JP2016072116A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a nonaqueous electrolyte which enables the materialization of a nonaqueous electrolyte secondary battery arranged so that the rise in direct current in the case of repetition of charge and discharge is suppressed; and a nonaqueous electrolyte battery arranged by use of such a nonaqueous electrolyte.SOLUTION: A nonaqueous electrolyte comprising sugar alcohol such as sorbitol is used. The inventors surmise as follows. Part of the sugar alcohol contributes to the formation of a coating on a negative electrode. While there are various kinds of materials as a material contributing to the formation of a coating on the negative electrode, sugar alcohol contributes to the formation of a low-resistance coating. Sugar alcohol forms a complex so as to take a very small amount of transition metal ions eluted from a positive electrode, especially Mn ions therein. It is considered that in this way the effect of transition metal ions, making a cause for the rise in DC resistance in a battery, on the negative electrode can be suppressed. From the point of view, it is considered to be preferable that the sugar alcohol is one which can act as a multidentate ligand. Also, it is considered to be preferable that the sugar alcohol is one which has, in its molecule, many oxygen-containing functional groups.SELECTED DRAWING: None

Description

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

  Nonaqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used as power sources for mobile devices represented by mobile phones because of their high energy density.

  Non-aqueous electrolyte secondary batteries are beginning to be used for applications such as power storage, electric vehicles, and hybrid vehicles. For example, in lithium ion secondary batteries used in HEVs (hybrid electric vehicles), PHEVs (plug-in hybrid electric vehicles), etc., electric power for driving the motors (starting / acceleration) is discharged by discharging the electric power accumulated therein. It is used as a time assist). Moreover, electric power can be stored by charging the secondary battery with regenerative electric power of the electric motor or electric power generated by the electric generator. When the resistance of the secondary battery increases, the power that can be output from the secondary battery decreases, and the output characteristics as assist decreases, or the input characteristics (charging) that can be stored as regenerative energy from the motor. A problem such as a decrease in acceptability occurs.

  That is, these automobile batteries are required to be non-aqueous electrolyte batteries that have a small decrease in input / output characteristics and discharge capacity even when the batteries are repeatedly used, that is, a small increase in DC resistance against repeated charging and discharging.

  Patent Document 1 discloses a non-aqueous solution containing, as a polyhydric alcohol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, or glycerin as an additive in order to suppress an increase in internal resistance of the non-aqueous electrolyte secondary battery. It describes that an electrolytic solution was used.

  Patent Document 2 describes that an electrolytic solution to which trimethylolpropane is added is used to suppress a decrease in contrast of an electrodeposition type or electrochromic type display element using a pigment such as titanium oxide. Yes. As polyhydric alcohol compounds containing three or more OH groups similar to trimethylolpropane, glycerin, trimethylolethane, erythritol, pentaerythritol, sorbitol, sucrose, quadrol, and their polymerization adducts are described.

  Patent Document 3 uses an electrolyte containing a saccharide such as monose, diose, octose, cellobiose, panose, levan, chitin, etc., in order to make the non-aqueous electrolyte battery excellent in charge / discharge cycle performance at high temperatures. It is described.

JP 2001-118599 A JP 2011-85622 A JP 2000-21443 A

  This invention is made | formed in view of the said problem, and it aims at providing the nonaqueous electrolyte secondary battery by which the resistance raise with respect to repeated charging / discharging was suppressed.

The present invention is a nonaqueous electrolyte for a nonaqueous electrolyte secondary battery containing a sugar alcohol having 5 to 10 carbon atoms. Moreover, it is the manufacturing method of the nonaqueous electrolyte secondary battery containing sugar alcohol, and the nonaqueous electrolyte secondary battery manufactured using sugar alcohol. Specifically, a sugar alcohol having a chain structure is represented by Chemical Formula 1.

(Where n is an integer from 3 to 8)

According to the nonaqueous electrolyte for a nonaqueous electrolyte secondary battery according to the present invention, it is possible to provide a nonaqueous electrolyte that can be a nonaqueous electrolyte secondary battery in which an increase in resistance is suppressed when charging and discharging are repeated.

1 is an external perspective view showing an embodiment of a nonaqueous electrolyte secondary battery according to the present invention. Schematic showing a power storage device configured by assembling a plurality of nonaqueous electrolyte secondary batteries according to the present invention Graph showing the relationship between the number of carbon atoms and the rate of increase in DC resistance

  The configuration and operational effects of the present invention will be described with the technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the following embodiments or experimental examples are merely examples in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  Examples of sugar alcohols include D-sorbitol, L-sorbitol, D-mannitol, L-mannitol, D-galactitol, L-galactitol, D-xylitol, L-xylitol, D-boretitol, L-boretitol, D-perceitol. , L-perceitol, D-erythro-D-galacto-octitol and the like.

  Sugar alcohol is easily decomposed when the number of carbon atoms is 3 or less, and the effect of suppressing increase in resistance cannot be sufficiently obtained. When the sugar alcohol has 5 or more carbon atoms, a remarkable resistance increase suppressing effect can be obtained. This is considered to be because the number of hydroxyl groups bonded to carbon between the carbon chains becomes three or more, and the probability that the hydroxyl group is arranged at a position advantageous for complexing with the metal ion is increased. On the other hand, when the number of carbon atoms is 12 or more, it is difficult to dissolve in the electrolytic solution, so that the effect of suppressing the resistance increase is hardly obtained. When the number of carbon atoms of the sugar alcohol is 10 or less, the effect of the present invention can be achieved in combination with excellent solubility in the electrolytic solution. Among these, sugar alcohols having 5 or 6 carbon atoms are preferable because they are hardly decomposed and are dissolved in the electrolytic solution.

  Further, when the carbon of the carbon chain of the sugar alcohol is arranged on a plane, it is preferable that the sugar alcohol contains three or more hydroxyl groups on the same side when the plane of the carbon is used as a boundary. . This is because it is considered that the hydroxyl group is arranged at a position advantageous for the sugar alcohol to complex with the metal ion. In addition, the hydroxyl group couple | bonded with carbon of the terminal carbon chain is not counted in the hydroxyl group which exists in the same side. In particular, D-xylitol, L-xylitol, D-sorbitol or L-sorbitol is preferable.

  Although the mechanism of action of the present invention is not necessarily clear, the present inventors presume as follows. Part of the sugar alcohol contributes to the formation of a film on the negative electrode. There are a wide variety of materials that contribute to film formation on the negative electrode, but sugar alcohols contribute to film formation with low resistance. In addition, the sugar alcohol is complexed so as to take in a small amount of transition metal ions, particularly Mn ions, eluted from the positive electrode. In this way, it is considered that the action of the transition metal ions that cause the resistance of the battery to increase is suppressed on the negative electrode. From these viewpoints, the sugar alcohol is desirably one that can act as a multidentate ligand, and it is considered preferable that the sugar alcohol has many oxygen-containing functional groups in the molecule.

  Since the sugar alcohol contained in the electrolyte partly contributes to the film formation on the negative electrode, the amount of sugar alcohol contained in the nonaqueous electrolyte provided in the nonaqueous electrolyte secondary battery produced using this is It is conceivable that the amount is reduced as compared with the amount added to the nonaqueous electrolyte used at the time of manufacture. However, even if the amount of sugar alcohol contained in the nonaqueous electrolyte included in the nonaqueous electrolyte secondary battery is very small, it can be detected by LC-MS analysis.

  The addition amount of the sugar alcohol is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, further preferably 0.05% by mass or more, and preferably 5.0% by mass or less, 3.0 The mass% or less is more preferable, and 1.0 mass% or less is more preferable. By making the addition amount 0.05% by mass or more, the effect of the present invention can be surely exhibited. Moreover, the possibility that the battery bulge increases excessively can be reduced by setting the addition amount to 1.0 mass% or less.

There is no restriction | limiting in particular as a positive electrode active material used for the nonaqueous electrolyte which concerns on this invention, The various materials which can occlude or discharge | release alkali metal ions, such as lithium, reversibly can be used suitably. For example, lithium transition metal complex oxide is mentioned. Representative lithium transition metal composite oxides include spinel type lithium manganese oxide represented by LiMn ₂ O _{4 and the} like, spinel type lithium nickel manganese oxide represented by LiNi _1/2 Mn _3/2 O _{4 and the} like. Lithium transition metal oxide having a spinel crystal structure, LiCoO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , Li _1.1 Co _2/3 Ni _1/6 Mn _1/6 O _{2 and the} like, LiMeO ₂ type (Me is a transition metal) lithium transition metal composite oxide having an α-NaFeO ₂ structure typified by, for example. Among these, it is preferable to include a lithium transition metal composite oxide containing Mn element, and it is particularly preferable to include a spinel type lithium manganese oxide.

  The positive electrode active material suppresses an increase in resistance when charging / discharging is repeated by applying the nonaqueous electrolyte of the present invention in a nonaqueous electrolyte secondary battery including a positive electrode including a lithium transition metal composite oxide containing Mn element. The effect is great. The nonaqueous electrolyte of the present invention is applied to a nonaqueous electrolyte secondary battery having a positive electrode active material that is a lithium transition metal composite oxide and includes a positive electrode containing an active material in which the proportion of Mn element in the transition metal is 30% or more. It is preferable to apply the nonaqueous electrolyte of the present invention to a nonaqueous electrolyte secondary battery including a positive electrode containing an active material having an Mn element ratio of 50% or more.

As the lithium transition metal composite oxide, a material that can be expressed as Li _{1 + α} Me _1-α O ₂ (Me includes Ni, Co, and Mn, and Mn / Me> 0.5, α> 0) may be used. Here, the Li / Me ratio is preferably 1.25 to 1.6. The ratio of elements such as Co, Ni and Mn constituting the transition metal element constituting the lithium transition metal composite oxide can be arbitrarily selected according to the required characteristics, but the discharge capacity is large and the initial charge / discharge is large. The molar ratio Co / Me of Co to the transition metal element Me is preferably 0.05 to 0.40, and preferably 0.10 to 0.30 in that a nonaqueous electrolyte secondary battery having excellent efficiency can be obtained. Is more preferable. In addition, the molar ratio Mn / Mn of the transition metal element Me is preferably 0.6 or more in that a nonaqueous electrolyte secondary battery having a large discharge capacity and excellent initial charge / discharge efficiency can be obtained. .65 to 0.75 is more preferable.

In the nonaqueous electrolyte secondary battery in which the positive electrode active material includes a positive electrode including a lithium transition metal composite oxide having an α-NaFeO ₂ structure, the nonaqueous electrolyte preferably contains a sugar alcohol. Furthermore, the positive electrode active material preferably includes a positive electrode containing 90% by mass or more of a lithium transition metal composite oxide having an α-NaFeO ₂ structure. Thereby, the fall of the discharge capacity of a battery accompanying charging / discharging cycle progress can be suppressed. This is because the sugar alcohol contained in the non-aqueous electrolyte forms a film on the positive electrode, which occurs when the lithium transition metal composite oxide having the α-NaFeO ₂ structure is included, and the discharge capacity of the battery with the progress of the charge / discharge cycle This is thought to be due to the fact that it is possible to suppress a rapid drop in the temperature.

  The positive electrode active material powder desirably has an average particle size of 100 μm or less. In particular, the positive electrode active material powder is desirably 40 μm or less for the purpose of improving the high output characteristics of the nonaqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  The nonaqueous electrolyte used for the nonaqueous electrolyte secondary battery according to the present invention is not limited, and those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof These may be used alone or as a mixture of two or more thereof, but are not limited thereto.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B _1.0 Cl _1.0 , NaClO ₄ , NaI. , NaSCN, NaBr, KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiN (FSO ₂ ) ₂ , LiCF ₃ SO ₃ , LiN (CF _{3 SO 2) 2, LiN (C} 2 F 5 SO 2) 2, LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) _{3, (CH 3) 4 NBF} 4, (CH 3) 4 NBr, (C 2 H 5) 4 NClO 4, (C 2 H 5) 4 NI, (C 3 H 7 _{4 NBr, (n-C 4} H 9) 4, NClO 4, (n-C 4 H 9) 4 NI, (C 2 H 5) 4 N-maleate, (C 2 H 5) 4 N-benzoate, ( Organic ion salts such as C ₂ H ₅ ) ₄ N-phtalate, lithium stearyl sulfonate, lithium octyl sulfonate, lithium dodecylbenzene sulfonate, etc., and these ionic compounds may be used alone or in combination of two or more. It is possible to use. Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

The negative electrode material is not limited, and any material can be selected as long as it is capable of reversibly occluding or releasing alkali metal ions such as lithium. For example, titanium-based materials such as lithium titanate having a spinel crystal structure typified by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based lithium metal, lithium alloys (Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) and the like can be given. In particular, it is desirable to use graphite from the viewpoint of energy density and life.

  The powder of the negative electrode material desirably has an average particle size of 100 μm or less. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  As described above, the positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, a filler, and the like. , May be added as another component.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect battery performance. Usually, natural graphite (such as scale-like graphite, scale-like graphite, earth-like graphite), artificial graphite, carbon black, acetylene black, A conductive material such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material can be included as one type or a mixture thereof. .

  Among these, as the conductive agent, acetylene black is desirable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by mass to 50% by mass, and particularly preferably 0.5% by mass to 10% by mass with respect to the total mass of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black by pulverizing into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet. Moreover, when using the material excellent in electroconductivity like graphite as an active material, scaly graphite is desirable as a electrically conductive agent.

  As the binder, thermoplastic resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene, and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene butadiene rubber are usually used. A polymer having rubber elasticity such as (SBR) or fluoro rubber can be used as one kind or a mixture of two or more kinds. The added amount of the binder is preferably 1 to 50% by mass, particularly preferably 1 to 10% by mass with respect to the total mass of the positive electrode or the negative electrode.

  As the filler, any material that does not adversely affect the battery performance may be used. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by mass or less with respect to the total mass of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode are obtained by kneading main constituents (positive electrode active material in the positive electrode, negative electrode material in the negative electrode) and other materials into a mixture and mixing them in an organic solvent such as N-methylpyrrolidone and toluene or water. The obtained liquid mixture is preferably produced by applying on a current collector described in detail below, or by pressure bonding and drying. Thermal vacuum drying can be performed as necessary. As for the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. Is not to be done.

  As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for nonaqueous electrolyte batteries include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  Further, as the separator, for example, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, and polyvinylidene fluoride and an electrolyte may be used. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is desirable that the separator be used in combination with the above-described porous film, nonwoven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, a film having a thickness of several μm or less coated with a solvophilic polymer is formed on the surface of the polyethylene microporous membrane and the microporous wall, and the electrolyte is held in the micropores of the film, whereby the solvophilic polymer is gelled. Turn into.

Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  FIG. 1 is a schematic view of a rectangular nonaqueous electrolyte secondary battery 1 which is an embodiment of the nonaqueous electrolyte secondary battery according to the present invention. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte secondary battery 1 shown in FIG. 1, an electrode group 2 is housed in a battery container 3. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.

  The configuration of the nonaqueous electrolyte secondary battery is not particularly limited, and examples thereof include a cylindrical battery having a positive electrode, a negative electrode, and a roll separator, a square battery, and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above non-aqueous electrolyte secondary batteries. One embodiment of a power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

Example 1
An electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. Mass% sorbitol (Wako Pure Chemical Industries, D-sorbitol) was added and dissolved. This is the nonaqueous electrolyte according to Example 1.

(Examples 2 and 3)
It was made to melt | dissolve with respect to electrolyte solution like Example 1 except having replaced with 0.1 mass% sorbitol and having added the quantity of sorbitol shown in Table 1. These are the nonaqueous electrolytes according to Examples 2 and 3.

Example 4
It was made to melt | dissolve with respect to electrolyte solution like Example 1 except having replaced with sorbitol and having added xylitol. These are the nonaqueous electrolytes according to Example 4.

(Example 5)
Instead of sorbitol, mannitol was added and stirred, and dissolved in the electrolytic solution in the same manner as in Example 1 except that the supernatant was collected after being left at 50 ° C. for 5 hours. These are the nonaqueous electrolytes according to Example 5.

(Comparative Example 1)
An electrolytic solution in which LiPF ₆ is dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 3: 7 is used as the nonaqueous electrolyte according to Comparative Example 1.

(Comparative Example 2)
An electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. Mass% glycerin was added. This is the nonaqueous electrolyte according to Comparative Example 2.

(Comparative Example 3)
Instead of sorbitol, maltitol was added and stirred, and dissolved in the electrolytic solution in the same manner as in Example 1 except that the supernatant was collected after leaving at 50 ° C. for 5 hours. These are the nonaqueous electrolytes according to Comparative Example 3.

(Preparation of non-aqueous electrolyte secondary battery)
Using each of these non-aqueous electrolytes, non-aqueous electrolyte secondary batteries were produced by the following procedure. In the following examples, a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure and represented by LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , and a spinel type crystal structure and LiMn _A mixture of lithium manganese oxide represented by ₂ O ₄ at a mass ratio of 7: 3 was used as the positive electrode active material.

  A positive electrode active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) are mixed at a mass ratio of 94: 3: 3 (in terms of solid content) to produce a positive electrode paste using N-methylpyrrolidone (NMP) as a solvent. And it apply | coated on both surfaces of the 20-micrometer-thick strip | belt-shaped aluminum foil electrical power collector. The positive electrode was pressure-molded with a roller press to form a positive electrode active material layer, and then vacuum dried at 100 ° C. for 14 hours to remove moisture in the electrode plate. In this way, a positive electrode plate was produced.

  Graphite, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed at a mass ratio of 97: 2: 1 (in terms of solid content) to prepare a negative electrode paste using water as a solvent, and having a thickness of 10 μm. It apply | coated to both surfaces of a strip | belt-shaped copper foil collector. The negative electrode was pressure-molded with a roller press to form a negative electrode active material layer, and then vacuum-dried at 100 ° C. for 12 hours to remove moisture in the electrode plate. In this way, a negative electrode plate was produced.

(Examples 2-1 to 2-4, Comparative Example 2-1)
In Examples 2-1 to 2-4 and Comparative Example 2-1, the positive electrode active material has an α-NaFeO ₂ type crystal structure and is represented by LiNi _1/3 Mn _1/3 Co _1/3 O ₂ A nonaqueous electrolyte battery was produced in the same manner as in Examples 1 to 4 and Comparative Example 1 except that the transition metal composite oxide was used.

<Assembly process>
A positive electrode plate and a negative electrode plate are laminated through a separator made of a polyethylene porous membrane, wound in a flat shape to produce a power generation element, housed in an aluminum square battery case, and attached with positive and negative electrode terminals . The container was sealed after injecting a nonaqueous electrolyte into the container. In this way, a nonaqueous electrolyte battery having a design capacity of 800 mAh (1 CmA = 800 mAh) was assembled.

<Initial charge / discharge process>
Next, it was subjected to an initial charge / discharge process of 2 cycles at 25 ° C. All voltage control was performed on the voltage between the positive and negative terminals. The first cycle charge was a constant current constant voltage charge with a current of 0.2 CmA and a voltage of 4.2 V for 8 hours, and the discharge was a constant current discharge with a current of 0.2 CmA and a final voltage of 2.75 V. Charging in the second cycle was constant current constant voltage charging with a current of 1.0 CmA and a voltage of 4.2 V for 3 hours, and discharging was constant current discharging with a current of 1.0 CmA and a final voltage of 2.75 V. In all cycles, a 10 minute rest period was set after charging and discharging.

<Charge / discharge cycle test>
About the nonaqueous electrolyte secondary battery completed through the said initial stage charging / discharging process, the charge / discharge cycle test of 800 cycles was done at 45 degreeC. All voltage control was performed on the voltage between the positive and negative terminals. Charging was performed at a constant current and constant voltage with a current of 1.0 CmA and a voltage of 4.2 V for 3 hours, and discharging was performed at a constant current of 1.0 CmA and a final voltage of 2.75 V. In all cycles, a 10 minute rest period was set after charging and discharging. Here, it is known that when the voltage between the positive and negative terminals is 4.2 V, the positive electrode potential is 4.3 V (vs. Li ^/ Li ⁺ ). In addition, the DC resistance of the battery in the SOC 50% state was determined by the following method at -20 ° C or 25 ° C as needed. First, discharge was performed for 30 seconds in the order of current 0.2 CmA, 0.5 CmA, and 1.0 CmA. Next, the relationship between the discharge current at that time and the voltage at 10 seconds was plotted, and the DC resistance was obtained from the slope of the obtained straight line. The rate of increase is determined by the formula {(DC resistance after test−DC resistance before test) / DC resistance before test}.

  For the nonaqueous electrolyte batteries according to Examples 1 to 5 and Comparative Examples 1, 2, and 3, “DC resistance before test” of charge / discharge cycle, DC resistance before charge / discharge cycle test, obtained at −20 ° C. Table 1 shows the DC resistance at 800th cycle as “increase rate”. Further, the discharge capacity at the second cycle before the charge / discharge cycle test is used as the “discharge capacity before cycle”, and the ratio of the discharge capacity at the 800th cycle to the discharge capacity at the second cycle is used as the “capacity maintenance ratio after 800 cycles”. Is shown in Table 1.

  As can be seen from Table 1, the nonaqueous electrolyte battery according to Example 1 using the nonaqueous electrolyte to which the sugar alcohol is added is the nonaqueous electrolyte according to Comparative Example 1 using the nonaqueous electrolyte to which the sugar alcohol is not added. It can be seen that an increase in DC resistance is suppressed as compared with the battery.

  Compared with the nonaqueous electrolyte battery according to Comparative Example 2 using the nonaqueous electrolyte to which glycerin was added, in the example using the sugar alcohol having 5 or more carbon atoms, the direct current resistance was remarkably increased as shown in FIG. It turns out that it is suppressed. Therefore, according to the present invention, a nonaqueous electrolyte secondary battery excellent in input / output characteristics can be obtained even when charging and discharging are repeated.

Non-related to Examples 2-1 to 2-4 and Comparative Example 2-1 using a lithium transition metal composite oxide represented by LiNi _1/3 Mn _1/3 Co _1/3 O _{2 as a} positive electrode active material Table 2 shows the “DC resistance before the test” of the charge / discharge cycle and the DC resistance at the 800th cycle with respect to the DC resistance before the charge / discharge cycle test, obtained at −20 ° C. Show. In addition, the discharge capacity of the second cycle before the charge / discharge cycle test is “pre-cycle discharge capacity”, and the ratio of the discharge capacity of the 800th cycle to the discharge capacity of the second cycle is “capacity maintenance ratio after 800 cycles” It shows in Table 2.

When Table 1 and Table 2 are compared, in Examples 1 to 4 including the positive electrode including the lithium manganese oxide represented by LiMn ₂ O ₄ , the effect of suppressing an increase in resistance when charging and discharging are repeated is large. I understand.

In Examples 2-1 to 2-4, from the cycle capacity retention rate of Table 2, the positive electrode active material used a lithium transition metal composite oxide represented by LiNi _1/3 Mn _1/3 Co _1/3 O ₂ It can be seen that the non-aqueous electrolyte secondary battery to which sugar alcohol is added has a large cycle capacity maintenance rate. Increasing the amount of sugar alcohol added improved the cycle capacity retention rate.

  Moreover, about the nonaqueous electrolyte battery which concerns on Examples 2-1 to 2-4 and Comparative Example 2-1, the result of having calculated | required the direct current | flow resistance of the battery at 25 degreeC is "DC resistance before a test" of a charging / discharging cycle. The DC resistance at the 800th cycle relative to the DC resistance before the charge / discharge cycle test is shown in Table 3 as “DC resistance increase rate”.

  The non-aqueous electrolyte batteries according to Examples 2-1 to 2-4 using the non-aqueous electrolyte added with the sugar alcohol are non-aqueous according to Comparative Example 2-1 using the non-aqueous electrolyte not added with the sugar alcohol. It can be seen that the increase in DC resistance is suppressed compared to the electrolyte battery.

(Explanation of symbols)
DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device

Claims (6)

A non-aqueous electrolyte for a non-aqueous electrolyte secondary battery containing a sugar alcohol having 5 to 10 carbon atoms.   The non-aqueous electrolyte for a non-aqueous electrolyte secondary battery according to claim 1, wherein the sugar alcohol has three or more hydroxyl groups arranged on the same side when the carbon of the carbon chain is arranged on a plane.   The non-aqueous electrolyte for a non-aqueous electrolyte secondary battery according to claim 2, wherein the sugar alcohol is sorbitol or xylitol.   A nonaqueous electrolyte secondary battery comprising: the nonaqueous electrolyte for a nonaqueous electrolyte secondary battery according to claim 1; a positive electrode including a positive electrode active material; and a negative electrode including a negative electrode active material.   5. The non-aqueous electrolyte secondary battery according to claim 4, wherein the positive electrode active material includes a lithium transition metal composite oxide in which a ratio of Mn element in the transition metal is 50% or more. The manufacturing method of the nonaqueous electrolyte secondary battery using the nonaqueous electrolyte for nonaqueous electrolyte secondary batteries of any one of Claim 1 to 3.