KR20220031290A - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery with improved battery performance at high temperatures including: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the positive electrode active material includes a lithium composite transition metal oxide including nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al), the non-aqueous electrolyte includes: a lithium salt; an organic solvent; lithium difluorophosphate as a first additive; and a compound represented by Chemical Formula 2 as a second additive; a content of the first additive is 0.1 wt% to 1.8 wt% based on the total weight of the non-aqueous electrolyte, and a content of the second additive is 0.05 wt% to 2.5 wt% based on the total weight of the non-aqueous electrolyte.

Description

Lithium secondary battery {LITHIUM SECONDARY BATTERY}

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery having improved high-temperature performance by strengthening the stability of the electrode film.

Lithium secondary batteries generally form an electrode assembly by interposing a separator between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode including a negative electrode active material capable of storing lithium ions, and the electrode It is manufactured by inserting the assembly into the battery case, injecting a non-aqueous electrolyte as a medium for transferring lithium ions, and then sealing the assembly.

Lithium secondary batteries can be miniaturized and have high energy density and operating voltage, so they are being applied to various fields such as mobile devices, electronic products, and electric vehicles. As the field of application of the lithium secondary battery is diversified, the required physical property conditions are gradually increasing, and in particular, there is a demand for the development of a lithium secondary battery that can be stably driven even in a high temperature condition.

At high temperatures, PF ₆ ⁻ anions may be thermally decomposed from lithium salts such as LiPF ₆ contained in the electrolyte to generate Lewis acids such as PF ₅ , which react with moisture to generate HF. Transition metals of the cathode material may be eluted into the electrolyte due to decomposition products such as PF ₅ and HF, and unstable structural changes of the anode due to charging and discharging. Do.

KR 10-2003-0061219 A

An object of the present invention is to provide a lithium secondary battery having less gas generation and improved battery performance at high temperatures by enhancing the stability of the electrode protective film in the lithium secondary battery.

According to one embodiment, the present invention provides a positive electrode comprising a positive electrode active material; a negative electrode comprising an anode active material; a separator interposed between the anode and the cathode; and a non-aqueous electrolyte;

The positive active material includes a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al),

The non-aqueous electrolyte may include a lithium salt; organic solvents; lithium difluorophosphate as a first additive; and a compound represented by the following formula (2) as a second additive,

The content of the first additive is 0.1 wt% to 1.8 wt% based on the total weight of the non-aqueous electrolyte,

The content of the second additive is 0.05 wt% to 2.5 wt% based on the total weight of the non-aqueous electrolyte.

[Formula 2]

In Formula 2,

n is 1 or 2,

R is hydrogen; halogen group; or an alkyl group having 1 to 10 carbon atoms.

The present invention maintains excellent performance even at high temperatures by using an electrolyte solution containing lithium difluorophosphate (LiDFP) and a compound represented by Formula 2 in an optimal content in the electrolyte solution together with a Ni-Co-Mn-Al-based positive electrode active material A lithium ion battery that does this can be realized.

Hereinafter, the present invention will be described in more detail.

Transition metals in the anode are easily eluted into the electrolyte due to decomposition products of the electrolyte and changes in the structure of the anode due to repeated charging and discharging. increase In addition, when the eluted transition metal moves to the negative electrode through the electrolyte, it is electrodeposited on the negative electrode and causes the destruction and regeneration of the SEI (solid electrolyte interphase) film, which causes problems such as consumption of lithium ions and increased resistance.

In addition, protective films are formed on the positive and negative electrodes due to the electrolyte reaction during initial activation of the battery. generate

Accordingly, the present inventors, lithium difluorophosphate (LiDFP) as an additive to the electrolyte; and a compound represented by the following formula 2, represented by prop-1-ene-1,3 sultone (PRS), and at the same time, a Ni-Co-Mn-Al-based lithium composite transition metal oxide was used as a positive electrode active material, It was confirmed that this leads to the improvement of stability and durability of the electrode film as well as the high-temperature performance of the battery. In particular, it was found that the optimal content of LiDFP and PRS was found, and if it was out of the range, the performance of the battery could be rather deteriorated.

a positive electrode including a positive electrode active material; a negative electrode comprising an anode active material; a separator interposed between the anode and the cathode; and a non-aqueous electrolyte, and the description of each configuration is as follows.

(1) non-aqueous electrolyte

The non-aqueous electrolyte of the present invention includes a lithium salt; organic solvents; lithium difluorophosphate (LiDFP) as a first additive; and a compound represented by the following formula (2) as a second additive.

[Formula 2]

In Formula 2,

n is 1 or 2,

R is hydrogen; halogen group; or an alkyl group having 1 to 10 carbon atoms.

(a) lithium salt

The lithium salt includes Li ⁺ as a cation, and F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , B ₁₀ Cl ₁₀ as an anion. ^- , AlCl ₄ ^- , AlO ₄ ^- , PF ₆ ^- , CF ₃ SO ₃ ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , AsF ₆ ^- , SbF ₆ ^- , CH ₃ SO ₃ ^- , (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , BF ₂ C ₂ O ₄ ^- , BC ₄ O ₈ ^- , BF ₂ C ₂ O ₄ CHF-, PF ₄ C ₂ O ₄ ^- , PF ₂ C ₄ O ₈ ^- , PO ₂ F ₂ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , C ₄ F ₉ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- and SCN ^- may include any one selected from the group consisting of.

Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiBF ₄ , LiFSI, LiTFSI, LiSO ₃ CF ₃ , LiPO ₂ F ₂ , lithium bis(oxalate)borate (LiBOB), lithium di Lithium difluoro(oxalate)borate (LiFOB), Lithium difluoro(bisoxalato)phosphate (LiDFBP), Lithium tetrafluoro(oxalate)phosphate (Lithium) It may be at least one selected from the group consisting of tetrafluoro(oxalate) phosphate, LiTFOP), and lithium fluoromalonato (difluoro) borate (LiFMDFB), preferably LiPF ₆ . LiPF ₆ is preferable as the lithium salt of the present invention from the viewpoint of being well soluble in a carbonate solvent and having high ionic conductivity.

The lithium salt may be contained in the non-aqueous electrolyte at a concentration of 0.5M to 2.0M, specifically, at a concentration of 1.0M to 1.5M. When the concentration of the lithium salt satisfies the above range, the lithium ion yield (Li ⁺ transference number) and the degree of dissociation of lithium ions may be improved, thereby improving the output characteristics of the battery.

If the concentration of the lithium salt is less than 0.5M, the mobility of lithium ions is reduced, so the effect of improving the low-temperature output and improving the cycle characteristics during high-temperature storage is insignificant. When the concentration of the lithium salt exceeds the concentration of 2.0M, the viscosity of the nonaqueous electrolyte is excessive increased, the non-aqueous electrolyte impregnation property may be deteriorated, and the film formation effect may be reduced.

(b) organic solvents

As the organic solvent, various organic solvents commonly used in lithium electrolytes may be used without limitation, but preferably, the organic solvent may include a cyclic carbonate-based solvent and a linear carbonate-based solvent.

The cyclic carbonate-based solvent is a high-viscosity organic solvent and has a high dielectric constant, so that it can well dissociate lithium salts in the electrolyte, and ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butyl It may be at least one selected from the group consisting of ene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate. Among them, ethylene carbonate (EC) may be included in terms of securing high ionic conductivity.

In addition, the linear carbonate-based solvent is an organic solvent having a low viscosity and a low dielectric constant, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methyl It may be at least one selected from the group consisting of propyl carbonate and ethylpropyl carbonate. Among them, ethylmethyl carbonate (EMC), which is preferable in terms of boiling point and viscosity, may be included.

In the present invention, the volume ratio of the cyclic carbonate-based solvent and the linear carbonate-based solvent may be 1:10 to 5:5, specifically 2:8 to 4:6.

In addition, the organic solvent has a low melting point in the cyclic carbonate-based solvent and/or the linear carbonate-based solvent in order to prepare an electrolyte solution having high ionic conductivity, and a linear ester-based solvent and/or a cyclic ester-based solvent having high stability at high temperature may further include.

The linear ester solvent may be at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate.

In addition, the cyclic ester solvent may be at least one selected from the group consisting of γ-butyrolactone, γ-buvalerolactone, γ-bucaprolactone, σ-valerolactone and ε-caprolactone.

Except for the organic solvent in the total weight of the non-aqueous electrolyte, the remainder except for the contents of the first additive, the second additive, and the lithium salt are all organic solvents unless otherwise specified.

(c) additives

The non-aqueous electrolyte of the present invention includes lithium difluorophosphate as a first additive; and a compound represented by Formula 2 as a second additive.

The lithium difluorophosphate forms a protective film containing LiF or PO bonds that are stable at high temperatures on the surface of the negative electrode, adsorbs on the surface of the positive electrode to stabilize the surface of the positive electrode, and suppresses the negative electrode side reaction of the electrolyte to improve the high temperature performance of the battery can play a role Specifically, the lithium ion component generated by decomposition during initial charging can form a stable SEI film on the surface of the anode, and by forming the SEI film, Li mobility to the anode can be improved, and the interfacial resistance can be lowered. . In particular, difluorophosphate anions generated by decomposition during initial charging are present on the surface of the positive electrode, stabilizing lattice oxygen of the positive electrode active material present on the surface of the positive electrode, and preventing further structural collapse.

The compound represented by Formula 2 serves to stabilize the battery by forming a film on the surface of the negative electrode through reduction and by forming a film on the surface of the positive electrode through oxidation.

When these two are used together, stable organic and inorganic protective films are formed on the cathode and anode to suppress gas generation due to oxidation of the electrolyte at high temperatures. When only the compound represented by Formula 2 is used without lithium difluorophosphate, a film centered on organic components is formed on the positive electrode. In the case of NCMA positive electrode, it is rich in Ni and is unstable at high temperature, so it is easy to decompose at high temperature. Since a lot of decomposition occurs, deterioration of the battery may be rather aggravated.

In an exemplary embodiment of the present invention, the compound represented by Formula 2 may be represented by any one of Formula 2-1 or 2-2, and preferably represented by Formula 2-1 below.

[Formula 2-1]

[Formula 2-2]

In Formulas 2-1 and 2-2,

R is hydrogen; halogen group; or an alkyl group having 1 to 10 carbon atoms.

In an exemplary embodiment of the present invention, R may be hydrogen or a methyl group, preferably hydrogen.

In addition, the compound represented by Formula 2 is prop-1-ene-1,3 sultone (prop-1-ene-1,3 sultone) and but-1-ene-1,3 sultone (but-1-ene) -1,4 sultone), and preferably prop-1-ene-1,3 sultone.

The content of the first additive is 0.1 wt% to 1.8 wt%, preferably 0.5 wt% to 1.5 wt%, more preferably 0.75 wt% to 1.2 wt%, based on the total weight of the non-aqueous electrolyte. When the content of the first additive is less than 0.1% by weight, there is a disadvantage in that a sufficient film is not formed and thus the performance improvement is insignificant. There may be problems that do not exist.

The content of the second additive is 0.05 wt% to 2.5 wt%, preferably 0.1 wt% to 0.5 wt%, more preferably 0.2 wt% to 0.25 wt% based on the total weight of the non-aqueous electrolyte. When the content of the second additive is less than 0.05% by weight, there is a disadvantage in that a sufficient film is not formed, so that the performance improvement is insignificant, and when the content of the second additive exceeds 2.5% by weight, the thickness of the film is too thick increases, and thus the resistance of the battery may also increase.

The weight ratio of the first additive and the second additive is 1:1 to 10:1, preferably 3:1 to 6:1. When the weight ratio of the first additive and the second additive is included in the above range, it is preferable in terms of improving battery performance at high temperature because it is possible to form a film in which an organic/inorganic component that is stable at high temperature without high resistance on the positive electrode is mixed. .

(d) third additive

On the other hand, the electrolyte for a lithium secondary battery according to the present invention forms a stable film on the surface of the negative electrode and the positive electrode without significantly increasing the initial resistance, suppresses the decomposition of the solvent in the non-aqueous electrolyte, and improves the mobility of lithium ions. It may additionally include a third additive that may play a role.

For example, the third additive may be a vinyl silane-based chemical, a phosphate-based compound, a sulfite-based compound, a sulfone-based compound, a sulfate-based compound, a sultone-based compound, a halogen-substituted carbonate-based compound, a nitrile-based compound, or a borate-based compound , and may include one or more compounds selected from the group consisting of lithium salt-based compounds.

The vinyl silane compound may be electrochemically reduced on the surface of the negative electrode to form a stable SEI, thereby improving battery durability. More specifically, the vinyl silane-based compound may include tetravinyl silane and the like.

The phosphate-based compound is electrochemically decomposed on the surfaces of the positive electrode and the negative electrode to help form the SEI film, and may improve the lifespan characteristics of the secondary battery. More specifically, lithium difluoro (bisoxalato) phosphate, tetramethyl trimethyl silyl phosphate (TMSPa), trimethyl silyl phosphite (TMSPi), tris (2,2,2-trifluoroethyl) phosphate (TFEPa) and tris(trifluoroethyl)phosphite (TFEPi).

The sulfite-based compound is ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfite at least one compound selected from the group consisting of phite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, and 1,3-butylene glycol sulfite may include

The sulfone-based compound may include at least one compound selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methylethyl sulfone, and methylvinyl sulfone.

The sulfate-based compound may include at least one compound selected from the group consisting of ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS). .

The sultone-based compound may include at least one compound selected from the group consisting of 1,3-propane sultone (PS) and 1,4-butane sultone, except for the compound represented by Formula 2 above.

As the halogen-substituted carbonate-based compound, fluoroethylene carbonate (FEC)) may be included.

In addition, the nitrile-based compound is succinonitrile (SN), adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptannitrile, cyclopentane carbonitrile, cyclohexane consisting of carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile and 4-fluorophenylacetonitrile It may include one or more compounds selected from the group.

The borate-based compound may include lithium oxalyldifluoroborate and the like.

The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and includes at least one compound selected from the group consisting of LiODFB, LiBOB (lithium bisoxalatoborate (LiB(C ₂ O ₄ ) ₂ ) and LiBF ₄ ). may include

The third additive may be included in an amount of 20 wt% or less, preferably 10 wt% or less, based on the total weight of the non-aqueous electrolyte. If the content of the additives exceeds the above range, side reactions in the electrolyte may excessively occur during charging and discharging of the lithium secondary battery, and may not be sufficiently decomposed at high temperature, and may exist as unreacted or precipitated in the non-aqueous electrolyte, Accordingly, the lifespan or resistance characteristics of the secondary battery may be reduced.

(2) anode

The positive electrode according to the present invention includes a positive electrode active material, and may be prepared by 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 has conductivity without causing a chemical change in the battery. For example, stainless steel; aluminum; nickel; titanium; calcined carbon; Alternatively, a surface treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used.

The positive active material may include a lithium composite transition metal oxide including nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al), and the lithium composite transition metal oxide may be represented by the following Chemical Formula 1 .

[Formula 1]

Li _x [Ni _y Co _z Mn _w Al _v M _p ]O ₂

In Formula 1,

M is W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B or Mo;

x, y, z, w, v and p are the atomic fractions of each element,

0.8≤x≤1.2, 0.7≤y<1, 0<z<0.3, 0<w<0.3, 0<v≤0.2, 0≤p<0.1,

y+z+w+v+p=1.

Where x means the atomic fraction of lithium relative to the total transition metal in the lithium composite transition metal oxide of Formula 1, and may be 0.8 to 1.2, preferably, 0.9 to 1.1.

In the lithium composite transition metal oxide of Formula 1, y means an atomic fraction of nickel among transition metals, and is 0.7 or more and less than 1, preferably 0.8 to less than 1, more preferably 0.82 to 0.98.

The z denotes the atomic fraction of cobalt in the transition metal in the lithium composite transition metal oxide of Formula 1, and is more than 0 and less than 0.3, preferably 0.01 or more and less than 0.3, more preferably 0.01 or more and less than 0.25.

The w denotes the atomic fraction of manganese in the transition metal in the lithium composite transition metal oxide of Formula 1, and is more than 0 and less than 0.3, preferably 0.01 or more and less than 0.3, more preferably 0.01 or more and less than 0.25.

In the lithium composite transition metal oxide of Formula 1, v means the atomic fraction of aluminum relative to the total transition metal, and may be greater than 0 and less than or equal to 0.2, preferably greater than or equal to 0 and less than or equal to 0.1. In this case, there is an advantage of improving the safety of an unstable positive electrode in a battery in which nickel is excessive.

In the lithium composite transition metal oxide of Formula 1, p denotes an atomic fraction of an additionally doped element among transition metals, and is 0 to 0.1.

The cathode active material may be included in an amount of 80 wt% to 99 wt%, specifically, 90 wt% to 99 wt%, based on the total weight of the solid content in the cathode slurry. In this case, when the content of the positive active material is 80% by weight or less, the energy density may be lowered, and thus the capacity may be lowered.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the solid content in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene , polyethylene, polypropylene, ethylene-propylene-diene ether monomer, styrene-butadiene rubber, fluororubber, or various copolymers thereof.

In addition, the conductive material is a material that imparts conductivity without causing a chemical change to the battery, and may be added in an amount of 0.5 to 20% by weight based on the total weight of the solid content in the positive electrode slurry.

Representative examples of the conductive material include carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; Graphite powder, such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

In addition, the solvent of the positive electrode slurry may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount having a desirable viscosity when the positive electrode active material and, optionally, a binder and a conductive material are included. can For example, the solid content concentration in the positive electrode slurry including the positive electrode active material and optionally the binder and the conductive material may be 10 wt% to 90 wt%, preferably 40 wt% to 85 wt%.

(3) cathode

The negative electrode may be prepared by 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, and then drying and rolling.

The negative electrode current collector generally has a thickness of 3 to 500 μm. Such a negative current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, copper; stainless steel; aluminum; nickel; titanium; calcined carbon; Copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc.; Alternatively, an aluminum-cadmium alloy or the like may be used. In addition, like 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, net, porous body, foam, non-woven body, and the like.

In addition, the negative active material may include lithium metal, a carbon material capable of reversibly intercalating/deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, and lithium doping and de-doping. It may include at least one selected from the group consisting of materials and transition metal oxides.

As a carbon material capable of reversibly intercalating/deintercalating lithium ions, any carbon-based negative active material generally used in lithium ion secondary batteries may be used without particular limitation, and representative examples thereof include crystalline carbon, Amorphous carbon or these may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon). or hard carbon, mesophase pitch carbide, and calcined coke.

Examples of the above 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 may be used.

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 or more selected from may be used.

Examples of materials capable of doping and dedoping lithium include Si, SiO _x (0<x≤2), Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, An element selected from the group consisting of rare earth elements and combinations thereof, but not Si), Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth) It is an element selected from the group consisting of elements and combinations thereof, and is not Sn), and at least one of these and SiO ₂ may be mixed and used. The 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, Ge, P, As, Sb, Bi, S, Se, It may be selected from the group consisting of Te, Po, and combinations thereof.

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

In the present invention, the negative active material is preferably graphite.

The negative active material may be included in an amount of 80% to 99% by weight based on the total weight of the solids in the negative electrode slurry.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the solid content in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene , polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, styrene-butadiene rubber-carboxymethylcellulose (SBR-CMC), or various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 0.5 wt % to 20 wt % based on the total weight of the solid content in the negative electrode slurry. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black. carbon powder; Graphite powder, such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The solvent of the negative electrode slurry is water; Alternatively, it may contain an organic solvent such as NMP or alcohol, and may be used in an amount that has a desirable viscosity when the negative electrode active material and optionally a binder and a conductive material are included. For example, the solid content concentration in the slurry including the negative electrode active material and optionally the binder and the conductive material may be 40 wt% to 75 wt%, preferably 40 wt% to 65 wt%.

(4) separator

The lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode.

The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and can be used without any particular limitation as long as it is normally used as a separator in a lithium secondary battery. Excellent is preferred.

Specifically, the separator is a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. Alternatively, a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

The lithium secondary battery according to the present invention as described above is a portable device such as a mobile phone, a notebook computer, a digital camera; and an electric vehicle field such as a hybrid electric vehicle (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium-to-large devices in a system for power storage.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a prismatic shape, a pouch type, or a coin type using a can.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source for a small device, but can also be preferably used as a unit cell in a medium or large battery module including a plurality of battery cells.

Hereinafter, the present invention will be described in detail through specific examples.

<Example: Preparation of lithium secondary battery>

Example 1.

(1) Preparation of non-aqueous electrolyte

A non-aqueous organic solution was prepared by dissolving LiPF ₆ (lithium hexafluorophosphate) to 1.2M in an organic solvent mixed with ethylene carbonate (EC):ethylmethyl carbonate (EMC) in a volume ratio of 3:7.

Then, based on 100% by weight of the non-aqueous electrolyte, 0.75% by weight of difluorophosphate (LiDFP), 0.25% by weight of prop-1-ene-1,3 sultone (PRS), 2% by weight of vinylene carbonate (VC), and ethylene sulfate (ESa) 1 wt% and 1,3-propane sultone (PS) 0.5 wt% were added and the balance was used as the non-aqueous organic solution to prepare a non-aqueous electrolyte.

(2) Lithium secondary battery manufacturing

Li[Ni _0.86 Co _0.05 Mn _0.07 Al _0.02 ]O ₂ as a cathode active material, carbon black as a conductive material, and polyvinylidene fluoride as a binder in a weight ratio of 98:0.7:1.3 to N-methyl-2-pyrrolidone as a solvent ( NMP) to prepare a positive electrode slurry (solid content 78.4 wt%). The positive electrode slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 15 μm, and dried and roll pressed to prepare a positive electrode.

In distilled water as a solvent, graphite as an anode active material (artificial graphite: natural graphite (8:2)), styrene-butadiene rubber-carboxymethylcellulose (SBR-CMC) as a binder, carbon black as a conductive material, and carboxymethylcellulose as a thickener After mixing sodium (CMC) in a weight ratio of 96.3:1.2:0.5:1, distilled water was mixed as a solvent to prepare a negative active material slurry having a solid content of 45.9% by weight. The negative electrode active material slurry was applied to a negative electrode current collector (Cu thin film) having a thickness of 8 μm, dried and rolled to prepare a negative electrode.

The positive electrode, the negative electrode, and the separator made of polypropylene/polyethylene/polypropylene (PP/PE/PP) were laminated in the order of the positive electrode/separator/negative electrode, and the laminated structure was placed in a pouch-type battery case and then the prepared non-aqueous electrolyte solution was injected to prepare a lithium secondary battery.

Example 2.

A lithium secondary battery was prepared in the same manner as in Example 1, except that the content of LiDFP was changed to 1.5 wt% during the preparation of the non-aqueous electrolyte.

Example 3.

A lithium secondary battery was prepared in the same manner as in Example 1, except that the content of LiDFP was changed to 1% by weight and the content of PRS to 0.2% by weight during the preparation of the non-aqueous electrolyte.

Comparative Example 1.

A lithium secondary battery was prepared in the same manner as in Example 1, except that LiDFP and PRS were not added during the preparation of the non-aqueous electrolyte.

Comparative Example 2.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that PRS was not added during the preparation of the non-aqueous electrolyte.

Comparative Example 3.

A lithium secondary battery was prepared in the same manner as in Example 1, except that LiDFP was not added during the preparation of the non-aqueous electrolyte.

Comparative Example 4.

LiDFP and PRS were not added when preparing the non-aqueous electrolyte, and Li[Ni _0.8 Co _0.1 Mn _0.1 ]O ₂ was used instead of Li[Ni _0.86 Co _0.05 Mn _0.07 Al _0.02 ]O ₂ as a positive electrode active material. A lithium secondary battery was manufactured in the same manner as in 1 .

Comparative Example 5.

A lithium secondary battery was prepared in the same manner as in Example 3, except that Li[Ni _0.8 Co _0.1 Mn _0.1 ]O ₂ was used instead of Li[Ni _0.86 Co _0.05 Mn _0.07 Al _0.02 ]O ₂ as a positive active material.

Comparative Example 6.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the content of LiDFP was changed to 2% by weight and the content of PRS to 3% by weight during the preparation of the non-aqueous electrolyte.

<Experimental Example: Evaluation of High-Temperature Storage of Lithium Secondary Battery>

Experimental Example 1. Measurement of capacity retention rate after high-temperature storage

For the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 5, formation was performed at a current of 200 mA (0.1 C rate), and then gas in the battery was removed (degas process). After transferring the degassed lithium secondary battery to a charge/discharger at room temperature (25°C), charging and 0.05C cut-off charging are performed under constant current/constant voltage conditions up to 4.2V at 0.33C rate, and discharge at 0.33C 2.5V did At this time, after each of the charging/discharging was performed 3 times, the discharge capacity was measured using a PNE-0506 charger/discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A), and the discharge capacity at this time was set as the initial discharge capacity did Then, after constant current/constant voltage charging up to 4.2V at 0.33C rate and 0.05C cut-off charging, it was stored at 60°C for 12 weeks.

Thereafter, the lithium secondary battery was transferred to a charger and discharger at room temperature (25° C.), charged at a rate of 0.33 C to 4.2 V under constant current/constant voltage conditions, and charged at 0.05 C cut off, and discharged at 0.33 C and 2.5 V. The discharge capacity after each of the charging/discharging was performed three times was measured using a PNE-0506 charger/discharger (manufacturer: PNE Solution, 5V, 6A). The discharge capacity at this time and the initial discharge capacity (100%) were compared to calculate the high-temperature capacity retention rate (%) and are shown in Table 1.

Experimental Example 2. Measurement of resistance increase rate after high temperature storage

For the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 5, formation was performed at a current of 200 mA (0.1 C rate), and then gas in the battery was removed (degas process). After transferring the degassed lithium secondary battery to a charge/discharger at room temperature (25°C), charging and 0.05C cut-off charging are performed under constant current/constant voltage conditions up to 4.2V at 0.33C rate, and discharge at 0.33C 2.5V was carried out. At this time, 50% of the SOC (State Of Charge) was set based on the discharge capacity after each of the three charging/discharging was performed at room temperature (25°C). At this time, a discharge pulse of 5A (2.5C) for 10 seconds The DC internal resistance was measured through the voltage drop that appears when (pulse) was applied (measured using a PNE-0506 charger/discharger (manufacturer: PNE Solution, 5V, 6A)), and the resistance at this time was set as the initial resistance. did

Thereafter, the lithium secondary battery was charged to 4.2V at a constant current/constant voltage condition at a rate of 0.33C at room temperature (25° C.) and a 0.05C cut-off charge was performed to fully charge it and stored at 60° C. for 12 weeks. After that, the lithium secondary battery was transferred to a charge/discharger at room temperature (25℃), set to 50% SOC (State Of Charge), and the voltage drop that appears when a discharge pulse is applied at 5A (2.5C) for 10 seconds The direct current internal resistance was measured (measured using a PNE-0506 charger/discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A)). This was compared with the initial resistance (0%) to calculate the resistance increase rate (%), and the results are shown in Table 1.

Experimental Example 3. Measurement of volume increase rate after high-temperature storage

For the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 5, the initial discharge capacity check of Experimental Example 1 was charged under constant current/constant voltage conditions up to 4.2V at 0.33C rate and 0.05C cut off After filling, the volume was measured by buoyancy method at room temperature. This was taken as the initial volume (0%). After the volumetric measurement was completed, the battery was stored at 60°C for 12 weeks, transferred to a charger and discharger at room temperature (25°C), and the capacity retention rate of Experimental Example 1 was measured. It was fully charged by performing C cut-off charging, and the volume was measured by the buoyancy method. This was compared with the initial volume (0%) to calculate the volume increase rate, and the results are shown in Table 1.

anode additive
(weight %) Experimental Example 1 Experimental Example 2 Experimental Example 3 DFP PRS Capacity retention rate (%) Resistance increase rate (%) Volume increase rate (%) Example 1 NCMA 0.75 0.25 93.47 -5.67 7.01 Example 2 NCMA 1.5 0.25 94.02 -6.66 5.97 Example 3 NCMA One 0.2 93.85 -6.03 6.23 Comparative Example 1 NCMA - - 92.36 8.22 10.29 Comparative Example 2 NCMA 0.75 - 93.00 -0.19 8.96 Comparative Example 3 NCMA - 0.25 91.42 37.44 12.96 Comparative Example 4 NCM - - 82.57 21.36 7.27 Comparative Example 5 NCM One 0.2 82.74 18.61 6.48

From the results of Table 1, the secondary batteries of Examples 1 to 3 including both the first additive and the second additive of the present invention did not include both additives (Comparative Example 1), as well as any one of the two It can be seen that the capacity retention rate, resistance increase rate, and volume increase rate are all improved compared to the case in which at least one is not included (Comparative Examples 2 and 3).

In particular, it can be seen that when both additives are not included and the positive electrode active material does not contain Al (Comparative Example 4), the characteristics are the worst, and even if both additives are used in an amount included in the scope of the present invention, the positive electrode active material When the active material does not contain Al (Comparative Example 5), it can be seen that the capacity retention rate is very low compared to the Example, and the resistance increase rate significantly increases.

Experimental Example 4. Measurement of initial resistance value

For the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Example 6, formation was performed at a current of 200 mA (0.1 C rate), and then gas in the battery was removed (degas process). After transferring the degassed lithium secondary battery to a charge/discharger at room temperature (25°C), charging and 0.05C cut-off charging are performed under constant current/constant voltage conditions up to 4.2V at 0.33C rate, and discharge at 0.33C 2.5V was carried out. At this time, 50% of the SOC (State Of Charge) was set based on the discharge capacity after each of the three charging/discharging was performed at room temperature (25°C). At this time, a discharge pulse of 5A (2.5C) for 10 seconds The DC internal resistance was measured through the voltage drop that appears when (pulse) was applied (measured using a PNE-0506 charger/discharger (manufacturer: PNE Solution, 5V, 6A)), and the resistance at this time was set as the initial resistance. did

anode additive
(weight %) Initial resistance (mohm) DFP PRS Example 1 NCMA 0.75 0.25 73.27 Example 2 NCMA 1.5 0.25 74.11 Example 3 NCMA One 0.2 72.86 Comparative Example 6 NCMA 2 3 116.25

Looking at Table 2, even if the positive active material includes both the first additive and the second additive of the present invention and the same material as in the embodiment is applied, when the content of the additive is outside the scope of the present invention, the initial resistance is very high. Able to know.

Claims (12)

a positive electrode including a positive electrode active material; a negative electrode comprising an anode active material; a separator interposed between the anode and the cathode; and a non-aqueous electrolyte;
The positive active material includes a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al),
The non-aqueous electrolyte may include a lithium salt; organic solvents; lithium difluorophosphate as a first additive; and a compound represented by the following formula (2) as a second additive,
The content of the first additive is 0.1 wt% to 1.8 wt% based on the total weight of the non-aqueous electrolyte,
The content of the second additive is 0.05 wt% to 2.5 wt% based on the total weight of the non-aqueous electrolyte lithium secondary battery:
[Formula 2]

In Formula 2,
n is 1 or 2,
R is hydrogen; halogen group; or an alkyl group having 1 to 10 carbon atoms.
The method according to claim 1,
The lithium composite transition metal oxide is a lithium secondary battery represented by the following formula 1:
[Formula 1]
Li _x [Ni _y Co _z Mn _w Al _v M _p ]O ₂
In Formula 1,
M is W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B or Mo;
x, y, z, w, v and p are the atomic fractions of each element,
0.8≤x≤1.2, 0.7≤y<1, 0<z<0.3, 0<w<0.3, 0<v≤0.2, 0≤p<0.1,
y+z+w+v+p=1.
3. The method according to claim 2,
In Formula 1, v is 0<v≤0.1 of a lithium secondary battery.
The method according to claim 1,
The compound represented by Formula 2 is prop-1-ene-1,3 sultone (prop-1-ene-1,3 sultone) and but-1-ene-1,3 sultone (but-1-ene-1) ,4 sultone) of at least one selected from a lithium secondary battery.
The method according to claim 1,
A weight ratio of the first additive to the second additive is 1:1 to 10:1.
6. The method of claim 5,
The weight ratio of the first additive and the second additive is 3:1 to 6:1 of a lithium secondary battery.
The method according to claim 1,
The content of the first additive is 0.5 wt% to 1.5 wt% based on the total weight of the non-aqueous electrolyte lithium secondary battery.
The method according to claim 1,
The content of the second additive is 0.1 wt% to 0.5 wt% based on the total weight of the non-aqueous electrolyte lithium secondary battery.
The method according to claim 1,
The organic solvent is a lithium secondary battery comprising a cyclic carbonate-based solvent and a linear carbonate-based solvent.
10. The method of claim 9,
The volume ratio of the cyclic carbonate-based solvent and the linear carbonate-based solvent is 1:10 to 5:5 of a lithium secondary battery.
The method according to claim 1,
The lithium salt is a lithium secondary battery comprising LiPF ₆ .
The method according to claim 1,
The negative active material is a lithium secondary battery comprising graphite.