WO2013151096A1

WO2013151096A1 - Lithium secondary cell

Info

Publication number: WO2013151096A1
Application number: PCT/JP2013/060218
Authority: WO
Inventors: 学落田; 安部　武志; 貴之土井; 小久見　善八
Original assignee: 新神戸電機株式会社
Priority date: 2012-04-05
Filing date: 2013-04-03
Publication date: 2013-10-10
Also published as: JPWO2013151096A1

Abstract

Provided is a lithium secondary cell in which the charge/discharge cycle characteristics and storage characteristics do not readily deteriorate, even under extreme usage conditions. There is configured a lithium secondary cell provided with: a positive electrode plate containing, as the positive electrode active material, a lithium-containing transition metal complex oxide; a negative electrode plate containing, as the negative electrode active material, a material in which oxidation and reduction or insertion and separation of lithium is possible; a separator positioned between the positive electrode plate and the negative electrode plate; and a non-aqueous electrolyte solution in which a lithium salt is dissolved. The non-aqueous electrolyte solution contains at least one type of cyclic ether selected from a thiacrown ether and an azacrown ether in which hydrogen bonded to a nitrogen atom is not substituted with another group.

Description

Lithium secondary battery

The present invention is interposed between a positive electrode plate using a lithium-containing transition metal complex oxide as a positive electrode active material, a negative electrode plate using a material capable of insertion / extraction or oxidation / reduction of lithium as a negative electrode active material, and the positive electrode plate and the negative electrode plate. The present invention relates to a lithium secondary battery including a separator and a non-aqueous electrolyte in which a lithium salt is dissolved.

A non-aqueous solution in which a lithium-containing transition metal composite oxide is used for the positive electrode plate, a material capable of lithium insertion / desorption or oxidation / reduction is used for the negative electrode plate, a separator is disposed between the positive electrode plate and the negative electrode plate, and a lithium salt is dissolved. Lithium secondary batteries using an electrolytic solution have a higher energy density and superior charge / discharge cycle characteristics as compared to aqueous secondary batteries. In particular, when a carbon material capable of inserting and removing lithium is used for the negative electrode, metal lithium is not used as the negative electrode, which is excellent in safety and is widely used as a lithium ion battery. Currently, lithium secondary batteries are being actively developed and improved for application to electric vehicles and power storage applications, and these applications require higher energy density than required for portable devices. Therefore, there are demands for charge / discharge cycle characteristics and storage characteristics under more severe use conditions.

In the case of a lithium ion battery using lithium manganate (LiMn ₂ O ₄ ) as the positive electrode active material, it is remarkable that Mn of the transition metal element elutes in the non-aqueous electrolyte at a high temperature. After being diffused and migrated, it is reduced and deposited on the negative electrode carbon material, and at this time, a film containing Li that reacts with the electrolytic solution and decomposition products of the electrolytic solution and cannot participate in charge / discharge is formed on the negative electrode carbon material. Therefore, the deterioration of cycle characteristics and storage characteristics at high temperatures is remarkable.

In order to solve this problem, a technique for preventing precipitation of eluted manganese by adding 1,3 dioxolane or succinic acid to the electrolytic solution (Patent Document 1: Japanese Patent Laid-Open No. 11-26018), and electrolysis of lithium borate oxide Technology for destabilizing eluting manganese by adding to liquid (Patent Document 2: Japanese Patent No. 4366724) and organic group having polymerizable unsaturated bond bonded to part of nitrogen atom of azacrown ethers There has been proposed a technique (Patent Document 3: Japanese Patent Application Laid-Open No. 2010-86954) that improves the charge / discharge cycle characteristics of a secondary battery by adding a compound to an electrolytic solution to form a protective film on the negative electrode.

Japanese Patent Laid-Open No. 11-26018 Japanese Patent No. 4366724 JP 2010-86954 A

However, even if the techniques of Patent Documents 1 and 2 are used, the phenomenon in which the transition metal element eluted from the positive electrode active material is reduced and precipitated on the negative electrode largely depends on the operating potential of the negative electrode, and is mainly based on the metal lithium potential standard. On the other hand, when a negative electrode using an operating potential range of 0 to 1 V is selected, reduction precipitation of the transition metal element on the negative electrode cannot be avoided. That is, when a negative electrode is selected as a carbon material capable of insertion / extraction of lithium, Sn, SnO, Si, SiO, metallic lithium, etc. capable of an oxidation-reduction reaction with lithium, the transition metal element is present on the negative electrode. A phenomenon of reduction precipitation occurs.

When a lithium-containing transition metal composite oxide such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), or lithium iron phosphate (LiFePO ₄ ) is used as the positive electrode active material, a relatively transition metal Although it is thought that element elution is small, it has been reported that transition metal elements (Co, Fe, Ni) are eluted in a non-aqueous electrolyte at a high temperature of 55 ° C. (Journal of The Electrochemical Society, 153). , 9, A1760-A1764, 2006). In this report, although the elution amount of transition metal elements (Co, Fe, Ni) is 6 to 25% lower than the elution amount of lithium manganate, lithium manganate was used as the positive electrode active material. Similar to the problem of elution Mn that occurs in some cases, it is assumed that a problem occurs in which the transition metal elements (Co, Fe, Ni) are reduced and deposited on the negative electrode carbon material. Assuming severe operating temperature conditions in electric vehicles and power storage applications, etc., electrolyte additives that prevent reduction deposition on the negative electrode due to elution of various transition metal elements are desired, not only Mn, It has not been put into practical use.

Further, in the technique of Patent Document 3 (Japanese Patent Laid-Open No. 2010-86954), azacrown ethers are bonded to other organic groups, and this compound exists as a protective film on the negative electrode surface. The protective film on the surface is composed of not only compounds in which azacrown ethers are bonded to other organic groups, but also a wide variety of components such as decomposition products of carbonates which are appropriately selected solvent components. The azacrown ethers that exist as a part of the compound in the protective film in such a state are fixed in the egg film in which lithium ions are embedded as a complex, and the transition metal ions eluted from the positive electrode are electrolyzed. When migrating and diffusing in the liquid to reach the surface of the negative electrode, an exchange reaction between lithium ions and transition metal ions cannot occur. Therefore, this technique cannot prevent the reduction precipitation reaction on the negative electrode surface of transition metal ions.

The purpose of the present invention is to prevent transition metals eluted from the positive electrode component from diffusing and migrating in the non-aqueous electrolyte and reducing and precipitating on the carbon material of the negative electrode, thereby suppressing deterioration in charge / discharge cycle characteristics and storage characteristics. An object of the present invention is to provide a rechargeable lithium battery.

A lithium secondary battery to be improved by the present invention includes a positive electrode plate containing a lithium-containing transition metal composite oxide as a positive electrode active material, and a negative electrode containing a material capable of insertion / extraction of lithium or redox as a negative electrode active material A plate, a separator interposed between the positive electrode plate and the negative electrode plate, and a non-aqueous electrolyte solution in which a lithium salt is dissolved. As the negative electrode active material, a carbon material capable of inserting and extracting lithium can be used.

In the lithium secondary battery of the present invention, the non-aqueous electrolyte contains cyclic ethers that can complex with transition metal ions dissolved in the electrolyte. The cyclic ether that can be used in the present invention is at least one cyclic ether selected from azacrown ethers in which hydrogen bonded to a nitrogen atom is not substituted with other groups, and thiacrown ethers. is there. That is, these cyclic ethers can be used alone or in combination. In azacrown ethers, the hydrogen bonded to the nitrogen atom in the azacrown ether is not substituted with another group, so the oxygen and nitrogen atoms in the constituent elements are negatively charged unpaired electrons in the ring. Oriented in the inner direction, various cations can be taken inside the ring and captured. Further, in the thiacrown ethers, the sulfur atom in the thiacrown ethers does not have other substituents, and the same effect as the azacrown ethers can be expected.

Lithium ion is the only cation present in the non-aqueous electrolyte at the beginning of use of the lithium secondary battery. In the non-aqueous electrolyte to which cyclic ethers are added, a part of this lithium ion is cyclic ether. It exists as a complex incorporated into a class. When the transition metal element in the lithium-containing transition metal composite oxide used as the positive electrode active material is eluted into the non-aqueous electrolyte due to the use condition history such as high temperature, the transition metal element is converted into a divalent cation as the electrolyte. Elute in. The divalent transition metal cation has a larger electrical interaction between the cyclic ethers and the cation in the non-aqueous electrolyte than the monovalent lithium-on. For this reason, the transition metal cation eluted from the positive electrode drives out lithium ions from the cyclic ethers complexed with the lithium ions, and newly forms a complex with the cyclic ethers. The transition metal ions once complexed with the cyclic ethers in this way are not released again into the electrolyte because their electrical interaction is larger than that of monovalent lithium ions. Even if this complexed complex diffuses and migrates in the electrolyte to the negative electrode material in a reducing atmosphere, it cannot approach the inside of the electric double layer where the reduction reaction accompanied by electron transfer on the negative electrode occurs. Precipitation does not occur. As described herein, the effect of capturing the transition metal element eluted from the positive electrode is most effective when cyclic ethers are present in the electrolyte solution in contact with the positive electrode.

A chain-like complex that forms a complex with lithium ions, such as ethylenediaminetetraacetic acid, can be applied, but when these are used as additives to non-aqueous electrolytes, transition metals are deposited on the negative electrode. The effect which suppresses was not acquired. The transition metal ions captured by the chain complex can approach the inside of the electric double layer on the carbon material of the negative electrode, and are considered to have received electrons and reduced and precipitated.

Further, the content of cyclic ethers in the non-aqueous electrolyte is preferably 0.001 to 1% by mass with respect to the non-aqueous electrolyte. When the content of the cyclic ether relative to the non-aqueous electrolyte is less than 0.001% by mass, the transition metal is likely to be deposited on the negative electrode plate, and when the content of the cyclic ether exceeds 1% by mass, the conductivity of the electrolyte This is because the rate and initial discharge capacity are likely to decrease.

In addition, it cannot be overemphasized that the nonaqueous electrolyte solution used with the above-mentioned lithium secondary battery may be used independently as a nonaqueous electrolyte solution for lithium secondary batteries.

It is a perspective view which shows the positive electrode plate, negative electrode plate, and separator which comprise the lithium secondary battery which is embodiment of this invention. It is a perspective view which shows the lithium secondary battery which is embodiment of this invention.

Hereinafter, embodiments of the lithium secondary battery according to the present invention will be described.

Examples of azacrown ethers added to the non-aqueous electrolyte include 1 aza-12-crown-4, 1,7 diaza-12-crown-4, 1 aza-15-crown-5, 1,7 diaza-15. Crown-5, 1,4,7 triaza-15-crown-5, 1aza-18-crown-6, 1,7 diaza-18-crown-6, 1,10 diaza-18-crown-6, 1 4,7 triaza-18-crown-6, and the like.

The thiacrown ethers added to the non-aqueous electrolyte include 1 thia-12-crown-4, 1,7 dithia-12-crown-4, 1 thia-15-crown-5, 1,7 dithia. -15-crown-5, 1,4,7 trithia-15-crown-5, 1 thia-18-crown-6, 1,7 dithia-18-crown-6, 1,10 dithia-18-crown-6 1,4,7 Trithia-18-crown-6, etc. are used.

The amount of cyclic ether added to the non-aqueous electrolyte is the amount of transition metal element eluted from the lithium-containing transition metal composite oxide as the positive electrode active material, as can be imagined from the capture form of the transition metal cation. The above addition amount is necessary. In general, it is difficult to accurately predict the amount of transition metal eluted from various positive electrode active materials under various usage conditions, but as a result of considering the assumed usage conditions, It was found that the effect can be obtained by adding 0.001 mass% to 10 mass% of crown ethers. However, the upper limit of the addition amount is desirably 1% by mass or less in consideration of the solubility of various crown ethers in the non-aqueous electrolyte and the conductivity of the electrolyte after dissolution. These cyclic ethers may be used alone or in combination of two or more.

The non-aqueous electrolyte used in the present invention was prepared by mixing LiPF ₆ as an electrolyte in a mixed solvent in which ethylene carbonate (EC) as a cyclic carbonate and diethyl carbonate (DEC) as a chain carbonate were mixed at a volume ratio of 1: 1. 1 mol · dm ⁻³ dissolved.

As the electrolyte, LiClO ₄ , LiBF ₄ , LiOSO ₂ CF ₃ , LiN (SO ₂ CF) ₂ , LiNC (SO ₂ CF) ₃ , lithium bisoxalate borate, etc. can be used other than those described here. .

As the solvent, cyclic carbonates, cyclic esters, ethers and the like are generally used. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinyl ethyl carbonate, fluoroethylene carbonate, and trifluoropropylene carbonate, and chain carbonates include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl. Carbonates, etc., cyclic esters such as γ-butyl lactone, 2-methyl-γ-butyl lactone, etc., ethers such as tetrahydrofurone, 1,4-dioxane, 1,3-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl ether, diethyl ether, ethylene glycol, etc. are generally used. These are used alone or in combination of two or more. Can be used as a mixture.

The lithium secondary battery according to the present invention can be constituted by adding the above-described crown ethers in a mass ratio, preferably 0.001% by mass to 1% by mass, with respect to the non-aqueous electrolyte.

As the positive electrode active material, two types are synthesized: Li (Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ assuming Ni, Co, Mn as eluting transition metal elements, and LiFePO ₄ assuming Fe. did. Li (Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ is Li ₂ CO ₃ , Ni (OH) ₂ , Co (OH) ₃ , Mn (OH) ₄ are weighed and mixed at a predetermined mixing ratio And heated in air at 900 ° C. to obtain a predetermined active material. For LiFePO ₄ , FeC ₂ O ₄ , NH ₄ H ₂ PO ₄ , and Li ₂ CO ₃ are weighed at a predetermined blending ratio, mixed in acetone, vacuum dried at 60 ° C., and then heated at 700 ° C. in a nitrogen stream. Thus, a predetermined active material was obtained. The present invention relates to an electrolytic solution additive, and the positive electrode active material only needs to contain a transition element, and is not limited to the active materials listed here. LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ Etc., and those obtained by substituting a part of the transition metal element in the positive electrode active material described herein can also be used.

A slurry is prepared by dispersing and mixing these active materials, acetylene black as a conductive aid, and polyvinylidene fluoride as a binder in a dispersion solvent of N-methyl-2-pyrrolidone in a weight ratio of 88: 6: 6, respectively. To do. This slurry is applied on a 20 μm thick aluminum foil serving as a positive electrode current collector, dried to evaporate and vaporize N-methyl-2-pyrrolidone as a dispersion solvent, and then a predetermined active material density by a roll press. To obtain a positive electrode mixture.

As shown in FIG. 1, this was cut into a width of 50 mm and a length of 80 mm to form a positive electrode plate 1, and a positive electrode current collecting tab 2 was attached to the positive electrode.

As a carbon material capable of inserting and desorbing lithium, natural graphite having an average particle diameter of 10 μm and polyvinylidene fluoride as a binder are dispersed in a dispersion solvent of N-methyl-2-pyrrolidone in a weight ratio of 92: 8. Mix to make a slurry. This slurry is applied onto a 10 μm thick copper foil serving as a negative electrode current collector, dried to evaporate and dry N-methyl-2-pyrrolidone as a dispersion solvent, and then a predetermined active material density by a roll press. To obtain a negative electrode mixture.

As shown in FIG. 1, this was cut into a width of 55 mm and a length of 85 mm to form a negative electrode plate 3, and a negative electrode current collecting tab 4 was attached to the negative electrode.

In this example, natural graphite is used as the carbon material. However, the present invention is not limited to this, and amorphous carbon, artificial graphite, hard carbon, and the like can be used as appropriate. As a material capable of oxidation and reduction of lithium, Sn, SnO, Si, SiO, metallic lithium, and the like can also be used. Moreover, although the fluoropolymer polyvinylidene fluoride is used as the binder, a styrene butadiene rubber that is a diene polymer, an acrylate ester that is an acrylate polymer, or the like can be used as appropriate.

The produced positive electrode plate 1 and the negative electrode plate 3 are opposed to each other through a separator 5 made of a polyethylene microporous film having a thickness of 30 μm, a width of 58 mm, and a length of 90 mm to produce a laminated electrode group. The separator is not limited to the polyethylene described here, but a polypropylene microporous film, a porous polyethylene / polypropylene multilayer film, polyester fiber, polyamide fiber, non-woven fabric made of glass fiber, etc., and their surfaces And ceramic fine particles such as silica, alumina, and titania attached thereto.

As shown in FIG. 2, the electrode group is housed in a battery container composed of an aluminum laminate film 6, and 1 ml of an electrolyte is injected into the battery container. A battery for testing was obtained by sealing the opening of the battery container so that the current collecting tab was taken out. The aluminum laminate film 6 is, for example, a laminate of polyethylene terephthalate (PET) film / aluminum foil / sealant layer (polypropylene or the like). The electrode size, electrode group shape, and battery shape to be produced can be arbitrarily selected and are not limited to the above-described configuration.

Experimental example

Specific examples of the present invention will be described below.

[Experimental Examples 1 to 24]
The electrolyte is a solution in which lithium hexafluorophosphate (LiPF ₆ ), which is an electrolyte, is dissolved at a concentration of 1 mol · dm ⁻³ in a solvent in which ethylene carbonate (EC) and dimethyl carbonate are mixed at a volume ratio of 1: 1. This was used as a standard electrolyte. Li (Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ was used as the positive electrode active material, natural graphite was used as the negative electrode active material, and a lithium secondary battery comprising an electrode group with a designed discharge capacity of 50 mAh was produced.

To the standard electrolyte, the following additives (a) to (j) were added in the mass% shown in Table 1. Note that Experimental Example 20 does not contain any of the additives (a) to (j).

(A) 1 aza 12-crown-4 ether (b) 1 aza 15-crown-5 ether (c) 1 aza 18-crown-6 ether (d) 1 thia 12-crown-4 ether (e) 1 thia 15 -Crown-5 ether (f) 1 thia 18-crown-6 ether (g) 12-crown-4 ether (h) 15-crown-5 ether (i) 18-crown-6 ether (j) ethylenediaminetetraacetic acid ( Experimental Example 1) To this standard electrolyte solution, 0.001 wt% of 1 aza 12-crown-4 ether was added by weight.

(Experimental Example 2) 1 aza 12-crown-4 ether having a weight ratio of 1 wt% was added to this standard electrolyte.

(Experimental Example 3) 10 wt% of 1 aza 12-crown-4 ether was added to the standard electrolyte solution in a weight ratio.

(Experimental Example 4) 0.001 wt% of 1 aza 15-crown-5 ether was added to this standard electrolyte solution in a weight ratio.

(Experimental example 5) 1 aza 15-crown-5 ether having a weight ratio of 1 wt% was added to the standard electrolyte.

(Experimental example 6) 1 aza 15-crown-5 ether having a weight ratio of 10 wt% was added to the standard electrolyte.

(Experimental Example 7) 0.001 wt% of 1 aza 18-crown-6 ether was added to this standard electrolyte solution in a weight ratio.

(Experimental Example 8) 1 aza 18-crown-6 ether having a weight ratio of 1 wt% was added to this standard electrolyte.

(Experimental Example 9) 10 wt% of 1 aza 18-crown-6 ether was added to the standard electrolyte solution in a weight ratio.

(Experimental Example 10) 0.001 wt% 1 thia 12-crown-4 ether was added to the standard electrolyte solution in a weight ratio.

(Experimental Example 11) 1 thia 12-crown-4 ether having a weight ratio of 1 wt% was added to this standard electrolyte.

(Experimental Example 12) 1 thia 12-crown-4 ether having a weight ratio of 10 wt% was added to this standard electrolyte.

(Experimental example 13) 0.001 wt% of 1 thia 15-crown-5 ether was added to the standard electrolyte solution in a weight ratio.

(Experimental example 14) 1 thia 15-crown-5 ether having a weight ratio of 1 wt% was added to this standard electrolyte.

(Experimental Example 15) 10% by weight of 1 thia 15-crown-5 ether was added to this standard electrolyte.

(Experimental Example 16) 0.001 wt% 1 thia 18-crown-6 ether was added to this standard electrolyte solution in a weight ratio.

(Experimental Example 17) 1 thia 18-crown-6 ether having a weight ratio of 1 wt% was added to this standard electrolyte.

(Experimental Example 18) 1 thia 18-crown-6 ether having a weight ratio of 10 wt% was added to this standard electrolyte.

(Experimental Example 19) A mixture of 1 aza 12-crown-4 ether and 1 aza 15-crown-5 ether in a weight ratio of 1: 1 was added to the standard electrolyte at 1 wt% by weight.

(Experiment 20) Only standard electrolyte was used.

(Experimental Example 21) 1 wt% of 12-crown-4 ether was added to the standard electrolyte solution.

(Experimental example 22) 15 wt% of 5 wt% ether was added to the standard electrolyte solution.

(Experimental example 23) 1 wt% 18-crown-6 ether was added to the standard electrolyte solution in a weight ratio.

(Experimental Example 24) 1 wt% ethylenediaminetetraacetic acid was added to the standard electrolyte solution in a weight ratio.

[Experimental Examples 25 to 34]
In Experimental Examples 25 to 34, a lithium secondary battery composed of an electrode group having a design discharge capacity of 50 mAh using LiFePO _{4 as} the positive electrode active material and natural graphite as the negative electrode active material was prepared in the same manner as in the above Experimental Examples 1 to 24. did.

To the standard electrolyte solution, the following additives (a) to (c) were added in mass% shown in Table 2. In Experimental Example 34, none of the additives (a) to (c) was blended.

(A) 1 aza 12-crown-4 ether (b) 1 aza 15-crown-5 ether (c) 1 aza 18-crown-6 ether (Experimental Example 25) 0.001 wt% by weight of standard electrolyte 1 Aza 12-crown-4 ether was added.

(Experimental Example 26) 1 aza 12-crown-4 ether at a weight ratio of 1 wt% was added to the standard electrolyte.

(Experimental example 27) 10 wt% of 1 aza 12-crown-4 ether was added to the standard electrolyte solution in a weight ratio.

(Experimental Example 28) 0.001 wt% of 1 aza 15-crown-5 ether was added to the standard electrolyte solution in a weight ratio.

(Experimental example 29) 1 aza 15-crown-5 ether having a weight ratio of 1 wt% was added to the standard electrolyte.

(Experimental example 30) 1 aza 15-crown-5 ether having a weight ratio of 10 wt% was added to the standard electrolyte.

(Experimental example 31) 0.001 wt% of 1 aza 18-crown-6 ether was added to the standard electrolyte.

(Experimental example 32) 1 aza 18-crown-6 ether having a weight ratio of 1 wt% was added to the standard electrolyte.

(Experimental example 33) 1 aza 18-crown-6 ether having a weight ratio of 10 wt% was added to the standard electrolyte.

(Experimental example 34) Only standard electrolyte was used.

The conductivity of the electrolyte solutions used in Experimental Examples 1 to 19, Experimental Examples 25 to 33, Experimental Examples 20 to 24, and Experimental Example 34 were measured using a conductivity meter DS-52 (manufactured by Horiba, Ltd.). The values are shown in Tables 1 and 2, respectively.

Using the charge / discharge device HJ1001 (manufactured by Hokuto Denko), the batteries of Experimental Examples 1 to 19, and Experimental Examples 25 to 33, Experimental Examples 20 to 24, and Experimental Example 34 were respectively charged at 25 ° C. with a charge end voltage of 4.3 V, 5 A constant current charge at a time rate (current value of 10 mA), a discharge end voltage of 2.8 V, and a constant current discharge at a time rate of 5 hours were performed, and the initial discharge capacity was confirmed. The values are shown in Tables 1 and 2, respectively.

Thereafter, constant current charging at a charge end voltage of 4.3 V and a 5-hour rate was performed at 25 ° C., and aging was performed in a constant temperature bath at 60 ° C. for 24 days while being charged. The battery after aging was taken out from the thermostat, and a constant current discharge at a discharge end voltage of 2.8 V and a 5-hour rate was performed at 25 ° C., and the ratio between the discharge capacity and the initial discharge capacity was stored as Tables 1 and 2. Respectively.

When the transition metal element is reduced and deposited on the negative electrode, it can be confirmed by elemental analysis of the transition metal remaining on the negative electrode after the test. Quantification of the transition metal element deposited on the negative electrode was carried out by the method shown below.

The battery after the test was disassembled without being exposed to air in an inert gas atmosphere, the negative electrode was immersed and washed with dimethyl carbonate (DMC) for 24 hours, and the negative electrode active material and binder mixture after the cleaning was peeled off from the negative electrode copper foil And collected. The collected mixture was immersed in a nitric acid solution in a sealed pressurized acid decomposition vessel and then heated and held at 121 ° C. for 48 hours, and the solution prepared therefrom was quantified using ICP-MS (7500CX manufactured by Agilent Technologies). The quantitative result was calculated as the abundance ratio by weight ratio of the detection element to the negative electrode active material. The results are shown in Tables 1 and 2.

In all of Experimental Examples 1 to 19 and 25 to 33 (Experimental examples excluding Experimental Examples 20 to 24 and Experimental Example 34) of the present invention, no detection due to precipitation of transition metal elements after aging at 60 ° C. was observed. 12-crown-4 (Experimental Example 21), 15-crown-5 (Experimental Example 22), and 18-crown-6 (Experimental Example 23), which were carried out as comparisons of cyclic ethers, had no additive (Experimental Example 20). Compared with Experimental Examples 1 to 19 and 25 to 33 (Experimental examples excluding Experimental Examples 20 to 24 and Experimental Example 34), the effect of slightly preventing the precipitation of transition metal elements was obtained. It was. Further, ethylenediaminetetraacetic acid (Experimental Example 24) carried out as a chain ether did not give any effect of preventing transition metal element precipitation.

In addition, in the experimental examples (Experimental Examples 3, 6, 9, 12, 15, 18, 27, 30 and 33) in which the additive was added by 10% by mass, the experimental examples in which 0.001% by mass and 1% by mass of the additive were added. Compared with (Experimental Examples 1, 2, 4, 5, 7, 8, 10, 11, 13, 14, 16, 17, 25, 26, 28, 29, 31 and 32), the conductivity of the electrolyte is lowered. In addition, since a decrease in the initial discharge capacity due to this was observed, the amount of additive added is preferably 0.001 to 1% by mass.

For these reasons, in the present invention, even if various transition metal ions are eluted from the positive electrode transition metal oxide, precipitation on the negative electrode can be prevented.

Although the embodiments and experimental examples of the present invention have been specifically described above, the present invention is not limited to these embodiments and experimental examples, and modifications based on the technical idea of the present invention are possible. Of course there is.

According to the present invention, the non-aqueous electrolyte contains at least one cyclic ether selected from azacrown ethers in which hydrogen bonded to a nitrogen atom is not substituted with other groups, and thiacrown ethers. Therefore, it is possible to prevent the transition metal eluted from the positive electrode active material into the non-aqueous electrolyte from being deposited on the negative electrode plate. As a result, deterioration of charge / discharge cycle characteristics and storage characteristics can be prevented even under severe use conditions.

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Positive electrode current collection tab 3 Negative electrode plate 4 Negative electrode current collection tab 5 Separator 6 Laminate film

Claims

A positive electrode plate containing a lithium-containing transition metal composite oxide as a positive electrode active material, a negative electrode plate containing a material capable of insertion / extraction of lithium or oxidation / reduction as a negative electrode active material, and interposed between the positive electrode plate and the negative electrode plate In a lithium secondary battery comprising a separator and a non-aqueous electrolyte in which a lithium salt is dissolved,
The non-aqueous electrolyte contains at least one cyclic ether selected from azacrown ethers in which hydrogen bonded to a nitrogen atom is not substituted with other groups, and thiacrown ethers,
The lithium secondary battery, wherein a content of the cyclic ether in the non-aqueous electrolyte is 0.001 to 1% by mass with respect to the non-aqueous electrolyte.
A positive electrode plate containing a lithium-containing transition metal composite oxide as a positive electrode active material, a negative electrode plate containing a material capable of insertion / extraction of lithium or oxidation / reduction as a negative electrode active material, and interposed between the positive electrode plate and the negative electrode plate In a lithium secondary battery comprising a separator and a non-aqueous electrolyte in which a lithium salt is dissolved,
The non-aqueous electrolyte contains at least one cyclic ether selected from azacrown ethers in which hydrogen bonded to a nitrogen atom is not substituted with other groups, and thiacrown ethers A lithium secondary battery characterized by.
3. The lithium secondary battery according to claim 2, wherein the content of the cyclic ether in the non-aqueous electrolyte is 0.001 to 1% by mass with respect to the non-aqueous electrolyte.
The lithium secondary battery according to claim 2 or 3, wherein the negative electrode active material is a carbon material.
A positive electrode plate containing a lithium-containing transition metal composite oxide as a positive electrode active material, a negative electrode plate containing a material capable of insertion / extraction of lithium or oxidation / reduction as a negative electrode active material, and interposed between the positive electrode plate and the negative electrode plate In a non-aqueous electrolyte for a lithium secondary battery comprising a separator and a non-aqueous electrolyte in which a lithium salt is dissolved,
Lithium disulfide characterized in that it contains at least one cyclic ether selected from azacrown ethers in which hydrogen bonded to a nitrogen atom is not substituted with other groups and thiacrown ethers Nonaqueous electrolyte for secondary batteries.
The non-aqueous electrolyte for a lithium secondary battery according to claim 5, wherein the content of the cyclic ether is 0.001 to 1% by mass with respect to the non-aqueous electrolyte.