Lithium manganese iron phosphate material, preparation method thereof, battery monomer, battery device and power utilization device

Abstract

The invention provides a lithium manganese iron phosphate material, a preparation method thereof, a battery monomer, a battery device and a power utilization device. The battery monomer comprises a positive pole piece, the positive pole piece 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 doped on the surfaces of the lithium manganese iron phosphate particles, and the sulfur element is doped at phosphorus element sites of the lithium manganese iron phosphate particles. The sulfur element comprises a + 6-valent sulfur element.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium manganese iron phosphate material, a preparation method thereof, a battery monomer, a battery device and a power utilization device. BACKGROUND

[0002] With the wide application of power batteries in electric vehicles and energy storage systems, the requirements for the energy density and cycle life of battery monomers are also increasing. Lithium manganese iron phosphate material has become one of the most promising candidate materials because it combines the high voltage advantage of lithium manganese phosphate and the cycle stability of lithium iron phosphate. However, the surface Mn 3+ of the lithium manganese iron phosphate positive electrode material is chemically unstable, which easily induces interface side reactions and accompanies manganese ion dissolution, degrading the ion conduction rate and rate performance of the material, and becoming the main bottleneck for the practical application of the material. SUMMARY

[0003] The present application provides a lithium manganese iron phosphate material, a preparation method thereof, a battery monomer, a battery device and a power utilization device to improve the rate performance and cycle performance of the battery monomer.

[0004] The first aspect of the present application provides a battery monomer, which comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active material, the positive electrode 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 doped on the surface of the lithium manganese iron phosphate particles, and the sulfur element is doped at the phosphorus element site of the lithium manganese iron phosphate particles, and the sulfur element comprises a +6 valence sulfur element.

[0005] The second aspect of the present application provides a lithium manganese iron phosphate material, which comprises lithium manganese iron phosphate particles and a 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 site of the lithium manganese iron phosphate particles, and the sulfur element comprises a +6 valence sulfur element.

[0006] When the sulfur element is doped at the surface phosphorus element site of the lithium manganese iron phosphate particles, and the sulfur element comprises a +6 valence sulfur element, the surface lithium manganese iron phosphate particles form sulfate, because the electronegativity of sulfate is higher than that of phosphate, it causes the change of local electron distribution in the lattice, which enhances the effect of surface oxygen atoms on lithium ions, i.e. the binding energy of lithium ions at the surface site is improved, which reduces the energy barrier in the migration process, thereby accelerating the ion diffusion at the surface and interface, reducing side reactions and mechanical damage, and improving the interface stability; at the same time, S 6+ substitutes P 5+The charge compensation caused by the lithium deficiency on the surface of the particles increases the local current density and promotes the reaction kinetics at the electrode / electrolyte interface, thus improving the rate capability. On the other hand, the lithium deficiency causes a certain capacity loss, but the strong electronegativity of the sulfate group weakens the covalence between the transition metal and oxygen, lowers the energy level of the transition metal-oxygen antibonding orbital, and thus increases the average discharge voltage of the material, offsetting the negative impact of the capacity loss on the energy density. Thus, the sulfur doping of the present application improves the rate capability and cycle performance significantly without sacrificing the energy density, through the synergistic effect of lowering the lithium ion migration energy barrier and increasing the working voltage.

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

[0008] In any embodiment of the first or second aspect, the doping depth of sulfur is 0.5nm-2nm. The above-mentioned doping depth can make the electronic structure and lithium deficiency mainly distributed in the surface or subsurface region of the particles, thus optimizing the reaction kinetics and ion diffusion path at the electrode / electrolyte interface, sufficiently improving the surface reaction rate, and better controlling the defect of reducing the bulk structure stability caused by the deepening of sulfur into the host lattice.

[0009] In any embodiment of the first or second aspect, the molar ratio of manganese and 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, 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 mass content of carbon in the lithium manganese iron phosphate material is 1.5%-5%.

[0014] The third aspect of the present application provides a preparation method of a lithium manganese iron phosphate material, the preparation method comprising: 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, The sulfur source comprises one or more of a sulfate or a pyrosulfate.

[0015] In any embodiment of the third aspect, the sulfur source comprises one or more of ferrous sulfate, ammonium sulfate, lithium sulfate or potassium pyrosulfate.

[0016] In any embodiment of the third aspect, the sintering satisfies one or more of the following conditions: the temperature of the sintering is 480-750℃; the time of the sintering is 6-10h; the sintering is performed in air, nitrogen or an inert gas.

[0017] 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.

[0018] In any embodiment of the third aspect, the preparation method further comprises the following steps: mixing the sulfur-doped precursor with a carbon source and a solvent to obtain a second mixed slurry, and the mixing is optionally sand milling; 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.

[0019] The fourth aspect of the present application provides a battery device comprising a battery cell, the battery cell comprising the battery cell provided by any embodiment of the first aspect and the battery cell prepared by any embodiment of the second aspect.

[0020] The fifth aspect of the present application provides a power-using device comprising a battery cell or a battery device, the battery cell comprising the battery cell provided by any embodiment of the first aspect and the battery cell prepared by any embodiment of the second aspect, and the battery device being the battery device provided by any embodiment of the third aspect. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from the drawings without creative labor.

[0022] Figure 1 Charge-discharge curves of the LMFP-73-S and LMFP-73 of Embodiment 1 of the present application.

[0023] Figure 2 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0024] Figure 3 is a schematic diagram of a battery cell according to an embodiment of the present application. Figure 2 is an exploded view of a battery cell according to an embodiment of the present application.

[0025] Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.

[0026] Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0027] Figure 6 is a schematic diagram of a battery pack according to an embodiment of the present application. Figure 5 is an exploded view of a battery pack according to an embodiment of the present application.

[0028] Figure 7 is a schematic diagram of an electrical device using a battery cell as a power source according to an embodiment of the present application.

[0029] In the drawings, the drawings are not drawn according to the actual proportions.

[0030] Explanation of reference signs: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0031] The embodiments of the present application will be further described in detail below in conjunction with the drawings and examples. The detailed description of the following examples and drawings are used to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application, i.e., the present application is not limited to the described examples.

[0032] Hereinafter, specific embodiments of the lithium iron manganese phosphate material and the method for producing the same, the battery cell, the battery device, and the electric device of the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases of omitting detailed description of matters known to those skilled in the art, and repeated description of substantially identical configurations. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0033] The ranges disclosed herein are defined by their lower and upper limits. Ranges can be comprised of any combination of the maximum and minimum defining the range. Unless otherwise stated, the ranges include both endpoints and all the numbers between. For example, the range "0-10" is intended to include all sub-ranges between (and including) the recited minimum and maximum values, e.g., 1-10, 2-10, 3-10, etc. In other words, a range of "0-10" means that the range includes any number between (and including) the minimum of zero and the maximum of 10. Similarly, a range of "0-5" means that the range includes any number between (and including) the minimum of zero and the maximum of 5. Also, a range of "2-6" means that the range includes any number between (and including) the minimum of 2 and the maximum of 6. It is specifically intended that the description set forth in this application include all of the various combinations of the various features recited herein.

[0034] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0036] If not specifically stated, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c) means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0037] If not specifically stated, the present application refers to "comprising" and "including" as open terms. For example, "comprising" and "including" can mean that other components not listed can also be included.

[0038] If not specifically stated, in the present application, the term "or" is inclusive. For example, any of the following conditions satisfy 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 A and B are both true (or exist).

[0039] [Lithium manganese iron phosphate material] As analyzed in the background section, although the lithium manganese iron phosphate positive electrode has the potential of improving the energy density, under the condition of unstable surface Mn³⁺ ions, it is easy to trigger the interface side reaction, which seriously affects the application value of the battery cell in the fast charging and high power output scene. In view of this problem, many schemes have been tried in the prior art, for example: by further reducing the particle size of the lithium manganese iron phosphate, the lithium ion diffusion path is shortened, and the kinetic performance is improved. However, reducing the particle size, although it improves the ion transmission, at the same time, it increases the specific surface area of the material, thereby aggravating the side reaction and manganese dissolution problem, and ultimately deteriorating the electrochemical performance and cycle life of the material.

[0040] To solve the problem of poor rate performance and insufficient cycle stability of the lithium manganese iron phosphate positive electrode, the present application provides a battery cell, a method for manufacturing a battery cell, a battery device and a power utilization device.

[0041] The first embodiment of the present application provides a lithium manganese iron phosphate material, which comprises lithium manganese iron phosphate particles and a 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 site of the lithium manganese iron phosphate particles, and the sulfur element comprises +6 valence sulfur element.

[0042] The applicant found that when the sulfur element is doped at the surface phosphorus element site of the lithium iron manganese phosphate particles, and the sulfur element includes +6 valence sulfur element, the surface lithium phosphate particles form sulfate, because the electronegativity of sulfate is higher than that of phosphate, the local electron distribution of the crystal lattice is changed, the effect of surface oxygen atoms on lithium ions is enhanced, that is, the binding energy of lithium ions at the surface site is improved, the energy barrier in the migration process is reduced, thereby accelerating the ion diffusion at the surface and interface, reducing the side reaction and mechanical damage, and improving the interface stability; at the same time, S 6+ Substituting P 5+ will cause charge compensation, resulting in the formation of a slightly lithium-poor state on the surface, thereby increasing the local current density and promoting the further optimization of the electrode / electrolyte interface reaction kinetics, which also helps to improve the rate capability. On the other hand, the lithium-poor state will cause a certain capacity sacrifice, but the strong electronegativity of sulfate weakens the covalence between transition metals and oxygen, reduces the energy level of transition metal-oxygen antibonding orbitals, and thus improves the average discharge voltage of the material, offsetting the adverse effects of capacity decline on energy density. Thus, the sulfur doping of the present application reduces the lithium ion migration energy barrier and improves the working voltage, thereby achieving significant improvement in rate capability (charging capacity) and cycle performance without sacrificing energy density.

[0043] The lithium intercalation voltages of undoped lithium iron manganese phosphate, lithium iron manganese phosphate doped with sulfur at the surface phosphorus site, and lithium iron manganese phosphate doped with sulfur at the surface oxygen site are different. Specifically, by comparing the lithium intercalation voltages of the above three models through first-principle calculation, it is found that doping sulfur at the phosphorus site can increase the lithium intercalation voltage, while doping sulfur at the oxygen site can decrease the lithium intercalation voltage, as shown in Table 1 below. Therefore, under the same negative electrode conditions, the discharge voltages of battery cells using the three models as positive active materials (≈lithium intercalation voltage of positive electrode - lithium extraction voltage of negative electrode) vary differently. When sulfur is doped at the phosphorus element site, the lithium intercalation voltage is the highest, and when sulfur is doped at the oxygen element site, the lithium intercalation voltage does not increase but decreases. Therefore, testing the lithium intercalation voltage variation of the corresponding battery cell can determine the doping site of sulfur.

[0044] Table 1 Lithium intercalation voltage calculation data of sulfur-doped and surface sulfur-doped

[0045] In some embodiments, the mass content of sulfur in the lithium manganese iron phosphate material is 0.01%-0.05%, for example, the mass content of sulfur in the lithium manganese iron phosphate material can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05% or within a range between any two of the above values. When the sulfur element is doped on the surface of the lithium manganese iron phosphate particles and the doping amount is controlled within the above trace interval, the electronic structure of the particle surface layer can be effectively adjusted without causing significant distortion to the host lattice, so that the doped lithium manganese iron phosphate can not only exhibit the optimization of local electronic distribution and the improvement of surface dynamics brought by sulfur doping, but also control the structural instability and side reactions caused by excessive doping, thereby improving the cycle stability and rate performance.

[0046] In this application, the mass content of sulfur in the lithium manganese iron phosphate material can be measured by the following method: the battery cell discharged to the cut-off voltage is disassembled to obtain the positive electrode sheet, which is cleaned with an organic solvent and high-temperature heat treated to completely remove the residual electrolyte, conductive agent and binder, and then inductively coupled plasma mass spectrometry (ICP-MS) equipped with a collision reaction cell (CRC) for eliminating interference of multi-atomic ions is used to measure the mass content of sulfur element in the obtained pure powder.

[0047] In some embodiments, the doping depth of sulfur element is 0.5nm-2nm, for example, the doping depth of sulfur element can be 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm, 1.5nm, 1.6nm, 1.7nm, 1.8nm, 1.9nm, 2nm or within a range between any two of the above values. The above doping depth can make the electronic structure and lithium-poor state mainly distributed in the surface layer or subsurface layer of the particles, thereby optimizing the reaction kinetics and ion diffusion path of the electrode / electrolyte interface and sufficiently improving the surface reaction rate, and better controlling the defect of reducing the bulk phase structure stability caused by the deepening of sulfur into the host lattice.

[0048] In this application, the doping depth of sulfur element can be measured by the following method: using ultra-high mass resolution time-of-flight secondary mass spectrometry (HR-ToF-SIMS) to perform ion sputtering depth profiling on the sample cross section, monitoring the change of ³²S characteristic signal with sputtering time, and converting the sputtering time into depth through standard sample calibration; the doping depth of sulfur element in the lithium manganese iron phosphate material is characterized by analyzing the distribution characteristics of the signal after penetrating the surface layer.

[0049] In some embodiments, the molar ratio of manganese element and iron element in the lithium manganese iron phosphate material is 6:4-8:2, for example, the molar ratio of manganese element and iron element in the lithium manganese iron phosphate material can be 6:4, 7:3, 8:2 or within the range of any two of the above values. By regulating the molar ratio of manganese / iron in the lithium manganese iron phosphate material within the above range, a balance between high voltage capacity and cycle stability can be achieved, thereby improving the overall electrochemical performance of the battery cell.

[0050] In this application, the elemental composition in the lithium manganese iron phosphate material can be confirmed by EDS combined with XRD.

[0051] In some embodiments, the lithium manganese iron phosphate particles have a chemical formula of Li a A x Mn 1-y R y PO4, 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 the lithium manganese iron phosphate positive electrode material can be further improved.

[0052] In some embodiments, the lithium manganese iron phosphate material further includes a carbon-containing coating layer. By introducing a carbon coating layer on the basis of sulfur doping, not only a continuous electron conduction network is provided, but also the possibility of direct corrosion of the electrolyte to the surface material is weakened, so that the long-term maintenance of the surface electronic structure and kinetic advantages optimized by sulfur doping is achieved, further improving the interface environment of the positive active material and the electrolyte and thereby improving the cycle characteristics of the battery cell.

[0053] 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 is beneficial to build a conductive network to improve 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 surface of the particles and provide multi-directional electron transmission channels. Compared with crystalline carbon materials, amorphous carbon has more defect sites, which is beneficial to improve the interface conductivity and enhance the synergistic effect with the sulfur-doped surface layer, thereby further reducing the interface charge transfer impedance while improving the electronic conductivity.

[0054] In some embodiments, the mass content of carbon element in the lithium manganese iron phosphate material is 1%-2%, for example, the mass content of carbon element 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 a range between any two of the above values. The above carbon element content range can form a uniform and continuous conductive network, improve the overall electronic conductivity of the material, avoid excessive carbon content to reduce the volume ratio of the active material, make the electronic / ion dual transport process more balanced, and thus comprehensively improve the rate performance and energy utilization efficiency.

[0055] [Battery cell] The second embodiment of the present application provides a battery cell, which comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active material, the positive electrode 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 doped on the surface of the lithium manganese iron phosphate particles, and the sulfur element is doped at the phosphorus element site of the lithium manganese iron phosphate particles, and the sulfur element comprises a +6 valence sulfur element.

[0056] When the sulfur element is doped at the surface phosphorus element site of the lithium manganese iron phosphate particles and the sulfur element comprises a +6 valence sulfur element, the surface lithium manganese iron phosphate particles form a sulfate radical. Since the electronegativity of the sulfate radical is higher than that of the phosphate radical, the local electron distribution of the crystal lattice is changed, the effect of the surface oxygen atom on the lithium ion is enhanced, that is, the binding energy of the lithium ion at the surface site is improved, the energy potential barrier in the migration process is reduced, the ion diffusion at the surface and the interface is accelerated, the side reaction and mechanical damage are reduced, and the interface stability is improved. At the same time, the S 6+ Substituting P 5+ will cause charge compensation, resulting in the formation of a slightly lithium-poor state on the surface, thereby increasing the local current density and promoting the further optimization of the electrode / electrolyte interface reaction kinetics, which also helps to improve the rate performance. On the other hand, the lithium-poor state will cause a certain capacity sacrifice, but the strong electronegativity of the sulfate radical weakens the covalence between the transition metal and oxygen, reduces the energy level of the transition metal-oxygen antibonding orbital, and thus improves the average discharge voltage of the material, offsetting the adverse effects of capacity decline on energy density. Thus, the sulfur doping of the present application reduces the lithium ion migration energy barrier and improves the working voltage, thereby achieving significant improvement in rate performance and cycle performance without sacrificing energy density.

[0057] The above lithium manganese iron phosphate material adopts any one of the embodiments provided above, and will not be repeated here.

[0058] [Manufacturing method of battery cell] The second embodiment of the present application provides a preparation method of a lithium manganese iron phosphate material, which comprises: The lithium manganese iron phosphate particles, a sulfur source, and a solvent are mixed to obtain a first mixed slurry, and the first mixed slurry is dried to obtain a sulfur-doped precursor; The sulfur-doped precursor is sintered to obtain a lithium manganese iron phosphate material, The sulfur source includes one or more of a sulfate or a pyrosulfate.

[0059] In the above preparation method, the lithium manganese iron phosphate particles are mixed with the sulfur source and then sintered, so that the sulfur element is doped on the surface of the lithium manganese iron phosphate material. The sulfur source includes one or more of a sulfate or a pyrosulfate, so that the doped sulfur element includes +6 valence sulfur element, and the +6 valence sulfur element tends to replace the P site. Since the electronegativity of the sulfate is higher than that of the phosphate, the local electronic distribution of the crystal lattice is changed, the effect of the surface oxygen atom on the lithium ion is enhanced, that is, the binding energy of the lithium ion at the surface site is increased, the energy barrier in the migration process is reduced, the ion diffusion on the surface and the interface is accelerated, the side reaction and mechanical damage are reduced, and the interface stability is improved. At the same time, S 6+ replaces P 5+ will cause charge compensation, resulting in the formation of a slightly lithium-poor state on the surface, thereby increasing the local current density and promoting the optimization of the electrode / electrolyte interface reaction kinetics, which also helps to improve the rate capability. On the other hand, the lithium-poor state will cause a certain capacity sacrifice, but the strong electronegativity of the sulfate weakens the covalence between the transition metal and oxygen, reduces the energy level of the transition metal-oxygen antibonding orbital, and thus improves the average discharge voltage of the material, offsetting the adverse effects of capacity decline on energy density. Thus, through the synergistic effect of reducing the lithium ion migration energy barrier and improving the working voltage, the rate capability and cycle performance are significantly improved without sacrificing the energy density.

[0060] In some embodiments, the sulfur source includes one or more of ferrous sulfate, ammonium sulfate, lithium sulfate, or potassium pyrosulfate.

[0061] In some embodiments, the sintering temperature is 480-750°C, for example, the sintering temperature can 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 a range between any two of the above values.

[0062] In some embodiments, the sintering time is 6-10h, for example, the sintering time can be 6h, 7h, 8h, 9h, 10h, or within a range between any two of the above values.

[0063] The 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 excessive sintering, thereby achieving a balance between structural order and doping activity at the micro level.

[0064] In some embodiments, the sintering is carried out in air, nitrogen or inert gas. Sintering in the above atmosphere can effectively inhibit side reactions under high temperature conditions, such as over-oxidation or excessive volatilization of the sulfur source, while protecting the valence state stability of the transition metal, not only improving the retention rate and uniformity of the doped sulfur, but also reducing the formation of surface defects of the material, thereby facilitating the maintenance of cycle stability.

[0065] As used herein, the term "inert gas" refers to a gas that does not substantially chemically react with the sintered material at the temperature and environment of the sintering, including but not limited to argon, helium, neon, krypton, xenon, and mixtures thereof.

[0066] In some embodiments, 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 the range of any two of the above values based on the total mass of the lithium manganese iron phosphate particles and the sulfur source. The above mass content of the sulfur source can achieve the regulation of the doping depth and the doping concentration, and achieve the best possible balance between kinetics improvement and structural stability, thereby obtaining the comprehensive advantages of considering both rate capability and energy density.

[0067] In some embodiments, the lithium manganese iron phosphate particles are prepared by mixing a lithium source, an iron source, a manganese source and a phosphorus source, preparing a lithium manganese iron phosphate precursor by spray drying, and sintering to obtain the lithium manganese iron phosphate particles. The spray drying method is beneficial to obtaining a particle structure with uniform particle size, regular morphology and large specific surface area. The morphology of the precursor particles is beneficial to the uniform distribution of sulfur elements on the particle surface in the subsequent doping and sintering process, thereby ensuring the consistency of the material performance on the macro level and providing a more stable basis for high rate capability. The above sintering can refer to the commonly used sintering temperature, time and atmosphere during the preparation of lithium manganese iron phosphate, such as sintering in air, nitrogen or inert atmosphere at 450°C-550°C for 4h-10h.

[0068] In some embodiments, the preparation method further comprises 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 comprises: sintering the carbon-coated precursor to obtain the lithium manganese iron phosphate material.

[0069] 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.

[0070] 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.

[0071] In some implementations, the carbon source includes one or more of glucose, sucrose, and ethanol.

[0072] [Positive electrode plate] 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.

[0073] 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.

[0074] 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.).

[0075] 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 can be referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(also can be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and modified compounds thereof. Examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, a composite of lithium manganese iron phosphate and carbon.

[0076] In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene-fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0077] In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0078] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode tab can be obtained.

[0079] [Negative electrode tab] In the following embodiments of the present application, the battery cell further includes a negative electrode tab. In some embodiments, the negative electrode can be a negative electrode tab, which can include a negative electrode current collector.

[0080] As an example, the negative electrode current collector can employ a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, a pure metal, an alloy, a surface-treated metal, including but not limited to stainless steel, copper, aluminum, nickel, nickel, titanium, or silver, etc. can be employed. The composite current collector can include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0081] As an example, the negative electrode tab can include a negative electrode current collector and a negative electrode active material disposed on at least one surface of the negative electrode current collector.

[0082] As an example, the negative electrode current collector has two opposite surfaces in the thickness direction thereof, and the negative electrode active material is disposed on either one or both of the two opposite surfaces of the negative electrode current collector.

[0083] As an example, the negative electrode active material can employ a negative electrode active material known in the art for a battery cell. As an example, the negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery cell can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0084] In some embodiments, the negative electrode can employ a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When the foamed metal is used as a negative electrode tab, the surface of the foamed metal can not be provided with a negative electrode active material, or of course can be provided with a negative electrode active material.

[0085] As an example, the negative electrode active material can be filled or / and deposited in the negative electrode current collector.

[0086] In some embodiments, the material of the positive electrode current collector can be aluminum, and the material of the negative electrode current collector can be copper.

[0087] [Electrolyte] In some embodiments, the battery cell further includes an electrolyte that functions to conduct ions between the positive and negative electrodes. The type of electrolyte is not particularly limited in the present application and can be selected as desired. The electrolyte can be liquid, gel, or solid.

[0088] In some embodiments, the liquid electrolyte includes an electrolyte salt and a solvent.

[0089] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium difluoro di-oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

[0090] In some embodiments, the solvent can 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, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butyrosulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent can also be selected from an ether solvent. The ether solvent can 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 a crown ether.

[0091] In some embodiments, the electrolyte solution can optionally further include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, an additive that improves certain properties of the battery cell, such as an additive that improves overcharge / rapid charge properties of the battery cell, an additive that improves high-temperature properties of the battery cell, an additive that improves low-temperature properties of the battery cell, etc.

[0092] In some embodiments, the gel electrolyte includes a polymer as a backbone network and can be used in combination with an ionic liquid-lithium salt.

[0093] In some embodiments, the solid electrolyte includes a polymer solid electrolyte, an inorganic solid electrolyte, a composite solid electrolyte.

[0094] As an example, the polymer of the polymer solid electrolyte can include a polyether (polyethylene oxide), a polysiloxane, a polycarbonate, a polyacrylonitrile, a polyvinylidene fluoride, a polymethyl methacrylate, a single-ion polymer, a polyionic liquid, cellulose, etc.

[0095] As an example, the inorganic solid-state electrolyte can be one or more of an oxide solid-state electrolyte (crystalline perovskite, sodium superionic conductor, garnet, amorphous LiPON film), a sulfide solid-state electrolyte (crystalline lithium superionic conductor (lithium germanium phosphorous sulfide, argyrodite), amorphous sulfide), and a halide solid-state electrolyte, a nitride solid-state electrolyte, and a hydride solid-state electrolyte.

[0096] As an example, the composite solid-state electrolyte is formed by adding an inorganic solid-state electrolyte filler to a polymer solid-state electrolyte.

[0097] [Separator] In some embodiments, the electrode assembly further comprises a separator disposed between the positive electrode and the negative electrode.

[0098] In some embodiments, the separator is a separator film. The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be used.

[0099] As an example, the main material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, and ceramic. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited. The separator can be a separate component located between the positive and negative electrodes, or can be attached to the surface 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 film.

[0100] In some embodiments, the separator is a solid-state electrolyte. The solid-state electrolyte is disposed between the positive electrode and the negative electrode, and functions to transport ions and separate the positive and negative electrodes.

[0101] [Electrode assembly] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of a wound structure and a stacked structure.

[0102] In some embodiments, the electrode assembly is a wound structure. The positive electrode sheet and the negative electrode sheet are wound into a wound structure.

[0103] In some embodiments, the electrode assembly is a stacked structure.

[0104] As an example, a plurality of positive electrode sheets and a plurality of negative electrode sheets can be alternately stacked.

[0105] As an example, a plurality of positive electrode sheets can be provided, and the negative electrode sheet can be folded to form a plurality of stacked folded sections, and one positive electrode sheet can be interposed between adjacent folded sections.

[0106] As an example, the positive electrode tab and the negative electrode tab are each folded to form a plurality of folded segments that are stacked.

[0107] As an example, the separator can be provided in plurality and disposed between any adjacent positive electrode tab or negative electrode tab.

[0108] As an example, the separator can be provided in plurality and disposed between any adjacent positive electrode tab or negative electrode tab.

[0109] In some embodiments, the electrode assembly can have a shape of a cylinder, a flat, or a polygonal prism, etc.

[0110] In some embodiments, the electrode assembly can be provided with a tab, which can lead current out of the electrode assembly. The tab can include a positive tab and a negative tab.

[0111] Casing In some embodiments, the battery cell can include a housing. The housing can be a steel housing, an aluminum housing, a plastic housing (e.g., polypropylene), a composite metal housing (e.g., a copper-aluminum composite housing), or an aluminum-plastic film, etc. In some embodiments, the housing can be a sealed structure or a non-sealed structure. As an example, when the housing is a non-sealed structure, the housing serves to protect the electrode assembly, and a sealing bag is further included between the housing and the electrode assembly, which is used to encapsulate the electrode assembly and the electrolyte. Specifically, the sealing bag can be a bag-shaped insulating member or an aluminum-plastic film. When the housing is a sealed structure, it is used to encapsulate the electrode assembly and the electrolyte, etc.

[0112] 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, including a square battery cell, a blade battery cell, a polygonal battery cell (e.g., a hexagonal battery cell), etc.

[0113] In some embodiments, the housing includes a top cover assembly and a housing body, the housing body is provided with an opening, and the top cover assembly is provided on the opening. The housing body can be provided with one or more openings. The top cover assembly can also be provided with one or more openings.

[0114] Figure 2 is a battery cell 5 of a square structure as an example.

[0115] In some embodiments, with reference to Figure 3The 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.

[0116] Electrode terminal 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.

[0117] Pressure relief mechanism 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.

[0118] 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.

[0119] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0120] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0121] 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.

[0122] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for discharging gas inside the battery cell.

[0123] The discharge from the battery cell mentioned in the present application includes, but is not limited to, electrolyte, dissolved or split positive and negative electrode sheets, fragments of separators, high-temperature and high-pressure gas generated by reaction, flame, and the like.

[0124] The third embodiment of the present application provides a battery apparatus including a battery cell including the battery cell of the first embodiment or the battery cell manufactured by the method of the second embodiment.

[0125] The battery apparatus mentioned in the embodiments of the present application can include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly can include a plurality of battery cells connected in series, in parallel, or in a mixed connection through a busbar.

[0126] In some embodiments, the battery cell assembly is generally formed by arranging a plurality of battery cells.

[0127] As an example, the battery cell assembly can be a battery module formed by arranging and fixing a plurality of battery cells into one independent module. As an example, the battery module can be formed by bundling a plurality of battery cells with a cable tie.

[0128] Figure 4 The battery module 4 is an example. Referring to FIG. 1, the battery module 4 includes a plurality of battery cells 5 arranged in series along the length direction of the battery module 4. Figure 4 In the battery module 4, the plurality of battery cells 5 can be arranged in series along the length direction of the battery module 4. Of course, the plurality of battery cells 5 can be arranged in any other manner. Further, the plurality of battery cells 5 can be fixed by a fastener.

[0129] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of battery cells 5 can be accommodated in the accommodation space.

[0130] In some embodiments, the battery apparatus can be a battery pack including a case and one or more battery cell assemblies accommodated in the case.

[0131] As an example, the battery cell assembly can be a battery module, and the battery cell assembly can be accommodated in the case by fixing the battery module in the case.

[0132] As an example, the battery cell assembly can also be accommodated in the case by directly fixing a plurality of battery cells in the case.

[0133] As an example, the case can include a first case and a second case. The first case and the second case are coupled so that an inside of the case forms a closed space to accommodate the battery cell assembly. The closed here means covered or closed, which can be sealed or unsealed. The first case can be a top cover or a bottom plate.

[0134] As an example, the case can include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected with the frame so that an inside of the case forms a closed space to accommodate the battery cell assembly. Figure 5 and Figure 6 is a battery pack 1 as an example. Referring to Figure 5 and Figure 6 In the battery pack 1, a battery case and a plurality of battery modules 4 disposed in the battery case can be included. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 is capable of being disposed on the lower case 3 and forming a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0135] In some embodiments, the case can be a part of a chassis structure of a vehicle. For example, a part of the case can be at least a part of a floor of the vehicle, or a part of the case can be at least a part of a cross beam and a longitudinal beam of the vehicle.

[0136] The fourth embodiment of the present application provides a power consuming device including a battery cell or a battery device, the battery cell including any battery cell provided by the first embodiment or a battery cell prepared by the method described in the second embodiment, and the battery device being any battery device provided by the third embodiment.

[0137] The technical solutions described in the embodiments of the present application are applicable to various power consuming devices using battery cells, such as mobile phones, portable devices, notebook computers, electric vehicles, electric toys, electric tools, vehicles, ships, and spacecraft, such as aircraft, rockets, space shuttles, and spaceships.

[0138] As the power consuming device, a secondary battery cell, a battery module, or a battery pack can be selected according to the use requirements thereof.

[0139] Figure 7 is a power consuming device as an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the power consuming device for secondary batteries, a battery pack or a battery module can be used. Embodiments

[0140] Hereinafter, the examples of the present application will be described. The examples described below are illustrative and are for the purpose of explanation only and are not to be taken as limiting the present application. Unless otherwise indicated, technical or conditions not specified in the examples are performed according to the techniques or conditions described in the literature in the field or according to the product manual. The reagents or instruments used are not specified by the manufacturer, but are all conventional products that can be obtained commercially.

[0141] Example 1 Preparation of positive electrode sheet Lithium carbonate, ferrous oxalate, manganese oxalate, and ammonium dihydrogen phosphate were weighed according to a molar ratio of lithium element:manganese element:iron element:phosphorus element = 1:0.7:0.3:1, and were put into a sand mill to obtain a slurry with a solid content of 50% by adding deionized water. A lithium manganese iron phosphate precursor was prepared by spray drying the slurry. A lithium manganese iron phosphate sample LMFP-73 was obtained by sintering the lithium manganese iron phosphate precursor at 480°C for 6h. The mass of LMFP-73 was weighed, and deionized water was added to disperse the mixture to obtain a slurry with a solid content of 50%. Ferrous sulfate was added to the slurry, and the mixture was continuously stirred for 2h until the ferrous sulfate was completely dissolved. A sulfur-doped precursor was obtained by spray drying the slurry. The 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 dispersed by sand milling. Zirconia balls with a diameter of about 0.5mm were used for sand milling, and the ball-to-material ratio was 3:1. After the sand milling was completed, the slurry was separated from the balls and was spray dried to obtain a carbon-coated precursor. A carbon-coated sulfur-surface-doped lithium manganese iron phosphate sample LMFP-73-S was obtained by sintering the carbon-coated precursor at 750°C for 10h under a nitrogen atmosphere.

[0142] The positive electrode active material LMFP-73-S, conductive carbon black Super P, and binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 92:5.5:2.5, and were dissolved in a solvent N-methyl pyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was coated on a current collector aluminum foil, and was dried, cold-pressed, trimmed, cut, and striped to obtain a positive electrode sheet.

[0143] Preparation of negative electrode sheet The negative electrode active material graphite, conductive carbon black Super P, binder styrene-butadiene rubber (SBR), and thickening agent carboxymethyl cellulose sodium (CMC-Na) were mixed in a mass ratio of 95:2.5:1.5:1, and were dissolved in a solvent deionized water to prepare a negative electrode slurry. The negative electrode slurry was coated on a current collector copper foil, and was dried, cold-pressed, trimmed, and cut to obtain a negative electrode sheet.

[0144] Electrolyte 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, and then lithium hexafluorophosphate (LiPF6) and the electrolyte solvent were mixed to prepare an electrolyte with a concentration of 1 mol / L.

[0145] Separator film : Porous polyethylene (PP) separator film.

[0146] Battery assembly The positive electrode sheet, the separator film, and the negative electrode sheet were prepared in sequence, and the separator film was placed between the positive electrode sheet and the negative electrode sheet to play a separation role. Then, the electrode assembly was obtained by winding, hot pressing, shaping, and welding. The electrode assembly was placed in a square aluminum shell, and after vacuum drying, the electrolyte was injected, and then the battery monomer was obtained after standing, formation test, aging, and capacity test.

[0147] Test: The mass content of sulfur element and the doping depth of sulfur element in the lithium manganese iron phosphate material were tested according to the above method.

[0148] Lithium intercalation voltage test: three-electrode test was performed on the battery monomer, and ultra-high precision blue electricity tester or electrochemical workstation was used. At 25℃, the battery monomer was charged at 0.33C constant current to 4.2V, and then charged at constant voltage to 0.05C current. After standing for 10 min, the battery monomer was discharged at 0.33C constant current to 2V, and the voltage-capacity curve in the charging and discharging process was recorded. The charging and discharging curves of LMFP-73-S and LMFP-73 are recorded in Figure 1 , and the voltage platform on the voltage-capacity curve is the lithium intercalation voltage. The results show that the lithium intercalation voltage of Example 1 does not decrease but increases relative to the undoped LMFP-73 and is near 3.62V, indicating that the sulfur element is doped at the P site. Since no reducing gas is used in the preparation process, the S element in the sulfur source remains +6 valence, and the improvement of the rate performance of the battery monomer also confirms that the 6+ substitution of P 5+ will cause charge compensation.

[0149] Test of carbon morphology in carbon-coated layer: the battery monomer discharged to the cut-off voltage was disassembled to obtain the positive electrode sheet, the positive electrode powder was scraped off from the current collector, and the powder was washed with high-purity dimethyl carbonate (DMC) to remove the electrolyte residues and lithium salt and then dried. A small amount of powder sample was ultrasonically dispersed in ethanol and then dropped on an ultrathin carbon film copper mesh, dried, and then placed under high-resolution transmission electron microscope analysis (HRTEM) for observation. First, a single particle located at the edge of the carbon film with appropriate contrast was found in low-magnification mode, and then the high-resolution mode was switched to focus on the edge of the particle. The carbon morphology in the carbon-coated layer was confirmed by identifying the typical morphological characteristics of carbon materials.

[0150] Cycle capacity retention rate test: Three-electrode test was performed on the battery monomer. An ultra-high precision blue electricity tester or an electrochemical workstation was used to charge the battery monomer to 4.2 V at 0.33 C, and then to a current of 0.05 C at constant voltage. After 10 min, 3 times of constant current charge-discharge cycle test was performed at different rates (0.33 C, 1 C, 2 C, 3 C). The voltage-capacity curve during each cycle was recorded, the charge capacity at different rates was calculated, and the capacity retention rate at 3 C was calculated: capacity retention rate = (3C rate capacity / 0.33C capacity) * 100%.

[0151] Example 2 The difference from Example 1 is that the same mass of potassium pyrosulfate is used to replace the ferrous sulfate in Example 1, and the others are the same as in Example 1.

[0152] Comparative Example 1 A lithium source, an iron source, a manganese source, a phosphorus source, and ferrous sulfate were weighed according to a molar ratio of lithium element: manganese element: iron element: phosphorus element: sulfur element = 1: 0.7: 0.3: 1: 0.0016, and were put into a sand mill to obtain a slurry with a solid content of 50% by adding deionized water. A sulfur-doped lithium manganese iron phosphate precursor was prepared by spray drying the slurry, a sulfur-doped lithium manganese iron phosphate sample LMFP-73-S-body was obtained by sintering the obtained precursor at 480°C for 6h. The 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 dispersed by sand milling, and zirconia with a diameter of about 0.5 mm was used as the grinding ball with a ball-to-material ratio of 3:1. After the sand milling was completed, the slurry was spray dried after the grinding balls were separated to obtain a carbon-coated precursor. A carbon-coated sulfur-doped lithium manganese iron phosphate sample LMFP-73-S-body was obtained by sintering the carbon-coated precursor at 750°C for 10h in a nitrogen atmosphere.

[0153] Comparative Example 2 The difference from Example 1 is only that ferrous sulfate of the same mass is used to replace the ferrous sulfate of Example 1, and the rest is the same as Example 1.

[0154] Comparative Example 3 The difference from Example 1 is only that ferrous sulfate of the same mass is used to replace the ferrous sulfate of Example 1, and the rest is the same as Example 1.

[0155] The test results of Example 1 and Comparative Examples 1 to 3 are recorded in Table 2.

[0156] Table 2

[0157] According to the data in Table 2, it can be seen that after the +6 valence sulfur element surface phosphorus site is doped in Example 1, the specific capacity under high rate charging is best, that is, the rate performance is best, and the capacity retention rate is also highest, indicating that the cycle performance is best. Comparative Examples 2 and 3 doped with low-valence sulfuric acid elements failed to improve the rate performance and cycle performance, and Comparative Example 3 did not doped in the positive valence position due to the use of negative valence sulfur, so it had no effect on the specific capacity.

[0158] Example 3 The difference from Example 1 is only that the mass percentage of ferrous sulfate added relative to the total mass of LMFP-73 and ferrous sulfate is 0.1%, and the rest is the same as Example 1.

[0159] Example 4 The difference from Example 1 is only that the mass percentage of ferrous sulfate added relative to the total mass of LMFP-73 and ferrous sulfate is 0.5%, and the rest is the same as Example 1.

[0160] Example 5 The difference from Example 1 is only that the mass percentage of ferrous sulfate added relative to the total mass of LMFP-73 and ferrous sulfate is 0.7%, and the rest is the same as Example 1.

[0161] The test results of Examples 3 to 5 are recorded in Table 3.

[0162] Table 3

[0163] According to the data in Table 3, it can be seen that as the mass content of sulfur element increases, the doping depth increases, the positive electrode charging specific capacity and capacity retention rate first increase, but when it exceeds 0.05%, the capacity retention rate decreases, which may be because the doping depth is too deep to affect the bulk phase of the positive electrode material, so the specific capacity and the cycle stability under high rate decrease.

[0164] Example 6 The difference from Example 1 is that the carbon-coated precursor is sintered at 550℃ for 6h under nitrogen atmosphere to obtain the carbon-coated sulfur surface-doped lithium manganese iron phosphate sample, and the rest is the same as Example 1.

[0165] Example 7 The difference from Example 1 is that the carbon-coated precursor is sintered at 750℃ for 4h under nitrogen atmosphere to obtain the carbon-coated sulfur surface-doped lithium manganese iron phosphate sample, and the rest is the same as Example 1.

[0166] Example 8 The difference from Example 1 is that the carbon-coated precursor is sintered at 750℃ for 12h under nitrogen atmosphere to obtain the carbon-coated sulfur surface-doped lithium manganese iron phosphate sample, and the rest is the same as Example 1.

[0167] Example 9 The difference from Example 1 is that the carbon-coated precursor is sintered at 750℃ for 10h under air atmosphere to obtain the carbon-coated sulfur surface-doped lithium manganese iron phosphate sample, and the rest is the same as Example 1.

[0168] The test results of Examples 6 to 9 are recorded in Table 4.

[0169] Table 4

[0170] According to the comparison of the data in Table 4, it can be seen that the sintering temperature and time will affect the doping amount and doping depth of sulfur element. Low sintering temperature and short sintering time will result in a decrease in the doping amount of sulfur element and a shallower doping depth, thus having a smaller impact on the specific capacity of 0.33C, but at the same time, the improvement of the rate performance and the cycle stability is weakened.

[0171] In addition, Example 9 is sintered in air, in which oxygen may cause the loss of sulfur element, resulting in a less improvement effect of sulfur doping than Example 1.

[0172] Although the present application has been described with reference to the preferred embodiments, various modifications can be made to it without departing from the scope of the application, and equivalent parts can be substituted for the parts thereof. In particular, the technical features mentioned in each embodiment can be combined in any manner as long as there is no structural conflict. The present 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 electrode sheet, the positive electrode sheet comprises a positive electrode active material, the positive electrode 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 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, and the sulfur element comprises a +6 valence sulfur element.

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 doping depth of the sulfur element is 0.5nm-2nm.

4. 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.

5. 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 and optionally one or more elements selected from the group consisting of 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.

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 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, and the sulfur element comprises a +6 valence sulfur element.

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 doping depth of the sulfur element is 0.5nm-2nm.

12. 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.

13. 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 and optionally one or more elements selected from the group consisting of 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.

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 a lithium iron manganese phosphate material, characterized by, 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 a sulfate or a pyrosulfate.

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 performed in air, nitrogen or an 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 with 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 or ethanol.

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

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

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