JP2008010253A - Electrode for lithium secondary battery, manufacturing method therefor, and the lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a lithium secondary battery capable of showing superior capacity maintenance rate, even if used at a high temperature of for example, 60°C or higher, and of showing high output, and to provide its manufacturing method, and the lithium secondary battery. <P>SOLUTION: This lithium secondary battery has an electrode body composed of a positive electrode, a negative electrode, and a separator pinched and installed between the positive electrode and the negative electrode, and having an electrolytic solution. The electrode for the lithium secondary battery, and its manufacturing method are provided. The electrode 2 (3) for the lithium secondary battery has metal current collectors 21 (31) and electrode material layers 22 (32) formed so as to pinch their both faces. At least one of the electrode material layers 22 (32) has an uneven structure 225 with a height difference of 5 to 100 μm on its surface. In manufacturing, an electrode material slurry is coated on the both faces of the metal current collectors 21 (31), and the electrode material layers 22 (32) are formed. After that, a metal die, having an uneven face of the height difference of up to 100 μm, is abutted against and is pressed against the electrode material layers 22 (32). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode used for a lithium secondary battery using lithium ions as a driving source, a method for producing the same, and a lithium secondary battery using the electrode.

Lithium secondary batteries are excellent in output performance, have been put into practical use in the fields of information equipment and communication equipment, mainly portable information terminals such as personal computers and mobile phones, and have been widely spread.
Generally, a lithium secondary battery includes a positive electrode, a negative electrode, an electrode body composed of a separator sandwiched between the positive electrode and the negative electrode, a battery case containing the electrode body, and a battery case filled therein. Electrolyte solution.

  In recent years, development of electric vehicles and hybrid vehicles has been urgently promoted due to environmental problems and resource issues, and the use of lithium secondary batteries as a power source for electric vehicles and hybrid vehicles has been studied. Therefore, further increase in output is required for the lithium secondary battery.

  Until now, in order to improve battery characteristics, a non-aqueous electrolyte battery using a microporous membrane whose surface has been processed into an uneven shape has been developed as a separator (see Patent Document 1). If such a nonaqueous electrolyte battery is applied to a lithium secondary battery, the output of the lithium secondary battery can be increased.

  However, in the lithium secondary battery, the separator is generally made of a microporous film made of polypropylene or polyethylene, and the positive electrode and the negative electrode are pressed against the separator with high pressure. Therefore, for example, at the use temperature (60 ° C. or higher) of the power source for a hybrid vehicle, the separator may be softened or deformed, and it has been difficult to maintain the unevenness of the separator surface for a long time. As a result, there has been a problem that the output tends to decrease when the charge and discharge are repeated, and the output maintenance rate is lowered. Therefore, it has been difficult to realize a lithium secondary battery having both a high capacity retention rate and a high output.

Japanese Patent Laid-Open No. 5-151951

  The present invention has been made in view of such conventional problems. For example, an electrode for a lithium secondary battery capable of exhibiting high output even when used at a high temperature of 60 ° C. or higher, a method for producing the same, and lithium The next battery is to be provided.

The first invention is an electrode body composed of a positive electrode, a negative electrode, and a separator sandwiched between the positive electrode and the negative electrode, a battery case containing the electrode body, and the battery case filled A sheet-like electrode for a lithium secondary battery used for the positive electrode and / or the negative electrode of a lithium secondary battery having an electrolyte solution,
The electrode for a lithium secondary battery has a sheet-like metal current collector and an electrode material layer formed so as to sandwich both surfaces of the metal current collector,
The electrode material layer is mainly composed of an inorganic positive electrode active material capable of occluding or releasing lithium ions or an inorganic negative electrode active material capable of occluding or releasing lithium ions,
At least one of the electrode material layers formed on both surfaces of the metal current collector has a concavo-convex structure with an elevation difference of 5 to 100 μm on the surface thereof. (Claim 1).

The electrode for a lithium secondary battery according to the first aspect of the invention has a concavo-convex structure with a height difference of 5 to 100 μm on the surface thereof. Therefore, when the electrode for a lithium secondary battery is used as the positive electrode and / or the negative electrode of the lithium secondary battery, the voids in the electrode body can be increased by the uneven structure. Therefore, in the lithium secondary battery, the electrolyte solution can be held in the voids in the electrode body. Therefore, the amount of the electrolytic solution in the electrode body can be increased. As a result, the battery reaction in the electrode body becomes smoother, and the output of the lithium secondary battery can be increased.
Moreover, since the said electrode for lithium secondary batteries has a large surface area, the contact area with the said electrolyte solution in the said lithium secondary battery is large. Thereby, the reaction area of a battery reaction becomes large, and high output can be achieved.

  The electrode material layer having the concavo-convex structure is mainly composed of the inorganic positive electrode active material or the inorganic negative electrode active material. Therefore, the concavo-convex structure is superior in heat resistance to the concavo-convex formed on the above-described conventional separator surface. Therefore, even when the lithium secondary battery having the lithium secondary battery electrode is repeatedly charged and discharged in a high temperature environment of, for example, 60 ° C., the lithium secondary battery electrode can maintain the uneven structure. . Accordingly, it is possible to suppress a decrease in output when the lithium secondary battery is repeatedly charged and discharged.

According to a second aspect of the present invention, there is provided an electrode body composed of a positive electrode, a negative electrode, and a separator sandwiched between the positive electrode and the negative electrode, a battery case containing the electrode body, and the battery case filled A method for producing a sheet-like electrode for a lithium secondary battery used for the positive electrode and / or the negative electrode of a lithium secondary battery having an electrolyte solution,
It has a sheet-like metal current collector and an electrode material layer formed so as to sandwich both surfaces of the metal current collector, and has an uneven structure with a height difference of 5 to 100 μm on at least one surface of the electrode material layer In the method for producing an electrode for a lithium secondary battery,
An electrode obtained by dispersing an electrode material mainly composed of an inorganic positive electrode active material capable of inserting or extracting lithium ions or an inorganic negative electrode active material capable of inserting or extracting lithium ions on both surfaces of the metal current collector in an organic solvent. Applying and drying a material slurry to form the electrode material layer sandwiching the metal current collector,
The concavo-convex structure is formed by pressing a mold having a concavo-convex surface with a height difference of 5 to 100 μm on the surface in contact with at least one surface of the electrode material layer formed on both surfaces of the metal current collector. It has the uneven | corrugated structure formation process to form, It exists in the manufacturing method of the electrode for lithium secondary batteries characterized by the above-mentioned (Claim 6).

In 2nd invention, the said electrode for lithium secondary batteries is manufactured by performing the said application | coating process and the said uneven | corrugated structure formation process.
In the coating step, an electrode material slurry in which an electrode material mainly composed of the positive electrode active material or the negative electrode active material is dispersed in an organic solvent is applied to both surfaces of the metal current collector and dried. Thereby, the said electrode material layer which has the said positive electrode active material or the said negative electrode active material as a main component can be formed in both surfaces of the said metal electrical power collector.
Moreover, in the said uneven | corrugated structure formation process, the metal mold | die which has an uneven surface with a height difference of 5-100 micrometers on the surface is made to contact at least one of the said electrode material layer, and is pressed. Thereby, the uneven structure having the same shape as the uneven surface of the mold can be formed on the surface of the electrode material layer.

In this manner, the lithium secondary battery electrode having a height difference of 5 to 100 μm on the surface can be easily produced.
In addition, the electrode for a lithium secondary battery manufactured according to the present invention has an unevenness with a height difference of 5 to 100 μm on the surface of the electrode material layer mainly composed of the inorganic positive electrode active material or the inorganic negative electrode active material. It has a structure. Therefore, the said lithium secondary battery electrode can improve the initial output, and can suppress the fall of the output when charging / discharging is repeated at high temperature of 60 degreeC or more, for example.

According to a third aspect of the present invention, there is provided an electrode body comprising a positive electrode, a negative electrode, and a separator sandwiched between the positive electrode and the negative electrode, a battery case containing the electrode body, and the battery case filled In a lithium secondary battery having an electrolyte solution,
At least one of the positive electrode and the negative electrode is the lithium secondary battery characterized in that it comprises the lithium secondary battery electrode of the first invention (claim 12).

In the lithium secondary battery of the third invention, at least one of the positive electrode and the negative electrode comprises the electrode for the lithium secondary battery of the first invention.
Therefore, taking advantage of the above-described characteristics of the electrode for the lithium secondary battery of the first invention, the lithium secondary battery can exhibit a high initial output and can be charged and discharged at a high temperature of, for example, 60 ° C. or higher. While being able to suppress a decrease in output when repeated,

Next, a preferred embodiment of the present invention will be described.
The electrode for a lithium secondary battery includes a sheet-shaped metal current collector and the electrode material layer formed so as to sandwich both surfaces of the current collector.
When the lithium secondary battery electrode is a positive electrode, the electrode material layer is mainly composed of an inorganic positive electrode active material. When the lithium secondary battery electrode is a negative electrode, the electrode material layer contains an inorganic negative electrode active material as a main component.

  When the height difference of the concavo-convex structure of the electrode material layer is less than 5 μm, it becomes difficult to form the concavo-convex substantially. In addition, the contact area between the lithium secondary battery electrode and the electrolytic solution is hardly increased. As a result, the output of the lithium secondary battery may not be sufficiently improved. On the other hand, when the thickness exceeds 100 μm, the electrode material may be easily broken. As a result, even in this case, there is a possibility that the output of the lithium secondary battery cannot be sufficiently improved. More preferably, the height difference of the concavo-convex structure is 5 to 20 μm.

The concavo-convex structure preferably includes a plurality of columnar convex portions having a diameter of 5 to 500 μm protruding from the periphery at intervals of 10 to 5000 μm.
The concavo-convex structure preferably includes a plurality of cup-shaped concave portions having a diameter of 5 to 500 μm that are recessed from the periphery at intervals of 10 to 5000 μm.
When the diameter of the said convex part or the said recessed part is less than 5 micrometers, there exists a possibility that the diameter of an uneven | corrugated | grooved part may be too small, and an effect may become small. On the other hand, when the thickness exceeds 500 μm, the effect may be reduced because the diameter of the concavo-convex portion is too large. Moreover, when the space | interval of the said convex part or the said recessed part is less than 10 micrometers, there exists a possibility that formation of an unevenness | corrugation may become difficult substantially. On the other hand, when it exceeds 5000 μm, the effect may be reduced.

Moreover, the said column-shaped convex part consists of column shape, elliptical column shape, polygonal column shape etc., for example. Further, the cup-shaped concave portion has a cross-sectional shape of, for example, a circular shape, an elliptical shape, or a polygonal shape.
In the case where the convex portion is cylindrical and the cross-sectional shape of the concave portion is circular, the diameter is the diameter of the bottom surface (upper surface or lower surface). Further, when the convex portion is elliptical columnar or polygonal columnar, and when the sectional shape of the concave portion is elliptical or polygonal, the diameter is the same as the ellipse or polygon of the bottom surface (upper surface or lower surface). The diameter of the area circle.

  Further, when the concavo-convex structure has the columnar convex portion, a concave portion is formed around the convex portion. On the other hand, when the concavo-convex structure has the cup-shaped concave portion, a convex portion is formed around the concave portion.

Next, it is preferable that the concavo-convex structure has a plurality of linear convex portions having a line width of 3 to 500 μm formed at intervals of 5 to 1000 μm.
The concavo-convex structure preferably has a plurality of linear recesses having a line width of 3 to 500 μm formed at intervals of 5 to 1000 μm.

When the line width is less than 5 μm, it may be difficult to form unevenness substantially. On the other hand, if it exceeds 1000 μm, the effect may be reduced.
Moreover, when the space | interval of the said linear recessed part or the space | interval of the said linear convex part is less than 5 micrometers, there exists a possibility that formation of an unevenness | corrugation may become difficult substantially. On the other hand, if it exceeds 1000 μm, the effect may be reduced.

Moreover, in this invention, the said electrode for lithium secondary batteries can be manufactured by performing the said application | coating process and the said uneven | corrugated structure formation process.
In the coating step, an electrode material slurry in which an inorganic positive electrode active material capable of occluding or releasing lithium ions or an electrode material mainly composed of an inorganic negative electrode active material capable of occluding or releasing lithium ions is dispersed in an organic solvent. It is applied to both sides of the metal current collector and dried.

The electrode material slurry can be produced by adding and mixing an organic solvent such as N-methyl-2-pyrrolidone to the electrode material mainly composed of the positive electrode active material or the negative electrode active material.
The electrode material can contain a binder, a conductive material, and the like in addition to the positive electrode active material or the negative electrode active material.
Examples of the binder include fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride, and fluororubber, or thermoplastic resins such as polypropylene and polyethylene. In addition, as the conductive material, for example, one or two or more carbon material powders such as carbon black, acetylene black, and graphite can be used.

  As said metal electrical power collector, metal foil, such as aluminum, stainless steel, copper, can be used, for example.

Moreover, in the said uneven | corrugated structure formation process, the metal mold | die which has an uneven surface with a height difference of 5-100 micrometers on the surface is made to contact | abut at least one of the said electrode material layer formed in both surfaces of the said metal electrical power collector, and is pressed.
When the unevenness of the uneven surface is less than 5 μm or exceeds 100 μm, the uneven structure having an unevenness of 5 μm to 100 μm may not be formed on the surface of the electrode material layer. As a result, the lithium secondary battery electrode that can sufficiently improve the output of the lithium secondary battery may not be produced.

Moreover, it is preferable that the said metal mold | die is roll shape (Claim 7).
In this case, the concavo-convex structure can be continuously formed on the surface of the electrode material layer by rotating the roll-shaped mold in contact with the surface of the electrode material layer.

The mold preferably has a plurality of cup-shaped recesses having a diameter of 5 to 500 μm that are recessed from the periphery on the surface thereof at intervals of 10 to 5000 μm.
In this case, a plurality of columnar convex portions having a diameter of 5 to 500 μm are formed at intervals of 10 to 5000 μm on the electrode material layer by pressing the mold in contact with the electrode material layer. The concave portion can be formed around the convex portion. Therefore, the concavo-convex structure can be easily formed.

Moreover, it is preferable that the mold has a plurality of columnar convex portions with a diameter of 5 to 500 μm protruding from the periphery at intervals of 10 to 5000 μm.
In this case, the mold is brought into contact with the electrode material layer and pressed to form a plurality of cup-shaped recesses having a diameter of 5 to 500 μm at intervals of 10 to 5000 μm in the electrode material layer. Can do. A convex portion can be formed around the concave portion. Therefore, the concavo-convex structure can be easily formed.

The mold preferably has a plurality of linear recesses having a line width of 3 to 500 μm formed at intervals of 5 to 1000 μm on the surface thereof (claim 10).
In this case, a plurality of linear protrusions having a line width of 3 to 500 μm are formed at intervals of 5 to 1000 μm on the electrode material layer by pressing the mold against the electrode material layer. be able to. Moreover, a linear recessed part can be formed between two adjacent linear convex parts.

Moreover, it is preferable that the said metal mold | die has a some linear convex part with the line | wire width of 3-500 micrometers formed with the space | interval of 5-1000 micrometers on the surface (Claim 11).
In this case, a plurality of linear recesses with a line width of 3 to 500 μm are formed at intervals of 5 to 1000 μm in the electrode material layer by pressing the mold against the electrode material layer. Can do. Moreover, a linear convex part can be formed between two adjacent linear concave parts.

Next, the lithium secondary battery includes a positive electrode, a negative electrode, and an electrode body composed of a separator sandwiched between the positive electrode and the negative electrode, a battery case containing the electrode body, and a battery case And filled electrolyte solution.
As the positive electrode and / or the negative electrode, the lithium secondary battery electrode can be used.

Preferably, both the positive electrode and the negative electrode are made of the electrode for a lithium secondary battery (claim 13).
In this case, both the positive electrode and the negative electrode have the uneven structure. Therefore, the output of the lithium secondary battery can be further improved.

  For the positive electrode, the electrode for a lithium secondary battery containing the positive electrode active material in the electrode material layer is used. On the other hand, for the negative electrode, the electrode for a lithium secondary battery containing the negative electrode active material in the electrode material layer is used.

  The separator to be narrowly attached to the positive electrode and the negative electrode separates the positive electrode and the negative electrode and holds the electrolytic solution. For example, a thin microporous film such as polyethylene or polypropylene can be used.

As the electrolytic solution, a nonaqueous electrolytic solution obtained by dissolving an electrolyte in an organic solvent or an aqueous electrolytic solution obtained by dissolving an electrolyte in water can be used.
As the electrolyte, it is possible to use, for example, _{LiPF 6, LiClO 4, LiBF 4} , LiAsF 6, or one or more selected from LiSbF ₆ like.
As the organic solvent, an aprotic organic solvent can be used. As such an organic solvent, for example, a mixed solvent composed of one or more selected from cyclic carbonate, chain carbonate, cyclic ester, cyclic ether, chain ether, and the like can be used.

  Here, examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of the cyclic ester carbonate include gamma butyrolactone and gamma valerolactone. Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the chain ether include dimethoxyethane and ethylene glycol dimethyl ether. As the organic solvent, any one of them can be used alone, or two or more kinds can be mixed and used.

Preferably, the electrolytic solution is a non-aqueous electrolytic solution obtained by dissolving a lithium salt in an organic solvent.
In this case, the effect of increasing the output can be further increased.

  Examples of the shape of the lithium secondary battery include a paper type, a coin type, a cylindrical type, and a square type. As the battery case containing the positive electrode, the negative electrode, and the electrolytic solution, those corresponding to these shapes can be used.

(Example 1)
Next, an embodiment of the present invention will be described with reference to FIGS.
In this example, an electrode for a lithium secondary battery (a positive electrode and a negative electrode) is produced, and a lithium secondary battery is produced using the electrode for the lithium secondary battery.
As shown in FIG. 1, the lithium secondary battery 1 of this example includes a positive electrode 2, a negative electrode 3, a separator 4, a gasket 59, a battery case 6, and the like. The battery case 6 is a 18650 type cylindrical case, and includes a cap 63 and an outer can 65. In the battery case 6, an electrode body formed by sandwiching a separator between the sheet-like positive electrode 2 and the negative electrode 3 is disposed in a wound state.
A gasket 59 is disposed inside the cap 63 of the battery case 6, and a non-aqueous electrolyte is injected into the battery case 6.

  The positive electrode 2 and the negative electrode 3 are respectively provided with a positive electrode current collecting lead 23 and a negative electrode current collecting lead 33 by welding. The positive electrode current collector lead 23 is connected to the positive electrode current collector tab 235 disposed on the cap 63 side by welding. Further, the negative electrode current collecting lead 33 is connected by welding to a negative electrode current collecting tab 335 disposed on the bottom of the outer can 65.

The nonaqueous electrolytic solution is prepared by adding LiPF ₆ as an electrolyte to an organic solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 30:70, and is injected into the battery case 6.

Moreover, as the positive electrode 2 and the negative electrode 3 of this example, as shown in FIGS. 2-4, the sheet-like electrode for lithium secondary batteries was used.
The lithium secondary battery electrodes 2 and 3 have a sheet-like metal current collector 21 (31) and an electrode material layer 22 (32) formed so as to sandwich both surfaces thereof.
The electrode 2 for a lithium secondary battery for positive electrode has an aluminum foil as the metal current collector 21, and the electrode material layer 22 is a lithium nickel composite oxide (LiNi _0.8 Co _0.15 Al) having a layered structure as a positive electrode active material. _0.05 O ₂ ) is the main component. The electrode material layer 22 contains carbon black as a conductive material and polyvinylidene fluoride as a binder.
Moreover, the electrode 3 for lithium secondary batteries for negative electrodes has copper foil as the metal electrical power collector 31, and the electrode material layer 32 has spherical artificial graphite which is a negative electrode active material as a main component. The electrode material layer 32 contains polyvinylidene fluoride as a binder.

  The electrode material layer 22 (32) has an uneven structure 225 (325) having a height difference h = 10 μm on the surface thereof. The concavo-convex structure 225 (325) has a plurality of cup-shaped concave portions 221 (321) having a diameter φ10 μm that are recessed from the periphery at intervals d = 10 μm. A convex portion 222 (322) is formed around the concave portion 221 (321).

Next, the manufacturing method of the electrode 2 (3) for lithium secondary batteries of this example is demonstrated.
In the manufacturing method of this example, an electrode for a lithium secondary battery is manufactured by performing a coating process and an uneven structure forming process.
As shown in FIG. 5, in the coating process, an electrode material slurry in which an electrode material is dispersed in an organic solvent is applied to both surfaces of the metal current collectors 21 and 31 and dried. Thereby, the electrode 20 (30) in which the electrode material layer 22 (32) is formed on both surfaces of the metal current collectors 21 and 31 is obtained.

  Further, in the concavo-convex structure forming step, the mold 7 (71, 72) having a concavo-convex surface 75 with a height difference of 10 μm on the surface is brought into contact with the electrode material layer 22 (32) of the electrode 20 (30) and pressed. (See FIGS. 6 and 9). Thereby, the uneven structure 225 (325) which consists of the recessed part 221 (321) and the convex part 222 (322) is formed in the electrode material layer 22 (32) (refer FIG. 2). Thus, the electrode 2 (3) for lithium secondary batteries which has the uneven structure 225 (325) of 10 micrometers in elevation difference on the surface is obtained.

Hereafter, the manufacturing method of the electrode for lithium secondary batteries of this example is demonstrated in detail.
First, the lithium secondary battery electrode 2 for positive electrodes is produced.
Specifically, first, lithium nickel composite oxide (LiNi _0.8 Co _0.15 Al _0.05 O ₂ ) having a layered structure as a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride as a binder were prepared. Next, 85 wt% of the positive electrode active material, 10 wt% of the conductive material, and 5 wt% of the binder were mixed, and an organic solvent (N-methyl-2-pyrrolidone) was added dropwise as a dispersion material. Furthermore, the positive electrode active material, the conductive material, and the binder were dispersed by mixing to obtain an electrode material slurry for the positive electrode. Next, this electrode material slurry was applied to both sides of a 20 μm thick aluminum foil current collector and dried. Thereby, as shown in FIG. 5, the electrode 20 in which the electrode material layer 22 was formed on both surfaces of the aluminum foil current collector 21 was obtained.

Next, an uneven structure forming step is performed using a mold having an uneven surface.
In the uneven | corrugated structure formation process of this example, as shown to FIGS. 6-8, the roll press apparatus 20 which has the roll-shaped metal mold | die 7 is used.
As shown in FIG. 6, the roll press device 70 includes an upper mold 71 and a lower mold 72 as the roll-shaped mold 7. In the roll press device 70, the upper mold 71 and the lower mold 72 are arranged with a certain gap between them. In this roll press device 70, the upper die 71 and the lower die 72 are rotated and the electrode 20 is passed through this gap, whereby the electrode material layer 22 formed on the metal current collector 21 is compressed. The electrode 2 that has passed through the roll press device 20 is taken up by a take-up roll 79.

  As shown in FIGS. 7 and 8, the mold 7 (the upper mold 71 and the lower mold 72) has an uneven surface 75 with a height difference of 10 μm on the surface thereof. The concavo-convex surface 75 has a plurality of columnar convex portions 73 with a diameter of 10 μm protruding from the periphery at intervals of 10 μm. A recess 74 is formed around the protrusion 73.

Therefore, as shown in FIG. 9, when the electrode 20 formed by forming the electrode material layer 22 on both surfaces of the metal current collector 21 is passed between the upper mold 71 and the lower mold 72, the upper mold 21 and the lower mold 22. The electrode material layer 22 is pressed and compressed by the surface, and the uneven structure 225 is formed in the electrode material layer 22 by the uneven surface 75 of the upper mold 71 and the lower mold 72. The lithium secondary battery electrode 2 on which the uneven structure 225 was formed was wound on a winding roll. In this example, the electrode material layer 22 was compressed to an electrode density of 2.5 g / cm ³ when compressed by the upper mold 71 and the lower mold 72. Moreover, the adhesion amount of the positive electrode active material was 7 mg / cm ² per side.
Subsequently, the electrode 2 for lithium secondary batteries was cut out to the size of width 52mm x length 450mm, and this was made into the positive electrode 2 for lithium secondary batteries.

Next, a negative electrode is produced as follows.
First, spherical artificial graphite was prepared as a negative electrode active material, and polyvinylidene fluoride was prepared as a binder. Next, 95 wt% of the negative electrode active material and 5 wt% of the binder were mixed, and a drop amount of N-methyl-2-pyrrolidone was added as a dispersion material. Furthermore, the negative electrode active material, the conductive material, and the binder were dispersed by mixing to obtain a negative electrode material slurry.
Next, this electrode material slurry was applied to both sides of a 10 μm thick copper foil current collector and dried. Thereby, the electrode 30 in which the electrode material layer 32 was formed on both surfaces of the copper foil current collector 31 was obtained (see FIG. 5).
Next, in the same manner as in the case of the positive electrode described above, compression was performed using the roll press device 70 to form the uneven structure 325 on both surfaces of the electrode material layer 32 of the electrode 30. And the obtained electrode 3 for lithium secondary batteries was wound up by the winding roll (refer FIG.6 and FIG.9). During compression, the electrode material layer 32 was compressed to an electrode density of 1.5 g / cm ³ . Moreover, the adhesion amount of the negative electrode active material was 5 mg / cm ² per side.
Next, the lithium secondary battery electrode 3 was cut into a size of 54 mm wide × 450 mm long, and this was used as the negative electrode 3 for the lithium secondary battery.

  Next, as shown in FIG. 1, a positive electrode current collecting lead 23 and a negative electrode current collecting lead 33 were welded to the sheet-like positive electrode 2 and negative electrode 3 obtained as described above, respectively. The positive electrode 2 and the negative electrode 3 were wound in a state where a polyethylene separator 4 having a width of 56 mm and a thickness of 25 μm was sandwiched between them, and a roll-shaped electrode body was produced.

  Subsequently, the roll-shaped electrode body was inserted into an 18650-type cylindrical battery case 6 including an outer can 65 and a cap 63. At this time, the positive electrode current collecting lead 23 is connected to the positive electrode current collecting tab 235 arranged on the cap 63 side of the battery case 6 by welding, and the negative electrode current collecting lead is arranged on the negative electrode current collecting tab 335 arranged on the bottom of the outer can 65. 33 was connected by welding.

  Next, the battery case 6 was impregnated with the non-aqueous electrolyte prepared as described above. A gasket 59 is disposed inside the cap 63, and the cap 63 is disposed in the opening of the outer can 65. Subsequently, the battery case 6 was sealed by caulking the cap 63, and the lithium secondary battery 1 was manufactured. This was designated as battery E1.

  Further, in this example, the battery E1 is different from the above-described battery E1 in three types of lithium secondary batteries (battery E2, battery E3, battery C) having a positive electrode and a negative electrode that are different in height in the concavo-convex structure, the diameter of the recesses, and the interval between the recesses. ) Was produced.

The battery E2 is a battery having a positive electrode and a negative electrode having a concavo-convex structure with a height difference h = 20 μm. The concavo-convex structure has a plurality of cup-shaped concave portions having a diameter of φ500 μm at intervals d = 500 μm. The other configuration is the same as that of the battery E1.
This battery E2 was produced in the same manner as the battery E1 except that a mold having a concavo-convex surface with a height difference of 20 μm, in which cylindrical convex portions having a diameter of 500 μm were arranged at intervals of 500 μm. .

The battery E3 is a battery having a positive electrode and a negative electrode having a concavo-convex structure with a height difference h = 5 μm. The concavo-convex structure has a plurality of cup-shaped concave portions having a diameter of 5 μm at intervals d = 10 μm. The other configuration is the same as that of the battery E1.
This battery E3 was produced in the same manner as the battery E1, except that a mold having a concavo-convex surface with a height difference of 5 μm, in which cylindrical convex portions with a diameter of 5 μm were arranged at intervals of 10 μm. .

The battery C is a battery having a positive electrode and a negative electrode having a concavo-convex structure with an elevation difference of 0.5 μm or less. The concave portion diameter φ of the concave-convex structure is 0.5 μm or less, and the interval d between the concave portions is also 0.5 μm or less. The other configuration is the same as that of the battery E1.
This battery E3 was used except that a mold having a surface structure in a normal mirror surface state (a height difference of 0.5 μm or less, a concave-convex concave portion diameter of 0.5 μm or smaller, and a concave interval of 0.5 μm or smaller) was used. Was produced in the same manner as the battery E1.

(Experimental example)
Next, about the said battery E1-battery E3 and the battery C, the following output test and charging / discharging cycle test were done, and the battery characteristic was evaluated.

"Output test"
Under the condition of a temperature of 20 ° C., each battery (battery E1 to battery E3 and battery C) is adjusted to 50% (SOC = 50%) of the battery capacity, and at any current value of 5 to 6 points of 100 mA to 10 A A current was passed, and the battery voltage after 10 seconds was measured. The applied current and voltage were linearly interpolated to determine the current value when the voltage after 10 seconds was 3.0 V, and the output (W) was calculated from the product of the current value and the voltage value. While calculating | requiring the initial output and the output after the charging / discharging cycle test mentioned later, the output maintenance factor was computed by the following formula | equation (a).
Output maintenance ratio (%) = output after charge / discharge cycle test / initial output × 100 (a)
Table 1 shows the initial output and the output maintenance ratio.

"Charge / discharge cycle test"
Under the temperature condition of 60 ° C., which is regarded as the upper limit of the actual use temperature range of the battery, each battery is charged to a charging upper limit voltage of 4.1 V with a constant current of 2.0 mA / cm ² , and then a current density of 2 Charge / discharge for discharging to a discharge lower limit voltage of 3 V at a constant current of 0.0 mA / cm ^{2 was} defined as one cycle, and this cycle was performed for a total of 500 cycles.
Then, when the discharge capacity before the charge / discharge cycle test was defined as the discharge capacity A (initial discharge capacity) and the discharge capacity after the charge / discharge cycle test was defined as the discharge capacity B, the capacity retention rate was calculated by the following formula (b). Table 1 shows the results of the initial discharge capacity and capacity retention rate.
Capacity maintenance rate (%) = discharge capacity B / discharge capacity A × 100 (b)

The discharge capacity A and the discharge capacity B were measured under the conditions of a temperature of 20 ° C. and a current density of 0.2 mA / cm ² before and after the charge / discharge cycle test. The discharge capacity is obtained by measuring the discharge current value (mA) and multiplying the discharge current value by the time (hr) required for discharge by the weight (g) of the positive electrode active material in the battery. Was calculated.

As is known from Table 1, each of the batteries E1 to E3 and the battery C showed a high initial discharge capacity of about 165 mAh / g, and further showed a high capacity maintenance rate of about 85%. From this, it can be seen that even when the concavo-convex structure is formed on the positive electrode and the negative electrode, the discharge capacity and the capacity retention rate are not adversely affected. Moreover, it can be said that the uneven structure formed in the positive electrode and the negative electrode of the batteries E1 to E3 is excellent in durability when charging and discharging are repeated at a high temperature.
On the other hand, the output of the battery C was 30 W, whereas the batteries E1 to E3 in which the concavo-convex structure having a height difference of 5 to 100 μm was formed on the positive electrode and the negative electrode were able to exhibit a high output of 41 W at the maximum. By forming the concavo-convex structure, a high output exceeding 10% as compared with the battery C could be achieved at the minimum. This is considered to be because the amount of the electrolyte solution present in the vicinity of the active material increased moderately and the battery reaction proceeded more smoothly by forming the uneven structure on the electrodes (positive electrode and negative electrode).

  Therefore, it can be seen that the output can be improved with almost no adverse effect on the capacity retention rate by using an electrode having a concavo-convex structure on the surface like the batteries E1 to E3. Therefore, a lithium secondary battery having an excellent capacity maintenance rate and a high output can be realized.

In the present embodiment, as described above, the electrode material layer 22 (32) is used by using the mold 7 having a plurality of cylindrical protrusions 73 protruding from the periphery on the surface (see FIGS. 7 and 8). A concavo-convex structure 225 (325) having a plurality of cup-shaped concave portions 221 (321) having a diameter of 5 to 500 μm recessed from the surroundings was formed on the surface (see FIG. 2).
As another embodiment, as shown in FIGS. 10 and 11, a concavo-convex structure can be formed using a mold 8 having a plurality of cup-shaped concave portions 82 that are recessed from the periphery. In the mold 8, a convex portion 81 is formed around the concave portion 82.
When this mold 8 is used, the concave-convex structure of the batteries E1 to E3 can form a concave-convex structure in which a concave portion and a convex portion are interchanged. That is, in this case, it is possible to form a concavo-convex structure having a plurality of columnar convex portions protruding from the periphery (not shown). Moreover, the said uneven | corrugated structure can also be formed using the metal mold | die which has multiple polygonal column-shaped recessed parts or convex parts on the surface instead of a cylindrical recessed part or convex part.

Moreover, as shown in FIG.12 and FIG.13, the said uneven | corrugated structure can also be formed using the metal mold | die 9 in which the several linear recessed part 92 was formed in the surface. In the mold 9, a convex portion 91 is formed between two adjacent concave portions 92.
When such a mold 9 is used, a hairline-like uneven structure in which a plurality of linear convex portions and a plurality of linear concave portions are alternately formed can be formed on the electrode material layer (illustrated). Abbreviation).
As described above, even when the concavo-convex structure having various patterns is formed, as in the case of the battery E1 to the battery E3, high output can be achieved without reducing the capacity retention rate of the lithium secondary battery. it can.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the structure of the lithium secondary battery concerning Example 1. FIG. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the cross-section of the electrode for lithium secondary batteries concerning Example 1. FIG. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the single side | surface of the electrode for lithium secondary batteries concerning Example 1. FIG. FIG. 3 is a partially enlarged view of a concavo-convex structure of an electrode for a lithium secondary battery according to Example 1. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the cross-section of the electrode concerning Example 1 which formed the electrode material layer on both surfaces of the metal electrical power collector. Explanatory drawing which shows a mode that the electrode material layer of the metal electrical power collector surface is compressed with the roll press apparatus concerning Example 1. FIG. Explanatory drawing which shows the cross-sectional structure of the roll-shaped metal mold | die in which the several convex part was formed in the surface concerning Example 1. FIG. Explanatory drawing which shows the surface structure of the roll-shaped metal mold | die in which the some convex part was formed in the surface concerning Example 1. FIG. Explanatory drawing which shows a mode that a concavo-convex structure is formed in an electrode material layer by the roll-shaped metal mold | die concerning Example 1. FIG. Explanatory drawing which shows the cross-section of the roll-shaped metal mold | die in which the some cylindrical recessed part was formed in the surface. Explanatory drawing which shows the surface structure of the roll-shaped metal mold | die with which the some cylindrical recessed part was formed in the surface. Explanatory drawing which shows the cross-section of the metal mold | die with which the several linear recessed part and the several linear convex part were alternately formed in the surface. Explanatory drawing which shows the cross-section of the metal mold | die with which the several linear recessed part and the several linear convex part were alternately formed in the surface.

Explanation of symbols

1 Lithium secondary battery 2 Positive electrode (electrode for lithium secondary battery)
3 Negative electrode (electrode for lithium secondary battery)
21 (31) Metal current collector 22 (32) Electrode material layer 221 (321) Concave part 222 (322) Convex part 225 (325) Concave and convex structure

Claims (14)

Lithium having a positive electrode, a negative electrode, and an electrode body composed of a separator sandwiched between the positive electrode and the negative electrode, a battery case containing the electrode body, and an electrolyte filled in the battery case A sheet-like electrode for a lithium secondary battery used for the positive electrode and / or the negative electrode of a secondary battery,
The electrode for a lithium secondary battery has a sheet-like metal current collector and an electrode material layer formed so as to sandwich both surfaces of the metal current collector,
The electrode material layer is mainly composed of an inorganic positive electrode active material capable of occluding or releasing lithium ions or an inorganic negative electrode active material capable of occluding or releasing lithium ions,
The electrode for a lithium secondary battery, wherein at least one of the electrode material layers formed on both surfaces of the metal current collector has a concavo-convex structure with a height difference of 5 to 100 μm on the surface thereof.   2. The electrode for a lithium secondary battery according to claim 1, wherein the concavo-convex structure has a plurality of columnar convex portions having a diameter of 5 to 500 [mu] m protruding from the periphery at intervals of 10 to 5000 [mu] m.   3. The electrode for a lithium secondary battery according to claim 1, wherein the concavo-convex structure has a plurality of cup-shaped concave portions having a diameter of 5 to 500 μm that are recessed from the periphery at intervals of 10 to 5000 μm.   2. The electrode for a lithium secondary battery according to claim 1, wherein the concavo-convex structure has a plurality of linear protrusions having a line width of 3 to 500 [mu] m formed at intervals of 5 to 1000 [mu] m.   3. The electrode for a lithium secondary battery according to claim 1, wherein the concavo-convex structure has a plurality of linear recesses having a line width of 3 to 500 [mu] m formed at intervals of 5 to 1000 [mu] m. Lithium having a positive electrode, a negative electrode, and an electrode body composed of a separator sandwiched between the positive electrode and the negative electrode, a battery case containing the electrode body, and an electrolyte filled in the battery case A method for producing a sheet-like electrode for a lithium secondary battery used for the positive electrode and / or the negative electrode of a secondary battery,
It has a sheet-like metal current collector and an electrode material layer formed so as to sandwich both surfaces of the metal current collector, and has an uneven structure with a height difference of 5 to 100 μm on at least one surface of the electrode material layer In the method for producing an electrode for a lithium secondary battery,
An electrode obtained by dispersing an electrode material mainly composed of an inorganic positive electrode active material capable of inserting or extracting lithium ions or an inorganic negative electrode active material capable of inserting or extracting lithium ions on both surfaces of the metal current collector in an organic solvent. Applying and drying a material slurry to form the electrode material layer sandwiching the metal current collector,
The concavo-convex structure is formed by pressing a mold having a concavo-convex surface with a height difference of 5 to 100 μm on the surface in contact with at least one surface of the electrode material layer formed on both surfaces of the metal current collector. A method for producing an electrode for a lithium secondary battery, comprising the step of forming an uneven structure.   7. The method for manufacturing an electrode for a lithium secondary battery according to claim 6, wherein the mold is in a roll shape.   8. The lithium secondary battery according to claim 6, wherein the mold has a plurality of cup-shaped recesses having a diameter of 5 to 500 [mu] m recessed from the periphery at intervals of 10 to 5000 [mu] m. For manufacturing an electrode.   8. The lithium secondary battery according to claim 6, wherein the mold has a plurality of columnar protrusions having a diameter of 5 to 500 μm protruding from the periphery at intervals of 10 to 5000 μm. For manufacturing an electrode.   10. The mold according to claim 6, wherein the mold has a plurality of linear recesses having a line width of 3 to 500 μm formed at intervals of 5 to 1000 μm on the surface thereof. A method for manufacturing an electrode for a lithium secondary battery.   10. The mold according to claim 6, wherein the mold has a plurality of linear protrusions having a line width of 3 to 500 μm formed at intervals of 5 to 1000 μm on the surface thereof. A method for producing an electrode for a lithium secondary battery. Lithium having a positive electrode, a negative electrode, and an electrode body composed of a separator sandwiched between the positive electrode and the negative electrode, a battery case containing the electrode body, and an electrolyte filled in the battery case In secondary batteries,
At least one of the said positive electrode and the said negative electrode consists of the said electrode for lithium secondary batteries as described in any one of Claims 1-5, The lithium secondary battery characterized by the above-mentioned.   The lithium secondary battery according to claim 12, wherein both the positive electrode and the negative electrode are composed of the electrode for the lithium secondary battery according to claim 1.   14. The lithium secondary battery according to claim 12, wherein the electrolytic solution is a nonaqueous electrolytic solution obtained by dissolving a lithium salt in an organic solvent.

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