JP2007299639A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To constitute a current collector so that physical stress can be absorbed even when a mix formed by mixing an active material, a conductive material, and a binder is expanded and contracted by charge discharge in a positive electrode and a negative electrode of a lithium secondary battery. <P>SOLUTION: The lithium secondary battery is equipped with a positive electrode A, a negative electrode B, a separator 2 electrically insulating the positive electrode A and the negative electrode B, and an electrolyte, the positive electrode A and the negative electrode B have current collectors 3, 6 having structure formed by accumulating two or more prismatic hollow parts, and the mix formed by mixing the active material, the conductive material, and the binder, filled in the prismatic hollow parts of the current collectors 3, 6, and the current collectors 3, 6 are constituted so that the prismatic hollow parts are deformed according to the expansion and contraction of the mix in charge discharge. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery having a current collector for achieving a long life.

Secondary batteries are often used as power sources for portable devices from the viewpoints of economy and resource saving. There are various types of secondary batteries, and the most common one at present is a nickel-cadmium battery. Recently, nickel metal hydride batteries have also become widespread. Furthermore, as the positive electrode material, cobalt lithium LiCoO ₂ , nickel lithium oxide LiNiO ₂ , these solid solution Li (Co _1-x Ni _x ) O ₂ or LiMn ₂ O ₄ having a spinel structure, etc. Lithium secondary batteries using carbon materials such as graphite, electrolytes with liquid organic compounds as solvents, and lithium compounds as solutes also have higher output voltage and higher energy density than nickel metal hydride batteries. It is becoming the main force.

Usually, a secondary battery having a capacity of about 1 Ah used for portable equipment or the like has a positive electrode plate and a negative electrode plate each having a thickness of about several hundreds of microns facing each other through a porous insulator separator. Is formed by encapsulating a metal or a resin film having a metal layer together with an electrolyte. In general, a positive electrode or a negative electrode is formed by adhering a positive electrode active material or a negative electrode active material and a conductive material for improving electronic conductivity to a current collector with a binder. In addition, current collectors used for the positive electrode plate and the negative electrode plate have been proposed in shapes such as punching, mesh, honeycomb, lath, lattice, expanded, screen, and lace ( For example, see Patent Document 1).
Japanese Patent Laid-Open No. 10-32006

  Lithium secondary batteries are known to have high output voltage and high energy density, as described above, and high energy efficiency (discharge power / charge power). Although preferred, there are several problems, the most important being capacity reduction and load characteristic degradation due to repeated cycles.

The lithium secondary battery supplies electrons to an external circuit by the following reaction during discharging. In the following reaction formula, Li _1-x CoO ₂ is a positive electrode active material, and C ₆ is a negative electrode active material.
The positive electrode _{Li 1-x CoO 2 + xLi} + xe - → LiCoO 2
The negative electrode _{xLiC 6 → C 6 + xLi +} xe -

As the above reaction proceeds, the positive electrode active material and the negative electrode active material decrease (shrink). During reverse charging, the reverse reaction proceeds, and the positive electrode active material and the negative electrode active material increase in volume (expand). That is, in the lithium secondary battery, the active material is repeatedly expanded and contracted by repeating charge and discharge, and as a result, physical stress is generated in the electrode sealed in the sealed container.
When the contact ratio between the active material and the conductive material decreases due to the physical stress, the current path inside the electrode is interrupted, so that the resistivity of the electrode increases, and as a result, the load characteristics of the battery decrease.
Furthermore, when stress repeatedly occurs, the active material is finally completely isolated and does not participate in charge / discharge, leading to a decrease in capacity as a battery. Therefore, in order to suppress a decrease in capacity and load characteristics due to repeated charge / discharge cycles and to provide a longer-life lithium secondary battery, the contact ratio between the active material and the conductive agent due to the expansion and contraction is reduced. It becomes a subject to suppress and to suppress an increase in internal resistance.
In the current collectors of various shapes described in Patent Document 1, it has not been studied to solve such a problem.

As a result of intensive studies, the inventors of the present application have gathered so that, in the positive electrode and the negative electrode, a mixture of an active material, a conductive material, and a binder can absorb physical stress even if it expands and contracts due to charge and discharge. By constructing the electric body, the present invention has been achieved.
Thus, according to the present invention, a positive electrode and a negative electrode, a separator that electrically insulates the positive electrode and the negative electrode, and an electrolyte are provided. The positive electrode and the negative electrode are a collection of structures in which a plurality of prismatic hollow portions are integrated. Each of the current collector and a mixed material obtained by mixing an active material, a conductive material, and a binder filled in each prismatic hollow portion of the current collector. There is provided a lithium secondary battery configured such that the shape of the prismatic hollow portion is deformed in accordance with expansion and contraction due to heat.

  According to the lithium secondary battery of the present invention, the current collector is configured such that the shape of the prismatic hollow portion is deformed in response to the expansion and contraction of the composite material due to heat. At the time of volume expansion of the material, each hollow portion becomes larger following it, and the physical stress applied to the positive electrode and the negative electrode is relaxed. As a result, the contact point between the active material and the conductive material in the composite material is not destroyed by stress (the contact state is maintained), and the increase in internal resistance and capacity decrease are suppressed even when the charge / discharge cycle is repeated. Longer life is achieved.

As shown in FIG. 1, the lithium secondary battery of the present invention includes a positive electrode A and a negative electrode B, a separator 2 that electrically insulates the positive electrode A and the negative electrode B, and an electrolyte. The current collectors 3 and 6 having a structure in which a plurality of prismatic hollow portions are integrated, and the active material, the conductive material, and the binder filled in each prismatic hollow portion of the current collectors 3 and 6. Each of the current collectors 3 and 6 is configured such that the shape of the prismatic hollow portion is deformed in accordance with expansion and contraction of the composite material due to heat. And
That is, the positive and negative electrode current collectors are configured by closely integrating deformable prismatic hollow portions for holding the composite material.
FIG. 1 shows a prismatic lithium secondary battery having a basic structure given as an example of the present invention. Reference numeral 50 denotes a lithium secondary battery according to an embodiment of the present invention. Reference numerals 4 and 5 denote a positive electrode plate and a negative electrode. Reference numerals 4a and 4b denote positive and negative terminals extending from the positive electrode 4 and the negative electrode 5, respectively, and reference numeral 7 denotes a battery container made of a resin sheet.
Hereinafter, each component of the lithium secondary battery of the present invention will be described. Note that the present invention is not limited to the following embodiments and examples.

(Current collector)
FIG. 2 is a partial plan view showing a state in which the positive electrode current collector 3 is viewed from the thickness direction. The current collector 3 includes a plurality of (five in FIG. 2) metal plates 11 and a plurality of coupling portions 12 that are coupled to each other in a state where the plurality of elongated metal plates 11 are overlapped. The joints 12 extend in parallel in the thickness direction at equal intervals, and the joints 12 in one stage between the pair of opposing metal plates 11, 11 are adjacent joints 12, 12 in other neighboring stages. By pulling the two outermost metal plates 11 and 11 in the state of FIG. 3 in the direction of arrows a and b (planar direction) in FIG. It is formed. In addition, about a negative electrode, a different point from a positive electrode is mainly demonstrated.

Examples of the material of the metal plate 11 of the current collectors 3 and 6 of the positive electrode A and the negative electrode B include aluminum, aluminum alloy, iron, stainless steel, titanium, copper, nickel, and the like. Aluminum or aluminum alloy is preferable for the positive electrode, and copper or nickel is preferable for the negative electrode.
If the thickness of the metal plate 11 is less than 10 μm, the physical structure cannot be maintained, and if it is more than 1 mm, the volume of the hollow portion 13 of the current collector 3 in the lithium secondary battery of a certain size decreases. Since the filling amount of the active material into the hollow portion 13 is reduced and the battery capacity is reduced, 10 μm to 1 mm is preferable.

  The assembly 3 configured as described above can form the joint portion 12 by joining the stacked metal plates 11 and 11 together by an adhesive or welding. The width and thickness of the coupling portion 12 can be arbitrarily set. For example, the width W can be set to 1 to 10 mm and the thickness T can be set to 1 mm or less. When the bonding portion 12 is made of an adhesive, the material is preferably a thermoplastic resin that is chemically stable and dissolves in a suitable solvent but does not corrode by the electrolyte. For example, low melting point polyethylene, polypropylene, and fluororesin are used. Can be mentioned.

  The current collector 3 shown in FIG. 1 is viewed from the plane direction, and the thickness T of the current collector 3 corresponding to the width of the metal plate 11 and the length of the hollow portion 13 increases as the distance to the counter electrode increases. Since internal resistance rises, 5 mm or less is preferable and 1-3 mm is more preferable. The positive electrode A is disposed with one opening of the prismatic hollow portion 13 of the current collector 3 facing the separator 2 and the other opening facing the positive electrode plate body 4. The same applies to the negative electrode B.

Next, the shape of the prismatic hollow portion 13 of the current collector 3 will be described.
In FIG. 2, since the thickness T is shown larger than the width W in order to explain the coupling portion 12, the prismatic hollow portion 13 (the second to fourth layers of metal) positioned inside the current collector 3. The plan view shape of the prismatic hollow portion 13 formed of the plate 11 looks like an octagon, and the prismatic hollow portion 13 (the first and second layers and the fourth to fifth layers of the metal plates 11) located outward. The prismatic hollow portion 13) formed in this manner appears to be a heptagon in plan view. However, since the thickness T of the coupling portion 12 is actually small as described above, the plan view shape of the prismatic hollow portion 13 is hexagonal when located inward of the current collector 3 as shown in FIG. The one located outside is a pentagon. 2 and 4, the mixture filled in the prismatic hollow portion 13 is not shown.

In the present invention, the hexagonal columnar hollow portion 13 having a hexagonal shape in plan view has a first inner angle θ _{1 that} is opposed to a second inner angle θ _{2 that} is opposed to a third inner angle that is opposite to the third inner angle. of and a interior angle theta _3, unlike the angle theta ₁ and the angle theta _2, the angle theta ₂ and the angle theta ₃ is made substantially equal.
In the hexagonal columnar hollow portion 13, the first interior angle θ ₁ satisfies 120 ° <θ ₁ <180 ° or 0 ° <θ ₁ <120 ° when the hollow portion 13 is filled with the composite material. Preferably 120 ° <θ ₁ <150 ° or 90 ° <θ ₁ <120 °, more preferably 120 ° <θ ₁ <130 ° or 110 ° <θ ₁ <120 °. The reason will be described below.

FIG. 5 is a graph showing the relationship between the angle θ ₁ of the first inner angle and the volume of the hollow portion in the hexagonal column-shaped hollow portion 13, where the volume of the hollow portion when the angle θ ₁ is 120 ° is set to 1. It represents the volume change due to the change of θ ₁ . The result of this graph is a result obtained on the basis of a current collector experimentally manufactured under the following conditions.
The thickness t of the coupling portion 12: 0.05 mm
Width W of coupling part 12: 1 mm
Current collector width: 3 mm
Length of one side (long side) of the hexagonal column shaped hollow portion L: 1 mm
The volume of the hollow part when the angle θ ₁ is changed can be calculated by the product of the cross-sectional area of the hollow part 13 and the width of the current collector. The cross-sectional area of the hollow portion 13 is divided into a rectangular region R1 corresponding to the thickness portion of the joint 12 and each trapezoidal region on both sides sandwiching the rectangular region R1 into two right-angled triangular regions R2 and one rectangular region R3, Each area | region R1-R3 can be calculated | required with the following formula | equation, and it can calculate by those sums.
R1 cross-sectional area = {2 * cos (θ ₁ /2)+1}*0.05
Sectional area of _{R2 = sin (θ 1/2} ) * cos (θ 1/2) / 2
R3 sectional area of _{= 1 * sin (θ 1/} 2)
Cross-sectional area of hollow portion = cross-sectional area of R1 + 4 × (cross-sectional area of R2) + 2 × (cross-sectional area of R3)
Although a hexagonal columnar hollow portion having an angle θ ₁ exceeding 180 ° can be produced, it is substantially difficult to produce such a hexagonal columnar hollow portion, and is omitted in FIG.

From FIG. 5, it can be seen that in the case of a hexagonal columnar hollow portion, the volume is the largest when the angle θ ₁ of the first inner angle is 120 °. Therefore, if the angle θ ₁ is larger or smaller than 120 °, even if the composite material (particularly the active material) filled in the hexagonal columnar hollow portion expands, the angle θ ₁ of the first inner angle becomes smaller. By deforming the shape of the hollow portion so as to increase, the volume of the hollow portion increases, so that no physical adaptation force is applied to the inside of the active material filled in the hollow portion. On the other hand, when the angle θ ₁ of the first inner angle is 120 °, the volume of the hollow portion does not increase any more even if the composite material expands. Contact points with the material are destroyed, cycle characteristics are deteriorated and battery life is shortened.
On the other hand, when shrinkage occurs in the composite material (particularly the active material), the volume of the hollow portion is increased according to the shrinkage of the entire filled composite material by increasing or decreasing the angle θ ₁ of the first internal angle. Therefore, the physical adaptability is not applied to the inside of the active material filled in the hollow portion.

As described above, according to the present invention, the stress applied to the current collectors 3 and 6 caused by the expansion and contraction of the mixture filled in the hollow portions 13 of the current collectors 3 and 6 of the positive electrode A and the negative electrode B is reduced. Because it is relaxed, the contact point between the active material and the conductive material is not destroyed by stress, and the long-life lithium secondary battery does not increase in internal resistance or decrease in capacity even after repeated charge / discharge cycles Is obtained.
As described above, in the hexagonal columnar hollow portion 13 of the current collector, the first interior angle θ ₁ is 120 ° <θ ₁ <180 ° or 0 when the hollow portion 13 is filled with the composite material. ° <θ ₁ <may be a 120 °, but preferably as large as possible is the volume of the hollow portion 13 in order to maximize the battery capacity, therefore 120 ° <θ ₁ <150 ° or 90 ° <θ ₁ < 120 ° is preferable, and 120 ° <θ ₁ <130 ° or 110 ° <θ ₁ <120 ° is particularly preferable.

  Further, the length L of one side of the prismatic hollow part 13 of the prismatic hollow part 13 of the current collector 3 is not particularly limited, but if the length of one side is 5 mm or more, the active part filled in the hollow part 13 is Since the distance from the substance to the current collector 3 is increased, the internal resistance of the electrode is likely to increase, and the load characteristics of the battery are liable to be reduced, it is preferably up to 5 mm, more preferably 1 to 3 mm.

(Positive electrode active material)
As the positive electrode active material, lithium transition metal composite oxide, lithium transition metal composite sulfide, lithium transition metal composite nitride, lithium phosphate transition metal compound, and the like can be used.

(Negative electrode active material)
As the negative electrode active material, a material capable of electrochemically inserting / extracting lithium is preferable. In order to constitute a high energy density battery, it is preferable that the potential at which lithium is inserted / desorbed is close to the deposition / dissolution potential of metallic lithium. A typical example is natural or artificial graphite in the form of particles (scale-like, lump-like, fibrous, whisker-like, spherical, pulverized particles, etc.). Artificial graphite obtained by graphitizing mesocarbon microbeads, mesophase pitch powder, isotropic pitch powder, and the like may be used. Also, graphite particles having amorphous carbon attached to the surface can be used. Alternatively, lithium transition metal oxide, lithium transition metal nitride, transition metal oxide, silicon oxide, or the like can be used. Among these, those that are difficult to change in composition and structure by heat treatment in a reducing atmosphere are preferable, and specifically, a carbon material is preferable.

(Conductive material)
Chemically stable materials such as graphite, carbon black, acetylene black, ketjen black, carbon fiber, and conductive metal oxide can be used as the conductive material. If necessary, multiple types can be mixed. May be used. The mixing ratio of the conductive material in the mixture can be 1 to 50 parts by weight with respect to 100 parts by weight of the positive electrode active material or the negative electrode active material, but is not limited to this range.

(Binder)
As the binder, fluorine-based polymers such as polytetrafluoroethylene and polyvinylidene fluoride, polyolefin-based polymers such as polyethylene and polypropylene, and the like can be used. The mixing ratio of the binder in the composite material can be 1 to 50 parts by weight with respect to 100 parts by weight of the positive electrode active material or the negative electrode active material, but is not limited to this range.

(Positive electrode plate, negative electrode plate and their electrode terminals)
The material of the positive electrode plate 4 and the positive electrode terminal 4a can be the same metal material as that of the positive electrode current collector 3, and the material of the negative electrode plate 5 and the negative electrode terminal 4b can be the same metal material as that of the negative electrode current collector 6. it can. The positive and negative terminals 4a and 4b are preferably connected in advance to the positive and negative electrodes 4 and 5 by welding. Alternatively, the positive and negative electrode plates 4 and 5 may be omitted, and the positive and negative electrode terminals 4a and 4b may be directly welded to the positive electrode current collector 3 and the negative electrode current collector 6.

(Electrolytes)
As the electrolyte, for example, an organic electrolyte, a gel electrolyte, a polymer solid electrolyte, an inorganic solid electrolyte, a molten salt, or the like can be used, and among them, an organic electrolyte is preferable. It is preferable to select an organic electrolyte that is most suitable for the combination of the positive electrode and the negative electrode active material to be used. Examples include the following combinations of positive electrode active material / electrolytic solution (salt: solvent) / negative electrode active material. Can do.
A combination of LiFePO ₄ / LiPF ₆ · ethylene carbonate + diethyl carbonate / graphite, a combination of LiCoO 2 / LiPF 6: propylene carbonate + diethyl carbonate / Li—C, and the like.

(Separator)
The material of the separator 7 is preferably one that does not dissolve or swell in the organic solvent contained in the electrolyte, and specifically includes an inorganic material such as a polyester polymer, a polyolefin polymer, an ether polymer, or glass. Specifically, a porous material or a nonwoven fabric formed from polyethylene or polypropylene can be used. The thickness of the separator 7 can be 0.005 to 0.1 mm.

Next, production of a lithium secondary battery will be described.
The current collector 3 can control the angle θ ₁ of the first inner angle of the hollow portion 13 by controlling the extension width between the metal plates 11 and 11 in the directions of the arrows a and b as described above. it can. Or after extending between the metal plates 11 and 11, it can also adjust later so that a 1st interior angle may become arbitrary angles. The same applies to the negative electrode current collector 6.

The active material, the conductive material, and the binder are mixed in predetermined amounts to produce a composite material, and the composite material is filled in all the hollow portions 13 of the current collector 3 without any gaps. At this time, the current collector 3 may be placed on the positive electrode plate 4, and the hollow part 13 opened upward may be filled with the mixture. Moreover, you may produce a compound material in paste form by adding a solvent. The solvent for forming the paste of the composite material is not particularly limited, but a solvent capable of dissolving the binder is preferable. For example, water can be used in addition to an organic solvent such as N-methylpyrrolidone, acetone and alcohol. The viscosity of the paste-like composite material is preferably within a viscosity range that does not leak from the hollow portion 13 due to its own weight, and is, for example, 20 to 100 Pa · s.
When a solvent is added to the composite material to form a paste, the composite material is preferably dried on the current collector 3 and then dried to remove the solvent. Drying may be performed in the air or under reduced pressure. Preferably, drying is performed at a temperature of about 80 ° C. in order to shorten the drying time. Similarly, each hollow portion 13 of the negative electrode current collector 6 is filled with a mixture of a negative electrode active material, a conductive material, and a binder.

A positive electrode current collector 3 superimposed on the positive electrode plate 4 and a negative electrode current collector 6 superimposed on the negative electrode plate 5 are stacked with the separator 2 interposed therebetween to produce an electrode group. In the case of FIG. 1, the positive electrode and the negative electrode have a two-layer structure, but at least one of the positive electrode and the negative electrode may be stacked on three or more layers with different polar sides overlapping each other.
The electrode group produced in this way is inserted into the battery container 7, and the positive terminal 4 a and the negative terminal 4 b are led out of the battery container 7. Thereafter, the battery container 7 is sealed in order to block the positive / negative electrodes A and B and the separator 2 from the outside air. In the case of a square battery, the sealing method can be sealed by attaching a lid called a metallic sealing plate to the opening and welding. In addition to these methods, sealing with an adhesive or fixing with bolts or the like via a gasket or the like may be used. Alternatively, sealing may be performed with a laminate film in which a thermoplastic resin is attached to a metal foil. An opening for injecting electrolyte can be provided at the time of sealing. In the case of a cylindrical battery, sealing is usually performed by fitting a lid having a resin packing into the opening of the battery container and caulking the container.
Thereafter, an electrolyte is injected into the battery container 7, and the opening of the battery container 7 is sealed to complete the production of the secondary battery. Note that the gas generated by energization before sealing may be removed from the battery container 7.

Example 1
A positive electrode was produced by the following procedure.
200 g of LiFePO ₄ as a positive electrode active material, 10 g of acetylene black as a conductive material, and 10 g of polyvinylidene fluoride as a binder are mixed, and 150 ml of N-methyl-2-pyrrolidone is added to the kneader. Kneading was performed to produce a positive electrode mixture.
The positive electrode current collector used was made of aluminum, had a length of 10 cm, a width of 10 cm, and a thickness of 1 mm. The length of one side of the hollow portion was 1.5 mm, and the angle θ ₁ of the first inner angle of the hollow portion was 125. °. Further, an aluminum positive electrode terminal having a width of 5 mm and a thickness of 100 μm is welded to the positive electrode current collector in advance. Each hollow part of the positive electrode current collector was filled with the paste-formed positive electrode mixture, and the current collector filled with the mixture was left in a dryer at 60 ° C. for 12 hours to remove the solvent.

A negative electrode was produced by the following procedure.
200 g of natural graphite as a negative electrode active material and 10 g of polyvinylidene fluoride as a binder are mixed, 150 ml of N-methyl-2-pyrrolidone is added thereto, and kneading is performed using a kneading apparatus to form a negative electrode. A composite material was prepared.
The negative electrode current collector used had the same structure as the positive electrode current collector, except that the material was copper. The negative electrode current collector was previously welded with a negative electrode terminal made of nickel having a width of 5 mm and a thickness of 100 μm. Has been. Each hollow part of the negative electrode current collector was filled with the pasted negative electrode mixture, and the current collector filled with the mixture was left in a dryer at 60 ° C. for 12 hours to remove the solvent.

Thereafter, in order to remove moisture, the positive electrode and the negative electrode were dried at 150 ° C. under a pressure of 0.01 MPa or less for 12 hours.
All subsequent operations were performed in an argon atmosphere dry box having a dew point temperature of −80 ° C. or lower.
Inside a laminated film bag (battery container), in which a positive electrode and a negative electrode are opposed to each other through a porous polyethylene separator having a thickness of 50 μm, and a low melting point polyethylene film having a thickness of 50 μm is welded to an aluminum foil having a thickness of 50 μm. The electrolyte solution was poured into the laminated film bag and the opening was sealed by heat welding to complete a lithium secondary battery. As the electrolytic solution, capacitance of ethylene carbonate and diethyl carbonate ratio of 1: a LiPF ₆ solvent as a salt mixed was used by dissolving 1.0 mol / l in 1.

The completed lithium secondary battery was charged with a constant current of 1 A until the voltage of the battery reached 4.0 V, and thereafter, 4.0 V constant voltage charging was performed for 2 hours to complete the charging. Thereafter, discharging was performed at 1 A until the battery voltage reached 2.5V. The discharge capacity at that time was defined as the initial capacity of the battery. The initial capacity of Example 1 was 10.3 Ah.
Next, the battery is charged at a constant current of 5 hours until the voltage of the battery reaches 4.0V, and thereafter, the battery is charged at a constant voltage of 4.0V for 2 hours to complete the charge, and discharged at the 5 hour rate One cycle was performed, and this was repeated 100 cycles. The discharge capacity after 100 cycles of Example 1 was 9.8 Ah, and the cycle characteristic indicated by the capacity ratio with respect to the initial capacity was 95.2%. Here, the 5-hour rate means a current value for discharging the entire capacity in 5 hours with respect to the rated capacity of the battery.

(Example 2)
A lithium secondary battery of Example 2 was fabricated in the same procedure as in Example 1 except that the angle θ ₁ of the first inner angle of the hollow part of the positive electrode current collector and the negative electrode current collector was 175 °. The cycle characteristics were measured by comparing the initial capacity of the battery of Example 2 and the discharge capacity after 100 cycles in the same manner as in Example 1. In Example 2, the initial capacity was 10.5 Ah, the discharge capacity after 100 cycles was 10.1 Ah, and the cycle characteristics were 96.3%.

(Example 3)
A lithium secondary battery of Example 3 was produced in the same procedure as Example 1 except that the first inner angle θ ₁ of the hollow part of the positive electrode current collector and the negative electrode current collector was 115 °. The cycle characteristics were measured by comparing the initial capacity of the battery of Example 3 and the discharge capacity after 100 cycles in the same manner as in Example 1. In Example 3, the initial capacity was 10.9 Ah, the discharge capacity after 100 cycles was 10.0 Ah, and the cycle characteristics were 91.3%.

(Comparative Example 1)
A lithium secondary battery of Comparative Example 1 was fabricated in the same procedure as in Example 1 except that the first interior angle θ ₁ of the hollow part of the positive electrode current collector and the negative electrode current collector was 120 °. The cycle characteristics were measured by comparing the initial capacity of the battery of Comparative Example 1 and the discharge capacity after 100 cycles in the same manner as in Example 1. In Comparative Example 1, the initial capacity was 10.9 Ah, the discharge capacity after 100 cycles was 7.1 Ah, and the cycle characteristics were 65.3%.

  Table 1 summarizes the cycle characteristics of Examples 1 to 3 and Comparative Example 1. It can be seen that the batteries of Examples 1 to 3 have good cycle characteristics. This is because the stress inside the electrode caused by the expansion and contraction of the active material due to charge and discharge is relieved, and the initial state is maintained even after 100 cycles of contact between the active material, the conductive material and the current collector. It is believed that there is.

It is sectional drawing which shows the whole structure of one Embodiment of the lithium secondary battery of this invention. It is the figure seen from the thickness direction explaining the electrical power collector in this invention. It is the figure seen from the thickness direction which shows the state before extending the electrical power collector of FIG. It is a figure explaining the shape of the prismatic hollow part of the electrical power collector of FIG. It is a graph which shows the relationship between the angle of the 1st interior angle in the prismatic hollow part of the electrical power collector of FIG. 2, and a hollow part volume.

Explanation of symbols

2 Separator 3 Positive electrode current collector 4 Positive electrode plate 4a Positive electrode terminal 5 Negative electrode plate 5a Negative electrode terminal 6 Negative electrode current collector 7 Battery container 12 Coupling portion 13 Rectangular column-shaped hollow portion (hexagonal column-shaped hollow portion)
A Positive electrode B Negative electrode L Length of one side of the prismatic hollow part T Current collector thickness t Coupling part thickness w Coupling part width θ ₁ First interior angle θ ₂ Second interior angle θ ₃ Third interior angle

Claims (5)

  A positive electrode and a negative electrode; a separator that electrically insulates the positive electrode and the negative electrode; and an electrolyte. Each of the prismatic hollow portions is filled with an active material, a conductive material and a binder mixed, and the current collector is expanded and contracted during charging and discharging. A lithium secondary battery characterized in that the shape of the prismatic hollow portion is deformed according to the above. Wherein the plurality of prismatic hollow part has a hexagonal prism-shaped hollow portion, the six internal angles in the 6 prismatic hollow portion, an angle theta ₁ of the first interior angle opposite, second interior angle opposite theta _2, and a third interior angle theta ₃ facing the different angles theta ₁ and the angle theta _2, the angle theta ₂ and the angle theta ₃ is a lithium secondary battery according to claim 1 equivalent. The lithium secondary battery according to claim 2, wherein the angle θ ₁ satisfies 120 ° <θ ₁ <180 ° or 0 ° <θ ₁ <120 °. The current collector has a plurality of metal plates and a plurality of coupling portions that are coupled to each other in a state where the plurality of metal plates are overlapped,
The plurality of joints extend in the same direction at equal intervals, a joint in one stage between a pair of opposing metal plates is located in the middle between adjacent joints in another adjacent stage,
The lithium secondary battery according to any one of claims 1 to 3, wherein a plurality of prismatic hollow portions are formed by separating two outermost metal plates.   The lithium secondary battery according to claim 4, wherein the positive electrode and the negative electrode are arranged such that one opening of a prismatic hollow portion of the current collector faces the separator.

Images