WO2024065387A1 - 正极活性材料、其制法以及包含其的二次电池、电池模块、电池包、用电装置 - Google Patents

正极活性材料、其制法以及包含其的二次电池、电池模块、电池包、用电装置 Download PDF

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WO2024065387A1
WO2024065387A1 PCT/CN2022/122554 CN2022122554W WO2024065387A1 WO 2024065387 A1 WO2024065387 A1 WO 2024065387A1 CN 2022122554 W CN2022122554 W CN 2022122554W WO 2024065387 A1 WO2024065387 A1 WO 2024065387A1
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positive electrode
electrode active
active material
battery
polymer
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PCT/CN2022/122554
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English (en)
French (fr)
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吴灿龙
许文竹
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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/CN2022/122554 priority Critical patent/WO2024065387A1/zh
Publication of WO2024065387A1 publication Critical patent/WO2024065387A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • 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 application relates to the technical field of lithium batteries, and in particular to a positive electrode active material and a method for preparing the positive electrode active material, and a secondary battery, a battery module, a battery pack, and an electrical device comprising the positive electrode active material.
  • lithium-ion batteries have been increasingly used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.
  • energy storage power systems such as hydropower, thermal power, wind power and solar power stations
  • power tools such as hydropower, thermal power, wind power and solar power stations
  • electric bicycles electric motorcycles
  • electric vehicles military equipment
  • aerospace and other fields lithium-ion batteries have made great progress, higher requirements have been placed on their cycle performance and power performance.
  • the positive active material of the current lithium-ion battery reacts with the electrolyte during fast charging, resulting in increased DC internal resistance, reduced cycle performance, and rapid battery temperature rise, posing a safety hazard. Therefore, designing and developing a lithium-ion battery with lower DC internal resistance and good cycle performance during fast charging has great application value.
  • the present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material, which includes a positive electrode active substance and a coating layer on its surface, wherein the coating layer includes a polymer of structural units derived from monomeric maleimide compounds and structural units derived from monomeric cyanuric acid compounds; when this positive electrode active material is applied to the positive electrode of a lithium ion battery, it can effectively improve the power performance and cycle performance of the battery.
  • the first aspect of the present application provides a positive electrode active material, which includes a positive electrode active substance and a coating layer on the surface thereof, wherein the coating layer includes a polymer of structural units derived from monomeric maleimide compounds and structural units derived from monomeric cyanuric acid compounds.
  • the polymer forms a uniform coating layer on the surface of the positive electrode active material (such as ternary material (NCM)), thereby protecting the positive electrode active material, reducing the side reaction between the positive electrode and the electrolyte, improving the cycle performance of the battery, and reducing the direct current internal resistance (DCR) of the battery during fast charging.
  • the positive electrode active material such as ternary material (NCM)
  • the structural unit derived from the monomer maleimide compound includes at least one of the following formulae (I-1) to (I-3):
  • R 1 is a group selected from the following:
  • n is an integer from 0 to 3, and n can be 1 or 2.
  • the structural unit derived from the monomer cyanuric acid compound comprises the following formula (II):
  • R 2 , R 3 and R 4 are independently oxygen atoms or sulfur atoms; in particular, the cyanuric acid compound is at least one selected from cyanuric acid and thiocyanuric acid.
  • the positive electrode active material is selected from lithium transition metal oxides, including at least one of LiCoO2 , LiNiO2 , LiMnO2 , LiMn2O4 , LiNi1 / 3Co1 / 3Mn1 / 3O2 , Li ( Ni0.5Co0.2Mn0.3 ) 1.07O2 , LiNi0.5Co0.2Mn0.3O2 , LiNi0.5Co0.25Mn0.25O2 , LiNi0.6Co0.2Mn0.2O2 , LiNi0.8Co0.1Mn0.1O2 , and LiNi0.85Co0.15Al0.05O2 .
  • the thickness of the coating layer is 0.8 nm to 2.5 nm, optionally 1.0 nm to 2 nm, and further optionally 1.1 nm to 1.5 nm, thereby further improving the cycle performance of the battery and reducing the DC internal resistance of the battery during fast charging.
  • the total molar amount of the structural units (I-1), (I-2), (I-3) and (II) accounts for 40-90 mol%, and can be 50-85 mol%; the molar amount of the structural unit (II) accounts for 10-60 mol%, and can be 15-50 mol%.
  • the polymer described in the present application is further optimized, so as to achieve the purpose of effectively improving the power performance and cycle performance of the battery.
  • the weight average molecular weight of the polymer is 3000 to 5000.
  • the mass fraction of the polymer is 0.3-2.5%, optionally 0.4-2%, and further optionally 0.5-1.5%, based on the total mass of the polymer and the positive electrode active material.
  • the composition of the positive electrode active material with the polymer coating layer is optimized, the DC internal resistance of the battery during fast charging is effectively reduced, and the DCR growth rate and cycle retention rate of the battery during cycling are improved.
  • the median particle size Dv50 of the positive electrode active material of the present application is 3.2 ⁇ m to 4.2 ⁇ m, and can be 3.5 ⁇ m to 3.6 ⁇ m; the specific surface area BET is 1.05 m 2 /g to 1.55 m 2 /g, and can be 1.50 m 2 /g to 1.53 m 2 /g.
  • effective coating of the positive electrode active material is achieved, thereby further reducing the DC internal resistance of the battery, and improving the cycle retention rate and DCR growth rate of the battery.
  • 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, which comprises the following steps:
  • Step S1 polymerizing a maleimide compound and a cyanuric acid compound to obtain a polymer
  • Step S2 adding a positive electrode active material to the polymer for coating to obtain a positive electrode active material having a polymer coating layer.
  • the mass ratio of the maleimide compound to the cyanuric acid compound is 2:1 to 10:1, and can be 2.5:1 to 6.5:1.
  • the mass ratio of the positive electrode active material to the polymer is 40:1 to 210:1, and optionally 49:1 to 199:1.
  • step S2 the coating is performed by heating to a temperature of 55° C. to 80° C. for a duration of 0.5 h to 2 h.
  • the third aspect of the present application provides a secondary battery, which includes the positive electrode active material described in the first aspect of the present application, or the positive electrode active material obtained by the preparation method described in the second aspect of the present application.
  • a fourth aspect of the present application provides a battery module, which includes the secondary battery described in the third aspect of the present application.
  • the fifth aspect of the present application provides a battery pack, which includes the battery module described in the fourth aspect of the present application.
  • the sixth aspect of the present application provides an electrical device, which includes at least one of the secondary battery described in the third aspect of the present application, the battery module described in the fourth aspect of the present application, or the battery pack described in the fifth aspect of the present application.
  • the present application can protect the positive electrode of the battery, reduce the side reaction between the positive electrode and the electrolyte, and effectively improve the cycle performance and power performance of the battery by coating the positive electrode active material with a polymer having a structural unit derived from a monomer maleimide compound and a structural unit derived from a cyanuric acid compound. Accordingly, the battery pack, battery module and power device provided by the present application also have good cycle performance and power performance.
  • FIG. 1 is an infrared spectrum of the positive electrode active material NCM523 of Example 1 of the present application before and after coating.
  • FIG. 2 is a transmission electron microscope (TEM) image of the positive electrode active material of Example 1 of the present application.
  • FIG. 3 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 4 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 3 .
  • FIG. 5 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG. 6 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 7 is an exploded view of the battery pack shown in FIG. 6 according to an embodiment of the present application.
  • FIG. 8 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.
  • Region I positive electrode active material NCM523; Region II: polymer coating layer; 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly.
  • Range disclosed in the present application is defined in the form of lower limit and upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range.
  • the range defined in this way can include or exclude end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range.
  • the range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected.
  • the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-6.
  • the numerical range "a-b” represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers.
  • the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just the abbreviation of these numerical combinations.
  • a parameter is expressed as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • the method may further include step (c), which means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
  • the “include” and “comprising” mentioned in this application represent open-ended or closed-ended expressions.
  • the “include” and “comprising” may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, any of the following conditions satisfies the condition "A or B”: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
  • the inventors of the present application have discovered through a large number of experiments that a polymer having structural units derived from monomeric maleimide compounds and structural units of cyanuric acid compounds, which is generated by the polymerization reaction of maleimide compounds and cyanuric acid compounds, is used to coat a positive electrode active material of a transition metal oxide.
  • the resulting positive electrode active material having the polymer coating layer is beneficial to improving the power performance and cycle performance of a lithium-ion battery.
  • the first aspect of the present application provides a positive electrode active material, which includes a positive electrode active substance and a coating layer on the surface thereof, wherein the coating layer includes a polymer of a structural unit derived from a monomer maleimide compound and a structural unit derived from a monomer cyanuric acid compound.
  • the positive electrode active material such as ternary material (NCM)
  • the positive electrode of the battery is protected, which is conducive to forming an interface film (CEI film) between the positive electrode and the electrolyte, reducing the side reaction between the positive electrode and the electrolyte, thereby improving the cycle performance of the battery and reducing the DC internal resistance (DCR) of the battery during fast charging.
  • CEI film interface film
  • the coating layer is composed of a polymer, wherein the polymer includes a structural unit derived from a monomeric maleimide compound and a structural unit derived from a monomeric cyanuric acid compound.
  • the coating layer includes or consists of a polymer, wherein the polymer is obtained by copolymerization of monomers of maleimide compounds and cyanuric acid compounds.
  • the structural unit derived from the monomer maleimide compound includes at least one of the following formulae (I-1) to (I-3):
  • R1 is at least one selected from the following groups:
  • n is an integer from 0 to 3, and n can be 1 or 2.
  • formula (1) represents 1,4-phenylene
  • formula (2) represents 1,3-phenylene
  • formula (3) represents 1,2-phenylene
  • connection site between it and the other parts of formula (I-3) can be on any carbon atom of each phenyl group; the preferred connection site is the para position, that is, at the 4,4' position of the diphenyl group.
  • the corresponding structural unit of formula (I-3) includes at least one of the following:
  • the structural unit of formula (I-2) or formula (I-3) is derived from a bismaleimide compound of the following formula (III),
  • A is a group selected from the following:
  • n is an integer from 0 to 3, and m can be 1 or 2.
  • the structural unit derived from the monomer cyanuric acid compound comprises the following formula (II):
  • R 2 , R 3 and R 4 are independently oxygen atoms or sulfur atoms; and optionally, the cyanuric acid compound includes at least one of cyanuric acid and thiocyanuric acid.
  • the positive electrode active material of the present application includes a positive electrode active substance and a coating layer on the surface thereof, wherein the coating layer includes or is composed of a polymer, and the polymer contains at least one of the structural unit formulas (I-1) to (I-3) derived from a monomer maleimide compound and a structural unit (II) derived from a monomer cyanuric acid compound.
  • the positive electrode active material of the present application includes a positive electrode active material and a coating layer on the surface thereof, wherein the coating layer includes a polymer or is composed of a polymer, wherein the polymer is obtained by polymerization of a monomer maleimide compound and a cyanuric acid compound; wherein the monomer maleimide compound is maleimide and a bismaleimide compound of the above formula (III), and the cyanuric acid compound is cyanuric acid or thiocyanuric acid.
  • the molar ratio of the maleimide compound to the cyanuric acid compound is 1:1 to 6:1.
  • the positive electrode active material is selected from lithium transition metal oxides, optionally selected from lithium transition metal oxides of the following formula:
  • M is selected from one of Mn and Al or a mixture thereof;
  • a, b, c, d, and e meet the valence requirements of the positive electrode active material.
  • the lithium transition metal oxide is selected from lithium cobalt oxide (such as LiCoO2 ), lithium nickel oxide (such as LiNiO2 ), lithium manganese oxide (such as LiMnO2 , LiMn2O4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1 / 3Co1 / 3Mn1 / 3O2 (also referred to as NCM333 ), Li( Ni0.5Co0.2Mn0.3 ) 1.07O2 (also referred to as NCM523 ) , LiNi0.5Co0.2Mn0.3O2 , LiNi0.5Co0.25Mn0.25O2 (also referred to as NCM211 ) , LiNi0.6Co0.2Mn0.2O2 (also referred to as NCM622 ) , LiNi0.8Co0.1Mn At least one of NCM 811 0.1 O 2 (also referred to as NCM 811 ), lithium nickel cobalt
  • the positive electrode active material is selected from at least one of LiCoO2 , LiNiO2 , LiMnO2 , LiMn2O4 , LiNi1 / 3Co1 / 3Mn1 / 3O2 , Li( Ni0.5Co0.2Mn0.3 ) 1.07O2 , LiNi0.5Co0.2Mn0.3O2 , LiNi0.5Co0.25Mn0.25O2 , LiNi0.6Co0.2Mn0.2O2 , LiNi0.8Co0.1Mn0.1O2 , and LiNi0.85Co0.15Al0.05O2 .
  • the specific surface area BET of the positive electrode active material is 0.5 m 2 /g to 1.5 m 2 /g, and the median particle size Dv50 is 3.2 ⁇ m to 4.2 ⁇ m.
  • the thickness of the coating layer is 0.8 nm to 2.5 nm, optionally 1.0 nm to 2 nm, and further optionally 1.1 nm to 1.5 nm, thereby further improving the cycle performance of the battery and reducing the DC internal resistance of the battery during fast charging.
  • the total molar amount of the structural units (I-1), (I-2), (I-3) and (II) accounts for 40-90 mol%, and can be 50-85 mol%; the molar proportion of the structural unit (II) is 10-60 mol%, and can be 15-50 mol%.
  • the molar ratio of the monomer maleimide compound and the cyanuric acid compound used is 1: 1 to 6: 1.
  • the molar proportion of the structural unit (I-1) is 0-90 mol%
  • the total molar proportion of (I-2) and (I-3) is 0-70 mol%
  • 51-67 mol% can be selected
  • the molar proportion of the structural unit (II) is 10-60 mol%, and 15-50 mol% can be selected.
  • the molar proportion of the structural unit (I-1) is not zero at the same time as the total molar proportion of the structural units (I-2) and (I-3).
  • the molar proportion of structural unit (I) (or based on the total molar amount of monomeric maleimide compounds and cyanuric acid compounds, the molar proportion of maleimide) may be about 0 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 80 mol%, about 82 mol%, about 85 mol%, about 87 mol% or about 89 mol%.
  • the molar proportion of structural unit (I) is within any range consisting of the above arbitrary values.
  • the molar amount of bismaleimide of formula (A) may be about 0 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 52 mol%, about 55 mol%, about 57 mol%, about 60 mol%, about 62 mol%, about 65 mol%, about 67 mol%, about 70 mol%, about 75 mol%, about 80 mol% or about 85 mol%.
  • the molar amount of the total molar amount of structural units (A)) may be about 0 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 52 mol%, about 55 mol%
  • the molar proportion of structural unit (II) (or based on the total molar amount of monomeric maleimide compounds and cyanuric acid compounds, the molar proportion of cyanuric acid compounds (especially cyanuric acid and thiocyanuric acid)) can be about 10 mol%, about 12 mol%, about 15 mol%, about 18 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 32 mol%, about 35 mol%, about 37 mol%, about 38 mol%, about 40 mol%, about 42 mol%, about 45 mol%, about 48 mol%, about 50 mol%, about 52 mol%, about 55 mol% or about 60 mol%.
  • the molar proportion of structural unit (II) is within any range consisting of the above arbitrary values.
  • a numerical value means a range, that is, a range of ⁇ 3% of the numerical value.
  • the weight average molecular weight of the polymer is 3000 to 5000.
  • the weight average molecular weight of the polymer is measured using a vapor osmometer OSMOMAT 070.
  • the mass fraction of the polymer is 0.3% to 2.5%, optionally 0.4% to 2%, and further optionally 0.5% to 1.5%, based on the total mass of the polymer and the positive electrode active material.
  • the composition of the positive electrode active material with a polymer coating layer is optimized, thereby effectively reducing the DC internal resistance of the battery during fast charging and improving the DCR growth rate and capacity retention rate of the battery during cycling.
  • the mass fraction of the coating layer i.e., the polymer coating layer
  • the mass fraction of the coating layer is 0.3% to 2.5%, optionally 0.4% to 2%, and further optionally 0.5% to 1.5%.
  • the mass fraction of the coating layer relative to the mass of the positive electrode active material is 0.3% to 2.5%, optionally 0.4% to 2%, and further optionally 0.5% to 1.5%.
  • the median particle size Dv50 of the positive electrode active material of the present application is 2.7 ⁇ m to 9.5 ⁇ m, optionally 3.2 ⁇ m to 4.2 ⁇ m, and further optionally 3.5 ⁇ m to 3.6 ⁇ m;
  • the specific surface area BET is 0.9 m 2 /g to 1.67 m 2 /g, optionally 1.05 m 2 /g to 1.55 m 2 /g, and further optionally 1.50 m 2 /g to 1.53 m 2 /g. This further reduces the DC internal resistance of the battery and improves the capacity retention rate and DCR growth rate of the battery.
  • 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, which comprises the following steps:
  • Step S1 polymerizing a maleimide compound and a cyanuric acid compound to obtain a polymer
  • Step S2 adding a positive electrode active material to the polymer for coating to obtain a positive electrode active material having a polymer coating layer.
  • the positive electrode active material with a polymer coating layer of the present application is obtained, and the secondary battery made using the positive electrode active material has improved cycle performance and power performance.
  • step S1 in the presence of an organic solvent (such as N-methylpyrrolidone, NMP), at 110°C to 135°C, a maleimide compound and a cyanuric acid compound are mixed, and reacted for 0.5h to 2h under stirring, and then cooled for standby use.
  • the mass ratio of the maleimide compound to the cyanuric acid compound is 1:2 to 17:1 or 1:1 to 12:1, optionally 2:1 to 10:1, optionally 2.5:1 to 6.5:1, for example, 2:1 to 5:1, or 3:1 to 3.5:1.
  • step S2 a positive electrode active material is added to the polymer solution obtained in step S1) by a liquid phase coating method, and air is removed after sufficient stirring, and the coating is performed at 55°C to 80°C for 0.5h to 2h. Then, the mixture is filtered and dried at 75°C to 90°C to obtain the positive electrode active material with a polymer coating layer of the present application.
  • the mass ratio of the added positive electrode active material to the mass ratio of the polymer obtained in step S1 is 40:1 to 210:1, and can be 49:1 to 199:1.
  • the positive electrode active material of the present application can be used not only in secondary batteries, but also in any other battery, battery module, battery pack or electrical device that needs to reduce power performance and improve cycle performance.
  • the secondary battery, battery module, battery pack and electric device of the present application are described below.
  • a secondary battery which includes the positive electrode active material described in the first aspect of the present application and the positive electrode active material prepared by the method described in the second aspect of the present application.
  • a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.
  • active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet.
  • the electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.
  • the separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the positive electrode active material described in the first aspect of the present application and the positive electrode active material prepared by the method described in the second aspect of the present application.
  • the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil may 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 may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode film layer may also optionally include a binder.
  • the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • the positive electrode film layer may also optionally include a conductive agent.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the mass content of the conductive agent in the negative electrode film layer is 1% to 5%, based on the total weight of the positive electrode film layer.
  • the preparation method of the positive electrode sheet of the present application is as follows:
  • Step S1 polymerizing a maleimide compound and a cyanuric acid compound to obtain a polymer
  • Step S2 adding a positive electrode active material to the polymer for coating to obtain a positive electrode active material (having a polymer coating layer);
  • Step S3 mixing the positive electrode active material (having a polymer coating layer), a conductive agent, and a binder to obtain a positive electrode slurry;
  • Step S4 coating the positive electrode slurry on the positive electrode current collector, and obtaining the positive electrode sheet after drying, cold pressing and other processes.
  • the positive electrode active material described in the first aspect of the present application is prepared.
  • step S1 in the presence of an organic solvent (such as N-methylpyrrolidone, NMP), at 110° C. to 135° C., a maleimide compound and a cyanuric acid compound are mixed, and reacted for 0.5 h to 2 h under stirring, and then cooled for standby use.
  • an organic solvent such as N-methylpyrrolidone, NMP
  • the mass ratio of the maleimide compound to the cyanuric acid compound is 1:1 to 12:1, optionally 2:1 to 10:1, and optionally 2.5:1 to 6.5:1, for example, 2:1 to 5:1 or 3:1 to 3.5:1.
  • step S2 a positive electrode active material is added to the polymer solution obtained in step S1) by a liquid phase coating method, and air is removed after sufficient stirring, and the reaction is carried out at 55°C to 80°C for 0.5-2h. Then, the mixture is filtered and dried at 75-90°C to obtain a positive electrode active material with a polymer coating layer.
  • the mass ratio of the added positive electrode active material to the mass ratio of the polymer obtained in step S1 is 40:1 to 210:1, and can be optionally 49:1 to 199:1.
  • step S3 according to the general method in the art, the positive electrode active material, conductive agent and binder prepared in step S2 are mixed in a mass ratio of (45-50):(1-1.4):1, and then added to an organic solvent (such as N-methylpyrrolidone, NMP), and after sufficient stirring, a positive electrode slurry with a solid content of 55-70% is obtained.
  • an organic solvent such as N-methylpyrrolidone, NMP
  • step S4 the positive electrode slurry is coated on the current collector with a coating surface density of 10 mg/ cm2 to 15 mg/ cm2 (dry weight); then dried in a vacuum drying oven at 100°C to 120°C for 12h to 16h, then naturally cooled to room temperature, and roller-pressed to obtain a positive electrode sheet with uniform thickness (85 ⁇ m to 110 ⁇ m).
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • a metal foil a copper foil may be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode active material may adopt the negative electrode active material for batteries known in the art.
  • the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used.
  • These negative electrode active materials may be used alone or in combination of two or more.
  • the mass content of the negative electrode active substance in the negative electrode film layer is 93% to 99%, based on the total weight measured for the negative electrode film layer.
  • the negative electrode film layer may further optionally include a binder.
  • the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAAS sodium polyacrylate
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • the negative electrode film layer may further include a conductive agent.
  • the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the mass content of the conductive agent in the negative electrode film layer is 1% to 5%, based on the total weight of the negative electrode film layer.
  • the negative electrode film layer may also optionally include other additives, such as a dispersant (such as sodium carboxymethyl cellulose (CMC-Na)), etc.
  • a dispersant such as sodium carboxymethyl cellulose (CMC-Na)
  • the mass content of the dispersant in the negative electrode film layer is 0.1% to 1.5%, based on the total weight of the negative electrode film layer.
  • the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry with a solid content of 55-70%; the negative electrode slurry is then coated on a current collector with a coating surface density of 7 mg/ cm2 to 8.5 mg/ cm2 (dry weight); and then dried in a vacuum drying oven at 85°C to 115°C for 9h to 16h, then naturally cooled to room temperature, and rolled to obtain a negative electrode sheet with uniform thickness (100 ⁇ m to 115 ⁇ m).
  • a solvent such as deionized water
  • the electrolyte plays the role of conducting ions between the positive electrode and the negative electrode.
  • the present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.
  • the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte).
  • the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.
  • the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).
  • LiPF 6 lithium hexafluorophosphate
  • 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 (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), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).
  • EC
  • the electrolyte may also optionally include additives.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature performance, etc.
  • the mass content of the additives in the electrolyte is 0% to 2%, based on the total weight of the electrolyte.
  • the secondary battery further includes a separator.
  • the separator is disposed between the positive electrode plate and the negative electrode plate to serve as a separator.
  • the present application has no particular restrictions on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation.
  • the materials of each layer can be the same or different, without particular limitation.
  • the isolation film has a thickness of 6-40 ⁇ m, and optionally 12-20 ⁇ m.
  • the secondary battery may include an outer package for packaging the positive electrode sheet, the negative electrode sheet and the electrolyte.
  • the positive electrode sheet, the negative electrode sheet and the separator may be stacked or wound to form a stacked structure battery cell or a wound structure battery cell, and the battery cell is packaged in the outer package;
  • the electrolyte may be an electrolyte, and the electrolyte is infiltrated in the battery cell.
  • the number of batteries in the secondary battery may be one or more, which can be adjusted according to demand.
  • the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly by a winding process or a lamination process.
  • the outer packaging can be used to package the above electrode assembly and the electrolyte.
  • the outer packaging of the secondary battery may be a soft package, such as a bag-type soft package.
  • the material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the present application provides a method for preparing a secondary battery, wherein the positive electrode sheet described in the present application or the positive electrode sheet prepared according to the method described in the present application is used.
  • the preparation of the secondary battery may also include the step of assembling the negative electrode sheet, the positive electrode sheet and the electrolyte of the present application to form a secondary battery.
  • the positive electrode sheet, the separator, and the negative electrode sheet may be wound or stacked in sequence, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, thereby obtaining a battery cell.
  • the battery cell is placed in an outer package, and the electrolyte is injected and sealed to obtain a secondary battery.
  • the battery group margin of the secondary battery is 90-95%.
  • the present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape.
  • 3 is a secondary battery 5 of a square structure as an example.
  • the outer package may include a shell 51 and a top cover assembly 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • the present application provides an electrical device, a battery module or a battery pack, wherein the electrical device, the battery module or the battery comprises a secondary battery as described in the present application or a secondary battery prepared according to the method described in the present application.
  • secondary batteries may be assembled into a battery module.
  • the number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.
  • FIG5 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.
  • the battery module 4 may further include a housing having a housing space, and the plurality of secondary batteries 5 are housed in the housing space.
  • the battery modules described above may also be assembled into a battery pack.
  • the battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.
  • FIG6 and FIG7 are battery packs 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4.
  • the plurality of battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application.
  • the secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device.
  • the electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • FIG8 is an example of an electric device.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module may be used.
  • a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.
  • the positive electrode active material of Example 1 refers to the positive electrode active material used in the preparation process of the lithium ion battery of Example 1;
  • the positive electrode plate of Example 1 refers to the positive electrode plate used in the preparation process of the lithium ion battery of Example 1;
  • the negative electrode plate of Example 1 refers to the positive electrode plate used in the preparation process of the lithium ion battery of Example 1;
  • the electrolyte of Example 1 refers to the electrolyte used in the preparation process of the lithium ion battery of Example 1;
  • the isolation membrane of Example 1 refers to the isolation membrane used in the preparation process of the lithium ion battery of Example 1;
  • the lithium ion battery of Example 1 refers to a lithium ion battery prepared by the positive electrode, isolation membrane, negative electrode and electrolyte of Example 1.
  • Cyanuric acid (CA, CAS: 108-80-5, Shanghai MacLean Biotechnology Co., Ltd.)
  • N, N′-(1,4-phenylene) bismaleimide (Shanghai MacLean Biotechnology Co., Ltd.)
  • NMP N-Methylpyrrolidone
  • PVDF Polyvinylidene fluoride
  • Carbon nanotubes (CNT, diameter ⁇ 2nm, length 0.5-3 ⁇ m, Aladdin Reagent Network)
  • CMC Sodium carboxymethyl cellulose
  • Styrene butadiene rubber (SBR, Guangdong Kaijin New Energy Technology Co., Ltd.)
  • Ethylene carbonate (EC, CAS: 96-49-1, Shanghai MacLean Biotechnology Co., Ltd.)
  • Lithium hexafluorophosphate LiPF6, CAS: 21324-40-3, Guangzhou Tianci High-tech Materials Co., Ltd.
  • the cyanuric acid compound thiocyanuric acid (TCA) and the maleimide compound N, N'-(4, 4'-bismaleimide) dimethylbenzene (BMI) are mixed in a mass ratio of 1:3 (molar ratio 1:1.48), and then a solvent N-methylpyrrolidone (NMP) is added to dilute to 20 times, and after sufficient stirring, an inert gas (such as nitrogen, etc.) is introduced into the solution to remove air, and the reaction is carried out at 120°C for 1 hour. After the reaction is completed, the solution is cooled to room temperature to obtain a polymer solution, in which the mass of the polymer contained is the sum of the mass of the cyanuric acid compound and the cyanuric acid compound.
  • NMP N-methylpyrrolidone
  • Step S2 Preparation of positive electrode active material
  • step S1 To the polymer solution prepared in step S1 above, add the positive electrode active material NCM523 (the mass ratio of NCM523 to polymer is 199:1). After the solution is fully stirred, remove the air and react at 60°C for 1 hour. After suction filtration, vacuum drying is carried out at 80°C for 12 hours to obtain a positive electrode active material with a polymer coating layer, i.e., the positive electrode active material of Example 1, wherein the mass percentage of the coating layer is 0.5%, based on the total mass of NCM523 and the polymer.
  • a positive electrode active material with a polymer coating layer i.e., the positive electrode active material of Example 1, wherein the mass percentage of the coating layer is 0.5%, based on the total mass of NCM523 and the polymer.
  • Step S3 Preparation of positive electrode slurry
  • the positive electrode active material (having a polymer coating layer) prepared in the above step S2, conductive carbon black, carbon nanotubes, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95.5:2:0.5:2, and then solvent N-methylpyrrolidone is added and stirred thoroughly to form a positive electrode slurry with a solid content of 60%.
  • PVDF polyvinylidene fluoride
  • Step S4 Preparation of positive electrode sheet
  • the positive electrode slurry prepared in the above step S3 is coated on the current collector aluminum foil, with a coating width of 70 mm and a coating surface density of the positive electrode material of 12.6 mg/ cm2 (dry weight); after double-sided coating, it is dried in a vacuum drying oven at 100°C for 14 hours, then naturally cooled to room temperature, and rolled to obtain a positive electrode sheet with uniform thickness (97 ⁇ m), which is the positive electrode sheet used in Example 1.
  • the negative electrode active material graphite, conductive agent carbon black (SP), dispersant CMC (sodium carboxymethyl cellulose), and binder styrene-butadiene rubber were added to deionized water at a mass ratio of 96.5:1.5:1:1, and stirred thoroughly to form a negative electrode slurry with a solid content of 60%; the negative electrode slurry was coated on the current collector copper foil with a coating width of 75mm and a coating surface density of 7.9mg/ cm2 . After double-sided coating, it was dried in a vacuum drying oven at 90-110°C for 10-15h, then naturally cooled to room temperature, and rolled to obtain a negative electrode sheet with uniform thickness (108 ⁇ m).
  • SP conductive agent carbon black
  • CMC sodium carboxymethyl cellulose
  • binder styrene-butadiene rubber were added to deionized water at a mass ratio of 96.5:1.5:1:1, and stirred thoroughly to form a negative electrode slurry with a solid content of
  • LiPF 6 lithium hexafluorophosphate
  • PE polyethylene
  • the positive electrode sheet, the isolation film, and the negative electrode sheet are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role, and then they are wound to obtain a bare battery cell; the bare battery cell with a capacity of 92mAh is placed in an outer plastic packaging, and the above-prepared 0.5g electrolyte is injected into the dried battery. After vacuum packaging, standing, formation, shaping and other processes, a lithium-ion battery is obtained.
  • FIG1 shows the infrared spectrum of the positive electrode active material (with a coating layer) prepared in step S2 of Example 1 and the infrared spectrum of the raw material NCM523 (before coating);
  • FIG2 shows the TEM imaging of the positive electrode active material prepared in Example 1.
  • the preparation process of the lithium-ion battery is generally similar to that of Example 1, except that the feed mass ratio of NCM523 to polymer in step S2 is changed to 99:1, thereby obtaining the positive electrode active material of Example 2 (having a polymer coating layer), and the mass percentage of the coating layer is 1%, based on the total mass of NCM523 and the polymer.
  • the preparation process of the lithium-ion battery as a whole refers to Example 2, except that the feed mass ratio of NCM523 to polymer in step S2 is changed to 65.75:1, thereby obtaining the positive electrode active material of Example 3 (with a polymer coating layer), and the mass percentage of the coating layer is 1.5%, based on the total mass of NCM523 and the polymer.
  • the preparation process of the lithium-ion battery is generally similar to that of Example 1, except that the feed mass ratio of NCM523 to polymer in step S2 is changed to 49:1, thereby obtaining the positive electrode active material of Example 4 (having a polymer coating layer), the mass percentage of the coating layer being 2%, based on the total mass of NCM523 and the polymer.
  • the preparation process of the lithium-ion battery is generally similar to that of Example 2, except that the reaction temperature in step S2 is changed to 55°C.
  • the preparation process of the lithium-ion battery is generally similar to that of Example 2, except that the reaction temperature in step S2 is changed to 80°C.
  • the preparation process of the lithium-ion battery is generally similar to that of Example 2, except that the monomer maleimide compound in the polymerization reaction in step S1 is changed to maleimide instead of N,N′-(4,4′-bismaleimide)xylene (BMI).
  • BMI N,N′-(4,4′-bismaleimide)xylene
  • the preparation process of the lithium-ion battery is generally referred to Example 2, except that the monomer maleimide compound in the polymerization reaction in step S1 is changed to N,N′-(1,4-phenylene)bismaleimide instead of N,N′-(4,4′-bismaleimido)xylene (BMI).
  • BMI N,N′-(1,4-phenylene)bismaleimide
  • the preparation process of the lithium-ion battery is generally referred to Example 2, except that the monomers of the polymerization reaction in step S1 are changed, wherein the cyanuric acid compound is cyanuric acid, and the maleimide compound is N,N′-(1,2-phenylene)bismaleimide.
  • step S2 is not included, and the specific process of step S3 is as follows:
  • the positive electrode active material NCM523, conductive carbon black, carbon nanotubes, and PVDF are mixed in a mass ratio of 94.545:2:0.5:2, and then N-methylpyrrolidone solvent is added and stirred thoroughly, and then the polymer prepared in the above step S1 is added (wherein the mass ratio of the polymer added to NCM523 is 1:99) to form a positive electrode slurry with a solid content of 60%.
  • step S2 is not included, and the specific process of step S3 is as follows:
  • the polymer, positive electrode active material NCM523, conductive carbon black, carbon nanotubes and PVDF were mixed in a mass ratio of 8.76:86.74:2:0.5:2, and then N-methylpyrrolidone solvent was added and stirred thoroughly to form a positive electrode slurry with a solid content of 60%.
  • step S2 is not included, and the specific process of step S3 is as follows:
  • the positive electrode active material NCM523, conductive carbon black, carbon nanotubes and PVDF were mixed in a mass ratio of 95.5:2:0.5:2, and then N-methylpyrrolidone solvent was added and stirred thoroughly to form a positive electrode slurry with a solid content of 60%.
  • NCM samples before and after coating were analyzed by infrared spectrum using SP100 advanced Fourier transform infrared spectrometer from Perkin Elmer Company, USA, with the scanning range of 4000 cm -1 to 500 cm -1 .
  • curve b represents the uncoated NCM sample, that is, the raw material NCM523 used in step 2 of Example 1
  • the positive electrode active material prepared in step S2 of Example 1 was tested using a TECNAI F20 transmission electron microscope (TEM, 600K magnification). As shown in FIG2 , the darker region I on the right side of the figure is NCM523, and the lighter region II on the left side is the polymer coating layer; thus, the interface between the polymer coating layer and NCM523 can be clearly observed, and the thickness of the coating layer is uniform; then, at any point at the junction of regions I and II, the vertical distance from the point to the boundary of region II (i.e., the outer surface of the positive electrode active material) is measured as the coating layer thickness; the coating layer thickness of any three points at the junction is measured by this method, and their average value is the coating layer thickness of the positive electrode active material of the present application.
  • TEM TECNAI F20 transmission electron microscope
  • Dv50 The physical definition of Dv50 is as follows: the particle size corresponding to when the cumulative volume distribution percentage of material particles reaches 50%.
  • the nitrogen adsorption specific surface area analysis test method was adopted, referring to GB/T 19587-2017, and the test was carried out by Micromeritics Tri-Star 3020 specific surface area pore size analysis tester; and the result was calculated by BET (Brunauer Emmett Teller) method.
  • the lithium-ion battery prepared in the embodiment and the comparative example is charged at a constant current of 4C to a charge cut-off voltage of 4.4V, then charged at a constant voltage to a current ⁇ 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 1C to a discharge cut-off voltage of 2.5V.
  • the first cycle discharge capacity of the battery is measured and left to stand for 5 minutes. This is a charge and discharge cycle.
  • the battery is tested for cyclic charge and discharge for a total of 200 cycles to obtain the discharge capacity of the last cycle.
  • Cycle capacity retention rate (%) last cycle discharge capacity/first cycle discharge capacity.
  • the lithium-ion battery prepared in the embodiment and comparative example was charged at a constant current of 0.33C to a charging cut-off voltage of 4.4V, and then charged at a constant voltage to a current of 0.05C, and the charging was stopped and left to stand for 60 minutes.
  • the battery was subjected to a cyclic charge and discharge test according to this method, with a total of 200 cycles.
  • the DCR growth rate (%) of 200 cycles (200th cycle fast charge DCR-first cycle fast charge DCR)/first cycle fast charge DCR.
  • the lithium-ion batteries prepared in the examples and comparative examples were charged at a constant current of 0.33C to a charge cutoff voltage of 4.4V, and then charged at a constant voltage to a current of 0.05C, and then stopped charging and left to stand for 60 minutes. After that, the battery was discharged at a rate of 0.33C to 50% SOC and the voltage V1 was recorded; then charged at a rate of 4C for 30 seconds and the voltage V2 was recorded.
  • DCR (V2-V1)/charging current, where the charging current is the current of the battery at a charging rate of 4C.
  • the molar ratio of TCA to BMI in the raw materials of step S1 corresponds to the ratio of the molar amount of structural unit (II) to the total molar amount of structural units (I-2) + (I-3), which is 1:1.48, as in Examples 1-6 and Comparative Examples 1-3;
  • the molar ratio of TCA to maleimide corresponds to the ratio of the molar amount of structural unit (II) to the molar amount of structural unit (I), which is 1:5.5, as in Example 7;
  • the molar ratio of cyanuric acid and N,N′-(1,2-phenylene)bismaleimide corresponds to the ratio of the molar amount of structural unit (II) to the total molar amount of structural units (I-2) + (I-3), which is 1:1.98, as in Example 8;
  • the molar ratio of cyanuric acid and N,N′-(1,2-phenylene)bismaleimide corresponds to the ratio of
  • the lithium ion batteries corresponding to Examples 1-9 have improved cycle capacity retention and reduced DC internal resistance.
  • the cycle capacity retention rate of the lithium-ion battery is in the range of 94.2% to 95.7%, and the DCR growth rate does not exceed 146%, and the DCR value during fast charging is not higher than 560m ⁇ .
  • the mass fraction of the coating layer containing the polymer relative to the mass of the positive electrode active material is 0.5% to 1.5%, and the thickness of the coating layer is 1.1nm to 1.5nm, the cycle capacity retention rate, DCR growth rate and DCR during fast charging of the lithium-ion battery are further improved.
  • step S2 when the positive electrode active material is coated with a polymer, when the reaction temperature is between 55°C and 80°C, the cycle capacity retention rate of the lithium-ion battery is higher than 93.8%, the DCR growth rate is lower than 150%, and the DCR during fast charging is not higher than 564m ⁇ . Furthermore, when the reaction temperature is 60°C, the cycle capacity retention rate, DCR growth rate, and DCR during fast charging of the lithium-ion battery are further improved.
  • step S2 described in the present application the polymer prepared by maleimide compounds and cyanuric acid compounds is directly coated on the positive electrode active material.
  • the positive electrode active material formed is applied to a lithium-ion battery, the cycle capacity retention rate, DCR growth rate and DCR during fast charging of the battery are improved.

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Abstract

正极活性材料包括正极活性物质以及在其表面上的包覆层，包覆层包括具有衍生自单体马来酰亚胺类化合物的结构单元和衍生自单体三聚氰酸类化合物的结构单元的聚合物。正极活性材料的制备方法，包括正极活性材料的二次电池和用电装置。二次电池具有改善的功率性能和循环性能。

Description

正极活性材料、其制法以及包含其的二次电池、电池模块、电池包、用电装置 技术领域
本申请涉及锂电池技术领域，尤其涉及一种正极活性材料及其制被方法、和包含该正极活性材料的二次电池、电池模块、电池包、用电装置。
背景技术
近年来，锂离子电池越来越广泛地应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。由于锂离子电池取得了极大的发展，因此对其循环性能和功率性能提出了更高的要求。
然而，目前的锂离子电池在快速充电时正极活性物质与电解液发生副反应，导致直流内阻增加，循环性能降低，并且电池快速升温，存在安全隐患。因此，设计开发一款在快充时具有较低的直流内阻和良好的循环性能的锂离子电池具有极大的应用价值。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种正极活性材料，其包括正极活性物质以及在其表面上的包覆层，该包覆层包括衍生自单体马来酰亚胺类化合物的结构单元和衍生自单体三聚氰酸类化合物的结构单元的聚合物；这种正极活性材料在应用于锂离子电池的正极时，能够有效地改善电池的功率性能和循环性能。
为了实现上述目的，本申请的第一方面提供了一种正极活性材料，其包括正极活性物质以及在其表面上的包覆层，该包覆层包括衍生自单体马来酰亚胺类化合物的结构单元和衍生自单体三聚氰酸类化合物的结构单元的聚合物。
通过包覆，使聚合物在正极活性物质(例如三元材料(NCM))的表面形成均匀的包覆层，从而保护正极活性物质，减少正极与电解液的副反应，以提高电池的循环性能，并且降低电池在快充时的直流内阻(DCR)。
在任意实施方式中，本申请的正极活性材料的包覆层中，衍生自单体马来酰亚胺类化合物的结构单元包括下式(I-1)至(I-3)中的至少一种：
Figure PCTCN2022122554-appb-000001
其中，R 1为选自以下的基团：
Figure PCTCN2022122554-appb-000002
n为0-3的整数，可选n为1或2。
由此，进一步改善电池在快充时的直流内阻，改善电池在循环时的DCR增长率和循环保持率。
在任意实施方式中，本申请的正极活性材料的包覆层中，衍生自单体三聚氰酸类化合物的结构单元包括下式(II)，
Figure PCTCN2022122554-appb-000003
其中，R 2、R 3和R 4彼此独立地为氧原子或硫原子；尤其是，所述三聚氰酸类化合物选自三聚氰酸和三聚硫氰酸中的至少一种。
在任意实施方式中，正极活性物质选自锂过渡金属氧化物，包括LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2、Li(Ni 0.5Co 0.2Mn 0.3) 1.07O 2、LiNi 0.5Co 0.2Mn 0.3O 2、LiNi 0.5Co 0.25Mn 0.25O 2、LiNi 0.6Co 0.2Mn 0.2O 2、LiNi 0.8Co 0.1Mn 0.1O 2、LiNi 0.85Co 0.15Al 0.05O 2中的至少一种。
在任意实施方式中，本申请的正极活性材料中，包覆层的厚度为0.8nm至2.5nm，可选1.0nm至2nm，进一步可选1.1nm至1.5nm。由此进一步提升电池的循环性能、降低电池在快充时的直流内阻。
在任意实施方式中，本申请正极活性材料中，基于结构单元(I-1)、(I-2)、(I-3)和(II)的总摩尔量计，结构单元(I-1)、(I-2)、(I-3)的摩尔量总和占比为40-90摩尔％，可选50-85摩尔％；结构单元(II)的摩尔占比为10-60摩尔％，可选15-50摩尔％。由此，进一步优化本申请所述的聚合物，从而达到有效地改善电池的功率性能和循环性能的目的。
在任意实施方式中，本申请正极活性材料中，聚合物的重均分子量为3000至5000。
在任意实施方式中，本申请正极活性材料中，聚合物的质量分数为0.3-2.5％，可选0.4-2％，进一步可选0.5-1.5％，基于聚合物与正极活性物质的总质量计。由此，通过进一步限定聚合物的质量含量，以优化具有聚合物包覆层的正极活性材料的组成，有效地降低电池在快充时的直流内阻，改善电池在循环时的DCR增长率和循环保持率。
在任意实施方式中，本申请正极活性材料的中值粒径Dv50为3.2μm至4.2μm，可选为3.5μm至3.6μm；比表面积BET为1.05m 2/g至1.55m 2/g，可选为1.50m 2/g至1.53m 2/g。由此，实现对于正极活性物质的有效包覆，从而进一步降低电池的直流内阻，改善电池的循环保持率和DCR增长率。
本申请的第二方面提供了一种制备本申请第一方面所述的正极活性材料的制备方法，其包括如下步骤：
步骤S1：将马来酰亚胺类化合物和三聚氰酸类化合物进行聚合反应，得到聚合物；
步骤S2：向所述聚合物中加入正极活性物质进行包覆，得到具有聚合物包覆层的正极活性材料。
在任意实施方式中，在本申请的制备正极活性材料的方法中，在步骤S1中，马来酰亚胺类化合物和三聚氰酸类化合物的质量比为2∶1至10∶1，可选2.5∶1至6.5∶1。
在任意实施方式中，在本申请的制备正极活性材料的方法中，在步骤S2中，所述正极活性物质与聚合物的质量比为40∶1至210∶1，可选49∶1至199∶1。
在任意实施方式中，在步骤S2中，加热至温度为55℃至80℃下进行包覆，时间持续0.5h至2h。
本申请的第三方面提供一种二次电池，其包括本申请第一方面所述的正极活性材料，或者本申请第二方面所述的制备方法获得的正极活性材料。
本申请的第四方面提供一种电池模块，其包括本申请第三方面所述的二次电池。
本申请的第五方面提供一种电池包，其包括本申请第四方面所述的电池模块。
本申请的第六方面提供一种用电装置，其包括本申请第三方面所述的二次电池、本申请第四方面所述的电池模块或本申请第五方面所述的电池包中的至少一种。
本申请通过在正极活性物质上包覆具有衍生自单体马来酰亚胺类化合物的结构单元和衍生自三聚氰酸类化合物的结构单元的聚合物，可以保护电池的正极，减少其与电解液发生副反应，有效地改善电池的循环性能和功率性能。相应地，本申请提供的电池包、电池模块和用电装置也具有良好的循环性能和功率性能。
附图说明
图1是本申请实施例1的正极活性物质NCM523在包覆前后的红外光谱图。
图2是本申请实施例1的正极活性材料透射电子显微镜(TEM)成像图。
图3是本申请一实施方式的二次电池的示意图。
图4是图3所示的本申请一实施方式的二次电池的分解图。
图5是本申请一实施方式的电池模块的示意图。
图6是本申请一实施方式的电池包的示意图。
图7是图6所示的本申请一实施方式的电池包的分解图。
图8是本申请一实施方式的二次电池用作电源的用电装置的示意图。
附图标记说明：
区域I：正极活性物质NCM523；区域II：聚合物包覆层；1电池包；2上箱体；3下箱体；4电池模块；5二次电池；51壳体；52电极组件；53顶盖组件。
具体实施方式
以下，适当地参照附图详细说明了本申请的正极活性材料及其制备方法、包含本申请的正极活性材料的二次电池、电池模块、电池包和用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-6。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩 略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
对于锂离子电池而言，在快速充电时，由于来自正极的传荷阻抗及扩散阻抗而导致电池的直流内阻增加，电池温度迅速升高；以及，在锂离子电池的循环过程中，由于正极与电解液中的氢氟酸(HF)及水(H 2O)发生副反应，导致电池的正极结构遭到破坏，循环容量发生不可逆地衰减，电池的循环性能降低。因此，仍然需要对正极材料进行改进，以改善电池的循环性能、功率性能和安全性能等。
本申请发明人通过大量的实验发现，通过马来酰亚胺类化合物和三聚氰酸类化合物的聚合反应而生成的具有衍生自单体马来酰亚胺类化合物的结构单元和三聚氰酸类化合物的结构单元的聚合物，在使用该聚合物对于过渡金属氧化物的正极活性物质进行包覆，所得到的具有该聚合物包覆层的正极活性材料，有利于提高锂离子电池的功率性能和循环性能。
本申请的第一方面提供了一种正极活性材料，其包括正极活性物质以及在其表面上的包覆层，该包覆层包括衍生自单体马来酰亚胺类化合物的结构单元和衍生自单体三聚氰酸类化合物的结构单元的聚合物。
通过在正极活性物质(例如三元材料(NCM))的表面形成该聚合物的包覆层，从而保护电池的正极，有利于在正极与电解液之间形成界面膜(CEI膜)，减少正极与电解液的副反应，以提高电池的循环性能，并且降低电池在快充时的直流内阻(DCR)
可选地，该包覆层由聚合物组成，所述聚合物包括衍生自单体马来酰亚胺类化合物的结构单元和衍生自单体三聚氰酸类化合物的结构单元。
可选地，该包覆层包括聚合物或由聚合物组成，所述聚合物由单体马来酰亚胺类化合物和三聚氰酸类化合物进行共聚反应而获得。
在一些实施方式中，本申请的正极活性材料的包覆层的聚合物中，衍生自单体马来酰亚胺类化合物的结构单元包括下式(I-1)至(I-3)中的至少一种：
Figure PCTCN2022122554-appb-000004
其中，R 1为选自以下的基团中的至少一种：
Figure PCTCN2022122554-appb-000005
n为0-3的整数，可选n为1或2。
上式(1)至(4)中，式(1)表示1，4-亚苯基，式(2)表示1，3-亚苯基，式(3)表示1，2-亚苯基，式(4)表示亚联苯基(n＝0)、亚甲基二苯基(n＝1)或亚乙基二苯基(n＝2)。
由此，进一步改善电池在快充时的直流内阻，改善电池在循环时的DCR增长率和容量保持率。
可选地，在R 1为式(4)时，其与式(I-3)的其他部分的连接位点可以是每个苯基的任一个碳原子上；优选连接位点为对位，即在二苯基的4，4’位上。
又可选地，在R 1为亚甲基二苯基(n＝1)，即为下式所示的基团时，
Figure PCTCN2022122554-appb-000006
对应的式(I-3)的结构单元包括以下的至少一种：
Figure PCTCN2022122554-appb-000007
这些结构单元衍生自以下的双马来酰胺类化合物：N，N′-(4，4′-双马来酰亚胺基)二甲苯烷(BMI)
Figure PCTCN2022122554-appb-000008
可选地，式(I-1)的结构单元衍生自马来酰亚胺
Figure PCTCN2022122554-appb-000009
又可选地，式(I-2)或式(I-3)的结构单元衍生自以下式(III)的双马来酰亚胺类化合物，
Figure PCTCN2022122554-appb-000010
其中，A为选自以下的基团：
Figure PCTCN2022122554-appb-000011
m为0-3的整数，可选m为1或2。
在一些实施方式中，本申请的正极活性材料的包覆层的聚合物中，衍生自单体三聚氰酸类化合物的结构单元包括下式(II)，
Figure PCTCN2022122554-appb-000012
其中，R 2、R 3和R 4彼此独立地为氧原子或硫原子；又可选地，所述三聚氰酸类化合物包括三聚氰酸和三聚硫氰酸中的至少一种。
可选地，本申请的正极活性材料包括正极活性物质以及在其表面上的包覆层，所述包覆层包括聚合物或由聚合物组成，该聚合物包含衍生自单体马来酰亚胺类化合物的结构单元式(I-1)至(I-3)中的至少一种和衍生自单体三聚氰酸类化合物的结构单元(II)。
在一些具体实施方案中，本申请的正极活性材料包括正极活性物质以及在其表面上的包覆层，所述包覆层包括聚合物，或者由聚合物组成，所述聚合物通过单体马来酰亚胺类化合物和三聚氰酸类化合物的聚合反应而获得；其中，所述单体马来酰亚胺类化合物为马来酰亚胺和上式(III)的双马来酰亚胺类化合物，所述三聚氰酸类化合物为三聚氰酸或三聚硫氰酸。马来酰亚胺类化合物与三聚氰酸类化合物的摩尔比为1∶1至6∶1。
在一些实施方式中，本申请的正极活性材料中，正极活性物质选自锂过渡金属氧化物，可选地选自下式锂过渡金属氧化物：
Li(Ni aCo bM c) dO e
其中，M选自Mn和Al之一或者是它们的混合物；
0≤a≤1；
0≤b≤1；
0≤c≤2；
0＜d≤1.2；
2≤e≤4；
a+b+c＞O；
a、b、c、d、e满足所述正极活性物质的价态要求。
可选地，在上述通式中，a+b＞O。
可选地，O＜a≤0.5；O＜b≤0.5；O＜c≤O.5；O.8≤d≤1.15。
可选地，锂过渡金属氧化物选自锂钴氧化物(如LiCoO 2)、锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn 2O 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NCM 333)、Li(Ni 0.5Co 0.2Mn 0.3) 1.07O 2(也可以简称为NCM 523)、LiNi 0.5Co 0.2Mn 0.3O 2、LiNi 0.5Co 0.25Mn 0.25O 2(也可以简称为NCM 211)、LiNi 0.6Co 0.2Mn 0.2O 2(也可以简称为NCM 622)、LiNi 0.8Co 0.1Mn 0.1O 2(也可以简称为NCM 811)、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。
可选地，正极活性物质选自LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2、Li(Ni 0.5Co 0.2Mn 0.3) 1.07O 2、LiNi 0.5Co 0.2Mn 0.3O 2、LiNi 0.5Co 0.25Mn 0.25O 2、LiNi 0.6Co 0.2Mn 0.2O 2、LiNi 0.8Co 0.1Mn 0.1O 2、LiNi 0.85Co 0.15Al 0.05O 2中的至少一种。
在本申请中，正极活性物质的比表面积BET为O.5m 2/g至1.5m 2/g，中值粒径Dv50为3.2μm至4.2μm。
在一些实施方式中，本申请的正极活性材料中，包覆层的厚度为0.8nm至2.5nm，可选1.0nm至2nm，进一步可选1.1nm至1.5nm。由此进一步提升电池的循环性能、降低电池在快充时的直流内阻。
在一些实施方式中，本申请的正极活性材料的包覆层的聚合物中，基于结构单元(I-1)、(I-2)、(I-3)和(II)的总摩尔量计，结构单元(I-1)、(I-2)、(I-3)的摩尔量总和占比为40-90摩尔％，可选50-85摩尔％；结构单元(II)的摩尔占比为10-60摩尔％，可选15-50摩尔％。在制备聚合物的聚合反应中，所用的单体马来酰亚胺类化合物和三聚氰酸类化合物的摩尔比为1∶1至6∶1。由此，进一步 优化本申请所述的聚合物的结构，从而达到有效地改善电池的功率性能和循环性能的目的。
在一些实施方式中，本申请正极活性材料中，基于结构单元(I-1)、(I-2)、(I-3)和(II)的总摩尔量计，结构单元(I-1)的摩尔占比为0-90摩尔％，(I-2)和(I-3)的摩尔量总和的占比为0-70摩尔％，可选51-67摩尔％；结构单元(II)的摩尔占比为10-60摩尔％，可选15-50摩尔％。其中，结构单元(I-1)的摩尔占比与结构单元(I-2)和(I-3)的摩尔量总和的占比不同时为零。
可选地，基于结构单元(I-1)、(I-2)、(I-3)和(II)的总摩尔量计，结构单元(I)的摩尔占比(或基于单体马来酰亚胺类化合物和三聚氰酸类化合物的总摩尔量计，马来酰亚胺的摩尔占比)可为约0摩尔％、约5摩尔％、约10摩尔％、约15摩尔％、约20摩尔％、约25摩尔％、约30摩尔％、约35摩尔％、约40摩尔％、约45摩尔％、约50摩尔％、约55摩尔％、约60摩尔％、约65摩尔％、约70摩尔％、约80摩尔％、约82摩尔％、约85摩尔％、约87摩尔％或约89摩尔％。或者，结构单元(I)的摩尔占比在上述任意值组成的任意范围内。
可选地，基于结构单元(I-1)、(I-2)、(I-3)和(II)的总摩尔量计，结构单元(I-2)和(I-3)的摩尔量总和的占比(或基于单体马来酰亚胺类化合物和三聚氰酸类化合物的总摩尔量计，式(A)的双马来酰亚胺的摩尔占比)可为约0摩尔％、约5摩尔％、约10摩尔％、约15摩尔％、约20摩尔％、约25摩尔％、约30摩尔％、约35摩尔％、约40摩尔％、约45摩尔％、约50摩尔％、约52摩尔％、约55摩尔％、约57摩尔％、约60摩尔％、约62摩尔％、约65摩尔％、约67摩尔％、约70摩尔％、约75摩尔％、约80摩尔％或约85摩尔％。或者，结构单元(I-2)和(I-3)的摩尔量总和的占比在上述任意值组成的任意范围内。
可选地，基于结构单元(I-1)、(I-2)、(I-3)和(II)的总摩尔量计，结构单元(II)的摩尔占比(或基于单体马来酰亚胺类化合物和三聚氰酸类化合物的总摩尔量计，三聚氰酸类化合物(特别是三 聚氰酸和三聚硫氰酸)的摩尔占比)可为为约10摩尔％、约12摩尔％、约15摩尔％、约18摩尔％、约20摩尔％、约25摩尔％、约30摩尔％、约32摩尔％、约35摩尔％、约37摩尔％、约38摩尔％、约40摩尔％、约42摩尔％、约45摩尔％、约48摩尔％、约50摩尔％、约52摩尔％、约55摩尔％或约60摩尔％。或者，结构单元(II)的摩尔量占比在上述任意值组成的任意范围内。
本申请中，“约”某个数值表示一个范围，即该数值的±3％的范围。
在一些实施方式中，本申请正极活性材料中，聚合物的重均分子量为3000至5000。使用蒸汽渗透压仪OSMOMAT 070测定聚合物的重均分子量。
在一些实施方式中，本申请正极活性材料中，基于聚合物与正极活性物质的总质量计，聚合物的质量分数为0.3％至2.5％，可选0.4％至2％，进一步可选0.5％至1.5％。由此，通过进一步限定聚合物的质量含量，以优化具有聚合物包覆层的正极活性材料的组成，从而有效地降低电池在快充时的直流内阻，改善电池在循环时的DCR增长率和容量保持率。
在一些实施方式中，本申请正极活性材料中，基于聚合物与正极活性物质的总质量计，包覆层(即聚合物包覆层)的质量分数为0.3％至2.5％，可选0.4％至2％，进一步可选0.5％至1.5％。
在一些实施方式中，本申请正极活性材料中，包覆层相对于正极活性材料的质量计的质量分数为0.3％至2.5％，可选0.4％至2％，进一步可选0.5％至1.5％。
在一些实施方式中，本申请正极活性材料的中值粒径Dv50为2.7μm至9.5μm，可选为3.2μm至4.2μm，进一步可选为3.5μm至3.6μm；比表面积BET为0.9m 2/g至1.67m 2/g，可选为1.05m 2/g至1.55m 2/g，进一步可选为1.50m 2/g至1.53m 2/g。由此进一步降低电池的直流内阻，改善电池的容量保持率和DCR增长率。
本申请的第二方面提供了一种制备本申请第一方面所述的正极活性材料的制备方法，其包括如下步骤：
步骤S1：将马来酰亚胺类化合物和三聚氰酸类化合物进行聚合反应，得到聚合物；
步骤S2：向所述聚合物中加入正极活性物质进行包覆，得到具有聚合物包覆层的正极活性材料。
由此得到本申请的具有聚合物包覆层的正极活性材料，使用该正极活性材料制成的二次电池具有改善的循环性能和功率性能。
其中，在步骤S1中，在有机溶剂(例如N-甲基吡咯烷酮，NMP)存在下，在110℃至135℃下，将马来酰亚胺类化合物和三聚氰酸类化合物混合，并且在搅拌下反应0.5h至2h，然后冷却备用。马来酰亚胺类化合物和三聚氰酸类化合物的质量比为1∶2至17∶1或1∶1至12∶1，可选2∶1至10∶1，可选2.5∶1至6.5∶1，例如2∶1至5∶1、或3∶1至3.5∶1。
在步骤S2中，采用液相包覆的方法，向步骤S1)得到的聚合物的溶液中加入正极活性物质，充分搅拌后除去空气，在55℃至80℃下进行包覆，时间持续0.5h至2h。然后抽滤、在75℃至90℃下干燥，得到本申请的具有聚合物包覆层的正极活性材料。其中，加入的正极活性物质的质量与步骤S1获得的聚合物的质量比为40∶1至210∶1，可选49∶1至199∶1。
应理解，本申请的正极活性材料，不仅可以用于二次电池，也可以用于任何其他需要降低功率性能且提高循环性能的任何电池、电池模块、电池包或用电装置。
下文对本申请的二次电池、电池模块、电池包和用电装置进行说明。
二次电池
本申请的一个实施方式中，提供一种二次电池，其包括本申请的第一方面所述的正极活性材料以及通过本申请第二方面所述的方法制备的正极活性材料。
通常情况下，二次电池包括正极极片、负极极片、电解质和隔离膜。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。
[正极极片]
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膜层，正极膜层包括本申请的第一方面所述的正极活性材料以及通过本申请第二方面所述的方法制备的正极活性材料。
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，正极膜层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。
在一些实施方式中，正极集流体可采用金属箔片或复合集流体。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)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
正极膜层还可选地包括粘结剂。作为示例，粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。粘结剂在正极膜层中的质量含量为1％至10％，基于正极膜层的总重量计。
正极膜层还可选地包括导电剂。作为示例，导电剂可以包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。导电剂在负极膜层中的质量含量为1％至5％，基于正极膜层的总重量计。
本申请的正极极片的制备方法如下：
步骤S1：将马来酰亚胺类化合物和三聚氰酸类化合物进行聚合反应，得到聚合物；
步骤S2：向所述聚合物中加入正极活性物质进行包覆，得到正极活性材料(具有聚合物包覆层)；
步骤S3：将所述正极活性材料(具有聚合物包覆层)、导电剂、粘结剂混合，得到正极浆料；
步骤S4：将所述正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
通过步骤S1和S2，制备本申请第一方面所述的正极活性材料。
其中，在步骤S1中，在有机溶剂(例如N-甲基吡咯烷酮，NMP)存在下，在110℃至135℃下，将马来酰亚胺类化合物和三聚氰酸类化合物混合，并且在搅拌下反应0.5h至2h，然后冷却备用。马来酰亚胺类化合物和三聚氰酸类化合物的质量比为1∶1至12∶1，可选为2∶1至10∶1，又可选2.5∶1至6.5∶1，例如2∶1至5∶1或3∶1至3.5∶1。
在步骤S2中，采用液相包覆的方法，向步骤S1)得到的聚合物的溶液中加入正极活性物质，充分搅拌后除去空气，在55℃至80℃下反应0.5-2h。然后抽滤、在75-90℃下干燥，得到具有聚合物包覆层的正极活性材料。其中，加入的正极活性物质的质量与步骤S1蝴蝶的聚合物的质量比为40∶1至210∶1，可选49∶1至199∶1。
在步骤S3中，按照本领域的一般方法，将步骤S2制备的正极活性材料、导电剂、粘结剂按照质量比例(45-50)∶(1-1.4)∶1混合，然后加入有机溶剂(例如N-甲基吡咯烷酮，NMP)中，充分搅拌后，得到固含量为55-70％的正极浆料。
在步骤S4中，将所述正极浆料涂布在集流体上，涂布面密度为10mg/cm 2至15mg/cm 2(干重)；然后在100℃至120℃下、在真空干燥箱中干燥12h至16h，随后自然降温至室温，进行辊压后，得到厚度均匀(85μm至110μm)的正极极片。
[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，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，负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。负极活性物质在负极膜层中的质量含量为93％至99％，基于负极膜层测定总重量计。
在一些实施方式中，负极膜层还可选地包括粘结剂。粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。粘结剂在负极膜层中的质量含量为1％至10％，负极膜层，基于负极膜层测定总重量计。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳 米纤维中的至少一种。导电剂在负极膜层中的质量含量为1％至5％，基于负极膜层测定总重量计。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如分散剂(如羧甲基纤维素钠(CMC-Na))等。分散剂在负极膜层中的质量含量为0.1％至1.5％，基于负极膜层测定总重量计。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成固含量为55-70％的负极浆料；然后将所述负极浆料涂布在集流体上，涂布面密度为7mg/cm 2至8.5mg/cm 2(干重)；然后在85℃至115℃下、在真空干燥箱中干燥9h至16h，随后自然降温至室温，进行辊压后，得到厚度均匀(100μm至115μm)的负极极片。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以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，电解质采用电解液。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)中的一种或几种。电解质盐在电解液中的摩尔浓度为0.5mol/L至5mol/L。
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)中的一种或几种。溶剂在电解液中的质量含量为60％至95％，基于电解液的总重量计。
在一些实施方式中，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、改善电池低温性能的添加剂等。添加剂在电解液中的质量含量为0％至2％，基于电解液的总重量计。
[隔离膜]
在一些实施方式中，二次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、聚丙烯及聚偏氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，所述隔离膜的厚度为6-40μm，可选为12-20μm。
[外包装]
在一些实施方式中，二次电池可以包括外包装，用于封装正极极片、负极极片和电解质。作为一个示例，正极极片、负极极片和隔离膜可经叠片或卷绕形成叠片结构电芯或卷绕结构电芯，电芯封装在外包装内；电解质可采用电解液，电解液浸润于电芯中。二次电池中电芯的数量可以为一个或几个，可以根据需求来调节。
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。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，二次电池的外包装可以是软包，例如袋式软包。软包的材质可以是塑料，如可包括聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的一种或几种。在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。
二次电池的制备方法
在一个实施方式中，本申请提供一种二次电池的制备方法，其中，使用本申请所述的正极极片或根据本申请所述的方法制备的正极极片。
二次电池的制备还可以包括将本申请的负极极片、正极极片和电解质组装形成二次电池的步骤。在一些实施方式中，可将正极极片、隔离膜、负极极片按顺序卷绕或叠片，使隔离膜处于正极极片与负极极片之间起到隔离的作用，得到电芯。将电芯置于外包装中，注入电解液并封口，得到二次电池。二次电池的电池群裕度为90-95％。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，3是作为一个示例的方形结构的二次电池5。
在一些实施方式中，参照图4，外包装可包括壳体51和顶盖组件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，顶盖组件53能够盖设于开口，以封闭容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
用电装置、电池模块或电池包
在一个实施方式中，本申请提供一种用电装置、电池模块或电池包，其中，所述用电装置、电池模块或电池包括如本申请所述的二次电池或根据本申请所述的方法制备的二次电池。
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为一个或多个，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5是作为一个示例的电池模块4。参照图5，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施方式中，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可以为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
图6和图7是作为一个示例的电池包1。参照图6和图7，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。
另外，本申请还提供一种用电装置，该用电装置包括本申请提供的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块、或电池包可以用作用电装置的电源，也可以用作用电装置的能量存储单元。用电装置可以包括移动设备(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，但不限于此。
作为用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图8是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对二次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，可以采用二次电池作为电源。
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，均为可以通过市购获得的常规产品。
以下描述用语：“实施例1的正极活性材料”是指实施例1的锂离子电池制备过程中的所用的正极活性材料；“实施例1的正极极片”是指实施例1的锂离子电池制备过程中的所用的正极极片；“实施例1的负极极片”是指实施例1的锂离子电池制备过程中的所用的正极极片；“实施例1的电解液”是指实施例1的锂离子电池制备过程中的所用的电解液；“实施例1的隔离膜”是指实施例1的锂离子电池制备过程中的所用的隔离膜；“实施例1的锂离子电池”是指由实施例1的正极、隔离膜、负极、电解液制备而成的锂离子电池。
原料：
正极活性物质(商用NCM523，化学式为Li(Ni 0.5Co 0.2Mn 0.3) 1.07O 2，BET＝1.41m 2/g，Dv50＝3.58μm)。
三聚硫氰酸(TCA，CAS：638-16-4，上海麦克林生物科技有限公司)
三聚氰酸(CA，CAS：108-80-5，上海麦克林生物科技有限公司)
N，N′-(4，4′-双马来酰亚胺基)二甲苯烷(BMI，CAS：13676-54-5，上海麦克林生物科技有限公司)
马来酰亚胺(MI，CAS：541-59-3，上海麦克林生物科技有限公司)
N，N′-(1，4-亚苯基)双马来酰亚胺(上海麦克林生物科技有限公司)
N，N′-(1，2-亚苯基)双马来酰亚胺(上海麦克林生物科技有限公司)
N-甲基吡咯烷酮(NMP，CAS：872-50-4，上海麦克林生物科技有限公司)
聚偏氟乙烯(PVDF，CAS：24937-79-9，上海麦克林生物科技有限公司)
导电炭黑(广东凯金新能源科技股份有限公司)
碳纳米管(CNT，直径≤2nm，长度0.5～3μm，阿拉丁试剂网)
石墨(广东凯金新能源科技股份有限公司)
羧甲基纤维素钠(CMC，CAS：9004-32-4，上海麦克林生物科技有限公司)
丁苯橡胶(SBR，广东凯金新能源科技股份有限公司)
碳酸亚乙酯(EC，CAS：96-49-1，上海麦克林生物科技有限公司)
碳酸二乙酯(DEC，上海麦克林生物科技有限公司)
六氟磷酸锂(LiPF6，CAS：21324-40-3，广州天赐高新材料股份有限公司)
实施例1
【正极极片的制备】
步骤S1：聚合物的制备
将三聚氰酸类化合物三聚硫氰酸(TCA)及马来酰亚胺类化合物N，N′-(4，4′-双马来酰亚胺基)二甲苯烷(BMI)以1∶3的质量比例混合(摩尔比1∶1.48)，然后加入溶剂N-甲基吡咯烷酮(NMP)稀释至20倍，充分搅拌后，向溶液中通入惰性气体(如氮气等)以除去空气，并于120℃下反应1h。反应完成后将溶液冷却至室温，得到聚合物的溶液，其中所包含的聚合物的质量为三聚氰酸类化合物和三聚氰酸类化合物的投料质量的总和。
步骤S2：正极活性材料的制备
向上述步骤S1制备的聚合物的溶液中，加入正极活性物质NCM523(NCM523与聚合物的质量比为199∶1)。溶液充分搅拌后除去空气，并于60℃下反应1h。抽滤后，于80℃下真空干燥12h，得到具有聚合物包覆层的正极活性材料，即实施例1的正极活性材料，其中包覆层质量百分比为0.5％，基于NCM523与聚合物的总质量计。
步骤S3：正极浆料的制备
将上述步骤S2制备的正极活性材料(具有聚合物包覆层)、导电炭黑、碳纳米管、聚偏氟乙烯(PVDF)按照95.5∶2∶0.5∶2的质量比混合，然后加入溶剂N-甲基吡咯烷酮充分搅拌后，形成固含量为60％的正极浆料。
步骤S4：正极极片的制备
将上述步骤S3制备的正极浆料涂布在集流体铝箔上，涂布宽度为70mm，正极材料的涂布面密度为12.6mg/cm 2(干重)；经过双面涂布后，在100℃下在真空干燥箱中干燥14h，然后自然降温至室温，进行辊压后，得到厚度均匀(97μm)的正极极片，即为实施例1所用的正极极片。
【负极极片的制备】
将负极活性材料石墨、导电剂炭黑(SP)、分散剂CMC(羧甲基纤维素钠)、粘结剂丁苯橡胶按照96.5∶1.5∶1∶1的质量比加入去离子水中，充分搅拌后，形成固含量为60％的负极浆料；将负极浆料涂布在集流体铜箔上，涂布宽度为75mm，涂布面密度为7.9mg/cm 2。双面涂布后，在90-110℃下、在真空干燥箱中干燥10-15h，然后自然降温至室温，进行辊压后，即得到厚度均匀(108μm)的负极极片。
【电解液的制备】
含水量＜10ppm的氩气气氛手套箱中，将碳酸亚乙酯与碳酸二乙酯以质量比3∶7的混合，加入六氟磷酸锂(LiPF 6)，充分溶解后，得到1mol/L的LiPF 6的电解液。
【隔膜膜】
采用聚乙烯(PE)隔离膜，厚度为16μm。
【二次电池的制备】
将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极极片之间起到隔离的作用，然后卷绕得到裸电芯；将容量为92mAh的裸电芯置于外包装塑料中，将上述制备好0.5g电解液注入到干燥后的电池中，经过真空封装、静置、化成、整形等工序，获得锂离子电池。
如图1示出，实施例1中步骤S2制备的正极活性材料(具有包覆层)的红外光谱图和原料NCM523(在包覆之前)的红外光谱图；图2示出实施例1制备的正极活性材料的TEM成像图。
实施例2
锂离子电池的制备过程整体上参照实施例1，区别在于，将步骤S2中NCM523与聚合物的投料质量比改变为99∶1，由此得到实施例2的正极活性材料(具有聚合物包覆层)，包覆层质量百分比为1％，基于NCM523与聚合物的总质量计。
实施例3
锂离子电池的制备过程整体上参照实施例2，区别在于，将步骤S2中NCM523与聚合物的投料质量比改变为65.75∶1，由此得到实施例3的正极活性材料(具有聚合物包覆层)，包覆层质量百分比为1.5％，基于NCM523与聚合物的总质量计。
实施例4
锂离子电池的制备过程整体上参照实施例1，区别在于，将步骤S2中NCM523与聚合物的投料质量比改变为49∶1，由此得到实施例4的正极活性材料(具有聚合物包覆层)，包覆层质量百分比为2％的，基于NCM523与聚合物的总质量计。
实施例5
锂离子电池的制备过程整体上参照实施例2，区别在于，改变步骤S2中的反应温度为55℃。
实施例6
锂离子电池的制备过程整体上参照实施例2，区别在于，改变步骤S2中的反应温度为80℃。
实施例7
锂离子电池的制备过程整体上参照实施例2，区别在于，改变步骤S1中聚合反应的单体马来酰亚胺类化合物，采用马来酰亚胺替代N，N′-(4，4′-双马来酰亚胺基)二甲苯烷(BMI)。
实施例8
锂离子电池的制备过程整体上参照实施例2，区别在于，改变步骤S1中聚合反应的单体马来酰亚胺类化合物，采用N，N′-(1，4-亚苯基)双马来酰亚胺替代N，N′-(4，4′-双马来酰亚胺基)二甲苯烷(BMI)。
实施例9
锂离子电池的制备过程整体上参照实施例2，区别在于，改变步骤S1中聚合反应的单体，其中三聚氰酸类化合物采用三聚氰酸，马来酰亚胺类化合物采用N，N′-(1，2-亚苯基)双马来酰亚胺。
对比例1
锂离子电池的制备过程整体上参照实施例2，区别在于，不包括步骤S2，并且步骤S3的具体过程如下：
将正极活性物质NCM523、导电炭黑、碳纳米管、PVDF按照94.545∶2∶0.5∶2的质量比混合，然后加入N-甲基吡咯烷酮溶剂充分搅拌后，加入上述步骤S1制备的聚合物(其中加入该聚合物的量与NCM523的质量比为1∶99)，形成固含量为60％的正极浆料。
对比例2
锂离子电池的制备过程整体上参照实施例2，区别在于，不包括步骤S2，并且步骤S3的具体过程如下：
将聚合物、正极活性物质NCM523、导电炭黑、碳纳米管、PVDF按照8.76∶86.74∶2∶0.5∶2的质量比混合，然后加入N-甲基吡咯烷酮溶剂充分搅拌后形成固含量为60％的正极浆料。
对比例3
锂离子电池的制备过程整体上参照实施例2，区别在于，不包括步骤S2，并且步骤S3的具体过程如下：
将正极活性物质NCM523、导电炭黑、碳纳米管、PVDF按照95.5∶2∶0.5∶2的质量比混合，然后加入N-甲基吡咯烷酮溶剂充分搅拌后，形成固含量为60％的正极浆料。
【相关参数及电池性能测试】
1.正极活性材料的包覆层的测定
使用美国Perkin Elmer公司的SP100型高级傅里叶变换红外光谱仪对包覆前后的NCM样品进行红外光谱分析，扫描范围为4000cm -1～500cm -1。
图1所示，曲线b表示未包覆的NCM样品，即为实施例1的步骤2中所用的原料NCM523；曲线a表示包覆后的NCM样品，即为实施例1的步骤S2制备的正极活性材料(具有聚合物包覆层的NCM523)，其中在1670.52cm -1及1507.55cm -1处分别出现C＝O及苯环的特征峰，由此证明在原料NCM523上包覆有聚合物包覆层，因此实施例1的正极活性材料具有聚合物包覆层。
2.正极活性材料的包覆层的厚度测定
使用TECNAI F20型透射电子显微镜(TEM，600K放大倍数)测试实施例1的步骤S2制备的正极活性材料。如图2所示，图中右侧颜色深的区域I为NCM523，左侧颜色较浅的区域II为聚合物包覆层；由此，可以清楚地观察到聚合物包覆层与NCM523之间的界面，并且包覆层的厚度均匀；然后在区域I和II的交界处任意取一点，测定从该点至区域II边界(即正极活性材料的外表面)的垂直距离即为包覆层厚度；通过该方法测定该交界处的任意3个点的包覆层厚度，它们的平均值即为本申请的正极活性材料的包覆层厚度。
3.正极活性材料的中值粒径(Dv50)
参照标准GB/T 19077.1-2016，使用激光粒度分析仪(Malvern Master Size 3000)测定。
其中，Dv50的物理定义如下：材料颗粒累计体积分布百分数达到50％时所对应的粒径。
4.正极活性材料的比表面积(BET)
采用氮气吸附比表面积分析测试方法，参照GB/T 19587-2017，通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪进行测试；并且利用BET(Brunauer Emmett Teller)法计算得出。
5.电池的容量保持率
25℃下，将实施例和对比例制备得到的锂离子电池以4C倍率恒流充电至充电截止电压4.4V，之后恒压充电至电流≤0.05C，静置5min，再以1C倍率恒流放电至放电截止电压2.5V，测得电池的首圈放电容量，静置5min，此为一个充放电循环。按照此方法对电池进行循环充放电测试，共计循环200圈，得到最后一圈的放电容量。循环容量保持率(％)＝最后一圈放电容量/首圈放电容量。
6.电池的直流内阻(DCR，Directive Current Resistance)增长率
在25℃下，将实施例和对比例制备得到的锂离子电池以0.33C倍率恒流充电至充电截止电压4.4V，然后进行恒压充电至电流0.05C，停止充电，静置60min。接下来电芯以0.33C倍率放电至50％SOC，并记录此时电压V1；之后以4C倍率充电30秒，并记录电压V2；首圈的快充DCR＝(V2-V1)/充电电流，其中充电电流为电池在4C倍率充电下的电流；之后电芯以0.33C倍率放电至2.5V，此为一个充放电循环。按照此方法对电池进行循环充放电测试，共计循环200圈。循环200圈的DCR增长率(％)＝(第200圈快充DCR-首圈快充DCR)/首圈快充DCR。
7.电池在快速充电时DCR的测定
在25℃下，将实施例和对比例制备得到的锂离子电池以0.33C倍率恒流充电至充电截止电压4.4V，然后进行恒压充电至电流0.05C，停止充电，静置60min。之后电芯以0.33C倍率放电至50％SOC并记 录电压V1；然后以4C倍率充电30秒，记录电压V2。DCR＝(V2-V1)/充电电流，其中充电电流为电池在4C倍率充电下的电流。
按照上述过程分别测试实施例1-9和对比例1-3，具体数值参见表1。
表1中，S1步骤的原料中TCA与BMI的摩尔量比对应于结构单元(II)的摩尔量与结构单元(I-2)+(I-3)的摩尔量总和之比，为1∶1.48，如在实施例1-6和对比例1-3中；TCA与马来酰亚胺的摩尔量比对应于结构单元(II)的摩尔量与结构单元(I)的摩尔量之比，为1∶5.5，如在实施例7中；TCA和N，N′-(1，4-亚苯基)双马来酰亚胺的摩尔量比对应于结构单元(II)的摩尔量与结构单元(I-2)+(I-3)的摩尔量总和之比，为1∶1.98，如在实施例8中；三聚氰酸和N，N′-(1，2-亚苯基)双马来酰亚胺的摩尔量比对应于结构单元(II)的摩尔量与结构单元(I-2)+(I-3)的摩尔量总和之比，为1∶1.08，如在实施例9中。
Figure PCTCN2022122554-appb-000013
Figure PCTCN2022122554-appb-000014
与对比例1-3相比，实施例1-9对应的锂离子电池具有提高的循环容量保持率和降低的直流内阻。
由实施例1-4可见，在正极活性材料中，当包含聚合物的包覆层相对于正极活性材料的质量计的质量分数为0.5％至2％，包覆层厚度为1.1nm至2nm时，锂离子电池的循环容量保持率在94.2％至95.7％范围内，并且DCR增长率均不超过146％，在快充时的DCR值都不高于560mΩ。进一步地，当包含聚合物的包覆层相对于正极活性材料的质量计的质量分数为0.5％至1.5％，包覆层的厚度为1.1nm至1.5nm，锂离子电池的循环容量保持率、DCR增长率以及在快充时的DCR得到进一步改善。
由实施例1和5-6可见，与对比例3比较，在S2步骤中，采用聚合物对正极活性物质进行包覆时，反应温度在55℃至80℃时，锂离子电池的循环容量保持率均高于93.8％、DCR增长率均低于150％以及在快充时的DCR都不高于564mΩ。进一步地，当反应温度在60℃时，锂离子电池的循环容量保持率、DCR增长率以及在快充时的DCR得到进一步改善。
由实施例1-9可见，通过本申请所述的步骤S2，将通过马来酰亚胺类化合物和三聚氰酸类化合物制备的聚合物对于正极活性物质直接进行包覆，由此形成的正极活性材料，在应用于锂离子电池时，该电池的循环容量保持率、DCR增长率以及在快充时的DCR得以改善。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，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 (17)

  1. 一种正极活性材料，其包括正极活性物质以及在其表面上的包覆层，其特征在于，所述包覆层包括衍生自单体马来酰亚胺类化合物的结构单元和衍生自单体三聚氰酸类化合物的结构单元的聚合物。
  2. 根据权利要求1所述的正极活性材料，其特征在于，所述衍生自单体马来酰亚胺类化合物的结构单元包括下式(I-1)至(I-3)中的至少一种：
    Figure PCTCN2022122554-appb-100001
    其中，R 1为选自以下的基团：
    Figure PCTCN2022122554-appb-100002
    n为0-3的整数，可选n为1或2。
  3. 根据权利要求1或2所述的正极活性材料，其特征在于，所述衍生自单体三聚氰酸类化合物的结构单元包括下式(II)，
    Figure PCTCN2022122554-appb-100003
    其中，R 2、R 3和R 4彼此独立地为氧原子或硫原子；尤其是，所述三聚氰酸类化合物选自三聚氰酸和三聚硫氰酸中的至少一种。
  4. 根据权利要求1至3中任一项所述的正极活性材料，其特征在于，所述正极活性物质选自下式锂过渡金属氧化物：
    Li(Ni aCo bM c) dO e
    其中，M选自Mn和Al之一或者是它们的混合物；
    0≤a≤1；
    0≤b≤1；
    0≤c≤2；
    0＜d≤1.2；
    2≤e≤4；
    a+b+c＞0；
    a、b、c、d、e满足所述正极活性物质的价态要求；
    可选地，a+b＞0；
    可选地，所述正极活性物质选自LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2、Li(Ni 0.5Co 0.2Mn 0.3) 1.07O 2、LiNi 0.5Co 0.2Mn 0.3O 2、LiNi 0.5Co 0.25Mn 0.25O 2、LiNi 0.6Co 0.2Mn 0.2O 2、LiNi 0.8Co 0.1Mn 0.1O 2、LiNi 0.85Co 0.15Al 0.05O 2中的至少一种。
  5. 根据权利要求1至4中任一项所述的正极活性材料，其特征在于，所述包覆层的厚度为0.8nm至2.5nm，可选1.0nm至2nm，进一步可选1.1nm至1.5nm。
  6. 根据权利要求2-5中任一项所述的正极活性材料，其特征在于，基于结构单元(I-1)、(I-2)、(I-3)和(II)的总摩尔量计，结构单元(I-1)、(I-2)、(I-3)的摩尔量总和占比为40-90摩尔％，可选50-85摩尔％；结构单元(II)的摩尔占比为10-60摩尔％，可选15-50摩尔％。
  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，所述聚合物的重均分子量为3000至5000。
  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，基于聚合物与正极活性物质的总质量计，所述聚合物的质量分数为0.3％至2.5％，可选0.4％至2％，进一步可选0.5％至1.5％。
  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，所述正极活性材料的中值粒径Dv50为3.2μm至4.2μm，可选为3.5μm至3.6μm；比表面积BET为1.05m 2/g至1.55m 2/g，可选为1.50m 2/g至1.53m 2/g。
  10. 制备权利要求1-9中任一项所述的正极活性材料的方法，其特征在于，包括如下步骤：
    步骤S1：将马来酰亚胺类化合物和三聚氰酸类化合物进行聚合反应，得到聚合物；
    步骤S2：向所述聚合物中加入正极活性物质进行包覆，得到所述正极活性材料。
  11. 根据权利要求10所述的方法，其中在步骤S1中，马来酰亚胺类化合物和三聚氰酸类化合物的质量比为2∶1至10∶1，可选2.5∶1至6.5∶1。
  12. 根据权利要求10或11所述的方法，其中在步骤S2中，所述正极活性物质与聚合物的质量比为40∶1至210∶1，可选49∶1至199∶1。
  13. 根据权利要求10-12中任一项所述的方法，其中在步骤S2中，在55℃至80℃温度下进行包覆，时间持续0.5至2h。
  14. 一种二次电池，所述二次电池包括权利要求1-9中任一项所述的正极活性材料，或通过权利要求10-13中任一项所述的方法制备的正极活性材料。
  15. 一种电池模块，其中包括权利要求14所述的二次电池。
  16. 一种电池包，其中包括权利要求14所述的二次电池或权利要求15所述的电池模块。
  17. 一种用电装置，其中包括选自权利要求14所述的二次电池、权利要求15所述的电池模块或权利要求16所述的电池包中的至少一种。
PCT/CN2022/122554 2022-09-29 2022-09-29 正极活性材料、其制法以及包含其的二次电池、电池模块、电池包、用电装置 WO2024065387A1 (zh)

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