Method for detecting conductivity and concentration of local electrolyte in battery and application of method

Abstract

The invention relates to the technical field of batteries, and discloses a method for detecting local electrolyte concentration and conductivity in a battery, which comprises the following steps: providing a test battery, the test battery comprises a battery body and a microelectrode positioned at a to-be-detected part in the battery body, and the volume ratio of the electrode of the battery body to the microelectrode is at least 100: 1; the surface of each microelectrode is provided with a pore structure capable of allowing electrolyte to enter; and testing the concentration and the conductivity of the electrolyte entering the pore structure by adopting an impedance spectroscopy detection method, or testing the concentration and the conductivity of the electrolyte entering the pore structure by adopting a single-point frequency testing method. According to the method, the local electrolyte can be detected, the uniformity of the electrolyte in the battery can be known, and the change of the conductivity of the electrolyte of the battery can also be known; the method can be used for knowing the electrolyte impedance change trend and the lithium salt consumption condition in the battery aging process. According to the method, the battery is not disassembled, and the test process is simple and efficient.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and more particularly, to a method for detecting the local electrolyte concentration in a battery and its application. Background Art

[0002] Lithium-ion batteries can experience performance degradation during long-term use and rapid charging, which is usually related to internal chemical and physical changes. Understanding and mitigating these aging mechanisms is crucial for improving the battery life. As a key component of lithium-ion batteries, the electrolyte affects the electrochemical performance and thermal stability of the battery. Compared with small-sized batteries, large-sized batteries (such as those used in electric vehicles) face greater challenges, including uneven internal temperature and pressure distribution, and uneven electrolyte movement. This phenomenon may lead to an uneven chemical environment inside the battery.

[0003] In high-electrolyte-volume batteries, the electrolyte movement caused by the volume change of the active material can form a significant lithium salt concentration gradient inside the battery, resulting in rapid battery capacity decay and increased internal resistance. The relaxation of this lithium salt concentration gradient often takes several weeks or even months. It has been reported that if the battery rests for several weeks to several months after cycling, both cylindrical and prismatic batteries can recover a large part of the significantly rapid capacity loss. The recovered capacity ranges from 8% to 30% of the total battery capacity, and is usually accompanied by a significant reduction in battery resistance.

[0004] Currently, there are methods for detecting the electrolyte concentration in a battery, such as computer tomography (CT) testing, ion chromatography, and liquid chromatography-mass spectrometry (LC-MS) testing; another example is a method for detecting the lithium salt content in a lithium-ion battery electrolyte disclosed in patent document CN201610294724.0, a method for detecting the lithium salt content in a lithium-ion battery electrolyte disclosed in patent document CN201711313440.2, and methods such as nuclear magnetic resonance (NMR), infrared spectroscopy, and Raman spectroscopy are also often used in papers to obtain the lithium salt concentration.

[0005] The above methods all have certain limitations, such as:

[0006] 1. Only the average electrolyte concentration of the entire battery can be obtained, and local information cannot be obtained;

[0007] 2. Only disassembly testing can be performed, and the damage to the battery is irreversible;

[0008] 3. The equipment is relatively high-end and the testing cost is extremely high. Only a simpler and more efficient method can collect sufficient information based on daily running vehicles to provide effective information for the design and improvement of the battery system and electrolyte.

[0009] In view of this, the present invention is specifically proposed. Summary of the Invention

[0010] The object of the present invention is to provide a method for detecting the local electrolyte concentration in a battery and its application.

[0011] The present invention is implemented as follows:

[0012] In a first aspect, the present invention provides a method for detecting the local electrolyte conductivity in a battery, including:

[0013] Providing a test battery, the test battery includes a battery body and a microelectrode located at a part to be detected in the battery body, the volume ratio of the electrode of the battery body to the microelectrode is at least 100:1, and the volume of the microelectrode is 0.5 - 1000 mm 3 ; each microelectrode surface has a pore structure that can allow the electrolyte to enter;

[0014] Applying a first voltage perturbation to the microelectrode - electrode, testing the impedance in the range of 10 Hz to 200 kHz, and using the blocking electrode pair of the transmission line model to fit the obtained impedance data to obtain the conductivity of the electrolyte; the first voltage perturbation value is a voltage value in the range of 5 - 50 mv;

[0015] Alternatively, applying a second voltage perturbation to the microelectrode - electrode, testing the resistance at a first frequency, and obtaining the conductivity of the electrolyte according to the resistance value; the second voltage perturbation value is a voltage value in the range of 5 - 50 mv, and the first frequency is a frequency value in the range of 50 - 1000 Hz;

[0016] Alternatively, applying a third voltage perturbation to the microelectrode - electrode, testing the impedance or capacitance at a second frequency, and obtaining the conductivity of the electrolyte according to the impedance or the capacitance; the third voltage perturbation value is a voltage value in the range of 5 - 50 mv, and the second frequency is a frequency value in the range of 50 - 1000 Hz.

[0017] In a second aspect, an embodiment of the present invention provides a method for detecting the local electrolyte concentration in a battery, including:

[0018] Providing a test battery, the test battery includes a battery body and a microelectrode located at a part to be detected in the battery body, the volume ratio of the electrode of the battery body to the microelectrode is at least 100:1; each microelectrode surface has a pore structure that can allow the electrolyte to enter;

[0019] Adopting an impedance spectrum detection method to test the concentration of the electrolyte entering the pore structure:

[0020] Pre - obtaining a first standard curve, the first standard curve is: a standard curve of the relationship between conductivity or resistance and the concentration of the electrolyte; the method for obtaining the first standard curve is:

[0021] Apply a first voltage perturbation to the microelectrode - electrode at multiple known different concentrations, measure the impedance in the range of 10 Hz to 200 kHz, and use the blocking electrode of the transmission line model to fit the obtained impedance data to obtain the conductivity or resistance of the electrolyte, and plot the standard curve of the relationship between conductivity or resistance and the concentration of the electrolyte;

[0022] At an unknown concentration, apply a first voltage perturbation to the microelectrode - electrode, measure the impedance in the range of 10 Hz to 200 kHz, use the blocking electrode of the transmission line model to fit the obtained impedance data to obtain the conductivity or resistance of the electrolyte, and substitute the conductivity or resistance into the first standard curve to obtain the local concentration of the unknown electrolyte;

[0023] The value of the first voltage perturbation is a voltage value in the range of 5 - 50 mV;

[0024] Alternatively, use the single - point frequency measurement method to measure the concentration of the electrolyte entering the pore structure:

[0025] Pre - obtain a second standard curve, where the second standard curve is the standard curve of the relationship between resistance and the concentration of the electrolyte; the method for obtaining the second standard curve is:

[0026] At multiple known different concentrations, apply a second voltage perturbation to the microelectrode - electrode respectively, measure the resistance at the first frequency, and plot the standard curve of the relationship between the electrolyte concentration and the resistance according to the measured multiple resistances;

[0027] At an unknown concentration, apply a second voltage perturbation to the microelectrode - electrode, measure the resistance at the first frequency, and substitute the resistance into the second standard curve to obtain the local concentration of the unknown electrolyte;

[0028] The value of the second voltage perturbation is a voltage value in the range of 5 - 50 mV, and the first frequency is a frequency value in the range of 50 - 1000 Hz;

[0029] Alternatively, use the single - point frequency measurement method to measure the concentration of the electrolyte entering the pore structure:

[0030] Pre - obtain a third standard curve, where the third standard curve is the standard curve of the relationship between the electrolyte concentration and impedance or capacitance, and the way to obtain the standard curve is:

[0031] At multiple known different concentrations, apply a third voltage perturbation to the microelectrode - electrode, measure the impedance or capacitance at the second frequency, and plot the standard curve of the relationship between the electrolyte concentration and impedance or capacitance according to the obtained impedance or capacitance data at multiple different concentrations;

[0032] Apply a third voltage perturbation to the microelectrode - electrode at an unknown concentration, measure the impedance or capacitance at a second frequency, and substitute the obtained impedance or capacitance into a third standard curve to obtain the local concentration of the unknown electrolyte.

[0033] The third voltage perturbation value is a voltage value within the range of 5 - 50 mV, and the second frequency is a frequency value within the range of 50 - 1000 Hz.

[0034] In an alternative embodiment, the test battery further includes a micro - diaphragm that isolates the microelectrode from the positive and negative electrodes of the battery body.

[0035] In an alternative embodiment, the volume ratio of the electrodes of the battery body to the microelectrode is 100 - 10 7 :1.

[0036] In an alternative embodiment, the microelectrode includes a conductive substrate and an active coating covering the surface of the conductive substrate;

[0037] The active coating includes an active material and an adhesive with a mass ratio of 7 - 99:1, and the active material is a conductive powder.

[0038] In an alternative embodiment, the active material is selected from at least one of carbon black, KB, activated carbon, metal powder, and electrode material powder.

[0039] In an alternative embodiment, the adhesive is selected from at least one of PTFE and PVDF.

[0040] In an alternative embodiment, the conductive substrate is a metal wire or a metal sheet.

[0041] In a third aspect, the present invention provides a method for detecting the uniformity of electrolyte distribution inside a battery, using the detection method mentioned in any of the foregoing embodiments to detect the conductivity or concentration of the electrolyte at different parts inside the battery;

[0042] Compare the conductivity or concentration of the electrolyte at different parts to determine the uniformity of electrolyte distribution inside the battery.

[0043] In a fourth aspect, the present invention provides a method for monitoring the change of electrolyte during the aging process of a battery, using the foregoing detection method to detect the conductivity of the local electrolyte inside the battery after different numbers of cycles, and analyzing the aging condition of the electrolyte based on the conductivity data of the local electrolyte after different numbers of cycles;

[0044] Alternatively, use the foregoing detection method to detect the concentration of the local electrolyte inside the battery after different numbers of cycles, and analyze the aging condition of the electrolyte based on the local concentration data of the electrolyte after different numbers of cycles.

[0045] The present invention has the following beneficial effects:

[0046] The detection method for the local electrolyte concentration inside the battery provided by the present invention can be used to detect the local electrolyte concentration of the battery. Based on the detection method provided by the present invention, for some batteries with unevenly distributed internal electrolyte concentration, the structure of the test battery provided by the present invention can be set, so that the local electrolyte can be detected by using the detection method provided by the present invention to understand the uniformity of the internal electrolyte of the battery; through the detection method provided by the present invention, it can be used to understand the change trend of the electrolyte impedance and the consumption of lithium salt during the battery aging process. This method does not require the disassembly of the battery, and the test process is simple and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0048] Figure 1 It is a structural schematic diagram of the battery to be detected provided by the present invention;

[0049] Figure 2 It is a schematic diagram of the data obtained by applying a voltage perturbation of 10 mV to the microelectrode - positive electrode at multiple different concentrations and testing the impedance from 10 Hz to 200 kHz;

[0050] Figure 3 It is a curve obtained by fitting the blocking electrode of the 0.2 M electrolyte in Example 1 using the transmission line model;

[0051] Figure 4 It is a standard curve graph of resistance - electrolyte concentration in Example 1;

[0052] Figure 5 It is a curve obtained by fitting the blocking electrode of the 0.2 M electrolyte in Example 2 using the transmission line model;

[0053] Figure 6 It is a standard curve graph of resistance - electrolyte concentration in Example 2;

[0054] Figures 7 to 9 They are respectively the standard curve graphs of resistance - electrolyte concentration at 10000 Hz, 200 Hz, and 20 Hz. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0056] The features and performance of the present invention will be further described in detail below in conjunction with the embodiments.

[0057] The embodiments of the present invention provide a method for detecting the local electrolyte conductivity and electrolyte concentration of a lithium-ion battery, which is specifically as follows:

[0058] I. As Figure 1 shown, a test battery is provided. The test battery includes a battery body and a microelectrode located at the part to be detected within the battery body. The volume ratio of the electrode of the battery body to the microelectrode is at least 100:1, preferably 100 to 10 7 :1. The surface of the microelectrode has a pore structure that allows the electrolyte to enter.

[0059] Specifically, the preparation method of the test battery is as follows:

[0060] S1. Prepare the microelectrode

[0061] Provide an active slurry. The specific preparation method of the active slurry is the same as the existing method for preparing the negative electrode slurry or the positive electrode slurry. For example: Mix the active material, binder, and solvent evenly to obtain the active slurry;

[0062] Generally, NMP is used as the solvent, corresponding to the PVDF binder; in addition, water can also be used as the solvent, corresponding to the use of PTFE or CMC, etc. as the binder. Coat the active slurry on the surface of the conductive substrate, and obtain the microelectrode after the solvent volatilizes.

[0063] The active coating on the surface of the microelectrode has micropores that can absorb the electrolyte, and the experiment detects the concentration of the electrolyte absorbed in the micropores.

[0064] Optionally, the mass ratio of the active material to the binder is 7 to 99:1 (such as 7:1, 8:1, 9:1, 10:1, 20:1, 50:1, 80:1, 90:1, or 99:1).

[0065] Optionally, the active material is selected from at least one of carbon black, KB (Ketjen black), activated carbon, metal powder, and electrode material powder.

[0066] Optionally, the binder is selected from one of CMC, PTFE, and PVDF.

[0067] Optionally, the conductive substrate is a metal wire or a metal sheet, such as a copper wire or a tiny copper sheet. A copper wire is preferred, and its diameter range is, for example, 10 - 100 μm (such as 10 μm, 20 μm, 50 μm, 80 μm or 100 μm).

[0068] Optionally, the volume of the microelectrode is 0.5 - 1000 mm 3 , and the volume ratio of the electrode of the battery body to the microelectrode is at least 100:1. The specific size can be determined according to the size of the electrode of the target battery to be tested.

[0069] S2. Assemble the test battery

[0070] Assemble the prepared microelectrode, microseparator and the battery body together to obtain the test battery. The battery body is a common battery. The microelectrode is located at the part to be inspected inside the battery body, and the microseparator is used to isolate the microelectrode from the positive and negative electrodes of the battery body.

[0071] II. Test of electrolyte conductivity

[0072] The electrolyte conductivity test is to test the conductivity of the electrolyte that enters the tiny pores in the surface coating of the microelectrode from the part to be tested inside the battery.

[0073] Since the proportion of the surface area of the microelectrode in the electrode (positive or negative electrode) of the battery body is extremely small, only the information of the microelectrode interface can be obtained, and the influence of the signal of the other electrode is shielded. Therefore, the following two test methods can be used to realize the test of battery conductivity.

[0074] 1. Impedance spectroscopy detection method:

[0075] Apply a first voltage perturbation to the microelectrode - electrode, test the impedance in the range of 10 Hz - 200 kHz, and the conductivity of the electrolyte can be obtained by fitting the obtained impedance data using the blocking electrode of the transmission line model; the first voltage perturbation value is a voltage value in the range of 5 - 50 mv.

[0076] 2. The first single - point frequency test method:

[0077] Apply a second voltage perturbation to the microelectrode - electrode, test the resistance at the first frequency, and obtain the conductivity of the electrolyte according to the resistance value; the second voltage perturbation value is a voltage value in the range of 5 - 50 mv, and the first frequency is a frequency value in the range of 50 - 1000 Hz.

[0078] 3. The second single - point frequency test method:

[0079] A third voltage disturbance is applied to the microelectrode-electrode, the impedance or capacitance at the second frequency is tested, and the conductivity of the electrolyte is obtained according to the impedance or the capacitance; the third voltage disturbance value is a voltage value in the range of 5 to 50 mv, and the second frequency is a frequency value in the range of 50 to 1000 Hz.

[0080] Therefore, the electrolyte conductivity detection method provided in the embodiment of the present invention can be used to detect the local electrolyte conductivity of the battery. The battery to be tested can be a lithium-ion battery or a sodium-ion battery. Taking the lithium-ion battery as an example, it can be a ternary lithium-ion battery, a lithium iron phosphate battery, a lithium metal battery, etc.

[0081] 3. Test of electrolyte concentration

[0082] The electrolyte concentration test is to test the electrolyte concentration in the tiny pores in the microelectrode surface coating at the test site in the battery.

[0083] Since the surface area of ​​the microelectrode accounts for a very small proportion of the electrode (positive or negative electrode) of the battery body, only the information of the microelectrode interface can be obtained, while the influence of the other electrode signal is shielded. Therefore, the following three test methods can be used to test the battery concentration.

[0084] There are two detection methods.

[0085] 1. Impedance spectrum detection method:

[0086] (1) Establishing a standard curve

[0087] Under multiple known different concentrations, a voltage disturbance of 5 to 50 mv (for example, 5 mv, 10 mv, 20 mv, 50 mv) is applied to the microelectrode-electrode (the positive or negative electrode of the battery body), and the impedance of the microelectrode in the range of 10 Hz to 200 kHz is tested. The conductivity or resistance of the electrolyte can be obtained by fitting the impedance data obtained using the blocking electrode of the transmission line model. A standard curve of the relationship between the measured conductivity or resistance and the concentration of the electrolyte is obtained by plotting the measured conductivity or resistance and the corresponding concentration.

[0088] (2) Test of unknown electrolyte concentration

[0089] Under unknown concentration, the same voltage perturbation as that used to establish the standard curve is applied to the microelectrode-electrode, and the impedance of the microelectrode in the range of 10 Hz to 200 kHz is tested. The conductivity or resistance of the electrolyte can be obtained by fitting the impedance data using the blocking electrode of the transmission line model. The conductivity or resistance is substituted into the standard curve established in step (1) to obtain the local concentration of the unknown electrolyte.

[0090] 2. The first single-point frequency test method:

[0091] (1) Establish a standard curve

[0092] Apply a voltage perturbation of 5 - 50 mV (such as 5 mV, 10 mV, 20 mV, 50 mV) to the microelectrode - electrode respectively at multiple known different concentrations, measure the resistance at the first frequency, and plot a standard curve of the relationship between the electrolyte concentration and the resistance based on the measured multiple resistances.

[0093] The method for measuring the resistance can be to directly measure it using a conventional impedance - measuring device, or a multimeter. The two probes of the multimeter are respectively connected to the microelectrode and the electrode, and the resistance value is obtained through the pointer reading of the multimeter. Each of these two testing methods has its advantages and disadvantages. Using a conventional impedance - measuring device for direct measurement has high accuracy, but is slightly less convenient than using a multimeter; while using a multimeter is convenient to operate, but has slightly lower accuracy compared to a conventional impedance - measuring device.

[0094] (2) Measurement of the unknown electrolyte concentration

[0095] At an unknown concentration, apply the same voltage perturbation as when establishing the standard curve to the microelectrode - electrode, measure the resistance at the first frequency, and substitute the resistance into the second standard curve to obtain the local concentration of the unknown electrolyte.

[0096] The first frequency is a frequency value within the range of 50 - 1000 Hz (such as 50 Hz, 100 Hz, 200 Hz, 500 Hz, or 1000 Hz).

[0097] 3. The second single - point frequency testing method:

[0098] (1) Obtain a standard curve

[0099] At multiple known different concentrations, apply a voltage perturbation of 5 - 50 mV (such as 5 mV, 10 mV, 20 mV, 50 mV) to the microelectrode - electrode, measure the impedance or capacitance at the second frequency, and plot a standard curve of the relationship between the electrolyte concentration and the impedance or capacitance based on the obtained impedance or capacitance data at multiple different concentrations.

[0100] (2) Measurement of the unknown electrolyte concentration

[0101] At an unknown concentration, apply the same voltage perturbation as when establishing the standard curve to the microelectrode - electrode, measure the impedance or capacitance at the second frequency, and substitute the obtained impedance or capacitance into the third standard curve to obtain the local concentration of the unknown electrolyte;

[0102] The second frequency is a frequency value within the range of 50 - 1000 Hz.

[0103] Therefore, the electrolyte concentration detection method provided by the embodiments of the present invention can be used to detect the local electrolyte concentration of a battery. The battery to be detected can be a lithium-ion battery or a sodium-ion battery. Taking a lithium-ion battery as an example, it can be a ternary lithium-ion battery, a lithium iron phosphate battery, a lithium metal battery, etc.

[0104] It should be noted that in the detection method provided by the present invention, the number of microelectrodes disposed in the battery body can be one or more. When one is set, the concentration of the electrolyte at the position where the microelectrode is located is detected; when multiple are set, the detection method is to first measure the concentration of the electrolyte at the position corresponding to one microelectrode, and then sequentially measure the concentrations of the electrolytes at the positions corresponding to other microelectrodes.

[0105] The embodiments of the present invention also provide a method for detecting the uniformity of the electrolyte distribution inside a battery. It uses the detection method for the conductivity of the local electrolyte inside the battery provided by the embodiments of the present invention to detect the conductivity of the electrolytes at different positions inside the battery; compares the conductivities of the electrolytes at different positions to determine the uniformity of the electrolyte distribution inside the battery.

[0106] There is a correlation between the conductivity of the electrolyte and its diffusion ability. The diffusion ability of the electrolyte or the uniformity of the electrolyte distribution can be evaluated by detecting the local conductivity of the electrolyte.

[0107] Alternatively, it uses the detection method for the concentration of the local electrolyte inside the battery provided by the embodiments of the present invention to detect the concentrations of the electrolytes at different positions inside the battery;

[0108] compares the concentrations of the electrolytes at different positions to determine the uniformity of the electrolyte distribution inside the battery.

[0109] The embodiments of the present invention also provide a method for monitoring the change trend of the electrolyte impedance and the consumption of lithium salt during the battery aging process. It uses the detection method provided by the embodiments of the present invention to detect the conductivity of the local electrolyte inside the battery after different numbers of cycles, and analyzes the aging condition of the electrolyte based on the conductivity data of the local electrolyte after different numbers of cycles.

[0110] Alternatively, it uses the detection method provided by the embodiments of the present invention to detect the concentration of the local electrolyte inside the battery after different numbers of cycles, and analyzes the aging condition of the electrolyte based on the local concentration data of the electrolyte after different numbers of cycles.

[0111] Based on the detection method provided by the present invention, for some batteries with uneven distribution of internal electrolyte concentration, the structure of the test battery provided by the present invention can be set, so that the local electrolyte can be detected by the detection method provided by the present invention to understand the uniformity of the internal electrolyte of the battery; the detection method provided by the present invention can be used to understand the change trend of electrolyte impedance and the consumption of lithium salt during the battery aging process; the aging condition of the electrolyte, such as the performance attenuation of conductivity and diffusion coefficient. This method does not involve disassembling the battery, and the test process is simple and efficient.

[0112] The aforementioned batteries with uneven distribution of internal electrolyte concentration are, for example, vehicle - used single - cell large battery cores of (1060±10)×(630±10)×(240±5)mm, or larger ones such as BYD's blade batteries. There are also smaller batteries, such as some 100 - mAh small laminated batteries.

[0113] Experimental Example

[0114] Four groups of test batteries are provided, and each group of test batteries is assembled from a common battery and a micro - electrode.

[0115] Remove the insulation coating from a 2 - cm long part at one end of the copper wire, and coat the active slurry on the surface of the part where the insulation coating of the copper wire is removed to form a micro - electrode with a diameter of 50μm and a length of 2 cm.

[0116] The ratio of the active ingredient to the binder in the active slurry is 9:1. The active ingredient is carbon black, and the binder is PVDF.

[0117] The common battery is a lithium iron phosphate battery. The active ingredient of its positive electrode is lithium iron phosphate, and the active ingredient of its negative electrode is graphite. The area of the positive electrode is 46*56mm, and the thickness is 140μm. The battery is a double - layer laminated battery with a structure of positive electrode - negative electrode - positive electrode.

[0118] The lithium salt in the electrolytes of the four groups of batteries is LiPF 6 , and the solvent is composed of EC and EMC with a volume ratio of 3:7. The lithium salt concentrations in the four groups of batteries are 1M, 0.8M, 0.5M, and 0.2M respectively.

[0119] Apply a voltage perturbation of 10mv to the micro - electrode - positive electrode, test the impedance from 10Hz to 200kHz, and obtain the data as Figure 2 shown.

[0120] From Figure 2 it can be seen that the four curves are 1M, 0.8M, 0.5M, and 0.2M from left to right in sequence, indicating that the high - frequency 45° line is caused by the electrolyte in the pores of the micro - electrode. Therefore, the solution conductivity Rion and the solution resistance Cdl can be directly obtained by fitting with the blocking electrode of the transmission line model.

[0121] Example 1

[0122] Provide multiple lithium salts as LiPF 6 , and electrolytes in which the solvent is composed of EC and EMC with a volume ratio of 3:7. The concentrations of these electrolytes are 1M, 0.9M, 0.8M, 0.6M, 0.5M, 0.3M, and 0.2M in sequence. Apply a voltage perturbation of 10 mV to the microelectrode - positive electrode, test the impedance of each electrolyte from 200 kHz to 10 Hz, and use the blocking electrode fitting of the transmission line model to obtain the resistance corresponding to each electrolyte.

[0123] Taking 0.2M as an example, the curve obtained by the blocking electrode fitting of the transmission line model is as Figure 3 shown, Figure 3 where the blue circles in it are the impedance data measured from 1000 kHz to 1 Hz. Through Figure 3 combining the following formula to calculate the corresponding resistance value:

[0124] where Zexp is the measured experimental data, j represents the imaginary number, ω = 2 * π * f, f is the impedance test frequency, that is, 1000 kHz to 1 Hz, L represents the inductance, and R 0 represents the ohmic impedance, and Rion is the required resistance value. During the impedance test, a feedback value of one amplitude at different frequencies f, that is, Zexp, will be input. It consists of two columns of real and imaginary parts, and the real and imaginary parts can be written together in the form of a - b * j. The above calculation process is carried out in a computer.

[0125] Under this formula, Rion and the interfacial capacitance C are obtained by fitting with the nonlinear least squares method.

[0126] Using the same method, the resistance values at other concentrations are calculated. Specifically, as shown in Table 1:

[0127] Table 1 Resistance values calculated at different concentrations

[0128] Concentration / M 0.20 0.30 0.50 0.60 0.80 0.90 1.00 Resistance / Ω 2195.71 1598.21 1192.58 1122.55 1004.37 981.87 978.36

[0129] Make a resistance - concentration relationship curve for the relationship between resistance and concentration as Figure 4 shown.

[0130] Provide 2 groups of batteries to be tested. The structure of the batteries to be tested is the same as that in the verification example, and the known concentrations of the electrolytes are 0.55M and 0.70M respectively. Apply a voltage perturbation of 10 mV to the microelectrode - positive electrode, test the impedance from 10 Hz to 200 kHz, use the blocking electrode fitting of the transmission line model to obtain the resistance corresponding to each electrolyte, and map this resistance to the standard curve to obtain the corresponding estimated concentration value, as shown in Table 2:

[0131] Table 2 Resistance and estimated concentration of the experimental group

[0132] Actual concentration / M 0.55 0.70 Resistance / Ω 1140.47 1049.15 Estimated concentration / M 0.57 0.72 Concentration error 0.02 0.02

[0133] As can be seen from Table 2, there is only a slight error between the concentration measured by this method (estimated concentration) and the actual concentration, indicating that the detection method provided in the embodiments of the present invention is feasible. In addition, as is well known in the art, if there is enough data for establishing the standard curve, the accuracy of the obtained standard curve will be higher. Therefore, if there is more data for establishing the standard curve provided in this embodiment, it can be predicted that the accuracy of the measured concentration value will also be higher.

[0134] Example 2

[0135] Provide a plurality of lithium salts as LiPF 6 , and electrolytes in which the solvent is composed of EC and EMC with a volume ratio of 3:7. The concentrations of these electrolytes are 1M, 0.9M, 0.8M, 0.6M, 0.5M, 0.3M, and 0.2M in sequence. Apply a voltage perturbation of 50 mv to the microelectrode - positive electrode, test the impedance of each electrolyte from 200 kHz to 10 Hz, and use the blocking electrode fitting using the transmission line model to obtain the resistance corresponding to each electrolyte.

[0136] Taking 0.2M as an example, the curve obtained by the blocking electrode fitting of the transmission line model is as Figure 5 shown, Figure 5 where the blue circles in are the impedance data measured from 1000 kHz to 1 Hz. Through Figure 5 combining the following formula to calculate the corresponding resistance value:

[0137] where Zexp is the measured experimental data, j represents the imaginary number, ω = 2 * π * f, f is the impedance test frequency, that is, from 1000 kHz to 1 Hz, L represents the inductance, R 0 represents the ohmic impedance, and Rion is the required resistance value. During the impedance test, a feedback value of one amplitude at different frequencies f, that is, Zexp, will be input. It consists of two columns of real part and imaginary part, and the real part and imaginary part can be written together in the form of a - b * j. The above calculation process is carried out in a computer.

[0138] Under this formula, Rion and the interface capacitance C are obtained by fitting with the non - linear least squares method.

[0139] In the same way, the resistance values at other concentrations are calculated. Specifically, as shown in Table 3:

[0140] Table 3 Impedance data at different frequencies

[0141] Concentration / M 0.20 0.30 0.50 0.60 0.80 0.90 1.00 Resistance / Ω 2153.89 1567.77 1169.86 1101.17 985.23 963.17 959.72

[0142] The relationship between resistance and concentration is made into a resistance-concentration relationship curve as Figure 6 shown.

[0143] Two groups of batteries to be tested are provided. The structure of the batteries to be tested is the same as that in the verification example. The known concentrations of the electrolytes are 0.55 M and 0.70 M respectively. A voltage perturbation of 50 mv is applied to the microelectrode - positive electrode, and the impedance is measured from 10 Hz to 200 kHz. The resistance corresponding to each electrolyte is obtained by fitting with the blocking electrode of the transmission line model, and the resistance is mapped to the standard curve to obtain the corresponding estimated concentration value, as shown in Table 4:

[0144] Table 4 Resistance and estimated concentration of the experimental group

[0145] Actual concentration / M 0.55 0.70 Resistance / Ω 1118.75 1029.17 Estimated concentration / M 0.57 0.72 Concentration error 0.02 0.02

[0146] As can be seen from Table 4, there is only a small error between the concentration (estimated concentration) measured by this method and the actual concentration, indicating that the detection method provided by the embodiment of the present invention is feasible. In addition, according to the common knowledge in the art, if there is enough data for establishing the standard curve, the accuracy of the obtained standard curve will be higher. Therefore, if there is more data for establishing the standard curve provided by this embodiment, it can be predicted that the accuracy of the measured concentration value will also be higher.

[0147] Example 3

[0148] Provide a plurality of electrolytes with lithium salt LiPF 6 , and the solvent is composed of EC and EMC with a volume ratio of 3:7. The concentrations of these electrolytes are 0.5 M, 0.6 M, 0.8 M, 0.9 M, and 1 M in sequence.

[0149] Apply a voltage perturbation of 10 mv to the microelectrode - positive electrode, and directly measure the resistance values at 10000 Hz, 200 Hz, and 20 Hz respectively. As shown in Table 5, the data in Table 5 are respectively plotted as standard curves of the relationship between different concentrations and resistances at specific frequencies, as Figures 7 to 9 shown.

[0150] Table 5 Resistance data at different concentrations for multiple frequencies

[0151] Frequency \ Concentration 1M 0.9M 0.8M 0.6M 0.5M 10000 Hz 121.36 Ω 126.56 Ω 131.76 Ω 140.27 Ω 148.78 Ω 200 Hz 344.06 Ω 350.60 Ω 362.58 Ω 394.60 Ω 418.03 Ω 20 Hz 527.23 Ω 530.42 Ω 536.56 Ω 573.78 Ω 621.85 Ω

[0152] Provide 3 groups of batteries to be tested, whose concentrations are known to be 0.85 M. Apply a voltage perturbation of 10 mv to the microelectrode - positive electrode at frequencies of 10000 Hz, 200 Hz, and 20 Hz respectively. The measured resistance value at 10000 Hz is 127.3 Ω, which is mapped to the Figure 7 standard curve, and the estimated concentration is 0.87 M, with an error of 0.02 M; the measured resistance value at 200 Hz is 355.2 Ω, which is mapped to the Figure 8In the standard curve, the estimated concentration is 0.86 M, and the error is 0.01 M; the measured resistance value at 20 Hz is 532.8 Ω, corresponding to Figure 9 In the standard curve, the estimated concentration is 0.86 M, and the error is 0.01 M.

[0153] It can be seen from the data in Table 5 that there is only a slight error between the concentration (estimated concentration) measured by this method and the actual concentration, indicating that the detection method provided in the embodiment of the present invention is feasible. In addition, as is well known in the art, if there is more data for establishing the standard curve, the accuracy of the obtained standard curve will be higher. Therefore, if there is more data for establishing the standard curve provided in this embodiment, it can be predicted that the accuracy of the measured concentration value will also be higher.

[0154] It can be illustrated by the above verification examples and embodiments that the detection method for the local electrolyte concentration inside the battery provided by the present invention is reliable. By detecting the local electrolyte concentration at different positions inside the battery, the uniformity of the electrolyte distribution inside the battery can be judged; the change trend of the electrolyte impedance and the consumption of lithium salt during the battery aging process can be detected based on the concentration data of the electrolyte after different numbers of cycles.

[0155] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for detecting the conductivity of a local electrolyte in a battery, characterized in that: include: A test battery is provided, the test battery comprising a battery body and a microelectrode located at a position to be tested in the battery body, the volume ratio of the electrode of the battery body to the microelectrode is at least 100:1, and the volume of the microelectrode is 0.5 to 1000 mm 3 ; Each of the microelectrode surfaces has a pore structure that allows electrolyte to enter; A first voltage disturbance is applied to the microelectrode-electrode, and the impedance in the range of 10 Hz to 200 kHz is tested. The conductivity of the electrolyte can be obtained by fitting the impedance data obtained by using the blocking electrode of the transmission line model; the first voltage disturbance value is a voltage value in the range of 5 to 50 mv; Alternatively, a second voltage disturbance is applied to the microelectrode-electrode, the resistance at the first frequency is tested, and the conductivity of the electrolyte is obtained according to the resistance value; the second voltage disturbance value is a voltage value in the range of 5 to 50 mv, and the first frequency is a frequency value in the range of 50 to 1000 Hz; Alternatively, a third voltage disturbance is applied to the microelectrode-electrode, the impedance or capacitance at the second frequency is tested, and the conductivity of the electrolyte is obtained based on the impedance or the capacitance; the third voltage disturbance value is a voltage value in the range of 5 to 50 mv, and the second frequency is a frequency value in the range of 50 to 1000 Hz.

2. A method for detecting local electrolyte concentration in a battery, characterized in that: include: A test battery is provided, the test battery comprising a battery body and a microelectrode located at a position to be tested in the battery body, the volume ratio of the electrode of the battery body to the microelectrode is at least 100:1; each microelectrode surface has a pore structure that allows electrolyte to enter; The concentration of the electrolyte entering the pore structure is tested by an impedance spectrum detection method: A first standard curve is obtained in advance, wherein the first standard curve is a standard curve of the relationship between conductivity or resistance and electrolyte concentration; the method for obtaining the first standard curve is: Under a plurality of known different concentrations, a first voltage disturbance is applied to the microelectrode-electrode, and the impedance in the range of 10 Hz to 200 kHz is tested, and the conductivity or resistance of the electrolyte can be obtained by fitting the impedance data obtained using the blocking electrode of the transmission line model, and a standard curve of the relationship between the conductivity or resistance and the concentration of the electrolyte is drawn; Under unknown concentration, applying the first voltage disturbance to the microelectrode-electrode, testing the impedance in the range of 10 Hz to 200 kHz, fitting the impedance data obtained using the blocking electrode of the transmission line model to obtain the conductivity or resistance of the electrolyte, and bringing the conductivity or resistance into the first standard curve to obtain the local concentration of the unknown electrolyte; The first voltage disturbance value is a voltage value in the range of 5 to 50 mv; Alternatively, the single-point frequency test method is used to test the concentration of the electrolyte entering the pore structure: A second standard curve is obtained in advance, where the second standard curve is a standard curve of the relationship between resistance and electrolyte concentration; the method for obtaining the second standard curve is: Under known multiple different concentrations, respectively applying a second voltage disturbance to the microelectrode-electrode, testing the resistance under the first frequency, and drawing a standard curve of the relationship between electrolyte concentration and resistance according to the measured multiple resistances; Under unknown concentration, applying the second voltage disturbance to the microelectrode-electrode, measuring the resistance under the first frequency, and inserting the resistance into the second standard curve to obtain the local concentration of the unknown electrolyte; The second voltage disturbance value is a voltage value in the range of 5 to 50 mv, and the first frequency is a frequency value in the range of 50 to 1000 Hz; Alternatively, the single-point frequency test method is used to test the concentration of the electrolyte entering the pore structure: A third standard curve is obtained in advance. The third standard curve is a standard curve of the relationship between electrolyte concentration and impedance or capacitance. The standard curve is obtained as follows: Applying a third voltage disturbance to the microelectrode-electrode at a plurality of known different concentrations, testing the impedance or capacitance at a second frequency, and drawing a standard curve of the relationship between electrolyte concentration and impedance or capacitance based on the impedance or capacitance data obtained at the plurality of different concentrations; Under unknown concentration, applying a third voltage disturbance to the microelectrode-electrode, measuring the impedance or capacitance at the second frequency, and substituting the obtained impedance or capacitance into the third standard curve to obtain the local concentration of the unknown electrolyte; The third voltage disturbance value is a voltage value in the range of 5 to 50 mV, and the second frequency is a frequency value in the range of 50 to 1000 Hz.

3. The detection method according to claim 2, characterized in that: The test cell also includes a micro-membrane that separates the micro-electrode from the positive and negative electrodes of the cell body.

4. The detection method according to claim 2, characterized in that: The volume ratio of the electrode of the battery body to the microelectrode is 100 to 10 7 :

1.

5. The detection method according to claim 2, characterized in that: The microelectrode comprises a conductive substrate and an active coating covering the surface of the conductive substrate; The active coating comprises an active substance and an adhesive in a mass ratio of 7 to 99:1, and the active substance is a conductive powder.

6. The detection method according to claim 5, characterized in that: The active substance is selected from at least one of carbon black, KB, activated carbon, metal powder, and electrode material powder.

7. The detection method according to claim 5, characterized in that: The adhesive is selected from at least one of PTFE and PVDF.

8. The detection method according to claim 5, characterized in that: The conductive substrate is a metal wire or a metal sheet.

9. A method for detecting the uniformity of electrolyte distribution inside a battery, characterized in that: The conductivity of different areas inside the battery is detected by the detection method as claimed in claim 1, or the concentration of the electrolyte in different parts inside the battery is detected by the detection method as claimed in any one of claims 2 to 8; Compare the conductivity or concentration of the electrolyte in different parts to determine the uniformity of the electrolyte distribution inside the battery.

10. A method for monitoring electrolyte changes during battery aging, characterized in that: The detection method as claimed in claim 1 is used to detect the conductivity of the local electrolyte in the battery after different numbers of cycles, and the electrolyte aging is analyzed according to the local conductivity data of the electrolyte after different numbers of cycles; Alternatively, the detection method as claimed in any one of claims 2 to 8 is used to detect the concentration of local electrolyte inside the battery after different numbers of cycles, and the aging of the electrolyte is analyzed based on the local concentration data of the electrolyte after different numbers of cycles.

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