KR102663797B1 - Cathode additives for lithium metal rechargeable battery, cathode including the same cathode additives, and formation methode for lithium metal rechargeable battery including the same cathode additives - Google Patents

Abstract

The present invention relates to a method for activating a lithium metal secondary battery,
1) At the discharge voltage of the battery formation process, select a positive electrode additive that can accommodate lithium ions with priority over the positive electrode active material,
2) The formation process of a general battery begins with charging, but the formation process of a battery to which the positive electrode additive is applied begins with discharging.

Description

A positive electrode additive for a lithium metal secondary battery, a positive electrode containing the same, and a method of activating a lithium metal secondary battery containing the same CATHODE ADDITIVES}

The present invention relates to a positive electrode additive for lithium metal secondary batteries, a positive electrode containing the same, and a method of activating a lithium metal secondary battery containing the same.

Commercial lithium secondary batteries mainly use carbon-based anodes. Here, the carbon-based negative electrode uses a carbon-based material as a negative electrode active material and applies it to the surface of the negative electrode current collector. Although this carbon-based negative electrode has the advantage of high stability, there is a limit to improving the energy density of the battery due to the low theoretical capacity of the carbon-based material that is the negative electrode active material.

Accordingly, in recent years, in order to utilize lithium secondary batteries as a power source for devices requiring high energy density and high output characteristics, research has been conducted to replace carbon-based negative electrodes and apply other negative electrodes to lithium secondary batteries.

As part of this, lithium metal anodes, which use lithium metal (Li-metal) itself as an anode active material, have recently emerged as a hot topic of research and development. Lithium metal (Li-metal) not only has a low density (0.54g/cm ³ ) and a large theoretical capacity (3840mAh/g), but also has a very low standard reduction potential (-3.045V SHE), making it useful as an anode active material for batteries. This can contribute to improving energy density and output characteristics.

However, due to the high reactivity of lithium metal (Li-metal), there is a problem in which a non-uniform passivation film is formed on the surface of the lithium metal negative electrode as soon as the lithium metal negative electrode and the electrolyte solution come into contact during the manufacturing process of the lithium metal secondary battery. .

In this way, the passive film formed unevenly on the surface of the lithium metal anode becomes a factor that inhibits the activation of the lithium metal anode and further shortens the lifespan of the lithium metal secondary battery.

To date, these problems have not been solved, and lithium metal secondary batteries have not been commercialized.

The present invention is intended to solve the problem pointed out above,

1) At the discharge voltage of the battery formation process, select a positive electrode additive that can accommodate lithium ions with priority over the positive electrode active material,

2) The formation process of a general battery begins with charging, but the formation process of a battery to which the positive electrode additive is applied begins with discharging.

Specifically, in one embodiment of the present invention,

A positive electrode additive containing lithium metal oxide; and a positive electrode active material; manufacturing a lithium metal secondary battery comprising a positive electrode, a lithium metal negative electrode, and an electrolyte;

Discharging the lithium metal secondary battery until it reaches a range of 1.8 V or more to 3.0 V or less;

Charging the discharged lithium metal secondary battery until it reaches a range of 4.2V to 4.6V; and

Aging the charged lithium metal secondary battery;

Including,

A method for activating a lithium metal secondary battery is provided.

According to one embodiment, the cathode surface is made uniform immediately after the activation process due to a synergistic effect according to 1) selection of the anode additive and 2) an activation process starting from the discharge; During the battery cycle after the activation process, lithium ion desorption/deposition on the cathode surface occurs smoothly; Ultimately, battery life (capacity maintenance rate) can be improved.

Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention.

In this specification, when a part “includes” a certain component, this means that it may further include other components rather than excluding other components unless specifically stated to the contrary. As used throughout the specification, the terms “about,” “substantially,” and the like are used to mean at or close to a numerical value when manufacturing and material tolerances inherent in the stated meaning are given, and are used to convey the understanding of the present application. Precise or absolute figures are used to assist in preventing unscrupulous infringers from taking unfair advantage of stated disclosures. As used throughout the specification, the terms “step of” or “step of” do not mean “step for.”

In this specification, the term "combination thereof" included in the Markushi format expression means a mixture or combination of one or more components selected from the group consisting of the components described in the Markushi format expression, It means including one or more selected from the group consisting of.

Based on the above definition, implementation examples of the present invention will be described in detail. However, these are presented as examples, and the present invention is not limited thereby, and the present invention is only defined by the scope of the claims to be described later.

How to activate a lithium metal secondary battery

In one embodiment of the present invention,

1) At the discharge voltage of the battery formation process, select a positive electrode additive that can accommodate lithium ions with priority over the positive electrode active material,

2) Unlike the general formation process of a battery that begins with charging, the formation process of a battery using the positive electrode additive begins with discharging, providing a method of activating a lithium metal secondary battery.

Specifically, the activation method of the embodiment is,

A positive electrode additive containing lithium metal oxide; and a positive electrode active material; manufacturing a lithium metal secondary battery comprising a positive electrode, a lithium metal negative electrode, and an electrolyte;

Discharging the lithium metal secondary battery until it reaches a range of 1.8 V or more to 3.0 V or less;

Charging the discharged lithium metal secondary battery until it reaches a range of 4.2V to 4.6V; and

Aging the charged lithium metal secondary battery;

It includes,

1) the selection of the positive electrode additive and 2) the synergistic effect of the activation process starting from the discharge, making the cathode surface uniform immediately after the activation process; During the battery cycle after the activation process, lithium ion desorption/deposition on the cathode surface occurs smoothly; Ultimately, battery life (capacity maintenance rate) can be improved.

Hereinafter, 1) the positive electrode additive, 2) the activation process starting from the discharge will be described in detail, and the configuration of the lithium metal secondary battery will be explained.

anode additive

As mentioned above, due to the high reactivity of lithium metal (Li-metal), as soon as the lithium metal negative electrode and the electrolyte solution come into contact in the process of manufacturing a lithium metal secondary battery, a non-uniform passivation film is formed on the surface of the lithium metal negative electrode. there is a problem.

In this way, with the passivation film formed unevenly on the surface of the lithium metal anode, if charging and discharging are performed according to an activation method generally known in the art, lithium metal is not uniformly plated on the surface of the lithium metal anode during charging, causing localized damage. There is a problem in that lithium dendrite is formed and not only the plated lithium metal but also the lithium metal under the plating layer (which was already included in the lithium metal cathode before activation) is detached during discharge.

To solve this problem, by first removing lithium ions from the lithium metal in the activation process after battery assembly, the passivation film formed on the surface of the lithium metal is also peeled off to make the surface composition and shape uniform, and at the same time, expand the surface area of the lithium metal, thereby increasing the surface area of the lithium metal. Methods to increase activity have been proposed. However, when using the above method, lithium ions removed from lithium metal are inserted into the positive electrode material, causing problems such as structural variation and reduced reversibility of the positive electrode active material, which still leads to a decrease in battery performance.

The positive electrode additive of the above embodiment was developed to fundamentally improve the performance of lithium metal secondary batteries, and includes one or more compounds capable of inserting lithium.

Specifically, the lithium secondary battery in which the positive electrode additive of the above embodiment is applied to the positive electrode may begin discharging after wetting of the electrolyte solution, unlike activation methods generally known in the art.

More specifically, when the lithium metal anode is sufficiently impregnated with the electrolyte solution, a passivation film may be formed on the surface as mentioned above. At this time, the passivation film formed through electrolyte impregnation has uneven characteristics due to the non-uniformity of impregnation within the battery, and if charging is performed first in this state, lithium metal is plated unevenly to form lithium dendrites. On the other hand, when discharge is started in this state, lithium ions are detached from the surface of the lithium metal negative electrode and stably inserted into the positive electrode additive of the embodiment, and at the same time, the non-uniform passivation film covering the lithium metal is peeled off, thereby changing the surface composition of the lithium metal. and shape can be made uniform.

In this way, when activation of a lithium metal secondary battery begins with discharge, unlike the case where lithium is unevenly plated on the surface of the lithium metal negative electrode by starting with charging while the passivation film is formed, the lithium metal under the passivation film is discharged in the form of lithium ions. It moves to the positive electrode additive, and the non-uniform passivation film formed before discharge is detached, so that the surface composition and shape of the lithium metal negative electrode can become uniform.

The positive electrode additive of the embodiment includes one or more compounds capable of inserting lithium, and can accommodate lithium ions released by discharge before the positive electrode active material. Here, lithium ions released by discharge mean that the lithium metal under the passivating film, as mentioned above, is discharged in the form of lithium ions.

In this regard, generally known positive electrode active materials such as LCO, LMO, NMO, NCM, LNO, and LFP allow lithium ions to be inserted at a potential of 1.6V (vs Li metal), while the positive electrode additive of the embodiment has a potential of 1.8V. Insertion of lithium ions may be possible at a level of V or more and 3.0 V or less, for example, 2.0 V or more and 2.5 V or less (vs Li metal).

Therefore, when the positive electrode additive of the above embodiment is applied to the positive electrode along with a typical positive electrode active material, and the resulting lithium metal secondary battery is discharged until it reaches the range of 2.0V to 2.5V, the positive electrode additive of the above embodiment is more effective than the typical positive electrode active material. Lithium ions may first be inserted into the positive electrode additive in the example.

The positive electrode additive of the embodiment may be lithium vanadium oxide or lithium titanium oxide, and may be, for example, represented by the following Chemical Formula 1:

[Formula 1] Li _x M _y A _z

In Formula 1, M is Ti or V, A is O, 0.8≤x≤3.2, 0.8≤y≤3.2, 2.8≤z≤8.2, and y and z are the oxidation number of M and the oxidation number of A. It is decided depending on

As described above, the compound represented by Formula 1 may have a crystal structure suitable for inserting lithium ions before generally known positive electrode active materials.

More specifically, the positive electrode additive of one embodiment may be a compound represented by the following formula 1-1 or 1-2.

[Formula 1-1] Li _x1 M _y1 O _z1

In Formula 1-1, M is Ti or V, and 0.8≤x1≤1.2, 2.8≤y1≤3.2, 7.8≤z1≤8.2.

[Formula 1-2] Li _x2 M _y2 O _z2

In Formula 1-2, M is Ti or V, and 0.8≤x2≤1.2, 0.8≤y2≤1.2, 2.8≤z2≤3.2.

For example, as the positive electrode additive of one embodiment, LiV ₃ O ₈ and LiVO ₃ may be used individually, or a mixture or composite thereof may be used. Here, the composite may be in the form of secondary particles in which individual primary particles are aggregated, or a core-shell in which the surface of one compound primary particle or secondary particle is coated with another compound primary particle or secondary particle. It can also have a structure. However, the present invention is not limited to these examples.

Meanwhile, the positive electrode additive of the embodiment may be converted to a compound represented by the following formula (2) after lithium is inserted during the activation process starting from discharge.

[Formula 2] Li _x+a M _y A _z

In Formula 2, 0.8≤a≤1.2, and M, A, x, y, and z are each the same as Formula 1.

For example, in the case of a compound represented by Formula 1-1 or 1-2, it can be converted to Formula 2-1 or 2-2, respectively.

[Formula 2-2] Li _x1+a1 M _y1 O _z1

In Formula 1-1, 0.8≤a1≤1.2, and M, A, x, y, and z are each the same as Formula 1-1.

[Formula 2-2]Li _x2+a2 M _y2 O _z2

In Formula 2-2, 0.8≤a2≤1.2, and M, A, x, y, and z are each the same as Formula 1-2.

Specifically, the compound represented by Formula 1-1 or 1-2 is higher than 1.6V (vs Li metal), which is the structural transition voltage of common positive electrode active materials, and is 3.0V to 4.3V (vs Li), which is the operating voltage of a typical secondary battery. Insertion of lithium ions is possible in a range lower than that of metal).

Accordingly, when a lithium metal secondary battery to which the compound represented by Formula 1-1 or 1-2 is applied to the positive electrode is discharged until it reaches the range of 2.0V to 2.5V, in the activation process, lithium ions are generated before the positive electrode active material. Insertion may be possible.

However, in the case of the compound represented by Formula 1-1 or 1-2, reversible insertion and desorption of lithium ions may not be possible at the operating voltage of 3.0V to 4.3V (vs Li metal) of a typical secondary battery.

activation process

When the activation process (i.e., a series of steps of discharging, charging, and aging) of a lithium metal battery to which the positive electrode additive of the embodiment is applied is performed at least once, due to the effect of the positive electrode additive of the above-described embodiment, the lithium metal negative electrode The surface can be made even. Accordingly, the charge/discharge cycle can proceed stably without additional processes after activation, and long-term operation can be possible.

The above series of steps must be performed at least once, and may be performed twice or more. When performed two or more times, the above-described effects may be increased, but the present invention is not limited thereby.

In the case of a general activation process, once the electrolyte impregnation of the manufactured secondary battery is completed, it is performed through a charging/discharging process and an aging process. At this time, since positive ions usually contain Li, the charging process in which Li ions move from the anode to the cathode precedes the discharging process.

On the other hand, as described above, according to the activation method of the embodiment, the passivation film is removed unevenly immediately upon injection of the electrolyte, and in order to control the composition and shape of the surface of the lithium metal anode, a discharge process is performed rather than a rechargeable battery after electrolyte impregnation is completed. Perform from Accordingly, the surface of the lithium metal cathode is evened and its surface area is expanded. Activity can be increased.

Specifically, the discharging step may be performed at 3.0V (vs Li metal) or less, which is the potential at which lithium can be inserted into the additive of the above-described embodiment.

More specifically, the discharging step may be performed under conditions generally known in the art, using a constant current of 1/50C or more and 1C or less, such as 1/20C or more and 1C or less, for 3 minutes or more to 5 hours. Hereinafter, the discharge may be performed for, for example, 30 minutes to 2 hours, and the discharge end voltage may be set to 1.8 V or more and 3.0 V or less, for example, 2.0 V or more and 2.5 V or less.

The charging step after the discharging step can also be performed under conditions generally known in the art, and can be carried out at a constant current and constant voltage of 1/10 C or more to 1/3 C or more for 30 minutes to 15 hours, for example, 30 minutes to 15 hours. It may be charged for 10 hours, and the charging end voltage may be 4.2V or more to 4.6V, for example, 4.3 V or more and 4.4V or less.

Additionally, the aging step after the charging step may be a process of sufficiently impregnating each electrode with the electrolyte solution again and leaving the battery cells at a certain temperature and humidity to stabilize the cells activated in the previous step. According to this aging step, the electrolyte is evenly spread inside the battery, and the spread electrolyte can be uniformly impregnated into each electrode. The aging step may also be performed under conditions generally known in the art, and may be performed at 20 to 30° C., for example, at room temperature, for about 7 to 30 days, and may be repeated two or more times before, after, or in the middle of charging and discharging for the activation. It can be.

anode

In another embodiment of the present invention, a positive electrode current collector; and a positive electrode mixture layer located on one or both sides of the positive electrode current collector and containing the positive electrode additive and the positive electrode active material of the above-described embodiment.

This is because the positive electrode additive of the above-described embodiment is applied, and thus can contribute to the activation of the lithium metal negative electrode by implementing the above-described mechanism.

Since the positive electrode additive of the above-described embodiment has been described in detail previously, only descriptions that do not overlap with the above-described content will be described below.

In the positive electrode of one embodiment, the positive electrode additive of the above-described embodiment may be included in an amount of 0.1 to 25% by weight based on the total weight (100% by weight) of the positive electrode mixture layer. Within this range, the cathode is activated by the cathode additive of the above-described embodiment, and capacity can be developed by an appropriate amount of the cathode active material included therewith.

Specifically, among the positive electrode additives of the above-described embodiment, when the lithium metal oxide represented by Chemical Formula 1-1 or 1-2 is included, the positive electrode additive is 0.1% of the total weight (100% by weight) of the positive electrode mixture layer. It may be included in 5 to 5% by weight.

This is taken into consideration that, if contained in a large amount exceeding the upper limit of the above range, capacity may not be developed at the operating voltage of the battery after activation and the energy density of the secondary battery may be reduced, as described above. Additionally, the lower limit of the above range takes into account the minimum amount that can accommodate the passivation film component (i.e., lithium ions) removed from the cathode surface during the activation process. However, the above range is only an example, and the present invention is not limited thereto.

The lower limit of the range is, similar to the lithium metal oxide represented by Formula 1-1 or 1-2, considering the minimum amount that can accommodate the passivation film component (i.e., lithium ion) removed from the cathode surface during the activation process. will be.

Meanwhile, in the positive electrode of the above embodiment, components other than the positive electrode additive may be those generally known in the art.

For example, the positive electrode of the embodiment may be manufactured by applying a mixture containing a positive electrode active material and the positive electrode additive to one or both sides of a positive electrode current collector and drying it to form a positive electrode mixture, and, if necessary, conductive Additional ash, binders, and fillers may be added.

The positive electrode current collector is generally made to have a thickness of 3 to 500 micrometers. These positive electrode current collectors and extension current collectors are not particularly limited as long as they have high conductivity without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum. Surface treatment of stainless steel with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector and extended current collector can increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and can be in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals; Lithium manganese oxide with the formula Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , etc.; lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); _{Chemical formula} LiMn _{2 - x M} Lithium manganese complex oxide expressed as Ni, Cu or Zn); LiMn ₂ O ₄ in which part of Li in the chemical formula is replaced with an alkaline earth metal ion; disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , lithium metal phosphate compounds expressed by the chemical formula LiFe _x Mn _y Co _z PO ₄ (where x, y, z≥0, x+y+z=1), etc. It is not limited to these alone.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive electrode active material. These conductive materials are not particularly limited as long as they have conductivity without causing chemical changes in the battery, and examples include graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The binder is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, and polyethylene. , polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butyrene rubber, fluorine rubber, and various copolymers.

The filler is selectively used as a component to suppress expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery. For example, olipine polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber are used.

However, the above contents merely exemplify components and methods generally known in the art, and may be modified according to the technical common sense of those skilled in the art.

Lithium metal secondary battery

For reference, when applying the positive electrode additive of one embodiment to an existing lithium ion secondary battery using a negative electrode coated with a carbon-based material, the potential of the negative electrode during overdischarge of the battery is lower than the ionization potential of copper metal (3.56V vs. Li). /Li ⁺ ), it can prevent the copper foil, which is the negative electrode current collector, from corroding.

On the other hand, in the lithium metal secondary battery of one embodiment, the lithium metal negative electrode includes: a negative electrode current collector; and a thin film located on one or both sides of the negative electrode current collector and containing lithium metal (Li-metal) or lithium alloy (Li-alloy).

In other words, in the lithium metal secondary battery of the above embodiment, lithium metal is attached to the copper foil, which is the negative electrode current collector, and a sufficient amount of lithium can be supplied from the negative electrode. Accordingly, even if overdischarge occurs, the potential of the negative electrode does not exceed the ionization potential of copper metal and is maintained at 0V (vs. Li/Li ⁺ ), causing corrosion of the copper foil negative electrode current collector that occurs in existing lithium-ion secondary batteries. Therefore, there is no reason to apply the above material for the purpose of a positive electrode additive used in existing lithium-ion secondary batteries.

Rather, applying the positive electrode additive of the above-described embodiment to the lithium metal secondary battery of the embodiment requires a discharge process that can control the composition and shape of the lithium metal surface in the activation process, and the additive as described above is required. This is to achieve the effect of preventing structural variation of the positive electrode active material by accepting lithium ions.

Since the positive electrode additive of the above-described embodiment has been described in detail previously, only descriptions that do not overlap with the above-described content will be described below.

The lithium metal secondary battery may further include a separator positioned between the positive electrode and the lithium metal negative electrode of the embodiment, and the electrolyte may be impregnated into the separator.

This structure follows a method generally known in the art, using the positive electrode and the lithium metal negative electrode of one embodiment, placing a separator between them to manufacture an electrode assembly, and then embedding the electrode assembly in a battery case. It can be formed by injecting an electrolyte solution into the separator.

With the electrolyte solution injected into the separator, the lithium metal anode can be activated by charging after discharging as described above while the lithium metal anode is sufficiently wet.

Meanwhile, in the lithium metal secondary battery of the above embodiment, components other than the positive electrode additive and the positive electrode containing the same may be those generally known in the art.

The lithium metal negative electrode can be manufactured by depositing lithium metal on one or both sides of a flat negative electrode current collector or rolling lithium foil. At this time, the negative electrode current collector may be specifically a copper foil.

The copper foil can generally be made to have a thickness of 3 to 100 micrometers, and the metal lithium formed in this copper foil can be formed to have a thickness of, for example, 1 to 300 micrometers. Alternatively, a negative electrode made only of lithium metal may be used.

The separator is sandwiched between the anode and the cathode, and a thin insulating film with high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 micrometers, and the thickness is typically 5 to 300 micrometers. Such separators include, for example, olefin-based polymers such as chemical-resistant and hydrophobic polypropylene; Sheets or non-woven fabrics made of glass fiber or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The electrode assembly is not limited in structure, and may include a stacked electrode assembly in which the anode, separator, and cathode are punched and stacked as unit electrodes, a jelly-roll type electrode assembly in which the anode sheet, separator, and cathode sheet are laminated and wound, or It may be a stack-and-fold type electrode assembly in which unit electrodes are arranged and wound on a sheet-like separation film.

The battery case may be a pouch-shaped battery case made of aluminum laminated sheet, or a square or cylindrical battery case made of a metal can.

The electrolyte solution may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used when manufacturing a lithium secondary battery.

Specifically, the organic liquid electrolyte, that is, the electrolyte solution, 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 solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; Ether-based solvents such as dibutyl ether or tetrahydrofuran; Ketone-based 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-based solvents such as PC); Ether-based solvents such as dimethoxyethane (DME), diethyl ether, ethylene glycol dimethyl ether (EGDME), and tetraethylene glycol dimethyl ether (TEGDME); Dioxolanes such as 1,3-dioxolane (DOL); Furans such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2MeTHF); Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 straight-chain, branched or ring-structured hydrocarbon group and may include a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Alternatively, sulfolane, etc. may be used. Among these, carbonate-based solvents or ether-based solvents are preferable, and cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) with high ionic conductivity and high dielectric constant that can improve the charging and discharging performance of the battery, and low-viscosity linear carbonates. A mixture of carbonate-based compounds (e.g., ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable. In this case, the performance of the electrolyte can be excellent when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

A mixture of linear ether (e.g., dimethoxy ether, ethylene glycol dimethyl ether, etc.) and cyclic dioxolane with excellent reduction stability that can increase the reversible charge/discharge performance of lithium metal can also be used.

The lithium salt can be used without particular restrictions as long as it is a compound that can provide lithium ions used in lithium secondary batteries. 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 may be used. The concentration of the lithium salt can be used within the range of 0.1M to 2.0M or within the range of 2.0M to 6.0M. When the concentration of lithium salt is in the range of 0.1M to 2.0M, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be achieved and lithium ions can move effectively. When the concentration of lithium salt is in the range of 2.0M to 6.0M, the transference number of lithium increases, allowing lithium ions to move effectively, and the electrolyte solvent is all coordinated to the lithium salt, improving the oxidation and reduction stability of the electrolyte solvent, and lithium metal And corrosion of the current collector can be suppressed.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and trifluoroethylene for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexanoic acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida. One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride may be further included. At this time, the additive may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte.

However, the above contents merely exemplify components and methods generally known in the art, and may be modified according to the technical common sense of those skilled in the art.

The lithium metal secondary battery of the above embodiment may also be provided as a battery module including the same as a unit cell and a battery pack including the same.

The battery module or battery pack is a power tool; Electric vehicles, including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); Alternatively, it can be used as a power source for any one or more mid- to large-sized devices among power storage systems.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement it. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein.

<Manufacture Example 1: LiV ₃ O ₈ Manufacturing>

LiOH, V ₂ O ₅ and aqueous ammonia (1 mol/l) were used as precursors to synthesize LiV ₃ O ₈ . LiOH and V ₂ O ₅ were added to distilled water so that the Li:V ratio was 1:3, and then ammonia water was added to dissolve the precursor. When all the precursors were melted, they were stirred at 70 ^o C until the water evaporated, and then completely dried in a vacuum oven at 80 ^o C. The dried precursor was pulverized in a mortar, compressed, and made into pellets, placed in an alumina crucible, and heat-treated at 800 ^o C for 12 hours to obtain LiV ₃ O ₈ .

<Preparation Example 2: LiVO ₃ Manufacturing>

Li ₂ CO ₃ and NH ₄ VO ₃ were used as precursors to synthesize LiVO ₃ . Li ₂ CO ₃ and NH ₄ VO ₃ were mixed at a molar ratio of 1:2, compressed to make pellets, placed in a platinum crucible, raised to 650 ^o C at 5 ^o C per minute in an argon gas atmosphere, and heat treated for 10 hours. LiVO ₃ was synthesized.

<Example 1: LiV ₃ O ₈ , included at 2% by weight in the anode mixture layer>

The positive electrode active material Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ , the conductive material Denka black, the binder polyvinylidene fluoride (PVDF), and the positive electrode additive LiV prepared in Preparation Example 1. A slurry was prepared in which ₃ O ₈ was mixed with NMP (Nmethyl pyrrolidone) at a weight ratio of 94:2:2:2. The slurry was coated on Al foil with a thickness of 20 μm to a thickness of 70 μm, dried at 120 degrees Celsius for 5 minutes, and compressed to prepare a positive electrode.

As a negative electrode, metal lithium was deposited (thickness: 100 μm) on a current collector made of copper (thickness: 20 μm) to prepare a lithium metal negative electrode sheet, and the lithium metal negative electrode sheet was punched to form a negative electrode.

The anode, the cathode, a polyethylene membrane (Celgard, thickness: 20 ㎛) as a separator, and an electrolyte solution containing 1M LiPF ₆ dissolved in a solvent containing ethylene carbonate, dimethylene carbonate, and diethyl carbonate mixed at a ratio of 1:2:1. It was used and built into a pouch-type case to manufacture a secondary battery.

<Example 2: LiVO ₃ , included at 2% by weight in the anode mixture layer>

A secondary battery was manufactured in the same manner as in Example 1, except that LiVO ₃ prepared in Preparation Example 2 was used as a positive electrode additive.

<Example 3: LiV ₃ O ₈ , included at 5% by weight in the anode mixture layer>

The positive electrode active material Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ , the conductive material Denka black, the binder polyvinylidene fluoride (PVDF), and the positive electrode additive LiV prepared in Preparation Example 1. A secondary battery was manufactured in the same manner as in Example 1, except that the ₃ O ₈ weight ratio of 91:2:2:5 was used.

<Example 4: LiVO ₃ , included at 5% by weight in the anode mixture layer>

Cathode active material Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ , conductive material Denka black, binder polyvinylidene fluoride (PVDF), and LiVO ₃ prepared in Preparation Example 2 above. A secondary battery was manufactured in the same manner as Example 1, except that the weight ratio of 91:2:2:5 was used.

<Example 5: LiV ₃ O ₈ , included at 10% by weight in the anode mixture layer>

The positive electrode active material Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ , the conductive material Denka black, the binder polyvinylidene fluoride (PVDF), and the positive electrode additive LiV prepared in Preparation Example 1. A secondary battery was manufactured in the same manner as in Example 1, except that the ₃ O ₈ weight ratio of 86:2:2:10 was used.

<Examples 6 to 10: Applying an activation process starting from discharge to each secondary battery in Examples 1 to 5>

Each secondary battery manufactured according to Examples 1 to 5 was left at room temperature for 3 days to sufficiently impregnate the electrolyte, then discharged at 0.05C for 1 hour until it reached 2.0V, and then discharged at 0.1C until it reached 4.35V. After charging with C for 10 hours, it was left at room temperature for 2 days to age.

<Comparative Example 1: No anode additive>

Except that the positive electrode active material Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ , the conductive material Denka black, and the binder polyvinylidene fluoride (PVDF) were used at a weight ratio of 96:2:2. Then, a secondary battery was manufactured in the same manner as in Example 1.

<Comparative Example 2: TiO _2, Included at 2% by weight in the anode mixture layer>

The positive electrode active material Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ , the conductive material Denka black, the binder polyvinylidene fluoride (PVDF), and the positive electrode additive TiO ₂ have a weight ratio of 94:2:2. A secondary battery was manufactured in the same manner as in Example 1, except that :2 was used.

<Comparative Example 3: V ₂ O _5, Included at 2% by weight in the anode mixture layer>

The positive electrode active material Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ , the conductive material Denka black, the binder polyvinylidene fluoride (PVDF), and the positive electrode additive V ₂ O ₅ have a weight ratio of 94:2. A secondary battery was manufactured in the same manner as in Example 1, except that :2:2 was used.

<Comparative Examples 4 to 6: Applying the activation process starting from discharge to each secondary battery of Comparative Examples 1 to 3>

Each secondary battery manufactured according to Comparative Examples 1 to 3 was left at room temperature for 3 days to sufficiently impregnate the electrolyte, then charged for 10 hours at 0.1C until it reached 4.35 V, and then left at room temperature for 2 days to age. .

<Comparative Example 7: Applying the activation process starting from charging to the secondary battery of Example 1>

The secondary battery manufactured according to Example 1 was left at room temperature for 3 days to sufficiently impregnate the electrolyte, then charged for 10 hours at 0.1C until it reached 4.35 V, and then left at room temperature for 2 days to age.

<Comparative Example 8: Applying the activation process starting from charging to the secondary battery of Comparative Example 1>

The secondary battery manufactured according to Comparative Example 1 was left at room temperature for 3 days to sufficiently impregnate the electrolyte, then charged for 10 hours at 0.1C until it reached 4.35 V, and then left at room temperature for 2 days to age.

<Experimental Example 1>

In order to compare the effects of applying the positive electrode additive of the above-described embodiment, the characteristics of Examples 6 to 10 and Comparative Examples 4 to 6, which applied an activation process starting from discharge, were compared.

Specifically, for each battery of Examples 6 to 10 and Comparative Examples 4 to 6, charging and discharging was performed at 0.1 C in the range of 3 V to 4.35 V, the initial discharge capacity was measured, and the results are shown in Table 1 below. It was. Afterwards, after performing 0.3C charging and 0.5C discharging 100 times, the discharge capacity maintenance ratio for 100 times compared to 1 time discharge capacity was calculated, and the results are shown in Table 1 below.

anode additive Lithium metal secondary battery evaluation type Content in anode mixture layer
(weight%) One-time discharge capacity Capacity maintenance rate after charging and discharging 100 times Example 6 LiV ₃ O ₈ 2 52.3mAh 66.0% Example 7 LiVO ₃ 2 52.2mAh 67.2% Example 8 LiV ₃ O ₈ 5 51.1mAh 65.1% Example 9 LiVO ₃ 5 52.4mAh 69.1% Example 10 LiV ₃ O ₈ 10 47.3mAh 61.8% Comparative Example 4 - - 53.4mAh 54.1% Comparative Example 5 TiO ₂ 2 51.8mAh 53.7% Comparative Example 6 V ₂ O ₅ 2 52.2mAh 51.2%

The positive electrode additive of the above-described embodiment is capable of accepting lithium ions preferentially over the positive electrode active material at the discharge voltage of the battery activation (formation) process.

Accordingly, when the activation process of the lithium metal battery using the positive electrode additive of the embodiment begins with discharge, the lithium metal located at the bottom of the passivation film of the lithium metal negative electrode is discharged in the form of lithium ions and moves to the positive electrode additive of the embodiment. , even the passivation film of the lithium metal anode may be detached.

As a result, the uniformity of the surface of the lithium metal anode is ensured, smooth lithium ion desorption/deposition on the surface of the lithium metal anode even during the charge and discharge process after the activation process, and battery life (capacity maintenance rate) can be improved. .

Table 1 above demonstrates that when activation of a lithium metal battery to which the positive electrode additive of the above-described embodiment is applied starts from discharge, the results are advantageous for increasing the initial (one time) discharge capacity and lifespan characteristics after the activation process.

Furthermore, in the case of Examples 6 to 9 using a specific amount of the positive electrode additive of the embodiment, it can be confirmed that the decrease in discharge capacity is not significant compared to Example 10 to the level without using the positive electrode additive of the embodiment. there is. Considering this, the positive electrode additive content of the embodiment can be determined.

On the other hand, in Comparative Example 4 in which the additive of the above embodiment was not used, it was confirmed that loss of lithium (under the passivation film) occurred in the lithium metal negative electrode and the lifespan characteristics were significantly reduced due to dendrite formation on the surface of the lithium metal. It can be seen that Comparative Examples 5 to 6 using a metal oxide as a positive electrode additive also did not perform the role of insertion/desorption of lithium ions, and thus the lifespan characteristics were not improved.

<Experimental Example 2>

Example 6 and Comparative Example 4, which applied an activation process starting from discharge, and Comparative Examples 7 and 8, which applied an activation process starting from charging, were compared.

For the batteries activated in each method, one-time discharge capacity and capacity maintenance rate after 100 charge and discharge were evaluated in the same manner as in Experimental Example 1, and the evaluation results are shown in Table 2 below.

anode additive activation process Lithium metal secondary battery evaluation type Content in anode mixture layer
(weight%) One-time discharge capacity Capacity maintenance rate after charging and discharging 100 times Example 6 LiV ₃ O ₈ 2 Start with discharge 52.3mAh 66.0% Comparative Example 7 LiV ₃ O ₈ 2 Start with charging 52.0mAh 55.0% Comparative Example 4 - - Start with discharge 53.4mAh 54.1% Comparative Example 8 - - Start with charging 55.1mAh 56.9%

Even if a lithium metal battery is manufactured using the positive electrode additive of the above-described embodiment, when the activation process of the manufactured lithium metal battery begins with charging, the lithium metal located at the bottom of the passivation film of the lithium metal negative electrode cannot be discharged into lithium ions, The passivation film may not be detached from the lithium metal anode.

Table 2 above shows that, even if the positive electrode additive of the embodiment is used, the positive electrode additive in case of applying the activation process starting from discharge (Example 6) and when applying the activation process starting from charging (Comparative Example 7) It is proven that the use is not effective.

On the other hand, for the lithium metal battery without using the positive electrode additive of the above embodiment, in contrast to the case where the activation process starting from charging was applied (Comparative Example 8) and the activation process starting from discharging (Comparative Example 4), , Rather, it can be seen that the initial (one-time) discharge capacity increases after the activation process, and the lifespan characteristics also increase. However, compared to the case where the activation process starting from discharge is applied using the positive electrode additive of the above embodiment (Example 6), the initial (one time) discharge capacity after the activation process is low and the lifespan characteristics are also inferior.

From these results, when a lithium metal battery is manufactured using the positive electrode additive of the above embodiment and an activation process starting from discharge is applied, the initial (one-time) discharge capacity and life characteristics after the activation process are significantly increased. It can be seen that there is a synergistic effect.

Here, for convenience, only the case where LiV ₃ O ₈ (Preparation Example 1) was used as the positive electrode additive in the above embodiment was tested. However, even when other positive electrode additives such as LiVO ₃ (Preparation Example 2) were used, the activation process starting from discharge can be applied. In this case, it is inferred that there will be a synergistic effect that significantly increases the initial (one time) discharge capacity and life characteristics after the activation process.

<Experimental Example 3>

For each battery of Example 6 and Comparative Example 4, the AC resistance at SOC 100% was measured, and the AC resistance was measured after 0.3 C charging and 0.5 C discharging 100 times, and the results are shown in Table 3 below. It was.

At this time, AC resistance is the value measured by measuring the resistance of each battery at 1 KHz using a Hioki resistance measurement device.

anode additive Resistance of lithium metal secondary battery type Content in anode mixture layer
(weight%) Resistance immediately after activation process
(Ohm) Resistance after charging and discharging 100 times
(Ohm) Resistance increase rate after charging and discharging 100 times compared to immediately after the activation process (%) Example 6 LiV ₃ O ₈ 2 0.514 0.755 46.9 Comparative Example 4 - - 0.651 1.278 96.3

Meanwhile, when the AC resistance was measured immediately after applying the activation process starting from discharge (Example 6) to the lithium metal battery manufactured using the positive electrode additive of the above embodiment, uniformity of the lithium metal negative electrode surface was secured. Due to this, a low resistance value can be confirmed. Even after charging and discharging 100 times, lithium ion desorption/deposition on the surface of the lithium metal cathode with guaranteed uniformity occurs smoothly in each cycle, and even if the resistance is measured after charging and discharging 100 times, the resistance is in a relatively low range. You can confirm that it is maintained.

On the other hand, even if an activation process starting from discharge is applied to the lithium metal battery manufactured without using the positive electrode additive of the above embodiment (Comparative Example 4), the uniformity of the lithium metal negative electrode surface is poor due to the absence of the positive electrode additive. As a result of this failure, the resistance value immediately after the activation process increases. In this state, the uniformity of the surface of the lithium metal cathode is not secured, the desorption/electrodeposition of lithium ions occurs unevenly, and side reactions with the electrolyte solution on the surface of the lithium metal cathode gradually increase, and as these side reactions accumulate with each cycle, After charging and discharging 100 times, the resistance value of a lithium metal battery may increase further.

Table 3 above demonstrates that even if the activation process starts from discharge, the initial resistance value, resistance value after long-term operation, and resistance increase rate of the lithium metal battery vary depending on whether or not the positive electrode additive of the embodiment is used.

Claims (13)

A positive electrode additive containing lithium metal oxide; and a positive electrode active material; manufacturing a lithium metal secondary battery comprising a positive electrode, a lithium metal negative electrode, and an electrolyte;
Discharging the lithium metal secondary battery until it reaches a range of 1.8 V or more to 3.0 V or less;
Charging the discharged lithium metal secondary battery until it reaches a range of 4.2V to 4.6V; and
Aging the charged lithium metal secondary battery; Including,
The positive electrode additive is,
Represented by the formula 1 below,
How to activate a lithium metal secondary battery:
[Formula 1]
Li _x M _y A _z
In Formula 1,
M is Ti or V,
A is O,
0.8 ≤x≤3.2, 0.8≤y≤3.2, 2.8≤z≤8.2,
The y and z are determined according to the oxidation number of M and the oxidation number of A.
According to paragraph 1,
In the discharging step, the positive electrode additive is,
Inserting lithium ions preferentially over the positive electrode active material,
Activation method of lithium metal secondary battery.
delete According to paragraph 1,
The positive electrode additive is,
Represented by the following formula 1-1 or 1-2,
How to activate a lithium metal secondary battery:
[Formula 1-1]
Li _x1 M _y1 O _z1
In Formula 1-1,
M is Ti or V,
0.8 ≤x1≤1.2, 2.8≤y1≤3.2, 7.8≤z1≤8.2,
[Formula 1-2] Li _x2 M _y2 O _z2
In Formula 1-2, M is Ti or V, and 0.8≤x2≤1.2, 0.8≤y2≤1.2, 2.8≤z2≤3.2.
According to paragraph 1,
The positive electrode additive is,
Containing at least one compound selected from the group consisting of LiV ₃ O ₈ and LiVO ₃ ,
Activation method of lithium metal secondary battery.
According to paragraph 1,
The discharge step is,
It is performed using a constant current of 1/50C or more and 1C or less,
Activation method of lithium metal secondary battery.
According to paragraph 1,
The discharge step is,
performed for at least 3 minutes and up to 5 hours,
Activation method of lithium metal secondary battery.
According to paragraph 1,
The end voltage of the discharge step is,
2.0V to 2.5V,
Activation method of lithium metal secondary battery.
According to paragraph 1,
The charging step is,
which is performed using a constant current of 1/10 C or more and 1/3 C or less,
Activation method of lithium metal secondary battery.
According to paragraph 1,
The charging step is,
performed for at least 30 minutes and up to 15 hours,
Activation method of lithium metal secondary battery.
According to paragraph 1,
The end voltage of the charging step is,
4.2V or more to 4.6V,
Activation method of lithium metal secondary battery.
According to paragraph 1,
The anode is,
positive electrode current collector; and
A positive electrode mixture layer located on one or both sides of the positive electrode current collector and containing the positive electrode additive and the positive electrode active material,
Activation method of lithium metal secondary battery.
According to clause 12,
The positive electrode additive is,
It is contained in 0.1 to 25% by weight of the total weight (100% by weight) of the positive electrode mixture layer,
Activation method of lithium metal secondary battery.