KR20140007128A - Positive electrode for lithium-sulfur battery and lithium-sulfur battery comprising the same - Google Patents

Abstract

TECHNICAL FIELD The present invention relates to a positive electrode for a lithium sulfur battery and a lithium sulfur battery including the same. And a cathode active material layer formed on the current collector, wherein the cathode active material layer comprises: a sulfur-based cathode active material; bookbinder; Conductive agent; And a metal nitride. The anode for a lithium-sulfur battery can be provided.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode for a lithium sulfur battery and a lithium sulfur battery including the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

A lithium sulfur battery positive electrode and a lithium sulfur battery including the same.

With the rapid development of portable electronic devices, the demand for secondary batteries is increasing. In particular, there is a continuous demand for the emergence of high energy density batteries that can meet the trend toward smaller, lighter, thinner and smaller portable electronic devices, and batteries that must satisfy inexpensive, safe and environmentally friendly aspects. It is required.

Lithium-sulfur batteries are inexpensive and environmentally friendly materials, and the energy density of lithium is 3830 mAh / g in terms of energy density, and the energy density of sulfur is expected to be high at 1675 mAh / g. It is emerging as the most promising battery which satisfies the above conditions.

The lithium-sulfur battery uses a sulfur-based compound having a sulfur-sulfur combination as a positive electrode active material, and an alkali metal such as lithium or a carbon-based material in which insertion and deintercalation of metal ions such as lithium ions occur. As a negative electrode active material, wherein the oxidation number of S decreases as the SS bond is broken during the reduction reaction (discharge), and the oxidation of the SS bond is formed again when the oxidation number of S increases during the oxidation reaction (charge). Reduction reactions are used to store and generate electrical energy.

The lithium-sulfur battery has an energy density of 3830 mAh / g when lithium metal is used as a negative electrode active material, and an energy density of 1675 mAh / g when elemental sulfur (S8) is used as a positive electrode active material. Is the most promising battery in the world. In addition, the sulfur-based material used as the positive electrode active material has the advantage that it is cheap and environmentally friendly material.

However, there are no examples of successful commercialization with lithium-sulfur battery systems. The reason why the lithium-sulfur battery is not commercialized is that when the sulfur is used as the active material, the utilization rate indicating the amount of sulfur participating in the electrochemical oxidation-reduction reaction in the battery with respect to the amount of sulfur introduced is low, .

Therefore, studies are ongoing to increase the capacity by increasing the electrochemical redox reaction, but the satisfactory effect has not yet been obtained.

One embodiment of the present invention is to solve the above-mentioned problems, and it is an object of the present invention to provide a positive electrode for a lithium-sulfur battery which can improve sulfur availability and improve battery performance.

Another embodiment of the present invention can provide a lithium-sulfur battery including the positive electrode.

In one embodiment of the present invention, the current collector; And a cathode active material layer formed on the current collector, wherein the cathode active material layer comprises: a sulfur-based cathode active material; bookbinder; Conductive agent; And a metal nitride. The positive electrode for a lithium-sulfur battery includes:

The metal nitride may be titanium nitride (TiN).

The particle size of the metal nitride may be 1 to 5 탆.

The content of the metal nitride in the cathode active material layer may be 3 to 15% by weight.

The cathode active material may be selected from the group consisting of: an organic sulfur compound and a carbon-sulfur polymer [(C ₂ Sx)] in which elemental sulfur (S 8), solid Li ₂ Sn (n ≥ 1), Li ₂ Sn n, x = 2.5 to 50, and n > = 2).

The anode may further include a coating layer selected from the group consisting of a polymer coating layer, an inorganic coating layer, and an organic coating layer.

The polymer may be selected from the group consisting of polyvinylidene fluoride, copolymers of polyvinylidene fluoride and hexafluoropropylene, poly (vinyl acetate), poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate) Vinyl acetate, polyvinyl pyrrolidone-co-vinyl acetate), cellulose acetate, polyvinyl pyrrolidone, polyvinyl pyrrolidone-co-ethylacrylate), polyacrylonitrile, polyvinyl chloride- Butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene styrene, sulfonated styrene / ethylene-butylene / styrene Triblock copolymers, polyethylene oxides, and mixtures thereof.

The inorganic material may be selected from the group consisting of colloidal silica, amorphous silica, surface treated silica, colloidal alumina, amorphous alumina, tin oxide, titanium oxide, titanium sulphide (TiS ₂ ), vanadium oxide, zirconium oxide (ZrO ₂ ) ), Iron sulphide (FeS), iron titanate (FeTiO ₃ ), vanadium titanate (BaTiO ₃ ), and mixtures thereof.

The organic material may be conductive carbon.

In another embodiment of the present invention, the current collector, And a cathode active material layer formed on the current collector, wherein the cathode active material layer comprises: a sulfur-based cathode active material; bookbinder; Conductive agent; And a metal nitride; A negative electrode including a negative electrode active material selected from the group consisting of a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of forming a compound reversibly with lithium, a lithium metal and a lithium alloy; And an electrolyte comprising a lithium salt and an organic solvent.

The metal nitride may be titanium nitride (TiN).

The particle size of the metal nitride may be 1 to 5 탆.

The content of the metal nitride in the cathode active material layer may be 3 to 15% by weight.

The organic solvent is benzene, fluorobenzene, toluene, trifluorotoluene, xylene, cyclohexane, tetrahydrofuran, 2-methyl tetrahydrofuran, cyclohexanone, ethanol, isopropyl alcohol, dimethyl carbonate, ethylmethyl Carbonate, diethyl carbonate, methylpropyl carbonate, methylpropionate, ethylpropionate, methyl acetate, ethyl acetate, propyl acetate, dimethoxy ethane, 1,3-dioxolane, diglyme, tetraglyme, ethylene carbonate, At least one solvent selected from the group consisting of propylene carbonate, γ-butyrolactone and sulfolane.

The lithium salt is lithium trifluoromethansulfonimide, lithium triflate, lithium perclorate, lithium hexafluoroazate (LiAsF ₆ ), lithium trifluoromethanesulfonate (CF ₃ SO ₃ Li), LiPF ₆ , LiBF ₄ , tetraalkylammonium, and at least one compound selected from the group consisting of a liquid salt at room temperature.

The electrolyte may include a lithium salt in a concentration of 0.5 to 2.0M.

One embodiment of the present invention is to solve the above-mentioned problems, and it is an object of the present invention to provide a positive electrode for a lithium-sulfur battery which can improve sulfur availability and improve battery performance.

Another embodiment of the present invention can provide a lithium-sulfur battery including the positive electrode.

1 is a perspective view of a lithium sulfur battery.
Fig. 2 shows life characteristics of the batteries according to Examples 1 and 2 and Comparative Example 1. Fig.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

In one embodiment of the present invention, the current collector; And a cathode active material layer formed on the current collector, wherein the cathode active material layer comprises: a sulfur-based cathode active material; bookbinder; Conductive agent; And a metal nitride. The positive electrode for a lithium-sulfur battery includes:

In a conventional lithium-sulfur battery, polysulfide is melted at the anode during charging and discharging, and the electrolyte moves between the anode and the cathode. This is generally referred to as a shuttle phenomenon.

As a result, the capacity and cycle characteristics of the battery may be problematic.

To solve this problem, in one embodiment of the present invention, a metal nitride can be used as an additive in the production of a cathode.

As a more specific example, the metal nitride may be excellent in electrical conductivity.

The metal nitride may activate the reaction of the metal nitride itself with sulfur.

In addition, since sulfur is adhered to the surface of the metal nitride, the shuttle phenomenon is less likely to occur and the utilization rate of sulfur can be increased.

The metal nitride may be titanium nitride (TiN). However, the present invention is not limited thereto unless it limits the effects of the present invention.

The particle size of the metal nitride may be 1 to 5 탆. When the above range is satisfied, the shuttle phenomenon can be effectively suppressed.

The content of the metal nitride in the cathode active material layer may be 3 to 15% by weight. More specifically from 3 to 11% by weight or from 3 to 10% by weight. When this range is satisfied, the shuttle phenomenon can be suppressed.

As the positive electrode active material is sulfur (elemental sulfur, S8) solid _{Li 2 Sn (n≥ 1),} Li 2 Sn (n≥ 1) is dissolved kaessol light, organic sulfur compounds, and carbon-sulfur polymer [(C ₂ Sx) n, x = 2.5 to 50, and n > = 2) may be used.

As a conductive agent for allowing electrons to move smoothly in the positive electrode active material together with the positive electrode active material, a conductive material such as a graphite based material, a carbon based material or the like or a conductive polymer may be preferably used. The graphite material is KS 6 (manufactured by Timcal) and the carbon material is super P (MMM company), ketjen black, denka black, acetylene black, carbon black, and the like. . Examples of the conductive polymer include polyaniline, polythiophene, polyacetylene, polypyrrole, and the like. These conductive conductive agents may be used alone or in combination of two or more.

The binder that serves to adhere the positive electrode active material to the current collector may include poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, crosslinked polyethylene oxide, polyvinyl ether , Poly (methyl methacrylate), polyvinylidene fluoride, copolymers of polyhexafluoropropylene and polyvinylidene fluoride (trade name: Kynar), poly (ethyl acrylate), polytetrafluoroethylene, polyvinyl Chlorides, polyacrylonitriles, polyvinylpyridines, polystyrenes, derivatives thereof, blends, copolymers and the like can be used.

The anode according to an embodiment of the present invention may further include a coating layer composed of a polymer, an inorganic material, an organic material, or a mixture thereof.

The polymer may be selected from the group consisting of polyvinylidene fluoride, copolymers of polyvinylidene fluoride and hexafluoropropylene, poly (vinyl acetate), poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate) Vinyl acetate, polyvinyl pyrrolidone-co-vinyl acetate), cellulose acetate, polyvinyl pyrrolidone, polyvinyl pyrrolidone-co-ethylacrylate), polyacrylonitrile, polyvinyl chloride- Butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene styrene, sulfonated styrene / ethylene-butylene / styrene Triblock copolymers, polyethylene oxides, and mixtures thereof.

Examples of the inorganic material include colloidal silica, amorphous silica, surface treated silica, colloidal alumina, amorphous alumina, tin oxide, titanium oxide, titanium sulphide (TiS ₂ ), vanadium oxide, zirconium oxide (ZrO ₂ ) Iron titanate, FeTiO ₃ , vanadium titanate (BaTiO ₃ ), and mixtures thereof, may be used as the metal oxide.

As the organic material, conductive carbon may be used.

The anode according to one embodiment of the present invention can be produced by coating a current collector with a composition in which a cathode active material, a conductive agent, a binder, and a metal nitride are dispersed in a solvent and drying the collector.

As the solvent for preparing the slurry, it is preferable to use a solvent which can uniformly disperse the sulfur-based active material, the binder, the conductive agent and the metal nitride, and is easily evaporated. Typical examples thereof include acetonitrile, methanol, ethanol, tetrahydrofuran, Water, isopropyl alcohol, dimethyl formamide, and the like.

The amount of the solvent, the sulfur compound or optionally the additive contained in the slurry is not particularly important in the present invention, and it is sufficient that the slurry has an appropriate viscosity to facilitate the coating of the slurry.

The current collector is not particularly limited, but conductive materials such as stainless steel, aluminum, copper, titanium, and the like are preferably used, and more preferably, a carbon-coated aluminum current collector is used. The use of an Al substrate coated with carbon has an advantage in that the adhesion to the active material is excellent, the contact resistance is low, and the corrosion by polysulfide of aluminum can be prevented, compared with the non-carbon coated Al substrate.

The lithium-sulfur battery 1 including the positive electrode is shown in FIG. As shown in FIG. 1, a lithium-sulfur battery includes a battery can 5 including a positive electrode 3, a negative electrode 4, and a separator positioned between the positive electrode 3 and the negative electrode 4.

As the negative electrode, a material made of a negative electrode active material including a material capable of reversibly intercalating lithium ions, a material capable of reversibly forming a compound with lithium metal, or a lithium metal or a lithium alloy is used.

As a material capable of reversibly intercalating lithium ions, any carbon negative active material generally used in a lithium ion secondary battery may be used, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Can be used. Representative examples of the material capable of reacting with the lithium ions to form a lithium-containing compound reversibly include tin oxide (SnO ₂ ), titanium nitrate, silicon (Si) and the like, but is not limited thereto. As the lithium alloy, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al and Sn can be used.

An inorganic protective layer, an organic protective layer, or a material in which these layers are stacked on a lithium metal surface may also be used as a cathode.

As the inorganic protective film, Mg, Al, B, C, Sn, Pb, Cd, Si, In, Ga, lithium silicate, lithium borate, lithium phosphate, lithium phosphoronide, lithium silicon sulfide, lithium borosulfide, lithium aluminium It consists of a material selected from the group consisting of nosulfide and lithium phosphosulfide. The organic protective film is poly (p-phenylene), polyacetylene, poly (p-phenylene vinylene), polyaniline, polypyrrole, polythiophene, poly (2,5-ethylene vinylene), acetylene, poly (ferry) Naphthalene), polyacene, and poly (naphthalene-2,6-diyl), and a monomer, oligomer or polymer having conductivity selected from the group consisting of.

In addition, in the process of charging and discharging the lithium-sulfur battery, sulfur used as the positive electrode active material may be changed into an inert material and adhered to the surface of the lithium negative electrode. As described above, inactive sulfur refers to sulfur in which sulfur can no longer participate in the electrochemical reaction of the anode through various electrochemical or chemical reactions, and inactive sulfur formed on the surface of the lithium anode is a protective layer of the lithium cathode. There is also an advantage to act as. Therefore, lithium metal and inert sulfur formed on the lithium metal, for example lithium sulfide, may be used as the negative electrode.

The electrolyte used with the positive electrode according to the embodiment of the present invention includes a lithium salt as a supporting electrolytic salt and a non-aqueous organic solvent. The organic solvent of the electrolyte used in the lithium-sulfur battery is appropriately selected from elemental sulfur (S8), lithium sulfide (Li ₂ S), and lithium polysulfide (Li ₂ Sn, n = 2, 4, 6, 8 ...). Use to dissolve. Examples of the organic solvent include benzene, fluorobenzene, toluene, trifluoro toluene, xylene, cyclohexane, tetrahydrofuran, 2-methyltetrahydrofuran, cyclodextrin, ethanol, isopropyl alcohol, dimethyl carbonate, ethyl Methyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl propionate, ethyl propionate, methyl acetate, ethyl acetate, propyl acetate, dimethoxyethane, 1,3-dioxolane, diglyme, tetraglyme, ethylene carbonate , Propylene carbonate,? -Butyrolactone, and sulfolane.

The lithium salt as the electrolytic salt is lithium trifluoromethansulfonimide, lithium triflate, lithium perclorate, lithium hexafluoroazate (LiAsF6), lithium trifluoro Methanesulfonate (CF ₃ SO ₃ Li), LiPF ₆ , LiBF ₄ or tetraalkylammonium, for example tetrabutylammonium tetrafluoroborate, or a liquid salt at room temperature, for example 1-ethyl-3-methyl One or more imidazolium salts such as midazolium bis (perfluoroethyl sulfonyl) imide and the like can be used. The electrolyte may include a lithium salt in a concentration of 0.5 to 2.0M.

The electrolyte may be used as a liquid electrolyte or as a solid electrolyte separator. When used as a liquid electrolyte, the separator further includes a separator made of porous glass, plastic, ceramic, or polymer as a physical separator having a function of physically separating the electrode.

The electrolyte separator functions as a physical separation of the electrode and a transfer medium for moving metal ions, and both electrochemically stable electric and ion conductive materials may be used. As such an electrically and ion conductive material, a glass electrolyte, a polymer electrolyte, or a ceramic electrolyte may be used. As a particularly preferred solid electrolyte, the supported electrolyte salt is mixed with a polymer electrolyte such as polyether, polyimine, polythioether, or the like. The solid

The electrolyte separator in a state may include less than about 20% by weight of a non-aqueous organic solvent, and in this case, may further include a suitable gelling agent to reduce the fluidity of the organic solvent.

Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto.

( Example )

Example  1: Preparation of Battery

0.18 g of a sulfur element (S8), 0.06 g of a carbon conductive agent, 0.03 g of titanium nitride and 0.6 g of a binder were mixed and ball milled for 1 hour to prepare a cathode active material slurry.

PVdF and NMP were used as the binder, and the content of PVdF in the binder was 5% by weight based on 100% by weight of the total binder.

The titanium nitride used had a grain size of 3 탆.

The prepared cathode active material slurry was coated on a carbon-coated Al current collector and then dried in a vacuum oven at 80 ° C. The dried electrode plate was cut into a size of 15 mm in diameter to prepare a cell for coin cell evaluation. A non-oxidized lithium metal foil (thickness 160 탆) was used as the cathode.

Example  2: Manufacture of batteries

0.12 g of a sulfur element (S8) powder, 0.06 g of a carbon conductive agent, 0.09 g of titanium nitride and 0.6 g of a binder were mixed and ball milled for 1 hour to prepare a cathode active material slurry.

PVdF and NMP were used as the binder, and the content of PVdF in the binder was 5% by weight based on 100% by weight of the total binder.

The titanium nitride used had a grain size of 3 탆.

The prepared cathode active material slurry was coated on a carbon-coated Al current collector and then dried in a vacuum oven at 80 ° C. The dried electrode plate was cut into a size of 15 mm in diameter to prepare a cell for coin cell evaluation. A non-oxidized lithium metal foil (thickness 160 탆) was used as the cathode.

Comparative Example  1: Preparation of Battery

In Example 1, a battery was prepared in the same manner as in Example 1, except that no titanium nitride was added.

( Experimental Example )

The batteries of Examples 1 and 2 and Comparative Example 1 were subjected to 0.1 C discharging and 0.1 C charging in a cut-off voltage range of 1.5 V to measure the life characteristics of the charge-discharge cycle 50 times.

As shown in FIG. 2, it was found that the battery made of the positive electrode according to the embodiment of the present invention has an excellent life characteristic as compared with Comparative Example 1.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

Claims (16)

Collecting house; And
And a cathode active material layer formed on the current collector,
The positive electrode active material layer
Sulfur cathode active material; bookbinder; Conducting agents; And metal nitride; and a cathode for a lithium-sulfur battery.
The method of claim 1,
Wherein the metal nitride is titanium nitride (TiN).
The method of claim 1,
Wherein the metal nitride has a particle size of 1 to 5 占 퐉.
The method of claim 1,
Wherein the content of the metal nitride in the cathode active material layer is 3 to 15% by weight.
The method of claim 1,
The cathode active material may be selected from the group consisting of: an organic sulfur compound and a carbon-sulfur polymer [(C ₂ Sx)] in which elemental sulfur (S 8), solid Li ₂ Sn (n ≥ 1), Li ₂ Sn n, x = 2.5 to 50, n? 2].
The method of claim 1,
Wherein the anode further comprises a coating layer selected from the group consisting of a polymer coating layer, an inorganic coating layer, and an organic coating layer.
The method according to claim 6,
The polymer may be selected from the group consisting of polyvinylidene fluoride, copolymers of polyvinylidene fluoride and hexafluoropropylene, poly (vinyl acetate), poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate) Vinyl acetate, polyvinyl pyrrolidone-co-vinyl acetate), cellulose acetate, polyvinyl pyrrolidone, polyvinyl pyrrolidone-co-ethylacrylate), polyacrylonitrile, polyvinyl chloride- Butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene styrene, sulfonated styrene / ethylene-butylene / styrene Triblock copolymers, polyethylene oxides, and mixtures thereof.
The method according to claim 6,
The inorganic material is colloidal silica, amorphous silica, surface treated silica, colloidal alumina, amorphous alumina, tin oxide, titanium oxide, titanium sulfide (TiS ₂ ), vanadium oxide, zirconium oxide (ZrO ₂ ), iron oxide (Iron Oxide) ), Iron sulfide (Iron Sulfide, FeS), iron titanate (Iron titanate, FeTiO ₃ ), barium titanate (Vanadium titanate, BaTiO ₃ ) and a mixture thereof.
The method according to claim 6,
The organic material is a conductive carbon lithium-sulfur battery.
Collecting house; And a cathode active material layer formed on the current collector, wherein the cathode active material layer comprises: a sulfur-based cathode active material; bookbinder; Conducting agents; And a metal nitride;
A negative electrode including a negative electrode active material selected from the group consisting of a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of forming a compound reversibly with lithium, a lithium metal and a lithium alloy; And
An electrolyte comprising a lithium salt and an organic solvent;
Lithium-sulfur battery comprising a.
The method of claim 10,
Wherein the metal nitride is titanium nitride (TiN).
The method of claim 10,
Wherein the metal nitride has a particle size of 1 to 5 占 퐉.
The method of claim 10,
Wherein the content of the metal nitride in the positive electrode active material layer is 3 to 15% by weight.
The method of claim 10,
The organic solvent is benzene, fluorobenzene, toluene, trifluorotoluene, xylene, cyclohexane, tetrahydrofuran, 2-methyl tetrahydrofuran, cyclohexanone, ethanol, isopropyl alcohol, dimethyl carbonate, ethylmethyl Carbonate, diethyl carbonate, methylpropyl carbonate, methylpropionate, ethylpropionate, methyl acetate, ethyl acetate, propyl acetate, dimethoxy ethane, 1,3-dioxolane, diglyme, tetraglyme, ethylene carbonate, Lithium-sulfur cell which is at least one solvent selected from the group consisting of propylene carbonate, γ-butyrolactone and sulfolane.
The method of claim 10,
The lithium salt is lithium trifluoromethansulfonimide, lithium triflate, lithium perclorate, lithium hexafluoroazate (LiAsF ₆ ), lithium trifluoromethanesulfonate At least one compound selected from the group consisting of (CF ₃ SO ₃ Li), LiPF ₆ , LiBF ₄ , tetraalkylammonium, and a liquid salt at room temperature.
The method of claim 10,
Wherein the electrolyte comprises a lithium salt in a concentration of 0.5 to 2.0M.

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