Method for measuring remaining amount of electrolyte inside battery by nuclear magnetic resonance

Abstract

The application discloses a method for measuring the residual amount of electrolyte in a battery by nuclear magnetic resonance, and belongs to the technical field of nuclear magnetic resonance measurement. The method comprises the following steps: cleaning the surface of a lithium battery after circulation, disassembling the lithium battery, immediately immersing all battery components, such as the positive electrode, the negative electrode, the diaphragm, the gasket, the spring sheet and the shell, which are attached with residual electrolyte, in deuterated solvent, performing oscillation treatment, and then performing static immersion treatment or ultrasonic treatment, so that the to-be-measured components in the residual electrolyte in the lithium battery are dissolved in the deuterated solvent to obtain an extraction solution, adding at least one internal standard substance with accurate weight to the extraction solution, then performing oscillation treatment to fully mix and uniformly distribute the internal standard substance, and finally performing nuclear magnetic resonance spectrum test. The application avoids the volatile loss caused by component cleaning through the "full-component integrated immersion extraction", and realizes the super-accurate determination of the complex components in the aged and dried battery by combining the absolute quantitative advantages of q-NMR, such as non-destructive and no need to establish a standard curve.

Description

Technical Field

[0001] This invention belongs to the field of nuclear magnetic resonance measurement technology, specifically relating to a method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance. Background Technology

[0002] Electrolyte, a crucial component of lithium-ion batteries, is often referred to as the battery's "blood," playing a vital role in transporting lithium ions between the positive and negative electrodes. During long-cycle or high-temperature storage aging, continuous side reactions (such as the growth of SEI / CEI films) occur on the surfaces of the positive and negative electrodes in lithium-ion batteries, leading to varying degrees of irreversible consumption of the electrolyte components (solvent, lithium salt, and additives). When the electrolyte is completely depleted, the battery exhibits a sharp decline in capacity and a rapid increase in internal resistance. Therefore, quantitative analysis of the remaining amounts of each electrolyte component inside the battery during the later stages of aging is of paramount practical value for diagnosing battery failure mechanisms and optimizing electrolyte formulation design.

[0003] However, existing methods for determining electrolyte consumption within batteries have serious flaws. Conventional methods, such as using syringes to extract free electrolyte or centrifugation to extract free electrolyte from the porous structure of the battery, often face the predicament of "no electrolyte left to collect" in the later stages of aging testing. Furthermore, the concentrations of electrolyte components bound within the porous electrodes have become polarized, meaning the extracted free electrolyte cannot represent the true residual status of each component within the battery, resulting in significant quantitative errors. Additionally, methods using conventional organic solvents for washing followed by heating, drying, and weighing for loss are lengthy, have uncontrollable evaporation losses, and cannot independently separate and quantify lithium salts, specific solvents, and additives.

[0004] Therefore, there is an urgent need to provide a simple, accurate, and widely applicable method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance, so as to achieve precise quantification of the remaining amounts of various components such as lithium salts, solvents, and additives in the electrolyte inside the battery after cycle aging. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a highly efficient and accurate method for precisely measuring the remaining electrolyte content of various components inside lithium batteries after cycling or storage, based on a direct immersion method of the entire component combined with quantitative nuclear magnetic resonance (q-NMR) spectroscopy. By employing an "integrated immersion extraction of the entire component," the method avoids the volatilization losses introduced by component cleaning, and combines the non-destructive nature of q-NMR with its absolute quantitative advantages of not requiring the establishment of standard curves, achieving high-precision determination of the complex components inside aged, dried-out batteries.

[0006] The present invention provides a method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance, the steps of which are as follows:

[0007] S1. After cleaning the surface of the cycled lithium battery to be tested, disassemble it. Immediately after disassembly, quickly immerse all battery components with residual electrolyte, including the positive electrode, negative electrode, separator, gasket, spring sheet, and casing, in a deuterated solvent. After shaking treatment, perform static soaking treatment or ultrasonic treatment to dissolve the test components in the residual electrolyte inside the lithium battery to be tested in the deuterated solvent to obtain the extract.

[0008] S2. Add at least one precisely weighed internal standard to the extract obtained in step S1, and then shake to mix it thoroughly.

[0009] S3. Perform nuclear magnetic resonance (NMR) spectroscopy on the extract containing the internal standard from step S2. Integrate the characteristic peaks of the internal standard and the analyte in the NMR spectrum to obtain the characteristic peak areas of the internal standard. and the characteristic peak area of ​​the analyte ;

[0010] S4. Based on the molecular structure of the internal standard and the molecular structure of the analyte, determine the equivalent nucleus number corresponding to the characteristic peak of the internal standard. and the equivalent nuclei corresponding to the characteristic peaks of the analyte Formula (2) is obtained from formula (1) of the area ratio method, thereby calculating the amount of residual substance of the component to be tested in the electrolyte inside the lithium battery. :

[0011] (1)

[0012] (2)

[0013] in, It is the amount of substance of the internal standard.

[0014] In step S1, before assembling the lithium battery, accurately weigh and record the initial mass of the electrolyte added to the lithium battery, as well as the amounts of each analyte component (lithium salt, organic solvent, additives, diluent, etc.). In step S2, the volume ratio of the internal standard to the deuterated solvent used in step S1 is between 1:100 and 1000. In step S3, the characteristic peak area is directly proportional to the amount of the analyte and the internal standard. In step S4, further determine the amount of the remaining analyte component. and the molar mass of the analyte The remaining mass of the component to be tested in the electrolyte inside the lithium battery to be tested is calculated using formula (3). :

[0015] (3)

[0016] Furthermore, the residual rate of the amount of the analyte is calculated using formula (4):

[0017] (4)

[0018] in, The initial amount of the component to be tested when injecting electrolyte into a lithium battery.

[0019] The advantages and technical effects of the testing method in this embodiment of the invention are as follows:

[0020] (1) In step S1 of this invention, all internal components (positive electrode, negative electrode, separator, gasket, spring sheet and shell) of the battery after disassembly are soaked in deuterated solvent, so that all the test components in the residual electrolyte inside the battery are extracted into the deuterated solvent. This solves the problem that the battery cannot be sampled and tested in the later stages of cycling, storage and other tests due to insufficient free electrolyte. It can also reflect the true content of each component in the electrolyte inside the battery. At the same time, this invention places the entire battery assembly after disassembly directly into the same extraction container without intermediate washing. Because the transfer to the sealed deuterated solvent is completed quickly (generally within 10 seconds), the volatilization distortion of the main solvent and low boiling point diluent in the electrolyte during the disassembly and washing operation is completely eliminated, and the complete capture of the residual components inside the battery in the later stages of drying and aging is achieved.

[0021] (2) In step S2 of this invention, nuclear magnetic resonance quantification is performed using an internal standard. The peak area is strictly proportional to the absolute number of quantitative nuclei in the solution. No standard curve needs to be established. The operation is simple and the analysis time is short. The remaining mass, amount of remaining substance or remaining rate can be calculated in a single test. This avoids the error caused by instrument fluctuations in the external standard method, and the quantitative results are highly accurate.

[0022] (3) By selecting suitable deuterated solvents and internal standards, this invention can be applied to 1 H NMR, 19 It can perform nuclear magnetic resonance spectroscopy tests of multiple nuclei such as F NMR, and can simultaneously quantify multiple components in the electrolyte such as lithium salt, organic solvent and additives, with a wide range of applications;

[0023] (4) In this invention, each component of the battery is directly immersed in a deuterated solvent, shaken, and then subjected to static soaking or ultrasonic treatment to homogenize the extract before it can be directly tested. There is no need for complex pretreatment processes such as extraction, digestion, and filtration. The testing efficiency is high and the human error is small.

[0024] Further, in step S1, the deuterated solvent is selected from at least one of deuterated dimethyl sulfoxide (DMSO-d6), deuterated chloroform (CDCl3), deuterated methanol (CD3OD), deuterated acetone (acetone-d6), deuterated acetonitrile (CD3CN), or heavy water (D2O). Preferably, the deuterated solvent is deuterated dimethyl sulfoxide (DMSO-d6), which has good dissolving power and can effectively dissolve lithium salts (such as LiFSI, LiPF6, etc.) and organic solvents in the electrolyte, and its residual... 1 H signal and 19 The F signal has minimal interference with the characteristic peaks of common electrolyte components.

[0025] Further, in step S1, the oscillation treatment is at least one of vortex oscillation, mechanical oscillation, or shaking table oscillation, and the oscillation treatment time is 3 to 10 minutes; after the oscillation treatment, a static soaking treatment is performed, the static soaking treatment temperature is 15 to 35°C, preferably room temperature (20 to 30°C), and the static soaking treatment time is 4 to 48 hours, preferably 8 to 24 hours, more preferably 12 hours; or ultrasonic treatment is used instead of static soaking treatment as an accelerated extraction method, the ultrasonic treatment time is 1 to 10 minutes, the ultrasonic power is 150 to 300W, and the ultrasonic frequency is 30 to 50kHz.

[0026] Furthermore, in step S1, after disassembling and obtaining the positive electrode, negative electrode, separator, gasket, spring sheet, and outer casing, each component is placed in a deuterated solvent within half a minute; preferably, it is placed within 10 seconds. Rapidly immersing the disassembled components in an organic solvent effectively avoids the loss of volatile components (such as low-boiling-point organic solvents) in the electrolyte, ensuring quantitative accuracy.

[0027] Furthermore, in step S2, the characteristic nuclei species of the internal standard are the same as those of the analyte; the selection principles for the internal standard include: (1) the internal standard contains the same NMR active nuclei species as the analyte ( 1 H, 19 (F); (2) The characteristic peaks of the internal standard on the NMR spectrum do not overlap with all the characteristic peaks of the analyte, and the characteristic peaks of multiple internal standards on the NMR spectrum do not overlap with each other; (3) The internal standard is chemically stable and does not react with other components in the extract; (4) The internal standard has known purity and the possibility of accurate weighing.

[0028] The internal standard is selected according to the type of analyte as follows:

[0029] (1) When adopting 19When performing quantitative analysis using F NMR, the analyte is a fluorinated lithium salt (such as lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), etc.), a fluorinated additive (fluoroethylene carbonate (FEC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), etc.), or a diluent (common hydrofluoroethers and fluoroalkanes, such as hexafluoroisopropyl methyl ether). When using hexafluorobenzene (HFPM), heptafluorocyclopentane (HFC), bis(2,2,2-trifluoroethyl) ether (BTFE), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE), etc., the internal standard can be selected from at least one of hexafluorobenzene (C6F6, δ≈-162.6ppm), trifluoroacetic acid (δ≈-76.5ppm), fluorobenzene (δ≈-113ppm), hexafluoroisopropanol (δ≈-76ppm), trifluorotoluene (δ≈-63ppm), and trifluoroethanol (δ≈-78ppm); hexafluorobenzene is preferred because it has a high concentration of fluorinated compounds. 19 The F NMR spectrum shows a single sharp signal peak, and its chemical shift does not overlap with the characteristic peaks of most fluorinated lithium salts (δ≈60~-200ppm);

[0030] (2) When adopting 1 When performing quantitative analysis using ¹H NMR, the analyte is in an organic solvent (such as common carbonate solvents, ether solvents, carboxylic acid ester solvents, etc., including dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), ethyl acetate (EA), propylene carbonate (PC), methyl ethyl carbonate (EMC), methyl acetate (MA), 1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL), dimethyltetrahydrofuran (2-Me-THF), 1,4-dioxane (DOX), tetrahydrofuran (THF), ethylene glycol diethyl ether (DEE), diethylene glycol...). When using dimethyl ether (DEGDME, etc.) or fluorine-free additives (such as vinylene carbonate (VC), vinyl sulfate (DTD), propane sulpholactone (PS), propylene sulfite (PES, etc.), the internal standard can be selected from at least one of acetonitrile (CH3CN, δ≈2.0ppm), 1,3,5-trimethoxybenzene (TMB, δ≈3.7ppm), dimethyl sulfoxide (DMSO, δ≈2.5ppm), dioxane (δ≈3.6ppm), cyclohexane (δ≈1.4ppm), and tetramethylsilane (TMS, δ≈0ppm); acetonitrile is preferred because acetonitrile has... 1 The H signal is a single peak, and the chemical shift is located in the blank region of most organic solvent signals (δ≈2.0ppm). Acetonitrile and DMSO-d6 are miscible.

[0031] Furthermore, when it is necessary to simultaneously quantify fluorinated lithium salts / fluorinated additives and organic solvents, hexafluorobenzene (used for...) can be added to the extract at the same time. 19 F NMR) and acetonitrile (used for F NMR) and acetonitrile (for 1 H NMR enables simultaneous quantification of multiple nuclei and components in a single sample preparation.

[0032] Furthermore, in step S3, the nuclear magnetic resonance spectroscopy test can be performed using a commercially available nuclear magnetic resonance spectrometer (such as the Bruker AVANCE series). The test parameters include: for 19 F NMR, spectral width 100~300ppm, center point -50~-100ppm, sampling times 16~128, relaxation delay time 10~30 seconds; for 1 ¹H NMR, spectral width 0–20 ppm, center point 5–10 ppm, sampling times 16–128, relaxation delay time 10–30 seconds; after spectral acquisition, NMR data processing software (such as MestreNova, TopSpin, etc.) was used to perform phase correction and baseline correction on the spectra, and then the characteristic peaks were integrated to obtain the integrated area of ​​the internal standard. The integral area of ​​the analyte Meanwhile, for ease of calculation, the integral area of ​​the internal standard is usually normalized to 1.0000. Attached Figure Description

[0033] Figure 1 The battery extract after 200 cycles in Example 1 of this invention 19 Fiber NMR quantitative spectrum;

[0034] Figure 2 The battery extract after 200 cycles in Example 2 of this invention 1 1H NMR quantitative spectrum;

[0035] Figure 3 The battery extract after 200 cycles in Example 3 of this invention 19 Fiber NMR quantitative spectrum;

[0036] Figure 4 The battery extract after 200 cycles in Example 3 of this invention 1 1H NMR quantitative spectrum. Detailed Implementation

[0037] Embodiments of the present invention are described in detail below, with examples of the embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0038] Example 1:

[0039] This embodiment illustrates an NMC811||Li full cell prepared using a locally concentrated electrolyte injection battery system. The locally concentrated electrolyte uses lithium bis(fluorosulfonyl)imide (LiFSI) as the lithium salt, 1,2-dimethoxyethane (DME) as the main solvent, and heptafluorocyclopentane (HFC) as the diluent. The molar ratio of LiFSI, DME, and HFC is 1:1:1.5. The battery described in this embodiment uses lithium nickel cobalt manganese oxide (NMC811) as the positive electrode (area capacity 2.5 mAh / cm³). 2 The battery is a full cell with an aluminum foil current collector and a lithium foil negative electrode (lithium foil thickness 50μm). The battery includes a separator (polypropylene / polyethylene composite separator), gaskets (stainless steel), spring contacts (stainless steel), and a casing (stainless steel or aluminum-plastic film). The electrolyte filling volume is 26.9mg (the filling volume is accurately weighed for each battery during assembly), with a LiFSI content of 4.71×10⁻⁶. -5 mol (approximately 8.81 mg), the DME content is 4.71 × 10⁻⁶. -5 The concentration of HFC was 7.06 × 10⁻⁶ mol (approximately 4.24 mg). -5 mol (approximately 13.86 mg). The remaining amounts of the analyte LiFSI and DME in the internal electrolyte of this battery after 200 charge-discharge cycles were tested. The specific procedures are as follows:

[0040] S1. After subjecting the above NMC811||Li full cell to 200 charge-discharge cycles, discharge it to an empty state. Disassemble it in an argon atmosphere glove box. Immediately after disassembly, immerse all battery components (positive electrode, negative electrode, separator, gasket, spring sheet, and outer casing) with residual electrolyte in a centrifuge tube containing 3 mL of deuterated dimethyl sulfoxide (DMSO-d6) within 10 seconds and seal it. Place the centrifuge tube on a vortex mixer and vortex at 2000 rpm for 5 minutes. Then, let it stand at room temperature for 12 hours to allow the components of the residual electrolyte inside the battery to fully dissolve in DMSO-d6, thus obtaining the extract.

[0041] S2. Accurately weigh the internal standard hexafluorobenzene (C6F6), the sample weight is 11.6 mg (equivalent to 6.2347 × 10⁻⁶ mg). -5 mol), used for 19 For quantitative determination of LiFSI by F NMR, the internal standard hexafluorobenzene (C6F6) was added to the extract obtained in step S1, and the mixture was vortexed to ensure thorough mixing.

[0042] S3. Transfer the well-mixed extract from step S2 through a needle filter into a 5 mm diameter NMR sample tube, and place it into the autosampler of the nuclear magnetic resonance spectrometer (Bruker AVANCE NEO 400MHz) for NMR spectroscopy testing. 19 The F NMR test parameters were as follows: zg pulse sequence, spectral width 301.8243ppm, center point -60ppm, 32 samplings, and relaxation delay time 20 seconds.

[0043] S4. Use MestreNova software to... 19 The F NMR spectrum was processed. For example... Figure 1 As shown, the characteristic peak of hexafluorobenzene (δ=-162.6ppm) was used as the internal standard peak, and its integrated area was calculated. Normalized to 1.0000; integral area of ​​the characteristic peak of LiFSI (δ=53.19ppm). The value is 0.1876. It is known that a hexafluorobenzene molecule contains 6 equivalent fluorine atoms (…). =6), the LiFSI molecule contains 2 equivalent fluorine atoms ( =2), the amount of hexafluorobenzene =6.2347×10 -5 mol; Calculate the remaining amount of LiFSI according to formula (2):

[0044]

[0045] The molar mass of LiFSI is 187.07 g / mol, therefore the remaining mass of LiFSI is 6.56 mg.

[0046] The initial electrolyte injection volume for this battery was 26.9 mg, of which the initial amount of LiFSI was 4.71 × 10⁻⁶. -5 Therefore, the remaining amount of LiFSI is: mol.

[0047] .

[0048] Example 2:

[0049] This embodiment uses the same NMC811||Li full cell and locally high-concentration electrolyte system as Example 1. The difference lies in the internal standard added in step S1 of this embodiment, which is different to quantitatively analyze the remaining content of organic solvent in the electrolyte. The specific operation is as follows:

[0050] Add the internal standard acetonitrile to the electrolyte extract, and accurately record the sample weight of acetonitrile (the sample weight of acetonitrile is 5.5 mg, equivalent to 13.398 × 10⁻⁶ mg). -5 mol), used for 1Quantitative DME by 1H NMR: vortexing was used to thoroughly mix the internal standard with the extract; the remaining steps (addition of internal standard, NMR testing, quantitative calculation) were the same as in Example 1.

[0051] 1 The H NMR test parameters were as follows: zg pulse sequence, spectral width 20ppm, center point 5ppm, 32 sampling times, and relaxation delay time 20 seconds.

[0052] Using the MestreNova software 1 The H NMR spectrum was processed. For example... Figure 2 As shown, the characteristic peak of acetonitrile (CH3CN) (δ≈2.0ppm) was used as the internal standard peak, and its integrated area was calculated. Normalized to 1.0000; integrate the characteristic peak of -CH3 in DME (δ≈3.34), and calculate the area of ​​integration. The value is 0.5941. It is known that an acetonitrile molecule contains three equivalent hydrogen atoms (…). =3), the DME molecule contains 6 equivalent -CH3 hydrogen atoms ( =6), amount of acetonitrile =13.398×10 - 5 mol. Calculate the amount of remaining DME according to formula (2):

[0053]

[0054] The molar mass of DME is 90.12 g / mol, therefore the remaining mass of DME is 3.58 mg.

[0055] The initial electrolyte injection volume for this battery was 26.9 mg, of which the initial amount of DME was 4.71 × 10⁻⁶. -5 Therefore, the molar percentage of DME is: mol.

[0056] .

[0057] Example 3:

[0058] This embodiment uses the same NMC811||Li full battery as in Examples 1 and 2. The electrolyte composition is lithium bis(fluorosulfonyl)imide (LiFSI) as the lithium salt, 1,2-dimethoxyethane (DME) as the main solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as an additive, with a molar ratio of LiFSI, DME, and TTE of 1:1:1.5. The injected electrolyte volume is 24.6 mg (the injected electrolyte volume is accurately weighed during assembly of each battery), and the LiFSI content is 3.94 × 10⁻⁶ mg / mL.-5 mol (approximately 7.37 mg), DME content is 3.94 × 10⁻⁶. -5 mol (approximately 3.55 mg), TTE content is 5.910 × 10 -5 The sample was collected in mol (approximately 13.71 mg), and the remaining lithium salt, solvent, and additive content in the battery after 200 cycles was analyzed. In step S2, both hexafluorobenzene and acetonitrile, two internal standards, were added, and samples were collected separately. 1 H NMR and 19 F NMR allows for the simultaneous testing of the remaining amounts of lithium salt, solvent, and additives in the electrolyte. The remaining steps (such as battery disassembly, electrolyte extraction, NMR testing parameters, integration processing method, and calculation principle) are the same as in Examples 1 and 2, as detailed below:

[0059] In the electrolyte extraction solution, hexafluorobenzene (C6F6) and acetonitrile (CH3CN) were accurately weighed, respectively. The sample weight of hexafluorobenzene was 7.6 mg (equivalent to 4.0848 × 10⁻⁶ mg). -5 mol), used for 19 Quantitative analysis of LiFSI using F NMR; acetonitrile sample weight was 4.4 mg (equivalent to 10.7181 × 10⁻⁶ mg / L). -5 mol), used for 1 Quantitative analysis of DME and TTE was performed using 1H NMR; two internal standards were added to the extract and vortexed to ensure thorough mixing; the homogeneous extract was transferred through a syringe filter to a 5mm diameter NMR sample tube and placed in the autosampler of a Bruker AVANCE NEO 400MHz NMR spectrometer for NMR spectroscopy analysis. 19 F NMR and 1 H NMR.

[0060] Test results show that, with the simultaneous addition of two internal standards, there is no mutual interference between the characteristic peaks: hexafluorobenzene's 19 The F signal is located at δ = -162.6 ppm, which is the value of LiFSI. 19 The F signal is located at δ=53.19ppm; acetonitrile 1 The H signal is located at δ≈2.0ppm, and the -CH3 in DME 1 The H characteristic peak is located at δ≈3.34ppm, and the -CH2- of TTE is... 1 The H signal is located at δ≈4.71ppm. The peaks are well separated and do not overlap.

[0061] Using the MestreNova software 19 Integrating the F NMR spectrum. For example... Figure 3 As shown, the characteristic peak of hexafluorobenzene is used as the internal standard peak, and its integrated area is calculated. Normalized to 1.0000; integral area of ​​the characteristic peak of LiFSI The value is 0.1821. It is known that a hexafluorobenzene molecule contains 6 equivalent fluorine atoms (…). =6), the LiFSI molecule contains 2 equivalent fluorine atoms ( =2), the amount of hexafluorobenzene =4.0848×10 -5 mol. Calculate the amount of remaining LiFSI according to formula (2):

[0062]

[0063] The molar mass of LiFSI is 187.07 g / mol, therefore the remaining mass of LiFSI is 4.17 mg.

[0064] The initial electrolyte injection volume for this battery was 24.6 mg, of which the initial amount of LiFSI was 3.94 × 10⁻⁶. -5 Therefore, the molar percentage of LiFSI is:

[0065] .

[0066] Using the MestreNova software 1 Integrating the H NMR spectrum. For example Figure 4 As shown, the characteristic peak of acetonitrile (CH3CN) was used as the internal standard peak, and its integrated area was calculated. Normalized to 1.0000; the characteristic peaks of -CH3 in DME and -CH2- in TTE were integrated, and the areas of integration were respectively... =0.6221 and =0.1738. It is known that an acetonitrile molecule contains 3 equivalent hydrogen atoms ( =3), the DME molecule contains 6 equivalent -CH3 hydrogen atoms ( =6), amount of acetonitrile =10.7181×10 -5 mol. Calculate the amount of remaining DME according to formula (2):

[0067]

[0068] The molar mass of DME is 90.12 g / mol, therefore the remaining mass of DME is 3.0 mg.

[0069] The initial electrolyte injection volume for this battery was 24.6 mg, of which the initial amount of DME was 3.94 × 10⁻⁶. -5 Therefore, the molar percentage of DME is: mol.

[0070] .

[0071] Furthermore, using acetonitrile as an internal standard, the remaining amount of additive TTE can also be calculated. For example... Figure 4 As shown, an acetonitrile molecule contains 3 equivalent hydrogen atoms ( =3), the integral area is 1.0000. The TTE molecule contains 2 equivalent -CH2- hydrogen atoms ( =2), the integral area is 0.1738. The amount of acetonitrile. = ×10 -5 mol. Calculate the amount of remaining substance in TTE according to formula (2):

[0072]

[0073] The molar mass of TTE is 232.07 g / mol, therefore the remaining mass of TTE is 6.48 mg.

[0074] The initial electrolyte injection volume for this battery was 24.6 mg, of which the initial amount of TTE was 5.910 × 10⁻⁶. -5 Therefore, the remaining amount of TTE is: mol.

[0075] .

[0076] The above results indicate that the method of the present invention can achieve simultaneous and accurate quantification of multiple components in the electrolyte.

[0077] Example 4:

[0078] This embodiment uses the same battery as in Example 1 (NMC811||Li full cell, locally high-concentration electrolyte system), the difference being that the soaking treatment in step 1 uses an ultrasonic-assisted method to accelerate the extraction speed. The specific operation is as follows:

[0079] After disassembling the battery, all components were placed into centrifuge tubes containing 3 mL of DMSO-d6 and sealed. The centrifuge tubes were then vortexed at 2000 rpm for 5 minutes. Next, the centrifuge tubes were placed in an ultrasonic cleaner (200 W ultrasonic power, 40 kHz frequency) and sonicated at room temperature for 10 minutes to fully dissolve any remaining electrolyte in the DMSO-d6. The remaining steps (internal standard addition, NMR testing, and quantitative calculation) were the same as in Example 1. The experimental results are shown in Table 1.

[0080] Table 1: Extraction efficiency data for oscillation + ultrasonic treatment and oscillation + soaking treatment

[0081]

[0082] The results showed that the extraction efficiency of ultrasound-assisted extraction for 10 minutes was comparable to that of oscillation treatment and static soaking for 12 hours, indicating that ultrasound treatment can effectively shorten the extraction time and improve the testing efficiency.

Claims

1. A method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance, characterized in that: The steps are as follows: S1. After cleaning the surface of the cycled lithium battery to be tested, disassemble it. Immediately after disassembly, quickly immerse all battery components with residual electrolyte, including the positive electrode, negative electrode, separator, gasket, spring sheet, and casing, in a deuterated solvent. After shaking treatment, perform static soaking treatment or ultrasonic treatment to dissolve the test components in the residual electrolyte inside the lithium battery to be tested in the deuterated solvent to obtain the extract. S2. Add at least one precisely weighed internal standard to the extract obtained in step S1, and then shake to mix it thoroughly. S3. Perform nuclear magnetic resonance (NMR) spectroscopy on the extract containing the internal standard from step S2. Integrate the characteristic peaks of the internal standard and the analyte in the NMR spectrum to obtain the characteristic peak areas of the internal standard. and the characteristic peak area of ​​the analyte ; S4. Based on the molecular structure of the internal standard and the molecular structure of the analyte, determine the equivalent nucleus number corresponding to the characteristic peak of the internal standard. and the equivalent nuclei corresponding to the characteristic peaks of the analyte ; Formula (2) is derived from formula (1) of the area ratio method, thereby calculating the amount of residual substance of the component to be tested in the electrolyte inside the lithium battery. : （1） （2） in, It is the amount of substance of the internal standard.

2. The method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance as described in claim 1, characterized in that: In step S1, the deuterated solvent is at least one of deuterated dimethyl sulfoxide, deuterated chloroform, deuterated methanol, deuterated acetone, deuterated acetonitrile, and heavy water.

3. The method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance as described in claim 1, characterized in that: In step S1, the oscillation treatment is at least one of vortex oscillation, mechanical oscillation, or shaking table oscillation, and the oscillation treatment time is 3 to 10 minutes; the temperature of the static soaking treatment is 15 to 35°C, and the static soaking treatment time is 4 to 48 hours; the ultrasonic treatment time is 1 to 10 minutes, the ultrasonic power is 150 to 300W, and the ultrasonic frequency is 30 to 50kHz.

4. The method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance as described in claim 1, characterized in that: In step S2, the volume ratio of the internal standard to the deuterated solvent is between 1:100 and 1000; the internal standard contains the same NMR active nuclei as the analyte. 1 H or 19 F, the characteristic peaks of the internal standard on the NMR spectrum do not overlap with all the characteristic peaks of the analyte, and the characteristic peaks of multiple internal standards on the NMR spectrum also do not overlap with each other; the internal standard is chemically stable and does not react with other components in the extract.

5. The method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance as described in claim 4, characterized in that: When the analyte is a fluorinated lithium salt, a fluorinated additive, or a diluent, the internal standard is at least one of hexafluorobenzene, trifluoroacetic acid, fluorobenzene, hexafluoroisopropanol, trifluorotoluene, and trifluoroethanol; when the analyte is an organic solvent or a non-fluorinated additive, the internal standard is at least one of acetonitrile, 1,3,5-trimethoxybenzene, dimethyl sulfoxide, dioxane, cyclohexane, and tetramethylsilane.

6. The method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance as described in claim 5, characterized in that: The fluorinated lithium salts are lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, or lithium difluorooxalate borate; the fluorinated additives are fluoroethylene carbonate or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; the non-fluorinated additives are vinylene carbonate, vinyl sulfate, propane sulpholactone, or propylene sulfite; and the diluents are hexafluoroisopropyl methyl ether, heptafluorocyclopentane, and bis(fluoromethyl)sulfonyl ether. (2,2,2-trifluoroethyl) ether or 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, wherein the organic solvent is dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethyl acetate, propylene carbonate, methyl ethyl carbonate, methyl acetate, 1,2-dimethoxyethane, 1,3-dioxolane, dimethyltetrahydrofuran, 1,4-dioxane, tetrahydrofuran, ethylene glycol diethyl ether, or diethylene glycol dimethyl ether.

7. The method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance as described in claim 1, characterized in that: In step S3, the nuclear magnetic resonance spectroscopy test is performed using a nuclear magnetic resonance spectrometer. 19 F NMR, spectral width 100~300ppm, center point -50~-100ppm, sampling times 16~128, relaxation delay time 10~30 seconds; for 1 H NMR, spectral width 0~20ppm, center point 5~10ppm, sampling number 16~128 times, relaxation delay time 10~30 seconds.

8. The method for measuring the remaining amount of electrolyte inside a battery using nuclear magnetic resonance as described in claim 1, characterized in that: In step S4, based on the amount of the remaining substance of the analyte... and the molar mass of the analyte The remaining mass of the component to be tested in the electrolyte inside the lithium battery to be tested is calculated using formula (3). : （3） The residual rate of the analyte is calculated using formula (4): （4） in, The initial amount of the component to be tested when injecting electrolyte into a lithium battery.

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