CN114113839B - A method for evaluating the current collecting capacity of a lithium-ion battery current collecting structure - Google Patents

Abstract

The invention provides an evaluation method for the current collecting capacity of a current collecting structure of a lithium battery, which comprises the following steps: (1) Preparing a series of sodium chloride solutions with concentration gradients, and measuring the conductivity of the sodium chloride solutions; (2) Injecting the sodium chloride solution into lithium sub-battery shells respectively, connecting the anode and the cathode of the battery shells with leads respectively, and electrifying to test the resistor; (3) The conductivity obtained in the step (1) and the resistance obtained in the step (2) are respectively corresponding, and a fitting curve is drawn by taking the conductivity as an abscissa and the resistance as an ordinate; (4) The resistance of the current collecting structure of the lithium battery to be measured is measured, the conductivity of sodium chloride obtained in the step (1) is used for drawing a fitting curve, and the current collecting effect of the current collecting structure of the lithium battery is obtained.

Description

A method for evaluating the current collecting capacity of a lithium-ion battery current collecting structure

Technical Field

The invention belongs to the field of lithium-ion batteries and relates to a method for evaluating the current collecting capacity of a current collecting structure of a lithium-ion battery.

Background Art

Lithium-ion battery is a liquid lithium primary battery with thionyl chloride as electrolyte solvent and cathode active material. It is the type with the highest specific energy and the widest operating temperature range among the current commercial battery products. At the same time, the characteristics of liquid batteries make its voltage stable for more than 90% of the time when the entire battery capacity is used. Nowadays, lithium-ion batteries are widely used in various types of smart meters such as electricity meters, water meters, and gas meters. They are also rapidly applied and promoted in the fields of automobile tire pressure monitoring systems (TPMS), radio frequency identification (RFID), and satellite positioning devices (GPS). The continuous application and development of lithium-ion batteries in the fields of smart meters, transportation, security, and the Internet of Things around the world also puts higher requirements on their performance.

In the process of battery design, manufacturing and quality control, the current collecting capacity of the current collecting structure is a key factor affecting the performance of the battery. However, its current collecting capacity is affected by other factors related to the battery assembly process, such as shape, size, battery shell size, etc., and does not entirely depend on the properties of the material itself. Traditional resistance measurement methods cannot be simulated, resulting in resistance measurement of only the performance of the material itself, but unable to measure the current transfer capacity of the internal structure of the battery in the actual battery, which makes the quality control of the battery current collecting structure design lack of corresponding quantifiable methods.

CN204793037U discloses a lithium-ion battery current collector structure, including a positive electrode body, a central pole, and a current collector. The current collector is matched and fitted in the central hole of the cylindrical positive electrode body. The current collector is cylindrical, and through holes are evenly designed on the cylindrical wall. The bottom of the cylinder is folded inwardly and the top is folded outwardly. The top outward folded edge is matched and attached to the top surface of the positive electrode body. A metal connecting strip connects the central pole and the current collector.

CN202423440U discloses a positive electrode current collecting device for a lithium-ion battery with improved load capacity, aiming to provide a lithium-ion battery that will not damage the preformed positive electrode structure inside the battery and has batch-stable performance. The lithium-ion battery comprises a cover plate, a stainless steel pole passing through the center of the cover plate, and a glass insulator arranged between the cover plate and the stainless steel pole. The positive electrode current collecting device for a lithium-ion battery with improved load capacity also comprises at least two nickel current collecting poles arranged at the bottom of the stainless steel pole.

The current collecting structures described in the above schemes cannot directly measure the current transfer capacity of the internal structure of the battery in the actual battery, which makes the quality control of the current collecting structure design of the battery lack a corresponding quantifiable method. Therefore, in the design and manufacturing process of lithium-ion batteries, there is an urgent need for a method that can more comprehensively simulate and measure the actual current transfer capacity of the current collecting structure inside the battery, and form specific data accumulation, which can also provide guidance for future battery design.

Summary of the invention

The purpose of the present invention is to provide a method for evaluating the current collecting capacity of a lithium-ion battery current collecting structure. The present invention proposes for the first time a quantitative standard for the current collecting effect of a battery current collecting structure and uses a fitting calculation method for data processing, which can minimize the impact of individual differences on the overall result.

In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

The present invention provides a method for evaluating the current collecting capacity of a lithium-ion battery current collecting structure, the method comprising the following steps:

(1) Preparing a series of sodium chloride solutions with concentration gradients and measuring the conductivity of the sodium chloride solutions;

(2) injecting the sodium chloride solution into the lithium-ion battery shells respectively, connecting the positive and negative electrodes of the battery shells to wires respectively, and testing the resistance by powering on;

(3) The conductivity obtained in step (1) and the resistance obtained in step (2) are respectively matched to each other, and a fitting curve is drawn with the conductivity as the horizontal axis and the resistance as the vertical axis;

(4) The resistance of the lithium sub-battery current collecting structure to be tested is measured, and the conductivity of sodium chloride obtained in step (1) is used to draw a fitting curve to obtain the current collecting effect of the lithium sub-battery current collecting structure.

The current collecting effect evaluation of the current collecting structure is a comprehensive evaluation that can perfectly simulate the actual situation. The battery shell is used as the negative electrode of the battery, and the current collecting structure is used as the positive electrode of the battery. The current collecting effect of the entire battery is a comprehensive result of the combination of these two parts. The present invention directly uses the standard battery shell as a measurement container to simulate the actual situation to the greatest extent.

Preferably, the tolerance of each concentration of the sodium chloride solution in step (1) is ≤0.002%, for example: 0.002%, 0.0015%, 0.001%, 0.001%, 0.0005% or 0.0002%, etc.

The tolerance of each concentration of the sodium chloride solution of the present invention is that the difference between the concentration of the prepared sodium chloride solution and the concentration of the required prepared sodium chloride solution is between ±0.002%, that is, to prepare a sodium chloride solution with a concentration of 0.02%, the concentration range of the prepared sodium chloride solution needs to be between 0.018 and 0.022%.

Preferably, the device for measuring the conductivity of the sodium chloride solution in step (1) comprises a conductivity meter.

Preferably, the volume of sodium chloride injected in step (2) varies according to the model, and the height reached by the injected sodium chloride solution is equivalent to the height of the lithium belt designed for the battery.

The method of the present invention is highly operable for batteries of different shapes and models.

Preferably, during the process of injecting the sodium chloride solution into the lithium-ion battery shell in step (2), the battery is kept vertically placed.

Preferably, the device for testing resistance in step (2) comprises an AC impedance tester.

Preferably, the relationship of the fitting curve in step (3) is y=a+b/x, wherein y is resistance and x is conductivity.

The present invention adopts a fitting calculation method for data processing, which can avoid the influence of individual differences on the overall results to the greatest extent.

Preferably, the method for determining the resistance of the current collecting structure of the lithium-ion battery to be tested in step (4) is to replace the standard cover group in the lithium-ion battery shell obtained in step (2) with the current collecting structure cover group to be tested, inject sodium chloride solution, connect the positive and negative electrodes of the battery shell with wires respectively, and test the resistance by powering on.

Preferably, the relationship of the fitting curve in step (4) is y=a+ _bn /x.

Preferably, the current collecting effect of the lithium sub-battery current collecting structure in step (4) is K=b/b _n , wherein the higher the K value, the better the current collecting effect.

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

(1) The present invention proposes for the first time a quantitative standard for the current collecting effect of a battery current collecting structure, and directly uses a standard battery shell as a measuring container, which can simulate the actual situation to the greatest extent.

(2) The present invention adopts a fitting calculation method for data processing, which can avoid the influence of individual differences on the overall results to the greatest extent and has extremely high operability for batteries of different shapes and models.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of a method for evaluating the current collecting capacity of a lithium-ion battery current collecting structure according to the present invention.

FIG. 2 is a resistance-conductivity relationship diagram of the standard cover assembly described in Example 1 of the present invention.

FIG. 3 is a resistance-conductivity relationship diagram of the sheet-shaped current collecting network described in Example 1 of the present invention.

FIG. 4 is a resistance-conductivity relationship diagram of the mesh current collecting network described in Example 1 of the present invention.

5 is a comparison diagram of the fitting curves of the 9 mm, 11 mm and 13 mm wide rapid flow nets described in Example 2 of the present invention and a standard cover group without a current collecting structure.

DETAILED DESCRIPTION

The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

Example 1

This embodiment provides a method for evaluating the current collecting capacity of a lithium-ion battery current collecting structure. The flow chart of the evaluation method is shown in FIG1 . The evaluation method specifically includes the following steps:

(1) In an environment of 20° C., a sodium chloride solution with a concentration gradient is prepared, and the conductivity of the sodium chloride aqueous solution is measured using a conductivity meter and recorded. The concentration of the sodium chloride solution is shown in Table 1 below:

Table 1

(2) Press the standard shell of the ER 26500 lithium-ion battery with the corresponding standard cover assembly, and inject the above sodium chloride solution through the injection hole in sequence. The volume of the injected sodium chloride solution is 15 ml. Use a clamp to ensure that the battery is placed vertically. Connect wires at both ends of the clamp to connect the positive and negative poles of the battery shell. In an environment of 20°C, use an AC impedance tester to measure the corresponding internal resistance. Record the resistance values one by one, and correspond them one by one with the sodium chloride solution and its actual measured conductivity. The results are shown in Table 2:

Table 2

(3) With the conductivity value as the horizontal axis and the resistance value as the vertical axis, draw the resistance-conductivity relationship diagram of the corresponding standard cover group, as shown in Figure 2, and perform fitting calculation. Obtain the relationship: y = a + b / x, b = 91.91; (4) Use the designed sheet-shaped current collecting net cover group and the ring-shaped current collecting net cover group to replace the standard cover group and press it with the standard shell of the ER 26500 lithium-ion battery, repeat the above steps (2)-(3), obtain the corresponding resistance value, and record the resistance value as shown in Table 2, and then obtain the relationship and fitting curve:

Sheet current collector: y = a + b ₁ /x, b ₁ = 51.50, the fitting curve is shown in Figure 3,

Ring current collecting network: y = a + b ₂ /x, b ₂ = 44.93, the fitting curve is shown in FIG4, K ₁ = b/b ₁ = 91.91/51.50 = 1.785, K ₂ = b/b ₂ = 91.91/44.93 = 2.046 are calculated, the K value reflects the quality of the current collecting effect, and can measure the current transfer capacity of the current collecting structure. The current collecting capacity of the ring current collecting structure is higher than that of the sheet current collecting structure.

The current collection effect evaluation of the current collection structure is a comprehensive evaluation that can perfectly simulate the actual situation. The battery shell is used as the negative electrode of the battery, and the current collection structure is used as the positive electrode of the battery. The current collection effect of the entire battery is a comprehensive result of the combination of these two parts. The present invention directly uses the standard battery shell as a measurement container to simulate the actual situation to the maximum extent. The present invention provides a simple method to obtain the current collection capacity of the annular current collection structure and the sheet current collection structure, and the effect is basically consistent with the actual application. The fitting calculation method is used for data processing, which can avoid the influence of individual differences on the overall result to the greatest extent.

Example 2

This embodiment provides a method for evaluating the current collecting capacity of a lithium-ion battery current collecting structure, and the evaluation method comprises the following steps:

(1) In an environment of 20° C., a sodium chloride solution with a concentration gradient is prepared, and the conductivity of the sodium chloride aqueous solution is measured using a conductivity meter and recorded. The concentration of the sodium chloride solution is shown in Table 3 below:

Table 3

(2) Press the standard shell of ER 26500 lithium-ion battery with the corresponding standard cover assembly, and inject the above sodium chloride solution through the injection hole in sequence. The volume of the injected sodium chloride solution is 15 ml. Use a clamp to ensure that the battery is placed vertically. Connect wires at both ends of the clamp to connect the positive and negative poles of the battery shell. In an environment of 20°C, use an AC impedance tester to measure the corresponding internal resistance. Record the resistance values one by one, and correspond them one by one with the sodium chloride solution and its actual measured conductivity. The results are shown in Table 4:

Table 4

(3) With the conductivity value as the horizontal coordinate and the resistance value as the vertical coordinate, draw the resistance-conductivity relationship diagram of the corresponding standard cover group, as shown in Figure 2, and perform fitting calculation. The relationship formula is: y=a+b/x, b=91.91;

(4) Use sheet-shaped current collecting mesh cover groups with widths of 9 mm, 11 mm, and 13 mm to replace the standard cover group and press them into the standard shell of ER 26500 lithium-ion battery. Repeat the above steps (2)-(3) to obtain the corresponding resistance values. The resistance values are recorded in Table 4, and then the relationship is obtained:

9mm wide current collecting net: y=a+ _b3 /x, _b3 =54.45, 11mm wide current collecting net: y=a+ _b4 /x, _b4 =51.50, 13mm wide current collecting net: y=a+ _b5 /x, _b5 =48.08. The fitting curves of 9mm, 11mm and 13mm wide rapid current nets and the comparison diagram of the standard cover group without current collecting structure are shown in Figure 5. _K3 =b/ _b3 =91.91/54.45=1.688, K4= _b / _b4 =91.91/51.50=1.784, _K5 =b/ _b5 =91.91/48.08=1.912 are calculated. The K value reflects the quality of the current collecting effect. It can be seen from the data that with the increase of the width of the current collecting net, the current collecting effect becomes stronger.

The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims (7)

1. The method for evaluating the current collecting capacity of the current collecting structure of the lithium battery is characterized by comprising the following steps of:

(1) Preparing a series of sodium chloride solutions with concentration gradients, and measuring the conductivity of the sodium chloride solutions;

(2) Injecting the sodium chloride solution into lithium-ion battery shells containing a standard shell and a standard cover group respectively, connecting the anode and the cathode of the battery shells with leads respectively, and electrifying to test a resistor;

(3) Respectively corresponding the conductivity obtained in the step (1) and the resistance obtained in the step (2), and drawing a standard fitting curve by taking the conductivity as an abscissa and the resistance as an ordinate;

the relation of the fitting curve in the step (3) is y=a+b/x, wherein y is resistance, and x is conductivity;

(4) Measuring the resistance of the current collecting structure of the lithium battery to be measured, drawing a fitting curve by adopting the conductivity of sodium chloride obtained in the step (1) to obtain the current collecting effect of the current collecting structure of the lithium battery;

the relation of the fitting curve in the step (4) is y=a+b _n/x;

And (3) the current collecting effect of the current collecting structure of the lithium-ion battery in the step (4) is K=b/b _n, wherein the higher the K value is, the better the current collecting effect is.

2. The assay of claim 1 wherein the sodium chloride solution of step (1) has a tolerance of 0.002% or less for each concentration.

3. The assay of claim 1, wherein the means for determining the conductivity of the sodium chloride solution of step (1) comprises a conductivity meter.

4. The method of claim 1, wherein the volume of sodium chloride injected in step (2) varies according to model, and the injected sodium chloride solution reaches a height equivalent to the lithium band height of the battery design.

5. The method of claim 1, wherein the cells are kept vertically in the process of injecting the sodium chloride solution into the lithium-ion battery case in step (2).

6. The method of claim 1, wherein the means for testing the resistance in step (2) comprises an ac impedance tester.

7. The method for evaluating the current collecting structure of the lithium-ion battery to be tested according to claim 1, wherein in the step (4), the standard cover set in the lithium-ion battery shell obtained in the step (2) is replaced by the cover set of the current collecting structure to be tested, sodium chloride solution is injected, the anode and the cathode of the battery shell are respectively connected with a wire, and the resistor is tested by electrifying.