WO2023023894A1 - 碳包覆的磷酸铁锂正极活性材料、其制备方法、包含其的正极极片以及锂离子电池 - Google Patents

碳包覆的磷酸铁锂正极活性材料、其制备方法、包含其的正极极片以及锂离子电池 Download PDF

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WO2023023894A1
WO2023023894A1 PCT/CN2021/114071 CN2021114071W WO2023023894A1 WO 2023023894 A1 WO2023023894 A1 WO 2023023894A1 CN 2021114071 W CN2021114071 W CN 2021114071W WO 2023023894 A1 WO2023023894 A1 WO 2023023894A1
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carbon
iron phosphate
positive electrode
lithium iron
active material
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PCT/CN2021/114071
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English (en)
French (fr)
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刘宏宇
别常峰
冷雪
柳娜
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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 PCT/CN2021/114071 priority Critical patent/WO2023023894A1/zh
Priority to CN202180083427.0A priority patent/CN116601798A/zh
Priority to JP2023501317A priority patent/JP2023538479A/ja
Priority to EP21927078.2A priority patent/EP4167314A4/en
Priority to KR1020237000446A priority patent/KR102593317B1/ko
Priority to US17/938,930 priority patent/US11721804B2/en
Publication of WO2023023894A1 publication Critical patent/WO2023023894A1/zh

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    • H01M4/139—Processes of manufacture
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    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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    • H01M2004/028—Positive electrodes
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    • 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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    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of electrochemistry, and in particular to a carbon-coated lithium iron phosphate positive electrode active material, a preparation method thereof, a positive electrode sheet containing the same, a lithium ion battery, a battery module, a battery pack and an electrical device.
  • lithium-ion batteries are widely used in various large-scale power devices, energy storage systems and various consumer products due to their excellent electrochemical performance, no memory effect, and low environmental pollution. Widely used in pure electric vehicles, hybrid electric vehicles and other new energy vehicles.
  • lithium iron phosphate is one of the most widely used positive electrode active materials in current industrial lithium-ion batteries.
  • the gram capacity of lithium iron phosphate is lower than that of ternary materials, in recent years people have mainly focused on improving the capacity of lithium iron phosphate as a research and development hotspot.
  • improving the capacity performance of lithium iron phosphate will inevitably lose other battery performances, such as cycle performance and processing performance.
  • the purpose of this application is to provide a carbon-coated lithium iron phosphate positive electrode active material, which has high capacity, high compaction density, and easy dehydration of the pole piece, so that the lithium-ion battery has both excellent Excellent energy density, cycle performance and excellent processing performance, and can significantly improve the production efficiency of the battery and reduce the production cost of the battery.
  • the first aspect of the present application provides a carbon-coated lithium iron phosphate positive electrode active material
  • the positive electrode active material includes a lithium iron phosphate substrate and a carbon coating layer on the surface of the substrate, the lithium iron phosphate substrate It has the general structural formula LiFe 1-a M a PO 4 , wherein M is selected from one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, 0 ⁇ a ⁇ 0.01, ;
  • the carbon coating factor of the carbon-coated lithium iron phosphate material Wherein, BET1 is the specific surface area of the mesopore and macroporous structure of the carbon-coated lithium iron phosphate, BET2 is the total specific surface area of the carbon-coated lithium iron phosphate, and ⁇ satisfies 0.81 ⁇ 0.95.
  • the ⁇ may be 0.85 ⁇ 0.93, and further may be 0.88 ⁇ 0.92.
  • the value range of the BET1 is 5.5-9.5 m 2 /g, and the value range of the BET2 is 6.0-11.5 m 2 /g.
  • the ratio H/D of the thickness H of the carbon coating layer to the average particle diameter D of the carbon-coated lithium iron phosphate is 0.01 ⁇ 0.04.
  • the carbon component in the carbon coating layer accounts for 0.7% to 1.3% of the total mass of the lithium iron phosphate positive electrode active material, optionally 0.9% to 1.3%, and more preferably 0.9% to 1.1% %.
  • the volume average particle size Dv50 of the carbon-coated lithium iron phosphate satisfies 840nm ⁇ Dv50 ⁇ 3570nm, optionally 1170nm ⁇ Dv50 ⁇ 1820nm.
  • the compacted density of the carbon-coated lithium iron phosphate powder is not less than 2.4 g/cm 3 , may be 2.5 g/cm 3 , and may be 2.6 g/cm 3 .
  • the degree of graphitization of the carbon-coated lithium iron phosphate is 0.15-0.32, optionally 0.19-0.26.
  • the powder resistivity of the carbon-coated lithium iron phosphate is not more than 60 ⁇ m, optionally not more than 30 ⁇ m, more preferably not more than 20 ⁇ m.
  • the second aspect of the present application provides a method for preparing the positive electrode active material described in the first aspect of the present application, the method comprising the following steps:
  • the positive electrode active material includes a lithium iron phosphate substrate and a carbon coating layer on the surface of the substrate, and the lithium iron phosphate
  • the material has the general structure LiFe 1-a M a PO 4 , where M is selected from more than one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, 0 ⁇ a ⁇ 0.01 ;
  • the carbon coating factor of the carbon-coated lithium iron phosphate material Wherein, BET1 is the specific surface area of the mesopore and macroporous structure of the carbon-coated lithium iron phosphate, BET2 is the total specific surface area of the carbon-coated lithium iron phosphate, and ⁇ satisfies 0.81 ⁇ 0.95.
  • the preparation method of the positive electrode active material comprises the following steps:
  • a lithium iron phosphate substrate is provided, wherein raw materials of Fe source, Li source, M source and/or P source and reagents as reducing agent and carbon source are mixed, and the resulting mixture is treated at high temperature under an inert atmosphere, Obtain a lithium iron phosphate substrate;
  • the Fe source may be one or more selected from FeSO 4 , FePO 4 , FeCl 2 , FeC 2 O 4 , and Fe 2 O 3 .
  • the Li source may be one or more selected from Li 2 CO 3 , LiH 2 PO 4 , and Li 3 PO 4 .
  • the P source may be one or more selected from NH 4 H 2 PO 4 and H 3 PO 4 .
  • the M source contains an element selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, or Ti.
  • the reducing agent and carbon source in step (1) may be one or more selected from C 2 H 2 , CH 4 , glucose, polyethylene glycol, sucrose, starch, H 2 , and CO.
  • the amount of the reagent used as the reducing agent and carbon source accounts for 4% to 8% of the total mass of the raw material, optionally 6%.
  • the carbon source can be materials such as acetone.
  • the treatment temperature in step (1) or (2) can vary within a wide range, for example, 500-800°C.
  • the third aspect of the present application provides a positive electrode sheet of a lithium ion battery, including a positive electrode current collector and a positive electrode active material disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material is the one described in the first aspect of the present application.
  • the saturated water content of the positive pole piece at 25°C and 45% relative humidity is no more than 500ppm.
  • the fourth aspect of the present application provides a lithium-ion battery
  • the lithium-ion battery includes a positive electrode sheet and a negative electrode sheet
  • the positive electrode sheet includes a positive electrode current collector and a positive active electrode disposed on at least one surface of the positive electrode current collector Material
  • the positive electrode active material is the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared by the method described in the second aspect of the present application
  • the positive electrode sheet is at 25°C and a relative humidity of 45%.
  • the saturated water content under the condition does not exceed 500ppm.
  • the pole piece compacted density of the positive pole piece is not lower than 2.35g/cm 3
  • the pole piece compacted density of the negative pole piece is not lower than 1.6g/cm 3
  • the negative pole piece The negative active material in the sheet is graphite coated with amorphous carbon.
  • a fifth aspect of the present application provides a battery module, including the lithium-ion battery of the fourth aspect of the present application.
  • the battery module can be prepared using methods known in the prior art for preparing battery modules.
  • the sixth aspect of the present application provides a battery pack, including the lithium-ion battery of the fourth aspect of the present application or the battery module of the fifth aspect of the present application.
  • the battery pack can be prepared using methods known in the prior art for preparing battery packs.
  • the seventh aspect of the present application provides an electric device, including the lithium-ion battery of the fourth aspect of the application, the battery module of the fifth aspect of the application, or the battery pack of the fifth aspect of the application, the lithium-ion battery or the The battery module or the battery pack is used as a power source of the electric device or an energy storage unit of the electric device.
  • the preparation of the electric device can adopt the methods known in the prior art for the preparation of the electric device.
  • the present application obtains the positive electrode active material of the present application by controlling the relative ratio of the specific surface area of the carbon structure of different microscopic forms in the surface layer of the carbon-coated lithium iron phosphate material.
  • the carbon-coated lithium iron phosphate material of the present application has a carbon coating factor ⁇ , and when the ⁇ satisfies 0.81 ⁇ 0.95, the carbon-coated lithium iron phosphate has high-quality carbon coating, which can significantly improve the difficulty of pole pieces.
  • the bottleneck of the dehydration process, the prepared lithium-ion battery has excellent energy density, cycle performance and excellent processability.
  • the battery module, battery pack and electrical device of the present application include the lithium-ion battery provided by the present application, and thus have at least the same advantages as the lithium-ion battery.
  • FIG. 1 is a TEM image of a carbon-coated lithium iron phosphate cathode active material under different magnifications according to an embodiment of the present application.
  • FIG. 2 is a schematic diagram of a lithium-ion battery according to an embodiment of the present application.
  • FIG. 3 is an exploded view of the lithium ion battery according to one embodiment of the present application shown in FIG. 2 .
  • FIG. 4 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG. 5 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 6 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG. 5 .
  • FIG. 7 is a schematic diagram of an electrical device according to an embodiment of the present application.
  • any lower limit can be combined with any upper limit to form the scope of the application; and any lower limit can be combined with any other lower limit to form the scope of the application, and likewise any upper limit can be combined with any other upper limit to form the scope of the application.
  • each individually disclosed point or individual value may by itself serve as a lower limit or upper limit in combination with any other point or single value or with other lower or upper limits to form the scope of the present application.
  • carbon coating layer refers to the part coated on the lithium iron phosphate substrate, which may but not necessarily completely cover the lithium iron phosphate substrate, and the use of “carbon coating layer” It is for ease of description only and is not intended to limit the application. Likewise, the term “thickness of the carbon coating layer” refers to the maximum thickness of the portion coated on the lithium iron phosphate substrate.
  • the inventors of the present application have found through research on the lithium iron phosphate positive electrode active material that the low electronic conductivity and low ion conductivity of the pure phase lithium iron phosphate positive electrode active material (without carbon) will deteriorate the capacity of the lithium iron phosphate positive electrode active material. , so that the energy density of lithium-ion batteries using lithium iron phosphate as the positive electrode active material is quite different from that of ternary lithium-ion batteries.
  • the material can be treated with carbon coating and nanometerization.
  • the inventors of the present application have found that both the carbon coating treatment and the nanonization treatment will inevitably deteriorate the performance of other aspects of the battery, especially the cycle performance and processing performance of the battery.
  • microporous structures Network structure with pores less than 2nm
  • mesoporous structure network structure with pores of 2nm-50nm
  • macroporous structure network structure with pores exceeding 50nm
  • other structures without obvious pores such as layered carbon structure wait.
  • the inventors also found in the actual operation process that the nano-processing will also increase the difficulty of dehydration of the pole piece, thereby deteriorating the cycle performance of the battery.
  • nanonization treatment will also reduce the powder compaction density of lithium iron phosphate cathode active material, thereby greatly reducing the energy density contributed by improving electronic conductance and ion conductance.
  • lithium iron phosphate positive electrode active materials have high capacity, high compaction density, and easy dehydration of the pole pieces, so that lithium-ion batteries have both excellent energy density and cycle life. Performance and excellent processing performance, and can significantly improve the production efficiency of the battery and reduce the production cost of the battery.
  • the present application provides a carbon-coated lithium iron phosphate positive electrode active material.
  • the positive electrode active material includes a lithium iron phosphate substrate and a carbon coating layer on the surface of the substrate.
  • the lithium iron phosphate substrate has a general structure.
  • Formula LiFe 1-a M a PO 4 wherein M is selected from one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, 0 ⁇ a ⁇ 0.01.
  • BET1 is the specific surface area of the mesopore and macroporous structure of the carbon-coated lithium iron phosphate
  • BET2 is the total specific surface area of the carbon-coated lithium iron phosphate
  • ⁇ satisfies 0.81 ⁇ 0.95.
  • the substrate has the general structure LiFe 1-a M a PO 4 , where M is selected from one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, 0 ⁇ a ⁇ 0.01.
  • M element is beneficial to improve the structural stability of the lithium iron phosphate substrate and prevent the structure collapse of the lithium iron phosphate positive electrode active material after several charge-discharge cycles.
  • the carbon coating can improve the electronic conductivity and ionic conductivity, and increase the energy density of the battery.
  • the carbon coating layer as a porous structure composed of carbon, will significantly increase the overall specific surface energy of the lithium iron phosphate positive electrode active material, thereby significantly increasing the water absorption capacity of the lithium iron phosphate positive electrode active material.
  • the inventors of the present application have found through a large number of experimental verifications that: when the carbon-coated lithium iron phosphate material satisfies When 0.81 ⁇ 0.95, the carbon-coated lithium iron phosphate has a reasonable specific surface energy while satisfying high-capacity performance, thereby significantly reducing the carbon-coated lithium iron phosphate positive electrode active material.
  • the overall specific surface energy of the pole piece can significantly improve the dehydration efficiency of the pole piece, and can significantly improve the process bottleneck that the pole piece is not easy to dehydrate. Therefore, the battery prepared from the carbon-coated lithium iron phosphate positive electrode active material with 0.81 ⁇ 0.95 has both excellent energy density, cycle performance and excellent processability.
  • the carbon coating factor ⁇ actually represents the relative proportion of the specific surface area contributed by the pore structure of different microscopic forms in the carbon-coated lithium iron phosphate material, which can reflect the micropores that contribute a lot to the surface energy
  • the proportion of the specific surface area of the structure to the specific surface area contributed by all pores reflects the effectiveness of the lithium iron phosphate carbon layer coating.
  • the carbon coating factor ⁇ is in the range of 0.85 ⁇ 0.93, the relative proportion of pores with different microscopic shapes in the surface layer is in a more reasonable range, and lithium iron phosphate has high quality
  • the carbon coating is beneficial to the capacity of the lithium iron phosphate positive electrode active material and significantly reduces the water absorption of the electrode sheet.
  • the prepared lithium-ion battery has excellent energy density, cycle performance and excellent processability.
  • the range of ⁇ is 0.88 ⁇ 0.92, and the electrochemical performance and processing performance of the lithium-ion battery are better.
  • the present application obtains the carbon-coated lithium iron phosphate positive electrode active material of the present application by controlling the relative ratio of the specific surface area of carbon structures with different microscopic morphologies in the surface layer of the carbon-coated lithium iron phosphate material.
  • the carbon coating factor ⁇ of the carbon-coated lithium iron phosphate material of the present application satisfies 0.81 ⁇ 0.95
  • the lithium iron phosphate material has high-quality carbon coating, which is conducive to significantly improving the dehydration efficiency of the pole piece, and the prepared lithium Ion batteries have excellent energy density, cycle performance and excellent processability. See Table 1 for details.
  • the value of ⁇ can be 0.811, 0.836, 0.862, 0.894, 0.915, 0.922, 0.928, 0.939, or its value is a numerical range composed of any two point values mentioned above.
  • the value range of BET1 is 5.5-9.5m 2 /g, and the value range of BET2 is 6.0-11.5m 2 /g.
  • the relative proportion of carbon structures with different microscopic forms in the surface layer In a more reasonable range, the pole piece is less likely to absorb water, which is more conducive to improving the energy density and cycle performance of the battery.
  • the BET1 may be 9.08, 8.86, 7.05, 6.68, 6.93, 6.46, 5.95, 5.82, or its value is a numerical range composed of any two point values mentioned above.
  • the BET2 can be 11.2, 10.6, 8.19, 7.48, 7.16, 7.01, 6.40, 6.20, or its value is a value range composed of any two point values mentioned above.
  • the ratio H/D of the thickness H of the carbon coating layer to the average particle diameter D of the carbon-coated lithium iron phosphate is 0.01-0.04 .
  • the ratio of the thickness of the carbon coating layer to the average particle size of the carbon-coated lithium iron phosphate is 0.01 to 0.04, the integrity and electronic conductivity of the carbon coating layer on the surface of the lithium iron phosphate material are better, and the material has a higher High electronic conductivity, and because the ratio of the thickness of the carbon coating layer to the overall particle size is within a reasonable range, the lithium iron phosphate material has a high powder compaction density, so that the energy density and cycle performance of the lithium-ion battery are relatively high. good.
  • a reasonable carbon coating thickness will also reduce the dehydration difficulty of the pole piece made of lithium iron phosphate material, which is beneficial to improve the processing performance.
  • the carbon component accounts for 0.7% to 1.3% of the total mass of the carbon-coated lithium iron phosphate, optionally 0.9% to 1.3%, and more preferably 0.8% to 1.1%. .
  • the carbon content is too low, the integrity of the carbon coating layer on the surface of the lithium iron phosphate material is poor, and the material kinetics is poor, resulting in a low energy density of the battery; while the carbon content is too high, it will hinder the growth of single particles during the sintering process. Large, so that the lithium iron phosphate material tends to form secondary particles formed by many small particles.
  • the carbon component does not contribute to the battery capacity, which also makes the energy density of lithium-ion batteries lower.
  • the carbon content satisfies 0.7% ⁇ C ⁇ 1.3%; optionally 0.9% ⁇ C ⁇ 1.3%; more optionally 0.8% ⁇ C ⁇ 1.1 %. See Table 2 for details.
  • the content of the carbon component can be 0.70%, 0.82%, 0.95%, 1.12%, 1.3%, or its value is any two points above Composed of numeric ranges.
  • the volume average particle diameter Dv50 of the carbon-coated lithium iron phosphate of the present application satisfies 840nm ⁇ Dv50 ⁇ 3570nm, optionally 1170nm ⁇ Dv50 ⁇ 1820nm.
  • the material in order to solve the problem of poor electronic conductivity and ionic conductivity of the lithium iron phosphate cathode active material, the material can be nanosized.
  • nano-processing will also increase the surface energy of the lithium iron phosphate positive electrode active material, increase the water absorption capacity of the pole piece, cause dehydration difficulties, and eventually deteriorate the battery cycle performance and processability.
  • nanonization treatment will also reduce the powder compaction density of lithium iron phosphate cathode active material, thereby greatly reducing the energy density contributed by improving electronic conductance and ion conductance.
  • the carbon-coated lithium iron phosphate when the carbon-coated lithium iron phosphate further satisfies the volume average particle size of 840nm ⁇ Dv50 ⁇ 3570nm, and can be selected as 1170nm ⁇ Dv50 ⁇ 1820nm, the carbon-coated The compacted density of lithium iron phosphate powder can be up to 2.64g/cm 3 , and the compacted density of pole piece can be up to 2.64g/cm 3 .
  • the volume average particle diameter Dv50 increases, both the compacted density of the powder and the compacted density of the electrode sheet show a downward trend, and the energy density of the battery gradually decreases.
  • the dehydration efficiency of the pole piece is improved, and the cycle performance of the corresponding lithium-ion battery is improved. See Table 4 for details.
  • the Dv50 may be 840, 1170, 1430, 1820, 3520, or its numerical value is a numerical range composed of any two above-mentioned point values.
  • the degree of graphitization of the carbon-coated lithium iron phosphate of the present application is 0.15-0.32.
  • the carbon coating factor of the carbon-coated lithium iron phosphate material in this application is 0.81 ⁇ 0.95
  • the graphitization degree of the carbon-coated lithium iron phosphate is 0.15-0.32, it is not only beneficial to the capacity of the lithium iron phosphate material, but also It is beneficial to improve the powder resistivity of the lithium iron phosphate material and increase the energy density of the battery. See Table 5 for details.
  • the "degree of graphitization" of carbon-coated lithium iron phosphate refers to the degree of graphitization of the carbon component, which reflects the completeness of the graphite crystal structure in the carbon-coated lithium iron phosphate of the present application, especially in the carbon coating layer.
  • the degree that is, the regularity of the arrangement of carbon atoms in the graphite structure.
  • the degree of graphitization may be 0.155, 0.197, 0.255, 0.245, 0.312, or its numerical value is a numerical range composed of any two above-mentioned point values.
  • the lithium iron phosphate substrate is doped with carbon, optionally 0.1% to 0.5% of carbon, based on the mass of the lithium iron phosphate substrate.
  • the powder resistivity of the carbon-coated lithium iron phosphate of the present application is not more than 60 ⁇ m, optionally not more than 30 ⁇ m, and more preferably not more than 20 ⁇ m.
  • the positive electrode active material of the present application also includes other conventional positive electrode active materials in the field, for example, lithium-containing phosphates of other olivine structures, lithium Transition metal oxides and their respective modifying compounds.
  • the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials of batteries can also be used. These positive electrode active materials may be used alone or in combination of two or more.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxides (such as LiNiO 2 ), lithium manganese oxides (such as LiMnO 2 , LiMn2O 4 ), lithium nickel cobalt oxides (such as LiMnO 2 , LiMn2O 4 ), lithium nickel cobalt oxides oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (also abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (also abbreviated as NCM211), LiNi0.6Co0.2Mn0.2O2 (also abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also may be abbreviated as NCM
  • lithium-containing phosphates of other olivine structures may include But not limited to at least one of lithium manganese phosphate (such as LiMnPO 4 ), composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and composite material of lithium manganese iron phosphate and carbon.
  • lithium manganese phosphate such as LiMnPO 4
  • composite material of lithium manganese phosphate and carbon lithium manganese iron phosphate
  • composite material of lithium manganese iron phosphate and carbon may include but not limited to at least one of lithium manganese phosphate (such as LiMnPO 4 ), composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and composite material of lithium manganese iron phosphate and carbon.
  • the present application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode active material disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material is the carbon-coated lithium iron phosphate according to one aspect of the present application.
  • the lithium ion battery of the present application includes a positive pole piece and a negative pole piece, and the positive pole piece comprises the aforementioned carbon-coated lithium iron phosphate positive electrode active material of the application, and the positive pole piece is at 25° C., 45% relative
  • the saturated water content under humidity is not more than 500ppm.
  • the lithium iron phosphate positive electrode active material coated with conventional carbon has a saturated water content of 1000ppm at 25°C and 45% relative humidity, which is significantly higher than that of carbon in this application. The water absorption of the electrode sheet prepared by the coated lithium iron phosphate positive electrode active material.
  • the pole piece compacted density of the positive pole piece of the present application can be up to 2.65g/cm 3 , and the pole piece compacted density of the negative pole piece is not less than 1.6g/cm 3 ,
  • the negative electrode active material in the negative electrode sheet is graphite covered by amorphous carbon.
  • a graphite negative electrode with a capacity of not less than 350mAh/g and a compacted density of the pole piece not lower than 1.6g/ cm3 is provided.
  • the surface has an amorphous carbon coating layer, which has the ability to intercalate lithium ions and a higher charging window to match the positive electrode of the present application.
  • the carbon-coated lithium iron phosphate positive electrode active material accounts for 90%-98% of the mass of the entire positive electrode film layer.
  • the carbon-coated lithium iron phosphate positive electrode active material of the present application has a reasonable specific surface area contributed by carbon structures with different microscopic forms, so it can bond more lithium iron phosphate under the same binder content.
  • Positive active material When the positive electrode film layer is matched with 2% PVDF, the coating amount is ⁇ 300mg/mm 2 , and the mass production coating speed can reach 60m/min, which significantly improves the processing efficiency in actual operation, and the energy density of the battery is also significantly improved.
  • the positive electrode sheet includes a positive electrode collector and a positive electrode material arranged on at least one surface of the positive electrode collector.
  • the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode material is disposed on any one or both of the two opposing surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil can be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector can be formed by forming metal materials (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalic acid Ethylene glycol ester (PET), polybutylene terephthalate (PBT), 1,3-propane sultone (PS), polyethylene (PE) and other substrates), but this Applications are not limited to these materials.
  • PP polypropylene
  • PET polyethylene terephthalic acid Ethylene glycol ester
  • PBT polybutylene terephthalate
  • PS 1,3-propane sultone
  • PE polyethylene
  • the positive electrode material also optionally includes a conductive agent.
  • a conductive agent there is no specific limitation on the type of conductive agent, which can be selected by those skilled in the art according to actual needs.
  • the conductive agent used for the positive electrode material may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode sheet can be prepared according to methods known in the art.
  • the positive electrode active material, conductive agent and binder of the present application can be dispersed in a solvent (such as N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode assembly On the fluid, after drying, cold pressing and other processes, the positive electrode sheet is obtained.
  • NMP N-methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposing surfaces of the negative electrode current collector.
  • the compacted density of the positive pole piece of the present application is not lower than 2.35g/cm 3
  • the compacted density of the negative pole piece is not lower than 1.6g/cm 3
  • the negative electrode active material in the negative electrode sheet is graphite covered by amorphous carbon.
  • a graphite negative electrode with a capacity of not less than 350mAh/g and a compacted density of the pole piece not lower than 1.6g/ cm3 is provided. It has an amorphous carbon coating layer, and has the ability of lithium ion intercalation and high charging window matched with the positive electrode of this application.
  • the negative electrode current collector can be a metal foil or a composite current collector.
  • copper foil can be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • Composite current collectors can be formed by metal materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyethylene terephthalic acid Ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) and other substrates), but the present application is not limited to these Material.
  • PP polypropylene
  • PET polyethylene terephthalic acid Ethylene glycol ester
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode film layer usually includes negative electrode active materials and optional binders, optional conductive agents and other optional additives, and is usually formed by coating and drying negative electrode slurry of.
  • Negative electrode slurry is usually formed by dispersing the negative electrode active material and optional conductive agent and binder in a solvent and stirring evenly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water.
  • the conductive agent may be selected from one or more 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 commonly used negative electrode active materials in addition to the negative electrode active material.
  • other commonly used negative electrode active materials artificial graphite, natural graphite, Soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate, etc.
  • the silicon-based material can be selected from more than one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • the tin-based material can be selected from more than one of elemental tin, tin oxide compounds and tin alloys.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the present application has no specific limitation on the type of electrolyte, which can be selected according to requirements.
  • the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (ie, electrolyte solution).
  • the electrolyte is an electrolytic solution.
  • the electrolytic solution includes an electrolytic salt and a solvent.
  • the electrolyte salt may be selected from lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), difluorosulfonyl Lithium amide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium difluorooxalate borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorooxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium perchlorate
  • the solvent may be 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), Fluoroethylene Carbonate (FEC), Methyl Formate (MF), Methyl Acetate Ester (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), methyl ethyl sulfone (EMS) and diethyl s
  • additives may optionally be included in the electrolyte.
  • additives can include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of batteries, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and battery low-temperature performance. additives, etc.
  • the electrolytic solution of the present application has an electrolytic conductivity not lower than 13 mS/cm, so as to be matched with the positive electrode sheet and the negative electrode sheet of the present application.
  • the separator is arranged between the positive pole piece and the negative pole piece to play the role of isolation.
  • the present application has no particular limitation on the type of the isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation film can be selected from more than one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.
  • the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process, and the positive pole piece includes the carbon-coated lithium iron phosphate of the present application.
  • a lithium ion battery can include an outer packaging.
  • the outer package can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the lithium-ion battery can be a hard case, such as a hard plastic case, aluminum case, steel case, and the like.
  • the outer packaging of the lithium-ion battery can also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of plastic include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • FIG. 2 shows a lithium-ion battery 5 with a square structure as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity.
  • the positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the accommodating cavity. Electrolyte is infiltrated in the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the lithium-ion battery 5 can be one or more, and those skilled in the art can select according to specific requirements.
  • lithium-ion batteries can be assembled into a battery module, and the number of lithium-ion batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.
  • FIG. 4 is a battery module 4 as an example.
  • a plurality of lithium-ion batteries 5 can be arranged sequentially along the length direction of the battery module 4 .
  • the plurality of lithium ion batteries 5 can be fixed by fasteners.
  • the battery module 4 may also include a housing with an accommodating space, and a plurality of lithium ion batteries 5 are accommodated in the accommodating space.
  • the above battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be selected by those skilled in the art according to the application and capacity of the battery pack.
  • 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 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electric device, which includes more than one of the lithium-ion battery, battery module, or battery pack provided in the present application.
  • the lithium-ion battery, battery module, or battery pack can be used as a power source for the device, or as an energy storage unit for the device.
  • the device can be, but not limited to, a mobile device (such as a mobile phone, a notebook 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 vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • a lithium-ion battery, a battery module or a battery pack can be selected according to its use requirements.
  • Figure 7 is an example device.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • battery packs or battery modules can be employed.
  • a device may be a cell phone, tablet, laptop, or the like.
  • the device is usually required to be light and thin, and a lithium-ion battery can be used as a power source.
  • lithium iron phosphate substrate Iron phosphate, lithium carbonate, and titanium oxide are used as raw materials, and iron phosphate , lithium carbonate , titanium oxide, and add glucose and polyethylene glycol (the mass ratio of glucose and polyethylene glycol is 1:1, and the carbon source charging amount accounts for 6% of raw material gross mass) as carbon source and reducing agent, then add Solvent water is wet-ground to obtain a mixed slurry; the obtained slurry is spray-dried, and then the dried product is put into a roller furnace for sintering at 500°C with air isolation for 20 hours, and cooled naturally until the material temperature is ⁇ 80°C.
  • the calcined material is obtained by crushing, screening and demagnetizing the calcined material to obtain the lithium iron phosphate base material LiFe 0.998 Ti 0.002 PO 4 , which is doped with about 0.3% carbon element.
  • Carbon coating put the above base material into a roller furnace and sinter it under nitrogen atmosphere, spray carbon source acetone solution in the sintering furnace at the same time, and sinter at a constant temperature of 770°C for 10h. After the material is naturally cooled to a temperature ⁇ 80° C., the material is discharged; after further pulverization by a jet mill, the carbon-coated lithium iron phosphate of Example 1-1 is obtained.
  • Negative electrode slurry was obtained as follows; the negative electrode slurry was evenly coated on a copper foil with a thickness of 8 ⁇ m; after drying, the negative electrode sheet was obtained by cold pressing and slitting, and the negative electrode sheet of Example 1-1 of the present application was obtained.
  • the "carbon coating" steps of Examples 1-3 are as follows: put the lithium iron phosphate base material of Examples 1-3 into a roller furnace with a nitrogen atmosphere for sintering, and spray acetone solution at the same time, and sinter at a constant temperature of 550°C for 10 hours. The material is naturally cooled to a temperature ⁇ 80°C and discharged. After being crushed and screened, the material is placed in a roller furnace and sprayed with acetone solution again, and sintered at a constant temperature of 770°C for 10 hours. After the material is naturally cooled to a temperature of ⁇ 80°C After discharge. The carbon-coated lithium iron phosphate of Example 1-3 was obtained after the second sintered product was pulverized by airflow.
  • the carbon source dosage is reduced to 4% of the total mass of raw materials, and in the "carbon coating” step, the constant temperature sintering temperature is 800°C and the constant temperature sintering time is 13h, other steps are the same as in Example 1-1 same.
  • the base material is doped with about 0.15% carbon element.
  • the carbon source dosage is 5% of the total mass of raw materials
  • the temperature of the first constant temperature sintering is 620°C (the time of constant temperature sintering is 12h)
  • the temperature of the second constant temperature sintering is Except for 820°C (constant temperature sintering time 12h), other steps are the same as in Example 2-5.
  • the carbon source dosage is 6% of the total mass of raw materials
  • the first constant temperature sintering temperature in the “carbon coating” step is 600°C (constant temperature sintering time 10h)
  • the second constant temperature sintering temperature is the same as in Example 3-1 except that the temperature is 780° C. (the sintering time at constant temperature is 10 h).
  • the first constant temperature sintering temperature in the "carbon coating” step is 600°C (constant temperature sintering time 10h) and the second constant temperature sintering temperature
  • the temperature is 780° C. (the constant temperature sintering time is 10 h).
  • the carbon source dosage is 3% of the total mass of raw materials
  • the temperature of the first constant temperature sintering is 650°C (the time of constant temperature sintering is 10h)
  • the temperature of the second constant temperature sintering is Other steps are the same as in Example 3-1 except that the temperature is 830°C (constant temperature sintering time 12h).
  • the carbon source dosage is 12% of the total mass of raw materials
  • the first constant temperature sintering temperature is 600°C (constant temperature sintering time 10h) and the second constant temperature sintering temperature Except for 780°C (constant temperature sintering time 10h), other steps are the same as Comparative Example 7.
  • Example 2 Except for the first constant temperature sintering temperature of 550°C (constant temperature sintering time 10h) and the second constant temperature sintering temperature of 790°C (constant temperature sintering time 15h) in the "carbon coating" step, other steps are the same as in Example 2-3 .
  • the volume average particle diameter Dv50 of the carbon-coated lithium iron phosphate cathode active material finally obtained in Example 4-1 was 530 nm.
  • the volume average particle diameter Dv50 of the carbon-coated lithium iron phosphate positive electrode active material obtained at last is 840nm, 1170nm, 1430nm, 1820nm, 3520nm, 5070nm respectively, by adjusting the classification frequency of the jet mill, the lithium iron phosphate with different Dv50 can be obtained Positive active material.
  • Example 1- 1 Except that in the "preparation of base material” step, the carbon source dosage is 8% of the total mass of raw materials, and the constant temperature sintering temperature in the "carbon coating” step is 750°C (constant temperature sintering time 10h), other steps are the same as in Example 1- 1 is the same.
  • the amount of carbon source is 6% of the total mass of raw materials
  • the temperature of the first constant temperature sintering in the step of “carbon coating” is 550°C (the time of constant temperature sintering is 10h)
  • the second constant temperature sintering Except that the temperature is 790°C (constant temperature sintering time 10h), other steps are the same as in Example 2-2.
  • the carbon source dosage is 5% of the total mass of raw materials
  • the first constant temperature sintering temperature in the "carbon coating” step is 600°C (constant temperature sintering time 10h)
  • the second constant temperature sintering Except that the temperature is 830°C (constant temperature sintering time 14h), other steps are the same as in Example 5-3.
  • the step of "preparation of base material” is the same as that of Comparative Example 7, except for the step of "carbon coating".
  • the specific "carbon coating” steps are as follows:
  • the specific surface area, the volume average particle diameter Dv50, the carbon content, the dehydration efficiency of the pole piece, the compacted density of the powder of the lithium iron phosphate positive electrode active material of the above examples and comparative examples, and the dehydration efficiency of the pole piece, the energy density of the battery, the energy density of the battery Please refer to Table 1 to Table 5 for specific data such as cycle retention rate.
  • the X-ray powder diffractometer used in this application is the X'pert PRO of the United States.
  • the detailed test process of average particle diameter D is as follows:
  • the lithium iron phosphate cathode active materials of all examples and comparative examples were tested with a ZEISS sigma300 scanning electron microscope, and then tested with reference to the standard JY/T010-1996 to observe the morphology of the samples.
  • the shape of the substrate lithium iron phosphate substrate in this application is not necessarily a perfect spherical shape, and may also be irregular, which is a primary particle. It should also be pointed out that the shape of the carbon-coated lithium iron phosphate cathode active material prepared in the present application is not necessarily spherical, and may also be random.
  • the lithium iron phosphate cathode active materials of all the examples and comparative examples were tested with a JEOL2010 transmission electron microscope.
  • the test standard is: GB/T 34002-2017.
  • the pole pieces of the example and the comparative example were cut into diaphragms with a length of 1000mm, and the pole pieces were rolled under a certain pressure. Due to the ductility of the aluminum foil, the length of the diaphragm was 1006mm. Then die-cut a small disc of 1540.25 mm 2 on the diaphragm, and measure the weight M and thickness L of the small disc. Die-cut the pure aluminum foil into small discs of 1540.25mm2 , weigh the mass M0 of the empty aluminum foil, then the compaction densities of the positive pole pieces corresponding to all the examples and all the comparative examples can be calculated by the following formula:
  • PD (M ⁇ M0)/1.54025/2/L.
  • the positive electrode active material in all above-mentioned examples and comparative examples is tested carbon content with infrared absorption method after burning with high-frequency induction furnace, and concrete test process is based on standard GB/T20123-2006/ISO 15350:2000 "the determination of the total carbon and sulfur content of iron and steel Infrared Absorption Method after Combustion in a High-Frequency Induction Furnace", it is conveniently measured by a carbon-sulfur analyzer, such as Dekai HCS infrared carbon-sulfur analyzer.
  • the specific surface area parameters related to the examples and comparative examples were tested with the 3Flex specific surface area analyzer of American Mike Company.
  • the specific surface area BET2 of the pore structure with a pore size of 0.5nm-100nm is obtained by fitting the T-Plot method, which reflects the sum of the surface areas of micropores, mesopores, and macropores in lithium iron phosphate materials; BET1 uses T-Plot The method obtains the specific surface area of mesoporous and macroporous structures with a pore diameter of not less than 2.0 nm and not more than 100 nm.
  • the lithium iron phosphate positive electrode active material, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black of the embodiment and the comparative example were mixed according to a mass ratio of 96.5:2.0:1.5, and an appropriate amount of N-methylpyrrolidone ( NMP) solvent, fully stirred and mixed to form a uniform positive electrode slurry; this slurry is coated on a carbon-coated aluminum foil with a positive electrode current collector thickness of 13 ⁇ m, and the coating surface density is 26 mg/cm 2 , followed by drying Cold-pressed and divided into strips for later use to obtain the positive electrode sheet.
  • NMP N-methylpyrrolidone
  • the diameter is greater than a certain D value, and there are other particles accounting for 50% of the total volume, the diameter is smaller than this D value, then this D value is the median particle size of the particle.
  • the degree of graphitization was tested using a Raman spectrometer.
  • the Raman spectrometer used is a new generation of high-resolution Raman spectrometer from HORIBA Jobin Yvon in France, the model is LabRAM HR Evolution, and the wavelength of the light source used is 532nm.
  • the spectrum in the range of 750-2000cm-1 is intercepted, and the following Gaussian function is used for fitting after buckling the background.
  • Ai, vi and wi are peak intensity, peak position and peak width, respectively.
  • the two peaks corresponding to the carbon coating can be fitted by four peaks, and the corresponding peak intensities are respectively recorded as D2, D1, D3 and G, and the degree of graphitization is G/(D3+G).
  • the lithium-ion batteries of all examples and comparative examples were placed in an oven at 25° C. for 2 hours, and then charged and discharged.
  • a charge and discharge process is as follows: 1C current constant current charge to 3.65V, continue constant voltage charge until the charge current is less than 0.05C, then stop; pause for 5min; 1C current constant current discharge to 2.0V; pause for 5min.
  • Battery mass energy density (Wh/kg) energy of the third discharge/mass of active material of lithium iron phosphate material in the battery.
  • a charging and discharging cycle process is as follows: 1C constant current charging to 3.65V, continue constant voltage charging until the charging current is less than 0.05C, then stop; pause for 5min; 1C constant current discharge to 2.5V; pause for 5min.
  • the above is a charging and discharging cycle of the battery, which is repeated continuously until the battery capacity decays to 80% of the initial value, and the number of cycles is recorded.
  • Table 1 Relevant parameters of lithium-ion batteries of examples and comparative examples
  • Table 4 Relevant parameters of lithium-ion batteries of examples and comparative examples
  • the lithium-ion battery has both good pole piece dehydration rate and excellent cycle Capacity retention and higher energy density; further, when the carbon content is 0.9% to 1.3%, the dehydration rate of the corresponding pole piece is better, and the cycle performance and energy density of the corresponding lithium-ion battery are also better; further , when the carbon content is 0.9% to 1.1%, the dehydration rate of the corresponding pole piece is better, and the cycle performance and energy density of the corresponding lithium-ion battery are also better, and the comprehensive performance of the lithium-ion battery is more excellent.
  • none of D4-D6 can simultaneously have a good pole piece dehydration rate, a high cycle capacity retention rate, and a high energy density.
  • the present application is not limited to the above-mentioned embodiments.
  • the above-mentioned embodiments are merely examples, and within the scope of the technical solutions of the present application, embodiments that have substantially the same configuration as the technical idea and exhibit the same effects are included in the technical scope of the present application.
  • various modifications conceivable by those skilled in the art are added to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of the present application. .

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Abstract

本申请提供一种碳包覆的磷酸铁锂正极活性材料。通过对碳包覆的磷酸铁锂材料的表层中不同微观形态的碳结构比表面积相对占比的调控，得到了本申请的碳包覆的磷酸铁锂正极活性材料。本申请的碳包覆的磷酸铁锂正极活性材料具有碳包覆因子η，并且所述η满足0.81≤η≤0.95时，磷酸铁锂正极活性材料具有高质量的碳包覆，有利于磷酸铁锂正极活性材料容量发挥、显著改善极片脱水效率，制备而成的锂离子电池兼具优良的能量密度、循环性能以及优良加工性能。

Description

碳包覆的磷酸铁锂正极活性材料、其制备方法、包含其的正极极片以及锂离子电池 技术领域
本申请涉及电化学领域，尤其涉及一种碳包覆的磷酸铁锂正极活性材料、其制备方法、包含其的正极极片、锂离子电池、电池模块、电池包和用电装置。
背景技术
随着新能源领域的快速发展，锂离子电池凭借其优良的电化学性能、无记忆效应、环境污染小等优势广泛应用于各类大型动力装置、储能系统以及各类消费类产品中，尤其广泛应用于纯电动汽车、混合电动汽车等新能源汽车领域。
在锂离子电池常用的正极活性材料中，磷酸铁锂是当前产业化锂离子电池中使用最广泛的正极活性材料之一。但是，因磷酸铁锂克容量低于三元材料，故近年来人们主要以提高磷酸铁锂容量发挥为研发热点。但是，仅着重提高磷酸铁锂容量性能会不可避免地损失电池其他性能，比如循环性能、加工性能等。
因此，期望设计出一款兼具高能量密度、高循环性能以及优良加工性能的锂离子电池。
发明内容
鉴于背景技术中存在的问题，本申请的目的在于提供一种碳包覆 的磷酸铁锂正极活性材料，其具有高容量发挥、高压实密度、极片易脱水，使锂离子电池兼具优良的能量密度、循环性能以及优良加工性能，并且能够显著提高电池的生产效率，降低电池生产成本。
本申请第一方面提供一种碳包覆的磷酸铁锂正极活性材料，所述正极活性材料包括磷酸铁锂基材以及位于所述基材表面的碳包覆层，所述磷酸铁锂基材具有结构通式LiFe 1-aM aPO 4，其中M选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr、Nb、Ti中的一种以上，0≤a≤0.01，；所述碳包覆的磷酸铁锂材料的碳包覆因子
Figure PCTCN2021114071-appb-000001
其中，BET1为所述碳包覆的磷酸铁锂中介孔和大孔结构的比表面积，BET2为所述碳包覆的磷酸铁锂的总比表面积，η满足0.81≤η≤0.95。
在任意实施方式中，所述η可选为0.85≤η≤0.93，进一步可选为0.88≤η≤0.92。
在任意实施方式中，所述BET1的数值范围为5.5～9.5m 2/g，所述BET2的数值范围为6.0～11.5m 2/g。
在任意实施方式中，碳包覆层的厚度H与所述碳包覆的磷酸铁锂的平均粒径D的比值H/D为0.01～0.04。
在任意实施方式中，碳包覆层中的碳组分占所述磷酸铁锂正极活性材料总质量的0.7％～1.3％，可选为0.9％～1.3％，更可选为0.9％～1.1％。
在任意实施方式中，所述碳包覆的磷酸铁锂的体积平均粒径Dv50满足840nm≤Dv50≤3570nm，可选为1170nm≤Dv50≤1820nm。
在任意实施方式中，所述碳包覆的磷酸铁锂的粉体压实密度不低于2.4g/cm 3，可选为2.5g/cm 3，更可选为2.6g/cm 3。
在任意实施方式中，所述碳包覆的磷酸铁锂的石墨化度为0.15～0.32，可选为0.19～0.26。
在任意实施方式中，所述碳包覆的磷酸铁锂的粉末电阻率不超过60Ω·m，可选为不超过30Ω·m，更可选为不超过20Ω·m。
本申请第二方面提供一种制备本申请第一方面所述的正极活性材料的方法，所述方法包括以下步骤：
提供磷酸铁锂基材；
对所述磷酸铁锂基材进行碳包覆，得到所述正极活性材料，其中，所述正极活性材料包括磷酸铁锂基材以及位于所述基材表面的碳包覆层，磷酸铁锂基材具有通式结构LiFe 1-aM aPO 4，其中M选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr、Nb、Ti中的一种以上，0≤a≤0.01；所述碳包覆的磷酸铁锂材料的碳包覆因子
Figure PCTCN2021114071-appb-000002
其中，BET1为所述碳包覆的磷酸铁锂中介孔和大孔结构的比表面积，BET2为所述碳包覆的磷酸铁锂的总比表面积，η满足0.81≤η≤0.95。
在任意实施方式中，所述正极活性材料的制备方法包括以下步骤：
(1)提供磷酸铁锂基材，其中将Fe源、Li源、M源和/或P源的原料以及作为还原剂和碳源的试剂混合，所得混合物在惰性气氛下在高温下进行处理，得到磷酸铁锂基材；
(2)对所述磷酸铁锂基材进行碳包覆，其中将磷酸铁锂基材在惰性气氛下在高温下进行处理，同时喷洒碳源，经化学气相沉积得到碳包覆的磷酸铁锂材料。
Fe源可以是选自FeSO 4、FePO 4、FeCl 2、FeC 2O 4、Fe 2O 3中的一种 或者多种。
Li源可以是选自Li 2CO 3、LiH 2PO 4、Li 3PO 4中的一种或者多种。
P源可以是选自NH 4H 2PO 4、H 3PO 4中的一种或者多种。M源包含选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr、Nb或Ti的元素。
步骤(1)中作为还原剂和碳源的试剂可以是选自C 2H 2、CH 4、葡萄糖、聚乙二醇、蔗糖、淀粉、H 2、CO中的一种或多种。可选地，所述作为还原剂和碳源的试剂的投料量占原料总质量的4％～8％，可选6％。
步骤(2)中碳源可以是丙酮等材料。
步骤(1)或(2)中的处理温度可以在宽范围内变化，例如500～800℃。
本申请第三方面提供一种锂离子电池的正极极片，包括正极集流体与设置在所述正极集流体的至少一个表面的正极活性材料，其中所述正极活性材料为本申请第一方面所述的正极活性材料或通过本申请第二方面所述的方法制备的正极活性材料。
在任意实施方式中，所述正极极片在25℃、45％的相对湿度下的饱和水含量不超过500ppm。
本申请第四方面提供一种锂离子电池，所述锂离子电池包括正极极片和负极极片，所述正极极片包括正极集流体与设置在所述正极集流体的至少一个表面的正极活性材料，所述正极活性材料为本申请第一方面所述的正极活性材料或通过本申请第二方面所述的方法制备的正极活性材料，所述正极极片在25℃、45％的相对湿度下的饱和水含 量不超过500ppm。
在任意实施方式中，所述正极极片的极片压实密度不低于2.35g/cm 3，所述负极极片的极片压实密度不低于1.6g/cm 3，所述负极极片中的负极活性材料为由无定形碳包覆的石墨。
本申请第五方面提供一种电池模块，包括本申请第四方面的锂离子电池。电池模块的制备可以采用现有技术已知的用于制备电池模块的方法。
本申请第六方面提供一种电池包，包括本申请第四方面的锂离子电池或本申请第五方面的电池模块。电池包的制备可以采用现有技术已知的用于制备电池包的方法。
本申请第七方面提供一种用电装置，包括本申请第四方面的锂离子电池、本申请第五方面的电池模块、或本申请第五方面的电池包，所述锂离子电池或所述电池模块或所述电池包用作所述用电装置的电源或所述用电装置的能量存储单元。用电装置的制备可以采用现有技术已知的用于制备用电装置的方法。
[有益效果]
本申请通过对碳包覆的磷酸铁锂材料的表层中不同微观形态的碳结构比表面积相对占比的调控，得到了本申请的正极活性材料。本申请碳包覆的磷酸铁锂材料具有碳包覆因子η，并且所述η满足0.81≤η≤0.95时，碳包覆的磷酸铁锂具有高质量的碳包覆，能显著改善极片不易脱水的工艺瓶颈，制备而成的锂离子电池兼具优良的能量密度、循环性能以及优良加工性能。
本申请的电池模块、电池包和用电装置包括本申请提供的锂离子 电池，因而至少具有与所述锂离子电池相同的优势。
附图说明
图1是本申请一实施方式的碳包覆的磷酸铁锂正极活性材料在不同放大倍率下的TEM图。
图2是本申请一实施方式的锂离子电池的示意图。
图3是图2所示的本申请一实施方式的锂离子电池的分解图。
图4是本申请一实施方式的电池模块的示意图。
图5是本申请一实施方式的电池包的示意图。
图6是图5所示的本申请一实施方式的电池包的分解图。
图7是本申请一实施方式的用电装置的示意图。
附图标记说明：
1电池包
2上箱体
3下箱体
4电池模块
5锂离子电池
51壳体
52电极组件
53顶盖组件
具体实施方式
以下，参照附图进行详细说明，具体公开本申请的碳包覆的磷酸铁锂正极活性材料及其制备方法、包含其的正极极片、锂离子电池、电池模块、电池包和用电装置，但是会有省略不必要的详细说明的情 况。例如，有省略对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。
为了简明，本申请具体地公开了一些数值范围，各种数值范围可以互相组合，形成相应的实施方案。任意下限可以与任意上限组合形成本申请的范围；以及任意下限可以与其他下限组合形成本申请的范围，同样任意上限可以与任意其他上限组合形成本申请的范围。此外，每个单独公开的点或单个数值自身可以作为下限或上限与任意其他点或单个数值组合或与其它下限或上限组合形成本申请的范围。
除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。在本申请中，除非另有说明，“以上”、“以下”包含本数，例如“a和b中的一种以上”是指a和b中的至少一种，例如a、b，或a和b。同样，“一种或多种”是指包含至少一种。在本文的描述中，除非另有说明，术语“或(or)”是包括性的，也就是说，短语“A或(or)B”表示“A、B，或A和B两者”。
需要说明的是，术语“碳包覆层”是指包覆在磷酸铁锂基材上的部分，所述部分可以但并不一定完全包覆磷酸铁锂基材，使用“碳包覆层”只是为了便于描述，并不意图限制本申请。同样地，术语“碳包覆层的厚度”是指包覆在磷酸铁锂基材上的所述部分的最大厚度。
本申请发明人经过对磷酸铁锂正极活性材料的研究发现，纯相磷酸铁锂正极活性材料(不含碳)的低电子导电和低离子导电特性，会恶化磷酸铁锂正极活性材料容量的发挥，使以磷酸铁锂作为正极活性材料的锂离子电池的能量密度与三元锂离子电池相差较大。
为了解决磷酸铁锂正极活性材料电子导电和离子导电性差的问题， 可以对材料进行碳包覆处理和纳米化处理。但是本申请发明人发现：无论是碳包覆处理还是纳米化处理都不可避免地会恶化电池其他方面的性能，特别是电池循环性能和加工性能。
特别地，发明人在实际作业过程中发现：对于碳包覆处理后的磷酸铁锂材料，不同的碳包覆工艺会导致正极活性材料中存在不同微观形态的孔道结构，比如，微孔结构(具有小于2nm孔的网络结构)、介孔结构(具有2nm-50nm孔的网络结构)、大孔结构(具有超过50nm孔的网络结构)，以及没有明显孔道的其他结构，比如层状的碳结构等。发明人经过大量实验发现：对于碳包覆后的磷酸铁锂材料，表层中各种孔结构的不合理搭配，不仅对改善磷酸铁锂正极活性材料电子导电性和离子导电性无明显作用，还会显著增加由磷酸铁锂正极活性材料制备而成的极片的脱水困难程度，使得由其制备的极片中的水分即使经过长时间脱水处理，脱水率也达不到制备电池的要求，特别地，当为增大电池能量密度而增大正极活性材料层的涂覆厚度时，极片脱水率更难达到要求。
特别地，发明人在实际作业过程中还发现：纳米化处理也会加剧极片脱水的难度，从而恶化电池循环性能。此外，纳米化处理还会降低磷酸铁锂正极活性材料的粉体压实密度，从而使其因提高电子电导和离子电导贡献的能量密度大打折扣。
极片中含有过高含量的水，一方面会导致极片中正极膜层易脱落、结构与化学性质不稳定等问题，最终影响电池循环性能；另一方面还会加大电池制备过程中不合格品的风险，不仅使得成本增加还严重影响电池生产效率。
综上所述，期望开发出一种兼具高容量发挥、高压实密度、极片易脱水的正极活性材料，进而设计出一款兼具高能量密度、高循环性 能以及优良加工性能的锂离子电池。
经过大量实验和研究，本申请发明人发现了使磷酸铁锂正极活性材料兼具高容量发挥、高压实密度、极片易脱水的技术方案，使锂离子电池兼具优良的能量密度、循环性能以及优良加工性能，并且能够显著提高电池的生产效率，降低电池生产成本。
[碳包覆的磷酸铁锂正极活性材料]
本申请提供一种碳包覆的磷酸铁锂正极活性材料，所述正极活性材料包括磷酸铁锂基材以及位于所述基材表面的碳包覆层，所述磷酸铁锂基材具有结构通式LiFe 1-aM aPO 4，其中M选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr、Nb、Ti中的一种以上，0≤a≤0.01。
所述碳包覆的磷酸铁锂材料的碳包覆因子
Figure PCTCN2021114071-appb-000003
其中，BET1为所述碳包覆的磷酸铁锂中介孔和大孔结构的比表面积，BET2为所述碳包覆的磷酸铁锂的总比表面积，η满足0.81≤η≤0.95。
基材具有通式结构LiFe 1-aM aPO 4，其中M选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr、Nb、Ti中的一种或多种，0≤a≤0.01。M元素的掺杂有利于提高磷酸铁锂基材的结构稳定性，防止磷酸铁锂正极活性材料在数次充放电循环后的结构坍塌。
碳包覆层能够提高电子电导率和离子导电率，提高电池能量密度。但是，碳包覆层作为一种由碳组成的多孔结构，会显著增大磷酸铁锂正极活性材料整体比表面能，进而使磷酸铁锂正极活性材料的吸水能力显著增加。本申请发明人经过大量实验验证发现：当碳包覆的磷酸铁锂材料满足
Figure PCTCN2021114071-appb-000004
0.81≤η≤0.95时，所述碳包覆的磷酸铁锂在满足高容量发挥的同时，还具有合理的比表面能，从而显著降低了由碳包覆的磷酸铁锂正极活性材料制备而成的极片的整体比表面能，使极片 脱水效率得到显著提高，能够显著改善极片不易脱水的工艺瓶颈。因此，由0.81≤η≤0.95的碳包覆的磷酸铁锂正极活性材料制备而成的电池兼具优良的能量密度、循环性能以及优良加工性能。
本申请中，碳包覆因子η实际表征了碳包覆后的磷酸铁锂材料中，不同微观形态的孔隙结构贡献的比表面积的相对占比，能反映出对表面能贡献很大的微孔结构的比表面积占所有孔道贡献的比表面积的比例的大小，其大小反应了磷酸铁锂碳层包覆的有效性。经过大量实验探究和制备正极材料的长期经验，发明人发现：当0.81≤η≤0.95时，致密高效的碳包覆层既能显著提高磷酸铁锂正极活性材料容量发挥，同时又能显著降低磷酸铁锂正极活性材料的表面能，从而使锂离子电池在具有优良能量密度的同时，电池的循环性能和加工性能也得到显著改善。
经过大量实验探究，发明人发现，当碳包覆因子η在0.85≤η≤0.93范围内时，此时表层中不同微观形态的孔隙的相对占比处于更合理范围内，磷酸铁锂具有高质量的碳包覆，有利于磷酸铁锂正极活性材料容量发挥、显著降低的极片吸水量，制备而成的锂离子电池兼具优良的能量密度、循环性能以及优良加工性能。
在一些实施方式中，可选地，η的范围为0.88≤η≤0.92，锂离子电池的电化学性能和加工性能更优。
综上所述，本申请通过对碳包覆的磷酸铁锂材料的表层中不同微观形态的碳结构比表面积相对占比的调控，得到了本申请的碳包覆的磷酸铁锂正极活性材料。本申请碳包覆的磷酸铁锂材料的碳包覆因子η满足0.81≤η≤0.95时，磷酸铁锂材料具有高质量的碳包覆，有利于显著改善极片脱水效率，制备而成的锂离子电池兼具优良的能量密度、 循环性能以及优良加工性能。具体参见表1。
可选地，所述η的值可以为0.811、0.836、0.862、0.894、0.915、0.922、0.928、0.939，或者其数值为上述任意两个点值组成的数值范围。
在一些实施方式中，可选地，BET1的数值范围为5.5～9.5m 2/g，BET2的数值范围为6.0～11.5m 2/g，此时表层中不同微观形态的碳结构的相对占比处于更加合理范围内，极片更不容易吸水，更有利于改善电池能量密度和循环性能。
可选地，所述BET1可以为9.08、8.86、7.05、6.68、6.93、6.46、5.95、5.82，或者其数值为上述任意两个点值组成的数值范围。所述BET2可以为11.2、10.6、8.19、7.48、7.16、7.01、6.40、6.20，或者其数值为上述任意两个点值组成的数值范围。
在一些实施方式中，可选地，本申请正极活性材料中，所述碳包覆层的厚度H与所述碳包覆的磷酸铁锂的平均粒径D的比值H/D为0.01～0.04。
碳包覆层的厚度与所述碳包覆的磷酸铁锂的平均粒径之比为0.01～0.04时，磷酸铁锂材料表面的碳包覆层完整度和电子导电能力较好，材料具有较高的电子电导率，同时因碳包覆层厚度占颗粒整体尺寸的比例位于合理范围内，磷酸铁锂材料兼具较高的粉末压实密度，从而使锂离子电池的能量密度和循环性能较好。合理的碳包覆层厚度还会降低由磷酸铁锂材料制备而成的极片的脱水困难，有利于提高加工性能。
在一些实施方式中，可选地，碳组分占所述碳包覆的磷酸铁锂总质量的0.7％～1.3％，可选为0.9％～1.3％，更可选为0.8％～1.1％。
碳含量过低，磷酸铁锂材料表面的碳包覆层的完整性较差，材料 动力学较差，导致电池的能量密度较低；而碳含量过高，会阻碍单颗粒在烧结过程中长大，进而使磷酸铁锂材料趋向于形成由众多小颗粒形成的二次颗粒，此外，碳组分并不贡献电池容量，同样使锂离子电池能量密度较低。在本申请中，基于碳包覆的磷酸铁锂的总质量计，碳含量满足0.7％≤C≤1.3％；可选为0.9％≤C≤1.3％；更可选为0.8％≤C≤1.1％。具体参见表2。
可选地，基于碳包覆的磷酸铁锂的总质量，所述碳组分的含量可以为0.70％、0.82％、0.95％、1.12％、1.3％，或者其数值为上述任意两个点值组成的数值范围。
在一些实施方式中，可选地，本申请碳包覆的磷酸铁锂的体积平均粒径Dv50满足840nm≤Dv50≤3570nm，可选为1170nm≤Dv50≤1820nm。
本申请发明人发现，为了解决磷酸铁锂正极活性材料电子导电和离子导电性差的问题，可以对材料进行纳米化处理。但是经过大量实践发现，纳米化处理同样会增大磷酸铁锂正极活性材料表面能，增大极片吸水能力而导致脱水困难，最终恶化电池循环性能和加工性能。此外，纳米化处理还会降低磷酸铁锂正极活性材料的粉体压实密度，从而使其因提高电子电导和离子电导贡献的能量密度大打折扣。
经过实验发现，在满足0.81≤η≤0.95范围内，当碳包覆的磷酸铁锂进一步满足体积平均粒径840nm≤Dv50≤3570nm，可选为1170nm≤Dv50≤1820nm时，所述碳包覆的磷酸铁锂的粉体压实密度可最高达2.64g/cm 3，极片压实密度可最高达2.64g/cm 3。本申请中，随着体积平均粒径Dv50增大，粉体压实密度和极片压实密度都呈现下降趋势，电池能量密度逐渐降低。但是，随着Dv50增大，极片脱水效 率提高，对应锂离子电池地循环性能有所提高。具体参见表4。
可选地，所述Dv50可以为840、1170、1430、1820、3520，或者其数值为上述任意两个点值组成的数值范围。
在一些实施方式中，可选地，本申请碳包覆的磷酸铁锂的石墨化度为0.15～0.32。本申请碳包覆的磷酸铁锂材料的碳包覆因子0.81≤η≤0.95、碳包覆的磷酸铁锂的石墨化度为0.15～0.32时，不仅有利于磷酸铁锂材料容量的发挥，更有利于改善磷酸铁锂材料的粉末电阻率，提高电池能量密度。具体参见表5。
碳包覆的磷酸铁锂的“石墨化度”是指碳组分的石墨化程度，反映了本申请的碳包覆的磷酸铁锂中，特别是碳包覆层中的石墨晶体结构的完整程度，也即石墨结构中碳原子排列的规整程度。
可选地，所述石墨化度可以为0.155、0.197、0.255、0.245、0.312，或者其数值为上述任意两个点值组成的数值范围。
在一些实施方式中，所述磷酸铁锂基材掺杂有碳元素，可选地0.1％至0.5％的碳元素，基于磷酸铁锂基材的质量计。
在一些实施方式中，可选地，本申请碳包覆的磷酸铁锂的粉末电阻率不超过60Ω·m，可选为不超过30Ω·m，更可选为不超过20Ω·m。
在一些实施方式中，可选地，本申请的正极活性材料除所述碳包覆的磷酸铁锂还包括其他本领域常规的正极活性材料，例如，其他橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。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正极活性材料的传统材料。这些正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。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO 2)、锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn2O 4)、锂镍钴氧化物、锂锰钴氧化物、锂镍锰 氧化物、锂镍钴锰氧化物(如LiNi 1/3Co 1/3Mn 1/3O 2(也可以简称为NCM333)、LiNi 0.5Co 0.2Mn 0.3O 2(也可以简称为NCM523)、LiNi 0.5Co 0.25Mn 0.25O 2(也可以简称为NCM211)、LiNi0.6Co0.2Mn0.2O2(也可以简称为NCM622)、LiNi 0.8Co 0.1Mn 0.1O 2(也可以简称为NCM811)、锂镍钴铝氧化物(如LiNi 0.85Co 0.15Al 0.05O 2)及其改性化合物等中的至少一种。其他橄榄石结构的含锂磷酸盐的示例可以包括但不限于磷酸锰锂(如LiMnPO 4)、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料中的至少一种。
[正极极片]
本申请提供一种正极极片，包括正极集流体与设置在所述正极集流体的至少一个表面的正极活性材料，其中所述正极活性材料为本申请一方面的碳包覆的磷酸铁锂。
本申请的锂离子电池，包括正极极片和负极极片，所述正极极片包括本申请前述的碳包覆的磷酸铁锂正极活性材料，所述正极极片在25℃、45％的相对湿度下的饱和水含量不超过500ppm。现有技术中，以常规碳包覆得到的磷酸铁锂正极活性材料，由其制得的极片在25℃、45％的相对湿度下的饱和水含量可达1000ppm，显著高于本申请碳包覆的磷酸铁锂正极活性材料制备的极片的吸水量。
在一些实施方式中，可选地，本申请正极极片的极片压实密度可最高达2.65g/cm 3，所述负极极片的极片压实密度不低于1.6g/cm 3，所述负极极片中负极活性材料为由无定形碳包覆的石墨。
本申请中，为了搭配本申请高容量发挥的磷酸铁锂正极活性材料，提供一种容量发挥不低于350mAh/g、极片压实密度不低于1.6g/cm 3的石墨负极，同时石墨表面具有无定形碳包覆层，具有与本申请正极相搭配的锂离子嵌锂能力和较高的充电窗口。
在一些实施方式中，可选地，本申请正极极片的正极膜层中，碳包覆的磷酸铁锂正极活性材料占整个正极膜层质量的90％-98％。本申请的碳包覆的磷酸铁锂正极活性材料，因搭配有合理的不同微观形态的碳结构贡献的比表面积，故在相同粘结剂含量的情况下，可以粘接较多的磷酸铁锂正极活性材料。当正极膜层搭配2％的PVDF时，涂覆量≥300mg/mm 2，量产涂布速度可达60m/min，显著提高实际作业中的加工效率，电池能量密度也得到显著提高。
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的正极材料。作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极材料设置在正极集流体相对的两个表面的其中任意一者或两者上。
本申请的锂离子电池中，所述正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，可采用铝箔。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层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、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)、1,3-丙烷磺酸内酯(PS)、聚乙烯(PE)等的基材)上而形成，但本申请并不限定于这些材料。
所述正极材料还可选地包括导电剂。但对导电剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正极材料的导电剂可以选自超导碳、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一种以上。
本申请中可按照本领域已知的方法制备正极极片。作为示例，可以将本申请的正极活性材料、导电剂和粘结剂分散于溶剂(例如N- 甲基吡咯烷酮(NMP))中，形成均匀的正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，得到正极极片。
[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，可选地，本申请正极极片的极片压实密度不低于2.35g/cm 3，所述负极极片的极片压实密度不低于1.6g/cm 3，所述负极极片中负极活性材料为由无定形碳包覆的石墨。
本申请中，为了搭配本申请高容量的磷酸铁锂正极活性材料，提供一种容量发挥不低于350mAh/g、极片压实密度不低于1.6g/cm 3的石墨负极，同时石墨表面具有无定形碳包覆层，具有与本申请正极相搭配的锂离子嵌锂能力和较高的充电窗口。
在本申请的锂离子电池中，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层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，但本申请并不限定于这些材料。
在本申请的负极极片中，所述负极膜层通常包含负极活性材料以及可选的粘结剂、可选的导电剂和其他可选助剂，通常是由负极浆料涂布干燥而成的。负极浆料通常是将负极活性材料以及可选的导电剂 和粘结剂等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)或去离子水。
作为示例，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一种以上。
在本申请的负极极片中，所述负极膜层除了包括负极活性材料外，还可选地包括其它常用负极活性材料，例如，作为其它常用负极活性材料，可列举出人造石墨、天然石墨、软炭、硬炭、硅基体料、锡基体料和钛酸锂等。所述硅基体料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的一种以上。所述锡基体料可选自单质锡、锡氧化合物以及锡合金中的一种以上。
[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，电解质可选自固态电解质及液态电解质(即电解液)中的至少一种。
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，电解质盐可选自六氟磷酸锂(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)及四氟草酸磷酸锂(LiTFOP)中的一种以上。
在一些实施方式中，溶剂可选自碳酸亚乙酯(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)、氟代碳酸亚乙酯(FEC)、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)及二乙砜(ESE)中的一种以上。
在一些实施方式中，所述电解液中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，也可以包括正极成膜添加剂，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、改善电池高温性能的添加剂、以及改善电池低温性能的添加剂等。
在一些实施方式中，可选地，本申请的电解液的电导率不低于13mS/cm的电解液，以与本申请的正极极片、负极极片搭配。
[隔离膜]
采用电解液的锂离子电池、以及一些采用固态电解质的锂离子电池中，还包括隔离膜。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。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一种以上。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。
[锂离子电池]
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，所述正极极片包括本申请的碳包覆的磷酸铁锂。
在一些实施方式中，锂离子电池可包括外包装。该外包装可用于 封装上述电极组件及电解质。
在一些实施方式中，锂离子电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。锂离子电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)以及聚丁二酸丁二醇酯(PBS)等。
本申请对锂离子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。例如，图2是作为一个示例的方形结构的锂离子电池5。
在一些实施方式中，参照图3，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能够盖设于所述开口，以封闭所述容纳腔。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封装于所述容纳腔内。电解液浸润于电极组件52中。锂离子电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体需求进行选择。
[电池模块]
在一些实施方式中，锂离子电池可以组装成电池模块，电池模块所含锂离子电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
图4是作为一个示例的电池模块4。参照图4，在电池模块4中，多个锂离子电池5可以沿电池模块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锂离子电池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，多个锂离 子电池5容纳于该容纳空间。
[电池包]
在一些实施方式中，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本领域技术人员可以根据电池包的应用和容量进行选择。
图5和图6是作为一个示例的电池包1。参照图5和图6，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能够盖设于下箱体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]
另外，本申请还提供一种用电装置，所述用电装置包括本申请提供的锂离子电池、电池模块、或电池包中的一种以上。所述锂离子电池、电池模块、或电池包可以用作所述装置的电源，也可以用作所述装置的能量存储单元。所述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。
作为所述用电装置，可以根据其使用需求来选择锂离子电池、电池模块或电池包。
图7是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对锂离子电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用锂离子电池作为电源。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例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，均为本领域通常使用的可以通过市购获得的常规产品。本申请实施例中各成分的含量，如果没有特别说明，均以质量计。
实施例
实施例1-1
【作为正极活性材料的碳包覆的磷酸铁锂的制备】
磷酸铁锂基材的制备：以磷酸铁、碳酸锂、氧化钛为原料，按照摩尔比FePO 4：Li 2CO 3：TiO 2＝0.996：0.498：0.004的化学计量比，将磷酸铁、碳酸锂、氧化钛混合，并加入作为碳源和还原剂的葡萄糖和聚乙二醇(葡萄糖和聚乙二醇的质量比为1:1，碳源投料量占原料总质量的6％)，随后加入溶剂水进行湿法研磨，得到混合浆料；将得到的浆料进行喷雾干燥，然后干燥后的产物放入辊道炉中在500℃隔绝空气烧结20h，自然冷却至物料温度＜80℃后出料，得到煅烧料；将煅烧料进行破碎、筛分、除磁，即得到磷酸铁锂基材LiFe 0.998Ti 0.002PO 4，其掺杂约0.3％的碳元素。
碳包覆：将上述基材放入辊道炉中在氮气气氛下烧结，同时在烧结炉中喷洒碳源丙酮溶液，770℃恒温烧结10h。待物料自然冷却至温度＜80℃后出料；进一步使用气流粉碎机粉碎后，即得实施例1-1的碳包覆的磷酸铁锂。
【正极极片】
将上述碳包覆的磷酸铁锂正极活性材料、粘结剂聚偏氟乙烯(PVDF)、导电剂乙炔黑按照96.5：2.0：1.5的质量比混合，然后加入N-甲基吡咯烷酮(NMP)溶剂以形成均匀的正极浆料；将此浆料涂覆于厚度为13μm的涂碳铝箔上，涂敷面密度为26mg/cm 2，烘干、冷压、分切后，得到本申请实施例1-1的正极极片。
【负极极片】
将负极活性材料石墨、增稠剂羧甲基纤维素钠、粘结剂丁苯橡胶、导电剂乙炔黑，按照质量比97：1：1：1进行混合，加入去离子水，在真空搅拌机作用下获得负极浆料；将负极浆料均匀涂覆在厚度为8μm的铜箔上；干燥后经过冷压、分切得到负极片，得到本申请实施例1-1的负极极片。
【电解液】
将溶剂碳酸亚乙酯(EC)和碳酸二甲酯(DMC)按30：70的质量比混合，溶解完全后，加入LiPF 6，然后加入碳酸亚乙烯酯(VC)和氟代碳酸亚乙酯(FEC)，混合均匀后，得到LiPF 6浓度为1mol/L、碳酸亚乙烯酯(VC)和氟代碳酸亚乙酯(FEC)的质量含量分别为3％的电解液。
【隔离膜】
选用12μm厚的聚丙烯隔离膜。
【锂离子电池的制备】
将极片置于110℃高温烘箱中烘烤7h，以除去极片中的水分，将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极片之间起到隔离的作用，再卷绕成方形的裸电芯后，装入铝塑膜，注入相应的非水电解液、封口，经静置、热冷压、化成、夹具、分 容等工序后，得到本申请实施例1-1的锂离子电池。
实施例1-2
除在“碳包覆”步骤中的恒温烧结的温度为780℃以外，其他步骤与实施例1-1相同。
实施例1-3
除“碳包覆”步骤，其他步骤与实施例1-1相同。
实施例1-3的“碳包覆”步骤如下：将实施例1-3的磷酸铁锂基材放入氮气气氛的辊道炉中烧结，并同时喷洒丙酮溶液，550℃恒温烧结10h，待物料自然冷却至温度＜80℃后出料，经粉碎、筛分后，继续将物料置于辊道炉中，并再次喷洒丙酮溶液，770℃恒温烧结10h，待物料自然冷却至温度＜80℃后出料。将第二次烧结的产物经气流粉碎后，得到实施例1-3的碳包覆的磷酸铁锂。
实施例1-4
除在“碳包覆”步骤中的第二次恒温烧结温度为780℃以外，其他步骤与实施例1-3相同。
实施例1-5
除在“碳包覆”步骤中的第二次恒温烧结温度为790℃以外，其他步骤与实施例1-3相同。
实施例1-6
除在“碳包覆”步骤中的第一次恒温烧结温度为600℃、第二次恒温烧结温度为770℃以外，其他步骤与实施例1-3相同。
实施例1-7
除在“碳包覆”步骤中的第二次恒温烧结温度为780℃以外，其他步骤与实施例1-6相同。
实施例1-8
除在“碳包覆”步骤中的第二次恒温烧结温度为790℃以外，其他步骤与实施例1-6相同。
对比例1
除在“碳包覆”步骤中的恒温烧结温度为750℃以外，其他步骤与实施例1-1相同。
对比例2
常规烧结：以磷酸铁、碳酸锂、氧化钛为原料，按照摩尔比FePO 4：Li 2CO 3：TiO 2＝0.996：0.498：0.004的化学计量比，将磷酸铁、碳酸锂、氧化钛混合，并加入作为碳源的葡萄糖和聚乙二醇(葡萄糖和聚乙二醇的质量比为1:1，碳源投料量占原料总质量的6％)，随后加入溶剂水进行湿法研磨，得到混合浆料；将得到的浆料进行喷雾干燥，然后干燥后的产物放入辊道炉中在750℃隔绝空气烧结10h，自然冷却至物料温度＜80℃后出料，得到煅烧料；将煅烧料进行破碎、筛分、除磁，即得到对比例2的磷酸铁锂。
对比例3
除在“碳包覆”步骤中的第一次恒温烧结温度为650℃、第二次恒温烧结温度为830℃以外，其他步骤与实施例1-6相同。
实施例2-1
除“基材的制备”步骤中碳源投料量降低到原料总质量的4％、“碳包覆”步骤中恒温烧结温度为800℃恒温烧结时间为13h以外，其他步骤与实施例1-1相同。基材中掺杂约0.15％的碳元素。
实施例2-2
除“基材的制备”步骤中碳源投料量降低到原料总质量的5％、“碳包覆”步骤中第一次恒温烧结温度为600℃且第二次恒温烧结温度为800℃以外，其他步骤与实施例1-3相同。
实施例2-3
除“基材的制备”步骤中碳源投料量为原料总质量的6％、“碳包覆”步骤中第一次恒温烧结温度为600℃且第二次恒温烧结温度为780℃以外，其他步骤与实施例2-2相同。
实施例2-4
除“基材的制备”步骤中碳源投料量提高到原料总质量的7％、“碳包覆”步骤中第一次恒温烧结温度为550℃且第二次恒温烧结温度为800℃以外，其他步骤与实施例2-3相同。
实施例2-5
除“基材的制备”步骤中碳源投料量提高到原料总质量的8％、“碳包覆”步骤中第一次恒温烧结温度为550℃且第二次恒温烧结温度为780℃以外，其他步骤与实施例2-4相同。
对比例4
除“基材的制备”步骤中碳源投料量降低为原料总质量的3％、恒温烧结温度为830℃、恒温烧结时间为15h以外，其他步骤与实施例2-1相同。
对比例5
除“基材的制备”步骤中碳源投料量提高到原料总质量的10％、“碳包覆”步骤中第一次恒温烧结温度为550℃且第二次恒温烧结温度为770℃以外，其他步骤与实施例2-5相同。
对比例6
除“基材的制备”步骤中碳源投料量提高到原料总质量的15％以外，其他步骤与对比例5相同。
实施例3-1
除“基材的制备”步骤中碳源投料量为原料总质量的5％、“碳 包覆”步骤中第一次恒温烧结温度为620℃(恒温烧结时间12h)且第二次恒温烧结温度为820℃(恒温烧结时间12h)以外，其他步骤与实施例2-5相同。
实施例3-2
除“基材的制备”步骤中碳源投料量为原料总质量的6％、“碳包覆”步骤中第一次恒温烧结温度为600℃(恒温烧结时间10h)且第二次恒温烧结温度为780℃(恒温烧结时间10h)以外，其他步骤与实施例3-1相同。
实施例3-3
除“基材的制备”步骤中碳源投料量为原料总质量的8％、“碳包覆”步骤中第一次恒温烧结温度为600℃(恒温烧结时间10h)且第二次恒温烧结温度为780℃(恒温烧结时间10h)以外，其他步骤与实施例3-2相同。
对比例7
除“基材的制备”步骤中碳源投料量为原料总质量的3％、“碳包覆”步骤中第一次恒温烧结温度为650℃(恒温烧结时间10h)且第二次恒温烧结温度为830℃(恒温烧结时间12h)以外，其他步骤与实施例3-1相同。
对比例8
除“基材的制备”步骤中碳源投料量为原料总质量的12％、“碳包覆”步骤中第一次恒温烧结温度为600℃(恒温烧结时间10h)且第二次恒温烧结温度为780℃(恒温烧结时间10h)以外，其他步骤与对比例7相同。
实施例4-1
除“碳包覆”步骤中第一次恒温烧结温度为550℃(恒温烧结 时间10h)且第二次恒温烧结温度为790℃(恒温烧结时间15h)以外，其他步骤与实施例2-3相同。实施例4-1最终得到的碳包覆的磷酸铁锂正极活性材料的体积平均粒径Dv50为530nm。
实施例4-2～实施例4-7
最终得到的碳包覆的磷酸铁锂正极活性材料的体积平均粒径Dv50分别为840nm、1170nm、1430nm、1820nm、3520nm、5070nm，通过调节气流粉碎机的分级频率，即得到不同Dv50的磷酸铁锂正极活性物质。
对比例9
常温烧结，除恒温烧结温度为750℃以外，其他步骤与实施例1-1相同。
实施例5-1
除“基材的制备”步骤中碳源投料量为原料总质量的8％、“碳包覆”步骤中的恒温烧结温度为750℃(恒温烧结时间10h)以外，其他步骤与实施例1-1相同。
实施例5-2
除“基材的制备”步骤中碳源投料量为原料总质量的6％、“碳包覆”步骤中的第一次恒温烧结温度为550℃(恒温烧结时间10h)且第二次恒温烧结温度为790℃(恒温烧结时间10h)以外，其他步骤与实施例2-2相同。
实施例5-3
除“基材的制备”步骤中碳源投料量为原料总质量的5％、“碳包覆”步骤中的第一次恒温烧结温度为600℃(恒温烧结时间10h)且第二次恒温烧结温度为830℃(恒温烧结时间14h)以外，其他步骤与实施例5-3相同。
对比例10
“基材的制备”步骤与对比例7相同，不同在于“碳包覆”步骤。具体的“碳包覆”步骤如下：
将对比例10的磷酸铁锂基材放入氮气气氛的辊道炉中烧结，并同时喷洒丙酮溶液，600℃恒温烧结10h，待物料自然冷却至温度＜80℃后出料，经粉碎、筛分后，继续将物料置于辊道炉中，并再次喷洒丙酮溶液，650℃恒温烧结10h，待物料自然冷却至温度＜80℃后出料，经粉碎、筛分后，继续将物料置于辊道炉中，并第三次喷洒丙酮溶液，830℃恒温烧结10h，待物料自然冷却至温度＜80℃后出料。将第三次烧结的产物经气流粉碎后，得到对比例10的磷酸铁锂正极活性材料。
以上实施例和对比例的磷酸铁锂正极活性材料的比表面积、体积平均粒径Dv50、碳含量、极片脱水效率、粉体压实密度，以及极片脱水效率、电池的能量密度、电池的循环保持率等数据具体参见表1～表5。
【磷酸铁锂正极活性材料相关参数测试】
1、平均粒径D
本申请所用的X射线粉末衍射仪为美国的X'pert PRO。平均粒径D的详细测试过程如下：
1)待测样品实测宽度Bm的测量。设置仪器扫描速率为2度/分钟，得到待测样品的XRD谱图。用JADE软件扣除Cu Kα2背底，得到各个衍射峰的Bm。
2)仪器宽化Bs测量。
用与待测样品同物质、晶粒度在5～20μm的标样，在与待测样品相同实验条件下，测定标样的XRD图谱，由图谱得到Bs。
3)半高宽B的计算。B＝Bm-Bs。(备注：如果计算出B的单位是角度，需转换成弧度)
4)平均粒径D的计算。使用谢乐公式D＝Kλ/Bcosθ，其中K取0.89，θ为衍射角，λ＝0.154056nm，代入B，即可得到单个衍射峰所代表的晶面法向的晶粒厚度D'。取多个衍射峰分别计算D'，取平均值后即得颗粒平均粒径D。
2、扫描电子显微镜SEM(Scanning Electron Microscope)
将所有实施例和对比例的磷酸铁锂正极活性材料用ZEISS sigma300扫描电子显微镜进行测试，然后参照标准JY/T010-1996进行测试，对样品形貌进行观测。
这里需要指出的是，本申请中基材磷酸铁锂基材的形状不一定是完美球形，也有可能是无规则的，为一次颗粒。还需指出的是，本申请制得的碳包覆的磷酸铁锂正极活性材料的形状也不一定是球形的，也有可能是无规则的。
3、透射电子显微镜TEM(Transmission Electron Microscope)
将所有实施例和对比例的磷酸铁锂正极活性材料用JEOL2010透射电子显微镜进行测试。测试标准为：GB/T 34002-2017。
4、粉体压实密度
分别称取所有实施例和对比例中的1g的磷酸铁锂正极活性材料，加入圆柱形模具中，模具圆孔的横截面积为S。对模具内粉体施加3t压力，并保压30s，记录粉体厚度为t。则所有实施例和所有对比例各自对应的磷酸铁锂正极活性材料的粉体压实密度ρ可通过以下公式计算得到：ρ＝m/(S×t)。
5、极片压实密度
将实施例和对比例的极片裁剪为1000mm长度的膜片，将极片通 过一定压力进行碾压，由于铝箔具备延展性，使其膜片长度为1006mm。然后在膜片上冲切1540.25mm 2的小圆片，测量小圆片重量M及厚度L。将纯铝箔冲切为1540.25mm 2的小圆片，称量空铝箔质量M0，则所有实施例和所有对比例各自对应的正极极片压实密度可通过以下公式计算得到：
PD＝(M-M0)/1.54025/2/L。
6、碳含量测试
将上述所有实施例和对比例中正极活性材料使用高频感应炉燃烧后用红外吸收法测试碳含量，具体测试过程依据标准GB/T20123-2006/ISO 15350:2000《钢铁总碳硫含量的测定高频感应炉燃烧后红外吸收法》，采用碳硫分析仪方便地测定，如德凯HCS红外碳硫分析仪。
7、比表面积测试
实施例和对比例相关比表面积参数用美国麦克公司的3Flex比表面积分析仪测试。本申请中，通过T-Plot法拟合得到孔径在0.5nm-100nm的孔结构的比表面积BET2，反映磷酸铁锂材料中微孔、介孔、大孔的表面积总和；BET1为使用T-Plot方法得到的孔径在2.0nm以上100nm以下的介孔和大孔结构的比表面积。
8、粉末电阻率
上述所有实施例和对比例正极活性材料的粉末电阻率，依据标准GB/T 30835-2014，使用粉末电阻率测试仪(ST2722)进行测试。
9、极片脱水效率
分别将实施例和对比例的磷酸铁锂正极活性材料、粘结剂聚偏氟乙烯(PVDF)、导电剂乙炔黑按照质量比96.5:2.0:1.5进行混合，加入 适量的N-甲基吡咯烷酮(NMP)溶剂，充分搅拌混合，使其形成均匀的正极浆料；将此浆料涂覆于正极集流体厚度为13μm的涂碳铝箔上，涂敷面密度为26mg/cm 2，随后进行烘干冷压，分条备用，得到正极极片。将极片皿置于50％水含量的湿度环境下，静置吸水24h至接近饱和，使用冲片设备，冲取直径为1.4cm的小圆片，剪碎成约为0.5cm×0.5cm的小块，置于水分测试仪器中，测试其水含量为A ppm。然后将剩余极片置于真空烘箱中，此过程使用塑封袋封好，避免极片吸脱水分，在110℃，7h的条件下烘干后，同样冲取小圆片并剪碎后测试其水含量为B ppm，材料脱水速率W＝(A-B)/420ppm/min。
10、体积平均粒径Dv50
在颗粒群中，有占总体积50％的颗粒，直径大于某D值，另有占总体积50％的颗粒，直径小于此D值，则此D值为颗粒的中值粒径。
设备型号：马尔文2000(MasterSizer 2000)激光粒度仪，参考标准流程：GB/T19077-2016/ISO 13320:2009，具体测试流程：取实施例和对比例的磷酸铁锂正极活性材料适量，加入20ml去离子水(样品浓度保证8-12％遮光度即可)，同时超声分散5min(53KHz/120W)，确保样品完全分散，之后按照GB/T19077-2016/ISO 13320:2009标准分别对实施例和对比例的样品进行测定。根据测试数据绘制粒径体积分布图和粒径数量分布图。从该分布图中得到：占总体积50％的颗粒直径大于某D值，另有占总体积50％的颗粒直径小于此D值，则此D值为颗粒的中值粒径。
11、石墨化度
石墨化度测试采用拉曼光谱仪进行表征。所用拉曼光谱仪为法国 HORIBA Jobin Yvon的新一代高分辨拉曼光谱仪，型号为LabRAM HR Evolution，所用光源波长为532nm。截取750-2000cm-1范围内的谱图，扣背底后用以下高斯函数进行拟合。Ai，vi和wi分别为为峰强、峰位置和峰宽。碳包覆层对应的两个峰可以用四个峰拟合，对应的峰强分别记为D2，D1，D3和G，则石墨化度为G/(D3+G)。
Figure PCTCN2021114071-appb-000005
Figure PCTCN2021114071-appb-000006
【电池性能测试】
1、能量密度测试方法
将所有实施例和对比例的锂离子电池置于25℃烘箱中，静置2h，然后进行充放电测试。一次充放电过程如下：1C电流恒流充电到3.65V，继续恒压充电，直至充电电流小于0.05C后截止；暂停5min；1C电流恒流放电到2.0V；暂停5min。以上为电池的一次充放电。电芯质量能量密度(Wh/kg)＝第三次放电的能量/电池中磷酸铁锂材料活性物质质量。
2、循环性能测试
将所有实施例和对比例的锂离子电池置于60℃烘箱中，静置2h，然后进行充放电测试。一个充放电循环过程如下：1C电流恒流充电到3.65V，继续恒压充电，直至充电电流小于0.05C后截止；暂停5min；1C电流恒流放电到2.5V；暂停5min。以上为电池的一个充放电循环，不断重复，直至电池容量衰减至初始值的80％，记录循环圈数。
表1：实施例和对比例锂离子电池相关参数
Figure PCTCN2021114071-appb-000007
表2：实施例和对比例锂离子电池相关参数
Figure PCTCN2021114071-appb-000008
表3：实施例和对比例锂离子电池相关参数
Figure PCTCN2021114071-appb-000009
Figure PCTCN2021114071-appb-000010
表4：实施例和对比例锂离子电池相关参数
Figure PCTCN2021114071-appb-000011
表5：实施例和对比例锂离子电池相关参数
Figure PCTCN2021114071-appb-000012
根据表1，综合比较S1-1～S1-8、以及D1～D3，当η在0.81～0.95(S1-1～S1-8)时，对应的极片脱水率整体显著优于D1～D3，同时对应锂离子电池还兼具优良的循环容量保持率和较高的能量密度；进一步地，当η在0.82～0.93(S1-2～S1-7)时，对应极片脱水率更优，同 时对应锂离子电池的循环性能和能量密度也更优；更进一步地，当η在0.88～0.92(S1-4～S1-6)时，对应极片脱水率更优，同时对应锂离子电池的循环性能和能量密度也更优，锂离子电池的综合性能优异。但是，对比例D1～D3都无法同时兼具良好的极片脱水率、较高的循环容量保持率和较高的能量密度。
根据表2，综合比较S2-1～S2-5以及D4～D6，当0.81≤η≤0.95，碳含量在0.82％～1.3％时，锂离子电池兼具良好的极片脱水率、优良的循环容量保持率和较高的能量密度；进一步地，当碳含量在0.9％～1.3％时，对应极片脱水率更优，同时对应锂离子电池的循环性能和能量密度也更优；更进一步地，当碳含量在0.9％～1.1％时，对应极片脱水率更优，同时对应锂离子电池的循环性能和能量密度也更优，锂离子电池的综合性能更优异。但是，D4～D6都无法同时兼具良好的极片脱水率、较高的循环容量保持率和较高的能量密度。
根据表3，综合比较S3-1～S3-3以及D7～D8，当0.81≤η≤0.95，H/D在0.01～0.04时，锂离子电池兼具良好的极片脱水率、优良的循环容量保持率和较高的能量密度。但是，D7～D8都无法同时兼具良好的极片脱水率、较高的循环容量保持率和较高的能量密度。
根据表4，综合比较S4-1～S4-7，当0.81≤η≤0.95，530nm≤Dv50≤5070nm，锂离子电池兼具良好的极片脱水率、优良的循环容量保持率和较高的能量密度；进一步地，当1170nm≤Dv50≤1820nm，对应极片脱水率更优，同时对应锂离子电池的循环性能和能量密度也更优，锂离子电池的综合性能更优异。
根据表5，综合比较S5-1～S5-3以及D9～D10，当正极活性材料的石墨化度在0.15～0.32时，锂离子电池兼具良好的极片脱水率、优良的循环容量保持率和较高的能量密度；进一步地，当碳包覆层的石墨 化度在0.19～0.26时，对应极片脱水率更优，同时对应锂离子电池的循环性能和能量密度也更优，锂离子电池的综合性能更优异。但是，对比例D9～D10都无法同时兼具良好的极片脱水率、较高的循环容量保持率和较高的能量密度。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为例示，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (19)

  1. 一种碳包覆的磷酸铁锂正极活性材料，其特征在于，
    所述正极活性材料包括磷酸铁锂基材以及位于所述基材表面的碳包覆层，所述磷酸铁锂基材具有结构通式LiFe 1-aM aPO 4，其中M选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr、Nb、Ti中的一种以上，0≤a≤0.01；
    碳包覆的磷酸铁锂材料的碳包覆因子
    Figure PCTCN2021114071-appb-100001
    其中，BET1为碳包覆的磷酸铁锂中介孔和大孔结构的比表面积，BET2为碳包覆的磷酸铁锂的总比表面积，η满足0.81≤η≤0.95。
  2. 根据权利要求1所述的正极活性材料，其特征在于，
    η可选为0.85≤η≤0.93，进一步可选为0.88≤η≤0.92。
  3. 根据权利要求1或2所述的正极活性材料，其特征在于，
    BET1的数值范围为5.5～9.5m 2/g，BET2的数值范围为6.0～11.5m 2/g。
  4. 根据权利要求1-3中任一项所述的正极活性材料，其特征在于，
    碳组分占碳包覆的磷酸铁锂总质量的0.7％～1.3％，可选为0.9％～1.3％，更可选为0.9％～1.1％。
  5. 根据权利要求1-4中任一项所述的正极活性材料，其特征在于，
    碳包覆层的厚度H与碳包覆的磷酸铁锂的平均粒径D的比值H/D为0.01～0.04。
  6. 根据权利要求1-5中任一项所述的正极活性材料，其特征在于，
    碳包覆的磷酸铁锂的体积平均粒径Dv50满足840nm≤Dv50≤3570nm，可选为1170nm≤Dv50≤1820nm。
  7. 根据权利要求1-6中任一项所述的正极活性材料，其特征在于，碳包覆的磷酸铁锂的粉体压实密度不低于2.4g/cm 3，可选为2.5g/cm 3，更可选为2.6g/cm 3。
  8. 根据权利要求1-7中任一项所述的正极活性材料，其特征在于，
    碳包覆的磷酸铁锂的石墨化度为0.15～0.32，可选为0.19～0.26。
  9. 根据权利要求1-8中任一项所述的正极活性材料，其特征在于，
    碳包覆的磷酸铁锂的粉末电阻率不超过60Ω·m，可选为不超过30Ω·m，更可选为不超过20Ω·m。
  10. 根据权利要求1所述的正极活性材料，其中所述磷酸铁锂基材掺杂有碳元素，可选地0.1％至0.5％的碳元素，基于磷酸铁锂基材的质量计。
  11. 一种制备权利要求1所述的正极活性材料的方法，所述方法包括以下步骤：
    提供磷酸铁锂基材；
    对所述磷酸铁锂基材进行碳包覆，得到碳包覆的磷酸铁锂正极活性材料，其中，
    所述正极活性材料包括磷酸铁锂基材以及位于所述基材表面的碳包覆层，所述磷酸铁锂基材具有结构通式LiFe 1-aM aPO 4，其中M选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr、Nb、Ti中的一种以上，0≤a≤0.01；
    碳包覆的磷酸铁锂材料的碳包覆因子
    Figure PCTCN2021114071-appb-100002
    其中，BET1为碳包覆的磷酸铁锂中介孔和大孔结构的比表面积，BET2为碳包覆的磷酸铁锂的总比表面积，η满足0.81≤η≤0.95。
  12. 根据权利要求11所述的方法，其中所述磷酸铁锂基材掺杂有碳元素，可选地0.1％至0.5％的碳元素，基于磷酸铁锂基材的质量计。
  13. 一种锂离子电池的正极极片，包括正极集流体与设置在所述正极集流体的至少一个表面的正极活性材料，其中所述正极活性材料为根据权利要求1-10中任一项所述的正极活性材料或通过权利要求11-12中任一项所述的方法制备的正极活性材料。
  14. 根据权利要求13所述的正极极片，其中所述正极极片在25℃、45％的相对湿度下的饱和水含量不超过500ppm。
  15. 一种锂离子电池，包括正极极片和负极极片，其特征在于，
    所述正极极片包括正极集流体与设置在所述正极集流体的至少一个表面的正极活性材料，其中所述正极活性材料为根据权利要求1-10中任一项所述的正极活性材料或通过权利要求11-12中任一项所述的方法制备的正极活性材料。
  16. 根据权利要求15所述的锂离子电池，其特征在于，
    所述正极极片的极片压实密度不低于2.35g/cm 3，所述负极极片的极片压实密度不低于1.6g/cm 3，所述负极极片中的负极活性材料为由无定形碳包覆的石墨。
  17. 一种电池模块，其特征在于，包括权利要求15或16所述的锂离子电池。
  18. 一种电池包，其特征在于，包括权利要求15或16所述的锂离子电池或权利要求17所述的电池模块。
  19. 一种用电装置，其特征在于，
    包括权利要求15或16所述的锂离子电池、权利要求17所述的电池模块或权利要求18所述的电池包，所述锂离子电池或所述电池模块或所述电池包用作所述用电装置的电源或所述用电装置的能量存储单元。
PCT/CN2021/114071 2021-08-23 2021-08-23 碳包覆的磷酸铁锂正极活性材料、其制备方法、包含其的正极极片以及锂离子电池 WO2023023894A1 (zh)

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CN202180083427.0A CN116601798A (zh) 2021-08-23 2021-08-23 碳包覆的磷酸铁锂正极活性材料、其制备方法、包含其的正极极片以及锂离子电池
JP2023501317A JP2023538479A (ja) 2021-08-23 2021-08-23 炭素被覆リン酸鉄リチウム正極活物質、その製造方法、それを含む正極シート及びリチウムイオン電池
EP21927078.2A EP4167314A4 (en) 2021-08-23 2021-08-23 CARBON-COATED LITHIUM IRON PHOSPHATE POSITIVE ELECTRODE ACTIVE MATERIAL, METHOD OF PRODUCING THE SAME, POSITIVE ELECTRODE POLE PIECE COMPRISING THE SAME, AND LITHIUM-ION BATTERY
KR1020237000446A KR102593317B1 (ko) 2021-08-23 2021-08-23 탄소 코팅 리튬인산철 캐소드 활물질, 이의 제조 방법, 이를 포함하는 캐소드 극판 및 리튬 이온 전지
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