Secondary battery and electronic device
By using a composite current collector and multiple positive electrode tabs in the secondary battery, and by appropriately adjusting the thickness of the negative electrode current collector and the parameters of the active material layer, the problem of positive electrode breakage caused by the volume expansion of silicon material was solved, and a balanced performance improvement was achieved.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- NINGDE AMPEREX TECHNOLOGY LTD
- Filing Date
- 2025-10-30
- Publication Date
- 2026-07-02
AI Technical Summary
Silicon materials in secondary batteries can cause the positive electrode to break due to volume expansion, affecting service life and safety. At the same time, setting multiple positive electrode tabs reduces energy density.
The positive electrode sheet employing a composite current collector includes a first metal layer, a polymer layer, and a second metal layer to increase ductility. Multiple positive electrode tabs are provided for parallel current splitting. The electrode sheet structure is optimized by appropriately reducing the thickness of the negative electrode current collector and adjusting the coating weight and compaction density of the active material layer.
It improves the fracture resistance, kinetic performance and energy density of secondary batteries, reduces the risk of fracture caused by volume expansion, and enhances service life and safety.
Smart Images
Figure CN2025131067_02072026_PF_FP_ABST
Abstract
Description
Secondary batteries and electronic devices Technical Field
[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and an electronic device having the secondary battery. Background Technology
[0002] Secondary batteries (such as lithium-ion batteries) are widely used in electronic mobile devices, power tools, and electric vehicles. Graphite is a widely used anode material in secondary batteries, offering advantages such as high efficiency and a stable charge-discharge platform. However, its relatively low specific capacity hinders its further application in high-demand fields. Compared to graphite, elemental silicon has a higher theoretical specific capacity, which can improve the energy density of secondary batteries when used as an anode material.
[0003] However, the significant volume expansion of silicon during cycling can lead to breakage of the positive electrode. This breakage not only causes secondary battery failure, but the resulting debris can also short-circuit with the negative electrode, generating excessive heat and reducing the battery's lifespan and safety. Summary of the Invention
[0004] Therefore, this application proposes a secondary battery that can improve the positive electrode breakage caused by the volume expansion of silicon material, and an electronic device having the secondary battery.
[0005] This application provides a secondary battery, including a casing and an electrode assembly disposed within the casing. The electrode assembly includes a negative electrode, a positive electrode, and a separator disposed between the negative and positive electrode. The negative electrode, separator, and positive electrode are stacked and wound together. The negative electrode includes a negative current collector, a negative active material layer, and a first negative electrode tab. The negative current collector is copper foil. The negative active material layer is disposed on the negative current collector. The negative active material layer contains a negative active material, which includes silicon. The negative active material layer has a first groove, and the first negative electrode tab is disposed in the first groove and electrically connected to the negative current collector. The positive electrode includes a positive current collector, a positive active material layer, and a plurality of positive electrode tabs. The positive current collector includes a first metal layer, a polymer layer, and a second metal layer stacked together. The positive active material layer is disposed on the first metal layer and the second metal layer.
[0006] This application addresses silicon-based secondary batteries by configuring the positive electrode current collector as a composite current collector comprising a first metal layer, a polymer layer, and a second metal layer. Compared to a pure metal current collector of the same thickness, this composite current collector exhibits higher elongation, thereby improving the elongation of the positive electrode sheet containing the current collector. This reduces the risk of breakage of the positive electrode sheet due to volume expansion caused by the insertion of active ions into the silicon material, thus enhancing the lifespan and safety of the secondary battery. Furthermore, this application also includes multiple positive electrode tabs on the positive electrode sheet. These tabs can shunt the current flowing through the positive electrode sheet in parallel, reducing its impedance. This minimizes the impact of the composite current collector on the impedance of the positive electrode sheet, and consequently reduces its impact on the kinetic performance of the positive electrode sheet. Moreover, with multiple positive electrode tabs, the first negative electrode tab is disposed in a first groove and connected to the negative current collector, supporting higher charge / discharge rates. Therefore, this approach effectively balances and matches the kinetic performance of the positive and negative electrode sheets. Furthermore, this application eliminates the need to die-cut multiple negative electrode tabs on the negative electrode sheet. On one hand, this reduces the risk of excessive energy density loss in the secondary battery. On the other hand, it eliminates the need for zebra coating or leaving empty foil areas at the edges of the negative electrode current collector during negative electrode sheet fabrication. Therefore, the risk of uneven stress due to differences in electrode sheet thickness during the slitting process, leading to wrinkling or breakage of the negative electrode sheet, is lower. Consequently, the thickness of the negative electrode current collector can be appropriately reduced, thereby mitigating the energy density reduction issue caused by multiple positive electrode tabs on the positive electrode sheet. Therefore, the secondary battery of this application achieves a good balance between fracture resistance, kinetic performance, and energy density.
[0007] Based on the first aspect, in some possible implementations, the thickness H0 of the negative electrode current collector is 5 μm to 10 μm. By reducing the thickness of the negative electrode current collector, the risk of wrinkling or breakage of the negative electrode sheet during the electrode slitting process can be reduced, while also mitigating the problem of reduced energy density of the secondary battery caused by multiple positive electrode tabs on the positive electrode sheet. Furthermore, it can also reduce the risk of over-soldering between the first negative electrode tab and the negative electrode current collector when the thickness of the negative electrode current collector is small.
[0008] Based on the first aspect, in some possible implementations, the coating weight w per unit area of the negative electrode active material layer is 70 mg / 1540.25 mm. 2 Up to 160mg / 1540.25mm 2 By setting a range for the coating weight per unit area of the negative electrode active material layer, it is beneficial to further improve the energy density of the secondary battery and mitigate the energy density reduction problem caused by the presence of multiple positive electrode tabs on the positive electrode. Simultaneously, it can also reduce the risk of positive electrode breakage when the coating weight per unit area is large, as well as the risk of hindered migration of active ions, leading to reduced kinetic performance of the negative electrode and lithium plating.
[0009] Based on the first aspect, in some possible implementations, the compaction density ρ of the negative electrode active material layer is 1.65 g / cm³. 3 Up to 1.78 g / cm 3 Increasing the compaction density of the negative electrode active material layer can further improve the energy density of the secondary battery and mitigate the energy density reduction caused by multiple positive electrode tabs on the positive electrode. Simultaneously, it can reduce the risk of positive electrode breakage when the compaction density is high, as well as the risk of hindered migration of active ions, leading to reduced kinetic performance of the negative electrode and lithium plating.
[0010] Based on the first aspect, in some possible implementations, the thickness H3 of the polymer layer is 2 μm to 13 μm, the thickness H1 of the first metal layer is 0.2 μm to 1.3 μm, and the thickness H2 of the second metal layer is 0.2 μm to 1.3 μm. By setting the thicknesses of the polymer layer, the first metal layer, and the second metal layer, the positive electrode current collector can have a higher elongation, thereby giving the positive electrode sheet containing the positive electrode current collector higher elongation and further reducing the risk of breakage of the positive electrode sheet due to the volume expansion of silicon material caused by the insertion of active ions. At the same time, it also reduces the risk of high impedance of the positive electrode sheet when the polymer layer thickness is large, resulting in high heat generation and mismatch of the kinetic performance of the positive and negative electrode sheets, and also reduces the risk of low impedance of the positive electrode sheet when the thickness of the first metal layer and / or the second polymer layer is large, leading to lithium plating on the negative electrode sheet.
[0011] Based on the first aspect, in some possible implementations, the polymer layer is made of at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyimide (PI), which have low density and good toughness and elongation.
[0012] Based on the first aspect, in some possible implementations, both the first metal layer and the second metal layer contain aluminum, thereby improving the conductivity, stability and mechanical strength of the positive current collector.
[0013] Based on the first aspect, in some possible implementations, the negative electrode sheet further includes a second negative electrode tab, and the negative electrode active material layer is further provided with a second groove. The second negative electrode tab is disposed in the second groove and is electrically connected to the negative electrode current collector. Therefore, the second negative electrode tab can also support a higher rate of charge and discharge current, which is beneficial for further balancing the dynamic performance of the positive and negative electrode sheets.
[0014] Based on the first aspect, in some possible implementations, the first negative electrode tab, the second negative electrode tab, and a plurality of positive electrode tabs are located on the same side of the electrode assembly and arranged along a first direction. In the first direction, the plurality of positive electrode tabs are located between the first and second negative electrode tabs. Therefore, this is advantageous for connection to external circuitry and also provides ample space for the arrangement of the plurality of positive electrode tabs.
[0015] Based on the first aspect, in some possible implementations, the secondary battery also includes a positive electrode adapter tab. The thickness direction of the electrode assembly is a second direction, which is perpendicular to the first direction. The projections of multiple positive electrode tabs in the second direction overlap and are connected to the positive electrode adapter tab. The casing is a packaging bag, and the first negative electrode tab, the second negative electrode tab, and the positive electrode adapter tab extend out of the packaging bag from the same side and are configured to be electrically connected to an external circuit, respectively.
[0016] Based on the first aspect, in some possible implementations, the silicon material includes at least one of silicon oxide, silicon carbide, and elemental silicon.
[0017] A second aspect of this application also provides an electronic device comprising a battery compartment and the aforementioned secondary battery disposed within the battery compartment. The electronic device is powered by the aforementioned secondary battery. In the secondary battery, the positive electrode current collector is a composite current collector, which reduces the risk of positive electrode breakage, thereby improving the service life and safety of the secondary battery. Simultaneously, the positive electrode includes multiple positive electrode tabs, reducing the impact of the composite current collector on the impedance of the positive electrode, thus matching the kinetic performance of the positive and negative electrodes. Furthermore, since the risk of wrinkling or breakage of the negative electrode during the electrode slitting process is relatively low, the thickness of the negative electrode current collector can be appropriately reduced, mitigating the problem of reduced energy density in the secondary battery caused by the multiple positive electrode tabs on the positive electrode. Therefore, the secondary battery of this application achieves a good balance between fracture resistance, kinetic performance, and energy density. Attached Figure Description
[0018] Figure 1 is a schematic diagram of the structure of a secondary battery provided in one embodiment of this application.
[0019] Figure 2 is a cross-sectional view of the secondary battery shown in Figure 1 along section line II-II.
[0020] Figure 3 is a cross-sectional view of the secondary battery shown in Figure 1 along section line III-III.
[0021] Figure 4 is a cross-sectional view of the secondary battery shown in Figure 1 along the cutting line IV-IV.
[0022] Figure 5 is an enlarged view of the secondary battery in Figure 3 at point V.
[0023] Figure 6 is a schematic diagram of the structure of an electronic device provided in one embodiment of this application.
[0024] Explanation of main component symbols
[0025] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation
[0026] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.
[0027] The embodiments of this application will be described in detail below. However, this application may 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 to provide a thorough and detailed understanding of this application to those skilled in the art.
[0028] Additionally, for brevity and clarity, the dimensions or thicknesses of various components and layers may be enlarged in the accompanying drawings. Throughout the text, the same numerical values refer to the same elements. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more of the associated enumerated items. Furthermore, it should be understood that when element A is referred to as "connecting" element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.
[0029] Furthermore, when describing the implementation of this application, the word "may" refers to "one or more implementations of this application".
[0030] The technical terms used herein are for the purpose of describing particular embodiments and are not intended to limit this 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," as used in this specification, means the presence of the described features, values, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof.
[0031] Spatial terms, such as "above," may be used herein for convenience in describing the relationship between one element or feature and another element (or feature) or feature (or feature) illustrated in the figures. It should be understood that, in addition to the directions depicted in the figures, spatial terms are intended to include different orientations of the device or apparatus during use or operation. For example, if the device in the figure is flipped, an element described as "above" or "on" other elements or features would be oriented "below" or "under" other elements or features. Therefore, the exemplary term "above" can include both above and below orientations. It should be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Therefore, a first element, component, region, layer, or portion discussed below may be referred to as a second element, component, region, layer, or portion without departing from the teachings of the exemplary embodiments.
[0032] In this application, the design relationships of greater than, less than, or not equal to parameter values need to exclude reasonable errors of the measuring equipment.
[0033] Referring to Figures 1 to 4, one embodiment of this application provides a secondary battery 100, including a housing 10, an electrode assembly 20, and an electrolyte (not shown). Both the electrode assembly 20 and the electrolyte are disposed within the housing 10. In some embodiments, the housing 10 is a packaging bag obtained by encapsulating with an aluminum-plastic film, which may include a receiving portion 11 and a sealing edge 12 connecting the receiving portion 11. The electrode assembly 20 and the electrolyte are disposed in the receiving portion 11. The sealing edge 12 is used to seal the receiving portion 11. In other embodiments, the housing 10 may also be a metal housing 10, such as a steel or aluminum housing.
[0034] As shown in Figure 2, the electrode assembly 20 has a wound structure. The electrode assembly 20 includes a positive electrode 21, a negative electrode 22, and a separator 23, with the separator 23 disposed between the positive electrode 21 and the negative electrode 22. The positive electrode 21, the separator 23, and the negative electrode 22 are stacked and wound together. A three-dimensional coordinate system is established based on three mutually perpendicular directions: a first direction X, a second direction Y, and a third direction Z, where the second direction Y is the thickness direction of the electrode assembly 20, and the third direction Z is the width direction of either the positive electrode 21 or the negative electrode 22. In some embodiments, the positive electrode 21 is located on the outermost side of the electrode assembly 20.
[0035] As shown in Figures 2 to 4, the negative electrode sheet 22 includes a negative electrode current collector 220, a negative electrode active material layer 221, and a first negative electrode tab 222. The negative electrode current collector 220 is a copper foil. The negative electrode active material layer 221 is disposed on the negative electrode current collector 220 and contains a negative electrode active material. The negative electrode active material includes silicon material capable of reversible insertion / extraction of active ions. By adding silicon material to the negative electrode active material, the negative electrode active material has a higher specific capacity, thereby increasing the energy density of the secondary battery 100. The negative electrode active material layer 221 has a first groove 2210, and the first negative electrode tab 222 is disposed within the first groove 2210 and electrically connected to the negative electrode current collector 220.
[0036] In some embodiments, the silicon material includes at least one of silicon oxide, silicon carbide, or elemental silicon. In the silicon-carbon material, elemental silicon can be dispersed within the pores of the porous carbon material, which helps to suppress the volume expansion of elemental silicon during cycling. The active material in the negative electrode active material layer 221 may also include graphite, such as natural or artificial graphite. Due to the flexibility of graphite, its combination with silicon material can alleviate the overall volume expansion of the negative electrode active material layer 221, improving the cycle performance of the secondary battery 100. Furthermore, the simultaneous use of graphite and silicon as active materials can fully utilize the advantages of both to achieve better electrochemical performance.
[0037] In some embodiments, the first negative electrode tab 222 is welded and fixed to the negative electrode current collector 220, thereby improving the connection strength between the first negative electrode tab 222 and the negative electrode current collector 220. During the fabrication of the negative electrode sheet 22, after processes such as electrode slurry coating, electrode rolling, and electrode slitting, a first groove 2210 can be created in the negative electrode active material layer 221 using laser cleaning, exposing part of the negative electrode current collector 220 to facilitate subsequent welding of the first negative electrode tab 222; alternatively, expanding foam can be pre-applied to part of the negative electrode current collector 220, and after coating with the negative electrode active material, heating can be applied to cause the expanding foam to detach, thus exposing that part of the negative electrode current collector 220; or, a scraper can be used to directly scrape off part of the negative electrode active material, thereby exposing part of the negative electrode current collector 220.
[0038] The positive electrode 21 includes a positive current collector 210, a positive active material layer 211, and a plurality of positive electrode tabs 212. The positive current collector 210 is a composite current collector, comprising a first metal layer 2101, a polymer layer 2103, and a second metal layer 2102 stacked together. The positive active material layer 211 is disposed on the first metal layer 2101 and the second metal layer 2102. The positive active material layer 211, disposed on the first metal layer 2101 and the second metal layer 2102, contains a positive active material, including a compound that reversibly inserts and deintercalates lithium ions (i.e., a lithiation intercalation compound). In some embodiments, the plurality of positive electrode tabs 212 are integrally disposed with the positive current collector 210; for example, the positive electrode tabs 212 can be formed by cutting the positive current collector 210. In the process of manufacturing the positive electrode 21, after processes such as electrode slurry coating (e.g., zebra coating), electrode rolling, and electrode slitting, a blank foil area can be reserved at the edge of the positive current collector 210. Then, the reserved blank foil area is die-cut to obtain multiple positive electrode tabs 212. Referring to Figure 5, the positive electrode tab 212 may include a first sub-layer 2121, a third sub-layer 2123, and a second sub-layer 2122 stacked together. The first sub-layer 2121 is integrally formed with the first metal layer 2101, the third sub-layer 2123 is integrally formed with the polymer layer 2103, and the second sub-layer 2122 is integrally formed with the second metal layer 2102.
[0039] In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material is selected from lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of O4 (lithium iron phosphate) or lithium iron phosphate (LiFePO4). In some embodiments, the polymer layer 2103 is made of at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide, which have low density and good toughness and elongation. The first metal layer 2101 and the second metal layer 2102 may respectively contain aluminum or nickel, thereby improving the conductivity, stability, and mechanical strength of the positive electrode current collector 210. In some embodiments, both the first metal layer 2101 and the second metal layer 2102 contain aluminum.
[0040] As shown in Figures 3 and 4, the negative current collector 220 includes a first end edge 220A and a second end edge 220B disposed opposite to each other in the third direction Z. In the third direction Z, the first end edge 220A is closer to the sealing edge 12 than the second end edge 220B. A first negative electrode tab 222 extends from the first end edge 220A to form a negative electrode sheet 22. The positive current collector 210 includes a third end edge 210A and a fourth end edge 210B disposed opposite to each other in the third direction Z. In the third direction Z, the third end edge 210A is closer to the sealing edge 12 than the fourth end edge 210B. A plurality of positive electrode tabs 212 are integrally connected to the third end edge 210A and extend from the third end edge 210A to form a positive electrode sheet 21.
[0041] The secondary battery 100 may further include a positive electrode adapter tab 30. The projections of multiple positive electrode tabs 212 onto the electrode assembly 20 in the second direction Y overlap, and the multiple positive electrode tabs 212 are connected to the positive electrode adapter tab 30. When the housing 10 is a packaging bag, the positive electrode adapter tab 30 and the first negative electrode tab 222 extend out of the packaging bag from the same side (e.g., from the sealing edge 12) and can be electrically connected to an external circuit (not shown). In the embodiments of this application, the overlapping of multiple positive electrode tabs 212 means that the multiple positive electrode tabs 212 at least partially cover each other in the second direction Y.
[0042] This application relates to a silicon-based secondary battery 100, wherein the positive electrode current collector 210 is configured as a composite current collector including a first metal layer 2101, a polymer layer 2103, and a second metal layer 2102. Compared with a conventional pure metal current collector of the same thickness, it has a higher elongation, thereby improving the elongation of the positive electrode 21 containing the positive electrode current collector 210, reducing the risk of breakage of the positive electrode 21 due to the volume expansion of silicon material due to the insertion of active ions, thereby improving the service life and safety of the secondary battery 100 (in particular, the outermost electrode of the electrode assembly 20 has a higher risk of breakage after the negative electrode 22 expands and deforms. If the outermost part of the electrode assembly 20 is set as the positive electrode 21, the risk of breakage of the outermost electrode due to the expansion and deformation of the negative electrode 22 can be reduced). Meanwhile, considering that the impedance of the positive current collector 210 will increase when it is a composite current collector, this application also provides that the positive electrode 21 includes multiple positive electrode tabs 212. The multiple positive electrode tabs 212 can shunt the current flowing through the positive electrode 21 in parallel, reduce the impedance of the positive electrode 21, thereby reducing the impact of the composite current collector on the impedance of the positive electrode 21, and further reducing the impact of the composite current collector on the dynamic performance of the positive electrode 21. Moreover, when the positive electrode 21 includes multiple positive electrode tabs 212, the first negative electrode tab 222 is disposed in the first groove 2210, which can also support a higher rate of charge and discharge current. Therefore, the dynamic performance of the positive electrode 21 and the negative electrode 22 can be better balanced and matched. In addition, this application does not require die-cutting multiple negative electrode tabs on the negative electrode sheet 22. On the one hand, this reduces the risk of excessive energy density loss in the secondary battery 100. On the other hand, the zebra coating method is not required when manufacturing the negative electrode sheet 22, nor is it necessary to reserve empty foil areas at the edges of the negative electrode current collector 220. Therefore, the risk of uneven stress caused by differences in electrode sheet thickness during the electrode sheet slitting process, which leads to wrinkling or breakage of the negative electrode sheet 22, is relatively small. Thus, the thickness of the negative electrode current collector 220 can be appropriately reduced, thereby improving the problem of reduced energy density in the secondary battery 100 caused by setting multiple positive electrode tabs 212 on the positive electrode sheet 21.
[0043] In some embodiments, the negative electrode 22 further includes a second negative electrode tab 223. The negative electrode active material layer 221 also includes a second groove 2211, and the second negative electrode tab 223 is disposed in the second groove 2211 and electrically connected to the negative electrode current collector 220. By adding the second negative electrode tab 223 and disposing of it in the second groove 2211, the second negative electrode tab 223 can also support a higher rate of charge and discharge current, thus facilitating a further balance in the dynamic performance of the positive electrode 21 and the negative electrode 22. The second negative electrode tab 223 can be welded and fixed to the negative electrode current collector 220, thereby improving the connection strength between the second negative electrode tab 223 and the negative electrode current collector 220. At this time, the positive electrode adapter tab 30, the first negative electrode tab 222, and the second negative electrode tab 223 extend out of the packaging bag from the same side and can be electrically connected to an external circuit.
[0044] In some embodiments, the first negative electrode tab 222, the second negative electrode tab 223, and a plurality of positive electrode tabs 212 are located on the same side of the electrode assembly 20 and arranged along a first direction X. In the first direction X, the plurality of positive electrode tabs 212 are located between the first negative electrode tab 222 and the second negative electrode tab 223. Correspondingly, in the first direction X, the positive electrode adapter tab 30 is located between the first negative electrode tab 222 and the second negative electrode tab 223. This arrangement facilitates connection to an external circuit and also provides sufficient space for the arrangement of the plurality of positive electrode tabs 212.
[0045] In some embodiments, the thickness H0 of the negative electrode current collector 220 is 5 μm to 10 μm. By reducing the thickness of the negative electrode current collector 220, the energy density of the secondary battery 100 can be increased while reducing the risk of wrinkling or breakage of the negative electrode sheet 22 during the electrode slitting process. This improves the problem of reduced energy density of the secondary battery 100 caused by the provision of multiple positive electrode tabs 212 on the positive electrode sheet 21. Moreover, it can also reduce the risk of over-soldering between the first negative electrode tab 222 or the second negative electrode tab 223 and the negative electrode current collector 220 when the thickness of the negative electrode current collector 220 is small.
[0046] In some embodiments, the coating weight w per unit area of the negative electrode active material layer 221 is 70 mg / 1540.25 mm. 2 Up to 160mg / 1540.25mm 2By setting the range of coating weight per unit area of the negative electrode active material layer 221, it is beneficial to further improve the energy density of the secondary battery 100 and improve the problem of reduced energy density of the secondary battery 100 caused by the setting of multiple positive electrode tabs 212 on the positive electrode sheet 21. In this application, the coating weight per unit area w can be measured in the following way: the secondary battery 100 is discharged to 0SOC%, the negative electrode sheet 22 is disassembled, cleaned with dimethyl carbonate (DMC) and dried; then, a negative electrode sheet 22 sample of a certain area S is punched out, and it is weighed using a balance, and the weight is recorded as W1; the negative electrode active material layer 221 of the sample is washed away with the solvent N-methylpyrrolidone (NMP), dried, and the weight of the negative electrode current collector 220 is recorded as W2; the coating weight per unit area is calculated by the following formula: w=(W1-W2) / S.
[0047] In some embodiments, the compaction density ρ of the negative electrode active material layer 221 is 1.65 g / cm³. 3 Up to 1.78 g / cm 3 By increasing the compaction density of the negative electrode active material layer 221, it is beneficial to further improve the energy density of the secondary battery 100 and alleviate the problem of reduced energy density of the secondary battery 100 caused by the multiple positive electrode tabs 212 on the positive electrode sheet 21. In this application, the compaction density ρ can be measured in the following way: the secondary battery 100 is discharged to 0SOC%, the negative electrode sheet 22 is disassembled, cleaned with dimethyl carbonate (DMC) and dried; then, a negative electrode sheet 22 sample of a certain area S is punched out, and it is weighed using a balance, and the weight is recorded as W1; the thickness of the sample is measured using a micrometer and recorded as d; the negative electrode active material layer 221 of the sample is washed away with the solvent N-methylpyrrolidone (NMP), dried, the weight of the negative electrode current collector 220 is weighed and recorded as W2, and the thickness of the negative electrode current collector 220 is measured using a micrometer and recorded as d2. Then, the compaction density ρ of the negative electrode active material layer 221 is calculated by the following formula: ρ=(W1-W2) / [(d-d2)×S].
[0048] In some embodiments, the thickness H3 of the polymer layer 2103 can be set to 2 μm to 13 μm, the thickness H1 of the first metal layer 2101 to 0.2 μm to 1.3 μm, and the thickness H2 of the second metal layer 2102 to 0.2 μm to 1.3 μm. By setting the thicknesses of the polymer layer 2103, the first metal layer 2101, and the second metal layer 2102, the positive current collector 210 can have a higher elongation, thereby giving the positive electrode 21 containing the positive current collector 210 higher elongation and further reducing the risk of breakage of the positive electrode 21 due to the volume expansion of the silicon material caused by the insertion of active ions. The thicknesses of the first metal layer 2101 and the second metal layer 2102 can be the same or different.
[0049] The secondary battery 100 of this application includes all devices capable of undergoing electrochemical reactions. Specifically, the secondary battery 100 includes all types of primary batteries, secondary batteries, fuel cells, solar cells, and capacitors (e.g., supercapacitors). Optionally, the secondary battery 100 can be a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, and lithium-ion polymer secondary batteries.
[0050] Please refer to Figure 6. One embodiment of this application also provides an electronic device 1, which includes a battery compartment 101 and a secondary battery 100 housed within the battery compartment 101. The electronic device 1 is powered by the secondary battery 100, and the secondary battery 100 achieves a good balance between fracture resistance, kinetic performance, and energy density. The secondary battery 100 of this application is applicable to electronic devices 1 in various fields. In one embodiment, the electronic device 1 of this application may be, but is not limited to, laptops, pen-based 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, household large-capacity batteries, and lithium-ion capacitors, etc.
[0051] The following uses a secondary battery 100 as an example of a lithium-ion pouch battery to illustrate the preparation method and performance of the secondary battery 100 provided in this application through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.
[0052] Example 1
[0053] (1) Preparation of positive electrode 21: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96.5:1.5:2. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly. A composite current collector (0.2 μm Al foil + 6 μm PET layer + 0.2 μm Al foil) was used as the positive electrode current collector 210. The slurry was uniformly coated on one surface of the composite current collector, leaving a blank foil area at the edge of the composite current collector. The mixture was dried at 110 °C. The above steps were repeated on the other surface of the composite current collector to obtain a double-coated positive electrode 21. The initial positive electrode 21 was cold-pressed to obtain a single coating layer 211 with a thickness of 77 μm. Then, the positive electrode 21 is pre-cut, and the reserved empty foil area is die-cut to obtain multiple positive electrode tabs 212, thus obtaining the positive electrode 21.
[0054] (2) Preparation of negative electrode sheet 22: Artificial graphite, silicon carbide, conductive carbon black (Super P), polyacrylic acid binder (PAA), and lithium difluorophosphate (LDPF) were mixed in a weight ratio of 69:5:6:19:1, with deionized water added as a solvent to prepare a slurry with a weight percentage of 55 wt%, and stirred evenly. Foaming adhesive was applied to the surface of the negative electrode current collector 220 (copper foil) with a thickness of 5 μm. The slurry was then uniformly coated onto one surface of the copper foil. Heating was performed to allow the foaming adhesive to detach, exposing a portion of the copper foil surface. The foil was then dried at 110°C. At this point, the exposed copper foil surface was located in the middle of the negative electrode active material along the length of the copper foil. The above coating steps were repeated on the other surface of the copper foil to obtain a double-coated negative electrode sheet 22. The initial negative electrode sheet 22 was rolled to obtain a negative electrode active material layer 221 with a coating thickness of 70 μm. Then, the first negative electrode tab 222 was welded onto the exposed copper foil. The negative electrode 22 is obtained.
[0055] (3) Preparation of electrolyte: In a dry argon atmosphere, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.
[0056] (4) Preparation of the isolation membrane 23: A polyethylene (PE) membrane with a thickness of 9 μm was selected.
[0057] (5) Assembly of the secondary battery 100: The positive electrode 21, the separator 23, and the negative electrode 22 are stacked and wound to obtain the electrode assembly 20. The positive electrode tab 212 is stacked and welded to the positive electrode adapter tab 30, which is made of copper. Then, the dented aluminum-plastic film (150 μm thick) is placed in the assembly fixture with the dent facing upward, and the electrode assembly 20 is placed in the dent. Electrolyte is injected into the dent of the aluminum-plastic film, and the positive electrode adapter tab 30 and the first negative electrode tab 222 are led out of the aluminum-plastic film. Then, formation and encapsulation are performed to obtain the secondary battery 100 shown in Figures 1 to 4.
[0058] Comparative Example 1
[0059] The difference from Example 1 lies in the preparation of the positive electrode and the assembly steps of the secondary battery, as follows:
[0060] Preparation of the positive electrode sheet: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96.5:1.5:2. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly. Using an aluminum foil of the same thickness as the composite current collector in Example 1 as the positive electrode current collector, foam adhesive was applied to the surface of the current collector. The slurry was then uniformly coated onto one surface of the current collector. Heating was performed to allow the foam adhesive to detach, exposing part of the aluminum foil surface. The foil was dried at 110°C. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. The initial positive electrode sheet was cold-pressed to obtain a single coating layer of positive active material with a thickness of 77 μm. Then, positive electrode tabs were welded onto the exposed aluminum foil. The positive electrode sheet was obtained.
[0061] Assembly of the secondary battery: The positive electrode, separator, and negative electrode are stacked and wound to obtain the electrode assembly. A 150μm thick aluminum-plastic film with a dented surface is placed in the assembly fixture with the dented surface facing upwards, and the electrode assembly is placed in the dent. Electrolyte is injected into the dent of the aluminum-plastic film, and the positive electrode tab and the first negative electrode tab are led out of the aluminum-plastic film. Then, formation and encapsulation are performed to obtain the secondary battery.
[0062] Comparative Example 2
[0063] The difference from Example 1 lies in the preparation of the positive electrode and the assembly steps of the secondary battery, as follows:
[0064] Preparation of the positive electrode sheet: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96.5:1.5:2. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly. A composite current collector (1 μm Al foil + 6 μm PET layer + 1 μm Al foil) was used as the positive electrode current collector. Foaming adhesive was applied to the surface of the composite current collector. The slurry was uniformly coated on one surface of the positive electrode current collector. Heating was performed to remove the foaming adhesive, exposing part of the aluminum foil surface. The mixture was dried at 110°C. The above steps were repeated on the other surface of the composite current collector to obtain a double-sided coated positive electrode sheet. The initial positive electrode sheet was cold-pressed to obtain a single coating layer with a thickness of 77 μm. Then, positive electrode tabs were welded onto the exposed aluminum foil. The positive electrode sheet was obtained.
[0065] Assembly of the secondary battery: The positive electrode, separator, and negative electrode are stacked and wound to obtain the electrode assembly. A 150μm thick aluminum-plastic film with a dented surface is placed in the assembly fixture with the dented surface facing upwards, and the electrode assembly is placed in the dent. Electrolyte is injected into the dent of the aluminum-plastic film, and the positive electrode tab and the first negative electrode tab are led out of the aluminum-plastic film. Then, formation and encapsulation are performed to obtain the secondary battery.
[0066] Comparative Example 3
[0067] The difference from Example 1 is that the negative electrode tab is welded to the empty foil area at the head of the negative electrode sheet.
[0068] The secondary batteries of each comparative example and embodiment were tested for positive electrode breakage rate, kinetic performance, and energy density. The kinetic performance was characterized by the impedance of the positive electrode and whether lithium plating occurred on the surface of the negative electrode after cycle testing. The test results are recorded in Table 1.
[0069] The test steps for the breakage rate of the positive electrode are as follows: 1) At a test temperature of 25℃, let the secondary battery stand for 5 minutes, charge it to 4.53V with a constant current of 1C, then charge it to 0.05C with a constant voltage, let it stand for 5 minutes, and then discharge it to 3.0V at 0.7C; 2) Repeat the above charge and discharge steps for 1000 cycles. After the cycle, disassemble the secondary battery and observe whether the positive electrode has broken. Repeat the test on 20 samples. The breakage rate is the number of secondary batteries with broken positive electrode divided by 20.
[0070] The steps for testing the impedance value of the positive electrode are as follows: 1) At a test temperature of 25℃, a copper wire is drawn out from the secondary battery, and after being plated with lithium, it is used as a reference electrode to obtain a three-electrode battery; 2) The reference electrode and the positive electrode are connected separately using an electrochemical workstation to test the impedance value of the positive electrode.
[0071] The lithium plating test procedure for the negative electrode is as follows: 1) At a test temperature of 25℃, let the secondary battery stand for 5 minutes, charge it at a constant current of 3C to 4.53V, and then charge it at a constant voltage of 4.53V to a current of 0.05C; 2) Disassemble the electrode assembly and check the surface of the negative electrode. If there is a gray area, it indicates lithium plating; if there is no gray area, there is no lithium plating. The degree of lithium plating is divided into slight lithium plating, moderate lithium plating, and severe lithium plating. Slight lithium plating is defined as a lithium plating area less than 0.5% of the entire negative electrode area; moderate lithium plating is defined as a lithium plating area of 0.5%-5% of the entire negative electrode area; and severe lithium plating is defined as a lithium plating area greater than 5% of the entire negative electrode area.
[0072] The energy density test steps for a secondary battery are as follows: 1) At a test temperature of 25℃, the secondary battery is left to stand for 5 minutes, discharged at a constant current of 0.2C to the termination voltage, left to stand for another 5 minutes, charged at a constant current of 0.2C to the limit voltage, and then charged under the limit voltage constant voltage condition until the current decreases to 0.02C. After standing for 5 minutes, it is discharged at a constant current of 0.2C to the termination voltage. The capacity of the secondary battery is recorded, and the energy D is obtained by multiplying the capacity by the plateau voltage; 2) The length, width, and thickness of the secondary battery are measured with an optical detector to calculate the volume T. The energy density (ED) = D / T, with the unit being Wh / L.
[0073] Table 1
[0074] As shown in Table 2, in Comparative Example 1, the negative electrode contained silicon-carbon material, leading to volume expansion of the negative electrode during cycling and subsequent breakage of the positive electrode. In Comparative Example 2, replacing the aluminum foil with a composite current collector with better elongation reduced the risk of positive electrode breakage; however, it also increased the impedance of the positive electrode, resulting in greater heat generation and a mismatch in the kinetic performance of the positive and negative electrodes. In Comparative Example 3, replacing the aluminum foil with a composite current collector with better elongation reduced the risk of positive electrode breakage; however, because the negative electrode tab was welded to the empty foil area at the head of the negative electrode, the kinetic performance of the negative electrode was lower, and lithium plating occurred on the negative electrode after cycling.
[0075] Compared to Comparative Examples 1-3, Example 1, while using a composite current collector to reduce the risk of positive electrode breakage, further includes multiple die-cut positive electrode tabs on the positive electrode to reduce the impact of the composite current collector on the impedance of the positive electrode. Simultaneously, the negative electrode tabs are located in the middle of the negative electrode active layer, ensuring kinetic performance matching between the positive and negative electrodes, resulting in no lithium deposition on the negative electrode after cycling. Furthermore, Example 1 does not also die-cut multiple negative electrode tabs on the negative electrode, reducing the risk of excessive energy density loss in the secondary battery. Therefore, the secondary battery achieves a better balance between resistance to positive electrode breakage, kinetic performance, and energy density.
[0076] Example 2-13
[0077] The difference from Example 1 is that the values of w, ρ, H0, etc. are specifically recorded in Table 2.
[0078] Examples 14-24
[0079] The difference from Example 3 is that the values of H1, H2, H3, etc. are specifically recorded in Table 2.
[0080] Table 2
[0081] As can be seen from the data in Table 2, compared with Examples 4-5, Examples 1-3 set the coating weight w per unit area of the negative electrode active material layer to a specific range, which not only further improved the energy density of the secondary battery, but also improved the problems of positive electrode breakage and negative electrode lithium plating when the coating weight w per unit area was high.
[0082] Compared to Examples 8-9, Examples 1 and 6-7 set the compaction density ρ of the negative electrode active material layer to a specific range, which not only further improved the energy density of the secondary battery, but also improved the problems of positive electrode breakage and negative electrode lithium deposition when the compaction density ρ is high.
[0083] Compared to Examples 12-13, Examples 1 and 10-11 set the thickness H0 of the negative electrode current collector to a specific range, which can further improve the energy density of the secondary battery without causing problems such as wrinkling or breakage of the negative electrode sheet during the electrode sheet slitting process. Moreover, compared to the smaller thickness H0 of the negative electrode current collector in Example 12, Examples 1 and 11-12 can reduce the risk of over-soldering between the first negative electrode tab and the negative electrode current collector.
[0084] Compared to Examples 18-19, Examples 3 and 14-17 set the polymer layer thickness H3 to a specific range, which further improved the elongation of the positive electrode sheet and improved the problem of positive electrode sheet breakage. Moreover, compared to the polymer layer thickness H3 of Example 19, which is larger, Examples 3 and 14-17 can improve the problem of large heat generation caused by large positive electrode sheet impedance.
[0085] Compared to Examples 23-24, Examples 3 and 20-22 set the thicknesses H1 and H2 of the first and second metal layers to a specific range, which further improved the elongation of the positive electrode sheet and improved the problem of positive electrode sheet breakage. Moreover, compared to the smaller thicknesses H1 and H2 of Example 23, Examples 3 and 20-22 can improve the problem of large heat generation caused by large positive electrode sheet impedance. Compared to the larger thicknesses H1 and H2 of Example 24, Examples 3 and 20-22 can improve the problem of lithium plating on the negative electrode sheet caused by small positive electrode sheet impedance.
[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application.
Claims
1. A secondary battery, comprising a housing and an electrode assembly disposed within the housing, the electrode assembly comprising a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode, wherein the negative electrode, the separator, and the positive electrode are stacked and wound together, wherein... The negative electrode sheet includes a negative current collector, a negative active material layer, and a first negative electrode tab; the negative current collector is a copper foil, the negative active material layer is disposed on the negative current collector, the negative active material layer contains a negative active material, and the negative active material contains silicon material; the negative active material layer has a first groove, and the first negative electrode tab is disposed in the first groove and electrically connected to the negative current collector; The positive electrode sheet includes a positive current collector, a positive active material layer, and multiple positive electrode tabs; the positive current collector includes a first metal layer, a polymer layer, and a second metal layer stacked together, and the positive active material layer is respectively disposed on the first metal layer and the second metal layer.
2. The secondary battery according to claim 1, wherein The thickness H0 of the negative electrode current collector is 5 μm to 10 μm.
3. The secondary battery according to claim 2, wherein The coating weight per unit area w of the negative electrode active material layer is 70 mg / 1540.25 mm 2 to 160 mg / 1540.25 mm 2 .
4. The secondary battery according to any one of claims 1 to 3, wherein The compacted density p of the negative electrode active material layer is 1.65 g / cm 3 to 1.78 g / cm 3 .
5. The secondary battery according to any one of claims 1 to 4, wherein The thickness H3 of the polymer layer is 2 μm to 13 μm, the thickness H1 of the first metal layer is 0.2 μm to 1.3 μm, and the thickness H2 of the second metal layer is 0.2 μm to 1.3 μm.
6. The secondary battery according to any one of claims 1 to 5, wherein The polymer layer is made of at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide.
7. The secondary battery according to any one of claims 1 to 6, wherein Both the first metal layer and the second metal layer comprise aluminum.
8. The secondary battery according to any one of claims 1 to 7, wherein The negative electrode sheet also includes a second negative electrode tab, and the negative electrode active material layer is further provided with a second groove. The second negative electrode tab is disposed in the second groove and is electrically connected to the negative electrode current collector.
9. The secondary battery according to claim 8, wherein The first negative electrode tab, the second negative electrode tab, and the plurality of positive electrode tabs are located on the same side of the electrode assembly and arranged along a first direction; in the first direction, the plurality of positive electrode tabs are located between the first negative electrode tab and the second negative electrode tab.
10. The secondary battery according to claim 9, wherein The secondary battery also includes a positive electrode adapter tab. The thickness direction of the electrode assembly is a second direction, which is perpendicular to the first direction. The projections of the plurality of positive electrode tabs in the second direction overlap and are connected to the positive electrode adapter tab. The housing is a packaging bag, and the first negative electrode tab, the second negative electrode tab, and the positive electrode adapter tab extend out of the packaging bag from the same side and are configured to be electrically connected to an external circuit, respectively.
11. The secondary battery according to any one of claims 1 to 10, wherein, The silicon material includes at least one of silicon oxide, silicon carbide, or elemental silicon.
12. An electronic device, wherein, It includes a battery compartment and a secondary battery as described in any one of claims 1 to 11 disposed within the battery compartment.