Composite reference electrode, preparation method thereof and three-electrode lithium ion battery

Abstract

The invention discloses a composite reference electrode and a preparation method thereof and a three-electrode lithium ion battery, and the preparation method of the composite reference electrode comprises the following steps: soaking a conductive wire part coated with an insulating medium in concentrated acid to obtain an effective part; and coating the insulating part of the conductive wire with foil, then placing the conductive wire in an ion sputtering instrument, and sputtering in a vacuum environment to form a metal film layer on the effective part of the conductive wire, so as to obtain the composite reference electrode. The copper wire is adopted as a conductive wire base material, a layer of precious metal is compounded on the periphery of the copper wire through the sputtering technology, the performance equivalent to that of a pure precious metal electrode can be achieved only through a small amount of precious metal, and the manufacturing cost is further reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy, and specifically to a composite reference electrode, a preparation method thereof, and a three-electrode lithium-ion battery. Background Art

[0002] With the booming development of the new energy vehicle industry, as a representative of the new energy battery industry, lithium-ion batteries have attracted much attention from users in terms of performance indicators such as service life, safety, and fast charging ability. In order to meet customer requirements and consumer usage needs, batteries often need to undergo repeated and stringent performance tests. According to the feedback of test results, improvements are made to battery materials, structural design, failure analysis, etc. until the design index requirements are met. Therefore, in order to further simplify and improve the test process and improve the R & D efficiency, researchers have introduced a three-electrode system into lithium-ion batteries to in-situ monitor the parameters of the electrochemical reaction process of the battery. The development of fast-charging lithium-ion battery technology is an important field, and non-destructive monitoring of the positive / negative electrode potential changes is very important for preventing battery performance degradation. During the charge and discharge process of a lithium-ion battery, an adverse side reaction at the negative electrode interface is that lithium metal deposits on the surface of graphite rather than being embedded in it, that is, lithium plating behavior, which will cause the negative electrode potential to be lower than 0 mV (relative to lithium metal), resulting in irreversible capacity loss, rapid decline of battery performance, battery failure, and even inducing safety accidents. If the electrode potentials of the positive and negative electrodes can be accurately monitored during the fast charging process, lithium plating can be effectively prevented.

[0003] For a three-electrode system, the reference electrode should have good chemical and electrochemical stability and no polarization in the electrolyte, and have as little impact on battery performance as possible when implanted. In the prior art, metal wires such as copper, silver, foil, and gold are often selected as substrates and inserted into the battery cell, and a small current electroplating method is used to plate lithium on the metal wire as the reference electrode. Chinese Patent CN219144259U uses metal wires such as gold wires, platinum wires, and copper wires as reference electrodes, and Chinese Patent CN 218827317U uses a silver reference electrode. However, using precious metals such as gold wires, platinum wires, and silver wires as reference electrodes not only has a high cost, but also has a soft texture, and is easily damaged and broken during subsequent implantation into the battery cell, resulting in the failure of the reference electrode and reducing the yield of the preparation of the three-electrode. When using a copper wire as the reference electrode, it has a small diameter and strong toughness, but the surface of the copper wire is easily oxidized, resulting in an unstable lithium plating layer on the reference electrode. Summary of the Invention

[0004] In view of this, the present invention aims to solve the drawbacks existing in the related technologies to at least some extent. For this reason, the present invention provides a new type of metal wire composite reference electrode, a preparation method, and a three-electrode lithium-ion battery, which increases the selectivity and stability of the reference electrode, and at the same time improves the success rate of preparing a three-electrode lithium-ion battery.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention discloses a preparation method of a composite reference electrode, comprising the following steps:

[0007] S1. Immerse a part of the conductive wire coated with an insulating medium in concentrated acid to obtain an effective part;

[0008] S2. Wrap the insulating part of the conductive wire with foil, and then place it in an ion sputtering instrument. Sputter a metal target in a vacuum environment to form a metal film layer on the effective part of the conductive wire, thus obtaining the composite reference electrode.

[0009] As a further scheme of the present invention: in step S2, the sputtering working parameters are: the distance between the target and the substrate is 40 - 50 mm, the sputtering power is 5 - 6 W, the target spraying pressure is 6 - 8 Pa, and the sputtering time is 80 - 160 s.

[0010] As a further scheme of the present invention: the target is at least one of titanium target, zinc target, chromium target, magnesium target, niobium target, tin target, aluminum target, indium target, iron target, zirconium aluminum target, titanium aluminum target, zirconium target, aluminum silicon target, silicon target, copper target, germanium target, silver target, cobalt target, gold target, gadolinium target, lanthanum target, yttrium target, cerium target, tungsten target, stainless steel target, nickel chromium target, hafnium target, molybdenum target, iron nickel target, tungsten target.

[0011] As a further scheme of the present invention: the diameter of the conductive wire is 50 - 150 um; the length of the effective part is 3 - 5 cm.

[0012] As a further scheme of the present invention: the conductive wire is a copper wire.

[0013] In a second aspect, the present invention discloses a composite reference electrode prepared by the above preparation method.

[0014] In a third aspect, the present invention discloses a three - electrode lithium - ion battery, comprising a stacked core formed by laminating a plurality of battery cell pole groups, a separator, and also comprising the composite reference electrode as described above. Among them, the effective part is laminated between the battery cell pole groups through the separator, and the joint of the foil and the conductive wire is fixed on the side of the stacked core.

[0015] In a fourth aspect, the present invention discloses a preparation method of the three - electrode lithium - ion battery as described above, comprising the following steps:

[0016] Pre - heat and press the stacked core, bury the composite reference electrode between the battery cell pole groups, separate them with a separator, and ensure that the reference electrode does not directly contact the material area of the battery cell pole groups;

[0017] Fix the lead - out end of the composite reference electrode on one side of the stacked core, perform secondary hot pressing on the stacked core, and obtain the three - electrode lithium - ion battery after post - treatment.

[0018] As a further solution of the present invention: the temperature of the preheating press is 60 - 90 °C, the pressure is 6 - 10 T, and the time is 120 - 300 s; and / or, the temperature of the secondary hot press is 60 - 90 °C, the pressure is 10 - 16 T, and the time is 150 - 300 s.

[0019] As a further solution of the present invention: the post-treatment sequentially includes shell encapsulation, baking, liquid injection, formation, grading, tab welding, supplementary charging, and lithium plating.

[0020] As a further solution of the present invention: the battery SOC for supplementary charging is 40 - 60%; and / or, the current for lithium plating is 20 - 70 μA, and the lithium plating time is 4 - 12 hours.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] The present invention realizes the composite of copper wire and precious metal through sputtering technology, which not only retains the advantages of low cost and high toughness of copper wire, but also inherits the high stability and conductivity of precious metal, and solves the problems of high cost and easy failure of traditional expensive metal reference electrodes.

[0023] The present invention is applicable to three-electrode lithium-ion batteries of multiple systems, has wide applicability and good repeatability, provides an efficient and economical solution for the performance testing and optimization of new energy batteries. In addition, it increases the selectivity and stability of the reference electrode, and at the same time improves the success rate of preparing three-electrode lithium-ion batteries.

[0024] The sputtering technology adopted is simple in operation and controllable in parameters (such as target material selection, sputtering time, power, etc.), and can accurately control the thickness and uniformity of the composite metal film, improving the preparation yield of the reference electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the voltage-charge state curve of the composite gold reference electrode in Example 1;

[0026] Figure 2 It is the voltage-charge state curve of the composite platinum reference electrode in Example 2;

[0027] Figure 3 It is the voltage-charge state curve of the composite silver wire reference electrode and the pure copper reference electrode in Example 3;

[0028] Figure 4 It is the voltage-charge state curve of the pure gold reference electrode in the comparative example and the composite gold reference electrode in Example 1;

[0029] Figure 5This is a schematic diagram of the assembly of the reference electrode and the battery cell stack in the present invention. The effective part of the composite reference electrode (precious metal-coated conductive wire) is placed in the battery cell stack. Detailed implementation mode

[0030] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0031] Embodiment 1

[0032] Preparation of the composite gold wire reference electrode:

[0033] (1) Pretreatment of the copper wire: The copper wire coated with insulating paint is fixed on the copper foil, and the effective part of the head end is immersed in concentrated sulfuric acid for 2 h; after the immersion is completed, it is washed with pure water and ethanol respectively and dried with nitrogen.

[0034] (2) Expose the effective part of the copper wire (the insulating paint has been removed), and wrap the remaining painted part (insulated) with copper foil; place the entire copper wire on the sample stage of the ion sputtering instrument, with a distance of 45 mm from the target base, close the upper cover, and evacuate.

[0035] (3) Select the gold target for the sputtering instrument, set the working pressure of the sputtering parameters to 6 Pa, the sputtering power to 5 W, and the sputtering time to 80 s. After sputtering is completed, turn it over and sputter again to ensure that the effective part of the copper wire is covered with a uniform gold film, and the gold composite copper wire, that is, the composite gold wire reference electrode, can be obtained.

[0036] Preparation of the three-electrode lithium-ion battery:

[0037] (1) Preheat and press the battery stack (pressure 6 T, time 150 s, temperature 90 °C), uncover the middle part of the stack without loosening; bury the treated composite gold wire into the battery cell stack, separate it with a separator, and ensure that the composite gold wire does not directly contact the material area.

[0038] (2) Restore the stack, perform secondary hot pressing (pressure 10 T, time 150 s, temperature 90 °C), assemble the stack implanted with the composite gold wire into the shell, lead out the redundant part of the copper wire from the shell and fix and protect it on the side, and then perform baking, liquid injection, formation, grading, and weld the tab to the electrode ear to obtain a three-electrode battery cell.

[0039] (3) Activate the three-electrode battery cell: Charge the three-electrode battery to 50% SOC, and then perform small-current lithium plating (current 35 uA, time 12 h) to obtain a three-electrode lithium-ion battery implanted with a gold wire reference electrode.

[0040] The obtained three-electrode lithium-ion battery was subjected to a fast charge test: the three-electrode battery cell was discharged and left for 30 minutes, and then a direct charge test was performed at different rates. When the negative parameter potential was monitored to be 0V, the next step was jumped to 0.33C discharge. The test results are shown in Figure 1 The results showed that the composite gold reference electrode could stably perform 11 repeated charge and discharge tests at different rates. No lithium replenishment test was performed on the reference electrode during the test, indicating that the composite gold reference electrode has a stable electrode potential.

[0041] Example 2

[0042] Preparation of composite platinum wire reference electrode:

[0043] (1) Copper wire pretreatment: The copper wire coated with insulating varnish is fixed on the copper foil, and the effective part of the head end is immersed in concentrated sulfuric acid for 2 hours. After the immersion is completed, it is washed with pure water and ethanol respectively, and dried with nitrogen gas;

[0044] (2) Expose the effective part of the copper wire (with the insulating paint removed) and wrap the remaining painted part (insulation) with copper foil; place the entire copper wire on the sample stage of the ion sputtering instrument, 50 mm away from the target base, close the upper cover, and evacuate;

[0045] (3) The target material of the sputtering instrument is a platinum target, and the working pressure of the platinum spraying parameters is set to 7Pa, the sputtering power is 6W, and the sputtering time is 40s. After the sputtering is completed, it is turned over and sputtered a second time to ensure that the effective part of the copper wire is covered with a uniform platinum metal film. Then, a platinum composite copper wire and a composite platinum wire reference electrode can be obtained.

[0046] Preparation of three-electrode lithium-ion battery:

[0047] (1) The battery core is preheated and pressed (pressure 8T, time 90s, temperature 90℃) to ensure that the middle part of the electrode group is not loose; the treated composite platinum wire is buried in the battery electrode group, separated by a diaphragm to ensure that the composite platinum wire does not directly contact the material area;

[0048] (2) The core stack is restored and hot pressed twice (pressure 12T, time 90s, temperature 90°C); the core stack with the composite platinum wire is assembled into the shell, and the excess copper wire is led out of the shell and fixed on the side for protection. Then it is baked, injected with liquid, formed, and divided into different volumes. The tabs are welded to obtain a three-electrode battery cell.

[0049] (3) After activating the three-electrode cell, the cell was charged to 50% SOC, and then a low-current lithium plating (current 30 uA, time 12 h) was performed to obtain a three-electrode lithium-ion battery implanted with a composite platinum wire reference electrode.

[0050] Fast charging test was conducted on a three - electrode lithium - ion battery: After the battery cell was discharged and left idle for 30 minutes, a stepped fast charging test was carried out. The change of the negative reference potential during fast charging could be monitored through a composite platinum wire. The results are as follows Figure 2 shown. By studying the change of the negative electrode potential at different rates (current densities), it is possible to evaluate whether there is a risk of lithium plating in the battery cell during fast charging; The rate (yellow line) simulates different stages of stepped fast charging, and the red line shows the potential of the negative reference at different SOCs; From Figure 2 it can be seen that when the SOC of the battery cell is about 50%, the negative reference is less than 0 mV, indicating that lithium plating may occur in the battery cell at this rate, and the fast charging strategy needs to be further adjusted. During the whole test process, the negative reference was monitored stably and there was no diving phenomenon, indicating that the composite platinum wire can effectively monitor the change of the negative reference potential at the battery cell end and help formulate a suitable fast charging strategy.

[0051] Example 3

[0052] Preparation of a composite silver wire reference electrode:

[0053] (1) Pretreatment of copper wire: The copper wire coated with insulating paint was fixed on the copper foil, and the effective part of the head end was immersed in concentrated sulfuric acid for 2 h; After immersion, it was washed with pure water and ethanol respectively and dried with nitrogen;

[0054] (2) Expose the effective part of the copper wire (the insulating paint has been removed), and wrap the remaining painted part (insulated) with copper foil; The whole copper wire was placed on the sample stage of the ion sputtering instrument, 40 mm away from the target base, the upper cover was closed, and the vacuum was pumped;

[0055] (3) Select a silver target for the sputtering instrument. The working pressure of the silver spraying parameter was set to 8 Pa, the sputtering power was 6 W, and the sputtering time was 60 s. After sputtering, turn it over and sputter again to ensure that the effective part of the copper wire is covered with a uniform silver metal film, and the silver - composite copper wire, that is, the composite silver wire reference electrode, can be obtained;

[0056] Preparation of a three - electrode lithium - ion battery:

[0057] (1) The battery stack was pre - heat - pressed (pressure: 5 T, time: 100 s, temperature: 70 °C) to ensure that the middle part of the electrode group did not become loose when uncovered; The processed composite silver wire was buried in the battery cell electrode group and separated by a separator to ensure that the composite silver wire did not directly contact the material area;

[0058] (2) The stack was restored, and secondary heat - pressing was carried out (pressure: 12 T, time: 90 s, temperature: 90 °C); The stack with the composite silver wire implanted was assembled into the shell. The excess part of the copper wire was led out of the shell and fixed and protected on the side. Then, baking, liquid injection, formation, grading, and welding the pole ear with a tab were carried out to obtain a three - electrode battery cell;

[0059] (3) Activate the three - electrode cell: Charge the three - electrode cell to 50% SOC, and then perform lithium plating with a small current (current 45 μA, time 8 h) to obtain a three - electrode lithium - ion battery implanted with a silver wire reference electrode.

[0060] Perform a fast - charge test on the obtained three - electrode lithium - ion battery: After the cell is discharged and left to stand for 30 min, perform a step - by - step fast - charge test and monitor the change in the negative reference potential. Figure 3 For the negative reference test of the composite silver and pure copper reference electrodes in the three - electrode lithium - ion battery, the results show that the composite silver reference electrode has a faster response speed. At the same SOC, the monitored negative reference potential is slightly higher than that of the copper reference electrode of the same specification. This is attributed to the fact that silver has better electrical and thermal conductivity than copper and higher chemical stability and is not easily oxidized.

[0061] Comparative example

[0062] In this comparative example, a pure gold wire is used to make the reference electrode, and the pure gold wire reference electrode has the same specifications (diameter, length of the effective part, etc.) as the composite gold wire reference electrode in Example 1.

[0063] Preparation of the three - electrode lithium - ion battery:

[0064] (1) Pre - heat and press the battery stack (pressure 6 T, time 150 s, temperature 90 °C), uncover the middle part of the electrode group without loosening; simultaneously bury the gold wire reference electrode and the composite gold wire reference electrode (prepared as in Example 1) in the middle position of the cell electrode group, and separate them with diaphragms respectively to ensure that the reference electrodes are not in direct contact with the material area.

[0065] (2) Restore the stack, perform secondary hot - pressing (pressure 9 T, time 150 s, temperature 90 °C), then assemble it into the shell, bake, inject electrolyte, form, and grade - separate. Weld the tab to the electrode ear to obtain a three - electrode cell.

[0066] (3) Activate the three - electrode cell: Charge the three - electrode battery to 50% SOC, and then perform lithium plating on the two reference electrodes simultaneously (current 35 μA, time 12 h) to obtain a three - electrode lithium - ion battery implanted with a pure gold wire and a composite gold wire reference electrode.

[0067] Perform a fast - charge test on the obtained three - electrode lithium - ion battery: After the three - electrode cell is discharged and left to stand for 30 min, perform a step - by - step fast - charge test, and the data acquisition instrument simultaneously monitors the negative reference potentials of the pure gold wire and the composite gold wire reference electrodes. The test results are shown in Figure 4 . The results show that the negative reference results monitored by the composite gold reference electrode are consistent with those monitored by the pure gold wire, indicating that the composite gold reference electrode has a stable electrode potential and can be comparable to the pure gold wire reference electrode, which can solve the problems of high cost and low reuse rate when using expensive gold wires as the reference electrode of the three - electrode battery.

[0068] Although this specification is described in terms of embodiments, not every embodiment contains only an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0069] Therefore, the above are only the preferred embodiments of this application and are not used to limit the scope of implementation of this application; that is, all equivalent transformations made according to the scope of the claims of this application are within the protection scope of the claims of this application.

Claims

1. A preparation method of a composite reference electrode, characterized in that, It includes the following steps: S1. Immerse the end of the conductive wire coated with an insulating medium in concentrated acid to obtain the effective part; S2. Wrap the insulating part of the conductive wire with foil, then place it in an ion sputtering instrument, sputter a metal target in a vacuum environment, and form a metal film layer on the surface of the effective part of the conductive wire to obtain a composite reference electrode.

2. The preparation method according to claim 1, characterized in that, In step S2, the sputtering working parameters are: the distance between the target and the substrate is 40 - 50 mm; the sputtering power is 5 - 6 W, the target spraying pressure is 6 - 8 Pa, and the sputtering time is 80 - 160 s.

3. The preparation method according to claim 1, characterized in that, The metal target is at least one of titanium target, zinc target, chromium target, magnesium target, niobium target, tin target, aluminum target, indium target, iron target, zirconium-aluminum target, titanium-aluminum target, zirconium target, aluminum-silicon target, silicon target, copper target, germanium target, silver target, cobalt target, gold target, gadolinium target, lanthanum target, yttrium target, cerium target, tungsten target, stainless steel target, nickel-chromium target, hafnium target, molybdenum target, iron-nickel target, tungsten target.

4. The preparation method according to claim 1, wherein, The diameter of the conductive wire is 50 - 150 um; the length of the effective part is 3 - 5 cm; the conductive wire is a copper wire.

5. A composite reference electrode prepared by the preparation method according to any one of claims 1 - 4.

6. A three-electrode lithium-ion battery, comprising a stacked core formed by laminating a plurality of cell electrode groups and a separator, characterized in that, It further includes the composite reference electrode according to claim 4, wherein the effective part is laminated between the electrode groups of the battery cell through a separator, and the joint of the foil and the conductive wire is fixed on the side of the laminated core.

7. The preparation method of the three-electrode lithium-ion battery according to claim 5, wherein It includes the following steps: Perform preheating pressing on the laminated core, bury the composite reference electrode between the electrode groups of the battery cell, and separate them with a separator to ensure that the reference electrode does not directly contact the material area of the electrode group of the battery cell; Fix the lead-out end of the composite reference electrode on one side of the laminated core, perform secondary hot pressing on the laminated core, and obtain a three-electrode lithium-ion battery after post-treatment.

8. The preparation method according to claim 7, characterized in that, The temperature of the preheating pressing is 60 - 90 °C, the pressure is 6 - 10 T, and the time is 120 - 300 s; and / or, the temperature of the secondary hot pressing is 60 - 90 °C, the pressure is 10 - 16 T, and the time is 150 - 300 s.

9. The preparation method according to claim 7, characterized in that, The post-treatment sequentially includes shell encapsulation, baking, liquid injection, formation, grading, tab welding, supplementary charging, and lithium plating.

10. The preparation method according to claim 9, characterized in that, The SOC of the battery for supplementary charging is 40 - 60%; and / or, the current for lithium plating is 20 - 70 uA, and the lithium plating time is 4 - 12 hours.

Images