KR20220092812A - Acid or moisture reducing agent in non-aqueous electrolyte, non-aqueous electrolyte containing the same, lithium secondary battery including non-aqueous electrolyte, and method for reducing acid or moisture in non-aqueous electrolyte - Google Patents

Abstract

The objective of the present invention is to provide an electrolyte that has an excellent cycle life by suppressing degradation of battery characteristics even under high temperature conditions by reducing acid and/or moisture. Provided are an acid or a water reducing agent of a non-aqueous electrolyte including a (meth)acrylate having an isocyanate group or an amide bond.

Description

Acid or moisture reducing agent of non-aqueous electrolyte, non-aqueous electrolyte containing same, lithium secondary battery having non-aqueous electrolyte, and method of reducing acid or moisture of non-aqueous electrolyte {Acid or moisture reducing agent in non-aqueous electrolyte , non-aqueous electrolyte containing the same, lithium secondary battery including non-aqueous electrolyte, and method for reducing acid or moisture in non-aqueous electrolyte}

The present invention relates to an acid or moisture reducing agent in a non-aqueous electrolyte, a non-aqueous electrolyte containing the same, a lithium secondary battery including the non-aqueous electrolyte, and a method for reducing acid or moisture in the non-aqueous electrolyte.

Lithium secondary batteries are widely used not only in portable devices such as mobile phones and notebook computers, but also as storage batteries for automobiles and industries, and further for new uses such as drones. Although lithium secondary batteries have a relatively higher energy density than other types of secondary batteries, in order to manufacture a lithium secondary battery with a higher energy density, the use of a material containing nickel in a high proportion as a positive electrode active material has been reviewed. have.

Conventionally, lithium cobaltate (LCO) has been used as a cathode active material of a lithium secondary battery, but nickel-cobalt-manganese (NCM) containing nickel is being used. In addition, the use of a nickel-cobalt-aluminum (NCA) ternary material is also being studied. These ternary materials are advantageous because they can reduce the use of cobalt not only from the viewpoint of high energy density but also from the viewpoint of cost competitiveness.

In addition, a technique of using a material containing silicon as an anode active material is also being developed. Since a material containing silicon has a large theoretical capacity, it is expected to be particularly applied to automotive applications requiring a large capacity.

In the case of using these positive electrode active materials and negative electrode active materials, examination of the optimal electrolyte solution is also in progress. Among the materials contained in the electrolyte, it is known that the electrolyte deteriorates under the influence of moisture contained in a trace amount. For example, when LiPF ₆ is used as the electrolyte, the following reaction occurs and the electrolyte is decomposed to generate acid.

LiPF ₆ +H ₂ O→LiF+POF ₃ +2HF

It is known that the acid powder generated in this way reacts with the surface of the negative electrode material containing silicon such as SiO or a film formed on the surface, and the impedance rises to deteriorate the battery characteristics. In addition, when a material containing nickel is used as the positive electrode active material, since there is a large amount of residual alkali in the material, there is a risk of accelerating the reaction for generating an acid content.

Patent Document 1 describes suppressing the production of hydrogen fluoride by including in the non-aqueous electrolyte at least one additive selected from the group consisting of compounds containing a nitrogen atom having a lone pair of electrons. However, although it has been demonstrated that graphite is effective in the case of using graphite as the negative electrode, the influence on the negative electrode and the film on the surface of the negative electrode in the case of using a material containing silicon is not known.

Patent Document 2 and Patent Document 3 disclose improving charge/discharge characteristics from a low temperature to a high temperature by adding a compound having an isocyanate group as an additive to a nonaqueous electrolyte solution for a secondary battery. However, although these documents disclose the formation of a film on the negative electrode, the effect on acid and moisture is not disclosed.

Patent Document 1: Japanese Patent Laid-Open No. 2019-186078 Patent Document 2: International Publication No. 2012/147502 Patent Document 3: International Publication No. 2014/125946

Therefore, an acid or moisture reducing agent capable of stabilizing the properties of the electrolyte even when a nickel-containing material for the positive electrode and a silicon-containing material for the negative electrode are used, and an electrolyte having excellent battery characteristics and cycle life by reducing acid and/or moisture is being demanded

The present invention has been made to solve the problems of the prior art, and it is an object of the present invention to provide an electrolyte solution having excellent cycle life by suppressing deterioration of battery characteristics even under high-temperature conditions by reducing acid and/or moisture. .

As a result of intensive examination of the above problems, the present inventors unexpectedly used (meth)acrylate having an isocyanate group or amide bond as an acid or moisture reducing agent in the electrolyte solution, so that excellent capacity density can be maintained even under high temperature conditions. found out and came to the present invention.

The object of the present invention is achieved by an acid or moisture reducing agent for a non-aqueous electrolytic solution containing a (meth)acrylate having an isocyanate group or an amide bond.

It is preferable that the (meth)acrylate which has the said isocyanate group or an amide bond is (meth)acrylate which has an isocyanate group.

The (meth)acrylate having an isocyanate group or an amide bond is preferably selected from the following compounds:

The (meth)acrylate having an isocyanate group or an amide bond is preferably 2-isocyanatoethyl acrylate or 2-isocyanatoethyl methacrylate. do.

Moreover, this invention relates to the non-aqueous electrolyte solution containing the acid or moisture reducing agent of this invention.

It is preferable to contain the (meth)acrylate which has the said isocyanate group or an amide bond in the quantity of 0.1-1 mass % with respect to the total mass of a non-aqueous electrolyte solution.

The non-aqueous electrolyte of the present invention preferably further contains a cyclic carbonate and a chain carbonate.

It is preferable that the non _- aqueous electrolyte solution of this invention contains a lithium salt further, and it is preferable that lithium salt contains LiPF6.

Further, the present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte of the present invention disposed between the positive electrode and the negative electrode.

The anode preferably includes a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary material.

It is preferable that the said negative electrode contains the material containing silicon.

Further, the present invention relates to a method for reducing acid or moisture in a non-aqueous electrolytic solution, comprising adding the (meth)acrylate having an isocyanate group or an amide bond to the non-aqueous electrolytic solution.

According to the present invention, by using (meth)acrylate having an isocyanate group or an amide bond as an acid or moisture reducing agent in the non-aqueous electrolyte, acid content is not easily generated even when water is mixed in a lithium secondary battery. Therefore, even under high-temperature conditions, deterioration of battery characteristics can be suppressed, and an electrolytic solution having an excellent cycle life can be provided.

1 is a graph showing the relationship between the number of cycles and the capacity obtained as a result of the charge/discharge cycle test of Examples 1, 2 and Comparative Example 1. FIG.

The acid or moisture reducing agent of the non-aqueous electrolyte of the present invention contains (meth)acrylate having an isocyanate group or an amide bond. Preferably, the acid or moisture reducing agent of the non-aqueous electrolyte solution of this invention contains the (meth)acrylate which has an isocyanate group.

The (meth)acrylate having an isocyanate group or amide bond contained in the acid or moisture reducing agent of the non-aqueous electrolyte of the present invention may contain one isocyanate group or amide bond in the molecule, or an isocyanate group or Two or more amide bonds may be included. In addition, other groups and bonds included in the molecule are not particularly limited.

In one embodiment, the (meth)acrylate having an isocyanate group or an amide bond contained in the acid or moisture reducing agent of the non-aqueous electrolyte of the present invention is selected from the following compounds:

In particular, (meth)acrylate having an isocyanate group at the terminal of the molecule is preferably used, and it is preferably a compound represented by the following formula (1):

(Wherein, R ₁ is a hydrogen atom or a methyl group, and R ₂ is a divalent organic group)

In the formula (1), R ₂ is a divalent organic group, and examples thereof include an alkylene group, an arylene group, and an alkenylene group. It is preferable that it is a C1-C6 alkylene group, and, as for R< ₂ >, it is more preferable that it is a C1-C3 alkylene group.

Preferably, the (meth)acrylate having an isocyanate group or an amide bond contained in the acid or moisture reducing agent of the non-aqueous electrolyte of the present invention is 2-isocyanatoethyl methacrylate, 2-isocyanato Ethyl acrylate, 1,1-(bisacryloyloxymethyl)ethyl isocyanate, 2-[0-(1′-methylpropylideneamino)carboxyamino]ethyl methacrylate or 2-[0-(1′- methylpropylideneamino)carboxyamino]ethyl acrylate. More preferably, the (meth)acrylate having an isocyanate group or an amide bond contained in the acid or moisture reducing agent of the non-aqueous electrolyte of the present invention is 2-isocyanatoethyl acrylate or 2-isocyanato ethyl methacrylate.

The (meth)acrylate which has an isocyanate group or an amide bond contained in the acid or moisture reducing agent of the non-aqueous electrolyte solution of this invention may be used individually by 1 type, and may be used combining several compounds.

Moreover, this invention relates to the non-aqueous electrolyte solution containing the acid or moisture reducing agent of this invention. The (meth)acrylate having an isocyanate group or an amide bond contained in the non-aqueous electrolytic solution is preferably contained in an amount of 0.1 to 1 mass %, and in an amount of 0.2 to 0.9 mass % with respect to the total mass of the non-aqueous electrolytic solution. More preferably, it is contained in an amount of 0.3 to 0.8 mass%, most preferably. By containing the (meth)acrylate having an isocyanate group or an amide bond as an acid or moisture reducing agent in an amount within the above range, it is possible to effectively suppress the acid or moisture generating reaction in the battery.

The non-aqueous electrolyte solution of the present invention preferably further contains an organic solvent such as a cyclic carbonate, a chain carbonate, an ether compound, an ester compound, and an amide compound. These organic solvents may be used independently and may be used in mixture of plurality. Preferably, the non-aqueous electrolyte of the present invention contains a cyclic carbonate and a chain carbonate as an organic solvent.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), methylvinylene carbonate, ethylvinylene carbonate, 1,2-diethylvinylene carbonate, vinylethylene carbonate (VEC) , 1-methyl-2-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1,1-divinylethylene carbonate, 1,2-divinylethylene carbonate, 1 ,1-Dimethyl-2-methyleneethylene carbonate, 1,1-diethyl-2-methyleneethylene carbonate, ethynylethylene carbonate, 1,2-diethynylethylene carbonate, 1,2-butylene carbonate, 2,3- butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, chloroethylene carbonate, and combinations thereof. In addition, as the chain carbonate, dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), methylisopropyl carbonate, methylbutyl carbonate, diethyl carbonate (DEC), ethylpropyl carbonate, ethylbutyl carbonate, dipropyl carbonate, propylbutyl carbonate, and combinations thereof.

As the cyclic carbonate, a cyclic carbonate containing a fluorine atom may be included. As the cyclic carbonate containing a fluorine atom, fluoro vinylene carbonate, trifluoro methyl vinylene carbonate, fluoro ethylene carbonate, 1,2-difluoro ethylene carbonate, 1, 1-difluoro ethylene carbonate, 1 ,1,2-Trifluoroethylene carbonate, tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl Ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, trifluoromethyl ethylene carbonate, 4-fluoro-1,3-dioxolan-2-one, trans or cis 4,5- difluoro-1,3-dioxolan-2-one, 4-ethynyl-1,3-dioxolan-2-one, and combinations thereof.

In particular, among carbonates, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are highly viscous organic solvents, and can be preferably used because of their high dielectric constant and easy dissociation of lithium salts in the electrolyte, and in such cyclic carbonates, dimethyl carbonate, diethyl carbonate and low-viscosity and low-dielectric-constant chain carbonate such as ethyl methyl carbonate, mixed in an appropriate ratio, is preferable because an electrolyte solution having high electrical conductivity can be prepared.

The non-aqueous electrolytic solution of the present invention may further contain an ether compound such as a cyclic ether or a chain ether. Examples of the cyclic ether include tetrahydrofuran and 2-methyl tetrahydrofuran. In addition, the non-aqueous electrolyte of the present invention may further contain a chain ether. Examples of the chain ether include dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether.

The non-aqueous electrolytic solution of the present invention may further contain an ester compound such as carbonic acid ester. Examples of the carbonic acid ester include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl valerate, ethyl valerate , propyl valerate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, ε-caprolactone, a compound in which some of the hydrogens in their carbonic acid esters are substituted with fluorine, and Combinations of these can be mentioned.

In addition to the above, the non-aqueous electrolyte of the present invention may contain other solvents such as polyethers, sulfur-containing solvents and phosphorus-containing solvents without particular limitation as long as the object of the present invention is not impaired.

The non-aqueous electrolyte of the present invention may contain a mixture of a cyclic carbonate and a chain carbonate, and the ratio of the cyclic carbonate and the chain carbonate is preferably 1:9 to 9:1 by volume, 2:8 to 8: It is more preferable that it is a volume ratio of 2.

The non-aqueous electrolyte of the present invention may contain an electrolyte generally used in secondary batteries. The electrolyte acts as a medium for transporting ions involved in an electrochemical reaction in a secondary battery. In particular, the present invention is useful as an electrolyte for a lithium secondary battery, and in this case, a lithium salt is contained as the electrolyte.

Examples of the lithium salt contained in the non-aqueous electrolyte of the present invention include LiPF ₆ , LiBF ₄ , LiB ₁₂ F ₁₂ , LiAsF ₆ , LiFSO ₃ , Li ₂ SiF ₆ , LiCF ₃ CO ₂ , LiCH ₃ CO ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiCF ₃ (CF ₂ ) ₇ SO ₃ , LiCF ₃ CF ₂ (CF ₃ ) ₂ CO, Li(CF ₃ SO ₂ ) ₂ CH, LiNO ₃ , LiN(CN) ₂ , LiN(FSO ₂ ) ₂ , LiN(F ₂ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ) ₃ , LiP(CF ₃ ) ₆ , LiPF(CF ₃ ) ₅ , LiPF ₂ (CF ₃ ) ₄ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (CF ₃ SO ₂ ) ₂ , LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₂ C ₂ O ₄ , LiBC ₄ O ₈ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂ , LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ , LiSbF ₆ , LiAlO ₄ , LiAlF ₄ , LiSCN, LiClO ₄ , LiCl, LiF, LiBr, LiI and LiAlCl ₄ , etc. can be heard _In particular, inorganic salts, such as LiPF6, _LiBF4 , _LiAsF6 , _and LiClO4, are preferable, and _LiPF6 is more preferable. A lithium salt can be used individually by 1 type, and can also be used combining several lithium salt.

Although the content of the electrolyte is not particularly limited, it is 0.1 mol/L to 5 mol/L or less, preferably 0.5 mol/L to 3 mol/L or less, more preferably 0.5 mol/L or less with respect to the total mass of the non-aqueous electrolyte solution. It is contained in an amount of L-2 mol/L or less. When the amount of the electrolyte is within the above range, sufficient battery characteristics can be obtained.

The non-aqueous electrolytic solution of the present invention may further contain at least one additive. Examples of the additive include a flame retardant, a wetting agent, a stabilizer, a corrosion inhibitor, a gelling agent, an overcharge inhibitor, and a negative electrode film forming additive.

Further, the present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte of the present invention disposed between the positive electrode and the negative electrode.

The lithium battery provided with the non-aqueous electrolyte of the present invention can use without limitation a positive electrode and a negative electrode that can be used in a known lithium secondary battery, and can be configured by accommodating it in a container together with the non-aqueous electrolyte of the present invention. In addition, a separator may be interposed between the positive electrode and the negative electrode.

The positive electrode used in the lithium secondary battery of the present invention may be manufactured by, for example, coating a positive electrode slurry including a positive electrode active material, a binder, a conductive material and a solvent on a positive electrode current collector, followed by drying and rolling.

The positive electrode current collector is not particularly limited as long as it does not cause chemical change in the lithium secondary battery of the present invention and has conductivity, for example, on the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. What has surface-treated with carbon, nickel, titanium, silver, etc. can be used.

The positive electrode active material is a compound capable of reversibly occluding and releasing lithium, and specifically, may include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (eg, LiMnO ₂ , LiMn ₂ O ₄ , etc.), a lithium-cobalt-based oxide (eg, LiCoO ₂ , etc.), lithium-nickel-based oxide. oxides (eg, LiNiO ₂ , etc.), lithium-nickel-manganese oxides (eg, LiNi _1-y1 Mn _y1 O ₂ (here, 0<y1<1), LiMn _2-z1 Ni _z O ₄ ) (here, 0<Z1<2), etc.), lithium-nickel-cobalt-based oxide (for example, LiNi _1-y2 Co _y2 O ₂ (here, 0<y2<1), etc.), lithium-manganese- Cobalt-based oxides (eg, LiCo _1-y3 Mn _y3 O ₂ (here, 0<y3<1), LiMn _2-z2 Co _z2 O ₄ (here, 0<Z2<2), etc.), lithium- Nickel-manganese-cobalt oxide (for example, Li(Ni _p1 Co _q1 Mn _r1 )O ₂ (here, 0<p1<1, 0<q1<1, 0<r1<1, p1+q1+r1) =1), or Li(Ni _p2 Co _q2 Mn _r2 )O ₄ (where 0<p2<2, 0<q2<2, 0<r2<2, p2+q2+r2=2), etc.), or Lithium-nickel-cobalt-transition metal (M) oxide (eg, Li(Ni _p3 Co _q3 Mn _r3 M _S3 )O ₂ , wherein M is Al, Fe, V, Cr, Ti, Ta, Mg and is selected from the group consisting of Mo, and p3, q3, r3 and s3 are each independently an atomic fraction of an element, 0 < p3 < 1, 0 < q3 < 1, 0 < r3 < 1, 0 < s 3 < 1, p3 +q3+r3+s3=1) etc.) etc. are mentioned, These may be included individually, or two or more may be included.

Preferably, from the viewpoint of improving the capacity characteristics and stability of the battery, the lithium composite metal oxide is preferably a lithium composite metal oxide containing a metal containing nickel and lithium. Specifically, lithium-nickel-based oxide (eg, LiNiO ₂ ), lithium-nickel-manganese-cobalt oxide (eg, Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 ) Co _0.2 )O ₂ , or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , etc.), or lithium-nickel-cobalt-aluminum oxide (eg, Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ , etc.) In particular, lithium-nickel-manganese-cobalt oxide or lithium-nickel-cobalt-aluminum oxide, which is a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary material, is preferably used in view of cost. do.

It is preferable to contain a positive electrode active material in the quantity of 80-99 mass % with respect to the total mass of solid content in a positive electrode slurry. By making content of a positive electrode active material into the said range, high energy density and capacity can be obtained.

The binder is a component that assists bonding between the positive electrode active material and the conductive material and bonding to the current collector, and is preferably contained in an amount of 1 to 30 mass % based on the total mass of the solid content in the positive electrode slurry. Examples of binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxy propyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene- and propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber.

The conductive material is a material that imparts conductivity to the lithium secondary battery of the present invention without causing a chemical change, and is preferably contained in an amount of 0.5 to 50 mass %, and 1 to 20 mass % with respect to the total mass of solid content in the positive electrode slurry. It is more preferable to contain. By containing the conductive material in the content within the above range, electrical conductivity is improved, and high energy density and capacity can be obtained.

Examples of the conductive material include carbon powders such as carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black, single-walled carbon nanotube (SWCNT) and double-walled carbon nanotube (MWCNT); Graphite powder, such as natural graphite, artificial graphite, and graphite with a developed crystal structure; conductive fibers such as carbon fibers and metal fibers; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

The solvent is not limited as long as it can slurry the positive electrode active material, binder and conductive material as the positive electrode material, for example, NMP (N-methyl-2-pyrrolidone), DMF (dimethyl formamide), acetone, dimethyl An organic solvent such as acetamide and water can be used. In addition, the positive electrode slurry can be used in an amount that has an appropriate viscosity, for example, it can be used in an amount such that the solid content concentration in the slurry is 10% by mass to 60% by mass, preferably 20% by mass to 50% by mass.

The negative electrode used in the lithium secondary battery of the present invention may be prepared by, for example, coating a negative electrode slurry including a negative electrode active material, a binder, a conductive material and a solvent on a negative electrode current collector, drying and rolling.

The negative electrode current collector generally has a thickness of 3 to 500 µm. The negative electrode current collector is not particularly limited as long as it does not cause chemical change in the lithium secondary battery of the present invention and has high conductivity, for example, copper, stainless steel, aluminum, nickel, titanium, carbon dioxide, copper or stainless steel. One in which the surface of steel is surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. can be used. In addition, similar to the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, sheet, foil, mesh, porous body, foam and nonwoven body.

The anode active material includes lithium metal, a carbon material capable of reversibly occluding and releasing lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide. At least one or more selected from the group consisting of may be included.

The carbon material capable of reversibly occluding and releasing lithium ions is not particularly limited as long as it is a carbon-based negative active material generally used in lithium secondary batteries, and for example, crystalline carbon, amorphous carbon, or a combination thereof. is available. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite and artificial graphite. Examples of the amorphous carbon include soft carbon (low temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, and the like.

Metals or alloys of these metals and lithium include Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al. and a metal selected from the group consisting of Sn, or an alloy of these metals and lithium.

Examples of the metal composite oxide include PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ . , Bi ₂ O ₅ , Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), and Sn _x Me _1-x Me′ _y O _z (Me: Mn, Fe , Pb, Ge; Me': Al, B, P, Si, elements of groups 1, 2, and 3 of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8) One selected from the group consisting of can be used.

Examples of the material capable of doping and dedoping lithium include Si, SiO _x (0<x<2), Si-Y alloy (where Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, An element selected from the group consisting of transition metals, rare earth elements, and combinations thereof, and not Si), Sn, SnO ₂ , Sn-Y (where Y is an alkali metal, alkaline earth metal, group 13 element, group 14 an element selected from the group consisting of an element, a transition metal, a rare earth element, and _a combination thereof, and is not Sn); Element Y is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, It may be selected from the group consisting of Se, Te, Po, and combinations thereof.

Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

As the negative electrode active material of the lithium secondary battery of the present invention, it is preferable to use a material containing silicon, for example, Si, SiO _x (0<x<2), Si-Y alloy (here, Y is an alkali metal , alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, and an element selected from the group consisting of combinations thereof, not Si), and a mixture of at least one of these and SiO ₂ may be used. . In particular, it is more preferable to use SiO.

The negative electrode active material is preferably contained in an amount of 80 to 99 mass% with respect to the total mass of the solid content in the negative electrode slurry.

The binder is a component that assists bonding between the conductive material, the negative electrode active material and the current collector, and is preferably contained in an amount of 1 to 30 mass % with respect to the total mass of the solid content in the negative electrode slurry. Examples of binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxy propyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene- and propylene-diene-terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber.

A conductive material is a component for further improving the electroconductivity of a negative electrode active material, It is preferable to contain in the quantity of 1-20 mass % with respect to the total mass of solid content in a negative electrode slurry. The conductive material is not particularly limited as long as it does not induce a chemical change in the lithium secondary battery and has conductivity, for example, graphite such as natural graphite and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, farness black, lamp black and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

The solvent is not limited as long as the negative electrode active material, binder and conductive material can be slurried as the negative electrode material, and for example, organic solvents such as water, NMP and alcohol can be used. Moreover, the negative electrode slurry can be used in an amount which becomes an appropriate viscosity, for example, the solid content concentration in a slurry can be used in 50 mass % - 75 mass %, Preferably it can be used in the quantity used as 50 mass % - 65 mass %.

The separator of the lithium secondary battery of the present invention is responsible for blocking the internal short circuit between the two electrodes and impregnating the electrolyte, and after preparing a separator composition by mixing a polymer resin, a filler and a solvent, the separator composition is applied to the electrode A separator film may be formed by coating and drying directly on the upper part, and after casting and drying a separator composition on a support body, you may form by laminating the separator film peeled from a support body on the upper part of an electrode.

As the separator, common porous polymer films conventionally used as separators, for example, polyolefin-based films such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer A porous polymer film made of a polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric such as a high melting point glass fiber or a polyethylene terephthalate fiber may be used. not.

The pore diameter of the porous separator is generally 0.01 to 50 µm, and the porosity may be 5 to 95%. In addition, the thickness of the porous separator may be generally in the range of 5 to 300 µm.

It is preferable that the charging voltage of the lithium secondary battery of this invention is 4.0V or more, and it is more preferable that it is 4.1V or more. In addition, it is preferable that the positive electrode potential at the time of full charge of the lithium secondary battery of the present invention is 4.0V or more.

In addition, the initial capacity density per positive electrode of the lithium secondary battery of the present invention is preferably 180 mAh/g or more, and more preferably 185 mAh/g or more.

The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape, a square shape, a pouch shape, or a coin shape.

Further, the present invention relates to a method for reducing acid or moisture in a non-aqueous electrolytic solution, comprising adding (meth)acrylate having an isocyanate group or an amide bond to the non-aqueous electrolytic solution. The compound mentioned above can be used as (meth)acrylate which has an isocyanate group or an amide bond.

《Example》

Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples. However, the scope of the present invention is not limited to the examples.

(Example 1)

(1) Preparation of lithium secondary battery

<Manufacture of anode>

In N-methyl-2-pyrrolidone as a solvent, 96.5 parts by mass of a nickel-cobalt-manganese (NCM) ternary material Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ as a positive electrode active material, and 1.5 parts by mass of acetylene black as a conductive material A positive electrode slurry was prepared by dispersing 2 parts by mass and 2 parts by mass of polyvinylidene fluoride as a binder. The prepared positive electrode slurry was uniformly applied on an aluminum foil, heated and vacuum dried, and then pressed to prepare a positive electrode.

<Production of negative electrode>

96 parts by mass of a mixture of graphite and SiO as a negative electrode active material in a 9:1 ratio in water, 1.0 parts by mass of acetylene black as a conductive material, and 3.0 parts by mass of styrene-butadiene rubber and carboxymethyl cellulose as a binder to disperse the negative electrode slurry was prepared The prepared negative electrode slurry was uniformly apply|coated on copper foil, after heating and vacuum drying, it pressed and manufactured the negative electrode.

<Production of non-aqueous electrolyte solution>

A solvent containing 30 parts by volume of ethylene carbonate (EC) and 70 parts by volume of ethyl methyl carbonate (EMC) was used as the solvent, and LiPF ₆ was dissolved therein so that the salt concentration was 1 M to prepare a solution. To 100 parts by mass of the obtained solution, 0.5 parts by mass of 2-isocyanatoethyl methacrylate (manufactured by Showa Denko) (A1) as an acid or water reducing agent was added to obtain a non-aqueous electrolyte solution of the present invention.

<Manufacture of lithium secondary battery>

Using the positive electrode, the negative electrode, and the non-aqueous electrolyte solution prepared by the above method, a polyolefin film was used as a separator to produce a pouch-type battery having a facing area of 12 cm 2 .

(Example 2)

The same method as in Example 1 was followed except that 2-isocyanatoethyl acrylate (manufactured by Showa Denko) (A2) was added to the non-aqueous electrolyte solution instead of 2-isocyanatoethyl methacrylate. An electrolyte solution and a lithium secondary battery having the same were manufactured.

(Example 3)

In the same manner as in Example 1, except that 1,1-(bisacryloyloxymethyl)ethyl isocyanate (manufactured by Showa Denko) was added to the non-aqueous electrolyte instead of 2-isocyanatoethyl methacrylate, A non-aqueous electrolyte solution and a lithium secondary battery having the same were manufactured.

(Example 4)

Example except that 2-[0-(1'-methylpropylideneamino)carboxyamino]ethyl methacrylate (manufactured by Showa Denko) was added to the non-aqueous electrolyte solution instead of 2-isocyanatoethyl methacrylate In the same manner as in 1, a non-aqueous electrolyte solution and a lithium secondary battery including the same were prepared.

(Example 5)

In the same manner as in Example 1, except that 2-[0-(1'-methylpropylideneamino)carboxyamino]ethyl acrylate (manufactured by Showa Denko) was added to the non-aqueous electrolyte, the non-aqueous electrolyte and the same A lithium secondary battery was manufactured.

(Comparative Example 1)

In the same manner as in Example 1, except that 2-isocyanatoethyl methacrylate was not added to the non-aqueous electrolyte, a non-aqueous electrolyte and a lithium secondary battery including the same were prepared.

(2) Measurement of acid content

The electrolytic solutions of Examples 1 to 5 and Comparative Example 1 prepared in (1) were stored at 60° C. for 1 week, and the results of measuring the acid content before and after storage are shown in Table 1 below.

As can be seen from the results in Table 1, 2-isocyanatoethyl methacrylate, 2-isocyanatoethyl acrylate, 1,1-(bisacryloyloxymethyl)ethyl isocyanate, 2 Example 1 using an electrolyte containing -[0-(1'-methylpropylideneamino)carboxyamino]ethyl methacrylate or 2-[0-(1'-methylpropylideneamino)carboxyamino]ethyl acrylate At ∼5, the amount of acid content was suppressed and the amount of acid content did not increase after storage. In particular, in the non-aqueous electrolytic solution containing 2-isocyanatoethyl acrylate, no acid was detected before and after storage.

(3) charge/discharge cycle test

Using the lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 prepared in (1), charge and discharge cycle test at 45° C. with a constant current of 0.5 C with an upper limit voltage of 4.20 V and a lower limit voltage of 2.80 V was carried out However, in 50 cycles, 100 cycles, and 200 cycles, in order to check the correct capacity, the test was conducted using a constant current of 0.1C.

The relationship between the number of cycles and the capacity obtained as a result of the above test is shown graphically in FIG. 1 . 1 , Examples 1 and 2 and Comparative Example 1 showed a significant difference in terms of capacity maintenance from a relatively early stage, and in Comparative Example 1 in which no additive was added to the non-aqueous electrolyte, the capacity was significantly reduced. On the other hand, in the case of Examples 1 and 2 containing 2-isocyanatoethyl methacrylate (A1) or 2-isocyanatoethyl acrylate (A2) in the non-aqueous electrolyte solution, the capacity was maintained over a long period of time. was found to have an effect.

(4) battery resistance increase rate

Using the lithium secondary batteries of Examples 1 to 5 and Comparative Example 1 prepared in (1), the lithium secondary battery in a charged state was left at 60° C. for 4 weeks, and the battery resistance increase rate was measured. As a result, 200 cycles of charge and discharge Table 2 below shows the results of measuring the cell resistance increase rate of the lithium secondary battery subjected to the cycle test.

As can be seen from the results in Table 2, especially in Examples 1 and 2 in which electrolytes containing 2-isocyanatoethyl methacrylate or 2-isocyanatoethyl acrylate were used as non-aqueous electrolytes, after high-temperature storage And the increase in battery resistance after a cycle test was suppressed low, and it was excellent in stability.

In addition, in the lithium secondary batteries of Example 2 and Comparative Example 1 tested, the results of measuring the amount of metal detected by ICP emission spectroscopy from the negative electrode active material after the test are shown in Table 3 below.

The metal amount measurement result shown in Table 3 has shown the influence of metal elution from an anode. As can be seen from the results in Table 3, it was found that, in particular, in Example 2 using an electrolyte containing 2-isocyanatoethyl acrylate as a non-aqueous electrolyte, the elution of metals, particularly cobalt, could be suppressed under high temperature. .

The acid or moisture reducing agent of the present invention and the non-aqueous electrolyte solution containing the same suppress the generation of acid content, thereby suppressing the elution of the anode metal even under high-temperature conditions, and can maintain capacity even after repeated charging and discharging several times. It is useful because it can suppress the increase in resistance.

Claims (15)

An acid or moisture reducing agent for a non-aqueous electrolyte, comprising (meth)acrylate having an isocyanate group or an amide bond. The method of claim 1,
The (meth)acrylate having an isocyanate group or an amide bond is a (meth)acrylate having an isocyanate group. An acid or moisture reducing agent. According to claim 1,
An acid or moisture reducing agent, wherein the (meth)acrylate having an isocyanate group or an amide bond is selected from the following compounds:

. According to claim 1,
The (meth)acrylate having an isocyanate group or an amide bond is 2-isocyanatoethyl acrylate or 2-isocyanatoethyl methacrylate. An acid or moisture reducing agent. The non-aqueous electrolyte solution containing the acid or moisture reducing agent in any one of Claims 1-4. 6. The method of claim 5,
A non-aqueous electrolytic solution characterized in that the (meth)acrylate having an isocyanate group or an amide bond is contained in an amount of 0.1 to 1 mass % with respect to the total mass of the non-aqueous electrolytic solution. 6. The method of claim 5,
A non-aqueous electrolyte solution further comprising a cyclic carbonate and a chain carbonate. 6. The method of claim 5,
A non-aqueous electrolyte solution further comprising a lithium salt. 9. The method of claim 8,
The non-aqueous electrolyte solution, characterized in that the lithium salt contains LiPF ₆ . A lithium secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte according to claim 5 disposed between the positive electrode and the negative electrode. 11. The method of claim 10,
The lithium secondary battery, characterized in that the positive electrode comprises a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary material. 11. The method of claim 10,
A lithium secondary battery, characterized in that the negative electrode comprises a material containing silicon. A method for reducing acid or moisture in a non-aqueous electrolyte, comprising adding (meth)acrylate having an isocyanate group or an amide bond to the non-aqueous electrolyte. 14. The method of claim 13,
The (meth)acrylate having an isocyanate group or an amide bond is a (meth)acrylate having an isocyanate group. 14. The method of claim 13,
A method characterized in that the (meth)acrylate having an isocyanate group or an amide bond is selected from the following compounds:

.

Images