JP2018133335A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery which enables the improvement of output characteristics.SOLUTION: A nonaqueous electrolyte battery comprises: a positive electrode 10 including a lithium vanadium compound represented by Li(M)(PO)(M=VO or V, 0.9≤a≤3.3, 0.9≤b≤2.2 and 0.9≤c≤3.3); and an electrolyte solution containing an additive agent (A) given by the chemical formula (1) below and at least one additive agent (B) selected from monofluorophosphate and difluorophosphate. (Rto Rindependently represent hydrogen, an alkyl group with 1-3 carbon atoms, a halogen, an alkyl group with 1-3 carbon atoms, which may include a halogen element, a cycloalkyl group or an alkenyl group, and n is an integer of 1-3.)SELECTED DRAWING: Figure 1

Description

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

  In recent years, a lithium ion secondary battery used as a main power source for mobile communication devices and portable electronic devices has a feature of high electromotive force and high energy density.

  The electrolyte for a lithium ion secondary battery is composed of a lithium salt that is an electrolyte and a non-aqueous organic solvent. The non-aqueous organic solvent is required to have a high dielectric constant for dissociating the lithium salt, to exhibit high ionic conductivity in a wide temperature range, and to be stable in the battery. Since it is difficult to achieve these requirements with a single solvent, usually a combination of a high-boiling solvent typified by propylene carbonate and ethylene carbonate and a low-boiling solvent such as dimethyl carbonate and diethyl carbonate is used. ing.

  In addition, many additives are added to the electrolyte to improve various battery characteristics such as initial capacity, rate characteristics, cycle characteristics, high temperature storage characteristics, continuous charge characteristics, self-discharge characteristics, and overcharge prevention characteristics. Has been studied. For example, it has been reported that lithium fluorophosphates are added as a method for suppressing self-discharge at high temperatures. (Patent Document 1)

Japanese Patent Laid-Open No. 11-67270

  However, the conventional methods still do not satisfy the various characteristics, and in particular, improvement of output characteristics is required.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a nonaqueous electrolytic solution capable of improving output characteristics and a nonaqueous electrolytic battery using the same.

In order to solve the above problems, a lithium ion secondary battery according to the present invention is a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolyte. The positive electrode is Li _a (M) _b (PO ₄ ) _c (where M = VO or V, and 0.9 ≦ a ≦ 3.3, 0.9 ≦ b ≦ 2.2, 0.9 ≦ a lithium vanadium compound represented by c ≦ 3.3),
The electrolytic solution includes an additive (A) represented by the following chemical formula (1) and at least one additive (B) selected from monofluorophosphate and difluorophosphate.
(Here, R ^{1 to} R ⁴ are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, a halogen, an alkyl group that may contain a halogen element having 1 to 3 carbon atoms, a cycloalkyl group, or an alkenyl group. And n is an integer of 1 to 3.)

  According to this, an output characteristic can be improved by including the said additives (A) and (B) in electrolyte solution.

  The details of the factors that cause these effects are not clear, but are considered as follows. That is, the additive (A) having a carbonate group decomposes to form a SEI film having high wettability to the solvent and low charge transfer resistance, and the additive (B) is concerted. By decomposing, the lithium ion conductivity in the SEI film is improved. As a result, the output characteristics are improved.

  Further, when a lithium vanadium compound is used as the positive electrode active material, the output characteristics are effectively improved. Although the exact mechanism of the above action is still unknown, it is considered that vanadium ions have a significant effect on film formation.

  In the nonaqueous electrolytic solution according to the present invention, it is preferable that the additive (A) is ethyl methyl 3-methyl-2,5-dioxahexanedioate.

According to this, it is suitable as the additive (A), and the output characteristics are further improved.

In the nonaqueous electrolytic solution according to the present invention, the additive (A) is preferably contained in the electrolytic solution in an amount of 1 × 10 ^{−4 to} 3 × 10 ⁻² mol / L.

  According to this, it is suitable as an addition amount and the output characteristics are further improved.

In the nonaqueous electrolytic solution according to the present invention, the additive (B) is preferably contained in the electrolytic solution in an amount of 1 × 10 ^{−3 to} 3 × 10 ⁻¹ mol / L.

  According to this, it is suitable as an addition amount and the output characteristics are further improved.

  In the nonaqueous electrolytic solution according to the present invention, it is further preferable that the additive (B) is lithium difluorophosphate.

  According to this, it is more suitable as an additive, and the output characteristics are further improved.

  According to the present invention, a nonaqueous electrolyte battery capable of improving output characteristics is provided.

It is a schematic cross section of the lithium ion secondary battery of this embodiment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments according to the invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

<Lithium ion secondary battery>
As shown in FIG. 1, a lithium ion secondary battery 100 according to the present embodiment is disposed adjacent to each other between a plate-like negative electrode 20 and a plate-like positive electrode 10 facing each other, and the negative electrode 20 and the positive electrode 10. One end is electrically connected to the negative electrode 20, a laminate 30 including a plate-like separator 18, a non-aqueous electrolyte containing lithium ions, a case 50 containing these in a sealed state, and the negative electrode 20. And a lead 62 whose other end protrudes outside the case and a lead 60 whose one end is electrically connected to the positive electrode 10 and whose other end protrudes outside the case. .

  The positive electrode 10 includes a positive electrode current collector 12 and a positive electrode active material layer 14 formed on the positive electrode current collector 12. The negative electrode 20 includes a negative electrode current collector 22 and a negative electrode active material layer 24 formed on the negative electrode current collector 22. The separator 18 is located between the negative electrode active material layer 24 and the positive electrode active material layer 14.

<Positive electrode>
The positive electrode according to the present embodiment has Li _a (M) _b (PO ₄ ) _c (where M = VO or V and 0.9 ≦ a ≦ 3.3, 0.9 ≦ b ≦ 2.2, The lithium vanadium compound represented by 0.9 ≦ c ≦ 3.3) is included.
(Positive electrode current collector)
The positive electrode current collector 12 may be a conductive plate material, and for example, a metal thin plate (metal foil) such as aluminum, an alloy thereof, or stainless steel can be used.

(Positive electrode active material layer)
The positive electrode active material layer 14 is mainly composed of a positive electrode active material, a positive electrode binder, a positive electrode conductive additive, and a positive electrode additive.

(Positive electrode active material)
The positive electrode active material according to the present embodiment is Li _a (M) _b (PO ₄ ) _c (where M = VO or V, and 0.9 ≦ a ≦ 3.3, 0.9 ≦ b ≦ 2. 2, 0.9 ≦ c ≦ 3.3) containing a lithium vanadium compound.

  According to this, when the lithium vanadium compound is used, the output characteristics are effectively improved when combined with the non-aqueous electrolyte according to the present embodiment. Although the exact mechanism of the above action is still unknown, it is considered that vanadium ions have a significant effect on film formation.

  Moreover, the positive electrode active material according to the present embodiment may include a second positive electrode active material.

Examples of the second positive electrode active material include occlusion and release of lithium ions, desorption and insertion (intercalation) of lithium ions, or doping and dedoping of a counter anion (for example, PF ₆ ⁻ ) of the lithium ions. The electrode is not particularly limited as long as it can be reversibly advanced, and a known electrode active material can be used. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and the chemical formula: LiNi _x Co _y Mn _z MaO ₂ (x + y + z + a = 1, 0 ≦ x ≦ 1) , 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a ≦ 1, and M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr) Olivine type LiMPO ₄ (wherein M represents one or more elements or VO selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), LiNi _x Co _y Al _z O ₂ (0.9 <x + y + z <1.1) and the like.

(Binder for positive electrode)
As the positive electrode binder, the positive electrode active materials are bonded together, and the positive electrode active material layer 14 and the positive electrode current collector 12 are bonded. The binder is not particularly limited as long as it can be bonded as described above. For example, fluorine resin such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide A resin, a polyamideimide resin, or the like may be used. Alternatively, an electron conductive conductive polymer or an ion conductive conductive polymer may be used as the binder. Examples of the electron conductive conductive polymer include polyacetylene, polythiophene, and polyaniline. Examples of the ion conductive conductive polymer include those obtained by combining a polyether polymer compound such as polyethylene oxide and polypropylene oxide and a lithium salt such as LiClO ₄ , LiBF ₄ , and LiPF _6. It is done.

  Although content of the binder in the positive electrode active material layer 14 is not specifically limited, When adding, it is preferable that it is 0.5-5 mass parts with respect to the mass of a positive electrode active material.

(Conductive aid for positive electrode)
The conductive auxiliary agent for positive electrode is not particularly limited as long as it improves the conductivity of the positive electrode active material layer 14, and a known conductive auxiliary agent can be used. Examples thereof include carbon-based materials such as graphite and carbon black, metal fine powders such as copper, nickel, stainless steel, and iron, and conductive oxides such as ITO.

<Negative electrode>
(Negative electrode current collector)
The negative electrode current collector 22 may be a conductive plate material, and for example, a metal thin plate (metal foil) such as copper can be used.

(Negative electrode active material layer)
The negative electrode active material layer 24 is mainly composed of a negative electrode active material, a negative electrode binder, and a negative electrode conductive additive.

(Negative electrode active material)
The negative electrode active material is not particularly limited as long as it can reversibly advance occlusion and release of lithium ions and desorption and insertion (intercalation) of lithium ions, and a known electrode active material can be used. . For example, carbon materials such as graphite and hard carbon, silicon materials such as silicon oxide (SiO _x ) metal silicon (Si), metal oxides such as lithium titanate (LTO), metal materials such as lithium, tin, and zinc Is mentioned.

  Of the above negative electrode active materials, the effect of the present invention can be further obtained when lithium is used. Although the details of the above factors are not clear, it is considered that the room temperature molten salt forms a SEI film having a higher donor property on lithium.

  When a metal material is not used as the negative electrode active material, the negative electrode active material layer 24 may further include a negative electrode binder and a negative electrode conductive additive.

(Binder for negative electrode)
There is no limitation in particular as a binder for negative electrodes, The thing similar to the binder for positive electrodes described above can be used.

(Conductive aid for negative electrode)
There is no limitation in particular as a conductive support agent for negative electrodes, The thing similar to the conductive support agent for positive electrodes described above can be used.

<Non-aqueous electrolyte>
The nonaqueous electrolytic solution according to the present embodiment includes a solvent composed of a cyclic carbonate and a chain carbonate, an additive (A) in which the electrolytic solution is represented by the chemical formula (1), and a monofluorophosphate or difluorophosphoric acid. It contains an additive (B) selected from salts.

  According to this, an output characteristic can be improved by including the said additives (A) and (B) in electrolyte solution.

  The details of the factors that cause these effects are not clear, but are considered as follows. That is, the additive (A) having a carbonate group decomposes to form a SEI film having high wettability to the solvent and low charge transfer resistance, and the additive (B) is concerted. By decomposing, the lithium ion conductivity in the SEI film is improved. As a result, the output characteristics are improved.

  In the nonaqueous electrolytic solution according to this embodiment, it is preferable that the additive (A) is ethyl methyl 3-methyl-2,5-dioxahexanedioate.

According to this, it is suitable as the additive (A), and the output characteristics are further improved.

In the nonaqueous electrolytic solution according to this embodiment, the additive (A) is preferably contained in the electrolytic solution in an amount of 1 × 10 ^{−4 to} 3 × 10 ⁻² mol / L.

  According to this, it is suitable as an addition amount and the output characteristics are further improved.

In the nonaqueous electrolytic solution according to this embodiment, the additive (B) is preferably contained in the electrolytic solution in an amount of 1 × 10 ^{−3 to} 3 × 10 ⁻¹ mol / L.

  According to this, it is suitable as an addition amount and the output characteristics are further improved.

  In the nonaqueous electrolytic solution according to this embodiment, it is further preferable that the additive (B) is lithium difluorophosphate.

  According to this, it is more suitable as an additive, and the output characteristics are further improved.

  In the non-aqueous electrolyte according to this embodiment, the additive (A) and the additive (B) are added in a molar ratio of additive (A): additive (B) = 1: 2-1. : 20 is preferable.

  According to this, it is suitable as a ratio of the addition amount, and the output characteristics are further improved.

(solvent)
Furthermore, the solvent generally used for the lithium ion secondary battery can be used as the solvent of the electrolytic solution. The solvent is not particularly limited. For example, cyclic carbonate compounds such as ethylene carbonate (EC) and propylene carbonate (PC), chain carbonate compounds such as diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), and γ-butyrolactone. A cyclic ester compound such as propyl propionate, a chain ester compound such as ethyl propionate and ethyl acetate, and the like can be mixed and used at an arbitrary ratio.

(Electrolytes)
The electrolyte is not particularly limited as long as it is a lithium salt used as an electrolyte of a lithium ion secondary battery. For example, inorganic acid anion salts such as LiPF ₆ , LiBF ₄ , lithium bisoxalate borate, LiCF ₃ SO ₃ , An organic acid anion salt such as (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, or the like can be used.

  As mentioned above, although preferred embodiment which concerns on this invention was described, this invention is not limited to the said embodiment.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

[Example 1]
(Preparation of positive electrode)
As a positive electrode active material, 85 parts by mass of LiVOPO ₄ , 5 parts by mass of carbon black, and 10 parts by mass of PVDF were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry for forming a positive electrode active material layer. This slurry was applied to one surface of an aluminum metal foil having a thickness of 20 μm so that the applied amount of the positive electrode active material was 9.0 mg / cm ² and dried at 100 ° C. to form a positive electrode active material layer. Then, it pressure-molded with the roller press and produced the positive electrode.

(Preparation of negative electrode)
90 parts by mass of natural graphite, 5 parts by mass of carbon black, and 5 parts by mass of PVDF were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry for forming a negative electrode active material layer. The slurry was applied to one surface of a copper foil having a thickness of 20 μm so that the amount of the negative electrode active material applied was 6.0 mg / cm ² and dried at 100 ° C. to form a negative electrode active material layer. Then, it pressure-molded with the roller press and produced the negative electrode.

(Preparation of electrolyte)
Were mixed so that EC / DEC = 3/7 by volume and this dissolved LiPF ₆ at a concentration of 1 mol / L. Thereafter, diethyl 2,5-dioxahexanedioate as an additive (A) is 1.0 × 10 ⁻³ mol / L, and lithium difluorophosphate (LiPO ₂ F ₂ ) is 1.0 × as an additive (A). It added so that it might become a density | concentration of 10 ^<-2 > mol / L, and produced electrolyte solution.

(Production of evaluation lithium-ion secondary battery)
The positive electrode and negative electrode produced above and a separator made of a polyethylene microporous film were sandwiched between them to be put in an aluminum laminate pack. After injecting the electrolytic solution prepared above into this aluminum laminate pack, vacuum sealing was performed to prepare a lithium ion secondary battery for evaluation.

(Measurement of 5C rate characteristics)
About the lithium ion secondary battery for evaluation produced above, using a secondary battery charge / discharge test apparatus (manufactured by Hokuto Denko Co., Ltd.), until the battery voltage becomes 4.2 V by constant current charging at a charge rate of 0.2 C. After charging, the battery was discharged at a constant current discharge rate of 0.2 C until the battery voltage reached 2.8 V, and the initial discharge capacity C ₁ was obtained. Subsequently, the battery is charged until the battery voltage becomes 4.2 V by constant current charging at a charge rate of 1 C, and then discharged by a constant current discharge at 5 C discharge rate until the battery voltage becomes 2.8 V. the discharge capacity _{C 2} was determined. In addition, nC (mA) of the said charging / discharging rate is an electric current value which can charge / discharge nominal capacity (mAh) by 1 / n (h).

From the initial discharge capacity _{C 1} and 5C discharge capacity _{C 2} obtained above, in accordance with equation (1), it was determined 5C rate characteristics. The obtained results are shown in Table 1.
5C rate characteristics [%] = C ₂ / C ₁ × 100 (1)

[Examples 2 to 6]
Lithium secondary batteries for evaluation of Examples 2 to 6 were produced in the same manner as in Example 5 except that the type of additive (A) used in the production of the electrolytic solution was changed as shown in Table 1. .

[Examples 7 to 12]
The evaluation lithium ion secondary batteries of Examples 7 to 12 were produced in the same manner as in Example 5 except that the amount of additive (A) used in the production of the electrolytic solution was changed as shown in Table 1. did.

[Examples 13 to 16]
The evaluation lithium ion secondary batteries of Examples 13 to 16 were produced in the same manner as in Example 5 except that the amount of additive (B) used in the production of the electrolytic solution was changed as shown in Table 1. did. Here, Li ₂ PO ₃ F is lithium monofluorophosphate.

[Examples 17 to 21]
Lithium ion secondary batteries for evaluation of Examples 17 to 21 were the same as Example 5 except that the type and amount of additive (B) used in the preparation of the electrolytic solution were changed as shown in Table 1. Was made. Here, Li ₂ PO ₃ F is lithium monofluorophosphate.

[Examples 22 and 23]
Lithium ion secondary batteries for evaluation of Examples 22 and 23 were produced in the same manner as in Example 5 except that the positive electrode active material used in the production of the positive electrode was changed as shown in Table 1.

[Example 24]
In the production of the positive electrode, an evaluation lithium ion secondary battery of Example 24 was produced in the same manner as in Example 5 except that 50 parts by mass of LiVOPO _{4 and} 35 parts by mass of LiCoO ₂ were used as the positive electrode active material.

[Comparative Example 1]
As shown in Table 1, a lithium ion secondary battery for evaluation of Comparative Example 1 was produced in the same manner as in Example 5 except that the additive (B) was not added in the production of the electrolytic solution.

[Comparative Example 2]
As shown in Table 1, a lithium ion secondary battery for evaluation of Comparative Example 1 was produced in the same manner as in Example 5 except that the additive (A) was not added in the production of the electrolytic solution.

[Comparative Example 3]
As shown in Table 1, a lithium ion secondary battery for evaluation of Comparative Example 1 was produced in the same manner as in Example 5 except that no additive was added in the production of the electrolytic solution.

[Comparative Example 4]
A lithium ion secondary battery for evaluation of Comparative Example 4 was produced in the same manner as Comparative Example 3 except that the positive electrode active material used in the production of the positive electrode was changed as shown in Table 1.

[Comparative Example 5]
A lithium ion secondary battery for evaluation of Comparative Example 5 was produced in the same manner as Comparative Example 3 except that the positive electrode active material used in the production of the positive electrode was changed as shown in Table 1.

[Comparative Example 6]
A lithium ion secondary battery for evaluation of Comparative Example 6 was produced in the same manner as Comparative Example 3 except that the positive electrode active material used in the production of the positive electrode was changed as shown in Table 1.

[Comparative Example 7]
A lithium ion secondary battery for evaluation of Comparative Example 7 was produced in the same manner as in Example 5 except that the positive electrode active material used in the production of the positive electrode was changed as shown in Table 1.

[Comparative Example 8]
A lithium ion secondary battery for evaluation of Comparative Example 8 was produced in the same manner as Comparative Example 3 except that the positive electrode active material used in the production of the positive electrode was changed as shown in Table 1.

[Comparative Example 9]
A lithium ion secondary battery for evaluation of Comparative Example 9 was produced in the same manner as in Example 5 except that the positive electrode active material used in the production of the positive electrode was changed as shown in Table 1.

  About the lithium ion secondary battery for evaluation produced in Examples 2-24 and Comparative Examples 1-9, similarly to Example 1, the 5C rate characteristic was measured. The results are shown in Table 1.

  In each of Examples 1 to 24, 5C rate characteristics were improved as compared with Comparative Examples 1 to 3 in which one or both of the additives were not added. From the results of Examples 1 to 6, it was confirmed that 5C rate characteristics were further improved by using ethyl methyl 3-methyl-2,5-dioxahexanedioate as the additive (A). Furthermore, from the results of Examples 7 to 12, it was confirmed that the 5C rate characteristics were further improved by optimizing the addition amount of the additive (A).

Similarly, for the additive (B), it was confirmed from the results of Examples 13 to 16 that the 5C rate characteristics were further improved by optimizing the addition amount. Furthermore, from the results of Examples 17 to 21, it was confirmed that 5C rate characteristics were further improved when LiPO ₂ F ₂ was used as an additive.

In addition, from the results of Examples 22 and 23, it was confirmed that 5C rate characteristics were further improved when LiPOVO ₄ was used as the positive electrode active material.

  According to the present invention, a nonaqueous electrolyte battery capable of improving output characteristics is provided.

  DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 20 ... Negative electrode, 22 ... Negative electrode collector, 24 ... Negative electrode active material layer, 30 ... Laminate, 50 ... Case, 60 62 ... Lead, 100 ... Lithium ion secondary battery.

Claims (5)

A non-aqueous electrolyte battery comprising a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is Li _a (M) _b (PO ₄ ) _c (where A lithium vanadium compound represented by M = VO or V and 0.9 ≦ a ≦ 3.3, 0.9 ≦ b ≦ 2.2, 0.9 ≦ c ≦ 3.3),
The electrolyte solution includes an additive (A) represented by the following chemical formula (1) and at least one additive (B) selected from monofluorophosphate and difluorophosphate. Water electrolyte battery.

(Here, R ^{1 to} R ⁴ are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, a halogen, an alkyl group that may contain a halogen element having 1 to 3 carbon atoms, a cycloalkyl group, or an alkenyl group. And n is an integer of 1 to 3.)   The non-aqueous electrolyte battery according to claim 1, wherein the additive (A) is ethyl methyl 3-methyl-2,5-dioxahexanedioate. 3. The non-aqueous electrolyte battery according to claim 1, wherein the additive (A) is contained in the electrolytic solution in an amount of 1 × 10 ^{−4 to} 3 × 10 ⁻² mol / L. The non-aqueous electrolysis according to any one of claims 1 to 3, wherein the additive (B) is contained in the electrolytic solution in an amount of 1 x ^{10-3 to} 3 x ^10-1 mol / L. Liquid battery.   The non-aqueous electrolyte battery according to any one of claims 1 to 4, wherein the additive (B) is lithium difluorophosphate.

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