JP2018133281A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery in which gas generation in a high temperature storage test can be suppressed.SOLUTION: The lithium ion secondary battery is provided that comprises: a positive electrode; a negative electrode; a separator positioned between the positive electrode and the negative electrode; and electrolytic solution. The positive electrode includes a lithium vanadium compound represented by Li(M)(PO)(where M=VO or V, and 0.9≤a≤3.3, 0.9≤b≤2.2, 0.9≤c≤3.3). The electrolytic solution includes a divalent nickel compound.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary 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.

  An electrolyte is present as one of the members constituting the lithium ion secondary battery. This electrolytic solution is generally a solution in which a solute such as lithium hexafluorophosphate is dissolved in a solvent in which a cyclic carbonate represented by ethylene carbonate and a chain carbonate represented by diethyl carbonate are mixed. Is used. However, these solvents have a problem in that they gradually react on the electrode surface during battery driving and high-temperature storage tests, and generate gases that adversely affect battery characteristics.

  Therefore, an attempt has been made to suppress the gas generation by adding an additive that decomposes in advance to form a stable film on the electrode surface. Patent Document 1 reports that gas generation can be effectively suppressed by adding a thiophene-based additive.

JP 2000-182673 A

  However, the properties of the prior art are not yet satisfactory, and there is a demand for further suppression of gas generation particularly in a high temperature storage test.

  As a result of intensive studies, the present inventors have found that cyclic carbonate is decomposed at the positive electrode and carbon monoxide is generated in a high-temperature storage test.

  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 lithium ion secondary battery capable of suppressing gas generation in a high temperature storage test.

In order to solve the above problems, a lithium ion secondary battery according to the present invention includes 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 ≦ c A lithium vanadium compound represented by ≦ 3.3),
The electrolytic solution contains a divalent nickel compound.

  According to this, a lithium ion secondary battery including a lithium vanadium compound in the positive electrode has a problem that a large amount of carbon monoxide is generated as a gas during a high temperature storage test. This is presumably because vanadium is strongly coordinated to the carbonyl oxygen of the cyclic carbonate, and the decomposition proceeds while maintaining the carbonyl structure. The divalent nickel ion reacts with carbon monoxide to form a carbonyl-containing nickel complex. Since carbon monoxide generated in the high temperature storage test is captured by this reaction, gas generation in the high temperature storage test can be suppressed.

  The lithium ion secondary battery according to the present invention is preferably a nickel complex in which the nickel compound takes a planar four-coordinate.

  According to this, it is more suitable from the viewpoint of reactivity with carbon monoxide, and it is possible to further suppress gas generation during the high-temperature storage test.

In the lithium ion secondary battery according to the present invention, the nickel compound is more preferably M ₂ [Ni (CN ⁻ ) ₄ ].
[M represents at least one selected from Li, Na, and K. ]

  According to this, it is more suitable from the viewpoint of reactivity with carbon monoxide, and it is possible to further suppress gas generation during the high-temperature storage test.

For the lithium ion secondary battery according to the present invention, the nickel compound is preferably contained in an amount of 1 × 10 ⁻⁴ mol / L or more and 3 × 10 ⁻² mol / L or less in terms of nickel element.

  For the lithium ion secondary battery according to the present invention, the nickel compound is 0.01 mol% or more and 1 mol% or less with respect to the molar amount of the vanadium element in the lithium vanadium compound contained in the positive electrode in terms of nickel element. It is preferably included.

  According to this, it is suitable as an addition amount, and gas generation during a high temperature storage test can be further suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery which can suppress gas generation | occurrence | production in a high temperature storage test 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. A plate-like separator 18, an electrolyte solution containing lithium ions, a case 50 containing these in a sealed state, and one end of the negative electrode 20 being electrically connected. 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 are provided.

  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 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 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 invention has 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.
(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, and a necessary amount of positive electrode conductive additive.

(Positive electrode active material)
The positive electrode active material 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 positive electrode active material has a problem that a large amount of carbon monoxide is generated as a gas during a high-temperature storage test. This is presumably because vanadium is strongly coordinated to the carbonyl oxygen of the cyclic carbonate, and the decomposition proceeds while maintaining the carbonyl structure. For this reason, when combined with the electrolytic solution according to the present embodiment, an effect of suppressing gas generation in a high temperature storage test is obtained.

(Binder for positive electrode)
The positive electrode binder bonds the positive electrode active materials to each other and bonds the positive electrode active material layer 14 to the positive electrode current collector 12. 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 aid 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 aid 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.

(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.

  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.

<Electrolyte>
The electrolytic solution according to this embodiment contains a divalent nickel compound.

  The electrolytic solution according to this embodiment is generated in a large amount in a high-temperature storage test when a positive electrode contains a lithium vanadium compound due to a reaction in which divalent nickel ions react with carbon monoxide to form a carbonyl-containing nickel complex. Carbon monoxide can be captured. Thereby, gas generation in the high temperature storage test can be suppressed.

  In the electrolytic solution according to this embodiment, it is preferable that the nickel compound further takes a planar four-coordinate.

  According to this, it is more suitable from the viewpoint of reactivity with carbon monoxide, and it is possible to further suppress gas generation during the high-temperature storage test.

In the electrolytic solution according to this embodiment, the nickel compound is preferably M ₂ [Ni (CN ⁻ ) ₄ ].
[M represents at least one selected from Li, Na, and K. ]

  According to this, it is more suitable from the viewpoint of reactivity with carbon monoxide, and it is possible to further suppress gas generation during the high-temperature storage test.

In the electrolytic solution according to the present embodiment, it is preferable that the nickel compound is contained in an amount of 1 × 10 ⁻⁴ mol / L or more and 3 × 10 ⁻² mol / L or less in terms of nickel element.

  In the electrolytic solution according to the present embodiment, the nickel compound is further contained in an amount of 0.01 mol% or more and 1 mol% or less with respect to the molar amount of the vanadium element in the lithium vanadium compound contained in the positive electrode in terms of nickel element. Preferably it is.

  According to this, it is suitable as an addition amount, and gas generation during a high temperature storage test can be further suppressed.

  The addition amount of the nickel compound can be adjusted by adding an arbitrary amount to the electrolytic solution, and can be measured by a high frequency inductively coupled plasma emission spectroscopy (ICP), a fluorescent X-ray analysis (XRF) or the like.

  The solvent of the electrolytic solution is not particularly limited as long as it is a solvent generally used in lithium ion secondary batteries. For example, cyclic carbonate compounds such as ethylene carbonate (EC) and propylene carbonate (PC), diethyl carbonate (DEC) ), A chain carbonate compound such as ethyl methyl carbonate (EMC), a cyclic ester compound such as γ-butyrolactone, a chain ester compound such as propyl propionate, ethyl propionate, ethyl acetate, etc. be able to.

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)
70 parts by mass of Li (Ni _0.85 Co _0.10 Al _0.05 ) O _2, 15 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 mixed with N-methyl-2-pyrrolidone (NMP The slurry for forming the positive electrode active material layer was prepared. 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)
A negative electrode was produced by attaching a 100 μm lithium foil on a 16 μm thick copper foil.

(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, bis (cyclopentadienyl) nickel was added to the solution as a nickel compound so as to have a concentration of 5 × 10 ⁻³ mol%, thereby preparing an electrolytic 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. The injection amount here is 1.1 mol% so that the nickel compound is in terms of nickel element with respect to the molar amount of vanadium element in the lithium vanadium compound contained in the positive electrode. went.
(Measurement of gas generation during high-temperature storage test)
About the lithium ion secondary battery for evaluation produced above, using a secondary battery charge / discharge test apparatus (manufactured by Hokuto Denko Co., Ltd.), a charge rate of 0.5 C (at constant current charging at 25 ° C. in 2 hours) The battery was charged until the battery voltage reached 4.2 V by constant current charging (current value at which charging was completed). After completion of charging, a cut was made in a part of the aluminum laminate pack, the gas was vented, and vacuum sealing was performed again. The volume of the battery was measured by the Archimedes method, were determined cell volume V ₁ of the previous high-temperature storage test.

The battery for which the battery volume V ₁ was determined as described above was allowed to stand for 4 hours in a thermostatic chamber (manufactured by ESPEC Corporation) whose temperature was set to 85 ° C. After 4 hours, allowed to heat radiation for 15 minutes at room temperature, remove the battery to measure the battery volume again by the Archimedes method, were determined cell volume V ₂ after high-temperature storage test.

From the volumes V ₁ and V ₂ before and after the high temperature storage test determined above, the gas generation amount V during the high temperature storage test was determined according to the following formula (1). The obtained results are shown in Table 1.
V = V ₂ −V ₁ (1)

[Examples 2 to 8]
Lithium ion secondary batteries for evaluation of Examples 2 to 8 were produced in the same manner as in Example 1 except that the nickel compound and concentration used in the production of the electrolytic solution were changed to the compounds shown in Table 1.

[Examples 9 and 10]
Evaluation lithium ion secondary batteries of Examples 9 and 10 were produced in the same manner as in Example 5 except that the lithium vanadium compound used in the production of the positive electrode was changed to the compounds shown in Table 1.

[Examples 11 and 12]
The injection amount of the electrolytic solution used for producing the evaluation lithium secondary battery is shown in Table 1 with respect to the molar amount of the vanadium element in the lithium vanadium compound in which the nickel compound is contained in the positive electrode in terms of nickel element. Except having changed so that it might become a value, it carried out similarly to Example 3, and produced the lithium ion secondary battery for evaluation of Examples 11 and 12.

[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 the nickel compound was not added in the production of the electrolytic solution.

  For the lithium ion secondary batteries for evaluation in Examples 2 to 12 and Comparative Example 1, the amount of gas generated during the high temperature storage test was measured in the same manner as in Example 1. The results are shown in Table 1.

  In each of Examples 1 to 9, the amount of gas generated during the high-temperature storage test was suppressed compared to Comparative Example 1 in which no nickel compound was added. Moreover, from the results of Examples 9 and 10, it was confirmed that the effect of suppressing the amount of gas generated during the high-temperature storage test was obtained for all the positive electrodes containing the lithium vanadium compound. Furthermore, from the results of Examples 11 and 12, it was confirmed that by optimizing the amount of the nickel compound relative to the lithium vanadium compound, an effect of further suppressing the amount of gas generated during the high temperature storage test was obtained.

  The present invention provides a lithium ion secondary battery capable of suppressing gas generation in a high temperature storage test.

  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 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 solution,
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 ≦ c A lithium vanadium compound represented by ≦ 3.3),
The lithium ion secondary battery, wherein the electrolytic solution contains a divalent nickel compound.   The lithium ion secondary battery according to claim 1, wherein the nickel compound is a nickel complex having a planar four-coordination. The lithium ion secondary battery according to claim 1, wherein the nickel compound is M ₂ [Ni (CN ⁻ ) ₄ ].
[M represents at least one selected from Li, Na, and K. ] 4. The nickel compound according to claim 1, wherein the nickel compound is contained in an amount of 1 × 10 ⁻⁴ mol / L or more and 3 × 10 ⁻² mol / L or less in terms of nickel element. Lithium ion secondary battery. The said nickel compound is 0.01 mol% or more and 1 mol% or less with respect to the molar amount of the vanadium element in the lithium vanadium compound contained in the said positive electrode in conversion of nickel element, The 1 thru | or characterized by the above-mentioned. The lithium ion secondary battery according to any one of 4.

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