JP2016207447A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having high durability and low internal resistance.SOLUTION: A nonaqueous electrolyte secondary battery 1 of the present invention includes a positive electrode 2 including a positive electrode active material, a negative electrode 3, and a nonaqueous electrolyte 4. The positive electrode active material includes a compound with an olivine structure having a potential of 4.0 V or less. The nonaqueous electrolyte 4 includes a first additive and a second additive. The nonaqueous electrolyte secondary battery 1 of the present invention exhibits an effect to achieve a secondary battery excellent in durability and conductivity.SELECTED DRAWING: None

Description

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

  With the spread of notebook computers, mobile phones, digital cameras, etc., the demand for secondary batteries for driving these small electronic devices is increasing. And since these electronic devices can be increased in capacity, the use of non-aqueous electrolyte secondary batteries (especially lithium ion secondary batteries) is being promoted.

  A nonaqueous electrolyte secondary battery is usually laminated with a separator interposed between a positive electrode plate and a negative electrode plate to form an electrode body, and is housed in a battery case together with the nonaqueous electrolyte solution. The electrode plate is manufactured by applying and drying a paste containing an electrode active material on the surface of a current collector made of a metal plate (metal foil) and molding the paste into a predetermined shape.

  Non-aqueous electrolyte secondary batteries are required to improve battery performance, and not only active materials but also non-aqueous electrolytes (non-aqueous electrolytes) are being studied as means for achieving this object. For example, a technique is known in which an additive that enhances durability is added to a non-aqueous electrolyte (non-aqueous electrolyte). This additive is oxidatively decomposed on the surface of the positive electrode (positive electrode active material) and forms a decomposition film on the surface of the negative electrode (negative electrode active material), thereby suppressing the decomposition of the active material and improving the durability.

However, the decomposed film formed on the negative electrode is a film having a high resistance, leading to an increase in internal resistance (a decrease in battery performance) in the secondary battery. In addition, this additive is oxidatively decomposed on the positive electrode, making it difficult to design the addition amount.
For such problems, for example, Patent Documents 1 and 2 describe a technique for suppressing the formation of a decomposed film by forming a low-resistance film on the negative electrode surface.

  Patent Document 1 discloses a non-aqueous electrolyte secondary battery including a positive electrode and a negative electrode together with a non-aqueous electrolyte, wherein the thickness of one side of the electrode active material layer is 40 μm or more, and the non-aqueous electrolyte is a sulfone. Non-aqueous electrolyte secondary batteries containing acid salts or sulfonimide salts are described.

  Patent Document 2 describes that an electrolyte having chemical structural characteristics is used as an additive in an electrolyte for a non-aqueous electrolyte battery. This electrolyte exhibits the effect of improving the cycle characteristics of the nonaqueous electrolyte battery.

JP 2009-302022 A JP 2010-257616 A

  However, although the additives described in Patent Documents 1 and 2 can reduce the resistance on the surface of the negative electrode, there is a problem that durability is lowered because a decomposition film is not formed.

  In addition, in the non-aqueous electrolyte secondary battery described in Patent Document 1, a sulfonate and a sulfonimide salt are added as additives, and a film formed therefrom is formed on the negative electrode surface. Due to its composition, this film has a problem that the lithium conductivity is small, and as a result, the effect of reducing the resistance is small. For this reason, when vinylene carbonate (VC) is added in a large amount as an additive for enhancing durability, the effect of suppressing an increase in resistance cannot be sufficiently obtained.

Moreover, the additive described in Patent Document 2 has a composition containing phosphorus (P), and has a negative electrode as compared with an additive having a composition containing sulfur (S) (additive of Patent Document 1). The driving force taken into the surface coating was small. For this reason, as in the case of Patent Document 1, when a large amount of VC is added, the effect of suppressing an increase in resistance cannot be sufficiently obtained.
This invention is made | formed in view of the said situation, and makes it a subject to provide the nonaqueous electrolyte secondary battery which has high durability and low internal resistance.

  The non-aqueous electrolyte secondary battery of the present invention that solves the above problems is a non-aqueous electrolyte secondary battery having a positive electrode having a positive electrode active material, a negative electrode, and a non-aqueous electrolyte solution, the positive electrode active material Has a olivine structure compound having a potential of 4.0 V or less, and the non-aqueous electrolyte comprises a first additive comprising a compound of the following formula (1) and a second additive comprising a compound of the following formula (2) And an additive.

  The non-aqueous electrolyte of the non-aqueous electrolyte secondary battery of the present invention has two additives, a first additive and a second additive.

The first additive exhibits the effect of increasing the durability of the secondary battery. The second additive generates a film having excellent conductivity on the surface of the negative electrode. As apparent from the formula, the second additive has a sulfonyl group (referred to as a sulfone moiety) and Li ions (referred to as a Li ion moiety) in its structure. For this reason, the film produced | generated on the negative electrode surface from the 2nd additive turns into a film containing two site | parts, a sulfone site | part and a Li ion site | part. These two portions exhibit conductivity (suppress the increase in resistance) and conduct Li ions (suppress the decrease in Li ion conductivity).
Thus, the non-aqueous electrolyte used in the present invention is one in which an increase in internal resistance and a decrease in Li ion conductivity are suppressed.

In addition, the nonaqueous electrolyte secondary battery of the present invention has an olivine structure compound having a potential of 4.0 V or less as a positive electrode active material. This compound has a plateau region when the potential change during discharge is measured. And since there is almost no potential change in the plateau region, there is no charge / discharge unevenness. That is, oxidative decomposition of the additive due to charge / discharge unevenness is suppressed. As a result, the effect of the non-aqueous electrolyte can be further exhibited.
As a result, in the nonaqueous electrolyte secondary battery of the present invention, an increase in internal resistance and a decrease in Li ion conductivity are reliably suppressed.

  In the non-aqueous electrolyte secondary battery of the present invention, the non-aqueous electrolyte preferably further includes a third additive composed of at least one of the following formula (3) and the following formula (4). . The third additive exhibits the effect of improving the durability of the secondary battery together with the first additive.

  In the non-aqueous electrolyte secondary battery of the present invention, the non-aqueous electrolyte includes a total of the content ratio of the first additive and the content ratio of the third additive, and the content ratio of the second additive. The ratio is preferably 0.2 or more and 3.0 or less. When the content ratio falls within this range, the above-described effect of the nonaqueous electrolytic solution can be exhibited.

1 is a diagram schematically illustrating a configuration of a lithium ion secondary battery 1 according to Embodiment 1. FIG. 4 is a perspective view showing a configuration of a lithium ion secondary battery 1 of Embodiment 2. FIG. 4 is a cross-sectional view showing a configuration of a lithium ion secondary battery 1 of Embodiment 2. FIG. It is the graph which plotted the relationship between the capacity | capacitance maintenance factor and resistance increase rate of each Example.

  Hereinafter, it demonstrates more concretely using embodiment which applied the nonaqueous electrolyte secondary battery of this invention to the lithium ion secondary battery.

[Embodiment 1]
The lithium ion secondary battery of this embodiment is a lithium ion secondary battery 1 whose configuration is schematically shown in FIG. The secondary battery 1 includes a positive electrode 2, a negative electrode 3, and a nonaqueous electrolyte solution 4.

[Positive electrode]
The positive electrode 2 has a positive electrode active material. The positive electrode 2 has a positive electrode active material layer 21 containing a positive electrode active material on the surface of the positive electrode current collector 20. The positive electrode active material layer 21 is formed by applying and drying a positive electrode mixture obtained by mixing a positive electrode active material, a conductive material, and a binder on the surface of the positive electrode current collector 20. The positive electrode mixture is made into a paste (slurry) with an appropriate solvent.

The positive electrode active material has a compound having an olivine structure with a potential of 4.0 V or less. Note that the potential of the positive electrode active material indicates an average potential. A compound having an olivine structure (sometimes referred to as a polyanion structure) has a plateau region when a potential change during charge / discharge is measured (capacitance-potential relationship). Almost no potential change occurs in the plateau region where the potential changes. This indicates that charging / discharging unevenness due to potential change does not occur. That is, oxidative decomposition of the additive due to charge / discharge unevenness is suppressed. It is possible to prevent the content of the additive from changing due to decomposition, and to adjust the content of the additive.
When the potential is 4.0 V or less, the positive electrode potential does not become a high potential exceeding 4.0 V. That is, decomposition of the additive (first additive) generated at a high potential is suppressed.

A specific configuration (composition) is not limited as long as the positive electrode active material has a compound having an olivine structure with a potential of 4.0 V or less.
The compounds of olivine structure (positive electrode active material), for example, be a _{Li α M β X η O 4} -γ Z γ. (M: one or more selected from M: Mn, Co, Ni, Fe, Cu, Cr, Mg, Ca, Zn, Ti, one or more selected from X: P, As, Si, Mo, Ge, Z : One or more selected from Al, Mg, Ca, Zn, Ti can be optionally contained, 0 <α ≦ 2.0, 0 ≦ β <1.5, 1 ≦ η ≦ 1.5, 0 ≦ γ ≦ 1.5) Of these, LiMnPO ₄ and LiFePO ₄ are more preferable.
The positive electrode active material may be formed from those having two or more different compositions within the range shown in the above composition formula.

  The positive electrode active material may be formed only from a compound having an olivine structure of 4.0 V or less, or may be mixed with another compound. In the case where the positive electrode active material is mixed with a compound having an olivine structure of 4.0 V or less and another compound, a compound having an olivine structure of 4.0 V or less is preferably contained as a main component. Here, the main component refers to a component having the highest content ratio, and is preferably a component that is included at 50 mass% or more.

  Another positive electrode active material is a material used as a positive electrode active material in a conventional lithium ion secondary battery. Examples of the positive electrode active material in the conventional lithium ion secondary battery include various oxides, sulfides, lithium-containing oxides, and conductive polymers. A lithium-transition metal composite oxide is preferable.

  Here, the other positive electrode active material may have either an olivine structure or a structure other than the olivine structure. In this case, a positive electrode active material having a potential of 4.0 V or less is preferable.

  The conductive material ensures the electrical conductivity of the positive electrode 2. Examples of the conductive material include, but are not limited to, graphite fine particles, acetylene black, ketjen black, carbon black such as carbon nanofiber, and amorphous carbon fine particles such as needle coke.

  The binder of the positive electrode mixture binds the positive electrode active material particles and the conductive material. As the binder, for example, PVDF, EPDM, SBR, NBR, fluororubber and the like can be used, but are not limited thereto.

  As the solvent for the positive electrode mixture, an organic solvent that dissolves the binder is usually used. Examples thereof include, but are not limited to, NMP, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. In some cases, a positive electrode active material is slurried with PTFE or the like by adding a dispersant, a thickener, or the like to water.

  As the positive electrode current collector 20, for example, a material obtained by processing a metal such as aluminum or stainless steel, for example, a foil processed into a plate shape, a net, a punched metal, a foam metal, or the like can be used, but is not limited thereto.

[Negative electrode]
The negative electrode 3 contains a negative electrode active material. The negative electrode 3 has a negative electrode active material layer 31 containing a negative electrode active material on the surface of the negative electrode current collector 30. The negative electrode active material layer 31 is formed by applying and drying a negative electrode mixture obtained by mixing a negative electrode active material and a binder on the surface of the negative electrode current collector 30. The negative electrode mixture is in the form of a paste (slurry) with an appropriate solvent.

  A conventional negative electrode active material can be used as the negative electrode active material of the negative electrode 3. A negative electrode active material containing at least one element of Sn, Si, Sb, Ge, and C can be given. Of these negative electrode active materials, C is preferably a carbon material capable of occluding and desorbing electrolyte ions of a lithium ion secondary battery (having Li storage ability), and more preferably graphite or graphite. .

  Of these negative electrode active materials, Sn, Sb, and Ge are alloy materials that have a large volume change. These negative electrode active materials may form an alloy with another metal such as Ti—Si, Ag—Sn, Sn—Sb, Ag—Ge, Cu—Sn, and Ni—Sn.

  As the conductive material of the negative electrode 3, a carbon material, metal powder, a conductive polymer, or the like can be used. From the viewpoint of conductivity and stability, it is preferable to use a carbon material such as acetylene black, ketjen black, or carbon black.

As the binder of the negative electrode 3, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluororesin copolymer (tetrafluoroethylene / hexafluoropropylene copolymer) SBR, acrylic rubber, fluorine And rubbers, polyvinyl alcohol (PVA), styrene / maleic acid resin, polyacrylate, carboxymethylcellulose (CMC), and the like.
Examples of the solvent for the mixture of the negative electrode 3 include organic solvents such as N-methyl-2-pyrrolidone (NMP), water, and the like.

  As the negative electrode current collector 30, a conventional current collector can be used, which is obtained by processing a metal such as copper, stainless steel, titanium, or nickel, for example, a foil processed into a plate shape, a net, a punched metal, a foam metal, or the like However, it is not limited to these.

[Non-aqueous electrolyte]
The nonaqueous electrolytic solution 4 has a first additive made of the compound of the above formula (1) and a second additive made of the compound of the formula (2). As a configuration other than these additives, those having a known material configuration can be used, and it is preferable that the supporting salt is dissolved in an organic solvent.

  A 1st additive consists of a compound of said (1) Formula. This first additive increases the durability of the non-aqueous electrolyte 4. The durability of the non-aqueous electrolyte 4 indicates a characteristic that can maintain the battery performance of the secondary battery 1. Specifically, the battery capacity of the secondary battery 1 is maintained, and a decrease in durability indicates a decrease in battery capacity maintenance rate (discharge capacity maintenance rate).

The first additive forms a film by reacting on the surfaces of the positive electrode 2 and the negative electrode 3 of the secondary battery 1.
The specific composition of the first additive is not limited as long as it is a compound of the formula (1). For example, the compound of the following formula (5) can be mentioned.

  Of these compounds, the first additive is preferably vinylene carbonate or fluoroethylene carbonate.

  A 2nd additive consists of a compound of said (2) Formula. This second additive increases the conductivity (ionic conductivity) in the non-aqueous electrolyte 4. By increasing the conductivity (ionic conductivity) by the second additive, an increase in the resistance of the nonaqueous electrolyte solution 4 can be suppressed even if an increase in the resistance due to the first additive occurs. Specifically, the first additive is polymerized on the surface of the negative electrode 3 of the secondary battery 1 to form a film. At this time, the second additive is present on the surface of the negative electrode 3 and prevents the negative electrode 3 from being completely covered. That is, the conductivity (ionic conductivity) of the negative electrode 3 is ensured by preventing the second additive from completely covering the surface of the negative electrode 3 with the polymer film of the first additive. That is, an increase in the internal resistance of the secondary battery 1 is suppressed.

As shown in the formula (2), the second additive has a sulfonyl group represented by —SO ₂ — and a lithium salt bond portion represented by Li ⁺ B ⁻ and Li ⁺ P ⁻ . The sulfonyl group is taken into the polymer film when the first additive forms the polymer film, and fixes the second additive to the polymer film. In addition, the second additive has a lithium salt bond and has conductivity (ionic conductivity). Even if the second additive is fixed to the polymer film of the first additive, the lithium salt bonding portion is maintained, and thus the second additive has conductivity (ionic conductivity). As a result, in the nonaqueous electrolytic solution 4 of this embodiment, high durability and conductivity are maintained.
The specific composition of the second additive is not limited as long as it is a compound of the formula (2). For example, the compound of following (6) Formula can be mentioned.

  It is preferable that the nonaqueous electrolytic solution 4 of this embodiment further has a third additive composed of at least one of the compound of the formula (3) and the compound of the formula (4). The 3rd additive comes to be able to exhibit more the effect acquired by the 1st additive.

  The specific composition of the third additive is not limited as long as it is a compound represented by formula (3) or formula (4). For example, the compound of formula (3) can be exemplified by the compound of formula (7) below, and the compound of formula (4) can be exemplified by the compound of formula (8) below.

  In the nonaqueous electrolytic solution 4 of the present embodiment, the content ratio of the first additive is not limited, but when the mass of the entire nonaqueous electrolytic solution 4 is 100 mass%, 0.1 to 5. It is preferably 0 mass%. When the content ratio of the first additive is within this range, the above-described effect of improving the durability is exhibited. When the content ratio is less than this range, the content ratio of the first additive is decreased, and the durability is lowered. Further, when the content ratio exceeds this range, the amount of reaction on the electrode surface increases and the resistance increases. A more preferable content rate is 0.5-4.0 mass%, and a still more preferable content rate is 1.0-3.5 mass%.

  In the nonaqueous electrolytic solution 4 of the present embodiment, the content ratio of the second additive is not limited, but when the mass of the entire nonaqueous electrolytic solution 4 is 100 mass%, 0.1 to 2. It is preferably 0 mass%. When the content ratio of the second additive is within this range, the above-described effect of improving conductivity is exhibited. When the content ratio is less than this range, the content ratio of the second additive is decreased, and the effect of improving conductivity cannot be obtained. Moreover, when a content rate becomes large exceeding this range, durability will fall by suppressing the film formation by a 1st additive. A more preferable content rate is 0.2-1.5 mass%, and a still more preferable content rate is 0.5-1.0 mass%.

  In the non-aqueous electrolyte solution 4 of the present embodiment, the content ratio of the third additive is not limited, but when the mass of the entire non-aqueous electrolyte solution 4 is 100 mass%, 0.1 to 1. It is preferable that it is 5 mass%. When the content ratio of the third additive is within this range, the effect of improving the durability described above is exhibited. When the content ratio is less than this range, the content ratio of the third additive is decreased, and the durability is lowered. Further, when the content ratio exceeds this range, the amount of reaction on the electrode surface increases and the resistance increases. A more preferable content rate is 0.2-1.0 mass%, and a still more preferable content rate is 0.3-0.7 mass%.

  In the nonaqueous electrolytic solution 4 of this embodiment, the ratio of the total content ratio of the first additive and the third additive content ratio to the content ratio of the second additive is 0.2 or more and 3. It is preferably 0 or less.

  When this ratio is in the range of 0.2 to 3.0, in the secondary battery 1 of this embodiment, the nonaqueous electrolyte solution 4 can be maintained having high durability and conductivity. When the value of the ratio is less than 0.2, the content ratio of the first additive (third additive) decreases, and the durability decreases. On the other hand, when the ratio value exceeds 3.0, the content ratio of the second additive decreases, the conductivity decreases, and the internal resistance of the secondary battery 1 increases. A more preferable ratio value is 0.5 to 2.5, and a further preferable ratio value is 1.0 to 2.0.

It is preferable that the nonaqueous electrolytic solution 4 of this embodiment further has an oxalate complex containing boron. The oxalate complex improves battery characteristics (durability and conductivity). The effect of improving the battery characteristics is not as high as the effect obtained by the first additive (third additive) and the second additive.
Examples of the oxalate complex include compounds of the following formula (9).

  In the nonaqueous electrolytic solution 4 of the present embodiment, the content ratio of the oxalate complex is not limited, but is 0.1 to 1.5 mass% when the mass of the entire nonaqueous electrolytic solution 4 is 100 mass%. Preferably there is. When the content of the oxalate complex is within this range, the above-described effects on durability and conductivity are exhibited. When the content ratio is less than this range, the effect of addition cannot be obtained. Further, when the content ratio exceeds this range, gas is generated in addition to an increase in resistance due to an increase in the amount of decomposition. A more preferable content rate is 0.1-1.2 mass%, and a still more preferable content rate is 0.3-1.0 mass%.

The kind of the supporting salt of the nonaqueous electrolytic solution 4 is not particularly limited. For example, an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , derivatives of these inorganic salts, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₃ and LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ) It is preferably at least one of organic salts and derivatives of these organic salts. These supporting salts can further improve the battery performance, and can maintain the battery performance higher even in a temperature range other than room temperature. The concentration of the supporting salt is not particularly limited, and it is preferable to select appropriately in consideration of the types of the supporting salt and the organic solvent.

  The organic solvent (non-aqueous solvent) in which the supporting salt dissolves is not particularly limited as long as it is an organic solvent used in ordinary non-aqueous electrolytes. For example, carbonates, halogenated hydrocarbons, ethers, ketones , Nitriles, lactones, oxolane compounds and the like can be used. In particular, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate and the like, and mixed solvents thereof are preferable. Among these organic solvents, the use of one or more non-aqueous solvents selected from the group consisting of carbonates and ethers is particularly excellent in the solubility, dielectric constant and viscosity of the supporting salt, and the lithium ion secondary battery 1 is preferable because the charge / discharge efficiency of No. 1 increases.

[Other configurations]
The secondary battery 1 of the present embodiment includes a battery case in which the positive electrode 2 and the negative electrode 3 are placed together with the nonaqueous electrolyte solution 4 with the separator 5 interposed therebetween with the positive electrode active material layer 21 and the negative electrode active material layer 31 facing each other. 6 to accommodate.

(Separator)
The separator 5 serves to electrically insulate the positive electrode 2 and the negative electrode 3 and hold the nonaqueous electrolyte solution 4. For example, the separator 5 is preferably a porous synthetic resin film, particularly a porous film of a polyolefin-based polymer (polyethylene, polypropylene).

(Battery case)
The battery case 6 accommodates (encloses) the positive electrode 2 and the negative electrode 3 together with the nonaqueous electrolyte solution 4 with the separator 5 interposed therebetween.
The battery case 6 is made of a material that inhibits moisture permeation between the inside and the outside. An example of such a material is a material having a metal layer.

[Effect of Embodiment 1]
(First effect)
The secondary battery 1 of this embodiment includes a compound having an olivine structure with a potential of 4.0 V or less as a positive electrode active material. In this positive electrode active material, generation of decomposition of the additive (first additive) can be suppressed due to the plateau region having a high potential.

In the secondary battery 1 of this embodiment, the non-aqueous electrolyte 4 contains the first additive and the second additive. The first additive improves the durability of the battery. The second additive increases conductivity.
As a result, the secondary battery 1 of this embodiment exhibits the effect of becoming a battery excellent in durability and conductivity.

(Second effect)
In the secondary battery 1 of the present embodiment, the non-aqueous electrolyte 4 further has a third additive. The 3rd additive comes to be able to exhibit more the effect acquired by the 1st additive. As a result, the secondary battery 1 of the present embodiment exhibits the effect of becoming a battery that is more excellent in durability and conductivity.

(Third effect)
In the secondary battery 1 of this embodiment, the ratio between the content ratio (total) of the first additive (and the third additive) and the content ratio of the second additive is 0.2 or more and 3.0. It is as follows. With this configuration, the secondary battery 1 of the present embodiment exhibits the effect of becoming a battery that is further excellent in durability and conductivity.

(Fourth effect)
In the secondary battery 1 of the present embodiment, the first additive is vinylene carbonate or fluoroethylene carbonate. According to this structure, the effect which improves the durability of the battery by a 1st additive can be exhibited more.

(Fifth effect)
The secondary battery 1 of this embodiment further has an oxalate complex in which the nonaqueous electrolytic solution 4 contains boron. According to this structure, the effect which improves battery characteristics (durability and electroconductivity) can be exhibited more.

[Embodiment 2]
In this embodiment, the secondary battery 1 of the first embodiment is applied to a laminate type battery, and the configuration of the positive electrode 2, the negative electrode 3, the nonaqueous electrolyte solution 4 and the like is the same as that of the first embodiment. The configuration of the secondary battery 1 of this embodiment is shown in FIGS. FIG. 2 is a perspective view of the secondary battery 1, and FIG. 3 is a cross-sectional view taken along the line III-III in FIG.

  The secondary battery 1 of this embodiment is configured by housing (enclosing) a positive electrode 2 and a negative electrode 3 in a battery case 6 made of a laminate case. Note that the structure not particularly limited in this embodiment is the same as that in the first embodiment.

  The positive electrode 2 is formed by forming a positive electrode active material layer 21 on the surface (both sides) of a substantially square positive electrode current collector 20. The positive electrode 2 has an uncoated portion 22 where a positive electrode current collector 20 is exposed (a positive electrode active material layer 21 is not formed) on one side of a square shape.

  The negative electrode 3 is formed by forming a negative electrode active material layer 31 on the surface (both surfaces) of a substantially square negative electrode current collector 30. The negative electrode 3 has an uncoated portion 32 where the negative electrode current collector 30 is exposed (the negative electrode active material layer 31 is not formed) on one side of the square shape.

In the negative electrode 3, the negative electrode active material layer 31 is formed wider than the positive electrode active material layer 21 of the positive electrode 2. When the negative electrode active material layer 31 of the negative electrode 3 is stacked on the positive electrode active material layer 21, the positive electrode active material layer 21 is formed in a size that can be completely covered without being exposed.
The positive electrode 2 and the negative electrode 3 are housed (enclosed) in a battery case 6 formed of a laminate film together with the non-aqueous electrolyte 4 in a state of being laminated via a separator 5.
The separator 5 is formed with a larger area than the negative electrode active material layer 31.

  The positive electrode 2 and the negative electrode 3 are stacked in a state where the centers of the positive electrode active material layer 21 and the negative electrode active material layer 31 overlap with the separator 5 interposed therebetween. At this time, the uncoated portion 22 of the positive electrode 2 and the uncoated portion 32 of the negative electrode 3 are arranged in opposite directions (directions facing away from each other).

(Battery case)
The battery case 6 is formed from a laminate film 60. The laminate film includes a plastic resin layer 601 / metal foil 602 / plastic resin layer 603 in this order. The battery case 6 is bonded by pressing the laminate film 60 bent in advance into a predetermined shape against another laminate film or the like in a state where the plastic resin layers 601 and 503 are softened by heat or some solvent.

  The battery case 6 has a laminate film 60 that is pre-molded (embossed) into a shape that can accommodate the positive electrode 2 and the negative electrode 3, and the outer peripheral edge portions are adhered to the entire periphery so that the positive electrode 2 and the negative electrode 3 are attached. It is sealed inside. A sealing part is formed by adhesion of the outer periphery. Adhesion of the outer periphery in this form was made by fusion.

  The battery case 6 is formed by overlapping another laminate film 60 on the laminate film 60. Here, the other laminate film 60 indicates a laminate film to be bonded (fused). That is, the battery case 6 includes not only an embodiment formed from two or more laminate films 60 but also an embodiment formed by folding back one laminate film.

  Bonding (assembling) the outer periphery of the battery case 6 is performed under a reduced pressure atmosphere (preferably vacuum). Thereby, only the electrode body is enclosed in the battery case 6 without containing air (water contained therein).

  As shown in FIGS. 2 to 3, the pre-formed laminate film 60 includes a flat plate portion 61 that forms a sealing portion 62 with another laminate film 60 when overlapped, and a flat plate portion 61. And a tank-like portion 63 capable of accommodating the positive electrode 2 and the negative electrode 3 formed in the central portion.

  As shown in FIGS. 2 to 3, the laminate films 60 and 60 are bent (formed) so as to have a concave shape that can accommodate the positive electrode 2 and the negative electrode 3. The laminate films 60, 60 have the same shape, and the flat plate portions 61, 61 are completely overlapped when they are overlapped with each other facing each other.

  In the laminate film 60, the flat plate portion 61 and the bottom 63A of the tank-like portion 63 (the portion forming the end portion in the stacking direction of the secondary battery 1) are formed in parallel. The flat plate part 61 and the bottom part 63A of the tank-like part 63 are connected by a standing part 63B. The standing portion 63B extends in a direction (inclined direction) intersecting the parallel direction of the flat plate portion 61 and the bottom portion 63A. The bottom 63A is formed smaller than the opening of the tank-shaped part 63 (the inner end of the flat plate part 61).

In the battery case 6, a sealing portion 62 is formed at the peripheral edge of the flat plate portions 61, 61, and the flat plate portions 61, 61 are overlapped on the inner side of the sealing portion 62 (in the direction close to the electrode body). The part of is formed. The unbonded portion where the flat plate portions 61 and 61 are overlapped may be in a contact state or in a state where a gap is formed. Further, the uncoated portions 22 and 32 of the electrode plates 2 and 3 and the separator 5 may be interposed.
Laminate films 60 and 60 are formed in advance in the shape shown in FIGS. For forming into this shape, a conventionally known forming method is used.
In the secondary battery 1, each of the positive electrode 2 and the negative electrode 3 is connected to electrode terminals (a positive electrode terminal 65 and a negative electrode terminal 66).

(Electrode terminal)
The positive terminal 65 is electrically connected to the uncoated part 22 of the positive electrode 2. The negative electrode terminal 66 is electrically connected to the uncoated part 32 of the negative electrode 3. In this embodiment, the uncoated portions 22 and 32 of the electrodes 2 and 3 are joined to the electrode terminals 65 and 66 by welding (vibration welding), respectively. Central portions in the width direction of the uncoated portions 22 and 32 of the electrodes 2 and 3 are joined to the electrode terminals 65 and 66.

  Each of the electrode terminals 65 and 66 is joined via a sealant 64 so that the plastic resin layer 601 of the laminate films 60 and 60 and the electrode terminals 65 and 66 are kept in a sealed state at a portion penetrating the battery case 6. ing.

The electrode terminals 65 and 66 are made of sheet-like (foil-like) metal, and the sealant 64 is made of resin that covers the sheet-like electrode terminals 65 and 66. The sealant 64 covers a portion where the electrode terminals 65 and 66 overlap the flat plate portion 61. By forming the electrode terminals 65 and 66 into a sheet shape, the deformation stress of the laminate film 60 due to the electrode terminals 65 and 66 being interposed at the portion penetrating the battery case 6 can be reduced. Further, welding (vibration welding) of the electrodes 2 and 3 to the uncoated portions 22 and 32 can be easily performed.
[Effect of Embodiment 2]
The secondary battery 1 of the present embodiment has the same configuration as that of the first embodiment except that the shape is different, and exhibits the same effect as that of the first embodiment.

[Deformation]
The secondary battery 1 of Embodiment 2 is a form in which the secondary battery 1 of Embodiment 1 is applied to a laminate type battery. That is, the secondary battery 1 of Embodiment 1 may be applied to a configuration other than the laminate type. For example, in addition to the laminate-type indeterminate secondary battery 1 of the second embodiment, various types of batteries such as a coin type, a cylindrical type, and a square type can be used.
The secondary battery 1 may be put to practical use by forming an assembled battery combined in series and / or in parallel.

Hereinafter, the present invention will be described using examples.
As an example for specifically explaining the present invention, the lithium ion secondary battery shown in Embodiment 2 was manufactured.

Example 1
In the positive electrode 2 of this example, LiFePO ₄ having an olivine structure was used as a positive electrode active material. LiFePO ₄ has a potential of 3.4 V (4.0 V or less).
Then, a positive electrode mixture obtained by mixing 80 parts by mass of a positive electrode active material, 10 parts by mass of acetylene black (AB), and 10 parts by mass of a PVDF binder with a solvent is applied to the positive electrode current collector 20 made of aluminum foil and dried. Then, the one in which the positive electrode active material layer 21 was formed was used.

The negative electrode 3 is made of graphite as a negative electrode active material. And the negative electrode mixture obtained by mixing 98 mass parts of negative electrode active materials, 1 mass part of CMC, and 1 mass part of SBR with the solvent was prepared. The negative electrode mixture was applied to both surfaces of a negative electrode current collector 30 made of a copper foil having a thickness of 0.01 mm and dried to form a negative electrode active material layer 31.
For the separator 5, a porous film made of polyethylene was used.

In the non-aqueous electrolyte solution 4, LiPF ₆ was dissolved to 1 mol% in a mixed solvent in which EC: DMC: EMC was mixed at a ratio of 30:30:40 (vol%). What added the 1st additive and the 2nd additive as described in Table 1 was used.

  The 1st additive added to the non-aqueous electrolyte 4 is the compound (vinylene carbonate) shown by (a). The 1st additive was added in the ratio used as 3 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.

The second additive added to the nonaqueous electrolytic solution 4 is the compound shown in (f). The 2nd additive was added in the ratio used as 1.5 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.
The ratio of the content ratio of the first additive and the content ratio of the second additive is 2.0. This ratio is shown in Table 1 as additive ratio.

  Table 1 also shows the configurations of the following examples.

(Example 2)
This example has the same configuration as that of Example 1 except that the content ratios of the first additive and the second additive added to the nonaqueous electrolytic solution 4 are different.

The 1st additive was added in the ratio used as 6 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%. The 2nd additive was added in the ratio used as 1 mass%, when the mass of the whole non-aqueous electrolyte solution 4 was 100 mass%.
The ratio of the content ratio of the first additive and the content ratio of the second additive is 6.0.

Example 3
This example has the same configuration as that of Example 1 except that the additive added to the nonaqueous electrolytic solution 4 is different.

  The first additive added to the non-aqueous electrolyte 4 is the compound (fluoroethylene carbonate) shown in (b). The 1st additive was added in the ratio used as 3 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.

The second additive is the compound shown in (f) as in Example 1. The 2nd additive was added in the ratio used as 3 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.
The ratio of the content ratio of the first additive and the content ratio of the second additive is 1.0.

Example 4
This example has the same configuration as that of Example 1 except that the additive added to the nonaqueous electrolytic solution 4 is different.

  The first additive added to the nonaqueous electrolytic solution 4 is the compound shown in (c). The 1st additive was added in the ratio used as 1.5 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.

The second additive is the compound represented by (h). The 2nd additive was added in the ratio used as 1.5 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.
The ratio of the content ratio of the first additive and the content ratio of the second additive is 1.0.

(Example 5)
This example has the same configuration as that of Example 1 except that the additive added to the nonaqueous electrolytic solution 4 is different.

In the non-aqueous electrolyte solution 4, LiPF ₆ was dissolved to 1 mol% in a mixed solvent in which EC: DMC: EMC was mixed at a ratio of 30:30:40 (vol%). What added the 1st additive, the 3rd additive, and the 2nd additive was used.

  The first additive added to the non-aqueous electrolyte 4 is the compound (vinylene carbonate) shown in (a) as in Example 1. The 1st additive was added in the ratio used as 1.5 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.

  The third additive added to the nonaqueous electrolytic solution 4 is the compound shown in (d). The 3rd additive was added in the ratio used as 1 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.

The second additive added to the nonaqueous electrolytic solution 4 is the compound shown in (5). The 2nd additive was added in the ratio used as 1 mass%, when the mass of the whole non-aqueous electrolyte solution 4 was 100 mass%.
The ratio of the total content ratio of the first additive and the third additive to the content ratio of the second additive is 2.5.

(Example 6)
This example has the same configuration as that of Example 5 except that the third additive added to the nonaqueous electrolytic solution 4 is different.
The third additive is the compound shown in (e). The 3rd additive was added in the ratio used as 1 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.
The ratio of the total content ratio of the first additive and the third additive to the content ratio of the second additive is 2.5.

(Example 7)
This example has the same configuration as that of Example 1 except that the additive added to the nonaqueous electrolytic solution 4 is different.

In the non-aqueous electrolyte solution 4, LiPF ₆ was dissolved to 1 mol% in a mixed solvent in which EC: DMC: EMC was mixed at a ratio of 30:30:40 (vol%). What added the 1st additive, the 2nd additive, and the oxalate complex containing a boron was used.

  The first additive added to the non-aqueous electrolyte 4 is the compound (vinylene carbonate) shown in (a) as in Example 1. The 1st additive was added in the ratio used as 1.5 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.

  The second additive added to the non-aqueous electrolyte 4 is the compound shown in (g). The 2nd additive was added in the ratio used as 1 mass%, when the mass of the whole non-aqueous electrolyte solution 4 was 100 mass%.

The oxalate complex containing boron is the compound represented by (i). When the mass of the whole non-aqueous electrolyte solution 4 was 100 mass%, it was added at a ratio of 0.5 mass%.
The ratio of the content ratio of the first additive and the content ratio of the second additive is 1.5.

(Example 8)
This example has the same configuration as that of Example 1 except that the material of the positive electrode active material and the content ratio of the first additive added to the nonaqueous electrolytic solution 4 are different.
The positive electrode 2 of this example uses LiMnPO ₄ having an olivine structure as a positive electrode active material. LiMnPO ₄ has a potential of 3.95 V (4.0 V or less).

  The first additive added to the non-aqueous electrolyte 4 is the compound (vinylene carbonate) shown in (a) as in Example 1. The 1st additive was added in the ratio used as 1.5 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.

The second additive added to the non-aqueous electrolyte 4 is the compound shown in (g). The 2nd additive was added in the ratio used as 1 mass%, when the mass of the whole non-aqueous electrolyte solution 4 was 100 mass%.
The ratio of the content ratio of the first additive and the content ratio of the second additive is 1.0.

(Comparative Example 1)
This example is a secondary battery 1 similar to that of Example 1 except that the nonaqueous electrolyte solution 4 is different.
The non-aqueous electrolyte 4 of this example is obtained by dissolving LiPF ₆ to 1 mol% in a mixed solvent in which EC: DMC: EMC is mixed at a ratio of 30:30:40 (vol%). In addition, a material obtained by adding only the first additive was used.

The first additive added to the non-aqueous electrolyte 4 is the compound (vinylene carbonate) shown in (a) as in Example 1. The 1st additive was added in the ratio used as 1.5 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.
In this example, the second additive is not added to the nonaqueous electrolytic solution 4.

(Comparative Example 2)
This example is a secondary battery 1 similar to that of Example 1 except that the material of the positive electrode active material is different.
The positive electrode 2 of this example uses LiCoO ₂ having a layered structure as a positive electrode active material. This positive electrode active material does not have an olivine structure. LiCoO ₂ has a potential of 3.8 V (4.0 V or less).

(Comparative Example 3)
This example is a secondary battery 1 similar to that of Example 1 except that the nonaqueous electrolyte solution 4 is different.
The non-aqueous electrolyte 4 of this example is obtained by dissolving LiPF ₆ to 1 mol% in a mixed solvent in which EC: DMC: EMC is mixed at a ratio of 30:30:40 (vol%). In addition, a material obtained by adding only the second additive was used.

The second additive added to the non-aqueous electrolyte 4 is the compound shown in (f) as in Example 1. The 1st additive was added in the ratio used as 1.5 mass%, when the mass of the nonaqueous electrolyte solution 4 whole was 100 mass%.
In this example, the first additive is not added to the nonaqueous electrolytic solution 4.

(Comparative Example 4)
This example is a secondary battery 1 similar to that of Example 1 except that the material of the positive electrode active material is different.
The positive electrode 2 of this example uses LiCoPO ₄ having an olivine structure as a positive electrode active material. LiCoPO ₄ has a potential of 4.8 V (a value exceeding 4.0 V).

[Evaluation]
The secondary battery 1 of each example was repeatedly charged and discharged, and the capacity retention rate and resistance increase rate after the test were measured. In addition, the secondary battery 1 of each example is formed so that all may become 25Ah.

(Charge / discharge test)
The secondary battery 1 was charged and discharged at a 1C rate for 300 cycles. Charging was performed by CC-CV charging at 4.2V, and discharging was performed by CC discharging at 2.0V.

(Capacity maintenance rate)
For the capacity maintenance rate, the battery capacity after the first and 300 cycles was measured, and the capacity maintenance rate of each secondary battery was determined from the ratio. The measurement results of the capacity retention rate are shown in Table 1. In Table 1, when the capacity maintenance rate of the comparative example 1 was set to 100%, it showed as a ratio of the capacity maintenance rate of each battery. That is, it was shown as a relative capacity maintenance rate.

(Resistance increase rate)
First, when the SOC is 60%, the resistance increase rate is the voltage at the time when 10 seconds have elapsed from the start of discharge in each of the cases where discharge was performed at discharge rates 1C, 2C, 3C, 5C, and 10C. The inclination was obtained, the internal resistance was measured from those values, and the resistance increase rate of each secondary battery was obtained from the ratio of the internal resistance after the first time and after 300 cycles. The results of measuring the capacity retention rate are shown in Table 1. In Table 1, when the resistance increase rate of the comparative example 1 was set to 100%, it showed as a ratio of the resistance increase rate of each battery. That is, it was shown as a relative resistance increase rate.

  A graph plotting the capacity retention rate and the resistance increase rate shown in Table 2 is shown in FIG. In addition, in FIG. 4, it becomes a secondary battery excellent in durability and electroconductivity, so that it is plotted on the lower right (high capacity maintenance rate, low resistance increase rate) of the plot area.

  As shown in Table 2 and FIG. 4, the secondary battery 1 of each example has a lower resistance increase rate than the secondary battery 1 of Comparative Example 1. That is, the secondary battery 1 of each example is superior in conductivity to the secondary battery of Comparative Example 1.

  Further, the secondary battery 1 of each example has a higher capacity retention rate than the secondary battery 1 of Comparative Example 3. That is, the secondary battery 1 of each example is excellent in durability as compared with the secondary battery of Comparative Example 3.

In addition, the secondary battery 1 of each example has a low resistance increase rate while maintaining a capacity maintenance rate equal to or higher than that of the secondary battery 1 of Comparative Example 2. That is, the secondary battery 1 of each example is excellent in durability and conductivity as compared with the secondary battery of Comparative Example 2.
As described above, it was confirmed that the secondary battery 1 of the example corresponding to the present invention was a secondary battery excellent in durability and conductivity.

1: Lithium ion secondary battery 2: Positive electrode 20: Positive electrode current collector 21: Positive electrode active material layer 3: Negative electrode 30: Negative electrode current collector 31: Negative electrode active material layer 4: Non-aqueous electrolyte 5: Separator 6: Battery case 60: Laminate film 61: Flat plate part 62: Sealing part 63: Tank-like part 64: Sealant 65: Positive electrode terminal 66: Negative electrode terminal

Claims (5)

A non-aqueous electrolyte secondary battery (1) having a positive electrode (2) having a positive electrode active material, a negative electrode (3), and a non-aqueous electrolyte (4),
The positive electrode active material has a compound having an olivine structure with a potential of 4.0 V or less,
The non-aqueous electrolyte comprises: a first additive comprising a compound of the following formula (1); and a second additive comprising a compound of the following formula (2): Next battery.

The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte further has a third additive composed of at least one of a compound represented by the following formula (3) and a compound represented by the following formula (4).

  In the non-aqueous electrolyte, the ratio of the total content of the first additive and the third additive and the content of the second additive is 0.2 or more and 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is 0 or less.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the first additive is vinylene carbonate or fluoroethylene carbonate.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte has an oxalate complex containing boron.

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