JP2018160380A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery with high cycle characteristics.SOLUTION: The lithium ion secondary battery is provided which includes a positive electrode capable of storing and releasing a lithium ion, a negative electrode, and electrolyte, and in which the electrolyte contains at least two kinds of chelating agents having different coordination number, and the positive electrode contains a lithium vanadium compound represented by the following formula (1). Li(M)(PO)... (1) (in the formula (1), M=VO or V, and 0.9≤a≤3.3, 0.9≤b≤2.2, and 0.9≤c≤3.3)SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery.

  Lithium ion secondary batteries currently used mainly use a material capable of inserting and removing lithium ions as a negative electrode and a positive electrode, sandwiching a porous separator between the positive electrode and the negative electrode, and using a non-aqueous electrolyte It is manufactured by filling, and electrical energy is generated by an oxidation reaction and a reduction reaction when lithium ions are inserted and removed from the positive electrode and the negative electrode.

When charging / discharging a lithium ion secondary battery, there is a known problem that the performance decreases due to dissolution of transition metal ions from the positive electrode active material. For example, when LiCoO ₂ is used as the positive electrode active material, Co ions are eluted into the electrolytic solution. The transition metal ions eluted in the electrolyte cause clogging of the separator or precipitate on the negative electrode, thereby deteriorating the cycle characteristics of the lithium ion secondary battery.

  In order to solve such a problem, a method of trapping transition metal ions with a chelating agent has been proposed. In Patent Document 1, a chelating agent that forms a complex with a transition metal ion while not reacting and coordinated with lithium ions is added to the electrolyte so that the transition metal ions are deposited from the negative electrode during charge and discharge of the battery. It has been shown to suppress reactions and improve battery performance and safety.

Special table 2009-517836

  However, the conventional methods have not yet satisfied various characteristics, and further improvement in cycle characteristics has been demanded.

  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 having high 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 having a positive electrode capable of inserting and extracting lithium ions, a negative electrode, and an electrolyte solution,
The electrolyte solution includes at least two kinds of chelating agents having different coordination numbers, and the positive electrode includes a lithium vanadium compound represented by the following formula (1).
Li _a (M) _b (PO ₄ ) _c (1)
(However, M = VO or V and 0.9 ≦ a ≦ 3.3, 0.9 ≦ b ≦ 2.2, 0.9 ≦ c ≦ 3.3)

  According to this, by combining two or more kinds of chelating agents having different conformational numbers, it becomes possible to efficiently capture ions even for vanadium ions having a large valence fluctuation, and vanadium ions eluted from the positive electrode are negative. It is possible to prevent precipitation on the surface and to improve the cycle characteristics.

The chelating agent preferably has at least one selected from chemical formulas A1 to A12.

  According to this, it is suitable as a chelating agent, the ability to capture vanadium ions is improved, and the cycle characteristics can be further improved.

  It is preferable that the total amount of the chelating agent is 0.01 mol / L to 1.0 mol / L with respect to the electrolytic solution.

  According to this, it is suitable as an addition amount, and the cycle characteristics can be further improved.

The lithium vanadium compound preferably contains at least one selected from Li ₃ V ₂ (PO ₄ ) _{3 and} LiVOPO ₄ .

  According to the present invention, a lithium ion secondary battery having high cycle 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>
In the positive electrode 10 according to the present embodiment, Li _a (M) _b (PO ₄ ) _c (where M = VO or V, and 0.9 ≦ a ≦ 3.3, 0.8. 9 ≦ b ≦ 2.2, 0.9 ≦ c ≦ 3.3) having a positive electrode active material layer 14 containing a lithium vanadium compound, a positive electrode binder, and a positive electrode conductive additive. .
(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.

  From the positive electrode active material, vanadium ions that cause cycle deterioration are eluted as the cycle progresses. For this reason, when combined with the electrolytic solution according to the present embodiment, an effect of improving the cycle characteristics can be obtained.

The lithium vanadium compound according to the present embodiment preferably further includes at least one selected from Li ₃ V ₂ (PO ₄ ) ₃ or LiVOPO ₄ .

As the lithium vanadium compound, it is particularly preferable to have LiVOPO ₄ . As a result, high cycle characteristics can be achieved and the capacity density can be improved.

The positive electrode active material according to the present embodiment is a normal lithium ion secondary battery such as LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.80 Co _0.15 Al _0.05 O _2. It is preferable to use a mixture of the compound used as the positive electrode material and the lithium vanadium compound described above.

In the positive electrode active material according to this embodiment, the ratio (δ) of the lithium vanadium compound to the total mass of the normal positive electrode material and the lithium vanadium compound is preferably 0.4 ≦ δ ≦ 20.
[Where δ is δ = (B / (A + B)) × 100, where A represents the mass of a normal positive electrode active material, and B represents the mass of a lithium vanadium compound. ]

(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.

  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 the present embodiment includes at least two types of chelating agents having different coordination numbers.

  According to this, when combined with the positive electrode according to the present embodiment, it becomes possible to efficiently capture ions with respect to vanadium ions having a large valence fluctuation eluted in the electrolytic solution, and vanadium eluted from the positive electrode. Since ions can be prevented from being deposited on the negative electrode, an effect of improving cycle characteristics can be obtained.

In the electrolytic solution according to this embodiment, the chelating agent is preferably represented by chemical formulas A1 to A12.

  According to this, it is suitable as a chelating agent, the ability to capture vanadium ions is improved, and the cycle characteristics can be further improved.

  These chelating agents can be identified by known analytical methods such as nuclear magnetic resonance spectroscopy (NMR).

  In the electrolytic solution according to this embodiment, the total amount of the chelating agent is preferably 0.01 mol / L to 1.0 mol / L with respect to the electrolytic solution.

  According to this, it is suitable as an addition amount, and the cycle characteristics can be further improved.

  The total amount of chelating agent relative to the electrolyte can be identified by known analytical methods such as thermogravimetric / differential thermal analysis (TG / DTA).

(solvent)
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, and ethyl acetate, etc. Can be used.

(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)
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 are N-methyl- A slurry for forming a positive electrode active material layer was prepared by dispersing in 2-pyrrolidone (NMP). 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 slurry for forming a negative electrode active material layer was prepared by dispersing natural graphite 90 in mass parts, carbon black 5 in mass parts, and PVDF5 in mass parts in N-methyl-2-pyrrolidone (NMP). 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, 1,2-ethylenediamine as a first chelating agent was added to the solution shown in Table 1 at a concentration of 0.1 mol / L, and diethylenetriamine was added as a second chelating agent to a concentration of 0.1 mol / L. Then, an electrolytic solution was produced.

(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.

(Total amount of anionic polymer)
The lithium ion secondary battery for evaluation produced above was disassembled, and the total amount of the chelating agent was measured using a thermogravimetric / differential thermal analysis method (TG / DTA).

[Example 2]
A lithium ion secondary battery for evaluation of Example 2 was produced in the same manner as in Example 1 except that triethylenetetramine was used as the second chelating agent.

[Example 3]
A lithium ion secondary battery for evaluation of Example 3 was produced in the same manner as in Example 1 except that tris (2-aminoethyl) amine was used as the second chelating agent.

[Example 4]
A lithium ion secondary battery for evaluation of Example 4 was produced in the same manner as in Example 1 except that phenylbis (diphenylphosphinoethyl) phosphine was used as the second chelating agent.

[Example 5]
A lithium ion secondary battery for evaluation of Example 5 was produced in the same manner as in Example 1 except that tris [2- (diphenylphosphino) ethyl] phosphine was used as the second chelating agent.

[Example 6]
A lithium ion secondary battery for evaluation of Example 6 was produced in the same manner as in Example 1 except that diethylenetriamine was used as the first chelating agent and bis (diphenylphosphino) methane was used as the second chelating agent.

[Example 7]
A lithium ion secondary battery for evaluation of Example 7 was prepared in the same manner as in Example 1 except that diethylenetriamine was used as the first chelating agent and 1,2-bis (diphenylphosphine) ethane was used as the second chelating agent. did.

[Example 8]
A lithium ion secondary battery for evaluation of Example 8 was produced in the same manner as in Example 1 except that diethylenetriamine was used as the first chelating agent and 1,3-propanediamine was used as the second chelating agent.

[Example 9]
The evaluation lithium ion secondary battery of Example 9 is the same as Example 1 except that diethylenetriamine is used as the first chelating agent and 1,3-bis (diphenylphosphino) propane is used as the second chelating agent. Produced.

[Example 10]
A lithium ion secondary battery for evaluation of Example 10 was produced in the same manner as in Example 1 except that diethylenetriamine was used as the first chelating agent and 1,4-butanediamine was used as the second chelating agent.

[Example 11]
The evaluation lithium ion secondary battery of Example 11 is the same as Example 1 except that diethylenetriamine is used as the first chelating agent and 1,4-bis (diphenylphosphino) butane is used as the second chelating agent. Produced.

[Example 12]
A lithium ion secondary battery for evaluation of Example 12 was produced in the same manner as in Example 1 except that diethylenetriamine was used as the first chelating agent and triethylenetetramine was used as the second chelating agent.

[Example 13]
A lithium ion secondary battery for evaluation of Example 13 was produced in the same manner as in Example 1 except that diethylenetriamine was used as the first chelating agent and tris (2-aminoethyl) amine was used as the second chelating agent.

[Example 14]
The lithium ion secondary battery for evaluation of Example 14 as in Example 1 except that diethylenetriamine was used as the first chelating agent and tris [2- (diphenylphosphino) ethyl] phosphine was used as the second chelating agent. Was made.

[Example 15]
Evaluation lithium of Example 15 as in Example 1 except that phenylbis (diphenylphosphinoethyl) phosphine was used as the first chelating agent and tris (2-aminoethyl) amine was used as the second chelating agent. An ion secondary battery was produced.

[Example 16]
A lithium ion secondary battery for evaluation of Example 16 was produced in the same manner as in Example 1 except that Li ₃ V ₂ (PO ₄ ) ₃ was used as the lithium vanadium compound.

[Example 17]
Except that the addition amount of the first chelating agent is 0.005 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent is 0.005 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 17 was produced in the same manner as Example 1.

[Example 18]
Except that the addition amount of the first chelating agent was 0.011 mol / L with respect to the electrolytic solution and the addition amount of the second chelating agent was 0.011 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 18 was produced in the same manner as Example 1.

[Example 19]
Except that the addition amount of the first chelating agent was 0.045 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent was 0.045 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 19 was produced in the same manner as Example 1.

[Example 20]
The addition amount of the first chelating agent was 0.050 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent was added so as to be 0.050 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 20 was produced in the same manner as Example 1.

[Example 21]
Except that the addition amount of the first chelating agent is 0.25 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent is 0.25 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 21 was produced in the same manner as Example 1.

[Example 22]
Except that the addition amount of the first chelating agent is 0.26 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent is 0.26 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 22 was produced in the same manner as Example 1.

[Example 23]
The addition amount of the first chelating agent was 0.49 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent was added so as to be 0.49 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 23 was produced in the same manner as Example 1.

[Example 24]
Except that the addition amount of the first chelating agent was 0.51 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent was 0.51 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 24 was produced in the same manner as Example 1.

[Example 25]
Except that the addition amount of the first chelating agent was 0.058 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent was 0.142 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 25 was produced in the same manner as Example 1.

[Example 26]
Except that the addition amount of the first chelating agent is 0.060 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent is 0.140 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 26 was produced in the same manner as Example 1.

[Example 27]
The addition amount of the first chelating agent was 0.140 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent was added so as to be 0.060 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 27 was produced in the same manner as Example 1.

[Example 28]
Except that the addition amount of the first chelating agent was 0.142 mol / L with respect to the electrolytic solution, and the addition amount of the second chelating agent was 0.058 mol / L with respect to the electrolytic solution, A lithium ion secondary battery for evaluation of Example 28 was produced in the same manner as Example 1.

[Comparative Example 1]
A lithium ion secondary battery for evaluation of Comparative Example 1 was prepared in the same manner as in Example 1 except that oxalic acid was used as the first chelating agent and ethylenediaminetetraacetic acid (EDTA) was used as the second chelating agent.

[Comparative Example 2]
A lithium ion secondary battery for evaluation of Comparative Example 2 was produced in the same manner as in Example 1 except that no chelating agent was added.

[Comparative Example 3]
A lithium ion secondary battery for evaluation of Comparative Example 3 was produced in the same manner as in Example 1 except that only the second chelating agent was not added.

  Table 1 shows structural formulas corresponding to the chelating agents used in Examples 1 to 28 and Comparative Example 3. These chelating agents are listed in Table 2 as A1 to A12.

(Measurement of capacity retention after 500 cycles)
About the lithium ion secondary battery for evaluation produced above, using a secondary battery charge / discharge test apparatus (manufactured by Hokuto Denko Co., Ltd.), the charge rate is 1.0 C (when constant current charging is performed at 25 ° C. in 1 hour) The battery was charged until the battery voltage reached 4.2 V by constant current charging (current value at which charging was completed), and was discharged until the battery voltage reached 2.8 V by constant current discharging at a discharge rate of 1.0 C. Detecting the discharge capacity after the charge and discharge ends, to determine the battery capacity to Q ₁ before the cycle test.

The battery determined battery capacity Q ₁ above, using the secondary battery charging and discharging test device again was charged until the battery voltage at a constant current charging charge rate 1.0C becomes 4.2 V, discharge rate 1. The battery was discharged at a constant current of 0 C until the battery voltage reached 2.8V. The charge / discharge was counted as one cycle, and 500 cycles of charge / discharge were performed. Then, to detect the discharge capacity after 500 cycles of charge and discharge termination, to determine the battery capacity Q ₂ after 500 cycles.

From the capacitor _Q 1, _{Q 2} obtained above, in accordance with equation (1), the capacity retention ratio was obtained E after 500 cycles. The obtained results are shown in Table 2.
E = Q ₂ / Q ₁ × 100 (1)

  Examples 1-28 were all compared to Comparative Example 1 in which no chelating agents A1 to A12 were added, Comparative Example 2 in which no chelating agent was added, and Comparative Example 3 in which only one chelating agent was added. The capacity retention rate after the cycle was improved, and a synergistic effect was obtained by adding two or more chelating agents A1 to A12. From the results of Examples 1 to 15, it was confirmed that the effect of improving the capacity retention after 500 cycles was obtained by combining two or more chelating agents having different conformational numbers. Further, it was confirmed that even when an amine-based or phosphine-based chelating agent was combined, an effect of improving the capacity retention after 500 cycles was obtained.

From the results of Examples 1 and 16, it was confirmed that the use of LiVOPO ₄ as the lithium vanadium compound has the effect of improving the capacity retention ratio after 500 cycles than using Li ₃ V ₂ (PO ₄ ) _3. It was done.

  From the results of Examples 17 to 24, it was confirmed that the effect of further improving the capacity retention after 500 cycles was obtained by optimizing the addition amounts of the two chelating agents. Furthermore, from the results of Examples 25 to 28, it was confirmed that by optimizing the ratio of the two types of chelating agents, the effect of further improving the capacity retention rate after 500 cycles was obtained.

  The present invention provides a lithium ion secondary battery having high cycle characteristics.

  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 (4)

A lithium ion secondary battery having a positive electrode capable of inserting and extracting lithium ions, a negative electrode, and an electrolyte solution,
A lithium ion secondary battery in which the electrolytic solution contains at least two kinds of chelating agents having different coordination numbers, and the positive electrode contains a lithium vanadium compound represented by the following formula (1).
Li _a (M) _b (PO ₄ ) _c (1)
(However, M = VO or V and 0.9 ≦ a ≦ 3.3, 0.9 ≦ b ≦ 2.2, 0.9 ≦ c ≦ 3.3) The lithium ion secondary battery according to claim 1, wherein the chelating agent has at least one selected from chemical formulas A1 to A12.

  The lithium ion secondary battery according to claim 1 or 2, wherein the total amount of the chelating agent is 0.01 mol / L to 1.0 mol / L with respect to the electrolytic solution. 4. The lithium ion secondary battery according to claim 1, wherein the lithium vanadium compound contains at least one selected from Li ₃ V ₂ (PO ₄ ) ₃ or LiVOPO _{4. 5} .

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