Patent Application
20240151697
The present disclosure relates to a method for analyzing a residual lithium compound not involved in charging and discharging in a cathode active material for a lithium secondary battery.
A lithium secondary battery generally has the structure that an electrode assembly comprising a cathode and an anode containing an electrode active material capable of intercalating/discharging lithium ions, and a separator for separating the two electrodes is impregnated with an electrolyte solution as a medium of transferring lithium ions. The battery is charged and discharged as lithium ions move between the anode and cathode through the electrolyte. The electrode is generally manufactured by coating a foil-shaped current collector with a slurry containing an electrode material (e.g., an active material, a conductive material and a binder) to dry same, and forming an active material layer through a pressing process.
The performance of such a secondary battery is influenced by various factors (e.g., the components such as a cathode, an anode, a separator and an electrolyte, the composition of each component, and charging and discharging characteristics thereof). In particular, since a lithium by-product generated during the manufacturing process of the cathode active material, i.e., a residual lithium compound present in the cathode active material but not involved in charging and discharging, may impair the performance of the cathode, analysis on the lithium by-product is important for evaluating the performance of the battery.
In general, LiOH, Li2CO3, Li2SO4, and Li2O are regarded as four major residual compounds of the cathode active material. Conventionally, a wet method of stirring a cathode active material sample in water to elute a residual compound and then measuring the pH of the filtrate was performed in order to analyze the residual components.
However, this wet method has the problems that, since Li2O mostly turns into LiOH when in contact with water, Li2O and LiOH are hardly distinguished from each other; and, since the pH of Li2SO4 cannot be measured, only the pH of LiOH and Li2CO3 among the four residual compounds are measured. In addition, when other metals are coated on the surface of the cathode active material, multiple peaks rather than a single peak appear during pH titration, which renders accurate analysis difficult.
Accordingly, the object of the present disclosure is to provide a method for analyzing all four residual lithium compounds of LiOH, Li2CO3, Li2SO4 and Li2O present in a cathode active material for a lithium secondary battery.
An aspect of the present invention provided is a method for analyzing residual lithium compounds in the cathode active material for the lithium secondary battery, an analysis method comprising the following steps:
An aspect of the present invention provides a process of measuring the amount of H by the ONH and Karl Fischer analysis methods when calculating the amount of LiOH in the cathode active material and then correcting for changes in the amount due to moisture.
In addition, an aspect of the present invention provides a cathode active material for a lithium secondary battery analyzed by the above-described methods, wherein the amount of residual LiOH is 0.1 to 0.4% by weight, the amount of residual Li2CO3 is 0.1 to 1.0% by weight, and the amount of residual Li2SO4 is 0.1% to 1.3% by weight, and the amount of residual Li2O is 0.2 to 0.5% by weight, based on the total amount of the cathode active material.
According to an aspect of the present invention, the cathode active material sample is subjected to ONH analysis, CS analysis and ICP-OES analysis, respectively, and the amounts of all four residual lithium compounds (i.e., LiOH, Li2CO3, Li2SO4 and Li2O) present in the cathode active material may be analyzed by using the amounts of H, C, S, and Li measured therefrom. In particular, unlike a conventional wet method through pH titration, the ONH analysis and CS analysis are performed in a dry method such that the amounts of Li2O and LiOH are separately measured, and the amount of Li2SO4 not pH titrated in the wet method is also measured, thereby contributing to accurate evaluation of the performance of the lithium secondary battery.
The terms or words used in the specification and claims of the present invention should not be construed as being limited to have ordinary or dictionary meanings, but be interpreted to have meanings and concepts consistent with the technical idea of the present invention, based on the principle that the inventor(s) of a patent may appropriately define the concept of terms in order to explain the invention in the best way.
In addition, the features exemplified in the embodiments described in the specification of the present invention are only one of the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention. Thus, it should be understood that there may be various equivalents and variations that can replace them at the time of the filing date of the present application.
One embodiment of the present invention relates to a method for analyzing all residual lithium compounds (i.e., LiOH, Li2CO3, Li2SO4 and Li2O) in the cathode active material for the lithium secondary battery.
The cathode active material to be analyzed by an embodiment of the present invention is a compound in which lithium ions are intercalated in a cathode of a lithium secondary battery, which may comprise, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi1-x-y-zCoxM1yM2zO2 (wherein M1 and M2 are independently any one 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 independently atomic fractions of oxide composition elements, and 0≤x≤0.5, 0≤y≤0.5, 0≤z≤0.5, and 0≤x+y+z≤1).
Such a cathode active material is produced into 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° C. or higher. Li not contained in the crystal structure may react with CO2 present in the air during the heat treatment process to become Li2CO3 or may react with water to generate LiOH. In addition, the unreacted lithium source used to produce the active material may remain on the surface of the final active material. In general, four lithium compounds (i.e., LiOH, Li2CO3, Li2SO4 and Li2O) are regarded as by-products present in the cathode active material but not involved in charging and discharging. In order to secure the performance of the cathode, accurate analysis on the four residual lithium compounds is required.
To this end, in the present application, the cathode active material samples are prepared and introduced into an oxygen nitrogen hydrogen analyzer (ONH analyzer) and a carbon-sulfur analyzer (CS analyzer) operated in a dry method, and an ICP-OES analyzer operated 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 through the measured values.
Specifically, the ONH analyzer is a device for detecting oxygen, nitrogen and hydrogen gas components discharged after melting the samples in a heating furnace, and the cathode active material samples may be introduced in the form of dried particles into the ONH analyzer commonly used in the art to measure the amount of the H component contained in the samples.
The CS analyzer is a device for detecting the amounts of carbon and sulfur produced by burning samples in an oxygen stream, and the cathode active material samples may be introduced in the form of dried particles together with a flame retardant into the ceramic heating furnace of the CS analyzer commonly used in the art, and oxygen gas may be supplied from a device for inducing a high frequency to measure the amounts of the C component and S component contained in the samples.
When using the ONH analyzer and the CS analyzer, the cathode active material samples do not contact with moisture allowing the amounts of Li2O and LiOH to be separately measured. As such, this method may overcome the limitation of the conventional analysis method of measuring the amount of residual lithium in the cathode active material by using pH titration in a wet method where Li2O changes to LiOH due to contact with moisture such that only the total amounts of LiOH and Li2CO3 may be measured. In addition, Li2SO4 that is not pH titrated in the wet method may be analyzed by using the amount of the S component measured by the CS analyzer.
In one embodiment of the present invention, the amount of LiOH is calculated by using the results of the H component measured by the ONH analysis, and the calculated amount of LiOH may be 0.1 to 0.4% by weight, based on the total weight of the cathode active material.
In addition, the amounts of Li2CO3 and Li2SO4 are calculated by using the results of the C component and the S component measured by the CS analysis, respectively, and the amount of Li2CO3 may be 0.1 to 1.0% by weight, based on the total weight of the cathode active material, and the amount of Li2SO4 may be 0.1 to 1.3% by weight, based on the total weight of the cathode active material.
On the other hand, the ICP-OES analysis may be performed by using a solution obtained by dispensing a cathode active material sample and dissolving same in ultrapure water. Specifically, for example, the ICP-OES analysis may comprise impregnating 1:50 to 1:500 parts by weight of the cathode active material sample 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 analyzed by the ICP-OES indicates the total amount of lithium (Li wt %) in the cathode active material, i.e., the amounts of all Li compounds such as LiOH, Li2CO3, Li2SO4 and Li2O.
The ICP-OES analysis is performed by applying high thermal energy to the sample by using a high-temperature plasma induced by an argon gas as an inert gas to generate atoms and ions in the sample in an excited state, and then detecting the line emitted by the atoms and ions returning to a low energy level to analyze the components, which allows the total residual Li component contained in the cathode active material sample to be measured.
In one embodiment of the present invention, the treatment of the cathode active material sample with ultrapure water may be performed by adding ultrapure water in a range of 0.1 to 100 ml, based on 100 mg of the dispensed 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, component analysis may be performed by introducing the remaining filtrate into an ICP-OES analyzer commonly used in the art.
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 cathode active material sample measured by the ICP-OES analysis, and the calculated amount of Li2O may be 0.2 to 0.5% by weight, based on the total weight of the cathode active material.
In the present application, the order of the steps of the ICP-OES analysis, CS analysis and ONH analysis is not particularly limited.
In order to solve the problem that, since Li2O is mostly changed to LiOH when in contact with water, Li2O and LiOH are hardly distinguished from each other, the ONH analysis and Karl Fischer analysis are performed on the cathode active material containing water, and the accuracy of measuring the amount of LiOH is improved through the correction of excluding the amount of LiOH generated due to contact with moisture, based on the amount value of water measured by the Karl Fischer analysis.
Specifically, the amount of LiOH in the cathode active material may be calculated as in Equation 1 to correct for changes in the amount due to moisture.
Accordingly, an embodiment of the present invention further provides a cathode active material for a lithium secondary battery analyzed by the above-described method.
In the cathode active material, the amount of residual LiOH may be 0.1 to 0.4% by weight, the amount of residual Li2CO3 may be 0.1 to 1.0% by weight, the amount of residual Li2SO4 may be 0.1 to 1.3% by weight, and the amount of residual Li2O may be 0.2 to 0.5% by weight, based on the total amount of the cathode active material.
Hereinafter, embodiments will be described in detail to aid understanding of the present invention. However, the embodiments according to the present invention may be modified in many different forms, and the scope of the present invention should not be construed as being limited to the following examples. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.
(Step 1) ONH Analysis
First, four types of cathode active material samples of Li[Ni0.86Co0.05Mn0.07Al0.02]O2 (Samples 1 and 2: calcinated products; and Samples 3 and 4: washed products) were prepared for analysis.
10 to 50 mg of each of the samples (in a solid state) was dispensed, introduced into the heating furnace of an ONH analyzer (ONH836, LECO) and melted at 2,200° C., and the discharged hydrogen gas was moved together with a carrier gas (He) and analyzed to measure the amount of H in the samples.
(Step 2) CS Analysis
200 to 300 mg of each of the samples (in a solid state) was dispensed, introduced into a CS analyzer (CS844, LECO) and then calcined together with a flame retardant under an oxygen atmosphere to obtain a carbon (C) compound and a sulfur (S) compound, and such compounds were analyzed to measure the amounts of C component and S component in the samples.
(Step 3) ICP-OES Analysis
100 to 200 mg of each of the samples was dispensed and dissolved in 10 ml of ultrapure water.
After 5 minutes, each sample solution was filtered with a 0.45 μm PTFE filter to remove undissolved components, and then the remaining filtrate (i.e., a supernatant) was introduced into an ICP-OES instrument (e.g., AVIO 500, Perkin Elmer) to perform component analysis. Thus, the components of the total residual Li contained in the samples were measured.
<Conditions for ICP-OES Analysis>
(Step 4) Calculation of the Amounts of LiOH, Li2CO3, Li2SO4 and Li2O
The amounts of LiOH, Li2CO3 and Li2SO4 in the samples were calculated by using the measurement results of the H, C and S components, respectively, in the four samples, and the amount of Li corresponding to LiOH, Li2CO3 and Li2SO4 was subtracted from the total residual Li components to calculate the amount of Li2O. The results are shown in Table 1 below.
Table 1 above shows that Samples 1 and 2 that are the calcinated products obtained by calcinating the precursors had a large amount of residual lithium, and Samples 3 and 4 that are washed products obtained by washing and drying the calcinated products had a small amount of residual lithium.
(Step 5)
A blank was measured three times by using a graphite crucible. Calibration was performed by using 0, C, and N standard samples. 0.02 g of the non-dried cathode active material of Li[Ni0.86Co0.05Mn0.07Al0.02]O2 was placed in a tin capsule and sealed. The tin capsule was then put into a nickel basket. The nickel basket was put into the sample inlet to perform H analysis. Quantitative analysis on the sample was repeatedly performed twice or more.
1 g of the cathode active material of Li[Ni0.86Co0.05Mn0.07Al0.02]O2 was dispensed into a sample bottle, sealed with a rubber stopper, and loaded into an instrument (e.g., C30 coulometric KF titrator, Mettler toledo) together with an empty bottle sample. After vaporizing the moisture while heating the sample at 200° C. for 600 seconds, the amount of moisture was measured by iodine titration. After correcting for moisture, the amount of LiOH was calculated as in Equation 1.
After preparing four types of cathode active material samples of Li[Ni0.86Co0.05Mn0.07Al0.02]O2, 5 g of each sample was dispensed and added to 1000 ml of ultrapure water to dissolve same.
After each sample solution was filtered through a 0.45 μm PTFE filter to remove undissolved components, pH titration was performed on the remaining filtrate (i.e., a supernatant) to measure the amounts of LiOH and Li2CO3 in the sample.
The amount results of the components calculated in the examples and comparative examples and indicated by the unit of weight % (wt %) are shown in Table 2 below.
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 performed on a cathode active material sample in dry and wet methods according to the examples. Further, it is confirmed that the amount of residual LiOH is 0.1 to 0.4% by weight, the amount of residual Li2CO3 is 0.1 to 1.0% by weight, the amount of residual Li2SO4 is 0.1 to 1.3% by weight, and the amount of residual Li2O is 0.2 to 0.5% by weight, based on the total amount of the sample.
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 is confirmed that the amount of LiOH measured according to the comparative examples includes the amount of Li2O changed to LiOH and is similar to the sum of the amounts of LiOH and Li2O according to the examples. Accordingly, 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.
1)RSD (Relative standard deviation) = Standard deviation/average × 100
From Table 3 above, it is confirmed that the relative standard deviation (RSD) of the amount of residual lithium of the examples is within 5% as compared to the comparative examples.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2021-0157632 | Nov 2021 | KR | national |
| 10-2022-0151580 | Nov 2022 | KR | national |
The present application is a national phase entry under 35 U.S.C § 371 of International Application No. PCT/KR2022/017993 filed on Nov. 15, 2022 which claims the benefit of priority based on Korean Patent Application No. 10-2022-0151580, filed on Nov. 14, 2022 and on Korean Patent Application No. 10-2021-0157632 filed on Nov. 16, 2021, all contents of which are incorporated herein by reference
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2022/017993 | 11/15/2022 | WO |
