Analysis method for residual lithium compounds in positive electrode active material

Abstract

The present invention provides a method for analyzing residual lithium compounds in a positive active material for a lithium secondary battery, and the analysis method includes the steps of: analyzing a sample of the positive active material with an oxygen, nitrogen, hydrogen analyzer and a Karl Fischer analyzer to measure the content of H component; analyzing the sample with a carbon-sulfur analyzer to measure the content of C component and S component; analyzing the sample with an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the content of Li component; and calculating the contents of LiOH, Li2CO3, and Li2SO4 in the sample using the measurement results of H, C, and S components, respectively, and calculating the content of Li2O in the sample using the measurement result of Li component. According to the analysis method of the present invention, the contents of all four types of residual lithium compounds, LiOH, Li2CO3, Li2SO4, and Li2O, present in the positive active material can be analyzed.

Description

[Technical field]

[0001] The present invention relates to a method for analyzing residual lithium compounds that are not involved in charge / discharge in a positive electrode active material for a lithium secondary battery. [Background technology]

[0002] A lithium secondary battery generally consists of an electrode assembly made up of a positive electrode and a negative electrode containing an electrode active material capable of inserting / extracting lithium ions, and a separator for separating the two electrodes, and is impregnated with an electrolyte, which is a lithium ion transfer medium, and the lithium ions travel between the negative electrode and the positive electrode through the electrolyte, thereby charging and discharging the battery. The electrodes are generally manufactured by coating a foil-shaped current collector with a slurry containing electrode materials such as an active material, a conductive material, and a binder, drying the slurry, and then forming an active material layer through a rolling process.

[0003] The performance of such secondary batteries is affected by various factors such as the components of the positive electrode, negative electrode, separator and electrolyte, the composition of each component, and the charge / discharge characteristics due to the components. In particular, lithium by-products generated during the manufacturing process of the positive electrode active material, i.e., residual lithium compounds that exist in the positive electrode active material but are not involved in charge / discharge, can impair the performance of the positive electrode, so their analysis is important for evaluating the battery performance.

[0004] In general, LiOH, Li 2 CO 3 , Li 2 SO 4 and Li 2 O is considered to be the four major residual compounds in the positive electrode active material, and in the past, to analyze these residual components, a wet method was used in which a positive electrode active material sample was stirred in water to elute the residual compounds, and the pH of the filtrate was then measured.

[0005] However, this wet method is 2 Since most of the O converted to LiOH when it comes into contact with water, Li 2It is difficult to distinguish between O and LiOH, 2 SO 4 The pH measurement itself is not possible, and among the four residual compounds, LiOH and Li 2 CO 3 In addition, if the surface of the positive electrode active material is coated with another metal, multiple peaks appear during pH titration instead of a single peak, making accurate analysis difficult. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to reduce the amount of LiOH, Li 2 CO 3 , Li 2 SO 4 and Li 2 The objective of the present invention is to provide a method for analyzing all four residual lithium compounds of O. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a method for analyzing residual lithium compounds in a positive electrode active material for a lithium secondary battery, comprising the steps of: analyzing a positive electrode active material sample with an oxygen, nitrogen, and hydrogen analyzer (ONH analyzer) and a Karl Fischer analyzer to measure the content of H components; analyzing the sample with a carbon-sulfur analyzer (CS analyzer) to measure the content of C components and S components; analyzing the sample with an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the content of Li components; and determining the content of LiOH, Li in the sample using the results of the measurements of H, C, and S components. 2 CO 3 and Li 2 SO 4 The content of each of the Li components was calculated, and the Li content in the sample was calculated using the results of the Li component measurement. 2 and calculating the content of O.

[0008] In the present invention, when calculating the LiOH content in the positive electrode active material, the H content is measured by the ONH analysis method and the Karl Fischer analysis method, and the change in content due to moisture is corrected.

[0009] Further, the present invention relates to a positive electrode active material for a lithium secondary battery analyzed by the above method, and the content of residual LiOH is 0.1 to 0.4 wt % based on the total content, and the content of residual Li is 0.5 to 1.0 wt % based on the total content. 2 CO 3 The content is 0.1-1.0 wt%, and residual Li 2 SO 4 The content is 0.1 to 1.3 wt.%, and residual Li 2 A positive electrode active material having an O content of 0.2 to 0.5 wt % is provided. Effect of the Invention

[0010] According to the present invention, a positive electrode active material sample is subjected to ONH analysis, CS analysis, and ICP-OES analysis, and the contents of H, C, S, and Li measured thereby are used to determine LiOH, Li, and Li that are present in the positive electrode active material. 2 CO 3 , Li 2 SO 4 and Li 2 In particular, the ONH and CS analyses are performed in a dry manner, which is different from the conventional wet method using pH titration, and therefore, the content of Li 2 The content of LiO and LiOH can be measured separately, and the pH titration of Li, which was impossible with the wet method, can be performed. 2 SO 4 By measuring the content of , it can contribute to accurate performance evaluation of lithium secondary batteries. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor can appropriately define the concept of the terms in order to best explain his invention, they must be construed as meanings and concepts that conform to the technical idea of the present invention.

[0012] In addition, the configurations illustrated in the embodiments described in this specification are merely the most desirable embodiments of the present invention and do not represent any of the technical ideas of the present invention. Therefore, it should be understood that there are various equivalents and modifications that can replace them at the time of this application.

[0013] One embodiment of the present invention relates to a method capable of analyzing any of LiOH, Li 2 CO 3 、Li 2 SO 4 and Li 2 O, which are residual lithium compounds in the positive electrode active material for a lithium secondary battery.

[0014] The positive electrode active material to be analyzed in the present invention is a compound into which lithium ions constituting a positive electrode of a lithium secondary battery are inserted. For example, LiCoO 2 、LiNiO 2 、LiMn 2 O 4 、LiCoPO 4 、LiFePO 4 、and LiNi 1-x-y-z Co x M1 y M2 z O 2 (M1 and M2 are each independently selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg, and Mo, and x, y, and z are each independently the atomic fraction of the oxide composition element, where 0 ≦ x < 0.5, 0 ≦ y < 0.5, 0 ≦ z < 0.5, and 0 < x + y + z ≦ 1) may include one or more selected from the group consisting of.

[0015] Such positive electrode active materials are prepared by mixing a precursor solution containing transition metals such as Ni, Co, and Mn with a lithium source (Li 2 CO 3 , LiNO 3 , Li 2 O, Li 2 SO 4 etc.) and then heat-treated at a temperature of 900°C or higher to produce crystals with a cubic spinel structure or layered structure. However, Li that is not included in the crystal structure is absorbed by CO present in the air during the heat treatment process. 2 reacts with Li 2 CO 3 In addition, unreacted lithium sources used in the preparation of the active material may remain on the surface of the final active material. 2 CO 3 , Li 2 SO 4 and Li 2 Although the four types of lithium compounds, O, are present in the positive electrode active material, they are considered to be by-products that are not involved in charging and discharging. In order to ensure the performance of the positive electrode, accurate analysis of the four types of residual lithium compounds is necessary.

[0016] For this purpose, in the present invention, a sample of the positive electrode active material is prepared and introduced into an oxygen, nitrogen, hydrogen analyzer and a carbon-sulfur analyzer operating in a dry mode, and an ICP-OES analyzer operating in a wet mode, respectively, to measure the contents of H, C, S, and Li. 2 CO 3 , Li 2 SO 4 and Li 2 The O content is calculated.

[0017] Specifically, the ONH analyzer is an instrument for detecting oxygen, nitrogen, and hydrogen gas components discharged after melting a sample in a heating furnace, and the content of H components contained in the sample can be measured by introducing a cathode active material sample in a dried granular form into an ONH analyzer commonly used in the field.

[0018] The CS analyzer is an instrument for detecting the content of carbon and sulfur produced by burning a sample in an oxygen stream. A cathode active material sample is introduced in a dried granular form together with a combustion improver into a ceramic heating furnace of a CS analyzer commonly used in the field, and oxygen gas is supplied by a high-frequency induction device to measure the content of C and S components contained in the sample.

[0019] When using such an ONH analyzer and a CS analyzer, the positive electrode active material sample does not come into contact with moisture, so Li 2 The content of LiO and LiOH can be measured separately. That is, when the residual lithium content in the positive electrode active material is measured using the existing wet pH titration method, Li 2 This is the phenomenon in which O changes to LiOH when it comes into contact with water. 2 CO 3 This overcomes the limitations of analytical methods that were previously limited to the measurement of Li. 2 SO 4 can be analyzed using the content of S components measured by a CS analyzer.

[0020] In one embodiment of the present invention, the content of LiOH is calculated using the result of the H component measured by the ONH analysis, and the calculated content of LiOH is 0.1 to 0.4 wt % based on the total weight of the positive active material.

[0021] In addition, the results of the C and S components measured in the CS analysis were used to determine Li 2 CO 3 and Li 2 SO 4 The content of each of the Li 2 CO 3 The content of is 0.1 to 1.0 wt% based on the total weight of the positive electrode active material, and Li 2 SO 4 The content of is 0.1 to 1.3 wt % based on the total weight of the positive electrode active material.

[0022] Meanwhile, the ICP-OES analysis is carried out by dissolving a sample of the positive electrode active material in ultrapure water to prepare a solution. For example, the ICP-OES analysis may include a step of immersing the positive electrode active material sample in ultrapure water at a ratio of 1:50 to 1:500 parts by weight, for example, 1:50 to 300 parts by weight, or 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, or 5 to 30 minutes, or 5 to 15 minutes. The value analyzed by ICP-OES is the total lithium content (Li wt%) in the positive electrode active material, i.e., LiOH, Li 2 CO 3 , Li 2 SO 4 , Li 2 This refers to the content of all Li compounds, including O.

[0023] The ICP-OES analysis applies high thermal energy to a sample using high-temperature plasma induced by argon gas, an inert gas, to create an excited state for atoms and ions in the sample, and then detects the rays emitted as the atoms and ions return to a lower energy level to perform component analysis. This allows the total amount of residual Li contained in a positive active material sample to be measured.

[0024] In one embodiment of the present invention, the ultrapure water treatment of the positive active material sample is performed by adding 0.1 to 100 ml of ultrapure water to 100 mg of the sample and stirring at room temperature for about 5 minutes. The ultrapure water-treated solution is filtered to remove undissolved components, and the remaining filtrate can be introduced into an ICP-OES analyzer commonly used in the art to perform component analysis.

[0025] The total residual Li components in the positive electrode active material sample measured by ICP-OES analysis were divided into LiOH, Li 2 CO 3 and Li 2 SO 4 Li content is subtracted from the Li content 2 The content of Li 2The content of O is 0.2 to 0.5 wt % based on the total weight of the positive electrode active material.

[0026] In the present invention, the order of the ICP-OES analysis, CS analysis, and ONH analysis steps is not particularly limited.

[0027] The present invention relates to Li 2 Since most of the O converted to LiOH when it comes into contact with water, Li 2 To solve the problem of difficulty in distinguishing between O and LiOH, ONH analysis and Karl Fischer analysis are performed on the positive active material containing moisture, and the accuracy of LiOH content measurement is improved by correcting the content of LiOH generated by contact with moisture based on the moisture content measured by Karl Fischer analysis.

[0028] Specifically, the LiOH content in the positive electrode active material can be calculated according to Equation 1 to correct for the change in content due to moisture.

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[0029] According to the above analysis, LiOH and Li 2 CO 3 , Li 2 SO 4 and Li 2 The content of any of the four types of residual lithium compounds in the above-mentioned 1H-COOH / O can be analyzed, and the content of these residual lithium compounds analyzed can be used to accurately evaluate the performance of the positive electrode and the lithium secondary battery.

[0030] Therefore, the present invention further provides a positive electrode active material for a lithium secondary battery analyzed by the above method.

[0031] The positive electrode active material has a residual LiOH content of 0.1 to 0.4 wt % based on the total content, and a residual Li 2 CO 3 The content is 0.1-1.0 wt%, and residual Li 2 SO 4 The content is 0.1 to 1.3 wt.%, and residual Li 2 The O content is 0.2 to 0.5 wt %.

[0032] The present invention will be described in detail below with reference to examples to aid in understanding the present invention. However, the examples according to the present invention may be modified in various other ways, and the scope of the present invention should not be construed as being limited to the following examples. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0033] Working Example

[0034] (Step 1) ONH analysis First, for the analysis, Li[Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 ]O 2 Four types of positive electrode active material samples (samples 1 and 2: fired products; samples 3 and 4: water-washed products) were prepared.

[0035] For each of the above samples (solid state), 10 to 50 mg was taken and introduced into the heating furnace of an ONH analyzer (ONH836, LECO), and then melted at 2,200°C. The discharged hydrogen gas was then transported together with a carrier gas (He) and analyzed to measure the H content in the sample.

[0036] (Step 2) CS analysis 200-300 mg of each of the samples (solid state) was taken and introduced into a CS analyzer (CS844, LECO), and then calcined together with a combustion improver under an oxygen atmosphere to analyze the carbon (C) compounds and sulfur (S) compounds obtained, thereby measuring the contents of C and S components in the samples.

[0037] (Step 3) ICP-OES analysis 100 to 200 mg of each of the samples was aliquoted and added to 10 ml of ultrapure water and dissolved.

[0038] After 5 minutes, each sample solution was filtered through a 0.45 μm PTFE filter to remove undissolved components, and then the remaining filtrate (supernatant) was introduced into an ICP-OES instrument (AVIO 500, Perkin Elmer) for component analysis to measure the total residual Li components contained in the sample.

[0039] <ICP-OES Analysis Conditions> Forward Power: 1300 W Torch Height: 15 mm Plasma Gas Flow Rate: 15.00 L / min Sample Gas Flow Rate: 0.8 L / min Auxiliary Gas Flow Rate: 0.20 L / min Pump Speed: 1.5 ml / min

[0040] (Step 4) LiOH, Li 2 CO 3 , Li 2 SO 4 and Li 2 O Content Calculation Using the measurement results of H, C, and S components obtained for the four samples, the contents of LiOH, Li 2 CO 3 and Li 2 SO 4 were calculated respectively, and the Li content corresponding to LiOH, Li 2 CO 3 and Li 2 SO 4 was subtracted from the total residual Li component to calculate the Li 2 O content, and the results are shown in Table 1 below.

[0041]

Table 1

[0042] In Table 1, it can be seen that samples 1 and 2 were obtained by calcining a precursor and using the calcined product as it is as a sample, and thus had a large amount of residual lithium, whereas samples 3 and 4 were obtained by washing and drying the calcined product and using the washed product as a sample, and thus had a small amount of residual lithium.

[0043] (Stage 5) A blank was measured in triplicate using a graphite crucible. Calibration was carried out using O, C, and N standard samples. 0.02 g of undried Li[Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 ]O 2 The positive electrode active material was placed in a tin capsule and sealed. The tin capsule was then placed in a nickel basket. The nickel basket was placed in the sample inlet and H analysis was performed. The sample was quantitatively analyzed twice or more.

[0044] 1g Li[Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 ]O 2 The positive active material was dispensed into a sample bottle, sealed with a rubber stopper, and placed in the equipment (C30 coulometric KF titrator, Mettler Toledo) together with an empty bottle sample. The sample was heated at 200°C for 600 seconds to evaporate the moisture, and the moisture content was measured by iodometric titration. After correcting for moisture, the LiOH content was calculated using Equation 1.

[0045]

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[0046] Comparative Example: Li[Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 ]O 2 After preparing the four types of positive electrode active material samples, 5 g of each sample was taken and added to 1000 ml of ultrapure water to dissolve.

[0047] Each sample solution was filtered through a 0.45 μm PTFE filter to remove undissolved components, and the remaining filtrate (supernatant) was subjected to pH titration to determine the LiOH and Li 2 CO 3 The content was measured.

[0048] The content of each component calculated from the examples and comparative examples is shown in Table 2 below, expressed in weight percent (wt%). [Table 2]

[0049] From Table 2, when the dry and wet component analyses were performed on the positive electrode active material samples according to the examples, the results were summarized as follows: LiOH, Li 2 CO 3 , Li 2 SO 4 and Li 2 The content of the four types of residual lithium compounds, LiOH, LiO, and LiOH, was 0.1-0.4 wt% based on the total content of the sample. 2 CO 3 The content is 0.1-1.0 wt%, and residual Li 2 SO 4 The content is 0.1 to 1.3 wt.%, and residual Li 2 It can be confirmed that the O content is 0.2 to 0.5 wt %.

[0050] On the other hand, in the comparative example, only the wet pH titration analysis was performed to determine the amount of LiOH and Li 2 CO 3 The LiOH measured by the comparative example was Li2 The content of LiOH is changed to LiOH according to the embodiment. 2 It can be confirmed that the total amount of LiOH and LiO measured in the embodiment is similar to that of LiOH and LiO. 2 O and Li 2 CO 3 The sum of LiOH and Li measured by the comparative example 2 CO 3 The residual lithium content was compared with the sum of the above, and the results are shown in Table 3 below.

[0051] [Table 3]

[0052] From Table 3, it can be seen that the relative standard deviation (RSD) of the residual lithium content of the examples is within 5% when compared with the comparative examples.

Claims

1. A method for analyzing residual lithium compounds in a positive electrode active material for a lithium secondary battery, comprising: Analyzing the positive active material sample using an oxygen, nitrogen, and hydrogen analyzer and a Karl Fischer analyzer to measure the content of H components; analyzing the positive active material sample using a carbon-sulfur analyzer to measure the contents of C and S components; Analyzing the positive electrode active material sample using an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the content of Li components; Using the results of the measurements of the H, C and S components, the LiOH, Li ２ CO ３ and Li ２ SO ４ The Li content in the positive electrode active material sample was calculated using the measurement results of the Li content. ２ and calculating the content of O, The analytical method includes the step of calculating the content of LiOH according to Equation 1: [0010] In the above formula 1, H1 is the hydrogen content (wt%) analyzed by the ONH analyzer; H2 is the hydrogen content (wt%) analyzed by Karl Fischer method; M.W. ＬｉＯＨ is the weight average molecular weight of LiOH, A.M. Ｈ is the atomic mass of hydrogen.

2. The analytical method according to claim 1 , wherein the ICP-OES analysis is performed on a solution in which a positive electrode active material sample is dissolved in ultrapure water.

3. 2. The method of claim 1, wherein the content of LiOH calculated using the result of the measurement of the content of H in the step of measuring the content of H is 0.1 to 0.4 wt % based on the total weight of the positive active material.

4. Li calculated using the result of the C component measured in the step of measuring the contents of the C component and the S component ２ CO ３ The method of claim 1, wherein the content of is 0.1 to 1.0 wt % based on the total weight of the positive electrode active material.

5. Li calculated using the results of the S component measured in the step of measuring the contents of the C component and the S component ２ SO ４ The method of claim 1, wherein the content of is 0.1 to 1.3 wt % based on the total weight of the positive electrode active material.

6. Li calculated using the results of the Li component measured by the ICP-OES analysis ２ The method of claim 1, wherein the O content is 0.2 to 0.5 wt % based on the total weight of the positive active material.

7. The Li ２ The content of O was determined by ICP-OES analysis, and was determined by dividing the total residual Li content in the positive electrode active material sample by LiOH, Li ２ CO ３ and Li ２ SO ４ The analytical method according to claim 6, wherein the Li content is calculated by subtracting the Li content corresponding to the above.

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