JP5310711B2 - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having high operating voltage (using a positive electrode material showing a high potential of &ge;4.5 V to lithium), which is improved in charge and discharge characteristic, particularly, in storage characteristic. <P>SOLUTION: The nonaqueous electrolyte secondary battery includes a positive electrode and a negative electrode capable of storing and releasing lithium, and a nonaqueous electrolyte containing lithium ion. The positive electrode contains a positive electrode active material which shows a discharge voltage of &ge;4.5 V to lithium, and the nonaqueous electrode contains a cyclic sulfonate. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte containing an active material having a potential of 5 V class in a positive electrode and containing a cyclic sulfonate ester. It is.

  Lithium ion secondary batteries, which are nonaqueous electrolyte secondary batteries, are widely used in applications such as portable electronic devices and personal computers. In the future, adaptation to automobile applications is also expected. In these applications, it has been conventionally required to reduce the size and weight of the battery. On the other hand, increasing the energy density of the battery is an important technical issue.

Several methods for increasing the energy density of a lithium ion secondary battery are conceivable. Among them, increasing the operating potential of the battery is an effective means. In a lithium ion secondary battery using a conventional lithium cobaltate or lithium manganate as a positive electrode active material, the operating potential is 4 V class (average operating potential = 3.6 to 3.8 V: lithium potential). This is because the expression potential is defined by the redox reaction of Co ions or Mn ions (Co ³⁺ ← → Co ⁴⁺ or Mn ³⁺ ← → Mn ⁴⁺ ). On the other hand, for example, it is known that an operating potential of 5 V class can be realized by using, as an active material, a spinel compound in which Mn of lithium manganate is substituted with Ni or the like. Specifically, it is known that a potential plateau is exhibited in a region of 4.5 V or more by using a spinel compound such as LiNi _0.5 Mn _1.5 O ₄ . In such a spinel compound, Mn exists in a tetravalent state, and the operating potential is regulated by oxidation / reduction of Ni ²⁺ ← → Ni ⁴⁺ instead of oxidation / reduction of Mn ³⁺ ← → Mn ^4+. Become.

LiNi _0.5 Mn _1.5 O ₄ has a capacity of 130 mAh / g or more, and an average operating voltage of 4.6 V or more with respect to Li metal. Although the capacity is smaller than LiCoO ₂ , the energy density of the battery is higher than LiCoO ₂ . For these reasons, LiNi _0.5 Mn _1.5 O ₄ is promising as a future positive electrode material.

However, since a battery using a positive electrode material exhibiting a high potential such as LiNi _0.5 Mn _1.5 O ₄ as an active material has a higher potential than the case where the positive electrode uses lithium cobaltate, lithium manganate, or the like, the positive electrode and the electrolyte solution It has been found that the decomposition reaction occurs at the contact portion with the battery, and the charge / discharge cycle characteristics are deteriorated and the capacity is significantly reduced when left in a charged state. In particular, the deterioration of the electrolytic solution tends to become conspicuous as the temperature rises, so these problems are serious in operation and storage at a high temperature such as 50 ° C.

  Conventionally, as a method for improving the cycle characteristics and storage characteristics of a battery, it has been proposed to add a sulfur element-containing compound as an additive to an electrolytic solution.

  Patent Document 1 (Japanese Patent Laid-Open No. 2000-235866) discloses the following chemical formula (A)

(Wherein R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a fluorine atom-substituted alkyl group having 1 to 6 carbon atoms. Represent)
And a secondary battery containing γ-sultone in a non-aqueous electrolyte.

However, the technique of the publication discloses that a stable film is formed on the surface of the negative electrode by containing γ-sultone in the electrolyte, and the contact between the negative electrode and the solvent molecules is cut off to suppress the decomposition reaction of the solvent on the negative electrode. Therefore, it was not a technique for suppressing the decomposition reaction of the solvent on the positive electrode. Although examples of applying the LiCoO ₂ in the positive electrode is shown an example of a battery using a positive electrode for performing the release occlusion of lithium 4.5V or more to the lithium it is not shown.

  Patent Document 2 (Japanese Patent Laid-Open No. 2000-268857) discloses a battery using a spinel-structured lithium manganese oxide as a positive electrode, and has improved charge / discharge characteristics by containing butane sultone or butadiene sultone in the organic electrolyte. Techniques to do this are disclosed.

However, although an example in which LiMn ₂ O ₄ is applied to the positive electrode is shown, an example of a battery using a positive electrode that releases and occludes lithium at 4.5 V or higher with respect to lithium is not shown. In addition, this technique describes that butane sultone or butadiene sultone decomposes during charging to form a film on the surface of the negative electrode.

  Patent Document 3 (Japanese Patent Application Laid-Open No. 2001-243982) discloses a positive electrode having a discharge potential of 4.2 V or higher and a chemical formula (B) or a chemical formula (C).

(However, R ₁ and R ₂ represent an alkyl group having 1 to 10 carbon atoms, and R ₁ and R ₂ may be the same.)

(However, R ₁ and R ₂ represent an alkyl group having 1 to 10 carbon atoms, and R ₁ and R ₂ may be the same.)
The technique which suppresses electrolyte solution decomposition reaction and improves cycling characteristics is disclosed by using the electrolyte solution containing the sulfur compound represented by these.

  This publication shows a system to which sulfate ester or sulfone is applied, but does not show an example to apply cyclic sulfonate ester. In addition, this publication describes that these sulfur compounds are adsorbed on the surface of the positive electrode, so that decomposition of the electrolytic solution is suppressed. However, even if these sulfur compounds are used, as described later, the high temperature It has been found that the storage properties below are not improved sufficiently.

JP 2000-235866 A JP 2000-268857 A Japanese Patent Laid-Open No. 2001-243982

  As described above, in the conventional technology, sufficient charge / discharge characteristics are not obtained in the non-aqueous electrolyte secondary battery using the positive electrode material exhibiting a high potential of 4.5 V or higher with respect to lithium.

  Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having a high operating voltage (using a positive electrode material exhibiting a high potential of 4.5 V or more with respect to lithium) with improved charge / discharge characteristics, particularly storage characteristics. Is to provide.

  The present invention is a non-aqueous electrolyte secondary battery having a positive electrode and a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte containing lithium ions, wherein the positive electrode is 4. The positive electrode active material which shows 5 V or more of discharge potential is contained, The said non-aqueous electrolyte is related with the non-aqueous electrolyte secondary battery containing cyclic sulfonate ester.

  According to the present invention, a non-aqueous electrolyte secondary battery having a high operating voltage (using a positive electrode material having a high potential of 4.5 V or higher with respect to lithium) having improved charge / discharge characteristics, particularly storage characteristics, is provided. Can be provided.

It is sectional drawing of one Embodiment of the nonaqueous electrolyte secondary battery of this invention.

  Embodiments of a lithium ion secondary battery will be described below as the nonaqueous electrolyte secondary battery of the present invention.

  In the present embodiment, in a lithium ion secondary battery having a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte containing lithium ions, 4.5 V or more with respect to lithium as the positive electrode The positive electrode that occludes and releases lithium is used, and as the non-aqueous electrolyte, an electrolytic solution in which a cyclic sulfonic acid ester is dissolved is used.

  As cyclic sulfonate ester, the following general formula (1)

(In the formula, A and B each independently represent an alkylene group or a fluoroalkylene group, and X represents a C—C single bond or —OSO ₂ — group.)
The compound represented by these can be used.

  As the alkylene group and fluoroalkylene group of A and B in the formula, those having 1 to 8 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 5 carbon atoms can be used.

Examples of such cyclic sulfonic acid esters include monosulfonic acid esters such as 1,3-propane sultone, 1,4-butane sultone, 1,3-butane sultone, 2,4-butane sultone (wherein X is a C—C simple substance). In the case of a bond), disulfonic acid esters such as methylenemethane disulfonic acid ester and ethylenemethane disulfonic acid ester (when X in the formula is an -OSO ₂ -group), and the like.

By including a cyclic sulfonic acid ester in the electrolyte, capacity deterioration can be suppressed in a battery having a charge / discharge potential of 4.5 V or more. As a result of the examination, compared with the improvement effect obtained when using a positive electrode active material that exhibits a discharge potential of less than 4.5 V with respect to Li, such as LiMn ₂ O ₄ , a discharge potential of 4.5 V or more is exhibited. When the positive electrode active material was used, the characteristics were dramatically improved. This is probably because the potential on the positive electrode side is as high as 4.5 V or higher, so that the cyclic sulfonic acid ester is oxidized and decomposed on the positive electrode side, and a film is formed on the surface of the positive electrode. On the other hand, in a battery that charges and discharges at less than 4.5 V, the cyclic sulfonic acid ester is reduced on the negative electrode side to form a film on the negative electrode surface, no oxidative decomposition occurs on the positive electrode side, and no film is formed on the positive electrode. It is considered a thing.

  Therefore, as the cyclic sulfonate ester in the present invention, a protective film can be formed on the surface of the positive electrode containing the positive electrode active material exhibiting a discharge potential of 4.5 V or more with respect to Li by being contained in the non-aqueous electrolyte. Those that can function with the positive electrode protective film forming agent are preferable. Moreover, what can form a protective film in the positive electrode surface and can form a protective film also in the negative electrode surface is preferable. As such a cyclic sulfonic acid ester, 1,3-propane sultone and 1,4-butane sultone are preferable from the viewpoint of desired effects, availability, and cost.

  The content of the cyclic sulfonic acid ester in the nonaqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less with respect to the solvent. The amount is preferably 0.01% by mass or more, and more preferably 0.1% by mass or more from the viewpoint that a sufficient film is formed on the surface of the positive electrode to suppress decomposition of the electrolytic solution. On the other hand, it is preferably 10% by mass or less, more preferably 5% by mass or less from the viewpoint of adjusting the viscosity and conductivity of the electrolytic solution within appropriate ranges and ensuring good cycle characteristics at a relatively low temperature. The property improvement effect at high temperature is preferably 10% by mass or less, more preferably 5% by mass or less, because there is a tendency to saturate at about 5 to 10% by mass.

  As the non-aqueous electrolyte solvent, cyclic carbonate compounds such as propylene carbonate (PC) and ethylene carbonate (EC) can be used in order to increase the dielectric constant of the solvent. For the purpose of reducing the viscosity, a chain monocarbonate such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC) can be used. Two or more of these may be used in combination.

  In the present invention, vinylene carbonate may be contained in the nonaqueous electrolyte. Thereby, the resistance rise derived from the film formed by decomposition | disassembly of cyclic sulfonate ester can be suppressed, and cycling characteristics and a storage characteristic can be improved. In addition, when vinylene carbonate is used as a non-aqueous solvent, it is easily decomposed on the surface of the positive electrode, and self-discharge tends to occur during storage, but self-discharge is suppressed by interaction with the cyclic sulfonate ester.

  As the solvent for the nonaqueous electrolyte, conventional nonaqueous electrolyte solvents other than those described above can be used. For example, aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, and chain structures such as 1,2-ethoxyethane (DEE) and ethoxymethoxyethane (EME) Ethers, cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphate triester, tri Methoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, ethylene carbonate derivative, propylene carbonate derivative Body, tetrahydrofuran derivative, ethyl ether, anisole, N-methylpyrrolidone, and the like.

Examples of the lithium salt dissolved in the nonaqueous solvent used for the electrolyte include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lithium of lower aliphatic carboxylate, lithium chloroborane, lithium tetraphenylborate, LiCl, LiBr , LiI, LiSCN, LiCl, imides and the like. As the electrolyte, an electrolytic solution obtained by dissolving these lithium salts in the above non-aqueous solvent can be preferably used. The concentration of the lithium salt can be, for example, 0.5 mol / l to 1.5 mol / l. This is because if the concentration is too high, the density and viscosity increase, and if the concentration is too low, the electrical conductivity decreases.

  The lithium ion secondary battery of this embodiment is sandwiched between a positive electrode including a lithium-containing metal composite oxide as a positive electrode active material, a negative electrode including a negative electrode active material capable of occluding and releasing lithium, and the positive electrode and the negative electrode The separator as the insulator, the positive electrode, and the negative electrode are in a state of being immersed in a lithium ion conductive electrolyte, and these can be in a sealed state in a battery case. By applying a voltage to the positive electrode and the negative electrode, the positive electrode active material releases lithium ions, the negative electrode active material occludes lithium ions, and the battery is charged. In the discharged state, the state is opposite to the charged state.

In the present invention, a material that exhibits a discharge potential of 4.5 V or higher with respect to lithium is used as the positive electrode active material. As such a positive electrode active material, lithium composite oxides such as LiNi _0.5 Mn _1.5 O ₄ , LiCoMnO ₄ , LiCrMnO ₄ , LiCu _0.5 Mn _1.5 O ₄ , LiFe _0.5 Mn _1.5 O ₄ , LiNiVO ₄ , and LiCoPO ₄ are used. be able to.

Among such positive electrode active materials, a spinel type lithium manganese metal composite oxide having a spinel structure and containing nickel is preferable. For example, the following general formula (2)
Li _a (M _x Mn _2-xy A _y ) O ₄ (2)
(In the formula, 0.4 <x, 0 ≦ y, x + y <2, 0 <a <1.2. M is selected from Ni, Co, Fe, Cr, and Cu, and at least one or more containing Ni. (A represents at least one metal selected from Si and Ti.)
It is preferable to use the compound represented by these. In the formula, 0.4 <x <0.6 is preferable, 0.8 <a <1.2 is preferable, and the ratio of Ni to M is 0.5 when the total amount of M is 1. The above is preferable, and 0.8 or more is more preferable. In the formula, a is the ratio of Li when (M _x Mn _{2 -xy} A _y ) is 2.

Among such metal complex oxides, the following general formula (3)
_{LiNi x Mn 2-xy A y} O 4 (3)
(In the formula, 0.4 <x <0.6, 0 ≦ y <0.3, A represents at least one metal selected from Si and Ti.)
The spinel type compound represented by these is preferable. In the formula, it is more preferable that 0 ≦ y <0.2.

Moreover, as a preferable positive electrode active material, a high capacity of 130 mAh / g or more can be obtained.
_{LiNi x Mn 2-x O 4} (4)
(Where 0.4 <x <0.6)
The spinel type compound represented by these can be used.

  If the Ni composition ratio x is too low, the 5V discharge region is reduced, and the energy density is lowered. On the other hand, if the Ni composition ratio x is too high, the capacity decreases. The Ni composition ratio x is desirably around 0.5 (0.4 <x <0.6). A compound having a Ni composition ratio x of 0.5 has a charge / discharge region in which Li is occluded / released between 4.5 V and 4.8 V with respect to Li, and a discharge region of 4.5 V or more is It has a very high capacity of 110 mAh / g or more.

  The reason why charge / discharge characteristics are improved by using a spinel type lithium manganese metal composite oxide, particularly a spinel type lithium manganese metal composite oxide containing nickel, as the positive electrode active material is that the active interface of the positive electrode is obtained by element substitution. This is considered to be because the decomposition of the electrolyte solvent is suppressed. At that time, if the electrolyte contains a cyclic sulfonic acid ester, it is considered that charge / discharge characteristics, particularly storage characteristics, are greatly improved in combination with the effect of the specific metal composite oxide.

  The positive electrode in the present invention preferably has a sulfur atom or a sulfur compound on the surface of the positive electrode, and preferably has a coating composed of these components. Thereby, the secondary battery having such a positive electrode has improved charge / discharge characteristics such as cycle characteristics and storage characteristics. The sulfur atom or sulfur compound on the surface of the positive electrode is a compound derived from a cyclic sulfonate ester, and exists as an unsupported film that suppresses the decomposition of the solvent on the surface of the positive electrode without impairing the normal reaction of the battery on the surface of the positive electrode. Conceivable.

  The positive electrode can be formed on a current collector by mixing a positive electrode active material, a conductivity-imparting agent, and a binder. As the conductivity-imparting agent, a carbon material, a metal substance such as Al, a conductive oxide powder, or the like can be used. As the binder, a resin binder such as polyvinylidene fluoride can be used. As the current collector, a metal thin film mainly composed of Al or the like can be used.

  The content of the conductivity imparting agent in the positive electrode is preferably about 1 to 10% by mass of the whole electrode, and the content of the binder is also preferably about 1 to 10% by mass of the electrode body. If it exists in such a range, the ratio of the amount of active materials in an electrode can fully be ensured, and sufficient capacity | capacitance per unit mass can be obtained. If the ratio between the conductivity-imparting agent and the binder is too small, the conductivity may not be maintained, or a problem of electrode peeling may occur.

The negative electrode active material used for the negative electrode is not particularly limited as long as lithium ions can be occluded during charging and released during discharging, and known materials can be used. Specific examples include graphite, coke, carbon materials such as hard carbon, a lithium - aluminum alloy, a lithium - lead alloy, lithium - lithium alloy such as a tin alloy, a lithium _{metal, Si, SnO 2, SnO,} TiO 2, Nb 2 Examples of the metal oxide include a base metal having a potential such as O ₃ SiO, which is lower than that of the positive electrode active material.

  The negative electrode can be formed on a current collector by mixing a negative electrode active material, a conductivity-imparting agent, and a binder. Examples of the conductivity-imparting agent include carbon materials and conductive oxide powders. As the binder, a resin binder such as polyvinylidene fluoride can be used. As the current collector, a metal thin film mainly composed of Cu or the like can be used.

  As the separator, for example, a polyolefin microporous film such as polyethylene or polypropylene can be used.

  The lithium secondary battery according to the present invention is, for example, laminated in a dry air or inert gas atmosphere with a negative electrode and a positive electrode laminated via a separator, or wound in a laminated case and then accommodated in an outer container such as a can case. A battery can be manufactured by injecting an electrolytic solution and sealing with a flexible film made of a laminate of a synthetic resin and a metal foil.

  The configuration and shape of the battery are not particularly limited, and can take the form of a positive electrode facing the separator, a wound type wound with the negative electrode, a laminated type, and a coin type, laminate pack, square type, etc. It can take the form of a cell, a cylindrical cell or the like. FIG. 1 shows a coin-type cell as an example of a battery. In the figure, reference numeral 1 denotes a positive electrode active material layer, reference numeral 2 denotes a negative electrode active material layer, reference numeral 3 denotes a positive electrode current collector, reference numeral 4 denotes a negative electrode current collector, reference numeral 5 denotes a separator, reference numeral 6 denotes a positive electrode side outer can, reference numeral 7 Is a negative electrode side exterior can, and the code | symbol 8 shows an insulation packing part.

[Example 1]
MnO ₂ , NiO, Li ₂ CO ₃ , and Ti ₂ O ₃ powders were used as raw materials for the positive electrode active material, and weighed to achieve the desired composition ratio and pulverized and mixed. Thereafter, the mixed powder was fired at 750 ° C. for 8 hours to produce LiNi _0.5 Mn _1.37 Ti _0.13 O ₄ . It was confirmed that the spinel structure was almost single phase.

  The produced positive electrode active material and carbon as a conductivity-imparting agent were mixed, and this mixture was dispersed in a solution in which polyvinylidene fluoride (PVDF) was dissolved in N-methylpyrrolidone as a binder to form a slurry. The mass ratio of the positive electrode active material, the conductivity-imparting agent, and the binder was 91/5/4. The slurry was applied on an Al current collector. Then, it was dried in vacuum for 12 hours, cut out into a circle having a diameter of 12 mm, and then pressure-molded to obtain a positive electrode.

  Hard carbon is used as the negative electrode active material, and carbon as a conductivity-imparting agent is mixed therewith, and this mixture is dispersed in a solution of polyvinylidene fluoride (PVDF) dissolved in N-methylpyrrolidone as a binder to form a slurry. . The mass ratio of the negative electrode active material, the conductivity-imparting agent, and the binder was 91/1/8. The slurry was applied on a Cu current collector. Then, after drying in vacuum for 12 hours and cutting out into a circle having a diameter of 13 mm, it was pressure-molded to obtain a negative electrode.

  A polypropylene (PP) film was used as the separator. The positive electrode and the negative electrode were insulated with a separator in between and placed in a coin cell, and then filled with an electrolyte solution and sealed.

The electrolytic solution was prepared by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) as a solvent so as to be 50:50 (vol.%), And adding 1 mass of 1,3-propane sultone (PS) to this mixed solution. % Was added. An electrolytic solution was prepared by dissolving LiPF _{6 in} this mixed solvent to a concentration of 1M.

[Example 2]
A secondary battery was fabricated in the same manner as in Example 1 except that 1,3-propane sultone (PS) was added to 2% by mass.

Example 3
A secondary battery was fabricated in the same manner as in Example 1 except that 1,3-propane sultone (PS) was added to 3% by mass.

Example 4
A secondary battery was fabricated in the same manner as in Example 1 except that 1,3-propane sultone (PS) was added to 5% by mass.

Example 5
A secondary battery was fabricated in the same manner as in Example 1 except that 1,3-propane sultone (PS) was added to 10% by mass.

Example 6
A secondary battery was fabricated in the same manner as in Example 1 except that 1,3-propane sultone (PS) was added to 15% by mass.

Example 7
A secondary battery was fabricated in the same manner as in Example 1 except that 1,3-propane sultone (PS) was added to 1% by mass and vinylene carbonate (VC) was added to 1% by mass. .

Example 8
A secondary battery was produced in the same manner as in Example 1 except that the positive electrode active material produced as follows was used. MnO ₂ , NiO, and Li ₂ CO ₃ powders were used as raw materials for the positive electrode active material, and weighed to achieve the target metal composition ratio, and pulverized and mixed. Thereafter, the mixed powder was fired at 750 ° C. for 8 hours to produce LiNi _0.5 Mn _1.5 O ₄ . It was confirmed that the spinel structure was almost single phase.

[Example 9]
A secondary battery was produced in the same manner as in Example 1 except that the electrolytic solution produced as follows was used. Ethylene carbonate (EC) and dimethyl carbonate (DMC) as a solvent are mixed so as to be 50:50 (vol.%), And 1,4-butane sultone (BS) is added to this mixed solution so as to be 1% by mass. added. An electrolytic solution was prepared by dissolving LiPF _{6 in} this mixed solution to a concentration of 1M.

Example 10
A secondary battery was fabricated in the same manner as in Example 9, except that 1,4-butane sultone (BS) was added to 3% by mass.

Example 11
A secondary battery was fabricated in the same manner as in Example 9, except that 1,4-butane sultone (BS) was added to 5% by mass.

Example 12
A secondary battery was fabricated in the same manner as in Example 9, except that 1,4-butane sultone (BS) was added to 10% by mass.

Example 13
A secondary battery was fabricated in the same manner as in Example 9, except that 1,4-butane sultone (BS) was added to 13 mass%.

[Comparative Example 1]
A secondary battery was fabricated in the same manner as in Example 1 except that 1,3-propane sultone (PS) was not added.

[Comparative Example 2]
A secondary battery was fabricated in the same manner as in Example 1 except that dimethyl sulfone was added to 1% by mass instead of 1,3-propane sultone (PS).

[Comparative Example 3]
A secondary battery was fabricated in the same manner as in Example 1 except that dimethyl sulfate was added to 1% by mass instead of 1,3-propane sultone (PS).

[Comparative Example 4]
A secondary battery was fabricated in the same manner as in Example 8 except that 1,3-propane sultone (PS) was not added.

[Reference Example 1]
A secondary battery was produced in the same manner as in Example 1 except that the positive electrode active material produced as follows was used. MnO ₂ and Li ₂ CO ₃ powders were used as raw materials, weighed so as to achieve the desired metal composition ratio, and pulverized and mixed. Thereafter, the mixed powder was fired at 750 ° C. for 8 hours to produce LiMn ₂ O ₄ . It was confirmed that the spinel structure was almost single phase.

[Reference Example 2]
A secondary battery was fabricated in the same manner as in Reference Example 1 except that 1,4-butane sultone was added to 1% by mass instead of 1,3-propane sultone (PS).

[Reference Example 3]
A secondary battery was fabricated in the same manner as in Reference Example 1 except that 1,3-propane sultone (PS) was not added.

[Evaluation test for storage characteristics]
The storage characteristics of the battery produced as described above were evaluated. At the time of evaluation, the batteries of Examples 1 to 13 and Comparative Examples 1 to 4 were charged to 4.75V and discharged to 2.5V. The batteries of Reference Examples 1 to 3 were charged to 4.2V and discharged to 2.5V.

First, charging and discharging were performed once at room temperature. The charging current and discharging current at this time are constant (2 mA) (corresponding to 1C), and the discharging capacity at this time is defined as the initial capacity. Thereafter, each battery was charged at a constant current constant voltage of 2 mA to a predetermined voltage for 2.5 hours, and then left in a constant temperature bath at 60 ° C. for 1 week. After leaving, the discharge operation was performed again at a constant current at room temperature. Subsequently, the same charge and discharge were repeated again at a constant current, and the discharge capacity at this time was defined as a recovery capacity. The following formula 100 × recovery capacity / initial capacity = capacity maintenance ratio (%)
Thus, the capacity maintenance rate of each battery was determined. The results are shown in Table 1.

  As is clear from Table 1, it was confirmed that the storage characteristics were improved by using a positive electrode active material that occludes and releases Li at 4.5 V or more and containing a cyclic sulfonic acid ester in the electrolytic solution.

DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Positive electrode collector 4 Negative electrode collector 5 Separator 6 Positive electrode outer can 7 Negative electrode outer can 8 Insulation packing part

Claims (9)

A non-aqueous electrolyte secondary battery having a positive electrode and a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte containing lithium ions,
The positive electrode contains a positive electrode active material that exhibits a discharge potential of 4.5 V or more with respect to lithium,
The non-aqueous electrolyte has the following general formula (1)

(In the formula, A and B each independently represent an alkylene group or fluoroalkylene group having 1 to 8 carbon atoms, and X represents a C—C single bond or —OSO ₂ — group.)
Containing a cyclic sulfonate ester represented by
The positive electrode active material has the following general formula (2)
Li _a (M _x Mn _2-xy A _y ) O ₄ (2)
(In the formula, 0.4 <x, y = 0, x + y <2, 0 <a <1.2. M is selected from Ni, Co, Fe, Cr, and Cu, and at least one or more containing Ni. (A represents at least one metal selected from Si and Ti.)
In Ri spinel compound der represented,
A nonaqueous electrolyte secondary battery in which the cyclic sulfonate ester is contained in the nonaqueous electrolyte in an amount of 0.01 to 15% by mass with respect to a solvent .   In the general formula (2), 0.4 <x <0.6, y = 0, x + y <2, 0.8 <a <1.2, and the ratio of Ni to M is 1 for the total amount of M. The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is 0.5 or more. The positive active material is represented by the following general formula LiNi _x Mn _2-x O ₄
(Where 0.4 <x <0.6)
The nonaqueous electrolyte secondary battery according to claim 1, which is a spinel type compound represented by the formula:   4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte contains the cyclic sulfonic acid ester in an amount of 0.01 to 10% by mass with respect to the solvent. 5. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4 , wherein the nonaqueous electrolyte contains a cyclic sulfonic acid ester as a positive electrode protective film forming agent. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5 , wherein the positive electrode surface has a sulfur atom or a sulfur-containing compound derived from the cyclic sulfonic acid ester. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6 , wherein vinylene carbonate is contained in the nonaqueous electrolyte. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 7 , wherein the cyclic sulfonic acid ester is 1,3-propane sultone. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 7 , wherein the cyclic sulfonate ester is 1,4-butane sultone.

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