WO2024065276A1 - 二次电池及其制备方法、用电装置 - Google Patents

二次电池及其制备方法、用电装置 Download PDF

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WO2024065276A1
WO2024065276A1 PCT/CN2022/122131 CN2022122131W WO2024065276A1 WO 2024065276 A1 WO2024065276 A1 WO 2024065276A1 CN 2022122131 W CN2022122131 W CN 2022122131W WO 2024065276 A1 WO2024065276 A1 WO 2024065276A1
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positive electrode
graphite
lithium
secondary battery
active material
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PCT/CN2022/122131
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English (en)
French (fr)
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黄瑛
刘江
姚斌
王红
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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/CN2022/122131 priority Critical patent/WO2024065276A1/zh
Publication of WO2024065276A1 publication Critical patent/WO2024065276A1/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
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present application relates to the field of secondary batteries, and more specifically to secondary batteries and methods for preparing the same, and electrical devices.
  • This passivation layer is an interface layer that has the characteristics of a solid electrolyte. It is an electronic insulator but an excellent conductor of lithium ions. Lithium ions can freely embed and detach through this passivation layer. Therefore, this passivation film is called a "solid electrolyte interface" (solid electrolyte interface), or SEI film for short.
  • the formation of the SEI film will consume some active lithium ions, increase the irreversible capacity of the first charge and discharge, and reduce the cycle performance of the battery. Therefore, in order to compensate for the performance loss caused by the formation of the SEI film, the battery often needs to be replenished with lithium.
  • traditional lithium replenishment technology often requires the introduction of lithium replenishers that have a negative impact on the battery's energy density or stability, or requires complex processes to achieve lithium replenishment. Therefore, how to further simplify the lithium replenishment of secondary batteries and avoid excessive negative impacts on other battery properties has always been a problem that needs to be solved in the field of secondary batteries.
  • a secondary battery and a method for preparing the same, and an electrical device are provided.
  • a secondary battery comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet;
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes modified graphite, and the modified graphite includes graphite and anions located between layers of the graphite.
  • anions between the layers of graphite as a positive electrode additive, these anions embedded in the graphite layers are not easy to escape during the cycle, and the lithium ions in the corresponding electrolyte are easily embedded in the negative electrode to maintain the charge balance, thereby achieving lithium replenishment in a simple and efficient manner without significantly changing the existing battery preparation process, which can effectively improve the battery's cycle performance.
  • the modified graphite with embedded anions is also conducive to enhancing conductivity, which can further improve the battery's electrical performance.
  • the anion is a monovalent anion; optionally, the monovalent anion includes one or more of PF 6 - , ClO 4 - , TFSI - , FSI - and NO 3 - .
  • Suitable types of anions can be better embedded in the graphite layer without affecting the battery performance, and the release rate during the cycle is lower, which is more conducive to improving the lithium replenishment efficiency.
  • the X-ray diffraction spectrum of the modified graphite has a characteristic peak in the range of 10° to 20°. After the anions that are difficult to be removed are embedded in the interlayer of the graphite during the cycle, an irreversible phase change occurs, so it can be detected that the obtained modified graphite has a characteristic X-ray diffraction peak in the range of 10° to 20°.
  • the working voltage of the appropriate type of positive electrode active material is more matched with the voltage required for inserting anions into the graphite interlayer, avoiding the failure of anion insertion into the graphite interlayer or the decomposition of the electrolyte due to voltage mismatch during preparation.
  • the mass percentage of the graphite in the positive electrode active material layer is 1% to 8%; alternatively, the mass percentage of the graphite in the positive electrode active material layer is 2% to 4%.
  • the mass percentage of graphite in the positive electrode active material layer is controlled within a suitable range, and while meeting the lithium replenishment demand, it does not occupy too much space of the positive electrode active material, causing the battery capacity to decrease, thereby achieving a balance between lithium replenishment and battery capacity.
  • the Dv50 particle size of the graphite is 10 ⁇ m to 20 ⁇ m; optionally, the Dv50 particle size of the graphite is 16 ⁇ m to 18 ⁇ m. Controlling the particle size of the graphite within a suitable range can make the positive electrode slurry more uniform during slurry preparation, the compaction density of the pole piece more appropriate, and the ion diffusion path moderate, thereby further improving the effects of lithium supplementation and conductivity.
  • a method for preparing a secondary battery according to one or more of the above embodiments comprising the following steps:
  • the positive electrode slurry is coated on at least one surface of a positive electrode current collector, and dried and pressed to obtain a positive electrode sheet;
  • the positive electrode sheet, the negative electrode sheet and the isolation membrane are assembled, and an electrolyte is injected to perform a formation treatment at a voltage of 4.5V to 4.8V.
  • the voltage of the formation treatment is controlled to be 4.5V ⁇ 4.8V, which can make the anions smoothly embedded in the interlayer of graphite and not easy to escape, and will not cause the decomposition of the electrolyte and affect the battery performance.
  • the electrolyte solute includes one or more of LiPF 6 , LiClO 4 , LiTFSI, LiFSI and LiNO 3.
  • Suitable electrolyte solute species provide suitable anion species, which can be better embedded in the interlayer of graphite during formation and are not easily removed during circulation, thereby better achieving lithium replenishment.
  • the concentration of lithium ions in the electrolyte is 1 mol/L to 1.5 mol/L; alternatively, the concentration of lithium ions in the electrolyte is 1.2 mol/L to 1.3 mol/L.
  • the electrolyte not only provides basic electron and ion conduction functions, but also provides a source of lithium ions after formation, playing a role in lithium supplementation. Therefore, the electrolyte having a suitable lithium ion concentration is an important prerequisite for maintaining the basic performance of the battery while achieving lithium supplementation.
  • the current of the formation treatment is less than 0.1 C. Controlling the formation current within a suitable range can make the anions more uniformly embedded in the interlayers of the graphite, reduce the escape of anions during circulation, and help improve the lithium replenishment efficiency.
  • the specific capacity range of the anions embedded in the graphite is 100mAh/g to 200m Ah/g.
  • the specific capacity of the anions released from the graphite is in the range of 20mAh/g to 100mAh/g.
  • the specific capacity of anions embedded in graphite can be made greater than the specific capacity of anions released, thereby achieving lithium replenishment.
  • an electrical device comprising a secondary battery as described in one or more of the aforementioned embodiments.
  • FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .
  • FIG. 3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.
  • FIG. 4 is an X-ray diffraction spectrum of the graphite raw material used in the positive electrode in each embodiment and comparative example of the present application.
  • FIG5 is an X-ray diffraction pattern of graphite in the positive electrode of the battery prepared in Example 1 of the present application (Test 1).
  • FIG6 is an X-ray diffraction pattern of graphite in the positive electrode of the battery prepared in Comparative Example 2 of the present application (Test 2).
  • FIG. 7 is an X-ray diffraction pattern of graphite in the positive electrode of the battery prepared in Comparative Example 3 of the present application (Test 3).
  • Example 8 is an X-ray diffraction pattern of graphite at the positive electrode of the battery prepared in Example 1 of the present application after being subjected to a 2.5V voltage formation treatment (Test 4).
  • range disclosed in this application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range.
  • the range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected.
  • the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers.
  • the numerical range "0 to 5" means that all real numbers between "0 to 5" have been fully listed in this article, and "0 to 5" is just an 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).
  • positive electrode lithium supplementation often introduces a certain amount of lithium salt lithium supplementation agent into the positive electrode active material layer, but these lithium salt lithium supplementation agents often cause the collapse of the corresponding position of the active material layer after being used for lithium supplementation. Therefore, it is necessary to strengthen the positive electrode active material layer or the entire pole piece structure accordingly, and it will occupy the position of the positive electrode active material.
  • lithium supplementation In addition to lithium supplementation, it has no other functions, which greatly reduces the capacity of the battery; negative electrode lithium supplementation often uses lithium as a lithium supplementation agent.
  • the nature of lithium is very active and easy to react with water and oxygen. Therefore, it is also necessary to specially design the pole piece structure or improve the preparation process to achieve it, and there are certain hidden dangers in terms of safety.
  • the first aspect of the present application provides a secondary battery, including a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet;
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode active material layer includes modified graphite.
  • the modified graphite includes graphite and anions located between graphite layers.
  • anions between the layers of graphite as a positive electrode additive, these anions embedded in the graphite layers are not easy to escape during the cycle, and the lithium ions in the corresponding electrolyte are easily embedded in the negative electrode to maintain the charge balance, thereby achieving lithium replenishment in a simple and efficient manner without significantly changing the existing battery preparation process, which can effectively improve the battery's cycle performance.
  • the modified graphite with embedded anions is also conducive to enhancing conductivity, which can further improve the battery's electrical performance.
  • the anion is a monovalent anion; optionally, the monovalent anion includes one or more of PF 6 - (hexafluorophosphate ion), ClO 4 - (perchlorate ion), TFSI - (bistrifluoromethanesulfonyl imide ion), FSI - (bisfluorosulfonyl imide ion) and NO 3 - (nitrate ion).
  • PF 6 - hexafluorophosphate ion
  • ClO 4 - perchlorate ion
  • TFSI - bistrifluoromethanesulfonyl imide ion
  • FSI - bisfluorosulfonyl imide ion
  • NO 3 - nitrate ion
  • the X-ray diffraction spectrum of the modified graphite has a characteristic peak in the range of 10° to 20°.
  • the X-ray diffraction spectrum of the modified graphite has a characteristic peak at any of the following values or in the range of any two values: 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18° or 19°.
  • the working voltage of the suitable type of positive electrode active material is more matched with the voltage required for inserting anions into the graphite interlayer, so as to avoid the failure of anion insertion into the graphite interlayer or the decomposition of the electrolyte due to voltage mismatch during preparation.
  • the mass percentage of graphite in the positive electrode active material layer, is 1% to 8%; alternatively, in the positive electrode active material layer, the mass percentage of graphite can be, for example, 3%, 5%, 6% or 7%, and can also be 2% to 4%.
  • the mass percentage of graphite in the positive electrode active material layer is controlled within a suitable range, while meeting the lithium replenishment demand, it will not occupy too much space of the positive electrode active material, causing the battery capacity to decrease, and achieve a balance between lithium replenishment and battery capacity.
  • the Dv50 particle size of the graphite is 10 ⁇ m to 20 ⁇ m; alternatively, the Dv50 particle size of the graphite can be, for example, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 17 ⁇ m, 18 ⁇ m or 19 ⁇ m, and can also be 16 ⁇ m to 18 ⁇ m. Controlling the particle size of the graphite within a suitable range can make the positive electrode slurry more uniform during slurry preparation, the compaction density of the pole piece more suitable, and the ion diffusion path moderate, thereby further improving the effects of lithium supplementation and conductivity.
  • Dv50 refers to the particle size corresponding to the cumulative volume distribution number of particles reaching 50% in the volume cumulative distribution curve of particle size. Its physical meaning is that the volume proportion of particles with a particle size smaller than (or larger than) this particle size value is 50%.
  • Dv50 can be conveniently measured by a laser particle size analyzer with reference to GB/T 19077-2016 particle size distribution laser diffraction method, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK.
  • a method for preparing a secondary battery according to one or more of the above embodiments comprising the following steps:
  • the positive electrode sheet, the negative electrode sheet and the separator are assembled, and the electrolyte is injected, and a chemical treatment is performed at a voltage of 4.5 V to 4.8 V.
  • the voltage of the chemical treatment can also be, for example, 4.55 V, 4.6 V, 4.65 V, 4.7 V or 4.75 V.
  • the voltage of the formation treatment is controlled to be 4.5V to 4.8V, which can make the anions smoothly embedded in the interlayer of graphite and not easy to escape, and will not cause the electrolyte to decompose and affect the battery performance.
  • the electrolyte solute includes one or more of LiPF 6 , LiClO 4 , LiTFSI, LiFSI and LiNO 3.
  • Suitable electrolyte solute species provide suitable anion species, which can be better embedded in the interlayer of graphite during formation and are not easily removed during circulation, thereby better achieving lithium replenishment.
  • the concentration of lithium ions in the electrolyte is 1 mol/L to 1.5 mol/L; alternatively, the concentration of lithium ions in the electrolyte can be, for example, 1.1 mol/L or 1.4 mol/L, or 1.2 mol/L to 1.3 mol/L.
  • the electrolyte not only provides basic electron and ion conductivity, but also provides a source of lithium ions after formation, thereby playing a role in lithium supplementation. Therefore, the electrolyte having a suitable lithium ion concentration is an important prerequisite for maintaining the basic performance of the battery while achieving lithium supplementation.
  • the current of the formation treatment is less than 0.1 C.
  • the current of the formation treatment may be, for example, 0.09 C, 0.08 C, 0.07 C, 0.06 C, 0.05 C, 0.04 C, 0.03 C, 0.02 C or 0.01 C. Controlling the formation current within a suitable range can make the anions more uniformly embedded in the interlayer of the graphite, reduce the escape of anions during circulation, and help improve the lithium replenishment efficiency.
  • the specific capacity of the anions embedded in the graphite ranges from 100mAh/g to 200m Ah/g.
  • the specific capacity of the anions embedded in the graphite can also be, for example, 110mAh/g, 120mAh/g, 130mAh/g, 140mAh/g, 150mAh/g, 160mAh/g, 170mAh/g, 180mAh/g or 190mAh/g.
  • the specific capacity of the anions released from the graphite is in the range of 20mAh/g to 100mAh/g.
  • the specific capacity of the anions released from the graphite can also be, for example, 30mAh/g, 40mAh/g, 50mAh/g, 60mAh/g, 70mAh/g, 80mAh/g or 90mAh/g.
  • specific capacity is mass specific capacity, which refers to the capacity value of anions that can be extracted or embedded in a unit mass of graphite.
  • specific capacity of anions embedded in graphite is 110 mAh/g, which means that the capacity value of anions that can be embedded in 1g of graphite is 110 mAh.
  • the specific capacity of anions embedded in graphite can be made greater than the specific capacity of anions released, thereby achieving lithium replenishment.
  • the specific capacity of anions embedded in or released from graphite is related to the specific type of anions.
  • the specific capacity of PF 6 - embedded in the positive electrode graphite is 140mAh/g
  • the specific capacity of PF 6 - released is 20mAh/g
  • the lithium replenishment capacity is 120mAh/g
  • the anion is FSI -
  • the specific capacity of FSI - embedded in the positive electrode graphite is 130mAh/g
  • the specific capacity of FSI - released is 20mAh/g
  • the lithium replenishment capacity is 110mAh/g.
  • an electrical device comprising a secondary battery according to one or more of the aforementioned embodiments.
  • a secondary battery is provided.
  • 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 disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.
  • 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 active material may be a positive electrode active material for a battery known in the art.
  • the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.
  • lithium transition metal oxides may include, but are not limited to , 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 ), LiNi0.5Co0.2Mn0.3O2 (also referred to as NCM523 ) , LiNi0.5Co0.25Mn0.25O2 (also referred to as NCM211 ) , LiNi0.6Co0.2Mn0.2O2 (also referred to as NCM622 ), LiNi0.8Co0.1Mn0.1O2 (also referred to as NCM811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05
  • lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • LiMnPO 4 lithium manganese phosphate
  • LiMnPO 4 lithium manganese phosphate
  • LiMnPO 4 lithium manganese phosphate and carbon
  • 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-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • a conductive agent which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
  • a solvent such as N-methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil may be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode active material may also include negative electrode active materials for batteries known in the art, such as artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode film layer may further include a binder.
  • the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • a conductive agent which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).
  • a thickener eg, sodium carboxymethyl cellulose (CMC-Na)
  • the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays the role of conducting ions between the positive electrode and the negative electrode.
  • the present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.
  • the electrolyte can be liquid, gel or all-solid.
  • the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.
  • the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.
  • the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • additives such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • the secondary battery further includes a separator.
  • the present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation.
  • the materials of each layer can be the same or different, without particular limitation.
  • the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.
  • the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.
  • 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 outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package.
  • the material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.
  • FIG1 is a secondary battery 1 of a square structure as an example.
  • the outer package may include a shell 11 and a cover plate 13.
  • the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity.
  • the shell 11 has an opening connected to the receiving cavity, and the cover plate 13 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 12 through a winding process or a lamination process.
  • the electrode assembly 12 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 12.
  • the number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to specific actual needs.
  • 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, and can also be used as an energy storage unit for the electrical device.
  • the electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.
  • the mobile device may be, for example, a mobile phone, a laptop computer, etc.;
  • the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.
  • a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.
  • Fig. 3 shows an example of an electric device 2.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • the device may be a mobile phone, a tablet computer, a laptop computer, etc.
  • Lithium iron phosphate, graphite (Dv50 particle size of 16.9 ⁇ m), conductive agent acetylene black, and binder PVDF (polyvinylidene fluoride) are mixed in a weight ratio of 92:2:4:2, and a solvent N-methylpyrrolidone is added, and the mixture is stirred and mixed to obtain a positive electrode slurry, which is then coated on both surfaces of the positive electrode current collector aluminum foil, and dried and cold pressed to obtain a positive electrode sheet;
  • Graphite, conductive agent acetylene black, binder SBR (styrene-butadiene rubber latex), binder CMC (sodium carboxymethyl cellulose) are mixed in a weight ratio of 95:1.5:3.1:0.4, deionized water is added as a solvent, and the mixture is stirred and mixed to obtain a negative electrode slurry, which is then coated on both surfaces of the negative electrode current collector copper foil, and dried and cold pressed to obtain a negative electrode sheet;
  • EC ethylene carbonate
  • PC polycarbonate
  • DMC dimethyl carbonate
  • PP/PE/PP composite film is used as the isolation film.
  • the positive electrode sheet prepared in step (1), the isolation film in step (4), and the negative electrode sheet prepared in step (2) are stacked in order, so that the isolation film is located between the positive and negative electrodes to play an isolating role, thereby obtaining a bare battery cell; the bare battery cell is placed in an outer package, the electrolyte prepared in step (3) is injected and packaged, and chemical formation is carried out at a voltage of 4.8V and a current of 0.05C.
  • the specific capacity of PF 6 - embedded in the positive electrode graphite is 140mAh/g
  • the specific capacity of PF 6 - released is 20mAh/g, thereby obtaining a lithium-ion secondary battery with a lithium supplement of 120mAh/g.
  • the method is basically the same as Example 1, except that in step (1), the weight ratio of lithium iron phosphate, graphite, conductive agent acetylene black, and binder PVDF is 93:1:4:2.
  • the method is basically the same as Example 1, except that in step (1), the weight ratio of lithium iron phosphate, graphite, conductive agent acetylene black, and binder PVDF is 86:8:4:2.
  • the method is basically the same as Example 1, except that the Dv50 particle size of the graphite in step (1) is 20 ⁇ m.
  • the method is basically the same as Example 1, except that the Dv50 particle size of the graphite in step (1) is 10 ⁇ m.
  • the method is basically the same as Example 1, except that the lithium ion concentration of the electrolyte obtained in step (3) is 1 mol/L.
  • the method is basically the same as Example 1, except that the lithium ion concentration of the electrolyte obtained in step (3) is 1.5 mol/L.
  • the method is basically the same as Example 1, except that the current formed in step (5) is 0.15C.
  • the method is basically the same as Example 1, except that the lithium iron phosphate in step (1) is replaced by NCM523, the solute of the electrolyte in step (3) is replaced by LiFSI, and the formation voltage in step (5) is adjusted to 4.5 V;
  • the specific capacity of FSI - embedded in the positive electrode graphite is 130 mAh/g, and the specific capacity of FSI - released is 20 mAh/g, thus obtaining a lithium-ion secondary battery with a lithium supplement of 110 mAh/g.
  • step (1) does not contain graphite, and the weight ratio of lithium iron phosphate, conductive agent acetylene black, and binder PVDF is 94:4:2.
  • step (5) Basically the same as Example 1, except that the formation voltage in step (5) is 4.0V.
  • step (5) Basically the same as Example 1, except that the formation voltage in step (5) is 4.9V.
  • Example 4 Analyzing the data in Table 1, compared with Example 1, the amount of graphite added in Example 2 is reduced, and the capacity that can be used to supplement lithium in SEI is reduced, and the battery cycle performance is reduced; the amount of graphite added in Example 3 is increased, although the capacity that can be used to supplement lithium is increased, but it occupies the space of the positive electrode active material, so it will also cause the overall battery cycle performance to decrease; in Example 4, the Dv50 particle size of the graphite is larger, which reduces the compaction density of the pole piece, so that the amount of active material that can be accommodated in the same volume is reduced, thereby reducing the cycle performance; in Example 5, the Dv50 particle size of the graphite is smaller, although the compaction density is high, but the ion diffusion path is increased, the polarization is increased, and a lower The rate and time required to replenish lithium are longer, so less lithium is replenished under the same conditions and the cycle performance is improved less; in Example 6, the concentration of lithium ions in the electrolyte is low.
  • the concentration of lithium ions in the electrolyte is lower than 1 mol/L, and the ion diffusion rate between the electrode layers is reduced, which ultimately reduces the cycle performance of the battery;
  • the concentration of lithium ions in the electrolyte is high, the electrolyte viscosity is high, the infiltration is difficult, and the ion diffusion rate between the electrode layers is low, which also leads to a decrease in the cycle performance of the battery;
  • the formation current is too large, resulting in excessive polarization, resulting in incomplete formation reaction and incomplete lithium replenishment reaction, and the expected lithium replenishment efficiency cannot be achieved.
  • Comparative Example 1 no graphite was added, and lithium replenishment could not be achieved; in Comparative Example 2, the formation voltage was too low, and the anions could not be normally embedded in the graphite, so lithium replenishment could not be achieved; in Comparative Example 3, the formation voltage was too high, resulting in irreversible decomposition of part of the electrolyte, which would seriously deteriorate the battery performance.

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Abstract

一种二次电池，包括正极极片、负极极片和隔离膜，隔离膜设置于正极极片和负极极片之间；正极极片包括正极集流体和设置于正极集流体至少一个表面之上的正极活性材料层，正极活性材料层包括改性石墨，改性石墨包括石墨和位于石墨的层间的阴离子。

Description

二次电池及其制备方法、用电装置 技术领域
本申请二次电池领域，更具体地涉及二次电池及其制备方法、用电装置。
背景技术
这里的陈述仅提供与本申请有关的背景信息，而不必然构成现有技术。
在锂离子电池的首次充放电过程中，电极材料与电解液会在固液相界面上发生反应，形成一层覆盖于电极材料表面的钝化层。这种钝化层是一种界面层，具有固体电解质的特征，是电子绝缘体却是锂离子的优良导体，锂离子可以经过该钝化层自由地嵌入和脱出，因此，这层钝化膜被称为“固体电解质界面膜”(solid electrolyte interface)，简称SEI膜。
SEI膜的形成会消耗部分活性锂离子，会使得首次充放电不可逆容量增加，降低电池的循环性能，因此，为了弥补SEI膜形成造成的性能损失，往往需要对电池进行补锂处理。然而，传统的补锂技术往往需要引入对电池能量密度或是稳定性存在负面影响的补锂剂，或是需要复杂的工艺才能实现补锂。因此，如何进一步简化二次电池的补锂，避免对电池的其他性能造成过多负面影响，一直是二次电池领域亟待解决的问题。
发明内容
根据本申请的各种实施例，提供一种二次电池及其制备方法、用电装置。
本申请的第一方面，提供了一种二次电池，包括正极极片、负极极片和隔离膜，所述隔离膜设置于所述正极极片和所述负极极片之间；
所述正极极片包括正极集流体和设置于所述正极集流体至少一个表面之上的正极活性材料层，所述正极活性材料层包括改性石墨，所述改性石墨包括石墨和位于所述石墨的层间的阴离子。
通过在作为正极添加剂的石墨的层间嵌入阴离子，在循环时这些嵌于石墨层间的阴离子不易脱出，为维持电荷平衡与之对应的电解液中的锂离子就容易嵌入负极，从而在无需大幅改变现有的电池制备工艺的前提下，简便高效地实现补锂，能有效提升电池的循环性能。此外，已嵌入阴离子的改性石墨还有利于增强导电性，能进一步提 升电池的电性能。
在一些实施方式中，所述阴离子为一价阴离子；可选地，所述一价阴离子包括PF 6 -、ClO 4 -、TFSI -、FSI -以及NO 3 -中的一种或多种。合适种类的阴离子能够在不影响电池性能的情况下，更好地嵌入石墨层间，且循环时脱出率更低，更有利于提升补锂效率。
在一些实施方式中，所述改性石墨的X射线衍射图谱在10°～20°范围内存在特征峰。石墨的层间嵌入循环时难以脱出的阴离子后，发生了不可逆的物相变化，因此能够检测到所得的改性石墨在10°～20°范围内存在X射线衍射特征峰。
在一些实施方式中，所述正极活性材料层采用的正极活性材料包括磷酸铁锂和三元正极材料中的一种或多种；可选地，所述三元正极材料包括Li aNi xCo yM zO 2，其中，M选自Mn、Al、Zr、Ti、V、Mg、Fe、Mo、B中的至少一种，0.95≤a≤1.2，x>0，y>0，z>0，且x+y+z＝1。合适种类的正极活性材料的工作电压与将阴离子嵌入石墨层间时所需的电压更匹配，避免制备时由于电压不匹配而造成阴离子嵌入石墨层间失败，或造成电解液分解。
在一些实施方式中，在所述正极活性材料层中，所述石墨的质量百分含量为1％～8％；可选地，在所述正极活性材料层中，所述石墨的质量百分含量为2％～4％。控制正极活性材料层中石墨的质量百分含量在合适范围内，在满足补锂需求的同时，不会挤占过多正极活性材料的空间，造成电池容量下降，实现了补锂和电池容量之间的平衡。
在一些实施方式中，所述石墨的Dv50粒径为10μm～20μm；可选地，所述石墨的Dv50粒径为16μm～18μm。控制石墨的粒径在合适范围内，可以使得制浆时正极浆料更加均匀，极片压实密度更合适，且离子扩散路径适中，从而进一步提升补锂和导电的效果。
本申请的第二方面，提供了前述一种或多种实施方式所述的二次电池的制备方法，包括以下步骤：
将所述石墨、制备所述正极活性材料层的其他原料以及溶剂混合，制备正极浆料；
将所述正极浆料涂覆于正极集流体的至少一个表面之上，经干燥、压制，得到正极极片；
将所述正极极片、负极极片和隔离膜组装，注入电解液，在4.5V～4.8V的电压下进行化成处理。
控制化成处理的电压为4.5V～4.8V，能够使得阴离子顺利嵌入石墨的层间不易 脱出，且不会造成电解液分解，影响电池性能。
在一些实施方式中，所述电解液的溶质包括LiPF 6、LiClO 4、LiTFSI、LiFSI以及LiNO 3中的一种或多种。合适的电解液溶质种类提供了合适的阴离子种类，能够在化成时更好地嵌入石墨的层间，且循环时不易脱出，从而更好地实现补锂。
在一些实施方式中，在所述电解液中，锂离子的浓度为1mol/L～1.5mol/L；可选地，在所述电解液中，锂离子的浓度为1.2mol/L～1.3mol/L。本申请中，电解液不仅提供了基本的导电子和导离子作用，且化成后提供了锂离子的来源，起到了补锂的作用。因此，电解液具有合适的锂离子浓度，是维持电池基本性能同时能实现补锂的重要前提。
在一些实施方式中，所述化成处理的电流小于0.1C。控制化成电流在合适的范围内，能够使得阴离子更均匀地嵌入石墨的层间，减少循环时阴离子的脱出，有利于提高补锂效率。
在一些实施方式中，在4.5V～4.8V的电压下进行化成处理时，所述石墨中嵌入所述阴离子的比容量范围为100mAh/g～200m Ah/g。
在一些实施方式中，在4.5V～4.8V的电压下进行化成处理时，所述石墨中脱出所述阴离子的比容量范围为20mAh/g～100mAh/g。
采用合适的化成条件进行处理，能够使得石墨中嵌入阴离子的比容量大于阴离子脱出的比容量，从而实现补锂。
本申请的第三方面，提供了一种用电装置，包括前述一种或多种实施方式所述的二次电池。
本申请的一个或多个实施例的细节在下面的附图和描述中提出。本申请的其他特征、目的和优点将从说明书、附图以及权利要求书变得明显。
附图说明
为了更好地描述和说明这里公开的那些发明的实施例或示例，可以参考一幅或多幅附图。用于描述附图的附加细节或示例不应当被认为是对所公开的发明、目前描述的实施例或示例以及目前理解的这些发明的最佳模式中的任何一者的范围的限制。
图1是本申请一实施方式的二次电池的示意图。
图2是图1所示的本申请一实施方式的二次电池的分解图。
图3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：
1：二次电池；11：壳体；12：电极组件；13：盖板；2：用电装置。
图4是本申请各实施例和对比例中正极采用的石墨原料的X射线衍射图谱。
图5是本申请实施例1制得的电池中正极的石墨的X射线衍射图谱(测试1)。
图6是本申请对比例2制得的电池中正极的石墨的X射线衍射图谱(测试2)。
图7是本申请对比例3制得的电池中正极的石墨的X射线衍射图谱(测试3)。
图8是本申请实施例1制得的电池经过2.5V的电压化成处理后正极的石墨的X射线衍射图谱(测试4)。
具体实施方式
为了使本申请的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本申请进行进一步详细说明。应当理解，此处描述的具体实施例仅仅用以解释本申请，并不用于限定本申请。
除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同。本文中在本申请的说明书中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60～120和80～110的范围，理解为60～110和80～120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1～3、1～4、1～5、2～3、2～4和2～5。在本申请中，除非有其他说明，数值范围“a～b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0～5”表示本文中已经全部列出了“0～5”之间的全部实数，“0～5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形 成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，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)。
由于市场对于电池长寿命的需求逐步提升，如何有效改善电池的循环性能成了二次电池领域的研究热点。SEI膜的形成是造成电池循环性能受损的一个重要原因，因此，通过额外补锂成了改善电池循环性能的一个有效措施。目前的补锂方式大致可以分为正极补锂和负极补锂两类，正极补锂往往是在正极活性材料层中引入一定用量的锂盐补锂剂，但这些锂盐补锂剂在用于补锂后往往会造成活性材料层相应位置的坍塌，因此需要相应对正极活性材料层或者整个极片结构进行加强设计，且会占据正极活性材料的位置，除了补锂以外不具备其他功效，大大降低了电池的容量；负极补锂则往往是将锂单质作为补锂剂，锂单质性质非常活泼，易于和水氧发生反应，因此也需要特别设计极片结构或者改进制备工艺才能实现，在安全方面也存在一定的隐患。
基于上述背景，本申请的第一方面，提供了一种二次电池，包括正极极片、负极极片和隔离膜，隔离膜设置于正极极片和负极极片之间；
正极极片包括正极集流体和设置于正极集流体至少一个表面之上的正极活性材料层，正极活性材料层包括改性石墨，改性石墨包括石墨和位于石墨的层间的阴离子。
通过在作为正极添加剂的石墨的层间嵌入阴离子，在循环时这些嵌于石墨层间的阴离子不易脱出，为维持电荷平衡与之对应的电解液中的锂离子就容易嵌入负极，从而在无需大幅改变现有的电池制备工艺的前提下，简便高效地实现补锂，能有效提升电池的循环性能。此外，已嵌入阴离子的改性石墨还有利于增强导电性，能进一步提 升电池的电性能。
在一些实施方式中，阴离子为一价阴离子；可选地，一价阴离子包括PF 6 -(六氟磷酸根离子)、ClO 4 -(高氯酸根离子)、TFSI -(双三氟甲磺酰亚胺根离子)、FSI -(双氟磺酰亚胺根离子)以及NO 3 -(硝酸根离子)中的一种或多种。合适种类的阴离子能够在不影响电池性能的情况下，更好地嵌入石墨层间，且循环时脱出率更低，更有利于提升补锂效率。
在一些实施方式中，改性石墨的X射线衍射图谱在10°～20°范围内存在特征峰。可选地，改性石墨的X射线衍射图谱在以下任意数值处或任意两个数值组成的范围内存在特征峰：11°、12°、13°、14°、15°、16°、17°、18°或19°。石墨的层间嵌入循环时难以脱出的阴离子后，发生了不可逆的物相变化，因此能够检测到所得的改性石墨在10°～20°范围内存在X射线衍射特征峰。
在一些实施方式中，正极活性材料层采用的正极活性材料包括磷酸铁锂和三元正极材料中的一种或多种；可选地，三元正极材料包括Li aNi xCo yM zO 2，其中，M选自Mn、Al、Zr、Ti、V、Mg、Fe、Mo、B中的至少一种，0.95≤a≤1.2，x>0，y>0，z>0，且x+y+z＝1。进一步可选地，M为Mn，LiNi xCo yMn zO 2材料包括NCM 523、NCM 622以及NCM 811中的一种或多种。合适种类的正极活性材料的工作电压与将阴离子嵌入石墨层间时所需的电压更匹配，避免制备时由于电压不匹配而造成阴离子嵌入石墨层间失败，或造成电解液分解。
在一些实施方式中，在正极活性材料层中，石墨的质量百分含量为1％～8％；可选地，在正极活性材料层中，石墨的质量百分含量例如可以是3％、5％、6％或7％，又如还可以是2％～4％。控制正极活性材料层中石墨的质量百分含量在合适范围内，在满足补锂需求的同时，不会挤占过多正极活性材料的空间，造成电池容量下降，实现了补锂和电池容量之间的平衡。
在一些实施方式中，石墨的Dv50粒径为10μm～20μm；可选地，石墨的Dv50粒径例如可以是11μm、12μm、13μm、14μm、15μm、16μm、17μm、18μm或19μm，又如还可以是16μm～18μm。控制石墨的粒径在合适范围内，可以使得制浆时正极浆料更加均匀，极片压实密度更合适，且离子扩散路径适中，从而进一步提升补锂和导电的效果。
本申请中，Dv50指在粒度的体积累积分布曲线中，颗粒的累计体积分布数达到50％时所对应的粒径，它的物理意义是粒径小于(或大于)该粒径值的颗粒的体积占比各 为50％。作为示例，Dv50可以参照GB/T 19077-2016粒度分布激光衍射法，采用激光粒度分析仪方便地测定，如英国马尔文仪器有限公司的Mastersizer 2000E型激光粒度分析仪。
本申请的第二方面，提供了前述一种或多种实施方式的二次电池的制备方法，包括以下步骤：
将石墨、正极活性材料层的其他原料以及溶剂混合，制备正极浆料；
将正极浆料涂覆于正极集流体的至少一个表面之上，经干燥、压制，得到正极极片；
将正极极片、负极极片和隔离膜组装，注入电解液，在4.5V～4.8V的电压下进行化成处理。化成处理的电压例如还可以是4.55V、4.6V、4.65V、4.7V或4.75V。
控制化成处理的电压为4.5V～4.8V，能够使得阴离子顺利嵌入石墨的层间不易脱出，且不会造成电解液分解，影响电池性能。
在一些实施方式中，电解液的溶质包括LiPF 6、LiClO 4、LiTFSI、LiFSI以及LiNO 3中的一种或多种。合适的电解液溶质种类提供了合适的阴离子种类，能够在化成时更好地嵌入石墨的层间，且循环时不易脱出，从而更好地实现补锂。
在一些实施方式中，在电解液中，锂离子的浓度为1mol/L～1.5mol/L；可选地，在电解液中，锂离子的浓度例如还可以是1.1mol/L或1.4mol/L，又如还可以是1.2mol/L～1.3mol/L。本申请中，电解液不仅提供了基本的导电子和导离子作用，且化成后提供了锂离子的来源，起到了补锂的作用。因此，电解液具有合适的锂离子浓度，是维持电池基本性能同时能实现补锂的重要前提。
在一些实施方式中，化成处理的电流小于0.1C。可选地，化成处理的电流例如可以是0.09C、0.08C、0.07C、0.06C、0.05C、0.04C、0.03C、0.02C或0.01C。控制化成电流在合适的范围内，能够使得阴离子更均匀地嵌入石墨的层间，减少循环时阴离子的脱出，有利于提高补锂效率。
在一些实施方式中，在4.5V～4.8V的电压下进行化成处理时，石墨中嵌入阴离子的比容量范围为100mAh/g～200m Ah/g。在4.5V～4.8V的电压下进行化成处理时，石墨中嵌入阴离子的比容量例如还可以是110mAh/g、120mAh/g、130mAh/g、140mAh/g、150mAh/g、160mAh/g、170mAh/g、180mAh/g或190mAh/g。
在一些实施方式中，在4.5V～4.8V的电压下进行化成处理时，石墨中脱出阴离子的比容量范围为20mAh/g～100mAh/g。在4.5V～4.8V的电压下进行化成处理时， 石墨中脱出阴离子的比容量例如还可以是30mAh/g、40mAh/g、50mAh/g、60mAh/g、70mAh/g、80mAh/g或90mAh/g。
本申请中，“比容量”是质量比容量，指单位质量的石墨可以脱出或者嵌入阴离子的容量值。例如，石墨中嵌入阴离子的比容量为110mAh/g是指：每1g的石墨中可嵌入阴离子的容量值为110mAh。
采用合适的化成条件进行处理，能够使得石墨中嵌入阴离子的比容量大于阴离子脱出的比容量，从而实现补锂。石墨中嵌入阴离子或脱出阴离子的比容量与具体的阴离子种类有关，例如，在一些实施方式中，当阴离子为PF 6 -时，正极石墨中嵌入PF 6 -的比容量为140mAh/g，脱出PF 6 -的比容量为20mAh/g，补锂容量为120mAh/g；在一些实施方式中，当阴离子为FSI -时，正极石墨中嵌入FSI -的比容量为130mAh/g，脱出FSI -的比容量为20mAh/g，补锂容量为110mAh/g。
本申请的第三方面，提供了一种用电装置，包括前述一种或多种实施方式的二次电池。
另外，以下适当参照附图对本申请的二次电池和用电装置进行说明。
本申请的一个实施方式中，提供一种二次电池。
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，所述正极膜层包括正极活性材料。
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，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)、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，正极活性材料可采用本领域公知的用于电池的正极活性材料。作为示例，正极活性材料可包括以下材料中的至少一种：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、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)、LiNi 0.5Co 0.2Mn 0.3O 2(也可以简称为NCM 523)、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。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂(如LiFePO 4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、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。
在一些实施方式中，正极膜层还可选地包括粘结剂。作为示例，所述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。
在一些实施方式中，正极膜层还可选地包括导电剂。作为示例，所述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。
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性材料、导电剂、粘结剂和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
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，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极活性材料还可包括本领域公知的用于电池的负极活性材料，例如：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，负极膜层还可选地包括粘结剂。所述粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
电解质
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
在一些实施方式中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟 砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
隔离膜
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，二次电池可包括外包装。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，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、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
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，图1是作为一个示例的方形结构的二次电池1。
在一些实施方式中，参照图2，外包装可包括壳体11和盖板13。其中，壳体11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11具有与容纳腔连通的开口，盖板13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12。电极组件12封装于所述容纳腔内。电解液浸润于电极组件12中。二次电池1所含电极组件12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。
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、或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备、电动车辆、电气列车、船舶及卫星、储能***等，但不限于此。其中，移动设备例如可以是手机、笔记本电脑等；电动车辆例如可以是纯电动车、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，但不限于此。
作为所述用电装置，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3是作为一个示例的用电装置2。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。
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。
本申请的一个或多个实施例的细节在下面的附图和描述中提出。本申请的其他特征、目的和优点将从说明书、附图以及权利要求书变得明显。
实施例1
(1)正极极片的制备
将磷酸铁锂、石墨(Dv50粒径为16.9μm)、导电剂乙炔黑、粘结剂PVDF(聚偏氟乙烯)按重量比92:2:4:2进行混合，加入溶剂N-甲基吡咯烷酮，充分搅拌混合均匀得到正极浆料，然后涂覆于正极集流体铝箔的两个表面上，经烘干、冷压，得到正极极片；
(2)负极极片的制备
将石墨、导电剂乙炔黑、粘结剂SBR(丁苯橡胶乳)、粘结剂CMC(羧甲基纤维素钠)按照重量比95:1.5:3.1:0.4进行混合，加入溶剂去离子水，充分搅拌混合均匀得到负极浆料，然后涂覆于负极集流体铜箔的两个表面上，经烘干、冷压，得到负极极片；
(3)电解液的制备
在含水量<10ppm的氩气气氛手套箱中，将EC(碳酸乙烯酯)、PC(聚碳酸酯)、DMC(碳酸二甲酯)按照重量比为EC:PC:DMC＝3:3:3进行混合，然后加入LiPF 6，VC，DTD以及PS，搅拌均匀后，获得电解液，其中，锂离子的浓度为1.2mol/L，VC，DTD，PS的质量百分数分别为3％，1％，1％；
(4)隔离膜的制备
以PP/PE/PP复合薄膜作为隔离膜。
(5)锂离子二次电池的制备
将步骤(1)制得的正极极片、步骤(4)中的隔离膜、步骤(2)制得的负极极片按顺序叠好，使隔离膜处于正负极中间起到隔离的作用，得到裸电芯；将裸电芯置于外包装中，注入步骤(3)中配好的电解液并封装，在4.8V电压、0.05C的电流下进行化成，此时，正极石墨中嵌入PF 6 -的比容量为140mAh/g，脱出PF 6 -的比容量为20mAh/g，获得补锂120mAh/g的锂离子二次电池。
实施例2
与实施例1基本相同，区别在于，步骤(1)中磷酸铁锂、石墨、导电剂乙炔黑、粘结剂PVDF的重量比为93:1:4:2。
实施例3
与实施例1基本相同，区别在于，步骤(1)中磷酸铁锂、石墨、导电剂乙炔黑、粘结剂PVDF的重量比为86:8:4:2。
实施例4
与实施例1基本相同，区别在于，步骤(1)中石墨的Dv50粒径为20μm。
实施例5
与实施例1基本相同，区别在于，步骤(1)中石墨的Dv50粒径为10μm。
实施例6
与实施例1基本相同，区别在于，步骤(3)中所得电解液的锂离子浓度为1mol/L。
实施例7
与实施例1基本相同，区别在于，步骤(3)中所得电解液的锂离子浓度为1.5mol/L。
实施例8
与实施例1基本相同，区别在于，步骤(5)中化成的电流为0.15C。
实施例9
与实施例1基本相同，区别在于，将步骤(1)中的磷酸铁锂替换为NCM523，将步骤(3)中电解液的溶质替换为LiFSI，将步骤(5)中的化成电压调整为4.5V；
化成时，正极石墨中嵌入FSI -的比容量为130mAh/g，脱出FSI -的比容量为20mAh/g，获得补锂110mAh/g的锂离子二次电池。
对比例1
与实施例1基本相同，区别在于，步骤(1)中不含石墨，磷酸铁锂、导电剂乙炔黑、粘结剂PVDF的重量比为94:4:2。
对比例2
与实施例1基本相同，区别在于，步骤(5)中的化成电压为4.0V。
对比例3
与实施例1基本相同，区别在于，步骤(5)中的化成电压为4.9V。
表征测试：
(1)X射线衍射(xrd)测试：
对石墨原料、实施例1、对比例2以及对比例3中制得的电池中正极的石墨进行xrd测试，分别记作石墨原料、测试1、测试2和测试3，所得谱图分别参见图4～7；
重复实施例1中的步骤(1)～(5)，然后将化成电压调低至2.5V，对制得的电池中正极的石墨进行xrd测试，记作测试4，所得谱图参见图8；
(2)循环性能测试：
在25℃的温度下，用0.5C的倍率恒流充电到3.65V，再恒压充电到0.05C,静置10min，用1C的倍率恒流放电到2.0V，静置10min，用该测试条件循环测试，循环到电芯容量衰减到80％SOH后测试停止，记录停止时的循环圈数，所得结果列入表1中。
表1
Figure PCTCN2022122131-appb-000001
Figure PCTCN2022122131-appb-000002
分析表1数据，相较于实施例1，实施例2中石墨的添加量降低，则可用于SEI补锂的容量降低，电池循环性能有所下降；实施例3中石墨的添加量升高，虽然可以用于补锂的容量提高，但挤占了正极活性材料的空间，因此也会总体上导致电池的循环性能有所下降；实施例4中，石墨的Dv50粒径较大，降低了极片压实密度，使得同体积可容纳的活性材料的量下降，从而使得循环性能有所下降；实施例5中，石墨的Dv50粒径较小，虽然压实密度高，但是离子扩散路径增加，极化增加，需要更低的倍率和更长的时间才能实现补锂，因此同等条件下补锂更少，循环性能提升更少；实施例6中，电解液中锂离子的浓度较低，充电补锂过程中，消耗部分锂盐后，电解液中锂离子的浓度低于1mol/L，极片层间离子扩散速率降低，最终使得电池的循环性能下降；实施例7中，电解液中锂离子的浓度较高，电解液粘度高，浸润难，极片层间离子扩散速率低，也会导致电池的循环性能下降；实施例8中，化成电流过大，使得极化过大，导致化成反应不彻底，补锂反应不彻底，不能达到预期的补锂效率。
对比例1中未添加石墨，不能实现补锂；对比例2中，化成电压过低，阴离子不能正常嵌入石墨，因此也不能实现补锂；对比例3中，化成电压过高，导致电解液部分不可逆分解，会严重恶化电池性能。
比较图4～7可知，相对于石墨原料的xrd谱图(图4)，实施例1中制得的正极石墨中由于嵌入了阴离子，形成了改性石墨，其谱图(测试1、图5)在10°～20°范围内存在特征峰；对比例2中，由于化成电压过低，阴离子不能正常嵌入石墨，未形成改性石墨，其xrd谱图(测试2、图6)在10°～20°范围内未出现特征峰；对比例3中，虽然其xrd谱图(测试3、图7)在10°～20°范围内出现了类似实施例1的特征峰，但由于化成电压过高，造成电解液部分不可逆分解，会严重恶化电池性能；测试4(图8)中，重复实施例1中的步骤(1)～(5)，然后将化成电压调低至2.5V，其xrd谱图在10°～20°范围内出现了类似实施例1的特征峰，说明本申请的方案中，阴离子嵌入石墨是不可逆的，即使后续使用电压下降，阴离子仍然能够保留在石墨中，从而持续实现补锂。
以上所述实施例的各技术特征可以进行任意的组合，为使描述简洁，未对上述实施例中的各个技术特征所有可能的组合都进行描述，然而，只要这些技术特征的组合不存在矛盾，都应当认为是本说明书记载的范围。
以上所述实施例仅表达了本申请的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本申请构思的前提下，还可以做出若干变形和改进，这些都属于本申请的保护范围。因此，本申请的保护范围应以所附权利要求为准。

Claims (13)

  1. 一种二次电池，包括正极极片、负极极片和隔离膜，所述隔离膜设置于所述正极极片和所述负极极片之间；
    所述正极极片包括正极集流体和设置于所述正极集流体至少一个表面之上的正极活性材料层，所述正极活性材料层包括改性石墨，所述改性石墨包括石墨和位于所述石墨的层间的阴离子。
  2. 根据权利要求1所述的二次电池，其特征在于，所述阴离子为一价阴离子；可选地，所述一价阴离子包括PF 6 -、ClO 4 -、TFSI -、FSI -以及NO 3 -中的一种或多种。
  3. 根据权利要求1～2任一项所述的二次电池，其特征在于，所述改性石墨的X射线衍射图谱在10°～20°范围内存在特征峰。
  4. 根据权利要求1～3任一项所述的二次电池，其特征在于，所述正极活性材料层采用的正极活性材料包括磷酸铁锂和三元正极材料中的一种或多种；可选地，Li aNi xCo yM zO 2，其中，M选自Mn、Al、Zr、Ti、V、Mg、Fe、Mo、B中的至少一种，0.95≤a≤1.2，x>0，y>0，z>0，且x+y+z＝1。
  5. 根据权利要求1～4任一项所述的二次电池，其特征在于，在所述正极活性材料层中，所述石墨的质量百分含量为1％～8％；可选地，在所述正极活性材料层中，所述石墨的质量百分含量为2％～4％。
  6. 根据权利要求1～5任一项所述的二次电池，其特征在于，所述石墨的Dv50粒径为10μm～20μm；可选地，所述石墨的Dv50粒径为16μm～18μm。
  7. 如权利要求1～6任一项所述的二次电池的制备方法，包括以下步骤：
    将所述石墨、制备所述正极活性材料层的其他原料以及溶剂混合，制备正极浆料；
    将所述正极浆料涂覆于正极集流体的至少一个表面之上，经干燥、压制，得到正极极片；
    将所述正极极片、负极极片和隔离膜组装，注入电解液，在4.5V～4.8V的电压下进行化成处理。
  8. 根据权利要求7所述的制备方法，其特征在于，所述电解液的溶质包括LiPF 6、LiClO 4、LiTFSI、LiFSI以及LiNO 3中的一种或多种。
  9. 根据权利要求7～8任一项所述的制备方法，其特征在于，在所述电解液中，锂离子的浓度为1mol/L～1.5mol/L；可选地，在所述电解液中，锂离子的浓度为1.2mol/L～1.3mol/L。
  10. 根据权利要求7～9任一项所述的制备方法，其特征在于，所述化成处理的电流小于0.1C。
  11. 根据权利要求7～10任一项所述的制备方法，其特征在于，在4.5V～4.8V的电压下进行化成处理时，所述石墨中嵌入所述阴离子的比容量范围为100mAh/g～200mAh/g。
  12. 根据权利要求7～11任一项所述的制备方法，其特征在于，在4.5V～4.8V的电压下进行化成处理时，所述石墨中脱出所述阴离子的比容量范围为20mAh/g～100mAh/g。
  13. 一种用电装置，包括权利要求1～6任一项所述的二次电池。
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