JP2016207557A - Lithium secondary battery - Google Patents

Abstract

In the prior art, it is desired to realize a high discharge capacity density of a negative electrode.
A lithium secondary battery of the present disclosure includes a positive electrode that occludes and releases lithium, a negative electrode that occludes and releases lithium, and a nonaqueous electrolytic solution including an electrolyte and an organic solvent, and the nonaqueous electrolyte includes the nonaqueous electrolyte. The electrolytic solution contains lithium oxide, and the content of the lithium oxide in the nonaqueous electrolytic solution is 0.1 M or more and 1.8 M or less with respect to the whole nonaqueous electrolytic solution. It is a battery. According to the present disclosure, a high negative electrode discharge capacity density can be realized.
[Selection] Figure 1

Description

  The present disclosure relates to a lithium secondary battery.

  Patent Document 1 discloses a non-aqueous solvent secondary battery using a carbon body as a negative electrode active material.

JP-A-8-203525

  In the prior art, it is desired to realize a high negative electrode discharge capacity density.

  A lithium secondary battery according to an embodiment of the present disclosure includes a positive electrode that occludes / releases lithium, a negative electrode that occludes / releases lithium, and a nonaqueous electrolytic solution including an electrolyte and an organic solvent, and the nonaqueous electrolysis The liquid contains lithium oxide, and the content of the lithium oxide in the non-aqueous electrolyte is 0.1 M or more and 1.8 M or less with respect to the whole non-aqueous electrolyte.

  According to the present disclosure, a high negative electrode discharge capacity density can be realized.

FIG. 1 is a diagram showing a schematic configuration of the lithium secondary battery in the first embodiment. FIG. 2 is a diagram showing the relationship between voltage and capacity density during initial charging and initial discharging. FIG. 3 is a diagram showing an X-ray diffraction pattern of the negative electrode after initial charging in Example 1.

  Hereinafter, embodiments of the present disclosure will be described in detail.

  However, this is presented by way of example, and the present disclosure is not limited thereby and is defined by the scope of the claims.

(Embodiment 1)
FIG. 1 is a diagram showing a schematic configuration of the lithium secondary battery in the first embodiment.

  A cylindrical battery shown in FIG. 1 includes a battery case 1, a sealing plate 2, an insulating packing 3, an electrode plate group 4, a positive electrode plate 5, a positive electrode lead 6, a negative electrode plate 7, and a negative electrode lead 8. The separator 9 and the insulating ring 10 are provided.

  The configuration of the battery shown in FIG. 1 is merely an example, and the battery of Embodiment 1 is not limited to this configuration.

  The nonaqueous electrolyte used in Embodiment 1 is composed of a nonaqueous solvent, a lithium salt dissolved in the solvent, and an additive.

As an additive, lithium oxide (Li ₂ O) is used.

  The added lithium oxide can be used in a state where it is completely dissolved in the non-aqueous solvent.

  Moreover, it can be used even in a state in which only a part of the added lithium oxide is dissolved and the rest is left as a solid in the non-aqueous electrolyte.

  That is, the lithium secondary battery according to Embodiment 1 includes a positive electrode that occludes and releases lithium, a negative electrode that occludes and releases lithium, and a nonaqueous electrolytic solution including an electrolyte and an organic solvent.

  At this time, the non-aqueous electrolyte contains lithium oxide. The content of lithium oxide in the non-aqueous electrolyte is 0.1 M or more and 1.8 M or less with respect to the whole non-aqueous electrolyte.

  According to the above configuration, in the non-aqueous electrolyte secondary battery, the use of the non-aqueous electrolyte containing lithium oxide causes controlled deposition of metallic lithium. For example, the theoretical capacity density of graphite is 372 mAh / A negative electrode discharge capacity density exceeding g can be achieved.

  And by making content of lithium oxide in a nonaqueous electrolyte into 0.1M or more and 1.8M or less with respect to the whole nonaqueous electrolyte, a nonaqueous electrolyte with a further large initial discharge capacity and favorable discharge characteristics A secondary battery can be obtained.

  By using the carbon material negative electrode in the nonaqueous electrolyte secondary battery, metallic lithium does not precipitate. For this reason, there is no problem of an internal short circuit due to dendrite. Furthermore, according to Embodiment 1, for example, a battery having a negative electrode with a capacity exceeding the theoretical capacity density of the carbon material can be realized without using a method of changing the charge end voltage condition.

  In the lithium secondary battery in the first embodiment, the content of lithium oxide in the non-aqueous electrolyte may be 1.8M with respect to the entire non-aqueous electrolyte.

  According to the above configuration, a lithium secondary battery having a larger initial discharge capacity can be realized.

  Moreover, in the lithium secondary battery in Embodiment 1, 0.2 to 4.5 weight% of lithium oxide may be contained in the non-aqueous electrolyte with respect to the total amount of the organic solvent.

For example, when 0.1 M to 1.8 M of Li ₂ O is added to an organic solvent of EC: EMC (= 1: 3) to which 1 M LiPF ₆ is added as an electrolyte, lithium oxide is 0.2 % By weight to 4.5% by weight.

  Further, in the lithium secondary battery in Embodiment 1, the organic solvent may include one or more compounds including a carbonate component.

  In the lithium secondary battery according to Embodiment 1, the organic solvent may include one or more compounds selected from the group consisting of ethylene carbonate and ethyl methyl carbonate.

Further, in the lithium secondary battery according to Embodiment 1, the nonaqueous electrolyte is 12.5 wt% to 13.2 wt% lithium hexafluorophosphate (LiPF _{6) with} respect to the total amount of the nonaqueous electrolyte. ) May be included.

For example, when 0.1 M to 1.8 M of Li ₂ O is added to an organic solvent of EC: EMC (= 1: 3) to which 1 M LiPF ₆ is added as an electrolyte, LiPF ₆ is 12.5 % By weight to 13.2% by weight.

  In the lithium secondary battery according to Embodiment 1, the negative electrode may include a negative electrode active material. At this time, the negative electrode active material may include one or more components selected from the group consisting of carbon materials, Si-based compounds, Sn-based compounds, lithium metals, lithium metal alloys, and transition metal oxides.

  In the lithium secondary battery according to Embodiment 1, the negative electrode active material may include a carbon material. At this time, the carbon material may be graphite.

  Nonaqueous solvents include cyclic carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), chain carbonates such as dipropyl carbonate (DPC), cyclic carboxylic acid esters such as γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane (DME), 1,2-diethoxyethane ( DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propyl nitrite Ril, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran Aprotic organic solvents such as derivatives, ethyl ether, 1,3-propane sultone, anisole, dimethyl sulfoxide, N-methylpyrrolidone and the like can be mentioned, and one or a combination of two or more of these can be used. Can do.

Examples of the lithium salt dissolved in these solvents include lithium hexafluorophosphate (LiPF ₆ ), LiClO ₄ , LiBF ₄ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF _{3 SO 2) 2, LiAsF 6} , LiB 10 Cl 10, lower aliphatic lithium carboxylate, LiCl, LiBr, LiI, chloroborane lithium, bis (1,2-benzene diolate (2 -) - O, O ') Lithium borate, bis (2,3-naphthalenedioleate (2-)-O, O ′) lithium borate, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, bis ( 5-Fluoro-2-olate-1-benzenesulfonic acid-O, O ′) borates such as lithium borate, bistet Trifluoromethane sulfonic acid imide lithium _{((CF 3 SO 2) 2} NLi), bispentafluoroethanesulfonyl imide lithium _{((C 2 F 5 SO 2} ) 2 NLi) can be exemplified imidates such as, these The electrolyte solution used can be used alone or in combination of two or more.

  Although the amount of the electrolyte added to the battery in Embodiment 1 is not particularly limited, a necessary amount can be used depending on the amount of the positive electrode material and the negative electrode material and the size of the battery. The amount of dissolution of the supporting electrolyte in the nonaqueous solvent is not particularly limited, but is preferably 0.2 to 2 mol / l. In particular, 0.5 to 1.5 mol / l is more preferable.

Examples of the negative electrode material include carbonaceous materials such as artificial graphite, graphite, non-graphitizable carbon, and graphitizable carbon, alloys of lithium with Al, Si, Pb, Sn, Zn, Cd, and the like, LiFe ₂ O ₃ , metal oxides such as WO ₂ , MoO ₂ , SiO, and CuO, lithium nitride such as Li ₃ N, metal lithium, lithium alloy, or a mixture thereof, or a composite may be used.

  The negative electrode conductive agent used in Embodiment 1 may be anything as long as it is an electron conductive material. For example, natural graphite (such as flake graphite), graphite such as artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, metal fiber, etc. The conductive fibers, metal powders such as carbon fluoride, copper and nickel, and organic conductive materials such as polyphenylene derivatives can be contained alone or as a mixture thereof. Among these conductive agents, artificial graphite, acetylene black, and carbon fiber are particularly preferable. Although the addition amount of a electrically conductive agent is not specifically limited, 1 to 50 weight% is preferable and especially 1 to 30 weight% is preferable. Moreover, since the negative electrode material in Embodiment 1 itself has electronic conductivity, it can function as a battery without adding a conductive agent.

  The negative electrode binder used in Embodiment 1 may be either a thermoplastic resin or a thermosetting resin. Preferred binders in Embodiment 1 are, for example, polypropylene, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, or (Na +) of the above materials An ionic cross-linked product, an ethylene-methacrylic acid copolymer or a (Na +) ionic cross-linked product of the material, an ethylene-methyl acrylate copolymer or a (Na +) ionic cross-linked product of the material, an ethylene-methyl methacrylate copolymer or The (Na +) ionic crosslinked body of the said material can be mentioned, These materials can be used individually or as a mixture. Among these materials, more preferable materials are styrene butadiene rubber, polyvinylidene fluoride, ethylene-acrylic acid copolymer, (Na +) ion-crosslinked product of the material, ethylene-methacrylic acid copolymer, or the material. A (Na +) ionic crosslinked product, an ethylene-methyl acrylate copolymer, or a (Na +) ionic crosslinked product of the material, an ethylene-methyl methacrylate copolymer, or a (Na +) ionic crosslinked product of the material.

  The negative electrode current collector used in Embodiment 1 may be anything as long as it is an electronic conductor that does not cause a chemical change in the constructed battery. For example, in addition to copper, stainless steel, nickel, titanium, carbon, conductive resin, etc., materials obtained by treating the surface of copper or stainless steel with carbon, nickel, or titanium are used. In particular, copper or a copper alloy is preferable. The surface of these materials can be oxidized and used. Further, it is desirable to make the current collector surface uneven by surface treatment. As the shape, a film, a sheet, a net, a punched product, a lath body, a porous body, a foamed body, a molded body of a fiber group, and the like are used in addition to the foil. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

As the positive electrode material used in Embodiment 1, metallic lithium or a lithium-containing compound can be used. For _{example, Li x CoO 2, Li x} MnO 2, Li x NiO 2, Li x Co y Ni 1-y O 2, Li x Co y M 1-y O z, Li x Ni 1-y M y O z, _{Li x Mn 2 O 4, Li} x Mn 2-y M y O 4 ( where, M = Na, Mg, Sc , Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb , B) (where 0 <x ≦ 1.2, 0 ≦ y ≦ 0.9, 2.0 ≦ z ≦ 2.3). Here, said x value is a value before the start of charging / discharging, and it increases / decreases by charging / discharging. However, it is also possible to use other positive electrode active materials such as transition metal chalcogenides, lithium compounds of vanadium oxide, lithium compounds of niobium oxide, conjugated polymers using organic conductive materials, and chevrel phase compounds. It is also possible to use a mixture of a plurality of different positive electrode active materials. The average particle diameter of the positive electrode active material particles is not particularly limited, but is preferably 1 to 30 μm.

  The conductive agent for positive electrode used in Embodiment 1 may be anything as long as it is an electron conductive material that does not cause a chemical change at the charge / discharge potential of the positive electrode material used. For example, natural graphite (such as flake graphite), graphite such as artificial graphite, carbon black such as ketjen black, acetylene black, channel black, furnace black, lamp black, thermal black, carbon fiber, metal fiber, etc. Conductive fibers, metal powders such as carbon fluoride, copper, nickel, aluminum and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide or polyphenylene derivatives An organic conductive material or the like can be contained alone or as a mixture thereof. Among these conductive agents, artificial graphite, acetylene black, and nickel powder are particularly preferable. Although the addition amount of a electrically conductive agent is not specifically limited, 1 to 50 weight% is preferable and especially 1 to 30 weight% is preferable. In the case of carbon or graphite, 2 to 15% by weight is particularly preferable.

  The positive electrode binder used in Embodiment 1 may be either a thermoplastic resin or a thermosetting resin. Preferred binders in Embodiment 1 are, for example, polypropylene, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene. Copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene Copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene Chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or (Na +) ion cross-linked product of the material, ethylene-methacrylic acid copolymer or (Na +) ion cross-linked product of the material, ethylene-methyl acrylate copolymer, or (Na +) ion cross-linked product of the material, ethylene-methacrylic acid Examples thereof include an acid methyl copolymer or a (Na +) ion crosslinked product of the above material. Particularly preferred among these are polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

  The positive electrode current collector used in Embodiment 1 may be any electronic conductor that does not cause a chemical change at the charge / discharge potential of the positive electrode material used. For example, in addition to aluminum, stainless steel, titanium, carbon, conductive resin, and the like, materials obtained by treating the surface of aluminum or stainless steel with carbon or titanium are used. In particular, aluminum or an aluminum alloy is preferable. The surface of these materials can be oxidized and used. Further, it is desirable to make the current collector surface uneven by surface treatment. As the shape, a film, a sheet, a net, a punched product, a lath body, a porous body, a foamed body, a fiber group, a non-woven body shaped body, and the like are used in addition to the foil. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

  In addition to the conductive agent and the binder, a filler, a dispersant, an ion conducting agent, a pressure enhancer, and other various additives can be used for the electrode mixture. Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constructed battery. Usually, olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0 to 30 weight% is preferable.

  In the configuration of the negative electrode plate and the positive electrode plate in the first embodiment, it is preferable that the negative electrode mixture surface is present at least on the surface facing the positive electrode mixture surface.

  As the separator used in Embodiment 1, an insulating microporous thin film having a large ion permeability and a predetermined mechanical strength is used. Moreover, it is preferable to have a function of closing the hole at a certain temperature or higher and increasing the resistance. A sheet, a nonwoven fabric, or a woven fabric made of an olefin polymer such as polypropylene or polyethylene, or glass fiber, or the like, is used because of its resistance to organic solvents and hydrophobicity. The pore diameter of the separator is desirably in a range in which the positive and negative electrode materials, the binder, and the conductive agent detached from the electrode sheet do not permeate, for example, 0.01 to 1 μm is desirable. The thickness of the separator is generally 10 to 300 μm. The porosity is determined according to the permeability of the electrons and ions, the material, and the film pressure, but is generally preferably 30 to 80%.

  The shape of the battery can be applied to any of a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, a square type, a large type used for an electric vehicle, and the like.

  Hereinafter, examples and comparative examples of the present disclosure will be described.

  However, the following embodiment is merely one embodiment of the present disclosure, and the present disclosure is not limited to the following embodiment.

<Example 1>
Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 1: 3, and LiPF ₆ is added so that the concentration of lithium hexafluorophosphate (LiPF ₆ ) is 1.0 M. Manufactured. Then, was produced added to the electrolyte solution so that the Li 2 _O to 1.8M to the mixed solution. However, all of Li ₂ O was not dissolved and partially remained as a solid.

  Artificial graphite and a binder were mixed in a 98: 2 weight ratio to produce a negative electrode active material slurry. The negative electrode active material slurry was uniformly applied onto a 15 μm thick copper current collector, dried, and then rolled to produce a negative electrode.

  In order to collect current on a part of the back surface of the metal lithium foil having a thickness of 30 μm, a copper mesh was pressed and adhered to produce a counter electrode.

  A lithium secondary battery was manufactured through a separator between the negative electrode and the counter electrode.

<Comparative Example 1>
A lithium secondary battery was produced by the same method as in Example 1 except that the step of adding Li ₂ O was omitted in the production of the electrolytic solution.

<Evaluation Example 1>
In order to evaluate the initial charge capacity density and the initial discharge capacity density for the lithium secondary batteries of Example 1 and Comparative Example 1 manufactured as described above, experiments were performed by the following methods. The batteries manufactured in Example 1 and Comparative Example 1 were charged at a charge current density of 18.6 mA / g and a charge end potential of 0 Vvs. The battery was charged at a constant current to Li / Li ⁺ and then rested for 20 minutes. Thereafter, the discharge end potential was 0.5 Vvs. At a discharge current density of 18.6 mA / g. The battery was discharged at a constant current to Li / Li ⁺ and the discharge capacity density was measured.

  The results of Example 1 and Comparative Example 1 are shown in Table 2 and FIG.

  FIG. 2 is a diagram showing the relationship between voltage and capacity density during initial charging and initial discharging.

  The initial discharge capacity density of Comparative Example 1 was 353 mAh / g, whereas in Example 1, the initial discharge capacity density was 413 mAh / g. Although the discharge capacity of Comparative Example 1 did not exceed the theoretical capacity density of artificial graphite, 372 mAh / g, in Example 1, the discharge capacity density exceeded the theoretical capacity density of artificial graphite.

<Evaluation Example 2>
In order to evaluate the production of metallic lithium during charging of the manufactured lithium secondary battery of Example 1, an experiment was conducted by the following method. The battery manufactured in Example 1 was charged at a charge current density of 18.6 mA / g and a charge end potential of 0 Vvs. After charging to Li / Li ⁺ with a constant current, the battery was rested for 20 minutes, then the battery was disassembled, the negative electrode was taken out, washed with EMC for 20 minutes, and then X-ray diffraction was measured. Irradiation X-rays were Cu-Kα rays, and the diffraction X-ray intensity distribution was measured in the angle range of 10 ° to 80 ° by the 2θ-θ method.

  The results of Evaluation Example 2 are shown in FIG.

  FIG. 3 is a diagram showing an X-ray diffraction pattern of the negative electrode after initial charging in Example 1.

Metallic lithium was detected at a diffraction angle of about 37 degrees. In addition, LiC ₆ was only detected as a carbon-derived compound, and it was found that LiC ₆ and metallic lithium coexist in the mixture layer of the electrode after charging.

As a result of measuring the negative electrode of Comparative Example 1 in which Li ₂ O was not added by the same method as in Evaluation Example 2, LiC ₆ was detected, but metallic lithium was not detected.

By adding Li ₂ O, a small amount of metallic lithium can be generated after LiC ₆ is formed during charging, and it is speculated that the metallic lithium covers the capacity exceeding the theoretical capacity during discharging. .

  The preferred embodiments of the present disclosure have been described in detail above, but the scope of the present disclosure is not limited thereto, and various modifications of those skilled in the art using the basic concept of the present disclosure defined in the claims. And improvements are also within the scope of this disclosure.

  The lithium secondary battery of the present disclosure can be used for a portable information terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle, an electric vehicle, a hybrid electric vehicle, and the like.

DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode plate group 5 Positive electrode plate 6 Positive electrode lead 7 Negative electrode plate 8 Negative electrode lead 9 Separator 10 Insulation ring

Claims (8)

A positive electrode that occludes and releases lithium;
A negative electrode that occludes and releases lithium;
A non-aqueous electrolyte containing an electrolyte and an organic solvent;
With
The non-aqueous electrolyte contains lithium oxide,
The lithium oxide content in the non-aqueous electrolyte is 0.1 M or more and 1.8 M or less with respect to the whole non-aqueous electrolyte.
Lithium secondary battery. The lithium oxide content in the non-aqueous electrolyte is 1.8M with respect to the whole non-aqueous electrolyte.
The lithium secondary battery according to claim 1. The lithium oxide is contained in the nonaqueous electrolytic solution in an amount of 0.2 wt% to 4.5 wt% based on the total amount of the organic solvent.
The lithium secondary battery according to claim 1 or 2. The organic solvent includes one or more compounds including a carbonate component,
The lithium secondary battery according to any one of claims 1 to 3. The organic solvent includes one or more compounds selected from the group consisting of ethylene carbonate and ethyl methyl carbonate.
The lithium secondary battery according to claim 1. The non-aqueous electrolyte contains 12.5 wt% to 13.2 wt% lithium hexafluorophosphate with respect to the total amount of the non-aqueous electrolyte.
The lithium secondary battery according to any one of claims 1 to 5. The negative electrode includes a negative electrode active material,
The negative electrode active material includes one or more components selected from the group consisting of carbon materials, Si-based compounds, Sn-based compounds, lithium metals, lithium metal alloys, and transition metal oxides.
The lithium secondary battery according to claim 1. The negative electrode active material includes a carbon material,
The carbon material is graphite;
The lithium secondary battery according to claim 7.