KR102460812B1 - A negative electrode for a lithium secondary battery into which a lithiation retardation layer is introduced and a method for manufacturing the same - Google Patents

Abstract

A negative electrode for a lithium secondary battery of the present invention, the negative electrode active material layer; a lithiation delay layer formed on the anode active material layer; and a lithium layer formed on the lithiation delay layer, wherein the lithiation delay layer is soluble in an electrolyte.

Description

A negative electrode for a lithium secondary battery into which a lithiation retardation layer is introduced and a method for manufacturing the same

The present invention relates to a negative electrode for a lithium secondary battery, a lithium secondary battery including the negative electrode, and a manufacturing method thereof.

As the price of energy sources increases due to the depletion of fossil fuels and interest in environmental pollution is increased, the demand for eco-friendly alternative energy sources is becoming an indispensable factor for future life, and in particular, technology development for mobile devices. As energy consumption increases, the demand for secondary batteries as an energy source is rapidly increasing.

Representatively, in terms of battery shape, there is a high demand for prismatic secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones with thin thickness, and in terms of materials, lithium ion batteries with high energy density, discharge voltage, and output stability, Demand for lithium secondary batteries such as lithium ion polymer batteries is high.

In general, secondary batteries apply an electrode mixture containing an electrode active material to the surface of a current collector to form a positive electrode and a negative electrode, and a separator is interposed therebetween to make an electrode assembly, then a cylindrical or prismatic metal can or aluminum laminate sheet It is mounted inside the pouch-type case of the electrode assembly, mainly by injecting or impregnating a liquid electrolyte or using a solid electrolyte.

Generally, a carbon material such as graphite is used for the negative electrode of a lithium secondary battery, but the theoretical capacity density of carbon is 372 mAh/g (833 mAh/cm ³ ). Therefore, in order to improve the energy density of the anode, silicon (Si), tin (Sn), oxides and alloys thereof, which are alloyed with lithium, are considered as anode materials. Among them, silicon-based materials have attracted attention due to their low price and high capacity (4200 mAh/g).

Although such a silicon-based material exhibits a high capacity, a problem arises in that the initial irreversible capacity is large. In the charging/discharging reaction of a lithium secondary battery, lithium released from the positive electrode is inserted into the negative electrode during charging, and during discharging, it is detached from the negative electrode and returns to the positive electrode. A large amount of lithium inserted into the negative electrode does not return to the positive electrode again, and thus the initial irreversible capacity increases. When the initial irreversible capacity increases, there is a problem in that the battery capacity and cycle rapidly decrease.

As one of the methods for solving the problems related to the initial irreversibility, a (pre-lithiation) technology in which lithium is pre-inserted into the negative electrode has been tried. Among them, the lithium direct contact method is a method of directly laminating a thin film lithium on the negative electrode layer. After cell assembly, an electrolyte is injected to cause diffusion of lithium in the lithium layer to the negative electrode, thereby increasing the lithium content in the negative electrode, thereby reducing irreversible capacity. tried to solve the problem.

However, in the lithiation method of the above method, the active material particles in direct contact with the lithium layer are rapidly lithiated, but the active material particles on the current collector side are far from the lithium layer, so the lithiation proceeds slowly. Such a difference according to the lithium diffusion distance may cause side effects such as detachment of the silicon-based active material electrode.

In addition, there is a time interval from cell assembly to injection of electrolyte or initial charging and discharging. Prior to injection of electrolyte, lithium in the lithium layer attached to the negative electrode is non-uniformly moved into the negative electrode (solid-diffusion), resulting in lower resistance. There is a problem in that the amount of lithium increases as lithium is diffused into the atmosphere and the amount of lithium is lost. Therefore, it is necessary to proceed with lithiation evenly in the thickness direction of the negative electrode.

On the other hand, Korean Patent Laid-Open Patent No. 10-2018-0057513 discloses that during (pre)lithiation by the lithium direct contact method, lithiation occurs as the material of the electrode layer and the lithium layer directly contact, raising the problem of fire or explosion. A technique of interposing a total lithiation prevention layer between lithium layers is disclosed. However, although the proposed technique is suitable for forming a lithium layer by lamination, the pre-lithiation prevention layer does not have sufficient heat resistance, so it is not suitable for forming a lithium layer by a thermal evaporation method. In addition, the total lithiation prevention layer continues to remain in the negative electrode, which may act as a resistance.

Therefore, in forming the lithium layer by the thermal deposition method, there is a need to develop a lithiation technology that does not increase resistance while proceeding lithiation slowly so that lithium is evenly diffused in the anode active material layer.

Korean Patent Publication No. 10-2018-0057513

The present invention has been devised to solve the above problems, and it is an object of the present invention to provide an anode and a method for manufacturing the same without increasing resistance while allowing lithium to be evenly spread in an anode active material layer by slowly lithiation.

A negative electrode for a lithium secondary battery according to an embodiment of the present invention includes an anode active material layer; a lithiation delay layer formed on the anode active material layer; and a lithium layer formed on the lithiation delay layer, wherein the lithium layer has an average surface roughness of a surface in contact with the lithiation delay layer and an opposite surface of 0.4 µm or less. In addition, the lithiation delay layer is soluble in the electrolyte.

In one embodiment of the present invention, the lithiation delay layer is a polymer including acrylate repeating units or carbonate repeating units.

In a specific embodiment, the lithiation delay layer includes a polymer having a carbonate repeating unit. In this case, the surface roughness of the surface of the lithium layer in contact with the lithiation retardation layer and the opposite surface is in the range of 0.05 to 0.35 μm on average.

In one embodiment of the present invention, the thickness of the lithiation delay layer is 0.1 to 5㎛.

In one embodiment of the present invention, the thickness of the lithium layer is 0.5 to 30㎛.

In an embodiment of the present invention, the negative active material included in the negative active material layer is a silicon-based negative active material.

In one embodiment of the present invention, the lithiation delay layer is dissolved in a carbonate-based electrolyte.

The method for manufacturing a negative electrode for a lithium secondary battery according to the present invention comprises the steps of: forming a lithiation delay layer on the negative electrode active material layer by supporting the negative electrode in a solution containing an amorphous polymer and drying the; and depositing lithium on the lithiation delay layer to form a lithium layer.

In an embodiment of the present invention, the forming of the lithium layer is deposited using a thermal evaporation method.

In one embodiment of the present invention, in the step of forming the lithiation delay layer, the amorphous polymer is a polymer including an acrylate repeating unit or a carbonate repeating unit.

In an embodiment of the present invention, the negative active material included in the negative active material layer is a silicon-based negative active material.

The lithium secondary battery of the present invention includes the above-described negative electrode, a separator positioned therebetween, and an electrolyte.

In the negative electrode for a lithium secondary battery according to the present invention, a lithiation delay layer including a polymer soluble in an electrolyte is introduced between the negative electrode active material layer and the lithium layer, and the lithiation delay layer delays the diffusion rate of lithium. , since lithiation of the anode active material progresses slowly, lithiation is uniformly lithiated in the thickness direction of the anode active material layer, and the irreversible capacity compensation effect is excellent. .

In addition, the lithiation delay layer of the negative electrode for a lithium secondary battery according to the present invention has excellent heat resistance, and has an advantage in that the lithiation layer can be more stably formed when the lithiation layer is formed by thermal evaporation.

1 is a cross-sectional view of a cathode according to an embodiment of the present invention.
2 is a flowchart of a method of manufacturing an anode according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined in

In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It is to be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof. Also, when a part of a layer, film, region, plate, etc. is said to be “on” another part, this includes not only cases where it is “directly on” another part, but also cases where another part is in between. Conversely, when a part of a layer, film, region, plate, etc. is said to be “under” another part, this includes not only cases where it is “directly under” another part, but also cases where there is another part in between. In addition, in the present application, “on” may include the case of being disposed not only on the upper part but also on the lower part.

Hereinafter, the present invention will be described in detail.

1 is a cross-sectional view of a negative electrode 100 according to an embodiment of the present invention, specifically showing the structure of the negative electrode before lithiation. Referring to FIG. 1 , the negative electrode 100 includes a current collector 110 ; a negative active material layer 120 formed on the current collector 110; a lithiation delay layer 130 formed on the anode active material layer 120; and a lithium layer 140 formed on the lithiation delay layer 130 is sequentially stacked.

Specifically, the lithium layer 140 has a surface roughness (Ra) of less than or equal to 0.4 µm, more specifically in the range of 0.05 to 0.4 µm, in the range of 0.1 to 0.4 µm, or 0.15 to 0.2 μm.

In the negative electrode of the present invention, a lithiation delay layer 130 is introduced between the negative electrode active material layer 120 and the lithium layer 140 to relieve the diffusion rate of lithium from the lithium layer, and thus lithium is introduced into the negative electrode active material layer. It helps to spread evenly. The lithiation delay layer of the present invention functions as a lithiation delay layer for delaying the rapid diffusion of lithium during the lithiation time according to the impregnation of the electrolyte. Therefore, since the anode active material particles are lithiated gradually and uniformly regardless of the distance from the lithium layer, the risk of explosion due to a sudden reaction between the anode active material and lithium particles is lowered, and the problem of desorption of the anode due to non-uniform lithiation is eliminated. is effective in preventing it.

In addition, after the entire amount or a significant amount of lithium in the lithium layer is inserted into the negative electrode active material layer by lithiation, the lithiation delay layer is soluble in the electrolyte and does not remain in the negative electrode, so that it does not act as a resistance of the battery.

The lithiation delay layer of the present invention is characterized in that a material soluble in an electrolyte is selected as a material constituting the lithiation delay layer so as not to act as a resistance after lithiation is completed.

In a specific embodiment of the present invention, the lithiation delay layer includes, as an amorphous polymer, a polymer including acrylate repeating units or carbonate repeating units. The polymer having the above characteristics is well dissolved in a typical electrolyte of a lithium secondary battery. Specific examples of such polymers may include polymethyl methacrylate (PMMA)-based or polycarbonate (PC)-based polymers. These polymers are known to dissolve well in carbonate-based pronuclear solutions commonly used as electrolytes.

In particular, since the lithiation delay layer is formed of a polymer including a carbonate repeating unit, excellent heat resistance and excellent surface uniformity at high temperatures can be realized.

On the other hand, in the present invention in which a lithium layer is formed on an anode by thermal evaporation, since the lithiation delay layer has the same function as a substrate, it is preferable that the lithiation delay layer of the present invention has heat resistance. desirable.
The thermal evaporation is characterized in that it is performed in the range of 460 to 850 °C based on the temperature of the supplied lithium.

In the thermal deposition method for forming the lithiation delay layer of the present invention, vaporized lithium is deposited on a substrate by heating a lithium ingot at 500 to 700 ° C. Since vaporized lithium has a high temperature, the substrate The silver must be able to withstand the heat of vaporized lithium sufficiently. That is, when the heat resistance of the lithiation delay layer serving as a substrate is low, the polymer chain has fluidity, and thus lithium deposition cannot be stably performed.

In this respect, it is preferable that the Tg of the polymer material constituting the lithiation delay layer of the present invention is 120° C. or higher. Therefore, it is more preferable to select a polymer having a Tg of 120°C or higher among the polymers including the acrylate repeating unit or the carbonate repeating unit. For example, polymethyl methacrylate-based polymers include repeating units on aromatic vinyl; imide-based repeating units; vinyl cyanide-based repeating units; and at least one repeating unit selected from the group consisting of a 3-membered to 6-month heterocyclic repeating unit substituted with at least one carbonyl group.

For example, polymethyl methacrylate having a phenyl maleimide functional group has a Tg of 120° C. or higher, and thus is particularly preferable as a material for the pre-lithiation delay layer of the present invention. In addition, since the polycarbonate-based polymer generally has a Tg of 120° C. or higher, it can be said that the polycarbonate-based polymer is also particularly preferable as a material for the pre-lithiation retardation layer of the present invention.

For example, when lithium is heated to 600° C. or higher during thermal deposition and supplied, it is advantageous to use a polymer including a carbonate repeating unit as the lithiation delay layer. In this case, the surface roughness (Ra) of the surface of the lithium layer in contact with the lithiation delay layer and the opposite surface can be controlled in the range of 0.05 to 0.35 μm. More specifically, the surface roughness (Ra) of the lithium layer is in the range of 0.05 to 0.3 μm, 0.1 to 0.3 μm, or 0.15 to 0.2 μm.

In a specific embodiment of the present invention, the thickness of the lithiation delay layer is 0.1 to 5 μm, specifically 0.3 to 3 μm, and more specifically 0.5 to 2 μm. If the thickness of the lithiation delay layer is too thick, it may take a long time to dissolve in the electrolyte, and it is not preferable because the ion conductivity may be lowered by increasing the viscosity of the electrolyte. Coating can be tricky in the process.
In a specific embodiment of the present invention, the thickness of the lithiation delay layer is in an average range of 0.5 to 1.5 μm, and the ratio of the average thickness (B) of the lithium layer to the average thickness (A) of the lithiation delay layer (B/ A) ranges from 3 to 7.

Hereinafter, the lithium layer will be described in detail.

The lithium layer is used as a source for lithiation of the anode active material contained in the anode active material layer, and as a certain amount of time passes after the electrolyte is injected, a predetermined amount of the lithium layer participates in pre-lithiation and the anode active material layer It moves to the inside, and a residual amount may exist on the surface of the negative electrode even after prelithiation is completed to some extent. The lithium layer includes lithium metal.

In a specific embodiment of the present invention, the thickness of the lithium layer is 0.5 to 30㎛, specifically 2 to 20㎛. The thickness of the lithium layer can be adjusted to an appropriate range depending on the irreversible capacity to be compensated, the material of the anode, etc., and in the case of an anode made of 100% pure silicon (Si) as in the embodiment of the present invention, the specific thickness range of the lithium layer is 3 to 20 μm, more specifically 5 to 15 μm or 6 to 14 μm.

Hereinafter, the current collector and the negative electrode active material layer constituting the negative electrode of the present invention will be described in detail.

The current collector is generally made to have a thickness of 3 μm to 500 μm. The current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a surface of aluminum or stainless steel. For example, a surface treated with carbon, nickel, titanium, or the like may be used.

In a specific embodiment of the present invention, the negative active material includes a silicon-based negative active material, and the silicon-based negative active material may be in the form of particles or a powder including the particles. The silicon-based negative active material may include one or more materials selected from the group consisting of silicon (Si), a silicon alloy (Si-alloy), silicon oxide (SiO _X ), and a silicon-carbon composite. In the silicon-carbon composite, the acid group carbon material may be bonded, attached, or coated to the surface of the silicon or silicon oxide particles. The carbon material may include at least one selected from the group consisting of crystalline carbon, natural graphite, artificial graphite, kish graphite, graphitized carbon fiber, graphitized mesocarbon microbead, and amorphous carbon. In addition, the graphite is soft carbon, hard carbon, pyrolytic carbon, liquid crystal pitch based carbon fiber (mesophase pitch based carbon fiber), carbon microspheres (meso-carbon microbeads), liquid crystal pitch (mesophase pices), petroleum coal-based coke (petroleum or coal tar pitch derived cokes), and may include those obtained by graphitizing one or more selected from the group consisting of activated carbon.

The negative active material layer of the present invention may further include a conductive material or a binder in addition to the negative active material.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the electrode mixture. As such a binder, the high molecular weight polyacrylonitrile-acrylic acid copolymer may be used, but is not limited thereto. Other examples include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene, alcohol and various copolymers such as ponized EDPM, styrene rubber, butyrene rubber, and fluororubber.

The conductive material may be added in an amount of 1 to 30% by weight based on the total weight of the mixture including the negative active material. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used, but is not limited thereto.

Hereinafter, a method for manufacturing the negative electrode for a lithium secondary battery of the present invention will be described.

2 is a flowchart of a method for manufacturing a negative electrode for a lithium secondary battery of the present invention. Referring to FIG. 2 , the method for manufacturing a negative electrode for a lithium secondary battery according to the present invention is after the negative electrode is supported in a solution containing an amorphous polymer. and drying to form a lithiation delay layer on the anode active material layer (S10) and depositing lithium on the lithiation delay layer to form a lithium layer (S20).

The forming of the lithiation delay layer is a step of forming a lithiation delay layer by coating an amorphous polymer material to a predetermined thickness on the anode active material layer. As long as the above-described polymer material can be coated on the anode active material layer, the coating method is not particularly limited. The amorphous polymer material constituting the lithiation delay layer is preferably a polymer including an acrylate repeating unit or a carbonate repeating unit. Since the description of this has been previously described, further detailed description thereof will be omitted.

In one embodiment of the present invention, a dip coating method that can be coated relatively easily was selected. In the dip coating method of the present invention, a solution in which a polymer material constituting the lithiation delay layer is dissolved in a solvent is prepared, the negative electrode is loaded in the prepared solution, and then the negative electrode is taken out, and the lithiation delay layer is coated on the negative electrode active material layer.

The forming of the lithium layer ( S20 ) is a step of forming a lithium layer serving as a lithium source for lithiation on the lithiation delay layer. In the step of forming the lithium layer of the present invention, a lithium film having a lithium layer formed on the release film is laminated on the anode active material layer, and then laminated to transfer the lithium metal of the lithium film onto the anode active material layer. Alternatively, the lithium layer may be formed on the anode active material layer by thermal evaporation.

Hereinafter, the lithiation process of the present invention will be described in detail.

In one embodiment of the present invention, lithiation of the negative electrode proceeds in the electrolyte solution injection and/or initial charge/discharge stage after the battery is manufactured, and at this time, at least a portion of the negative electrode active material included in the negative electrode active material layer is lithiated. In one embodiment of the present invention, the battery comprises a negative electrode, a positive electrode, and an electrode assembly having a separator interposed between the negative electrode and the positive electrode, and after inserting the electrode assembly into a suitable casing, the electrolyte is injected and sealed can be prepared in this way.

In the present invention, lithiation may be performed by injection of an electrolyte solution. That is, when the electrolyte is injected, the electrode assembly including components such as electrodes is impregnated with the electrolyte. At this time, as the lithiation delay layer of the present invention is slowly dissolved, lithium in the lithium layer may be gradually and uniformly diffused into the anode active material layer.

After the electrolyte is injected, the battery is activated by first applying a current to the battery to perform initial charge/discharge (formation). The activation process may be performed while a predetermined pressure is applied to the battery.

By such lithiation, the anode active material included in the anode active material layer, in particular, the above-described silicon-based anode active material and lithium may be complexed to form an alloy, and in addition, a portion of lithium may be inserted into the crystal structure of the anode active material.

In the present invention, since the lithiation delay layer is interposed between the negative electrode active material layer and the lithium layer, in the state before the electrolyte is injected, the diffusion of lithium is prevented by the lithiation delay layer, so that lithiation hardly proceeds. . Almost all lithiation may be performed in the electrode assembly and after the electrolyte is injected into the electrode assembly and/or in the initial charge/discharge step.

Meanwhile, it is preferable that the initial charge/discharge is performed in a state where a predetermined pressure is applied to the battery to energize the lithiation delay layer and the negative electrode in some cases. Thereafter, as long as the lithium metal remains in the lithium layer, lithiation may continue, and may be affected, such as being accelerated by charging and discharging of the battery.

Hereinafter, the lithium secondary battery of the present invention will be described.

The present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the negative electrode has the above-described structural characteristics.

The positive electrode may be prepared by coating a mixture of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector and then drying the mixture, and if necessary, may further include a filler in the mixture. The positive active material may include a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxide, such as Formula Li _1+x Mn _2-x O ₄ (here, x is 0-0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, lithium manganese composite oxide represented by Ni, Cu or Zn; LiMn ₂ O ₄ in which a part of Li in the formula is substituted with an alkaline earth metal ion; disulfide compounds; Although Fe2 _{(MoO4)3 etc. are} mentioned, It is not limited only to these.

For the positive electrode, the conductive material, the current collector, and the binder may refer to the above-described negative electrode.

As the separator, an insulating thin film having high ion permeability and mechanical strength may be used. The processing diameter of the separator is generally 0.01 to 10 μm, and the thickness may be 5 to 300 μm. Non-limiting examples of such a separator include olefin-based polymers such as chemical-resistant and hydrophobic polypropylene; and a sheet or a nonwoven fabric made of glass fiber or polyethylene. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

In the present invention, the electrolyte contains an organic solvent and a predetermined amount of a lithium salt, and the organic solvent includes N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene. carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1, 3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, Aprotic organic solvents such as 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyropionate, and ethyl propionate can be used.

The lithium salt is a material readily soluble in the electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenyl borate, imide, or the like may be used.

The secondary battery of the present invention may be manufactured by housing/sealing the electrode assembly in which the positive electrode and the negative electrode are alternately stacked with a separator together with an electrolyte solution in an exterior material such as a battery case. For the manufacturing method of the secondary battery, a conventional method may be used without limitation.

According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include a secondary battery exhibiting excellent fast charging characteristics at high loading, they may be used as power sources for electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

Hereinafter, examples will be described in detail to help the understanding of the present invention. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the following examples. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example 1

<Production of cathode>

A negative electrode in which a negative active material made of pure silicon (Si) was coated on a copper current collector was prepared. After dissolving PMMA (Polymethylmethacrylate, IH 830Grade: Manufactured by LG Chem) at a concentration of 1% in methylene chloride solvent (Methylene chloride, Manufactured by Daejung Hwageum), the anode is supported in the solution and PMMA is dip-coated on the anode active material layer (dip coating). Then, it was dried at room temperature for 10 minutes. At this time, the thickness of the PMMA coating layer was 1㎛. Lithium was deposited on the PMMA coating layer of the PMMA-coated negative electrode by thermal evaporation to form a lithium layer of 5 μm. In this case, the deposition equipment was EWK-060 of ULVAC, the speed was 2.5 m/min, the temperature of the lithium supply part was 500°C, and the temperature of the main roll was set to -25°C, and the deposition process was performed.

<Manufacture of lithium secondary battery>

After punching the negative electrode with the lithium layer formed to have a size of 34 mm in width and 51 mm in length, a porous polyethylene separator is interposed between the positive electrodes containing Li(Ni _0.8 Co _0.1 Mn _0.1 )O ₂ as a positive electrode active material. was stored in the battery case of the pouch, and then an electrolyte solution containing 1M LiPF ₆ was added to a mixed solvent in which EC (ethylene carbonate) and EMC (ethyl methyl carbonate) were mixed in a 3:7 ratio to prepare a monocell.

Example 2

A negative electrode in which a negative active material made of pure silicon was coated on a copper current collector was prepared. Polycarbonate (DVD1080 Grade: Manufactured by LG Chem) was dissolved in methylene chloride solvent (Methylene chloride, Manufactured by: Daejeong Hwageum) at a concentration of 1%, and then the anode was loaded in the solution to form polycarbonate on the anode active material layer. Dip coating was carried out. Then, it was dried at room temperature for 10 minutes. In this case, the thickness of the polycarbonate coating layer was 1 μm. Lithium was deposited on the polycarbonate coating layer of the polycarbonate-coated negative electrode by thermal evaporation to form a lithium layer of 5 μm. In this case, the deposition equipment was EWK-060 of ULVAC, the speed was 2.5 m/min, the temperature of the lithium supply part was 500°C, and the temperature of the main roll was set to -25°C, and the deposition process was performed.

Thereafter, a monocell was prepared in the same manner as in Example 1.

Example 3

An anode was manufactured in the same manner as in Example 3, except that the lithium supply rate was controlled to 3.5 m/min and the temperature of the lithium supply part to 650° C. during the thermal deposition process.

Using the prepared negative electrode, a monocell was prepared in the same manner as in Example 3.

Comparative Example 1

A negative electrode in which a negative active material made of pure silicon was coated on a copper current collector was prepared. On the negative electrode active material layer of the negative electrode, lithium was deposited by thermal evaporation in the same manner as in Example 1 to form a lithium layer having a thickness of 5 μm.

Thereafter, a monocell was prepared in the same manner as in Example 1.

Comparative Example 2

A negative electrode in which a negative active material made of pure silicon was coated on a copper current collector was prepared. A coating solution was prepared by adding polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) to an acetone solvent. A free-standing film (1 μm) was prepared by solution casting the coating solution on a substrate (PTFE). The film was dried in a vacuum oven at 80° C. for 24 hours.

The film and lithium foil (5 μm) were sequentially laminated on the negative electrode and then rolled to prepare a negative electrode. Thereafter, a monocell was prepared in the same manner as in Example 1.

Comparative Example 3

In the thermal deposition process, a negative electrode was manufactured in the same manner as in Example 1, except that the lithium supply rate was controlled to 3.5 m/min and the temperature of the lithium supply part was controlled to 650°C.

Using the prepared negative electrode, a monocell was prepared in the same manner as in Example 1.

Experimental Example 1: SEM observation of the anode cross-section

The cross-section of each cathode was observed by SEM. As a result, it was confirmed that the negative electrode of Examples 1 and 2 had a deep and uniform lithiation depth, whereas the negative electrode of Comparative Example 1 was lithiated only to 1/3 in the depth direction. This is thought to be due to the slow diffusion of lithium by the lithiation delay layer.

Experimental Example 2: Initial dose measurement

The discharge capacity of each of the monocells prepared in Examples 1 and 2 and Comparative Example 1 was measured. As a result, it was confirmed that the monocells of Examples 1 and 2 had a larger capacity than the monocells of Comparative Example 1. This is considered to be because the negative electrode according to the present invention completely compensated for the irreversible capacity by lithiation, but the monocell of Comparative Example 1 did not sufficiently compensate for the irreversible capacity due to non-uniform lithiation.

Experimental Example 3: Confirmation of solubility of the lithiation delay layer

Each of the anodes prepared in Examples 1 and 2 and Comparative Example 2 was immersed in an electrolyte in which 1M LiPF ₆ was added to a mixed solvent in which EC (ethylene carbonate) and EMC (ethyl methyl carbonate) were mixed at a ratio of 3:7, After 24 hours, the cross-section of each cathode was observed by SEM. As a result, in the cross-sections of each negative electrode of Examples 1 and 2, the PMMA coating layer and the PC coating layer, which were the lithiation retardation layers, were not observed. On the other hand, it was confirmed that the PVdF-HFP layer of Comparative Example 2 did not dissolve in the electrolyte and remained. From these experimental results, it could be predicted that, in the negative electrode including the lithiation delay layer of the present invention, the lithiation delay layer is dissolved in the electrolyte and will not act as a resistance in the electrode.

Experimental Example 4: Confirmation of surface roughness

For each negative electrode prepared in Examples 1 to 4, the surface roughness was measured. Specifically, the arithmetic mean roughness (Ra) of the surface of the surface on which the lithium layer was formed of each negative electrode was measured.

Specifically, the arithmetic mean roughness (Ra, surface roughness) of the surface was measured in a chamber under an argon gas atmosphere, and was measured with a 3D profiler, which is an optical non-contact surface roughness meter. In this case, the magnification was 50 times the combined magnification of the viewing angle lens and the objective lens, and the measurement area was measured for an area of 10 μm x 10 μm. The measured results are shown in Table 1 below.

division Lithation retardation layer composition Lithium supply temperature Surface roughness (Ra) of lithium layer Example 1 PMMA 500℃ 0.18㎛ Example 2 polycarbonate 500℃ 0.15㎛ Example 3 polycarbonate 650℃ 0.19㎛ Comparative Example 1 - 500℃ 0.75㎛ Comparative Example 3 PMMA 650℃ 0.48㎛

In Table 1, the surface roughness of the lithium layer is directly affected by the surface roughness of the lithiation delay layer. Referring to the results of Table 1, in the case of Examples 1 and 2, it was confirmed that the arithmetic mean roughness (Ra) of the lithium layer was controlled to a low level. This is because, when the temperature of the lithium supply part is 500° C., the surface can be maintained uniformly even if the lithiation delay layer is applied to PMMA (Example 1) or polycarbonate (Example 2).

In the case of Example 3, the arithmetic mean roughness of the lithium layer was maintained at a low level even though the temperature of the lithium supply part was 650°C. In Example 3, polycarbonate was applied as a lithiation delay layer. Polycarbonate can maintain heat resistance even at high temperatures, thereby maintaining excellent surface uniformity. The lithium layer deposited on the lithiation retardation layer having excellent surface uniformity can also maintain a low calculated average roughness.

In contrast, in Comparative Example 1 in which the lithiation delay layer was not formed, it was confirmed that the arithmetic mean roughness of the lithium layer was high. In addition, in the case of Comparative Example 3 in which PMMA is applied as the lithiation delay layer, when the temperature of the lithium supply part is 650° C., it can be seen that the heat resistance range of PMMA is out of range.

The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Accordingly, the drawings disclosed in the present invention are for explanation rather than limiting the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by these drawings. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

110: current collector
120: negative electrode mixture layer
130: lithium diffusion rate control layer
140: lithium layer

Claims (13)

negative electrode current collector;
a negative active material layer formed on one or both sides of the negative electrode current collector;
a lithiation delay layer formed on the anode active material layer; and
a lithium layer deposited on the lithiation delay layer;
In the lithium layer, the surface roughness of the surface located on the opposite side to the surface in contact with the lithiation delay layer is in an average range of 0.05 to 0.35 μm,
The lithiation delay layer includes a polymer having at least one repeating unit of an acrylate repeating unit and a carbonate repeating unit,
The thickness of the lithiation delay layer ranges from 0.5 to 1.5 μm on average,
A negative electrode for a lithium secondary battery, characterized in that the ratio (B/A) of the average thickness (B) of the lithium layer to the average thickness (A) of the lithiation delay layer is in the range of 3 to 7.
The method of claim 1,
The lithiation delay layer is an anode for a lithium secondary battery comprising a polymer having a carbonate repeating unit.
The method of claim 1,
The polymer included in the lithiation delay layer has a glass transition temperature (Tg) of 120° C. or higher for a lithium secondary battery.
The negative electrode for a lithium secondary battery according to claim 1, wherein the average thickness of the lithium layer is in the range of 0.5 to 30 µm.
delete The negative electrode for a lithium secondary battery according to claim 1, wherein the negative active material included in the negative active material layer is a silicon-based negative active material.
The negative electrode for a lithium secondary battery according to claim 1, wherein the lithiation delay layer has solubility in a carbonate-based electrolyte.
forming a lithiation delay layer on the anode active material layer by supporting the anode in a solution containing an amorphous polymer and drying the anode; and
Depositing lithium through thermal evaporation on the lithiation delay layer to form a lithium layer,
In the step of forming the lithiation delay layer,
The method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, wherein the amorphous polymer includes at least one of an acrylate repeating unit and a carbonate repeating unit as a repeating unit.
9. The method of claim 8,
The amorphous polymer has a glass transition temperature (Tg) of 120° C. or more.
9. The method of claim 8,
The thermal evaporation is based on the temperature of supplied lithium,
A method of manufacturing a negative electrode for a lithium secondary battery, characterized in that it is carried out in the range of 460 to 850 °C.
9. The method of claim 8,
The negative electrode active material included in the negative electrode active material layer is a method of manufacturing a negative electrode for a lithium secondary battery, characterized in that the silicon-based negative electrode active material. delete delete

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