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

Abstract

The invention relates to the technical field of new energy, in particular to a reference electrode, a three-electrode battery and a preparation method of the three-electrode battery. The reference electrode comprises a porous conductive substrate and a first attachment, and the first attachment is located in pores of the porous conductive substrate; the porous conductive substrate meets at least one of the following conditions 1)-2): 1) the density of the porous conductive substrate is rho0, the density of a solid conductive substrate made of the same material as the porous conductive substrate is rho1, and rho0 meets the condition that rho0 is greater than or equal to rho1 * 0.7; and 2) the specific surface area of the porous conductive substrate is S0, the specific surface area of the solid conductive substrate with the same shape as the porous conductive substrate is S1, and S0 is greater than or equal to S1 * 5. The reference electrode can stably monitor the positive and negative electrode potentials of the lithium ion battery so as to evaluate the positive and negative electrode performance of the battery, and is long in service life.

Description

Technical Field

[0001] This application relates to the field of new energy technologies, and particularly to a reference electrode, a three-electrode battery, and a preparation method thereof. Background Art

[0002] Power batteries are an important option to alleviate energy shortages. Taking lithium-ion batteries as an example, lithium-ion batteries have advantages such as high energy density, low self-discharge rate, high voltage, and long cycle life, and have currently been widely used in various fields, such as consumer products, medical devices, automobiles, airplanes, etc. With the progress of technology.

[0003] In order to evaluate the more microscopic and specific conditions of the positive and negative electrodes of power batteries during charge and discharge, a reference electrode is usually set in the battery to monitor the potential change between the positive and negative electrodes. Currently, the reference electrode has the problem of short service life. Summary of the Invention

[0004] Based on this, this application provides a reference electrode, a three-electrode battery, and a preparation method thereof to improve the problem of short service life of the reference electrode.

[0005] The first aspect of this application provides a reference electrode, and its technical solution is as follows:

[0006] A reference electrode includes a porous conductive matrix and a first attachment, and the first attachment is located in the pores of the porous conductive matrix;

[0007] The porous conductive matrix satisfies at least one of the following conditions 1) to 2):

[0008] 1) The density of the porous conductive matrix is ρ0, and the density of a solid conductive matrix made of the same material as the porous conductive matrix is ρ1, and ρ0 satisfies: ρ0 ≤ ρ1 × 0.7;

[0009] 2) The specific surface area of the porous conductive matrix is S0, and the specific surface area of a solid conductive matrix with the same shape as the porous conductive matrix is S1, and S0 satisfies: S0 ≥ S1 × 5.

[0010] The second aspect of this application provides a three-electrode battery, and its technical solution is as follows:

[0011] A three-electrode battery includes a battery housing, an electrolyte, and a three-electrode cell located in the battery housing. The three-electrode cell includes the reference electrode, a positive electrode plate, a negative electrode plate, a first separator, and a second separator as described above. The first separator is disposed between the reference electrode and the positive electrode plate, and the second separator is disposed between the reference electrode and the negative electrode plate.

[0012] The third aspect of the present application provides a method for preparing a three - electrode battery, and its technical solution is as follows:

[0013] A method for preparing a three - electrode battery includes the following steps:

[0014] Stack a prefabricated electrode, a positive electrode plate, a negative electrode plate, a first separator, and a second separator to prepare a prefabricated battery cell; wherein, the first separator is disposed between the prefabricated electrode and the positive electrode plate, the second separator is disposed between the prefabricated electrode and the negative electrode plate, the prefabricated electrode includes a porous conductive matrix, and the porous conductive matrix satisfies at least one of the following conditions 1) - 2): 1) The density of the porous conductive matrix is ρ0, and the density of a solid conductive matrix made of the same material as the porous conductive matrix is ρ1, and ρ0 satisfies: ρ0 ≤ ρ1×0.7; 2) The specific surface area of the porous conductive matrix is S0, and the specific surface area of a solid conductive matrix having the same shape as the porous conductive matrix is S1, and S0 satisfies: S0 ≥ S1×5;

[0015] Package the prefabricated battery cell, inject an electrolyte, and prepare a prefabricated battery;

[0016] Activate the prefabricated electrode to form a first attachment in the pores of the porous conductive matrix, form a reference electrode, and obtain a three - electrode battery.

[0017] The present application has the following beneficial effects:

[0018] In the reference electrode of the present application, the porous conductive matrix has pores, and the density ρ0 of the porous conductive matrix having pores satisfies ρ0 ≤ ρ1×0.7 and / or the specific surface area S0 of the porous conductive matrix having pores satisfies S0 ≥ S1×5. The first attachment is located in the pores of the porous conductive matrix that meet the above conditions. During the use of the reference electrode, the pore structure of the porous conductive matrix that meets the above conditions provides sufficient hindrance to the outflow of the first attachment, and the first attachment can stably adhere to the porous conductive matrix, effectively delaying the corrosion and damage of the attachment of the electrolyte to the reference electrode, facilitating the stable monitoring of the positive and negative electrode potentials by the reference electrode for a long time, and improving the service life of the reference electrode. Specific Embodiments

[0019] The following further elaborates on the present application in detail with specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosed content of the present application more thorough and comprehensive.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application herein are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0021] The term

[0022] Unless otherwise stated or there is a contradiction, the terms or phrases used in this application have the following meanings:

[0023] In this application, the terms "optionally", "optional", and "option" mean that it is optional, that is, it refers to any one of the two alternative schemes of "having" or "not having". If the term "optional" appears multiple times in a technical solution, without special instructions, and without contradictions or mutual restrictions, each "optional" is independent of each other.

[0024] In this application, in "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc., the terms "first", "second", "third", "fourth", etc. are only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive listing and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0025] In this application, the first feature being "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over", and "on top of" the second feature can be that the first feature is directly above or obliquely above the second feature, or it merely means that the first feature is at a higher horizontal level than the second feature. The first feature being "under", "beneath", and "underneath" the second feature can be that the first feature is directly below or obliquely below the second feature, or it merely means that the first feature is at a lower horizontal level than the second feature.

[0026] In view of the problem that the current reference electrode has a relatively short service life, in the first aspect of this application, a reference electrode is provided. In some embodiments, the reference electrode includes a porous conductive matrix and a first attachment, and the first attachment is located in the pores of the porous conductive matrix;

[0027] The porous conductive matrix satisfies at least one of the following conditions 1) to 2):

[0028] 1) The density of the porous conductive matrix is ρ0, and the density of the solid conductive matrix made of the same material as the porous conductive matrix is ρ1, and ρ0 satisfies: ρ0 ≤ ρ1 × 0.7;

[0029] 2) The specific surface area of the porous conductive substrate is S0, and the specific surface area of the solid conductive substrate with the same shape as the porous conductive substrate is S1. S0 satisfies: S0 ≥ S1 × 5.

[0030] In the above reference electrode, the porous conductive substrate has pores, and the density ρ0 of the porous conductive substrate with pores satisfies ρ0 ≤ ρ1 × 0.7 and / or the specific surface area S0 of the porous conductive substrate with pores satisfies S0 ≥ S1 × 5. The first attachment is located in the pores of the porous conductive substrate that meet the above conditions. During the use of the reference electrode, the pore structure of the porous conductive substrate that meets the above conditions provides sufficient hindrance for the outflow of the first attachment, and the first attachment can stably adhere to the porous conductive substrate, effectively delaying the corrosion damage of the attachment of the electrolyte to the reference electrode, which is beneficial for the reference electrode to stably monitor the positive and negative electrode potentials for a long time and improve the service life of the reference electrode.

[0031] It can be understood that considering that the mechanical properties of the reference electrode meet the actual use conditions, ρ0 satisfies: ρ0 ≥ ρ1 × 0.3. For example: ρ0 / ρ1 can be 0.3, 0.4, 0.5, 0.6, 0.7. S0 satisfies: S0 ≤ S1 × 330. For example: S0 / S1 can be 5, 10, 50, 100, 150, 200, 250, 300, 330.

[0032] Optionally, the reference electrode further includes a second attachment, and the second attachment is located on the surface of the porous conductive substrate and covers the pores of the porous conductive substrate. Through the covering of the second attachment, it is beneficial to maintain the stable attachment of the first attachment in the pores, delay the corrosion of the first attachment by the electrolyte, and improve the service life of the reference battery.

[0033] Considering factors such as the volume of the three-electrode cell, the volume occupied by the reference electrode needs to be small. Optionally, the porous conductive substrate is a porous conductive wire. Using a porous conductive wire as the porous conductive substrate is beneficial for saving the volume occupied by the reference electrode in the three-electrode cell. Optionally, the wire diameter of the porous conductive wire is D, and the thickness of the second attachment is T. D and T satisfy the following conditions: 32μm ≤ 2T + D ≤ 260μm. It can be understood that the wire diameter D of the porous conductive wire refers to the diameter of the radial cross-section of the porous conductive wire.

[0034] Generally speaking, the larger the T value, the longer the service life of the reference electrode. However, as the T value continues to increase, the lamination flatness of the subsequent laminated three-electrode battery will decrease, and even the interface between the positive electrode and the negative electrode will be damaged, affecting the battery performance. To control the influence of the addition of the reference electrode on the battery performance, control 2T + D ≤ 260 μm, so that the service life of the reference electrode can be relatively long without damaging the interface between the positive electrode and the negative electrode. 2T + D can be 32 μm, 50 μm, 100 μm, 150 μm, 200 μm, 260 μm. Optionally, D satisfies: 30 μm ≤ D ≤ 200 μm. D can be 30 μm, 50 μm, 100 μm, 150 μm, 200 μm. Optionally, T satisfies: 1 μm ≤ T ≤ 50 μm. T can be 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm. Preferably, D satisfies: 30 μm ≤ D ≤ 100 μm. Preferably, T satisfies: 1 μm ≤ T ≤ 10 μm.

[0035] In the reference electrode, the porous conductive matrix has the function of conducting electricity. Optionally, the material of the porous conductive substrate is metal. Optionally, the material of the porous conductive matrix includes at least one of copper, nickel, gold, and tin. The porous conductive substrate can be a single substance, an alloy, or can have a coating layer. For example, the porous conductive matrix can include a copper matrix and a tin layer coated on the copper matrix.

[0036] In some examples, the porous conductive matrix is porous copper wire. The density of solid copper wire is 8.96 g / cm 3 , and the density of the porous copper wire ≤ 6.272 g / cm 3 . For example: the density of the porous copper wire is 5.376 g / cm 3 , 4.48 g / cm 3 , 3.584 g / cm 3 . When the diameter D of the porous copper wire is 50 μm, the specific surface area of the solid copper wire is 0.0089 m 2 / g, and the specific surface area of the porous copper wire is ≥ 0.0445 m 2 / g. For example, the specific surface area of the porous copper wire is 0.12 m 2 / g, 0.49 m 2 / g, 1.24 m 2 / g, 2.81 m 2 .

[0037] In the reference electrode, the first attachment and the second attachment have a preset potential. With the preset potential as a reference, the potentials of the positive and negative electrodes are monitored in real time. The more stable the potentials of the first attachment and the second attachment, the higher the detection accuracy. Optionally, the chemical formulas of the first attachment and the second attachment are independently selected from Li, Li n FePO 4, Na or K, where 0.1 ≤ n ≤ 0.9. LiFePO 4 (lithium iron phosphate) has an unstable potential. Therefore, LiFePO 4 is not suitable as the attachment in this application, and the detection result is inaccurate. However, by charging lithium iron phosphate, some lithium ions in lithium iron phosphate are removed, and Li n FePO 4 (0.1 ≤ n ≤ 0.9) has a stable potential and the detection result is accurate.

[0038] The reference electrode of the above embodiment is stable, has a long service life, and high detection accuracy. It can be applied not only in lithium-ion batteries to monitor the potentials of the positive and negative electrodes and evaluate the performance of the positive and negative electrodes, but also in other types of batteries, such as sodium-ion batteries or potassium-ion batteries.

[0039] The second aspect of this application provides a three-electrode battery. In some embodiments, the three-electrode battery includes a battery housing, an electrolyte, and a three-electrode cell located within the battery housing. The three-electrode cell includes the reference electrode, a positive electrode plate, a negative electrode plate, a first separator, and a second separator as described above. The first separator is disposed between the reference electrode and the positive electrode plate, and the second separator is disposed between the reference electrode and the negative electrode plate.

[0040] In the above three-electrode cell, the reference electrode and the positive electrode plate are separated by the first separator, which can prevent a short circuit between the reference electrode and the positive electrode plate. The reference electrode and the negative electrode plate are separated by the second separator, which can prevent a short circuit between the reference electrode and the negative electrode plate.

[0041] Optionally, the positive electrode plate includes a positive current collector and a positive active layer located on the positive current collector. The positive active layer includes a lithium-containing positive active material, a sodium-containing positive active material, or a potassium-containing positive active material.

[0042] Optionally, the negative electrode plate includes a negative current collector and a negative active layer located on the negative current collector. The negative active layer includes a carbon-based material and / or a silicon-based material. Optionally, the carbon-based material includes graphite or hard carbon.

[0043] Taking a lithium-ion battery as an example, optionally, the positive current collector can be aluminum foil. Optionally, the positive active layer includes a lithium-containing positive active material, a positive binder, and a positive conductive agent. Optionally, the lithium-containing positive active material is selected from lithium iron phosphate, lithium cobaltate, etc. The positive binder is selected from polyvinylidene fluoride (PVDF), etc. The positive conductive agent is selected from carbon nanotubes (CNT), etc. Optionally, the negative current collector can be copper foil. Optionally, the negative active layer includes a carbon material, a negative binder, and a negative conductive agent. Optionally, the carbon material is selected from graphite, silicon carbon, etc. The negative binder is selected from lithiated polyacrylic acid (PAALi), styrene-butadiene rubber (SBR), etc. The negative conductive agent is selected from carbon nanotubes (CNT), conductive carbon black (SP), etc. Optionally, the first separator and the second separator each independently include a polyethylene (PE) film and composite layers on both sides of the PE film, and the composite layer includes polyvinylidene fluoride (PVDF) and Al 2 O 3 。Optionally, the electrolyte includes a lithium salt, an organic solvent, and an additive. Optionally, the lithium salt is selected from LiPF 6 。The organic solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC). Optionally, the additive is selected from fluoroethylene carbonate (FEC), etc.

[0044] Optionally, the battery case can be a soft-pack case or a hard case. When the battery case is a soft-pack case, the material can be an aluminum-plastic film. When the battery case is a hard case, the material can be aluminum alloy, stainless steel, etc.

[0045] It can be understood that the three-electrode battery cell further includes a third separator, and the third separator is disposed between the positive electrode plate and the negative electrode plate. The positive electrode plate and the negative electrode plate are separated by the third separator, which can prevent a short circuit between the positive electrode plate and the negative electrode plate. The third separator includes a polyethylene (PE) film and composite layers on both sides of the PE film, and the composite layer includes polyvinylidene fluoride (PVDF) and Al 2 O 3 。

[0046] It can be understood that the three-electrode battery further includes accessories well-known to those skilled in the art such as electrode tabs and adhesive tapes.

[0047] The above three-electrode battery has all the advantages of the above reference electrode, which will not be elaborated here.

[0048] The third aspect of the present application provides a method for manufacturing a three-electrode battery. In some embodiments, the method for manufacturing a three-electrode battery includes the following steps:

[0049] S10. Stack the prefabricated electrode, the positive electrode plate, the negative electrode plate, the first separator, and the second separator to prepare a prefabricated battery cell.

[0050] Among them, the first separator is disposed between the prefabricated electrode and the positive electrode sheet, and the second separator is disposed between the prefabricated electrode and the negative electrode sheet. The number of the positive electrode sheet, the negative electrode sheet, the first separator and the first separator can be one or more. When the number is more than one, a third separator is further disposed between the positive electrode sheet and the negative electrode sheet. The prefabricated electrode can be disposed between any positive electrode sheet and negative electrode sheet.

[0051] After stacking, a prefabricated battery cell is prepared by winding or laminating.

[0052] The prefabricated electrode includes a porous conductive matrix, and the porous conductive matrix satisfies at least one of the following conditions 1) to 2):

[0053] 1) The density of the porous conductive matrix is ρ0, and the density of the solid conductive matrix made of the same material as the porous conductive matrix is ρ1. ρ0 satisfies: ρ0 ≤ ρ1 × 0.7;

[0054] 2) The specific surface area of the porous conductive matrix is S0, and the specific surface area of the solid conductive matrix with the same shape as the porous conductive matrix is S1. S0 satisfies: S0 ≥ S1 × 5.

[0055] The porous conductive matrix can be obtained by subjecting the conductive matrix to a corrosion treatment. Optionally, the preparation method of the porous conductive matrix includes the following steps: placing the conductive matrix in a corrosion solution for corrosion treatment. Through the corrosion of the corrosion solution, pores can be formed on the conductive matrix.

[0056] Optionally, the corrosion solution is a strongly corrosive acid solution. For example, the corrosion solution is an aqueous hydrochloric acid solution with a mass fraction greater than 30%. The material of the conductive matrix includes at least one of copper, nickel, gold and tin. The conductive matrix is continuously corroded in the corrosion solution to generate pores.

[0057] Considering the corrosion depth of the corrosion treatment to obtain a porous conductive matrix with an ideally controllable density and / or specific surface area, optionally, the material of the conductive matrix includes a conductive material and an etching material. Among them, the conductive material can be retained in the corrosion treatment, and the etching material can be removed in the corrosion treatment to form pores. The distribution of the etching material in the conductive matrix can be controlled to control the pore distribution of the porous conductive matrix and obtain a porous conductive matrix with an ideally controllable density and / or specific surface area. Optionally, the corrosion solution is a weakly corrosive acid solution. For example, the corrosion solution is an aqueous hydrochloric acid solution with a mass fraction of 5% to 30%. Optionally, the conductive material is a metal. Optionally, the conductive material includes at least one of copper, nickel, gold and tin. Optionally, the etching material includes at least one of aluminum, manganese and iron.

[0058] S20. Package the prefabricated battery cell, inject electrolyte, and prepare a prefabricated battery.

[0059] Optionally, the material for encapsulating the prefabricated battery cell can be a soft material or a hard material. When it is a soft material, the battery housing is a soft-pack housing; when it is a hard material, the battery housing is a hard housing. Among them, the soft material can be an aluminum-plastic film. The hard material can be aluminum alloy, stainless steel, etc.

[0060] After encapsulation, electrolyte is injected into the battery housing. Before injecting the electrolyte, processes such as high-temperature baking can also be included. After injecting the electrolyte, processes such as vacuum packaging, standing, formation, and capacity measurement can also be included.

[0061] S30. Activate the prefabricated electrode to form a first attachment in the pores of the porous conductive matrix, form a reference electrode, and obtain a three-electrode battery.

[0062] Optionally, activating the prefabricated electrode further includes the following steps: forming a second attachment on the surface of the porous conductive matrix to cover the pores of the porous conductive matrix.

[0063] The appropriate activation method can be selected according to the situation of the prefabricated electrode.

[0064] In some examples, the prefabricated electrode includes a porous conductive matrix, and the chemical formula of the first attachment is Li, Na, or K. Activating the prefabricated electrode includes the following steps:

[0065] Charge the prefabricated electrode using the positive electrode plate and / or the negative electrode plate. Preferably, charge the prefabricated electrode using the positive electrode plate and the negative electrode plate respectively.

[0066] Optionally, after forming the first attachment, control the charging time and current to form a second attachment on the surface of the porous conductive matrix to cover the pores of the porous conductive matrix. The chemical formula of the second attachment is Li, Na, or K.

[0067] Optionally, the porous conductive matrix is a porous conductive wire with a wire diameter of D. Control the thickness T of the second attachment so that D and T satisfy the following conditions: 32μm ≤ 2T + D ≤ 260μm, so as to have a longer service life of the reference electrode without damaging the interface between the positive electrode plate and the negative electrode plate. Optionally, make D and T satisfy at least one of the following conditions 1) - 2): 1) 30μm ≤ D ≤ 200μm; 2) 1μm ≤ T ≤ 50μm.

[0068] It can be understood that during activation charging, the charging current is small. Optionally, the charging current is 20μA - 40μA. Optionally, the charging time is 2h - 10h.

[0069] In some examples, the prefabricated electrode includes a porous conductive matrix and a first pre-attachment, and the first pre-attachment is located in the pores of the porous conductive matrix. The chemical formula of the first pre-attachment is LiFePO 4, activating the prefabricated electrode includes the following steps:

[0070] Charge the prefabricated electrode using the positive electrode plate or the negative electrode plate, control the charging time and current, so that the first pre-attachment is converted into the first attachment, and the chemical formula of the first attachment is Li n FePO 4 , where 0.1 ≤ n ≤ 0.9.

[0071] Optionally, the preparation method of the prefabricated electrode includes the following steps: Immerse the porous conductive substrate in the slurry containing the first pre-attachment. It can be understood that the number of immersions can be one or multiple.

[0072] Optionally, the prefabricated electrode further includes a second pre-attachment, the second pre-attachment is located on the surface of the porous conductive substrate, covering the pores of the porous conductive substrate, and the chemical formula of the second pre-attachment is LiFePO 4 , activating the prefabricated electrode further includes the following steps:

[0073] Charge the prefabricated electrode using the positive electrode plate or the negative electrode plate, control the charging time and current, so that the second pre-attachment is converted into the second attachment, and the chemical formula of the second attachment is Li n FePO 4 , where 0.1 ≤ n ≤ 0.9.

[0074] Optionally, the preparation method of the prefabricated electrode further includes the following steps: Immerse the porous conductive substrate with the first pre-attachment in the pores in the slurry containing the second pre-attachment. It can be understood that the number of immersions can be one or multiple.

[0075] Optionally, the porous conductive substrate is a porous conductive wire, the wire diameter of the porous conductive wire is D, control the thickness T of the second attachment, so that D and T satisfy the following conditions: 32μm ≤ 2T + D ≤ 260μm, so as to have a longer service life of the reference electrode while not damaging the interface between the positive electrode plate and the negative electrode plate. Optionally, make D and T satisfy at least one of the following conditions 1) - 2): 1) 30μm ≤ D ≤ 200μm; 2) 1μm ≤ T ≤ 50μm.

[0076] It can be understood that the thickness of the second pre-attachment is basically the same as the thickness T of the second attachment, and can be controlled by controlling the solid content, immersion time and number of immersions of the slurry containing the second pre-attachment.

[0077] Optionally, the solid content of the slurry containing the first pre-attachment and the slurry containing the second pre-attachment are each independently 20wt% - 90wt%. Optionally, the total immersion time in the slurry containing the first pre-attachment and the slurry containing the second pre-attachment is 1h - 15h.

[0078] When both the first pre-attached substance and the second pre-attached substance in the prefabricated electrode are LiFePO 4 at this time, the porous conductive matrix can be immersed in a slurry containing LiFePO 4 to form the first pre-attached substance and the second pre-attached substance. Optionally, the slurry containing LiFePO 4 includes LiFePO 4 , a binder, a conductive agent, and a solvent. The binder, the conductive agent, and the solvent can refer to the cathode binder and the cathode conductive agent above. The solvent can be N-methylpyrrolidone (NMP).

[0079] In this embodiment, the prefabricated electrode is charged using the negative electrode sheet, and part of the lithium ions in LiFePO 4 are removed, so that the chemical formulas of the first attached substance and the second attached substance are Li n FePO 4 (0.1≤n≤0.9). At this time, the voltage of the prefabricated electrode is 3.0V - 3.4V, and the potential is stable. It can be understood that during the activation charging, the charging current is small. Optionally, the charging current is 20μA - 40μA.

[0080] Through activation, a reference electrode is formed. The reference electrode, the positive electrode sheet, the negative electrode sheet, the first separator, and the second separator constitute a three-electrode battery cell, and a three-electrode battery is obtained. The preparation method of the above three-electrode battery is simple, the prepared three-electrode battery has a long service life, good stability, and does not damage the interface between the positive electrode and the negative electrode.

[0081] The following is further described in combination with specific examples and comparative examples. The raw materials involved in the following specific examples and comparative examples, unless otherwise specified, can all be obtained commercially. The instruments used, unless otherwise specified, can all be obtained commercially. The processes involved, unless otherwise specified, are all conventional selections of those skilled in the art. The parts involved, unless otherwise specified, are all parts by weight.

[0082] Preparation of the positive electrode sheet: Prepare 97 parts of lithium cobaltate, 2.5 parts of PVDF, 0.5 parts of CNT, and 100 parts of NMP. Mix these materials evenly, coat the obtained slurry evenly on one surface of a 16μm aluminum foil, and after drying, the coating weight of the electrode sheet is 15mg / cm 2 , and then perform rolling, slitting, and cutting to obtain the positive electrode sheet. The density of the rolled electrode sheet is 4.2g / cc.

[0083] Preparation of the negative electrode sheet: Prepare 86.7 parts of graphite, 10 parts of silicon carbon, 2.8 parts of PAALi, 0.3 parts of SBR, 0.2 parts of CNT, and 150 parts of deionized water. Mix these materials evenly, coat the obtained slurry on one surface of a 10μm copper foil, and after drying, the coating weight of each side of the electrode sheet is 5.5mg / cm2 , and then roll pressing, slitting, and cutting to obtain a negative electrode sheet, with the compaction of the electrode sheet after roll pressing being 1.65 g / cc.

[0084] Electrolyte preparation: EC, PC, and DMC are mixed in a mass ratio of 1:1:1 to obtain an organic solvent. Then, LiPF 6 is dissolved in the above-mentioned organic solvent, and then FEC is added and mixed evenly to obtain an electrolyte; finally, the concentration of the lithium salt is 1 mol / L, and the mass content of FEC is 20%.

[0085] Separator preparation: 50 parts of PVDF, 50 parts of Al 2 O 3 and 100 parts of NMP are mixed, and the mixed slurry is evenly coated on both surfaces of a 10-μm PE separator substrate by a micro-embossing roll coating method, and then dried. After drying, the coating thickness on both sides of the separator is 1 μm, and the total thickness is 12 μm.

[0086] Example 1

[0087] This example provides a reference electrode, a three-electrode battery, and a preparation method thereof, and the steps are as follows:

[0088] Step 1: Provide a porous copper wire with a diameter D of 50 μm as a prefabricated electrode. The density, porosity, and specific surface area of the porous copper wire are shown in Table 1. After sequentially laminating the positive electrode sheet, separator, prefabricated electrode, separator, and negative electrode sheet, a prefabricated battery core is formed by lamination.

[0089] Step 2: Encapsulate the prefabricated battery core with an aluminum-plastic film, and then through high-temperature baking, liquid injection, vacuum packaging, standing, formation, and capacity measurement, a single-piece soft-pack prefabricated battery is obtained.

[0090] Step 3: Use a charge and discharge device to charge with a current of 20 μA between the positive electrode sheet and the porous copper wire for 4 h, and then charge with a current of 20 μA between the negative electrode sheet and the porous copper wire for 4 h to obtain a reference electrode. At this time, after activation, lithium metal is formed in the pores and on the surface of the porous copper wire, and the lithium metal on the surface covers the pores. Measure the thickness T of the lithium metal on the surface of the porous copper wire, see Table 1. At this time, the porous copper wire attached with lithium metal is the reference electrode, and a three-electrode battery is obtained.

[0091] Table 1

[0092] <![CDATA[Density (g / cm 3 )]]> <![CDATA[Specific surface area (m 2 / g)]]> D (μm) T (μm) 2T + D (μm) Example 1 4.48 1.24 50 5 60 Example 2 5.376 0.49 50 5 60 Example 3 6.272 0.12 50 5 60 Example 4 4.48 1.24 50 32 114 Example 5 4.48 1.24 50 51 152 Example 6 4.48 1.24 50 125 300 Example 7 4.48 1.24 50 6 72 Example 8 6.272 0.12 50 6 72 Example 9 4.48 1.24 50 12 74 Example 10 4.48 1.24 50 6 72 Comparative Example 1 8.96 0.0089 50 60 170 Comparative Example 2 8.2 0.013 50 51 114 Comparative Example 3 7.1 0.038 50 32 152

[0093] Examples 2 to 3

[0094] Examples 2 to 3 provide a reference electrode, a three-electrode battery, and a preparation method thereof, and the steps are as follows:

[0095] Step 1: Provide a porous copper wire with a diameter D of 50 μm. The density, porosity and specific surface area of ​​the porous copper wire are shown in Table 1. Refer to Step 1 of Example 1 to prepare a prefabricated battery cell.

[0096] Step 2, refer to step 2 of Example 1 to prepare a prefabricated battery.

[0097] Step 3, use a charging and discharging device to charge between the positive electrode plate and the porous copper wire with a current of 20μA for a period of time, and then use a current of 20μA to charge between the negative electrode plate and the porous copper wire for a period of time, and lithium monomers are formed in the pores and on the surface of the porous copper wire. The charging time is controlled so that the thickness T of the lithium monomers on the surface of the porous copper wire is as shown in Table 1. At this time, the porous copper wire with lithium monomers attached is the reference electrode, and a three-electrode battery is obtained.

[0098] Example 4 to Example 6

[0099] Examples 4 to 6 provide a reference electrode, a three-electrode battery and a preparation method thereof, the steps are as follows:

[0100] Step 1, refer to step 1 of Example 1, prepare a prefabricated battery cell.

[0101] Step 2, refer to step 2 of Example 1 to prepare a prefabricated battery.

[0102] Step 3, use a charging and discharging device to charge between the positive electrode plate and the porous copper wire with a current of 20μA for a period of time, and then use a current of 20μA to charge between the negative electrode plate and the porous copper wire for a period of time, and lithium monomers are formed in the pores and on the surface of the porous copper wire. The charging time is controlled so that the thickness T of the lithium monomers on the surface of the porous copper wire is as shown in Table 1. At this time, the porous copper wire with lithium monomers attached is the reference electrode, and a three-electrode battery is obtained.

[0103] Example 7

[0104] This embodiment provides a reference electrode, a three-electrode battery and a preparation method thereof, the steps are as follows:

[0105] Step 1: Provide a porous copper wire with a diameter D of 50 μm. The density, porosity, and specific surface area of the porous copper wire are shown in Table 1. Immerse the porous copper wire into a slurry containing lithium iron phosphate with a solid content of 30 wt% (by weight, including 95 parts of lithium iron phosphate, 2.8 parts of PVDF, 0.5 parts of CNT, and 1.7 parts of SP). After 3 hours, take it out and dry it, then immerse it again. After 3 hours, take it out and dry it to obtain a prefabricated electrode. At this time, a lithium iron phosphate layer is formed in the pores and on the surface of the porous copper wire, and the lithium iron phosphate layer on the surface covers the pores. The thickness of the lithium iron phosphate layer on the surface of the porous copper wire is basically the same as the thickness of the subsequent second attachment. Measure the thickness T of the lithium iron phosphate layer on the surface of the porous copper wire, see Table 1. Refer to Step 1 of Example 1 to prepare a prefabricated battery cell.

[0106] Step 2: Refer to Step 2 of Example 1 to prepare a prefabricated battery.

[0107] Step 3: Use a charge-discharge device to charge between the negative electrode plate and the prefabricated electrode with a current of 20 μA until the chemical formula of the lithium iron phosphate layer in the pores and on the surface of the porous copper wire at this time is Li n FePO 4 , where 0.1 ≤ n ≤ 0.9. At this time, the voltage of the prefabricated electrode is 3.2 V, which is used as a reference electrode to obtain a three-electrode battery.

[0108] Example 8

[0109] This example provides a reference electrode, a three-electrode battery, and a preparation method thereof, and the steps are as follows:

[0110] Step 1: Provide a porous copper wire with a diameter D of 50 μm. The density, porosity, and specific surface area of the porous copper wire are shown in Table 1. Immerse the porous copper wire into the slurry of Example 7. After a period of time, take it out and dry it, then immerse it again. After a period of time, take it out and dry it to form a lithium iron phosphate layer in the pores and on the surface of the porous copper wire, and the lithium iron phosphate layer on the surface covers the pores to obtain a prefabricated electrode. Measure the thickness T of the lithium iron phosphate layer on the surface of the porous copper wire, see Table 1. Refer to Step 1 of Example 1 to prepare a prefabricated battery cell.

[0111] Step 2: Refer to Step 2 of Example 1 to prepare a prefabricated battery.

[0112] Step 3: Refer to Step 3 of Example 7 to obtain a three-electrode battery.

[0113] Example 9

[0114] This example provides a reference electrode, a three-electrode battery, and a preparation method thereof, and the steps are as follows:

[0115] Step 1, see step 1 of Example 7, provide a porous copper wire, immerse the porous copper wire in the slurry of Example 7, take it out and dry it after a period of time, immerse it again, take it out and dry it after a period of time, form a lithium iron phosphate layer in the pores and on the surface of the porous copper wire, and the lithium iron phosphate layer on the surface covers the pores to obtain a prefabricated electrode. Test the thickness T of the lithium iron phosphate layer on the surface of the porous copper wire, see Table 1. See step 1 of Example 1, prepare a prefabricated battery cell.

[0116] Step 2, refer to step 2 of Example 1 to prepare a prefabricated battery.

[0117] Step 3, refer to step 3 of Example 7 to obtain a three-electrode battery.

[0118] Example 10

[0119] This embodiment provides a reference electrode, a three-electrode battery and a preparation method thereof, the steps are as follows:

[0120] Step 1, refer to step 1 of Example 7, prepare a prefabricated battery cell.

[0121] Step 2, refer to step 2 of Example 1 to prepare a prefabricated battery.

[0122] Step 3: Use a charging and discharging device to charge between the negative electrode and the prefabricated electrode with a current of 20μA. The chemical formula of the lithium iron phosphate layer in the pores and on the surface of the porous copper wire is Li n FePO 4 , where n < 0.1, at this time, the prefabricated electrode voltage is 3.8V, which is the reference electrode, and a three-electrode battery is obtained.

[0123] Comparative Example 1

[0124] This comparative example provides a reference electrode, a three-electrode battery and a preparation method thereof, and the steps are as follows:

[0125] Step 1: Provide a copper wire with a diameter D of 50 μm as a prefabricated electrode, refer to step 1 of Example 1, and prepare a prefabricated battery cell.

[0126] Step 2, refer to step 2 of Example 1 to prepare a prefabricated battery.

[0127] Step 3, refer to step 3 of Example 1, test the thickness T of the lithium element on the surface of the copper wire, refer to Table 1, at this time, the copper wire with lithium element attached is the reference electrode, and the three battery electrodes are obtained.

[0128] Comparative Example 2~Comparative Example 3

[0129] Comparative Examples 2 and 3 provide a reference electrode, a three-electrode battery and a preparation method thereof, and the steps are as follows:

[0130] Step 1: Provide a porous copper wire with a diameter D of 50 μm. The density, porosity and specific surface area of ​​the porous copper wire are shown in Table 1. Refer to Step 1 of Example 1 to prepare a prefabricated battery cell.

[0131] Step 2, refer to step 2 of Example 1 to prepare a prefabricated battery.

[0132] Step 3, refer to step 3 of Example 1, test the thickness T of the lithium element on the surface of the copper wire, refer to Table 1, at this time, the copper wire with lithium element attached is the reference electrode, and the three battery electrodes are obtained.

[0133] The three-electrode batteries of the above-mentioned embodiments and comparative examples were tested as follows, and the results are shown in Table 2.

[0134] The battery's cyclic charge and discharge performance was tested using a charge rate of 0.5C and a discharge rate of 0.2C, and the positive and negative electrode potentials were monitored in real time through three electrodes. During the cycle, if the following conditions 1) and 2) are met at the same time, the three electrodes are determined to be effective in the cycle. Among them: 1) The voltage difference between the positive electrode and the three electrodes increases with the increase of the battery voltage, and decreases with the decrease of the battery voltage; 2) The voltage difference between the negative electrode and the three electrodes decreases with the increase of the battery voltage, and increases with the decrease of the battery voltage. In order to further determine whether the detected positive and negative electrode potentials are stable and effective, the battery is charged to 60% of the power after 20 cycles. After charging is completed, the battery is allowed to stand for 48 hours to confirm the potential difference between the positive and negative electrodes and the third electrode. After 48 hours, the potential difference between the positive and negative electrodes and the third electrode is tested to confirm the voltage change rate of the two tests. The smaller the change rate, the more stable the three electrodes.

[0135] Table 2

[0136]

[0137] Combining Table 1 and Table 2, it can be seen that when the first attachment in the pores is used as the reference electrode, the density and specific surface area of ​​the porous copper wire are controlled within a certain range, and the reference electrode can still be effective after 20 cycles, and a three-electrode battery with good stability, high test accuracy and long service life can be obtained. If the thickness of the second attachment is large, although the reference electrode is still effective, the traces of the reference electrode can be clearly seen on the appearance of the single-chip soft-pack battery, and the interface of the positive and negative electrodes is also damaged when the interface is disassembled, which is not conducive to evaluating the performance of the positive and negative electrodes.

[0138] In Comparative Example 1, when using traditional copper wire with a large thickness of single-element lithium, after 5 cycles, it was impossible to continue to use the reference electrode to monitor the positive and negative electrode potentials; in Comparative Examples 2 and 3, the density, porosity, and specific surface area of ​​the porous copper wire were not appropriate. Similarly, when the thickness of single-element lithium was large, they failed after 10 and 15 cycles.

[0139] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0140] The above-described embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, 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 appended claims.

Claims

1. A reference electrode, characterized in that It includes a porous conductive substrate and a first attachment, wherein the first attachment is located in the pores of the porous conductive substrate; The porous conductive substrate satisfies at least one of the following conditions 1) to 2): 1) The density of the porous conductive matrix is ​​ρ0, and the density of the solid conductive matrix made of the same material as the porous conductive matrix is ​​ρ1, and ρ0 satisfies: ρ0≤ρ1×0.7; 2) The specific surface area of ​​the porous conductive matrix is ​​S0, the specific surface area of ​​the solid conductive matrix having the same shape as the porous conductive matrix is ​​S1, and S0 satisfies: S0≥S1×5.

2. The reference electrode according to claim 1, characterized in that It also includes a second attachment, which is located on the surface of the porous conductive substrate and covers the pores of the porous conductive substrate.

3. The reference electrode according to claim 2, characterized in that The porous conductive substrate is a porous conductive wire, the wire diameter of the porous conductive wire is D, the thickness of the second attachment is T, and D and T satisfy the following condition: 32μm≤2T+D≤260μm.

4. The reference electrode according to claim 3, characterized in that The D and the T satisfy at least one of the following conditions 1) to 2): 1)30μm≤D≤200μm; 2)1μm≤T≤50μm.

5. The reference electrode according to any one of claims 2 to 4, characterized in that The chemical formulas of the first attachment and the second attachment are independently selected from Li, Li n FePO4, Na or K, wherein 0.1≤n≤0.

9.

6. The reference electrode according to any one of claims 1 to 4, characterized in that The material of the porous conductive matrix includes at least one of copper, nickel, gold and tin.

7. A three-electrode battery, characterized in that: It comprises a battery shell, an electrolyte and a three-electrode battery cell located in the battery shell, wherein the three-electrode battery cell comprises a reference electrode according to any one of claims 1 to 6, a positive electrode sheet, a negative electrode sheet, a first diaphragm and a second diaphragm, wherein the first diaphragm is arranged between the reference electrode and the positive electrode sheet, and the second diaphragm is arranged between the reference electrode and the negative electrode sheet.

8. The three-electrode battery according to claim 7, characterized in that: Includes at least one of the following features: 1) The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on the positive electrode current collector, wherein the positive electrode active layer comprises a lithium-containing positive electrode active material, a sodium-containing positive electrode active material or a potassium-containing positive electrode active material; 2) The negative electrode plate includes a negative electrode current collector and a negative electrode active layer located on the negative electrode current collector, and the negative electrode active layer includes a carbon-based material and / or a silicon-based material.

9. A method for preparing a three-electrode battery, characterized in that: The following steps are involved: A prefabricated electrode, a positive electrode sheet, a negative electrode sheet, a first separator and a second separator are stacked to prepare a prefabricated battery cell; wherein the first separator is arranged between the prefabricated electrode and the positive electrode sheet, the second separator is arranged between the prefabricated electrode and the negative electrode sheet, the prefabricated electrode comprises a porous conductive matrix, and the porous conductive matrix satisfies at least one of the following conditions 1) to 2): 1) the density of the porous conductive matrix is ​​ρ0, the density of a solid conductive matrix of the same material as the porous conductive matrix is ​​ρ1, and ρ0 satisfies: ρ0≤ρ1×0.7; 2) the specific surface area of ​​the porous conductive matrix is ​​S0, the specific surface area of ​​a solid conductive matrix of the same shape as the porous conductive matrix is ​​S1, and S0 satisfies: S0≥S1×5; Encapsulating the prefabricated battery core, injecting electrolyte, and preparing a prefabricated battery; The prefabricated electrode is activated to form a first attachment in the pores of the porous conductive substrate to form a reference electrode, resulting in a three-electrode battery.

10. The method for preparing a three-electrode battery according to claim 9, characterized in that: The method for preparing the porous conductive substrate comprises the following steps: placing the conductive substrate in a corrosive solution for corrosion treatment.

11. The method for preparing a three-electrode battery according to claim 10, characterized in that: The conductive substrate is made of a conductive material and an etching material. The conductive material can be retained during the etching process, and the etching material can be removed during the etching process to form the pores.

12. The method for preparing a three-electrode battery according to claim 11, characterized in that: Includes at least one of the following features: 1) The conductive material includes at least one of copper, nickel, gold and tin; 2) The etched material includes at least one of aluminum, manganese and iron; 3) The etching solution is a hydrochloric acid aqueous solution with a mass fraction of 5% to 30%.

13. The method for preparing a three-electrode battery according to any one of claims 9 to 12, characterized in that: Activating the prefabricated electrode further comprises the following steps: forming a second attachment on the surface of the porous conductive substrate to cover the pores of the porous conductive substrate.

14. The method for preparing a three-electrode battery according to any one of claims 9 to 12, characterized in that: The chemical formula of the first attachment is Li, Na or K, and activating the prefabricated electrode comprises the following steps: The prefabricated electrode is charged using the positive electrode sheet and / or the negative electrode sheet.

15. The method for preparing a three-electrode battery according to claim 14, characterized in that: After the first attachment is formed, the charging time and current are controlled to form a second attachment covering the pores of the porous conductive substrate on the surface of the porous conductive substrate, wherein the chemical formula of the second attachment is Li, Na or K.

16. The method for preparing a three-electrode battery according to claim 15, characterized in that: The porous conductive substrate is a porous conductive wire, the wire diameter of the porous conductive wire is D, and the thickness T of the second attachment is controlled so that D and T meet the following condition: 32μm≤2T+D≤260μm.

17. The method for preparing a three-electrode battery according to any one of claims 9 to 12, characterized in that: The prefabricated electrode further comprises a first pre-attachment, the first pre-attachment is located in the pores of the porous conductive substrate, the chemical formula of the first pre-attachment is LiFePO4, and activating the prefabricated electrode comprises the following steps: The prefabricated electrode is charged by using a positive electrode sheet or a negative electrode sheet, and the charging time and current are controlled to convert the first pre-attached substance into a first attached substance, wherein the chemical formula of the first attached substance is Li n FePO4, wherein 0.1≤n≤0.

9.

18. The method for preparing a three-electrode battery according to claim 17, characterized in that: The method for preparing the prefabricated electrode comprises the following steps: immersing the porous conductive substrate in a slurry containing the first pre-attached substance.

19. The method for preparing a three-electrode battery according to claim 17, characterized in that: The prefabricated electrode further includes a second pre-attachment, which is located on the surface of the porous conductive substrate and covers the pores of the porous conductive substrate. The chemical formula of the second pre-attachment is LiFePO4. Activating the prefabricated electrode further includes the following steps: The prefabricated electrode is charged by using a positive electrode sheet or a negative electrode sheet, and the charging time and current are controlled to convert the second pre-attached substance into a second attached substance, wherein the chemical formula of the second attached substance is Li n FePO4, wherein 0.1≤n≤0.

9.

20. The method for preparing a three-electrode battery according to claim 19, characterized in that: The method for preparing the prefabricated electrode further comprises the following steps: immersing the porous conductive substrate containing the first pre-attached substance in pores in a slurry containing the second pre-attached substance.

21. The method for preparing a three-electrode battery according to claim 20, characterized in that: The porous conductive matrix is ​​a porous conductive wire, the wire diameter of the porous conductive wire is D, and the thickness T of the second pre-attachment is controlled so that D and T meet the following condition: 32μm≤2T+D≤260μm.

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