阅读说明：本技术 锂离子电池检测用参比电极和三电极系统及制备方法 (Reference electrode and three-electrode system for lithium ion battery detection and preparation method thereof ) 是由 王钢 李可心 刘杰 于 2020-05-29 设计创作，主要内容包括：本发明公开了一种锂离子电池检测用参比电极,包括材质为预浸料碳纤维的参比电极本体,所述参比电极本体一端通过氧化形成裸露碳纤维,所述裸露碳纤维位于锂离子电池的正极片和负极片之间。其稳定性好,参比电极不影响锂离子在正极片和负极片间的传输,提高检测的准确性。本发明还公开了具有上述参比电极的锂离子电池检测用三电极系统以及该三电极系统的制备方法,其结构稳定性好,成本低廉,制备方法简单易操作。(The invention discloses a reference electrode for detecting a lithium ion battery, which comprises a reference electrode body made of prepreg carbon fibers, wherein one end of the reference electrode body is oxidized to form bare carbon fibers, and the bare carbon fibers are positioned between a positive plate and a negative plate of the lithium ion battery. The stability is good, the reference electrode does not influence the transmission of lithium ions between the positive plate and the negative plate, and the detection accuracy is improved. The invention also discloses a three-electrode system with the reference electrode for detecting the lithium ion battery and a preparation method of the three-electrode system, and the three-electrode system has the advantages of good structural stability, low cost and simple and easy operation of the preparation method.)

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.

Technical Field

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

Background

The rapidly-developed pure electric vehicle greatly stimulates the demand of the lithium ion battery, and the global power battery shipment 106GWH in 2018 is increased by 55.2% on a par with the data of the research data of GGII of the high industry research institute; the annual composite growth rate of global power batteries in 2014-2018 is 69.6%. While the demand of the power battery is increased, the requirements on the energy, the power and the like of the power battery are also higher and higher. Especially, the demand of customers for quick charging is a big bottleneck limiting the development of new energy automobiles.

During the charging process of the lithium ion battery, the negative electrode potential is continuously reduced. If the charging current of the quick charge is too large, the battery has the risk of lithium precipitation. Meanwhile, with the increase of the mileage of the electric vehicle, the battery is continuously aged, such as electrolyte consumption, a negative electrode SEI film is thickened, electronic impedance is increased, and the like, so that the state of the battery is further deteriorated. Therefore, there is a need for a method for in-situ detection of electrode potential variation during battery charging and discharging process, which can prevent lithium precipitation during fast charging and can detect the aging state of battery core. The three-electrode method is a method for effectively monitoring the charging lithium precipitation and aging state of the battery in the service process.

CN202949008U discloses a three-electrode device of lithium ion battery, and the reference electrode that adopts is the metal lithium piece, and the diameter of metal lithium piece is 10~ 20mm, and thickness is 0.2 cm. However, in the process of cyclic charge and discharge of the lithium ion battery, the reference electrode of the metal lithium sheet can block the transmission of lithium ions, and lithium cannot be released and embedded in the corresponding positive and negative electrode regions to form a dead zone, so that the result of researching the service life of the three-electrode system adopting the metal lithium sheet as the reference electrode is unreliable.

CN105470577A discloses a three-electrode assembly method for a flexible package lithium ion battery, CN204130649U is a three-electrode battery, and reference electrodes in three-electrode systems of the two are selected to plate lithium on the surfaces of copper, silver and gold metal wires. Because the metal wire or the surface of the metal wire is plated with lithium and is exposed in the electrolyte, the electrolyte can interfere the electric signals of the tested anode-reference electrode and the tested cathode-reference electrode, and the test result is influenced.

CN107293778A discloses a three-electrode battery and a preparation method thereof, wherein a copper wire enameled wire with one exposed end is selected as a three-electrode, and the surface of the exposed copper wire is subjected to lithium plating treatment before testing alternating current impedance. However, the micron-sized copper wire has poor mechanical properties, so the micron-sized copper wire is easy to break off in the manufacturing process, and the stability of the three-electrode battery is poor. And the affinity of the surface of the copper wire to lithium is poor, the lithium and the copper wire are not firmly combined, and the lithium-plated layer is easy to fall off, so that the test result is influenced.

Disclosure of Invention

The invention aims to provide a reference electrode and a three-electrode system for lithium ion battery detection and a preparation method thereof, the stability is good, the reference electrode does not influence the transmission of lithium ions between a positive plate and a negative plate, and the detection accuracy is improved.

The reference electrode for detecting the lithium ion battery comprises a reference electrode body made of prepreg carbon fibers, wherein one end of the reference electrode body is oxidized to form bare carbon fibers, and the bare carbon fibers are positioned between a positive plate and a negative plate of the lithium ion battery.

Further, the reference electrode body is in a filiform shape, a sheet shape or a columnar shape.

Furthermore, the reference electrode body is in a filamentous shape with the diameter of 5-20 microns.

Further, the surface of the bare carbon fiber is plated with lithium.

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

A three-electrode system for detecting a lithium ion battery comprises a shell, and an electric core and electrolyte which are packaged in the shell, wherein the electric core comprises a positive plate, a negative plate and the reference electrode body; the anode plate is connected with one end of an anode tab, one end of the reference electrode body, which is far away from the exposed carbon fibers, is connected with one end of the reference electrode tab, and the cathode plate is connected with one end of a cathode tab; the other ends of the anode tab, the reference electrode tab and the cathode tab extend out of the shell.

Further, one of the diaphragms completely separates the positive plate from the negative plate, and the other diaphragm separates the bare carbon fiber of the reference electrode body from the positive plate or the negative plate. The diaphragm has the functions of preventing the positive plate and the negative plate from being in physical contact, and allowing ion current to pass through the micro-channel of the diaphragm, so that the lithium ions are rapidly transmitted between the positive electrode and the negative electrode in the charging and discharging processes of the battery.

Furthermore, the shell is made of aluminum or aluminum alloy.

A preparation method of a three-electrode system for detecting a lithium ion battery comprises 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, and washing to obtain a reference electrode body; the oxidant is concentrated sulfuric acid, concentrated nitric acid, KMnO₄、H₂O₂At least one of;

s2, placing the bare carbon fibers of the reference electrode body between the positive plate and the negative plate, and separating the positive plate and the reference electrode body and the negative plate by using diaphragms;

s3, winding the positive plate, the negative plate, the reference electrode body and the diaphragm integrally to obtain an electric core, wherein the positive plate is connected with one end of a positive electrode lug, one end of the reference electrode body, which is far away from the exposed carbon fiber, is connected with one end of the reference electrode lug, the negative plate is connected with one end of a negative electrode lug, and the other ends of the positive electrode lug, the reference electrode lug and the negative electrode lug extend out of the shell; and then packaging the battery cell in a shell, and filling electrolyte into the shell.

Further, the positive plate and the negative plate are adopted to plate lithium on the surface of the exposed carbon fiber of the reference electrode body, the lithium plating current is 0.001-1 mA, and the lithium plating time is 20-120 min.

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

1. The reference electrode is made of prepreg carbon fibers, one end of the reference electrode is oxidized to form bare carbon fibers, and the carbon fibers have tensile strength far higher than that of copper, so that the risk of breakage of the reference electrode in the manufacturing and using processes is reduced, and the stability and durability of a three-electrode system are improved. And the reference electrode is arranged without influencing the transmission of lithium ions between the positive plate and the negative plate, so that the electric signal is not interfered, the manufacturing cost is low, and the potential stability of the reference electrode is improved.

2. According to the three-electrode system, the bare carbon fibers of the reference electrode body are positioned between the positive plate and the negative plate, and the diaphragms are arranged between the positive plate and the reference electrode body and between the reference electrode body and the negative plate, so that the bare carbon fibers are prevented from being directly exposed in the electrolyte to interfere with the electric signal of the test, the continuous in-situ monitoring of the positive electrode potential, the negative electrode potential and the impedance in the use process of the lithium ion battery is facilitated, and the research on the service life of the lithium ion battery is promoted.

3. One end of the prepreg carbon fiber is placed in an oxidant to react for 10-60 min, so that on one hand, exposed carbon fiber can be formed at one end of the prepreg carbon fiber through the oxidation action of the oxidant, and on the other hand, the oxidant acts on the exposed carbon fiber along with the continuous reaction, so that the exposed carbon fiber is provided with oxygen-containing groups, the oxygen-containing groups can promote the combination of a lithium plating layer and the surface of the exposed carbon fiber, and the structural stability of the lithium plating layer is improved.

4. According to the invention, the surface lithium plating treatment is carried out on the bare carbon fiber of the reference electrode through the positive plate and the negative plate of the three-electrode system, the operation is simple, and the effect of in-situ detection of the chemical and electrochemical reactions in the lithium ion battery by the three-electrode system is ensured.

Drawings

FIG. 1 is a schematic diagram of the position distribution of the positive plate, the negative plate, the diaphragm and the reference electrode according to the present invention;

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

fig. 3 is a negative potential-time curve of a cell.

In the figure, 1 is a reference electrode body, 2 is bare carbon fiber, 3 is a positive plate, 4 is a negative plate, 5 is a diaphragm, 51 is a first diaphragm, 52 is a second diaphragm, 6 is a shell, 7 is a positive pole lug, 8 is a reference electrode lug, and 9 is a negative pole lug.

Detailed Description

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

Referring to fig. 1, the reference electrode for detecting the lithium ion battery comprises a reference electrode body 1 made of prepreg carbon fibers, wherein the reference electrode body is in a filament shape with the diameter of 5-20 μm, namely the diameter of the prepreg carbon fibers is 5-20 μm, and specific numerical values are reasonably selected according to actual detection conditions. One end of the reference electrode body 1 is oxidized to form bare carbon fibers 2, and the bare carbon fibers 1 are located between a positive plate 3 and a negative plate 4 of the lithium ion battery. The length of the bare carbon fiber 2 is 2-5 cm, and the specific numerical value is reasonably selected according to actual detection conditions.

In order to ensure the effect of the three-electrode system for in-situ detection of the chemical and electrochemical reactions inside the lithium ion battery, the surface of the bare carbon fiber 2 is plated with lithium.

Referring to fig. 2, the three-electrode system for detecting the lithium ion battery includes a housing, and a battery cell and an electrolyte enclosed in the housing 6. The shell 6 is made of aluminum or aluminum alloy, specifically an aluminum-plastic bag or an aluminum shell, and is reasonably selected according to actual working conditions.

The battery core comprises a positive plate 3, a negative plate 4 and the reference electrode body 1, 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 exposed 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 tab 7, one end of the reference electrode body 1, which is far away from the exposed carbon fibers 2, is connected with one end of a reference electrode tab 8, and the negative plate 4 is connected with one end of a negative electrode tab 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.

The diaphragm 5 comprises a first diaphragm 51 and a second diaphragm 52, wherein the first diaphragm 51 is arranged between the positive plate 3 and the reference electrode body 1, and the positive plate 3 and the negative plate 4 are completely separated by the first diaphragm 51, namely, the length of the first diaphragm 51 is more than or equal to that of the positive plate 3. The second diaphragm 52 is arranged between the reference electrode body 1 and the negative electrode sheet 4, and the bare carbon fibers 2 of the reference electrode body 1 are separated from the positive electrode sheet 3 by the first diaphragm 51 and from the negative electrode sheet 4 by the second diaphragm 52. The function of the diaphragm 5 is to prevent the physical contact between the positive plate 3 and the negative plate 4 and allow ion flow to pass through the micro-channels of the diaphragm 5, thereby ensuring the rapid transmission of lithium ions between the positive and negative electrodes during the charging and discharging process of the battery.

The preparation method of the three-electrode system for detecting the lithium ion battery comprises the following steps.

S1, placing one end of the prepreg carbon fiber in concentrated sulfuric acid to react for 10-60 min, adjusting the reaction time according to the resin group of the prepreg carbon fiber, oxidizing to form bare carbon fiber 2, and carrying out surface oxidation treatment on the bare carbon fiber 2 through the concentrated sulfuric acid to carry an oxidizing group. And then, cleaning for 3-5 times by using distilled water to remove the concentrated sulfuric acid remained in the prepreg carbon fibers and the bare carbon fibers, so as to obtain the reference electrode body 1.

S2, the bare carbon fibers 2 of the reference electrode body 1 are placed between the positive plate 3 and the negative plate 4, and the positive plate 3 and the reference electrode body 1, and the reference electrode body 1 and the negative plate 4 are separated by the 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, which is far away from the bare carbon fibers 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. Wherein, the reference electrode tab 8 is a nickel tab.

Before testing, the surface of the bare carbon fiber 2 of the reference electrode body 1 is plated with lithium by adopting the positive plate 3 and the negative plate 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 condition.

Three cells are prepared by the same technological parameters, the three cells are sequentially numbered as 1#, 2#, and 3#, then the three cells are respectively subjected to charge-discharge test and negative electrode-reference electrode potential monitoring by the same charge-discharge machine and the same multiplexer equipment, the charging process is step charging, and the current is sequentially reduced. See figure 3 and table 1 for results.

Referring to fig. 3, the negative electrode potential-time curves of the three cells and the negative electrode-reference potential curves of the three cells have higher contact ratios under different charging currents, which indicates that the reference electrode of the invention has high repeatability.

TABLE 1 cell first to fourth order charging terminal negative electrode potential

As can be seen from table 1, the three cells still have good uniformity at the end of charging.

The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.