Method for analyzing residual lithium compounds in anode active material

Abstract

The present invention provides a method of analyzing residual lithium compounds in an anode active material for a lithium secondary battery, the analysis method comprising the steps of: analyzing a sample of an anode active material to determine the amount of H component using an oxygen / nitrogen / hydrogen analyzer (ONH analyzer) and a Karl Fischer analyzer; analyzing the sample to determine the amounts of C component and S component using a carbon / sulfur analyzer (CS analyzer); analyzing the sample to determine the amount of Li component using an inductively coupled plasma optical emission spectrometer (ICP-OES); and calculating the amounts of each of LiOH, Li2CO3, and Li2SO4 in the sample using the quantitative results of the H, C, and S components, and calculating the amount of Li2O in the sample using the quantitative result of the Li component. According to the analysis method of the present invention, the amounts of all four residual lithium compounds LiOH, Li2CO3, Li2SO4, and Li2O present in the anode active material can be analyzed.

Description

TECHNICAL FIELD

[0001] The present application relates to a method of analyzing residual lithium compounds not involved in charging and discharging in an anode active material for a lithium secondary battery. BACKGROUND

[0002] A lithium secondary battery generally has a structure of an electrode assembly including a cathode and an anode including an electrode active material capable of intercalating / deintercalating lithium ions, and a separator for separating the two electrodes, which is impregnated with an electrolyte solution as a medium for transferring lithium ions. When lithium ions move between the anode and the cathode through the electrolyte, the battery is charged and discharged. The electrodes are generally manufactured by coating a foil-like current collector with a slurry including an electrode material (e.g., an active material, a conductive material, and a binder) to dry them, and forming an active material layer by a pressing process.

[0003] The performance of such a secondary battery is affected by various factors (e.g., components such as a cathode, an anode, a separator, and an electrolyte, the composition of each component, and their charging and discharging characteristics). In particular, since lithium by-products, i.e., residual lithium compounds present in the anode active material but not involved in charging and discharging, generated during the manufacturing process of the anode active material, can impair the performance of the anode, analysis of the lithium by-products is important for evaluating the performance of the battery.

[0004] Generally, LiOH, Li2CO3, Li2SO4, and Li2O are considered as four main residual compounds of the anode active material. Conventionally, the following wet method is performed to analyze the residual components: stirring an anode active material sample in water to elute the residual compounds, and then measuring the pH of the filtrate.

[0005] However, such a wet method has the following problems: since Li2O is mostly changed into LiOH when in contact with water, Li2O and LiOH are hardly distinguishable from each other; and since the pH of Li2SO4 cannot be measured, the pH of only LiOH and Li2CO3 is measured among the four residual compounds. In addition, when other metals are coated on the surface of the anode active material, a multi-peak rather than a single peak occurs in the pH titration process, which makes it difficult to perform accurate analysis. SUMMARY

[0006] TECHNICAL PROBLEM

[0007] Accordingly, an object of the present application is to provide a method of analyzing all four residual lithium compounds of LiOH, Li2CO3, Li2SO4, and Li2O present in an anode active material for a lithium secondary battery.

[0008] TECHNICAL SOLUTION

[0009] According to one aspect of the present application, there is provided a method of analyzing residual lithium compounds in an anode active material for a lithium secondary battery, the analysis method comprising the steps of:

[0010] analyzing an anode active material sample with an oxygen-nitrogen-hydrogen analyzer (ONH analyzer) and a Karl Fischer analyzer to measure the amount of H component;

[0011] analyzing the sample with a carbon-sulfur analyzer (CS analyzer) to measure the amounts of C component and S component;

[0012] analyzing the sample with an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the amount of Li component; and

[0013] calculating the respective amounts of LiOH, Li2CO3, and Li2SO4 in the sample by using the measured results of the H, C, and S components, and calculating the amount of Li2O in the sample by using the measured result of the Li component.

[0014] The present application provides a process in which, when calculating the amount of LiOH in an anode active material, the amount of H is measured by ONH and Karl Fischer analysis methods, and then the amount change due to moisture is corrected.

[0015] Further, the present application provides an anode active material for a lithium secondary battery analyzed by the above-described method, in which, based on the total amount of the anode active material, the amount of residual LiOH is 0.1 to 0.4 wt%, the amount of residual Li2CO3 is 0.1 to 1.0 wt%, the amount of residual Li2SO4 is 0.1 to 1.3 wt%, and the amount of residual Li2O is 0.2 to 0.5 wt%.

[0016] Advantageous Effects

[0017] According to the present application, ONH analysis, CS analysis, and ICP-OES analysis are respectively performed on an anode active material sample, and all four residual lithium compounds (i.e., LiOH, Li2CO3, Li2SO4, and Li2O) present in the anode active material can be analyzed by using the amounts of H, C, S, and Li thus measured. Specifically, unlike a conventional wet method by pH titration, ONH analysis and CS analysis are performed in a dry method, so that the amounts of Li2O and LiOH are respectively measured, and the amount of Li2SO4, which is not titrated in pH in a wet method, is also measured, thereby contributing to accurate evaluation of the performance of a lithium secondary battery. DETAILED DESCRIPTION

[0018] The terms or words used in the present specification and claims should not be understood as being limited to the meanings that are commonly used in the conventional use of the terms and words and instead should be understood based on the concept and principles of the present invention based on the idea of the inventor of the present patent to most suitably explain the present invention in the best way.

[0019] Further, the features illustrated in the embodiments described in the specification of the present application are only a part of the most preferred embodiments of the present application and do not represent all technical ideas of the present application. Therefore, it should be understood that, at the filing date of the present application, various equivalents and modifications can exist which can replace them.

[0020] One embodiment of the present application relates to a method of analyzing all residual lithium compounds (i.e., LiOH, Li2CO3, Li2SO4, and Li2O) in an anode active material for a lithium secondary battery.

[0021] The anode active material to be analyzed by the present application is a compound in which lithium ions that can be used to constitute an anode of a lithium secondary battery are intercalated, and the compound can include, for example, at least one selected from LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi 1-x-y-z Co x Ml y M2 z O2(wherein M1 and M2 are independently any one selected from Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg, and Mo; x, y, and z are independently atomic fractions of oxide constituent elements, and 0≤x<0.5, 0≤y<0.5, 0≤z<0.5, and 0<x+y+z≤1).

[0022] Such an anode active material is prepared as a crystal having a cubic spinel structure or a layered structure by mixing a precursor solution containing transition metals such as Ni, Co, and Mn with a lithium source (e.g., Li2CO3, LiNO3, Li2O, and Li2SO4) and heat-treating the mixture at a temperature of 900℃ or more. Li not included in the crystal structure can react with CO2 present in the air to become Li2CO3 or can react with water to produce LiOH during the heat-treatment process. In addition, an unreacted lithium source used to prepare the active material can remain on the surface of the final active material. In general, the four lithium compounds (i.e., LiOH, Li2CO3, Li2SO4, and Li2O) are considered to be by-products present in the anode active material but not participating in charging and discharging. In order to secure the performance of the anode, accurate analysis of the four residual lithium compounds is required.

[0023] To this end, in the present application, a sample of anode active material is prepared and introduced into an oxygen-nitrogen-hydrogen analyzer (ONH analyzer) and a carbon-sulfur analyzer (CS analyzer) which operate in a dry method, and an ICP-OES analyzer which operates in a wet method, respectively, to measure the amounts of H, C, S, and Li components and calculate the amounts of LiOH, Li2CO3, Li2SO4, and Li2O from the measured values.

[0024] Specifically, the ONH analyzer is a device for detecting oxygen, nitrogen, and hydrogen components discharged after melting a sample in a heating furnace, and the sample of anode active material can be introduced into the ONH analyzer commonly used in the art in the form of dry particles to measure the amount of H component contained in the sample.

[0025] The CS analyzer is a device for detecting the amounts of carbon and sulfur generated by burning a sample in an oxygen stream, and the sample of anode active material can be introduced into a ceramic heating furnace of the CS analyzer commonly used in the art in the form of dry particles together with a flame retardant, and oxygen can be supplied from a device for inducing high frequency to measure the amounts of C component and S component contained in the sample.

[0026] When the ONH analyzer and the CS analyzer are used, the sample of anode active material is not in contact with moisture, so that the amounts of Li2O and LiOH can be measured separately. Therefore, the method can overcome the limitations of a conventional analysis method of measuring the amount of residual lithium in anode active material by using pH titration in a wet method in which Li2O becomes LiOH due to contact with moisture, so that only the total amount of LiOH and Li2CO3 can be measured. In addition, Li2SO4 which is not titrated in pH in the wet method can be analyzed by using the amount of S component measured by the CS analyzer.

[0027] In one embodiment of the present application, the amount of LiOH is calculated by using the result of H component measured by the ONH analyzer, and the calculated amount of LiOH can be 0.1 to 0.4% by weight based on the total weight of anode active material.

[0028] In addition, the amounts of Li2CO3 and Li2SO4 are calculated by using the results of C component and S component measured by CS analysis, respectively, and the amount of Li2CO3 can be 0.1 to 1.0% by weight based on the total weight of anode active material, and the amount of Li2SO4 can be 0.1 to 1.3% by weight based on the total weight of anode active material.

[0029] On the other hand, the ICP-OES analysis can be performed by using a solution obtained by taking a sample of the anode active material and dissolving it in ultrapure water. Specifically, for example, the ICP-OES analysis can include immersing a sample of the anode active material in a range of 1:50 to 1:500 parts by weight and ultrapure water, for example, 1:50 to 300 parts by weight, 1:50 to 200 parts by weight, or 1:80 to 150 parts by weight, for 1 to 60 minutes, for example, 1 to 40 minutes, 5 to 30 minutes, or 5 to 15 minutes. The value by the ICP-OES analysis indicates the total amount of lithium (Li wt%) in the anode active material, that is, the amount of all Li compounds such as LiOH, Li2CO3, Li2SO4, and Li2O.

[0030] The ICP-OES analysis is performed by applying high thermal energy to a sample by using a high-temperature plasma induced by argon gas as an inert gas to generate atoms and ions in the sample in an excited state, and then analyzing components by detecting lines emitted by atoms and ions returning to a low energy level, which enables the total residual Li component contained in the sample of the anode active material to be measured.

[0031] In one embodiment of the present application, the treatment of the sample of the anode active material with ultrapure water can be performed by adding ultrapure water in a range of 0.1 ml to 100 ml based on 100 mg of the taken sample, and then stirring the mixture at room temperature for about 5 minutes. After filtering the solution treated with ultrapure water to remove undissolved components, the component analysis can be performed by introducing the remaining filtrate into an ICP-OES analyzer commonly used in the art.

[0032] The amount of Li2O is calculated by subtracting the amount of Li corresponding to LiOH, Li2CO3, and Li2SO4 from the total residual Li component in the sample of the anode active material measured by the ICP-OES analysis, and the calculated amount of Li2O can be 0.2 to 0.5 wt% based on the total weight of the anode active material.

[0033] In the present application, the order of the steps of the ICP-OES analysis, the CS analysis, and the ONH analysis is not particularly limited.

[0034] To solve the problem that Li2O and LiOH are hardly distinguished from each other because Li2O is mostly changed into LiOH when in contact with water, the ONH analysis and the Karl Fischer analysis are performed on the anode active material containing water, and based on the amount of water measured by the Karl Fischer analysis, the accuracy of measuring the amount of LiOH is improved by excluding correction of the amount of LiOH generated by contact with moisture.

[0035] Specifically, the amount of LiOH in the anode active material can be calculated as in Equation 1 to correct the amount change due to moisture.

[0036] [Equation 1]

[0037]

[0038] wherein,

[0039] H1 is the amount of hydrogen (wt%) analyzed by the ONH analyzer,

[0040] H2 is the amount of hydrogen (wt%) analyzed by the Karl Fischer method,

[0041] MW LiOH is the weight average molecular weight of LiOH,

[0042] AM H is the atomic mass of hydrogen.

[0043] The above analysis process can include analyzing the amounts of all four residual lithium compounds (i.e., LiOH, Li2CO3, Li2SO4, and Li2O) present in the anode active material of the lithium secondary battery but not participating in charging and discharging, and can accurately evaluate the performance of the anode and the lithium secondary battery by applying the amounts of the analyzed residual lithium compounds.

[0044] Accordingly, the present application further provides an anode active material for a lithium secondary battery analyzed by the above method.

[0045] In the anode active material, the amount of residual LiOH can be 0.1 to 0.4 wt%, the amount of residual Li2CO3 can be 0.1 to 1.0 wt%, the amount of residual Li2SO4 can be 0.1 to 1.3 wt%, and the amount of residual Li2O can be 0.2 to 0.5 wt%, based on the total amount of the anode active material.

[0046] Hereinafter, the embodiments will be described in detail to help the understanding of the present application. However, the embodiments according to the present application can be modified in many different forms, and the scope of the present application should not be construed as being limited to the following examples. The embodiments of the present application are provided to more fully explain the present application to those skilled in the art.

[0047] (Examples)

[0048] (Step 1) ONH analysis

[0049] First, Li[Ni 0.86 Co 0.05 Mn 0.07 Al 0.02Four types of anode active material samples (Samples 1 and 2: calcination products; Samples 3 and 4: washing products) of Li2O.

[0050] Take 10 mg to 50 mg of each sample (in a solid state), introduce into a heating furnace of an ONH analyzer (ONH 836, LECO) and melt at 2,200°C, and move and analyze the discharged hydrogen gas together with a carrier gas (He) to measure the amount of H in the sample.

[0051] (Step 2) CS analysis

[0052] Take 200 mg to 300 mg of each sample (in a solid state), introduce into a CS analyzer (CS 844, LECO), and then calcine with a flame retardant under an oxygen atmosphere to obtain carbon (C) compounds and sulfur (S) compounds, and analyze these compounds to measure the amounts of C components and S components in the sample.

[0053] (Step 3) ICP-OES analysis

[0054] Take 100 mg to 200 mg of each sample and dissolve in 10 ml of ultrapure water.

[0055] After 5 minutes, filter each sample solution with a 0.45 pm PTFE filter to remove undissolved components, and then introduce the remaining filtrate (i.e., supernatant) into an ICP-OES instrument (e.g., AVIO 500, Perkin Elmer) to perform component analysis. Thereby, the component of total residual Li contained in the sample is measured.

[0056] <Conditions for ICP-OES analysis>

[0057] Forward power: 1300 W

[0058] Torch height: 15 mm

[0059] Plasma gas flow: 15.00 L / min

[0060] Sample gas flow: 0.8 L / min

[0061] Auxiliary gas flow: 0.20 L / min

[0062] Pump speed: 1.5 mL / min

[0063] (Step 4) Calculation of the amounts of LiOH, Li2CO3, Li2SO4, and Li2O

[0064] The amounts of LiOH, Li2CO3, and Li2SO4 in the samples were calculated using the measured results of H, C, and S components in the four samples, respectively, and the amounts of Li corresponding to LiOH, Li2CO3, and Li2SO4 were subtracted from the total residual Li component to calculate the amount of Li2O. The results are shown in Table 1 below.

[0065] [Table 1]

[0066]

[0067] Table 1 above shows that samples 1 and 2, which are calcined products obtained by calcining a precursor, have a large amount of residual lithium, and samples 3 and 4, which are washed products obtained by washing and drying the calcined products, have a small amount of residual lithium.

[0068] (Step 5)

[0069] The blank sample was measured three times using a graphite crucible. Calibration was performed using O, C, and N standard samples. 0.02 g of the anode active material of Li[Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 ]O2, which was not dried, was placed in a tin capsule and sealed. The tin capsule was then placed in a nickel basket. The nickel basket was placed in a sample inlet for H analysis. The quantitative analysis of the sample was repeated more than twice.

[0070] 1 g of the anode active material of Li[Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 ]O2 was divided into sample bottles, sealed with a rubber plug, and loaded into an instrument (e.g., C30 coulometric KF titrator, Mettler toledo) together with a blank sample. After evaporating moisture at 200°C for 600 seconds while heating the sample, the amount of moisture was measured by iodine titration. After correction for moisture, the amount of LiOH was calculated as in Equation 1.

[0071] [Equation 1]

[0072]

[0073] wherein,

[0074] H1 is the amount of hydrogen (wt%) analyzed by the ONH analyzer,

[0075] H2 is the amount of hydrogen (wt%) analyzed by the Karl Fischer method,

[0076] MW LiOH is the weight average molecular weight of LiOH,

[0077] AM H is the atomic mass of hydrogen.

[0078] (Comparative Example)

[0079] After preparing four types of anode active material samples of Li[Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 ]O2, 5 g of each sample was taken out and added to 1000 ml of ultrapure water to be dissolved.

[0080] After each sample solution was filtered through a 0.45 μm PTFE filter to remove undissolved components, the remaining filtrate (i.e., supernatant) was subjected to pH titration to measure the amounts of LiOH and Li2CO3 in the sample.

[0081] The results of the amounts of components calculated in the examples and comparative examples and expressed in units of weight % (wt %) are shown in Table 2 below.

[0082] [Table 2]

[0083]

[0084] From Table 2 above, the amounts of all four residual lithium compounds of LiOH, Li2CO3, Li2SO4, and Li2O can be measured by combining the results of component analysis of the anode active material samples according to the examples by dry and wet methods. In addition, it was confirmed that the amount of residual LiOH was 0.1 to 0.4 wt %, the amount of residual Li2CO3 was 0.1 to 1.0 wt %, the amount of residual Li2SO4 was 0.1 to 1.3 wt %, and the amount of residual Li2O was 0.2 to 0.5 wt % based on the total amount of the sample.

[0085] On the other hand, in the comparative examples, since only wet pH titration analysis was performed, only the amounts of LiOH and Li2CO3 were measured. It can be confirmed that the amount of LiOH measured according to the comparative examples includes the amount of Li2O that becomes LiOH, and is similar to the sum of the amounts of LiOH and Li2O according to the examples. Therefore, the total amount of LiOH, Li2O, and Li2CO3 measured according to the examples was compared with the total amount of LiOH and Li2CO3 measured according to the comparative examples as the amount of residual lithium, and the results are shown in Table 3 below.

[0086] [Table 3]

[0087]

[0088] As can be confirmed from Table 3 above, the relative standard deviation (RSD) of the amount of residual lithium of the examples is within 5% compared to the comparative example.

Claims

1. A method of analyzing residual lithium compounds in an anode active material for a lithium secondary battery, comprising: analyzing an anode active material sample with an oxygen-nitrogen-hydrogen analyzer (ONH analyzer) and a Karl Fischer analyzer to measure the amount of H component; analyzing the sample with a carbon-sulfur analyzer (CS analyzer) to measure the amount of C component and S component; analyzing the sample with an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the amount of Li component; and calculating the respective amounts of LiOH, Li2CO3 and Li2SO4 in the sample by using the measurement results of the H, C and S components, and calculating the amount of Li2O in the sample by using the measurement result of the Li component, and calculating the amount of LiOH by Equation 1: [Equation 1] wherein, H1 is the amount of hydrogen analyzed by the ONH analyzer, wt. %, H2 is the amount of hydrogen analyzed by the Karl Fischer analyzer, wt. %, MW LiOH is the weight average molecular weight of LiOH, AM H is the atomic mass of hydrogen, wherein, the amount of Li2O is calculated by subtracting the amount of Li corresponding to LiOH, Li2CO3 and Li2SO4 from the total residual Li component in the anode active material sample measured by ICP-OES analysis.

2. The method of analyzing residual lithium compounds in an anode active material for a lithium secondary battery according to claim 1, wherein, The inductively coupled plasma optical emission spectrometer (ICP-OES) analysis is performed with a solution in which the anode active material sample is dissolved in ultrapure water.

3. The method of analyzing residual lithium compounds in an anode active material for a lithium secondary battery according to claim 1, wherein, The amount of LiOH calculated by using the result of H component measured by ONH analysis is 0.1 to 0.4 wt. % based on the total weight of the anode active material.

4. The method of analyzing residual lithium compounds in an anode active material for a lithium secondary battery according to claim 1, wherein, The amount of Li2CO3 calculated by using the result of C component measured by CS analysis is 0.1 to 1.0 wt. % based on the total weight of the anode active material.

5. The method of analyzing residual lithium compounds in an anode active material for a lithium secondary battery according to claim 1, wherein, The amount of Li2SO4 calculated by using the result of S component measured by CS analysis is 0.1 to 1.3 wt. % based on the total weight of the anode active material.

6. The method of analyzing residual lithium compounds in an anode active material for a lithium secondary battery according to claim 1, wherein, The amount of Li2O calculated by using the result of Li component measured by ICP-OES analysis is 0.2 to 0.5 wt. % based on the total weight of the anode active material.

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