Reference electrode and preparation method and application thereof

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a reference electrode and a preparation method and application thereof. According to the reference electrode provided by the invention, the composition and the thickness of the solid electrolyte coating layer are limited, so that the test precision, the response time and the like of the reference electrode can be further improved, and higher detection requirements are met; according to the reference electrode provided by the invention, while the test precision is ensured, the problem that the lithium plating layer is quickly damaged due to direct contact between the electrolyte and the lithium plating layer is solved, and the electric signal interference of the direct contact between the lithium plating layer and the electrolyte on the tested positive electrode-reference electrode and negative electrode-reference electrode is avoided; meanwhile, a diaphragm is prevented from being additionally arranged in a reference electrode area, and the fast charging test accuracy of the battery cell is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to a reference electrode and a preparation method and application thereof. Background Art

[0002] In recent years, lithium-ion batteries have been used in digital products, power and energy storage, and with the demand of the consumer market, the fast charging capability of batteries is getting higher and higher. The fast charging capability of batteries is usually affected by the selection of battery cell materials, electrolyte formula adaptation, charging temperature and charging strategy. When the charging rate exceeds the upper limit of the battery, the lithium ions released from the positive electrode cannot be normally embedded in the negative electrode material, causing lithium deposition on the surface of the negative electrode, which in turn affects the battery cell cycle performance and safety performance. For the development of battery cell platforms, step charging is often used to obtain the most suitable charging rate for the battery cell. Therefore, how to accurately identify lithium metal deposition is the key to confirming the upper limit of the battery charging rate.

[0003] Identification of lithium deposition can be confirmed by a three-electrode method (i.e., adding a reference electrode). The current common three-electrode solution for lithium-ion batteries is usually to connect a reference electrode to the battery cell. This type of reference electrode is usually composed of a metal wire or metal foil with a metal pole ear. In order to reduce the voltage hysteresis and accuracy problems during the three-electrode test, and to avoid the metal wire after lithium plating being directly exposed to the electrolyte, the lithium plating layer will react with the electrolyte, causing the lithium plating layer to be destroyed and lose the detection potential function, affecting the service life of the reference electrode, etc., the reference electrode in the prior art will be configured with a coating layer on the outside of the lithium plating layer, and the reference electrode is coated with a solid electrolyte, so that the reference electrode can directly contact the positive and negative electrodes, and no additional diaphragm is required for insulation. Due to the coating effect of the solid electrolyte, the reference electrode does not directly react with the electrolyte, which can effectively reduce the occurrence of side reactions and is conducive to long-term stable potential monitoring.

[0004] In the prior art, the coating layer is generally prepared by mixing a solid electrolyte into a slurry and then coating it on a metal wire. However, the solid electrolyte has a large particle size, which is more than several hundred nanometers after being crushed. This means that it is very difficult to coat it on the metal wire and the coating layer is thicker. In addition, since the solid electrolyte is difficult to distribute evenly in the slurry, this will seriously affect the accuracy of the metal wire as a reference electrode, especially for measuring the gradient of a fast charging system, which requires a high reaction time of the reference electrode. The three electrodes prepared by this method have poor response accuracy and can only cope with ordinary working conditions. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present application is to overcome the defects of the reference electrode in the prior art, such as detection accuracy and response time, which cannot meet the higher detection requirements of the fast charging system, thereby providing a reference electrode and its preparation method and application.

[0006] To this end, this application provides the following technical solutions:

[0007] According to one aspect of the present application, a reference electrode is provided, comprising:

[0008] The metal wire is provided with an active area and an inactive area in its own length direction, the surface of the active area is provided with a lithium plating layer and a coating layer covering the lithium plating layer; the thickness of the coating layer is 0.2-0.8 μm;

[0009] Wherein, the coating layer includes a component having the following general composition formula: Li3MX6, M includes at least one of In, Sc, Y, Fe, V, Ga, Ru, Rh, Bi, Au, Ir, Re, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; X is a halogen;

[0010] The pole ear is arranged at one end of the inactive area of ​​the metal wire.

[0011] In some optional embodiments, the thickness of the lithium plating layer is 5-50 nm; as an example, the thickness of the lithium plating layer can be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or within the range of any of the above values;

[0012] And / or, the length of the active area is 0.5-2 cm; as an example, the length of the active area can be 0.5 cm, 0.7 cm, 0.9 cm, 1 cm, 1.2 cm, 1.4 cm, 1.5 cm, 1.6 cm, 1.8 cm, 2 cm, or within a range consisting of any of the above values;

[0013] And / or, the length of the coating layer is 3-8 cm; as an example, the length of the coating layer can be 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, or within the range of any of the above values;

[0014] And / or, the length of the lithium plating layer is 0.5-2 cm; as an example, the length of the lithium plating layer can be 0.5 cm, 0.7 cm, 0.9 cm, 1 cm, 1.2 cm, 1.4 cm, 1.5 cm, 1.6 cm, 1.8 cm, 2 cm, or within the range of any of the above values;

[0015] And / or, the length of the metal wire is 12-20 cm, and the diameter is 20-200 μm. As an example, the length of the metal wire can be 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, 18 cm, 19 cm, 20 cm, or within the range of any of the above values; the diameter of the metal wire can be 20 μm, 40 μm, 50 μm, 80 μm, 100 μm, 120 μm, 140 μm, 150 μm, 160 μm, 180 μm, 200 μm, or within the range of any of the above values.

[0016] In some optional embodiments, the material of the metal wire includes at least one of copper, gold, and silver;

[0017] And / or, X includes at least one of F, Cl, Br, and I.

[0018] According to another aspect of the present application, a method for preparing the reference electrode is provided, comprising the following steps:

[0019] S1, providing a metal wire with an insulating layer, removing the insulating layer at one end thereof to obtain an active region, and the portion where the insulating layer is not removed is an inactive region;

[0020] S2, dissolving a lithium halide and a halide containing an M element in water to obtain a hydrate solution, and adding a binder to obtain a coating slurry;

[0021] S3, immersing one end of the active area of ​​the metal wire into the coating slurry, freezing, and drying to obtain a coated metal wire;

[0022] S4, configuring a pole ear at one end of the inactive area of ​​the coated metal wire, and plating lithium in the active area to form a lithium plating layer.

[0023] In the present application, the metal wire with an insulating layer may be an enameled wire including a corresponding metal wire, for example, it may be one of enameled copper wire, enameled gold wire, and enameled silver wire;

[0024] In some optional embodiments, in S1, the step of removing the insulating layer includes: immersing the metal wire in sulfuric acid with a mass concentration of 30-50% for 1-3 hours. As an example, the mass concentration of the sulfuric acid can be 30%, 35%, 40%, 45%, 50%, or within the range of any of the above values; the immersion time can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or within the range of any of the above values.

[0025] In some optional embodiments, in S2, the mass ratio of the total mass of the lithium-containing halide and the halide containing the M element to water is 50-200:50-500; as an example, the mass ratio of the total mass of the lithium-containing halide and the halide containing the M element to water can be 50:50, 50:100, 50:200, 50:300, 50:400, 50:500, 100:50, 100:300, 100:500, 150:50, 150:100, 150:200, 150:300, 150:400, 150:500, 200:50, 200:100, 200:300, 200:500, or within the range of any of the above values;

[0026] And / or, the mass ratio of the total mass of the lithium-containing halide and the halide containing the M element to the binder is 50-200:1-10. As an example, the mass ratio of the total mass of the lithium-containing halide and the halide containing the M element to the binder can be 50:1, 50:3, 50:5, 50:8, 50:10, 100:1, 100:3, 100:5, 100:8, 100:10, 200:1, 200:3, 200:5, 200:8, 200:10, or within the range of any of the above values.

[0027] In some optional embodiments, in S3, the freezing temperature is -20℃ to -30℃, and the time is 12-48h; as an example, the freezing temperature can be -20℃, -22℃, -25℃, -27℃, -30℃, or within the range of any of the above values; the freezing time can be 12h, 16h, 20h, 24h, 28h, 32h, 36h, 40h, 44h, 48h, or within the range of any of the above values.

[0028] And / or, the drying temperature is 80-200°C, and the drying time is 12-48h. As an example, the drying temperature can be 80°C, 100°C, 120°C, 140°C, 150°C, 160°C, 180°C, 200°C, or within the range of any of the above values; the drying time can be 12h, 16h, 20h, 24h, 28h, 32h, 36h, 40h, 44h, 48h, or within the range of any of the above values.

[0029] In some optional embodiments, in S4, the lithium plating current is 0.001-1mA, and the lithium plating time is 20-120min. As an example, the lithium plating current can be 0.001mA, 0.002mA, 0.005mA, 0.008mA, 0.1mA, 0.15mA, 0.2mA, 0.25mA, 0.3mA, 0.4mA, 0.5mA, 0.6mA, 0.7mA, 0.8mA, 0.9mA, 1mA, or in the range of any of the above values; the lithium plating time can be 20min, 40min, 50min, 60min, 80min, 100min, 120min, or in the range of any of the above values.

[0030] In some optional embodiments, the binder includes at least one of polyacrylic acid adhesive, polyacrylonitrile adhesive, polyvinylidene fluoride adhesive, polyvinyl alcohol adhesive, sodium alginate, and carboxymethyl chitosan;

[0031] And / or, the metal wire with the insulating layer includes an enameled wire.

[0032] According to another aspect of the present application, there is provided an application of the reference electrode or the reference electrode prepared by the preparation method in detecting the electrochemical properties of lithium-ion batteries.

[0033] It is particularly suitable for applications in basic electrochemistry and material research of lithium-ion batteries.

[0034] The technical solution of this application has the following advantages:

[0035] The reference electrode provided in the present application comprises: a metal wire, an active area and an inactive area are arranged in the length direction of the metal wire, a lithium plating layer and a coating layer covering the lithium plating layer are arranged on the surface of the active area; the thickness of the coating layer is 0.2-0.8 μm; wherein the coating layer comprises a component having the following general composition formula: Li3MX6, M comprises at least one of In, Sc, Y, Fe, V, Ga, Ru, Rh, Bi, Au, Ir, Re, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; X is a halogen; and a pole ear is arranged at one end of the inactive area of ​​the metal wire. The reference electrode provided in the present application can further improve the test accuracy and response time of the reference electrode by limiting the composition and thickness of the solid electrolyte coating layer, thereby meeting higher detection requirements; while ensuring the test accuracy, it overcomes the problem of rapid damage to the lithium plating layer caused by direct contact between the electrolyte and the lithium plating layer, avoids direct contact between the lithium plating layer and the electrolyte to interfere with the electrical signals of the tested positive electrode-reference electrode and negative electrode-reference electrode, and at the same time avoids the need to add a diaphragm in the reference electrode area, thereby improving the accuracy of the battery cell fast charging test.

[0036] The preparation method of the reference electrode provided in the present application adopts an aqueous phase synthesis method to prepare the coating layer, and the active area of ​​the metal wire is directly processed into a film in the coating slurry, so there is no problem of excessively thick or uneven coating caused by excessive electrolyte particle size; in addition, the aqueous phase synthesis method can also regulate the thickness and morphology of the coating layer according to actual needs. The reference electrode prepared by this method, thanks to the high ionic conductivity of the halide solid electrolyte and the precise control of the coating layer, greatly improves the applicability of the three-electrode system containing the reference electrode to working conditions with high response accuracy requirements and strong stability requirements (for example, for fast charging system detection).

[0037] Additional aspects and advantages of the embodiments of the present application will be described and shown in part in the subsequent description, or explained through the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 is a schematic diagram of the structure of the reference electrolysis provided in the examples of the present application;

[0040] Figure 2 is a schematic diagram of preparing a coating layer in an embodiment of the present application;

[0041] Figure 3 It is a schematic diagram of the assembly structure of the three-electrode system in this application;

[0042] Figure 4 This is a comparison diagram of the reference voltage distribution of the fast charging test of the 1# three-electrode system in Example 1 of the present application;

[0043] Figure 5 It is a comparison diagram of the consistency of the reference voltage difference potential-time curve and the negative electrode reference potential-time curve of the three-electrode system in Example 1 of the present invention;

[0044] Figure 6 This is a comparison diagram of the reference voltage distribution of the fast charging test of the 1# three-electrode system in Comparative Example 1 of the present application;

[0045] Figure 7 It is a comparison diagram of the consistency of the reference voltage difference potential-time curve and the negative electrode reference potential-time curve of the 1# and 2# three-electrode systems in Comparative Example 1 of the present invention;

[0046] Reference numerals:

[0047] 1. Reference electrode; 2. Metal wire; 3. Coating layer; 4. Positive ear; 5. Negative ear; 6. Aluminum-plastic film shell; 7. Positive electrode sheet; 8. Negative electrode sheet; 9. Diaphragm; 10. Coating slurry; 11. Tape. DETAILED DESCRIPTION

[0048] The following examples are provided for a better understanding of the present application, but are not limited to the best implementation mode described, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the protection scope of the present application.

[0049] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0050] As described in the background technology, in order to overcome the defects of the reference electrode detection accuracy and response time in the prior art that cannot meet the higher detection requirements of the fast charging system, the present application coats the metal wire to isolate the direct contact between the electrolyte and the metal wire, thereby reducing the side reaction between the lithium plating layer and the electrolyte after electrochemical lithium plating, so that the lithium plating layer can exist longer in the charge and discharge cycle, thereby improving the service life of the reference electrode. The main component of the coating layer on the metal wire is an oxide solid electrolyte, which can make the coating layer thinner and more uniform. Therefore, the coating layer itself provides excellent ionic conductivity compared to the coating layer in the prior art, and can quickly provide lithium ion channels during lithium plating and charging and discharging, reducing voltage hysteresis and other problems; at the same time, the coating layer isolates electrons and can replace the diaphragm, so when the reference electrode is assembled, the metal wire does not need to be filled with an additional diaphragm in the vicinity, simplifying the assembly process; when testing the fast charging and lithium deposition, the introduction of the additional diaphragm will not cause the nearby lithium deposition potential test data deviation, thereby improving the test accuracy.

[0051] As mentioned above, the present application provides a new reference electrode and a preparation method thereof. By limiting the composition and thickness of the solid electrolyte coating layer, the test accuracy and response time of the reference electrode can be further improved to meet higher detection requirements; while ensuring the test accuracy, it overcomes the problem of rapid damage to the lithium plating layer caused by direct contact between the electrolyte and the lithium plating layer, avoids direct contact between the lithium plating layer and the electrolyte to interfere with the electrical signals of the tested positive electrode-reference electrode and negative electrode-reference electrode, and at the same time avoids the use of laying a diaphragm in the reference electrode area, thereby improving the accuracy of the battery cell fast charging test.

[0052] Specifically, Figure 1As shown, the reference electrode 1 provided in the present application adopts a structure of a metal wire externally connected to a pole ear, including a metal wire 2, which is divided into an active area and an inactive area, and a lithium plating layer (not shown in the figure) and a coating layer 3 covering the lithium plating layer are provided on the surface of the active area;

[0053] The preparation method of the reference electrode may include the following steps:

[0054] (1) Preparation of coating slurry:

[0055] Take raw materials containing lithium halide and halide containing M element, dissolve them in deionized water, put the solution into an ultrasonic cleaner for ultrasonic dispersion for 10-60 minutes, then magnetically stir at 300-800 rpm for 1-3 hours to form a Li3MX6·nH2O hydrate solution for use; add a binder to the solution, and magnetically stir at 300-800 rpm for 1-3 hours; after dispersion, a coating slurry is obtained for use.

[0056] (2) Treatment of reference electrode wire:

[0057] Take a 12-20 cm long metal wire (copper wire, silver wire, gold wire) with a diameter of 20-200 μm, immerse the bottom 0.5-2 cm of the wire in concentrated sulfuric acid for 1-3 hours, treat the surface lacquer coating, expose the wire (i.e., the active area), wash it with deionized water 2-5 times and dry it for later use.

[0058] (3) Preparation of coating layer:

[0059] Schematic diagram of preparing the coating layer in the active area of ​​the metal wire Figure 2 As shown, the coating slurry 10 is poured into a glass tube (with a tube mouth diameter of 1-3 cm) and placed vertically upward, the treated metal wire 2 is vertically adhered to the inside of the centrifuge tube by means of tape 11, and the bottom 3-8 cm of the metal wire 2 is immersed in the coating slurry 10. The glass tube is moved into a freeze dryer to quickly freeze the solution into a solid, and then placed in a vacuum drying oven and heated at 80-200°C for 12-48 hours to obtain a metal wire with a coating layer on the surface, which is taken out for use.

[0060] (4) Preparation of tabs:

[0061] The end of the metal wire with the coating layer prepared in the above steps on one side of the inactive region is welded with a pole ear.

[0062] (5) Preparation of lithium plating layer:

[0063] according to Figure 3The structure shown is assembled into a three-electrode system, and the aluminum-plastic film shell 6 encapsulates the battery cell, the battery cell includes a positive electrode sheet 7, a negative electrode sheet 8 and an electrolyte, and a diaphragm 9 is located between the positive electrode sheet 7 and the negative electrode sheet 8. The reference electrode 1 is placed between the negative electrode sheet 8 and the diaphragm 9 (in this application, the reference electrode is actually added to the conventional battery cell structure, and the normal battery cell structure is not changed, and there is no need to add a diaphragm again). The tail end of the coating layer 3 is placed in the middle of the battery cell, and the positive electrode ear 4 and the negative electrode ear 5, and the reference electrode ear are encapsulated at the head of the battery cell. The positive electrode sheet 7 and the negative electrode sheet 8 are used to plate lithium on the bottom 0.5-2cm surface of the metal wire 2 in the coating layer 3. The lithium plating current is 0.001-1mA, and the lithium plating time is 20-120min. The specific process parameters can be adjusted according to the actual working conditions.

[0064] In the present application, after lithium plating is completed, the three-electrode system can directly perform electrical performance testing of the lithium-ion battery, and is particularly suitable for testing fast charging performance.

[0065] It can be understood by those skilled in the art that during the charge and discharge process of the battery, lithium ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet, the electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet, and the diaphragm is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing lithium ions to pass through.

[0066] As an example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is arranged on any one or both of the two opposite surfaces of the negative electrode current collector. The material, composition and manufacturing method of the negative electrode sheet used in the three-electrode system of the present application may include any technology disclosed in the prior art.

[0067] The material and shape of the separator used in the three-electrode system of the present application are not particularly limited, and may include any technology disclosed in the prior art.

[0068] The electrolyte used in the three-electrode system of the present application may include any technology disclosed in the prior art.

[0069] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0070] Example 1

[0071] This embodiment provides a reference electrode, and its structural schematic diagram is as follows Figure 1As shown, it includes: a metal wire 2, which is provided with an active area and an inactive area in its own length direction, and the surface of the active area is provided with a lithium plating layer and a coating layer 3 coating the lithium plating layer; wherein the coating layer 3 includes a component with the following general composition formula: Li3InCl6; a pole ear, which is arranged at one end of the inactive area of ​​the metal wire.

[0072] The preparation method of the reference electrode comprises the following steps:

[0073] (1) Preparation of coating slurry:

[0074] Take 64g of LiCl and 110g of InCl3 as raw materials, dissolve them in 100g of deionized water, put the solution into an ultrasonic cleaner for ultrasonic dispersion for 30min, and then magnetically stir at 600rpm for 2h to form a Li3InCl6·nH2O hydrate solution for use; add 5g of polyacrylic acid binder (model La136DL) to the solution, and magnetically stir at 600rpm for 2h; after dispersion, a coating slurry is obtained for use.

[0075] (2) Treatment of reference electrode wire:

[0076] Take a 15 cm long metal wire (copper enameled wire in this embodiment) with a diameter of 50 μm, immerse the bottom 1.5 cm of the metal wire in concentrated sulfuric acid for 2 hours to treat the surface enameling layer, expose the metal wire (i.e., the active area), wash it with deionized water 3 times and dry it for later use.

[0077] (3) Preparation of coating layer:

[0078] Schematic diagram of preparing the coating layer in the active area of ​​the metal wire Figure 2 As shown, the coating slurry 10 is poured into a glass tube (with a tube mouth diameter of 2 cm) and placed vertically upward, the treated metal wire 2 is vertically adhered to the inside of the centrifuge tube by means of tape 11, and the bottom 5 cm of the metal wire 2 is immersed in the coating slurry 10. The glass tube is moved into a freeze dryer to quickly freeze the solution into a solid at a freezing temperature of -20°C for 18 hours, and then placed in a vacuum drying oven and heated at 120°C for 24 hours to obtain a metal wire with a coating layer on the surface, which is taken out for use.

[0079] (4) Preparation of tabs:

[0080] The end of the metal wire with the coating layer prepared in the above steps on one side of the inactive region is welded with a pole ear.

[0081] (5) Preparation of lithium plating layer:

[0082] according to Figure 3 The structure shown in the figure assembles a three-electrode system, and the aluminum-plastic film shell 6 encapsulates the battery cell. The battery cell includes a positive electrode sheet 7 (specifically composed of positive electrode active material Li (Ni0.9 Co 0.05 Mn 0.05 )O2, conductive agent (SP), single-walled carbon nanotube (SWNT) and binder polyvinylidene fluoride (PVDF) in a mass ratio of 96:2:1:1), negative electrode sheet 8 (specific composition: graphite, conductive agent (SP), thickener CMC, binder SBR in a mass ratio of 95:2:1:2) and electrolyte (specific composition: 1M LiPF6, the solvent is ethylene carbonate (EC) and dimethyl carbonate (DMC) in a mass ratio of 1:1, and 0.5M vinylene carbonate (VC) additive is added), the reference electrode 1 is located between the positive and negative electrodes, and a diaphragm 9 (specific composition: 7μm PE base film, a 2μm thick PVDF layer on one side of the base film and a 2μm thick ceramic layer on the other side (the ceramic layer is made of aluminum oxide), wherein the PVDF layer faces the positive electrode) is arranged between the positive electrode 7 and the reference electrode 1, and there is no need to add a diaphragm again between the negative electrode 8 and the reference electrode 1, the tail end of the coating layer 3 is placed in the middle of the battery cell, and the positive and negative electrodes 4 and 5, and the reference electrode electrodes are encapsulated at the head of the battery cell. The positive electrode 7 and the negative electrode 8 are used to plate lithium on the bottom 1.5cm surface of the metal wire 2 in the coating layer 3 of the reference electrode 1, the lithium plating current is 0.002mA, and the lithium plating time is 120min.

[0083] The thickness of the coating layer and the lithium-plated layer was tested by cross-sectional polishing-scanning electron microscopy (CP-SEM). The test showed that the thickness of the lithium-plated layer was 20 nm, and the thickness of the coating layer was 0.5 μm.

[0084] Example 2

[0085] This embodiment provides a reference electrode, which is different from that of embodiment 1 only in that the coating layer is prepared differently, as follows:

[0086] Schematic diagram of preparing the coating layer in the active area of ​​the metal wire Figure 2 As shown, the coating slurry 10 is poured into a glass tube (with a tube mouth diameter of 2 cm) and placed vertically upward, the treated metal wire 2 is vertically adhered to the inside of the centrifuge tube by means of tape 11, and the bottom 5 cm of the metal wire 2 is immersed in the coating slurry 10. The glass tube is moved into a freeze dryer to quickly freeze the solution into a solid at a freezing temperature of -30°C for 12 hours, and then placed in a vacuum drying oven and heated at 80°C for 48 hours to obtain a metal wire with a coating layer on the surface, which is taken out for use.

[0087] Example 3

[0088] This embodiment provides a reference electrode, which is different from that of embodiment 1 only in that the coating slurry is prepared differently, as follows:

[0089] Take 127g of LiCl and 221g of InCl3 as raw materials, dissolve them in 100g of deionized water, put the solution into an ultrasonic cleaner for ultrasonic dispersion for 30min, and then magnetically stir at 600rpm for 2h to form a Li3InCl3·nH2O hydrate solution for use; add 10g of polyacrylic acid binder to the solution and magnetically stir at 600rpm for 2h; after dispersion, a coating slurry is obtained for use.

[0090] Example 4

[0091] This embodiment provides a reference electrode, which is different from that of embodiment 1 only in that the coating slurry is prepared differently, as follows:

[0092] Take 64g of LiCl and 110g of InCl3 as raw materials, dissolve them in 100g of deionized water, put the solution into an ultrasonic cleaner for ultrasonic dispersion for 10min, and then magnetically stir at 300rpm for 1h to form a Li3InCl3·nH2O hydrate solution for use; add 5g of polyacrylic acid binder to the solution and magnetically stir at 300rpm for 1h; after dispersion, a coating slurry is obtained for use.

[0093] Example 5

[0094] This embodiment provides a reference electrode, which is different from that of embodiment 1 only in that the coating slurry is prepared differently, as follows:

[0095] Take 87g of LiCl and 110g of FeCl3 as raw materials, dissolve them in 100g of deionized water, put the solution into an ultrasonic cleaner for ultrasonic dispersion for 30min, and then magnetically stir at 600rpm for 2h to form a Li3FeCl3·nH2O hydrate solution for use; add 5g of polyacrylonitrile binder to the solution and magnetically stir at 600rpm for 2h; after dispersion, a coating slurry is obtained for use.

[0096] Example 6

[0097] This embodiment provides a reference electrode, which is different from Embodiment 1 only in that the coating slurry is prepared differently, specifically as follows: the lithium plating current is 0.001 mA, and the lithium plating time is 60 min.

[0098] Example 7

[0099] This embodiment provides a reference electrode, which is different from Embodiment 1 only in that the coating slurry is prepared differently, specifically as follows: the lithium plating current is 1 mA, and the lithium plating time is 120 min.

[0100] Comparative Example 1

[0101] This comparative example provides a reference electrode, which is different from Example 1 in that the coating slurry is prepared differently, as follows:

[0102] Take 50g of solid electrolyte Dv50 of 150nm Li 1.5 Al 0.5 Ti 1.5 (PO4)3(LATP) was dispersed in 100g of deionized water, and the solution was ultrasonically dispersed in an ultrasonic cleaning machine for 30min, followed by magnetic stirring at 600rpm for 2h, and 5g of polyacrylonitrile binder was added to the solution, and magnetic stirring was continued at 600rpm for 2h; after dispersion, a coating slurry was obtained for standby use. The other steps were the same as those in Example 1.

[0103] Three-electrode test

[0104] Three battery cells are prepared with the same process parameters in each embodiment and comparative example. The three battery cells are numbered 1#, 2#, and 3# in sequence. Then, the same charging and discharging machine and the same multi-channel instrument are used to perform charge and discharge tests and negative electrode-reference electrode potential monitoring on the three battery cells. The charging process is step charging, and the battery cell charging rate is step-type, which is 4C, 3C, 2C, and 1C in sequence. The negative electrode reference voltage is used as the jump condition of the charging rate. When the negative electrode reference voltage is reduced to the set voltage of 60mV, 40mV, 20mV, and 10mV, the battery cell charging rate triggers a jump from high to low, so as to achieve the purpose of testing the fast charging capability of the battery cell. See the test results for details. Figure 4-Figure 7 and Table 1.

[0105] Table 1 Negative electrode reference potential of the battery cell at the end of the first to fourth stage of charging

[0106]

[0107]

[0108] From the data in the above table, it can be seen that the test accuracy of Examples 1 to 7 is better than that of Comparative Example 1 as a whole, among which, the test accuracy of Example 1 is the highest. Compared with Example 1, it can be seen that the adjustment of the coating preparation parameters will affect the test accuracy; compared with Example 1, it can be seen that the different compositions of the coating will affect the test accuracy, and the halide electrolyte Li3InCl6 has the best performance; compared with Example 1, it can be seen that the adjustment of the lithium plating parameters will lead to a decrease in the accuracy of the three-electrode test. Compared with the examples, Comparative Example 1 shows that the particle size of the traditional solid electrolyte LATP is too large, and it is difficult to form a film on the surface of the copper wire or the film is too thick and uneven, and the accuracy of the three-electrode test and the maintenance time of the lithium plating layer are greatly attenuated.

[0109] See also Figure 4In the 1# three-electrode system fast charge test in Example 1, the reference positive electrode voltage curve (left coordinate axis)-reference negative electrode voltage curve (right coordinate axis) = reference voltage difference (left coordinate axis), and the obtained reference voltage difference is completely consistent with the full battery voltage curve, showing that the reference electrode test of this application is accurate and the voltage hysteresis is small. The test results of other embodiments are close to this embodiment and are not shown one by one.

[0110] See also Figure 5 , the reference voltage difference potential-time curve and negative electrode reference potential-time curve of the three three-electrode systems in Example 1, the negative electrode reference potential curve and reference voltage difference potential curve of the three cells under different charging currents all have a high degree of coincidence, indicating that the reference electrode of the present application has high repeatability. The test results of other embodiments are similar to this embodiment and are not shown one by one.

[0111] See also Figure 6 In the fast charging test of the 1# three-electrode system in Comparative Example 1, the reference positive electrode voltage curve-reference negative electrode voltage curve=reference voltage difference. The obtained reference voltage difference cannot coincide with the full battery voltage curve, indicating that there is a deviation in the reference electrode test of Comparative Example 1 and the voltage lags.

[0112] See also Figure 7 The reference voltage difference potential-time curve and negative electrode reference potential-time curve of the 1# and 2# three-electrode systems in comparative example 1, the negative electrode reference potential curves and reference voltage difference potential of the three battery cells under different charging currents can hardly overlap, indicating that the repeatability of the reference electrode provided in the comparative example is relatively poor.

[0113] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A reference electrode, characterized in that include: The metal wire is provided with an active area and an inactive area in its own length direction, the surface of the active area is provided with a lithium plating layer and a coating layer covering the lithium plating layer; the thickness of the coating layer is 0.2-0.8 μm; Wherein, the coating layer includes a component having the following general composition formula: Li3MX6, M includes at least one of In, Sc, Y, Fe, V, Ga, Ru, Rh, Bi, Au, Ir, Re, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; X is a halogen; The pole ear is arranged at one end of the inactive area of ​​the metal wire.

2. The reference electrode according to claim 1, characterized in that The thickness of the lithium plating layer is 5-50nm; And / or, the length of the active area is 0.5-2 cm; And / or, the length of the coating layer is 3-8 cm; And / or, the length of the lithium plating layer is 0.5-2 cm; And / or, the length of the metal wire is 12-20 cm and the diameter is 20-200 μm.

3. The reference electrode according to claim 1 or 2, characterized in that The material of the metal wire includes at least one of copper, gold and silver; And / or, X includes at least one of F, Cl, Br, and I.

4. A method for preparing a reference electrode according to any one of claims 1 to 3, characterized in that: The steps include: S1, providing a metal wire with an insulating layer, removing the insulating layer at one end thereof to obtain an active region, and the portion where the insulating layer is not removed is an inactive region; S2, dissolving a lithium halide and a halide containing an M element in water to obtain a hydrate solution, and adding a binder to obtain a coating slurry; S3, immersing one end of the active area of ​​the metal wire into the coating slurry, freezing, and drying to obtain a coated metal wire; S4, configuring a pole ear at one end of the inactive area of ​​the coated metal wire, and plating lithium in the active area to form a lithium plating layer.

5. The method for preparing a reference electrode according to claim 4, characterized in that: In S1, the step of removing the insulating layer includes: soaking the metal wire in sulfuric acid with a mass concentration of 30-50% for 1-3 hours.

6. The method for preparing a reference electrode according to claim 4, characterized in that: In S2, the mass ratio of the total mass of the lithium-containing halide and the halide containing the M element to water is 50-200:50-500; And / or, the mass ratio of the total mass of the lithium-containing halide and the halide containing the M element to the binder is 50-200:1-10.

7. The method for preparing a reference electrode according to claim 4, characterized in that: In S3, the freezing temperature is -20°C to -30°C, and the freezing time is 12-48h; And / or, the drying temperature is 80-200° C. and the drying time is 12-48 hours.

8. The method for preparing a reference electrode according to claim 4, characterized in that: In S4, the lithium plating current is 0.001-1 mA, and the lithium plating time is 20-240 min.

9. The method for preparing a reference electrode according to any one of claims 4 to 8, characterized in that: The adhesive includes at least one of polyacrylic acid adhesive, polyacrylonitrile adhesive, polyvinylidene fluoride adhesive, polyvinyl alcohol adhesive, sodium alginate, and carboxymethyl chitosan; And / or, the metal wire with the insulating layer includes an enameled wire.

10. An application of a reference electrode in detecting the electrochemical performance of a lithium-ion battery, characterized in that: The reference electrode is the reference electrode described in any one of claims 1 to 3 or the reference electrode prepared by the preparation method described in any one of claims 4 to 9.

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