JP7091574B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

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

Non-aqueous electrolyte secondary batteries represented by lithium secondary batteries are widely used as power sources for mobile devices such as mobile phones by taking advantage of their high energy density. Further, in recent years, it has been developed not only for power sources for small devices but also for medium- and large-sized industrial applications such as power storage, electric vehicles and hybrid vehicles.

A non-aqueous electrolyte secondary battery generally includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator, and a non-aqueous electrolyte containing a non-aqueous solvent and a lithium salt. A lithium-containing transition metal oxide is widely used as the positive electrode active material constituting the non-aqueous electrolyte secondary battery, and a carbon material typified by graphite is widely used as the negative electrode active material. As the non-aqueous electrolyte, an electrolyte such as lithium hexafluorophosphate (LiPF ₆ ) dissolved in a non-aqueous solvent at various concentrations is widely used.

Patent Document 1 describes a lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) of 1.5 mol / L or more and 3.5 mol / L or less for the purpose of providing a highly safe secondary battery in which an electrolytic solution is incombustible. ) And an electrolytic solution containing 20 to 60% by volume of a phosphate ester derivative are described, a battery using LiMn ₂ O ₄ as a positive electrode is specifically described, and LiTFSI is used at a high concentration. It is stated that corrosion of aluminum is suppressed.

Patent Document 2 describes LiPF ₆ of 1.2 M or more and 3 M or less for the purpose of providing a lithium secondary battery in which both characteristics of high input / output characteristics and good high temperature cycle characteristics are well-balanced.
It is described that a non-aqueous electrolytic solution in which is dissolved is used, and a battery using LiNi _0.8 Co _0.15 Al _0.05 O ₂ for the positive electrode is specifically described, and LiCoO ₂ , LiNiO ₂ and LiMn are described. It is described that _{2O 4} , LiMnO ₂ , and the like can be used (paragraph 0014).

In Patent Document 3, the porosity of the positive electrode is 25% or less for the purpose of providing a non-aqueous electrolyte battery in which the high rate characteristics and low temperature characteristics of the battery do not deteriorate even when a low porosity electrode is used. A non-aqueous electrolyte battery in which the amount of active material carried per unit area of the positive electrode is 20 mg / cm ² or more and the salt concentration of the non-aqueous electrolyte exceeds the concentration giving the conductivity peak is described. The concentration given is "in the salt exemplified below such as lithium hexafluoride phosphate (LiPF ₆ ), it is around 1 mol · dm ^-3 , ^and it is preferable that the concentration is higher than that, especially 1.3 mol · dm-. ³ or more. The upper limit thereof is about 3 mol · dm ^-3 . ”(Section 0013), a battery using LiCoO ₂ as the positive electrode active material and having a salt concentration of 2.5 mol · dm ^-3 . (Examples 5 and 14) and the like are specifically described, and the positive electrode active material includes “LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiV ₂ O ₄ and the like” (paragraph 0022). There is.

Patent Document 4 describes lithium bis (perfluoroethanesulfonyl) in a PC for the purpose of making it possible to use an organic electrolytic solution containing propylene carbonate (PC) even in a negative electrode made of a graphite-based carbon material. It is described that an electrolytic solution in which imide (LiBETI) is dissolved at a concentration of 2.12 to 3.15 mol / L is used.

Non-Patent Document 1 describes a definition and a method for obtaining the number of donors of a solvent. The number of donors is a negative value of the enthalpy of formation of a 1: 1 addition compound between antimony trichloride in 1,2-dichloroethane and a solvent of interest, which was proposed by Gutmann, the author of Non-Patent Document 1. It is a parameter representing the electron pair donating ability of the solvent defined in.

Japanese Patent No. 5557337 Japanese Patent Application Laid-Open No. 2002-025606 Japanese Patent No. 4180335 Japanese Unexamined Patent Publication No. 2004-09552

Viktor Gutmann, "The Donor-Acceptor Approach to Molecular Interactions", Springer, 1978 (ISBN-13: 978-0306310645)

As the lithium-containing transition metal oxide used as the positive electrode active material of the non-aqueous electrolyte secondary battery, those mainly containing Mn, Ni, Co and the like which are transition metal elements are often used. Of these, since Mn is abundant as an earth resource and inexpensive, it has been desired to use a lithium-containing transition metal oxide having a high ratio of Mn element in the transition metal.

However, such a non-aqueous electrolyte secondary battery has a problem that Mn is likely to elute from the positive electrode active material into the non-aqueous electrolyte, and the charge / discharge efficiency cannot be sufficiently increased. An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent charge / discharge efficiency.

In the present invention, the following means are adopted in order to solve the above problems.
Positive electrode containing positive electrode active material containing Mn element Positive electrode, negative electrode, and
A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte in which the non-aqueous solvent contains an alkali metal salt.
The non-aqueous electrolyte is
Contains a non-aqueous solvent with 15 or more donors,
The ratio of the number of moles of the non-aqueous solvent having 15 or more donors to the number of moles of the alkali metal salt is 4 times or less.
Non-aqueous electrolyte secondary battery.

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having excellent charge / discharge efficiency.

External perspective view showing an embodiment of a non-aqueous electrolyte secondary battery according to the present invention. Schematic diagram showing a power storage device including a plurality of non-aqueous electrolyte secondary batteries according to the present invention.

The non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode and a negative electrode containing a positive electrode active material containing an Mn element, and a non-aqueous electrolyte containing an alkali metal salt as a non-aqueous solvent. In the next battery, the non-aqueous electrolyte contains a non-aqueous solvent having 15 or more donors, and the ratio of the number of moles of the non-aqueous solvent having 15 or more donors to the number of moles of the alkali metal salt is 4. It is characterized by being less than double.

Although the mechanism of action of the present invention is not always clear, the present inventors infer as follows. The elution of Mn from the positive electrode active material to the non-aqueous electrolyte occurs when the non-aqueous solvent liberated in the non-aqueous electrolyte without solvating the alkali metal ions solvates the Mn ions. In the non-aqueous electrolyte according to the present invention, the ratio of the number of moles of the non-aqueous solvent having 15 or more donors to the number of moles of the alkali metal salt is 4 times or less, so that the non-aqueous solvent having 15 or more donors is used. Most of them are solvents in alkali metal ions. That is, in the non-aqueous electrolyte, there is almost no non-aqueous solvent having 15 or more donors freed without solvation. Therefore, since there is almost no non-aqueous solvent that can be solvated with Mn ions, the elution of Mn from the positive electrode active material to the non-aqueous electrolyte is suppressed.

The positive electrode active material is not limited as long as it contains an Mn element. For example, a composite oxide represented by Li _x MO _y (M represents one or more transition metals containing Mn) (Li _x Ny Mn (2- _{y )} O ₄ , Li _x Mn ₂ O ₄ ). , Li _{x Ny Mn z Co (1-y-z)} O ₂ , Li _{1 + x} ( _{Ny Mn z Co (1-y-z)} ) _1-x O ₂ etc.), Li _w M _x (XO _y ) Examples thereof include polyanionic compounds (LiMnPO ₄ , Li ₂ MnSiO ₄ , etc.) represented by _z (M represents one or more kinds of transition metals containing Mn, and X represents, for example, P, Si, B, V). .. The elements or polyanions in these compounds may be partially substituted with other elements or anion species.

The elution of Mn from the positive electrode active material tends to be promoted when the operating potential of the positive electrode active material is noble. Therefore, it is preferable to apply the present invention to a non-aqueous electrolyte battery in which the positive electrode active material is operated at a more noble potential, because the effect of the present invention is remarkably exhibited.

The number of donors of the non-aqueous solvent used for the non-aqueous electrolyte can be confirmed by handbook or the like. Alternatively, it can be obtained by the method described in Non-Patent Document 1.

The non-aqueous solvent having 15 or more donors is not limited. For example, propylene carbonate (number of donors: 15.1), ethylene carbonate (16.4), diethyl carbonate (16.4), dimethyl carbonate (15.2), ethyl methyl carbonate, butylene carbonate, chloroethylene carbonate, fluoroethylene. Cyclic or chain such as carbonate, 1,2-difluoroethylene carbonate, trifluoropropylene carbonate, vinylene carbonate, vinylethylene carbonate, styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, diphenylcarbonate, etc. Cyclic carboxylic acid esters such as carbonate, γ-butyrolactone (18), γ-valerolactone, propiolactone, chain carboxylic acid esters such as methyl acetate, ethyl acetate (17.1), methyl butyrate, tetrahydrofuran (20) or Derivatives thereof, ethers such as 1,3-dioxane, 1,2-dimethoxyethane (20), diethoxyethane, methoxyethoxyethane, diglyme (19.2), tetraglyme (16.6), methyl diglyme, etc. Examples thereof include a single substance such as nitriles, dioxalane or a derivative thereof, or a mixture of two or more thereof. In particular, those containing cyclic carbonate such as ethylene carbonate and / or chain carbonate such as diethyl carbonate are preferable. Further, these non-aqueous solvents can be used by mixing two or more kinds at an arbitrary ratio.

As the non-aqueous solvent having 15 or more donors used for the non-aqueous electrolyte, it is preferable to select and use a non-aqueous solvent in which the number of donors is not too large. By selecting and using a non-aqueous solvent in which the number of donors is not too large, it is possible to reduce the possibility that the coordinating force of the non-aqueous solvent to solvate the alkali metal ions becomes too strong. Therefore, it is possible to reduce the possibility that the energy required for desolvation of the alkali metal ions on the surface of the active material becomes too large, and it is possible to reduce the concern that the progress of the electrode reaction is hindered. From this viewpoint, it is preferable to use a non-aqueous solvent containing 15 or more donors in the non-aqueous electrolyte, which has 16.5 or less donors.

The non-aqueous electrolyte according to the present invention may contain a non-aqueous solvent having less than 15 donors. For example, triglyme (number of donors: 14.0), acetonitrile (14.1), benzonitrile (11.9), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoro. Propyl ether (6-7), 1,1,2,2-tetrafluoroethyl-1,1,1-trifluoroethyl ether, 1,1,2,2-tetrafluoropropyl-1,1,1,2 , 3,3-A non-aqueous solvent such as hydrofluoroethers such as hexafluoropropyl ether can be mixed and used. In particular, by containing a non-aqueous solvent having excellent oxidation resistance and reduction resistance with a non-aqueous solvent alone and having a low viscosity of less than 15, the non-aqueous solvent does not impair the action and effect of the present invention. This is preferable because the viscosity of the electrolytic solution can be reduced.

As the non-aqueous solvent containing less than 15 donors in the non-aqueous electrolyte according to the present invention, it is preferable to select and use a non-aqueous solvent having a small number of donors. By selecting and using a non-aqueous solvent having a small number of donors, the coordinating power of the non-aqueous solvent to harmonize with alkali metal ions can be reduced, and a non-aqueous solvent having 15 or more donors selectively becomes alkali metal ions. Does not prevent solvating. Further, the non-aqueous solvent does not solvate the Mn ion, and the elution of Mn from the positive electrode active material to the non-aqueous electrolyte can be suppressed.

Even when the non-aqueous electrolyte contains a non-aqueous solvent having less than 15 donors, the "ratio of the number of moles of the non-aqueous solvent having 15 or more donors to the number of moles of the alkali metal salt" can be obtained. The calculation does not take into account the content of non-aqueous solvents with less than 15 donors. The reason is that the mechanism of action of the present invention is that a non-aqueous solvent having 15 or more donors can selectively solvate the alkali metal ion to suppress the elution of Mn from the positive electrode active material to the non-aqueous electrolyte. It is considered that there is a non-aqueous solvent having a donor number of less than 15 in the non-aqueous electrolyte, which is considered to be hardly solvent to the alkali metal ion or the Mn ion eluted from the positive electrode active material. Therefore, the number of donors is considered to be present. Is considered to hardly inhibit the solvent addition of 15 or more non-aqueous solvents to alkali metal ions.

The alkali metal salt contained in the non-aqueous electrolyte according to the present invention is not limited. Lithium salts that are stable in the wide potential range commonly used in non-aqueous electrolyte secondary batteries can be used. For example, LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (FSO ₂ ) ₂ , 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 , and the like can be mentioned. These may be used alone or in combination of two or more.

The concentration of the alkali metal salt in the non-aqueous electrolyte according to the present invention can be determined in relation to the number of moles of the non-aqueous solvent having 15 or more donors. For example, when propylene carbonate (PC) is used alone as a non-aqueous solvent having 15 or more donors and LiPF ₆ is used alone as an alkali metal salt, the number of donors of PC is 15.1 and the molecular weight of PC is 102. Since the molecular weight of LiPF ₆ is 151.9, the ratio of the number of moles of PC to the number of moles of LiPF ₆ is 4 times or less. It is a non-aqueous electrolyte (corresponding to a salt concentration of 2.45 mol / L or more) containing 372 g (2.45 mol) or more of LiPF ₆ .

The lower limit of the ratio of the number of moles of the non-aqueous solvent having 15 or more donors to the number of moles of the alkali metal salt, that is, the upper limit of the alkali metal salt concentration is not limited as long as the mechanism of action of the present invention is considered. .. Further, the type of non-aqueous solvent and the composition ratio when two or more types are mixed and used are not limited as long as the mechanism of action of the present invention is taken into consideration. However, it is preferable to adjust these matters as appropriate in consideration of design reasons and circumstances. For example, it is preferable that the viscosity of the non-aqueous electrolyte is not too high by not making the alkali metal salt concentration too high to facilitate the production of the non-aqueous electrolyte battery, or to facilitate the impregnation of the separator. .. From this viewpoint, the ratio of the number of moles of the non-aqueous solvent having 15 or more donors to the number of moles of the alkali metal salt is preferably 1 times or more.

Further, for example, it is preferable to reduce the risk of alkali metal salt precipitation by not making the composition ratio of the non-aqueous solvent having a low dielectric constant too high.

Further, for example, since ethers such as triglyme and tetraglyme are known to be easily decomposed at a noble potential, a non-aqueous solvent that is easily decomposed at a noble potential according to the operating potential of the positive electrode active material. It is preferable to avoid using it.

The material of the positive electrode current collector is not particularly limited, and any known material can be used. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbonaceous materials such as carbon cloth and carbon paper. Of these, metal materials are preferable, and aluminum is particularly preferable because it is lightweight and inexpensive.

For example, when LiN (CF ₃ SO ₂ ) ₂ is used in a high ratio as the alkali metal salt contained in the non-aqueous electrolyte, the positive electrode using the aluminum current collector is 4V (vs. Li / Li ⁺ ). Since it is known that the aluminum current collector may corrode when operated at a nobler potential, the aluminum current collector and LiN (CF ₃ SO ₂ ) depend on the operating potential of the positive electrode active material. It is preferable to avoid the combination with ₂ .

The negative electrode active material used for the negative electrode constituting the non-aqueous electrolyte secondary battery of the present invention is not particularly limited as long as it is electrochemically capable of inserting and removing lithium ions, and is a carbonaceous material and oxidation. Examples thereof include metal oxides such as tin and silicon oxide, metal composite oxides such as lithium titanate, lithium alloys such as lithium alone and lithium-aluminum alloys, and metals capable of forming alloys with lithium such as Sn and Si. Examples of the carbonaceous material include natural graphite, artificial graphite, coke, non-graphitizable carbon, low-temperature calcinable graphitizable carbon, fullerene, carbon nanotube, carbon black, activated carbon and the like. These may be used alone or in combination of two or more in any combination and ratio. Of these, carbonaceous materials or metal composite oxides are preferably used from the viewpoint of safety.

As the current collector of the negative electrode, a known one can be arbitrarily used. For example, metal materials such as copper, nickel, stainless steel, and nickel-plated steel can be mentioned, and copper is particularly preferable from the viewpoint of ease of processing and cost.

As the separator, it is preferable to use a microporous membrane, a non-woven fabric, or the like alone or in combination. Examples of the material constituting the separator include a polyolefin resin typified by polyethylene and polypropylene, a polyester resin typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and a vinylidene fluoride-hexafluoropropylene copolymer. , Fluoride vinylidene-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoro Acecone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, foot Examples thereof include polyvinylidene fluoride represented by a vinylidene compound-ethylene-tetrafluoroethylene copolymer and its copolymer, polyimide, polyamide, polyamideimide, cellulose and the like. Further, a glass filter can also be used. Of these, a microporous film containing a polyolefin resin typified by polyethylene, polypropylene or the like as a main component is preferable.

Other components of the battery include terminals, an insulating plate, a battery case, and the like, but these parts may be the same as those conventionally used.

FIG. 1 shows an external perspective view of a rectangular non-aqueous electrolyte secondary battery 1 which is an embodiment of the non-aqueous electrolyte secondary battery according to the present invention. The figure is a perspective view of the inside of the container. In the non-aqueous electrolyte secondary battery 1 shown in FIG. 1, the electrode group 2 is housed in the battery container 3. The electrode group 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having 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 shape of the non-aqueous electrolyte secondary battery according to the present invention is not particularly limited, and examples thereof include a coin-type battery, a cylindrical battery, a square battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device in which a plurality of the above-mentioned non-aqueous electrolyte secondary batteries are assembled. An embodiment of the 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 non-aqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for an electric vehicle (EV), a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), or the like.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples as long as the gist of the present invention is not exceeded.

(Non-aqueous electrolyte A)
A non-aqueous electrolyte was prepared using lithium hexafluorophosphate (LiPF ₆ ) at a ratio of 0.83 mol (126 g) to 1 kg of propylene carbonate (PC). The LiPF ₆ concentration corresponds to 1.0 mol / L. The ratio of the number of moles of PC to the number of moles of LiPF ₆ is 11
.. It is calculated as 8.

(Non-aqueous electrolyte B)
A non-aqueous electrolyte was prepared using LiPF ₆ at a ratio of 2.45 mol (372 g) to 1 kg of PC. The LiPF ₆ concentration corresponds to 2.9 mol / L. The ratio of the number of moles of PC to the number of moles of LiPF ₆ is calculated to be 4.0.

(Non-aqueous electrolyte C)
A non-aqueous electrolyte was prepared using LiPF ₆ at a ratio of 3.26 mol (495 g) to 1 kg of PC. The LiPF ₆ concentration corresponds to 3.9 mol / L. The ratio of the number of moles of PC to the number of moles of LiPF ₆ is calculated to be 3.0.

(Non-aqueous electrolyte D)
A non-aqueous electrolyte was prepared using LiPF ₆ at a ratio of 4.45 mol (676 g) to 1 kg of PC. The LiPF ₆ concentration corresponds to 5.9 mol / L. The ratio of the number of moles of PC to the number of moles of LiPF ₆ is calculated to be 2.2.

(Example 1)
(Manufacturing of positive electrode plate)
Using N-methylpyrrolidone as a dispersion medium, LiNi _0.5 Mn _1.5 O ₄ as a positive electrode active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) are kneaded and dispersed at a mass ratio of 80:10:10. A paste for coating was prepared. The coating paste was applied to one side of an aluminum foil current collector having a thickness of 20 μm, and a positive electrode plate was prepared through a drying step and a pressing step.

(Assembly of non-aqueous electrolyte battery)
A non-aqueous electrolyte battery was assembled using the positive electrode plate for the following tests. The positive electrode plate was cut out into a disk shape having a diameter of 13 mm and used. As the negative electrode, 50 μm of metallic lithium was used in close contact with the nickel foil current collector. The negative electrode, the glass filter as a separator, and the positive electrode were laminated in this order on a sealable stainless steel battery test cell, and a non-aqueous electrolytic solution was sealed and sealed. Batteries assembled using the non-aqueous electrolytes A to D in this way are designated as non-aqueous electrolyte batteries A1 to D1, respectively.

(Mn elution amount quantitative test)
Using the non-aqueous electrolyte batteries A1 to D1, a quantitative test of the amount of Mn elution from the positive electrode active material to the non-aqueous electrolyte was conducted under the following conditions. The non-aqueous electrolyte battery was charged with a constant current of 0.1 CmA and a final voltage of 5.0 V at 25 ° C., and then stored in a constant temperature bath at 60 ° C. for 3 days in an open circuit state. Next, the battery was disassembled, the negative electrode was taken out, dissolved in hydrochloric acid having a concentration of 0.05 mol / L, the amount of Mn in the negative electrode was quantified by ICP emission spectroscopic analysis, and recorded as "Mn elution amount (mg)". In this way, the amount of Mn eluted from the positive electrode active material to the non-aqueous electrolyte during storage and deposited on the negative electrode was compared. The results are shown in Table 1. In the table below, the ratio of the number of moles of the non-aqueous solvent having a donor number of 15 or more to the number of moles of the alkali metal salt is shown in the column of "high DN solvent / salt (molar ratio)".

As shown in Table 1, the non-aqueous electrolyte has a larger ratio of the number of moles of the non-aqueous solvent having a donor number of 15 or more to the number of moles of the alkali metal salt contained in the non-aqueous electrolyte, as compared with the non-aqueous electrolyte battery A1. In the non-aqueous electrolyte batteries B1 to D1 in which the ratio of the number of moles of the non-aqueous solvent having a donor number of 15 or more to the number of moles of the alkali metal salt contained is 4 times or less, the amount of Mn eluted from the positive electrode active material to the non-aqueous electrolyte. Was found to be suppressed. It was also found that the higher the alkali metal salt concentration, the higher the effect of suppressing Mn elution from the positive electrode active material into the non-aqueous electrolyte.

The non-aqueous electrolytes E to H were adjusted according to the following formulations.

(Non-water electrolyte E)
A non-aqueous electrolyte was prepared by using LiPF ₆ at a ratio of 2.53 mol (384 g) with respect to 1 kg of a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a mass ratio of 1: 1. The LiPF ₆ concentration corresponds to 2.9 mol / L. The ratio of the number of moles of the mixed solvent to the number of moles of LiPF ₆ is calculated to be 3.8.

(Non-aqueous electrolyte F)
A non-aqueous electrolyte was prepared using lithium tetrafluoroborate (LiBF ₄ ) at a ratio of 4.90 mol (459 g) to 1 kg of PC. The LiBF ₄ concentration corresponds to 5.9 mol / L. The ratio of the number of moles of PC to the number of moles of LiBF ₄ is calculated to be 2.0.

(Non-aqueous electrolyte G)
A non-aqueous electrolyte was prepared by using LiPF ₆ at a ratio of 0.87 mol (132 g) with respect to 1 kg of a mixed solvent in which EC and DEC were mixed at a volume ratio of 1: 1. The LiPF ₆ concentration corresponds to 1.0 mol / L. The ratio of the number of moles of the mixed solvent to the number of moles of LiPF ₆ is calculated to be 11.6.

(Non-water electrolyte H)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 0.83 mol (78 g) to 1 kg of PC. The LiBF ₄ concentration corresponds to 1.0 mol / L. The ratio of the number of moles of PC to the number of moles of LiBF ₄ is calculated to be 11.8.

(Example 2)
(Assembly of non-aqueous electrolyte battery)
Using the non-aqueous electrolytes A to H, respectively, the non-aqueous electrolyte batteries A2 to H2 were assembled in the same manner as in Example 1.

(Charge / discharge cycle test)
Using the non-aqueous electrolyte batteries A2 to H2, a charge / discharge test of 15 cycles was performed at 25 ° C. under the following conditions. The charging was a constant current charge with a current of 0.25 CmA and an upper limit voltage of 5.0 V, and the discharge was a constant current charge with a current of 0.25 CmA and a lower limit voltage of 3.55 V. In this way, the charge electricity amount (mAh) and the discharge electricity amount (mAh) in all cycles were recorded. Based on this data, the Coulomb efficiency in the first cycle was determined as the "initial Coulomb efficiency (%)". In addition, the difference between the sum of the charge electricity amounts from the 1st cycle to the 15th cycle and the discharge electricity amount from the 1st cycle to the 15th cycle is the "integral non-reverse capacity (mAh / g)" per positive electrode active material mass. ) ”. The results are shown in Table 2.

As can be seen from Table 2, the ratio of the number of moles of the non-aqueous solvent having a donor number of 15 or more to the number of moles of the alkali metal salt contained in the non-aqueous electrolyte is large as compared with the non-aqueous electrolyte batteries A2, G2 and H2. In the non-aqueous electrolyte batteries B2 to F2 in which the ratio of the number of moles of the non-aqueous solvent having a donor number of 15 or more to the number of moles of the alkali metal salt contained in the aqueous electrolyte is 4 times or less, the "initial Coulomb efficiency (%)" is high. It was found that the improvement was achieved and the "non-integral reverse capacity (mAh / g)" could be reduced. It was also found that the higher the alkali metal salt concentration, the better these effects.

The non-aqueous electrolytes I to R were adjusted according to the following formulations.

(Non-water electrolyte I)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 5.31 mol (498 g) to 1 kg of PC. The LiBF ₄ concentration corresponds to 6.4 mol / L. The ratio of the number of moles of PC to the number of moles of LiBF ₄ is calculated to be 1.8.

(Non-water electrolyte J)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 6.22 mol (583 g) to 1 kg of PC. The LiBF ₄ concentration corresponds to 7.5 mol / L. The ratio of the number of moles of PC to the number of moles of LiBF ₄ is calculated to be 1.6.

(Non-water electrolyte K)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 7.30 mol (684 g) to 1 kg of PC. The LiBF ₄ concentration corresponds to 8.8 mol / L. The ratio of the number of moles of PC to the number of moles of LiBF ₄ is calculated to be 1.3.

(Non-water electrolyte L)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 6.62 mol (621 g) and LiN (FSO ₂ ) ₂ (LiFSI) at a ratio of 0.0833 mol (16 g) to 1 kg of PC. The total concentration of LiBF ₄ and LiFSI corresponds to 8.1 mol / L. The ratio of the number of moles of PC to the total number of moles of LiBF ₄ and LiFSI is calculated to be 1.5.

(Non-water electrolyte M)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 2.90 mol (272 g) to 1 kg of GBL. The LiBF ₄ concentration corresponds to 3.3 mol / L. The ratio of the number of moles of GBL to the number of moles of LiBF ₄ is calculated to be 4.0.

(Non-water electrolyte N)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 3.87 mol (363 g) to 1 kg of GBL. The LiBF ₄ concentration corresponds to 4.3 mol / L. The ratio of the number of moles of GBL to the number of moles of LiBF ₄ is calculated to be 3.0.

(Non-water electrolyte O)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 4.65 mol (436 g) to 1 kg of GBL. The LiBF ₄ concentration corresponds to 5.2 mol / L. The ratio of the number of moles of GBL to the number of moles of LiBF ₄ is calculated to be 2.5.

(Non-water electrolyte P)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 7.84 mol (735 g) to 1 kg of a mixed solvent in which PC and dimethyl carbonate (DMC) were mixed in a volume ratio of 2: 1. The LiBF ₄ concentration corresponds to 9.1 mol / L. The ratio of the number of moles of the mixed solvent to the number of moles of LiBF ₄ is calculated to be 1.3.

(Non-water electrolyte Q)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 3.75 mol (352 g) to 1 kg of PC. The LiBF ₄ concentration corresponds to 4.5 mol / L. The ratio of the number of moles of PC to the number of moles of LiBF ₄ is calculated to be 2.6.

(Non-water electrolyte R)
2. LiBF ₄ was added to 1 kg of a mixed solvent in which PC and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) were mixed in a volume ratio of 2: 1. A non-aqueous electrolyte was prepared using a ratio of 50 mol (234 g). The ratio of the number of moles of PC to the number of moles of LiBF ₄ is calculated to be 2.4.

(Example 3)
(Assembly of non-aqueous electrolyte battery)
A non-aqueous electrolyte battery was assembled using the non-aqueous electrolyte H, the non-aqueous electrolyte F, and the non-aqueous electrolytes I to R, respectively. These are referred to as a non-aqueous electrolyte battery H3, a non-aqueous electrolyte battery F3, and a non-aqueous electrolyte battery I3 to R3, respectively.

(Charge / discharge cycle test)
Using the non-aqueous electrolyte battery H3, the non-aqueous electrolyte battery F3, and the non-aqueous electrolyte batteries I3 to R3, a 50-cycle charge / discharge test was performed at 25 ° C. under the following conditions. The charging was a constant current charge with a current of 0.1 CmA and an upper limit voltage of 5.0 V, and the discharge was a constant current charge with a current of 0.1 CmA and a lower limit voltage of 3.55 V. In this way, the charge electricity amount (mAh) and the discharge electricity amount (mAh) in all cycles were recorded. Based on this data, the Coulomb efficiency in the first cycle was determined as the "initial Coulomb efficiency (%)". In addition, the sum of the amount of electricity charged from the 1st cycle to the 50th cycle (however, the 40th cycle for the non-aqueous electrolyte batteries Q3 and R3) and the 1st cycle to the 50th cycle (however, the non-aqueous electrolyte battery Q3 and the non-aqueous electrolyte battery Q3 and) For R3, the difference from the sum of the amount of discharged electricity up to the 40th cycle) was calculated as the "integral irreversible capacity (mAh / g)" per mass of the positive electrode active material. The results are shown in Table 3.

As can be seen from the results of the non-aqueous electrolyte batteries I3 to K3, even when the non-aqueous electrolytes I to K in which the LiBF ₄ concentration with respect to the PC is higher than that of the non-aqueous electrolyte Q and the non-aqueous electrolyte F are used, this It was confirmed that the effect of the invention was exhibited.
As can be seen from the results of the non-aqueous electrolyte battery L3, it was confirmed that the effect of the present invention is exhibited even when a plurality of alkali metal salts are mixed and used.
As can be seen from the results of the non-aqueous electrolyte batteries M3 to O3, it was confirmed that the initial Coulomb efficiency can be improved even if the non-aqueous solvent having 15 or more donors is a solvent other than the cyclic carbonate or the chain carbonate.
As can be seen from the results of the non-aqueous electrolyte battery P3, it was confirmed that the effect of the present invention is exhibited even when a plurality of non-aqueous solvents having 15 or more donors are mixed and used.
As can be seen from the results of the non-aqueous electrolyte battery R3, if the ratio of the number of moles of the non-aqueous solvent having a donor number of 15 or more to the number of moles of the alkali metal salt contained in the non-aqueous electrolyte is 4 times or less, the number of donors is It was confirmed that the effect of the present invention is exhibited even when a non-aqueous solvent of less than 15 is mixed and used.

The non-aqueous electrolyte S was prepared according to the following formulation.

(Non-water electrolyte S)
A non-aqueous electrolyte was prepared using LiBF ₄ at a ratio of 2.30 mol (216 g) to 1 kg of a mixed solvent in which PC and HFE were mixed at a volume ratio of 2: 1. The ratio of the number of moles of PC to the number of moles of LiBF ₄ is calculated to be 2.6.

(Example 4)
(Manufacturing of positive electrode plate)
Using N-methylpyrrolidone as a dispersion medium, Li _1.2 Mn _0.56 Co _0.08 Ni _0.16 O ₂ as a positive electrode active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) have a mass ratio of 80: A coating paste prepared by kneading and dispersing at a ratio of 10:10 was prepared. The coating paste was applied to one side of an aluminum foil current collector having a thickness of 20 μm, and a positive electrode plate was prepared through a drying step and a pressing step.

(Assembly of non-aqueous electrolyte battery)
A non-aqueous electrolyte battery A4, a non-aqueous electrolyte battery D4, and a non-aqueous electrolyte are used in the same manner as in Example 1 except that the positive electrode plates are used and the non-aqueous electrolytes A, D, K, and S are used, respectively. The battery K4 and the non-aqueous electrolyte battery S4 were assembled.

(Charge / discharge cycle test)
Using the non-aqueous electrolyte battery A4, the non-aqueous electrolyte battery D4, the non-aqueous electrolyte battery K4, and the non-aqueous electrolyte battery S4, a 50-cycle charge / discharge test was performed at 25 ° C. under the following conditions. The charging was a constant current charge with a current of 0.1 CmA and an upper limit voltage of 4.8 V, and the discharge was a constant current charge with a current of 0.1 CmA and a lower limit voltage of 2.5 V. In this way, the charge electricity amount (mAh) and the discharge electricity amount (mAh) in all cycles were recorded. Based on this data, the Coulomb efficiency in the first cycle was determined as the "initial Coulomb efficiency (%)". Further, the difference between the sum of the charge electricity amounts from the first cycle to the 100th cycle and the discharge electricity amount from the first cycle to the 100th cycle is the "integral non-reverse capacity (mAh / g)" per positive electrode active material mass. ) ”. The results are shown in Table 4.

As can be seen from this result, it was confirmed that the effect of the present invention is exhibited regardless of the type of the positive electrode active material.

(Explanation of code)
1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive terminal 4'Positive lead 5 Negative terminal 5'Negative lead 20 Power storage unit 30 Power storage device

Claims (1)

Positive electrode containing positive electrode active material containing Mn element Positive electrode, negative electrode, and
A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte in which the non-aqueous solvent contains an alkali metal salt.
The non-aqueous electrolyte is
Contains a non-aqueous solvent with 15 or more donors,
The ratio of the number of moles of the non-aqueous solvent having 15 or more donors to the number of moles of the alkali metal salt is 4 times or less.
Non-aqueous electrolyte secondary battery (However, the positive electrode active material is LiMn ₂ O4 system active material, and the non _- aqueous solvent is trimethyl phosphate, diethyl fluorophosphate, or Tris (trifluoromethyl) phosphate, and ethylene carbonate: diethyl. It is composed of carbonate (3: 7) or dimethoxyethane, and the content ratio of the trimethyl phosphate, diethyl fluorophosphate, or Tris (trifluoromethyl) phosphate in the non-aqueous solvent is 40% by volume or more, and The positive electrode active material is LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and the non-aqueous solvent contains ethylene carbonate, propylene carbonate, or dimethyl carbonate, acetonitrile or propionitrile, and vinylene carbonate. , Except for those in which the content ratio of the acetonitrile or propionitrile in the non-aqueous solvent is 27% by mass or more) .

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