Method of analyzing amount of lithium carbonate as impurity in lithium sulfate

Abstract

A step of preparing a sample by mixing lithium carbonate of a predetermined content with lithium sulfide, and manufacturing an electrode sample containing lithium sulfide using said sample; a step of measuring the rate of change of capacity Q with respect to voltage V by a constant current charge / discharge method for said electrode sample, obtaining a normalized rate of change by dividing the rate of change dQ / dV by a theoretical capacity value, and obtaining a graph showing said normalized rate of change against voltage V; a step of measuring the area of ​​a peak appearing at a predetermined numerical range of voltage in the graph showing said normalized rate of change against voltage V, wherein the predetermined numerical range of voltage is a numerical range in which the peak of said normalized rate of change appears due to the reaction of said mixed lithium carbonate; a step of measuring the area of ​​said peak by a constant current charge / discharge method in the same manner for a plurality of electrode samples manufactured by changing the content of said lithium carbonate, and collecting data on the area of ​​said peak measured for each of the contents of said lithium carbonate; and a step of analyzing the correlation between the content of said lithium carbonate and the area of ​​said peak using said data. A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide is provided, comprising: a step of manufacturing an electrode for the lithium sulfide to be analyzed in the same manner as the step of manufacturing the electrode sample, and measuring the area of ​​the peak by a constant current charge / discharge method; and a step of determining the content of lithium carbonate corresponding to the peak area measured for the lithium sulfide to be analyzed by applying the analyzed correlation, and determining this as the content of lithium carbonate mixed as an impurity in the lithium sulfide to be analyzed.

Description

Technology Field

[0001] The present invention relates to a method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide. Background Technology

[0003] The content of a specific substance in a mixture can be analyzed using methods such as XRD (X-ray diffraction) analysis, BET analysis, and ICP (inductively coupled plasma spectrometry). The problem to be solved

[0005] The objective of the present invention is to provide a method for analyzing the content of lithium carbonate in cases where the content of lithium carbonate mixed as an impurity in lithium sulfide is very low and difficult to measure with known measuring instruments.

[0006] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims. means of solving the problem

[0008] In one embodiment of the present invention, the method comprises the steps of: preparing a sample by mixing lithium carbonate of a predetermined content with lithium sulfide, and manufacturing an electrode sample containing lithium sulfide using the sample; measuring the rate of change of capacity Q with respect to voltage V by a constant current charge / discharge method for the electrode sample, obtaining a normalized rate of change by dividing the rate of change dQ / dV by a theoretical capacity value, and obtaining a graph showing the normalized rate of change against voltage V; measuring the area of ​​a peak appearing at a predetermined numerical range of voltages in the graph showing the normalized rate of change against voltage V, wherein the predetermined numerical range of voltages is a numerical range in which the peak of the normalized rate of change appears due to the reaction of the mixed lithium carbonate; measuring the area of ​​the peak by the constant current charge / discharge method in the same manner for a plurality of electrode samples manufactured by changing the content of the lithium carbonate, and collecting data on the area of ​​the peak measured for each of the plurality of lithium carbonate contents; and analyzing the correlation between the content of the lithium carbonate and the area of ​​the peak using the data. A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide comprises: a step of manufacturing an electrode for the lithium sulfide to be analyzed in the same manner as the step of manufacturing the electrode sample, and measuring the area of ​​the peak by a constant current charge-discharge method; and a step of determining the content of lithium carbonate corresponding to the peak area measured for the lithium sulfide to be analyzed by applying the analyzed correlation, and determining this as the content of lithium carbonate mixed as an impurity in the lithium sulfide to be analyzed.

[0009] A method for analyzing the content of lithium carbonate included as an impurity in the above lithium sulfide can determine the correlation by using the above data and linear regression analysis.

[0010] The above linear regression analysis can obtain constant values ​​of a and b in Equation 1 below by setting the independent variable X as the content of lithium carbonate in the sample and the dependent variable Y as the area of ​​the peak.

[0011] <Equation 1>

[0012] Y = aX + b

[0013] In the above Equation 1, the unit of X is wt%, and a is 7.2 x 10 -5 Up to 4.1 x 10 -4 and, the above b is 9.99 x 10 -5 Up to 5.01 x 10 -4 It could be.

[0014] In one embodiment, Y may be 0.0051 to 0.00273.

[0015] In a method for analyzing the content of lithium carbonate included as an impurity in the lithium sulfide, for measurement by the constant current charging and discharging method, a battery including the electrode sample or the electrode is manufactured, and the battery is charged at a charging and discharging rate of 0.01 C-rate and under charging and discharging conditions in the range of 1.5 V to 4.5 V, so that the rate of change of capacity with respect to voltage can be measured.

[0016] The voltage of the above predetermined numerical range may be 3.9 V to 4.1 V.

[0017] In a method for analyzing the content of lithium carbonate included as an impurity in the lithium sulfide, the area of ​​the peak can be measured for the plurality of electrode samples prepared using the sample prepared with different content of lithium carbonate within the range of 0 to 10 wt%.

[0018] The above electrode sample and the electrode can be manufactured using a dry electrode manufacturing method.

[0019] The electrode sample and the electrode each comprise an active material layer comprising the lithium sulfide, a conductive material, and a binder, and the active material layer may contain 55 to 75 wt% of the lithium sulfide based on a total amount of 100 wt% of the lithium sulfide, the conductive material, and the binder.

[0020] The method for analyzing the content of lithium carbonate included as an impurity in the above lithium sulfide can evaluate the quality of the lithium sulfide to be analyzed based on the determined content of lithium carbonate. Effects of the invention

[0022] The content of lithium carbonate can be analyzed by a method that analyzes the content of lithium carbonate included as an impurity in lithium sulfide. Furthermore, this method enables the analysis of the content of lithium carbonate included as an impurity in lithium sulfide even when the amount of lithium carbonate mixed as an impurity is low.

[0023] In addition to the effects described above, the specific effects of the present invention are described together with the specific details for implementing the invention below. Brief explanation of the drawing

[0025] FIG. 1 is a charge / discharge graph measured by a constant voltage charge / discharge method for each electrode sample prepared according to the lithium carbonate content in a method according to one embodiment of the present invention. Figure 2 is a graph plotting the normalized rate of change of capacity Q with respect to voltage V, obtained by processing the charge / discharge graph of the electrode sample of Figure 1 and dividing the rate of change of capacity Q with respect to voltage V, dQ / dV, by the theoretical capacity value. Figure 3 is an enlarged graph of the portion of Figure 2 where the normalized rate of change peaks at voltages around 3.9 to 4.1 V. Figure 4 is a graph showing the area of ​​the peak obtained as the integral value of the normalized rate of change at 3.9 to 4.1 V for each lithium carbonate content in Figure 3, plotted against the lithium carbonate content, and confirming the linear calibration curve. Figure 5 is a graph showing the peak area obtained as an integral value of the normalized rate of change for electrode samples prepared with different electrode sizes, plotted against the lithium carbonate content, and confirming the linear calibration curve. Specific details for implementing the invention

[0026] The aforementioned objectives, features, and advantages are described in detail below with reference to the attached drawings, thereby enabling those skilled in the art to easily implement the technical concept of the present invention. In describing the present invention, detailed descriptions of known technologies related to the present invention are omitted if it is determined that such descriptions would unnecessarily obscure the essence of the invention. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0027] In the following, the statement that any configuration is placed on the "upper (or lower)" of a component or on the "upper (or lower)" of a component may mean not only that any configuration is placed in contact with the upper (or lower) surface of said component, but also that another configuration may be interposed between said component and any configuration placed on (or below) said component.

[0028] In addition, where it is stated that one component is "connected," "combined," or "connected" to another component, it should be understood that while the components may be directly connected or connected to each other, another component may be "interposed" between each component, or each component may be "connected," "combined," or "connected" through another component.

[0029] In this specification, lithium, sulfur, magnesium, calcium, sodium, potassium, etc., may be in a form that exists in raw materials, extracts, or precipitates, and are collectively referred to as types of elements without being limited to a specific form, such as metal atoms, atoms, ions, or salts, and when distinction is necessary, they may be understood as being in a state that exists according to the laws of nature.

[0030] In one embodiment of the present invention:

[0031] A step of preparing a sample by mixing lithium carbonate of a predetermined content with lithium sulfide, and manufacturing an electrode sample containing lithium sulfide using said sample;

[0032] For the electrode sample, the step of measuring the rate of change of capacitance Q with respect to voltage V, dQ / dV, by a constant current charging and discharging method, obtaining a normalized rate of change by dividing the rate of change dQ / dV by a theoretical capacitance value, and obtaining a graph showing the normalized rate of change with respect to voltage V;

[0033] A step of measuring the area of ​​a peak appearing at a voltage within a predetermined numerical range in a graph showing the normalized rate of change with respect to voltage V, wherein the voltage within the predetermined numerical range is a numerical range in which the peak of the normalized rate of change appears due to the reaction of the mixed lithium carbonate;

[0034] A step of measuring the area of ​​the peak by the same constant current charging and discharging method for a plurality of electrode samples prepared by changing the content of the lithium carbonate, and collecting data on the area of ​​the peak measured for each of the plurality of lithium carbonate contents;

[0035] A step of analyzing the correlation between the content of lithium carbonate and the area of ​​the peak using the above data;

[0036] A step of manufacturing an electrode for the lithium sulfide subject to analysis using the same method as the step of manufacturing the electrode sample, and measuring the area of ​​the peak by a constant current charge / discharge method;

[0037] A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide is provided, comprising the step of determining the content of lithium carbonate corresponding to the peak area measured for the lithium sulfide of the analysis target by applying the above-described correlation, and determining this as the content of lithium carbonate mixed as an impurity in the lithium sulfide of the analysis target.

[0038] Lithium sulfide (Li2S), used as a battery material such as a solid electrolyte or electrode, must have a low content of mixed impurities. The quality of lithium sulfide can be analyzed by evaluating the content of lithium carbonate (Li2CO3) included as an impurity in the lithium sulfide, using a method that analyzes the content of lithium carbonate included as an impurity.

[0039] Since lithium sulfide used as a battery material requires high purity, the lithium carbonate content is generally low. However, the content of lithium carbonate mixed as an impurity can significantly affect battery efficiency during application. Therefore, it is necessary to verify the purity of lithium sulfide, which can be prepared in forms such as powder, by analyzing the content of impurities like lithium carbonate before it is used as a battery material.

[0040] As such, because the content of lithium carbonate mixed as an impurity is very low, it may be difficult to measure using methods widely used for analyzing the content of materials, such as XRD (X-ray diffraction), BET analysis, and ICP (inductively coupled plasma spectrometry). The method for analyzing the content of lithium carbonate included as an impurity in the lithium sulfide above enables the analysis of the content even when the content of lithium carbonate mixed as an impurity is low. For example, the method for analyzing the content of lithium carbonate included as an impurity in the lithium sulfide above can be applied to analyze the content of lithium carbonate in residual lithium that is mixed as an impurity during the manufacture of lithium sulfide.

[0041] The method for analyzing the content of lithium carbonate included as an impurity in the lithium sulfide above is to first perform a constant current charge-discharge test on samples prepared according to the lithium carbonate content to obtain a predetermined target data value, namely the rate of change of capacity Q with respect to voltage V, dQ / dV, determine the relationship between the rate of change dQ / dV and the lithium carbonate content, and then use this to determine the content of lithium carbonate included as an impurity in the lithium sulfide to be analyzed.

[0042] Below, each of the aforementioned steps will be explained in detail in sequence.

[0044] (s1) A step of preparing a sample by mixing lithium carbonate of a predetermined amount with lithium sulfide, and manufacturing an electrode sample containing lithium sulfide using the sample:

[0045] First, a first sample is prepared by mixing lithium sulfide to have a predetermined content, for example, 1 wt% lithium carbonate content, and an electrode is manufactured using this sample, which is referred to as the first electrode sample.

[0047] (s2) A step of measuring the rate of change of capacitance Q with respect to voltage V by a constant current charge / discharge method for the electrode sample, obtaining a normalized rate of change by dividing the rate of change dQ / dV by a theoretical capacitance value, and obtaining a graph showing the normalized rate of change with respect to voltage V:

[0048] The first electrode sample prepared above is charged by a constant current charging and discharging method to evaluate the capacitance Q according to voltage V. From this, the rate of change dQ / dV of capacitance Q with respect to voltage V can be measured, and subsequently, the rate of change dQ / dV is divided by the theoretical capacitance value to obtain a normalized rate of change, and a graph showing the normalized rate of change with respect to voltage V can be obtained.

[0049] Specifically, the first electrode sample prepared above can be charged by a constant current charging and discharging method to first obtain a graph showing voltage V relative to battery capacity Q (or a graph showing battery capacity Q relative to voltage V), and then the rate of change dQ / dV can be processed into a normalized rate of change by dividing it by the theoretical capacity value to obtain a graph showing the normalized rate of change relative to voltage V. The graph showing voltage V relative to battery capacity Q (or a graph showing battery capacity Q relative to voltage V) can be obtained by charging the first electrode sample under charging and discharging conditions in the range of 1.5 V to 4.5 V at a charging and discharging rate of 0.01 C-rate. By measuring at a voltage within the above range, excessive overvoltage can be prevented and the accuracy of the analysis can be increased, while preventing the decomposition of the electrolyte.

[0050] Although the measurement conditions of the above constant current charging and discharging method may be set appropriately according to the situation, they must be applied consistently throughout the entire method of analyzing the content of lithium carbonate included as an impurity in the lithium sulfide.

[0051] In one embodiment, the constant current charging and discharging method may be performed by charging the battery sample at a charging and discharging rate of 0.01 C-rate and under charging and discharging conditions in the range of 1.5 V to 4.5 V, and measuring the rate of change of capacity with respect to voltage, and the charging and discharging conditions are not limited thereto as long as they are consistently applied throughout the entire method of analyzing the content of lithium carbonate included as an impurity in the lithium sulfide.

[0053] ( s3) A step of measuring the area of ​​the peak appearing at a voltage within a predetermined numerical range in a graph showing the normalized rate of change with respect to voltage V:

[0054] In the graph showing the normalized rate of change against voltage V, the normalized rate of change has a positive value and a peak appears in a voltage range within a predetermined numerical range due to the reaction of the mixed lithium carbonate.

[0055] In one embodiment, the voltage of the predetermined numerical range may be 3.9 V to 4.1 V. That is, a peak appears in the voltage range, for example, 3.9 V to 4.1 V, in the graph, and the peak appearing in this range is understood to be measured at the result of the reaction of the lithium carbonate.

[0056] The area ratio of the peaks appearing in the above-mentioned predetermined numerical range of voltage, for example, from 3.9 V to 4.1 V, is obtained. Specifically, the normalized rate of change can be obtained by finding a function of a graph plotted against voltage V, and then obtaining the integral value of the function over the above-mentioned predetermined numerical range, for example, the voltage interval from 3.9 V to 4.1 V.

[0057] In this way, the area of ​​the peak is obtained by measuring the area of ​​the peak for a sample with a predetermined content, for example, 1 wt% lithium carbonate content.

[0059] (s4) A step of measuring the area of ​​the peak by the same constant current charge / discharge method for a plurality of electrode samples prepared by changing the content of the lithium carbonate, and collecting data on the area of ​​the peak measured for each of the plurality of lithium carbonate contents:

[0060] Previously, the area of ​​the peak was obtained by measuring a sample with a predetermined content, for example, 1 wt% lithium carbonate content, and in the same way, a sample with a different content is prepared and the area of ​​the peak is obtained by measuring a sample with that content.

[0061] For example, a second sample, a third sample, a fourth sample, or a fifth sample is prepared with a lithium carbonate content of 2 wt%, 3 wt%, 4 wt%, or 5 wt%, respectively, and then the second electrode sample, the third electrode sample, the fourth electrode sample, or the fifth electrode sample is prepared in the same manner as the method for preparing the first electrode sample, and for each, the area of ​​the peak is measured to obtain.

[0062] In one embodiment, data can be collected by measuring the area of ​​the peak for the plurality of electrode samples prepared using the plurality of samples prepared with different amounts of lithium carbonate within the range of 0 to 10 wt%.

[0063] As mentioned above, if the analysis is performed on cases where the content of lithium carbonate mixed as an impurity in lithium sulfide is a trace amount of about a few wt%, multiple samples can be prepared and measured within a low content range.

[0064] In one embodiment, data can be collected by measuring the area of ​​the peak for a plurality of electrode samples prepared using the sample prepared with different amounts of lithium carbonate within the range of 1 to 5 wt%.

[0066] (s5) A step of analyzing the correlation between the content of lithium carbonate and the area of ​​the peak using the above data:

[0067] In one embodiment, the correlation between the lithium carbonate content and the peak area can be analyzed by linear regression analysis using the data. When using linear regression analysis, data obtained by measuring the peak area for at least three predetermined lithium carbonate contents can be collected.

[0068] The above linear regression analysis obtains constant values ​​of a and b in Equation 1 below by setting the independent variable X as the content of lithium carbonate in the sample and the dependent variable Y as the area of ​​the peak.

[0069] <Equation 1>

[0070] Y = aX + b

[0072] Data can be obtained showing a tendency for the peak area Y to increase as the lithium carbonate content X of the sample increases. This implies that the higher the lithium carbonate content, the greater the reactivity when evaluated by the constant current charge / discharge method, resulting in a larger peak area.

[0073] In addition, the electrode sample prepared for the above correlation analysis may have a linear trend between the lithium carbonate content X and the peak area Y, regardless of size. For example, the electrode sample is 0.5 cm 2up to 1.55 cm 2 It can be manufactured in terms of area. For example, the electrode sample can be manufactured in a size of 14 pi or 8 pi.

[0074] According to one embodiment, in Equation 1 above, when the unit of X is wt%, a is 7.2 x 10 -5 Up to 4.1 x 10 -4 and, the above b is 9.99 x 10 -5 Up to 5.01 x 10 -4 It could be.

[0075] In one embodiment, the peak area Y may be 0.0051 to 0.00273.

[0077] (s6) A step of manufacturing an electrode for the lithium sulfide to be analyzed in the same manner as the step of manufacturing the electrode sample, and measuring the area of ​​the peak by a constant current charge / discharge method:

[0078] Since the correlation between the lithium carbonate content and the peak area has been determined by Equation 1, if the peak area for lithium sulfide of the subject of analysis is measured, the corresponding lithium carbonate content can be determined using Equation 1.

[0079] Therefore, for the lithium sulfide under analysis, the area of ​​the peak is measured using the same method as that used to measure the sample.

[0080] That is, for the lithium sulfide subject to analysis, an electrode is prepared using the same method as used to prepare the electrode sample from the sample. For the electrode prepared in this way, the area of ​​the peak is measured by the constant current charge-discharge method under the same conditions as with the electrode sample.

[0081] In one embodiment, the electrode sample and the electrode can be manufactured using a dry electrode manufacturing method.

[0082] Specifically, the electrode sample and the electrode may each include an active material layer comprising the lithium sulfide, a conductive material, and a binder.

[0083] The above electrode sample and the electrode can be manufactured according to a known method for manufacturing electrodes, specifically a known method for manufacturing electrodes for secondary batteries.

[0084] In one embodiment, the active material layer may contain 55 to 75 wt%, specifically 60 to 70 wt%, of lithium sulfide based on a total amount of 100 wt% of the lithium sulfide, the conductive material, and the binder.

[0085] The specific method for manufacturing the above electrode is not limited to that exemplified above, provided that the electrode sample and the electrode are manufactured under the same conditions.

[0087] (s7) A step of determining the lithium carbonate content corresponding to the peak area measured for the lithium sulfide of the analysis target by applying the above-analyzed correlation, and determining this as the content of lithium carbonate mixed as an impurity in the lithium sulfide of the analysis target:

[0088] When the area of ​​the peak measured by the constant current charge / discharge method for the electrode prepared from the lithium sulfide subject to analysis is taken as the Y value of Equation 1 obtained by linear regression analysis, the X value of the lithium carbonate content can be obtained. The lithium carbonate content obtained in this way represents the content of lithium carbonate mixed as an impurity in the lithium sulfide subject to analysis.

[0090] As described above, since the content of lithium carbonate mixed as an impurity in the lithium sulfide subject to analysis can be determined by the method for analyzing the content of lithium carbonate included as an impurity in the lithium sulfide subject to analysis, the quality of the lithium sulfide powder subject to analysis can be evaluated from this.

[0092] Examples and comparative examples of the present invention are described below. The following examples are merely embodiments of the present invention, and the present invention is not limited to the following examples.

[0094] (Example)

[0095] Example 1

[0096] (1) Preparation of electrode sample

[0097] Five samples of lithium sulfide (Li2S) mixed with lithium carbonate contents of 1.0 wt%, 2.0 wt%, 3.0 wt%, 4.0 wt%, and 5.0 wt%, respectively, were prepared. For each of the five samples, electrode samples were prepared as follows.

[0098] A positive electrode was prepared by dry method, in which an active material layer satisfying a total of 0.1 g of lithium sulfide (Li2S), a conductive material, and a binder was formed in a mass ratio of 65:30:5, respectively. Super C was used as the conductive material, and polytetrafluoroethylene (PTEE) was used as the binder. Additionally, a lithium metal negative electrode with a thickness of 200 μm was used. The size of the positive electrode was 14 pi, and the negative electrode was 16 pi.

[0099] An electrode sample was prepared as a Li-S anode half-cell using an electrolyte in which lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved at a concentration of 1.0 M in a solvent mixed with dimethoxyethane / 1,3-dioxolane (DME / DOL) in a 1:1 volume ratio and LiNO3 2.0 wt% was added.

[0101] (2) Derivation of charge / discharge graph of electrode sample

[0102] The above Li-S anode half-cell was charged only once at 0.01 C in a voltage range of 1.5 V to 4.5 V. Subsequently, the graph shape was derived through charging only without a separation process. Figure 1 is a charge-discharge graph measured by the constant voltage charge-discharge method for the above electrode sample.

[0103] Referring to FIG. 1, a charge-discharge graph is shown when a lithium-sulfur electrode is charged at 0.01 C in a voltage range of 1.5 V to 4.5 V. Specifically, it is a graph of voltage according to the specific capacity of the lithium-sulfur electrode.

[0104] In the general shape of the charge-discharge graph above, a trend is observed regarding quantification in terms of overvoltage trends or capacity development ranges, but it was confirmed that there is no one-to-one matching as the Li2CO3 content increases. However, it was confirmed that there is a specific trend around 3.9 to 4.1 V in the charge-discharge graph above, so the graph was further processed as follows.

[0106] (3) Primary processing of the charge / discharge graph of the electrode sample

[0107] Figure 2 is a graph plotting the normalized rate of change of capacity Q with respect to voltage V, obtained by processing the charge / discharge graph of the electrode sample of Figure 1 and dividing the rate of change of capacity Q with respect to voltage V, dQ / dV, by the theoretical capacity value.

[0108] Referring to FIG. 2, the charge / discharge graph of the electrode sample of FIG. 1 is a graph obtained as a differential function using a charge / discharge program (Origin program). dQ / dV represents the value obtained by differentiating the battery capacity (Q) with respect to the voltage (V). This is then divided by the theoretical capacity (Q0) to obtain a graph of the normalized rate of change ( FIG. 2). The area of ​​the normalized rate of change (peak area) according to the voltage V can be obtained by integrating the graph of FIG. 2 with respect to the voltage, and the area of ​​the normalized rate of change (peak area) may represent the capacity of Li2CO3 reacting in lithium sulfide.

[0109] Figure 3 is an enlarged graph of the portion of Figure 2 where the normalized rate of change peaks at voltages around 3.9 to 4.1 V.

[0110] Referring to Figure 3, it was confirmed that as the Li2CO3 content increased, the area of ​​the normalized rate of change (peak area) increased around the voltage of 3.9 to 4.1 V, where Li2CO3 is expected to react. A linear calibration curve (Equation 2 below) was confirmed for the correlation between the Li2CO3 content and the area of ​​the normalized rate of change (peak area) through the method below.

[0112] (4) Secondary processing of the charge / discharge graph of the primary processed electrode sample

[0113] Figure 4 is a graph showing the area of ​​the peak obtained as an integral value of the voltage of the normalized rate of change at 3.9 to 4.1 V for each lithium carbonate content in Figure 3, plotted against the lithium carbonate content, and confirming the linear calibration curve.

[0114] Specifically, in Figure 3, for each Li2CO3 content, the integral value (peak area) of the normalized rate of change function in the 3.9 to 4.1 V range was measured using the integral function of the Origin program. The results are listed in Table 1 below.

[0115] In Figure 4, a linear trend can be observed when the Li2CO3 content is 0 to 5 wt%.

[0116] Using a linear regression analysis program, the correlation between the Li2CO3 content X and the peak area Y in Fig. 4 was obtained using Equation 2 below. The confidence value R for the linearity of the linear regression analysis when the Li2CO3 content is 0 to 5 wt%. 2 A high confidence level of = 0.96499 was confirmed. R 2 The value represents the reliability of the calculated value within the range of Li2CO3 content from 0 to 5 wt%. Using the Origin program, the peak area according to Li2CO3 content is displayed as a scatter graph, and R is calculated using the Linear fitting function. 2 The value was calculated.

[0118] number ingredient Li2CO3 content [wt%] Area of ​​normalized rate of change (peak area) [Unit: mAh] R1 2 Satisfaction of Formula 2 1 Li2S 0 0.00051 ±0.00013 0.96499 ○ 2 Li2S + Li2CO3 1 0.00085 ±0.00095 ○ 3 Li2S + Li2CO3 2 0.00127 ±0.00040 ○ 4 Li2S + Li2CO3 3 0.00193 ±0.00060 ○ 5 Li2S + Li2CO3 4 0.00176 ±0.00038 ○ 6 Li2S + Li2CO3 5 0.00273 ±0.00031 ○

[0120] <Equation 2>

[0121] Y = (4.09459 × 10 -4 ) × X + (5.0064 × 10 -4 )

[0123] Equation 2 above represents high reliability R 2Since linearity was confirmed with the value, the content of Li2CO3 could be determined by applying the above Equation 2 to the lithium sulfide subject to analysis. For the lithium sulfide subject to analysis, the peak area was measured using the same method as the electrode sample, and this was applied as the Y value of Equation 2 to derive the corresponding X value. The X value derived in this way was analyzed as the content of Li2CO3 mixed as an impurity in the lithium sulfide subject to analysis.

[0124] Since the above Equation 2 is a correlation equation with high linearity reliability for samples with a Li2CO3 content of 5 wt% or less, it can be expected that the accurate Li2CO3 content can be analyzed for lithium sulfide mixed with Li2CO3 as an impurity with a content of 5 wt% or less.

[0126] Example 2

[0127] Samples were prepared in the same manner as in Example 1, and electrode samples were manufactured and data were collected by constant current charge / discharge method. However, four samples were prepared with lithium carbonate content of 1.0 wt%, 2.0 wt%, 3.0 wt%, and 4.0 wt%, and electrode samples with a positive electrode size of 8 pi were manufactured and data were measured.

[0128] Figure 5 is a graph showing the peak area obtained as the integral value of the normalized rate of change at 3.9 to 4.1 V for each lithium carbonate content, plotted against the lithium carbonate content in the same manner as in Example 1, and confirming the linear calibration curve. Likewise, in Example 2 with an electrode size of 8 pi, a high R 2 Value (R 2 The reliability of (= 0.99805) could be confirmed. The data measured in Example 2 is listed in Table 2.

[0129] Using a linear regression analysis program, the correlation between the Li2CO3 content X and the peak area Y in Fig. 5 was obtained using Equation 3 below. The confidence value R for the linearity of the linear regression analysis when the Li2CO3 content is 1 to 4 wt%. 2 A high confidence level of = 0.99805 was confirmed. R 2 The value represents the reliability of the calculated value within the range of Li2CO3 content to 4 wt%. Using the Origin program, the peak area according to Li2CO3 content is displayed as a scatter graph, and R is calculated using the Linear fitting function. 2 The value was calculated.

[0131] number ingredient Li2CO3 content [wt%] Area of ​​normalized rate of change (peak area) [Unit: mAh] R1 2 Meal 3 satisfaction 1 Li2S + Li2CO3 1 0.000173 ±0.00001 0.99805 ○ 2 Li2S + Li2CO3 2 0.000237 ±0.000048 ○ 3 Li2S + Li2CO3 3 0.000318 ±0.000017 ○ 4 Li2S + Li2CO3 4 0.000413 ±0.000112 ○

[0133] <Equation 3>

[0134] Y = (7.27594 × 10 -5 ) × X + (9.99688 × 10 -5 )

[0136] Although the present invention has been described above with reference to embodiments, the present invention is not limited by the embodiments disclosed in this specification, and it is obvious that various modifications can be made by a person skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention were not explicitly described while describing the embodiments of the present invention above, it is natural to acknowledge that the effects predictable by said configuration should also be recognized.

Claims

Claim 1 A step of preparing a sample by mixing lithium carbonate of a predetermined content with lithium sulfide, and manufacturing an electrode sample containing lithium sulfide using the sample; a step of measuring the rate of change of capacity Q with respect to voltage V by a constant current charge / discharge method for the electrode sample, obtaining a normalized rate of change by dividing the rate of change dQ / dV by a theoretical capacity value, and obtaining a graph showing the normalized rate of change with respect to voltage V; a step of measuring the area of ​​a peak appearing at a predetermined numerical range of voltage in the graph showing the normalized rate of change with respect to voltage V, wherein the predetermined numerical range of voltage is a numerical range in which the peak of the normalized rate of change appears due to the reaction of the mixed lithium carbonate; A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide, comprising: a step of measuring the area of ​​the peak by a constant current charge-discharge method in the same manner for a plurality of electrode samples prepared by changing the content of the lithium carbonate, and collecting data on the area of ​​the peak measured for each of the plurality of lithium carbonate contents; a step of analyzing the correlation between the content of the lithium carbonate and the area of ​​the peak using the data; a step of preparing an electrode for the lithium sulfide to be analyzed in the same manner as the step of preparing the electrode sample and measuring the area of ​​the peak by a constant current charge-discharge method; and a step of determining the content of lithium carbonate corresponding to the area of ​​the peak measured for the lithium sulfide to be analyzed by applying the analyzed correlation, and determining this as the content of lithium carbonate mixed as an impurity in the lithium sulfide to be analyzed. Claim 2 A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide, wherein the correlation is determined by linear regression analysis using the data in claim 1. Claim 3 In paragraph 2, the linear regression analysis is a method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide, wherein the independent variable X is the content of lithium carbonate in the sample and the dependent variable Y is the area of ​​the peak, and constant values ​​of a and b in the following Equation 1 are obtained. <Equation 1> Y = aX + b Claim 4 In paragraph 3, the unit of X is wt%, and the above a is 7.2 x 10 -5 Up to 4.1 x 10 -4 and, the above b is 9.99 x 10 -5 Up to 5.01 x 10 -4 A method for analyzing the content of lithium carbonate included as an impurity in lithium phosphate. Claim 5 A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide, wherein Y is 0.0051 to 0.00273 in paragraph 3. Claim 6 A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide, wherein, for measurement by the constant current charging and discharging method, a battery including the electrode sample or the electrode is manufactured, and the battery is charged at a charging and discharging rate of 0.01 C-rate and under charging and discharging conditions in the range of 1.5 V to 4.5 V to measure the rate of change of capacity with respect to voltage. Claim 7 A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide, wherein the voltage in the predetermined numerical range is 3.9 V to 4.1 V in claim 1. Claim 8 A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide, wherein, in claim 1, the area of ​​the peak is measured for a plurality of electrode samples prepared using the sample prepared with different plurality of lithium carbonate contents within the range of 0 to 10 wt%. Claim 9 A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide, wherein the electrode sample and the electrode are manufactured by a dry electrode manufacturing method. Claim 10 A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide, wherein, in claim 1, the electrode sample and the electrode each comprise an active material layer comprising the lithium sulfide, a conductive material, and a binder, and the active material layer comprises 55 to 75 wt% of the lithium sulfide based on a total amount of 100 wt% of the lithium sulfide, the conductive material, and the binder. Claim 11 A method for analyzing the content of lithium carbonate included as an impurity in lithium sulfide, wherein the quality of the lithium sulfide to be analyzed is evaluated based on the determined content of lithium carbonate in claim 1.

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