Method for determining the content of battery liquid electrolyte components

Abstract

The present application discloses a method for determining the content of components in a battery liquid electrolyte. The method comprises: S1. providing an extraction solution containing an organic acid titrant and a relaxation enhancer; S2. contacting the battery liquid electrolyte obtained by disassembling the battery and / or the components in the battery that are in contact with the battery liquid electrolyte with the extraction solution to obtain an extraction mixture; S3. adding an internal standard compound to the sample obtained from the extraction mixture to obtain a sample to be tested; S4. obtaining at least two first nuclear magnetic resonance spectra of the sample to be tested measured for the nuclear magnetic element; S5. determining the content of the component to be tested in the battery liquid electrolyte based on the first nuclear magnetic resonance spectrum. The relaxation enhancer in the method provided by the present application can reduce the relaxation time; reduce data errors through the internal standard cross-calibration formula; and accurately realize the quantitative detection of solutes and solvents in the liquid electrolyte.

Description

Technical Field

[0001] The present application belongs to the technical field of electrolyte detection, and specifically relates to a method for determining the content of liquid electrolyte components in a battery. Background Art

[0002] Batteries are widely used in products such as mobile phones, laptops, cameras, and automobiles, and have characteristics such as high energy density and high operating voltage. Depending on different application scenarios, the amount of liquid electrolyte injected into the battery can be a few grams or tens of grams to hundreds of grams, and the liquid electrolyte will undergo a decomposition reaction during use. The electrolyte interface film (SEI) produced during the decomposition reaction determines the transmission rate and uniformity of metal ions, such as lithium ions and sodium ions, at the anode / electrolyte interface, and determines the reversibility of the negative electrode. Understanding and quantifying the electrolyte decomposition reaction process is crucial to understanding the battery failure mechanism and the working principle of liquid electrolytes. Therefore, it is very important to understand and quantify the component content of the liquid electrolyte.

[0003] Numerous attempts have been made, both theoretically and experimentally, to quantify the solute and solvent content in liquid electrolytes. However, current technologies lack accurate quantitative methods. Common methods for determining component content in liquid electrolytes include ion chromatography (IC), gas chromatography-mass spectrometry (GC / MS), and inductively coupled plasma-mass spectrometry (ICP-MS). However, these methods can only determine the concentration of organic solvents or inorganic salts individually, and are unable to provide a unified and accurate measurement of solutes and solvents in liquid electrolytes after charge and discharge. Furthermore, they are unable to accurately detect the solvent and solute content in liquid electrolytes after electrochemical cycling. Summary of the Invention

[0004] In view of this, the present application provides a method for determining the content of battery liquid electrolyte components, aiming to accurately detect the content of solvent and solute in the battery liquid electrolyte at one time.

[0005] The present invention provides a method for determining the content of a liquid electrolyte component in a battery, the method comprising:

[0006] The present invention provides a method for determining the content of a liquid electrolyte component in a battery, the method comprising:

[0007] S1 provides an extraction solution containing an organic acid titrant and a relaxation enhancer, wherein the metal element or reducing metal compound in the battery component is completely dissolved by controlling the content of the organic acid titrant;

[0008] S2. The battery liquid electrolyte obtained by disassembling the battery and / or the battery components in contact with the battery liquid electrolyte are contacted with the extraction solution to obtain an extraction mixture;

[0009] S3. An internal standard compound is added to the sample obtained by the extraction mixture to obtain a sample to be tested, wherein the internal standard compound comprises: at least one element with nuclear magnetic properties; and each component of the liquid electrolyte to be tested independently contains the element with nuclear magnetic properties;

[0010] S4. Obtain at least two first nuclear magnetic resonance spectra of the sample to be tested measured for the element with nuclear magnetic properties;

[0011] S5. Determine the content of the component to be measured in the battery liquid electrolyte based on the first nuclear magnetic resonance spectrum.

[0012] According to an embodiment of one aspect of the present application, the concentration of the organic acid titrant in the extraction solution is 95-105 mmol / l.

[0013] According to an embodiment of one aspect of the present application, the concentration of the relaxation enhancer in the extraction solution is 0.5-3 mmol / l.

[0014] According to an embodiment of one aspect of the present application, the molecular weight of the organic acid titrant is ≤1000 Da.

[0015] According to an embodiment of one aspect of the present application, the relaxation enhancer makes the relaxation time ≤1S.

[0016] According to an embodiment of one aspect of the present application, the organic acid titrant is selected from maleic acid, dihydroxytartaric acid, oxaloacetic acid, pyruvic acid, malonic acid, phthalic acid, tartaric acid, fumaric acid, methylmalonic acid, terephthalic acid, adipic acid, acetic acid, propionic acid, tert-pentanoic acid or a combination thereof.

[0017] According to an embodiment of one aspect of the present application, the relaxation enhancer is selected from manganese acetylacetonate, manganese chloride, chromium acetylacetonate, nickel acetylacetonate, iron acetylacetonate, copper acetylacetonate, cobalt acetylacetonate, gadolinium acetylacetonate, or a combination thereof.

[0018] According to an embodiment of one aspect of the present application, the internal standard compound is selected from trifluorotoluene, 3,4-dichlorotrifluorotoluene, 2,4-dichlorotrifluorotoluene, 2,5-dichlorotrifluorotoluene, 2,3-dichlorotrifluorotoluene, 3,5-dichlorotrifluorotoluene, 3,4,5-trichlorotrifluorotoluene, 4,4'-difluorobenzophenone, 2-chloro-4-fluorotoluene or a combination thereof.

[0019] According to an embodiment of one aspect of the present application, the extraction solution further comprises a deuterated reagent, and the deuterated reagent is selected from dichloromethane, deuterated methanol, deuterated dimethyl sulfoxide, deuterated chloroform, deuterated acetonitrile, or a combination thereof.

[0020] According to an embodiment of one aspect of the present application, the battery is a battery that has undergone electrochemical cycling.

[0021] According to an embodiment of one aspect of the present application, the components in the liquid electrolyte include any one or more of a solvent, a solute, and an additive.

[0022] According to an embodiment of one aspect of the present application, step S5 includes: determining the relative content of the solvent in the battery liquid electrolyte by formula (1) based on the first nuclear magnetic resonance spectrum;

[0023]

[0024] in, is the relative content of solvent A in the liquid electrolyte after i electrochemical cycles;

[0025] is the characteristic peak area of ​​element y in solvent A in the liquid electrolyte after i electrochemical cycles after NMR detection;

[0026] N(A) y is the number of y elements in the molecular formula of solvent A;

[0027] is the characteristic peak area of ​​solute B or additive C in the liquid electrolyte after i electrochemical cycles after NMR detection of element x;

[0028] N(B or C) x is the number of x elements in the molecular formula of solute B or additive C;

[0029] is the characteristic peak area of ​​the internal standard compound after NMR detection of element y, which can be normalized to 100;

[0030] N(IR) y is the number of y elements in the molecular formula of the internal standard compound;

[0031] is the characteristic peak area of ​​the internal standard compound after NMR detection of element x, which can be normalized to a constant of 100;

[0032] N(IR) x is the number of x elements in the molecular formula of the internal standard compound; the x elements and y elements are independently selected from hydrogen, boron, carbon, oxygen, fluorine, and phosphorus.

[0033] According to an embodiment of one aspect of the present application, step S5 includes: determining the relative content of the solute in the liquid electrolyte of the battery by formula (2) based on the first nuclear magnetic resonance spectrum;

[0034]

[0035] in, is the relative content of solute B in the liquid electrolyte after i electrochemical cycles;

[0036] is the characteristic peak area of ​​solute B in the liquid electrolyte after i electrochemical cycles detected by element x by NMR;

[0037] is the number of x elements in the molecular formula of solute B;

[0038] is the characteristic peak area of ​​solvent A or additive C in the liquid electrolyte after i electrochemical cycles detected by NMR of element y;

[0039] N(A or C) y is the number of y elements in the molecular formula of solvent A or additive C;

[0040] is the characteristic peak area of ​​the internal standard compound after NMR detection of element y, which can be normalized to a constant of 100;

[0041] N(IR) y is the number of y elements in the molecular formula of the internal standard compound;

[0042] is the characteristic peak area of ​​the internal standard compound after NMR detection of element x, which can be normalized to a constant of 100;

[0043] N(IR) x is the number of x elements in the molecular formula of the internal standard compound;

[0044] The x element and the y element are independently selected from hydrogen, boron, carbon, oxygen, fluorine, and phosphorus.

[0045] According to an embodiment of one aspect of the present application, the method further includes:

[0046] S6. The battery containing a known volume of electrolyte that has not been electrochemically cycled is disassembled in a protective atmosphere, and the battery liquid electrolyte and the components in contact with the battery liquid electrolyte are contacted with an additional extraction solution to obtain the total volume of the mixed solution and the liquid electrolyte and the extract that has not been electrochemically cycled;

[0047] S7. Add an internal standard compound to the sample obtained from the mixed solution to obtain a sample to be subjected to NMR detection;

[0048] S8. The sample to be tested by nuclear magnetic resonance is subjected to nuclear magnetic resonance detection for the element with nuclear magnetic properties to obtain at least two second nuclear magnetic resonance spectra;

[0049] S9. Determine the absolute content of the substance in the liquid electrolyte of the battery based on the volume of the test mixture, the volume of the extract, the volume of the internal standard compound, the amount of the internal standard compound in the test mixture, the first nuclear magnetic resonance spectrum, and the second nuclear magnetic resonance spectrum obtained in part S7.

[0050] According to an embodiment of one aspect of the present application, step S9 specifically includes:

[0051] According to formula (3), the absolute content of the substance in the battery liquid electrolyte is determined:

[0052]

[0053] in, It is an internal standard cross calibration type;

[0054] n(Z) i The absolute content of substance Z in the liquid electrolyte after i electrochemical cycles;

[0055] I(Z) i is the characteristic peak area of ​​substance Z after NMR detection of the predetermined element;

[0056] I(IR) i is the characteristic peak area of ​​the y element in the internal standard compound in NMR detection, which can be normalized to a constant of 100;

[0057] N3 is the amount of the internal standard compound in the test mixture, in moles,

[0058] is the characteristic peak area of ​​the deuterated reagent in the mixed solution of liquid electrolyte and extract after i electrochemical cycles after NMR detection of the predetermined element, which can be normalized to a constant of 100;

[0059] It is the characteristic peak area of ​​the deuterated reagent in the mixture of the liquid electrolyte and the extract that has not been electrochemically cycled after nuclear magnetic resonance detection of the predetermined element;

[0060] It is the characteristic peak area after NMR detection of the predetermined element, which can be normalized to a constant of 100;

[0061] V1 is the sum of the volume of the extract and the volume of the internal standard compound;

[0062] V2 is the volume of the sample to be detected by NMR

[0063] According to an embodiment of one aspect of the present application,

[0064] Compared with the prior art, this application has at least the following beneficial effects:

[0065] The method provided in the present application disassembles the battery in a protective atmosphere, so that the battery liquid electrolyte and the components in contact with the battery liquid electrolyte are in contact with the extraction solution. Since the spatial distribution of the SEI components formed in the battery may be uneven, it is impossible to accurately detect the content of each component of the liquid electrolyte decomposition reaction. After contact with the extraction solution and homogenization, the uneven distribution of components in the liquid electrolyte can be avoided, and the accuracy of the component detection results in the liquid electrolyte can be improved. The organic acid titrant can make the elemental metal or reducing metal compound in the battery negative electrode lose its reducing activity, thereby avoiding the reaction of the elemental metal or reducing metal compound with the liquid electrolyte during the measurement process, which affects the measurement of the content of each component of the electrolyte during disassembly. The relaxation enhancer can reduce the relaxation time and shorten the sampling time, avoiding the relaxation time difference caused by the dissolution of metal ions in the battery positive electrode. The internal standard cross-calibration formula can reduce data errors. By controlling the organic acid titrant, it is ensured that the composition of the liquid electrolyte remains unchanged during disassembly and can be detected in time, and the solute and solvent in the liquid electrolyte can be accurately quantitatively measured.

[0066] In addition, the method of the present application can simultaneously determine the relative contents of solvents and solutes in liquid electrolytes; the method of the present application is simple, rigorous, and low-cost, and is not limited by the types of liquid electrolytes and batteries. It can be applied to different liquid electrolytes and different battery configurations under conventional laboratory conditions, and can also be used for lithium-ion batteries, sodium-ion batteries, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0068] Figure 1 This is a nuclear magnetic resonance image of the uncycled battery provided in Example 1 of the present application;

[0069] Figure 2 This is a nuclear magnetic resonance image of the cycled battery provided in Example 1 of the present application;

[0070] Figure 3 This is a nuclear magnetic resonance image of the uncycled battery provided in Example 2 of the present application;

[0071] Figure 4 This is a nuclear magnetic resonance image of the cycled battery provided in Example 2 of the present application;

[0072] Figure 5 This is a nuclear magnetic resonance image of the uncycled battery provided in Example 3 of the present application;

[0073] Figure 6 This is the nuclear magnetic resonance image of the cycled battery provided in Example 3 of the present application. DETAILED DESCRIPTION

[0074] In order to make the application purpose, technical solution and beneficial technical effects of this application clearer, the application is further described in detail below with reference to the embodiments. It should be understood that the embodiments described in this specification are only for explaining this application and are not intended to limit this application.

[0075] For simplicity, this application only explicitly discloses certain numerical ranges. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is included in the range. Thus, each point or individual value may serve as its own lower limit or upper limit and be combined with any other point or individual value, or with other lower limits or upper limits, to form an unspecified range.

[0076] In the description of this application, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number, and “a variety” in “one or more” means two or more.

[0077] The above disclosure of the present application is not intended to describe every disclosed embodiment or every implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided through a series of examples, which can be used in various combinations. In each example, the enumeration is intended only as a representative group and should not be construed as exhaustive.

[0078] With the development of society, energy has experienced a steady transition from fossil fuels to renewable and efficient energy. Among them, high-efficiency energy represented by secondary batteries is an important electrochemical device that stores and provides electricity on demand.

[0079] In order to promote the development of secondary batteries, the inventors conducted a lot of research and found that the failure mechanism of secondary batteries and the scientific principles behind them are subject to many limitations such as testing methods, and there are many parts that are not fully recognized and understood.

[0080] The inventors found that in secondary batteries, the negative electrode, electrolyte interface and related electrolyte decomposition reactions are considered to be important and need to be understood parts of secondary batteries. For example, in lithium-containing secondary batteries, due to the high reactivity of lithium and lithiated graphite anodes, the electrolyte undergoes complex decomposition reactions during the electrochemical cycle. The solid electrolyte interface film (SEI) produced during this decomposition reaction determines the transfer rate and uniformity of lithium ions at the anode or electrolyte interface, and also determines the reversibility of the negative electrode. Therefore, the inventors found that understanding and quantifying the electrolyte decomposition reaction process is crucial to understanding the battery failure mechanism and the working principle of the electrolyte.

[0081] In order to understand the decomposition process of the electrolyte, the inventors have made a lot of attempts from both theoretical and experimental aspects, but there is currently a lack of accurate quantitative methods. For example, computational methods such as density functional theory (DFT) and molecular dynamics (MD) can predict the reaction path and mechanism of the electrolyte decomposition reaction from thermodynamics, but theoretical simulations cannot quantify the changes in electrolyte content at the battery cycle scale. Conventional characterization techniques such as X-ray photoelectron spectroscopy (XPS) and (low temperature) transmission electron microscopy (TEM) can determine the components of the reaction product, namely SEI, as well as its content and distribution, thereby providing the necessary information for inferring the electrolyte decomposition process. However, the spatial resolution of XPS (hundreds of microns) and TEM (tens of nanometers) is suitable for detecting reaction products in local areas, while the spatial distribution of SEI components is uneven in both horizontal and vertical directions, making it impossible to quantify the electrolyte decomposition reaction and battery failure mechanism.

[0082] The inventors discovered that, compared to measuring the reaction products obtained from the electrolyte decomposition reaction, quantifying the changes in the content of each electrolyte component before and after circulation provides an alternative approach to understanding the electrolyte decomposition process. Currently, common methods for measuring the content of electrolyte components include ion chromatography (IC), gas chromatography-mass spectrometry (GC / MS), and inductively coupled plasma-mass spectrometry (ICP-MS). However, these methods can only measure the content of organic solvents or inorganic salts separately and cannot simultaneously perform more complex sample preparation processes such as separation or digestion.

[0083] In order to simultaneously measure the content of solvent and salt components in the electrolyte, the inventors found that quantitative nuclear magnetic technology (qNMR) can provide the nuclei in the solvent and the anion-containing molecules, so that these nuclei can reach signals that are easy to identify and quantify. However, in addition to the continuous consumption of anions and solvents, due to the presence of deposited metals and reducing metal compounds, the electrolyte will also continue to react with the deposited metals and reducing metal compounds when the battery is not cycled, thereby causing interference. At the same time, the transition metal ions dissolved by the positive electrode material will also affect the relaxation of the nuclear magnetic signal before and after the electrolyte cycle. Therefore, although quantitative nuclear magnetic technology has been used for electrolyte quantification, the residual metal lithium, the relaxation differences of different substances and the errors caused by sample preparation have not been accurately studied, resulting in the inability to accurately measure the content of each component in the electrolyte before and after the battery cycle.

[0084] After research, the inventors found that the titration gas chromatography (TGC) method can be used to react with residual metallic lithium and quantify the product by using heavy water as a titrant. Other alternative techniques, such as in situ solid-state NMR, electron paramagnetic resonance (EPR), and mass spectrometry (MS)-based titration, can also quantify residual metallic lithium by detecting gas or solid products, but are not suitable for the case of this application. The above studies mainly focus on residual metallic lithium and lack quantitative information about the simultaneous evolution of the electrolyte.

[0085] Based on the above-mentioned problems, the inventors provide a testing method to eliminate the influence of residual metallic lithium in battery samples, relaxation differences between different substances, and sample preparation errors during quantitative nuclear magnetic resonance sampling and testing, and ensure accurate measurement of the content of each component in the electrolyte through rigorous methods.

[0086] Method for determining the content of battery liquid electrolyte components

[0087] The present invention provides a method for determining the content of a liquid electrolyte component in a battery, the method comprising:

[0088] S1 provides an extraction solution containing an organic acid titrant and a relaxation enhancer, wherein the metal element or reducing metal compound in the battery component is completely dissolved by controlling the content of the organic acid titrant;

[0089] S2. The battery liquid electrolyte obtained by disassembling the battery and / or the battery components in contact with the battery liquid electrolyte are contacted with the extraction solution to obtain an extraction mixture;

[0090] S3. An internal standard compound is added to the sample obtained by the extraction mixture to obtain a sample to be tested, wherein the internal standard compound comprises: at least one element with nuclear magnetic properties; and each component of the liquid electrolyte to be tested independently contains the element with nuclear magnetic properties;

[0091] In step S3, the internal standard compound may include a first element with nuclear magnetism and a second element with nuclear magnetism, and each component to be measured in the liquid electrolyte independently contains the first element and / or the second element; or the internal standard compound may include a first element with nuclear magnetism, a second element with nuclear magnetism, and a third element with nuclear magnetism, and each component to be measured in the liquid electrolyte independently contains the first element, the second element, and the third element.

[0092] S4. Obtain at least two first nuclear magnetic resonance spectra of the sample to be tested measured for the element with nuclear magnetism;

[0093] S5. Determine the content of the component to be measured in the battery liquid electrolyte based on the first nuclear magnetic resonance spectrum.

[0094] According to the embodiments of the present application, the organic acid titrant, relaxation enhancer, and internal standard calibration treatment can respectively eliminate the influence of residual metallic lithium in the battery sample, the relaxation difference of different substances, and the sample preparation error, thereby ensuring that the content of each component of the electrolyte before and after the battery cycle can be accurately measured. The method for determining the content of each component in the electrolyte before and after the battery cycle provided in the present application can simultaneously determine the content of each component in the electrolyte, including the content of each component of the solvent, salts, and additives. The method is simple and rigorous, low-cost, and is not limited by the type of electrolyte. It can be applied to different electrolytes and battery configurations under conventional laboratory conditions.

[0095] In some embodiments, the extraction solution has predetermined ions. The extraction solution can be selected based on the composition of the battery liquid electrolyte so that the predetermined ions do not exist in the liquid electrolyte, and preferably the predetermined ions do not react with the electrolyte.

[0096] In some examples, the predetermined ions may be alkali metal ions. For example, for lithium-ion batteries, the predetermined ions may be sodium ions or potassium ions. For sodium-ion batteries, the predetermined ions may be potassium ions, rubidium ions, or cesium ions. In another example, the predetermined ions may also be anions, such as halogen ions such as bromide, chloride, or iodide.

[0097] In some embodiments, the concentration of the organic acid titrant in the extraction solution is 95-105 mmol / L.

[0098] According to the embodiments of the present application, the upper limit of the organic acid titrant is its solubility in the extraction solution. It should be noted that since the method for determining the electrolyte content in this application does not require knowing the concentration of the organic acid titrant in the extraction solution, this application does not impose specific restrictions. However, to ensure the accuracy of subsequent measurements, an organic acid titrant with high solubility and strong reactivity with metal elements and reducing metal compounds can be selected. The organic acid titrant can optionally be 195-205 mmol / L, or optionally 995-1005 mmol / L.

[0099] In some embodiments, the concentration of the relaxation enhancer in the extraction solution is 0.5-3 mmol / l.

[0100] According to the embodiments of the present application, by using the first element and the second element for nuclear magnetic resonance detection, the concentration of the relaxation enhancer in the extraction solution is controlled within the above-mentioned range, thereby overcoming the problem that a single surface relaxation rate value cannot truly reflect the content of the liquid electrolyte, and effectively improving the accuracy of the nuclear magnetic resonance results of the liquid electrolyte at a certain relaxation rate.

[0101] In some embodiments, the molecular weight of the organic acid titrant is ≤1000 Da. By controlling the molecular weight of the organic acid titrant within the above range, a higher diffusion rate and other better effects can be achieved.

[0102] In some embodiments, the relaxation enhancer makes the relaxation time ≤ 1 s. In order to accelerate relaxation, reduce the relaxation time, and make various types of elements relax within a relatively close time, the quantitative detection results can be made more accurate.

[0103] In some embodiments, the organic acid titrant is selected from maleic acid, dihydroxytartaric acid, oxaloacetic acid, pyruvic acid, malonic acid, phthalic acid, tartaric acid, fumaric acid, methylmalonic acid, terephthalic acid, adipic acid, acetic acid, propionic acid, p-pentanoic acid, or a combination thereof.

[0104] According to an embodiment of the present application, the organic acid titrant can be a carboxylic acid organic acid; on the one hand, it can be miscible with other components in the extraction solution, and on the other hand, it can react with metal elements and reducing metal-containing compounds to avoid interference with the accuracy of the measurement.

[0105] In some embodiments, the relaxation enhancer is selected from manganese acetylacetonate, manganese chloride, chromium acetylacetonate, nickel acetylacetonate, iron acetylacetonate, copper acetylacetonate, cobalt acetylacetonate, gadolinium acetylacetonate, or a combination thereof.

[0106] According to an embodiment of the present application, the relaxation enhancer may be a paramagnetic metal salt, which is magnetic in a nuclear magnetic field but non-magnetic outside the nuclear magnetic field and has no hysteresis phenomenon, thereby enhancing the accuracy of detection.

[0107] According to an embodiment of the present application, in step S2, any one of the button batteries, soft-pack batteries, square batteries and cylindrical batteries can be opened, and then the extracting liquid can be put into the battery to mix it with the liquid electrolyte in the battery; or, the opened battery can be immersed in the extracting liquid to mix it with the liquid electrolyte in the battery to obtain a solution in which the liquid electrolyte and the extracting liquid are evenly mixed.

[0108] In some embodiments, when the reaction of the mixture of liquid electrolyte and extract with the residual solid (metal element or reducing metal compound) in the battery sample is completed, the mixture can be mixed using an oscillator or a rotator to improve the uniformity of the components in the mixture.

[0109] In some embodiments, the internal standard compound is selected from trifluorotoluene, 3,4-dichlorobenzotrifluoride, 2,4-dichlorobenzotrifluoride, 2,5-dichlorobenzotrifluoride, 2,3-dichlorobenzotrifluoride, 3,5-dichlorobenzotrifluoride, 3,4,5-trichlorobenzotrifluoride, 4,4'-difluorobenzophenone, 2-chloro-4-fluorotoluene, or a combination thereof.

[0110] According to the embodiments of the present application, the internal standard compound can be a fluorinated organic compound, which can be used to determine the content and control the quality of the liquid electrolyte control group. In the absence of relevant reference substances, the determination of the content of the internal standard compound is an effective method that can provide a certain reference for the content of the liquid electrolyte.

[0111] In some embodiments, the extraction solution further comprises a deuterated reagent, and the deuterated reagent is selected from dichloromethane, deuterated methanol, deuterated dimethyl sulfoxide, deuterated chloroform, deuterated acetonitrile or a combination thereof. In the embodiments of the present application, it is necessary to ensure that each component in the extraction solution is completely dissolved into a transparent and clear solution. The deuterated solvent needs to consider its deuteration rate. Different deuterated solvents have different deuteration rates. For example, in deuterated chloroform, the content of CHCl3 is significantly greater than the content of H2O in D2O; for example, substances containing active hydrogen cannot be dissolved with deuterated reagents containing active hydrogen, such as alcohols, carboxylic acids, pyrrole, etc. cannot be dissolved with heavy water to avoid proton exchange.

[0112] In some embodiments, in step S2, in order to ensure that the electrolyte and the extract are fully mixed, the mixed solution can be allowed to stand for a period of time, and then a vibrating device such as a vibrator or a rotator can be used to accelerate the mixing of the mixed solution, and the above-mentioned standing and vibrating steps can be repeated to ensure that the concentration of each ion in the mixed solution is uniform.

[0113] In some embodiments, the battery is a battery that has undergone electrochemical cycling. Nuclear magnetic resonance (NMR) testing of the electrolyte of the battery that has undergone electrochemical cycling can determine the relative content of each component in the liquid electrolyte and understand the consumption of each component in the liquid electrolyte.

[0114] In some embodiments, the components of the liquid electrolyte include any one or more of a solvent, a solute, and an additive. A solute is defined as a substance with a content exceeding 1 mol / l in the liquid electrolyte, and a substance that dissolves the solute is defined as a solvent. Furthermore, an additive is defined as a solute with a content less than 1 mol / l or that does not function as an electrolyte. The contents of the solvent, solute, and additive in the liquid electrolyte can be measured separately or in combination.

[0115] In some embodiments, step S5 includes: determining the relative content of the solvent in the battery liquid electrolyte by formula (1) based on the first nuclear magnetic resonance spectrum;

[0116]

[0117] in, is the relative content of solvent A in the liquid electrolyte after i electrochemical cycles;

[0118] is the characteristic peak area of ​​element y in solvent A in the liquid electrolyte after i electrochemical cycles after NMR detection;

[0119] N(A) y is the number of y elements in the molecular formula of solvent A;

[0120] is the characteristic peak area of ​​solute B or additive C in the liquid electrolyte after i electrochemical cycles after NMR detection of element x;

[0121] N(B or C) x is the number of x elements in the molecular formula of solute B or additive C;

[0122] is the characteristic peak area of ​​the internal standard compound after NMR detection of element y, preferably a constant of 100;

[0123] N(IR) y is the number of y elements in the molecular formula of the internal standard compound;

[0124] is the characteristic peak area of ​​the internal standard compound after NMR detection of element x, preferably a constant of 100;

[0125] N(IR) x is the number of x elements in the molecular formula of the internal standard compound; x and y are independently selected from hydrogen, boron, carbon, oxygen, fluorine, and phosphorus. Preferably, x is hydrogen and y is fluorine.

[0126] In the embodiments of the present application, the relative content can be understood as the relative content of solvent A relative to solute B, or the relative content of solute B relative to solvent A, or the relative content of solute B relative to additive C.

[0127] In some embodiments, step S5 includes: determining the relative content of the solute in the liquid electrolyte of the battery according to the first nuclear magnetic resonance spectrum using formula (2);

[0128]

[0129] in, is the relative content of solute B in the liquid electrolyte after i electrochemical cycles;

[0130] is the characteristic peak area of ​​solute B in the liquid electrolyte after i electrochemical cycles detected by element x by NMR;

[0131] is the number of x elements in the molecular formula of solute B;

[0132] is the characteristic peak area of ​​solvent A or additive C in the liquid electrolyte after i electrochemical cycles detected by NMR of element y;

[0133] N(A or C) y is the number of y elements in the molecular formula of solvent A or additive C;

[0134] is the characteristic peak area of ​​the internal standard compound after NMR detection of element y, which can be normalized to a constant of 100;

[0135] N(IR) y is the number of y elements in the molecular formula of the internal standard compound;

[0136] is the characteristic peak area of ​​the internal standard compound after NMR detection of element x, preferably a constant of 100;

[0137] N(IR) x is the number of x elements in the molecular formula of the internal standard compound;

[0138] The x element and the y element are independently selected from hydrogen, boron, carbon, oxygen, fluorine, and phosphorus.

[0139] In some embodiments, the step S5 further includes: determining the relative content of the additive in the battery liquid electrolyte by formula (3) based on the first nuclear magnetic resonance spectrum;

[0140]

[0141] in, is the characteristic peak area of ​​element y in additive C in the liquid electrolyte after i electrochemical cycles in NMR detection;

[0142] N(C) y is the number of y elements in the molecular formula of solute C;

[0143] is the characteristic peak area of ​​solvent A or additive C in the liquid electrolyte after i electrochemical cycles after NMR detection of element x;

[0144] N(A or C) x is the number of x elements in the molecular formula of solvent A or additive C;

[0145] is the characteristic peak area of ​​the internal standard compound after NMR detection of element y, which can be normalized to a constant of 100;

[0146] N(IR) y is the number of y elements in the molecular formula of the internal standard compound;

[0147] is the characteristic peak area of ​​the internal standard compound after NMR detection of element x, which can be normalized to a constant of 100;

[0148] N(IR) y is the number of x elements in the molecular formula of the internal standard compound;

[0149] The x element and the y element are independently selected from hydrogen, boron, carbon, oxygen, fluorine, and phosphorus.

[0150] In some embodiments, the first element is selected from hydrogen, boron, carbon, oxygen, fluorine, and phosphorus.

[0151] In some embodiments, the second element is selected from hydrogen, boron, carbon, oxygen, fluorine, and phosphorus.

[0152] In some embodiments, the first element is different from the second element. In some embodiments, the method further comprises:

[0153] S6. The battery containing a known volume of electrolyte that has not been electrochemically cycled is disassembled in a protective atmosphere, and the battery liquid electrolyte and the components in contact with the battery liquid electrolyte are contacted with an additional extraction solution to obtain the total volume of the mixed solution and the liquid electrolyte and the extract that has not been electrochemically cycled;

[0154] S7. Add an internal standard compound to the sample obtained from the mixed solution to obtain a sample to be subjected to NMR detection;

[0155] S8. Performing nuclear magnetic resonance testing on the sample to be tested for the element with nuclear magnetic properties to obtain at least two second nuclear magnetic resonance spectra;

[0156] S9. Determine the absolute content of the substance in the liquid electrolyte of the battery based on the volume of the test mixture, the volume of the extract, the volume of the internal standard compound, the amount of the internal standard compound in the test mixture, the first nuclear magnetic resonance spectrum, and the second nuclear magnetic resonance spectrum obtained in part S7.

[0157] According to an embodiment of the present application, steps S2 to S5 and steps S6 to S8 may be performed simultaneously or sequentially, and the present application does not impose any specific limitation thereto.

[0158] According to the embodiments of the present application, the volume of the mixed solution to be tested and the volume of the extract can be determined by the volume transferred by a pipette, and the volume of the internal standard compound is calculated by weighing on a digital balance.

[0159] According to the embodiments of the present application, the method for determining the content of solvents, solutes, and additives in the liquid electrolyte before and after battery cycling can measure the electrolyte before and after the battery cycling to obtain the relative content and absolute content of each component before and after the battery cycling, respectively, avoiding the one-to-one comparison of each component of the nuclear magnetic resonance according to its standard nuclear magnetic resonance spectrum. The above method can be used for quantitative analysis of battery failure and is a testing method with great research value and application prospects.

[0160] In the examples of the present application, the absolute content can be understood as the absolute content of solvent A, solute B, and additive C independently relative to the blank control liquid electrolyte that has not undergone electrochemical cycling.

[0161] In some embodiments, step S9 specifically includes:

[0162] According to formula (4), the absolute content of the substance in the battery liquid electrolyte is determined:

[0163]

[0164] in, It is an internal standard cross calibration type;

[0165] n(Z) i The absolute content of substance Z in the liquid electrolyte after i electrochemical cycles;

[0166] I(Z) i is the characteristic peak area of ​​substance Z after NMR detection of the predetermined element;

[0167] I(IR) i is the characteristic peak area of ​​element y in the internal standard compound in NMR detection, preferably a constant of 100;

[0168] N3 is the amount of the internal standard compound in the test mixture, in moles,

[0169] is the characteristic peak area of ​​the deuterated reagent in the mixed solution of liquid electrolyte and extract after i electrochemical cycles after NMR detection of the predetermined element, which can be normalized to 100;

[0170] It is the characteristic peak area of ​​the deuterated reagent in the mixture of the liquid electrolyte and the extract that has not been electrochemically cycled after nuclear magnetic resonance detection of the predetermined element;

[0171] It is the characteristic peak area after NMR detection of the predetermined element, which can be normalized to 100;

[0172] V1 is the sum of the volume of the extract and the volume of the internal standard compound;

[0173] V2 is the volume of the sample to be detected by NMR.

[0174] The preparation method provided in this application can be used for the preparation method, which has a simple process, short time consumption, low equipment requirements, and compared with the measurement of reaction products in related technologies, it quantitatively measures the relative content of each component of the liquid electrolyte after circulation, providing another idea for understanding the decomposition process of the electrolyte.

[0175] Example

[0176] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0177] Example 1

[0178] The present invention provides a method for determining the content of a liquid electrolyte component in a battery, the method comprising:

[0179] S1. Providing an extraction solution containing an organic acid titrant and a relaxation enhancer, wherein the metal element or reducing metal compound in the battery component is completely dissolved by controlling the content of the organic acid titrant; the extract is prepared by adding 1 mM chromium acetylacetonate and 100 mM maleic acid as a relaxation enhancer and a titration reagent, respectively, to deuterated dimethyl sulfoxide.

[0180] S2. contacting the battery liquid electrolyte obtained by disassembling the battery and / or the components of the battery in contact with the battery liquid electrolyte with the extraction solution to obtain an extraction mixed solution; wherein the electrolyte is prepared by mixing lithium bis(fluorosulfonyl)imide (LiFSI) and dimethyl carbonate (DMC) as salt and solvent in a molar ratio of 1.0:1.8; wherein 3 copper||NCM523(LiNi 0.5 Co 0.2 Mn 0.3 ) button cell (2032 type), consisting of a single-side coated positive electrode, a polyethylene (PE) separator, and a copper foil, 20 μL of electrolyte was added to each cell using a pipette.

[0181] S3. Add an internal standard compound to the sample obtained from the extraction mixture to obtain a sample to be tested, wherein the internal standard compound comprises: a first element with nuclear magnetism, hydrogen; and a second element with nuclear magnetism, fluorine. Each component to be tested in the liquid electrolyte independently contains the first element and / or the second element; wherein 0.6 mL of the mixed solution is transferred to a nuclear magnetic tube containing 20 μL of the internal standard compound (2,4-dichlorotrifluorotoluene) to obtain a test solution and perform a qNMR test. The liquid nuclear magnetic tube used is a 5 mm high-throughput liquid nuclear magnetic tube.

[0182] S4. Obtain two first NMR spectra of the sample for the magnetically active element. The NMR detection methods in step 4 are as follows: obtain a proton and fluorine spectrum of the sample on an NMR spectrometer using a 90° pulse angle and a d1 of 15 s. The scan range is set to 120% of the signal range, with the emitter offset centered at the signal. The number of scans is 8. Area extraction and integration are performed using automatic peak selection and automatic integration methods to ensure the same integration width for each signal.

[0183] S5. Determine the content of the component to be tested in the battery liquid electrolyte according to the first nuclear magnetic resonance spectrum; substitute the qNMR test result into formula (1), formula (2) or formula (3) to calculate and obtain the relative content of lithium salt and solvent before and after the electrolyte cycle:

[0184] S6. Disassemble an un-electrochemically cycled battery containing a known volume of electrolyte in a protective atmosphere, and contact the battery liquid electrolyte and components in contact with the battery liquid electrolyte with an additional extraction solution to obtain a mixed solution and the total volume of the un-electrochemically cycled liquid electrolyte and the extraction solution. Two of these batteries were charge-discharge cycled using a battery tester at 25°C within a voltage range of 2.8-4.3V, designated as Examples 1-b and 1-c. The un-cycled battery was designated as Example 1-a. After 30 charge-discharge cycles of Examples 1-b and 1-c, the un-cycled and cycled coin cells of Example 1 were disassembled in an argon-filled glove box. All disassembled battery components were quickly transferred to a sample tube containing 2 mL of the extraction solution. After all the residual metallic lithium was reacted with the titration reagent (~5 minutes), the sample tube was vortexed for 30 minutes and then allowed to stand for 30 minutes to thoroughly mix and obtain a mixed solution. The sample tubes used are 30 mL PET sample bottles with an inner diameter of >20 mm or 25 / 50 mL PP centrifuge tubes.

[0185] S7. Add the internal standard compound to the sample obtained from the mixed solution to obtain a sample for NMR analysis. Transfer 0.6 mL of the mixed solution to an NMR tube containing 20 μL of the internal standard compound (2,4-dichlorotrifluorotoluene) to obtain a test solution and perform qNMR analysis. The liquid NMR tube used is a 5 mm high-throughput liquid NMR tube.

[0186] S8. Perform nuclear magnetic resonance detection on the sample to be detected for the first element and the second element to obtain at least two second nuclear magnetic resonance spectra; the nuclear magnetic detection methods of step 8 are as follows: use a 90° pulse angle and a d1 of 15s on the nuclear magnetic spectrometer to obtain the hydrogen spectrum and fluorine spectrum of the sample. The scanning range is set to 120% of the signal range, and the emitter offset is located at the center of the signal. The number of scans is 8. Area extraction and integration are completed using automatic peak selection and automatic integration methods to ensure that the integration width of each signal is the same. The nuclear magnetic resonance image of Example 1-a is as follows Figure 1 As shown, the nuclear magnetic resonance images of Example 1-b and Example 1-c are as follows Figure 2 As shown, the left side is the NMR image of Example 1-b, and the right side is the NMR image of Example 1-c.

[0187] S9. Determine the absolute content of the substance in the battery liquid electrolyte based on the volume of the test mixture, the volume of the extract, the volume of the internal standard compound, the amount of the internal standard compound in the test mixture, the first nuclear magnetic resonance spectrum, and the second nuclear magnetic resonance spectrum obtained in part S7. Substitute the qNMR test results into formula (3) to calculate the absolute content of lithium salt and solvent in the electrolyte before and after circulation:

[0188] The NMR detection methods in step 4 and step 8 are:

[0189] The model of the above-mentioned nuclear magnetic resonance detector is JEOL JNM-ECZ400S, and its operating parameters are: hydrogen spectrum 399.98 MHz, hydrogen spectrum midpoint 7 ppm, hydrogen spectrum width 7512.02 Hz, fluorine spectrum 376.36 MHz, fluorine spectrum midpoint -4 ppm, fluorine spectrum width 93.985 kHz, measurement temperature 293 K, time 6.5 μs, spectrum points 29999, sampling time 4 s, and delay time 15 s.

[0190] Example 2

[0191] The present embodiment provides a method for determining the content of liquid electrolyte components in a battery, the difference being that:

[0192] (1) The electrolyte solution was prepared by mixing lithium bis(fluorosulfonyl)imide (LiFSI) and dimethyl carbonate (DMC) as a salt and a solvent at a molar ratio of 1.0:1.8.

[0193] (2) An extract was prepared by adding 1 mM chromium acetylacetonate and 100 mM maleic acid as a relaxation enhancer and titration reagent, respectively, to deuterated dimethyl sulfoxide.

[0194] (3) Assemble three copper||NCM523(LiNi 0.5 Co 0.2 Mn 0.3 ) button cell (2025 type), consisting of a single-sided coated positive electrode, a polyethylene (PE) separator, and a copper foil, 20 μL of electrolyte was added to each cell using a pipette.

[0195] (4) Two of the batteries were subjected to charge-discharge cycles at 25° C. and within a voltage range of 2.8-4.3 V using a battery tester, and designated as Example 2-b and Example 2-c, respectively. The uncycled battery was designated as Example 2-a.

[0196] (5) After 30 charge-discharge cycles of Example 2-b and Example 2-c, the button batteries of Example 2-a that had not been cycled and the button batteries of Example 2-b and Example 2-c that had been cycled were disassembled in an argon-filled glove box. All parts of the disassembled battery were quickly transferred to a sample tube containing 2 mL of the extract. After all the residual metallic lithium was reacted by the titration reagent (~5 minutes), the sample tube was shaken on a vortex oscillator for 30 minutes, and then allowed to stand for 30 minutes to fully mix and obtain a mixed solution. The sample tube used was a 30 mL PET sample bottle with an inner diameter of the bottle mouth >20 mm or a 25 / 50 mL PP centrifuge tube.

[0197] (6) Transfer 0.6 mL of the mixed solution into a 5 mm high-throughput liquid NMR tube containing 20 μL of the internal standard compound (2,4-dichlorotrifluorotoluene) to obtain the test solution and perform qNMR analysis.

[0198] (7) Proton and fluorine spectra of the sample were acquired on an NMR spectrometer using a 90° pulse angle and a d1 of 15 s. The scan range was set to 120% of the signal range, with the emitter offset centered at the signal. The number of scans was 8. Area extraction and integration were performed using automatic peak selection and automatic integration methods, ensuring that the integration width was the same for each signal.

[0199] (8) Substitute the qNMR test results into the formula to calculate the relative and absolute contents of lithium salt and solvent before and after the electrolyte cycle.

[0200] The NMR spectra of Example 2-a are as follows: Figure 3 As shown, the nuclear magnetic resonance images of Example 2-b and Example 2-c are as follows Figure 4 As shown, the left side is the NMR image of Example 2-b, and the right side is the NMR image of Example 2-c.

[0201] Example 3

[0202] The present embodiment provides a method for determining the content of liquid electrolyte components in a battery, the difference being that:

[0203] (1) The electrolyte was prepared by mixing lithium bis(fluorosulfonyl)imide (LiFSI), dimethyl carbonate (DMC), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) as salt, solvent, and additive in a molar ratio of 1.0:1.8:2.0.

[0204] (2) An extract was prepared by adding 1 mM chromium acetylacetonate and 100 mM maleic acid as a relaxation enhancer and titration reagent, respectively, to deuterated dimethyl sulfoxide (molecular formula: [2H]6C2OS).

[0205] (3) Assemble three copper||NCM soft pack batteries (7×4cm) in a dry room with a dew point of -60℃. 2 ), consisting of a double-sided coated positive electrode, a polyethylene (PE) separator, and copper foil, and 0.5 g of electrolyte was added.

[0206] (4) Two of the batteries were subjected to charge-discharge cycles using a battery tester at 25° C. within a voltage range of 2.8-4.3 V, respectively designated as Example 3-b and Example 3-c. The uncycled electrolyte was used as Example 3-a.

[0207] (5) For soft-pack batteries, inject 2 mL of the extract into the soft-pack battery, seal it, and knead it for 5 minutes to allow the extract to fully enter the battery, then let it stand for 30 minutes.

[0208] (9) Transfer 0.6 mL of the mixed solution into a NMR tube containing 50 μL of the internal standard compound (2,4-dichlorotrifluorotoluene) to obtain the test solution and perform qNMR analysis. The liquid NMR tube used was a 5 mm high-throughput liquid NMR tube.

[0209] (6) Proton and fluorine spectra of the sample were acquired on an NMR spectrometer using a 90° pulse angle and a d1 of 15 s. The scan range was set to 120% of the signal range, with the emitter offset centered at the signal. The number of scans was 8. Area extraction and integration were performed using automatic peak selection and automatic integration methods, ensuring that the integration width was the same for each signal.

[0210] (7) Substitute the qNMR test results into the formula to calculate the relative and absolute contents of lithium salt and solvent before and after the electrolyte cycle.

[0211] The NMR spectra of Example 3-a are as follows: Figure 5 As shown, the nuclear magnetic resonance images of Example 3-b and Example 3-c are as follows Figure 6 As shown, the left side is the nuclear magnetic resonance image of Example 3-b, and the right side is the nuclear magnetic resonance image of Example 3-c.

[0212] Comparative Example

[0213] In the prior art, when a method without using a relaxation enhancer and an internal standard is used, the error of the calculated result increases by 30%, and the data result is relatively random and inaccurate.

[0214] Test section

[0215] The methods of the above examples are recorded in a table, and the obtained NMR spectra are Figure 1-6 shown.

[0216] Table 1 NMR test results of Examples 1-3.

[0217]

[0218]

[0219] By the following calculation formula:

[0220] Relative content:

[0221] Absolute content:

[0222] Wherein for all embodiments, N(A) 1H The corresponding value is 6; N(IR)1H The corresponding value is 3; N(B) 19F The corresponding value is 2; N(C) 1H The corresponding value is 2; N(IR) 19F The corresponding value is 3; M IR The corresponding value is 215.00, V2 is 0.60mL, for Example 1-3, the corresponding value of V1 is 2.02mL; the corresponding value of M3 is 32.90μg, for Example 1-3, the corresponding value of V1 is 2.31mL; the corresponding value of M3 is 82.27μg. The corresponding value of V2 is 0.60mL, the above n(Z) i represents the content of substance Z in the electrolyte after i electrochemical cycles, I(Z) is the integrated area of ​​the hydrogen spectrum or fluorine spectrum of substance Z, X is the characteristic atomic nucleus of fluorine-containing salt B or fluorine-containing or hydrogen-containing additive C, D is the deuterated solvent in the extract, V1 is the volume of the blank mixed solution after adding the first predetermined amount of extract, V2 is the volume of the second predetermined amount of mixed solution, M3 is the mass of the second predetermined amount of internal standard, and M IR is the molecular mass of the internal standard.

[0223] For example, in Example 3-b, the solvent is dimethyl carbonate (DMC), whose chemical formula is C3H6O3; the solute is lithium bis(fluorosulfonyl)imide (LiFSI), and the additive is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE); the internal standard compound is 2,4-dichlorobenzotrifluoride, which is an organic compound with a chemical formula of C7H3Cl2F3;

[0224] Relative content of dimethyl carbonate = [(123.78 / 6) / (100 / 3)] / [(21.98 / 2) / (100 / 3)] = 1.88

[0225] Absolute content of dimethyl carbonate = [(123.78 / 6) / (100 / 3)] × (82.27 / 215.00) / [(12.57 / 100) / (11.04 / 100)] × (2.31 / 0.6) = 0.80079 mmol

[0226] Table 2 Determination results of the content of each component in the electrolyte of Examples 1-3.

[0227]

[0228] Examples 1-3 demonstrate that the method provided by the present invention can measure the relative and absolute contents of solvents, salts, and additives in the electrolyte before and after battery cycling, with high data reproducibility and accuracy. Examples 1-3 utilize different battery configurations for sample collection, demonstrating the robust applicability of the method provided by the present invention to electrolyte testing across various battery configurations.

[0229] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for determining the content of a liquid electrolyte component in a battery, the method comprising: S1. Providing an extraction solution containing an organic acid titrant and a relaxation enhancer, wherein the metal element or reducing metal compound in the battery component is completely deactivated by controlling the content of the organic acid titrant, and the concentration of the relaxation enhancer in the extraction solution is 0.5-3 mmol / l; the relaxation enhancer is selected from manganese acetylacetonate, manganese chloride, chromium acetylacetonate, nickel acetylacetonate, iron acetylacetonate, copper acetylacetonate, cobalt acetylacetonate, gadolinium acetylacetonate, or a combination thereof; S2. The liquid electrolyte of the battery obtained by disassembling the battery and / or the battery components in contact with the liquid electrolyte are contacted with the extraction solution to obtain an extraction mixture; S3. Adding an internal standard compound to the sample obtained by the extraction mixture to obtain a sample to be tested, wherein the internal standard compound comprises: at least one element with nuclear magnetism; and each component to be tested in the liquid electrolyte independently contains the element with nuclear magnetism; S4. Obtaining at least two first nuclear magnetic resonance spectra of the sample to be tested measured for the element with nuclear magnetism; S5. Determine the content of the component to be measured in the battery liquid electrolyte according to the first nuclear magnetic resonance spectrum.

2. The method according to claim 1, characterized in that The concentration of the organic acid titrant in the extraction solution is 95-105 mmol / l; and / or, The molecular weight of the organic acid titrant is ≤1000Da, and / or The relaxation enhancer makes the relaxation time ≤ 1 s.

3. The method according to claim 1, characterized in that The organic acid titrant is selected from maleic acid, dihydroxytartaric acid, oxaloacetic acid, pyruvic acid, malonic acid, phthalic acid, tartaric acid, fumaric acid, methylmalonic acid, terephthalic acid, adipic acid, acetic acid, propionic acid, p-pentanoic acid or a combination thereof; and / or, The internal standard compound is selected from trifluorotoluene, 3,4-dichlorobenzotrifluoride, 2,4-dichlorobenzotrifluoride, 2,5-dichlorobenzotrifluoride, 2,3-dichlorobenzotrifluoride, 3,5-dichlorobenzotrifluoride, 3,4,5-trichlorobenzotrifluoride, 4,4'-difluorobenzophenone, 2-chloro-4-fluorotoluene or a combination thereof.

4. The method according to claim 1, wherein The extraction solution further comprises a deuterated reagent, and the deuterated reagent is selected from dichloromethane, deuterated methanol, deuterated dimethyl sulfoxide, deuterated chloroform, deuterated acetonitrile or a combination thereof.

5. The method according to claim 1, wherein The battery is a battery that has undergone electrochemical cycling.

6. The method according to claim 5, characterized in that The components of the liquid electrolyte include any one or more of a solvent, a solute and an additive.

7. The method according to claim 6, characterized in that The step S5 comprises: determining the relative content of the solvent in the liquid electrolyte of the battery by formula (1) according to the first nuclear magnetic resonance spectrum; in, is the relative content of solvent A in the liquid electrolyte after i electrochemical cycles; is the characteristic peak area of ​​element y in solvent A in the liquid electrolyte after i electrochemical cycles after NMR detection; N(A) y is the number of y elements in the molecular formula of solvent A; is the characteristic peak area of ​​solute B or additive C in the liquid electrolyte after i electrochemical cycles after NMR detection of element x; N(B or C) x is the number of x elements in the molecular formula of solute B or additive C; is the characteristic peak area of ​​the internal standard compound after NMR detection of element y, which can be normalized to a constant of 100; N(IR) y is the number of y elements in the molecular formula of the internal standard compound; is the characteristic peak area of ​​the internal standard compound after NMR detection of element x, which can be normalized to 100; N(IR) x is the number of x elements in the molecular formula of the internal standard compound; the x elements and y elements are independently selected from hydrogen, boron, carbon, oxygen, fluorine, and phosphorus.

8. The method according to claim 6, characterized in that The step S5 includes: determining the relative content of the solute in the liquid electrolyte of the battery by formula (2) according to the first nuclear magnetic resonance spectrum; in, is the relative content of solute B in the liquid electrolyte after i electrochemical cycles; is the characteristic peak area of ​​solute B in the liquid electrolyte after i electrochemical cycles detected by element x by NMR; N(B) x is the number of x elements in the molecular formula of solute B; is the characteristic peak area of ​​solvent A or additive C in the liquid electrolyte after i electrochemical cycles detected by NMR of element y; N(A or C) y is the number of y elements in the molecular formula of solvent A or additive C; is the characteristic peak area of ​​the internal standard compound after NMR detection of element y, which can be normalized to a constant of 100; N(IR) y is the number of y elements in the molecular formula of the internal standard compound; is the characteristic peak area of ​​the internal standard compound after NMR detection of element x, which can be normalized to a constant of 100; N(IR) x is the number of x elements in the molecular formula of the internal standard compound; The x element and the y element are independently selected from hydrogen, boron, carbon, oxygen, fluorine, and phosphorus.

9. The method according to any one of claims 6 to 8, characterized in that: The method further comprises: S6. disassembling a battery containing a known volume of electrolyte that has not been electrochemically cycled in a protective atmosphere, contacting the battery liquid electrolyte and components in contact with the battery liquid electrolyte with an additional extraction solution to obtain a total volume of a mixed solution, a liquid electrolyte that has not been electrochemically cycled, and the extraction solution; S7. Add the internal standard compound to the sample obtained from the mixed solution to obtain a sample to be subjected to NMR detection; S8. The sample to be tested by nuclear magnetic resonance is subjected to nuclear magnetic resonance detection for the element with nuclear magnetic properties to obtain at least two second nuclear magnetic resonance spectra; S9. Determine the absolute content of the substance in the liquid electrolyte of the battery based on the volume of the test mixture obtained in part S7, the volume of the extraction solution, the volume of the internal standard compound, the amount of the internal standard compound in the test mixture, the first nuclear magnetic resonance spectrum, and the second nuclear magnetic resonance spectrum.

10. The method according to claim 9, characterized in that The S9 step specifically includes: The absolute content of the substance in the liquid electrolyte of the battery is determined according to formula (3), in, is the internal standard cross calibration formula; n(Z) i The absolute content of substance Z in the liquid electrolyte after i electrochemical cycles; is the characteristic peak area of ​​substance Z after NMR detection of the predetermined element; It is the characteristic peak area of ​​the predetermined element in the internal standard compound in the NMR detection, which can be normalized to a constant of 100; N(Z) X is the number of predetermined elements in the molecular formula of substance Z; N(IR) X is the number of predetermined elements in the molecular formula of the internal standard compound; N3 is the amount of the internal standard compound in the test mixture, in moles, is the characteristic peak area of ​​the deuterated reagent in the mixture of liquid electrolyte and extraction solution after i electrochemical cycles after NMR detection of the predetermined element, which can be normalized to 100; It is the characteristic peak area of ​​the deuterated reagent in the mixture of the liquid electrolyte and the extraction solution that has not been electrochemically cycled after nuclear magnetic resonance detection of the predetermined element; It is the characteristic peak area of ​​the internal standard compound after NMR detection of the predetermined element, which can be normalized to a constant of 100; It is the characteristic peak area of ​​the internal standard compound after NMR detection of the predetermined element without electrochemical cycling; V1 is the sum of the volume of the extraction solution and the volume of the internal standard compound; V2 is the volume of the sample to be detected by NMR.

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