JP2004193139A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery having an improved over-discharge cycle performance. <P>SOLUTION: The non-aqueous electrolyte secondary battery comprises a covering material 2 formed of a metal plate or a resin impregnated sheet with a thickness of 0.05-0.25 mm, a positive electrode housed inside the covering material 2, a collector formed of aluminum or an aluminum alloy housed inside the covering material 2, a negative electrode held by the collector, and contains a negative electrode active material for occluding lithium at an potential of 0.4V or higher to the electrode potential of Li, and a non-aqueous electrolyte containing γ-butyrolactone, housed inside the covering material 2. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries using a lithium metal, lithium alloy, lithium compound or carbon material for the negative electrode are expected as high energy density batteries, and are being actively researched and developed. Heretofore, lithium ion batteries including a positive electrode containing LiCoO ₂ or LiMn ₂ O ₄ as an active material and a negative electrode containing a carbon material capable of inserting and extracting lithium have been widely put into practical use. Also, the use of metal oxides or alloys in the negative electrode instead of the carbon material has been studied.

  By the way, the current collector of these negative electrodes is currently a copper foil. When a secondary battery including a negative electrode including a copper foil as a current collector is put into an overdischarge state, the potential of the negative electrode increases, so that the copper foil is melted, the discharge capacity is rapidly reduced, and the battery life is shortened. For this reason, the secondary battery is provided with a protection circuit for preventing an overdischarge state. However, such a secondary battery is disadvantageous in terms of energy density because the protection circuit is mounted.

  An object of the present invention is to provide a nonaqueous electrolyte secondary battery with improved overdischarge cycle performance.

The nonaqueous electrolyte secondary battery according to the present invention has a thickness of 0.05 to 0.25 mm, and a packaging material formed from a metal plate or a resin-containing sheet,
A positive electrode housed in the exterior material,
A current collector formed of aluminum or an aluminum alloy and housed in the exterior material; and a negative electrode active supported on the current collector and absorbing lithium at a potential of 0.4 V or more with respect to the electrode potential of Li. A negative electrode including a negative electrode layer containing a substance,
And a non-aqueous electrolyte containing γ-butyrolactone, which is housed in the exterior material.

  According to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery having a high capacity and a long life even in an overdischarge cycle.

  The non-aqueous electrolyte secondary battery according to the present invention has an exterior material, a positive electrode housed in the exterior material, a negative electrode housed in the exterior material, and a non-aqueous electrolyte housed in the exterior material. Is provided.

  The negative electrode contains a current collector made of aluminum or an aluminum alloy, and at least one type of negative electrode active material selected from the group consisting of a metal, an alloy, and a compound supported on the current collector and absorbing and releasing lithium. And a negative electrode layer.

  In the non-aqueous electrolyte, a liquid non-aqueous electrolyte prepared by dissolving an electrolyte in an organic solvent, a gel electrolyte in which the liquid non-aqueous electrolyte and a polymer material are combined, or a composite of an electrolyte and a polymer material Solid electrolytes that have been used can be used. As the electrolyte and the organic solvent, those described in the section of liquid non-aqueous electrolyte described later can be used. Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

  Hereinafter, an example of the nonaqueous electrolyte secondary battery according to the present invention will be described in detail.

  This non-aqueous electrolyte secondary battery includes an electrode group having a separator interposed between a positive electrode and a negative electrode, a liquid non-aqueous electrolyte impregnated in the electrode group, and a packaging material in which the electrode group is housed.

  Hereinafter, the positive electrode, the negative electrode, the separator, the liquid nonaqueous electrolyte, and the exterior material will be described.

1) Positive electrode This positive electrode has a positive electrode current collector and a positive electrode layer supported on one or both surfaces of the positive electrode current collector and containing an active material and a binder.

As the positive electrode active material, various oxides, for example, manganese dioxide (MnO ₂ ), lithium manganese composite oxide (for example, LiMn ₂ O ₄ , LiMnO ₂ ), lithium nickel composite oxide (for example, LiNiO ₂ ), lithium Cobalt composite oxide (for example, LiCoO ₂ ), lithium nickel cobalt composite oxide (for example, LiNi _1-x Co _x O ₂ , where the molar ratio x is 0 <x <1), and lithium manganese cobalt composite oxide (for example, , LiMn _x Co _1-x O ₂ , where the molar ratio x is 0 <x <1), vanadium oxide (for example, V ₂ O ₅ ), and the like. Further, an organic material such as a conductive polymer material or a disulfide-based polymer material may be used as the positive electrode active material. Among the positive electrode active materials, more preferred are lithium manganese composite oxide (LiMn ₂ O ₄ ), lithium nickel composite oxide (eg, LiNiO ₂ ), and lithium cobalt composite oxide (eg, LiCoO ₂ ) that can provide a high battery voltage. ), lithium nickel cobalt composite oxide _{(e.g., LiNi 0.8 Co 0.2 O 2)} , lithium manganese cobalt composite oxides (for _{example, LiMn x Co 1-x O} 2).

  As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, or the like can be used.

  The positive electrode layer may further include a conductive agent. Examples of such a conductive agent include acetylene black, carbon black, and graphite.

  The mixing ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.

  The positive electrode is produced by, for example, suspending a positive electrode active material, a conductive agent and a binder in a suitable solvent, applying the suspension to a current collector such as an aluminum foil, drying, and pressing. You.

2) Negative electrode The current collector of this negative electrode is aluminum or an aluminum alloy. The aluminum alloy preferably contains at least one or more metal components selected from the group consisting of Mg, Mn, Cr, Zn, Si, Fe and Ni. The current collector made of such an aluminum alloy can be improved in strength and can be reduced in thickness.

  The current collector may have a porous structure (for example, a mesh) or a non-porous (for example, a foil).

  The thickness of the current collector is preferably in the range of 5 to 50 μm.

  On one or both surfaces of the current collector, a negative electrode layer containing at least one type of negative electrode active material selected from the group consisting of a metal or an alloy that stores and releases lithium and a compound that stores and releases lithium is supported.

The metal or alloy contains, for example, one or more elements selected from the group consisting of Sb, Ti, Fe, V, W, Nb, Mo, Mn, Bi, Sn, Co, Si and Se. Can be mentioned. Above all, Sb, Bi, SnSb, CoSb _x (where the molar ratio x is 0 <x <3), NiSb _x (where the molar ratio x is 0 <x <3), and FeSb _x (where the molar ratio x is 0 <X <3) is preferred.

As the compound, at least one element selected from the group consisting of Sb, Ti, Fe, V, W, Nb, Mo, Mn, Bi, Sn, Co, Si, Se, B, S, C and N And the like. Examples of such compounds include oxides of at least one metal selected from the group consisting of Sb, Ti, Fe, V, W, Nb, Mo, Mn, Bi, Sn, Co, and Si; , A sulfide of the at least one metal, a sulfide of the at least one metal, Sb, Ti, Fe, V, W, Nb, Mo, Mn, Bi, Sn, Co, Si, At least one element selected from the group consisting of Se, B, S, and N; Sb, Ti, Fe, V, W, Nb, Mo, Mn, Bi, Sn, Co, Si, B, S And selenium compounds of at least one element selected from the group consisting of N. The metal _{oxide, SnO, CoO, TiO 2,} Li 4/3 Ti 5/3 O 4, WO 2, Fe 2 O 3, MoO 2 are preferred. As the metal sulfide, MoS ₂ , TiS ₂ , Li _2-y FeS ₂ , FeS ₂ , FeS, SiS ₂ , CoS ₂ , VS ₂ , and MnS ₂ are preferable. As the metal nitride, Li _3-x Co _x N (where the molar ratio x is 0 <x <3) and Li ₇ MnN ₄ are preferable. The carbonized material is preferably BCN, B _1-y C _y (where the molar ratio y is 0 <y <1). VSe ₂ is preferred as the selenium compound.

  It is preferable that the negative electrode active material absorbs lithium at a potential of 0.4 V or more with respect to the electrode potential of Li. If the lithium storage potential is lower than 0.4 V, the formation reaction of the lithium-aluminum alloy is likely to proceed, and the current collector may be pulverized. The lithium storage potential (relative to the electrode potential of Li) of the negative electrode active material is preferably in the range of 0.4 V to 3 V, and more preferably 0.4 V to 2 V.

  The negative electrode is produced, for example, by mixing a negative electrode active material, a conductive material, and a binder in the presence of a solvent, applying the obtained slurry to a current collector, drying, and then pressing.

  Examples of the conductive material include carbon materials such as graphite and carbon black, and have little effect on the reaction between the current collector and lithium. It is preferable that the compounding ratio of the conductive material is in the range of 3 to 20 parts by weight based on 100 parts by weight of the negative electrode active material.

  As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, or the like can be used.

3) Separator A porous separator is used as the separator.

  Examples of the porous separator include a porous film containing polyethylene, polypropylene, cellulose, or polyvinylidene fluoride (PVdF), and a synthetic resin nonwoven fabric. Among them, a porous film made of polyethylene, polypropylene, or both is preferable because the safety of the secondary battery can be improved.

4) Liquid non-aqueous electrolyte This liquid non-aqueous electrolyte is prepared by dissolving the electrolyte in an organic solvent.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), and trifluoroelectrolyte. Lithium salts such as lithium metasulfonate (LiCF ₃ SO ₃ ) and bistrifluoromethylsulfonylimitolithium [LiN (CF ₃ SO ₂ ) ₂ ] are exemplified.

  Examples of the organic solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC). Examples thereof include chain carbonates, cyclic ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2MeTHF), chain ethers such as dimethoxyethane (DME), and γ-butyrolactone (BL). These organic solvents can be used alone or in the form of a mixture of two or more.

  Preferable mixed solvents among the organic solvents include EC and PC, EC and BL, EC and PC and VC, EC and BL and VC, EC and PC and BL, EC and PC and BL and VC. Among them, EC, BL and VC, and EC, PC, BL and VC are preferable. In this case, the volume ratio of BL in the organic solvent is 50% by volume or more, and the volume ratio of VC is 0.1 to 10% by volume. It is desirable to do. A more preferable range of the volume ratio of VC is 0.1 to 2% by volume.

5) Exterior material This exterior material can be formed from, for example, a metal plate, a sheet having a resin layer, or the like.

  The metal plate can be formed from, for example, iron, stainless steel, or aluminum. The thickness of the metal plate is preferably in the range of 0.05 to 0.25 mm, and more preferably 0.05 to 0.2 mm.

  The sheet is preferably composed of a metal layer and a resin layer covering the metal layer. The thickness of the sheet is preferably in the range of 0.05 to 0.25 mm, and more preferably 0.05 to 0.2 mm. The metal layer is preferably formed from an aluminum foil having a thickness of 0.01 to 0.15 mm. Meanwhile, the resin layer can be formed from a thermoplastic resin such as polyethylene or polypropylene. The resin layer may have a single layer or a multilayer structure.

  FIG. 1 shows an example of the nonaqueous electrolyte secondary battery according to the present invention.

  FIG. 1 is a sectional view showing an example of a lithium ion secondary battery according to the present invention.

  The electrode group 1 has a structure in which a positive electrode and a negative electrode are wound in a flat shape with a separator interposed therebetween. The electrode group 1 is manufactured by winding a positive electrode and a negative electrode into a flat shape with a separator interposed therebetween, and then applying a hot press. A liquid non-aqueous electrolyte is impregnated in the electrode group 1. Such an electrode group 1 is housed in an exterior material 2 in the form of a bag made of a sheet including a resin layer, for example. One end of the strip-shaped positive electrode lead 3 is connected to the positive electrode of the electrode group 1, and the other end is extended from the exterior material 1. On the other hand, the strip-shaped negative electrode lead 4 has one end connected to the negative electrode of the electrode group 1 and the other end extended from the exterior material 1.

  In FIG. 1 described above, the positive electrode, the negative electrode, and the separator in the electrode group are integrated by hot pressing. However, the positive electrode, the negative electrode, and the separator can be integrated using an adhesive polymer.

  The non-aqueous electrolyte secondary battery according to the present invention has an exterior material, a positive electrode housed in the exterior material, a negative electrode housed in the exterior material, and a non-aqueous electrolyte housed in the exterior material. Is provided. The negative electrode is selected from the group consisting of a current collector made of aluminum or an aluminum alloy, a metal supported on the current collector and absorbing and releasing lithium, an alloy absorbing and releasing lithium, and a compound absorbing and releasing lithium. And a negative electrode layer containing at least one type of negative electrode active material.

  ADVANTAGE OF THE INVENTION According to the secondary battery which concerns on this invention, while being able to obtain high capacity | capacitance, long life can be maintained also in an overdischarge cycle.

  That is, when a current collector of aluminum or an aluminum alloy is used as the current collector of the negative electrode, the current collector does not dissolve even in an overdischarged state, so that good cycle characteristics can be obtained even if overdischarge to 0 V is repeated. Can be obtained. When the current collector is used, if a carbonaceous material that absorbs and releases lithium ions is used as the negative electrode active material, the lithium occlusion potential (relative to the Li electrode) of the carbonaceous material is lower than the lithium aluminum alloy formation potential, Reacts with lithium to cause a lithium-aluminum alloy forming reaction to proceed, and the current collector is pulverized.

  When a current collector made of aluminum or an aluminum alloy is used as in the present invention, by using a metal, an alloy or a compound that absorbs and releases lithium as a negative electrode active material, the lithium storage potential (Li electrode ) Is higher than the lithium aluminum alloy forming potential, so that the reaction between the current collector and lithium can be suppressed, and the pulverization of the negative electrode current collector can be suppressed. Therefore, it is possible to realize a non-aqueous electrolyte secondary battery having a high capacity and a long life maintained even in an overdischarge cycle.

  In the secondary battery according to the present invention, a metal or alloy containing at least one selected from the group consisting of Sb, Ti, Fe, V, W, Nb, Mo, Mn, Bi, Sn, Co, Si, and Se And at least one element selected from the group consisting of Sb, Ti, Fe, V, W, Nb, Mo, Mn, Bi, Sn, Co, Si, Se, B, S, C and N. By using at least one selected from the group consisting of compounds as the negative electrode active material, pulverization of the current collector can be further suppressed.

  Further, in the secondary battery according to the present invention, by using a sheet including a resin layer as the exterior material, in addition to the fact that the current collector of the negative electrode is formed of lightweight aluminum or aluminum alloy, Since the weight can be reduced, the weight of the secondary battery can be reduced, and the energy density by weight can be improved. In particular, by forming the sheet from an aluminum foil having a thickness of 0.01 to 0.15 mm and a resin layer formed on one or both sides of the aluminum foil, the weight of the secondary battery can be reduced. In addition, it is possible to prevent dissolution and corrosion of the exterior material in the overdischarge cycle.

[Example]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings described above.

(Example 1)
<Preparation of positive electrode>
First, 91% by weight of lithium cobalt oxide (LiCoO ₂ ) powder, 2.5% by weight of acetylene black, 3% by weight of graphite and 4% by weight of polyvinylidene fluoride (PVdF) as a positive electrode active material were added to N-methylpyrrolidone (NMP). The slurry was further mixed to form a slurry. The slurry was applied to both sides of a current collector made of aluminum foil of 15 μm, dried, and pressed to produce a positive electrode having an electrode density of 3.0 g / cm ³ .

<Preparation of negative electrode>
Li _4/3 Ti _5/3 O ₄ as a negative electrode active material, graphite as a conductive material, and polyvinylidene fluoride (PVdF) in a N-methylpyrrolidone (NMP) solution in a weight ratio of 90: 5: 5. The resulting slurry was applied to an aluminum foil having a thickness of 15 μm, dried, and then pressed to produce a negative electrode.

<Preparation of electrode group>
The positive electrode, a separator made of a porous film made of polyethylene having a thickness of 25 μm, the negative electrode, and the separator were laminated in this order, and then spirally wound. Next, this was hot-pressed at 90 ° C. to produce a flat electrode group having a width of 30 mm and a thickness of 3.0 mm. The obtained electrode group was housed in a pack made of a laminated film having a thickness of 0.1 mm and composed of an aluminum foil having a thickness of 40 μm and polypropylene layers formed on both surfaces of the aluminum foil. Vacuum drying was performed for 24 hours.

<Preparation of liquid non-aqueous electrolyte>
1.5 mol / L lithium tetrafluoroborate (LiBF ₄ ) as an electrolyte in a mixed solvent (volume ratio 24: 75: 1) of ethylene carbonate (EC), γ-butyrolactone (BL) and vinylene carbonate (VC) By dissolving, a liquid non-aqueous electrolyte (non-aqueous electrolyte) was prepared.

  After injecting the liquid non-aqueous electrolyte into the laminate film pack containing the electrode group, the pack was completely sealed by heat sealing, and had the structure shown in FIG. 1 described above, a width of 35 mm, and a thickness of 35 mm. A non-aqueous electrolyte secondary battery having a size of 3.2 mm and a height of 65 mm was manufactured.

(Examples 2 to 14)
A non-aqueous electrolyte secondary battery having the same configuration as in Example 1 described above was manufactured except that the negative electrode active materials shown in Table 1 below were used.

(Examples 15 and 16)
A non-aqueous electrolyte secondary battery having the same configuration as in Example 1 described above was manufactured except that an aluminum alloy having a composition shown in Table 1 below was used as the negative electrode current collector.

(Comparative Examples 1 to 5)
A non-aqueous electrolyte secondary battery having the same configuration as in Example 1 described above was manufactured except that the negative electrode active material and the negative electrode current collector shown in Table 1 below were used.

The obtained secondary batteries of Examples 1 to 16 and Comparative Examples 3 to 5 were subjected to a constant voltage charge of 3.8 V at 500 mA for 3 hours, and then subjected to an overdischarge cycle test of discharging to 0 V at 500 mA. In addition, the secondary batteries of Comparative Examples 1 and 2 were subjected to an overdischarge cycle test in which a 4.2 V constant voltage charge was performed at 500 mA for 3 hours, and then the battery was discharged to 0 V at 500 mA. The first cycle capacity (initial capacity) and cycle life in the overdischarge cycle test were measured, and the results are shown in Table 1 below. The cycle life was the number of cycles at which the capacity reached 80% based on the capacity of the first cycle.

  As is apparent from Table 1, the secondary batteries of Examples 1 to 16 each including a negative electrode including a negative electrode active material made of a metal, an alloy or a compound capable of inserting and extracting lithium, and a negative electrode current collector made of aluminum or an aluminum alloy. It can be seen that the battery has a high battery capacity and a longer overdischarge cycle life than Comparative Examples 1 to 5.

  On the other hand, the secondary batteries of Comparative Examples 1 and 3 to 5 including the negative electrode including the copper current collector, and the negative electrode including the negative electrode active material including a carbonaceous material that absorbs and releases lithium ions and the negative electrode including the aluminum current collector were used. It can be seen that the secondary battery of Comparative Example 2 provided had a short overdischarge cycle life.

  In the above-described embodiment, an example in which the present invention is applied to a thin non-aqueous electrolyte secondary battery has been described. However, the form of the non-aqueous electrolyte secondary battery according to the present invention is not limited to a thin type. It can be square, cylindrical, button-shaped or the like.

FIG. 1 is a cross-sectional view showing a thin non-aqueous electrolyte secondary battery as an example of the non-aqueous electrolyte secondary battery according to the present invention.

Explanation of reference numerals

  DESCRIPTION OF SYMBOLS 1 ... electrode group, 2 ... exterior material, 3 ... positive electrode terminal, 4 ... negative electrode terminal.

Claims (3)

An exterior material formed from a metal plate or a resin-containing sheet having a thickness of 0.05 to 0.25 mm;
A positive electrode housed in the exterior material,
A current collector formed of aluminum or an aluminum alloy and housed in the exterior material; and a negative electrode active supported on the current collector and absorbing lithium at a potential of 0.4 V or more with respect to the electrode potential of Li. A negative electrode including a negative electrode layer containing a substance,
A non-aqueous electrolyte secondary battery which is housed in the exterior material and contains γ-butyrolactone. The negative active _{material, SnO, CoO, TiO 2,} Li 4/3 Ti 5/3 O 4, FeS 2, WO 2, Fe 2 O 3, MoO 2, MoS 2, TiS 2, Li 2-y FeS 2 _{, FeS, SiS 2, CoS 2} , VS 2, MnS 2, Li 3-x Co x N ( where the molar ratio x is 0 <x <3), Li 7 MnN 4, BCN, B 1-y C y ( However, the molar ratio y is 0 <y <1) and VSe nonaqueous electrolyte secondary battery according to claim 1, characterized in that it comprises at least one selected from the group consisting of _2.   The non-aqueous electrolyte includes an organic solvent containing at least one selected from the group consisting of ethylene carbonate, γ-butyrolactone, methyl ethyl carbonate, dimethyl carbonate and diethyl carbonate, and an electrolyte dissolved in the organic solvent. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte is a liquid non-aqueous electrolyte.

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