WO2024096414A1 - Lithium secondary battery - Google Patents

Abstract

A lithium secondary battery, according to embodiments of the present disclosure, comprises: a positive electrode comprising a positive electrode active material including lithium metal oxide particles in which the ratio of the number of moles of lithium to the total number of moles of metals excluding lithium is 1.05 or more; a negative electrode facing the positive electrode; and a non-aqueous electrolyte comprising a non-aqueous organic solvent and a lithium salt, wherein the content of a cyclic carbonate-based compound included in the non-aqueous electrolyte is less than 2% by weight compared to the total weight of the non-aqueous electrolyte.

Description

lithium secondary battery

The disclosure of this application relates to lithium secondary batteries.

Secondary batteries are batteries that can be repeatedly charged and discharged, and with the development of the information and communication and display industries, they are widely used as a power source for portable electronic communication devices such as camcorders, mobile phones, and laptop PCs. Additionally, recently, battery packs including secondary batteries have been developed and applied as a power source for eco-friendly vehicles such as hybrid vehicles.

Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, lithium secondary batteries have a high operating voltage and energy density per unit weight, and are advantageous for charging speed and weight reduction. In this regard, active research and development is underway.

The positive electrode active material of a lithium secondary battery may include a lithium-excessive positive electrode active material having a lithium molar ratio of 1.1 or more. The lithium-excessive positive electrode active material has high capacity characteristics, but requires high voltage operation, which may deteriorate its lifespan characteristics.

According to one aspect of the present disclosure, a lithium secondary battery with improved capacity characteristics and driving stability can be provided.

A lithium secondary battery according to exemplary embodiments includes a positive electrode containing a positive electrode active material containing lithium metal oxide particles, a negative electrode opposing the positive electrode, and a non-aqueous electrolyte solution containing a non-aqueous organic solvent and a lithium salt, The ratio of the number of moles of lithium contained in the lithium metal oxide particles to the total number of moles of metal excluding lithium contained in the lithium metal oxide particles is 1.05 or more, and the cyclic carbonate-based compound contained in the non-aqueous electrolyte solution relative to the total weight of the non-aqueous electrolyte solution. The content is less than 2% by weight.

In some embodiments, the cyclic carbonate-based compound may include at least one selected from the group consisting of ethylene carbonate, propylene carbonate, gamma-butyrolactone, and fluoroethylene carbonate.

In some embodiments, the non-aqueous electrolyte solution may not include the cyclic carbonate-based compound.

In some embodiments, the non-aqueous organic solvent may include a linear carbonate-based compound and a propionate-based compound.

In some embodiments, the content of the propionate-based compound relative to the total volume of the non-aqueous organic solvent may be 5 to 60% by volume.

In some embodiments, the content of the propionate-based compound relative to the total volume of the non-aqueous organic solvent may be 5 to 15% by volume.

In some embodiments, the propionate-based compound may include at least one selected from the group consisting of methyl propionate, ethyl propionate, and propyl propionate.

In some embodiments, the linear carbonate-based compound may include at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, and ethylpropyl carbonate.

In some embodiments, the lithium salt is at least one selected from the group consisting of lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium difluorophosphate (LiPO ₂ F ₂ ). may include.

In some embodiments, the lithium metal oxide particles may be represented by Formula 1 below.

[Formula 1]

Li _a [M _x Ni _y Mn _z ]O _b

In Formula 1, M is Co, Na, Ca, Y, Hf, Ta, Fe, B, Si, Ba, Ra, Mg, V, Ti, Al, Ru, Zr, W, Sn, Nb, Mo, Cu, At least one of Zn, Cr, Ga, V and Bi, 0≤x≤0.9, 0≤y≤0.9, x+y>0, 0.1≤z≤0.9, 1.8≤a+x+y+z≤2.2, 1.05≤a/(x+y+z)≤1.95 and 1.8≤b≤2.2.

The positive electrode according to embodiments of the present disclosure includes a positive electrode active material including lithium metal oxide particles containing excessive lithium. In this case, lithium may exist in the transition metal layer of the layered structure of lithium metal oxide particles. Accordingly, the capacity characteristics of the positive electrode active material can be improved.

According to exemplary embodiments, the lithium secondary battery includes a non-aqueous electrolyte solution. The content of the cyclic carbonate-based compound contained in the non-aqueous electrolyte solution is less than 2% by weight. Within the above range, the content of cyclic carbonate-based compounds that are easily decomposed in a high-voltage environment is reduced, so that life characteristics during high-voltage charging and discharging can be improved.

The lithium secondary battery of the present disclosure can be widely applied in green technology fields such as electric vehicles, battery charging stations, and solar power generation and wind power generation using other batteries. The lithium secondary battery of the present disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, etc. to prevent climate change by suppressing air pollution and greenhouse gas emissions.

1 and 2 are schematic plan views and cross-sectional views, respectively, showing lithium secondary batteries according to example embodiments.

Embodiments of the present disclosure provide a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte solution.

Hereinafter, embodiments of the present disclosure will be described in detail. However, this is merely illustrative and the present disclosure is not limited to the specific embodiments described as examples.

In exemplary embodiments, a lithium secondary battery includes a positive electrode, a negative electrode opposite the positive electrode, and a non-aqueous electrolyte solution.

The detailed structure of the lithium secondary battery will be described later with reference to FIGS. 1 and 2.

In exemplary embodiments, the positive electrode includes a positive electrode active material including lithium metal oxide particles containing excess lithium. For example, lithium may exist in the transition metal layer of the layered structure of lithium metal oxide particles. Accordingly, the capacity characteristics of the positive electrode active material can be improved similar to the theoretical capacity of the layered structure (250 mAh/g).

In exemplary embodiments, the ratio of the number of moles of lithium contained in the lithium metal oxide particles to the total number of moles of metal excluding lithium contained in the lithium metal oxide particles is 1.05 or more, and in some embodiments, is 1.2 or more. You can. Within the above range, lithium may sufficiently exist in the transition metal layer in addition to the lithium layer in the layered structure of lithium metal oxide particles.

In some embodiments, lithium metal oxide particles may be represented by Formula 1 below.

[Formula 1]

Li _a [M _x Ni _y Mn _z ]O _b

In Formula 1, M is Co, Na, Ca, Y, Hf, Ta, Fe, B, Si, Ba, Ra, Mg, V, Ti, Al, Ru, Zr, W, Sn, Nb, Mo, Cu, At least one of Zn, Cr, Ga, V and Bi, 0≤x≤0.9, 0≤y≤0.9, x+y>0, 0.1≤z≤0.9, 1.8≤a+x+y+z≤2.2, 1.05≤a/(x+y+z)≤1.95 and 1.8≤b≤2.2.

According to some embodiments, in Formula 1, 1.2≤a/(x+y+z)≤1.8. For example, a/(x+y+z) may mean the number of moles of lithium contained in the lithium metal oxide particles compared to the number of moles of transition metals contained in the lithium metal oxide particles.

In the a/(x+y+z) range, a sufficient amount of lithium is present in the transition metal layer, thereby improving capacity characteristics and suppressing an excessive decrease in the number of moles of the transition metal.

The chemical structure represented by Formula 1 represents a bonding relationship included in the layered structure or crystal structure of lithium metal oxide particles and does not exclude other additional elements. For example, M, Ni, and Mn in Chemical Formula 1 may serve as the main active elements of the positive electrode active material. Formula 1 is provided to express the bonding relationship of the main active elements and should be understood as encompassing the introduction and substitution of additional elements.

In one embodiment, in addition to the main active element, auxiliary elements to improve the chemical stability of the lithium metal oxide particles or the layered structure/crystal structure may be further included. The auxiliary elements may be incorporated together in the layered structure/crystal structure to form a bond, and in this case, it should be understood that they are included within the range of the chemical structure represented by Formula 1.

The auxiliary elements include, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, It may include at least one selected from the group consisting of Sn, Sr, Ba, Ra, P, and Zr. For example, the auxiliary element, such as Al, may act as an auxiliary active element that contributes to the capacity/output activity of the positive electrode active material together with Co or Mn.

The positive electrode active material may further include a coating element or a doping element. For example, elements substantially the same as or similar to the above-described auxiliary elements may be used as coating elements or doping elements. For example, any of the above-mentioned elements alone or in combination of two or more may be used as a coating element or a doping element.

The coating element or doping element may exist on the surface of the lithium metal oxide particle, or may penetrate through the surface of the lithium metal composite oxide particle and be included in the layered structure or bonded structure represented by Chemical Formula 1.

The positive electrode active material may include nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.

Ni may serve as a transition metal related to the output and capacity of lithium secondary batteries. Therefore, by adopting a high-Ni composition as the positive electrode active material as described above, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

However, as the Ni content increases, the long-term storage stability and lifetime stability of the positive electrode or secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. However, according to exemplary embodiments, electrical conductivity can be maintained by including Co, while life stability and capacity maintenance characteristics can be improved through Mn.

The content of Ni (for example, the mole fraction of nickel in the total number of moles of nickel, cobalt, and manganese) in the NCM-based lithium oxide may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

According to exemplary embodiments, the lithium secondary battery includes a non-aqueous electrolyte solution. For example, the non-aqueous electrolyte solution includes a non-aqueous organic solvent and a lithium salt.

For example, the positive electrode active material containing the above-described lithium metal oxide particles can be driven at a high voltage of 4.5 V or more. For example, lithium metal oxide particles having the composition of Formula 1 may be activated under a high voltage environment of 4.5 V or more.

In the comparative example, when the lithium secondary battery is driven in the high voltage environment, the non-aqueous electrolyte may be decomposed and the amount of gas generated may increase. Accordingly, the lifespan characteristics and driving stability of the lithium secondary battery may be reduced.

According to exemplary embodiments, the content of the cyclic carbonate-based compound contained in the non-aqueous electrolyte is less than 2% by weight. Within the above range, the content of cyclic carbonate-based compounds that are easily decomposed in a high-voltage environment is reduced, so that life characteristics during high-voltage charging and discharging can be improved.

According to one embodiment, the non-aqueous electrolyte solution may not contain a cyclic carbonate-based compound. Accordingly, gas generation due to decomposition of the non-aqueous electrolyte can be further suppressed.

The cyclic carbonate-based compounds include, for example, ethylene carbonate (EC), propylene carbonate (PC), gamma-butyrolactone (GBL), and fluoroethylene carbonate (FEC). ) may include at least one selected from the group consisting of.

According to some embodiments, the non-aqueous organic solvent may include a linear carbonate-based compound and a propionate-based compound.

For example, linear carbonate-based compounds include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), and ethylmethyl carbonate. , EMC), methylpropyl carbonate (MPC), and ethylpropyl carbonate (EPC).

For example, the oxidation resistance of the non-aqueous electrolyte is improved through the propionate-based compound, and the driving stability of the lithium secondary battery can be further improved.

The propionate-based compound is, for example, at least one selected from the group consisting of methyl propionate (MP), ethyl propionate (EP), and propyl propionate (PP). may include.

According to some embodiments, the content of the propionate-based compound relative to the total volume of the non-aqueous organic solvent may be 5 vol% to 60 vol% or 5 vol% to 15 vol%. Within the above range, ion conductivity can be improved while improving the oxidation resistance of the non-aqueous electrolyte solution.

In exemplary embodiments, a lithium salt may serve as the electrolyte. For example, the lithium salt can be expressed ^as Li ⁺

For example, the anion (X ^- ) of the lithium salt is

F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , Examples include CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

In some embodiments, the lithium salt is at least selected from the group consisting of lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF _6- ), and lithium difluorophosphate (LiPO ₂ F ₂ ). It can contain one. In this case, a film with excellent thermal stability can be formed on the electrode surface. Accordingly, the ionic conductivity and electrode protection characteristics of the non-aqueous electrolyte can be improved.

In one embodiment, the lithium salt may be included in a concentration of about 0.01M to 5M, or about 0.01M to 2M relative to the non-aqueous organic solvent. Within the above range, the transfer of lithium ions and/or electrons may be promoted during charging and discharging of a lithium secondary battery, thereby improving output characteristics.

Below, a lithium secondary battery including the positive electrode and non-aqueous electrolyte solution described above with reference to FIGS. 1 and 2 is provided.

Referring to Figures 1 and 2, a lithium secondary battery may include a positive electrode 100 containing a positive electrode active material containing the above-described lithium metal oxide particles and a negative electrode 130 opposing the positive electrode 100.

The positive electrode 100 may include a positive electrode current collector 105, and a positive electrode active material layer 110 disposed on at least one side of the positive electrode current collector 105 and containing a positive electrode active material containing the above-described lithium metal oxide particles. You can.

The positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector 105 may include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive electrode current collector 105 may be 10 ㎛ to 50 ㎛.

A positive electrode slurry can be prepared by mixing the positive electrode active material in a solvent. The positive electrode slurry may be coated on at least one side of the positive electrode current collector 105, then dried and rolled to manufacture the positive electrode active material layer 110. The coating includes methods such as gravure coating, slot die coating, multi-layer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting. can do. The positive active material layer 110 may further include a binder and optionally may further include a conductive material, a thickener, etc.

As the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. may be used.

The binder is polyvinylidenefluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethyl methacrylate ( polymethylmethacrylate), acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These may be used alone or in combination of two or more.

In one embodiment, a PVDF-based binder can be used as the anode binder. In this case, the amount of binder for forming the positive electrode active material layer 110 may decrease and the amount of positive electrode active material may relatively increase. Accordingly, the output characteristics and capacity characteristics of the secondary battery can be improved.

The conductive material may be added to improve the conductivity of the positive electrode active material layer 110 and/or the mobility of lithium ions or electrons. For example, the conductive material may be a carbon-based conductive material such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), carbon fiber, and/or tin, tin oxide, It may include a metal-based conductive material including perovskite materials such as titanium oxide, LaSrCoO ₃ , and LaSrMnO ₃ . These may be used alone or in combination of two or more.

The positive electrode slurry may further include a thickener and/or a dispersant. In one embodiment, the positive electrode slurry may include a thickener such as carboxymethyl cellulose (CMC).

The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 disposed on at least one side of the negative electrode current collector 125.

The negative electrode current collector 125 may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, etc. These may be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector 125 may be 10 ㎛ to 50 ㎛.

The negative electrode active material layer 120 may include a negative electrode active material. A material capable of adsorbing and desorbing lithium ions may be used as the negative electrode active material. For example, the negative electrode active material may include carbon-based materials such as crystalline carbon, amorphous carbon, carbon composite, and carbon fiber; lithium metal; lithium alloy; Silicon (Si)-containing materials or tin (Sn)-containing materials, etc. may be used. These may be used alone or in combination of two or more.

The amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber (MPCF), etc.

The crystalline carbon may include graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

The lithium metal may include pure lithium metal and/or lithium metal with a protective layer formed to inhibit dendrite growth. In one embodiment, a lithium metal-containing layer deposited or coated on the negative electrode current collector 125 may be used as the negative electrode active material layer 120. In one embodiment, a lithium thin film layer may be used as the negative electrode active material layer 120.

Elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, and indium. These may be used alone or in combination of two or more.

The silicon-containing materials can provide increased capacitance properties. The silicon-containing material may include Si, SiO _x (0<x<2), metal-doped SiO _x (0<x<2), silicon-carbon composite, etc.

The metal may include lithium and/or magnesium, and the metal-doped SiO _x (0<x<2) may include a metal silicate.

A negative electrode slurry can be prepared by mixing the negative electrode active material in a solvent. After coating/depositing the negative electrode slurry on the negative electrode current collector 125, the negative electrode active material layer 120 can be manufactured by drying and rolling. The coating includes methods such as gravure coating, slot die coating, multi-layer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting. can do. The negative electrode active material layer 120 may further include a binder and optionally may further include a conductive material, a thickener, etc.

Solvents included in the cathode slurry may include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc. These may be used alone or in combination of two or more.

The above-described materials that can be used in manufacturing the positive electrode 100 may be used as the binder, conductive material, and thickener.

In some embodiments, the negative electrode binder includes a styrene-butadiene-rubber (SBR)-based binder, carboxymethyl cellulose (CMC), polyacrylic acid-based binder, and polyethylenedioxythiophene (poly(). 3,4-ethylenedioxythiophene), PEDOT)-based binders, etc. may be used. These may be used alone or in combination of two or more.

In exemplary embodiments, a separator 140 may be interposed between the anode 100 and the cathode 130. The separator 140 may be configured to prevent an electrical short circuit between the anode 100 and the cathode 130 and to generate a flow of ions. For example, the thickness of the separator may be 10 ㎛ to 20 ㎛.

For example, the separator 140 may include a porous polymer film or a porous non-woven fabric.

The porous polymer film is an ethylene polymer, a propylene polymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer. It may include polyolefin-based polymers such as polymers. These may be used alone or in combination of two or more.

The porous nonwoven fabric may include high melting point glass fibers, polyethylene terephthalate fibers, etc.

The separator 140 may include a ceramic-based material. For example, inorganic particles can be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

The separator 140 may have a single-layer or multi-layer structure including the polymer film and/or non-woven fabric described above.

According to exemplary embodiments, an electrode cell is defined by an anode 100, a cathode 130, and a separator 140, and a plurality of electrode cells are stacked, for example, an electrode in the form of a jelly roll. Assembly 150 may be formed. For example, the electrode assembly 150 can be formed through winding, stacking, zigzag folding, stack-folding, etc. of the separator 140.

The electrode assembly 150 may be accommodated in the case 160 together with the non-aqueous electrolyte solution described above to form a lithium secondary battery.

Hereinafter, embodiments of the present disclosure will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended patent claims, and various changes and modifications to the examples are possible within the scope and technical idea of the present disclosure. It is obvious to those skilled in the art, and it is natural that such variations and modifications fall within the scope of the appended patent claims.

Example 1

(1) Manufacture of positive electrode active material

Distilled water from which dissolved oxygen was removed was added to the closed reactor, and NiSO ₄ ·6H ₂ O and MnSO ₄ ·H ₂ O were further added at a molar ratio of 38.1:61.9.

NaOH as a precipitant and NH ₄ OH as a chelating agent were additionally added to the reactor, and coprecipitation reaction was performed for 60 hours to prepare metal hydroxide particles.

The metal hydroxide particles were dried at 100° C. for 12 hours.

Dried metal hydroxide particles and lithium hydroxide were added to a dry mixer to prepare a mixture.

The mixing ratio of the metal hydroxide particles and lithium hydroxide was adjusted so that the composition of the manufactured lithium metal oxide particles according to inductively coupled plasma (ICP) analysis was Li _1.11 Ni _0.34 Mn _0.55 O ₂ .

The ICP analysis was performed using Agilent's 5800 ICP-OES device.

The mixture was placed in a firing furnace, the temperature of the firing furnace was raised to 250°C at 2°C/min, and maintained at 250°C for 3 hours (first firing).

After the first firing, the temperature of the furnace was raised to 850°C at a rate of 2°C/min, and the second firing was performed while maintaining the temperature at 850°C for 8 hours.

Oxygen gas was continuously passed through the furnace at a rate of 10 mL/min during the first and second calcinations.

After completion of firing, the fired product was naturally cooled to room temperature, pulverized and classified to prepare lithium metal oxide particles.

As a result of performing ICP analysis on the lithium metal oxide particle by normalizing the number of oxygen atoms to 2, it was confirmed to be Li _1.11 Ni _0.34 Mn _0.55 O ₂ .

The prepared lithium metal oxide particles were used as a positive electrode active material.

(2) Preparation of non-aqueous electrolyte

A non-aqueous electrolyte solution was prepared by dissolving LiPF ₆ at a concentration of 1.0 M in a mixed solvent of EMC/EP (90:10; volume ratio).

(3) Lithium secondary battery manufacturing

A lithium secondary battery was manufactured using the prepared positive electrode active material and non-aqueous electrolyte solution.

Specifically, a positive electrode slurry was prepared by mixing the prepared positive electrode active material, Denka Black as a conductive material, and PVDF as a binder in a mass ratio of 93:5:2, respectively. The positive electrode slurry was coated on an aluminum current collector (thickness: 15 ㎛), vacuum dried at 130°C, and then rolled to prepare a positive electrode.

Lithium metal (Li metal) with a thickness of 15 ㎛ was used as the cathode.

The anode and cathode manufactured as described above are notched and stacked in a circular shape with diameters of Φ14 and Φ16, respectively, and an electrode cell is formed by interposing a separator (polyethylene, thickness 13 ㎛) notched at Φ19 between the anode and the cathode. did. The electrode cell was placed in a coin cell exterior material with a diameter of 20 mm and a height of 1.6 mm and assembled by injecting an electrolyte solution, and was aged for more than 12 hours to allow the electrolyte solution to impregnate the inside of the electrode.

Chemical charging and discharging was performed on the lithium secondary battery manufactured as above (charging conditions CC-CV 1C 4.6V 0.05C CUT-OFF, discharging conditions CC 1C 2.0V CUT-OFF).

Examples 2 to 9

A positive electrode active material, a non-aqueous electrolyte solution, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the composition of the non-aqueous organic solvent was adjusted to be as shown in Table 1 below.

Example 10

The input amounts of LiOH·H ₂ O, NiSO ₄ ·6H ₂ O, CoSO ₄ ·7H ₂ O and MnSO ₄ ·H ₂ O were adjusted so that the composition of _the lithium metal oxide particles was Li _1.19 Ni _0.21 Co _{0.02 Mn} 0.58 0 2 Except for this, a positive electrode active material, a non-aqueous electrolyte solution, and a lithium secondary battery were prepared in the same manner as in Example 1.

Comparative Examples 1 to 3

A positive electrode active material, a non-aqueous electrolyte, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the composition of the non-aqueous organic solvent and the content of EC relative to the total weight of the non-aqueous electrolyte were adjusted to be as shown in Table 1 below.

Comparative Example 4

Same as Example ₁ , except that the input amounts of LiOH·H ₂ O, NiSO ₄ ·6H ₂ O, and MnSO ₄ ·H ₂ O were adjusted so that the composition of the lithium metal oxide particles was Li _1.02 Ni _0.38 Mn _0.60 O 2 A positive electrode active material, non-aqueous electrolyte solution, and lithium secondary battery were manufactured using this method.

Composition (chemical formula) of the positive electrode active material, ratio of the number of moles of lithium contained in the lithium metal oxide particles to the total number of moles of metal excluding lithium contained in the lithium metal oxide particles (Li/Me), composition of the non-aqueous electrolyte solvent (volume ratio), and The content of the cyclic carbonate-based compound is shown in Table 1 below.

division	positive electrode active material		non-aqueous electrolyte
	Composition (chemical formula)	Li/Me	Non-aqueous organic solvent composition (volume ratio)	Content of cyclic carbonate compounds (weight%)
Example 1	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	EMC:EP(90:10)	0
Example 2	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	DEC:EP(90:10)	0
Example 3	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	EMC:PP(90:10)	0
Example 4	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	EMC:EP(96:4)	0
Example 5	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	EMC:EP(35:65)	0
Example 6	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	EMC:EP(80:20)	0
Example 7	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	EMC:EP(70:30)	0
Example 8	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	EMC:EP(50:50)	0
Example 9	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	EMC:EP(40:60)	0
Example 10	Li 1.19 Ni 0.21 Co 0.02 Mn 0.58 0 2	1.47	EMC:EP(90:10)	0
Comparative Example 1	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	EC:EMC:DEC (25:45:30)	26.64
Comparative Example 2	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	FEC:EMC(10:90)	12.25
Comparative Example 3	Li 1.11 Ni 0.34 Mn 0.55 O 2	1.25	FEC:DMC(50:50)	51.84
Comparative Example 4	Li 1.02 Ni 0.38 Mn 0.60 O 2	1.04	EMC:EP(90:10)	0

Experiment example

(1) Measurement of gas generation - 45℃

The lithium secondary battery manufactured according to the above-described examples and comparative examples was charged (CC-CV 1C 4.6V 0.05C CUT-OFF) and left in a chamber at 45°C for 8 weeks. Afterwards, the lithium secondary battery was left at room temperature for 30 minutes and placed into a chamber to measure the amount of gas generated.

After forming a vacuum in the chamber, nitrogen gas was filled to create normal pressure, and the volume of nitrogen at normal pressure (V ₀ ) and the internal pressure of the chamber (P ₀ ) were measured.

After forming a vacuum again inside the chamber, a hole was drilled in the lithium secondary battery and left for 1 hour. Afterwards, the internal pressure (P ₁ ) of the chamber was measured and the amount of gas generated was measured by substituting the following equation.

Gas generation amount (mL) = (V ₀ /P ₀ )*P ₁

(2) Capacity maintenance rate evaluation - 45℃

Charging (CC/CV 1C 4.6V 0.05C CUT-OFF) and discharging (CC 1C 2.0V CUT-OFF) of the lithium secondary battery manufactured according to the above-described examples and comparative examples were repeated 100 times in a chamber at 45°C. did.

The capacity maintenance rate was calculated as a percentage by dividing the discharge capacity measured in the 100th discharge by the discharge capacity measured in the first discharge.

Capacity maintenance rate (%) = (100th discharge capacity/1st discharge capacity) × 100

(3) Initial discharge capacity measurement

Charging (CC/CV 0.1C 4.6V 0.05C CUT-OFF) and discharging (CC 0.1C 2.0V CUT-OFF) are performed once for the lithium secondary battery manufactured according to the above-described examples and comparative examples. The initial discharge capacity was measured.

The initial discharge capacity is defined as the absolute capacity (mAh) of the lithium secondary battery divided by the total weight (g) of the positive electrode active material in the battery.

The evaluation results are shown in Table 2 below.

division	Gas generation amount (45℃) (mL)	Capacity maintenance rate (45℃) (%, 100cyc)	initial discharge capacity (mAh/g)
Example 1	8.6	93.5	210
Example 2	8.3	93.3	210
Example 3	8.9	93.7	210
Example 4	13.7	92.5	210
Example 5	15.2	91.3	210
Example 6	9.1	92.9	210
Example 7	9.4	92.6	210
Example 8	10.2	92.5	210
Example 9	11.3	91.9	210
Example 10	9.0	92.8	247
Comparative Example 1	76.9	73.9	210
Comparative Example 2	55.3	80.1	210
Comparative Example 3	164.2	61.5	210
Comparative Example 4	8.5	92.1	140

Referring to Tables 1 and 2, in Examples containing less than 2% by weight of the cyclic carbonate-based compound based on the total weight of the non-aqueous electrolyte, the amount of gas generated in a high voltage environment was reduced and the capacity maintenance rate was improved compared to the Comparative Examples.

Additionally, in Examples using a positive electrode active material containing excess lithium, capacity characteristics were improved compared to Comparative Examples.

In Example 4, where the content of the propionate-based compound was less than 5% by volume relative to the total volume of the non-aqueous organic solvent, oxidation resistance was relatively lowered and the lifetime capacity retention rate was decreased.

In Example 5, where the content of the propionate-based compound exceeded 60% by volume relative to the total volume of the non-aqueous organic solvent, side reactions of the electrolyte solution relatively increased.

In Comparative Example 4, where the ratio of the number of moles of lithium contained in the lithium metal oxide particles to the total number of moles of metal excluding lithium contained in the lithium metal oxide particles is less than 1.05, the amount of lithium present in the transition metal layer of the layered structure is reduced compared to the Examples. And the initial capacity was lowered.

Claims (11)

1. A positive electrode containing a positive electrode active material containing lithium metal oxide particles;

   a cathode opposite the anode; and

   Comprising a non-aqueous electrolyte solution containing a non-aqueous organic solvent and a lithium salt,

   The ratio of the number of moles of lithium contained in the lithium metal oxide particles to the total number of moles of metal excluding lithium contained in the lithium metal oxide particles is 1.05 or more,

   A lithium secondary battery, wherein the content of the cyclic carbonate-based compound contained in the non-aqueous electrolyte is less than 2% by weight relative to the total weight of the non-aqueous electrolyte.
2. The lithium secondary battery according to claim 1, wherein the cyclic carbonate-based compound includes at least one selected from the group consisting of ethylene carbonate, propylene carbonate, gamma-butyrolactone, and fluoroethylene carbonate.
3. The lithium secondary battery according to claim 1, wherein the non-aqueous electrolyte solution does not include the cyclic carbonate-based compound.
4. The lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent includes a linear carbonate-based compound and a propionate-based compound.
5. The lithium secondary battery according to claim 1, wherein the content of the propionate-based compound relative to the total volume of the non-aqueous organic solvent is 5 vol% to 60 vol%.
6. The lithium secondary battery according to claim 5, wherein the content of the propionate-based compound relative to the total volume of the non-aqueous organic solvent is 5 vol% to 15 vol%.
7. The lithium secondary battery according to claim 4, wherein the propionate-based compound includes at least one selected from the group consisting of methyl propionate, ethyl propionate, and propyl propionate.
8. The lithium secondary battery according to claim 4, wherein the linear carbonate-based compound includes at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, and ethylpropyl carbonate.
9. The method of claim 1, wherein the lithium salt comprises at least one selected from the group consisting of lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium difluorophosphate (LiPO ₂ F ₂ ). Lithium secondary battery.
10. The lithium secondary battery according to claim 1, wherein the lithium metal oxide particles are represented by the following formula (1):

    [Formula 1]

    Li _a [M _x Ni _y Mn _z ]O _b

    (In Formula 1, M is Co, Na, Ca, Y, Hf, Ta, Fe, B, Si, Ba, Ra, Mg, V, Ti, Al, Ru, Zr, W, Sn, Nb, Mo, Cu , Zn, Cr, Ga, V and Bi, 0≤x≤0.9, 0≤y≤0.9, x+y>0, 0.1≤z≤0.9, 1.8≤a+x+y+z≤2.2 , 1.05≤a/(x+y+z)≤1.95 and 1.8≤b≤2.2).
11. The lithium secondary battery according to claim 10, wherein 1.2≤a/(x+y+z)≤1.8.

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