JP2010086717A - Electrode for lithium secondary battery, and lithium secondary cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a lithium secondary battery with active material layers provided on both surfaces of a collector capable of improving discharge rate characteristics and as well as excellent in adhesiveness between the active material layers and the collector, and obtainable high charge-discharge cycle characteristics and provide a lithium secondary battery. <P>SOLUTION: In the electrode for a lithium secondary battery with active material layers 1 and 2 provided on both opposing surfaces of a collector, a plurality of slit-shaped grooves 4 and 5 nearly parallel with each other are formed each on the active material layers 1 and 2 on both surfaces, and a smaller angle θ out of the angles made by an extending direction of the groove 4 formed on the one surface of the active material layer and the extending direction of the groove 5 formed on the other surface of the active material layer is ≥15 degrees. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lithium secondary power electrode and a lithium secondary battery using the same.

  The current lithium secondary battery is formed by stacking an electrode group consisting of a positive electrode, a negative electrode, and a separator in layers such as a spiral or a stack together with an electrolyte in an outer package such as a battery can. . In each electrode, an active material layer is formed on the current collector. Therefore, if the active material layer is made thick and the number of electrode groups stacked is reduced, the volume of the active material layer in the battery can increases and the battery capacity can be increased.

  However, when the active material layer is thickened, the current density per electrode surface area is increased under the same charge / discharge current time ratio. In addition, since the active material near the current collector has a long distance to the electrode surface, lithium ions cannot be smoothly diffused from the reaction site of the active material to the electrolyte phase during charging and discharging. For this reason, the utilization factor of an active material falls in the range of the practically effective charging / discharging voltage for the operation of the lithium secondary battery, and as a result, the merit of increasing the capacity by thickening the active material layer cannot be obtained.

  In order to solve the above problem, it is conceivable to make the electrolyte easily penetrate into the active material layer.

  Patent Document 1 proposes a nonaqueous electrolyte secondary battery improved by forming a hole or groove in at least one of a positive electrode and a negative electrode so that the efficiency of the battery does not decrease even when the electrode area is increased. Has been. In Patent Document 2, it is proposed that an electrolyte guide groove is formed on the surface of the negative electrode active material layer in the permeation direction of the nonaqueous electrolytic solution, and the central portion of the negative electrode is sufficiently impregnated with the electrolytic solution. In Patent Document 3, an uncoated portion that becomes a slit-like gap is formed in the active material layer so as to reach the end face, and the injection time when impregnating with the electrolytic solution is shortened.

  In Patent Document 4, a large number of grooves are formed on the surface of the positive electrode to which the separator is bonded via the adhesive layer, and the solvent of the adhesive layer is easily volatilized through the grooves, and the electrolytic solution passes through the grooves. It is possible to penetrate inside. In Patent Document 5, it is proposed to form grooves in the current collector to promote internal diffusion of the nonaqueous electrolyte.

However, in these conventional techniques, when the groove is formed in each of the active material layers formed on both sides of the current collector, sufficient examination has not been made on how to form the grooves.
JP-A-9-283116 JP-A-9-298057 JP 2001-35484 A JP 2001-357836 A JP 2005-267955 A

  An object of the present invention is to improve the discharge rate characteristics in an electrode for a lithium secondary battery in which an active material layer is provided on both sides of a current collector, and to improve the adhesion between the active material layer and the current collector. An object of the present invention is to provide an electrode for a lithium secondary battery capable of obtaining excellent and high charge / discharge cycle characteristics and a lithium secondary battery using the same.

  An electrode for a lithium secondary battery of the present invention is an electrode for a lithium secondary battery in which an active material layer is provided on both sides of a current collector facing each other, and a plurality of slit-like grooves substantially parallel to each other are provided on both sides. Formed in each of the upper active material layers, and an angle formed by the extending direction of the groove formed in the active material layer on one surface and the extending direction of the groove formed in the active material layer on the other surface. Among them, the smaller angle is 15 degrees or more.

  In the present invention, the smaller one of the angles formed by the extending direction of the groove formed in the active material layer on one surface and the extending direction of the groove formed in the active material layer on the other surface is 15 degrees. Each groove is formed so as to be the above. When slit-like grooves are formed in the active material layer, the current collector and the active material layer are easily bent in a direction substantially perpendicular to the extending direction of the grooves. For this reason, the smaller one of the angles formed by the extending direction of the groove formed in the active material layer on one surface and the extending direction of the groove formed in the active material layer on the other surface is less than 15 degrees. Then, since the extending direction of each groove approaches, the current collector and the active material layer are easily bent with respect to a specific direction. As a result, the adhesion between the active material layer and the current collector is lowered, and the charge / discharge cycle characteristics are lowered.

  According to the present invention, the smaller one of the angles formed by the extending direction of the groove formed in the active material layer on the one surface and the extending direction of the groove formed in the active material layer on the other surface is 15 degrees or more. By forming each groove, the current collector and the active material layer can be prevented from being easily bent in a specific direction, and the adhesion between the active material layer and the current collector is excellent. It can be set as the electrode for lithium secondary batteries which shows a high charging / discharging cycling characteristic.

  The angle is more preferably in the range of 45 degrees to 90 degrees. By setting it as such a range, it can prevent still more effectively that a collector and an active material layer become easy to bend in a specific direction.

  In addition, after forming a groove in the active material layer on one surface and then forming a groove in the active material layer on the other surface, stress is applied to the current collector and the active material layer on the one surface. Such stress is likely to be applied in a direction substantially perpendicular to the extending direction of the groove to be formed. For this reason, the smaller one of the angles formed by the extending direction of the groove formed in the active material layer on the other surface and the extending direction of the groove formed in the active material layer on the one surface is less than 15 degrees. When the groove is formed in the active material layer on the other surface, a large stress is applied to the current collector and the active material layer on one surface, and the active material layer on one surface and the current collector are in close contact with each other. Sex is reduced. As a result, the charge / discharge cycle characteristics deteriorate. According to the present invention, by forming each groove so that the angle is in the range of 15 degrees or more, preferably 45 degrees to 90 degrees, the adhesion between the active material layer and the current collector is excellent, and high charge / discharge It can be set as the electrode for lithium secondary batteries which shows cycling characteristics.

  Further, in the present invention, the end of the groove in the extending direction of the groove on the one surface is not located on the line when the groove on the other surface is projected on the one surface. Each groove is preferably formed. As described above, when the active material layer and the current collector are bent or when the groove is formed on the other surface, stress tends to concentrate on the end of the groove in the direction in which the groove extends. Therefore, if the end of the groove on one surface is located on the line when the groove on the other surface is projected on one surface, a larger stress is concentrated and the adhesion between the active material layer and the current collector is reduced. To do. For this reason, as described above, the end of the groove in the extending direction of the groove on the one surface is not positioned on the line when the groove on the other surface is projected onto the one surface. It is preferable that the upper grooves are respectively formed.

  Moreover, in this invention, the groove | channel may be formed so that the space | interval between grooves may expand gradually. In the region where the interval between the grooves is narrow, the nonaqueous electrolyte is more easily introduced into the electrode. Therefore, in a secondary battery in which a separator is disposed between a positive electrode and a negative electrode, and this is wound in a spiral shape and housed in an outer package, a portion with a narrow gap between the grooves is positioned at the center of the battery. By assembling the battery, the nonaqueous electrolyte can be introduced into the central portion where the nonaqueous electrolyte is difficult to penetrate, and the battery characteristics can be improved.

  In the present invention, the groove is preferably formed so that the end of the groove in the extending direction of the groove does not reach the peripheral edge of the active material layer. When the end portion of the groove reaches the peripheral edge portion of the active material layer, the active material layer and the current collector are liable to be peeled off from that portion. By forming the groove so that the end portion of the groove does not reach the peripheral edge of the active material layer, peeling of the active material layer from the current collector can be prevented.

  Moreover, it is preferable that the groove | channel is not formed in the area | region to 1 mm inside from the peripheral part of an active material layer. By not forming a groove in this region, it is possible to more effectively prevent the active material layer from being separated from the current collector.

  Moreover, in this invention, it is preferable that the groove | channel is formed in the depth which does not reach the electrical power collector surface. By forming the groove at a depth that does not reach the current collector surface, it is possible to more effectively prevent the active material layer from peeling from the current collector.

  A lithium secondary battery of the present invention includes a positive electrode, a negative electrode, a separator provided between the positive electrode and the negative electrode, a nonaqueous electrolyte, and an exterior body that houses the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte. The secondary battery is characterized in that the electrode of the present invention is used as a positive electrode and / or a negative electrode.

  In the lithium secondary battery of the present invention, since the electrode for the lithium secondary battery of the present invention is used as a positive electrode and / or a negative electrode, the discharge rate characteristics can be improved, and a current collector as an active material layer It is excellent in adhesiveness, and high charge / discharge cycle characteristics can be obtained.

  The lithium secondary battery of the present invention may be a lithium secondary battery that is wound in a spiral shape in a state in which a positive electrode, a negative electrode, and a separator are stacked and is housed in an outer package. In this case, it is preferable to use the electrode of the present invention in which grooves are formed so that the distance between the grooves gradually increases, and the grooves are formed so that the distance between the grooves increases from the center of the battery toward the outside. . As a result, the nonaqueous electrolyte can be preferentially introduced into the central portion where the nonaqueous electrolyte is difficult to penetrate, and the battery characteristics can be improved.

  The lithium secondary battery of the present invention may also be a stack type secondary battery in which a plurality of positive electrodes, negative electrodes, and separators are stacked.

  Except as described above, the grooves in the present invention are preferably arranged uniformly in the groove forming region in the active material layer. Thereby, lithium ions are more uniformly diffused in the electrode, and damage to the active material layer due to deformation of the electrode can be prevented.

  In the present invention, the method for forming the groove is not particularly limited, but a method for physically removing the active material layer to form the groove or a laser irradiation to melt the active material layer to form the groove. And a method of forming grooves using mechanical stress by, for example, applying particles to the surface of the active material layer at high speed. Further, the groove may be formed by chemical etching.

  It is also possible to form grooves in the stage of forming the active material layer. For example, a method of forming an active material layer by patterning so as to form a groove by using various printers such as screen printing and inkjet may be used. In addition, the current collector is previously masked in a slit shape, and after applying a slurry on it, or by physically or chemically attaching an active material by sputtering, vapor deposition, electrodeposition, etc., the mask is removed, A method of forming a groove is also included. The thickness of the active material layer in the present invention is preferably in the range of 20 to 300 μm.

The active material layer in the present invention may be a positive electrode active material layer or a negative electrode active material layer. Examples of the positive electrode active material include layered transition metal oxides such as LiCoO ₂ and LiNiO ₂ , spinel type transition metal oxides such as LiMn ₂ O ₄ and Li ₄ Ti ₅ O ₁₂ , and olivine types such as LiFePO ₄ and LiCoPO _4. A phosphoric acid compound etc. are mentioned. Examples of the negative electrode active material include spinel transition metal oxides such as Li ₄ Ti ₅ O ₁₂ , carbon materials such as graphite and coke, silicon, tin, and alloy materials thereof. Since the positive electrode active material layer is generally formed thick, the effect of the lithium secondary battery electrode of the present invention is particularly significant when used as a positive electrode.

  The lithium secondary battery of the present invention is characterized by comprising a positive electrode comprising the electrode of the present invention, a negative electrode, and a nonaqueous electrolyte.

  Since the lithium secondary battery of the present invention uses the electrode of the present invention, the battery can have a high active material utilization rate and excellent discharge rate characteristics.

The electrolyte salt used for the non-aqueous electrolyte is not particularly limited, but LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl _12, and mixtures thereof are exemplified.

  In the present invention, the effect of the present invention is further exhibited particularly when the concentration of the electrolyte salt in the nonaqueous electrolyte is 1.5 mol / liter or more. When the concentration of the electrolyte salt is 1.5 mol / liter or more, the viscosity of the nonaqueous electrolyte increases and lithium ions are difficult to diffuse. According to the present invention, by using an electrode in which slit-like or lattice-like grooves are formed in the active material layer, the contact area between the nonaqueous electrolyte and the electrode surface can be increased, and lithium ions can be further diffused. Therefore, the effect of the present invention is further exhibited.

  The solvent used for the non-aqueous electrolyte is not particularly limited, but a cyclic carbonate or a chain carbonate is preferable. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and the like. Among these, ethylene carbonate is particularly preferably used. Examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and the like. Further, the solvent is preferably a mixed solvent obtained by mixing two or more solvents. In particular, a mixed solvent containing a cyclic carbonate and a chain carbonate is preferable.

  A mixed solvent of the cyclic carbonate and an ether solvent such as 1,2-dimethoxyethane or 1,2-diethoxyethane is also preferably used.

  The current collector used in the present invention is not particularly limited, and a current collector that has been conventionally used as a current collector for an electrode of a lithium secondary battery can be used. In the case of the positive electrode current collector, a metal foil such as an aluminum foil can be used, and in the case of the negative electrode current collector, a metal foil such as a copper foil can be used.

  By using the electrode for a lithium secondary battery of the present invention, the discharge rate characteristics can be improved, the adhesiveness between the active material layer and the current collector is excellent, and high charge / discharge cycle characteristics can be obtained.

  In addition, since the lithium secondary battery of the present invention uses the electrode of the present invention as a positive electrode and / or a negative electrode, the discharge rate characteristics can be improved and the adhesion between the active material layer and the current collector can be improved. And high charge / discharge cycle characteristics can be obtained.

  Hereinafter, the present invention will be described with reference to specific embodiments. However, the present invention is not limited to the following embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention. It is.

(First embodiment)
FIG. 1 is a plan view showing an electrode for a lithium secondary battery of a first embodiment according to the present invention.

  As shown in FIG. 1A, the active material layer 1 is formed with a plurality of slit-like grooves 4 extending in the vertical direction. The plurality of slit-shaped grooves 4 extend in directions substantially parallel to each other.

  The active material layer 1 is provided on one surface of a current collector (not shown). An active material layer 2 is provided on the other surface opposite to one surface of the current collector. A plurality of slit-like grooves 5 are formed in the active material layer 2 in the lateral direction. The plurality of slit-like grooves 5 extend in directions substantially parallel to each other.

  In this embodiment, the groove 4 and the groove 5 are formed such that an angle θ formed by the extending direction of the groove 4 formed in the active material layer 1 and the extending direction of the groove 5 formed in the active material layer 2 is 90 degrees. Is formed.

  A current collector tab 6 is attached to the current collector.

  As shown in FIG. 1A, the end portions 4a and 4b in the extending direction of the groove 4 are not positioned on the line when the groove 5 is projected onto the surface of the current collector on the surface side including the groove 4. A groove 4 is formed in the groove. Similarly, the grooves 5 are formed so that the end portions 5a and 5b in the extending direction of the groove 5 are not positioned on the line when the groove 4 is projected onto the surface of the current collector on the surface side including the groove 5. .

  Further, the groove 4 and the groove 5 are formed so as not to reach the peripheral portions 1 a and 2 a of the active material layers 1 and 2. It is preferable that the groove 4 and the groove 5 are not formed in a region of 1 mm inward from the peripheral edges 1a and 2a of the active material layers 1 and 2.

  FIG.1 (b) is a top view which shows the front side of an electrode. As shown in FIG. 1B, a plurality of slit-like grooves 4 are formed in the vertical direction in the active material layer 1 located on the front side.

  FIG.1 (c) is a top view which shows the back side of an electrode. As shown in FIG. 1C, a plurality of slit-like grooves 5 are formed in the lateral direction in the active material layer 2 located on the back side.

  As described above, in this embodiment, the angle θ formed by the extending direction of the groove 4 formed in the active material layer 1 and the extending direction of the groove 5 formed in the active material layer 2 is 15 degrees or more. It is formed to be 90 degrees. According to the present invention, by forming the grooves 4 and 5 so that the angle θ is 15 degrees or more, the adhesion between the active material layers 1 and 2 and the current collector can be improved, and high charge / discharge cycle characteristics Can be obtained. The reason will be specifically described below.

  In FIG. 2, the active material layer 1 is provided on one surface 3a of the current collector 3, the active material layer 2 is provided on the other surface 3b, and a plurality of slit-like grooves 4 are formed in the active material layer 1, 3 is a cross-sectional view showing an electrode in which a plurality of slit-like grooves 5 are formed in an active material layer 2. FIG.

  With reference to FIG. 2, the dimension shape etc. of the groove | channel formed in this invention are demonstrated. Although the width W of the groove | channel 4 and the groove | channel 5 is not specifically limited, It is preferable to form so that it may become the width | variety of the range of 10-100 micrometers. By forming in such a range, the current density per surface area can be reduced without significantly reducing the capacity.

  Moreover, it is preferable that the groove | channel 4 and the groove | channel 5 in this invention are formed in the depth d from which the bottom parts 4a and 5a do not reach the surface 3a and 3b of an electrical power collector. Accordingly, the depth d of the grooves 4 and 5 is preferably formed to be smaller than the thickness t of the active material layer 1 and the active material layer 2. By forming the grooves 4 and 5 at a depth that does not reach the current collector surfaces 3a and 3b, it is possible to effectively prevent the active material layers 1 and 2 from being separated from the current collector 3 due to the groove formation. it can.

  Further, the depth d of the grooves 4 and 5 is preferably formed to be equal to or greater than ½ of the thickness t of the active material layer 1 and the active material layer 2. Thereby, the nonaqueous electrolyte can be disposed up to the vicinity of the current collector 3 of the active material layers 1 and 2, lithium ions can be diffused more smoothly, the utilization rate of the active material is increased, and the discharge rate is increased. Characteristics can be improved.

  The depth d of the grooves 4 and 5 is more preferably in the range of 50 to 99.5% of the thickness of the active material layers 1 and 2.

  The grooves 4 and 5 are preferably formed such that the distance D between the adjacent grooves 4 and 5 is 1000 μm or less. The distance D in this case is the distance between the centers in the surface direction of the grooves 4 and 5. The distance D is more preferably in the range of 100 to 800 μm. By setting it as such a range, the surface area of an active material layer increases, the current density per surface area can be reduced, and lithium ion can be spread | diffused smoothly.

  In the state shown in FIG. 2, the groove 4 formed in the active material layer 1 and the groove 5 formed in the active material layer 2 are formed so as to extend in a substantially parallel direction. Accordingly, a state is shown in which the grooves 4 and 5 are formed so that the angle θ shown in FIG. 1 is approximately 0 degrees.

  FIG. 3 is a cross-sectional view showing a state where the electrode shown in FIG. 2 is bent. In the state shown in FIG. 3, the active material layer 1 is curved outward and the active material layer 2 is curved inward.

  As shown in FIG. 3, the groove 4 of the active material layer 1 located outside is deformed so that the width of the groove 4 expands as indicated by an arrow A. On the other hand, in the active material layer 2 located on the inner side, as shown by the arrow B, the groove 5 is deformed so as to become narrower.

  In the active material layer 1, since there is a space along the direction in which the groove 4 extends, the active material layer 1 is easily deformed in a direction substantially perpendicular to the direction in which the groove 4 extends. Moreover, in the active material layer 2, since a space exists in the direction in which the groove 5 extends, the active material layer 2 is easily deformed in a direction substantially perpendicular to the direction in which the groove 5 extends.

  When the direction in which the groove 4 extends and the direction in which the groove 5 extends are substantially parallel, the direction in which the active material layer 1 is easily deformed and the direction in which the active material layer 2 is easily deformed are substantially the same direction. The electrode is easily deformed with respect to the direction. For this reason, it becomes an electrode which is easily deformed by an external stress, and peeling between the active material layer 1 and the current collector 3 and between the active material layer 2 and the current collector 3 are likely to occur. Adhesiveness between the material layer 1 and the active material layer 2 and the current collector 3 is lowered.

  Moreover, since the active material layer 1 and the active material layer 2 are easily deformed, the active material layer 1 between the grooves 4 and the active material layer 2 between the grooves 5 are formed during battery assembly or charge / discharge reaction. Problems such as chipping and detachment tend to occur, and charge / discharge cycle characteristics deteriorate.

  The decrease in the adhesion between the active material layer and the current collector and the decrease in charge / discharge cycle characteristics as described above are the angle formed by the direction in which the groove 4 extends and the direction in which the groove 5 extends, as shown in the examples described later. This is likely to occur when θ is less than 15 degrees.

  The above problem also occurs when stress is applied when forming a groove in the active material layer.

  4 and 5 are cross-sectional views for explaining a case where stress is applied when the groove is formed.

  FIG. 4 is a cross-sectional view showing a state after the grooves 4 are formed in the active material layer 1 on the one surface 3 a of the current collector 3. FIG. 5 is a cross-sectional view showing a state in which the groove 5 is formed in the active material layer 2 on the other surface 3 b of the current collector 3. When the groove 5 is formed, for example, when cutting is performed using a knife or the like, stress during cutting is applied to the active material layer 2, the current collector 3, and the active material layer 1. When the direction in which the groove 5 extends is substantially parallel to the direction in which the groove 4 extends, a space is formed in the direction in which the groove 4 extends. Therefore, the active material layer 1 is deformed by the stress when the groove 5 is formed. It becomes easy to do. For this reason, the current collector 3 and the active material layer 1 are easily separated. Also, in the active material layer 2, when the groove 5 is formed to some extent, the active material layer 2 itself is easily deformed, and peeling between the active material layer 2 and the current collector 3 is likely to occur. For this reason, peeling or the like is likely to occur between the current collector 3, the active material layer 1, and the active material layer 2 due to the stress applied when forming the groove 5, and the adhesion is reduced.

  The above problem is also likely to occur when the angle θ is less than 15 degrees.

  Therefore, according to the present invention, the angle θ formed by the direction in which the groove 4 extends and the direction in which the groove 5 extends is 15 degrees or more, so that the adhesion between the active material layer and the current collector is excellent, and a high charge / discharge cycle. Characteristics can be obtained.

(Second Embodiment)
FIG. 6 is a plan view showing an electrode for a lithium secondary battery of a second embodiment according to the present invention.

  In this embodiment, as shown in FIG. 6, the groove 4 formed in the active material layer 1 extends in the vertical direction, and the groove 5 formed in the opposite active material layer 2 extends in the oblique direction. Yes. Therefore, the angle θ formed by the extending direction of the groove 4 and the extending direction of the groove 5 is an angle of 15 degrees or more and less than 90 degrees. In the present invention, the angle formed by the groove 4 and the groove 5 is an angle θ which is a smaller angle. Accordingly, in the present invention, the angle θ is in the range of 15 degrees to 90 degrees.

  FIG. 6B shows the groove 4 formed in the active material layer 1 on the front side, and FIG. 6C shows the groove 5 formed in the active material layer 2 on the back side.

(Third embodiment)
FIG. 7 is a plan view showing an electrode for a lithium secondary battery of a third embodiment according to the present invention.

  As shown in FIG. 7A, a groove 4 extending in the vertical direction is formed in the active material layer 1 on the front side. A groove 5 extending in an oblique direction is formed in the active material layer 2 on the back side.

In the present embodiment, the interval D ₁ of the between the grooves 4 are grooves 4 are formed so as to extend with increasing distance from the current collector tab 6. The groove 5 Similarly, spacing D ₂ between the grooves 5 is formed so as to extend with increasing distance from the current collector tab 6.

  FIG. 7B shows the groove 4 formed in the active material layer 1 on the front side. FIG. 7C shows the groove 5 formed in the active material layer 2 on the back side.

In the present embodiment, the groove 4 and the groove 5 are formed so that the distance D ₁ between the grooves 4 and the distance D ₂ between the grooves 5 increase as the distance from the current collector tab 6 increases. In the vicinity of the current collector tab 6, more grooves 4 and 5 are formed per area, so that it is easier to introduce the nonaqueous electrolyte into the electrode in the vicinity of the current collector tab 6. Accordingly, in the cylindrical battery in which the electrode is wound in a spiral shape, the nonaqueous electrolyte is likely to be insufficiently penetrated at the center of the battery. Therefore, the current collector tab 6 is arranged at the center of the battery, and the spiral shape is obtained. By winding, introduction of the electrolytic solution in the center of the battery can be promoted.

  FIG. 8 is a plan view showing another embodiment of the groove 4. In the present invention, the groove may be divided into a plurality of grooves 4 as shown in FIG.

  FIG. 9 is a plan view for explaining a preferable position of the end portion of the groove. As described above, the end of the groove on the one surface is preferably formed so as not to be positioned on a line when the groove on the other surface is projected onto the other surface. As shown in FIG. 9, the end 5 b of the groove 5 is preferably not located on the line of the groove 4. FIG. 10 shows a state where the end 5 b of the groove 5 is located on the line of the groove 4. In the present invention, it is preferable that the end 5 b of the groove 5 is not located at the end of the groove 4 as shown in FIG. 9.

(Example of lithium secondary battery)
FIG. 11 is an exploded perspective view showing an example of a lithium secondary battery according to the present invention. A lithium secondary battery 10 shown in FIG. 11 is a cylindrical secondary battery, and in a state where a separator 13 is disposed between the negative electrode 12 and the positive electrode 11 and a separator 13 is further disposed outside the positive electrode 11. The electrode group is wound in a spiral shape and is housed in an exterior body composed of a negative electrode can 14 and a positive electrode can 15.

  In such a cylindrical battery, as described above, the nonaqueous electrolyte may not be sufficiently supplied into the electrode at the center of the battery, so an electrode as shown in FIG. By disposing a relatively large number of grooves, it is possible to improve the shortage of non-aqueous electrolyte in the center of the battery.

(Other examples of lithium secondary batteries)
FIG. 12 is a perspective view showing another example of the lithium secondary battery according to the present invention. FIG. 12 shows an electrode portion in which a part of a stack type lithium secondary battery in which a positive electrode, a negative electrode, and a separator are stacked is cut out. The positive electrode 21, the negative electrode 22, and the separator 23 are stacked so that the separator 23 is disposed between the positive electrode 21 and the negative electrode 22. A positive electrode tab 21 a is attached to the positive electrode 21, and a negative electrode tab 22 a is attached to the negative electrode 22. Thus, the positive electrode 21, the negative electrode 22, and the separator 23 are stacked and stored in the battery exterior body.

  FIG. 13 is a perspective view showing a stacked lithium secondary battery 20 in which the electrode portion shown in FIG. 12 is housed. A positive electrode tab 21a and a negative electrode tab 22a are taken out from the stacked lithium secondary battery 20.

  Also in the above-described stack type lithium secondary battery, by using the electrode for the lithium secondary battery of the present invention, the discharge rate characteristics can be improved, and excellent adhesion between the active material layer and the current collector, It can be set as the lithium secondary battery which shows a high charging / discharging cycling characteristic.

  The electrode for a lithium secondary battery of the present invention may be used for both the positive electrode and the negative electrode, or may be used for only one of the positive electrode and the negative electrode.

  Hereinafter, the present invention will be described with reference to specific examples. However, the present invention is not limited to the following examples, and can be appropriately modified and implemented without departing from the scope of the present invention. .

[Production of positive electrode]
And LiCoO ₂ 90% by weight as a positive electrode active material, carbon black 5 wt% as a conductive agent, and polyvinylidene fluoride 5 wt% as a binder, N- methyl-2-pyrrolidone (NMP) solution as the solvent Were mixed to prepare a positive electrode slurry, and this positive electrode slurry was applied to both surfaces of an aluminum foil as a positive electrode current collector. Thereafter, the solvent was dried, compressed to a thickness of 0.1 mm with a roller, and then cut to a width of 95 mm and a height of 95 mm to produce a positive electrode.

(Production of negative electrode)
A slurry was prepared by mixing 95% by weight of graphite powder as a negative electrode active material, 5% by weight of polyvinylidene fluoride as a binder, and an NMP solution as a solvent, and then using the slurry as a negative electrode current collector. It applied to both sides of copper foil. Thereafter, the solvent was dried, compressed to a thickness of 0.08 mm with a roller, and then cut to a width of 100 mm and a height of 100 mm.

  Next, grooves having a depth of 30 μm were formed in the active material at intervals of 400 μm in parallel with one side of the electrode using a cutter knife in a range of 90 mm × 90 mm at the center of the negative electrode. Thereafter, grooves of the same depth were provided at 400 μm intervals in the same range on the back side of the surface on which the grooves were formed so as to form a constant angle θ with the previously formed grooves. At this time, if the starting point of the groove overlaps the line formed when the previously formed groove is projected onto the surface on which the groove is to be formed, the active material is collected with high probability regardless of the angle θ of each other groove. It was found to peel off. Therefore, the groove was provided with care so that the start point of the groove does not overlap the projection line. In this way, a negative electrode having grooves formed on both sides was produced.

  The adhesion between the active material layer and the current collector after forming the negative electrode was evaluated. Evaluated as “Yes” if there was any separation between the active material layer and the current collector, and evaluated “None” if there was no separation between the active material layer and the current collector. . The evaluation results are shown in Table 1.

(Preparation of non-aqueous electrolyte)
An electrolyte solution was prepared by dissolving LiPF _{6 at} a ratio of 1 mol / liter in a mixed solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 3: 7.

[Production of lithium secondary battery]
5 positive electrodes and 6 negative electrodes with the same groove pattern are laminated via a polypropylene separator thickness (30 μm), and both end surfaces of the electrode plate are negative electrodes, and both end surfaces are connected with insulating tape to maintain the shape. Then, a laminated electrode body was produced. For comparison, an electrode body using a negative electrode without a groove was also produced. Next, current collecting tabs (positive electrode: aluminum foil, negative electrode: copper foil) were welded to the positive electrode and the negative electrode by ultrasonic welding. Insert this electrode body into an exterior body made of a laminate film formed so that the electrode body can be installed in advance, and heat-seal the surface with the current collection tab so that only the current collection tab protrudes from the exterior body, Two of the remaining three sides were heat-sealed. Finally, an electrolytic solution was injected, and one side that was not thermally fused was thermally fused to produce a battery.

<Evaluation of charge / discharge cycle characteristics>
Charging / discharging at a constant current of up to 4.2V at a current of 1A and constant current discharging at a current of 1A to 2.75V is defined as one cycle. The ratio of eye discharge capacity was determined. In addition, for batteries using a negative electrode with a groove angle θ of 90 ° and batteries without grooves, the capacity when charging at a constant current up to 4.2 V with a current of 3 A is measured separately, and the ratio to the charge capacity at 1 A is measured. (3A / 1A) was determined.

  Table 1 shows the evaluation results of charge / discharge cycle characteristics and discharge rate characteristics.

  As shown in Table 1, in the battery using the negative electrode in which the groove angle θ is 15 ° or more according to the present invention, no peeling occurs between the active material layer and the current collector, and good charge / discharge is achieved. Cycle characteristics are obtained. Further, by forming the groove, the charge capacity ratio of 3A / 1A is increased, and the discharge rate characteristics can be improved.

The top view which shows the electrode for lithium secondary batteries of one Embodiment according to this invention. Sectional drawing which shows the electrode in which the groove | channel formed in each in the front side active material layer and the back side active material layer is substantially parallel. Sectional drawing which shows a state when the electrode shown in FIG. 2 is curved. Sectional drawing which shows a state when a groove | channel is formed in the active material layer of a front side. Sectional drawing which shows a state when a groove | channel is formed in the active material layer of a back side. The top view which shows the electrode for lithium secondary batteries of 2nd Embodiment according to this invention. The top view which shows the electrode for lithium secondary batteries of 3rd Embodiment according to this invention. The top view which shows the example of the other form of the groove | channel in this invention. The top view which shows a state when the edge part of a groove | channel is not located on the line of another groove | channel. The top view which shows a state when the edge part of a groove | channel is located on the line of another groove | channel. The disassembled perspective view which shows an example of the lithium secondary battery according to this invention. The perspective view which shows the electrode part which notched some in the other example of the lithium secondary battery according to this invention. The perspective view which shows the other example of the lithium secondary battery according to this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Active material layer 1a ... Peripheral part of active material layer 2 ... Active material layer 2a ... Peripheral part of active material layer 3 ... Current collector 3a ... One side of current collector 3b ... Other side of current collector 4 ... Groove 4a, 4b ... end of groove 4c ... bottom of groove 5 ... groove 5a, 5b ... end of groove 5c ... bottom of groove 6 ... current collector tab 10 ... cylindrical lithium secondary battery 11 ... positive electrode 12 ... negative electrode 13 DESCRIPTION OF SYMBOLS ... Separator 14 ... Negative electrode can 15 ... Positive electrode can 20 ... Stack type lithium secondary battery 21 ... Positive electrode 21a ... Positive electrode tab 22 ... Negative electrode 22a ... Negative electrode tab 23 ... Separator θ ... Extension direction of one groove and extension direction of the other groove D, D ₁ , D ₂ ... spacing between grooves d ... depth of grooves t ... thickness of active material layer W ... width of grooves

Claims (10)

An electrode for a lithium secondary battery in which active material layers are provided on both sides of a current collector,
A plurality of slit-like grooves that are substantially parallel to each other are formed in each of the active material layers on the both surfaces. The electrode for a lithium secondary battery, wherein a smaller one of the angles formed by the extending direction of the groove formed in the material layer is 15 degrees or more.   2. The electrode for a lithium secondary battery according to claim 1, wherein the angle is in a range of 45 to 90 degrees.   The end of the groove in the extending direction of the groove on the one surface is not positioned on a line when the groove on the other surface is projected onto the one surface. The electrode for a lithium secondary battery according to claim 1, wherein the groove is formed.   The electrode for a lithium secondary battery according to any one of claims 1 to 3, wherein the gap between the grooves is formed so as to gradually increase.   5. The groove according to claim 1, wherein the groove is formed so that an end of the groove in a direction in which the groove extends does not reach a peripheral edge of the active material layer. Electrode for lithium secondary battery.   The electrode for a lithium secondary battery according to any one of claims 1 to 5, wherein the groove is formed to a depth that does not reach the surface of the current collector. Lithium secondary battery comprising a positive electrode, a negative electrode, a separator provided between the positive electrode and the negative electrode, a nonaqueous electrolyte, and an exterior body that houses the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte Because
The lithium secondary battery in which the electrode according to any one of claims 1 to 6 is used as the positive electrode and / or the negative electrode.   The lithium secondary battery according to claim 7, wherein the positive electrode, the negative electrode, and the separator are spirally wound in a stacked state and stored in the outer package.   The electrode according to claim 4 is used as the positive electrode and / or the negative electrode, and the groove is formed so that an interval between the grooves increases from the center of the battery toward the outside. The lithium secondary battery according to claim 8.   The lithium secondary battery according to claim 7, wherein the secondary battery is a stack type secondary battery in which a plurality of the positive electrode, the negative electrode, and the separator are stacked.

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