JP2010153289A - Method of measuring amount of hf in electrolytic solution and method of manufacturing lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measuring the amount of an HF (Hydrogen Fluoride) in an electrolytic solution, by which method the amount of the HF in the electrolytic solution can be made constant; and to provide a method of manufacturing a lithium ion secondary battery using the method. <P>SOLUTION: According to the method of measuring the amount of the HF in the nonaqueous electrolytic solution 140 of the lithium ion secondary battery 100, the nonaqueous electrolytic solution 140 is a nonaqueous electrolytic solution containing an ethylene carbonate. The method includes: a separating step (steps S45 and S47) of separating the components of the nonaqueous electrolytic solution 140 into the ethylene carbonate and other electrolytic components; and a neutralizing/titrating step (step S46) of neutralizing/titrating other electrolytic components under an inert gas atmosphere. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for quantifying HF in an electrolyte and a method for producing a lithium ion secondary battery using the same.

Secondary batteries such as lithium ion secondary batteries are attracting attention as power sources for portable devices and as power sources for electric vehicles and hybrid vehicles. As a lithium ion secondary battery, a positive electrode active material made of LiMO ₂ (M is Co, Ni, Mn, V, Al, Mg, etc.), a negative electrode active material made of a carbon material, a Li salt, and a non-aqueous solvent are used. What has the nonaqueous electrolyte solution which becomes becomes mainstream. This lithium ion secondary battery has the advantage of exhibiting a high discharge voltage and high output.

However, in the process of manufacturing the lithium ion secondary battery, moisture may be mixed in the battery. Then, HF (hydrofluoric acid) is generated by hydrolysis of a lithium salt (for example, LiPF ₆ ) contained in the electrolytic solution. When the amount of HF in the electrolytic solution increases, there is a problem that the battery capacity and charge / discharge characteristics are lowered, and further, corrosion inside the battery proceeds. For this reason, it is necessary to grasp how much HF is generated in the electrolyte of the manufactured lithium ion secondary battery. This is because the above problem may occur when the amount of HF exceeds the reference value.

  For example, Patent Document 1 discloses the following HF quantification method. Take 20 g of the electrolyte, add a few drops of the indicator 0.1% bromothymol blue / ethanol solution, and use a 0.01N sodium methoxide / ethanol solution to determine the amount by neutralization titration. The amount of HF in the electrolytic solution is quantified by converting the obtained acid equivalent to the amount of hydrofluoric acid (HF).

WO99 / 34471

However, with the method described in Patent Document 1, there is a possibility that the amount of HF in the electrolytic solution cannot be accurately determined. Specifically, for example, there is a possibility that the amount of HF in the electrolyte cannot be appropriately quantified due to the influence of CO _{2 in} the atmosphere. This is because CO ₂ in the atmosphere dissolves in the titration solvent and acts as an acid. In addition, when ethylene carbonate (EC) is included as a solvent of the electrolytic solution, CO ₂ is generated by hydrolysis of ethylene carbonate, and the amount of HF in the electrolytic solution cannot be appropriately determined due to the influence of this CO _2. was there.

  The present invention has been made in view of the present situation, and it is possible to accurately determine HF in an electrolytic solution and to determine a HF determination method in an electrolytic solution, and a lithium ion secondary battery using the same. An object is to provide a manufacturing method.

  The solution is a method for quantifying HF in an electrolyte solution of a lithium ion secondary battery, wherein the electrolyte solution is an electrolyte solution containing ethylene carbonate, and the electrolyte solution is mixed with the ethylene carbonate and other electrolytes. A method for quantifying HF in an electrolytic solution, comprising: a separation step of separating into a liquid component; and a neutralization titration step of performing neutralization titration in an inert gas atmosphere for the other electrolytic solution component.

In the HF determination method of the present invention, the electrolytic solution is separated into ethylene carbonate (EC) and other electrolytic solution components, and neutralization titration is performed on the other electrolytic solution components not containing EC. Thereby, in the neutralization titration step, HF (hydrofluoric acid) in other electrolytic solution components can be accurately quantified without being affected by CO ₂ generated by hydrolysis of ethylene carbonate. In addition, the amount of HF in other electrolyte components is equal to the amount of HF in the electrolyte. Therefore, according to the HF determination method of the present invention, HF in the electrolyte can be accurately determined.

Furthermore, in the HF determination method of the present invention, neutralization titration is performed in an inert gas atmosphere in the neutralization titration step. Specifically, neutralization titration is performed with an inert gas flowing into the neutralization titration apparatus and the atmosphere contained in the neutralization titration apparatus being replaced with an inert gas. Thereby, the amount of HF in the electrolytic solution can be accurately determined without being affected by CO ₂ contained in the atmosphere.

  The "electrolyte of the lithium ion secondary battery" refers to the electrolyte existing in the lithium ion secondary battery (electrolyte after injection), as well as the electrolysis before being injected into the lithium ion secondary battery. Including liquid. That is, the HF determination method of the present invention can be applied to, for example, an electrolyte present in a lithium ion secondary battery (for example, a completed lithium ion secondary battery before shipment). In this case, the electrolytic solution is taken out from the lithium ion secondary battery, and the HF determination method of the present invention is applied to the electrolytic solution. Moreover, you may apply the HF determination method of this invention with respect to the electrolyte solution before inject | pouring in a lithium ion secondary battery.

  Further, the neutralization titration may be performed on the other amount of the electrolyte component after the separation step (that is, after the electrolyte solution is separated into ethylene carbonate and another electrolyte component). Alternatively, neutralization titration may be performed while performing the separation step. Specifically, in the separation step, when the electrolytic solution is separated into EC and other electrolytic solution components (boiling point lower than EC) by distillation, the other electrolytic solution components are gradually added during the distillation period (during the separation step). Evaporates to separate from EC, and finally, the total amount of other electrolyte components separate from EC. Therefore, while performing distillation (separation step), the operation of performing neutralization titration on other electrolyte components that have been separated from EC so far in the middle of distillation is repeated several times, and finally the total amount of other electrolysis Neutralization titration may be performed on the liquid component.

  Moreover, in the neutralization titration process of this invention, it is preferable to use the indicator which changes color in the range of pH 7-10. Specific examples include thymolphthalein, cresol red, phenolphthalein, thymol blue, and bromothymol blue.

  Moreover, as a titration liquid used at the neutralization titration process of this invention, the solution which melt | dissolved tetrabutylammonium hydroxide (TBAOH) in the solvent can be mentioned. In addition to TBAOH, tetraethylammonium hydroxide, tetramethylammonium hydroxide, potassium hydroxide, sodium hydroxide and the like can also be used.

  Furthermore, it is preferable that the method for quantifying HF in the electrolytic solution described above, wherein the electrolytic solution includes a lithium salt having a fluorine element.

When the electrolytic solution contains a lithium salt having a fluorine element, HF is easily generated by hydrolysis of the lithium salt. On the other hand, the HF determination method of the present invention is preferable because the generated HF can be accurately determined. As the lithium salt having a fluorine element, for example, a LiPF _6.

  Furthermore, in any one of the above HF determination methods in the electrolytic solution, in the neutralization titration step, the other electrolytic solution components are dissolved in a basic non-aqueous solvent to perform neutralization titration. It is preferable to use an HF quantitative method.

  In a lithium ion secondary battery, much of the electrolyte injected into the battery may be absorbed by the electrode body (particularly the separator). For this reason, when HF in the electrolyte solution in the lithium ion secondary battery is quantified, only a small amount (for example, about 1.0 mL) of the electrolyte solution may be extracted from the battery. In such a case, with the conventional HF determination method (see Patent Document 1), the sensitivity is too low to quantitate a trace amount (for example, 100 μg or less) of HF contained in a small amount of electrolyte. It was.

  On the other hand, in the HF determination method of the present invention, neutralization titration is performed by dissolving other electrolyte components in a basic nonaqueous solvent in the neutralization titration step. By dissolving other electrolyte components in a basic non-aqueous solvent, the dissociation constant of HF contained in the other electrolyte components can be increased. Thereby, the sensitivity of neutralization titration can be improved. That is, even a trace amount (for example, 100 μg or less) of HF can be appropriately quantified. Therefore, according to the HF determination method of the present invention, the amount of HF in the electrolyte can be accurately determined even if the amount of HF in the electrolyte is very small (for example, 100 μg or less).

  Examples of the basic non-aqueous solvent include dimethylformamide (DMF), pyridine, ethylene diamine, butyl amine, dioxane, ethanol and the like.

  Moreover, it is preferable to use a neutral or basic nonaqueous solvent for the solvent of the titrant. Thereby, since the dissociation constant of HF is not lowered by the solvent of the dropped titrant, highly sensitive neutralization titration can be performed. Examples of the neutral non-aqueous solvent include benzene and ethanol. The basic non-aqueous solvent is as described above.

  Furthermore, in the above-described method for quantifying HF in an electrolytic solution, in the neutralization titration step, dimethylformamide is used as the basic nonaqueous solvent, and a nonaqueous solvent in which benzene and methanol are mixed as a titrant. A titration solution in which tetrabutylammonium hydroxide is dissolved may be used as a method for quantifying HF in an electrolyte solution for neutralization titration.

  In the present invention, neutralization titration is performed using dimethylformamide as a basic nonaqueous solvent for dissolving other electrolyte components. Thereby, since the dissociation constant of HF becomes very high, the sensitivity of neutralization titration can be increased.

  Furthermore, in the present invention, neutralization titration is performed using a titration solution in which tetrabutylammonium hydroxide is dissolved in a nonaqueous solvent in which benzene and methanol are mixed as the titration solution. That is, a titration solution in which tetrabutylammonium hydroxide is dissolved in a nonaqueous solvent in which benzene and methanol are mixed is added dropwise to a titration solution in which other electrolyte components are dissolved in dimethylformamide, and neutralization titration is performed. Do. By using tetrabutylammonium hydroxide, HF in the electrolytic solution can be appropriately quantified. In addition, since a neutral non-aqueous solvent (benzene and methanol) is used, the dissociation constant of HF is not lowered by the solvent of the dropped titrant. For this reason, highly sensitive neutralization titration can be performed.

  Further, the method for determining HF in any one of the above electrolytic solutions, wherein the electrolytic solution includes the ethylene carbonate and a low boiling point solvent having a boiling point lower than that of the ethylene carbonate, and the separation step is performed by distillation. The electrolytic solution may be a method for quantifying HF in an electrolytic solution that separates the ethylene carbonate and the other electrolytic solution component containing the low-boiling solvent.

The HF quantification method of the present invention quantifies HF in an electrolytic solution containing ethylene carbonate and a low-boiling solvent having a boiling point lower than that of ethylene carbonate.
In the present invention, in the separation step, the electrolytic solution is separated by distillation into other electrolytic solution components including ethylene carbonate and a low boiling point solvent. Specifically, by raising the electrolytic solution to a temperature lower than the boiling point of ethylene carbonate (about 240 ° C.) and higher than the boiling point of the low-boiling solvent, other low-boiling solvents and other HF containing HF are obtained. The electrolyte component can be taken out. Thereby, EC can be appropriately separated from the electrolytic solution.

  Another solution is a method of manufacturing a lithium ion secondary battery having an electrolyte solution containing ethylene carbonate, wherein the lithium ion secondary battery is assembled, and the electrolyte solution is injected into the lithium ion secondary battery. And an inspection step of inspecting the lithium ion secondary battery after completing the lithium ion secondary battery, taking out the electrolytic solution from the lithium ion secondary battery, It is a manufacturing method of a lithium ion secondary battery provided with the test | inspection process which quantifies HF using the HF quantification method in electrolyte solution.

  The production method of the present invention is a method for producing a lithium ion secondary battery having an electrolytic solution containing ethylene carbonate. In the manufacturing method of the present invention, in the inspection step, the electrolytic solution is taken out from the lithium ion secondary battery, and HF is quantified with respect to this electrolytic solution by using any one of the HF quantification methods in the electrolytic solution. Thereby, HF generated in the manufacturing process can be accurately quantified. Therefore, for example, when it is determined that the HF amount is higher than the reference value, it can be determined with high accuracy.

  The inspection process may be performed on all completed batteries, but in the case of mass production, one of the completed batteries (for example, 1000) is extracted and inspected (quantification of HF). ) May be performed.

  In a lithium ion secondary battery, much of the electrolyte injected into the battery may be absorbed by the electrode body (particularly the separator). For this reason, only a small amount (for example, about 1.0 mL) of electrolyte solution can be taken out from the lithium ion secondary battery. In such a case, as described above, in the neutralization titration step, a method for quantifying HF in an electrolyte solution in which other electrolyte components are dissolved in a basic nonaqueous solvent for neutralization titration (see claim 2). It is preferable to provide a method for manufacturing a lithium ion secondary battery comprising an inspection step for quantifying the amount of HF using As a result, the sensitivity of neutralization titration can be increased as described above, and therefore, in a test process, a small amount (for example, 100 μg or less) of HF contained in a small amount of electrolyte should be appropriately quantified. Can do.

  Furthermore, in the above method for manufacturing a lithium ion secondary battery, the electrolytic solution is preferably a method for manufacturing a lithium ion secondary battery containing a lithium salt having a fluorine element.

When the electrolytic solution contains a lithium salt containing a fluorine element, HF may be generated by hydrolysis of the lithium salt after injecting the electrolytic solution containing ethylene carbonate into the lithium ion secondary battery. On the other hand, the production method of the present invention is preferable because the generated HF can be accurately quantified in the inspection process. As the lithium salt having a fluorine element, for example, a LiPF _6.

  Furthermore, in any one of the above-described methods for manufacturing a lithium ion secondary battery, in the inspection step, a method for manufacturing a lithium ion secondary battery that determines whether or not the quantified amount of HF is below a reference value is determined. good.

  In the manufacturing method of the present invention, in the inspection step, it is determined whether or not the amount of HF determined by neutralization titration is below a reference value. As described above, since the generated HF can be accurately quantified, it is possible to accurately determine whether or not the HF is below the reference value.

  In addition, when the amount of HF is larger than the reference value, for example, it can be considered that a large amount of HF is generated by hydrolysis of the lithium salt. That is, it can be considered that a large amount of moisture exceeding the standard was mixed in the battery during the manufacturing process. Therefore, it is possible to check the production line, find out a process in which a large amount of moisture is mixed, and take measures to improve the process. Thereby, after that, the lithium ion secondary battery which suppressed the amount of HF to the reference value or less can be manufactured.

Example 1
First, the lithium ion secondary battery 100 manufactured by the manufacturing method of Example 1 will be described. As shown in FIGS. 1 and 2, the lithium ion secondary battery 100 is a lithium ion secondary battery including a rectangular parallelepiped battery case 110, a positive electrode external terminal 120, and a negative electrode external terminal 130.

  The battery case 110 is made of metal and has a battery case main body 117 having a rectangular parallelepiped housing part 117b and a battery case lid 118 for closing the housing part 117b of the battery case main body 117, as shown in FIG. . The electrode body 150, the non-aqueous electrolyte 140, and the like are accommodated in the accommodating portion 117b of the battery case main body 117.

  As shown in FIGS. 3 and 4, the electrode body 150 is a flat wound body that is formed by laminating and laminating a sheet-like positive electrode 155, a negative electrode 156, and a separator 157. . Among these, the positive electrode 155 includes a positive electrode current collector 151 (aluminum foil) and a positive electrode mixture layer 152 (including a positive electrode active material 153) formed on the surface of the positive electrode current collector 151. The negative electrode 156 has a negative electrode current collector 158 (copper foil) and a negative electrode mixture layer 159 (including a negative electrode active material 154) formed on the surface of the negative electrode current collector 158.

  This electrode body 150 is located at one end (right end in FIG. 2) in the axial direction (left and right in FIG. 2), and only the positive current collecting member 151 of the positive electrode 155 overlaps in a spiral shape. 150b and a negative electrode current collecting terminal portion 150c which is located at the other end (left end in FIG. 2) and in which only the negative electrode current collecting member 158 of the negative electrode 156 overlaps in a spiral shape. The positive electrode current collecting terminal portion 150 b is electrically connected to the positive electrode external terminal 120 through the positive electrode connecting member 122. The negative electrode current collecting terminal portion 150 c is electrically connected to the negative electrode external terminal 130 through the negative electrode connecting member 132.

In Example 1, lithium nickelate is used as the positive electrode active material 153. Further, a carbon-based material (specifically, natural graphite) is used as the negative electrode active material 154. Further, a polyethylene sheet is used as the separator 157. Further, as a non-aqueous electrolyte, a solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a ratio of 1: 1: 1 (volume ratio) at a rate of 1 mol / L. A solution in which LiPF ₆ is dissolved is used.

Next, a method for manufacturing the lithium ion secondary battery 100 will be described with reference to FIGS.
First, as shown in FIG. 5, the secondary battery is assembled in step S1. Specifically, first, lithium nickelate (positive electrode active material 153), acetylene black, polytetrafluoroethylene, and carboxymethylcellulose are mixed at a ratio of 88: 10: 1: 1 (weight ratio) and dispersed therein. A solvent was mixed to prepare a positive electrode slurry. Next, this positive electrode slurry was applied to the surface of an aluminum foil 151 having a thickness of 15 μm, dried, and then pressed. Thereby, the positive electrode 155 in which the positive electrode mixture 152 was coated on the surface of the aluminum foil 151 was obtained (see FIG. 4).

  Natural graphite (negative electrode active material 154), styrene-butadiene rubber, and carboxymethylcellulose were mixed in water at a ratio of 98: 1: 1 (weight ratio) to prepare a negative electrode slurry. Next, this negative electrode slurry was applied to the surface of a copper foil 158 having a thickness of 10 μm, dried, and then pressed. Thereby, the negative electrode 156 by which the negative electrode compound material 159 was coated on the surface of the copper foil 158 was obtained (refer FIG. 4).

  Next, a positive electrode 155, a negative electrode 156, and a separator 157 were stacked and wound to form an electrode body 150 having an oval cross section (see FIG. 3). However, when laminating the positive electrode 155, the negative electrode 156, and the separator 157, an uncoated portion of the positive electrode 155 that is not coated with the positive electrode mixture 152 protrudes from one end portion of the electrode body 150. The positive electrode 155 is disposed. Furthermore, the negative electrode 156 is disposed so that an uncoated portion of the negative electrode 156 that is not coated with the negative electrode mixture 159 protrudes from the side opposite to the uncoated portion of the positive electrode 155. Thereby, the electrode body 150 having the positive electrode current collecting terminal portion 150b in which only the positive electrode current collecting member 151 of the positive electrode 155 overlaps in a spiral shape and the negative electrode current collection terminal portion 150c in which only the negative electrode current collecting member 158 of the negative electrode 156 overlaps in a spiral shape. (See FIG. 2) is formed. In Example 1, a polyethylene sheet having a thickness of 25 μm is used as the separator 157.

  Next, the positive electrode current collecting terminal portion 150 b of the electrode body 150 and the positive electrode external terminal 120 are connected through the positive electrode current collecting member 122. Further, the negative electrode current collecting terminal portion 150 c of the electrode body 150 and the negative electrode external terminal 130 are connected through the negative electrode current collecting member 132. Then, this was accommodated in the battery case main body 117, the battery case main body 117 and the battery case cover 118 were welded, and the battery case 110 was sealed.

Next, proceeding to step S <b> 2, the nonaqueous electrolytic solution 140 was injected into the battery case 110 through a liquid injection port (not shown) provided in the battery case lid 118. Thereafter, a liquid injection port (not shown) was sealed. In Example 1, as a non-aqueous electrolyte solution 140, LiPF ₆ was added at a concentration of 1 mol / L in a solvent in which ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate were mixed at a ratio of 1: 1: 1 (volume ratio). Is used.

  Then, it progressed to step S3 and the lithium ion secondary battery 100 was initially charged. Specifically, using a known power supply device, the lithium ion secondary battery 100 was charged to SOC 50% at a current value of 0.1 C. Furthermore, it charged to SOC100% with the electric current value of 0.5C. Thereafter, the lithium ion secondary battery 100 is completed through a predetermined process.

Next, the process proceeds to step S4, and the completed secondary battery 100 is inspected. Specifically, HF in the electrolytic solution 140 in the secondary battery 100 was quantified, and it was inspected whether the HF amount was below a reference value.
In Example 1, all the completed lithium ion secondary batteries 100 are not inspected. Specifically, when the number of completed lithium ion secondary batteries 100 reaches a predetermined number (for example, 1000), one lithium ion secondary battery 100 is removed from the predetermined number of lithium ion secondary batteries 100. An inspection process is performed on the extracted lithium ion secondary battery 100.

  Here, the inspection process of the first embodiment will be specifically described. First, it progresses to step S41 and the non-aqueous electrolyte solution 140 is taken out from the lithium ion secondary battery 100 inside. Specifically, the battery case 110 of the lithium ion secondary battery 100 was cut, and the nonaqueous electrolyte solution 140 in the battery case 110 was collected. In the lithium ion secondary battery 100 of Example 1, most of the injected electrolyte solution 140 is absorbed by the electrode body 150 (particularly, the separator 157), and therefore a small amount of the nonaqueous electrolyte solution 140 that can be collected ( About 1.0 mL).

Next, it progresses to step S42, and as shown in FIG. 7, the inert gas (specifically nitrogen gas) flows in into the neutralization titration apparatus 1, and the atmosphere contained in the neutralization titration apparatus 1 Was replaced with an inert gas. Thereby, since the inside of neutralization titration apparatus 1 can be made into an inert gas atmosphere, in the subsequent neutralization titration process (Step S46), quantification of HF by neutralization titration is performed under an inert gas atmosphere. Can do. In Example 1, an inert gas (specifically, nitrogen gas) is allowed to flow into the neutralization titration apparatus 1 until the neutralization titration is completed, and the neutralization titration apparatus 1 is always inert. Gas atmosphere. Further, an inert gas (specifically, nitrogen gas) is also introduced into the burette 2 to prevent the concentration of the titrant from changing due to the influence of atmospheric CO ₂ .

  Here, the neutralization titration apparatus 1 of the first embodiment will be described. As shown in FIG. 7, the neutralization titration apparatus 1 includes a burette 2 that contains a titrant, a test tube 3 that contains a titrant, and a container 4 that contains a non-aqueous electrolyte 140 collected from the lithium ion secondary battery 100. And a heater 5 for heating the container 4 (non-aqueous electrolyte 140). The test tube 3 and the container 4 are connected by a connecting tube 8. A thermocouple 6 is disposed in the container 4, and the temperature (gas temperature) in the container 4 can be detected by a temperature monitor 7 connected to the thermocouple 6. The surfaces of the container 4 and the connecting pipe 8 are processed with a fluororesin.

  Next, it progresses to step S43 and the reagent used by neutralization titration is prepared. Specifically, about 10 mL of dimethylformamide (DMF) is put into the test tube 3, and one drop of 0.1% thymolphthalein (indicator) is added. Furthermore, a titrant solution in which tetrabutylammonium hydroxide (TBAOH) is dissolved in a non-aqueous solvent in which benzene and methanol are mixed is placed in the burette 2. In addition, this titrant (TBAOH solution) was adjusted just before putting in the burette 2, and when TBAOH density | concentration was measured, it was 0.00238 mol / L. A method for measuring the TBAOH concentration of the titrant (TBAOH solution) will be described in detail later.

  Subsequently, it progresses to step S44 and a blank measurement is performed. Specifically, a titrant (TBAOH solution) is dropped from the burette 2 into the test tube 3, and the color of the liquid in the test tube 3 (liquid obtained by adding thymolphthalein to DMF) changes from transparent to blue. Then, the dropping of the titrant (TBAOH solution) is finished. Thereby, the influence of DMF can be eliminated in the subsequent neutralization titration.

  Next, it progresses to step S45 and distillation (separation process) is started. Specifically, with the heating temperature of the heater 5 set to 190 ° C., 1.0 mL of the nonaqueous electrolyte solution 140 collected from the lithium ion secondary battery 100 is placed in the container 4. Thereby, the nonaqueous electrolyte solution 140 in the container 4 can be heated and the temperature of the nonaqueous electrolyte solution 140 can be gradually raised. At this time, the components contained in the non-aqueous electrolyte 140 gradually evaporate (vaporize) in order from the one having the lowest boiling point, and the gas flows into the test tube 3 through the connecting tube 8. Dissolve in DMF in 3.

In Example 1, ethylene carbonate (boiling point 240 ° C.), ethyl methyl carbonate (boiling point 107 ° C.) and dimethyl carbonate (boiling point 90 ° C.) are 1: 1: 1 (volume ratio) as the non-aqueous electrolyte solution 140. A solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent is used. Therefore, when the temperature of the non-aqueous electrolyte 140 in the container 4 rises, dimethyl carbonate and ethyl methyl carbonate gradually evaporate and flow into the test tube 3 through the connecting tube 8 and dissolve in the DMF in the test tube 3. To do. At this time, HF present in the nonaqueous electrolytic solution 140 also flows into the test tube 3 through the connecting tube 8 and is dissolved in the DMF in the test tube 3. In Example 1, dimethyl carbonate and ethyl methyl carbonate correspond to the low boiling point solvent.

  In addition, since the boiling point of ethylene carbonate is 240 ° C., even when the non-aqueous electrolyte 140 is heated by the heater 5 whose heating temperature is set to 190 ° C., the ethylene carbonate does not evaporate. As a result, ethylene carbonate remains in the container 4 out of the non-aqueous electrolyte 140, while other electrolyte components including dimethyl carbonate, ethylmethyl carbonate, and HF are taken out from the container 4 and stored in the test tube 3. In DMF. Note that DMF (containing 0.1% thymolphthalein) in which other electrolyte components are dissolved corresponds to the titrant.

  In this manner, in Example 1, the nonaqueous electrolytic solution 140 can be separated into ethylene carbonate and other electrolytic solution components including dimethyl carbonate, ethyl methyl carbonate, and HF by distillation.

  By the way, in the lithium ion secondary battery 100 of the first embodiment, most of the injected nonaqueous electrolytic solution 140 is absorbed by the electrode body 150 (particularly, the separator 157). Was 1.0 mL. In order to quantify a small amount of HF contained in such a small amount of non-aqueous electrolyte 140, highly sensitive neutralization titration is required.

  On the other hand, in Example 1, a basic nonaqueous solvent (specifically, DMF) is used as the solvent of the titrant. That is, other electrolyte components are dissolved in a basic nonaqueous solvent (specifically, DMF). When a basic non-aqueous solvent is used as the solvent for the titration solution, the dissociation constant of HF increases, so that the sensitivity of neutralization titration can be increased. That is, even a trace amount (for example, 100 μg or less) of HF can be appropriately quantified. Therefore, according to the HF determination method (inspection step) of the first embodiment, the amount of HF in the electrolyte can be accurately determined even if the amount of HF in the electrolyte is very small (for example, 100 μg or less). Can do.

  Moreover, in Example 1, a neutral nonaqueous solvent (benzene and methanol) is used as a solvent for the titrant. Thereby, since the dissociation constant of HF is not lowered by the solvent of the dropped titrant, highly sensitive neutralization titration can be performed.

  Next, it progresses to step S46 and neutralization titration is performed. Specifically, after starting distillation (heating of the non-aqueous electrolyte 140 in the container 4 by the heater 5) and confirming that the color of the titrant in the test tube 3 has changed from blue to transparent, The titrant (tetrabutylammonium hydroxide-benzene / methanol) in the burette 1 is dropped into the test tube 3. In addition, because the color of the titrant containing thymolphthalein changed from blue to transparent, a part of HF contained in the nonaqueous electrolyte solution 140 in the container 4 was dissolved in DMF in the test tube 3. You can confirm that When the color of the liquid to be titrated in the test tube 3 is changed from transparent to blue (neutralization point) by dropping the titrant, the titration liquid is stopped to be dropped.

  Thereafter, when a part of HF contained in the non-aqueous electrolyte solution 140 in the container 4 is newly dissolved in DMF in the test tube 3 by distillation, the color of the titrant in the test tube 3 changes from blue. It changes to transparency. When this discoloration is confirmed, the dropping of the titrant in the burette 1 is started again, and the dropping is stopped when the color of the titrant in the test tube 3 changes from transparent to blue (neutralization point).

Thereafter, as described above, the titration liquid in the burette 1 is repeatedly dropped (neutralization titration), the temperature in the container 4 does not increase (becomes constant), and the liquid to be titrated in the test tube 3 is maintained. When it is confirmed that is no longer discolored (discoloration from blue to transparent), the neutralization titration is finished. The temperature in the container 4 did not increase, and the titrated liquid in the test tube 3 did not change color (discoloration from blue to transparent), so that it was contained in the non-aqueous electrolyte 140 in the container 4. This is because it can be determined that all of the HF was taken out from the container 4 and dissolved in the DMF in the test tube 3.
Then, it progresses to step S47 and distillation (heating of the nonaqueous electrolyte solution 140 in the container 4 by the heater 5) is complete | finished.

Thus, in the present Example 1, neutralization titration is performed, performing distillation (separation process). That is, an operation of performing neutralization titration on other electrolyte components (components containing dimethyl carbonate, ethyl methyl carbonate, and HF) that have been separated from EC so far during the distillation period while performing distillation (separation step). This is repeated several times, and finally, neutralization titration is performed on the other amount of the other electrolyte components. Thereby, in the present Example 1, HF in the nonaqueous electrolytic solution 140 can be appropriately quantified.
In Example 1, the temperature in the container 4 is monitored by the temperature monitor 7 from the time when the distillation is started until the neutralization titration is completed.

Subsequently, it progressed to step S48 and the HF amount (HF density | concentration) in the nonaqueous electrolyte solution 140 was computed. Specifically, the HF concentration (ppm) in the non-aqueous electrolyte 140 is calculated from the following formula (1) based on the titration amount of the titrant dropped from the start of neutralization titration to the end point. did.
HF concentration (ppm) = {TBAOH concentration (mol / L) × Titration volume of titrant (L) × HF molecular weight (g / mol) × 10 ⁶ } / {Nonaqueous electrolyte amount (mL) × Nonaqueous electrolyte solution Specific gravity (g / mL)} ... (1)

  In Example 1, the temperature in the container 4 does not increase (that is, the temperature of the non-aqueous electrolyte 140 in the container 4 increases to 190 ° C.), and the titrated liquid in the test tube 3 The end point of neutralization titration is defined as the point at which the color change from blue to clear is ceased. At the end point of the neutralization titration, all of the other electrolyte components except the ethylene carbonate in the non-aqueous electrolyte solution 140 are dissolved in the DMF in the test tube 3. That is, all of the HF in the nonaqueous electrolytic solution 140 is dissolved in the DMF in the test tube 3.

  Then, it progresses to step S49 and it is determined whether the calculated HF density | concentration is below a reference value (for example, 150 ppm). When the HF concentration is equal to or lower than the reference value (Yes), the HF concentration is also applied to a predetermined number (for example, 1000) of lithium ion secondary batteries 100 manufactured at the same time as the lithium ion secondary battery 100 that has been inspected. Can be estimated to be below the reference value. Therefore, when the HF concentration is equal to or lower than the reference value (Yes), the process proceeds to step S4A, and all of the predetermined number of lithium ion secondary batteries 100 are accepted.

  On the other hand, when the HF concentration is larger than the reference value (No), the HF of the predetermined number (for example, 1000) of lithium ion secondary batteries 100 manufactured at the same time as the tested lithium ion secondary battery 100 is also HF. The concentration is likely to be greater than the reference value. Therefore, when the HF concentration is larger than the reference value (No), the process proceeds to step S4B, and all of the predetermined number of lithium ion secondary batteries 100 are determined to be defective (failed products). Thereafter, the process returns to the main routine (see FIG. 5), and the series of processes is terminated.

  In addition, when the HF concentration of the lithium ion secondary battery 100 that has been inspected is larger than the reference value, it can be considered that a large amount of HF is generated in the lithium ion secondary battery 100 due to hydrolysis of the lithium salt. . That is, it can be considered that a large amount of moisture exceeding the standard was mixed in the battery during the manufacturing process. Therefore, it is advisable to check the production line, identify the process in which a large amount of moisture is mixed, and take measures to improve the process. Thereby, after that, the lithium ion secondary battery 100 in which the amount of HF is suppressed to a reference value or less can be manufactured.

  In the first embodiment, step S4 (steps S41 to S49) corresponds to the inspection process. Steps S45 and S46 (specifically, distillation performed during the period from the start of the process of step S45 to the process of step S48) correspond to the separation step. Step S46 corresponds to a neutralization titration step.

Here, a method for measuring the TBAOH concentration of the titrant (TBAOH solution) used in Example 1 will be described. The TBAOH concentration was calculated by neutralization titration.
First, an inert gas (specifically, nitrogen gas) was introduced into the neutralization titration apparatus 1 to replace the atmosphere contained in the neutralization titration apparatus 1 with an inert gas. Next, about 10 mL of dimethylformamide (DMF) was placed in the test tube 3, and one drop of 0.1% thymolphthalein (indicator) was added. Further, in the burette 2, a titration solution (adjusted to about 0.0025 mol / L) in which tetrabutylammonium hydroxide (TBAOH) is dissolved in a nonaqueous solvent in which benzene and methanol are mixed is placed.

  Thereafter, blank measurement was performed. Specifically, a titrant (TBAOH solution) is dropped from the burette 2 into the test tube 3, and the color of the liquid in the test tube 3 (liquid obtained by adding thymolphthalein to DMF) changes from transparent to blue. Then, the dropping of the titrant (TBAOH solution) is finished. Thereby, the influence of DMF can be eliminated in the subsequent neutralization titration. Next, 1.0 mL of a 0.005 mol / L benzoic acid-toluene solution was added to the test tube 3. Thereafter, a titrant (TBAOH solution) was dropped from the burette 2 one by one into the test tube 3, and the time when the color of the liquid in the test tube 3 changed from transparent to blue was defined as the neutralization point.

Next, based on the titration of the titrant (TBAOH solution) dropped from the start of neutralization titration to the neutralization point, the TBAOH concentration (mol / L) of the TBAOH solution is calculated from the following formula (2). Calculated.
TBAOH concentration (mol / L) = {benzoic acid concentration (mol / L) × benzoic acid addition amount (mL)} / titer of TBAOH solution (mL) (2)

  In this measurement, the benzoic acid concentration was 0.005 mol / L, the benzoic acid addition amount was 1.0 mL, and the titration amount of the TBAOH solution was 2.10 mL. Therefore, from the formula (2), the TBAOH concentration was 0.00238 mol. Calculated as / L. In Example 1, since the titration solution (TBAOH solution) in which the TBAOH concentration was strictly measured was used, neutralization titration was performed in the inspection process, and the HF concentration was calculated. The amount of HF in the water electrolyte solution 140 can be quantified.

(Verification experiment)
Next, an experiment was conducted to verify the validity of the HF determination method (steps S42 to S48) of the first embodiment. Specifically, a nonaqueous electrolytic solution 140 having an HF concentration of 31.8 ppm and a TBAOH solution (titrant) having a TBAOH concentration of 0.0026 mol / L are prepared, and the neutralization titrator 1 (see FIG. 7). ) Was used for neutralization titration in the same procedure as in Example 1 (processing of steps S42 to S47). In addition, when the theoretical value of the titration amount of the TBAOH solution (titrant) in this experimental example is calculated based on the formula (1), it is 0.62 mL.

  Here, in the period from the start of distillation (heating of the non-aqueous electrolyte 140 in the container 4 by the heater 5) to the end of neutralization titration, the relationship between the heating time, the temperature in the container, and the titration amount is expressed. The obtained graph is shown in FIG. The heating time is the time when the nonaqueous electrolyte solution 140 in the container 4 is heated by the heater 5. The container temperature is the temperature in the container 4 and is the temperature detected by the temperature monitor 7. The titration amount is the amount of titration solution (TBAOH solution) dropped in neutralization titration.

  As shown in FIG. 8, in this verification experiment, when the heating time has passed about 28 minutes, the temperature in the container 4 becomes substantially constant at around 62 ° C. after the TBAOH solution (titrant) is dropped. The temperature inside the container 4 no longer increases. Moreover, after that, the liquid to be titrated in the test tube 3 did not change from blue to transparent. For this reason, it was judged that the end point of the neutralization titration was reached by the dropwise addition of the TBAOH solution (titrant) performed when the heating time passed about 28 minutes. The titer of the titrant (TBAOH solution) until the end point was about 0.64 mL, which was very close to the theoretical value (0.62 mL). From this result, it can be said that the HF determination method (inspection process) of Example 1 is a highly accurate HF determination method.

(Comparison with conventional method)
Next, a comparison test of the accuracy and sensitivity of neutralization titration was performed for the HF quantification method of the present invention (hereinafter also referred to as the method of the present invention) and the conventional HF quantification method (hereinafter also referred to as the conventional method).

  Specifically, as a method of the present invention, a nonaqueous electrolytic solution containing 32 μg of HF and a TBAOH solution (titrant) having a TBAOH concentration of 0.002 mol / L are prepared, and the neutralization titrator 1 (FIG. 7). Was used for neutralization titration of the non-aqueous electrolyte (specifically, other electrolyte components) in the same procedure as in Example 1 (processing in steps S42 to S47). In addition, the solvent of the nonaqueous electrolytic solution is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate at a ratio of 1: 1: 1 (volume ratio), as in Example 1.

  In this test, neutralization titration according to the above-described method of the present invention was performed 10 times, and each time, titration volume M1 (mL) of the titration liquid in the blank measurement and titration volume M2 (mL) to the end point of the titration liquid in the neutralization titration. ). Further, for the titration amounts M1 and M2, an average value (mL), a standard deviation (mL), and a coefficient of variation (%) were calculated, respectively. The results are shown in Table 1.

In addition, as a conventional method, a nonaqueous electrolytic solution containing 190 μg of HF and a NaOH solution (a titrant) having a NaOH concentration of 0.01 mol / L are prepared. Neutralization titration of the liquid was performed. Specifically, unlike Example 1 (similar to Patent Document 1), the titration solution was dropped directly into the nonaqueous electrolyte solution without performing distillation of the nonaqueous electrolyte solution, and neutralization titration was performed. . That is, neutralization titration was performed by dropping the titrant directly into a non-aqueous electrolyte containing ethylene carbonate. Further, unlike Example 1 (similar to Patent Document 1), neutralization titration was performed without replacing the atmosphere contained in the neutralization titration apparatus with an inert gas. That is, neutralization titration was performed in an atmosphere containing CO ₂ .

  Further, in the conventional method, unlike Example 1, water was used as a solvent for the titrated liquid (including nonaqueous electrolyte) without using a basic nonaqueous solvent. In the conventional method, a BTB solution is used as an indicator. However, as in Example 1, the solvent of the non-aqueous electrolyte is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a 1: 1: 1 (volume ratio).

  In this test, neutralization titration by the conventional method described above was performed 10 times, and each time, titration volume M1 (mL) of the titration liquid in the blank measurement and titration volume M2 (mL) to the end point of the titration liquid in the neutralization titration. Acquired. Further, for the titration amounts M1 and M2, an average value (mL), a standard deviation (mL), and a coefficient of variation (%) were calculated, respectively. The results are shown in Table 1.

  As shown in Table 1, in the conventional method, the variation coefficients of the titration amounts M1 and M2 were 10.01% and 7.11%, respectively. In contrast, according to the method of the present invention, the coefficients of variation of the titration amounts M1 and M2 are 3.71% and 3.84%, respectively, and the method of the present invention uses a HF-containing nonaqueous electrolyte having a lower concentration. Despite this, the value was considerably smaller than that of the conventional method. That is, in the method of the present invention, variation in titration in neutralization titration was considerably smaller than that in the conventional method. From this result, it can be said that the method of the present invention (specifically, the HF quantification method of Example 1) can quantitate HF in the non-aqueous electrolyte with higher accuracy than the conventional method.

This is because in the method of the present invention, the non-aqueous electrolyte is separated into ethylene carbonate (EC) and other electrolyte components, and neutralization titration is performed on other electrolyte components that do not contain EC. . Thereby, in neutralization titration, it is considered that HF (hydrofluoric acid) could be accurately quantified without being affected by CO ₂ generated by hydrolysis of ethylene carbonate. On the other hand, in the conventional method, the titration solution is directly dropped onto the non-aqueous electrolyte containing ethylene carbonate and neutralization titration is performed. Therefore, the titration amount is affected by CO ₂ generated by the hydrolysis of ethylene carbonate. The variation is thought to have increased.

Furthermore, in the method of the present invention, the atmosphere contained in the neutralization titration apparatus is replaced with an inert gas, and neutralization titration is performed in an inert gas atmosphere. Therefore, CO ₂ contained in the atmosphere It is considered that HF in the electrolytic solution could be quantified with high accuracy without being influenced by. On the other hand, in the conventional method, neutralization titration is performed in an atmosphere containing CO ₂ without replacing the atmosphere contained in the neutralization titration system with an inert gas. It is considered that the variation in titration amount has increased due to the influence of CO ₂ .

Next, the lower limit of quantification was calculated by the following formula (3) for the method of the present invention and the conventional method. The lower limit of quantification refers to the lower limit of the amount of HF that can be quantified by neutralization titration, and HF less than the lower limit of quantification cannot be quantified.
Lower limit of quantification (μg) = 10 × standard deviation of titration amount M1 (mL) × {amount of HF in nonaqueous electrolyte (μg) / average value of titration amount M2 (mL)} (3)

  When the lower limit of quantification was calculated from Equation (3), it was 210 μg in the conventional method. That is, when the amount of HF in the electrolytic solution is less than 210 μg, quantification of HF becomes impossible. In contrast, in the method of the present invention, the lower limit of quantification was 8.2 μg. That is, even when the amount of HF in the electrolytic solution is as small as 8.2 μm, HF can be quantified. Thus, the lower limit of quantification of the method of the present invention was about 1/25 of the conventional method. That is, the method of the present invention (specifically, the HF quantification method of Example 1) was about 25 times more sensitive to neutralization titration than the conventional method. From this result, it can be said that the method of the present invention (specifically, the HF quantification method of Example 1) is an extremely sensitive HF quantification method.

  This is because, in the method of the present invention, neutralization titration is performed by dissolving other electrolyte components in a basic non-aqueous solvent. Since the dissociation constant of HF contained in other electrolyte components can be increased by dissolving other electrolyte components in a basic non-aqueous solvent, the sensitivity of neutralization titration can be increased. Conceivable. On the other hand, in the conventional method, water is used without using a basic non-aqueous solvent as a solvent for the titrated liquid (including non-aqueous electrolyte), so the dissociation constant of HF cannot be increased. It is considered that the sensitivity of neutralization titration was lowered.

(Example 2)
Next, two lithium ion secondary batteries 100 (samples 1 and 2) manufactured by the manufacturing method of Example 1 were prepared, and each was subjected to a cycle test at different environmental temperatures. Specifically, for Sample 1, constant current charging was performed at a current of 20 A under a temperature environment of 25 ° C. until the battery voltage (inter-terminal voltage) reached 4.1V. Next, constant current discharge was performed at a current of 20 A until the battery voltage (terminal voltage) reached 3.0V. This charging / discharging was made into 1 cycle and this charging / discharging cycle was performed 1000 cycles. On the other hand, with respect to Sample 2, 1000 cycles of the above charge / discharge cycle were performed in a temperature environment of 60 ° C.

  About samples 1 and 2 which finished the cycle test, HF in the non-aqueous electrolyte solution 140 was quantified. Specifically, HF in the nonaqueous electrolytic solution 140 was quantified in the same manner as in Example 1 except that the TBAOH concentration of the TBAOH solution (titrant) was 0.0021 mol / L. That is, neutralization titration was performed using the neutralization titration apparatus 1 (see FIG. 7) in the same procedure as in Example 1 (processing in steps S41 to S48). The amount of the non-aqueous electrolyte solution 140 collected from the samples 1 and 2 was 1.0 mL as in Example 1.

  Here, with respect to the nonaqueous electrolyte solutions 140 of Samples 1 and 2, the heating time in the period from the start of distillation (heating of the nonaqueous electrolyte solution 140 in the container 4 by the heater 5) to the end of neutralization titration. FIG. 9 and FIG. 10 show graphs showing the relationship between the temperature in the container and the titration amount. The heating time is the time when the nonaqueous electrolyte solution 140 in the container 4 is heated by the heater 5. The container temperature is the temperature in the container 4 and is the temperature detected by the temperature monitor 7. The titration amount is the amount of titration solution (TBAOH solution) dropped in neutralization titration.

  As shown in FIG. 9, with respect to the non-aqueous electrolyte 140 of Sample 1, when the heating time passed about 28 minutes, the TBAOH solution (titrant) was dropped, and the temperature in the container 4 was 60. The temperature in the container 4 became almost constant near 0 ° C., and the temperature in the container 4 no longer increased. Moreover, after that, the liquid to be titrated in the test tube 3 did not change from blue to transparent. For this reason, it can be judged that the end point of the neutralization titration has been reached by the dropwise addition of the TBAOH solution (titrant) performed when the heating time has passed about 28 minutes. The titer of the titrant (TBAOH solution) until reaching the end point was 0.66 mL.

  On the other hand, as shown in FIG. 10, with respect to the non-aqueous electrolyte 140 of sample 2, when the heating time passed about 32 minutes, the TBAOH solution (titration solution) was dropped, and then the temperature in the container 4 However, the temperature in the container 4 no longer increased. Moreover, after that, the liquid to be titrated in the test tube 3 did not change from blue to transparent. For this reason, it can be judged that the end point of the neutralization titration has been reached by the dropwise addition of the TBAOH solution (titrant) performed when the heating time has passed about 32 minutes. The titer of the titrant (TBAOH solution) until reaching the end point was 1.60 mL.

Next, for samples 1 and 2, the amount of HF (HF concentration) in the non-aqueous electrolyte solution 140 was calculated. Specifically, as in Example 1, the HF concentration (ppm) in the nonaqueous electrolytic solution 140 was calculated from the formula (1).
HF concentration (ppm) = {TBAOH concentration (mol / L) × Titration volume of titrant (L) × HF molecular weight (g / mol) × 10 ⁶ } / {Nonaqueous electrolyte amount (mL) × Nonaqueous electrolyte solution Specific gravity (g / mL)} ... (1)

For sample 1, HF concentration (ppm) = {0.0021 (mol / L) × 0.66 × 10 ⁻³ (L) × 20.0 (g / mol) × 10 ⁶ } / {1.0 ( mL) × 1.2 (g / mL)} = 23 (ppm).
For sample 2, HF concentration (ppm) = {0.0021 (mol / L) × 1.60 × 10 ⁻³ (L) × 20.0 (g / mol) × 10 ⁶ } / {1.0 ( mL) × 1.2 (g / mL)} = 56 (ppm).
From this result, it can be seen that when the lithium ion secondary battery 100 is used in a high-temperature environment of 60 ° C., the amount of HF generated is twice or more that in the case of using it in a room-temperature environment. It is considered that, when used in a high temperature environment, hydrolysis of the lithium salt (LiPF ₆ ) contained in the non-aqueous electrolyte 140 is promoted, and the amount of HF (hydrofluoric acid) generated increases.

  In the above, the present invention has been described with reference to the first and second embodiments. However, the present invention is not limited to the above-described embodiments, and it can be applied as appropriate without departing from the scope of the present invention. Nor.

  For example, in Examples 1 and 2, neutralization titration was performed while performing distillation (separation step). Specifically, after starting distillation in step S45, the process proceeds to step S46, neutralization titration is performed while performing distillation, and then the process proceeds to step S47 to complete the distillation. Specifically, neutralization titration is performed on other electrolyte components (components containing dimethyl carbonate, ethyl methyl carbonate, and HF) that have been separated from EC in the middle of the distillation period while performing distillation (separation step). The operation was repeated several times, and finally, neutralization titration was carried out for the total amount of other electrolyte components.

  However, after the distillation (separation step) is completed (that is, after separation of the non-aqueous electrolyte 140 into ethylene carbonate and other electrolyte components by distillation), the entire amount of other electrolyte components is neutralized. Titration may be performed. Specifically, after starting the distillation in step S45, if it is confirmed by the temperature monitor 7 that the temperature in the container 4 has not increased, the process proceeds to step S47 and the distillation is terminated. Then, it progresses to step S46 and you may make it perform neutralization titration about the whole quantity of the other electrolyte solution component isolate | separated from ethylene carbonate by distillation.

1 is a top view of a lithium ion secondary battery 100. FIG. It is a figure which shows the internal structure of the lithium ion secondary battery 100, and is equivalent to CC sectional view taken on the line of FIG. It is a figure which shows the internal structure of the lithium ion secondary battery 100, and is equivalent to the FF arrow sectional drawing of FIG. FIG. 4 is an enlarged cross-sectional view of an electrode body 150, and corresponds to an enlarged view of a portion B in FIG. 3 is a flowchart (main routine) showing a flow of a method of manufacturing a lithium ion secondary battery according to Example 1; 3 is a flowchart (subroutine) showing a flow of a manufacturing method of a lithium ion secondary battery according to Example 1; 1 is a diagram showing a configuration of a neutralization titration apparatus 1 according to Example 1. FIG. It is a graph which shows the relationship between heating time, the temperature in a container, and titration when HF is determined by the HF determination method of Example 1. It is a graph which shows the relationship between a heating time, the temperature in a container, and titration amount when quantification of HF is performed about the electrolyte solution concerning the lithium ion secondary battery 100 (sample 1) after a cycle test. It is a graph which shows the relationship between heating time, the temperature in a container, and titration amount when quantification of HF is performed about the electrolyte solution concerning the lithium ion secondary battery 100 (sample 2) after a cycle test.

Explanation of symbols

1 Neutralization titration apparatus 100 Lithium ion secondary battery 110 Battery case 140 Non-aqueous electrolyte (electrolyte)
150 Electrode body 155 Positive electrode 156 Negative electrode 157 Separator

Claims (6)

A method for quantifying HF in an electrolyte solution of a lithium ion secondary battery, comprising:
The electrolytic solution is an electrolytic solution containing ethylene carbonate,
A separation step of separating the electrolytic solution into the ethylene carbonate and other electrolytic solution components;
A neutralization titration step of performing neutralization titration in an inert gas atmosphere for the other electrolyte solution component, and a method for quantifying HF in the electrolyte solution. A method for quantifying HF in an electrolyte solution according to claim 1,
In the neutralization titration step, a method for quantifying HF in an electrolyte solution, in which the other electrolyte component is dissolved in a basic nonaqueous solvent and neutralization titration is performed. A method for quantifying HF in an electrolyte solution according to claim 2,
In the neutralization titration step,
As the basic non-aqueous solvent, dimethylformamide is used,
A method for quantifying HF in an electrolytic solution in which neutralization titration is performed using a titration solution in which tetrabutylammonium hydroxide is dissolved in a nonaqueous solvent in which benzene and methanol are mixed as a titration solution. A method for quantifying HF in an electrolyte solution according to any one of claims 1 to 3,
The electrolytic solution includes the ethylene carbonate and a low boiling point solvent having a lower boiling point than the ethylene carbonate,
The separation step is a method for quantifying HF in an electrolytic solution by separating the electrolytic solution into the ethylene carbonate and the other electrolytic solution component containing the low boiling point solvent by distillation. A method for producing a lithium ion secondary battery having an electrolytic solution containing ethylene carbonate,
This is an inspection process for inspecting the lithium ion secondary battery after assembling the lithium ion secondary battery and injecting the electrolyte into the lithium ion secondary battery to complete the lithium ion secondary battery. Then, the electrolyte solution is taken out from the lithium ion secondary battery, and HF is quantified by using the HF determination method in the electrolyte solution according to any one of claims 1 to 4 for the electrolyte solution. A manufacturing method of a lithium ion secondary battery provided with an inspection process. It is a manufacturing method of the lithium ion secondary battery according to claim 5,
In the inspection step, a method of manufacturing a lithium ion secondary battery that determines whether or not the quantified amount of HF is equal to or less than a reference value.

Images