JP4067258B2 - Method for evaluating cycle life characteristics of secondary batteries - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for evaluating cycle life characteristics of a secondary battery.
[0002]
[Prior art]
In recent years, non-aqueous electrolyte batteries such as secondary batteries, particularly lithium secondary batteries, have been actively developed, and the development of non-aqueous electrolyte secondary batteries having excellent charge / discharge cycle life characteristics has become an important issue. Yes.
[0003]
Among these, a lithium secondary battery using a metal chalcogen compound combined with lithium as a positive electrode active material is disclosed (Japanese Patent Laid-Open No. 5-325964). In this battery, the use of a metal chalcogen compound as an active material with less expansion associated with charge / discharge makes it possible to improve charge / discharge cycle life characteristics.
[0004]
Thus, the expansion of the active material accompanying charge / discharge has a great influence on the charge / discharge cycle life characteristics, and the cycle life characteristics are greatly influenced by the pressure applied to the positive electrode and the negative electrode.
[0005]
[Problems to be solved by the invention]
However, a method for evaluating the relationship between the pressure applied to the positive electrode and the negative electrode and cycle life characteristics has not been known.
[0006]
An object of the present invention is to provide a method capable of simply and reliably evaluating the relationship between the pressure applied to a positive electrode and a negative electrode and cycle life characteristics.
[0007]
[Means for Solving the Problems]
In the present invention, at least one electrode group composed of a positive electrode and a negative electrode is housed in a battery case formed of a separator that separates both electrodes and a film material in which a metal foil is laminated with a synthetic resin together with an electrolyte. a method for evaluating the cycle life characteristics of the next cell by charging and discharging cycle test in a state where the pressure in the interior of the positive electrode and the negative electrode was added by applying pressure from the outside to the battery case, evaluate the cycle life characteristics It is characterized by doing.
[0008]
In the present invention, the battery case is preferably formed of a flexible material so that when a pressure is applied to the battery case from the outside, the pressure is applied to the positive electrode and the negative electrode inside the battery case. An example of such a material is a film material obtained by laminating a metal foil with a synthetic resin.
[0009]
In the present invention, a charge / discharge cycle test is performed in a state in which pressure is applied from the outside to a battery case formed of a film material obtained by laminating a metal foil with a synthetic resin, and pressure is applied to the positive electrode and the negative electrode inside the battery case. During the charge / discharge cycle test, the active material of the positive electrode and the negative electrode is restrained from expanding due to charge / discharge and is subjected to a load by this pressure. By repeatedly performing the charge / discharge cycle test under such a pressure load, the electrode is deteriorated according to the degree of expansion of various positive and negative electrode active materials, and the charge / discharge cycle characteristics are lowered. That is, by performing a charge / discharge cycle test with pressure applied to the positive electrode and the negative electrode, it is possible to promote the influence on the charge / discharge cycle characteristics due to expansion associated with charge / discharge of the positive electrode and the negative electrode active material. In addition, the cycle life characteristics when the negative electrode active material is used can be easily and reliably evaluated.
[0010]
In a preferred embodiment according to the present invention, the attachment fastening 冶 again and again for applying clamping pressure to the battery case being formed from a laminated film material of the metal foil with synthetic resin, clamping at least a portion of said battery case by applying a biasing pressure, applying pressure from outside to the battery case. When the electrode group has an electrode surface extending in a specific surface direction, the clamping pressure is applied so as to be perpendicular to the electrode surface.
[0011]
State 冶 fastening tool, for example, that pinched a flat 冶 tool for sandwiching the battery case being formed from a laminated film material of the metal foil with synthetic resin from both sides, the battery case tabular 冶 tool in and has a stationary 冶 device for fixing a flat 冶 tool.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications within a range not changing the gist thereof. Is.
[0013]
(Example)
A thin battery using natural graphite as the negative electrode active material, lithium-containing cobalt oxide (LiCoO ₂ ) as the positive electrode active material, natural graphite as the negative electrode active material, and lithium-containing manganese oxide (LiMn ₂ as the positive electrode active material) Thin batteries using O ₄ ) were prepared, and the charge / discharge cycle life characteristics were evaluated while applying pressure to the battery case. These thin batteries were produced as follows.
[0014]
[Fabrication 1: LiCoO ₂ ]
90 parts by weight of lithium-containing cobalt oxide (LiCoO ₂ ) powder as a positive electrode main material, 5 parts by weight of artificial graphite powder, and N-methyl-2-pyrrolidone (NMP) solution of 5 parts by weight of polyvinylidene fluoride were mixed. A slurry was prepared. This slurry was applied to both surfaces of an aluminum foil by a doctor blade method to form an active material layer. Then, it vacuum-dried at 150 degreeC for 2 hours, and produced the positive electrode.
[0015]
[Preparation of positive electrode 2: LiMn ₂ O ₄ ]
LiOH and MnO ₂ were mixed in a mortar so that the molar ratio of each element was Li: Mn (= 1: 2), heat-treated at 750 ° C. for 20 hours in an oxygen atmosphere, pulverized, and lithium-containing manganese The oxide LiMn ₂ O ₄ was obtained.
[0016]
Mixing 90 parts by weight of lithium-containing manganese oxide LiMn ₂ O ₄ powder as the positive electrode main material, 5 parts by weight of artificial graphite powder, and 5 parts by weight of polyvinylidene fluoride in N-methyl-2-pyrrolidone (NMP) solution Thus, a slurry was prepared. This slurry was applied to both surfaces of an aluminum foil by a doctor blade method to form an active material layer. Then, it vacuum-dried at 150 degreeC for 2 hours, and produced the positive electrode.
[0017]
(Production of negative electrode)
A natural graphite powder is mixed with 95 parts by weight and a polyvinylidene fluoride powder is mixed with 5 parts by weight. This is mixed with an NMP solution to prepare a slurry, and this slurry is coated on one side of a copper current collector having a thickness of 20 μm. An active material layer was formed by coating with a doctor blade method, and then dried at 150 ° C. to prepare a negative electrode.
[0018]
(Preparation of electrolyte)
LiPF ₆ was dissolved in an equal volume mixed solvent of ethylene carbonate and diethyl carbonate so as to be 1.0 mol / liter to prepare a nonaqueous electrolytic solution.
[0019]
[Production of battery]
A thin nonaqueous electrolyte battery (lithium secondary battery, battery dimensions: thickness 3 mm, width 30 mm, length 50 mm) as shown in FIG. 2 is obtained using the positive electrode, negative electrode, and electrolytic solution obtained as described above. Produced. As shown in FIG. 2, a separator 14 is sandwiched between a positive electrode 12 and a negative electrode 13, and this is wound into a flat spiral shape to produce an electrode group. After storing and injecting the non-aqueous electrolyte, the opening of the bag-shaped storage body 15 was sealed by heat welding to produce a non-aqueous electrolyte battery 10. A positive electrode current collecting tab 11 a is connected to the positive electrode 12, and a negative electrode current collecting tab 11 b is connected to the negative electrode 13. As the separator 14, a polypropylene microporous film was used.
[0020]
In FIG. 2, only one surface of the bag-shaped storage body 15 is illustrated and the other surface is not illustrated, but the bag-shaped storage body 15 is formed in a bag shape. Moreover, the bag-shaped storage body 15 is formed from the film which laminated polyethylene on both surfaces of the aluminum foil.
[0021]
[Measurement of charge / discharge cycle life characteristics]
Using 冶 fasteners shown in FIG. 1, the charge-discharge cycle test was carried out while applying pressure to the positive and negative electrodes therein by applying pressure from the outside to the battery case of the nonaqueous electrolyte battery. FIG. 1A is a side view, and FIG. 1B is a plan view. As shown in FIG. 1, 冶 fastener is comprised of tabular 冶 tool 1 and 2 and the fixed 冶 fixture 3. The flat 冶 instrument 1 and 2, iron flat plate (dimensions: thickness 5 mm, width 50 mm, length 80 mm) was used. The fixed 冶 device 3, using bolts (diameter 5mm of the thread).
[0022]
Tabular 冶 instrument 1 and 2, is provided with a hole for each pass a screw portion of the bolt 3 six, with the holes of the flat 冶 device 2, screw holes that mate with the threaded portion of the bolt 3 Is formed. Therefore, by turning the bolt 3, the flat 冶 device 2 can be brought close to the flat 冶 device 1 side, by inserting the battery 10 between the flat 冶 instrument 1 and tabular 冶 tool 2, A tightening pressure can be applied to the battery 10. To prevent a short circuit between the battery 10, the surface of the plate-like 冶 tool 1 and 2 have been subjected to coating treatment with an insulating material.
[0023]
The procedure for assembling the 冶 tool with the above clamping, the first battery 10, sandwiched between the flat 冶 tool 1 and 2. In this case, arranged between the flat 冶 tool 1 and 2 as clamping pressure is applied in the direction perpendicular to the electrode surface extending in flat direction of the electrode group of the battery 10. Then, as the tightening pressure on the cell 10 becomes a predetermined value, tightening the battery 10 by turning the fixing 冶 fixture 3. Adjustment of the pressure clamping, the torque when tightening the fixing 冶 fixture 3, respectively carried out by changing the 10, 20, 30 and 40 kgf · cm. Incidentally, tightening pressure (tightening torque) as the those of 0 kgf · cm, using a battery that is not fitted with 冶 fastener.
[0024]
A charge / discharge cycle test was performed on each battery to which a clamping pressure was applied as described above. The experimental conditions were as follows: each battery was charged at a constant current of up to 4.2 V at a current value of 200 mA at 25 ° C., and then discharged at a current value of 200 mA to 2.75 V to obtain an initial discharge capacity.
[0025]
Next, after charging at a constant current of up to 4.2 V at 200 mA, a charge / discharge cycle test was repeated in which the process of discharging at a constant current of up to 2.75 V at 200 mA was repeated, and the remaining capacity was determined from the discharge capacity after 200 cycles. The rate was calculated. The results are shown in FIG.
[0026]
As is clear from the results shown in FIG. 3, the thin battery using lithium-containing manganese oxide (LiMn ₂ O ₄ ) as the positive electrode active material exhibits excellent charge / discharge cycle characteristics regardless of the tightening pressure of the battery. It was. On the other hand, in the thin battery using lithium-containing cobalt oxide (LiCoO ₂ ) as the positive electrode active material, a decrease in charge / discharge cycle characteristics was observed as the tightening pressure increased.
[0027]
This is because the expansion associated with charging / discharging of lithium-containing manganese oxide (LiMn ₂ O ₄ ) is small, and it is difficult to receive a load due to the clamping pressure applied to the electrode. This is probably because the material does not deteriorate. On the other hand, since lithium-containing cobalt oxide (LiCoO ₂ ) has a large expansion associated with charging and discharging, it receives a large pressure load when a clamping pressure is applied to the electrode. It is considered that the repeated charge / discharge cycle test under such a large pressure load resulted in the deterioration of the active material and consequently the cycle life characteristics.
[0028]
As described above, the charge / discharge cycle test is performed with the pressure applied to the battery, and the relationship between the pressure applied to the positive electrode and the negative electrode and the cycle life characteristics is easily and reliably evaluated for the battery using various materials. can do.
[0029]
In the above embodiment, the cycle life characteristics of the nonaqueous electrolyte secondary battery are evaluated as the secondary battery, but the present invention is not limited to this, and other secondary batteries such as alkaline storage batteries are used. Can also be applied.
[0030]
【The invention's effect】
According to the present invention, the relationship between the pressure applied to the positive electrode and the negative electrode and the cycle life characteristics can be easily and reliably evaluated. Therefore, it is possible to easily and reliably evaluate the deterioration of the active material due to the expansion and contraction associated with the charge / discharge of the electrode active material.
[Brief description of the drawings]
[1] The present invention a side view showing the fastening 冶 tool used in the example according (a) and a plan view (b).
FIG. 2 is an exploded perspective view showing the structure of a nonaqueous electrolyte secondary battery used as an evaluation object in an example according to the present invention.
FIG. 3 is a diagram showing a relationship between a tightening pressure and a capacity retention rate of a nonaqueous electrolyte secondary battery evaluated in an example according to the present invention.
[Explanation of symbols]
1, 2, flat 冶 instrument 3 ... fixed 冶 fixture 10 ... non-aqueous electrolyte secondary battery 11a, 11b ... electrode current collector tab 12 ... cathode 13 ... anode 14 ..・ Separator 15 ... Battery case (bag-like storage)

Claims (5)

A cycle of a secondary battery housed in a battery case in which at least one electrode group consisting of a positive electrode and a negative electrode is formed of a separator that separates both electrodes, and a film material obtained by laminating a metal foil with a synthetic resin together with an electrolyte In a method for evaluating life characteristics,
A cycle life characteristic of a secondary battery, characterized by evaluating a cycle life characteristic by performing a charge / discharge cycle test in a state where pressure is applied to a positive electrode and a negative electrode inside the battery case from the outside. Evaluation methods. Attaching the tightening 冶 tool for applying clamping pressure to the battery case, by applying a clamping pressure to at least a portion of the battery case, to claim 1, characterized in that applying pressure from the outside The cycle life characteristic evaluation method of the described secondary battery.   The cycle life of the secondary battery according to claim 2, wherein the electrode group has an electrode surface extending in a specific surface direction, and the clamping pressure is applied in a direction perpendicular to the electrode surface. Characterization method. 冶 device the tightening is a flat 冶 device for sandwiching the battery case from both sides, and fixed 冶 device for fixing the flat 冶 instrument in a state of sandwiching the battery case in the flat 冶 tool The cycle life characteristics evaluation method for a secondary battery according to claim 2 or 3, wherein The method for evaluating cycle life characteristics of a secondary battery according to any one of claims 1 to 4 , wherein the secondary battery is a nonaqueous electrolyte secondary battery.

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