JP5447517B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention generally relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having improved characteristics in a high temperature environment.

  Conventionally, in a non-aqueous electrolyte secondary battery, generally, for example, a non-aqueous electrolyte obtained by dissolving a lithium salt such as lithium hexafluorophosphate as an electrolyte in a non-aqueous solvent such as ethylene carbonate or dimethyl carbonate. , A lithium transition metal composite oxide as a positive electrode active material, and a carbon material as a negative electrode active material. In such a non-aqueous electrolyte secondary battery, in order to improve cycle characteristics, it has been proposed to use a spinel type lithium titanium composite oxide as a negative electrode active material.

  For example, Japanese Patent Application Laid-Open No. 2007-273154 (hereinafter referred to as Patent Document 1) proposes a non-aqueous electrolyte secondary battery with improved cycle characteristics at a high temperature such as 60 ° C. In this non-aqueous electrolyte secondary battery, a lithium transition metal oxide having a layered crystal structure as a positive electrode active material, a spinel-type lithium titanium composite oxide as a negative electrode active material, ethylene carbonate, A solution obtained by dissolving a lithium salt such as lithium hexafluorophosphate or lithium tetrafluoroborate as an electrolyte in a non-aqueous solvent such as dimethyl carbonate is used. Patent Document 1 describes that a non-aqueous electrolyte may be a room temperature molten salt (ionic liquid) containing lithium ions.

JP 2007-273154 A

  However, in Patent Document 1, a lithium cobalt composite oxide, a lithium nickel cobalt aluminum composite oxide, or a lithium nickel cobalt composite oxide is used as a positive electrode active material, and a spinel-type lithium titanium composite oxide is used as a negative electrode active material. As a non-aqueous electrolyte solution, a non-aqueous electrolyte secondary battery using a mixed solvent of ethylene carbonate and γ-butyrolactone in which lithium tetrafluoroborate is dissolved as an electrolyte is used in an environment of 60 ° C. Only the charge / discharge cycle test was conducted and the capacity retention rate was evaluated. There is no disclosure or suggestion about the configuration of the non-aqueous electrolyte secondary battery that can withstand a high temperature environment exceeding 60 ° C.

  In addition, carbon materials such as acetylene black, carbon black, and graphite are used as a conductive agent for the positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery proposed in Patent Document 1.

  In Patent Document 1, an example of a non-aqueous electrolyte secondary battery using an ionic liquid as a non-aqueous electrolyte is not specifically disclosed, and the characteristics under a high temperature environment are not evaluated at all. Not.

  Then, the objective of this invention is providing the structure of the nonaqueous electrolyte secondary battery which can improve the heat resistance in the high temperature environment over 60 degreeC.

A non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator, the non-aqueous electrolyte containing an ionic liquid, In addition, a negative electrode active material having a lithium occlusion / release potential of 1.0 V (vs Li / Li ⁺ ) or more is included, and substantially no conductive agent is included.

In the non-aqueous electrolyte secondary battery of the present invention, the non-aqueous electrolyte includes an ionic liquid, and the negative electrode includes a negative electrode active material having a lithium storage / release potential of 1.0 V (vs Li / Li ⁺ ) or more, And by not containing a electrically conductive agent substantially, even if it heats to the high temperature over 60 degreeC, a battery voltage hardly falls, and a battery voltage can be substantially maintained in a high temperature environment. Thereby, the heat resistance of a nonaqueous electrolyte secondary battery can be improved.

In the non-aqueous electrolyte secondary battery of the present invention, a separator, a polyethylene terephthalate, cellulose, polyamide-imide, at least one of including selected from the group consisting of polyimide and an inorganic filler.

Thus, by adopting a material having high heat resistance as the separator, the heat resistance of the non-aqueous electrolyte secondary battery can be further improved.

  In the non-aqueous electrolyte secondary battery of the present invention, the binder used for forming the positive electrode and the negative electrode preferably contains at least one selected from the group consisting of polyvinylidene fluoride and polyamideimide. .

  Furthermore, in the nonaqueous electrolyte secondary battery of the present invention, the negative electrode active material is preferably a spinel type lithium titanium composite oxide.

  As described above, according to the present invention, since the heat resistance of the nonaqueous electrolyte secondary battery in a high temperature environment exceeding 60 ° C. can be improved, it can be surface-mounted on a substrate by reflow soldering. A nonaqueous electrolyte secondary battery can be obtained.

It is a front view which decomposes | disassembles and shows schematically the internal structure of the nonaqueous electrolyte secondary battery produced in one Example of this invention. It is a front view which shows roughly the external appearance of the nonaqueous electrolyte secondary battery produced in one Example of this invention. It is a figure which shows the change of battery temperature and battery voltage in the non-aqueous-electrolyte secondary battery produced in Example 1 of this invention. It is a figure which shows the change of battery temperature and battery voltage in the nonaqueous electrolyte secondary battery produced by the comparative example 1 of this invention.

The inventor of the present application has made various studies on the configuration of the nonaqueous electrolyte secondary battery for improving the heat resistance in a high temperature environment exceeding 60 ° C. As a result, the non-aqueous electrolyte contains an ionic liquid, the negative electrode contains a noble negative electrode active material having a lithium storage / release potential of 1.0 V (vs Li / Li ⁺ ) or more, and substantially contains a conductive agent . In other words, the present inventors have found that even when heated to a high temperature exceeding 60 ° C., the battery voltage hardly decreases and the battery voltage can be substantially maintained in a high temperature environment. The present invention has been made based on such knowledge of the present inventor.

That is, the non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator, the non-aqueous electrolyte containing an ionic liquid, In addition, a negative electrode active material having a lithium occlusion / release potential of 1.0 V (vs Li / Li ⁺ ) or more is included, and substantially no conductive agent is included.

  Preferably, the separator includes at least one selected from the group consisting of polyethylene terephthalate (PET), cellulose, polyamideimide (PAI), polyimide (PI), and inorganic filler, and a material having high heat resistance as the separator. By adopting, the heat resistance of the non-aqueous electrolyte secondary battery can be further improved.

  Furthermore, in the nonaqueous electrolyte secondary battery of the present invention, the binder used to form the positive electrode and the negative electrode is at least selected from the group consisting of polyvinylidene fluoride (PVDF) and polyamideimide (PAI). It is preferable to include one kind.

  In one embodiment of the present invention, as the ionic liquid constituting the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery, for example, 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (EMITFSI) Is used.

  Examples of cations constituting the ionic liquid include the following five types. R1 to R4 are alkyl groups or H (hydrogen). R1 to R4 may be the same group or different from each other.

  Examples of the anion that constitutes the ionic liquid include the following three types.

BF ₄ ^-

PF ₆ ^-

  The ionic liquid which comprises the optimal combination of a cation and an anion which comprises the nonaqueous electrolyte solution of the nonaqueous electrolyte secondary battery of this invention is as follows.

  1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (EMITFSI) or 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4).

  Furthermore, in one embodiment of the present invention, the positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery are alternately stacked via a separator. The structure of the battery element may be composed of a laminate of a plurality of strip-shaped positive electrodes, a plurality of strip-shaped separators and a plurality of strip-shaped negative electrodes, a laminate of so-called single-wafer structures. It may be configured by folding and interposing a strip-shaped positive electrode and a strip-shaped negative electrode alternately. Moreover, as a structure of the battery element, a winding type structure in which a long positive electrode, a long separator, and a long negative electrode are wound may be employed. In the following examples, a single-wafer structure laminate is adopted as the structure of the battery element.

In the positive electrode, a positive electrode mixture layer including a positive electrode active material, a conductive agent, and a binder is formed on both surfaces of the positive electrode current collector. As an example, the positive electrode current collector is made of aluminum. The positive electrode active material is lithium cobalt oxide composite oxide (LCO), lithium manganate composite oxide (LMO), lithium nickelate composite oxide (LNO), lithium-nickel-manganese-cobalt composite oxide (LNMCO), lithium -Manganese-nickel composite oxide (LMNO), lithium-manganese-cobalt composite oxide (LMCO), lithium-nickel-cobalt composite oxide (LNCO), or the like can be used. Furthermore, the positive electrode active material may be a mixture of the above materials. The positive electrode active material may be an olivine-based material such as LiFePO ₄ . Carbon or the like is used as a conductive agent for the positive electrode. Polyvinylidene fluoride (PVDF) or polyamideimide (PAI) is used as the binder for binding the positive electrode active material and the conductive agent.

On the other hand, in the negative electrode, a negative electrode mixture layer including a negative electrode active material and a binder is formed on both surfaces of a negative electrode current collector. As an example, the negative electrode current collector is made of aluminum, and the negative electrode active material is made of a spinel-type lithium titanium composite oxide which is a noble material having a lithium occlusion / release potential of 1.0 V (vs Li / Li ⁺ ) or more. The negative electrode is substantially free of carbon that acts as a conductive agent. Polyvinylidene fluoride (PVDF) or polyamideimide (PAI) is used as a binder for binding the negative electrode active material.

  The separator is made of polyethylene terephthalate (PET), cellulose, polyamideimide (PAI), polyimide (PI), or an inorganic filler.

  Presence / absence of a conductive agent used to form a negative electrode using a positive electrode, a negative electrode and a non-aqueous electrolyte prepared as follows, a binder material for forming the positive electrode and the negative electrode, and a separator material The non-aqueous electrolyte secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 7 were produced by making the composition of the non-aqueous electrolyte different as shown in Table 1 and Table 2 below.

(Preparation of positive electrode)
Lithium-nickel-manganese-cobalt composite oxide (LNMCO) represented by the composition formula LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as a positive electrode active material, carbon as a conductive agent, and as a binder The slurry was prepared by blending with polyvinylidene fluoride (PVDF) in a weight ratio of 94: 3: 3 and kneading with N-methyl 2-pyrrolidone (NMP). This slurry was applied to both surfaces of an aluminum foil as a current collector, dried, and then rolled with a roll press to produce a positive electrode.

(Preparation of negative electrode)
In Examples 1 and 2 and Comparative Examples 1, 2, 5, and 6, a spinel type lithium titanium composite oxide represented by Li ₄ Ti ₅ O ₁₂ as a negative electrode active material and PVDF as a binder A slurry was prepared by blending in a weight ratio of 97: 3 and kneading with NMP. This slurry was applied to both surfaces of an aluminum foil as a current collector, dried, and then rolled with a roll press to produce a negative electrode.

In Examples 3 and 4 and Comparative Examples 3 and 4, a spinel type lithium titanium composite oxide represented by Li ₄ Ti ₅ O ₁₂ as a negative electrode active material and polyamideimide (PAI) as a binder were used. A slurry was prepared by blending in a weight ratio of 97: 3 and kneading with NMP. This slurry was applied to both surfaces of an aluminum foil as a current collector, dried, and then rolled with a roll press to produce a negative electrode.

In Comparative Example 7, a spinel type lithium titanium composite oxide represented by Li ₄ Ti ₅ O ₁₂ as a negative electrode active material, carbon as a conductive agent, and PVDF as a binder in a weight ratio of 94: The slurry was prepared by blending to 3: 3 and kneading with NMP. This slurry was applied to both surfaces of an aluminum foil as a current collector, dried, and then rolled with a roll press to produce a negative electrode.

(Preparation of non-aqueous electrolyte)
In Examples 1 to 4 and Comparative Examples 6 and 7, 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (EMITFSI) was used as the ionic liquid, and lithium bis (trifluoromethyl) was added to the ionic liquid. A non-aqueous electrolyte solution was prepared by dissolving sulfonyl) imide at a rate of 1.0 mol / L.

In Comparative Examples 1 to 5, the solvent was prepared by preparing ethylene carbonate (EC) and γ-butyrolactone (GBL) at a volume ratio of 1: 2. A non-aqueous electrolyte was prepared by dissolving lithium tetrafluoroborate (LiBF ₄ ) as an electrolyte in this solvent at a rate of 1.5 mol / L.

(Production of battery)
As shown in FIG. 1, lead tabs 14 and 15 were provided on the positive electrode 11 and the negative electrode 12 produced as described above. Between the positive electrode 11 and the negative electrode 12, polyethylene terephthalate (PET) was used in Examples 1 and 3 and Comparative Examples 1 and 3, cellulose was used in Examples 2 and 4 and Comparative Examples 2 and 4, and polypropylene ( Laminated with a porous separator 13 made of PP). Thus, the battery element 10 was produced. Sealants 16 and 17 were attached to the lead tabs 14 and 15, and as shown in FIG. 2, the above laminate was accommodated in an outer packaging material made of a laminate film 20 containing aluminum as an intermediate layer. Then, after injecting the non-aqueous electrolyte solution produced above into the outer packaging material, the non-aqueous electrolyte secondary battery 1 was produced by sealing the opening of the outer packaging material.

  A heating test was performed using the non-aqueous electrolyte secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 7 obtained as described above. The test results are shown in Tables 1 and 2.

(Heating test)
After performing constant current charging with each battery at an electric current of 4 mA in an atmosphere at a temperature of 25 ° C., constant voltage charging was performed with a voltage of 2.75 V and a charging current of 0.1 mA. Thereafter, constant current discharge was performed until the voltage became approximately 2.0 V at a current of 4 mA. At this time, the battery voltage was measured and used as the voltage before the heating test (Tables 1 and 2). The battery temperature (temperature of the atmosphere around the battery) was raised to 200 ° C. at a rate of temperature increase of 4 ° C./min. The battery voltage at that time was measured and used as the voltage when reaching 200 ° C. (Tables 1 and 2). In addition, changes in battery temperature and battery voltage during the heating test were measured. Changes in battery temperature and battery voltage in Example 1 and Comparative Example 1 are shown in FIGS.

  From the results shown in Table 1, in Examples 1 to 4, even when the temperature of the atmosphere around the battery was heated to 200 ° C., the decrease in the battery voltage was less than 0.1V. On the other hand, from the results shown in Table 2, in Comparative Examples 1 to 7, when the temperature of the atmosphere around the battery was heated to 200 ° C., the decrease in the battery voltage was 0.1 V or more. Therefore, it can be seen that the non-aqueous electrolyte secondary batteries of Examples 1 to 4 can improve the heat resistance.

  It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments or examples but by the scope of claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the scope of claims.

1: non-aqueous electrolyte secondary battery, 10: battery element, 11: positive electrode, 12: negative electrode, 13: separator.

Claims (3)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator,
The non-aqueous electrolyte contains an ionic liquid;
The negative electrode includes a noble negative electrode active material having a lithium occlusion / release potential of 1.0 V (vs Li / Li ⁺ ) or more and substantially free of a conductive agent ,
A non-aqueous electrolyte secondary battery , wherein the separator includes at least one selected from the group consisting of polyethylene terephthalate, cellulose, polyamideimide, polyimide, and inorganic filler . The nonaqueous electrolyte secondary battery according to claim 1, wherein the binder used to form the positive electrode and the negative electrode includes at least one selected from the group consisting of polyvinylidene fluoride and polyamideimide. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is a spinel type lithium titanium composite oxide.

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