JP2010135115A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery excellent in float characteristics. <P>SOLUTION: In the nonaqueous electrolyte secondary battery provided with a cathode with a cathode active material layer arranged on a cathode collector, an anode with an anode active material layer arranged on an anode collector and a nonaqueous electrolyte, the cathode active material layer contains as a principal composition lithium-cobalt oxide (LiCoO<SB>2</SB>) of a cathode active material or a lithium-cobalt composite oxide containing different kinds of atoms(LiCo<SB>x</SB>M<SB>1-x</SB>O<SB>2</SB>: wherein M is one or more kinds of metal, and 0<x<1), and the anode active material layer contains as a principal composition a carbon system material of an anode active material, and the nonaqueous electrolyte contains at least one kind out of sulfone compounds as shown in a formula (1) and a formula (2). Here, R1 is C<SB>m</SB>H<SB>2m-n</SB>X<SB>n</SB>, wherein X is halogen, provided that m is integral numbers of 2 to 4, and n is integral numbers of 0 to 2m. R2: C<SB>j</SB>H<SB>2j-k</SB>Z<SB>k</SB>, wherein Zi s halogen, provided that j is integral numbers of 2 to 4, and k is integral numbers of 0 to 2j. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

Among non-aqueous electrolyte batteries, lithium ion secondary batteries are rapidly developing as power sources for portable electronic devices such as mobile phones and portable personal computers. In these power sources for portable devices, the most required characteristic is energy density, that is, energy storage amount per unit volume, and there is an interest in how long a portable device can be used. As positive electrode materials for lithium ion secondary batteries, lithium / cobalt composite oxide, lithium nickel cobalt composite oxide, lithium nickel cobalt manganese composite oxide, etc. have been developed. It is.
Patent Document 1 discloses a lithium secondary battery having excellent characteristics such as energy density and electromotive force using an electrolytic solution containing a sulfonic acid anhydride in an aprotic organic solvent, and having excellent cycle life and safety. There is a description to obtain.
In Patent Document 2, in a non-aqueous electrolyte secondary battery using a positive electrode active material containing cobalt, cobalt ions eluted in the electrolyte solution are added to the electrolyte solution by adding a compound that forms a complex with cobalt. Provides a non-aqueous electrolyte secondary battery with excellent high-temperature storage characteristics and high-temperature charge / discharge cycle characteristics by stabilizing and suppressing deposition on the negative electrode to reduce the negative electrode reaction area and gas generation due to the catalytic reaction of cobalt There is a statement that it can be done.
However, for example, if the power supply is continuously connected to the portable personal computer, the battery in the battery pack is exposed to a charged state (float state), and the battery capacity is rapidly deteriorated. This is because the cobalt contained in the positive electrode active material is easily eluted in an oxidizing environment, and the interface resistance increases, and at the same time, the capacity decreases due to the layered structure change. Furthermore, the rise in ambient temperature accompanying the driving of a portable personal computer is a factor that accelerates deterioration.
As an improvement measure, there is a technique in which even if Co is eluted from the lithium cobalt composite oxide, it is stabilized by an electrolytic solution additive to avoid an adverse effect on the negative electrode. However, the adverse effect on the negative electrode due to Co elution can be avoided, but the positive electrode resistance increases due to the positive electrode structure change, and the capacity deteriorates. That is, unless the elution of Co itself is suppressed, a highly reliable battery cannot be obtained.
That is, there is a demand for a non-aqueous electrolyte secondary battery that is further excellent in float characteristics.

Special table 2002-22336 gazette JP 2002-134170 A

  The present invention has been made in view of such problems, and an object thereof is to provide a nonaqueous electrolyte secondary battery having excellent float characteristics.

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本願明細書において、非水電解質とは、液状、ゲル状を含む。 The present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material layer provided on a positive electrode current collector, a negative electrode having a negative electrode active material layer provided on a negative electrode current collector, and a non-aqueous electrolyte. The positive electrode active material layer includes one or more types of lithium cobalt oxide (LiCoO ₂ ), which is a positive electrode active material, or a lithium cobalt composite oxide containing different atoms (LiCo _x M _1-x O ₂ : M). And x is 0 <x <1) as a main component, the negative electrode active material layer mainly includes a carbon-based material as a negative electrode active material, and the nonaqueous electrolyte is represented by the formula (1 ) And at least one of the sulfone compounds of formula (2).

(R1 is a _{C m H 2m-n X n} , X is halogen. However, m is an integer of 2 to 4, n is an integer of 0 to 2m .R2 is _C j _{H 2j-k} Z _k and Z is halogen, where j is an integer of 2 to 4 and k is an integer of 0 to 2j.)
In the specification of the present application, the nonaqueous electrolyte includes liquid and gel.

  According to the present invention, since the non-aqueous electrolyte contains the sulfone compound, even if the battery uses an oxide containing cobalt for the positive electrode, a good protective film is formed on the surface of the positive electrode active material by the first charge. Even if formed and exposed in a charging environment, the elution of cobalt itself can be suppressed. This makes it possible to obtain a lithium ion secondary battery with little deterioration in an actual use environment such as an actual portable personal computer.

Hereinafter, the present invention will be described in detail. In the present specification, “%” means mass% unless otherwise specified.
In the present invention, the positive electrode active material layer includes one or more types of lithium cobalt oxide (LiCoO ₂ ), which is a positive electrode active material, or a lithium cobalt composite oxide containing different atoms (LiCo _x M _1-x O ₂ : M). In which x is 0 <x <1). Here, the “main body” means 50% or more of the total mass of the positive electrode active material in the positive electrode active material layer. Further, when M is two or more kinds, M is selected so that the sum of the subscripts is 1-x. Examples of M include transition elements, IIA group elements, IIIA group elements, IIIB group elements, IVB group elements, etc., but cobalt (Co), nickel, manganese (Mn), iron, aluminum, vanadium as transition metal elements. Those containing at least one of (V) and titanium (Ti) are preferred.
The positive electrode active material is formed on the surface of lithium cobalt oxide or lithium cobalt composite oxide, a metal oxide having a composition different from that of the oxide (for example, one selected from Ni, Mn, Li, etc.) or a phosphoric acid compound ( For example, the coating layer containing lithium phosphate etc. may be given.
In the present invention, the positive electrode active material means a positive electrode material capable of inserting and extracting lithium as an electrode reactant.
In the present specification, the above-described lithium cobalt oxide particles and lithium cobalt composite oxide particles containing different atoms are collectively referred to as “composite oxide particles”.

In the present invention, the negative electrode active material layer mainly contains a carbon-based material that is a negative electrode active material. Here, the “main body” means 50% or more of the total mass of the negative electrode active material in the negative electrode active material layer. The carbon material means a material containing 90% by mass or more of carbon. Examples of the carbon-based material include graphite, non-graphitizable carbon, and graphitizable carbon. These carbon-based materials are preferable because a change in crystal structure that occurs during charge / discharge is very small, a high charge / discharge capacity can be obtained, and good charge / discharge cycle characteristics can be obtained. The graphite may be natural graphite or artificial graphite.
The non-graphitizable carbon has a (002) plane spacing of 0.37 nm or more, a true density of less than 1.70 g / cm ³ , and differential thermal analysis (DTA) in air. Those that do not show an exothermic peak at 700 ° C. or higher are preferred.

Next, the nonaqueous electrolyte will be described.
The nonaqueous electrolyte contains at least one of the sulfone compounds of the formula (1) and the formula (2). That is, the non-aqueous electrolyte may contain only the sulfone compound of formula (1), may contain only the sulfone compound of formula (2), or may contain both of them. In this case, one or more kinds can be used on a structural basis. The sulfone compound of the formula (1) is also referred to as the sulfone compound (1). The same applies to equation (2) and the like. Moreover, when using by the meaning containing both, it is only called a sulfone compound. The content of the sulfone compound in the nonaqueous electrolyte is preferably 0.05 to 5% by mass. If the amount exceeds 5% by mass, the positive electrode film becomes thick and the film resistance becomes too large. If the amount is less than 0.05% by mass, the effect of the present invention cannot be expected.
Hereinafter, the sulfone compound of the formula (1) is also referred to as a sulfone compound (1). The same applies to equation (2) and the like.
The sulfone compound (1) will be described.
R1 is _{C m H 2m-n X n} , m is an integer of 2 to 4, preferably, 2 to 3 integer, n represents an integer of 0 to 2m, preferably, an integer of 4-6 . X is a halogen, preferably fluorine or chlorine.
As the sulfone compound (1), a compound of the formula (1-1) is preferable.

  Although the specific example of a sulfone compound (1) is given to the following, this invention is not limited to these.

The sulfone compound (2) will be described.
R2 is _{C j H 2j-k Z k} , j is an integer from 2 to 4, preferably, 2 to 3 integer, k is an integer of 0～2J, preferably, an integer of 4-6 . Z is a halogen, preferably fluorine or chlorine.
Although the specific example of a sulfone compound (2) is given to the following, this invention is not limited to these.

  The nonaqueous electrolyte includes a solvent and an electrolyte salt. Examples of the solvent include 4-fluoro-1,3-dioxolan-2-one (FEC), ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, γ -Valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate, methyl propionate, ethyl propionate, acetonitrile, glutaronitrile , Adiponitrile, methoxyacetonitrile, 3-methoxypropyronitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide, triphosphate Room temperature molten salts such as methyl, triethyl phosphate, ethylene sulfide, and bistrifluoromethylsulfonylimide trimethylhexylammonium. Among them, at least one of the group consisting of 4-fluoro-1,3-dioxolan-2-one, ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethylene sulfite is used as a mixture. It is preferable because excellent charge / discharge capacity characteristics and charge / discharge cycle characteristics can be obtained.

The electrolyte salt contained in the non-aqueous electrolyte may contain one kind or a mixture of two or more kinds of materials. Examples of the electrolyte salt include lithium hexafluorophosphate (LiPF ₆ ), bis (pentafluoroethanesulfonyl) imide lithium (Li (C ₂ F ₅ SO ₂ ) ₂ N), lithium perchlorate (LiClO ₄ ), Lithium hexafluoroarsenate (LiAsF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiSO ₃ CF ₃ ), lithium bis (trifluoromethanesulfonyl) imide (Li (CF ₃ SO ₂ ) ₂ N), tris (trifluoromethanesulfonyl) methyllithium (LiC (SO ₂ CF ₃ ) ₃ ), lithium chloride (LiCl) and lithium bromide (LiBr).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a cross-sectional structure of a secondary battery according to an embodiment of the present invention. This secondary battery is a so-called cylindrical type, and a wound electrode body 20 in which a belt-like positive electrode 21 and a negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. have. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14, and a heat sensitive resistance element (PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  For example, a center pin 24 is inserted in the center of the wound electrode body 20. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG.
The positive electrode 21 has, for example, a structure in which a positive electrode active material layer 21B is provided on both surfaces of a positive electrode current collector 21A having a pair of opposed surfaces. Although not shown, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil.

  The positive electrode active material layer 21B is required to contain the lithium oxide containing the specific cobalt (Co) as the positive electrode active material, but the positive electrode capable of inserting and extracting lithium as the electrode reactant. Other materials may be included. Moreover, the electrically conductive agent may be included as needed. The binder preferably includes, for example, polyvinylidene fluoride, but may further contain polyacrylonitrile, a rubber-based binder, or the like. Polyvinylidene fluoride is, for example, PVDF-CTFE copolymer (vinylidene fluoride-chlorotrifluoroethylene copolymer), PVDF-PTFE (vinylidene fluoride-polytrifluoroethylene copolymer), polyvinylidene fluoride maleic acid modified It may be a body.

Examples of the positive electrode material capable of inserting and extracting lithium include lithium-containing compounds such as lithium oxide, lithium sulfide, an intercalation compound containing lithium, and a lithium phosphate compound. Among them, a composite oxide containing lithium and a transition metal element, or a phosphoric acid compound containing lithium and a transition metal element is preferable. In particular, cobalt (Co), nickel, manganese (Mn), iron, aluminum, Those containing at least one of vanadium (V) and titanium (Ti) are preferred. The chemical formula is represented by, for example, Li _x1 M1O ₂ and Li _y M2PO ₄ . In the formula, M1 and M2 contain one or more transition metal elements, and the values of x and y vary depending on the charge / discharge state of the battery, and are generally 0.05 ≦ x1 ≦ 1.10 and 0.05 ≦ y ≦ 1. .10.

Specific examples of the composite oxide containing lithium and a transition metal element include lithium-cobalt composite oxide (Li _x1 CoO ₂ ), lithium nickel composite oxide (Li _x1 NiO ₂ ), lithium nickel cobalt composite oxide (Li _{x1 Ni 1-z Co z O} 2 (z <1)), a lithium nickel cobalt manganese complex oxide _{(Li x1 Ni (1-v} -w) Co v Mn w O 2 (v + w <1)), and spinel Examples thereof include lithium manganese composite oxide (LiMn ₂ O ₄ ) having a structure. Specific examples of the phosphate compound containing lithium and a transition metal element include, for example, a lithium iron phosphate compound (LiFePO ₄ ) and a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (u <1)). Can be mentioned.

  Examples of the positive electrode material capable of inserting and extracting lithium include other metal compounds and polymer materials. Examples of other metal compounds include oxides such as titanium oxide, vanadium oxide and manganese dioxide, or disulfides such as titanium sulfide and molybdenum sulfide. Examples of the polymer material include polyaniline and polythiophene.

The specific surface area of the positive electrode active material, _{N 2} gas BET (Brunauer, Emmett, Teller) as measured by method, 0.05~2.0m ² / g, preferably a range of 0.2~0.7m ² / g It is comprised so that it may become. This is because a more effective film can be formed within this range.

  The positive electrode active material layer 21B may contain a conductive material as necessary. Examples of the conductive material include carbon materials such as graphite, carbon black, and ketjen black, and one kind or a mixture of two or more kinds is used. In addition to the carbon material, a metal material, a conductive polymer material, or the like may be used as long as the material has conductivity.

The negative electrode 22 has, for example, a configuration in which a negative electrode active material layer 22B is provided on both surfaces of a negative electrode current collector 22A having a pair of opposed surfaces. Although not shown, the negative electrode active material layer 22B may be provided only on one surface of the negative electrode current collector 22A. The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.
The negative electrode active material layer 22B mainly includes a carbon-based material capable of occluding and releasing lithium, which is an electrode reactant, as a negative electrode active material, but other negative electrode active materials may be used in combination. Moreover, the negative electrode active material layer may contain the same electrically conductive agent as the positive electrode active material layer 21B as needed, for example.

The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 23 is made of, for example, a porous film made of synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of ceramic, and these two or more kinds of porous films are laminated. It may be a structure. Among these, a porous film made of polyolefin is preferable because it is excellent in the effect of preventing short circuit and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable as a material constituting the separator 23 because a shutdown effect can be obtained at 100 to 160 ° C. and the electrochemical stability is excellent. Polypropylene is also preferable. In addition, any resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.
The separator 23 is impregnated with a nonaqueous electrolyte.

For example, the secondary battery can be manufactured as follows.
First, for the positive electrode, for example, polyvinylidene fluoride is dispersed in a solvent such as N-methyl-2-pyrrolidone. Next, a positive electrode active material containing cobalt and a conductive agent are mixed with this mixed liquid to prepare a positive electrode mixture coating liquid as a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture coating liquid is applied to the positive electrode current collector 21A, and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like, and the positive electrode 21 is manufactured. Further, the positive electrode active material layer 21B may be formed by attaching a positive electrode mixture to the positive electrode current collector 21A.

  Also, for example, a negative electrode active material is mixed with a carbon-based material and a binder to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste. A negative electrode mixture coating solution prepared by slurrying the negative electrode mixture was prepared. Subsequently, the negative electrode mixture coating liquid is applied to the negative electrode current collector 22A and the solvent is dried. Then, the negative electrode active material layer 22B is formed by compression molding using a roll press or the like, and the negative electrode 22 is manufactured. The negative electrode active material layer 22B may be formed by sticking a negative electrode mixture to the negative electrode current collector 22A.

  Next, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, an electrolytic solution containing a sulfone compound is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through the gasket 17. Thereby, the secondary battery shown in FIG. 1 is completed.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode active material layer 21B and inserted into the negative electrode active material layer 22B through the electrolytic solution. In addition, when discharging is performed, for example, lithium ions are released from the negative electrode active material layer 22B and inserted into the positive electrode active material layer 21B through the electrolytic solution.

  In the above embodiment, the cylindrical secondary battery having a winding structure has been specifically described. However, the present invention is not limited to an elliptical or polygonal secondary battery having a winding structure, or The present invention can be similarly applied to secondary batteries having other shapes in which a positive electrode and a negative electrode are folded or a plurality of layers are stacked. In addition, the present invention can be similarly applied to secondary batteries having other shapes such as a coin shape, a button shape, a square shape, or a laminate film shape.

  Furthermore, in the above embodiment, the case where a liquid electrolytic solution is used as the nonaqueous electrolyte has been described. However, a gel-like nonaqueous electrolyte in which the electrolytic solution is held by a holding body such as a polymer compound is used. Also good. Examples of such a polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, and polyphosphazene. , Polysiloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene and polycarbonate. In particular, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene and polyethylene oxide are preferable from the viewpoint of electrochemical stability. Although the ratio of the polymer compound to the electrolytic solution varies depending on the compatibility thereof, it is usually preferable to add a polymer compound corresponding to 5% by mass or more and 50% by mass or less in the electrolytic solution.

Specific examples of the present invention will be described in detail, but the present invention is not limited thereto.
(Examples 1-1 to 1-3, Comparative Example 1-1)
The cylindrical secondary battery shown in FIGS.
As the positive electrode active material, lithium cobaltate (LiCoO ₂ ) having a cumulative 50% particle size (median particle size) of 12 μm obtained by a laser diffraction method was used. Subsequently, the positive electrode was prepared by adding 94% by mass of lithium cobaltate powder and 3% by mass of ketjen black as a conductive material to a mixed liquid in which 3.0% by mass of polyvinylidene fluoride was well dispersed in N-methyl-2-pyrrolidone. The mixture was mixed to prepare a positive electrode mixture and used as a positive electrode mixture coating solution.

Next, this positive electrode mixture coating solution is uniformly applied to both surfaces of a positive electrode current collector 21A made of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and compression-molded to form a positive electrode active material layer 21B to produce the positive electrode 21. did. At that time, the thickness of one surface of the positive electrode active material layer 21B is 80 μm. It was. After that, an aluminum positive electrode lead 25 was attached to one end of the positive electrode current collector 21A.

Further, as a negative electrode active material, 95% by mass of granular graphite powder composed of mesophase spherules having a lattice plane distance d ₀₀₂ in the C-axis direction of 0.336 nm and a median particle size of 15.6 μm in X-ray diffraction, and polyfluoride serving as a binder are used. The mixture was mixed with 5.0% by mass of vinylidene chloride and dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a negative electrode mixture coating solution.

Next, this negative electrode mixture coating solution was uniformly applied to both surfaces of a negative electrode current collector 22A made of a strip-shaped copper foil having a thickness of 15 μm, dried, and compression-molded to form a negative electrode active material layer 22B to produce a negative electrode 22. . At that time, the thickness of one surface of the negative electrode active material layer 22B is 70 μm. It was. Subsequently, nickel negative electrode leads 26 were attached to one end of the negative electrode current collector 22A at three locations.

  After preparing the positive electrode 21 and the negative electrode 22, the positive electrode 21 and the negative electrode 22 are laminated in the order of the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 through a separator 23 made of a microporous polyethylene stretched film having a thickness of 18 μm. The jelly roll type wound electrode body 20 was produced by winding a large number of turns. Next, the wound electrode body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. 11 was stored inside. Subsequently, an electrolytic solution was injected into the battery can 11, and the battery lid 14 was caulked to the battery can 11 through the gasket 17 to produce a cylindrical secondary battery.

  As the electrolyte, phosphorus hexafluoride as an electrolyte salt was mixed with a solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) were mixed at a ratio of 20/70/10 (mass). What dissolved lithium acid in the ratio of 1.28 mol / kg was used. At that time, 1.0% by weight of a sulfone compound as an additive was added to the total electrolyte. In Examples 1-1 to 1-3, the sulfone compound was changed to the following compounds 1 to 3. In Comparative Example 1-1, no sulfone compound was used.

(Measurement of capacity maintenance rate)
The prepared lithium batteries of Examples 1-1 to 1-3 and Comparative Example 1-1 were subjected to a 45 ° C. float test, and the capacity retention rate after 2000 hours was examined. First, the battery was charged with a constant current of 1 C until the battery voltage reached 4.2 V, and then switched to a constant voltage charge of 4.2 V to be in a float state. As for the capacity retention rate, the batteries after 1 hour and 2000 hours were discharged at a constant current of 1 C, and when the battery voltage reached 3.0 V, the discharge was terminated and the discharge capacity was measured. From {(battery capacity after 2000 hours) / (battery capacity after 1 hour)} × 100, the capacity retention rate after 2000 hours was determined.

  As shown in Table 1, in Examples 1-1 to 1-3, the capacity retention rate was significantly improved as compared with Comparative Example 1-1 in which no sulfone compound was added. Moreover, it turned out that the structure of the compound 1 can express an effect especially.

(Examples 2-1 to 2-6)
In Examples 2-1 to 2-6, cylindrical secondary batteries were produced in the same manner as in Example 1-1 except that the addition amount of the sulfone compound (Compound 1) was changed.

  In Examples 2-1 to 2-6, it was confirmed that the capacity retention rate was improved by adding the sulfone compound (Compound 1). If the amount added is small, the effect of forming a sufficient film on the surface of the positive electrode is small. If the amount added is large, the film on the surface of the positive electrode becomes too thick. The effect of a decrease in capacity maintenance rate increases. From this, it was found that the optimum addition amount was in the range of 0.05 wt% to 5.0 wt%.

(Examples 3-1 to 3-11, Comparative examples 3-1 to 3-11)
A cylindrical secondary battery was produced in the same manner as in Example 1-1 except that the type of the positive electrode active material was changed.
In addition, the positive electrode active material of Example 3-10 and Comparative Example 3-10 was produced as follows.
First, as the composite oxide particles, lithium cobaltate powder having an average composition of LiCoO ₂ and an average particle diameter of 13 μm measured by a laser scattering method is prepared, and lithium carbonate (Li ₂ CO _{3) is used} as a raw material for the coating layer. ) Powder, nickel hydroxide (Ni (OH) ₂ ) powder, manganese carbonate (MnCO ₃ ) powder, and a mole of Li ₂ CO ₃ : Ni (OH) ₂ : MnCO ₃ = 1.08: 1: 1 The precursor powder mixed in the ratio was pulverized with a ball mill device until the average particle size became 1 μm or less.
10 parts by mass of Li _1.08 Ni _0.5 Mn _0.5 O ₂ is obtained by pulverizing the precursor powder until the average particle size becomes 1 μm or less with respect to 100 parts by mass of the composite oxide particles. And a precursor layer was formed on the surface of the composite oxide particles by treatment with a mechanofusion apparatus.
Subsequently, this was heated at a rate of 3 ° C./min, held at 800 ° C. for 3 hours, and then gradually cooled to form a coating layer to obtain a positive electrode active material.
When the positive electrode active material of the produced Example was observed using a scanning electron microscope (Scanning Electron Microscope; SEM) and an energy dispersive X-ray fluorescence spectrometer (Energy Dispersive X-ray Fluorescence Spectrometer; EDX) in combination, Oxide particles containing nickel and manganese having a particle size of about 0.1 μm are deposited on the surface of the oxide particles, and nickel and manganese are present almost uniformly on the surface of the composite oxide particles. The situation was seen.
Moreover, the positive electrode active materials of Example 3-11 and Comparative Example 3-11 were prepared as follows.
First, as the composite oxide particles, lithium cobaltate powder having an average composition of LiCoO ₂ and an average particle diameter of 13 μm measured by a laser scattering method is prepared, and lithium carbonate (Li ₂ CO _{3) is used} as a raw material for the coating layer. ) Powder and manganese phosphate Mn ₃ (PO ₄ ) ₂ powder mixed at a molar ratio of Li ₂ CO ₃ : Mn ₃ (PO ₄ ) ₂ = 1: 1, the average particle diameter was measured by a ball mill device. Was pulverized until it became 1 μm or less.
To 100 parts by mass of the composite oxide particles, a powder obtained by pulverizing the precursor powder until the average particle size becomes 1 μm or less is added so as to be 10 parts by mass in terms of Li ₃ PO ₄ and processed by a mechanofusion apparatus. Thus, a precursor layer was formed on the surface of the composite oxide particle.
Subsequently, this was heated at a rate of 3 ° C./min, held at 800 ° C. for 3 hours, and then gradually cooled to form a coating layer to obtain a positive electrode active material.
When the positive electrode active material of the produced example was observed using both SEM and EDX, particles containing a phosphoric acid compound having a particle size of about 0.1 μm were deposited on the surface of the composite oxide particles. Manganese was dissolved in the surface part of lithium cobaltate.

From the results in Table 3, in the battery using lithium nickelate (LiNiO ₂ ) or lithium manganate (LiMn ₂ O ₄ ), the deterioration in the charged state is extremely small, and the effect of adding the sulfone compound is small. It was also found that the effect of adding the sulfone compound is greatly exhibited when cobalt is dissolved or mixed in the positive electrode active material.

(Examples 4-1 to 4-2, Comparative examples 4-1 to 4-2)
A cylindrical secondary battery was produced in the same manner as in Example 1-1 except that the type of the electrolyte solvent was changed.

  From the results in Table 4, it was confirmed that the capacity retention rate was improved by adding the sulfone compound, regardless of which electrolyte solution was used.

(Comparative Examples 5-1 to 5-4)
The type of negative electrode active material was changed. In Comparative Examples 5-1 to 5-2, a negative electrode active material containing tin as the first constituent element was synthesized using a mechanochemical reaction. The composition analysis was performed about the obtained negative electrode active material powder. The carbon content was measured by a carbon / sulfur analyzer, and the content of other elements was measured by ICP (Inductively Coupled Plasma) emission analysis. The obtained results are shown in parentheses in the negative electrode active material column of the table. Note that the numbers shown in parentheses separated by slashes indicate the content (mass%) of the elements described above in order. Next, 80 parts by mass of the obtained negative electrode active material powder, 11 parts by mass of graphite (KS-15 manufactured by Lonza) and 1 part by mass of acetylene black as a conductive material, and 8 parts by mass of polyvinylidene fluoride as a binder were mixed. The negative electrode mixture slurry was dispersed in N-methyl-2-pyrrolidone as a solvent. Subsequently, the negative electrode mixture slurry is uniformly applied to both surfaces of a negative electrode current collector 22A made of a strip-shaped copper foil having a thickness of 10 μm, dried, and compression-molded at a constant pressure to form a negative electrode active material layer 22B. Was made. After that, a nickel negative electrode lead 26 was attached to one end of the negative electrode current collector 22A.
In Comparative Examples 5-3 to 5-4, the negative electrode active material layer 22B made of silicon was formed on the negative electrode current collector 22A by electron beam vapor deposition, and then the negative electrode 22 was produced by heat treatment. A cylindrical secondary battery was produced in the same manner as in Example 1-1 and Comparative Example 1-1 except that the type of the negative electrode active material was changed.

(Example 5-1 and Comparative Example 5-5)
In Example 5-1 and Comparative Example 5-5, natural graphite having an active material made of granular graphite powder made of mesophase spherules and having a lattice plane distance d ₀₀₂ in the C-axis direction of 0.3357 nm and a median particle diameter of 18 μm in X-ray diffraction. Changed to powder. A mixture of 95% by mass of natural graphite powder, 4.0% by mass of styrene butadiene rubber (SBR) and 1.0% by mass of carboxymethyl cellulose (CMC), which are binders, is dispersed in water and mixed with a negative electrode mixture. It was. Cylindrical secondary batteries were produced in the same manner as in Example 1-1 and Comparative Example 1-1 except that the type of the negative electrode active material and the type of the binder were changed.

From the results shown in Table 5, when an active material such as Sn-based or Si-based active material having a very strong activity with respect to the electrolytic solution is used for the negative electrode, the electrolytic solution is severely decomposed and the float characteristics are reduced regardless of the deterioration on the positive electrode side. Intense. Even if the sulfone compound is used, deterioration due to cobalt elution on the positive electrode side can be suppressed, but decomposition of the electrolyte solution on the negative electrode side cannot be suppressed, and the film on the surface of the negative electrode becomes thick and capacity deterioration due to increased resistance cannot be suppressed. From this, it was found that the sulfone compound exerts an effect on a battery of a combination of a carbon-based negative electrode and a cobalt-based positive electrode.
From Example 5-1 and Comparative Example 5-5, it was found that the sulfone compound exhibited an effect even when natural graphite was used as the active material and styrene butadiene rubber (SBR) or carboxymethyl cellulose was used as the binder.

It is sectional drawing showing the structure of the secondary battery which concerns on embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body in the secondary battery shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20 ... Winding electrode body, 21 ... Positive electrode, 21A DESCRIPTION OF SYMBOLS ... Positive electrode collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode collector, 22B ... Negative electrode active material layer, 23 ... Separator, 24 ... Center pin, 25 ... Positive electrode lead, 26 ... Negative electrode lead.

Claims (3)

A non-aqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material layer provided on a positive electrode current collector, a negative electrode having a negative electrode active material layer provided on a negative electrode current collector, and a non-aqueous electrolyte, The positive electrode active material layer includes a lithium cobalt oxide (LiCoO ₂ ) that is a positive electrode active material, or a lithium cobalt composite oxide containing different atoms (LiCo _x M _1-x O ₂ : M is one or more metals, x 0 <x <1) as a main component, the negative electrode active material layer mainly includes a carbon-based material that is a negative electrode active material, and the non-aqueous electrolyte has the formula (1) and the formula ( A nonaqueous electrolyte secondary battery containing at least one of the sulfone compounds of 2).

(R1 is a _{C m H 2m-n X n} , X is halogen. However, m is an integer of 2 to 4, n is an integer of 0 to 2m .R2 is _C j _{H 2j-k} Z _k and Z is halogen, where j is an integer of 2 to 4 and k is an integer of 0 to 2j.) The nonaqueous electrolyte secondary battery according to claim 1, wherein the sulfone compound of the formula (1) is a compound of the formula (1-1).

  The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the sulfone compound according to claim 1 or 2 in the nonelectrolyte is 0.05 to 5 mass%.

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