JP6780263B2 - Manufacturing method of non-aqueous electrolyte for secondary batteries, non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary batteries - Google Patents

Description

The present invention relates to a method for producing a non-aqueous electrolyte for a secondary battery, a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used in personal computers, electronic devices such as communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically separated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge.

In non-aqueous electrolyte secondary batteries, techniques for adding various additives to non-aqueous electrolytes are being studied in order to improve charge / discharge cycle characteristics and the like. As a specific technique, a secondary battery using a non-aqueous electrolyte containing a scavenger such as ascorbic acid as an additive has been proposed (see Patent Document 1). In the above-mentioned secondary battery, it is said that by capturing impurities generated in the battery with a scavenger, deterioration of battery characteristics can be reduced even if the charge / discharge cycle is repeated. However, even in the non-aqueous electrolyte containing ascorbic acid and the like, the capacity retention rate in the charge / discharge cycle is not sufficient, and a non-aqueous electrolyte secondary battery having a higher capacity retention rate is required.

Japanese Unexamined Patent Publication No. 2014-22321

The present invention has been made based on the above circumstances, and an object of the present invention is a non-aqueous electrolyte for a secondary battery capable of increasing the capacity retention rate in a charge / discharge cycle, and a non-aqueous electrolyte containing the non-aqueous electrolyte. The present invention provides a method for manufacturing an electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

The invention made to solve the above problems is a non-aqueous electrolyte for a secondary battery in which an electrolyte salt is dissolved in a non-aqueous solvent, a compound having a five-membered ring structure and a phosphate group, a salt of the above compound, and the above. It is characterized by containing an additive composed of a hydrate of a compound or the above-mentioned salt or a combination thereof.

Another invention made to solve the above problems is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is a non-aqueous electrolyte for a secondary battery. Is used.

Yet another invention made to solve the above problems is a method for manufacturing a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the secondary battery is used as the non-aqueous electrolyte. It is characterized by using a non-aqueous electrolyte.

According to the present invention, a method for producing a non-aqueous electrolyte for a secondary battery capable of increasing the capacity retention rate in a charge / discharge cycle, a non-aqueous electrolyte secondary battery provided with this non-aqueous electrolyte, and a non-aqueous electrolyte secondary battery Can be provided.

Hereinafter, a method for producing a non-aqueous electrolyte for a secondary battery, a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described in detail.

<Non-aqueous electrolyte for secondary batteries>
The non-aqueous electrolyte for a secondary battery according to an embodiment of the present invention (hereinafter, may be simply referred to as “non-aqueous electrolyte”) is a non-aqueous electrolyte for a secondary battery in which an electrolyte salt is dissolved in a non-aqueous solvent. It contains an additive consisting of a compound having a five-membered ring structure and a phosphate group, a salt of the above compound, a hydrate of the above compound or the above salt, or a combination thereof.

<Additives>
The additive comprises a compound having a five-membered ring structure and a phosphoric acid group, a salt of the compound, a hydrate of the compound or the salt, or a combination thereof. The above additives may be used alone or in admixture of two or more.

<Compound>
The above compound is not particularly limited as long as it is a compound having a five-membered ring structure and a phosphoric acid group (-H ₂ PO ₄ ). The five-membered ring structure and the number of phosphoric acid groups are not particularly limited, and the compound may have a plurality of five-membered ring structures and a plurality of phosphoric acid groups. However, the above compound preferably has a 5-membered ring structure of 1 and a phosphate group of 1. In addition, the above compound can have any group other than the five-membered ring structure and the phosphoric acid group.

Examples of the five-membered ring structure include an alicyclic (aliphatic carbocycle), an aliphatic heterocycle, and an aromatic heterocycle.

Examples of the alicyclic ring (aliphatic carbocyclic ring) having a five-membered ring structure include a cyclopentane ring and a cyclopentene ring.

Examples of the five-membered cyclic aliphatic heterocycle include a pyrrolidine ring, a tetrahydrofuran ring (an example of a cyclic ether structure), a tetrahydrothiophene ring, an ethylene carbonate ring (an example of a cyclic carbonate structure), and a γ-butyrolactone ring (an example of a cyclic ester structure). ) Etc. can be mentioned.

Examples of the aromatic heterocycle having a five-membered ring structure include a pyrrole ring, a furan ring, a thiophene ring, and an oxazole ring.

Among the above-mentioned five-membered ring structures, a five-membered ring aliphatic heterocycle is preferable. Further, as the five-membered ring structure, a five-membered ring structure containing oxygen atoms constituting the ring structure is preferable.

The five-membered ring structure containing oxygen atoms constituting the ring structure may be an aliphatic heterocyclic structure such as a cyclic ether structure, a cyclic ester structure, or a cyclic carbonate structure, or an aromatic heterocycle such as a furan ring. It may be a structure. Further, in the case of the above-mentioned aliphatic heterocycle, it may be a saturated aliphatic heterocycle or an unsaturated aliphatic heterocycle.

The five-membered ring structure containing oxygen atoms constituting the ring structure is preferably a cyclic ether structure or a cyclic ester structure, and more preferably a cyclic ester structure. The cyclic ether structure includes a saturated ring structure such as a tetrahydrofuran ring and a 1,3-dioxorane ring represented by the following formula (3), and a 2,3-dihydrofuran ring, a 2,5-dihydrofuran ring and a furan ring. The unsaturated ring structure can be mentioned, but the saturated ring structure is preferable, and the tetrahydrofuran ring is more preferable. Examples of the cyclic ester structure include a saturated ring structure such as a γ-butyrolactone ring and an unsaturated ring structure such as a γ-crotonolactone ring represented by the following formula (4). Is preferable, and the γ-crotonolactone ring is more preferable.

Specific examples of the above compound include a compound represented by the following formula (1).

In formula (1), R ¹ is a five-membered ring structure containing oxygen atoms constituting the ring structure. R ² is a single bond or a divalent hydrocarbon group having 1 to 3 carbon atoms. R ³ is an independent polar group or a group containing the above polar groups. n is an integer of 2 to 7.

The specific structure and preferable structure of the five-membered ring structure containing the oxygen atom constituting the ring structure represented by R ¹ are as described above.

The above R ² is a structure in which a ring structure represented by R ¹ and a phosphoric acid group (−H ₂ PO ₄ ) are linked. Examples of the divalent hydrocarbon group having 1 to 3 carbon atoms represented by R ^2,
Alcandiyl groups such as methanediyl group, ethanediyl group, propanediyl group;
Arkendiyl groups such as etendil groups;
An alkindiyl group such as an ethyndiyl group can be mentioned.

As the above R ² , a single bond and a methanediyl group (−CH ₂₋ ) are preferable.

Examples of the polar group in the group containing a polar group or the polar group represented by R ^3, hydroxy group, amino group, carboxy group, cyano group, halogenated hydrocarbon group, alkoxy group, include a heterocyclic group such as Can be done. Examples of the group containing the polar group include a hydrocarbon group having these polar groups as a substituent.

As the R ^3, hydroxy group, hydroxyalkyl group, or a group represented by the following formula (2) preferably.

In the formula (2), R ⁴ and R ⁵ are independently hydrogen atoms, halogen atoms, hydroxy groups, phosphate groups or organic groups having 1 to 4 carbon atoms.

The organic group means a group containing one or more carbon atoms. The organic group having 1 to 4 carbon atoms includes a hydrocarbon group having 1 to 4 carbon atoms, a group containing a heteroatom-containing group between carbons or at the terminal of the hydrocarbon group, and one of the hydrogen atoms of these groups. Examples thereof include a group in which a part or the whole is substituted with a substituent, a carboxy group, a cyano group and the like.

Examples of the hydrocarbon group having 1 to 4 carbon atoms include an alkyl group such as a methyl group, an ethyl group, a propyl group and a butyl group, an alkenyl group such as an ethenyl group and a propenyl group, and an alkynyl group such as an ethynyl group. it can.

The heteroatom-containing group refers to a group having a divalent or higher valent heteroatom in the structure. The heteroatom-containing group may have one heteroatom or two or more heteroatoms. Further, the heteroatom-containing group may be composed of only one heteroatom.

The divalent or higher valent heteroatom possessed by the heteroatom-containing group is not particularly limited as long as it is a heteroatom having a divalent or higher valence, for example, an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, or a phosphorus atom. , Boron atom and the like.

As the hetero atom-containing group, for example -O -, - S -, - SO -, - SO 2 -, - SO 2 O -, - SO 3 - groups consist of a hetero atom such as;
Combining carbon atoms such as -CO-, -COO-, -COS-, -CONH-, -OCOO-, -OCOS-, -OCONH-, -SCONH-, -SCSNH-, -SCSS- and heteroatoms. The group and the like can be mentioned. The carbon number of the organic group also includes the carbon number in these heteroatom-containing groups.

Examples of the substituent include a halogen atom, a hydroxy group, a carboxy group, a nitro group, a cyano group and the like. The carbon number of the organic group also includes the carbon number in these substituents.

A hydrogen atom is preferable as R ⁴ and R ⁵ .

The hydroxyalkyl group represented by R ³ refers to an alkyl group in which one or more hydrogen atoms are substituted with a hydroxy group. Examples of the hydroxyalkyl group include hydroxymethyl group, dihydroxymethyl group, 1-hydroxyethyl group, 2-hydroxyethyl group, 1,2-dihydroxyethyl group, 1-hydroxypropyl group, 2-hydroxypropyl group and 3-hydroxy. A hydroxyalkyl group having 1 to 4 carbon atoms such as a propyl group can be mentioned. Among these, hydroxyalkyl groups having 1 and 2 carbon atoms are preferable, and 1,2-dihydroxyethyl groups are more preferable.

The n represents the number of polar groups represented by R ³ or groups containing the polar groups bonded to the ring structure represented by R ¹ . As the lower limit of n, 2 is preferable. On the other hand, as the upper limit of n, 4 is preferable, and 3 is more preferable.

The compound is preferably an ester of a compound having a five-membered ring structure and a hydroxy group and phosphoric acid.

Examples of the compound having a five-membered ring structure and a hydroxy group include
Cytidine, 2'-deoxycytidine, 2', 3'-dideoxycytidine, 5-fluorocytidine, 2'-o-methylcytidine, citarabin, deoxyribofuranose, hydroxymethylfurfural, furfuryl alcohol, tetrahydrofurfuryl alcohol and other rings A compound having a cyclic ether structure having 5 members and a hydroxy group;
Compounds having a cyclic ester structure with 5 rings and a hydroxy group, such as ascorbic acid (L-ascorbic acid, etc.), erythorbic acid, pantolactone, etc.;
In addition, cyclopentanol and the like can be mentioned.

Among these, a compound having a cyclic ether structure having 5 ring members and a hydroxy group, a compound having a cyclic ester structure having 5 ring members and a hydroxy group are preferable, and a compound having a cyclic ester structure having 5 ring members and a hydroxy group is more preferable. preferable.

Examples of the compound having a cyclic ether structure having 5 ring members and a hydroxy group include cytidine and its derivatives (2'-deoxycytidine, 2', 3'-dideoxycytidine, 5-fluorocytidine, 2'-o-methylcytidine and the like. ) Is preferable, and cytidine is more preferable.

As the compound having a cyclic ester structure having 5 ring members and a hydroxy group, ascorbic acid and erythorbic acid are preferable, and ascorbic acid is more preferable.

Examples of the ester of citidine and phosphoric acid include cytidine-2'-monophosphate (2'-cytidinelic acid), cytidine-3'-monophosphate (3'-cytidinelic acid), and cytidine-5'-monophosphate. Examples thereof include cytidilic acid such as acid (5'-cytidinelic acid), but cytidine-5'-monophosphate is preferable.

Examples of the ester of ascorbic acid and phosphoric acid include L-ascorbic acid-2-phosphoric acid and L-ascorbic acid-3-phosphate, but L-ascorbic acid-2-phosphoric acid is preferable. ..

<Salts and hydrates>
Examples of the salt of the above compound include alkali metal salts such as potassium salt and sodium salt, and alkaline earth metal salts such as magnesium salt and calcium salt. Among these, alkaline earth metal salts are preferable, and magnesium salts are more preferable.

The hydrate may be a hydrate of the compound or a hydrate of the salt. Examples of the hydrate include L-ascorbic acid-2-phosphate sesquimagnesium hydrate and the like.

As the additive, a magnesium salt or a hydrate thereof is preferable. By using such an additive, the capacity retention rate in the charge / discharge cycle can be further increased.

The lower limit of the content of the additive in the non-aqueous electrolyte is not particularly limited, but is preferably 0.1% by mass, more preferably 0.5% by mass, still more preferably 1% by mass. By setting the content of the additive to the above lower limit or more, the capacity retention rate in the charge / discharge cycle can be further increased. The upper limit of this content is not particularly limited, but may be, for example, 5% by mass, 3% by mass, or 2% by mass. The above additives may be used alone or in admixture of two or more.

<Non-aqueous solvent>
As the non-aqueous solvent, a known non-aqueous solvent usually used as a non-aqueous solvent for a general non-aqueous electrolyte for a secondary battery can be used. Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, ester, ether, amide, sulfonamide, lactone, nitrile and the like. Among these, it is preferable to use at least cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is not particularly limited, but is, for example, 5:95 or more and 50:50 or less. Is preferable.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene. Examples thereof include carbonate (DFEC), styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, and among these, EC is preferable.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate and the like, and among these, EMC is preferable.

<Electrolyte salt>
As the electrolyte salt, a known electrolyte salt usually used as an electrolyte salt of a general non-aqueous electrolyte for a secondary battery can be used. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like, but lithium salt is preferable.

Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO). ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) _{3 and} other fluorinated hydrocarbon groups Lithium salt having the above can be mentioned. Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

The lower limit of the content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 M, more preferably 0.3 M, further preferably 0.5 M, and particularly preferably 0.7 M. On the other hand, the upper limit is not particularly limited, but is preferably 2.5M, more preferably 2M, and even more preferably 1.5M.

The non-aqueous electrolyte may contain components other than the above additives, the above non-aqueous solvent and the above electrolyte as long as the effects of the present invention are not impaired. Examples of the other components include various additives contained in a general non-aqueous electrolyte for a secondary battery. However, the content of these other components is preferably 5% by mass or less, and more preferably 1% by mass or less.

The non-aqueous electrolyte can be obtained by adding the electrolyte salt and the additive to the non-aqueous solvent and dissolving them.

<Non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery according to the embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode and the negative electrode usually form power generation elements that are alternately superimposed by stacking or winding through a separator. The power generation element is housed in a case, and the case is filled with the non-aqueous electrolyte. In the non-aqueous electrolyte secondary battery, the above-mentioned non-aqueous electrolyte for a secondary battery is used as the non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the above case, a known aluminum case or the like which is usually used as a case of a non-aqueous electrolyte secondary battery can be used.

According to the non-aqueous electrolyte secondary battery, the capacity retention rate in the charge / discharge cycle can be increased by using the non-aqueous electrolyte containing the above additive.

<Positive electrode>
The positive electrode has a positive electrode current collector and a positive electrode active material layer arranged directly on the positive electrode current collector or via an intermediate layer.

The positive electrode current collector has conductivity. As the material of the current collector, metals such as aluminum, titanium, tantalum, and stainless steel or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of balance of potential resistance, high conductivity and cost. Further, as a form of forming the positive electrode current collector, a foil, a vapor-deposited film and the like can be mentioned, and the foil is preferable from the viewpoint of cost. That is, an aluminum foil is preferable as the positive electrode current collector. Examples of aluminum or aluminum alloy include A1085P and A3003P specified in JIS-H-4000 (2014).

The intermediate layer is a coating layer on the surface of the positive electrode current collector, and by containing conductive particles such as carbon particles, the contact resistance between the positive electrode current collector and the positive electrode active material layer is reduced. The composition of the intermediate layer is not particularly limited, and can be formed by, for example, a composition containing a resin binder and conductive particles. Incidentally, to have a "conductive" means that the volume resistivity is measured according to JIS-H-0505 (1975 years) is not more than 10 ⁷ Ω · cm, and "non-conductive" means that the volume resistivity is 10 ⁷ Ω · cm greater.

The positive electrode active material layer is formed from a so-called positive electrode mixture containing a positive electrode active material. In addition, the positive electrode mixture forming the positive electrode active material layer contains optional components such as a conductive agent, a binder (binder), a thickener, and a filler, if necessary.

Examples of the positive electrode active material include composite oxides represented by Li _x MO _y (M represents at least one kind of transition metal) (Li _x CoO ₂ and Li _x NiO having a layered α-NaFeO type ₂ crystal structure). ₂ , Li _x MnO ₃ , Li _x Ni _α Co _(1-α) O ₂ , Li _x Ni _α Mn _β Co _(1-α-β) O _2, etc., Li _x Mn ₂ O ₄ having a spinel type crystal structure , Li _x Ni _α Mn _(2-α) O ₄ etc.), Li _w Me _x (XO _y ) _z (Me represents at least one kind of transition metal, and X represents, for example, P, Si, B, V, etc.) Examples thereof include polyanionic compounds represented by (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc.). The elements or polyanions in these compounds may be partially substituted with other elements or anion species. In the positive electrode active material layer, one of these compounds may be used alone, or two or more of these compounds may be mixed and used.

The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect the battery performance. Examples of such a conductive agent include natural or artificial graphite, carbon black such as furnace black, acetylene black, and Ketjen black, metal, and conductive ceramics. Examples of the shape of the conductive agent include powder and fibrous.

Examples of the binder (binding agent) include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, and polyimide; ethylene-propylene-diene rubber (EPDM), Elastomers such as sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and thermoplastic polymers can be mentioned.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium, it is preferable to deactivate the functional group by methylation or the like in advance.

The filler is not particularly limited as long as it does not adversely affect the battery performance. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, carbon and the like.

<Negative electrode>
The negative electrode has a negative electrode current collector and a negative electrode active material layer arranged directly or via an intermediate layer on the negative electrode current collector. The intermediate layer may have the same structure as the intermediate layer of the positive electrode.

The negative electrode current collector may have the same configuration as the positive electrode current collector, but as a material, a metal such as copper, nickel, stainless steel, nickel-plated steel or an alloy thereof is used, and copper or copper is used. Alloys are preferred. That is, a copper foil is preferable as the negative electrode current collector. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The negative electrode active material layer is formed from a so-called negative electrode mixture containing a negative electrode active material. Further, the negative electrode mixture forming the negative electrode active material layer contains optional components such as a conductive agent, a binder (binder), a thickener, and a filler, if necessary. As the optional component such as the conductive agent, the binder, the thickener, and the filler, the same one as that of the positive electrode active material layer can be used.

As the negative electrode active material, a material capable of occluding and releasing lithium ions is usually used. Specific negative electrode active materials include, for example, metals or metalloids such as Si and Sn; metal oxides or metalloids such as Si oxide and Sn oxide; polyphosphate compounds; graphite and amorphous carbon (easy). Examples include carbon materials such as graphitized carbon or non-graphitizable carbon).

Further, the negative electrode mixture (negative electrode active material layer) is a typical non-metal element such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge. It may contain a typical metal element such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W and the like.

<Separator>
As the material of the separator, for example, a woven fabric, a non-woven fabric, a porous resin film or the like is used. Among these, a porous resin film is preferable. As the main component of the porous resin film, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of strength. Further, a porous resin film obtained by combining these resins with a resin such as aramid or polyimide may be used.

<Manufacturing method of non-aqueous electrolyte secondary battery>
The method for producing a non-aqueous electrolyte secondary battery according to an embodiment of the present invention is a method for producing a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the non-aqueous electrolyte secondary battery is used as the non-aqueous electrolyte. It is characterized by using the non-aqueous electrolyte for a secondary battery. The manufacturing method includes, for example, a step of injecting a non-aqueous electrolyte into a case containing a positive electrode and a negative electrode.

The above injection can be performed by a known method. After injection, a non-aqueous electrolyte secondary battery can be obtained by sealing the injection port. Details of each element constituting the non-aqueous electrolyte secondary battery obtained by the manufacturing method are as described above. According to the method for producing a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery having a high capacity retention rate in a charge / discharge cycle can be produced by using a non-aqueous electrolyte containing the above additive.

<Other Embodiments>
The present invention is not limited to the above-described embodiment, and can be implemented in various modifications and improvements in addition to the above-described embodiment. For example, it is not necessary to provide an intermediate layer in the positive electrode or the negative electrode. Further, for example, when a polymer solid electrolyte is used as the non-aqueous electrolyte, the above-mentioned injection step may not be provided in the method for producing a non-aqueous electrolyte secondary battery of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

The compounds used in Examples and Comparative Examples are shown below. The structural formulas of each compound are also shown below.
A-1: L-ascorbic acid-2-phosphate sesquimagnesium hydrate A-2: Cytidine-5'-monophosphate a-1: Ascorbic acid a-2: Erythorbic acid

[Example 1]
LiPF ₆ was dissolved at 1M in a solvent in which EC and EMC were mixed at a volume ratio of 30:70. To this, a saturated dissolved amount of L-ascorbic acid-2-phosphate sesquimagnesium hydrate (A-1) was further added to obtain the non-aqueous electrolyte of Example 1.

[Example 2, Comparative Examples 1 to 3]
The non-aqueous electrolytes of Example 2 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1 except that the types of additives used were listed in Table 1 or no additives were used. It was.

[Evaluation 1]
A positive electrode in which the positive electrode active material was LiNi _1/3 Co _1/3 Mn _1/3 O ₂ having an α-NaFeO type ₂ crystal structure and a negative electrode in which the negative electrode active material was graphite were prepared. A power generation element was produced by winding the positive electrode and the negative electrode through a porous resin film separator made of polyolefin. After inserting this power generation element into the aluminum case, the lid of the case was welded by laser welding. After injecting the non-aqueous electrolytes of Examples 1 and 2 and Comparative Examples 1 to 3 through the liquid injection holes provided in the lid, the liquid injection holes are sealed to seal the non-aqueous electrolyte secondary battery (square lithium ion battery). ) Was obtained.

Each of the obtained non-aqueous electrolyte secondary batteries was charged and discharged at 25 ° C. with a charge termination voltage of 4.2 V and a discharge termination voltage of 2.75 V, and the initial capacity was confirmed. Next, 500 cycles of constant current constant voltage charging with a charging current of 1.0 CmA and a charging voltage of 4.2 V, and constant current discharge with a discharge current of 1.0 CmA and a discharge end voltage of 2.75 V were performed at 45 ° C. .. A 10-minute rest period was provided between charging and discharging and between discharging and charging. The 1.0 CmA discharge capacity (25 ° C) before the charge / discharge cycle test and after 500 cycles was measured, and the capacity retention rate of each non-aqueous electrolyte secondary battery (discharge after 500 cycles with respect to the discharge capacity before the charge / discharge cycle test). The volume ratio) was calculated. The results are shown in Table 1.

[Evaluation 2]
A positive electrode in which the positive electrode active material was LiNi _1/3 Co _1/3 Mn _1/3 O ₂ having an α-NaFeO type ₂ crystal structure and a negative electrode in which the negative electrode active material was graphite were prepared. A power generation element was produced by winding the positive electrode and the negative electrode through a porous resin film separator made of polyolefin. After inserting this power generation element into the aluminum case, the lid of the case was welded by laser welding. After injecting the non-aqueous electrolytes of Examples 1 and 2 and Comparative Examples 1 to 3 through the liquid injection holes provided in the lid, the liquid injection holes are sealed to seal the non-aqueous electrolyte secondary battery (square lithium ion battery). ) Was obtained.

Each of the obtained non-aqueous electrolyte secondary batteries was charged and discharged at 25 ° C. with a charge termination voltage of 4.35 V and a discharge termination voltage of 2.75 V, and the initial capacity was confirmed. Next, 100 cycles of constant current constant voltage charging with a charging current of 1.0 CmA and a charging voltage of 4.35 V and constant current discharge with a discharge current of 1.0 CmA and a discharge end voltage of 2.75 V were performed at 45 ° C. .. A 10-minute rest period was provided between charging and discharging and between discharging and charging. The 1.0 CmA discharge capacity (25 ° C.) before the charge / discharge cycle test and after 100 cycles was measured, and the capacity retention rate of each non-aqueous electrolyte secondary battery (discharge after 100 cycles with respect to the discharge capacity before the charge / discharge cycle test). The volume ratio) was calculated. The results are shown in Table 2.

As shown in Tables 1 and 2 above, it can be seen that the non-aqueous electrolyte secondary batteries provided with the non-aqueous electrolytes of Examples 1 and 2 have a high capacity retention rate. In particular, as shown in Table 2, when charging at 4.35 V, Comparative Example 2 to which L-ascorbic acid was added had a lower capacity retention rate than Comparative Example 1 to which L-ascorbic acid was not added, and erythorbic acid. Comparative Example 3 to which was added has only a slightly higher volume retention rate than Comparative Example 1 to which no addition was added. On the other hand, it can be seen that Examples 1 and 2 have a remarkably high capacity retention rate.

The present invention can be applied to a non-aqueous electrolyte secondary battery used as a power source for a personal computer, an electronic device such as a communication terminal, an automobile, and a non-aqueous electrolyte for a secondary battery provided therein.

Claims (8)

A non-aqueous electrolyte for secondary batteries in which an electrolyte salt dissolves in a non-aqueous solvent.
It contains an additive consisting of a compound having a five-membered ring structure and a phosphoric acid group, a salt of the above compound, a hydrate of the above compound or the above salt, or a combination thereof .
A non-aqueous electrolyte for a secondary battery , wherein the five-membered ring structure is an aliphatic heterocycle or an aromatic heterocycle . The non-aqueous electrolyte for a secondary battery according to claim 1, wherein the five-membered ring structure contains oxygen atoms constituting the ring structure. The non-aqueous electrolyte for a secondary battery according to claim 2, wherein the five-membered ring structure containing oxygen atoms constituting the ring structure is a cyclic ether structure or a cyclic ester structure. The non-aqueous electrolyte for a secondary battery according to claim 2 or 3, wherein the compound is represented by the following formula (1).

(In the formula (1), R ¹ is a five-membered ring structure containing oxygen atoms constituting the ring structure. R ² is a single bond or a divalent hydrocarbon group having 1 to 3 carbon atoms. R ³ is an independent polar group or a group containing the above polar groups. N is an integer of 2 to 7). The non-aqueous electrolyte for a secondary battery according to claim 4, wherein R ³ is a hydroxy group, a hydroxyalkyl group, or a group represented by the following formula (2).

(In the formula (2), R ⁴ and R ⁵ are independently hydrogen atoms, halogen atoms, hydroxy groups, phosphate groups or organic groups having 1 to 4 carbon atoms.) The non-aqueous electrolyte for a secondary battery according to any one of claims 1 to 5, wherein the additive is a magnesium salt or a hydrate thereof. A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte.
As the non-aqueous electrolyte, the non-aqueous electrolyte for a secondary battery according to any one of claims 1 to 6 is used.
As the positive electrode, a non-aqueous electrolyte secondary battery comprising a composite oxide having a layered α-NaFeO type ₂ crystal structure or a spinel type crystal structure, or a positive electrode containing a polyanion compound as a positive electrode active material is used. .. A method for manufacturing a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte.
As the non-aqueous electrolyte, the non-aqueous electrolyte for a secondary battery according to any one of claims 1 to 6 is used.
A method for producing a non-aqueous electrolyte secondary battery, which comprises using as the positive electrode a positive electrode containing a layered α-NaFeO type ₂ crystal structure or a composite oxide having a spinel type crystal structure, or a polyanion compound as a positive electrode active material. ..