JP2012089303A - Lithium secondary battery electrode and lithium secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for lithium secondary batteries which is sufficiently impregnated with an electrolyte to exhibit increased ion conductivity and can thereby significantly increase battery characteristics such as load characteristics, etc., and a lithium secondary battery using the electrode.SOLUTION: In a lithium secondary battery constructed in such a way that aluminum fiber 5 molded in sheet form is used for a cathode current collector 1, with a cathode active material carried on the cathode current collector 1, a groove 2 is formed on the surface of the cathode current collector 1 and space 3 exists inside the groove while the cathode active material is being carried on the cathode current collector 1.

Description

  The present invention relates to a lithium secondary battery, and more particularly to an improvement of a current collector used in the battery.

  In recent years, mobile information terminals such as mobile phones, notebook personal computers, and PDAs have been rapidly reduced in size and weight, and batteries as drive power sources are required to have higher capacities. A lithium secondary battery that performs charging / discharging by moving lithium ions between the positive and negative electrodes along with charging / discharging has a high energy density and high capacity. As widely used. Furthermore, with the miniaturization of the mobile information terminal, a secondary battery having a higher energy density is demanded. For such a high energy density secondary battery, as shown in (1) to (3), a battery using a metal nonwoven fabric as a current collector has been proposed.

(1) A proposal to use a porous sheet of aluminum fibers as a core material of a positive electrode (see Patent Document 1 below).
(2) A proposal using an aluminum non-woven fabric formed by melting and spinning metal fibers containing aluminum as a main component so as to have a three-dimensional network structure (see Patent Document 2 below).
(3) A positive electrode current collector made of an aluminum nonwoven fabric made of pure aluminum or aluminum alloy fibers, having a fiber diameter of 50 to 100 μm, a basis weight of 300 to 600 g / m ² , and a porosity of 50 to 96% is used. Proposal (see Patent Document 3 below).

JP-A-6-196170 JP 2001-155739 A JP 2010-33891 A

  The proposals shown in the above (1) to (3) have a structure in which the active material is supported on the nonwoven fabric, but the surface of the nonwoven fabric has a flat shape (microscopically because there are protrusions of metal fibers, etc.) Therefore, the flat shape means that large unevenness is not formed on the surface of the nonwoven fabric). For this reason, when an active material is carry | supported on a nonwoven fabric and an electrode plate is produced, the surface of an electrode plate also becomes a flat shape. Therefore, when the battery is manufactured, the electrolytic solution is less likely to penetrate into the electrode plate. In particular, in a stacked battery, the electrolytic solution is less likely to penetrate into the center portion of the electrode plate. Further, the electrolyte does not easily permeate in the thickness direction of the electrode, and is particularly remarkable when the packing density of the active material is increased or the thickness of the electrode is increased in order to increase the capacity of the battery. For these reasons, the lithium ion conductivity is lowered, and battery characteristics such as load characteristics are lowered.

  The present invention takes the above-mentioned conventional problems into consideration, and improves the ionic conductivity by sufficiently infiltrating the electrolyte into the electrode plate, thereby dramatically improving the battery characteristics such as load characteristics. An object of the present invention is to provide an electrode for a lithium secondary battery, and a lithium secondary battery using the electrode.

In order to achieve the above object, the present invention uses a current collector formed by molding a metal fiber in a sheet shape, and in the electrode for a lithium secondary battery having a structure in which an active material is supported on the current collector, A groove is formed on the surface of the electric body, and a space exists in the groove in a state where an active material is supported on the current collector.
As in the above configuration, a groove is formed on the surface of the current collector, and if there is a space in the groove with the active material supported on the current collector (the inside of the groove is the active material). When the battery is manufactured, a space (gap) is formed between the separator and the electrode. Therefore, the electrolytic solution easily passes through the space in the groove and spreads over the entire electrode (that is, the electrolytic solution is sufficiently supplied to the central portion of the electrode). Further, when the electrolytic solution penetrates into the electrode, it penetrates from the surface of the electrode and also from the side surface of the groove. As described above, the electrolytic solution penetrates from the portion where the electrode is thinned into the planar direction of the electrode and the thickness direction of the electrode, so that the electrolytic solution is more easily penetrated. From these things, it becomes possible to impregnate the whole electrode with electrolyte solution, and the lithium ion conductivity in an electrode improves. As a result, the electrode reaction becomes uniform, and battery characteristics such as load characteristics are dramatically improved. In particular, the present invention is effective in an electrode plate in which the thickness of the electrode plate is increased or the packing density of the active material is improved in order to increase the capacity and output of the battery.

The density of the metal fibers of the current collector in the part corresponding to the groove is desirably higher than the density of the metal fibers of the current collector in the part other than the groove.
If the density of the metal fiber of the current collector in the part corresponding to the groove is higher than the density of the metal fiber of the current collector in the part other than the groove, the part corresponding to the groove is more electron than the part other than the groove. The conductivity is increased. As described above, if a portion where the electronic conductivity is increased is provided in a part of the current collector, an electron highway path is easily formed, so that the electronic conductivity of the entire current collector is improved. As a result, the electrode reaction becomes uniform and battery characteristics such as cycle characteristics are improved.

Also, if the density of the metal fiber of the current collector at the part corresponding to the groove is increased, fraying and fluffing of the metal fiber is suppressed at the part, so that the electrode may be damaged starting from fraying, etc. It can suppress that a short circuit arises.
In the same manner as described above, the electrode plate is effective in increasing the electrode plate thickness or improving the packing density of the active material in order to increase the capacity and output of the battery.

It is desirable that the density of the metal fibers of the current collector in the outer peripheral portion of the current collector is higher than the density of the metal fibers of the current collector in a portion other than the outer peripheral portion.
The current collector is produced by cutting a sheet (nonwoven fabric) obtained by molding large metal fibers into a sheet shape. In this case, the cut portion has fraying or fluffing of the metal fibers as compared to the portion other than the cut portion. Become more. Therefore, if the density of the metal fibers of the current collector at the outer peripheral part (cut part) of the current collector is increased, fraying and fluffing of the metal fibers at the part can be suppressed, so that the electrode is damaged or short-circuited inside the battery. Can be further suppressed.

The width of the groove is desirably 1 mm or more and 10 mm or less.
If the width of the groove is less than 1 mm, the width of the groove is too small, and it may be difficult to provide a space in the groove in a state where the active material is supported on the current collector. Grooves can be made by pressing a metal fiber molded into a sheet shape, but if the groove width is too small, the press pressure increases and the current collector can break during pressing. There is sex. On the other hand, when the width of the groove exceeds 10 mm, the amount of the active material carried on the current collector is reduced, and the electrode capacity may be reduced. This is because the density of the metal fibers of the current collector in the part corresponding to the groove is higher than the density of the metal fibers of the current collector in the part other than the groove. It cannot be supported. For this reason, if the groove width becomes too large, the proportion of the groove in the current collector increases, and the amount of active material carried on the current collector decreases.

It is desirable that the ratio of the thickness of the current collector in the portion corresponding to the groove to the thickness of the current collector in the portion other than the groove is 10% or more and 90% or less.
When the ratio is less than 10%, when a groove is produced by a pressing method, the pressing pressure increases, and the current collector may break at a portion corresponding to the groove. On the other hand, when the ratio exceeds 90%, the density of the metal fibers of the current collector in the portion corresponding to the groove is not much different from the density of the metal fibers of the current collector in the portion other than the groove. For this reason, the improvement effect of the battery characteristic by the improvement of ion conductivity and electronic conductivity, and the improvement effect of the reliability of the battery by short circuit suppression inside a battery may not fully be exhibited.

It is desirable that a plurality of the grooves are provided.
If a plurality of grooves are provided, the above-described effects are further exhibited. However, in the case of an electrode having an extremely small area (1 cm ² or less), even if there is a single groove, the above effect is sufficiently exhibited.

The interval between the grooves is preferably not less than twice the width of the groove and not more than 50 mm.
If the groove interval is less than twice the groove width, the proportion of the groove in the current collector increases, and the amount of active material carried on the current collector decreases, resulting in a decrease in electrode capacity. . On the other hand, when the groove interval exceeds 50 mm, the electronic conductivity and the lithium ion conductivity cannot be improved so much, and fraying and fluffing of fibers are likely to occur.

It is desirable that the grooves have a lattice shape.
If the grooves are in the form of a lattice, a highway path for electrons is formed, the conductivity of the entire current collector is improved, and the ability of the electrolyte solution to flow is improved at any part of the electrode. The effect of improving characteristics is further exhibited. Further, as described above, fraying and fluffing of the current collector portion where the metal fiber density is high (current collector portion corresponding to the groove) are suppressed, but if the groove is in a lattice shape, the current collector As a whole, fraying and fluffing of metal fibers are greatly reduced.

It is desirable that no active material exists in the groove.
If there is no active material in the groove, a larger amount of electrolytic solution can pass through the groove (the amount of electrolytic solution present on the electrode surface increases), so that the ionic conductivity is further improved.

  In a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, the above-described electrode for a lithium secondary battery is used for at least one of positive and negative electrodes. Moreover, it is desirable that the above-mentioned electrode for a lithium secondary battery is used as a positive electrode, and the metal fiber is made of aluminum fiber.

  According to the present invention, since the ionic conductivity can be improved by sufficiently impregnating the electrolyte into the electrode, battery characteristics such as load characteristics can be drastically improved. Moreover, since electronic conductivity becomes high, the electronic conductivity in the whole collector improves. Therefore, the electrode reaction can be made uniform and battery characteristics such as cycle characteristics can be improved. In addition, since fraying and fluffing of the metal fiber can be suppressed, an excellent effect can be achieved in that the electrode can be prevented from being damaged starting from fraying and the like, and a short circuit can be prevented from occurring inside the battery.

It is a top view which shows the positive electrode electrical power collector of this invention. It is sectional drawing which shows the positive electrode electrical power collector of this invention. It is sectional drawing of the positive electrode using the positive electrode electrical power collector of this invention. It is explanatory drawing which shows the method of making the positive electrode electrical power collector of this invention carry | support a positive electrode active material. It is a partial expanded sectional view which shows the positive electrode electrical power collector of this invention. It is a top view which shows the modification of the positive electrode electrical power collector of this invention. It is a top view which shows the other modification of the positive electrode electrical power collector of this invention. It is a top view which shows the other modification of the positive electrode electrical power collector of this invention. It is a top view which shows the other modification of the positive electrode electrical power collector of this invention. It is a top view which shows the other modification of the positive electrode electrical power collector of this invention. It is a top view of the nonwoven fabric sheet used for the positive electrode electrical power collector of this invention. It is explanatory drawing which shows the method of making the positive electrode electrical power collector of this invention carry | support a positive electrode active material. It is sectional drawing which shows the other modification of the positive electrode electrical power collector of this invention. It is sectional drawing which shows the other modification of the positive electrode electrical power collector of this invention. It is a partial expanded sectional view which shows the positive electrode electrical power collector of this invention. It is sectional drawing which shows the positive electrode electrical power collector of a comparative example. It is sectional drawing which shows the positive electrode electrical power collector of a comparative example. It is sectional drawing of the positive electrode using the positive electrode electrical power collector of a comparative example.

  Hereinafter, the present invention will be described in more detail based on the following embodiments, but 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.

(Preparation of positive electrode)
As shown in FIG. 1, a grid-like groove 2 was formed on a nonwoven fabric sheet made of aluminum fibers 5 having a diameter of 100 μm by pressing, and then the sheet was cut into a square shape to obtain a positive electrode current collector 1. As shown in FIG. 2, in the positive electrode current collector 1, the thickness L1 of the current collector other than the portion corresponding to the groove 2 is 0.6 mm, and the thickness L2 of the current collector in the portion corresponding to the groove 2 is 0.4 mm. The width L3 of the groove 2 was 1.5 mm, and the distance L4 between the grooves 2 was 10 mm.

  Next, as shown in FIG. 4, the positive electrode current collector 1 was completely immersed in a container 15 filled with the positive electrode slurry 10 (moved in the direction A in the drawing and completely immersed), and then the positive electrode collector The electric body 1 was pulled up from the container (in the figure, it was moved in the anti-A direction and pulled up). Thereafter, the positive electrode slurry 10 was dried to produce a positive electrode carrying a positive electrode active material. The positive electrode slurry 10 was prepared by dissolving lithium cobaltate, a carbon conductive agent, and PVdF in a mass ratio of 94: 3: 3 in NMP. As shown in FIG. 3, in the obtained positive electrode, the thickness L5 of the positive electrode at the portion corresponding to the groove 2 was smaller than the thickness L6 of the positive electrode other than the portion corresponding to the groove 2. As a result, a space 3 is formed above the groove 2.

  Here, such a structure is formed because, as shown in FIG. 5, the positive electrode current collector 1a corresponding to the groove 2 is pressed, so that the density of the aluminum fibers 5 is increased. Since the positive electrode current collector 1b other than the portion corresponding to the groove 2 is not pressed, the density of the aluminum fibers 5 is lowered. Therefore, the anchor effect on the slurry is smaller at the bottom surface 2 a of the groove 2 than at the normal surface 4. In addition, since the groove 2 is a space (the aluminum fiber 5 is not present), the fluidity of the slurry is higher than that in the case where the aluminum fiber 5 is present. From these, even when the positive electrode current collector 1 is immersed in the positive electrode slurry 10 and the positive electrode slurry 10 is difficult to be disposed in the groove 2 and the positive electrode slurry 10 is disposed in the groove 2, This is because when the positive electrode current collector 1 is pulled up from the container, the positive electrode slurry 10 slides down due to its own weight.

(Preparation of negative electrode)
First, graphite powder as a negative electrode active material, CMC, and SBR as a binder were mixed in an aqueous solution as a solvent to prepare a negative electrode slurry. Next, this negative electrode slurry was applied to both sides of a copper foil as a negative electrode current collector, dried, and then rolled to prepare a negative electrode.

[Production of battery]
A large number of power generating elements each having a separator disposed between the positive electrode and the negative electrode were laminated to produce a laminated electrode body, and the laminated electrode body was inserted into an outer package made of a laminate film. Finally, an electrolyte was injected into the outer package, and the opening of the outer package was thermally welded to produce a battery. As the above electrolyte solution, ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3: 7 to mixed mixed solvent at a ratio of, LiPF ₆ is dissolved in a proportion of 1M (mol / l) What was done was used.

(Other matters)
(1) As shown in FIG. 1, the lattice shape of the grooves is not limited to a square lattice shape in which the grooves are orthogonal to each other, and the shape constituted by the grooves is, for example, a triangular lattice shape (see FIG. 6) or a parallelogram lattice shape (see FIG. 7). Further, it is not necessary for the grooves to intersect each other, and the grooves 2 may be formed in a flat direction as shown in FIG. 8, and further, the grooves 2 may be formed in a spiral shape as shown in FIG. . That is, it suffices if it is continuous on the current collector and opens toward the outer periphery of the current collector. However, in the groove-shaped positive electrode current collector shown in FIG. 8 and the groove-shaped positive electrode current collector shown in FIG. 9, the end of the positive electrode current collector is compared with the groove-shaped positive electrode current collector shown in FIG. There are few extended grooves 2 (that is, there are few end openings 6 of the grooves 2). Therefore, the function of evenly penetrating the electrolyte into the positive electrode current collector is reduced. Therefore, it is desirable to form the grooves 2 in a lattice shape. Furthermore, it is desirable that the grooves 2 be provided at a uniform interval in order to further exhibit the function of allowing the electrolytic solution to penetrate evenly.

  In addition, the positive electrode current collector can be manufactured by cutting an aluminum fiber molded into a large sheet (nonwoven fabric). In this case, the cut portion is made of aluminum as compared with a portion other than the cut portion. Increases fiber fraying and fuzz. Therefore, as shown in FIG. 11, when the nonwoven fabric 12 in which the groove 2 is formed is cut to produce a positive electrode current collector, cutting along the groove 2 (cut along line segments 13 and 14 in FIG. 11). )do it. As shown in FIG. 10, the positive electrode current collector manufactured in this way has a density of aluminum fibers 5 in the outer peripheral portion 11 of the positive electrode current collector 1 such that the aluminum fibers 5 in other than the outer peripheral portion 11 of the positive electrode current collector 1. Higher than the density of. With such a configuration, fraying and fluffing of the metal fibers at the cut portion can be suppressed, and therefore it is possible to further suppress the electrode from being damaged or short-circuiting from occurring inside the battery.

(2) The method of allowing the positive electrode slurry to permeate the positive electrode current collector is not limited to the method of completely immersing the positive electrode current collector 1 in the positive electrode slurry 10 as shown in FIG. 12, only the lower surface (the surface opposite to the surface on which the groove 2 is formed) 20 of the positive electrode current collector 1 is brought into contact with the positive electrode slurry 10 and the positive electrode slurry 10 is allowed to penetrate from the lower surface 20. good. In such a method, since the positive electrode current collector 1b other than the portion corresponding to the groove 2 has a low density of the aluminum fibers 5, the amount of slurry passing through the positive electrode current collector 1b increases, and the positive electrode current collector The inside of 1b is filled with the positive electrode slurry. On the other hand, the positive electrode current collector 1a corresponding to the groove 2 has a high density of aluminum fibers 5, so that the amount of slurry that passes through the positive electrode current collector 1b is reduced. Accordingly, since the amount of the positive electrode slurry reaching the groove 2 is small, the space 3 can be formed in the groove 2.

(3) Further, when forming the grid-like grooves by pressing, as shown in FIG. 2, the method is not limited to pressing only on one side (pressing only in one direction), as shown in FIG. A double-sided press (bidirectional press) may be used. In this case, if the grooves 2 are not opposed, the current collector may be wavy when pressing, so the grooves 2 formed on both sides are provided to face each other. It is preferable.

(4) As shown in FIG. 14, if no positive electrode slurry exists in the groove 2, the space in the groove 2 becomes large, and thus the above-described effects are further exhibited. The following methods are exemplified as a method for providing such a structure.
A method in which the positive electrode current collector is dipped in the positive electrode slurry and then the positive electrode slurry is scraped out from the groove.
A method of decreasing the viscosity of the positive electrode slurry and increasing the amount by which the positive electrode slurry slides down due to its own weight when the positive electrode current collector 1 is pulled up from the container filled with the positive electrode slurry.
A method in which the groove is covered with a masking tape or resist before the positive electrode current collector is immersed in the positive electrode slurry, and after the positive electrode current collector 1 is filled with the positive electrode slurry, the masking tape or resist is removed.

(5) In the above embodiment, the positive electrode has been described as an example, but the present invention can also be applied to the negative electrode. When applied to the negative electrode, copper fiber, nickel fiber, or the like can be used as the metal fiber.

[First embodiment]
(Example)
A positive electrode current collector (50 mm × 100 mm) was obtained by forming grid-like grooves on a nonwoven fabric sheet made of aluminum fibers having a diameter of 100 μm by pressing. In this positive electrode current collector, the thickness L1 of the current collector other than the part corresponding to the groove 2 is 1.2 mm, the thickness L2 of the current collector in the part corresponding to the groove 2 is 0.4 mm, and the width L3 of the groove 2 is The distance L4 between the grooves 2 was 1.5 mm and 10 mm (see FIG. 2 for L1 to L4). The mass of the positive electrode current collector was 2.4 g (also 2.4 g in the following comparative example).

Next, a positive electrode active material similar to that described above was supported on a positive electrode current collector in the same manner as in the embodiment for carrying out the invention. Finally, the positive electrode current collector carrying the positive electrode active material was cut into 20 mm × 20 mm and further tabbed to produce a positive electrode. In this positive electrode, the thickness L5 of the positive electrode at the portion corresponding to the groove 2 was 1.2 mm. Further, the thickness L6 of the positive electrode other than the portion corresponding to the groove 2 was 1.4 mm, and the thickness L5 was about 86% of the thickness L6 (see FIG. 3 for L5 and L6).
Finally, a three-electrode cell in which the positive electrode was used as a working electrode and the counter electrode and reference electrode were made of lithium foil was produced. In addition, as an electrolyte solution, the thing similar to the form for implementing the said invention was used.
The cell thus produced is hereinafter referred to as cell A.

(Comparative example)
A cell was fabricated in the same manner as in the above example except that a positive electrode current collector that did not form grooves was used.
The cell thus produced is hereinafter referred to as cell Z.

(Experiment)
The cells A and Z were charged / discharged under the following conditions, and the load characteristics (discharge capacity ratio) were examined. The results are shown in Table 1.
After charging to-discharge condition 0.5 mA / cm ² current at 4.4V (vs.Li/Li ^+), with the current 0.5 mA / cm ² until 3.0V (vs.Li/Li ⁺⁾ After discharging, the discharge capacity at a current of 0.5 mA / cm ² was examined. Then, after charging with a current 0.5 mA / cm ² until 4.4V (vs.Li/Li ^+), with the current 5.0 mA / cm ² until 3.0V (vs.Li/Li ⁺⁾ discharge Then, the discharge capacity at a current of 5.0 mA / cm ² was examined.
Then, the discharge capacity at a current 0.5 mA / cm discharge capacity when the ² and the current 5.0 mA / cm ^2, was calculated discharge capacity ratio using the following equation (1).

Discharge capacity ratio = [(discharge capacity at a current 5.0mA / cm ²⁾ / (discharge capacity at a current 0.5 mA / cm ^2)] × 100 · · · (1)

  As is apparent from Table 1 above, it can be seen that the cell A has a larger discharge capacity ratio than the cell Z, and is excellent in load characteristics. In the above experiment, since the current density is small, the influence of the voltage drop due to the ohmic resistance of the electrode on the load characteristics is small. Therefore, the cell A is considered to have excellent load characteristics due to the lithium ion conductivity being higher than that of the cell Z. In addition, it is thought that it is based on the reason shown below that lithium ion conductivity becomes high.

(1) The electrolyte easily spreads over the entire electrode through the groove space. Therefore, the electrolytic solution is sufficiently supplied even to the central portion of the electrode where it is difficult to supply the electrolytic solution.
(2) Since the electrolytic solution passes through the space 3 of the groove 2 as shown in FIG. 15, the electrolytic solution is supplied not only from the positive electrode surface 31 but also from the side surface 30 of the groove 2 to the inside of the positive electrode and lithium ions. Can go in and out. As described above, since the electrolytic solution penetrates in the planar direction (B direction in the figure) and the thickness direction (C direction in the figure) from the portion where the electrode is thinned, lithium ions can enter and exit. The liquid becomes more easily penetrated and the diffusion distance of lithium ions in the electrode is shortened.
From the above (1) and (2), in the electrode to which the present invention is applied, lithium ion conductivity is increased.

[Second Embodiment]
(Example)
A positive electrode current collector was produced in the same manner as in the method for carrying out the invention.
The positive electrode current collector thus produced is hereinafter referred to as current collector b.

(Comparative example)
As shown in FIGS. 16 and 17, a positive electrode current collector was produced in the same manner as in the above example, except that the grid-like grooves were not formed.
The positive electrode current collector thus fabricated is hereinafter referred to as current collector y.

(Experiment)
The resistance of the current collectors b and y and the presence or absence of fiber fluff were examined, and the results are shown in Table 2 below. The resistance of the current collector was measured using an AC milliohm high tester 3560 (manufactured by Hioki Electric Co., Ltd.) with the current collector sandwiched between clip-type leads. The clip was placed on a diagonal line of a 50 × 100 mm sheet within a 10 mm square including the corners of the current collector and at a site that was not a groove. The presence or absence of fiber fluff was visually examined.

  As is clear from Table 2, the current collector b provided with the grooves has a lower resistance of the current collector than the current collector y provided with no grooves, and fuzz is suppressed. I understand. Therefore, in order to improve the battery characteristics by improving the electronic conductivity of the current collector, and to suppress the fraying and fluffing of the metal fibers to suppress the electrode from being damaged or short-circuiting inside the battery It is understood that it is effective to form grooves in the current collector. Incidentally, the current collector y without grooves is fluffed at the production stage as shown in FIG. 17 (the aluminum fibers 5 are protruding), and further, as shown in FIG. The fuzz is maintained even in the supported state.

[Third embodiment]
(Example)
A positive electrode current collector was produced in the same manner as in the second example except that the width of the groove of the positive electrode current collector was 1.0 mm.
The positive electrode current collector thus produced is hereinafter referred to as current collector c.

(Experiment)
Since the resistance of the current collector c and the presence or absence of fiber fluff were examined in the same manner as in the experiment of the second example, the results are shown in Table 3 below. Table 3 also shows the results of the current collector b.

  As is clear from Table 3 above, it can be seen that the current collector b and the current collector c have no fuzz and the resistance is substantially the same. However, although not clear from Table 3, the groove width is preferably 1 mm or more and 10 mm or less. If the groove width is less than 1 mm, the groove width is too narrow, and it may be difficult to provide a space in the groove while the active material is supported on the current collector, and the press pressure is large. Thus, the current collector may break during pressing. On the other hand, when the width of the groove exceeds 10 mm, the amount of the active material carried on the current collector is reduced, and the electrode capacity may be reduced. This is because the current collector at the site corresponding to the groove has a higher density of metal fibers than the current collector at the site other than the groove, so that the active material cannot be supported so much at the site. For this reason, if the groove width becomes too large, the proportion of the groove in the current collector increases, and the amount of active material carried on the current collector decreases.

[Fourth embodiment]
Example 1
A positive electrode current collector was produced in the same manner as in the second example except that the mass of the positive electrode current collector was 2.5 g. That is, the current collector of this example has the same thickness as the current collector b, but its mass is larger than that of the current collector b. The density of aluminum fiber is high.
The positive electrode current collector thus fabricated is hereinafter referred to as current collector d1.

(Example 2)
A positive electrode current collector was produced in the same manner as in Example 1 except that the thickness of the positive electrode current collector was 1.0 mm. In other words, the current collector of this example has a thickness greater than that of the current collector d1, although the mass is the same as that of the current collector d1, so that the density of the aluminum fibers is higher than that of the current collector d1. Is low.
The positive electrode current collector thus fabricated is hereinafter referred to as current collector d2.

(Example 3)
A positive electrode current collector was produced in the same manner as in Example 1 except that the thickness of the positive electrode current collector was 1.2 mm and the mass of the positive electrode current collector was 2.5 g. That is, the current collector of the present example has a thickness larger than that of the current collector d2 although the mass is smaller than that of the current collector d2, and therefore, the aluminum fiber compared with the current collector d2. The density is low.
The positive electrode current collector thus fabricated is hereinafter referred to as current collector d3.

(Experiment)
Since the resistances of the current collectors d1 to d3 and the presence or absence of fiber fluff were examined in the same manner as in the experiment of the second example, the results are shown in Table 4 below.

  As is clear from Table 4, it can be seen that the current collectors d1 to d3 have substantially the same resistance although the density of the aluminum fibers is different. Therefore, even if the current collector has a low aluminum fiber density, the resistance of the current collector can be reduced by pressing to provide a portion of the current collector with a high aluminum fiber density. I understand.

[Fifth embodiment]
Example 1
A positive electrode current collector was produced in the same manner as in the second example except that the interval between the grooves of the positive electrode current collector was 50 mm.
The positive electrode current collector thus fabricated is hereinafter referred to as current collector e1.

(Example 2)
A positive electrode current collector was produced in the same manner as in the second example except that the interval between the grooves of the positive electrode current collector was 80 mm.
The positive electrode current collector thus produced is hereinafter referred to as current collector e2.

(Experiment)
Since the resistances of the current collectors e1 and e2 and the presence or absence of fiber fluff were examined in the same manner as in the experiment of the second example, the results are shown in Table 5 below. Table 5 also shows the results of the current collector b.

As is apparent from Table 5, the current collectors b and e1 having a groove interval of 50 mm or less have low resistance and fuzz is suppressed, whereas the current collector e2 having a groove interval exceeding 50 mm has resistance. Is low and slightly fuzzy (however, it is less fuzzy and less resistant than the current collector y without grooves). Therefore, it can be seen that the groove spacing is preferably 50 mm or less in order to improve conductivity and suppress fuzz.
If the interval between the grooves exceeds 50 mm, the ratio of the grooves to the current collector becomes too small, and the effect of providing the grooves may not be sufficiently exhibited. The groove interval is preferably at least twice the width of the groove. If the groove spacing is less than twice the groove width, the proportion of the groove in the current collector increases and the amount of active material carried on the current collector decreases, resulting in a decrease in electrode capacity. is there.

[Sixth embodiment]
Example 1
The thickness of the current collector at the site corresponding to the groove was 0.2 mm (ratio to the thickness of the current collector other than the site corresponding to the groove (0.6 mm) was 33%). A positive electrode current collector was produced in the same manner as in the example.
The positive electrode current collector thus produced is hereinafter referred to as current collector f1.

(Example 2)
The thickness of the current collector at the site corresponding to the groove was 0.5 mm (ratio to the thickness of the current collector other than the site corresponding to the groove (0.6 mm) was 83%). A positive electrode current collector was produced in the same manner as in the example.
The positive electrode current collector thus fabricated is hereinafter referred to as current collector f2.

(Experiment)
The resistance of the current collectors f1 and f2 and the presence or absence of fiber fluff were examined in the same manner as in the experiment of the second example, and the results are shown in Table 6 below. Table 6 also shows the results of the current collector b.

  The current collectors f1 and b where the current collector at the portion corresponding to the groove is small (the press pressure is large and the depth of the groove is large) are large at the current collector at the portion corresponding to the groove (press It can be seen that the resistance is small compared to the current collector f2 where the pressure is small and the groove depth is small. Therefore, in order to improve conductivity, it is desirable that the thickness of the current collector at the portion corresponding to the groove is small, and in particular, it corresponds to the groove for the thickness of the current collector other than the portion corresponding to the groove. It is preferable that the ratio of the thickness of the current collector at the site to be 90% or less.

  When the ratio exceeds 90%, the density of the metal fibers of the current collector in the portion corresponding to the groove is not much different from the density of the metal fibers of the current collector in the portion other than the groove, and the effect of the present invention ( This is because the effect of improving lithium ion conductivity and the effect of suppressing fuzz are not sufficiently exhibited in addition to the effect of improving the electronic conductivity by reducing the resistance. In addition, it is preferable that the ratio of the thickness of the electrical power collector of the site | part corresponding to a groove | channel with respect to the thickness of electrical power collectors other than the site | part corresponding to a groove | channel is 10% or more. When the ratio is less than 10%, when a groove is produced by a pressing method, the pressing pressure increases, and the current collector may break at a portion corresponding to the groove.

  The present invention can be expected to be applied to a driving power source for mobile information terminals such as mobile phones, notebook computers, and PDAs, and a driving power source for high output such as HEVs and electric tools.

1: Positive electrode current collector 2: Groove 3: Space 5: Aluminum fiber

Claims (11)

In the electrode for a lithium secondary battery having a structure in which an active material is supported on the current collector using a metal fiber molded into a sheet shape,
An electrode for a lithium secondary battery, wherein a groove is formed on a surface of the current collector, and a space exists in the groove in a state where an active material is supported on the current collector.   2. The electrode for a lithium secondary battery according to claim 1, wherein the density of the metal fibers of the current collector in a portion corresponding to the groove is higher than the density of the metal fibers of the current collector in a portion other than the groove.   3. The lithium secondary battery according to claim 2, wherein the density of the metal fibers of the current collector in the outer peripheral portion of the current collector is higher than the density of the metal fibers of the current collector in a portion other than the outer peripheral portion. electrode.   The electrode for a lithium secondary battery according to claim 2 or 3, wherein the width of the groove is 1 mm or more and 10 mm or less.   The ratio of the thickness of the current collector in a portion corresponding to the groove to the thickness of the current collector in a portion other than the groove is 10% or more and 90% or less. An electrode for a lithium secondary battery as described in 1.   The electrode for a lithium secondary battery according to any one of claims 1 to 5, wherein a plurality of the grooves are provided.   The electrode for a lithium secondary battery according to claim 6, wherein the interval between the grooves is not less than twice the width of the groove and not more than 50 mm.   The electrode for a lithium secondary battery according to claim 6 or 7, wherein the groove has a lattice shape.   The electrode for a lithium secondary battery according to any one of claims 1 to 8, wherein no active material is present in the groove.   A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the lithium secondary battery electrode according to any one of claims 1 to 9 is used for at least one of positive and negative electrodes. A lithium secondary battery characterized by comprising:   The lithium secondary battery according to any one of claims 1 to 9, wherein the electrode for a lithium secondary battery according to any one of claims 1 to 9 is used as a positive electrode, and the metal fibers are made of aluminum fibers.

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