Separator and preparation method thereof, lithium ion battery and power utilization device

Abstract

The embodiment of the invention discloses a separator and a preparation method thereof, a lithium ion battery and an electric device. The separator comprises an isolating membrane and a coating arranged on at least one side of the isolating membrane, the coating comprises a metal salt, the metal salt comprises metal ions, and the reduction potential of the metal ions is higher than that of the lithium ions. The separator is applied to the lithium ion battery, can effectively inhibit lithium precipitation, and helps to improve the cycle performance of the lithium ion battery.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to an isolating element and a preparation method thereof, a lithium-ion battery and an electrical device. Background Art

[0002] 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 power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and have thus achieved great development.

[0003] During the cycle of lithium-ion batteries, as the internal resistance of the battery increases and the current density of the electrode is uneven, it is easy to cause lithium deposition on the negative electrode. In severe cases, it leads to the growth of lithium dendrites, threatening the reversible capacity and cycle life of lithium-ion batteries. Therefore, how to improve lithium deposition in lithium-ion batteries has become a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above-mentioned technical problems, and its purpose is to provide an isolation member and a preparation method thereof, a lithium-ion battery and an electrical device. The isolation member is applied to a lithium-ion battery to effectively inhibit lithium plating and help improve the cycle performance of the lithium-ion battery.

[0005] In a first aspect, an isolation member is provided, the isolation member 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.

[0006] 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 sheet of the lithium-ion battery, the potential at the lithium deposition position is relatively low. The free metal ions in the electrolyte can freely move to the position with lower potential on the negative electrode sheet, forming a local positive charge electrostatic field, thereby uniformizing the current density on the negative electrode sheet 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.

[0007] 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.

[0008] 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.

[0009] In a possible implementation, the metal salt includes anions, and the anions include one or more of fluorine, phosphorus, sulfur, and nitrogen.

[0010] 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.

[0011] 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 isolation member can be controlled, thereby helping to improve the mechanical strength of the isolation member.

[0012] 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 .

[0013] In a possible implementation, the thickness d of the coating satisfies: 0.01 μm≤d≤200 μm; optionally, 0.5 μm≤d≤50 μm.

[0014] 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 element can also be controlled, thereby helping to improve the mechanical strength of the isolation element.

[0015] In a possible implementation manner, 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.

[0016] 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%.

[0017] In the embodiments of the present application, by controlling the content of metal salt on the isolation member 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 lithium-ion batteries and helping to improve the cycle performance and coulombic efficiency of lithium-ion batteries.

[0018] In a second aspect, a method for preparing an isolation element is provided, the method comprising: providing a coating on at least one side of an isolation membrane to obtain the isolation element; 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.

[0019] 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.

[0020] In a possible implementation, the rolling of the isolation film and the coating layer includes: rolling the isolation film and the coating layer at a pressure of 2MPa-70MPa; optionally, rolling the isolation film and the coating layer at a pressure of 10MPa-35MPa.

[0021] In a third aspect, a lithium-ion battery is provided, wherein the lithium-ion battery comprises the separator in any possible implementation of the first aspect; and / or the separator prepared by the method in any possible implementation of the second aspect.

[0022] In a possible implementation, the lithium-ion battery includes an electrolyte, and the electrolyte includes the metal ions.

[0023] 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%.

[0024] In a fourth aspect, an electrical device is provided, wherein the electrical device comprises a lithium-ion battery according to any possible implementation of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. 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 paying creative work.

[0026] Figure 1 The present invention is a schematic flow chart of a method for preparing an isolating element.

[0027] Figure 2 Another schematic flow chart of a method for preparing an isolation element according to the present application.

[0028] Figure 3 A schematic diagram of a battery cell of a lithium-ion battery.

[0029] Figure 4 A schematic diagram of a battery module for a lithium-ion battery.

[0030] Figure 5A schematic diagram of a lithium-ion battery.

[0031] Figure 6 Another schematic diagram of a lithium-ion battery. DETAILED DESCRIPTION

[0032] Hereinafter, 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 structures 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 descriptions 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.

[0033] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a 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 a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present 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 real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0035] If not specifically stated, in this application, the term "and / or" is inclusive. For example, the phrase "A and / or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A and / or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0036] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means 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.

[0037] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0038] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0039] 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 by placing the substance in a galvanic cell with a standard hydrogen electrode.

[0040] Where referred to, "metal salt" refers to a compound consisting of a metal cation and an anion.

[0041] Next, embodiments of the present application are introduced.

[0042] 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 achieved great development. Usually, 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 a role in 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.

[0043] Take lithium-ion batteries as an example. Lithium-ion batteries are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and disintercalating between the positive and negative electrodes for charging and discharging, lithium-ion batteries are also called rocking-chair batteries. During the charging process of lithium-ion batteries, lithium ions are released from the positive electrode active material, move to the negative electrode through the conduction of the electrolyte and embed into the negative electrode active material; and during the discharge process, lithium ions are released from the negative electrode active material, move to the positive electrode through the conduction of the electrolyte and embed into the positive electrode active material.

[0044] It should be understood that the "lithium insertion" and "embedding" 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 "extraction", "delithium" and "extraction" processes described in this application refer to the process in which lithium ions are extracted from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0045] During the cycle of lithium-ion batteries, the process of lithium ion embedding into the negative electrode active material is hindered by factors such as battery preparation technology and battery aging, and lithium deposition will occur on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode tends to be in the form of dendrites. As lithium deposition continues, the lithium dendrites grow, and in severe cases, they pierce the SEI (solid electrolyte interface) membrane, react with the electrolyte, consume the active lithium ions in the battery, and cause the reversible capacity of the battery to decay and the cycle life to decrease. Once the lithium dendrites pierce the separator, it will also cause serious safety problems.

[0046] In view of this, the embodiments of the present application provide a separator and a preparation method thereof, a lithium-ion battery and an electrical device, wherein the separator includes a separator provided with a coating, and the coating includes a metal salt. When the separator is applied to a lithium-ion battery, the metal salt can be dissolved or partially dissolved in the electrolyte, so that free metal ions exist in the electrolyte. The free metal ions can move freely to a position with a lower potential on the negative electrode plate, that is, a position where lithium deposition is likely to occur or has already occurred, and an electrostatic shield is formed at this position, thereby uniformizing the current density on the negative electrode plate and suppressing lithium deposition.

[0047] 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.

[0048] Specifically, when the separator is used in a lithium-ion battery, the metal salt in the coating can be dissolved or partially dissolved in the electrolyte, so that free metal ions exist in the electrolyte. During the cycle of the lithium-ion battery, these metal ions can move freely to the area with lower potential on the negative electrode plate, forming a local high-concentration positive charge electrostatic field in this area, thereby forming an electrostatic shield and uniformizing the current density on the negative electrode plate.

[0049] In this embodiment, by introducing a coating including a metal salt into the isolation element, the problem of uneven current density of the electrode during the cycle of the lithium-ion battery can be effectively improved, thereby improving lithium precipitation, thereby reducing side reactions during the lithium-ion cycle and helping to improve the lithium-ion cycle performance and coulombic efficiency.

[0050] Generally, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. Next, the lithium-ion battery provided in the present application and various parts of the lithium-ion battery are introduced.

[0051] [Negative electrode]

[0052] 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.

[0053] 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 any one or both of the two facing surfaces of the negative electrode current collector.

[0054] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0055] In one embodiment, the negative electrode active material may adopt the negative electrode active material for batteries 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 oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. 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.

[0056] 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).

[0057] In one embodiment, the negative electrode active material layer further includes a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0058] In one embodiment, the negative electrode active material layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0059] In one embodiment, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet are formed into a negative electrode slurry. For example, the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a negative electrode slurry. Then, the negative electrode slurry is coated on the negative electrode current collector, and after drying, rolling and other processes, the negative electrode sheet can be obtained.

[0060] [Positive electrode]

[0061] 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.

[0062] 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 disposed on any one or both of the two facing surfaces of the positive electrode current collector.

[0063] 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 and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0064] In one embodiment, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, 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. Among them, 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 0.2 Mn 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 0.05O2) 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 charging and discharging 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.

[0065] 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), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0066] 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.

[0067] In one embodiment, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet are respectively formed into positive electrode slurries. For example, the first positive electrode active material and / or the second positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry. Then, the positive electrode slurry is coated on the positive electrode current collector, and after drying, rolling and other processes, the positive electrode sheet can be obtained.

[0068] [Electrolyte]

[0069] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. The electrolyte includes electrolyte salt and solvent.

[0070] In one embodiment, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0071] 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, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0072] 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 performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, etc.

[0073] [Isolator]

[0074] 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.

[0075] 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.

[0076] Specifically, metal salts can be dissolved or partially dissolved 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 precipitation and improving the cycle performance and coulombic efficiency of lithium-ion batteries.

[0077] It should be understood that the present application has no particular restrictions on the structure and type of the isolation membrane. For example, any known porous structure isolation membrane with good chemical stability and mechanical stability can 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.

[0078] 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.

[0079] In one embodiment, the metal salt includes anions, and the anions include one or more of fluorine, phosphorus, sulfur, and nitrogen.

[0080] Specifically, after the metal salt is dissolved or partially dissolved in the electrolyte, the electrolyte also includes 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 coulomb efficiency of lithium-ion batteries.

[0081] For example, the anion may be an acetate ion, a nitrate ion, a hexafluorophosphate ion, or a bis(fluorosulfonyl)imide ion.

[0082] 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.

[0083] Specifically, by selecting metal ions whose reduction potential is close to that of lithium ions, the possibility of metal ions being reduced during the battery cycle can be reduced, so that there are sufficient free metal ions in the electrolyte.

[0084] 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.

[0085] 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.

[0086] It should be understood that there are two situations in the dissolution process of the metal salt according to the different dissolution speeds of the metal salt in the electrolyte. One is that the metal salt can dissolve quickly, in which case no metal salt remains on the isolation membrane or only a small amount of metal salt remains. The other is that the metal salt gradually dissolves, in which case some metal salt remains on the isolation membrane.

[0087] In this embodiment, the solubility of the metal salt in the electrolyte is controlled within a suitable range, which can indirectly control the amount of metal salt remaining on the separator. Generally, the metal salt helps to enhance the mechanical strength of the separator. Therefore, by controlling the solubility of the metal salt in the electrolyte within a suitable range, it helps to enhance the mechanical strength of the separator and reduce the risk of the separator being punctured by lithium dendrites.

[0088] 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 .

[0089] 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 / cm 3 , 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.

[0090] If the powder compaction density ρ of the coating is too small, it is not conducive to the molding of the coating; if the powder compaction density ρ of the coating is too large, it is not conducive to the coating to fully contact with the electrolyte and dissolve. In addition, a higher powder compaction density is conducive to the gradual dissolution of the metal salt, so that part of the metal salt remains on the isolation membrane to improve the mechanical strength of the isolation member. Therefore, in this embodiment, by controlling the powder compaction density ρ of the coating within a suitable range, it is helpful to not only help the coating to be molded on the isolation membrane, but also to improve the mechanical strength of the isolation member.

[0091] In one embodiment, the thickness d of the coating satisfies: 0.01 μm≤d≤200 μm; optionally, 0.5 μm≤d≤50 μm.

[0092] 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.

[0093] 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 other 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 thickness d of the coating, the higher the content of metal salt on the separator. Therefore, by controlling the thickness d of the coating, the content of metal salt 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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%.

[0098] 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.

[0099] On the one hand, metal salts do not participate in the electrochemical reaction of charging and discharging in lithium-ion batteries. If the mass content of metal salts is too high, the mass of lithium-ion batteries will increase but not contribute to the capacity, which will have a greater impact on the energy density of lithium-ion batteries. On the other hand, if the mass content of metal salts is too low, the number of free metal ions in the electrolyte is limited, which has limited inhibitory effect on lithium precipitation.

[0100] 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 effect of the metal salt on the energy density of the lithium-ion battery.

[0101] [Preparation method]

[0102] Next, the preparation method of the isolation element in the aforementioned embodiment is introduced.

[0103] The present application also provides a method for preparing an isolation element. Figure 1 A schematic flow chart of a method for preparing a separator.

[0104] like Figure 1 As shown, the method 100 includes:

[0105] S101, providing a coating on at least one side of the isolation film to obtain an isolation member.

[0106] 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.

[0107] Figure 2 Another schematic flow chart of a method for preparing a separator.

[0108] Alternatively, if Figure 2 As shown, in S101, providing a coating on at least one side of the isolated film includes:

[0109] S1011, preparing a slurry, wherein the slurry includes a metal salt.

[0110] S1012, coating the slurry on at least one side of the isolation film.

[0111] S1013, drying the slurry to form a coating layer on the isolation film.

[0112] S1014, rolling the isolation film and the coating layer to obtain an isolation member.

[0113] 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.

[0114] 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.

[0115] It should be understood that the rolling process can be one-time rolling or multiple-time rolling, which is not limited in the present application. The rolling process can be cold pressing or hot pressing, which is not limited in the present application.

[0116] The roller 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.

[0117] Based on a similar principle, the isolation member prepared by method 100, when applied to a lithium-ion battery, can allow the electrolyte to contain free metal ions, and can achieve the corresponding technical effects of the aforementioned isolation member, which will not be described in detail here.

[0118] The present application also provides a lithium-ion battery, which includes the separator in any of the above embodiments, and / or the separator prepared by the preparation method 100 in any of the above embodiments. Based on similar principles, the lithium-ion battery includes the separator in the above embodiments, which can achieve the corresponding technical effects, and will not be described in detail here.

[0119] In one embodiment, a lithium ion battery includes an electrolyte including metal ions.

[0120] 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%.

[0121] 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.

[0122] In one embodiment, the negative electrode sheet, the positive electrode sheet and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0123] In one embodiment, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0124] In one embodiment, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0125] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 3 The battery cell 300 is a square structure as an example.

[0126] It should be understood that the battery cell 300 may include the lithium-ion battery in the aforementioned embodiment.

[0127] Figure 4 4 is a battery module 400 as an example. Figure 4 In the battery module 400, the plurality of battery cells 300 may be arranged in sequence along the length direction of the battery module 400. Of course, they may also be arranged in any other manner. The plurality of battery cells 300 may be further fixed by fasteners. The plurality of battery cells 300 may be battery cells 300 of the same chemical system or battery cells 300 of different chemical systems.

[0128] Optionally, in one embodiment, the battery module 400 may further include a housing having an accommodation space, and the plurality of battery cells 300 are accommodated in the accommodation space.

[0129] Optionally, in one embodiment, the battery modules 400 may also be assembled into a battery. The number of battery modules 400 contained in the battery may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0130] Figure 5 and Figure 6 500 is an example of a battery. Figure 5 and Figure 6 The battery 500 may include a battery box and a plurality of battery modules 400 disposed in the battery box. The battery box includes an upper box body 501 and a lower box body 502. The upper box body 501 can cover the lower box body 502 and form a closed space for accommodating the battery modules 400. The plurality of battery modules 400 may be arranged in the battery box in any manner.

[0131] 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 form a battery module 400, and the battery 500 may be formed by the battery module 400. Alternatively, the battery 500 may be directly formed by the battery cells 300, omitting the intermediate form of the battery module 400.

[0132] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0133] In another embodiment, the electrical device includes at least one of the battery cell 300, battery module 400, or battery 500 provided in the present application. 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 mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0134] As an electric device, a battery cell 300, a battery module 400, or a battery 500 may be selected according to its usage requirements.

[0135] 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, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

[0136] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0137] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0138] [Examples 1-25 and Comparative Examples 1-2]

[0139] Example 1

[0140] (1) Preparation of negative electrode sheet

[0141] 1 kg of artificial graphite, anode active material, 10 g of acetylene black, 30 g of styrene butadiene rubber (SBR), and 20 g of carboxymethyl cellulose sodium (CMC) were dissolved in 1 kg of deionized water and mixed evenly to obtain cathode slurry. Then, the cathode slurry was evenly coated on the cathode current collector copper foil. Then, the cathode pole sheet was obtained by rolling and cutting.

[0142] (2) Preparation of positive electrode sheet

[0143] 1 kg of positive electrode active material LiNi5Co2Mn3O2, 20 g of conductive agent carbon nanotubes, and 20 g of binder polyvinylidene fluoride (PVDF) were dissolved in 1 kg of N-methylpyrrolidone and mixed evenly to obtain positive electrode slurry. Then, the positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil. After rolling and cutting, the positive electrode sheet was obtained.

[0144] (3) Preparation of spacers

[0145] 1 kg of metal salt potassium nitrate and 20 g of binder polyvinylidene fluoride (PVDF) were dissolved in 1 kg of N-methylpyrrolidone, and mixed evenly to obtain a slurry including metal salts. 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 piece.

[0146] (4) Preparation of lithium-ion batteries

[0147] The positive electrode sheet, the negative electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet and can separate the positive electrode sheet from the negative electrode sheet; then the stacked components are wound and placed in a shell, and after drying, a lithium hexafluorophosphate (LiPF6) electrolyte with a concentration of 1 mol / L is injected, and a lithium-ion battery is obtained after packaging.

[0148] 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 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%.

[0149] 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.

[0150] Example 2

[0151] 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%.

[0152] Example 3

[0153] 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%.

[0154] Example 4

[0155] Compared with Example 1, in Example 4, the metal salt is potassium hexafluorophosphate, S=0.035 g / mL, and b=2.9%.

[0156] Example 5

[0157] 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%.

[0158] Example 6

[0159] 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%.

[0160] Example 7

[0161] 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%.

[0162] Example 8

[0163] 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%.

[0164] Example 9

[0165] 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%.

[0166] Example 10

[0167] 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%.

[0168] Embodiment 11

[0169] 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%.

[0170] Example 12

[0171] 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%.

[0172] Example 13

[0173] 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%.

[0174] Embodiment 14

[0175] 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%.

[0176] Embodiment 15

[0177] 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%.

[0178] Example 16

[0179] Compared with Example 1, in Example 16, d=0.1 μm, a=1.5%, and b=0.14%.

[0180] Embodiment 17

[0181] Compared with Example 1, in Example 17, d=200 μm, a=99.9%, and b=2.7%.

[0182] Embodiment 18

[0183] Compared with Example 1, in Example 18, d=50 μm, a=96.2%, and b=2.7%.

[0184] Embodiment 19

[0185] Compared with Example 1, in Example 19, d=0.66 μm, a=10%, and b=0.87%.

[0186] Embodiment 20

[0187] Compared with Example 1, in Example 20, d=2.2 μm, a=40%, and b=2.7%.

[0188] Embodiment 21

[0189] Compared with Example 1, in Example 21, d=4.95 μm, a=90%, and b=2.7%.

[0190] Embodiment 22

[0191] Compared with Example 1, in Example 22, d=0.02 μm, a=0.25%, and b=0.02%.

[0192] Embodiment 23

[0193] Compared with Example 1, in Example 23, d=2.0 μm, a=0.35%, and b=0.03%.

[0194] Embodiment 24

[0195] 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%.

[0196] Embodiment 25

[0197] 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%.

[0198] Comparative Example 1

[0199] Compared with Example 1, Comparative Example 1 directly uses the isolation film in Example 1 as an isolation member.

[0200] Comparative Example 2

[0201] Compared with Example 1, the preparation process of the separator of Comparative Example 2 is as follows:

[0202] 20 g of polyvinylidene fluoride (PVDF) was dissolved in 50 g of N-methylpyrrolidone, and the mixture was uniformly mixed to obtain a slurry including polyvinylidene fluoride. The slurry was uniformly coated on one side of a polyethylene separator, dried in an oven at 80° C., and then rolled at a pressure of 2 MPa to obtain a separator. In other words, the separator of Comparative Example 2 includes a coating layer, but the coating layer does not contain a metal salt.

[0203] The product parameters of Examples 1-25 and Comparative Examples 1-2 are detailed in Table 1.

[0204] Table 1: Product parameters of Examples 1-25 and Comparative Examples 1-2

[0205] 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; "rolling pressure" represents the pressure applied to the isolation membrane and the coating when rolling them.

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

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

[0208] In Table 2, "Number of cycles" indicates the number of cycles when the lithium-ion battery is cycled to SOH 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, and "Whether lithium dendrites appear" indicates whether obvious dendrite-like lithium precipitation appears on the negative electrode sheet obtained by disassembling the lithium-ion battery after the lithium-ion battery cycle is completed.

[0209] According to the comparative analysis of the above-mentioned embodiment and the comparative example, it can be seen that the number of cycles and the average coulombic efficiency of the embodiment are better than those of the comparative example, and no lithium dendrites are found in the lithium ion batteries of the embodiment after cycling, while lithium dendrites appear in the lithium ion batteries of the comparative example after cycling. 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 inhibited, thereby helping to improve the cycling performance and coulombic efficiency of the lithium ion battery.

[0210] Through comparative analysis of Examples 1-4, it can be seen that providing metal salts containing multiple metal ions whose reduction potentials are 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.

[0211] 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 inhibition of lithium precipitation and lithium dendrites. In addition, for metal salts with low solubility, the amount remaining on the isolation membrane will be higher than that of metal salts with high solubility. Therefore, by selecting metal salts with solubility within a suitable range, it is possible to achieve the inhibition of lithium precipitation and lithium dendrites while helping to improve the mechanical strength of the isolation membrane.

[0212] 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 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 the roller pressure of the coating within a suitable 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.

[0213] 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 small and the content of metal salt on the separator is low. In order to effectively inhibit 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 isolation membrane. 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 lithium-ion batteries.

[0214] Through comparative analysis of Examples 1, 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 in 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.

[0215] 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, a lithium-ion battery with a higher energy density is configured with a separator with a higher metal salt mass content.

[0216] 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 the growth of lithium dendrites is also limited. Therefore, by comparing and analyzing Examples 1, 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 improve the inhibitory effect of the separator on lithium precipitation and lithium dendrite growth.

[0217] The following is a brief introduction to the test methods of the physical and chemical parameters and performance parameters involved in the embodiments of the present application. It should be understood that the following test methods are only examples, and other test methods known in the art may also be used for testing.

[0218] 1. Test method of reduction potential

[0219] The substance to be tested is dissolved in an appropriate solvent, and then a reference electrode (such as a standard hydrogen electrode) and a working electrode (such as a glassy carbon electrode) are used to form a battery. 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.

[0220] 2. Test method for solubility of metal salts in electrolyte

[0221] Dissolve the metal salt in 100 mL of 1 mol / L lithium hexafluorophosphate electrolyte until crystals are precipitated, calculate the total amount of metal salt added m, and measure the total volume of the solution at this time V. The solubility S can be calculated by the following formula: S = m / V.

[0222] 3. Test method for compacted powder density

[0223] Cut the roller-pressed spacer and weigh it (m1), measure its thickness as h1, and its area as P. Then wash off the surface powder coating, weigh it again (m2) and measure its thickness (h2). The compacted density is: (m1-m2) / (P×(h1-h2)).

[0224] 4. Test method for mass content

[0225] Disassemble the lithium-ion battery, weigh the total mass m3 of the separator, scrape the coating on the surface of the separator, and obtain the mass m4 of the metal salt in the coating and the mass m5 of the metal salt in the electrolyte through ICP testing, and weigh the mass m6 of the remaining separator. Based on the total mass of the coating, the mass content of the metal salt a = (m4 + m5) / (m3 + m5 - m6).

[0226] 5. Test method for the number of cycles of lithium-ion batteries

[0227] After formation, the lithium-ion battery is fully charged and discharged at a current of 0.33C, and the number of battery cycles is counted when the battery SOH reaches 80%.

[0228] 6. Test method for average coulombic efficiency of lithium-ion batteries

[0229] The discharge capacity of each cycle of the lithium-ion battery charge and discharge cycle is divided by the charge capacity to obtain the coulombic efficiency of each cycle, and then the coulombic efficiency of each cycle is added up and divided by the number of cycles to obtain the average coulombic efficiency.

[0230] 7. Test method for the presence of lithium dendrites

[0231] 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.

[0232] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned 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 includes all technical solutions falling 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 coating is provided on at least one side of the isolation film, comprising: 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 2 MPa-70 MPa; Optionally, the isolation film and the coating layer are rolled at a pressure of 10 MPa to 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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