Method for stripping negative electrode sheets in metal batteries and testing method for metal batteries

Abstract

The present application provides a method for stripping a negative electrode sheet in a metal battery and a method for testing a metal battery. The stripping method includes the following steps: disassembling the metal battery to obtain a negative electrode sheet with a diaphragm on the surface; the negative electrode sheet includes an active metal layer; applying a treatment liquid to the negative electrode sheet with a diaphragm on the surface, so that the treatment liquid acts at least on the interface between the active metal layer and the diaphragm to strip the negative electrode sheet from the diaphragm; wherein the treatment liquid contains a polar aprotic solvent, the dielectric constant of the polar aprotic solvent at 25°C is ≥7, and the standard reduction potential of the polar aprotic solvent relative to the standard hydrogen electrode is <-1.1V. The above-mentioned stripping method can reduce the risk of metal adhesion and oxidation blackening, improve the deposition morphology integrity of the metal layer of the negative electrode sheet obtained by stripping, and is conducive to improving the accuracy of judging the metal deposition condition on the negative electrode interface of the metal battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for stripping a negative electrode sheet in a metal battery and a method for testing a metal battery. Background Art

[0002] With the increasing global demand for energy-intensive energy storage, developing energy storage devices with higher energy density, longer cycle life, and greater safety has become a key goal of battery development. Lithium-ion batteries, due to their high energy density, excellent cycle performance, and lack of memory effect, have already dominated the mainstream energy storage market and are widely used in mobile electronic devices, electric vehicles, and energy storage power stations. Currently, the energy density of lithium-ion batteries can reach 250 Wh / Kg, but this is still approximately an order of magnitude lower than the energy density of gasoline. Metal batteries based on metal anodes offer significant advantages over traditional lithium-ion batteries in terms of energy density. For example, sodium metal batteries have an extremely high theoretical specific capacity of approximately 1166 mAh / g and a low electrochemical potential of approximately -2.71 V relative to a standard hydrogen electrode.

[0003] The electrochemical energy storage mechanism of metal batteries differs fundamentally from that of lithium-ion batteries. During cycling, uneven deposits often form on the negative electrode surface, resulting in poor cycling performance. Therefore, during R&D and production, it is often necessary to disassemble the battery to assess the negative electrode interface and evaluate the impact of negative electrode metal deposition, such as the morphology of the deposited metal, on battery performance.

[0004] However, the current method is to directly disassemble and separate the negative electrode plate and the separator. This method may cause the problem of destroying the deposition morphology of the negative electrode metal, thereby affecting the judgment of the metal deposition situation on the negative electrode interface of the metal battery. Summary of the Invention

[0005] Based on this, the present application provides a method for stripping negative electrode sheets from metal batteries. This method can reduce the risk of metal adhesion and oxidation blackening, improve the deposition morphology integrity of the metal layer of the stripped negative electrode sheet, and facilitate the accurate assessment of the metal deposition conditions at the negative electrode interface of the metal battery. Furthermore, a method for testing metal batteries is provided.

[0006] In a first aspect of the present application, a method for stripping a negative electrode sheet in a metal battery is provided, comprising the following steps:

[0007] Disassembling the metal battery to obtain a negative electrode sheet having a separator on its surface; the negative electrode sheet includes an active metal layer;

[0008] Applying a treatment liquid to the negative electrode sheet having a separator on its surface, so that the treatment liquid acts at least on the interface between the active metal layer and the separator;

[0009] Peeling the negative electrode sheet from the separator;

[0010] The treatment liquid contains a polar aprotic solvent, the dielectric constant of the polar aprotic solvent at 25° C. is ≥7, and the standard reduction potential of the polar aprotic solvent relative to a standard hydrogen electrode is <-1.1V.

[0011] In the above-mentioned method for stripping the negative electrode sheet in the metal battery, the polar aprotic solvent in the treatment liquid has a good effect of dissolving the binder, and the polar aprotic solvent has a specific dielectric constant and reduction potential. It basically has no reaction activity with the active metal and thus will not react with the active metal layer of the negative electrode sheet or the reaction degree is low. Applying and acting on the interface between the active metal layer and the diaphragm with the treatment liquid containing the polar aprotic solvent can reduce the interfacial adhesion between the active metal layer and the diaphragm, reduce the probability of metal adhesion to the diaphragm and the risk of oxidation and blackening, improve the deposition morphology integrity of the active metal layer of the negative electrode sheet obtained by stripping, and help to improve the accuracy of the judgment of the metal deposition condition on the negative electrode interface of the metal battery.

[0012] In some embodiments, applying the treatment liquid includes the following steps: applying the treatment liquid to the negative electrode sheet having the separator on its surface from the side where the treatment liquid is located, so that the treatment liquid penetrates the interface between the active metal layer and the separator. This application method is easy to operate and control, and it is also easy to control the amount of treatment liquid applied. It is also less likely to cause the metal layer to fall off the surface, further improving the deposited morphology integrity of the metal layer of the negative electrode sheet obtained by peeling.

[0013] In some embodiments, the treatment liquid is applied in a manner comprising one or more of spraying, showering, and dripping, which facilitates control of the application location and amount.

[0014] In some embodiments, the polar aprotic solvent has a dielectric constant of 7 to 50 at 25° C.; and / or,

[0015] The polar aprotic solvent has a standard reduction potential of -1.15 V to -3 V relative to a standard hydrogen electrode; and / or

[0016] The polar aprotic solvent has a pKa of ≥25 in dimethyl sulfoxide at 25°C.

[0017] Such polar aprotic solvents have a better dissolving effect on the binder.

[0018] The pKa of the polar aprotic solvent in dimethyl sulfoxide at 25° C. is controlled to be ≥25, that is, its acidity is controlled to be low, that is, the hydrogen in the structure of the polar aprotic solvent is controlled to not react with the metal in the active metal layer or to have low reaction activity with the metal in the active metal layer.

[0019] In some embodiments, the polar aprotic solvent includes one or more of an amide solvent and an ether solvent.

[0020] In some embodiments, the amide solvent includes NN dimethylacetamide; and / or,

[0021] The ether solvent includes one or more of tetrahydrofuran and 1,3-dioxolane.

[0022] In some embodiments, the amount of the treatment liquid applied is based on the mass of the polar aprotic solvent, and relative to the area of ​​the negative electrode sheet containing the separator on the surface, the average amount of the polar aprotic solvent applied is ≥0.04 g / cm 2 By controlling the average amount of polar aprotic solvent applied, the amount applied can be moderate, which can reduce the interfacial adhesion and not easily cause the metal layer to fall off the surface, thereby improving the deposition morphology integrity of the metal layer of the negative electrode obtained by peeling.

[0023] In some embodiments, after applying the treatment solution and before peeling the negative electrode sheet from the separator, a step of standing and soaking is further included;

[0024] The static infiltration time is ≥3 min.

[0025] Controlling the static immersion time can take into account the sufficiency of the treatment liquid infiltration, effectively separate the diaphragm and the metal layer, while reducing the oxidation of sodium and lithium metals by air, and maximizing the original deposition morphology of the metal layer of the negative electrode obtained by stripping.

[0026] In some embodiments, the active metal layer includes one of a metallic sodium layer, a metallic lithium layer, and a metallic zinc layer.

[0027] In some embodiments, the diaphragm includes a base film and a coating layer provided on the base film, wherein the coating layer contains a binder; the binder includes one or more of polyvinylidene fluoride, polyacrylic acid, and polyethylene oxide.

[0028] In some embodiments, the binder comprises polyvinylidene fluoride, and the polar aprotic solvent comprises an amide solvent; or

[0029] The binder includes one or more of polyacrylic acid and polyethylene oxide, and the polar aprotic solvent includes an ether solvent.

[0030] According to the different types of binders contained in the coating of the separator, the use of specific solvents for treatment can further improve the solubility of the binder, thereby improving the stripping efficiency between the negative electrode sheet and the separator.

[0031] In a second aspect of the present application, a method for testing a metal battery is provided, comprising the following steps:

[0032] The metal battery to be tested is stripped using the method for stripping the negative electrode sheet in the metal battery provided in the first aspect of the present application to obtain the negative electrode sheet;

[0033] The active metal layer of the negative electrode plate is subjected to morphological analysis.

[0034] The above-mentioned metal battery testing method adopts a negative electrode sheet stripping method to reduce the probability of metal adhesion to the diaphragm, improve the deposition morphology integrity of the active metal layer of the negative electrode sheet obtained by stripping, and is conducive to improving the accuracy of the morphology analysis of the active metal layer of the negative electrode sheet, thereby improving the accuracy of the judgment of the metal deposition situation on the negative electrode interface of the metal battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0036] Figure 1 This is a flow chart of a method for stripping a negative electrode sheet in a metal battery according to one embodiment of the present application.

[0037] Figure 2 This is a flow chart of a metal battery testing method according to one embodiment of the present application. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0039] " scope " disclosed in the present application can be limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are also listed, then the following scope can all be 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 all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for a combination of these values. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0040] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0042] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0043] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0044] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0045] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0046] In batteries, the surface of the separator is usually provided with a coating containing a binder, such as a bonding layer, based on considerations such as the mechanical strength and stability of the separator, improved electrochemical performance, improved electrolyte wetting performance, and providing a physical barrier to metal dendrites piercing the separator. During the cycling process of the metal battery, an active metal layer is formed on the surface of the negative electrode. This active metal layer contacts the separator's binder-containing coating, thereby tightly bonding the active metal on the negative electrode surface to the separator. In addition, the binder-containing coating may also undergo side reactions with the electrolyte and metals such as sodium and lithium, increasing the viscosity of the binder-containing coating and further tightly bonding the active metal on the negative electrode surface to the separator.

[0047] Therefore, the current method of directly disassembling and separating the negative electrode plate and the diaphragm will cause the problem of damage to the deposition morphology of the negative electrode metal, thereby affecting the judgment of the metal deposition situation on the negative electrode interface of the metal battery. Studies have found that the problems of damage to the deposition morphology of the negative electrode metal include the adhesion of the diaphragm to the metal, resulting in an incomplete active metal layer and inability to effectively evaluate the interface, and the oxidation and blackening of the active metal layer, resulting in the loss of the original morphology and inability to effectively evaluate the interface. In short, the integrity of the deposition morphology of the active metal layer of the negative electrode plate is destroyed, thereby reducing the accuracy of the judgment of the metal deposition situation on the negative electrode interface of the metal battery.

[0048] See also Figure 1 In one embodiment of the present application, a method for stripping a negative electrode sheet in a metal battery is provided, comprising the following steps S100 to S300:

[0049] Step S100: disassemble the metal battery to obtain a negative electrode sheet with a separator on its surface, wherein the negative electrode sheet includes an active metal layer.

[0050] Furthermore, the negative electrode plate includes a negative electrode current collector and an active metal layer disposed on the negative electrode current collector. In a negative electrode plate having a separator on its surface, the active metal layer is located between the negative electrode current collector and the separator.

[0051] Step S200: applying a treatment liquid to the negative electrode sheet having a separator on its surface, so that the treatment liquid acts on at least the interface between the active metal layer and the separator.

[0052] Step S300: peeling off the negative electrode plate and the separator.

[0053] The treatment liquid contains a polar aprotic solvent, wherein the treatment liquid contains a polar aprotic solvent, wherein the dielectric constant of the polar aprotic solvent at 25° C. is greater than or equal to 7, and the standard reduction potential of the polar aprotic solvent relative to a standard hydrogen electrode is less than -1.1 V.

[0054] The standard hydrogen electrode (SHE) is a polar aprotic solvent with a standard reduction potential of less than -1.1 V relative to the standard hydrogen electrode, meaning the potential is more negative than -1.1 V.

[0055] Polar aprotic solvents have the same definition as those in the art, meaning they are polar but lack transferable protons in their molecules. Because polar aprotic solvent molecules lack transferable protons, the hydrogen in their structure does not react with the metal in the active metal layer, or has a low reactivity with the metal in the active metal layer.

[0056] The dielectric constant of a polar aprotic solvent at 25°C represents the solvent's ability to shield charges and its influence on the interaction between solute molecules. The dielectric constant of a polar aprotic solvent at 25°C is controlled to be ≥7, so that it has a good effect of dissolving the binder.

[0057] The polar aprotic solvent is controlled to have a standard reduction potential of less than -1.1 V relative to a standard hydrogen electrode. Thus, even if the polar aprotic solvent contains oxidizing groups, the oxidizing groups will not react with the metal in the active metal layer or will have low reactivity with the metal in the active metal layer, thereby preventing oxidation of the active metal layer and causing morphological changes such as blackening. The oxidizing groups include, but are not limited to, hydroxyl, carboxyl, carbonyl, and sulfoxide groups.

[0058] In the above-mentioned method for stripping the negative electrode sheet in the metal battery, the polar aprotic solvent in the treatment liquid has a good effect of dissolving the binder, and the polar aprotic solvent has a specific dielectric constant and reduction potential. It basically has no reaction activity with the active metal and thus will not react with the active metal layer of the negative electrode sheet or the reaction degree is low. Applying and acting on the interface between the active metal layer of the negative electrode sheet and the diaphragm of the treatment liquid containing the polar aprotic solvent can reduce the interfacial adhesion between the active metal layer and the diaphragm, reduce the probability of metal adhesion to the diaphragm and the risk of oxidation and blackening, improve the deposition morphology integrity of the active metal layer of the negative electrode sheet obtained by stripping, and help to improve the accuracy of the judgment of the metal deposition condition on the negative electrode interface of the metal battery.

[0059] As an example, the dielectric constant of the polar aprotic solvent can be 7, 8, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, or any value within a range consisting of any two of the above values ​​as end values. In some embodiments, the dielectric constant of the polar aprotic solvent at 25°C can be selected to be ≥10, so that the polar aprotic solvent has a better dissolving effect on the binder. In some embodiments, the dielectric constant of the polar aprotic solvent at 25°C is 7-50, and can be selected to be 10-50.

[0060] As an example, the standard reduction potential of the polar aprotic solvent relative to a standard hydrogen electrode can be within a range consisting of any two of -1.15 V, -1.2 V, -1.3 V, -1.5 V, -1.8 V, -2 V, -2.3 V, -2.5 V, -2.8 V, or -3 V. In some embodiments, the standard reduction potential of the polar aprotic solvent relative to a standard hydrogen electrode is ≤ -1.15 V, and can further be between -1.15 V and -3 V.

[0061] In some embodiments, the polar aprotic solvent has a pKa of ≥ 25 in dimethyl sulfoxide at 25°C, where pKa is the negative logarithm of the acid dissociation constant (Ka), which is used to quantitatively describe the strength of an acid and reflects the rate at which an acid (HA) loses a proton (H + ) difficulty; the smaller the pKa, the stronger the acidity. The pKa of the polar aprotic solvent in dimethyl sulfoxide at 25°C is controlled to be ≥ 25, i.e., its acidity is controlled to be low. Specifically, the hydrogen in the structure of the polar aprotic solvent is controlled to not react with the metal in the active metal layer, or to have low reactivity with the metal in the active metal layer. Furthermore, the pKa of the polar aprotic solvent in dimethyl sulfoxide at 25°C is between 25 and 45; illustratively, it can be 25, 28, 30, 35, 40, 45, etc., or within a range consisting of any two of the aforementioned values ​​as endpoints.

[0062] It is understandable that the steps of disassembling the metal battery can adopt traditional methods in the field, including removing the outer packaging, the tabs, separating the electrolyte, separating the positive electrode sheets, etc. The positive electrode sheets can be separated by directly tearing off the positive electrode sheets in the electrode assembly, that is, obtaining the negative electrode sheets with a diaphragm on the surface. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a diaphragm, and the positive electrode sheet, the negative electrode sheet and the diaphragm can be made by a winding process or a lamination process. The electrolyte is infiltrated into the electrode assembly, and the metal battery includes an outer packaging, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are arranged in the outer packaging, and the outer packaging can be used to encapsulate the above-mentioned electrode assembly and the electrolyte.

[0063] It is understandable that the negative electrode sheet and the separator can be peeled off by directly tearing the negative electrode sheet and the separator apart.

[0064] In some embodiments, the metal battery is fully charged before being disassembled, and then fully charged using the cyclic charge and discharge conditions required by the cycle test.

[0065] In some embodiments, the active metal layer comprises one of a sodium metal layer, a lithium metal layer, and a zinc metal layer. For example, if the metal battery is a sodium metal battery, the active metal layer comprises a sodium metal layer. For example, if the metal battery is a lithium metal battery, the active metal layer comprises a lithium metal layer. For example, if the metal battery is a zinc metal battery, the active metal layer comprises a zinc metal layer.

[0066] In some embodiments, the separator includes a base film and a coating disposed on the base film, wherein the coating contains a binder. Furthermore, the coating includes an adhesive layer, i.e., the separator includes a base film and an adhesive layer disposed on the base film, wherein the adhesive layer contains a binder. Furthermore, the binder includes one or more of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), and polyethylene oxide (PEO). It is understood that the treatment liquid is applied to the negative electrode plate having the separator on its surface, so that the treatment liquid acts on at least the coating between the negative electrode plate and the separator, thereby acting on the binder in the coating.

[0067] It is understandable that the material of the base film may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0068] In some embodiments, after applying the treatment liquid and before peeling the negative electrode sheet from the separator, a static soaking step is also included to allow the treatment liquid to fully penetrate the interface between the active metal layer and the separator.

[0069] Furthermore, the time for static infiltration is ≥ 3 minutes, and can be selected from 3 minutes to 10 minutes, and more preferably from 3 minutes to 5 minutes. As an example, the time for static infiltration is 3 minutes, 4 minutes, 5 minutes, 8 minutes, 10 minutes, or any value within the range formed by any two of the above point values ​​as end values. Controlling the time for static infiltration can take into account the sufficiency of the infiltration of the treatment liquid, effectively separate the diaphragm and the metal layer, while reducing the oxidation of sodium and lithium metals by air, and maximizing the original deposition morphology of the metal layer of the negative electrode obtained by stripping.

[0070] In some embodiments, applying the treatment liquid includes applying the treatment liquid to the negative electrode sheet having the separator on its surface from the side where the treatment liquid is located, so that the treatment liquid penetrates the interface between the active metal layer and the separator. This application method is easy to operate and control, and also facilitates controlling the amount of treatment liquid applied, further improving the deposited morphology integrity of the metal layer of the negative electrode sheet obtained by stripping.

[0071] Furthermore, the static infiltration step is performed after applying the treatment liquid from the side where the separator is located to the negative electrode plate with the separator on its surface.

[0072] Furthermore, the method for applying the treatment liquid from the side where the separator is located to the negative electrode sheet with the separator on its surface includes, but is not limited to, one or more of spraying, showering, and dripping. These methods facilitate control over the application location and amount. Furthermore, spraying or showering are used as the method for applying the treatment liquid, which provides better uniformity in the application of the treatment liquid. Furthermore, when applying the treatment liquid, the negative electrode sheet with the separator on its surface is laid flat with the separator facing upward.

[0073] It is understood that applying the treatment liquid includes, but is not limited to, the aforementioned methods. For example, immersing the negative electrode sheet having a separator on its surface may also be employed. Compared to immersion, applying the treatment liquid from the side where the separator is located to the negative electrode sheet having a separator on its surface facilitates control of the amount of treatment liquid applied, is less likely to cause the metal layer to fall off, and improves the integrity of the deposited morphology of the metal layer of the negative electrode sheet obtained by stripping.

[0074] Furthermore, the step of applying the treatment liquid in step S200 is performed at room temperature and pressure. Room temperature refers to a temperature between 20° C. and 30° C., and room pressure refers to a standard atmospheric pressure.

[0075] Furthermore, the temperature of the treatment liquid in step S200 is controlled to be 20°C to 30°C.

[0076] Furthermore, for example, the process can be carried out in a dry room environment, with the relative humidity controlled to be less than 1%.

[0077] Furthermore, the amount of treatment liquid applied is calculated as the mass of the polar aprotic solvent, and the average amount of polar aprotic solvent applied relative to the area of ​​the negative electrode sheet containing the separator is ≥ 0.04 g / cm 2 , optional 0.04g / cm 2 ~0.1g / cm 2 , and 0.04g / cm 2 ~0.06g / cm 2 As an example, the average amount of polar aprotic solvent applied may be 0.04 g / cm 2 , 0.05g / cm 2 , 0.06g / cm 2 , 0.08g / cm 2 , 0.1g / cm 2 , or any value within the range defined by any two of the aforementioned points. By controlling the average amount of polar aprotic solvent applied, the amount can be moderated, reducing interfacial adhesion while preventing the metal layer from detaching from the surface. This improves the integrity of the deposited morphology of the metal layer obtained after stripping the negative electrode sheet.

[0078] It can be understood that the average amount of polar aprotic solvent applied refers to the ratio of the total amount of polar aprotic solvent applied to the area of ​​the negative electrode sheet with a separator on its surface to the area of ​​the negative electrode sheet with a separator on its surface. Furthermore, to improve the uniformity of the application of the treatment liquid to the negative electrode sheet with a separator on its surface, the entire surface of the negative electrode sheet with a separator on its surface can be divided into multiple application sub-areas, for example, divided into multiple sub-areas of equal or identical area along multiple rows and columns, and an equal amount of treatment liquid (i.e., an equal amount of polar aprotic solvent) is applied to each sub-area.

[0079] In some embodiments, the treatment liquid is the aforementioned polar aprotic solvent, without the need for the addition of other reagents. In other words, the mass content of the aforementioned polar aprotic solvent in the treatment liquid is 100%. It is understood that in other examples, the addition of other reagents to the treatment liquid is not excluded; as long as the treatment liquid contains the aforementioned polar aprotic solvent, it is within the scope of this application.

[0080] In some embodiments, the mass content of the polar aprotic solvent in the treatment liquid is 80% to 100%; for example, it can be 80%, 85%, 90%, 95%, 100%, or any value within a range consisting of any two of the aforementioned values. Furthermore, the treatment liquid does not contain any other solvents, that is, the solvent in the treatment liquid is the polar aprotic solvent. This can reduce the adverse effects of other solvents on the metal layer deposition morphology caused by reactions with the metal layer, further improving the deposition morphology integrity of the metal layer of the negative electrode sheet obtained by stripping.

[0081] In some embodiments, the polar aprotic solvent includes one or more of an amide solvent and an ether solvent. These solvents not only effectively dissolve the binder but also substantially do not react with the metal layer, thereby improving the deposited morphology integrity of the metal layer of the negative electrode sheet obtained by stripping.

[0082] Furthermore, the amide solvent includes but is not limited to N-dimethylacetamide (DMAC). Furthermore, the ether solvent includes one or more of tetrahydrofuran (THF) and 1,3-dioxolane (DOL).

[0083] In some embodiments, the binder in the coating of the separator includes polyvinylidene fluoride (PVDF), and the polar aprotic solvent includes an amide solvent, including but not limited to NN dimethylacetamide (DMAC).

[0084] In some embodiments, the binder in the coating of the separator includes one or more of polyacrylic acid and polyethylene oxide, and the polar aprotic solvent includes an ether solvent, including but not limited to one or more of tetrahydrofuran and 1,3-dioxolane.

[0085] According to the different types of binders contained in the coating of the separator, the use of specific solvents for treatment can further improve the solubility of the binder, thereby improving the stripping efficiency between the negative electrode sheet and the separator.

[0086] See also Figure 2 Another embodiment of the present application provides a metal battery testing method, comprising the following steps S100 to S400:

[0087] The metal battery to be tested is stripped using the above-mentioned stripping method for the negative electrode sheet of the metal battery to obtain the negative electrode sheet; that is, the method includes steps S100 to S300;

[0088] S400: Perform morphology analysis on the active metal layer of the negative electrode.

[0089] The metal batteries to be tested include but are not limited to failed batteries, or batteries in the battery production process, including normal or abnormal batteries. As an example, for failed batteries, it is necessary to detect and analyze the cause of their failure, and it is necessary to analyze the morphology of the active metal layer of the failed metal battery. As an example, for batteries after formation in the battery production process, when one or more of its gas production and interface are judged to be abnormal, it is necessary to analyze its abnormality, and it is necessary to analyze the morphology of the active metal layer of the failed metal battery; in a specific example, such as a battery analyzed after formation, generally only the battery is fully charged once or the battery directly after formation is analyzed, and the charging SOC is about 30%.

[0090] The above-mentioned metal battery testing method adopts a negative electrode sheet stripping method to reduce the probability of metal adhesion to the diaphragm, improve the deposition morphology integrity of the active metal layer of the negative electrode sheet obtained by stripping, and is conducive to improving the accuracy of the morphology analysis of the active metal layer of the negative electrode sheet, thereby improving the accuracy of the judgment of the metal deposition situation on the negative electrode interface of the metal battery.

[0091] In some embodiments, the morphology analysis includes, but is not limited to, direct observation and morphology analysis assisted by electron microscopy. Electron microscopy includes, but is not limited to, a CCD camera, and through image analysis, the area ratio of the active metal layer to the negative electrode sheet and / or the area ratio of the region without the active metal layer to the negative electrode sheet are calculated based on the color difference between the negative electrode current collector and the active metal layer.

[0092] The area of ​​the region without the active metal layer includes the region where the active metal layer is adhered to the diaphragm and / or falls off due to the reaction with the solvent.

[0093] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0094] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0095] Example 1

[0096] The sodium metal battery used in Example 1 includes an outer packaging, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are arranged in the outer packaging. The outer packaging can be used to encapsulate the above-mentioned electrode assembly and electrolyte. The electrode assembly can be made by winding a positive electrode sheet, a negative electrode sheet and a separator; wherein the negative electrode sheet includes a copper foil with a thickness of 60 μm and an active sodium metal layer with a thickness of about 40 μm arranged on the copper foil, and the separator includes a base film (specifically made of polyethylene with a thickness of 8 μm) and an adhesive layer (specifically made of PVDF with a thickness of 4 μm) arranged on the base film.

[0097] The sodium metal battery in this embodiment is a failed battery, and a failure analysis is performed on it, including a morphology analysis of the metal deposition interface of the sodium metal battery. The failed battery has undergone a large number of full charge and discharge cycles before failure, >500 cycles.

[0098] The method for stripping the negative electrode sheet in a sodium metal battery comprises the following steps:

[0099] (1) Disassemble the sodium metal battery, specifically remove the outer packaging, tabs, separate the electrolyte, separate the positive electrode sheet, and obtain the negative electrode sheet with a diaphragm on the surface.

[0100] (2) At room temperature and pressure, lay the negative electrode sheet with the diaphragm on the surface flat with the diaphragm facing upwards, and apply the treatment liquid NN dimethylacetamide (DMAC) solvent to the negative electrode sheet with the diaphragm on the surface by spraying from the side where the diaphragm is located. The amount of DMAC applied (relative to the area of ​​the negative electrode sheet with the diaphragm on the surface) is controlled to be 0.05 g / cm 2 , let it soak for 4 minutes.

[0101] (3) Then tear and peel off the negative electrode sheet and the separator.

[0102] Comparative Example 1

[0103] Comparative Example 1 is substantially the same as Example 1, except that step (2) is omitted, and after obtaining the negative electrode sheet with the separator on the surface in step (1), the negative electrode sheet and the separator are directly torn and peeled off.

[0104] Comparative Example 2

[0105] Comparative Example 2 is substantially the same as Example 1, except that the N-dimethylacetamide (DMAC) solvent in Example 1 is replaced by dimethyl carbonate (DMC) of the same mass in the treatment liquid.

[0106] Comparative Example 3

[0107] Comparative Example 3 is substantially the same as Example 1, except that the N-dimethylformamide (DMF) of the same mass is used as the treatment liquid to replace the N-dimethylacetamide (DMAC) solvent in Example 1.

[0108] Example 2

[0109] Example 2 is substantially the same as Example 1, except that the N-dimethylacetamide (DMAC) solvent in Example 1 is replaced by tetrahydrofuran (THF) of the same mass as the treatment liquid.

[0110] Example 3

[0111] Example 3 is basically the same as Example 1, except that the material of the adhesive layer of the separator in the sodium metal battery is different, specifically polyacrylic acid (PAA); and the treatment liquid uses tetrahydrofuran (THF) of the same mass instead of the N-dimethylacetamide (DMAC) solvent in Example 1.

[0112] Example 4

[0113] Example 4 is basically the same as Example 3, except that the material of the adhesive layer of the separator in the sodium metal battery is different, specifically polyethylene oxide (PEO).

[0114] Example 5

[0115] Example 5 is substantially the same as Example 4, except that the treatment liquid uses 1,3-dioxolane (DOL) of the same mass to replace the tetrahydrofuran (THF) solvent in Example 4.

[0116] Example 6

[0117] Example 6 is basically the same as Example 1, except that step (2) is different, specifically as follows: at room temperature and pressure, the negative electrode sheet with the diaphragm on the surface is laid flat with the diaphragm facing upward, and completely immersed in the treatment liquid NN dimethylacetamide (DMAC) solvent for 4 minutes.

[0118] Example 7

[0119] Example 7 is basically the same as Example 1, except that the amount of DMAC applied in step (2) is different, specifically as follows: the amount of DMAC applied (relative to the area of ​​the negative electrode sheet containing the diaphragm on the surface) is controlled to be 0.1 g / cm 2 .

[0120] Example 8

[0121] Example 8 is basically the same as Example 1, except that the standing and soaking time in the treatment liquid in step (2) is different, specifically as follows: standing and soaking for 10 minutes.

[0122] The following is a performance test.

[0123] (1) Peeling morphology test of negative electrode sheet and separator.

[0124] The peeling morphologies of the negative electrode sheets and separators obtained by tearing and peeling off Example 1 and Comparative Example 1 were physically observed, and the following results were obtained.

[0125] The surface of the diaphragm obtained by tearing and peeling off Example 1 is clean and complete, with basically no sodium metal layer adhered. At the same time, most of the sodium metal deposited on the negative electrode plate obtained by tearing and peeling off Example 1 is completely retained, and is not adhered to the diaphragm by the adhesive layer of the diaphragm, resulting in exposed copper foil. The surface of the diaphragm obtained by tearing and peeling off Comparative Example 1 has a large amount of sodium metal layer adhered to it. At the same time, the copper foil in most areas of the negative electrode plate obtained by tearing and peeling off Comparative Example 1 is exposed. This is because most of the sodium metal originally deposited on the negative electrode plate adheres to the diaphragm during peeling, making it impossible to perform interface judgment. Therefore, the peeling method of Example 1 of the present application can effectively separate the sodium metal adhered to the diaphragm, and basically will not cause the reaction of the sodium metal, and can achieve efficient, rapid and non-destructive peeling of the anode plate and the diaphragm in the sodium metal battery.

[0126] (2) Quantitative analysis of adhesion was performed using a high-precision CCD detector.

[0127] The specific analysis and quantification method is as follows: a CCD camera is used to capture an image of the surface of the negative electrode sheet on which the active metal layer resides. This image is then analyzed and, based on the color difference between the negative current collector and the active metal layer, the percentage of the active metal layer area in the negative electrode sheet and the percentage of the area of ​​the area of ​​the negative electrode sheet without the active metal layer are calculated. The area of ​​the area without the active metal layer includes areas where the active metal layer has adhered to the separator and / or has detached due to interaction with the solvent. The percentage of the area of ​​the area without the active metal layer to the area of ​​the negative electrode sheet is denoted as K.

[0128] The test results of various embodiments and comparative examples are shown in Table 1.

[0129] Table 1

[0130]

[0131] As can be seen from the table above, Comparative Example 1 was directly torn apart. While Comparative Example 2 employed a solvent treatment, the solvent used was DMC, which has a dielectric constant of approximately 3.1 at 25°C and poor solubility in the adhesive. Therefore, the adhesion area percentages in Comparative Examples 1 and 2 were relatively large. Comparative Example 3 employed DMF (with a standard reduction potential of -1.1 V relative to a standard hydrogen electrode), which is more easily reduced by sodium than DMAC. Therefore, DMF reacted with the active sodium metal layer, causing it to darken significantly. Therefore, the adhesion area percentage was not tested.

[0132] Compared with Comparative Examples 1 to 2, the active metal layers of Examples 1 to 8 were not found to be obviously blackened, and the area of ​​the region without the active metal layer accounted for a relatively low proportion of the area of ​​the negative electrode plate. This shows that the stripping method of the embodiments of the present application effectively reduces the probability of metal adhesion to the diaphragm and the risk of oxidation and blackening, improves the deposition morphology integrity of the metal layer of the negative electrode plate obtained by stripping, and is conducive to improving the accuracy of judging the metal deposition situation on the negative electrode interface of the metal battery.

[0133] The area without an active metal layer in Examples 1-5 is mainly due to the active metal layer adhering to the diaphragm, and therefore mainly reflects the area ratio of the adhesion area. The area without an active metal layer in Examples 1 and 3-5 is relatively low, while in Example 2, due to the relatively low solubility of THF in PVDF, the area without an active metal layer is relatively large. The area without an active metal layer in Examples 6-8 is mainly due to the shedding of the active metal layer due to factors such as the effect of the solvent, and therefore mainly reflects the area ratio of the shedding active metal layer. The immersion method used in Example 6, the large amount of solvent applied in Example 7, and the long soaking time after spraying in Example 8 all increase the area without an active metal layer.

[0134] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art could make several modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the appended claims, and the specification and drawings shall be used to interpret the scope of the claims.

Claims

1. A method for stripping a negative electrode sheet in a metal battery, characterized in that: The steps include: Disassembling the metal battery to obtain a negative electrode sheet having a separator on its surface; the negative electrode sheet includes an active metal layer; Applying a treatment liquid to the negative electrode sheet having a separator on its surface, so that the treatment liquid acts at least on the interface between the active metal layer and the separator; Peeling the negative electrode sheet from the separator; The treatment liquid contains a polar aprotic solvent, the dielectric constant of the polar aprotic solvent at 25°C is ≥7, and the standard reduction potential of the polar aprotic solvent relative to the standard hydrogen electrode is <-1.1V; applying the treatment liquid includes the following steps: applying the treatment liquid from the side where the diaphragm is located to the negative electrode plate with the diaphragm on the surface, so that the treatment liquid is infiltrated into the interface between the active metal layer and the diaphragm; the mass content of the polar aprotic solvent in the treatment liquid is 80%~100%; the amount of the treatment liquid applied is based on the mass of the polar aprotic solvent, and the average amount of the polar aprotic solvent applied relative to the area of ​​the negative electrode plate with the diaphragm on the surface is 0.04g / cm 2 ~0.08g / cm 2 ; After applying the treatment liquid and before peeling the negative electrode sheet from the separator, the method further includes a step of standing and soaking; the time for standing and soaking is 3 minutes to 8 minutes; The diaphragm includes a base film and a coating provided on the base film, wherein the coating contains a binder; wherein the binder includes polyvinylidene fluoride, and the polar aprotic solvent includes an amide solvent; or, the binder includes one or more of polyacrylic acid and polyethylene oxide, and the polar aprotic solvent includes an ether solvent.

2. The method for stripping the negative electrode sheet in a metal battery according to claim 1, wherein: The treatment liquid is applied in one or more ways including spraying, showering and dripping.

3. The method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 2, characterized in that: The polar aprotic solvent has a dielectric constant of 7 to 50 at 25° C.; and / or, The polar aprotic solvent has a standard reduction potential of -1.15 V to -3 V relative to a standard hydrogen electrode; and / or The polar aprotic solvent has a pKa of ≥25 in dimethyl sulfoxide at 25°C.

4. The method for stripping the negative electrode sheet in a metal battery according to claim 1, wherein: The amide solvent includes NN dimethylacetamide.

5. The method for stripping the negative electrode sheet in a metal battery according to claim 1, wherein: The ether solvent includes one or more of tetrahydrofuran and 1,3-dioxolane.

6. The method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 2, 4 to 5, wherein: The amount of the treatment liquid applied is based on the mass of the polar aprotic solvent. The average amount of the polar aprotic solvent applied relative to the area of ​​the negative electrode sheet with the separator on the surface is 0.04 g / cm 2 ~0.06g / cm 2 .

7. The method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 2, 4 to 5, wherein: After applying the treatment liquid and before peeling the negative electrode sheet from the separator, the method further includes a step of standing and soaking; The time for the static infiltration is 3 min to 5 min.

8. The method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 2, 4 to 5, wherein: The active metal layer includes one of a metal sodium layer, a metal lithium layer and a metal zinc layer.

9. A metal battery testing method, characterized in that: The steps include: The metal battery to be tested is stripped using the method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 8 to obtain the negative electrode sheet; The active metal layer of the negative electrode plate is subjected to morphological analysis.

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