A method for detecting wettability of lithium-ion battery electrolyte

Abstract

The present invention discloses a method for detecting the wettability of lithium-ion battery electrolytes, comprising the following steps: a first step of pre-fabricating a plurality of identical batteries that have been dried; a second step of injecting a plurality of different electrolytes into a battery to obtain a plurality of batteries injected with different electrolytes; a third step of placing all the batteries in a static state and performing AC internal resistance tests respectively; a fourth step of, for each battery, when the AC internal resistance of the two previous and subsequent tests does not change, using the detection time corresponding to the AC internal resistance of the latter test as the soaking time consumed by the electrolyte injected into the battery; and comparing and judging the wettability of the electrolytes injected into the multiple batteries based on the soaking time consumed by the electrolytes injected into the multiple batteries. The present invention can quickly and accurately detect the wettability of different electrolytes, compare and judge the wettability of different electrolytes in the same battery, and the detection results are reliable, which can significantly reduce the detection time.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a method for detecting the wettability of an electrolyte of a lithium ion battery. Background Art

[0002] At present, lithium-ion batteries are widely used in the field of new energy vehicles due to their advantages such as high energy density, long cycle life, and long storage time.

[0003] The consistency, cycle performance, energy density, etc. of lithium-ion batteries are the main battery performance contents that are currently of concern. The manufacturing process of the battery directly affects the battery performance. Among them, the formation is the first charging process of the battery, which directly affects the formation quality of the battery electrolyte membrane and the uniformity of the electrode, and directly affects the consistency and long-term cycle performance of the battery. The wetting state of the electrolyte directly affects the uniformity of the electrode's lithium insertion and extraction during the formation process. If the electrolyte's wetting is poor, it will cause the electrode to have a lithium insertion dead zone phenomenon, affecting the battery performance. The length of time the battery is left standing after liquid injection affects the wetting state of the battery electrode, and too long a standing time will also lead to negative effects such as low battery production efficiency.

[0004] Currently, there are two main methods for determining the electrolyte wetting status in battery production. The first is observation, which involves disassembling the battery to observe the distribution of the electrolyte or colorants added to the electrolyte, or by weighing to determine the electrolyte absorption and wetting. The second method is performance judgment, which involves manufacturing the battery and then conducting electrical performance tests to determine the wetting effect based on the test results. However, these existing methods all have problems such as cumbersome overall operation procedures, long time consumption, and high costs. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for detecting the wettability of lithium ion battery electrolyte in view of the technical defects in the prior art.

[0006] To this end, the present invention provides a method for detecting the wettability of a lithium ion battery electrolyte, comprising the following steps:

[0007] The first step is to pre-fabricate multiple identical batteries, wherein the battery electrode groups in the multiple batteries have not yet been filled with electrolyte, and the multiple batteries are dried under the same conditions;

[0008] In the second step, multiple different electrolytes to be tested for wettability are respectively injected into one of the batteries obtained in the first step, and the electrolyte injection ports in all batteries are sealed to obtain multiple batteries injected with different electrolytes;

[0009] In the third step, the multiple batteries obtained in the second step and injected with different electrolytes are placed in a static state and then subjected to AC internal resistance tests. Specifically, for each battery, the AC internal resistance of the battery is measured in real time at a preset fixed interval and the detection time corresponding to the AC resistance is recorded;

[0010] In the fourth step, for each battery, when the AC internal resistance of the two tests before and after does not change, the detection time corresponding to the AC internal resistance of the latter test is used as the infiltration time consumed by the electrolyte injected into the battery; then, based on the infiltration time consumed by the electrolyte injected into multiple batteries, the infiltration performance of the electrolyte injected into multiple batteries is compared and judged.

[0011] Preferably, between the third step and the fourth step, the method further comprises the following steps:

[0012] For each battery, the battery's AC internal resistance is used as the vertical coordinate, and the detection time corresponding to the battery's AC resistance is used as the horizontal coordinate. A corresponding curve of the detection time and AC resistance of each battery is drawn on the same graph.

[0013] Preferably, in the third step, for each battery, the preset fixed time interval between the first test and the second test is 30 minutes; and subsequently, the preset fixed time interval between any two adjacent tests is 2 hours.

[0014] Preferably, in the third step, an AC internal resistance tester is used to test the AC internal resistance of the battery.

[0015] It can be seen from the technical solution provided by the present invention above that, compared with the prior art, the present invention provides a method for detecting the wetting performance of lithium-ion battery electrolytes. The method is scientifically designed and can quickly and accurately detect the wetting performance of different electrolytes, and compare and judge the wetting performance of different electrolytes in the same battery (for example, the relationship between the size of the wetting rate). The operation is simple, the test results are reliable, and the detection time can be significantly reduced, which has important practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A flow chart of a method for detecting the wettability of a lithium-ion battery electrolyte provided by the present invention;

[0017] Figure 2 The present invention provides a method for detecting the wettability of a lithium-ion battery electrolyte. In Example 3, a schematic diagram of the capacity retention rate of two lithium-ion batteries with different standing times when cyclically charged and discharged at 1C in a test environment of 45°C is shown. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and implementation methods.

[0019] See also Figure 1 The present invention provides a method for detecting the wettability of a lithium-ion battery electrolyte, comprising the following steps:

[0020] In the first step, multiple identical batteries are prefabricated, wherein the battery electrode groups in the multiple batteries have not yet been filled with electrolyte, and the multiple batteries are dried under the same conditions (e.g., the same drying time and drying temperature);

[0021] In the second step, multiple different electrolytes whose wettability needs to be tested are respectively injected into a battery obtained in the first step (specifically, into the battery electrode group), and the electrolyte injection ports in all batteries are sealed to obtain multiple batteries injected with different electrolytes (i.e., sample batteries);

[0022] In the third step, the multiple batteries obtained in the second step and injected with different electrolytes are placed in a static state, and then the AC internal resistance is tested respectively. Specifically, for each battery, the AC internal resistance of the battery is tested in real time at a preset fixed interval (for example, 30 minutes or 2 hours), and the detection time corresponding to the AC resistance is recorded (that is, the time from the beginning of the test to the time when the AC resistance is obtained, that is, the total static time);

[0023] Fourth, for each battery, when the AC internal resistance of the battery does not change between the two previous and subsequent tests (i.e., the AC internal resistance ACR has stabilized), the detection time corresponding to the AC internal resistance of the latter test is used as the infiltration time consumed by the electrolyte injected into the battery; then, based on the infiltration time consumed by the electrolyte injected into multiple batteries, the infiltration performance (e.g., the infiltration rate) of the electrolyte injected into multiple batteries is compared and judged.

[0024] It should be noted that the longer the electrolyte infiltration time is, the worse the infiltration performance is and the slower the infiltration rate is. Conversely, the shorter the electrolyte infiltration time is, the better the infiltration performance is and the faster the infiltration rate is.

[0025] Between the third and fourth steps, there are also steps:

[0026] For each battery, the test time (i.e., rest time) and AC resistance curve are plotted on the same graph, with the battery's AC internal resistance as the ordinate and the test time corresponding to the battery's AC resistance as the abscissa. This graph allows for intuitive comparison and assessment of the wetting performance and wetting rates of the electrolytes injected into multiple batteries at different time periods.

[0027] In the first step, the battery electrode group can be formed by laminating or winding. For example, the battery electrode group is formed by winding a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

[0028] In the third step, in terms of specific implementation, for each battery, the preset fixed time between the first test and the second test (i.e., the initial time interval) is 30 minutes; thereafter, the preset fixed time between any two adjacent tests is 2 hours, until the AC internal resistance value of the battery reaches stability (i.e., no longer changes).

[0029] In the third step, the battery's AC internal resistance is tested using an AC internal resistance tester with a test current frequency of 1000 Hz.

[0030] In the present invention, in a specific implementation, the first to fourth steps are all performed in an environment with a stable temperature (±2° C.).

[0031] Based on the above technical solution, it can be seen that the present invention has certain guiding significance for determining the standing time required for batteries after injection when different electrolytes are injected into batteries of the same structure during battery production.

[0032] In order to more clearly understand the technical solution of the present invention, the technical solution of the present invention is described below through specific embodiments.

[0033] Example 1.

[0034] The present invention provides a method for detecting the wettability of a lithium-ion battery electrolyte, which may include the following steps:

[0035] In the first step, the main materials, conductive agents, and binders are prepared according to the existing component ratio requirements to prepare positive and negative electrode slurries, and then the positive and negative electrode sheets are prepared through coating and rolling operations;

[0036] In the second step, the electrode sheets and separators are wound to form multiple electrode groups, which are then assembled into multiple identical batteries (with the same battery shell). The battery size is 60mm×220mm×112mm and the rated capacity is 172Ah.

[0037] The third step is to inject electrolyte A and electrolyte B into two batteries that have not yet been injected with electrolyte and have been dried at room temperature. After sealing with rubber stoppers, the changes in the AC internal resistance of the two batteries are monitored until the AC internal resistance ACR of the two batteries does not change.

[0038] Table 1 is a table showing the changes in the AC internal resistance of the battery of Example 1 as a function of the soaking time. It can be seen that as the soaking time of the electrolyte increases, the AC internal resistance of the battery gradually decreases. After 20 hours and 24 hours respectively, the AC internal resistance of the two batteries injected with electrolytes A and B basically stabilizes. Therefore, it is concluded that the AC internal resistance of the battery after injection can be used to indirectly characterize whether the electrolyte is completely soaked. That is, when the AC internal resistance reaches stability (i.e., unchanged), it can be considered that the pole group in the battery is completely soaked by the electrolyte. Therefore, for batteries with the same structure injected with electrolytes of different compositions and proportions, the shorter the time required for the AC internal resistance of the battery injected with a certain electrolyte to reach stability, the faster the soaking rate of the electrolyte on the pole group in the battery and the better the soaking effect.

[0039] Table 1: Changes in AC internal resistance of batteries using electrolyte A and electrolyte B as a function of standing time in Example 1.

[0040]

[0041] Example 2.

[0042] The present invention provides a method for characterizing electrolyte wettability by AC internal resistance, comprising the following steps:

[0043] In the first step, the main materials, conductive agents, and binders are prepared according to the existing component ratio requirements to prepare positive and negative electrode slurries, and then the positive and negative electrode sheets are prepared through coating and rolling operations;

[0044] In the second step, the electrode sheets and separators are wound to form multiple electrode groups, which are then assembled into multiple identical batteries (with the same battery shell). The battery size is 60mm×220mm×112mm and the rated capacity is 172Ah.

[0045] In the third step, electrolyte A is injected into two batteries that have not yet been injected with electrolyte and have been dried. After sealing with rubber stoppers, they are placed in room temperature and 45°C environments respectively, and the changes in the AC internal resistance of the battery are monitored until the AC internal resistance ACR does not change.

[0046] Table 2 shows the change in AC internal resistance of the battery in Example 2 as a function of time, when placed at room temperature and at elevated temperatures. Table 2 shows that by monitoring the change in AC internal resistance of identical batteries filled with the same electrolyte and placed at different temperatures, the effect of varying temperatures on the rate and duration of electrolyte penetration into the battery can be determined. The results indicate that elevated temperatures are more conducive to electrolyte penetration into the battery.

[0047] Therefore, it was concluded that the AC internal resistance of the battery after injection can indirectly indicate whether the electrolyte is fully infiltrated. That is, when the AC internal resistance reaches a stable state, the battery's electrode group can be considered to be fully infiltrated by the electrolyte. Therefore, the electrolyte infiltration rate and effect in the battery vary at different temperatures. Appropriately increasing the static temperature is conducive to electrolyte infiltration. In addition, in battery production, this method can be used to determine the time required for complete electrolyte infiltration under different processes, which has significant production practical significance.

[0048] Table 2: Changes in battery AC internal resistance with standing time at room temperature and high temperature.

[0049]

[0050]

[0051] Example 3.

[0052] The present invention provides a method for detecting the wettability of a lithium-ion battery electrolyte, comprising the following steps:

[0053] In the first step, the main materials, conductive agents, and binders are prepared according to the existing component ratio requirements to prepare positive and negative electrode slurries, and then the positive and negative electrode sheets are prepared through coating and rolling operations;

[0054] In the second step, the electrode sheets and separators are wound to form multiple electrode groups, which are then assembled into multiple identical batteries (with the same battery shell). The battery size is 60mm×220mm×112mm and the rated capacity is 172Ah.

[0055] The third step is to inject electrolyte B into two batteries that have not yet been injected with electrolyte and have been dried. They are marked as battery 1# and battery 2# respectively. After sealing with rubber stoppers, they are placed in room temperature environment and the changes in AC internal resistance are monitored.

[0056] In the fourth step, the 1# battery is left standing until the AC internal resistance reaches a stable state, that is, after standing for 28 hours, the subsequent processes such as formation and aging are continued; after the 2# battery is left standing for only 18 hours, the AC internal resistance has not reached a stable state, so the subsequent processes such as formation and aging are directly carried out to complete the production of 1# and 2# batteries, and the cycle life test is carried out.

[0057] Table 3 shows the changes in the AC internal resistance of the two batteries in Example 3 as a function of the standing time.

[0058] Figure 2 The results of the cycle life test on two batteries in Example 3 are as follows: Figure 2 The 45℃ in the figure is the temperature during the battery cycle life test. Figure 2It can be seen that the cycle performance of the 2# battery, which has not been fully soaked for 18 hours, is poor. However, as the standing time is extended until the AC internal resistance stabilizes, the cycle life of the 1# battery is good, indicating that the change in AC internal resistance can reflect the soaking condition of the electrolyte in the battery.

[0059] In summary, a standing time that is too short will result in poor electrolyte infiltration in the battery, resulting in poor cycle performance. Therefore, the battery's infiltration effect can be reflected by the change in the battery's AC internal resistance. At the same time, the difference in the battery's cycle performance also reflects the different degree of electrolyte infiltration.

[0060] Table 3 Changes of AC internal resistance of 1# and 2# batteries with standing time

[0061]

[0062] It should be noted that the scope of application of the present invention includes but is not limited to square, circular, polymer and soft-pack batteries.

[0063] In summary, compared with the prior art, the method for detecting the wetting performance of lithium-ion battery electrolytes provided by the present invention is scientifically designed, can quickly and accurately detect the wetting performance of different electrolytes, and compare and judge the wetting performance of different electrolytes in the same battery (for example, the relationship between the size of the wetting rates). It is simple to operate, the test results are reliable, and the detection time can be significantly reduced, which has important practical significance.

[0064] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for detecting the wettability of a lithium-ion battery electrolyte, characterized in that: The following steps are involved: The first step is to pre-fabricate multiple identical batteries, wherein the battery electrode groups in the multiple batteries have not yet been filled with electrolyte, and the multiple batteries are dried under the same conditions; In the second step, multiple different electrolytes to be tested for wettability are respectively injected into one of the batteries obtained in the first step, and the electrolyte injection ports in all batteries are sealed to obtain multiple batteries injected with different electrolytes; In the third step, the multiple batteries obtained in the second step and injected with different electrolytes are placed in a static state and then subjected to AC internal resistance tests. Specifically, for each battery, the AC internal resistance of the battery is measured in real time at a preset fixed interval and the detection time corresponding to the AC internal resistance is recorded; Step 4: For each battery, if the AC internal resistance between the two tests remains unchanged, the test time corresponding to the AC internal resistance of the latter test is used as the soaking time of the electrolyte injected into the battery. The soaking times of the electrolyte injected into the multiple batteries are then used to compare and determine the soaking performance of the electrolyte injected into the multiple batteries. Between the third and fourth steps, there are also steps: For each battery, the AC internal resistance of the battery is used as the vertical coordinate, and the detection time corresponding to the AC internal resistance of the battery is used as the horizontal coordinate. A corresponding curve of the detection time and AC internal resistance of each battery is drawn on the same graph.

2. The method for detecting the wettability of a lithium-ion battery electrolyte according to claim 1, wherein: In the third step, for each battery, the preset fixed time interval between the first test and the second test is 30 minutes; and then, the preset fixed time interval between any two adjacent tests is 2 hours.

3. The method for detecting wettability of a lithium ion battery electrolyte according to any one of claims 1 or 2, wherein: In the third step, the battery's AC internal resistance is tested using an AC internal resistance tester.

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