KR20190125716A - Pellet composition for negative electrode, negative electrode for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a pellet composition for a negative electrode and a manufacturing method thereof, a negative electrode for a lithium secondary battery comprising a negative electrode layer consisting of the pellet composition for the negative electrode and a manufacturing method thereof, and a lithium secondary battery comprising the negative electrode and, more specifically, to a pellet composition for a negative electrode having a pellet form enabling pre-lithiation of the negative electrode without a liquid electrolyte, a negative electrode comprising the same and a lithium secondary battery comprising the negative electrode.

Description

Pellet composition for negative electrode, negative electrode for lithium secondary battery and lithium secondary battery comprising same {PELLET COMPOSITION FOR NEGATIVE ELECTRODE, NEGATIVE ELECTRODE FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a negative electrode pellet composition and a method for manufacturing the same, a negative electrode for a lithium secondary battery comprising a negative electrode layer consisting of the pellet composition for the negative electrode and a method for manufacturing the same, a lithium secondary battery comprising the negative electrode. In particular, the present invention relates to a pellet composition for a negative electrode having a pellet form that can easily lithium ionize a negative electrode without a liquid electrolyte, a negative electrode including the same, and a lithium secondary battery including the negative electrode.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among them, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries have been commercialized and widely used.

On the other hand, metal oxides such as LiCoO ₂ , LiMnO ₂ , LiMn ₂ O _4, or LiCrO ₂ are used as positive electrode active materials constituting the positive electrode of a lithium secondary battery, and metal lithium and graphite are used as negative active materials constituting the negative electrode. Carbon-based materials such as graphite or activated carbon, or materials such as silicon oxide (SiO _x ) are used. Among the negative active materials, metal lithium was initially used, but as the charge and discharge cycles progress, lithium atoms grow on the surface of the metal lithium to damage the separator and damage the battery. Recently, carbon-based materials are mainly used. However, the carbon-based material has a disadvantage in that the theoretical capacity is only about 400 mAh / g, so the capacity is small. Therefore, a silicon (Si) -based material having a high theoretical capacity (4,200 mAh / g) is used as the negative electrode active material. Various studies have been conducted to replace the carbonaceous material.

The lithium secondary battery charges and discharges while repeating a process in which lithium ions of the positive electrode active material of the positive electrode are intercalated and deintercalated into the negative electrode active material of the negative electrode.

In theory, the lithium insertion and desorption reaction into the negative electrode active material layer is completely reversible, but in reality more lithium is consumed than the theoretical capacity of the negative electrode active material, only a part of which is recovered upon discharge. Thus, after the second cycle, less lithium ions are inserted during charging but almost all of the lithium ions are released during discharge. This difference in capacity in the first charge and discharge reaction is called irreversible capacity loss.In commercialized lithium secondary batteries, since lithium ions are supplied from the positive electrode and manufactured without lithium at the negative electrode, irreversible capacity during initial charge and discharge It is important to minimize losses.

It is known that the initial irreversible capacity loss is mainly due to the electrolyte decomposition reaction on the surface of the negative electrode active material, and the SEI film (solid electrolyte membrane, Solid Electrolyte Interface) on the surface of the negative electrode active material by the electrochemical reaction through the electrolyte decomposition. ) Is formed. Such SEI film formation causes a problem of irreversible capacity loss because a large amount of lithium ions are consumed. However, the SEI film formed at the beginning of charging prevents reaction between lithium ions and a negative electrode or other materials during charge and discharge, and ion tunnels. It serves to pass only lithium ions by the role of) to suppress further electrolyte decomposition reactions contribute to the improvement of cycle characteristics of the lithium secondary battery.

Therefore, there is a need for a method for improving the initial irreversibility caused by the formation of the SEI film, etc. As one method, a pre-lithiation is performed prior to fabricating a lithium secondary battery to advance side reactions generated during the first charge. How to suffer. As such, when the prelithiation is performed, the first cycle proceeds in a state where the irreversibility is reduced by the charge / discharge of the actually manufactured secondary battery, thereby reducing the initial irreversibility.

Conventional alllithiation methods include a method of depositing lithium on a negative electrode, and a method of directly contacting a negative electrode with lithium. However, in order to deposit lithium on the cathode, it is expensive to set up a device for deposition, and in the case of mass production, it has a disadvantage in that processability is not good over time. In addition, the method of directly contacting the negative electrode with lithium requires a process of immersing the negative electrode in the electrolyte before the contact with lithium, so that it takes time, and the electrode that has been immersed in the electrolyte may cause problems in adhesion. have.

Accordingly, the development of a new negative electrode for a lithium secondary battery that can be more effective prelithiation is required.

KR 2014-0137371 A

The present invention can not only increase the capacity of the cell by ensuring the initial reversibility of the negative electrode, but also a pellet composition for a negative electrode that can easily lithium ionize the negative electrode without a liquid electrolyte, a negative electrode comprising the same and a lithium secondary battery comprising the negative electrode To provide.

In order to solve the above problems, the present invention first,

Provided is a pellet composition for a negative electrode including a negative electrode active material, a solid electrolyte, lithium metal powder and a conductive material, and having a pellet form.

In addition, the present invention

Mixing a negative electrode active material, a solid electrolyte, lithium metal powder and a conductive material, and

It provides a method for producing the pellet composition for the negative electrode, comprising the step of obtaining a pellet-shaped molded article by pressing the mixed mixture.

In addition, the present invention

A pellet composition for a negative electrode having a pellet form, comprising a negative electrode active material, a solid electrolyte, and a conductive material, wherein lithium ions diffuse into the pellet composition and are bonded to the negative electrode active material. To provide.

In addition, the present invention

Mixing a negative electrode active material, a solid electrolyte, lithium metal powder and a conductive material,

Pressurizing the mixed mixture to obtain a pellet shaped article, and

It provides a method for producing a pellet composition for the pre-lithiated negative electrode comprising the step of pre-lithiating the pellet-shaped molded article at a temperature of 10 ℃ to 180 ℃ for 2 hours to 48 hours.

In addition, the present invention

A negative electrode current collector, and

Provided on the negative electrode current collector, comprising a negative electrode layer made of the pelletized composition for the pre-lithiated negative electrode, provides a negative electrode for a lithium secondary battery.

In addition, the present invention

Distributing the pellet composition for the pre-lithiated negative electrode on a negative electrode current collector, and

It provides a method for manufacturing the negative electrode for a lithium secondary battery comprising the step of pressing the resultant to form a negative electrode layer.

In addition, the present invention

A lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte,

The negative electrode provides a lithium secondary battery which is the negative electrode for the lithium secondary battery described above.

The pellet composition for the negative electrode of the present invention can not only easily lithium ionize the negative electrode without a liquid electrolyte solution, it is possible to manufacture an all-solid-state battery excellent in reliability and stability using such a pellet composition for the negative electrode. The lithium secondary battery manufactured in the present invention greatly increases the cycle efficiency.

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

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

Pellet composition for negative electrode

The negative electrode composition of the present invention is a negative electrode pellet composition containing a negative electrode active material, a solid electrolyte, lithium metal powder and a conductive material, and has a pellet form.

The lithium metal powder may be included in an amount of 1/143 to 1/2 of the weight of the negative electrode active material.

Specifically, in the case of using a graphite-based material having a small theoretical capacity, the lithium powder may be used in an amount of 1/20 to 1/143, specifically, 1/20 to 1/100 of the weight of the negative electrode active material. On the other hand, in the case of using a cathode active material with a large theoretical capacity such as silicon, the amount of 1/2 to 1/20 of the weight of the negative electrode active material can be increased because lithium lithiation may be increased when the lithium powder is used in comparison with the graphite-based anode active material. Can be used as

If the lithium metal powder is contained in an amount less than 1/143 of the weight of the negative electrode active material, it is not sufficiently lithiated. If the lithium metal powder is contained in an amount exceeding 1/2, the lithium dendrite is formed at the negative electrode during charging. Deterioration of the cell performance can be accelerated.

In the pellet composition for the negative electrode, the weight ratio of the negative electrode active material, the solid electrolyte and the conductive material may be 60-90: 5-30: 5-15, specifically 65-85: 10-25: 8-12.

When the negative electrode active material is used in less than 60 weight ratio, the capacity of the cell may be reduced, and when the negative electrode active material is used in excess of 90 weight ratio, the amount of the solid electrolyte and the conductive material may be small, so that the electrode may not be properly formed. When the solid electrolyte is used in less than 5 weight ratio, the electrode is not configured and may be insufficient to dissociate the lithium metal powder to pre-lithiate the negative electrode, and when used in excess of 30 weight ratio, the negative electrode capacity may be reduced. In addition, the conductivity of the cell may be lowered when the conductive material is used in less than 5 weight ratio, and the capacity of the negative electrode may be reduced when used in an amount exceeding 15 weight ratio.

The negative electrode active material is a carbon-based material; At least one selected from the group consisting of Si, Sn, Al, Sb, and Zn or oxides thereof; And Co _x1 O _y1 ( ₁ ≦ _x1 ≦ 3, ₁ ≦ _y1 ≦ 4), Ni _x2 O _y2 (1 ≦ _x2 ≦ 3, 1 ≦ _y2 ≦ 4), Fe _x3 O _y3 (1 ≦ _x3 ≦ ₃ , 1 ≦ y 3 ≤ 4), TiO ₂ , MoO ₂ , V ₂ O ₅ And Li ₄ Ti ₅ O _{12 It} may be one or more selected from the group consisting of;

The solid electrolyte may be an inorganic solid electrolyte or a polymer solid electrolyte.

The inorganic solid electrolyte may be an oxide-based inorganic solid electrolyte, a phosphate-based inorganic solid electrolyte, a nitride-based inorganic solid electrolyte, a sulfide-based inorganic solid electrolyte, or a mixture thereof.

The oxide-based inorganic solid electrolyte is a lithium-lanthanum-titanium oxide (LLTO) -based, lithium-lanthanum-zirconium oxide (LLZO) -based, lisicon-based or a mixture thereof,

The phosphate inorganic solid electrolyte is any one selected from the group consisting of lithium-aluminum-titanium-phosphate (LATP), lithium-aluminum-germanium-phosphate (LAGP), and mixtures thereof,

The nitride-based inorganic solid electrolyte is LiPON (lithium phosphorous oxynitride),

The sulfide-based inorganic solid electrolyte is Li ₁₀ GeP ₂ S ₁₂ , Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O -LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S _3- LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n ( _where m and n are positive numbers and Z is Ge, Zn or Ga), L _i2 S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (where x and y are positive numbers, M may be any one of P, Si, Ge, B, Al, Ga, In), and mixtures thereof.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any conductive material can be used without particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, and the like, or a mixture of two or more kinds thereof may be used.

The pellet composition for the negative electrode of the present invention comprises the steps of mixing a negative electrode active material, a solid electrolyte, lithium metal powder and a conductive material, and

Pressing the mixed mixture is prepared to obtain a pellet-shaped molded article.

The negative electrode pellet composition of the present invention is prepared by a dry method using no solvent, the negative electrode pellet composition thus prepared also does not contain a solvent.

Meanwhile, the negative electrode pellet composition may be a lithium ion negative electrode pellet composition in which lithium ions derived from lithium powder are diffused into the pellet composition and combined with a negative electrode active material.

Such prelithiated pellet composition for negative electrode may be prepared by performing the step of leaving the pellet-shaped molded article after manufacture.

The leaving step may be performed for 2 hours to 48 hours at a temperature of 10 ℃ to 180 ℃, preferably 13 hours to 36 hours at a temperature of 20 ℃ to 70 ℃ as a prelithiation step.

If the standing temperature is less than 10 ℃ lithium ion diffusion rate is slow may not be sufficiently pre-lithiation, the lithium metal is melted at a temperature exceeding 180 ℃ it is difficult to maintain its shape and may not be smooth alliation. In addition, if the leaving time is less than 2 hours, the prelithiation may not be sufficiently performed, and if it is 48 hours, the prelithiation is sufficiently performed, and thus it is not necessary to leave it for more than 48 hours.

Through this prelithiation process, lithium ions are diffused into the pellet composition or combined with the negative electrode active material.

Cathode and Manufacturing Method of Cathode

The negative electrode of the present invention

A negative electrode current collector, and

It is distributed on the negative electrode current collector, and comprises a negative electrode layer made of the above-described pellet composition of the present invention.

The negative electrode layer may be formed in a ratio of 1: 3 to 300, specifically, 1: 3 to 200 with respect to the thickness of the negative electrode current collector, and may be generally formed in a thickness of 50 μm to 2000 μm. If the thickness of the negative electrode layer is less than 1: 3 with respect to the current collector, the capacity may be too small. If the thickness of the negative electrode layer is greater than 1: 300, the electrode resistance may increase, thereby preventing smooth charging and discharging.

The negative electrode according to the present invention can be prepared through the following steps:

Distributing the pellet composition for the negative electrode on a negative electrode current collector, and

Pressing the resultant to form a cathode layer.

When distributing the pellet composition for the negative electrode on the negative electrode current collector, a binder and an additional conductive material may be mixed with the pellet composition and distributed. These binders and conductive materials are mixed with the pellet composition in a dry state without a solvent, distributed on a negative electrode current collector, and then pressurized to form a negative electrode layer.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The binder serves to improve adhesion between the pellet compositions and adhesion between the negative electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber Or various copolymers thereof, and the like may be used alone or in a mixture of two or more thereof. The binder may be included in an amount of 1 wt% to 30 wt% with respect to the total weight of the negative electrode layer made of a pellet composition, a binder, and optionally a conductive material.

The additional conductive material may be the same as or different from the conductive material contained in the pellet composition, and specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, and the like, or a mixture of two or more kinds thereof may be used. The conductive material may include 1 wt% to 30 wt% of the total weight of the negative electrode layer, which is composed of a pellet composition, a binder, and a conductive material.

Lithium secondary battery

Next, a lithium secondary battery according to the present invention will be described.

The negative electrode prepared according to the present invention can be usefully used for manufacturing a lithium secondary battery.

Specifically, the lithium secondary battery according to the present invention

A lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is a negative electrode manufactured according to the present invention described above.

Meanwhile, the secondary battery may further include a battery container for accommodating the structure including the positive electrode, the negative electrode, and the electrolyte, and a sealing member for sealing the battery container.

The lithium secondary battery may be manufactured according to a conventional secondary battery manufacturing method except for using the negative electrode according to the present invention.

In the secondary battery, the positive electrode includes a positive electrode current collector and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector.

The positive electrode may be prepared according to a conventional positive electrode manufacturing method generally known in the art. For example, the positive electrode may be prepared by dissolving or dispersing components constituting the positive electrode active material layer, that is, the positive electrode active material, a conductive material and / or a binder, and the like in a solvent, and manufacturing the positive electrode mixture of the positive electrode current collector. After coating on at least one surface, it may be prepared by drying and pressing, or by casting the positive electrode mixture on a separate support, and then laminating the film obtained by peeling from the support onto a positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, carbon, nickel, titanium on the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with silver, silver or the like can be used. In addition, the positive electrode current collector may have a thickness of typically 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

As the positive electrode active material, for example, 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; Formula _{Li 1 + y Mn 2 - y} O 4 ( where, y is from 0 to 0.33), LiMnO _3, the lithium manganese oxide such as 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 , Cu ₂ V ₂ O ₇ and the like; 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 , wherein M = Co, Ni, Fe, Cr, Zn or Ta, y = 0.01-0.1, 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 alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like may be used, but are not limited thereto.

In addition, the binder and the conductive material may be the same as described above in the negative electrode.

Meanwhile, in the secondary battery, although the solid electrolyte may play a role of a separator, a separate separator may be added. When a separate separator is added, the separator separates the negative electrode from the positive electrode and provides a passage for moving lithium ions. If the separator is used as a separator in a secondary battery, the separator can be used without particular limitation. It is preferable that it is low resistance and excellent in electrolyte solution moisture-wetting ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.

Meanwhile, the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, or the like that can be used in manufacturing a secondary battery.

Preferably, the electrolyte in the present invention may be a solid electrolyte interposed between the positive electrode and the negative electrode, the solid electrolyte may be an inorganic solid electrolyte or a polymer solid electrolyte.

The inorganic solid electrolyte may be an oxide-based inorganic solid electrolyte, a phosphate-based inorganic solid electrolyte, a nitride-based inorganic solid electrolyte, a sulfide-based inorganic solid electrolyte, or a mixture thereof.

The oxide-based inorganic solid electrolyte is a lithium-lanthanum-titanium oxide (LLTO) -based, lithium-lanthanum-zirconium oxide (LLZO) -based, lisicon-based or a mixture thereof,

The phosphate inorganic solid electrolyte is any one selected from the group consisting of lithium-aluminum-titanium-phosphate (LATP), lithium-aluminum-germanium-phosphate (LAGP), and mixtures thereof,

The nitride-based inorganic solid electrolyte is LiPON (lithium phosphorous oxynitride),

The sulfide-based inorganic solid electrolyte is Li ₁₀ GeP ₂ S ₁₂ , Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O -LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S _3- LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n ( _where m and n are positive numbers and Z is Ge, Zn or Ga), L _i2 S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (where x and y are positive numbers, M may be any one of P, Si, Ge, B, Al, Ga, In), and mixtures thereof.

The solid electrolyte may simultaneously play a role of an electrolyte and a role of a separator.

On the other hand, when the electrolyte is a liquid electrolyte, the liquid electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc .; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles, such as Ra-CN (Ra is a C2-C20 linear, branched, or cyclic hydrocarbon group, and may include a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Among these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge / discharge performance of a battery, and low viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1: 1 to 9, the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

The electrolyte includes, in addition to the electrolyte components, haloalkylene carbonate-based compounds such as difluoroethylene carbonate and the like for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity; Or pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N One or more additives such as -substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be included. In this case, the additive may be included in an amount of 0.1% by weight to 5% by weight based on the total weight of the electrolyte.

As described above, the lithium secondary battery according to the present invention may be an all-solid-state battery containing no liquid electrolyte by including a solid electrolyte layer.

Example

Hereinafter, the present invention will be described in detail by way of examples. However, the following examples are only for illustrating the present invention and are not intended to limit the present invention.

Example 1.

Preparation of pellet composition for negative electrode

70 wt% of graphite (D ₅₀ = 20 μm) as a negative electrode active material, 10 wt% of carbon fiber as a conductive material, and 20 wt% of LLZO (Li ₇ La ₃ Zr ₂ O ₁₂ ) as a solid electrolyte were mixed. A lithium metal powder (D ₅₀ = 10 μm) was further added thereto in an amount of 1/70 to a negative electrode active material, mixed, and pressed to prepare a pellet composition for a negative electrode having a pellet form.

Prelithiation

The pellet composition for the negative electrode prepared above was left at 25 ° C. for 30 hours to be prelithiated.

Preparation of Cathode

The prepared pre-lithiated negative electrode pellet composition was distributed on one surface of a copper current collector and compressed to prepare a negative electrode (thickness of copper current collector: 20 μm, thickness of the compressed negative electrode layer: 60 μm).

Fabrication of All Solid Battery

On one surface of the negative electrode prepared above, LLZO was raised to a thickness of 2 mm as a solid electrolyte and then pressed to attach a negative electrode and a solid electrolyte. Then, a lithium metal foil (thickness of 40 μm) was placed on the top surface of the solid electrolyte and pressurized to attach a lithium metal foil. Through this cell manufacturing process, a coin-type half cell of Li / LLZO / cathode type was manufactured.

Example 2.

Except that the lithium metal powder was added in a weight ratio of 1/80 to the negative electrode active material in the preparation process of the pellet composition for the negative electrode of Example 1 was carried out the same process to prepare a coin-type half-cell.

Example 3.

The embodiment as a first solid electrolyte from the cathode pellet composition manufacturing process for the LLTO instead _{LLZO (Li 0. 35 La 0} . 55 TiO 3) of the Example 1, and a coin-type half-cell by following the same procedure but using Prepared.

Comparative Example 1.

Except that the lithium metal powder was not added during the preparation of the pellet composition for the negative electrode of Example 1 was carried out in the same manner to prepare a coin-type half cell.

Comparative Example 2.

A coin-type half cell was manufactured in the same manner as in Example 1, except that LLZO was not added as a solid electrolyte in the preparation process of the pellet composition for the negative electrode, and 70 wt% graphite and 30 wt% carbon fiber were used. .

Experimental Example 1. Initial Reversibility Test

The coin-type half-cells prepared in Examples and Comparative Examples were subjected to a charge / discharge reversibility test using an electrochemical charger.

During charging, a current was charged at a current density of 0.1 C-rate to a voltage of 0.005 V ( vs. Li / Li ⁺ ), and discharged at a voltage of 1.5 V at the same current density. At this time, the charge capacity and the discharge capacity were measured and the first cycle efficiency was calculated and shown in Table 1 below.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Charge capacity (mAh / g) 320 343 321 388 21 Discharge Capacity (mAh / g) 339 336 337 341 5 First cycle efficiency (%) 106 98 105 88 24

As can be seen from the results of Table 1, in Examples 1 to 3 and Comparative Example 1, the discharge capacity is almost similar, but the charge capacity is different because of the difference in the degree of prelithiation. In Examples 1 to 3 in which the lithium metal powder was put in a weight ratio of 1/70 to 1/80 relative to the active material, the negative electrode was pre-lithiated to reduce irreversibility generated during charging, thereby improving efficiency. On the other hand, in Comparative Example 1, in which no lithium metal powder is added, the initial efficiency is not as good as in Examples 1 to 3 because the negative electrode is not prelithiated. In Comparative Example 2, the charging capacity and the discharging capacity were hardly expressed because the solid electrolyte did not enter the negative electrode, and thus, there was no medium capable of moving lithium ions in the negative electrode itself, and thus, the deep solid state battery was not deeply charged and discharged. It is believed that only a part of the solid electrolyte used in the manufacture participated in charging and discharging.

Claims (19)

A pellet composition for a negative electrode, comprising a negative electrode active material, a solid electrolyte, lithium metal powder, and a conductive material, and having a pellet form.
The method according to claim 1,
The lithium metal powder is a pellet composition for the negative electrode contained in an amount of 1/143 ~ 1/2 relative to the weight of the negative electrode active material.
The method according to claim 1,
The weight ratio of the negative electrode active material, the solid electrolyte and the conductive material is 60-90: 5-30: 5-15 pellet composition for the negative electrode.
The method according to claim 1,
The negative electrode active material is a carbon-based material; At least one selected from the group consisting of Si, Sn, Al, Sb, and Zn or oxides thereof; And Co _x1 O _y1 ( ₁ ≦ _x1 ≦ 3, ₁ ≦ _y1 ≦ 4), Ni _x2 O _y2 (1 ≦ _x2 ≦ 3, 1 ≦ _y2 ≦ 4), Fe _x3 O _y3 (1 ≦ _x3 ≦ ₃ , 1 ≦ y3 ≦ 4), TiO ₂ , MoO ₂ , V ₂ O ₅ and Li ₄ Ti ₅ O ₁₂ ; a metal oxide selected from the group consisting of; at least one member selected from the group consisting of pellet composition for a negative electrode.
The method according to claim 1,
The solid electrolyte is at least one selected from an inorganic solid electrolyte and a polymer solid electrolyte, pellet composition for the negative electrode.
The method according to claim 1,
The negative electrode pellet composition does not contain a solvent, pellet composition for negative electrode.
Mixing a negative electrode active material, a solid electrolyte, lithium metal powder and a conductive material, and
Pressing the mixed mixture to obtain a pellet-shaped molded article, the method of producing a pellet composition for negative electrode of claim 1.
The method according to claim 7,
The manufacturing method is a method for producing a pellet composition for the negative electrode, which is a dry manufacturing method using no solvent.
A pellet composition for a negative electrode, comprising a negative electrode active material, a solid electrolyte, and a conductive material, having a pellet form, wherein lithium ions diffuse into the pellet composition and are bonded to the negative electrode active material.
Mixing a negative electrode active material, a solid electrolyte, lithium metal powder and a conductive material,
Pressurizing the mixed mixture to obtain a pellet shaped article, and
Leaving the pellet-shaped molded article for 2 hours to 48 hours at a temperature of 10 ℃ to 180 ℃
A method for producing a pellet composition for negative electrode, comprising a.
A negative electrode current collector, and
Distributing on the negative electrode current collector, comprising a negative electrode layer made of the pellet composition for negative electrode of claim 9, the negative electrode for a lithium secondary battery.
The method according to claim 11,
The thickness of the negative electrode current collector: the thickness of the negative electrode layer is formed in a ratio of 1: 3 to 300, the lithium secondary battery negative electrode.
Distributing the pellet composition for negative electrode on the negative electrode current collector, and
Method of manufacturing a negative electrode for a lithium secondary battery of claim 11 comprising the step of pressing the resultant to form a negative electrode layer.
A lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte,
The negative electrode is a lithium secondary battery of claim 11.
The method according to claim 14,
The electrolyte is a lithium secondary battery is a solid electrolyte layer.
The method according to claim 15,
The solid electrolyte layer is at least one selected from an inorganic solid electrolyte layer and a polymer solid electrolyte layer lithium secondary battery.
The method according to claim 15,
The solid electrolyte layer is a lithium secondary battery disposed between the positive electrode and the negative electrode.
The method according to claim 14,
The lithium secondary battery is a lithium secondary battery that is an all-solid-state battery.
The method according to claim 14,
The lithium secondary battery further comprises a separator.