JP5092232B2 - Non-aqueous electrolyte battery - Google Patents

Description

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

  In recent years, nonaqueous electrolyte batteries, particularly lithium secondary batteries, have attracted attention as power supplies for portable devices such as mobile phones, PHS (simple mobile phones), and small computers, power storage power supplies, and power supplies for electric vehicles.

  A lithium secondary battery is generally composed of a positive electrode having a positive electrode active material as a main constituent, a negative electrode having a negative electrode active material as a main constituent, and a nonaqueous electrolyte.

The positive electrode active material constituting the lithium secondary battery is a lithium-containing transition metal oxide, the negative electrode active material is a carbonaceous material typified by graphite, and the nonaqueous electrolyte is lithium hexafluorophosphate ( A solution in which an electrolyte such as LiPF ₆ ) is dissolved in a non-aqueous solvent of a carbonate derivative is widely known. As the carbonate derivative, for example, Patent Document 1 includes ethylene carbonate having a 5-membered ring whose molecular structure includes a carbonate group in a non-aqueous electrolyte secondary battery. However, ethylene carbonate has a low melting point, and the electrolyte is easily solidified at a low temperature.

  Therefore, a method is known in which propylene carbonate having a higher melting point is used as the non-aqueous solvent for the electrolyte instead of ethylene carbonate. Although propylene carbonate has a structural formula similar to that of a solid solvent at normal temperature such as ethylene carbonate, it has a low freezing point, so it is considered that propylene carbonate has a function of hardly precipitating ethylene carbonate at low temperatures. Therefore, ionic conduction of the nonaqueous electrolyte can be ensured without causing ethylene carbonate to precipitate even at low temperatures. However, since propylene carbonate decomposes on the graphite negative electrode during the charging operation, there is a problem that charging cannot be performed sufficiently.

  As means for solving this problem, Patent Document 2 discloses a technique in which a nonaqueous electrolyte solution containing a cyclic carbonate having a phenyl group is applied to a nonaqueous electrolyte battery in order to minimize decomposition of the electrolyte solution. Therefore, it is said that a nonaqueous electrolyte battery having high battery characteristics can be obtained. However, even with the means described in the above publication, improvement in high-temperature storage characteristics is insufficient, and a nonaqueous electrolyte battery that achieves both excellent high-temperature storage characteristics and high battery characteristic batteries at a high level is demanded.

  In addition, it has been proposed to add a disulfide compound to suppress swelling during high-temperature storage (Patent Documents 3 and 4).

In Examples of Patent Document 3, “artificial graphite as a negative electrode active material” is used for a negative electrode plate (paragraph 0035), and a solute is mixed in a mixed solvent in which the weight ratio of EC, EMC, and DEC is 4: 5: 2. Non-aqueous solution in which 1.35M LiPF ₆ is dissolved as follows, and 2.0% by weight of PC (propylene carbonate), 4.0% by weight of PS (1,3-propane sultone) and a disulfide compound are added and mixed. A battery assembled by adjusting the electrolyte solution (Examples 17 to 30) is described. "PC and PS contained in the nonaqueous solvent in the nonaqueous electrolyte contribute to the formation of a stable protective film on the surface of the negative electrode carbon material" (paragraph 0024), "DPDS, DPTS and BMPDS (invention). Note: A kind of disulfide compound) contributes to the formation of a stable protective film on the surface of the negative electrode carbon material.This protective film is maintained in a stable state even after repeated charging and discharging. It is described that the nonaqueous solvent in the electrolytic solution is electrochemically reduced to generate gas ”(paragraph 0025). That is, in the battery described in Patent Document 3, the amount of propylene carbonate used is only 2% by weight and is used as an additive that contributes to the formation of a stable protective film on the surface of the negative electrode carbon material. Alternatively, it is presumed that propylene carbonate is not present in the electrolyte solution of the battery after shipment because it is consumed at least in an initial cycle process performed at the time of manufacture.

  When propylene carbonate is used as the main solvent of the non-aqueous electrolyte, as shown in the examples described later, propylene carbonate is severely decomposed on the surface of the graphite negative electrode. There was a problem that could not be obtained.

In an example of Patent Document 4, 1M LiPF ₆ is added to a non-aqueous organic solvent in which ethylene carbonate / dimethyl carbonate (EC / DMC) is mixed in 1/1, and a disulfide compound is added (Example 1). To 6), a battery using “crystalline artificial graphite as a negative electrode active material” is described. However, a battery using propylene carbonate is not specifically described.
JP 02-172162 A JP 11-354152 A JP 2002-083632 A JP 2005-019409 A

  The present invention has been made in view of the above problems, and provides a non-aqueous electrolyte battery having excellent performance by suppressing decomposition of the non-aqueous electrolyte on the negative electrode using graphite as a negative electrode active material. For the purpose.

In order to achieve the above-described object, the present inventors have intensively studied to make the nonaqueous solvent constituting the nonaqueous electrolyte specific, and surprisingly, have excellent high temperature storage characteristics and high The present inventors have found that a battery characteristic battery, that is, a nonaqueous electrolyte battery having a high energy density can be obtained, and the present invention has been achieved. The technical configuration and operational effects of the present invention are as follows. However, the action mechanism includes estimation, and its correctness does not limit the present invention.
(1) A nonaqueous electrolyte battery including a positive electrode and a negative electrode, wherein the negative electrode includes a polymerization product of a disulfide derivative having an acrylic group.
(2) The nonaqueous electrolyte battery according to (1) above, comprising a nonaqueous electrolyte containing propylene carbonate.
(3) The non-aqueous electrolyte battery according to any one of (1) or ( 2 ), wherein the negative electrode contains graphite as a negative electrode active material.

  That is, in order to obtain a non-aqueous electrolyte according to the present invention, a non-aqueous electrolyte battery is manufactured using a non-aqueous electrolyte containing a disulfide derivative having an acrylic group. Since the disulfide derivative having a group is polymerized, the negative electrode has a polymerization product of the disulfide derivative having an acrylic group. The negative electrode thus obtained suppresses the decomposition of the solvent at the time of charging very effectively, so even if a nonaqueous electrolyte containing propylene carbonate as a main solvent is used, the negative electrode is graphite as the negative electrode active material. Even if it contains, the battery swelling by decomposition | disassembly of a nonaqueous electrolyte is suppressed effectively, and the nonaqueous electrolyte battery which has the outstanding battery performance can be provided. And since the polymerization product of the disulfide derivative which has an acryl group does not melt | dissolve even if it preserve | saves at high temperature, it can be set as the nonaqueous electrolyte battery which has the outstanding high temperature storage characteristic and high energy density.

  Here, examples of the disulfide derivative having an acrylic group include compounds represented by the following chemical formula.

  According to the present invention, since propylene carbonate, which could not be used because of severe decomposition, can be used as a solvent for non-aqueous electrolytes, it has a low temperature performance compared to a battery using ethylene carbonate as a main solvent. A water electrolyte battery can be provided. In order to ensure this effect, the amount of propylene carbonate in the solvent constituting the nonaqueous electrolyte is preferably 10% by volume or more, and more preferably 20% by volume or more.

  The nonaqueous electrolyte battery of the present invention is manufactured using a nonaqueous electrolyte containing a disulfide derivative having an acrylic group, and the negative electrode includes a polymerization product of a disulfide derivative having an acrylic group. Whether using a non-aqueous electrolyte containing carbonate or using a negative electrode containing graphite as the negative electrode active material, the decomposition of the non-aqueous electrolyte during charging is suppressed. Therefore, a non-aqueous electrolyte battery having excellent performance can be provided.

  Hereinafter, embodiments of the present invention will be exemplified, but the present invention is not limited to the following embodiments.

  The non-aqueous electrolyte battery according to the present invention includes a positive electrode having a positive electrode active material as a main constituent, a negative electrode having a negative electrode active material as a main constituent, and a non-aqueous electrolyte containing an electrolyte salt in a non-aqueous solvent. In general, a separator for a nonaqueous electrolyte battery is provided between the positive electrode and the negative electrode.

  The amount of the disulfide derivative having an acrylic group is preferably 0.01% by weight to 5% by weight, and more preferably 0.10% by weight to 2% by weight with respect to the total weight of the electrolytic solution. When the amount of the disulfide derivative having an acrylic group is 0.01% by weight or more with respect to the total weight of the electrolytic solution, the decomposition of propylene carbonate during the charging operation is almost completely suppressed and charging is performed more reliably. be able to. Moreover, since the ionic conductivity of the disulfide derivative itself having an acrylic group is low, the ionic conductivity of the electrolytic solution can be ensured by being 5% by weight or less.

  In addition to propylene carbonate, other organic solvents can be mixed and used for the non-aqueous electrolyte as required. For example, cyclic carbonates such as ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethylmethyl carbonate; cyclics such as γ-butyrolactone Esters; chain esters such as methyl acetate and methyl butyrate; ethers such as tetrahydrofuran or derivatives thereof, 1,3-dioxane, 1,2-dimethoxyethane, methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxalane or Examples thereof include, but are not limited to, sulfolane, sultone or a derivative thereof alone or a mixture of two or more thereof.

Examples of the electrolyte salt used for the nonaqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiSCN. , LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN, etc., one kind of lithium (Li), sodium (Na) or potassium (K) Inorganic ion salt containing, LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , _{(C 2 H 5) 4 NI} , (C 3 H 7) 4 NBr, (n-C 4 H 9) 4 NClO 4, (n-C 4 H 9) 4 NI, (C 2 H 5) 4 N- _{maleate, (C 2 H 5)} 4 N-benzoat _{, (C 2 H 5) 4} N-phtalate quaternary ammonium salts such as lithium stearyl sulfonate, lithium octyl sulfonate, and organic ion salts of lithium dodecylbenzenesulfonate, alone these ionic compounds, Alternatively, two or more types can be mixed and used.

  The concentration of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 1 mol / l to 2.5 mol in order to reliably obtain a nonaqueous electrolyte battery having high battery characteristics. / L.

  As a positive electrode active material which is a main component of the positive electrode, a self-evident material can be used in a self-evident formula.

As a negative electrode active material that is a main component of the negative electrode, among carbonaceous materials, graphite has an operating potential very close to that of metallic lithium. Therefore, when lithium salt is used as an electrolyte salt, self-discharge can be reduced, and charge and discharge can be reduced. Since the irreversible capacity can be reduced, it is preferable as the negative electrode active material. More specifically, the lattice spacing (d ₀₀₂ ) is 0.333 to 0.350 nm, the crystallite size (La) in the a-axis direction is 20 nm or more, and the crystallite size (Lc) in the c-axis direction is What has 20 nm or more and a true density of 2.00-2.25 g / cm < ³ > is preferable.

  It is also possible to modify graphite by adding a metal oxide such as tin oxide or silicon oxide, phosphorus, boron, amorphous carbon or the like. In particular, by modifying the surface of graphite by the above method, it is possible to suppress the decomposition of the electrolytic solution and improve the battery characteristics, which is desirable. In addition to graphite, lithium metal-containing alloys such as lithium metal, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys can be used in combination. Graphite in which lithium is inserted by chemical reduction can also be used as the negative electrode active material.

  The positive electrode and the negative electrode may contain a conductive agent, a binder and a filler as other components in addition to the active material which is a main component.

  The exterior material is preferably a thin material from the viewpoint of reducing the weight of the nonaqueous electrolyte battery. For example, a metal resin composite film having a structure in which a metal foil is sandwiched between resin films is preferable. Specific examples of the metal foil include aluminum, iron, nickel, copper, stainless steel, titanium, gold, silver, and the like, as long as the foil does not have a pinhole. However, a lightweight and inexpensive aluminum foil is preferable. In addition, as the resin film on the battery outer side, a resin film having excellent piercing strength such as polyethylene terephthalate film and nylon film can be heat-sealed as the resin film on the battery inner side such as polyethylene film and nylon film. Preferred is a film having solvent resistance.

  EXAMPLES Hereinafter, although the detail of this invention is demonstrated by an Example, this invention is not limited to these.

Example 1
After mixing LiCoO ₂ as a positive electrode active material, acetylene black as a conductive agent and polyvinylidene fluoride as a binder in a weight ratio of 90: 5: 5, a positive electrode slurry of the above material was prepared using N-methylpyrrolidone as a solvent. The obtained slurry was applied to both surfaces of a 20 μm aluminum foil as a positive electrode current collector and dried to remove N-methylpyrrolidone. This positive electrode plate was pressed by a roll press to obtain a positive electrode.

  After mixing graphite having Lc of 100 nm or more as a negative electrode active material and SBR (styrene-butadiene rubber) and carboxymethyl cellulose as a binder in a weight ratio of 97: 1: 2, a negative electrode slurry of the above materials is prepared using purified water as a solvent. Produced. The obtained slurry was applied to both surfaces of an electrolytic copper foil having a rough surface roughness of 0.3 μmRa as a negative electrode current collector, and water was removed by drying. This negative electrode plate was pressed by a roll press to obtain a negative electrode.

The positive electrode and the negative electrode are laminated via a non-woven fabric made of polyethylene which is a separator for a nonaqueous electrolyte battery (10 g / m ² per unit area, thickness 100 μm), and subsequently an aluminum terminal (width 5 mm, thickness 100 μm) (positive electrode terminal) Was connected to the positive electrode current collector, and a nickel terminal (width 5 mm, thickness 100 μm) (negative electrode terminal) was connected to the negative electrode current collector by electric resistance welding. After this laminate is installed in an exterior material made of a cylindrical metal resin composite film (battery outer side resin, metal foil, and battery inner side resin are polyethylene terephthalate, aluminum foil, and modified polypropylene, respectively) The nonaqueous electrolyte was vacuum-injected (1333 Pa) into the exterior material, and further vacuum sealed (1333 Pa).

Here, as the non-aqueous electrolyte, 15 parts by weight of LiPF _6, 20 parts by weight of propylene carbonate, 30 parts by weight of dimethyl carbonate, 30 parts by weight of ethyl methyl carbonate, and an acrylic group having a structure represented by the above (Chemical Formula 1) are used. What mixed 1 weight part of disulfide derivative which has was used.

  Next, one charge / discharge was performed as an initial cycle process. Charging is performed at a temperature of 20 ° C., a charging current of 0.2 ItmA, a charging voltage of 4.2 V, a charging time of 7 hours, and a discharging is performed at a temperature of 20 ° C., a discharging current of 0.2 ItmA, a final voltage. The constant current discharge was 2.7V. The energy density of this battery was evaluated by the discharge capacity. Thus, the nonaqueous electrolyte battery of Example 1 was produced.

(Comparative Example 1)
As the non-aqueous electrolyte, 15 parts by weight of LiPF _6, 20 parts by weight of propylene carbonate, 30 parts by weight of dimethyl carbonate, and 30 parts by weight of ethyl methyl carbonate are mixed, and a disulfide derivative having an acrylic group is not mixed. A nonaqueous electrolyte battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the above was found.

(Comparative Example 2)
The non-aqueous electrolyte is the same as in the above examples except that a mixture of 15 parts by weight of LiPF _6, 20 parts by weight of ethylene carbonate, 30 parts by weight of dimethyl carbonate, and 30 parts by weight of ethyl methyl carbonate was used. A nonaqueous electrolyte battery of Comparative Example 2 was produced in the same manner as the water electrolyte battery.

(Comparative Example 3)
As the non-aqueous electrolyte, 15 parts by weight of LiPF _6, 20 parts by weight of propylene carbonate, 30 parts by weight of dimethyl carbonate, 30 parts by weight of ethyl methyl carbonate, 1 part by weight of diphenyl disulfide which is a disulfide compound having no acrylic group, A non-aqueous electrolyte battery of Comparative Example 1 was produced in the same manner as in Example 1 except that a mixture of was used.

  In the nonaqueous electrolyte battery of Example 1, an energy density equivalent to that of the nonaqueous electrolyte battery of Comparative Example 2 was obtained. On the other hand, in the nonaqueous electrolyte batteries of Comparative Examples 1 and 3, the batteries were swollen by the charging operation, and the discharge capacity was not obtained. That is, in these batteries, it is considered that the discharge could not be performed because the propylene carbonate used as the main solvent of the nonaqueous electrolyte was decomposed on the graphite.

  Using the nonaqueous electrolyte battery of Example and the nonaqueous electrolyte battery of Comparative Example 2, the high temperature storage characteristics at 60 ° C. were measured. At a temperature of 20 ° C., the battery was charged at a constant current and a constant voltage at a charging current of 0.2 ItmA, a charging voltage of 4.2 V, and a charging time of 7 hours, and then stored at 60 ° C. for 1 month. After storage, a constant current discharge with a discharge current of 0.2 ItmA and a final voltage of 2.7 V was performed at a temperature of 20 ° C., and the self-discharge rate was determined to be 15% in the battery of Example 1. In the battery of Comparative Example 2, it was 40%.

This is a disulfide derivative having an acrylic group of the non-aqueous electrolyte is considered to not be eluted at high temperatures to the negative electrode graphite surface polymerization the film (SEI) is formed.

  The state of the nonaqueous electrolyte used in Examples and Comparative Examples at −30 ° C. was observed. In the non-aqueous electrolyte used in Comparative Examples 1 and 2, precipitation like crystals was observed. On the other hand, no precipitation of crystals was observed in the electrolytic solutions used in Examples and Comparative Example 3. This is considered that the crystallization of the solvent was inhibited by containing propylene carbonate in the nonaqueous electrolyte.

According to the present invention, the charging of the propylene carbonate on the negative electrode during charging can be reliably suppressed and charging can be sufficiently performed, so that ionic conduction is ensured without the solidification of the electrolyte even at low temperatures. it can be used for the main solvent of propylene carbonate can, it is possible to further form a strong target film to withstand high temperatures, provide a nonaqueous electrolyte battery having both an excellent high-temperature storage characteristics and high energy density it can.

Claims (3)

A non-aqueous electrolyte battery comprising a positive electrode and a negative electrode, the negative electrode comprising a polymerization product of a disulfide derivative having an acrylic group derived from (Chemical Formula 1) .
The nonaqueous electrolyte battery according to claim 1, further comprising a nonaqueous electrolyte containing propylene carbonate. The nonaqueous electrolyte battery according to claim 1, wherein the negative electrode contains graphite as a negative electrode active material.