Reference electrode, preparation method and preparation device of reference electrode, three-electrode battery and preparation method of three-electrode battery

Abstract

The embodiment of the invention provides a reference electrode, a preparation method and a preparation device of the reference electrode, a three-electrode battery and a preparation method of the three-electrode battery. The reference electrode comprises: a metal substrate; the coating is arranged on at least part of the surface of the metal base material, the coating comprises an electrode material, a voltage platform of a charging and discharging curve of the electrode material comprises a first interval, and the difference value between the maximum voltage value and the minimum voltage value of the first interval is smaller than 10 mV. According to the technical scheme provided by the embodiment of the invention, the electrochemical characteristic information of the battery can be effectively monitored for a long time.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a reference electrode and a preparation method and device thereof, a three-electrode battery and a preparation method thereof. Background Art

[0002] In recent years, the application scope of secondary batteries has become increasingly wide. They are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] During the use of secondary batteries, their capacity, voltage, impedance, etc. will continue to change with the increase of charge and discharge times. Accurately obtaining and monitoring the electrochemical characteristics of the battery is of great significance for the battery life and safety monitoring. Therefore, how to effectively monitor the electrochemical characteristics of the battery is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above-mentioned technical problems, and its purpose is to provide a reference electrode to achieve long-term and effective monitoring of the electrochemical characteristic information of the battery.

[0005] In order to achieve the above-mentioned objectives, the present application provides a reference electrode and a preparation method and a preparation device thereof, a three-electrode battery and a preparation method thereof.

[0006] In a first aspect, a reference electrode is provided, comprising: a metal substrate; a coating, wherein the coating is disposed on at least a portion of the surface of the metal substrate, the coating comprises an electrode material, the voltage platform of the charge and discharge curve of the electrode material comprises a first interval, and the difference between the maximum voltage and the minimum voltage in the first interval is less than 10 mV.

[0007] In an embodiment of the present application, the reference electrode includes a metal substrate and a coating disposed on at least a portion of the surface of the metal substrate. The voltage platform of the charge-discharge curve of the electrode material in the coating includes a first interval, and the difference between the maximum voltage and the minimum voltage in the first interval is less than 10mV, that is, the electrode material has a stable voltage platform. When used as an electrode material for a reference electrode, the reference electrode has high potential repeatability, small polarization, good stability, good cycle performance, and long service life. The use of the above-mentioned reference electrode can effectively monitor the electrochemical characteristics of the battery for a long time.

[0008] In a possible implementation, the absolute value of the difference between the capacity value in the charge-discharge curve corresponding to one endpoint of the first interval and the capacity value in the charge-discharge curve corresponding to another endpoint of the first interval is greater than 10%. During the use of the battery, the capacity of the reference electrode will change slightly due to the influence of itself and the outside world. When the electrode material meets the above conditions, even if the capacity of the reference electrode changes, its capacity can still be within the capacity range corresponding to the first interval, and the performance of the reference electrode remains stable.

[0009] In a possible implementation, the thickness of the coating ranges from 100 μm to 200 μm.

[0010] The thickness of the coating is set within the above range, so that the reference electrode has an appropriate reference capacity, which is beneficial to improving the cycle performance and service life of the reference electrode.

[0011] In one possible implementation, the reference electrode is used in a lithium battery, and the electrode material includes a lithium-containing olivine structure phosphate material, a lithium-containing spinel material, and a carbon material; optionally, the lithium-containing olivine structure phosphate material includes at least one of lithium iron phosphate and lithium iron manganese phosphate; optionally, the lithium-containing spinel material includes lithium manganate; optionally, the carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon nanotubes, and graphene.

[0012] Olivine structure is a crystal structure of materials, and materials with olivine structure have higher stability. Olivine structure phosphates have the advantages of higher theoretical specific capacity, better cycle stability, low cost and environmental friendliness. For example, lithium iron phosphate and lithium iron manganese phosphate both have the advantages of long cycle life and good thermal stability. Spinel is a mineral composed of magnesium aluminum oxide, with tetrahedral and octahedral crystal forms. For example, spinel-type lithium manganese oxide materials have outstanding characteristics such as higher specific capacity, low cost and less environmental pollution. Due to the unique composition of the carbon structure, carbon materials have good electrical conductivity.

[0013] In one possible implementation, the reference electrode is used in a sodium battery, and the electrode material includes at least one of a carbon material, sodium vanadium phosphate, sodium titanate, and Na4Fe3(PO4)2(P2O7); optionally, the carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon nanotubes, and graphene.

[0014] In a possible implementation, the metal substrate includes at least one of aluminum, copper, tin, sodium-tin alloy, stainless steel, silver, gold, and platinum.

[0015] In a possible implementation, the metal substrate is a metal wire, and the diameter of the metal wire ranges from 30 μm to 400 μm.

[0016] The diameter of the metal wire is set within the above range. On the one hand, it is beneficial to the adhesion of the coating on the surface of the metal wire and to improve the performance of the reference electrode. On the other hand, it controls the reference electrode to have a suitable volume and reduces the influence of the reference electrode on the battery interface.

[0017] In a possible implementation, the metal substrate is a metal foil, and the thickness of the metal foil ranges from 4 μm to 30 μm.

[0018] The thickness of the metal foil is set within the above range. On the one hand, it is beneficial to the adhesion of the coating on the surface of the metal foil and to improve the performance of the reference electrode. On the other hand, it controls the reference electrode to have a suitable volume and reduces the influence of the reference electrode on the battery interface.

[0019] In a possible implementation, the width of the reference electrode ranges from 0.5 mm to 1 mm.

[0020] The width of the reference electrode is set within the above range, so that the reference electrode has a suitable size and reduces the influence of the reference electrode on the battery interface.

[0021] In a possible implementation, the length of the coating ranges from 10 mm to 25 mm.

[0022] The length of the coating is set within the above range so that the reference electrode as a whole has a suitable size, thereby reducing the influence of the reference electrode on the battery interface.

[0023] In a possible implementation, the coating further includes a conductive agent. Optionally, the conductive agent includes at least one of conductive carbon black, superconducting carbon, carbon dots, Ketjen black, and carbon nanotubes.

[0024] Conductive agents collect microcurrents between electrode materials to reduce the contact resistance of the electrodes and accelerate the movement of electrons. They can also effectively increase the migration rate of metal ions in the electrode materials, thereby improving the charge and discharge efficiency of the electrodes. Due to the unique composition of the carbon structure, carbon material conductive agents have good electrical conductivity. For example, conductive carbon black has the advantages of low resistance and high conductivity, small particle size, large and rough specific surface area, high structure, and clean surface (few compounds); Ketjen black has a unique branched morphology, so it has high conductivity; carbon atoms in carbon nanotubes adopt SP 2 Hybridization, thus having high modulus and high strength, carbon nanotubes also have good flexibility, stretchability and conductivity. Conductive carbon black, superconducting carbon, carbon dots, Ketjen black, and carbon nanotubes as conductive agents can improve the conductivity of batteries.

[0025] In a possible implementation, the coating also includes a binder. Optionally, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trichloroethylene copolymer and fluorine-containing acrylic resin, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, and styrene-butadiene rubber.

[0026] The binder can bond the electrode material to the conductive agent, enhance the electrical contact between the electrode material and the conductive agent, and enhance the structural stability of the reference electrode. The above substances all have good bonding properties, and can be used as binders to enhance the bonding force between the electrode material and the conductive agent and the structural stability of the reference electrode.

[0027] In a possible implementation, based on the total mass of the coating, the mass content of the electrode material in the coating ranges from 90% to 98%.

[0028] The mass content of the electrode material in the coating is set within an appropriate range so that the reference electrode has an appropriate reference capacity, which is beneficial to improving the cycle performance and service life of the reference electrode.

[0029] In a possible implementation, based on the total mass of the coating, the mass content of the conductive agent in the coating ranges from 0.1% to 5%.

[0030] Setting the mass content of the conductive agent in the coating within an appropriate range is beneficial to improving the conductivity of the reference electrode, allowing the reference electrode to better play its role in obtaining electrochemical characteristic information such as battery capacity, voltage, impedance, etc.

[0031] In a possible implementation, based on the total mass of the coating, the mass content of the binder in the coating ranges from 0.5% to 5%.

[0032] Setting the mass content of the binder in the coating within an appropriate range is beneficial to enhancing the electrical contact between the electrode material and the conductive agent, and is also beneficial to improving the structural stability of the reference electrode.

[0033] In a second aspect, a method for preparing a reference electrode is provided, comprising: coating an electrode slurry on at least a portion of the surface of a metal substrate; wherein the electrode slurry comprises an electrode material, the voltage platform of the charge and discharge curve of the electrode material comprises a first interval, and the difference between the maximum voltage and the minimum voltage in the first interval is less than 10 mV; and drying the electrode slurry coated on at least a portion of the surface of the metal substrate to obtain the reference electrode.

[0034] In a possible implementation, the thickness of the coating ranges from 100 μm to 200 μm.

[0035] The thickness of the coating is set within the above range, so that the reference electrode has an appropriate reference capacity, which is beneficial to improving the cycle performance and service life of the reference electrode.

[0036] In one possible implementation, the reference electrode is used in a lithium battery, and the electrode material includes a lithium-containing olivine structure phosphate material, a lithium-containing spinel material, and a carbon material; optionally, the lithium-containing olivine structure phosphate material includes at least one of lithium iron phosphate and lithium iron manganese phosphate; optionally, the lithium-containing spinel material includes lithium manganate; optionally, the carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon nanotubes, and graphene.

[0037] Olivine structure is a crystal structure of materials, and materials with olivine structure have higher stability. Olivine structure phosphates have the advantages of higher theoretical specific capacity, better cycle stability, low cost and environmental friendliness. For example, lithium iron phosphate and lithium iron manganese phosphate both have the advantages of long cycle life and good thermal stability. Spinel is a mineral composed of magnesium aluminum oxide, with tetrahedral and octahedral crystal forms. For example, spinel-type lithium manganese oxide materials have outstanding characteristics such as higher specific capacity, low cost and less environmental pollution. Due to the unique composition of the carbon structure, carbon materials have good electrical conductivity.

[0038] In one possible implementation, the reference electrode is used in a sodium battery, and the electrode material includes at least one of a carbon material, sodium vanadium phosphate, sodium titanate, and Na4Fe3(PO4)2(P2O7); optionally, the carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon nanotubes, and graphene.

[0039] In a possible implementation, the metal substrate includes at least one of aluminum, copper, tin, sodium-tin alloy, stainless steel, silver, gold, and platinum.

[0040] In one possible implementation, the metal substrate is a metal wire, and coating the electrode slurry on at least a portion of the surface of the metal substrate includes: fixing the metal wire to a winding pole of a preparation device; and scraping the electrode slurry on at least a portion of the surface of the metal wire with a film applicator.

[0041] In one possible implementation, the metal substrate is a metal foil, and the preparation method further includes: after drying the electrode slurry coated on at least a portion of the surface of the metal substrate, shearing the metal foil having at least a portion of the surface coated with the electrode material along its length direction to obtain at least two reference electrodes.

[0042] In a third aspect, a reference electrode preparation device is provided, comprising: a providing module for providing a metal substrate; a preparing module for preparing an electrode slurry, wherein the electrode slurry comprises an electrode material, and the voltage platform of the charge and discharge curve of the electrode material comprises a first interval, and the difference between the maximum voltage and the minimum voltage in the first interval is less than 10 mV; a coating module for coating the electrode slurry on at least a portion of the surface of the metal substrate; and a drying module for drying the electrode slurry coated on at least a portion of the surface of the metal substrate.

[0043] In a possible implementation, the metal substrate is a metal wire, and the coating module includes a fixing device and a film applicator;

[0044] The fixing device is used to fix the metal wire;

[0045] The film applicator is used to scrape the electrode slurry onto at least a portion of the surface of the metal wire.

[0046] In a possible implementation, the fixing device includes a winding post, and the fixing device includes an upper plate, the upper plate is provided with a winding post, and the winding post is used to fix the metal wire.

[0047] In a possible implementation, the upper plate is provided with a through groove, and the fixing device also includes a lower plate; the first surface of the lower plate close to the upper plate is provided with a protrusion protruding from the first surface, the protrusion extends along a first direction, and the protrusion is embedded in the through groove to form a material trough for accommodating the electrode slurry.

[0048] In a possible implementation manner, in the first direction, a size of the through groove is larger than a size of the protrusion.

[0049] In a fourth aspect, a three-electrode battery is provided, comprising the reference electrode in the first aspect and any possible implementation thereof; a positive electrode plate; a negative electrode plate; and a separation membrane; the positive electrode plate, the reference electrode, and the negative electrode plate are arranged in sequence at intervals, and the separation membrane is provided between the positive electrode plate and the reference electrode, and between the reference electrode and the negative electrode plate.

[0050] In a fifth aspect, a method for preparing a three-electrode battery is provided, comprising: assembling the reference electrode, positive electrode sheet, negative electrode sheet and isolation membrane in the first aspect and any possible implementation thereof into an electrode assembly; packaging the electrode assembly with an outer packaging; and injecting an electrolyte into the outer packaging to obtain the three-electrode battery.

[0051] In a possible implementation, the preparation method also includes: forming the three-electrode battery; charging the reference electrode to a preset cutoff voltage, and then discharging the reference electrode until the capacity of the reference electrode is within the range of the capacity of the electrode material corresponding to the first interval. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0053] Figure 1 A schematic diagram of a reference electrode according to an embodiment of the present application;

[0054] Figure 2 A schematic diagram of a reference electrode according to an embodiment of the present application;

[0055] Figure 3 A charge and discharge curve diagram of lithium iron phosphate according to an embodiment of the present application;

[0056] Figure 4 is a cross-sectional view of a reference electrode according to an embodiment of the present application;

[0057] Figure 5 A schematic diagram of a method for preparing a reference electrode according to an embodiment of the present application;

[0058] Figure 6 A schematic block diagram of a reference electrode preparation device according to an embodiment of the present application;

[0059] Figure 7 This is a schematic diagram of the structure of a fixing device according to an embodiment of the present application;

[0060] Figure 8Schematic diagram of a three-electrode battery disclosed in one embodiment of the present application.

[0061] In the drawings, the drawings are not drawn to scale. DETAILED DESCRIPTION

[0062] Hereinafter, the reference electrode and its preparation method and preparation device, the three-electrode battery and its preparation method of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0063] In the description of the present application, it should be noted that, unless otherwise specified, "multiple" means more than two; the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0064] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0065] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0066] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0067] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0068] A secondary battery is a battery that can be used again after being discharged by recharging the active materials. Usually, a secondary battery includes a positive electrode, a negative electrode, a separator and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode and the negative electrode. The separator is set between the positive electrode and the negative electrode to play an isolating role. The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode.

[0069] During the use of secondary batteries, their capacity, voltage, impedance, etc. will change with the increase of charge and discharge times. Accurately obtaining and monitoring the electrochemical characteristics of the battery is of great significance to the battery life and safety monitoring. The reference electrode currently used is usually made of copper wire or copper sheet electrochemically plated with lithium metal, and the lithium metal on the surface will react with the electrolyte, resulting in the consumption of the metal lithium coating of the reference electrode, shortening the service life of the reference electrode, and affecting the stability of the reference potential of the reference electrode, thus failing to effectively monitor the electrochemical characteristics of the battery in the long term.

[0070] In view of this, an embodiment of the present application provides a reference electrode, including a metal substrate and a coating disposed on at least part of the surface of the metal substrate, the coating including an electrode material, the voltage platform of the charge-discharge curve of the electrode material including a first interval, the difference between the maximum voltage and the minimum voltage in the first interval is less than 10mV, that is, the electrode material has a stable voltage platform, and when used as an electrode material of a reference electrode, the reference electrode has high potential repeatability, small polarization, good stability, good cycle performance, and long service life. The use of the above-mentioned reference electrode can effectively monitor the capacity, voltage, impedance and other electrochemical characteristics of the battery for a long time.

[0071] Several embodiments of the present application are described in detail below.

[0072] [Reference electrode]

[0073] Figure 1 FIG. 1 is a schematic diagram of a reference electrode according to an embodiment of the present application. Figure 2 FIG. 1 is a schematic diagram of a reference electrode according to another embodiment of the present application. Figure 1 and Figure 2 As shown, the reference electrode 1 includes a metal substrate 10 and a coating 11 disposed on at least a portion of the surface of the metal substrate 10 .

[0074] The metal substrate 10 can be a metal wire, such as Figure 1 As shown, the coating 11 is provided on at least a portion of the circumferential surface of the metal wire.

[0075] The metal substrate 10 may be a metal foil having two surfaces arranged along its thickness direction. Figure 2 As shown, at least parts of both surfaces of the metal foil are provided with a coating 11 .

[0076] It should be understood that the coating 11 can be disposed on a partial area of ​​the surface of the metal substrate 10 , which means that a portion of the surface of the metal substrate 10 is covered by the coating 11 , and another portion is exposed.

[0077] The coating 11 includes an electrode material, and a voltage platform of a charge-discharge curve of the electrode material includes a first interval, and a difference between a maximum voltage and a minimum voltage in the first interval is less than 10 mV.

[0078] The charge and discharge curve of an electrode material refers to a curve showing the relationship between time or capacity and voltage of an electrode material under the action of current. For example, under a constant current charging condition of a certain magnitude, the voltage gradually increases with time until the set upper limit voltage is reached; under a constant current discharging condition of a certain magnitude, the voltage gradually decreases with time until the set lower limit voltage is reached.

[0079] The voltage platform refers to a relatively stable curve in which the voltage of the electrode changes little during the charging and discharging process.

[0080] For example, Figure 3 (a) shows the charge and discharge curve of lithium iron phosphate (LFP) material. Curve M is the charge curve of LFP, and curve N is the charge curve of LFP. In curve M or curve N, the part of the curve where the voltage changes slowly with the change of SOC is the voltage platform. Here SOC refers to the state of charge of the battery, that is, the remaining power. It indicates the ratio of the remaining dischargeable power to the fully charged power after the battery has been used for a period of time or stored for a long time.

[0081] refer to Figure 3 (b) in FIG. 1 is a partial curve of the charging curve M of lithium iron phosphate. Figure 3 As shown in (b), the first interval is the curve segment between point A and point B, the point with the maximum voltage in the first interval is point B, and the point with the minimum voltage is point A. The voltage value of the ordinate of the charging curve M corresponding to point B is 3.465V, and the voltage value of the ordinate of the charging curve M corresponding to point A is 3.456V. Therefore, the difference ΔU between the maximum voltage and the minimum voltage in the first interval is 9mV.

[0082] It should be understood that the embodiment of the present application is described by taking the charging curve of lithium iron phosphate as an example, which does not constitute any limitation on the technical solution of the present application. The electrode material in the embodiment of the present application can be but is not limited to lithium iron phosphate.

[0083] In the embodiment of the present application, the reference electrode 1 includes a metal substrate 10 and a coating 11 disposed on at least part of the surface of the metal substrate 10. Specifically, the coating 11 includes an electrode material, and the voltage platform of the charge-discharge curve of the electrode material includes a first interval, and the difference between the maximum voltage and the minimum voltage in the first interval is less than 10mV, that is, the electrode material has a stable voltage platform. When used as an electrode material of the reference electrode 1, the reference electrode 1 has high potential repeatability, small polarization, good stability, and good cycle performance and long service life. The use of the above-mentioned reference electrode 1 can effectively monitor the capacity, voltage, impedance and other electrochemical characteristics of the battery for a long time.

[0084] In some embodiments, the absolute value of the difference between the capacity value in the charge-discharge curve corresponding to one end point of the first interval and the capacity value in the charge-discharge curve corresponding to another end point of the first interval is greater than 10%. Figure 3 As shown in (b), the battery capacity in the charge-discharge curve corresponding to one endpoint A of the first interval is 7.8%, and the battery capacity in the charge-discharge curve corresponding to the other endpoint B of the first interval is 72.4%, and the difference ΔSOC between the two is 64.6%.

[0085] During the use of the battery, the capacity of the reference electrode will change slightly due to its own and external influences. When the electrode material meets the above conditions, even if the capacity of the reference electrode changes, its capacity can still be within the capacity range corresponding to the first interval, and the performance of the reference electrode remains stable.

[0086] Optionally, in some embodiments, the reference electrode 1 is applied to a lithium battery, and the electrode material includes a lithium-containing olivine-structured phosphate material, a lithium-containing spinel material, and a carbon material.

[0087] It should be understood that the lithium battery can be a lithium ion battery or a lithium metal battery.

[0088] Olivine structure is a crystal structure of materials, and materials with olivine structure have higher stability. Olivine structure phosphate has the advantages of higher theoretical specific capacity, better cycle stability, low cost and environmental friendliness. For example, lithium iron phosphate and lithium iron manganese phosphate both have the advantages of long cycle life and good thermal stability.

[0089] Spinel is a mineral composed of magnesium aluminum oxide, with tetrahedral and octahedral crystal forms. For example, spinel-type lithium manganese oxide materials have outstanding characteristics such as high specific capacity, low cost and low environmental pollution.

[0090] Due to the unique composition of carbon structure, carbon materials have good electrical conductivity.

[0091] In some embodiments, the olivine structure phosphate material includes Li a Fe b M 1-b P 1-m O 4-n , wherein M includes at least one of the other metal elements except Fe, wherein 0≤a≤1.1, 0.3≤b≤1, 0≤m≤0.1, 0≤n≤0.1, and optionally, M includes at least one of Mn, Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge.

[0092] Optionally, the olivine structure phosphate material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0093] In some embodiments, the spinel material includes LiNi c Mn 2-c O4, where 0≤c<2.

[0094] Optionally, the spinel material comprises lithium manganate.

[0095] In some embodiments, the carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon nanotubes, and graphene. Due to the unique composition of the carbon structure, the carbon material has good electrical conductivity.

[0096] Optionally, in some embodiments, the reference electrode 1 is applied to a sodium battery, and the electrode material includes at least one of a carbon material, sodium vanadium phosphate, sodium titanate, and Na4Fe3(PO4)2(P2O7).

[0097] It should be understood that the sodium battery can be a sodium ion battery or a sodium metal battery.

[0098] In some embodiments, the metal substrate 10 includes at least one of aluminum, copper, tin, sodium-tin alloy, stainless steel, silver, gold, and platinum.

[0099] It should be understood that in the technical solution of the present application, the type of metal substrate can be selected according to the type of electrode material. For example, when using an electrode material with a higher voltage platform, a metal substrate that can withstand high voltage is selected accordingly; when using an electrode material with a lower voltage platform, a metal substrate that can withstand low voltage is selected accordingly. For example, lithium iron phosphate and sodium vanadium phosphate materials can use metal aluminum materials and metal tin materials; sodium titanate materials can use metal copper materials.

[0100] In some embodiments, Figure 1 As shown, the metal substrate 10 is a metal wire, and the diameter D of the metal wire ranges from 30 μm to 400 μm.

[0101] Specifically, the diameter D of the metal wire may be 30 μm, 50 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, or a value between any two of the above values.

[0102] The diameter D of the metal wire is set within the above range. On the one hand, it is beneficial to the adhesion of the coating on the surface of the metal wire and to improve the performance of the reference electrode. On the other hand, it controls the reference electrode to have a suitable volume and reduces the influence of the reference electrode on the battery interface.

[0103] In some embodiments, Figure 2 As shown, the metal substrate 10 is a metal foil, and the thickness d of the metal foil ranges from 4 μm to 30 μm.

[0104] Specifically, the thickness d of the metal foil may be 4 μm, 5 μm, 10 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, or a value between any two of the above values.

[0105] The thickness d of the metal foil is set within the above range. On the one hand, it is beneficial to the adhesion of the coating on the surface of the metal foil and to improve the performance of the reference electrode. On the other hand, it controls the reference electrode to have a suitable volume and reduces the influence of the reference electrode on the battery interface.

[0106] In some embodiments, continue to refer to Figure 2 The width L1 of the reference electrode 1 ranges from 0.5 mm to 1 mm.

[0107] Specifically, the width L1 of the reference electrode 1 may be 0.5 mm, 0.6 mm, 0.75 mm, 0.8 mm, 0.9 mm, 1 mm, or a value between any two of the above values.

[0108] The width L1 of the reference electrode 1 is set within the above range, so that the reference electrode 1 has a suitable size and reduces the influence of the reference electrode 1 on the battery interface.

[0109] In some embodiments, Figure 4 As shown, the thickness d1 of the coating 11 ranges from 100 μm to 200 μm.

[0110] Specifically, the thickness d1 of the coating 11 may be 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, or a value between any two of the above values.

[0111] The thickness d1 of the coating 11 is set within the above range, so that the reference electrode 1 has a suitable reference capacity, which is beneficial to improving the cycle performance and service life of the reference electrode 1.

[0112] In some embodiments, continue to refer to Figure 4 The length L2 of the coating 11 ranges from 10 mm to 25 mm.

[0113] Specifically, the length L2 of the coating 11 can be 10 mm, 12 mm, 15 mm, 17 mm, 20 mm, 25 mm, or a value between any two of the above values.

[0114] The length L2 of the coating 11 is set within the above range, so that the reference electrode 1 as a whole has a suitable size, reducing the influence of the reference electrode 1 on the battery interface.

[0115] In some embodiments, the coating 11 further includes a conductive agent.

[0116] Optionally, the conductive agent includes at least one of conductive carbon black, superconducting carbon, carbon dots, Ketjen black, and carbon nanotubes.

[0117] Conductive agents collect microcurrents between electrode materials to reduce the contact resistance of the electrodes and accelerate the movement of electrons. They can also effectively increase the migration rate of metal ions in the electrode materials, thereby improving the charge and discharge efficiency of the electrodes. Due to the unique composition of the carbon structure, carbon material conductive agents have good electrical conductivity. For example, conductive carbon black has the advantages of low resistance and high conductivity, small particle size, large and rough specific surface area, high structure, and clean surface (few compounds); Ketjen black has a unique branched morphology, so it has high conductivity; carbon atoms in carbon nanotubes adopt SP 2 Hybridization, thus having high modulus and high strength, carbon nanotubes also have good flexibility, stretchability and conductivity. Conductive carbon black, superconducting carbon, carbon dots, Ketjen black, and carbon nanotubes as conductive agents can improve the conductivity of batteries.

[0118] In some embodiments, the coating 11 further includes a binder.

[0119] Optionally, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trichloroethylene copolymer and fluorine-containing acrylic resin, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, and styrene-butadiene rubber.

[0120] The binder can bond the electrode material and the conductive agent, enhance the electrical contact between the electrode material and the conductive agent, and enhance the structural stability of the reference electrode 1. The above substances all have good bonding properties, and can be used as a binder to enhance the bonding force between the electrode material and the conductive agent and the structural stability of the reference electrode 1.

[0121] In some embodiments, based on the total mass of the coating 11 , the mass content of the electrode material in the coating 11 ranges from 90% to 98%.

[0122] Specifically, the mass content of the electrode material in the coating layer 11 may be 90%, 91%, 93%, 95%, 97%, 98%, or a value between any two of the above values.

[0123] The mass content of the electrode material in the coating 11 is set within a suitable range so that the reference electrode 1 has a suitable reference capacity, which is beneficial to improving the cycle performance and service life of the reference electrode 1 .

[0124] In some embodiments, based on the total mass of the coating 11 , the mass content of the conductive agent in the coating 11 ranges from 0.1% to 5%.

[0125] Specifically, the mass content of the conductive agent in the coating 11 can be 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 3%, 4%, 4.5%, 5%, or a value between any two of the above values.

[0126] Setting the mass content of the conductive agent in the coating 11 within an appropriate range is beneficial to improving the conductivity of the reference electrode 1, so that the reference electrode 1 can better play its role in obtaining electrochemical characteristic information such as capacity, voltage, impedance, etc. of the battery.

[0127] In some embodiments, based on the total mass of the coating 11 , the mass content of the binder in the coating 11 ranges from 0.5% to 5%.

[0128] Specifically, the mass content of the binder in the coating 11 can be 0.5%, 1%, 1.5%, 2%, 3%, 4%, 4.5%, 5%, or a value between any two of the above values.

[0129] Setting the mass content of the binder in the coating 11 within an appropriate range is beneficial to enhancing the electrical contact between the electrode material and the conductive agent, and is also beneficial to improving the structural stability of the reference electrode 1 .

[0130] [Method for preparing reference electrode]

[0131] Figure 5 This is a method for preparing a reference electrode according to an embodiment of the present application. Figure 5 As shown, the preparation method 500 includes the following steps.

[0132] Step 510, providing a metal substrate;

[0133] Step 520, preparing electrode slurry;

[0134] The electrode slurry includes an electrode material, and a voltage platform of a charge-discharge curve of the electrode material includes a first interval, and a difference between a maximum voltage and a minimum voltage in the first interval is less than 10 mV.

[0135] Step 530, coating the electrode slurry on at least a portion of the surface of the metal substrate;

[0136] Step 540, drying the electrode slurry coated on at least a portion of the surface of the metal substrate to obtain a reference electrode.

[0137] In some embodiments, the absolute value of the difference between the capacity value in the charge-discharge curve corresponding to one end point of the first interval and the capacity value in the charge-discharge curve corresponding to the other end point of the first interval is greater than 10%. During the use of the battery, the capacity of the reference electrode will change slightly due to the influence of itself and the outside world. When the electrode material meets the above conditions, even if the capacity of the reference electrode changes, its capacity can still be within the capacity range corresponding to the first interval, and the performance of the reference electrode remains stable.

[0138] Optionally, in some embodiments, the reference electrode is applied to a lithium battery, and the electrode material includes a lithium-containing olivine-structured phosphate material, a lithium-containing spinel material, and a carbon material.

[0139] It should be understood that the lithium battery can be a lithium ion battery or a lithium metal battery.

[0140] Olivine structure is a crystal structure of materials, and materials with olivine structure have higher stability. Olivine structure phosphate has the advantages of higher theoretical specific capacity, better cycle stability, low cost and environmental friendliness. For example, lithium iron phosphate and lithium iron manganese phosphate both have the advantages of long cycle life and good thermal stability.

[0141] Spinel is a mineral composed of magnesium aluminum oxide, with tetrahedral and octahedral crystal forms. For example, spinel-type lithium manganese oxide materials have outstanding characteristics such as high specific capacity, low cost and low environmental pollution.

[0142] Due to the unique composition of carbon structure, carbon materials have good electrical conductivity.

[0143] In some embodiments, the olivine structure phosphate material includes Li a Fe b M 1-b P 1-m O 4-n , wherein M includes at least one of the other metal elements except Fe, wherein 0≤a≤1.1, 0.3≤b≤1, 0≤m≤0.1, 0≤n≤0.1, and optionally, M includes at least one of Mn, Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge.

[0144] Optionally, the olivine structure phosphate material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0145] In some embodiments, the spinel material includes LiNi c Mn 2-c O4, where 0≤c<2.

[0146] Optionally, the spinel material comprises lithium manganate.

[0147] In some embodiments, the carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon nanotubes, and graphene. Due to the unique composition of the carbon structure, the carbon material has good electrical conductivity.

[0148] In some embodiments, the metal substrate includes at least one of aluminum, copper, tin, sodium-tin alloy, stainless steel, silver, gold, and platinum.

[0149] Optionally, in some embodiments, the reference electrode is applied to a sodium battery, and the electrode material includes at least one of a carbon material, sodium vanadium phosphate, sodium titanate, and Na4Fe3(PO4)2(P2O7).

[0150] It should be understood that the sodium battery can be a sodium ion battery or a sodium metal battery.

[0151] Optionally, in some embodiments, the metal substrate is a metal wire, and the preparation method includes: fixing the metal wire to a winding pole of a preparation device; and applying the electrode slurry to at least a portion of the surface of the metal wire using a coating applicator.

[0152] Fixing the metal wire to the winding rod makes it easier to scrape the electrode slurry on the surface of the metal wire, thereby improving the processing efficiency and the processing quality of the reference electrode.

[0153] Optionally, in some embodiments, the metal substrate is a metal foil, and the preparation method further includes: after drying the electrode slurry coated on at least a portion of the surface of the metal substrate, shearing the metal foil having at least a portion of the surface coated with the electrode material along its length direction to obtain at least two reference electrodes.

[0154] A larger metal foil (for example, a metal foil with a larger width) can be selected to prepare a larger reference electrode to be processed at one time, and then the reference electrode to be processed can be cut into multiple reference electrodes required for actual use, which can greatly improve production efficiency.

[0155] [Reference electrode preparation device]

[0156] Figure 6 FIG. 6 is a schematic block diagram of a reference electrode preparation device 600 according to an embodiment of the present application. Figure 6 As shown, the reference electrode preparation device 600 may include:

[0157] A module 610 is provided for providing a metal substrate;

[0158] Preparation module 620, for preparing electrode slurry;

[0159] The electrode slurry includes an electrode material, and a voltage platform of a charge-discharge curve of the electrode material includes a first interval, and a difference between a maximum voltage and a minimum voltage in the first interval is less than 10 mV.

[0160] A coating module 630 is used to coat the electrode slurry on at least a portion of the surface of the metal substrate;

[0161] The drying module 640 is used to dry the electrode slurry coated on at least a portion of the surface of the metal substrate.

[0162] Optionally, in some embodiments, the metal substrate is a metal wire, and the coating module 630 includes a fixing device and a film coater. The fixing device is used to fix the metal wire, and the film coater is used to scrape the electrode slurry onto at least a portion of the surface of the metal wire.

[0163] Figure 7 This is a schematic diagram of the structure of a fixing device according to an embodiment of the present application. Figure 7As shown, the fixing device 700 includes an upper plate 703 , and a winding post 701 is disposed on the upper plate 703 . The winding post 701 is used to fix the metal wire 702 .

[0164] In some embodiments, Figure 7 As shown, the upper plate 703 is provided with a through slot 7031 , and the fixing device 700 further includes a lower plate 704 .

[0165] Specifically, a first surface 7041 of the lower plate 704 close to the upper plate 703 is provided with a protrusion 7042 protruding from the first surface 7041 , the protrusion 7042 extends along a first direction, and the protrusion 7042 is embedded in the through groove 7031 to form a material groove for accommodating the electrode slurry.

[0166] The first direction may be the thickness direction of the lower plate 704, for example, Figure 7 The z' direction is shown.

[0167] In some embodiments, continue to refer to Figure 7 In the first direction z′, the dimension H1 of the through groove 7031 is greater than the dimension H2 of the protrusion 7042 .

[0168] Thus, when the protrusion 7042 is embedded in the through groove 7031, a portion of the space of the through groove 7031 is filled by the protrusion 7042, and the remaining space and the protrusion 7042 together form a material groove to accommodate the electrode slurry. For example, the dimension H1 of the through groove 7031 is 5.00 mm, and the dimension H2 of the protrusion 7042 is 4.90 mm, so that a material groove with a depth of 0.10 mm can be formed.

[0169] In an embodiment of the present application, the metal substrate can be a metal wire, and the metal wire can be wound and fixed on the winding post of the fixing device, and the electrode slurry is poured between the winding post and the material tank (the side where the winding post and the material tank are closer), and the electrode slurry is scraped from the position of the electrode slurry close to the winding post in the direction close to the material tank with a film applicator. When the electrode slurry is scraped to the material tank position, it will enter the material tank. As the scraping progresses, the electrode slurry in the material tank gradually increases until it covers part of the metal wire. In this way, the surface of the metal wire can be fully in contact with the electrode slurry, thereby avoiding the phenomenon of uneven scraping of the electrode slurry on the surface of the metal wire. After the electrode slurry is scraped, the upper plate and the lower plate are separated, so that the protrusion of the lower plate is pulled out of the through groove of the upper plate, and the excess electrode slurry in the through groove flows out of the through groove due to the lack of the obstruction of the protrusion. After the excess electrode slurry in the through groove has basically flowed out, the metal wire fixed to the winding post and the upper plate are placed in an oven together to dry the electrode slurry on the surface of the metal wire.

[0170] It should be understood that Figure 7As shown, a plurality of winding posts 701 may be provided on the fixing device 700, so that a plurality of metal wires may be scraped and coated at the same time, and a plurality of reference electrodes may be formed at the same time, thereby greatly improving the production efficiency.

[0171] In some embodiments, the material of the fixing device may be polytetrafluoroethylene material.

[0172] [Positive electrode]

[0173] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0174] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0175] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0176] In some embodiments, the positive electrode active material may adopt the positive electrode active material for lithium ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates containing olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for lithium ion batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0177] The battery will be accompanied by Li deintercalation and consumption during the charging and discharging process. The molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the list of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system. After the charge and discharge cycle, the molar content of Li will change. In the list of positive electrode active materials in this application, the molar content of O is only an ideal state value. Lattice oxygen release will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0178] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0179] In some embodiments, the positive electrode film layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0180] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0181] [Negative electrode]

[0182] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0183] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0184] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0185] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0186] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0187] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0188] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0189] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0190] [Isolation film]

[0191] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0192] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0193] [Three-electrode battery]

[0194] In some embodiments, the positive electrode sheet, the negative electrode sheet, the reference electrode, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0195] In some embodiments, the three-electrode battery may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0196] In some embodiments, the outer packaging of the three-electrode battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the three-electrode battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed.

[0197] The present application has no particular limitation on the shape of the three-electrode battery, which may be cylindrical, square or any other shape. Figure 8 A three-electrode battery 80 of a square structure is shown as an example.

[0198] In some embodiments, Figure 8 As shown, the uncoated metal substrate of the reference electrode 1 can partially extend out of the outer package 81 of the three-electrode battery 80 and be connected to a monitoring device outside the battery to monitor the electrochemical characteristics of the battery. The end of the metal substrate extending out of the outer package 81 of the three-electrode battery 80 can be welded with a nickel sheet or an aluminum sheet to facilitate connection with an external monitoring device, and the welding method can be soldering or ultrasonic welding.

[0199] [Method for preparing three-electrode battery]

[0200] The following introduces a method for preparing a three-electrode battery, wherein the contents related to the above-mentioned three-electrode battery are not repeated.

[0201] In an embodiment of the present application, a method for preparing a three-electrode battery includes: assembling a reference electrode, a positive electrode sheet, a negative electrode sheet and an isolation membrane into an electrode assembly; packaging the electrode assembly with an outer package; and injecting an electrolyte into the package to prepare a three-electrode battery.

[0202] In some embodiments, the preparation method of the three-electrode battery also includes: forming the three-electrode battery; charging the reference electrode to a preset cutoff voltage, and then discharging the reference electrode until the capacity of the reference electrode is within the range of the capacity of the electrode material corresponding to the first interval.

[0203] Here, the preset cut-off voltage is selected according to the type of electrode material of the reference electrode.

[0204] The reference electrode is discharged until the capacity of the reference electrode is within the capacity range of the electrode material corresponding to the first interval, and the activation of the reference electrode is completed. In this way, during the cyclic use of the three-electrode battery, the positive and negative electrodes participate in the cycle, and the reference electrode does not participate in the cycle, and its capacity remains the remaining capacity after formation, that is, its capacity remains within the capacity range of the electrode material corresponding to the first interval, and the reference electrode has better performance at this time.

[0205] [Example]

[0206] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0207] 1. Preparation of reference electrode

[0208] Reference electrode 1: The electrode material lithium iron phosphate, the binder polyvinylidene fluoride (PVDF), and the conductive agent superconducting carbon (SP) are dissolved in a solvent N-methylpyrrolidone (NMP) in a mass ratio of 97.0%:2.0%:1.0%, and the electrode slurry is obtained after being fully stirred and mixed. Then, the electrode slurry is evenly coated on an aluminum foil (aluminum foil width 0.8 mm, thickness 15 μm) to form a coating, and then dried and cold pressed to form a reference electrode 1, wherein the thickness of the coating is 150 μm.

[0209] Reference electrode 2: The preparation of reference electrode 2 is similar to that of reference electrode 1, except that the thickness of the coating of the prepared reference electrode 2 is 100 μm.

[0210] Reference electrode 3: The preparation of reference electrode 3 is similar to that of reference electrode 1, except that the thickness of the coating of the prepared reference electrode 3 is 200 μm.

[0211] Reference electrode 4: The preparation of reference electrode 4 is similar to that of reference electrode 1, except that the thickness of the coating of reference electrode 4 is 50 μm.

[0212] Reference electrode 5: The preparation of reference electrode 5 is similar to that of reference electrode 1, except that the thickness of the coating of reference electrode 5 is 250 μm.

[0213] Reference electrode 6: The preparation of reference electrode 6 is similar to that of reference electrode 1, except that during the preparation of reference electrode 6, the electrode material in the electrode slurry is lithium manganese oxide.

[0214] Reference electrode 7: The preparation of reference electrode 7 is similar to that of reference electrode 1, except that during the preparation of reference electrode 7, the electrode material in the electrode slurry is lithium manganese iron phosphate.

[0215] Reference electrode 8: The preparation of reference electrode 8 is similar to that of reference electrode 1, except that, during the preparation of reference electrode 8, the electrode material in the electrode slurry is sodium vanadium phosphate, and the metal substrate is tin foil.

[0216] Reference electrode 9: The preparation of reference electrode 9 is similar to that of reference electrode 1, except that, during the preparation of reference electrode 9, the electrode material in the electrode slurry is sodium titanate, and the metal substrate is copper foil.

[0217] Reference electrode 10: The preparation of reference electrode 10 is similar to that of reference electrode 1, except that, during the preparation of reference electrode 10, the electrode material in the electrode slurry is Na4Fe3(PO4)2(P2O7) and the metal substrate is tin foil.

[0218] Reference electrode 11: The preparation of reference electrode 11 is similar to that of reference electrode 1, except that during the preparation of reference electrode 11, the metal substrate is aluminum wire (with a diameter of 100 μm).

[0219] Reference electrode 12: Place one end of the enameled copper wire in concentrated sulfuric acid and soak it for 1 hour. Then wash it with deionized water and anhydrous ethanol. Implant the soaked end of the copper wire into a battery, use the battery cathode or anode as the positive electrode, and the copper wire as the negative electrode. Charge it for 1 hour at a current of 20μA for lithium plating. The thickness of the lithium coating on the surface of the copper wire is 200μm, and a reference electrode 12 is obtained.

[0220] Reference electrode 13: Place one end of the enameled copper wire in concentrated sulfuric acid and soak it for 1 hour. Then wash it with deionized water and anhydrous ethanol. Implant the soaked end of the copper wire into a battery, use the battery cathode or anode as the positive electrode, and the copper wire as the negative electrode. Charge it at a current of 20μA for 1 hour to plate sodium. The thickness of the sodium coating on the surface of the copper wire is 200μm, and a reference electrode 13 is obtained.

[0221] 2. Preparation of secondary batteries

[0222] [Example 1]

[0223] (1) Reference electrode

[0224] The reference electrode 1 prepared above was used as the reference electrode.

[0225] (2) Preparation of positive electrode sheet

[0226] Positive electrode sheet: The positive electrode active material lithium manganese oxide (LiMn2O4), the conductive agent acetylene black, and the binder PVDF are dissolved in the solvent NMP at a mass ratio of 90%:5%:5%, and after being fully stirred and mixed, they are coated on Al foil, dried, and cold pressed to obtain the positive electrode sheet.

[0227] (3) Preparation of negative electrode sheet

[0228] The negative electrode active material artificial graphite, the conductive agent acetylene black and the binder PVDF were fully stirred and mixed in an N-methylpyrrolidone solvent system in a mass ratio of 90%:5%:5%, and then coated on a Cu foil, dried and cold pressed to obtain a negative electrode sheet.

[0229] (4) Preparation of isolation membrane

[0230] A conventional polypropylene film was used as the isolation film.

[0231] (5) Preparation of electrolyte

[0232] Electrolyte 1: In an argon atmosphere glove box with a water content of <10ppm, fully dried lithium salt (LiPF6) was dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 20:20:60, and then the additive vinylene carbonate (VC) was added and mixed evenly to obtain an electrolyte. The concentration of the lithium salt was 1 mol / L.

[0233] Electrolyte 2: In an argon atmosphere glove box with a water content of <10ppm, fully dried sodium salt (NaPF6) was dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 20:20:60, and then the additive vinylene carbonate (VC) was added and mixed evenly to obtain an electrolyte. The concentration of the sodium salt was 1 mol / L.

[0234] (6) Assembly of secondary batteries

[0235] The above-mentioned positive electrode sheet, isolation membrane, reference electrode 1, isolation membrane, and negative electrode sheet are stacked in order, so that one isolation membrane is between the positive electrode sheet and the reference electrode 1, and the other isolation membrane is between the reference electrode 1 and the negative electrode sheet to play an isolating role, and then wound to obtain an electrode assembly; the electrode assembly is placed in a battery casing, and after drying, the electrolyte 1 is injected, and then a secondary battery 1 is obtained through processes such as formation and standing, which is Example 1.

[0236] Using high-precision equipment such as an electrochemical workstation, use a current of 1μA to 10μA to charge the positive electrode of the battery to the reference electrode to the cut-off voltage of the reference electrode to activate the electrode material. Then use a current of 1μA to 10μA to release a certain amount of lithium / sodium insertion capacity to ensure that the lithium / sodium plating state of the reference electrode is in the middle of the discharge platform so that the reference electrode potential is in a stable state.

[0237] Here, the cutoff voltage of the reference electrode and the capacity of lithium / sodium intercalation released after the electrode material is activated are related to the type of electrode material of the reference electrode. An appropriate cutoff voltage and appropriate lithium / sodium intercalation capacity can be selected according to the type of electrode material of the reference electrode.

[0238] [Examples 2-7, 11, Comparative Example 1]

[0239] The preparation methods of the secondary batteries of Examples 2-7, 11 and Comparative Example 1 are similar to that of the secondary battery of Example 1, except that different reference electrodes are used (Examples 1-7 and 11 use reference electrodes 1-7 and 11, respectively, and Comparative Example 1 uses reference electrode 12).

[0240] [Examples 8-10, Comparative Example 2]

[0241] The preparation methods of the secondary batteries of Examples 8-10 and Comparative Example 2 are similar to those of the secondary battery of Example 1, except that different reference electrodes and electrolytes are used (Example 1 uses reference electrode 1 and electrolyte 1, and Examples 8-10 and Comparative Example 2 use reference electrodes 8-10 and 13 respectively, and the electrolyte used is electrolyte 2).

[0242] Next, the battery performance testing process is described.

[0243] 3. Battery performance test

[0244] (1) Battery potential difference test: After the reference electrode is adjusted to the corresponding operating potential, use a multimeter or other voltage measuring equipment to measure the voltage difference between the positive and negative electrodes of the secondary battery as E1, the voltage difference between the positive electrode and the reference electrode as E2, and the voltage difference between the negative electrode and the reference electrode as E3; calculate the difference between E2 and E3, recorded as E4, that is, E4 = E2-E3, and finally calculate the absolute value of the difference between E4 and E1, recorded as ΔE, that is, ΔE = |E4-E1|, which is the potential difference of the battery.

[0245] (2) Life test of reference electrode: Use a 5V, 1A Xinwei tester with an auxiliary channel to perform a cyclic charge and discharge test on the battery. Place the Xinwei tester channel test line and the secondary battery in a Harding high and low temperature box to control the test temperature. The auxiliary channel test line is clamped on the tabs of the negative / positive electrode and the reference electrode to monitor the voltage between the negative / positive electrode and the reference electrode. If the curve suddenly rises or falls, it proves that the reference electrode has failed. Terminate the test and record the number of cycles of the reference electrode at this time.

[0246] The battery cycle charge and discharge test process is as follows: at 25°C, the secondary battery is charged to 4.2V at a constant current of 1C, then charged to 0.05C at a constant voltage of the upper voltage limit, and after 15 minutes, the secondary battery is discharged to 2.5V at a constant current of 1C. This is one charge and discharge process. Follow this charge and discharge process to cycle charge and discharge.

[0247] According to the above method, the battery performance tests were carried out on the prepared Examples 1-11 and Comparative Examples 1-2, and the results are shown in Table 1. Wherein, d1 represents the thickness of the coating, and ΔE represents the potential difference of the battery.

[0248] Table 1: Product parameters and performance test results of Examples 1 to 11 and Comparative Examples 1-2

[0249]

[0250] From the comparison of the results of Examples 1-11 and Comparative Examples 1-2, it can be seen that using lithium iron phosphate, lithium manganese oxide, lithium iron manganese phosphate, sodium vanadium phosphate, sodium titanate, and Na4Fe3(PO4)2(P2O7) as electrode materials for the reference electrode can greatly improve the cycle life of the reference electrode.

[0251] From the comparison of the results of Examples 1-5, it can be seen that within a certain range, the thicker the coating thickness of the reference electrode, the longer the service life of the reference electrode. When the coating thickness reaches a certain value, as the coating thickness increases, the extension time of the service life of the reference electrode is shorter. For example, in Example 5 relative to Example 3, the coating thickness increases by 50 μm, and the service life of the reference electrode increases, but the number of increased cycles is small. The increase in the coating thickness of the reference electrode increases the volume of the reference electrode, hinders the deintercalation of lithium between the positive and negative pole pieces, and causes uneven distribution of lithium embedded in the negative pole piece, resulting in distortion of the data monitored by the reference electrode. Therefore, in the embodiment of the present application, under the same other conditions, the thickness of the coating of the reference electrode is in the range of 100 μm to 200 μm, and the corresponding service life of the reference electrode is significantly improved.

[0252] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A reference electrode, characterized in that include: Metal substrate; A coating is disposed on at least a portion of the surface of the metal substrate, the coating includes an electrode material, the voltage platform of the charge and discharge curve of the electrode material includes a first interval, and the difference between the maximum voltage and the minimum voltage in the first interval is less than 10mV.

2. The reference electrode according to claim 1, characterized in that An absolute value of a difference between a capacity value in the charge-discharge curve corresponding to one end point of the first interval and a capacity value in the charge-discharge curve corresponding to another end point of the first interval is greater than 10%.

3. The reference electrode according to claim 1 or 2, characterized in that The thickness of the coating ranges from 100 μm to 200 μm.

4. The reference electrode according to any one of claims 1 to 3, characterized in that The reference electrode is used for lithium batteries, and the electrode material includes a lithium-containing olivine structure phosphate material, a lithium-containing spinel material, and a carbon material; Optionally, the lithium-containing olivine-structured phosphate material includes at least one of lithium iron phosphate and lithium manganese iron phosphate; Optionally, the lithium-containing spinel material includes lithium manganate; Optionally, the carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon nanotubes, and graphene.

5. The reference electrode according to any one of claims 1 to 3, characterized in that The reference electrode is used for a sodium battery, and the electrode material includes at least one of a carbon material, sodium vanadium phosphate, sodium titanate, and Na4Fe3(PO4)2(P2O7); Optionally, the carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon nanotubes, and graphene.

6. The reference electrode according to any one of claims 1 to 5, characterized in that The metal substrate includes at least one of aluminum, copper, tin, sodium-tin alloy, stainless steel, silver, gold, and platinum.

7. The reference electrode according to any one of claims 1 to 6, characterized in that The metal substrate is a metal wire, and the diameter of the metal wire ranges from 30 μm to 400 μm.

8. The reference electrode according to any one of claims 1 to 7, characterized in that The metal substrate is a metal foil, and the thickness of the metal foil ranges from 4 μm to 30 μm.

9. The reference electrode according to claim 8, characterized in that The width of the reference electrode ranges from 0.5 mm to 1 mm.

10. The reference electrode according to any one of claims 1 to 9, characterized in that The length of the coating ranges from 10 mm to 25 mm.

11. The reference electrode according to any one of claims 1 to 10, characterized in that The coating further comprises a conductive agent. Optionally, the conductive agent comprises at least one of conductive carbon black, superconducting carbon, carbon dots, Ketjen black and carbon nanotubes.

12. The reference electrode according to any one of claims 1 to 11, characterized in that The coating also includes a binder. Optionally, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trichloroethylene copolymer and fluorine-containing acrylic resin, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, and styrene-butadiene rubber.

13. The reference electrode according to any one of claims 1 to 12, characterized in that Based on the total mass of the coating, the mass content of the electrode material in the coating ranges from 90% to 98%.

14. The reference electrode according to claim 11, characterized in that Based on the total mass of the coating, the mass content of the conductive agent in the coating ranges from 0.1% to 5%.

15. The reference electrode according to claim 12, characterized in that Based on the total mass of the coating, the mass content of the binder in the coating ranges from 0.5% to 5%.

16. A method for preparing a reference electrode, characterized in that: include: applying an electrode slurry to at least a portion of the surface of a metal substrate; The electrode slurry includes an electrode material, the voltage platform of the charge-discharge curve of the electrode material includes a first interval, and the difference between the maximum voltage and the minimum voltage in the first interval is less than 10 mV; The electrode slurry coated on at least a portion of the surface of the metal substrate is dried to obtain the reference electrode.

17. The preparation method according to claim 16, characterized in that: An absolute value of a difference between a capacity value in the charge-discharge curve corresponding to one end point of the first interval and a capacity value in the charge-discharge curve corresponding to another end point of the first interval is greater than 10%.

18. The preparation method according to claim 16 or 17, characterized in that: The thickness of the coating ranges from 100 μm to 200 μm.

19. The preparation method according to any one of claims 16 to 18, characterized in that: The reference electrode is used for lithium batteries, and the electrode material includes a lithium-containing olivine structure phosphate material, a lithium-containing spinel material, and a carbon material; Optionally, the lithium-containing olivine-structured phosphate material includes at least one of lithium iron phosphate and lithium manganese iron phosphate; Optionally, the lithium-containing spinel material includes lithium manganate; Optionally, the carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon nanotubes, and graphene.

20. The preparation method according to any one of claims 16 to 18, characterized in that: The reference electrode is used for a sodium battery, and the electrode material includes at least one of a carbon material, sodium vanadium phosphate, sodium titanate, and Na4Fe3(PO4)2(P2O7); Optionally, the carbon material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon nanotubes, and graphene.

21. The preparation method according to any one of claims 16 to 20, characterized in that: The metal substrate includes at least one of aluminum, copper, tin, sodium-tin alloy, stainless steel, silver, gold, and platinum.

22. The preparation method according to any one of claims 16 to 21, characterized in that: The metal substrate is a metal wire, and the preparation method comprises: Fixing the metal wire to a winding post of a preparation device; The electrode slurry is scraped onto at least a portion of the surface of the metal wire using a film applicator.

23. The preparation method according to any one of claims 16 to 21, characterized in that: The metal substrate is a metal foil, and the preparation method further comprises: After drying the electrode slurry coated on at least a portion of the surface of the metal substrate, the metal foil having at least a portion of the surface coated with the electrode material is sheared along its length direction to obtain at least two reference electrodes.

24. A reference electrode preparation device, characterized in that: include: providing a module for providing a metal substrate; A preparation module, for preparing an electrode slurry, wherein the electrode slurry includes an electrode material, wherein a voltage platform of a charge-discharge curve of the electrode material includes a first interval, and a difference between a maximum voltage and a minimum voltage in the first interval is less than 10 mV; A coating module, used for coating the electrode slurry on at least a portion of the surface of the metal substrate; The drying module is used to dry the electrode slurry coated on at least a portion of the surface of the metal substrate.

25. The preparation device according to claim 24, characterized in that: The metal substrate is a metal wire, and the coating module includes a fixing device and a film applicator; The fixing device is used to fix the metal wire; The film applicator is used to scrape the electrode slurry onto at least a portion of the surface of the metal wire.

26. The preparation device according to claim 25, characterized in that: The fixing device comprises an upper plate, and the upper plate is provided with a winding post, and the winding post is used to fix the metal wire.

27. The preparation device according to claim 26, characterized in that: The upper plate is provided with a through slot, and the fixing device further comprises a lower plate; A first surface of the lower plate close to the upper plate is provided with a protrusion protruding from the first surface, the protrusion extends along a first direction, and the protrusion is embedded in the through groove to form a material groove for accommodating the electrode slurry.

28. The preparation device according to claim 27, characterized in that: In the first direction, a size of the through slot is larger than a size of the protrusion.

29. A three-electrode battery, characterized in that: include: A reference electrode according to any one of claims 1 to 15; Positive electrode; Negative electrode; and Isolation film; The positive electrode sheet, the reference electrode, and the negative electrode sheet are arranged in sequence and spaced apart from each other. The isolation film is provided between the positive electrode sheet and the reference electrode, and between the reference electrode and the negative electrode sheet.

30. A method for preparing a three-electrode battery, characterized in that: include: Assembling a reference electrode according to any one of claims 1 to 15, a positive electrode sheet, a negative electrode sheet and a separator into an electrode assembly; packaging the electrode assembly with an outer package; An electrolyte is injected into the outer package to obtain the three-electrode battery.

31. The preparation method according to claim 30, characterized in that: The preparation method further comprises: forming the three-electrode battery; The reference electrode is charged to a preset cut-off voltage, and then the reference electrode is discharged until the capacity of the reference electrode is within the range of the capacity of the electrode material corresponding to the first interval.

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