Battery cell and preparation method therefor, secondary battery and electric device

Abstract

The present application belongs to the technical field of secondary batteries. Provided are a battery cell and a preparation method therefor, a secondary battery and an electric device. The battery cell comprises a positive electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least part of the surface of the positive electrode current collector. The positive electrode film layer contains a positive electrode active material and a dopant. The dopant contains a first doping element and a second doping element, wherein the first doping element comprises at least one of boron or aluminum, and the second doping element comprises at least one of phosphorus, silicon or fluorine. Any region having a size of 1 μm×1 μm in a longitudinal cross-section of the positive electrode film layer contains the dopant. The dopant is uniformly dispersed in the positive electrode film layer, such that the cycle performance and safety performance of the battery can be synchronously improved.

Description

Battery cells and their preparation methods, secondary batteries and electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese patent application CN202510365554.X, filed on March 26, 2025, entitled “Battery cell and method of preparation thereof, secondary battery and power device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of secondary battery technology, and more specifically, to a battery cell and its preparation method, a secondary battery, and an electrical device. Background Technology

[0004] In recent years, with the development of secondary batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace. At the same time, higher requirements have been put forward for the cycle performance and safety performance of secondary batteries.

[0005] To simultaneously improve the safety and cycle performance of secondary batteries, common strategies include electrolyte modification, separator modification, and cathode coating or doping modification. However, existing modification methods cannot effectively improve both safety and cycle performance simultaneously. Summary of the Invention

[0006] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell and its preparation method, a secondary battery and an electrical device, so as to simultaneously improve the cycle performance and safety performance of the secondary battery.

[0007] In a first aspect, this application provides a battery cell, including a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least a portion of the surface of the positive current collector. The positive electrode film layer contains a positive electrode active material and a dopant. The dopant contains a first dopant element and a second dopant element. The first dopant element includes at least one of boron or aluminum, and the second dopant element includes at least one of phosphorus, silicon, or fluorine. Any 1μm × 1μm region in the longitudinal section of the positive electrode film layer contains the dopant.

[0008] In the above technical solution, the dopant contains a first dopant element and a second dopant element. The first dopant element includes at least one of boron or aluminum, and the second dopant element includes at least one of phosphorus, silicon, or fluorine. Stable chemical bonds can be formed between the first and second dopant elements, giving the dopant high thermal stability and making it less soluble in the electrolyte. In the longitudinal section of the positive electrode film, any 1μm × 1μm region contains the dopant. This allows some of the dopant to coat the surface of the positive electrode active material, reducing the contact area between the positive electrode active material and the electrolyte, reducing side reactions, and thus improving the cycle performance of the battery cell. Furthermore, some of the dopant is dispersed freely in the positive electrode film, which can make the heat distribution more uniform, reducing local overheating and thus improving the safety performance of the battery cell.

[0009] In some embodiments, the molar ratio of the first dopant element to the second dopant element is (0.1~10):1. A suitable molar ratio of the first dopant element to the second dopant element allows the corresponding dopant to possess good thermal stability and be insoluble in the electrolyte.

[0010] In some embodiments, the molar ratio of the first dopant element to the second dopant element is 1:(1~5). By further limiting the molar ratio of the first dopant element to the second dopant element to a suitable range, the safety performance and cycle performance of the battery cell can be further improved.

[0011] In some embodiments, based on the mass meter of the positive electrode film, the mass content of the first dopant element is 100ppm to 10000ppm, and the mass content of the second dopant element is 300ppm to 30000ppm. The mass contents of the first and second dopant elements are within a certain range, corresponding to an appropriate amount of dopant. This allows for simultaneous improvement of the cycle performance and safety performance of the battery cell, while ensuring that the mass proportion of the positive electrode active material in the positive electrode film does not significantly decrease.

[0012] In some embodiments, based on the mass meter of the positive electrode film, the mass content of the first dopant element is 500ppm to 3000ppm, and the mass content of the second dopant element is 500ppm to 3000ppm. By further limiting the contents of the first and second dopant elements to appropriate ranges, the safety performance and cycle performance of the battery cell can be further improved.

[0013] In some embodiments, based on the mass of the positive electrode film, the mass percentage of the dopant is 0.1% to 5%. When the amount of dopant is within a suitable range, it can simultaneously improve the cycle performance and safety performance of the battery cell, while ensuring that the mass percentage of the positive electrode active material in the positive electrode film does not decrease significantly.

[0014] In some embodiments, the dopant includes B 3+ Or Al 3+ At least one of them, including PO4 3- SiO5 6- or F - At least one of the following. Dopant B 3+ Or Al 3+ As a cation, with PO4 3- SiO5 6- or F - These anions or polyanions combine to give the dopants high thermal stability and make them less soluble in electrolyte. When uniformly dispersed in the positive electrode, they can effectively improve the safety and cycle performance of the battery cell.

[0015] In some embodiments, the dopant includes at least one selected from boron phosphate, aluminum phosphate, boron silicate, aluminum silicate, boron fluoride, or aluminum fluoride. Boron phosphate, aluminum phosphate, boron silicate, aluminum silicate, boron fluoride, and aluminum fluoride all possess high thermal stability and are heat-absorbing and heat-insulating materials. Their uniform dispersion in the positive electrode film can reduce heat diffusion and improve the safety performance of the battery cell. Furthermore, these substances also have high ionic conductivity. Coating the surface of the positive electrode active material reduces the contact between the positive electrode active material and the electrolyte while also improving the ionic conductivity of the positive electrode active material, thereby further enhancing the cycle performance of the battery cell.

[0016] In some embodiments, at least a portion of the dopant is coated onto the surface of the positive electrode active material to form a coating layer, and the thickness of the coating layer is 1 nm to 200 nm. The dopant is uniformly distributed in the positive electrode film layer, and at least a portion of the dopant coats the surface of the positive electrode active material to form a coating layer with a suitable thickness range, which can further reduce the contact between the electrolyte and the positive electrode active material, improve the stability of the positive electrode active material, and thus further improve the cycle performance of the battery cell.

[0017] Secondly, this application provides a method for preparing a battery cell, including the preparation of a positive electrode sheet. The method for preparing the positive electrode sheet includes: dispersing a positive active material, a first doped precursor containing a first doping element, and a second doped precursor containing a second doping element in a solvent; dissolving the first doped precursor and the second doped precursor in the solvent and reacting during dispersion to form a dopant, thereby obtaining a positive electrode slurry; coating the positive electrode slurry onto at least a portion of the surface of a positive current collector, and drying it to form a positive electrode film layer, thereby obtaining a positive electrode sheet; wherein the dopant contains a first doping element and a second doping element, the first doping element including at least one of boron or aluminum, and the second doping element including at least one of phosphorus, silicon, or fluorine; and assembling the positive electrode sheet, the negative electrode sheet, and the electrolyte to form a battery cell.

[0018] In the above technical solution, this application dissolves a first doped precursor containing a first dopant element and a second doped precursor containing a second dopant element in a solvent of the positive electrode slurry. During dispersion, a dopant is formed through an in-situ reaction, resulting in a dopant with good thermal stability and insolubility in the electrolyte. This allows the dopant to be uniformly dispersed in the positive electrode slurry. Further coating and drying allow a portion of the dopant to coat the surface of the positive electrode active material, while another portion remains freely dispersed within the positive electrode film. This preparation method, while preparing the positive electrode sheet, uniformly distributes dopant that improves the stability of the positive electrode active material and reduces thermal diffusion within the positive electrode film, effectively enhancing both the cycle performance and safety performance of the battery cell.

[0019] In some embodiments, the molar ratio of the first dopant element to the second dopant element in the positive electrode slurry is (0.1~10):1. Controlling the molar ratio of the first dopant element to the second dopant element within a suitable range allows the first dopant element and the second dopant element to react fully to form the dopant.

[0020] In some embodiments, the first doped precursor includes BO3. 3- Or Al 3+ At least one of them, the second doped precursor includes PO4 3- SiO3 2- or F - At least one of the following. Contains BO3. 3- Or Al 3+ The first doped precursor and containing PO4 3- SiO3 2- or F - The second doping precursor can react in situ during the dispersion process to form a dopant, and the formed dopant has high thermal stability and is insoluble in electrolyte.

[0021] In some embodiments, the first doping precursor includes at least one of boric acid or aluminum isopropoxide, and the second doping precursor includes at least one of lithium dihydrogen phosphate, sodium silicate, or ammonium fluoride. Both the first and second doping precursors are soluble in the solvent of the cathode slurry, and they can react in situ during dispersion to form dopants. The formed dopants exhibit high thermal stability, acting as heat-absorbing and heat-insulating materials, and also possess high ionic conductivity. This results in a cathode electrode with uniformly dispersed dopants and cathode active materials, simultaneously improving the cycle performance and safety performance of the battery cell.

[0022] In some embodiments, the method for preparing the positive electrode slurry includes: dissolving a second doped precursor in a solvent to form a precursor solution; mixing a positive electrode active material, a conductive agent, and a binder, and then dispersing the mixture in the precursor solution to form a mixed slurry; and dissolving a first doped precursor in the mixed slurry to form a positive electrode slurry. Dispersing the positive electrode active material first in the precursor solution, followed by adding and dissolving the first doped precursor, can improve the dispersion uniformity of each component, shorten the slurry preparation time, and allow the first and second doped precursors to react in situ during uniform dispersion to form dopants. At least a portion of the dopants can coat the surface of the positive electrode active material, and at least a portion of the dopants can be freely dispersed in the positive electrode slurry.

[0023] In some embodiments, the precursor solution has a mass concentration of 0.1% to 5%; the solid content of the mixed slurry is 50% to 75%. This can further improve the dispersion uniformity of the positive electrode active material and dopants, thereby further improving the cycle performance and safety performance of the battery cell.

[0024] Thirdly, this application provides a secondary battery, including the battery cell provided in the first aspect or the battery cell prepared by the preparation method provided in the second aspect.

[0025] Fourthly, this application provides an electrical device including the secondary battery provided in the third aspect. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 is a schematic diagram of a battery cell according to one embodiment of this application.

[0028] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1.

[0029] Figure 3 is a schematic diagram of a battery module according to one embodiment of this application.

[0030] Figure 4 is a schematic diagram of a secondary battery according to an embodiment of this application.

[0031] Figure 5 is an exploded view of the secondary battery according to one embodiment of this application, as shown in Figure 4.

[0032] Figure 6 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0033] Figure 7 is an EDS cross-sectional view of element B in the positive electrode sheet provided in Embodiment 1 of this application.

[0034] Figure 8 is an enlarged view of Figure 7.

[0035] Figure 9 is an EDS cross-sectional view of the P element in the positive electrode sheet provided in Embodiment 1 of this application.

[0036] Figure 10 is an enlarged view of Figure 9.

[0037] Figure 11 is an EDS cross-sectional view of element B in the positive electrode sheet provided in Comparative Example 1 of this application.

[0038] Figure 12 is an enlarged view of Figure 11.

[0039] Figure 13 is an EDS cross-sectional view of the P element in the positive electrode sheet provided in Comparative Example 1 of this application.

[0040] Figure 14 is an enlarged view of Figure 13.

[0041] Figure 15 is an EDS cross-sectional view of element B in the positive electrode sheet provided in Comparative Example 2 of this application.

[0042] Figure 16 is an enlarged view of Figure 15.

[0043] Figure 17 is an EDS cross-sectional view of the P element in the positive electrode sheet provided in Comparative Example 2 of this application.

[0044] Figure 18 is an enlarged view of Figure 17.

[0045] Figure 19 is an EDS diagram of element B in the positive electrode active material of the positive electrode sheet provided in Embodiment 1 of this application.

[0046] Figure 20 is an EDS diagram of the P element in the positive electrode active material of the positive electrode sheet provided in Embodiment 1 of this application.

[0047] Figure 21 is an XPS B1s peak fitting diagram of the positive electrode powder obtained after scraping the positive electrode sheet according to Embodiment 1 of this application.

[0048] Figure 22 is an XPS P2p peak fitting diagram of the positive electrode powder obtained after scraping the positive electrode sheet according to Embodiment 1 of this application.

[0049] Explanation of reference numerals in the attached diagram: 1-Secondary battery; 2-Upper casing; 3-Lower casing; 4-Battery module; 5-Battery cell; 51-Housing shell; 52-Electrode assembly; 53-Cover plate. Embodiments of the present invention

[0050] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, the method for preparing the battery cell, the secondary battery, and the power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0051] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0053] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0054] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0055] Secondary batteries are susceptible to thermal runaway when used at high temperatures. To improve their safety, flame retardants can be added to reduce the destructive potential during thermal runaway. However, flame retardants are typically insoluble solid particles, and nano-sizing is difficult, making it hard to directly and uniformly disperse them within the electrodes. Consequently, their effectiveness in mitigating thermal runaway is limited, and they do not improve cycle performance.

[0056] Based on this, this application provides a battery cell including a positive electrode, a negative electrode, and an electrolyte.

[0057] [Positive electrode plate]

[0058] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least a portion of the surface of the positive current collector. The positive electrode film layer contains a positive electrode active material and a dopant. The dopant contains a first dopant element and a second dopant element. The first dopant element includes at least one of boron or aluminum, and the second dopant element includes at least one of phosphorus, silicon, or fluorine. Any 1 μm × 1 μm region in the longitudinal section of the positive electrode film layer contains the dopant.

[0059] In this application, "doping" refers to the mixing of multiple substances together. In order to improve the performance of the positive electrode, a small amount of other compounds besides the positive electrode active material are mixed into the positive electrode. The dopant and the positive electrode active material are in a physically mixed state, and the dopant is not incorporated into the interior of the crystal structure of the positive electrode active material.

[0060] In this application, "any 1μm×1μm region in the longitudinal section of the positive electrode film contains dopant" means that when testing the longitudinal section of the positive electrode sheet, part of the region is the positive current collector region and part of the region is the positive electrode film region. Any 1μm×1μm region of the positive electrode film is selected, and the selected region is not limited. Any 1μm×1μm region contains dopant, indicating that the dopant is uniformly distributed in the positive electrode film.

[0061] For example, EDS testing of the cross-section of the positive electrode sheet can demonstrate that "any 1μm × 1μm region in the longitudinal section of the positive electrode film contains dopants." The specific method is as follows: Disassemble the finished battery cell, take the positive electrode sheet, immerse it in dimethyl carbonate (DMC) solvent for cleaning, then dry it, immerse it in liquid nitrogen for 3 minutes, remove it, break it / cut it with scissors to expose the cross-section, and then attach it to the sample stage for EDS testing to obtain a cross-sectional EDS image. During EDS testing, the type of dopant to be analyzed is determined. In the resulting EDS image, the region containing that dopant will form a bright spot, displaying the distribution of that dopant. The distribution of the dopant can also indicate the distribution of the dopant.

[0062] In the above technical solution, the first dopant element includes at least one of boron or aluminum, and the second dopant element includes at least one of phosphorus, silicon, or fluorine, forming a stable chemical bond between the first and second dopant elements. The dopant exhibits high thermal stability and is insoluble in the electrolyte. In the longitudinal section of the positive electrode film, any 1μm × 1μm region contains the dopant. This allows some of the dopant to coat the surface of the positive electrode active material, reducing the contact area between the positive electrode active material and the electrolyte, reducing side reactions, and thus improving the cycle performance of the battery cell. Furthermore, some of the dopant is dispersed freely within the positive electrode film, which can ensure uniform heat distribution and reduce localized overheating, thereby simultaneously improving the safety performance of the battery cell.

[0063] In some embodiments, the molar ratio of the first dopant element to the second dopant element is (0.1~10):1. As an example, the molar ratio of the first dopant element to the second dopant element is 0.1:1, 0.3:1, 0.5:1, 1:1, 1:2, 1:5, 2:1, 5:1 or 10:1, etc.

[0064] Furthermore, the molar ratio of the first dopant element to the second dopant element is 1:(1~5).

[0065] In some embodiments, based on the mass meter of the positive electrode film, the mass content of the first dopant element is 100ppm to 10000ppm, and the mass content of the second dopant element is 300ppm to 30000ppm.

[0066] Furthermore, the mass content of the first dopant element is 500ppm to 3000ppm, and the mass content of the second dopant element is 500ppm to 3000ppm.

[0067] As an example, based on the mass meter of the positive electrode film, the mass content of the first dopant element is 100ppm, 500ppm, 1000ppm, 3000ppm, 5000ppm, 9000ppm, or 10000ppm; and the mass content of the second dopant element is 300ppm, 500ppm, 1000ppm, 3000ppm, 10000ppm, 20000ppm, or 30000ppm.

[0068] In some embodiments, based on the mass meter of the positive electrode film, the mass percentage of the dopant is 0.1% to 5%. As an example, based on the mass meter of the positive electrode film, the mass percentage of the dopant is 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, or 5%.

[0069] The mass content of the first and second dopant elements can be obtained using common methods and equipment. The molar ratio of the first and second dopant elements can be calculated from their mass content, and the mass percentage of the dopant in the positive electrode film can be calculated from this molar ratio. As an example, according to EPA 6010D-2018 and JY / T 0567-2020 standards, the battery is first disassembled, the positive electrode sheet is removed, washed, and powder is scraped off to obtain the positive electrode powder. After digestion according to EPA 6010D-2018, the positive electrode powder is tested using inductively coupled plasma atomic emission spectrometry (ICP) according to JY / T 0567-2020.

[0070] In some embodiments, the dopant includes B 3+ Or Al 3+ At least one of them, the dopant also includes PO4 3- SiO5 6- F - At least one of the following. Further, the dopant includes at least one of boron phosphate (BPO4), aluminum phosphate (AlPO4), boron silicate (B2SiO5), aluminum silicate (Al2SiO5), boron fluoride (BF3), or aluminum fluoride (AlF3).

[0071] The composition of the dopant in the positive electrode film can be determined using conventional methods and equipment. For example, the positive electrode can be disassembled, the positive electrode sheet removed, washed, and the powder scraped off to obtain positive electrode powder. The first and second dopant elements are analyzed separately. X-ray photoelectron spectroscopy (XPS) is performed on the sample, and peak fitting is performed using XPS Peak chemical processing software to obtain XPS peak fitting diagrams for each dopant element. By comparing the electron binding energy shifts of the first and second dopant elements with standard spectral data, the chemical bonding mode and chemical valence state of the first and second dopant elements can be analyzed, thereby determining the dopant composition. For example, when the dopant is boron phosphate, the XPS B1s peak fitting diagram of the cathode powder shows the presence of a characteristic peak of a BP bond with an electron binding energy of approximately 193.5 eV; the XPS P2p peak fitting diagram of the cathode powder shows the presence of a characteristic peak of a PB bond with an electron binding energy of approximately 135.5 eV. This confirms that the dopant is boron phosphate, and the high bond energy of the BP bond indicates good stability and resistance to reaction with the electrolyte. Furthermore, it does not burn and can be used as a catalytic char-forming additive. Through catalysis, it alters the polymer's thermal degradation mode, promoting char formation and thus exerting a flame-retardant function. Specifically, the BP bond promotes the cross-linking of pyrolysis products during polymer thermal degradation, increasing the thermal stability of the char layer and reducing the release of combustion smoke and toxic products, thereby achieving its flame-retardant effect.

[0072] In some embodiments, at least a portion of the dopant is coated onto the surface of the positive electrode active material to form a coating layer, the thickness of which is 1 nm to 200 nm. As an example, the thickness of the coating layer can be 1 nm, 10 nm, 20 nm, 50 nm, 100 nm, 200 nm, etc.

[0073] "At least some dopant is coated on the surface of the positive electrode active material to form a coating layer" can be determined by taking the positive electrode sheet, removing the positive electrode current collector, retaining the positive electrode film layer, immersing the positive electrode film layer in DMC, washing out the positive electrode active material particles, analyzing the first dopant element and the second dopant element separately, and performing EDS testing on the positive electrode active material particles. By observing the first dopant element and the second dopant element simultaneously on the surface of the positive electrode active material, it can be known that "at least some dopant is coated on the surface of the positive electrode active material".

[0074] In some embodiments, the battery cell is a lithium-ion battery cell, and the positive electrode active material may also be a positive electrode active material for lithium-ion batteries well known in the art to prepare a lithium-ion battery. By way of example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphate with olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials may be used alone in one kind, or two or more kinds may be used in combination.

[0075] Wherein, examples of the lithium transition metal oxide include, but are not limited to, lithium cobalt oxide (e.g., LiCoO₂), lithium nickel oxide (e.g., LiNiO₂), lithium manganese oxide (e.g., LiMnO₂, LiMn₂O₄), lithium nickel cobalt oxide, lithium manganese cobalt oxide, and lithium nickel manganese oxide. Examples of the lithium-containing phosphate with olivine structure include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO₄, which may also be abbreviated as LFP), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO₄), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0076] In some embodiments, in order to further increase the energy density of the secondary battery, the positive electrode active material for a lithium-ion battery may include lithium of the general formula Li a Ni b Co c M d O e A f one or more of transition metal oxides and modified compounds thereof, wherein 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M comprises at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from at least one of N, F, S and Cl.

[0077] As an example, the positive electrode active material for a lithium-ion battery may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O₂ (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O₂ (NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O₂ (NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O₂ (NCM622), LiNi 0.8Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, LiNi 0.8 Co 0.15 Al 0.05 At least one of O2.

[0078] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0079] As an optional technical approach in this application, the polyanionic compound can be Li 1+x Mn 1-y A y P 1-z R z O4. Wherein, x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes at least one element selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes at least one element selected from B, S, Si and N.

[0080] As an optional technical approach in this application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n Wherein, A includes at least one element selected from Zn, Al, Na, K, Mg, Nb, Mo, and W. B includes at least one element selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge. C includes at least one element selected from B, S, Si, and N. D includes at least one element selected from S, F, Cl, and Br. a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0081] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of cathode materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0082] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0083] In some embodiments, the battery cell is a sodium-ion battery cell, and the positive electrode active material can be a known positive electrode active material for sodium-ion batteries to prepare the sodium-ion battery. As an example, the positive electrode active material may include at least one of the following materials: polyanionic compounds, sodium transition metal oxides, Prussian blue compounds, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0084] In some embodiments, the positive electrode active material of a sodium-ion battery may be a sodium transition metal compound, with the general formula Na. x XO2, where X includes a transition metal that can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, where 0 < x ≤ 1. As an example, the positive electrode active material of a sodium-ion battery includes Na. x MnO2, Na x CoO2, Na x FeO2, NaNi 0.2 Fe 0.6 Mn 0.2 At least one of O2.

[0085] In some embodiments, the polyanionic compound may be Na a A e Mn 1-f B f P 1-g C g O 4-n D n, wherein A comprises at least one element selected from Zn, Al, Na, K, Mg, Nb, Mo and W. B comprises at least one element selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge. C comprises at least one element selected from B, S, Si and N. D comprises at least one element selected from S, F, Cl and Br. a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0086] As an optional technical solution of the present application, the polyanionic compound may be Na 4+x R 3-y P 4-m O 15 / C. Wherein 0<x<0.5, 0<y≤0.5, 0<m≤0.2, and R comprises at least one selected from Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W and Pb.

[0087] As an optional technical solution of the present application, the polyanionic compound may be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d , wherein element A represents an alkali metal element that is doped to substitute Na element, element M represents a metal element that substitutes V element, element D represents a doping element that substitutes phosphorus element, element Q represents a doping element that substitutes F element, said element D comprises at least one of Si and S, and said element Q comprises at least one of Cl and O. 3.5≤x≤4.5, 0≤a≤0.15x, 0.8≤y≤1.1, 0≤b≤0.3y, 0≤c≤0.15, 0.8≤z≤1.1, 0≤d≤0.2z. Optionally, said element A comprises at least one of K and Li. Said element M comprises at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu and Co.

[0088] The Prussian blue-type compound may be a class of compound having sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The Prussian blue-type compound is, for example, Na aMe b Me' c (CN)6, wherein Me and Me' are each independently at least one of Mn, Fe, Ni, Co, Cu and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0089] In some embodiments, the positive electrode may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0090] In some embodiments, the positive electrode may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0092] [Preparation method of positive electrode sheet]

[0093] In this embodiment of the application, the method for preparing the above-mentioned positive electrode sheet includes the following steps:

[0094] S11: The positive electrode active material, a first doped precursor containing a first doping element, and a second doped precursor containing a second doping element are dispersed in a solvent. The first and second doped precursors dissolve in the solvent and react during dispersion to form a dopant, thereby obtaining a positive electrode slurry. The dopant contains a first doping element and a second doping element. The first doping element includes at least one of boron or aluminum, and the second doping element includes at least one of phosphorus, silicon, or fluorine.

[0095] S12: The positive electrode slurry is coated on at least part of the surface of the positive electrode current collector, and after drying, a positive electrode film is formed to obtain a positive electrode sheet.

[0096] "Reaction to form dopant during dispersion" means that the first doping precursor and the second doping precursor, which are completely dissolved in the solvent, react completely or at least partially during the dispersion of the slurry to form dopant. The first doping element in the first doping precursor corresponds to the cation in the dopant, and the second doping element in the second doping precursor corresponds to the anion or polyanion in the dopant.

[0097] In the preparation of the positive electrode sheet of a battery cell, a first doping precursor containing a first doping element and a second doping precursor containing a second doping element are dissolved in the solvent of the positive electrode slurry. During the dispersion process, a dopant is formed in situ, which allows a stable chemical bond to be formed between the first and second doping elements. The formed dopant has good thermal stability and is insoluble in the electrolyte. It also allows the dopant to be uniformly dispersed in the positive electrode slurry. Through further coating and drying, some of the dopant can be coated on the surface of the positive electrode active material, which can improve the cycle performance of the battery cell. In addition, some of the dopant is dispersed freely in the positive electrode film layer, which can improve the safety performance of the battery cell.

[0098] If the dopant is directly dispersed in the positive electrode slurry, since the dopant is a highly stable solid particle and insoluble in the electrolyte, it is difficult to dissolve in the solvent of the positive electrode slurry. The dopant is in a solid physical dispersion state, and the dopant particles are prone to agglomeration in the positive electrode slurry. After subsequent heating and drying, the dispersion effect of the dopant in the obtained positive electrode sheet will be relatively poor compared with the positive electrode sheet prepared in this application, which will lead to poor cycle performance and safety performance of the secondary battery.

[0099] If a dry coating method is used, the solid particles of the coating agent are physically mixed with the particles of the positive electrode active material, and then sintered to obtain the coated positive electrode active material, and then the coated positive electrode active material is used to prepare a positive electrode slurry, which is then coated and dried to form a positive electrode sheet. Compared with the preparation method of this application, the dry coating process is more difficult to disperse the coating agent. The coating agent is prone to agglomeration and cannot be uniformly coated on the surface of the positive electrode active material, nor can it be uniformly dispersed in the positive electrode sheet. Furthermore, the dry coating process requires additional mixing and sintering steps, making the preparation process more complex and resulting in higher production costs for battery cells, which is not conducive to industrial production.

[0100] If a wet coating method is used, the coating agent is dispersed in a dispersion, and then the dispersion is wet-mixed with the positive electrode active material. The solvent in the dispersion is evaporated, sintered, and then the sintered positive electrode active material is used to prepare a positive electrode slurry, which is then coated and dried. Compared with the preparation method of this application, the wet coating method cannot uniformly disperse the coating agent in the positive electrode sheet. In addition to the solvent in the positive electrode slurry, the wet coating process requires the use of a dispersion solvent in addition to the solvent in the positive electrode slurry, and additional wet mixing, evaporation, and sintering steps are required. The preparation process is more complex, the preparation cost of the battery cell is higher, and it is not conducive to industrial production.

[0101] In this application, while preparing the positive electrode sheet, dopants that can improve the stability of the positive electrode active material and reduce the thermal diffusion of the electrode sheet are uniformly distributed in the positive electrode film layer. This can simultaneously improve the cycle performance and safety performance of the battery cell, avoid adding flame retardants to the electrolyte to degrade the conductivity of the electrolyte, and avoid the step of separately preparing the coating of the positive electrode active material, thus saving the battery manufacturing cost.

[0102] In some embodiments, the solvent for the positive electrode slurry may include N-methylpyrrolidone (NMP). This solvent has good solubility, which not only improves the dispersibility of substances such as the positive electrode active material, but also dissolves the first and second doping precursors, thereby improving the coating quality and stability of the positive electrode sheet. In this application, the type of solvent is not limited; any solvent that can be used as a dispersion solvent for the positive electrode slurry and can dissolve both the first and second doping precursors is within the scope of protection of this application. This includes existing solvents and potential future solvents, all of which are included in the inventive concept of this application.

[0103] In step S11, the positive electrode active material is dispersed in the solvent, while the first doped precursor and the second doped precursor are dissolved in the solvent. "The first doped precursor and the second doped precursor are dissolved in the solvent" means that the first doped precursor and the second doped precursor can mix with the solvent to form a homogeneous phase. "The positive electrode active material is dispersed in the solvent" means that the positive electrode active material and the solvent are in a mixed state, and both the positive electrode active material and the solvent retain their original states.

[0104] In some embodiments, the first doped precursor includes BO3. 3- Or Al 3+ At least one of them, the second doped precursor includes PO4 3- SiO3 2- or F - At least one of them.

[0105] Furthermore, the first doped precursor includes boric acid (H3BO3) or aluminum isopropoxide (C9H2O). 21The second doped precursor includes at least one of the following: lithium dihydrogen phosphate (LiH2PO4), sodium silicate (Na2SiO3), or ammonium fluoride (NH4F). Specifically, H3BO3 reacts with LiH2PO4 to form BPO4, H3BO3 reacts with Na2SiO3 to form B2SiO5, and H3BO3 reacts with NH4F to form BF3. C9H 21 AlO3 reacts with LiH2PO4 to form AlPO4, C9H 21 AlO3 and Na2SiO3 react to form Al2SiO5, C9H 21 AlO3 reacts with NH4F to form AlF3.

[0106] In some embodiments, the molar ratio of the first dopant element to the second dopant element is (0.1~10):1. As an example, the molar ratio of the first dopant element to the second dopant element is 0.1:1, 0.3:1, 0.5:1, 1:1, 2:1, 5:1 or 10:1, etc.

[0107] In some embodiments, the method for preparing the positive electrode slurry includes: dissolving a second doped precursor in a solvent to form a precursor solution; mixing a positive electrode active material, a conductive agent, and a binder, and then dispersing them in the precursor solution to form a mixed slurry; and dissolving a first doped precursor in the mixed slurry to form a positive electrode slurry.

[0108] The phrase "mixing the positive electrode active material, conductive agent, and binder" refers to mixing these materials using a dry method. This method of first dry mixing and then solvent dispersion can shorten the slurry preparation time and also improve dispersion uniformity.

[0109] In other embodiments, the positive electrode active material, conductive agent and binder may also be dispersed in a portion of the solvent, wet-mixed and then dispersed in the precursor solution.

[0110] Further, the precursor solution has a mass concentration of 0.1% to 5%, and the solid content of the mixed slurry is 50% to 75%. "Solid content of the mixed slurry" refers to the mass percentage of substances other than the solvent in the total mass of the mixed slurry. For example, the mass concentration of the precursor solution can be 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any two of the above values. The solid content of the mixed slurry can be 50%, 55%, 60%, 65%, 70%, 75%, or any two of the above values.

[0111] In step S12, "coating the positive electrode slurry onto at least a portion of the surface of the positive electrode current collector" means that the positive electrode current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode slurry is applied to either or both of the two opposite surfaces of the positive electrode current collector.

[0112] As an example, the positive electrode slurry can be applied to one surface of the positive electrode current collector.

[0113] As an example, positive electrode slurry can be coated on both surfaces of the positive electrode current collector.

[0114] In some embodiments, the dried positive electrode sheet can be cold-pressed and cut.

[0115] The positive electrode sheet prepared by the above method has dopants and positive active materials uniformly dispersed in it.

[0116] [Negative electrode plate]

[0117] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material.

[0118] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0119] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0120] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, and tin-based materials, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0121] When it is necessary to prepare lithium-ion batteries, the negative electrode active material may also include lithium titanate.

[0122] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0123] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0125] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained.

[0126] In other embodiments, the current collector of the negative electrode sheet typically includes a current collector body and a base coating. The base coating can be disposed on at least one side of the current collector body. The base coating essentially does not contain negative electrode active material, but may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the film layer can be disposed on the surface of at least one side of the current collector. When the current collector of the negative electrode sheet includes a base coating, the film layer can be disposed on the surface of the base coating away from the current collector.

[0127] In some embodiments, the membrane layer may also include a binder for fixing the additive to the negative electrode sheet. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0128] [Electrolytes]

[0129] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0130] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0131] In some embodiments, when it is necessary to prepare a lithium-ion battery, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0132] In some embodiments, when it is necessary to prepare a sodium-ion battery, the electrolyte salt includes at least one of sodium hexafluorophosphate and sodium perchlorate.

[0133] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0134] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0135] In some embodiments, the secondary battery further includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0136] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0137] [Battery cell]

[0138] In some embodiments, a battery cell includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process, and the electrolyte is filled in the electrode assembly.

[0139] In some embodiments, the battery cell may also include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte described above.

[0140] In some embodiments, the outer packaging of a single battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0141] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a schematic diagram of a battery cell 5 according to an embodiment of this application.

[0142] In some embodiments, FIG2 is an exploded view of a battery cell 5 according to an embodiment of the present application shown in FIG1. ​​Referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0143] In some embodiments, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0144] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0145] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0146] In some embodiments, the battery modules described above can also be assembled into a secondary battery. The secondary battery may contain one or more battery modules, and the specific number can be selected by those skilled in the art based on the application and capacity of the secondary battery.

[0147] Figure 4 is a schematic diagram of a secondary battery according to an embodiment of this application, and Figure 5 is an exploded view of the secondary battery according to an embodiment of this application shown in Figure 4. Referring to Figures 4 and 5, the secondary battery 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3. The upper box 2 can cover the lower box 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner. In the embodiments of this application, the secondary battery 1 may also be referred to as a battery pack.

[0148] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or secondary battery provided in this application. The battery cell, battery module, or secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0149] As an electrical device, you can choose individual battery cells, battery modules, or secondary batteries according to your usage requirements.

[0150] Figure 6 is a schematic diagram of an electrical device using a single battery cell as a power source according to an embodiment of this application. Please refer to Figure 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device, a single battery cell or a battery module can be used.

[0151] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0152] Example

[0153] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0154] Example 1

[0155] This embodiment provides a lithium-ion battery, the preparation method of which is as follows:

[0156] (1) Preparation of positive electrode: Lithium dihydrogen phosphate (LiH2PO4) was dissolved in N-methylpyrrolidone (NMP) solvent to form a precursor solution with a mass concentration of 1%; the positive electrode active material LiNi 0.83 Co 0.12 Mn 0.05 O2, conductive carbon black (Super P), and binder PVDF are dry-mixed in a mass ratio of 97:2:1 until homogeneous. The aforementioned precursor solution is then added, and the mixture is stirred again until homogeneous, yielding a slurry with a solid content of 60%. Boric acid (H3BO3) is added to the slurry, dissolved, and stirred until homogeneous, yielding a positive electrode slurry. The homogeneous positive electrode slurry is then uniformly coated onto one surface of an aluminum foil and baked at 150°C for 10 hours to form a positive electrode film, thus obtaining the positive electrode sheet.

[0157] In the positive electrode slurry, the molar ratio of boron in boric acid to phosphorus in lithium dihydrogen phosphate is 1:1. Boric acid and lithium dihydrogen phosphate react during dispersion to form boron phosphate, and the chemical reaction equation is as follows:

[0158] LiH2PO4+H3BO3→BPO4+LiOH+2H2O.

[0159] (2) Battery assembly: The positive electrode sheet obtained in step (1) is cut into small round pieces of 14mm, and lithium sheet is used as the negative electrode to assemble into a button cell, and then formation is performed.

[0160] The separator is a polyethylene membrane. The electrolyte is prepared by mixing ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1, and dissolving LiPF6 in the mixed solvent to obtain the electrolyte. The concentration of LiPF6 in the electrolyte is 1 mol / L.

[0161] Example 2

[0162] Example 2 provides a lithium-ion battery, which differs from Example 1 in that:

[0163] In step (1), the molar ratio of boron in boric acid to phosphorus in lithium dihydrogen phosphate in the positive electrode slurry is 2:1.

[0164] Example 3

[0165] Example 3 provides a lithium-ion battery, which differs from Example 1 in that: in step (1), the molar ratio of boron in boric acid and phosphorus in lithium dihydrogen phosphate in the positive electrode slurry is 1:2.

[0166] Example 4

[0167] Example 4 provides a lithium-ion battery, which differs from Example 1 in that: in step (1), lithium dihydrogen phosphate (LiH2PO4) is dissolved in N-methylpyrrolidone (NMP) solvent to form a precursor solution with a mass concentration of 0.2%.

[0168] Example 5

[0169] Example 5 provides a lithium-ion battery, which differs from Example 1 in that: in step (1), lithium dihydrogen phosphate (LiH2PO4) is dissolved in N-methylpyrrolidone (NMP) solvent to form a precursor solution with a mass concentration of 3%.

[0170] Example 6

[0171] Example 6 provides a lithium-ion battery, which differs from Example 1 in that: in step (1), lithium dihydrogen phosphate (LiH2PO4) is dissolved in N-methylpyrrolidone (NMP) solvent to form a precursor solution with a mass concentration of 5%.

[0172] Example 7

[0173] Example 7 provides a lithium-ion battery, which differs from Example 1 in that: in step (1), the positive electrode active material is LiFePO4.

[0174] Example 8

[0175] Example 8 provides a lithium-ion battery, which differs from Example 1 in that: in step (1), lithium dihydrogen phosphate (LiH2PO4) is dissolved in N-methylpyrrolidone (NMP) solvent to form a precursor solution with a mass concentration of 1%; and the positive electrode active material LiNi 0.83 Co 0.12 Mn 0.05 O2, conductive carbon black (Super P), and binder PVDF are dry-mixed in a mass ratio of 97:2:1 until homogeneous. This mixture is then added to the precursor solution along with boric acid (H3BO3) and mixed again to obtain a slurry with a solid content of 60%. The homogeneous positive electrode slurry is then uniformly coated onto one surface of an aluminum foil and baked at 150°C for 10 hours to form a positive electrode film, thus obtaining the positive electrode sheet.

[0176] In the positive electrode slurry, the molar ratio of boron in boric acid to phosphorus in lithium dihydrogen phosphate is 1:1.

[0177] Example 9

[0178] Example 9 provides a lithium-ion battery, which differs from Example 1 in that: in step (1), lithium dihydrogen phosphate (LiH2PO4) is dissolved in N-methylpyrrolidone (NMP) solvent to form a precursor solution with a mass concentration of 1%; the positive electrode active material LiNi 0.83 Co 0.12 Mn 0.05 O2, conductive carbon black (Super P), and binder PVDF are dry-mixed uniformly in a mass ratio of 97:2:1. The aforementioned precursor solution is then added, and the mixture is mixed uniformly again to obtain a mixed slurry with a solid content of 60%. Aluminum isopropoxide (C9H) is then added... 21 AlO3 is added to the above mixed slurry and dissolved and mixed evenly to obtain a positive electrode slurry. The evenly mixed positive electrode slurry is uniformly coated on one surface of an aluminum foil and baked at 150°C for 10 hours to form a positive electrode film, thus obtaining a positive electrode sheet. In the positive electrode slurry, the molar ratio of aluminum in aluminum isopropoxide to phosphorus in lithium dihydrogen phosphate is 1:1.

[0179] Comparative Example 1

[0180] Comparative Example 1 provides a lithium-ion battery, which differs from Example 1 in that step (1) preparation of the positive electrode: the positive electrode active material LiNi is prepared... 0.83 Co 0.12 Mn 0.05 O2, conductive carbon black (Super P), binder PVDF, and boron phosphate (BPO4) were uniformly dispersed in NMP solvent at a mass ratio of 97:2:1:1 to obtain a positive electrode slurry with a solid content of 60%. The uniformly mixed positive electrode slurry was coated evenly on a positive electrode current collector aluminum foil. The electrode was then vacuum baked at 150°C for 10 hours to remove the NMP solvent, thus obtaining the positive electrode film and the positive electrode sheet.

[0181] Comparative Example 2

[0182] Comparative Example 2 provides a lithium-ion battery, which differs from Example 1 in that step (1), the preparation of the positive electrode: LiNi 0.83 Co 0.12 Mn 0.05 O2 and boron phosphate (BPO4, 1% by mass) were dry-mixed until homogeneous, and then sintered at 500℃ for 10 h. The boron phosphate-coated LiNi was then... 0.83 Co 0.12 Mn 0.05O2, conductive carbon black (Super P), and binder PVDF are uniformly dispersed in NMP solvent at a mass ratio of 97:2:1 to obtain a positive electrode slurry with a solid content of 60%. The uniformly mixed positive electrode slurry is coated evenly on a positive electrode current collector aluminum foil. The electrode is then vacuum baked at 150°C for 10 hours to remove the NMP solvent, thus obtaining the positive electrode film and the positive electrode sheet.

[0183] Comparative Example 3

[0184] Comparative Example 3 provides a lithium-ion battery, which differs from Example 1 in that, in step (1), LiNi is used... 0.83 Co 0.12 Mn 0.05 O2, conductive carbon black (Super P), and binder PVDF are uniformly dispersed in NMP solution at a mass ratio of 97:2:1 and stirred to form a positive electrode slurry with a solid content of 60%. That is, the positive electrode does not contain any dopants.

[0185] Comparative Example 4

[0186] Comparative Example 4 provides a lithium-ion battery, which differs from Comparative Example 3 in that, in step (1), the positive electrode active material is LiFePO4.

[0187] Test case

[0188] 1. The distribution and composition of dopants in the positive electrode sheets of Example 1, Comparative Example 1, and Comparative Example 2 were tested. The test methods and results are analyzed below:

[0189] (1) Disassemble the lithium-ion batteries provided in Example 1, Comparative Example 1 and Comparative Example 2 respectively, take the positive electrode sheet, immerse the positive electrode sheet in dimethyl carbonate (DMC) solvent for cleaning, then dry it, immerse it in liquid nitrogen for 3 minutes, take it out and cut it with scissors to expose the cross section, and then perform EDS test.

[0190] Figure 7 is an EDS cross-sectional view of element B in the positive electrode sheet provided in Embodiment 1 of this application, and Figure 8 is an enlarged view of Figure 7; Figure 9 is an EDS cross-sectional view of element P in the positive electrode sheet provided in Embodiment 1 of this application, and Figure 10 is an enlarged view of Figure 9. Figure 11 is an EDS cross-sectional view of element B in the positive electrode sheet provided in Comparative Example 1 of this application, and Figure 12 is an enlarged view of Figure 11; Figure 13 is an EDS cross-sectional view of element P in the positive electrode sheet provided in Comparative Example 1 of this application, and Figure 14 is an enlarged view of Figure 13. Figure 15 is an EDS cross-sectional view of element B in the positive electrode sheet provided in Comparative Example 2 of this application, and Figure 16 is an enlarged view of Figure 15; Figure 17 is an EDS cross-sectional view of element P in the positive electrode sheet provided in Comparative Example 2 of this application, and Figure 18 is an enlarged view of Figure 17.

[0191] In Figures 7 and 8, 11 and 12, and 15 and 16, the bright spot areas represent the distribution areas of the first dopant element, B. Similarly, the bright spot areas in Figures 9 and 10, 13 and 14, and 17 and 18 represent the distribution areas of the second dopant element, P. Compared to Figures 11 and 13, and 15 and 17, the bright spot areas in Figures 7 and 9 are more uniformly distributed and cover a wider area. This indicates that the distribution of B and P dopant elements is more uniform in the positive electrode sheet provided in Embodiment 1 of this application, and also suggests that the distribution of boron phosphate is more uniform. As can be seen from Figures 8 and 10, Figures 12 and 14, and Figures 14 and 18, any 1μm × 1μm region in Figures 8 and 10 (all boxed areas in Figures 8 and 10) contains areas with partial bright spots (the areas indicated by the arrows in the boxes are bright spot areas). Some 1μm × 1μm regions in Figures 12 and 14 (some boxed areas in Figures 12 and 14) and some 1μm × 1μm regions in Figures 16 and 18 (some boxed areas in Figures 16 and 18) do not contain bright spots. Therefore, in the positive electrode sheet provided in Embodiment 1 of this application, any 1μm × 1μm region of the active material layer contains bright spots of boron dopant and phosphorus dopant, that is, any 1μm × 1μm region in the longitudinal section of the positive electrode film layer contains boron phosphate dopant.

[0192] (2) Disassemble the lithium-ion battery provided in Example 1, take the positive electrode sheet, remove the positive current collector, retain the positive electrode film, immerse the positive electrode film in DMC, wash out the positive active material particles, dry it, and perform EDS test to obtain Figure 19 and Figure 20.

[0193] Figure 19 is an EDS diagram of element B in the positive electrode active material of the positive electrode sheet provided in Embodiment 1 of this application, and Figure 20 is an EDS diagram of element P in the positive electrode active material of the positive electrode sheet provided in Embodiment 1 of this application. In Figure 19, the bright spot area represents the distribution area of ​​the first dopant element B, and in Figure 20, the bright spot area represents the distribution area of ​​the second dopant element P. As can be seen from Figures 19 and 20, the preparation method provided in this application can coat the surface of the positive electrode active material with dopants containing both B and P elements.

[0194] (3) The lithium-ion battery in Example 1 was disassembled, and the positive electrode sheet was taken out. The positive electrode sheet was immersed in DMC solvent for cleaning, then dried, and powder was scraped off to obtain positive electrode powder. The first dopant element boron and the second dopant element phosphorus were analyzed separately. The sample was subjected to XPS test. Before performing peak fitting on the test results, the XPS spectrum was first corrected for background, and the external carbon source (284.8 eV) was used as the reference for calibration. Then, the peak area of ​​the XPS spectrum was normalized to eliminate the influence of factors such as sample surface morphology and chemical state on signal intensity. Finally, the identified peaks were fitted to determine the position, shape and intensity of the peaks. By comparing the electron binding energy shifts of the first and second dopant elements with the standard spectrum database, the chemical bonding mode and chemical valence state of the first and second dopant elements can be analyzed, thereby determining the dopant composition.

[0195] Figure 21 is an XPS B1s peak fitting diagram of the positive electrode powder obtained after scraping the positive electrode sheet according to Example 1 of this application, and Figure 22 is an XPS P2p peak fitting diagram of the positive electrode powder obtained after scraping the positive electrode sheet according to Example 1 of this application. As can be seen from Figure 21, the positive electrode powder contains BP bonds, and the electron binding energy of the boron 1s orbital (B1s) is 193.5 ± 1 eV. As can be seen from Figure 22, the positive electrode powder contains PB bonds, and the electron binding energy of the phosphorus 2p orbital (P2p) is 135.5 ± 1 eV. Therefore, the dopant composition can be determined to be boron phosphate. Furthermore, the BP bond has a high bond energy, indicating good stability and resistance to reaction with the electrolyte, as well as good thermal conductivity.

[0196] 2. The lithium-ion batteries provided in Examples 1 to 9 and Comparative Examples 1 to 4 were subjected to battery performance tests, and the content of doping elements in the positive electrode and the thermal stability of the positive electrode were detected. The test results are shown in Table 1. The test methods are as follows:

[0197] (1) Doping element content: The lithium-ion battery was disassembled, the positive electrode sheet was taken, the positive electrode sheet was immersed in DMC solvent for cleaning, then dried, and the positive electrode powder was scraped off. According to the national standards EPA 6010D-2018 and JY / T 0567-2020, the content of the first and second doping elements in the positive electrode powder was tested by inductively coupled plasma atomic emission spectrometry (ICP). Specifically, weigh approximately 0.05 g of sample using an analytical balance, add 1 mL of water to moisten the sample, then add 8 mL of nitric acid (68% by mass), 1 mL of hydrochloric acid (38% by mass), and 1 mL of hydrofluoric acid (40% by mass). Tighten the lid, place the container in a microwave digester, and pre-digest at 120°C for 30 min. Then, raise the temperature to 130°C and heat for 3 min, then hold at 130°C for 3 min. Next, raise the temperature to 150°C and heat for 3 min, then hold at 150°C for 10 min. Then, raise the temperature to 180°C and heat for 3 min, then hold at 180°C for 30 min. Finally, cool to 60°C and bring the volume to 25 mL with deionized water. The mass content of the doped elements is then determined using ICP.

[0198] (2) Thermal stability of the positive electrode: The lithium-ion battery was disassembled, the positive electrode was taken out, and the positive electrode was immersed in DMC solvent for cleaning, then dried and scraped to obtain positive electrode powder. 30mg of sample was weighed and placed into an Al2O3 crucible. The sample crucible was gently placed on the sample position on the support. The reference position was an empty crucible. The heating rate was set to 10℃ / min, and the exothermic temperature was tested using a differential scanning calorimeter (DSC).

[0199] (3) Battery capacity retention rate: Under a constant temperature environment of 25℃, the battery was charged to 4.25V at a rate of 0.33C at a voltage of 2.8V~4.25V, and then charged at a constant voltage of 4.25V until the current ≤0.05C. After resting for 5 minutes, the battery was discharged to 2.8V at a rate of 0.33C, and the discharge capacity was recorded. The process was repeated to obtain the capacity retention rate after 500 cycles. The capacity retention rate = discharge capacity of the first cycle / discharge capacity at the specified number of cycles × 100%.

[0200] Table 1. Partial fabrication process of the positive electrode sheet and performance test results of the positive electrode sheet and battery.

[0201]

[0202] As shown in Table 1, compared to Comparative Examples 1 to 4, the lithium-ion batteries provided in Examples 1 to 9 of this application exhibit both high safety performance and excellent cycle performance. Specifically, the DSC exothermic temperature of the positive electrode is greater than or equal to 205°C, and the capacity retention rate after 500 cycles is greater than or equal to 93%. A comparison of the performance test results of Examples 1 and 2 shows that by controlling the reaction of boron (B) and phosphorus (P) elements in a 1:1 molar ratio to generate boron phosphate, the DSC exothermic temperature of the positive electrode can be further increased, thereby improving the battery's safety performance. A comparison of the performance test results of Examples 1 and 3 shows that the presence of more phosphorus (P) allows the excess phosphate ions to react with lithium ions in the positive electrode active material to form lithium phosphate (Li3PO4). The strong bond energy of lithium phosphate further increases the DSC exothermic temperature of the positive electrode, thus further improving the battery's safety performance.

[0203] A comparison of the performance test results of Example 1 and Comparative Example 1 shows that in Comparative Example 1, where the dopant boron phosphate was directly added to the positive electrode slurry, the dopant was unevenly dispersed in the positive electrode sheet. Consequently, the DSC exothermic temperature and cycle capacity retention rate in Comparative Example 1 were significantly lower than those in Example 1. This demonstrates that adding the first and second doping precursors during the positive electrode slurry preparation process in this application, allowing them to react in situ to form the dopant, can effectively improve the uniformity of dopant dispersion, thereby enhancing the safety and cycle performance of the battery cell.

[0204] Comparing the performance test results of Example 1 and Comparative Example 2, it can be seen that Comparative Example 2 uses a dry doping coating method, where the dopant boron phosphate is dry-mixed with the positive electrode active material and then sintered. The sintered positive electrode active material is then used to prepare a positive electrode slurry, which is coated and dried to obtain the positive electrode sheet. In the positive electrode sheet obtained in Comparative Example 2, the dopant boron phosphate is not evenly dispersed. The DSC exothermic temperature and cycle capacity retention rate in Comparative Example 2 are significantly lower than those in Example 1. This demonstrates that the in-situ reaction method for forming dopant in this application not only allows some dopant to be coated on the surface of the positive electrode active material but also allows some dopant to be uniformly dispersed in the positive electrode film layer, thereby simultaneously improving the cycle performance and safety performance of the battery.

[0205] Comparing the performance test results of Example 1 and Comparative Example 3, and Example 7 and Comparative Example 4, it can be seen that, compared with Comparative Example 3 and Comparative Example 4 where no dopant is added, the dopant formed in situ during the positive electrode slurry preparation process in Example 1 and Example 7 can effectively improve the safety performance of the battery cell and improve the cycle performance of the battery cell.

[0206] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, The device includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least a portion of the surface of the positive current collector. The positive electrode film layer contains a positive electrode active material and a dopant. The dopant contains a first dopant element and a second dopant element. The first dopant element includes at least one of boron or aluminum, and the second dopant element includes at least one of phosphorus, silicon, or fluorine. The dopant is present in any 1μm×1μm region in the longitudinal section of the positive electrode film.

2. The battery cell according to claim 1, characterized in that, The molar ratio of the first dopant element to the second dopant element is (0.1~10):1; And / or, based on the mass of the positive electrode film, the mass content of the first dopant element is 100ppm to 10000ppm, and the mass content of the second dopant element is 300ppm to 30000ppm.

3. The battery cell according to claim 1 or 2, characterized in that, The molar ratio of the first dopant element to the second dopant element is 1:(1~5); And / or, based on the mass of the positive electrode film, the mass content of the first dopant element is 500ppm to 3000ppm, and the mass content of the second dopant element is 500ppm to 3000ppm.

4. The battery cell according to any one of claims 1 to 3, characterized in that, Based on the mass of the positive electrode film, the mass percentage of the dopant is 0.1% to 5%.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The dopant includes B 3+ Or Al 3+ At least one of the following, the dopant also includes PO4. 3- SiO5 6- or F - At least one of them.

6. The battery cell according to claim 5, characterized in that, The dopant includes at least one of boron phosphate, aluminum phosphate, boron silicate, aluminum silicate, boron fluoride, or aluminum fluoride.

7. The battery cell according to any one of claims 1 to 6, characterized in that, At least a portion of the dopant is coated onto the surface of the positive electrode active material to form a coating layer, the thickness of which is 1 nm to 200 nm.

8. A method for preparing a single battery cell, characterized in that, include: Preparation of positive electrode sheet: A positive electrode active material, a first doped precursor containing a first dopant element, and a second doped precursor containing a second dopant element are dispersed in a solvent. The first and second doped precursors dissolve in the solvent and react during dispersion to form a dopant, thereby obtaining a positive electrode slurry. The positive electrode slurry is coated onto at least a portion of the surface of a positive electrode current collector and dried to form a positive electrode film, thereby obtaining a positive electrode sheet. The dopant contains the first and second doped elements, wherein the first doped element includes at least one of boron or aluminum, and the second doped element includes at least one of phosphorus, silicon, or fluorine. The positive electrode, negative electrode, and electrolyte are assembled to form a battery cell.

9. The preparation method according to claim 8, characterized in that, In the positive electrode slurry, the molar ratio of the first dopant element to the second dopant element is (0.1~10):1; And / or, based on the mass of the positive electrode film, the mass content of the first dopant element is 100ppm to 10000ppm, and the mass content of the second dopant element is 300ppm to 30000ppm.

10. The preparation method according to claim 8 or 9, characterized in that, The first doped precursor includes BO3 3- Or Al 3+ At least one of them, wherein the second doped precursor includes PO4. 3- SiO5 6- or F - At least one of them; And / or, the first doped precursor includes at least one of boric acid or aluminum isopropoxide, and the second doped precursor includes at least one of lithium dihydrogen phosphate, sodium silicate, or ammonium fluoride.

11. The preparation method according to any one of claims 8 to 10, characterized in that, The method for preparing the positive electrode slurry includes: The second doped precursor is dissolved in the solvent to form a precursor solution; The positive electrode active material, conductive agent, and binder are mixed and dispersed in the precursor solution to form a mixed slurry; The first doped precursor is dissolved in the mixed slurry to form the positive electrode slurry.

12. The preparation method according to claim 11, characterized in that, The precursor solution has a mass concentration of 0.1% to 5%; the mixed slurry has a solid content of 50% to 75%.

13. A secondary battery, characterized in that, It includes battery cells as described in any one of claims 1 to 7, or battery cells prepared by the preparation method as described in any one of claims 8 to 12.

14. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 13.

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