KR20190083304A - A method of pre-lithiating anode and Anode manufactured therefrom - Google Patents

Abstract

The present invention provides a pre-lithiation method of a negative electrode. The method comprises the steps of: (S1) preparing a negative electrode including a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, wherein uncoated portions are formed at both ends of the negative electrode current collector; and (S2) depositing a lithium metal sheet on the negative electrode active material layer in a first electrolyte solution and fixing both ends of the metal sheet and the negative electrode current collector uncoated portion to be in contact with each other. The pre-lithiation can occur simultaneously not only in an upper portion of the electrode but also in a lower portion of the electrode, and thus can be uniformly performed in a thickness direction.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of pre-lithiating a cathode and a cathode made therefrom,

The present invention relates to a method for total lithization of a cathode and a cathode made therefrom.

High capacity silicon cathodes are now recognized as a key factor in increasing the energy density of lithium secondary batteries (LIBs). Particularly in applying lithium secondary batteries to electric vehicles, high energy densities are particularly important because they ensure greater distance travel.

However, despite this advantage, a large volume change of a high capacity silicon anode during charging and discharging leads to undifferentiation of the active material, detachment of the electrode and formation of an unstable solid electrolyte interface coating (SEI), deteriorating the cycle characteristics of the battery.

In addition, high capacity silicon cathodes also have problems exhibiting degraded properties at initial Coulombic efficiency (ICE).

One of the causes of this problem is the trapping phenomenon that the surface oxide film of pure silicon or silicon oxide (SiOx, 0 <x <2) base material and lithium ion trapped inside the SEI layer during the first charge.

One of the attempts to simultaneously improve the initial coulombic efficiency and cycle problems described above is known as pre-lithiation.

Pre-lithization is generally used to solve the problem of low initial efficiency due to the consumption of lithium to form SEI and various irreversible phases during initial charging at a lithium secondary battery cathode, (SEI layer, Li ₂ O, Li _x SiO _y ) by injecting Li as much as possible to increase the initial efficiency.

1, a lithium metal foil may be laminated on a negative electrode active material layer formed on an anode current collector 300 to perform preliminary lithium ionization.

If the pre-lithiation is insufficient, it still causes trapping of lithium, resulting in deterioration of the initial coulombic efficiency (ICE). Conversely, excessive pre-lithization can lead to the introduction of lithium in advance to the extent that it contributes to capacity implementation during actual charging, which is disadvantageous to initial capacity implementation. From this point of view, controlling the level of pre-lithization at an appropriate level is critical for stable full-cell operation.

On the other hand, there is known a technique of prelithiation of silicon particles or silicon oxide particles. However, in this technique, it is not easy to pre-lithize the particles to a desired extent, and the cohesion of silicon particles or silicon oxide particles themselves There is a problem that it is difficult to expect reliable performance from a lithium secondary battery employing such a cathode.

The present inventors have found that in a technique of directly bringing a lithium metal sheet and a negative electrode into direct contact with each other to form a pre-lithiated lithium metal sheet, the lithium metal sheet is excessively pre-lithiated at the portion of the negative electrode directly contacting the lithium metal sheet, And the non-uniformity of the lithium ionization in the negative electrode portion in the opposite direction (toward the collector) with respect to the portion in contact with the lithium ion secondary battery.

That is, a problem to be solved by the present invention is to provide a method for uniformly performing pre-lithization in the entire negative electrode, particularly in the negative electrode thickness direction.

Another object of the present invention is to provide a cathode that is uniformly pre-lithiated by the above method and a lithium secondary battery including the same.

According to a first aspect of the present invention, there is provided a negative electrode collector comprising: a negative electrode collector; And a negative electrode active material layer formed on at least one surface of the negative electrode current collector, wherein (S1) the negative electrode active material layer is formed on at least a portion of the negative electrode current collector such that the uncoated portion is provided on at least one end of the negative electrode current collector, Applying a layer to form a cathode; And (S2) laminating a lithium metal sheet so that the lithium metal sheet is in contact with the negative active material layer and the uncoated portion in a state of immersing the negative electrode in an electrolyte ('first electrolyte') composition. A method of painting is provided.

According to a second aspect of the present invention, in the first aspect, between the step (S1) and the step (S2), the step of wetting the cathode with the first electrolyte may be further included.

According to a third aspect of the present invention, in the first aspect, the contact may be made only at one end of the negative electrode collector uncoated portion.

According to a fourth aspect of the present invention, in the first aspect, the contact may be made at both ends of the negative electrode collector uncoated portion.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the anode active material layer is a silicon oxide represented by SiO _x (0 <x <2); A silicon oxide-based composite in which a metal such as Al and Mg is doped or chemically bonded to SiO _x (0 <x <2); Or a mixture thereof may be included as a negative electrode active material.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, a copper mesh thin plate may be interposed between the lithium metal sheet and the negative electrode collector uncoated portion.

According to a seventh aspect of the present invention, in the sixth aspect, the copper mesh thin plate may be welded to the negative electrode collector uncoated portion.

According to an eighth aspect of the present invention, in the sixth or seventh aspect, the copper mesh thin plate may have a thickness of 3 to 500 탆.

According to a ninth aspect of the present invention, in any one of the first to eighth aspects, the copper mesh thin plate may have 10 mesh to 200 mesh.

According to a tenth aspect of the present invention, there is provided a pre-lithiated anode produced in any one of the first to ninth aspects.

According to one aspect of the present invention, a cathode that is uniformly pre-lithiated in the entire cathode, particularly in the direction of the cathode thickness, is obtained.

As a result, the problem that the lithium ion secondary battery according to the present invention exhibits excellent capacity retention at the time of cycle charge / discharge is solved.

1 is a side view schematically showing a prior art embodiment in which a lithium metal sheet 300 is directly brought into contact with a negative electrode made of an electrode current collector 100 and a negative electrode active material layer 200 to pre-lithize the negative electrode.
2 is a top view of an embodiment of the present invention in which a negative electrode active material layer 100 'is formed on a negative electrode current collector 200'.
3A is a side view showing an anode current collector 100 'and a lithium metal sheet 300' in which the anode active material layer 200 'is formed. FIG. 3B and FIG. 3C are side views showing the anode active material layer 200' And the lithium metal sheet 300 'is in direct contact with the non-coated portion of the negative electrode current collector 100' formed thereon.
FIG. 4 is a side view schematically illustrating a process in which only one end of an anode current collector is directly contacted with a lithium metal sheet in the electrolyte solution 500 according to an embodiment of the present invention, thereby forming a pre-lithium electrode.
5 is a side view schematically illustrating a process in which both ends of an anode current collector are directly contacted with a lithium metal sheet in an electrolytic solution 500 according to an embodiment of the present invention.

Hereinafter, embodiments and examples of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention.

It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments and examples described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

The terms "about "," substantially ", etc. used to the extent that they are used herein are intended to be taken to indicate a manufacturing and material tolerance inherent in the stated sense, Accurate or absolute numbers are used to prevent unauthorized exploitation by unauthorized intruders of the mentioned disclosure. Also, throughout the present specification, the phrase " step "or" step "does not mean" step for.

Throughout this specification, the term "combination thereof" included in the expression of the machine form means one or more combinations or combinations selected from the group consisting of the constituents described in the expression of the machine form, And the like.

Throughout this specification, the description of "A and / or B" means "A or B, or A and B".

According to one aspect of the present invention, there is provided a negative electrode collector comprising: an anode current collector; And a negative electrode active material layer formed on at least one surface of the negative electrode current collector, wherein (S1) the negative electrode active material layer is formed on at least a portion of the negative electrode current collector such that the uncoated portion is provided on at least one end of the negative electrode current collector, Applying a layer to form a cathode; And (S2) laminating a lithium metal sheet such that the lithium metal sheet is in contact with at least one end of the negative electrode active material layer and the negative electrode collector uncoated portion in a state where the negative electrode is immersed in the electrolyte ('first electrolyte') composition There is provided a method for full lithification of a cathode comprising

The step of wetting the cathode with the first electrolyte may be further included between the steps (S1) and (S2).

The negative electrode current collector usable in the present invention is not particularly limited as long as it is commonly used in the art and includes, but not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foil, copper foil, Coated polymer base, or a combination thereof.

According to an aspect of the present invention, the oxide film on the surface of the collector may be removed by pre-treating the surface of the collector with an acidic solution to improve the electrical conductivity of the collector.

Referring to FIG. 2, the negative electrode collector is designed to be larger than the desired negative electrode active material layer 200 ', that is, to generate margins 100a and 100b at both ends, It is referred to as a &quot; plain portion &quot;. The size of the margin is not particularly limited as long as it can make direct contact with the lithium metal sheet, but can be designed to have a size of from 0.1 cm to 2 cm or from 0.5 cm to 1.5 cm or from 0.7 cm to 1 cm, have.

According to an embodiment of the present invention, a copper mesh thin plate may be interposed between the lithium metal sheet and the negative electrode collector nonwoven fabric so as to improve the contact property between the lithium metal sheet and the negative electrode collector. In one example, the copper mesh foil may be welded to the negative electrode current collector. The welding may be ultrasonic welding.

The copper mesh thin plate may have a thickness of 3 [mu] m to 500 [mu] m or a thickness of 10 [mu] m to 200 [mu] m. When the copper mesh thin plate has a thickness of 3 μm or more, the contactability between the anode current collector and the lithium metal sheet by the copper mesh thin plate can be improved. When the copper mesh thin plate has a thickness of 500 μm or less, The resistance value of the mesh thin plate can be prevented from increasing excessively.

When the copper mesh thin plate is placed in a plane, the mesh of the copper mesh thin plate may be in the form of a hole formed in the copper mesh thin plate, and the mesh may be formed on at least a part of the copper mesh thin plate, .

The copper mesh sheet may have 10 mesh to 200 mesh or 30 mesh to 100 mesh. When the mesh size is formed in such a range, it is possible to increase the contact property between the lithium metal sheet and the non-collector portion of the current collector while providing appropriate lithium ion conductivity.

The ratio of the total mesh in the mesh metal thin plate is preferably 20 to 80% based on 100% of the mesh metal thin plate area. When the opening ratio is in the above range, the contactability between the lithium metal sheet and the collector uncoated portion can be increased while providing appropriate lithium ion conductivity.

The lithium metal sheet generally has a soft physical property. When the thin metal mesh plate is provided between the lithium metal sheet and the non-collecting portion of the collector, lithium metal is interposed between the meshes of the thin metal mesh plate, (In D3 form) with the lithium metal sheet. In contrast, the collector in the form of a foil is brought into contact with the lithium metal sheet in planar form (in 2D form). Thus, ultimately, the contact between the lithium metal sheet and the current collector portion can be improved when the mesh metal thin plate is interposed between the lithium metal sheet and the current collector non-current portion.

On the other hand, when the lithium metal sheet is manufactured in a concavo-convex shape or a mesh shape, irregularities or mesh shapes are flattened due to soft physical properties of the lithium metal sheet, and the contactability between the lithium metal sheet and the non- It is difficult.

In addition, when the current collectors are manufactured in a concavo-convex shape, when the current collector is loaded in a concavo-convex shape, there is a fear of unfavorable in terms of the amount of loading of the active material or uneven charging of the active material during charging and discharging have. Therefore, it is preferable that the current collector portion where the active material is loaded does not have concavity and convexity and only concave and convex portions are formed in the portion corresponding to the current collector blank portion. However, in this case, the manufacturing method becomes complicated and increases the manufacturing cost.

The negative electrode active material layer may be composed of a negative electrode active material, a binder polymer, a conductive material and, if necessary, an additive. The negative electrode active material, the binder polymer, the conductive material, and other additives are added to the solvent to form a negative electrode active material slurry. The negative electrode active material slurry may be coated on at least one surface of the negative electrode collector, followed by drying and rolling.

The active material used for the negative electrode active material is not particularly limited, but it may include a silicon oxide or a silicon oxide based composite in consideration of the object of the present invention that lithium is converted to lithium.

The silicon oxide or silicon oxide-based composite is a silicon oxide-based material in which silicon oxides represented by SiO _x (0 <x <2) and / or SiO _x (0 <x <2) are doped or chemically bonded to metals such as Al and Mg Compound, but a compound in which Li metal is doped or chemically bonded to SiO _x (0 < x < 2) does not correspond to the present invention. When a compound in which Li metal is doped or chemically bonded to SiO _x (0 < x < 2) is used as a negative electrode active material, it is vulnerable to oxidation through moisture and oxygen.

The silicon oxide or silicon oxide-based composite may be crystalline, amorphous or a mixture thereof.

The silicon oxide or silicon oxide based composite may have an average particle size (D50) of 7 mu m or less or an average particle size (D50) of 200 to 500 nm, but is not limited thereto. The term "average particle diameter (D50)" used herein means a value obtained by measuring the weight average value D50 (particle diameter or median diameter when the cumulative weight becomes 50% of the total weight) in the particle size distribution measurement by laser light diffraction Lt; / RTI &gt;

The silicon oxide or silicon oxide-based composite may have a surface coated with carbon. The surface of the silicon oxide or silicon oxide-based composite is coated with carbon, whereby the reaction with the electrolyte can be suppressed, and the effect of improving the conductivity and suppressing expansion of the active material particle can be obtained. For example, the carbon coating layer may be formed in an amount of 1 to 20 wt% or 5 to 17 wt% to 10 to 15 wt% based on the weight of the silicon oxide or silicon oxide based composite including the coating layer.

The negative electrode active material may further include a carbonaceous material, and the carbonaceous material may be, for example, natural graphite, artificial graphite, soft carbon, hard carbon, or a combination thereof. The negative electrode active material may include 80 to 95% by weight of the carbon-based material. By blending the carbon-based material and the silicon oxide or silicon oxide based composite, the capacity per weight can be controlled.

The binder polymer may be used to bind the active material particles to maintain the formed body. The binder polymer is not particularly limited as long as it is a common binder polymer used in the production of electrodes. For example, polyvinyl alcohol, carboxymethyl cellulose, Cellulose, diacetylene cellulose, polyvinyl chloride, polyvinyl pyrrolidone, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene or polypropylene, Economical and eco-friendly water-based binders can be used. Examples of the aqueous binder include styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), acrylonitrile-butadiene rubber, acrylic resin, hydroxyethylcellulose, or a combination thereof. The binder polymer used for the negative electrode is preferably an aqueous binder polymer. The aqueous binder may be included in an amount of 1 to 30% by weight, preferably 1 to 2% by weight based on the total amount of the negative electrode active material layer composition.

The conductive material is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum and nickel powder, and the like.

As shown in FIGS. 3A to 3C, the lithium metal sheet 300 'is larger than the negative electrode active material layer 200' so that it can cover the entire negative electrode active material layer and can contact the end of the negative electrode current collector 100 ' It is preferable to have a size of

The lithium metal sheet may have a thickness in the range of 15 to 300 占 퐉 or 20 to 100 占 퐉. As shown in Fig. 3B, the non-coated portion and the lithium metal sheet of the negative electrode current collector are bent so that the ends of the non-coated portion of the negative electrode current collector 100 'and the ends of the lithium metal sheet 200' . Alternatively, as shown in FIG. 3C, the non-coated portion and the lithium metal sheet of the negative electrode current collector may be formed such that the negative electrode current collector 100 'is flat and the end portion of the lithium metal sheet 200' As shown in Fig.

A lithium metal sheet is laminated on the negative electrode active material layer and these are pressed and fixed with a flat jig so that both end portions of the lithium metal sheet come into contact with the uncoated portions of the negative electrode collector. Further, in addition to the flat jig, a separate jig ('end jig') may be additionally provided to enhance the contact of the portion where the collector blank and the lithium metal sheet are in contact with each other. In this case, the contact surface between the lithium metal sheet and the current collector may be between 5% and 20%, and preferably between 7% and 13% of the contact area between the lithium metal sheet and the holding part coated with the active material.

An embodiment in contact with the lithium metal sheet and the negative electrode current collector uncoated portion is shown in Figs.

4 and 5, total lithization is performed in the electrolyte 500. To this end, a negative electrode active material layer 200 'is formed on one surface of the negative electrode current collector 100', and the negative active material layer 200 ' The flat plate jig 400a is positioned above and below the cathode and the lithium metal sheet and a constant pressure P is applied to the flat plate jig 400a The lithium metal sheet 300 'is brought into contact with the negative electrode under pressure. And the lithium metal sheet is pressed toward the negative electrode active material layer with a force of 0.1 to 30 kgf per 1.5 cm ² by the jig. If the pressing force is smaller than the lower limit value, the entire lithium ionization is not smoothly performed. If the pressing force is larger than the upper limit value, the electrode is physically damaged.

Also, an end jig 400b for contacting the end portion of the negative electrode current collector 100 'with the end portion of the lithium metal sheet 300' may be applied. The contact between the negative electrode collector uncoated portion and the lithium metal sheet end portion may be made only on one side of the negative electrode collector uncoated portion as shown in FIG. 4 or on both sides of the negative electrode collector uncoated portion as shown in FIG. The end jig 400b for contact between the non-coated portion of the negative electrode current collector 100 'and the end of the lithium metal sheet 300' is pressed with a force of 0.1 to 5 kgf per 1.0 cm ² to make contact. If the pressing force is smaller than the lower limit value, the entire lithization is not smoothly performed. If the pressing force is larger than the upper limit value, the cathode collector end and / or the lithium metal sheet end portion may be physically damaged.

The method of applying the pressure can be used without any particular limitation as long as it is a method generally known in the art. For example, there is a method of changing the distance between jigs constituting a pair of flat jigs and / or end jigs using equipment.

The knife jig 400a and / or the end jig 400b may be made of a material that is not reactive with the organic electrolyte, and may be made of, for example, polyetheretherketone (PEEK).

As a result, cracks or cracks do not occur in the negative electrode active material layer, and the ends of the negative electrode collector and the lithium metal sheet are contacted without rupture, thereby further generating an electrically conductive channel between the lithium metal sheet and the end of the negative electrode collector.

Next, the negative electrode and the lithium metal sheet press-fixed by the jig are wetted and dipped into an electrolytic solution ('first electrolyte') to be pre-lithiated.

In the present invention, the first electrolyte used for the preliminary lithium ionization may include a first organic solvent and a first electrolyte salt.

The first organic solvent may be any organic solvent conventionally used in the art without any particular limitation, but a high boiling organic solvent may be preferably used to minimize electrolyte consumption due to evaporation during pre-lithization. Specific examples of the first organic solvent may include ethylene carbonate (EC) and ethylmethyl carbonate, preferably ethylene carbonate and ethylmethyl carbonate alone, and more preferably ethylene carbonate and ethylmethyl carbonate 50:50 And an organic solvent having a volume ratio.

In a further embodiment, the first electrolyte may be selected from the group consisting of 1,2-dimethoxyethane (DME), gamma -butyrolactone (GBL), tetrahydrofuran (THF) (DOXL), dimethyl ether (DEE), methyl propionate (MP), sulfolane (S), dimethylsulfoxide (DMSO), acetonitrile (AN), and tetraethylene glycol dimethyl ether ) May be further included.

The electrolyte salt is _{LiBF 4, LiClO 4, LiPF 6} , LiAsF 6, LiCF 3 SO 3, Li (CF 3 SO 2) 2 N, LiC 4 F 9 SO 3, Li (CF 3 SO 2) 3 C, and LiBPh _{4. &} Lt; / RTI &gt; The electrolyte salt may be contained in the first organic solvent at a concentration of 1 to 2 M.

The negative electrode of the present invention is immersed in the first electrolyte solution for 1 hour to 30 hours so that the negative electrode is wetted with the first electrolyte solution. If the immersion time is shorter than 1 hour, the negative active material is not sufficiently wetted by the electrolyte, and the subsequent lithium ionization is not smoothly performed. If the immersion time is longer than 30 hours, the durability of the electrode The active material easily falls off from the collector during the process. When the electrolyte is uniformly penetrated into the electrode through the wetting, the lithium ion is uniformly diffused to the electrode when it is in direct contact with the lithium metal sheet, so that the lithium ion can be uniformly distributed throughout the electrode.

To make the wetting better, the reactor in which the wetting occurs can be evacuated to less than 760 mmHg. In this case, the first electrolytic solution temperature at which wetting is performed may be in the range of 30 to 60 占 폚.

Subsequently, the lithium metal sheet is immersed in the first electrolyte solution, and is held in contact with both surfaces of the lithium metal sheet and both end portions of the negative electrode current collector by a flat jig and end jig for 10 minutes to 1 hour or 15 Min to 45 min or 20 to 30 min.

In addition, when the former lithium ionization is performed shorter than the above, the effect of improving the initial efficiency and cycle performance of the battery becomes insignificant. When the former lithium ionization is performed longer than the above, lithium electrodeposition occurs, which is disadvantageous from a safety standpoint.

Subsequently, the negative electrode is taken out from the first electrolyte, washed with dimethyl carbonate and dried. When dimethyl carbonate is used as a washing solution, the lithium salt can sufficiently be dissolved and washed without damaging the cathode. The drying can be carried out in a manner customary in the art and can be carried out in a dry room at 20 ° C to 40 ° C for 1 hour to 5 hours, as a non-limiting example.

The negative electrode constitutes an electrode assembly together with a positive electrode and a separator including a positive electrode active material, and the electrode assembly and the electrolyte are housed in a casing of a lithium secondary battery.

The positive electrode active material may be 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 oxides such as Li _{1 + y} Mn _{2 - y} O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and 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 ; Formula LiNi _{1 -y} M _y O ₂ (where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 - 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2 - y M y O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 - 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); a ternary lithium manganese composite oxide; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Ternary lithium (Fe ₂ (MoO ₄ ) ₃ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + Transition metal complex oxides, and the like, but the present invention is not limited to these.

The cathode active material may be dispersed in a solvent together with a binder polymer, a conductive material and other additives to form a cathode mixture slurry. The cathode active material may be coated on at least one surface of the cathode current collector, followed by drying and rolling to form an anode.

Non-limiting examples of the positive electrode current collector include aluminum, nickel, or a foil produced by a combination of these. Non-limiting examples of the negative electrode current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil and so on.

The binder polymer, conductive material and other additives used in the anode may be the same as or different from those used in the cathode. For binder polymers and conductive materials, refer to the matters related to the negative electrode.

The second electrolyte comprises conventional electrolyte components such as a second organic solvent and a second electrolyte salt. A second electrolyte salt that can be used, A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+,, and comprising an alkali metal cation or an ion composed of a combination thereof, such as K ⁺ B ^- is PF _{6 ^{-, BF 4 -, Cl -}} , Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO ₂ ) ₃ ^- , or an ion consisting of a combination of these. In particular, a lithium salt is preferable. For example, LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) _2, or a mixture thereof can be used.

The organic solvent used for the second electrolyte may be a solvent commonly known in the art, for example, a cyclic carbonate system with or without a halogen substituent; Linear carbonate system; Ester-based, nitrile-based, phosphate-based solvents, or mixtures thereof. For example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, acetic acid Methyl, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate and butyl propionate or mixtures thereof.

The lithium secondary battery according to an embodiment of the present invention is not limited to the outer shape or the case, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

In addition, the lithium secondary battery according to an embodiment of the present invention may include all conventional lithium secondary batteries such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited by these Examples and Experimental Examples. The embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example  One

&Lt; Preparation of negative electrode &

92 weight% of negative electrode active material (graphite: SiO = 7: 3), 3 weight% of Denka black (conductive agent) and 3.5 weight% of SBR (binder) and 1.5 weight% of CMC (thickener) .

The prepared negative electrode mixture slurry is coated on one surface of a copper current collector used as a negative electrode collector, dried and rolled to form a negative electrode active material layer. At this time, the negative active material layer is coated on the copper current collector so that the active material layer is formed over a width of 5 cm, and the uncoated portion is made 1 cm wide on both sides of the negative active material layer. The negative electrode thus cut is cut to a width of 7 cm and a length of 5 cm.

<Lithiumization before high voltage direct contact>

The negative electrode prepared above was wetted for 10 hours in an electrolyte composition (first electrolyte solution) in which 1 M LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate were mixed in a volume ratio of 50:50, , A lithium metal sheet was laminated on the negative electrode active material layer and the non-coated portion such that a lithium metal sheet having a width of 7 cm and a length of 6 cm was in contact with the jig. The jig was tightened and pressed with a force of 30 kgf / 1.5 cm ² . It is kept for 30 minutes, and the lithium metal sheet is removed, followed by washing with dimethyl carbonate (DMC) and drying with minimal water exposure.

&Lt; Production of lithium secondary battery >

A polyolefin separator was interposed between the negative electrode and the LiCoO ₂ positive electrode prepared in the above manner to form a coin cell size, followed by dissolving 1 M LiPF ₆ in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate at a volume ratio of 50:50 Was injected to prepare a coin-type full cell.

Example  2

&Lt; Preparation of negative electrode &

92 weight% of negative electrode active material (graphite: SiO = 7: 3), 3 weight% of Denka black (conductive agent) and 3.5 weight% of SBR (binder) and 1.5 weight% of CMC (thickener) .

The prepared anode mixture slurry is coated on one side of the copper collector, dried and rolled. At this time, the negative electrode active material layer is coated on the copper collector such that the active material layer is formed over a width of 5 cm, and the uncoated portion is made 1 cm wide only on one side of the negative electrode active material layer. The negative electrode thus cut is cut into a width of 6 cm and a length of 5 cm.

<Lithiumization before high voltage direct contact>

The negative electrode prepared above was wetted with an electrolytic solution (1 M LiPF ₆ dissolved in a solvent mixture of ethylene carbonate (EC) and ethylmethyl carbonate in a volume ratio of 50:50) for 10 hours. Thereafter, , A lithium metal sheet having a length of 6 cm was placed on the negative electrode and the jig was tightened and pressed with a force of 30 kgf. At this time, the uncoated portion and the negative electrode active material layer adjacent to the negative electrode active material layer are brought into contact with the lithium metal sheet. This is held for 30 minutes and the lithium metal sheet is removed, washed with dimethyl carbonate (DMC) and dried with minimal water exposure.

&Lt; Production of lithium secondary battery >

A lithium secondary battery was produced in the same manner as in Example 1 above.

Example  3

&Lt; Preparation of negative electrode &

Except that a copper mesh thin plate (Sigma-aldrich, thickness 50 m, 60 mesh) (0.5 cm x 5 cm) was welded to both of the non-coated portions of the negative electrode prepared in Example 1, .

Example  4

&Lt; Preparation of negative electrode &

Except that a copper mesh thin plate (Sigma-aldrich, thickness 50 m, 60 mesh) (0.5 cm x 5 cm) was welded to one of the non-coated portions of the negative electrode prepared in Example 2, .

Comparative Example  One

Other steps were carried out in the same manner as in Example 1 except that no uncoated portions were formed on both sides of the electrode during the manufacture of the negative electrode, thereby manufacturing a lithium secondary battery.

Comparative Example  2

&Lt; Preparation of negative electrode &

A negative electrode was prepared in the same manner as in Example 1 above.

<Lithiumization before high voltage direct contact>

An electrolytic solution in which 1 M LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate were mixed in a 50:50 volume ratio was prepared. The negative electrode prepared above was wetted with the electrolyte solution for 10 hours. Then, a lithium metal sheet having a width of 7 cm and a length of 6 cm was placed on the negative electrode in the state of the electrolyte solution, and the jig was tightened and pressed with a force of 30 kgf. At this time, a Teflon plate (thickness: 0.1 mm) was attached to both uncoated portions on the sides of the negative electrode active material layer so that the electrode collector uncoated portion and the lithium metal sheet were not in direct contact with each other and only the negative electrode active material layer and the lithium metal sheet were in contact with each other . This was held for 30 minutes and the lithium metal sheet was removed, followed by washing with dimethyl carbonate (DMC) and drying with minimal water exposure.

Evaluation experiment

<Cycle charge / discharge test>

The coin-type full-cell prepared in Example 1 and Comparative Example 1 was subjected to charge-discharge reversibility test using an electrochemical charging / discharging device. The battery was charged at a current density of 0.1 C-rate up to a voltage of 4.2 V (vs. Li / Li ⁺ ) at the time of charging, and discharged to a voltage of 2.5 V at the same current density at the time of discharging. At this time, the 100-cycle capacity retention rate is shown in Table 1.

100 cycle capacity retention rate (%) Example 1 88 Example 2 87 Example 3 92 Example 4 91 Comparative Example 1 79 Comparative Example 2 79

The reason why the capacity retention ratios are different in Example 1 and Comparative Example 1 is that in the case of Comparative Example 1 in the case of lithium ionization, the electrons and ions are concentrated on the upper portions of the electrodes to cause lithization and the contact damage between the electrode active materials In the case of Example 1, a channel through which the electrons can move through the non-coated portion is further secured, so that the electrode is uniformly lithium-ized in the upper portion and the damage of the electrode is greatly reduced.

The reason why the capacity retention ratio is excellent in Examples 3 and 4 is that the copper mesh thin plate is interposed between the collector uncoated portion and the lithium metal sheet to improve the contact between the collector uncoated portion and the lithium metal sheet, This is because it moves more toward the igniter part of the current collector, resulting in more uniform pre-lithization of the electrode, thereby reducing electrode damage.

Claims (10)

Cathode collector; And a negative electrode active material layer formed on at least one surface of the negative electrode current collector,
(S1) forming a negative electrode by coating a negative electrode active material layer on at least a part of the negative electrode current collector such that the uncoated portion is provided at least at one end of the negative electrode current collector; And
(S2) stacking the lithium metal sheet so that the lithium metal sheet is in contact with the negative active material layer and the non-coated portion in a state where the negative electrode is immersed in the electrolyte composition
A method for full lithification of a cathode.
The method according to claim 1,
Further comprising the step of wetting the cathode with the electrolyte composition between steps (S1) and (S2).
The method according to claim 1,
Wherein the contact is made at one end of the negative electrode current collector uncoated portion.
The method according to claim 1,
Wherein the contact is made at both ends of the uncoated portion of the negative electrode collector.
The method according to claim 1,
Wherein the anode active material layer is represented by SiO _x (0 < x &lt;2); A silicon oxide-based composite in which a metal such as Al and Mg is doped or chemically bonded to SiO _x (0 <x <2); Or a mixture thereof is used as a negative electrode active material.
The method according to claim 1,
Wherein a copper mesh thin plate is interposed between the lithium metal sheet and the negative electrode collector non-coated portion.
The method according to claim 6,
Wherein the copper mesh thin plate is welded to the uncoated portion of the negative electrode current collector.
The method according to claim 6,
Wherein the copper mesh thin plate has a thickness of 3 to 500 占 퐉.
The method according to claim 6,
Wherein the copper mesh thin plate has 10 mesh to 200 mesh.
A pre-lithiated cathode produced by the method of any one of claims 1 to 9.

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