KR20160136248A - Negative electrode for rechargeable sodium battery comprising protective layer and rechargeable sodium battery comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode for a rechargeable sodium battery comprising a protective layer and a rechargeable sodium battery comprising the same. Provided is the negative electrode for a rechargeable sodium battery, the negative electrode comprising a negative electrode active material and a protective layer, wherein the protective layer includes a composite of a hydrophobic polymer and a sodium ion conductive polymer. According to the present invention, a sodium metal is coated with the protective layer including the composite of a hydrophobic polymer and a sodium ion conductive polymer. Accordingly, the sodium metal can be protected from moisture, and driving is enabled by transferring Na ions after the construction of a battery.

Description

TECHNICAL FIELD [0001] The present invention relates to a negative electrode for a sodium secondary battery including a protective layer and a sodium secondary battery including the negative electrode. [0002]

The present invention relates to a negative electrode for a sodium secondary battery including a protective layer and a sodium secondary battery comprising the same. More particularly, the present invention relates to a negative electrode for a sodium secondary battery comprising a protective layer, And a negative electrode for a sodium secondary battery and a sodium secondary battery including the negative electrode.

BACKGROUND ART [0002] In recent years, secondary batteries have been used in a wide range of applications, ranging from large capacity batteries for power storage, mid-sized batteries for transportation, and small batteries used as power sources for portable devices. have. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate are commercially available and widely used. However, since a lithium secondary battery uses a large amount of rare metals such as cobalt, nickel, and lithium, there is a concern about supply of the rare metal due to an increase in demand for a large secondary battery.

On the other hand, interest is focused on the next-generation sodium secondary battery, which is richly buried in an even distribution throughout the world with an alkali metal belonging to Group 1 of the periodic table together with lithium and has an oxidation-reduction potential value equal to that of lithium and a high energy density .

The sodium secondary battery is composed of a positive electrode containing a positive electrode active material capable of doping and dedoping sodium ions, a negative electrode containing a negative electrode active material capable of doping and dedoping sodium ions, and a nonaqueous electrolyte containing sodium ions , As in the lithium ion of the lithium secondary battery, the sodium ion reciprocates between the negative electrode and the positive electrode through the electrolyte, thereby charging and discharging the battery. A state in which sodium ions are occluded (doped) in a negative electrode active material corresponds to charging, and a state in which sodium ions are desorbed (de-doped) from a negative electrode active material corresponds to a discharge.

However, there is a problem that sodium metal reacts with moisture in the atmosphere rapidly and is poor in fairness. In order to solve this problem, there has been an attempt to prevent moisture by coating a protective layer on the sodium metal. However, in such a case, there is a limit in that the battery can not be driven after the battery is constructed.

Korean Registered Patent No. 10-1499586 (registered on March 2, 2015)

An object of the present invention is to provide a negative electrode for a sodium secondary battery that protects sodium metal from moisture by coating a sodium metal on a protective layer composed of a complex of a hydrophobic polymer and a sodium ion conductive polymer, .

Another object of the present invention is to provide an electrode assembly including the negative electrode and a sodium secondary battery.

According to an embodiment of the present invention, there is provided a negative electrode for a sodium secondary battery comprising a protective layer composed of a complex of a hydrophobic polymer and a sodium ion conductive polymer.

In the negative electrode for a sodium secondary battery, the hydrophobic polymer may be selected from the group consisting of polydimethylsiloxane (PDMS), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene , polychlorotrifluoroethylene, polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), and combinations thereof.

The sodium ion conductive polymer may be at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polymethylmethacrylate (PMMA), polyethylene oxide (PEO) And a combination thereof.

In addition, the protective layer may include 10 to 50% by weight of the hydrophobic polymer and 50 to 90% by weight of the sodium ion conductive polymer based on the total weight of the protective layer.

In the negative electrode for a sodium secondary battery, the protective layer may have a thickness of 0.1 to 20 탆.

In the negative electrode for a sodium secondary battery, the contact angle of the protective layer may be 80 to 170 degrees.

According to another embodiment of the present invention, there is provided an electrode assembly for a sodium secondary battery including the negative electrode.

According to another embodiment of the present invention, there is provided a sodium secondary battery including the electrode assembly.

According to the present invention, a protective layer composed of a complex of a hydrophobic polymer and a sodium ion conductive polymer is coated on a sodium metal to protect the sodium metal by blocking water in a battery manufacturing process. After the electrolyte is injected, the protective layer is activated, A negative electrode for a sodium secondary battery can be provided.

Hereinafter, the present invention will be described in detail with reference to the following examples. However, the following examples are illustrative of the present invention, and the contents of the present invention are not limited by the following examples.

According to an embodiment of the present invention, there is provided a negative electrode for a sodium secondary battery comprising a protective layer composed of a complex of a hydrophobic polymer and a sodium ion conductive polymer.

Specifically, the negative electrode may be an alloy of sodium metal or sodium metal. The sodium alloy may be an alloy of any one selected from the group consisting of Al, Sn, Bi, Si, Sb, B and their alloys and sodium.

The negative electrode active material may be a carbon-based material such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbon materials, carbon fibers, sintered organic polymer compounds, amorphous hard carbon and the like capable of storing and releasing sodium ions; Transition metal oxides such as Na ₂ Ti ₃ O, Li ₄ Ti ₅ O ₁₂ and the like; Metal sodium or an alloy thereof; And a phosphate, and optionally a mixture of two or more thereof.

The negative electrode active material layer may further include a binder optionally in combination with the negative electrode active material.

The binder acts as a paste for the anode active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, buffering effect on expansion and contraction of the active material, and the like. Specifically, the binder is selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer including ethylene oxide, polyvinyl pyrrolidone, polyurethane , Polytetrafluoroethylene, polyvinylidene difluoride (PVDF), polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like. The binder may be contained in an amount of 20 wt% or less, or 5 to 15 wt%, based on the total weight of the negative electrode active material layer.

The protective layer is composed of a complex of a hydrophobic polymer and a sodium ion conductive polymer. The complex may be a blending form of the hydrophobic polymer and the sodium ion conductive polymer, or may be a copolymer of the hydrophobic polymer and the sodium ion conductive polymer.

The hydrophobic polymer may be selected from the group consisting of polydimethylsiloxane (PDMS), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinyl fluoride (PVF), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), and combinations thereof.

The sodium ion conductive polymer may be at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polymethylmethacrylate (PMMA), polyethylene oxide (PEO) And a combination thereof. The polymer is swelled into an electrolyte and is driven, so that the polymer itself can be ion-exchanged.

The protective layer may include 10 to 50% by weight of the hydrophobic polymer and 50 to 90% by weight of the sodium ion conductive polymer based on the total weight of the protective layer, preferably 20 to 30% by weight of the hydrophobic polymer, And 70 to 80% by weight of the sodium ion conductive polymer.

When the content of the hydrophobic polymer is less than 10% by weight or the content of the sodium ion conductive polymer is more than 90% by weight, the sodium metal may be oxidized due to the lowering of the moisture blocking ability of the protective layer. The content of the hydrophobic polymer Is more than 50% by weight or the content of the sodium ion conductive polymer is less than 50% by weight, the resistance of the battery may increase due to the lowering of sodium ion conductivity of the protective layer.

In addition, the protective layer may further include a curing agent for mixing the hydrophobic polymer and the sodium ion conductive polymer. The curing agent may be any one selected from the group consisting of silicon, acrylic, and combinations thereof. More specifically, carbosilane may be used. The curing agent may be added in an amount of 5 to 15% by weight, preferably 8 to 12% by weight based on the total weight of the protective layer. If the content of the curing agent is less than 5% by weight, the strength of the protective layer may be weakened and the growth of sodium dendrites may not be inhibited. If the content of the curing agent is more than 15% by weight, the protective layer may be broken due to high film strength.

In the negative electrode for a sodium secondary battery, the protective layer may have a thickness of 0.1 to 20 m, and when the thickness of the protective layer is less than 0.1 m, it may be difficult to block moisture during the process, The output characteristics of the battery may be deteriorated due to the resistance.

In the negative electrode for a sodium secondary battery, the contact angle of the protective layer may be in the range of 80 to 170 degrees. If the contact angle is less than 80 degrees, the hydrophobicity may be insufficient and blocking of moisture may be difficult. Fairness may be reduced.

According to another embodiment of the present invention, there is provided an electrode assembly for a sodium secondary battery including the negative electrode.

Specifically, the electrode assembly has the positive electrode and the negative electrode alternately stacked with the separator as a boundary, and the negative electrode is as described above.

In the electrode assembly, the positive electrode includes a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode collector.

The positive electrode collector is particularly limited as long as it has conductivity without causing chemical changes in the battery. Specifically, the positive electrode and the negative electrode are laminated alternately with a separator as a boundary, wherein the negative electrode is as described above .

In the electrode assembly, the positive electrode includes a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode collector.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, titanium, , Silver or the like may be used. In addition, the cathode current collector may have a thickness of 3 to 500 탆, and fine unevenness may be formed on the surface of the current collector to increase the adhesive force of the cathode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

In addition, the cathode active material layer includes a cathode active material, and optionally, a conductive material and a binder.

As the cathode active material, Na _x CoO ₂ , Na _x Co _2/3 Mn _1/3 O ₂ , Na _x Fe _1/2 Mn _1/2 O ₂ , NaCrO ₂ , NaLi _0.2 Ni _0.25 Mn _0.75 O _2.35 , Sodium metal oxides such as Na _0.44 MnO ₂ , NaMnO ₂ , Na ₂ Fe ₅ Si ₁₂ O ₃₀ , Na _0.7 VO ₂ , or Na _0.33 V ₂ O ₅ (where 0 <x≤1); Oxides such as Na ₃ V ₂ (PO ₄ ) ₃ , NaFePO ₄ , NaMn _0.5 Fe _0.5 PO ₄ , Na ₃ V ₂ (PO ₄ ) ₃ , Na ₃ Fe ₂ (PO ₄ ) ₃ and the like; Na ₂ FePO ₄ F, Na ₃ V ₂ (PO ₄ ) _3, and the like; Sodium or metal fluoride such as sulfur oxides NaFeSO ₄ F; Composite metal oxide of the transition metal _{- NaFeO 2, NaMnO 2, NaNiO} 2 and ₂ NaCoO sodium and the like; Sodium metal fluorides such as Na ₃ FeF ₆ or Na ₂ MnF ₆ ; Sodium metal borates such as NaFeBO ₄ , or Na ₃ Fe ₂ (BO ₄ ) ₃ ; And chalcogen compounds such as TiS ₂ , ZrS ₂ , VS ₂ , V ₂ S ₂ , TaS ₂ , FeS ₂ or NiS _2, and any one or a mixture of two or more of them may be used. Among them, the Fe-containing compound can suppress the elution of the transition metal ions even when the temperature of the electrolyte in the battery rises, and as a result, the cycle characteristics and the discharge capacity retention rate of the sodium secondary battery can be improved. In addition, chalcogen compounds such as TiS ₂ , ZrS ₂ , and the like can store and desorb sodium ions at a higher potential than the negative electrode when used in combination with metal sodium or its alloy based negative active material, And can exhibit further increased reactivity.

In addition, the binder plays a role of attaching the positive electrode active material particles to each other well and attaching the positive electrode active material to the current collector well. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropylcellulose, diacetylcellulose, Polyvinyl fluoride, polymers comprising ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene difluoride, polyethylene, polypropylene &lt; RTI ID = 0.0 &gt; , Styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black , Ketjen black, carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

The positive electrode having the above structure can be produced according to a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, the positive electrode active material layer forming material containing the positive electrode active material, the binder and the conductive material may be coated on the positive electrode current collector, followed by drying and rolling.

Meanwhile, in the electrode assembly, the separation membrane is interposed between the positive electrode and the negative electrode to insulate the positive electrode from the negative electrode, thereby interrupting the internal short circuit of the electrode and impregnating the electrolyte.

As the separation membrane, an insulating thin film having high ion permeability and mechanical strength can be used. The thickness of the separator may be preferably as thin as long as the mechanical strength is maintained because the volume energy density of the battery becomes high and the internal resistance becomes small. Specifically, the separation membrane may have a pore diameter of 0.01 to 10 탆, an air permeability of 50 to 300 sec / 100 cc, and a thickness of 5 to 310 탆.

The separator may be any of those generally used in the art. More specifically, it is possible to use a polymer resin having a chemical resistance and a hydrophobic property, or a glass fiber, and more specifically, a high-density polyethylene, a low density polyethylene, a linear low density polyethylene, a ultra high molecular weight polyethylene, a polypropylene, a polyethylene terephthalate, But are not limited to, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyethersulfone, polyphenylene oxide, polyphenylenesulfrode, polyethylenenaphthalene, and copolymers thereof. Any one or a mixture of two or more of them may be used.

According to another embodiment of the present invention, there is provided a sodium secondary battery including the electrode assembly.

Specifically, the sodium secondary battery includes the electrode assembly and the electrolyte. At this time, the electrolyte rapidly and uniformly conducts sodium ions, and may be an electrolytic solution or a solid electrolyte.

When the electrolyte is an electrolytic solution, it includes an electrolyte salt and a solvent.

Specific examples of the electrolytic salt include sodium hydroxide (for example, sodium hydroxide (NaOH)), borate (for example, sodium metaborate (NaBO ₂ ), borax (Na ₂ B ₄ O ₇ ) (H ₃ BO _3), and the like), phosphates (e.g., trisodium phosphate (Na ₃ PO _4), sodium pyrophosphate (Na ₂ HPO ₄₎ and the like), acid (for example, NaClO _4, etc.), NaAlCl _{4 , NaAsF 6, NaBF 4, NaPF} 6, NaSbF 6, NaCF 3 SO 3 or NaN (SO ₂ CF _{3) 2} or the like may be, there is any one or a mixture of two or more of them may be used.

The electrolyte may contain 2 to 50% by weight of the electrolyte salt based on the total weight of the electrolyte.

In addition, the solvent can be used without any particular limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the solvent may be an aqueous solvent such as water, alcohol, or the like; Or a nonaqueous system such as an ester solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an alkoxyalkane solvent, or a carbonate solvent. These may be used singly or in combination of two or more.

Specific examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, But are not limited to, ethyl propionate,? -Butyrolactone, decanolide,? -Valerolactone, mevalonolactone,? -Caprolactone (? -caprolactone, 隆 -valerolactone, 竜 -caprolactone, and the like.

Specific examples of the ether solvent include dibutyl ether, tetraglyme, 2-methyltetrahydrofuran, tetrahydrofuran, and the like.

Specific examples of the ketone-based solvents include cyclohexanone and the like. Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, chlorobenzene, iodobenzene, toluene, fluorotoluene, xylene, (xylene), and the like. Examples of the alkoxyalkane solvent include dimethoxy ethane and diethoxy ethane.

Specific examples of the carbonate solvent include dimethylcarbonate (DMC), diethylcarbonate (DEC), dipropylcarbonate (DPC), methylpropylcarbonate (MPC), ethylpropylcarbonate (EPC) , Methyl ethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylenes carbonate (BC) And fluoroethylene carbonate (FEC).

When the electrolyte is a solid electrolyte, specifically, an organic polymer electrolyte such as a polymer compound containing at least one of a polyethylene oxide-based polymer compound, a polyorganosiloxane chain, and a polyoxyalkylene chain may be used. A so-called gel type in which a non-aqueous electrolyte solution is held in a polymer compound may also be used. In addition, inorganic solid electrolytes such as sulfide electrolytes such as Na ₂ S-SiS ₂ and Na ₂ S-GeS ₂ and NASICON electrolytes such as NaZr ₂ (PO ₄ ) ₃ may be used. When these solid electrolytes are used, there are cases where safety can be further increased.

In the case of using the solid electrolyte in the sodium secondary battery of the present invention, the solid electrolyte may serve as a separator, and in this case, a separator may not be required.

In addition to the above electrolyte components, the electrolyte may further contain an additive (hereinafter, referred to as "other additive") that can be generally used for an electrolyte for the purpose of improving lifetime characteristics of the battery, suppressing reduction in battery capacity, .

It is preferable that 0.1 to 5% by weight of fluorinated ethylene carbonate is further added to the electrolyte.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. However, the following embodiments are intended to illustrate the invention, but the invention is not limited thereto.

(Example 1)

A mixture of PDMS (SYLGARD 184) and a curing agent (184B, carbosilane) in a ratio of 10: 1 was added to PVdF-HFP while controlling the content of PVdF-HFP as shown in the following Table 1. DME (dimethoxyethane) And the mixture was stirred for 30 minutes. The stirred solution was coated on a sodium electrode with a doctor blade to form a 5 mu m protective layer.

At this time, the contents of PDMS and PVdF-HFP in Table 1 are shown based on the sum of the weights of PDMS and PVdF-HFP.

(Comparative Example 1)

A protective layer was formed in the same manner as in Example 1 except that the protective layer was formed without PDMS in Example 1.

(Comparative Example 2)

A protective layer was formed in the same manner as in Example 1 except that a protective layer was formed without PVdF-HFP in Example 1.

[Experimental Example 1: Measurement of sodium cycle efficiency]

The embodiments the sodium electrode (20㎛) prepared in Examples and Comparative Examples, polyethylene (PE) separator and DOL (Dioxolane) and DME (Dimethoxyethane) (DOL: DME = 1: 1v / v) NaPF 6 as an electrolyte salt in a solvent To prepare 2032 coin cells as a 1M electrolytic solution.

The cyclic efficiency of the thus prepared symmetric cell was measured with a 1C DOD of 83%, and the results are shown in Table 1. The 1C DOD 83% means that the amount of 16.6 탆 corresponding to 83% of 20 탆 of Na is charged and discharged. The rate of 3.7 mA / cm ² Current density &quot;

[Experimental Example 2: Measurement of sodium ion conductivity]

Sodium ion conductivity was measured using the symmetric cell prepared in Experimental Example 1, and the results are also shown in Table 1 below.

[Experimental Example 3: Measurement of water stability]

The sodium electrode prepared in Examples and Comparative Examples was left in air at 25 ° C and RH 40% to measure the degree of oxidation of the sodium electrode surface. The results are also shown in Table 1 below.

At this time, the measurement standard is as follows.

DELTA: oxidation within 3 hours

○: oxidation within 6 hours

◎: Stable for more than 6 hours

PDMS content
(wt.%) PVdF-HFP
Content (wt.%) Na efficiency
(%) Ion conductivity
(S / cm) Water stability Example 1 10 90 94 5.3 × 10 ^-3 △ Example 2 30 70 92 9.1 × 10 ^-3 ○ Example 3 50 50 85 1.8 X 10 ^-4 ◎ Comparative Example 1 0 100 95 2.7 X 10 ^-3 △ Comparative Example 2 100 0 N / A N / A ◎

From Table 1, the moisture stability was poor in Comparative Example 1 without PDMS, and Na efficiency and ionic conductivity were not measured in Comparative Example 2 in which PVdF-HFP was absent.

On the other hand, it can be seen that Examples 1 to 3 have moisture stability with Na efficiency and ion conductivity higher than a certain level, and Example 2 shows a better effect.

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, Of the right.

Claims (8)

A negative electrode active material layer comprising an alloy of sodium metal or sodium metal, and
And a protective layer disposed on the negative active material layer,
Wherein the protective layer comprises a complex of a hydrophobic polymer and a sodium ion conductive polymer. The method according to claim 1,
The hydrophobic polymer may be selected from the group consisting of polydimethylsiloxane (PDMS), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinyl fluoride Wherein the negative electrode is any one selected from the group consisting of polyvinylidene fluoride (PVF), polyvinyl fluoride (PVDF), polyvinylidene fluoride (PVDF), and combinations thereof. The method according to claim 1,
The sodium ion conductive polymer may be at least one selected from the group consisting of polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), polymethyl methacrylate (PMMA), polyethylene oxide (PEO) Wherein the negative electrode is a negative electrode. The method according to claim 1,
Also, the protective layer comprises 10 to 50% by weight of the hydrophobic polymer and 50 to 90% by weight of the sodium ion conductive polymer based on the total weight of the protective layer. The method according to claim 1,
Wherein the protective layer has a thickness of 0.1 占 퐉 to 20 占 퐉. The negative electrode for a sodium secondary battery according to claim 1, wherein the protective layer has a contact angle of 80 to 170 degrees. In an electrode assembly in which an anode and a cathode are alternately stacked with a separator as a boundary,
The electrode assembly for a sodium secondary battery according to any one of claims 1 to 6, A sodium secondary battery comprising an electrode assembly according to claim 7.