JP2008234851A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery for restraining decomposition of a nonaqueous electrolyte and degradation of a positive electrode active material and having high capacity, superior cycle performance, and high-temperature preservation characteristics. <P>SOLUTION: In the nonaqueous electrolyte secondary battery having a group of electrode plates 1 winding a positive electrode plate and negative electrode plate via a separator and a nonaqueous electrolyte, and a charge and discharge control device connected with a main body of the nonaqueous electrolyte secondary battery, the positive electrode plate includes a binding agent mainly made of PTFE, a compound layer with high oxidation resistance having fine holes is arranged on at least one surface of the separator facing to the positive electrode plate, and charge terminating voltage of the charge and discharge control device is set up to be 4.3 V or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery using lithium ions, and more particularly to a non-aqueous electrolyte secondary battery that operates well even when the end-of-charge voltage is set to 4.3 V or higher.

In recent years, non-aqueous electrolyte secondary batteries used as a main power source for mobile communication devices and portable electronic devices have a high electromotive force and a high energy density. Examples of the positive electrode active material used here include lithium cobaltate (LiCoO ₂ ) and lithium nickelate (LiNiO ₂ ). These positive electrode active materials have a voltage of 4 V or more with respect to lithium (Li).

  In these lithium ion secondary batteries using lithium ions, a higher capacity battery can be realized as the charge end voltage of the battery is set higher. Therefore, higher charge end voltage has been studied.

  Among them, since a lithium spinel oxide containing manganese (Mn) is stable even at a high potential, a configuration in which a charge end voltage is set in a range of 4.0 V to 4.5 V has been proposed (for example, Patent Document 1). reference).

It has also been proposed that by mixing two specific positive electrode active materials, good cycle characteristics can be obtained even when operated at a charge end voltage of 4.3 V or more (see, for example, Patent Document 2). .
JP 2001-307781 A JP 2006-164934 A

  However, when the end-of-charge voltage is set to 4.3 V or higher, a battery with a higher capacity can be realized. However, by increasing the end-of-charge voltage, structural degradation of the positive electrode active material, decomposition of the electrolyte on the surface of the positive electrode active material, etc. There is a problem that the capacity of the battery is greatly reduced by a high-temperature storage test or a charge / discharge cycle test.

  In particular, the structural deterioration of the positive electrode active material is accelerated rapidly in the region where the end-of-charge voltage is 4.3 V or more, and as disclosed in Patent Documents 1 and 2, polyvinylidene is used as a binder for the positive electrode plate. When difluoride (PVDF) is used, it cannot be said that the structure deterioration of the positive electrode active material is suppressed.

  The present invention solves this problem, and even when the end-of-charge voltage in a normal operation state is set to 4.3 V or higher, the battery function such as high-temperature storage characteristics and charge / discharge cycle characteristics is high enough to operate normally. An object is to provide a non-aqueous electrolyte secondary battery.

In order to achieve the above object, the present invention provides a non-aqueous electrolyte secondary battery comprising an electrode plate group obtained by winding a positive electrode plate and a negative electrode plate via a separator, and a non-aqueous electrolyte, and the non-aqueous electrolyte secondary battery. A non-aqueous electrolyte secondary battery including a charge / discharge control device connected to a main body of the secondary battery, wherein the positive electrode plate includes a binder mainly composed of polytetrafluoroethylene (PTFE), and the positive electrode plate includes A layer of a compound having high oxidation resistance having fine holes is provided on at least one surface of the facing separator, and a charge end voltage of the charge / discharge control device is set to 4.3 V or more.

  According to this configuration, even when the end-of-charge voltage is set to 4.3 V or more, the oxidation reaction of the binder of the separator and the positive electrode plate hardly occurs, the structure of the positive electrode active material is deteriorated and the surface of the positive electrode active material is electrolyzed. Since the decomposition of the liquid is greatly suppressed, it is possible to solve the problem that the capacity is drastically reduced in the high temperature storage test and the charge / discharge cycle test. An electrolyte secondary battery is obtained.

  When the end-of-charge voltage is set to 4.3 V or more, the structure deterioration of the positive electrode active material and the decomposition of the electrolyte on the surface of the positive electrode active material are greatly accelerated. As a result, the high temperature storage characteristics and charge / discharge cycle characteristics are greatly increased. A downward trend is observed. Furthermore, as a result of examining these batteries in detail, in the battery produced using a separator mainly composed of polyethylene (PE), the PE on the separator surface in contact with the positive electrode plate was greatly oxidized, and the positive electrode plate It was revealed that the PVDF as the binder was greatly oxidized in the battery manufactured using PVDF as the main binder. It is considered that these were subjected to an oxidation reaction when a separator mainly composed of PE and a binder mainly composed of PVDF were in direct contact with a positive electrode active material charged at a high voltage.

  From these results, the structural deterioration of the positive electrode active material and the decomposition of the electrolyte solution on the surface of the positive electrode active material when the end-of-charge voltage is set to 4.3 V or higher are the oxidation reaction of the separator mainly composed of PE, PVDF Oxidation reaction of the binder mainly composed of is greatly involved, and by suppressing these oxidation reactions, there is a possibility that structural degradation of the positive electrode active material and decomposition of the electrolyte solution on the surface of the positive electrode active material can be suppressed. It was suggested.

  According to the present invention, the surface of the separator that is in contact with the positive electrode plate is formed of a highly oxidation-resistant compound having fine pores, and the binder of the positive electrode plate is mainly composed of PTFE. Significantly suppresses structural deterioration of the positive electrode active material and decomposition of the electrolyte solution on the surface of the positive electrode active material when the voltage is set to 4.3 V or higher, and has high capacity and excellent high-temperature storage characteristics and charge / discharge cycle characteristics. A water electrolyte secondary battery can be provided.

  In the present invention, a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte and an electrode plate group formed by winding a positive electrode plate and a negative electrode plate through a separator, and connected to the main body of the non-aqueous electrolyte secondary battery A non-aqueous electrolyte secondary battery including a charge / discharge control device, wherein the positive electrode plate includes a binder mainly composed of PTFE, and at least one surface of the separator facing the positive electrode plate has micropores. A layer of a compound having high oxidation resistance and having a charge endurance voltage of 4.3 V or higher was set.

  Thus, by using PTFE as a binder for the positive electrode plate, and providing a layer of a compound having high oxidation resistance having fine holes on at least one surface of the separator facing the positive electrode plate, Even when the end-of-charge voltage is set to 4.3 V or more, it becomes possible to suppress the oxidation reaction of the positive electrode binder and the oxidation reaction of PE when a separator mainly composed of PE is used. By suppressing the reaction, the structure deterioration of the positive electrode active material and the decomposition of the electrolyte solution on the surface of the positive electrode active material can be suppressed. As a result, a non-aqueous electrolyte secondary battery having a high capacity and excellent in high-temperature storage characteristics and charge / discharge cycle characteristics can be provided.

The highly oxidation-resistant compound having micropores provided on the surface of the separator facing the positive electrode plate may include at least one material selected from the group consisting of polypropylene, polyaramid, polyamideimide, and polyimide. More preferred.
According to this, an effect that enables formation of a layer having both oxidation resistance and flexibility can be obtained.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  In addition, the figure shown here is an example of the nonaqueous electrolyte secondary battery of this invention, Comprising: If it has the structure represented to the claim of this invention, the same effect can be acquired.

(Production of battery)
FIG. 1 is a partially cutaway perspective view showing an embodiment of the nonaqueous electrolyte secondary battery of the present embodiment.

  As shown in FIG. 1, a strip-shaped positive electrode plate and a negative electrode plate were wound in a spiral shape a plurality of times through a separator to constitute an electrode plate group 1. A positive electrode lead 2 made of aluminum and a negative electrode lead 3 made of nickel were connected to the positive electrode plate and the negative electrode plate, respectively. It was housed in a battery case 4 made of aluminum. The other end of the positive electrode lead 2 was spot welded to the aluminum sealing plate 5, and the other end of the negative electrode lead 3 was spot welded to the lower part of the nickel negative electrode terminal 6 at the center of the sealing plate 5. The periphery of the opening of the battery case 4 and the sealing plate 5 were laser welded, and a predetermined amount of non-aqueous electrolyte was injected from the inlet 7. Finally, the injection port 7 was laser welded using an aluminum plug to complete a nonaqueous electrolyte secondary battery.

(1) Production of positive electrode plate (1-1) Production of positive electrode plate using PVDF as binder LiCo _0.94 Mg _0.05 Al _0.01 O ₂ was used as a positive electrode active material. An N-methylpyrrolidinone (NMP) solution was prepared so that 3 parts by weight of acetylene black as a conductive agent and 5 parts by weight of PVDF as a binder were added to 100 parts by weight of the positive electrode active material, and the mixture was stirred and mixed to obtain a paste-like positive electrode A mixture was obtained. Next, an aluminum foil having a thickness of 20 μm was used as a positive electrode current collector, the paste-like positive electrode mixture was applied to both surfaces thereof, dried and rolled with a rolling roller, and cut into a predetermined size to obtain a positive electrode plate.

(1-2) Preparation of positive electrode plate using PTFE as binder LiCo _0.94 Mg _0.05 Al _0.01 O ₂ was used as a positive electrode active material. 100 parts by weight of the positive electrode active material was mixed with 3 parts by weight of acetylene black as a conductive agent and 5 parts by weight of PTFE as a binder, and the mixture was made turbid in an aqueous solution of carboxymethyl cellulose to obtain a paste-like positive electrode mixture. Next, an aluminum foil having a thickness of 20 μm was used as a positive electrode current collector, the paste-like positive electrode mixture was applied to both surfaces thereof, dried and rolled with a rolling roller, and cut into a predetermined size to obtain a positive electrode plate.

  The conductive agent for the positive electrode plate may be any electron conductive material that is substantially chemically stable in the constructed nonaqueous electrolyte secondary battery. For example, graphites, carbon blacks, conductive fibers, metal powders, conductive whiskers, conductive metal oxides, organic conductive materials such as polyphenylene derivatives, and the like can be used alone or as a mixture. Also good.

(2) Production of negative electrode plate After pulverized and classified so as to have an average particle size of about 20 μm and 3 parts by weight of styrene / butadiene rubber as a binder, carboxymethyl cellulose is 1% of graphite. A carboxymethyl cellulose aqueous solution was added so that the mixture was stirred and mixed to obtain a paste-like negative electrode mixture. A copper foil having a thickness of 15 μm was used as a negative electrode current collector, a paste-like negative electrode mixture was applied to both surfaces thereof, dried and then rolled using a rolling roller, and cut into a predetermined size to obtain a negative electrode plate.

  Examples of the negative electrode active material include pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, and the like, which are mainly carbonaceous materials that can be doped and dedoped with lithium. , Glassy carbons, organic polymer compound fired bodies (phenol resins, furan resins, etc., fired at a suitable temperature and carbonized), carbon fibers, activated carbon, etc., and these may be used alone or in combination of two or more. It can be used by mixing. The average particle size of the negative electrode active material is not particularly limited, but is preferably 1 to 30 μm.

  The conductive agent for the negative electrode is not particularly limited as long as it is an electron conductive material. For example, artificial graphite, acetylene black, carbon fiber and the like are preferable.

  Examples of the binder for the negative electrode include styrene butadiene rubber, polyvinylidene fluoride, an ethylene-acrylic acid copolymer, or a (Na +) ion crosslinked product of the above material, an ethylene-methacrylic acid copolymer, or a (Na + of the above material). An ionic cross-linked product, an ethylene-methyl acrylate copolymer, or a (Na +) ionic cross-linked product of the material, an ethylene-methyl methacrylate copolymer, or a (Na +) ionic cross-linked product of the material are preferred.

(3) Production of separator (3-1) Production of separator provided with a layer made of polypropylene on the surface in contact with the positive electrode plate Using a polyethylene microporous membrane as a base material, a polypropylene microporous membrane is multilayered on the surface in contact with the positive electrode plate Thus, a separator in which a layer made of polypropylene was provided on the surface in contact with the positive electrode plate was produced.

(3-2) Production of separator having a layer made of polyaramid on the surface in contact with the positive electrode plate 5 parts by weight of anhydrous calcium chloride was added to 100 parts by weight of NMP and completely dissolved. After adding 3 parts by weight of paraphenylenediamine (PPD) to this solution, 5 parts by weight of terephthalic acid dichloride (TPC) was added dropwise little by little to synthesize polyparaphenylene terephthalamide (PPTA) by a polymerization reaction. The obtained polymerization solution was further diluted with an NMP solution to which calcium chloride was added. This PPTA solution was thinly coated with a bar coater on the surface of the base material made of a polyethylene microporous film, which was in contact with the positive electrode plate, and heated and dried at 60 ° C. to form an aramid resin layer made of PPTA to obtain a composite film. The composite membrane was sufficiently washed with pure water to remove calcium chloride, thereby making the aramid resin layer porous, and a separator having a layer made of polyaramid on the surface in contact with the positive electrode plate was produced.

(4) Production of non-aqueous electrolyte A solution prepared by dissolving 1.0 mol / l LiPF ₆ in a solvent prepared by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 30:70 at 20 ° C. was used.

(5) Battery assembly <Example 1 and Comparative Example 1>
A separator provided with a layer made of polypropylene prepared in (3-1) above is spirally wound on a surface in contact with a positive electrode plate and a negative electrode plate using PTFE as a binder, and the positive electrode plate. After injecting the non-aqueous electrolyte adjusted in 4), a charge / discharge control device was connected to the main body of the prismatic lithium ion secondary battery assembled by sealing and sealing.

(Battery A1-1 of Example 1)
Using the prismatic lithium ion secondary battery produced as described above, constant voltage charging was performed for 2 hours at a maximum current of 600 mA and a charge end voltage of 4.3 V. This square lithium ion secondary battery was designated as battery A1-1 of Example 1 of the present invention.

(Battery A1-2 of Example 1)
A square lithium ion secondary battery produced in the same manner as the battery A1-1 of Example 1 except that the end-of-charge voltage was 4.4 V was designated as the battery A1-2 of Example 1 of the present invention.

(Battery A1-3 of Example 1)
A square lithium ion secondary battery produced in the same manner as the battery A1-1 of Example 1 except that the end-of-charge voltage was set to 4.5 V was designated as battery A1-3 of Example 1 of the present invention.

(Battery B1-1 of Comparative Example 1)
A square lithium ion secondary battery produced in the same manner as the battery A1-1 of Example 1 except that the end-of-charge voltage was 4.1 V was designated as a battery B1-1 of Comparative Example 1.

(Battery B1-2 of Comparative Example 1)
A square lithium ion secondary battery produced in the same manner as the battery A1-1 of Example 1 except that the end-of-charge voltage was 4.2 V was designated as battery B1-2 of Comparative Example 1.

<Example 2 and Comparative Example 2>
A prismatic lithium ion secondary battery connected to a charge / discharge control device in the same manner as in Example 1 and Comparative Example 1 except that the separator provided with the layer made of polyaramid prepared in (3-2) was used as the separator. Produced.

(Battery A2-1 of Example 2)
Using the prismatic lithium ion secondary battery produced as described above, constant voltage charging was performed for 2 hours at a maximum current of 600 mA and a charge end voltage of 4.3 V. This square lithium ion secondary battery was designated as Battery A2-1 of Example 2 of the present invention.

(Battery A2-2 of Example 2)
A square lithium ion secondary battery produced in the same manner as the battery A2-1 of Example 2 except that the end-of-charge voltage was 4.4 V was designated as a battery A2-2 of Example 2 of the present invention.

(Battery A2-3 of Example 2)
A square lithium ion secondary battery produced in the same manner as the battery A2-1 of Example 2 except that the end-of-charge voltage was 4.5 V was designated as a battery A2-3 of Example 2 of the present invention.

(Battery B2-1 of Comparative Example 2)
A square lithium ion secondary battery produced in the same manner as the battery A2-1 of Example 2 except that the end-of-charge voltage was 4.1 V was designated as a battery B2-1 of Comparative Example 2.

(Battery B2-2 of Comparative Example 2)
A square lithium ion secondary battery produced in the same manner as the battery A2-1 of Example 2 except that the end-of-charge voltage was 4.2 V was designated as a battery B2-2 of Comparative Example 2.

<Comparative Example 3>
A charge / discharge control device as in Example 1 and Comparative Example 1 except that PVDF was used as the binder and a polyethylene microporous membrane without fine oxidation-resistant compound layers having fine pores was used as the separator. A square-shaped lithium ion secondary battery connected with was prepared.

(Battery B3-1 of Comparative Example 3)
Using the prismatic lithium ion secondary battery produced as described above, constant voltage charging was performed for 2 hours at a maximum current of 600 mA and a charge end voltage of 4.1 V. This square lithium ion secondary battery was designated as Battery B3-1 of Comparative Example 3.

(Battery B3-2 of Comparative Example 3)
A square lithium ion secondary battery produced in the same manner as the battery B3-1 of Comparative Example 3 except that the end-of-charge voltage was 4.2 V was designated as Battery B3-2 of Comparative Example 3.

(Battery B3-3 of Comparative Example 3)
A square lithium ion secondary battery produced in the same manner as the battery B3-1 of Comparative Example 3 except that the end-of-charge voltage was 4.3 V was designated as Battery B3-3 of Comparative Example 3.

(Battery B3-4 of Comparative Example 3)
A square lithium ion secondary battery produced in the same manner as the battery B3-1 of Comparative Example 3 except that the end-of-charge voltage was 4.4V was designated as Battery B3-4 of Comparative Example 3.

(Battery B3-5 of Comparative Example 3)
A square lithium ion secondary battery produced in the same manner as the battery B3-1 of Comparative Example 3 except that the end-of-charge voltage was 4.5 V was designated as Battery B3-5 of Comparative Example 3.

<Comparative Example 4>
A square lithium ion secondary battery connected to a charge / discharge control device was produced in the same manner as in Example 1 and Comparative Example 1 except that PVDF was used as the binder.

(Battery B4-1 of Comparative Example 4)
Using the prismatic lithium ion secondary battery produced as described above, constant voltage charging was performed for 2 hours at a maximum current of 600 mA and a charge end voltage of 4.1 V. This square lithium ion secondary battery was designated as Battery B4-1 of Comparative Example 4.

(Battery B4-2 of Comparative Example 4)
A square lithium ion secondary battery produced in the same manner as the battery B4-1 of Comparative Example 4 except that the end-of-charge voltage was 4.2 V was designated as Battery B4-2 of Comparative Example 4.

(Battery B4-3 of Comparative Example 4)
A square lithium ion secondary battery produced in the same manner as the battery B4-1 of Comparative Example 4 except that the end-of-charge voltage was 4.3 V was designated as Battery B4-3 of Comparative Example 4.

(Battery B4-4 of Comparative Example 4)
A square lithium ion secondary battery produced in the same manner as the battery B4-1 of Comparative Example 4 except that the end-of-charge voltage was 4.4V was designated as Battery B4-4 of Comparative Example 4.

(Battery B4-5 of Comparative Example 4)
A square lithium ion secondary battery produced in the same manner as the battery B4-1 of Comparative Example 4 except that the end-of-charge voltage was set to 4.5 V was designated as Battery B4-5 of Comparative Example 4.

<Comparative Example 5>
A corner to which a charge / discharge control device is connected in the same manner as in Example 1 and Comparative Example 1 except that PVDF is used as a binder and a separator provided with a layer made of polyaramid prepared in (3-2) is used as a separator. Type lithium ion secondary battery was produced.

(Battery B5-1 of Comparative Example 5)
Using the prismatic lithium ion secondary battery produced as described above, constant voltage charging was performed for 2 hours at a maximum current of 600 mA and a charge end voltage of 4.1 V. This square lithium ion secondary battery was designated as battery B5-1 of Comparative Example 5.

(Battery B5-2 of Comparative Example 5)
A square lithium ion secondary battery produced in the same manner as the battery B5-1 of Comparative Example 5 except that the end-of-charge voltage was 4.2 V was designated as Battery B5-2 of Comparative Example 5.

(Battery B5-3 of Comparative Example 5)
A square lithium ion secondary battery produced in the same manner as the battery B5-1 of Comparative Example 5 except that the end-of-charge voltage was 4.3 V was designated as Battery B5-3 of Comparative Example 5.

(Battery B5-4 of Comparative Example 5)
A square lithium ion secondary battery produced in the same manner as the battery B5-1 of Comparative Example 5 except that the end-of-charge voltage was 4.4 V was designated as Battery B5-4 of Comparative Example 5.

(Battery B5-5 of Comparative Example 5)
A square lithium ion secondary battery produced in the same manner as the battery B5-1 of Comparative Example 5 except that the end-of-charge voltage was set to 4.5 V was designated as Battery B5-5 of Comparative Example 5.

<Comparative Example 6>
As a separator, a square lithium ion connected to a charge / discharge control device was used in the same manner as in Example 1 and Comparative Example 1 except that a polyethylene microporous membrane having fine pores and not having a layer of high oxidation resistance was used. A secondary battery was produced.

(Battery B6-1 of Comparative Example 6)
Using the prismatic lithium ion secondary battery produced as described above, constant voltage charging was performed for 2 hours at a maximum current of 600 mA and a charge end voltage of 4.1 V. This square lithium ion secondary battery was designated as Battery B6-1 of Comparative Example 6.

(Battery B6-2 of Comparative Example 6)
A square lithium ion secondary battery produced in the same manner as the battery B6-1 of Comparative Example 6 except that the end-of-charge voltage was 4.2 V was designated as Battery B6-2 of Comparative Example 6.

(Battery B6-3 of Comparative Example 6)
A square lithium ion secondary battery produced in the same manner as the battery B6-1 of Comparative Example 6 except that the end-of-charge voltage was 4.3 V was designated as Battery B6-3 of Comparative Example 6.

(Battery B6-4 of Comparative Example 6)
A square lithium ion secondary battery produced in the same manner as the battery B6-1 of Comparative Example 6 except that the end-of-charge voltage was 4.4 V was designated as Battery B6-4 of Comparative Example 6.

(Battery B6-5 of Comparative Example 6)
A square lithium ion secondary battery produced in the same manner as the battery B6-1 of Comparative Example 6 except that the end-of-charge voltage was 4.5 V was designated as Battery B6-5 of Comparative Example 6.

<Evaluation of discharge capacity>
Using the prismatic lithium ion secondary batteries of Example 1, Example 2, and Comparative Examples 1 to 6, the discharge capacity was measured at an environmental temperature of 20 ° C. The discharge conditions were a constant current with a current value of 200 mA and a discharge end voltage of 3.0 V.

<Evaluation of cycle life characteristics>
Using the prismatic lithium ion secondary batteries of Example 1, Example 2, and Comparative Examples 1 to 4, the charge / discharge cycle was performed 500 times at an environmental temperature of 20 ° C. The charging conditions were a maximum current of 600 mA, a charging end voltage was constant voltage charging for 2 hours as the charging end voltage of each battery produced in Example 1, Example 2 and Comparative Examples 1 to 4. The discharge conditions were a constant current with a current value of 600 mA and a discharge end voltage of 3.0 V, the discharge capacity after 500 cycles was measured, and the ratio was evaluated with respect to the initial capacity.

<Evaluation of high-temperature storage characteristics>
Using the prismatic lithium ion secondary batteries of Example 1, Example 2, and Comparative Examples 1 to 4, a high temperature storage test at 85 ° C. for 24 hours was performed. Charging conditions were an environmental temperature of 20 ° C., a maximum current of 600 mA, a charge end voltage of constant charge as a charge end voltage of each battery produced in Example 1, Example 2 and Comparative Examples 1 to 4 for 2 hours. . The discharge conditions were an environmental temperature of 20 ° C., a constant current of 600 mA and a final discharge voltage of 3.0 V, and the discharge capacity of each battery was measured. In each battery, the ratio of the discharge capacity after high temperature storage to the discharge capacity before high temperature storage was evaluated.

  The evaluation results of discharge capacity, cycle life characteristics, and high temperature storage characteristics are shown in Table 1.

  As can be seen from (Table 1), the evaluation results of the discharge capacity were as follows: Comparative Example 1 and Example 1, Comparative Example 2 and Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6 It was confirmed that the discharge capacity of the ion secondary battery increased as the end-of-charge voltage increased, and that a higher capacity battery could be realized by increasing the end-of-charge voltage.

  The capacity retention rate after 500 cycles was determined by comparing the square lithium ion 2 of Comparative Examples 3 to 6 using at least one of a positive electrode plate using PVDF as a binder and a separator of polyethylene microporous membrane. In the secondary battery, when the end-of-charge voltage was set to 4.3 V or more, an extreme decrease in capacity retention rate was observed.

On the other hand, produced by combining a positive electrode plate using PTFE as a binder and a separator provided with a layer made of polypropylene on the surface facing the positive electrode plate, or a separator provided with a layer made of polyaramid on the surface facing the positive electrode plate The battery A1-1 to battery A1-3 of Example 1 and the battery A2-1 to battery A2-3 of Example 2 in which the end-of-charge voltage was 4.3 V to 4.5 V were:
It was found that the capacity retention rate after 500 cycles was good as well as the end-of-charge voltage of 4.2 V or less.

  Battery B3-3 to Battery B3-5 of Comparative Example 3, Battery B4-3 to Battery B4-5 of Comparative Example 4, and Battery B5-3 of Comparative Example 5 were greatly reduced in capacity retention after 500 cycles. B5-5, battery B6-3 of Comparative Example 6 and battery B6-5 were disassembled and analyzed. As a result, when the X-ray diffraction analysis of the positive electrode plate was performed, the crystal structure of the positive electrode active material changed and the positive electrode active The material was found to be significantly degraded. Moreover, the electrolyte was also greatly depleted by decomposition.

  The same tendency as the capacity retention rate after 500 cycles was observed for the capacity retention rate after high-temperature storage.

  From the above results, in Example 1 and Example 2, the positive electrode plate using PTFE as the binder, the separator provided with a layer made of polypropylene on the surface facing the positive electrode plate, or the surface facing the positive electrode plate In a prismatic lithium ion secondary battery in which the end-of-charge voltage is set to 4.3 V or higher by combining a separator provided with a layer made of polyaramid, a charge-discharge cycle and a high temperature It was found that decomposition of the non-aqueous electrolyte and deterioration of the positive electrode active material during storage were suppressed, and good cycle life characteristics and high temperature storage characteristics were obtained.

  In addition, even if a layer made of polyamideimide or a layer made of polyimide is provided as a layer of a compound with high oxidation resistance having fine pores on at least one surface of the separator facing the positive electrode plate, good cycle life characteristics and high temperature It was confirmed that storage characteristics were obtained.

  The non-aqueous electrolyte secondary battery according to the present invention is useful as a non-aqueous electrolyte secondary battery because of its high capacity and excellent cycle life characteristics and high-temperature storage characteristics.

The partially cutaway perspective view showing one embodiment of the nonaqueous electrolyte secondary battery of the present invention

Explanation of symbols

1 Electrode Plate Group 2 Positive Electrode Lead 3 Negative Electrode Lead 4 Battery Case 5 Sealing Plate 6 Negative Electrode Terminal 7 Inlet

Claims (2)

A non-aqueous electrolyte secondary battery comprising a group of electrode plates formed by winding a positive electrode plate and a negative electrode plate via a separator and a non-aqueous electrolyte, and a charge / discharge control device connected to the main body of the non-aqueous electrolyte secondary battery A non-aqueous electrolyte secondary battery comprising:
The positive electrode plate includes a binder mainly composed of polytetrafluoroethylene, and a layer of a highly oxidation-resistant compound having fine holes is provided on at least one surface of the separator facing the positive electrode plate, and the charge / discharge A non-aqueous electrolyte secondary battery, characterized in that the end-of-charge voltage of the control device is set to 4.3 V or higher.   2. The non-aqueous electrolyte 2 according to claim 1, wherein the oxidation-resistant compound having micropores includes at least one material selected from the group consisting of polypropylene, polyaramid, polyamideimide, and polyimide. Next battery.

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