Multilayer composite separator film, and secondary battery and electric device comprising the same

Abstract

The application discloses a multilayer composite separator, and a secondary battery and a power utilization device comprising the same. The multilayer composite separator comprises a first substrate layer and a second substrate layer, wherein the multilayer composite separator further comprises a water removal material and an acid removal material, the acid removal 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 secondary battery of the application can simultaneously meet high energy density and long service life.

Description

Technical Field

[0001] This application belongs to the field of battery technology, and particularly relates to a multilayer composite separator, a secondary battery containing the separator, and an electrical device. Background Technology

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the increasing application and promotion of secondary batteries, their energy density and lifespan have received increasing attention. Therefore, effective technical means are needed to improve the energy density and extend the lifespan of secondary batteries. Summary of the Invention

[0003] The purpose of this application is to provide a multilayer composite separator, a secondary battery containing the separator, and an electrical device, wherein the secondary battery can simultaneously achieve high energy density and long service life.

[0004] The first aspect of this application provides a multilayer composite separator membrane, including a first substrate layer and a second substrate layer, wherein the multilayer composite separator membrane further includes a water-removing material and an acid-removing material, the acid-removing material being located between the first substrate layer and the second substrate layer, and the water-removing material being located on at least one surface of the first substrate layer and the second substrate layer.

[0005] The multilayer composite separator of this application uses both dehydration and deacidification materials. Through physical adsorption, chemical bonding and other effects, it effectively fixes the free water and HF inside the battery onto the dehydration and deacidification materials. Therefore, it can continuously and effectively reduce the content of free water and HF inside the battery, thereby reducing the negative impact of water and HF on the secondary battery, and enabling the secondary battery to simultaneously achieve high energy density and long service life.

[0006] In any embodiment of this application, 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-removing material and an acid-removing material.

[0007] In any embodiment of this application, based on the total mass of the functional layer, the mass percentage of the acid-removing material is 20% to 50%, and the mass percentage of the water-removing material is 15% to 50%.

[0008] In any embodiment of this application, the thickness of the functional layer is 1 μm to 100 μm. Optionally, the thickness of the functional layer is 4 μm to 50 μm. When the thickness of the functional layer is within a suitable range, it can continuously and effectively reduce the content of free water and HF inside the battery during long-term charge-discharge cycles, while ensuring that the secondary battery has high energy density and good kinetic performance.

[0009] In any embodiment of this application, the mass ratio of the acid-removing material to the water-removing material in the multilayer composite separator is 1 to 3. Optionally, the mass ratio of the acid-removing material to the water-removing material in the multilayer composite separator is 1 to 1.5. The mass of the acid-removing material can be greater than or equal to the mass of the water-removing material, thereby ensuring that the acid-removing material can continuously and effectively reduce the free HF content inside the battery, and thus reduce the free water content inside the battery.

[0010] In any embodiment of this application, the dewatering material includes at least one of molecular sieve and superabsorbent resin.

[0011] In any embodiment of this application, the molecular sieve has a static water adsorption capacity of more than 15% at 25°C and 30% relative humidity.

[0012] In any embodiment of this application, the pore size of the molecular sieve is 0.3 nm to 50 nm, optionally 0.5 nm to 15 nm. When the pore size of the molecular sieve is within a suitable range, the molecular sieve can have better water adsorption capacity and worse water desorption capacity, thereby ensuring that the secondary battery has less free water and HF content during long-term charge-discharge cycles, and thus the cycle performance of the secondary battery is better.

[0013] In any embodiment of this application, the volume average particle size Dv50 of the molecular sieve is 1 μm to 10 μm, optionally 2 μm to 6 μm. When the volume average particle size Dv50 of the molecular sieve is within a suitable range, the secondary battery can be guaranteed to have good kinetic performance.

[0014] In any embodiment of this application, the specific surface area of ​​the molecular sieve is 350 m². 2 / g~1000m 2 / g, optionally 650m 2 / g~800m 2 / g. When the specific surface area of ​​the molecular sieve is within a suitable range, the molecular sieve can have better water adsorption capacity, thereby ensuring that the secondary battery has less free water and HF content during long-term charge-discharge cycles, and thus the cycle performance of the secondary battery is better.

[0015] In any embodiment of this application, 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 thicker pore walls, higher pore volume and better hydrothermal stability, thus ensuring that the secondary battery has less free water and HF content during long-term charge-discharge cycles, thereby improving the cycle performance of the secondary battery.

[0016] In any embodiment of this application, the superabsorbent resin has a water absorption ratio of more than 100 times.

[0017] In any embodiment of this application, the solubility of the superabsorbent resin in water at 25°C is less than 5%.

[0018] In any embodiment of this application, the superabsorbent resin includes at least one selected from starch-grafted acrylonitrile, starch-grafted acrylic, starch-grafted acrylamide, cellulose-grafted acrylonitrile, cellulose-grafted acrylic, cellulose-grafted acrylamide, polyvinyl alcohol, polyacrylate (salt), polyacrylamide, polyoxyethylene, polyurethane, vinyl acetate copolymer, and their respective modified compounds. Optionally, the superabsorbent resin includes at least one selected from polyvinyl alcohol and cyclic anhydride copolymer, sodium polyacrylate resin, and vinyl acetate and acrylate copolymer.

[0019] In any embodiment of this application, the pH of the deacidifying material is 7–11.5. Optionally, the pH of the deacidifying material is 7–10. In this application, the deacidifying material is weakly alkaline and can fix HF and water molecules through acid-base neutralization reactions, thereby continuously and effectively reducing the content of free water and HF inside the battery, thus reducing the negative impact of water and HF on the secondary battery, enabling the secondary battery to simultaneously achieve high energy density and long service life.

[0020] In any embodiment of this application, the acid-removing material includes at least one of inorganic alkaline lithium salt and organic compound.

[0021] In any embodiment of this application, the inorganic alkaline lithium salt includes at least one of lithium carbonate and lithium bicarbonate.

[0022] In any embodiment of this application, the molecular structure of the organic compound includes at least one selected from amide group, silazine group, silyl group, carbonazine group, sulfonate group, and carboxylate ion. Optionally, the organic compound includes at least one selected from lithium acetate, hexamethyldisilazane, heptamethyldisilazane, trimethylsilyldiethylamine, trimethylsilylmethanesulfonate, bis(trimethylsilyl)carbodiimide, N,N-dimethylpropionamide, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0023] The second aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, an electrolyte, and a multilayer composite separator as described in the first aspect of this application.

[0024] In any embodiment of this application, based on the total mass of the positive electrode and the negative electrode, the water content in the secondary battery is A ppm, and based on the total mass of the multilayer composite separator, the content of the dehydrating material is B ppm, and A and B satisfy the following relationship: 3 ≤ B / A ≤ 5. When B / A is within a suitable range, the free water and HF content inside the battery can be continuously and effectively reduced, thereby reducing the negative impact of water and HF on the secondary battery, giving the secondary battery a long service life, and also giving the secondary battery a high energy density.

[0025] Optionally, 20 ≤ A ≤ 600.

[0026] Optionally, 60 ≤ B ≤ 3000.

[0027] In any embodiment of this application, based on the total mass of the electrolyte, the HF content in the electrolyte is C ppm, and based on the total mass of the electrolyte, the content of the deacidifying material is D ppm, and C and D satisfy the following relationship: 1 ≤ D / C ≤ 2. When D / C is within a suitable range, the free water and HF content inside the battery can be continuously and effectively reduced, thereby reducing the negative impact of water and HF on the secondary battery, giving the secondary battery a long service life, and at the same time, the secondary battery also has a high energy density.

[0028] Optionally, 20 ≤ C ≤ 500.

[0029] Optionally, 20 ≤ D ≤ 1000.

[0030] In any embodiment of this application, the pH of the deacidifying material, the HF content C ppm in the electrolyte, and the content D ppm of the deacidifying material also satisfy the following relationship: lgpH + 0.5 ≤ D / C ≤ 2. In this case, the secondary battery contains less free HF and moisture, resulting in a longer lifespan and higher energy density.

[0031] A third aspect of this application provides an electrical device that includes a secondary battery as described in the second aspect of this application.

[0032] The secondary battery of this application includes a multi-layer composite separator membrane that simultaneously employs dehydration and deacidification materials. This multi-layer composite separator membrane can continuously and effectively reduce the content of free moisture and HF inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery. Therefore, the secondary battery of this application can simultaneously achieve high energy density and long service life. The electrical device of this application includes the secondary battery provided in this application, and thus has at least the same advantages as the secondary battery. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0035] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0036] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0037] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0038] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0039] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application. Detailed Implementation

[0040] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the multilayer composite separator membrane, and secondary batteries and power-consuming devices incorporating the membrane. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0041] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0044] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0046] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0047] Unless otherwise specified, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. The term "multiple" means two or more, unless otherwise explicitly defined.

[0048] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions, sodium ions, etc.

[0049] In this application, the term "molecular sieve" refers to a type of material with pores of uniform size, whose crystalline state is mainly silicate or aluminosilicate; the term "superabsorbent resin" refers to a type of synthetic resin with hydrophilic groups that can absorb a large amount of water, swell, and retain the water without leakage.

[0050] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, acting as a conductor between the positive and negative electrodes, conducts the active ions. Currently, secondary batteries are widely used in energy storage systems such as hydroelectric, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields.

[0051] With the increasing application and promotion of rechargeable batteries, their energy density and lifespan have received growing attention. Therefore, developing rechargeable batteries with high energy density and long lifespan is a common pursuit in the industry. However, during long-term charge-discharge cycles, bound water in the electrode plates gradually releases and enters the electrolyte. Water readily reacts with fluorinated electrolyte salts in the electrolyte to produce HF. HF not only induces the decomposition of organic solvents in the electrolyte (e.g., inducing ring-opening polymerization of ethylene carbonate), but also damages the protective films on the surfaces of the positive and negative electrode active materials. In particular, when HF damages the protective film on the surface of the positive electrode active material, transition metal ions in the crystal structure of the positive electrode active material dissolve, leading to crystal structure destruction, affecting the extraction and insertion of active ions, and reducing the energy density and lifespan of the rechargeable battery. Therefore, effective technical means are needed to reduce the negative impact of moisture on rechargeable batteries.

[0052] Existing technologies typically employ the following strategies: (1) adding additives to the electrolyte to improve its stability; and (2) setting a coating layer on the surface of the positive electrode active material. However, when the amount of additives added is small, it is insufficient to complex all the HF; when the amount added is large, it can easily change the kinetic properties of the electrolyte and affect the kinetic performance of the secondary battery. Furthermore, setting a coating layer on the surface of the positive electrode active material is not only complex in process but also easily affects the capacity of the secondary battery and reduces its energy density.

[0053] In view of the above problems, the inventors, through extensive research and practice, and by using reverse thinking and lateral thinking, proposed a new type of multilayer composite separator membrane, which can effectively reduce the free water and HF inside the battery, enabling the secondary battery to simultaneously achieve high energy density and long service life.

[0054] Multilayer composite separator

[0055] The first aspect of this application provides a multilayer composite separator membrane, including a first substrate layer and a second substrate layer, wherein the multilayer composite separator membrane further includes a water-removing material and an acid-removing material, the acid-removing material being located between the first substrate layer and the second substrate layer, and the water-removing material being located on at least one surface of the first substrate layer and the second substrate layer.

[0056] Through extensive research and practice, the inventors discovered that bound water released from the electrode sheet into the electrolyte reacts with fluorine-containing electrolyte salts to generate HF. Similarly, HF can react with inorganic electrolyte salt components (such as lithium carbonate) in the solid electrolyte interface film on the surface of the negative electrode active material, transforming back into water. Therefore, simply using dehydrating or deacidifying materials alone cannot effectively improve the lifespan of a secondary battery. The multilayer composite separator of this application employs both dehydrating and deacidifying materials. Through physical adsorption, chemical bonding, and other mechanisms, it effectively fixes free water and HF inside the battery onto the dehydrating and deacidifying materials. This continuously and effectively reduces the content of free water and HF inside the battery, thereby reducing the negative impact of water and HF on the secondary battery and enabling the secondary battery to simultaneously achieve high energy density and long lifespan.

[0057] The multilayer composite separator of this application has a multilayer structure, in which the acid removal material is located between two substrate layers, thereby avoiding the oxidation and decomposition reaction of the acid removal material under high voltage and ensuring that the acid removal material has a better effect.

[0058] This application does not impose any particular limitation on the location of the dewatering material, which can be located on at least one surface of the first substrate layer and the second substrate layer. For example, both the first substrate layer and the second substrate layer have two surfaces opposite each other in their thickness direction; therefore, the dewatering material can be located on at least one of the four surfaces. For example, the dewatering material can be located on the surface of the first substrate layer away from the deacidifying material and close to the electrode sheet, or on the surface of the second substrate layer away from the deacidifying material and close to the electrode sheet, or between the first substrate layer and the second substrate layer.

[0059] In some embodiments, the multilayer composite barrier membrane includes a functional layer located between the first substrate layer and the second substrate layer, and the functional layer includes a water-removing material and an acid-removing material.

[0060] The thickness of the functional layer is not specifically limited and can be selected according to actual needs. When the thickness of the functional layer is small, the amount of dehydrating and deacidifying materials loaded inside is insufficient, which may not be able to continuously and effectively reduce the free water and HF content inside the battery during long-term charge-discharge cycles. When the thickness of the functional layer is large, the weight of the secondary battery increases significantly, and the mass energy density and kinetic performance may decrease. Therefore, the thickness of the functional layer should not be too small or too large. In some embodiments, the thickness of the functional layer can be 1 μm to 100 μm. Optionally, the thickness of the functional layer is 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, or 6μm–20μm. When the thickness of the functional layer is within a suitable range, it can continuously and effectively reduce the content of free water and HF inside the battery during long-term charge-discharge cycles, while ensuring that the secondary battery has high energy density and good kinetic performance.

[0061] The specific content of each component in the functional layer is not specifically limited and can be selected according to actual needs. In some embodiments, optionally, based on the total mass of the functional layer, the mass percentage of the acid-removing material is 20% to 50%, and the mass percentage of the water-removing material is 15% to 50%.

[0062] In some embodiments, the functional layer may further include an adhesive. This application does not impose any particular limitation on the type of adhesive, which can be selected according to actual needs. As an example, the adhesive used for the functional layer includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the adhesive can be from 1% to 35% based on the total mass of the functional layer.

[0063] The deacidifying material primarily reduces the free HF content inside the battery through chemical bonding (e.g., hydrogen bonds, covalent bonds, etc.). Therefore, in the multilayer composite separator of this application, the mass of the deacidifying material can be greater than or equal to the mass of the dehydrating material, thereby ensuring that the deacidifying material can continuously and effectively reduce the free HF content inside the battery, and consequently reduce the free water content inside the battery. In some embodiments, the mass ratio of the deacidifying material to the dehydrating material in the multilayer composite separator can be 1 to 3. Optionally, the mass ratio of the deacidifying material to the dehydrating material in the multilayer composite separator can be 1 to 2.5, 1 to 2, or 1 to 1.5.

[0064] In some embodiments, the dewatering material may include at least one of molecular sieve and superabsorbent polymer (SAP).

[0065] In this application, molecular sieves with high water absorption capacity are preferred. For example, in some embodiments, the static water adsorption capacity of the molecular sieve at 25°C and 30% relative humidity can be above 15%. The static water adsorption capacity of the molecular sieve can be tested according to GB 6287-86 Method for Determination of Static Water Adsorption of Molecular Sieves.

[0066] According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), porous materials with pore sizes between 2 nm and 50 nm are called mesoporous materials, porous materials with pore sizes less than 2 nm are called microporous materials, and porous materials with pore sizes greater than 50 nm are called macroporous materials. In this application, the molecular sieve may include at least one of microporous molecular sieves and mesoporous molecular sieves. Compared with macroporous molecular sieves, microporous and mesoporous molecular sieves can have higher specific surface areas, thus enabling them to play a better role in water adsorption. Meanwhile, the pore size of the molecular sieve should not be less than 0.3 nm. If the pore size of the molecular sieve is too small, water molecules are difficult to be adsorbed into the pore structure of the molecular sieve, thus the molecular sieve will not have a good water adsorption and removal effect.

[0067] In some embodiments, the pore size of the molecular sieve can be 0.3 nm to 50 nm. Optionally, 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, 0.4nm~8nm, 0.5nm~8nm, 1nm~8nm, or 2nm~8nm. When the pore size of the molecular sieve is within a suitable range, the molecular sieve can have better water adsorption capacity and worse water desorption capacity, thereby ensuring that the secondary battery has less free water and HF content during long-term charge-discharge cycles, and thus the cycle performance of the secondary battery is better.

[0068] When the volume average particle size Dv50 of the molecular sieve is large, the transport path of active ions becomes longer, which may reduce the kinetic performance of the secondary battery. Conversely, when the volume average particle size Dv50 of the molecular sieve is small, it may increase the risk of pore blockage in the separator, which may also reduce the kinetic performance of the secondary battery. To ensure good kinetic performance of the secondary battery, the volume average particle size Dv50 of the molecular sieve should not be too large or too small. In some embodiments, the volume average particle size Dv50 of the molecular sieve can be 1 μm to 10 μm. Optionally, the volume average particle size Dv50 of the molecular sieve can be 1 μm to 10 μm, 1 μm to 8 μm, 1 μm to 6 μm, 1 μm to 4 μm, 2 μm to 10 μm, 2 μm to 8 μm, 2 μm to 6 μm, 2 μm to 4 μm, 4 μm to 10 μm, 4 μm to 8 μm, or 4 μm to 6 μm.

[0069] In this application, the volume average particle size Dv50 of the material has a well-known meaning in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50%, which can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0070] When the molecular sieve has a high specific surface area (BET), it can quickly adsorb free water inside the battery. However, the specific surface area of ​​the molecular sieve should not be too high, otherwise the water adsorption capacity of the molecular sieve will not increase further, while the manufacturing cost will increase significantly. Simultaneously, the molecular sieve may also absorb a large amount of electrolyte, which is not conducive to electrolyte wetting of the electrode plates. At the same time, the specific surface area of ​​the molecular sieve should not be too small. When the specific surface area of ​​the molecular sieve is small, its adsorption capacity for free water inside the battery is poor, which may prevent the secondary battery from maintaining low levels of free water and HF content during long-term charge-discharge cycles. In some embodiments, the specific surface area of ​​the molecular sieve can be 350 m². 2 / g~1000m 2 / g. Optionally, the specific surface area of ​​the molecular sieve is 350m². 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. When the specific surface area of ​​the molecular sieve is within a suitable range, the molecular sieve can have better water adsorption capacity, thereby ensuring that the secondary battery has less free water and HF content during long-term charge-discharge cycles, and thus the cycle performance of the secondary battery is better.

[0071] In this application, the specific surface area of ​​the material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0072] The type of molecular sieve is not specifically limited and can be selected according to actual needs. In some embodiments, classified according to pore structure, the molecular sieve may include, but is not limited to, at least one of type A molecular sieves (e.g., type 3A, type 4A, type 5A, etc.), type X molecular sieves (e.g., type 10X, type 13X), and type Y molecular sieves. In some embodiments, classified according to framework elements, the molecular sieve may include, but is not limited to, at least one of silica-alumina molecular sieves, titanium-silicon molecular sieves, and phosphorus-alumina molecular sieves.

[0073] As an example, in some embodiments, the molecular sieve may include, but is 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 may have a mesoporous structure with thicker pore walls, higher pore volume, and better hydrothermal stability, thus ensuring that the secondary battery has less free water and HF content during long-term charge-discharge cycles, resulting in better cycle performance. Of course, SBA-15 and TS-1 may also have a microporous structure.

[0074] In this application, a superabsorbent polymer (SAP) with high water absorption capacity is preferred. In some embodiments, the SAP's water absorption ratio can be greater than 100 times. Here, water absorption ratio refers to the ratio of the mass of water that a unit mass of SAP can absorb to its own mass. The water absorption ratio test of the SAP can be performed with reference to GB / T 22875-2008 and GB / T 22905-2008.

[0075] In this application, a superabsorbent resin with high water absorption and low solubility in water is preferred. In some embodiments, the solubility of the superabsorbent resin in water at 25°C may be less than 5%.

[0076] As an example, in some embodiments, the superabsorbent resin may include, but is not limited to, at least one of starch-grafted acrylonitrile, starch-grafted acrylic, starch-grafted acrylamide, cellulose-grafted acrylonitrile, cellulose-grafted acrylic, cellulose-grafted acrylamide, polyvinyl alcohol, polyacrylate (salt), polyacrylamide, polyoxyethylene, polyurethane, vinyl acetate copolymer, and their respective modified compounds.

[0077] Optionally, the superabsorbent resin includes at least one of polyvinyl alcohol and cyclic anhydride copolymer, sodium polyacrylate resin, and vinyl acetate and acrylate copolymer.

[0078] The deacidifying material should not be acidic or acidic after hydrolysis, as this may not effectively reduce the free HF content inside the battery. Simultaneously, the deacidifying material should not be too alkaline. Strong alkalinity can easily induce electrolyte salt decomposition, increasing side reactions within the battery, reducing the energy density, lifespan, and kinetic performance of the secondary battery, and may even increase the HF content. In some embodiments, the pH of the deacidifying material is 7–11.5. In this application, the deacidifying material is weakly alkaline, which can fix HF and water molecules through acid-base neutralization reactions, thereby continuously and effectively reducing the free water and HF content inside the battery, thus reducing the negative impact of water and HF on the secondary battery, allowing the secondary battery to simultaneously achieve high energy density and long lifespan. Optionally, the pH of the deacidifying material is 7–10. Further, the pH of the deacidifying material is 7.2–9.3.

[0079] In this application, the pH of the deacidifying material has a meaning known in the art and can be measured using instruments and methods known in the art. An exemplary test method includes the following steps: at 25°C, add 5g of the deacidifying material to 100g of deionized water, stir thoroughly to dissolve, and then use the pH value of the test solution as specified in GB / T 6920-86 as the pH of the deacidifying material.

[0080] In some embodiments, the acid-removing material may include at least one of inorganic alkaline lithium salts and organic compounds.

[0081] In some embodiments, the inorganic alkaline lithium salt may include, but is not limited to, at least one of lithium carbonate and lithium bicarbonate.

[0082] In some embodiments, the molecular structure of the organic compound may include at least one selected from amide, silazine, silyl, carbonazine, sulfonate, and carboxylate ions. For example, the organic compound may include, but is not limited to, at least one selected from organic basic lithium salts and small organic molecule compounds. As examples, the organic compound includes, but is not limited to, at least one selected from lithium acetate, hexamethyldisilazane, heptamethyldisilazane, trimethylsilyldiethylamine, trimethylsilylmethanesulfonate, bis(trimethylsilyl)carbodiimide, N,N-dimethylpropionamide, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0083] In this application, the deacidifying material can fix HF and water molecules through chemical reactions (such as acid-base neutralization reactions) and hydrogen bonding, thereby continuously and effectively reducing the content of free water and HF inside the battery, thus reducing the negative impact of water and HF on the secondary battery, and enabling the secondary battery to simultaneously achieve high energy density and long service life.

[0084] This application does not impose any particular limitation on the thickness of the first substrate layer and the second substrate layer, and they can be selected according to actual needs. This application also does not impose any particular limitation on the types of the first substrate layer and the second substrate layer; any known porous membrane structure with good chemical and mechanical stability can be selected. In some embodiments, the materials of the first substrate layer and the second substrate layer may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The first substrate layer and the second substrate layer may be the same or different.

[0085] The multilayer composite separator membrane of this application does not exclude other components besides those described above. In some embodiments, the multilayer composite separator membrane may further include fillers, such as inorganic ceramic particles. Optionally, the inorganic ceramic particles may be located on the surface of the first substrate layer away from the deacidifying material and close to the electrode sheet, on the surface of the second substrate layer away from the deacidifying material and close to the electrode sheet, or within the pores of the first and second substrate layers.

[0086] In some embodiments, the multilayer composite separator includes a first substrate layer and a second substrate layer, wherein the multilayer composite separator further includes a water-removing material and an acid-removing material, the acid-removing material being located between the first substrate layer and the second substrate layer, and the water-removing material being located on at least one surface of the first substrate layer and the second substrate layer; the water-removing material includes at least one of molecular sieve and superabsorbent resin; the pH of the acid-removing material is 7 to 11.5, optionally 7 to 10, and further 7.2 to 9.3; the mass ratio of the acid-removing material to the water-removing material in the multilayer composite separator is 1 to 3, optionally 1 to 1.5. The multi-layer composite separator, by employing a highly absorbent dehydrating material and a weakly alkaline deacidifying material, effectively fixes free water and HF inside the battery onto the dehydrating and deacidifying materials through various processes such as physical adsorption and chemical bonding (e.g., acid-base neutralization reaction). Therefore, it can continuously and effectively reduce the content of free water and HF inside the battery, thereby reducing the negative impact of water and HF on the secondary battery and enabling the secondary battery to simultaneously achieve high energy density and long service life.

[0087] In some embodiments, the multilayer composite separator includes a first substrate layer, a second substrate layer, and a functional layer located between the first substrate layer and the second substrate layer. The functional layer includes a dehydrating material and an acid-removing material. Based on the total mass of the functional layer, the acid-removing material has a mass percentage content of 20% to 50%, the dehydrating material has a mass percentage content of 15% to 50%, and the mass ratio of the acid-removing material to the dehydrating material is 1 to 3, optionally 1 to 1.5. The dehydrating material includes at least one of molecular sieve and superabsorbent resin. The pH of the acid-removing material is 7 to 11.5, optionally 7 to 10, and further 7.2 to 9.3. The multi-layer composite separator, by employing a highly absorbent dehydrating material and a weakly alkaline deacidifying material, effectively fixes free water and HF inside the battery onto the dehydrating and deacidifying materials through various processes such as physical adsorption and chemical bonding (e.g., acid-base neutralization reaction). Therefore, it can continuously and effectively reduce the content of free water and HF inside the battery, thereby reducing the negative impact of water and HF on the secondary battery and enabling the secondary battery to simultaneously achieve high energy density and long service life.

[0088] [Preparation Method]

[0089] The first aspect of this 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.

[0090] In some embodiments, the multilayer composite separator can be prepared by the following steps: dispersing dehydrating materials, deacidifying materials, binders and optional additives in a solvent and stirring evenly to form a slurry; coating the slurry on the surface of one of the substrate layers, and then covering the slurry surface with another substrate layer, and obtaining the multilayer composite separator after drying and cold pressing.

[0091] In other embodiments, the multilayer composite separator can also be prepared by the following steps: dispersing the deacidifying material, binder, and optional additives in a solvent and stirring evenly to form a first slurry; dispersing the dehydrating material, binder, and optional additives in a solvent and stirring evenly to form a second slurry; coating the first slurry onto the surface of one of the substrate layers, and then covering the surface of the first slurry with another substrate layer; coating the second slurry onto the surface of any one of the substrate layers away from the deacidifying material; and obtaining the multilayer composite separator after drying and cold pressing.

[0092] The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto. The binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. The additives may include dispersants, such as hexadecyltrimethylammonium bromide.

[0093] It should be noted that the structure of the multilayer composite separator prepared by the above preparation method can be found in the multilayer composite separators provided in the above embodiments.

[0094] Secondary batteries

[0095] A second aspect of this application provides a secondary battery. This application does not particularly limit the type of secondary battery; for example, the secondary battery can be a lithium-ion battery, a sodium-ion battery, etc. Specifically, the secondary battery is a lithium-ion secondary battery.

[0096] In some embodiments, the secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The separator is a multilayer composite separator as described in any embodiment of the first aspect of this application. The separator is disposed between the positive electrode and the negative electrode to prevent short circuits between the positive and negative electrodes and to reduce the content of free water and HF inside the battery.

[0097] In some embodiments, the water content in the secondary battery is A ppm based on the total mass of the positive electrode and the negative electrode, and the water removal material content is B ppm based on the total mass of the multilayer composite separator, and A and B satisfy the following relationship: 3≤B / A≤5.

[0098] When the B / A ratio is low, it may not effectively reduce the free moisture and HF content inside the battery; while when the B / A ratio is high, the amount of dehydrating 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 will increase, thereby reducing the energy density of the secondary battery. When the B / A ratio is within a suitable range, it can continuously and effectively reduce the content of free moisture and HF inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, giving the secondary battery a long service life, while also maintaining a high energy density.

[0099] The moisture in the secondary battery mainly consists of three parts: trace amounts of moisture remaining in the positive electrode, trace amounts of moisture remaining in the negative electrode, and trace amounts of moisture in the electrolyte. The moisture content in the secondary battery is obtained as follows: the mass of moisture in the prepared positive electrode, negative electrode, and electrolyte is measured separately to obtain the total mass of moisture; the total mass of moisture is then divided by the total mass of the positive and negative electrode to obtain the moisture content (Appm) of the secondary battery. The moisture in the positive electrode, negative electrode, and electrolyte can be measured using a Karl Fischer moisture analyzer, such as the MA-30 intelligent Karl Fischer moisture analyzer.

[0100] Selecting the appropriate dehydration material quality based on the moisture content (A ppm) in the secondary battery can not only continuously and effectively reduce the free moisture and HF content inside the battery, thus reducing the negative impact of moisture and HF on the secondary battery and giving it a long service life, but also enable the secondary battery to have a high energy density.

[0101] Typically, based on the total mass of the positive and negative electrode sheets, the water content (Appm) in the secondary battery is between 20 ppm and 600 ppm. Furthermore, the amount of dehydrating material added can be such that, based on the total mass of the multilayer composite separator, the content (B ppm) of the dehydrating material is between 60 ppm and 3000 ppm.

[0102] In some embodiments, the HF content in the electrolyte is C ppm based on the total mass of the electrolyte, the content of the acid removal material is D ppm based on the total mass of the electrolyte, and C and D satisfy the following relationship: 1≤D / C≤2.

[0103] When the D / C ratio is low, it may not effectively reduce the free moisture and HF inside the battery; while when the D / C ratio is high, the amount of deacidifying 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 will increase, thereby reducing the energy density of the secondary battery. When the D / C ratio is within a suitable range, it can continuously and effectively reduce the content of free moisture and HF inside the battery, thereby reducing the negative impact of moisture and HF on the secondary battery, giving the secondary battery a long service life, while also maintaining a high energy density.

[0104] Selecting the appropriate quality of deacidification material based on the HF content (C ppm) in the electrolyte can not only continuously and effectively reduce the free water and HF content inside the battery, thus reducing the negative impact of water and HF on the secondary battery and giving it a long service life, but also enable the secondary battery to have a high energy density.

[0105] The HF content (C ppm) in the electrolyte can be determined by titration, for example, according to HG / T4067-2015. An exemplary test method includes the following steps: Add 15g of electrolyte sample to 100ml of an ice-water mixture; using bromothymol blue as an indicator, titrate with sodium hydroxide standard solution until the solution turns blue as the reaction endpoint, and record the volume V1 of the sodium hydroxide standard titration solution; add bromothymol blue as an indicator to 100ml of the ice-water mixture, titrate with sodium hydroxide standard solution until the solution turns blue as the reaction endpoint, and record the volume V0 of the sodium hydroxide standard titration solution. V1-V0 represents the actual volume of sodium hydroxide standard titration solution consumed, from which the mass of HF and its content in the electrolyte can be calculated.

[0106] Typically, based on the total mass of the electrolyte, the HF content C in the electrolyte is between 20 ppm and 500 ppm. Further, the amount of the deacidifying material added can be such that, based on the total mass of the electrolyte, the content D of the deacidifying material is between 20 ppm and 1000 ppm.

[0107] In some embodiments, the pH of the deacidifying material, the HF content C ppm in the electrolyte, and the content of the deacidifying material D ppm also satisfy the following relationship: lgpH+0.5≤D / C≤2. Through extensive research and practice, the inventors have discovered that when the content of the deacidifying material D ppm satisfies the above relationship lgpH+0.5≤D / C≤2, the secondary battery contains less free HF and moisture, resulting in a longer lifespan and higher energy density.

[0108] Electrolyte

[0109] In some embodiments, the electrolyte comprises an electrolyte salt and a solvent. The types of electrolyte salt and solvent are not specifically limited and can be selected according to actual needs.

[0110] When the secondary battery of this application is a lithium-ion battery, particularly a lithium-ion secondary battery, as an example, the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0111] When the secondary battery of this application is a sodium-ion battery, the electrolyte salt may include at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0112] In some embodiments, as an example, the solvent may include at least one selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0113] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain battery performance, such as additives improving battery overcharge performance, battery high-temperature performance, and battery low-temperature power performance. As an example, the additives may include, but are not limited to, at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3-propanesulfonate lactone (PS).

[0114] [Positive electrode plate]

[0115] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0116] The positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0117] The positive electrode film typically comprises a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film is typically formed by coating a positive electrode slurry onto the positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to it. As an example, the binder used for the positive electrode film may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. As an example, the conductive agent used for the positive electrode film includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0118] The positive electrode active material may be a positive electrode active material known in the art for use in secondary batteries.

[0119] When the secondary battery of this application is a lithium-ion battery, particularly a lithium-ion secondary battery, the positive electrode active material may include at least one of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for lithium-ion batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0120] In some embodiments, to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery may include at least one of the lithium transition metal oxides and their modified compounds represented by Formula 1.

[0121] Li a Ni b Co c M d O e A f Formula 1

[0122] In Formula 1, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from at least one of N, F, S and Cl.

[0123] As an example, positive electrode active materials for lithium-ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co0.15 Al 0.05 At least one of O2, LiFePO4, and LiMnPO4.

[0124] When the secondary battery of this application is a sodium-ion battery, the positive electrode active material may include at least one of sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials. This application is not limited to these materials; other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0125] As an example, positive electrode active materials for sodium-ion batteries may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials, with the general formula A a M b (PO4) c O x Y 3-x At least one of the materials. Wherein, A is selected from H. + Li + Na + K + and NH4 + At least one of the following: M is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu and Zn; 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.

[0126] In this application, the modified compounds of the above-mentioned positive electrode active materials can be used to dope or surface-coat the positive electrode active materials.

[0127] [Negative electrode plate]

[0128] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0129] The negative electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0130] The negative electrode film typically comprises a negative electrode active material, an optional binder, an optional conductive agent, and other optional additives. The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry coating is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these. As an example, the binder used for the negative electrode film may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). As an example, the conductive agent used for the negative electrode film 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 (e.g., sodium carboxymethyl cellulose, CMC-Na), PTC thermistor materials, etc.

[0131] The negative electrode active material can be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. Tin-based materials may include at least one of elemental tin, tin oxide, and tin alloy materials. This 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.

[0132] The negative electrode sheet of this application does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0133] In some embodiments, the positive electrode sheet, the multilayer composite separator, and the negative electrode sheet can be fabricated into an electrode assembly using a winding process or a stacking process.

[0134] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0135] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0136] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0137] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0138] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. 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.

[0139] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0140] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0141] In some embodiments, the battery modules described above 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.

[0142] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0143] [Preparation Method]

[0144] A second aspect of this application also provides a method for preparing a secondary battery. The method includes the following steps: S100, providing a positive electrode, a negative electrode, a multilayer composite separator, and an electrolyte, wherein the multilayer composite separator includes a first substrate layer, a second substrate layer, a dehydrating material, and an acid-removing material, the acid-removing material being located between the first substrate layer and the second substrate layer, and the dehydrating material being located on at least one surface of the first substrate layer and the second substrate layer; S200, assembling the positive electrode, the multilayer composite separator, the negative electrode, and the electrolyte into a secondary battery.

[0145] In some embodiments, S100 further includes the following steps: S101, testing the mass of water in the positive electrode and the negative electrode, and the mass of water and HF in the electrolyte, and calculating the water content A ppm in the secondary battery based on the total mass of the positive electrode and the negative electrode, and the HF content C ppm in the electrolyte based on the total mass of the electrolyte; S102, the amount of water-removing material added is such that the water-removing material content B ppm based on the total mass of the multilayer composite separator membrane satisfies 3≤B / A≤5, and the amount of acid-removing material added is such that the acid-removing material content D ppm based on the total mass of the electrolyte satisfies 1≤D / C≤2. Optionally, the amount of acid-removing material added is such that lgpH+0.5≤D / C≤2, where pH is the pH of the acid-removing material.

[0146] By selecting appropriate dehydration materials based on the water content (A ppm) in the secondary battery and appropriate deacidification materials based on the HF content (C ppm) in the electrolyte, it is possible to continuously and effectively reduce the free water and HF content inside the battery, thereby reducing the negative impact of water and HF on the secondary battery, resulting in a long service life and high energy density.

[0147] In some embodiments, S200 may further include the steps of: forming an electrode assembly by winding or stacking the above-mentioned positive electrode sheet, separator, and negative electrode sheet; placing the electrode assembly in an outer packaging; drying and injecting electrolyte; and obtaining a secondary battery by vacuum sealing, standing, formation, shaping and other processes.

[0148] It should be noted that the structure of the secondary battery prepared by the above-described secondary battery preparation method can be found in the secondary batteries provided in the above embodiments.

[0149] Electrical appliances

[0150] A third aspect of this application provides an electrical device. The electrical device includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0151] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0152] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0153] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0154] Example

[0155] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0156] Example 1

[0157] Preparation of the separating membrane

[0158] With a specific surface area of ​​650m 2 A slurry is formed by mixing TS-1 titanium silicate molecular sieve (dehydration material) with a pore size of 3 nm and a Dv50 of 2 μm, hexamethyldisilazane (acid removal material) with a pH of 7.5, polyvinylidene fluoride (binder), and hexadecyltrimethylammonium bromide in a suitable amount of NMP solvent at a mass ratio of 35:45:19:1 for 2-3 hours. The slurry is then coated onto the surface of a porous polyethylene membrane (first substrate layer) with a thickness of 14 μm, and then another porous polyethylene membrane (second substrate layer) with a thickness of 8 μm is placed on the slurry surface. After drying and cold pressing, a multilayer composite isolation membrane is obtained. The thickness of the slurry layer is 6 μm.

[0159] Preparation of positive electrode sheet

[0160] The positive electrode active material LiFePO4, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of solvent NMP at a mass ratio of 80:10:10 to form a positive electrode slurry with a solid content of 50%. The positive electrode slurry was uniformly coated on the surface of the positive electrode current collector aluminum foil, dried at 85°C, and then cold-pressed. After trimming, cutting, and slitting, it was dried under vacuum at 85°C for 4 hours to obtain the positive electrode sheet.

[0161] Preparation of negative electrode sheet

[0162] The negative electrode active material graphite, conductive agent carbon black (Super P), thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) are thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 80:15:3:2 to form a negative electrode slurry with a solid content of 30%. The negative electrode slurry is uniformly coated on the surface of the negative electrode current collector copper foil, dried at 85°C, and then cold-pressed. After trimming, cutting, and slitting, it is dried under vacuum at 120°C for 12 hours to obtain the negative electrode sheet.

[0163] Preparation of electrolyte

[0164] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent; LiPF6 was uniformly dissolved in the above organic solvent to obtain an electrolyte, wherein the concentration of LiPF6 was 1 mol / L.

[0165] Preparation of secondary batteries

[0166] The positive electrode, multilayer composite separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, the electrolyte is added, and after processes such as encapsulation, standing, formation, and aging, a secondary battery is obtained.

[0167] The water content in the secondary battery is obtained by the following method: the mass of water in the prepared positive electrode, negative electrode, and electrolyte is measured by an MA-30 intelligent Karl Fischer moisture analyzer to obtain the total mass of water; the water content (Appm) in the secondary battery is obtained by dividing the obtained total mass of water by the total mass of the positive electrode and negative electrode.

[0168] Add 15g of the above electrolyte sample to 100ml of ice-water mixture. Using bromothymol blue as an indicator, titrate with sodium hydroxide standard solution until the solution turns blue, marking the reaction endpoint. Record the volume V1 of the sodium hydroxide standard titration solution. Repeat the process, adding bromothymol blue to the same 100ml mixture and titrating with sodium hydroxide standard solution until the solution turns blue, marking the reaction endpoint again. Record the volume V0 of the sodium hydroxide standard titration solution. V1-V0 represents the actual volume of sodium hydroxide standard titration solution consumed. Calculate the mass of HF and its concentration (C ppm) in the electrolyte using this method.

[0169] Specifically, based on the total mass of the positive and negative electrode plates, the water content (Appm) in the secondary battery is 50 ppm; based on the total mass of the electrolyte, the HF content (C ppm) in the electrolyte is 100 ppm; based on the total mass of the multilayer composite separator, the water removal material content (B ppm) is 150 ppm; and based on the total mass of the electrolyte, the acid removal material content (D ppm) is 187 ppm.

[0170] Examples 2-16

[0171] The preparation method of the secondary battery is similar to that of Example 1, except that the preparation parameters of the separator are different, as detailed in Table 1. Specifically, by adjusting one or more parameters of the separator composition 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, and the types and mass percentages of each component in the functional layer, a secondary battery that meets the requirements of the dehydration and deacidification material content for each embodiment can be obtained.

[0172] Comparative Example 1

[0173] The preparation method of the secondary battery is similar to that in Example 1, except that a porous polyethylene membrane with a thickness of 14 μm is used as the separator.

[0174] Comparative Example 2

[0175] The preparation method of the secondary battery is similar to that of Example 1, except that no dehydrating material is added when preparing the separator.

[0176] Comparative Example 3

[0177] The preparation method of the secondary battery is similar to that in Example 1, except that no acid-removing material is added when preparing the separator.

[0178] Comparative Example 4

[0179] The preparation method of the secondary battery is similar to that of Example 1, except that the preparation parameters of the separator and electrolyte are different. In this example, a porous polyethylene membrane with a thickness of 14 μm is used as the separator, and 1% hexamethyldisilazane is added to the electrolyte as an additive.

[0180] Test section

[0181] At 25°C, the secondary batteries of each embodiment and comparative example were charged at a constant current of 1C to 3.8V, and then charged at a constant voltage to 0.05C. At this point, the secondary batteries were fully charged, and the charging capacity at this point was recorded as the first charging capacity. After the secondary batteries were left to stand for 5 minutes, they were discharged at a constant current of 1C to 2.0V. This constituted one charge-discharge cycle, and the discharge capacity at this point was recorded as the first discharge capacity. The secondary batteries were subjected to cyclic charge-discharge tests according to the above method, and the discharge capacity after each cycle was recorded.

[0182] The capacity retention rate (%) of a secondary battery after 200 cycles = discharge capacity of the 200th cycle / discharge capacity of the 1st cycle × 100%.

[0183] Table 1 shows the test results of Examples 1-16 and Comparative Examples 1-4.

[0184] As can be seen from the test results in Table 1, the multilayer composite separator of this application uses both dehydration and deacidification materials. Under the combined effects of physical adsorption and chemical bonding, it effectively fixes the free water and HF inside the battery onto the dehydration and deacidification materials. Therefore, it can continuously and effectively reduce the content of free water and HF inside the battery, thereby reducing the negative impact of water and HF on the secondary battery and giving the secondary battery better cycle performance.

[0185] Comparative Examples 2 and 3, which used only deacidifying or dehydrating materials, showed some improvement in cycle performance compared to Comparative Example 1, but the improvement was not significant. A possible reason is that bound water released from the electrode sheets into the electrolyte reacts with fluorine-containing electrolyte salts to form HF. Similarly, HF can react with inorganic electrolyte salt components (such as lithium carbonate) in the solid electrolyte interface film on the surface of the negative electrode active material, transforming back into water. Therefore, using only deacidifying or dehydrating materials cannot effectively improve the cycle performance of the secondary battery.

[0186] Comparative Example 4 added hexamethyldisilazane, an acid-removing material, 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 significant. The possible reason is that hexamethyldisilazane has poor compatibility with the electrolyte; after prolonged use, it easily forms precipitates, thus affecting the acid removal effect. Simultaneously, the precipitates deposited on the separator surface can easily clog the separator pores, affecting the cycle performance of the secondary battery.

[0187] The test results from Examples 1-5 show that the mass of the dehydrating material should not be too high or too low. When the B / A ratio is within a suitable range, it can continuously and effectively reduce the content of free water and HF inside the battery, thereby reducing the negative impact of water and HF on the secondary battery, resulting in a long service life and high energy density. When the B / A ratio is low, it may not effectively reduce the free water and HF inside the battery, leading to poor cycle performance. Conversely, when the B / A ratio is high, there is an excess of dehydrating material, and its effect on improving the performance of the secondary battery will not continue to increase, but the mass of the secondary battery will increase, thus reducing its energy density. Therefore, optionally, 3 ≤ B / A ≤ 5.

[0188] The test results from Examples 6-9 show that the quality of the deacidifying material should not be too high or too low. When the D / C ratio is within a suitable range, it can continuously and effectively reduce the content of free water and HF inside the battery, thereby reducing the negative impact of water and HF on the secondary battery, resulting in a long service life and high energy density. When the D / C ratio is low, it may not effectively reduce the free water and HF inside the battery, leading to poor cycle performance. Conversely, when the D / C ratio is high, there is an excess of deacidifying material, which does not further improve the performance of the secondary battery, but increases the mass of the secondary battery, thus reducing its energy density. Therefore, optionally, 1 ≤ D / C ≤ 2.

[0189] The test results from Examples 2, 6 to 9 also show that when the pH of the deacidifying material, the HF content C ppm in the electrolyte, and the content D ppm of the deacidifying material satisfy 1gpH+0.5≤D / C≤2, the secondary battery can have better cycle performance.

[0190] The test results from Examples 10-13 show that the pH of the acid removal material should not be too high. A high pH may induce electrolyte salt decomposition, thereby reducing the cycle performance of the secondary battery. Therefore, the pH of the acid removal material can be 7-11.5, optionally 7-10, and more preferably 7.2-9.3.

[0191] The test results from Examples 14-16 show that the specific surface area of ​​the molecular sieve used as a dehydration material should not be too high or too low. A higher specific surface area may result in the absorption of more electrolyte, hindering electrolyte wetting of the electrode plates and consequently leading to slightly poorer cycle performance of the secondary battery. Conversely, a lower specific surface area results in poorer adsorption of free water inside the battery, potentially preventing the secondary battery from maintaining low levels of free water and HF during long-term charge-discharge cycles, thus also slightly impairing cycle performance. Therefore, optionally, the specific surface area of ​​the molecular sieve is 350 m² / g. 2 / g~1000m 2 / g, further to 650m 2 / g~800m 2 / g.

[0192] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

[0193]

Claims

1. A multilayer composite separator, comprising a first substrate layer and a second substrate layer, in, The multilayer composite isolation membrane further includes a water-removing material and an acid-removing material, wherein the acid-removing material is located between the first substrate layer and the second substrate layer, and the water-removing material is located on at least one surface of the first substrate layer and the second substrate layer.

2. The multilayer composite separator according to claim 1, characterized in that, The multilayer composite isolation membrane includes a functional layer located between the first substrate layer and the second substrate layer, and the functional layer includes a water-removing material and an acid-removing material.

3. The multilayer composite separator according to claim 2, characterized in that, 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%.

4. The multilayer composite separator according to claim 2, characterized in that, The thickness of the functional layer is 1μm to 100μm.

5. The multilayer composite separator according to claim 4, characterized in that, The thickness of the functional layer is 4μm~50μm.

6. The multilayer composite separator membrane according to any one of claims 1-5, characterized in that, The mass ratio of the acid-removing material to the water-removing material in the multilayer composite isolation membrane is 1 to 3.

7. The multilayer composite separator according to claim 6, characterized in that, The mass ratio of the acid-removing material to the water-removing material in the multilayer composite isolation membrane is 1 to 1.

5.

8. The multilayer composite separator according to any one of claims 1-5 or claim 7, characterized in that, The dewatering material includes at least one of molecular sieve and superabsorbent resin.

9. The multilayer composite separator according to claim 8, characterized in that, The molecular sieve satisfies at least one of the following conditions (1) to (4): (1) The molecular sieve has a static water adsorption capacity of more than 15% at 25℃ and 30% relative humidity. (2) The pore size of the molecular sieve is 0.3 nm to 50 nm. (3) The volume average particle size Dv50 of the molecular sieve is 1 μm to 10 μm. (4) The specific surface area of ​​the molecular sieve is 350 m². 2 / g~1000m 2 / g; The superabsorbent resin satisfies at least one of the following conditions (5) to (6): (5) The water absorption ratio of the superabsorbent resin is more than 100 times. (6) The solubility of the superabsorbent resin in water at 25°C is less than 5%.

10. The multilayer composite separator according to claim 9, characterized in that, The molecular sieve has a pore size of 0.5 nm to 15 nm.

11. The multilayer composite separator according to claim 9, characterized in that, The volume average particle size Dv50 of the molecular sieve is 2μm~6μm.

12. The multilayer composite separator according to claim 9, characterized in that, The specific surface area of ​​the molecular sieve is 650 m². 2 / g~800m 2 / g.

13. The multilayer composite separator according to claim 8, characterized in that, The molecular sieve includes at least one of silicon-based molecular sieve SBA-15 and titanium-silicon molecular sieve TS-1; and / or, The superabsorbent resin includes at least one of starch-grafted acrylonitrile, starch-grafted acrylic, starch-grafted acrylamide, cellulose-grafted acrylonitrile, cellulose-grafted acrylic, cellulose-grafted acrylamide, polyvinyl alcohol, polyacrylate, polyacrylamide, polyoxyethylene, polyurethane, vinyl acetate copolymer, and their respective modified compounds.

14. The multilayer composite separator according to claim 13, characterized in that, The superabsorbent resin includes at least one of polyvinyl alcohol and cyclic anhydride copolymer, sodium polyacrylate resin, and vinyl acetate and acrylate copolymer.

15. The multilayer composite separator according to any one of claims 1-5 or claim 7, characterized in that, The pH of the deacidifying material is 7~11.

5.

16. The multilayer composite separator according to claim 15, characterized in that, The pH of the deacidifying material is 7-10.

17. The multilayer composite separator according to claim 15, characterized in that, The acid-removing material includes at least one of inorganic alkaline lithium salts and organic compounds.

18. The multilayer composite separator according to claim 17, characterized in that, The inorganic alkaline lithium salt includes at least one of lithium carbonate and lithium bicarbonate; and / or, The molecular structure of the organic compound includes at least one of the following: amide group, silazine group, silicon group, carbonazine group, sulfonate group, and carboxylate ion.

19. The multilayer composite separator according to claim 18, characterized in that, The organic compound includes at least one of lithium acetate, hexamethyldisilazane, heptamethyldisilazane, trimethylsilyldiethylamine, trimethylsilylmethanesulfonate, di(trimethylsilyl)carbodiimide, N,N-dimethylpropionamide, N,N-dimethylacetamide, and N,N-dimethylformamide.

20. A secondary battery, comprising a positive electrode, a negative electrode, an electrolyte, and a multilayer composite separator according to any one of claims 1-19.

21. The secondary battery according to claim 20, characterized in that, Based on the total mass of the positive electrode and the negative electrode, the water content in the secondary battery is A ppm, and based on the total mass of the multilayer composite separator, the water removal material content is B ppm, and A and B satisfy the following relationship: 3≤B / A≤5.

22. The secondary battery according to claim 21, characterized in that, 20≤A≤600。 23. The secondary battery according to claim 21, characterized in that, 60≤B≤3000。 24. The secondary battery according to claim 20 or 21, characterized in that, Based on the total mass of the electrolyte, the HF content in the electrolyte is C ppm, and based on the total mass of the electrolyte, the content of the acid removal material is D ppm, and C and D satisfy the following relationship: 1≤D / C≤2.

25. The secondary battery according to claim 24, characterized in that, 20≤C≤500。 26. The secondary battery according to claim 24, characterized in that, 20≤D≤1000。 27. The secondary battery according to claim 24, characterized in that, The pH of the deacidifying material, the HF content C ppm in the electrolyte, and the content D ppm of the deacidifying material also satisfy the following relationship: lgpH+0.5≤D / C≤2.

28. An electrical device comprising a secondary battery according to any one of claims 20-27.

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