Separator and preparation method therefor, lithium ion battery, and electric device

Abstract

Disclosed in embodiments of the present application are a separator and a preparation method therefor, a lithium ion battery, and an electric device. The separator comprises a membrane and a coating arranged on at least one side of the membrane; the coating comprises a metal salt, the metal salt comprises metal ions, and the reduction potential of the metal ions is higher than the reduction potential of lithium ions. The separator is applied to a lithium ion battery, and can effectively inhibit lithium plating and facilitate the improvement of the cycle performance of the lithium ion battery.

Description

Isolator and preparation method thereof, lithium-ion battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent document claims priority to and the benefit of Chinese patent application No. 202310798215.1, filed on June 30, 2023, entitled "Separator and method for preparing the same, lithium-ion battery, and electrical device." The entire contents of the aforementioned patent application are incorporated by reference into this patent document. Technical Field

[0003] The present application relates to the field of batteries, and more specifically, to an isolator and a preparation method thereof, a lithium-ion battery, and an electrical device. Background Art

[0004] In recent years, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and have thus achieved great development.

[0005] During the cycling of lithium-ion batteries, increased internal resistance and uneven current density between the electrodes can easily lead to lithium deposition on the negative electrode. In severe cases, this can lead to the growth of lithium dendrites, threatening the reversible capacity and cycle life of the lithium-ion battery. Therefore, improving lithium deposition in lithium-ion batteries has become a pressing technical issue.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned technical problems, and its purpose is to provide an isolation member and its preparation method, a lithium-ion battery and an electrical device. The isolation member can be applied to lithium-ion batteries to effectively inhibit lithium plating and help improve the cycle performance of lithium-ion batteries.

[0008] In a first aspect, an isolation member is provided, comprising an isolation membrane and a coating disposed on at least one side of the isolation membrane; the coating comprises a metal salt, the metal salt comprises metal ions, and the reduction potential of the metal ions is higher than the reduction potential of lithium ions.

[0009] In an embodiment of the present application, a coating including a metal salt is provided on at least one side of the isolation membrane so that after the isolation member is applied to a lithium-ion battery, free metal ions are present in the electrolyte. In the case of lithium deposition on the negative electrode of the lithium-ion battery, the potential at the location of lithium deposition is relatively low. The free metal ions in the electrolyte can freely move to the location with lower potential on the negative electrode, forming a local positive charge electrostatic field, thereby uniformizing the current density on the negative electrode and suppressing lithium deposition. Thus, the isolation member provided by the present application can effectively suppress lithium deposition and reduce side reactions during the cycle of the lithium-ion battery, thereby helping to improve the cycle performance of the lithium-ion battery and improve the coulombic efficiency of the lithium-ion battery.

[0010] In a possible implementation, the difference between the reduction potential of the metal ions and the reduction potential of the lithium ions is less than or equal to 0.8V.

[0011] In a possible implementation, the metal salt includes at least one of a sodium salt, a potassium salt, a calcium salt, a magnesium salt, and a cesium salt.

[0012] In a possible implementation, the metal salt includes anions, and the anions include one or more of fluorine, phosphorus, sulfur, and nitrogen.

[0013] In a possible implementation, the solubility S of the metal salt in the electrolyte satisfies: 0.0006 g / mL≤S; optionally, 0.005 g / mL≤S≤0.06 g / mL.

[0014] In the embodiments of the present application, by controlling the solubility of the metal salt within a suitable range, the amount of the metal salt that can be dissolved on the separator can be controlled, thereby helping to improve the mechanical strength of the separator.

[0015] In a possible implementation, the powder compaction density ρ of the coating satisfies: 0.5 g / cm 3 ≤ρ≤5.0g / cm 3 ; Optionally, 1.0 g / cm 3 ≤ρ≤2.0g / cm 3 .

[0016] In a possible implementation, the thickness d of the coating satisfies: 0.01 μm≤d≤200 μm; optionally, 0.5 μm≤d≤50 μm.

[0017] In the embodiments of the present application, by controlling the powder compaction density and thickness of the coating within a suitable range, the amount of metal salt dissolved on the isolation member can also be controlled, thereby helping to improve the mechanical strength of the isolation member.

[0018] In a possible implementation, the isolation film includes at least one of a polyolefin film, a polyester film, a cellulose film, a polyimide film, a polyamide film, a spandex film, and an aramid film.

[0019] In a possible implementation, based on the total mass of the coating, the mass content a of the metal salt satisfies: 10%≤a≤90%; optionally, 40%≤a≤90%.

[0020] In the embodiments of the present application, by controlling the content of the metal salt on the separator within a suitable range, the content of metal ions in the electrolyte can be indirectly controlled within a suitable range, thereby further suppressing lithium plating in the lithium-ion battery and helping to improve the cycle performance and coulombic efficiency of the lithium-ion battery.

[0021] In a second aspect, a method for preparing an isolation member is provided, the method comprising: providing a coating on at least one side of an isolation membrane to obtain the isolation member; the coating comprises a metal salt, the metal salt comprises metal ions, and the reduction potential of the metal ions is higher than the reduction potential of lithium ions.

[0022] In one possible implementation, providing a coating on at least one side of the isolation membrane includes: preparing a slurry, the slurry including the metal salt; applying the slurry to at least one side of the isolation membrane; drying the slurry to form a coating layer on the isolation membrane; and rolling the isolation membrane and the coating layer to obtain the isolation member.

[0023] In a possible implementation, rolling the isolation film and the coating layer includes: rolling the isolation film and the coating layer at a pressure of 2 MPa-70 MPa; optionally, rolling the isolation film and the coating layer at a pressure of 10 MPa-35 MPa.

[0024] In a third aspect, a lithium-ion battery is provided, comprising the separator according to any possible implementation of the first aspect; and / or the separator prepared by the method according to any possible implementation of the second aspect.

[0025] In a possible implementation, the lithium-ion battery includes an electrolyte, and the electrolyte includes the metal ions.

[0026] In a possible implementation, based on the total mass of the electrolyte, the mass content b of the metal ions satisfies: 0.02%≤b≤30%; optionally, 0.03%≤b≤6%.

[0027] In a fourth aspect, an electrical device is provided, wherein the electrical device includes the lithium-ion battery in any possible implementation of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0029] FIG1 is a schematic flow chart of a method for preparing an isolation element according to the present application.

[0030] FIG2 is another schematic flow chart of a method for preparing an isolation element according to the present application.

[0031] FIG3 is a schematic diagram of a battery cell of a lithium-ion battery.

[0032] FIG4 is a schematic diagram of a battery module of a lithium-ion battery.

[0033] FIG5 is a schematic diagram of a lithium-ion battery.

[0034] FIG6 is another schematic diagram of a lithium-ion battery. DETAILED DESCRIPTION

[0035] Below, the embodiments of the separator and its preparation method, lithium-ion battery and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0036] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] In the description of this application, it should be noted that, unless otherwise specified, "plurality" means more than two; terms such as "upper," "lower," "left," "right," "inner," and "outer" indicating directions or positional relationships are merely for the purpose of facilitating the description of this application and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting this application. Furthermore, terms such as "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] Unless otherwise specified, the term "and / or" is inclusive in this application. For example, the phrase "A and / or B" means "A, B, or both A and B." More specifically, the condition "A and / or B" is satisfied if any of the following conditions are met: 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).

[0039] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0040] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0041] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0042] Where mentioned, "reduction potential" refers to the electrode potential of a substance relative to a standard hydrogen electrode. Specifically, the reduction potential is the electrode potential of a substance measured when a galvanic cell is formed between the substance and a standard hydrogen electrode.

[0043] Where referred to, "metal salt" refers to a compound consisting of a metal cation and an anion.

[0044] Next, embodiments of the present application are introduced.

[0045] In recent years, secondary batteries have been widely used in power tools, electronic products, electric vehicles, aerospace and other fields due to their high energy density and long service life, and have thus achieved great development. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. Among them, the electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which allows active ions to pass through while preventing the positive and negative electrodes from short-circuiting, so that the electrochemical reaction of the secondary battery proceeds normally.

[0046] Take lithium-ion batteries, for example. They are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and deintercalating between the positive and negative electrodes for charging and discharging, they are also called rocking-chair batteries. During the charging process, lithium ions are released from the positive electrode active material, transferred through the electrolyte to the negative electrode, and then embedded in the negative electrode active material. During the discharge process, lithium ions are released from the negative electrode active material, transferred through the electrolyte to the positive electrode, and then embedded in the positive electrode active material.

[0047] It should be understood that the "lithium insertion" and "intercalation" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the "de-lithiumization", "de-lithiumization" and "de-intercalation" processes described in this application refer to the process in which lithium ions are removed from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0048] During the cycling of lithium-ion batteries, the process of lithium ion intercalation into the negative electrode active material is hindered by factors such as battery manufacturing technology and battery aging, leading to lithium deposition on the surface of the negative electrode. The deposited lithium metal tends to form dendrites. As lithium deposition continues, the dendrites grow and, in severe cases, can pierce the solid electrolyte interface (SEI) membrane, reacting with the electrolyte and consuming the active lithium ions in the battery, causing reversible capacity degradation and shortening the battery's cycle life. Once the dendrites pierce the separator, they can also pose serious safety risks.

[0049] In view of this, an embodiment of the present application provides an isolating element and a method for preparing the same, a lithium-ion battery, and an electrical device, wherein the isolating element includes an isolating membrane provided with a coating, and the coating includes a metal salt. When the isolating element is applied to a lithium-ion battery, the metal salt can be dissolved or partially dissolved in the electrolyte, so that free metal ions are present in the electrolyte. The free metal ions can freely move to a position on the negative electrode sheet with a lower potential, that is, a position where lithium deposition is likely to occur or where lithium deposition has already occurred, and form an electrostatic shield at this position, thereby uniformizing the current density on the negative electrode sheet and suppressing lithium deposition.

[0050] First, an isolation member is provided. The isolation member includes an isolation membrane and a coating disposed on at least one side of the isolation membrane. The coating includes a metal salt. The metal salt includes metal ions. The reduction potential of the metal ions is higher than the reduction potential of lithium ions.

[0051] Specifically, when the separator is used in a lithium-ion battery, the metal salt in the coating can dissolve or partially dissolve in the electrolyte, resulting in the presence of free metal ions in the electrolyte. During the cycle of the lithium-ion battery, these metal ions can freely move to the area of ​​lower potential on the negative electrode plate, forming a localized high-concentration positive charge electrostatic field in this area, thereby forming an electrostatic shield and uniformizing the current density on the negative electrode plate.

[0052] In this embodiment, by introducing a coating including a metal salt into the isolation member, the problem of uneven current density of the electrode during the cycle of the lithium-ion battery can be effectively improved, thereby improving lithium plating, thereby reducing side reactions during the lithium-ion cycle and helping to improve the lithium-ion cycle performance and coulombic efficiency.

[0053] Typically, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The lithium-ion battery provided in this application and its various components are described below.

[0054] [Negative electrode]

[0055] The negative electrode sheet generally includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0056] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0057] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0058] In one embodiment, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0059] In one embodiment, the negative electrode active material layer further includes a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0060] In one embodiment, the negative electrode active material layer further includes a conductive agent, which can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0061] In one embodiment, the negative electrode active material layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0062] In one embodiment, the negative electrode sheet can be prepared by forming a negative electrode slurry using the aforementioned components for preparing the negative electrode sheet. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector. After drying and roller pressing, the negative electrode sheet is obtained.

[0063] [Positive electrode]

[0064] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0065] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0066] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0067] In one embodiment, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and at least one of a composite material of lithium iron manganese phosphate and carbon. The battery is accompanied by the deintercalation and consumption of Li during the charge and discharge process, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after charge and discharge cycles. In the enumeration of positive electrode active materials in this application, the molar content of O is only an ideal state value. The release of lattice oxygen will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0068] In one embodiment, the positive electrode active material layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0069] In one embodiment, the positive electrode active material layer further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In one embodiment, the positive electrode sheet can be prepared by separately forming a positive electrode slurry from the components used to prepare the positive electrode sheet. For example, the first positive electrode active material and / or the second positive electrode active material, a conductive agent, a binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated on a positive electrode current collector. After drying and rolling, the positive electrode sheet can be obtained.

[0071] [Electrolyte]

[0072] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and you can choose one based on your needs. The electrolyte includes an electrolyte salt and a solvent.

[0073] In one embodiment, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0074] In one embodiment, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0075] In one embodiment, the electrolyte may further include additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0076] [Isolator]

[0077] An embodiment of the present application provides an isolation member, which includes an isolation membrane and a coating disposed on at least one side of the isolation membrane.

[0078] The coating layer includes a metal salt, the metal salt includes metal ions, and the reduction potential of the metal ions is higher than the reduction potential of lithium ions.

[0079] Specifically, metal salts can dissolve or partially dissolve in the electrolyte, so that free metal ions exist in the electrolyte. The free metal ions can form an electrostatic shield in the area with lower potential of the negative electrode, thereby inhibiting lithium plating and improving the cycle performance and coulombic efficiency of lithium-ion batteries.

[0080] It should be understood that the present application does not particularly limit the structure and type of the isolation membrane. For example, any known porous isolation membrane with good chemical and mechanical stability may be selected. The isolation membrane may include a base membrane and a functional coating disposed on at least one side of the base membrane, such as a CCS coating or a PCS coating.

[0081] In one embodiment, the metal salt includes at least one of a sodium salt, a potassium salt, a calcium salt, a magnesium salt, and a cesium salt.

[0082] In one embodiment, the metal salt includes anions, and the anions include one or more of fluorine, phosphorus, sulfur, and nitrogen.

[0083] Specifically, after the metal salt is dissolved or partially dissolved in the electrolyte, the electrolyte also contains free anions, which may participate in the formation of the SEI film. Therefore, by selecting anions including the above elements, it is beneficial to form a uniform and dense SEI film. In the case of lithium deposition on the negative electrode, a uniform and dense SEI film helps to induce uniform deposition of lithium ions. In other words, it makes lithium deposition more uniform, thereby further inhibiting the formation or growth of lithium dendrites and improving the cycle performance and coulombic efficiency of lithium-ion batteries.

[0084] For example, the anion may be an acetate ion, a nitrate ion, a hexafluorophosphate ion, or a bis(fluorosulfonyl)imide ion.

[0085] In one embodiment, the difference between the reduction potential of the metal ion and the reduction potential of the lithium ion battery is less than or equal to 0.8V.

[0086] Specifically, by selecting metal ions with a reduction potential close to that of lithium ions, the possibility of metal ions being reduced during battery cycling can be reduced, so that there are sufficient free metal ions in the electrolyte.

[0087] In one embodiment, the solubility S of the metal salt in the electrolyte satisfies: 0.0006 g / mL≤S; optionally, 0.005 g / mL≤S≤0.06 g / mL.

[0088] Specifically, S can be 0.0006 g / mL, 0.0008 g / mL, 0.001 g / mL, 0.002 g / mL, 0.003 g / mL, 0.004 g / mL, 0.005 g / mL, 0.006 g / mL, 0.007 g / mL, 0.008 g / mL, 0.009 g / mL, 0.01 g / mL, 0.015 g / mL, 0.02 g / mL, 0.025 g / mL, 0.03 g / mL, 0.035 g / mL, 0.04 g / mL, 0.045 g / mL, 0.05 g / mL, 0.055 g / mL, 0.06 g / mL, or its value can be within the range obtained by combining any two of the above values.

[0089] It should be understood that depending on the dissolution rate of the metal salt in the electrolyte, there are two scenarios for the dissolution process. One is that the metal salt dissolves rapidly, in which case no or only a small amount of metal salt remains on the separator. The other is that the metal salt dissolves gradually, in which case some metal salt remains on the separator.

[0090] In this embodiment, controlling the solubility of the metal salt in the electrolyte within a suitable range can indirectly control the amount of metal salt remaining on the separator. Generally, metal salts help enhance the mechanical strength of the separator. Therefore, controlling the solubility of the metal salt in the electrolyte within a suitable range helps enhance the mechanical strength of the separator and reduces the risk of the separator being punctured by lithium dendrites.

[0091] In one embodiment, the powder compaction density ρ of the coating satisfies: 0.5 g / cm 3 ≤ρ≤5.0g / cm 3 ; Optionally, 1.0 g / cm 3 ≤ρ≤2.0g / cm 3 .

[0092] Specifically, ρ can be 0.5 g / cm 3 , 0.55g / cm 3 , 0.6g / cm 3 , 0.65g / cm 3 , 0.7g / cm 3 , 0.75g / cm 3 , 0.8g / cm 3 , 0.85g / cm 3 , 0.9g / cm 3 , 0.95g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3.0g / cm 3 , 3.1g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 、3.4g / cm 3 、3.5g / cm 3 、3.6g / cm 3 、3.7g / cm 3 、3.8g / cm 3 、3.9g / cm 3 , 4.0g / cm 3 , 4.1g / cm 3 , 4.2g / cm 3 , 4.3g / cm 3 , 4.4g / cm 3 , 4.5g / cm 3 , 4.6g / cm 3 , 4.7g / cm 3 , 4.8g / cm 3 , 4.9g / cm 3 , 5.0g / cm 3 , or its value is within the range obtained by combining any two of the above values.

[0093] A coating with too low a powder compaction density, ρ, is not conducive to coating formation; a coating with too high a powder compaction density, ρ, is not conducive to sufficient contact between the coating and the electrolyte, thereby dissolving. Furthermore, a higher powder compaction density facilitates the gradual dissolution of the metal salt, leaving some metal salt remaining on the separator, thereby improving the mechanical strength of the separator. Therefore, in this embodiment, controlling the coating powder compaction density, ρ, within an appropriate range facilitates the coating's formation on the separator while also improving the mechanical strength of the separator.

[0094] In one embodiment, the thickness d of the coating satisfies: 0.01 μm≤d≤200 μm; optionally, 0.5 μm≤d≤50 μm.

[0095] Specifically, d can be 0.01μm, 0.02μm, 0.05μm, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0. 7μm, 0.8μm, 0.9μm, 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm , 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, or its value is within the range obtained by combining any two of the above values.

[0096] It should be understood that the thickness d of the coating is affected by factors such as the powder compaction density ρ and the amount of metal salt added. Under the same conditions, the thickness d of the coating is inversely proportional to the powder compaction density ρ of the coating. The greater the powder compaction density ρ of the coating, the smaller the thickness d of the coating. When the powder compaction density ρ is constant, the thicker the coating thickness d, the higher the metal salt content on the separator. Therefore, by controlling the thickness d of the coating, the metal salt content on the separator can also be indirectly controlled, thereby affecting the amount of metal salt dissolved in the electrolyte and the amount of metal salt remaining on the separator.

[0097] In one embodiment, the isolation film includes at least one of a polyolefin film, a polyester film, a cellulose film, a polyimide film, a polyamide film, a spandex film, and an aramid film.

[0098] In another embodiment, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0099] In one embodiment, the isolation film can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0100] In one embodiment, based on the total mass of the coating, the mass content a of the metal salt satisfies: 10%≤a≤90%; alternatively, 40%≤a≤90%.

[0101] Specifically, a can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or its value is within the range obtained by combining any two of the above values.

[0102] On the one hand, metal salts do not participate in the electrochemical reactions of charge and discharge in lithium-ion batteries. Excessive metal salt content increases the mass of the lithium-ion battery but does not contribute to its capacity, significantly impacting its energy density. On the other hand, excessively low metal salt content limits the number of free metal ions in the electrolyte, limiting its inhibitory effect on lithium deposition.

[0103] In this embodiment, by controlling the mass content a of the metal salt within a suitable range, lithium precipitation is effectively suppressed while also helping to reduce the impact of the metal salt on the energy density of the lithium-ion battery.

[0104] [Preparation method]

[0105] Next, the preparation method of the isolation member in the aforementioned embodiment is introduced.

[0106] The present application also provides a method for preparing an isolator. Figure 1 is a schematic flow chart of the method for preparing an isolator.

[0107] As shown in FIG1 , the method 100 includes:

[0108] S101, providing a coating on at least one side of the isolation film to obtain an isolation member.

[0109] The coating layer includes a metal salt, the metal salt includes metal ions, and the reduction potential of the metal ions is higher than the reduction potential of lithium ions.

[0110] FIG2 is another schematic flow chart of a method for preparing a separator.

[0111] Optionally, as shown in FIG2 , in S101 , providing a coating on at least one side of the isolation film includes:

[0112] S1011, preparing a slurry, the slurry including a metal salt.

[0113] S1012, coating the slurry on at least one side of the isolation film.

[0114] S1013, drying the slurry to form a coating layer on the isolation film.

[0115] S1014, rolling the separator and the coating layer to obtain a separator.

[0116] Optionally, in S1014 , rolling the isolation film and the coating layer includes: rolling the isolation film and the coating layer at a pressure of 2 MPa-70 MPa.

[0117] Optionally, in S1014 , rolling the isolation film and the coating layer includes: rolling the isolation film and the coating layer at a pressure of 10 MPa-35 MPa.

[0118] It should be understood that the rolling process can be a single rolling process or multiple rolling processes, which is not limited in this application. The rolling process can be a cold pressing process or a hot pressing process, which is not limited in this application.

[0119] The rolling pressure can be 2MPa, 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa, 15MPa, 20MPa, 25MPa, 30MPa, 35MPa, 40MPa, 45MPa, 50MPa, 55MPa, 60MPa, 65MPa, 70MPa, or its value is within the range obtained by combining any two of the above values.

[0120] Based on a similar principle, the separator prepared by method 100 can allow free metal ions to be contained in the electrolyte when applied to a lithium-ion battery, thereby achieving the corresponding technical effects of the aforementioned separator, which will not be elaborated here.

[0121] The present application also provides a lithium-ion battery, comprising the separator of any of the aforementioned embodiments and / or the separator prepared by the preparation method 100 of any of the aforementioned embodiments. Based on similar principles, the lithium-ion battery comprising the separator of the aforementioned embodiments can achieve corresponding technical effects, which will not be further described here.

[0122] In one embodiment, a lithium-ion battery includes an electrolyte comprising metal ions.

[0123] In one embodiment, based on the total mass of the electrolyte, the mass content b of the metal ions satisfies: 0.02%≤b≤30%; optionally, 0.03%≤b≤6%.

[0124] Specifically, b can be 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or its value is within the range obtained by combining any two of the above values.

[0125] In one embodiment, the negative electrode sheet, the positive electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0126] In one embodiment, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0127] In one embodiment, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0128] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG3 shows a battery cell 300 having a square structure as an example.

[0129] It should be understood that the battery cell 300 may include the lithium-ion battery in the aforementioned embodiment.

[0130] Figure 4 shows an example battery module 400. Referring to Figure 4 , in the battery module 400, multiple battery cells 300 may be arranged sequentially along the length of the battery module 400. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 300 may be secured by fasteners. The multiple battery cells 300 may be of the same chemical system or of different chemical systems.

[0131] Optionally, in one embodiment, the battery module 400 may further include a housing having an accommodation space, and the plurality of battery cells 300 may be accommodated in the accommodation space.

[0132] Optionally, in one embodiment, the battery modules 400 may be assembled into a battery. The battery may contain one or more battery modules 400. The specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0133] Figures 5 and 6 illustrate an example battery 500. Referring to Figures 5 and 6, the battery 500 may include a battery box and multiple battery modules 400 disposed within the box. The battery box includes an upper case 501 and a lower case 502. The upper case 501 can be placed over the lower case 502 to form an enclosed space for accommodating the battery modules 400. The multiple battery modules 400 can be arranged in any manner within the battery box.

[0134] It should be understood that in other embodiments, the battery 500 is also referred to as a battery pack. The battery cells 300 may first be assembled into the battery module 400, and the battery 500 may be assembled from the battery module 400. Alternatively, the battery 500 may be assembled directly from the battery cells 300, omitting the intermediate battery module 400.

[0135] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0136] In another embodiment, an electrical device includes at least one of the battery cell 300, battery module 400, or battery 500 provided herein. The battery cell 300, battery module 400, or battery 500 can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, 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, satellites, energy storage systems, etc.

[0137] As an electric device, a battery cell 300 , a battery module 400 , or a battery 500 may be selected according to its usage requirements.

[0138] As an example of an electric device, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0139] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0140] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0141] [Examples 1-25 and Comparative Examples 1-2]

[0142] Example 1

[0143] (1) Preparation of negative electrode sheet

[0144] Dissolve 1 kg of artificial graphite (the negative electrode active material), 10 g of acetylene black (the conductive agent), 30 g of styrene-butadiene rubber (SBR) (the binder), and 20 g of sodium carboxymethyl cellulose (CMC) (the thickener) in 1 kg of deionized water and mix thoroughly to create a negative electrode slurry. The slurry is then evenly coated onto the negative electrode current collector copper foil. The negative electrode sheets are then rolled and slit.

[0145] (2) Preparation of positive electrode sheet

[0146] 1 kg of the positive electrode active material LiNi5Co2Mn3O2, 20 g of the conductive carbon nanotubes, and 20 g of the binder polyvinylidene fluoride (PVDF) were dissolved in 1 kg of N-methylpyrrolidone and mixed thoroughly to create a positive electrode slurry. The slurry was then evenly coated onto the positive electrode current collector aluminum foil. The positive electrode sheets were then rolled and slit.

[0147] (3) Preparation of spacers

[0148] 1 kg of metal salt potassium nitrate and 20 g of binder polyvinylidene fluoride (PVDF) were dissolved in 1 kg of N-methylpyrrolidone, and the mixture was evenly mixed to obtain a slurry including the metal salt. The slurry was evenly coated on one side of the polyethylene isolation film, dried in an oven at 80°C, and then rolled at a pressure of 2 MPa to obtain an isolation member.

[0149] (4) Preparation of lithium-ion batteries

[0150] The positive electrode sheet, negative electrode sheet, separator and negative electrode sheet are stacked in order so that the separator is between the positive electrode sheet and the negative electrode sheet and can isolate the positive electrode sheet and the negative electrode sheet; then the stacked components are wound and placed in a shell, and after drying, lithium hexafluorophosphate (LiPF6) electrolyte with a concentration of 1 mol / L is injected, and a lithium-ion battery is obtained after packaging.

[0151] In the separator of Example 1, the metal salt is potassium nitrate, and the metal ion is potassium ion K + , the solubility of the metal salt in the electrolyte S = 0.032 g / mL, the powder compaction density of the coating ρ = 1.65 g / cm 3 The thickness of the coating layer is d = 2 μm, the mass content of the metal salt in the separator is a = 30%. In the lithium-ion battery of Example 1, the mass content of the metal salt in the electrolyte is b = 2.7%.

[0152] In order to verify the inhibitory effect of the separator on lithium plating, the CB value of the lithium-ion battery can be designed to be less than 1.

[0153] Example 2

[0154] Compared with Example 1, in Example 2, the metal salt is magnesium nitrate, the metal ion is magnesium ion, S=0.054 g / mL, and b=4.7%.

[0155] Example 3

[0156] Compared with Example 1, in the separator of Example 3, the metal salts are potassium nitrate and magnesium nitrate, the metal ions are potassium ions and magnesium ions, S=0.047 g / mL, and b=1.8% and 4.2%.

[0157] Example 4

[0158] Compared with Example 1, in Example 4, the metal salt is potassium hexafluorophosphate, S=0.035 g / mL, and b=2.9%.

[0159] Example 5

[0160] Compared with Example 1, in Example 5, the metal salt is barium sulfate, the metal ion is barium ion, S=0.0006 g / mL, and b=0.02%.

[0161] Example 6

[0162] Compared with Example 1, in Example 6, the metal salt is calcium sulfate, the metal ion is calcium ion, S=0.005 g / mL, and b=0.41%.

[0163] Example 7

[0164] Compared with Example 1, in Example 7, the metal salt is sodium nitrate, the metal ion is sodium ion, S=0.06 g / mL, and b=5%.

[0165] Example 8

[0166] Compared with Example 1, in Example 8, during the rolling process of the separator, the pressure was 0.6 MPa, ρ = 0.5 g / cm 3 , d=6.5μm, b=2.73%.

[0167] Example 9

[0168] Compared with Example 1, in Example 9, during the rolling process of the separator, the pressure was 1.3 MPa, ρ = 1 g / cm 3 , d=3.3μm, b=2.72%.

[0169] Example 10

[0170] Compared with Example 1, in Example 10, during the rolling process of the separator, the pressure was 2.4 MPa, ρ = 2 g / cm 3 , d=1.6μm, b=2.68%.

[0171] Example 11

[0172] Compared with Example 1, in Example 11, during the rolling process of the separator, the pressure was 6.0 MPa, ρ = 5 g / cm 3 , d=0.7μm, b=2.65%.

[0173] Example 12

[0174] Compared with Example 1, in Example 12, during the rolling process of the separator, the pressure was 30.0 MPa, ρ = 6.5 g / cm 3 , d=0.54μm, b=2.63%.

[0175] Example 13

[0176] Compared with Example 1, in Example 13, during the rolling process of the separator, the pressure was 70.0 MPa, ρ = 7.8 g / cm 3 , d=0.45μm, b=2.55%.

[0177] Example 14

[0178] Compared with Example 1, in Example 14, during the rolling process of the separator, the pressure was 10.0 MPa, ρ = 5.4 g / cm 3 , d=0.65μm, b=2.66%.

[0179] Example 15

[0180] Compared with Example 1, in Example 15, during the rolling process of the separator, the pressure was 35.0 MPa, ρ = 6.7 g / cm 3 , d=0.52μm, b=2.62%.

[0181] Example 16

[0182] Compared with Example 1, in Example 16, d=0.1 μm, a=1.5%, and b=0.14%.

[0183] Example 17

[0184] Compared with Example 1, in Example 17, d=200 μm, a=99.9%, and b=2.7%.

[0185] Example 18

[0186] Compared with Example 1, in Example 18, d=50 μm, a=96.2%, and b=2.7%.

[0187] Example 19

[0188] Compared with Example 1, in Example 19, d=0.66 μm, a=10%, and b=0.87%.

[0189] Example 20

[0190] Compared with Example 1, in Example 20, d=2.2 μm, a=40%, and b=2.7%.

[0191] Example 21

[0192] Compared with Example 1, in Example 21, d=4.95 μm, a=90%, and b=2.7%.

[0193] Example 22

[0194] Compared with Example 1, in Example 22, d=0.02 μm, a=0.25%, and b=0.02%.

[0195] Example 23

[0196] Compared with Example 1, in Example 23, d=2.0 μm, a=0.35%, and b=0.03%.

[0197] Example 24

[0198] Compared with Example 1, in Example 24, the metal salt is sodium hexafluorophosphate, the metal ion is sodium ion, S=0.07 g / mL, d=3.0 μm, a=30%, and b=6%.

[0199] Example 25

[0200] Compared with Example 1, in Example 25, the metal salt is bis(sulfonyl)imide, the metal ion is sodium ion, S=0.4 g / mL, a=50%, and b=30%.

[0201] Comparative Example 1

[0202] Compared with Example 1, Comparative Example 1 directly uses the isolation film in Example 1 as the isolation member.

[0203] Comparative Example 2

[0204] Compared with Example 1, the preparation process of the separator of Comparative Example 2 is as follows:

[0205] 20g of polyvinylidene fluoride (PVDF) was dissolved in 50g of N-methylpyrrolidone and mixed thoroughly to obtain a slurry containing polyvinylidene fluoride. The slurry was evenly coated on one side of a polyethylene separator, dried in an 80°C oven, and then roller-pressed at a pressure of 2MPa to obtain a separator. In other words, the separator of Comparative Example 2 included a coating layer, but the coating layer did not contain a metal salt.

[0206] The product parameters of Examples 1-25 and Comparative Examples 1-2 are detailed in Table 1.

[0207] Table 1: Product parameters of Examples 1-25 and Comparative Examples 1-2

[0208] In Table 1, "S" represents the solubility of the metal salt in the electrolyte; "ρ" represents the powder compaction density of the coating; "d" represents the thickness of the coating; "a" represents the mass content of the metal salt in the coating based on the total mass of the coating; "b" represents the mass content of the metal ion in the electrolyte based on the total mass of the electrolyte; and "rolling pressure" represents the pressure applied to the separator and coating when rolling them.

[0209] The product performance tests of Examples 1-25 and Comparative Examples 1-2 are detailed in Table 2.

[0210] Table 2: Product performance parameters of Examples 1-25 and Comparative Examples 1-2

[0211] In Table 2, "Number of Cycles" indicates the number of cycles the lithium-ion battery has cycled to when its SOH is less than or equal to 80%. "Average Coulombic Efficiency" indicates the average value of the ratio of discharge capacity to charge capacity during the battery cycle. "Presence of Lithium Dendrites" indicates whether obvious dendritic lithium deposition occurs on the negative electrode sheet obtained by disassembling the lithium-ion battery after the battery cycle is completed.

[0212] According to the comparative analysis of the above-mentioned embodiments and comparative examples, it can be seen that the number of cycles and average coulombic efficiency of the embodiments are both better than those of the comparative examples. In addition, no lithium dendrites were found in the lithium-ion batteries of the embodiments after cycling, while lithium dendrites were found in the lithium-ion batteries of the comparative examples. Therefore, it is shown that by introducing the separator provided by the present application into the lithium-ion battery, lithium precipitation and the growth of lithium dendrites can be effectively suppressed, thereby helping to improve the cycling performance and coulombic efficiency of the lithium-ion battery.

[0213] Through comparative analysis of Examples 1-4, it can be seen that providing metal salts containing multiple metal ions with reduction potentials close to that of lithium ions in the separator can effectively inhibit lithium precipitation and improve the cycle performance and coulombic efficiency of lithium-ion batteries.

[0214] Through comparative analysis of Example 1 and Examples 5-7, it can be seen that for metal salts with low solubility, such as the metal salts in Examples 5 and 6, the amount of metal salt can be increased by increasing the coating thickness or the powder compaction density to achieve the inhibitory effect on lithium precipitation and lithium dendrites. In addition, for metal salts with low solubility, the amount remaining on the separator will be higher than that of metal salts with high solubility. Therefore, by selecting metal salts with solubility within the appropriate range, it is possible to achieve the inhibition of lithium precipitation and lithium dendrites while helping to improve the mechanical strength of the separator.

[0215] On the one hand, the thickness of the coating, the powder compaction density and the pressure of the roller-pressed coating and the isolation membrane are related. Under the same other conditions, the greater the roller pressure, the smaller the thickness of the coating and the greater the powder compaction density. On the other hand, when the powder compaction density is large, the dissolution rate of the metal salt in the electrolyte will decrease, and thus, the mass content of the metal ions in the electrolyte will be affected by the powder compaction density. Therefore, by adjusting the roller pressure, coatings with different powder compaction densities and different thicknesses in Example 1 and Examples 8-15 can be obtained. Through the comparative analysis of Example 1 and Examples 8-15, it can be seen that by controlling the powder compaction density and roller pressure of the coating within an appropriate range, effective inhibition of lithium precipitation and lithium dendrite growth can be achieved, thereby improving the cycle performance and coulombic efficiency of lithium-ion batteries.

[0216] Under the same other conditions, as the thickness of the coating increases, the mass content of the metal salt in the separator will increase. Through the comparative analysis of Example 1 and Examples 16-18, it can be seen that in Example 16, the thickness of the coating is smaller and the content of metal salt on the separator is lower. In order to achieve effective inhibition of lithium precipitation and lithium dendrite growth, the powder compaction density of the coating can be increased by increasing the rolling pressure, so that more metal salt is loaded on the separator. Thus, by controlling the thickness of the coating on the separator within a suitable range, the mass content of the metal salt loaded on the separator can be controlled, thereby achieving effective inhibition of lithium precipitation and lithium dendrite growth and improving the cycle performance of the lithium-ion battery.

[0217] Through the comparative analysis of Examples 1 and 19-21, it can be seen that, under the same other conditions, the thicker the coating thickness, the higher the mass content of the metal salt in the separator. On the one hand, the number of cycles of the lithium-ion battery increases with the increase of the mass content of the metal salt; on the other hand, the metal salt does not participate in the charge and discharge reaction of the lithium-ion battery and therefore does not contribute to the capacity. Therefore, by controlling the mass content of the metal salt within a suitable range, while achieving effective inhibition of lithium precipitation and lithium dendrite growth, it helps to reduce the impact of the metal salt on the energy density of the lithium-ion battery.

[0218] Generally speaking, separators with different metal salt mass contents can be selected according to different types of lithium-ion batteries, for example, lithium-ion batteries with different energy densities. For example, lithium-ion batteries with higher energy densities are configured with separators with higher metal salt mass contents.

[0219] It should be understood that in the lithium-ion battery after cycling, the free metal ions are gradually consumed in the process of suppressing lithium precipitation. For example, the lithium that is partially precipitated is reduced to a metal element, or is reduced to a metal element and then forms an alloy with lithium. Therefore, after the lithium-ion battery is cycled, the mass content of the metal ions in the electrolyte is affected by multiple factors such as the mass content of the metal salt in the separator (before cycling) and the number of cycles. For the lithium-ion battery after cycling, the mass content of the metal ions in the electrolyte is too high, indicating that the metal ions are consumed less, and its inhibitory effect on lithium precipitation and lithium dendrite growth is limited. The mass content of the metal ions in the electrolyte is too low, indicating that the metal ions are basically all consumed. It may be that the load of the metal salt on the separator does not match the lithium-ion battery, and the effect on lithium precipitation and lithium dendrite growth is also limited. Therefore, by comparing and analyzing Examples 1 and 22-25, it can be seen that by controlling the mass content of the metal ions in the electrolyte within a suitable range, it can help to improve the inhibitory effect of the separator on lithium precipitation and lithium dendrite growth.

[0220] The following is a brief introduction to the test methods for the physical and chemical parameters and performance parameters involved in the embodiments of this application. It should be understood that the following test methods are only examples, and other test methods known in the art can also be used for testing.

[0221] 1. Test method of reduction potential

[0222] The substance to be tested is dissolved in an appropriate solvent, and then a cell is formed using a reference electrode (such as a standard hydrogen electrode) and a working electrode (such as a glassy carbon electrode). The cyclic voltammetry curve is tested under different conditions (such as pH value, temperature, etc.), and the reduction peak potential of the substance to be tested is read to obtain the reduction potential of the substance to be tested.

[0223] 2. Test method for the solubility of metal salts in electrolyte

[0224] Dissolve a metal salt in 100 mL of 1 mol / L lithium hexafluorophosphate electrolyte until crystals form. Calculate the total amount of metal salt added (m) and measure the total volume of the solution (V). The solubility (S) can be calculated using the following formula: S = m / V.

[0225] 3. Test method for powder compaction density

[0226] Cut the roller-pressed spacer and weigh it (m1). Measure its thickness as h1 and its area as P. Wash off the powder coating and reweigh it (m2) and measure its thickness (h2). The compacted density is: (m1 - m2) / (P × (h1 - h2)).

[0227] 4. Test method for mass content

[0228] Disassemble the lithium-ion battery, weigh the total mass of the separator (m3), scrape the coating off the separator surface, and use ICP testing to determine the mass of metal salt in the coating (m4) and the mass of metal salt in the electrolyte (m5). Weigh the remaining separator (m6). Based on the total mass of the coating, the metal salt mass content (a) is (m4 + m5) / (m3 + m5 - m6).

[0229] 5. Test method for the number of cycles of lithium-ion batteries

[0230] After formation, the lithium-ion battery is fully charged and discharged at a current of 0.33C, and the number of cycles of the battery is counted when the battery SOH reaches 80%.

[0231] 6. Test method for average coulombic efficiency of lithium-ion batteries

[0232] The discharge capacity of each cycle of the lithium-ion battery charge and discharge process is divided by the charge capacity to obtain the coulombic efficiency of each cycle. The coulombic efficiency of each cycle is then added up and divided by the number of cycles to obtain the average coulombic efficiency.

[0233] 7. Test method for the presence of lithium dendrites

[0234] The cycled lithium-ion battery is disassembled to obtain the cycled negative electrode sheet, and whether lithium dendrites appear on the negative electrode sheet can be directly observed.

[0235] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A spacer, characterized in that: The isolating element comprises: An isolation membrane and a coating disposed on at least one side of the isolation membrane; The coating layer includes a metal salt including metal ions having a reduction potential higher than a reduction potential of lithium ions.

2. The isolating element according to claim 1, characterized in that: The difference between the reduction potential of the metal ions and the reduction potential of the lithium ions is less than or equal to 0.8V.

3. The isolating element according to claim 1 or 2, characterized in that: The metal salt includes at least one of sodium salt, potassium salt, calcium salt, magnesium salt and cesium salt.

4. The isolating element according to any one of claims 1 to 3, characterized in that: The metal salt includes anions, and the anions include one or more of fluorine, phosphorus, sulfur, and nitrogen.

5. The isolating element according to any one of claims 1 to 4, characterized in that: The solubility S of the metal salt in the electrolyte satisfies: 0.0006 g / mL≤S; optionally, 0.005 g / mL≤S≤0.06 g / mL.

6. The isolating element according to any one of claims 1 to 5, characterized in that: The powder compaction density ρ of the coating satisfies: 0.5 g / cm 3 ≤ρ≤5.0g / cm 3 ; Optionally, 1.0 g / cm 3 ≤ρ≤2.0g / cm 3 .

7. The isolating element according to any one of claims 1 to 6, characterized in that: The thickness d of the coating satisfies: 0.1 μm≤d≤200 μm, optionally, 0.5 μm≤d≤50 μm.

8. The isolating element according to any one of claims 1 to 7, characterized in that: The isolation film includes at least one of a polyolefin film, a polyester film, a cellulose film, a polyimide film, a polyamide film, a spandex film, and an aramid film.

9. The isolating element according to any one of claims 1 to 8, characterized in that: Based on the total mass of the coating, the mass content a of the metal salt satisfies: 10%≤a≤90%; optionally, 40%≤a≤90%.

10. A method for preparing a spacer, characterized in that: The method comprises: Disposing a coating on at least one side of the isolation film to obtain the isolation member; The coating layer includes a metal salt including metal ions having a redox potential lower than that of lithium ions.

11. The method according to claim 10, characterized in that The provision of a coating on at least one side of the isolation film comprises: preparing a slurry, the slurry comprising the metal salt; Applying the slurry on at least one side of the isolation film; Drying the slurry to form a coating layer on the isolation film; The separator is obtained by rolling the separator film and the coating layer.

12. The method according to claim 11, characterized in that The rolling of the isolation film and the coating layer comprises: Rolling the isolation film and the coating layer at a pressure of 2MPa-70MPa; Optionally, the isolation film and the coating layer are rolled at a pressure of 10 MPa-35 MPa.

13. A lithium ion battery, characterized in that: The lithium-ion battery comprises an isolation member as described in any one of claims 1 to 9; and / or an isolation member prepared by the method as described in any one of claims 10 to 12.

14. The lithium ion battery according to claim 13, characterized in that: The lithium ion battery includes an electrolyte, and the electrolyte includes the metal ions.

15. The lithium ion battery according to claim 14, characterized in that: Based on the total mass of the electrolyte, the mass content b of the metal ions satisfies: 0.02%≤b≤30%; optionally, 0.03%≤b≤6%.

16. An electrical device, characterized in that: The electrical device comprises a lithium-ion battery as claimed in any one of claims 13 to 15.

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