Lithium secondary battery and method of manufacturing the same

Abstract

The present disclosure provides a lithium secondary battery and a method for manufacturing the same, comprising: a positive electrode comprising a positive active material comprising a lithium metal oxide comprising nickel (Ni); a negative electrode comprising a negative active material comprising artificial graphite; and an electrolyte comprising a solvent comprising propylene carbonate, wherein the ratio (B / A) of the volume ratio (B) of the propylene carbonate to the total volume of the solvent to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the negative active material is 0.01 to 0.15.

Description

Technology Field

[0001] The present disclosure relates to a lithium secondary battery and a method for manufacturing the same. Background Technology

[0002] Rechargeable batteries are batteries capable of repeated charging and discharging, and with the advancement of the information and communication and display industries, they are widely applied as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop PCs. Furthermore, recently, battery packs containing rechargeable batteries are also being developed and applied as power sources for eco-friendly vehicles, such as hybrid cars.

[0003] Among the aforementioned secondary batteries, active research and development is being conducted on lithium secondary batteries due to their high operating voltage and energy density per unit weight, as well as their advantages in charging speed and weight reduction.

[0004] Recently, research has been conducted on lithium secondary batteries using lithium nickel manganese oxide (LNMO) cathode materials. However, lithium secondary batteries using LNMO cathode materials generate more gas compared to other cathode materials under harsh conditions such as high-temperature storage and high-temperature cycling.

[0005] To reduce gas generation under harsh conditions in lithium secondary batteries equipped with lithium nickel manganese oxide (LNMO) cathode material, a method of increasing the content of propylene carbonate (PC) solvent in the electrolyte can be used.

[0006] However, due to the high reactivity of propylene carbonate solvent with graphite in the cathode, its decomposition products penetrate between the cathode graphite layers upon introduction, causing graphite delamination on the cathode surface. This delamination of the cathode surface graphite leads to problems such as reduced battery capacity, lifespan, and output performance of lithium-ion batteries. The problem to be solved

[0007] According to one aspect of the present disclosure, a lithium secondary battery in which graphite peeling does not occur on the negative electrode surface and a method for manufacturing the same can be provided.

[0008] According to another aspect of the present disclosure, a lithium secondary battery with reduced gas generation under harsh conditions and a method for manufacturing the same can be provided.

[0009] The lithium secondary battery of the present disclosure can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other applications utilizing batteries, such as solar power generation and wind power generation. Furthermore, 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. means of solving the problem

[0010] The present disclosure provides a lithium secondary battery comprising: a positive electrode comprising a positive active material comprising a lithium metal oxide comprising nickel (Ni); a negative electrode comprising a negative active material comprising artificial graphite; and an electrolyte comprising a solvent comprising propylene carbonate, wherein the ratio (B / A) of the volume ratio (B) of the propylene carbonate to the total volume of the solvent to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the negative active material is 0.01 to 0.15.

[0011] In one embodiment according to the present disclosure, the lithium secondary battery may have a ratio (B / A) of the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent relative to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the negative electrode active material, which is 0.05 to 0.15.

[0012] In one embodiment according to the present disclosure, the lithium secondary battery may have a weight ratio (A) of artificial graphite to the total weight of artificial graphite and natural graphite in the negative electrode active material of 50 to 100%.

[0013] In one embodiment according to the present disclosure, the lithium metal oxide may have a nickel content of 70 mol% or more among the total metals excluding lithium.

[0014] In one embodiment according to the present disclosure, the lithium metal oxide may have a cobalt content of less than 5 mol% among the total metals excluding lithium.

[0015] In one embodiment according to the present disclosure, the lithium metal oxide may be represented by the following chemical formula 1.

[0016] [Chemical Formula 1]

[0017] Li x Ni a Co b Mn c M d O 2+y

[0018] (In the above Chemical Formula 1, M is at least one element selected from the group consisting of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr, and 0.5≤x≤1.5, -1≤y≤1, 0.7≤a≤1, 0≤b≤0.05, 0≤c≤0.3, 0≤d≤0.3, and a+b+c+d=1.)

[0019] In one embodiment according to the present disclosure, the anode may have a layered structure.

[0020] In one embodiment according to the present disclosure, the lithium secondary battery may have a volume ratio (B) of the propylene carbonate relative to the total volume of the solvent of 3 to 15%.

[0021] In addition, the present disclosure provides a method for manufacturing a lithium secondary battery comprising: a step of manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a step of inserting the electrode assembly into a battery case and then injecting an electrolyte into the battery case, wherein the positive electrode comprises a positive active material comprising a lithium metal oxide comprising nickel (Ni), the negative electrode comprises a negative active material comprising artificial graphite, the electrolyte comprises a solvent comprising propylene carbonate, and the ratio (B / A) of the volume ratio (B) of the propylene carbonate to the total volume of the solvent to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the negative active material is 0.01 to 0.15.

[0022] In one embodiment according to the present disclosure, the ratio (B / A) of the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent relative to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the cathode active material may be 0.05 to 0.15.

[0023] In one embodiment according to the present disclosure, the weight ratio (A) of artificial graphite relative to the total weight of artificial graphite and natural graphite in the cathode active material may be 50 to 100%.

[0024] In one embodiment according to the present disclosure, the lithium metal oxide may have a nickel content of 70 mol% or more among the total metals excluding lithium.

[0025] In one embodiment according to the present disclosure, the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent may be 3 to 15%. Effects of the invention

[0026] According to one embodiment of the present disclosure, graphite peeling on the negative electrode surface of a lithium secondary battery can be prevented.

[0027] According to another embodiment of the present disclosure, a lithium secondary battery with reduced gas generation under harsh conditions can be provided. Brief explanation of the drawing

[0028] Figure 1 is a photograph of the cathode surface graphite after the formation process of Example 1 of the present disclosure. Figure 2 is a photograph of the cathode surface graphite after the formation process of Example 2 of the present disclosure. Figure 3 is a photograph of the cathode surface graphite after the formation process of Example 3 of the present disclosure. Figure 4 is a photograph of the cathode surface graphite after the formation process of Comparative Example 1 of the present disclosure. Figure 5 is a photograph of the cathode surface graphite after the formation process of Comparative Example 2 of the present disclosure. Figure 6 is a photograph of the cathode surface graphite after the formation process of Comparative Example 3 of the present disclosure. Figure 7 is a photograph of the cathode surface graphite after the formation process of Comparative Example 4 of the present disclosure. Figure 8 is a photograph of the cathode surface graphite after the formation process of Example 4 of the present disclosure. Figure 9 is a photograph of the cathode surface graphite after the formation process of Example 5 of the present disclosure. FIG. 10 is a photograph of the cathode surface graphite after the formation process of Example 6 of the present disclosure. Figure 11 is a photograph of the cathode surface graphite after the formation process of Comparative Example 5 of the present disclosure. FIG. 12 is a photograph of the cathode surface graphite after the formation process of Comparative Example 6 of the present disclosure. FIG. 13 is a photograph of the cathode surface graphite after the formation process of Comparative Example 7 of the present disclosure. Specific details for implementing the invention

[0029] The embodiments of the present disclosure provide a lithium secondary battery and a method for manufacturing the same.

[0030] The present disclosure will be described in detail below. However, this is merely illustrative and the present disclosure is not limited to the specific embodiments described illustratively.

[0031] Unless otherwise specifically indicated, the singular form of a term used in this disclosure may be interpreted to include the plural form.

[0032] The numerical ranges used in this disclosure include lower and upper limits and all values ​​within the range, increments logically derived from the form and width of the defined range, all of which are limited values, and all possible combinations of upper and lower limits of the numerical range defined in different forms. Unless specifically defined in this disclosure, values ​​outside the numerical range that may occur due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0033] The term "comprising" as used in this disclosure is an open description having an equivalent meaning to expressions such as "comprising," "containing," "having," and "characteristics," and does not exclude elements, materials, or processes not additionally listed.

[0034] The term 'formation process' as used in the present disclosure may be a process that imparts electrical characteristics to a lithium secondary battery to activate it and performs defect inspection, etc., after stabilizing the battery.

[0035] The term 'layered structure' as used in this disclosure may be a structure in which octahedral layers of lithium and transition metal surrounded by oxygen are regularly stacked.

[0036] lithium secondary battery

[0037] The present disclosure provides a lithium secondary battery comprising: a positive electrode comprising a positive active material comprising a lithium metal oxide comprising nickel (Ni); a negative electrode comprising a negative active material comprising artificial graphite; and an electrolyte comprising a solvent comprising propylene carbonate, wherein the ratio (B / A) of the volume ratio (B) of the propylene carbonate to the total volume of the solvent to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the negative active material is 0.01 to 0.15.

[0038] To reduce gas generation under harsh conditions in lithium secondary batteries, a method of increasing the content of propylene carbonate solvent in the electrolyte can be used. However, due to the high reactivity of propylene carbonate solvent with graphite in the anode, its decomposition products penetrate between the anode graphite layers upon introduction, causing graphite delamination on the anode surface. Specifically, this penetration occurs before the Solid Electrolyte Interphase (SEI) film is fully formed on the anode surface, generating propylene carbonate decomposition products between the graphite layers and inducing graphite delamination. As such graphite delamination occurs, the battery capacity, lifespan, and output performance of the lithium secondary battery can be severely degraded.

[0039] In the case of a lithium secondary battery in which the ratio (B / A) of the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent relative to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the negative electrode active material is 0.15 or less, the delamination of the graphite on the negative electrode surface can be prevented, thereby improving battery capacity, lifespan, and output performance.

[0040] The ratio (B / A) of the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent relative to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the cathode active material may be 0.00001 or more, 0.0001 or more, 0.001 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.15 or less, or a value between the above values, and specifically may be 0.01 to 0.15.

[0041] The ratio (B / A) of the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent relative to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the cathode active material may be 0.05 to 0.15.

[0042] In the case of a lithium secondary battery in which the ratio (B / A) of the volume ratio (B) of the propylene carbonate to the total volume of the solvent to the weight ratio (A) of the artificial graphite to the total weight of the artificial graphite and natural graphite in the negative electrode active material is 0.05 or higher, the amount of gas generated can be significantly reduced under harsh conditions.

[0043] The ratio (B / A) of the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent relative to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the cathode active material may be 0.05 or more, 0.07 or more, or 0.09 or more.

[0044] In one embodiment according to the present disclosure, the weight ratio (A) of artificial graphite to the total weight of artificial graphite and natural graphite in the cathode active material may be 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 100% or less, 95% or less, 90% or less, or 80% or less, and may be in the range of 30 to 100%, 50 to 100%, or 70 to 100%.

[0045] In one embodiment according to the present disclosure, the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent may be 0.5% or more, 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 7% or more, 10% or more, 12% or more, 14% or more, 25% or less, 20% or less, 18% or less, 15% or less, 13% or less, 11% or less, 10% or less, 8% or less, 6% or less, 5% or less, 4% or less, or an intermediate value between the above figures, and specifically may be 3 to 15%.

[0046] The lithium secondary battery of the present disclosure may be formed in other shapes, such as cylindrical or pouch types, in addition to the prismatic type. The lithium secondary battery is suitable for applications requiring high voltage and high output, such as electric vehicles, in addition to existing applications such as mobile phones and portable computers. Furthermore, the lithium secondary battery can be used in hybrid vehicles by combining it with existing internal combustion engines, fuel cells, supercapacitors, etc., and can be used in electric bicycles, power tools, and all other applications requiring high output and high voltage operation.

[0047] anode

[0048] The above anode may include an anode current collector and an anode composite layer disposed on at least one surface of the anode current collector.

[0049] The above anode composite layer may include an anode active material, an anode conductive material, and an anode binder.

[0050] The above-mentioned positive electrode active material may include a lithium metal oxide containing nickel (Ni). In one embodiment according to the present disclosure, the lithium metal oxide may have a nickel content of 30 mol% or more, 50 mol% or more, 70 mol% or more, 99 mol% or less, 95 mol% or less, 90 mol% or less, or 80 mol% or less among the total metals excluding lithium. Since the above-mentioned positive electrode active material contains a high content of nickel having a high capacity, the positive electrode to which the above-mentioned positive electrode active material is applied may have a high capacity and a high energy density.

[0051] In one embodiment according to the present disclosure, the lithium metal oxide may have a cobalt content of less than 5 mol%, less than 3 mol%, less than 1 mol%, or less than 0.5 mol% among the total metals excluding lithium. Additionally, the lithium metal oxide may not contain cobalt. The lithium secondary battery according to the present disclosure may use less cobalt, which is expensive among the lithium metal oxides. Therefore, economic feasibility can be secured when manufacturing the lithium secondary battery.

[0052] In one embodiment according to the present disclosure, the lithium metal oxide may be represented by the following chemical formula 1.

[0053] [Chemical Formula 1]

[0054] Li x Ni a Co b Mn c M d O 2+y

[0055] (In the above Chemical Formula 1, M is at least one element selected from the group consisting of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr, and 0.5≤x≤1.5, -1≤y≤1, 0.7≤a≤1, 0≤b≤0.05, 0≤c≤0.3, 0≤d≤0.3, and a+b+c+d=1.)

[0056] In one embodiment, the lithium metal oxide is, for example, LiNi 0.75 Mn 0.25 O 2, LiNi 0.765 Co 0.015 Mn 0.22 It may be O2 or a mixture thereof.

[0057] Additionally, the lithium metal oxide may be coated or doped with at least one selected from the group consisting of Al, Ti, Ba, Zr, Si, B, Mg, P, V, W, alloys thereof, and oxides thereof. Accordingly, the structural stability, thermal stability, and electronic conductivity of the lithium metal oxide are improved, and at least one selected from the group acts as a physical barrier, thereby reducing adverse reactions of the lithium metal oxide with the electrolyte.

[0058] Meanwhile, the lithium metal oxide may include nickel, and in the charged state, oxygen of the lithium metal oxide may be oxidized, and the oxidized oxygen may react with the electrolyte to generate gas at high temperatures. In exemplary embodiments, the gas may include carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), ethane (C2H6), propane (C3H8), propene (C3H6), acetylene (C2H2), ethylene (C2H4), and hydrogen (H2).

[0059] The above-mentioned positive electrode active material may include lithium metal oxide in the form of a single particle or lithium metal oxide in the form of a secondary particle. Here, the single particle form may mean, for example, excluding secondary particles formed substantially as a single particle by assembling or aggregating a plurality of primary particles (e.g., more than 10). However, the single particle form does not exclude the formation of a substantially monolithic form (e.g., a structure converted into a single particle) in which 2 to 10 single particles are attached or closely bonded to each other.

[0060] In the case of lithium metal oxide in the form of a single particle, cracks do not occur during the charging and discharging of the secondary battery, and accordingly, the generation of gas is reduced, thereby preventing swelling of the secondary battery, and thus the lifespan characteristics, storage characteristics, and stability of the secondary battery can be improved.

[0061] In one embodiment, the positive active material may be about 95 to about 99.5 wt% based on the total weight of the positive composite layer.

[0062] The positive electrode conductive material is used to impart conductivity to the positive electrode, and any material commonly used in secondary batteries may be used without limitation. The positive electrode conductive material may be a conductive material comprising, for example, carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc., metal-based materials such as metal powder or metal fiber such as copper, nickel, aluminum, silver, etc., conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0063] In one embodiment, the anode conductive material may be about 0.1 to about 2.5 wt% based on the total weight of the anode composite layer.

[0064] The anode binder may not be particularly limited as long as it is a component that assists in the bonding of the anode active material, the anode conductive material, etc., and the bonding to the anode current collector. The anode binder may include, for example, at least one selected from the group consisting of polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl methylcellulose (HPMC), polyvinyl pyrrolidone, polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), non-aromatic hydrocarbon butadiene rubber, and fluorinated rubber.

[0065] In one embodiment, the anode binder may be about 0.5 to about 3 wt% based on the total weight of the anode composite layer.

[0066] The positive current collector is a material commonly used in the manufacture of the positive electrode of a secondary battery, and can be used without special restrictions as long as it is conductive and does not cause chemical changes within the secondary battery. For example, the positive current collector may be a plate or foil made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.

[0067] In one embodiment according to the present disclosure, the anode may have a layered structure. The layered structure may be a structure in which octahedral layers in which lithium and a transition metal are surrounded by oxygen are regularly stacked. Since the anode has a layered structure, lithium ions can move between the layers during charging and discharging, thereby improving the electrochemical performance of the lithium secondary battery.

[0068] cathode

[0069] The above cathode may include a cathode current collector and a cathode composite layer formed on at least one surface of the cathode current collector.

[0070] The above cathode composite layer may include a cathode active material, a cathode conductive material, and a cathode binder.

[0071] The above-mentioned negative electrode active material may include a carbon-based active material.

[0072] The above carbon-based active material is not specifically limited, but may include one or more selected from the group consisting of, for example, artificial graphite, natural graphite, and graphitized mesocarbon micro beads.

[0073] In exemplary embodiments, the carbon-based active material may comprise artificial graphite alone, or may comprise artificial graphite and natural graphite.

[0074] In one embodiment according to the present disclosure, the weight ratio (A) of artificial graphite to the total weight of artificial graphite and natural graphite in the cathode active material may be 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 100% or less, 95% or less, 90% or less, or 80% or less, and may be in the range of 30 to 100%, 50 to 100%, or 70 to 100%.

[0075] If the weight ratio (A) of artificial graphite relative to the total weight of artificial graphite and natural graphite in the above cathode material satisfies the range of 50 to 100%, graphite peeling on the cathode surface can be prevented.

[0076] The above negative electrode active material may further include a silicon-based active material in addition to the carbon-based active material. The above negative electrode active material may include the silicon-based active material having a higher discharge capacity compared to the carbon-based active material, thereby improving the capacity and energy density of the negative electrode.

[0077] The above silicon-based active material can be suitably used in the present invention if it is a material that can be conventionally used as a negative electrode active material, for example, SiO x (0 <x<2), Si-C 복합체 및 Si-Y 합금(여기서, Y는 알칼리 금속, 알칼리 토금속, 전이금속, 13족 원소, 14족 원소, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소임)으로 이루어진 군에서 선택되는 적어도 어느 하나를 포함할 수 있다. 일 실시예에 있어서, 상기 규소계 활물질은 SiO x (0 <x<2) 또는 Si-C 복합체를 포함할 수 있다.

[0078] In exemplary embodiments, the negative electrode active material may comprise about 1 to about 15 wt% of the silicon-based active material based on the total weight of the negative electrode active material.

[0079] The cathode conductive material is used to impart conductivity to the cathode, and any material commonly used in secondary batteries may be used without limitation. The cathode conductive material may include, for example, one or more selected from the group consisting of graphite, carbon black, carbon nanotubes, metal powder, and conductive oxide.

[0080] In one embodiment, the cathode conductive material may be about 0.05 to about 5 wt% based on the total weight of the cathode composite layer.

[0081] The above-mentioned cathode binder may not be particularly limited as long as it is a component that assists in the bonding of the cathode active material, the cathode conductive material, etc., and the bonding to the cathode current collector. The above-mentioned cathode binder may include at least one type selected from the group consisting of rubber-based binders and water-soluble polymer-based binders.

[0082] The above rubber-based binder may be one that is not soluble in water-based solvents such as water but has water dispersibility capable of smooth dispersion in water-based solvents, and may include, for example, at least one selected from styrene butadiene rubber (SBR), hydrogenated nitrile butadiene rubber (HNBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, and fluoro rubber. Specifically, it may include at least one selected from the group consisting of styrene butadiene rubber and hydrogenated nitrile butadiene rubber, more specifically, styrene butadiene rubber, in terms of ease of dispersion and excellent phase stability.

[0083] In addition, the above-mentioned water-soluble polymer-based binder is soluble in an aqueous solvent such as water and may include, for example, at least one selected from polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyacrylamide (PAM), and carboxymethylcellulose (CMC). In one embodiment, the cathode binder may be about 0.5 to about 6 wt% based on the total weight of the cathode composite layer.

[0084] The above-mentioned negative current collector is commonly used in the manufacture of negative electrodes for secondary batteries and can be used without special restrictions as long as it is conductive and does not cause chemical changes within the secondary battery. Examples of the above-mentioned negative current collectors may include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys. Additionally, fine irregularities may be formed on the surface to strengthen the bonding strength of the negative active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics may be used.

[0085] electrolytes

[0086] A lithium secondary battery can be defined by housing an electrode assembly together with an electrolyte within a case. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

[0087] The above-mentioned non-aqueous electrolyte comprises a lithium salt as an electrolyte and a solvent, and the lithium salt is, for example, Li + X - It is expressed as and the anion (X) of the above lithium salt -As F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Examples of the back can be given.

[0088] The above solvent may include an organic compound that has sufficient solubility for the lithium salt and additive and does not have reactivity in the battery. As an example of the above solvent, it may include at least one of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.As the above solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, and tetraethylene glycol Dimethyl ether (tetraethylene glycol dimethyl ether, TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF) and 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, and propylene sulfite may be used. These may be used alone or in combination of two or more. Specifically, the solvent may include propylene carbonate (PC).

[0089] In particular, when propylene carbonate (PC) is used as the solvent, the amount of gas generated can be reduced under harsh conditions such as high-temperature storage and high-temperature cycles.

[0090] In one embodiment according to the present disclosure, the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent may be 0.5% or more, 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 7% or more, 10% or more, 12% or more, 14% or more, 25% or less, 20% or less, 18% or less, 15% or less, 13% or less, 11% or less, 10% or less, 8% or less, 6% or less, 5% or less, 4% or less, or an intermediate value between the above figures, and specifically may be 3 to 15%.

[0091] If the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent satisfies the range of 3 to 15%, the amount of gas generated under harsh conditions can be significantly reduced.

[0092] The above-mentioned non-aqueous electrolyte may further include additives. The additives may include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sulfone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate compounds.

[0093] The above-mentioned cyclic carbonate compounds may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0094] The above fluorine-substituted cyclic carbonate compounds may include fluoroethylene carbonate (FEC), etc.

[0095] The above sulfone-based compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0096] The above-mentioned cyclic sulfate compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0097] The above-mentioned cyclic sulfite compounds may include ethylene sulfite, butylene sulfite, etc.

[0098] The above phosphate-based compounds may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0099] The above borate-based compounds may include lithium bis(oxalate) borate, etc.

[0100] Separator

[0101] A separator may be interposed between the anode and the cathode. The separator may be configured to prevent an electrical short circuit between the anode and the cathode and to allow for the flow of ions. According to an embodiment, the thickness of the separator may be 10 μm to 20 μm, but the present disclosure is not limited thereto.

[0102] For example, the separator may comprise a porous polymer film or a porous nonwoven fabric. The porous polymer film may comprise polyolefin-based polymers such as ethylene polymer, propylene polymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. The porous nonwoven fabric may comprise high-melting-point glass fibers, polyethylene terephthalate fibers, etc. The separator may also comprise ceramic-based materials. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0103] The separator may have a single-layer or multi-layer structure comprising the aforementioned polymer film and / or nonwoven fabric.

[0104] Method for manufacturing a lithium secondary battery

[0105] In addition, the present disclosure provides a method for manufacturing a lithium secondary battery comprising: a step of manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a step of inserting the electrode assembly into a battery case and then injecting an electrolyte into the battery case, wherein the positive electrode comprises a positive active material comprising a lithium metal oxide comprising nickel (Ni), the negative electrode comprises a negative active material comprising artificial graphite, the electrolyte comprises a solvent comprising propylene carbonate, and the ratio (B / A) of the volume ratio (B) of the propylene carbonate to the total volume of the solvent to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the negative active material is 0.01 to 0.15.

[0106] The description of the above lithium secondary battery may be applied in the same way to the description of the manufacturing method of the lithium secondary battery to the extent of overlap.

[0107] In one embodiment according to the present disclosure, the anode, the cathode, and the separator may be repeatedly arranged to form an electrode assembly.

[0108] The above electrode assembly may be a winding type, a stacking type, a zigzag folding (z-folding) type, or a stack-folding type.

[0109] In the above method for manufacturing a lithium secondary battery, the ratio (B / A) of the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent relative to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the negative electrode active material may be 0.05 to 0.15.

[0110] The above method for manufacturing a lithium secondary battery may have a weight ratio (A) of artificial graphite relative to the total weight of artificial graphite and natural graphite in the negative electrode active material of 50 to 100%.

[0111] The above lithium metal oxide may have a nickel content of 70 mol% or more among the total metals excluding lithium.

[0112] The above method for manufacturing a lithium secondary battery may have a volume ratio (B) of the propylene carbonate relative to the total volume of the solvent of 3 to 15%.

[0113] In the following, embodiments of the present invention are further described with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are merely illustrative of the present invention and are not intended to limit the appended claims. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and spirit of the present invention, and that such variations and modifications fall within the scope of the appended claims.

[0114] Example 1

[0115] Manufacturing of anodes

[0116] Based on the weight of the solids, a cathode slurry was prepared by mixing 97.86 wt% of single-particle lithium nickel manganese oxide (LNMO) with a nickel-to-manganese molar ratio of 75:25 as the cathode active material, 1 wt% of polyvinylidene fluoride (PVDF) binder, and 1.14 wt% of carbon nanotubes (CNT) and carbon black conductive material in an N-methyl-2-pyrrolidone (NMP) solvent.

[0117] An anode was manufactured by applying the prepared anode slurry to both sides of an aluminum foil, drying it, and then rolling it.

[0118] Manufacturing of the cathode

[0119] A cathode slurry was prepared by dispersing synthetic graphite, natural graphite, styrene butadiene rubber (SBR), and carboxymethylcellulose (CMC) in distilled water in a weight ratio of 97.4 : 0 : 1.4 : 1.2.

[0120] A cathode was manufactured by applying a manufactured cathode slurry to an area excluding the protrusion (cathode tab) of a copper foil including a protrusion on one side, and then drying and rolling it.

[0121] Preparation of electrolyte

[0122] An electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 26:4:70.

[0123] Manufacturing of lithium secondary batteries

[0124] An electrode assembly was manufactured by interposing a polyolefin separator between the anode and cathode manufactured above, and the manufactured electrode assembly was inserted into a pouch for a secondary battery, after which the electrolyte manufactured above was injected into the pouch for the secondary battery and sealed to manufacture a lithium secondary battery.

[0125] Example 2

[0126] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 25:5:70.

[0127] Example 3

[0128] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 15:15:70.

[0129] Comparative Example 1

[0130] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:0:70.

[0131] Comparative Example 2

[0132] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 14:16:70.

[0133] Comparative Example 3

[0134] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 10:20:70.

[0135] Comparative Example 4

[0136] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 5:25:70.

[0137] Example 4

[0138] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a negative electrode slurry was prepared by dispersing artificial graphite, natural graphite, styrene butadiene rubber (SBR), and carboxymethylcellulose (CMC) in distilled water in a weight ratio of 68.18:29.22:1.4:1.2, and an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 27:3:70.

[0139] Example 5

[0140] A lithium secondary battery was prepared in the same manner as in Example 4, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 26:4:70.

[0141] Example 6

[0142] A lithium secondary battery was prepared in the same manner as in Example 4, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 20:10:70.

[0143] Comparative Example 5

[0144] A lithium secondary battery was prepared in the same manner as in Example 4, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:0:70.

[0145] Comparative Example 6

[0146] A lithium secondary battery was prepared in the same manner as in Example 4, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 19:11:70.

[0147] Comparative Example 7

[0148] A lithium secondary battery was prepared in the same manner as in Example 4, except that an electrolyte was prepared by dissolving 1.0 M LiPF6 in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 15:15:70.

[0149] Experimental Example

[0150] 1. Measurement of graphite peeling on the cathode surface

[0151] After removing the pouch from the cell (SOC 30%) that was shipped following the formation process, the jelly roll was unfolded to separate the positive and negative electrodes and the separator, and the condition of the negative electrode surface was visually inspected. The results regarding graphite peeling on the negative electrode surface are shown in Table 1.

[0152] FIGS. 1 to 3 are photographs of the cathode graphite surface after the formation process of Examples 1 to 3, FIGS. 4 to 7 are photographs of the cathode graphite surface after the formation process of Comparative Examples 1 to 4, FIGS. 8 to 10 are photographs of the cathode graphite surface after the formation process of Examples 4 to 6, and FIGS. 11 to 13 are photographs of the cathode graphite surface after the formation process of Comparative Examples 5 to 7.

[0153] 2. Measurement of Gas Generation and Calculation of Gas Generation Reduction Rate

[0154] Among the lithium secondary batteries prepared according to each example and comparative example, the lithium secondary battery in which graphite peeling did not occur on the negative electrode surface was charged to 100% state of charge (SOC) under 0.3C, 4.2V, and 0.05C cut-off conditions, and then stored at a high temperature of 60°C for 12 weeks (84 days).

[0155] To measure the amount of gas generated, a battery that had completed high-temperature storage was placed in a vacuum chamber, air was injected, and the amount of gas generated from the battery was measured through the air pressure inside the chamber. The results are shown in Table 1 below.

[0156] The gas generation reduction rate of Examples 1 to 3 was calculated based on the gas generation rate of Comparative Example 1, in which propylene carbonate was not included in the electrolyte. The gas generation reduction rate of Examples 4 to 6 was calculated based on the gas generation rate of Comparative Example 5, in which propylene carbonate was not included in the electrolyte.

[0157] A B B / A Whether peeling Gas production (mL) Gas generation reduction rate Example 1 100% 4% 0.04 X 219.6 1.3% Example 2 100% 5% 0.05 X 184.1 17.2% Example 3 100% 15% 0.15 X 147.2 33.8% Comparative Example 1 100% 0% 0 X 222.4 0% Comparative Example 2 100% 16% 0.16 O - - Comparative Example 3 100% 20% 0.2 O - - Comparative Example 4 100% 25% 0.25 O - - Example 4 70% 3% 0.043 X 221.5 1.6% Example 5 70% 4% 0.057 X 182.1 19.1% Example 6 70% 10% 0.143 X 158.9 29.4% Comparative Example 5 70% 0% 0 X 225.1 0% Comparative Example 6 70% 11% 0.157 O - - Comparative Example 7 70% 15% 0.214 O - -

[0158] Referring to FIGS. 1 to 3, it was confirmed that when the weight ratio (A) of artificial graphite relative to the total weight of artificial graphite and natural graphite in the cathode active material is 100%, surface graphite peeling does not occur in the cathodes of Examples 1 to 3, where B / A is 0.15 or less.

[0159] On the other hand, referring to FIGS. 5 to 7, when the weight ratio (A) of artificial graphite to the total weight of artificial graphite and natural graphite in the cathode active material is 100%, it was confirmed that surface graphite peeling occurs after the formation process in the cathodes of Comparative Examples 2 to 4, where B / A is greater than 0.15.

[0160] Referring to FIGS. 8 to 10, it was confirmed that when the weight ratio (A) of artificial graphite relative to the total weight of artificial graphite and natural graphite in the cathode active material is 70%, surface graphite peeling does not occur in the cathodes of Examples 4 to 6, where B / A is 0.15 or less.

[0161] Referring to Figures 12 and 13, it was confirmed that when the weight ratio (A) of artificial graphite to the total weight of artificial graphite and natural graphite in the cathode active material is 70%, surface graphite peeling occurs after the formation process in the cathodes of Comparative Examples 6 and 7, where B / A is greater than 0.15.

[0162] When the weight ratio (A) of artificial graphite relative to the total weight of artificial graphite and natural graphite in the cathode active material is 100%, Example 1, in which B / A is 0.04, showed a reduction rate of 1.3% in gas generation compared to Comparative Example 1, in which propylene carbonate was not included in the electrolyte.

[0163] On the other hand, Example 2, in which the weight ratio (A) of artificial graphite to the total weight of artificial graphite and natural graphite in the cathode active material is 100% and B / A is 0.05, showed a reduction rate of 17.2% in gas generation compared to Comparative Example 1, in which propylene carbonate was not included in the electrolyte.

[0164] That is, Example 2, in which B / A is 0.05 or higher, shows a reduction rate of gas generation of more than 10 times compared to Example 1, and it was confirmed that gas generation is significantly reduced at a B / A of around 0.05.

[0165] Example 4, in which the weight ratio (A) of artificial graphite to the total weight of artificial graphite and natural graphite in the cathode active material is 70% and B / A is 0.043, showed a reduction rate of 1.6% in gas generation compared to Comparative Example 1, in which propylene carbonate was not included in the electrolyte.

[0166] On the other hand, Example 5, in which the weight ratio (A) of artificial graphite to the total weight of artificial graphite and natural graphite in the cathode active material is 70% and B / A is 0.057, showed a reduction rate of 19.1% in gas generation compared to Comparative Example 1, in which propylene carbonate was not included in the electrolyte.

[0167] That is, Example 5, in which B / A is 0.05 or higher, shows a gas generation reduction rate of more than 10 times compared to Example 4, and it was confirmed that gas generation is significantly reduced at a B / A of around 0.05.

[0168] The above description is merely an example of applying the principles of the present disclosure, and other configurations may be included without departing from the scope of the present invention.

Claims

Claim 1 A lithium secondary battery comprising: a positive electrode comprising a positive active material comprising a lithium metal oxide comprising nickel (Ni); a negative electrode comprising a negative active material comprising artificial graphite; and an electrolyte comprising a solvent comprising propylene carbonate; wherein the ratio (B / A) of the volume ratio (B) of the propylene carbonate to the total volume of the solvent to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the negative active material is 0.01 to 0.

15. Claim 2 A lithium secondary battery according to claim 1, wherein the ratio (B / A) of the volume ratio (B) of the propylene carbonate to the total volume of the solvent to the weight ratio (A) of the artificial graphite to the total weight of the artificial graphite and natural graphite in the negative electrode active material is 0.05 to 0.

15. Claim 3 A lithium secondary battery according to claim 1, wherein the weight ratio (A) of artificial graphite relative to the total weight of artificial graphite and natural graphite in the negative electrode active material is 50 to 100%. Claim 4 A lithium secondary battery according to claim 1, wherein the lithium metal oxide has a nickel content of 70 mol% or more among the total metals excluding lithium. Claim 5 A lithium secondary battery according to claim 1, wherein the lithium metal oxide has a cobalt content of less than 5 mol% among the total metals excluding lithium. Claim 6 A lithium secondary battery according to claim 1, wherein the lithium metal oxide is represented by the following chemical formula 1. [Chemical Formula 1] Li x Ni a Co b Mn c M d O 2+y (In the above chemical formula 1, M is at least one element selected from the group consisting of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr, and 0.5≤x≤1.5, -1≤y≤1, 0.7≤a≤1, 0≤b≤0.05, 0≤c≤0.3, 0≤d≤0.3, and a+b+c+d=1.) Claim 7 A lithium secondary battery according to claim 1, wherein the positive electrode has a layered structure. Claim 8 A lithium secondary battery according to claim 1, wherein the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent is 3 to 15%. Claim 9 A method for manufacturing a lithium secondary battery comprising: a step of manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a step of inserting the electrode assembly into a battery case and then injecting an electrolyte into the battery case; wherein the positive electrode comprises a positive active material comprising a lithium metal oxide comprising nickel (Ni), the negative electrode comprises a negative active material comprising artificial graphite, the electrolyte comprises a solvent comprising propylene carbonate, and the ratio (B / A) of the volume ratio (B) of the propylene carbonate to the total volume of the solvent to the weight ratio (A) of the artificial graphite relative to the total weight of the artificial graphite and natural graphite in the negative active material is 0.01 to 0.

15. Claim 10 A method for manufacturing a lithium secondary battery according to claim 9, wherein the ratio (B / A) of the volume ratio (B) of the propylene carbonate to the total volume of the solvent to the weight ratio (A) of the artificial graphite to the total weight of the artificial graphite and natural graphite in the negative electrode active material is 0.05 to 0.

15. Claim 11 A method for manufacturing a lithium secondary battery according to claim 9, wherein the weight ratio (A) of artificial graphite relative to the total weight of artificial graphite and natural graphite in the negative electrode active material is 50 to 100%. Claim 12 A method for manufacturing a lithium secondary battery according to claim 9, wherein the lithium metal oxide has a nickel content of 70 mol% or more among the total metals excluding lithium. Claim 13 A method for manufacturing a lithium secondary battery according to claim 9, wherein the volume ratio (B) of the propylene carbonate relative to the total volume of the solvent is 3 to 15%.

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