WO2023174012A1 - 正极极片、锂离子二次电池、电池模块、电池包和用电装置 - Google Patents

正极极片、锂离子二次电池、电池模块、电池包和用电装置 Download PDF

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WO2023174012A1
WO2023174012A1 PCT/CN2023/077399 CN2023077399W WO2023174012A1 WO 2023174012 A1 WO2023174012 A1 WO 2023174012A1 CN 2023077399 W CN2023077399 W CN 2023077399W WO 2023174012 A1 WO2023174012 A1 WO 2023174012A1
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lithium
positive electrode
battery
coating
transition metal
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PCT/CN2023/077399
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English (en)
French (fr)
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朱映华
史松君
来佑磊
童星
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宁德时代新能源科技股份有限公司
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Publication of WO2023174012A1 publication Critical patent/WO2023174012A1/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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • 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 field of batteries, and in particular to a positive electrode plate, a lithium-ion secondary battery, a battery module, a battery pack and an electrical device.
  • Lithium-ion secondary batteries have been widely used in various power tools due to their high energy density, such as electric vehicles, mobile phones, etc. Users continue to put forward higher requirements for the cost, energy density and safety of lithium-ion secondary batteries.
  • This application was made in view of the above-mentioned issues, and its purpose is to provide a positive electrode sheet, a lithium ion secondary battery, a battery module, a battery pack and a power consumption device, which can suppress overdischarge of lithium surface and improve lithium The charge and discharge capabilities of ion secondary batteries enhance cycle stability.
  • olivine structure phosphate compounds such as lithium iron phosphate and lithium iron manganese phosphate are generally nanoparticles. If nanolithium iron phosphate or lithium iron manganese phosphate is directly combined with layered transition metal oxides Mixed use will cause stirring gel and rapid performance decay. Therefore, consider dividing olivine structure phosphate compounds such as lithium iron phosphate and lithium iron manganese phosphate into small particle parts and large particle parts, and coat the small particle parts separately. On both sides of the current collector, the large particles are further mixed with layered transition metal oxides or pure layered transition metal oxides and coated on the aforementioned coating, which can solve the problems of stirring gel and rapid performance decay. This suppresses overdischarge on the surface of layered transition metal oxides, improves the charge and discharge capabilities of lithium-ion secondary batteries, and enhances cycle stability.
  • the first aspect of the present application is to provide a positive electrode plate, which includes: a current collector, a first coating coated on both sides of the current collector, and a second coating coated on the surface of the first coating ,in,
  • the first coating contains: small particles of olivine structure phosphate compound, and the particle size of the small particles of olivine structure phosphate compound is 0.5 to 2 ⁇ m;
  • the second coating contains: large particles of olivine structure phosphate compounds and layered transition metal oxides; or large particles of olivine structure phosphate compounds and pure layered transition metal oxides, and the large particles of olivine structures
  • the particle size of the stone structure phosphate compound is larger than the particle size of the small particles of the olivine structure phosphate compound.
  • Small-grain olivine structure phosphate compounds with a particle size of 0.5 to 2 ⁇ m are individually coated on both sides of the current collector to form the first coating, and large-grain olivine structure phosphate compounds with a particle size larger than the small-grain olivine structure phosphate compound are applied separately.
  • the salt compound is mixed with a layered transition metal oxide material or a pure layered transition metal oxide material is mixed and then coated on the first coating to form a second coating, which can retain the small particle olivine structure phosphate compound
  • the charge and discharge ability of the small-grain olivine structure phosphate compound can be isolated from the layered transition metal oxide, which solves the problem that during the charge and discharge process, the solid phase concentration polarization of the small-grain olivine structure phosphate compound is small, and the layered transition metal oxide
  • the solid phase concentration polarization of layered transition metal oxide materials is large, and the two contacts produce an equilibrium potential difference, which leads to the problem of overdischarge of layered transition metal oxide materials.
  • the olivine structure phosphate compound is at least one selected from the group consisting of lithium iron phosphate and lithium manganese iron phosphate.
  • the layered transition metal oxide is at least one selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganate and lithium nickel cobalt aluminate, and the pure The layered transition metal oxide is at least one selected from lithium nickel cobalt manganate and lithium nickel cobalt aluminate.
  • the thickness of the first coating layer is 2-200 ⁇ m. If the first coating is too thick, there will be problems with the pole piece decoating and powder falling off; if the thickness of the first coating is too thin, there will be problems such as the inability to effectively utilize the dynamics of the small particle material in the lower layer, the inability to improve the charging capacity of the electrode, and low processing efficiency. question. Therefore, by setting the thickness of the first coating in the range of 2 to 200 ⁇ m, the dynamic performance of the electrode can be improved, the deterioration of the charge and discharge capabilities of the underlying material due to the long diffusion path can be compensated, and the pole piece can be prevented from peeling off. pink.
  • the thickness of the second coating is 2-400 ⁇ m. If the second coating is too thick, there will be problems with the pole piece being decoated and powdered and poor kinetics; if the second coating is too thin, the high capacity characteristics of layered transition metal oxides cannot be fully utilized. Therefore, by setting the thickness of the second coating layer in the range of 2 to 400 ⁇ m, excellent processing performance, dynamic performance, and energy density can be obtained.
  • a second aspect of the present application is to provide a lithium ion secondary battery.
  • the lithium ion secondary battery includes the positive electrode sheet according to the first aspect of the present application.
  • a third aspect of the present application is to provide a battery module, which includes the lithium ion secondary battery according to the second aspect of the present application.
  • a fourth aspect of the present application is to provide a battery pack, which includes the battery module according to the third aspect of the present application.
  • the fifth aspect of the present application is to provide an electric device, which includes the lithium ion secondary battery according to the second aspect of the present application, the battery module according to the third aspect of the present application and the fourth aspect of the present application. At least one of the battery packs described in the aspect.
  • the olivine structure phosphate compound is divided into a small particle part and a large particle part, the small particle part is separately coated on both sides of the current collector, and then the large particle part is further transitioned into a layered Metal oxides or pure layered transition metal oxides are mixed and coated on the aforementioned coating, which can solve the problems of stirring gel and rapid performance attenuation, thereby suppressing overdischarge on the surface of layered transition metal oxides and improving the secondary lithium ion
  • the battery's charge and discharge capabilities enhance cycle stability.
  • Figure 1 is a schematic structural diagram of a positive electrode plate according to an embodiment of the present application.
  • FIG. 2 is a schematic diagram of a lithium ion secondary battery according to an embodiment of the present application.
  • FIG. 3 is an exploded view of the lithium ion secondary battery according to one embodiment of the present application shown in FIG. 2 .
  • Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 6 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG. 5 .
  • FIG. 7 is a schematic diagram of a power consumption device using a lithium ion secondary battery as a power source according to an embodiment of the present application.
  • Figure 8 is a schematic diagram of the cycle stability of a battery using the positive electrode sheet of Example 1 of the present application.
  • Figure 9 is a schematic diagram of the cycle stability of a battery using the positive electrode sheet of Example 2 of the present application.
  • Figure 10 is a schematic diagram of the cycle stability of a battery using the positive electrode sheet of Comparative Example 1 of the present application.
  • Figure 11 is a schematic diagram of the rate performance of a battery using the positive electrode sheet of Comparative Example 2 of the present application.
  • Figure 12 is a schematic diagram of the cycle stability of a battery using the positive electrode sheet of Comparative Example 3 of the present application.
  • 1 battery pack 2 upper box; 3 lower box; 4 battery module; 5 lithium-ion secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Additionally, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 ⁇ 4 and 2 ⁇ 5.
  • the numerical range “a ⁇ b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0 ⁇ 5" means that all real numbers between "0 ⁇ 5" have been listed in this article, and "0 ⁇ 5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • condition "A or B” is satisfied by any of the following conditions: 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).
  • Olivine structure phosphate compounds such as lithium iron phosphate and lithium iron manganese phosphate have wide sources and stable structures and have good application prospects. However, their energy density is low and it is difficult to be used in products with high energy density requirements. Layer transition Cathode materials such as metal oxides have high energy density and are therefore used in high-energy-density products. However, due to their more active chemical properties, unstable structure and poor safety, olivine structure phosphate compounds and layers are Mixing transition metal oxides like this, and adjusting the mixing ratio can be used in products suitable for different application scenarios, taking into account the advantages of both.
  • Olivine structure phosphate compounds have poor kinetics and need to be made into nanoparticles and carbon coated to be commercially applied. When mixed with layered transition metal oxides, it can cause processing and performance problems. Binders are not suitable because binders suitable for layered transition metal oxides generally have large molecular weights and strong polarity, which can easily lead to physical agglomeration of olivine structure phosphate compounds that are made into nanoparticles. Nanoparticle olivine structure phosphate compounds have small solid phase concentration polarization. Layered transition metal oxides generally have larger particles and have large solid phase concentration polarization. Nanoparticle olivine structure phosphate compounds are easily wrapped in large particles.
  • the olivine structure phosphate compound of the nanoparticles causes the liquid phase diffusion path of the pole piece to become longer, resulting in the layered transition metal oxide having insufficient capacity.
  • a positive electrode piece is provided.
  • the positive electrode sheet of the present application includes a current collector, a first coating coated on both sides of the current collector, and a second coating coated on the surface of the first coating.
  • the current collector has two surfaces opposite in its own thickness direction, the first coating is disposed on the two opposite surfaces of the current collector, and the second coating is further on the first coating.
  • the current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil can 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 base layer.
  • the composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • composite current collectors can solve the problem of thermal runaway in batteries caused by internal short circuits; transfer more space in the battery to active materials to increase the energy density of the battery; maintain the long-term integrity of the electrode plate interface and improve the cycle life of the battery; and It can be directly applied to power batteries of various specifications and systems.
  • the first coating coated on both sides of the current collector contains: small particles of an olivine structure phosphate compound, and the particle size of the small particles of the olivine structure phosphate compound is 0.5 to 2 ⁇ m;
  • the second coating coated on the surface of the first coating contains: large particles of olivine structure phosphate compounds and layered transition metal oxides; or large particles of olivine structure phosphate compounds and Pure layered transition metal oxide, and the particle size of the large-grained olivine structure phosphate compound is larger than the particle size of the small-grained olivine structure phosphate compound.
  • the small particle olivine structure phosphate compound has a large specific surface area and is coated on the electrode, the liquid phase diffusion path is long and the dynamic performance of the battery core is poor. Therefore, it is coated separately on the current collector. On both sides, the liquid phase diffusion path of the upper electrode can be reduced, significantly improving the charge and discharge capacity of the battery core. Moreover, the small particle olivine structure phosphate compound itself has a large active specific surface area. Even if it is coated on both sides of the current collector, the dynamic performance of the electrode is still good, which to a certain extent compensates for the charge and discharge capabilities of the underlying material due to the long diffusion path. deterioration.
  • layered transition metal oxide materials usually require large molecular weight and strong polarity binders to improve the bonding force, the use of such binders in olivine structure phosphate compounds can easily lead to agglomeration and the occurrence of physical gels. Therefore, by stirring the small-grain olivine structure phosphate compound separately and coating it separately, the slurry gel problem caused by the mismatch of the binder when it is mixed and stirred with the layered transition metal oxide material can be avoided.
  • a large particle olivine structure phosphate compound is mixed with a layered transition metal oxide or a pure layered transition metal oxide, and then coated on the first coating, thus taking into account the advantages of both. .
  • the olivine structure phosphate compound includes at least one selected from the group consisting of lithium iron phosphate (LiFePO 4 ) and lithium iron manganese phosphate (LiMnPO 4 ).
  • Lithium iron phosphate (LiFePO 4 ) and lithium iron manganese phosphate (LiMnPO 4 ) which are olivine structure phosphate compounds, have a polyanionic framework structure. Their structural basic unit is PO 4 tetrahedron. The strong PO covalent bond in the phosphate group is In the fully charged state, the oxygen atoms are stabilized to prevent them from being oxidized to produce oxygen and released. The existence of this structure makes the olivine structure phosphate compound have a stable charging and discharging platform. During the charging and discharging process, the structure has good structural stability, high safety, and good cycle performance. Performance is very good.
  • the layered transition metal oxide is at least one selected from lithium cobalt oxide (LiCoO 2 ), lithium nickel cobalt manganate (LiNiMnCoO 2 ), and lithium nickel cobalt aluminate (LiNiCoAlO 2 ).
  • the pure layered transition metal The oxide is at least one selected from the group consisting of lithium nickel cobalt manganate and lithium nickel cobalt aluminate. Only one type of these materials may be used alone, or two or more types may be used in combination.
  • the layered transition metal oxide or pure layered transition metal oxide has good high rate performance and long cycle stability.
  • the first coating layer and the second coating layer optionally further include a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • the first coating layer and the second coating layer optionally further 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 positive electrode sheet can be prepared in the following manner: sieving the olivine structure phosphate compound into a large particle part and a small particle part, and sieving out: the small particle part with a particle size in the range of 0.01 to 10 ⁇ m, as small particles.
  • the above-mentioned small particles of olivine structure phosphate compound are mixed with a binder, conductive carbon and any other components dispersed in a solvent (such as N-methylpyrrolidone), and coated on both sides of the current collector to form a third One coating layer, the coating thickness of the first coating layer is 2-200 ⁇ m, preferably 30-100 ⁇ m.
  • the above-mentioned large-particle olivine structure phosphate compound, layered transition metal oxide or pure layered transition metal oxide, binder and conductive carbon, and any other components are dispersed in a solvent (such as N- Methyl pyrrolidone) is mixed and coated on the surface of the first coating layer formed on both sides of the aluminum foil to form a second coating layer.
  • a solvent such as N- Methyl pyrrolidone
  • the coating thickness of the second coating layer is 2 to 400 ⁇ m, preferably 50 to 200 ⁇ m.
  • the positive electrode sheet of the present application can be obtained.
  • a lithium ion secondary battery is provided.
  • the lithium ion secondary battery of the present application includes the above-mentioned positive electrode sheet of the present application, as well as the negative electrode sheet, electrolyte and separator.
  • active ions are inserted and detached back and forth between the positive and negative electrodes.
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.
  • 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.
  • the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposite surfaces in its own 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 composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material.
  • the composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative active material may be a negative active material known in the art for batteries.
  • the negative 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, and the like.
  • 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 battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.
  • the negative electrode film layer optionally further includes a binder.
  • the binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylic acid sodium (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylate At least one of acrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer optionally further includes 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 negative electrode film layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the type of electrolyte in this application can be selected according to needs.
  • the electrolyte can be liquid, gel, or completely solid.
  • the electrolyte is an electrolyte solution.
  • the electrolyte solution includes electrolyte salts and solvents.
  • the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.
  • the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte optionally further includes additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the secondary battery further includes a separator film.
  • a separator film There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • 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 film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the lithium ion secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the lithium ion 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 lithium-ion secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • FIG. 2 shows a square-structured lithium ion secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the lithium ion secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • lithium-ion secondary batteries can be assembled into battery modules.
  • the number of lithium-ion secondary batteries contained in the battery module can be one or more. The specific number can be determined by those skilled in the art according to the application and capacity of the battery module. choose.
  • FIG. 4 is a battery module 4 as an example.
  • a plurality of lithium-ion secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of lithium ion secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having an accommodation space in which a plurality of lithium ion secondary batteries 5 are accommodated.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes at least one of the lithium ion secondary battery, battery module, or battery pack provided by the present application.
  • the lithium ion secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit of 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 to these.
  • a lithium-ion secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • Fig. 7 is an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • a battery pack or battery module can be used.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • This device is usually required to be thin and light, and a lithium-ion secondary battery can be used as a power source.
  • Example 1 as the olivine structure phosphate compound, lithium iron phosphate particles with a particle size in the range of 0.01 to 10 ⁇ m are used; As the layered transition metal oxide, lithium nickel cobalt manganate particles with a particle diameter in the range of 0.5 to 20 ⁇ m are used.
  • lithium iron phosphate particles with a particle size in the range of 0.01 to 10 ⁇ m Use a sieve with a mesh size of 12,500 to screen lithium iron phosphate particles with a particle size in the range of 0.01 to 10 ⁇ m, and screen out: lithium iron phosphate particles with a particle size below 1 ⁇ m as small particles of lithium iron phosphate.
  • the range is 0.01 to 1 ⁇ m; and lithium iron phosphate particles with a particle size greater than 1 ⁇ m.
  • the particle size range is greater than 1 ⁇ m and below 10 ⁇ m.
  • the above-mentioned small particle lithium iron phosphate is mixed with a binder and conductive carbon, and is coated on both sides of the aluminum foil serving as a current collector to form a first coating layer.
  • the coating thickness of the first coating layer is 50 ⁇ m.
  • the above-mentioned large particle lithium iron phosphate, the above-mentioned lithium nickel cobalt manganate particles with a particle size in the range of 0.5-20 ⁇ m, a binder and conductive carbon are mixed and coated on the first coating surface formed on both sides of the aluminum foil, A second coating layer was formed with a coating thickness of 150 ⁇ m.
  • the positive electrode sheet was combined with the graphite negative electrode sheet, electrolyte (1M LiPF6 in EC/DMC/DEC) and isolation film (commercial 12 ⁇ mPE) to form a square aluminum shell battery, which was charged at 1C to 4.35V, 1C discharge to 2.5V, record the discharge capacity retention rate, and measure its cycle characteristics at 25°C. As shown in Figure 8, the battery shows good cycle stability at 25°C.
  • Example 2 the positive electrode sheet of Example 2 was prepared according to the same method as Example 1, except that a sieve with a mesh number of 25,000 and a particle size of 0.5 ⁇ m was used for sieving, and the particle size range was: Small particle lithium iron phosphate with a particle size range of 0.01 to 0.5 ⁇ m; and large particle lithium iron phosphate with a particle size range of greater than 0.5 ⁇ m and less than 10 ⁇ m.
  • the positive electrode sheet was combined with the graphite negative electrode sheet, electrolyte (1M LiPF6 in EC/DMC/DEC) and separator (commercial 12 ⁇ mPE) to form a square aluminum shell battery, and its cycle characteristics at 25°C were measured. As shown in Figure 9, the battery exhibits good cycling stability at 25°C.
  • Example 3 the positive electrode sheet of Example 3 was prepared according to the same method as Example 1, except that a sieve with a mesh number of 6250 mesh and a particle size of 2 ⁇ m was used for sieving, and the particle size range was: Small particle lithium iron phosphate of 0.01 to 2 ⁇ m; and large particle lithium iron phosphate with a particle size range of greater than 2 ⁇ m and less than 10 ⁇ m.
  • Example 4 to 7 the positive electrode sheets of Examples 4 to 7 were prepared according to the same method as Example 1, except for the thickness of the first coating and/or the thickness of the second coating.
  • Example 8 the positive electrode sheet of Example 8 was prepared according to the same method as Example 1, except that: as the olivine structure phosphate compound, lithium manganese iron phosphate particles with a particle size in the range of 0.01 to 10 ⁇ m were used; as For layered transition metal oxides, lithium nickel cobalt aluminate particles with a particle size in the range of 0.5 to 20 ⁇ m are used.
  • the olivine structure phosphate compound lithium manganese iron phosphate particles with a particle size in the range of 0.01 to 10 ⁇ m were used; as For layered transition metal oxides, lithium nickel cobalt aluminate particles with a particle size in the range of 0.5 to 20 ⁇ m are used.
  • Comparative Example 1 the positive electrode sheet of Comparative Example 1 was prepared according to the same method as Example 1, except that a sieve with a mesh number of 31250 and a particle size of 0.4 ⁇ m was used for sieving, and the particle size range was: Small particle lithium iron phosphate of 0.01 to 0.4 ⁇ m; and large particle lithium iron phosphate with a particle size range of greater than 0.4 ⁇ m and less than 10 ⁇ m; and the thickness of the first coating is 30 ⁇ m, and the thickness of the second coating is 170 ⁇ m. .
  • Comparative Example 2 the positive electrode sheet of Comparative Example 2 was prepared according to the same method as Example 1, except that a sieve with a mesh number of 5900 and a particle size of 2.1 ⁇ m was used for sieving, and the particle size range was: Small particle lithium iron phosphate of 0.01 to 2.1 ⁇ m; and large particle lithium iron phosphate with a particle size range of greater than 2.1 ⁇ m and less than 10 ⁇ m; and the thickness of the first coating is 50 ⁇ m, and the thickness of the second coating is 150 ⁇ m. .
  • Comparative Example 3 the positive electrode sheet of Comparative Example 3 was prepared according to the same method as Example 1, with the following differences:
  • large particle lithium iron phosphate with a particle size range of greater than 1 ⁇ m and less than 10 ⁇ m, lithium nickel cobalt manganate particles with a particle size in the range of 0.5-20 ⁇ m, a binder, and conductive carbon are mixed and coated on the aluminum foil.
  • a second coating is formed on the first coating surface on both sides, and the coating thickness of the second coating is 150 ⁇ m.
  • the particle size of small particles of lithium iron phosphate as an olivine structure phosphate is smaller than that of lithium nickel cobalt manganate particles as a layered transition metal oxide, and the two are mixed in the first coating on both sides of the aluminum foil.
  • there are differences in solid phase concentration polarization and there is an uncontrollable equilibrium current, which causes the rapid decay of layered transition metal oxides.
  • the mixing and stirring of small particles of lithium iron phosphate and high pH layered transition metal oxide materials has the problem of unsuitable binders, resulting in serious mixing gel and difficult production.
  • Comparative Example 4 the positive electrode sheet of Comparative Example 4 was prepared according to the same method as Example 1, with the following differences:
  • the cloth thickness is 50 ⁇ m.
  • small-particle lithium iron phosphate with a particle size ranging from 0.01 to 1 ⁇ m, lithium nickel cobalt manganate particles with a particle size ranging from 0.5-20 ⁇ m, a binder, and conductive carbon are mixed and coated on both sides of the aluminum foil.
  • a second coating layer is formed on the surface of the first coating layer, and the coating thickness of the second coating layer is 150 ⁇ m.

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Abstract

本申请提供一种正极极片、锂离子二次电池、电池模块、电池包和用电装置。本申请的正极极片，其包括：集流体、涂布在集流体两侧的第一涂层和涂布在第一涂层表面的第二涂层，其中，第一涂层含有：小颗粒的橄榄石结构磷酸盐化合物，并且，所述小颗粒的橄榄石结构磷酸盐化合物的粒径为0.5～2μm；第二涂层含有：大颗粒的橄榄石结构磷酸盐化合物与层状过渡金属氧化物；或大颗粒的橄榄石结构磷酸盐化合物与纯层状过渡金属氧化物，并且，所述大颗粒的橄榄石结构磷酸盐化合物的粒径大于所述小颗粒的橄榄石结构磷酸盐化合物的粒径。通过本申请的正极极片能够抑制层状过渡金属氧化物表面过放，提升锂离子二次电池的充放电能力，增强循环稳定性。

Description

正极极片、锂离子二次电池、电池模块、电池包和用电装置
本申请要求于2022年3月14日提交中国专利局、申请号为202210246572.2的中国专利申请的优先权，其全部内容通过引用结合在申请中。
技术领域
本申请涉及电池领域，尤其涉及一种正极极片、锂离子二次电池、电池模块、电池包和用电装置。
背景技术
锂离子二次电池因其高能量密度已被广泛运用在各种电动工具中，如电动汽车、手机等，用户也持续对锂离子二次电池的成本、能量密度和安全提出更高要求。
技术问题
本申请是鉴于上述课题而进行的，其目的在于，提供一种正极极片、锂离子二次电池、电池模块、电池包和用电装置，该正极极片能够抑制锂表面过放，提升锂离子二次电池的充放电能力，增强循环稳定性。
发明人考虑到：磷酸铁锂、磷酸锰铁锂等橄榄石结构磷酸盐化合物为提升充放电能力，一般为纳米颗粒，如果将纳米磷酸铁锂或磷酸锰铁锂直接与层状过渡金属氧化物混合使用，会出现搅拌凝胶及性能快速衰减，因此考虑到将磷酸铁锂、磷酸锰铁锂等橄榄石结构磷酸盐化合物区分成小颗粒部分和大颗粒部分，通过将小颗粒部分单独涂布在集流体的两侧，然后进一步将大颗粒部分与层状过渡金属氧化物或纯层状过渡金属氧化物混合而涂布在前述涂层之上，可以解决搅拌凝胶及性能快速衰减问题，从而抑制层状过渡金属氧化物表面过放，提升锂离子二次电池的充放电能力，增强循环稳定性。
技术解决方案
为了实现上述目的，本申请第一方面在于提供一种正极极片，其包括：集流体、涂布在集流体两侧的第一涂层和涂布在第一涂层表面的第二涂层，其中，
第一涂层含有：小颗粒的橄榄石结构磷酸盐化合物，并且，所述小颗粒的橄榄石结构磷酸盐化合物的粒径为0.5～2μm；
第二涂层含有：大颗粒的橄榄石结构磷酸盐化合物与层状过渡金属氧化物；或大颗粒的橄榄石结构磷酸盐化合物与纯层状过渡金属氧化物，并且，所述大颗粒的橄榄石结构磷酸盐化合物的粒径大于所述小颗粒的橄榄石结构磷酸盐化合物的粒径。
将粒径为0.5～2μm的小颗粒橄榄石结构磷酸盐化合物单独涂布在集流体两侧以形成第一涂层，将粒径大于小颗粒橄榄石结构磷酸盐化合物的大颗粒橄榄石结构磷酸盐化合物与层状过渡金属氧化物材料混合或纯层状过渡金属氧化物材料混合后涂布在第一涂层之上，以形成第二涂层，既可以保留小颗粒橄榄石结构磷酸盐化合物的充放电能力，又能够将小颗粒橄榄石结构磷酸盐化合物与层状过渡金属氧化物隔离开，解决充放电过程中，小颗粒橄榄石结构磷酸盐化合物固相浓差极化小，而层状过渡金属氧化物材料固相浓差极化大，两种接触产生均衡电势差，从而导致层状过渡金属氧化物材料过放的问题。
在一些实施方式中，在本申请的正极极片中，所述橄榄石结构磷酸盐化合物为选自磷酸铁锂和磷酸锰铁锂中的至少一种。
在一些实施方式中，在本申请的正极极片中，所述层状过渡金属氧化物为选自钴酸锂、镍钴锰酸锂和镍钴铝酸锂中的至少一种，所述纯层状过渡金属氧化物为选自镍钴锰酸锂和镍钴铝酸锂中的至少一种。
在一些实施方式中，在本申请的正极极片中，所述第一涂层的厚度为2～200μm。如果第一涂层过厚，存在极片脱膜掉粉的问题；如果第一涂层的厚度过薄，存在不能有效利用下层小颗粒材料动力学，无法提高电极充电能力，以及加工效率低的问题。因此，通过使第一涂层的厚度在2～200μm的范围内，从而能够提高电极的动力学性能，弥补下层材料因扩散路径长带来的充放电能力的恶化，同时避免极片脱膜掉粉。
在一些实施方式中，在本申请的正极极片中，所述第二涂层的厚度为2～400μm。如果第二涂层过厚，存在极片脱膜掉粉和动力学差的问题；如果第二涂层过薄，存在不能充分利用层状过渡金属氧化物高容量的特性。因此，通过使第二涂层的厚度在2～400μm的范围内，从而能够获得优良的加工性能、动力学性能和能量密度。
本申请第二方面在于提供一种锂离子二次电池，该锂离子二次电池包括根据本申请第一方面所述的正极极片。
本申请第三方面在于提供一种电池模块，该电池模块包括根据本申请第二方面所述的锂离子二次电池。
本申请第四方面在于提供一种电池包，该电池包包括根据本申请第三方面所述的电池模块。
本申请第五方面在于提供一种用电装置，该用电装置包括根据本申请第二方面所述的锂离子二次电池、根据本申请第三方面所述的电池模块和根据本申请第四方面所述的电池包中的至少一种。
有益效果
根据本申请的正极极片，通过将橄榄石结构磷酸盐化合物区分出小颗粒部分和大颗粒部分，将小颗粒部分单独涂布在集流体的两侧，然后进一步将大颗粒部分与层状过渡金属氧化物或纯层状过渡金属氧化物混合后涂布在前述涂层之上，可以解决搅拌凝胶及性能快速衰减问题，从而抑制层状过渡金属氧化物表面过放，提升锂离子二次电池的充放电能力，增强循环稳定性。
附图说明
图1是本申请一个实施方式的正极极片的结构示意图。
图2是本申请一个实施方式的锂离子二次电池的示意图。
图3是图2所示的本申请一个实施方式的锂离子二次电池的分解图。
图4是本申请一个实施方式的电池模块的示意图。
图5是本申请一个实施方式的电池包的示意图。
图6是图5所示的本申请一个实施方式的电池包的分解图。
图7是本申请一个实施方式的锂离子二次电池用作电源的用电装置的示意图。
图8是使用本申请实施例1的正极极片的电池的循环稳定性的示意图。
图9是使用本申请实施例2的正极极片的电池的循环稳定性的示意图。
图10是使用本申请对比例1的正极极片的电池的循环稳定性的示意图。
图11是使用本申请对比例2的正极极片的电池的倍率性能的示意图。
图12是使用本申请对比例3的正极极片的电池的循环稳定性的示意图。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5锂离子二次电池；51壳体；52电极组件；53顶盖组件。
本发明的实施方式
以下，适当地参照附图详细说明具体公开了本申请的负极集流体及其制造方法、负极极片、锂离子二次电池、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2～5。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)。
磷酸铁锂、磷酸锰铁锂等橄榄石结构磷酸盐化合物来源广泛、结构稳定，具有很好的应用前景，但是其能量密度较低，较难运用于对能量密度高要求的产品，层状过渡金属氧化物等正极材料具有较高的能量密度，因而用于高能量密度的产品，但因其化学性质较活泼，结构不太稳定，安全性较差，因此将橄榄石结构磷酸盐化合物和层状过渡金属氧化物混合，调控混合比例能够适用于不同运用场景的产品，兼顾两者优势。
橄榄石结构磷酸盐化合物的动力学较差，需要制成纳米颗粒，并进行碳包覆才能被商业化应用， 当其与层状过渡金属氧化物混合时，会导致加工和性能上的问题。包括粘结剂不适用，因为适用于层状过渡金属氧化物的粘结剂一般分子量大、极性较强，易导致被制成纳米颗粒的橄榄石结构磷酸盐化合物的物理团聚。纳米颗粒的橄榄石结构磷酸盐化合物的固相浓差极化小，层状过渡金属氧化物一般颗粒较大固相浓差极化大，纳米颗粒的橄榄石结构磷酸盐化合物易包裹在大颗粒层状过渡金属氧化物表面，会由于两者浓差极化差异大产生均衡电势差，导致层状过渡金属氧化物表面过放，循环恶化。纳米颗粒的橄榄石结构磷酸盐化合物的加入导致极片液相扩散路径变长，导致层状过渡金属氧化物容量发挥不全。
以下适当参照附图对本申请的锂离子二次电池、电池模块、电池包和用电装置进行说明。
正极极片
本申请的一个实施方式中，提供一种正极极片。
本申请的正极极片包括集流体、涂布在集流体两侧的第一涂层和涂布在第一涂层表面的第二涂层。
作为示例，集流体具有在其自身厚度方向相对的两个表面，第一涂层设置在集流体相对的两个表面上，第二涂层进一步在第一涂层上。
在一些实施方式中，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。采用复合集流体，能够解决电池因内短路易引发热失控的问题；将电池内更多空间让渡给活性物质，提升电池能量密度；保持极片界面长期完整性，提升电池的循环寿命；并且能够直接运用于各种规格、不同体系的动力电池。
作为涂布在集流体两侧的第一涂层，该第一涂层含有：小颗粒的橄榄石结构磷酸盐化合物，并且，小颗粒的橄榄石结构磷酸盐化合物的粒径为0.5～2μm；作为涂布在第一涂层表面的第二涂层，该第二涂层含有：大颗粒的橄榄石结构磷酸盐化合物与层状过渡金属氧化物；或大颗粒的橄榄石结构磷酸盐化合物与纯层状过渡金属氧化物，并且，大颗粒的橄榄石结构磷酸盐化合物的粒径大于小颗粒的橄榄石结构磷酸盐化合物的粒径。
作为第一涂层，由于小颗粒橄榄石结构磷酸盐化合物因比表面积大，涂布在电极上，液相扩散路径较长，电芯的动力学性能较差，将其单独涂布在集流体两侧，可以降低上层电极的液相扩散路径，显著提高电芯的充放电能力。而且，小颗粒橄榄石结构磷酸盐化合物本身活性比表面积大，即使涂布在集流体两侧，电极的动力学性能依然较好，一定程度弥补下层材料因扩散路径长带来的充放电能力的恶化。
另外，由于层状过渡金属氧化物材料通常需要分子量大、强极性粘结剂来提高粘结力，而这类粘结剂使用在橄榄石结构磷酸盐化合物中易导致团聚，出现物理凝胶问题，因此，通过单独搅拌小颗粒橄榄石结构磷酸盐化合物并单独涂布，可以避免其与层状过渡金属氧化物材料混合搅拌时，由于粘结剂不匹配而产生的浆料凝胶问题。
进而，作为第二涂层，将大颗粒橄榄石结构磷酸盐化合物与层状过渡金属氧化物或者纯层状过渡金属氧化物混合，进而涂布在第一涂层之上，从而兼顾两者优势。
在一些实施方式中，橄榄石结构磷酸盐化合物包括选自磷酸铁锂(LiFePO4)、和磷酸锰铁锂(LiMnPO4)中的至少一种。作为橄榄石结构磷酸盐化合物的磷酸铁锂(LiFePO4)和磷酸锰铁锂(LiMnPO4)具有聚阴离子框架结构，其结构基元是PO4四面体，磷酸根中强的P-O共价键在完全充电状态下稳定了氧原子，避免其被氧化生产氧气而释放，该结构的存在使得橄榄石结构磷酸盐化合物具有稳定的充放电平台，充放电过程中结构稳定性好、安全性高、循环性能非常好。
该层状过渡金属氧化物为选自钴酸锂(LiCoO2)、镍钴锰酸锂(LiNiMnCoO2)、和镍钴铝酸锂(LiNiCoAlO2)中的至少一种，该纯层状过渡金属氧化物为选自镍钴锰酸锂、和镍钴铝酸锂中的至少一种。这些材料可以仅单独使用一种，也可以将两种以上组合使用。该层状过渡金属氧化物或纯层状过渡金属氧化物具有良好的高倍率性能与长循环稳定性，通过与上述橄榄石结构磷酸盐化合物混用，可以兼顾两者优势。
在一些实施方式中，第一涂层、第二涂层还可选地包括粘结剂。作为示例，该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，第一涂层、第二涂层还可选地包括导电剂。作为示例，该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：将橄榄石结构磷酸盐化合物筛分成大颗粒部分和小颗粒部分，筛出：粒径在0.01～10μm范围内的小颗粒部分，作为小颗粒的橄榄石结构磷酸盐 化合物；以及粒径大于小颗粒部分的大颗粒部分，作为大颗粒的橄榄石结构磷酸盐化合物。
接着，将上述小颗粒的橄榄石结构磷酸盐化合物与粘结剂、导电碳和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)混合，涂布在集流体的两侧，形成第一涂层，该第一涂层的涂布厚度为2～200μm，优选为30～100μm。通过设置第一涂层的厚度在上述范围内，从而能够提高电极的动力学性能，弥补下层材料因扩散路径长带来的充放电能力的恶化，同时避免极片脱膜掉粉。
然后，将上述大颗粒的橄榄石结构磷酸盐化合物、层状过渡金属氧化物或纯层状过渡金属氧化物、粘结剂和导电碳、以及和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)混合，涂布在形成于铝箔两侧的第一涂层表面，形成第二涂层，该第二涂层的涂布厚度为2～400μm，优选为50～200μm。通过设置第二涂层的厚度在上述范围内，从而能够获得优良的加工性能、动力学性能和能量密度。
进一步，经烘干、冷压等工序后，即可得到本申请的正极极片。
锂离子二次电池
本申请的一个实施方式中，提供一种锂离子二次电池。
本申请的锂离子二次电池包括上述本申请的正极极片、以及负极极片、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。
[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，该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，该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。该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。该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。该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，该电解质采用电解液。该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，该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，锂离子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，锂离子二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。锂离子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。
本申请对锂离子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2是作为一个示例的方形结构的锂离子二次电池5。
在一些实施方式中，参照图3，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于该开口，以封闭该容纳腔。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封装于该容纳腔内。电解液浸润于电极组件52中。锂离子二次电池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。
电池模块
在一些实施方式中，锂离子二次电池可以组装成电池模块，电池模块所含锂离子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4是作为一个示例的电池模块4。参照图4，在电池模块4中，多个锂离子二次电池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锂离子二次电池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，多个锂离子二次电池5容纳于该容纳空间。
电池包
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以为一个或多个，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5和图6是作为一个示例的电池包1。参照图5和图6，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
用电装置
另外，本申请还提供一种用电装置，该用电装置包括本申请提供的锂离子二次电池、电池模块、或电池包中的至少一种。该锂离子二次电池、电池模块、或电池包可以用作该用电装置的电源，也可以用作该用电装置的能量存储单元。该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。
作为该用电装置，可以根据其使用需求来选择锂离子二次电池、电池模块或电池包。
图7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锂离子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，可以采用锂离子二次电池作为电源。
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。
<实施例>
实施例1
在实施例1中，作为橄榄石结构磷酸盐化合物，使用粒径在0.01～10μm范围内的磷酸铁锂颗粒； 作为层状过渡金属氧化物，使用粒径在0.5～20μm范围内的镍钴锰酸锂颗粒。
使用目数为12500目的筛网对粒径在0.01～10μm范围内的磷酸铁锂颗粒进行筛分，筛出：粒径在1μm以下的磷酸铁锂颗粒，作为小颗粒磷酸铁锂，其粒径范围为0.01～1μm；以及粒径大于1μm的磷酸铁锂颗粒，作为大颗粒磷酸铁锂，其粒径范围为大于1μm且在10μm以下。
接着，将上述小颗粒磷酸铁锂与粘结剂、导电碳混合，涂布在作为集流体的铝箔两侧，形成第一涂层，该第一涂层的涂布厚度为50μm。
然后，将上述大颗粒磷酸铁锂、上述粒径在0.5-20μm范围内的镍钴锰酸锂颗粒、粘结剂和导电碳混合，涂布在形成于铝箔两侧的第一涂层表面，形成第二涂层，该第二涂层的涂布厚度为150μm。
由此形成具有如图1所示的结构的本申请实施例1的正极极片。
进而，将该正极极片与石墨负极极片、电解液(1M LiPF6 in EC/DMC/DEC)和隔离膜(商业化12μmPE)组合形成方形铝壳电池，在25℃环境下，采用1C充电至4.35V，1C放电至2.5V的方法，记录放电容量保持率，测定其在25℃下的循环特性，如图8所示，该电池在25℃下表现出良好的循环稳定性。
实施例2
在实施例2中，按照实施例1相同的方法制备实施例2的正极极片，区别在于：使用目数为25000目、粒径为0.5μm的筛网进行筛分，筛出：粒径范围为0.01～0.5μm的小颗粒磷酸铁锂；以及粒径范围为大于0.5μm且在10μm以下的大颗粒磷酸铁锂。
进而，将该正极极片与石墨负极极片、电解液(1M LiPF6 in EC/DMC/DEC)和隔离膜(商业化12μmPE)组合形成方形铝壳电池，测定其在25℃下的循环特性，如图9所示，该电池在25℃下表现出良好的循环稳定性。
实施例3
在实施例3中，按照实施例1相同的方法制备实施例3的正极极片，区别在于：使用目数为6250目、粒径为2μm的筛网进行筛分，筛出：粒径范围为0.01～2μm的小颗粒磷酸铁锂；以及粒径范围为大于2μm且在10μm以下的大颗粒磷酸铁锂。
进而，同样制备具备上述实施例3的正极极片的方形铝壳电池，测定该电池在25℃下的循环特性，表现出良好的循环稳定性。
实施例4～7
在实施例4～7中，按照实施例1相同的方法制备实施例4～7的正极极片，区别在于：第一涂层的厚度和/或第二涂层的厚度。
进而，同样制备具备上述实施例4～7的正极极片的方形铝壳电池，测定它们在25℃下的循环特性，均在25℃下表现出良好的循环稳定性。
实施例8
在实施例8中，按照实施例1相同的方法制备实施例8的正极极片，区别在于：作为橄榄石结构磷酸盐化合物，使用粒径在0.01～10μm范围内的磷酸锰铁锂颗粒；作为层状过渡金属氧化物，使用粒径在0.5～20μm范围内的镍钴铝酸锂颗粒。
进而，同样制备具备上述实施例4～7的正极极片的方形铝壳电池，测定它们在25℃下的循环特性，均在25℃下表现出良好的循环稳定性。
<对比例>
对比例1
在对比例1中，按照实施例1相同的方法制备对比例1的正极极片，区别在于：使用目数为31250目、粒径为0.4μm的筛网进行筛分，筛出：粒径范围为0.01～0.4μm的小颗粒磷酸铁锂；以及粒径范围为大于0.4μm且在10μm以下的大颗粒磷酸铁锂；并且，第一涂层的厚度为30μm，第二涂层的厚度为170μm。
进而，同样制备具备上述对比例1的正极极片的方形铝壳电池，测定它们在25℃下的循环特性，如图10所示，该电池表现出较差的循环稳定性，容量快速衰减。
推测其原因在于：0.4μm的层状结构磷酸盐化合物与层状过渡金属氧化物材料混合在上层，由于充放电过程中的固相浓差极化差异，导致产生颗粒间不可控的均衡电流，从而导致层状过渡金属氧化物材料过放，加速了容量衰减。
对比例2
在对比例2中，按照实施例1相同的方法制备对比例2的正极极片，区别在于：使用目数为5900目、粒径为2.1μm的筛网进行筛分，筛出：粒径范围为0.01～2.1μm的小颗粒磷酸铁锂；以及粒径范围为大于2.1μm且在10μm以下的大颗粒磷酸铁锂；并且，第一涂层的厚度为50μm，第二涂层的厚度为150μm。
进而，同样制备具备上述对比例2的正极极片的方形铝壳电池，测定它们在25℃下的循环特性， 如图11所示，虽然该电池表现出良好的循环稳定性，但是倍率性能显著恶化。
对比例3
在对比例3中，按照实施例1相同的方法制备对比例3的正极极片，区别在于：
将粒径范围为0.01～1μm的小颗粒磷酸铁锂粒径、粒径在0.5-20μm范围内的镍钴锰酸锂颗粒、粘结剂和导电碳混合，涂布在作为集流体的铝箔两侧，形成第一涂层，该第一涂层的涂布厚度为50μm。
然后，将粒径范围为大于1μm且在10μm以下的大颗粒磷酸铁锂、粒径在0.5-20μm范围内的镍钴锰酸锂颗粒、粘结剂、导电碳混合，涂布在形成于铝箔两侧的第一涂层表面，形成第二涂层，该第二涂层的涂布厚度为150μm。
进而，同样制备具备上述对比例3的正极极片的方形铝壳电池，测定它们在25℃下的循环特性，如图12所示，电池表现出较差的循环稳定性，并存在搅拌凝胶问题。
推测其原因在于：作为橄榄石结构磷酸盐的小颗粒磷酸铁锂，其粒径小于作为层状过渡金属氧化物的镍钴锰酸锂颗粒，两者混合在铝箔两侧的第一涂层中，存在固相浓差极化的差异，存在不可控均衡电流，造成层状过渡金属氧化物快速衰减。另外小颗粒磷酸铁锂与高PH值的层状过渡金属氧化物材料混合搅拌存在粘结剂不适用的问题，导致搅拌凝胶严重，生产难度大。
对比例4
在对比例4中，按照实施例1相同的方法制备对比例4的正极极片，区别在于：
将粒径范围为大于1μm且在10μm以下的大颗粒磷酸铁锂、粘结剂和导电碳混合，涂布在作为集流体的铝箔两侧，形成第一涂层，该第一涂层的涂布厚度为50μm。
然后，将粒径范围为0.01～1μm的小颗粒磷酸铁锂、粒径在0.5-20μm范围内的镍钴锰酸锂颗粒、粘结剂、导电碳混合，涂布在形成于铝箔两侧的第一涂层表面，形成第二涂层，该第二涂层的涂布厚度为150μm。
进而，同样制备具备上述对比例4的正极极片的方形铝壳电池，测定它们在25℃下的循环特性，该电池表现出较差的循环稳定性。
表1
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 (9)

  1. 一种正极极片，其中，
    所述正极极片包括：集流体、涂布在所述集流体两侧的第一涂层和涂布在所述第一涂层表面的第二涂层，其中，
    所述第一涂层含有：小颗粒的橄榄石结构磷酸盐化合物，并且，所述小颗粒的橄榄石结构磷酸盐化合物的粒径为0.5～2μm；
    所述第二涂层含有：大颗粒的橄榄石结构磷酸盐化合物与层状过渡金属氧化物；或大颗粒的橄榄石结构磷酸盐化合物与纯层状过渡金属氧化物，并且，所述大颗粒的橄榄石结构磷酸盐化合物的粒径大于所述小颗粒的橄榄石结构磷酸盐化合物的粒径。
  2. 根据权利要求1所述的正极极片，其中，
    所述橄榄石结构磷酸盐化合物为选自磷酸铁锂和磷酸锰铁锂中的至少一种。
  3. 根据权利要求1或2所述的正极极片，其中，
    所述层状过渡金属氧化物为选自钴酸锂、镍钴锰酸锂和镍钴铝酸锂中的至少一种，
    所述纯层状过渡金属氧化物为选自镍钴锰酸锂和镍钴铝酸锂中的至少一种。
  4. 根据权利要求1～3中任一项所述的正极极片，其中，所述第一涂层的厚度为2～200μm，可选为30～100μm。
  5. 根据权利要求1～4中任一项所述的正极极片，其中，所述第二涂层的厚度为2～400μm，可选为50～200μm。
  6. 一种锂离子二次电池，其中，所述锂离子二次电池具备权利要求1～5中任一项所述的正极极片。
  7. 一种电池模块，其中，
    所述电池模块包括权利要求6所述的锂离子二次电池。
  8. 一种电池包，其中，
    所述电池包包括权利要求7所述的电池模块。
  9. 一种用电装置，其中，
    所述用电装置包括选自权利要求6所述的锂离子二次电池、权利要求7所述的电池模块和权利要求8所述的电池包中的至少一种。
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