KR20210024975A - Lithium secondary battery and method for manufacturing the same - Google Patents

Abstract

The present invention relates to: a lithium secondary battery including a pre-lithiation carbon-based negative electrode, a positive electrode, a separator, and an inorganic electrolyte represented by the following chemical formula 1: LiMX-n(SO_2); and a method for manufacturing the same. In the chemical formula 1, M is at least one metal selected from alkali metals, transition metals, and post-transition metals, X is a halogen element, and n is an integer of any one of 1 to 4.

Description

Lithium secondary battery and its manufacturing method {LITHIUM SECONDARY BATTERY AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a lithium secondary battery and a method of manufacturing the same, and specifically, a lithium secondary battery having improved capacity characteristics and cycle characteristics by including a pre-lithiation carbon-based negative electrode and a sulfur dioxide-based inorganic electrolyte, and a manufacturing method thereof. It's about the method.

Lithium secondary batteries are not only portable power sources for mobile phones, notebook computers, digital cameras and camcorders, but also power tools, electric bicycles, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (plug-in). HEV, PHEV) and other medium and large-sized power supplies are rapidly expanding their application.

Lithium-ion secondary batteries have the highest energy density theoretically and can be miniaturized enough to be applied to personal IT devices, and thus are proposed as batteries that can be used in various fields such as electric vehicles and power storage devices.

Meanwhile, a lithium secondary battery is composed of a negative electrode including a negative electrode active material, a positive electrode including a positive electrode active material, and an electrolyte. Of these, the electrolyte is a constituent component that greatly affects the stability and capacity characteristics of the lithium secondary battery. As it is known, research is being actively conducted on this.

Currently, most of the electrolytes use organic electrolytes, and when such organic electrolytes are stored for a long period of time, the electrolyte is depleted, resulting in deterioration of the performance of the secondary battery, such as deteriorating the stability of the secondary battery.

Accordingly, in order to improve the depletion and stability of the electrolyte, research for applying an inorganic electrolyte having high ion conduction, flame retardancy, and excellent low-temperature characteristics instead of an organic electrolyte has been on the rise.

However, the inorganic electrolyte has a disadvantage in that the capacity characteristics and cycle characteristics of the secondary battery are inferior due to a large number of irreversible reactions during charging and discharging.

Accordingly, there is a need for research on a method capable of suppressing the decomposition reaction of the inorganic electrolyte and minimizing the irreversible capacity when manufacturing a secondary battery to which an inorganic electrolyte is applied.

Korean Patent Publication No. 2019-0007296

The present invention is to provide a lithium secondary battery with improved capacity characteristics and cycle characteristics by suppressing the irreversible reaction of the inorganic electrolyte during charging and discharging.

In addition, the present invention is to provide a method of manufacturing the lithium secondary battery.

According to one embodiment, the present invention

Pre-lithiation carbon-based cathode, anode, separator, and

It provides a lithium secondary battery including an inorganic electrolyte represented by the following formula (1).

[Formula 1]

LiMX-n(SO ₂ )

In Formula 1,

M is at least one metal selected from an alkali metal, a transition metal, and a post-transition metal,

X is a halogen element,

n is an integer of 1 to 4.

The prelithiated carbon-based negative electrode may have a capacity of 30% to 90% of the total capacity of the negative electrode active material by prelithiation.

In addition, the positive electrode may include a lithium transition metal phosphate.

In addition, the inorganic electrolyte may be LiAlCl ₄ -3SO ₂ .

According to another embodiment, the present invention

Preparing an all-lithiated carbon-based negative electrode;

Manufacturing an electrode assembly by sequentially laminating the pre-lithiated carbon-based negative electrode, a separator, and a positive electrode; And

It provides a method for manufacturing a lithium secondary battery of the present invention, including the step of inserting the electrode assembly into a battery case and injecting an inorganic electrolyte represented by the following formula (1).

[Formula 1]

LiMX-n(SO ₂ )

In Formula 1,

M is at least one metal selected from alkali metal, transition metal and post-transition metal, X is a halogen element,

n is an integer of 1 to 4.

According to the present invention, since a solid electrolyte interface (SEI) is formed in advance on the surface of the carbon-based negative electrode through prelithiation before the charging and discharging process, the decomposition reaction of the inorganic electrolyte accompanying the process of forming the interface film is prevented. It is possible to manufacture a lithium secondary battery with improved capacity characteristics and cycle characteristics by suppressing and minimizing irreversible capacity.

The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the content of the above-described invention, so the present invention is limited to the matters described in such drawings. It is limited and should not be interpreted.
1 is a graph showing the results of observing the charging and discharging capacity of the lithium secondary battery prepared in Example 1.
2 is a graph showing the results of observing the charging and discharging capacity of the lithium secondary battery prepared in Comparative Example 1.
3 is a graph showing the results of observing the charging and discharging capacity of the lithium secondary battery prepared in Comparative Example 2.
4 is a graph showing cycle characteristics and Coulombic efficiency (CE) of a lithium secondary battery prepared in Example 1. FIG.
5 is a graph showing cycle characteristics and Coulomb efficiency of a lithium secondary battery prepared in Comparative Example 1.
6 is a graph showing an oxidation/reduction voltage range of an inorganic electrolyte and a voltage profile of _{lithium iron phosphate (LiFePO 4 ).}

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

The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The terms used in the present specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In the present specification, terms such as "comprise", "include", or "have" are intended to designate the existence of a feature, number, step, element, or combination of the implemented features, but one or more other features or It is to be understood that the possibility of the presence or addition of numbers, steps, elements, or combinations thereof is not preliminarily excluded.

Lithium secondary battery

In the present invention, pre-lithiation carbon-based cathode, anode, separator, and

It provides a lithium secondary battery including an inorganic electrolyte represented by the following formula (1).

[Formula 1]

LiMX-n(SO ₂ )

In Formula 1,

M is at least one metal selected from an alkali metal, a transition metal, and a post-transition metal, X is a halogen element, and n is an integer from 1 to 4.

(1) pre-lithiated carbon-based cathode

First, an all-lithiated carbon-based negative electrode according to the present invention will be described.

The pre-lithiated carbon-based negative electrode may be prepared by laminating a carbon-based negative electrode active material layer on a negative electrode current collector to prepare a negative electrode, and then performing a pre-lithiation process.

The negative electrode current collector generally has a thickness of 50 to 300 μm. Such a negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc. may be used on the surface. In addition, like the positive electrode current collector, it is possible to enhance the bonding strength of the negative electrode active material by forming fine irregularities on the surface, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The carbon-based negative active material layer may be prepared by coating a negative electrode slurry including a carbon-based negative active material and optionally a binder, a conductive material, and a solvent on a negative electrode current collector, followed by drying and rolling.

The carbon-based negative active material may include a carbon-based material capable of reversibly intercalating and deintercalating lithium ions.

As the carbon-based material, any carbon-based negative active material generally used in lithium ion secondary batteries may be used without particular limitation, and representative examples thereof may be crystalline carbon, amorphous carbon, or a mixture thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon). Alternatively, hard carbon, mesophase pitch carbide, and fired coke may be used.

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

The binder is a component that aids in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the solid content in the negative electrode slurry. Examples of such a binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber (SBR), styrene-butadiene rubber, fluorine rubber. And various copolymers thereof. The binder may further include a thickener such as carboxymethylcellulose (CMC), starch, hydroxypropylcellulose or regenerated cellulose.

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% by weight based on the total weight of the solid content in the negative electrode slurry. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, carbon black (eg, Denka black), acetylene black, Ketjen black, channel black, furnace black, lamp black , Or a carbon powder such as thermal black; Graphite powders such as natural graphite, artificial graphite, or graphite having a very developed crystal structure; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The solvent may include water or an organic solvent such as NMP or alcohol, and may be used in an amount having a desirable viscosity when the negative electrode active material and optionally a binder and a conductive material are included. For example, it may be included so that the solid content concentration in the slurry including the negative electrode active material and optionally a binder and a conductive material is 50% to 75% by weight, preferably 50% to 65% by weight.

Meanwhile, the prelithiation process includes (1) impregnating lithium (Li) metal, which is a negative electrode and a counter electrode, into an electrolyte solution, then connecting the negative electrode and the lithium metal, and inducing a short circuit to lithify the surface of the negative electrode; (2) a method of directly depositing gaseous lithium on the negative electrode by high-temperature heat treatment of lithium (Li) metal in a vacuum state (about 10 torr); (3) A method of dispersing particles containing an excessive amount of lithium (eg, Stabilized Lithium Metal Powder (SLMP ^® )) in a binder polymer, applying it to the negative electrode, and passing through a roll press to make the negative electrode lithium; Or (4) contacting the negative electrode and the positive electrode containing lithium, and then flowing a current at a low current so that the negative electrode is charged with lithium (Li) by an electrochemical method; And the like, and a more specific method will be described in more detail below.

On the other hand, the prelithiated carbon-based negative electrode obtained through the prelithiation process may have a capacity of 30% to 90% of the total capacity of the negative electrode active material to be lithiated, specifically 40% to 80%, more specifically 50 % To 75% of the capacity may be lithiated. When the amount of prelithiation is greater than 90%, the lithium metal powder may be present on the negative electrode in the form of a metal, thereby causing a side reaction. When the total amount of lithiation is lower than the range of 20%, sufficient pre-lithiation may not be achieved, and the effect of suppressing side reactions of the inorganic electrolyte may be insignificant.

(2) anode

The positive electrode of the present invention preferably includes a lithium transition metal phosphate having a driving voltage of 3.9V or less as a positive electrode active material.

Specifically, the lithium transition metal phosphate is preferably a lithium iron phosphate _{(LiFePO 4} ) ^{that can secure high discharge capacity (170 mAhg -1} ) and excellent thermal stability under a driving voltage of 3.9V or less. .

Meanwhile, as shown in FIG. 6, the lithium secondary battery of the present invention is characterized in that the inorganic electrolyte is driven in a voltage range of 2.9V-3.9V, which is an electrochemically safe voltage range. If the secondary battery is driven in a voltage range above or below that, there is a disadvantage in that the driving efficiency of the secondary battery is lowered as the inorganic electrolyte itself is oxidized and/or reduced.

Accordingly, the positive electrode active material of the present invention is a lithium transition metal phosphate capable of realizing the maximum reversible capacity in a voltage range in which the inorganic electrolyte can stably operate, that is, a driving voltage of 3.9 V or less, preferably lithium iron phosphate having an olivine structure. It is preferred to include (LiFePO _{4 ).}

When a positive electrode employing such a lithium transition metal phosphate as a positive electrode active material and an inorganic electrolyte are provided together, a secondary battery with improved structural safety and battery driving stability may be realized through stable voltage behavior characteristics.

_{Meanwhile, lithium-cobalt oxide (LiCO 2} ), lithium nickel oxide (LiNiO ₂ ), lithium-nickel-cobalt oxide (LiNi _1-Y1 Co _Y1 O ₂ ), which is used as a general positive electrode active material in manufacturing lithium secondary batteries (here In, 0<Y1<1), etc.), lithium-manganese-cobalt-based oxide (LiCo _1-Y2 Mn _Y2 O ₂ (here, 0<Y2<1), lithium-nickel-manganese-cobalt-based oxide (Li( Ni _x Co _y Mn _z )O ₂ , 0<x<1, 0<y<1, 0<z<1, x+y+z=1), or lithium-nickel-cobalt-transition metal (M) oxide (Li(Ni _a Co _b Mn _c M _d )O ₂ (M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and a, b, c and d are each independent As the atomic fraction of the elements, lithium transition metal oxides such as 0<a<1, 0<b<1, 0<c<1, 0<d<1, a+b+c+d=1 are the most reversible. In order to realize the capacity, it is necessary to perform charging to a voltage range exceeding 3.9V.

If the lithium transition metal oxide is employed as the positive electrode active material of the present invention, but charging is performed at 3.9V or less in which the inorganic electrolyte can stably operate, about 25% to about 25% of the total reversible capacity of the lithium transition metal oxide Since 30% of the capacity is not used, the capacity characteristics of the battery may deteriorate. On the other hand, when the lithium transition metal oxide is employed as the positive electrode active material of the present invention and the charging voltage is performed up to a voltage exceeding 3.9 V, for example, 3.9 V, the reversible capacity of the lithium transition metal oxide is used, oxidation of the inorganic electrolyte , Since the reduction is intensified, the driving efficiency of the secondary battery may be lowered and the lifespan characteristics may be deteriorated.

As described above, when the inorganic electrolyte of the present invention and the lithium transition metal oxide having a driving voltage range wider than the driving voltage range of the inorganic electrolyte are mixed together as a positive electrode active material, it may be a factor of lowering the positive electrode use efficiency. Therefore, when manufacturing a secondary battery employing the inorganic electrolyte of the present invention, the lithium transition metal oxide is not preferably used as a positive electrode active material.

Meanwhile, the positive electrode may be manufactured and used by a conventional method.

That is, the 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 collects a positive electrode slurry including a positive electrode active material and optionally a binder, a conductive material, and a solvent. After coating on the whole, it can be prepared by drying and rolling.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , Nickel, titanium, silver, or the like may be used.

The positive electrode active material may be included in an amount of 80% to 99% by weight, specifically 93% to 98% by weight, based on the total weight of the solid content in the positive electrode slurry. In this case, when the content of the positive active material is 80% by weight or less, the energy density may be lowered and the capacity may be lowered.

The binder is a component that aids in bonding of an active material and a conductive material and bonding to a current collector, and is typically added in an amount of 1% to 30% by weight based on the total weight of the solid content in the positive electrode slurry. Examples of such a binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, fluorine rubber, and various copolymers. have.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black. Carbon powder; Graphite powders such as natural graphite, artificial graphite, or graphite having a very developed crystal structure; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the solid content in the positive electrode slurry.

The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount having a desirable viscosity when the positive electrode active material and optionally a binder and a conductive material are included. For example, the solid content concentration in the positive electrode slurry including the positive electrode active material and optionally a binder and a conductive material may be 10% to 70% by weight, preferably 20% to 60% by weight.

(3) separator

In the lithium secondary battery of the present invention, the separator separates the negative electrode and the positive electrode to block an internal short circuit, and impregnates a non-aqueous electrolyte to provide a passage for lithium ions. Although it can be used without limitation, it is specifically preferable to have low resistance to lithium ion migration and to have excellent electrolyte moisture content.

The separator is prepared by mixing a polymer resin, a filler, and a solvent to prepare a separator composition, and then directly coating and drying the separator composition on an electrode to form a separator film, or casting and drying the separator composition on a support, The separator film peeled off from the support may be formed by laminating an upper portion of the electrode.

Specifically, the separator is a polyolefin-based polymer such as a commonly used porous polymer film, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer. The prepared porous polymer film may be used alone or two or more layers thereof may be laminated, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength.

The pore diameter of the porous separator is generally 0.01 to 50 μm, and the porosity may be 5 to 95%. In addition, the thickness of the porous separator may generally be in the range of 18 to 300 μm.

(4) inorganic electrolyte

Meanwhile, the lithium secondary battery of the present invention may include an inorganic electrolyte represented by Formula 1 below.

[Formula 1]

LiMX-n(SO ₂ )

In Formula 1,

M is at least one metal selected from an alkali metal, a transition metal, and a post-transition metal, X is a halogen element, and n is an integer from 1 to 4.

Specifically, in Formula 1, M may be one or more metals selected from the group consisting of Al, Ga, Cu, Mn, Co, Ni, Zn, and Pd. In addition, the halogen element may be selected from the group consisting of F, Cl, Br and I.

Specifically, the inorganic electrolyte may be LiAlCl ₄ -3SO ₂ .

In general, an organic electrolyte containing a lithium salt and an organic solvent has been used as an electrolyte for a lithium secondary battery, but since such an organic electrolyte is highly flammable, it may cause serious problems in safety during battery operation. Therefore, in order to improve this problem, the use of an inorganic (liquid) electrolyte has been proposed. In the case of the inorganic electrolyte, while having the advantage of having high ion conductivity, flame retardancy, and excellent low temperature characteristics, there is a disadvantage in that capacity characteristics and life characteristics are deteriorated due to a large number of irreversible reactions during charging and discharging.

Accordingly, the inventors of the present invention devised a lithium secondary battery including an all-lithiated negative electrode and an inorganic electrolyte in order to solve the above problems.

That is, in the secondary battery according to the present invention, by mixing an electrolithiated negative electrode and an inorganic electrolyte in which a solid electrolyte interface (SEI) is formed in advance through electrolithiation on the surface of a carbon-based negative electrode, SEI on the surface of the negative electrode. It is possible to suppress the decomposition reaction of the inorganic electrolyte during the charge/discharge process of forming the film and minimize the irreversible capacity. Accordingly, the lithium secondary battery of the present invention to which the prelithiated negative electrode and the inorganic electrolyte are applied can sufficiently exhibit capacity even at high and low temperatures, and obtain an effect of operating normally.

In particular, the inorganic electrolyte of the present invention is characterized in that it is driven in a voltage range of 2.9V-3.9V, which is an electrochemically safe voltage range, as shown in FIG. 6. If the secondary battery is driven in a higher voltage range, there is a disadvantage in that the driving efficiency of the secondary battery is lowered as the inorganic electrolyte itself is oxidized and/or reduced.

Accordingly, in the present invention, a positive electrode including a lithium transition metal phosphate capable of driving within the driving voltage range of the inorganic electrolyte, for example, lithium iron phosphate having an olivine structure (LiFePO ₄ ) as a positive electrode active material, is mixed together to improve positive electrode efficiency. You can increase it.

Lithium secondary battery manufacturing method

In addition, in an embodiment of the present invention, a method of manufacturing a lithium secondary battery may be provided.

The lithium secondary battery manufacturing method includes the steps of preparing an all-lithiated carbon-based negative electrode, sequentially stacking the all-lithiated carbon-based negative electrode, a separator, and a positive electrode to prepare an electrode assembly, and attaching the electrode assembly to a battery case. Inserting and injecting the inorganic electrolyte represented by Chemical Formula 1 may be included.

In the method of the present invention, since the detailed description of the negative electrode, the positive electrode, the separator, and the inorganic electrolyte is duplicated with the above description, the description thereof will be omitted.

On the other hand, the step of preparing the pre-lithiated carbon-based negative electrode will be described in more detail below.

(1) preparing an all-lithiated carbon-based anode

Specifically, the manufacturing of the pre-lithiated carbon-based negative electrode may include preparing a negative electrode by laminating a carbon-based negative electrode active material layer on a negative electrode current collector; Preparing a prelithiation solution; Impregnating the negative electrode into the prelithiation solution; Manufacturing a negative electrode laminate for prelithiation by sequentially laminating a separator and a lithium metal as a counter electrode on the negative electrode; And performing a pre-lithiation process on the negative electrode laminate to prepare a pre-lithiated carbon-based negative electrode.

(1-1) Step of preparing a negative electrode

The manufacturing of the pre-lithiated carbon-based negative electrode may be prepared by a conventional method of laminating a carbon-based negative electrode active material layer on a negative electrode current collector.

At this time, since the detailed description of the negative electrode current collector and the carbon-based negative electrode active material layer overlaps with the above description, the description thereof will be omitted.

(1-2) Preparing a prelithiation solution

The prelithiation solution is a solution containing an ionizable lithium salt and an organic solvent, and a general liquid electrolyte for a lithium secondary battery may be used.

The ionizable lithium salt comprises a Li ⁺ as the cation, and the anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, AlO 4 _{^{-, AlCl 4 -, PF 6}} -, SbF 6 -, AsF 6 -, B 10 Cl 10 -, BF 2 C 2 O 4 -, BC 4 O 8 -, PF 4 C 2 O 4 -, PF 2 C 4 _{^{O 8 -, (CF 3)}} 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO _{^{3 -, C 4 F 9 SO}} 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, ( ^{_{CF 3 SO 2) 2 CH -}} , CH 3 SO 3 -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 What is selected from the group consisting of ^{N-can be used.}

The concentration of the ionizable lithium salt can be appropriately changed within the range that can be used normally, but in order to obtain an optimum effect of forming a film for preventing corrosion on the electrode surface, a concentration of 0.8 M to 3.0 M in the electrolyte solution, specifically 1.0 M to 3.0 M Can be included in concentration.

In addition, the organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixed organic solvent thereof.

The cyclic carbonate-based organic solvent is an organic solvent of high viscosity and is an organic solvent capable of dissociating lithium salts in an electrolyte well due to a high dielectric constant, and specific examples thereof are ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene Carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate may contain at least one or more organic solvents selected from the group consisting of carbonate, among which ethylene carbonate It may include.

In addition, the linear carbonate-based organic solvent is an organic solvent having a low viscosity and a low dielectric constant, and representative examples thereof are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate ( EMC), at least one organic solvent selected from the group consisting of methylpropyl carbonate and ethylpropyl carbonate may be used, and specifically ethylmethyl carbonate (EMC) may be included.

The organic solvent may include a cyclic carbonate organic solvent and a linear carbonate organic solvent in a volume ratio of 1:9 to 5:5, specifically 2:8 to 4:6 so as to have high ionic conductivity.

In addition, the organic solvent may further include a cyclic carbonate-based organic solvent and/or a linear carbonate-based organic solvent, a linear ester-based organic solvent and/or a cyclic ester-based organic solvent commonly used in an electrolyte solution for a lithium secondary battery, if necessary. May be

Such a linear ester-based organic solvent is a specific example of at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. Can be lifted.

The cyclic ester-based organic solvent is a specific example thereof, any one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or two of them. The above organic solvents are mentioned.

(1-3) Step of impregnating the negative electrode in the prelithiation solution

In the method of the present invention, after preparing a negative electrode, in order to secure wettability to the negative electrode and increase the efficiency of a subsequent prelithiation process, the prepared negative electrode may be impregnated with an electrolithiation solution.

The impregnating step may be performed at a temperature of 10° C. to 75° C. for 30 minutes to 48 hours, and preferably at a temperature of 20° C. to 40° C. for 30 minutes to 36 hours.

When the above impregnation conditions are satisfied, sufficient wettability of the negative electrode with respect to the prelithiation solution can be ensured. If the temperature in the impregnation step is less than 10°C or the time is less than 30 minutes, it is difficult to secure a sufficient impregnation effect, and the lithiation efficiency may decrease during the prelithiation process performed as a subsequent process. In addition, if the temperature exceeds 75°C during the impregnation process, it is difficult to uniformly ensure impregnation of the electrolyte solution due to the volatility of the organic solvent used in the prelithiation solution, and thus there is a disadvantage in that the processability decreases during the subsequent process. In addition, if the impregnation step is performed within 48 hours, since the electrode is sufficiently impregnated with the electrolyte, there is no need to increase the impregnation time in consideration of cost and time.

(1-4) preparing a negative electrode laminate for prelithiation

Subsequently, in the present invention, a separator and a lithium metal as a counter electrode are sequentially stacked on the negative electrode. A negative electrode laminate for prelithiation can be prepared.

(1-5) preparing an all-lithiated carbon-based negative electrode

Then, in the present invention, a pre-lithiation process may be performed on the pre-lithiation negative electrode laminate to prepare a pre-lithiation negative electrode.

In the prelithiation process, the negative electrode active material layer of the negative electrode stack and the lithium metal as the counter electrode are connected together using a wire or copper foil, and then added to the prelithiation solution, and then through the conductive wire or copper foil. It can be done by inducing a short-circuit.

The pre-lithiation solution is a pre-lithiation solution used for impregnation of the negative electrode, and a detailed description thereof is duplicated with the above description, and thus description thereof will be omitted.

The prelithiation process is It may be performed at 10°C to 35°C for 30 minutes to 2 hours, specifically 30 minutes to 90 minutes.

That is, within the prelithiation process temperature and time range, the OCV of the cathode can be secured in the range of 3V or more at SOC 30%, specifically 3.05V to 3.29V, and more specifically 3.20V to 3.29V. . Specifically, when the prelithiation process is performed for 30 minutes or more to less than 45 minutes, the OCV of the negative electrode may implement 3.26 OCV. In addition, when the prelithiation process is performed for 45 minutes or more to less than 1 hour, the OCV of the negative electrode can implement 3.26 OCV, and when the prelithiation process is more than 1 hour, the OCV of the negative electrode can implement 3.29 OCV. . The open-circuit voltage of the negative electrode can be determined by measuring using a charge/discharger after assembling the full cell. On the other hand, when the prelithiation process is performed in less than 30 minutes, it is difficult to secure an OCV of 3V or more at an SOC of 30%.

On the other hand, when performing the prelithiation process, an appropriate pressure, for example, ^{1 kgf to 2 kgf per 1.5 cm 2} may be applied to prepare a prelithiation negative electrode.

In this case, if a pressure exceeding 2 kgf is applied, the electrode may be damaged, resulting in a risk of deteriorating the capacity characteristics of the secondary battery or generating heat.

Meanwhile, as part of the carbon-based negative electrode is lithiated through the prelithiation process, a large amount of lithium to compensate for the irreversible capacity loss of the negative electrode may be supplied to the negative electrode. Lithium electrodeposited on the negative electrode (Li-plating) can continuously electrodeposit and release lithium ions during the charging and discharging process of the lithium secondary battery, and thus can contribute as an available capacity of the negative electrode. In addition, lithium electrodeposited on the negative electrode (Li-plating) may function as an additional lithium source supplying lithium ions to the positive or negative electrode when the lithium secondary battery is degraded. Accordingly, in the lithium secondary battery according to an example of the present invention including a negative electrode including electrodeposited lithium, the electrodeposited lithium acts as an additional supplemental lithium source without supplying a separate lithium source due to deterioration of the battery. Characteristics can be exhibited.

Meanwhile, in the method of the present invention, after the step of preparing the prelithiated anode, the step of washing the prelithiated anode with an organic solvent may be further included.

The organic solvent may be selected from the organic solvents used in the above-described prelithiation solution.

In addition, the washing step may be performed for 1 minute to 3 hours at a temperature of 10 ℃ to 75 ℃, specifically 10 ℃ to 40 ℃. If the temperature is less than 10°C, the lithium salt may solidify and not be sufficiently washed, and if it exceeds 75°C, the electrode may be damaged by heat. In addition, if the washing time is less than 1 minute, the lithium salt may not be sufficiently washed, and if it exceeds 3 hours, the electrode active material may fall off and the electrode may be damaged.

On the other hand, the method of manufacturing a lithium secondary battery of the present invention is a general lithium secondary battery manufacturing method described in Korean Publication No. 2017-0111513 and Korean Publication No. 2019-0007296, except for the step of preparing the pre-lithiated negative electrode. It can be manufactured according to the method.

Hereinafter, the present invention will be described in more detail through specific examples. However, the following examples are only examples to aid understanding of the present invention, and do not limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications are possible within the scope of the present disclosure and the scope of the technical idea, and it is natural that such modifications and modifications fall within the appended claims.

Example

Example 1.

(Cathode manufacturing)

A negative electrode active material (graphite), a conductive material (Denka Black), a binder (SBR), and a thickener (CMC) were added to water in a weight ratio of 92:3:3.5:1.5 to prepare a negative electrode active material slurry. The prepared negative electrode active material slurry was coated on one surface of a copper current collector, and then dried and rolled to prepare a negative electrode having a negative electrode active material layer laminated on the copper current collector.

_{Then, LiPF 6} was dissolved in a solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were mixed at a volume ratio of 3:7 to a concentration of 1M to prepare a prelithiation solution.

The prepared negative electrode was impregnated in the prelithiation solution at 25° C. for 12 hours or longer.

Then, a separator made of a polyethylene material-based porous film and a lithium (Li) metal as a counter electrode are sequentially stacked on the negative electrode to prepare a negative electrode laminate for prelithiation, and the negative electrode active material layer and the lithium metal as a counter electrode are connected to a copper conductor. After connecting through, a short circuit was induced at 25° C. for 30 minutes in a prelithiation solution, and a prelithiation process was performed on the negative electrode. At this time, during the prelithiation process, a pressure was applied to the stacked electrodes with a force of 1 kgf per ^{1.5 cm 2, thereby preparing a prelithiation negative electrode.}

Lastly, the pre-lithiated negative electrode was washed with ethyl methyl carbonate (EMC) for 30 minutes at 25° C. and then dried at room temperature to pre-lithiated negative electrode (lithiation: 50% of the total capacity of the negative electrode active material, OCV : 3.21V) was produced.

(Anode manufacturing)

Positive electrode active material (LiFePO ₄ ): conductive material (carbon black): binder (polyvinylidene fluoride (PVDF)) was added to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 90:5:5 A slurry (55% by weight solid content) was prepared. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 20 μm, and dried and roll pressed to prepare a positive electrode.

(Secondary battery manufacturing)

An electrode assembly was prepared by interposing a polyethylene material-based porous film between the negative electrode and the pre-lithiated negative electrode prepared above, and then placed in a battery case and an inorganic electrolyte (LiAlCl ₄ -3SO ₂ ) was injected into a lithium secondary battery. Was prepared.

Comparative Example 1.

(Cathode manufacturing)

A negative electrode active material (graphite), a conductive material (Denka Black), a binder (SBR), and a thickener (CMC) were added to water in a weight ratio of 92:3:3.5:1.5 to prepare a negative electrode active material slurry. The prepared negative electrode active material slurry was coated on one surface of a copper current collector, and dried and rolled to prepare a negative electrode. At this time, the prelithiation process is not performed on the negative electrode.

(Secondary battery manufacturing)

A lithium secondary battery was manufactured in the same manner as in Example 1, except that a negative electrode not subjected to the prelithiation process was used.

Comparative Example 2.

(Non-aqueous electrolyte manufacturing)

_{LiPF 6} was dissolved in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7 to a concentration of 1M to prepare a non-aqueous electrolyte for a lithium secondary battery.

(Secondary battery manufacturing)

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the prepared non-aqueous electrolyte was injected instead of the inorganic electrolyte.

Experimental example

Experimental Example 1. Evaluation of initial dose characteristics

For each of the lithium secondary battery prepared in Example 1 and the lithium secondary battery prepared in Comparative Examples 1 and 2, formation was performed at a current of 37 mA (0.1 C rate), and then 0.005 V at a rate of 0.1 C. Charging was performed under constant current conditions until, and discharged to 2.0 V at a 0.1C rate. At this time, after performing 2 cycles with the charge/discharge as 1 cycle, the specific capacity of the secondary battery is measured using a charge/discharger (manufacturer: TOYO, 5V), and the measured battery capacity is used as the initial battery capacity. It is set and shown in FIGS. 1 to 3 respectively. At this time, in FIGS. 1 to 3, a rising curve (solid line) of battery capacity indicates initial charging capacity, and a falling curve (dotted line) of battery capacity indicates initial discharge capacity.

Then, Coulombic efficiency (CE) was calculated using the initial battery capacity of the secondary batteries prepared in Example 1, Comparative Example 1, and Comparative Example 2, and the results are shown in Table 1 below. At this time, the Coulomb efficiency (%) is a value calculated using Equation 1 below.

[Equation 1]

Coulomb efficiency (%) = (discharge capacity after 2 cycles/2 charge capacity after cycles)×100

Coulomb efficiency (%) Example 1 98 Comparative Example 1 46.6 Comparative Example 2 92.8

Referring to Figure 1 and Table 1, the secondary battery of Example 1 using the pre-lithiated negative electrode and inorganic electrolyte (LiAlCl ₄ -3SO ₂ ) has reduced irreversible capacity, the initial discharge capacity is 153.29 mAh/g, and Coulomb efficiency. It can be seen that is 98%. On the other hand, looking at Figure 2 and Table 1, the initial discharge capacity of the secondary battery of Comparative Example 1 including the negative electrode and the inorganic electrolyte not prelithiated is 73.8 mAh / g, Coulomb efficiency is 46.6% of Example 1 It can be seen that it is deteriorated compared to the secondary battery. In addition, referring to FIG. 3 and Table 1, the initial discharge capacity of the secondary battery of Comparative Example 2 including an electrolithiated negative electrode and an electrolyte solution including a general carbonate-based organic solvent was 144.17 mAh/g, and the Coulomb efficiency was 92.8%. It can be seen that it is deteriorated compared to the secondary battery of Example 1.

Experimental Example 2. Cycle capacity evaluation

The lithium secondary battery prepared in Example 1 and the lithium secondary battery prepared in Comparative Example 1 were formed at a current of 37 mA (0.1 C rate), and then charged at a constant current condition to 0.005V at a 0.1C rate. And discharged to 2.0V at a 0.1C rate. After the charging/discharging was performed as 1 cycle, 2 cycles were performed, and the initial discharge capacity was measured using a PNE-0506 charging/discharging machine (manufacturer: PNE Solution Co., Ltd., 5V, 6A).

Then, 50 cycles were each performed under the above charging and discharging conditions, and then the charging capacity and the discharging capacity after 50 cycles were measured using a charging/discharging machine (manufacturer: TOYO, 5V). The capacity retention rate (%) after 50 cycles was calculated using Equation 2 below, and the results are shown in FIGS. 4 and 5, respectively. In addition, the Coulomb efficiency of the secondary batteries prepared in Example 1 and Comparative Example 1 was calculated using Equation 3 below, and the result values are shown in FIGS. 4 and 5, respectively.

[Equation 2]

Capacity retention rate (%) = (discharge capacity after 50 cycles/initial discharge capacity) × 100

[Equation 3]

Coulomb efficiency (%) = (discharge capacity after 50 cycles/charge capacity after 50 cycles)×100

Referring to FIG. 4, it can be seen that the capacity retention rate after 50 cycles of the secondary battery of Example 1 including the prelithiated negative electrode and the inorganic electrolyte (LiAlCl ₄ -3SO _{2) was 81.5% and the Coulomb efficiency was 100%.} .

On the other hand, referring to FIG. 5, the capacity retention rate after 50 cycles of the secondary battery of Comparative Example 1 including the non-lithiated negative electrode and the inorganic electrolyte was 8.1%, and the Coulomb efficiency was 95%. It can be seen that it is lower than that.

Claims (11)

Pre-lithiation carbon-based cathode, anode, separator, and
Lithium secondary battery comprising an inorganic electrolyte represented by the following formula (1).
[Formula 1]
LiMX-n(SO ₂ )
In Formula 1,
M is at least one metal selected from an alkali metal, a transition metal, and a post-transition metal, X is a halogen element, and n is an integer from 1 to 4.
The method according to claim 1,
The lithium secondary battery in which the pre-lithiated carbon-based negative electrode has a capacity of 30% to 90% of the total capacity of the negative electrode active material through pre-lithiation.
The method according to claim 1,
The positive electrode is a lithium secondary battery comprising a lithium transition metal phosphate.
The method according to claim 1,
In Formula 1, M is at least one metal selected from the group consisting of Al, Ga, Cu, Mn, Co, Ni, Zn, and Pd, and the halogen element is selected from the group consisting of F, Cl, Br, and I. At least one lithium secondary battery.
The method according to claim 1,
The inorganic electrolyte is a lithium secondary battery containing _{LiAlCl 4} -3SO _2.
Preparing an all-lithiated carbon-based negative electrode;
Manufacturing an electrode assembly by sequentially laminating the pre-lithiated carbon-based negative electrode, a separator, and a positive electrode; And
The method for manufacturing a lithium secondary battery according to claim 1, comprising the step of inserting the electrode assembly into a battery case and injecting an inorganic electrolyte represented by the following formula (1).
[Formula 1]
LiMX-n(SO ₂ )
In Formula 1,
M is at least one metal selected from an alkali metal, a transition metal, and a post-transition metal, X is a halogen element, and n is an integer from 1 to 4.
The method of claim 6,
The step of preparing the pre-lithiated carbon-based negative electrode
Manufacturing a negative electrode by laminating a carbon-based negative electrode active material layer on the negative electrode current collector;
Preparing a prelithiation solution;
Impregnating the negative electrode into the prelithiation solution;
Manufacturing a negative electrode laminate for prelithiation by sequentially laminating a separator and a lithium metal as a counter electrode on the negative electrode; And
A method for manufacturing a lithium secondary battery comprising a; performing an electrolithiation process on the prelithiation negative electrode laminate to prepare a prelithiation carbon-based negative electrode.
The method of claim 7,
The prelithiation solution is a method of manufacturing a lithium secondary battery containing a lithium salt and an organic solvent.
The method of claim 7,
The impregnating step is carried out at a temperature of 10 ℃ to 75 ℃ for 30 minutes to 48 hours is a lithium secondary battery manufacturing method.
The method of claim 7,
The prelithiation process is performed by connecting the negative electrode active material layer of the negative electrode laminate and the lithium metal together using a conducting wire or copper foil, and then inducing a short circuit through the conducting wire or copper foil under the prelithiation solution. Secondary battery manufacturing method.
The method of claim 7,
The prelithiation process is performed at 10°C to 35°C for 30 minutes to 2 hours.

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