Method for determining liquid injection amount of high-power lithium ion battery

Abstract

The invention discloses a method for determining the liquid injection amount of a high-power lithium ion battery, relates to the technical field of batteries, and determines the liquid injection amount of the lithium ion battery by determining the liquid injection amount range and monitoring the alternating current internal resistance change after formation and aging. In addition, after the battery is subjected to multiple charging and discharging tests and the interface is stable, the alternating current internal resistance value tends to be stable, and at the moment, the electrolyte injection amount conforms to the actual use working condition of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a method for determining the electrolyte volume of a high-power lithium-ion battery. Background Technology

[0002] Determining the electrolyte injection volume is a critical process in lithium-ion battery manufacturing, directly impacting the battery's energy density, cycle life, and safety performance. High-power batteries, in particular, prioritize low internal resistance and high rate performance, making the electrolyte injection volume even more crucial. Traditional methods for determining the electrolyte injection volume rely heavily on empirical formulas and experimental trial and error, resulting in insufficient accuracy, high costs, and low efficiency. With the diversification of battery material systems and continuously increasing performance requirements, the precise control and optimization of the electrolyte injection volume has become increasingly complex and critical.

[0003] CN202310543995.5 provides a method for determining the electrolyte injection amount based on the relationship between the injection volume and internal resistance, thereby optimizing the battery manufacturing process. This method determines the final electrolyte injection amount by analyzing the change in AC internal resistance before and after electrolyte injection. However, this requires multiple injections, making the process cumbersome. Furthermore, the AC internal resistance is the resistance after the electrolyte has settled; during charging and discharging, the electrolyte is further consumed, leading to battery instability and subsequent changes in the AC internal resistance value. Therefore, considering only the internal resistance after settling differs from the battery's normal operating conditions, making it impossible to determine whether the injection volume is appropriate.

[0004] Currently, the core of existing battery electrolyte injection technology lies in improving accuracy and efficiency through methods such as porosity calculation combined with gradient experiments, disassembly and measurement of free electrolyte volume, process innovation using staged injection or high-pressure injection, and intelligent control, using real-time monitoring and equipment control. However, all of the above methods have shortcomings: gradient experiments have long testing cycles; destructive disassembly is complex to operate; and real-time monitoring requires extensive preliminary evaluation and data parameter collection. High-power batteries generally have lower positive and negative electrode compaction, larger separator porosity, and require more electrolyte, making it more difficult to determine the appropriate electrolyte injection volume. Therefore, developing a method for determining the electrolyte injection volume of high-power batteries is particularly important. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for determining the electrolyte volume of a high-power lithium-ion battery, which is applicable to various types of batteries, including ternary lithium and lithium iron phosphate batteries, and can more comprehensively and accurately determine the electrolyte volume of a high-power lithium-ion battery.

[0006] This invention is implemented as follows: a method for determining the electrolyte volume of a high-power lithium-ion battery, comprising the following steps: S1. Determine the electrolyte injection range for high-power lithium batteries: First, select an appropriate electrolyte injection coefficient based on the type of lithium battery to determine the electrolyte injection range, m=k*C*a, where k is the electrolyte injection coefficient, which is 6.5 for high-power lithium iron phosphate batteries and 3.2 for high-power ternary batteries; C is the theoretical capacity of the battery; and a is the electrolyte injection fluctuation coefficient, which is 0.8~1.3. S2. Battery electrolyte filling volume design: Within the battery electrolyte filling volume range, by adjusting the electrolyte filling fluctuation coefficient, determine the electrolyte filling volumes for three or more batteries, namely m1~m n Gradient injection is then performed; S3. Battery formation and aging: Perform formation and aging steps on the battery after electrolyte injection, and record the AC internal resistance r1 after formation and the internal resistance r2 after aging. S4. Battery Rate Cycling Test: Perform high-rate cycling on a high-power battery and record the DC internal resistance before and after the cycle. S5. Determine the optimal injection volume: Based on the injection volume and the change in AC internal resistance, select an appropriate injection fluctuation coefficient, evaluate the battery reliability based on the battery rate cycle test, and determine the optimal injection volume.

[0007] The advantages and technical effects of this invention are as follows: This invention obtains the AC internal resistance of a gradient electrolyte-filled battery after formation by testing its AC internal resistance. During aging and resting, the electrolyte inside the battery decomposes and is consumed, affecting the battery's state. Therefore, the AC internal resistance is measured again after aging, and the amount of electrolyte injected is evaluated by the change in AC internal resistance before and after aging. This invention provides a comprehensive evaluation of the actual high-rate usage conditions of high-power batteries. During high-rate charge and discharge, lithium ions need to migrate and escape rapidly. Insufficient electrolyte injection directly leads to obstruction of the ion transport path, increasing the battery's internal resistance, affecting its rate performance, and shortening its lifespan. This invention examines the change in the battery's DC internal resistance at the end of the cycle and its impact on battery performance, ensuring battery reliability. Attached Figure Description

[0008] Figure 1 Box plot of AC internal resistance change of high-power lithium-ion battery before and after aging, measured using the present invention.

[0009] Figure 2 This is a comparison chart of the AC internal resistance of a high-power lithium-ion battery before and after cycling, measured using the present invention. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0011] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a method for determining the electrolyte volume of a high-power lithium-ion battery according to the present invention.

[0012] Example 1 This embodiment takes an 11Ah lithium iron phosphate battery as an example and specifically includes the following steps: S1. Determine the electrolyte filling range for high-power lithium batteries: First, select an appropriate electrolyte filling coefficient according to the type of lithium battery to determine the battery electrolyte filling range, m=k*C*a, where k is the electrolyte filling coefficient, which is 6.5 for lithium iron phosphate batteries; C is the theoretical capacity of the battery, which is 11; a is the electrolyte filling fluctuation coefficient, which is 0.8~1.3; therefore, the electrolyte filling range m is 59.4g~85.8g; S2. Battery electrolyte injection design: Within the range of battery electrolyte injection volume, adjust the electrolyte injection fluctuation coefficient to 0.9, 1, and 1.1 to determine the electrolyte injection volumes of three batteries, namely m1=64.3g, m2=71.5g, and m3=78.7g, and carry out gradient electrolyte injection; S3. Battery formation and aging: Perform formation and aging steps on the battery after electrolyte injection, and record the AC internal resistance r1 before and after aging and the internal resistance r2 after aging. See Table 1 for details. S4. Battery Rate Cycling Test: The 11Ah lithium iron phosphate battery was subjected to 1000 cycles of 3C charge-rate cycling. The DC internal resistance test was performed by adjusting the battery to 50% SOC, allowing it to stand for 1 hour, then discharging at 0.5C (5A) for 10 seconds, followed by discharging at 3C (30A) for 10 seconds. The voltage V1 at 0.5C discharge for 10 seconds and the voltage V2 at 3C discharge for 10 seconds were recorded. The DC internal resistance r was calculated. x = Record the DC internal resistances r3 and r4 before and after the cycle.

[0013] S5. Determine the optimal injection volume: According to Table 1. Figure 1 Based on the changes in injection volume and AC internal resistance, suitable injection fluctuation coefficients α were selected as 1 and 1.1. According to the battery rate cycle test, the battery capacity retention rate was >90% after 1000 3C cycles, meeting the lifespan requirements. (See Table 2.) Figure 2 The test batteries with electrolyte injection volumes of m2 and m3 showed minimal changes in DC internal resistance before and after cycling, ensuring battery reliability. Considering battery safety and cost, the optimal electrolyte injection volume was determined to be m2.

[0014] Table 1. AC internal resistance data before and after battery aging

[0015] Table 2 DC internal resistance data before and after battery cycling

[0016] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the electrolyte volume of a high-power lithium-ion battery, characterized in that, Includes the following steps: S1. Determine the electrolyte injection range for high-power lithium batteries: First, select an appropriate electrolyte injection coefficient based on the type of lithium battery to determine the electrolyte injection range, m=k*C*a, where k is the electrolyte injection coefficient, which is 6.5 for high-power lithium iron phosphate batteries and 3.2 for high-power ternary batteries; C is the theoretical capacity of the battery; and a is the electrolyte injection fluctuation coefficient, which is 0.8~1.

3. S2. Battery electrolyte filling volume design: Within the battery electrolyte filling volume range, by adjusting the electrolyte filling fluctuation coefficient, determine the electrolyte filling volumes for three or more batteries, namely m1~m n Gradient injection is performed; S3. Battery formation and aging: Perform formation and aging steps on the battery after electrolyte injection, and record the AC internal resistance r1 after formation and the internal resistance r2 after aging. S4. Battery Rate Cycling Test: Perform high-rate cycling on a high-power battery and record the DC internal resistance before and after the cycle. S5. Determine the optimal injection volume: Based on the injection volume and the change in AC internal resistance, select an appropriate injection fluctuation coefficient, evaluate the battery reliability based on the battery rate cycle test, and determine the optimal injection volume.

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