JP6961338B2 - Negative electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery - Google Patents

Description

The present disclosure relates to a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

In non-aqueous electrolyte secondary batteries such as lithium ion batteries, a method of filling the active material of the positive electrode and the negative electrode at a high density is adopted as a means for increasing the capacity. Therefore, as the capacity is increased, the space inside the electrode body is reduced, so that the problem that the electrolytic solution is difficult to permeate into the electrode body becomes remarkable. For example, in Patent Documents 1 to 3, a plurality of grooves are formed on the surface of the negative electrode mixture layer so that the electrolytic solution injected into the battery case into which the electrode body is inserted quickly permeates into the electrode body. The negative electrode is disclosed.

Japanese Unexamined Patent Publication No. 9-298057 Japanese Unexamined Patent Publication No. 2008-27633 Japanese Unexamined Patent Publication No. 2009-59686

Certainly, by using the negative electrode disclosed in Patent Documents 1 to 3, the permeability of the electrolytic solution into the electrode body at the time of injecting liquid is improved. However, there are cases where the cycle characteristics are not sufficient when a negative electrode active material having a large amount of expansion / contraction during charging / discharging is used or when the rest time after charging is short. It was speculated by the present inventors that the cause of this is that the speed at which the electrolytic solution extruded from the expanded electrode body during charging returns to the electrode body is not sufficient. The present disclosure has been made in view of such problems, and an object of the present disclosure is to provide a non-aqueous electrolyte secondary battery having excellent cycle characteristics.

The negative electrode for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a non-aqueous electrolyte secondary battery having a long negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. On the surface of the negative electrode mixture layer, a plurality of grooves extending in the width direction of the negative electrode current collector and the bottoms of the plurality of grooves are partitioned in the width direction of the negative electrode current collector. A plurality of extended strip-shaped regions are formed, and the surface of the negative electrode mixture layer in at least one strip-shaped region of the plurality of strip-shaped regions is convex toward the bottom of each of the grooves and opposite to the negative electrode current collector. It is characterized in that it is curved so as to become.

According to the negative electrode for a non-aqueous electrolyte secondary battery, which is one aspect of the present disclosure, it is possible to provide a non-aqueous electrolyte secondary battery having excellent cycle characteristics.

It is sectional drawing of the non-aqueous electrolyte secondary battery which is an example of embodiment. It is a top view of the negative electrode which is an example of an embodiment. FIG. 2 is a cross-sectional view taken along the line AA in FIG. It is sectional drawing of the negative electrode which is an example of a reference example. It is a figure which shows the pressing member for manufacturing the negative electrode which is an example of an embodiment. It is sectional drawing of the conventional negative electrode (the negative electrode produced in Comparative Example 1). It is a figure which shows the pressing member for manufacturing the negative electrode of FIG.

As described above, in the non-aqueous electrolyte secondary battery, the electrolytic solution is pushed out from the inside of the electrode to the surroundings due to the expansion of the electrode due to charging and discharging. In particular, when a high-capacity negative electrode active material is used, the negative electrode expands significantly during charging. Then, when the amount of the electrolytic solution in the electrode body is reduced, a non-uniform battery reaction may occur in the electrode body, which is considered to cause deterioration of the cycle characteristics.

FIG. 6 is a cross-sectional view showing a conventional negative electrode 100. The negative electrode 100 illustrated in FIG. 6 has a plurality of grooves 102 formed on the surface of the negative electrode mixture layer 101 in order to quickly return the electrolytic solution extruded from the electrode body to the electrode body. However, as a result of the studies by the present inventors, it was found that even if the groove 102 as shown in FIG. 6 is formed on the surface of the negative electrode mixture layer 101, the effect of improving the cycle characteristics is small or hardly obtained. ..

As a result of further studies by the present inventors, a plurality of grooves are formed on the surface of the negative electrode mixture layer, and the surface of the negative electrode mixture layer in the band-shaped region partitioned at the bottom of the plurality of grooves is opposite to that of the negative electrode current collector. It was found that the cycle characteristics of the battery were specifically improved by bending it so as to be convex to the side. It is considered that by curving the surface of the negative electrode mixture layer in the band-shaped region and eliminating the angular portion at the edge of the groove, the electrolytic solution can easily return to the inside of the electrode along the groove. Therefore, it is presumed that the non-uniform battery reaction accompanying the decrease in the electrolytic solution is suppressed and the cycle characteristics are improved.

Hereinafter, as an example of the embodiment, the non-aqueous electrolyte secondary battery 10 which is a cylindrical battery provided with a cylindrical metal case will be illustrated, but the non-aqueous electrolyte secondary battery of the present disclosure is not limited thereto. The non-aqueous electrolyte secondary battery of the present disclosure may be, for example, a square battery having a square metal case, a laminated battery having an exterior body made of a resin sheet, or the like.

FIG. 1 is a cross-sectional view of the non-aqueous electrolyte secondary battery 10. As illustrated in FIG. 1, the non-aqueous electrolyte secondary battery 10 includes an electrode body 14 having a wound structure and a non-aqueous electrolyte (not shown). The electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and the positive electrode 11 and the negative electrode 12 are spirally wound via the separator 13. In the following, one side in the axial direction of the electrode body 14 may be referred to as “upper”, and the other side in the axial direction may be referred to as “lower”.

The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved or dispersed in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and a mixed solvent of two or more of these can be used. The non-aqueous solvent may contain a halogen substituent in which at least a part of hydrogen in these solvents is substituted with a halogen atom such as fluorine.

The positive electrode 11, the negative electrode 12, and the separator 13 constituting the electrode body 14 are all formed in a long shape. Each of these members is spirally wound so that the electrode body 14 is alternately laminated in the radial direction. In the electrode body 14, the longitudinal direction of each electrode is the winding direction, and the width direction of each electrode is the axial direction. The positive electrode lead 19 that electrically connects the positive electrode 11 and the positive electrode terminal is connected to, for example, the central portion in the longitudinal direction of the positive electrode 11 and extends from the upper end of the electrode group. The negative electrode lead 20 that electrically connects the negative electrode 12 and the negative electrode terminal is connected to, for example, the longitudinal end of the negative electrode 12 and extends from the lower end of the electrode group.

In the example shown in FIG. 1, the case body 15 and the sealing body 16 constitute a metal battery case that houses the electrode body 14 and the non-aqueous electrolyte. Insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode lead 19 extends to the sealing body 16 side through the through hole of the insulating plate 17 and is welded to the lower surface of the filter 22 which is the bottom plate of the sealing body 16. In the non-aqueous electrolyte secondary battery 10, the cap 26 of the sealing body 16 electrically connected to the filter 22 serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends toward the bottom of the case body 15 and is welded to the inner surface of the bottom of the case body 15. In the non-aqueous electrolyte secondary battery 10, the case body 15 serves as a negative electrode terminal.

The case body 15 is a bottomed cylindrical metal container. A gasket 27 is provided between the case body 15 and the sealing body 16 to ensure the airtightness inside the battery case. The case body 15 has, for example, an overhanging portion 21 that supports the sealing body 16 formed by pressing a side surface portion from the outside. The overhanging portion 21 is preferably formed in an annular shape along the circumferential direction of the case body 15, and the sealing body 16 is supported on the upper surface thereof.

The sealing body 16 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are laminated in this order from the electrode body 14 side. Each member constituting the sealing body 16 has, for example, a disk shape or a ring shape, and each member except the insulating member 24 is electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at the central portion thereof, and an insulating member 24 is interposed between the peripheral portions thereof. Since the lower valve body 23 is provided with a ventilation hole, when the internal pressure of the battery rises due to abnormal heat generation, the upper valve body 25 swells toward the cap 26 side and separates from the lower valve body 23, so that the electrical connection between the two is established. It is blocked. When the internal pressure further rises, the upper valve body 25 breaks and gas is discharged from the opening of the cap 26.

Hereinafter, each component (positive electrode 11, negative electrode 12, separator 13) of the electrode body 14 will be described in detail with reference to FIGS. 2 and 3, particularly the negative electrode 12.

[Positive electrode]
The positive electrode 11 has a long positive electrode current collector 11a and a positive electrode mixture layer 11b formed on the positive electrode current collector 11a. The positive electrode current collector 11a is, for example, a strip-shaped body having a thickness of 5 μm to 20 μm and a substantially constant width. As the positive electrode current collector 11a, a metal foil stable in the potential range of the positive electrode 11 such as aluminum, a film in which the metal is arranged on the surface layer, or the like can be used. The positive electrode mixture layer 11b contains, for example, a positive electrode active material, a conductive agent, and a resin binder. For the positive electrode 11, for example, a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a resin binder, and the like is applied to both surfaces of the positive electrode current collector 11a, the coating film is dried, and then compressed to compress the positive electrode mixture layer 11b. Can be produced by forming on both sides of the current collector.

The positive electrode mixture layer 11b is formed on the entire surface of both sides of the positive electrode current collector 11a except for a portion where the positive electrode lead 19 is welded and a portion located on the opposite side thereof, for example. The thickness of the positive electrode mixture layer 11b is not particularly limited, but is preferably 40 μm to 80 μm on one side of the positive electrode current collector 11a. Examples of the positive electrode active material contained in the positive electrode mixture layer 11b include lithium-containing transition metal 14 oxides containing transition metal elements such as Ni, Co, and Mn. The lithium-containing transition metal oxide is not particularly limited, but the general formula Li _{1 + x} MO ₂ (in the formula, −0.2 <x ≦ 0.2, M is at least one of Ni, Co, Mn, and Al). It is preferably a composite oxide represented by).

Examples of the conductive agent contained in the positive electrode mixture layer 11b include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the resin binder contained in the positive electrode mixture layer 11b include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. .. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or salts thereof, polyethylene oxide (PEO) and the like.

[Negative electrode]
The negative electrode 12 has a long negative electrode current collector 30 and a negative electrode mixture layer 31 formed on the negative electrode current collector 30. The negative electrode current collector 30 is, for example, a strip-shaped body having a thickness of 5 μm to 20 μm and a substantially constant width. For the negative electrode current collector 30, a metal foil stable in the potential range of the negative electrode 12 such as copper, a film in which the metal is arranged on the surface layer, or the like can be used. The negative electrode mixture layer 31 contains, for example, a negative electrode active material and a resin binder. For the negative electrode 12, for example, a negative electrode mixture slurry containing a negative electrode active material, a resin binder, and the like is applied to both sides of the negative electrode current collector 30, the coating film is dried, and then compressed to form the negative electrode mixture layer 31. It can be produced by forming on both sides of. As will be described in detail later, the negative electrode mixture layer 31 is compressed twice, for example, and the groove 32 is formed in the second compression step.

The negative electrode mixture layer 31 is formed on both sides of the negative electrode current collector 30 except for a portion where the negative electrode lead 20 is welded and a portion located on the opposite side thereof, for example. The thickness of the negative electrode mixture layer 31 is not particularly limited, but preferably the thickness T ₃₁ of the thickest portion on one side of the negative electrode current collector 30 is 40 μm to 80 μm. The negative electrode active material contained in the negative electrode mixture layer 31 is not particularly limited as long as it can reversibly occlude and release lithium ions, for example, carbon materials such as natural graphite and artificial graphite, silicon (Si), and tin. A metal alloying with lithium such as (Sn) or an oxide containing a metal element such as Si or Sn can be used.

Preferable examples of the negative electrode active material include graphite and silicon oxide represented by _{SiO x.} The negative electrode mixture layer 31 may contain either graphite or silicon oxide represented by _{SiO x} as the negative electrode active material, or may contain both. When graphite and the silicon oxide are used in combination, the mass ratio of graphite and the silicon oxide is, for example, 99: 1 to 80:20, preferably 97: 3 to 90:10.

Silicon oxide represented by SiO _x has a structure in which fine particles of Si are dispersed in, for example, an amorphous SiO _{2 matrix.} An example of a suitable silicon oxide is SiO _x (0.5 ≦ x ≦ 1.6). Silicon oxide represented by SiO _{x may contain lithium silicate represented by Li 2y} SiO _{(2 + y)} (0 <y <2), and Si fine particles are dispersed in the lithium silicate phase. It may have a structure.

It is preferable that a conductive film made of a material having a higher conductivity than silicon oxide is formed on the surface of silicon oxide particles represented by SiO _x. The material constituting the conductive coating is preferably at least one selected from a carbon material, a metal, and a metal compound. Above all, it is particularly preferable to use a carbon material. The carbon film is formed, for example, at 0.5 to 10% by mass with respect to the mass of _{SiO x particles.}

As the resin binder contained in the negative electrode mixture layer 31, a fluororesin, a PAN, a polyimide resin, an acrylic resin, a polyolefin resin or the like can be used as in the case of the positive electrode. When preparing a mixture slurry using an aqueous solvent, it is preferable to use CMC or a salt thereof, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

As illustrated in FIGS. 2 and 3, a plurality of grooves 32 extending in the width direction of the negative electrode current collector 30 are formed on the surface of the negative electrode mixture layer 31. Further, the negative electrode mixture layer 31 is formed with a plurality of band-shaped regions 34 partitioned by the bottom 33 of the groove 32 and extending in the width direction of the negative electrode current collector 30. The surface of the negative electrode mixture layer 31 in the band-shaped region 34 is curved toward the bottom 33 of each groove 32 so as to be convex on the side opposite to the negative electrode current collector 30. That is, in the negative electrode mixture layer 31, the groove edge portion 35 is rounded, and the groove edge portion 35 has no corners. As a result, even when the electrode body 14 is expanded by charging, the electrolytic solution easily permeates into the electrode body 14 along the groove 32. If the surface of the negative electrode mixture layer 31 in at least one band-shaped region 34 is curved toward the bottom 33 of each groove 32, the effect of the present disclosure is exerted. However, it is preferable that the surface of the negative electrode mixture layer 31 in all the band-shaped regions 34 is curved toward the bottom 33 of the groove 32.

In the present embodiment, a plurality of grooves 32 are formed in each of the negative electrode mixture layers 31 formed on both sides of the negative electrode current collector 30. The number of grooves 32 in each negative electrode mixture layer 31 is the same, and the grooves 32 in each negative electrode mixture layer 31 are formed at substantially the same spacing, width, and depth, and overlap in the thickness direction of the negative electrode 12. The number of grooves 32 may be different in each negative electrode mixture layer 31. Further, the intervals, widths, and depths of the grooves 32 of each negative electrode mixture layer 31 may be different from each other, and the grooves 32 may not overlap in the thickness direction of the negative electrode 12.

The plurality of grooves 32 may be formed, for example, from both ends in the width direction of the negative electrode mixture layer 31 to the vicinity of the central portion in the width direction, but are preferably formed over the entire width of the negative electrode mixture layer 31 (the present embodiment). Then, it is formed over the entire width of the negative electrode current collector 30). The groove 32 may be inclined with respect to the width direction of the negative electrode current collector 30, but is preferably formed substantially parallel to the width direction. Further, it is preferable that the grooves 32 are formed substantially parallel to each other.

_{The distance P 32 in} the longitudinal direction of the negative electrode current collectors 30 of the plurality of grooves 32 is, for example, 150 μm to 250 μm with respect to the center line α perpendicular to the longitudinal direction of the negative electrode current collectors 30 of each bottom 33 (see FIG. 2). ). The spacing P _{32 of the} grooves 32 is more preferably 150 μm to 200 μm. Each interval P ₃₂ may be irregular, but is preferably substantially constant. The width W ₃₂ (see FIG. 2) of each groove 32 is, for example, 5 μm to 15 μm. The width W ₃₂ is the width of the bottom 33 of the groove 32. In the example shown in FIG. 3, the bottom 33 of the groove 32 is formed substantially flat, but the bottom 33 is curved so as to be convex toward the negative electrode current collector 30 or protrudes so as to be V-shaped. May be good. In that case, the width of the curved portion or the protruding portion _{matches the width W 32} of the groove. The widths W ₃₂ of each groove 32 may be different from each other, but are preferably substantially the same.

The depth D ₃₂ (see FIG. 3) of each groove 32 is, for example, 7 μm to 20 μm. Here, the depth D ₃₂ is the length along the thickness direction of the negative electrode 12 from the surface of the thickest portion of the negative electrode mixture layer 31 to the deepest portion of the groove 32. The depth D ₃₂ of each groove 32, is 5% to 40% relative to the thickness T ₃₁ of the thickest portion of the example the negative electrode mixture layer 31. The depth D ₃₂ of each groove 32 may be different but are preferably substantially the same.

The band-shaped regions 34 are formed side by side in the longitudinal direction of the negative electrode current collector 30. In the example shown in FIG. 3, the surface of the negative electrode mixture layer 31 in the band-shaped region 34 is curved so as to be convex on the opposite side to the negative electrode current collector 30 over the entire width of the region. That is, the entire surface of the negative electrode mixture layer 31 in the band-shaped region 34 is curved, and the surface of the negative electrode mixture layer 31 in the band-shaped region 34 is a gentle curve in the cross section obtained by cutting the negative electrode 12 in the longitudinal direction.

It is preferable that each band-shaped region 34 is curved so as to be at a position substantially equidistant from both ends in the width direction of the region, that is, the central portion in the width direction of the band-shaped region 34 is the top. That is, the thickness of the strip-shaped region 34 becomes thicker as it approaches the central portion in the width direction from both ends in the width direction. In other words, the negative electrode mixture layer 31 gradually becomes thinner from the central portion in the width direction of the strip-shaped region 34 toward the bottom 33 of each groove 32 formed on both sides of the region. The groove edge portion 35 has no corners and does not have a surface shape such that the thickness of the negative electrode mixture layer 31 sharply decreases only in the portion where the groove 32 is formed.

In the negative electrode mixture layer 31, for example, the difference between the density of the negative electrode mixture layer 31 in the band-shaped region 34 and the density of the negative electrode mixture layer 31 in the bottom region 35 is within 5%. Here, the bottom region 35 is a region located between the bottom 33 of each groove 32 and the negative electrode current collector 30. When the groove 102 as illustrated in FIG. 6 is formed, the density of the negative electrode mixture layer 101 tends to be higher in the bottom region 106 than in the other regions, but the surface of the band-shaped region 34 should have a gentle curved surface. Therefore, the increase in density in the bottom region 35 can be suppressed. Making the density of the negative electrode mixture layer 31 uniform facilitates the permeation of the electrolytic solution into the electrode body expanded by charging, suppresses the non-uniform battery reaction, and contributes to the improvement of the cycle characteristics.

In the example shown in FIG. 4, the surface of the negative electrode mixture layer 31X is curved so as to be convex on the opposite side to the negative electrode current collector 30 only in the vicinity of both ends in the width direction of each band-shaped region 34X. In the negative electrode 12X illustrated in FIG. 4, the bottom portion 33X of each groove 32X is substantially flat. Further, it is common with the negative electrode 12 in that the groove edge portion 35X is curved and the groove edge portion 35X has no corner. On the other hand, the strip-shaped region 34X is different from the strip-shaped region 34 of the negative electrode 12 in that the central portion in the width direction is not curved and the surface thereof is substantially flat. The dimensions of the groove 32X and the like can be the same as those of the groove 32 of the negative electrode 12.

FIG. 5 shows a pressing member 50 for forming a plurality of grooves 32 on the surface of the negative electrode mixture layer 31. In the plurality of grooves 32, the negative electrode mixture layer 31 is compressed by a pressing member such as a roller having no unevenness on the surface, and then the negative electrode mixture layer 31 is compressed again by using the pressing member 50 illustrated in FIG. Is formed by. A plurality of convex portions 51 are formed on the surface of the pressing member 50. The convex portions 51 are formed elongated in a direction orthogonal to the direction in which the convex portions 51 are lined up at a substantially constant interval from each other. The concave portions 52 having a gently curved surface are formed on both sides of each convex portion 51. The pressing member 50 is, for example, a roller in which a plurality of convex portions 51 and a plurality of concave portions 52 are formed on a surface that abuts on the negative electrode mixture layer 31.

The negative electrode mixture layer 31 has a groove 32 in a portion compressed by the convex portion 51, and a strip-shaped region 34 in a portion compressed by the concave portion 52. In the example shown in FIG. 5, since the tip of the convex portion 51 is substantially flat, the bottom portion 33 of the groove 32 is substantially flat. Since the surface of the recess 52 is curved as described above, the entire surface of the negative electrode mixture layer 31 in the band-shaped region 34 is curved so as to be convex on the opposite side to the negative electrode current collector 30. .. By changing the surface shape of the recess 52, the band-shaped region 34X illustrated in FIG. 4 can be formed.

[Separator]
As the separator 13, a porous sheet having ion permeability and insulating property is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a non-woven fabric. As the material of the separator 13, olefin resin such as polyethylene and polypropylene, cellulose and the like are suitable. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer containing a heat-resistant material may be formed on the surface of the separator 13.

Hereinafter, the present disclosure will be further described with reference to Examples, but the present disclosure is not limited to these Examples.

<Example 1>
[Preparation of positive electrode]
98 parts by mass of lithium nickel composite oxide, 1 part by mass of conductive carbon powder, 1 part by mass of polyvinylidene fluoride, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) are mixed to form a positive electrode. An agent slurry was prepared. Next, the positive electrode mixture slurry was applied to both sides of the positive electrode current collector made of aluminum foil having a thickness of 15 μm, the coating film was dried, and then the coating film was compressed to form the positive electrode mixture layer. A current collector having a positive electrode mixture layer formed on both sides was cut into a predetermined electrode size, and an aluminum lead was connected to a portion where the surface of the current collector was exposed to obtain a positive electrode. The thickness of the positive electrode was 143 μm at the portion where the positive electrode mixture layer was formed on both sides of the current collector.

[Preparation of negative electrode]
98 parts by mass of graphite powder, 1 part by mass of styrene-butadiene rubber, and 1 part by mass of carboxymethyl cellulose were mixed, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of the negative electrode current collector made of copper foil having a thickness of 10 μm, the coating film was dried, and then the coating film was compressed to form the negative electrode mixture layer. The density of the negative electrode mixture layer at this time was 1.6 g / cc.

Next, the negative electrode mixture layer is compressed using an embossed roll having a surface shape as shown in FIG. 5 (width of the apex of the convex portion 51: 10 μm, distance between the convex portions 51: 200 μm), and the negative electrode mixture layer is used. Multiple grooves were formed on the surface of the. Each groove had a width of 10 μm, a depth of 10 μm, and an interval of 200 μm, and was formed over the entire width of the negative electrode current collector, and the surface was curved so as to be convex on the opposite side of the current collector between the grooves. Multiple strips were formed. The entire surface of the band-shaped region is gently curved, and there are no corners at the edges along the grooves. The density of the negative electrode mixture layer in the band-shaped region and the bottom region was 1.6 g / cc.

Subsequently, a current collector having grooved negative electrode mixture layers formed on both sides was cut to a predetermined electrode size, and a nickel lead was connected to a portion where the surface of the current collector was exposed to obtain a negative electrode. The thickness of the negative electrode was 160 μm at the portion where the negative electrode mixture layer was formed on both sides of the current collector and corresponding to the top of the band-shaped region.

[Preparation of non-aqueous electrolyte solution]
Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in an argon atmosphere at a volume ratio of 3: 7. A non-aqueous electrolyte solution was prepared by dissolving _{LiPF 6} in the mixed solvent so as to have a concentration of 1 mol / L.

[Battery production]
A wound electrode body was produced by spirally winding the positive electrode and the negative electrode through a separator made of a polyethylene microporous film having a thickness of 20 μm. The electrode body is housed in a bottomed cylindrical battery case body under a nitrogen atmosphere of 25 ° C. and 1 atmosphere, and after injecting the non-aqueous electrolyte solution, the opening of the battery case body is sealed with a gasket and a sealing body. Then, a cylindrical non-aqueous electrolyte secondary battery was produced.

<Example 2>
As the negative electrode active material, non-aqueous material was used in the same manner as in Example 1 except that a mixture of 93 parts by mass of graphite and _{7 parts by mass of silicon oxide represented by SiO x (x = 1) was used.} An electrolyte secondary battery was manufactured.

<Comparative example 1>
The negative electrode mixture layer is compressed using an embossed roll having a surface shape as shown in FIG. 7 (width of vertices of convex portions 111: 10 μm, distance between convex portions 111: 200 μm), and the surface of the negative electrode mixture layer is formed. A negative electrode and a battery were produced in the same manner as in Example 1 except that a plurality of grooves were formed. Each groove was formed over the entire width of the negative electrode current collector with a width of 10 μm, a depth of 10 μm, and an interval of 200 μm. A plurality of strip-shaped regions having a substantially flat surface were formed between the grooves, and corners were formed at the edges along the grooves. The density of the negative electrode mixture layer in the band-shaped region was 1.6 g / cc, and the density of the negative electrode mixture layer in the bottom region was 1.65 g / cc.

<Comparative example 2>
A negative electrode and a battery were produced in the same manner as in Example 1 except that the negative electrode mixture layer was not compressed using embossed rolls and no grooves were formed on the surface of the negative electrode mixture layer.

<Comparative example 3>
Non-aqueous in the same manner as in Comparative Example 1 except that a mixture of 93 parts by mass of graphite and _{7 parts by mass of silicon oxide represented by SiO x (x = 1) was used as the negative electrode active material.} An electrolyte secondary battery was manufactured.

<Comparative example 4>
Non-aqueous in the same manner as in Comparative Example 2 except that a mixture of 93 parts by mass of graphite and _{7 parts by mass of silicon oxide represented by SiO x (x = 1) was used as the negative electrode active material.} An electrolyte secondary battery was manufactured.

The performance of each of the above non-aqueous electrolyte secondary batteries was evaluated by the following method, and the evaluation results are shown in Table 1. Table 1 shows the negative electrode active material, the expansion coefficient of the electrode body during charging, the dimensions of the grooves formed on the surface of the negative electrode mixture layer, and the like, as well as the evaluation results.

[Evaluation of cycle characteristics]
Under the temperature condition of 25 ° C., the battery was charged with a constant current of 1 C until the battery voltage became 4.2 V, and then charged with a constant voltage of 4.2 V until the final current became 0.02 C. After resting for 1 minute, the battery was discharged with a constant current of 1C until the battery voltage became 2.5V, and then rested for 1 minute. This charge / discharge cycle was repeated for 500 cycles, and the ratio of the discharge capacity at the 500th cycle (capacity retention rate) to the discharge capacity at the first cycle was determined. The battery capacity retention rate of Example 2 and each Comparative Example shown in Table 1 is a value when the capacity retention rate of the battery of Example 1 is 100.

As shown in Table 1, the battery of Example 1 is superior in cycle characteristics to the batteries of Comparative Examples 1 and 2. It was found that there was no difference in the cycle characteristics between the batteries of Comparative Examples 1 and 2, and that the grooves formed on the surface of the negative electrode mixture layer of Comparative Example 1 did not contribute to the cycle characteristics. That is, when the expansion coefficient of the electrode body at the time of charging is 120%, there is no effect of improving the cycle characteristics even if a groove having a corner exists at the groove edge portion, and there is no corner at the groove edge portion. Cycle characteristics are improved only when grooves are formed.

On the other hand, when the expansion coefficient of the electrode body at the time of charging was 150%, the cycle characteristics were significantly deteriorated in the battery of Comparative Example 4 in which the groove was not formed on the surface of the negative electrode mixture layer. In this case, even if the groove has an angle at the groove edge, the effect of improving the cycle characteristics can be seen by forming the groove on the surface of the negative electrode mixture layer (Comparative Example 3). Further, the battery of Example 2 has significantly improved cycle characteristics as compared with the battery of Comparative Example 3, and the cycle characteristics equal to or higher than those of the battery of Example 1 have been obtained.

As described above, by using the negative electrode in which the groove having no corner at the groove edge portion is formed on the surface of the negative electrode mixture layer, a non-aqueous electrolyte secondary battery having excellent cycle characteristics can be obtained. In particular, when the non-aqueous electrolyte secondary battery includes an electrode body having a large volume change due to charging / discharging, the effect of improving the cycle characteristics is remarkably exhibited.

10 Non-aqueous electrolyte secondary battery, 11 positive electrode, 12, 12X negative electrode, 13 separator, 14 electrode body, 15 case body, 16 sealing body, 17, 18 insulating plate, 19 positive electrode lead, 20 negative electrode lead, 21 overhang, 22 Filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 27 gasket, 30 negative electrode current collector, 31, 31X negative electrode mixture layer, 32, 32X groove, 33, 33X bottom, 34, 34X strip Region, 35, 35X groove edge, 36 bottom region, 50 pressing member, 51 convex, 52 concave, 100 negative electrode, 101 negative electrode mixture layer, 102 groove, 106 bottom region, 110 pressing member, 111 convex, 112 concave , Α Center line

Claims (7)

A negative electrode for a non-aqueous electrolyte secondary battery having a long negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector.
On the surface of the negative electrode mixture layer, a plurality of grooves extending in the width direction of the negative electrode current collector and a plurality of strip-shaped regions partitioned at the bottom of the plurality of grooves and extending in the width direction of the negative electrode current collector. Is formed,
At least one surface of said at strip area anode mixture layer of said plurality of band-like regions, over the entire width of the region is curved to be convex on the negative electrode current collector opposite,
A negative electrode for a non-aqueous electrolyte secondary battery , wherein the thickness of the negative electrode mixture layer in the at least one band-shaped region becomes thicker from both ends in the width direction of the region toward the center in the width direction of the region. The difference between the density of the negative electrode mixture layer in the bottom region located between each bottom of the plurality of grooves and the negative electrode current collector and the density of the negative electrode mixture layer in the band-shaped region is within 5%. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2 , wherein the negative electrode mixture layer contains silicon oxide represented by _{SiO x} (0.5 ≦ x ≦ 1.6). The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3 , wherein the plurality of grooves are formed over the entire width of the negative electrode mixture layer. The distance between the plurality of grooves in the longitudinal direction of the negative electrode current collector is 150 μm to 250 μm with respect to a center line perpendicular to the longitudinal direction of the negative electrode current collector at the bottom of each of the plurality of grooves. The negative electrode for a non-aqueous electrolyte secondary battery according to any one of 4 to 4. The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5 , wherein the width of each bottom of the plurality of grooves is 5 μm to 15 μm, and the depth of each groove is 7 μm to 20 μm. .. The negative electrode, the positive electrode, the separator, the negative electrode and the positive electrode in which the negative electrode and the positive electrode are spirally wound via the separator, and a non-water type electrode body according to any one of claims 1 to 6. A non-aqueous electrolyte secondary battery with an electrolyte.

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