JP2008311171A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery with high capacity, long life in a high current charge and discharge, and high safety. <P>SOLUTION: The lithium secondary battery includes an electrode group formed by laminating or winding a negative electrode having a foil-shaped negative electrode collector in a negative electrode mixture layer and a positive electrode having a foil-shaped positive electrode collector in a positive electrode mixture layer, through a separator, and an electrolyte in which the electrode group is immersed. The foil-shaped negative electrode collector and the foil-shaped positive electrode collector are provided with a plurality of holes penetrating the collectors, a circumference of each of the holes projects to at least one surface side of the foil-shaped collector, and a thickness of the foil-shaped collector, including the projection portion of the circumference of the hole is more than 3% and 25% or less of a total thickness of one electrode plate in which the collector of the negative electrode or the positive electrode and the mixture layer are put together. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery.

A lithium secondary battery in which a negative electrode is formed using a material capable of occluding and releasing lithium ions can suppress dendrite precipitation compared to a lithium battery in which a negative electrode is formed using metallic lithium. Therefore, there is an advantage that a battery having a high capacity and a high energy density can be provided while safety is improved by preventing a short circuit of the battery.
In recent years, further increase in capacity of this lithium secondary battery is demanded, while improvement of large current charge / discharge performance accompanying reduction in battery resistance is demanded. In this regard, the capacity of the lithium metal oxide positive electrode material or negative electrode material itself, which is a battery reactant in the past, has been increased. Further, the specific surface area of these reactant particles and the electrode area due to battery design have increased, and the separator has been made thinner. Ingenuity has been devised such as an increase in the amount of reactants due to. On the other hand, the reactants peel and fall from the current collector metal foil inside the battery, causing an internal short circuit, which may impair the safety of the lithium secondary battery such as battery voltage drop or heat runaway. It was. Therefore, in order to increase the binding between the reactants and the foil, the amount of the binder is increased, the type is changed (Patent Document 1), and the other secondary battery is used for preventing peeling. It is conceivable to use a metal foil having irregularities on the surface (Patent Document 2, Patent Document 3).

However, the means proposed so far can be increased simply in terms of capacity, but is still unresolved in terms of improving large current charge / discharge characteristics by reducing resistance. Compared with the secondary battery, it has been impossible to expand to the use of electric tools and hybrid cars that require large current charge / discharge, which is a large performance barrier of the lithium secondary battery. In addition, repeated charge and discharge cycles with a large current cause expansion and shrinkage of the positive and negative electrode materials, thereby damaging the binding between the positive and negative electrode particles and the metal foil, increasing resistance, and accelerating the peeling and dropping from the foil. As a result, a large current could not flow as a battery, resulting in an early life, and the battery could run out of heat and become unsafe.
JP-A-5-226004 JP 2004-342519 A JP 2002-198055 A

  The present invention has been made to address such problems, and an object of the present invention is to provide a lithium secondary battery with high capacity, long life and high safety as well as high capacity.

  In the lithium secondary battery of the present invention, a negative electrode having a foil-like negative electrode current collector in a negative electrode mixture layer and a positive electrode having a foil-like positive electrode current collector in a positive electrode mixture layer are laminated or wound via a separator. A lithium secondary battery comprising an electrode group formed by being formed and an electrolyte solution in which the electrode group is immersed, wherein the foil-shaped negative electrode current collector and the foil-shaped positive electrode current collector are: A plurality of holes penetrating the current collector, wherein the hole has a periphery projecting toward at least one side of the foil-shaped current collector, and the projecting portion around the hole of the foil-shaped current collector The thickness including the current collector and the mixture layer of the negative electrode or the positive electrode exceeds 3% of the total thickness of one electrode plate and is 25% or less.

  The foil-shaped negative electrode current collector and the foil-shaped positive electrode current collector are provided with holes having the protrusions on the entire surface of the current collector, or holes in the longitudinal direction or the width direction of the current collector. The hole which has the said protrusion part is provided in the surface of this electrical power collector, leaving the part which does not have, It is characterized by the above-mentioned.

  The density of the positive electrode mixture layer excluding the foil-like positive electrode current collector is 1.8 to 3.6 g / cc, and the density of the negative electrode mixture layer excluding the foil-like negative electrode current collector is 1.2 to 1.6 g / cc. It is characterized by being.

In the lithium secondary battery of the present invention, as the battery constituent member, a negative electrode having a foil-like negative electrode current collector in a negative electrode mixture layer, and a positive electrode having a foil-like positive electrode current collector in a positive electrode mixture layer are separators. And an electrode group formed by being laminated or wound via, and an electrolytic solution in which the electrode group is immersed. Further, the negative electrode and the positive electrode foil-shaped current collector have a plurality of holes penetrating the current collector, and the holes are formed so that the periphery of the hole protrudes to at least one surface side of the foil-shaped current collector, In addition, the thickness of the foil-shaped current collector including the projecting portion around the hole exceeds 3% of the total thickness of one electrode plate including the current collector and the mixture layer of the negative electrode or the positive electrode, 25% It is as follows. The protrusion around the hole improves the holding ability of the active material mixture layer formed on the surface of the current collector, and can prevent the mixture layer from peeling off. Moreover, by providing the some hole which has a protrusion part around the said hole, the electron conduction network as a collector improves, electrode resistance is reduced, and large current charging / discharging is attained.
Furthermore, the positive or negative electrode expands and contracts during the charging / discharging due to the protrusions around the holes, and the adhesion between the particles and the current collector is improved. Allows prevention.
In addition, the current collector has a plurality of holes, so that the melt responsiveness at the time of heat generation is good, and the foil is instantaneously cut, so that a partial current path shuts down, resulting in a higher safety battery. Is obtained.

  Moreover, the lithium secondary battery of the present invention is provided with a hole having the protruding portion on the entire surface of the foil-shaped current collector, or a portion having no hole in the longitudinal direction or the width direction of the current collector. The hole which has the said protrusion part in the surface of this collector is left behind. By leaving a portion of the current collector that is not perforated, the strength of the current collector itself increases, and the current collector is not cut when pressed or bent, resulting in an electrode plate that is difficult to break. Thus, an internal short circuit can be prevented.

  The lithium secondary battery of the present invention has protrusions around a plurality of holes penetrating the positive electrode or negative electrode foil-shaped current collector, and the density of the positive electrode mixture layer excluding the positive electrode current collector is 1.8 to 3.6 g. By increasing the density of the negative electrode mixture layer excluding / cc and the negative electrode current collector to 1.2 to 1.6 g / cc, the active material itself can be increased or the mixture layer can be thickened, enabling large current charge / discharge. Become.

  An example of the lithium secondary battery of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of the lithium secondary battery of the present invention, and particularly shows a cross-sectional view of an electrode group formed by laminating a positive electrode, a negative electrode and a separator.

  As shown in FIG. 1, the lithium secondary battery of the present invention has a negative electrode 1 having a foil-like negative electrode current collector 1a in a negative electrode mixture layer 1b, and a foil-like positive electrode current collector 2a in a positive electrode mixture layer 2b. A positive electrode 2 is provided with an electrode group 4 formed by being laminated via a separator 3. In addition to the electrode group 4 laminated as described above, an electrode group 4 in which a negative electrode and a positive electrode are wound with a separator interposed therebetween may be used. The electrode group 4 is immersed in an electrolytic solution inside a sealed battery case (not shown).

The negative electrode 1 for a lithium secondary battery according to the present invention has, as the negative electrode mixture layer 1b, a material capable of occluding and releasing lithium ions as an active material as a main material, the material, a binder, a dispersion solvent, and the like. Can be kneaded into a paste and applied to both sides of the foil-shaped negative electrode current collector 1a.
Examples of materials that can store and release lithium ions include carbon materials, lithium-aluminum alloys, silicon-based or tin-based lithium alloys, and the like. Among these, it is preferable to use a carbon material for reasons such as a large amount of occlusion / release of lithium ions and a small irreversible capacity.
Moreover, as the negative electrode current collector 1a that can be used in the present invention, a copper foil is used from the viewpoint of electrochemical properties, processability to a foil shape, and cost.

The positive electrode 2 for a lithium secondary battery according to the present invention is mainly composed of a lithium-containing metal oxide, a lithium-containing metal phosphate compound or a lithium-containing compound as an active material for forming the positive electrode mixture layer 2b. It can be formed by kneading an adhesive, a dispersion solvent, and the like to form a paste and applying it to both surfaces of the positive electrode current collector 2a.
Examples of the lithium-containing metal oxide include LiCoO ₂ , Li (Ni / Co / Mn) O ₂ , and Li ₂ MnO _4. Examples of the lithium-containing metal phosphate compound include LiFePO ₄ and LiCoPO ₄ . Examples of the lithium-containing compound include LiTi ₂ (PO ₄ ) ₃ and LiFeO ₂ . Among these, LiCoO ₂ , Li (Ni / Co / Mn) O ₂ , and LiFePO ₄ are preferably used in terms of electrochemical characteristics, safety, and cost.
In addition, as the positive electrode current collector 2a that can be used in the present invention, an aluminum foil is used in terms of performance.

  In the present invention, the density of the positive electrode mixture layer excluding the positive electrode current collector is 1.8 to 3.6 g / cc, and the density of the negative electrode mixture layer excluding the negative electrode current collector is 1.2 to 1.6 g / cc. Preferably there is. If it is out of the above range, the lower limit side particularly has a risk of reducing the cycle performance because the adhesion between the active material mixture layer and the current collector is lowered. On the upper limit side, the porosity of the electrode plate is not ensured, and the diffusibility of the electrolytic solution is suppressed, resulting in a decrease in large current charge / discharge performance.

  As shown in FIG. 1, in the negative electrode current collector 1a and the positive electrode current collector 2a used in the lithium secondary battery of the present invention, the periphery of the hole penetrating the foil current collector is a foil current collector. A plurality of holes (1c, 2c) having protrusions (1d, 2d) protruding toward at least one surface side are provided.

FIG. 2 is an end view showing an example of a current collector provided with a plurality of holes having protrusions. Even if the hole 1c has a protrusion 1d on one surface side of the current collector 1a (FIG. 2 (a) or FIG. 2 (c)), the hole 1c has a protrusion 1d on both surfaces of the current collector 1a. It may be a thing (FIG.2 (b) or FIG.2 (d)). Here, it is preferable that the protrusion 1d protrudes at least on the surface side on which the mixture layer is formed. Further, it may have a protruding portion 1d ′ having a tip extending outward from the opening direction of the hole or a curved shape, and a mixture layer formed on the current collector 1a by this shape The adhesion is further increased (FIG. 2C or FIG. 2D). The pattern of the plurality of holes 1c provided in the current collector 1a may be either periodically or continuously provided, or randomly provided, but the adhesiveness with the mixture layer formed thereon may be For reasons such as electrode resistance, it is preferably periodic or continuous. Although the above has described the negative electrode current collector 1a as an example, the same applies to the positive electrode current collector 2a.
As a method for providing the foil-shaped current collector 1a with a plurality of holes 1c having protrusions 1d or 1d 'around the above-described holes, a method such as roll processing or die press processing can be used. Further, in order to obtain the protruding portion 1d ′ having a shape in which the tip extends outward from the opening direction of the hole or a curved shape, a method such as roll pressing or die pressing is used in addition to the above-described drilling method. be able to.

FIG. 3 is a cross-sectional view of a single negative electrode plate comprising a foil-like current collector having a plurality of holes having protrusions and a mixture layer. The thickness t ₁ of the negative electrode current collector 1a provided with the hole 1c having the protruding portion 1d around the hole is the total thickness t _{0 of} one electrode plate including the negative electrode current collector 1a and the negative electrode mixture layer 1b. Preferably, it is more than 3% and 25% or less. Here, the thickness t ₁ of the current collector 1a means that the protrusion 1d around the hole 1c provided in the current collector 1a protrudes only to one surface side of the current collector 1a. It is the height from the non-projecting surface to the tip of the projecting portion 1d (FIG. 3 (a)), and when the projecting portion 1d around the hole 1c projects to both sides of the current collector 1a, it projects from one surface side. This is the height from the tip of the portion 1d to the tip of the protruding portion 1d on the opposite surface side (FIG. 3B). If the ratio of the thickness t ₁ of the current collector 1a including the protrusion around the hole is 3% or less, the desired adhesion between the active material mixture layer and the current collector cannot be obtained. If the content exceeds 25%, it will be difficult to apply the mixture onto the current collector. Although the above has described the negative electrode current collector 1a as an example, the same applies to the positive electrode.

  Even if the foil-like negative electrode current collector and the foil-like positive electrode current collector in the lithium secondary battery of the present invention are provided with the above-described holes on the entire surface of the current collector, You may equip the surface of an electrical power collector with the hole which has the above-mentioned protrusion part, leaving the part which does not have a hole with respect to a longitudinal direction or the width direction. In this invention, an active material is apply | coated to the part in which the hole which has the said protrusion part on the surface of an electrical power collector is provided, and a mixture layer is formed. By leaving the part that does not have holes in the longitudinal direction or width direction of the current collector, that is, the part that does not form the mixture layer, the strength in the longitudinal direction or width direction of the current collector increases, and during plate processing In addition, it is possible to prevent the electrode plate from being cut when the battery is incorporated such as stacking or winding.

  The separator that can be used in the lithium secondary battery of the present invention is to electrically insulate the positive electrode and the negative electrode to hold the electrolytic solution. Examples of the separator include a synthetic resin, and specific examples thereof include polyethylene and polypropylene. It is preferable to use a porous film because the electrolyte retainability is good.

  In the lithium secondary battery of the present invention, it is preferable to use a non-aqueous electrolyte containing a lithium salt, an ion conductive polymer, or the like as the electrolyte in which the electrode group described above is immersed.

Examples of the nonaqueous solvent for the nonaqueous electrolyte in the nonaqueous electrolyte containing a lithium salt include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC). Is mentioned.
Examples of lithium salts that can be dissolved in the non-aqueous solvent include lithium hexafluorophosphate (LiPF ₆ ), lithium borotetrafluoride (LiBF ₄ ), and lithium trifluoromethanesulfonate (LiSO ₃ CF ₄ ). .

  Hereinafter, the lithium secondary battery according to the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples unless it exceeds the gist. An example of the positive electrode, negative electrode, and battery manufacturing method in the present invention is shown below. In each Example, a battery was obtained by combining the following positive electrode, negative electrode, and separator.

<Preparation of positive electrode>
Lithium cobalt oxide was used as a positive electrode active material, and 2.2 parts by weight of a conductive agent and 2.5 parts by weight of polyvinylidene fluoride as a binder were added to 95.3 parts by weight of the active material. A positive electrode mixture (slurry) in which N-methylpyrrolidone was added and kneaded as a dispersion solvent was prepared.
Perforation processing is performed on 20 μm aluminum foil, and the thickness of the processed aluminum foil is shown in Table 1 for the predetermined total thickness of the positive electrode (thickness when the above material is applied on both sides of the aluminum foil, dried and pressed). What was shown was prepared. The positive electrode slurry was applied to both sides of the processed aluminum foil, dried, then pressed and cut to obtain a positive electrode for a lithium secondary battery.

<Production of negative electrode>
A negative electrode mixture (slurry) was prepared by adding 7 parts by weight of polyvinylidene fluoride as a binder to 93 parts by weight of graphite powder and adding and kneading N-methylpyrrolidone as a dispersion solvent thereto.
Perforation processing is performed on 10 μm copper foil, and the thickness of the processed copper foil is compared to the predetermined total thickness of the negative electrode (the thickness when the above material is applied to both sides of the copper foil, dried and then pressed). What was made into the ratio shown in Table 1 was prepared. The negative electrode slurry was applied to both sides of the processed copper foil, dried, then pressed and cut to obtain a negative electrode for a lithium secondary battery.

  The surfaces of the positive electrode and the negative electrode obtained above were observed visually and with an optical microscope. The coated surface having a smooth surface shape was evaluated as “good”, and the other results were also shown in Table 1 together with the reasons.

表１に示すように、スラリー塗工面の表面状態は、突出部を有する穿孔加工箔厚さの極板総厚さに対する割合は、正極および負極共に 3〜25 ％の範囲のものが良好な結果であり、特に 5〜25 ％の範囲のものが良好であった。25 ％のものでは、塗工面がやや肌荒れとなったが、電池作製に問題はなかった。26 ％のものでは、穿孔した孔径が大きく、スラリーの塗工が困難であった。一方、割合が逆に小さくなると、通常の平滑な金属箔（穿孔加工を施していない金属箔）に近づくために塗工としては問題がない。
上記の結果から、以下の実施例４および実施例５〜７では、正・負極ともに正極３および負極３の箔仕様のものを用いることとした。

As shown in Table 1, the surface condition of the slurry coated surface is such that the ratio of the thickness of the punched foil having protrusions to the total thickness of the electrode plate is in the range of 3 to 25% for both the positive electrode and the negative electrode. Especially, the range of 5 to 25% was good. In the case of 25%, the coated surface was slightly rough, but there was no problem in battery production. In the case of 26%, the diameter of the perforated holes was large and it was difficult to apply the slurry. On the other hand, when the ratio becomes smaller, there is no problem as coating because it approaches a normal smooth metal foil (metal foil not subjected to perforation).
From the above results, in the following Example 4 and Examples 5 to 7, the positive and negative electrodes having the foil specifications of the positive electrode 3 and the negative electrode 3 were used.

Examples 1 to 3 and Comparative Examples 1 to 2
A battery was prepared using the positive and negative electrode plates prepared as described above. However, for the combination of positive and negative electrodes, as shown in Table 2, the positive electrode 2 and the negative electrode 2 as Example 1, the positive electrode 3 and the negative electrode 3 as Example 2, and so on to show the difference in battery performance. Combined. Further, as Comparative Example 1, the positive electrode 6 and the negative electrode 6 produced by the same method as the positive electrode 2 and the negative electrode 2, respectively, using a metal foil not subjected to perforation processing were used, and as the Comparative Example 2, the above-described foil thickness was used. A positive electrode 1 and a negative electrode 1 having a thickness ratio close to that of a smooth foil were used in combination.
The above positive electrode and negative electrode are wound through a polyethylene separator with a thickness of 20 μm to form an electrode group. This electrode group is inserted into a cylindrical battery can, a predetermined amount of electrolyte is injected, and the upper lid is caulked and sealed. Thus, a cylindrical lithium secondary battery was obtained. As the electrolytic solution, a solution obtained by dissolving 1 mol / l of lithium hexafluorophosphate (LiPF ₆ ) in a solution in which EC and MEC were mixed at a volume ratio of 30:70 was used. The design capacity of this battery is 1800 mAh.
The battery performance test includes battery internal resistance measurement using 1 kHz AC wave, capacity ratio during 2 ItA and 0.2 ItA constant current discharge, and 2 ItA constant current discharge (EV = 3.0 V), 4.2 V (2 ItA Cut- off) The capacity ratio of the 200th cycle to the capacity of the initial 5th cycle in the charge / discharge cycle of CCCV 3 hr charge was measured. The test performance results are also shown in Table 2.

Example 4
An electrode plate was prepared using a current collector foil that was perforated to the foil specifications of the positive electrode 3 and the negative electrode 3 described above, and left a portion that was not perforated in the width direction of the current collector. In the same manner, a cylindrical lithium secondary battery was obtained. The design capacity of this battery is 1800 mAh.
As a battery performance test, the above-mentioned battery internal resistance measurement, capacity ratio during current discharge, and cycle capacity ratio were measured. The test performance results are also shown in Table 2.

表２に示すように、突出部を有する穿孔加工箔厚さの割合が 3 ％である比較例２は、穿孔加工を施していない比較例１と変化がないことがわかった。また、25 ％の金属箔を用いた実施例３は、比較例１と比べて性能は向上するが、正比例しないことがわかり、上記割合の上限と考えられる。25 ％をこえると塗工面が平滑でなくなり、セパレータと極板との界面で隙間が開いて、液の拡散性が悪くなり、所期の効果が得られなくなると考えられる。
したがって、突出部を有する穿孔加工箔厚さの割合は 3 ％をこえ 25 ％以下が好ましく、5〜25 ％がさらに好ましいと言える。これは比較例１の平滑箔に比べ、孔周囲に突出部を有する孔の存在により合剤活物質中での電子伝導性が向上して抵抗が小さくなる。またこのことにより大電流での放電容量が大きくなることがわかる。さらには孔周囲の突出部により箔と活物質合剤との密着性が向上して、かつ抵抗が小さいのでサイクル特性は向上することになる。
また、実施例４の部分的に穿孔加工をしない箔で極板を作製すると、全面加工されたものに比べて、通電部が広くなり抵抗が下がる場合がある。そして特に集電箔幅方向の強度が増加してプレス時の極板切断等の生産上の不具合が改善されることがわかった。

As shown in Table 2, it was found that Comparative Example 2 in which the ratio of the thickness of the punched foil having protrusions was 3% was not different from Comparative Example 1 in which punching was not performed. Moreover, although Example 3 using 25% of metal foil improves performance compared with the comparative example 1, it turns out that it is not directly proportional, and is considered to be the upper limit of the said ratio. If it exceeds 25%, the coated surface becomes unsmooth, and a gap is formed at the interface between the separator and the electrode plate, so that the diffusibility of the liquid deteriorates and the expected effect cannot be obtained.
Therefore, it can be said that the ratio of the thickness of the perforated foil having protrusions is preferably more than 3% and not more than 25%, and more preferably 5 to 25%. Compared with the smooth foil of the comparative example 1, this improves electronic conductivity in a mixture active material by presence of the hole which has a protrusion part around a hole, and resistance becomes small. This also shows that the discharge capacity at a large current increases. Furthermore, since the protrusions around the holes improve the adhesion between the foil and the active material mixture and the resistance is small, the cycle characteristics are improved.
Further, when the electrode plate is made of a foil that is not partially perforated in Example 4, the energized portion may be widened and the resistance may be reduced as compared with the case where the entire surface is processed. And it turned out that especially the intensity | strength of the collector foil width direction increases and the malfunctions in production, such as the electrode plate cutting | disconnection at the time of a press, are improved.

Examples 5 to 7 and Comparative Examples 3 to 4
Using the current collector foil having the foil specifications of the positive electrode 3 and the negative electrode 3 described above, when pressing was performed after coating and drying, electrodes set to the positive electrode mixture density and the negative electrode mixture density shown in Table 3 were produced. .
Using these electrode plates, a cylindrical lithium secondary battery was obtained in the same manner as in Example 1. The design capacity of this battery is 1800 mAh.
Capacitance ratio between 2 ItA and 0.2 ItA constant current discharge, as well as 2 ItA constant current discharge (EV = 3.0 V), 4.2 V (2 ItA Cut-off) CCCV 3 hr The capacity ratio of the 200th cycle to the capacity of the 5th cycle was measured. The results are also shown in Table 3.

Comparative Example 5
Except for using the electrode plate pressed to the positive electrode mixture density and negative electrode mixture density shown in Table 3, respectively, using 20 μm aluminum foil and 10 μm copper foil without punching the current collector. A cylindrical lithium secondary battery was obtained in the same manner as in Example 1. The design capacity of this battery is 1800 mAh.
Capacitance ratio between 2 ItA and 0.2 ItA constant current discharge, and 2 ItA constant current discharge (EV = 3.0 V), 4.2 V (2 ItA Cut-off) CCCV 3 hr The capacity ratio at the 200th cycle to the capacity at the 5th cycle was measured. The results are also shown in Table 3.

表３の結果より、合剤密度の限界は正極下限が 1.8 g/cc で、負極が 1.2 g/cc、上限については正極が 3.6 g/cc で、負極が 1.6 g/cc であることがわかる。これは下限値側になると極板の多孔度が大きくなるので電解液の拡散が良好となるが、電子伝導性が低下するので大電流放電容量は逆に小さくなる。そして寿命においても活物質の密着性が低下するのでサイクル寿命が低下することになる。特に、正極の 1.7 g/cc や負極の 1.1 g/cc の密度は塗工した状態の密度であり、プレスされていないのでさらに集電箔との密着性は劣る。一方上限値側になると多孔度が小さくなるので大電流放電容量は小さくなる。しかしサイクル寿命は良くなるように推定されるが、極板をプレスして極板密度を上げていくと、本発明の集電体の穿孔の孔周囲の突出部の高さが結果として押しつぶされて低下することになるので、比較例５の通常平滑箔に近づくため、かえって箔との密着性は劣ることになり、サイクル性能は低下すると考えられる。

From the results in Table 3, it can be seen that the mixture density limit is 1.8 g / cc for the lower limit of the positive electrode, 1.2 g / cc for the negative electrode, 3.6 g / cc for the positive electrode, and 1.6 g / cc for the negative electrode. . On the lower limit side, the porosity of the electrode plate increases, so that the electrolyte solution is diffused better. However, since the electron conductivity is reduced, the large current discharge capacity is decreased. And since the adhesiveness of an active material falls also in lifetime, cycle life will fall. In particular, the density of 1.7 g / cc of the positive electrode and 1.1 g / cc of the negative electrode is the density in the coated state, and since it is not pressed, the adhesion to the current collector foil is further inferior. On the other hand, when the upper limit value is reached, the porosity is reduced, so the large current discharge capacity is reduced. However, although the cycle life is estimated to be improved, when the electrode plate is pressed to increase the electrode plate density, the height of the protrusion around the hole of the current collector perforation of the present invention is crushed as a result. Therefore, since it approaches the normal smooth foil of Comparative Example 5, the adhesion with the foil is rather inferior, and the cycle performance is considered to be lowered.

  The lithium battery of the present invention has a high capacity, can be repeatedly charged and discharged with a large current, and has high safety. Therefore, the lithium battery is suitably used for applications that require charging and discharging with a large current such as electric tools and hybrid cars. it can.

It is sectional drawing which shows an example of the lithium secondary battery of this invention. It is an end view which shows the example of the electrical power collector provided with the some hole which has a protrusion part. It is sectional drawing of the electrical power collector provided with the some hole which has a protrusion part, and a mixture layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode 1a Negative electrode collector 1b Negative electrode mixture layer 1c Hole 1d Protrusion part 2 Positive electrode 2a Positive electrode collector 2b Positive electrode mixture layer 2c Hole 2d Protrusion part 3 Separator 4 Electrode group

Claims (3)

An electrode group formed by laminating or winding a negative electrode having a foil-like negative electrode current collector in a negative electrode mixture layer and a positive electrode having a foil-like positive electrode current collector in a positive electrode mixture layer via a separator And a lithium secondary battery comprising an electrolyte solution in which the electrode group is immersed,
The foil-shaped negative electrode current collector and the foil-shaped positive electrode current collector have a plurality of holes penetrating the current collector, and the periphery of the holes is directed to at least one surface side of the foil-shaped current collector. Protruding,
The thickness of the foil-shaped current collector including the protruding portion around the hole is 3% of the total thickness of one electrode plate including the current collector and the mixture layer of the negative electrode or the positive electrode. This is a lithium secondary battery characterized by being 25% or less.   The foil-shaped negative electrode current collector and the foil-shaped positive electrode current collector are provided with holes having the protrusions on the entire surface of the current collector, or holes in the longitudinal direction or the width direction of the current collector. 2. The lithium secondary battery according to claim 1, wherein a hole having the protruding portion is provided on a surface of the current collector, leaving a portion not having a surface. 3.   The density of the positive electrode mixture layer excluding the foil-like positive electrode current collector is 1.8 to 3.6 g / cc, and the density of the negative electrode mixture layer excluding the foil-like negative electrode current collector is 1.2 to 1.6 g / cc. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is provided.

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