KR102509138B1 - 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 method for producing the same, a negative electrode for a lithium secondary battery including a negative electrode layer made of the pellet composition for the negative electrode, a method for manufacturing the same, and a lithium secondary battery including the negative electrode. Specifically, the present invention relates to a pellet composition for a negative electrode having a pellet form capable of easily pre-lithiation of a negative electrode without a liquid electrolyte, a negative electrode including the same, and a lithium secondary battery including the negative electrode.

Description

Pellet composition for negative electrode, negative electrode for lithium secondary battery and lithium secondary battery containing the same

The present invention relates to a pellet composition for a negative electrode and a method for producing the same, a negative electrode for a lithium secondary battery including a negative electrode layer made of the pellet composition for the negative electrode, a method for manufacturing the same, and a lithium secondary battery including the negative electrode. Specifically, the present invention relates to a pellet composition for a negative electrode having a pellet form capable of easily pre-lithiation of a negative electrode without a liquid electrolyte, a negative electrode including the same, and a lithium secondary battery including the negative electrode.

As the technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Batteries have been commercialized and are 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 lithium secondary batteries, and metal lithium and graphite are used as negative electrode active materials constituting the negative electrode. A carbon based material such as graphite or activated carbon, or a material such as silicon oxide (SiO _x ) is used. Among the negative electrode active materials, metal lithium was initially mainly used, but as the charge and discharge cycle progresses, lithium atoms grow on the surface of metal lithium to damage the separator and damage the battery. Recently, carbon-based materials are mainly used. However, in the case of carbon-based materials, the theoretical capacity is only about 400 mAh/g, which has the disadvantage of low capacity. As an anode active material, a silicon (Si)-based material with a high theoretical capacity (4,200 mAh/g) is used. Thus, various studies have been conducted to replace the carbon-based material.

The lithium secondary battery is charged and discharged while repeating processes of intercalation and deintercalation of lithium ions from a positive electrode active material of a positive electrode into a negative electrode active material of a negative electrode.

Theoretically, lithium insertion and desorption reactions into the anode active material layer are completely reversible, but in practice, more lithium is consumed than the theoretical capacity of the anode active material, and only a part of it is recovered during discharge. Therefore, after the second cycle, a smaller amount of lithium ions are inserted during charging, but most of the inserted lithium ions are desorbed during discharging. In this way, the difference in capacity that appears in the first charge and discharge reaction is called irreversible capacity loss. In commercialized lithium secondary batteries, lithium ions are supplied from the positive electrode and the negative electrode is manufactured without lithium, so irreversible capacity in the initial charge and discharge It is important to minimize losses.

It is known that most of this initial irreversible capacity loss is due to an electrolyte decomposition reaction on the surface of the negative electrode active material, and an SEI film (Solid Electrolyte Interface) is formed on the surface of the negative electrode active material by the electrochemical reaction through the electrolyte decomposition. ) is formed. Forming such an SEI film has a problem of causing irreversible capacity loss because many lithium ions are consumed, but the SEI film formed at the beginning of charging prevents the reaction between lithium ions and the negative electrode or other materials during charging and discharging, and the ion tunnel (Ion Tunnel) ) to pass only lithium ions, thereby suppressing further electrolyte decomposition reactions and contributing to the improvement of cycle characteristics of lithium secondary batteries.

Therefore, there is a need for a method for improving the initial irreversibility caused by the formation of the SEI film, etc., and as one method, pre-lithiation is performed before manufacturing a lithium secondary battery to prevent side reactions occurring during the first charge in advance. You can tell how to make it happen. In this way, when prelithiation is performed, when charging and discharging are performed on the actually manufactured secondary battery, the first cycle proceeds in a state in which the irreversibility is reduced by that much, so there is an advantage in that the initial irreversibility can be reduced.

Conventional prelithiation methods include, for example, 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 negative electrode, it is expensive to set up equipment for deposition, and in mass production, there are disadvantages in that processability is not good depending on the time required. In addition, since the method of directly contacting the negative electrode and lithium requires a process of immersing the negative electrode in the electrolyte before wetting the lithium, not only does it take time, but the electrode immersed in the electrolyte may have problems with adhesion. there is.

Accordingly, there is a need to develop a new negative electrode for a lithium secondary battery capable of more effective pre-lithiation.

KR 2014-0137371 A

The present invention provides a pellet composition for a negative electrode that can increase the capacity of a cell by securing the initial reversibility of the negative electrode and can easily prelithiate the negative electrode without a liquid electrolyte, a negative electrode including the same, and a lithium secondary battery including the negative electrode want 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

In the pellet composition for a negative electrode including a negative electrode active material, a solid electrolyte, and a conductive material and having a pellet form, lithium ions are diffused in the pellet composition and combined with the negative electrode active material at the same time, a prelithiated negative electrode pellet composition provides

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 molded article, and

It provides a method for producing the pre-lithiated negative electrode pellet composition, comprising the step of prelithiation by leaving the pellet-shaped molded article at a temperature of 10 ° C to 180 ° C for 2 hours to 48 hours.

In addition, the present invention

a negative electrode current collector, and

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

In addition, the present invention

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

It provides a method for manufacturing a negative electrode for a lithium secondary battery comprising the step of forming a negative electrode layer by pressing the resulting product.

In addition, the present invention

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

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

The pellet composition for a negative electrode of the present invention can easily pre-lithiate a negative electrode without a liquid electrolyte, and an all-solid-state battery with excellent reliability and stability can be manufactured using the pellet composition for a negative electrode. The lithium secondary battery manufactured in the present invention has greatly increased cycle efficiency.

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

The terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to explain their invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Pellet composition for negative electrode

The negative electrode composition of the present invention includes a negative electrode active material, a solid electrolyte, lithium metal powder, and a conductive material, and is a pellet composition for a negative electrode having 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, when a graphite-based material having a small theoretical capacity is used as the negative electrode active material, 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, when using an anode active material with a large theoretical capacity such as silicon, a relatively large amount of lithium powder must be used compared to graphite-based anode active materials to increase the prelithiation degree, so the amount of 1/2 to 1/20 of the weight of the anode active material can be used as

If the lithium metal powder is included in an amount less than 1/143 of the weight of the anode active material, prelithiation is not sufficiently performed, and if it is included in an amount exceeding 1/2, prelithiation is excessively performed, and lithium dendrites are formed in the anode during charging. As a result, cell performance degradation may 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.

If the negative electrode active material is used in a weight ratio of less than 60, the capacity of the cell may be reduced, and if the weight ratio is greater than 90, the amount of the solid electrolyte and the conductive material may be reduced, so that the electrode may not be properly formed. When the solid electrolyte is used in a weight ratio of less than 5, an electrode may not be formed and the lithium metal powder may be insufficient to pre-lithiate the negative electrode by dissociating the lithium metal powder, and when the solid electrolyte is used in a weight ratio exceeding 30, the negative electrode capacity may decrease. In addition, when the conductive material is used in an amount of less than 5 weight ratio, the conductivity of the cell may decrease, and when the amount of the conductive material exceeds 15 weight ratio, the capacity of the negative electrode may decrease.

The anode active material is a carbon-based material; Si, Sn, Al, at least one selected from the group consisting of 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), a metal oxide selected from the group consisting of TiO ₂ , MoO ₂ , V ₂ O ₅ and Li ₄ Ti ₅ O ₁₂ ; may be at least one 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-based 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 lithium phosphorous oxynitride (LiPON),

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 (provided that m and n are positive numbers, Z is Ge, any one of Zn and Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (provided that x and y are positive numbers, M is 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, any material that does not cause chemical change and has electronic conductivity can be used without particular limitation. Specific examples include graphite such as natural graphite or 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 powders 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, and one of them alone or a mixture of two or more may be used.

The negative electrode pellet composition 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

and pressurizing the mixed mixture to obtain a pellet-shaped molded product.

The pellet composition for a negative electrode of the present invention is prepared by a dry method without using a solvent, and the pellet composition for a negative electrode prepared according to this method also does not contain a solvent.

On the other hand, the negative electrode pellet composition may be a pre-lithiated negative electrode pellet composition in which lithium ions derived from lithium powder are diffused into the pellet composition and combined with the negative electrode active material.

Such a pre-lithiated pellet composition for a negative electrode may be prepared by performing a step of leaving the pellet-shaped molded article to be prepared.

The leaving step is a pre-lithiation step, which may be performed at a temperature of 10 °C to 180 °C for 2 hours to 48 hours, preferably at a temperature of 20 °C to 70 °C for 13 hours to 36 hours.

If the standing temperature is less than 10 ° C, the diffusion rate of lithium ions is slow, and prelithiation may not be sufficiently performed. In addition, if the leaving time is less than 2 hours, the prelithiation may not be sufficiently performed, and if the leaving time is 48 hours, the prelithiation is sufficiently performed, so there is no need to leave it for more than 48 hours.

Through this pre-lithiation process, lithium ions are diffused into the pellet composition or bonded to the negative electrode active material.

Cathode and cathode manufacturing method

The cathode of the present invention is

a negative electrode current collector, and

Distributed on the negative electrode current collector, and a negative electrode layer made of the pellet composition of the present invention described above.

The negative electrode layer may be formed at 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 generally have 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, and if it is formed in excess of 1:300, the electrode resistance may increase and smooth charging and discharging may not be performed.

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

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

Pressing the resultant to form a cathode layer.

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

The anode current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. For example, it is formed on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. A surface treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance bonding strength of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The binder serves to improve the adhesion between the pellet compositions and the 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, carboxymethylcellulose (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, and one of them alone or a mixture of two or more may be used. The binder may be included in an amount of 1% to 30% by weight based on the total weight of the negative electrode layer made of the pellet composition, the binder, and a conductive material that may optionally be added.

In addition, the additional conductive material may be the same as or different from the conductive material included in the pellet composition, and specific examples include graphite such as natural graphite or 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 powders 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, and one of them alone or a mixture of two or more may be used. The conductive material may include a pellet composition, a binder, and a conductive material in an amount of 1% to 30% by weight based on the total weight of the negative electrode layer.

lithium secondary battery

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

The negative electrode manufactured 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 prepared according to the present invention described above.

Meanwhile, the secondary battery may selectively further include a battery container accommodating a structure including the positive electrode, the negative electrode, and the electrolyte, and a sealing member 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 manufactured according to a conventional positive electrode manufacturing method generally known in the art. For example, the positive electrode is prepared by dissolving or dispersing components constituting the positive electrode active material layer, that is, a positive electrode active material, a conductive material and/or a binder, etc. It can be prepared by coating at least one surface, then drying and compressing, or by casting the positive electrode mixture on a separate support and then laminating a film obtained by peeling from the support on a positive electrode current collector.

The positive current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , those surface-treated with silver, etc. may be used. In addition, the cathode current collector may have a thickness of typically 3 μm to 500 μm, and adhesion of the cathode active material may be increased by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

Examples of the cathode active material include layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), or compounds 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 ; Ni site type lithium nickel oxide represented by the formula LiNi _{1 - y} M _y O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and y = 0.01 to 0.3); Formula LiMn _2-y M _y O ₂ (Where M = Co, Ni, Fe, Cr, Zn or Ta, and y = 0.01-0.1) or Li ₂ Mn ₃ MO ₈ (Where M = Fe, Co, Ni, Cu or Zn) lithium manganese composite oxide; LiMn ₂ O ₄ in which Li part of the formula is substituted with an alkaline earth metal ion; 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 those described above for the negative electrode.

Meanwhile, in the secondary battery, a solid electrolyte may serve as a separator, but a separate separator may be added. When a separate separator is added, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ion movement. If it is normally used as a separator in a secondary battery, it can be used without particular limitation. In particular, regarding the movement of ions in the electrolyte It is preferable to have low resistance and excellent ability to absorb electrolyte. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminated structure of two or more layers of may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting 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 selectively used in a single layer or multilayer structure.

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

Preferably, as an electrolyte in the present invention, a solid electrolyte may be interposed between an anode and a cathode, and 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-based 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 lithium phosphorous oxynitride (LiPON),

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 (provided that m and n are positive numbers, Z is Ge, any one of Zn and Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (provided that x and y are positive numbers, M is any one of P, Si, Ge, B, Al, Ga, In) and mixtures thereof.

The solid electrolyte may simultaneously serve as an electrolyte and a separator.

Meanwhile, 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 includes ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, PC) and other carbonate-based solvents; alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as Ra-CN (Ra is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolane (sulfolane) and the like may be used. Among these, carbonate-based solvents are preferable, and cyclic carbonates (eg, ethylene carbonate or propylene carbonate, etc.) having high ion conductivity and high permittivity capable of increasing the charge and discharge performance of batteries, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) 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.

Any compound capable of providing lithium ions used in a lithium secondary battery may be used as the lithium salt without particular limitation. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO _{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 or the like may 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 within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

In addition to the components of the electrolyte, the electrolyte may include, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate for the purpose of improving life characteristics of a battery, suppressing a decrease in battery capacity, and improving a discharge capacity of a battery; or pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid 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 further included. In this case, the additive may be included in an amount of 0.1% 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 that does not include a liquid electrolyte by including a solid electrolyte layer.

Example

Hereinafter, the present invention will be described in detail by examples. However, the following examples are only intended to illustrate 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 an anode 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. Here, lithium metal powder (D ₅₀ = 10 μm) was additionally added in a weight ratio of 1/70 to the negative electrode active material, mixed, and then pressed to prepare a pellet composition for an anode having a pellet form.

prelithiation

The pellet composition for the negative electrode prepared above was left at 25° C. for 30 hours to pre-lithiate.

cathode fabrication

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

Manufacture of all-solid-state battery

After raising LLZO to a thickness of 2 mm as a solid electrolyte on one side of the negative electrode prepared above, the negative electrode and the solid electrolyte were attached by pressing. Then, a lithium metal foil (thickness of 40 μm) was placed on the upper surface of the solid electrolyte, and then the lithium metal foil was attached by pressing. Through this cell manufacturing process, a coin-type half-cell in the form of Li/LLZO/cathode was manufactured.

Example 2.

A coin-type half-cell was prepared in the same manner as in Example 1, except that the lithium metal powder was added in a weight ratio of 1/80 to the negative electrode active material in the process of preparing the pellet composition for the negative electrode of Example 1.

Example 3.

A coin-type half-cell was prepared in the same manner as in Example 1, except that LLTO (Li _0.35 La _0.55 TiO ₃ ) was used instead of LLZO as the solid electrolyte in the _process of preparing _the pellet _composition for the negative electrode of Example ₁ . manufactured.

Comparative Example 1.

A coin-type half-cell was prepared in the same manner as in Example 1, except that the lithium metal powder was not added during the manufacturing process of the negative electrode pellet composition.

Comparative Example 2.

A coin-type half-cell was prepared in the same manner as in Example 1, except that 70% by weight of graphite and 30% by weight of carbon fiber were used without adding LLZO as the solid electrolyte during the manufacturing process of the pellet composition for the negative electrode. .

Experimental Example 1. Initial reversibility test

The charge/discharge reversibility test was performed on the coin-type half-cell prepared in Examples and Comparative Examples using an electrochemical charge/discharge machine.

During charging, a current was applied at a current density of 0.1 C-rate up to a voltage of 0.005 V ( vs. Li/Li ⁺ ) to charge, and during discharge, a voltage of 1.5 V was discharged at the same current density. At this time, the charge capacity and 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, the discharge capacities of Examples 1 to 3 and Comparative Example 1 are almost similar, but the reason for the difference in charge capacities is due to the difference in prelithiation degree. In the case of Examples 1 to 3 in which the lithium metal powder was added at a weight ratio of 1/70 to 1/80 relative to the active material, the negative electrode was pre-lithiated, reducing irreversible occurrence during charging and improving efficiency. On the other hand, in the case of Comparative Example 1 in which no lithium metal powder was added, the initial efficiency was lower than that of Examples 1 to 3 because the anode was not pre-lithiated. In the case of Comparative Example 2, the charge capacity and discharge capacity were hardly expressed. This is because the solid electrolyte did not enter the negative electrode and there was no medium to move lithium ions in the negative electrode itself, so charging and discharging did not occur deeply. It is believed that this is because only a portion of the solid electrolyte used during manufacturing participated in charging and discharging.

Claims (19)

Distributing and pressurizing a pellet composition for a negative electrode on a negative electrode current collector to form a negative electrode layer,
The negative electrode pellet composition includes a negative electrode active material, a solid electrolyte, lithium metal powder and a conductive material and has a pellet form, a method for producing a negative electrode for a lithium secondary battery.
The method of claim 1,
The lithium metal powder is a method for producing a negative electrode for a lithium secondary battery, which is included in an amount of 1/143 to 1/2 by weight of the negative electrode active material.
The method of 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, a method for producing a negative electrode for a lithium secondary battery.
The method of claim 1,
The anode active material is a carbon-based material; Si, Sn, Al, at least one selected from the group consisting of 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), a metal oxide selected from the group consisting of TiO ₂ , MoO ₂ , V ₂ O ₅ and Li ₄ Ti ₅ O ₁₂ ; at least one selected from the group consisting of, a method for producing a negative electrode for a lithium secondary battery.
The method of claim 1,
The solid electrolyte is at least one selected from an inorganic solid electrolyte and a polymer solid electrolyte, a method for producing a negative electrode for a lithium secondary battery.
The method of claim 1,
The pellet composition for the negative electrode is a method for producing a negative electrode for a lithium secondary battery that does not contain a solvent.
The method of claim 1,
The pellet composition for the negative electrode,
A method for producing a negative electrode for a lithium secondary battery, which is produced by 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 product.
The method of claim 1,
The negative electrode pellet composition is a method for producing a negative electrode for a lithium secondary battery, which is prepared by a dry manufacturing method that does not use a solvent.
Distributing and pressurizing a pellet composition for a negative electrode on a negative electrode current collector to form a negative electrode layer,
The negative electrode pellet composition includes a negative electrode active material, a solid electrolyte, and a conductive material, has a pellet form, and lithium ions are diffused in the pellet composition and combined with the negative electrode active material, manufacturing a negative electrode for a lithium secondary battery method.
The method of claim 9,
The pellet composition for the negative electrode,
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 molded article, and
Leaving the pellet-shaped molded article at a temperature of 10 ° C to 180 ° C for 2 hours to 48 hours
A method for producing a negative electrode for a lithium secondary battery, which is prepared by including.
delete The method of claim 9,
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, a method for manufacturing a negative electrode for a lithium secondary battery. delete delete delete delete delete delete delete