Separator and preparation method thereof, secondary battery, battery module, battery pack and power-consuming device

Abstract

The present application provides an isolation membrane and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device, wherein the isolation membrane comprises: an isolation membrane substrate and a coating on at least one surface of the isolation membrane substrate; the coating comprises an iodine-containing substance; wherein the coating on the surface of the isolation membrane substrate facing the negative electrode comprises an iodate; and / or the coating on the surface of the isolation membrane substrate facing the positive electrode comprises an iodide. The isolation membrane provided by the present application can convert metallic lithium precipitated from the negative electrode into active lithium ions, thereby preventing lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing an internal short circuit of the battery, reducing the irreversible attenuation of battery capacity caused by the loss of active lithium ions, and improving the performance stability, service life and safety performance of the secondary battery.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to an isolation membrane and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device. Background Art

[0002] In recent years, as the application scope of secondary batteries becomes wider and wider, secondary batteries are 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. Secondary battery separator is an important component of the battery in addition to the positive electrode material, negative electrode material and electrolyte. It plays an important role in isolating the positive and negative electrodes and achieving electronic insulation and ion conduction.

[0003] However, during the charging process of secondary batteries, lithium deposition is prone to occur at the negative electrode, and the current separator is easily pierced by lithium dendrites formed by the deposition, causing internal short circuits in the battery and thermal runaway, which seriously affects the service life and safety performance of the secondary battery. Therefore, the existing separator still needs to be improved. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to convert the precipitated metallic lithium into lithium ions, thereby preventing the lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing an internal short circuit in the battery, thereby improving the service life and safety performance of the secondary battery.

[0005] In order to achieve the above-mentioned objectives, the present application provides an isolation film and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device.

[0006] The first aspect of the present application provides an isolation membrane, comprising: an isolation membrane substrate and a coating on at least one surface of the isolation membrane substrate; the coating comprises an iodine-containing substance; wherein the coating on the surface of the isolation membrane substrate facing the negative electrode contains iodate; and / or the coating on the surface of the isolation membrane substrate facing the positive electrode contains iodide.

[0007] Therefore, the present application arranges the iodine-containing substance in the coating on at least one surface of the isolation membrane substrate. When metallic lithium is precipitated at the negative electrode, the iodine-containing substance undergoes a series of reactions with the metallic lithium to convert the metallic lithium into active lithium ions, thereby preventing the lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing an internal short circuit in the battery, thereby improving the service life and safety performance of the secondary battery. In addition, since the metallic lithium is converted into active lithium ions, the irreversible attenuation of the battery capacity caused by the loss of active lithium ions can be reduced, thereby improving the capacity retention rate of the secondary battery, and improving the stability of the performance and service life of the secondary battery.

[0008] In any embodiment, the coating is provided on both surfaces of the separator substrate, wherein the coating on the surface of the separator substrate facing the positive electrode comprises one or more of iodate and iodide. When the coating on the surface of the separator substrate facing the positive electrode comprises iodate, the iodate can react with lithium dendrites in the electrolyte that pierces the separator and reaches between the positive electrode and the separator, thereby eliminating lithium dendrites and reducing the negative impact of lithium deposition on the negative electrode.

[0009] In any embodiment, the iodate is selected from one or more of KIO3, Fe(IO3)3, NaIO3, Ca(IO3)2, LiIO3 and Mg(IO3)2; the iodide is selected from one or more of KI, NaI, HI, LiI, AgI, AlI3, MgI2, MnI2, ZnI2, BiI3 and NH4I. The above iodine-containing substances can convert metallic lithium into active lithium ions by a series of reactions with metallic lithium, thereby preventing lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing internal short circuit of the battery, and reducing the irreversible attenuation of battery capacity caused by the loss of active lithium ions.

[0010] In any embodiment, the total amount of iodine-containing substance in the coating on the surface of the isolation membrane substrate is 65 mg / m 2 -1300mg / m 2 When the total amount of iodine-containing substances is controlled within the above range, metallic lithium can be converted into active lithium ions to a large extent, thereby minimizing problems such as internal short circuit of the battery and irreversible attenuation of battery capacity caused by lithium plating.

[0011] The second aspect of the present application also provides a method for preparing an isolation membrane, comprising: coating a coating comprising an iodine-containing substance on at least one surface of an isolation membrane substrate, and drying to obtain the isolation membrane.

[0012] Therefore, when metallic lithium is precipitated at the negative electrode, the iodate or iodide in the coating formed after the coating is dried can convert the metallic lithium into active lithium ions through a series of reactions with the metallic lithium, thereby preventing the lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing an internal short circuit in the battery, thereby improving the service life and safety performance of the secondary battery; and can reduce the irreversible attenuation of the battery capacity caused by the loss of active lithium ions, thereby improving the capacity retention rate of the secondary battery, and improving the stability of the performance and service life of the secondary battery.

[0013] In any embodiment, the coating further comprises an adhesive, and the mass ratio of the adhesive to the iodine-containing substance is 1.11:(10-100). The adhesive is used to bond the iodine-containing substance to the surface of the isolation film substrate; the amount of the adhesive used is controlled within the above range, so that the iodine-containing substance can be bonded to the surface of the isolation film substrate without falling off, and at the same time, the coating is ensured not to agglomerate during the coating process.

[0014] A third aspect of the present application provides a secondary battery, comprising the isolation membrane of the first aspect of the present application or the isolation membrane prepared according to the method of the second aspect of the present application.

[0015] A fourth aspect of the present application provides a battery module, comprising the secondary battery of the third aspect of the present application.

[0016] A fifth aspect of the present application provides a battery pack comprising the battery module of the fourth aspect of the present application.

[0017] The sixth aspect of the present application provides an electrical device comprising one or more selected from the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application.

[0018] Beneficial effects of this application:

[0019] The present application provides an isolation membrane, a secondary battery, a battery module, a battery pack and an electrical device. By providing a coating including an iodine-containing substance on the surface of the isolation membrane, the iodine-containing substance can convert metallic lithium precipitated from the negative electrode into active lithium ions, thereby preventing lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing an internal short circuit in the battery, thereby improving the service life and safety performance of the secondary battery; in addition, converting metallic lithium into active lithium ions can reduce the irreversible attenuation of the battery capacity caused by the loss of active lithium ions, improve the capacity retention rate of the secondary battery, and improve the stability of the secondary battery performance and service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of an isolation membrane according to one embodiment of the present application.

[0021] Figure 2 Schematic diagram of the working mechanism of the isolation membrane according to one embodiment of the present application.

[0022] Figure 3 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0023] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0024] Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application.

[0025] Figure 6 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0026] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0027] Figure 8 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0028] Description of reference numerals:

[0029] 11 isolation film substrate; 12 coating; 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0030] Below, the isolation membrane and its preparation method, secondary battery, battery module, battery pack and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there are 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 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.

[0031] "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.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0034] 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.

[0035] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0036] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A 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).

[0037] In the process of studying secondary batteries, the applicant discovered that during the charging process of the secondary battery, lithium deposition is prone to occur at the negative electrode, and lithium deposition at the negative electrode will have a negative impact on the secondary battery: on the one hand, the lithium dendrites formed by lithium deposition can easily pierce the isolation membrane, thereby causing an internal short circuit in the battery and causing thermal runaway, seriously affecting the service life and safety performance of the secondary battery; on the other hand, because the active lithium ions are converted into metallic lithium, the active lithium ions are lost, resulting in irreversible decay of the battery capacity and shortening the battery life.

[0038] In order to prevent the lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing an internal short circuit in the battery, and to reduce the loss of active lithium ions, the applicant has found that the metallic lithium precipitated from the negative electrode can be converted into active lithium ions through chemical reactions. After in-depth research, it was found that when metallic lithium is precipitated from the negative electrode, iodates or iodides can convert metallic lithium into active lithium ions through a series of reactions with metallic lithium, thereby preventing the lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing an internal short circuit in the battery, thereby improving the service life and safety performance of the secondary battery; and reducing the irreversible attenuation of the battery capacity caused by the loss of active lithium ions, thereby improving the capacity retention rate of the secondary battery, and improving the stability and service life of the secondary battery performance.

[0039] The isolation membrane provided by the present application can be used in secondary batteries; secondary batteries can be used in electrical devices such as vehicles, ships or aircraft, but are not limited thereto. A power supply system comprising the electrical device and the secondary battery disclosed in the present application can be used, which is conducive to preventing lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing internal short circuits in the battery, thereby improving the service life and safety performance of the secondary battery; and reducing the irreversible attenuation of the secondary battery capacity caused by the loss of active lithium ions, improving the capacity retention rate of the secondary battery, and improving the stability and service life of the secondary battery performance.

[0040] The present application provides an electric device using a secondary battery as a power source, and the electric device may be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, for example, a game console, an electric car toy, an electric ship toy, an electric airplane toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, a spacecraft, etc.

[0041] In order to prevent lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing internal short circuit of the battery, reduce the loss of active lithium ions, and improve the service life and safety performance of the secondary battery, the present application provides an isolation membrane and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device.

[0042] Isolation film

[0043] In one embodiment of the present application, the present application proposes an isolation membrane, the structural schematic diagram of which is as follows: Figure 1 As shown, the isolation membrane includes an isolation membrane substrate 11 and a coating 12 on at least one surface of the isolation membrane substrate 11; the coating 12 includes an iodine-containing substance; wherein the coating 12 on the surface of the isolation membrane substrate 11 facing the negative electrode contains iodate; and / or the coating 12 on the surface of the isolation membrane substrate 11 facing the positive electrode contains iodide.

[0044] The applicant unexpectedly discovered that: by setting an iodine-containing substance in a coating on at least one surface of the isolation membrane substrate, when metallic lithium is precipitated at the negative electrode, the iodine-containing substance undergoes a series of reactions with the metallic lithium to convert the metallic lithium into active lithium ions, thereby preventing lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing an internal short circuit in the battery, thereby improving the service life and safety performance of the secondary battery; in addition, since the metallic lithium is converted into active lithium ions, the irreversible attenuation of the battery capacity caused by the loss of active lithium ions can be reduced, thereby improving the capacity retention rate of the secondary battery, and improving the stability of the performance and service life of the secondary battery.

[0045] The schematic diagram of the mechanism of action of the isolation membrane provided in one embodiment of the present application is as follows Figure 2 As shown, the isolation membrane includes an isolation membrane substrate and a coating on the surface of the isolation membrane substrate facing the negative electrode; the iodine-containing substance included in the coating is iodate.

[0046] When metallic lithium (Li) is precipitated at the negative electrode, the IO3 in the iodate - It will enter the electrolyte between the negative electrode and the separator and react with Li as shown in formula (1):

[0047] 6Li+IO3 - =I - +3Li2O. (1)

[0048] I generated by reaction equation (1) - Entering the electrolyte between the positive electrode and the separator through the separator, a reaction as shown in formula (2) occurs:

[0049] 3I - -2e - =I3 - (2)

[0050] I3 generated by reaction equation (2) - Entering the electrolyte between the negative electrode and the separator through the separator, it reacts with the Li precipitated from the negative electrode as shown in formula (3):

[0051] 2Li+I3 - =2Li + +3I - ; (3)

[0052] The Li2O generated by reaction equation (1) undergoes a reaction as shown in equation (4):

[0053] 3Li2O+3I3 - =6Li + +IO3 - +8I - (4)

[0054] I generated by reaction equations (3) and (4) - It can enter the electrolyte between the positive electrode and the isolation membrane through the isolation membrane, and the reaction shown in formula (2) will occur, and the cycle will continue.

[0055] From the above content, it can be seen that the metallic lithium deposited from the negative electrode can be converted into active lithium ions, thereby preventing the lithium dendrites formed during lithium deposition from piercing the isolation membrane and causing internal short circuit of the battery, and reducing the irreversible attenuation of the battery capacity caused by the loss of active lithium ions.

[0056] Another embodiment of the present application provides an isolation membrane, which includes an isolation membrane substrate and a coating on the surface of the isolation membrane substrate on the side facing the positive electrode; the iodine-containing substance included in the coating is iodide.

[0057] When metallic lithium (Li) is precipitated at the negative electrode, the I in the iodide - It will enter the electrolyte between the positive electrode and the separator, and the reaction shown in formula (2) will occur:

[0058] 3I - -2e - =I3 - (2)

[0059] I3 generated by reaction equation (2) - Entering the electrolyte between the negative electrode and the separator through the separator, a reaction as shown in formula (3) occurs:

[0060] 2Li+I3 - =2Li + +3I - (3)

[0061] I generated by reaction equation (3) - It can enter the electrolyte between the positive electrode and the isolation membrane through the isolation membrane, and the reaction shown in formula (2) will occur, and the cycle will continue.

[0062] From the above content, it can be seen that the metallic lithium deposited from the negative electrode can be converted into active lithium ions, thereby preventing the lithium dendrites formed during lithium deposition from piercing the isolation membrane and causing internal short circuit of the battery, and reducing the irreversible attenuation of the battery capacity caused by the loss of active lithium ions.

[0063] Another embodiment of the present application provides an isolation membrane, comprising: an isolation membrane substrate; a coating is provided on the surface of the isolation membrane substrate facing the negative electrode, and the iodine-containing substance included in the coating is iodate; a coating is provided on the surface of the isolation membrane substrate facing the positive electrode, and the iodine-containing substance included in the coating is iodide.

[0064] When metallic lithium (Li) is precipitated at the negative electrode, the IO3 in the iodate- It will enter the electrolyte between the negative electrode and the separator and react with Li as shown in formula (1):

[0065] 6Li+IO3 - =I - +3Li2O. (1)

[0066] I generated by reaction equation (1) - The I in the iodide enters the electrolyte between the positive electrode and the separator through the separator. - It will enter the electrolyte between the positive electrode and the separator, and the reaction shown in formula (2) will occur:

[0067] 3I - -2e - =I3 - (2)

[0068] I3 generated by reaction equation (2) - Entering the electrolyte between the negative electrode and the separator through the separator, it reacts with the Li precipitated from the negative electrode as shown in formula (3):

[0069] 2Li+I3 - =2Li + +3I - ; (3)

[0070] The Li2O generated by reaction equation (1) undergoes a reaction as shown in equation (4):

[0071] 3Li2O+3I3 - =6Li + +IO3 - +8I - (4)

[0072] I generated by reaction equations (3) and (4) - It can enter the electrolyte between the positive electrode and the isolation membrane through the isolation membrane, and the reaction shown in formula (2) will occur, and the cycle will continue.

[0073] From the above content, it can be seen that the metallic lithium deposited from the negative electrode can be converted into active lithium ions, thereby preventing the lithium dendrites formed during lithium deposition from piercing the isolation membrane and causing internal short circuit of the battery, and reducing the irreversible attenuation of the battery capacity caused by the loss of active lithium ions.

[0074] The present application has no particular restrictions on the type of the isolation film substrate, as long as the purpose of the present application can be achieved. For example, the isolation film substrate can be directly selected from a polymer film bare film, or a ceramic coating (hereinafter referred to as CCS layer) and a polymer adhesive coating (hereinafter referred to as PCS layer) can be sequentially provided on one side or both sides of the polymer film, and the CCS layer is located between the polymer film and the PCS layer; wherein the polymer film can be selected from one or more of a polypropylene film and a polyethylene film.

[0075] The present application does not limit the thickness of the isolation membrane substrate, as long as the purpose of the present application can be achieved. For example, the thickness of the isolation membrane substrate can be 5μm-54μm. The present application does not limit the thickness of the polymer film, the thickness of the CCS layer and the thickness of the PCS layer in the isolation membrane substrate, as long as the purpose of the present application can be achieved. For example, the thickness of the polymer film is 5μm-50μm, the thickness of the CCS layer is 3μm, and the thickness of the PCS layer is 1μm.

[0076] The CCS layer described in the present application refers to a coating layer comprising a ceramic material, wherein the ceramic material is selected from one or more of SiO2, TiO2, ZrO2, Al2O3, MgO and SiC. In some embodiments, the CCS layer optionally further comprises a binder, wherein the binder is selected from one or more of polyvinylidene fluoride (PVDF), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, polyurethane (PU), and styrene acrylic latex (SA).

[0077] The PCS layer described in the present application refers to a coating layer containing a polymer binder, and the polymer binder is selected from one or more of polyvinylidene fluoride (PVDF), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, polyurethane (PU), and styrene acrylic latex (SA).

[0078] The present application does not limit the preparation method of the isolation membrane substrate, as long as the purpose of the present application can be achieved. For example, a CCS layer can be coated on a polymer film, and then a PCS layer can be coated on the CCS layer to obtain an isolation membrane substrate. Coating a CCS layer on a polymer film and coating a PCS layer on a CCS layer are both commonly used methods in the art and are not limited here.

[0079] In some embodiments, both surfaces of the separator are provided with coatings, wherein the coating on the surface of the separator substrate facing the positive electrode comprises one or more selected from iodates and iodides. When the coating on the surface of the separator substrate facing the positive electrode comprises iodates, if lithium dendrites formed during lithium precipitation penetrate the separator and reach the electrolyte between the positive electrode and the separator, the IO3 in the iodate -It will react with Li as shown in formula (1):

[0080] 6Li+IO3 - =I - +3Li2O. (1)

[0081] In this way, lithium dendrites in the electrolyte between the positive electrode and the isolation membrane can be eliminated in time, thereby reducing the negative impact of lithium plating at the negative electrode.

[0082] In some embodiments, the iodate is selected from one or more of KIO3, Fe(IO3)3, NaIO3, Ca(IO3)2, LiIO3 and Mg(IO3)2; the iodide is selected from one or more of KI, NaI, HI, LiI, AgI, AlI3, MgI2, MnI2, ZnI2, BiI3 and NH4I. The above iodates and iodides can convert metallic lithium into active lithium ions by a series of reactions with metallic lithium, thereby preventing the lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing an internal short circuit in the battery, and reducing the irreversible attenuation of the battery capacity caused by the loss of active lithium ions.

[0083] In some embodiments, the total amount of iodine-containing material in the coating on the surface of the isolation film substrate is 65 mg / m 2 -1300mg / m 2 , that is, for each m 2 The total mass of the iodine-containing substance in the coating provided on the two surfaces of the isolation membrane substrate is 65mg-1300mg. If the total mass of the iodine-containing substance in the coating is low, it is difficult to effectively eliminate lithium and convert the precipitated lithium into active lithium ions to a large extent, resulting in the secondary battery still having a relatively obvious lithium precipitation situation, and the capacity retention rate and cycle life have not been effectively improved; if the total mass of the iodine-containing substance in the coating is high, the thickness of the anode and cathode plates will increase, resulting in the number of pole plates wound in the same volume of the battery cell will be reduced, thereby reducing the mass energy density, and ultimately affecting the battery's endurance and other performance. Therefore, the inventor of the present application believes that the use of iodine-containing substances is controlled within the above range, which can effectively convert metallic lithium into active lithium ions to a large extent, so that the lithium precipitation of the secondary battery is significantly improved, with a better first discharge capacity, and at the same time, a better capacity retention rate and cycle life.

[0084] The coating described in the present application can be set in a local area or all areas on at least one surface of the isolation membrane substrate. The coating is set in a local area on the surface of the isolation membrane substrate, and the iodine-containing substance in the coating can undergo a series of reactions with metallic lithium to convert metallic lithium into active lithium ions, thereby preventing lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing internal short circuits in the battery, thereby reducing the irreversible attenuation of battery capacity caused by the loss of active lithium ions. The coating is set in all areas on the surface of the isolation membrane substrate, and the iodine-containing substance in the coating can undergo a series of reactions with metallic lithium more promptly and efficiently, which can further improve the reaction efficiency.

[0085] Preparation method of isolation film

[0086] In one embodiment of the present application, the present application proposes a method for preparing an isolation membrane, comprising: coating a coating comprising an iodine-containing substance on at least one surface of an isolation membrane substrate, and drying to obtain the isolation membrane.

[0087] When the coating is applied on the surface of the isolation membrane substrate facing the negative electrode, the iodine-containing substance includes iodate; when the coating is applied on the surface of the isolation membrane substrate facing the positive electrode, the iodine-containing substance includes iodide; when the two surfaces of the isolation membrane substrate are provided with coatings, the iodine-containing substance of the coating on the surface of the isolation membrane substrate facing the positive electrode includes one or more selected from iodate and iodide.

[0088] The present application coats a coating including an iodine-containing substance on at least one surface of an isolation membrane substrate to prepare an isolation membrane with a coating on the surface of the isolation membrane substrate. When metallic lithium is precipitated at the negative electrode, the iodine-containing substance in the coating can convert the metallic lithium into active lithium ions through a series of reactions with the metallic lithium, thereby preventing lithium dendrites formed during lithium precipitation from piercing the isolation membrane and causing an internal short circuit in the battery, thereby improving the service life and safety performance of the secondary battery; and can reduce the irreversible attenuation of the battery capacity caused by the loss of active lithium ions, thereby improving the capacity retention rate of the secondary battery, and improving the stability of the performance and service life of the secondary battery.

[0089] In some embodiments, the coating further comprises an adhesive, and the mass ratio of the adhesive to the iodine-containing substance is 1.11:(10-100). The adhesive can bond the iodine-containing substance to the surface of the isolation membrane substrate. If the amount of the adhesive used is low, it is difficult to bond the iodine-containing substance to the surface of the isolation membrane substrate without falling off; if the amount of the adhesive used is high, agglomeration is likely to occur during the coating process, and the mass energy density of the secondary battery will be reduced.

[0090] The present application has no particular limitation on the specific type of adhesive, as long as the purpose of the present application can be achieved. For example, the adhesive can be one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR).

[0091] The present application has no particular restrictions on the specific preparation method of the coating, as long as the purpose of the present application can be achieved. For example, the iodine-containing substance can be dissolved in deionized water, a binder is added, and the mixture is stirred evenly to prepare the coating. When preparing the coating, the present application uses deionized water to dissolve the iodine-containing substance, and the amount thereof is not particularly limited, as long as the purpose of the present application can be achieved.

[0092] The present application has no particular limitation on the coating method, as long as the purpose of the present application can be achieved. For example, coating can be performed by gravure, extrusion or spraying.

[0093] The purpose of drying in this application is to remove deionized water. There is no particular limitation on the equipment, drying time and drying temperature used for drying, as long as the purpose of this application can be achieved. For example, the drying temperature is 30°C-50°C.

[0094] In addition, the secondary battery, battery module, battery pack, and electric device of the present application will be described below with reference to the drawings as appropriate.

[0095] In one embodiment of the present application, a secondary battery is provided.

[0096] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0097] [Positive electrode]

[0098] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0099] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0100] In some embodiments, 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.).

[0101] In some embodiments, 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 one or more 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. 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 NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of 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 a composite material of lithium iron manganese phosphate and carbon.

[0102] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0103] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0104] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the 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; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0105] [Negative electrode]

[0106] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0107] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0108] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, 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.).

[0109] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include one or more 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 one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from one or more 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.

[0110] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from one or more 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).

[0111] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0112] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0113] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0114] [Electrolytes]

[0115] The electrolyte plays the role of 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. For example, the electrolyte can be liquid, gel or all-solid.

[0116] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0117] In some embodiments, the electrolyte salt can be selected from one or more 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.

[0118] In some embodiments, the solvent can be selected from one or more 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.

[0119] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and 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.

[0120] [Isolation film]

[0121] In some embodiments, the secondary battery further includes the isolation membrane provided in the present application.

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

[0123] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0124] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery 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 secondary battery, which may be cylindrical, square or any other shape. Figure 3 The secondary battery 5 is a square structure as an example.

[0126] In some embodiments, reference Figure 4, the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0127] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module 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 module.

[0128] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0129] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0130] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0131] Figure 6 and Figure 7 1 is a battery pack 1 as an example. Figure 6 and Figure 7 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0132] In addition, the present application also provides an electrical device, which includes one or more of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used 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 to these.

[0133] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0134] Figure 8 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0135] 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.

[0136] Example

[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] Example 1

[0139] <Preparation of positive electrode sheet>

[0140] The positive electrode active material lithium iron phosphate (LiFePO4), the conductive agent carbon black, and the binder polyvinylidene fluoride are mixed in a weight ratio of 8:1:1, and then N-methylpyrrolidone (NMP) is added as a solvent, and stirred under the action of a vacuum mixer until the system is uniform, to obtain a positive electrode slurry with a solid content of 65%. The positive electrode slurry is evenly coated on both surfaces of a positive electrode current collector aluminum foil with a thickness of 12μm, dried at 120℃, and cold pressed to obtain a positive electrode sheet with a positive electrode active material layer thickness of 60μm, and then the positive electrode sheet is obtained through processes such as ear forming and slitting.

[0141] <Preparation of negative electrode sheet>

[0142] The negative electrode active material artificial graphite, conductive agent carbon black, and binder polyacrylic acid are mixed in a weight ratio of 7:1.5:1.5, deionized water is added as a solvent, and the system is stirred under the action of a vacuum mixer until the system is uniform to obtain a negative electrode slurry with a solid content of 50%. The negative electrode slurry is evenly coated on both surfaces of a negative electrode current collector copper foil with a thickness of 8μm, dried at 110°C, and cold pressed to obtain a negative electrode sheet with a thickness of 50μm, and then the negative electrode sheet is obtained through processes such as ear forming and slitting.

[0143] <Preparation of Electrolyte>

[0144] In an environment with a water content of less than 10ppm, non-aqueous organic solvents ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an electrolyte solvent, and then the lithium salt LiPF6 is dissolved in the mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0145] <Preparation of Separator Film>

[0146] With a thickness of 20μm and a single sheet area of ​​1540.25mm 2 The polypropylene film is a bare film, a CCS layer with a thickness of 3 μm is coated on the surface of the polypropylene film, and then a PCS layer with a thickness of 1 μm is coated on the surface of the CCS layer to obtain an isolation film substrate.

[0147] Dissolve 100 mg KIO3 in 50 mL deionized water, then add 2.564 mg of binder polyvinylidene fluoride, stir evenly to make a coating, and then use extrusion coating to coat all areas on the surface of the separator substrate facing the negative electrode, and control the KIO3 coating mass to 975 mg / m 2 After coating, put it into a drying box for drying to obtain an isolation film.

[0148] <Preparation of lithium-ion batteries>

[0149] The positive 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 to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0150] Example 2 to Example 15

[0151] Except for the difference in <Preparation of Isolation Film> from Example 1, the rest is the same as Example 1.

[0152] In <Preparation of Isolation Film>, except for adjusting the type of iodine-containing substance, the coating mass of the iodine-containing substance, and the position where the coating is applied on the isolation film substrate as shown in Table 1, the rest is the same as Example 1.

[0153] Comparative Example 1

[0154] Except for the difference in <Preparation of Isolation Film> from Example 1, the rest is the same as Example 1.

[0155] <Preparation of Separator Film>

[0156] With a thickness of 20μm and a single sheet area of ​​1540.25mm 2 The polypropylene film is a bare film, a CCS layer with a thickness of 3 μm is coated on the surface of the polypropylene film, and then a PCS layer with a thickness of 1 μm is coated on the surface of the CCS layer to obtain an isolation film substrate; the isolation film substrate is directly used as an isolation film.

[0157] Comparative Example 2 to Comparative Example 4

[0158] Except for the difference in <Preparation of Isolation Film> from Example 1, the rest is the same as Example 1.

[0159] In <Preparation of Isolation Film>, except for using other substances ((NH4)2CO3 and / or NH4HCO3) to replace the iodine-containing substance and adjusting the coating quality of other substances and the position of the coating on the isolation film substrate as shown in Table 1, the rest is the same as Example 1.

[0160] Table 1: Relevant parameters of Examples 1 to 15 and Comparative Examples 1 to 4

[0161]

[0162]

[0163] In addition, the lithium ion batteries obtained in the above Examples 1 to 15 and Comparative Examples 1 to 4 were subjected to performance tests. The test results are shown in Table 2 below.

[0164] (1) Initial discharge capacity test and lithium deposition test

[0165] The test temperature is 25° C. The lithium ion batteries prepared in the embodiments and comparative examples are charged to 4.35V at a constant current of 1 / 3C, then charged to 0.05C at a constant voltage, and then discharged to 2.8V at a constant current of 1 / 3C. The obtained capacity is recorded as the first discharge capacity value C0.

[0166] After that, 10 cycles were performed using 1 / 3C constant current charging to 4.35V, constant voltage charging to 0.05C, and 1 / 3C constant current discharging to 2.8V. The lithium-ion battery was then disassembled in a dry room with a humidity of less than 5% to check the status of the negative electrode.

[0167] The degree of lithium plating of lithium-ion batteries is determined according to the following standards:

[0168] No lithium deposition: no lithium deposition on the surface of the negative electrode;

[0169] Slight lithium deposition: The lithium deposition area on the surface of the negative electrode is less than 10%;

[0170] Moderate lithium deposition: The lithium deposition area on the surface of the negative electrode is 10% to 30%;

[0171] Severe lithium deposition: The lithium deposition area on the surface of the negative electrode is greater than 30%.

[0172] (2) Lithium-ion battery performance cycle test

[0173] The test temperature is 25°C. The lithium ion batteries prepared in the embodiments and comparative examples are charged to 4.35V at 1 / 3C constant current, then charged to 0.05C at constant voltage, and then discharged to 3.3V at 1 / 3C constant current. The discharge capacity value during the cycle is recorded, and the capacity retention rate of 1000 cycles is calculated. The capacity retention rate of the Nth cycle = (discharge capacity of the Nth cycle / first discharge capacity) × 100%. The number of cycles when the capacity retention rate drops to 80% is recorded as the cycle life of the battery.

[0174] (3) Lithium-ion battery mass energy density test

[0175] The test temperature is 25°C, and the lithium ion batteries prepared in each embodiment and comparative example are charged to 4.35V at a 1 / 3C constant current, then charged to 0.05C at a constant voltage, and then discharged to 2.8V at a 1 / 3C constant current. The discharge energy is recorded, and then the 1 / 3C discharge energy density is calculated according to the following formula: mass energy density (Wh / kg) = discharge energy (Wh) / electrochemical device weight (kg).

[0176] Table 2: Performance test results of Examples 1 to 15 and Comparative Examples 1 to 4

[0177]

[0178] According to the above results, the separators of the lithium-ion batteries of Examples 1 to 11 include a coating on at least one surface of the separator substrate, the type of iodine-containing substance in the coating is controlled within the scope of the present application, and the coating quality is controlled at 65 mg / m 2 -1300mg / m 2 Within this range, the lithium plating of lithium-ion batteries has been significantly improved, with better initial discharge capacity, as well as better capacity retention rate, cycle life and mass energy density.

[0179] It can be seen from Examples 1 to 3 that the coating mass of the iodate in the coating on the surface of the separator substrate facing the negative electrode is controlled at 65 mg / m 2 -1300mg / m2 Within this range, the lithium-ion battery has slight or no lithium deposition, and the lithium deposition situation is significantly improved. It has a better first discharge capacity, as well as better capacity retention rate, cycle life and mass energy density.

[0180] It can be seen from Examples 4 to 6 that the coating mass of the iodide in the coating on the surface of the separator substrate facing the positive electrode is controlled at 65 mg / m 2 -1300mg / m 2 Within this range, the lithium-ion battery has slight or no lithium deposition, and the lithium deposition situation is significantly improved. It has a better first discharge capacity, as well as better capacity retention rate, cycle life and mass energy density.

[0181] It can be seen from Examples 1 and 4 that the capacity retention rate and cycle life of Example 1 are better than those of Example 4. Without being limited to any theory, the inventors of the present application believe that when negative electrode lithium deposition occurs in the battery cell, iodate can directly react with metallic lithium to convert metallic lithium into lithium ions, which can solve the lithium deposition problem in a timely manner and reduce the negative impact of metallic lithium on the safety and performance of the battery; while iodide needs to go through the charging and ion transfer process to consume metallic lithium, and its efficiency in removing metallic lithium is affected by ion diffusion and charge and discharge cycles. Therefore, the effect of using iodate is better than that of using iodide.

[0182] It can be seen from Examples 7 to 11 that both sides of the separator substrate are coated, and the total coating mass of the iodate in the coating on the side of the separator substrate facing the negative electrode and the iodine-containing substance in the coating on the side of the separator substrate facing the positive electrode is controlled at 65 mg / m 2 -1300mg / m 2 Within this range, the lithium-ion battery has slight or no lithium deposition, and the lithium deposition situation is significantly improved. It has a better first discharge capacity, as well as better capacity retention rate, cycle life and mass energy density.

[0183] The separator of the lithium ion battery of Example 12 includes iodate in the coating on the surface of the separator substrate facing the negative electrode, but the coating quality is low, which is 32.5 mg / m 2 , which is not enough to convert the precipitated metallic lithium into lithium ions as much as possible, resulting in moderate lithium precipitation in lithium-ion batteries, and the capacity retention rate and cycle life have not been effectively improved.

[0184] The separators of the lithium ion batteries of Examples 13 to 15 include iodine-containing substances in the coatings on the surfaces of one or both sides of the separator substrates, but the coating quality is relatively high, which is 1950 mg / m 2, resulting in a decrease in mass energy density, while the capacity retention rate and cycle life are difficult to further improve. Without being limited to any theory, the inventors of the present application believe that a high coating quality of the iodine-containing substance will lead to an increase in the thickness of the anode and cathode electrodes, and a decrease in the number of electrode turns of the same volume of the battery cell, thereby reducing the mass energy density; in addition, there is an upper limit to the amount of lithium ion battery deposition, so there is also an upper limit to the required iodine-containing substance. When the coating quality of the iodine-containing substance is too high, it is impossible to further significantly improve the capacity retention rate and cycle life, but instead cause a waste of iodine-containing substances and increase production costs.

[0185] In contrast, the isolation membrane of the lithium-ion battery of Comparative Example 1 does not include a coating containing an iodine-containing substance, and the lithium-ion battery suffers from severe lithium plating. The capacity retention rate after 1,000 cycles is only 85.1%, and the cycle life is only 1,320 cycles, which is difficult to meet the requirements of lithium-ion battery life in many application scenarios.

[0186] The coating of the isolation membrane of the lithium-ion battery of Comparative Examples 2 to 4 includes (NH4)2CO3 and / or NH4HCO3, but does not include iodine-containing substances. The lithium-ion batteries suffer from severe lithium plating and cannot effectively solve the lithium plating problem. The capacity retention rate after 1,000 cycles does not exceed 84.3%, and the cycle life does not exceed 1,260 cycles, which makes it difficult to meet the requirements of lithium-ion battery life in many application scenarios.

[0187] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A separation film, characterized in that: include: a separator substrate and a coating on at least one surface of the separator substrate; The coating includes an iodine-containing substance; wherein the coating on the surface of the separator substrate facing the negative electrode comprises iodate; and / or The coating layer on the surface of the separator substrate facing the positive electrode contains one or more of iodide and iodate.

2. The isolation film according to claim 1, characterized in that: The coating is provided on both surfaces of the isolation film substrate.

3. The isolation membrane according to claim 1 or 2, characterized in that: The iodate is selected from one or more of KIO3, Fe(IO3)3, NaIO3, Ca(IO3)2, LiIO3 and Mg(IO3)2; the iodide is selected from one or more of KI, NaI, HI, LiI, AgI, AlI3, MgI2, MnI2, ZnI2, BiI3 and NH4I.

4. The isolation film according to claim 1, characterized in that: The total amount of iodine-containing substances in the coating on the surface of the isolation film substrate is 65 mg / m 2 -1300mg / m 2 .

5. A method for preparing the isolation film according to any one of claims 1 to 4, characterized in that: include: The coating including the iodine-containing substance is coated on at least one surface of the isolation film substrate and dried to obtain the isolation film.

6. The method for preparing the isolation film according to claim 5, characterized in that: The coating also includes an adhesive, and the mass ratio of the adhesive to the iodine-containing substance is 1.11:(10-100).

7. A secondary battery, characterized in that: The invention comprises the isolation film according to any one of claims 1 to 4 or an isolation film prepared by the method for preparing the isolation film according to claim 5 or 6.

8. A battery module, characterized in that: A secondary battery comprising the secondary battery according to claim 7.

9. A battery pack, characterized in that: Comprising the battery module as claimed in claim 8.

10. An electrical device, characterized in that: The battery comprises one or more selected from the secondary battery of claim 7, the battery module of claim 8 or the battery pack of claim 9.

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