Battery cell and method for producing the same, battery, electric device

Abstract

This application provides a battery cell and its preparation method, a battery, and an electrical device. The battery cell includes a positive electrode sheet, the positive electrode sheet includes a positive electrode film, and the positive electrode film includes lithium iron sulfate fluoride; the chemical formula of lithium iron sulfate fluoride satisfies: Li 1+a Fe x M y SO4F, -0.05≤a≤0.1, x≥0.95, y>0, x+y=1, the X-ray diffraction pattern of lithium iron sulfate fluoride shows a diffraction peak C at 29.5°~30.5° and a diffraction peak D at 31.5°~32.5°; the integrated area of ​​diffraction peaks C and D is S. C and S D The integral area of ​​the diffraction peak of lithium iron sulfate fluoride at 20°–40° is S, where: (S C +S D ) / S≥0.3, S C / S≥0.15, S D / S≥0.15. The technical solution of this application can improve the conductivity and stability of the battery cell, thereby enabling the battery cell to achieve both rate performance and cycle performance.

Description

Technical Field

[0001] This application relates to the field of batteries, and more specifically, to a battery cell and its preparation method, a battery, and an electrical device. Background Technology

[0002] With increasing environmental pollution, the new energy industry is attracting more and more attention. Within the new energy industry, battery technology is a crucial factor in its development.

[0003] The development of battery technology requires consideration of various design factors, such as energy density, cycle life, capacity, and reliability. Therefore, improving the rate performance and cycle performance of individual battery cells is a pressing issue that needs to be addressed. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell that improves the conductivity and stability of the material to improve the rate performance and cycle performance of the battery cell.

[0005] To achieve the above objectives, this application provides a battery cell and its preparation method, a battery, and an electrical device.

[0006] In a first aspect, a battery cell is provided, comprising: a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer, the positive electrode film layer being disposed on at least one surface of the positive current collector, the positive electrode film layer comprising lithium iron sulfate fluoride; the chemical formula of lithium iron sulfate fluoride satisfies: Li 1+a Fe x M y SO4F, -0.05≤a≤0.1, x≥0.95, y>0, x+y=1, M includes at least one of Ni, Co, Mn, Ti, V, Zr, Y, Al, Mg, B, Sr, Na, K, Nb, La, Si, Cl, Br; the X-ray diffraction pattern of lithium iron sulfate fluoride has a diffraction peak C at a diffraction angle of 2θ of 29.5°~30.5° and a diffraction peak D at a diffraction angle of 2θ of 31.5°~32.5°; the integral area of ​​diffraction peak C is S. C The integral area of ​​the diffraction peak D is S. D The integral area of ​​the diffraction peaks in the X-ray diffraction pattern of lithium iron sulfate fluoride at diffraction angles of 2θ ranging from 20° to 40° is S, where: (S C +S D ) / S≥0.3, S C / S≥0.15, S D / S≥0.15.

[0007] In this embodiment, the battery cell includes a positive electrode sheet, which includes a positive current collector and a positive electrode film. The positive electrode film is disposed on at least one surface of the positive current collector and includes lithium iron fluoride sulfate. The lithium iron fluoride sulfate introduces doping elements that stabilize the structure. These doping elements can support lithium-ion insertion / extraction channels in the material. In the crystal form formed by the positive electrode material, the crystal planes corresponding to diffraction peaks C and D are lithium extraction channels. When the integrated area ratio of diffraction peaks C and D is greater than 30%, it is beneficial to improve the material's lithium extraction capability, enhance the electronic conductivity and ion migration and transport efficiency of the positive electrode material, and improve the rate performance of the battery cell. Simultaneously, the doping elements can reduce structural degradation during charge and discharge, enhance the stability of the positive electrode material structure, and improve the cycle performance of the battery cell.

[0008] In one possible implementation, the positive electrode film layer further includes a coating layer that coats lithium iron sulfate fluoride. The coating layer comprises a carbon material, and the resistivity ρ of the carbon material satisfies: ρ≤0.01Ω·m.

[0009] In this embodiment, the surface of the positive electrode material contains a coating layer made of highly conductive carbon material. Therefore, after coating, the lithium iron fluoride sulfate exhibits improved conductivity and ion transport efficiency, thereby enhancing the rate performance of the material. Furthermore, coating reduces direct contact between the electrolyte and the lithium iron fluoride sulfate, minimizing the dissolution of the positive electrode material and reducing side reactions, thus improving the cycle performance of the battery cell.

[0010] In one possible implementation, the carbon material includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0011] In this embodiment, by using the carbon material described above, the conductivity of the coating layer can be improved, which is beneficial to the electron-ion transport of the cathode material, thereby improving the rate performance of the battery cell. At the same time, the structure of the material is stable and has a good coating effect.

[0012] In one possible implementation, the positive electrode includes a positive electrode film layer, in which the carbon material accounts for 0.3 wt% to 5 wt% by mass.

[0013] In the embodiments of this application, the content of carbon material coating layer in the positive electrode film layer is within the above range, which can ensure that the carbon material fully and completely coats the lithium iron sulfate fluoride, improve the cycle life of the battery, and at the same time improve the conductivity and rate performance of lithium iron sulfate fluoride.

[0014] In one possible implementation, the X-ray diffraction pattern of lithium iron sulfate fluoride has a diffraction peak A at a diffraction angle of 2θ between 26° and 27°, and a diffraction peak B at a diffraction angle of 2θ between 27.5° and 28.5°. The peak intensity of diffraction peak A is I. AThe peak intensity of diffraction peak B is I B The peak intensity of diffraction peak C is I C The peak intensity of diffraction peak D is I D , where: I C +I D ≥2(I A +I B ).

[0015] In this embodiment, the crystal plane (02-1) corresponding to diffraction peak C and the crystal plane (202) corresponding to diffraction peak D are lithium removal channels. After lithium ions are removed, the positions of these two peaks will shift to a lower angle. Conversely, the crystal plane (31-2) corresponding to diffraction peak A and the crystal plane (402) corresponding to diffraction peak B have a higher iron atom distribution. After lithium ions are removed, Fe attracts SO42-. 2- The crystal structure further shrinks, and the crystal planes (31-2) and (402) shift to higher angles. When the peak intensity of the diffraction peaks meets the above conditions, it is beneficial to improve the delithiation capability of lithium iron fluoride sulfate, thereby improving the electronic conductivity and ion migration and transport efficiency of the cathode material, and improving the rate performance of the battery cell.

[0016] In one possible implementation, I C / I A ≥1.2.

[0017] In the embodiments of this application, the peak intensity satisfies I C / I A A concentration of ≥1.2 can improve the delithiation capability of lithium iron fluoride sulfate, thereby improving the conductivity of the battery cell.

[0018] In one possible implementation, I C Greater than I A I C Greater than I B I C Greater than I D .

[0019] In the embodiments of this application, the peak intensity of diffraction peak C is the highest, which can improve the electronic conductivity of the material and thus improve the rate performance of the battery cell.

[0020] Secondly, a method for preparing a battery cell is provided, wherein FeSO4·7H2O is mixed with a dopant and sintered to obtain a first product, the dopant including at least one of sulfate and fluoride containing a dopant element, the dopant element including at least one of Ni, Co, Mn, Ti, V, Zr, Y, Al, Mg, B, Sr, Na, K, Nb, La, Si, Cl, Br; the first product is mixed with LiF and sintered in an inert atmosphere for 1 h to 5 h to obtain lithium iron fluoride sulfate, the sintering temperature being 350℃ to 450℃; a positive electrode sheet is prepared using lithium iron fluoride sulfate to obtain a battery cell.

[0021] In this embodiment, FeSO4·7H2O is first sintered with a dopant to remove the water of crystallization, and then mixed with LiF. By controlling the sintering temperature to be relatively high and the sintering time to be relatively short, doped lithium iron sulfate fluoride is obtained. The high sintering temperature allows the dopant element to diffuse into the particle interior, while the short sintering time ensures the crystal orientation of the lithium iron sulfate fluoride, thereby improving the conductivity and cycle performance of the material. In addition, the dopant includes at least one of sulfate and fluoride, avoiding the introduction of impurity elements, making the dopant element compatible with the existing system, and improving the stability of the structure.

[0022] In one possible implementation, the preparation of a positive electrode sheet using lithium iron fluoride sulfate includes: crushing lithium iron fluoride sulfate and mixing it with carbon material by ball milling, and then heat-treating the mixture to obtain a positive active material for preparing a positive electrode sheet.

[0023] In this embodiment, lithium iron fluoride sulfate and carbon material are ball-milled and mixed, so that the carbon material coats the surface of lithium iron fluoride sulfate to form a coating layer, thereby improving the conductivity and cycle life of the cathode material.

[0024] In one possible implementation, the resistivity ρ of the carbon material satisfies: ρ≤0.01Ω·m.

[0025] In the embodiments of this application, the carbon material has a low resistivity, which can improve the high conductivity of the coating material, enhance the electron-ion transport efficiency of the cathode material, and improve the rate performance of the battery cell.

[0026] In one possible implementation, the heat treatment includes heat treatment in an inert atmosphere at 300°C.

[0027] In this embodiment, the sintering temperature of the heat treatment is 300°C, which allows the surface of lithium iron fluoride sulfate to be fully coated with carbon material, improving the stability of lithium iron fluoride sulfate and thus ensuring the cycle life of the battery cell.

[0028] In one possible implementation, the carbon material includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0029] In the embodiments of this application, by coating the surface of lithium iron fluoride sulfate with the above-mentioned carbon material, the stability and conductivity of the coating layer can be improved, thereby improving the electrochemical performance of the battery cell.

[0030] In one possible implementation, the carbon material accounts for 0.3 wt% to 5 wt% of the total mass of the positive electrode active material.

[0031] In the embodiments of this application, when the mass ratio of carbon material is within the above range, the surface of lithium iron sulfate fluoride can have a coating layer, thereby improving the conductivity and cycle life of the cathode material.

[0032] In one possible implementation, the dopant includes at least one of NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and MnF2.

[0033] In the embodiments of this application, the use of the above-mentioned dopant can avoid the introduction of impurity elements and at the same time improve the conductivity of lithium iron sulfate fluoride.

[0034] In one possible implementation, the molar ratio of the first product to LiF is (0.95–1.1):1.

[0035] In the embodiments of this application, the molar ratio of the first product to LiF is within the above range, which can improve the delithiation ability of lithium iron sulfate fluoride, thereby improving the electronic and ionic conductivity of the material and improving the cycle performance and rate performance of the battery cell.

[0036] In one possible implementation, mixing FeSO4·7H2O with a dopant and sintering it comprises: mixing FeSO4·7H2O with the dopant and then sintering it in an inert atmosphere at 400°C for 3 hours.

[0037] In this embodiment, FeSO4·7H2O and the dopant are treated at a high sintering temperature to remove the water of crystallization from FeSO4 and the dopant, thereby avoiding the generation of impurity elements.

[0038] Thirdly, a battery is provided, comprising a battery cell according to the first aspect and any possible implementation thereof, and / or a battery cell obtained by a preparation method according to the second aspect and any possible implementation thereof.

[0039] Fourthly, an electrical device is provided, including the battery of the third aspect. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application.

[0041] Figure 2 This is a schematic diagram of a method for preparing a battery cell according to an embodiment of this application.

[0042] Figure 3 This is a schematic diagram of a battery cell according to an embodiment of this application.

[0043] Figure 4 This is a schematic diagram of a battery according to an embodiment of this application.

[0044] Figure 5 This is a schematic diagram of an electrical device according to an embodiment of this application.

[0045] Figure 6 This is an XRD pattern of an embodiment of this application.

[0046] Figure 7 This is a scanning electron microscope image of the positive electrode film layer according to an embodiment of this application.

[0047] Figure 8 This is a first charge-discharge curve diagram of an embodiment of this application.

[0048] Explanation of reference numerals in the attached figures:

[0049] 1 Positive electrode sheet; 10 Positive current collector; 11 Positive electrode film layer; 3 Battery cell; 31 Housing; 32 End cap assembly; 33 Electrode assembly; 34 Connecting component; 322 Electrode terminal; 330 Electrode assembly body; 331 Tab; 4 Battery; 5 Electrical device. Detailed Implementation

[0050] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, its manufacturing method, the 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 for the purpose of enabling 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 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 "ab" 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] In recent years, rechargeable batteries have been widely used in many fields such as power tools, electronic products, electric vehicles, and aerospace due to their high energy density and long service life, thus achieving significant development.

[0056] The development of battery technology must consider multiple design factors simultaneously, such as energy density, cycle life, discharge capacity, charge / discharge rate, fast charging capability, reliability, and initial charge capacity. With the widespread use of batteries, the requirements for charge / discharge rate and cycle performance are gradually increasing. For lithium-ion batteries, cathode materials play a crucial role in both cost and performance. Currently, lithium iron fluorosulfate, as a promising cathode material, requires further improvement in its ionic and electronic conductivity and cycle performance. Therefore, research on improving its electronic conductivity, ion diffusion rate, and cycle performance is of great significance.

[0057] In view of this, in one embodiment of this application, a battery cell is provided, comprising: a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer, the positive electrode film layer being disposed on at least one surface of the positive current collector, the positive electrode film layer including lithium iron sulfate fluoride; the chemical formula of lithium iron sulfate fluoride satisfies: Li 1+a Fe x M y SO4F, -0.05≤a≤0.1, x≥0.95, y>0, x+y=1, M includes at least one of Ni, Co, Mn, Ti, V, Zr, Y, Al, Mg, B, Sr, Na, K, Nb, La, Si, Cl, Br; the X-ray diffraction pattern of lithium iron sulfate fluoride has a diffraction peak C at a diffraction angle of 2θ of 29.5°~30.5° and a diffraction peak D at a diffraction angle of 2θ of 31.5°~32.5°; the integral area of ​​diffraction peak C is S. C The integral area of ​​diffraction peak D is S D The integral area of ​​the diffraction peaks in the X-ray diffraction pattern of lithium iron sulfate fluoride at diffraction angles of 2θ ranging from 20° to 40° is S, where: (S C +S D ) / S≥0.3, S C / S≥0.15, S D / S≥0.15. The crystal planes corresponding to diffraction peaks C and D are lithium extraction channels. When the integral area S of diffraction peak C... C The integral area S of the diffraction peak D DThe sum of the percentages is not less than 0.3, reflecting that the lithium-ion extraction channels of lithium iron fluoride sulfate are dominant in the material, which is conducive to the rapid insertion and extraction of lithium ions, thereby improving the rate performance of the battery cell. At the same time, the increase in the percentage of peak area indicates that the crystal structure of the material changes less during charge and discharge, thus improving cycle stability. Furthermore, by doping elements into lithium iron fluoride sulfate, the interlayer spacing of the material can be expanded, further increasing the lithium extraction channels, promoting the extraction of lithium ions, improving the material's lithium extraction capability, thereby enhancing the ionic and electronic conductivity, improving the charge and discharge rate, and improving the stability of the material through doping, reducing structural degradation during charge and discharge, and thus improving the cycle performance of the battery cell.

[0058] In addition, the following description, with appropriate reference to the accompanying drawings, will illustrate the battery cell, the method for preparing the battery cell, the battery, and the power-consuming device of this application.

[0059] [Battery cell]

[0060] In one embodiment of this application, a battery cell is provided.

[0061] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0062] Figure 1 This is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application. For example, as shown... Figure 1 As shown, the positive electrode 1 includes a positive current collector 10 and a positive electrode film layer 11 disposed on at least one side surface of the positive current collector 10.

[0063] The positive current collector 10 has two opposing surfaces along its thickness direction. The positive electrode film layer 11 can be disposed on one surface of the positive current collector 10 or on both surfaces of the positive current collector 10. As an example, such as... Figure 1 As shown, the positive electrode film layer 11 is disposed on both sides of the positive electrode current collector 10.

[0064] The positive electrode film layer 11 includes lithium iron fluoride sulfate, wherein the chemical formula of lithium iron fluoride sulfate satisfies: Li 1+ a Fe x M ySO4F, -0.05≤a≤0.1, x≥0.95, y>0, x+y=1, M includes at least one of Ni, Co, Mn, Ti, V, Zr, Y, Al, Mg, B, Sr, Na, K, Nb, La, Si, Cl, Br; the X-ray diffraction pattern of lithium iron sulfate fluoride has a diffraction peak C at a diffraction angle of 2θ of 29.5°~30.5° and a diffraction peak D at a diffraction angle of 2θ of 31.5°~32.5°; the integral area of ​​diffraction peak C is S. C The integral area of ​​diffraction peak D is S D The integral area of ​​the diffraction peaks in the X-ray diffraction pattern of lithium iron sulfate fluoride at diffraction angles of 2θ ranging from 20° to 40° is S, where: (S C +S D ) / S≥0.3, S C / S≥0.15, S D / S≥0.15.

[0065] Therefore, by adding lithium iron fluoride that meets the above conditions to the positive electrode film layer 11, the present application can improve the delithiation capability of the positive electrode active material by doping lithium iron fluoride, which is beneficial to improving the electronic conductivity and ion diffusion of the material, thereby improving the charge and discharge rate of the battery cell, and at the same time enhancing the stability of the structure and improving the cycle performance of the battery cell.

[0066] In some embodiments, the X-ray diffraction pattern of lithium iron sulfate fluoride shows a diffraction peak A at a diffraction angle of 2θ between 26° and 27°, and a diffraction peak B at a diffraction angle of 2θ between 27.5° and 28.5°, with a peak intensity of I0. A The peak intensity of diffraction peak B is I B The peak intensity of diffraction peak C is I C The peak intensity of diffraction peak D is I D , where: I C +I D ≥2(I A +I B ).

[0067] Diffraction peak A corresponds to crystal plane (31-2), diffraction peak B corresponds to crystal plane (40-2), diffraction peak C corresponds to crystal plane (02-1), and diffraction peak D corresponds to crystal plane (202). Crystal planes (02-1) and (202) are lithium extraction channels, while crystal planes (31-2) and (40-2) have a higher concentration of iron atoms. Therefore, when lithium iron fluoride sulfate meets the above conditions, it is beneficial to further improve the material's lithium extraction capability and enhance its rate performance.

[0068] In some embodiments, the peak intensities of diffraction peak A and diffraction peak C satisfy: I C / IA ≥1.2. This increases the peak intensity of the delithiation channel in lithium iron fluoride sulfate, which helps the material maintain better structural stability during delithiation, improves ion electron transport performance, and enhances electrochemical performance.

[0069] In some embodiments, the peak intensity of the diffraction peak satisfies: I C Greater than I A I C Greater than I B and I C Greater than I D This helps to improve electron conductivity and ion diffusion rate, thereby improving the charge / discharge rate performance of individual battery cells.

[0070] In some embodiments, the positive electrode film 11 further includes a coating layer that coats the lithium iron fluoride sulfate. The coating layer comprises a carbon material, and the resistivity ρ of the carbon material satisfies: ρ ≤ 0.01 Ω·m. Thus, coating the surface of the lithium iron fluoride sulfate with the aforementioned coating layer, which is a highly conductive carbon coating layer, can further improve the conductivity of the positive electrode material, making it more conducive to electron and ion transport and improving the rate performance of the material. Simultaneously, the coating can reduce the direct contact between the electrolyte and the material, reducing the dissolution of the positive electrode material and the occurrence of side reactions, thereby improving cycle performance.

[0071] In some embodiments, the carbon material includes at least one selected from conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene. Using highly stable carbon materials for solid-phase coating results in good coating performance, improving material stability and thus enhancing the cycle performance of the battery cell. Simultaneously, the highly conductive carbon material further improves the conductivity of the cathode material, thereby increasing the rate performance of the battery cell.

[0072] In some embodiments, the mass percentage of the coating layer is 0.3 wt% to 5 wt% based on the total mass of the positive electrode film layer 11.

[0073] Specifically, the mass percentage of the coating layer can be 0.3wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, or a value within the range obtained by any combination of the above values.

[0074] In the above embodiments, under these conditions, the carbon material coating layer in the positive electrode film 11 ensures sufficient and complete coating of lithium iron sulfate fluoride, improves the conductivity of the positive electrode material, and helps reduce internal resistance and polarization, thereby improving the battery's cycle life, fast charging performance, and energy efficiency. Simultaneously, the carbon material coating layer's mass content not exceeding 5 wt% avoids the risks associated with excessive carbon material introduction, such as reduced capacity of the positive electrode active material, decreased coulombic efficiency, increased carrier migration and transport paths, increased impedance, and increased side reactions.

[0075] [Preparation methods for battery cells]

[0076] In one embodiment of this application, a method for preparing a battery cell is provided.

[0077] Figure 2 This is a schematic diagram illustrating a method for preparing a single battery cell according to an embodiment of this application. (In conjunction with...) Figure 2 As shown, the preparation method 2 of the battery cell may include the following steps.

[0078] Step 210: FeSO4·7H2O is mixed with a dopant and sintered to obtain the first product.

[0079] Step 220: The first product and LiF are mixed and sintered in an inert atmosphere for 1 h to 5 h to obtain lithium iron sulfate fluoride. The sintering temperature is 350 to 450 °C.

[0080] Step 230: Prepare a positive electrode sheet using lithium iron fluoride sulfate to obtain a battery cell.

[0081] In step 210, the dopant includes at least one of sulfates and fluorides containing a dopant element, and the dopant element includes at least one of Ni, Co, Mn, Ti, V, Zr, Y, Al, Mg, B, Sr, Na, K, Nb, La, Si, Cl, and Br. As an example, the dopant includes at least one of NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and MnF2.

[0082] The inert atmosphere in step 220 includes one of nitrogen, argon, and helium.

[0083] Therefore, this application uses the aforementioned dopant, which has a similar structure to the raw materials used in the preparation of lithium iron fluorosulfate, avoiding the introduction of impurity elements and ensuring good compatibility between the dopant elements and the existing system. When sintering the first product with LiF, the sintering temperature is controlled at a relatively high level and the sintering time at a relatively short level, thereby controlling the crystal orientation. With a sintering temperature not less than 350℃, metal elements can diffuse into the particle interior. As time increases, Li / Fe begin to mutually occupy sites, at which point the peak intensities of diffraction peaks C and D begin to strengthen. Due to the volatility of LiF, a deficiency of Li and F occurs within the material, and more Fe begins to occupy Li sites. At this point, the peak intensities of diffraction peaks C and D begin to weaken, and the crystal structure further shrinks. This method can improve the electronic conductivity and ion diffusion rate of lithium iron fluorosulfate, thereby improving the rate performance of the battery cell, while also enhancing the structural stability of the material and improving the cycle life of the battery cell.

[0084] In some embodiments, step 210 further includes: mixing FeSO4·7H2O with the dopant and then sintering it in an inert atmosphere at 400°C for 3 hours. This can effectively remove the water of crystallization from FeSO4·7H2O and the dopant, reduce the occurrence of side reactions, improve the stability of the structure, and thus improve the cycle performance of the battery cell.

[0085] In some embodiments, step 230 further includes: crushing lithium iron fluoride sulfate and mixing it with carbon material through ball milling, followed by heat treatment to obtain a positive electrode active material for preparing a positive electrode sheet. In this way, the heat treatment of the carbon material mixed with lithium iron fluoride sulfate allows the carbon material to coat the surface of the lithium iron fluoride sulfate, forming a coating layer. This carbon material coating further improves the conductivity of the material, facilitating electron and ion transport. Simultaneously, the coating reduces direct contact between the electrolyte and the material, minimizing the dissolution of the positive electrode material and the occurrence of side reactions, thereby improving cycle performance.

[0086] In some embodiments, the resistivity ρ of the carbon material satisfies: ρ≤0.01Ω·m.

[0087] Specifically, the resistivity ρ of the carbon material can be 0.01 Ω·m, 0.008 Ω·m, 0.005 Ω·m, or a value within the range obtained by any combination of the above values.

[0088] Under the above conditions, the carbon material used for coating lithium iron fluoride sulfate has high conductivity, which can further improve the conductivity of the cathode material and improve the rate performance of the battery cell.

[0089] In some embodiments, the heat treatment includes heat treatment in an inert atmosphere at 300°C. This allows the carbon material to be better coated on the surface of lithium iron fluoride sulfate, forming a structurally stable coating layer, thereby improving the conductivity and cycle life of the battery cell.

[0090] In some embodiments, a positive electrode film layer is disposed on the surface of the positive electrode sheet, and the mass percentage of carbon material in the positive electrode film layer is 0.3wt% to 5wt%.

[0091] Specifically, the mass percentage of carbon material can be 0.3wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, or a value within the range obtained by any combination of the above values.

[0092] In some embodiments, the carbon material includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0093] Using the above materials can ensure the stability of the coating and the conductivity of the materials, thereby improving the rate performance of the battery cells.

[0094] In some embodiments, the molar ratio of the first product to LiF is (0.95 to 1.1):1.

[0095] Specifically, the molar ratio of the first product to LiF can be 0.95:1, 0.97:1, 0.98:1, 1:1, 1.08:1, 1.1:1, or a value within the range obtained by any combination of the above values.

[0096] When the molar ratio of the first product to LiF is within the above range, the occurrence of side reactions is reduced, the reaction efficiency is improved, the performance of the material is avoided, and the stability of the structure is guaranteed.

[0097] In some embodiments, the second aggregate is kneaded with the binder at the softening point of the binder, which is between 50°C and 80°C. Optionally, the binder includes at least one selected from asphalt, phenolic resin, furfural resin, and epoxy resin.

[0098] [Positive electrode plate]

[0099] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0100] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0101] 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.).

[0102] In some embodiments, the positive electrode film layer comprises lithium iron fluoride; the chemical formula of lithium iron fluoride satisfies: Li 1+ a Fe x M ySO4F, -0.05≤a≤0.1, x≥0.95, y>0, x+y=1, M includes at least one of Ni, Co, Mn, Ti, V, Zr, Y, Al, Mg, B, Sr, Na, K, Nb, La, Si, Cl, Br; the X-ray diffraction pattern of lithium iron sulfate fluoride has a diffraction peak C at a diffraction angle of 2θ of 29.5°~30.5° and a diffraction peak D at a diffraction angle of 2θ of 31.5°~32.5°; the integral area of ​​diffraction peak C is S. C The integral area of ​​diffraction peak D is S D The integral area of ​​the diffraction peaks in the X-ray diffraction pattern of lithium iron sulfate fluoride at diffraction angles of 2θ ranging from 20° to 40° is S, where: (S C +S D ) / S≥0.3, S C / S≥0.15, S D / S≥0.15.

[0103] In some embodiments, the positive electrode film layer further includes a coating layer, which coats lithium iron fluoride sulfate and includes a carbon material, wherein the resistivity ρ of the carbon material satisfies: ρ≤0.01Ω·m.

[0104] In some embodiments, the positive electrode film layer may further include at least one of the positive electrode active materials known in the art for use in batteries: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0105] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0106] In some embodiments, the positive electrode film 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.

[0107] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0108] [Negative electrode plate]

[0109] As described above, the negative electrode current collector has two opposing surfaces along its thickness direction. The negative electrode film layer can be disposed on one surface of the negative electrode current collector or on both surfaces.

[0110] 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 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 (copper, copper 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.).

[0111] In some embodiments, the negative electrode active material may be a 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, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material 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.

[0112] In some embodiments, the negative electrode film layer may optionally include a binder. The binder 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).

[0113] As described above, in some embodiments, the negative electrode film may optionally include conductive carbon. The conductive carbon may be selected from at least one of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0115] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive carbon, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0116] [Electrolytes]

[0117] 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.

[0118] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0119] For lithium-ion battery cells or lithium metal battery cells, the electrolyte salt may include one or more 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.

[0120] For lithium-ion battery cells or lithium metal battery cells, the solvent may include one or more of the following: 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.

[0121] For sodium-ion battery cells or sodium metal battery cells, the electrolyte salt may include at least one of NaPF6, NaBF4, NaN(SO2F)2, NaClO4, NaAsF6, NaB(C2O4)2, NaBF2(C2O4), NaN(SO2RF)2, and NaN(SO2F)(SO2RF), where RF includes C b F 2b+1 b is an integer from 1 to 10; optionally, the electrolyte salt includes at least one of NaPF6, NaN(SO2F)2, and NaBF2(C2O4); optionally, b is an integer from 1 to 3; optionally, RF includes at least one of CF3, C2F5, and CF2CF2CF3.

[0122] For sodium-ion battery cells or sodium metal battery cells, the solvent may include 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, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, 1,3-dioxolane, tetrahydrofuran, ethylene glycol dimethyl ether, and acetonitrile; optionally, the solvent may include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and butyl carbonate.

[0123] 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.

[0124] [Isolation membrane]

[0125] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0126] 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.

[0127] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0128] [Battery Device]

[0129] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0130] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the 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.

[0131] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3This is a square-structured battery cell 3, used as an example.

[0132] In some implementations, refer to Figure 3 The battery cell 3 includes a housing 31, an end cap assembly 32, and an electrode assembly 33 disposed within the housing 31. The housing 31 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 31 has an opening communicating with the receiving cavity, and the end cap assembly 32 can be closed by covering the opening. The end cap assembly 32 includes electrode terminals 322, such as... Figure 3 As shown, the end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal. The electrode assembly 33 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 33. The positive electrode sheet, negative electrode sheet, and separator can be formed into the electrode assembly 33 via a winding process or a stacking process. The electrode assembly 33 includes an electrode assembly body 330 and tabs 331 extending from the electrode assembly body 330. The battery cell 3 also includes a connecting member 34 for connecting the tabs 331 and the electrode terminals 322 of the electrode assembly 33. The battery cell 3 can contain one or more electrode assemblies 33, which can be selected by those skilled in the art according to specific practical needs.

[0133] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0134] Figure 4 This is a battery 4 as an example. Referring to the figure, in battery 4, multiple battery cells 3 can be arranged sequentially along the length of battery 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, these multiple battery cells 3 can be fixed in place by fasteners.

[0135] Optionally, the battery 4 may also include a housing with a receiving space in which multiple battery cells 3 are housed.

[0136] In some embodiments, the battery modules described above can also be assembled into a battery / battery pack. The number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0137] [Electrical appliances]

[0138] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack 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.

[0139] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0140] Figure 5 Here is an example of an electrical device 5. 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 the secondary battery for this electrical device, a battery pack or battery module can be used.

[0141] 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.

[0142] [Example]

[0143] 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.

[0144] Example 1

[0145] (1) Preparation of positive electrode sheet

[0146] FeSO4·7H2O and dopant MnSO4·H2O were mixed uniformly at a molar ratio of 98:2 using a high-speed mixer, and then sintered at 400℃ under a nitrogen atmosphere for 3 hours to remove the water of crystallization, obtaining the first product. LiF was mixed uniformly with the first product at a molar ratio of 1.03:1, and the above materials were placed in a mortar and sintered at 400℃ under a nitrogen atmosphere for 3 hours to obtain lithium iron sulfate fluoride. The lithium iron sulfate fluoride was crushed and then ball-milled with carbon nanotubes, wherein the mass proportion of carbon nanotubes was 2wt%. After heat treatment at 300℃ under a nitrogen atmosphere, the positive electrode active material was obtained. The positive electrode active material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were dissolved in the solvent N-methylpyrrolidone at a mass ratio of 90:5:5 and mixed uniformly to obtain the positive electrode slurry. The positive electrode slurry was then uniformly coated onto the positive electrode current collector aluminum foil. After drying, rolling, and slitting, the positive electrode sheet was obtained.

[0147] (2) Separating membrane

[0148] A polyethylene film with a thickness of 10 μm was used as the separator.

[0149] (3) Preparation of electrolyte

[0150] The organic solvents ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (EMC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. Then, a thoroughly dried lithium salt (LiPF6) was dissolved in the above mixed solvent at a ratio of 1 mol / L to obtain an electrolyte.

[0151] (4) Preparation of battery cells

[0152] The above-mentioned positive electrode sheet, separator, and lithium metal sheet with a diameter of 16 mm as counter electrode are stacked in sequence into a CR2032 button cell, the electrolyte prepared above is added, and the cell is obtained by encapsulation and standing.

[0153] Example 2

[0154] Compared with Example 1, the molar ratio of LiF to the first product in Example 2 is 0.98:1.

[0155] Example 3

[0156] Compared with Example 1, the molar ratio of LiF to the first product in Example 3 is 1.08:1.

[0157] Example 4

[0158] Compared with Example 1, in Example 4, FeSO4·7H2O and dopant MnSO4·H2O were mixed evenly at a molar ratio of 95:5.

[0159] Example 5

[0160] Compared with Example 1, the dopant in Example 5 is NiSO4·6H2O.

[0161] Example 6

[0162] Compared to Example 1, the dopant in Example 6 is MgSO4.

[0163] Example 7

[0164] Compared with Example 1, the dopant in Example 7 is Na2SO4·10H2O.

[0165] Example 8

[0166] Compared with Example 1, in Example 8, FeSO4·7H2O and dopants MnSO4·H2O and Ti(SO4)2·9H2O were mixed evenly in a molar ratio of 98:1:1.

[0167] Example 9

[0168] Compared to Example 1, the coating layer in Example 9 has a mass percentage of 0.5 wt%.

[0169] Example 10

[0170] Compared to Example 1, the coating layer in Example 10 has a mass percentage of 4 wt%.

[0171] Example 11

[0172] Compared to Example 1, the coating layer in Example 11 is Super P.

[0173] Example 12

[0174] Compared with Example 1, in Example 12, after LiF and the first product were mixed evenly and placed in a mortar, the sintering time was 2 hours.

[0175] Example 13

[0176] Compared with Example 1, in Example 13, after LiF and the first product were mixed evenly and placed in a mortar, the sintering time was 5 hours.

[0177] Example 14

[0178] Compared with Example 1, in Example 14, after LiF and the first product were mixed evenly and placed in a mortar, the sintering temperature was 350°C.

[0179] Example 15

[0180] Compared with Example 1, in Example 15, after LiF and the first product were mixed evenly and placed in a mortar, the sintering temperature was 450°C.

[0181] Example 16

[0182] Compared to Example 1, the lithium iron fluoride in Example 16 did not have a coating layer on its surface.

[0183] Comparative Example 1

[0184] Compared with Example 1, no dopant was added in Comparative Example 1, and only FeSO4·7H2O was used as raw material.

[0185] Comparative Example 2

[0186] Compared with Example 1, in Comparative Example 2, after LiF and the first product were mixed evenly and placed in a mortar, the sintering temperature was 550°C.

[0187] Comparative Example 3

[0188] Compared with Example 1, in Comparative Example 3, after LiF and the first product were mixed evenly and placed in a mortar, the sintering temperature was 300°C.

[0189] Comparative Example 4

[0190] Compared with Example 1, in Comparative Example 4, after LiF and the first product were mixed evenly and placed in a mortar, the sintering time was 8 hours.

[0191] The battery cells obtained in Example 1 and Comparative Example 1 were subjected to parameter and performance tests. The test results are shown in Table 1 below.

[0192] Table 1: Specific parameters of Examples 1-16 and Comparative Examples 1-4

[0193]

[0194]

[0195] (1) Element detection method

[0196] The content of the coating carbon material in the above samples was tested according to the national standard EPA 6010D-2018JY / T 0567-2020 inductively coupled plasma atomic emission spectrometry.

[0197] (2) Ratio retention test

[0198] At 25°C, the tested battery cells were charged at a constant current rate of 0.1C to 100% State of Charge (SOC), i.e., charged at a constant current rate of 0.1C to 4.5V, and then charged at a constant voltage of 4.5V to a cutoff current of 0.05C. They were then discharged at a constant current rate of 1C, with a discharge cutoff voltage of 2V. The capacity retention rate of 1C / 0.1C can be used to characterize the battery's rate performance.

[0199] (3) Capacity retention test

[0200] At 25℃, a single battery cell is charged to 4.5V at a constant current of 0.5C, then charged to 0.05C at a constant voltage of 4.5V. After resting for 5 minutes, it is discharged to 2.0V at 0.5C. The resulting discharge capacity is recorded as the initial capacity C0. The above steps are repeated for the same battery cell, and the discharge capacity Cn of the battery after the nth cycle is recorded. The battery capacity retention rate after each cycle is Pn = (Cn / C0) × 100%. The battery cell is charged and discharged in this way until the battery has been cycled 40 times. The capacity retention rate at this time is recorded. For detailed test results, please refer to Table 2.

[0201] (4) Peak height and peak area test

[0202] The XRD pattern of the sample was tested according to the JIS / K0131-1996 testing standard. The corresponding diffraction peaks of the target crystal were located based on the XRD pattern of the sample, and the peak height was determined based on the diffraction peaks. The peak height refers to the height of the peak value (vertical axis of the peak value).

[0203] After fitting a baseline to the XRD pattern, the minimum value of the diffraction peaks with diffraction angles between 20° and 40° is set as 0. The baseline-fitted data is obtained by subtracting this value from the intensities of other peaks. Then, integration is performed to obtain the peak area. Integrating the peak intensities between 20° and 40° yields the total peak area S, and the peak area between 29.5° and 30.5° is S0. C The peak area at 31.5°–32.5° is S. D .

[0204] Figure 6 This is an XRD pattern of an embodiment of this application, provided by... Figure 6 The peak heights and peak areas of diffraction peaks A, B, C, and D can be determined, and thus S can be obtained. C S D The ratio of S to the crystalline form that meets the above conditions is beneficial to improving the electron-ion transport efficiency of lithium iron fluoride sulfate, thereby improving the rate performance and cycle performance of the battery cell.

[0205] Figure 7 This is a scanning electron microscope (SEM) image of the positive electrode film layer according to an embodiment of this application. Figure 7 It is known that lithium iron fluoride sulfate has a coating layer on its surface, which has a good coating effect and is beneficial to improving the cycle performance and rate performance of the cathode material.

[0206] (5) Gram volume test

[0207] At 25℃, the cathode is charged at a constant current rate of 0.1C to 4.5V, and then charged at a constant voltage rate of 4.5V until the cutoff current is 0.05C. It is then discharged at a constant current rate of 0.1C, with a discharge cutoff voltage of 2V. The specific capacity of the cathode active material can be calculated by combining this with the mass of the positive electrode active material.

[0208] Figure 8 This is a charge-discharge curve diagram of an embodiment of this application, provided by... Figure 8 It is known that more than 80% of the specific capacity is above 3V. Therefore, by doping elements into lithium iron fluoride sulfate, the charge and discharge performance of the battery cells is improved, and the energy density of the battery cells is increased.

[0209] The test results for the above parameters are shown in Table 2.

[0210] Table 2: Test results of Examples 1-16 and Comparative Examples 1-4

[0211]

[0212]

[0213] As can be seen from Examples 1-16 and Comparative Example 1, by doping elements into lithium iron fluoride sulfate and thereby controlling the crystal orientation, the specific capacity and rate performance of the battery cell can be improved, while the cycle performance of the battery cell can be enhanced.

[0214] As can be seen from Examples 1-3, maintaining the molar ratio of LiF to the first product at (0.95-1.1):1 is beneficial to the crystal stability of lithium iron sulfate fluoride, thereby improving the conductivity of the material and enhancing the specific capacity, rate performance, and cycle life of the battery cell.

[0215] Combining Examples 1 and 4, maintaining the molar ratio of FeSO4·7H2O to dopant MnSO4·H2O at (95-100):(0-5) is beneficial for material structure stability, can improve delithiation capability, and enhance the rate performance and cycle retention of battery cells.

[0216] In conjunction with Examples 1 and 5-8, different types of dopants can improve the rate performance and cycle life of battery cells.

[0217] Combining Examples 1 and 9-10, by maintaining the mass percentage of the coating layer between 0.3wt% and 5wt%, the rate performance of the battery cell can be improved, and it increases with the increase of the mass percentage.

[0218] Combining Examples 1 and 11, different types of coating materials can improve the conductivity of battery cells, thereby improving the rate performance of battery cells.

[0219] By combining Examples 1, 12-13 and Comparative Example 4, the sintering time after uniformly mixing LiF with the first product and packing it into a mortar can be controlled within the range of 1h to 5h, which can ensure the stability of the crystal structure and is beneficial to improving the specific capacity, rate performance and cycle performance of the material.

[0220] Combining Examples 1, 14-15 and Comparative Examples 2-3, by maintaining the sintering temperature of the LiF-first product mixture at 350℃~450℃ after uniform mixing and sintering in a mortar, the unstable crystal structure caused by excessively high temperature can be avoided, thereby improving the rate performance of the battery cell.

[0221] In conjunction with Examples 16 and Comparative Examples 1-4, the cycle performance of battery cells can be improved by controlling the sintering time and sintering temperature of lithium iron fluoride for doping.

[0222] 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, include: A positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode film layer, the positive electrode film layer being disposed on at least one surface of the positive current collector, the positive electrode film layer comprising lithium iron sulfate fluoride; The chemical formula of the lithium iron sulfate fluoride satisfies: Li 1+a Fe x M y SO4F, -0.05≤a≤0.1, x≥0.95, y>0, x+y=1, M includes at least one of Ni, Co, Mn, Ti, V, Zr, Y, Al, Mg, B, Sr, Na, K, Nb, La, Si, Cl, Br; The X-ray diffraction pattern of the lithium iron sulfate fluoride has a diffraction peak C at a diffraction angle of 2θ of 29.5° to 30.5° and a diffraction peak D at a diffraction angle of 2θ of 31.5° to 32.5°. The integral area of ​​the diffraction peak C is S. C The integral area of ​​the diffraction peak D is S. D The integral area of ​​the diffraction peaks in the X-ray diffraction pattern of the lithium iron sulfate fluoride at diffraction angles of 2θ ranging from 20° to 40° is S, where: (S C +S D ) / S≥0.3, S C / S≥0.15, S D / S≥0.

15.

2. The battery cell according to claim 1, characterized in that, The positive electrode film layer further includes a coating layer, which coats the lithium iron sulfate fluoride. The coating layer includes a carbon material, and the resistivity ρ of the carbon material satisfies: ρ≤0.01Ω·m.

3. The battery cell according to claim 2, characterized in that, The carbon material includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

4. The battery cell according to claim 2 or 3, characterized in that, Based on the total mass of the positive electrode film, the mass percentage of the coating layer is 0.3 wt% to 5 wt%.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The X-ray diffraction pattern of the lithium iron sulfate fluoride shows a diffraction peak A at a diffraction angle of 2θ between 26° and 27°, and a diffraction peak B at a diffraction angle of 2θ between 27.5° and 28.5°. The peak intensity of diffraction peak A is I. A The peak intensity of the diffraction peak B is I. B The peak intensity of the diffraction peak C is I. C The peak intensity of the diffraction peak D is I. D , where: I C +I D ≥2(I A +I B ).

6. The battery cell according to any one of claims 1 to 5, characterized in that, I C / I A ≥1.2。 7. The battery cell according to any one of claims 1 to 6, characterized in that, I C Daeyu I A , I C Daeyu I B , I C Daeyu I D .

8. A method for preparing a single battery cell, characterized in that, include: FeSO4·7H2O is mixed with a dopant and sintered to obtain a first product. The dopant includes at least one of sulfate and fluoride containing a dopant element. The dopant element includes at least one of Ni, Co, Mn, Ti, V, Zr, Y, Al, Mg, B, Sr, Na, K, Nb, La, Si, Cl, and Br. The first product was mixed with LiF and sintered in an inert atmosphere for 1 h to 5 h to obtain lithium iron sulfate fluoride. The sintering temperature was 350℃ to 450℃. The positive electrode sheet is prepared using the lithium iron fluoride sulfate to obtain a battery cell.

9. The method according to claim 8, characterized in that, The preparation of the positive electrode sheet using the lithium iron fluoride sulfate includes: crushing the lithium iron fluoride sulfate and mixing it with carbon material by ball milling, and then heat-treating the mixture to obtain the positive electrode active material, so as to prepare the positive electrode sheet.

10. The method according to claim 9, characterized in that, The resistivity ρ of the carbon material satisfies: ρ≤0.01Ω·m.

11. The method according to claim 9 or 10, characterized in that, The heat treatment includes: heat treatment in an inert atmosphere at 300°C.

12. The method according to any one of claims 9 to 11, characterized in that, The carbon material includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

13. The method according to any one of claims 9 to 12, characterized in that, The positive electrode includes a positive electrode film layer, and the carbon material in the positive electrode film layer accounts for 0.3wt% to 5wt% by mass.

14. The method according to any one of claims 8 to 13, characterized in that, The dopant includes at least one of NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and MnF2.

15. The method according to any one of claims 8 to 14, characterized in that, The molar ratio of the first product to LiF is (0.95–1.1):

1.

16. The method according to any one of claims 8 to 15, characterized in that, The process of mixing FeSO4·7H2O with the dopant and sintering includes: mixing FeSO4·7H2O with the dopant and then sintering it in an inert atmosphere at 400°C for 3 hours.

17. A battery, characterized in that, Includes battery cells as described in any one of claims 1-7, and / or battery cells prepared by the method as described in any one of claims 8-16.

18. An electrical appliance, characterized in that, Includes the battery as described in claim 17.

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