Negative electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

Abstract

A negative electrode for a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure includes: a negative electrode core; and a negative electrode mixture layer arranged on the surface of the negative electrode core. The negative electrode mixture layer contains a negative electrode active material and a binder component; and the binder component contains a binder compound and a chelating agent. In the thickness direction of the negative electrode mixture layer, when the side closer to the negative electrode core is defined as a lower side, the side farther from the negative electrode core is defined as an upper side, a layer above the central part is defined as an upper negative electrode mixture layer, and a layer below the central part is defined as a lower negative electrode mixture layer, the upper negative electrode mixture layer contains more of the chelating agent than the lower negative electrode mixture layer.

Description

Negative electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

[0001] This invention relates to a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

[0002] Non-aqueous electrolyte secondary batteries are used in a variety of applications as high-capacity secondary batteries. A non-aqueous electrolyte secondary battery comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte. Various proposals have been made regarding the negative electrode of such non-aqueous electrolyte secondary batteries.

[0003] Patent Document 1 describes a negative electrode for a non-aqueous electrolyte secondary battery, wherein the negative electrode comprises a negative electrode active material, a binder, and a conductive additive, and the negative electrode active material is SiO ｘ A negative electrode for a non-aqueous electrolyte secondary battery has been proposed, comprising a silicon-based active material (A) containing (wherein x is a number satisfying 0.5 ≤ x ≤ 1.6), a carbon-based active material (B) consisting of secondary particles formed by the aggregation of primary particles, and a carbon-based active material (C) consisting of primary particles different from those of the carbon-based active material (B), wherein the average particle diameter of the metallic silicon particles contained in the silicon-based active material (A) is 0.5 nm or more and 10 nm, and the conductive additive has the shape of a wire, with a wire diameter of 1 nm or more and 4 nm or less, and a wire length of 2 μm or more and 15 μm or less.

[0004] Patent Document 1 discloses that by using the above-described negative electrode for a non-aqueous electrolyte secondary battery, the lifespan (cycle characteristics) of the non-aqueous electrolyte secondary battery, in other words, the capacity retention rate of the non-aqueous electrolyte secondary battery, can be improved.

[0005] Japanese Patent Publication No. 2024-141386

[0006] A negative electrode for a non-aqueous electrolyte secondary battery typically comprises a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. The negative electrode mixture layer includes, for example, a negative electrode active material, a binder, and a conductive additive. In the negative electrode mixture layer, conductive paths are formed by the negative electrode active materials connecting to each other via, for example, the conductive additive. In such a negative electrode mixture layer, the negative electrode active material expands during charging and contracts during discharging. Therefore, in a non-aqueous electrolyte secondary battery, the negative electrode mixture layer also repeatedly expands and contracts during charging and discharging in accordance with the expansion and contraction of the negative electrode active material.

[0007] When expansion and contraction are repeated in the negative electrode mixture layer, the conductive paths formed in the negative electrode mixture layer may disconnect, resulting in a decrease in the capacity retention rate of the non-aqueous electrolyte secondary battery. Also, due to factors such as an increase in resistance in the vicinity of the negative electrode core, the resistance of the entire negative electrode may increase

[0008] However, in any known document including Patent Document 1, sufficient consideration has not yet been given to achieving both suppression of a decrease in the capacity retention rate of the non-aqueous electrolyte secondary battery and suppression of an increase in the resistance of the negative electrode.

[0009] Therefore, an object of the present disclosure is to provide a negative electrode for a non-aqueous electrolyte secondary battery that can achieve both suppression of a decrease in the capacity retention rate and suppression of an increase in resistance of the non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery including such a negative electrode for a non-aqueous electrolyte secondary battery.

[0010] One aspect of the present invention includes a negative electrode core and a negative electrode mixture layer disposed on the surface of the negative electrode core. The negative electrode mixture layer includes a negative electrode active material and a binder component. The binder component includes a binder compound and a chelating agent. In the thickness direction of the negative electrode mixture layer, with the side closer to the negative electrode core being the lower side and the side farther from the negative electrode core being the upper side, when the layer above the central portion is the upper negative electrode mixture layer and the layer below the central portion is the lower negative electrode mixture layer, the upper negative electrode mixture layer contains more chelating agent than the lower negative electrode mixture layer, and relates to a negative electrode for a non-aqueous electrolyte secondary battery.

[0011] Another aspect of the present disclosure relates to a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is the above-described negative electrode for a non-aqueous electrolyte secondary battery.

[0012] According to the present disclosure, it is possible to provide a negative electrode for a non-aqueous electrolyte secondary battery that can achieve both suppression of a decrease in the capacity retention rate and suppression of an increase in resistance. Also, it is possible to provide a non-aqueous electrolyte secondary battery including such a negative electrode for a non-aqueous electrolyte secondary battery.

[0013] This is a schematic cross-sectional view showing an example of a negative electrode for a non-aqueous electrolyte secondary battery according to an embodiment of this disclosure. This is a schematic cross-sectional view showing another example of a negative electrode for a non-aqueous electrolyte secondary battery according to an embodiment of this disclosure. This is a schematic cross-sectional view showing a non-aqueous electrolyte secondary battery according to one embodiment of this disclosure.

[0014] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values, materials, etc. may be applied as long as the effects of this disclosure are obtained. Notwithstanding, known components may be applied to components of parts that are characteristic of this disclosure. In this specification, when "the range of numerical values ​​A to numerical values ​​B" is used, that range includes numerical values ​​A and B.

[0015] In the following explanation, when examples are given for the lower and upper limits of numerical values ​​related to specific physical properties or conditions, any combination of either of the given lower limits and any of the given upper limits is permitted, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, unless otherwise specified, one type may be selected and used alone, or two or more types may be used in combination.

[0016] This disclosure includes any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims. In other words, any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims is possible, as long as it does not result in a technical inconsistency.

[0017] [Negative electrode for non-aqueous electrolyte secondary battery] The negative electrode for a non-aqueous electrolyte secondary battery according to the embodiments of this disclosure includes a negative electrode core and a negative electrode mixture layer disposed on the surface of the negative electrode core. In the non-aqueous electrolyte secondary battery according to the embodiments of this disclosure, the negative electrode mixture layer includes a negative electrode active material and a binder component, and the binder component includes a binder compound and a chelating agent.

[0018] In the non-aqueous electrolyte secondary battery according to the embodiment of this disclosure, when the side closer to the negative electrode core is considered downward and the side further away from the negative electrode core is considered upward in the thickness direction of the negative electrode mixture layer, and the layer above the center is considered the upper negative electrode mixture layer and the layer below the center is considered the lower negative electrode mixture layer, the upper negative electrode mixture layer contains more chelating agent than the lower negative electrode mixture layer.

[0019] In the negative electrode for a non-aqueous electrolyte secondary battery according to the embodiments of this disclosure, it is important that (i) the binder component includes a binder compound and a chelating agent, and (ii) the upper negative electrode mixture layer contains more chelating agent than the lower negative electrode mixture layer. The reasons for this are explained below.

[0020] A negative electrode for a non-aqueous electrolyte secondary battery typically comprises a negative electrode core and a negative electrode mixture layer placed on the negative electrode core. The negative electrode mixture layer includes, for example, a negative electrode active material, a binder compound, and a conductive additive. In the negative electrode mixture layer, conductive paths are formed by the negative electrode active materials connecting to each other via, for example, the conductive additive. In such a negative electrode mixture layer, the negative electrode active material expands during charging and contracts during discharging. Therefore, in a non-aqueous electrolyte secondary battery, the negative electrode mixture layer also repeatedly expands and contracts during charging and discharging in accordance with the expansion and contraction of the negative electrode active material.

[0021] Repeated expansion and contraction in the negative electrode mixture layer can cause conductive paths formed within the layer to break, potentially reducing the capacity retention rate of the non-aqueous electrolyte secondary battery. When using a swelling inhibitor to suppress the expansion of the negative electrode mixture layer, it is necessary to adjust the amount of the swelling inhibitor in the negative electrode mixture layer depending on the degree of expansion. Furthermore, if the degree of expansion of the negative electrode mixture layer is small despite a high amount of swelling inhibitor, the excess swelling inhibitor in the negative electrode mixture layer may act as a resistive component. For example, the degree of expansion of the negative electrode mixture layer varies depending on the charging depth; the surface side with a deeper charging depth (higher charge) expands more, while the negative electrode core side with a shallower charging depth (lower charge) expands less. Therefore, if the amount of swelling inhibitor in the negative electrode mixture layer is adjusted considering the degree of expansion on the surface side, excess swelling inhibitor will remain on the negative electrode core side. In this case, the negative electrode for the non-aqueous electrolyte secondary battery will become highly resistive.

[0022] In the negative electrode for a non-aqueous electrolyte secondary battery according to the embodiment of this disclosure, the binder component contained in the negative electrode mixture layer includes a binder compound and a chelating agent, and the binder compound and the chelating agent typically have a structure that can form hydrogen bonds. Therefore, the binder compound and the chelating agent can bond the negative electrode active materials together while forming hydrogen bonds. Furthermore, since the bond formed by hydrogen bonds between the binder compound and the chelating agent is thought to possess both rigidity and elasticity, it is thought that the degree of expansion (swelling) of the negative electrode mixture layer during charging can be reduced. This suppresses the disconnection of conductive paths within the negative electrode mixture layer, thereby suppressing a decrease in the capacity retention rate of the non-aqueous electrolyte secondary battery caused by this. The bond formed by hydrogen bonds between the binder compound and the chelating agent corresponds to a swelling inhibitor.

[0023] Furthermore, in the negative electrode for a non-aqueous electrolyte secondary battery according to the embodiment of this disclosure, the upper negative electrode mixture layer contains more chelating agent than the lower negative electrode mixture layer. That is, in the negative electrode mixture layer, there is less chelating agent on the negative electrode core side. Therefore, it is possible to suppress the presence of excess chelating agent in the negative electrode mixture layer on the negative electrode core side, thereby suppressing the increase in resistance of the negative electrode for a non-aqueous electrolyte secondary battery.

[0024] The configuration of the negative electrode for a non-aqueous electrolyte secondary battery according to the embodiments of this disclosure will be described in more detail below with reference to the drawings.

[0025] As shown in Figure 1, the negative electrode 12 for a non-aqueous electrolyte secondary battery includes a negative electrode core 121 and a negative electrode mixture layer 122 disposed on the surface of the negative electrode core. In addition to the negative electrode active material and binder components, the negative electrode mixture layer 122 may contain other additives. Examples of other additives include conductive additives.

[0026] In the negative electrode 12 for a non-aqueous electrolyte secondary battery, when the thickness direction TD of the negative electrode mixture layer 122 is defined as the side closer to the negative electrode core 121 being downward and the side further from the negative electrode core 121 being upward, and the layer above the center being defined as the upper negative electrode mixture layer 122a and the layer below the center being defined as the lower negative electrode mixture layer 122b, the upper negative electrode mixture layer 122a contains more chelating agent than the lower negative electrode mixture layer 122b. That is, in the negative electrode mixture layer 122, there is less chelating agent present on the negative electrode core 121 side. Therefore, it is possible to suppress the presence of excess chelating agent in the negative electrode mixture layer 122 on the negative electrode core 121 side, thereby suppressing the increase in resistance of the negative electrode 12 for the non-aqueous electrolyte secondary battery.

[0027] As described above, a negative electrode mixture layer 122 in which the upper negative electrode mixture layer 122a contains more chelating agent than the lower negative electrode mixture layer 122b can be obtained using two types of negative electrode mixture slurries with different chelating agent content. Specifically, a first negative electrode mixture slurry with a high chelating agent content and a second negative electrode mixture slurry with a low chelating agent content are prepared, the second negative electrode mixture slurry is applied to the surface of the negative electrode core body 121 to form a second coating film, and then the first negative electrode mixture slurry is applied to the surface of the second coating film to form a first coating film, thereby obtaining the negative electrode mixture layer described above.

[0028] The thickness of the second coating film may be thinner than the thickness of the first coating film, the same as the thickness of the first coating film, or thicker than the thickness of the first coating film. When the thickness of the second coating film is the same as the thickness of the first coating film, a lower negative electrode mixture layer 122b, composed of the second coating film, exists below the center of the thickness direction TD of the negative electrode mixture layer 122, and an upper negative electrode mixture layer 122a, composed of the first coating film, exists above the center of the thickness direction TD of the negative electrode mixture layer 122. When the thickness of the second coating film is thinner than the thickness of the first coating film, a lower negative electrode mixture layer 122b, composed of the second coating film and a part of the first coating film, exists below the center of the thickness direction TD of the negative electrode mixture layer 122, and an upper negative electrode mixture layer 122a, composed of the remaining part of the first coating film, exists above the center of the thickness direction TD of the negative electrode mixture layer 122. Furthermore, if the thickness of the second coating is greater than the thickness of the first coating, a lower negative electrode mixture layer 122b, composed of a portion of the second coating, exists below the center of the thickness direction TD of the negative electrode mixture layer 122, and an upper negative electrode mixture layer 122a, composed of the remainder of the second coating and the first coating, exists above it. In either of the above cases, the lower negative electrode mixture layer 122b contains at least a portion of the second coating which has a low chelating agent content, and the upper negative electrode mixture layer 122a contains at least a portion of the first coating which has a high chelating agent content. Therefore, the amount of chelating agent contained in the upper negative electrode mixture layer 122a is greater than the amount of chelating agent contained in the lower negative electrode mixture layer 122b.

[0029] As shown in Figure 2, the negative electrode mixture layer 122 includes a second negative electrode mixture layer 1222 disposed on the surface of the negative electrode core 121 and a first negative electrode mixture layer 1221 disposed on the surface of the second negative electrode mixture layer 1222. Preferably, the ratio of the thickness T1 of the first negative electrode mixture layer 1221 to the total thickness Tt of the negative electrode mixture layer 122 is 10% or more and 50% or less, and the ratio of the thickness T2 of the second negative electrode mixture layer 1222 to the total thickness Tt of the negative electrode mixture layer 122 is 50% or more and 90% or less. Preferably, the second negative electrode mixture layer 1222 is formed using the above-mentioned second negative electrode mixture slurry (a negative electrode mixture slurry with a low chelating agent content), and preferably, the first negative electrode mixture layer 1221 is formed using the above-mentioned first negative electrode mixture slurry (a negative electrode mixture slurry with a high chelating agent content).

[0030] As the negative electrode active material, a material that reversibly intercepts and releases lithium ions can be used. Examples of such materials include carbonaceous materials and silicon-containing materials.

[0031] Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). One type of carbonaceous material may be used alone, or two or more types may be used in combination. Graphite is preferred as the carbonaceous material due to its excellent charge-discharge stability and low irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0032] Examples of silicon-containing materials include silicon oxide, silicon, and composite materials. A composite material may contain at least one phase selected from the group consisting of a carbon phase, a lithium silicate phase, a silicon phase, and a silicon oxide phase. One example of a composite material may contain a carbon phase and particulate silicon phase dispersed in the carbon phase. Another example of a composite material may contain a lithium silicate phase and particulate silicon phase dispersed in the lithium silicate phase.

[0033] The negative electrode 12 for a non-aqueous electrolyte secondary battery preferably contains artificial graphite as the negative electrode active material. Furthermore, if the negative electrode mixture layer 122 includes a second negative electrode mixture layer 1222 disposed on the surface of the negative electrode core body 121 and a first negative electrode mixture layer 1221 disposed on the surface of the second negative electrode mixture layer 1222, it is preferable that the first negative electrode mixture layer 1221 contains at least one of artificial graphite and a silicon-containing material as the negative electrode active material. Among the negative electrode active materials, artificial graphite and silicon-containing materials have high hardness. Therefore, as will be described later, even if the negative electrode mixture layer 122 (a laminate of the first negative electrode mixture layer 1221 and the second negative electrode mixture layer 1222) is formed by rolling, the voids formed between these active materials are not easily crushed, so the porosity of the first negative electrode mixture layer 1221 can be increased. This improves the liquid flow of the non-aqueous electrolyte in the first negative electrode mixture layer 1221.

[0034] High-hardness negative electrode active materials, such as graphite and silicon-containing materials, may have a Vickers hardness of 300 Hv or higher, or 500 Hv or higher. The Vickers hardness may be 1000 Hv or lower, or 700 Hv or lower. The Vickers hardness is measured by embedding the negative electrode active material in a thermosetting resin and exposing the cross-section of the negative electrode active material with 400-grit abrasive paper. Furthermore, the cross-section is polished to a mirror finish using 2000-grit abrasive paper. The Vickers hardness of the polished cross-section is measured using a Vickers hardness tester with a load of 1 kg and a holding time of 15 seconds.

[0035] When the porosity of the first negative electrode mixture layer 1221 is ε1%, it is preferable that ε1 satisfies the relationship 5 < ε1 ≤ 30. By satisfying this relationship, the liquid flow of the non-aqueous electrolyte can be improved in the first negative electrode mixture layer 1221. Furthermore, if the porosity ε1 is within the above range, an appropriate amount of binder compound and chelating agent bonded by hydrogen bonding can be inserted into the voids of the first negative electrode mixture layer 1221, thereby sufficiently suppressing the expansion of the first negative electrode mixture layer 1221.

[0036] When the porosity of the second negative electrode mixture layer 1222 is ε2%, it is preferable that the relationship ε1 and ε2 satisfy ε2 < ε1. By satisfying this relationship, it is possible to suppress the excess chelating agent contained in the second negative electrode mixture layer 1222. Therefore, since it is possible to suppress the presence of excess chelating agent in the negative electrode mixture layer 122 on the negative electrode core body 121 side, it is possible to suppress the increase in resistance of the negative electrode 12 for the non-aqueous electrolyte secondary battery. Furthermore, it is possible to suppress the decrease in the capacity retention rate of the non-aqueous electrolyte secondary battery. In addition, from the viewpoint of ensuring a certain degree of liquid flowability in the second negative electrode mixture layer 1222, it is preferable that the porosity ε2 of the second negative electrode mixture layer 1222 is 1 < ε2 ≤ 30.

[0037] The porosity ε1 of the first anode mixture layer 1221 and the porosity ε2 of the second anode mixture layer 1222 can be adjusted by using multiple anode active materials with different hardnesses and then adjusting the mass ratio of these multiple anode active materials. Among the anode active materials, artificial graphite and silicon-containing materials have high hardness, so by using such hard anode active materials, the values ​​of porosity ε1 and ε2 can be increased. On the other hand, among the anode active materials, natural graphite has low hardness, so by using such low hardness anode active materials, the values ​​of porosity ε1 and ε2 can be decreased. Then, by including a hard anode active material and a low hardness anode active material in an appropriate mass ratio in the first anode mixture layer 1221 and the second anode mixture layer 1222, respectively, the porosity ε1 and ε2 can be adjusted to the desired values.

[0038] When the first negative electrode mixture layer 1221 contains at least one of artificial graphite and silicon-containing material as the negative electrode active material, it is preferable that a1 and b1 satisfy the relationship 0 ≤ a1 ≤ 90 and 10a1 + b1 ≥ 80, where a1 and b1 are the total negative electrode active material (100% by mass), the mass ratio of the silicon-containing material to the total negative electrode active material (a1% by mass), and the mass ratio of the artificial graphite to the total negative electrode active material (b1% by mass). By including the silicon-containing material and artificial graphite in the first negative electrode mixture layer 1221 in such a way that satisfies the above relationship, the decrease in the capacity retention rate of the non-aqueous electrolyte secondary battery can be further sufficiently suppressed.

[0039] In the negative electrode 12 for a non-aqueous electrolyte secondary battery, the porosity ε1 of the first negative electrode mixture layer 1221 and the porosity ε2 of the second negative electrode mixture layer 1222 are two-dimensional values ​​obtained from the ratio of the area of ​​voids to the cross-sectional area of ​​each region in the cross-sections of the first negative electrode mixture layer 1221 and the second negative electrode mixture layer 1222, respectively. The porosity ε1 of the first negative electrode mixture layer 1221 can be measured according to the following procedure. The porosity ε2 of the second negative electrode mixture layer 1222 can also be measured by replacing the first negative electrode mixture layer 1221 with the second negative electrode mixture layer 1222 and replacing the porosity ε1 with the porosity ε2 in the following procedure. The first negative electrode mixture layer 1221 and the second negative electrode mixture layer 1222 can be distinguished by differences in the size of voids in the cross-section of the negative electrode mixture layer 122. Furthermore, reference numbers will not be assigned to the negative electrode mixture layer and other components below.

[0040] (1) Disassemble the battery to be evaluated and cut out the negative electrode to expose the cross-section of the negative electrode mixture layer. One method for exposing the cross-section is to cut out a part of the negative electrode and process it with an ion milling device (for example, Hitachi High-Tech Corporation's IM4000PLUS) to expose the cross-section of the negative electrode mixture layer. Then, in the negative electrode mixture layer, the formation region of the first negative electrode mixture layer is determined by differences in the size of the voids. (2) Using a SEM, backscattered electron images of the exposed cross-section of the first negative electrode mixture layer are taken for each region of the first negative electrode mixture layer. The magnification when taking the backscattered electron images is, for example, 800x. The following processes (3) and (4) are performed for each region of the first negative electrode mixture layer and the void ratio of each is calculated. (3) The cross-sectional image obtained in (2) above is imported into a computer and binarized using image analysis software (for example, ImageJ from the National Institutes of Health, USA) to obtain a binarized image in which the particle cross-sections in the cross-sectional image are converted to black and the voids present in the particle cross-sections are converted to white. (4) In the binarized image obtained in (3) above, the area of ​​the voids is calculated by excluding the voids inside the particles (pores not connected to the particle surface) and pores with a width of 3 μm or less that are connected to the particle surface from the voids converted to white. The porosity ε is calculated based on the following formula: Porosity ε1 (%) = Area of ​​voids / Area of ​​each region in the cross-section of the first negative electrode mixture layer × 100 (5) The calculation of the porosity by (3) and (4) above is performed three times, and the arithmetic mean of the three calculated values ​​is taken as the porosity ε1 of the first negative electrode mixture layer.

[0041] The binder compound included in the binder component is preferably a compound that binds to the chelating agent. Examples of such bonds include covalent bonds, ionic bonds, and hydrogen bonds, but hydrogen bonds are preferred. The binder compound preferably contains at least one selected from the group consisting of polyacrylic acid and salts of polyacrylic acid. Examples of cations constituting the salt of a salt of polyacrylic acid include lithium ions, sodium ions, potassium ions, and ammonium ions. The weight-average molecular weight of the binder compound may be in the range of 5,000 to 5,000,000 or in the range of 100,000 to 1,000,000.

[0042] The chelating agent contained in the binder component preferably contains at least one functional group selected from the group consisting of carboxylic acid groups, carboxylic acid bases, phosphonic acid groups, and phosphonic acid bases. Examples of cations constituting the salt in carboxylic acid bases and phosphonic acid bases include lithium ions, sodium ions, potassium ions, and ammonium ions. The chelating agent preferably contains at least one selected from the group consisting of ethylenediamine derivatives, bisphosphonate derivatives, and inositol derivatives. Examples of ethylenediamine derivatives include the compound shown in the following chemical formula (1), examples of bisphosphonate derivatives include the compound shown in the following chemical formula (2), and examples of inositol derivatives include the compound shown in the following chemical formula (3).

[0043]

[0044]

[0045]

[0046] When the negative electrode mixture layer 122 includes a second negative electrode mixture layer 1222 disposed on the surface of the negative electrode core 121 and a first negative electrode mixture layer 1221 disposed on the surface of the second negative electrode mixture layer 1222, in the first negative electrode mixture layer 1221, when the content of the binder compound is Wp1 and the content of the chelating agent is Wc1, and in the second negative electrode mixture layer 1222, when the content of the binder compound is Wp2 and the content of the chelating agent is Wc2, it is preferable that Wp1, Wc1, Wp2, and Wc2 satisfy the relationship of 0 ≦ Wc2 / Wp2 < Wc1 / Wp1 ≦ 0.75. When the relationship of 0 ≦ Wc2 / Wp2 < Wc1 / Wp1 is satisfied, the amount of the chelating agent present in the vicinity of the negative electrode core 121 can be reduced, so that an increase in the resistance of the entire negative electrode 12 for a non-aqueous electrolyte secondary battery can be suppressed. Further, when the relationship of Wc2 / Wp2 < Wc1 / Wp1 ≦ 0.75 is satisfied, in the first negative electrode mixture layer 1221, a conjugate formed by hydrogen bonding between the binder compound and the chelating agent can be sufficiently formed, so that a decrease in the capacity retention rate of the non-aqueous electrolyte secondary battery can be suppressed.

[0047] The binder component may contain a polyvalent cation. When the binder component contains a polyvalent cation, when the chelating agent is a phosphorus-containing compound as represented by the above chemical formulas (2) and (3), the phosphorus-containing compounds can be linked via the polyvalent cation. Also by this, the expansion of the negative electrode mixture layer can be suppressed. The polyvalent cation may be included in the binder component by, for example, including the polyvalent cation in the non-aqueous electrolyte and allowing this polyvalent cation to penetrate into the negative electrode mixture layer.

[0048] The polyvalent cation is a cation having a valence of 2 or more. Examples of the polyvalent cation include divalent cations, trivalent cations, and tetravalent cations. The polyvalent cation is Ca ２＋ , Mg ２＋ , Ba ２＋ , Ge ２＋ , Cu ２＋ , Ni ２＋ , Co ２＋ , Sn ２＋ , Sr ２＋ , Zn ２＋ , Pd ２＋ , Pt２＋ Mn ２＋ Mn ３＋ Ti ３＋ , Nb ３＋ , Bi ３＋ Ce ３＋ , Cr ３＋ La ３＋ In ３＋ , Rh ３＋ Sb ３＋ Sm ３＋ , Dy ３＋ , Eu ３＋ Mn ３＋ Fe ３＋ Al ３＋ , Hf ４＋ , Zr ４＋ , and, Th ４＋ It may include at least one selected from the group consisting of the above. The polyvalent cation may be any one selected from the above group.

[0049] The polyvalent cation may contain a divalent cation or may be a divalent cation only. Divalent cations are thought to readily and stably bond with other phosphorus-containing compounds. The polyvalent cation is Ca ２＋ Mg ２＋ , and Sr ２＋ It may include at least one selected from the group consisting of the following. The polyvalent cation is Ca ２＋ It may also be Mg ２＋ It may also be Sr ２＋ That's fine.

[0050] Conductive carbon materials can be used as conductive additives. Examples of conductive carbon materials include carbon black, carbon nanotubes, and graphite.

[0051] [Non-aqueous electrolyte secondary battery] A non-aqueous electrolyte secondary battery according to an embodiment of this disclosure comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte. In the non-aqueous electrolyte secondary battery according to an embodiment of this disclosure, the negative electrode is a negative electrode for a non-aqueous electrolyte secondary battery according to an embodiment of this disclosure. In addition to the positive electrode, negative electrode, and non-aqueous electrolyte, the non-aqueous electrolyte secondary battery according to an embodiment of this disclosure may also include a separator interposed between the positive electrode and the negative electrode, and an outer casing. Examples of non-aqueous electrolyte secondary batteries include lithium-ion secondary batteries and lithium metal secondary batteries. The components other than the negative electrode will be described below.

[0052] (Positive electrode) The positive electrode includes a positive electrode mixture layer. The positive electrode may also include a positive electrode current collector (positive electrode core) and a positive electrode mixture layer disposed on the positive electrode current collector. The positive electrode current collector and the positive electrode mixture layer are not particularly limited, and those used in the positive electrodes of various known non-aqueous electrolyte secondary batteries may be used.

[0053] Examples of materials that constitute the positive electrode current collector include metallic materials such as Al, Ti, and Fe. The metallic material may also be Al, Al alloy, Ti, Ti alloy, and Fe alloy. The Fe alloy may be stainless steel (SUS).

[0054] The positive electrode mixture layer contains a positive electrode active material. As the positive electrode active material, a substance that reversibly intercepts and releases lithium ions can be used. Examples of positive electrode active materials include composite oxides containing lithium and a metal element other than lithium (Me), transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. The composite oxide containing lithium and the metal element Me may be a lithium-containing transition metal oxide containing at least a transition metal as the metal element Me. Because it has low manufacturing costs and a high average discharge voltage, it is preferable to use a lithium-containing transition metal oxide as the positive electrode active material.

[0055] Examples of transition metal elements included in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. A lithium-containing transition metal oxide may contain one transition metal element or two or more transition metal elements. Preferably, a lithium-containing transition metal oxide contains at least one element selected from the group consisting of Ni, Co, Mn, and Al.

[0056] The positive electrode mixture layer may contain additives other than the positive electrode active material. Examples of additives include binder compounds (binding agents) and conductive materials. Examples of binder compounds include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluororesins include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF). Conductive materials can be conductive carbon materials. Examples of conductive carbon materials include carbon black, carbon nanotubes, and graphite.

[0057] (Separator) As the separator, a porous sheet having ion permeability and insulating properties can be used. As the porous sheet, for example, a thin film, woven fabric, and nonwoven fabric having microporous properties can be used. The material constituting the separator is not particularly limited, and for example, polymer materials can be used. Examples of polymer materials include polyolefin resins, polyamide resins, and cellulose. Examples of polyolefin resins include polyethylene resins, polypropylene resins, and copolymers of ethylene and propylene. The separator may contain additives (such as inorganic fillers) as needed. The thickness of the separator is not particularly limited and may be 10 μm or more, or 15 μm or more. The thickness of the separator may be 30 μm or less, or 20 μm or less.

[0058] (Non-aqueous electrolyte) As the non-aqueous electrolyte, a non-aqueous electrolyte having lithium ion conductivity can be used. The non-aqueous electrolyte contains a non-aqueous solvent and ions dissolved in the non-aqueous solvent. Examples of ions include lithium ions and anions. The non-aqueous electrolyte may be in liquid or gel form.

[0059] Non-aqueous electrolytes can be prepared by dissolving lithium salts in a non-aqueous solvent. By dissolving lithium salts in a non-aqueous solvent, lithium ions and anions can be generated. Furthermore, by dissolving salts of polyvalent cations in a non-aqueous solvent, polyvalent cations and anions can also be generated.

[0060] Examples of lithium salts include lithium salts of chlorine-containing acids (e.g., LiClO ４ LiAlCl ４ , and LiB １０ Cl １０ (e.g., lithium salts of fluorine-containing acids (e.g., LiPF)) ６ LiPF ２ O ２ LiBF ４ LiSbF ６ LiAsF ６ LiCF ３ SO ３ , and LiCF ３ CO ２ (e.g., lithium salts of fluorine-containing acidimides (e.g., LiN(FSO)) ２ ) ２ ,LiN(CF ３ SO ２ ) ２ ,LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ), and LiN(C ２ F ５ SO ２ ) ２Examples include lithium halides (e.g., LiCl, LiBr, and LiI). The lithium salt may be used alone or in combination of two or more types. The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less.

[0061] Non-aqueous electrolytes may be substantially free of chloride ions. For example, the concentration of chloride ions in a non-aqueous electrolyte may be less than 0.001 mol / L or less than 0.0001 mol / L. Non-aqueous electrolytes that are substantially free of chloride ions are preferable in that they substantially do not generate chlorine-based gases derived from chloride ions during the charging and discharging process. Non-aqueous electrolytes that are substantially free of chloride ions can be prepared by using salts that do not contain the element chlorine.

[0062] The non-aqueous solvent is not particularly limited, and various known non-aqueous solvents can be used. Examples of non-aqueous solvents include cyclic carbonate esters, linear carbonate esters, cyclic carboxylic acid esters, and linear carboxylic acid esters. Examples of cyclic carbonate esters include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC). Examples of linear carbonate esters include dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone. Examples of linear carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, and ethyl propionate. The non-aqueous solvent may be used alone or in combination of two or more types.

[0063] The non-aqueous electrolyte may contain various known additives. Examples of additives include 1,3-propanesalton, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene. Cyclic carbonate esters such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC), which were exemplified as solvents, may also be used as additives.

[0064] (Outer casing) Various known outer casings (battery cases) can be used. The outer casing may include an outer can and a sealing body that seals the opening of the outer can. In this case, the outer can functions as the negative terminal, and the sealing body functions as the positive terminal. The sealing body may include a sealing plate and a gasket.

[0065] The outer casing (battery case) houses the electrode group and the non-aqueous electrolyte. The electrode group consists of a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes. The configuration of the electrode group is not particularly limited. The electrode group may be wound or laminated. A wound electrode group is formed by winding a laminate of a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes. The form of the non-aqueous electrolyte secondary battery is not particularly limited. The form of the non-aqueous electrolyte secondary battery may be cylindrical, prismatic, coin-shaped, button-shaped, or laminated.

[0066] Hereinafter, an example of a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure will be described with reference to the drawings. The components of the example described below can be the components described above. Furthermore, the components of the example described below can be modified based on the above description. In addition, the matters described below may be applied to the above embodiment. Furthermore, in the example described below, components that are not essential to the non-aqueous electrolyte secondary battery according to the present disclosure may be omitted.

[0067] Figure 1 is a schematic longitudinal cross-sectional view showing a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure. The non-aqueous electrolyte secondary battery 10 shown in Figure 1 has a cylindrical shape. The non-aqueous electrolyte secondary battery 10 includes a cylindrical battery case and an electrode group 14 and a non-aqueous electrolyte (not shown) housed within the battery case. The electrode group 14 is a wound electrode group and includes a positive electrode 11, a negative electrode 12, and a separator 13 interposed between the positive electrode 11 and the negative electrode 12. The wound electrode group is formed by winding a laminate of the positive electrode 11, the negative electrode 12, and the separator 13.

[0068] The battery case includes a case body 15, which is a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the case body 15. A gasket 27 is placed between the case body 15 and the sealing body 16. The placement of the gasket 27 ensures that the battery case is airtight. Inside the case body 15, insulating plates 17 and 18 are placed at both ends of the electrode group 14 in the direction of the winding axis, respectively. The case body 15 has a stepped portion 21.

[0069] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. The lower valve body 23 and the upper valve body 25 are connected at their respective centers. The insulating member 24 is positioned between the peripheral edge of the lower valve body 23 and the peripheral edge of the upper valve body 25. The filter 22 and the lower valve body 23 are connected at their respective peripheral edges. The upper valve body 25 and the cap 26 are connected at their respective peripheral edges. Of the components of the sealing body 16, all components except the insulating member 24 are electrically connected.

[0070] The lower valve body 23 has a ventilation hole. Therefore, if the internal pressure of the battery case rises due to abnormal heat generation or other reasons, the upper valve body 25 bulges towards the cap 26 and separates from the lower valve body 23. This disconnects the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures, and gas is released through the opening formed in the cap 26.

[0071] The positive electrode 11 is electrically connected to the cap 26, which functions as a positive electrode terminal, via the positive electrode lead 19. The negative electrode 12 is electrically connected to the case body 15, which functions as a negative electrode terminal, via the negative electrode lead 20. The negative electrode 12 is the negative electrode for a non-aqueous electrolyte secondary battery according to the embodiment of this disclosure.

[0072] [Method for Manufacturing a Non-Aqueous Electrolyte Secondary Battery] A method for manufacturing a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure will be described below. In the following, an example will be described in which the negative electrode includes a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, and a separator is interposed between the negative electrode and the positive electrode. Furthermore, in the following, a case will be described in which the negative electrode mixture layer includes a second negative electrode mixture layer disposed on the surface of the negative electrode core and a first negative electrode mixture layer disposed on the surface of the second negative electrode mixture layer.

[0073] (First step) The first step includes a first substep for manufacturing a negative electrode, a second substep for manufacturing a positive electrode, and a third substep for manufacturing an electrode group by interposing a separator between the positive electrode and the negative electrode.

[0074] In the first substep, a negative electrode mixture containing a negative electrode active material and a binder component is mixed with a dispersion medium to prepare a negative electrode mixture slurry. As the dispersion medium, for example, water, alcohol (e.g., ethanol), ether (e.g., tetrahydrafuran), N-methyl-2-pyrrolidone (NMP), or a mixture thereof can be used. The negative electrode active material preferably contains at least one of artificial graphite and a silicon-containing material. The negative electrode mixture may optionally contain other substances besides the negative electrode active material and binder component. As negative electrode mixture slurries, a first negative electrode mixture slurry with a high chelating agent content and a second negative electrode mixture slurry with a low chelating agent content are prepared.

[0075] Next, a second negative electrode mixture slurry is applied to the negative electrode core to obtain a second coating film, and then a first negative electrode mixture slurry is applied to this second coating film to obtain a first coating film. After that, the laminate of the first and second coating films is dried. This yields a laminate containing a negative electrode core, a second negative electrode mixture layer placed on the surface of the negative electrode core, and a first negative electrode mixture layer placed on the surface of the second negative electrode mixture layer. Next, the negative electrode is manufactured by rolling this laminate. After rolling, the thickness of the negative electrode mixture layer (first negative electrode mixture layer + second negative electrode mixture layer) may be 3 μm or more, or 5 μm or more. The thickness of the negative electrode mixture layer may be 200 μm or less, or 150 μm or less. The negative electrode may be cut to a predetermined size as needed. The negative electrode mixture layer may be formed on only one side of the negative electrode current collector, or on both sides.

[0076] The second substep can be carried out in the same manner as the first substep, except that a positive electrode slurry is used instead of a negative electrode slurry, and a positive electrode core is used instead of a negative electrode core. The positive electrode slurry contains a positive electrode active material, a binder compound (binding agent), and a conductive material as the positive electrode slurry, and further contains a dispersion medium. As the dispersion medium, those exemplified in the first substep can be used.

[0077] In the third substep, as described above, an electrode group is fabricated by interposing a separator between the positive and negative electrodes. The electrode group may be of the wound type or the stacked type. A wound electrode group is fabricated by winding the positive electrode, negative electrode, and separator together. A stacked electrode group is fabricated by stacking one or more flat positive electrodes, one or more flat negative electrodes, and one or more flat separators so that their main surfaces overlap. In both the wound and stacked electrode groups, a separator is interposed between the positive and negative electrodes.

[0078] (Second Step) In the second step, the electrode group and the non-aqueous electrolyte are housed inside the outer casing. The method for housing the electrode group and the non-aqueous electrolyte inside the outer casing is not particularly limited, and various known methods can be employed. The non-aqueous electrolyte can be prepared, for example, by dissolving predetermined components (salts, additives, etc.) in a non-aqueous solvent. The outer casing is not particularly limited, and various known outer casings can be used.

[0079] (Note) The following technologies are disclosed by the above description. (Technology 1) A negative electrode for a non-aqueous electrolyte secondary battery, comprising a negative electrode core and a negative electrode mixture layer disposed on the surface of the negative electrode core, wherein the negative electrode mixture layer comprises a negative electrode active material and a binder component, the binder component comprises a binder compound and a chelating agent, and in the thickness direction of the negative electrode mixture layer, the side closer to the negative electrode core is considered downward, the side further away from the negative electrode core is considered upward, the layer above the center is considered the upper negative electrode mixture layer, and the layer below the center is considered the lower negative electrode mixture layer, wherein the upper negative electrode mixture layer contains more chelating agent than the lower negative electrode mixture layer. (Technology 2) The negative electrode for a non-aqueous electrolyte secondary battery according to Technology 1, wherein the binder compound comprises at least one selected from the group consisting of polyacrylic acid and salts of polyacrylic acid. (Technology 3) The negative electrode for a non-aqueous electrolyte secondary battery according to Technology 1 or 2, wherein the chelating agent comprises at least one functional group selected from the group consisting of a carboxylic acid group, a carboxylic acid base, a phosphonic acid group, and a phosphonic acid base. (Technology 4) The negative electrode for a non-aqueous electrolyte secondary battery according to any one of Technology 1 to 3, wherein the chelating agent comprises at least one selected from the group consisting of an ethylenediamine derivative, a bisphosphonate derivative, and an inositol derivative. (Technology 5) The negative electrode for a non-aqueous electrolyte secondary battery according to any one of Technology 1 to 4, wherein the negative electrode active material comprises artificial graphite. (Technical 6) The negative electrode for a non-aqueous electrolyte secondary battery according to any one of Technical 1 to 5, wherein the negative electrode mixture layer comprises a second negative electrode mixture layer disposed on the surface of the negative electrode core and a first negative electrode mixture layer disposed on the surface of the second negative electrode mixture layer, the ratio of the thickness of the first negative electrode mixture layer to the thickness of the negative electrode mixture layer is 10% or more and 50% or less, and the ratio of the thickness of the second negative electrode mixture layer to the thickness of the negative electrode mixture layer is 50% or more and 90% or less. (Technical 7) When the porosity of the first negative electrode mixture layer is ε1%, ε1 satisfies the relationship 5 < ε1 ≤ 30. (Technical 8) When the porosity of the second negative electrode mixture layer is ε2%, ε1 and ε2 satisfy the relationship ε2 < ε1.(Technical 9) The first negative electrode mixture layer comprises at least one of artificial graphite and a silicon-containing material as the negative electrode active material, and when the total amount of the negative electrode active material is 100% by mass, the mass ratio of the silicon-containing material to the total amount of the negative electrode active material is a1% by mass, and the mass ratio of the artificial graphite to the total amount of the negative electrode active material is b1% by mass, then a1 and b1 satisfy the relationship 0 ≤ a1 ≤ 90 and 10a1 + b1 ≥ 80, the negative electrode for a non-aqueous electrolyte secondary battery according to any one of Technical 6 to 8. (Technology 10) A negative electrode for a non-aqueous electrolyte secondary battery according to any one of Technologies 6 to 9, wherein in the first negative electrode mixture layer, the content of the binder compound is Wp1 and the content of the chelating agent is Wc1, and in the second negative electrode mixture layer, the content of the binder compound is Wp2 and the content of the chelating agent is Wc2, such that Wp1, Wc1, Wp2, and Wc2 satisfy the relationship 0 ≤ Wc2 / Wp2 < Wc1 / Wp1 ≤ 0.75. (Technology 11) A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is a negative electrode for a non-aqueous electrolyte secondary battery according to any one of Technologies 1 to 10.

[0080] The present disclosure will be described below in detail based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0081] (Example 1) (1) Preparation of the negative electrode A first negative electrode slurry was prepared by mixing the negative electrode active material, polyacrylic acid (PAA), styrene-butadiene copolymer rubber (SBR), carboxymethylcellulose (CMC), carbon nanotubes (CNT), ethylenediaminetetraacetic acid (EDTA), and an appropriate amount of water. The negative electrode active material contained silicon-containing material, natural graphite, and artificial graphite. Silicon-carbon composite particles (GSS manufactured by Giga Solar Materials) were used as the silicon-containing material. The mass ratio of these materials was silicon-containing material:natural graphite:artificial graphite = 10:45:45. In the first negative electrode mixture slurry, the mass ratio of the negative electrode active material, PAA, SBR, CMC, CNT, and EDTA was set to negative electrode active material:PAA:SBR:CMC:CNT:EDTA = 100:1:1:1:0.1:0.5.

[0082] The second anode mixture slurry was prepared in the same manner as the first anode mixture slurry, except that the anode active material ratio was set to PAA:SBR:CMC:CNT:EDTA = 100:1:1:1:0.1:0.3.

[0083] A second negative electrode mixture slurry was applied to one side of an electrolytic copper foil (core) to form a second coating film. Then, a first negative electrode mixture slurry was applied on the second coating film to form a first coating film, thereby obtaining a laminate in which the electrolytic copper foil, the second coating film, and the first coating film were laminated in this order. Next, this laminate was punched out to a predetermined size (2 cm x 2 cm) and then dried. In this way, a negative electrode was obtained in which the second negative electrode mixture layer and the first negative electrode mixture layer were laminated on the electrolytic copper foil in this order. The ratio of the thickness of the first negative electrode mixture layer to the thickness of the negative electrode mixture layer was 50%, and the ratio of the thickness of the second negative electrode mixture layer to the thickness of the negative electrode mixture layer was also 50%. Furthermore, regarding the negative electrode according to Example 1, the porosity ε1 of the first negative electrode mixture layer and the porosity ε2 of the second negative electrode mixture layer were measured according to the method described in the above section on embodiments, and the ratio of the porosity ε1 to the porosity ε2 (porosity ratio) was found to be 1.0.

[0084] (2) Fabrication of the counter electrode A lithium metal foil was attached to one side of an electrolytic copper foil (current collector), and then the counter electrode was fabricated by punching out a square shape with sides of 2.5 cm. Leads were also attached to the counter electrode.

[0085] (3) Preparation of non-aqueous electrolyte Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:EMC:DMC = 4:1:15 to obtain a non-aqueous solvent. LiPF ６ It was dissolved at a concentration of 1.3 mol / L. In this way, a non-aqueous electrolyte was prepared.

[0086] (4) Test cell assembly An electrode group was fabricated by arranging the negative electrode and counter electrode prepared as described above opposite each other via a separator. A microporous film made of polyolefin was used as the separator. Next, the electrode group was housed inside an outer casing. An outer casing made of aluminum laminate sheet was used. Next, the non-aqueous electrolyte prepared as described above was injected into the inside of the outer casing, and then the opening of the outer casing was sealed. At this time, a portion of the lead attached to the negative electrode and a portion of the lead attached to the counter electrode were exposed from the outer casing. In this way, the test cell according to Example 1 was fabricated.

[0087] (Example 2) A test cell according to Example 2 was prepared in the same manner as in Example 1, except that the mass ratio of silicon-containing material, natural graphite, and artificial graphite in the first negative electrode mixture slurry was changed to silicon-containing material:natural graphite:artificial graphite = 10:90:0. The void ratio (void ratio ε1 / void ratio ε2) of the negative electrode according to Example 2 was found to be 0.8. The void ratios ε1 and ε2 were measured according to the method described in the above embodiment section.

[0088] (Example 3) A test cell according to Example 3 was prepared in the same manner as in Example 1, except that the mass ratio of silicon-containing material, natural graphite, and artificial graphite in the second negative electrode mixture slurry was changed to silicon-containing material:natural graphite:artificial graphite = 10:90:0. The void ratio (void ratio ε1 / void ratio ε2) of the negative electrode according to Example 3 was found to be 1.2. The void ratios ε1 and ε2 were measured according to the method described in the above embodiment section.

[0089] (Comparative Example 1) A test cell according to Comparative Example 1 was prepared in the same manner as in Example 1, except that the composition of each component of the second negative electrode mixture slurry was the same as that of the first negative electrode mixture slurry. The void ratio (void ratio ε1 / void ratio ε2) of the negative electrode according to Comparative Example 1 was found to be 1.0. The void ratios ε1 and ε2 were measured according to the method described in the above embodiment section.

[0090] (Comparative Example 2) A test cell according to Comparative Example 2 was prepared in the same manner as in Example 1, except that the composition of each component of the first negative electrode mixture slurry was swapped with the composition of each component of the second negative electrode mixture slurry. The void ratio (void ratio ε1 / void ratio ε2) of the negative electrode according to Comparative Example 2 was found to be 1.0. The void ratios ε1 and ε2 were measured according to the method described in the above embodiment section.

[0091] (Comparative Example 3) A test cell according to Comparative Example 3 was prepared in the same manner as in Example 2, except that the amount of EDTA in the second negative electrode mixture slurry was 0.5 parts by mass per 100 parts by mass of negative electrode active material. The void ratio (void ratio ε1 / void ratio ε2) of the negative electrode according to Comparative Example 3 was found to be 0.8. The void ratios ε1 and ε2 were measured according to the method described in the above embodiment section.

[0092] (Comparative Example 4) A test cell according to Comparative Example 4 was prepared in the same manner as in Example 3, except that the amount of EDTA in the second negative electrode mixture slurry was 0.5 parts by mass per 100 parts by mass of negative electrode active material. The void ratio (porosity ε1 / porosity ε2) of the negative electrode according to Comparative Example 4 was found to be 1.2. The void ratios ε1 and ε2 were measured according to the method described in the above embodiment section.

[0093] [Evaluation] (Initial Capacity) The non-aqueous electrolyte secondary batteries according to each example (Examples 1 to 11 and Comparative Examples 1 to 5) were left in an environment of 25°C, and constant current charging was performed with a current of 0.5 It until the voltage reached 4.2 V. Then, constant voltage charging was performed with a constant voltage of 4.2 V until the current reached 0.02 It. Next, constant current discharge was performed with a current of 1.0 It until the voltage reached 2.5 V. The discharge capacity during the first discharge performed in this manner was defined as the initial capacity C. ０ This was the request.

[0094] (Capacity Retention Rate) After the initial discharge, the non-aqueous secondary batteries for each example were left for 20 minutes, and then the charge-discharge cycle was repeated 300 times. In the charge-discharge cycle, (1) constant current charging was performed with a current of 1.0 It until the voltage reached 4.2 V, followed by constant voltage charging at a constant voltage of 4.2 V until the current reached 0.02 It, and (2) constant current discharge was performed with a current of 1.0 It until the voltage reached 2.5 V, and this was repeated.

[0095] After repeating the charge-discharge cycle 300 times, the discharge capacity at the 300th discharge is defined as discharge capacity C. ３００ It was measured as follows. The obtained initial capacity C ０ and discharge capacity C ３００ Using the following formula (1), the capacity retention rate X (%) was calculated. Note that the capacity retention rate of the non-aqueous electrolyte secondary battery in each example was determined as a relative value when the capacity retention rate X of the non-aqueous electrolyte secondary battery in Comparative Example 1 was set to 100. • Capacity retention rate X (%) = (C ３００ / C ０ ) × 100 ... (1)

[0096] (DC Resistance (DCR)) For each example of the non-aqueous electrolyte secondary battery, the battery was charged with a constant current of 0.3 It at a temperature of 25°C until the voltage reached 4.1 V, and then charged with a constant voltage of 4.1 V until the current reached 0.05 It. Next, it was discharged with a constant current of 0.3 It for 100 minutes to bring the State of Charge (SOC) to 50%.

[0097] Then, for a battery with an SOC of 50%, the DCR was determined by ΔV / I when discharged at a constant current (0.5It) for a predetermined time (10s). The DCR of the non-aqueous electrolyte secondary battery in each example was determined as a relative value with the DCR of the non-aqueous electrolyte secondary battery in Comparative Example 1 set to 100. The greater the relative value is compared to 100, the better the DCR is considered to be.

[0098] The results of determining the capacity retention rate and DCR for each example of the non-aqueous electrolyte secondary battery are shown in Table 1 below. Table 1 also shows the results of determining the void ratio (void ratio ε1 / void ratio ε2).

[0099]

[0100] Table 1 shows that in each of the test cells for each example (Examples 1 to 3), the relative values ​​of DCR and the relative values ​​of volume retention rate all exceeded 100, indicating an improvement compared to Comparative Example 1. In contrast, in the test cells for Comparative Examples 2 and 4, while the relative values ​​of DCR improved, the relative values ​​of volume retention rate did not. Furthermore, in the test cell for Comparative Example 3, neither the relative value of DCR nor the relative value of volume retention rate improved.

[0101] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0102] The negative electrode for non-aqueous electrolyte secondary batteries relating to this disclosure can be used in applications where it is necessary to suppress both the decrease in the capacity retention rate of the non-aqueous electrolyte secondary battery and the suppression of increased resistance.

[0103] 10: Non-aqueous electrolyte secondary battery, 11: Positive electrode, 12: Negative electrode (negative electrode for non-aqueous electrolyte secondary battery), 13: Separator, 14: Electrode group, 121: Negative electrode core, 122: Negative electrode mixture layer, 122a: Upper negative electrode mixture layer, 122b: Lower negative electrode mixture layer, 1221: First negative electrode mixture layer, 1222: Second negative electrode mixture layer

Claims

It comprises a negative electrode core and a negative electrode mixture layer disposed on the surface of the negative electrode core, The aforementioned negative electrode mixture layer comprises a negative electrode active material and a binder component. The aforementioned binder component comprises a binder compound and a chelating agent. In the thickness direction of the negative electrode mixture layer, the side closer to the negative electrode core is considered downward, the side further from the negative electrode core is considered upward, the layer above the center is considered the upper negative electrode mixture layer, and the layer below the center is considered the lower negative electrode mixture layer. The upper negative electrode mixture layer contains a larger amount of chelating agent than the lower negative electrode mixture layer. Negative electrode for non-aqueous electrolyte secondary batteries. 　 The binder compound comprises at least one selected from the group consisting of polyacrylic acid and salts of polyacrylic acid. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1. 　 The chelating agent comprises at least one functional group selected from the group consisting of a carboxylic acid group, a carboxylic acid base, a phosphonic acid group, and a phosphonic acid base. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1. 　 The chelating agent comprises at least one selected from the group consisting of ethylenediamine derivatives, bisphosphonate derivatives, and inositol derivatives. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1. 　 The negative electrode active material includes artificial graphite. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1. 　 The negative electrode mixture layer includes a second negative electrode mixture layer disposed on the surface of the negative electrode core and a first negative electrode mixture layer disposed on the surface of the second negative electrode mixture layer. The ratio of the thickness of the first negative electrode mixture layer to the total thickness of the negative electrode mixture layer is 10% or more and 50% or less. The ratio of the thickness of the second negative electrode mixture layer to the thickness of the aforementioned negative electrode mixture layer is 50% or more and 90% or less. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1. 　 When the porosity of the first negative electrode mixture layer is ε1%, then ε1 satisfies the relationship 5 < ε1 ≤ 30. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 6. 　 When the porosity of the second negative electrode mixture layer is ε2%, the relationship between ε1 and ε2 satisfies ε2 < ε1. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 7. 　 The first negative electrode mixture layer contains at least one of artificial graphite and a silicon-containing material as the negative electrode active material. When the total mass of the negative electrode active material is 100% by mass, the mass ratio of the silicon-containing material to the total negative electrode active material is a1% by mass, and the mass ratio of the artificial graphite to the total negative electrode active material is b1% by mass, The above a1 and b1 satisfy the relationship 0 ≤ a1 ≤ 90 and 10a1 + b1 ≥ 80. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 6. 　 When the content of the binder compound in the first negative electrode mixture layer is Wp1 and the content of the chelating agent is Wc1, and the content of the binder compound in the second negative electrode mixture layer is Wp2 and the content of the chelating agent is Wc2, The Wp1, Wc1, Wp2, and Wc2 satisfy the relationship 0 ≤ Wc2 / Wp2 < Wc1 / Wp1 ≤ 0.

75. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 6. 　 It includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode is the negative electrode for a non-aqueous electrolyte secondary battery described in any one of claims 1 to 10. Nonaqueous electrolyte secondary battery.

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