Non-aqueous secondary battery and non-aqueous electrolyte used therein

Abstract

This invention provides a non-aqueous electrolyte that suppresses the voltage drop in non-aqueous secondary batteries caused by metal dissolution and leaching reactions. [Solution] The non-aqueous electrolyte for non-aqueous secondary batteries comprises a non-aqueous solvent, an electrolyte salt, an isocyanate compound, and a nitrile compound having two or more nitrile groups, wherein the content of the isocyanate compound is C NCO However, the content of the nitrile compound C CN It is greater in terms of mass.

Description

[Technical Field]

[0001] This disclosure relates primarily to non-aqueous electrolytes for non-aqueous secondary batteries. [Background technology]

[0002] Patent Document 1 proposes a non-aqueous electrolyte comprising a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent, characterized in that it comprises (A) at least one compound selected from the group consisting of unsaturated carbonates and specific cyclic compounds, (B) a fluorine-containing ethylene carbonate derivative, and (C) a specific CN compound.

[0003] Patent Document 2 proposes a non-aqueous electrolyte for lithium batteries, characterized in that an electrolyte is dissolved in a non-aqueous solvent, and the non-aqueous electrolyte further contains a nitrile compound and an S=O group-containing compound.

[0004] Patent Document 3 proposes a non-aqueous electrolyte for a non-aqueous electrolyte battery having a positive electrode and a negative electrode capable of intercalating and releasing metal ions, characterized in that the non-aqueous electrolyte contains, together with the electrolyte and a non-aqueous solvent, (A) a compound having at least two isocyanate groups in its molecule and a compound having at least two cyano groups in its molecule, and (B) the content ratio (mass ratio) of the compound having at least two isocyanate groups in its molecule to the compound having at least two cyano groups in its molecule is 50:50 to 1:99. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-51202 [Patent Document 2] Japanese Patent Publication No. 2004-179146 [Patent Document 3] Japanese Patent Publication No. 2013-65540 [Overview of the project]

[0006] Non-aqueous secondary batteries typified by lithium-ion secondary batteries include a positive electrode, a negative electrode, and a non-aqueous electrolyte. When metals such as copper and iron are present in a non-aqueous secondary battery that utilizes an electrochemical oxidation-reduction reaction, a metal dissolution and precipitation reaction occurs, and the voltage of the non-aqueous secondary battery decreases.

[0007] One aspect of the present disclosure includes a non-aqueous solvent, an electrolyte salt, an isocyanate compound, and a nitrile compound having two or more nitrile groups (hereinafter, also referred to as "nitrile compound P"), and the content C of the isocyanate compound NCO is more on a mass basis than the content C of the nitrile compound CN and relates to a non-aqueous electrolyte for a non-aqueous secondary battery.

[0008] Another aspect of the present disclosure includes a positive electrode containing a positive electrode active material, a separator, a negative electrode facing the positive electrode through the separator, and a non-aqueous electrolyte, and the non-aqueous electrolyte includes a non-aqueous solvent, an electrolyte salt, an isocyanate compound, and a nitrile compound having two or more nitrile groups, and in the non-aqueous electrolyte, the content C of the isocyanate compound NCO is more on a mass basis than the content C of the nitrile compound CN and relates to a non-aqueous secondary battery. According to the present disclosure, it is possible to suppress a decrease in the voltage of a non-aqueous secondary battery due to a metal dissolution and precipitation reaction.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a perspective view of a non-aqueous secondary battery according to an embodiment of the present disclosure with a part cut away.

Embodiments for Carrying Out the Invention

[0010] The non-aqueous electrolyte for a non-aqueous secondary battery according to the present disclosure includes a non-aqueous solvent, an electrolyte salt, an isocyanate compound, and a nitrile compound having two or more nitrile groups (hereinafter, also referred to as "nitrile compound P"). However, the content C of the isocyanate compoundNCO is more in terms of mass content C of the nitrile compound P CN than (C NCO >C CN ). In addition, the non-aqueous secondary battery according to the present disclosure includes a positive electrode containing a positive electrode active material, a separator, a negative electrode facing the positive electrode through the separator, and the non-aqueous electrolyte.

[0011] When a metal is exposed to the positive electrode potential, metal ions may elute from the metal into the non-aqueous electrolyte. Also, metal ions may elute from the positive electrode active material. For example, the positive electrode of a non-aqueous secondary battery contains a positive electrode active material, and the positive electrode active material has a high potential and contains a metal component (in many cases, a transition metal). The metal ions eluted into the non-aqueous electrolyte move from the positive electrode side to the negative electrode side and precipitate on the negative electrode side. When such dissolution and precipitation reactions proceed, the voltage of the non-aqueous secondary battery decreases. In a non-aqueous secondary battery, it is important to suppress the dissolution and precipitation of metals.

[0012] On the other hand, when the content (mass %) of the isocyanate compound and the content (mass %) of the nitrile compound P in the non-aqueous electrolyte are C NCO >C CN is satisfied, the dissolution and precipitation reaction of the metal is significantly suppressed, and the decrease in the battery voltage is suppressed.

[0013] Even by adding the isocyanate compound or the nitrile compound P alone to the non-aqueous electrolyte, the dissolution and precipitation reaction of the metal is suppressed, but the effect of suppressing the decrease in the battery voltage is limited. Also, even when the isocyanate compound and the nitrile compound P are used in combination, when C NCO >C CN is not satisfied (that is, C NCO ≦C CNIn this case, the effect of suppressing the decrease in battery voltage is limited. Although the detailed mechanism is not clear, surface analysis results have revealed that the isocyanate compound is reduced at the negative electrode and forms a film on the negative electrode active material, while the nitrile compound P is oxidized at the positive electrode and forms a film on the positive electrode active material. It is thought that the metal dissolution reaction is suppressed when the total amount of film on the negative electrode active material is greater than the total amount of film on the positive electrode active material. It is presumed that the ratio of the amount of film formed on the positive and negative electrodes affects the metal dissolution reaction, and therefore more isocyanate compound is needed to form a film on the negative electrode active material than nitrile compound P.

[0014] The non-aqueous electrolyte secondary battery of this disclosure will be described in more detail below, component by component. The non-aqueous electrolyte secondary battery comprises, for example, a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator as follows. [Non-aqueous electrolytes] Non-aqueous electrolytes consist of a non-aqueous solvent, an electrolyte salt, an isocyanate compound, and a nitrile compound P.

[0015] Isocyanate compound content C NCO and the content of nitrile compound P C CN is C NCO >C CN The following conditions must be met, but the content of the isocyanate compound C NCO and the content of nitrile compounds C CN Ratio to: C NCO / C CN For example, the range could be 55 / 45 to 99 / 1, 70 / 30 to 99 / 1, or 80 / 20 to 99 / 1.

[0016] Content of isocyanate compounds in non-aqueous electrolytes C NCO For example, it may be 0.001% by mass or more and 5% by mass or less, or 0.001% by mass or more and less than 4% by mass, or 0.01% by mass or more and less than 4% by mass, or 0.1% by mass or more and 2% by mass or less.

[0017] Content of nitrile compound P in non-aqueous electrolytes C CNFor example, this could be 0.001% by mass or more and 5% by mass or less, or 0.001% by mass or more and 2% by mass or less, or 0.001% by mass or more and less than 1.6% by mass, or 0.01% by mass or more and 1.5% by mass or less, or 0.02% by mass or more and 0.8% by mass or less.

[0018] In non-aqueous secondary batteries, the content of isocyanate compounds and nitrile compounds P in the non-aqueous electrolyte may change during storage or charging / discharging. Therefore, it is sufficient that isocyanate compounds and nitrile compounds P remain in the non-aqueous electrolyte sampled from a non-aqueous secondary battery at concentrations above the detection limit. The content of isocyanate compounds in the non-aqueous electrolyte sampled from a non-aqueous secondary battery may be 0.0001% by mass or more. The content of nitrile compounds P in the non-aqueous electrolyte sampled from a non-aqueous secondary battery may be 0.0001% by mass or more. The content of isocyanate compounds and nitrile compounds P in a non-aqueous electrolyte can be determined, for example, by gas chromatography under the following conditions. Equipment used: Manufactured by Shimadzu Corporation, GC-2010 Plus Column: J&W HP-1 (film thickness 1 μm, inner diameter 0.32 mm, length 60 m)

[0019] Column temperature: Increase the temperature from 50°C to 90°C at a rate of 5°C / min, maintain at 90°C for 15 minutes, then increase the temperature from 90°C to 250°C at a rate of 10°C / min, maintain at 250°C for 15 minutes. Split ratio: 1 / 50 Linear speed: 30.0cm / sec Inlet temperature: 270℃ Injection volume: 1μL Detector: FID 290℃ (sens.10 1 ) (Isocyanate compounds)

[0020] The isocyanate compound may be a monoisocyanate having one isocyanate group, a diisocyanate having two isocyanate groups, or a polyisocyanate having three or more isocyanate groups. The isocyanate compound may have five or fewer isocyanate groups, or four or fewer. Among these, diisocyanates are particularly effective at suppressing metal leaching reactions even when used in small amounts, and offer excellent stability within the battery.

[0021] Isocyanate compounds form a film on the surface of the negative electrode active material (e.g., carbon material such as graphite), suppressing the reductive decomposition of non-aqueous electrolytes. However, the film formed on the negative electrode surface also functions as a resistor that restricts the movement of lithium ions. The properties of the formed film differ depending on the number of isocyanate groups. Diisocyanates form a film with lower resistance than monoisocyanates and a more homogeneous film than triisocyanates. To form a low-resistance and homogeneous film and effectively suppress the metal dissolution reaction, diisocyanates with two isocyanate groups are desirable.

[0022] The following are specific examples of isocyanate compounds, but isocyanate compounds are not limited to those listed below. Furthermore, isocyanate compounds may be used individually, or two or more may be used in any combination.

[0023] Specific examples of monoisocyanates include isocyanatomethane, isocyanatoethane, 1-isocyanatopropane, 1-isocyanatobutane, 1-isocyanatopentane, 1-isocyanatohexane, 1-isocyanathheptane, 1-isocyanatooctane, 1-isocyanatononane, 1-isocyanatodecane, isocyanatocyclohexane, methoxycarbonyl isocyanate, ethoxycarbonyl isocyanate, propoxycarbonyl isocyanate, butoxycarbonyl isocyanate, methoxysulfonyl isocyanate, ethoxysulfonyl isocyanate, propoxysulfonyl isocyanate, butoxysulfonyl isocyanate, fluorosulfonyl isocyanate, methyl isocyanate, butyl isocyanate, phenyl isocyanate, 2-isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate, and ethyl isocyanate.

[0024] Specific examples of diisocyanates include 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane (hexamethylene diisocyanate), 1,7-diisocyanatoheptane, 1,8-diisocyanatooctane, 1,9-diisocyanatononane, 1,10-diisocyanatodecane, 1,3-diisocyanatopropene, 1,4-diisocyanato-2-butene, 1,4-diisocyanato-2-fluorobutane, 1,4-diisocyanato-2,3-difluorobutane, 1,5-diisocyanato-2-pentene, 1,5- Diisocyanato-2-methylpentane, 1,6-diisocyanato-2-hexene, 1,6-diisocyanato-3-hexene, 1,6-diisocyanato-3-fluorohexane, 1,6-diisocyanato-3,4-difluorohexane, toluene diisocyanate, xylene diisocyanate, tolylene diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane, 1,4-diisocyanatocyclohexane, dicyclohexylmethane-1,1'-diisocyanate, dicyclohexylmethane-2,2'- Examples include diisocyanates, dicyclohexylmethane-3,3'-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate (isophorone diisocyanate), bicyclo[2.2.1]heptane-2,5-diirbis(methylisocyanate), bicyclo[2.2.1]heptane-2,6-diirbis(methylisocyanate), 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylenediisocyanate, octamethylene diisocyanate, tetramethylene diisocyanate, etc.

[0025] Specific examples of triisocyanates include 1,6,11-triisocyanatoundecane, 4-isocyanatomethyl-1,8-octamethylenediisocyanate, 1,3,5-triisocyanatemethylbenzene, 1,3,5-tris(6-isocyanatohexa-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and 4-(isocyanatomethyl)octamethylenediisocyanate.

[0026] Among them, OCN-C n H 2n Compounds represented as -NCO(n is an integer from 1 to 10) (e.g., hexamethylene diisocyanate), compounds having an alicyclic diyl group (e.g., 1,3-bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-diylbis(methylisocyanate), bicyclo[2.2.1]heptane-2,6-diylbis(methylisocyanate), isophorone diisocyanate), 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, etc. are readily available. These may be used individually or in combination of two or more. These compounds may account for 50% or more by mass, and even more than 70% or 90% or more by mass, of the isocyanate compounds in the nonaqueous electrolyte. (Nitrile compound P)

[0027] Nitrile compound P may be a dinitrile having two nitrile groups, or a nitrile compound having three or more nitrile groups. The number of nitrile groups in nitrile compound P may be five or fewer, or four or fewer. Among these, dinitrile is highly effective in suppressing the dissolution reaction of metals and has little impact on battery characteristics. Note that when mononitrile is added to a non-aqueous electrolyte, the dissolution of metals is actually promoted. Nitrile compounds having three or more nitrile groups suppress the dissolution of metals, but tend to increase the viscosity of the non-aqueous electrolyte. Therefore, dinitrile having two nitrile groups is preferable.

[0028] The following are specific examples of nitrile compound P, but nitrile compound P is not limited to those listed below. Furthermore, nitrile compound P may be used alone, or two or more types may be used in any combination.

[0029] Specific examples of nitrile compound P include malononitrile, succinonitrile, glutalonitrile, adiponitrile, pimelonitrile, suberonitrile, azeranitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinonitrile, 2,2-dimethylsuccinonitrile, and 2,3-dimethylsuccinonitrile. , 2,3,3-trimethylsuccinonitrile, 2,2,3,3-tetramethylsuccinonitrile, 2,3-diethyl-2,3-dimethylsuccinonitrile, 2,2-diethyl-3,3-dimethylsuccinonitrile, bicyclohexyl-1,1-dicarbonitrile, bicyclohexyl-2,2-dicarbonitrile, bicyclohexyl-3,3-dicarbonitrile, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,3-diisobutyl-2, 3-dimethylsuccinonitrile, 2,2-diisobutyl-3,3-dimethylsuccinonitrile, 2-methylglutaronitrile, 2,3-dimethylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,3,3-tetramethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 2,2,3,4-tetramethylglutaronitrile, 2,3,3,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 2,6-di Examples include cyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,3'-(ethylenedioxy)dipropionitrile, 3,3'-(ethylenedithio)dipropionitrile, 3,9-bis(2-cyanoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, butanenitrile, phthalonitrile, etc.

[0030] Among them, NC-C m H2m Compounds represented by -CN (where m is an integer from 1 to 10), and compounds having one phenyl group, are readily available. Examples of such compounds include succinonitrile (NC-C2H4-CN), glutalonitrile (NC-C3H6-CN), adiponitrile (NC-C4H8-CN), and pimeronitrile (NC-C5H 10 -CN), Suberonitrile (NC-C6H 12 Examples include nitrile compound P (-CN) and phthalonitrile (NC-C6H5-CN). These may be used individually or in combination of two or more. These compounds may constitute 50% by mass or more, and even 70% by mass or 90% by mass or more, of the nitrile compound P in the non-aqueous electrolyte. (Non-aqueous solvent)

[0031] Examples of non-aqueous solvents include cyclic carbonate esters, linear carbonate esters, cyclic carboxylic acid esters, and linear carboxylic acid esters. Examples of cyclic carbonate esters include propylene carbonate (PC) and ethylene carbonate (EC). Examples of linear carbonate esters include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of linear carboxylic acid esters include methyl formate, ethyl formate, propyl formate, methyl acetate (MA), ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The non-aqueous electrolyte may contain one non-aqueous solvent or a combination of two or more non-aqueous solvents. (Electrolyte salts)

[0032] Lithium salts are preferred as the electrolyte salt. Examples of lithium salts include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, and LiB 10 Cl 10Examples include lithium lower aliphatic carboxylates, LiCl, LiBr, LiI, borates, and imide salts. Examples of borates include lithium difluorooxalate borate and lithium bisoxalate borate. Examples of imide salts include lithium bisfluorosulfonylimide (LiN(FSO2)2) and lithium bistrifluoromethanesulfonate (LiN(CF3SO2)2). Non-aqueous electrolytes may contain one electrolyte salt or a combination of two or more electrolyte salts. The concentration of the electrolyte salt in a non-aqueous electrolyte is, for example, between 0.5 mol / L and 2 mol / L.

[0033] The non-aqueous electrolyte may contain other additives. Examples of other additives include at least one selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, and vinylethylene carbonate. [Positive electrode]

[0034] The positive electrode contains a positive electrode active material. The positive electrode typically comprises a positive electrode current collector and a layered positive electrode mixture (hereinafter referred to as the "positive electrode mixture layer") held by the positive electrode current collector. The positive electrode mixture layer can be formed by coating a positive electrode slurry, which is obtained by dispersing the components of the positive electrode mixture in a dispersion medium, onto the surface of the positive electrode current collector and drying it. The dried coating may be rolled if necessary. The positive electrode mixture contains a positive electrode active material as an essential component and may contain binders, thickeners, etc., as optional components. (Cathode active material)

[0035] The positive electrode active material can be any material that can be used as a positive electrode active material in a non-aqueous secondary battery (especially a lithium-ion secondary battery), and is not particularly limited. Preferred positive electrode active materials include, for example, lithium transition metal composite oxides having a layered rock salt type structure and containing Ni and at least one selected from the group consisting of Co, Mn, and Al.

[0036] From the viewpoint of obtaining high capacity, it is desirable that the proportion of Ni among the metal elements other than Li in the lithium transition metal composite oxide be 80 atomic percent or more. The proportion of Ni among the metal elements other than Li may be 85 atomic percent or more, or 90 atomic percent or more. For example, it is desirable that the proportion of Ni among the metal elements other than Li be 95 atomic percent or less. When limiting the range, these upper and lower limits can be combined arbitrarily.

[0037] Hereinafter, lithium transition metal composite oxides having a layered rock salt structure and containing Ni and at least one element selected from the group consisting of Co, Mn, and Al, with Ni accounting for 80 atomic percent or more of the metal elements other than Li, will also be referred to as "composite oxide HN". Reversible insertion and removal of Li ions is possible between the layers of the layered rock salt structure of composite oxide HN.

[0038] The higher the proportion of Ni, the more lithium ions can be extracted from the composite oxide HN during charging, thereby increasing the capacity. However, the Ni in composite oxide HN with increased capacity tends to have a higher valence state. Also, as the proportion of Ni increases, the proportion of other elements decreases relatively. In this case, the crystal structure tends to become unstable, especially in the fully charged state, and transition metals such as Ni are more likely to dissolve with repeated charging and discharging. When Ni dissolves from composite oxide HN with a high Ni content, the particle surface tends to change to a crystal structure that makes reversible intercalation and release of lithium ions difficult. In the non-aqueous secondary battery according to this disclosure, even though composite oxide HN with a high Ni content is used, the dissolution of transition metals can be highly suppressed by using a non-aqueous electrolyte containing an isocyanate compound and a nitrile compound P.

[0039] Co, Mn, and Al contribute to stabilizing the crystal structure of composite oxides HN with a high Ni content. However, from the standpoint of reducing manufacturing costs, a lower Co content is preferable. Composite oxides HN with a low Co content or no Co at all may also contain Mn and Al.

[0040] The proportion of Co among metal elements other than Li is preferably 10 atomic percent or less, more preferably 5 atomic percent or less, and it is not necessary to include Co at all. From the viewpoint of stabilizing the crystal structure of the composite oxide HN, it is desirable to include 1 atomic percent or more, or 1.5 atomic percent or more, of Co.

[0041] The proportion of Mn in the metal elements other than Li may be 10 atomic percent or less, or 5 atomic percent or less. The proportion of Mn in the metal elements other than Li may be 1 atomic percent or more, or 3 atomic percent or more, or 5 atomic percent or more. When limiting the range, these upper and lower limits can be combined arbitrarily.

[0042] The proportion of Al among metal elements other than Li may be 10 atomic percent or less, or 5 atomic percent or less. The proportion of Al among metal elements other than Li may be 1 atomic percent or more, 3 atomic percent or more, or 5 atomic percent or more. When limiting the range, these upper and lower limits can be combined arbitrarily.

[0043] A composite oxide HN is, for example, one with the formula: Li α Ni (1-x1-x2-y-z) Co x1 Mn x2 Al y M z O 2+β It is represented as follows: Element M is an element other than Li, Ni, Co, Mn, Al, and oxygen.

[0044] In the above formula, α, which represents the atomic ratio of lithium, is, for example, 0.95 ≤ α ≤ 1.05. However, α increases or decreases with charging and discharging. In (2 + β), which represents the atomic ratio of oxygen, β satisfies -0.05 ≤ β ≤ 0.05.

[0045] The atomic ratio of Ni, represented by 1-x1-x2-yz (=v), is 0.8 or greater, may be 0.85 or greater, or 0.90 or greater, or 0.95 or greater. Similarly, the atomic ratio of Ni, represented by v, may be 0.98 or less, or 0.95 or less. When limiting the range, these upper and lower limits can be combined in any way.

[0046] The x1 indicating the atomic ratio of Co is, for example, 0.1 or less (0 ≦ x1 ≦ 0.1), and may be 0.08 or less, may be 0.05 or less, and may be 0.01 or less. When x1 is 0, the case where Co is below the detection limit is included.

[0047] The x2 indicating the atomic ratio of Mn is, for example, 0.1 or less (0 ≦ x2 ≦ 0.1), and may be also 0.08 or less, may be 0.好5 or less, and may be 0.03 or less. x2 may be 0.01 or more, and may be 0.03 or more. Mn contributes to the stabilization of the crystal structure of the composite oxide HN, and the fact that the composite oxide HN contains inexpensive Mn is advantageous for cost reduction. When limiting the range, these upper and lower limits can be arbitrarily combined.

[0048] The y indicating the atomic ratio of Al is, for example, 0.1 or less (0 ≦ y ≦ 0.1), and may be 0.08 or less, may be 0.05 or less, and may be 0.03 or less. y may be 0.01 or more, and may be 0.03 or more. Al contributes to the stabilization of the crystal structure of the composite oxide HN. When limiting the range, these upper and lower limits can be arbitrarily combined.

[0049] The z indicating the atomic ratio of the element M is, for example, 0 ≦ z ≦ 0.10, and may be 0 < z ≦ 0.05, and may be 0.001 ≦ z ≦ 0.01. When limiting the range, these upper and lower limits can be arbitrarily combined.

[0050] The element M may be at least one selected from the group consisting of Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, Sc, and Y. Among them, when at least one selected from the group consisting of Nb, Sr, and Ca is contained in the composite oxide HN, it is considered that the surface structure of the composite oxide HN is stabilized, the resistance is reduced, and the elution of the metal is further suppressed. It is more effective if the element M is unevenly distributed in the vicinity of the particle surface of the composite oxide HN.

[0051] The elemental content of the composite oxide HN can be measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), electron probe microanalyzer (EPMA), or energy dispersive X-ray spectroscopy (EDX), among other methods.

[0052] The composite oxide HN is, for example, a secondary particle formed by the aggregation of multiple primary particles. The particle size of the primary particles is, for example, between 0.05 μm and 1 μm. The average particle size of the secondary particles of the composite oxide HN is, for example, between 3 μm and 30 μm, and may also be between 5 μm and 25 μm.

[0053] In this specification, the average particle size of secondary particles refers to the particle size at which the integrated volume value in the particle size distribution measured by laser diffraction scattering (volume-average particle size) becomes 50%. Such a particle size is sometimes referred to as D50. For the measuring device, for example, the "LA-750" manufactured by HORIBA, Ltd. can be used.

[0054] The positive electrode active material may contain lithium transition metal composite oxides other than composite oxide HN, but it is preferable that the proportion of composite oxide HN is high. The proportion of composite oxide HN in the positive electrode active material is, for example, 90% by mass or more, may be 95% by mass or more, or may be 100%. (others)

[0055] For example, resin materials can be used as binders. Examples of binders include fluororesins, polyolefin resins, polyamide resins, polyimide resins, acrylic resins, vinyl resins, and rubber-like materials (e.g., styrene-butadiene copolymer (SBR)). A single binder may be used, or two or more may be used in combination.

[0056] Examples of thickening agents include cellulose derivatives such as cellulose ether. Examples of cellulose derivatives include carboxymethylcellulose (CMC) and its modified forms, and methylcellulose. A single thickening agent may be used alone, or two or more may be used in combination. Examples of conductive materials include carbon nanotubes (CNTs), carbon fibers other than CNTs, and conductive particles (e.g., carbon black, graphite).

[0057] The dispersion medium used in the positive electrode slurry is not particularly limited, but examples include water, alcohol, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof.

[0058] For example, a metal foil may be used as the positive electrode current collector. The positive electrode current collector may be porous. Examples of porous current collectors include nets, perforated sheets, and expanded metal. Examples of materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloys, and titanium. The thickness of the positive electrode current collector is not particularly limited, but for example, it may be 1 to 50 μm, or 5 to 30 μm. [Negative electrode]

[0059] The negative electrode contains a negative electrode active material. The negative electrode typically comprises a negative electrode current collector and a layered negative electrode mixture (hereinafter referred to as the negative electrode mixture layer) held by the negative electrode current collector. The negative electrode mixture layer can be formed by coating the surface of the negative electrode current collector with a negative electrode slurry, which is obtained by dispersing the components of the negative electrode mixture in a dispersion medium, and drying it. The dried coating may be rolled if necessary. The negative electrode mixture may contain a negative electrode active material as an essential component, and may also contain binders, thickeners, conductive agents, etc., as optional components. (Negative electrode active material)

[0060] As the negative electrode active material, metallic lithium, lithium alloys, etc., may be used, but materials capable of electrochemically intercalating and releasing lithium ions are preferably used. Examples of such materials include carbonaceous materials and Si-containing materials. The negative electrode may contain one type of negative electrode active material, or a combination of two or more types.

[0061] Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). A single carbonaceous material may be used, or two or more may be used in combination. Among these, graphite is preferred as the carbonaceous material due to its excellent charge-discharge stability and low irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0062] Si-containing materials include elemental Si, silicon alloys, silicon compounds (such as silicon oxides), and composite materials in which the silicon phase is dispersed within the lithium-ion conductive phase (matrix). Examples of silicon oxides include SiO2. x Particles are an example. x may be, for example, 0.5 ≤ x < 2, and also 0.8 ≤ x ≤ 1.6. As the lithium ion conducting phase, at least one selected from the group consisting of SiO2 phase, silicate phase, and carbon phase may be used. For example, the materials exemplified for the positive electrode can be used as the binder, thickener, conductive agent, and dispersion medium for the negative electrode slurry.

[0063] For example, a metal foil may be used as the negative electrode current collector. The negative electrode current collector may be porous. Examples of materials for the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy. The thickness of the negative electrode current collector is not particularly limited, but for example, it may be 1 to 50 μm, or 5 to 30 μm. [Separator]

[0064] It is desirable to interpose a separator between the positive and negative electrodes. The separator should have high ion permeability and appropriate mechanical strength and insulating properties. As the separator, a microporous thin film, woven fabric, nonwoven fabric, etc., can be used. As the material of the separator, polyolefins such as polypropylene and polyethylene are preferred.

[0065] One example of the structure of a non-aqueous electrolyte secondary battery is a structure in which an electrode group, in which a positive electrode and a negative electrode are wound around each other with a separator, is housed together with a non-aqueous electrolyte in an outer casing. However, it is not limited to this, and other forms of electrode groups may be used. For example, a stacked electrode group in which the positive electrode and negative electrode are stacked with a separator in between may also be used. The form of the non-aqueous electrolyte secondary battery is also not limited, and may be cylindrical, prismatic, coin-type, button-type, laminate-type, etc. The following describes the structure of a rectangular non-aqueous electrolyte secondary battery as an example of a non-aqueous electrolyte secondary battery related to this disclosure, with reference to Figure 1.

[0066] The battery comprises a bottomed rectangular battery case 4, an electrode group 1 housed within the battery case 4, and a non-aqueous electrolyte. The electrode group 1 has a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator interposed between them. The negative electrode current collector is electrically connected to a negative electrode terminal 6 provided on a sealing plate 5 via a negative electrode lead 3. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode current collector is electrically connected to the back surface of the sealing plate 5 via a positive electrode lead 2. That is, the positive electrode is electrically connected to the battery case 4, which also serves as the positive electrode terminal. The periphery of the sealing plate 5 fits into the open end of the battery case 4, and the fitting portion is laser-welded. The sealing plate 5 has an injection hole for the non-aqueous electrolyte, which is sealed by a seal 8 after injection. The present disclosure will be described in detail below based on examples and comparative examples, but the present disclosure is not limited to the following examples. Examples 1-38 and Comparative Examples 1-5 A non-aqueous secondary battery was fabricated and evaluated using the following procedure. (1) Preparation of the positive electrode

[0067] Positive electrode active material particles (LiNi 0.88 Co 0.09 Al 0.03 A positive electrode slurry was obtained by mixing 100 parts by mass of O2, 1 part by mass of carbon nanotubes, 1 part by mass of polyvinylidene fluoride, and an appropriate amount of NMP. Next, the positive electrode slurry was applied to one side of an aluminum foil, the coating was dried, and then the foil was rolled to form a positive electrode mixture layer (thickness 95 μm, density 3.6 g / cm³) on both sides of the aluminum foil. 3 A positive electrode was obtained by forming a positive electrode. (2) Fabrication of the negative electrode

[0068] A negative electrode slurry was prepared by mixing 98 parts by mass of negative electrode active material (graphite), 1 part by mass of sodium carboxymethylcellulose (CMC-Na), 1 part by mass of SBR, and an appropriate amount of water. Next, the negative electrode slurry was applied to one side of a copper foil, which was to be used as the negative electrode current collector. After the coating was dried, the foil was rolled to form negative electrode mixture layers on both sides of the copper foil. (3) Preparation of non-aqueous electrolytes (electrolyte)

[0069] An electrolyte was prepared by dissolving LiPF6 and the isocyanate compounds and nitrile compounds P shown in Table 1 and 2 in a mixed solvent of EC and EMC (EC:EMC = 3:7 (volume ratio)). The concentration of LiPF6 in the electrolyte was 1.0 mol / L. The concentrations of isocyanate compounds and nitrile compounds P in the electrolyte are the initial concentrations of the electrolyte immediately after preparation. The isocyanate compounds and nitrile compounds P shown in Tables 1 and 2 are listed below. <Isocyanate compounds> BIMCH13: 1,3-Bis(isocyanatomethyl)cyclohexane HMDI: 1,6-Diisocyanatohexane (Hexamethylene-1,6-diisocyanate) <Nitrile compound P> ScCN: Sucinonitrile (NC-C2H4-CN) AdCN: Adiponitrile (NC-C4H8-CN) (4) Fabrication of non-aqueous electrolyte secondary batteries

[0070] The positive electrode was cut into a predetermined shape to obtain a positive electrode for evaluation. The positive electrode had a 20mm x 20mm region to function as a positive electrode and a 5mm x 5mm region for connection to the tab lead. Subsequently, the positive electrode mixture layer formed on the connection region was scraped off to expose the positive electrode current collector. Then, the exposed portion of the positive electrode current collector was connected to the positive electrode tab lead, and a predetermined region on the outer circumference of the positive electrode tab lead was covered with an insulating tab film. In Examples 1 to 38 and Comparative Examples 1 to 5, a metallic copper sphere with a diameter of approximately 100 μm was intentionally embedded near the center of the positive electrode mixture layer.

[0071] The negative electrode was cut to the same shape as the positive electrode to obtain a negative electrode for evaluation. The negative electrode mixture layer formed on the connection region, which was formed in the same way as the positive electrode, was peeled off to expose the negative electrode current collector. Then, the exposed portion of the negative electrode current collector was connected to the negative electrode tab lead, and a predetermined area on the outer circumference of the negative electrode tab lead was covered with an insulating tab film.

[0072] Cells were fabricated using evaluation positive and negative electrodes. First, the positive and negative electrodes were placed opposite each other via a polypropylene separator (30 μm thick) so that the positive electrode mixture layer and the negative electrode mixture layer overlapped to obtain an electrode plate group. Next, a 60 × 90 mm rectangle of Al laminate film (100 μm thick) was folded in half, and the 60 mm long side end was heat-sealed to form a 60 × 45 mm cylinder. Then, the fabricated electrode plate group was placed inside the cylinder, and the end face of the Al laminate film was aligned with the position of the heat-sealing resin on each tab lead and sealed. Next, a non-aqueous electrolyte was poured into the short side of the Al laminate film that was not heat-sealed, impregnating each mixture layer with the non-aqueous electrolyte. Finally, the end face of the Al laminate film on the side where the electrolyte was poured was sealed to obtain evaluation cells A1 to A38 for Examples 1 to 38 and evaluation cells B1 to B5 for Comparative Examples 1 to 5. (5) Battery evaluation The evaluation cell was clamped between a pair of 80 x 80 cm stainless steel (2 mm thick) clamps and fixed under pressure at 0.2 MPa.

[0073] First, the battery was charged and discharged five times in a constant current of 0.05C (1C is the current value that discharges the design capacity in one hour) in a constant temperature bath at 25°C. Charging was terminated at a battery voltage of 4.2V, and discharging at a battery voltage of 2.5V. The battery was left undisturbed in an open circuit for 20 minutes between charging and discharging. (6) Evaluation

[0074] At a temperature of 25°C, the battery was charged with a constant current of 0.3 It until the voltage reached 4.1V, and then charged with a constant voltage of 4.1V until the current reached 0.05 It. The battery was then stored at 25°C, and the voltage drop and DC resistance (DCIR) increase rate after 100 hours were measured. The results are shown in Tables 1 and 2.

[0075] The DCIR increase rate was determined by measuring the voltage values ​​when discharging the battery for 10 seconds at currents of 0A, 0.1A, 0.5A, and 1.0A, respectively, in a 25°C environment before and after 100 hours of storage. The battery was then charged with a constant current of 0.3It until the voltage reached 4.1V, then charged with a constant voltage of 4.1V until the current reached 0.05It, and then discharged with a constant current of 0.3It for 100 minutes, bringing the State of Charge (SOC) to 50%. The DCIR (initial DCIR) was calculated from the absolute value of the slope when the relationship between the discharge current and the voltage after 10 seconds was approximated by the least squares method as a straight line. The DCIR increase rate was calculated as the ratio of the DCIR after 100 hours of storage to the initial DCIR using the following formula. DCIR increase rate (%) = {(DCIR at 100 cycles - initial DCIR)} / initial DCIR × 100

[0076] [Table 1]

[0077] [Table 2]

[0078] From Table 1, batteries B1, B2, and C do not use diisocyanate. NCO ≤C CN In batteries B3 to B5 that satisfy the conditions, the voltage drop is extremely significant. Furthermore, when comparing batteries B2 and B5, which have the same amount of nitrile compound P, it can be seen that B2, which does not use diisocyanate, actually experiences a smaller voltage drop than B5, which does use diisocyanate. On the other hand, C NCO >C CN In batteries A1 to A38 that satisfy the criteria, voltage drop is significantly suppressed. Furthermore, while the addition of isocyanate compounds or nitrile compounds P to the electrolyte tends to increase DCIR, it can be understood that the rate of increase can be suppressed by limiting the amount added. [Industrial applicability]

[0079] The non-aqueous secondary battery described herein is suitable for use as a main power source for mobile communication devices, portable electronic devices, and in-vehicle power sources, but its applications are not limited to these. [Explanation of symbols]

[0080] 1 electrode group 2 Positive leads 3 Negative lead 4 Battery case 5 Sealing plate 6 Negative terminal 7 Gasket 8. Sealing

Claims

1. Non-aqueous solvents and Electrolyte salts, Isocyanate compounds and, A nitrile compound having two or more nitrile groups, Content C of the isocyanate compound NCO However, the nitrile compound content C CN A non-aqueous electrolyte for non-aqueous secondary batteries, which is more abundant by mass.

2. Content C of the isocyanate compound NCO However, it is between 0.001% by mass and 5% by mass. Content C of the nitrile compound CN The non-aqueous electrolyte for a non-aqueous secondary battery according to claim 1, wherein the concentration is 0.001% by mass or more and 5% by mass or less.

3. Content C of the isocyanate compound NCO However, it is less than 4% by mass, Content C of the nitrile compound CN However, the non-aqueous electrolyte for a non-aqueous secondary battery according to claim 2, wherein the amount is less than 1.6% by mass.

4. The content C of the isocyanate compound NCO and the content C of the nitrile compound CN The ratio of: C NCO / C CN is within the range of 70 / 30 to 99 / 1. The non-aqueous electrolyte for a non-aqueous secondary battery according to any one of claims 1 to 3.

5. The isocyanate compound has two or more isocyanate groups, and is a non-aqueous electrolyte for a non-aqueous secondary battery according to any one of claims 1 to 4.

6. The non-aqueous electrolyte for a non-aqueous secondary battery according to claim 5, wherein the isocyanate compound is a diisocyanate compound.

7. The non-aqueous electrolyte for a non-aqueous secondary battery according to claim 5, wherein the diisocyanate compound comprises at least one selected from the group consisting of hexamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-diylbis(methylisocyanate), bicyclo[2.2.1]heptane-2,6-diylbis(methylisocyanate), isophorone diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

8. The non-aqueous electrolyte for a non-aqueous secondary battery according to any one of claims 1 to 7, wherein the nitrile compound is a dinitrile compound.

9. The non-aqueous electrolyte for a non-aqueous secondary battery according to claim 8, wherein the dinitrile compound comprises at least one selected from the group consisting of succinonitrile, glutalonitrile, adiponitrile, pimeronitrile, and suberonitrile.

10. The device comprises a positive electrode containing a positive electrode active material, a separator, a negative electrode facing the positive electrode via the separator, and a non-aqueous electrolyte. The non-aqueous electrolyte comprises a non-aqueous solvent, an electrolyte salt, an isocyanate compound, and a nitrile compound having two or more nitrile groups. In the aforementioned non-aqueous electrolyte, the content C of the isocyanate compound NCO However, the nitrile compound content C CN Non-aqueous secondary batteries that are more numerous by mass.

11. The positive electrode active material has a layered rock salt type structure and includes a lithium transition metal composite oxide comprising Ni and at least one selected from the group consisting of Co, Mn, and Al. The non-aqueous secondary battery according to claim 10, wherein the proportion of Ni among the metal elements other than Li contained in the lithium transition metal composite oxide is 80 atomic percent or more.

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