] 2) The mixture slurry is coated on one surface of the base film 1 (polyethylene diaphragm, thickness d is 9 μm) in the thickness direction, and dried in an oven at 45°C for 0.5 h to obtain a diaphragm. A second primer layer 4 is formed on the surface of the diaphragm, with a thickness d1 = 2 μm. An organic coating layer 5 is stacked on the surface of the second primer layer 4 away from the base film, and the coverage of the organic coating layer 5 on the second primer layer 4 can be 50%. The thickness d3 of the organic coating layer is 1 μm, and a composite diaphragm is obtained, the structural schematic of which is shown in FIG. Figure 2 shown.

[0070] The NCM811 positive electrode, composite separator, and graphite negative electrode are stacked in order, then wound to obtain an electrode assembly and placed in an outer package. After welding the tabs, the coil core is placed in a steel shell. After vacuum packaging, liquid injection, standing at room temperature for 24 hours, formation (0.02C constant current charging to 3.75V, then 0.1C constant current charging to 4.3V), shaping, and capacity testing, a cylindrical lithium-ion battery is obtained. Its group margin is γ, which is 94.9%, and the spacing d between the composite separator and the electrode piece is d. gap =d3=1μm, where d3 / d1=0.5, d gap / γ is 1.05μm.

[0071] Example 3

[0072] The difference from Example 1 is that when the other surface opposite to the first surface of the base film also has the first primer layer 2, the d gap =2×(d2-d1)=2μm, d gap / γ is 2.09μm, and an embedded separator is obtained, and finally a cylindrical lithium-ion battery is obtained.

[0073] Example 4

[0074] The difference from Example 2 is that when the other surface opposite to the first surface of the base film also has a second primer layer 4, the d gap =2×d3=2μm, d gap / γ is 2.11μm, a composite separator is obtained, and finally a cylindrical lithium-ion battery is obtained.

[0075] Example 5

[0076] The difference from Example 1 is that the group margin of the cylindrical lithium-ion battery is γ is 95.0%, d gap =d2-d1=0.95, d gap / γ is 1μm, an embedded separator is obtained, and finally a cylindrical lithium-ion battery is obtained.

[0077] Example 6

[0078] The difference from Example 1 is that the group margin of the cylindrical lithium-ion battery is γ is 95%, d gap =d2-d1=2.85, d gap / γ is 3μm, an embedded separator is obtained, and finally a cylindrical lithium-ion battery is obtained.

[0079] Example 7

[0080] The difference from Example 1 is that d2 is 5 μm, d1 is 3 μm, d2 / d1=1.67, d gap =d2-d1=2μm, d gap / γ=2.09μm, an embedded separator is obtained, and finally a cylindrical lithium-ion battery is obtained.

[0081] Example 8

[0082] The difference from Example 1 is that d2 is 3.5 μm, d1 is 1 μm, d2 / d1=3.5, d gap =d2-d1=2.5μm, d gap / γ=2.61μm, an embedded separator is obtained, and finally a lithium-ion battery is obtained.

[0083] Example 9

[0084] The difference from Example 1 is that d3 is 2 μm, d1 is 2 μm, d3 / d1=1, d2 / d1=2, d gap =d2-d1=2μm, d gap / γ=2.09μm, an embedded separator is obtained, and finally a cylindrical lithium-ion battery is obtained.

[0085] Example 10

[0086] The difference from Example 1 is that d3 is 3 μm, d1 is 1.4 μm, d3 / d1=2.14, d2 / d1=2.14, d gap =d2-d1=2.6μm, d gap / γ=2.71μm, an embedded separator is obtained, and finally a cylindrical lithium-ion battery is obtained.

[0087] Example 11

[0088] The difference from Example 2 is that the coverage of the organic coating 5 on the second primer layer 4 can be 70%, thereby obtaining an embedded separator and ultimately a cylindrical lithium-ion battery.

[0089] Example 12

[0090] The difference from Example 2 is that the coverage of the organic coating 5 on the second primer layer 4 can be 25%, thereby obtaining an embedded separator and ultimately a cylindrical lithium-ion battery.

[0091] Example 13

[0092] The difference from Example 1 is that D50 is 3.3 μm, (D99-D10) / D50=1, and an embedded separator is obtained, and finally a lithium-ion battery is obtained.

[0093] Example 14

[0094] The difference from Example 1 is that D50 is 2 μm, (D99-D10) / D50=3, and an embedded separator is obtained, and finally a cylindrical lithium-ion battery is obtained.

[0095] Comparative Example 1

[0096] The difference from Example 1 is that the group margin of the cylindrical lithium-ion battery is γ is 90.0%, d2 is 4.45 μm, d1 is 4 μm, and the distance d between the embedded diaphragm and the pole piece is gap =d2-d1=0.45, d gap / γ is 0.5μm, and an embedded separator is obtained, and finally a cylindrical lithium-ion battery is obtained.

[0097] Comparative Example 2

[0098] The difference from Example 1 is that the group margin of the cylindrical lithium-ion battery is γ is 98.0%, d2 is 5.92 μm, d1 is 2 μm, and the distance d between the embedded diaphragm and the pole piece is gap =d2-d1=3.92μm, d gap / γ is 4μm, an embedded separator is obtained, and finally a cylindrical lithium-ion battery is obtained.

[0099] Test method:

[0100] Cut the diaphragm into 50 mm x 50 mm pieces and weigh them. Record the weight as m1. Soak the weighed diaphragm in electrolyte at room temperature for 30 minutes. Remove and wipe the electrolyte off the diaphragm surface completely. Let it sit for 1 hour before weighing it. Record the weight as m2. Diaphragm liquid retention (%) = (m2 - m1) / m1 × 100.

[0101] Cycle capacity retention rate: Calculate the capacity retention rate after 800 cycles.

[0102] The lithium-ion batteries of the embodiment and comparative example were respectively subjected to energy density and cycle capacity retention rate tests on a charge and discharge device, and were charged to 4.3V at a charge rate of 0.3C and then discharged to 3V at a discharge rate of 1C, thereby performing a cycle.

[0103] The energy density, cycle capacity retention rate and liquid retention rate of the above lithium-ion batteries are listed in Table 1.

[0104] Table 1

[0105] Example Energy density (Wh / kg) Cycle capacity retention rate / % Fluid retention rate / % Example 1 172 85 93 Example 2 170 80 91 Example 3 165 82 98 Example 4 168 86 96 Example 5 171 79 90 Example 6 169 85 97 Example 7 167 81 90 Example 8 168 73 87 Example 9 164 88 93 Example 10 156 75 92 Example 11 171 85 88 Example 12 170 81 85 Example 13 173 85 96 Example 14 172 73 85 Comparative Example 1 160 65 82 Comparative Example 2 The core cannot be inserted into the shell The core cannot be inserted into the shell 95

[0106] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0107] The present invention takes into account γ and d when designing the diaphragm structure. gap This helps to achieve precise control of the diaphragm during the battery manufacturing process, which can not only effectively improve the liquid retention and infiltration ability of the battery cell, but also avoid the risk of poor battery cell shell entry, and at the same time improve production consistency and yield.

[0108] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A lithium-ion battery comprising a cell, wherein the cell comprises a separator and an electrode, wherein the group margin of the lithium-ion battery is γ, expressed in %, and wherein: The distance between the diaphragm and the pole piece is defined as d gap ; Among them, the γ and the d gap Satisfy the relationship: 1μm≤d gap / γ≤3μm; The γ is 90% to 98%.

2. The lithium-ion battery according to claim 1, wherein The diaphragm is a first diaphragm, comprising a base film and a first primer layer stacked on at least a first surface of the base film along a thickness direction of the base film, wherein the first primer layer comprises a first organic polymer, and the first organic polymer protrudes from a surface of the first primer layer; The thickness of the base film is d, the thickness of the first primer layer is d1, and the D50 particle size of the first organic polymer is d2; When the surface of the base film has only one first primer layer, the d gap =d2-d1; When the other surface opposite to the first surface of the base film also has a first primer layer, the d gap =2×(d2-d1); The d1 and the d2 satisfy: 1 <d2 / d1≤3。 3. The lithium-ion battery according to claim 1, wherein The diaphragm is a second diaphragm, comprising a base film and a second primer layer stacked on at least a first surface of the base film along a thickness direction of the base film, and an organic coating layer stacked on a surface of the second primer layer away from the base film; The thickness of the base film is d, the thickness of the second primer layer is d1, and the thickness of the organic coating layer is d3; When the surface of the base film has only one second primer layer, the d gap =d3; When the other surface opposite to the first surface of the base film also has a second primer layer, the d gap =2×d3; The d1 and the d3 satisfy: 0 <d3 / d1≤2。 4. The lithium-ion battery according to claim 2, wherein The glass transition temperature of the first organic polymer is 80-110° C.; the particle size of the first organic polymer must satisfy the following condition: 0<(D99-D10) / D50≤2.

5.

5. The lithium-ion battery according to any one of claims 2 to 4, characterized in that The d gap 0.5~4.0μm.

6. The lithium-ion battery according to any one of claims 2 to 5, characterized in that The d is 5 to 15 μm, and / or the base film is a polyolefin membrane, and the base film is a polyethylene membrane and / or a polypropylene membrane.

7. The lithium-ion battery according to any one of claims 2 to 6, characterized in that The d1 is 1 to 5 μm, and / or the first primer layer and the second primer layer each independently include inorganic particles and a first binder, and the inorganic particles are selected from any one or more of boehmite, aluminum oxide, magnesium hydroxide, magnesium oxide, titanium dioxide, silicon dioxide, titanium oxide, barium titanate, zinc oxide, nickel oxide, magnesium fluoride, zirconium oxide, cerium oxide and barium sulfate; and / or the first binder is a homopolymer and / or copolymer of an acrylate monomer, and the acrylate monomer is selected from any one or more of an acrylic acid monomer, a hydrocarbon acrylic acid monomer, an acrylate monomer and a hydrocarbon acrylate monomer.

8. The lithium-ion battery according to claim 3, wherein The coverage of the organic coating on the second primer layer is 10 to 90%.

9. The lithium-ion battery according to claim 3, characterized in that The d3 is 0.5 to 4.0 μm, and / or the organic coating includes a second organic polymer and a second binder, and / or the second organic polymer is selected from any one or more of polyvinylidene fluoride, polytetrafluoroethylene and polyhexafluoroethylene; and / or the second binder is a homopolymer and / or copolymer of an acrylate monomer, and the acrylate monomer is selected from any one or more of an acrylic acid monomer, a hydrocarbon acrylic acid monomer, an acrylate monomer and a hydrocarbon acrylate monomer.

10. The lithium-ion battery according to claim 2, wherein The first organic polymer is a styrene-acrylate polymer; and / or D50 is 2 to 8 μm.

Images