Analysis method for the content and distribution of boron introduced into the positive electrode active material

Abstract

The present invention provides an analytical method for introducing the boron content in a positive electrode active material. The method includes the following steps: (S1) preparing a positive electrode active material sample in which boron is introduced; (S2) separating a first liquid layer and a first precipitate by dissolving the positive electrode active material sample in water, and then analyzing the solution obtained by acid-treating the first liquid layer using inductively coupled plasma optical emission spectrometry (ICP-OES) to measure the boron concentration; (S3) separating a second liquid layer and a second precipitate by dissolving the first precipitate in water, and then analyzing the solution obtained by acid-treating the second liquid layer using ICP-OES to measure the boron concentration; and (S4) analyzing the solution obtained by adding acid and hydrogen peroxide to the second precipitate using ICP-OES to measure the boron concentration. According to the present invention, by sequentially extracting and analyzing boron introduced to improve the performance of the positive electrode active material for a lithium secondary battery using the solubility differences in water and acid according to the distribution position, the optimal boron content for improving the performance of the positive electrode active material can be obtained based on the distribution of boron in the positive electrode active material.

Description

Technical Field

[0001] This application claims the priority benefits of Korean Patent Application No. 10-2020-0181058, filed on December 22, 2020, and Korean Patent Application No. 10-2021-0107445, filed on August 13, 2021. The entire disclosures of the Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to an analysis method for introducing a distribution pattern of boron and the content of each distribution position into a positive electrode active material for a lithium secondary battery. Background Art

[0003] A lithium secondary battery generally has a structure including an electrode assembly composed of a positive electrode (cathode) and a negative electrode (anode) each containing an electrode active material capable of embedding / releasing lithium ions and a separator interposed between the two electrodes, and an electrolyte as a lithium ion transport medium. Lithium ions move between the negative electrode and the positive electrode through the electrolyte, causing charging and discharging of the battery.

[0004] Problems such as deterioration of life characteristics, decomposition of the electrolyte, or deterioration of the active material may occur during repeated charging and discharging of the secondary battery. In addition, during the manufacture of a secondary battery electrode, when impurities are present on the surface of the active material, the battery may expand due to changes over time and the reaction between the impurities and the electrolyte.

[0005] To overcome the above problems, the electrode active material can be coated or doped with various materials. For example, when using a lithium transition metal oxide such as a lithium-nickel-manganese-cobalt-based oxide as the positive electrode active material, coating or doping with boron results in the formation of an oxygen-closed structure, thereby enabling a slowdown in capacity decline. In addition, boron contained in the positive electrode active material can improve the structural stability by strengthening the bond between the transition metal and oxygen. Generally, introducing boron into the positive electrode active material is performed by mixing the positive electrode active material and boric acid (H 3 BO 3 ) and firing at a high temperature, where boron can penetrate into the interior of the positive electrode active material or can remain in the form of a Li-B-O compound on its surface and outside.

[0006] To evaluate the effect of boron on the performance of the positive electrode active material, it is important to understand the distribution pattern of boron inside and outside the active material, particularly to measure the content of boron that penetrates into the interior. Currently, the method for analyzing the composition of the positive electrode active material is measurement by inductively coupled plasma optical emission spectrometry (ICP-OES) after acid pretreatment. In this method, even boron that penetrates into the interior of the primary particles of the structurally stable positive electrode active material can be quantified by using an acid.

[0007] However, a technique for separately analyzing boron inside and outside the positive electrode active material has not been developed yet. Summary of the Invention

[0008] Technical Problem

[0009] Therefore, an object of the present invention is to provide an analysis method for the content of each distribution position of boron introduced to improve the performance of the positive electrode active material used in a lithium secondary battery.

[0010] Solution to the Problem

[0011] According to one aspect of the present invention, there is provided an analysis method for the content of boron introduced into a positive electrode active material, the method comprising:

[0012] (S1) Preparing a positive electrode active material sample into which boron has been introduced;

[0013] (S2) Dissolving the positive electrode active material sample in water to obtain a first liquid layer and a first precipitate, treating the first liquid layer with an acid, and then analyzing the resulting solution by inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the boron concentration;

[0014] (S3) Dissolving the first precipitate in water to obtain a second liquid layer and a second precipitate, treating the second liquid layer with an acid, and then analyzing the resulting solution by ICP-OES to determine the boron concentration; and

[0015] (S4) Adding an acid and hydrogen peroxide to the second precipitate, and then analyzing the resulting solution by ICP-OES to determine the boron concentration.

[0016] In addition, the present invention provides a positive electrode active material for a secondary battery, the boron content of which is determined by the above analysis method, wherein boron is introduced into a lithium transition metal oxide such that boron is present at at least one of the surface, grain boundaries, and inside the lattice of the lithium transition metal oxide particles.

[0017] Advantageous Effects of the Invention

[0018] According to the present invention, boron introduced to improve the performance of the positive electrode active material for a lithium secondary battery can be sequentially extracted and analyzed by utilizing the difference in solubility in water and acid depending on the distribution position of boron, and thus, the optimum boron content required to improve the performance of the positive electrode active material can be determined based on the distribution pattern of boron in the positive electrode active material. Brief Description of the Drawings

[0019] Figure 1 Shows the distribution pattern of boron introduced into the positive electrode active material.

[0020] Figure 2Shows the extraction results of boron and lithium according to the dissolution time of the positive electrode active material sample in water during the analysis according to the embodiment. Detailed Embodiment

[0021] Hereinafter, terms or words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings, but rather should be interpreted in accordance with the meaning and concept that conforms to the technical gist of the present invention on the basis of the principle that the inventor can appropriately define the concept of the term in order to best describe his invention.

[0022] In addition, the embodiments described in this specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, it should be understood that various equivalents and modifications may replace them when this application is filed.

[0023] One embodiment of the present invention relates to an analysis method for the content of boron introduced according to the distribution position to improve the performance of the positive electrode active material for lithium secondary batteries. Hereinafter, this method will be described in detail for each step.

[0024] First, prepare a positive electrode active material sample (S1) into which boron is introduced.

[0025] Specifically, the positive electrode active material sample can be prepared by dry-mixing a boron-containing compound and a positive electrode active material, and then firing at a high temperature.

[0026] The boron-containing compound may include at least one compound selected from the group consisting of: H 3 BO 3 , B 2 O 3 , C 6 H 5 B(OH) 2 , (C 6 H 5 O) 3 B, [CH 3 (CH 2 ) 3 O] 3 B, C 13 H 19 BO 3 , C 3 H 9 B 3 O 6 and (C 3 H 7 O) 3 B.

[0027] The positive electrode active material may include a lithium transition metal oxide represented by the following formula 1.

[0028] [Formula 1]

[0029] Li[Ni x Mn y Co z M v O 2

[0030] In the formula, M is one or more selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga, and In; 0 ≤ x ≤ 1.0, 0 ≤ y ≤ 0.6, 0 ≤ z ≤ 0.6, and 0 ≤ v ≤ 0.1.

[0031] In addition, the firing can be carried out near the melting point of the boron-containing compound, for example, at 130 °C to 300 °C, such as 130 °C to 200 °C, for 3 hours to 10 hours. When the firing temperature satisfies the above temperature range, the boron-containing compound is sufficiently melted and can prevent non-uniform reactions caused by excessive temperature.

[0032] After the firing process, boron can be coated on the surface of the positive electrode active material or penetrate into the interior of the positive electrode active material to be distributed between primary particles or secondary particles. Refer to Figure 1 , boron is introduced into the positive electrode active material so that it exists in the coating layer on the surface (A), at the grain boundary (B), or within the lattice (C) to form lithium borate oxides such as LiBO 2 , LiB 4 O 7 etc.

[0033] The solubility of boron in water can vary depending on its distribution position in the positive electrode active material. For example, boron present in the coating layer (A) of the positive electrode active material is easily soluble in water, while boron present at the grain boundary (B) dissolves in water after a long time, and boron doped within the lattice (C) is hardly soluble in water and can be dissolved by acid treatment. Therefore, in the present invention, by utilizing the solubility differences at each distribution position, boron present in the positive electrode active material sample is sequentially extracted.

[0034] In particular, the positive electrode active material sample is dissolved in water to obtain a first liquid layer and an insoluble first precipitate, and then the first liquid layer is acid-treated (S2). At this time, the dissolution of the sample in water can be carried out at room temperature for 1 to 10 minutes.

[0035] The first liquid layer is the result of boron coated on the surface of the positive electrode active material rapidly dissolving in water. Therefore, the first liquid layer is acid-treated to induce the dissolution of the remaining boron. In addition, through the acid treatment, the acid concentration and solution viscosity can be maintained at the same level as in the single extraction of boron.

[0036] The acid-treated first liquid layer solution can be analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) to measure the boron concentration. The ICP-OES can be carried out in a conventional manner in the art, for example, under the conditions illustrated in the following examples. The boron content (A) coated on the surface of the positive electrode active material can be calculated using the boron concentration measured as above.

[0037] Then, in order to extract the boron present at the grain boundaries of the positive electrode active material sample, the first precipitate is dissolved in water to obtain a second liquid layer and an insoluble second precipitate, and then the second liquid layer is treated with an acid (S3). At this time, the dissolution of the first precipitate in water can be carried out at room temperature for 1 to 10 hours.

[0038] The acid-treated second liquid layer solution can be analyzed by ICP-OES to measure the boron concentration, and the boron content (B) present at the grain boundaries of the positive electrode active material can be calculated using the boron concentration measured as above.

[0039] Then, in order to extract the boron doped in the lattice of the positive electrode active material sample, the second precipitate is dissolved by adding an acid and hydrogen peroxide (S4). At this time, the dissolution of the second precipitate can be carried out for 1 to 5 hours.

[0040] The solution obtained by treating the second precipitate with an acid and hydrogen peroxide is analyzed by ICP-OES to measure the boron concentration, and the boron content (C) doped in the lattice of the positive electrode active material can be calculated using the boron concentration measured as above.

[0041] The boron content (C) doped in the lattice of the active material particles determined by extraction and ICP-OES analysis in the sequential process corresponds to the value according to the following Equation 1:

[0042] [Equation 1]

[0043] Lattice boron content (C) = Total boron content (D) in the sample – (Boron content (A) in the coating layer + Boron content (B) at the grain boundaries).

[0044] In the boron extraction step at each distribution position, the acid that can be used for the first liquid layer, the second liquid layer, and the second precipitate can be hydrochloric acid, and based on 1 g of each object to be treated, the amount of the acid can be 0.01 to 10 mL, preferably 5 to 10 mL.

[0045] On the other hand, hydrogen peroxide is used to extract the remaining boron that is not dissolved by the acid, and the acid and hydrogen peroxide can be used in a volume ratio of 1:0.3 to 1:0.7, for example, 1:0.5.

[0046] As described above, when boron introduced into the positive electrode active material is sequentially extracted and analyzed by taking advantage of the difference in solubility in water and acid, the amount of boron present at each position can be quantified according to the distribution pattern of boron in the positive electrode active material, thereby identifying the correlation between performance improvement and boron introduction amount. From this, the optimal boron content contributing to the improvement of the positive electrode material performance can be confirmed.

[0047] Accordingly, the present invention also provides a positive electrode active material for a secondary battery, the boron content of which is determined by the above analysis method, wherein boron is introduced into lithium transition metal oxide particles such that boron is present at at least one of the surface, grain boundaries, and within the crystal lattice of the lithium transition metal oxide particles.

[0048] In the positive electrode active material according to the present invention, based on the total amount of boron introduced, 80% to 100% of boron may be present on the surface of the lithium transition metal oxide particles, 0 to 1% of boron may be present at the grain boundaries of the lithium transition metal oxide particles, and 0 to 20% of boron may be present within the crystal lattice of the lithium transition metal oxide particles.

[0049] Mode for Carrying Out the Invention

[0050] Hereinafter, embodiments will be described in detail to assist in understanding the present invention. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the following embodiments. The embodiments of the present invention are provided to more fully explain the present invention to those of ordinary skill in the art.

[0051] Example 1: Extraction and Content Analysis Based on the Distribution Position of Boron Introduced into the Positive Electrode Active Material

[0052] (Step 1) Preparation of the positive electrode active material sample

[0053] LiNi, which is a positive electrode active material, 0.78 Mn 0.11 Co 0.11 O 2 and H, which is a boron-containing compound, 3 BO 3 were mixed in a dry mixer (CYCLOMIX, Hosokawa Micron Corporation), and then the resulting powder was fired at 150 °C for 5 hours. Through this process, three samples in which boron was introduced into the positive electrode active material were obtained, wherein the positive electrode active material and the boron-containing compound were applied to the samples in the amounts shown in Table 1, respectively.

[0054] (Step 2) Extraction and content measurement of boron present in the coating layer of the positive electrode active material

[0055] Take out 0.1 g of each of the three samples obtained in Step 1 and put them into vials. Dissolve them by adding 20 g of ultrapure water thereto and then shaking for 5 minutes at room temperature. Let the resulting solution stand to separate the first liquid layer and the first precipitate (insoluble), and then filter through a 0.45-μm filter.

[0056] After filtration, add 0.5 mL of concentrated hydrochloric acid and 0.1 mL of internal standard solution (Sc, 1000 μg / mL) to 10 g of the first liquid layer, and analyze the resulting solution by ICP-OES. At this time, run ICP-OES (AVIO500, PerkinElmer) under the following 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; and pump speed 1.5 mL / min.

[0057] Based on the boron concentration measured by ICP-OES, calculate the boron content (A) present in the coating layer of the positive electrode active material.

[0058] (Step 3) Extraction and content measurement of boron present at the grain boundaries of the positive electrode active material

[0059] Put 0.1 g of the first precipitate (insoluble) separated in Step 2 into a vial, and dissolve it by adding 20 g of ultrapure water thereto and then shaking for 5 hours at room temperature. Let the resulting solution stand to separate the second liquid layer and the second precipitate (insoluble), and then filter through a 0.45-μm filter.

[0060] After filtration, add 0.5 mL of concentrated hydrochloric acid and 0.1 mL of internal standard solution (Sc, 1000 μg / mL) to 10 g of the second liquid layer, and analyze the resulting solution by ICP-OES under the same conditions as in Step 2.

[0061] Based on the boron concentration measured by ICP-OES, calculate the boron content (B) present at the grain boundaries of the positive electrode active material.

[0062] (Step 4) Extraction and content measurement of boron within the crystal lattice of the positive electrode active material

[0063] Put 0.1 g of the second precipitate (insoluble) separated in Step 3 into a vial, and dissolve it by adding 1 mL of concentrated hydrochloric acid and 0.5 mL of hydrogen peroxide at room temperature for 3 hours. Bubbles and heat are generated during the dissolution process.

[0064] Add 0.1 mL of internal standard solution (Sc, 1000 μg / mL) to the resulting solution, and perform ICP-OES analysis under the same conditions as in Step 2.

[0065] The boron content (C) within the lattice of the positive electrode active material was calculated from the boron concentration measured by ICP-OES.

[0066] Comparative Example 1: Single extraction and content analysis of boron introduced into the positive electrode active material

[0067] 0.1 g of each of the three samples obtained in Step 1 of the Example was separated and placed in a vial, and it was dissolved at room temperature for 3 hours by adding 1 mL of concentrated hydrochloric acid and 0.5 mL of hydrogen peroxide. Bubbles and heat were generated during the dissolution process.

[0068] 0.1 mL of an internal standard solution (Sc, 1000 μg / mL) was added to the resulting solution, and ICP-OES analysis was performed under the same conditions as in Step 2.

[0069] The boron content (D) introduced into the positive electrode active material was calculated from the boron concentration measured by ICP-OES.

[0070] The analysis results of the Example and the Comparative Example are shown in Table 1 below.

[0071] [Table 1]

[0072]

[0073] From Table 1, even though the amount of boron used in the sample preparation was the same, the content of boron coated or doped in each sample differed depending on the reactivity between boron and the active material (especially for Sample 1, it was found that due to the weight error in weighing the boron raw material or the purity of boron, the content in the active material was different from the amount of boron introduced). By sequentially extracting boron using the difference in solubility in water and acid depending on the distribution position of boron, the content of boron that penetrated into the interior could be measured. That is to say, it can be seen that in Sample 1, most of the boron introduced into the positive electrode active material existed in the coating layer (A) on the surface, while in Samples 2 and 3, the introduced boron was dispersed and distributed in the coating layer (A), at the grain boundaries (B), and within the lattice (C). From the distribution pattern of boron, the optimal boron content required to improve the performance of the positive electrode active material could be determined.

[0074] In addition, from the results of the Comparative Example, it was confirmed that the boron content (C) within the lattice of the positive electrode active material particles corresponded to the value according to Equation 1 below.

[0075] [Equation 1]

[0076] Boron content within the lattice (C) = Total boron content in the sample (D) – (Boron content in the coating layer (A) + Boron content at the grain boundaries (B))

[0077] Therefore, as in Example 1, when boron introduced into the positive electrode active material is extracted and analyzed according to the distribution position, the amount of boron present at each position can be quantified according to the distribution pattern of boron in the positive electrode active material, thereby identifying the correlation between performance improvement and boron introduction amount. Thus, the optimal boron content contributing to the performance improvement of the positive electrode material can be determined.

[0078] Example 2:

[0079] To confirm the extraction contents of boron and lithium corresponding to the dissolution time of the positive electrode active material into which boron has been introduced, LiNi 0.78 Mn 0.11 Co 0.11 O 2 and H 3 BO 3 were dry-mixed and fired as in Step 1 of Example 1 to prepare a sample (1000 mg boron / 1 kg positive electrode active material), and then 0.1 g of the sample was separated and placed in a vial, dissolved by adding 20 g of ultrapure water thereto at room temperature, and subjected to ICP-OES analysis according to the dissolution time under the same conditions as in Example 1.

[0080] As a result, the boron and lithium contents according to the dissolution time are shown in Table 2 and Figure 2 as follows.

[0081] [Table 2]

[0082]

[0083] From Table 2 and Figure 2 , the content (extraction concentration) of boron did not change significantly with the dissolution time and most of the boron was present in the coating layer, while the slope of the content (extraction concentration) of lithium was divided into three stages with the dissolution time and the results of lithium were similar to those of Samples 2 and 3 used in Example 1. These results will be used as indirect evidence that lithium applied to the positive electrode active material at a high concentration has different distribution patterns in the active material particles according to the dissolution rate. It is speculated that the difference in the dissolution rate of the lithium component is due to the partial detachment and dissolution of lithium from the structure of the NCM-based positive electrode active material (Li[Ni / Co / Mn]O 2 ).

Claims

1. A method for analyzing the boron content introduced into a positive electrode active material, the method comprises: (S1) Prepare a positive electrode active material sample into which boron is introduced; (S2) Dissolve the positive electrode active material sample in water to obtain a first liquid layer and a first precipitate, treat the first liquid layer with an acid, and then analyze the resulting solution by inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the boron concentration; (S3) Dissolve the first precipitate in water to obtain a second liquid layer and a second precipitate, treat the second liquid layer with an acid, and then analyze the resulting solution by ICP-OES to determine the boron concentration; and (S4) Add an acid and hydrogen peroxide to the second precipitate, and then analyze the resulting solution by ICP-OES to determine the boron concentration; wherein the positive electrode active material sample is prepared by dry-mixing a boron-containing compound and a positive electrode active material, followed by firing, such that boron is present on the surface, at grain boundaries, and within the crystal lattice of the positive electrode active material particles; wherein the method comprises: Calculating the boron content (A) coated on the surface of the positive electrode active material using the boron concentration measured in step (S2), Calculating the boron content (B) present at the grain boundaries of the positive electrode active material using the boron concentration measured in step (S3), and Calculating the boron content (C) doped within the crystal lattice of the positive electrode active material using the boron concentration measured in step (S4); wherein the boron content (C) present within the crystal lattice of the positive electrode active material corresponds to the value according to the following Equation 1: [Equation 1] Boron content within the lattice (C) = Total boron content in the sample (D) – (Boron content in the coating layer (A) + Boron content at grain boundaries (B)).

2. The analytical method according to claim 1, wherein the boron-containing compound comprises at least one compound selected from the group consisting of: H 3 BO 3 , B 2 O 3 , C 6 H 5 B(OH) 2 , (C 6 H 5 O) 3 B. [CH 3 (CH 2 ) 3 O] 3 B.C 13 H 19 BO 3 , C 3 H 9 B 3 O 6 and (C 3 H 7 O) 3 B.

3. The analysis method according to claim 1, wherein the positive electrode active material comprises a lithium transition metal oxide represented by the following formula 1 [Formula 1] Li[Ni x Mn y Co z M v O 2 In the formula, M is one or more selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga, and In; 0 ≤ x ≤ 1.0, 0 ≤ y ≤ 0.6, 0 ≤ z ≤ 0.6, and 0 ≤ v ≤ 0.

1.

4. The analysis method according to claim 1, wherein the firing is carried out at a temperature of 130°C to 300°C.

5. The analysis method according to claim 1, wherein based on 1 g of the object to be treated, the amount of acid used in steps (S2) to (S4) is in the range of 0.01 to 10 mL.

6. The analysis method according to claim 1, wherein the acid used in steps (S2) to (S4) comprises hydrochloric acid.

7. A positive electrode active material for a secondary battery, wherein the boron content of the positive electrode active material is determined by the analysis method according to claim 1, and boron is introduced into lithium transition metal oxide particles such that boron is present at least at one of the surface, grain boundaries, and within the crystal lattice of the lithium transition metal oxide particles.

8. The positive electrode active material for a secondary battery according to claim 7, wherein, based on the total amount of boron introduced, 80% to 100% of boron is present on the surface of the lithium transition metal oxide particles, 0% to 1% of boron is present at the grain boundaries of the lithium transition metal oxide particles, and 0% to 20% of boron is present within the lattice of the lithium transition metal oxide particles.

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