JP2013152849A - Lithium-ion secondary battery subjected to aging treatment and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery which is excellent in cycle characteristics by an aging treatment and has large capacity and high output.SOLUTION: There are provided: the lithium-ion secondary battery having a polymer electrolyte, wherein when an internal resistance of the battery after initial charge/discharge is (A) and an internal resistance of the battery after an aging treatment is (B), the value of (B)/(A) is <0.7; and a method for manufacturing the same.

Description

  The present invention relates to a lithium secondary battery utilizing the phenomenon of insertion and extraction of lithium ions, and provides a lithium secondary battery excellent in output characteristics and low-temperature characteristics.

  With the miniaturization of electronic devices such as personal computers, video cameras, and mobile phones, lithium secondary batteries having a high energy density have already been put into practical use and widely used in the field of information and communication-related devices. On the other hand, it is considered that this lithium secondary battery will be used for large-capacity applications such as power sources for electric vehicles and power storage, and it is expected that the demand will increase in the future.

The performance required for secondary batteries in general is that the characteristics do not change with time. Even if charging and discharging are repeated, cycle characteristics with a small reduction rate of the discharge capacity are required. So far, in order to improve the cycle characteristics of lithium secondary batteries, the development of positive and negative electrode active materials, the structure of positive and negative electrodes Many technologies have been studied and developed, such as strengthening of non-aqueous electrolyte and improvement of non-aqueous electrolyte.
Among them, in order to improve the cycle characteristics of the lithium secondary battery, a technique for performing an aging process of storing at a predetermined temperature for a predetermined time has been proposed.
For example, after a predetermined preliminary charge / discharge is performed on the assembled battery, a predetermined aging process is performed, and the main charge is sequentially performed (Patent Document 1), and the preliminary charge process is performed up to a predetermined voltage value under a room temperature range. Filling the battery case space of the pre-charged battery with a mixed gas of oxygen gas and inert gas, the oxygen gas concentration of which is adjusted to 10 to 20 vol%, and sealing, and There has been proposed a method (Patent Document 2) in which a sealed battery is kept at a predetermined temperature for a predetermined time and subjected to an aging treatment.

  A positive electrode formed by binding a positive electrode active material made of a lithium transition metal composite oxide with a positive electrode binder; a negative electrode formed by binding a negative electrode active material made of a carbon material with a negative electrode binder; The temperature at which the non-aqueous electrolyte solidifies with respect to a lithium secondary battery that has a non-aqueous electrolyte and is assembled by impregnating the positive and negative electrodes with the positive and negative electrodes facing each other. A lithium secondary battery formed by assembling a positive electrode and a negative electrode using a layered rock salt structure lithium-nickel composite oxide as a positive electrode active material is applied at 40 ° C. or higher 90 ° C. Aging process for storing at a storage temperature of ℃ or less, including a low temperature aging process for increasing initial discharge capacity and a high temperature aging process for improving charge / discharge cycle characteristics (patented) Document 4) the aging process, such as has been proposed.

JP-A-11-102729 JP 2010-153337 A JP 2001-52754 A JP 2000-340262 A

In the future, the market for large-sized lithium secondary batteries for power storage will rapidly expand, and the forecast for the 2016 market is expected to be 12.6 times that of 2010 (the forecast for the 2016 market is 1,200 billion yen). As a performance of the storage battery required in the storage battery market, a battery that can be used in a wide temperature range is required. Among them, the lithium polymer secondary battery has a problem that the durability is relatively high in a high temperature environment but the durability is low in a low temperature region.
Until now, in lithium ion secondary batteries, a technology to improve the room temperature and high temperature cycle by forming a stable surface film on the negative electrode material by performing aging treatment has been developed. The technology to improve this has not been realized yet.
Therefore, the present inventors have succeeded in finding a solution by advancing earnest research and development to solve the problems of the conventional technology, and provide a lithium ion secondary battery with improved output characteristics and low temperature characteristics. The present invention has been reached.
An object of the present invention is to provide a lithium polymer secondary battery having excellent durability and output characteristics in a high temperature environment and a low temperature environment.

The present invention is constituted by the following technical matters.
(1) A lithium ion secondary battery having a polymer electrolyte, where the internal resistance value of the battery after initial charge / discharge is (A) and the internal resistance value of the battery after aging treatment is (B), B) A lithium ion secondary battery with improved output characteristics and low temperature characteristics, wherein the value of (A) is <0.7.
(2) The lithium ion secondary battery with improved output characteristics and low temperature characteristics as described in (1) above, wherein the aging treatment comprises holding the lithium ion secondary battery at 40 to 90 ° C.
(3) The lithium ion secondary battery having improved output characteristics and low-temperature characteristics as described in (1) or (2) above, wherein the aging treatment is performed in a charged state with an SOC of 40% or more.
(4) The lithium ion secondary battery having improved output characteristics and low temperature characteristics according to any one of (1) to (3), wherein the polymer electrolyte contains a polymer composed of an acrylic monomer.
(5) Acrylic monomers are acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, polyethylene glycol diacrylate, ethylene oxide modified acrylate, ethoxyethyl methacrylate , Ethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N, N-diethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, poly Propylene glycol dimethacrylate, polyalkylene glycol dimethacrylate, polyalkylene glycol dimethacrylate, trimethylolpropane alkoxylate triacrylate, pentaerythritol alkoxylate tetraacrylate, dipentaerythritol polyacrylate, dipentaerythritol hexaacrylate, pentaerythritol alkoxylate tetraacrylate A lithium ion secondary battery having improved output characteristics and low temperature characteristics according to the above (1), which is one or more selected from:

(6) In the production of a lithium ion secondary battery having a polymer electrolyte, the internal resistance value of the battery after initial charge / discharge is set to (A) by aging treatment, and the internal resistance value of the battery after aging treatment is set to (B). A method of manufacturing a lithium ion secondary battery with improved output characteristics and low temperature characteristics, wherein the value of (B) / (A) is <0.7.
(7) The method for producing a lithium ion secondary battery having improved output characteristics and low temperature characteristics according to (6), wherein the aging treatment comprises holding the lithium ion secondary battery at 40 to 90 ° C.
(8) The method for producing a lithium ion secondary battery having improved output characteristics and low temperature characteristics as described in (6) or (7) above, wherein the aging treatment is performed in a charged state with an SOC (charged state) of 40% or more .
(9) The method for producing a lithium ion secondary battery having improved output characteristics and low temperature characteristics according to any one of (6) to (8), wherein the polymer electrolyte contains a polymer composed of an acrylic monomer.
(10) Acrylic monomers are acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, polyethylene glycol diacrylate, ethylene oxide modified acrylate, ethoxyethyl methacrylate , Ethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N, N-diethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, Ripropylene glycol dimethacrylate, polyalkylene glycol dimethacrylate, polyalkylene glycol dimethacrylate, trimethylolpropane alkoxylate triacrylate, pentaerythritol alkoxylate tetraacrylate, dipentaerythritol polyacrylate, dipentaerythritol hexaacrylate, pentaerythritol alkoxylate tetra The method for producing a lithium ion secondary battery having improved output characteristics and low temperature characteristics according to the above (9), which is one or more selected from acrylates.

  The present invention can produce and provide a large capacity, high output lithium ion secondary battery by reducing the internal resistance of the lithium ion secondary battery by aging treatment. In addition, the cycle characteristics at a low temperature are good, and the drawbacks of the conventional lithium ion secondary battery can be improved.

It shows that the internal resistance of the lithium ion secondary battery is reduced by the aging process in which the SOC (charged state) is changed during the aging process. It shows that the low temperature cycle characteristics are improved by changing the SOC (charge state) during the aging process.

  The lithium secondary battery of the present invention is a lithium ion secondary battery having a polymer electrolyte, wherein the internal resistance value of the battery after initial charge / discharge is (A), and the internal resistance value of the battery after aging treatment is (B ), A lithium ion secondary battery with improved output characteristics and low temperature characteristics characterized in that the value of (B) / (A) is <0.7, and a method for producing the same, for example, In a lithium secondary battery comprising a negative electrode containing a carbon material as a negative electrode active material, a positive electrode, and a non-aqueous electrolyte, an aging treatment is performed on a battery having a polymer electrolyte between electrode bodies in which the negative electrode and the positive electrode face each other. This improves the durability under a low temperature environment.

  The lithium ion secondary battery of the present invention has a characteristic that the internal resistance value of the battery after the aging treatment is low, and further, the aging treatment is performed at 40 to 90 ° C. in a charged state of SOC of 40% or more. (Internal resistance value of battery after initial charging) / (Internal resistance value of battery after aging treatment) can be set to the above value, especially when the aging treatment is in a charged state of SOC 40% or more. It is preferred that processing be performed.

  Usually, when the aging treatment is performed at a high temperature of about 80 ° C., the battery internal resistance is increased to about 1.05 to 2.5 times. The increase in the battery internal resistance is caused by power characteristics (output characteristics), This is a major factor in battery capacity reduction. It is said that the increase in internal resistance is largely due to the increase in liquid resistance. However, in the present invention, the battery internal resistance after the aging treatment is reduced. The reason is not clear, but the electrical characteristics of the battery have been improved due to the decrease in internal resistance.

Below, an example of the manufacturing method of the lithium secondary battery of the present invention will be described, including each component and the aging process.
[Components of lithium secondary battery]
A lithium ion secondary battery targeted by the present manufacturing method includes, for example, a negative electrode including a carbon material as a negative electrode active material, a positive electrode, a nonaqueous electrolytic solution, and a polymer electrolyte as main components. However, it is not particularly limited to those components, and may be configured by combining already known components. Below, a general aspect is shown as an example.

[Negative electrode]
A negative electrode containing a carbon material as a negative electrode active material is used for a lithium secondary battery targeted by the present negative electrode manufacturing method. Carbon materials that can be used as the negative electrode active material include graphite materials such as natural graphite, spherical or fibrous artificial graphite, non-graphitizable carbon materials, and organic compound fired bodies such as phenol resins, coke, etc. Mention may be made of powders of graphitizable carbon materials. These carbon materials have respective advantages, and may be selected according to the characteristics of the lithium secondary battery to be manufactured.

  Since the graphite material has a high true density and excellent conductivity, it has an advantage that a lithium secondary battery having a large capacity (high energy density) and good power characteristics can be constituted. In addition, artificial graphite can be manufactured by heat-treating graphitizable carbon at a high temperature of 2800 ° C. or higher, for example. As graphitizable carbon, tar pitch generally obtained from petroleum or coal is used as a raw material, and examples thereof include coke, MCMB, mesophase pitch carbon fiber, and pyrolytic vapor grown carbon fiber. Moreover, organic compound baked bodies, such as a phenol resin, can also be used.

  Non-graphitizable carbon is so-called hard carbon, and is a carbon material having a structure close to an amorphous typified by glassy carbon. Generally, it is a material obtained by carbonizing a thermosetting resin. Non-graphitizable carbon has the advantages of high safety and relatively low cost. It is desirable to use as.

  The negative electrode is prepared by mixing a binder in these carbon material powders, applying a paste-like negative electrode mixture onto the surface of a current collector made of a metal foil such as copper, and then drying. Accordingly, the density of the negative electrode mixture is increased by a press or the like to form and manufacture a sheet-like material. The binder plays a role of bonding the active material particles and the conductive material particles, such as polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, carbomethoxy cellulose, fluorine-containing resin such as fluoro rubber, polypropylene, polyethylene, etc. A thermoplastic resin can be used. As a solvent for dispersing the active material and the binder, an organic solvent such as N-methyl-2-pyrrolidone or water can be used.

[Positive electrode]
Various known materials can be used for the positive electrode active material. In general, composite oxides of Li and transition metals such as Co, Mn, Ni, Mo, V, Cr, Fe, Cu, and Ti can be used, but layered rock salt structure lithium cobalt composite oxide, layered rock salt structure It is preferable to use lithium nickel composite oxide, spinel structure lithium manganese composite oxide, or the like. It is also possible to use those obtained by substituting a part of the Li site or Co, Ni, or Mn site with another transition metal element, alkali metal element, alkaline earth element, or the like.

  The positive electrode is made by mixing a conductive material and a binder with a powder of a substance that can be a positive electrode active material, and adding a solvent to form a paste-like positive electrode mixture. It can be made into a sheet-like material formed by applying and drying the material and compressing it to increase the electrode density as necessary. The conductive material is for ensuring the electrical conductivity of the positive electrode, and a material obtained by mixing one or more carbon material powders such as carbon black, acetylene black, and graphite can be used. As in the case of the negative electrode, the binder may be a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluorine rubber, or a thermoplastic resin such as polypropylene or polyethylene. An organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing these active material, conductive material, and binder.

[Non-aqueous electrolyte]
The nonaqueous electrolytic solution is obtained by dissolving a lithium salt as an electrolyte in an organic solvent. The lithium salt is dissociated by dissolving in an organic solvent, and becomes lithium ions and exists in the electrolytic solution. Examples of the lithium salt that can be used include LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _{2 and the} like. These lithium salts may be used alone, or two or more of these may be used in combination.

  As the organic solvent for dissolving the lithium salt, an aprotic organic solvent is used. For example, a mixed solvent composed of one or more of cyclic carbonate, chain carbonate, cyclic ester, cyclic ether, or chain ether can be used. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and the like. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, and examples of the cyclic ester include gamma butyrolactone and gamma valerolactone. Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the chain ether include dimethoxyethane and ethylene glycol dimethyl ether.

[Polymer electrolyte]
The method for producing the polymer electrolyte is, for example, a monomer having an unsaturated double bond such as acryloyl group, methacryloyl group, vinyl group or allyl group, or a monomer having a cationic polymerizable cyclic ether group such as epoxy, oxetane or formal. An example is a method in which the monomer is polymerized after being contained in the non-aqueous electrolyte. The time when this monomer is polymerized may be after the battery is assembled. Among these materials, the monomer having an unsaturated double bond can be polymerized by heat, ultraviolet light, electron beam or the like, but a polymerization initiator may be added in order to advance the reaction effectively.

  As an acrylic acid-based monomer having an unsaturated double bond, acrylic monomers are acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, polyethylene Glycol diacrylate, ethylene oxide modified acrylate, ethoxyethyl methacrylate, ethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N, N-diethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate , Polyethylene glycol dimethacrylate Polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, polyalkylene glycol dimethacrylate, polyalkylene glycol dimethacrylate, trimethylolpropane alkoxylate triacrylate, pentaerythritol alkoxylate tetraacrylate, dipentaerythritol polyacrylate, dipentaerythritol hexaacrylate Pentaerythritol alkoxylate tetraacrylate and the like can be used. Examples of the monomer having a cyclic ether group include a copolymer of methyl methacrylate and (3-ethyl-3-oxetanyl) methyl acrylate, tetraethylene glycol bisoxetane, and polyvinyl formal. In addition, siloxane-based, phosphazene-based polymers, and polyalkylene oxide polymers can be used.

[Manufacturing process]
The manufacturing process of the lithium secondary battery of the present invention includes a battery assembly process in which a negative electrode and a positive electrode are opposed to each other to form an electrode body, and the battery body is assembled by impregnating the electrode body with a non-aqueous electrolyte and a polymer electrolyte. It is manufactured by a known method. For example, a sheet-like positive electrode and a negative electrode are made to face each other to form an electrode body, and a separator that separates the positive electrode and the negative electrode and holds the electrolyte is interposed between the positive electrode and the negative electrode. For this separator, a thin microporous film such as polyethylene or polypropylene can be used.

  The shape of the electrode body is determined according to the shape of the battery to be manufactured. For example, a disk-shaped or card-shaped positive electrode and negative electrode can be made to face each other to form a circular or card-type battery electrode body. Also, a plurality of card-shaped positive electrodes and negative electrodes are used, and the layers are alternately stacked. Also, the electrode body of a square battery can be formed by overlapping. Furthermore, the belt-like positive electrode and negative electrode can be wound to form an electrode body of a cylindrical battery. Also, the size of the electrode body is appropriately determined according to the application.

[Aging process]
The aging treatment process is to perform aging treatment on the battery assembled in the battery assembling process, and is intended to improve the cycle characteristics of the lithium secondary battery and is assembled at a predetermined temperature for a predetermined time. This means that the battery is stored or retained, and is left for a certain period of time in a discharged state or a charged state, but is preferably aged in a charged state having a constant charge capacity. The charge capacity during aging is preferably 40 to 100% of the charge capacity during main charge. The holding temperature in the aging treatment is desirably 40 ° C. or higher and 90 ° C. or lower. This is because if the temperature is lower than 40 ° C., the effect of improving the cycle characteristics is small, and if the temperature exceeds 90 ° C., the separator may be adversely affected. Note that the higher the storage temperature, the greater the effect of the aging process.

  The storage time in the aging process is not particularly limited, but may be any time necessary for obtaining the effect of improving the cycle characteristics. The longer the storage time is, the greater the effect of the aging process is. However, even if the storage time is longer than necessary, only the time elapses and it is not efficient. Although it differs depending on the storage temperature, it may be a period of about 3 hours to 15 days.

[Measurement of internal resistance and initial charge / discharge]
In the production method of the present invention, it is preferable to perform initial charge / discharge called so-called formation before the aging treatment. The formation conditions are not particularly limited, and may be performed at a relatively low current as applied to a normal lithium secondary battery. Further, the aging process may be performed after the formation or without performing the formation until the precharge is performed until the state of charge (SOC) is reached and the state of charge is maintained.
The initial charging / discharging (formation) conditions are, for example, charging at a constant current / constant voltage to a charge end voltage of 4.1V in a 24 ° C. environment, and then discharging at a constant current of 0.5A to a discharge end voltage of 3.0V. This can be done by making one cycle one cycle. After the formation is completed, the internal resistance of the battery at 50% SOC can be measured in a 24 ° C. environment, and the measured value can be used as the battery internal resistance before the aging treatment.

[SOC (charging state)]
When the aging process is performed with the battery charged, the characteristics are greatly improved. That is, it is preferable to perform an aging process between SOC = 100% and 40% in a fully charged state in which the battery is charged with all the amount of electricity that can be reversibly charged and discharged. When the SOC is aged at 40% or less, the battery internal resistance is not sufficiently lowered, so that the battery performance improvement effect is small.

Aging treatment improves cycle characteristics at low temperatures. Further, the greater the cycle characteristic improvement effect, the smaller the internal resistance of the battery. As a measure of the effect of the aging treatment, the battery internal resistance (A) before the aging treatment may be compared with the battery internal resistance (B) after the aging treatment. This battery internal resistance ratio is determined by a value defined by the following equation.
It is desirable to perform an aging treatment so that the battery internal resistance ratio does not exceed 0.7. When the battery internal resistance ratio exceeds 0.7, the effect of improving battery characteristics is reduced.

[Battery internal resistance after aging treatment (B)] / [Charged / discharged battery internal resistance before aging treatment (A)]

[Test with 10Ah cell]
Changes in internal resistance and low-temperature cycle characteristics with different aging treatment conditions were measured. FIG. 1 shows the dependence of internal resistance on aging treatment conditions, and FIG. 2 shows the dependence of low temperature cycle characteristics on aging treatment conditions.
A 10Ah cell, which is a lithium ion secondary battery, was prepared using a polymer electrolyte containing an acrylic polymer, and the dependency of internal resistance on aging treatment conditions was measured. A battery having a state of charge (SOC) before aging treatment of 30, 50, 80, and 100% was produced, and aging treatment was performed at 45 ° C. for 10 days. FIG. 1 shows the result of measuring the internal resistance value at each SOC value and comparing it with the value before the aging treatment. In a battery with an SOC of 30%, the decrease in the internal resistance value after the aging treatment is not so large, and FIG. 1 shows that the internal resistance value is significantly decreased when the SOC is 50% or more. Further, when the reduction of the SOC and the internal resistance value was examined, it was found that when the SOC was 40% or more, the internal resistance value was reduced and the battery performance could be remarkably improved.

The influence of the aging treatment on the cycle characteristics at low temperature was examined using a 10 Ah cell which is a lithium ion secondary battery. Before the aging treatment, the cycle characteristics of a battery in which the state of charge (SOC) before aging treatment is 30, 50, 80, 100% and aged at 45 ° C. for 10 days are measured under a temperature condition of 0 ° C. FIG. 2 shows the result of comparison with this battery.
The evaluation condition for the 0 ° C. cycle characteristics is that the charge current is 0.5 C in a 0 ° C. environment, the battery is charged at a constant current and constant voltage with a charge voltage of 4.10 V until the current value becomes C / 20, and then the discharge current is 1.0 C. The charge and discharge were repeated 50 cycles under the condition of a final voltage of 3.00 V, and the capacity retention rate was calculated from the discharge capacity (Ah) at the first cycle and the discharge capacity (Ah) at the 50th cycle by the following formula (2).

Capacity retention rate (%) = (discharge capacity at 50th cycle) × 100 / (discharge capacity at the first cycle) ................................. (2)

It was found from FIG. 2 that the battery of the present invention that was aged at SOC of 50, 80, and 100% had significantly improved low-temperature cycle characteristics. Among samples with different SOCs, the larger the SOC, the better the characteristics. In a battery that was aged at 30% SOC, the capacity retention rate decreased rapidly as the number of cycles increased, and no aging effect was observed.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to the Example shown below, unless the meaning is impaired. The raw materials and members used in both the examples and comparative examples were pre-dried. In the following examples, “part” means “part by mass”.

<Adjustment of electrode slurry>
A positive slurry and a negative slurry were prepared by kneading and dispersing with a planetary mixer according to the composition shown below.

(Slurry composition for positive electrode)
LiNi _0.80 Co _0.15 Al _0.05 O ₂ (active material): 41.6 parts LiCoO ₂ (active material): 18.2 parts Acetylene black (conductive material): 2.6 parts Polyvinylidene fluoride (binder) ): 2.6 parts N-methylpyrrolidone (solvent): 35.0 parts

(Slurry composition for negative electrode)
Amorphous carbon surface-coated graphite (active material): 38.7 parts Mesocarbon microbeads (active material): 7.8 parts Styrene butadiene rubber (binder): 0.9 parts Carbomethoxycellulose: 0.4 parts Ion exchange Water: 52.2 parts

<Adjustment of electrolyte>
The raw materials used for the preparation of the electrolytic solution are as follows. And it melt | dissolved according to the composition shown below, and prepared the uniform electrolyte solution.

(Electrolytic solution composition)
Propylene carbonate: 35.4 parts Ethylene carbonate: 38.8 parts LiPF ₆ : 18.5 parts Dipentaerythritol polyacrylate polyundecylate: 7.1 parts (ADP-51 manufactured by Shin-Nakamura Chemical Co., Ltd.)
Cross-linking initiator (Trigonox 23C-70 manufactured by Kayaku Akzo Co., Ltd.): 0.2 part

<Manufacture of secondary batteries>
First, a positive electrode coating material was applied on one side onto a 20 μm thick aluminum foil with a doctor blade and dried to obtain a sheet on which a positive electrode active material layer having voids was formed. Thereafter, a calendar process was performed to obtain a final layer thickness of about 60 μm. Similarly to the above, a negative electrode coating material was applied on one side onto a 10 μm thick copper foil and dried to obtain a sheet on which a negative electrode active material layer having voids was formed. Next, calendering was performed to obtain a final layer thickness of about 54 μm.
Thereafter, the coating film was re-dried at 120 ° C. in a dry environment, and then punched into a predetermined shape.

Next, the electrolytic solution was applied and impregnated on the active material layer side of each of the above sheets with an electrolytic solution application pin. At that time, by adjusting the height of the electrolyte solution application pin, an amount more than the amount that fills the gap was applied, and the electrolyte solution was present on the surface.
Then, after impregnating the electrolyte in the voids of a polyethylene microporous film having a thickness of 16 μm, the positive electrode sheet and the negative electrode sheet are laminated with the microporous film interposed therebetween, and then the whole is heated to 115 ° C. Thus, the electrolyte solution was gelled to form a gel electrolyte continuous with the voids in the active material layer and the electrolyte layer, and a battery element A composed of a positive electrode, an electrolyte layer, and a negative electrode was obtained.

Next, 34 battery elements A were stacked in parallel to obtain battery element B.
After a terminal was attached to the battery element B, it was sealed in a vacuum pack, and a lithium secondary battery having a 1C capacity of 10.0 Ah was produced.

  The prepared 10.0 Ah lithium secondary battery was subjected to initial charge / discharge (formation). Then, after adjusting to SOC 100%, it aged for 10 days in a 45 degreeC thermostat. After the aging, the SOC was adjusted to 50% and the internal resistance was measured. Then, the cycle characteristics were evaluated between 3.0 and 4.10 V at a charging current of 5 A and a discharging current of 10 A in an environment of 0 ° C.

  A 10.0 Ah lithium secondary battery produced in the same manner as in Example 1 was initially charged and discharged (formation), adjusted to 80% SOC, and aged for 10 days in a 45 ° C. thermostat. Thereafter, after adjusting the SOC to 50% and measuring the internal resistance, the cycle characteristics were evaluated between 3.0 and 4.10 V at a charging current of 5 A and a discharging current of 10 A in an environment of 0 ° C.

  A 10.0 Ah lithium secondary battery produced in the same manner as in Example 1 was initially charged and discharged (formation), adjusted to 50% SOC, and aged for 10 days in a 45 ° C. thermostat. Thereafter, after adjusting the SOC to 50% and measuring the internal resistance, the cycle characteristics were evaluated between 3.0 and 4.10 V at a charging current of 5 A and a discharging current of 10 A in an environment of 0 ° C.

Comparative Example 1

  A 10.0 Ah lithium secondary battery produced in the same manner as in Example 1 was initially charged and discharged (formation), adjusted to SOC 30%, and aged in a 45 ° C. thermostat for 10 days. Thereafter, after adjusting the SOC to 50% and measuring the internal resistance, the cycle characteristics were evaluated between 3.0 and 4.10 V at a charging current of 5 A and a discharging current of 10 A in an environment of 0 ° C.

In Examples 1 to 3 and Comparative Example 1, capacitance and internal resistance were measured before aging.
Moreover, initial charge / discharge (formation), capacity confirmation, internal resistance measurement, and cycle characteristics at low temperatures were evaluated by the methods described below.

<Initial charge / discharge>
Initial charge / discharge (formation) is performed at a constant current of 5 A to a discharge end voltage of 3.0 V under a constant current and constant voltage charge of 2 A and a charge voltage of 4.10 V for 8 hours in a 24 ° C. environment. It was.

<Confirmation of capacity>
In a 24 ° C. environment, constant current and constant voltage charging with a charging current of 10 A and a charging voltage of 4.10 V was performed, and the charging was terminated when the current value reached 500 mA. After the completion of charging, discharging was performed under the conditions of a discharging current of 10 A and a final voltage of 3.00 V.
The above charge / discharge was repeated twice, and the second discharge capacity (Ah) was defined as 1C discharge capacity.
In addition, the second charge capacity was set to 100% SOC.

<Measurement of internal resistance>
After adjusting to SOC 50% in a 24 ° C. environment, discharging was performed at a discharge current of 20 A for 10 seconds. The internal resistance value was calculated from the voltage (V) before discharge and the voltage (V) at 10 seconds after discharge by the following mathematical formula (3).

Internal resistance (mΩ) = ((Voltage before discharge) − (Voltage at discharge 10 seconds)) × 1000 / Discharge current value (3)

<Evaluation of cycle characteristics at low temperature>
After charging until a current value of 500 mA is obtained at a constant current and constant voltage of 5 A and a charging voltage of 4.10 V in an environment of 0 ° C., charging and discharging are repeated 100 cycles under the conditions of a discharging current of 10 A and a final voltage of 3.00 V. From the discharge capacity (Ah) at the cycle and the discharge capacity (Ah) at the 100th cycle, the capacity retention rate was calculated by the following mathematical formula (4).

Capacity maintenance ratio (%) = (discharge capacity at the 100th cycle) × 100 / (discharge capacity at the first cycle)... (4)

  As a result of the test, a result showing the same tendency as the battery of SOC = 100% shown in FIGS. 1 and 2 was obtained, and it was found that the cycle characteristics under a low temperature environment were excellent. By performing the aging treatment, the internal resistance of the battery is lowered, and the capacity retention rate in the charge / discharge cycle test is improved. It has been confirmed that the method for producing a lithium secondary battery of the present invention is a production method capable of producing a lithium secondary battery having a large discharge capacity and excellent power characteristics while maintaining high cycle characteristics.

  The lithium ion secondary battery of the present invention can provide a large-capacity, high-power lithium ion secondary battery by aging treatment, and has good cycle characteristics at low temperatures, and is a conventional lithium ion secondary battery. This is a significant improvement in the disadvantages. Thus, the lithium ion secondary battery with improved performance in a low temperature environment is not only useful as a power source for electronic devices, but also devices used in special low temperature environments, or power sources for electric vehicles, Since it can be widely used for large-capacity applications such as power storage, it is expected that demand will increase in the future and contribute to the progress of a wide range of industries.

Claims (10)

  A lithium ion secondary battery having a polymer electrolyte, wherein the internal resistance value of the battery after initial charge / discharge is (A) and the internal resistance value of the battery after aging treatment is (B), (B) A lithium ion secondary battery with improved output characteristics and low temperature characteristics, wherein the value of / (A) is <0.7.   The lithium ion secondary battery with improved output characteristics and low temperature characteristics according to claim 1, wherein the aging treatment comprises holding the lithium ion secondary battery at 40 to 90 ° C.   The lithium ion secondary battery with improved output characteristics and low temperature characteristics according to claim 1 or 2, wherein the aging treatment is performed in a charged state in which the SOC (charged state) is 40% or more.   The lithium ion secondary battery with improved output characteristics and low temperature characteristics according to any one of claims 1 to 3, wherein the polymer electrolyte contains a polymer composed of an acrylic monomer.   Acrylic monomers are acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, polyethylene glycol diacrylate, ethylene oxide modified acrylate, ethoxyethyl methacrylate, ethoxyethyl Methacrylate, polyethylene glycol monomethacrylate, N, N-diethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, polypro Lenglycol dimethacrylate, polyalkylene glycol dimethacrylate, polyalkylene glycol dimethacrylate, trimethylolpropane alkoxylate triacrylate, pentaerythritol alkoxylate tetraacrylate, dipentaerythritol polyacrylate, dipentaerythritol hexaacrylate, pentaerythritol alkoxylate tetraacrylate The lithium ion secondary battery having improved output characteristics and low-temperature characteristics according to claim 4, which is one or more selected from the group consisting of:   In the production of a lithium ion secondary battery having a polymer electrolyte, when the internal resistance value of the battery after initial charge / discharge is (A) and the internal resistance value of the battery after the aging process is (B) by aging treatment A method for producing a lithium ion secondary battery with improved output characteristics and low temperature characteristics, wherein the value of (B) / (A) is <0.7.   The method for producing a lithium ion secondary battery with improved output characteristics and low temperature characteristics according to claim 6, wherein the aging treatment comprises holding the lithium ion secondary battery at 40 to 90 ° C.   The method for producing a lithium ion secondary battery with improved output characteristics and low temperature characteristics according to claim 6 or 7, wherein the aging treatment is performed in a charged state in which the SOC (charged state) is 40% or more.   The method for producing a lithium ion secondary battery with improved output characteristics and low temperature characteristics according to any one of claims 6 to 8, wherein the polymer electrolyte contains a polymer comprising an acrylic monomer. Acrylic monomers are acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, polyethylene glycol diacrylate, ethylene oxide modified acrylate, ethoxyethyl methacrylate, ethoxyethyl Methacrylate, polyethylene glycol monomethacrylate, N, N-diethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, polypro Lenglycol dimethacrylate, polyalkylene glycol dimethacrylate, polyalkylene glycol dimethacrylate, trimethylolpropane alkoxylate triacrylate, pentaerythritol alkoxylate tetraacrylate, dipentaerythritol polyacrylate, dipentaerythritol hexaacrylate, pentaerythritol alkoxylate tetraacrylate The method for producing a lithium ion secondary battery having improved output characteristics and low-temperature characteristics according to claim 9, which is one or more selected from the group consisting of: