A secondary battery and an electronic device
By setting an inert layer on the surface of the positive electrode active material layer of a lithium-ion battery and controlling its thickness and silicon content, the lithium plating problem in a specific region of the overhang was solved, thereby improving the energy density and performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NINGDE AMPEREX TECHNOLOGY LTD
- Filing Date
- 2023-06-26
- Publication Date
- 2026-07-24
AI Technical Summary
Existing lithium-ion batteries are prone to lithium plating in specific overhang areas, which is difficult to avoid, especially under extreme conditions, affecting battery performance and energy density.
By setting an inert layer on the surface of the positive electrode active material layer, controlling the thickness of the positive electrode active material layer, the mass percentage of silicon element, and the coverage of the inert layer, the rate of lithium ion extraction can be reduced, thereby improving the lithium plating phenomenon in a specific region of the overhang.
It effectively reduces the rate of lithium ion extraction, improves lithium plating, and enhances the energy density and performance of secondary batteries.
Smart Images
Figure CN116632160B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology
[0002] With the widespread adoption of fast charging technology, people are placing increasingly higher demands on the charging speed of rechargeable batteries (such as lithium-ion batteries). Charging speed is closely related to the kinetics of lithium-ion batteries, requiring the battery's chemical system to support high-rate charging while preventing problems such as lithium plating at the positive and negative electrode interfaces. For lithium-ion batteries, the overhang region (hereinafter referred to as the kinetic weakness region) at the head (where the tabs extend) or tail (the end opposite the tab extension) of the negative electrode is the most prone to lithium plating. Therefore, improving the lithium plating phenomenon in the overhang region of lithium-ion batteries has become a pressing technical problem for those skilled in the art. Summary of the Invention
[0003] The purpose of this application is to provide a secondary battery and electronic device to improve lithium plating in a specific region of the overhang of a secondary battery.
[0004] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:
[0005] The first aspect of this application provides a secondary battery, including an electrode assembly. The electrode assembly includes a positive electrode and a negative electrode, which are stacked. The positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The thickness of the positive active material layer is D μm, and 30 ≤ D ≤ 200. The negative electrode includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector, with the positive and negative active material layers facing each other. In the width direction of the positive electrode, the negative electrode... The positive electrode active material layer includes two opposing first edges, and the positive electrode active material layer includes two opposing second edges, with the two second edges located between the two first edges. The width direction of the positive electrode sheet is perpendicular to the thickness direction of the electrode assembly. An inert layer is disposed on the surface of the positive electrode active material layer, the inert layer overlapping at least part of the second edges. Within a 15μm × 15μm region on the inert layer, the mass percentage content of silicon is B%, 0.1 ≤ B ≤ 6.0; and B and D satisfy: 0.15 ≤ BD / 100 ≤ 12.00. This application, by controlling the thickness D μm of the positive electrode active material layer, the mass percentage content of silicon B%, and the value of BD / 100 within the range of this application, reduces the rate of lithium ion extraction in the inert layer-covered area, thereby improving the lithium plating phenomenon in a specific region of the secondary battery. Furthermore, the secondary battery exhibits a high energy density.
[0006] In one embodiment of this application, 0.60 ≤ BD / 100 ≤ 4.00. Adjusting the value of BD / 100 within this range helps to reduce the rate of lithium ion extraction from the inert layer coverage area, thereby improving lithium plating in specific regions of the secondary battery overhang. Furthermore, the secondary battery exhibits a higher energy density.
[0007] In one embodiment of this application, the width of the inert layer along the width direction of the positive electrode sheet is E mm, where 1 ≤ E ≤ 20. Controlling the width of the inert layer within the above range is beneficial for improving lithium plating in specific regions of the secondary battery overhang.
[0008] In one embodiment of this application, 30≤D≤80, 15≤E≤18. Adjusting the values of D and E within these ranges helps to reduce the rate of lithium ion extraction, thereby improving lithium plating in specific regions of the secondary battery overhang.
[0009] In one embodiment of this application, 80 < D ≤ 100, and 0.03 < E / D < 0.15. Adjusting the values of D and E within these ranges helps to reduce the rate of lithium ion extraction, thereby improving lithium plating in specific regions of the secondary battery.
[0010] In one embodiment of this application, 100 < D ≤ 200, and 1 ≤ E ≤ 2.5. Adjusting the values of D and E within these ranges helps to reduce the rate of lithium ion extraction, thereby improving lithium plating in specific regions of the secondary battery overhang.
[0011] In one embodiment of this application, the inert layer comprises a linear fluorinated polysiloxane F(-SiF2-O-). n H, and n is 3 to 100. The inert layer includes the above-mentioned linear fluorinated polysiloxane, which can reduce the rate of lithium ion extraction in the inert layer-covered area, thereby improving the lithium plating phenomenon in a specific region of the secondary battery overhang.
[0012] In one embodiment of this application, the thickness of the inert layer is from 0.5 μm to 2.0 μm. Controlling the thickness of the inert layer within this range is beneficial for improving lithium plating in specific regions of the secondary battery overhang without affecting the energy density of the secondary battery.
[0013] In one embodiment of this application, the electrode assembly is a wound structure.
[0014] A second aspect of this application provides an electronic device comprising the secondary battery described in any of the foregoing embodiments. Therefore, the electronic device exhibits good performance.
[0015] The beneficial effects of this application are:
[0016] This application provides a secondary battery and an electronic device. In the secondary battery, by controlling the thickness Dμm of the positive electrode active material layer, the mass percentage of silicon B%, and the value of BD / 100 within the range specified in this application, the rate of lithium ion extraction in the inert layer covered region is reduced, thereby improving the lithium plating phenomenon in a specific region of the secondary battery. Furthermore, the secondary battery exhibits a high energy density.
[0017] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description
[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.
[0019] Figure 1 This is a partial schematic diagram of the cross-sectional structure of a secondary battery along its thickness direction in one embodiment of this application;
[0020] Figure 2 This is a schematic diagram of the structure of the positive electrode sheet in one embodiment of this application;
[0021] Figure 3 for Figure 2 Schematic diagram of the cross-sectional structure along the AA direction;
[0022] Figure 4 This is a schematic diagram showing the positional relationship between the positive and negative electrode plates in one embodiment of this application;
[0023] Figure 5 for Figure 4 Schematic diagram of the cross-sectional structure along the BB direction;
[0024] Figure 6 This is a schematic diagram of the inert layer thickness test;
[0025] Figure 7 This is a schematic diagram illustrating the degree of lithium deposition. Detailed Implementation
[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.
[0027] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.
[0028] In existing technologies, the overhang region at the head or tail of a lithium-ion battery is a kineticly weak area, making it highly susceptible to lithium plating. This is due to the edge effect; in secondary batteries, the delithiation rate at the edge of the positive electrode is faster than in the main body, often leading to lithium plating at the edge of the negative electrode, resulting in localized lithium plating in the overhang region. Current common methods aim to mitigate this risk by improving negative electrode kinetics, such as reducing coating weight and achieving a thinner negative electrode thickness to shorten the lithium-ion diffusion path and accelerate reaction kinetics, thereby preventing lithium plating. However, this often results in a loss of energy density. Furthermore, these methods do not fundamentally solve the problem; under extreme testing conditions, the risk of lithium plating in the overhang region still exists. For example, during low-temperature cycling, the lithium-ion conductivity of the electrolyte decreases, and the impedance of lithium ions intercalating and deintercalating from the positive electrode to the negative electrode increases significantly, with a greater increase in impedance during intercalation into the negative electrode, thus triggering lithium plating. Based on this, this application provides a secondary battery and an electronic device.
[0029] It should be noted that, in this application, the overhang specific region, i.e., the negative electrode super-positive electrode specific region, refers to, for example... Figure 1 As shown, the diaphragm 30 is located between the positive electrode 10 and the negative electrode 20. Figure 1 The area 40 marked with a dashed box is the overhang specific area. Specifically, the overhang specific area includes the region along the width direction of the secondary battery where the negative electrode 20 extends beyond the positive electrode 10, and a local area 21 of the negative electrode 20 extending Lmm from a position flush with the edge of the positive electrode 10 along its own center direction (only in...). Figure 1 An example of a negative electrode 20 is shown (for illustrative purposes only, and not as a limitation thereof), and L is from 0 to 10. Those skilled in the art will understand that the width direction of the negative electrode, positive electrode, and separator is the same as the width direction of the secondary battery.
[0030] like Figures 2 to 5 As shown, the first aspect of this application provides a secondary battery, including an electrode assembly comprising a positive electrode 10 and a negative electrode 20, which are stacked together. For ease of understanding, a three-dimensional Cartesian coordinate system is established with the length direction of the positive electrode 10 as the X-direction, the width direction of the positive electrode 10 as the Y-direction, and the thickness direction of the positive electrode 10 as the Z-direction. It is understood that the length direction, width direction, and thickness direction of the positive current collector 13, the positive active material layer 12, and the inert layer 11 are the same as those of the positive electrode 10. The length direction, width direction, and thickness direction of the negative electrode 20, the negative current collector 23, and the negative active material layer 22 are also the same as those of the positive electrode 10. The positive electrode 10 includes the positive current collector 13 and the positive active material layer 12 disposed on the surface of the positive current collector 13, the thickness of the positive active material layer 12 being D μm, where 30 ≤ D ≤ 200. The negative electrode 20 includes a negative electrode current collector 23 and a negative electrode active material layer 22 disposed on the surface of the negative electrode current collector 23. See also... Figure 4 and Figure 5The positive electrode active material layer 12 and the negative electrode active material layer 22 are disposed facing each other. In the width direction Y of the positive electrode sheet 10, the negative electrode active material layer 22 includes two opposing first edges 24, and the positive electrode active material layer 12 includes two opposing second edges 14. The two second edges 14 are located between the two first edges 24, and the first edges 24 of the negative electrode active material layer 22 extend beyond the second edges 14 of the positive electrode active material layer 12. Those skilled in the art should understand that this means one of the first edges 24 of the negative electrode active material layer 22 extends beyond one of the second edges 14 of the positive electrode active material layer 12 that is closer to it. The width direction of the positive electrode sheet 10 is perpendicular to the thickness direction of the electrode assembly (not shown). It should be noted that, in order to more clearly illustrate the positional relationship between the positive electrode active material layer 12 and the negative electrode active material layer 22, Figure 4 and Figure 5 The separator is not shown, but in a secondary battery, a separator is provided between the positive electrode 10 and the negative electrode 20; this application is not limited to this. An inert layer 11 is provided on the surface of the positive electrode active material layer 12, and the inert layer 11 overlaps with at least a portion of the second edge 14. The mass percentage content of silicon in a 15μm × 15μm region on the inert layer 11 is B%, 0.1 ≤ B ≤ 6.0; B and D satisfy: 0.15 ≤ BD / 100 ≤ 12.00. For example, the value of D is 30, 50, 70, 90, 110, 130, 150, 170, 190, 200, or any value between any two of the above ranges. The value of B is 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, or any value between any two of the above ranges. The value of BD / 100 is 0.15, 0.60, 1.00, 2.00, 3.00, 4.00, 5.00, 6.00, 7.00, 8.00, 9.00, 10.00, 11.00, 12.00 or any value between any two of the above ranges.
[0031] This application provides an inert layer 11 on the surface of the positive electrode active material layer 12, with the inert layer 11 overlapping at least part of the second edge, to reduce the rate of lithium ion extraction in the area covered by the inert layer 11. When the mass percentage of silicon in a 15μm × 15μm region on the inert layer 11 is less than 0.1%, the thickness of the inert layer 11 is too small to function effectively; when the mass percentage of silicon in a 15μm × 15μm region on the inert layer 11 is greater than 6.0%, the thickness of the inert layer 11 is too large, which will lead to an excessive difference in lithium insertion / extraction rates between the covered and uncovered areas of the inert layer 11, resulting in lithium plating at the boundary between the covered and uncovered areas of the inert layer 11. When the BD / 100 value is less than 0.15, the thickness of the positive electrode active material layer 12 is too small and / or the mass percentage of silicon is too small, resulting in an insufficient thickness of the inert layer 11 to perform its function and thus failing to improve the lithium deposition phenomenon of the negative electrode 20; or the content of positive electrode active material in the positive electrode 10 is too low, which will affect the energy density of the secondary battery. When the BD / 100 value is greater than 80, the thickness of the positive electrode active material layer 12 is too large and / or the mass percentage of silicon is too large, which will cause lithium deposition at the interface between the covered area and the uncovered area of the inert layer 11, affecting the energy density of the secondary battery. When the thickness of the positive electrode active material layer 12 is less than 30 μm, the thickness is too small, and the positive electrode 10 is excessively affected by the edge effect. This increases the edge region of the positive electrode 10, leading to a larger area of lithium plating on the negative electrode 20. Furthermore, the insufficient content of positive electrode active material in the positive electrode active material layer 12 affects the energy density of the secondary battery. When the thickness of the positive electrode active material layer 12 is greater than 200 μm, it results in energy density loss due to the increased volume of the secondary battery, also affecting its energy density. This application addresses this by controlling the thickness D μm of the positive electrode active material layer 12, the mass percentage of silicon B%, and the value of BD / 100 within the range specified in this application. This reduces the rate of lithium ion extraction in the inert layer 11 coverage area, thereby improving the lithium plating phenomenon in the specific region 40 of the secondary battery. Furthermore, the secondary battery exhibits a higher energy density.
[0032] The aforementioned "positive electrode active material layer disposed on the surface of the positive electrode current collector" refers to a positive electrode active material layer disposed on one surface of the positive electrode current collector, or a positive electrode active material layer disposed on both surfaces of the positive electrode current collector. Here, "surface" can be part or all of the surface of the positive electrode current collector. It can be understood that, along the width direction of the positive electrode sheet, the inert layer is disposed on both sides of the positive electrode active material layer. In some embodiments of this application, if the positive electrode active material layer is disposed on one surface of the positive electrode current collector, then the inert layer is disposed on one surface of the positive electrode current collector; in other embodiments of this application, if the positive electrode active material layer is disposed on both surfaces of the positive electrode current collector, then the inert layer is also disposed on both surfaces of the positive electrode current collector.
[0033] The aforementioned "negative electrode active material layer disposed on the surface of the negative electrode current collector" refers to a negative electrode active material layer disposed on one surface of the negative electrode current collector, or a negative electrode active material layer disposed on both surfaces of the negative electrode current collector. Here, "surface" can refer to part or all of the surface of the negative electrode current collector.
[0034] In one embodiment of this application, 0.60 ≤ BD / 100 ≤ 4.00. For example, the value of BD / 100 is 0.60, 1.00, 1.50, 2.00, 2.50, 3.00, 3.50, 4.00, or any value between any two of the above ranges. Adjusting the value of BD / 100 within the above range helps to reduce the rate of lithium ion extraction from the inert layer coverage area, thereby improving lithium plating in specific regions of the secondary battery overhang. Furthermore, the secondary battery exhibits a higher energy density.
[0035] In one embodiment of this application, such as Figure 1 and Figure 2 As shown, along the width direction Y of the positive electrode 10, the width of the inert layer 11 is E mm, where 1 ≤ E ≤ 20. For example, the value of E is 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, or any value within any two of the above ranges. By controlling the width of the inert layer within the above range, the rate of lithium delithiation in the inert layer coverage area and the rate of lithium insertion in the corresponding area of the negative electrode can be reduced, thereby improving the lithium plating phenomenon in specific areas of the secondary battery overhang.
[0036] In one embodiment of this application, 30 ≤ D ≤ 80, and 15 ≤ E ≤ 18. For example, the value of D is 30, 40, 50, 60, 70, 80, or any value between any two of the above ranges. The value of E is 15, 16, 17, 18, or any value between any two of the above ranges. By adjusting the values of D and E within the above ranges, a good matching effect is achieved between the thickness of the positive electrode active material layer and the width of the inert layer. While maintaining the capacity of the secondary battery, the rate of lithium ion extraction is reduced, thereby improving the lithium plating phenomenon in specific areas of the secondary battery overhang.
[0037] In one embodiment of this application, 80 < D ≤ 100, and 0.03 < E / D < 0.15. Further, in some embodiments, 2.4 < E < 15. For example, the value of D is 81, 100, 120, 140, 160, 180, 200, or any value between any two of the above ranges. The value of E / D is 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, or any value between any two of the above ranges. By adjusting the values of D and E within the above ranges, a good matching effect is achieved between the thickness of the positive electrode active material layer and the width of the inert layer. While maintaining the capacity of the secondary battery, the rate of lithium ion extraction is reduced, thereby improving the lithium plating phenomenon in specific areas of the secondary battery overhang.
[0038] In one embodiment of this application, 100 < D ≤ 200, and 1 ≤ E ≤ 2.5. For example, the value of D is 101, 120, 140, 160, 180, 200, or any value between any two of the above ranges. The value of E is 1, 1.5, 2, 2.5, or any value between any two of the above ranges. By adjusting the values of D and E within the above ranges, a good matching effect is achieved between the thickness of the positive electrode active material layer and the width of the inert layer. While taking into account the capacity of the secondary battery, the rate of lithium ion extraction is reduced, thereby improving the lithium plating phenomenon in specific areas of the secondary battery overhang.
[0039] In one embodiment of this application, the inert layer comprises a linear fluorinated polysiloxane F(-SiF2-O-). n H, and n is between 3 and 100. For example, the value of n is 3, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or any value between any two of the above ranges. The above-mentioned linear fluorinated polysiloxane has excellent chemical stability, thermal stability, and electrochemical inertness, and is not easily soluble in common electrolyte solvent systems. The inert layer including the above-mentioned linear fluorinated polysiloxane is a dense passivation layer, which can reduce the rate of lithium ion extraction in the inert layer covered area, thereby improving the lithium plating phenomenon in specific areas of the secondary battery overhang.
[0040] In one embodiment of this application, such as Figure 2 As shown, the thickness H1 of the inert layer 11 is from 0.5 μm to 2.0 μm. For example, the thickness H1 of the inert layer 11 can be 0.5 μm, 0.8 μm, 1.1 μm, 1.4 μm, 1.7 μm, 2.0 μm, or any value between any two of the above ranges. By controlling the thickness of the inert layer within the above range, without affecting the energy density of the secondary battery, the inert layer can achieve good coverage of the positive electrode active material layer, reduce the lithium ion extraction rate in the inert layer-covered area, and thus improve the lithium plating phenomenon in specific areas of the secondary battery overhang.
[0041] In one embodiment of this application, the electrode assembly is a stacked structure. In another embodiment of this application, the electrode assembly is a wound structure.
[0042] This application does not impose any particular limitation on the type of positive electrode current collector, as long as it can achieve the purpose of this application. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, etc. The positive electrode active material layer of this application includes a positive electrode active material. This application does not impose any particular limitation on the type of positive electrode active material, as long as it includes the transition metal element of this application and can achieve the purpose of this application. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1 At least one of the following: lithium nickel cobalt aluminum oxide (LiCO2), lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur, which can further improve the stability of the positive electrode active material. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application is achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the positive electrode active material layer is 30 μm to 120 μm.
[0043] Optionally, the positive electrode active material layer may further include a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the types of positive electrode conductive agents and positive electrode binders in the positive electrode active material layer, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the mass ratio of positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode active material layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. For example, the mass ratio of positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode active material layer is (95~98):(0.5~2.5):(1.5~3.4).
[0044] The present application does not particularly limit the method for preparing the positive electrode sheet, as long as the object of the present application can be achieved. For example, the preparation steps of the positive electrode sheet include but are not limited to the following steps: (1) Coating a positive electrode slurry on one surface of the positive electrode current collector, and after drying, forming a positive electrode sheet with a single-sided coated positive electrode active material layer; or, (1) Coating a positive electrode slurry on both surfaces of the positive electrode current collector, and after drying, forming a positive electrode sheet with a double-sided coated positive electrode active material layer; (2) After exposing the target area of the positive electrode sheet obtained in step (1) to a mixed atmosphere of an inert gas and SiF4 for 0.5 h to 1 h, a positive electrode sheet with inert layers provided on both surfaces of the positive electrode active material layer is obtained. Among them, the volume ratio of Ar to SiF4 in the mixed atmosphere is 1 to 10. The above "target area" refers to the area on the positive electrode sheet where an inert layer needs to be provided, and those skilled in the art can select according to actual needs, as long as the width of the inert layer is within the scope of the present application.
[0045] In the present application, there is no particular limitation on the method for regulating the mass percentage content B% of silicon element, as long as the object of the present application can be achieved. For example, the mass percentage content B% of silicon element can be regulated by regulating the volume ratio of SiF4 to Ar during the preparation process of the inert layer. Further, in some embodiments, the volume ratio of SiF4 to the inert gas is 1 to 10, and the mass percentage content B% of silicon element in an area with a size of 15 μm × 15 μm on the inert layer is 0.1% to 6.0%.
[0046] The present application does not particularly limit the type of the above-mentioned inert gas, as long as the object of the present application can be achieved. For example, the inert gas includes but is not limited to Ar or He.
[0047] In an embodiment of the present application, the secondary battery further includes a negative electrode sheet. The present application does not particularly limit the negative electrode sheet, as long as the object of the present application can be achieved. For example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The present application does not particularly limit the negative electrode current collector, as long as the object of the present application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam or copper foam, etc. The negative electrode active material layer of the present application includes a negative electrode active material. The present application does not particularly limit the type of the negative electrode active material, as long as the object of the present application can be achieved. For example, the negative electrode active material can include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12The negative electrode active material layer contains at least one of the following: Li-Al alloy or metallic lithium. In this application, there are no particular limitations on the thickness of the negative electrode current collector or the negative electrode active material layer, as long as the purpose of this application is achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode active material layer is 30 μm to 130 μm. Optionally, the negative electrode active material layer may further include at least one of a conductive agent, a thickener, and a binder. This application does not particularly limit the types of negative electrode conductive agents, thickeners, and negative electrode binders in the negative electrode active material layer, as long as the purpose of this application is achieved. This application does not particularly limit the mass ratio of the negative electrode active material, negative electrode conductive agent, negative electrode binder, and thickener in the negative electrode active material layer, as long as the purpose of this application is achieved. For example, the mass ratio of the negative electrode active material, negative electrode conductive agent, negative electrode binder, and thickener in the negative electrode active material layer is (83.5~98.0):(0.5~10.0):(0.1~5.0):(1.0~1.9).
[0048] In one embodiment of this application, the secondary battery further includes a separator disposed between the positive electrode and the negative electrode to separate them. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The separator type may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.
[0049] In one embodiment of this application, the secondary battery further includes a packaging bag and an electrolyte. This application does not impose any particular limitation on the packaging bag and electrolyte; they can be any packaging bag and electrolyte known in the art, as long as they achieve the purpose of this application.
[0050] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. For example, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), sodium-ion secondary batteries (sodium-ion batteries), lithium polymer secondary batteries, and lithium-ion polymer secondary batteries.
[0051] This application does not impose any particular limitation on the preparation method of the secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery.
[0052] A second aspect of this application provides an electronic device comprising the secondary battery described in any of the foregoing embodiments. Therefore, the electronic device exhibits good performance.
[0053] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.
[0054] Example
[0055] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.
[0056] Test methods and equipment:
[0057] Test for silicon content B:
[0058] After disassembling the lithium-ion batteries of each embodiment and comparative example under fully discharged conditions, the positive electrode sheets were cleaned three times with dimethyl carbonate (DMC), dried, and then elemental analysis was performed using an X-ray energy dispersive spectroscopy (EDS) instrument.
[0059] The mass percentage of silicon in any region with a size of 15μm×15μm on the inert layer is denoted as B.
[0060] Testing the width E of the inert layer:
[0061] A noticeable color difference will appear on the surface of the positive electrode sheet with an inert layer. Use a ruler to select the position with the maximum width along the width direction of the positive electrode sheet in the dark area and measure it. Record this as the width of the inert layer, E.
[0062] Testing of inert layer thickness H1:
[0063] After disassembling the lithium-ion batteries of each embodiment and comparative example under full discharge, the disassembled positive electrode sheet was cleaned three times using DMC. After drying, it was first subjected to ion polishing to obtain the cross-section of the positive electrode sheet. See [link to documentation]. Figure 6 The test diagram shows the results of testing using EDS. Figure 6 Line scan testing was performed on the cross-section of the positive electrode shown in (a). From Figure 6 By determining the peak intervals of the F and Si signals in (b) and (c) respectively, the thickness of the inert layer can be obtained. Specifically: Figure 6 In (b) and (c), the horizontal axis represents the slicing distance of the positive electrode sheet, with the start and end points corresponding to... Figure 6 The distance of the horizontal coordinate covered by line segment O in (a) is used to determine that F signal and Si signal appear at this position.
[0064] Testing the thickness D of the positive electrode active material layer:
[0065] After discharging the lithium-ion batteries of each embodiment and comparative example to 3.0V, they were disassembled. The positive electrode sheet was cleaned twice with DMC and dried. The thickness of the positive electrode sheet was measured with a micrometer and recorded as thickness T1. Then, the positive active material layer and inert layer were cleaned with N-methylpyrrolidone (NMP) and the thickness of the positive current collector was measured and recorded as thickness T2.
[0066] The thickness of the positive electrode active material layer is D = (T1 - T2) / 2.
[0067] Determining the lithium plating situation:
[0068] Different lithium plating detection charging methods are used depending on the thickness D of the positive electrode active material layer:
[0069] The thickness D of the positive electrode active material layer satisfies: D < 70 μm, and the voltage can be charged to the design upper limit voltage at 5C.
[0070] The thickness D of the positive electrode active material layer satisfies: 70μm≤D<100μm, and the voltage is charged to the design upper limit voltage at 4C.
[0071] The thickness D of the positive electrode active material layer satisfies: 100μm≤D<115μm, 3C charging to the design upper limit voltage;
[0072] The thickness D of the positive electrode active material layer satisfies: 115μm≤D<130μm, 2C direct charge to the design upper limit voltage;
[0073] The thickness D of the positive electrode active material layer satisfies: 130μm≤D<150μm, allowing for direct charging to the design upper limit voltage at 1C.
[0074] The thickness D of the positive electrode active material layer satisfies: D≥150μm, 0.5C direct charge to the design upper limit voltage;
[0075] After fully discharging the lithium-ion batteries in each embodiment and comparative example, they were charged at different rates (refer to the charging method selection logic described above). After charging, the lithium-ion batteries were disassembled to obtain the disassembly interface. The degree of lithium plating in the lithium-ion batteries was as follows: Figure 7 As shown, the degree of lithium plating is: severe lithium plating > lithium plating > slight lithium plating > no lithium plating.
[0076] Example 1
[0077] <Preparation of the positive electrode>
[0078] The positive electrode active material is lithium cobalt oxide (LiCoO2), the positive electrode conductive agent is conductive carbon black (SP), and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight-average molecular weight of 7×10⁻⁶). 6 The materials were mixed at a mass ratio of 96:2:2, with NMP added as a solvent, and stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% was obtained. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil current collector and dried at 90°C to obtain a positive electrode sheet with a single-sided coating of the positive active material layer. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive active material layer. After cold pressing, cutting, and welding of tabs, a positive electrode sheet with dimensions of 74 mm × 851 mm was obtained for use. The thickness of the positive active material layer, D μm, was 190 μm.
[0079] In an environment with a water content of <100ppm, the target area of the positive electrode sheet was exposed to a mixed atmosphere of Ar and SiF4 (volume ratio of Ar to SiF4 = 1). After 1 hour, a positive electrode sheet with an inert layer (width Emm = 6mm, thickness 0.8μm) formed on both sides of the positive electrode active material layer was obtained. The inert layer comprises F(-SiF2-O-). n H and n is 4 to 50.
[0080] <Preparation of Negative Electrode Sheets>
[0081] The negative electrode active material is artificial graphite, the negative electrode conductive agent is SP, and the negative electrode binder is polyacrylic acid (weight average molecular weight is 8×10). 6 Thickener sodium carboxymethyl cellulose (weight average molecular weight 1×10⁻⁶) 7Mix the components in a mass ratio of 83.5:10.0:5.0:1.5, then add deionized water as a solvent, and stir under vacuum until a uniform negative electrode slurry with a solid content of 75wt% is obtained.
[0082] Polyacrylic acid (weight average molecular weight of 8,000,000) and SP were mixed at a mass ratio of 50:50. Then, deionized water was added as a solvent, and the mixture was stirred under vacuum until a base coating slurry with a solid content of 75 wt% and a uniform system was obtained.
[0083] First, a base coating slurry is applied to one surface of a 12μm thick copper foil used as the negative electrode current collector. This is then dried at 120℃ to obtain a negative electrode sheet with a single-sided base coating (30μm thick). The above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided base coating. Next, a negative electrode slurry is applied to one surface of the copper foil with the base coating and dried at 120℃ to obtain a negative electrode sheet with a single-sided negative electrode active material layer (130μm thick). This process is repeated on the other surface of the copper foil with the base coating to obtain a negative electrode sheet with a double-sided negative electrode active material layer. After cold pressing, cutting, and welding of tabs, a negative electrode sheet with dimensions of 76mm × 867mm is obtained for later use.
[0084] <Septum>
[0085] A 4μm thick polyethylene-based membrane (manufacturer: Zhuogao New Materials Technology Co., Ltd.) was used as the separator.
[0086] <Preparation of Electrolyte>
[0087] In a dry argon atmosphere, non-aqueous organic solvents ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) were mixed in a mass ratio of 1:1:1. Then, lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvents, dissolved, and mixed evenly to obtain an electrolyte, wherein the concentration of LiPF6 was 1.15 mol / L.
[0088] <Preparation of Lithium-ion Batteries>
[0089] The negative electrode sheet, separator, and positive electrode sheet prepared above are stacked and wound in sequence to obtain a wound electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, capacity testing, degassing, and edge trimming, a lithium-ion battery is obtained.
[0090] Examples 2 to 15
[0091] Except for adjusting the relevant parameters according to Table 1, everything else is the same as in Example 1.
[0092] Comparative Examples 1 to 4
[0093] Except for adjusting the relevant parameters according to Table 1, everything else is the same as in Example 1.
[0094] Comparative Example 5
[0095] Except for the absence of an inert layer in the positive electrode, it is the same as in Example 3.
[0096] The preparation and performance parameters of each embodiment and comparative example are shown in Table 1.
[0097] Table 1
[0098]
[0099]
[0100] Note: In Table 1, "\" indicates that there is no corresponding parameter.
[0101] As can be seen from Examples 1 to 15 and Comparative Examples 1 to 5, the secondary batteries in these examples have an inert layer on the surface of the positive electrode active material layer, and the thickness D μm of the positive electrode active material layer, the mass percentage of silicon B%, and the value of BD / 100 are controlled within the range of this application. The degree of lithium plating in the overhang specific region is relatively mild, indicating that the lithium plating phenomenon in the overhang specific region of the secondary battery is improved. However, the secondary batteries in Comparative Examples 1, 2, and 5 do not have an inert layer on the surface of the positive electrode active material layer, or at least one of the mass percentage of silicon B% or the value of BD / 100 in the secondary battery is outside the range of this application, resulting in a more severe degree of lithium plating in the overhang specific region. Although the secondary battery in Comparative Example 3 does not plating lithium, its positive electrode active material layer is too thin, the coating weight of the positive electrode active material layer is too thin, and the energy density of the secondary battery is too low, which does not meet the normal performance requirements of a secondary battery and is therefore outside the scope of this application. In Comparative Example 4, the secondary battery was unable to form a secondary battery because the thickness of the positive electrode active material layer was too thick. During the cold pressing process of the positive electrode sheet, light transmission occurred, and during the winding process, there was a break in the process and powder shedding.
[0102] When the thickness of the positive electrode active material layer changes, the width of the inert layer also typically affects the degree of lithium plating in a specific area of the overhang of the secondary battery. Examples 11 to 15 show that secondary batteries with a positive electrode active material layer thickness and an inert layer width satisfying 30 ≤ D ≤ 80 and 15 ≤ E ≤ 18 exhibit improved lithium plating in the overhang area. Examples 2 to 4 show that secondary batteries with a positive electrode active material layer thickness and an inert layer width satisfying 80 < D ≤ 100 and 0.03 < E / D < 0.15 exhibit improved lithium plating in the overhang area. Examples 6 to 10 show that secondary batteries with a positive electrode active material layer thickness and an inert layer width satisfying 100 < D ≤ 200 and 1 ≤ E ≤ 3 exhibit improved lithium plating in the overhang area. In Example 8, E = 3 mm, resulting in a large area of the inert layer covering the positive electrode active material layer; therefore, a "roofing effect" type of lithium plating occurs, i.e., lithium plating at the edge of the inert layer.
[0103] The thickness of the inert layer also typically affects the degree of lithium plating in specific regions of the overhang of a secondary battery. As can be seen from Examples 1 to 5, the degree of lithium plating in specific regions of the overhang of secondary batteries with selected inert layer thicknesses within the scope of this application is improved.
[0104] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0105] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.
[0106] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.
Claims
1. A secondary battery, comprising an electrode assembly, the electrode assembly comprising a positive electrode and a negative electrode, the positive electrode and the negative electrode being stacked; The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector, wherein the thickness of the positive active material layer is D μm, and 30≤D≤200; The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector, with the positive active material layer facing the negative active material layer; in the width direction of the positive electrode sheet, the negative active material layer includes two opposing first edges and two opposing second edges, the two second edges being located between the two first edges; the width direction of the positive electrode sheet is perpendicular to the thickness direction of the electrode assembly; An inert layer is disposed on the surface of the positive electrode active material layer, and the inert layer overlaps with at least part of the second edge; the positive electrode sheet of the secondary battery in a fully discharged state is cleaned with dimethyl carbonate three times, dried, and then subjected to elemental analysis by X-ray energy dispersive spectroscopy. The mass percentage content of silicon element in a region with a size of 15μm×15μm on the inert layer is B%, 0.1≤B≤6.0; The relationship between B and D satisfies: 0.15 ≤ BD / 100 ≤ 12.00; The positive electrode sheet of the secondary battery discharged to 3.0V was cleaned twice with dimethyl carbonate. After drying, the thickness T1 of the positive electrode sheet was measured. Then, the positive active material layer and the inert layer were cleaned with N-methylpyrrolidone. The thickness T2 of the positive current collector was measured. The thickness D of the positive active material layer is D=(T1-T2) / 2. The inert layer comprises linear fluorinated polysiloxane F(-SiF2-O-). n H, and n is between 3 and 100.
2. The secondary battery according to claim 1, wherein, 0.60≤BD / 100≤4.
00.
3. The secondary battery according to claim 1, wherein, Along the width direction of the positive electrode sheet, the width of the inert layer is E mm, where 1 ≤ E ≤ 20.
4. The secondary battery according to claim 3, wherein, 30≤D≤80, 15≤E≤18.
5. The secondary battery according to claim 3, wherein, 80<D≤100, 0.03<E / D<0.
15.
6. The secondary battery according to claim 3, wherein, 100<D≤200,1≤E≤2.5。 7. The secondary battery according to claim 1, wherein, The thickness of the inert layer is from 0.5 μm to 2.0 μm; The positive electrode of the secondary battery in a fully discharged state was cleaned three times with dimethyl carbonate and dried to obtain the cross-section of the positive electrode. The cross-section of the positive electrode was then subjected to line scan testing using an X-ray energy dispersive spectroscopy (EDS) instrument. The thickness of the inert layer was determined based on the peak ranges of the F and Si signals.
8. The secondary battery according to claim 1, wherein, The electrode assembly has a wound structure.
9. An electronic device, wherein, The electronic device includes a secondary battery as described in any one of claims 1 to 8.