Lithium iron manganese phosphate material, method of making same, battery cell, battery device, and power using device

Abstract

This application provides a lithium manganese iron phosphate material, its preparation method, a battery cell, a battery device, and an electrical device. The battery cell includes a positive electrode sheet, which includes a positive electrode active material. The positive electrode active material includes lithium manganese iron phosphate material, which includes lithium manganese iron phosphate particles and sulfur element. The sulfur element is doped on the surface of the lithium manganese iron phosphate particles, and the sulfur element is doped at the phosphorus sites of the lithium manganese iron phosphate particles. The sulfur element includes +6 valent sulfur.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a lithium manganese iron phosphate material and its preparation method, a battery cell, a battery device, and an electrical device. Background Technology

[0002] With the widespread application of power batteries in electric vehicles and energy storage systems, the requirements for battery cell energy density and cycle life are constantly increasing. Lithium manganese iron phosphate (LFP) has become one of the most promising candidate materials due to its combination of the high voltage advantage of lithium manganese phosphate and the cycle stability of lithium iron phosphate. However, the surface Mn content of LFP cathode materials... 3+ The unstable ionic chemical properties of the material easily induce interfacial side reactions and are accompanied by the dissolution of manganese ions, which degrades the ion conduction rate and rate performance of the material, becoming the main bottleneck for its practical application. Summary of the Invention

[0003] This application provides a lithium manganese iron phosphate material and its preparation method, a battery cell, a battery device, and an electrical device to improve the rate performance and cycle performance of the battery cell.

[0004] The first aspect of this application provides a battery cell, which includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, the positive electrode active material includes lithium manganese iron phosphate material, the lithium manganese iron phosphate material includes lithium manganese iron phosphate particles and sulfur element, the sulfur element is doped on the surface of the lithium manganese iron phosphate particles, and the sulfur element is doped at the phosphorus element sites of the lithium manganese iron phosphate particles, the sulfur element includes +6 valent sulfur element.

[0005] The second aspect of this application provides a lithium manganese iron phosphate material comprising lithium manganese iron phosphate particles and sulfur element, wherein the sulfur element is doped on the surface of the lithium manganese iron phosphate particles and the sulfur element is doped at the phosphorus sites of the lithium manganese iron phosphate particles, and the sulfur element includes +6 valent sulfur element.

[0006] When sulfur is doped at phosphorus sites on the surface of lithium manganese iron phosphate particles, including +6 valent sulfur, sulfate ions are formed on the surface. Since sulfate ions are more electronegative than phosphate ions, this causes a change in the electron distribution of the crystal structure, enhancing the effect of surface oxygen atoms on lithium ions. This increases the binding energy of lithium ions at surface sites, lowers the energy barrier during migration, accelerates ion diffusion at the surface and interface, reduces side reactions and mechanical damage, and improves interface stability. Simultaneously, S... 6+ Replace P 5+This process induces charge compensation, leading to a slightly lithium-deficient state on the surface. This increases the local current density, further optimizing the reaction kinetics at the electrode / electrolyte interface and contributing to improved rate performance. On the other hand, while the lithium-deficient state causes some capacity loss, the strong electronegativity of sulfate weakens the covalent bond between the transition metal and oxygen, lowering the energy level of the transition metal-oxygen antibonding orbitals. This, in turn, increases the average discharge voltage of the material, compensating for the adverse effect of capacity reduction on energy density. Therefore, the sulfur doping in this application, through the synergistic effect of lowering the lithium-ion migration barrier and increasing the operating voltage, achieves significant improvements in rate and cycle performance without sacrificing energy density.

[0007] In any embodiment of the first or second aspect, the sulfur content in the lithium manganese iron phosphate material is 0.01%-0.05% by mass.

[0008] In any embodiment of the first or second aspect, the sulfur doping depth is 0.5 nm to 2 nm. This doping depth allows the electronic structure and lithium-poor state to be primarily distributed in the surface or subsurface region of the particles, thereby optimizing the reaction kinetics and ion diffusion pathways at the electrode / electrolyte interface, significantly improving the surface reaction rate, and better controlling the defect of reduced bulk structural stability caused by sulfur penetrating deep into the bulk lattice.

[0009] In any embodiment of the first or second aspect, the molar ratio of manganese to iron in the lithium manganese iron phosphate material is 6:4-8:2.

[0010] In any embodiment of the first or second aspect, the lithium manganese iron phosphate particles have the chemical formula Li a A x Mn 1- y R y PO4, where A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; R includes Fe and optionally one or more elements selected from Ti, V, Zr, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; a is selected from the range of 0.9 to 1.1; x is selected from the range of 0.001 to 0.1; and y is selected from the range of 0.001 to 0.5.

[0011] In any embodiment of the first or second aspect, the lithium manganese iron phosphate material further includes a carbon-containing coating layer.

[0012] In any embodiment of the first or second aspect, the carbon-containing coating layer includes at least one of amorphous carbon and carbon black.

[0013] In any embodiment of the first or second aspect, the carbon content in the lithium manganese iron phosphate material is 1.5%-5% by mass.

[0014] A third aspect of this application provides a method for preparing lithium manganese iron phosphate material, the method comprising:

[0015] Lithium manganese iron phosphate particles, sulfur source and solvent are mixed to obtain a first mixed slurry, and the first mixed slurry is dried to obtain a sulfur-doped precursor.

[0016] The sulfur-doped precursor was sintered to obtain lithium manganese iron phosphate material.

[0017] The sulfur source includes one or more of sulfates or pyrosulfates.

[0018] In any embodiment of the third aspect, the sulfur source includes one or more of ferrous sulfate, ammonium sulfate, lithium sulfate, or potassium pyrosulfate.

[0019] In any embodiment of the third aspect, sintering satisfies one or more of the following conditions: the sintering temperature is 480°C-750°C;

[0020] The sintering time is 6-10 hours.

[0021] Sintering is carried out in air, nitrogen, or an inert gas.

[0022] In any embodiment of the third aspect, the mass content of the sulfur source is 0.1%-0.5% based on the total mass of the lithium manganese iron phosphate particles and the sulfur source.

[0023] In any embodiment of the third aspect, the preparation method further includes the following steps:

[0024] The sulfur-doped precursor is mixed with a carbon source and a solvent to obtain a second mixed slurry, wherein the mixing is optionally carried out by sand milling;

[0025] The second mixed slurry was dried to obtain the carbon-coated precursor.

[0026] The process of sintering the sulfur-doped precursor includes:

[0027] The carbon-coated precursor is sintered to obtain lithium manganese iron phosphate material.

[0028] The fourth aspect of this application provides a battery device including a battery cell, the battery cell including a battery cell provided in any embodiment of the first aspect and a battery cell obtained in any embodiment of the second aspect.

[0029] The fifth aspect of this application provides an electrical device including a battery cell or a battery device, wherein the battery cell includes a battery cell provided by any embodiment of the first aspect and a battery cell obtained by any embodiment of the second aspect, and the battery device is a battery device provided by any embodiment of the third aspect. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0031] Figure 1 The charge / discharge curves of LMFP-73-S and LMFP-73 in Embodiment 1 of this application are shown.

[0032] Figure 2 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0033] Figure 3 yes Figure 2 An exploded view of a battery cell according to one embodiment of this application is shown.

[0034] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0035] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0036] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0037] Figure 7 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application.

[0038] The accompanying drawings are not drawn to scale.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0041] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0042] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the lithium manganese iron phosphate material, its preparation method, battery cell, battery device, and 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 a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0043] 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.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0045] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0046] 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.

[0047] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0048] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0049] [Lithium iron manganese phosphate materials]

[0050] As analyzed in the background section, although lithium manganese iron phosphate (LFP) cathodes have the potential to improve energy density, the unstable Mn³⁺ ions on the surface easily trigger interfacial side reactions, severely impacting the application value of individual cells in fast charging and high-power output scenarios. To address this issue, existing technologies have attempted many solutions, such as further reducing the particle size of LFP particles to shorten the lithium-ion diffusion path and improve kinetic performance. However, while reducing particle size improves ion transport, it also increases the specific surface area of ​​the material, thereby exacerbating side reactions and manganese dissolution, ultimately worsening the material's electrochemical performance and cycle life.

[0051] To address the issues of poor rate performance and insufficient cycle stability of lithium manganese iron phosphate cathodes, this application provides a single battery cell, a method for manufacturing the single battery cell, a battery device, and an electrical device.

[0052] The first embodiment of this application provides a lithium manganese iron phosphate material, which includes lithium manganese iron phosphate particles and sulfur element. The sulfur element is doped on the surface of the lithium manganese iron phosphate particles and is doped at the phosphorus sites of the lithium manganese iron phosphate particles. The sulfur element includes +6 valent sulfur element.

[0053] The applicant discovered that when sulfur is doped at phosphorus sites on the surface of lithium manganese iron phosphate particles, and the sulfur includes +6 valent sulfur, sulfate ions are formed on the surface of the lithium manganese iron phosphate particles. Since sulfate ions are more electronegative than phosphate ions, this causes a change in the electron distribution of the crystal structure, enhancing the effect of surface oxygen atoms on lithium ions, i.e., increasing the binding energy of lithium ions at surface sites, lowering the energy barrier during their migration, thereby accelerating ion diffusion at the surface and interface, reducing side reactions and mechanical damage, and improving interface stability; simultaneously, S 6+ Replace P 5+ This process induces charge compensation, leading to a slightly lithium-deficient state on the surface. This increases the local current density, further optimizing the reaction kinetics at the electrode / electrolyte interface and contributing to improved rate performance. On the other hand, while the lithium-deficient state causes some capacity loss, the strong electronegativity of sulfate weakens the covalent bond between the transition metal and oxygen, lowering the energy level of the transition metal-oxygen antibonding orbitals. This, in turn, increases the average discharge voltage of the material, compensating for the adverse effect of capacity reduction on energy density. Therefore, the sulfur doping in this application, through the synergistic effect of lowering the lithium-ion migration barrier and increasing the operating voltage, achieves significant improvements in rate performance (charging capability) and cycle performance without sacrificing energy density.

[0054] The lithium intercalation voltages of undoped lithium manganese iron phosphate (LFP), LFP doped with sulfur at phosphorus sites, and LFP doped with sulfur at oxygen sites differ. Specifically, first-principles calculations comparing the lithium intercalation voltages of these three models revealed that sulfur doping at phosphorus sites increases the lithium intercalation voltage, while oxygen doping decreases it, as shown in Table 1. Therefore, under the same negative electrode conditions, the discharge voltage (≈ lithium intercalation voltage of the positive electrode - lithium delithiation voltage of the negative electrode) of the battery cells using the three models as positive electrode active materials exhibits different trends. The lithium intercalation voltage is highest when sulfur is doped at phosphorus sites, and decreases instead of increasing when sulfur is doped at oxygen sites. Therefore, testing the lithium intercalation voltage changes of the corresponding battery cells can determine the sulfur doping sites.

[0055] Table 1. Calculated lithium intercalation voltage data for sulfur-free and surface sulfur-doped lithium.

[0056]

[0057] In some embodiments, the sulfur content in the lithium manganese iron phosphate material is 0.01%-0.05% by mass. For example, the sulfur content in the lithium manganese iron phosphate material can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, or within any two of the above values. When sulfur is doped onto the surface of lithium manganese iron phosphate particles and the doping amount is controlled within the above-mentioned trace range, the electronic structure of the particle surface can be effectively adjusted without causing significant distortion to the main crystal lattice. This allows the doped lithium manganese iron phosphate to leverage the local electron distribution optimization and surface kinetic improvement brought about by sulfur doping, while controlling the structural instability and side reactions that may be caused by excessive doping. Thus, it improves both cycle stability and rate performance.

[0058] In this application, the sulfur content in lithium manganese iron phosphate material can be measured by the following method: the battery cell discharged to the cutoff voltage is disassembled to obtain the positive electrode sheet, which is then cleaned with an organic solvent and subjected to high-temperature heat treatment to thoroughly remove electrolyte residue, conductive agent and binder. The sulfur content in the obtained pure powder is then determined by inductively coupled plasma mass spectrometry (ICP-MS) equipped with a collision reaction cell (CRC) to eliminate polyatomic ion interference.

[0059] In some embodiments, the sulfur doping depth is 0.5 nm to 2 nm. For example, the sulfur doping depth can be 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2 nm, or within any two of the above values. This doping depth allows the electronic structure and lithium-deficient state to be mainly distributed in the surface or subsurface region of the particles, thereby optimizing the reaction kinetics and ion diffusion paths at the electrode / electrolyte interface, significantly improving the surface reaction rate, and better controlling the defect of reduced bulk structural stability caused by sulfur penetrating deep into the bulk lattice.

[0060] In this application, the doping depth of sulfur can be measured by the following method: using ultra-high quality resolution time-of-flight secondary spectroscopy (HR-ToF-SIMS), the sample cross-section is analyzed for ion sputtering depth, the change of the ³²S characteristic signal with sputtering time is monitored, and the sputtering time is converted into depth by standard calibration; the doping depth of sulfur in lithium manganese iron phosphate material is characterized by analyzing the distribution characteristics of the signal after penetrating the surface layer.

[0061] In some embodiments, the molar ratio of manganese to iron in lithium manganese iron phosphate (LFP) materials is 6:4-8:2. For example, the molar ratio of manganese to iron in LFP materials can be 6:4, 7:3, 8:2, or within any two of the above ratios. Adjusting the manganese / iron molar ratio within the above range in LFP materials can achieve a balance between high voltage capacity and cycle stability, thereby improving the overall electrochemical performance of the battery cell.

[0062] In this application, the elemental composition of the lithium manganese iron phosphate material can be confirmed by EDS combined with XRD.

[0063] In some embodiments, lithium manganese iron phosphate particles have the chemical formula Li a A x Mn 1-y R y PO4, where A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; R includes Fe and optionally one or more elements selected from Ti, V, Zr, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; a is selected from the range of 0.9 to 1.1; x is selected from the range of 0.001 to 0.1; and y is selected from the range of 0.001 to 0.5. Through multi-metal synergistic doping, the energy density and cycle stability of lithium manganese iron phosphate cathode materials can be further improved.

[0064] In some embodiments, lithium manganese iron phosphate materials also include a carbon coating layer. Introducing a carbon coating layer on the basis of sulfur doping not only provides a continuous electronic conduction network, but also reduces the possibility of electrolyte directly corroding the surface material. This allows the surface electronic structure and kinetic advantages optimized by sulfur doping to be maintained for a long time, further improving the interfacial environment between the positive electrode active material and the electrolyte, thereby improving the cycle characteristics of the battery cell.

[0065] In some embodiments, the carbon-containing coating layer includes at least one of amorphous carbon and carbon black. When the carbon-containing coating layer includes carbon black, it facilitates the construction of a conductive network, thereby improving the conductivity of the positive electrode. When amorphous carbon is used as the coating layer, its highly dispersed and disordered structure can tightly cover the particle surface and provide multidirectional electron transport channels. Compared to crystalline carbon materials, amorphous carbon has more defect sites, which is beneficial for improving interfacial conductivity and enhancing the synergistic effect with the sulfur-doped surface layer, thereby further reducing interfacial charge transfer impedance while improving electronic conductivity.

[0066] In some embodiments, the carbon content in the lithium manganese iron phosphate material is 1%-2% by mass. For example, the carbon content in the lithium manganese iron phosphate material can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or within any two of the above ratios. This range of carbon content allows for the formation of a uniform and continuous conductive network, improving the overall electronic conductivity of the material, while avoiding excessively high carbon content that reduces the volume ratio of the active material. This results in a more balanced electron / ion transport process, thereby comprehensively improving rate performance and energy utilization efficiency.

[0067] [Battery cell]

[0068] The second embodiment of this application provides a battery cell, which includes a positive electrode sheet, a positive electrode active material, a lithium manganese iron phosphate material, a lithium manganese iron phosphate particle and sulfur element, wherein the sulfur element is doped on the surface of the lithium manganese iron phosphate particle, and the sulfur element is doped at the phosphorus site of the lithium manganese iron phosphate particle, and the sulfur element includes +6 valent sulfur element.

[0069] When sulfur is doped at phosphorus sites on the surface of lithium manganese iron phosphate particles, including +6 valent sulfur, sulfate ions are formed on the surface. Since sulfate ions are more electronegative than phosphate ions, this causes a change in the electron distribution of the crystal structure, enhancing the effect of surface oxygen atoms on lithium ions. This increases the binding energy of lithium ions at surface sites, lowers the energy barrier during migration, accelerates ion diffusion at the surface and interface, reduces side reactions and mechanical damage, and improves interface stability. Simultaneously, S... 6+ Replace P 5+ This process induces charge compensation, leading to a slightly lithium-deficient state on the surface. This increases the local current density, further optimizing the reaction kinetics at the electrode / electrolyte interface and contributing to improved rate performance. On the other hand, while the lithium-deficient state causes some capacity loss, the strong electronegativity of sulfate weakens the covalent bond between the transition metal and oxygen, lowering the energy level of the transition metal-oxygen antibonding orbitals. This, in turn, increases the average discharge voltage of the material, compensating for the adverse effect of capacity reduction on energy density. Therefore, the sulfur doping in this application, through the synergistic effect of lowering the lithium-ion migration barrier and increasing the operating voltage, achieves significant improvements in rate and cycle performance without sacrificing energy density.

[0070] The above-mentioned lithium manganese iron phosphate material can be any one of the embodiments provided above, and will not be described in detail again.

[0071] [Manufacturing method of a single battery cell]

[0072] A second embodiment of this application provides a method for preparing lithium manganese iron phosphate material, the method comprising:

[0073] Lithium manganese iron phosphate particles, sulfur source and solvent are mixed to obtain a first mixed slurry, and the first mixed slurry is dried to obtain a sulfur-doped precursor.

[0074] The sulfur-doped precursor was sintered to obtain lithium manganese iron phosphate material.

[0075] The sulfur source includes one or more of sulfates or pyrosulfates.

[0076] In the above preparation method, lithium manganese iron phosphate particles are mixed with a sulfur source and then sintered, allowing sulfur to be doped onto the surface of the lithium manganese iron phosphate material. One or more sulfur sources, such as sulfate or pyrosulfate, are used, ensuring that the doped sulfur includes +6 valent sulfur. Since +6 valent sulfur tends to substitute for P sites, and because sulfate is more electronegative than phosphate, this causes a change in the electron distribution of the crystal structure, enhancing the effect of surface oxygen atoms on lithium ions, i.e., increasing the binding energy of lithium ions at surface sites. This lowers the energy barrier during their migration, thereby accelerating ion diffusion at the surface and interface, reducing side reactions and mechanical damage, and improving interface stability. Simultaneously, S... 6+ Replace P 5+ This process induces charge compensation, leading to a slightly lithium-deficient state on the surface. This increases the local current density, further optimizing the electrode / electrolyte interface reaction kinetics and contributing to improved rate performance. On the other hand, while the lithium-deficient state causes some capacity loss, the strong electronegativity of sulfate weakens the covalent bond between the transition metal and oxygen, lowering the energy level of the transition metal-oxygen antibonding orbitals. This, in turn, increases the average discharge voltage of the material, compensating for the adverse effect of capacity reduction on energy density. Therefore, sulfur doping, through the synergistic effect of lowering the lithium-ion migration barrier and increasing the operating voltage, achieves significant improvements in rate and cycle performance without sacrificing energy density.

[0077] In some embodiments, the sulfur source includes one or more of ferrous sulfate, ammonium sulfate, lithium sulfate, or potassium pyrosulfate.

[0078] In some embodiments, the sintering temperature is 480°C-750°C. For example, the sintering temperature may be 480°C, 500°C, 520°C, 540°C, 550°C, 560°C, 580°C, 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 750°C, or within any two of the above values.

[0079] In some implementations, the sintering time is 6h-10h, for example, the sintering time can be 6h, 7h, 8h, 9h, 10h or within any two of the above values.

[0080] The aforementioned sintering temperature and sintering time can better control the depth and degree of S element doping, while avoiding grain growth or surface sulfur volatilization caused by over-sintering, thereby achieving a balance between structural order and doping activity at the microscopic level.

[0081] In some embodiments, sintering is carried out in air, nitrogen, or an inert gas. Sintering under these atmospheres can effectively suppress side reactions under high-temperature conditions, such as peroxidation or excessive volatilization of the sulfur source, while protecting the valence stability of the transition metal. This not only improves the retention rate and uniformity of sulfur doping but also reduces the formation of surface defects in the material, thereby contributing to the maintenance of cycle stability.

[0082] As used herein, the term "inert gas" refers to a gas that does not substantially react chemically with the sintered material at the sintering temperature and environment, including but not limited to argon, helium, neon, krypton, xenon, and mixtures thereof.

[0083] In some implementations, the mass content of the sulfur source is 0.1%-0.5% based on the total mass of the lithium manganese iron phosphate particles and the sulfur source. For example, the mass content of the sulfur source can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or within any two of the above values. This sulfur source mass content allows for the control of doping depth and concentration, achieving a balance between improved kinetics and structural stability, thereby obtaining a comprehensive advantage that balances rate performance and energy density.

[0084] In some embodiments, lithium manganese iron phosphate (LFP) particles are prepared by mixing lithium, iron, manganese, and phosphorus sources, preparing a LFP precursor by spray drying, and then sintering to obtain LFP particles. Spray drying is advantageous for obtaining particles with uniform size, regular morphology, and a large specific surface area. This precursor particle morphology facilitates the uniform distribution of sulfur on the particle surface during subsequent doping and sintering, thereby ensuring the consistency of material properties macroscopically and providing a more stable foundation for high-rate performance. The sintering process can refer to the sintering temperature, time, and atmosphere commonly used in LFP preparation, such as sintering in air, nitrogen, or an inert atmosphere at 450℃-550℃ for 4-10 hours.

[0085] In some embodiments, the preparation method further includes the following steps: mixing the sulfur-doped precursor with a carbon source and a solvent to obtain a second mixed slurry; drying the second mixed slurry to obtain a carbon-coated precursor; and sintering the sulfur-doped precursor to obtain lithium manganese iron phosphate material.

[0086] Through the above steps, a carbon coating layer is introduced on the basis of sulfur doping, which not only provides a continuous electronic conduction network, but also reduces the possibility of electrolyte directly corroding the surface material. This allows the optimized surface electronic structure and kinetic advantages of sulfur doping to be maintained for a long time, further improving the interfacial environment between the positive electrode active material and the electrolyte, thereby improving the cycle characteristics of the battery cell.

[0087] In some embodiments, the mixing is performed by sand milling. Sand milling facilitates the ultrafine grinding and uniform mixing of raw materials, shortens the synthesis time, and improves the synthesis efficiency. In some embodiments, the grinding media used in sand milling are zirconia grinding balls with a diameter of 0.3-0.7 mm.

[0088] In some implementations, the carbon source includes one or more of glucose, sucrose, and ethanol.

[0089] [Positive electrode plate]

[0090] A positive electrode typically 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.

[0091] 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.

[0092] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0093] In some embodiments, the positive electrode active material may also include other positive electrode active materials known in the art for use in batteries. As an example, the positive electrode active material may also include at least one of the following materials: other 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 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 / 3 Co 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 LiNi 0.8 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, and lithium manganese iron phosphate and carbon composites.

[0094] In some embodiments, the positive electrode film layer 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.

[0095] 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.

[0096] 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.

[0097] [Negative electrode plate]

[0098] In the following embodiments of this application, the battery cell further includes a negative electrode sheet. In some embodiments, the negative electrode may be a negative electrode sheet, and the negative electrode sheet may include a negative electrode current collector.

[0099] As an example, the negative electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0100] As an example, the negative electrode sheet may include a negative current collector and a negative active material disposed on at least one surface of the negative current collector.

[0101] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0102] As an example, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. 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. 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 battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0103] In some embodiments, the negative electrode can be made of foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not contain a negative electrode active material.

[0104] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0105] In some embodiments, the positive current collector can be made of aluminum, and the negative current collector can be made of copper.

[0106] [Electrolytes]

[0107] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0108] Liquid electrolytes include electrolyte salts and solvents.

[0109] In some embodiments, the electrolyte salt may be selected from 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.

[0110] 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. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0111] 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 additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0112] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0113] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0114] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0115] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium germanium phosphorus sulfide, silver sulfide germanium ore), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0116] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0117] [Isolation Component]

[0118] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0119] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0120] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. 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. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0121] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0122] [Electrode Assembly]

[0123] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0124] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0125] In some implementations, the electrode assembly is a stacked structure.

[0126] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0127] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0128] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0129] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0130] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0131] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0132] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0133] shell

[0134] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0135] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0136] In some embodiments, the housing includes a top cover assembly and a housing, the housing having an opening, and the top cover assembly covering the opening. The housing may have one or more openings. The top cover assembly may also have one or more.

[0137] Figure 2 The example shown is a square-structured battery cell 5.

[0138] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 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 51 has an opening communicating with the receiving cavity, and the top cover assembly 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 through 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 a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0139] electrode terminals

[0140] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab or indirectly connected to the tab through a current collector. The electrode terminal can be provided on the top cover assembly or on the housing.

[0141] Pressure relief mechanism

[0142] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0143] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0144] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0145] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0146] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0147] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0148] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0149] The third embodiment of this application provides a battery device including a battery cell, which includes the battery cell described in the first embodiment or the battery cell obtained by the method described in the second embodiment.

[0150] The battery device mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0151] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0152] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0153] Figure 4 This is battery module 4 as an example. (See reference...) Figure 4 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 way. Furthermore, these multiple secondary battery cells 5 can be fixed in place using fasteners.

[0154] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0155] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0156] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0157] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0158] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0159] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells. Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0160] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0161] The fourth embodiment of this application provides an electrical device, including a battery cell or a battery device. The battery cell includes any battery cell provided in the first embodiment or a battery cell obtained by the method described in the second embodiment. The battery device is any battery device provided in the third embodiment.

[0162] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0163] As the electrical device, a single secondary battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0164] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used. Example

[0165] 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.

[0166] Example 1

[0167] Preparation of positive electrode sheet

[0168] Lithium carbonate, ferrous oxalate, manganese oxalate, and ammonium dihydrogen phosphate were weighed and added to a sand mill according to the molar ratio of lithium:manganese:iron:phosphorus = 1:0.7:0.3:1. Deionized water was added to obtain a slurry with a solid content of 50%. After spray drying the slurry, lithium manganese iron phosphate precursor was prepared. The obtained lithium manganese iron phosphate precursor was sintered at 480℃ for 6 hours to obtain lithium manganese iron phosphate sample LMFP-73.

[0169] Weigh the mass of LMFP-73, add deionized water and stir to disperse to obtain a slurry with a solid content of 50%. Add 0.15% ferrous sulfate (this mass percentage is the mass percentage of ferrous sulfate relative to the total mass of LMFP-73 and ferrous sulfate) to the slurry and stir continuously for 2 hours until completely dissolved. Then, spray dry to obtain the sulfur-doped precursor.

[0170] Sulfur-doped precursor, water, and glucose were added to a sand mill to form a slurry with a solid content of 50%. The slurry was then dispersed by sand milling. The grinding balls used for sand milling were zirconium oxide with a diameter of about 0.5 mm and a ball-to-material ratio of 3:1. After sand milling, the grinding balls were separated and the slurry was spray-dried to obtain a carbon-coated precursor. The carbon-coated precursor was then sintered at 750°C for 10 h under a nitrogen atmosphere to obtain a carbon-coated sulfur-doped lithium manganese iron phosphate sample LMFP-73-S.

[0171] The positive electrode active material LMFP-73-S, conductive carbon black Super P, and binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 92:5.5:2.5 and dissolved in the solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry is coated on the current collector aluminum foil, dried, and then cold-pressed, trimmed, cut, and slit to obtain the positive electrode sheet.

[0172] Preparation of negative electrode sheet

[0173] A negative electrode slurry is prepared by mixing graphite (a negative electrode active material), Super P (conductive carbon black), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) in a mass ratio of 95:2.5:1.5:1 and dissolving them in deionized water. The negative electrode slurry is then coated onto copper foil (current collector), dried, and subjected to cold pressing, edge trimming, and cutting to obtain the negative electrode sheet.

[0174] electrolyte

[0175] Ethylene carbonate (EC), diethyl carbonate (DMC), and vinylene carbonate (VC) were mixed in a mass ratio of 29:69:2 to obtain an electrolyte solvent. Subsequently, lithium hexafluorophosphate (LiPF6) was mixed with the electrolyte solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0176] Separating membrane : Porous polyethylene (PP) separator film.

[0177] Battery assembly:

[0178] The positive electrode, separator, and negative electrode are prepared in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound, hot-pressed, shaped, and welded to obtain the electrode assembly. The electrode assembly is placed in a square aluminum shell, vacuum-dried, and then injected with electrolyte. It is then left to stand, undergoes formation testing, aging, and capacity testing to finally obtain the battery cell.

[0179] test:

[0180] The mass content of sulfur and the doping depth of sulfur in lithium manganese iron phosphate materials were tested using the methods described above.

[0181] Lithium intercalation voltage test: Three-electrode testing was performed on the battery cells using an ultra-high precision blue electrode tester or electrochemical workstation. At 25°C, the battery cells were charged at a constant current of 0.33C to 4.2V, then charged at a constant voltage to a current of 0.05C. After resting for 10 minutes, the battery cells were discharged at a constant current of 0.33C to 2V. The voltage-capacity curves during the charge-discharge process were recorded. The charge-discharge curves of LMFP-73-S and LMFP-73 were recorded in [the relevant section]. Figure 1 In the voltage-capacity curve, the voltage plateau represents the lithium intercalation voltage. The results show that the lithium intercalation voltage of Example 1, compared to the undoped LMFP-73, did not decrease but rather increased, remaining around 3.62V, indicating sulfur doping at the p-site. Since no reducing gas was used during the preparation process, the sulfur in the sulfur source maintained a +6 valence, and the improved rate performance of the battery cell further confirms the presence of sulfur doping. 6+ Replace P 5+ This will cause charge compensation.

[0182] Testing of carbon morphology in the carbon coating: A single battery cell discharged to its cutoff voltage was disassembled to obtain the positive electrode. Positive electrode powder was scraped from the current collector and cleaned with high-purity dimethyl carbonate (DMC) to remove electrolyte residue and lithium salts, then dried. A small amount of powder sample was ultrasonically dispersed in ethanol and dropped onto an ultrathin carbon film copper grid. After drying, it was observed under a high-resolution transmission electron microscope (HRTEM). First, in low-magnification mode, individual particles with suitable contrast located at the edge of the carbon film were identified. Then, the high-resolution mode was switched to focus on the particle edges. The carbon morphology in the carbon coating was confirmed by identifying the typical morphological characteristics of the carbon material.

[0183] Cyclic capacity retention test:

[0184] Three-electrode testing was performed on individual battery cells using an ultra-high precision blue electrode tester or an electrochemical workstation. At 25°C, the individual cells were charged to 4.2V at a constant current of 0.33C, and then charged to 0.05C at a constant voltage. After resting for 10 minutes, three constant current charge-discharge cycles were performed at different rates (0.33C, 1C, 2C, 3C). The voltage-capacity curves during the charge-discharge process were recorded after each cycle. The charging capacity at different rates was calculated, and the capacity retention rate at 3C was calculated: Capacity retention rate = (3C capacity / 0.33C capacity) * 100%.

[0185] Example 2

[0186] The only difference from Example 1 is that the same mass of potassium pyrosulfate is used instead of ferrous sulfate in Example 1; otherwise, they are the same as in Example 1.

[0187] Comparative Example 1

[0188] According to the molar ratio of lithium:manganese:iron:phosphorus:sulfur = 1:0.7:0.3:1:0.0016, lithium source, iron source, manganese source, phosphorus source and ferrous sulfate were weighed and put into a sand mill. Deionized water was added to obtain a slurry with a solid content of 50%. After spray drying the slurry, sulfur-doped lithium manganese iron phosphate precursor was prepared. The obtained precursor was sintered at 480℃ for 6 hours to obtain sulfur-doped lithium manganese iron phosphate sample LMFP-73-S-body.

[0189] A sulfur-doped lithium manganese iron phosphate sample LMFP-73-S-body, water, and glucose were added to a sand mill to form a slurry with a solid content of 50%. The slurry was then dispersed by sand milling. The grinding balls used were zirconium oxide balls with a diameter of approximately 0.5 mm and a ball-to-material ratio of 3:1. After sand milling, the grinding balls were separated and the slurry was spray-dried to obtain a carbon-coated precursor. The carbon-coated precursor was then sintered at 750°C for 10 hours under a nitrogen atmosphere to obtain the carbon-coated sulfur-doped lithium manganese iron phosphate sample LMFP-73-S-body.

[0190] Comparative Example 2

[0191] The only difference from Example 1 is that the same mass of ferrous sulfite is used instead of ferrous sulfate in Example 1; otherwise, they are the same as in Example 1.

[0192] Comparative Example 3

[0193] The only difference from Example 1 is that ferrous sulfide of the same mass is used instead of ferrous sulfate in Example 1; otherwise, they are the same as in Example 1.

[0194] The test results of Examples 1 and Comparative Examples 1 to 3 are recorded in Table 2.

[0195] Table 2

[0196]

[0197] As can be seen from the data in Table 2, the +6 valence sulfur element doped with phosphorus sites in Example 1 exhibits the best specific capacity under high-rate charging, indicating the best rate performance. Simultaneously, the highest capacity retention also indicates the best cycle performance. Comparative Examples 2 and 3, doped with low-valence sulfuric acid, failed to improve rate and cycle performance. In Comparative Example 3, because it uses negatively valence sulfur, it does not have a significant impact on specific capacity as it does not have positive valence sites.

[0198] Example 3

[0199] The only difference from Example 1 is that the added ferrous sulfate is 0.1% of the total mass of LMFP-73 and ferrous sulfate; otherwise, it is the same as Example 1.

[0200] Example 4

[0201] The only difference from Example 1 is that the added ferrous sulfate is 0.5% of the total mass of LMFP-73 and ferrous sulfate; otherwise, it is the same as Example 1.

[0202] Example 5

[0203] The only difference from Example 1 is that the added ferrous sulfate is 0.7% of the total mass of LMFP-73 and ferrous sulfate; otherwise, it is the same as Example 1.

[0204] The test results of Examples 3 to 5 are recorded in Table 3.

[0205] Table 3

[0206]

[0207] As can be seen from the data in Table 3, with the increase of sulfur content and doping depth, the specific capacity and capacity retention of the positive electrode increase first. However, the capacity retention decreases after exceeding 0.05%, which may be because the excessive doping depth affects the bulk phase of the positive electrode material, thus reducing the specific capacity and cycling stability at high rates.

[0208] Example 6

[0209] The only difference from Example 1 is that the carbon-coated precursor was sintered at 550°C for 6 hours in a nitrogen atmosphere to obtain a carbon-coated sulfur-doped lithium manganese iron phosphate sample. The rest is the same as in Example 1.

[0210] Example 7

[0211] The only difference from Example 1 is that the carbon-coated precursor was sintered at 750°C for 4 hours in a nitrogen atmosphere to obtain a carbon-coated sulfur-doped lithium manganese iron phosphate sample. The rest is the same as in Example 1.

[0212] Example 8

[0213] The only difference from Example 1 is that the carbon-coated precursor was sintered at 750°C for 12 hours in a nitrogen atmosphere to obtain a carbon-coated sulfur-doped lithium manganese iron phosphate sample. The rest is the same as in Example 1.

[0214] Example 9

[0215] The only difference from Example 1 is that the carbon-coated precursor was sintered in air at 750°C for 10 hours to obtain a carbon-coated sulfur-doped lithium manganese iron phosphate sample. The rest is the same as in Example 1.

[0216] The test results of Examples 6 to 9 are recorded in Table 4.

[0217] Table 4

[0218]

[0219] As can be seen from the data comparison in Table 4, both sintering temperature and time affect the amount and depth of sulfur doping. Lower sintering temperature and shorter sintering time will lead to a decrease in the amount of sulfur doping and a shallower doping depth, thus having a smaller impact on the specific capacity of 0.33C. However, the improvement in rate performance and cycle stability is also weakened.

[0220] In addition, in Example 9, sintering was carried out in air, where the oxygen may cause the sulfur to burn off, resulting in a less effective improvement in sulfur doping compared to Example 1.

[0221] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, characterized by, The battery cell comprises a positive pole sheet, the positive pole sheet comprises a positive active material, the positive active material comprises a lithium manganese iron phosphate material, the lithium manganese iron phosphate material comprises lithium manganese iron phosphate particles and a sulfur element, the sulfur element is only doped on the surface of the lithium manganese iron phosphate particles, the sulfur element is doped at the site of phosphorus elements of the lithium manganese iron phosphate particles, the sulfur element is a +6 valence sulfur element, the doping depth of the sulfur element is 0.5nm-2nm.

2. The battery cell of claim 1, wherein, The mass content of the sulfur element in the lithium manganese iron phosphate material is 0.01%-0.05%.

3. The battery cell according to claim 1 or 2, characterized in that, The molar ratio of manganese elements and iron elements in the lithium manganese iron phosphate material is 6:4-8:

2.

4. The battery cell according to claim 1 or 2, characterized in that, The lithium iron manganese phosphate particles have the chemical formula Li a A x Mn 1-y R y PO4, A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W; R comprises Fe, a is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.1, and y is selected from the range of 0.001 to 0.

5.

5. The battery cell of claim 4, wherein, R further comprises one or more elements selected from Ti, V, Zr, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge.

6. The battery cell according to claim 1 or 2, characterized in that, The lithium manganese iron phosphate material further comprises a carbon-containing coating layer.

7. The battery cell of claim 6, wherein, The carbon-containing coating layer comprises at least one of amorphous carbon and carbon black.

8. The battery cell of claim 6, wherein, The mass content of carbon elements in the lithium manganese iron phosphate material is 1%-2%.

9. A lithium iron manganese phosphate material, characterized in that, The lithium manganese iron phosphate material comprises lithium manganese iron phosphate particles and a sulfur element, the sulfur element is only doped on the surface of the lithium manganese iron phosphate particles, the sulfur element is doped at the site of phosphorus elements of the lithium manganese iron phosphate particles, the sulfur element is a +6 valence sulfur element, the doping depth of the sulfur element is 0.5nm-2nm.

10. The lithium iron manganese phosphate material of claim 9, wherein, The mass content of the sulfur element in the lithium manganese iron phosphate material is 0.01%-0.05%.

11. The lithium iron manganese phosphate material of claim 9 or 10, wherein, The molar ratio of manganese elements and iron elements in the lithium manganese iron phosphate material is 6:4-8:

2.

12. The lithium iron manganese phosphate material of claim 9 or 10, wherein, The lithium iron manganese phosphate particles have the chemical formula Li a A x Mn 1-y R y PO4, A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W; R comprises Fe, a is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.1, and y is selected from the range of 0.001 to 0.

5.

13. The lithium iron manganese phosphate material of claim 12, wherein, R further comprises one or more elements selected from Ti, V, Zr, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge.

14. The lithium iron manganese phosphate material of claim 9 or 10, wherein, The lithium manganese iron phosphate material further comprises a carbon-containing coating layer.

15. The lithium iron manganese phosphate material of claim 14, wherein, The carbon-containing coating layer comprises at least one of amorphous carbon and carbon black.

16. The lithium iron manganese phosphate material of claim 14, wherein, The mass content of carbon elements in the lithium manganese iron phosphate material is 1%-2%.

17. A method of producing the lithium iron manganese phosphate material according to any one of claims 9 to 16, characterized in that, The preparation method comprises: mixing lithium manganese iron phosphate particles, a sulfur source and a solvent to obtain a first mixed slurry, drying the first mixed slurry to obtain a sulfur-doped precursor; sintering the sulfur-doped precursor to obtain the lithium manganese iron phosphate material, wherein the sulfur source comprises one or more of sulfates or pyrosulfates.

18. The method of claim 17, wherein, The sulfur source comprises one or more of ferrous sulfate, ammonium sulfate, lithium sulfate or potassium pyrosulfate.

19. The method of manufacturing according to claim 17 or 18, wherein, The sintering satisfies one or more of the following conditions: the temperature of the sintering is 480°C-750°C; The sintering time is 6h-10h; The sintering is carried out in air, nitrogen or inert gas.

20. The method of manufacturing according to claim 17 or 18, wherein, Based on the total mass of the lithium manganese iron phosphate particles and the sulfur source, the mass content of the sulfur source is 0.1%-0.5%.

21. The method of manufacturing according to claim 17 or 18, wherein, The preparation method further comprises the following steps: mixing the sulfur-doped precursor, a carbon source and a solvent to obtain a second mixed slurry; drying the second mixed slurry to obtain a carbon-coated precursor, The process of sintering the sulfur-doped precursor comprises: sintering the carbon-coated precursor to obtain the lithium manganese iron phosphate material.

22. The method of claim 21, wherein, The mixing is sand milling.

23. The preparation method according to claim 21, characterized in that, The carbon source comprises one or more of glucose, sucrose and ethanol.

24. A battery device, characterized by A battery comprising one or more battery cells according to any one of claims 1 to 8.

25. An electrical device, comprising: A battery device according to claim 24, comprising a battery cell according to any one of claims 1 to 8.

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