Method for identifying composite lithium salt in lithium battery electrolyte containing lithium oxalylborate

Abstract

The invention discloses a method for identifying composite lithium salt in a lithium battery electrolyte containing lithium oxalato borate. The method comprises the following steps: firstly, carrying out ion chromatography test on the electrolyte to be tested to obtain the type and content of conventional lithium salt and the total peak area of the lithium oxalato borate; then carrying out 400M nuclear magnetic resonance boron spectrum test, accurately identifying various types of oxalic acid-containing lithium borate salts, and obtaining the peak area proportion of hydrolyzed lithium salt products possibly existing in the oxalic acid-containing lithium borate salts and generated by part of easily-hydrolyzed lithium salts in the ion chromatography test; and finally, correcting and redistributing the total peak area measured by the ion chromatography according to the proportion, so as to calculate the accurate contents of various products containing the lithium oxalylborate and the hydrolyzed lithium salt of the lithium oxalylborate. The method effectively solves the problems that the traditional ion chromatography cannot distinguish the oxalic acid-containing lithium borate with similar structures and the quantification is interfered by hydrolysis, realizes the accurate qualitative and quantitative analysis of the composite lithium salt in the electrolyte, and provides reliable technical support for the research and development and quality control of the electrolyte.

Description

Technical Field

[0001] This invention relates to the field of lithium salt detection methods in lithium battery electrolytes, and particularly to a method for identifying complex lithium salts in lithium battery electrolytes containing lithium oxalate-borate salt. Background Technology

[0002] Lithium salts in lithium-ion battery electrolytes are crucial carriers and sources of lithium ions, playing an irreplaceable core role in the battery system. Specifically, the core functions of lithium salts are mainly reflected in the following aspects: First, improving ionic conductivity. Lithium salts dissociate into lithium ions in organic solvents, forming an ionic conductive network. Their dissociation ability and ion migration rate directly determine the ionic conductivity of the electrolyte, thus affecting the battery's rate performance and fast-charging capability. Second, regulating interfacial electrochemistry. The anions of lithium salts participate in the formation of the electrode / electrolyte interface (SEI film and CEI film). A stable, ion-conducting interfacial film is essential for inhibiting continuous electrolyte decomposition, improving initial coulombic efficiency, and extending cycle life. For example, some lithium salts can promote the formation of a more uniform and dense SEI film, effectively preventing the damage to the electrode structure caused by solvent molecule co-intercalation. Finally, ensuring system stability. High-quality lithium salts can inhibit the oxidative decomposition of the electrolyte at high voltages and solidification at low temperatures, while reducing the generation of gaseous byproducts during charging and discharging, thereby comprehensively improving the battery's safety window, high and low temperature performance, and lifespan. Therefore, precise control of the lithium salt composition in the electrolyte is a key aspect of designing and optimizing high-performance lithium batteries.

[0003] Currently, ion chromatography is the mainstream method for identifying and quantifying lithium salt components in electrolytes in industry and laboratories. This method separates different ions based on the difference in their partition coefficients between the stationary and mobile phases of the chromatographic column, and then uses a detector (such as a conductivity detector) to perform qualitative and quantitative analysis of the separated ions. This method has good separation performance for conventional lithium salts such as lithium hexafluorophosphate. However, its technical bottleneck lies in separating highly similar anionic salts, especially lithium oxalate-borate salts. When anions are highly similar in molecular size, charge distribution, and polarity, their retention behavior on conventional ion chromatography columns is almost identical, and their elution times are extremely close. This similarity in physicochemical properties directly leads to peak overlap or insufficient resolution in the chromatogram. Overlapping chromatographic peaks not only make accurate quantification of their respective contents difficult but also introduce uncertainty into qualitative identification, making it difficult to determine whether one or both exist simultaneously. This poses a hidden danger for electrolyte formulation development, quality control, and battery failure analysis.

[0004] Therefore, to overcome the limitations of traditional ion chromatography, it is urgent to develop a novel analytical method that can efficiently distinguish structurally similar lithium oxalate-borate salts based on information beyond the physicochemical properties of the ions themselves. By constructing these highly selective and sensitive new analytical methods, we can achieve rapid and accurate identification of various lithium salt components in complex multi-component lithium salt electrolyte systems. This will not only accelerate the development of new lithium salt formulations but also provide solid and reliable technical support for raw material inspection, finished electrolyte quality monitoring, and traceability analysis of failed batteries during lithium battery production, ultimately promoting the iteration and development of high-performance and high-safety lithium-ion battery technology. Summary of the Invention

[0005] This invention addresses the problems in existing technologies where ion chromatography cannot effectively identify the types of lithium oxalate-borate salts and cannot accurately quantify them during the identification of complex lithium salts. It provides a method for identifying lithium oxalate-borate salts in lithium battery electrolytes, offering reliable technical support for product development and improving the long-term quality stability of products.

[0006] This invention is achieved through the following technical solution: This invention provides a method for identifying composite lithium salts in lithium battery electrolytes containing lithium oxalate borate, comprising the following steps: S1: Perform ion chromatography tests on the lithium battery electrolyte to be tested, and confirm the types and contents of conventional lithium salts in the composite lithium salt, as well as the total peak area of ​​lithium salt containing lithium oxalate borate, based on the peak time and peak area. S2: Perform 400M nuclear magnetic resonance boron spectrum test on the lithium battery electrolyte to be tested, and identify the various types of lithium oxalate-borate salts and the hydrolyzed lithium salt products of various types of easily hydrolyzed lithium salts in lithium oxalate-borate salts according to the peak time, and obtain the peak area ratio of various types of lithium oxalate-borate salts and various types of hydrolyzed lithium salt products. S3: The sum of the total peak area of ​​lithium oxalate-borate salt and the peak area of ​​each type of corresponding hydrolyzed lithium salt product in the ion chromatography test in step S1 is redistributed according to the peak area ratio in step S2 to obtain the corrected peak areas of each type of lithium oxalate-borate salt and each type of hydrolyzed lithium salt product, and the content of each type of composite lithium salt is confirmed based on the corrected peak areas.

[0007] This invention innovatively proposes a synergistic analytical strategy combining ion chromatography and nuclear magnetic resonance (NMR) boron spectroscopy. This method fully leverages the advantages of ion chromatography in rapid screening and multi-component quantification, as well as the high specificity of NMR in molecular structure identification, successfully solving the challenge of accurately distinguishing various structurally similar lithium salts containing lithium oxalate-borate. Specifically, this method uses a 400 M NMR spectrometer for boron spectroscopy detection, achieving an optimal balance between instrument cost and analytical performance. Although higher-frequency NMR equipment can provide higher theoretical resolution, the 400 M boron spectrum has sufficient resolution to clearly and stably distinguish the characteristic chemical shifts of the two lithium salts containing lithium oxalate-borate, ensuring the reliability of the identification results. Furthermore, this frequency of NMR equipment is more widely available and has lower maintenance costs, greatly enhancing the practicality and promotional value of this method. Therefore, this invention's strategy of combining ion chromatography with 400 M NMR boron spectroscopy provides efficient and reliable technical support for the precise development of high-performance lithium battery electrolytes, quality control in the production process, and failure analysis. This invention innovatively discovers that in the ion chromatography detection of lithium oxalate-borate salts, the detected content deviates from the theoretical value. This is because, during the detection of some lithium oxalate-borate salts using ion chromatography, some components in the eluent may react with some of the lithium oxalate-borate salt, leading to the hydrolysis of the lithium oxalate-borate salt and the generation of hydrolyzed lithium salt products, affecting the accuracy of quantitative analysis. These products can originate from the hydrolyzed lithium salts generated during ion chromatography testing, or they can originate from the lithium salts originally present in the battery electrolyte. Therefore, in subsequent quantitative analysis, because ion chromatography cannot distinguish between the detected hydrolyzed lithium salt products that are originally present in the electrolyte and those generated by the hydrolysis of lithium oxalate-borate salts, the measured concentration is actually the sum of the two. At this point, the present invention innovatively uses the peak area ratio of the nuclear magnetic resonance boron spectrum to redistribute the total peak area of ​​lithium oxalate-borate salt and hydrolyzed lithium salt products measured by ion chromatography. This allows for the separation of the concentration corresponding to the hydrolyzed lithium salt products generated by the hydrolysis of easily hydrolyzable lithium salts, and the correction of this concentration to the original concentration of the easily hydrolyzable lithium salt. This enables accurate calculation and correction of the true content of lithium oxalate-borate salt. This innovative correction strategy effectively eliminates systematic analysis errors caused by the instability of lithium salt chemical properties, significantly improving the accuracy and reliability of qualitative and quantitative analysis of lithium oxalate-borate salt in complex electrolyte systems, and providing a more reliable data foundation and technical support for product quality control and formulation development.

[0008] As one example, when the lithium battery electrolyte is tested with 400M nuclear magnetic resonance boron spectrum in S2 to obtain the peak area at different elution times, and only the various types of lithium oxalate borate salts are obtained according to the elution time, the total peak area of ​​lithium oxalate borate salts in the ion chromatography test is allocated according to the peak area ratio of various lithium oxalate borate salts in the nuclear magnetic resonance boron spectrum to confirm the content of each type.

[0009] As a further embodiment, the eluent for the ion chromatography test includes carbonate and acetonitrile, and the flow rate of the eluent for the ion chromatography test is 0.6~0.8 mL / min.

[0010] This method utilizes a mixture of carbonate and acetonitrile as the eluent. The carbonate provides the ionic strength and pH environment required for gradient elution, while the addition of an appropriate amount of acetonitrile adjusts the polarity and selectivity of the mobile phase, effectively improving the interaction differences between structurally similar lithium salts and promoting their separation. Combined with an optimized flow rate of 0.6–0.8 mL / min, the target components can reach kinetic and thermodynamic equilibrium on the column within a reasonable analytical time, resulting in sharp chromatographic peaks with well-separated baselines. Further optimization of these parameters lays a solid technical foundation for accurate qualitative and quantitative analysis.

[0011] As a further embodiment, the injection volume of the ion chromatography test is 20~30 μL, the chromatographic column model of the ion chromatography test is A5-150, and the column temperature of the ion chromatography test is 33~37℃.

[0012] This invention further limits the injection volume, column type, and column temperature for ion chromatography testing. This allows for better separation of lithium salts, and a sufficient injection volume ensures adequate detection sensitivity while avoiding peak broadening and tailing caused by excessive injection volume. The use of an A5-150 column, with its packing particle size and functional group design, is suitable for the efficient separation of various anions. Precisely controlling the column temperature at 33–37°C helps maintain a stable eluent mass transfer rate, thereby achieving reproducible retention times.

[0013] As a further option, the carbonate is selected from one or more of sodium carbonate and sodium bicarbonate.

[0014] As a further embodiment, the volume ratio of carbonate to acetonitrile in the rinsing solution is (65~75):(25~35).

[0015] This invention further optimizes the volume ratio of carbonate to acetonitrile in the eluent, selecting a ratio of (65-75):(25-35). This specific ratio is the result of systematic optimization and verification, aiming to achieve the best balance between separation efficiency, analysis speed, and peak shape characteristics. At this ratio, the carbonate-dominated aqueous phase system ensures the necessary ion exchange forces between the target anion and the stationary phase of the column, providing sufficient retention and separation. Simultaneously, 30% acetonitrile acts as an organic modifier, effectively adjusting the overall polarity and elution intensity of the mobile phase. This ratio optimizes the peak shape, suppresses peak tailing, and controls the analysis time within a reasonable range under suitable elution intensity, while ensuring sufficient resolution. This optimized eluent ratio further provides a reliable guarantee for the accurate quantification of target lithium salts in complex electrolyte samples.

[0016] As a further step, in step S1, the electrolyte of the lithium battery to be tested is subjected to ion chromatography, and the content of various types of conventional lithium salts in the composite lithium salt is confirmed by external standard method based on the peak time and peak area according to the standard curve.

[0017] As a further step, in step S3, the corrected peak areas of various types of lithium salt containing oxalate-borate and various types of hydrolyzed lithium salt products are obtained, and the content of various types in the composite lithium salt is confirmed by external standard method according to the standard curve based on the corrected peak areas.

[0018] As a further option, the conventional lithium salts include lithium difluorophosphate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, etc.

[0019] As a further embodiment, the lithium oxalate-borate salt includes lithium difluorooxalate-borate, lithium dioxalate-borate, etc.

[0020] As a further embodiment, the easily hydrolyzable lithium salt in the ion chromatography test includes lithium difluorooxalate borate, and the hydrolysis lithium salt product of lithium difluorooxalate borate in the ion chromatography test is lithium tetrafluoroborate.

[0021] As a further embodiment, the method for nuclear magnetic resonance boron spectroscopy testing includes the following steps: s1: First, the gyromagnetic ratio of the B11 nucleus is found to be 8.5794. 10 7 rad s -1 T -1 The natural abundance of B11 was 80.1%; s2: First, borrow the standard experiment of C spectrum and create a new experiment. When the gyromagnetic ratio is positive, select C13CPD as the standard experiment; when the gyromagnetic ratio is negative, select C13IG as the standard experiment. s3: To view the Acqpar parameters of C13, enter the command getprosol to read the pulse width and power of C; s4: Enter the edsp command, change C13 in F1 dimension to B11, leave 1H in F2 dimension unchanged, and save the settings; Returning to the Acqupars parameters, change the number of scans (NS) to 1024, the spectral width (SW) to 400, assign O1P to 0, and set D1 (relaxation time) to 2s; s5: Enter the command to lock the field, homogenize the field, and enter the command ATMM to perform received tuning. The first time is manual tuning. After tuning is completed, enter the command ATMA again to perform automatic tuning. s6: Input command to perform signal amplification (rga), spectrum acquisition (zg), Fourier transform (efp), phase correction (apk), and finally input command sref to perform data calibration.

[0022] This invention further establishes and optimizes the testing method for 400M NMR boron spectroscopy. Since a standardized testing method for boron spectroscopy in routine 400M NMR analysis has not been established, and the nuclear properties of different boron-containing substances, such as gyromagnetic ratio, differ significantly from those of common hydrogen and carbon nuclei, this invention establishes a more stable, reliable, and highly sensitive standard testing procedure for lithium oxalate-borate salts based on standard C-spectroscopy experiments at 400M NMR. The establishment of this standardized method not only fills the gap in high-precision analysis of lithium oxalate-borate salts in electrolyte systems but also provides a more applicable NMR boron spectroscopy testing method for the entire identification process.

[0023] As a further embodiment, the peak elution time of the lithium difluorooxalate boron spectroscopy is 3.08 ppm, and the peak elution time of the lithium difluorooxalate boron spectroscopy is 7.52 ppm.

[0024] In NMR boron spectroscopy, the characteristic chemical shifts of lithium difluorooxalate borate and lithium dioxalate borate can fluctuate due to various factors. These factors mainly include the instrument's magnetic field strength, solvent type, sample concentration, temperature, choice of reference material, and spectral processing parameters. Inherent field drift and calibration differences may exist between different NMR devices, and solvent effects can cause subtle changes in the electronic environment around molecules, thus affecting the shielding constant and peak position. Therefore, in practical analysis, chemical shift correction should be performed using internal or external standards, and comparisons with control samples under the same conditions should be conducted to ensure accurate identification.

[0025] As a further embodiment, the ion chromatography elution times of lithium difluorophosphate, lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonyl)imide are 5.62 min, 26.08 min, and 34.93 min, respectively.

[0026] In actual testing, the elution time of ion chromatography in this invention may vary due to factors such as instrument model, column brand, column efficiency, column temperature, eluent composition, flow rate, and the complexity of the sample matrix. Furthermore, the separation effect and retention time may be affected by differences in the performance of the packing material and the wear and tear of different laboratories or different batches of columns. Therefore, in actual analysis, it is necessary to rely on standards for comparison and calibration to confirm the attribution of the target peak.

[0027] The beneficial effects of this invention are: (1) Achieved accurate qualitative identification of lithium oxalate-borate salts: This invention creatively combines ion chromatography (IC) with nuclear magnetic resonance boron spectroscopy, making full use of the high sensitivity of nuclear magnetic resonance boron spectroscopy to the chemical environment of boron atoms. The chemical environment of boron atoms in different lithium oxalate-borate salts varies significantly, resulting in distinctly different characteristic chemical shifts in the spectra (e.g., LiODFB at approximately 3.08 ppm, LiBOB at approximately 7.52 ppm), thus completely solving the industry problem that ion chromatography cannot distinguish between different types of lithium oxalate-borate salts due to their similar retention times, achieving unambiguous and accurate qualitative identification.

[0028] (2) A complete analytical scheme combining qualitative and quantitative methods was constructed: This invention does not simply replace the detection method, but rather constructs an efficient analytical workflow. The method first utilizes ion chromatography for rapid screening and routine lithium salt quantification. When lithium oxalate-borate salts are suspected, confirmation can be achieved through nuclear magnetic resonance boron spectroscopy. In the quantification stage, the confirmed results can guide ion chromatography external standard quantification, and nuclear magnetic resonance boron spectroscopy can be used to correct ion chromatography quantification results due to factors such as hydrolysis, significantly improving the accuracy and reliability of the quantification results.

[0029] (3) Effective identification and correction of interfering factors in the analysis process: This invention accurately identifies the problem that some lithium oxalate-borate salts may hydrolyze to form hydrolyzed lithium salt products under ion chromatography testing conditions. The presence or absence of hydrolyzed lithium salt products can be clearly determined by nuclear magnetic resonance boron spectrum, thereby distinguishing between the lithium salt originally contained in the sample and the hydrolyzed lithium salt products generated during the detection process, avoiding misjudgment of the content of lithium oxalate-borate salts, and providing more accurate data support for the true composition and stability assessment of electrolyte formulation.

[0030] (4) A universally applicable NMR detection method has been established, broadening its application scope: Addressing the possibility that conventional NMR equipment may not have a pre-installed standard method for NMR boron spectroscopy, this invention provides a standardized and operable set of steps for creating a 400M NMR boron spectroscopy detection method based on existing carbon spectral sequences. This method possesses strong versatility and repeatability, lowering the technical implementation threshold and enabling the identification method of this invention to be widely applied and promoted in most laboratories equipped with 400M NMR spectrometers.

[0031] (5) Improved the overall level of reverse analysis and quality control of electrolytes: This method provides an efficient and accurate component analysis scheme for lithium battery electrolytes, especially those containing complex and easily confused lithium salt components. It not only serves the research and development of new formulations, but also has important application value in product quality monitoring, competitor product analysis, and failure analysis during use, providing key technical support for improving the long-term quality stability and safety of lithium battery products.

[0032] Therefore, by combining multiple technologies and optimizing processes, this invention has successfully overcome the technical bottlenecks of difficulty in identifying lithium oxalate-borate salts and low accuracy in the identification process, forming a scientific, rigorous, and practical detection system, which is of great significance for promoting the advancement of analytical technology in the lithium battery industry. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 These are the ion chromatograms of LiODFB and LiBOB.

[0035] Figure 2 This is the ion chromatography chromatogram of lithium salt in the electrolyte of Example 1.

[0036] Figure 3 The image shows the NMR fluorine spectrum of the lithium salt containing fluorine in the electrolyte of Example 1.

[0037] Figure 4 This is the ion chromatography chromatogram of lithium salt in the electrolyte of Example 2.

[0038] Figure 5 The image shows the boron NMR spectrum of lithium salt in the electrolyte of Example 2.

[0039] Figure 6Nuclear magnetic boron spectra of lithium difluorooxalate borate (LiODFB) and lithium difluorooxalate borate (LiBOB) standards. Detailed Implementation

[0040] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0041] As a specific example of the implementation of this invention, detailed cases are provided below.

[0042] Example 1: The lithium salt component in the test electrolyte sample of Example 1 consisted only of fluorinated lithium salts, without LiODFB or LiBOB. The lithium salt components in the test electrolyte sample were analyzed using IC ion chromatography. The qualitative and quantitative process using the ion chromatograph (model: Metrohm 930) was as follows: 25 μL of the electrolyte sample was diluted with acetonitrile and filtered through a 0.22 μm nylon membrane. Separation was performed using a chromatographic column (model: A5-150) at 35℃, with isocratic elution using a carbonate (sodium carbonate / sodium bicarbonate)-acetonitrile system (70:30, v / v) at a flow rate of 0.7 mL / min. The IC ion chromatography results for lithium salts in the test electrolyte sample are as follows: Figure 2 As shown, the lithium salt information includes LiPO2F2, LiPF6, and LiTFSI. Ion chromatography (IC) can distinguish fluorinated lithium salts, achieving qualitative analysis. Standard curves for LiPO2F2, LiPF6, and LiTFSI are then established using IC ion chromatography, and external standard curves are used for quantification of these substances. The content of each lithium salt component in the test sample is shown in Table 1, and the IC ion chromatography values ​​are close to the theoretical values. To further verify and confirm the presence of fluorinated lithium salts in the test sample, nuclear magnetic resonance (NMR) fluorine spectroscopy can be performed. IC ion chromatography combined with NMR analysis will determine the lithium salt composition. Figure 3 The image shows the NMR fluorine spectrum of common fluorine-containing substances in lithium-ion electrolytes. The NMR fluorine spectrum test confirmed that the electrolyte in Example 1 contained three lithium salts: LiPO2F2, LiPF6, and LiTFSI.

[0043]

[0044] Example 2: The lithium salt component in the test electrolyte sample of Example 2 included lithium difluorooxalate borate. The lithium salt component in the test electrolyte sample was analyzed using IC ion chromatography. The qualitative and quantitative process using an ion chromatograph (model: Metrohm 930, Switzerland) was as follows: The electrolyte sample was diluted with acetonitrile and filtered through a 0.22 μm nylon membrane. 25 μL of the sample was injected and separated using a chromatographic column (model: A5-150) at 35℃. Isocratic elution was performed using a carbonate (sodium carbonate / sodium bicarbonate)-acetonitrile system (70:30, v / v) at a flow rate of 0.7 mL / min. The IC ion chromatography results are as follows: Figure 4 As shown, the lithium salt information includes LiPO2F2, LiBF4, lithium difluorooxalate borate and / or lithium difluorooxalate borate (LiBOB) which cannot be determined by IC ion chromatography, LiPF6, and LiFSI. Based on actual testing conditions, [the information is provided in the original text]. Figure 1 It can be seen that the ion elution times of LiODFB and LiBOB are similar, making them indistinguishable. LiODFB requires further confirmation.

[0045] Step 1: Perform NMR boron spectroscopy analysis on electrolytes containing LiODFB and mark the positions of chemical shift peaks.

[0046] Step 2: Perform NMR boron spectroscopy on lithium salt LiODFB and LiBOB standards and mark the peak positions. Figure 6 The figures show the NMR boron spectra of LiODFB and LiBOB lithium salt standards. The peak at 3.08 ppm is attributed to LiODFB, and the peak at 7.52 ppm is attributed to LiBOB. LiODFB and LiBOB can be distinguished using NMR. The chemical shifts of boron atoms in the NMR boron spectra of LiODFB and LiBOB differ due to their structural differences. In LiODFB, boron atoms experience a deshielding effect from neighboring fluorine atoms, causing the chemical shift of boron atoms to move to higher fields.

[0047] Step 3: For the boron NMR spectroscopy test in step 2. Figure 5 In the boron NMR spectrum of the LiODFB-containing electrolyte, the peak at a chemical shift of 3.13 ppm can be identified as belonging to LiODFB.

[0048] Step 4: Based on NMR boron spectroscopy, the composition of each lithium salt in the electrolyte can be determined. External standard curves are established using IC ion chromatography to quantify the lithium salts in the electrolyte. External standard curves are established for LiPO2F2, LiBF4, LiODFB, LiPF6, and LiFSI, respectively. Table 2 shows the content data of each component in the lithium salts of the electrolyte detected by IC ion chromatography. The IC detection revealed trace amounts of lithium tetrafluoroborate (LiBF4) that were not detected in the NMR boron spectroscopy. This may originate from impurities generated during the hydrolysis of LiODFB during the detection process or from lithium tetrafluoroborate already present in the electrolyte.

[0049]

[0050] Step 5: The content of each lithium salt component detected by IC reveals a deviation between the detected content of LiODFB and the theoretical value. This is because when LiODFB is detected by ion chromatography, components such as carbonates in the eluent may react with LiODFB, leading to hydrolysis and the production of other substances, which affects the accuracy of quantitative analysis. Figure 5 In the NMR boron spectrum analysis of the intermediate sample electrolyte, only LiODFB peaks were found, indicating that LiBF4 was an impurity generated by LiODFB during the IC assay. To obtain a more accurate LiODFB content in the lithium salt, inductively coupled plasma optical emission spectrometry (ICP-OES) was used to detect the boron content in the electrolyte, as shown in Table 3 below. The detected boron content was attributed to LiODFB to calculate the LiODFB content in the lithium salt, which was close to the theoretical value.

[0051]

[0052] In view of the above problems, if both LiODFB and LiBF4 are present in the electrolyte lithium salt during IC detection, NMR boron spectroscopy can be used for testing, and the conversion can be made by combining the peak area ratio of the two.

[0053] In this embodiment, the NMR boron spectroscopy test did not contain LiBF4; therefore, all LiBF4 was a hydrolyzed lithium salt product generated from LiODFB during the IC assay. This invention sums the peak areas of lithium oxalate borate and hydrolyzed lithium salt products in the ion chromatography test and then redistributes them, assigning all the summed peak areas to LiODFB. At this point, the LiODFB content obtained by the external standard method is 0.37%, which is close to the theoretical value.

[0054] Example 3: The lithium salt components in the test electrolyte sample of Example 3 included lithium difluorooxalate borate and lithium tetrafluoroborate. The lithium salt components in the test electrolyte sample were analyzed using IC ion chromatography. The qualitative and quantitative process using an ion chromatograph (model: Metrohm 930, Switzerland) was as follows: The electrolyte sample was diluted with acetonitrile and filtered through a 0.22 μm nylon membrane. 25 μL of the sample was injected and separated using a chromatographic column (model: A5-150) at 35℃. Isocratic elution was performed using a carbonate (sodium carbonate / sodium bicarbonate)-acetonitrile system (70:30, v / v) at a flow rate of 0.7 mL / min. The IC ion test results are as follows: Figure 4 The lithium salt information shown includes LiPO2F2, LiBF4, lithium difluorooxalate borate (LiODFB) and / or lithium difluorooxalate borate (LiBOB) which cannot be determined by IC ion chromatography, LiPF6, and LiFSI. The information is based on actual testing conditions. Figure 1 It can be seen that the ion elution times of LiODFB and LiBOB are similar, making them indistinguishable. LiODFB requires further confirmation.

[0055] Step 1: Perform NMR boron spectroscopy analysis on electrolytes containing LiODFB and mark the positions of chemical shift peaks.

[0056] Step 2: Perform NMR boron spectroscopy on lithium salt LiODFB and LiBOB standards and mark the peak positions. Figure 6 The figures show the NMR boron spectra of LiODFB and LiBOB lithium salt standards. The peak at 3.08 ppm is attributed to LiODFB, and the peak at 7.52 ppm is attributed to LiBOB. LiODFB and LiBOB can be distinguished using NMR. The chemical shifts of boron atoms in the NMR boron spectra of LiODFB and LiBOB differ due to their structural differences. In LiODFB, boron atoms experience a deshielding effect from neighboring fluorine atoms, causing the chemical shift of boron atoms to move to higher fields.

[0057] Step 3: The boron NMR spectrum test in Step 2 shows that the peak at the chemical shift of 3.13 ppm is attributed to LiODFB.

[0058] Step 4: Based on NMR boron spectroscopy, the composition of each lithium salt in the electrolyte can be determined. External standard curves are established using IC ion chromatography to quantify the lithium salts in the electrolyte. External standard curves are established for LiPO2F2, LiBF4, LiODFB, LiPF6, and LiFSI, respectively. Table 4 shows the content data of each component in the lithium salts of the electrolyte detected by IC ion chromatography. The detection of lithium tetrafluoroborate (LiBF4) by IC ion chromatography may originate from impurities generated by the hydrolysis of LiODFB during the detection process or from lithium tetrafluoroborate already present in the electrolyte.

[0059]

[0060] Step 5: The analysis of the lithium salt content detected by IC revealed a discrepancy between the detected LiODFB content and the theoretical value. This is because during ion chromatography detection of LiODFB, components such as carbonates in the eluent may react with LiODFB, leading to hydrolysis and the production of other substances, thus affecting the accuracy of quantitative analysis. The NMR boron spectrum analysis of the electrolyte showed peaks for both LiODFB and LiBF4, indicating that LiBF4 originates from both lithium tetrafluoroborate present in the electrolyte and the hydrolyzed lithium salt products generated by LiODFB during IC testing.

[0061] In view of the above problems, if both LiODFB and LiBF4 are present in the electrolyte lithium salt during IC detection, NMR boron spectroscopy can be used for testing, and the conversion can be made by combining the peak area ratio of the two.

[0062] In this embodiment, the NMR boron spectroscopy test included LiBF4. Therefore, LiBF4 originated from both lithium tetrafluoroborate present in the electrolyte and impurities generated by LiODFB during the IC assay. The peak area ratio of LiBF4 to LiODFB in the NMR boron spectrum is 1:8. Therefore, this invention sums the peak areas of LiBF4 and LiODFB obtained in IC ion chromatography, and then redistributes this summed peak area according to the 1:8 ratio of LiBF4 to LiODFB in the NMR boron spectrum. Using the external standard method, the concentration of LiBF4 is obtained as 0.049%, and the concentration of LiODFB is as 0.39%.

[0063] To further verify the content of lithium salt LiODFB, inductively coupled plasma optical emission spectrometry (ICP-OES) was used to detect the boron content in the electrolyte, as shown in Table 5 below. The detected boron content was attributed to LiODFB to calculate the content of lithium salt LiODFB, which was close to the theoretical value.

[0064]

[0065] Based on the above technical solutions, this invention provides a method for the precise qualitative and quantitative analysis of lithium salts in electrolytes, and also provides a method for identifying lithium salts containing oxalate-borate in lithium salts. This method is based on nuclear magnetic resonance (NMR) boron spectroscopy for detection. The addition of NMR detection technology compensates for the shortcomings of ion chromatography (IC) in detecting lithium salts in electrolytes. Based on the above embodiments, it is clear that qualitative analysis of lithium salts is achieved through NMR boron spectroscopy, followed by IC ion chromatography detection, and quantitative analysis is performed using the external standard curve method. During the testing process, NMR boron spectroscopy simultaneously addresses the issue of impurities.

[0066] The identification and testing method for lithium oxalate borate salt in lithium salt components of lithium battery electrolyte provided by this invention is easy to implement and can reliably distinguish lithium oxalate borate salt in test samples, facilitating the analysis of various components of the electrolyte.

[0067] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can modify, alter, substitute, and transform the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A method for identifying composite lithium salts in lithium battery electrolytes containing lithium oxalate-borate salt, characterized in that, Includes the following steps: S1: Perform ion chromatography tests on the lithium battery electrolyte to be tested, and confirm the types and contents of conventional lithium salts in the composite lithium salt, as well as the total peak area of ​​lithium salt containing lithium oxalate borate, based on the peak time and peak area. S2: Perform 400M nuclear magnetic resonance boron spectrum test on the lithium battery electrolyte to be tested, and identify the various types of lithium oxalate-borate salts and the hydrolyzed lithium salt products of various types of easily hydrolyzed lithium salts in lithium oxalate-borate salts according to the peak time, and obtain the peak area ratio of various types of lithium oxalate-borate salts and various types of hydrolyzed lithium salt products. S3: The sum of the total peak area of ​​lithium oxalate-borate salt and the peak area of ​​each type of corresponding hydrolyzed lithium salt product in the ion chromatography test in step S1 is redistributed according to the peak area ratio in step S2 to obtain the corrected peak areas of each type of lithium oxalate-borate salt and each type of hydrolyzed lithium salt product, and the content of each type in the composite lithium salt is confirmed based on the corrected peak areas.

2. The preparation method according to claim 1, characterized in that, The eluent for the ion chromatography test includes carbonate and acetonitrile, and the flow rate of the eluent for the ion chromatography test is 0.6~0.8 mL / min.

3. The identification method according to claim 2, characterized in that, The carbonate is selected from one or more of sodium carbonate and sodium bicarbonate; Preferably, the volume ratio of carbonate to acetonitrile in the rinsing solution is (65~75):(25~35).

4. The identification method according to claim 1, characterized in that, In step S1, the lithium battery electrolyte to be tested is subjected to ion chromatography. Based on the peak time and peak area, the content of various types of conventional lithium salts in the composite lithium salt is confirmed according to the standard curve using the external standard method. Preferably, in step S3, the corrected peak areas of various types of lithium salt containing oxalate-borate and various types of hydrolyzed lithium salt products are obtained, and the content of various types in the composite lithium salt is confirmed by external standard method according to the standard curve based on the corrected peak areas.

5. The identification method according to claim 1, characterized in that, The conventional lithium salts include lithium difluorophosphate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate.

6. The identification method according to claim 1, characterized in that, The lithium oxalate borate salts include lithium difluorooxalate borate and lithium dioxalate borate.

7. The identification method according to claim 1, characterized in that, The easily hydrolyzable lithium salts in the ion chromatography test include lithium difluorooxalate borate, and the hydrolysis lithium salt product of lithium difluorooxalate borate in the ion chromatography test is lithium tetrafluoroborate.

8. The identification method according to claim 1, characterized in that, The method for nuclear magnetic resonance boron spectroscopy testing includes the following steps: s1: First, the gyromagnetic ratio of the B11 nucleus is found to be 8.5794. 10 7 rad s -1 T -1 The natural abundance of B11 was 80.1%; s2: First, borrow the standard experiment of C spectrum and create a new experiment. When the gyromagnetic ratio is positive, select C13CPD as the standard experiment; when the gyromagnetic ratio is negative, select C13IG as the standard experiment. s3: To view the Acqpar parameters of C13, enter the command getprosol to read the pulse width and power of C; s4: Enter the edsp command, change C13 in F1 dimension to B11, leave 1H in F2 dimension unchanged, and save the settings; Returning to the Acqupars parameters, change the number of scans (NS) to 1024, the spectral width (SW) to 400, assign O1P to 0, and set D1 (relaxation time) to 2s; s5: Enter the command to lock the field, homogenize the field, and enter the command ATMM to perform received tuning. The first time is manual tuning. After tuning is completed, enter the command ATMA again to perform automatic tuning. s6: Input command to perform signal amplification (rga), spectrum acquisition (zg), Fourier transform (efp), phase correction (apk), and finally input command sref to perform data calibration.

9. The identification method according to claim 6, characterized in that, The peak elution time of the lithium difluorooxalate boronate in the NMR boron spectrum was 3.08 ppm, and the peak elution time of the lithium difluorooxalate boronate in the NMR boron spectrum was 7.52 ppm.

10. The identification method according to claim 5, characterized in that, The ion chromatography elution times of lithium difluorophosphate, lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonylimide) were 5.62 min, 26.08 min, and 34.93 min, respectively.

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