Secondary battery and electronic device

Abstract

The application provides a secondary battery and an electronic device. The secondary battery comprises a positive electrode sheet. The positive electrode sheet comprises a current collector, a tab protruding from the current collector, and at least one surface insulation layer arranged on the current collector. The insulation layer is arranged along the side of the current collector close to the tab and is adjacent to the active material layer. The ratio of the thickness of the insulation layer to the thickness of the active material layer is 0.5-0.7, and the thickness of the active material layer is 200-400 μm.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage devices, in particular to a secondary battery and an electronic device comprising the secondary battery. BACKGROUND

[0002] The edge of the electrode tab is usually provided with an insulation layer for burr prevention. The active material layer and the insulation layer are usually coated synchronously on the current collector surface of the electrode tab. However, during the drying process, the active material layer and the insulation layer can interpenetrate and mix at the boundary position, resulting in blurred boundary position between the active material layer and the insulation layer after final drying, and causing deviation in the judgment of the position of the active material layer, affecting the size of the electrode tab, and further causing low capacity risk of the battery. SUMMARY

[0003] An object of the present application is to provide a secondary battery and an electronic device, which can improve the problem of affecting the size of the electrode tab due to the interaction zone at the interface between the active material layer and the insulation layer.

[0004] The first aspect of the present application provides a secondary battery comprising a positive electrode tab. The positive electrode tab comprises a current collector, a tab protruding from the current collector, and at least one surface insulation layer provided on the current collector. The insulation layer is provided along the side of the current collector close to the tab and is adjacent to the active material layer. The ratio of the thickness of the insulation layer to the thickness of the active material layer is 0.5-0.7, and the thickness of the active material layer is 200-400 μm.

[0005] In the secondary battery provided by the present application, the thickness of the active material layer is controlled to be 200-400 μm, and the ratio of the thickness of the insulation layer to the thickness of the active material layer is controlled to be 0.5-0.7, which can reduce the size of the interaction zone at the interface between the active material layer and the insulation layer formed by the interpenetration and mixing of the active slurry and the insulation slurry during the coating process, and improve the influence of the interaction zone on the size of the electrode tab.

[0006] According to some embodiments of the present application, the ratio of the thickness of the insulation layer to the thickness of the active material layer is 0.6-0.7, which is more conducive to reducing the size of the interaction zone.

[0007] According to some embodiments of the present application, the thickness of the active material layer is further controlled to be 200-370 μm, further reducing the size of the interaction zone.

[0008] According to some embodiments of the present application, the coating weight of the active material layer is 427-740 mg / 1540.25 mm 2 , which is conducive to reducing the size of the interaction zone.

[0009] According to some embodiments of the present application, the coating weight of the active material layer is 427-640 mg / 1540.25 mm 2.

[0010] According to some embodiments of the present application, the active material layer has a compacted density of 2.6-3 g / cc, which is conducive to reducing the size of the interaction region.

[0011] According to some embodiments of the present application, the insulating layer comprises inorganic particles, and the inorganic particles comprise one or more of alumina, boehmite, zirconia, boron oxide, or hexagonal boron nitride.

[0012] According to some embodiments of the present application, the active material layer comprises an active material, and the active material comprises one or more of lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron phosphate, or lithium manganese iron phosphate.

[0013] According to some embodiments of the present application, the active material consists of lithium manganese oxide and lithium iron phosphate, and the mass ratio of lithium manganese oxide to lithium iron phosphate is 3.5-12, which makes the width of the interaction region of the secondary battery appropriate and the thickness expansion rate of the secondary battery after storage appropriate.

[0014] According to some embodiments of the present application, the active material consists of lithium manganese oxide and lithium iron phosphate, and the mass ratio of lithium manganese oxide to lithium iron phosphate is 4-10, which can further reduce the thickness expansion rate of the secondary battery after storage.

[0015] The second aspect of the present application provides an electronic device comprising the secondary battery of any of the above embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0016] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which:

[0017] Figure 1 A partial plan view of a positive electrode tab is provided for an embodiment of the present application.

[0018] Figure 2 A cross-sectional view of the positive electrode tab shown along I-I is provided. Figure 1

[0019] Explanation of main element symbols

[0020] Positive electrode tab 10

[0021] Current collector 11

[0022] Tab 12

[0023] Active material layer 13

[0024] Insulating layer 14

[0025] First surface 11a

[0026] Second surface 11b ​DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Unless otherwise defined, all the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application.

[0028] Hereinafter, the embodiments of the present application will be described in detail. However, the present application can be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that the present application will be thorough and complete, and fully convey the scope of the present application to those skilled in the art.

[0029] In addition, for the sake of brevity and clarity, in the drawings, the size or thickness of various components, layers, or regions can be exaggerated. Throughout the specification, like numbers refer to like elements throughout. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. In addition, it should be understood that, when an element A is referred to as being "connected" to another element B, it can be directly connected to the other element B or intervening elements C can be present and the element A and the other element B can be indirectly connected to each other.

[0030] Further, use of "may" when describing embodiments of the present application means that one or more embodiments of the present application.

[0031] The professional terms used herein are for the purpose of describing the specific embodiments and are not intended to limit the present application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. It should be further understood that the term "comprising" when used in this specification, specifies the presence of stated features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0032] Spatially relative terms, such as "on", "above", and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device or apparatus in use or operation in addition to the orientations depicted in the figures. For example, if a device or apparatus is turned over, then an element or feature that is described as being "above" or "on" another element or feature would then be oriented "below" or "on" the other element or feature. Thus, the exemplary term "above" can encompass both an orientation that is above and then below. It will be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the exemplary embodiments.

[0033] In the prior art, as the demand for high energy density batteries increases, it is often necessary to provide a large coating weight of active material layer on the pole piece to achieve the increase of the battery capacity. A large coating weight will result in a large thickness of the active material layer. The applicant found that when forming an active material layer with a large thickness, the boundary position between the active material layer and the insulating layer is blurred, and the active material layer and the insulating layer interpenetrate and mix at the boundary position to form an interaction zone, which affects the size of the pole piece.

[0034] Based on the above problems found by the applicant, the applicant improves the thickness of the active material layer and the insulating layer of the pole piece to reduce the size of the interaction zone, and thus reduce the impact of the interaction zone on the size of the pole piece. The embodiments of the present application are further described below.

[0035] An embodiment of the present application provides a secondary battery, comprising a shell and a positive pole piece, a negative pole piece, a separator and an electrolyte contained in the shell, and the positive pole piece and the negative pole piece are provided with the separator therebetween.

[0036] Please refer to Figure 1 and Figure 2The positive electrode sheet 10 includes a current collector 11, a tab 12, an active material layer 13, and an insulating layer 14. The current collector 11 includes a first surface 11a and a second surface 11b disposed opposite to each other. The tab 12 protrudes from a side edge of the current collector 11 and is connected to the first surface 11a and the second surface 11b. The active material layer 13 is disposed on the first surface 11a and is separated from the tab 12. In other embodiments, the active material layer 13 can be disposed on the first surface 11a and the second surface 11b to increase the energy density. The insulating layer 14 is disposed on the first surface 11a along the side edge of the current collector 11 near the tab 12 and is adjacent to the active material layer 13. In a direction perpendicular to the first surface 11a (a thickness direction of the positive electrode sheet 10), the thickness of the active material layer 13 is 200 to 400 μm, and the ratio of the thickness H of the insulating layer 14 to the thickness T of the active material layer 13 is 0.5 to 0.7.

[0037] The current collector 11 can use any positive electrode current collector known in the art, such as a copper foil, a copper alloy foil, or a composite current collector. The tab 12 and the current collector 11 are integrally formed, for example, by cutting a copper foil to form the current collector 11 and the tab 12.

[0038] The insulating layer 14 includes inorganic particles and a binder. The inorganic particles include one or more of alumina, boehmite, zirconia, boron oxide, or hexagonal boron nitride. The binder includes one or more of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, sodium carboxymethyl cellulose.

[0039] The active material layer 13 includes an active material, a conductive agent, and a binder. The active material includes one or more of lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron phosphate, or lithium manganese iron phosphate. The conductive agent can use any conductive agent known in the art, for example, the conductive agent includes one or more of Ketjen black, Super-P, acetylene black, graphene, carbon nanotube, carbon fiber, etc. The binder can use any binder known in the art, for example, the binder includes one or more of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, sodium carboxymethyl cellulose.

[0040] The active material layer 13 and the insulation layer 14 are prepared by a synchronous coating process. In some embodiments, the method for preparing the secondary battery comprises the following steps: dissolving the active material, the conductive agent and the binder in a solvent to form an active slurry with a solid content greater than or equal to 65%, wherein the proportion of the active material is greater than or equal to 95.5%; dissolving the inorganic particles and the binder in a solvent to form an insulation slurry with a solid content of 30-50%, wherein the proportion of the inorganic particles is greater than or equal to 80%; synchronously coating the active slurry and the insulation slurry on the surface of the current collector 11; drying the active slurry coating and the insulation slurry coating to form the active material layer 13 and the insulation layer 14, thereby preparing the positive electrode sheet 10; and stacking or winding the positive electrode sheet 10, the separator and the negative electrode sheet to prepare the secondary battery. The solvent can include, but is not limited to, one or more of N-methyl pyrrolidone, anhydrous ethanol and acetone.

[0041] In the present application, the thickness of the active material layer 13 is controlled to be 200-400 μm, and the ratio of the thickness of the insulation layer 14 to the thickness of the active material layer 13 is controlled to be 0.5-0.7, which can reduce the size of the interaction zone formed by the penetration and fusion of the active slurry and the insulation slurry at the boundary position between the active material layer 13 and the insulation layer 14, and improve the influence of the interaction zone on the size of the electrode sheet.

[0042] When the ratio of the thickness H of the insulation layer 14 to the thickness T of the active material layer 13 is less than 0.5, the thickness difference between the insulation layer 14 and the active material layer 13 is too large, and in the drying process, due to the flowability of the active slurry and the surface tension of the active slurry, the active slurry and the insulation slurry are easily fused to form an interaction zone at the boundary position, and the size of the interaction zone is too large to affect the size of the positive electrode sheet 10. In addition, when the ratio of the thickness H of the insulation layer 14 to the thickness T of the active material layer 13 is less than 0.5, the thickness H of the insulation layer 14 can be small, and when the height of the burr formed by cutting is greater than the thickness H of the insulation layer 14, the burr can pierce the insulation layer 14, which can easily cause internal short circuit between the positive electrode and the negative electrode, and cause safety problems.

[0043] When the ratio of the thickness H of the insulation layer 14 to the thickness T of the active material layer 13 is greater than 0.7, the thickness H of the insulation layer 14 is close to the thickness T of the active material layer 13, so that in the cold pressing process of the secondary battery 100, the insulation layer 14 can be pressed, and due to the incompressibility of the inorganic particles, the part of the current collector 11 corresponding to the insulation layer 14 can be damaged by the pressure, thereby causing the problem of cold pressing belt breakage. In addition, when the ratio of the thickness H of the insulation layer 14 to the thickness T of the active material layer 13 is greater than 0.7, due to the large difference in solid content between the insulation slurry and the active slurry, when the coating weight is increased (up to 740 mg / 1540.25 mm 2) When the thickness of the insulation layer 14 is increased, the insulation layer does not dry completely during the coating process and can adhere to the rubber roll, causing scratches and breakage of the electrode tab.

[0044] In some embodiments, the ratio of the thickness H of the insulation layer 14 to the thickness T of the active material layer 13 is 0.6 to 0.7, which is more advantageous for reducing the size of the interaction region.

[0045] In some embodiments, the thickness of the active material layer is further controlled to be 200 to 370 μm, which is more advantageous for reducing the size of the interaction region.

[0046] In some embodiments, the thickness of the active material layer 13 is adjusted by controlling the coating weight of the active material layer 13 and the compaction density of the active material layer 13. In some embodiments, the coating weight of the active material layer 13 is 427 to 740 mg / 1540.25 mm 2 , and the compaction density of the active material layer 13 is 2.6 to 3 g / cc, which can control the active material layer 13 to have a suitable thickness and is advantageous for reducing the size of the interaction region. Preferably, the coating weight of the active material layer 13 is 427 to 640 mg / 1540.25 mm 2 In some embodiments, the thickness of the insulation layer 14 is adjusted by controlling the solid content of the insulation paste and the coating weight of the insulation layer 14.

[0047] In some embodiments, the active material of the active material layer 13 is composed of lithium manganate and lithium iron phosphate, and the mass ratio of lithium manganate to lithium iron phosphate is 3.5 to 12. The higher the content of lithium manganate, the more gas is generated in the secondary battery. Controlling the mass ratio of lithium manganate to lithium iron phosphate to be 3.5 to 12 can make the width of the interaction region and the thickness expansion rate of the secondary battery after storage both more appropriate. In some embodiments, the active material is composed of lithium manganate and lithium iron phosphate, and the mass ratio of lithium manganate to lithium iron phosphate is 4 to 10, which can further reduce the thickness expansion rate of the secondary battery after storage.

[0048] The negative electrode tab includes a negative current collector and a negative active material disposed on the surface of the negative current collector. The negative current collector can use any negative current collector known in the art, such as a copper foil, a copper alloy foil, or a composite current collector. The negative active material can use any negative active material known in the art, such as at least one of graphite, hard carbon, soft carbon, silicon, silicon-carbon, or silicon oxide. The negative active material can further include a conductive agent and a binder, the conductive agent can include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, or graphene, and the binder can include at least one of styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or sodium carboxymethyl cellulose (CMC-Na).

[0049] The separator film can be any separator film known in the art. For example, the separator film can be selected from a film of one or more of polyethylene, polypropylene, non-woven fabric, and polyfiber.

[0050] The electrolyte can be any electrolyte known in the art. For example, the electrolyte can be selected from a solution of one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate as solvent, and one or more of LiPF6, LiBF4, LiBOB, LiAsF6, Li(CF3SO2)2N, LiCF3SO3, and LiCIO4 as solute.

[0051] The shell can be any shell known in the art. For example, the shell can be a packaging bag obtained by packaging with a packaging film, such as an aluminum-plastic film or a steel-plastic film, or the shell can be a metal shell, such as a steel shell or an aluminum shell.

[0052] An embodiment of the present application also provides an electronic device comprising the secondary battery of the present application. The electronic device can be any electrically powered equipment using an electrochemical device, for example, the electronic device can be a mobile phone, a portable device, a notebook computer, an electric vehicle, an electric automobile, a ship, a spacecraft, an electric toy, an electric tool, etc.

[0053] Some specific examples and comparative examples are listed below to better illustrate the present application.

[0054] Example 1

[0055] 9.64% lithium iron phosphate, 86.76% lithium manganese oxide (the mass ratio of lithium manganese oxide to lithium iron phosphate is 9), 0.6% conductive carbon paste, 1.2% conductive carbon black, and 1.8% polyvinylidene fluoride were dispersed in N-methylpyrrolidone to obtain an active paste with a solid content of 67%. 88% boehmite and 12% polyvinylidene fluoride were dispersed in N-methylpyrrolidone to obtain an insulating paste with a solid content of 35%. The active paste and the insulating paste were coated on an aluminum foil to form an active coating layer and an insulating coating layer, the active coating layer and the insulating coating layer were adjacent, and the thickness of the active coating layer was equal to the thickness of the insulating coating layer. The active coating layer and the insulating coating layer were dried to obtain an active material layer and an insulating layer. Then, after cold pressing, die cutting, and slitting, a positive electrode tab as shown in FIG. 1 was obtained. Figure 1 The coated weight of the active material layer was 427 mg / 1540.25 mm 2 , the compacted density of the active material layer was 3 g / cc, the thickness T of the active material layer was 200 μm, the thickness H of the insulating layer was 130 μm, and H / T was 0.65.

[0056] The graphite, polyvinylidene fluoride and conductive carbon black are mixed and coated on a copper foil, and after cold pressing, die cutting and striping, a negative electrode sheet is obtained.

[0057] The positive electrode sheet, the polyethylene separator and the negative electrode sheet are sequentially stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet, and are wound to obtain an electrode assembly; the electrode assembly is placed in an aluminum plastic film, and after liquid injection and formation, a lithium ion battery is obtained.

[0058] Examples 2-11

[0059] Except that at least one of the coating weight of the active material layer, the thickness T of the active material layer, the compaction density of the active material layer, the thickness H of the insulating layer, and H / T is different, the rest is the same as Example 1. Among them, T is 200-400 μm, and H / T is 0.5-0.7.

[0060] Examples 12-17

[0061] Except that the content of lithium manganate, the content of lithium iron phosphate, and the thickness H of the insulating layer are different, the rest is the same as Example 3.

[0062] Example 18

[0063] Except that the lithium iron phosphate, the coating weight of the active material layer, and the compaction density of the active material layer are different, the rest is the same as Example 3.

[0064] Comparative Examples 1-5

[0065] Comparative Examples 1-5 are the same as Example 1 except that the coating weight of the active material layer, the thickness T of the active material layer, the compaction density of the active material layer, and the thickness H of the insulating layer are different.

[0066] The size of the interaction zone in Examples 1-18 and Comparative Examples 1-5 is observed and measured:

[0067] The positive electrode sheet is cut transversely with a slitting knife, and the cross section is analyzed with a high-power microscope (SEM). The white insulating layer, the black active material layer, and the gray interaction zone between the white insulating layer and the black active material layer in the width direction of the positive electrode sheet can be seen.

[0068] The distance from the highest point of the white insulating layer to the current collector is tested using the "dot line mode", and the average value obtained by repeating the above steps three times is the thickness H of the insulating layer. Along the width direction of the sheet, 3 points are taken to measure the distance from the surface of the white active material layer to the current collector at a transverse translation of 25-35 mm from the edge of the black active material layer, and then the average value is obtained, which is the thickness T of the active material layer.

[0069] Along the width direction of the pole piece, the intersection point of the white insulating layer and the gray interaction zone as the starting point, the intersection point of the black active material layer and the gray interaction zone as the ending point, the distance between the two parallel lines is measured, which is the width of the interaction zone. The above steps are repeated three times to obtain the average value, which is the measured width of the interaction zone.

[0070] The frequency of belt breakage during the cold pressing process of the positive pole piece was observed.

[0071] When the width of the interaction zone is less than or equal to 0.5 mm, and the frequency of belt breakage is greater than or equal to 20,000 m / time, it is determined that it is within the acceptable range of product and process, and the effect is "OK"; otherwise, the effect is "NG".

[0072] High-temperature storage performance of lithium ion batteries of Examples 1-18 and Comparative Examples 1-5:

[0073] The lithium ion battery was placed in a 25°C constant temperature oven for 5 minutes to allow the lithium ion battery to reach a constant temperature. It was charged to 4.2V at 0.5C constant current, charged to a constant voltage when the current was 0.05C, and then discharged to 2.8V at 0.2C constant current, and then placed in a 25°C constant temperature oven for 5 minutes to allow the lithium ion battery to reach a constant temperature. The thickness of the lithium ion battery was measured and recorded as the initial thickness. The test lithium ion battery was transferred to a 60°C constant temperature oven for storage for 60 days, then taken out and placed in a 25°C constant temperature oven for 5 minutes to allow the lithium ion battery to reach a constant temperature, and the thickness of the lithium ion battery was measured as the thickness after storage.

[0074] Thickness expansion rate = (thickness after storage - initial thickness) / initial thickness x 100%.

[0075] The data and measurement results of Examples 1-18 and Comparative Examples 1-5 are shown in Table 1.

[0076] Table 1

[0077]

[0078] Comparing Examples 1-12 and Comparative Examples 1-5, when the thickness T of the active material layer is 200-400 μm, and the ratio H / T of the thickness H of the insulating layer to the thickness T of the active material layer is 0.5-0.7, the width of the interaction zone is 0.13-0.4 mm, and the frequency of belt breakage is 20,000-26,000 m / time, the effect is OK. When H / T is 0.6-0.7, the width of the interaction zone is 0.13-0.23 mm, and the width of the interaction zone is smaller.

[0079] It can be seen from Examples 3, 12-17 that when the thickness of the active material layer and the thickness of the insulation layer are within a suitable range, the mass ratio of lithium manganate and lithium iron phosphate has a greater influence on the high-temperature storage performance; when the mass ratio of lithium manganate and lithium iron phosphate is small, the thickness expansion rate after storage is small; when the mass ratio of lithium manganate and lithium iron phosphate is large, the thickness expansion rate after storage is large; in addition, it can be seen from Example 18 that when the positive electrode active material is only lithium iron phosphate, the width of the interzone will be large; when the positive electrode active material only contains lithium iron phosphate, the drying of the active layer is relatively fast, and the drying rate of the insulation layer is slow, and under the action of capillary stress, the insulation layer flows to the active layer; and the surface tension of the lithium iron phosphate slurry is high, and during the drying process, the edge of the positive electrode active material layer shrinks, causing the insulation layer slurry to further flow to the positive electrode active material layer, interpenetrate with the positive electrode active material layer, and thus form a wide interzone.

[0080] The above disclosure is only the preferred embodiments of the present application, and of course cannot be used to limit the present application, so equivalent changes made according to the present application still fall within the scope of the present application.

Claims

1. A secondary battery, comprising a positive electrode, wherein, The positive electrode sheet includes: current collector; The tab protrudes from the current collector; An active material layer is disposed on at least one surface of the current collector; An insulating layer is disposed along the side of the current collector near the tab and adjacent to the active material layer, wherein the ratio of the thickness of the insulating layer to the thickness of the active material layer is 0.5 to 0.7, and the thickness of the active material layer is 200 to 400 μm; The active material layer includes an active material composed of lithium manganese oxide and lithium iron phosphate, wherein the mass ratio of lithium manganese oxide to lithium iron phosphate is 3.5 to 12.

2. The secondary battery as described in claim 1, wherein, The ratio of the thickness of the insulating layer to the thickness of the active material layer is 0.6 to 0.

7.

3. The secondary battery as described in claim 1, wherein, The thickness of the active material layer is 200~370 μm.

4. The secondary battery as described in claim 1, wherein, The coating weight of the active material layer is 427~740 mg / 1540.25 mm. 2 .

5. The secondary battery as described in claim 4, wherein, The coating weight of the active material layer is 427~640 mg / 1540.25 mm. 2 .

6. The secondary battery as described in claim 1, wherein, The compaction density of the active material layer is 2.6~3 g / cc.

7. The secondary battery as described in claim 1, wherein, The insulating layer comprises inorganic particles, which include one or more of alumina, boehmite, zirconium oxide, boron oxide, or hexagonal boron nitride.

8. The secondary battery as described in claim 1, wherein, The mass ratio of lithium manganese oxide to lithium iron phosphate is 4 to 10.

9. An electronic device, wherein, Includes the secondary battery as described in any one of claims 1-8.

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