Non-combustible lithium ion battery electrolyte and preparation method thereof

Abstract

The invention relates to the field of lithium ion batteries, in particular to a non-combustible lithium ion battery electrolyte and a preparation method thereof. The method comprises the following steps: preparing a plurality of target electrolytes; performance testing; and electrolyte preparation parameters are corrected. According to the method, the optimal electrolyte formula and injection amount are determined through the fine leakage test and the high-temperature infiltration test, the performance of the electrolyte is comprehensively evaluated, the safety and effectiveness of the electrolyte in practical application are ensured, in the high-temperature infiltration test, the standard electrolyte injection amount is adjusted in time according to the bubble condition of an electrode and an electrolyte interface, and the reliability of the electrolyte is improved. The performance change of the electrolyte can be quickly responded, the formula of the electrolyte can be optimized, the qualification of the electrolyte can be effectively judged according to the results of a leakage test and a high-temperature infiltration test, and cause analysis is carried out, so that electrolyte preparation parameters are adaptively selected, regulated and controlled, the preparation convenience is improved, the adaptability and optimization space of the electrolyte are enhanced, and the production cost is reduced. And through strict testing and parameter adjustment, the stability and reliability of the battery are ensured.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to a non-flammable lithium ion battery electrolyte and a preparation method thereof. Background Art

[0002] The electrolyte is generally composed of electrolyte lithium salt and high-purity organic solvent, and is the carrier of lithium ion migration and charge transfer. As one of the key materials of the four major liquid batteries, the electrolyte plays the role of conducting conductive ions between the positive and negative electrode materials inside the battery, ensuring the effectiveness of the internal circuit, and plays a key role in the energy density, power density, cycle life, safety performance, and wide temperature performance of the conductive ion battery. Improving the electrolyte is a key method to improve the safety of lithium-ion batteries.

[0003] Chinese Patent Publication No.: CN107293785B discloses a non-flammable lithium-ion battery electrolyte and a preparation method thereof, wherein the prepared electrolyte is composed of four components: (A) lithium salt, (B) carbonate and / or ether organic solvents, (C) trifluoropropylmethylcyclotrisiloxane flame retardant additive and (D) other functional additives. Among them, the molar concentration range of lithium salt in this electrolyte is: 0.001-2 mol / L; the mass proportion range of flame retardant additive in this electrolyte is: 0.1%-60%; the molar concentration range of other functional additives in this electrolyte is: 0.01-0.5 mol / L; the flame retardant additive is trifluoropropylmethylcyclotrisiloxane; It can be seen that in the existing electrolyte preparation method, there is a lack of precise control of the injection amount of electrolyte into the battery according to leakage test and charge and discharge test, resulting in inaccurate energy density of the battery. Summary of the invention

[0004] To this end, the present invention provides a method for preparing a non-flammable lithium-ion battery electrolyte, which is used to overcome the problem in the prior art that the electrolyte injection amount cannot be accurately controlled through leakage testing and charge and discharge testing, resulting in inaccurate battery performance evaluation data.

[0005] To achieve the above object, the present invention provides a method for preparing a non-flammable lithium-ion battery electrolyte.

[0006] Prepare corresponding target electrolytes according to several recipes;

[0007] Mixing the solvent raw materials according to a preset volume ratio to form a mixed solvent;

[0008] gradually adding lithium salt into the mixed solution to form an initial electrolyte;

[0009] Slowly adding a flame retardant to the initial electrolyte and stirring and dispersing the mixture to form a target electrolyte;

[0010] For any of the target electrolytes, the target electrolytes are respectively injected into each battery cell with a standard injection volume to perform a performance test on each of the battery cells, wherein the performance test includes a leakage test, a high temperature immersion test, and a charge and discharge test;

[0011] Obtaining corresponding charge and discharge curves and battery performance parameters according to the charge and discharge test, and determining whether to modify electrolyte preparation parameters according to the leakage test and the high-temperature immersion test;

[0012] Wherein, when performing the high-temperature infiltration test, it is determined whether to increase the standard injection volume to the first corrected injection volume according to the bubble situation at the interface between the electrode and the electrolyte, and when it is determined that there are no bubbles at the interface between the electrode and the electrolyte, a leakage test is performed, and it is determined whether the target electrolyte is qualified according to the leakage test result, and the reason is analyzed, and the electrolyte preparation parameters are corrected according to the analysis result;

[0013] The electrolyte preparation parameters include a standard injection volume and a flame retardant addition volume.

[0014] Furthermore, the battery cell is placed in a preset high temperature environment for a high temperature soaking test. During the standing period, the real-time soaking duration is recorded and the real-time soaking duration is determined according to the standard soaking duration.

[0015] If the real-time infiltration time is less than or equal to the standard infiltration time, the real-time ambient temperature difference is obtained in a preset collection period, and the standard ambient temperature difference is compared with the real-time ambient temperature difference to determine whether to perform inspection processing;

[0016] If the real-time infiltration time is longer than the standard infiltration time, the droplet to be tested is taken for infiltration test to obtain the wettability index, and the wettability of the target electrolyte is analyzed according to the wettability index. When the wettability is judged to be unqualified, the bubble situation at the interface between the electrode and the electrolyte is analyzed.

[0017] Furthermore, the high temperature soaking test includes:

[0018] Aspirating the target electrolyte with a preset sampling volume to obtain a droplet to be detected;

[0019] Add the droplet to be detected onto the electrode surface, and take a picture with a contact angle measuring instrument to identify the droplet shape and output the real-time contact angle;

[0020] Calculate the wettability index based on the real-time contact angle;

[0021] Wherein, W=cos(θ), W is the wettability index, and θ is the real-time contact angle.

[0022] Further, analyzing the wettability of the target electrolyte according to the wettability index includes:

[0023] The positive and negative values ​​of the wettability index are analyzed.

[0024] If the wettability index is a positive number, the wettability is determined to be qualified and a charge and discharge test is performed;

[0025] If the wettability index is a negative number, the wettability is judged to be unqualified.

[0026] Furthermore, when the wettability is judged to be unqualified, the bubble situation at the interface between the electrode and the electrolyte is analyzed, including:

[0027] Taking an image of the interface between the electrode and the electrolyte to obtain a real-time interface image, analyzing the real-time interface image,

[0028] If there are bubbles in the real-time interface image, increase the standard injection volume to the first corrected injection volume, and test again with the first corrected injection volume;

[0029] If there are no bubbles in the real-time interface image, perform a leak test.

[0030] Further, the leakage test includes,

[0031] Get the real-time gas flow rate and compare it with the first standard gas flow rate and the second standard gas flow rate.

[0032] When the real-time gas flow rate is less than the first standard gas flow rate, it is determined to be qualified and the charge and discharge test is performed;

[0033] When the real-time gas flow is between the first standard gas flow and the second standard gas flow, the target electrolyte is determined to be unqualified, the real-time flow rate change rate is monitored, and the reason for the unqualified target electrolyte is analyzed based on the monitoring result.

[0034] Further, monitoring the real-time flow rate change includes:

[0035] Respectively obtain the initial gas flow rate and the ending gas flow rate corresponding to the start time and the end time within the preset unit time, calculate the difference between the ending gas flow rate and the initial gas flow rate, divide the difference by the preset unit time, and obtain the real-time flow rate change rate;

[0036] The real-time flow rate change rate is compared with the standard flow rate change rate, and the reason why the target electrolyte is unqualified is analyzed based on the comparison result.

[0037] Further, according to the comparison results, the reasons why the target electrolyte is unqualified include:

[0038] When the real-time flow rate change rate is less than the standard flow rate change rate, it is determined that the standard injection volume is excessive, and the standard injection volume is reduced to the second corrected injection volume, and the test is performed again;

[0039] When the real-time flow rate change rate is greater than or equal to the standard flow rate change rate, the real-time ambient temperature difference is obtained, and the standard ambient temperature difference is compared with the real-time ambient temperature difference to analyze the temperature impact.

[0040] Further, the analysis of temperature effects includes,

[0041] When the real-time ambient temperature difference is less than the standard ambient temperature difference, the gas composition is detected, and whether the amount of flame retardant added is adjusted is determined based on the detection results;

[0042] When the real-time ambient temperature difference is greater than or equal to the standard ambient temperature difference, on-site inspection and processing shall be carried out.

[0043] Further, determining whether to adjust the standard injection volume according to the test results includes:

[0044] If the gas composition contains a type of gas, it is determined that the amount of flame retardant added is insufficient, and the amount of flame retardant added is increased to the corrected amount of flame retardant added, and the test is performed again;

[0045] If the gas composition does not contain a type of gas, it is determined that the formula of the target electrolyte is unqualified, and another target electrolyte is tested;

[0046] Wherein, Gb'=Gb×[1+(ΔTb-ΔTc) / ΔTb], Gb' is the corrected flame retardant addition amount, Gb is the flame retardant addition amount, ΔTb is the standard ambient temperature difference, and ΔTc is the real-time ambient temperature difference.

[0047] Compared with the prior art, the beneficial effect of the present invention lies in that, by setting multiple groups of electrolyte formulas and conducting precise leakage tests and high-temperature infiltration tests, the optimal electrolyte formula and injection amount are determined according to the test results, the performance of the electrolyte is comprehensively evaluated, and its safety and effectiveness in practical applications are ensured. In the high-temperature infiltration test, the standard injection amount is timely adjusted according to the bubble situation at the interface between the electrode and the electrolyte, which can quickly respond to changes in the performance of the electrolyte and optimize the electrolyte formula. Through the results of the leakage test and the high-temperature infiltration test, the qualification of the electrolyte can be effectively judged, and the cause analysis can be performed, so as to adaptively select and adjust the electrolyte preparation parameters, improve the convenience of preparation, enhance the adaptability and optimization space of the electrolyte, reduce the safety risk of the electrolyte during use through strict testing and parameter adjustment, ensure the stability and reliability of the battery, and ensure the balance between safety and performance by identifying abnormal situations and prompting timely processing, so as to achieve fast, convenient and flexible screening of qualified products in large-scale production tests and ensure that the performance of the final product meets the expected standards.

[0048] Furthermore, the wettability of the electrolyte is analyzed to accurately test the performance of the electrolyte formulation, and the method is simple and effective.

[0049] Furthermore, when it is determined that the wettability of the electrode and the electrolyte is unqualified, the bubble situation at the interface of the electrode and the electrolyte is analyzed. If it is determined that there are bubbles, it means that this situation is due to uneven distribution inside the battery due to insufficient injection of the electrolyte, and the bubbles appear. In this case, the standard injection amount is adjusted according to the real-time contact angle to optimize the injection amount. If it is determined that there are no bubbles, it means that the injection amount of the electrolyte is sufficient, but excessive injection of the electrolyte will also lead to reduced battery performance. In this case, a leakage test is performed to accurately analyze whether the electrolyte is qualified, analyze the reasons, and adaptively adjust the electrolyte preparation parameters to continuously optimize the electrolyte formula and improve the safety of non-flammable lithium-ion battery electrolytes.

[0050] Furthermore, when the real-time gas flow rate is less than the first standard gas flow rate, it indicates that no leakage gas is generated, and the formula is judged to be qualified, and the charge and discharge test is continued to obtain the battery performance parameters. The second standard gas flow rate indicates the maximum leakage flow rate allowed under extreme conditions. When the real-time gas flow rate is greater than the second standard gas flow rate, it indicates that the battery cell under the formula has serious leakage, and it is directly judged as unqualified, and a prompt instruction to isolate and cool the battery cell is sent. The high-temperature static test is continued on the next target electrolyte. When the real-time gas flow rate is between the first standard gas flow rate and the second standard gas flow rate, the cause of the failure is further analyzed to adaptively optimize the preparation parameters and improve the efficiency of electrolyte preparation.

[0051] Furthermore, by monitoring the ambient temperature, when it is determined that the real-time ambient temperature difference is less than the standard ambient temperature difference, it indicates that the temperature fluctuation is not large. The reason for the sudden increase in gas generation is that the gas component generated by the electrolyte is harmful gas, which may be due to insufficient flame retardant or decomposition of the electrolyte. By analyzing the components of the generated gas, when it is determined that the real-time ambient temperature difference is greater than or equal to the standard ambient temperature difference, it indicates that the temperature fluctuation is large. This is because the unstable components in the electrolyte decompose rapidly under specific conditions, that is, high temperature accelerates the degradation reaction of the electrolyte, causing the electrolyte to evaporate rapidly and generate a large amount of gas. By conducting on-site inspections and processing, temperature control failure can be avoided to ensure the safety and accuracy of the test.

[0052] Furthermore, by analyzing the gas composition, if it is determined that the gas composition contains harmful gases, indicating that the gas generation is related to insufficient flame retardancy, then an appropriate amount of flame retardant is added to the current electrolyte formula and the test is performed again. When it is determined that the gas composition contains unstable and unpredictable components, the formula of the target electrolyte is determined to be unqualified, and another target electrolyte is tested to screen more stable solvents and salts, reduce highly reactive components, and ensure the reliability and effectiveness of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a schematic diagram of a process for preparing a non-flammable lithium-ion battery electrolyte according to an embodiment of the present invention;

[0054] Figure 2 A schematic diagram of a process for preparing a target electrolyte according to an embodiment of the present invention;

[0055] Figure 3 A schematic diagram of a process for performing a high temperature soaking test according to an embodiment of the present invention;

[0056] Figure 4 The figure is a flow chart of monitoring the real-time flow rate change according to an embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0058] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0059] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0060] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0061] See also Figure 1 and Figure 2 As shown, Figure 1 Schematic diagram of a process for preparing a non-flammable lithium-ion battery electrolyte according to an embodiment of the present invention. Figure 2 The present invention provides a method for preparing a non-flammable lithium-ion battery electrolyte, comprising: step S1, preparing a target electrolyte; step S101, solvent blending; step S102, adding a lithium salt; step S103, adding a flame retardant; step S2, performance testing; step S3, parameter optimization; wherein,

[0062] Step S1, preparing corresponding target electrolytes according to several recipes;

[0063] Step S101, mixing solvent raw materials according to a preset volume ratio to form a mixed solvent;

[0064] Step S102, gradually adding lithium salt into the mixed solution to form an initial electrolyte;

[0065] Step S103, slowly adding the flame retardant into the initial electrolyte and stirring and dispersing the mixture to form a target electrolyte;

[0066] Step S2, for any of the target electrolytes, injecting the target electrolyte into each battery cell with a standard injection volume to perform a performance test on each battery cell, wherein the performance test includes a leakage test, a high temperature immersion test, and a charge and discharge test;

[0067] Step S3, obtaining corresponding charge and discharge curves and battery performance parameters according to the charge and discharge test, and determining whether to modify electrolyte preparation parameters according to the leakage test and the high-temperature immersion test;

[0068] Wherein, when performing the high-temperature infiltration test, it is determined whether to increase the standard injection volume to the first corrected injection volume according to the bubble situation at the interface between the electrode and the electrolyte, and when it is determined that there are no bubbles at the interface between the electrode and the electrolyte, a leakage test is performed, and it is determined whether the target electrolyte is qualified according to the leakage test result, and the reason is analyzed, and the electrolyte preparation parameters are corrected according to the analysis result;

[0069] The electrolyte preparation parameters include a standard injection volume and a flame retardant addition volume.

[0070] In this embodiment, multiple groups of electrolyte formulas are set, and detailed leakage tests and high-temperature infiltration tests are performed. According to the test results, the optimal electrolyte formula and injection amount are determined, the performance of the electrolyte is comprehensively evaluated, and its safety and effectiveness in practical applications are ensured. In the high-temperature infiltration test, the standard injection amount is adjusted in time according to the bubble situation at the interface between the electrode and the electrolyte, which can quickly respond to changes in the performance of the electrolyte and optimize the electrolyte formula. Through the results of the leakage test and the high-temperature infiltration test, the qualification of the electrolyte can be effectively judged, and the cause analysis can be performed, so as to adaptively select and adjust the electrolyte preparation parameters, improve the convenience of preparation, enhance the adaptability and optimization space of the electrolyte, reduce the safety risk of the electrolyte during use through strict testing and parameter adjustment, ensure the stability and reliability of the battery, and ensure the balance between safety and performance by identifying abnormal situations and prompting them in time, so as to achieve fast, convenient and flexible screening of qualified products in large-scale production tests and ensure that the performance of the final product meets the expected standards.

[0071] Specifically, the battery cell is placed in a preset high temperature environment for a high temperature soaking test. During the standing period, the real-time soaking duration is recorded and the real-time soaking duration is determined according to the standard soaking duration.

[0072] If the real-time infiltration time is less than or equal to the standard infiltration time, the real-time ambient temperature difference is obtained in a preset collection period, and the standard ambient temperature difference is compared with the real-time ambient temperature difference to determine whether to perform inspection processing;

[0073] If the real-time infiltration time is longer than the standard infiltration time, the droplet to be tested is taken for infiltration test to obtain the wettability index, and the wettability of the target electrolyte is analyzed according to the wettability index. When the wettability is judged to be unqualified, the bubble situation at the interface between the electrode and the electrolyte is analyzed.

[0074] The standard soaking time set in this embodiment is 24 hours. During the standing process, the temperature fluctuation value is monitored in real time to avoid inaccurate testing caused by temperature fluctuations. By setting the standard soaking time, sufficient soaking of the electrolyte is guaranteed. As the soaking time increases, the discharge rate performance is better. At the same time, excessive soaking time is avoided to save testing time. When the standard soaking time is reached, a high-temperature soaking test is performed to accurately obtain the wettability data of the electrode and the electrolyte by measuring the contact angle, so as to perform more detailed safety tests on the battery cells.

[0075] Specifically, comparing the standard ambient temperature difference with the real-time ambient temperature difference includes,

[0076] When the real-time ambient temperature difference is less than the standard ambient temperature difference, no on-site inspection will be carried out;

[0077] When the real-time ambient temperature difference is greater than or equal to the standard ambient temperature difference, conduct on-site inspection and processing;

[0078] By regularly analyzing the temperature changes of the battery cells while they are stationary at high temperatures, the temperature is strictly controlled during the test to ensure the reliability and effectiveness of the test.

[0079] See also Figure 3 As shown, it is a schematic diagram of the process of performing a high temperature wetting test according to an embodiment of the present invention;

[0080] Specifically, the high temperature soaking test includes:

[0081] Step S301, aspirating the target electrolyte with a preset sampling volume to obtain a droplet to be detected;

[0082] Step S302, adding the liquid drop to be detected onto the electrode surface, and taking pictures with a contact angle measuring instrument to identify the shape of the liquid drop and output a real-time contact angle;

[0083] Step S303, calculating the wettability index according to the real-time contact angle;

[0084] Wherein, W=cos(θ), W is the wettability index, and θ is the real-time contact angle.

[0085] The contact angle measuring instrument in this embodiment is an optical contact angle measuring instrument, which is equipped with a high-resolution camera and software, and can accurately measure the contact angle formed by a liquid drop on a solid surface. The drop to be tested is evenly dropped on the electrode surface using a micro-syringe. After the drop is stably formed, the camera of the contact angle measuring instrument is used to capture images of the drop and the electrode surface. The software will automatically identify the shape of the drop and calculate the contact angle. The unit of the contact angle is degree, which represents the angle between the drop and the electrode surface. When θ<90°, W is a positive value, indicating good wettability. When θ>90°, W is a negative value, indicating poor wettability.

[0086] Specifically, analyzing the wettability of the target electrolyte according to the wettability index includes:

[0087] The positive and negative values ​​of the wettability index are analyzed.

[0088] If the wettability index is a positive number, the wettability is determined to be qualified and a charge and discharge test is performed;

[0089] If the wettability index is a negative number, the wettability is judged to be unqualified.

[0090] The wettability of the electrolyte is analyzed to accurately test the performance of the electrolyte formula, and the method is simple and effective.

[0091] Specifically, when the wettability is judged to be unqualified, the bubble situation at the interface between the electrode and the electrolyte is analyzed, including:

[0092] Taking an image of the interface between the electrode and the electrolyte to obtain a real-time interface image, analyzing the real-time interface image,

[0093] If there are bubbles in the real-time interface image, increase the standard injection volume to the first corrected injection volume, and test again with the first corrected injection volume;

[0094] If there are no bubbles in the real-time interface image, perform a leak test;

[0095] Among them, Rb1'=min{Rb×[1+(θ-90°) / θ], Rbmax}, Rbmax=A×3.8, A is the rated capacity of the battery cell, Rbmax is the maximum value of the standard injection volume of the battery cell, Rb1' is the first corrected injection volume, Rb is the standard injection volume, and θ is the real-time contact angle.

[0096] In this embodiment, a threshold segmentation method is used to extract bubble features from real-time interface images, that is, the bubble edges are segmented by a watershed algorithm, which compares the maximum grayscale value to a peak and the minimum grayscale value to a valley, and realizes areas separated by peaks according to different grayscale values. Superimposed bubbles can be processed. At the same time, in order to avoid over-segmentation by segmenting the noise into small basins when the image has more noise and texture, limited contrast adaptive histogram equalization is used before segmentation to perform preprocessing operations on the enhanced image, so as to improve the contrast of the image, avoid amplification of image noise, and improve the accuracy of bubble recognition and processing.

[0097] The standard injection amount in this embodiment is the amount of electrolyte injected into the battery for the first time during the battery production process. The proportional relationship between the standard injection amount and the rated capacity of the battery cell is 3.2 grams per ampere hour to 3.8 grams per ampere hour (g / Ah). The proportional range allows a certain degree of flexibility, but it is also necessary to adapt to batteries of different types and uses to provide a more accurate standard injection amount. The standard injection amount is calculated by using a proportional relationship of 3.5 grams per ampere hour, that is, the standard injection amount is calculated according to the rated capacity of the battery cell. For example, for a battery cell with a rated capacity of 2Ah, the standard injection amount is set to 7g, and the standard injection amount is fine-tuned by performing detailed performance tests on the battery cell to obtain a more accurate electrolyte injection amount to ensure optimal battery performance and safety and reliability.

[0098] When the wettability of the electrode and the electrolyte is judged to be unqualified, the bubble situation at the interface of the electrode and the electrolyte is analyzed. If it is judged that there are bubbles, it means that this situation is due to the uneven distribution of the electrolyte inside the battery due to insufficient injection of the electrolyte. In this case, the standard injection amount is adjusted according to the real-time contact angle to optimize the injection amount. If it is judged that there are no bubbles, it means that the injection amount of the electrolyte is sufficient, but the excessive injection amount of the electrolyte will also lead to reduced battery performance. In this case, a leakage test is performed to accurately analyze whether the electrolyte is qualified, analyze the reasons, and adaptively adjust the electrolyte preparation parameters to continuously optimize the electrolyte formula and improve the safety of non-flammable lithium-ion battery electrolytes.

[0099] Specifically, the leakage test includes:

[0100] Get the real-time gas flow rate and compare it with the first standard gas flow rate and the second standard gas flow rate.

[0101] When the real-time gas flow rate is less than the first standard gas flow rate, it is determined to be qualified and the charge and discharge test is performed;

[0102] When the real-time gas flow rate is between the first standard gas flow rate and the second standard gas flow rate, the target electrolyte is determined to be unqualified, the real-time flow rate change rate is monitored, and the reason why the target electrolyte is unqualified is analyzed according to the monitoring result;

[0103] When the real-time gas flow rate is greater than the second standard gas flow rate, the formulation of the target electrolyte is determined to be unqualified, and a prompt instruction to isolate and cool the battery cell is sent, and another target electrolyte is tested.

[0104] In the leakage test of this embodiment, the flow rate of the leaking gas is detected in a closed high-temperature environment by a pressure sensor to provide effective real-time monitoring and evaluation. A qualified battery cell is placed in a closed high-temperature environment under the same conditions in advance to obtain an initial static pressure value through the pressure sensor. In the actual test process, the real-time pressure difference is calculated according to the initial static pressure value and the real-time static pressure value, and the first standard gas flow is calculated according to the real-time pressure difference and the flow constant; the first standard gas flow represents a qualified battery cell, that is, a gas flow detected in a closed high-temperature environment for a battery cell that is considered to be leaking, and the second standard gas flow represents the maximum leakage flow allowed under extreme conditions. The second standard gas flow is greater than the first standard gas flow. The second standard gas flow can be set to 1.5L / min, indicating that under extreme conditions, the gas leakage flow should not exceed this value to prevent potential safety risks. Qb1 is 0.5L / min;

[0105] Wherein, Qb1=k×ΔP, Qb1 is the first standard gas flow rate, ΔP is the real-time pressure difference, k is the flow constant, k is 0.005L / (min·Pa);

[0106] The k value in this embodiment is related to the characteristics of the device and is obtained through experimental calibration, that is, in a closed high-temperature environment under the same conditions, a gas source is connected to fill the closed high-temperature environment with test gas, and the gas flow rate is gradually increased by adjusting the flow valve of the gas source. At each set flow rate Q', the corresponding pressure value is recorded and the corresponding pressure difference ΔP' is calculated. A scatter plot is drawn with the flow rate as the horizontal axis and the pressure difference as the vertical axis, and a linear fit is performed to fit the relationship between the flow rate and the pressure difference: Q'=k·ΔP', that is, the flow constant k is determined by the slope of the linear regression; the test gas is air, nitrogen, etc.; the flow rate is directly read by a flow meter.

[0107] When the real-time gas flow rate is less than the first standard gas flow rate, it indicates that no leakage gas is generated, and the formula is judged to be qualified. The charge and discharge test is continued to obtain the battery performance parameters. The second standard gas flow rate indicates the maximum leakage flow rate allowed under extreme conditions. When the real-time gas flow rate is greater than the second standard gas flow rate, it indicates that the battery cell under the formula has serious leakage, and it is directly judged to be unqualified, and a prompt instruction to isolate and cool the battery cell is sent. The high-temperature static test is continued on the next target electrolyte. When the real-time gas flow rate is between the first standard gas flow rate and the second standard gas flow rate, the cause of the failure is further analyzed to adaptively optimize the preparation parameters and improve the efficiency of electrolyte preparation.

[0108] See also Figure 4 As shown, it is a schematic diagram of a process of monitoring the real-time flow rate change rate according to an embodiment of the present invention;

[0109] Specifically, monitoring the real-time traffic change rate includes:

[0110] Step S311, respectively obtaining the initial gas flow rate and the ending gas flow rate corresponding to the start time and the end time within the preset unit time length;

[0111] Step S312, calculating the difference between the end gas flow rate and the initial gas flow rate, dividing the difference by a preset unit time length, and obtaining a real-time flow rate change rate;

[0112] Step S313, comparing the real-time flow rate change rate with the standard flow rate change rate, and analyzing the reason why the target electrolyte is unqualified according to the comparison result.

[0113] In this embodiment, the preset unit time length is set to 10s. By comparing the real-time flow rate change rate with the standard flow rate change rate, the reason for the electrolyte failure is deeply analyzed according to the gas generation situation. When it is determined that the real-time flow rate change rate is less than the standard flow rate change rate, it means that the gas generation is steadily increasing. This is caused by the excessive standard injection amount. The excessive electrolyte cannot be completely absorbed and bound, thereby generating a decomposition reaction inside the battery to generate gas. When it is determined that the real-time flow rate change rate is greater than or equal to the standard flow rate change rate, it means that the gas generation suddenly increases. This may be due to the presence of unstable components in the electrolyte. These components may decompose rapidly under specific conditions to generate a large amount of gas, and this sudden gas release may be accompanied by the generation of heat, which in turn causes the temperature to accelerate the degradation reaction of the electrolyte, resulting in accelerated gas generation, thereby increasing the risk of thermal runaway of the battery. Therefore, by monitoring the ambient temperature, it is determined whether the response temperature remains effectively controlled, and gas changes caused by temperature fluctuations are eliminated to ensure the validity and reliability of the detection results.

[0114] Specifically, according to the comparison results, the reasons why the target electrolyte is unqualified include:

[0115] When the real-time flow rate change rate is less than the standard flow rate change rate, it is determined that the standard injection volume is excessive, and the standard injection volume is reduced to the second corrected injection volume, and the test is performed again;

[0116] When the real-time flow rate change rate is greater than or equal to the standard flow rate change rate, the real-time ambient temperature difference is obtained, and the standard ambient temperature difference is compared with the real-time ambient temperature difference to analyze the temperature impact;

[0117] Among them, Rb2'=max{Rb×[1-(Vb-Vs) / Vb],Rbmin}, Rbmin=A×3.2, A is the rated capacity of the battery cell, Rbmin is the minimum value of the standard filling amount of the battery cell, Rb2' is the second corrected filling amount, Rb is the standard filling amount, Vb is the standard flow change rate, and Vs is the real-time flow change rate.

[0118] In this embodiment, the standard flow rate change rate is set to 1.2 L / min and is adjusted according to actual safety standards.

[0119] Specifically, analyzing the temperature impact includes,

[0120] When the real-time ambient temperature difference is less than the standard ambient temperature difference, the gas composition is detected, and whether the amount of flame retardant added is adjusted is determined based on the detection results;

[0121] When the real-time ambient temperature difference is greater than or equal to the standard ambient temperature difference, conduct on-site inspection and processing;

[0122] The standard ambient temperature difference set in this embodiment is the difference between the actual temperature and the standard temperature. The standard temperature is set within the range of 60°C-80°C. The standard ambient temperature difference is set to 2°C according to the safety requirements.

[0123] By monitoring the ambient temperature, when it is determined that the real-time ambient temperature difference is less than the standard ambient temperature difference, it means that the temperature fluctuation is not large. The reason for the sudden increase in gas generation is that the gas component generated by the electrolyte is harmful gas, which may be insufficient flame retardant or electrolyte decomposition. By analyzing the generated gas components, when it is determined that the real-time ambient temperature difference is greater than or equal to the standard ambient temperature difference, it means that the temperature fluctuation is large. This is because the unstable components in the electrolyte decompose rapidly under specific conditions, that is, high temperature accelerates the degradation reaction of the electrolyte, causing the electrolyte to evaporate rapidly and generate a large amount of gas. Through on-site inspection and processing, temperature control failure is avoided to ensure the safety and accuracy of the test.

[0124] Specifically, whether to adjust the standard injection volume according to the test results includes:

[0125] If the gas composition contains a type of gas, it is determined that the amount of flame retardant added is insufficient, and the amount of flame retardant added is increased to the corrected amount of flame retardant added, and the test is performed again;

[0126] If the gas composition does not contain a type of gas, it is determined that the formula of the target electrolyte is unqualified, and another target electrolyte is tested;

[0127] Wherein, Gb'=Gb×[1+(ΔTb-ΔTc) / ΔTb], Gb' is the amount of modified flame retardant added, Gb is the amount of flame retardant added, ΔTb is the standard ambient temperature difference, and ΔTc is the real-time ambient temperature difference;

[0128] In this embodiment, one type of gas is a stable, predictable harmful gas, such as hydrogen fluoride and ammonia;

[0129] By analyzing the gas composition, if it is determined that the gas composition contains harmful gases, it means that the gas generation is related to insufficient flame retardancy. In this case, an appropriate amount of flame retardant is added to the current electrolyte formula and the test is performed again. When it is determined that the gas composition contains unstable and unpredictable components, the formula of the target electrolyte is determined to be unqualified, and another target electrolyte is tested to screen more stable solvents and salts, reduce highly reactive components, and ensure the reliability and effectiveness of the test.

[0130] Specifically, the charge and discharge test includes:

[0131] Generate charge and discharge curves, including voltage-time graphs and capacity-time graphs;

[0132] Obtain the integral of current and time during the discharge process to obtain the discharge capacity of the battery;

[0133] Calculate the energy density of the battery based on its voltage and mass;

[0134] Wherein, the battery performance parameters include discharge capacity and energy density;

[0135] Gravimetric energy density = (battery rated capacity × battery average operating voltage) / battery mass.

[0136] The battery is charged and discharged to evaluate its performance, stability and cycle life. The battery performance parameters are calculated to gradually screen out the target energy density based on the composition and ratio of the electrolyte.

[0137] Specifically, in Example 1, the electrolyte formula is: LiPF 6 The concentration is 1M, the preset volume ratio of the mixed solvent is 70:30 (EC:DMC), LiPF 6 : The mixed solvent is 3:7, the flame retardant is diammonium hydrogen phosphate, and the amount of flame retardant added is 5% of the mixed solvent;

[0138] The measured energy density is 150Wh / kg.

[0139] Example 2, LiPF 6 The concentration is 1.5M, the preset volume ratio of the mixed solvent is 50:50 (EC:DMC), LiPF 6 : The mixed solvent is 1:8, the flame retardant is diammonium hydrogen phosphate, and the amount of flame retardant added is 3% of the mixed solvent;

[0140] The measured energy density is 180Wh / kg.

[0141] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

[0142] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a non-flammable lithium-ion battery electrolyte, characterized in that: include, Prepare corresponding target electrolytes according to several recipes; Mixing the solvent raw materials according to a preset volume ratio to form a mixed solvent; gradually adding lithium salt into the mixed solution to form an initial electrolyte; Slowly adding a flame retardant to the initial electrolyte and stirring and dispersing the mixture to form a target electrolyte; For any of the target electrolytes, the target electrolytes are respectively injected into each battery cell with a standard injection volume to perform a performance test on each of the battery cells, wherein the performance test includes a leakage test, a high temperature immersion test, and a charge and discharge test; Obtaining corresponding charge and discharge curves and battery performance parameters according to the charge and discharge test, and determining whether to modify electrolyte preparation parameters according to the leakage test and the high-temperature immersion test; Wherein, when performing the high-temperature infiltration test, it is determined whether to increase the standard injection volume to the first corrected injection volume according to the bubble situation at the interface between the electrode and the electrolyte, and when it is determined that there are no bubbles at the interface between the electrode and the electrolyte, a leakage test is performed, and it is determined whether the target electrolyte is qualified according to the leakage test result, and the reason is analyzed, and the electrolyte preparation parameters are corrected according to the analysis result; The electrolyte preparation parameters include a standard injection volume and a flame retardant addition volume.

2. The method for preparing a non-flammable lithium-ion battery electrolyte according to claim 1, characterized in that: The battery cell is placed in a preset high temperature environment for a high temperature soaking test. During the standing period, the real-time soaking duration is recorded and the real-time soaking duration is determined according to the standard soaking duration. If the real-time infiltration time is less than or equal to the standard infiltration time, the real-time ambient temperature difference is obtained in a preset collection period, and the standard ambient temperature difference is compared with the real-time ambient temperature difference to determine whether to perform inspection processing; If the real-time infiltration time is longer than the standard infiltration time, the droplet to be tested is taken for infiltration test to obtain the wettability index, and the wettability of the target electrolyte is analyzed according to the wettability index. When the wettability is judged to be unqualified, the bubble situation at the interface between the electrode and the electrolyte is analyzed.

3. The method for preparing a non-flammable lithium-ion battery electrolyte according to claim 2, characterized in that: The high temperature soaking test includes: Aspirating the target electrolyte with a preset sampling volume to obtain a droplet to be detected; Add the droplet to be detected onto the electrode surface, and take a picture with a contact angle measuring instrument to identify the droplet shape and output the real-time contact angle; Calculate the wettability index based on the real-time contact angle; Wherein, W=cos(θ), W is the wettability index, and θ is the real-time contact angle.

4. The method for preparing a non-flammable lithium-ion battery electrolyte according to claim 2, characterized in that: Analyzing the wettability of the target electrolyte according to the wettability index includes: The positive and negative values ​​of the wettability index are analyzed. If the wettability index is a positive number, the wettability is determined to be qualified and a charge and discharge test is performed; If the wettability index is a negative number, the wettability is judged to be unqualified.

5. The method for preparing a non-flammable lithium-ion battery electrolyte according to claim 4, characterized in that: When the wettability is judged to be unqualified, the bubble situation at the interface between the electrode and the electrolyte is analyzed, including: Taking an image of the interface between the electrode and the electrolyte to obtain a real-time interface image, analyzing the real-time interface image, If there are bubbles in the real-time interface image, increase the standard injection volume to the first corrected injection volume, and test again with the first corrected injection volume; If there are no bubbles in the real-time interface image, perform a leak test.

6. The method for preparing a non-flammable lithium-ion battery electrolyte according to claim 5, characterized in that: The leak test includes, Get the real-time gas flow rate and compare it with the first standard gas flow rate and the second standard gas flow rate. When the real-time gas flow rate is less than the first standard gas flow rate, it is determined to be qualified and the charge and discharge test is performed; When the real-time gas flow is between the first standard gas flow and the second standard gas flow, the target electrolyte is determined to be unqualified, the real-time flow rate change rate is monitored, and the reason for the unqualified target electrolyte is analyzed based on the monitoring result.

7. The method for preparing a non-flammable lithium-ion battery electrolyte according to claim 6, characterized in that: Monitoring of real-time traffic change rate includes: Respectively obtain the initial gas flow rate and the ending gas flow rate corresponding to the start time and the end time within the preset unit time, calculate the difference between the ending gas flow rate and the initial gas flow rate, divide the difference by the preset unit time, and obtain the real-time flow rate change rate; The real-time flow rate change rate is compared with the standard flow rate change rate, and the reason why the target electrolyte is unqualified is analyzed based on the comparison result.

8. The method for preparing a non-flammable lithium-ion battery electrolyte according to claim 7, characterized in that: According to the comparison results, the reasons why the target electrolyte is unqualified include: When the real-time flow rate change rate is less than the standard flow rate change rate, it is determined that the standard injection volume is excessive, and the standard injection volume is reduced to the second corrected injection volume, and the test is performed again; When the real-time flow rate change rate is greater than or equal to the standard flow rate change rate, the real-time ambient temperature difference is obtained, and the standard ambient temperature difference is compared with the real-time ambient temperature difference to analyze the temperature impact.

9. The method for preparing a non-flammable lithium-ion battery electrolyte according to claim 8, characterized in that: Analysis of temperature effects includes, When the real-time ambient temperature difference is less than the standard ambient temperature difference, the gas composition is detected, and whether the amount of flame retardant added is adjusted is determined based on the detection results; When the real-time ambient temperature difference is greater than or equal to the standard ambient temperature difference, on-site inspection and processing shall be carried out.

10. The method for preparing a non-flammable lithium-ion battery electrolyte according to claim 9, characterized in that: Determine whether to adjust the standard injection volume based on the test results, including: If the gas composition contains a type of gas, it is determined that the amount of flame retardant added is insufficient, and the amount of flame retardant added is increased to the corrected amount of flame retardant added, and the test is performed again; If the gas composition does not contain a type of gas, it is determined that the formula of the target electrolyte is unqualified, and another target electrolyte is tested; Wherein, Gb'=Gb×[1+(ΔTb-ΔTc) / ΔTb], Gb' is the corrected flame retardant addition amount, Gb is the flame retardant addition amount, ΔTb is the standard ambient temperature difference, and ΔTc is the real-time ambient temperature difference.

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