KR20210055586A - Manufacturing method of lithium secondary battery - Google Patents

Abstract

The present invention relates to a method for manufacturing a lithium secondary battery capable of exhibiting improved capacity and energy density compared to a conventional lithium ion battery and a lithium metal secondary battery, and providing excellent safety and lifespan characteristics.

Description

Manufacturing method of lithium secondary battery {MANUFACTURING METHOD OF LITHIUM SECONDARY BATTERY}

Cross-reference with related application(s)

This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0141790 filed on November 7, 2019, and all contents disclosed in the documents of the Korean patent application are included as part of this specification.

The present invention relates to a method of manufacturing a lithium secondary battery.

Lithium secondary batteries developed in the early 1990s are in the spotlight because of their higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using aqueous electrolyte solutions. In particular, as the demand for electric vehicles (EV) has recently increased, the need for a lithium secondary battery having a high energy density is expanding.

Lithium metal secondary batteries using lithium metal as a negative electrode active material can significantly improve energy density compared to lithium ion batteries using conventional carbon-based and silicon-based active materials, and thus, continuous research is being conducted.

However, since lithium metal is highly reactive and reacts easily with moisture and oxygen in the air, the assembling process is difficult, and lithium metal grows into a dendrite as the lithium metal dissolves and precipitates during operation, causing a battery short circuit.

Accordingly, efforts to develop a lithium secondary battery having improved safety and lifespan characteristics while having a high capacity compared to a conventional lithium ion battery are being continued.

An object of the present invention is to provide a lithium secondary battery that can achieve a higher energy density and has more excellent safety and lifespan characteristics compared to conventional lithium ion batteries and lithium metal secondary batteries.

According to one embodiment of the present invention, a negative electrode coated with a negative active material layer on a negative electrode current collector; A positive electrode coated with a positive electrode active material layer on the positive electrode current collector; Separator; And assembling a battery containing an electrolyte, and

As a method of manufacturing a lithium secondary battery comprising the step of charging the battery,

In the battery assembly step, the negative electrode loading amount ratio (N/P ratio) to the positive electrode loading amount is 0.01 to 0.99,

In the battery charging step, charging is made by the amount of positive electrode loading,

A method of manufacturing a lithium secondary battery is provided.

According to the present invention, it is possible to manufacture a lithium secondary battery having improved capacity and energy density and excellent safety and lifespan characteristics compared to conventional lithium ion batteries and lithium metal secondary batteries.

1 is a schematic diagram illustrating a change of a negative electrode in a method of manufacturing a lithium secondary battery of the present invention.

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, step, component, or combination of the implemented features, one or more other features or steps, It is to be understood that the possibility of the presence or addition of components, or combinations thereof, is not preliminarily excluded.

The present invention will be described in detail below and exemplify specific embodiments, as various modifications can be made and various forms can be obtained. However, this is not intended to limit the present invention to a specific form disclosed, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

The present invention relates to a method of manufacturing a lithium secondary battery that exhibits high energy density and has excellent safety and lifespan characteristics compared to conventional lithium ion batteries and lithium metal secondary batteries.

Accordingly, according to an embodiment of the present invention,

A negative electrode coated with a negative electrode active material layer on the negative electrode current collector; A positive electrode coated with a positive electrode active material layer on the positive electrode current collector; Separator; And assembling a battery containing an electrolyte, and

As a method of manufacturing a lithium secondary battery comprising the step of charging the battery,

In the battery assembly step, the negative electrode loading amount ratio (N/P ratio) to the positive electrode loading amount is 0.01 to 0.99,

In the battery charging step, charging is made by the amount of positive electrode loading,

A method of manufacturing a lithium secondary battery is provided.

Conventional lithium-ion batteries have widely applied carbon-based materials such as artificial graphite, natural graphite, and hard carbon capable of intercalation/deintercalation of lithium as an anode active material. In particular, graphite is mainly used in commercial batteries due to its structural stability, low electron chemical reactivity, and excellent lithium ion storage capacity, but its theoretical capacity is about 372 mAh/g, and its application to high-capacity batteries is limited.

Accordingly, silicon, tin, etc., which can react with lithium to form an alloy as a high-capacity negative electrode material, are being studied as substitutes, but these have a problem that a significant volume change occurs when lithium ions are inserted/desorbed.

On the other hand, in the case of lithium metal, which can theoretically achieve the highest capacity, it is difficult to handle because of its high reactivity with moisture and oxygen and its soft nature, and there is a problem that fairness is inferior when manufacturing a lithium metal electrode. In addition, a lithium metal electrode made of a current collector and a thin film of lithium metal may cause a phenomenon in which lithium metal is deposited as a dendritic due to uneven electron density on the electrode surface during the lithium plating and dissolution process when the battery is driven. . In this case, the lithium metal (lithium dendrite) deposited in the dendritic form cannot be used as an active material, and there is a problem that a battery short circuit occurs when the dendritic lithium continues to grow.

Accordingly, in the present invention, a battery is assembled using a negative electrode including a conventional negative electrode active material excluding lithium metal, but the ratio of the negative electrode loading amount to the positive electrode loading amount, that is, the N/P ratio, is set lower than that of a conventional battery. Then, the lithium secondary battery is manufactured by charging it by a positive electrode loading amount higher than that of the negative electrode loading amount so that intercalation of the negative electrode active material and plating of lithium metal occur continuously. The lithium secondary battery manufactured in this way uses both the negative electrode active material included in the battery assembly and the plated lithium metal as an active material for the negative electrode, so it has a higher capacity compared to the existing lithium ion battery and the lithium metal secondary battery. It shows remarkably improved safety and longevity characteristics.

That is, according to the manufacturing method of the present invention, the negative electrode of the finally manufactured lithium secondary battery has a structure including a negative electrode active material layer coated on a current collector and a lithium metal layer formed on the negative electrode active material layer during charging, but assembling a battery Since lithium metal is not separately handled in the step, it is not necessary to block moisture and oxygen, thus simplifying the assembly process. In addition, when the lithium metal is plated, the specific surface area of the negative electrode active material layer, which is the plating surface, is very large, so that the current density and overvoltage are significantly lower than that of the lithium metal thin film. Accordingly, lithium metal can be uniformly plated on the surface of the negative electrode active material layer without growing dendritic, and thus the plated lithium metal can be used as an active material.

Hereinafter, the present invention will be described in detail.

In the manufacturing method of the present invention, first, a negative electrode coated with a negative electrode active material layer including a carbon-based negative active material on a negative electrode current collector; A positive electrode coated with a positive electrode active material layer on the positive electrode current collector; Separator; And a battery containing an electrolyte is assembled. At this time, the negative electrode loading amount ratio (N/P ratio) to the positive electrode loading amount is set to satisfy the range of 0.01 to 0.99.

The positive electrode and negative electrode current collectors are not particularly limited as long as they have conductivity without causing chemical changes to the battery.

For example, as the positive electrode current collector, stainless steel, aluminum, nickel, titanium, calcined carbon, or a surface-treated aluminum or stainless steel surface with carbon, nickel, titanium, silver, or the like may be used.

In addition, as the negative electrode current collector, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, a surface-treated copper or stainless steel surface with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. have.

The current collector may be in various forms such as a film, a sheet, a foil, a net, a porous material, a foam, and a nonwoven fabric. The thickness of the current collector may be in the range of 3 to 500 μm, but is not limited thereto.

The negative active material layer includes a negative active material, a binder, and optionally a conductive material.

As the negative active material, a carbon-based active material, an alloy of lithium metal, and/or a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions may be used. However, lithium metal is excluded.

As the carbon-based active material, crystalline carbon, amorphous carbon, or a combination thereof may be used. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite, and such graphite may be in the form of amorphous, plate, flake, spherical or fibrous. Examples of the amorphous carbon include soft carbon (low temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, and the like.

Lithium metal alloys include lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), and calcium (Ca ), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), germanium (Ge), and an alloy of a metal selected from the group consisting of tin (Sn).

Examples of a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions include a silicon-based active material and a tin-based active material. Specifically, Si, SiO _x (0 <x <2), Si-C composite, Si-Q alloy (where Q is an alkali metal, alkaline earth metal, group 13 to 16 element, transition metal, rare earth element, or a combination thereof And not Si), Sn, SnO ₂ , Sn-C complex, Sn-R (wherein R is an alkali metal, alkaline earth metal, group 13-16 element, transition metal, rare earth element, or a combination thereof, Sn is Or not). Specific elements of Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, or combinations thereof.

In addition, lithium titanium oxide (LTO) may be used as the negative active material. Lithium titanium oxide may be represented by Li _a Ti _b O ₄ (0.5 ≤ a ≤ 3, 1 ≤ b ≤ 2.5), specifically Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , It may be Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O _4- or the like, but is not limited thereto.

The negative electrode active material described above is included in an amount of 70 to 99.5% by weight, or 80 to 99% by weight of the total weight of the negative electrode active material layer (that is, before the lithium metal layer is formed, as the negative electrode active material layer in the battery assembly step, the same applies hereinafter). desirable. If the content of the negative active material is less than 70% by weight, there may be a disadvantage in energy density, and if it exceeds 99.5% by weight, there may be a problem in that the active material is peeled off due to insufficient amount of the binder. However, in the case of an alloy of lithium metal, since it can be used by electrolytic plating on the current collector in the form of a foil without a binder, it can be used in an amount of 100% by weight.

The binder adheres the active material particles well to each other and also plays a role in adhering the active material to the current collector, and representative examples thereof include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, polyvinyl chloride, carboxylated poly Vinyl chloride, polyvinylfluoride, polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene -Butadiene rubber, epoxy resin, nylon, etc. may be used, but the present invention is not limited thereto.

The conductive material is used for imparting conductivity to the electrode, and does not cause chemical changes in the battery to be constituted, and any electronically conductive material may be used. For example, carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; Metal-based materials such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

The positive electrode active material layer includes a positive electrode active material, a binder, and optionally a conductive material, wherein the binder and the conductive material described above may be used.

As the positive electrode active material, a compound known in the art as a compound capable of reversible insertion and desorption of lithium may be used without limitation. Specifically, the positive electrode active material may be a lithium composite metal oxide containing at least one metal such as cobalt, manganese, nickel, or aluminum, and lithium.

Examples of the lithium composite metal oxide include lithium-manganese-based oxides (eg, LiMnO ₂ , LiMn ₂ O _4, etc.), lithium-cobalt-based oxides (eg, LiCoO _2, etc.), and lithium-nickel-based oxides (eg For example, LiNiO ₂ ), lithium-nickel-manganese oxide (e.g., LiNi _1-Y Mn _Y O ₂ (here, 0<Y<1), LiMn _2-z Ni _z O ₄ (here, 0<Z<2), lithium-nickel-cobalt oxide (e.g., LiNi _1-Y1 Co _Y1 O ₂ (here, 0<Y1<1), etc.), lithium-manganese-cobalt oxide ( For example, 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 oxide (for example, Li(Ni _p Co _q Mn _r1 )O ₂ (here, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (here, 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 from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo) Is at least one selected, and p2, q2, r3, and s2 are the atomic fractions of each independent element, 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 compounds may be included.

In addition, Ni-rich cathode material (NCM811, NCM911) or Li-rich cathode material (Over-Lithiated layered (1-x)LiMO ₂ , where, in order to supply a sufficient amount of lithium ions to the anode when charging after assembling the battery, 0<x<1) may be used, and specifically, it is preferable to use _{Li[Li 0.2} Mn _0.54 Ni _0.13 Co _0.13 ]O _2.

In addition, it is preferable that the loading amount per unit area of the positive active material layer is 4 to 15 mAh/cm ² , 5 to 10 mAh/cm ² , or 5 to 8 mAh/cm ^2. When the above-described loading amount range is satisfied, a sufficient amount of lithium ions may be supplied to the negative electrode from the positive electrode active material in the charging step of the battery.

Meanwhile, the positive electrode active material layer of the present invention may further include an irreversible additive in order to supply a sufficient amount of lithium ions to the negative electrode. The irreversible additive refers to a material in which lithium ions are desorbed during the initial charging of a battery, and then in an irreversible phase, that is, a material that does not occlude the desorbed lithium ions.

At this time, lithium ions may remain in the irreversible additive converted to the irreversible phase, and the remaining lithium ions are reversibly occluded and released, but the lithium ions released during the initial charge are returned to the irreversible compensation additive during subsequent discharge. It is not occluded and is plated on the cathode.

The irreversible additive is not particularly limited as long as it is a compound having the above-described effect, but specifically Li _7/3 Ti _5/3 O ₄ , Li _2.3 Mo ₆ S _7.7 , Li ₂ NiO ₂ , Li ₂ CuO _2, Li ₆ CoO ₄ , Li ₅ FeO ₄ , Li ₆ MnO ₄ , Li ₂ MoO ₃ , Li ₃ N, Li ₂ O, LiOH and Li ₂ CO ₃ selected from the group consisting of There may be more than one type. Among them, in terms of stable life performance and energy density, preferably at least one selected from the group _{consisting of Li 2} NiO ₂ , Li ₆ CoO ₄ , and Li _{3 N may be used.}

It is preferable that the irreversible additive is included in an amount of 10% by weight or less of the total weight of the positive electrode active material layer. When the irreversible additive exceeds 10% by weight of the total weight of the positive electrode active material layer, a problem of gelation may occur during preparation of the positive electrode slurry. The irreversible additive is a material that is selectively used to supply a larger amount of lithium ions to the negative electrode, and there is no limit to the lower limit.

The method of manufacturing the negative electrode and the positive electrode is not particularly limited. For example, an active material slurry prepared by mixing an active material, a binder, optionally, a conductive material and/or an irreversible additive in an organic solvent, is applied and dried on the current collector, and optionally compression molded on the current collector to improve the electrode density. It can be manufactured by doing.

As the organic solvent, an active material, a binder, a conductive material, and an irreversible additive can be uniformly dispersed, and it is preferable to use one that evaporates easily. Specifically, N-methylpyrrolidone, acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol may be exemplified, but are not limited thereto.

On the other hand, the loading amount of the negative electrode and the positive electrode, the N/P ratio (= negative electrode loading amount / positive electrode loading amount) is in the range of 0.01 to 0.99. In this way, when the negative electrode loading amount is significantly lower than that of the positive electrode loading amount during the initial assembly of the electrode, lithium ions are supplied from the positive electrode when charging the battery to be plated on the negative active material layer. Accordingly, the lithium metal layer is formed on the negative active material layer. Can be produced to obtain a high-capacity negative electrode.

The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions, and any one commonly used in a lithium battery may be used. That is, those having low resistance to ion migration of the electrolyte and excellent in impregnating the electrolyte may be used. For example, as selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, it may be in the form of a non-woven fabric or a woven fabric.

For example, a polyolefin-based polymer separator such as polyethylene, polypropylene, etc., or a separator including a coating layer containing a ceramic component or a polymer material to secure heat resistance or mechanical strength, may be used, and such a separator may be used in a single layer or a multilayer structure. I can. In one embodiment, as the separator, a separator prepared by coating a ceramic coating material containing ceramic particles and an ionic binder polymer on both surfaces of a polyolefin-based polymer substrate may be used.

As the electrolyte, an electrolyte solution including a lithium salt and a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like, which are usually used in a lithium secondary battery, may be used.

The electrolyte solution contains a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent may be used. As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), and the like may be used, and as the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methylpropionate , Ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and the like may be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether solvent, and cyclohexanone may be used as the ketone solvent. have. In addition, ethyl alcohol, isopropyl alcohol, and the like may be used as the alcohol-based solvent, and R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, wherein A bonded aromatic ring or an ether bond), such as nitriles, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like may be used.

The non-aqueous organic solvent may be used alone or in combination of one or more, and the mixing ratio in the case of using one or more mixtures may be appropriately adjusted according to the desired battery performance, which is widely understood by those in the field. Can be.

In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte may exhibit excellent performance.

The non-aqueous organic solvent may further include the aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. At this time, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

The non-aqueous electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound to improve battery life.

Representative examples of the ethylene carbonate-based compound include difluoro ethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, vinylene. Ethylene carbonate, etc. are mentioned. When the vinylene carbonate or the ethylene carbonate-based compound is further used, the lifespan may be improved by appropriately adjusting the amount of the vinylene carbonate or the ethylene carbonate-based compound.

The lithium salt is dissolved in the non-aqueous organic solvent, acts as a source of lithium ions in the battery, enables the operation of a basic lithium secondary battery, and promotes the movement of lithium ions between the positive electrode and the negative electrode. to be. Representative examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _{2y +1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate; LiBOB) or a combination thereof The lithium salt is preferably used in the range of 0.1 to 2.0 M. If the concentration of the lithium salt falls within the above range, the electrolyte has an appropriate conductivity and viscosity. It can exhibit excellent electrolyte performance, and lithium ions can move effectively.

Among the above electrolytes, an electrolyte containing a large amount of FEC (Fluoroehtylene carbonate), which is known as an electrolyte suitable for lithium metal batteries, high concentration electrolyte, TTE (1,1,2,2-tetrafluoroethyl-2,2,3,3 -tetrafluoropropyl ether), OTE (1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether). This can be the most desirable example for this experiment. That is, an electrolyte for suppressing a side reaction of the electrolyte may be preferably used in the present invention.

In addition, as the organic solid electrolyte, for example, polyethylene derivative, polyethylene oxide derivative, polypropylene oxide derivative, phosphate ester polymer, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride , A polymer containing a secondary dissociation group, and the like may be used.

As the inorganic solid electrolyte, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS _{2 may be used.}

The method of manufacturing a lithium secondary battery is not particularly limited, and as an example, an electrode assembly is manufactured by sequentially stacking the positive electrode, the separator, and the negative electrode, placing it in a battery case, and then injecting an electrolyte solution into the upper part of the case, and It can be manufactured by sealing with a plate and a gasket. When a solid electrolyte is included as an electrolyte, a solid electrolyte may be positioned between the positive electrode and the negative electrode in place of the separator.

Next, for the battery assembled as described above, overcharging is performed as much as the positive electrode loading designed to be higher than the negative electrode loading, thereby manufacturing a final lithium secondary battery.

1 is a schematic diagram briefly explaining a process of changing a negative electrode in a method of manufacturing a lithium secondary battery of the present invention.

When initially assembled, the negative electrode includes a negative electrode current collector 10 and a negative electrode active material layer 21. Subsequently, when the assembled battery is overcharged, lithium desorbed from the positive electrode active material layer is first intercalated with the active material included in the negative electrode active material layer, and after all intercalation is completed, the voids and surfaces in the negative electrode active material layer are plated. Since the negative active material layer has a very large specific surface area and thus has a low current density and a low overvoltage for a lithium plating reaction, the lithium metal does not grow into a dendrite during the lithium metal plating process, and uniform plating may occur. As a result, the plated lithium metal can serve as a second negative electrode active material.

The negative electrode 100 of the lithium secondary battery finally manufactured after the overcharging step is completed includes a current collector 10, an intercalated negative electrode active material layer 22 and a lithium metal layer 23, and the negative active material Both the negative electrode active material and the lithium metal included in the layer 22 and the lithium metal layer 23 may be used as an active material of the negative electrode.

The overcharging step may be performed by one charging, or may be performed by two or more consecutive charging. The charging method can use various charging methods such as constant current-constant voltage mode (CC-CV mode), constant current mode (CC mode), constant voltage mode (CV mode), and constant power mode (CP mode) charging, and is not particularly limited.

When the overcharging step is performed in a single charge, charging of the negative active material (lithium intercalation) and plating of lithium metal occur continuously. As the filling method, an appropriate method may be selected from among various filling methods as described above. However, when the positive electrode capacity designed to be higher than the negative electrode is charged, overcharge proceeds to the negative electrode, so that a lithium plating layer may be generated after charging the negative active material.

When the overcharging step is performed by two consecutive charging, the active material included in the negative active material layer is first charged to the extent that the first charging occurs, and then the secondary charging may be performed so that the lithium metal can be continuously plated. . At this time, the conditions for charging once and charging twice may be set differently in consideration of the characteristics of each step.

Specifically, the first charging is performed as much as the initial loading amount of the negative active material layer, and when the second charging is performed, the remaining positive electrode loading amount is charged, so that two consecutive charging may be performed. In this case, if a high rate charging is performed in the step of plating lithium metal, the side reaction of the electrolyte may become severe and the internal resistance may increase. Therefore, it is preferable to lower the current during the secondary charging than during the primary charging.

The thickness of the lithium metal layer generated after the overcharging step may be in the range of 1 to 5000%, or 1 to 200% of the thickness of the negative active material layer. By satisfying this range, high capacity and long life can be realized.

Hereinafter, preferred examples of the present invention, comparative examples in contrast thereto, and experimental examples for evaluating them will be described. However, it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the present description and the scope of the technical idea, and such modifications and modifications belong to the appended claims. will be.

<Example 1>

Manufacture of anode

_{LiNi 0.6} Co _0.2 Mn _0.2 O ₂ was used as a positive electrode active material, and a conductive material (carbon black) and a binder (PVdF) were mixed in NMP (N-methyl-2-pyrrolidone) at a weight ratio of 94:3:3, respectively. A positive electrode mixture was prepared.

The prepared positive electrode mixture was coated on an aluminum foil having a thickness of 20 μm at ^{a loading amount of 4.5 mAh/cm 2} , and then rolled and dried to prepare a positive electrode.

Preparation of cathode

Artificial graphite was used as the negative electrode, and a conductive material (carbon black) and a binder (PVdF) were mixed in NMP (N-methyl-2-pyrrolidone) at a weight ratio of 95:3:2 to prepare a negative electrode mixture.

The prepared negative electrode mixture was coated on a 20 μm-thick copper foil at 3.0 mAh/cm ² , and then rolled and dried to prepare a negative electrode.

Manufacturing of secondary battery

A separator (DB307B, BA1 SRS composition, thickness: 15 µm, fabric 7 µm, applied in a thickness of 4 µm per side of SRS, total 8 µm) was interposed between the cathode and the anode, and the electrode assembly was laminated at a pressure of 1 kgf/mm line pressure. After manufacture, the electrode assembly was accommodated in a pouch-type battery case, propylene carbonate and dimethyl carbonate were mixed at a volume ratio of 2:8, and a non-aqueous electrolyte containing 3.8 M LiFSI as a lithium salt was added. A pouch-type lithium secondary battery was prepared.

Charging process

The lithium secondary battery prepared above was charged at ^{0.2C by 4.5mAh/cm 2} , which is equivalent to the positive electrode loading amount.

<Example 2 >

In the charging process of the first embodiment, the filling ² is manufactured as a lithium secondary battery negative electrode loading amounts to 3mAh 0.2C / cm, and except that the back rest by charging 1.5mAh / cm ² to 0.1C Example 1 In the same manner as, a lithium secondary battery was manufactured.

<Example 3>

When manufacturing the positive electrode of Example 1, LiNi _0.6 Co _0.2 Mn _0.2 O ₂ was used as a positive electrode active material, and an irreversible additive (Li ₂ NiO ₂ ), a conductive material (carbon black), and a binder (PVdF) were each 88: 2: A lithium secondary battery was manufactured in the same manner as in Example 1, except that a positive electrode mixture was prepared by mixing in NMP (N-methyl-2-pyrrolidone) at a weight ratio of 5:4.

<Example 4>

In the charging process of the first embodiment, and is carried out except that the 3mAh / cm ² as the negative electrode loading amounts of the lithium secondary battery is manufactured by a 0.2C charge and re-charge the 1.5mAh / cm ² to 0.3C Example 1 In the same manner as, a lithium secondary battery was manufactured.

<Comparative Example 1>

In the charging process of Example 1, a lithium secondary battery was manufactured in the same manner as in Example 1, except that the prepared lithium secondary battery was charged ^{at 0.2 C by 3 mAh/cm 2 equal to the negative electrode loading amount.}

<Comparative Example 2>

A lithium secondary battery was manufactured in the same manner as in Example 1, except that a lithium metal negative electrode of 60 μm was applied as the negative electrode active material in Example 1 above.

<Experimental Example 1>

In Examples 1 to 3 and Comparative Example 1, the loading amounts of the positive and negative electrodes were measured as follows.

To measure the amount of positive electrode loading, the positive electrode ^{was coin-punched with 1.6 cm 2} , and the coin half cell was evaluated using a Li metal electrode as the counter electrode to measure the expression capacity. By dividing the anode area from the measured expression capacity, the anode loading amount can be calculated. Then, coin-puncture the cathode with 1.6 cm ² and measure the expression capacity by conducting coin half cell evaluation using a Li metal electrode as the counter electrode. The negative electrode loading amount can be calculated by dividing the area of the negative electrode from the measured expression capacity. The positive electrode loading amount was divided by the calculated negative electrode loading amount and shown in Table 1 below.

Loading ratio Example 1 0.67 Example 2 0.67 Example 3 0.60 Example 4 0.67 Comparative Example 1 0.67

<Experimental Example 2>

The charging/discharging capacity values measured after completely discharging the lithium secondary battery charged in Examples 1 to 4 and Comparative Examples 1 to 2 at 0.5C are shown in Table 2, and again 200th at room temperature under the same charging and discharging conditions. The cycle evaluation was performed until the cycle, and the capacity retention rate was calculated and shown in Table 2. (Discharge capacity after 200 cycles/discharge capacity after cycle) x 100 is expressed as a life retention rate (%))

Initial charging capacity (mAh) Initial discharge capacity (mAh) Capacity retention rate
@ 200th cycle Example 1 75 69 96% Example 2 76 70 99% Example 3 80 69 99% Example 4 75 70 95% Comparative Example 1 50 46 96% Comparative Example 2 75 69 75%

Referring to Table 2, in the case of Examples 1 to 4, the initial charge/discharge capacity is expressed high by charging so that intercalation of the negative electrode active material and plating of lithium metal occur continuously. It was confirmed that it could be manufactured. In addition ^{, when checking the capacity retention rate in the 200 th} cycle, it was confirmed that the charging was performed only as much as the loading amount of the negative electrode and the same lifespan characteristics as Comparative Example 1 in which only intercalation was performed on the negative electrode active material was displayed. Only lithium metal was used as the negative electrode active material. Thus, it was confirmed that the lifespan characteristics were superior to those of Comparative Example 2, in which charging was performed only by lithium plating. On the other hand, Comparative Example 1, in which charging was performed by the amount of negative electrode loading, had good life characteristics, but the basic capacity was the invention according to the present invention. Compared with, it can be seen that it is significantly smaller.

Furthermore, it can be seen that Example 2, which is charged twice, exhibits more excellent life characteristics than Example 1, which is charged once. However, since Example 4, in which the secondary charging was performed at a high current in the second charge, is similar to Example 1, the second charging while performing the secondary charging at a low current is the best in terms of life characteristics. I can confirm.

10: negative electrode current collector
21: negative active material layer
22: negative active material layer on which lithium intercalation has been completed
23: lithium metal layer
100: negative electrode of the final manufactured lithium secondary battery

Claims (9)

A negative electrode coated with a negative electrode active material layer on the negative electrode current collector; A positive electrode coated with a positive electrode active material layer on the positive electrode current collector; Separator; And assembling a battery containing an electrolyte, and
As a method of manufacturing a lithium secondary battery comprising the step of charging the battery,
In the battery assembly step, the negative electrode loading amount ratio (N/P ratio) to the positive electrode loading amount is 0.01 to 0.99,
In the battery charging step, charging is made by the amount of positive electrode loading,
Method of manufacturing a lithium secondary battery.
The method of claim 1,
In the step of charging the battery, lithium is plated on the pores and surfaces of the negative active material layer to form a lithium metal layer on the negative active material layer.
The method of claim 2,
The thickness of the lithium metal layer is a method of manufacturing a lithium secondary battery of 1 to 5000% of the thickness of the negative electrode active material layer.
The method of claim 1,
A method of manufacturing a lithium secondary battery in which the loading amount per unit area of the positive active material layer is 4 to 15 mAh/cm ^2.
The method of claim 1,
The positive active material layer is Li _7/3 Ti _5/3 O ₄ , Li _2.3 Mo ₆ S _7.7 , Li ₂ NiO ₂ , Li ₂ CuO _2, Li ₆ CoO ₄ , Li ₅ FeO ₄ , Li ₆ MnO ₄ , Li ₂ MoO ₃ , Li ₃ N, Li ₂ O, LiOH and Li ₂ CO ₃ selected from the group consisting of A method of manufacturing a lithium secondary battery further comprising at least one irreversible additive.
The method of claim 5,
The method of manufacturing a lithium secondary battery, wherein the irreversible additive is contained in an amount of 10% by weight or less of the total weight of the positive electrode active material layer.
The method of claim 1,
The negative active material may include a carbon-based active material; An alloy of lithium with a metal selected from the group consisting of sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, radium, aluminum, germanium and tin; Silicon-based active material; Tin-based active material; And at least one lithium secondary battery selected from the group consisting of lithium titanium oxide.
The method of claim 1,
The battery charging step is a method of manufacturing a lithium secondary battery that is performed twice in a row.
The method of claim 8,
In the step of charging the battery, the charging current at the time of charging twice is lower than the charging current at the time of charging once.

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