KR102631720B1 - Manufacturing method of lithium secondary battery - Google Patents

Abstract

The present invention relates to a method of manufacturing a lithium secondary battery that can exhibit improved capacity and energy density compared to existing lithium ion batteries and lithium metal secondary batteries, and has excellent safety and lifespan characteristics.

Description

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

Cross-Citation with Related Application(s)

This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0141790 dated November 7, 2019, and all contents disclosed in the document 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 they have a higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and lead sulfate batteries that use aqueous electrolyte solutions. In particular, as demand for electric vehicles (EVs) increases, the need for lithium secondary batteries with high energy density is increasing.

Lithium metal secondary batteries that use lithium metal as a negative electrode active material can significantly improve energy density compared to lithium-ion batteries that use conventional carbon-based or silicon-based active materials, so ongoing research is being conducted.

However, lithium metal is highly reactive and easily reacts with moisture and oxygen in the air, making the assembly process difficult, and as dissolution and precipitation reactions of lithium metal occur during operation, the lithium metal grows into dendrites, causing a short circuit in the battery.

Accordingly, efforts are continuing to develop lithium secondary batteries that have higher capacity and improved safety and lifespan characteristics compared to existing lithium ion batteries.

The purpose of the present invention is to provide a lithium secondary battery that can achieve higher energy density and has better safety and lifespan characteristics compared to existing lithium ion batteries and lithium metal secondary batteries.

According to one embodiment of the present invention, a negative electrode coated with a negative electrode 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; separation membrane; and assembling a battery containing an electrolyte, and

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

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

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

A method for manufacturing a lithium secondary battery is provided.

According to the present invention, a lithium secondary battery can be manufactured that can exhibit improved capacity and energy density compared to existing lithium ion batteries and lithium metal secondary batteries, and has excellent safety and lifespan characteristics.

Figure 1 is a schematic diagram explaining changes in the negative electrode in the manufacturing method of the lithium secondary battery of the present invention.

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as “comprise,” “comprise,” or “have” are intended to designate the presence of implemented features, steps, components, or a combination thereof, and are intended to indicate the presence of one or more other features or steps, It should be understood that the existence or addition possibility of components or combinations thereof is not excluded in advance.

Since the present invention can be subject to various changes and can take various forms, specific embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to a specific disclosed form, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical 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 existing lithium ion batteries and lithium metal secondary batteries.

Accordingly, according to one embodiment of the present invention,

A negative electrode coated with a negative electrode 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; separation membrane; and assembling a battery containing an electrolyte, and

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

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

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

A method for manufacturing a lithium secondary battery is provided.

Existing lithium-ion batteries have widely used carbon-based materials such as artificial graphite, natural graphite, and hard carbon that allow insertion/desorption of lithium as anode active materials. In particular, graphite is mainly used in commercial batteries due to its structural stability, low electrochemical reactivity, and excellent lithium ion storage ability, but its theoretical capacity is about 372 mAh/g, which limits its application to high-capacity batteries.

Accordingly, silicon, tin, etc., which can react with lithium to form an alloy, are being studied as replacement high-capacity anode materials, but these have the problem of accompanied by a significant volume change when lithium ions are inserted/desorbed.

Meanwhile, in the case of lithium metal, which can theoretically achieve the highest capacity, it is highly reactive with moisture and oxygen and is difficult to handle due to its brittle nature, resulting in poor fairness in the manufacture of lithium metal electrodes. In addition, lithium metal electrodes made of a current collector and a thin film of lithium metal may cause dendritic precipitation of lithium metal due to uneven electron density on the electrode surface during the lithium plating and dissolution process during battery operation. . In this case, the lithium metal (lithium dendrite) precipitated in dendrites cannot be used as an active material, and if dendritic lithium continues to grow, there is a problem of causing a short circuit in the battery.

Therefore, in the present invention, a battery is assembled using a negative electrode containing a typical 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 normal battery. After assembling it, it is charged with a positive electrode loading amount that is higher than the negative electrode loading amount, so that intercalation of the negative electrode active material and plating of lithium metal occur continuously to manufacture a lithium secondary battery. The lithium secondary battery manufactured in this way uses both the negative electrode active material included during battery assembly and the lithium metal plated during charging as the negative electrode active material, so it has high capacity compared to existing lithium-ion batteries and lithium metal secondary batteries. It exhibits significantly 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 the charging process, but assembly of the battery Since lithium metal is not handled separately at this stage, blocking moisture and oxygen is not necessary, making the assembly process simple. Additionally, when lithium metal is plated, the specific surface area of the anode active material layer, which is the plating surface, is very large, so the current density and overvoltage are significantly lower than those of a lithium metal thin film. Therefore, lithium metal can be uniformly plated on the surface of the negative electrode active material layer without growing in a dendritic form, 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 is coated with a negative electrode active material layer containing a carbon-based negative electrode 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; separation membrane; and assemble a battery containing the electrolyte. At this time, the ratio of the cathode loading amount to the anode loading amount (N/P ratio) is set to satisfy the range of 0.01 to 0.99.

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

For example, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc.

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

The current collector can take various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics. The thickness of the current collector may range from 3 to 500 ㎛, but is not limited thereto.

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

As the negative electrode active material, a carbon-based active material, an alloy of lithium metal, and/or a material that can react with lithium ions to reversibly form a lithium-containing compound may be used. However, lithium metal is excluded.

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

Alloys of lithium metal include lithium (Li), 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 tin (Sn).

Examples of materials that can react with lithium ions to reversibly form lithium-containing compounds include silicon-based active materials and tin-based active materials. Specifically, Si, _SiO , but not Si), Sn, SnO ₂ , Sn-C composite, Sn-R (where R is an alkali metal, an alkaline earth metal, a Group 13 to Group 16 element, a transition metal, a rare earth element, or a combination thereof, and Sn is (not), etc. 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 a combination thereof may be mentioned.

Additionally, lithium titanium oxide (LTO) can be used as the negative electrode active material. Lithium titanium oxide may be expressed as 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- , etc., but is not limited thereto.

The above-mentioned negative electrode active material is contained in 70 to 99.5% by weight, or 80 to 99% by weight of the total weight of the negative electrode active material layer (i.e., the negative electrode active material layer in the battery assembly stage before the lithium metal layer is formed, the same applies hereinafter). desirable. If the negative electrode active material content is less than 70% by weight, there may be a problem with energy density, and if it exceeds 99.5% by weight, there may be a problem with the active material peeling off due to insufficient binder content. However, in the case of lithium metal alloy, it can be used by electrolytic plating on the current collector in the form of a foil without a binder, so it can be used at 100% by weight.

The binder serves to adhere the active material particles to each other and also to adhere the active material to the current collector. Representative examples include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, and carboxylated poly. Vinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene. -Butadiene rubber, epoxy resin, nylon, etc. can be used, but are not limited to these.

The conductive material is used to provide conductivity to the electrode, and any electronically conductive material can be used as long as it does not cause chemical changes in the battery being constructed. For example, carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber; Metallic substances 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. In this case, the binder and conductive material described above may be used.

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

The lithium composite metal oxide includes lithium-manganese-based oxide (e.g., LiMnO ₂ , LiMn ₂ O ₄ , etc.), lithium-cobalt-based oxide (e.g., LiCoO _{2 ,} etc.), and lithium-nickel-based oxide (e.g. For example, LiNiO _2, etc.), lithium-nickel-manganese oxide (for example, LiNi _1-Y Mn _Y O ₂ (where, 0<Y<1), LiMn _2-z Ni _z O ₄ (where, 0<Z<2), etc.), lithium-nickel-cobalt-based oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (where 0<Y1<1), etc.), lithium-manganese-cobalt-based oxide ( For example, LiCo _1-Y2 Mn _Y2 O ₂ (where 0<Y2<1), LiMn _2-Z1 Co _Z1 O ₄ (where 0<Z1<2), etc.), lithium-nickel-manganese- Cobalt-based oxide (for example, Li(Ni _p Co _q Mn _r1 )O ₂ (where 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (where 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), or lithium-nickel-cobalt -Transition metal (M) oxide (for example, Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ (where M is from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo) One or more types are selected, and p2, q2, r3 and s2 are independent atomic fractions of elements, respectively, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2+ q2+r3+s2=1), etc.), and any one or two or more of these compounds may be included.

In addition, in order to supply a sufficient amount of lithium ions to the cathode when charging after assembling the battery, Ni-rich anode material (NCM811, NCM911) or Li-rich cathode material (Over -Lithiated layered (1-x)LiMO ₂ , where, 0<x<1) can 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, the loading amount per unit area of the positive active material layer is preferably 4 to 15 mAh/cm ² , 5 to 10 mAh/cm ² , or 5 to 8 mAh/cm ² . When the above-mentioned loading amount range is satisfied, a sufficient amount of lithium ions can be supplied from the positive electrode active material to the negative electrode during the charging stage 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 that does not occlude the irreversible phase, that is, the desorbed lithium ions again, after the lithium ions are desorbed during the initial charging of the battery.

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

The irreversible additive is not particularly limited as long as it is a compound having the above-mentioned effects, and specifically includes 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 these, one or more types selected from the group consisting of Li ₂ NiO ₂ , Li ₆ CoO ₄ , and Li ₃ N may be preferably used in terms of stable life performance and energy density.

The irreversible additive is preferably included in an amount of 10% by weight or less of the total weight of the positive electrode active material layer. If the irreversible additive exceeds 10% by weight of the total weight of the positive electrode active material layer, gelation problems may occur when manufacturing 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 cathode and anode is not particularly limited. For example, an active material slurry prepared by mixing an active material, a binder, and optionally a conductive material and/or an irreversible additive in an organic solvent is applied and dried on a current collector, and optionally compression molded on the current collector to improve electrode density. It can be manufactured.

The organic solvent is preferably one that can uniformly disperse the active material, binder, conductive material, and irreversible additive and that evaporates easily. Specific examples include, but are not limited to, N-methylpyrrolidone, acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol.

Meanwhile, the loading amount of the cathode and anode has an N/P ratio (=cathode loading amount/anode loading amount) in the range of 0.01 to 0.99. In this way, if the negative electrode loading amount is significantly lower than the positive electrode loading amount during the initial electrode assembly, lithium ions can be supplied from the positive electrode and plated on the negative electrode active material layer when the battery is charged. As a result, a lithium metal layer is formed on the negative electrode active material layer. It is possible to obtain a high-capacity cathode.

The separator separates the cathode from the anode and provides a passage for lithium ions to move, and any type commonly used in lithium batteries can be used. That is, one that has low resistance to ion movement in the electrolyte and has excellent electrolyte impregnation ability can be used. For example, it is selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of non-woven or woven fabric.

For example, a polyolefin-based polymer separator such as polyethylene or polypropylene, or a separator containing a coating layer containing a ceramic component or polymer material to ensure heat resistance or mechanical strength may be used. Such a separator may be used in a single-layer or multi-layer structure. You can. In one embodiment, the separator may be a separator manufactured by coating both sides of a polyolefin-based polymer substrate with a ceramic coating material containing ceramic particles and an ionic binder polymer.

The electrolyte may be an electrolyte solution containing lithium salt and a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc., which are commonly used in lithium secondary batteries.

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

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

The non-aqueous organic solvent may be carbonate-based, ester-based, ether-based, ketone-based, alcohol-based or aprotic solvent. The carbonate-based solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used, and the ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, and methyl propionate. , ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, etc. can be used. The ether-based solvent may be dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., and the ketone-based solvent may include cyclohexanone. there is. In addition, the alcohol-based solvent may be ethyl alcohol, isopropyl alcohol, etc., and the aprotic solvent may be R-CN (R is a C2 to C20 straight-chain, branched or ring-structured hydrocarbon group, of which Nitriles such as (may include an aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. may be used.

The non-aqueous organic solvents can be used alone or in a mixture of one or more, and when used in a mixture of more than one, the mixing ratio can be appropriately adjusted according to the desired battery performance, which is widely understood by those working in the field. It can be.

In addition, in the case of the carbonate-based solvent, it is recommended to use a mixture of cyclic carbonate and chain carbonate. In this case, excellent electrolyte performance can be obtained by mixing cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9.

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

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

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

The lithium salt is dissolved in the non-aqueous organic solvent and acts as a source of lithium ions in the battery, enabling the operation of a basic lithium secondary battery and serving as a substance that promotes the movement of lithium ions between the positive and negative electrodes. am. 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 combinations thereof. It can be used as a supporting electrolytic salt. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity. It can exhibit excellent electrolyte performance and lithium ions can move effectively.

Among the above electrolytes, electrolyte containing a large amount of FEC (Fluoroehtylene carbonate), which is known as an electrolyte suitable for lithium metal batteries, high concentrated electrolyte, TTE (1,1,2,2-tetrafluoroethyl-2,2,3,3) In the case of electrolytes containing fluorinated ether dilution solvents such as -tetrafluoropropyl ether) and OTE (1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether), suppression of electrolyte side reactions with the lithium plating layer is maximized. This may be the most desirable example for this experiment. That is, an electrolyte for suppressing electrolyte side reactions can be preferably used in the present invention.

In addition, the organic solid electrolyte includes, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, and polyvinylidene fluoride. , polymers containing secondary dissociation groups, etc. may be used.

Examples of the inorganic solid electrolyte include 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 , Nitride, halide, sulfate, etc. 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. For example, an electrode assembly is manufactured by sequentially stacking the positive electrode, separator, and negative electrode, placed in a battery case, and then injecting an electrolyte into the upper part of the case and capping the battery. It can be manufactured by sealing with a plate and gasket. When a solid electrolyte is included as the electrolyte, a solid electrolyte may be positioned between the anode and the cathode instead of a separator.

Next, the battery assembled as above is overcharged by an anode loading designed to be higher than the anode loading, to manufacture a final lithium secondary battery.

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

When initially assembling a battery, the negative electrode includes a negative electrode current collector 10 and a negative electrode active material layer 21. When the assembled battery is overcharged, the lithium desorbed from the positive electrode active material layer is first intercalated with the active material contained in the negative electrode active material layer, and after all intercalation is completed, it is plated on the pores and surfaces within the negative electrode active material layer. The negative active material layer has a very large specific surface area, low current density, and low overvoltage for lithium plating reaction, so lithium metal does not grow into dendrites during the lithium metal plating process and uniform plating can 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 completing the overcharge step includes a current collector 10, a negative electrode active material layer 22 intercalated with lithium, and a lithium metal layer 23, and the negative electrode active material Both the negative electrode active material and lithium metal contained in the layer 22 and the lithium metal layer 23 can be used as the active material of the negative electrode.

The overcharging step may be performed in one charge, or may be performed in two or more consecutive charges. Various charging methods can be used, 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 are not particularly limited.

When the overcharging step is performed in one charge, charging of the negative electrode active material (lithium intercalation) and plating of lithium metal occur continuously. The charging method may be an appropriate method selected from among the various charging methods described above. However, the positive electrode capacity must be charged to be higher than the negative electrode capacity, which may cause overcharging of the negative electrode and create a lithium plating layer after charging the negative electrode active material.

When the overcharging step is performed in two consecutive charges, the first charge is performed enough to cause the first charge of the active material included in the negative electrode active material layer, and then the second charge can be performed so that lithium metal can be continuously plated. . At this time, the conditions for one-time charging and two-time charging can be set differently considering the characteristics of each stage.

Specifically, two consecutive charges can be performed by performing primary charging equal to the initial loading amount of the negative electrode active material layer, and charging equal to the remaining positive loading amount during secondary charging. At this time, if high rate charging is performed during the lithium metal plating step, electrolyte side reactions may become more severe and internal resistance may increase, so it is desirable to lower the current during secondary charging than during primary charging.

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

Hereinafter, preferred examples of the present invention, comparative examples, and experimental examples for evaluating them will be described. However, the above examples are merely illustrative of the present description, and it is clear to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended patent claims. will be.

<Example 1>

Manufacturing of anode

LiNi _0.6 Co _0.2 Mn _0.2 O ₂ was used as the positive electrode active material, and the conductive material (carbon black) and binder (PVdF) were added to NMP (N-methyl-2-pyrrolidone) at a weight ratio of 94:3:3, respectively, and mixed. A positive electrode mixture was prepared.

The prepared positive electrode mixture was coated on a 20 ㎛ thick aluminum foil 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 cathode, and a conductive material (carbon black) and binder (PVdF) were added to NMP (N-methyl-2-pyrrolidone) at a weight ratio of 95:3:2 and mixed to prepare a cathode mixture.

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

Manufacturing of secondary batteries

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

Charging process

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

<Example 2 >

In the charging process of Example 1, the manufactured lithium secondary battery was charged at 0.2C to 3 mAh/cm ² , which is equivalent to the negative electrode loading, and then again at 0.1 C for the remaining 1.5 mAh/cm ² . A lithium secondary battery was manufactured in the same manner as above.

<Example 3>

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

<Example 4>

In the charging process of Example 1, the manufactured lithium secondary battery was charged at 0.2C to 3 mAh/cm ² , equivalent to the negative electrode loading, and then again at 0.3 C to 1.5 mAh/cm ² . A lithium secondary battery was manufactured in the same manner as above.

<Comparative Example 1>

In the charging process of Example 1, a lithium secondary battery was manufactured in the same manner as Example 1, except that the manufactured lithium secondary battery was charged at 0.2C at 3 mAh/cm ² , which is equivalent to the negative electrode loading amount.

<Comparative Example 2>

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

<Experimental Example 1>

In Examples 1 to 3 and Comparative Example 1, the loading amounts of the anode and cathode were measured as follows.

To measure the anode loading amount, coin punch the anode to 1.6 cm ² and conduct a coin half cell evaluation using a Li metal electrode as the counter electrode to measure the expressed capacity. The anode loading can be calculated by dividing the anode area by the measured capacity. Next, coin punch the cathode to 1.6 cm ² and proceed with coin half cell evaluation using a Li metal electrode as the counter electrode to measure the generated capacity. The cathode loading amount can be calculated by dividing the area of the cathode by the measured capacity. The anode loading amount was divided by the calculated cathode loading amount and is shown in Table 1 below.

Loading amount 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 charge/discharge capacity values measured after fully discharging the lithium secondary batteries in Examples 1 to 4 and Comparative Examples 1 to 2 at 0.5C are shown in Table 2, and again at room temperature for 200 times under the same charge and discharge conditions. Cycle evaluation was performed from cycle to cycle, and the capacity maintenance rate was calculated and shown in Table 2. (Discharge capacity after 200 cycles/discharge capacity after 1 cycle) × 100, expressed as life maintenance rate (%))

Initial charge capacity (mAh) Initial discharge capacity (mAh) Capacity maintenance 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 Examples 1 to 4, charging was performed so that intercalation of the negative electrode active material and plating of lithium metal occurred continuously, resulting in a high initial charge and discharge capacity, resulting in a high-capacity battery. It was confirmed that it could be manufactured. In addition, when checking the capacity maintenance rate at the 200 ^th cycle, it was confirmed that the battery life characteristics were similar to those of Comparative Example 1, in which only intercalation was performed on the negative electrode active material by charging only as much as the loading amount of the negative electrode, and only lithium metal was used as the negative electrode active material. Therefore, it was confirmed that it exhibited superior lifespan characteristics than Comparative Example 2, in which charging was carried out only by lithium plating. Meanwhile, Comparative Example 1, in which charging was carried out by the amount of negative electrode loading, had good lifespan characteristics, but the basic capacity was lower than that of the invention according to the present invention. It can be seen that it is significantly smaller compared to .

Furthermore, it can be confirmed that Example 2, which was charged twice, exhibited better lifespan characteristics than Example 1, which was charged once. However, Example 4, in which secondary charging was performed at a high current during two charging, is similar to Example 1, so performing secondary charging at a low current while charging twice was the best in terms of lifespan characteristics. You can check it.

10: cathode current collector
21: Negative active material layer
22: Negative active material layer with completed lithium intercalation
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 a negative electrode current collector; A positive electrode coated with a positive electrode active material layer on the positive electrode current collector; separation membrane; and assembling a battery containing an electrolyte, and
A method of manufacturing a lithium secondary battery comprising the step of charging the battery,
In the battery assembly step, the ratio of the negative electrode loading amount to the positive electrode loading amount (N/P ratio) is 0.01 to 0.99,
In the battery charging step, charging is performed according to the positive electrode loading amount, and lithium is plated on the pores and surface of the negative electrode active material layer to form a lithium metal layer on the negative electrode active material layer,
The battery charging step is performed twice in succession, with first charging equal to the initial loading of the negative electrode active material layer and secondary charging equal to the remaining positive positive loading, and the charging current during secondary charging is the same as that during primary charging. which is lower than the current,
Manufacturing method of lithium secondary battery.
delete According to paragraph 1,
A method of manufacturing a lithium secondary battery wherein the thickness of the lithium metal layer is 1 to 5000% of the thickness of the negative electrode active material layer.
According to paragraph 1,
A method of manufacturing a lithium secondary battery wherein the loading amount per unit area of the positive active material layer is 4 to 15 mAh/cm ² .
According to paragraph 1,
The positive electrode 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 one or more types of irreversible additives.
According to clause 5,
A 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.
According to paragraph 1,
The negative electrode active material includes: a carbon-based active material; alloys of lithium and a metal selected from the group consisting of sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, radium, aluminum, germanium and tin; Silicone-based active material; tin-based active material; and a method of manufacturing a lithium secondary battery comprising at least one selected from the group consisting of lithium titanium oxide.
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