JP2019061836A - Lithium ion secondary battery - Google Patents

Abstract

To provide a lithium ion secondary battery capable of improving cycle characteristics.SOLUTION: In a lithium ion secondary battery including a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, an electrolyte, the positive electrode contains a lithium vanadium compound, and the electrolyte contains disulfonic acid.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery.

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

Conventionally, layered compounds such as LiCoO ₂ and LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and spinel compounds such as LiMn ₂ O ₄ have been used as positive electrode materials (positive electrode active materials) for lithium ion secondary batteries. The In recent years, olivine type compounds represented by LiFePO ₄ have attracted attention. It is known that positive electrode materials having an olivine structure have high thermal stability at high temperatures and high safety.

However, a lithium ion secondary battery using LiFePO ₄ has a disadvantage that the charge and discharge voltage is as low as about 3.5 V and the energy density is low. Therefore, LiCoPO ₄ , LiNiPO _{4 and the} like have been proposed as phosphoric acid based positive electrode materials capable of realizing high charge and discharge voltage. However, even in lithium ion secondary batteries using these positive electrode materials, at present, sufficient capacity is not obtained.

Among the above-described phosphoric acid-based positive electrode materials, vanadium phosphate compounds having a structure of LiVOPO ₄ or Li ₃ V ₂ (PO ₄ ) ₃ are known as compounds capable of achieving 4V class charge and discharge voltage. However, when these compounds are repeatedly charged and discharged under high voltage, vanadium elutes and is deposited on the negative electrode, so that there is a problem that cycle characteristics deteriorate.

  Therefore, Patent Document 1 reports that fluorinated carbonate contained as a solvent in an electrolytic solution suppresses the elution of vanadium by forming a film on the positive electrode.

JP 2013-77424

  However, in the method of the prior art, various properties are not satisfied yet, and further improvement of cycle characteristics is required.

  The present invention has been made in view of the problems of the above-mentioned prior art, and it is an object of the present invention to provide a lithium ion secondary battery capable of improving cycle characteristics.

  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 electrolytic solution. The positive electrode contains a lithium vanadium compound, and the electrolytic solution contains a disulfonic acid.

  According to this, since the oxygen bonded to sulfur has a large negative charge density, the disulfonic acid has a high donor property, can form a stable complex with vanadium eluted from the lithium vanadium compound, and can suppress vanadium precipitation on the negative electrode. , Improve the cycle characteristics.

  Furthermore, in the lithium ion secondary battery according to the present invention, the molecular weight of the disulfonic acid is preferably 280 g / mol or less.

  According to this, it is suitable as a molecular weight of disulfonic acid, and the cycle characteristics are further improved.

Furthermore, in the lithium ion secondary battery according to the present invention, the disulfonic acid is preferably represented by the following chemical formula (1).
(R1 is a linear substituted or unsubstituted alkyl chain of 1 to 5 carbon atoms.)

  According to this, it is suitable as a disulfonic acid, and the cycle characteristics are further improved.

  In the lithium ion secondary battery according to the present invention, preferably, the disulfonic acid is methanedisulfonic acid or 1,2-ethanedisulfonic acid.

  According to this, it is suitable as a disulfonic acid, and the cycle characteristics are further improved.

  In the lithium ion secondary battery according to the present invention, preferably, the above-mentioned disulfonic acid is contained in the above-mentioned electrolytic solution in an amount of 0.01% by weight or more and 3.0% by weight or less.

  According to this, it is suitable as the addition amount of disulfonic acid, and the cycle characteristics are further improved.

Lithium-ion secondary battery according to the present invention preferably further the lithium vanadium compound is LiVOPO _4.

  According to the present invention, a lithium ion secondary battery capable of improving cycle characteristics is provided.

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

  Hereinafter, preferred embodiments according to the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments. Further, the components described below include those which can be easily conceived by those skilled in the art and those substantially the same. Furthermore, the components described below can be combined as appropriate.

<Lithium ion secondary battery>
As shown in FIG. 1, the lithium ion secondary battery 100 according to this embodiment is disposed adjacent to each other between the plate-like negative electrode 20 and the plate-like positive electrode 10 facing each other, and between the negative electrode 20 and the positive electrode 10. And an electrolytic solution containing lithium ions, a case 50 for accommodating these in a sealed state, and one end of the negative electrode 20 are electrically connected. It has 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 has a positive electrode current collector 12 and a positive electrode active material layer 14 formed on the positive electrode current collector 12. Further, the negative electrode 20 has 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 contains a lithium vanadium compound.
(Positive current collector)
The positive electrode current collector 12 may be any conductive plate material, and for example, aluminum or an alloy thereof, or a thin metal plate (metal foil) such as 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, and a positive electrode conductive aid.

(Positive electrode active material)
The positive electrode active material according to the present embodiment contains a lithium vanadium compound.

The positive electrode active material according to the present embodiment further includes 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) is preferable, and LiVOPO ₄ is more preferable.

  In the case of the positive electrode using the above-mentioned positive electrode active material, when combined with the electrolytic solution according to this embodiment, a stable complex is formed with the eluted vanadium, so that the precipitation of vanadium can be suppressed and the cycle characteristics improvement effect can be obtained. .

(Binder for positive electrode)
The positive electrode binder bonds the positive electrode active materials to one another, and also bonds the positive electrode active material layer 14 and the positive electrode current collector 12. The binder may be any one as long as the above-mentioned bonding is possible, for example, a fluorine resin such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), cellulose, styrene butadiene rubber, ethylene / propylene rubber, polyimide Resin, polyamide imide resin, etc. may be used. In addition, 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, polyaniline and the like. As the ion conductive conductive polymer, for example, those obtained by combining a polyether type polymer compound such as polyethylene oxide or polypropylene oxide with a lithium salt such as LiClO ₄ , LiBF ₄ or LiPF ₆ are listed. Be

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

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

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

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

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

(Binder for negative electrode)
The negative electrode binder is not particularly limited, and the same positive electrode binder as described above can be used.

(Conductive additive 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.

<Electrolyte solution>
The electrolytic solution according to this embodiment contains disulfonic acid.

  According to this, since the oxygen bonded to sulfur has a large negative charge density, the disulfonic acid has a high donor property, can form a stable complex with vanadium eluted from the lithium vanadium compound, and can suppress vanadium precipitation on the negative electrode. , Improve the cycle characteristics.

  Further, in the lithium ion secondary battery according to the present embodiment, the molecular weight of the disulfonic acid is preferably 280 g / mol or less.

  According to this, it is suitable as a molecular weight of disulfonic acid, and the cycle characteristics are further improved.

  Further, in the lithium ion secondary battery according to the present embodiment, the disulfonic acid is preferably represented by the chemical formula (1), and more preferably methanedisulfonic acid or 1,2-ethanedisulfonic acid.

  According to this, it is suitable as a disulfonic acid, and the cycle characteristics are further improved.

  In the lithium ion secondary battery according to the present embodiment, the above-mentioned disulfonic acid is preferably further contained in the above-mentioned electrolytic solution at 0.01 wt% or more and 3.0 wt% or less.

  According to this, it is suitable as the addition amount of disulfonic acid, and the cycle characteristics are further improved.

(Other solvents)
A solvent generally used for a lithium ion secondary battery can be used for the electrolytic solution according to the present embodiment. The solvent is not particularly limited, and examples thereof include cyclic carbonate compounds such as ethylene carbonate (EC) and propylene carbonate (PC), linear carbonate compounds such as diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), and the like. It can be mixed and used in the ratio of

(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, and examples thereof include inorganic acid anion salts such as LiPF ₆ , LiBF ₄ and lithium bis oxalate borate, LiCF ₃ SO ₃ , Organic acid anionic salts such as (CF ₃ SO ₂ ) ₂ NLi and (FSO ₂ ) ₂ NLi can be used.

  As mentioned above, although the suitable embodiment concerning the present invention was described, the present invention is not limited to the above-mentioned embodiment.

  Hereinafter, the present invention will be more specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
(Production of positive electrode)
85 parts by mass of LiVOPO ₄ as a lithium vanadium compound, 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. The slurry was applied to one surface of a 20 μm thick aluminum metal foil so that the coating 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 by the roller press, and produced the positive electrode.

(Fabrication 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 20 μm thick copper foil so that the coating amount of the negative electrode active material was 6.0 mg / cm ^2, and dried at 100 ° C. to form a negative electrode active material layer. Then, it pressure-molded by the roller press, and produced the negative electrode.

(Preparation of electrolyte)
Dissolve LiPF ₆ in a solvent adjusted to EC / DEC = 3/7 by volume ratio to a concentration of 1 mol / L, and add 1.0% by weight of methanedisulfonic acid as disulfonic acid to this To make an electrolyte.

(Preparation of lithium ion secondary battery for evaluation)
The positive electrode and the negative electrode produced above and a separator made of a polyethylene microporous film were interposed between them and placed in an aluminum laminate pack. The electrolytic solution prepared above was injected into the aluminum laminate pack, and vacuum sealing was performed to prepare a lithium ion secondary battery for evaluation.

(Measurement of capacity retention rate after 300 cycles)
For the lithium ion secondary battery for evaluation prepared above, using a secondary battery charge and discharge test device (manufactured by Hokuto Denko Corporation), charging rate 1.0 C (constant current charging at 25 ° C.) takes 1 hour The battery was charged until the battery voltage reached 4.2 V by constant current charging (the current value at which the charging is completed), and was discharged until the battery voltage reached 2.8 V by constant current discharging at a discharge rate of 1.0C. The charge / discharge cycle was defined as one cycle, followed by 300 cycles of charge / discharge, and after 300 cycles, the capacity retention ratio (300th cycle discharge capacity / 1st cycle discharge capacity × 100) was determined. The obtained results are shown in Table 1.

Example 2
A lithium ion secondary battery for evaluation of Example 2 was produced in the same manner as Example 1, except that the disulfonic acid used in the production of the electrolytic solution was changed as shown in Table 1.

[Example 3]
A lithium ion secondary battery for evaluation of Example 3 was produced in the same manner as Example 1, except that the disulfonic acid used in the production of the electrolytic solution was changed as shown in Table 1.

Example 4
A lithium ion secondary battery for evaluation of Example 4 was produced in the same manner as in Example 1 except that the disulfonic acid used in producing the electrolytic solution was changed as shown in Table 1.

[Example 5]
A lithium ion secondary battery for evaluation of Example 5 was produced in the same manner as in Example 1 except that the disulfonic acid used for producing the electrolytic solution was changed as shown in Table 1.

[Example 6]
A lithium ion secondary battery for evaluation of Example 6 was produced in the same manner as in Example 1 except that the disulfonic acid used in the production of the electrolytic solution was changed as shown in Table 1.

[Example 7]
A lithium ion secondary battery for evaluation of Example 7 was produced in the same manner as in Example 1 except that the disulfonic acid used in the production of the electrolytic solution was changed as shown in Table 1.

[Example 8]
A lithium ion secondary battery for evaluation of Example 8 was produced in the same manner as in Example 1 except that the addition amount of disulfonic acid was changed as shown in Table 1.

[Example 9]
A lithium ion secondary battery for evaluation of Example 9 was produced in the same manner as in Example 1 except that the amount of disulfonic acid added was changed as shown in Table 1.

[Example 10]
A lithium ion secondary battery for evaluation of Example 10 was produced in the same manner as in Example 1 except that the amount of disulfonic acid added was changed as shown in Table 1.

[Example 11]
A lithium ion secondary battery for evaluation of Example 11 was produced as in Example 1 except that the amount of disulfonic acid added was changed as shown in Table 1.

[Example 12]
A lithium ion secondary battery for evaluation of Example 12 was produced in the same manner as in Example 1 except that the amount of disulfonic acid added was changed as shown in Table 1.

[Example 13]
A lithium ion secondary battery for evaluation of Example 13 was produced as in Example 1 except that the amount of disulfonic acid added was changed as shown in Table 1.

Example 14
A lithium ion secondary battery for evaluation of Example 14 was produced in the same manner as Example 1, except that the lithium vanadium compound used in the production of the positive electrode was changed as shown in Table 1.

[Example 15]
A lithium ion secondary battery for evaluation of Example 15 was produced in the same manner as Example 1, except that the lithium vanadium compound used in the production of the positive electrode was changed as shown in Table 1.

Comparative Example 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 disulfonic acid was added.

Comparative Example 2
A lithium ion secondary battery for evaluation of Comparative Example 2 was produced in the same manner as in Example 14 except that the disulfonic acid was not added.

Comparative Example 3
A lithium ion secondary battery for evaluation of Comparative Example 3 was produced in the same manner as in Example 15 except that the disulfonic acid was not added.

Comparative Example 4
The composition of the slurry for forming a positive electrode active material layer produced in manufacturing the positive electrode, LiCoO ₂ 85 parts by weight of carbon black 5 parts by mass, and PVDF10 parts by mass to prepare a positive electrode. A lithium ion secondary battery for evaluation of Comparative Example 4 was produced in the same manner as Example 1 except for the above.

Comparative Example 5
The composition of the slurry for forming the positive electrode active material layer prepared in the preparation of the positive electrode was 85 parts by mass of LiNi _0.85 Co _0.10 Al _0.05 O ₂ , 5 parts by mass of carbon black, 10 parts by mass of PVDF, and the positive electrode was prepared. did. A lithium ion secondary battery for evaluation of Comparative Example 5 was produced in the same manner as Example 1 except for the above.

Comparative Example 6
A lithium ion secondary battery for evaluation of Comparative Example 6 was produced in the same manner as in Comparative Example 4 except that no disulfonic acid was added.

Comparative Example 7
A lithium ion secondary battery for evaluation of Comparative Example 7 was produced in the same manner as in Comparative Example 5 except that no disulfonic acid was added.

  About the lithium ion secondary battery for evaluation produced in Examples 2-15 and Comparative Examples 1-7, the measurement of the capacity retention after 300 cycles was performed in the same manner as in Example 1. The results are shown in Table 1.

  In all of Examples 1 to 15, the capacity retention rate improved after 300 cycles as compared with Comparative Example 1 in which no disulfonic acid was used.

  From the results of Example 7, it was confirmed that setting the molecular weight of the disulfonic acid to 280 g / mol or less provides the effect of further improving the capacity retention after 300 cycles.

  From the results of Example 6, it was confirmed that, by setting the total carbon number of the disulfonic acid to 5 or less, the effect of further improving the capacity retention rate after 300 cycles can be obtained.

  From the results of Examples 1 to 5, it was confirmed that by using methanedisulfonic acid or 1,2-ethanedisulfonic acid as the disulfonic acid, the effect of further improving the capacity retention after 300 cycles was obtained.

  From the results of Examples 8 to 13, it was confirmed that the effect of further improving the capacity retention rate after 300 cycles can be obtained by optimizing the addition amount of disulfonic acid.

Example 14 and 15, from the results of Comparative Examples 2 and 3, when using the LiVOPO ₄ as a lithium vanadium compound, that higher improving effect after 300 cycles the capacity retention ratio were obtained.

  According to the present invention, a lithium ion secondary battery capable of improving cycle 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 (6)

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 electrolytic solution,
The positive electrode contains a lithium vanadium compound,
The lithium ion secondary battery, wherein the electrolytic solution contains disulfonic acid.   The molecular weight of the said disulfonic acid is 280 g / mol or less, The lithium ion secondary battery of Claim 1 characterized by the above-mentioned. The lithium ion secondary battery according to claim 1 or 2, wherein the disulfonic acid is represented by the following chemical formula (1).
(R1 is a linear substituted or unsubstituted alkyl chain of 1 to 5 carbon atoms.)

  The lithium ion secondary battery according to any one of claims 1 to 3, wherein the disulfonic acid is methanedisulfonic acid or 1,2-ethanedisulfonic acid.   The lithium ion secondary battery according to any one of claims 1 to 4, wherein the disulfonic acid is contained in the electrolyte solution in an amount of 0.01% by weight or more and 3.0% by weight or less. The lithium ion secondary battery according to any one of claims 1 to 5 wherein the lithium vanadium compound characterized in that it is a LiVOPO _4.

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