A secondary battery and electronic device

Abstract

This application provides a secondary battery and an electronic device. The secondary battery includes a separator, which comprises a polymer substrate and a first coating and a second coating disposed on at least one surface of the polymer substrate. The surface of the polymer substrate includes a first region and a second region. The first region is the area where the separator overlaps with the negative electrode, and the second region is the area where the separator extends beyond the negative electrode in the width direction. The second region extends from both sides of the first region along the width direction of the separator, and the width of the second region on each side is A mm, where 1 < A ≤ 5. The first coating comprises ceramic particles, and the second coating comprises porous plastic. The secondary battery of this application has good drop resistance and cycle performance while also possessing high energy density.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] The rapid development of electric vehicles, consumer electronics, and various portable smart devices in recent years has placed higher demands on the energy density and capacity of secondary batteries (such as lithium-ion batteries) to meet the evolving needs of intelligence, multifunctionality, and high portability. However, high-energy-density and high-capacity batteries can be damaged internally when dropped, which is detrimental to their long-term use. Therefore, research on the drop resistance of lithium-ion batteries is increasing. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery and electronic device to improve the energy density, drop resistance and cycle performance of the secondary battery.

[0004] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0005] The first aspect of this application provides a secondary battery, which includes a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and a negative electrode material layer on at least one surface of the negative current collector. The positive electrode includes a positive current collector and a positive electrode material layer on at least one surface of the positive current collector. A separator is disposed between the positive and negative electrodes. The separator includes a polymer substrate and a first coating and a second coating disposed on at least one surface of the polymer substrate. The surface of the polymer substrate includes a first region and a second region. The first region is the region where the separator overlaps with the negative electrode, and the second region is the region where the separator extends beyond the negative electrode in the width direction. The second region extends from both sides of the first region along the width direction of the separator, wherein the width of the second region on each side is A mm, 1 < A ≤ 5. The first coating is disposed on at least one surface of the first region, and the second coating is disposed on at least one surface of the second region. The first coating includes ceramic particles, and the second coating includes porous plastic. When the separator of the secondary battery has the coating structure of this application, and 1 < A ≤ 5, when the secondary battery is dropped, the porous plastic coating (i.e., the second coating) provided on the second region at both ends of the separator in the width direction can absorb energy through structural deformation, thereby playing a shock-absorbing role, reducing the loss caused by the drop to the secondary battery, improving the drop resistance of the secondary battery, and the porous structure of the porous plastic can provide channels for electrolyte replenishment, improving the cycle performance of the secondary battery while having a high energy density. It is worth noting that in the width direction of the separator, there is a second region on each side of the first region. The widths of the two second regions can be the same or different, as long as the widths of the two second regions are greater than 1 mm and less than or equal to 5 mm, which will not be elaborated further below.

[0006] In one embodiment of this application, 1.5≤A≤4.0, where A is within the above range, can improve the utilization rate of the internal space of the secondary battery while taking into account the improved drop resistance and cycle performance brought by the porous plastic second coating, thereby increasing the battery energy density.

[0007] In one embodiment of this application, the thickness of the polymer substrate is from 4 μm to 30 μm, and the polymer substrate includes at least one of polyethylene or polypropylene. The secondary battery can increase its energy density by reducing the thickness of the polymer substrate. When the polymer substrate is selected from the above materials and its thickness is within the above range, the secondary battery also has good drop resistance.

[0008] In one embodiment of this application, the ceramic particles include at least one of Al2O3, ZrO2, SnO2, SiO2, or TiO2. When the ceramic particles are selected from the above materials, the stability of the separator under high-temperature environments can be improved, thermal runaway can be reduced, thereby improving the safety performance of the battery.

[0009] In one embodiment of this application, the porous plastic includes at least one of polyethylene, polystyrene, polyvinyl chloride, polypropylene, or polyurethane. When the porous plastic is selected from the above materials, it can absorb energy through structural deformation when subjected to impact, thereby achieving a shock absorption effect and improving the safety performance of the secondary battery. At the same time, the above materials are lightweight and do not have a significant impact on energy density.

[0010] In one embodiment of this application, the porosity of the second coating is 50% to 90%. When the porosity of the second coating is within this range, it helps the separator to better store electrolyte during cycling, improving the cycle performance of the secondary battery, while maintaining appropriate mechanical strength and improving the drop resistance of the secondary battery. Preferably, the porosity of the second coating is 60% to 85%. When the porosity of the second coating is within this range, it further improves the drop resistance of the secondary battery while also exhibiting better cycle performance.

[0011] In one embodiment of this application, the thickness of the first coating is 1 μm to 5 μm. When the thickness of the first coating is within the above range, the thermal stability of the separator can be improved, the puncture resistance of the separator can be enhanced, the internal self-discharge of the secondary battery can be reduced, and the cycle performance and drop resistance of the secondary battery can be improved.

[0012] In one embodiment of this application, the surface of the polymer substrate facing the positive electrode sheet is the first surface. The ratio B of the thickness of the second coating on the first surface to the thickness of the positive electrode material layer is 0.7 to 0.9, that is, the thickness ratio of a single layer of the second coating to a single layer of the positive electrode material layer is 0.7 to 0.9. When the value of B is within the above range, the separator and the positive electrode sheet can support each other, reducing the impact of electrolyte on the electrode assembly during drop, thus preventing short circuits. In addition, a suitable thickness can also achieve a shock absorption effect, reducing tearing caused by rigid stress on the electrode sheet and improving the drop resistance of the secondary battery.

[0013] In one embodiment of this application, the surface of the polymer substrate facing the negative electrode sheet is a second surface. The ratio C of the thickness of the second coating on the second surface to the thickness of the negative electrode material layer is 0.7 to 0.9, that is, the thickness ratio of a single layer of the second coating to a single layer of the negative electrode material layer is 0.7 to 0.9. When the value of C is within the above range, the separator and the negative electrode sheet can support each other, reducing the impact of electrolyte on the electrode assembly during drop, thus preventing short circuits. In addition, a suitable thickness can also achieve a shock absorption effect, reducing the tearing caused by rigid stress on the electrode sheet and improving the drop resistance of the secondary battery.

[0014] A second aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments.

[0015] The beneficial effects of this application are:

[0016] This application provides a secondary battery and an electronic device. The secondary battery includes a separator, a negative electrode sheet including a negative current collector and a negative electrode material layer located on at least one surface of the negative current collector, and a positive electrode sheet including a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector. A separator is disposed between the positive electrode sheet and the negative electrode sheet. The separator includes a polymer substrate and a first coating and a second coating disposed on at least one surface of the polymer substrate. The surface of the polymer substrate includes a first region and a second region. The first region is the region where the separator overlaps with the negative electrode sheet, and the second region is the region where the separator extends beyond the negative electrode sheet in the width direction. The second region extends from both sides of the first region along the width direction of the separator, and the width of the second region on each side is A mm, where 1 < A ≤ 5. The first coating is disposed on at least one surface of the first region, and the second coating is disposed on at least one surface of the second region. The first coating includes ceramic particles, and the second coating includes porous plastic. When the separator of the secondary battery has the coating structure of this application, and 1 < A ≤ 5, when the secondary battery is dropped, the porous plastic coating (i.e., the second coating) provided on the second region at both ends of the separator in the width direction can absorb energy through structural deformation, thereby playing a shock absorption role, reducing the loss caused by the drop to the secondary battery, improving the drop resistance performance of the secondary battery, and the porous structure of the porous plastic can provide channels for electrolyte replenishment, improving the cycle performance of the secondary battery while having a high energy density.

[0017] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0019] Figure 1 This is a cross-sectional view of the isolation membrane in the second region according to one embodiment of this application;

[0020] Figure 2 This is a cross-sectional view of the isolation membrane in the first region according to one embodiment of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0022] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries, and can also be applied to secondary batteries such as sodium-ion batteries.

[0023] The purpose of this application is to provide a secondary battery and electronic device to improve the energy density, drop resistance and cycle performance of the secondary battery.

[0024] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0025] The first aspect of this application provides a secondary battery, comprising a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and a negative electrode material layer on at least one surface of the negative current collector. The positive electrode includes a positive current collector and a positive electrode material layer on at least one surface of the positive current collector. A separator is disposed between the positive and negative electrodes. The separator includes a polymer substrate and a first coating and a second coating disposed on at least one surface of the polymer substrate. The surface of the polymer substrate includes a first region and a second region. The first region is the region where the separator overlaps with the negative electrode, and the second region is the region where the separator extends beyond the width of the negative electrode in the width direction. The second region extends from both sides of the first region along the width direction of the separator, and the width of the second region on each side is A mm, where 1 < A ≤ 5. The first coating is disposed on at least one surface of the first region, and the second coating is disposed on at least one surface of the second region. The first coating includes ceramic particles, and the second coating includes porous plastic. For example, the width of the second region can be 1.5 mm, 2 mm, 3 mm, 4 mm, 5 mm, or a range consisting of any two of these values. Without being limited to any theory, the inventors of this application have discovered that when the separator of a secondary battery has the coating structure of this application, and 1 < A ≤ 5, the porous plastic coating (i.e., the second coating) provided on the second region at both ends of the separator in the width direction can absorb energy through structural deformation when the secondary battery is dropped, thereby playing a shock-absorbing role, reducing the loss caused by the drop to the secondary battery, improving the drop resistance of the secondary battery, and the porous structure of the porous plastic can provide channels for electrolyte replenishment, thus improving the cycle performance of the secondary battery while having a high energy density.

[0026] In one embodiment of this application, 1.5≤A≤4.0, where A is within the above range, can improve the utilization rate of the internal space of the secondary battery while taking into account the improved drop resistance and cycle performance brought by the porous plastic second coating, thereby increasing the battery energy density.

[0027] A cross-sectional view of the isolation membrane in the second region in one embodiment of this application is shown below. Figure 1 As shown, the separator membrane includes 11 a polymer substrate and 12 a second coating.

[0028] A cross-sectional view of the isolation membrane in the first region in one embodiment of this application is shown below. Figure 2 As shown, the separator membrane comprises 11 a polymer substrate and 13 a first coating.

[0029] In one embodiment of this application, the thickness of the polymer substrate is from 4 μm to 30 μm, and the polymer substrate includes at least one of polyethylene or polypropylene. For example, the thickness of the polymer substrate can be 4 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or a range of any two of these values. The secondary battery can increase its energy density by reducing the thickness of the polymer substrate. When the polymer substrate is selected from the above-mentioned materials and its thickness is within the above-mentioned range, the secondary battery also has good drop resistance.

[0030] In one embodiment of this application, the ceramic particles include at least one of Al2O3, ZrO2, SnO2, SiO2, or TiO2. Ceramic materials have high melting points, thermal stability, high hardness, good mechanical strength, and puncture resistance. When the first coating is selected from the above materials, the stability of the separator in high-temperature environments can be improved, thermal runaway can be reduced, thereby improving the safety performance of the battery.

[0031] In one embodiment of this application, the porous plastic includes at least one of polyethylene, polystyrene, polyvinyl chloride, polypropylene, or polyurethane. When the second coating is selected from the above materials, it can absorb energy through structural deformation when subjected to impact, thereby achieving a shock absorption effect and improving the safety performance of the secondary battery. At the same time, the above materials are lightweight and do not have a significant impact on energy density.

[0032] In one embodiment of this application, the porosity of the second coating is 50% to 90%. For example, the porosity of the second coating can be 50%, 60%, 70%, 80%, 90%, or a range consisting of any two of these values. When the porosity of the second coating is within the above range, it helps the separator to better store electrolyte during cycling, improving the cycle performance of the secondary battery, while maintaining appropriate mechanical strength and improving the drop resistance of the secondary battery. Preferably, the porosity of the second coating is 60% to 85%. When the porosity of the second coating is within the above range, the drop resistance of the secondary battery can be further improved while also having better cycle performance.

[0033] In one embodiment of this application, the thickness of the first coating is from 1 μm to 5 μm. For example, the thickness of the first coating can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or a range consisting of any two of these values. When the thickness of the first coating is within the above range, the thermal stability of the separator can be improved, the puncture resistance of the separator can be enhanced, and the internal self-discharge of the secondary battery can be reduced, thereby improving the cycle performance and drop resistance of the secondary battery.

[0034] In one embodiment of this application, the surface of the polymer substrate facing the positive electrode sheet is the first surface, and the ratio B of the thickness of the second coating on the first surface to the thickness of the positive electrode material layer is 0.7 to 0.9. For example, the value of B can be 0.7, 0.75, 0.8, 0.85, 0.9, or a range of any two of these values. When the value of B is within the above range, the separator and the positive electrode sheet can support each other, reducing the impact of electrolyte on the electrode assembly during drop, thus preventing short circuits. In addition, a suitable thickness can also achieve a shock absorption effect, reducing tearing caused by rigid stress on the electrode sheet and improving the drop resistance of the secondary battery.

[0035] In one embodiment of this application, the surface of the polymer substrate facing the negative electrode sheet is a second surface, and the ratio C of the thickness of the second coating on the second surface to the thickness of the positive electrode material layer is 0.7 to 0.9. For example, the value of C can be 0.7, 0.75, 0.8, 0.85, 0.9, or a range of any two of these values. When the value of C is within the above range, the separator and the negative electrode sheet can support each other, reducing the impact of electrolyte on the electrode assembly during drop, thus preventing short circuits. In addition, a suitable thickness can also achieve a shock absorption effect, reducing tearing caused by rigid stress on the electrode sheet and improving the drop resistance of the secondary battery.

[0036] In one embodiment of this application, the separator may further include an adhesive, which includes at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, polyvinylidene fluoride, or polyacrylonitrile.

[0037] This application does not impose any particular limitation on the method for preparing the first coating, as long as it achieves the purpose of this application. For example, the method for preparing the first coating may include, but is not limited to, spraying or gravure coating.

[0038] This application does not impose any particular limitation on the preparation method of the second coating, as long as it can achieve the purpose of this application. For example, the preparation method of the second coating may include, but is not limited to, the following steps: (1) adding 5% to 10% by mass of polyvinylidene fluoride (PVDF) to 90% to 95% by mass of N-methylpyrrolidone (NMP), and using an ultrasonic stirring device to form a uniform suspension; (2) adding 3% to 8% by mass of plastic material to the above suspension at a mass ratio of 97% to 92%, continuing to stir, and then filtering to obtain a uniform plastic material slurry; (3) continuously coating the second region of the separator membrane and drying to obtain the second coating. The plastic material includes at least one of polyethylene, polystyrene, polyvinyl chloride, polypropylene, or polyurethane.

[0039] Typically, the thickness of the first coating can be controlled by changing the viscosity, solid content, or coating speed of the slurry; the thickness of the second coating can be controlled by changing the viscosity, solid content, or coating speed of the plastic material slurry.

[0040] In this application, the secondary battery further includes a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the positive current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0041] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0042] In this application, the positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0043] In this application, the positive electrode material layer may further include a conductive agent and a binder. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0044] This application does not impose any particular limitation on the conductive agent, as long as it can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. Conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0045] This application does not impose any particular limitation on the adhesive, as long as it can achieve the purpose of this application. For example, the adhesive may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0046] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer can be 30 μm to 120 μm.

[0047] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0048] In this application, the secondary battery further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion thereof; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0049] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0050] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0051] In some embodiments of this application, the negative electrode material layer may further include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it may be at least one of the aforementioned conductive agents and binders. This application does not impose any particular restrictions on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0052] In some embodiments of this application, the negative electrode material layer may further include a conductive agent, a binder, and a thickener. This application does not particularly limit the types of conductive agents and thickeners, as long as they achieve the purpose of this application. For example, the conductive agent and binder may be at least one of the aforementioned conductive agents and binders. The thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0053] This application does not impose any particular restrictions on the thickness of the negative electrode current collector and the thickness of the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 120 μm.

[0054] Optionally, the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, which can be at least one of the aforementioned conductive agents and binders.

[0055] In this application, the secondary battery also includes an electrolyte, which includes lithium salts and non-aqueous solvents.

[0056] This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application.

[0057] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0058] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.

[0059] In this application, the secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0060] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to reduce the pressure rise and overcharge / discharge inside the secondary battery.

[0061] A second aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments.

[0062] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In some embodiments of this application, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0063] Example

[0064] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0065] Test methods and equipment:

[0066] Capacity retention test after 1000 cycles at 25°C:

[0067] The lithium-ion batteries of each embodiment and comparative example were repeatedly charged and discharged through the following steps, and the discharge capacity retention rate of the lithium-ion batteries was calculated.

[0068] The lithium-ion battery was subjected to its first charge and discharge cycle at 25°C. It was charged at a constant current of 2C until the full charge voltage of 4.48V was reached, followed by constant voltage charging at the full charge voltage until the current reached 0.05C. Then, it was discharged at a constant current of 0.5C until the final voltage reached 3.0V. This constituted one charge-discharge cycle, and the discharge capacity of the first cycle was recorded. The above steps were then repeated for 1000 charge-discharge cycles, and the discharge capacity of the 1000th cycle was recorded.

[0069] Cycle capacity retention rate = (discharge capacity of the 1000th cycle / discharge capacity of the first cycle) × 100%, denoted as "25℃-1000 cycle capacity retention rate".

[0070] Drop test at 25℃:

[0071] In an environment of 25℃, the lithium-ion battery is charged at a constant current of 2C to a full charge voltage of 3.8V. The lithium-ion battery is then fixed in a drop test fixture with double-sided tape. The six sides of the fixture are numbered 1, 2, 3, 4, 5, and 6 in sequence, and the four corners of the fixture are numbered C1, C2, C3, and C4 in sequence.

[0072] At 25℃, place the fixture on a test platform 1.5m high, and drop the lithium-ion batteries sequentially in the order of numbers 1 to 6. Then drop them sequentially in the order of numbers C1 to C4. This completes one cycle. Repeat the above steps 10 times to complete the drop test. After standing for 1 hour, observe whether the lithium-ion batteries exhibit the following conditions:

[0073] A. Disassemble the lithium-ion battery and observe whether the separator films on both sides of the electrode assembly in the width direction have shifted or wrinkled;

[0074] B. Whether the lithium-ion battery packaging is damaged;

[0075] C. Whether the top seal of the lithium-ion battery has been punctured;

[0076] D. Is the aluminum foil of the positive electrode current collector of the lithium-ion battery torn?

[0077] If none of the above conditions occur, the test is considered passed. Each group consists of 15 lithium-ion batteries, and the number of lithium-ion batteries that pass the drop test is recorded.

[0078] Room temperature volumetric energy density test

[0079] Take the lithium-ion battery to be tested, and charge it to 4.48V at a current of 0.2C under a test temperature of 25℃. Then charge it to 0.05C at a constant voltage of 4.48V. Let it stand for 5 minutes, and then discharge it to 3.0V at a constant current of 0.2C. Let it stand for 5 minutes. Record the capacity D at this time in mAh. Measure the length, width and thickness of the battery at this time and calculate the volume V of the cell. Calculate the volumetric energy density: VED=(D×3.89) / V, in Wh / L.

[0080] Example 1

[0081] <Preparation of the positive electrode>

[0082] LiCoO2 (positive electrode active material), Super P (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were mixed in a mass ratio of 97.9:0.9:1.2. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was then stirred under vacuum until homogeneous to obtain the positive electrode slurry. This slurry was uniformly coated onto one surface of a 9 μm thick aluminum foil used as a positive electrode current collector. The foil was then dried at 120°C to obtain a single-sided coated positive electrode sheet with a coating weight of 0.143 mg / mm². 2 Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a positive electrode sheet with a size of 67.9mm×1614mm for later use. The thickness of the single-sided positive electrode material layer is 34.35μm.

[0083] <Preparation of Negative Electrode Sheets>

[0084] Artificial graphite (negative electrode active material), styrene-butadiene rubber (binder), and acetylene black (conductive agent) were mixed in a mass ratio of 97.4:1.4:1.2. Deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated on one surface of a 6 μm thick copper foil used as a negative electrode current collector and dried at 120°C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The coating weight of the negative electrode material layer was 0.076 mg / mm². 2 Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a negative electrode sheet with a size of 69.4mm×1598mm for later use. The thickness of the single-sided negative electrode material layer is 44.4μm.

[0085] <Preparation of Electrolyte>

[0086] In an environment with a water content of less than 10 ppm, dimethyl carbonate, diethyl carbonate, and ethylene carbonate were mixed in a mass ratio of 1:1:1 to obtain an organic solvent. Then, the electrolyte salt LiPF6 was added to the organic solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the electrolyte salt comprised 12.5% ​​by mass, with the remainder being the organic solvent.

[0087] <Preparation of the separating membrane>

[0088] A 5 μm thick polyethylene was used as the polymer substrate. A 2 μm thick alumina (Al₂O₃) ceramic layer was coated on the first surface of the first region of the polymer substrate, and then a 0.003 mg / mm² alumina ceramic layer was coated on the second surface of the first region of the polymer substrate. 2 Polyvinylidene fluoride (PVDF) is dried to obtain a first coating. Then, polyethylene with a thickness of 27.48 μm and a porosity of 70% is continuously coated onto the first surface of the second region of the polymer substrate. Next, polyethylene with a thickness of 35.52 μm and a porosity of 70% is continuously coated onto the second surface of the second region of the polymer substrate, and dried to obtain a separator film. The width of the second region is 2.4 mm. The ratio B of the thickness of the second coating on the first surface to the thickness of the single-sided positive electrode material layer is 0.8, and the ratio C of the thickness of the second coating on the second surface to the thickness of the single-sided negative electrode material layer is 0.8.

[0089] <Preparation of Lithium-ion Batteries>

[0090] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. The electrolyte prepared above is then injected, and the battery undergoes vacuum sealing, settling, formation, degassing, and edge trimming to obtain a lithium-ion battery. The formation upper limit voltage is 4.15V, the formation temperature is 70°C, and the formation settling time is 2 hours.

[0091] Examples 2 to 24

[0092] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1. Specifically, when adjusting the values ​​of B and C, the thicknesses of the positive and negative electrode material layers remain unchanged, while the thickness of the second coating on the first and second surfaces changes accordingly.

[0093] Comparative Example 1

[0094] Except for the fact that the second coating is prepared using the same method as the first coating in the preparation of the isolation membrane, the rest is the same as in Example 1.

[0095] Comparative Example 2

[0096] Except for the fact that the width of the second region is set to 1 mm in the <Preparation of the Separating Membrane>, it is the same as in Example 1.

[0097] The preparation parameters and performance tests of each embodiment and comparative example are shown in Table 1.

[0098]

[0099]

[0100] As can be seen from Examples 1 to 24 and Comparative Examples 1 to 2, when the separator has the regional coating structure of this application, the resulting lithium-ion battery exhibits higher drop test pass rate, 1000-cycle capacity retention rate, and capacity at room temperature. In Comparative Example 1, the second coating is prepared using the same method as the first coating, resulting in a lower drop test pass rate for the lithium-ion battery; in Comparative Example 2, the width of the second region is 1 mm, resulting in a lower drop test pass rate for the lithium-ion battery. Therefore, the drop resistance and cycle performance of the lithium-ion battery of this application are improved, while also possessing a higher volumetric energy density. Furthermore, as can be seen from Examples 1 to 6 and Example 24, a smaller value of A (e.g., Example 24) indicates a poorer ability to absorb drop impact energy, while a larger value of A (e.g., Example 6) results in a larger space occupied by the second region in the packaging bag, lower battery energy density, and a longer path for the electrolyte through the porous plastic layer (second coating), affecting battery cycle performance. Examples 1 to 5 show better overall performance.

[0101] As can be seen from Examples 1 to 24, when the value of A, the material and thickness of the first coating, the material and thickness of the second coating, the porosity of the second coating, the ratio B of the thickness of the second coating on the first surface to the thickness of the positive electrode material layer, the ratio C of the thickness of the second coating on the second surface to the thickness of the negative electrode material layer, and the thickness of the substrate layer are within the range of this application, the resulting lithium-ion battery has a higher drop test pass rate, 1000-cycle capacity retention rate, and capacity at room temperature, thus indicating that the drop resistance and cycle performance of the lithium-ion battery are improved while having a higher volumetric energy density.

[0102] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

[0103] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0104] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. A secondary battery, the secondary battery comprising a positive electrode, a negative electrode, and a separator, the negative electrode comprising a negative current collector and a negative electrode material layer located on at least one surface of the negative current collector, the positive electrode comprising a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector, the separator being disposed between the positive electrode and the negative electrode; the separator comprising a polymer substrate and a first coating and a second coating disposed on at least one surface of the polymer substrate; The surface of the polymer substrate includes a first region and a second region. The first region is the area where the separator overlaps with the negative electrode sheet. The second region is the area where the separator extends beyond the negative electrode sheet in the width direction. The second region extends from both sides of the first region along the width direction of the separator. The width of the second region on each side is A mm, where 1.5 ≤ A ≤ 4.

0. The first coating is disposed on at least one surface of the first region, and the second coating is disposed on at least one surface of the second region; the first coating comprises ceramic particles, and the second coating comprises porous plastic.

2. The secondary battery according to claim 1, wherein, The thickness of the polymer substrate is from 4 μm to 20 μm, and the polymer substrate includes at least one of polyethylene or polypropylene.

3. The secondary battery according to claim 1, wherein, The ceramic particles include at least one of Al2O3, ZrO2, SnO2, SiO2, or TiO2.

4. The secondary battery according to claim 1, wherein, The porous plastic includes at least one of polyethylene, polystyrene, polyvinyl chloride, polypropylene, or polyurethane.

5. The secondary battery according to claim 1, wherein, The porosity of the second coating is 50% to 90%.

6. The secondary battery according to claim 5, wherein, The porosity of the second coating is 60% to 85%.

7. The secondary battery according to claim 1, wherein, The thickness of the first coating is 1 μm to 5 μm.

8. The secondary battery according to claim 1, wherein, The surface of the polymer substrate facing the positive electrode sheet is the first surface, and the ratio B of the thickness of the second coating on the first surface to the thickness of the positive electrode material layer is 0.7 to 0.

9.

9. The secondary battery according to claim 1, wherein, The surface of the polymer substrate facing the negative electrode sheet is the second surface, and the ratio C of the thickness of the second coating on the second surface to the thickness of the negative electrode material layer is 0.7 to 0.

9.

10. An electronic device comprising a secondary battery according to any one of claims 1 to 9.

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