JP2018133284A - Nonaqueous electrolyte and nonaqueous electrolyte battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte and a nonaqueous electrolyte battery using the same capable of improving output characteristics.SOLUTION: There is provided a nonaqueous electrolytic solution containing a cyclic sulfate represented by the chemical formula (1) and an additive selected from a monofluorophosphate or a difluorophosphate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte battery using the same.

  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)

JP 2013-229303 A

  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-mentioned problems, the nonaqueous electrolytic solution according to the present invention contains a cyclic sulfate represented by the following chemical formula (1) and an additive selected from monofluorophosphate or difluorophosphate. It is characterized by.
(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 0 to 2.)

  According to this, an output characteristic can be improved by including the said cyclic sulfate and the said additive in electrolyte solution.

  The details of the factors that cause these effects are not clear, but are considered as follows. That is, the cyclic ester and the additive are decomposed at the positive electrode, whereby a low donor film in which phosphorus and sulfur coexist is formed. Thereby, the lithium ion trap property in a positive electrode membrane | film | coat becomes low, and an output characteristic improves.

  In the nonaqueous electrolytic solution according to the present invention, the cyclic sulfate is preferably 1,3,2-dioxathiolane-2,2-dioxide.

  According to this, it is suitable as a cyclic sulfate and the output characteristics are further improved.

In the nonaqueous electrolytic solution according to the present invention, it is preferable that the cyclic sulfate is contained in the electrolytic solution in an amount of 1 × 10 ⁻³ to 2 × 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, the additive 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 is lithium difluorophosphate.

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

  ADVANTAGE OF THE INVENTION According to this invention, the non-aqueous electrolyte which can improve an output characteristic and a non-aqueous electrolyte battery using the same are 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>
(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)
As the positive electrode active material, lithium ion occlusion and release, lithium ion desorption and insertion (intercalation), or doping and dedoping of a counter anion (for example, PF ₆ ⁻ ) of the lithium ion are reversibly performed. If it can be made to advance, it will not specifically limit, A well-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) , Lithium vanadium compound 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), olivine-type LiMPO ₄ (wherein M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr or VO), titanium Lithium acid (Li ₄ Ti ₅ O ₁₂ ), LiNi _x Co _y Al _z O ₂ (0.9 <x + y + z <1.1) and the like.

  Among the positive electrode active materials, particularly when a lithium vanadium compound is used, 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.

(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 this embodiment includes a cyclic sulfate represented by the chemical formula (1) and an additive selected from monofluorophosphate or difluorophosphate.

  According to this, an output characteristic can be improved by including the said cyclic sulfate and the said additive in electrolyte solution.

  The details of the factors that cause these effects are not clear, but are considered as follows. That is, the cyclic ester and the additive are decomposed at the positive electrode, whereby a low donor film in which phosphorus and sulfur coexist is formed. Thereby, the lithium ion trap property in a positive electrode membrane | film | coat becomes low, and an output characteristic improves.

  In the nonaqueous electrolytic solution according to this embodiment, the cyclic sulfate is preferably 1,3,2-dioxathiolane-2,2-dioxide.

  According to this, it is suitable as a cyclic sulfate and the output characteristics are further improved.

In the nonaqueous electrolytic solution according to the present embodiment, the cyclic sulfate is preferably contained in the electrolytic solution in an amount of 1 × 10 ⁻³ to 2 × 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, the additive 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, the additive is preferably 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 the present embodiment, it is preferable that the cyclic sulfate and the additive are added in a molar ratio of cyclic sulfate: additive = 5: 1 to 20: 1.

  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, 1.0 × 10 ⁻¹ mol / L of 1,3,2-dioxathiolane-2,2-dioxide as a cyclic sulfate and 1.0 of lithium difluorophosphate (LiPO ₂ F ₂ ) are added to this solution. 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 5]
Lithium secondary batteries for evaluation of Examples 2 to 5 were produced in the same manner as in Example 1 except that the type of cyclic sulfate used in the production of the electrolytic solution was changed as shown in Table 1.

[Examples 6 to 11]
Lithium secondary batteries for evaluation of Examples 6 to 11 were produced in the same manner as in Example 1 except that the addition amount of the cyclic sulfate used in the production of the electrolytic solution was changed as shown in Table 1.

[Examples 12 to 15]
Lithium ion secondary batteries for evaluation of Examples 12 to 15 were produced in the same manner as in Example 1 except that the additive amount used in the production of the electrolytic solution was changed as shown in Table 1.

[Examples 16 to 20]
Lithium ion secondary batteries for evaluation of Examples 16 to 20 were produced in the same manner as in Example 1 except that the types and amounts of additives used in the production of the electrolytic solution were changed as shown in Table 1. . Here, Li ₂ PO ₃ F is lithium monofluorophosphate.

[Examples 21 to 24]
Lithium ion secondary batteries for evaluation of Examples 21 to 24 were produced in the same manner as in Example 1 except that the positive electrode active material used in the production of the positive electrode was changed as shown in Table 1.

[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 1 except that no additive was 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 prepared in the same manner as in Example 1 except that no cyclic sulfate was added in the preparation 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 1 except that the cyclic sulfate and the additive were not added in the production of the electrolytic solution.

[Comparative Examples 4 to 7]
Lithium ion secondary batteries for evaluation of Comparative Examples 4 to 7 were 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.

  About the lithium ion secondary battery for evaluation produced in Examples 2-24 and Comparative Examples 1-7, 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 5, it was confirmed that 5C rate characteristics were further improved by using 1,3,2-dioxadiolane-2,2-dioxide as the cyclic sulfate. Furthermore, from the results of Examples 6 to 11, it was confirmed that the 5C rate characteristics were further improved by optimizing the amount of cyclic sulfate added.

Similarly, for the additives, it was confirmed from the results of Examples 12 to 15 that the 5C rate characteristics were further improved by optimizing the addition amount. Furthermore, from the results of Examples 16 to 20, it was confirmed that when LiPO ₂ F ₂ was used as an additive, the 5C rate characteristics were further improved.

In addition, from the results of Examples 21 to 24, it was confirmed that when LiPOVO ₄ was used as the positive electrode active material, the output characteristics were further improved.

  According to the present invention, a non-aqueous electrolyte capable of improving output characteristics and a non-aqueous electrolyte battery using the same are 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 (6)

A cyclic sulfate represented by the following chemical formula (1);
A non-aqueous electrolyte comprising an additive selected from monofluorophosphate or 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.)   The non-aqueous electrolytic solution according to claim 1, wherein the cyclic sulfate is 1,3,2-dioxathiolane-2,2-dioxide. 3. The non-aqueous electrolyte according to claim 1, wherein the cyclic sulfate is contained in the electrolytic solution in an amount of 1 × 10 ⁻³ to 2 × 10 ⁻¹ mol / L. The non-aqueous electrolyte according to any one of claims 1 to 3, wherein the additive is contained in the electrolytic solution in an amount of 1 x ^{10-3 to} 3 x ^10-1 mol / L.   The non-aqueous electrolyte according to any one of claims 1 to 4, wherein the additive is lithium difluorophosphate. A nonaqueous electrolyte secondary battery comprising the nonaqueous electrolyte solution according to any one of claims 1 to 5.

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