Binder polymers for non-aqueous secondary batteries, binder compositions for non-aqueous secondary batteries, and electrodes for non-aqueous secondary batteries

Abstract

A binder polymer for nonaqueous secondary batteries according to the present invention is characterized in that: if an aqueous dispersion that contains this binder polymer for nonaqueous secondary batteries at a solid content concentration of 8.0% by mass, while having a pH of 12.0 at 23°C is prepared and a 1.0 mol / L aqueous hydrochloric acid solution is added to 125 g of the aqueous dispersion at a rate of 0.5 mL / 30 seconds, linear functions obtained, by a least-squares method, from the relationship between the cumulative amount (x mL) of added aqueous hydrochloric acid solution from the start of the addition of the aqueous hydrochloric acid solution to the time when the electrical conductivity of the aqueous dispersion reaches 2.0 S / m and the electrical conductivity (y S / m) are only the first line L1 and the second line L2; and the first line L1 is expressed by formula y = a1x + b1 (wherein a1 and b1 are more than 0), while the second line L2 is expressed by formula y = a2x + b2 (wherein a2 is more than a1).

Description

[Technical Field]

[0001] This invention relates to binder polymers for non-aqueous secondary batteries, binder compositions for non-aqueous secondary batteries, and electrodes for non-aqueous secondary batteries. This application claims priority based on Japanese Patent Application No. 2021-214258, filed in Japan on December 28, 2021, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] Non-aqueous secondary batteries are widely used as power sources for laptop computers, mobile phones, power tools, and electronic and communication equipment because they can be made smaller and lighter. In recent years, non-aqueous secondary batteries have also been used as power sources for electric vehicles and hybrid vehicles. A specific example of a non-aqueous secondary battery is the lithium-ion secondary battery.

[0003] Non-aqueous secondary batteries include a positive electrode with a metal oxide or the like as the active material, a negative electrode with a carbon material such as graphite as the active material, and an electrolyte. The positive and negative electrodes usually contain a binder that binds the active materials together and to the current collector. Conventionally, binders used in non-aqueous secondary batteries are known to be those described in Patent Documents 1 and 2.

[0004] Patent Document 1 describes a binder composition comprising a particulate polymer having block regions composed of aromatic vinyl monomer units, with a surface acid content within a predetermined range, and water. Patent Document 1 also describes that by adding an aqueous hydrochloric acid solution to a pH-adjusted sample of an aqueous dispersion of the particulate polymer and measuring the electrical conductivity, a hydrochloric acid content-electrical conductivity curve with three inflection points can be obtained.

[0005] Patent Document 2 describes a binder composition for secondary battery electrodes containing 100 parts by mass of at least one polymer aqueous dispersion selected from the group consisting of styrene-butadiene copolymer latex and acrylic emulsion, and 1 to 20 parts by mass of a compound having a cloud point of 70°C or lower. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2019 / 107229 [Patent Document 2] Japanese Patent Publication No. 2014-239070 [Overview of the project] [Problems that the invention aims to solve]

[0007] In recent years, there has been a strong demand for higher power output, higher capacity, and longer lifespan in non-aqueous secondary batteries. Therefore, binders used in non-aqueous secondary batteries are increasingly required to reduce the internal resistance of the batteries and improve their cycle characteristics.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a binder polymer for non-aqueous secondary batteries that can be used as a binder material to obtain a non-aqueous secondary battery with low internal resistance (DCR) and excellent cycle characteristics, a binder composition for non-aqueous secondary batteries containing the same, a binder for non-aqueous secondary batteries, and a slurry for non-aqueous secondary battery electrodes. Furthermore, the present invention aims to provide a non-aqueous secondary battery electrode containing a binder polymer for non-aqueous secondary batteries, which yields a non-aqueous secondary battery with low internal resistance and excellent cycle characteristics, and a non-aqueous secondary battery equipped with the same. [Means for solving the problem]

[0009] The present invention includes the following embodiments. A first aspect of the present invention provides the following binder polymer for non-aqueous secondary batteries. [1] A binder polymer for non-aqueous secondary batteries, When an aqueous dispersion containing 8.0% by mass of the non-aqueous secondary battery binder polymer is prepared at 23°C with a pH of 12.0, and a 1.0 mol / L hydrochloric acid aqueous solution is added to 125 g of the aqueous dispersion at a rate of 0.5 mL / 30 seconds, A binder polymer for non-aqueous secondary batteries, characterized in that, from the relationship between the cumulative amount of hydrochloric acid aqueous solution added x mL from the start of adding the hydrochloric acid aqueous solution until the electrical conductivity of the aqueous dispersion becomes 2.0 S / m, and the electrical conductivity y S / m, the linear functions that can be obtained by the least squares method are only two lines, a first line L1 and a second line L2, the first line L1 is represented by the following equation (1), and the second line L2 is represented by the following equation (2). y = a1x + b1 ... (1) (In equation (1), a1 and b1 are greater than 0.) y = a²x + b² ···(2) (In equation (2), a2 is greater than a1.)

[0010] The binder polymer for non-aqueous secondary batteries according to the first embodiment of the present invention preferably has the following features [2] to [9]. It is also preferable to combine two or more of the following features. [2] The binder polymer for non-aqueous secondary batteries according to [1], wherein a1 in formula (1) is 0.05 or more and 0.1 or less. [3] A binder polymer for non-aqueous secondary batteries according to [1] or [2], wherein a2 in formula (2) is 0.15 or more and 0.3 or less. [4] A binder polymer for non-aqueous secondary batteries according to any one of [1] to [3], wherein b1 in formula (1) is 0.05 or more and 0.3 or less.

[0011] [5] The first structural unit derived from the monomer (a1), The second structural unit derived from the monomer (a2), It has a third structural unit derived from an internal crosslinking agent (a3), The monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, The monomer (a2) is a compound having only one ethylenically unsaturated bond and an anionic functional group. The internal crosslinking agent (a3) ​​is a compound having a plurality of independent ethylenically unsaturated bonds, as described in any of [1] to [4], for a binder polymer for a non-aqueous secondary battery.

[0012] [6] The binder polymer for non-aqueous secondary batteries according to [5], wherein the anionic functional group is at least one of a carboxyl group and a sulfo group. [7] The monomer (a2) comprises at least one of methacrylic acid, fumaric acid, and crotonic acid, as described in [5] or [6], a binder polymer for non-aqueous secondary batteries.

[0013] [8] A binder polymer for non-aqueous secondary batteries according to any one of [5] to [7], comprising 80% by mass or more in total of the first structural unit and the second structural unit. [9] A binder polymer for non-aqueous secondary batteries according to any one of [5] to [8], wherein the content of the second structural unit per 100 parts by mass of the first structural unit is 1.0 part by mass or more and 30 parts by mass or less.

[0014] A second aspect of the present invention provides the following binder composition for non-aqueous secondary batteries. A binder composition for a non-aqueous secondary battery, comprising a binder polymer for a non-aqueous secondary battery described in any of [1] to [9] and an aqueous medium. A third aspect of the present invention provides the following binder for non-aqueous secondary batteries. A binder for non-aqueous secondary batteries comprising a binder polymer for non-aqueous secondary batteries as described in any of [1] to [9]. A fourth aspect of the present invention provides the following slurry for non-aqueous secondary battery electrodes.

[12] A binder polymer for non-aqueous secondary batteries as described in any of [1] to [9], an electrode active material, and an aqueous medium, The aqueous medium is one selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent, wherein the slurry is for a non-aqueous secondary battery electrode.

[0015] A fifth aspect of the present invention provides the following non-aqueous secondary battery electrode.

[13] A non-aqueous secondary battery electrode comprising a binder polymer for non-aqueous secondary batteries as described in any of [1] to [9]. A sixth aspect of the present invention provides the following non-aqueous secondary battery. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrodes described in

[14]

[13] . [Effects of the Invention]

[0016] According to the present invention, a binder polymer for non-aqueous secondary batteries can be provided that can be used as a binder material to obtain non-aqueous secondary batteries with low internal resistance and excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide a binder composition for non-aqueous secondary batteries, a binder for non-aqueous secondary batteries, and a slurry for non-aqueous secondary battery electrodes, which yield non-aqueous secondary batteries with low internal resistance and excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery electrode that yields a non-aqueous secondary battery with low internal resistance and excellent cycle characteristics, and a non-aqueous secondary battery equipped with the same that has low internal resistance and excellent cycle characteristics. [Brief explanation of the drawing]

[0017] [Figure 1] This graph shows an example of the relationship between the cumulative amount of hydrochloric acid solution added (x, mL) and the electrical conductivity (y, S / m) when hydrochloric acid solution is added to the electrical conductivity titration sample of Example 1. [Figure 2] This graph shows an example of the relationship between the cumulative amount of hydrochloric acid solution added (x, mL) and the electrical conductivity (y, S / m) when hydrochloric acid solution is added to the electrical conductivity titration sample of Comparative Example 1. [Modes for carrying out the invention]

[0018] The following describes in detail preferred examples of the binder polymer for non-aqueous secondary batteries (also referred to as the polymer used in the binder for non-aqueous secondary batteries), the binder composition for non-aqueous secondary batteries, the binder for non-aqueous secondary batteries, the slurry for non-aqueous secondary battery electrodes, the non-aqueous secondary battery, and the non-aqueous secondary battery of the present invention. It should be noted that the present invention is not limited to the embodiments shown below. For example, additions, omissions, substitutions, and changes can be made to the number, types, positions, quantities, ratios, materials, and configurations, without departing from the spirit of the present invention.

[0019] Herein, we will explain the following terms used in this specification. "(Meth)acrylic" is a general term for acrylic and methacrylic. "(Meth)acrylate" is a general term for acrylate and methacrylate. Unless otherwise specified, "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond that exhibits radical polymerization properties.

[0020] In a polymer using a compound having an ethylenically unsaturated bond, the structural unit derived from the compound having the ethylenically unsaturated bond may mean a structural unit in which the chemical structure of the part of the compound other than the ethylenically unsaturated bond is the same as the chemical structure of the part of the polymer other than the part corresponding to the ethylenically unsaturated bond. The ethylenically unsaturated bond of the compound may be changed to a single bond when forming the polymer. For example, in a polymer of methyl methacrylate, the structural unit derived from methyl methacrylate is represented by -CH2-C(CH3)(COOCH3)-.

[0021] Furthermore, in the case of polymers of compounds having ionic functional groups and ethylenically unsaturated bonds, for example, as shown in the second structural unit described later, structural units having ionic functional groups such as carboxyl groups may be considered structural units derived from the same ionic compound even if some of the functional groups are ion-exchanged or not. For example, the structural unit represented by -CH2-C(CH3)(COONa)- may also be considered a structural unit derived from methacrylic acid.

[0022] Furthermore, for compounds having multiple independent ethylenically unsaturated bonds, one or more ethylenically unsaturated bonds may remain within the structural unit as a structural unit of the polymer of the compound. Multiple independent ethylenically unsaturated bonds may mean multiple ethylenically unsaturated bonds that do not form conjugated dienes with each other. For example, in the case of a polymer of divinylbenzene, the structural unit derived from divinylbenzene may be a structure without ethylenically unsaturated bonds (a form in which both parts corresponding to the two ethylenically unsaturated bonds of divinylbenzene are incorporated into the polymer chain), or it may be a structure having one ethylenically unsaturated bond (a form in which only the part corresponding to one of the ethylenically unsaturated bonds is incorporated into the polymer chain).

[0023] Furthermore, if, after polymerization, the parts of the polymer other than the chain structure corresponding to the ethylenically unsaturated bond, such as functional groups like carboxyl groups, no longer correspond to the chemical structure of the monomer due to chemical reactions, then the structural units of the polymer shall be considered to be structural units derived from the compound containing the ethylenically unsaturated bond in the polymer. For example, when vinyl acetate is polymerized and then saponified, the structural units of the polymer shall be considered to be derived from vinyl alcohol, rather than from vinyl acetate, based on the chemical structure of the polymer.

[0024] <1. Binder polymer (P) for non-aqueous secondary batteries> The binder polymer for non-aqueous secondary batteries of this embodiment (hereinafter sometimes referred to as "binder polymer") (P) has the following characteristics with respect to a linear function. First, an aqueous dispersion with a pH of 12.0 containing 8.0% by mass of the binder polymer (P) in solid content is prepared. A 1.0 mol / L hydrochloric acid aqueous solution is added to 125 g of this aqueous dispersion at a rate of 0.5 mL / 30 seconds. At this time, the relationship between the cumulative amount of hydrochloric acid aqueous solution added x (mL) from the start of addition of the hydrochloric acid aqueous solution until the electrical conductivity of the aqueous dispersion becomes 2.0 S / m, and the electrical conductivity y (S / m), can be determined by the least squares method to obtain only two linear functions: the first line L1 and the second line L2. In this embodiment, the 1.0 mol / L hydrochloric acid aqueous solution is also referred to as hydrochloric acid aqueous solution. Furthermore, an aqueous dispersion with a pH of 12.0 containing 8.0% by mass of the binder polymer (P) in solid content can be prepared, for example, by creating a binder composition for a non-aqueous secondary battery containing the binder polymer (P) and water, as described later, and then subjecting it to appropriate treatment. Alternatively, the binder polymer (P) alone can be prepared first, water or the like can be added to create a binder composition for a non-aqueous secondary battery, and then the aqueous dispersion can be prepared by subjecting the prepared non-aqueous secondary battery binder composition to appropriate treatment.

[0025] Figure 1 is a graph showing an example of the relationship between the cumulative amount of hydrochloric acid aqueous solution added (x, mL) and the electrical conductivity (y, S / m) when hydrochloric acid aqueous solution is added to an aqueous dispersion containing the binder polymer (P) (the sample for electrical conductivity titration in Example 1, described later) under the above conditions. In Figure 1, the horizontal axis (X coordinate axis) shows the cumulative amount of 1.0 mol / L hydrochloric acid aqueous solution added (mL), and the vertical axis (Y coordinate axis) shows the electrical conductivity (S / m) of the aqueous dispersion. The plots on the XY coordinate system shown in Figure 1 represent the measured values ​​of electrical conductivity (y, S / m). The method for determining the first line L1 and the second line L2 in the binder polymer (P) of this embodiment will be explained below using Figure 1.

[0026] [How to find the first line L1 and the second line L2] In this embodiment, a linear function is obtained by the least squares method using five or more measured values ​​of the electrical conductivity y(S / m) of the aqueous dispersion, and the square of the correlation coefficient (r) is calculated. 2 ) to find r 2 r is a parameter that indicates the variability between the regression line (linear function) obtained by the least squares method and the measured value of the electrical conductivity y (S / m). 2 This value is in the range of 0 to 1, and the closer it is to 1, the smaller the variation.

[0027] In this embodiment, r 2 Using the values ​​shown below, the inflection point p1(x) on the graph shown in Figure 1 is obtained using the method described below. p1 , y p1 ) is determined. Then, the measured value (y) of the electrical conductivity y(S / m) at the inflection point p1 is obtained by the method shown below. p1 Using the measured values ​​less than (7 measured values ​​in the example shown in Figure 1), the linear function obtained by the least squares method is defined as the straight line L1. In addition, the measured value of the electrical conductivity y(S / m) at the inflection point p1 (y p1 Using the above measurements, the linear function obtained by the least squares method is defined as the line L2.

[0028] To determine the first and second lines L1 and L2, first measure the electrical conductivity y (S / m) of the aqueous dispersion when the cumulative amount x (mL) of 1.0 mol / L hydrochloric acid solution added is zero. Then, measure the electrical conductivity y (S / m) of the aqueous dispersion at the time of each 0.5 mL addition of hydrochloric acid solution. Continue adding hydrochloric acid solution and measuring the electrical conductivity of the aqueous dispersion at the time of addition until the electrical conductivity of the aqueous dispersion reaches 2.0 S / m.

[0029] If, due to limitations in the experimental apparatus, a measurement of the electrical conductivity y(S / m) of the aqueous dispersion at 2.0 S / m cannot be obtained, the measurement results up to the cumulative amount of hydrochloric acid aqueous solution added x(mL) at which the measured electrical conductivity y(S / m) is less than 2.0 S / m but closest to 2.0 S / m will be used to calculate the first straight line L1 and the second straight line L2.

[0030] Next, using a total of five points, namely, the measured value of the electrical conductivity y (S / m) when the cumulative addition amount x (mL) is zero and the measured values of four electrical conductivities y (S / m) where the cumulative addition amount x (mL) is greater than zero and close to zero, a linear function is obtained by the least squares method, and the square (r 2 ) of the correlation coefficient (r) is obtained. Then, it is confirmed whether r 2 is 0.992 or more. If r 2 is less than 0.992, it is assumed that the linear function (straight line L1) obtained by the least squares method does not exist. In this embodiment, when r 2 is 0.992 or more, it is considered that the variation in the measured values used for calculating the linear function is sufficiently small and the error of the linear function calculated by the least squares method is sufficiently small.

[0031] When r 2 is 0.992 or more for the total of five points including the measured value of the electrical conductivity y (S / m) when the cumulative addition amount x (mL) is zero and the measured values of four electrical conductivities y (S / m) where the cumulative addition amount x (mL) is greater than zero and close to zero, the number of measured values of the electrical conductivity y (S / m) where the cumulative addition amount x (mL) is greater than zero and close to zero is increased one by one from four, and each time, a linear function is obtained by the least squares method. For each obtained linear function, the square (r 2 ) of the correlation coefficient (r) is obtained, and it is confirmed whether r 2 is 0.992 or more. In this embodiment, this operation is performed, and when r 2 changes to less than 0.992, it is considered that a change has occurred in the components contributing to the neutralization reaction between the aqueous dispersion and the hydrochloric acid aqueous solution within the measurement range of the measured values of a plurality of electrical conductivities y (S / m) used to obtain the linear function by the least squares method.

[0032] Then, among the linear functions for which r 2 becomes less than 0.992, the linear function with the smallest number of measured values used for calculating the linear function is obtained. That is, this linear function is the linear function for which r 2 first drops below 0.992 using five or more measurement points greater than zero and close to zero. The maximum value of the cumulative addition amount x used for calculating that linear function is designated as "xp1 " and the measured value of the electrical conductivity y(S / m) at that time is "y p1 " and the inflection point p1(x p1 , y p1 )

[0033] Then, the cumulative amount added x is the value of the inflection point p1 "x p1 Using all the measured values ​​of electrical conductivity y(S / m) when it is less than , the linear function obtained by the least squares method is defined as the first line L1. Therefore, the r of the first line L1 2 This is 0.992 or higher. Figure 1 shows, as an example, the first linear line L1 and its equation obtained from the electrical conductivity titration sample of Example 1 described later, and r 2 Enter the value.

[0034] Furthermore, in the linear function obtained by the above method, within the range from when the hydrochloric acid aqueous solution is added to the aqueous dispersion until the measured electrical conductivity y(S / m) becomes 2.0 S / m, r 2 If no linear function has a value less than 0.992, then no inflection points exist. In this case, the only linear function found by the least squares method is the first line L1, and the second line L2 does not exist.

[0035] Next, the cumulative amount added x is the value of the inflection point p1 "x p1 The above conditions apply, and the value of the inflection point p1 is "x p1 Five of the closest to " (i.e., x p1 In addition, using the measured values ​​of electrical conductivity y (S / m) for four other parameters, a linear function was obtained by the least squares method, and the square of the correlation coefficient (r) was calculated. 2 ) And then, r 2 Check whether it is 0.992 or greater. As a result, r 2 If the result is less than 0.992, the only linear function found by the least squares method is the first line L1, and the second line L2 does not exist. Also, r 2Even if the value is 0.992 or greater, if the slope of the resulting linear function is less than or equal to the slope (a1) of the first line L1, the second line L2 is considered not to exist.

[0036] On the other hand, the cumulative amount added x is the value of the inflection point p1 "x p1 The value of the inflection point p1 is "x" p1 Five of the closest to " (i.e., x p1 In addition, r was determined using the measured values ​​of the electrical conductivity y (S / m) of four other factors. 2 If the value becomes 0.992 or higher, the cumulative amount added x will be equal to the value of the inflection point p1, "x p1 The value of the inflection point p1 is "x" p1 The number of measured values ​​of electrical conductivity y(S / m) that are close to ' is increased from four to one each time. Then, a linear function is found using the least squares method each time the number of measured values ​​is increased. Next, for each obtained linear function, the square of the correlation coefficient (r) is calculated. 2 ) to find, r 2 Check whether the value is 0.992 or higher.

[0037] If the number of measured values ​​of electrical conductivity y(S / m) used when determining a linear function is such that the cumulative amount of addition x is equal to the value of the inflection point p1 "x p1 The number of measurements is increased until all measurements with electrical conductivity y(S / m) of 2.0 S / m or less are included, and each time it is increased, the linear function r obtained by the least squares method is used. 2 However, if all values ​​are 0.992 or higher, the cumulative amount added x will be equal to the value of the inflection point p1, "x p1 Using all the measured values ​​of electrical conductivity y(S / m) when the value is greater than or equal to , a linear function is obtained by the least squares method. Then, it is checked whether the slope of the obtained linear function is greater than the slope (a1) of the first line L1, and if it is greater than the slope (a1) of the first line L1, it is designated as the second line L2. In Figure 1, as an example, the second line L2 and its equation obtained from the electrical conductivity titration sample of Example 1 described later, and r 2 Enter the value.

[0038] In other words, by the above method, the cumulative amount added x is equal to the value of the inflection point p1 "x p1The linear function obtained using measured values ​​within the range where the measured electrical conductivity y(S / m) is 2.0 S / m or less, is r 2 If there is no linear function where the cumulative amount x is less than 0.992, then the value of the inflection point p1 "x" is equal to the value of x p1 Within the range where the measured value of electrical conductivity y(S / m) is 2.0 S / m, there are no inflection points. Also, the r of the second straight line L2 2 This will be 0.992 or higher.

[0039] Therefore, there is only one inflection point within the range from when the hydrochloric acid solution is added to the aqueous dispersion until the measured electrical conductivity y(S / m) becomes 2.0 S / m (in the example shown in Figure 1, point p1(x) on the graph). p1 , y p1 In this case, the only linear functions that can be obtained by the least squares method are the first line L1 and the second line L2, and no other regression lines exist.

[0040] Here, using the method described above, the cumulative amount added x is equal to the value of the inflection point p1 "x p1 The value of the inflection point p1 is "x" and is greater than or equal to the measured value of the electrical conductivity y(S / m) which is 2.0 S / m or less. p1 Six of the closest to " (i.e., x p1 In addition to the value of , using five or more measured values ​​of electrical conductivity y(S / m), among the multiple linear functions obtained by the least squares method, r 2 The case where a linear function exists in which is less than 0.992 will be explained using Figure 2. In this case, the cumulative amount added x is "x p1 The value of the inflection point p1 is "x" and is greater than or equal to the measured value of the electrical conductivity y(S / m) which is 2.0 S / m or less. p1 Five of the closest to " (i.e., x p1 In addition, using the measured values ​​of electrical conductivity y(S / m) (four other values), multiple linear functions r were obtained by the least squares method. 2 It is 0.992 or higher.

[0041] Figure 2 is a graph showing an example of the relationship between the cumulative amount of hydrochloric acid aqueous solution added (x, mL) and the electrical conductivity (y, S / m) when hydrochloric acid aqueous solution is added to an aqueous dispersion containing a binder polymer (the sample used for electrical conductivity titration in Comparative Example 1, described later) under the above conditions. In Figure 2, the horizontal axis (X coordinate axis) shows the cumulative amount of 1.0 mol / L hydrochloric acid aqueous solution added (mL), and the vertical axis (Y coordinate axis) shows the electrical conductivity (S / m) of the aqueous dispersion. The plots on the XY coordinate system shown in Figure 2 represent the measured values ​​of electrical conductivity (y, S / m). Figure 2 shows, as an example, the first linear interval L1 and its equation obtained from the electrical conductivity titration sample of Comparative Example 1 described later, and r 2 The value of , the second line L'2 and its equation, and r 2 Enter the value.

[0042] The cumulative amount of additive x is greater than or equal to the value of the inflection point p1, and the measured value of electrical conductivity y (S / m) is within the range of 2.0 S / m or less, and the value of the inflection point p1 is "x p1 Six of the closest to " (i.e., x p1 In addition to the value of , using five or more measured values ​​of electrical conductivity y(S / m), among the multiple linear functions obtained by the least squares method, r 2 If there exists a linear function for which r is less than 0.992, 2 We will find the linear function whose value is less than 0.992, and which uses the fewest number of measured values ​​to calculate the linear function. In other words, this linear function is the one whose value at the inflection point p1 is "x p1 Using a total of six or more measurement points close to ', for the first time r 2 This is a linear function in which the value of x falls below 0.992. The maximum value of the cumulative amount of addition x used to calculate this linear function is "x p2 " and the measured value of the electrical conductivity y(S / m) at that time is "y p2 " and the inflection point p2(x) on the graph shown in Figure 2 p2 , y p2 ) In this case, as shown in Figure 2, there are two or more inflection points (two, p1 and p2, in the example shown in Figure 2) within the range from when the hydrochloric acid solution is added to the aqueous dispersion until the measured electrical conductivity y(S / m) becomes 2.0 S / m.

[0043] Then, using all the measured values ​​of electrical conductivity y(S / m) when the cumulative amount added x is greater than or equal to the value at inflection point p1 and less than the value at inflection point p2, the linear function obtained by the least squares method is defined as the second line L'2. After that, it is checked whether the slope (a2) of the second line L'2 is greater than the slope (a1) of the first line L1. If the slope (a2) of the second line L'2 is greater than the slope (a1) of the first line L1, then it is defined as the second line L2. At this time, the r of the second line L2 2 This will be 0.992 or higher. In the example shown in Figure 2, the slope (a2) of the second line L'2 is less than or equal to the slope (a1) of the first line L1, therefore the second line L'2 is not the second line L2 in this embodiment. In this case, the r of the second line L'2 2 This will be 0.992 or higher.

[0044] Subsequently, in the same manner as when the second line L2 was determined after the first line L1 was determined, the cumulative amount of additive x is greater than or equal to the value of the inflection point p2, and the measured value of the electrical conductivity y (S / m) is within the range of 2.0 S / m or less, and the five values ​​close to the value of the inflection point p2 (i.e., x) p2 In addition to the value of , four measured values ​​of electrical conductivity y(S / m) were used to determine the linear function by the least squares method, and the square of the correlation coefficient (r) was also calculated. 2 ) And then, r 2 Check whether it is 0.992 or greater. As a result, r 2 If the value is less than 0.992, then in this embodiment, it is assumed that there is not only the first line L1 and the second line L2 (the second line L'2 in the example shown in Figure 2), but also another line L'3 that is not a linear function obtained by the least squares method.

[0045] The cumulative amount of additive x is greater than or equal to the value of the inflection point p2, and the measured value of electrical conductivity y(S / m) is within the range of 2.0 S / m or less, and r is determined using the five measured values ​​of electrical conductivity y(S / m) that are close to the value of the inflection point p2. 2If the value is 0.992 or greater, the linear functions that can be found by the least squares method are not just the first line L1 and the second line L2 (the second line L'2 in the example shown in Figure 2), but there is one or more more (the third line L3 in the example shown in Figure 2). In other words, there are three or more linear functions that can be found by the least squares method. At this time, the r of the third line L3 2 This is 0.992 or higher. In Figure 2, as an example, the third line L3 and its equation obtained from the electrical conductivity titration sample of Comparative Example 1 described later, and r 2 Enter the value.

[0046] The binder polymer (P) of this embodiment is such that, under the above conditions, the linear functions obtained by the least squares method from the relationship between the cumulative amount of hydrochloric acid aqueous solution added x (mL) and the electrical conductivity y (S / m) are only two lines: the first line L1 and the second line L2. The first line L1 is represented by the following equation (1), and the second line L2 is represented by the following equation (2). y = a1x + b1 ... (1) (In equation (1), a1 and b1 are greater than 0.) y = a²x + b² ···(2) (In equation (2), a2 is greater than a1.)

[0047] In formula (1), a1 is a value derived from the neutralization reaction in which the alkali used to adjust the pH of the aqueous dispersion containing the binder polymer (P) is neutralized, and the neutralization reaction caused by the components contained in the binder polymer (P). Since a1 in formula (1) is greater than 0, it can be confirmed that the components that cause the neutralization reaction have been sufficiently introduced into the binder polymer (P), so it is preferably 0.05 to 0.1, more preferably 0.055 to 0.9, and even more preferably 0.06 to 0.8.

[0048] In equation (2), a2 is a value derived from the reaction in which the alkali used to adjust the pH of the aqueous dispersion containing the binder polymer (P) is neutralized. The change in the electrical conductivity y (S / m) of the aqueous dispersion containing the binder polymer (P) is more pronounced when a neutralization reaction caused by the components of the binder polymer (P) does not occur, compared to when a neutralization reaction caused by the components of the binder polymer (P) occurs in addition to the reaction in which the alkali used to adjust the pH of the aqueous dispersion is neutralized. For this reason, a2 in equation (2) is a positive value greater than a1 in equation (1). In formula (2), a2 is greater than a1, and the endpoint of the neutralization reaction caused by the components in the binder polymer (P) can be sufficiently confirmed, so it is preferably 0.15 or more and 0.3 or less, more preferably 0.016 or more and 0.28 or less, and even more preferably 0.017 or more and 0.25 or less.

[0049] In formula (1), b1 is greater than 0, which confirms that the binder polymer (P) has been sufficiently introduced with components that undergo a neutralization reaction. Therefore, it is preferably 0.05 or more and 0.3 or less, more preferably 0.08 or more and 0.2 or less, and even more preferably 0.1 or more and 0.18 or less. A binder polymer (P) in formula (1) where b1 is 0.05 or greater contains a sufficient amount of components that undergo a neutralization reaction, and can therefore be used as a binder material to obtain a non-aqueous secondary battery with lower internal resistance (DCR) and superior cycle characteristics. In equation (2), b2 can be a value smaller than b1.

[0050] The binder polymer (P) of this embodiment can be used as a binder material to obtain non-aqueous secondary batteries with lower internal resistance (DCR) and superior cycle characteristics. The reason why the binder polymer (P) exhibits the above effects is not clear, but it is presumed to be as follows. The following describes one embodiment of the binder polymer (P a I will use this as an example to explain, but it is not limited to this example.

[0051] The binder polymer (P) of this embodiment has only two linear functions that can be obtained under the above conditions: the first line L1 represented by equation (1) and the second line L2 represented by equation (2) (see Figure 1). When an aqueous dispersion of the binder polymer (P) of this embodiment is prepared to pH 12.0 and then a hydrochloric acid aqueous solution is added to the aqueous dispersion to perform a neutralization reaction, if the component neutralized by the hydrochloric acid aqueous solution changes during the neutralization reaction, the relationship between the cumulative amount of hydrochloric acid aqueous solution added x (mL) and the electrical conductivity y (S / m) changes accordingly, and an inflection point appears. Since the binder polymer (P) of this embodiment has only two linear functions that can be obtained under the above conditions: the first line L1 and the second line L2, the inflection point that appears when a neutralization reaction is performed under the above conditions is point p1(x p1 , y p1 ) There is only one. In other words, in the aqueous dispersion of the binder polymer (P) of this embodiment, the component neutralized by the hydrochloric acid aqueous solution changes only once.

[0052] In the neutralization reaction from the start of adding the hydrochloric acid solution to the aqueous dispersion up to the inflection point p1, a first neutralization reaction occurs where the alkali used to adjust the pH of the aqueous dispersion of the binder polymer (P) to pH 12.0 is neutralized before the addition of the hydrochloric acid solution. At this time, it is presumed that not only the first neutralization reaction but also a second neutralization reaction occurs, caused by the anionic functional groups of the binder polymer (P). The second neutralization reaction is a reaction in which the anionic functional groups of the binder polymer (P), which were neutralized by the pH adjustment before the addition of the hydrochloric acid solution, are reneutralized by the hydrochloric acid solution.

[0053] In contrast, in the neutralization reaction from the appearance of the inflection point p1 until the measured electrical conductivity y(S / m) becomes 2.0 S / m, it is presumed that only the first neutralization reaction occurs because the anionic functional groups of the binder polymer (P) that are reneutralized in the second neutralization reaction have disappeared.

[0054] From these observations, it is presumed that when the binder polymer (P) of this embodiment is dispersed in an aqueous medium, anionic functional groups such as -COOH, which tend to be present on the outermost surface of particles made of the binder polymer (P), do not become liberated into the aqueous dispersion, but rather remain unevenly distributed within the particles made of the binder polymer (P). Therefore, it is considered that a non-aqueous secondary battery (e.g., a lithium-ion secondary battery) having a non-aqueous secondary battery electrode (e.g., a negative electrode) containing the binder polymer (P) of this embodiment allows Li ions to move easily within the negative electrode, and Li ions are less likely to accumulate locally. As a result, it is presumed that this lithium-ion secondary battery will have suppressed Li deposition, low internal resistance (DCR), and high capacity retention.

[0055] In contrast, for example, as shown in Figure 2, if the binder polymer is one in which the linear functions obtained under the above conditions are not only the first line L1 and the second line L'2, but also one or more other linear functions (three in the example shown in Figure 2), then there will be two or more inflection points (two in the example shown in Figure 2, p1 and p2) when the neutralization reaction is carried out under the above conditions. Therefore, in an aqueous dispersion of such a binder polymer, the components neutralized by the hydrochloric acid solution change at least twice.

[0056] More specifically, in the example shown in Figure 2, it is presumed that in the neutralization reaction from the start of adding the hydrochloric acid aqueous solution to the inflection point p1, a first neutralization reaction and a second neutralization reaction caused by the anionic functional groups of the binder polymer (P) occur, similar to the binder polymer (P) of this embodiment. However, in the neutralization reaction from the appearance of inflection point p1 to the appearance of inflection point p2, unlike the binder polymer (P) of this embodiment, it is presumed that not only the first neutralization reaction occurs, but also a third neutralization reaction occurs, caused by the liberation of anionic functional groups such as -COOH, which tend to be present on the outermost surface of particles made of the binder polymer (P), into the aqueous dispersion. Furthermore, in the neutralization reaction from the appearance of inflection point p2 to the measurement value of electrical conductivity y(S / m) reaching 2.0 S / m, it is presumed that only the first neutralization reaction occurs because the anionic functional groups liberated from the binder polymer (P) that were neutralized in the third neutralization reaction are gone.

[0057] From these observations, it is presumed that in binder polymers that exhibit two or more inflection points when neutralized under the above conditions, anionic functional groups such as -COOH will be released from the outermost surface of the binder polymer into the aqueous dispersion when dispersed in an aqueous medium. Therefore, it is presumed that a non-aqueous secondary battery (e.g., a lithium-ion secondary battery) having a non-aqueous secondary battery electrode (e.g., a negative electrode) containing a binder polymer with two or more of the above inflection points will have a tendency for Li ions to accumulate locally within the negative electrode, leading to easy Li deposition, high internal resistance (DCR), and poor capacity retention.

[0058] Here, the binder polymer (P) in this embodiment is not particularly limited as long as it satisfies the above conditions in the electrical conductivity test. For example, it may be a particulate polymer or a polymer of other form. More specifically, the binder polymer (P) preferably has a first structural unit derived from the monomer (a1) shown below, a second structural unit derived from the monomer (a2) shown below, and a third structural unit derived from the internal crosslinking agent (a3) ​​shown below. This polymer is called the binder polymer (P a This is also called [another term]. This is because the binder polymer (P) of this embodiment is easily obtained in which the linear functions obtained by the above conditions are only two lines: the first line L1 represented by equation (1) and the second line L2 represented by equation (2). The binder of this embodiment: That(P a ) may include a fourth structural unit derived from another monomer (a4) that does not fall under any of monomer (a1), monomer (a2), or internal crosslinking agent (a3).

[0059] [First structural unit] The binder of this embodiment: That(P a The first structural unit in ) originates from the monomer (a1). Monomer (a1) is a nonionic compound (having neither anionic nor cationic functional groups) having only one ethylenically unsaturated bond. Monomer (a1) may consist of only one compound or may contain two or more compounds.

[0060] The monomer (a1) is preferably at least one of (meth)acrylic acid esters and aromatic compounds having ethylenically unsaturated bonds, and more preferably both. The (meth)acrylic acid ester is more preferably an alkyl (meth)acrylate ester. The monomer (a1) preferably does not have either a hydroxyl group or a cyano group, and more preferably does not have a polar functional group, because it facilitates the adjustment of the glass transition temperature and hydrophilicity / hydrophobicity of the copolymer.

[0061] When the monomer (a1) contains a (meth)acrylic acid ester and an aromatic vinyl compound, the total content of the (meth)acrylic acid ester and the aromatic vinyl compound in the monomer (a1) is preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass.

[0062] Examples of the alkyl (meth)acrylate contained in the (meth)acrylic acid ester used for the monomer (a1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and the like. Among these, when producing the binder polymer (P a ), good polymerization stability can be obtained, and since it is suitable for adjusting the uneven distribution of anionic functional groups in the binder polymer (P a ) particles, it is preferable to contain at least one of methyl (meth)acrylate and 2-ethylhexyl (meth)acrylate.

[0063] Examples of the aromatic compound having an ethylenically unsaturated bond used for the monomer (a1) include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, 1,1-diphenylethylene, and the like. When the monomer (a1) contains an aromatic compound having an ethylenically unsaturated bond, it is more preferable to contain at least one of styrene and α-methylstyrene. In particular, when producing the binder polymer (P a ), good polymerization stability can be obtained, and since it is suitable for adjusting the uneven distribution of anionic functional groups in the binder polymer (P a ) particles, it is more preferable to contain styrene. The monomer (a1) is not limited to the compounds described above, but may also include, for example, aliphatic hydrocarbon compounds having an ethylenically unsaturated bond, alicyclic hydrocarbon compounds having an ethylenically unsaturated bond, and the like.

[0064] Regarding the composition of monomer (a1), the binder polymer (P a In order to adjust the glass transition temperature of ) or to adjust the polymerization rate according to the molecular design, it is preferable to appropriately adjust the preferred compound and its amount within the range defined in this embodiment.

[0065] [Second structural unit] The binder of this embodiment: That(P a The second structural unit in ) originates from the monomer (a2). Monomer (a2) is a compound having only one ethylenically unsaturated bond and an anionic functional group. Monomer (a2) may consist of only one compound or may contain two or more compounds.

[0066] Examples of anionic functional groups possessed by monomer (a2) include carboxyl groups, sulfo groups, and phosphate groups. Monomer (a2) is a polymer for binders (P a ) provides good polymerization stability when manufacturing polymers for binders (P a Since it is suitable for adjusting the uneven distribution of anionic functional groups within particles, it is preferable to include a compound having at least one of a carboxyl group and a sulfo group, and more preferably to include both a compound having a carboxyl group and a compound having a sulfo group.

[0067] The monomer (a2) may contain a compound having multiple identical anionic functional groups in one molecule. That is, a binder polymer (P a ) may contain multiple identical anionic functional groups in a single structural unit. Monomer (a2) may contain compounds having two or more different anionic functional groups in one molecule. That is, binder polymer (P a) may contain two or more different anionic functional groups in one structural unit. Further, the monomer (a2) may contain two or more compounds containing different anionic functional groups. That is, the polymer for binder (P a ) may contain two or more structural units containing different anionic functional groups.

[0068] Examples of the monomer (a2) include unsaturated monocarboxylic acids such as methacrylic acid and crotonic acid; unsaturated dicarboxylic acids such as fumaric acid. Among these, when the monomer (a2) is dispersed in an aqueous medium, the carboxy groups (-COOH) derived from the polymer for binder (P a ) are difficult to be liberated into the aqueous dispersion and tend to be unevenly distributed in the particles composed of the polymer for binder (P a ). Therefore, it is preferable to contain at least one of methacrylic acid, fumaric acid, and crotonic acid. In particular, since good polymerization stability is obtained when producing the polymer for binder (P a ) and it is suitable for adjusting the uneven distribution of anionic functional groups in the particles of the polymer for binder (P a ), it is particularly preferable to contain methacrylic acid.

[0069] At least a part of the structural unit derived from the monomer (a2) may form a salt with a basic substance. Examples of the monomer (a2) forming a salt include sodium (meth)acrylate, sodium p-styrenesulfonate, and the like.

[0070] The monomer (a2) preferably contains at least one of a sulfonic acid having an ethylenic unsaturated bond and its salt, and more preferably contains a sulfonate having an ethylenic unsaturated bond. The sulfonic acid preferably contains an aromatic vinyl compound having a sulfo group, and more preferably contains p-styrenesulfonic acid. The sulfonate preferably contains a salt of an aromatic vinyl compound having a sulfo group, and more preferably contains a p-styrenesulfonate. The polymer for binder (P aIt is even more preferable to include sodium parastyrene sulfonate, as this provides good polymerization stability when manufacturing the product.

[0071] [Third structural unit] The binder of this embodiment: That(P a The third structural unit in ) originates from the internal crosslinking agent (a3). The internal crosslinking agent (a3) ​​is a compound having multiple independent ethylenically unsaturated bonds. In this embodiment, the internal crosslinking agent (a3) ​​is a compound capable of forming a crosslinked structure in the radical polymerization of monomers including monomer (a1) and monomer (a2). Only one compound may be used as the internal crosslinking agent (a3), or two or more different compounds may be used.

[0072] Examples of internal crosslinking agents (a3) ​​include compounds having two ethylenically unsaturated bonds, such as divinylbenzene, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate, and compounds having three or more ethylenically unsaturated bonds, such as trimethylolpropane tri(meth)acrylate. The internal crosslinking agent (a3) ​​is a polymer for binders (P a ) provides good polymerization stability when manufacturing polymers for binders (P a It is preferable that the material contains at least one of divinylbenzene and trimethylolpropane tri(meth)acrylate, as this is suitable for regulating the uneven distribution of anionic functional groups within the particles.

[0073] [Fourth structural unit] The binder of this embodiment: That(P a The fourth structural unit that ) may have originates from other monomers (a4). Other monomers (a4) do not fall under monomers (a1) and monomers (a2), nor do they fall under internal crosslinking agents (a3). Examples of other monomers (a4) include, but are not limited to, compounds having ethylenically unsaturated bonds and polar functional groups, surfactants having ethylenically unsaturated bonds (hereinafter sometimes referred to as "polymerizable surfactants"), and compounds having ethylenically unsaturated bonds and functioning as silane coupling agents.

[0074] In compounds having an ethylenically unsaturated bond and a polar functional group, the polar functional group preferably includes at least one of a hydroxyl group and a cyano group, and more preferably a hydroxyl group. Examples of compounds having ethylenically unsaturated bonds and polar functional groups include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and (meth)acrylonitrile, with the inclusion of 2-hydroxyethyl (meth)acrylate being preferable.

[0075] As an example of a polymerizable surfactant, which is another monomer (a4), compounds having an ethylenically unsaturated bond and functioning as a surfactant can be used. Examples of polymerizable surfactants include compounds represented by the following chemical formulas (1) to (4).

[0076] [ka]

[0077] In formula (1), R 1 R is an alkyl group. p is an integer between 10 and 40. 1 It is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms.

[0078] [ka]

[0079] In formula (2), R 2 is an alkyl group. q is an integer between 10 and 12. R 2 The C1 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms. Examples of compounds represented by formula (2) include polyoxyethylene alkyl ether sulfate salts (Aqualon KH-10, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0080] [ka]

[0081] In formula (3), R 3 M is an alkyl group. 1 R is either NH4 or Na. 3 It is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms.

[0082] [ka]

[0083] In formula (4), R 4 M is an alkyl group. 2 R is either NH4 or Na. 4 The C1 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms. Examples of compounds represented by formula (4) include sodium alkylallyl sulfosuccinate (Sanyo Chemical Industries, Ltd., Eleminol JS-20).

[0084] Examples of compounds that have an ethylenically unsaturated bond and function as a silane coupling agent include vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloxypropyltriethoxysilane.

[0085] [For binders, use (P a [Content of each structural unit in the above] The binder of this embodiment: That(P a The polymer (P) preferably contains 80% by mass or more of the first structural unit and the second structural unit in total, more preferably 85% by mass or more, and even more preferably 90% by mass or more. a By increasing the content of the first and second structural units contained in ), a binder polymer (P a When manufacturing the polymer (P), good polymerization stability can be obtained, and the polymer for binder (P a This is because it is suitable for regulating the uneven distribution of anionic functional groups within particles.

[0086] The binder of this embodiment: That(P a The polymer for binder (P a A binder polymer (P) that provides good polymerization stability when manufacturing and is suitable for adjusting the uneven distribution of anionic functional groups within particles. a This is because it results in the following:

[0087] The binder of this embodiment: That(P a The polymer for the binder (P a A binder polymer (P) that provides good polymerization stability when manufacturing and is suitable for adjusting the uneven distribution of anionic functional groups within particles. a This is because it results in the following:

[0088] The binder of this embodiment: That(Pa The polymer for binder (P a A binder polymer (P) that can be used as a binder material to suppress the degradation of ) and obtain a non-aqueous secondary battery with excellent cycle characteristics. a This is because it results in the following:

[0089] The binder of this embodiment: That(P a The polymer for the binder (P a This is because it can suppress the gelation of the substance.

[0090] The binder of this embodiment: That(P a When the polymer (P) contains a fourth structural unit derived from a polymerizable surfactant which is another monomer (a4), the content of the fourth structural unit derived from the other monomer (a4) relative to 100 parts by mass of the first structural unit derived from monomer (a1) is preferably 0.050 parts by mass or more, more preferably 0.075 parts by mass or more, and even more preferably 0.50 parts by mass or more. a A binder polymer (P) that provides good polymerization stability when manufacturing and is suitable for adjusting the uneven distribution of anionic functional groups within particles. a This is because it results in the following:

[0091] The binder of this embodiment: That(P aIf the polymer (P) contains a fourth structural unit derived from a polymerizable surfactant which is another monomer (a4), the content of the fourth structural unit derived from the other monomer (a4) relative to 100 parts by mass of the first structural unit derived from monomer (a1) is preferably 30 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 7.5 parts by mass or less. This is because the particle size, viscosity, etc. of the binder polymer (P) can be appropriately adjusted.

[0092] [For binders, use (P a ) Glass transition temperature Tg The binder of this embodiment: That(P a The glass transition temperature Tg in ) is the peak top temperature of the DDSC chart obtained as the temperature derivative of the DSC, measured using a Differential Scanning Calorimetry (DSC) instrument (EXSTAR DSC / SS7020, Hitachi High-Tech Science Corporation) at a heating rate of 10°C / min under a nitrogen gas atmosphere.

[0093] Binder enhancer (P a The glass transition temperature Tg of the polymer (P) is preferably -30°C or higher, more preferably -10°C or higher, and even more preferably 0°C or higher. a This is because a non-aqueous secondary battery equipped with electrodes containing a binder for non-aqueous secondary batteries, including ), will have excellent cycle characteristics. Binder enhancer (P a The glass transition temperature Tg of the polymer (P) is preferably 100°C or lower, more preferably 50°C or lower, and even more preferably 40°C or lower. a The film-forming properties of the polymer (P) are improved, and the binder polymer (P a This is because a non-aqueous secondary battery equipped with electrodes containing a binder for non-aqueous secondary batteries, including ), will have excellent cycle characteristics.

[0094] [For binders, use (P a (Manufacturing method) A polymer for binders in one embodiment (P a ) is obtained by copolymerizing monomers containing monomer (a1) and monomer (a2), an internal crosslinking agent (a3), and optionally other monomers (a4). Binder polymer (P a The monomers (components (a1) to (a4)) used to synthesize ) are sometimes collectively referred to as monomer (a).

[0095] One method for copolymerizing monomer (a) is, for example, an emulsion polymerization method in which monomer (a) is emulsion polymerized in an aqueous medium (b). By emulsion polymerization, a polymer for binder (P a When manufacturing (a), in addition to monomers (a) and an aqueous medium (b), components such as a nonpolymerizable surfactant (c), a basic substance (d), a radical polymerization initiator (e), and a chain transfer agent (f) can be used.

[0096] [Aqueous medium (b)] The aqueous medium (b) is selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent. Examples of hydrophilic solvents include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. From the viewpoint of polymerization stability, the aqueous medium (b) is preferably water. As long as polymerization stability is not impaired, a mixture of water and a hydrophilic solvent may be used as the aqueous medium (b).

[0097] [Non-polymerizable surfactants (c)] Binder polymer (P) produced by emulsion polymerization a When producing (a), emulsion polymerization may be carried out by including a nonpolymerizable surfactant (c) in a solution containing an aqueous medium (b) and a monomer (a). A nonpolymerizable surfactant (c) is a surfactant (c) that does not have an ethylenically unsaturated bond in its chemical structure. The surfactant (c) improves the dispersion stability of the solution during emulsion polymerization and / or the dispersion (emulsion) obtained after polymerization. It is preferable to use an anionic surfactant or a nonionic surfactant as the surfactant (c).

[0098] Examples of anionic surfactants include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. The surfactant (c) described above may be used alone or in combination of two or more types.

[0099] [Basic substances (d)] Binder polymer (P) produced by emulsion polymerization a When manufacturing the emulsion polymer, a basic substance (d) may be added to the emulsion polymerization solution and / or the dispersion after emulsion polymerization, which contain the aqueous medium (b) and monomer (a). By adding the basic substance (d), the acidic components contained in monomer (a) are neutralized. As a result, the pH of the solution during emulsion polymerization and / or the dispersion after emulsion polymerization is within an appropriate range, and the stability of the solution during emulsion polymerization and / or the dispersion after emulsion polymerization is improved.

[0100] The dispersion after emulsion polymerization contains a binder polymer (P a When manufacturing electrodes using a slurry containing a non-aqueous secondary battery binder and electrode active material, the pH at 23°C is preferably 1.5 to 10, more preferably 6.0 to 9.0, and even more preferably 5.0 to 9.0. This is because it is possible to suppress the settling of the electrode active material in the slurry containing the non-aqueous secondary battery binder and electrode active material.

[0101] Examples of basic substances (d) to be added to the emulsion polymerization solution and / or the dispersion after emulsion polymerization include ammonia, triethylamine, sodium hydroxide, and lithium hydroxide. These basic substances (d) may be used individually or in combination of two or more.

[0102] [Radical polymerization initiator (e)] Binder polymer (P) produced by emulsion polymerization a The radical polymerization initiator (e) used in the production of ) is not particularly limited and known ones can be used. Examples of radical polymerization initiators (e) include persulfates such as ammonium persulfate and potassium persulfate; hydrogen peroxide; azo compounds; and organic peroxides such as tert-butyl hydroperoxide, tert-butyl peroxybenzoate, and cumene hydroperoxide. It is preferable to use persulfates and organic peroxides as radical polymerization initiators (e).

[0103] In this embodiment, a binder polymer (P) is produced by emulsion polymerization. a When producing (), redox polymerization may be carried out by using a reducing agent such as sodium bisulfite, rongalit, or ascorbic acid in combination with a radical polymerization initiator (e).

[0104] The amount of radical polymerization initiator (e) added (including the reducing agent if used in combination) is preferably 0.001 parts by mass or more, and more preferably 0.005 parts by mass or more, per 100 parts by mass of monomer (a). The polymer for binder (P) is polymerized by emulsion polymerization. a When manufacturing the monomer (a), the binder polymer (P a This is because the conversion rate to ) can be increased. The amount of radical polymerization initiator (e) added is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of monomer (a). Binder polymer (P a The molecular weight of the polymer (P) can be increased, and the polymer for the binder of this embodiment can be increased. a This is because it can reduce the swelling rate of non-aqueous secondary battery electrodes containing ) in relation to the electrolyte.

[0105] [Chain transfer agent (f)] Binder polymer (P) produced by emulsion polymerization aThe chain transfer agent (f) used in the production of ) is a binder polymer (P) obtained by emulsion polymerization. a It is used to adjust the molecular weight of ). Examples of chain transfer agents (f) include n-dodecyl mercaptan, tert-dodecyl mercaptan, n-butyl mercaptan, 2-ethylhexyl thioglycolate, 2-mercaptoethanol, β-mercaptopropionic acid, methyl alcohol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, and benzyl alcohol.

[0106] [Emulsion polymerization method] Binder enhancer (P a Examples of emulsion polymerization methods used in the production of ) include a method in which each component used for emulsion polymerization is continuously supplied into the reaction vessel while emulsion polymerization is carried out. The temperature of emulsion polymerization is not particularly limited, but for example, it is 30 to 90°C, preferably 50 to 85°C, and more preferably 55 to 85°C. Emulsion polymerization is preferably carried out while stirring. Furthermore, it is preferable to continuously supply monomer (a) and radical polymerization initiator (e) to the solution during emulsion polymerization so that the concentrations of monomer (a) and radical polymerization initiator (e) in the solution during emulsion polymerization become uniform.

[0107] <2. Binder for non-aqueous secondary batteries> The binder for non-aqueous secondary batteries of this embodiment includes the binder polymer (P) of this embodiment. The electrode binder for non-aqueous secondary batteries may contain other components along with the binder polymer (P). Specifically, the electrode binder for non-aqueous secondary batteries may contain, for example, polymers other than the binder polymer (P), surfactants, etc.

[0108] The binder for non-aqueous secondary batteries consists of components that remain without volatilizing even after heating processes in the manufacturing method of non-aqueous secondary batteries described later. Specifically, the components constituting the binder for non-aqueous secondary batteries are those that remain after weighing 1 g of a binder composition for non-aqueous secondary batteries containing a binder polymer (P), placing it on a 5 cm diameter aluminum dish, and drying it in a dryer at 1 atmosphere (1013 hPa) and a temperature of 105°C for 1 hour while circulating the air inside the dryer.

[0109] The content of the binder polymer (P) in the binder for non-aqueous secondary batteries is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more. This is because the effects of including the binder polymer (P) become significant.

[0110] <3. Binder composition for non-aqueous secondary batteries> The binder composition for non-aqueous secondary batteries of this embodiment comprises the binder polymer (P) of this embodiment and an aqueous medium (B). Preferably, the binder polymer (P) is dispersed in the aqueous medium (B) in the binder composition for non-aqueous secondary batteries. The binder composition for non-aqueous secondary batteries may also contain other components, such as various additives, along with the binder polymer (P) and the aqueous medium (B). Specifically, the binder composition for non-aqueous secondary batteries may contain, for example, the components used in the synthesis of the binder polymer (P).

[0111] The binder composition for non-aqueous secondary batteries of this embodiment may be a dispersion obtained by producing a binder polymer (P) by emulsion polymerization. Alternatively, the binder composition for non-aqueous secondary batteries of this embodiment may be a dispersion obtained by dispersing a binder polymer (P) obtained by a method other than emulsion polymerization in an aqueous medium (B). In this case, a known method can be used to disperse the binder polymer (P) in the aqueous medium (B).

[0112] [Aqueous medium (B)] The aqueous medium (B) in the binder composition for non-aqueous secondary batteries of this embodiment is water, a hydrophilic solvent, or a mixture thereof. Examples of hydrophilic solvents include those exemplified as the aqueous medium (b) used in the synthesis of the binder polymer (P). The aqueous medium (B) may be the same as, or different from, the aqueous medium (b) used in the synthesis of the binder polymer (P).

[0113] If the binder composition for non-aqueous secondary batteries is a dispersion obtained by producing a binder polymer (P) by emulsion polymerization, the aqueous medium (B) may be the aqueous medium (b) used in the synthesis of the binder polymer (P). Alternatively, the aqueous medium (B) may be the aqueous medium (b) used in the synthesis of the binder polymer (P) with a new aqueous medium added. Alternatively, the aqueous medium (B) may be obtained by replacing part or all of the aqueous medium (b) contained in the dispersion obtained by producing the binder polymer (P) by emulsion polymerization with a new aqueous solvent. In this case, the new aqueous medium used may have the same composition as the aqueous medium (b) used in the synthesis of the binder polymer (P), or it may have a different composition.

[0114] [Non-volatile content concentration of binder compositions for non-aqueous secondary batteries] The non-volatile content concentration of the binder composition for non-aqueous secondary batteries in this embodiment is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. This is to increase the amount of active ingredients contained in the binder composition for non-aqueous secondary batteries. The non-volatile content concentration of the binder composition for non-aqueous secondary batteries can be adjusted by the content of the aqueous medium (B) contained in the binder composition for non-aqueous secondary batteries. The non-volatile content concentration of the binder composition for non-aqueous secondary batteries is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. This is because it suppresses the increase in viscosity of the binder composition for non-aqueous secondary batteries, making it easier to prepare a slurry for non-aqueous secondary battery electrodes.

[0115] <4. Slurry for non-aqueous secondary battery electrodes> Next, the slurry for non-aqueous secondary battery electrodes of this embodiment will be described in detail. The slurry for non-aqueous secondary battery electrodes includes the binder polymer (P) of this embodiment, an electrode active material, and an aqueous medium. Preferably, the binder polymer (P) and electrode active material contained in the slurry for non-aqueous secondary battery electrodes are dispersed in the aqueous medium. In addition to the binder polymer (P), electrode active material, and aqueous medium, the slurry for non-aqueous secondary battery electrodes may also contain a thickener, a conductive additive, the above-mentioned components used in the synthesis of the binder polymer (P), etc.

[0116] [Content of binder polymer (P)] The amount of binder polymer (P) contained in the slurry for non-aqueous secondary battery electrodes is preferably 0.50 parts by mass or more, and more preferably 1.0 part by mass or more, per 100 parts by mass of electrode active material. This is to allow the effects of including binder polymer (P) to be fully realized. The content of the binder polymer (P) in the slurry for non-aqueous secondary battery electrodes is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100 parts by mass of electrode active material. This is because it allows for a higher content of electrode active material in the slurry for non-aqueous secondary battery electrodes.

[0117] [Electrode active material] The electrode active material contained in the slurry for non-aqueous secondary battery electrodes is a material that can intercarry and deintercalate charge carrier ions such as lithium ions. The charge carrier ions are preferably alkali metal ions, more preferably lithium ions, sodium ions, and potassium ions, and even more preferably lithium ions.

[0118] When a non-aqueous secondary battery electrode manufactured using a slurry for non-aqueous secondary battery electrodes is the aqueductor, the electrode active material is the aqueductor active material. The aqueductor active material preferably contains at least one of the following: carbon materials, silicon-containing materials, and titanium-containing materials. Examples of carbon materials used as aqueductor active materials include coke such as petroleum coke, pitch coke, and coal coke; carbonized organic polymers; and graphite such as artificial graphite and natural graphite. Examples of silicon-containing materials used as aqueductor active materials include elemental silicon and silicon compounds such as silicon oxide. Examples of titanium-containing materials used as aqueductor active materials include lithium titanate. These materials used as aqueductor active materials may be used individually, or they may be used in mixtures or composites.

[0119] The negative electrode active material preferably contains at least one of a carbon material or a silicon-containing material, and more preferably a carbon material. This is because the binder polymer (P) contained in the non-aqueous secondary battery electrode slurry has a significant effect in improving the binding between negative electrode active materials and between the negative electrode active material and the current collector.

[0120] When a non-aqueous secondary battery electrode manufactured using a slurry for non-aqueous secondary battery electrodes is the positive electrode, the electrode active material is the positive electrode active material. As the positive electrode active material, a material with a higher standard electrode potential than the negative electrode active material is used. Specifically, examples of positive electrode active materials include lithium composite oxides containing nickel, such as Ni-Co-Mn lithium composite oxides, Ni-Mn-Al lithium composite oxides, and Ni-Co-Al lithium composite oxides, as well as chalcogen compounds such as lithium cobalt oxide (LiCoO2), spinel-type lithium manganate (LiMn2O4), olivine-type lithium iron phosphate, TiS2, MnO2, MoO3, and V2O5. These materials used as positive electrode active materials may be used individually or in combination of two or more types.

[0121] [Aqueous medium] The aqueous medium contained in the slurry for non-aqueous secondary battery electrodes of this embodiment is selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent. Examples of the hydrophilic solvent include the same hydrophilic solvent exemplified as the aqueous medium (b) used in the synthesis of the binder polymer (P). The aqueous medium contained in the slurry for non-aqueous secondary battery electrodes may be the same as or different from the aqueous medium (b) used in the synthesis of the binder polymer (P).

[0122] [Thickening agent] Examples of thickeners that may be included in the slurry for non-aqueous secondary battery electrodes include celluloses such as carboxymethylcellulose (CMC), hydroxyethylcellulose, and hydroxypropylcellulose, ammonium salts of celluloses, alkali metal salts of celluloses, polyvinyl alcohol, and polyvinylpyrrolidone. It is preferable that the thickener contains at least one of carboxymethylcellulose, ammonium salts of carboxymethylcellulose, or alkali metal salts of carboxymethylcellulose, as this facilitates the dispersion of the electrode active material in the slurry for non-aqueous secondary battery electrodes.

[0123] The amount of thickener contained in the slurry for non-aqueous secondary battery electrodes is preferably 0.50 parts by mass or more, and more preferably 0.80 parts by mass or more, per 100 parts by mass of electrode active material. This is because it improves the bonding between the electrode active materials contained in the non-aqueous secondary battery electrodes prepared using the slurry, and between the electrode active materials and the current collector. The amount of thickener contained in the slurry for non-aqueous secondary battery electrodes is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and even more preferably 1.5 parts by mass or less, per 100 parts by mass of electrode active material. This is because it improves the coating properties of the slurry for non-aqueous secondary battery electrodes.

[0124] [Conductive additive] Examples of conductive additives that may be included in the slurry for non-aqueous secondary battery electrodes of this embodiment include carbon black and carbon fibers. Examples of carbon black include furnace black, acetylene black, Denka Black (registered trademark) (manufactured by Denka Co., Ltd.), and Ketjen Black (registered trademark) (manufactured by Ketjen Black International Co., Ltd.). Examples of carbon fibers include carbon nanotubes and carbon nanofibers. As a carbon nanotube, VGCF (registered trademark, manufactured by Showa Denko K.K.), which is a gas-phase carbon fiber, is a preferred example.

[0125] [Properties of slurries for non-aqueous secondary battery electrodes] The non-volatile content concentration of the slurry for non-aqueous secondary battery electrodes is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. This is because the concentration of the active ingredient in the slurry for non-aqueous secondary battery electrodes is high, allowing the formation of non-aqueous secondary battery electrodes with a small amount of material. The non-volatile content concentration of the slurry for non-aqueous secondary battery electrodes can be adjusted by the amount of aqueous medium contained in the slurry for non-aqueous secondary battery electrodes. The non-volatile content concentration of the slurry for non-aqueous secondary battery electrodes is preferably 85% by mass or less, more preferably 75% by mass or less, and even more preferably 65% ​​by mass or less. This is because it results in good coating properties for the slurry for non-aqueous secondary battery electrodes.

[0126] The viscosity of the slurry for non-aqueous secondary battery electrodes is preferably 20,000 mPa·s or less, more preferably 10,000 mPa·s or less, and even more preferably 5,000 mPa·s or less. This is because it improves the applicability of the slurry to the current collector and increases the productivity of the non-aqueous secondary battery electrodes. The viscosity of the slurry for non-aqueous secondary battery electrodes can be adjusted by the concentration of non-volatile components in the slurry, the type and amount of thickener.

[0127] The pH of the slurry for non-aqueous secondary battery electrodes can be adjusted as appropriate depending on the specifications of the non-aqueous secondary battery electrodes, and is not limited to this, but preferably the pH at 23°C is 2.0 to 10, more preferably 4.0 to 9.0, and even more preferably 6.0 to 9.0. This is because the durability of a non-aqueous secondary battery equipped with non-aqueous secondary battery electrodes made using the slurry for non-aqueous secondary battery electrodes is improved.

[0128] [Method for manufacturing slurry for non-aqueous secondary battery electrodes] A method for producing the slurry for non-aqueous secondary battery electrodes according to this embodiment includes, but is not limited to, a method of mixing the binder polymer (P) of this embodiment, the electrode active material, an aqueous medium, a thickener as needed, a conductive additive as needed, and other components as needed. The mixing order of each component, which is the raw material for the slurry for non-aqueous secondary battery electrodes, is not particularly limited and can be determined as appropriate. Methods for mixing each component include using a mixing device such as a stirring type, rotary type, or shaking type.

[0129] <5. Non-aqueous secondary battery electrode> Next, the non-aqueous secondary battery electrode (hereinafter sometimes referred to as "electrode") of this embodiment will be described in detail. The electrode of this embodiment includes the binder polymer (P) of this embodiment. The electrode of this embodiment comprises a current collector and an electrode active material layer formed on the current collector. The shape of the electrode of this embodiment is not particularly limited and includes, for example, a laminate or a wound body. The area in which the electrode active material layer is formed on the current collector is not particularly limited, and the electrode active material layer may be formed on the entire surface of the current collector, or on only a part of the surface of the current collector. If the current collector is in the shape of a plate, foil, etc., the electrode active material layer may be formed on both sides of the current collector, or on only one side.

[0130] [Current collector] The current collector is preferably a metal sheet with a thickness of 0.001 mm or more and 0.5 mm or less. Examples of metals forming the metal sheet include iron, copper, aluminum, nickel, and stainless steel. When the electrode in this embodiment is the negative electrode of a lithium-ion secondary battery, the current collector is preferably copper foil.

[0131] [Electrode active material layer] The electrode active material layer includes the binder polymer (P) and electrode active material of this embodiment. The electrode active material layer may also contain conductive additives, thickeners, etc. The electrode active material, conductive additives, and thickeners can all be the same as those exemplified as components of the slurry for non-aqueous secondary battery electrodes.

[0132] [Method for manufacturing electrodes of non-aqueous secondary batteries] The electrode of this embodiment can be manufactured, for example, by the method shown below. First, the slurry for non-aqueous secondary battery electrodes of this embodiment is applied to a current collector. Next, the slurry for non-aqueous secondary battery electrodes is dried. This forms an electrode active material layer containing a binder polymer (P) on the current collector, forming an electrode sheet. After that, the electrode sheet is cut to an appropriate size as needed. By performing the above steps, the electrode of this embodiment is obtained.

[0133] There are no particular limitations on the method for applying the slurry for non-aqueous secondary battery electrodes onto a current collector, but examples include the reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, gravure method, bar method, dip method, and squeeze method. Among these application methods, considering the viscosity and other physical properties and drying properties of the slurry for non-aqueous secondary battery electrodes, it is preferable to use one of the methods selected from the doctor blade method, knife method, or extrusion method. This is because it is possible to obtain an electrode active material layer with a smooth surface and small variation in thickness.

[0134] When applying a slurry for non-aqueous secondary battery electrodes to both sides of a current collector, it may be applied sequentially to one side at a time, or to both sides simultaneously. Furthermore, the slurry for non-aqueous secondary battery electrodes may be applied continuously or intermittently to the current collector. The amount of slurry applied to the non-aqueous secondary battery electrode can be appropriately determined according to the battery's design capacity and the composition of the slurry.

[0135] The method for drying the slurry for non-aqueous secondary battery electrodes applied to the current collector is not particularly limited, but for example, methods selected from hot air, reduced pressure or vacuum environment, (far) infrared radiation, and low-temperature air can be used alone or in combination. The drying temperature and drying time when drying the slurry for non-aqueous secondary battery electrodes can be appropriately adjusted depending on the concentration of non-volatile components in the slurry, the amount applied to the current collector, etc. The drying temperature is preferably 40°C to 350°C, and more preferably 60°C to 100°C from the viewpoint of productivity. The drying time is preferably 1 minute to 30 minutes.

[0136] An electrode sheet, on which an electrode active material layer is formed on a current collector, may be cut to a size and shape suitable for use as an electrode. The method of cutting the electrode sheet is not particularly limited, and for example, slitting, laser cutting, wire cutting, cutting machines, die cutting machines, etc., can be used.

[0137] In this embodiment, the electrode sheet may be pressed before or after cutting, if necessary. This allows the electrode active material to be firmly bonded to the current collector, and the non-aqueous secondary battery can be miniaturized by reducing the thickness of the electrode. A general method can be used for pressing the electrode sheet. In particular, it is preferable to use a die press method or a roll press method. When using the die pressing method, the press pressure is not particularly limited, but 0.5 t / cm 2 5 t / cm² or more 2 The following is preferable. When using the roll press method, the press load is not particularly limited, but it is preferable to set it to 0.5 t / cm or more and 8 t / cm or less. This is because it is possible to obtain the above-mentioned effects of pressing while suppressing a decrease in the insertion and desorption capacity of charge carriers such as lithium ions into the electrode active material.

[0138] <6.Nonaqueous secondary battery> Next, a lithium-ion secondary battery will be described as a preferred example of a non-aqueous secondary battery according to this embodiment. Note that the configuration of the non-aqueous secondary battery in this embodiment is not limited to the example shown below. The lithium-ion secondary battery of this embodiment has a positive electrode, a negative electrode, an electrolyte, and known components such as separators, which may be provided as needed, housed in an outer casing. The shape of the lithium-ion secondary battery may be any shape, such as coin-shaped, button-shaped, sheet-shaped, cylindrical, prismatic, or flat.

[0139] [Positive electrode / Negative electrode] In this embodiment, the lithium-ion secondary battery comprises an electrode active material layer containing the binder polymer (P) of this embodiment in one or both of the positive and negative electrodes. In this embodiment, it is preferable that at least the negative electrode of the lithium-ion secondary battery comprises an electrode active material layer containing the binder polymer (P). In the lithium-ion secondary battery of this embodiment, if only one of the electrodes, the positive electrode or the negative electrode, is equipped with an electrode active material layer containing the binder polymer (P) of this embodiment, then, as an electrode that does not contain the binder polymer (P) of this embodiment, a known binder such as polyvinylidene fluoride is used instead of the binder polymer (P) of this embodiment.

[0140] [Electrolyte] As the electrolyte, a non-aqueous liquid with ionic conductivity is used. Examples of electrolytes include solutions in which the electrolyte is dissolved in an organic solvent, and ionic liquids, with the former being preferred. This is because it allows for the production of lithium-ion secondary batteries with low manufacturing costs and low internal resistance.

[0141] Alkali metal salts can be used as electrolytes and can be appropriately selected depending on the type of electrode active material, etc. Examples of electrolytes include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, and LiB 10 Cl 10 Examples include LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N, and lithium aliphatic carboxylates. Other alkali metal salts can also be used as electrolytes.

[0142] The organic solvent used to dissolve the electrolyte is not particularly limited, but examples include carbonate ester compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC); nitrile compounds such as acetonitrile; and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. These organic solvents may be used individually or in combination of two or more. Among these, it is preferable to use a combination of linear carbonate solvents as the organic solvent.

[0143] [Exterior] As for the exterior, for example, a material formed from aluminum laminate consisting of aluminum foil and resin film can be used as appropriate, but is not limited to this. [Examples]

[0144] The present invention will be described in detail below with reference to examples and comparative examples. The following examples are provided to facilitate understanding of the present invention. The present invention is not limited to these examples. In the following embodiments, a negative electrode for a lithium-ion secondary battery was fabricated as an example of a non-aqueous secondary battery electrode of the present invention, and a lithium-ion secondary battery was fabricated as an example of a non-aqueous secondary battery. The effects of the present invention were confirmed by comparing it with the negative electrode and lithium-ion secondary battery of the comparative example. Furthermore, unless otherwise specified, the water used in the following examples and comparative examples is deionized water.

[0145] <1. Manufacturing of Binder Polymers> 150 parts by mass of water were placed in a separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel, and the temperature was raised to 80°C. Monomers (a1) and (a2) shown in Table 1 or Table 2, an internal crosslinking agent (a3), a polymerizable surfactant (a4) which is another monomer, and a radical polymerization initiator (e) were continuously supplied to this separable flask in the proportions shown in Table 1 or Table 2 over 3 hours while stirring at 80°C to carry out emulsion polymerization and obtain aqueous emulsions containing the binder polymers of Examples 1 to 6 and Comparative Examples 1 to 3.

[0146] The obtained aqueous emulsion was cooled to room temperature, and 160 parts by mass of water and 25% by mass of aqueous ammonia were added. This produced the non-aqueous binder compositions for secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3, in which the particulate binder polymers of Examples 1 to 6 and Comparative Examples 1 to 3 were dispersed in an aqueous medium (b).

[0147] [Table 1]

[0148] [Table 2]

[0149] The amounts of ammonia as a basic substance (d) shown in Tables 1 and 2 represent the amount of ammonia contained in aqueous ammonia (parts by mass). The amount of water as aqueous medium (b) shown in Tables 1 and 2 represents the total amount of water (parts by mass) contained in the binder composition for non-aqueous secondary batteries.

[0150] The polymerizable surfactant (a4) shown in Tables 1 and 2 is polyoxyethylene alkyl ether sulfate salt (compound represented by chemical formula (2), manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Aqualon KH-10). The polymerization initiator (e-2) is tert-butyl peroxybenzoate (Kayabutyl B, manufactured by Kayaku Akzo Co., Ltd.). The polymerization initiator (e-3) is tert-butyl hydroperoxide (manufactured by Kayaku Akzo Co., Ltd., Kayabutyl H-70).

[0151] <2. Evaluation of binder polymers and binder compositions for non-aqueous secondary batteries> The glass transition temperature (Tg) of the binder polymers in Examples 1 to 6 and Comparative Examples 1 to 3 was measured using the method described below. The results are shown in Tables 1 and 2. In addition, the non-volatile content concentration of the binder compositions for non-aqueous secondary batteries in Examples 1 to 6 and Comparative Examples 1 to 3 was measured using the method described below. The results are shown in Tables 1 and 2.

[0152] [Glass transition temperature Tg] A binder composition for non-aqueous secondary batteries was applied to a release PET (polyethylene terephthalate) film and dried at 50°C for 5 hours to obtain a 2 mm thick film made of a binder polymer. Square test specimens measuring 2 mm in length and 2 mm in width were cut from the obtained film. The test specimens were sealed in aluminum pans, and differential scanning calorimetry (DSC) measurements were performed on the specimens using a differential scanning calorimeter (EXSTAR DSC / SS7020, Hitachi High-Tech Science Corporation) under a nitrogen gas atmosphere at a heating rate of 10°C / min. The temperature range for DSC measurement was -40°C to 200°C. The peak top temperature of the DDSC chart obtained as the temperature derivative of the DSC was measured, and this temperature was defined as the glass transition temperature Tg (°C) of the binder polymer.

[0153] [Non-volatile content concentration] One g of the binder composition for non-aqueous secondary batteries was weighed, placed on a 5 cm diameter aluminum dish, and placed in a drying oven. The mixture was dried for one hour at 1 atmosphere (1013 hPa) and 105°C while circulating the air inside the oven, and the mass of the remaining components was measured. The mass ratio (mass%) of the components remaining after drying to the mass (1 g) of the binder composition for non-aqueous secondary batteries before drying was calculated and defined as the non-volatile content concentration.

[0154] Furthermore, using the non-aqueous secondary battery binder compositions of Examples 1 to 6 and Comparative Examples 1 to 3, the electrical conductivity titration of the binder polymers of Examples 1 to 6 and Comparative Examples 1 to 3 was performed by the method described below.

[0155] [Electrical conductivity titration] (Preparation of titration sample) A binder composition for non-aqueous secondary batteries was diluted with a 0.3% aqueous dodecylbenzenesulfonic acid solution to adjust the solid content to 8%, and 200 g of aqueous dispersion was obtained. The obtained aqueous dispersion was centrifuged at 7000 G for 30 minutes, and light liquid (1) was separated. The obtained light liquid (1) was diluted with a 0.3% aqueous dodecylbenzenesulfonic acid solution to adjust the solid content to 8%, and this was obtained as adjusted light liquid (1). The adjusted light liquid (1) was centrifuged at 7000 G for 30 minutes, and light liquid (2) was separated. The obtained light liquid (2) was diluted with a 0.3% aqueous dodecylbenzenesulfonic acid solution to adjust the solid content to 8%, and this was obtained as adjusted light liquid (2). The adjusted light liquid (2) was centrifuged at 7000 G for 30 minutes, and light liquid (3) was separated. The obtained light liquid (3) was diluted with a 0.3% aqueous solution of dodecylbenzenesulfonic acid to adjust the solid content to 8%, and the adjusted light liquid (3) was then used. Using a 1% sodium hydroxide aqueous solution, the pH of the prepared light solution (3) at 23°C was adjusted to obtain a conductivity titration sample (titration sample) consisting of an aqueous dispersion containing 8.0% by mass of the binder polymer in solid content and having a pH of 12.0 at 23°C.

[0156] (Measurement of electrical conductivity) 125 g (10.0 g in solid content) of the titration sample was placed in a 100 mL beaker, and the electrical conductivity (unit: S / m) of the titration sample was measured before adding the hydrochloric acid solution while stirring with a stirrer at 150 rpm. Subsequently, while stirring the titration sample in the beaker with a stirrer at 150 rpm, 1 mol / L hydrochloric acid solution was added to the titration sample at a rate of 0.5 mL / 30 seconds (0.5 ml every 30 seconds), and the electrical conductivity (unit: S / m) of the titration sample was measured every 30 seconds. The electrical conductivity was measured at a temperature of 23°C using a portable electrical conductivity / pH meter (WM-32EP) (manufactured by Toa DKK Co., Ltd.). The addition of hydrochloric acid solution to the titration sample and the measurement of the electrical conductivity of the titration sample were repeated until the electrical conductivity of the titration sample reached 2.0 S / m.

[0157] (Data processing) The measured electrical conductivity of the titration sample against the cumulative amount of hydrochloric acid solution added was then plotted on an XY coordinate system (orthogonal coordinate system) with the cumulative amount of hydrochloric acid solution added (mL) on the horizontal axis (X-axis) and the electrical conductivity of the titration sample (S / m) on the vertical axis (Y-axis).

[0158] Then, using the method for finding the first and second lines L1 and L2 described above, the first and second lines L1 and L2 were determined. If the linear functions obtained by the least squares method using the method described above consisted only of the first and second lines L1 and L2, the slope (a1) and y-intercept (b1) of the first line L1 and the slope (a2) of the second line L2 were determined. Furthermore, if the linear functions obtained by the least squares method using the method described above consisted not only of the first and second lines L1 and L2, but also of one or more additional linear functions, the number of such additional linear functions was determined. The results are shown in Tables 1 and 2.

[0159] <3. Manufacturing of non-aqueous secondary batteries> Using the binder compositions for non-aqueous secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3, negative electrodes were prepared by the methods described below, and lithium-ion secondary batteries, which are non-aqueous secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3, were prepared using these negative electrodes.

[0160] [Fabrication of the positive electrode] LiNi as a positive electrode active material 0.6 Mn 0.2 Co 0.2 A mixture was obtained by mixing 4 parts by mass of O294, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder. 50 parts by mass of N-methylpyrrolidone were added to the mixture and further mixed to obtain a positive electrode slurry.

[0161] A 15 μm thick aluminum foil was prepared as the positive electrode current collector. The positive electrode slurry was applied to both sides of the positive electrode current collector using the direct roll method. The amount of positive electrode slurry applied to the positive electrode current collector was adjusted so that the thickness after the roll press treatment described later was 125 μm per side. The positive electrode slurry applied to the positive electrode current collector was dried at 120°C for 5 minutes, and then pressed using a roll press (manufactured by Sankmetal Co., Ltd., press load 5 t / cm, roll width 7 cm) by the roll press method to obtain a positive electrode sheet having positive electrode active material layers on both sides of the positive electrode current collector. The obtained positive electrode sheet was cut into a rectangle measuring 50 mm in length and 40 mm in width, and conductive tabs were attached to form the positive electrode.

[0162] [Fabrication of negative electrode (non-aqueous secondary battery electrode)] 100 parts by mass of artificial graphite (G49, manufactured by Jiangxi Zichen Technology Co., Ltd.) as the negative electrode active material, 3.9 parts by mass of any non-aqueous secondary battery binder composition produced in Examples 1 to 6 or Comparative Examples 1 to 3 (1.5 parts by mass of non-volatile content (binder polymer)), and 62 parts by mass of a 2% by mass aqueous solution of CMC (carboxymethylcellulose-sodium salt, manufactured by Nippon Paper Chemicals Co., Ltd., Sunrose® MAC500LC) were mixed, and 28 parts by mass of water were added. The mixture was then mixed using a rotation-orbit mixer (ARE-310, manufactured by Thinky Co., Ltd.) to obtain a negative electrode slurry (slurry for non-aqueous secondary battery electrodes).

[0163] A 10 μm thick copper foil was prepared as the negative electrode current collector. The negative electrode slurry was applied to both sides of the negative electrode current collector using the direct roll method. The amount of negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness after the roll press treatment described later was 170 μm per side. The negative electrode slurry applied to the negative electrode current collector was dried at 90°C for 10 minutes, and then pressed using a roll press (manufactured by Sankmetal Co., Ltd., press load 8 t / cm, roll width 7 cm) by the roll press method to obtain a negative electrode sheet having negative electrode active material layers on both sides of the negative electrode current collector. The obtained negative electrode sheet was cut into a rectangle measuring 52 mm in length and 42 mm in width, and conductive tabs were attached to form the negative electrode.

[0164] [Fabrication of non-aqueous secondary batteries] A separator made of a porous polyolefin film (polyethylene, 25 μm thick) was interposed between the positive and negative electrodes, and the positive electrode active material layer and the negative electrode active material layer were laminated so that they faced each other. These were then housed in an outer casing (battery pack) made of aluminum laminate material. Subsequently, an electrolyte solution was injected into the outer casing, vacuum impregnation was performed, and the battery was packed using a vacuum heat sealer to obtain a lithium-ion secondary battery. As the electrolyte, a mixture was used consisting of 99 parts by mass of a solution in which LiPF6 was dissolved at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DEC = 30:50:20, and 1 part by mass of vinylene carbonate.

[0165] <4. Evaluation of non-aqueous secondary batteries> For the lithium-ion secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3, the internal resistance, discharge capacity retention rate after 100 cycles, and Li deposition were evaluated using the methods described below. The results are shown in Tables 1 and 2.

[0166] [Internal resistance (DCR)] Under conditions of 25°C, the internal resistance (DCR(Ω)) of a lithium-ion secondary battery was measured using the following procedure. Specifically, the battery was charged at a constant current of 0.2C from rest potential until the voltage reached 3.6V, bringing the charge state to 50% of the initial capacity (SOC50%). Subsequently, discharge was performed for 60 seconds at current values ​​of 0.2C, 0.5C, 1C, and 2C. The internal resistance DCR(Ω) at SOC50% was determined from the relationship between these four current values ​​(values ​​per second) and voltage.

[0167] [Discharge capacity retention rate after 100 cycles] Under conditions of 45°C, charging and discharging were performed with each cycle consisting of the following steps (i) to (iv) as defined. The time integral of the current in steps (i) and (ii) was defined as the charging capacity, and the time integral of the current in step (iv) was defined as the discharging capacity. The discharging capacity after the first cycle and the discharging capacity after the 100th cycle were measured, and the discharge capacity retention rate after 100 cycles was calculated using the following formula. Discharge capacity retention rate (%) = 100 × (Discharge capacity at 100 cycles / Discharge capacity at 1 cycle)

[0168] (i) Charge at a current of 1C until the voltage reaches 4.2V (constant current (CC) charging). (ii) Charge at a voltage of 4.2V until the current reaches 0.05C (constant voltage (CV) charging). (iii) Let stand for 30 minutes. (iv) Discharge at a current of 1C until the voltage reaches 2.75V (constant current (CC) discharge).

[0169] [Evaluation of Li precipitation] Under conditions of 10°C, the lithium-ion secondary battery was adjusted to a fully charged state (SOC 100%) by performing the series of operations described in steps (i) to (iii) above only once, except that the current was set to 1.5C. The fully charged lithium-ion secondary battery was disassembled in a glove box under an argon atmosphere, and the surface of the negative electrode electrode active material layer was visually inspected.

[0170] On the surface of the negative electrode's electrode active material layer, the normally charged region is gold-colored. However, when Li is deposited in the electrode active material layer, the electrode active material layer turns gray. Therefore, a higher ratio of the gray area to the total area of ​​the electrode active material layer indicates a greater degree of Li deposition. In this embodiment, the ratio of the gray area to the total area of ​​the negative electrode's electrode active material layer was used to evaluate the degree of Li deposition in the negative electrode based on the following criteria.

[0171] [standard] ◎(Excellent); The degree of Li deposition (area of ​​the gray portion) is less than 30% of the entire electrode active material layer. ○ (Good); The degree of Li deposition (area of ​​the gray portion) is between 30% and 50% of the entire electrode active material layer. △ (Acceptable); The degree of Li deposition (area of ​​the gray portion) is 50% or more of the entire electrode active material layer.

[0172] <5. Evaluation Results> As shown in Tables 1 and 2, the lithium-ion secondary batteries of Examples 1 to 6 all exhibited lower internal resistance and higher capacity retention compared to the lithium-ion secondary batteries of Comparative Examples 1 to 3. Furthermore, it was confirmed that the lithium-ion secondary batteries of Examples 1 to 6, compared to the lithium-ion secondary batteries of Comparative Examples 1 to 3, all exhibited suppressed Li deposition, a secondary effect other than the main effect of the present invention. This is presumed to be because the binder polymer contained in the negative electrode of the lithium-ion secondary batteries of Examples 1 to 6 has only two linear functions, the first line L1 and the second line L2, which can be determined by the least squares method, while the binder polymer contained in the negative electrode of the lithium-ion secondary batteries of Comparative Examples 1 to 3 has three linear functions, which can be determined by the least squares method. [Industrial applicability]

[0173] According to the present invention, a binder polymer for non-aqueous secondary batteries can be provided that can be used as a binder material to obtain non-aqueous secondary batteries with low internal resistance and excellent cycle characteristics.

Claims

1. A binder polymer for non-aqueous secondary batteries, When an aqueous dispersion containing 8.0% by mass of the non-aqueous secondary battery binder polymer is prepared at 23°C and pH 12.0, and a 1.0 mol / L hydrochloric acid aqueous solution is added to 125 g of the aqueous dispersion at a rate of 0.5 mL / 30 seconds, A binder polymer for non-aqueous secondary batteries, characterized in that, from the relationship between the cumulative amount of hydrochloric acid aqueous solution added x mL from the start of adding the hydrochloric acid aqueous solution until the electrical conductivity of the aqueous dispersion becomes 2.0 S / m, and the electrical conductivity y S / m, the linear functions that can be obtained by the least squares method are only two lines, a first line L1 and a second line L2, the first line L1 is represented by the following equation (1), and the second line L2 is represented by the following equation (2). y=a １ x+b １ ・・・(1) (In formula (1), a １ and b １ (It is greater than 0.) y=a ２ x+b ２ ・・・(2) (In formula (2), a ２ a １ It's incredible.

2. a in the formula (1) above １ The binder polymer for non-aqueous secondary batteries according to claim 1, wherein a is 0.05 or more and 0.1 or less.

3. a in formula (2) ２ The binder polymer for non-aqueous secondary batteries according to claim 1, wherein the ratio is 0.15 or more and 0.3 or less.

4. b in formula (1) １ However, the binder polymer for non-aqueous secondary batteries according to claim 1, wherein the ratio is 0.05 or more and 0.3 or less.

5. The first structural unit derived from the monomer (a1), The second structural unit derived from the monomer (a2), It has a third structural unit derived from an internal crosslinking agent (a3), The monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, The monomer (a2) is a compound having only one ethylenically unsaturated bond and an anionic functional group. The binder polymer for a non-aqueous secondary battery according to claim 1, wherein the internal crosslinking agent (a3) ​​is a compound having a plurality of independent ethylenically unsaturated bonds.

6. The binder polymer for non-aqueous secondary batteries according to claim 5, wherein the anionic functional group is at least one of a carboxyl group and a sulfo group.

7. The monomer (a2) comprises at least one of methacrylic acid, fumaric acid, and crotonic acid, as described in claim 5, for a binder polymer for a non-aqueous secondary battery.

8. The binder polymer for non-aqueous secondary batteries according to claim 5, comprising a total of 80% by mass or more of the first structural unit and the second structural unit.

9. The binder polymer for non-aqueous secondary batteries according to claim 5, wherein the content of the second structural unit relative to 100 parts by mass of the first structural unit is 1.0 part by mass or more and 30 parts by mass or less.

10. A binder composition for a non-aqueous secondary battery, comprising a binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 9, and an aqueous medium.

11. A binder for a non-aqueous secondary battery, comprising the binder polymer for a non-aqueous secondary battery described in any one of claims 1 to 9.

12. A binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 9, an electrode active material, and an aqueous medium, The aqueous medium is one selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent, wherein the slurry is for a non-aqueous secondary battery electrode.

13. A non-aqueous secondary battery electrode comprising a binder polymer for non-aqueous secondary batteries according to any one of claims 1 to 9.

14. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode described in claim 13.

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