CN111600087A - Reference electrode and three-electrode system for lithium ion battery detection and preparation method thereof - Google Patents

Abstract

The invention discloses a reference electrode for lithium ion battery detection, comprising a reference electrode body made of prepreg carbon fiber, one end of the reference electrode body is oxidized to form a bare carbon fiber, and the bare carbon fiber is located in the lithium ion battery. between the positive and negative electrodes. Its stability is good, and the reference electrode does not affect the transmission of lithium ions between the positive electrode sheet and the negative electrode sheet, which improves the detection accuracy. The invention also discloses a three-electrode system for lithium ion battery detection with the above-mentioned reference electrode and a preparation method of the three-electrode system, which have good structural stability, low cost, and simple and easy-to-operate preparation method.

Description

Reference electrode and three-electrode system for detection of lithium ion battery and preparation method thereof

technical field

The invention relates to a lithium ion battery, in particular to a reference electrode and a three-electrode system for detection of the lithium ion battery and a preparation method.

Background technique

The rapid development of pure electric vehicles has greatly stimulated the demand for lithium-ion batteries. According to the research data of GGII of the Advanced Industrial Research Institute, the global power battery shipments in 2018 were 106GWh, a year-on-year increase of 55.2%; the global power battery year from 2014 to 2018 The compound growth rate is 69.6%. At the same time as the demand for power batteries increases, the requirements for energy and power of power batteries are also getting higher and higher. In particular, customer demand for fast charging is a major bottleneck restricting the development of new energy vehicles.

During the charging process of lithium-ion batteries, the potential of the negative electrode decreases continuously. If the charging current of the fast charge is too large, the battery will have the risk of lithium precipitation. At the same time, with the increase of the mileage of the electric vehicle, the battery continues to age, such as the consumption of electrolyte, the thickening of the negative electrode SEI film, and the increase of electronic impedance, which will further deteriorate the state of the battery. Therefore, there is a need for a method for in-situ detection of electrode potential changes during battery charging and discharging, so as to prevent lithium precipitation during fast charging and to detect the aging state of battery cells. Among them, the three-electrode method is an effective method to monitor the lithium evolution and aging state of the battery during charging.

CN202949008U discloses a three-electrode device for a lithium ion battery. The reference electrode used is a metal lithium sheet, and the metal lithium sheet has a diameter of 10-20 mm and a thickness of 0.2 cm. However, in the process of cyclic charge and discharge of lithium-ion batteries, the reference electrode of the metal lithium sheet will block the transmission of lithium ions, and the corresponding positive and negative regions cannot deintercalate lithium, forming a dead zone. Therefore, the metal lithium sheet is used as the reference electrode. The results of the lifetime studies of the three-electrode system are unreliable.

CN105470577A discloses a three-electrode assembly method of a flexible packaging lithium ion battery, and CN204130649U is a three-electrode battery, in which the reference electrodes in the three-electrode systems of both are selected to be plated with lithium on the surface of copper, silver and gold metal wires. Since the surface of the metal wire or metal wire is exposed in the electrolyte, the electrolyte will interfere with the electrical signals of the positive electrode-reference electrode and the negative electrode-reference electrode, which will affect the test results.

CN107293778A discloses a three-electrode battery and a preparation method thereof. A copper wire enameled wire with one end exposed is selected as the three electrodes, and the surface of the bare copper wire is subjected to lithium plating treatment before the AC impedance test. However, the micron-scale copper wire has poor mechanical properties, so it is easy to break during the production process, so the stability of the three-electrode battery is poor. In addition, the surface of the copper wire has a poor affinity for lithium, and the combination of lithium and copper wire is not strong, and the lithium plating layer is prone to fall off, which affects the test results.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a reference electrode and a three-electrode system for detection of a lithium ion battery and a preparation method thereof, which have good stability, the reference electrode does not affect the transmission of lithium ions between the positive electrode sheet and the negative electrode sheet, and improves the accuracy of detection sex.

The reference electrode for detection of a lithium ion battery according to the present invention includes a reference electrode body made of prepreg carbon fiber, one end of the reference electrode body is oxidized to form a bare carbon fiber, and the bare carbon fiber is located at the positive electrode of the lithium ion battery. between the plate and the negative plate.

Further, the reference electrode body is in a filament shape, a sheet shape or a column shape.

Further, the reference electrode body is in the shape of a filament with a diameter of 5-20 μm.

Further, the surface of the exposed carbon fiber is subjected to lithium plating treatment.

Further, the length of the bare carbon fibers is 2-5 cm.

A three-electrode system for detection of a lithium ion battery, comprising a casing, a battery core and an electrolyte packaged in the casing, the battery core comprising a positive electrode sheet, a negative electrode sheet and the above-mentioned reference electrode body, the positive electrode sheet and the A separator is arranged between the reference electrode body, the reference electrode body and the negative electrode piece, and the exposed carbon fiber of the reference electrode body is located between the positive electrode piece and the negative electrode piece; the positive electrode piece is connected with one end of the positive electrode tab, and the One end of the reference electrode body away from the exposed carbon fiber is connected with one end of the reference electrode tab, and the negative electrode sheet is connected with one end of the negative electrode tab; the other ends of the positive electrode tab, the reference electrode tab and the negative electrode tab extend out of the shell in vitro.

Further, one of the separators completely separates the positive electrode sheet and the negative electrode sheet, and the other separates the bare carbon fiber of the reference electrode body from the positive electrode sheet or the negative electrode sheet. The function of the separator is to prevent the physical contact between the positive electrode and the negative electrode, and to allow the ion flow to pass through the micropores of the separator, thereby ensuring the rapid transmission of lithium ions between the positive and negative electrodes during the charging and discharging of the battery.

Further, the housing material is aluminum or aluminum alloy.

A preparation method of a three-electrode system for detection of a lithium ion battery, comprising the following steps:

S1, place one end of the prepreg carbon fiber in an oxidizing agent for 10-60 minutes, oxidize to form a bare carbon fiber, and wash to obtain a reference electrode body; the oxidizing agent is at least one of concentrated sulfuric acid, concentrated nitric acid, KMnO ₄ , and H ₂ O ₂ A sort of;

S2, the exposed carbon fiber of the reference electrode body is placed between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet and the reference electrode body, the reference electrode body and the negative electrode sheet are separated by a diaphragm;

S3, coil the positive electrode sheet, the negative electrode sheet, the reference electrode body and the separator as a whole to obtain a battery cell, the positive electrode sheet is connected to one end of the positive electrode tab, and the reference electrode body is far away from the exposed carbon fiber at one end and the reference electrode tab. One end is connected, the negative electrode piece is connected with one end of the negative electrode tab, the other end of the positive electrode tab, the reference electrode tab and the negative electrode tab protrude out of the casing; liquid.

Further, the exposed carbon fiber surface of the reference electrode body is plated with lithium by using a positive electrode sheet and a negative electrode sheet, the lithium plating current is 0.001-1 mA, and the lithium plating time is 20-120 min.

Compared with the prior art, the present invention has the following beneficial effects.

1. The material of the reference electrode in the present invention is prepreg carbon fiber, and one end is oxidized to form a bare carbon fiber. Since the carbon fiber has a tensile strength far higher than that of copper, the risk of breakage of the reference electrode during manufacture and use is reduced. , thereby improving the stability and durability of the three-electrode system. In addition, the setting of the reference electrode does not affect the transmission of lithium ions between the positive electrode sheet and the negative electrode sheet, and does not cause interference to electrical signals, the manufacturing cost is low, and the potential stability of the reference electrode is improved.

2. The exposed carbon fiber of the reference electrode body of the three-electrode system of the present invention is located between the positive electrode sheet and the negative electrode sheet, and a separator is provided between the positive electrode sheet and the reference electrode body, and between the reference electrode body and the negative electrode sheet to avoid exposure. Carbon fiber is directly exposed to the electrolyte to interfere with the electrical signal of the test, which is conducive to continuous in-situ monitoring of the positive electrode potential, negative electrode potential and impedance during the use of lithium-ion batteries, and promotes the life research of lithium-ion batteries.

3. In the present invention, one end of the prepreg carbon fiber is placed in the oxidant to react for 10 to 60 minutes. On the one hand, the exposed carbon fiber can be formed at one end of the prepreg carbon fiber through the oxidation of the oxidant. On the other hand, as the reaction continues, the oxidant will Acting on the bare carbon fiber makes the oxygen-containing group on the bare carbon fiber, and the oxygen-containing group can promote the combination of the lithium plating layer and the surface of the bare carbon fiber, and improve the structural stability of the lithium plating layer.

4. In the present invention, the exposed carbon fibers of the reference electrode are subjected to surface lithium plating treatment through the positive and negative electrodes of the three-electrode system, which is simple to operate and ensures the effect of the three-electrode system for in-situ detection of the internal chemical and electrochemical reactions of the lithium-ion battery. .

Description of drawings

Fig. 1 is the positional distribution schematic diagram of positive electrode sheet, negative electrode sheet, separator and reference electrode of the present invention;

2 is a schematic structural diagram of a three-electrode system for lithium-ion battery detection according to the present invention;

Figure 3 is a negative electrode potential-time curve of a cell.

In the figure, 1—reference electrode body, 2—bare carbon fiber, 3—positive electrode sheet, 4—negative electrode sheet, 5—diaphragm, 51—first diaphragm, 52—second diaphragm, 6—shell, 7—positive electrode ear, 8—reference electrode tab, 9—negative electrode tab.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings.

Referring to FIG. 1 , the reference electrode for lithium-ion battery detection includes a reference electrode body 1 made of prepreg carbon fiber, and the reference electrode body is in the shape of a filament with a diameter of 5-20 μm, that is, a prepreg The diameter of the carbon fiber is 5-20 μm, and the specific value is reasonably selected according to the actual detection conditions. One end of the reference electrode body 1 is oxidized to form a bare carbon fiber 2 , and the bare carbon fiber 1 is located between the positive electrode sheet 3 and the negative electrode sheet 4 of the lithium ion battery. The length of the exposed carbon fiber 2 is 2-5 cm, and the specific value is reasonably selected according to the actual detection conditions.

In order to ensure the effect of the three-electrode system in detecting the chemical and electrochemical reactions inside the lithium-ion battery in situ, the surface of the exposed carbon fiber 2 is subjected to lithium plating treatment.

Referring to FIG. 2 , the three-electrode system for detection of a lithium ion battery is shown, including a case, a battery cell and an electrolyte packaged in the case 6 . The shell 6 is made of aluminum or aluminum alloy, specifically aluminum-plastic bags or aluminum shells, which can be reasonably selected according to the actual working conditions.

The battery cell includes a positive electrode sheet 3, a negative electrode sheet 4 and the above-mentioned reference electrode body 1, and a separator 5 is provided between the positive electrode sheet 3 and the reference electrode body 1, the reference electrode body 1 and the negative electrode sheet 4, so The exposed carbon fiber 2 of the reference electrode body 1 is located between the positive electrode sheet 3 and the negative electrode sheet 4; the positive electrode sheet 3 is connected with one end of the positive electrode tab 7, and the reference electrode body 1 is away from one end of the exposed carbon fiber 2 and the reference electrode body 1. One end of the electrode tab 8 is connected, and the negative electrode sheet 4 is connected to one end of the negative electrode tab 9;

The separator 5 includes a first separator 51 and a second separator 52, wherein the first separator 51 is arranged between the positive electrode sheet 3 and the reference electrode body 1, and the first separator 51 completely separates the positive electrode sheet 3 and the negative electrode sheet 4 , that is, the length of the first separator 51 ≥ the length of the positive electrode sheet 3 . The second separator 52 is provided between the reference electrode body 1 and the negative electrode sheet 4 . The exposed carbon fibers 2 of the reference electrode body 1 are separated from the positive electrode sheet 3 by the first separator 51 , and separated from the negative electrode sheet 4 by the second separator 52 . open. The function of the separator 5 is to prevent the physical contact between the positive electrode sheet 3 and the negative electrode sheet 4, and allow the ion flow to pass through the micropores of the separator 5, thereby ensuring the rapid transmission of lithium ions between the positive and negative electrodes during the charging and discharging of the battery.

The preparation method of the above-mentioned three-electrode system for lithium ion battery detection includes the following steps.

S1, one end of the prepreg carbon fiber is placed in concentrated sulfuric acid to react for 10-60 minutes, the reaction time is adjusted according to the resin group of the prepreg carbon fiber, oxidized to form the bare carbon fiber 2, and the exposed carbon fiber 2 is subjected to surface oxidation treatment by concentrated sulfuric acid , with an oxidizing group. Then use distilled water to wash 3-5 times to remove the concentrated sulfuric acid remaining in the prepreg carbon fibers and the bare carbon fibers, and obtain the reference electrode body 1 .

S2, the exposed carbon fiber 2 of the reference electrode body 1 is placed between the positive electrode sheet 3 and the negative electrode sheet 4, and the separator 5 is used between the positive electrode sheet 3 and the reference electrode body 1, the reference electrode body 1 and the negative electrode sheet 4 separated.

S3, the positive electrode sheet 3, the negative electrode sheet 4, the reference electrode body 1 and the separator 5 are wound as a whole to obtain a battery cell, the positive electrode sheet 3 is connected to one end of the positive electrode tab 7, and the reference electrode body 1 is far away from the exposed carbon fiber 2. One end is connected with one end of the reference electrode tab 8, the negative electrode sheet 4 is connected with one end of the negative electrode tab 9, and the other end of the positive electrode tab 7, the reference electrode tab 8 and the negative electrode tab 9 extends out of the housing 6; Then, the cells are packaged in the casing 6 , and the electrolyte solution is filled in the casing 6 . Wherein, the reference electrode tab 8 is a nickel tab.

Before the test, the surface of the exposed carbon fiber 2 of the reference electrode body 1 is plated with lithium using the positive electrode sheet 3 and the negative electrode sheet 4, the lithium plating current is 0.001-1 mA, and the lithium plating time is 20-120 min. The specific process parameters are adjusted according to the actual working conditions.

Three cells are prepared with the same process parameters, and the three cells are numbered as 1#, 2#, and 3# in turn. Charge and discharge test and negative electrode-reference electrode potential monitoring, the charging process is step charging, and the current decreases in turn. See Figure 3 and Table 1 for the results.

Referring to Fig. 3, the negative electrode potential-time curves of the three battery cells shown, the negative electrode-reference potential curves of the three battery cores all have a high degree of coincidence under different charging currents, indicating the reference of the present invention. Electrode repeatability is high.

Table 1 The negative electrode potential of the first to the fourth stage charging terminal of the battery cell

It can be seen from Table 1 that the three cells still have good consistency at the charging end.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection of the present application. within the range.

Claims (10)

1. A reference electrode for detecting a lithium ion battery is characterized in that: the reference electrode comprises a reference electrode body (1) made of prepreg carbon fibers, wherein bare carbon fibers (2) are formed at one end of the reference electrode body (1) through oxidation, and the bare carbon fibers (2) are located between a positive plate (3) and a negative plate (4) of a lithium ion battery.

2. The reference electrode for lithium ion battery detection according to claim 1, wherein: the reference electrode body (1) is filamentous, flaky or columnar.

3. The reference electrode for lithium ion battery detection according to claim 1 or 2, characterized in that: the reference electrode body (1) is in a filament shape with the diameter of 5-20 mu m.

4. The reference electrode for lithium ion battery detection according to claim 1 or 2, characterized in that: and carrying out lithium plating treatment on the surface of the bare carbon fiber (2).

5. The reference electrode for lithium ion battery detection according to claim 1 or 2, characterized in that: the length of the bare carbon fiber (2) is 2-5 cm.

6. The utility model provides a three electrode system are used in lithium ion battery detection, includes casing (6) and encapsulates electric core and electrolyte in casing (6), its characterized in that: the battery core comprises a positive plate (3), a negative plate (4) and the reference electrode body (1) as claimed in any one of claims 1 to 5, wherein a diaphragm (5) is arranged between the positive plate (3) and the reference electrode body (1) and between the reference electrode body (1) and the negative plate (4), and the bare carbon fibers (2) of the reference electrode body (1) are positioned between the positive plate (3) and the negative plate (4);

the positive plate (3) is connected with one end of a positive electrode lug (7), one end of the reference electrode body (1) far away from the exposed carbon fiber (2) is connected with one end of a reference electrode lug (8), and the negative plate (4) is connected with one end of a negative electrode lug (9); the other ends of the anode tab (7), the reference electrode tab (8) and the cathode tab (9) extend out of the shell (6).

7. The three-electrode system for lithium ion battery detection according to claim 6, wherein: one of the diaphragms (5) completely separates the positive plate (3) from the negative plate (4), and the other diaphragm separates the bare carbon fiber (2) of the reference electrode body (1) from the positive plate (3) or the negative plate (4).

8. The three-electrode system for lithium ion battery detection according to claim 6 or 7, characterized in that: the shell (6) is made of aluminum or aluminum alloy.

9. A preparation method of a three-electrode system for detecting a lithium ion battery is characterized by comprising the following steps:

s1, placing one end of the prepreg carbon fiber in an oxidant to react for 10-60 min, oxidizing to form bare carbon fiber (2), and washing to obtain a reference electrode body (1); the oxidant is concentrated sulfuric acid, concentrated nitric acid, KMnO₄、H₂O₂At least one of;

s2, placing the bare carbon fibers (2) of the reference electrode body (1) between the positive plate (3) and the negative plate (4), and separating the positive plate (3) from the reference electrode body (1) and separating the reference electrode body (1) from the negative plate (4) by using a diaphragm (5);

s3, winding the positive plate (3), the negative plate (4), the reference electrode body (1) and the diaphragm (5) integrally to obtain an electric core, wherein the positive plate (3) is connected with one end of a positive electrode tab (7), one end of the reference electrode body (1) far away from the bare carbon fiber (2) is connected with one end of a reference electrode tab (8), the negative plate (4) is connected with one end of a negative electrode tab (9), and the other ends of the positive electrode tab (7), the reference electrode tab (8) and the negative electrode tab (9) extend out of the shell (6); then the battery core is packaged in the shell (6), and the electrolyte is filled in the shell (6).

10. The method for preparing a three-electrode system for lithium ion battery detection according to claim 9, wherein: the surface of the bare carbon fiber (2) of the reference electrode body (1) is plated with lithium by adopting a positive plate (3) and a negative plate (4), wherein the lithium plating current is 0.001-1 mA, and the lithium plating time is 20-120 min.

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