WO2023142673A1 - 多层复合隔离膜、以及包含其的二次电池、用电装置 - Google Patents

多层复合隔离膜、以及包含其的二次电池、用电装置 Download PDF

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WO2023142673A1
WO2023142673A1 PCT/CN2022/135796 CN2022135796W WO2023142673A1 WO 2023142673 A1 WO2023142673 A1 WO 2023142673A1 CN 2022135796 W CN2022135796 W CN 2022135796W WO 2023142673 A1 WO2023142673 A1 WO 2023142673A1
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Prior art keywords
secondary battery
acid
multilayer composite
optionally
water
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PCT/CN2022/135796
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English (en)
French (fr)
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张翠平
韩昌隆
范朋
吴则利
黄磊
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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 EP22923464.6A priority Critical patent/EP4354628A1/en
Publication of WO2023142673A1 publication Critical patent/WO2023142673A1/zh
Priority to US18/412,608 priority patent/US20240195016A1/en

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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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • 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
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/61—Types of temperature control
    • H01M10/613—Cooling or keeping cold
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/42—Acrylic resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/431—Inorganic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
    • 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
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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 application belongs to the field of battery technology, and in particular relates to a multilayer composite separator, a secondary battery and an electrical device containing the same.
  • the purpose of the present application is to provide a multi-layer composite separator, a secondary battery containing it, and an electrical device.
  • the secondary battery can simultaneously take into account high energy density and long service life.
  • the first aspect of the present application provides a multilayer composite isolation membrane, including a first substrate layer and a second substrate layer, wherein the multilayer composite isolation membrane also includes a water removal material and an acid removal material, and the acid removal A material is located between the first substrate layer and the second substrate layer, and the water removal material is located on at least one surface of the first substrate layer and the second substrate layer.
  • the multi-layer composite separator of the present application adopts water-removing materials and acid-removing materials at the same time, and effectively fixes the free moisture and HF inside the battery on the water-removing materials and the On the acid removal material, it can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, so that the secondary battery can take into account both high energy density and long service life.
  • the multilayer composite separator includes a functional layer located between the first substrate layer and the second substrate layer, and the functional layer includes a water removal material and a water removal material. acid material.
  • the mass percentage of the acid removal material is 20% to 50%, and the mass percentage of the water removal material is 15% to 50%. %.
  • the thickness of the functional layer is 1 ⁇ m ⁇ 100 ⁇ m.
  • the thickness of the functional layer is 4 ⁇ m ⁇ 50 ⁇ m.
  • the ratio of the mass of the acid-scavenging material to the mass of the water-scavenging material in the multilayer composite isolation membrane is 1-3.
  • the ratio of the mass of the acid-scavenging material to the mass of the water-scavenging material in the multilayer composite isolation membrane is 1-1.5.
  • the mass of the acid-removing material can be greater than or equal to the mass of the water-removing material, so as to ensure that the acid-removing material can continuously and effectively reduce the free HF content inside the battery, thereby reducing the free water content inside the battery.
  • the water-removing material includes at least one of molecular sieves and superabsorbent resins.
  • the static water adsorption capacity of the molecular sieve at 25°C and 30% relative humidity is above 15%.
  • the pore size of the molecular sieve is 0.3nm-50nm, optionally 0.5nm-15nm.
  • the molecular sieve can have better water adsorption capacity and poorer water desorption capacity, thereby ensuring that the secondary battery has less free water during long-term charge and discharge cycles and HF content, and thus the cycle performance of the secondary battery is better.
  • the volume average particle diameter Dv50 of the molecular sieve is 1 ⁇ m-10 ⁇ m, optionally 2 ⁇ m-6 ⁇ m.
  • the volume-average particle diameter Dv50 of the molecular sieve is within an appropriate range, it can ensure good kinetic performance of the secondary battery at the same time.
  • the specific surface area of the molecular sieve is 350m 2 /g-1000m 2 /g, optionally 650m 2 /g-800m 2 /g.
  • the molecular sieve can have better water adsorption capacity, thereby ensuring that the secondary battery has less free water and HF content during the long-term charge and discharge cycle, and the secondary battery cycle performance is better.
  • the molecular sieve includes at least one of silicon-based molecular sieve SBA-15 and titanium-silicon molecular sieve TS-1.
  • SBA-15 and TS-1 can have a mesoporous structure and have thicker pore walls, higher pore volume and better hydrothermal stability, so it can ensure that the secondary battery has less damage during long-term charge and discharge cycles.
  • the content of free moisture and HF is higher, and the cycle performance of the secondary battery is better.
  • the water absorption ratio of the superabsorbent resin is more than 100 times.
  • the solubility of the superabsorbent resin in water at 25°C is below 5%.
  • the superabsorbent resin includes starch-grafted acrylonitrile, starch-grafted acrylic, starch-grafted acrylamide, cellulose-grafted acrylonitrile, cellulose-grafted acrylic, At least one of cellulose grafted acrylamide series, polyvinyl alcohol series, polyacrylic acid (salt) series, polyacrylamide series, polyoxyethylene series, polyurethane series, vinyl acetate copolymers, and their respective modified compounds kind.
  • the superabsorbent resin includes at least one of polyvinyl alcohol and cyclic acid anhydride copolymer, sodium polyacrylate resin, and vinyl acetate and acrylate copolymer.
  • the pH of the acid removal material is 7-11.5.
  • the pH of the acid removal material is 7-10.
  • the acid-removing material has weak alkalinity, and can fix HF and water molecules through acid-base neutralization reaction, so as to continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the impact of moisture and HF on The negative impact of the secondary battery makes the secondary battery take into account both high energy density and long service life.
  • the acid-scavenging material includes at least one of inorganic alkaline lithium salts and organic compounds.
  • the inorganic alkaline lithium salt includes at least one of lithium carbonate and lithium bicarbonate.
  • the molecular structure of the organic compound includes at least one of amide groups, silicon nitrogen groups, silicon groups, carbon nitrogen groups, sulfonate groups, and carboxylate ions.
  • the organic compound includes lithium acetate, hexamethyldisilazane, heptamethyldisilazane, trimethylsilyldiethylamine, trimethylsilyl methanesulfonate, bis(tri At least one of (methylsilyl) carbodiimide, N,N-dimethylpropionamide, N,N-dimethylacetamide, N,N-dimethylformamide.
  • the second aspect of the present application provides a secondary battery, including a positive pole piece, a negative pole piece, an electrolyte, and the multilayer composite separator according to the first aspect of the present application.
  • the moisture content in the secondary battery is Apppm, based on the total mass of the multilayer composite separator,
  • the content of the dewatering material is B ppm, and A and B satisfy the following relationship: 3 ⁇ B/A ⁇ 5.
  • B/A is in the appropriate range, it can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, so that the secondary battery has a long service life.
  • the secondary battery also has a high energy density.
  • the content of HF in the electrolyte is C ppm
  • the content of the acid removal material is D ppm
  • C and D satisfy the following relationship: 1 ⁇ D/C ⁇ 2.
  • the pH of the acid removal material, the content C ppm of HF in the electrolyte, and the content D ppm of the acid removal material also satisfy the following relationship: lgpH+0.5 ⁇ D/C ⁇ 2.
  • the free HF and moisture content in the secondary battery are less, and the secondary battery can have a longer service life and a higher energy density.
  • the third aspect of the present application provides an electric device, which includes the secondary battery according to the second aspect of the present application.
  • the secondary battery of the present application includes a multi-layer composite separator that uses both water-removing materials and acid-removing materials.
  • the multi-layer composite separator can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing moisture and HF has a negative impact on the secondary battery, so the secondary battery of the present application can take into account both high energy density and long service life.
  • the electrical device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic diagram of an embodiment of a secondary battery of the present application.
  • FIG. 2 is an exploded schematic view of an embodiment of the secondary battery of FIG. 1 .
  • Fig. 3 is a schematic diagram of an embodiment of the battery module of the present application.
  • Fig. 4 is a schematic diagram of an embodiment of the battery pack of the present application.
  • FIG. 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of an embodiment of an electrical device including the secondary battery of the present application as a power source.
  • ranges disclosed herein are defined in terms of lower and upper limits, and 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 and may be combined arbitrarily, ie 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, it is understood that ranges of 60-110 and 80-120 are contemplated. Additionally, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all expected: 1-3, 1-4, 1-5, 2- 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" indicates that all real numbers between "0-5" have been listed in this article, and "0-5" is only an abbreviated representation of the combination of these values.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed in sequence, and may also include steps (b) and (a) performed in sequence.
  • steps (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c) , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b) and so on.
  • the “comprising” and “comprising” mentioned in this application mean open or closed.
  • the “comprising” and “comprising” may mean that other components not listed may be included or included, or only listed components may be included or included.
  • the term "or” is inclusive unless otherwise stated.
  • the phrase "A or B” means “A, B, or both A and B.” More specifically, the condition "A or B” is satisfied by either of the following: 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).
  • active ion refers to ions that can intercalate and deintercalate back and forth between the positive and negative electrodes of the secondary battery, including but not limited to lithium ions, sodium ions, etc.
  • molecular sieve refers to a class of materials with pores of uniform size, and its crystalline state is mainly silicate or aluminosilicate;
  • superabsorbent resin refers to a class of materials with hydrophilic groups.
  • Secondary batteries also known as rechargeable batteries or accumulators, refer to batteries that can be activated by charging the active materials and continue to be used after the battery is discharged.
  • a secondary battery includes a positive pole piece, a negative pole piece, an electrolyte, and a separator.
  • active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode.
  • the separator is arranged between the positive pole piece and the negative pole piece, which mainly plays a role in preventing the short circuit of the positive and negative poles, and at the same time allows active ions to pass through.
  • the electrolyte plays the role of conducting active ions between the positive pole piece and the negative pole piece.
  • secondary batteries are widely used in energy storage power systems such as hydraulic power, thermal power, wind power and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.
  • the countermeasures usually adopted in the prior art include: (1) adding additives to the electrolyte to improve the stability of the electrolyte; (2) setting a coating layer on the surface of the positive electrode active material.
  • adding additives to the electrolyte to improve the stability of the electrolyte include: (1) adding additives to the electrolyte to improve the stability of the electrolyte; (2) setting a coating layer on the surface of the positive electrode active material.
  • the amount of additive added is small, it is not enough to complex all HF, and when the amount added is large, it is easy to change the kinetic properties of the electrolyte and affect the kinetic performance of the secondary battery; The process is complicated, and it is easy to affect the capacity of the secondary battery and reduce the energy density of the secondary battery.
  • the inventor after a lot of research and practice, and using reverse thinking and horizontal thinking, proposed a new type of multi-layer composite separator, which can effectively reduce the free moisture and HF inside the battery, so that the secondary battery can take into account the high Energy density and long service life.
  • the first aspect of the embodiment of the present application provides a multilayer composite isolation membrane, including a first substrate layer and a second substrate layer, the multilayer composite isolation membrane also includes a water removal material and an acid removal material, and the removal An acid material is located between the first substrate layer and the second substrate layer, and the water removal material is located on at least one surface of the first substrate layer and the second substrate layer.
  • the multi-layer composite separator of the present application adopts water-removing materials and acid-removing materials at the same time, and effectively fixes the free moisture and HF inside the battery on the water-removing materials and the On the acid removal material, it can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, so that the secondary battery can take into account both high energy density and long service life.
  • the multi-layer composite isolation membrane of the present application has a multi-layer structure, and the acid removal material is located between the two substrate layers, so as to avoid the oxidation and decomposition reaction of the acid removal material under high voltage, and ensure that the acid removal material has a better effect .
  • the present application has no particular limitation on the location of the water removal material, which may be located on at least one surface of the first substrate layer and the second substrate layer.
  • both the first base material layer and the second base material layer have two opposite surfaces in their thickness direction, therefore, the water removal material may be located on at least one of the above four surfaces.
  • the water removal material is located on the surface of the first substrate layer away from the acid removal material and close to the electrode sheet, or is located on the surface of the second substrate layer away from the acid removal material and close to the electrode sheet. On the surface of the electrode sheet, or between the first base material layer and the second base material layer.
  • the multilayer composite separator includes a functional layer between the first substrate layer and the second substrate layer, and the functional layer includes a water-scavenging material and an acid-scavenging material.
  • the thickness of the functional layer is not specifically limited, and can be selected according to actual needs.
  • the thickness of the functional layer is small, there are less water-removing materials and acid-removing materials loaded inside it, which may not be able to continuously and effectively reduce the free moisture and HF content inside the battery during the long-term charge-discharge cycle of the secondary battery;
  • the thickness of the above-mentioned functional layer is large, the weight of the secondary battery will increase significantly, and the mass energy density and kinetic performance may decrease. Therefore, the thickness of the functional layer should neither be too small nor too large.
  • the thickness of the functional layer may be 1 ⁇ m ⁇ 100 ⁇ m.
  • the thickness of the functional layer is 2 ⁇ m-80 ⁇ m, 2 ⁇ m-60 ⁇ m, 2 ⁇ m-50 ⁇ m, 2 ⁇ m-40 ⁇ m, 2 ⁇ m-30 ⁇ m, 2 ⁇ m-20 ⁇ m, 4 ⁇ m-80 ⁇ m, 4 ⁇ m-60 ⁇ m, 4 ⁇ m-50 ⁇ m, 4 ⁇ m-40 ⁇ m , 4 ⁇ m to 30 ⁇ m, 4 ⁇ m to 20 ⁇ m, 6 ⁇ m to 80 ⁇ m, 6 ⁇ m to 60 ⁇ m, 6 ⁇ m to 50 ⁇ m, 6 ⁇ m to 40 ⁇ m, 6 ⁇ m to 30 ⁇ m, or 6 ⁇ m to 20 ⁇ m.
  • the thickness of the functional layer When the thickness of the functional layer is in an appropriate range, it can continuously and effectively reduce the free moisture and HF content inside the battery during the long-term charge-discharge cycle of the secondary battery, while ensuring that the secondary battery has a high energy density and good performance. dynamic performance.
  • each component in the functional layer is not specifically limited, and can be selected according to actual needs.
  • the mass percentage of the acid removal material is 20% to 50%, and the mass percentage of the water removal material is 15% to 50%. 50%.
  • the functional layer may further include an adhesive.
  • the binder used for the functional layer includes but not limited to polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride - at least one of hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.
  • the binder may have a mass percentage of 1%-35%.
  • the acid removal material mainly reduces the free HF content inside the battery through chemical bonding (such as hydrogen bond, covalent bond, etc.). Therefore, in the multilayer composite separator of the present application, the quality of the acid removal material can be greater than or equal to The quality of the water removal material can ensure that the acid removal material can continuously and effectively reduce the free HF content inside the battery, thereby reducing the free water content inside the battery.
  • the ratio of the mass of the acid-removing material to the mass of the water-removing material in the multilayer composite isolation membrane may be 1-3.
  • the ratio of the mass of the acid-scavenging material to the mass of the water-scavenging material in the multilayer composite isolation membrane is 1-2.5, 1-2, or 1-1.5.
  • the water removal material may include at least one of molecular sieves and super absorbent polymers (Super Absorbent Polymer, SAP).
  • super absorbent polymers Super Absorbent Polymer, SAP
  • molecular sieves with higher water absorption are preferred.
  • the static water adsorption capacity of the molecular sieve at 25° C. and 30% relative humidity may be above 15%.
  • the static water adsorption test of the molecular sieve can refer to GB 6287-86 molecular sieve static water adsorption determination method.
  • the molecular sieve may include at least one of microporous molecular sieves and mesoporous molecular sieves.
  • microporous molecular sieves and mesoporous molecular sieves can have a higher specific surface area, so that they can play a better role in moisture adsorption.
  • the pore size of the molecular sieve should not be less than 0.3nm. If the pore size of the molecular sieve is too small, it is difficult for water molecules to be absorbed into the pore structure of the molecular sieve, so it is difficult for the molecular sieve to have a good adsorption and dewatering effect.
  • the pore size of the molecular sieve may be 0.3nm-50nm.
  • the pore size of the molecular sieve is 0.4nm-50nm, 0.5nm-50nm, 1nm-50nm, 2nm-50nm, 0.3nm-35nm, 0.4nm-35nm, 0.5nm-35nm, 1nm-35nm, 2nm-35nm , 0.3nm ⁇ 25nm, 0.4nm ⁇ 25nm, 0.5nm ⁇ 25nm, 1nm ⁇ 25nm, 2nm ⁇ 25nm, 0.3nm ⁇ 15nm, 0.4nm ⁇ 15nm, 0.5nm ⁇ 15nm, 1nm ⁇ 15nm, 2nm ⁇ 15nm, 0.3nm ⁇ 11nm, 0.4nm ⁇ 11nm, 0.5nm ⁇ 11nm, 1nm ⁇ 11nm, 2nm ⁇ 11nm, 0.3nm ⁇ 8nm, 0.4
  • the molecular sieve can have better water adsorption capacity and poorer water desorption capacity, thereby ensuring that the secondary battery has less free water during long-term charge and discharge cycles and HF content, and thus the cycle performance of the secondary battery is better.
  • the volume average particle diameter Dv50 of the molecular sieve When the volume average particle diameter Dv50 of the molecular sieve is large, the transmission path of active ions becomes longer, and the kinetic performance of the secondary battery may decrease; The risk of pores, and thus the kinetic performance of the secondary battery may also decrease. In order to ensure good kinetic performance of the secondary battery at the same time, the volume average particle diameter Dv50 of the molecular sieve should not be too large or too small. In some embodiments, the volume average particle diameter Dv50 of the molecular sieve may be 1 ⁇ m ⁇ 10 ⁇ m.
  • the volume average particle diameter Dv50 of the molecular sieve is 1 ⁇ m to 10 ⁇ m, 1 ⁇ m to 8 ⁇ m, 1 ⁇ m to 6 ⁇ m, 1 ⁇ m to 4 ⁇ m, 2 ⁇ m to 10 ⁇ m, 2 ⁇ m to 8 ⁇ m, 2 ⁇ m to 6 ⁇ m, 2 ⁇ m to 4 ⁇ m, 4 ⁇ m to 10 ⁇ m, 4 ⁇ m to 8 ⁇ m, or 4 ⁇ m to 6 ⁇ m.
  • the volume average particle diameter Dv50 of a material is a well-known meaning in the art, which means the particle diameter corresponding to when the cumulative volume distribution percentage of the material reaches 50%, which can be measured by instruments and methods known in the art. For example, it can be conveniently measured by 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 Co., Ltd., UK.
  • the molecular sieve When the molecular sieve has a relatively high specific surface area (BET), it can quickly absorb the free water inside the battery. However, the specific surface area of the molecular sieve should not be too high. At this time, the water adsorption capacity of the molecular sieve will not be further increased. , and the manufacturing cost is significantly increased; at the same time, the molecular sieve may also absorb more electrolyte, which is not conducive to the electrolyte to infiltrate the electrode sheet. At the same time, the specific surface area of the molecular sieve should not be too small.
  • BET specific surface area
  • the molecular sieve may have a specific surface area ranging from 350m 2 /g to 1000m 2 /g.
  • the specific surface area of the molecular sieve is 350m 2 /g-900m 2 /g, 350m 2 /g-800m 2 /g, 350m 2 /g-700m 2 /g, 350m 2 /g-600m 2 /g , 350m 2 /g ⁇ 500m 2 /g, 500m 2 /g ⁇ 1000m 2 /g, 500m 2 / g ⁇ 900m 2 /g, 500m 2 /g ⁇ 800m 2 /g, 500m 2 /g ⁇ 700m 2 /g , 500m 2 /g ⁇ 600m 2 /g, 650m 2 /g ⁇ 1000m 2 /g, 650m 2 /g ⁇ 900m 2 /g, 650m 2 /g ⁇ 800m 2 /g, or 650m 2 /g ⁇ 700m 2 /g g.
  • the molecular sieve can have better water adsorption capacity, thereby ensuring that the secondary battery has less free water and HF content during the long-term charge and discharge cycle, and the secondary battery cycle performance is better.
  • the specific surface area of a material is a well-known meaning in the art, and can be measured with instruments and methods known in the art.
  • it can refer to GB/T 19587-2017, use the nitrogen adsorption specific surface area analysis test method to test, and use the BET (Brunauer Emmett Teller) method to calculate, the nitrogen adsorption specific surface area analysis test can pass the Tri-Star 3020 specific surface area of Micromeritics in the United States Pore size analysis tester.
  • the type of the molecular sieve is not specifically limited, and can be selected according to actual needs.
  • the molecular sieves may include but not limited to type A molecular sieves (such as type 3A molecular sieves, type 4A molecular sieves, type 5A molecular sieves, etc.), type X molecular sieves (such as type 10X molecular sieves, type 13X molecular sieves, etc.) ), at least one of Y-type molecular sieves.
  • the molecular sieves may include, but are not limited to, at least one of silica-alumina molecular sieves, titanium-silicon molecular sieves, and phosphorus-aluminum molecular sieves according to the classification of framework elements.
  • the molecular sieve may include but not limited to at least one of silicon-based molecular sieve SBA-15 and titanium-silicon molecular sieve TS-1.
  • SBA-15 and TS-1 can have a mesoporous structure and have thicker pore walls, higher pore volume and better hydrothermal stability, so it can ensure that the secondary battery has less damage during long-term charge and discharge cycles. The content of free moisture and HF is higher, and the cycle performance of the secondary battery is better.
  • SBA-15 and TS-1 can also have a microporous structure.
  • a superabsorbent resin having a higher water absorption is preferable.
  • the water absorption rate of the superabsorbent resin may be more than 100 times.
  • the water absorption capacity refers to the ratio of the water mass that a unit mass of superabsorbent resin can absorb to its own mass.
  • the water absorption rate test of the superabsorbent resin can refer to GB/T 22875-2008 and GB/T 22905-2008.
  • a superabsorbent resin that has a relatively high water absorption and is not easily soluble in water is preferable.
  • the solubility of the superabsorbent resin in water at 25°C may be below 5%.
  • the super absorbent resin may include but not limited to starch-grafted acrylic, starch-grafted acrylic, starch-grafted acrylamide, cellulose-grafted acrylonitrile, cellulose-grafted Branch acrylic series, cellulose grafted acrylamide series, polyvinyl alcohol series, polyacrylic acid (salt) series, polyacrylamide series, polyoxyethylene series, polyurethane series, vinyl acetate copolymers, and their respective modified compounds at least one of the
  • the superabsorbent resin includes at least one of polyvinyl alcohol and cyclic acid anhydride copolymer, sodium polyacrylate resin, and vinyl acetate and acrylate copolymer.
  • the acid removal material should not be selected to be acidic or acidic after hydrolysis, and it may not be possible to effectively reduce the free HF content inside the battery at this time.
  • the alkalinity of the acid removal material should not be too strong.
  • the alkalinity of the acid-removing material is strong, it is easy to induce electrolyte salt decomposition, increase free side reactions inside the battery, reduce the energy density, service life and kinetic performance of the secondary battery, and may even increase the HF content.
  • the pH of the acid-scavenging material is 7-11.5.
  • the acid-removing material has weak alkalinity, and can fix HF and water molecules through acid-base neutralization reaction, so as to continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the impact of moisture and HF on
  • the negative impact of the secondary battery makes the secondary battery take into account both high energy density and long service life.
  • the pH of the acid removal material is 7-10. Further, the pH of the acid removal material is 7.2-9.3.
  • the pH of the acid-removing material has a well-known meaning in the art, and can be measured with instruments and methods known in the art.
  • An exemplary test method includes the steps: at 25°C, add 5g of the acid-removing material into 100g of deionized water, stir and dissolve it thoroughly, and test the pH value of the solution with reference to GB/T 6920-86 as the pH of the acid-removing material.
  • the acid removal material may include at least one of inorganic alkaline lithium salts and organic compounds.
  • the inorganic alkaline lithium salt may include but not limited to at least one of lithium carbonate and lithium bicarbonate.
  • the molecular structure of the organic compound may include at least one of amide groups, silicon nitrogen groups, silicon groups, carbon nitrogen groups, sulfonate groups, and carboxylate ions.
  • the organic compound may include, but not limited to, at least one of an organic basic lithium salt and an organic small molecule compound.
  • the organic compounds include, but are not limited to, lithium acetate, hexamethyldisilazane, heptamethyldisilazane, trimethylsilyldiethylamine, trimethylsilyl methanesulfonate, di At least one of (trimethylsilyl)carbodiimide, N,N-dimethylpropionamide, N,N-dimethylacetamide, and N,N-dimethylformamide.
  • the acid-removing material can fix HF and water molecules through chemical reactions (such as acid-base neutralization reaction), hydrogen bonding, etc., so as to continuously and effectively reduce the free moisture and HF content inside the battery, and then Reduce the negative impact of moisture and HF on the secondary battery, so that the secondary battery can take into account both high energy density and long service life.
  • chemical reactions such as acid-base neutralization reaction
  • hydrogen bonding etc.
  • the thicknesses of the first base material layer and the second base material layer there is no particular limitation on the thicknesses of the first base material layer and the second base material layer, which can be selected according to actual needs.
  • the types of the first substrate layer and the second substrate layer there is no particular limitation on the types of the first substrate layer and the second substrate layer, and any known porous structure membrane with good chemical stability and mechanical stability can be selected.
  • the material of the first base material layer and the second base material layer may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the first substrate layer and the second substrate layer may be the same or different.
  • the multilayer composite separator of the present application does not exclude other components other than the above-mentioned components.
  • the multilayer composite separator may further include fillers, such as inorganic ceramic particles and the like.
  • the inorganic ceramic particles may be located on the surface of the first substrate layer away from the acid-scavenging material and close to the electrode sheet, on the surface of the second substrate layer away from the acid-scavenging material and close to the electrode sheet. on the surface of the electrode sheet, or located in the pores of the first base material layer and the second base material layer.
  • the multilayer composite isolation membrane includes a first substrate layer and a second substrate layer, and the multilayer composite isolation membrane also includes a water removal material and an acid removal material, and the acid removal material is located in the Between the first substrate layer and the second substrate layer, the water removal material is located on at least one surface of the first substrate layer and the second substrate layer; the water removal material Including at least one of molecular sieves and superabsorbent resins; the pH of the acid-removing material is 7-11.5, optionally 7-10, and further 7.2-9.3; the multilayer composite isolation membrane The ratio of the mass of the acid-removing material to the mass of the water-removing material is 1-3, optionally 1-1.5.
  • the multi-layer composite separator adopts a water-removing material with high water-absorbing capacity and a weakly alkaline acid-removing material to effectively dissociate the inside of the battery under various actions such as physical adsorption and chemical bonding (such as acid-base neutralization reaction).
  • the moisture and HF are fixed on the water-removing material and the acid-removing material, so it can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, making the secondary battery
  • the secondary battery combines high energy density and long service life at the same time.
  • the multilayer composite separator includes a first substrate layer, a second substrate layer, and a functional layer between the first substrate layer and the second substrate layer, and the The functional layer includes a water removal material and an acid removal material. Based on the total mass of the functional layer, the mass percentage of the acid removal material is 20% to 50%, and the mass percentage of the water removal material is 15%. % to 50%, and the ratio of the mass of the acid removal material to the mass of the water removal material is 1 to 3, optionally 1 to 1.5; the water removal material includes at least one of molecular sieves and superabsorbent resins One: the pH of the acid removal material is 7-11.5, optionally 7-10, further 7.2-9.3.
  • the multi-layer composite separator adopts a water-removing material with high water-absorbing capacity and a weakly alkaline acid-removing material to effectively dissociate the inside of the battery under various actions such as physical adsorption and chemical bonding (such as acid-base neutralization reaction).
  • the moisture and HF are fixed on the water-removing material and the acid-removing material, so it can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, making the secondary battery
  • the secondary battery combines high energy density and long service life at the same time.
  • the first aspect of the embodiment of the present application also provides a method for preparing a multilayer composite separator.
  • the multilayer composite separator can be prepared according to methods known in the art.
  • the multi-layer composite separator can be prepared according to the following steps: disperse the water removal material, acid removal material, binder and optional additives in a solvent and stir to form a slurry; The slurry is coated on the surface of one of the substrate layers, and then another substrate layer is covered on the surface of the slurry. After drying and cold pressing, a multi-layer composite isolation film is obtained.
  • the multi-layer composite separator can also be prepared according to the following steps: disperse the acid-removing material, binder and optional additives in a solvent and stir evenly to form the first slurry;
  • the water material, binder and optional additives are dispersed in a solvent and stirred evenly to form a second slurry;
  • the first slurry is coated on the surface of one of the substrate layers, and then the surface of the first slurry is covered with another layer substrate layer; coating the second slurry on the surface of any one substrate layer away from the acid-scavenging material, drying and cold pressing to obtain a multi-layer composite isolation film.
  • the solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the binder may include but not limited to polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoro At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.
  • the auxiliary agent may include a dispersant, such as cetyltrimethylammonium bromide and the like.
  • a second aspect of the embodiments of the present application provides a secondary battery.
  • the present application has no special limitation on the type of the secondary battery, for example, the secondary battery may be a lithium ion battery, a sodium ion battery, etc., especially, the secondary battery is a lithium ion secondary battery.
  • the secondary battery includes a positive pole piece, a negative pole piece, an electrolyte, and a separator
  • the separator adopts the multilayer composite separator described in any embodiment of the first aspect of the present application.
  • the separator is arranged between the positive pole piece and the negative pole piece to prevent the short circuit of the positive and negative poles and reduce the free moisture and HF content inside the battery.
  • the moisture content in the secondary battery is Applied ppm, based on the total mass of the multilayer composite separator, the except The content of water material is B ppm, and A and B satisfy the following relationship: 3 ⁇ B/A ⁇ 5.
  • B/A When B/A is small, it may not be able to effectively reduce the free moisture and HF inside the battery; and when B/A is large, the excess of the water removal material will increase, and its effect on improving the performance of the secondary battery will not continue to increase , but the mass of the secondary battery increases, thereby reducing the energy density of the secondary battery.
  • B/A When B/A is in the appropriate range, it can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, so that the secondary battery has a long service life.
  • the secondary battery also has a high energy density.
  • the moisture in the secondary battery is mainly composed of three parts: trace moisture remaining in the positive electrode sheet, trace moisture remaining in the negative electrode sheet, and trace moisture in the electrolyte solution.
  • the content of moisture in the secondary battery is obtained by the following method: respectively test the quality of water in the prepared positive electrode sheet, negative electrode sheet, and electrolyte to obtain the total mass of water; divide the obtained total mass of water by the positive electrode sheet And the total mass of the negative electrode sheet, promptly obtain the content (App ppm) of moisture in the above-mentioned secondary battery.
  • the moisture in the positive pole piece, the negative pole piece and the electrolyte can be tested by a Karl Fischer moisture analyzer, such as the MA-30 intelligent Karl Fischer moisture analyzer.
  • the secondary battery Based on the above-mentioned moisture content (App ppm) in the secondary battery, selecting the appropriate quality of water-removing material can not only continuously and effectively reduce the free moisture and HF content inside the battery, but also reduce the negative impact of moisture and HF on the secondary battery.
  • the secondary battery has a long service life, and at the same time, the secondary battery has a high energy density.
  • the moisture content Appm in the secondary battery is between 20ppm and 600ppm.
  • the added amount of the water removal material can be satisfied based on the total mass of the multilayer composite isolation membrane, and the content B ppm of the water removal material is between 60ppm and 3000ppm.
  • the content of HF in the electrolyte is C ppm
  • the content of the acid removal material is D ppm
  • C and D satisfies the following relationship: 1 ⁇ D/C ⁇ 2.
  • the D/C When the D/C is small, it may not be able to effectively reduce the free moisture and HF inside the battery; and when the D/C is large, the acid removal material is excessive, and its effect on improving the performance of the secondary battery will not continue to increase , but the mass of the secondary battery increases, thereby reducing the energy density of the secondary battery.
  • the D/C When the D/C is within an appropriate range, it can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, so that the secondary battery has a long service life.
  • the secondary battery also has a high energy density.
  • the secondary battery has a long service life, and at the same time, the secondary battery has a high energy density.
  • the content of HF in the electrolyte can be obtained by titration test, for example, refer to HG/T4067-2015.
  • An exemplary test method comprises the steps of: adding 15g of electrolyte sample to 100ml of ice-water mixture, using bromothymol blue as indicator, titrating with sodium hydroxide standard titration solution until the solution turns blue as the reaction end point, Record the volume V 1 of the sodium hydroxide standard titration solution; add bromothymol blue to the 100ml ice-water mixture as an indicator, titrate with the sodium hydroxide standard titration solution until the solution turns blue as the reaction end point, and record the sodium hydroxide The volume V 0 of the standard titration solution.
  • V 1 -V 0 is the volume of the sodium hydroxide standard titration solution actually consumed, from which the mass of HF and its content in the electrolyte can be calculated.
  • the content C ppm of HF in the electrolyte is between 20 ppm and 500 ppm.
  • the added amount of the acid-scavenging material can be satisfied based on the total mass of the electrolyte, and the content D ppm of the acid-scavenging material is between 20ppm and 1000ppm.
  • the pH of the acid-scavenging material, the content C ppm of HF in the electrolyte, and the content D ppm of the acid-scavenging material also satisfy the following relationship: lgpH+0.5 ⁇ D/C ⁇ 2.
  • the electrolyte solution includes an electrolyte salt and a solvent.
  • the types of the electrolyte salt and the solvent are not specifically limited, and can be selected according to actual needs.
  • the electrolyte salt may include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), di At least one of lithium fluorine oxalate borate (LiDFOB), lithium difluorooxalate borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorooxalate phosphate (LiDFOP), lithium tetrafluorooxalate phosphate (LiPF 6 ), lithium tetrafluorooxalate phosphate (LiPF 6 ), lithium t
  • the electrolyte salt may include sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), hexafluoroarsenic acid Sodium (NaAsF 6 ), sodium bisfluorosulfonimide (NaFSI), sodium bistrifluoromethanesulfonimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), di At least one of sodium oxalate borate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ), sodium difluorodioxalate phosphate (NaDFOP), sodium tetrafluorooxalate phosphate (NaTFOP).
  • NaPF 6 sodium hexafluorophosphate
  • NaBF 4 sodium tetrafluoroborate
  • the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate ( DMC), Dipropyl Carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Butylene Carbonate (BC), Methyl Formate (MF), Methyl Acetate (MA), Ethyl Acetate Ester (EA), Propyl Acetate (PA), Methyl Propionate (MP), Ethyl Propionate (EP), Propyl Propionate (PP), Methyl Butyrate (MB), Ethyl Butyrate (EB ), 1,4-butyrolactone (GBL), sulfolane (SF), dimethylsulfone (MSM), methylethylsulfone (EMS) and diethylsulfone (ESE).
  • EC ethylene carbonate
  • PC propylene carbon
  • the electrolyte may optionally include additives.
  • the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and improve battery performance. Additives for low temperature power performance, etc.
  • the additive may include but not limited to at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3-propane sultone (PS).
  • 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.
  • the positive electrode current collector has two opposite surfaces 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 current collector can 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 and a metal material layer formed on at least one surface of the polymer material base.
  • the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) at least one.
  • the positive film layer generally includes a positive active material, an optional binder, and an optional conductive agent.
  • the positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder and any other components in a solvent and stirring them uniformly.
  • the solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the binder used for the positive film layer may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoro At least one of propylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • VFE vinylidene fluoride-tetrafluoroethylene-propylene terpolymer
  • the conductive agent used for the positive electrode film layer includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode active material may be a positive electrode active material known in the art for secondary batteries.
  • the positive electrode active material may include lithium transition metal oxides, olivine-structured lithium-containing phosphates and their respective modified compounds at least one of the Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide At least one of lithium nickel cobalt aluminum oxide and modified compounds thereof.
  • olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium manganese iron phosphate, lithium manganese iron phosphate At least one of composite materials with carbon and their respective modifying compounds.
  • the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials of lithium ion batteries can also be used. These positive electrode active materials may be used alone or in combination of two or more.
  • the positive electrode active material for the lithium ion battery may include at least one of the lithium transition metal oxide and its modified compound shown in Formula 1,
  • M is selected from Mn, Al, Zr, Zn , at least one of Cu, Cr, Mg, Fe, V, Ti and B, and A is at least one selected from N, F, S and Cl.
  • positive active materials for lithium-ion batteries may include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM333), LiNi 0.5 Co 0.2 At least one of Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 , LiMnPO 4 kind.
  • the positive electrode active material may include sodium-containing transition metal oxides, polyanion materials (such as phosphate, fluorophosphate, pyrophosphate, sulfate, etc.), Prussian blue At least one of the class materials.
  • the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries can also be used. These positive electrode active materials may be used alone or in combination of two or more.
  • positive active materials for sodium ion batteries may include NaFeO 2 , NaCoO 2 , NaCrO 2 , NaMnO 2 , NaNiO 2 , NaNi 1/2 Ti 1/2 O 2 , NaNi 1/2 Mn 1/2 O 2 , Na 2/3 Fe 1/3 Mn 2/3 O 2 , NaNi 1/3 Co 1/3 Mn 1/3 O 2 , NaFePO 4 , NaMnPO 4 , NaCoPO 4 , Prussian blue materials, the general formula is A a At least one of the materials of M b (PO 4 ) c O x Y 3-x .
  • A is selected from at least one of H + , Li + , Na + , K + and NH 4 + ;
  • M is a transition metal cation, optionally V, Ti, Mn, Fe, Co, Ni, Cu and Zn at least one of;
  • Y is a halide anion, optionally at least one of F, Cl and Br; 0 ⁇ a ⁇ 4;0 ⁇ b ⁇ 2;1 ⁇ c ⁇ 3; 0 ⁇ x ⁇ 2.
  • the modified compounds of the above-mentioned positive electrode active materials may be modified by doping or surface coating of the positive electrode active materials.
  • 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 anode current collector has two opposite surfaces in its own thickness direction, and the anode film layer is disposed on any one or both of the two opposite surfaces of the anode current collector.
  • the negative electrode current collector can be a metal foil or a composite current collector.
  • the metal foil copper foil can be used.
  • the composite current collector may include a polymer material base and a metal material layer formed on at least one surface of the polymer material base.
  • the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy.
  • the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) at least one.
  • the negative electrode film layer usually includes negative electrode active materials, optional binders, optional conductive agents and other optional additives.
  • the negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying and cold pressing.
  • the negative electrode slurry coating is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring them evenly.
  • the solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.
  • the binder used for the negative film layer may include styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS ), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), carboxymethyl chitosan (CMCS) at least one.
  • the conductive agent used in the negative electrode film layer may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • Other optional additives may include thickeners (eg, sodium carboxymethylcellulose CMC-Na), PTC thermistor materials, and the like.
  • the negative active material known negative active materials for secondary batteries can be used in the art.
  • the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate.
  • the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials.
  • the tin-based material may include at least one of simple tin, tin oxide, and tin alloy materials. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode sheet of the present application does not exclude other additional functional layers other than the negative electrode film layer.
  • the negative electrode sheet of the present application further includes a conductive primer layer (for example, composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and provided on the surface of the negative electrode current collector.
  • the negative electrode sheet of the present application further includes a protective layer covering the surface of the negative electrode film layer.
  • the positive electrode sheet, the multilayer composite separator and the negative electrode sheet can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer package.
  • the outer package can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer package of the secondary battery may be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, and the like.
  • the outer packaging of the secondary battery may also be a soft bag, such as a pouch-type soft bag.
  • the material of the soft bag can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS) and the like.
  • FIG. 1 shows a secondary battery 5 with a square structure as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and the side plates enclose to form a receiving cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 is used to cover the opening to close the accommodating cavity.
  • the positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the accommodating chamber. Electrolyte is infiltrated in the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or several, and can be adjusted according to requirements.
  • the secondary battery according to the present application can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 3 is a schematic diagram of a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 may be fixed by fasteners.
  • the battery module 4 may also include a case having a housing space in which a plurality of secondary batteries 5 are accommodated.
  • the above battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3 , the upper box body 2 is used to cover the lower box body 3 and forms a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the second aspect of the embodiment of the present application also provides a method for preparing a secondary battery.
  • the method includes the following steps: S100, providing a positive electrode sheet, a negative electrode sheet, a multilayer composite separator, and an electrolyte, wherein the multilayer composite separator includes a first substrate layer, a second substrate layer, Water material and acid removal material, the acid removal material is located between the first substrate layer and the second substrate layer, the water removal material is located between the first substrate layer and the second substrate layer At least one surface of the material layer; S200, assembling the above-mentioned positive electrode sheet, multi-layer composite separator, negative electrode sheet and electrolyte into a secondary battery.
  • S100 further includes the following steps: S101, testing the quality of water in the positive pole piece and the negative pole piece, and the water and HF quality in the electrolyte, and calculating based on the weight of the positive pole piece and the water in the negative pole piece.
  • the addition amount makes it meet the content B ppm of the water removal material based on the total mass of the multilayer composite separator to meet 3 ⁇ B/A ⁇ 5, the addition amount of the acid removal material makes it meet the requirement based on the electrolysis
  • the content D ppm of the acid-removing material in the total mass of the liquid satisfies 1 ⁇ D/C ⁇ 2, optionally, the added amount of the acid-removing material further satisfies lgpH+0.5 ⁇ D/C ⁇ 2, and the pH is The pH of the acid scavenging material.
  • Selecting the appropriate quality of dewatering material based on the content (App ppm) of moisture in the above-mentioned secondary battery and selecting the appropriate quality of deacidifying material based on the content (C ppm) of HF in the electrolyte can not only continuously and effectively Reduce the free moisture and HF content inside the battery, reduce the negative impact of moisture and HF on the secondary battery, make the secondary battery have a long service life, and at the same time make the secondary battery have a high energy density.
  • S200 may further include the step of forming an electrode assembly through the above-mentioned positive electrode sheet, separator, and negative electrode sheet through a winding process or a lamination process, placing the electrode assembly in an outer package, drying it, and injecting it into an electrolytic liquid, and undergo processes such as vacuum packaging, standing still, chemical formation, and shaping to obtain a secondary battery.
  • a third aspect of the embodiments of the present application provides an electrical device.
  • the electric device includes at least one of the secondary battery, battery module, or battery pack of the present application.
  • the secondary battery, battery module or battery pack can be used as a power source of the electric device, and can also be used as an energy storage unit of the electric device.
  • the electric device can be, but not limited to, mobile devices (such as mobile phones, notebook computers, 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.
  • the electric device can select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • FIG. 6 is a schematic diagram of an example electrical device.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • a battery pack or a battery module can be used.
  • the electric device may be a mobile phone, a tablet computer, a notebook computer, and the like.
  • the electrical device is usually required to be light and thin, and a secondary battery can be used as a power source.
  • Titanium-silicon molecular sieve TS-1 (water removal material) with a specific surface area of 650m 2 /g, a pore size of 3nm, and a Dv50 of 2 ⁇ m was mixed with hexamethyldisilazane (acid removal material) and polyvinylidene fluoride with a pH of 7.5 (Binder) and hexadecyltrimethylammonium bromide are stirred in an appropriate amount of solvent NMP for 2h to 3h according to the mass ratio of 35:45:19:1 to form a slurry; the slurry is coated with a thickness of 14 ⁇ m porous polyethylene film (first substrate layer) surface, and then cover another layer of porous polyethylene film (second substrate layer) with a thickness of 8 ⁇ m on the surface of the slurry, after drying and cold pressing to obtain a multi-layer Composite isolation film.
  • the thickness of the slurry layer was 6 ⁇ m.
  • the positive electrode active material LiFePO 4 , conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of solvent NMP according to the mass ratio of 80:10:10 to form a solid content of 50 % positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the aluminum foil of the positive electrode current collector, dried at 85°C and then cold pressed, then trimmed, cut into pieces, and slitted, and then dried at 85°C Dry under vacuum condition for 4h to obtain the positive electrode sheet.
  • Negative electrode active material graphite, conductive agent carbon black (Super P), thickener carboxymethylcellulose sodium (CMC-Na), binder styrene-butadiene rubber (SBR) are mixed according to the mass ratio of 80:15:3:2
  • An appropriate amount of solvent in deionized water is fully stirred and mixed to form a negative electrode slurry with a solid content of 30%; the negative electrode slurry is evenly coated on the surface of the copper foil of the negative electrode current collector, dried at 85°C and then cold pressed. Then edge trimming, cutting into pieces, and slitting were carried out, and then dried under a vacuum condition of 120° C. for 12 hours to obtain negative electrode sheets.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • the content of moisture in the secondary battery is obtained by the following method: respectively test the quality of water in the positive pole piece, negative pole piece, and electrolyte prepared by the MA-30 intelligent Karl Fischer moisture meter to obtain the total mass of water; The total mass of moisture obtained is divided by the total mass of the positive electrode sheet and the negative electrode sheet to obtain the moisture content (A ppm) in the secondary battery.
  • the moisture content A ppm in the secondary battery is 50 ppm; based on the total mass of the electrolyte, the HF content C ppm in the electrolyte is 100ppm; based on the total mass of the multilayer composite separator, the content B ppm of the water removal material is 150 ppm; based on the total mass of the electrolyte, the content D ppm of the acid removal material is 187 ppm.
  • the preparation method of the secondary battery is similar to that of Example 1, except that the preparation parameters of the separator are different, see Table 1 for details.
  • the composition of the isolation film in each embodiment including the type and thickness of the first substrate layer, the type and thickness of the second substrate layer, the thickness of the functional layer, the type and mass percentage of each component in the functional layer, etc.
  • One or more of the parameters can be used to obtain a secondary battery that satisfies the content of the water-removing material and the content of the acid-removing material required by each embodiment.
  • the preparation method of the secondary battery is similar to that of Example 1, except that a porous polyethylene film with a thickness of 14 ⁇ m is used as the separator.
  • the preparation method of the secondary battery is similar to that of Example 1, except that no water-removing material is added when preparing the separator.
  • the preparation method of the secondary battery is similar to that of Example 1, except that no acid-scavenging material is added when preparing the separator.
  • the preparation method of the secondary battery is similar to that of Example 1, except that the preparation parameters of the separator and the electrolyte are different.
  • a porous polyethylene film with a thickness of 14 ⁇ m is used as the separator, and 1% of Hexa Disilazane as an additive.
  • the capacity retention rate (%) of the secondary battery after 200 cycles 200th cycle discharge capacity/1st cycle discharge capacity ⁇ 100%.
  • Table 1 shows the test results of Examples 1-16 and Comparative Examples 1-4.
  • the multi-layer composite separator of the present application uses both water-removing materials and acid-removing materials, and effectively removes the free moisture and HF inside the battery under various functions such as physical adsorption and chemical bonding. fixed on the water-removing material and the acid-removing material, so it can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, making the secondary battery more Good cycle performance.
  • Comparative Example 2 and Comparative Example 3 only use acid-removing materials or water-removing materials. Compared with Comparative Example 1, the cycle performance of the secondary battery is improved to some extent, but the improvement effect is not good. The possible reason is that after the bound water in the electrode sheet is released into the electrolyte, it will react with the fluorine-containing electrolyte salt to generate HF. Similarly, HF can also combine with the inorganic electrolyte salt in the solid electrolyte interface film on the surface of the negative active material. Partitions (such as lithium carbonate, etc.) react to convert into moisture again. Therefore, only using acid-removing materials or water-removing materials alone cannot effectively improve the cycle performance of the secondary battery.
  • Comparative Example 4 the acid-removing material hexamethyldisilazane was added to the electrolyte. Compared with Comparative Example 1, the cycle performance of the secondary battery was improved to some extent, but the improvement effect was not good. The possible reason is that hexamethyldisilazane is not compatible with the electrolyte, and hexamethyldisilazane is easy to form precipitates after long-term use, which affects the acid removal effect; at the same time, the precipitates are deposited on the surface of the isolation membrane It is easy to cause the pore blocking of the separator and affect the cycle performance of the secondary battery.
  • the quality of the water removal material should not be too high or too low.
  • B/A When B/A is in the appropriate range, it can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, so that the secondary battery has a long service life.
  • the secondary battery also has a high energy density.
  • B/A When B/A is small, it may not be able to effectively reduce the free moisture and HF inside the battery, and thus the cycle performance of the secondary battery is poor; and when the B/A is large, there are more excess water removal materials, which is harmful to the secondary battery.
  • the effect of improvement in performance does not continue to increase, but the mass of the secondary battery increases, thereby reducing the energy density of the secondary battery. Therefore, optionally, 3 ⁇ B/A ⁇ 5.
  • the quality of the acid removal material should not be too high or too low.
  • the D/C When the D/C is within an appropriate range, it can continuously and effectively reduce the free moisture and HF content inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, so that the secondary battery has a long service life.
  • the secondary battery also has a high energy density.
  • the D/C When the D/C is small, it may not be able to effectively reduce the free moisture and HF inside the battery, and the cycle performance of the secondary battery is poor; and when the D/C is large, there are more acid removal materials, which is harmful to the secondary battery.
  • the effect of improvement in performance does not continue to increase, but the mass of the secondary battery increases, thereby reducing the energy density of the secondary battery. Therefore, optionally, 1 ⁇ D/C ⁇ 2.
  • the pH of the acid-removing material should not be too high. Higher pH of the acid-removing material may induce electrolyte salt decomposition, thereby reducing the cycle performance of the secondary battery. Therefore, the pH of the acid removal material may be 7-11.5, optionally 7-10, further 7.2-9.3.
  • the specific surface area of the molecular sieve as the water removal material should not be too high or too low.
  • the specific surface area is high, it may absorb more electrolyte, which is not conducive to the electrolyte infiltrating the electrode sheet, and the cycle performance of the secondary battery is slightly poor; when the specific surface area is small, the adsorption capacity for free moisture inside the battery is poor. It may not be possible to ensure that the secondary battery has less free moisture and HF content during long-term charge-discharge cycles, and then the cycle performance of the secondary battery will be slightly poor. Therefore, optionally, the specific surface area of the molecular sieve is 350m 2 /g-1000m 2 /g, further 650m 2 /g-800m 2 /g.
  • the present application is not limited to the above-mentioned embodiments.
  • the above-mentioned embodiments are merely examples, and within the scope of the technical solutions of the present application, embodiments that have substantially the same configuration as the technical idea and exert the same effects are included in the technical scope of the present application.
  • various modifications conceivable by those skilled in the art are added to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of the present application. .

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Abstract

本申请公开了一种多层复合隔离膜、以及包含其的二次电池、用电装置，所述多层复合隔离膜包括第一基材层以及第二基材层，其中，所述多层复合隔离膜还包括除水材料以及除酸材料，所述除酸材料位于所述第一基材层和所述第二基材层之间，所述除水材料位于所述第一基材层和所述第二基材层中的至少一个表面上。本申请的二次电池能够同时兼顾高能量密度和长使用寿命。

Description

多层复合隔离膜、以及包含其的二次电池、用电装置
相关申请的交叉引用
本申请要求享有于2022年01月27日提交的名称为“多层复合隔离膜、以及包含其的二次电池、用电装置”的中国专利申请202210099661.9的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请属于电池技术领域，尤其涉及一种多层复合隔离膜、以及包含其的二次电池、用电装置。
背景技术
近年来，二次电池被广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。随着二次电池的应用及推广，其能量密度和使用寿命受到越来越多的关注，因此需要有效的技术手段提高二次电池的能量密度、延长二次电池的使用寿命。
发明内容
本申请的目的在于提供一种多层复合隔离膜、以及包含其的二次电池、用电装置，所述二次电池能够同时兼顾高能量密度和长使用寿命。
本申请第一方面提供一种多层复合隔离膜，包括第一基材层以及第二基材层，其中，所述多层复合隔离膜还包括除水材料以及除酸材料，所述除酸材料位于所述第一基材层和所述第二基材层之间，所述除水材料位于所述第一基材层和所述第二基材层中的至少一个表面上。
本申请的多层复合隔离膜同时采用了除水材料和除酸材料，在物理吸附、化学键合等多种作用下，有效将电池内部游离的水分和HF固定在所述除水材料和所述除酸材料上，因此能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池同时兼顾高能量密度和长使用寿命。
在本申请的任意实施方式中，所述多层复合隔离膜包括位于所述第一基材层和所述第二基材层之间的功能层，并且所述功能层包括除水材料以及除酸材料。
在本申请的任意实施方式中，基于所述功能层的总质量，所述除酸材料的质量百分含量为20％～50％，所述除水材料的质量百分含量为15％～50％。
在本申请的任意实施方式中，所述功能层的厚度为1μm～100μm。可选地，所述功能层的厚度为4μm～50μm。所述功能层的厚度在合适的范围时，能在二次电池长期充放电循环过程中持续且有效地减少电池内部游离的水分和HF含量，同时保证二次电池具有较高的能量密度和良好的动力学性能。
在本申请的任意实施方式中，所述多层复合隔离膜中的所述除酸材料的质量和所述除水材料的质量之比为1～3。可选地，所述多层复合隔离膜中的所述除酸材料的质量和所述除水材料的质量之比为1～1.5。所述除酸材料的质量可以大于等于所述除水材料的质量，从而能够保证所述除酸材料能够持续且有效地减少电池内部游离的HF含量，进而减少电池内部游离的水分含量。
在本申请的任意实施方式中，所述除水材料包括分子筛、高吸水树脂中的至少一种。
在本申请的任意实施方式中，所述分子筛在25℃、30％相对湿度的静态水吸附量在15％以上。
在本申请的任意实施方式中，所述分子筛的孔径为0.3nm～50nm，可选地为0.5nm～15nm。所述分子筛的孔径在合适的范围内时，所述分子筛可以具有更好的水吸附能力以及更差的水脱附能力，从而保证二次电池在长期充放电循环过程中具有较少的游离水分和HF含量，进而二次电池的循环性能更好。
在本申请的任意实施方式中，所述分子筛的体积平均粒径Dv50为1μm～10μm，可选地为2μm～6μm。所述分子筛的体积平均粒径Dv50在合适的范围内时，可以保证二次电池同时兼顾较好的动力学性能。
在本申请的任意实施方式中，所述分子筛的比表面积为350m 2/g～1000m 2/g，可选地为650m 2/g～800m 2/g。所述分子筛的比表面积在合适的范围内时，所述分子筛可以具有更好水吸附能力，从而保证二次电池在长期充放电循环过程中具有较少的游离水分和HF含量，进而二次电池的循环性能更好。
在本申请的任意实施方式中，所述分子筛包括硅基分子筛SBA-15、钛硅分子筛TS-1中的至少一种。SBA-15、TS-1可以具有介孔结构以及具有更厚的孔壁、更高的孔容和更好的水热稳定性，因此可以保证二次电池在长期充放电循环过程中具有较少的游离水分和HF含量，进而二次电池的循环性能更好。
在本申请的任意实施方式中，所述高吸水树脂的吸水倍率在100倍以上。
在本申请的任意实施方式中，所述高吸水树脂25℃下在水中的溶解度在5％以下。
在本申请的任意实施方式中，所述高吸水树脂包括淀粉接枝丙烯腈系、淀粉接枝丙烯酸系、淀粉接枝丙烯酰胺系、纤维素接枝丙烯腈系、纤维素接枝丙烯酸系、纤维素接枝丙烯酰胺系、聚乙烯醇系、聚丙烯酸(盐)系、聚丙烯酰胺系、聚氧乙烯系、聚氨酯系、醋酸乙烯酯共聚物、及其各自的改性化合物中的至少一种。可选地，所述高吸水树脂包括聚乙烯醇与环状酸酐共聚物、聚丙烯酸钠树脂、醋酸乙烯酯与丙烯酸盐共聚物中的至少一种。
在本申请的任意实施方式中，所述除酸材料的pH为7～11.5。可选地，所述除酸材料的pH为7～10。在本申请中，所述除酸材料具有弱碱性，可以通过酸碱中和反应固定 HF和水分子，从而能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池同时兼顾高能量密度和长使用寿命。
在本申请的任意实施方式中，所述除酸材料包括无机碱性锂盐、有机化合物中的至少一种。
在本申请的任意实施方式中，所述无机碱性锂盐包括碳酸锂、碳酸氢锂中的至少一种。
在本申请的任意实施方式中，所述有机化合物的分子结构包括酰胺基、硅氮基、硅基、碳氮基、磺酸酯基、羧酸盐离子中的至少一种。可选地，所述有机化合物包括醋酸锂、六甲基二硅氮烷、七甲基二硅氮烷、三甲基硅烷基二乙胺、甲基磺酸三甲基硅酯、二(三甲基硅基)碳酰二亚胺、N,N-二甲基丙酰胺、N,N-二甲基乙酰胺、N,N-二甲基甲酰胺中的至少一种。
本申请第二方面提供一种二次电池，包括正极极片、负极极片、电解液以及本申请第一方面的多层复合隔离膜。
在本申请的任意实施方式中，基于所述正极极片和所述负极极片的总质量，所述二次电池中水分的含量为A ppm，基于所述多层复合隔离膜的总质量，所述除水材料的含量为B ppm，并且A和B满足如下关系式：3≤B/A≤5。当B/A在合适的范围内时，能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池具有长使用寿命，同时二次电池还具有高能量密度。
可选地，20≤A≤600。
可选地，60≤B≤3000。
在本申请的任意实施方式中，基于所述电解液的总质量，所述电解液中HF的含量为C ppm，基于所述电解液的总质量，所述除酸材料的含量为D ppm，并且C和D满足如下关系式：1≤D/C≤2。当D/C在合适的范围内时，能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池具有长使用寿命，同时二次电池还具有高能量密度。
可选地，20≤C≤500。
可选地，20≤D≤1000。
在本申请的任意实施方式中，所述除酸材料的pH、所述电解液中HF的含量C ppm、所述除酸材料的含量D ppm还满足如下关系式：lgpH+0.5≤D/C≤2。此时，二次电池内部游离的HF以及水分含量更少，二次电池可以具有更长的使用寿命和更高的能量密度。
本申请第三方面提供一种用电装置，其包括本申请第二方面的二次电池。
本申请的二次电池包括同时采用了除水材料和除酸材料的多层复合隔离膜，所述多层复合隔离膜能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，因此本申请的二次电池能够同时兼顾高能量密度和长使用寿命。本申请的用电装置包括本申请提供的二次电池，因而至少具有与所述二次电池相同的优势。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的二次电池的一实施方式的示意图。
图2是图1的二次电池的实施方式的分解示意图。
图3是本申请的电池模块的一实施方式的示意图。
图4是本申请的电池包的一实施方式的示意图。
图5是图4所示的电池包的实施方式的分解示意图。
图6是包含本申请的二次电池作为电源的用电装置的一实施方式的示意图。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的多层复合隔离膜、以及包含其的二次电池、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，并且这样的技术方案应被认为包含在本申请的公开内容中。
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，并且这样的技术方案应被认为包含在本申请的公开内容中。
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)。
如果没有特别的说明，在本申请中，术语“第一”、“第二”等仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。术语“多个”的含义是两个以上，除非另有明确具体的限定。
如果没有特别的说明，在本申请中，术语“活性离子”是指能在二次电池正负极之间往返嵌入和脱出的离子，包括但不限于锂离子、钠离子等。
在本申请中，术语“分子筛”是指一类具有均匀大小的孔的材料，其结晶态主要为硅酸盐或硅铝酸盐；术语“高吸水树脂”是指一类具有亲水基团、能大量吸收水分溶胀并保持住水分不外流的一类合成树脂。
二次电池又称为充电电池或蓄电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。通常情况下，二次电池包括正极极片、负极极片、电解液以及隔离膜。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。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，同时可以使活性离子通过。电解液在正极极片和负极极片之间起到传导活性离子的作用。目前，二次电池被广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。
随着二次电池的应用及推广，其能量密度和使用寿命受到越来越多的关注，因此开发具有高能量密度和长使用寿命的二次电池是业界的普遍追求。但是，二次电池在长期充放电循环过程中，电极片中的结合水会逐渐释放出来并进入电解液中。水与电解液中的含氟电解质盐容易发生副反应并产生HF，HF不仅会诱导电解液中的有机溶剂分解(例如，诱导碳酸乙烯酯开环聚合)，而且会破坏正负极活性材料表面的保护膜。特别地，当HF破坏正极活性材料表面的保护膜后，正极活性材料晶体结构中的过渡金属离子会溶出，进而导致晶体结构被破坏，影响活性离子的脱出的嵌入，降低二次电池的能量密度和使用寿命。因此，需要有效的技术手段减少水分对二次电池的负面影响。
现有技术通常采取的应对策略包括：(1)在电解液中加入添加剂，提高电解液的稳定性；(2)在正极活性材料表面设置包覆层。但是，添加剂加入量较少时不足以络合全部的HF，加入量较多时又容易改变电解液的动力学性质，影响二次电池的动力学 性能；而在正极活性材料表面设置包覆层不仅工艺复杂，而且还容易影响二次电池容量的发挥，降低二次电池的能量密度。
鉴于上述问题，发明人经过大量研究和实践，并运用逆向思维和水平思维提出了一种新型的多层复合隔离膜，其能有效减少电池内部游离的水分和HF，使二次电池同时兼顾高能量密度和长使用寿命。
多层复合隔离膜
本申请实施方式第一方面提供了一种多层复合隔离膜，包括第一基材层以及第二基材层，所述多层复合隔离膜还包括除水材料以及除酸材料，所述除酸材料位于所述第一基材层和所述第二基材层之间，所述除水材料位于所述第一基材层和所述第二基材层中的至少一个表面上。
发明人经过大量研究和实践发现，电极片中的结合水释放到电解液中后，会与含氟的电解质盐反应生成HF，同样地，HF也可以与负极活性材料表面固体电解质界面膜中的无机电解质盐组分(例如碳酸锂等)反应再次转变成水分，因此，仅单一地采用除水材料或除酸材料并不能有效提升二次电池的使用寿命。本申请的多层复合隔离膜同时采用了除水材料和除酸材料，在物理吸附、化学键合等多种作用下，有效将电池内部游离的水分和HF固定在所述除水材料和所述除酸材料上，因此能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池同时兼顾高能量密度和长使用寿命。
本申请的多层复合隔离膜具有多层结构，除酸材料位于两层基材层之间，从而可以避免除酸材料在高电压下发生氧化分解反应，保证除酸材料具有更好的作用效果。
本申请对所述除水材料的位置没有特别的限制，其可以位于所述第一基材层和所述第二基材层中的至少一个表面上。例如，所述第一基材层和所述第二基材层均具有在自身厚度方向相对的两个表面，因此，所述除水材料可位于上述四个表面中的至少一个表面上。例如，所述除水材料位于所述第一基材层远离所述除酸材料、靠近所述电极片的表面上，或位于所述第二基材层远离所述除酸材料、靠近所述电极片的表面上，或位于所述第一基材层和所述第二基材层之间。
在一些实施例中，所述多层复合隔离膜包括位于所述第一基材层和所述第二基材层之间的功能层，并且所述功能层包括除水材料以及除酸材料。
所述功能层的厚度不受具体的限制，可根据实际需求进行选择。所述功能层的厚度较小时，其内部负载的除水材料和除酸材料较少，可能无法在二次电池长期充放电循环过程中持续且有效地减少电池内部游离的水分和HF含量；所述功能层的厚度较大时，二次电池增重明显，质量能量密度和动力学性能可能下降。因此，所述功能层的厚度不宜过小，也不宜过大。在一些实施例中，所述功能层的厚度可以为1μm～100μm。可选地，所述功能层的厚度为2μm～80μm，2μm～60μm，2μm～50μm，2μm～40μm，2μm～30μm，2μm～20μm，4μm～80μm，4μm～60μm，4μm～50μm，4μm～40μm，4μm～30μm，4μm～20μm，6μm～80μm，6μm～60μm，6μm～50μm，6μm～40μm，6μm～30μm，或6μm～20μm。所述功能层的厚度在合适的范围时，能在二次电池长期充 放电循环过程中持续且有效地减少电池内部游离的水分和HF含量，同时保证二次电池具有较高的能量密度和良好的动力学性能。
所述功能层中各组分的具体含量不受具体的限制，可根据实际需求进行选择。在一些实施例中，可选地，基于所述功能层的总质量，所述除酸材料的质量百分含量为20％～50％，所述除水材料的质量百分含量为15％～50％。
在一些实施例中，所述功能层还可以包括粘结剂。本申请对所述粘结剂的种类没有特别的限制，可根据实际需求进行选择。作为示例，用于所述功能层的粘结剂包括但不限于聚偏氟乙烯(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、含氟丙烯酸酯树脂中的至少一种。在一些实施例中，基于所述功能层的总质量，所述粘结剂的质量百分含量可以为1％～35％。
所述除酸材料主要通过化学键合(例如氢键、共价键等)减少电池内部游离的HF含量，因此，在本申请的多层复合隔离膜中，所述除酸材料的质量可以大于等于所述除水材料的质量，从而能够保证所述除酸材料能够持续且有效地减少电池内部游离的HF含量，进而减少电池内部游离的水分含量。在一些实施例中，所述多层复合隔离膜中的所述除酸材料的质量和所述除水材料的质量之比可以为1～3。可选地，所述多层复合隔离膜中的所述除酸材料的质量和所述除水材料的质量之比为1～2.5，1～2，或1～1.5。
在一些实施例中，所述除水材料可以包括分子筛、高吸水树脂(Super Absorbent Polymer，SAP)中的至少一种。
在本申请中，具有较高吸水量的分子筛是优选的。例如，在一些实施例中，所述分子筛在25℃、30％相对湿度的静态水吸附量可以在15％以上。所述分子筛的静态水吸附量测试可以参照GB 6287-86分子筛静态水吸附测定方法。
按照国际纯粹与应用化学联合会(IUPAC)的定义，把孔径在2nm～50nm之间的多孔材料称为介孔材料，把孔径小于2nm的多孔材料称为微孔材料，把孔径大于50nm的多孔材料称为大孔材料。在本申请中，所述分子筛可以包括微孔分子筛、介孔分子筛中的至少一种。相对于大孔分子筛而言，微孔分子筛和介孔分子筛可以具有较高的比表面积，从而使其在水分吸附中发挥出更好的作用。同时，所述分子筛的孔径不宜小于0.3nm，所述分子筛的孔径过小时，水分子难以被吸附进入所述分子筛的孔道结构中，从而所述分子筛难以具有较好的吸附除水效果。
在一些实施例中，所述分子筛的孔径可以为0.3nm～50nm。可选地，所述分子筛的孔径为0.4nm～50nm，0.5nm～50nm，1nm～50nm，2nm～50nm，0.3nm～35nm，0.4nm～35nm，0.5nm～35nm，1nm～35nm，2nm～35nm，0.3nm～25nm，0.4nm～25nm，0.5nm～25nm，1nm～25nm，2nm～25nm，0.3nm～15nm，0.4nm～15nm，0.5nm～15nm，1nm～15nm，2nm～15nm，0.3nm～11nm，0.4nm～11nm，0.5nm～11nm，1nm～11nm，2nm～11nm，0.3nm～8nm，0.4nm～8nm，0.5nm～8nm，1nm～8nm，或2nm～8nm。所述分子筛的孔径在合适的范围内时，所述分子筛可以具有更好的水吸附能力以及更差的水脱附能力，从而保证二次电池在长期充放电循环过程中具有较少的游离水分和HF含量，进而二次电池的循环性能更好。
所述分子筛的体积平均粒径Dv50较大时，活性离子的传输路径变长，二次电池的动力学性能可能下降；所述分子筛的体积平均粒径Dv50较小时，可能增加所述隔离膜堵孔的风险，进而二次电池的动力学性能也可能下降。为了保证二次电池同时兼顾较好的动力学性能，所述分子筛的体积平均粒径Dv50不宜过大，也不宜过小。在一些实施例中，所述分子筛的体积平均粒径Dv50可以为1μm～10μm。可选地，所述分子筛的体积平均粒径Dv50为1μm～10μm，1μm～8μm，1μm～6μm，1μm～4μm，2μm～10μm，2μm～8μm，2μm～6μm，2μm～4μm，4μm～10μm，4μm～8μm，或4μm～6μm。
在本申请中，材料的体积平均粒径Dv50为本领域公知的含义，其表示材料累计体积分布百分数达到50％时所对应的粒径，可以用本领域公知的仪器及方法进行测定。例如可以参照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。
所述分子筛具有较高的比表面积(BET)时，能够快速吸附电池内部游离的水分，但是，所述分子筛的比表面积也不宜过高，此时，所述分子筛的水吸附能力不会进一步增加，而制造成本明显增加；同时，所述分子筛可能还会吸收较多的电解液，不利于电解液浸润电极片。同时，所述分子筛的比表面积不宜过小。所述分子筛的比表面积较小时，对电池内部游离的水分的吸附能力较差，进而可能无法保证二次电池在长期充放电循环过程中具有较少的游离水分和HF含量。在一些实施例中，所述分子筛的比表面积可以为350m 2/g～1000m 2/g。可选地，所述分子筛的比表面积为350m 2/g～900m 2/g，350m 2/g～800m 2/g，350m 2/g～700m 2/g，350m 2/g～600m 2/g，350m 2/g～500m 2/g，500m 2/g～1000m 2/g，500m 2/g～900m 2/g，500m 2/g～800m 2/g，500m 2/g～700m 2/g，500m 2/g～600m 2/g，650m 2/g～1000m 2/g，650m 2/g～900m 2/g，650m 2/g～800m 2/g，或650m 2/g～700m 2/g。所述分子筛的比表面积在合适的范围内时，所述分子筛可以具有更好水吸附能力，从而保证二次电池在长期充放电循环过程中具有较少的游离水分和HF含量，进而二次电池的循环性能更好。
在本申请中，材料的比表面积为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如可以参照GB/T 19587-2017，采用氮气吸附比表面积分析测试方法测试，并用BET(BrunauerEmmett Teller)法计算得出，氮气吸附比表面积分析测试可以通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪进行。
所述分子筛的种类不受具体的限制，可根据实际需求进行选择。在一些实施例中，按照孔道结构分类，所述分子筛可以包括但不限于A型分子筛(例如3A型分子筛、4A型分子筛、5A型分子筛等)、X型分子筛(例如10X型分子筛、13X型分子筛)、Y型分子筛中的至少一种。在一些实施例中，按照骨架元素分类，所述分子筛可以包括但不限于硅铝分子筛、钛硅分子筛、磷铝分子筛中的至少一种。
作为示例，在一些实施例中，所述分子筛可以包括但不限于硅基分子筛SBA-15、钛硅分子筛TS-1中的至少一种。SBA-15、TS-1可以具有介孔结构以及具有更厚的孔壁、更高的孔容和更好的水热稳定性，因此可以保证二次电池在长期充放电循环过程中具有较少的游离水分和HF含量，进而二次电池的循环性能更好。当然，SBA-15、TS-1也可以具有微孔结构。
在本申请中，具有较高吸水量的高吸水树脂是优选的。在一些实施例中，所述高吸水树脂的吸水倍率可以在100倍以上。吸水倍率是指单位质量的高吸水树脂能够吸收的水分质量与自身质量的比值。所述高吸水树脂的吸水倍率测试可以参考GB/T 22875-2008、GB/T 22905-2008。
在本申请中，具有较高吸水量并且不易在水中溶解的高吸水树脂是优选的。在一些实施例中，所述高吸水树脂25℃下在水中的溶解度可以在5％以下。
作为示例，在一些实施例中，所述高吸水树脂可以包括但不限于淀粉接枝丙烯腈系、淀粉接枝丙烯酸系、淀粉接枝丙烯酰胺系、纤维素接枝丙烯腈系、纤维素接枝丙烯酸系、纤维素接枝丙烯酰胺系、聚乙烯醇系、聚丙烯酸(盐)系、聚丙烯酰胺系、聚氧乙烯系、聚氨酯系、醋酸乙烯酯共聚物、及其各自的改性化合物中的至少一种。
可选地，所述高吸水树脂包括聚乙烯醇与环状酸酐共聚物、聚丙烯酸钠树脂、醋酸乙烯酯与丙烯酸盐共聚物中的至少一种。
所述除酸材料不宜选择具有酸性或水解后呈酸性的材料，此时可能无法有效减少电池内部游离的HF含量。同时，所述除酸材料的碱性也不宜过强。所述除酸材料的碱性较强时，容易诱发电解质盐分解，增加电池内部游离的副反应，降低二次电池的能量密度、使用寿命和动力学性能，甚至还可能增加HF含量。在一些实施例中，所述除酸材料的pH为7～11.5。在本申请中，所述除酸材料具有弱碱性，可以通过酸碱中和反应固定HF和水分子，从而能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池同时兼顾高能量密度和长使用寿命。可选地，所述除酸材料的pH为7～10。进一步地，所述除酸材料的pH为7.2～9.3。
在本申请中，所述除酸材料的pH为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。一个示例性测试方法包括步骤：25℃下，将5g除酸材料加入100g去离子水中，充分搅拌溶解后参照GB/T 6920-86测试溶液的pH值，作为所述除酸材料的pH。
在一些实施例中，所述除酸材料可以包括无机碱性锂盐、有机化合物中的至少一种。
在一些实施例中，所述无机碱性锂盐可以包括但不限于碳酸锂、碳酸氢锂中的至少一种。
在一些实施例中，所述有机化合物的分子结构可以包括酰胺基、硅氮基、硅基、碳氮基、磺酸酯基、羧酸盐离子中的至少一种。例如，所述有机化合物可以包括但不限于有机碱性锂盐以及有机小分子化合物中的至少一种。作为示例，所述有机化合物包括但不限于醋酸锂、六甲基二硅氮烷、七甲基二硅氮烷、三甲基硅烷基二乙胺、甲基磺酸三甲基硅酯、二(三甲基硅基)碳酰二亚胺、N,N-二甲基丙酰胺、N,N-二甲基乙酰胺、N,N-二甲基甲酰胺中的至少一种。
在本申请中，所述除酸材料可以通过化学反应(例如酸碱中和反应)、氢键作用等固定HF和水分子，从而能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池同时兼顾高能量密度和长使用寿命。
本申请对所述第一基材层和所述第二基材层的厚度没有特别的限制，可根据实际需求进行选择。本申请对所述第一基材层和所述第二基材层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膜。在一些实施例中，所述第一基材层和所述第二基材层的材质可以包括玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏氟乙烯中的至少一种。所述第一基材层和所述第二基材层可以相同也可以不同。
本申请的多层复合隔离膜并不排除除了上述组分外的其他组分。在一些实施例中，所述多层复合隔离膜还可以包括填料，例如无机陶瓷颗粒等。可选地，所述无机陶瓷颗粒可为位于所述第一基材层远离所述除酸材料靠近所述电极片的表面上、位于所述第二基材层远离所述除酸材料靠近所述电极片的表面上、或者位于所述第一基材层和所述第二基材层的孔内。
在一些实施例中，所述多层复合隔离膜包括第一基材层以及第二基材层，所述多层复合隔离膜还包括除水材料以及除酸材料，所述除酸材料位于所述第一基材层和所述第二基材层之间，所述除水材料位于所述第一基材层和所述第二基材层中的至少一个表面上；所述除水材料包括分子筛、高吸水树脂中的至少一种；所述除酸材料的pH为7～11.5，可选地为7～10，进一步地为7.2～9.3；所述多层复合隔离膜中的所述除酸材料的质量和所述除水材料的质量之比为1～3，可选地为1～1.5。所述多层复合隔离膜通过采用高吸水能力的除水材料和弱碱性的除酸材料，在物理吸附、化学键合(例如酸碱中和反应)等多种作用下，有效将电池内部游离的水分和HF固定在所述除水材料和所述除酸材料上，因此能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池同时兼顾高能量密度和长使用寿命。
在一些实施例中，所述多层复合隔离膜包括第一基材层、第二基材层以及位于所述第一基材层和所述第二基材层之间的功能层，并且所述功能层包括除水材料以及除酸材料，基于所述功能层的总质量，所述除酸材料的质量百分含量为20％～50％，所述除水材料的质量百分含量为15％～50％，并且所述除酸材料的质量和所述除水材料的质量之比为1～3，可选地为1～1.5；所述除水材料包括分子筛、高吸水树脂中的至少一种；所述除酸材料的pH为7～11.5，可选地为7～10，进一步地为7.2～9.3。所述多层复合隔离膜通过采用高吸水能力的除水材料和弱碱性的除酸材料，在物理吸附、化学键合(例如酸碱中和反应)等多种作用下，有效将电池内部游离的水分和HF固定在所述除水材料和所述除酸材料上，因此能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池同时兼顾高能量密度和长使用寿命。
[制备方法]
本申请实施方式第一方面还提供了一种多层复合隔离膜的制备方法。所述多层复合隔离膜可以按照本领域公知的方法进行制备。
在一些实施例中，所述多层复合隔离膜可以按照如下步骤进行制备：将除水材料、除酸材料、粘结剂以及可选的助剂分散于溶剂中搅拌均匀形成浆料；将浆料涂覆在其 中一个基材层表面，之后再在浆料表面覆盖另一层基材层，经干燥、冷压后得到多层复合隔离膜。
在另一些实施例中，所述多层复合隔离膜还可以按照如下步骤进行制备：将除酸材料、粘结剂以及可选的助剂分散于溶剂中搅拌均匀形成第一浆料，将除水材料、粘结剂以及可选的助剂分散于溶剂中搅拌均匀形成第二浆料；将第一浆料涂覆在其中一个基材层表面，之后再在第一浆料表面覆盖另一层基材层；将第二浆料涂覆在任意一个基材层远离所述除酸材料的表面上，经干燥、冷压后得到多层复合隔离膜。
所述溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。所述粘结剂可包括但不限于聚偏氟乙烯(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、含氟丙烯酸酯树脂中的至少一种。所述助剂可包括分散剂，例如十六烷基三甲基溴化铵等。
需要说明的是，通过上述制备方法制备出的多层复合隔离膜的相关结构，可参见上述各实施例提供的多层复合隔离膜。
二次电池
本申请实施方式的第二方面提供一种二次电池。本申请对所述二次电池种类没有特别的限制，例如，所述二次电池可以为锂离子电池、钠离子电池等，特别地，所述二次电池为锂离子二次电池。
在一些实施例中，所述二次电池包括正极极片、负极极片、电解液以及隔离膜，所述隔离膜采用本申请实施方式第一方面任一实施例所述的多层复合隔离膜，所述隔离膜设置在所述正极极片和所述负极极片之间，起到防止正负极短路以及减少电池内部游离的水分和HF含量的作用。
在一些实施例中，基于所述正极极片和所述负极极片的总质量，所述二次电池中水分的含量为A ppm，基于所述多层复合隔离膜的总质量，所述除水材料的含量为B ppm，并且A和B满足如下关系式：3≤B/A≤5。
当B/A较小时，可能不能有效减少电池内部游离的水分和HF；而当B/A较大时，所述除水材料过量较多，其对二次电池性能的改善效果不会继续增加，但是二次电池的质量增加，由此降低了二次电池的能量密度。当B/A在合适的范围内时，能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池具有长使用寿命，同时二次电池还具有高能量密度。
所述二次电池中水分主要由正极极片中残存的微量水分、负极极片中残存的微量水分以及电解液中的微量水分三部分组成。所述二次电池中水分的含量通过如下方法得到：分别测试制备的正极极片、负极极片、电解液中水分的质量，得到水分总质量；以所得到的水分总质量除以正极极片和负极极片的总质量，即得到上述二次电池中水分的含量(A ppm)。正极极片、负极极片以及电解液中的水分可以通过卡尔费休水分测定仪测试得到，例如MA-30智能卡尔费休水分测定仪。
基于上述二次电池中水分的含量(A ppm)来选择合适的除水材料质量，不仅能够持续且有效地减少电池内部游离的水分和HF含量，减少水分和HF对二次电池的负面影响，使二次电池具有长使用寿命，同时还能使二次电池具有高能量密度。
通常，基于所述正极极片和所述负极极片的总质量，所述二次电池中水分的含量A ppm在20ppm至600ppm之间。进一步地，所述除水材料的添加量可以使其满足基于所述多层复合隔离膜的总质量，所述除水材料的含量B ppm在60ppm和3000ppm之间。
在一些实施例中，基于所述电解液的总质量，所述电解液中HF的含量为C ppm，基于所述电解液的总质量，所述除酸材料的含量为D ppm，并且C和D满足如下关系式：1≤D/C≤2。
当D/C较小时，可能不能有效减少电池内部游离的水分和HF；而当D/C较大时，所述除酸材料过量较多，其对二次电池性能的改善效果不会继续增加，但是二次电池的质量增加，由此降低了二次电池的能量密度。当D/C在合适的范围内时，能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池具有长使用寿命，同时二次电池还具有高能量密度。
基于所述电解液中HF的含量(C ppm)来选择合适的除酸材料质量，不仅能够持续且有效地减少电池内部游离的水分和HF含量，减少水分和HF对二次电池的负面影响，使二次电池具有长使用寿命，同时还能使二次电池具有高能量密度。
所述电解液中HF的含量(C ppm)可以通过滴定法测试得到，例如可以参照HG/T4067-2015。一个示例性的测试方法包括如下步骤：在100ml冰水混合物中加入15g电解液样品，以溴百里酚蓝作为指示剂，以氢氧化钠标准滴定溶液滴定至溶液变成蓝色作为反应终点，记录氢氧化钠标准滴定溶液的体积V 1；在100ml冰水混合物中加入溴百里酚蓝作为指示剂，以氢氧化钠标准滴定溶液滴定至溶液变成蓝色作为反应终点，记录氢氧化钠标准滴定溶液的体积V 0。V 1-V 0为实际消耗的氢氧化钠标准滴定溶液的体积，以此可以计算得到HF质量以及其在电解液中的含量。
通常，基于所述电解液的总质量，所述电解液中HF的含量C ppm在20ppm至500ppm之间。进一步地，所述除酸材料的添加量可以使其满足基于所述电解液的总质量，所述除酸材料的含量D ppm在20ppm至1000ppm之间。
在一些实施例中，所述除酸材料的pH、所述电解液中HF的含量C ppm、所述除酸材料的含量D ppm还满足如下关系式：lgpH+0.5≤D/C≤2。发明人经过大量研究和实践发现，当所述除酸材料的含量D ppm满足上述关系式lgpH+0.5≤D/C≤2时，二次电池内部游离的HF以及水分含量更少，二次电池可以具有更长的使用寿命和更高的能量密度。
[电解液]
在一些实施例中，所述电解液包括电解质盐和溶剂。所述电解质盐和所述溶剂的种类不受具体的限制，可根据实际需求进行选择。
当本申请的二次电池为锂离子电池，特别地为锂离子二次电池时，作为示例，所述电解质盐可包括六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)、四氟草酸磷酸锂(LiTFOP) 中的至少一种。
当本申请的二次电池为钠离子电池时，所述电解质盐可包括六氟磷酸钠(NaPF 6)、四氟硼酸钠(NaBF 4)、高氯酸钠(NaClO 4)、六氟砷酸钠(NaAsF 6)、双氟磺酰亚胺钠(NaFSI)、双三氟甲磺酰亚胺钠(NaTFSI)、三氟甲磺酸钠(NaTFS)、二氟草酸硼酸钠(NaDFOB)、二草酸硼酸钠(NaBOB)、二氟磷酸钠(NaPO 2F 2)、二氟二草酸磷酸钠(NaDFOP)、四氟草酸磷酸钠(NaTFOP)中的至少一种。
在一些实施例中，作为示例，所述溶剂可包括碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的至少一种。
在一些实施例中，所述电解液还可选地包括添加剂。例如，所述添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温功率性能的添加剂等。作为示例，所述添加剂可以包括但不限于碳酸亚乙烯酯(VC)、氟代碳酸乙烯酯(FEC)、1,3-丙磺酸内酯(PS)中的至少一种。
[正极极片]
在一些实施例中，所述正极极片包括正极集流体以及设置在所述正极集流体至少一个表面的正极膜层。例如，所述正极集流体具有在自身厚度方向相对的两个表面，所述正极膜层设置于所述正极集流体的两个相对表面中的任意一者或两者上。
所述正极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铝箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层。作为示例，金属材料可包括铝、铝合金、镍、镍合金、钛、钛合金、银、银合金中的至少一种。作为示例，高分子材料基层可包括聚丙烯(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)中的至少一种。
所述正极膜层通常包含正极活性材料、可选的粘结剂和可选的导电剂。所述正极膜层通常是将正极浆料涂布在所述正极集流体上，经干燥、冷压而成的。所述正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。作为示例，用于正极膜层的粘结剂可包括聚偏氟乙烯(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、含氟丙烯酸酯树脂中的至少一种。作为示例，用于正极膜层的导电剂包括超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维中的至少一种。
所述正极活性材料可采用本领域公知的用于二次电池的正极活性材料。
当本申请的二次电池为锂离子电池，特别地为锂离子二次电池时，所述正极活性材料可包括锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的至少一种。锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、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、锂镍钴铝氧化物及其改性化合物中的至少一种。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、磷酸铁锂与碳的复合材料、磷酸锰锂、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及其各自的改性化合物中的至少一种。本申请并不限定于这些材料，还可以使用其他可被用作锂离子电池正极活性材料的传统公知的材料。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。
在一些实施例中，为了进一步提高二次电池的能量密度，用于锂离子电池的正极活性材料可以包括式1所示的锂过渡金属氧化物及其改性化合物中的至少一种，
Li aNi bCo cM dO eA f    式1
式1中，0.8≤a≤1.2，0.5≤b＜1，0＜c＜1，0＜d＜1，1≤e≤2，0≤f≤1，M选自Mn、Al、Zr、Zn、Cu、Cr、Mg、Fe、V、Ti及B中的至少一种，A选自N、F、S及Cl中的至少一种。
作为示例，用于锂离子电池的正极活性材料可包括LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2(NCM333)、LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)、LiNi 0.6Co 0.2Mn 0.2O 2(NCM622)、LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、LiNi 0.85Co 0.15Al 0.05O 2、LiFePO 4、LiMnPO 4中的至少一种。
当本申请的二次电池为钠离子电池时，所述正极活性材料可包括含钠过渡金属氧化物、聚阴离子材料(如磷酸盐、氟磷酸盐、焦磷酸盐、硫酸盐等)、普鲁士蓝类材料中的至少一种。本申请并不限定于这些材料，还可以使用其他可被用作钠离子电池正极活性材料的传统公知的材料。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。
作为示例，用于钠离子电池的正极活性材料可包括NaFeO 2、NaCoO 2、NaCrO 2、NaMnO 2、NaNiO 2、NaNi 1/2Ti 1/2O 2、NaNi 1/2Mn 1/2O 2、Na 2/3Fe 1/3Mn 2/3O 2、NaNi 1/3Co 1/3Mn 1/3O 2、NaFePO 4、NaMnPO 4、NaCoPO 4、普鲁士蓝类材料、通式为A aM b(PO 4) cO xY 3-x的材料中的至少一种。A选自H +、Li +、Na +、K +及NH 4 +中的至少一种；M为过渡金属阳离子，可选地为V、Ti、Mn、Fe、Co、Ni、Cu及Zn中的至少一种；Y为卤素阴离子，可选地为F、Cl及Br中的至少一种；0＜a≤4；0＜b≤2；1≤c≤3；0≤x≤2。
在本申请中，上述各正极活性材料的改性化合物可以是对正极活性材料进行掺杂改性、或表面包覆改性。
[负极极片]
在一些实施例中，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面的负极膜层。例如，所述负极集流体具有在自身厚度方向相对的两个表面，所述负极膜层设置在所述负极集流体的两个相对表面中的任意一者或两者上。
所述负极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铜箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层。作为示例，金属材料可包括铜、铜合金、镍、镍合金、钛、钛合金、银、银合金中的至少一种。作为示例，高分子材料基层可包括聚丙烯(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)中的至少一种。
负极膜层通常包含负极活性材料、可选的粘结剂、可选的导电剂以及其他可选的助剂。负极膜层通常是将负极浆料涂布在负极集流体上，经干燥、冷压而成的。负极浆料涂通常是将负极活性材料、可选的导电剂、可选地粘结剂、其他可选的助剂分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，但不限于此。作为示例，用于负极膜层的粘结剂可包括丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸树脂(例如，聚丙烯酸PAA、聚甲基丙烯酸PMAA、聚丙烯酸钠PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、羧甲基壳聚糖(CMCS)中的至少一种。作为示例，用于负极膜层的导电剂可包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维中至少一种。其他可选的助剂可包括增稠剂(例如，羧甲基纤维素钠CMC-Na)、PTC热敏电阻材料等。
负极活性材料可采用本领域公知的用于二次电池的负极活性材料。作为示例，负极活性材料可包括天然石墨、人造石墨、软炭、硬炭、硅基材料、锡基材料、钛酸锂中的至少一种。硅基材料可包括单质硅、硅氧化物、硅碳复合物、硅氮复合物、硅合金材料中的至少一种。锡基材料可包括单质锡、锡氧化物、锡合金材料中的至少一种。本申请并不限定于这些材料，还可以使用其他可被用作二次电池负极活性材料的传统公知的材料。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。
本申请的负极极片并不排除除了负极膜层之外的其他附加功能层。例如在一些实施例中，本申请的负极极片还包括夹在负极集流体和负极膜层之间、设置于负极集流体表面的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施例中，本申请的负极极片还包括覆盖在负极膜层表面的保护层。
在一些实施例中，所述正极极片、所述多层复合隔离膜和所述负极极片可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施例中，所述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液。
在一些实施例中，所述二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。所述二次电池的外包装也可以是软包，例如袋式软包。所述软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的至少一种。
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。如图1是作为一个示例的方形结构的二次电池5。
在一些实施例中，如图2所示，外包装可包括壳体51和盖板53。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用于盖设所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或几个，可根据需求来调节。
在本申请的一些实施例中，根据本申请的二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图3是作为一个示例的电池模块4的示意图。如图3所示，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施例中，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根据电池包的应用和容量进行调节。
图4和图5是作为一个示例的电池包1的示意图。如图4和图5所示，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用于盖设下箱体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。
[制备方法]
本申请实施方式第二方面还提供一种二次电池的制备方法。所述方法包括如下步骤：S100，提供正极极片、负极极片、多层复合隔离膜以及电解液，其中，所述多层复合隔离膜包括第一基材层、第二基材层、除水材料以及除酸材料，所述除酸材料位于所述第一基材层和所述第二基材层之间，所述除水材料位于所述第一基材层和所述第二基材层中的至少一个表面上；S200，将上述正极极片、多层复合隔离膜、负极极片和电解液组装成二次电池。
在一些实施例中，S100进一步包括如下步骤：S101，测试所述正极极片和所述负极极片中水分的质量、以及所述电解液中水分和HF质量，计算基于所述正极极片和所述负极极片的总质量得到的所述二次电池中水分的含量A ppm、基于所述电解液的总质量得到的所述电解液中HF的含量C ppm；S102，所述除水材料的添加量使其满足基于所述多层复合隔离膜的总质量所述除水材料的含量B ppm满足3≤B/A≤5，所述除酸材料的添加量使其满足基于所述电解液的总质量所述除酸材料的含量D ppm满足1≤D/C≤2，可选地，所述除酸材料的添加量使其进一步满足lgpH+0.5≤D/C≤2，pH为所述除酸材料的pH。
基于上述二次电池中水分的含量(A ppm)来选择合适的除水材料质量、基于所述电解液中HF的含量(C ppm)来选择合适的除酸材料质量，不仅能够持续且有效地减少电池内部游离的水分和HF含量，减少水分和HF对二次电池的负面影响，使二次电池具有长使用寿命，同时还能使二次电池具有高能量密度。
在一些实施例中，S200可进一步包括步骤：将上述正极极片、隔离膜、负极极片经卷绕工艺或叠片工艺形成电极组件，将电极组件置于外包装中，烘干后注入电解液， 经过真空封装、静置、化成、整形等工序，得到二次电池。
需要说明的是，通过上述二次电池的制备方法制备出的二次电池的相关结构，可参见上述各实施例提供的二次电池。
用电装置
本申请实施方式第三方面提供一种用电装置。所述用电装置包括本申请的二次电池、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。所述用电装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
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6是作为一个示例的用电装置的示意图。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。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于质量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
实施例1
隔离膜的制备
将比表面积为650m 2/g、孔径为3nm、Dv50为2μm的钛硅分子筛TS-1(除水材料)与pH为7.5的六甲基二硅氮烷(除酸材料)、聚偏氟乙烯(粘结剂)以及十六烷基三甲基溴化铵按照质量比为35:45:19:1在适量的溶剂NMP中搅拌2h～3h混合形成浆料；将浆料涂覆在厚度为14μm的多孔聚乙烯膜(第一基材层)表面，之后再在浆料表面覆盖另一层厚度为8μm的多孔聚乙烯膜(第二基材层)，经干燥、冷压后得到多层复合隔离膜。浆料层的厚度为6μm。
正极极片的制备
将正极活性材料LiFePO 4、导电剂炭黑(Super P)、粘结剂聚偏氟乙烯(PVDF)按照质量比80:10:10在适量的溶剂NMP中充分搅拌混合，形成固体成分含量为50％的正极浆料；将正极浆料均匀涂覆于正极集流体铝箔的表面上，在85℃下烘干后进行冷压，然后进行切边、裁片、分条后，再在85℃的真空条件下烘干4h，得到正极极片。
负极极片的制备
将负极活性材料石墨、导电剂炭黑(Super P)、增稠剂羧甲基纤维素钠(CMC-Na)、粘结剂丁苯橡胶(SBR)按照质量比80:15:3:2在适量的溶剂去离子水中充分搅 拌混合，形成固体成分含量为30％的负极浆料；将负极浆料均匀涂覆于负极集流体铜箔的表面上，在85℃下烘干后进行冷压，然后进行切边、裁片、分条后，再在120℃的真空条件下烘干12h，得到负极极片。
电解液的制备
将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照体积比1:1:1混合，得到有机溶剂；将LiPF 6均匀溶解在上述有机溶剂中得到电解液，LiPF 6的浓度为1mol/L。
二次电池的制备
将正极极片、多层复合隔离膜、负极极片按顺序堆叠并卷绕，得到电极组件；将电极组件放入外包装中，加入上述电解液，经封装、静置、化成、老化等工序后，得到二次电池。
所述二次电池中水分的含量通过如下方法得到：分别通过MA-30智能卡尔费休水分测定仪测试制备的正极极片、负极极片、电解液中水分的质量，得到水分总质量；以所得到的水分总质量除以正极极片和负极极片的总质量，即得到二次电池中水分的含量(A ppm)。
在100ml冰水混合物中加入15g上述电解液样品，以溴百里酚蓝作为指示剂，以氢氧化钠标准滴定溶液滴定至溶液变成蓝色作为反应终点，记录氢氧化钠标准滴定溶液的体积V 1；在100ml冰水混合物中加入溴百里酚蓝作为指示剂，以氢氧化钠标准滴定溶液滴定至溶液变成蓝色作为反应终点，记录氢氧化钠标准滴定溶液的体积V 0。V 1-V 0为实际消耗的氢氧化钠标准滴定溶液的体积，以此计算得到HF质量以及其在电解液中的含量(C ppm)。
基于所述正极极片和所述负极极片的总质量，所述二次电池中水分的含量A ppm为50ppm；基于所述电解液的总质量，所述电解液中HF的含量C ppm为100ppm；基于所述多层复合隔离膜的总质量，所述除水材料的含量B ppm为150ppm；基于所述电解液的总质量，所述除酸材料的含量D ppm为187ppm。
实施例2～16
二次电池的制备方法与实施例1类似，不同之处在于隔离膜的制备参数不同，具体详见表1。通过调节各个实施例的隔离膜组成，包括第一基材层的种类及厚度、第二基材层的种类及厚度、功能层的厚度、功能层中各组分的种类以及质量百分含量等中的一个或多个参数，可以得到满足各个实施例所需除水材料含量和除酸材料含量的二次电池。
对比例1
二次电池的制备方法与实施例1类似，不同之处在于采用厚度为14μm的多孔聚乙烯膜作为隔离膜。
对比例2
二次电池的制备方法与实施例1类似，不同之处在于制备隔离膜时未加入除水材料。
对比例3
二次电池的制备方法与实施例1类似，不同之处在于制备隔离膜时未加入除酸材料。
对比例4
二次电池的制备方法与实施例1类似，不同之处在于隔离膜和电解液的制备参数不同，采用厚度为14μm的多孔聚乙烯膜作为隔离膜，电解液中还加入了1％的六甲基二硅氮烷作为添加剂。
测试部分
25℃下，将各实施例和对比例的二次电池以1C恒流充电至3.8V，继续恒压充电至0.05C，此时二次电池为满充状态，记录此时的充电容量，即为第1圈充电容量；将上述二次电池静置5min后，以1C恒流放电至2.0V，此为一个循环充放电过程，记录此时的放电容量，即为第1圈放电容量。将二次电池按照上述方法进行循环充放电测试，记录每圈循环后的放电容量。
二次电池循环200圈后的容量保持率(％)＝第200圈放电容量/第1圈放电容量×100％。
表1给出实施例1～16和对比例1～4的测试结果。
从表1的测试结果可以看出，本申请的多层复合隔离膜同时采用了除水材料和除酸材料，在物理吸附、化学键合等多种作用下，有效将电池内部游离的水分和HF固定在所述除水材料和所述除酸材料上，因此能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池具有更好的循环性能。
对比例2和对比例3仅单一地采用除酸材料或除水材料，与对比例1相比，二次电池的循环性能有一定改善，但是改善效果不佳。可能的原因在于，电极片中的结合水释放到电解液中后，会与含氟的电解质盐反应生成HF，同样地，HF也可以与负极活性材料表面固体电解质界面膜中的无机电解质盐组分(例如碳酸锂等)反应再次转变成水分。因此，仅单一地采用除酸材料或除水材料并不能有效提升二次电池的循环性能。
对比例4在电解液中加入了除酸材料六甲基二硅氮烷，与对比例1相比，二次电池的循环性能有一定改善，但是改善效果不佳。可能的原因在于，六甲基二硅氮烷与电解液兼容性不佳，长时间使用后六甲基二硅氮烷容易形成沉淀，进而影响除酸效果；同时沉淀物沉积在隔离膜表面后容易导致隔离膜堵孔，影响二次电池的循环性能。
从实施例1～5的测试结果可以看出，除水材料的质量不宜过高也不宜过低。当B/A在合适的范围内时，能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池具有长使用寿命，同时二次电池还具有高能量密度。当B/A较小时，可能不能有效减少电池内部游离的水分和HF，进而二次电池的循环性能较差；而当B/A较大时，除水材料过量较多，其对二次电池性能的改善效果不会继续增加，但是二次电池的质量增加，由此降低了二次电池的能量密度。因此，可选地，3≤B/A≤5。
从实施例6～9的测试结果可以看出，除酸材料的质量不宜过高也不宜过低。当D/C在合适的范围内时，能够持续且有效地减少电池内部游离的水分和HF含量，进而减少水分和HF对二次电池的负面影响，使二次电池具有长使用寿命，同时二次电池还具有高能量密度。当D/C较小时，可能不能有效减少电池内部游离的水分和HF，进而二次电池的循环性能较差；而当D/C较大时，除酸材料过量较多，其对二次电池性能的改善效果不会继续增加，但是二次电池的质量增加，由此降低了二次电池的能量密度。因此，可选地，1≤D/C≤2。
从实施例2、6～9的测试结果还可以看出，当所述除酸材料的pH、所述电解液中HF的含量C ppm、所述除酸材料的含量D ppm还满足lgpH+0.5≤D/C≤2时，二次电池可以具有更好的循环性能。
从实施例10～13的测试结果可以看出，除酸材料的pH不宜过高，除酸材料的pH较高时可能会诱导电解质盐分解，进而降低二次电池的循环性能。因此，所述除酸材料的pH可以为7～11.5，可选地为7～10，进一步地为7.2～9.3。
从实施例14～16的测试结果可以看出，作为除水材料的分子筛的比表面积不宜太高也不宜太低。比表面积较高时，可能会吸收较多的电解液，不利于电解液浸润电极片，进而二次电池的循环性能略差；比表面积较小时，对电池内部游离的水分的吸附能力较差，可能无法保证二次电池在长期充放电循环过程中具有较少的游离水分和HF含量，进而二次电池的循环性能也会略差。因此，可选地，所述分子筛的比表面积为350m 2/g～1000m 2/g，进一步地为650m 2/g～800m 2/g。
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。
Figure PCTCN2022135796-appb-000001

Claims (14)

  1. 一种多层复合隔离膜，包括第一基材层以及第二基材层，
    其中，
    所述多层复合隔离膜还包括除水材料以及除酸材料，所述除酸材料位于所述第一基材层和所述第二基材层之间，所述除水材料位于所述第一基材层和所述第二基材层中的至少一个表面上。
  2. 根据权利要求1所述的多层复合隔离膜，其中，所述多层复合隔离膜包括位于所述第一基材层和所述第二基材层之间的功能层，并且所述功能层包括除水材料以及除酸材料；
    可选地，基于所述功能层的总质量，所述除酸材料的质量百分含量为20％～50％，所述除水材料的质量百分含量为15％～50％；
    可选地，所述功能层的厚度为1μm～100μm，进一步地为4μm～50μm。
  3. 根据权利要求1或2所述的多层复合隔离膜，其中，所述多层复合隔离膜中的所述除酸材料的质量和所述除水材料的质量之比为1～3，可选地为1～1.5。
  4. 根据权利要求1-3中任一项所述的多层复合隔离膜，其中，所述除水材料包括分子筛、高吸水树脂中的至少一种。
  5. 根据权利要求4所述的多层复合隔离膜，其中，
    所述分子筛满足如下条件(1)至(4)中的至少一者：
    (1)所述分子筛在25℃、30％相对湿度的静态水吸附量在15％以上，
    (2)所述分子筛的孔径为0.3nm～50nm，可选地为0.5nm～15nm，
    (3)所述分子筛的体积平均粒径Dv50为1μm～10μm，可选地为2μm～6μm，
    (4)所述分子筛的比表面积为350m 2/g～1000m 2/g，可选地为650m 2/g～800m 2/g；
    所述高吸水树脂满足如下条件(5)至(6)中的至少一者：
    (5)所述高吸水树脂的吸水倍率在100倍以上，
    (6)所述高吸水树脂25℃下在水中的溶解度在5％以下。
  6. 根据权利要求4或5所述的多层复合隔离膜，其中，
    所述分子筛包括硅基分子筛SBA-15、钛硅分子筛TS-1中的至少一种；和/或，
    所述高吸水树脂包括淀粉接枝丙烯腈系、淀粉接枝丙烯酸系、淀粉接枝丙烯酰胺系、纤维素接枝丙烯腈系、纤维素接枝丙烯酸系、纤维素接枝丙烯酰胺系、聚乙烯醇系、聚丙烯酸(盐)系、聚丙烯酰胺系、聚氧乙烯系、聚氨酯系、醋酸乙烯酯共聚物、及其各自的改性化合物中的至少一种，
    可选地，所述高吸水树脂包括聚乙烯醇与环状酸酐共聚物、聚丙烯酸钠树脂、醋酸乙烯酯与丙烯酸盐共聚物中的至少一种。
  7. 根据权利要求1-6中任一项所述的多层复合隔离膜，其中，所述除酸材料的pH为7～11.5，可选地为7～10。
  8. 根据权利要求7所述的多层复合隔离膜，其中，所述除酸材料包括无机碱性锂盐、有机化合物中的至少一种。
  9. 根据权利要求8所述的多层复合隔离膜，其中，
    所述无机碱性锂盐包括碳酸锂、碳酸氢锂中的至少一种；和/或，
    所述有机化合物的分子结构包括酰胺基、硅氮基、硅基、碳氮基、磺酸酯基、羧酸盐离子中的至少一种，可选地，所述有机化合物包括醋酸锂、六甲基二硅氮烷、七甲基二硅氮烷、三甲基硅烷基二乙胺、甲基磺酸三甲基硅酯、二(三甲基硅基)碳酰二亚胺、N,N-二甲基丙酰胺、N,N-二甲基乙酰胺、N,N-二甲基甲酰胺中的至少一种。
  10. 一种二次电池，包括正极极片、负极极片、电解液以及根据权利要求1-9中任一项所述的多层复合隔离膜。
  11. 根据权利要求10所述的二次电池，其中，基于所述正极极片和所述负极极片的总质量，所述二次电池中水分的含量为A ppm，基于所述多层复合隔离膜的总质量，所述除水材料的含量为B ppm，并且A和B满足如下关系式：3≤B/A≤5，
    可选地，20≤A≤600；
    可选地，60≤B≤3000。
  12. 根据权利要求10或11所述的二次电池，其中，基于所述电解液的总质量，所述电解液中HF的含量为C ppm，基于所述电解液的总质量，所述除酸材料的含量为D ppm，并且C和D满足如下关系式：1≤D/C≤2，
    可选地，20≤C≤500；
    可选地，20≤D≤1000。
  13. 根据权利要求12所述的二次电池，其中，所述除酸材料的pH、所述电解液中HF的含量C ppm、所述除酸材料的含量D ppm还满足如下关系式：
    lgpH+0.5≤D/C≤2。
  14. 一种用电装置，包括根据权利要求10-13中任一项所述的二次电池。
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