KR20190133982A - Method for preparing lithium secondary battery - Google Patents

Abstract

The present invention relates to a method for manufacturing a lithium secondary battery. The method comprises the following steps: preparing a non-aqueous electrolyte including LiPF_6 and a non-aqueous organic solvent; manufacturing an electrode assembly by sequentially stacking a positive electrode, a separation membrane, and a negative electrode; storing the electrode assembly in a battery case under an atmosphere of a dry room; injecting the non-aqueous electrolyte into the battery case in which the electrode assembly is accommodated, and controlling a water content of the inside of the battery case to 750 to 2,250 ppm; manufacturing a preliminary secondary battery by sealing the battery case; performing a formation and aging process on the preliminary secondary battery at a temperature equal to or greater than 60°C to convert a part of the LiPF_6 included in the non-aqueous electrolyte into lithium difluorophosphate (LiDFP); and removing gas. According to the present invention, it is possible to manufacture a lithium secondary battery including a non-aqueous electrolyte with high purity LiDFP by an economical method without a dangerous process.

Description

Manufacturing method of lithium secondary battery {METHOD FOR PREPARING LITHIUM SECONDARY BATTERY}

The present invention relates to a method for producing a lithium secondary battery having a nonaqueous electrolyte containing lithium difluorophosphate (LiDFP) of high purity simply and economically.

As personal IT devices and computer networks are developed due to the development of the information society, and as the dependence on electric energy increases, the development of technology for efficiently storing and utilizing electric energy is required.

Secondary batteries are known to be the most suitable technology for various purposes because they can be miniaturized to be applied to personal IT devices, and also can be applied to electric vehicles, power storage devices, and the like. In particular, the lithium ion secondary battery with the highest energy density has been in the spotlight, and is currently being applied to various devices.

In the case of lithium ion secondary batteries, unlike the early days when lithium metal was directly applied to electrodes, a transition metal oxide material containing lithium is used as a cathode material, and carbon-based materials such as graphite and alloy-based materials such as silicon are used. It is applied as a negative electrode material.

Specifically, a lithium ion secondary battery is composed of a positive electrode composed of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte serving as a medium for transferring lithium ions, and a separator.

On the other hand, the lithium ion secondary battery is a case of using a graphite-based negative electrode as the negative electrode material, the electrochemical stability window of the electrolyte used in the lithium ion secondary battery with the operating potential of graphite is 0.3 V ( vs. Li / Li ⁺ ) or less. As it is lower than the Electrochemical Stability Window, currently used electrolytes are first reduced and decomposed. The reduced-decomposed electrolyte product forms a solid electrolyte interphase (SEI) membrane that permeates lithium ions at the initial stage of charging and inhibits decomposition of the electrolyte.

Recently, a method for maintaining the passivation capability of the SEI film at a high temperature has been studied in order to prevent an increase in resistance and a capacity deterioration during charging and discharging at a high temperature.

For example, lithium difluorophosphate (hereinafter referred to as "LiDFP"), which is a kind of lithium salt, has been found to have excellent performance in forming a solid SEI film on the surface of the cathode, thereby developing an electrolyte solution containing high purity LiDFP. Research to do is emerging.

However, in the production of the lithium difluorophosphate, not only acid gases and salts are generated, but also as a starting material, since they are highly corrosive and easily decomposed in the air, they are difficult to handle or have low reactivity. This is cumbersome and has a disadvantage of low safety in the manufacturing process. In particular, a by-product is inevitably generated during the process of synthesizing the lithium difluorophosphate.

Korean Patent Registration Publication No. 1739936

An object of the present invention is to provide a method for manufacturing a lithium secondary battery having a nonaqueous electrolyte containing LiDFP of high purity simply and economically.

Specifically, in one embodiment of the present invention

Preparing a non-aqueous electrolyte comprising LiPF ₆ and a non-aqueous organic solvent;

Manufacturing an electrode assembly by sequentially stacking an anode, a separator, and a cathode;

Storing the electrode assembly in a battery case in a dry room atmosphere;

Injecting the nonaqueous electrolyte into the battery case in which the electrode assembly is accommodated, and controlling the moisture content of the battery case to be 750 ppm to 2,250 ppm;

Manufacturing a secondary battery by sealing the battery case;

Performing a formation and aging process on the preliminary secondary battery at a temperature of 60 ° C. or higher to convert a portion of LiPF ₆ contained in the nonaqueous electrolyte into lithium difluorophosphate (LiDFP); And

It provides a method for producing a lithium secondary battery comprising a; degassing.

In the lithium secondary battery manufacturing method according to an embodiment of the present invention, the initial LiPF ₆ concentration in the non-aqueous electrolyte may be 1.0M to 2.0M, specifically 1.0M to 1.5M.

The non-aqueous organic solvent may include a carbonate-based organic solvent.

In the electrode assembly manufacturing step, since a separate drying step is not performed for the positive electrode and the negative electrode, the moisture content of the positive electrode and the negative electrode may be 700 ppm to 2250 ppm, respectively.

The pouring of the non-aqueous electrolyte may be performed in a draw room atmosphere in which dew point temperature of -10 ° C. under which external humidity is controlled is maintained.

After the non-aqueous electrolyte solution, the moisture content in the battery case can be controlled to 1,000ppm to 2,000ppm.

The internal moisture content of the battery case may be controlled by drying the battery case in which the nonaqueous electrolyte is injected after the nonaqueous electrolyte is injected under high temperature vacuum or by exposing it to nitrogen (N ₂ ) containing moisture.

The formation step may be carried out at 60 ℃ to 80 ℃ 3 hours or less, the aging step may be carried out at 60 ℃ to 80 ℃ 48 hours or less.

After the formation and aging step, the moisture content in the battery case may be 5ppm or less.

After the formation and aging step, the concentration of LiPF _{6 in} the non-aqueous electrolyte may be 0.85M to 1.5M, the concentration of lithium difluorophosphate may be 0.0040M to 0.015M.

According to the method of the present invention, the lithium content of the lithium secondary battery having a non-aqueous electrolyte containing LiPF ₆ as a lithium salt by controlling the moisture content and the temperature conditions during the formation step in the battery case is dangerous by a simple, economical method A lithium secondary battery having a nonaqueous electrolyte containing high purity LiDFP can be manufactured without a process. In the lithium secondary battery, a solid SEI film is formed on the surface of the cathode and the anode during initial charging, thereby improving high temperature storage characteristics and cycle life characteristics.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to the ordinary or dictionary meanings, and the inventors appropriately define the concept of terms in order to explain their invention in the best way. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that it can.

Recently, the necessity of high performance secondary batteries is increasing according to the commercialization of various mobile devices. With the commercialization of electric vehicles, hybrid electric vehicles, and the development of electric storage devices, high power, high energy density, high discharge voltage, etc. A secondary battery was needed. In particular, the importance of lithium salts in the non-aqueous electrolyte composition is emerging, and as lithium difluorophosphate is known to form a solid SEI film on the surface of the negative electrode, among lithium salts, it contains economically high purity lithium difluorophosphate. In order to manufacture a non-aqueous electrolyte, research for producing a secondary battery having improved low-temperature output characteristics and high-temperature cycle life characteristics is emerging.

Hereinafter, the present invention is to provide a method for producing a lithium secondary battery having a non-aqueous electrolyte containing a high purity lithium difluorophosphate (LiDFP) without a dangerous process in a simple, economical way.

Specifically, in one embodiment of the present invention

Preparing a non-aqueous electrolyte comprising LiPF ₆ and a non-aqueous organic solvent;

Manufacturing an electrode assembly by sequentially stacking an anode, a separator, and a cathode;

Storing the electrode assembly in a battery case in a dry room atmosphere;

Injecting the nonaqueous electrolyte into the battery case in which the electrode assembly is accommodated, and controlling the moisture content of the battery case to be 750 ppm to 2,250 ppm;

Manufacturing a secondary battery by sealing the battery case;

Performing a formation and aging process on the preliminary secondary battery at a temperature of 60 ° C. or higher to convert a portion of LiPF ₆ contained in the nonaqueous electrolyte into lithium difluorophosphate (LiDFP); And

It provides a method for producing a lithium secondary battery comprising a; degassing.

The manufacturing method of the lithium secondary battery of the present invention will be described in more detail below.

Steps to prepare a nonaqueous electrolyte

In the lithium secondary battery manufacturing method according to an embodiment of the present invention, the concentration of LiPF _{6 in} the non-aqueous electrolyte may be 1.0M to 2.0M, specifically 1.0M to 1.5M, more specifically 1.0M to 1.4M.

At this time, when the concentration of the lithium salt is less than 1.0M, the effect of improving the low temperature output and the high temperature cycle characteristics of the battery is insignificant, and the LiPF ₆ is partially converted to LiDFP during the formation and aging process, and thus, LiPF in the non-aqueous electrolyte. _{Since the} amount of ₆ ? Decreases to 0.8 M or less, there is a disadvantage in that cycle life characteristics and resistance deteriorate. On the other hand, when the concentration of LiPF ₆ is high, side reactions are excessively generated during the formation and aging process described later, and by-products are excessively generated, and the electrode wettability is deteriorated due to an increase in the viscosity of the electrolyte. _{Even if 6} is converted to some LiDFP, output inferiority may appear due to an increase in film resistance due to side reactions. Thus, the concentration of LiPF ₆ may be 2.0M or less, 1.5M or less, preferably 1.4M.

In addition, in the lithium secondary battery manufacturing method according to an embodiment of the present invention, the organic solvent contained in the non-aqueous electrolyte may be minimized by the oxidation reaction, etc. in the charge and discharge process of the secondary battery, with the additive There is no limitation as long as it can exhibit the characteristics, and specifically, it may include an ester solvent.

The ester solvent may include at least one compound selected from the group consisting of a cyclic carbonate organic solvent, a linear carbonate organic solvent, a linear ester organic solvent, and a cyclic ester organic solvent. Specifically, the cyclic carbonate organic solvent and At least one carbonate solvent of the linear carbonate organic solvent may be included.

Specific examples of the cyclic carbonate organic solvent include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, and 1,2-pene. One or a mixture of two or more thereof selected from the group consisting of methylene carbonate, 2,3-pentylene carbonate, vinylene carbonate and fluoroethylene carbonate (FEC).

In addition, specific examples of the linear carbonate organic solvent include dimethyl carbonate (dimethyl carbonate, DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate. Any one selected from the group consisting of, or a mixture of two or more thereof may be representatively used, but is not limited thereto.

The linear ester organic solvent may be any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. Two or more kinds of mixtures and the like may be representatively used, but are not limited thereto.

Specific examples of the cyclic ester organic solvent include any one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone. Mixtures of more than one species may be used, but are not limited thereto.

The cyclic carbonate organic solvent in the ester solvent may be preferably used because it has a high dielectric constant and dissociates lithium salts in the electrolyte, and the cyclic carbonate organic solvent and low viscosity such as dimethyl carbonate and diethyl carbonate. In the case where a low dielectric constant linear carbonate-based organic solvent and a linear ester compound are used in an appropriate ratio, an electrolyte having a high electrical conductivity can be prepared, and thus it can be used more preferably.

In addition, in the present invention, the non-aqueous electrolyte may further include at least one solvent of an ether solvent and an amide solvent.

The ether solvent may be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more thereof. It doesn't happen.

The non-aqueous electrolyte may further include an additive, if necessary, in order to increase the SEI film forming effect.

The additive may include at least one compound selected from the group consisting of ethylene sulfate (Esa), tetravinylsilane, 1,3-propanesultone (PS), fluorobenzene (FB), and lithium tetrafluoroborate (LiBF ₄ ). Can be mentioned.

The additive may be included in 6% by weight, more specifically 3% by weight, more specifically 1% by weight or less so as not to inhibit the conversion efficiency from LiPF ₆ to LiDFP.

When the additive exceeds 6% by weight, not only the conversion efficiency from LiPF ₆ to LiDFP may be lowered, but also side reactions and an increase in resistance may be caused to lower output characteristics.

Step to manufacture anode

The secondary battery positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector, wherein the positive electrode mixture layer includes a positive electrode slurry including a positive electrode active material and optionally a binder, a conductive material, a solvent, and the like. After coating on the whole, it can be produced by rolling, except for the drying step.

That is, in the conventional positive electrode manufacturing, after coating the positive electrode active material slurry, the drying step was performed as an essential process to control the positive electrode moisture content to 30 ppm or less, in the present invention, to increase the moisture content in the battery case, the positive electrode manufacturing It is desirable to produce a positive electrode with a water content of about 750 ppm to 2250 ppm, specifically about 1000 ppm to 2000 ppm, maintained without additional drying steps.

At this time, the positive electrode moisture content is a Karl Fisher device (moisture measuring instrument, Metrohm) using a Karl Fisher (Karl-Fischer Reagent: Merck, KF solution, 1.09255.0500) of the moisture produced by burning the prepared positive electrode at high temperature 756 KF Coulometer / 703 Ti stand / 832 KF Thermoprep).

The Karl Fischer moisture measurement method using the Karl Fischer reagent is disclosed in Korean Patent No. 1425797, dissolving a homogeneous sample with a Karl Fischer titration solvent containing methanol or extracting water from a sample using a solvent. It is a chemical volume analysis method that calculates the water content from the consumption of Karl Fisher reagent, which is titrated with the Karl Fischer reagent previously titrated and reacted chemically with water. Specifically, the titrant is electrically generated in the titration cell and weighed in the 832 KF Thermoprep by measuring the weight of the electrode (sample) to be measured. _By reacting with ₂ , the moisture content in the sample can be calculated from the amount of current used for the end point measurement through the potential difference measurement.

On the other hand, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, for example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver, or the like can be used.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may specifically include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. have. More specifically, the lithium composite metal oxide may be lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O _4, etc.), lithium-cobalt oxide (eg, LiCoO _2, etc.), lithium-nickel oxide (Eg, LiNiO _2, etc.), lithium-nickel-manganese oxides (eg, LiNi _1-Y Mn _Y O ₂ (here 0 <Y <1), LiMn _2-z Ni _z O ₄ ( Here, 0 <Z <2) and the like, lithium-nickel-cobalt-based oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (here, 0 <Y1 <1) and the like), lithium-manganese-cobalt System oxides (e.g., LiCo _1-Y2 Mn _Y2 O ₂ (here, 0 <Y2 <1), LiMn _2-z1 Co _z1 O ₄ (here, 0 <Z1 <2), etc.), lithium-nickel Manganese-cobalt-based oxides (e.g., Li (Ni _p Co _q Mn _r1 ) O ₂ , where 0 <p <1, 0 <q <1, 0 <r1 <1, p + q + r1 = 1) or Li (Ni _p1 Co _q1 Mn _r2 ) O ₄ (where 0 <p1 <2, 0 <q1 <2, 0 <r2 <2, p1 + q1 + r2 = 2, etc.), or lithium- Nickel-cobalt-transition metal (M) oxide (e.g., Li (Ni _p2 Co _q2 Mn _r3 M _S2 ) O ₂ (here, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of freestanding elements, respectively, 0 <p2 <1, 0 <q2 <1, 0 <r3 <1, 0 <s2 <1, p2 + q2 + r3 + s2 = 1), etc.), and any one or two or more of these compounds may be included.

Among them, the lithium composite metal oxide may be LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (eg, Li (Ni _1/3 Mn _1/3 Co ₁₎ in that the capacity characteristics and stability of the battery may be improved. _{/ 3) O 2, Li (} Ni 0.6 Mn 0.2 Co 0.2) O 2, Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , Li (Ni _0.7 Mn _0.15 Co _0.15 ) O _2, and Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ , or the like, or lithium nickel cobalt aluminum oxide (eg, Li (Ni _0.8 Co _0.15 Al _0.05 ) O ₂ , and the like.

The cathode active material may be included in an amount of 80 wt% to 99.5 wt%, specifically 85 wt% to 95 wt%, based on the total weight of solids in the cathode slurry. In this case, when the content of the positive electrode active material is 80% by weight or less, the energy density may be lowered, thereby lowering the capacity characteristic.

The binder is a component that assists in bonding the active material and the conductive material and bonding to the current collector, and is generally added in an amount of 1 to 30% by weight based on the total weight of solids in the positive electrode slurry. When the binder is less than 1% by weight, the adhesion between the electrode active material and the current collector may be insufficient. If the binder exceeds 30% by weight, the adhesion may be improved, but the content of the electrode active material may decrease, thereby lowering the battery capacity.

Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers, and the like.

In addition, the conductive material may be added in 1 to 20% by weight based on the total weight of solids in the positive electrode slurry. If the content of the conductive material is less than 1% by weight, it is difficult to expect the effect of improving the electrical conductivity or the electrochemical characteristics of the battery may be reduced. And energy density may be lowered.

Such a conductive material is not particularly limited as long as it is conductive without causing chemical change in the battery, and examples thereof include carbon black, acetylene black (or denka black), Ketjenblack, channel black, furnace black, Carbon powders such as lamp black or thermal black; Graphite powders such as natural graphite, artificial graphite, or graphite with very advanced crystal structure; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The solvent is dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (N-methyl-2-pyrrolidone, NMP), acetone (acetone) or water alone or these It can be mixed and used. The amount of the solvent used may be appropriately adjusted in consideration of the coating thickness of the slurry, the production yield, the viscosity, and the like. For example, the solvent may be included so that the solid content concentration in the slurry including the positive electrode active material and optionally the binder and the conductive material is 10% by weight to 60% by weight, preferably 30% by weight to 60% by weight.

Step of preparing a cathode

The negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector, wherein the negative electrode mixture layer comprises a negative electrode slurry containing a negative electrode active material and optionally a binder, a conductive material, a solvent, and the like. After coating on, it can be prepared by rolling directly.

That is, in the conventional negative electrode manufacturing, after coating the negative electrode active material slurry, in order to control the negative electrode moisture content to 30 ppm or less, the drying step was performed as an essential process, in the present invention, to increase the moisture content in the battery case, the negative electrode It is preferable to prepare a negative electrode in which a water content of about 750 ppm to 2,250 ppm, specifically about 1000 ppm to 2000 ppm is maintained, without additionally performing a drying step in preparation.

In this case, the negative electrode moisture content may be analyzed by using a Karl Fischer device using a Karl Fisher reagent as described above for the moisture produced by burning the prepared negative electrode at high heat.

On the other hand, the negative electrode current collector generally has a thickness of 3 to 500㎛. Such a negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like on the surface, aluminum-cadmium alloy and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

In addition, the negative electrode active material may be lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal complex oxide, and may dope and undo lithium. Materials, and at least one selected from the group consisting of transition metal oxides.

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

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

The metal complex oxide may include PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , Bi ₂ O ₅ , Li _x4 Fe ₂ O ₃ (0 _{≦ x4} ≦ ₁ ), Li _x5 WO ₂ (0 ≦ _x5 ≦ 1), and Sn _x6 Me _1-x6 Me ' _y4 O _z4 (Me: Mn, Fe Me ': Al, B, P, Si, Group 1, 2, 3, Periodic Table of Elements, Halogen; 0 <x6≤1;1≤4y≤3; 1≤z4≤8 Any one selected from the group can be used.

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

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

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

In addition, the binder and the conductive material may be the same as or different from those described above for the positive electrode.

That is, the binder is a component that assists in the bonding between the conductive material, the active material and the current collector, and is typically added in an amount of 1 to 30 wt% based on the total weight of solids in the negative electrode active material slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Low ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers thereof, and the like.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 1 to 20 wt% based on the total weight of solids in the negative electrode active material slurry. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The solvent may include an organic solvent such as water or NMP, alcohol, etc. The amount of the solvent may be appropriately adjusted in consideration of the coating thickness of the slurry, production yield, viscosity, and the like. For example, the solvent may be included so that the solid content concentration in the slurry including the negative electrode active material and optionally the binder and the conductive material is 50% to 90% by weight, preferably 60% to 80% by weight.

In addition, the separator serves to block internal short circuits of both electrodes and to impregnate the electrolyte, to prepare a separator composition by mixing a polymer resin, a filler, and a solvent, and then directly coating and drying the separator composition on the electrode. After forming the separator film or casting and drying the separator composition on the support, the separator film separated from the support may be formed by lamination on the electrode.

The separator is a porous polymer film commonly used, for example, a porous polymer made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer The polymer film may be used alone or in a stack thereof, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used, but is not limited thereto.

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

Step of preparing an electrode assembly

In the method of manufacturing a lithium secondary battery according to an embodiment of the present invention, the electrode assembly has a separator that does not perform a drying step between a positive electrode and a negative electrode having a water content of 750 ppm or more, specifically 1,000 ppm or more, and sequentially It can be manufactured by lamination (stack) to.

The electrode assembly manufacturing method may be manufactured by a conventional winding method such as winding in the form of jelly roll in addition to the general lamination method.

At this time, the present invention does not perform a separate drying step even after the production of the electrode assembly.

Receiving the electrode assembly

Subsequently, in the method of the present invention, the prepared electrode assembly is stored in a battery case in a dry room atmosphere.

Conventionally, a drying step after manufacturing an electrode assembly is included as an essential process step. However, in the present invention, since the electrode assembly is accommodated without performing the drying step after manufacturing the electrode assembly, the moisture content in the battery case is about. 750 ppm to 2250 ppm, specifically about 1,000 ppm to 2,000 ppm.

Injecting non-aqueous electrolyte

Next, the prepared non-aqueous electrolyte may be injected into a battery case in which the electrode assembly is housed in a draw room atmosphere in which dew point of −10 ° C. or less at which external humidity is controlled is maintained.

After the nonaqueous electrolyte injection, the moisture content in the battery case in which the nonaqueous electrolyte and the electrode assembly are accommodated is controlled to maintain about 750 ppm to 2,250 ppm, specifically about 1,000 ppm to 2,000 ppm.

The moisture content in the battery case may be adjusted by drying the preliminary secondary battery under vacuum after pouring the non-aqueous electrolyte solution or by exposing it to nitrogen (N ₂ ) gas containing moisture to adjust the moisture content. That is, if the water content in the preliminary secondary battery after the non-aqueous electrolyte solution exceeds about 2,250 ppm, the self-decomposition reaction of LiPF ₆ by water and the excessive formation of side reaction products, the amount of LiPF _6- in the non-aqueous electrolyte solution is reduced, or by-products Since this excess is generated, cycle life characteristics and resistance may deteriorate. Therefore, when the moisture content in the battery case exceeds about 2,250 ppm, the battery can be dried under high temperature vacuum to remove the moisture to a certain concentration or less.

If the moisture content of the preliminary secondary battery after the non-aqueous electrolyte solution is less than about 750 ppm, the conversion rate from LiPF ₆ to LiDFP is low, and the SEI film forming effect is insignificant, thereby deteriorating high temperature characteristics. Therefore, when the moisture content in the battery case is less than about 750 ppm, the battery case may be exposed to nitrogen (N ₂ ) gas containing water to increase the moisture content in the nonaqueous electrolyte solution to a predetermined content or more.

On the other hand, the moisture content of the inside of the battery case is a non-aqueous electrolyte in a dry room atmosphere after the completion of the injection, take the electrode assembly and separated into a positive electrode, a negative electrode and a separator, respectively, and then measured their respective water content by Karl Fischer method, Can be calculated by adding up.

Step of manufacturing a spare secondary battery

Subsequently, in the method of the present invention, the secondary battery may be manufactured by sealing the nonaqueous electrolyte injection hole.

The sealing step may be carried out by a conventional method, and specifically, may be carried out by pressing the edge of the battery case under a vacuum pressure of −85 kPa using a sealing bar of 135 ° C. to 150 ° C. for 3 seconds or less.

Perform the formation and aging process

Subsequently, in the method of the present invention, after sealing, the formed secondary battery can be subjected to a formation and aging step at a temperature of 60 ° C. or higher.

Specifically, the formation process may be carried out at 60 ℃ to 80 ℃, specifically 60 ℃ to 75 ℃ 3 hours or less, specifically 0.5 hours to 3 hours. The formation process may be performed at a pressure of 5 kg / cm 2 or less, specifically, 0.5 kg / cm 2 to 5 kg / cm 2.

Moreover, in the method of this invention, an aging process can be performed at the temperature of 60 degreeC or more after a formation process. Specifically, the aging step may be carried out at 60 ℃ to 80 ℃, specifically 60 ℃ to 75 ℃ 48 hours or less, specifically 1 hour to 48 hours.

When the formation and aging process is performed at a temperature of 60 ° C. or higher as described above, LiDFP may be generated while part of LiPF ₆ contained in the nonaqueous electrolyte reacts with moisture in the preliminary secondary battery by heat (see Scheme 1 below).

Scheme 1

In this case, when the formation process and the aging process is performed at a temperature of less than 60 ° C., the conversion effect of the consumed LiPF ₆ to LiDFP may be low, and thus, it may be difficult to generate LiDFP having a desired concentration. In addition, when the formation process and the aging process is performed at a temperature of more than 80 ° C., instead of the high effect of LiDFP from the consumed LiPF ₆ , the decomposition product (eg, LiPOF) through side reaction between the LiPF ₆ self-decomposition product and the solvent. ₃ , HF, etc.) may be generated together, resulting in deterioration of the performance of the secondary battery.

On the other hand, after the formation step, the moisture content in the battery case can be maintained at 5ppm or less.

After the formation and aging step, the concentration of LiPF _{6 in} the non-aqueous electrolyte is 0.85M to 1.5M, specifically 0.9M to 1.4M, the concentration of LiDFP may be 0.0040M to 0.015M, specifically 0.0045M to 0.014M have.

If the excess is LiDFP switches from LiPF _6, the concentration of LiPF ₆ to be increased initial resistance and low-temperature output decrease is less than 0.85M, there is a side reaction due to the LiDFP generated in excess may be caused. In addition, when a small amount of LiDFP is converted from LiPF ₆ , and the LiDFP concentration is less than 0.0040M, the SEI film forming effect is insignificant, and thus high temperature characteristics may be deteriorated.

At this time, the concentration of LiPF ₆ and the converted LiDFP in the non-aqueous electrolyte may be measured by extracting the non-aqueous electrolyte from the secondary battery after the aging process, and then by MASS analysis.

Specifically, after the formation and aging process step, LiDFP in the non-aqueous electrolyte may be generated from about 0.5% to 1.5% by weight based on the total weight of the non-aqueous electrolyte.

Meanwhile, the LiDFP conversion rate from LiPF ₆ may be 96% or more, specifically 96% to 100%, and more specifically 96% to 99%. In addition, in the conversion of LiPF ₆ to LiDFP, the production rate (eg, conversion) of the byproduct is preferably 4% or less.

That is, during the formation and aging process steps, part of LiPF ₆ may be consumed through other side reactions such as SEI formation and reaction with solvents, and the LiDFP conversion is preferably calculated as a value relative to the consumed LiPF ₆ . , Which may be defined from Equation 1 below.

[Equation 1]

On the other hand, since the gas generated during the formation and aging process is moved to the gas pocket by using the high temperature pressurizing jig used to fix the preliminary secondary battery and trapped, and then removed during the subsequent degassing step, No deformation takes place.

The degassing step can be carried out in less than 10 seconds under -95 kPa vacuum.

Meanwhile, HF generated as a reaction byproduct during the conversion of LiDFP may be reconverted to LiF and H ₂ gas, wherein LiF may be removed by participating in the formation of the SEI film on the electrode surface, and the H ₂ gas may be subjected to a subsequent degassing process. It can be easily removed at the time.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example

Example 1.

(Manufacture of Electrode Assembly)

N- as the solvent (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ; NCM), carbon black as the conductive material, polyvinylidene fluoride (PVDF) (80: 5: 15 wt%) as the binder Addition to methyl-2-pyrrolidone (NMP) produced a positive electrode mixture slurry (solid content 55% by weight). After applying the positive electrode mixture slurry to a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, without performing a drying process, a roll press is immediately performed to obtain a positive electrode having a moisture content of 1,000 ppm. Prepared.

A negative electrode mixture slurry (solid content 70 wt%) was prepared by adding natural graphite as a negative electrode active material, PVDF as a binder, and carbon black (96: 3: 1 wt%) as a conductive material to NMP as a solvent. After applying the negative electrode mixture slurry to a thin film of copper (Cu), a negative electrode current collector having a thickness of 10㎛, without performing a drying process, by performing a roll press directly to prepare a negative electrode having a moisture content of 1,000 ppm It was.

An electrode assembly was prepared by sequentially stacking a separator made of polypropylene / polyethylene / polypropylene (PP / PE / PP) between the anode and the cathode.

(Non-aqueous electrolyte preparation)

Ethylene carbonate (EC): 1 M LiPF ₆ was dissolved in a non-aqueous organic solvent of ethyl methyl carbonate (EMC) (3: 7% by volume) to prepare a nonaqueous electrolyte.

(Lithium secondary battery manufacturing)

After storing the dried electrode assembly in a battery case, pouring the non-aqueous electrolyte in a draw room atmosphere maintaining a dew point of -10 ° C. or lower, and then the moisture content inside the battery case containing the electrode assembly and the non-aqueous electrolyte It was dried to 1,000 ppm. The battery case edges were sealed for 2 seconds using a sealing bar at 140 ° C. under a vacuum pressure of −85 kPa.

Then, the formation process was carried out at 60 ° C. at 0.5 kgf / cm ² pressure for 1 hour, followed by the aging process at 60 ° C. for 24 hours.

Then, extract the electrolyte in the secondary battery to measure the LiPF ₆ and LiDFP concentration through MASS analysis, and calculate the conversion rate of LiDFP from the consumed LiPF ₆ using Equation 1 below, the results are shown in Table 1 Indicated.

[Equation 1]

Subsequently, a degassing process was performed for 3 seconds under -95 kPa vacuum to prepare a lithium secondary battery of the present invention.

Example 2.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the moisture content of the battery case was controlled to 2,000 ppm in manufacturing the lithium secondary battery, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 3.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the formation and aging of the lithium secondary battery were performed at 80 ° C., and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 4.

In manufacturing a lithium secondary battery, a lithium secondary battery was manufactured in the same manner as in Example 3 except that the moisture content in the battery case was controlled to 2,000 ppm, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 5.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1.4M LiPF ₆ was dissolved in a non-aqueous organic solvent to prepare a nonaqueous electrolyte, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 6.

A lithium secondary battery was manufactured in the same manner as in Example 2, except that 1.4M LiPF ₆ was dissolved in a non-aqueous organic solvent to prepare a nonaqueous electrolyte, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 7.

A lithium secondary battery was manufactured in the same manner as in Example 3, except that 1.4M LiPF ₆ was dissolved in a non-aqueous organic solvent to prepare a nonaqueous electrolyte, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 8.

A lithium secondary battery was manufactured in the same manner as in Example 4, except that 1.4M LiPF ₆ was dissolved in a non-aqueous organic solvent to prepare a nonaqueous electrolyte, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 9.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1.5M LiPF ₆ was dissolved in a non-aqueous organic solvent to prepare a nonaqueous electrolyte, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 10.

In manufacturing a lithium secondary battery, a lithium secondary battery was manufactured in the same manner as in Example 9 except that the moisture content in the battery case was controlled to 2,000 ppm, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 11.

A lithium secondary battery was manufactured in the same manner as in Example 3, except that 0.8 M LiPF ₆ was dissolved in a non-aqueous organic solvent to prepare a non-aqueous electrolyte, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 12.

A lithium secondary battery was manufactured in the same manner as in Example 10, except that 0.8 M LiPF ₆ was dissolved in a non-aqueous organic solvent to prepare a non-aqueous electrolyte, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Example 13.

In preparing the lithium secondary battery, except that the aging step was performed at 90 ° C., a lithium secondary battery was prepared in the same manner as in Example 1, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ , and as a result, It is shown in Table 1 below.

Example 14.

In preparing the lithium secondary battery, except that the aging step was performed at 50 ° C., a lithium secondary battery was manufactured in the same manner as in Example 1, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ , and as a result, It is shown in Table 1 below.

Comparative Example 1.

In manufacturing the lithium secondary battery, except that the internal moisture content of the battery case is controlled to 2,500 ppm, a lithium secondary battery was manufactured in the same manner as in Example 1, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ The results are shown in Table 1 below.

Comparative Example 2.

(Manufacture of Electrode Assembly)

N- as the solvent (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ; NCM), carbon black as the conductive material, polyvinylidene fluoride (PVDF) (80: 5: 15 wt%) as the binder Addition to methyl-2-pyrrolidone (NMP) produced a positive electrode mixture slurry (solid content 55% by weight). The positive electrode mixture slurry is applied to a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, and an internal moisture content of 30 ppm at 100 ° C. for 2 to 3 hours in a vacuum atmosphere chamber of -0.1 Mpa or less. It dried so that it might be below. Next, a roll press was performed to prepare a positive electrode.

A negative electrode mixture slurry (solid content 70 wt%) was prepared by adding natural graphite as a negative electrode active material, PVDF as a binder, and carbon black (96: 3: 1 wt%) as a conductive material to NMP as a solvent. The negative electrode mixture slurry was applied to a thin film of copper (Cu), which is a negative electrode current collector having a thickness of 10 μm, and dried at 100 ° C. for 3 to 4 hours in a vacuum atmosphere chamber of -0.1 Mpa or less to obtain internal moisture content. It dried to 30 ppm or less. Next, a roll press was performed to prepare a negative electrode.

An electrode assembly was prepared by sequentially stacking a separator made of polypropylene / polyethylene / polypropylene (PP / PE / PP) between the positive electrode and the negative electrode.

(Non-aqueous electrolyte preparation)

Ethylene carbonate (EC): 1.4 M LiPF ₆ was dissolved in ethyl methyl carbonate (EMC) (3: 7% by volume) to prepare a non-aqueous electrolyte.

(Lithium secondary battery manufacturing)

In manufacturing the lithium secondary battery, except that the internal moisture content of the battery case is controlled to 100 ppm, a lithium secondary battery was prepared in the same manner as in Comparative Example 1, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ The results are shown in Table 1 below.

Comparative Example 3.

(Manufacture of Electrode Assembly)

N- as the solvent (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ; NCM), carbon black as the conductive material, polyvinylidene fluoride (PVDF) (80: 5: 15 wt%) as the binder Addition to methyl-2-pyrrolidone (NMP) produced a positive electrode mixture slurry (solid content 55% by weight). The positive electrode mixture slurry was applied to a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, and the internal moisture content was 500 ppm for 2 to 3 hours at 100 ° C. in a vacuum atmosphere chamber of -0.1 Mpa or less. It dried so that it might be below. Next, a roll press was performed to prepare a positive electrode.

A negative electrode mixture slurry (solid content 70 wt%) was prepared by adding natural graphite as a negative electrode active material, PVDF as a binder, and carbon black (96: 3: 1 wt%) as a conductive material to NMP as a solvent. The negative electrode mixture slurry was applied to a thin film of copper (Cu), which is a negative electrode current collector having a thickness of 10 μm, and dried at 100 ° C. for 3 to 4 hours in a vacuum atmosphere chamber of -0.1 Mpa or less to obtain internal moisture content. It dried to 500 ppm or less. Next, a roll press was performed to prepare a negative electrode.

An electrode assembly was prepared by sequentially stacking a separator made of polypropylene / polyethylene / polypropylene (PP / PE / PP) between the anode and the cathode.

(Non-aqueous electrolyte preparation)

Ethylene carbonate (EC): 1.4 M LiPF ₆ was dissolved in ethyl methyl carbonate (EMC) (3: 7% by volume) to prepare a non-aqueous electrolyte.

(Lithium secondary battery manufacturing)

In preparing the lithium secondary battery, except that the internal moisture content of the battery case is controlled to 500 ppm, a lithium secondary battery was manufactured in the same manner as in Comparative Example 1, and the conversion rate of LiDFP was calculated from the consumed LiPF ₆ . The results are shown in Table 1 below.

Referring to Table 1, when the formation and aging process of the same temperature range, the moisture content in the battery case compared to the secondary batteries of Examples 1, 3, 5, and 7 each having a moisture content of 1,000 ppm, respectively It can be seen that the conversion rate of LiDFP from LiPF ₆ is relatively high in the secondary batteries of Examples 2, 4, 6, and 8 each containing 2,000 ppm.

On the other hand, in the case of the secondary battery of Example 1 having a non-aqueous electrolyte having a lithium salt concentration of 1.0 M, LiPF ₆ was lower than the secondary battery of Example 5 having a non-aqueous electrolyte having a relatively high lithium salt concentration of 1.4 M. It can be seen that the formation rate of by-products during the LiDFP conversion is relatively low. Similarly, in the case of the secondary batteries of Examples 2 to 4 with nonaqueous electrolytes having a lithium salt concentration of 1.0 M, the secondary cells of Examples 6 to 8 with nonaqueous electrolytes having a relatively high lithium salt concentration of 1.4 M, respectively. Compared with the battery, it can be seen that the production rate of by-products during LiDFP conversion from LiPF ₆ is relatively low.

On the other hand, in the case of the secondary batteries of Examples 9 and 10 having a non-aqueous electrolyte having a high lithium salt concentration of 1.5 M, compared to the secondary batteries of Examples 1 to 8 having a non-aqueous electrolyte having a relatively low lithium salt concentration, LiPF It can be seen from ₆ that the LiDFP conversion rate is low and the byproduct formation rate is relatively high.

On the other hand, in the case of the secondary batteries of Examples 11 and 12 having a non-aqueous electrolyte having a low lithium salt concentration of 0.8 M, LiPF compared to the secondary batteries of Examples 1 to 8 having a non-aqueous electrolyte having a relatively high lithium salt concentration. _{It can be seen} from ₆ that the LiDFP conversion rate and the byproduct production rate are at the same level, while the concentration of LiPF _{6 in} the non-aqueous electrolyte after formation and aging is low, below 0.79.

On the other hand, the secondary battery of Example 13 subjected to the high temperature aging process at 90 ° C. at the time of manufacturing the lithium secondary battery, has an excessive amount of by-products in the nonaqueous electrolyte solution compared to the secondary batteries of Examples 1 to 8 that performed the aging step at 80 ° C. or lower. It can be seen that the generated rate and the conversion rate from LiPF ₆ to LiDFP deteriorate.

On the other hand, in the case of the secondary battery of Example 14 subjected to the low temperature aging process at 50 ° C. at the time of manufacturing the lithium secondary battery, the conversion rate from LiPF ₆ to LiDFP is lower than that of the secondary batteries of Examples 1 to 8 subjected to the aging step at 60 ° C. or higher. It can be seen that low.

On the other hand, the secondary battery of Comparative Example 1 in which the moisture content in the battery case was controlled at 2,500 ppm, compared to the secondary batteries of Examples 1 to 8 in which the moisture content in the battery case was controlled at 2,000 ppm or less, It can be seen that the by-products are excessively generated and the conversion rate from LiPF ₆ to LiDFP is degraded.

On the other hand, by including the electrode assembly prepared by drying the positive electrode and the negative electrode when manufacturing a lithium secondary battery as in the conventional method, the moisture content of the secondary battery and the battery case of Comparative Example 2 in which the moisture content of the battery case is controlled to 100 ppm In the case of the secondary battery of Comparative Example 7 controlled to 500 ppm, the conversion rate from LiPF ₆ to LiDFP was lower than that of the secondary batteries of Examples 1 to 8, wherein the moisture content in the battery case was controlled to 1,000 ppm to 12,000 ppm. It can be seen that the concentration of LiDFP in the electrolyte is very low, 0.00083M.

Claims (13)

Preparing a non-aqueous electrolyte comprising LiPF ₆ and a non-aqueous organic solvent;
Manufacturing an electrode assembly by sequentially stacking an anode, a separator, and a cathode;
Storing the electrode assembly in a battery case in a dry room atmosphere;
Injecting the nonaqueous electrolyte into the battery case in which the electrode assembly is accommodated, and controlling the moisture content of the battery case to be 750 ppm to 2,250 ppm;
Manufacturing a secondary battery by sealing the battery case;
Performing a formation and aging process on the preliminary secondary battery at a temperature of 60 ° C. or higher to convert a portion of LiPF ₆ contained in the nonaqueous electrolyte into lithium difluorophosphate (LiDFP); And
Lithium secondary battery manufacturing method comprising the step of degassing.
The method according to claim 1,
In the non-aqueous electrolyte manufacturing step, the initial LiPF ₆ concentration in the non-aqueous electrolyte is a lithium secondary battery manufacturing method of 1.0M to 2.0M.
The method according to claim 2,
In the non-aqueous electrolyte manufacturing step, the initial LiPF ₆ concentration in the non-aqueous electrolyte is a lithium secondary battery manufacturing method of 1.0M to 1.5M.
The method according to claim 1,
The non-aqueous organic solvent is a lithium secondary battery manufacturing method comprising a carbonate-based organic solvent.
The method according to claim 1,
In the electrode assembly manufacturing step, the moisture content of the positive electrode is a 700 to 2,250ppm lithium secondary battery manufacturing method.
The method according to claim 1,
In the electrode assembly manufacturing step, the moisture content of the negative electrode is a lithium secondary battery manufacturing method is 700ppm to 2,250ppm.
The method according to claim 1,
Wherein the step of pouring the non-aqueous electrolyte is a lithium secondary battery manufacturing method that is carried out in a draw room atmosphere to maintain the dew point temperature (Dew Point) -10 ℃ or less controlled outside humidity.
The method according to claim 1,
After the non-aqueous electrolyte solution is injected, the moisture content of the inside of the battery case is controlled to 1,000ppm to 2,000ppm.
The method according to claim 1,
The internal moisture content of the inside of the battery case is a lithium secondary battery manufacturing method that is controlled by drying the battery case in which the non-aqueous electrolyte solution is injected after the non-aqueous electrolyte solution or exposed to nitrogen (N ₂ ) containing water.
The method according to claim 1,
The formation step is a lithium secondary battery manufacturing method that is carried out within 60 hours at 60 ℃ to 80 ℃.
The method according to claim 1,
The aging step is a lithium secondary battery manufacturing method that is carried out within 60 hours to 80 ℃ 48 hours.
The method according to claim 1,
After the formation and aging step, the moisture content in the battery case is less than 5ppm lithium secondary battery manufacturing method.
The method according to claim 1,
After the formation and aging step, the concentration of LiPF ₆ in the non-aqueous electrolyte is 0.85M to 1.5M, the concentration of lithium difluorophosphate is 0.0040M to 0.015M lithium secondary battery manufacturing method.