WO2024077636A1 - 复合磷酸锰铁锂材料、其制备方法、二次电池和用电装置 - Google Patents

复合磷酸锰铁锂材料、其制备方法、二次电池和用电装置 Download PDF

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WO2024077636A1
WO2024077636A1 PCT/CN2022/125524 CN2022125524W WO2024077636A1 WO 2024077636 A1 WO2024077636 A1 WO 2024077636A1 CN 2022125524 W CN2022125524 W CN 2022125524W WO 2024077636 A1 WO2024077636 A1 WO 2024077636A1
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lithium
lithium iron
manganese
coating layer
phosphate particles
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PCT/CN2022/125524
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English (en)
French (fr)
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杨成龙
张海明
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宁德时代新能源科技股份有限公司
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Priority to CN202280084148.0A priority Critical patent/CN118402097A/zh
Priority to PCT/CN2022/125524 priority patent/WO2024077636A1/zh
Publication of WO2024077636A1 publication Critical patent/WO2024077636A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates

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  • the present application relates to the field of batteries, and in particular to a composite lithium iron manganese phosphate material, a preparation method thereof, a secondary battery and an electrical device.
  • Secondary batteries have the characteristics of high capacity and long life, so they are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and electric tools, etc.
  • the positive electrode active materials in the secondary batteries are usually optimized and improved.
  • the positive electrode active materials are currently used in secondary batteries, their specific capacity is poorly exerted, and the cycle performance of the secondary batteries is poor.
  • the present application is made in view of the above-mentioned problems, and its purpose is to provide a composite manganese iron lithium phosphate material, a preparation method thereof, a secondary battery and an electrical device.
  • a first aspect of the present application provides a composite lithium iron manganese phosphate material, which includes lithium iron manganese phosphate particles and a coating layer; the upper limit voltage of the lithium iron manganese phosphate particles is denoted by V1, with a unit of V; the coating layer is coated on at least a portion of the surface of the lithium iron manganese phosphate particles, the coating layer includes metal nanoparticles, and the oxidation voltage of the metal nanoparticles is denoted by V2, with a unit of V, wherein the composite lithium iron manganese phosphate material satisfies: V1 ⁇ V2.
  • the present application can improve the conductivity of the coated material and reduce its conductive resistance by coating the surface of the lithium iron manganese phosphate particles with metal nanoparticles; and the metal nanoparticles have stable performance and are not easily oxidized under high pressure, thereby ensuring the stability of the conductivity of the coated material during the use cycle, reducing the risk of rapid increase in polarization and rapid capacity decay of the material in the late cycle, and ensuring the cycle stability and stable performance of the capacity of the material.
  • the structural formula of the lithium iron manganese phosphate particles is LiMn 1-x Fe x M y PO 4 , wherein 0.05 ⁇ x ⁇ 0.95; 0 ⁇ y ⁇ 1; optionally, 0 ⁇ y ⁇ 0.2; M represents a doping element, and the lithium iron manganese phosphate particles include a doping element M, and the doping element M includes one or more elements of sulfur, nitrogen, boron, fluorine, chlorine, bromine and iodine; optionally, the doping element M includes sulfur.
  • the doping element M of the present application can form a bond with the metal nanoparticles, play an anchoring role on the metal nanoparticles, and achieve the localized growth and small-size growth of the metal nanoparticles. Therefore, the uniform doping of the doping element M is conducive to the uniform distribution of the metal nanoparticles and improves the coating performance of the lithium manganese iron phosphate particles.
  • the metal nanoparticles include nanoparticles of one or more of silver, gold, platinum, palladium, rhodium, iridium, osmium, and ruthenium.
  • the metal nanoparticles can exist stably under the working voltage of lithium manganese iron phosphate, and play a role in improving the conductive properties of lithium manganese iron phosphate.
  • the mass content of the coating layer is recorded as A%, 0.3 ⁇ A ⁇ 10; optionally, 0.3 ⁇ A ⁇ 3.
  • the thickness of the coating layer will not be too thick, which is conducive to the smooth migration of lithium ions and ensures the normal progress of the cycle process, and the coating layer will not excessively occupy the space of the lithium iron manganese phosphate, ensuring the gram capacity of the composite lithium iron manganese phosphate; the thickness of the coating layer will not be too thin, so that it can have a good coating effect on the surface of the lithium iron manganese phosphate particles and improve the overall conductivity of the lithium iron manganese phosphate particles after coating.
  • the thickness of the coating layer is denoted as H, in nm, 2 ⁇ H ⁇ 100; optionally, 5 ⁇ H ⁇ 20.
  • the thickness of the coating layer of the present application when the thickness of the coating layer of the present application is within the above range, the thickness of the coating layer will not be too thick, which is conducive to the smooth migration of lithium ions and ensures the normal progress of the cycle process; the thickness of the coating layer will not be too thin, so that it can have a good coating effect on the surface of the lithium iron manganese phosphate particles and improve the overall conductivity of the lithium iron manganese phosphate particles after coating.
  • the composite lithium manganese iron phosphate material satisfies: the average particle size D of the metal nanoparticles is denoted as D1, in nm, D1 ⁇ 20; optionally, D1 ⁇ 10.
  • the average particle size D of the metal nanoparticles of the present application is within the above range, the average particle size will not be too large, and the lithium iron manganese phosphate particles can be tightly coated, thereby evenly improving the overall conductivity of the lithium iron manganese phosphate particles and reducing the coating amount; the average particle size D of the metal nanoparticles will not be too small, and the metal nanoparticles have certain gaps that are beneficial to the migration of lithium ions, thereby ensuring the smooth progress of the cycle process.
  • the composite lithium iron manganese phosphate material satisfies: the volume average particle size Dv50 of the lithium iron manganese phosphate particles is denoted as D2, in ⁇ m, 0.1 ⁇ D2 ⁇ 10; optionally, 0.2 ⁇ D2 ⁇ 5.
  • the structure of the lithium iron manganese phosphate particles of the present application is relatively stable and the kinetic performance is relatively good, which is beneficial to improving the first coulomb efficiency of the composite lithium iron manganese phosphate particles; and is beneficial to the formation of uniform coating of metal nanoparticles on the surface of the lithium iron manganese phosphate particles.
  • the composite lithium manganese iron phosphate material satisfies: the volume average particle size Dv50 of the composite lithium manganese iron phosphate material is denoted as D, the unit is ⁇ m, 0.1 ⁇ D ⁇ 10; optionally, 0.2 ⁇ D ⁇ 5.
  • the composite manganese iron lithium phosphate material of the present application meets the above range, its structure is relatively stable and its dynamic performance is relatively good, which is beneficial to improving the first coulombic efficiency of the composite manganese iron lithium phosphate material.
  • the second aspect of the present application provides a method for preparing a composite lithium iron manganese phosphate material, the method comprising: providing lithium iron manganese phosphate particles; providing a conductive precursor to the lithium iron manganese phosphate particles, and heat treating the conductive precursor to reduce the conductive precursor to form a coating layer coating the lithium iron manganese phosphate particles, the coating layer comprising metal nanoparticles, wherein the upper limit voltage of the use of the lithium iron manganese phosphate particles is denoted as V1, in V; the coating layer is coated on at least a portion of the surface of the lithium iron manganese phosphate particles, the coating layer comprises metal nanoparticles, the oxidation voltage of the metal nanoparticles is denoted as V2, in V, and the composite lithium iron manganese phosphate material satisfies: V1 ⁇ V2.
  • the step of providing lithium iron manganese phosphate particles includes: doping a doping element M into the lithium iron manganese phosphate particles, wherein the doping element M includes one or more elements of sulfur, nitrogen, boron, fluorine, chlorine, bromine and iodine; optionally, the doping element M includes sulfur.
  • the heat treatment temperature is 400° C. to 1000° C.; and/or the heat treatment time is 2 h to 6 h.
  • the present application can control the size of the metal nanoparticles formed by regulating the conditions of the heat treatment; the temperature of the heat treatment will not be too high, which is conducive to the moderate growth of the metal nanoparticles, the particles will not be too large, and the doping elements can easily play an anchoring effect, so that the metal nanoparticles are evenly distributed on the surface of the lithium manganese iron phosphate particles, and the particle size of the formed particles is relatively moderate, which is conducive to forming a good coating effect on the lithium manganese iron phosphate particles.
  • the conductive precursor includes one or more of nitrate, chloride, bromide, iodide, sulfate, phosphate, acetate, and acetylacetonate; and/or the conductive precursor includes one or more of silver, gold, platinum, palladium, rhodium, iridium, osmium, and ruthenium.
  • the molar content of the conductive precursor is b%, 0.25 ⁇ b ⁇ 14.5; optionally, 0.40 ⁇ b ⁇ 4.60.
  • the present application regulates the molar content of the conductive precursor so that the quality of the coating layer formed by the conductive precursor on the surface of the lithium iron manganese phosphate particles is regulated.
  • the lithium iron manganese phosphate in the composite lithium iron manganese phosphate is the main material, and the coating layer has little effect on the overall gram capacity of the material, which can ensure the overall gram capacity of the material; and the coating layer can form a uniform coating on the lithium iron manganese phosphate, improve the overall conductivity of the composite lithium iron manganese phosphate, and is beneficial to the capacity of the lithium iron manganese phosphate.
  • the third aspect of the present application provides a secondary battery, including a positive electrode plate, wherein the positive electrode plate includes a composite lithium iron manganese phosphate material as described in any embodiment of the first aspect of the present application or a composite lithium iron manganese phosphate material obtained by the method described in any implementation method of the second aspect of the present application.
  • the fourth aspect of the present application further provides an electrical device, comprising the secondary battery as described in the third aspect of the present application.
  • FIG. 1 is a schematic diagram of an embodiment of a secondary battery of the present application.
  • FIG. 2 is an exploded schematic diagram of an embodiment of the secondary battery of FIG. 1 .
  • FIG. 3 is a schematic diagram of an embodiment of a battery module of the present application.
  • FIG. 4 is a schematic diagram of an embodiment of a battery pack of the present application.
  • FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present application as a power source.
  • FIG. 7 is a cycle curve diagram of Example 1 and Comparative Example 1.
  • range disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range.
  • the range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected.
  • the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers.
  • the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just the abbreviation of these numerical combinations.
  • a parameter is expressed as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • a method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, 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).
  • Lithium manganese iron phosphate has an olivine structure, and its theoretical capacity is comparable to that of lithium iron phosphate materials. Due to the presence of Mn elements, its electrode potential is relatively high, and the high potential makes this type of material have the potential advantage of high energy density; but at the same time, lithium manganese iron phosphate crystals have a hexagonal close-packed structure, lithium and iron atoms occupy the octahedral 4a and 4c sites respectively, and phosphorus atoms occupy the tetrahedral 4c site, wherein the FeO 6 (MnO 6 ) octahedron and the PO 4 tetrahedron are cross-connected, and this structure has good stability, and even if all lithium ions are removed during charging, it is not easy to have the problem of structural collapse.
  • MnO 6 FeO 6
  • the P atoms in the material form PO 4 tetrahedrons through strong covalent bonds of PO, and it is difficult for O atoms to escape from the structure, so the material has high stability; however, since the material is connected by PO 4 tetrahedrons, it does not have a continuous FeO 6 (MnO 6 ) octahedral network with common edges, resulting in poor electrical conductivity of the material, low electronic conductivity, and low diffusion coefficient of lithium ions. It is difficult to synthesize lithium manganese iron phosphate that can be reversibly charged and discharged, and its electrical conductivity limits its development.
  • MnO 6 FeO 6
  • the inventors have found that in order to improve the conductivity of lithium manganese iron phosphate, a conductive carbon layer is usually coated on the surface of the lithium manganese iron phosphate particles.
  • the voltage system suitable for lithium manganese iron phosphate is a high voltage, such as >4V
  • the oxidation of the carbon layer is enhanced under the high voltage system, which may cause the carbon layer to oxidize and produce gas.
  • the conductivity of the material decreases, the impedance increases, and the cycle performance decays.
  • the inventor has improved the coating structure of lithium manganese iron phosphate, and a coating layer containing metal nanoparticles is coated on the surface of lithium manganese iron phosphate particles.
  • the coating layer can improve the conductivity of lithium manganese iron phosphate, which is beneficial to the capacity of lithium manganese iron phosphate.
  • the coating layer has stable performance and can improve the overall structural stability of lithium manganese iron phosphate, which is beneficial to improving the cycle performance of the secondary battery used in it.
  • the present application is described in detail below.
  • the present application proposes a composite lithium manganese iron phosphate material.
  • the composite lithium iron manganese phosphate material includes lithium iron manganese phosphate particles and a coating layer; the upper limit voltage of the lithium iron manganese phosphate particles is recorded as V1, with a unit of V; the coating layer is coated on at least a portion of the surface of the lithium iron manganese phosphate particles, and the coating layer includes metal nanoparticles, and the oxidation voltage of the metal nanoparticles is recorded as V2, with a unit of V, wherein the composite lithium iron manganese phosphate material satisfies: V1 ⁇ V2.
  • the upper limit voltage V1 of lithium manganese iron phosphate refers to the upper limit voltage of charging when lithium manganese iron phosphate is used as a positive electrode active material in a secondary battery. At this voltage, lithium manganese iron phosphate can basically ensure the stability of the material.
  • the upper limit voltage V1 of lithium manganese iron phosphate can be set to 3.7V to 4.5V. V1 can be set by the manufacturer.
  • the oxidation voltage V2 of metal nanoparticles refers to the voltage at which metal nanoparticles lose electrons and become metal ions.
  • V2 can be tested by linear sweep voltammetry LSV, using the metal to be measured as the working electrode and the lithium sheet as the reference electrode, and scanning from 0V to 5V or higher voltage at a scanning speed of 0.15mV/s to 50mV/s.
  • the voltage when the oxidation current increases significantly is V2.
  • the scanning speed can be selected from 1mV/s to 5mV/s.
  • the present application sets V1 ⁇ V2, so that during the long-term cycle charge and discharge process of the secondary battery, the metal nanoparticles will basically not be oxidized, thereby ensuring the structural stability of the composite manganese iron phosphate lithium material.
  • the lithium manganese iron phosphate particles have a structural formula of LiMn 1-x Fe x My PO 4 , wherein 0.05 ⁇ x ⁇ 0.95; 0 ⁇ y ⁇ 1; optionally, 0 ⁇ y ⁇ 0.2.
  • M represents a doping element, that is, lithium manganese iron phosphate can be a material modified by a doping element, or a material without a doping element.
  • the doping element can be a cation doping element or an anion doping element.
  • Lithium manganese iron phosphate can be charged and discharged at a high voltage of about 4.45V.
  • the metal nanoparticles can exist stably under the working voltage of lithium manganese iron phosphate and are not easily oxidized, thereby being able to play a long-term and stable coating role on the lithium manganese iron phosphate particles, improving the structural stability of the coated lithium manganese iron phosphate, and improving the cycle performance of the composite lithium manganese iron phosphate material.
  • the particle size of the lithium iron manganese phosphate particles themselves is usually small, and the particles in the coating layer in the related art are relatively large in particle size, so it is not easy for the coating layer to form a coating on the surface of the lithium iron manganese phosphate particles, resulting in the inability to play a good coating role on the lithium iron manganese phosphate.
  • the coating layer of the present application includes metal nanoparticles, and the particle size of the metal in the coating layer is small and nanometer-level, which can be dispersed on the surface of the lithium iron manganese phosphate particles to form a uniform coating, thereby having a good overall coating performance for the lithium iron manganese phosphate particles; and because the particle size of the metal nanoparticles is small, the contact between adjacent metal nanoparticles is closer, and the metal nanoparticles can fill the gaps in the adjacent layers inside the coating layer, so that the coating layer composed of the metal nanoparticles has better conductivity, which can reduce the conductive resistance to a certain extent, which is conducive to improving the conductivity of the lithium iron manganese phosphate particles after coating, and the improvement of the conductivity is conducive to the capacity of the lithium iron manganese phosphate particles.
  • the present application can improve the conductivity of the coated material and reduce its conductive resistance by coating the surface of lithium manganese iron phosphate particles with metal nanoparticles; and the metal nanoparticles have stable performance and are not easily oxidized under high pressure, thereby ensuring the stability of the conductivity of the coated material during the use cycle, reducing the risk of rapid increase in polarization and rapid capacity decay of the material in the late stage of the cycle, and ensuring the cycle stability of the material and the stable performance of the capacity.
  • the lithium manganese iron phosphate particles include a doping element M, and the doping element M includes one or more elements of sulfur, nitrogen, boron, fluorine, chlorine, bromine, iodine, etc.; optionally, the doping element M includes sulfur.
  • the doping element M is doped in the form of anions, which can occupy oxygen vacancies in the lithium iron manganese phosphate particles during the charge and discharge process, and play a role in stabilizing the structure of the lithium iron manganese phosphate; and the doping element M can increase the electron density of the lithium iron manganese phosphate particles, improve the conductivity and lithium capacity of the lithium iron manganese phosphate, improve the overall conductivity of the composite lithium iron manganese phosphate material, and is beneficial to capacity utilization and improved cycle performance.
  • the doping element M can form a bond with the metal nanoparticles, play an anchoring role on the metal nanoparticles, and achieve the localized growth and small-size growth of the metal nanoparticles. Therefore, the uniform doping of the doping element M is conducive to the uniform distribution of the metal nanoparticles and improves the coating performance of the lithium manganese iron phosphate particles.
  • the metal nanoparticles include one or more nanoparticles of silver, gold, platinum, palladium, rhodium, iridium, osmium, ruthenium, mercury, thallium, etc.
  • the metal nanoparticles can stably exist under the operating voltage of lithium manganese iron phosphate, and play a role in improving the conductive properties of lithium manganese iron phosphate.
  • the metal nanoparticles include one or more nanoparticles of silver, gold, platinum, palladium, rhodium, iridium, osmium, ruthenium, etc. Such metals are less toxic and more suitable for battery systems.
  • the mass content of the coating layer is recorded as A%, 0.3 ⁇ A ⁇ 10; optionally, 0.3 ⁇ A ⁇ 3.
  • the mass content of the coating layer has a meaning well known in the art, which can be measured by methods or equipment well known in the art; specifically, a certain weight of the composite lithium manganese iron phosphate material is weighed, digested with aqua regia, and then the solution is diluted, and the weight of the coated metal in the diluted solution is tested by ICP, and the mass proportion of the coating layer is calculated based on the tested metal weight and the weight of the composite lithium manganese iron phosphate material taken.
  • the thickness of the coating layer will not be too thick, which is conducive to the smooth migration of lithium ions and ensures the normal progress of the cycle process, and the coating layer will not excessively occupy the space of lithium iron manganese phosphate, ensuring the gram capacity of the composite lithium iron manganese phosphate; the thickness of the coating layer will not be too thin, so that it can play a good coating role on the surface of the lithium iron manganese phosphate particles and improve the overall conductivity of the lithium iron manganese phosphate particles after coating.
  • the mass content A% of the coating layer can be 0.3%, 0.5%, 0.8%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0% or 10%; or a range consisting of any two of the above values.
  • the thickness of the coating layer is denoted as H, in nm, 2 ⁇ H ⁇ 100; optionally, 5 ⁇ H ⁇ 20.
  • the thickness of the coating layer is a well-known meaning in the art, and it can be measured by methods or equipment well-known in the art; specifically, a certain amount of composite lithium manganese iron phosphate material can be taken as a sample, and a high-resolution transmission electron microscope analysis test can be performed to obtain an HRTEM image, and then the thickness of multiple (for example, more than 30) different positions on the HRTEM image is measured, and the average value is taken as the average thickness of the coating layer. From the HRTEM image, it can be seen that there is a clear grain boundary between the coating layer and the lithium manganese iron phosphate particles.
  • the thickness of the coating layer When the thickness of the coating layer is within the above range, the thickness of the coating layer will not be too thick, which is conducive to the smooth migration of lithium ions and ensures the normal progress of the cycle process; the thickness of the coating layer will not be too thin, so that it can have a good coating effect on the surface of the lithium iron manganese phosphate particles and improve the overall conductivity of the lithium iron manganese phosphate particles after coating.
  • the thickness H nm of the coating layer can be 2 nm, 3 nm, 5 nm, 10 nm, 20 nm, 30 nm, 50 nm, 60 nm, 80 nm or 100 nm; or a range consisting of any two of the above values.
  • the average particle size D of the metal nanoparticles is denoted as D1, in nm, and D1 ⁇ 20; optionally, D1 ⁇ 10.
  • the average particle size D of the metal nanoparticles has a meaning well known in the art, and can be measured by methods or equipment well known in the art; the metal of the coating layer is granular, and a certain amount of composite lithium manganese iron phosphate material can be taken as a sample, and a high-resolution transmission electron microscopy analysis test can be performed to obtain an HRTEM image, and then the particle sizes of the metal nanoparticles at multiple (for example, more than 30) different positions are measured on the HRTEM image, and the average value is taken as the average particle size D of the metal nanoparticles.
  • the average particle size D of the metal nanoparticles When the average particle size D of the metal nanoparticles is within the above range, the average particle size will not be too large, and the lithium iron manganese phosphate particles can be tightly coated, thereby evenly improving the overall conductivity of the lithium iron manganese phosphate particles and reducing the coating amount; the average particle size D of the metal nanoparticles will not be too small, and the metal nanoparticles have certain gaps that are conducive to the migration of lithium ions and ensure the smooth progress of the cycle process.
  • the average particle size of the metal nanoparticles can be 2nm, 3nm, 5nm, 6nm, 8nm, 10nm, 12nm, 15nm, 18nm or 20nm; or a range consisting of any two of the above values.
  • the volume average particle size Dv50 of the lithium manganese iron phosphate particles is denoted as D2, in ⁇ m, 0.1 ⁇ D2 ⁇ 10; optionally, 0.2 ⁇ D2 ⁇ 5.
  • the volume average particle size Dv50 of the material has a well-known meaning in the art, which indicates the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%, and can be tested using instruments and methods known in the art. For example, it can be conveniently tested using a laser particle size analyzer with reference to GB/T19077-2016 particle size distribution laser diffraction method, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK.
  • the first particles and the second particles in the lithium iron manganese phosphate particles may exist at the same time, and of course only one of them may exist.
  • the structure of the lithium iron manganese phosphate particles is relatively stable and the dynamic performance is relatively good, which is beneficial to improving the first coulomb efficiency of the composite lithium iron manganese phosphate particles; and it is beneficial to the formation of a uniform coating of metal nanoparticles on the surface of the lithium iron manganese phosphate particles.
  • the volume average particle size Dv50 of the composite lithium manganese iron phosphate material is denoted as D, in ⁇ m, 0.1 ⁇ D ⁇ 10; optionally, 0.2 ⁇ D ⁇ 5.
  • the thickness of the coating layer is an order of magnitude different from the particle size of lithium iron manganese phosphate.
  • the thickness of the coating layer contributes little to the particle size of the composite lithium iron manganese phosphate, so the particle size difference between lithium iron manganese phosphate particles and composite lithium iron manganese phosphate particles is not obvious at the micron level.
  • the composite lithium iron manganese phosphate material meets the above range, its structure is relatively stable and its kinetic performance is relatively good, which is conducive to improving the first coulomb efficiency of the composite lithium iron manganese phosphate material.
  • the present application proposes a method for preparing a composite lithium iron manganese phosphate material, which can prepare the composite lithium iron manganese phosphate material of any embodiment of the first aspect of the present application.
  • the method comprises:
  • Step S100 providing lithium manganese iron phosphate particles
  • Step S200 providing a conductive precursor to the lithium iron manganese phosphate particles, and heat-treating the conductive precursor to reduce the conductive precursor to form a coating layer covering the lithium iron manganese phosphate particles, wherein the coating layer includes metal nanoparticles.
  • the surface of the lithium manganese iron phosphate particles is coated with metal nanoparticles, which can improve the conductivity of the coated material and reduce its conductive resistance.
  • the metal nanoparticles have stable performance and are not easily oxidized under high voltage, thereby ensuring the conductivity of the coated material during its use cycle, reducing the risk of rapid increase in polarization and rapid capacity decay in the late stage of the cycle, and ensuring the cycle stability of the material and the stable performance of its capacity.
  • the composite lithium iron phosphate material meets the following requirements: the upper limit voltage of the use of the lithium manganese iron phosphate particles is recorded as V1, and the unit is V; the coating layer is coated on at least part of the surface of the lithium manganese iron phosphate particles, and the coating layer includes metal nanoparticles, and the oxidation voltage of the metal nanoparticles is recorded as V2, and the unit is V.
  • the composite lithium manganese iron phosphate material satisfies: V1 ⁇ V2, which can improve the conductivity and cycle performance of the composite lithium iron phosphate material.
  • the lithium manganese iron phosphate particles can be prepared by a variety of methods, such as solid phase method, coprecipitation method, sol-gel method, hydrothermal/solvothermal method, etc., and the solid phase method is used as an example for description.
  • the lithium source, manganese source, iron source, phosphorus source, etc. are added to the solvent according to a set molar ratio, such as 1: (1-m): m: 1, and mixed into a slurry, and the slurry is ball-milled and dried; then, it is sintered at high temperature under protective gas to form a lithium iron phosphate material.
  • 0.05 ⁇ m ⁇ 0.95, preferably 0.2 ⁇ m ⁇ 0.5 0.05 ⁇ m ⁇ 0.95, preferably 0.2 ⁇ m ⁇ 0.5.
  • the lithium source may include one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, and lithium oxalate.
  • the manganese source may include manganese carbonate and/or manganese oxalate.
  • the iron source may include one or more of ferrous carbonate, ferrous acetate, ferrous sulfate, ferrous nitrate, ferric phosphate, ferric acrylate, and ferrous oxalate.
  • the phosphorus source may include one or more of ammonium phosphate, diammonium phosphate, diammonium hydrogen phosphate, and iron phosphate.
  • the solvent may be deionized water and/or ethanol.
  • the shielding gas may include one or more of nitrogen, argon and helium.
  • a doping element M is doped into the lithium iron manganese phosphate particles, wherein the doping element M includes one or more elements selected from sulfur, nitrogen, boron, fluorine, chlorine, bromine, iodine, etc.; optionally, the doping element M includes sulfur.
  • raw materials including the doping element M can be added to the slurry and then ball-milled, dried after ball-milling, and then sintered at high temperature under protective gas to obtain a lithium iron manganese phosphate material doped with the doping element.
  • the sulfur source may include one or more of thiourea, carbon disulfide, hydrogen sulfide, sulfur powder and sodium dodecylbenzene sulfonate.
  • the nitrogen source may include one or more of ammonium chloride, ammonium iodide, ammonium formate, ammonium acetate, hexamethylenetetramine and glucosamine.
  • the boron source may include one or more of boron dioxide, boron trioxide, boric acid, tetraphenylboric acid, boron carbide, and tributyl borate.
  • the molar ratio of sulfur element to lithium element is (0.01-0.05):1.
  • the lithium manganese iron phosphate particles can also be prepared by a dry mixing method, and the specific preparation process can adopt the existing process in the field.
  • the conductive precursor may include one or more of nitrate, chloride, bromide, iodide, sulfate, phosphate, acetate, and acetylacetonate. That is, the anion of the conductive precursor is one or more of nitrate, chloride, bromide, iodide, sulfate, phosphate, acetate, and acetylacetonate.
  • the cations of the conductive precursor may include one or more ions of silver ions, gold ions, platinum ions, palladium ions, rhodium ions, iridium ions, osmium ions, and ruthenium ions.
  • the conductive precursor is a reasonable combination of any of the above anions and any of the cations.
  • the conductive precursor can be an inorganic precursor or an organic precursor, such as silver nitrate, silver chloride, gold nitrate, silver acetylacetonate, and the like.
  • the conductive precursor is conducive to reduction under a reducing atmosphere, and nitrate ions can be decomposed and are not easily left in the composite lithium iron manganese phosphate material; chloride ions, bromide ions, etc. can form hydrogen chloride or hydrogen bromide gas with hydrogen ions and evaporate out of the system, and are not easily left in the composite lithium iron manganese phosphate material, and have little effect on the composite lithium iron manganese phosphate material.
  • the molar content of the conductive precursor is b%, 0.25 ⁇ b ⁇ 14.5; alternatively, 0.40 ⁇ b ⁇ 4.60.
  • the cation of the conductive precursor is a silver ion, 0.45 ⁇ b ⁇ 13.7; alternatively, 0.70 ⁇ b ⁇ 4.20.
  • the quality of the coating formed by the conductive precursor on the surface of the lithium iron manganese phosphate particles can be regulated.
  • the lithium iron manganese phosphate in the composite lithium iron manganese phosphate is the main material, and the coating has little effect on the overall gram capacity of the material, which can ensure the overall gram capacity of the material; and the coating can form a uniform coating on the lithium iron manganese phosphate, improve the overall conductivity of the composite lithium iron manganese phosphate, and is beneficial to the capacity of the lithium iron manganese phosphate.
  • the temperature of the heat treatment may be 400° C. to 1000° C.; and/or the time of the heat treatment may be 2 h to 6 h.
  • the size of the metal nanoparticles can be controlled; the temperature of the heat treatment will not be too high, which is conducive to the moderate growth of the metal nanoparticles, the particles will not be too large, and the doping elements will easily play an anchoring effect, so that the metal nanoparticles are evenly distributed on the surface of the lithium manganese iron phosphate particles, and the particle size of the formed particles is relatively moderate, which is conducive to forming a good coating effect on the lithium manganese iron phosphate particles.
  • the temperature of the heat treatment will not be too low, so that the metal ions in the conductive precursor can be fully reduced to metal elements.
  • the heat treatment can be performed under the protection of a reducing atmosphere, so that the conductive precursor can be fully reduced to generate metal nanoparticles.
  • the reducing atmosphere can be a mixed gas of argon and hydrogen, and the proportion of hydrogen can be relatively small, for example, 5%.
  • the present application proposes a secondary battery.
  • Secondary batteries include positive electrode sheets, negative electrode sheets, electrolytes, and separators.
  • active ions are embedded and released back and forth between the positive electrode sheets and the negative electrode sheets.
  • the electrolyte plays the role of conducting ions between the positive electrode sheets and the negative electrode sheets.
  • the separator is set between the positive electrode sheets and the negative electrode sheets, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.
  • the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode film layer includes a positive electrode active material
  • the positive electrode active material may include the composite lithium iron manganese oxide material of any embodiment of the first aspect of the present application or the composite lithium iron manganese oxide material prepared by the method described in any embodiment of the second aspect of the present application.
  • the positive electrode film layer may further include a positive electrode conductive agent.
  • a positive electrode conductive agent includes a combination of one or more selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the mass percentage of the positive electrode conductive agent is less than 5%.
  • the positive electrode film layer may also optionally include a positive electrode binder.
  • the present application does not particularly limit the type of positive electrode binder.
  • the positive electrode binder may include a combination of one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • a metal foil an aluminum foil or an aluminum alloy foil may be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include a combination of one or more selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy
  • the polymer material base layer may include a combination of one or more selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).
  • the positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring them uniformly.
  • the solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil may be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode active material may adopt the negative electrode active material for the battery known in the art.
  • 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, lithium titanate, etc.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode film layer may further include a binder.
  • the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • a conductive agent which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).
  • a thickener eg, sodium carboxymethyl cellulose (CMC-Na)
  • the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays the role of conducting ions between the positive electrode and the negative electrode.
  • the present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.
  • the electrolyte can be liquid, gel or all-solid.
  • the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.
  • the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.
  • the lithium salt may include a combination of one or more selected from lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium te
  • the organic solvent may include a combination of one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).
  • EC ethylene carbon
  • the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • additives such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • the secondary battery further includes a separator.
  • the present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation.
  • the materials of each layer can be the same or different, without particular limitation.
  • the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.
  • FIG1 is a secondary battery 5 of a square structure as an example.
  • the outer package may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.
  • the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery.
  • the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying, and the secondary battery is obtained through vacuum packaging, standing, forming, shaping and other processes.
  • the secondary batteries according to the present application can be assembled into a battery module.
  • the battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG3 is a schematic diagram of a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.
  • the battery module 4 may further include a housing having a housing space, and the plurality of secondary batteries 5 are housed in the housing space.
  • the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.
  • FIG4 and FIG5 are schematic diagrams of a battery pack 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3, wherein the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4.
  • the plurality of battery modules 4 may be arranged in the battery box in any manner.
  • the present application provides an electrical device, which includes at least one of the secondary battery, battery module and battery pack of the present application.
  • the secondary battery, battery module and battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device.
  • the electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.
  • the electric device can select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • Fig. 6 is a schematic diagram of an electric device as an example.
  • the electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack 1 or a battery module can be used.
  • the electric device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • the electric device is usually required to be light and thin, and a secondary battery may be used as a power source.
  • lithium source e.g., lithium hydroxide
  • manganese source e.g., manganese carbonate
  • iron source e.g., ferrous carbonate
  • phosphorus source e.g., ammonium phosphate
  • sulfur source e.g., sulfur powder
  • 0.03 mol of sulfur source e.g., sulfur powder
  • 0.03 mol of sulfur source is slowly added to the mixed slurry, ball milled at 600 rpm for 6 hours, then vacuum dried at 80°C for 12 hours, calcined at 800°C in a nitrogen atmosphere for 12 hours, and the obtained solid product is ground and crushed to obtain sulfur-doped lithium manganese iron phosphate particles.
  • Lithium manganese iron phosphate particles are used as positive electrode active materials.
  • the positive electrode active materials and silver nitrate are mixed in a molar ratio of 1:0.027, and then treated at 600°C for 4 hours under a reducing atmosphere (Ar/H 2 ) to obtain a silver-coated lithium manganese iron phosphate material, namely a composite lithium manganese iron phosphate material.
  • the composite lithium manganese iron phosphate material, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in a proper amount of solvent NMP at a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil (thickness of 12 ⁇ m), and after drying and cold pressing, a positive electrode sheet is obtained.
  • a copper foil with a thickness of 8 ⁇ m was used as the negative electrode current collector.
  • the negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (Super P) are fully stirred and mixed in an appropriate amount of solvent deionized water at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode collector copper foil, and after drying and cold pressing, a negative electrode sheet is obtained.
  • SBR binder styrene-butadiene rubber
  • CMC-Na thickener sodium carboxymethyl cellulose
  • Super P conductive agent carbon black
  • a porous polyethylene (PE) membrane was used as the isolation membrane.
  • non-aqueous organic solvents ethylene carbonate EC and diethyl carbonate DMC are mixed in a volume ratio of 1:1 to obtain an electrolyte solvent, and then lithium salt and the mixed solvent are mixed to prepare an electrolyte with a lithium salt concentration of 1 mol/L.
  • the positive electrode sheet, separator and negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.
  • Examples 2-1 to 2-3 secondary batteries were prepared in a similar manner to that in Example 1. The difference from Example 1 was that the types of conductive precursors were adjusted in Examples 2-1 to 2-3.
  • Examples 3-1 to 3-8 prepared secondary batteries in a similar manner to Example 1. The difference from Example 1 was that the molar amount of the conductive precursor silver nitrate was adjusted in Examples 3-1 to 3-8.
  • Example 4-1 and Example 4-5 Secondary batteries were prepared in Example 4-1 and Example 4-5 according to a method similar to that in Example 1. The difference from Example 1 was that the heat treatment conditions were adjusted in Example 4-1 and Example 4-5.
  • Example 5 A secondary battery was prepared in a similar manner to Example 1. The difference from Example 1 was that the composite lithium manganese iron phosphate particles of Example 5 were not doped with sulfur. The preparation process was as follows:
  • lithium source e.g. lithium hydroxide
  • manganese source e.g. manganese carbonate
  • iron source e.g. ferrous carbonate
  • phosphorus source e.g. ammonium phosphate
  • the lithium manganese iron phosphate particles and silver nitrate were mixed in a molar ratio of 1:0.027, and then treated at 600°C for 4 hours under a reducing atmosphere (Ar/H 2 ) to obtain a silver-coated lithium manganese iron phosphate material, namely a composite lithium manganese iron phosphate material.
  • Comparative Example 1 A secondary battery was prepared in a similar manner to Example 1. The difference from Example 1 was that the composite lithium manganese iron phosphate particles of Comparative Example 1 were not provided with a coating layer.
  • Comparative Example 2 A secondary battery was prepared in a similar manner to that of Example 1. The difference from Example 1 was that the coating layer of the composite lithium manganese iron phosphate particles of Comparative Example 2 was a carbon coating layer.
  • the specific preparation process was as follows:
  • lithium source e.g. lithium hydroxide
  • manganese source e.g. manganese carbonate
  • iron source e.g. ferrous carbonate
  • phosphorus source e.g. ammonium phosphate
  • Comparative Example 1 As can be seen from Table 1, the lithium iron manganese phosphate particles of Comparative Example 1 are not provided with a coating layer, and their structure is unstable during long-term cycle charge and discharge. Compared with Comparative Example 1, Comparative Example 2 sets a carbon-containing coating layer on the surface of the lithium iron manganese phosphate particles, which has a good protective effect on the lithium iron manganese phosphate particles and can improve the cycle performance of the secondary battery; however, carbon may be oxidized under a high voltage system, resulting in a decrease in the cycle performance of the system.
  • Figure 7 shows the cycle curves of Comparative Example 1 and Example 1; since the embodiment of the present application is provided with a coating layer containing metal nanoparticles, its performance is relatively stable, which can significantly improve the cycle performance of the system; and it can ensure the full use of the lithium iron manganese phosphate capacity.
  • Examples 3-1 to 3-8 regulate the mass content of the coating layer, which can improve the cycle performance of the secondary battery; among them, although the mass content of the coating layer of Example 3-8 is lower and the coated silver content is less, it still shows the effect of improving the cycle performance relative to Comparative Example 1.
  • Example 1 sulfur is added to the lithium manganese iron phosphate particles, which can play an anchoring role on the metal nanoparticles, improve the coating uniformity of the metal nanoparticles, and improve the cycle performance of the system.
  • the positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) prepared above are mixed evenly in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 91.6:1.8:6.6 to prepare a slurry; the prepared slurry is coated on a copper foil, dried in an oven and set aside; then a metal lithium sheet is used as a counter electrode, a polyethylene (PE) film is used as an isolation membrane, a few drops of the same electrolyte as the above secondary battery are dripped, and a CR2430 button battery is assembled in an argon-protected glove box.
  • NMP solvent N-methylpyrrolidone
  • the button cell was left to stand for 12 hours, it was discharged at 0.05C constant current to 0.005V at 25°C, left to stand for 10 minutes, and then discharged at 50 ⁇ A constant current to 0.005V, left to stand for 10 minutes, and then discharged at 10 ⁇ A constant current to 0.005V; then it was charged at 0.1C constant current to 2V, and the charging capacity was recorded.
  • the ratio of the charging capacity to the mass of the negative electrode active material is the initial gram capacity of the negative electrode active material.
  • the secondary battery prepared above was charged at a constant current of 0.33C to a charge cut-off voltage of 4.4V, then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.8V, and its initial capacity was recorded as C0. Then, the battery was charged according to the strategy shown in Table 2, discharged at 0.33C, and the discharge capacity Cn of each cycle was recorded until the cycle capacity retention rate (i.e., Cn/C0 ⁇ 100%) was 80%, and the number of cycles was recorded. The more cycles, the better the cycle performance of the secondary battery.

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Abstract

本申请提供了一种复合磷酸锰铁锂材料、其制备方法、二次电池和用电装置。所述复合磷酸锰铁锂材料包括磷酸锰铁锂颗粒和包覆层；磷酸锰铁锂颗粒的使用上限电压记为V1，单位为V；包覆层包覆于磷酸锰铁锂颗粒的至少部分表面，包覆层包括金属纳米颗粒，金属纳米颗粒的氧化电压记为V2，单位为V，其中，复合磷酸锰铁锂材料满足：V1＜V2。本申请通过在磷酸锰铁锂颗粒的表面包覆有金属纳米颗粒，能够改善材料的循环稳定性，并保证容量的稳定发挥。

Description

复合磷酸锰铁锂材料、其制备方法、二次电池和用电装置 技术领域
本申请涉及电池领域，具体涉及一种复合磷酸锰铁锂材料、其制备方法、二次电池和用电装置。
背景技术
二次电池具有容量高、寿命长等特性，因此广泛应用于电子设备，例如手机、笔记本电脑、电瓶车、电动汽车、电动飞机、电动轮船、电动玩具汽车、电动玩具轮船、电动玩具飞机和电动工具等等。
随着电池应用范围越来越广泛，对二次电池性能的要求也逐渐严苛。为了提高二次电池的性能，通常对二次电池内的正极活性材料进行优化改善。然而，目前正极活性材料应用于二次电池时，其克容量发挥较差，且二次电池的循环性能较差。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种复合磷酸锰铁锂材料、其制备方法、二次电池和用电装置。
本申请的第一方面提供了一种复合磷酸锰铁锂材料，所述复合磷酸锰铁锂材料包括磷酸锰铁锂颗粒和包覆层；磷酸锰铁锂颗粒的使用上限电压记为V1，单位为V；包覆层包覆于磷酸锰铁锂颗粒的至少部分表面，包覆层包括金属纳米颗粒，金属纳米颗粒的氧化电压记为V2，单位为V，其中，复合磷酸锰铁锂材料满足：V1＜V2。
由此，本申请通过在磷酸锰铁锂颗粒的表面包覆有金属纳米颗粒，可以改善包覆后材料的导电性，减小其导电阻力；且金属纳米颗粒的性能稳定，不容易在高压下发生氧化，从而能够保证包覆后材料在使用周期内导电的稳定性，降低材料在循环后期极化迅速增大和容量快速衰减的风险，保证材料的循环稳定性和容量的稳定发挥。在一些实施方式中，磷酸锰铁锂颗粒的结构式为LiMn 1-xFe xM yPO 4，式中，0.05≤x≤0.95；0≤y≤1；可选地，0≤y≤0.2；M表示掺杂元素，磷酸锰铁锂颗粒包括掺杂元素M，掺杂元素M包括硫、氮、硼、氟、氯、溴和碘中的一种元素或多种元素；可选地，掺杂元素M包括硫元素。
由此，本申请的掺杂元素M在金属纳米颗粒的形成过程中，掺杂元素M能够和金属纳米颗粒之间形成键合作用，起到对金属纳米颗粒的锚定作用，实现金属纳米颗粒的定位生长和小尺寸生长。因此，掺杂元素M的均匀掺杂，有利于金属纳米颗粒 的均匀分布，改善对磷酸锰铁锂颗粒的包覆性能。
在一些实施方式中，金属纳米颗粒包括银、金、铂、钯、铑、铱、锇和钌中的一种或多种纳米颗粒。
金属纳米颗粒在磷酸锰铁锂的工作电压下能够稳定存在，起到改善磷酸锰铁锂的导电性能的作用。
在一些实施方式中，基于复合磷酸锰铁锂材料的总质量计，包覆层的质量含量记为A％，0.3≤A≤10；可选地，0.3≤A≤3。
由此，本申请的包覆层的质量含量在上述范围时，包覆层的厚度不会过厚，从而有利于锂离子的顺利迁移，保证循环过程的正常进行，且包覆层不会过度侵占磷酸锰铁锂的空间，保证复合磷酸锰铁锂的克容量；包覆层的厚度不会过薄，从而能够对磷酸锰铁锂颗粒的表面起到良好的包覆作用，改善包覆后的磷酸锰铁锂颗粒整体的导电性能。
在一些实施方式中，包覆层的厚度记为H，单位为nm，2≤H≤100；可选地，5≤H≤20。
由此，本申请的包覆层的厚度在上述范围时，包覆层的厚度不会过厚，从而有利于锂离子的顺利迁移，保证循环过程的正常进行；包覆层的厚度不会过薄，从而能够对磷酸锰铁锂颗粒的表面起到良好的包覆作用，改善包覆后的磷酸锰铁锂颗粒整体的导电性能。
在一些实施方式中，复合磷酸锰铁锂材料满足：金属纳米颗粒的平均粒径记D为D1，单位为nm，D1≤20；可选地，D1≤10。
由此，本申请的金属纳米颗粒的平均粒径D在上述范围时，其平均粒径不会过大，其对磷酸锰铁锂颗粒可以起到紧密的包覆，从而能够均匀改善磷酸锰铁锂颗粒整体的导电性，且能够降低包覆量；金属纳米颗粒的平均粒径D不会过小，其具有一定的空隙有利于锂离子的迁移，保证循环过程的顺利进行。
在一些实施方式中，复合磷酸锰铁锂材料满足：磷酸锰铁锂颗粒的体积平均粒径Dv50记为D2，单位为μm，0.1≤D2≤10；可选地，0.2≤D2≤5。
由此，本申请的磷酸锰铁锂颗粒的结构相对稳定，动力学性能相对较好，有利于提高复合磷酸锰铁锂颗粒的首次库伦效率；并且有利于金属纳米颗粒在磷酸锰铁锂颗粒的表面形成均匀包覆。
在一些实施方式中，复合磷酸锰铁锂材料满足：复合磷酸锰铁锂材料的体积平均粒径Dv50记为D，单位为μm，0.1≤D≤10；可选地，0.2≤D≤5。
由此，本申请的复合磷酸锰铁锂材料满足上述范围时，其结构相对稳定，动力学性能相对较好，有利于提高复合磷酸锰铁锂材料的首次库伦效率。
本申请的第二方面提供了一种复合磷酸锰铁锂材料的制备方法，所述方法包括：提供磷酸锰铁锂颗粒；将导电前驱体提供至磷酸锰铁锂颗粒，热处理导电前驱体以使导电前驱体还原形成包覆磷酸锰铁锂颗粒的包覆层，包覆层包括金属纳米颗粒，其中， 磷酸锰铁锂颗粒的使用上限电压记为V1，单位为V；包覆层包覆于磷酸锰铁锂颗粒的至少部分表面，包覆层包括金属纳米颗粒，金属纳米颗粒的氧化电压记为V2，单位为V，复合磷酸锰铁锂材料满足：V1＜V2。
在一些实施方式中，提供磷酸锰铁锂颗粒的步骤，包括：将掺杂元素M掺杂至磷酸锰铁锂颗粒内，掺杂元素M包括硫、氮、硼、氟、氯、溴和碘中的一种元素或多种元素；可选地，掺杂元素M包括硫元素。
在一些实施方式中，热处理的温度为400℃至1000℃；和/或热处理的时间为2h至6h。
由此，本申请通过调控热处理的条件，能够控制金属纳米颗粒形成的尺寸大小；热处理的温度不会过高，有利于金属纳米颗粒的适度生长，其颗粒不会过大，且掺杂元素容易发挥锚定效果，从而使得金属纳米颗粒在磷酸锰铁锂颗粒的表面均匀分布，且所形成的颗粒的粒径大小相对适中，有利于对磷酸锰铁锂颗粒形成良好的包覆作用。
在一些实施方式中，导电前驱体包括硝酸根、氯离子、溴离子、碘离子、硫酸根、磷酸根、醋酸根、乙酰丙酮根中的一种或多种；和/或导电前驱体包括银离子、金离子、铂离子、钯离子、铑离子、铱离子、锇离子和钌离子中的一种或多种。
在一些实施方式中，基于导电前驱体和磷酸锰铁锂颗粒的总摩尔比计，导电前驱体的摩尔含量为b％，0.25≤b≤14.5；可选地，0.40≤b≤4.60。
由此，本申请通过调控导电前驱体的摩尔含量，使得导电前驱体在磷酸锰铁锂颗粒表面所形成的包覆层的质量得到调控，复合磷酸锰铁锂中的磷酸锰铁锂为主体材料，包覆层对材料整体的克容量影响较小，能够保证材料整体的克容量；且包覆层能够对磷酸锰铁锂形成均匀包覆，改善复合磷酸锰铁锂整体的导电性，有利于磷酸锰铁锂的容量发挥。
本申请的第三方面提供了一种二次电池，包括正极极片，所述正极极片包括如本申请第一方面任一实施例方式所述的复合磷酸锰铁锂材料或如本申请第二方面任一实施方式所述的方法得到的复合磷酸锰铁锂材料。
本申请第四方面还提供了一种用电装置，包括如本申请第三方面所述的二次电池。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍，显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的二次电池的一实施方式的示意图。
图2是图1的二次电池的实施方式的分解示意图。
图3是本申请的电池模块的一实施方式的示意图。
图4是本申请的电池包的一实施方式的示意图。
图5是图4所示的电池包的实施方式的分解示意图。
图6是包含本申请的二次电池作为电源的用电装置的一实施方式的示意图。
图7是实施例1和对比例1的循环曲线图。
附图未必按照实际的比例绘制。
附图标记说明如下：
1、电池包；2、上箱体；3、下箱体；4、电池模块；
5、二次电池；51、壳体；52、电极组件；
53、盖板；
6、用电装置。
具体实施方式
以下，详细说明具体公开了本申请的复合磷酸锰铁锂材料、其制备方法、二次电池和用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，方法包括步骤(a)和(b)，表示方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，提到方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到方法，例如，方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是 封闭式。例如，“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
在本申请中，术语“多个”、“多种”是指两个或两种以上。
磷酸锰铁锂具有橄榄石结构，理论容量与磷酸铁锂材料相当，由于Mn元素的存在，其电极电势相对较高，高电势使得该类材料具有潜在的高能量密度优点；但同时磷酸锰铁锂晶体具有六方密堆结构，锂、铁原子分别占据八面体4a和4c位点，磷原子占据四面体4c位点，其中，FeO 6(MnO 6)八面体和PO 4四面体交叉连接，这种结构的稳定性较好，即使在充电的过程中锂离子全部脱出，也不容易存在结构崩塌的问题。同时材料中的P原子通过P-O强共价键形成PO 4四面体，O原子很难从结构中脱出，因此材料具有较高的稳定性；但是由于材料通过PO 4四面体连接，其没有连续的FeO 6(MnO 6)共棱八面体网络，导致材料的导电性较差，电子电导率较低，锂离子的扩散系数较低，合成能够可逆充放电的磷酸锰铁锂较为困难，其导电性限制了其发展。
发明人研究发现，目前为了改善磷酸锰铁锂的导电性，通常在磷酸锰铁锂的颗粒表面包覆有导电碳层，但是经发明人深入研究发现，由于磷酸锰铁锂适用的电压体系为高电压例如＞4V，高电压体系下对碳层的氧化增强，可能会导致使用碳层氧化产气，长时间使用后材料导电性降低，阻抗增加，循环性能衰减。
鉴于此，发明人对磷酸锰铁锂的包覆结构进行了改进，在磷酸锰铁锂的颗粒表面包覆有含有金属纳米颗粒的包覆层，包覆层能够改善磷酸锰铁锂的导电性能，有利于磷酸锰铁锂的容量发挥，并且包覆层的性能稳定，能够改善磷酸锰铁锂整体的结构稳定性，有利于改善其所应用的二次电池的循环性能。接下来对本申请进行详细说明。
复合磷酸锰铁锂材料
第一方面，本申请提出了一种复合磷酸锰铁锂材料。
所述的复合磷酸锰铁锂材料包括磷酸锰铁锂颗粒和包覆层；所述磷酸锰铁锂颗粒的使用上限电压记为V1，单位为V；包覆层包覆于所述磷酸锰铁锂颗粒的至少部分表面，所述包覆层包括金属纳米颗粒，所述金属纳米颗粒的氧化电压记为V2，单位为V，其中，所述复合磷酸锰铁锂材料满足：V1＜V2。
磷酸锰铁锂的使用上限电压V1是指磷酸锰铁锂作为正极活性材料应用到二次电池时的充电上限电压，在此电压下磷酸锰铁锂基本可以保证材料的稳定性。例如，磷酸锰铁锂的使用上限电压V1可以设定为3.7V至4.5V。V1可以由生产方进行设置。
金属纳米颗粒的氧化电压V2是指金属纳米颗粒失去电子变成金属离子的电压，V2可以通过线性扫描伏安法LSV进行测试，使用所需要测定的金属为工作电极，锂片为参比电极，以0.15mV/s至50mV/s扫描速度从0V扫至5V或更高电压，氧化电流明显增大时的电压即为V2。扫描速度可选为1mV/s至5mV/s。
本申请设置V1＜V2，可以使得在二次电池长期循环充放电过程中，金属纳米颗粒基本不会被氧化，保证复合磷酸锰铁锂材料的结构稳定性。
磷酸锰铁锂颗粒具有结构式LiMn 1-xFe xM yPO 4，式中，0.05≤x≤0.95；0≤y≤1；可选地，0≤y≤0.2。
M表示掺杂元素，即磷酸锰铁锂可以为掺杂元素改性的材料，也可以为不具有掺杂元素的材料。掺杂元素可以为阳离子掺杂元素，也可以为阴离子掺杂元素。磷酸锰铁锂可以在4.45V左右的高压下进行充放电，由于复合磷酸锰铁锂满足上述电位关系，使得金属纳米颗粒在磷酸锰铁锂的工作电压下可以稳定存在，不容易被氧化，从而能够对磷酸锰铁锂颗粒起到长期稳定的包覆作用，提高包覆后的磷酸锰铁锂的结构稳定性，改善复合磷酸锰铁锂材料的循环性能。
磷酸锰铁锂颗粒自身的粒径通常较小，而相关技术中的包覆层中的颗粒由于粒径相对较大，包覆层不易在磷酸锰铁锂颗粒表面形成包覆，导致无法对磷酸锰铁锂起到良好的包覆作用。而本申请的包覆层包括金属纳米颗粒，包覆层中的金属的粒径较小为纳米级，可以分散于磷酸锰铁锂颗粒的表面形成均匀包覆，从而对磷酸锰铁锂颗粒的整体包覆性能较好；并且由于金属纳米颗粒的粒径较小，相邻金属纳米颗粒之间的接触更为紧密，金属纳米颗粒能够填充包覆层内部相邻层中的空隙，从而使得金属纳米颗粒所构成的包覆层的导电性能较好，能够在一定程度上减小导电阻力，有利于改善包覆后的磷酸锰铁锂颗粒导电性，导电性能的提高有利于磷酸锰铁锂颗粒的容量发挥。
本申请通过在磷酸锰铁锂颗粒的表面包覆有金属纳米颗粒，可以改善包覆后材料的导电性，减小其导电阻力；且金属纳米颗粒的性能稳定，不容易在高压下发生氧化，从而能够保证包覆后材料在使用周期内导电的稳定性，降低材料在循环后期极化迅速增大和容量快速衰减的风险，保证材料的循环稳定性和容量的稳定发挥。
为了进一步提高包覆层的包覆效果，改善复合磷酸锰铁锂材料的导电性，在一些实施方式中，磷酸锰铁锂颗粒包括掺杂元素M，所述掺杂元素M包括硫、氮、硼、氟、氯、溴、碘等中的一种元素或多种元素；可选地，所述掺杂元素M包括硫元素。
所述掺杂元素M以阴离子的形式掺入，能够占据磷酸锰铁锂颗粒在充放电过程中氧空位，起到稳定磷酸锰铁锂结构的作用；并且所述掺杂元素M能够提高磷酸锰铁锂颗粒的电子密度，提高磷酸锰铁锂的导电性能和容锂性能，能够改善复合磷酸锰铁锂材料整体的导电性，并有利于容量发挥和改善循环性能。
所述掺杂元素M在金属纳米颗粒的形成过程中，掺杂元素M能够和金属纳米颗粒之间形成键合作用，起到对金属纳米颗粒的锚定作用，实现金属纳米颗粒的定位生长和小尺寸生长。因此，掺杂元素M的均匀掺杂，有利于金属纳米颗粒的均匀分布，改善对磷酸锰铁锂颗粒的包覆性能。
在一些实施方式中，金属纳米颗粒包括银、金、铂、钯、铑、铱、锇、钌、汞、铊等中的一种或多种纳米颗粒。所述金属纳米颗粒在磷酸锰铁锂的工作电压下能够稳定存在，起到改善磷酸锰铁锂的导电性能的作用。可选地，金属纳米颗粒包括银、金、 铂、钯、铑、铱、锇、钌、中的一种或多种纳米颗粒。该类金属毒性较小，更适用于电池体系。
在一些实施方式中，基于所述复合磷酸锰铁锂材料的总质量计，所述包覆层的质量含量记为A％，0.3≤A≤10；可选地，0.3≤A≤3。
在本申请中，包覆层的质量含量是本领域公知的含义，其可以采用本领域公知的方法或设备测定；具体地，称取一定重量的复合磷酸锰铁锂材料，用王水消解，随后将溶液稀释后，通过ICP测试稀释后溶液中的包覆金属重量，根据测试的金属重量并根据取用的复合磷酸锰铁锂材料的重量计算包覆层的质量占比。
包覆层的质量含量在上述范围时，包覆层的厚度不会过厚，从而有利于锂离子的顺利迁移，保证循环过程的正常进行，且包覆层不会过度侵占磷酸锰铁锂的空间，保证复合磷酸锰铁锂的克容量；包覆层的厚度不会过薄，从而能够对磷酸锰铁锂颗粒的表面起到良好的包覆作用，改善包覆后的磷酸锰铁锂颗粒整体的导电性能。示例性地，所述包覆层的质量含量A％可以为0.3％、0.5％、0.8％、1.0％、1.5％、2.0％、2.5％、3.0％、3.5％、4.0％、5.0％、6.0％、7.0％、8.0％、9.0％或10％；或者是上述任意两个数值组成的范围。
在一些实施方式中，所述包覆层的厚度记为H，单位为nm，2≤H≤100；可选地，5≤H≤20。
在本申请中，包覆层的厚度是本领域公知的含义，其可以采用本领域公知的方法或设备测定；具体地，可以取一定量的复合磷酸锰铁锂材料作为样品，进行高分辨透射电子显微镜分析测试，得到HRTEM图片，然后在HRTEM图片上量取多个(例如30个以上)不同位置的厚度，并取其平均值作为包覆层的平均厚度。从HRTEM图片上，可以看出包覆层和磷酸锰铁锂颗粒之间存在明显的晶界。
包覆层的厚度在上述范围时，包覆层的厚度不会过厚，从而有利于锂离子的顺利迁移，保证循环过程的正常进行；包覆层的厚度不会过薄，从而能够对磷酸锰铁锂颗粒的表面起到良好的包覆作用，改善包覆后的磷酸锰铁锂颗粒整体的导电性能。
示例性地，所述包覆层的厚度H nm可以为2nm、3nm、5nm、10nm、20nm、30nm、50nm、60nm、80nm或100nm；或者是上述任意两个数值组成的范围。
在一些实施方式中，金属纳米颗粒的平均粒径D记为D1，单位为nm，D1≤20；可选地，D1≤10。
在本申请中，金属纳米颗粒的平均粒径D为本领域公知的含义，其可以采用本领域公知的方法或设备测定；包覆层的金属为颗粒状，可以通过取一定量的复合磷酸锰铁锂材料作为样品，进行高分辨透射电子显微镜分析测试，得到HRTEM图片，然后在HRTEM图片上量取多个(例如30个以上)不同位置的金属纳米颗粒的粒径，并取其平均值作为金属纳米颗粒的平均粒径D。
金属纳米颗粒的平均粒径D在上述范围时，其平均粒径不会过大，其对磷酸锰铁锂颗粒可以起到紧密的包覆，从而能够均匀改善磷酸锰铁锂颗粒整体的导电性，且能够降低包覆量；金属纳米颗粒的平均粒径D不会过小，其具有一定的空隙有利于锂 离子的迁移，保证循环过程的顺利进行。示例性地，金属纳米颗粒的平均粒径可以为2nm、3nm、5nm、6nm、8nm、10nm、12nm、15nm、18nm或20nm；或者是上述任意两个数值组成的范围。
在一些实施方式中，所述磷酸锰铁锂颗粒的体积平均粒径Dv50记为D2，单位为μm，0.1≤D2≤10；可选地，0.2≤D2≤5。
在本申请中，材料的体积平均粒径Dv50为本领域公知的含义，其表示材料累计体积分布百分数达到50％时所对应的粒径，可以用本领域公知的仪器及方法进行测试。例如可以参照GB/T19077-2016粒度分布激光衍射法，采用激光粒度分析仪方便地测试，如英国马尔文仪器有限公司的Mastersizer 2000E型激光粒度分析仪。
磷酸锰铁锂颗粒满足上述范围时，磷酸锰铁锂颗粒中第一颗粒和第二颗粒可能同时存在，当然也可以仅存在其中一种，磷酸锰铁锂颗粒的结构相对稳定，动力学性能相对较好，有利于提高复合磷酸锰铁锂颗粒的首次库伦效率；并且有利于金属纳米颗粒在磷酸锰铁锂颗粒的表面形成均匀包覆。
在一些实施方式中，所述复合磷酸锰铁锂材料的体积平均粒径Dv50记为D，单位为μm，0.1≤D≤10；可选地，0.2≤D≤5。
包覆层的厚度与磷酸锰铁锂的粒径为数量级的差异，包覆层的厚度对复合磷酸锰铁锂的粒径贡献甚微，故磷酸锰铁锂颗粒和复合磷酸锰铁锂颗粒的粒径在微米级别区别并不明显。复合磷酸锰铁锂材料满足上述范围时，其结构相对稳定，动力学性能相对较好，有利于提高复合磷酸锰铁锂材料的首次库伦效率。
复合磷酸铁锂材料的制备方法
第二方面，本申请提出了一种复合磷酸锰铁锂材料的制备方法，所述方法能够制备得到本申请第一方面任一实施方式的复合磷酸锰铁锂材料。
所述方法包括：
步骤S100，提供磷酸锰铁锂颗粒；
步骤S200，将导电前驱体提供至所述磷酸锰铁锂颗粒，热处理所述导电前驱体以使所述导电前驱体还原形成包覆磷酸锰铁锂颗粒的包覆层，所述包覆层包括金属纳米颗粒。
磷酸锰铁锂颗粒的表面包覆有金属纳米颗粒，可以改善包覆后材料的导电性，减小其导电阻力；且金属纳米颗粒的性能稳定，不容易在高压下发生氧化，从而能够保证包覆后材料在使用周期内的导电性，降低材料在循环后期极化迅速增大，容量快速衰减的风险，保证材料的循环稳定性和容量的稳定发挥。
尤其是复合磷酸铁锂材料满足以下要求时：所述磷酸锰铁锂颗粒的使用上限电压记为V1，单位为V；包覆层包覆于所述磷酸锰铁锂颗粒的至少部分表面，所述包覆层包括金属纳米颗粒，所述金属纳米颗粒的氧化电压记为V2，单位为V，所述复合磷酸锰铁锂材料满足：V1＜V2，能够改善复合磷酸铁锂材料的导电性和循环性能。
在一些实施方式中，步骤S100中，磷酸锰铁锂颗粒可以采用多种方法制备，例如，固相法、共沉淀法、溶胶-凝胶法、水热/溶剂热法等，接下来以固相法为例进行 说明。将锂源、锰源、铁源、磷源等按照设定的摩尔比例如1：(1-m)：m：1加入溶剂中混合成浆料，将该浆料球磨后干燥；然后在保护气体下高温烧结为磷酸铁锂材料。其中，0.05≤m≤0.95，优选为0.2≤m≤0.5。
锂源可以包括氢氧化锂、碳酸锂、硝酸锂、磷酸二氢锂、磷酸氢二锂、草酸锂中的一种或多种。
锰源可以包括碳酸锰和/或草酸锰。
铁源可以包括碳酸亚铁、醋酸亚铁、硫酸亚铁、硝酸铁、磷酸铁、丙烯酸铁和草酸亚铁中的一种或多种。
磷源可以包括磷酸铵、磷酸二氢铵、磷酸氢二铵、磷酸铁中的一种或多种。
溶剂可以为去离子水和/或乙醇。
保护气体可以包括氮气、氩气和氦气中的一种或多种。
进一步地，将掺杂元素M掺杂至磷酸锰铁锂颗粒内，所述掺杂元素M包括硫、氮、硼、氟、氯、溴、碘等中的一种元素或多种元素；可选地，所述掺杂元素M包括硫元素。具体地，可以在浆料中继续加入包含掺杂元素M的原料后球磨，球磨后干燥，然后在保护气体下高温烧结为掺杂有掺杂元素的磷酸锰铁锂材料。
硫源可以包括硫脲、二硫化碳、硫化氢、硫粉和十二烷基苯磺酸钠中的一种或几种。氮源可以包括氯化铵、碘化铵、甲酸铵、乙酸铵、六次甲基四胺、氨基葡萄糖中的一种或多种。
硼源可以包括二氧化硼、三氧化二硼、硼酸、四苯硼酸、碳化硼、硼酸三丁酯中的一种或多种。
硫元素与锂元素的摩尔比为(0.01-0.05):1。
磷酸锰铁锂颗粒还可以采用干混法制备，具体制备工艺可采用本领域现有工艺。
在一些实施方式中，步骤S200中，导电前驱体可以包括硝酸盐、氯盐、溴盐、碘盐、硫酸盐、磷酸盐、乙酸盐、乙酰丙酮盐中的一种或多种。即，导电前驱体的阴离子为硝酸根、氯离子、溴离子、碘离子、硫酸根、磷酸根、醋酸根、乙酰丙酮根中的一种或多种。
导电前驱体的阳离子可以包括银离子、金离子、铂离子、钯离子、铑离子、铱离子、锇离子和钌离子中的一种或多种离子。
示例性地，导电前驱体为上述任一阴离子和任一阳离子的合理搭配，例如，导电前驱体可以为无机前驱体或有机前驱体，例如可以为硝酸银、氯化银、硝酸金、乙酰丙酮银等等。
所述导电前驱体有利于在还原性气氛下的还原，同时硝酸根能够分解不容易残留在复合磷酸锰铁锂材料中；氯离子、溴离子等能够与氢离子形成氯化氢或溴化氢气体从而挥发出体系外，不易残留在复合磷酸锰铁锂材料中，对复合磷酸锰铁锂材料的影响较小。
在一些实施方式中，步骤S200中，基于导电前驱体和磷酸锰铁锂颗粒的总摩尔比计，导电前驱体的摩尔含量为b％，0.25≤b≤14.5；可选地，0.40≤b≤4.60。以导电前 驱体的阳离子为银离子示例，0.45≤b≤13.7；可选地，0.70≤b≤4.20。
通过调控导电前驱体的摩尔含量，使得导电前驱体在磷酸锰铁锂颗粒表面所形成的包覆层的质量得到调控，复合磷酸锰铁锂中的磷酸锰铁锂为主体材料，包覆层对材料整体的克容量影响较小，能够保证材料整体的克容量；且包覆层能够对磷酸锰铁锂形成均匀包覆，改善复合磷酸锰铁锂整体的导电性，有利于磷酸锰铁锂的容量发挥。
在一些实施方式中，步骤S200中，热处理的温度可以为400℃至1000℃；和/或热处理的时间可以为2h至6h。
通过调控热处理的条件，能够控制金属纳米颗粒形成的尺寸大小；热处理的温度不会过高，有利于金属纳米颗粒的适度生长，其颗粒不会过大，且掺杂元素容易发挥锚定效果，从而使得金属纳米颗粒在磷酸锰铁锂颗粒的表面均匀分布，且所形成的颗粒的粒径大小相对适中，有利于对磷酸锰铁锂颗粒形成良好的包覆作用。热处理的温度不会过低，能够使得导电前驱体中的金属离子能够充分还原为金属单质。
相应地，调控热处理的时间也能够得到相似的效果，具体地，热处理时间充足能够使得导电前驱体中的金属离子充分还原为金属单质，且能够保证金属单质不会过度生长，其纳米颗粒的粒径相对较小，能够对磷酸锰铁锂颗粒的表面进行均匀包覆。
在一些实施方式中，步骤S200中，可以在还原性气氛保护下进行热处理，导电前驱体能够充分进行还原生成金属纳米颗粒。示例性地，还原性气氛可以为氩气和氢气的混合气体，氢气占比可以相对较少，例如其占比为5％。
二次电池
第三方面，本申请提出了一种二次电池。
二次电池包括正极极片、负极极片、电解质和隔离膜。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。
[正极极片]
在一些实施方式中，正极极片包括正极集流体以及设置在正极集流体至少一个表面上的正极膜层。例如，正极集流体具有在自身厚度方向相对的两个表面，正极膜层设置于正极集流体的两个相对表面中的任意一者或两者上。
在一些实施方式中，所述正极膜层包括正极活性材料，所述正极活性材料可以包括本申请第一方面任一实施方式的复合锰酸铁锂材料或本申请第二方面任一实施方式所述的方法制备的饿到的复合锰酸铁锂材料。
在一些实施方式中，正极膜层还可选地包括正极导电剂。本申请对正极导电剂的种类没有特别的限制，作为示例，正极导电剂包括选自超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的一种或多种的组合。在一些实施方式中，基于正极膜层的总质量，正极导电剂的质量百分含量在5％以下。
在一些实施方式中，正极膜层还可选地包括正极粘结剂。本申请对正极粘结剂的种类没有特别的限制，作为示例，正极粘结剂可包括选自聚偏氟乙烯(PVDF)、聚 四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物和含氟丙烯酸酯类树脂中的一种或多种的组合。在一些实施方式中，基于正极膜层的总质量，正极粘结剂的质量百分含量在5％以下。
在一些实施方式中，正极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铝箔或铝合金箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层，作为示例，金属材料可包括选自铝、铝合金、镍、镍合金、钛、钛合金、银和银合金中的一种或多种的组合，高分子材料基层可包括选自聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)和聚乙烯(PE)中的一种或多种的组合。
正极膜层通常是将正极浆料涂布在正极集流体上，经干燥、冷压而成的。正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层，所述负极膜层包括负极活性材料。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，负极膜层还可选地包括粘结剂。所述粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
作为示例，锂盐可包括选自六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)和四氟草酸磷酸锂(LiTFOP)中的一种或多种的组合。
作为示例，有机溶剂可包括选自碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)和二乙砜(ESE)中的一种或多种的组合。
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
[隔离膜]
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图1是作为一个示例的方形结构的二次电池5。
在一些实施例中，如图1和图2所示，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53用于盖设开口，以封闭容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于容纳腔。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，可根据需求来调节。
本申请的二次电池的制备方法是公知的。在一些实施例中，可将正极极片、隔离膜、负极极片和电解液组装形成二次电池。作为示例，可将正极极片、隔离膜、负极极片经卷绕工艺或叠片工艺形成电极组件，将电极组件置于外包装中，烘干后注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
在本申请的一些实施例中，根据本申请的二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图3是作为一个示例的电池模块4的示意图。如图3所示，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图4和图5是作为一个示例的电池包1的示意图。如图4和图5所示，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2用于盖设下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
用电装置
第四方面，本申请提供一种用电装置，用电装置包括本申请的二次电池、电池模块和电池包中的至少一种。二次电池、电池模块和电池包可以用作用电装置的电源，也可以用作用电装置的能量存储单元。用电装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
用电装置可以根据其使用需求来选择二次电池、电池模块或电池包。
图6是作为一个示例的用电装置的示意图。该用电装置6为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对高功率和高能量密度的需求，可以采用电池包1或电池模块。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
以下，说明本申请的实施方式。下面描述的实施方式是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施方式中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
实施例1
1、正极极片的制备
将1mol锂源(例如氢氧化锂)、0.6mol锰源(例如碳酸锰)、0.4mol铁源(例如碳酸亚铁)、1mol磷源(例如磷酸铵)逐次加入到35mol去离子水中，搅拌均匀，得到混合浆料。将0.03mol硫源(例如硫粉)缓慢加入混合浆料中，在每分钟转速600下球磨6小时后，然后80℃下真空干燥12小时，在氮气气氛下800℃的温度下煅烧12小时，将得到的固体产物进行研磨粉碎得到硫掺杂的磷酸锰铁锂颗粒。
将磷酸锰铁锂颗粒作为正极活性材料，正极活性材料和硝酸银按照摩尔比1：0.027混合后，在还原性气氛保护下(Ar/H 2)600℃处理4h，得到银包覆的磷酸锰铁锂材料，即复合磷酸锰铁锂材料。
将复合磷酸锰铁锂材料、导电剂炭黑、粘结剂聚偏氟乙烯(PVDF)按重量比97.5:1.4:1.1在适量的溶剂NMP中充分搅拌混合，形成均匀的正极浆料；将正极浆料均匀涂覆于正极集流体铝箔(厚度为12μm)的表面上，经干燥、冷压后，得到正极极片。
2、负极极片的制备
采用厚度为8μm的铜箔作为负极集流体。
将负极活性材料石墨、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)、导电剂炭黑(Super P)按重量比96.2:1.8:1.2:0.8在适量的溶剂去离子水中充分搅拌混合，形成均匀的负极浆料；将负极浆料均匀涂覆于负极集流体铜箔的表面上，经干燥、冷压后，得到负极极片。
3、隔离膜
采用多孔聚乙烯(PE)膜作为隔离膜。
4、电解液的制备
在含水量小于10ppm的环境下，将非水有机溶剂碳酸乙烯酯EC、碳酸二乙酯DMC按照体积比1:1进行混合得到电解液溶剂，随后将锂盐和混合后的溶剂混合，配置成锂盐浓度为1mol/L的电解液。
5、二次电池的制备
将上述正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正极极片和负极极片之间起到隔离作用，然后卷绕得到电极组件；将电极组件置于外包装壳中，干燥后注入电解液，经过真空封装、静置、化成、整形等工序，得到锂离子电池。
实施例2
实施例2-1至2-3按照实施例1类似的方法制备二次电池，与实施例1不同的是，实施例2-1至2-3调整了导电前驱体的种类。
实施例3
实施例3-1至3-8按照实施例1类似的方法制备二次电池，与实施例1不同的是，实施例3-1至3-8调整了导电前驱体硝酸银的摩尔量。
实施例4
实施例4-1至实施例4-5按照实施例1类似的方法制备二次电池，与实施例1不同的是，实施例4-1至实施例4-5调整了热处理的条件。
实施例5
实施例5按照实施例1类似的方法制备二次电池，与实施例1不同的是，实施例5的复合磷酸锰铁锂颗粒中未掺杂硫元素，其制备过程如下：
将1mol锂源(例如氢氧化锂)、0.6mol锰源(例如碳酸锰)、0.4mol铁源(例如碳酸亚铁)、1mol磷源(例如磷酸铵)逐次加入到35mol去离子中，搅拌均匀，得到混合浆料。在每分钟转速600下球磨6小时后，然后80℃下真空干燥12小时，在氮气气氛下800℃的温度下煅烧12小时，将得到的固体产物进行研磨粉碎得到磷酸锰铁锂颗粒。
将磷酸锰铁锂颗粒和硝酸银按照摩尔比1：0.027混合后，在还原性气氛保护下(Ar/H 2)600℃处理4h，得到银包覆的磷酸锰铁锂材料，即复合磷酸锰铁锂材料。
对比例1
对比例1按照实施例1类似的方法制备二次电池，与实施例1不同的是，对比例1的复合磷酸锰铁锂颗粒未设置包覆层。
对比例2
对比例2按照实施例1类似的方法制备二次电池，与实施例1不同的是，对比例2的复合磷酸锰铁锂颗粒的包覆层为碳包覆层，其具体制备过程如下：
将1mol锂源(例如氢氧化锂)、0.6mol锰源(例如碳酸锰)、0.4mol铁源(例如碳酸亚铁)、1mol磷源(例如磷酸铵)逐次加入到35mol去离子中，搅拌均匀，得到混合浆料。在每分钟转速600下球磨6小时后，然后80℃下真空干燥12小时，在氮气气氛下800℃的温度下煅烧12小时，将得到的固体产物进行研磨粉碎得到磷酸锰铁锂颗粒。
将磷酸锰铁锂颗粒和葡萄糖按照摩尔比1：0.1混合后，在还原性气氛保护下(Ar/H 2)600℃处理4h，得到碳包覆的磷酸锰铁锂材料，即复合磷酸锰铁锂材料。
实施例以及对比例的相关参数如表1所示。
表1
Figure PCTCN2022125524-appb-000001
由表1可知，对比例1的磷酸锰铁锂颗粒未设置有包覆层，在长期循环充放电过程中，其结构不稳定。相较于对比例1，对比例2在磷酸锰铁锂颗粒表面设置含碳包覆层，对磷酸锰铁锂颗粒具有良好的防护作用，可以改善二次电池的循环性能；但是碳在高电压体系下可能会被氧化，导致其体系循环性能衰减。图7中示出了对比例1和实施例1的循环曲线图；本申请实施例由于设置了包含金属纳米颗粒的包覆层，其性能较为稳定，可以显著改善体系的循环性能；并且能够保证磷酸锰铁锂克容量的发挥。
相较于对比例1，实施例3-1至实施例3-8对包覆层的质量含量进行了调控，可以改善二次电池的循环性能；其中，虽然实施例3-8包覆层的质量含量较低，包覆的银含量较少，但是仍然相对于对比例1显示出改善循环性能的效果。
对比例2在充足碳包覆的情况下，其具有改善循环性能的作用；由于碳的氧化作用会弱化其对磷酸锰铁锂颗粒防护能力，一定程度上恶化循环性能；相较于对比例2，实施例3-1至实施例3-8中的一些实施例，在其包覆层质量含量与对比例2中碳包覆量相近时，实施例3-1至实施例3-8明显能够显著改善包覆效果，提高循环性能。
相较于实施例5，实施例1在磷酸锰铁锂颗粒中掺入了硫元素，能够起到对金属纳米颗粒的锚定作用，改善金属纳米颗粒的包覆均匀性，体系的循环性能更好。
测试部分：
1、正极活性材料的克容量
将上述制备的正极活性材料、导电剂炭黑、粘结剂聚偏氟乙烯(PVDF)按质量比91.6:1.8:6.6与溶剂N-甲基吡咯烷酮(NMP)中混合均匀，制成浆料；将制备好的浆料涂覆于铜箔上，于烘箱中干燥后备用；之后以金属锂片为对电极，以聚乙烯(PE)薄膜作为隔离膜，滴入几滴与上述二次电池相同的电解液，并在氩气保护的手套箱中组装成CR2430型扣式电池。
将所得扣式电池静置12h后，在25℃下，以0.05C恒流放电至0.005V，静置10min，以50μA的电流再恒流放电至0.005V，静置10min，以10μA再恒流放电至0.005V；然后以0.1C恒流充电至2V，记录充电容量。充电容量与负极活性材料质量的比值即为负极活性材料的初始克容量。
2、二次电池的循环性能
在25℃下，将上述制备的二次电池以0.33C恒流充电至充电截止电压4.4V，之后恒压充电至电流为0.05C，静置5min，再以0.33C恒流放电至放电截止电压2.8V，记录其初始容量为C0。然后按照表2所示策略进行充电，以0.33C放电，记录每次循环的放电容量Cn，直至循环容量保持率(即Cn/C0×100％)为80％，记录循环圈数。循环圈数越多，则代表二次电池的循环性能越好。
表2
二次电池的荷电状态SOC 充电倍率(C)
0～10％ 0.33
10％～20％ 5.2
20％～30％ 4.5
30％～40％ 4.2
40％～50％ 3.3
50％～60％ 2.6
60％～70％ 2.0
70％～80％ 1.5
80％～100％ 0.33
虽然已经参考优选实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件。尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (13)

  1. 一种复合磷酸锰铁锂材料，包括：
    磷酸锰铁锂颗粒，其使用上限电压记为V1，单位为V；
    包覆层，其包覆于所述磷酸锰铁锂颗粒的至少部分表面，所述包覆层包括金属纳米颗粒，所述金属纳米颗粒的氧化电压记为V2，单位为V，
    其中，所述复合磷酸锰铁锂材料满足：V1＜V2。
  2. 根据权利要求1所述的复合磷酸锰铁锂材料，其中，
    所述磷酸锰铁锂颗粒的结构式为LiMn 1-xFe xM yPO 4，
    式中，
    0.05≤x≤0.95；
    0≤y≤1；可选地，0≤y≤0.2；
    M表示掺杂元素，所述掺杂元素M包括硫、氮、硼、氟、氯、溴和碘中的一种元素或多种元素；可选地，所述掺杂元素M包括硫元素。
  3. 根据权利要求1或2所述的复合磷酸锰铁锂材料，其中，所述金属纳米颗粒包括银、金、铂、钯、铑、铱、锇和钌中的一种或多种纳米颗粒。
  4. 根据权利要求1至3中任一项所述的复合磷酸锰铁锂材料，其中，基于所述复合磷酸锰铁锂材料的总质量计，所述包覆层的质量含量记为A％，0.3≤A≤10；
    可选地，0.3≤A≤3。
  5. 根据权利要求1至4中任一项所述的复合磷酸锰铁锂材料，其中，
    所述包覆层的厚度记为H，单位为nm，2≤H≤100；可选地，5≤H≤20。
  6. 根据权利要求1至5中任一项所述的复合磷酸锰铁锂材料，其中，所述复合磷酸锰铁锂材料满足条件(1)至条件(3)中的至少一者：
    (1)所述金属纳米颗粒的平均粒径记D为D1，单位为nm，D1≤20；可选地，D1≤10；
    (2)所述磷酸锰铁锂颗粒的体积平均粒径Dv50记为D2，单位为μm，0.1≤D2≤10；可选地，0.2≤D2≤5；
    (3)所述复合磷酸锰铁锂材料的体积平均粒径Dv50记为D，单位为μm，0.1≤D≤10；可选地，0.2≤D≤5。
  7. 一种如权利要求1至6中任一项所述的复合磷酸锰铁锂材料的制备方法，包括：
    提供磷酸锰铁锂颗粒；
    将导电前驱体提供至所述磷酸锰铁锂颗粒，热处理所述导电前驱体以使所述导电前驱体还原形成包覆所述磷酸锰铁锂颗粒的包覆层，所述包覆层包括金属纳米颗粒，
    其中，
    所述磷酸锰铁锂颗粒的使用上限电压记为V1，单位为V；
    包覆层包覆于所述磷酸锰铁锂颗粒的至少部分表面，所述包覆层包括金属纳米颗粒，所述金属纳米颗粒的氧化电压记为V2，单位为V，
    所述复合磷酸锰铁锂材料满足：V1＜V2。
  8. 根据权利要求7所述的方法，其中，所述提供磷酸锰铁锂颗粒的步骤，包括：
    将掺杂元素M掺杂至所述磷酸锰铁锂颗粒内，所述掺杂元素M包括硫、氮、硼、氟、氯、溴和碘中的一种元素或多种元素；
    可选地，所述掺杂元素M包括硫元素。
  9. 根据权利要求7或8所述的方法，其中，
    所述热处理的温度为400℃至1000℃；和/或
    所述热处理的时间为2h至6h。
  10. 根据权利要求7至9中任一项所述的方法，其中，
    所述导电前驱体包括硝酸根、氯离子、溴离子、碘离子、硫酸根、磷酸根、醋酸根、乙酰丙酮根中的一种或多种；和/或
    所述导电前驱体包括银离子、金离子、铂离子、钯离子、铑离子、铱离子、锇离子和钌离子中的一种或多种。
  11. 根据权利要求7至10中任一项所述的方法，其中，基于所述导电前驱体和所述磷酸锰铁锂颗粒的总摩尔比计，所述导电前驱体的摩尔含量为b％，0.25≤b≤14.5；可选地，0.40≤b≤4.60。
  12. 一种二次电池，包括正极极片，所述正极极片包括如权利要求1至6中任一项所述的复合磷酸锰铁锂材料或如权利要求1至11中任一项所述的方法得到的复合磷酸锰铁锂材料。
  13. 一种用电装置，包括如权利要求12所述的二次电池。
PCT/CN2022/125524 2022-10-14 2022-10-14 复合磷酸锰铁锂材料、其制备方法、二次电池和用电装置 WO2024077636A1 (zh)

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JP2001110414A (ja) * 1999-10-04 2001-04-20 Nippon Telegr & Teleph Corp <Ntt> リチウム二次電池正極活物質およびリチウム二次電池
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