WO2023184960A1 - 磷酸锰铁锂的制备方法，正极材料及锂离子电池 - Google Patents

磷酸锰铁锂的制备方法，正极材料及锂离子电池 Download PDF

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WO2023184960A1
WO2023184960A1 PCT/CN2022/128489 CN2022128489W WO2023184960A1 WO 2023184960 A1 WO2023184960 A1 WO 2023184960A1 CN 2022128489 W CN2022128489 W CN 2022128489W WO 2023184960 A1 WO2023184960 A1 WO 2023184960A1
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lithium
manganese
phosphate
source
iron
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French (fr)
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王正伟
王永琛
李娜
朱华君
刘付召
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星恒电源股份有限公司
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Priority to KR1020237021069A priority patent/KR20230142698A/ko
Priority to US18/210,054 priority patent/US20230322557A1/en
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    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
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    • C01B25/00—Phosphorus; Compounds thereof
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    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/37—Phosphates of heavy metals
    • C01B25/377—Phosphates of heavy metals of manganese
    • H—ELECTRICITY
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    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
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    • C01P2006/11—Powder tap density
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to the technical field of lithium-ion battery preparation, and specifically relates to a preparation method of lithium manganese iron phosphate, a positive electrode material prepared therefrom and a lithium-ion battery.
  • cathode materials are shown in Table 1 below:
  • ternary cathode materials lithium nickel cobalt manganate or lithium nickel cobalt aluminate
  • the ternary cathode material has low-temperature discharge capability, normal temperature cycle, and high-temperature cycle, and has the highest energy density. It can be seen from the table that as the nickel content increases, the gram capacity of the material gradually increases, but at the same time the thermal decomposition temperature of the material decreases, resulting in a decrease in the safety of lithium-ion batteries in the ternary cathode material system.
  • low-nickel ternary such as 111 ternary has a high cobalt content, so the material price is high, and when the nickel content exceeds 70% (nickel content accounts for the sum of nickel, cobalt, manganese or aluminum), such as high-nickel 811 ternary material requires an oxygen atmosphere during the sintering process, so the material price is also high.
  • nickel content accounts for the sum of nickel, cobalt, manganese or aluminum
  • high-nickel 811 ternary material requires an oxygen atmosphere during the sintering process, so the material price is also high.
  • due to the low abundance of cobalt and nickel in the earth they are expensive. Based on this, ternary materials are more suitable for use in mid-to-high-end vehicles with longer driving ranges.
  • lithium manganate materials The safety performance of lithium manganate materials is significantly better than that of ternary cathode materials. It has excellent low temperature and rate performance and is the cheapest. However, its gram capacity is low ( ⁇ 110mAh/g) and its cycle life, especially high temperature cycle, is poor. Therefore, it is difficult to use lithium manganate alone as a cathode material.
  • lithium-rich manganese-based materials have a specific capacity of more than 250mAh/g when charged to 4.8V, but the cycle is unstable.
  • the mainstream of mature commercial electrolytes is still 4.2V system.
  • Single crystal ternary is equipped with electrolyte of 4.3 ⁇ 4.4V system.
  • the electrolyte of 5V high voltage system is not yet mature, so lithium-rich manganese-based materials have not been widely used. , only a small amount is used for doping with lithium manganate to delay the problem of rapid decay in the early stages of the lithium manganate cycle.
  • Lithium iron phosphate is a common cathode material for lithium-ion batteries. It has a long cycle life and excellent safety performance. However, due to poor conductivity, small particle size is used to make up for its rate performance in commercial applications. Even so, lithium iron phosphate is difficult to discharge electricity at low temperatures. In addition, because its discharge capacity is concentrated in the platform area, it is difficult to calibrate the state of charge with the voltage, resulting in a poor user experience. The compacted density of lithium iron phosphate is low, only 2.4 ⁇ 2.5g/cm 3 , while lithium manganate can reach 3.1g/cm 3 , and the ternary cathode can reach 3.4/cm 3 . In addition, the voltage of lithium iron is only 3.2V.
  • LiMnPO 4 , LiCoPO 4 , LiNiPO 4 , LiMnSiO 4 , LiFeSiO 4 , LiCoSiO 4 , and LiNiPSiO 4 are materials that are expected to replace lithium iron phosphate.
  • the commercialization of the phosphoric acid system is more mature.
  • manganese, cobalt, nickel, and iron, cobalt and nickel are the most expensive, while manganese and iron are the cheapest.
  • the conductivity of lithium manganese phosphate is extremely poor, worse than that of lithium iron phosphate.
  • the structural stability of lithium iron manganese phosphate is used to synthesize lithium manganese iron phosphate, so lithium manganese iron phosphate has the characteristics of both lithium manganese phosphate and lithium iron phosphate through the doping of manganese or iron.
  • the three substances can also be called the same category of materials. Expressed by a chemical formula LiMn x Fe 1-x PO 4 . Lithium iron manganese phosphate is currently mature for commercialization, but its conductivity is worse than that of lithium iron phosphate and its low-temperature discharge capability is weaker.
  • the platform voltage of lithium iron manganese phosphate is as high as 4.1V, and the medium voltage is up to 3.9V. Its gram capacity and cycle life are consistent with those of lithium iron phosphate. Its safety performance is extremely high in the 4.2-4.3V system, and it can be used to blend into ternary materials to improve Safety performance against overcharging and acupuncture.
  • the synthesis methods of lithium iron phosphate are divided into solid phase method and liquid phase method.
  • the liquid phase method mainly uses ferrous sulfate heptahydrate, phosphoric acid, and lithium hydroxide to hydrothermally generate lithium iron phosphate, lithium sulfate, and water.
  • the equipment is expensive, and three times the amount of lithium hydroxide is generally used as the precipitant, which requires more consumption. 200% lithium hydroxide thus increasing the cost.
  • the solid phase method is divided into ferrous oxalate, iron oxide red, and ferric orthophosphate methods. A large amount of carbon dioxide gas is produced during the reaction of the ferrous oxalate method.
  • the carbon band loss is large, the carbon content is easy to fluctuate, the product consistency is poor, the product tap density is low, and ammonia gas is released, which pollutes the environment.
  • the cost of the iron oxide red method is lower.
  • the density of the synthesized lithium iron phosphate is higher, but the capacity is low, and ammonia gas is released, which pollutes the environment.
  • the ferric orthophosphate method does not produce ammonia, the production process is environmentally friendly, and the output is large, and it has become a mainstream production process.
  • There are two methods for synthesizing ferric orthophosphate one is the ferrous sulfate method and the other is the iron powder-phosphoric acid method. Both methods require the use of phosphoric acid and hydrogen peroxide.
  • Equipment anti-corrosion requirements result in high costs and greater pressure on environmental protection. big.
  • the synthesis methods of lithium iron manganese phosphate are mainly divided into solid phase method and co-precipitation method.
  • the solid phase method uses manganese source, iron source, phosphorus source, and lithium source for sintering. The process is the simplest, but the synthesized material has the worst performance, so the co-precipitation method is the mainstream.
  • the co-precipitation method uses manganese source, iron source and complexing agent to co-precipitate to generate a precursor. The precursor reacts with the phosphorus source and lithium source in solid phase or liquid phase to generate lithium iron manganese phosphate, such as Chinese invention patent CN105047922A.
  • the material synthesis is divided into solid phase and liquid phase methods.
  • the solid phase method has a simple process.
  • the synthesized materials have the worst performance.
  • the liquid-phase synthesis method has good performance, but the anti-corrosion requirements of the equipment cause high costs and put great pressure on environmental protection. Therefore, a new design process is needed to synthesize LiMn x Fe 1-x PO 4 materials to improve the performance of the material while having low cost.
  • the invention provides a method for preparing lithium manganese iron phosphate, through which a lithium manganese iron phosphate material with high tap density, long cycle life, low price and high cost performance can be prepared.
  • the invention also provides cathode materials and lithium-ion batteries prepared from the materials.
  • the preparation method of lithium iron manganese phosphate provided by the invention includes the following steps:
  • the solid-phase method of lithium iron manganese phosphate is to mix manganese source, iron source, phosphorus source and lithium source and then sinter them.
  • the process is simple, the synthesized material has the worst performance.
  • the present invention provides a new preparation method.
  • the manganese source and the iron source are mixed and then solid-phase sintering is performed, so that the manganese source and the iron source are thermally decomposed to obtain manganese iron oxide (Mn x Fe 1 -xy ) m O n ; then, the manganese iron oxide (Mn x Fe 1-xy ) m O n is mixed with a lithium source and a phosphorus source, and then solid-phase sintering is performed for the second time to obtain lithium iron manganese phosphate LiMn x Fe 1-xy PO 4-z .
  • lithium iron manganese phosphate prepared by solid phase method and liquid phase method. This is mainly because the method of the present invention first synthesizes manganese iron oxide, the precursor of lithium iron manganese phosphate.
  • the true density of manganese iron oxide is higher than that of iron oxide, but lower than that of manganese oxide.
  • the true density of iron oxide is Higher than iron salts such as ferrous sulfate.
  • the traditional solid-phase method uses iron sources, manganese sources, lithium sources, and phosphorus sources to synthesize lithium iron manganese phosphate. Due to the presence of low-density iron sources, Therefore, the synthesized lithium iron manganese phosphate material has a low tap density and a large specific surface. After being made into a pole piece, the compaction density is low, the energy density is low, the self-discharge is large, and the cycle is slightly poor; the traditional liquid phase method is to co-precipitate manganese iron carbonate Salt or ferromanganese hydroxide has a porous and fluffy appearance and low density.
  • the lithium ferromanganese phosphate material synthesized using co-precipitated ferromanganese sources, lithium sources, and phosphorus sources also has low tap density and large specific surface area, and is made of The post-pole piece compaction density is low, the energy density is low, the self-discharge is large, and the cycle is slightly poor.
  • the lithium iron manganese phosphate precursor manganese iron oxide particles synthesized by the method of the present invention have a large single crystal morphology and a high true density, resulting in a high tap density of the finally synthesized lithium iron manganese phosphate material and a compact density of the pole piece. High, high battery energy density, small material specific surface, small self-discharge, and long cycle life.
  • the manganese source can be various manganese compounds commonly used in this field, and the present invention is not limited thereto.
  • the manganese source may or may not contain crystal water.
  • the manganese source is one or more of manganese sulfate, manganese carbonate, manganese acetate, manganese phosphate, manganese nitrate, manganese oxalate, and manganese citrate.
  • the iron source can be various iron compounds commonly used in this field, and the present invention is not limited thereto.
  • the iron source may or may not contain crystal water.
  • the iron source is ferrous sulfate, ferrous carbonate, ferrous acetate, ferrous phosphate, ferrous nitrate, ferrous oxalate, ferrous citrate, ferric sulfate, ferric carbonate, ferric acetate, ferric phosphate, nitric acid
  • iron, iron oxalate, and iron citrate is one or more of iron, iron oxalate, and iron citrate.
  • the lithium source can use various lithium compounds commonly used in this field, and the present invention is not limited thereto.
  • the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium phosphate, lithium oxalate, lithium acetate, lithium sulfate, lithium nitrate, and lithium chloride.
  • the phosphorus source can be various phosphorus-containing compounds commonly used in this field, and the present invention is not limited thereto.
  • the phosphorus source is ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium tripolyphosphate, phosphoric acid, calcium phosphate, phosphate ester, lithium dihydrogen phosphate, iron phosphate, phosphoric acid One or more of lithium, lithium dihydrogen phosphate, and manganese phosphate.
  • manganese source or iron source can also be used alone.
  • either lithium manganese phosphate or lithium iron manganese phosphate can be prepared (the iron source is supplemented in step S3).
  • the iron source is used alone, either lithium iron phosphate or lithium manganese iron phosphate can be prepared (the manganese source is supplemented in step S3).
  • the iron source and/or manganese source supplemented in step S3 is preferably iron oxide and/or manganese oxide.
  • the addition amounts of manganese source, iron source, lithium source and phosphorus source mainly refer to the synthesis of manganese iron oxide (Mn x Fe 1-xy ) m O n and lithium manganese iron phosphate LiMn x Fe 1-xy PO 4 The stoichiometric ratio of the reaction equation is determined.
  • steps S1 and S3 one or more of a carbon source, an M source, and an N source may be added during solid phase mixing.
  • ferromanganese oxide (Mn x Fe 1-xy M y ) m O n N z /C and lithium iron manganese phosphate LiMn x Fe 1-xy M y PO 4- are obtained respectively.
  • a carbon-coated lithium iron manganese phosphate material when a carbon source is added, a carbon-coated lithium iron manganese phosphate material can be formed.
  • the carbon source may be one or more of organic carbon sources and inorganic carbon sources.
  • the carbon source is one of sucrose, glucose, fructose, citric acid, phenolic resin, polyvinyl alcohol, polyethylene glycol, starch, carbon black, acetylene black, graphite, graphene, conductive carbon tubes, or Various.
  • the M source when M source is added, cation-doped lithium manganese iron phosphate material can be obtained.
  • the M source can be one cation source or a combination of multiple cation sources; preferably, the cation source includes aluminum, magnesium, nickel, cobalt, titanium, copper, calcium, niobium, chromium, zinc, lanthanum, antimony, One or more of tellurium, strontium, tungsten, indium, yttrium and other elements.
  • anion-doped lithium manganese iron phosphate material when an N source is added, anion-doped lithium manganese iron phosphate material can be obtained.
  • the N source can be one anion source or a combination of multiple anion sources.
  • the anion source includes one or more elements such as fluorine and sulfur.
  • materials such as olivine-structured lithium iron manganese phosphate materials, layered polybasic acid lithium, spinel-type lithium manganate, layered manganese-rich lithium base and other materials can be obtained.
  • the invention provides a cathode material, which is composed of one or more of the above-mentioned olivine structure lithium manganese iron phosphate material, layered polybasic acid lithium, spinel type lithium manganate, and layered manganese-rich lithium base. owned.
  • the invention provides a lithium ion battery, which includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.
  • the positive electrode sheet is prepared from the above-mentioned positive electrode material.
  • the present invention provides a new solid-phase synthesis method of lithium iron manganese phosphate by improving the synthesis process.
  • the lithium iron manganese phosphate material synthesized by this method has high tap density, high compaction density and specific surface area. Small, the lithium-ion battery prepared by it has the characteristics of high energy density, small self-discharge and long cycle life.
  • the lithium iron manganese phosphate material synthesized by the present invention has the advantages of low price and high cost performance.
  • Figure 1 is the XRD pattern of (Mn 0.9 Fe 0.1 ) 2 O 3 in Example 1 of the present invention
  • Figure 2 is an SEM image of (Mn 0.9 Fe 0.1 ) 2 O 3 in Example 1 of the present invention
  • Figure 3 is an SEM image of LiMn 0.9 Fe 0.1 PO 4 in Example 1 of the present invention.
  • Figure 4 is an SEM image of LiMn 0.9 Fe 0.1 PO 4 in Example 2 of the present invention.
  • Figure 5 is a cycle performance test chart of the cylindrical full battery prepared in Example 3 and Comparative Example 1 of the present invention.
  • MnSO 4 ⁇ H 2 O is used as the manganese source
  • FeSO 4 ⁇ 7H 2 O is used as the iron source
  • the molar ratio of MnSO 4 ⁇ H 2 O and FeSO 4 ⁇ 7H 2 O is 9:1, and then solid phase mixing is performed;
  • the uniformly mixed material is heated to 600°C for high-temperature solid phase sintering to obtain the lithium manganese iron phosphate precursor (Mn 0.9 Fe 0.1 ) 2 O 3 .
  • the reaction equation is:
  • the thick black line in Figure 1 is the X-ray diffraction XRD pattern of the LiMn 0.9 Fe 0.1 PO 4 precursor (Mn 0.9 Fe 0.1 ) 2 O 3. It can be seen that the substances synthesized in this scheme are consistent with the color comparison card PDF#24-0507. The (Mn 0.983 Fe 0.017 ) 2 O 3 peak corresponds better.
  • Figure 2 is the SEM image of (Mn 0.9 Fe 0.1 ) 2 O 3. It can be seen that the material is a uniform material with good morphology. The particle size and tap density of the test material were tested. D50 was 6 ⁇ m and the tap density was as high as 2.4g/cm 3 . Therefore, what is synthesized in this scheme is manganese iron oxide, rather than a simple mixture of manganese oxide and iron oxide.
  • Figure 3 shows the scanning electron microscope SEM image of lithium iron manganese phosphate LiMn 0.9 Fe 0.1 PO 4.
  • the morphology of the material is good.
  • the particle size and tap density of the test material were tested. D50 was 2 ⁇ m and the tap density was as high as 1.5 g/cm 3 .
  • MnSO 4 ⁇ H 2 O is used as the manganese source
  • FeSO 4 ⁇ 7H 2 O is used as the iron source
  • the molar ratio of MnSO 4 ⁇ H 2 O and FeSO 4 ⁇ 7H 2 O is 6:4, and then solid phase mixing is performed;
  • the uniformly mixed material is heated to 500°C for high-temperature solid phase sintering to obtain the lithium manganese iron phosphate precursor (Mn 0.6 Fe 0.4 ) 2 O 3 .
  • the reaction equation is:
  • Figure 4 is a scanning electron microscope SEM image of lithium iron manganese phosphate LiMn 0.6 Fe 0.4 PO 4. It can be seen from the figure that the morphology of the prepared lithium iron manganese phosphate material is good.
  • the particle size, specific surface area, and tap density of the material were tested. The results showed that the D50 of the material was 1.5 ⁇ m, the specific surface area was 15 m 2 /g, the tap density was as high as 1.3 g/cm 3 , and the compacted density of the material was as high as 2.8 g/ cm 3 , which is much higher than the currently common tap density of 0.8-1.0g/cm 3 and the compacted density of 2.3g/cm 3 , and much lower than the currently common commercial specific surface area of 20m 2 /g. Higher compaction density can make the rolling density of pole pieces higher. Thin pole pieces allow more pole pieces to be accommodated in a given battery case, ultimately making the battery have a higher energy density.
  • the low specific surface area can reduce the content of the binder, making the active material account for a higher proportion, further improving the energy density of the battery; and the low specific surface area allows fewer side reactions between the material and the electrolyte, improving the shelf performance and cycle of the battery. life.
  • a mixture of spinel lithium manganese oxide LiMn2O4 and lithium iron manganese phosphate LiMn 0.6 Fe 0.4 PO 4 prepared in Example 2 is used as the active material of the positive electrode sheet of the lithium ion battery.
  • the spinel lithium manganate material accounts for the positive electrode.
  • the proportion of active materials is 80%, and lithium iron manganese phosphate material accounts for 20%.
  • the above-mentioned positive electrode active material is mixed with a conductive agent and a binder to prepare a positive electrode slurry.
  • the proportion of solid matter in the slurry active materials account for 97.2%, conductive agents (conductive carbon black, conductive graphite, conductive carbon nanotubes, graphene) account for 1.7%, and binders (polyvinylidene fluoride) account for 1.7%.
  • the ratio is 1.1%. Adjust the content of the solvent N-methylpyrrolidone so that the solid content of the slurry is about 75%.
  • the evenly stirred slurry is coated on the surface of the current collector aluminum foil, and after drying, it is rolled and sliced to obtain the positive electrode piece.
  • a cylindrical full battery assembled with the above positive electrode plates was used to conduct a 0.5C charge and discharge cycle performance test.
  • the cylindrical battery model is R34235, with a diameter of 34mm and a height of 235mm.
  • spinel Lithium manganate material accounts for 80% of the cathode active material
  • lithium iron manganese phosphate material accounts for 20%.
  • the above positive electrode active material was prepared into a cylindrical full battery according to the same method as Example 3.
  • the battery assembled from the lithium iron manganese phosphate synthesized in Example 2 can be cycled 1100 times and has an energy density of 140Wh/kg.
  • the battery assembled from the lithium manganese iron phosphate prepared by the traditional liquid phase method in Comparative Example 1 can be cycled 800 times and has an energy density of 130Wh/kg.
  • the improvement in cycle performance and energy density is mainly due to the high compaction density of the material.
  • the battery is left fully charged at room temperature for 28 days, and the capacity before storage is taken as 100%.
  • the remaining capacity ratio after storage and the charge-discharge recovery capacity ratio can reflect the self-discharge of the battery and the side reactions between the material and the electrolyte.
  • the batteries of Example 3 and Comparative Example 1 were tested for 28-day storage performance at room temperature when fully charged, and the results are shown in Table 2 below.
  • the remaining capacity ratio of the battery of Comparative Example 1 after being put aside is 92.44%, and the recovery capacity ratio is 96.35%; while the remaining capacity ratio of the battery of Example 3 after being put aside is 94.79%, and the recovery capacity ratio is 98.05%.
  • the materials synthesized in the present invention have less side reactions with the electrolyte, which is mainly due to the smaller specific surface area of the materials in the embodiments.
  • MnSO 4 ⁇ H 2 O Industrial grade MnSO 4 ⁇ H 2 O is used as a manganese source. After grinding to micron size using a sand mill, it is heated to 150°C. Manganese sulfate loses crystal water and is then heated to 900°C to thermally decompose to generate lithium manganese phosphate precursor Mn. 3 O 4 .
  • the overall reaction equation is:
  • MnSO 4 ⁇ H 2 O Industrial grade MnSO 4 ⁇ H 2 O is used as the manganese source. After grinding to micron size using a sand mill, it is heated to 150°C. Manganese sulfate loses crystal water and is then heated to 900°C to thermally decompose to generate lithium manganese iron phosphate precursor. Mn 3 O 4 . The total reaction equation is: 3MnSO 4 ⁇ H 2 O ⁇ Mn 3 O 4 +3SO 2 ⁇ +3H 2 O ⁇ .
  • lithium carbonate, iron phosphate, and ammonium dihydrogen phosphate are solid-phase mixed and sand-ground, and solid-phase sintered at a high temperature of 600°C to obtain lithium iron manganese phosphate LiMn 0.6 Fe 0.4 PO 4 .
  • the reaction equation is:

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Abstract

本发明公开了一种磷酸锰铁锂的制备方法，包括以下步骤：S1.将锰源和/或铁源固相混合，得到第一混合物；S2.将所述第一混合物于300～1200℃下进行固相烧结，获得锰铁氧化物(Mn xFe 1-x-y) mO n；S3.将所述锰铁氧化物(Mn xFe 1-x-y) mO n与锂源、磷源以及可选的锰源和/或铁源进行固相混合，得到第二混合物；S4.将所述第二混合物于350～900℃下进行固相烧结，得到磷酸锰铁锂LiMn xFe 1-x-yPO 4；其中，0≤x≤1，0≤y≤1。本发明的方法能够制备得到振实密度高、循环寿命长、价格低、性价比高的磷酸锰铁锂材料。

Description

磷酸锰铁锂的制备方法，正极材料及锂离子电池 技术领域
本发明涉及锂离子电池制备技术领域，具体涉及一种磷酸锰铁锂的制备方法，由其制备的正极材料及锂离子电池。
背景技术
在锂离子电池中，常用的正极材料如下表1所示：
表1
Figure PCTCN2022128489-appb-000001
其中，三元正极材料(镍钴锰酸锂或镍钴铝酸锂)一般用于替代钴酸锂，应用于动力电池领域。三元正极材料兼具有低温放电能力、常温循环、高温循环，并且能量密度最高。从表中可以看出，随着镍含量的增加，材料克容量逐渐提升，但与此同时材料的热分解温度降低，导致三元正极材料体系的锂离子电池安全性下降。另一方面，低镍三元如111三元的钴含量高，所以材料价格高，而当镍含量超过70％(镍含量占比镍、钴、锰或铝的总和)时，例如高镍的811三元材料，烧结过程中需要通氧气气氛，所以材料价格也偏高。除此之外，由于钴、镍在地球中的丰度低，所以价格昂贵，基于此，三元材料更适合用于续航里程较长 的中高端车辆领域。
正极三元材料的合成需要氧参与反应，一般在中低镍条件下，生产厂家只在空气条件下烧结，而在高镍条件(镍＞0.7)，则需要在氧气气氛下烧结。另外由于高镍对空气湿度比较敏感，很容易吸潮导致材料表面生成碳酸锂，包装和电池配料涂布对湿度要求严格，所以高镍的工费要高于中镍。近几年来，高镍三元搭配的长续航里程电动汽车的安全事故频发，导致行业内对高镍三元的热度下降，目前由追求高镍逐渐转向中镍三元的使用。随着研发的进步以及追求降成本市场驱动，导致低钴无钴三元的应用加速，目前已逐渐将钴含量降低至0.05甚至0.03。但由于矿产中钴和镍天然相伴，纯镍中也会有3～5％的钴，所以没有必要花费成本来去除高镍三元中钴的含量。
锰酸锂材料的安全性能明显优于三元正极材料，低温和倍率性能优异，同时价格最低廉，但其克容量低(～110mAh/g)，循环寿命尤其是高温循环差。所以锰酸锂很难单独作为正极材料去使用。
富锂锰基材料作为新兴正极材料代表，充电至4.8V时比容量可达250mAh/g以上，但循环不稳定。目前成熟的商品化电解液主流还是4.2V体系，单晶三元配有4.3～4.4V体系的电解液，5V高电压体系的电解液还不成熟，所以富锂锰基材料未能被广泛使用，仅少量用于和锰酸锂掺杂使用，以延缓锰酸锂循环前期衰减快的问题。
磷酸铁锂是一种常见的锂离子电池正极材料，其循环寿命长，安全性能优异，但由于导电性差，所以商业化应用时以小粒径来弥补其倍率性能。即便如此，磷酸铁锂在低温下很难放出电来，另外由于其放电容量集中于平台区，导致荷电状态很难与电压标定，导致用户使用体验很差。磷酸铁锂的压实密度低，仅为2.4～2.5g/cm 3，而锰酸锂可达3.1g/cm 3，三元正极可达3.4/cm 3，另外铁锂电压仅为3.2V，所以磷酸铁锂的体积能量密度非常低。基于此，LiMnPO 4、LiCoPO 4、LiNiPO 4、LiMnSiO 4、LiFeSiO 4、LiCoSiO 4、LiNiPSiO 4是有望代替磷酸铁锂的材料。相比于硅酸盐体系，磷酸体系的商业化更成熟一些。锰、钴、镍、铁这四种元素，钴、镍价格最高，锰、铁最便宜。但磷酸锰锂的导电性极差，比磷酸铁锂还差，折中的，无论是用锰掺杂磷酸铁锂还是用铁掺杂磷酸锰锂，均是利用锰的高电位平台和铁的结构稳定特性来合成磷酸锰铁锂，所以磷酸锰铁锂通过锰或铁的掺杂兼具有磷酸锰锂和磷酸铁锂的特性，也可以将该三种物质其称为同一大类材料，用一个化学式LiMn xFe 1-xPO 4表示。磷酸锰铁锂目前商业化已成熟，但其导电性比磷酸铁锂还差，低温放电能力更弱，目前还没有单独作为正极材料来使用。磷酸锰铁锂的平台电压高达4.1V，中压达3.9V，克容量和循环寿命与磷酸铁锂一致，4.2～4.3V体系下安全性能极高，有应用于混掺至三元材料中提升过充及针刺的安全性能。
目前磷酸铁锂的合成方法分为固相法、液相法。液相法主要采用七水硫酸亚铁、磷酸、氢氧化锂水热生成磷酸铁锂、硫酸锂和水，但设备昂贵，而且一般使用三倍量的氢氧化锂作为沉淀剂，这需要多消耗200％的氢氧化锂从而增加了成本。固相法分为草酸亚铁、氧化铁红、正磷酸铁法。草酸亚铁法反应过程中产生大量二氧化碳气体，碳的带损大，碳含量易波动，产品一致性差，且产品振实密度低，并且含有氨气放出，污染环境。氧化铁红法成本较低，合成的磷酸铁锂密度较大，但容量偏低，并且有氨气放出，污染环境。正磷酸铁法没有氨气产生，生产过程环保，产量大，已成为主流生产工艺。正磷酸铁的合成方法有两种，一种是硫酸亚铁法，另一种是铁粉-磷酸法，两种方法均需使用磷酸和双氧水，设备防腐要求造成成本高并且对环保的压力较大。
目前磷酸锰铁锂的合成方法主要分为固相法和共沉淀法。固相法采用锰源、铁源、磷源、锂源烧结，工艺最简单，但合成的材料性能最差，所以主流是用共沉淀法。共沉淀法采用锰源、铁源、络合剂共沉淀生成前驱体，前驱体和磷源、锂源固相或液相反应生成磷酸锰铁锂，如中国发明专利CN105047922A。
可以看到，LiMn xFe 1-xPO 4无论是x＝0时的磷酸铁锂还是x≠0时的磷酸锰铁锂，材料合成均分为固相和液相法，固相法工艺简单但合成的材料性能最差，液相法合成的性能好但设备防腐要求造成成本高并且对环保的压力较大。所以，需要一种全新的设计工艺来合成LiMn xFe 1-xPO 4材料，提高材料的性能，同时具有成本低的特性。
发明内容
本发明提供一种磷酸锰铁锂的制备方法，通过该方法能够制备得到振实密度高、循环寿命长、价格低、性价比高的磷酸锰铁锂材料。本发明还提供了由所述材料制备的正极材料及锂离子电池。
本发明提供的磷酸锰铁锂的制备方法，包括以下步骤：
S1.将锰源和/或铁源固相混合，得到第一混合物；
S2.将所述第一混合物于300～1200℃下进行固相烧结，获得锰铁氧化物(Mn xFe 1-x-y) mO n；
S3.将所述锰铁氧化物(Mn xFe 1-x-y) mO n与锂源、磷源以及可选的锰源和/或铁源进行固相混合，得到第二混合物；
S4.将所述第二混合物于350～900℃下进行固相烧结，得到磷酸锰铁锂LiMn xFe 1-x-yPO 4；
其中，0≤x≤1，0≤y≤1。
现有技术中，磷酸锰铁锂的固相法是将锰源、铁源、磷源和锂源混合后烧结，虽然工艺简单，但合成的材料性能最差。本发明在此基础上，提供了一种新的制备方法，先将锰源与铁源混合后进行固相烧结，使得锰源、铁源发生热分解，获得锰铁氧化物(Mn xFe 1-x-y) mO n；接着，将锰铁氧化物(Mn xFe 1-x-y) mO n再与锂源、磷源混合后，进行第二次固相烧结，得到磷酸锰铁锂LiMn xFe 1-x-yPO 4-z。这种制备方法同样简单，得到的磷酸锰铁锂价格低，且具有振实密度和压实密度高、能量密度高、比表面小、自放电小、循环寿命长的特点，明显优于现有的固相法和液相法制备的磷酸锰铁锂。这主要是因为本发明的方法先合成的是磷酸锰铁锂前驱体锰铁氧化物，锰铁氧化物的真密度要高于铁氧化物，而低于锰氧化物，铁氧化物的真密度高于铁盐如硫酸亚铁，随后在合成磷酸锰铁锂时，由于传统固相法是利用铁源、锰源、锂源、磷源合成磷酸锰铁锂，由于低密度的铁源存在，所以合成的磷酸锰铁锂材料振实密度低、比表面大，做成极片后压实密度低、能量密度低、自放电大、循环略差；传统液相法是共沉淀锰铁碳酸盐或锰铁氢氧化物，形貌多孔蓬松，密度小，随后用共沉淀的锰铁源、锂源、磷源合成的磷酸锰铁锂材料同样具有振实密度低、比表面大，做成极片后压实密度低、能量密度低、自放电大、循环略差特点。此外，本发明的方法合成的磷酸锰铁锂前驱体锰铁氧化物颗粒为一次大单晶形貌，真密度高，导致最终合成的磷酸锰铁锂材料振实密度高、极片压实密度高、电池能量密度高、材料比表面小、自放电小、循环寿命长。
所述锰源可采用本领域常用的各种锰化合物，本发明对此不作限制。所述锰源可含有结晶水，也可不含有结晶水。优选地，所述锰源为硫酸锰、碳酸锰、醋酸锰、磷酸锰、硝酸锰、草酸锰、柠檬酸锰中的一种或多种。
所述铁源可采用本领域常用的各种铁化合物，本发明对此不作限制。所述铁源可含有结晶水，也可不含有结晶水。优选地，所述铁源为硫酸亚铁、碳酸亚铁、醋酸亚铁、磷酸亚铁、硝酸亚铁、草酸亚铁、柠檬酸亚铁、硫酸铁、碳酸铁、醋酸铁、磷酸铁、硝酸铁、草酸铁、柠檬酸铁中的一种或多种。
所述锂源可采用本领域常用的各种锂化合物，本发明对此不作限制。优选地，所述锂源为碳酸锂、氢氧化锂、磷酸锂、草酸锂、醋酸锂、硫酸锂、硝酸锂、氯化锂中的一种或多种。
所述磷源可采用本领域常用的各种含磷化合物，本发明对此不作限制。优选地，所述磷源为磷酸二氢铵、磷酸氢二铵、磷酸二氢钠、磷酸氢二钠、三聚磷酸钠、磷酸、磷酸钙、磷 酸酯、磷酸二氢锂、磷酸铁、磷酸锂、磷酸二氢锂、磷酸锰中的一种或多种。
本发明步骤S1中，也可单独采用锰源或铁源。当单独采用锰源时，既可以制备得到磷酸锰锂，也可以制备得到磷酸锰铁锂(在步骤S3中补充铁源)。同样的，当单独采用铁源时，既可以制备得到磷酸铁锂，也可以制备得到磷酸锰铁锂(在步骤S3中补充锰源)。其中，在步骤S3中补充的铁源和/或锰源优选为铁氧化物和/或锰氧化物。
本发明中，锰源、铁源、锂源、磷源的添加量主要参考锰铁氧化物(Mn xFe 1-x-y) mO n和磷酸锰铁锂LiMn xFe 1-x-yPO 4的合成反应方程式的化学计算比确定。
进一步地，步骤S1和S3中，固相混合时还可加入了碳源、M源、N源中的一种或多种。经过步骤S2和S4的固相烧结后，分别得到锰铁氧化物(Mn xFe 1-x-yM y) mO nN z/C和磷酸锰铁锂LiMn xFe 1-x-yM yPO 4-zN z/C；其中，所述M源为掺杂阳离子源，所述N源为掺杂阴离子源；0≤x≤1，0≤y≤1，0≤z≤0.1，1：3.5≤m：(n+z)≤1:1。如FeO、Fe 2O 3、Fe 3O 4。
本发明中，当加入碳源时，可以形成碳包覆的磷酸锰铁锂材料。所述碳源可为有机碳源、无机碳源中的一种或多种。优选地，所述碳源为蔗糖、葡萄糖、果糖、柠檬酸、酚醛树脂、聚乙烯醇、聚乙二醇、淀粉、炭黑、乙炔黑、石墨、石墨烯、导电碳管中的一种或多种。
本发明中，当加入M源时，可以得到掺杂阳离子的磷酸锰铁锂材料。其中，M源可以为一种阳离子源或多种阳离子源复合添加；优选地，所述阳离子源包括铝、镁、镍、钴、钛、铜、钙、铌、铬、锌、镧、锑、碲、锶、钨、铟、钇等元素中的一种或多种。
本发明中，当加入N源时，可以得到掺杂阴离子的磷酸锰铁锂材料。其中，N源可以为一种阴离子源或多种阴离子源复合添加。优选地，所述阴离子源包括氟、硫等元素中的一种或多种。
通过本发明的制备方法，可以得到橄榄石结构的磷酸锰铁锂材料、层状多元酸锂、尖晶石型锰酸锂、层状富锰锂基等材料。
本发明提供的一种正极材料，由上述橄榄石结构的磷酸锰铁锂材料、层状多元酸锂、尖晶石型锰酸锂、层状富锰锂基中的一种或多种混合后得到的。
本发明提供的一种锂离子电池，包括正极片、负极片、电解液和隔膜，所述正极片是由上述的正极材料制备而成的。
与现有技术相比，本发明的有益效果在于：
1、本发明通过对合成工艺方法的改进，提供了一种新的磷酸锰铁锂的固相合成方法，该方法合成出的磷酸锰铁锂材料振实密度高、压实密度高、比表面小，由其制备的锂离子电池，具有能量密度高、自放电小、循环寿命长的特点。
2、本发明合成的磷酸锰铁锂材料，具有价格低、性价比高的优点。
附图说明
图1是本发明实施例1中(Mn 0.9Fe 0.1) 2O 3的XRD图；
图2是本发明实施例1中(Mn 0.9Fe 0.1) 2O 3的SEM图；
图3是本发明实施例1中LiMn 0.9Fe 0.1PO 4的SEM图；
图4是本发明实施例2中LiMn 0.9Fe 0.1PO 4的SEM图；
图5是本发明实施例3和对比例1制备的圆柱全电池的循环性能测试图。
具体实施方式
除非另有定义，本文所使用的所有的技术和科学术语与属于本发明的技术领域的技术人员通常理解的含义相同。本文中在本发明的说明书中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本发明。本文所使用的术语“及/或”包括一个或多个相关的所列项目的任意的和所有的组合。
下面结合附图和具体实施例对本发明作进一步说明，以使本领域的技术人员可以更好地理解本发明并能予以实施，但所举实施例不作为对本发明的限定。
下述实施例中所使用的实验方法如无特殊说明，均为常规方法，所用的材料、试剂等，如无特殊说明，均可从商业途径得到。
实施例1
采用MnSO 4·H 2O作为锰源，FeSO 4·7H 2O作为铁源，MnSO 4·H 2O与FeSO 4·7H 2O的摩尔比为9:1，随后进行固相混料；将混合均匀的料升温至600℃进行高温固相烧结，获得磷酸锰铁锂前驱体(Mn 0.9Fe 0.1) 2O 3。反应方程式为：
18MnSO 4·H 2O+2FeSO 4·7H 2O→10(Mn 0.9Fe 0.1) 2O 3+20SO 2↑+32H 2O↑+5O 2↑。
将(Mn 0.9Fe 0.1) 2O 3、碳酸锂、磷酸二氢铵固相混合砂磨，500℃高温固相烧结， 获得磷酸锰铁锂LiMn 0.9Fe 0.1PO 4。反应方程式为：
2(Mn 0.9Fe 0.1) 2O 3+2Li 2CO 3+4NH 4H 2PO 4→4LiMn 0.9Fe 0.1PO 4+2CO 2↑+4NH 3↑+6H 2O↑+O 2↑。
图1中黑色粗线为LiMn 0.9Fe 0.1PO 4前驱体(Mn 0.9Fe 0.1) 2O 3的X射线衍射XRD图，可以看到，本方案合成的物质与比色卡PDF#24-0507的(Mn 0.983Fe 0.017) 2O 3峰对应的较好。
图2为(Mn 0.9Fe 0.1) 2O 3的SEM图，可以看到该物质为一种均一的物质，形貌较好。测试材料的粒径和振实密度，D50为6μm，振实密度高达2.4g/cm 3。所以，本方案的合成出的是锰铁氧化物，而不是简单的氧化锰与氧化铁的混合物。
图3为磷酸锰铁锂LiMn 0.9Fe 0.1PO 4的扫描电子显微镜SEM图，材料的形貌较好。测试材料的粒径和振实密度，D50为2μm，振实密度高达1.5g/cm 3。
实施例2
采用MnSO 4·H 2O作为锰源，FeSO 4·7H 2O作为铁源，MnSO 4·H 2O与FeSO 4·7H 2O的摩尔比为6:4，随后进行固相混料；将混合均匀的料升温至500℃进行高温固相烧结，获得磷酸锰铁锂前驱体(Mn 0.6Fe 0.4) 2O 3。反应方程式为：
12MnSO 4·H 2O+8FeSO 4·7H 2O→10(Mn 0.6Fe 0.4) 2O 3+20SO 2↑+68H 2O↑+5O 2↑。
将(Mn 0.6Fe 0.4) 2O 3、碳酸锂、磷酸二氢铵固相混合砂磨，500℃高温固相烧结，获得磷酸锰铁锂LiMn 0.6Fe 0.4PO 4。反应方程式为：
2(Mn 0.6Fe 0.4) 2O 3+2Li 2CO 3+4NH 4H 2PO 4→4LiMn 0.6Fe 0.4PO 4+2CO 2↑+4NH 3↑+6H 2O↑+O 2↑。
图4为磷酸锰铁锂LiMn 0.6Fe 0.4PO 4的扫描电子显微镜SEM图，从图中可以看出，制备的磷酸锰铁锂材料的形貌较好。
测试材料的粒径、比表面积、振实密度，结果显示，材料的D50为1.5μm，比表面积15m 2/g，振实密度高达1.3g/cm 3，材料的压实密度可达2.8g/cm 3，远高于目前商业化常见的0.8～1.0g/cm 3的振实密度以及2.3g/cm 3的压实密度，远低于目前商业化常见的20m 2/g的比表面积。更高的压实密度可以使得极片辊压密度做的高，极片薄后使得给定的电池壳内可以容纳更多的极片，最终使得电池具有更高的能量密度。同时低比表面积可以降低粘结剂的含量，使得活性物质的占比更高，进一步提高电池的能量密度；并且低比表面积使得材料与电解液的副 反应更少，提高电池的搁置性能和循环寿命。
实施例3
采用尖晶石锰酸锂LiMn2O4和实施例2制备的磷酸锰铁锂LiMn 0.6Fe 0.4PO 4两种物质的混合物作为锂离子电池正极片的活性材料，其中，尖晶石锰酸锂材料占正极活性材料的比例为80％，磷酸锰铁锂材料占20％。
将上述正极活性材料与导电剂和粘结剂混合，制成正极浆料。浆料中固体物质的比例，活性材料占比为97.2％，导电剂(导电炭黑、导电石墨、导电碳纳米管、石墨烯)占比为1.7％，粘结剂(聚偏氟乙烯)占比为1.1％。调节溶剂N-甲基吡咯烷酮的含量，使浆料固含量为75％左右。将搅拌均匀后的浆料分别涂覆在集流体铝箔表面，干燥后经辊压和切片，获得正极极片。
采用上述正极极片组装成的圆柱全电池，进行0.5C充1C放循环性能测试。圆柱电池型号为R34235，直径34mm，高度235mm。
对比例1
采用尖晶石锰酸锂LiMn 2O 4和传统液相法制备的磷酸锰铁锂LiMn 0.6Fe 0.4PO 4两种物质的混合物作为锂离子电池正极片的活性材料，作为对比样，尖晶石锰酸锂材料占正极活性材料的比例为80％，磷酸锰铁锂材料占20％。
按照实施例3同样的方法将上述正极活性材料制备成圆柱全电池。
如图5所示，按循环衰减至70％结束，由实施例2合成的磷酸锰铁锂组装的电池可循环1100次，能量密度为140Wh/kg。而由对比例1传统液相法制备的磷酸锰铁锂组装的电池可循环800次，能量密度为130Wh/kg。循环性能和能量密度的提升主要得益于材料的高压实密度。
将电池常温满电28天搁置，以搁置前的容量作为100％，搁置后的剩余容量比以及充放电恢复容量比，可以反应电池的自放电以及材料与电解液的副反应情况。测试了实施例3以及对比例1电池的常温满电28天搁置性能，结果如下表2所示。
表2
常温满电28天搁置 对比例1 实施例3
搁置前 100.00％ 100.00％
剩余 92.44％ 94.79％
恢复 96.35％ 98.05％
从表2中可以看到，对比例1电池搁置后的剩余容量比为92.44％，恢复容量比为96.35％；而实施例3电池搁置后的剩余容量比为94.79％，恢复容量比为98.05％，均优于对比例1电池，说明本发明合成的材料与电解液副反应少，这主要得益于实施例的材料的比表面积较小。
实施例4
将工业级MnSO 4·H 2O作为锰源，使用砂磨机砂磨至微米级尺寸后，加热至150℃，硫酸锰失去结晶水，随后加热至900℃热分解生成磷酸锰锂前驱体Mn 3O 4。总反应方程式为：
3MnSO 4·H 2O→Mn 3O 4+3SO 2↑+3H 2O↑。
将Mn 3O 4、碳酸锂、磷酸二氢铵固相混合砂磨，600℃高温固相烧结，获得磷酸锰锂LiMnPO 4。反应方程式为：
4Mn 3O 4+6Li 2CO 3+12NH 4H 2PO 4→12LiMnPO 4+6CO 2↑+12NH 3↑+12H 2O↑+5O 2↑。
实施例5
将工业级FeSO 4·7H 2O作为铁源，使用砂磨机砂磨至微米级尺寸后，加热至70～98℃，硫酸铁开始失去结晶水变成FeSO 4·4H 2O，继续加热，从86～159℃继续失去结晶水变成FeSO 4·H 2O，最终在227～283℃完全失去结晶水变成FeSO 4，300℃后FeSO 4开始熔融准备热分解，随后加热至653～716℃热分解生成磷酸铁锂前驱体Fe 2O 3。总反应方程式为：
4FeSO 4·7H 2O→2Fe 2O 3+4SO 2↑+28H 2O↑+O 2↑。
将Fe 2O 3、碳酸锂、磷酸二氢铵固相混合砂磨，700℃高温固相烧结，获得磷酸铁锂LiFePO 4。反应方程式为：
Fe 2O 3+Li 2CO 3+2NH 4H 2PO 4→2LiFePO 4+CO 2↑+2NH 3↑+2H 2O↑+O 2↑。
实施例6
将工业级FeSO 4·7H 2O作为铁源，使用砂磨机砂磨至微米级尺寸后，加热至200℃，硫酸铁失去结晶水，随后加热至1000℃热分解生成磷酸锰铁锂前驱体Fe 2O 3。总反应方程式为：
4FeSO 4·7H 2O→2Fe 2O 3+4SO 2↑+28H 2O↑+O 2↑。
将Fe 2O 3、碳酸锂、磷酸二氢锰、Mn 2O 3固相混合砂磨，700℃高温固相烧结，获得磷酸锰铁锂LiFeMnPO 4。反应方程式为：
2Mn 2O 3+8Fe 2O 3+20Li 2CO 3+20Mn(H 2PO 4) 2·2H 2O→40LiMn 0.6Fe 0.4PO 4+20CO 2↑+80H 2O↑+5O 2↑。
实施例7
将工业级MnSO 4·H 2O作为锰源，使用砂磨机砂磨至微米级尺寸后，加热至150℃，硫酸锰失去结晶水，随后加热至900℃热分解生成磷酸锰铁锂前驱体Mn 3O 4。总反应方程式为：3MnSO 4·H 2O→Mn 3O 4+3SO 2↑+3H 2O↑。
将Mn 3O 4、碳酸锂、磷酸铁、磷酸二氢铵固相混合砂磨，600℃高温固相烧结，获得磷酸锰铁锂LiMn 0.6Fe 0.4PO 4。反应方程式为：
6NH 4H 2PO 4+2Mn 3O 4+5Li 2CO 3+4FePO 4·2H 2O→10LiMn 0.6Fe 0.4PO 4+5CO 2↑+17H 2O↑+2O 2↑+6NH 3↑。
以上所述实施例仅是为充分说明本发明而所举的较佳的实施例，本发明的保护范围不限于此。本技术领域的技术人员在本发明基础上所作的等同替代或变换，均在本发明的保护范围之内。本发明的保护范围以权利要求书为准。

Claims (10)

  1. 一种磷酸锰铁锂的制备方法，其特征在于，包括以下步骤：
    S1.将锰源和/或铁源固相混合，得到第一混合物；
    S2.将所述第一混合物于300～1200℃下进行固相烧结，获得锰铁氧化物(Mn xFe 1-x-y) mO n；
    S3.将所述锰铁氧化物(Mn xFe 1-x-y) mO n与锂源、磷源以及可选的锰源和/或铁源进行固相混合，得到第二混合物；
    S4.将所述第二混合物于350～900℃下进行固相烧结，得到磷酸锰铁锂LiMn xFe 1-x-yPO 4；
    其中，0≤x≤1，0≤y≤1。
  2. 根据权利要求1所述的一种磷酸锰铁锂的制备方法，其特征在于，所述锰源为含有结晶水或不含有结晶水的硫酸锰、碳酸锰、醋酸锰、磷酸锰、硝酸锰、草酸锰、柠檬酸锰中的一种或多种。
  3. 根据权利要求1所述的一种磷酸锰铁锂的制备方法，其特征在于，所述铁源为含有结晶水或不含有结晶水的硫酸亚铁、碳酸亚铁、醋酸亚铁、磷酸亚铁、硝酸亚铁、草酸亚铁、柠檬酸亚铁、硫酸铁、碳酸铁、醋酸铁、磷酸铁、硝酸铁、草酸铁、柠檬酸铁中的一种或多种。
  4. 根据权利要求1所述的一种磷酸锰铁锂的制备方法，其特征在于，所述锂源为碳酸锂、氢氧化锂、磷酸锂、草酸锂、醋酸锂、硫酸锂、硝酸锂、氯化锂中的一种或多种。
  5. 根据权利要求1所述的一种磷酸锰铁锂的制备方法，其特征在于，所述磷源为磷酸二氢铵、磷酸氢二铵、磷酸二氢钠、磷酸氢二钠、三聚磷酸钠、磷酸、磷酸钙、磷酸酯、磷酸二氢锂、磷酸铁、磷酸锂、磷酸二氢锂、磷酸锰中的一种或多种。
  6. 根据权利要求1所述的一种磷酸锰铁锂的制备方法，其特征在于，步骤S1和S3中，固相混合时还加入了碳源、M源、N源中的一种或多种；经过步骤S2和S4的固相烧结后，分别得到锰铁氧化物(Mn xFe 1-x-yM y) mO nN z/C和磷酸锰铁锂LiMn xFe 1-x-yM yPO 4-zN z/C；
    其中，所述M源为掺杂阳离子源，所述N源为掺杂阴离子源；0≤x≤1，0≤y≤1，0≤z≤0.1，1：3.5≤m：(n+z)≤1:1。
  7. 根据权利要求6所述的一种磷酸锰铁锂的制备方法，其特征在于，所述碳源为蔗糖、葡萄糖、果糖、柠檬酸、酚醛树脂、聚乙烯醇、聚乙二醇、淀粉、炭黑、乙炔黑、石墨、石墨烯、导电碳管中的一种或多种。
  8. 根据权利要求6所述的一种磷酸锰铁锂的制备方法，其特征在于，所述阳离子源包括铝、镁、镍、钴、钛、铜、钙、铌、铬、锌、镧、锑、碲、锶、钨、铟、钇中的一种或多种，所述阴离子源包括氟或/和硫。
  9. 一种正极材料，其特征在于，所述正极材料是由橄榄石结构的磷酸锰铁锂材料、层状多元酸锂、尖晶石型锰酸锂、层状富锰锂基中的一种或多种混合后得到的；其中，所述橄榄石结构的磷酸锰铁锂材料、层状多元酸锂、尖晶石型锰酸锂、层状富锰锂基材料是由权利要求1～8任一项所述的方法制备得到的。
  10. 一种锂离子电池，包括正极片、负极片、电解液和隔膜，其特征在于，所述正极片是由权利要求9所述的正极材料制备而成的。
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