Positive electrode current collector, electrochemical device and electronic device

Abstract

This application provides a positive electrode current collector, an electrochemical device, and an electronic device. The positive electrode current collector is an aluminum foil and includes silicon, with the silicon content in the current collector being m% by mass (0.03 ≤ m ≤ 0.13). The silicon includes 0-valent and +4-valent silicon, with the 0-valent silicon content in the current collector being n% by mass (50 ≤ n ≤ 100). Applying the positive electrode current collector to the electrochemical device can reduce the risk of failure during charge-discharge cycles.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a positive current collector, an electrochemical device, and an electronic device. Background Technology

[0002] Most existing secondary batteries (such as lithium-ion batteries) have exposed positive electrode current collectors (usually aluminum foil), such as wound structures with the positive electrode current collector ending, wound structures with die-cut aluminum tabs, or stacked structures with the positive electrode ending on one side. As the voltage of lithium-ion batteries continues to increase, the oxidation capacity of the positive electrode sheet to the electrolyte during full charging also increases. To reduce the oxidation of the electrolyte by the positive electrode sheet, existing technologies often improve the protection of both the positive and negative electrode sheets under high voltage by continuously increasing the content of fluorine compounds in the electrolyte.

[0003] However, fluorinated compounds, such as fluorinated additives and fluorinated lithium salts, are prone to undergoing a defluorination reaction under the influence of Lewis acids (such as PF5) produced by electrolyte decomposition, generating HF. In this situation, after the lithium-ion battery is filled with electrolyte, the electrolyte comes into contact with the exposed positive electrode current collector. The HF in the electrolyte and the positive electrode current collector easily react to generate impurities. These impurities diffuse within the lithium-ion battery along with the electrolyte and accumulate in specific areas of the positive electrode (e.g., at the edge of the positive active material layer on one side of the positive electrode current collector), causing abnormalities in the positive electrode and leading to battery failure during charge-discharge cycles. Therefore, how to reduce the risk of lithium-ion battery failure during charge-discharge cycles has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode current collector, an electrochemical device, and an electronic device to reduce the risk of failure of the electrochemical device during charge-discharge cycles.

[0005] It should be noted that while this application uses lithium-ion batteries as an example of an electrochemical device to explain the invention, the electrochemical device is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0006] The first aspect of this application provides a positive electrode current collector, which is an aluminum foil and includes silicon. The mass percentage of silicon in the positive electrode current collector is m%, 0.03≤m≤0.13. The silicon includes 0-valent silicon and +4-valent silicon, and the mass percentage of 0-valent silicon in the silicon is n%, 50≤n≤100, preferably 70≤n≤100. By controlling the mass percentage m% of silicon in the positive electrode current collector and the mass percentage n% of 0-valent silicon in the silicon within the above range, it is possible to reduce manufacturing abnormalities of the positive electrode current collector. While ensuring that the strength and toughness of the positive electrode current collector meet the requirements of its manufacturing process, the reactivity between silicon in the positive electrode current collector and HF in the electrolyte is reduced, thus reducing the content of the byproduct fluorosilicone compound. This reduces the risk of abnormalities in the positive electrode, thereby reducing the risk of failure of the electrochemical device during charge-discharge cycles.

[0007] In one embodiment of this application, the positive electrode current collector further includes an alkaline earth metal, which includes at least one of beryllium, magnesium, or calcium. The mass percentage of the alkaline earth metal in the positive electrode current collector is a%, 0.01 ≤ a ≤ 0.50. By selecting the above-mentioned alkaline earth metals and controlling the mass percentage of the alkaline earth metals in the positive electrode current collector within the above range, the risk of abnormality of the positive electrode sheet is reduced, thereby reducing the risk of failure of the electrochemical device during charge-discharge cycles.

[0008] In one embodiment of this application, 5 ≤ m(100-n) / a ≤ 70. By controlling the value of m(100-n) / a within the above range, the risk of abnormality of the positive electrode is further reduced, and the risk of failure of the electrochemical device during charge-discharge cycles is further reduced.

[0009] The second aspect of this application provides an electrochemical device including an electrode assembly and an electrolyte. The electrolyte includes a fluorine-containing compound. The electrode assembly includes a positive electrode, a negative electrode, and a membrane disposed between the positive and negative electrode. The positive electrode includes a positive current collector provided in the first aspect of this application and a positive active material layer disposed on the positive current collector.

[0010] In one embodiment of this application, the fluorinated compound includes a fluorinated additive, and the fluorinated additive has a mass percentage of b% in the electrolyte, where 0.1 ≤ b ≤ 40.0%. When the electrolyte includes a fluorinated compound, by selecting the positive electrode current collector provided in the first aspect of this application, the protective capability of the electrolyte for the negative electrode sheet can be enhanced, forming a uniform and dense protective film on the surface of the negative electrode sheet, thereby improving the cycle performance of the electrochemical device; simultaneously, it reduces the content of fluorosilicone compounds, byproducts generated from the reaction of HF in the electrolyte and silicon in the positive electrode current collector. This reduces the risk of abnormalities in the positive electrode sheet, thereby reducing the risk of failure of the electrochemical device during charge-discharge cycles.

[0011] In one embodiment of this application, the fluorinated additive includes at least one of fluoroethylene carbonate, bis(fluoromethyl)ethylene carbonate, bis(difluoromethyl)ethylene carbonate, bis(trifluoromethyl)ethylene carbonate, bis(2-fluoroethyl)ethylene carbonate, bis(2,2-difluoroethyl)ethylene carbonate, bis(2,2,2-trifluoroethyl)ethylene carbonate, 2-fluoroethylmethylethylene carbonate, 2,2-difluoroethylmethylethylene carbonate, or 2,2,2-trifluoroethylmethylethylene carbonate. Using the above-mentioned types of fluorinated additives is more effective in reducing the oxidizing power of the positive electrode sheet on the electrolyte, forming a uniform and dense protective film on the surfaces of both the positive and negative electrode sheets, thus protecting them.

[0012] In one embodiment of this application, m(100-n)b / 100 ≤ 80. By adjusting the value of m(100-n)b / 100 within the above range, the mass percentage of silicon in the positive electrode current collector and the mass percentage of fluorine-containing additives in the electrolyte are matched, resulting in a synergistic effect, which is more conducive to reducing the risk of failure of the electrochemical device during charge-discharge cycles.

[0013] In one embodiment of this application, the fluorinated compound further includes a fluorinated lithium salt, which includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(trifluoromethane)sulfonylimide, lithium bisfluorosulfonylimide, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium perfluorobutylsulfonate, lithium bissulfonylimide, or lithium fluoride. The addition of the fluorinated lithium salt further facilitates the provision of high ionic conductivity, resulting in a faster lithium-ion transport rate.

[0014] In one embodiment of this application, the positive electrode current collector includes opposing first and second surfaces. The positive electrode current collector includes a single-sided region. The first surface of the single-sided region is provided with a positive electrode active material layer, while the second surface of the single-sided region is not provided with a positive electrode active material layer. The single-sided region includes a first portion, and the second surface of the first portion is located on the outer surface of the electrode assembly. This reduces the likelihood of direct contact between the negative electrode current collector (e.g., copper foil) and the packaging bag, thus reducing the risk of corrosion from contact between the copper foil and the aluminum foil in the packaging bag, thereby improving the encapsulation performance and safety of the electrochemical device. Simultaneously, the first portion being a single-sided region, located at the end of the electrode assembly, can save on the amount of positive electrode active material used, reducing the production cost of the electrochemical device.

[0015] In one embodiment of this application, the electrochemical device further includes a packaging bag containing electrode components and electrolyte, with the second surface of the first portion in contact with the packaging bag.

[0016] In one embodiment of this application, the electrode assembly has a stacked structure; or, the electrode assembly has a wound structure, and the positive current collector further includes a double-sided region, with the double-sided region and the single-sided region connected sequentially along the winding direction.

[0017] A third aspect of this application provides an electronic device that includes the electrochemical device provided in the second aspect of this application. Therefore, the beneficial effects of the electrochemical device provided in the second aspect of this application can be obtained.

[0018] 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

[0019] 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.

[0020] Figure 1 This is a schematic diagram of the electrode assembly structure of some embodiments of this application;

[0021] Figure 2 for Figure 1 A schematic diagram of the cross-sectional structure of the positive electrode sheet in the electrode assembly in its unfolded state along its own thickness direction;

[0022] Figure 3 This is a schematic diagram of the electrode assembly structure of some embodiments of this application;

[0023] Figure 4 for Figure 3A schematic diagram of the cross-sectional structure of the positive electrode sheet in the electrode assembly in its unfolded state along its own thickness direction;

[0024] Figure 5 This is a schematic diagram of the structure of the positive electrode sheet in some embodiments of this application. Detailed Implementation

[0025] 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. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0027] Electrochemical devices (such as lithium-ion batteries) typically have exposed positive electrode current collectors. Current technologies often use aluminum foil with a silicon content of 0.06% to 0.18% by mass, with most silicon existing as silicon dioxide or silicates. As the voltage of electrochemical devices increases, the oxidation of the electrolyte by the positive electrode at full charge also increases. To reduce this oxidation, current technologies often increase the content of fluorine compounds in the electrolyte to improve protection of both the positive and negative electrodes at high voltages.

[0028] However, fluorinated compounds, such as fluorinated additives and fluorinated lithium salts, undergo a de-fluorination reaction under the action of Lewis acids (such as PF5) produced by electrolyte decomposition, generating HF. In this case, after the electrochemical device is filled with electrolyte, the electrolyte comes into contact with the bare aluminum foil. The HF in the electrolyte may react with components in the aluminum foil, such as silicon dioxide or silicates, to generate byproduct fluorosilicone compounds. These byproduct fluorosilicone compounds diffuse inside the electrochemical device and accumulate in specific areas of the positive electrode (e.g., at the edge of the positive active material layer on one side of the positive electrode current collector), causing abnormalities in the positive electrode (e.g., significant color difference in local areas due to increased silicon content). The abnormal areas of the positive electrode cannot properly delithiate, and lithium ions escape from the edges of these abnormal areas, resulting in insufficient lithium intercalation sites on the corresponding negative electrode, leading to lithium plating and ultimately causing the electrochemical device to fail during charge-discharge cycles. To solve the problem of electrochemical device failure during charge-discharge cycles, this application provides a positive electrode current collector, an electrochemical device, and an electronic device.

[0029] The first aspect of this application provides a positive electrode current collector, which is an aluminum foil and includes silicon. The mass percentage of silicon in the positive electrode current collector is m%, where 0.03 ≤ m ≤ 0.13. Preferably, 0.06 ≤ m ≤ 0.13. The silicon includes 0-valent silicon and +4-valent silicon, where the mass percentage of 0-valent silicon is n%, where 50 ≤ n ≤ 100. Preferably, 70 ≤ n ≤ 100. More preferably, 65 ≤ n ≤ 85.

[0030] For example, the value of m is 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, or any value between any two of the above ranges. The value of n is 50, 60, 65, 70, 80, 85, 90, 100, or any value between any two of the above ranges. When the mass percentage of silicon in the positive electrode current collector is too low (m value less than 0.03), the aluminum foil has insufficient strength and poor wear resistance, increasing the risk of cold-pressing breakage during positive electrode preparation. Conversely, when the mass percentage of silicon in the positive electrode current collector is too high (m value greater than 0.13), the current collector has excessive strength, leading to poor ductility and increasing the risk of breakage during subsequent winding processes (such as winding the current collector, winding the positive electrode sheet, and winding during electrode assembly preparation). Simultaneously, the conductivity of the current collector deteriorates. Furthermore, +4 valent silicon readily reacts with HF in the electrolyte to generate fluorosilicon compounds as a byproduct. If the mass percentage of 0-valent silicon in the silicon element is too low (n = less than 50), and the mass percentage of +4-valent silicon is too high, the reactivity between silicon in the positive electrode current collector and HF in the electrolyte will be too high, generating a large amount of byproduct fluorosilicon compounds. This will cause abnormalities in the positive electrode, preventing proper lithium delithiation in the abnormal areas. Lithium ions will escape from the edges of the abnormal areas, resulting in insufficient lithium insertion sites on the corresponding negative electrode. This leads to the failure of the electrochemical device in the later stages of charge-discharge cycles due to lithium plating. By controlling both the mass percentage m% of silicon in the positive electrode current collector and the mass percentage n% of 0-valent silicon within the aforementioned range, the manufacturing abnormalities of the positive electrode current collector (such as cold-pressing fracture and winding fracture) can be reduced. This ensures that the strength and toughness of the positive electrode current collector meet the requirements of its manufacturing process, while reducing the reactivity between silicon in the positive electrode current collector and HF in the electrolyte, thus reducing the content of byproduct fluorosilicon compounds. This reduces the risk of abnormalities in the positive electrode, thereby reducing the risk of failure of the electrochemical device during charge-discharge cycles.

[0031] By controlling the mass percentage m% of silicon in the positive electrode current collector within the aforementioned preferred range, the fabrication anomalies of the positive electrode current collector can be further reduced, making its strength and toughness better meet the requirements of its fabrication process, and also providing better conductivity. By controlling the mass percentage n% of 0-valent silicon in the silicon element within the aforementioned preferred range, while ensuring the strength of the positive electrode current collector meets the requirements of its fabrication process, the content of fluorosilicone compounds, a byproduct formed by the reaction of HF in the electrolyte with silicon in the positive electrode current collector, is further reduced. This reduces the risk of anomalies in the positive electrode sheet, thereby further reducing the risk of failure of the electrochemical device during charge-discharge cycles.

[0032] This application does not specifically limit the type of aluminum foil; it can be any aluminum foil known in the art, as long as it can achieve the purpose of this application.

[0033] This application does not impose any particular restrictions on the method for controlling the mass percentage of silicon in the positive electrode current collector, or the mass percentage of 0-valent silicon and +4-valent silicon, as long as the purpose of this application can be achieved. For example, it can be achieved by adjusting the types of raw materials used to prepare the positive electrode current collector and the proportions of each raw material.

[0034] In one embodiment of this application, the positive electrode current collector further includes an alkaline earth metal, which includes at least one of beryllium, magnesium, or calcium. The mass percentage of the alkaline earth metal in the positive electrode current collector is a%, 0.01 ≤ a ≤ 0.50. For example, the value of a is 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, or any value between any two of the above ranges. The aforementioned alkaline earth metals have strong reducing properties and can reduce the +4 valent silicon element in the positive electrode current collector to 0 valent silicon element, further increasing the mass percentage of 0 valent silicon element in silicon. At the same time, the alkaline earth metal and the 0 valent silicon element in the positive electrode current collector combine to form a stable alloy phase M2Si (M represents alkaline earth metal). By controlling the mass percentage of alkaline earth metals in the positive electrode current collector within the aforementioned range, the reactivity between silicon in the current collector and HF in the electrolyte can be reduced, thus decreasing the content of the byproduct fluorosilicon compounds. This reduces the risk of abnormalities in the positive electrode, thereby lowering the risk of failure of the electrochemical device during charge-discharge cycles.

[0035] This application does not impose any particular limitation on the method for controlling the mass percentage of alkaline earth metals in the cathode current collector, as long as the purpose of this application can be achieved. For example, it can be achieved by adjusting the types of raw materials used to prepare the cathode current collector, adding substances containing alkaline earth metals to the raw materials, and adjusting the ratio of each raw material. Specifically, if it is necessary to add alkaline earth metal beryllium, it can be achieved by adding elemental beryllium metal; if it is necessary to add alkaline earth metal magnesium, it can be achieved by adding elemental magnesium metal; and if it is necessary to add alkaline earth metal calcium, it can be achieved by adding elemental calcium metal.

[0036] In one embodiment of this application, 5 ≤ m(100-n) / a ≤ 70. The value of m(100-n) / a is 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, or any value between any two of the above ranges. By controlling the value of m(100-n) / a within the above range, the strength and toughness of the positive electrode current collector meet the requirements of its preparation process, resulting in a good yield. The content of alkaline earth metals and +4 valent silicon is matched, enabling more +4 valent silicon to be reduced to 0 valent silicon, thus reducing the content of +4 valent silicon and increasing the content of 0 valent silicon in silicon. The alkaline earth metals and 0 valent silicon in the positive electrode current collector combine to form more stable alloy phase M2Si, further reducing the reactivity between silicon in the positive electrode current collector and HF in the electrolyte, and reducing the content of the byproduct fluorosilicon compounds produced by the reaction. As a result, the risk of abnormality in the positive electrode is further reduced, and the risk of failure of the electrochemical device during charge-discharge cycles is further reduced.

[0037] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be from 8 μm to 20 μm.

[0038] This application does not impose any particular restrictions on the preparation method of the positive electrode current collector. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, a preparation method including the following steps can be adopted: (1) Select appropriate raw materials according to the content of each element in the positive electrode current collector of any of the above embodiments, and obtain ingots by melting and casting; (2) Sawing, milling, annealing, hot rolling, cold rough rolling, and cold finish rolling of the ingots to obtain strip billets; (3) Rolling the strip billets obtained above to obtain a positive electrode current collector of the required thickness.

[0039] This application does not impose any particular restrictions on the production processes of smelting, casting, sawing, milling, annealing, hot rolling, cold roughing, cold finishing, and strip billet rolling. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0040] A second aspect of this application provides an electrochemical device comprising an electrode assembly and an electrolyte. The electrolyte includes a fluorinated compound. The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The positive electrode includes a positive current collector provided in the first aspect of this application and a positive active material layer disposed on the positive current collector. When the electrolyte includes a fluorinated compound, by selecting the positive current collector provided in the first aspect of this application, the protective capability of the electrolyte for the negative electrode can be enhanced, forming a uniform and dense protective film on the surface of the negative electrode, thereby improving the cycle performance of the electrochemical device. Simultaneously, it reduces the content of fluorine-silicon compounds, byproducts generated from the reaction of HF in the electrolyte and silicon in the positive current collector. This reduces the risk of abnormalities in the positive electrode, thereby reducing the risk of failure of the electrochemical device during charge-discharge cycles.

[0041] In one embodiment of this application, the electrochemical device further includes an electrolyte comprising a fluorinated additive, wherein the mass percentage of the fluorinated additive in the electrolyte is b%, and 0.1 ≤ b ≤ 40.0. For example, the value of b is 0.1, 2.0, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, 40.0, or any value between any two of the above ranges. By controlling the mass percentage of fluorinated additives in the electrochemical device within the aforementioned range, when the electrochemical device is fully charged under a high voltage (e.g., 4.35V to 4.6V) system, the electrolyte's protective ability for the negative electrode is enhanced, and a uniform and dense protective film is more easily formed on the surface of the negative electrode. Simultaneously, the fluorinated additives undergo a defluorination reaction under the action of Lewis acids (e.g., PF5) produced by the decomposition of the electrolyte, resulting in a lower content of HF. This reduces the risk of fluorinated silicon compounds, a byproduct of the reaction between HF and silicon in the positive electrode current collector, diffusing within the electrochemical device and accumulating in specific areas of the positive electrode. Consequently, the likelihood of abnormalities in the positive electrode is reduced, thus further mitigating the risk of failure of the electrochemical device during charge-discharge cycles.

[0042] This application does not impose any particular limitation on the compaction density of the positive and negative electrode sheets after cold pressing, as long as the purpose of this application can be achieved. For example, the compaction density of the positive and negative electrode sheets after cold pressing is 3.9 g / cm³. 3 Up to 4.3 g / cm 3 .

[0043] In one embodiment of this application, the fluorinated additive includes at least one of fluoroethylene carbonate (FEC), bis(fluoromethyl)ethylene carbonate (DFEC), bis(difluoromethyl)ethylene carbonate, bis(trifluoromethyl)ethylene carbonate, bis(2-fluoroethyl)ethylene carbonate, bis(2,2-difluoroethyl)ethylene carbonate, bis(2,2,2-trifluoroethyl)ethylene carbonate, 2-fluoroethylmethylethylene carbonate, 2,2-difluoroethylmethylethylene carbonate, or 2,2,2-trifluoroethylmethylethylene carbonate. Using the above-mentioned types of fluorinated additives is more effective in reducing the oxidizing power of the positive electrode sheet on the electrolyte, forming a uniform and dense protective film on the surfaces of both the positive and negative electrode sheets, thus protecting them.

[0044] In one embodiment of this application, m(100-n)b ≤ 80. Preferably, 1.6 ≤ m(100-n)b ≤ 48. The value of mb / 100 is 0.01, 0.24, 1.00, 1.6, 5, 10, 15, 16, 20, 24, 28, 32, 38, 42, 48, 56, 64, 68, 72, 78, 80, or any value between any two of the above ranges. By adjusting the value of mb / 100 within the above range, the mass percentage of silicon in the positive electrode current collector and the mass percentage of fluorine-containing additives in the electrolyte are matched, resulting in a synergistic effect, which is more conducive to reducing the risk of failure of the electrochemical device during charge-discharge cycles.

[0045] In one embodiment of this application, the electrolyte further includes a fluorinated lithium salt, including lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2), lithium bis(trifluoromethane)sulfonylimide (LiTFSI), lithium bis(fluorosulfonylimide) (LiTSI), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiBF2(C2O4), LiDFOB), lithium hexafluoroantimonyate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium perfluorobutyl sulfonate (LiC4F9SO3), and lithium bis(sulfonylimide) (LiN(CxF) 2x+ 1SO2)(CyF 2y+1 The lithium salt comprises at least one of SO2, where x and y are positive integers and x≤10, y≤10, or lithium fluoride (LiF). The addition of a fluorinated lithium salt further enhances the provision of high ionic conductivity, resulting in faster lithium-ion transport. Preferably, the fluorinated lithium salt comprises at least one of LiPF6, LiTFSI, or LiTSI, which further reduces the production cost of the electrochemical device.

[0046] This application does not impose any particular limitation on the mass percentage of fluorinated lithium salt in the electrolyte, as long as the purpose of this application is achieved. For example, the mass percentage of fluorinated lithium salt in the electrolyte can be 8% to 20%.

[0047] In one embodiment of this application, the positive electrode current collector includes opposing first and second surfaces. The positive electrode current collector includes a single-sided region. The first surface of the single-sided region is provided with a positive electrode active material layer, and the second surface of the single-sided region is not provided with a positive electrode active material layer. The single-sided region includes a first portion, and the second surface of the first portion is located on the outer surface of the electrode assembly. It can be understood that the single-sided region is a segment of the positive electrode current collector; therefore, the first surface of the single-sided region is the first surface of the positive electrode current collector, and the second surface of the single-sided region is the second surface of the positive electrode current collector. The first portion is a segment of the single-sided region, which is also a segment of the positive electrode current collector; therefore, the first surface of the first portion is the first surface of the positive electrode current collector, and the second surface of the first portion is the second surface of the positive electrode current collector. The second surface of the first portion is located on the outer surface of the electrode assembly, thus concluding the electrode assembly with a positive electrode sheet. This reduces the possibility of direct contact between the negative electrode current collector (such as copper foil) and the packaging bag, reducing the risk of corrosion from contact between the copper foil and the aluminum foil in the packaging bag, thereby improving the encapsulation performance and safety of the electrochemical device. Meanwhile, the first part is a single-sided area, which is set in the end area of ​​the electrode assembly. This can save the amount of positive electrode active material layer and reduce the production cost of the electrochemical device.

[0048] Exemplary examples, in some embodiments of this application, such as Figures 1 to 4 As shown, the electrode assembly 001 has a wound structure, with the winding direction indicated by W. The electrode assembly 001 includes a positive electrode 100, a negative electrode 200, and a separator 300 disposed between the positive electrode 100 and the negative electrode 200. The positive electrode 100 includes a positive current collector 10 and a positive active material layer 20 disposed on the positive current collector 10. The positive current collector 10 includes opposing first surfaces 10a and second surfaces 10b, and includes a single-sided region 30. The first surface 10a of the single-sided region 30 is provided with the positive active material layer 20, while the second surface 10b of the single-sided region 30 is not provided with the positive active material layer 20. The single-sided region 30 includes a first portion 301, and the second surface 10b of the first portion 301 is located on the outer surface of the electrode assembly 001. Figure 1 and Figure 2 As shown, the positive current collector 10 also includes a double-sided region 40, a first double-sided empty foil region 61 and a second double-sided empty foil region 62. The portion of the single-sided region 30 other than the first portion 301 is not located on the outer surface of the electrode assembly 001. Figure 3 The positive current collector in the electrode assembly shown does not include the second double-sided empty foil region 62, which includes a double-sided region 40, a single-sided region 30, and a first double-sided empty foil region 61, as shown. Figure 3 and Figure 4As shown, the first part 301 can be understood as a single-sided area 30, and the second surface 10b of the first part 301 can also be understood as the second surface 10b of the single-sided area 30, that is, the second surface 10b of the single-sided area 30 is located on the outer surface of the electrode assembly 001.

[0049] Exemplary, in some embodiments of this application, the electrode assembly has a stacked structure, consisting of a positive electrode, a negative electrode, and a separator between the positive and negative electrode layers. The two outermost layers of the electrode assembly along its thickness direction are both single-sided positive electrode sheets. Specifically, as shown... Figure 5 As shown, a single-sided positive electrode includes a positive current collector 10, which includes a first surface 10a and a second surface 10b. The positive current collector 10 includes a single-sided region 30. The first surface 10a of the single-sided region 30 is provided with a positive active material layer 20, while the second surface 10b of the single-sided region 30 is not provided with the positive active material layer 20. The single-sided region 30 includes a first portion 301, and the second surface 10b of the first portion 301 is located on the outer surface of the electrode assembly 001. The first portion 301 can be understood as the single-sided region 30, and the second surface 10b of the first portion 301 can also be understood as the second surface 10b of the single-sided region 30, meaning the second surface 10b of the single-sided region 30 is located on the outer surface of the electrode assembly. Typically, a positive electrode not located on the outer surface of the electrode assembly is a double-sided positive electrode. A double-sided positive electrode includes a positive current collector, which includes a first surface and a second surface, both of which are provided with a positive active material layer.

[0050] In one embodiment of this application, the electrochemical device further includes a packaging bag containing the electrode assembly and the electrolyte, with the second surface of the first portion in contact with the packaging bag. In this application, "in contact" can mean that the second surface of the first portion is in direct contact with the inner side of the packaging bag near the electrode assembly, or that a separator, such as adhesive tape or a diaphragm, is provided between the second surface of the first portion and the inner side of the packaging bag near the electrode assembly.

[0051] In one embodiment of this application, the electrode assembly has a stacked structure. In another embodiment of this application, the electrode assembly has a wound structure, such as... Figure 1 and Figure 2 As shown, the positive electrode current collector 10 also includes a double-sided region 40, which is connected to the single-sided region 30 in sequence along the winding direction W. A positive electrode active material layer 20 is disposed on both the first surface 10a and the second surface 10b of the double-sided region 40.

[0052] 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 achieves the purpose of this application. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (e.g., common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also include non-metallic elements, such as fluorine, phosphorus, boron, chlorine, silicon, sulfur, etc., which can further improve the stability of the positive electrode active material. Optionally, the positive electrode active material layer also includes a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders in the positive electrode active material layer, as long as they achieve the purpose of this application. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode 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, conductive agent and binder in the positive electrode active material layer is (97.5~97.9):(0.9~1.7):(1.0~2.0).

[0053] This application does not impose any particular limitation on the thickness of the positive electrode active material layer, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode active material layer can be from 30 μm to 120 μm.

[0054] The negative electrode sheet of this application includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The aforementioned "negative electrode active material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or only a part of it; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the negative electrode current collector, as long as the purpose of this application is achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam, or copper foam, etc. The negative electrode active material layer includes a negative electrode active material. This application has no particular limitation on the type of negative electrode active material, as long as the purpose of this application is achieved. For example, the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, tin-based materials, silicon-based materials, lithium titanate, transition metal nitrides, or natural flake graphite. Optionally, the negative electrode active material layer may also include at least one of a conductive agent, a stabilizer, and a binder. This application does not impose any particular limitation on the types of conductive agents, stabilizers, and binders in the negative 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 the negative electrode active material, conductive agent, stabilizer, and binder 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, conductive agent, stabilizer, and binder in the negative electrode active material layer may be (97–98):(0.5–1.5):(0.5–1.5):(1.0–1.9).

[0055] This application does not impose any particular limitations on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector can be 5 μm to 20 μm, and the thickness of the negative electrode active material layer can be 30 μm to 120 μm.

[0056] The electrolyte of this application also includes non-aqueous solvents. This application does not have any particular limitation on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, the non-aqueous solvent may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate.

[0057] This application does not impose any particular limitation on the mass percentage of non-aqueous solvents in the electrolyte, as long as the purpose of this application can be achieved. For example, the mass percentage of non-aqueous solvents in the electrolyte can be between 70% and 99%.

[0058] This application does not impose any particular restrictions on the diaphragm and packaging bag; they can be any diaphragm and packaging bag known in the art, as long as they can achieve the purpose of this application.

[0059] The electrochemical device described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device may include, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries, sodium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0060] This application does not impose any particular restrictions on the preparation method of the electrochemical device; any preparation method known in the art can be used, as long as it can achieve the purpose of this application.

[0061] A third aspect of this application provides an electronic device that includes the electrochemical device provided in the second aspect of this application. Therefore, the beneficial effects of the electrochemical device provided in the second aspect of this application can be obtained.

[0062] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, 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, large household batteries, lithium-ion capacitors, etc.

[0063] Example

[0064] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0065] Test methods and equipment:

[0066] Detection of different element contents:

[0067] After fully discharging the lithium-ion batteries of each embodiment and comparative example, disassemble them, wash away the positive electrode active material layer on the surface of the positive electrode current collector with N-methylpyrrolidone, and finally clean the positive electrode current collector with DMC; after cleaning, perform inductively coupled plasma spectroscopy (ICP) on the positive electrode current collector to obtain the content of aluminum, silicon and alkaline earth metals.

[0068] Detection of +4 valent silicon and 0 valent silicon:

[0069] The lithium-ion batteries from each embodiment and comparative example were fully discharged and disassembled. The positive electrode active material layer on the surface of the positive electrode current collector was washed away with N-methylpyrrolidone, and finally the positive electrode current collector was cleaned with DMC. After cleaning, X-ray photoelectron spectroscopy (XPS) was performed on the positive electrode current collector. The peaks at ~99eV / 102eV corresponded to Si elements in the 0 / +4 valence states, respectively, and the integral areas of the two peaks were S1 and S2, respectively. Wherein, n(%) = S1 / (S1+S2)×100. Here, n is the mass percentage of 0-valent silicon in the silicon element, and (100-n) is the mass percentage of +4-valent silicon in the silicon element.

[0070] Detection of abnormalities in the positive electrode:

[0071] After fully discharging and disassembling the lithium-ion batteries of each embodiment and comparative example, the positive electrode was visually inspected. An abnormal appearance (also called an abnormal area) was observed, where a localized area showed a significant color difference from its surrounding area. X-ray energy dispersive spectroscopy (EDS) was performed on the positive electrode in the abnormal area. If the silicon content in the abnormal area was >2 wt%, the positive electrode was considered to have an abnormal appearance. If no abnormal appearance of discolored markings was observed on the positive electrode, it was considered that the positive electrode did not have an abnormal appearance, and EDS testing was not performed on the positive electrode.

[0072] An abnormal appearance of the positive electrode and a silicon content >2wt% in the abnormal area are used to characterize the failure of the electrochemical device during charge-discharge cycles.

[0073] Determining whether there are any abnormalities in the manufacturing of the positive electrode:

[0074] In the <Preparation of Positive Electrode> of each embodiment or comparative example, during the cold pressing process of the positive electrode, it is determined whether the positive current collector breaks or the electrode band breaks.

[0075] Example 1

[0076] <Preparation of Positive Electrode Current Collector>

[0077] The positive electrode current collector is made of aluminum foil with a thickness of 10 μm. The mass percentage of silicon in the positive electrode current collector is m% = 0.08%, the mass percentage of 0-valent silicon is n% = 2%, and the mass percentage of +4-valent silicon is W%. Si +4 (%) = 98%.

[0078] <Preparation of the positive electrode>

[0079] The positive electrode active material LiCoO2, conductive agent conductive carbon black, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was then uniformly coated onto a substrate such as… Figure 4 The positive electrode current collector 10 is applied to the first surface 10a of the double-sided region 40 and the single-sided region 30, and then dried at 120°C for 1 hour. The above steps are repeated on the second surface 10b of the double-sided region of the positive electrode current collector 10 to obtain the desired result. Figure 2 The positive electrode sheet shown is dried at 120°C for 1 hour, then cold-pressed, slit, and cut to obtain a positive electrode sheet with dimensions of 78mm × 875mm. Specifically, the double-sided region 40 has dimensions of 78mm × 780mm, the single-sided region 30 has dimensions of 78mm × 80mm, and the first double-sided empty foil region 61 has dimensions of 78mm × 15mm. The thickness of the positive electrode active material layer is 12μm.

[0080] <Preparation of Negative Electrode Sheets>

[0081] Graphite (anode active material), styrene-butadiene rubber (binder), and sodium carboxymethyl cellulose (thickener) were mixed in a mass ratio of 97.4:1.4:1.2. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a cathode slurry with a solid content of 75 wt%. The cathode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector, and then dried at 120 °C for 1 hour to obtain a cathode with a single-sided coating of 130 μm thick and a cathode active material layer. The above steps were repeated on the other surface of the cathode current collector to obtain a cathode sheet with a double-sided coating of cathode active material. After drying at 120 °C for 1 hour, the cathode sheet was cold-pressed, slit, and cut to size to obtain a cathode sheet with dimensions of 74 mm × 867 mm.

[0082] <Preparation of Electrolyte>

[0083] In an argon-atmospheric glove box with a water content of <10 ppm, EC, PC, and DEC were mixed in a mass ratio of 1:1:1 to obtain an organic solvent. Then, a fluorinated lithium salt, LiPF6, was added to the organic solvent to obtain a basic electrolyte. A fluorinated additive, FEC, was then added to the basic electrolyte to obtain the final electrolyte. The mass percentage of the fluorinated lithium salt, LiPF6, in the electrolyte was 13.8%, and the mass percentage of the fluorinated additive, FEC, was b% = 20%.

[0084] <Preparation of the separating membrane>

[0085] A porous polyethylene film with a thickness of 7μm is used.

[0086] <Preparation of Lithium-ion Batteries>

[0087] The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode to provide separation. The electrodes are then wound to obtain the desired shape. Figure 3 The electrode assembly with the spiral wound structure shown is then placed in an aluminum-plastic film packaging bag, dried, and injected with electrolyte. After vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0088] Examples 2 to 6

[0089] Except for adjusting the raw material feeding ratio in the positive electrode current collector to make n% as shown in Table 1, the rest is the same as in Example 1.

[0090] Examples 7 to 8

[0091] Except for adjusting the raw material feeding ratio in the positive electrode current collector to make m% as shown in Table 1, the rest is the same as in Example 3.

[0092] Examples 9 to 23

[0093] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0094] Comparative Examples 1 to 3

[0095] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0096] The relevant preparation parameters and performance tests for each embodiment and comparative example are shown in Table 1.

[0097] Table 1

[0098]

[0099]

[0100] Note: "\" in Table 1 indicates that there are no corresponding preparation parameters; "-" in Table 1 indicates that there are no abnormalities in the positive electrode and there is no need to test the Si content.

[0101] As can be seen from Examples 1 to 23 and Comparative Examples 1 to 3, when a positive electrode current collector with a silicon content of m% and a silicon content of n% within the scope of this application is selected, the probability of abnormal appearance of the positive electrode sheet is reduced, the Si content in the abnormal area of ​​the positive electrode sheet is less than 2wt%, and the risk of abnormal positive electrode sheet fabrication is reduced, indicating that the risk of failure of lithium-ion battery during charge-discharge cycle is reduced.

[0102] As can be seen from Examples 1 to 8 and Comparative Examples 1 to 3, Examples 1 to 8 used positive electrode current collectors with a silicon content of m% and an 0-valent silicon content of n% within the scope of this application. This reduced the probability of abnormal appearance of the positive electrode sheet, and the Si content in the abnormal area of ​​the positive electrode sheet was less than 2 wt%, thus reducing the risk of abnormal positive electrode sheet fabrication. This indicates that the risk of lithium-ion battery failure during charge-discharge cycles was reduced. However, in Comparative Examples 1 to 3, positive electrode current collectors with an 0-valent silicon content outside the scope of this application were used. This resulted in abnormal appearance of the positive electrode sheet, and the Si content in the abnormal area of ​​the positive electrode sheet was greater than 2 wt%, indicating that the risk of lithium-ion battery failure during charge-discharge cycles was not reduced.

[0103] The type of alkaline earth metal and its mass percentage in the positive electrode current collector typically affect the probability of lithium-ion battery failure during charge-discharge cycles. As can be seen from Examples 1, 9 to 17, by selecting the type of alkaline earth metal and the mass percentage of alkaline earth metal in the positive electrode current collector within the scope of this application, the probability of abnormal appearance of the positive electrode sheet is reduced, the Si content in the abnormal area of ​​the positive electrode sheet is less than 2wt%, and the risk of abnormal positive electrode sheet fabrication is reduced, indicating that the risk of lithium-ion battery failure during charge-discharge cycles is reduced.

[0104] The mass percentage (b%) of fluorinated additives in the electrolyte also typically affects the probability of lithium-ion battery failure during charge-discharge cycles. As can be seen from Examples 3, 18 to 21, when lithium-ion batteries with a mass percentage (b%) of fluorinated additives in the electrolyte within the scope of this application are used, the fluorinated compound and the positive electrode current collector work together to reduce the probability of abnormal appearance of the positive electrode, and the Si content in the abnormal areas of the positive electrode is less than 2 wt%. This reduces the risk of abnormal positive electrode fabrication, indicating that the risk of lithium-ion battery failure during charge-discharge cycles is reduced.

[0105] The type of fluorinated additives also typically affects the probability of lithium-ion battery failure during charge-discharge cycles. As can be seen from Examples 1 and 22, when the type of fluorinated additive used is within the scope of this application for the positive electrode current collector, the probability of abnormal appearance of the positive electrode sheet is reduced, the Si content in the abnormal area of ​​the positive electrode sheet is less than 2wt%, and the risk of abnormal positive electrode sheet fabrication is reduced, indicating that the risk of lithium-ion battery failure during charge-discharge cycles is reduced.

[0106] The type of fluorinated lithium salt also typically affects the probability of lithium-ion battery failure during charge-discharge cycles. As can be seen from Examples 1 and 23, when the type of fluorinated lithium salt used is selected as the positive electrode current collector within the scope of this application, the probability of abnormal appearance of the positive electrode sheet is reduced, the Si content in the abnormal area of ​​the positive electrode sheet is less than 2wt%, and the risk of abnormal positive electrode sheet fabrication is reduced, indicating that the risk of lithium-ion battery failure during charge-discharge cycles is reduced.

[0107] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity from another, and do not necessarily require or imply any such actual relationship or order between these entities. Furthermore, 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.

[0108] 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.

[0109] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A positive electrode current collector, which is an aluminum foil and includes silicon, wherein the mass percentage of silicon in the positive electrode current collector is m%, and 0.03≤m≤0.13; The silicon element includes 0-valent silicon and +4-valent silicon, and the mass percentage of 0-valent silicon in the silicon element is n%, 50≤n<100.

2. The positive electrode current collector according to claim 1, wherein 70≤n＜100。 3. The positive current collector according to claim 1, wherein, The positive electrode current collector also includes an alkaline earth metal, which includes at least one of beryllium, magnesium, or calcium. The mass percentage of the alkaline earth metal in the positive electrode current collector is a%, where 0.01 ≤ a ≤ 0.

50.

4. The positive current collector according to claim 3, wherein, 5≤m(100-n) / a≤70.

5. An electrochemical device comprising an electrode assembly and an electrolyte, the electrolyte comprising a fluorine-containing compound, the electrode assembly comprising a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, the positive electrode comprising a positive current collector as described in any one of claims 1 to 4 and a positive active material layer disposed on the positive current collector.

6. The electrochemical device according to claim 5, wherein, The fluorinated compound includes a fluorinated additive, and the fluorinated additive has a mass percentage of b% in the electrolyte, where 0.1 ≤ b ≤ 40.0%.

7. The electrochemical device according to claim 6, wherein, The fluorinated additive includes at least one of fluoroethylene carbonate, bis(fluoromethyl)ethylene carbonate, bis(difluoromethyl)ethylene carbonate, bis(trifluoromethyl)ethylene carbonate, bis(2-fluoroethyl)ethylene carbonate, bis(2,2-difluoroethyl)ethylene carbonate, bis(2,2,2-trifluoroethyl)ethylene carbonate, 2-fluoroethylmethylethylene carbonate, 2,2-difluoroethylmethylethylene carbonate, or 2,2,2-trifluoroethylmethylethylene carbonate.

8. The electrochemical device according to claim 6, wherein, m(100-n)b≤80.

9. The electrochemical device according to claim 5, wherein, The fluorinated compound further includes a fluorinated lithium salt, which includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(trifluoromethane)sulfonylimide, lithium bis(fluorosulfonylimide), lithium tetrafluoroborate, lithium difluorooxalate borate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium perfluorobutyl sulfonate, lithium bis(sulfonylimide), or lithium fluoride.

10. The electrochemical device according to claim 5, wherein, The positive current collector includes a first surface and a second surface opposite to each other. The positive current collector includes a single-sided region. The first surface of the single-sided region is provided with the positive active material layer. The second surface of the single-sided region is not provided with the positive active material layer. The single-sided region includes a first portion. The second surface of the first portion is located on the outer surface of the electrode assembly.

11. The electrochemical device according to claim 10, wherein, The electrochemical device further includes a packaging bag containing the electrode assembly and the electrolyte, wherein the second surface of the first portion is in contact with the packaging bag.

12. The electrochemical device according to claim 10, wherein, The electrode assembly has a stacked structure; or... The electrode assembly has a wound structure, and the positive current collector further includes a double-sided region. Along the winding direction, the double-sided region and the single-sided region are connected in sequence.

13. An electronic device comprising the electrochemical device according to any one of claims 5 to 12.

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