Method for stripping negative pole piece in metal battery and method for testing metal battery

Abstract

The invention provides a stripping method of a negative pole piece in a metal battery and a testing method of the metal battery. The stripping method comprises the following steps: disassembling the metal battery to obtain a negative pole piece with a diaphragm on the surface; the negative pole piece comprises an active metal layer; applying the treating fluid to the negative pole piece with the diaphragm on the surface, enabling the treating fluid to at least act on an interface between the active metal layer and the diaphragm, and stripping the negative pole piece from the diaphragm; wherein the treating fluid comprises a polar aprotic solvent, the dielectric constant of the polar aprotic solvent at 25 DEG C is larger than or equal to 7, and the standard reduction potential of the polar aprotic solvent relative to a standard hydrogen electrode is smaller than-1.1 V. According to the stripping method, the risks of metal adhesion and oxidation blackening can be reduced, the deposition morphology integrity of the metal layer of the cathode pole piece obtained by stripping is improved, and the accuracy of judging the metal deposition condition on the cathode interface of the metal battery is improved.

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] As the global demand for energy-intensive energy storage increases, the development of energy storage devices with higher energy density, longer cycle life and safer energy storage devices has become an important goal of battery development. Among them, lithium-ion batteries have occupied the mainstream energy storage market and are widely used in mobile electronic devices, electric vehicles, energy storage power stations, etc. due to their high energy density, excellent cycle performance and no memory effect. At present, the energy density of lithium-ion batteries can reach 250 Wh / Kg, but it is still about an order of magnitude lower than the energy density of gasoline. Metal batteries based on metal negative electrodes have great advantages over traditional lithium-ion batteries in terms of energy density. Take sodium metal batteries as an example: they have extremely high theoretical specific capacity, about 1166mAh / g and low electrochemical potential, about -2.71V relative to the standard hydrogen electrode.

[0003] The electrochemical energy storage mechanism of metal batteries is fundamentally different from that of lithium-ion batteries. During the cycle, uneven deposition often occurs on the negative electrode surface, resulting in poor cycle performance. Therefore, during the R&D and production process, it is generally necessary to disassemble the battery to determine the negative electrode interface in order to evaluate the impact of deposition conditions such as the negative electrode metal deposition morphology on battery performance.

[0004] However, currently, a method of directly disassembling and separating the negative electrode plate and the separator is generally adopted. This method may cause the problem of destroying the deposition morphology of the negative electrode metal, thereby affecting the judgment of the metal deposition condition on the negative electrode interface of the metal battery. Summary of the invention

[0005] Based on this, it is necessary for this application to provide a method for stripping the negative electrode sheet in a metal battery, which 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 help improve the accuracy of judging the metal deposition situation on the negative electrode interface of the metal battery. In addition, a metal battery testing method is also 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 the surface; the negative electrode sheet includes an active metal layer;

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

[0009] Peeling off the negative electrode sheet and the separator;

[0010] The treatment solution 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, and 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 reacts to a low degree. Applying and acting the treatment liquid containing the polar aprotic solvent on the interface between the active metal layer and the diaphragm 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 judging the metal deposition situation 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 from the side where the separator is located to the negative electrode sheet having the separator on the surface, so that the treatment liquid infiltrates the interface between the active metal layer and the separator. This application method is easy to operate and control, and is also easy to control the amount of the treatment liquid applied, and is not likely to cause the metal layer surface to fall off, further improving the deposition morphology integrity of the metal layer of the negative electrode sheet obtained by peeling.

[0013] In some embodiments, the treatment liquid is applied in one or more ways including spraying, showering and dripping, which facilitates controlling the application position and application 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, the acidity thereof is controlled to be low, that is, the hydrogen in the structure of the polar aprotic solvent is controlled not to 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 measured by the mass of the polar aprotic solvent, and relative to the area of ​​the negative electrode sheet having 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, thereby improving the deposition morphology integrity of the metal layer of the negative electrode sheet 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 also included;

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

[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 metal sodium layer, a metal lithium layer and a metal zinc layer.

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

[0028] In some embodiments, the binder includes polyvinylidene fluoride, and the polar aprotic solvent includes 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 metal battery testing method is provided, comprising the following steps:

[0032] The metal battery to be tested is stripped by 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 testing method for metal batteries 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, which is beneficial to improve the accuracy of the morphology analysis of the active metal layer of the negative electrode sheet, and further improve the accuracy of the judgment of the metal deposition condition 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 by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the 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 of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0036] Figure 1 The present invention 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 the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work 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 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 excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, 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 listed, and if the maximum range values ​​3,4 and 5 are also listed, 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 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 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", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0040] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater 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] Reference to "embodiments" herein means 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 the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0043] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean 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 internal logic. 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), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can 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, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0046] In batteries, the surface of the diaphragm is usually provided with a coating containing a binder, such as a bonding layer, based on considerations such as the improvement of the mechanical strength and stability of the diaphragm, the improvement of the electrochemical performance, the improvement of the electrolyte infiltration performance, and the provision of a physical barrier for metal dendrites to pierce the diaphragm. During the cycle of the metal battery, an active metal layer is formed on the negative electrode surface, and the active metal layer contacts the coating containing the binder of the diaphragm, thereby making the active metal on the negative electrode surface tightly bonded to the diaphragm. In addition, the coating containing the binder may also react with the electrolyte and metals such as sodium and lithium, which increases the viscosity of the coating containing the binder, further making the active metal on the negative electrode surface tightly bonded to the diaphragm.

[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, thus affecting the judgment of the metal deposition 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 that cannot effectively evaluate the interface, and the oxidation and blackening of the active metal layer, resulting in the loss of the original morphology and the 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 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 the surface, wherein the negative electrode sheet includes an active metal layer.

[0050] Furthermore, the negative electrode sheet includes a negative electrode current collector and an active metal layer disposed on the negative electrode current collector. In the negative electrode sheet 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 plate 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 ≥ 7, and the standard reduction potential of the polar aprotic solvent relative to a standard hydrogen electrode is <-1.1V.

[0054] The English name of the standard hydrogen electrode is Standard Hydrogen Electrode, abbreviated as SHE. The standard reduction potential of a polar aprotic solvent relative to the standard hydrogen electrode is less than -1.1V, which means that the potential is more negative than -1.1V.

[0055] Polar aprotic solvents have the same definition as in the art, which means that the solvent has polarity but has no transferable protons in the molecule. Since there are no transferable protons in the polar aprotic solvent molecule, hydrogen in the structure of the polar aprotic solvent does not react with the metal in the active metal layer or has a low reaction activity with the metal in the active metal layer.

[0056] The dielectric constant of a polar aprotic solvent at 25°C represents the shielding ability of the solvent to 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 dissolving binder effect.

[0057] The standard reduction potential of the polar aprotic solvent relative to the standard hydrogen electrode is controlled to be less than -1.1V, so that even if the polar aprotic solvent contains oxidizing groups, the oxidizing groups do not react with the metal in the active metal layer or have low reactivity with the metal in the active metal layer, thereby preventing the active metal layer from being oxidized and causing morphological changes such as blackening. The oxidizing groups refer to groups with oxidizing properties, including but not limited to hydroxyl, carboxyl, carbonyl, sulfoxide and other 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, and 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 reacts to a low degree. The treatment liquid containing the polar aprotic solvent is applied and acts on the interface between the active metal layer of the negative electrode sheet and the diaphragm, which 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 is conducive to improving the accuracy of judging the metal deposition condition on the negative electrode interface of the metal battery.

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

[0060] As an example, the standard reduction potential of the polar aprotic solvent relative to the standard hydrogen electrode may be within the range of any two of the above values ​​as end values, such as -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 the standard hydrogen electrode is ≤ -1.15 V, and may further be -1.15 V to -3 V.

[0061] In some of the 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. Controlling the pKa of the polar aprotic solvent in dimethyl sulfoxide at 25°C ≥ 25, that is, controlling its acidity to be relatively low, that is, controlling the hydrogen in the structure of the polar aprotic solvent not to react with the metal in the active metal layer or to have a relatively low reaction activity with the metal in the active metal layer. Further, the pKa of the polar aprotic solvent in dimethyl sulfoxide at 25°C is 25-45; as examples, it can be 25, 28, 30, 35, 40, 45, etc. or within the range consisting of any two of the above point values ​​as end values.

[0062] Understandably, the steps of disassembling the metal battery can adopt the traditional methods in the field, including removing the outer packaging, the pole ears, separating the electrolyte, separating the positive electrode sheet and the like. To separate the positive electrode sheet, the positive electrode sheet in the electrode assembly can be directly torn apart, that is, the negative electrode sheet with a diaphragm on the surface is obtained. 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 in a fully charged state before the metal battery is disassembled, and can be fully charged after further adopting the cycle charge and discharge conditions required by the cycle test.

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

[0066] In some of the embodiments, the diaphragm includes a base film and a coating provided on the base film, and the coating contains a binder. Further, the coating includes a bonding layer, that is, the diaphragm includes a base film and a bonding layer provided on the base film, and the bonding layer contains a binder. Further, the binder includes one or more of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and polyethylene oxide (PEO). It can be understood that the treatment liquid is applied to the negative electrode plate having a diaphragm on the surface, so that the treatment liquid acts on at least the coating between the negative electrode plate and the diaphragm to act on the binder in the coating.

[0067] It can be understood 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 of the embodiments, after applying the treatment liquid and before peeling the negative electrode plate from the separator, a static soaking step is also included to allow the treatment liquid to fully infiltrate the interface between the active metal layer and the separator.

[0069] Furthermore, the time of standing and soaking is ≥ 3min, and can be selected as 3min~10min, and can be selected as 3min~5min. As an example, the time of standing and soaking is 3min, 4min, 5min, 8min, 10min, or any value within the range formed by any two of the above point values ​​as end values. Controlling the time of standing and soaking can take into account the sufficiency of the infiltration of the treatment liquid, effectively separate the diaphragm and the metal layer, and at the same time reduce the oxidation of sodium and lithium metals by air, and maximize the original deposition morphology of the metal layer of the negative electrode obtained by stripping.

[0070] In some embodiments, applying the treatment liquid includes the following steps: applying the treatment liquid from the side where the separator is located to the negative electrode sheet having the separator on the surface, so that the treatment liquid infiltrates 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 the treatment liquid applied, further improving the deposition 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 having the separator on its surface.

[0072] Further, the method of applying the treatment liquid from the side where the diaphragm is located to the negative electrode plate with the diaphragm on the surface includes but is not limited to one or more of spraying, showering and dripping. These methods are convenient for controlling the application position and application amount. Further, the treatment liquid is applied by spraying and showering, and the uniformity of applying the treatment liquid is good. Further, when applying the treatment liquid, the negative electrode plate with the diaphragm on the surface is laid flat with the diaphragm facing upward.

[0073] It is understandable that the application of the treatment liquid includes but is not limited to the above-mentioned methods, for example, the method of soaking the negative electrode sheet with a separator on the surface can also be adopted. Compared with the soaking method, the method of applying the treatment liquid from the side where the separator is located to the negative electrode sheet with a separator on the surface can facilitate the control of the amount of treatment liquid applied, and is not likely to cause the metal layer surface to fall off, thereby improving the deposition morphology integrity of the metal layer of the negative electrode sheet obtained by peeling.

[0074] Furthermore, the step of applying the treatment liquid in step S200 is performed at room temperature and pressure. Room temperature refers to between 20° C. and 30° C. 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 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 sheet containing the separator on the surface is ≥ 0.04 g / cm 2 , optional 0.04g / cm 2 ~0.1g / cm 2 , and can be selected as 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 formed by any two of the above point values ​​as end values. By controlling the average amount of polar aprotic solvent applied, the amount of application can be moderate, which can reduce the interfacial adhesion and not easily cause the metal layer to fall off, thereby improving the deposition morphology integrity of the metal layer of the negative electrode sheet obtained by peeling.

[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 the surface to the area of ​​the negative electrode sheet with a separator on the surface. Further, in order to improve the uniformity of the application of the treatment liquid on the negative electrode sheet with a separator on the surface, the entire surface of the negative electrode sheet with a separator on the surface can be divided into multiple application sub-areas, for example, divided into multiple sub-areas with equal or identical areas according to multiple rows and columns, and the same amount of treatment liquid is applied to each sub-area (i.e., the same amount of polar aprotic solvent is applied).

[0079] In some embodiments, the treatment liquid is the polar aprotic solvent, and no other reagents need to be added. In other words, the mass content of the polar aprotic solvent in the treatment liquid is 100%. It is understandable that in other examples, it is not excluded to add other reagents to the treatment liquid, as long as the treatment liquid contains the polar aprotic solvent, it is within the scope of the present application.

[0080] In some embodiments, the mass content of the polar aprotic solvent in the treatment liquid is 80% to 100%; as an example, it can be 80%, 85%, 90%, 95%, 100%, or any value within the range formed by any two of the above point values ​​as end values. Further, the treatment liquid does not contain other solvents, that is, the solvent in the treatment liquid is the polar aprotic solvent, which can reduce the adverse effects of other solvents on the deposition morphology of the metal layer caused by the reaction with the metal layer, and further improve 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 agents can not only dissolve the binder well, but also basically do not react with the metal layer, so as to improve the deposition morphology integrity of the metal layer of the negative electrode sheet obtained by stripping.

[0082] Further, the amide solvent includes but is not limited to N-N-dimethylacetamide (DMAC). Further, 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 diaphragm 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-S400:

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

[0088] S400, performing morphological analysis on the active metal layer of the negative electrode plate.

[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 failure, and the morphology of the active metal layer of the failed metal battery needs to be analyzed. 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 the morphology of the active metal layer of the failed metal battery needs to be analyzed; in a specific example, for example, as a battery for analysis after formation, the battery is generally only fully charged once or the battery is analyzed directly after formation, and the charging SOC is about 30%.

[0090] The above-mentioned testing method for metal batteries 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, which is beneficial to improve the accuracy of the morphology analysis of the active metal layer of the negative electrode sheet, and further improve the accuracy of the judgment of the metal deposition condition on the negative electrode interface of the metal battery.

[0091] In some embodiments, the above-mentioned morphology analysis includes but is not limited to direct observation, morphology analysis assisted by electron microscope, etc. The electron microscope includes but is not limited to 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 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 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 the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0094] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0095] Example 1

[0096] The sodium metal battery used in Example 1 includes an outer package, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are arranged in the outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and the electrolyte. The electrode assembly can be made by winding a positive electrode plate, a negative electrode plate and a diaphragm; wherein the negative electrode plate 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 diaphragm 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 the sodium metal battery comprises the following steps:

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

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

[0101] (3) Then tear and peel off the negative electrode plate 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 having a separator on its 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 treatment liquid uses dimethyl carbonate (DMC) of the same mass to replace the N-N-dimethylacetamide (DMAC) solvent in Example 1.

[0106] Comparative Example 3

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

[0108] Example 2

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

[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 to replace the N-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, lay the negative electrode sheet with the separator on the surface flat with the separator facing upward, and completely immerse it in a 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 separator 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 solution 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, most areas of the negative electrode plate obtained by tearing and peeling off Comparative Example 1 have exposed copper foil. 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 stripping method of Example 1 of the present application can effectively separate the sodium metal adhered to the diaphragm, and basically does not cause the reaction of the sodium metal, and can achieve efficient, rapid and non-destructive stripping of the anode plate and the diaphragm in the sodium metal battery.

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

[0127] The specific analysis and quantitative method are as follows: a CCD camera is used to capture an image of the surface of the negative electrode sheet where the active metal layer is located, and the image is analyzed to calculate the area ratio of the active metal layer to the negative electrode sheet and the area ratio of the region without the active metal layer to the negative electrode sheet based on the color difference between the negative electrode current collector and the active metal layer, where the area without the active metal layer includes the area where the active metal layer is adhered to the diaphragm and / or reacts with the solvent and falls off. The area ratio of the region without the active metal layer to the area of ​​the negative electrode sheet is recorded 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, and although Comparative Example 2 was treated with a solvent, the solvent used was DMC, whose dielectric constant at 25°C was about 3.1. DMC had poor solubility in the binder, so the area ratio of the adhesion area in Comparative Examples 1 and 2 was relatively large. Comparative Example 3 used DMF (with a standard reduction potential of -1.1V relative to a standard hydrogen electrode), which was more easily reduced by sodium than DMAC. Therefore, DMF reacted with the active sodium metal layer, causing the color of the active sodium metal layer to become obviously black, and the area ratio test of the adhesion area was not performed.

[0132] Compared with comparative examples 1-2, no obvious blackening was found in the active metal layers of embodiments 1-8, and the area of ​​the region without the active metal layer accounts for a relatively low proportion of the area of ​​the negative electrode plate, indicating 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 of ​​the region without active metal layer in Examples 1 to 5 is mainly caused by the adhesion of the active metal layer to the diaphragm, so it mainly reflects the area ratio of the adhesion area, among which the area ratio of the region without active metal layer in Examples 1 and 3 to 5 is relatively low, and the area ratio of the region without active metal layer in Example 2 is relatively large due to the relatively low solubility of THF in PVDF. The area of ​​the region without active metal layer in Examples 6 to 8 is mainly caused by the fall of the active metal layer due to the effect of solvents and other reasons, so it mainly reflects the area ratio of the fall of the active metal layer. In Example 6, the immersion method is adopted, the amount of solvent applied in Example 7 is large, and the immersion time after spraying in Example 8 is long, all of which increase the area of ​​the region without active metal layer.

[0134] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims, and the description and drawings may 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 the 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 off the negative electrode sheet from the separator; The treatment solution 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.

2. The method for stripping the negative electrode sheet in a metal battery according to claim 1, characterized in that: Applying the treatment liquid includes the following steps: applying the treatment liquid from the side where the separator is located to the negative electrode plate whose surface contains the separator, so that the treatment liquid infiltrates the interface between the active metal layer and the separator.

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

4. The method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 3, 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.

5. The method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 3, characterized in that: The polar aprotic solvent includes one or more of an amide solvent and an ether solvent.

6. The method for stripping the negative electrode sheet in a metal battery according to claim 5, characterized in that: The amide solvent includes NN dimethylacetamide; and / or, The ether solvent includes one or more of tetrahydrofuran and 1,3-dioxolane.

7. The method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 3 and 6, characterized in that: 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 with the separator on the surface, the average amount of the polar aprotic solvent applied is ≥ 0.04 g / cm 2 .

8. The method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 3 and 6, characterized in that: 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 static infiltration time is ≥3 minutes.

9. The method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 3 and 6, characterized in that: The active metal layer includes one of a metal sodium layer, a metal lithium layer and a metal zinc layer.

10. The method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 3 and 6, characterized in that: The diaphragm comprises a base film and a coating layer arranged on the base film, wherein the coating layer contains a binder; the binder comprises one or more of polyvinylidene fluoride, polyacrylic acid and polyethylene oxide.

11. The method for stripping the negative electrode sheet in a metal battery according to claim 10, characterized in that: 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.

12. A metal battery testing method, characterized in that: The steps include: The metal battery to be tested is stripped by the method for stripping the negative electrode sheet in a metal battery according to any one of claims 1 to 11 to obtain the negative electrode sheet; The active metal layer of the negative electrode plate is subjected to morphological analysis.

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