Capsule for lithium-sulfur secondary battery and lithium-sulfur secondary battery comprising the same

Abstract

The present invention relates to a capsule for a lithium-sulfur secondary battery, wherein the capsule comprises: a core containing a material required for formation and restoration of a solid electrolyte interface (SEI layer) and a hydrogel; and a shell made of a polymer surrounding the core, whereby the solid electrolyte interface (SEI layer) on the negative electrode can be maintained for a long time by keeping the material required for formation and restoration of a solid electrolyte interface (SEI layer) at a constant level during battery operation.

Description

Technical Field

[0001] This invention relates to a capsule for lithium-sulfur secondary batteries.

[0002] This application claims priority to Korean Patent Application No. 10-2020-0116127, filed on September 10, 2020, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Recently, with the rapid development of miniaturization, lightweighting, and high performance in electronic and communication devices, and the significant increase in demand for electric vehicles related to environmental issues, the need for improved performance of secondary batteries used as energy sources for these products is growing. For secondary batteries that meet these requirements, extensive research is being conducted on lithium-sulfur batteries using sulfur-based materials as the positive electrode active material.

[0004] Lithium-sulfur batteries are secondary batteries that use sulfur compounds containing sulfur-sulfur bonds as positive electrode active materials and alkali metals such as lithium or carbon materials that allow for the insertion / deintercalation of metal ions such as lithium ions as negative electrode active materials.

[0005] Specifically, lithium-sulfur batteries have a theoretical discharge capacity of 1675 mAh / g and a theoretical energy density of 2600 Wh / kg, which is about five times the theoretical energy density of currently researched lithium-ion batteries (approximately 570 Wh / kg). Therefore, lithium-sulfur batteries are a type of battery capable of achieving high capacity, high energy density, and long lifespan. Furthermore, because sulfur, the main material for the positive electrode, has a low atomic weight, is abundant and easily supplied and absorbed, is inexpensive, non-toxic, and environmentally friendly, lithium-sulfur batteries are attracting considerable attention as an energy source for medium to large-sized devices such as electric vehicles and portable electronic devices.

[0006] This type of lithium-sulfur secondary battery uses lithium metal as the negative electrode. Therefore, to protect the lithium metal negative electrode, additives are added to the electrolyte. Accordingly, a solid electrolyte interface (SEI layer) is formed through the reaction of the additives with the lithium metal. However, in this type of lithium-sulfur secondary battery, when repeatedly charged and discharged, the solid electrolyte interface (SEI layer) on the negative electrode is damaged and the lithium metal is exposed. As a result, the battery efficiency drops sharply and the discharge capacity decreases, leading to battery degradation.

[0007] To prevent such damage to the solid electrolyte interphase (SEI) layer of the negative electrode, if the content of materials (additives) that can easily form and restore the SEI layer as battery components is increased, the additives may act as resistors in the battery, resulting in reduced energy density and shortened lifespan.

[0008] Therefore, in order to prevent damage to the solid electrolyte interface (SEI layer) and maintain the SEI layer at a constant level, a method is needed to maintain the content of materials capable of forming and restoring the SEI layer at a constant level even during the operation of the lithium-sulfur secondary battery.

[0009] [Existing technical documents]

[0010] [Patent Literature]

[0011] (Patent Document 1) Korean Patent Publication No. 10-2007-0008405 (January 17, 2007), "Lithium Secondary Battery Containing Capsule for Controlled-release of Additives" Summary of the Invention

[0012] Technical issues

[0013] Therefore, in this invention, it was discovered that for the negative electrode of a lithium-sulfur secondary battery, when a capsule comprising a core containing a hydrogel and a material capable of forming and restoring a solid electrolyte interface (SEI layer) on the negative electrode and a shell made of a polymer surrounding the core is used as an additive for lithium-sulfur secondary batteries, so that even during the operation of the lithium-sulfur secondary battery, the material (additive) capable of reacting with lithium metal to form and restore the solid electrolyte interface (SEI layer) on the negative electrode is kept at a constant level, the sudden drop in battery efficiency and the decrease in discharge capacity can be suppressed by preventing damage to the solid electrolyte interface (SEI layer) on the negative electrode and thus preventing lithium metal from being exposed to the electrolyte, even during the operation of the lithium-sulfur secondary battery.

[0014] Therefore, one object of the present invention is to provide a capsule for lithium-sulfur secondary batteries and a method for preparing the same, wherein the capsule can prevent damage to the solid electrolyte interface (SEI layer) formed on the negative electrode of the lithium-sulfur secondary battery, thereby improving the lifespan characteristics of the lithium-sulfur secondary battery. In particular, one object of the present invention is to provide a capsule for lithium-sulfur secondary batteries and a method for preparing the same, wherein the capsule can maintain the solid electrolyte interface (SEI layer) on the negative electrode at a constant level even during the operation of the lithium-sulfur secondary battery by continuously supplying materials (additives) capable of forming and restoring the solid electrolyte interface (SEI layer).

[0015] Another object of the present invention is to provide a lithium-sulfur secondary battery comprising the capsule.

[0016] Technical solution

[0017] To achieve the above objectives, the present invention provides a capsule for lithium-sulfur secondary batteries, the capsule comprising a core containing a hydrogel and a material capable of forming and restoring a solid electrolyte interface (SEI layer) and a shell made of a polymer surrounding the core.

[0018] Furthermore, the present invention provides a capsule for lithium-sulfur secondary batteries, wherein the material required for forming and restoring the solid electrolyte interface (SEI layer) is selected from at least one of the following: LiNO3, Be(NO3)2, NaNO3, Mg(NO3)2, Al(NO3)3, KNO3, Ca(NO3)2, Sc(NO3)3, Ti(NO3)4, VO(NO3)3, Cr(NO3)3, Mn(NO3)2, Fe(NO3)3, Fe(NO3)2, Co(NO3)2, Co(NO3)3, Ni(NO3)2, Cu(NO3)2, Zn(NO3)2, Ga(NO3) 3. RbNO3, Sr(NO3)2, Y(NO3)3, Zr(NO3)4, Pd(NO3)2, AgNO3, Cd(NO3)2, Sb(NO3)3, Xe(NO3)2, CsNO3, Ba(NO3)2, Hg2(NO3)2, Hg(NO3)2, Tl(NO 3)3. TlNO3, Pb(NO3)2, Bi(NO3)3, BiO(NO3), FrNO3, Ra(NO3)2, La(NO3)3, Ce(NO3)3, Ce(NO3)4, Nd(NO3)3, Eu(NO3)3, Gd(NO3)3 and Tb(NO3)3.

[0019] Furthermore, the present invention provides a capsule for lithium-sulfur secondary batteries, wherein the hydrogel is selected from acrylate polymers, polysaccharides, polyamino acids, and combinations thereof, wherein the acrylate polymers include monomer-derived units having two or more acrylate groups containing ethylene glycol groups.

[0020] Furthermore, the present invention provides a capsule for lithium-sulfur secondary batteries, wherein the polymer is formed by crosslinking an epoxy compound having two or more epoxy groups with a crosslinking agent having two or more amino groups.

[0021] Furthermore, the present invention provides a capsule for lithium-sulfur secondary batteries, wherein the epoxy compound having two or more epoxy groups is selected from at least one of the following: 1,4-butanediol diglycidyl ether (BDDE), ethylene glycol diglycidyl ether (EGDGE), 1,6-hexanediol diglycidyl ether, propylene glycol diglycidyl ether, poly(propylene glycol) diglycidyl ether, poly(butanediol) diglycidyl ether, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, polyglycerol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, 1,2-(bis(2,3-epoxypropoxy)ethane), pentaerythritol polyglycidyl ether, or sorbitol polyglycidyl ether.

[0022] Furthermore, the present invention provides a capsule for lithium-sulfur secondary batteries, wherein the crosslinking agent having two or more amino groups is selected from at least one of the following: ethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 1,8-diaminooctane, 1,10-diaminodecane, 1,12-diaminododecane, isophorone diamine, 1,2-cyclohexanediamine, piperazine, 2,5-diaminopyridine, 4,4'-diaminodicyclohexylmethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 1,3-bis(aminoethyl)cyclohexane, phenylenediamine, m-phenylenediamine, and diaminodiphenylmethane.

[0023] Furthermore, the present invention provides a capsule for lithium-sulfur secondary batteries, wherein the particle size of the capsule for lithium-sulfur secondary batteries is from 0.1 μm to 5.0 μm.

[0024] Furthermore, the present invention provides a capsule for lithium-sulfur secondary batteries, wherein, based on the total weight of the capsule for lithium-sulfur secondary batteries, the content of the material required for forming and restoring the solid electrolyte interface is from 10% to 70% by weight.

[0025] Furthermore, the present invention provides a lithium-sulfur secondary battery, which includes a capsule for the lithium-sulfur secondary battery, a positive electrode, a negative electrode, a separator, and an electrolyte.

[0026] Furthermore, the present invention provides a lithium-sulfur secondary battery, which also includes materials separately required for forming and restoring the solid electrolyte interface.

[0027] Furthermore, the present invention provides a lithium-sulfur secondary battery, wherein the content of the lithium-sulfur secondary battery capsule is from 0.1% to 6.0% by weight, based on the total weight of the electrolyte.

[0028] Furthermore, the present invention provides a lithium-sulfur secondary battery, wherein, based on the total weight of the electrolyte, the total amount of materials contained in the capsule for forming and restoring the solid electrolyte interface, together with additionally contained materials required for forming and restoring the solid electrolyte interface, is 0.1% to 10% by weight.

[0029] Furthermore, the present invention provides a method for preparing capsules for lithium-sulfur secondary batteries, the method comprising the following steps: dissolving in water materials required for forming and restoring a solid electrolyte interface (SEI layer), a monomer capable of forming a hydrogel, and a crosslinking agent having two or more amino groups to prepare an aqueous phase portion; preparing a water-in-oil emulsion by mixing the aqueous phase portion with an oil phase portion containing an oil phase component and a surfactant; adding an epoxy compound having two or more epoxy groups to the emulsion to form a shell; forming a hydrogel core using free radical polymerization; and removing the oil phase component from the emulsion and drying it.

[0030] Furthermore, the present invention provides a method for preparing capsules for lithium-sulfur secondary batteries, wherein the hydrogel is selected from acrylate polymers, polysaccharides, polyamino acids, and combinations thereof, wherein the acrylate polymers include monomer-derived units having two or more acrylate groups containing ethylene glycol groups.

[0031] Furthermore, the present invention provides a method for preparing capsules for lithium-sulfur secondary batteries, wherein the surfactant has a hydrophilic / lipophilic balance (HLB) value of 1 to 6.

[0032] Beneficial effects

[0033] The lithium-sulfur secondary battery capsule according to the present invention comprises a core containing materials and hydrogel required for forming and restoring the solid electrolyte interface (SEI layer) and a shell made of a polymer surrounding the core, thereby maintaining the materials required for forming and restoring the solid electrolyte interface (SEI layer) at a constant level during battery operation, thus exhibiting the effect of maintaining the solid electrolyte interface (SEI layer) on the negative electrode for a long time.

[0034] Furthermore, by using the capsule for lithium-sulfur secondary batteries according to the present invention, the present invention exhibits the effect of suppressing sudden drops in battery efficiency and decreases in battery discharge capacity by preventing damage to the solid electrolyte interface (SEI layer) on the negative electrode and thus preventing lithium metal from being exposed to the electrolyte, even during the operation of the lithium-sulfur secondary battery. In other words, the present invention demonstrates the effect of improving the lifespan characteristics of lithium-sulfur secondary batteries. Attached Figure Description

[0035] Figure 1The graph shows the initial discharge capacity of the coin battery type lithium-sulfur secondary batteries according to Examples 2-1 and 2-2, and Comparative Examples 2-1 and 2-2.

[0036] Figure 2 The graph shows the fourth discharge capacity of the coin battery type lithium-sulfur secondary batteries according to Examples 2-1 and 2-2, and Comparative Examples 2-1 and 2-2.

[0037] Figure 3 The graph shows the life characteristics of the coin battery type lithium-sulfur secondary battery according to Example 2-1, Comparative Example 2-1, and Comparative Example 2-3.

[0038] Figure 4 The graph shows the life characteristics of the coin battery type lithium-sulfur secondary batteries according to Example 2-2, Comparative Examples 2-2 and 2-4.

[0039] Figure 5 The graph shows the thermogravimetric analysis of the capsule for lithium-sulfur secondary batteries according to Example 1.

[0040] Figure 6 The images are SEM images of the lithium-sulfur secondary battery capsule and pure LiNO3 according to Example 1. Detailed Implementation

[0041] The embodiments provided by the present invention can all be implemented through the following description. It will be understood that the following description describes preferred embodiments of the present invention, and the present invention is not necessarily limited thereto.

[0042] The present invention provides a capsule for lithium-sulfur secondary batteries, the capsule comprising a core containing materials and hydrogel required for forming and restoring the solid electrolyte interface (SEI layer) and a shell made of a polymer surrounding the core.

[0043] The material required for forming and restoring the solid electrolyte interface (SEI layer) can be at least one selected from the following: LiNO3, Be(NO3)2, NaNO3, Mg(NO3)2, Al(NO3)3, KNO3, Ca(NO3)2, Sc(NO3)3, Ti(NO3)4, VO(NO3)3, Cr(NO3)3, Mn(NO3)2, Fe(NO3)3, Fe(NO3)2, Co(NO3)2, Co(NO3)3, Ni(NO3)2, Cu(NO3)2, Zn(NO3)2, Ga(NO3)3, RbNO3, Sr(NO3)2, Y(NO3)2, etc. NO3)3, Zr(NO3)4, Pd(NO3)2, AgNO3, Cd(NO3)2, Sb(NO3)3, Xe(NO3)2, CsNO3, Ba(NO3)2, Hg2(NO3)2, Hg(NO3)2, Tl(NO3)3, TlNO3, Pb(NO3) 2. Bi(NO3)3, BiO(NO3), FrNO3, Ra(NO3)2, La(NO3)3, Ce(NO3)3, Ce(NO3)4, Nd(NO3)3, Eu(NO3)3, Gd(NO3)3 and Tb(NO3)3, preferably lithium nitrate (LiNO3).

[0044] Furthermore, the hydrogel can be selected from acrylate polymers, polysaccharides, polyamino acids, and combinations thereof. Preferably, the hydrogel is selected from acrylate polymers, hyaluronic acid, gelatin, and combinations thereof. The acrylate polymer can include monomer-derived units containing ethylene glycol groups and having two or more acrylate groups. Furthermore, the number-average molecular weight of the monomers containing ethylene glycol groups and having two or more acrylate groups can be 500 to 1000, preferably 550 to 800, and more preferably 575 to 700. If the number-average molecular weight of the monomers containing ethylene glycol groups and having two or more acrylate groups is lower than the above range, the solubility in water is too low, making it difficult for the monomers to exist in the aqueous phase, thus making it difficult to form a hydrogel in the capsule. If the number-average molecular weight of the monomers containing ethylene glycol groups and having two or more acrylate groups exceeds the above range, the number of acrylate groups per unit weight of the monomer decreases, thus accelerating dissolution and reducing the degree of crosslinking of the capsule. Therefore, it is preferable that the number-average molecular weight of the monomers containing ethylene glycol groups and having two or more acrylate groups meets the above range.

[0045] The hydrogel can be formed by free radical polymerization of monomers containing ethylene glycol groups and having two or more acrylate groups, and the hydrogel formed as described above can prevent the materials contained in the core required for the formation and restoration of the solid electrolyte interface from dissolving into the electrolyte all at once, and the hydrogel can swell in the electrolyte so that the materials required for the formation and restoration of the solid electrolyte interface can slowly dissolve into the electrolyte.

[0046] Furthermore, the polymer can be formed by crosslinking an epoxy compound having two or more epoxy groups with a crosslinking agent having two or more amino groups.

[0047] Specifically, the shell, made of a polymer surrounding the core, can be formed by crosslinking an epoxy compound having two or more epoxy groups on the surface of an aqueous portion containing a crosslinking agent having two or more amino groups. The shell formed as described above prevents the materials contained in the core required for the formation and restoration of the solid electrolyte interface from dissolving into the electrolyte all at once, and the shell is capable of swelling in the electrolyte so that the materials contained in the core required for the formation and restoration of the solid electrolyte interface can slowly dissolve into the electrolyte.

[0048] As a result, because the materials required for the formation and restoration of the solid electrolyte interface (SEI layer) slowly dissolve into the electrolyte, the solid electrolyte interface (SEI layer) on the negative electrode can be maintained for a long time.

[0049] Furthermore, the epoxy compound having two or more epoxy groups can be selected from at least one of the following: 1,4-butanediol diglycidyl ether (BDDE), ethylene glycol diglycidyl ether (EGDGE), 1,6-hexanediol diglycidyl ether, propylene glycol diglycidyl ether, poly(propylene glycol) diglycidyl ether, poly(butanediol) diglycidyl ether, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, polyglycerol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, 1,2-(bis(2,3-epoxypropoxy)ethane), pentaerythritol polyglycidyl ether, or sorbitol polyglycidyl ether, preferably 1,4-butanediol diglycidyl ether (BDDE).

[0050] Furthermore, the crosslinking agent having two or more amino groups can be at least one selected from the following: ethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 1,8-diaminooctane, 1,10-diaminodecane, 1,12-diaminododecane, isophorone diamine, 1,2-cyclohexanediamine, piperazine, 2,5-diaminopyridine, 4,4'-diaminodicyclohexylmethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 1,3-bis(aminoethyl)cyclohexane, phenylenediamine, m-phenylenediamine, and diaminodiphenylmethane, preferably dipropylenetriamine.

[0051] The particle size of the lithium-sulfur secondary battery capsule can be from 0.1 μm to 5.0 μm, preferably from 0.3 μm to 3.0 μm, and more preferably from 0.35 μm to 2.5 μm. If the particle size of the lithium-sulfur secondary battery capsule is smaller than the above range, it is difficult to fully dissolve the material contained in the core required for forming and restoring the solid electrolyte interface (SEI layer). If the particle size of the lithium-sulfur secondary battery capsule exceeds the above range, the material contained in the core required for forming and restoring the solid electrolyte interface (SEI layer) may be over-dissolved at once. Therefore, it is preferable that the particle size of the lithium-sulfur secondary battery capsule meets the above range.

[0052] In the capsule for lithium-sulfur secondary batteries, based on the total weight of the capsule, the content of the material required for forming and restoring the solid electrolyte interface can be from 10% to 70% by weight, preferably from 30% to 60% by weight, and more preferably from 40% to 50% by weight. If the content of the material required for forming and restoring the solid electrolyte interface is less than the above range, it is difficult to sufficiently dissolve the material contained in the core. If the content of the material required for forming and restoring the solid electrolyte interface exceeds the above range, the material contained in the core may be excessively dissolved at once because the shell cannot adequately cover the core. Therefore, it is preferable that the content of the material required for forming and restoring the solid electrolyte interface meets the above range.

[0053] Furthermore, the present invention provides a method for preparing the capsule for a lithium-sulfur secondary battery, the method comprising the following steps: dissolving in water a material required for forming and restoring a solid electrolyte interface (SEI layer), a monomer capable of forming a hydrogel, and a crosslinking agent having two or more amino groups to prepare an aqueous phase portion; preparing a water-in-oil emulsion by mixing the aqueous phase portion with an oil phase portion containing an oil phase component and a surfactant; adding an epoxy compound having two or more epoxy groups to the emulsion to form a shell; forming a hydrogel core using free radical polymerization; and removing the oil phase component from the emulsion and drying it.

[0054] The step of preparing the aqueous phase may also include a free radical initiator.

[0055] The free radical initiator can be a water-soluble free radical initiator, and the water-soluble free radical initiator can be a water-soluble azo free radical initiator with a 10-hour half-life temperature of 40°C to 70°C. Specifically, the water-soluble azo free radical initiator can be an azomididine initiator (V-057, V-50 (Wako Chemical)), an azonitrile initiator (VA-501 (Wako Chemical)), etc., but is not limited to these. In addition, as a water-soluble free radical initiator, ammonium persulfate, potassium persulfate, sodium persulfate, etc., can be used alone or in combination with reducing agents such as sodium bisulfate and sodium formaldehyde bisulfite, but is not limited to these.

[0056] In the step of forming the hydrogel core, the free radical initiator can form the hydrogel by free radical polymerization of monomers containing ethylene glycol groups and having two or more acrylate groups.

[0057] The material required for forming and restoring the solid electrolyte interface (SEI layer) can be at least one selected from the following: LiNO3, Be(NO3)2, NaNO3, Mg(NO3)2, Al(NO3)3, KNO3, Ca(NO3)2, Sc(NO3)3, Ti(NO3)4, VO(NO3)3, Cr(NO3)3, Mn(NO3)2, Fe(NO3)3, Fe(NO3)2, Co(NO3)2, Co(NO3)3, Ni(NO3)2, Cu(NO3)2, Zn(NO3)2, Ga(NO3)3, RbNO3, Sr(NO3)2, Y(NO3)2, etc. NO3)3, Zr(NO3)4, Pd(NO3)2, AgNO3, Cd(NO3)2, Sb(NO3)3, Xe(NO3)2, CsNO3, Ba(NO3)2, Hg2(NO3)2, Hg(NO3)2, Tl(NO3)3, TlNO3, Pb(NO3) 2. Bi(NO3)3, BiO(NO3), FrNO3, Ra(NO3)2, La(NO3)3, Ce(NO3)3, Ce(NO3)4, Nd(NO3)3, Eu(NO3)3, Gd(NO3)3 and Tb(NO3)3, preferably lithium nitrate (LiNO3).

[0058] Furthermore, the epoxy compound having two or more epoxy groups can be selected from at least one of the following: 1,4-butanediol diglycidyl ether (BDDE), ethylene glycol diglycidyl ether (EGDGE), 1,6-hexanediol diglycidyl ether, propylene glycol diglycidyl ether, poly(propylene glycol) diglycidyl ether, poly(butanediol) diglycidyl ether, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, polyglycerol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, 1,2-(bis(2,3-epoxypropoxy)ethane), pentaerythritol polyglycidyl ether, or sorbitol polyglycidyl ether, preferably 1,4-butanediol diglycidyl ether (BDDE).

[0059] Furthermore, the crosslinking agent having two or more amino groups can be at least one selected from the following: ethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 1,8-diaminooctane, 1,10-diaminodecane, 1,12-diaminododecane, isophorone diamine, 1,2-cyclohexanediamine, piperazine, 2,5-diaminopyridine, 4,4'-diaminodicyclohexylmethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 1,3-bis(aminoethyl)cyclohexane, phenylenediamine, m-phenylenediamine, and diaminodiphenylmethane, preferably dipropylenetriamine.

[0060] In addition, the oil phase component may be selected from at least one of the following: decane, hexane, pentane, cyclopentane, benzene, toluene, o-xylene, m-xylene, p-xylene, diethyl ether, methyl ethyl ketone, dichloromethane, tetrahydrofuran, mineral oil, paraffin oil and plant-derived oil, preferably paraffin oil.

[0061] Furthermore, the hydrophilic / lipophilic balance (HLB) value of the surfactant can be from 1 to 6, preferably from 3 to 5. Specific examples of surfactants may be, but are not limited to, at least one selected from the following: SPAN120, SPAN83, SPAN85, SPAN80, SPAN60, SPAN40, Brij52, Brij72, Brij93, Triton X35, and Triton X15.

[0062] Furthermore, the particle size of the lithium-sulfur secondary battery capsules prepared by the above method can be from 0.1 μm to 5.0 μm, preferably from 0.3 μm to 3.0 μm, and more preferably from 0.35 μm to 2.5 μm. If the particle size of the lithium-sulfur secondary battery capsules is smaller than the above range, it is difficult to fully dissolve the materials contained in the core required for forming and restoring the solid electrolyte interface (SEI layer). If the particle size of the lithium-sulfur secondary battery capsules exceeds the above range, the materials contained in the core required for forming and restoring the solid electrolyte interface (SEI layer) may be over-dissolved at once. Therefore, it is preferable that the particle size of the lithium-sulfur secondary battery capsules meets the above range.

[0063] Furthermore, in the lithium-sulfur secondary battery capsule prepared by the above-described method, based on the total weight of the lithium-sulfur secondary battery capsule, the content of the material required for forming and restoring the solid electrolyte interface (SEI layer) can be from 10% to 70% by weight, preferably from 30% to 60% by weight, and more preferably from 40% to 50% by weight. If the content of the material required for forming and restoring the SEI layer is less than the above range, it is difficult to sufficiently dissolve the material contained in the core. If the content of the material required for forming and restoring the SEI layer exceeds the above range, the material contained in the core may be excessively dissolved at once because the shell cannot adequately cover the core. Therefore, it is preferable that the content of the material required for forming and restoring the SEI layer meets the above range.

[0064] Furthermore, the present invention provides a lithium-sulfur secondary battery comprising the aforementioned lithium-sulfur secondary battery capsule, positive electrode, negative electrode, separator, and electrolyte, and further comprising materials required for forming and restoring the solid electrolyte interface.

[0065] Furthermore, based on the total weight of the electrolyte, the content of lithium-sulfur secondary battery capsules included in the lithium-sulfur secondary battery can be from 0.1% by weight to 6.0% by weight, preferably from 0.5% by weight to 3.0% by weight. If the content of lithium-sulfur secondary battery capsules is outside the above range, the discharge capacity, average voltage, and lifespan characteristics of the lithium-sulfur secondary battery may deteriorate, and it will be difficult to achieve the effect of improving battery performance. Therefore, it is preferable that the content of lithium-sulfur secondary battery capsules meets the above range.

[0066] Furthermore, based on the total weight of the electrolyte, the total amount of materials required for forming and restoring the solid electrolyte interface contained in the capsule for lithium-sulfur secondary batteries, along with any additional materials required for forming and restoring the solid electrolyte interface, can be from 0.1% to 10% by weight, preferably from 0.2% to 8% by weight, and more preferably from 0.5% to 7% by weight. If the total amount of materials required for forming and restoring the solid electrolyte interface is less than the above range, damage to the solid electrolyte interface cannot be sufficiently suppressed. If the total amount of materials required for forming and restoring the solid electrolyte interface exceeds the above range, it may act as a resistor in the battery, thereby reducing energy density and shortening lifespan. Therefore, it is preferable that the total amount of materials required for forming and restoring the solid electrolyte interface meets the above range.

[0067] Furthermore, the present invention can also provide a battery module comprising the lithium-sulfur secondary battery as a unit cell, and a battery pack comprising the battery module. The battery module or battery pack can be used as a power source for any one or more medium to large-sized devices, including: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or energy storage systems, etc.

[0068] Furthermore, the capsule for lithium-sulfur secondary batteries can be contained in any one or more of the positive electrode, negative electrode, separator, and electrolyte, preferably contained in the electrolyte.

[0069] Because the capsule for lithium-sulfur secondary batteries is contained in the electrolyte, the materials contained in the core required for the formation and restoration of the solid electrolyte interface (SEI layer) dissolve into the electrolyte during battery operation and remain at a constant concentration in the electrolyte, thus enabling the solid electrolyte interface (SEI layer) on the negative electrode to be maintained at a constant level.

[0070] The following description includes the positive electrode, negative electrode, and electrolyte used in the lithium-sulfur secondary battery according to the present invention.

[0071] positive electrode

[0072] The positive electrode used in this invention will be described below. After preparing a positive electrode composition containing a positive electrode active material, a conductive material, and a binder, a slurry prepared by diluting this composition in a predetermined solvent (dispersion medium) can be directly coated onto a positive electrode current collector and dried to form a positive electrode layer. Alternatively, after casting the slurry onto a separate carrier, a film layer obtained by peeling it from the carrier can be pressed onto the positive electrode current collector to manufacture the positive electrode layer. Furthermore, the positive electrode can be manufactured in various ways using methods well known to those skilled in the art.

[0073] The conductive material not only acts as a pathway for electrons to move from the positive electrode current collector to the positive electrode active material, thus imparting electronic conductivity, but also electrically connects the electrolyte and the positive electrode active material, thereby simultaneously acting as a pathway for lithium ions (Li+) to move to sulfur in the electrolyte and react with sulfur. Therefore, if the amount of conductive material is insufficient or if the conductive material does not function properly, the unreacted portion of sulfur in the electrode increases, ultimately leading to a decrease in capacity. Furthermore, high-rate discharge characteristics and charge / discharge cycle life are adversely affected. Therefore, it is necessary to add an appropriate amount of conductive material. Based on the total weight of the composition for the positive electrode, the amount of conductive material added is preferably from 0.01% to 30% by weight.

[0074] There are no particular restrictions on conductive materials, as long as they are conductive and do not cause chemical changes in the battery. Examples include: graphite; carbon black such as Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers such as carbon fiber and metal fiber; fluorinated carbon; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include: Chevron Chemical Company's acetylene black series, Denka black (Denka Singapore Private Limited), Gulf Oil Company's products, Ketjen black, Armak Company's EC series, Cabot Company's Vulcan XC-72, and Super P (Timcal Company's product).

[0075] An adhesive is used to ensure good adhesion of the positive electrode active material to the current collector. The adhesive should be readily soluble in a solvent and should not only form a conductive network between the positive electrode active material and the conductive material, but also possess suitable electrolyte permeation properties. The adhesive can be any adhesive known in the art, specifically, but not limited to, any one of the following: fluoropolymer adhesives, including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); rubber adhesives, including styrene-butadiene rubber, acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose adhesives, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyol adhesives; polyolefin adhesives, including polyethylene and polypropylene; polyimide adhesives; polyester adhesives; silane adhesives; and mixtures or copolymers of two or more of the above materials.

[0076] Based on the total weight of the cathode composition, the binder content can be, but is not limited to, 0.5% by weight to 30% by weight. If the binder resin content is less than 0.5% by weight, the physical properties of the cathode may deteriorate, and the active and conductive materials may detach. If the content exceeds 30% by weight, the ratio of active to conductive materials in the cathode is relatively reduced, which may reduce the battery capacity, and the contents may act as resistive elements, thereby reducing efficiency.

[0077] A positive electrode, comprising a positive electrode active material, a conductive material, and a binder, can be diluted in a predetermined solvent and coated onto a positive electrode current collector using conventional methods known in the art. First, the positive electrode current collector is prepared. The thickness of the positive electrode current collector is typically from 3 μm to 500 μm. There are no particular limitations on the positive electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery; for example, it can be made of stainless steel, aluminum, nickel, titanium, sintered carbon; or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The current collector can also enhance the adhesion of the positive electrode active material by forming fine irregularities on its surface, and can take various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0078] Next, a slurry obtained by diluting a positive electrode composition containing a positive electrode active material, a conductive material, and a binder in a solvent is coated onto the positive electrode current collector. The positive electrode composition containing the aforementioned positive electrode active material, conductive material, and binder can be mixed with a predetermined solvent to prepare the slurry. At this time, the solvent should be easy to dry; preferably, the solvent can dissolve the binder well, but keep the positive electrode active material and conductive material in a dispersed but not dissolved state. If the solvent dissolves the positive electrode active material, there is a tendency for sulfur to be submerged in the slurry due to its high specific gravity (D = 2.07). This leads to sulfur flowing into the current collector during coating and causing problems with the conductive network, resulting in battery operation issues. The solvent (dispersion medium) can be water or an organic solvent. The organic solvent can be at least one selected from: dimethylformamide, isopropanol, acetonitrile, methanol, ethanol, and tetrahydrofuran.

[0079] Subsequently, there are no particular limitations on the method for coating the cathode composition in a slurry state. For example, the coating can be prepared by blade coating, dip coating, gravure coating, stencil coating, spin coating, comma coating, rod coating, reverse roller coating, screen coating, and cap coating. Afterward, in the cathode composition that has undergone this coating process, a drying process is used to achieve the evaporation of the solvent (dispersion medium), the compaction of the coating film, and the adhesion between the coating film and the current collector. At this time, drying is performed according to conventional methods and is not particularly limited.

[0080] negative electrode

[0081] As a negative electrode, any negative electrode capable of intercalating and deintercalating lithium ions can be used. Examples include: metallic materials such as lithium metal and lithium alloys; and carbon materials such as low-crystallinity carbon and high-crystallinity carbon. Typical low-crystallinity carbons include soft carbon and hard carbon. Typical high-crystallinity carbons include high-temperature sintered carbons such as natural graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and coke derived from petroleum or coal tar pitch. Additionally, silicon-containing alloys, such as Li₄Ti₆O₅, are also suitable. 18 Oxides, etc., are also well-known negative electrodes.

[0082] In this case, the negative electrode may contain an adhesive. The adhesive may be a variety of adhesive polymers, such as polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, and styrene-butadiene rubber.

[0083] The negative electrode may optionally include a negative electrode current collector for supporting the negative electrode active layer containing the negative electrode active material and binder. Specifically, the negative electrode current collector may be selected from copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium, or silver, and an aluminum-cadmium alloy may be used as the alloy. In addition, sintered carbon, non-conductive polymers surface-treated with conductive materials, or conductive polymers may be used.

[0084] The adhesive is used to bond the negative electrode active material, to bind the active materials together, to bond the active material to the current collector, and to buffer the expansion and contraction of the active material. Specifically, the adhesive is the same as the positive electrode adhesive described above. Furthermore, the negative electrode can be lithium metal or a lithium alloy. A non-limiting example of the negative electrode is a lithium metal film, and it can be an alloy of lithium with at least one metal selected from the following: Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn.

[0085] electrolyte

[0086] The electrolyte contains a solvent and a lithium salt, and may also contain additives if necessary. The solvent can be used without particular restriction, as long as it is a conventional non-aqueous solvent that serves as a medium through which ions participating in the battery's electrochemical reactions can move. Examples of non-aqueous solvents include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, etc.

[0087] More specifically, examples of carbonate solvents can include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), or butyl carbonate (BC). Specifically, examples of ester solvents can include methyl acetate, ethyl acetate, n-propyl acetate, ethyl 1,1-dimethylacetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolactone, valerate, mevalonolactone, caprolactone, etc. Specifically, examples of ether solvents can include diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and polyethylene glycol dimethyl ether. In addition, examples of ketone solvents may include cyclohexanone, etc. Examples of alcohol solvents may include ethanol and isopropanol, etc. Examples of aprotic solvents may include: nitriles, such as acetonitrile; amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane (DOL); and sulfolane, etc. Non-aqueous organic solvents may be used alone or in combination of two or more. When used in combination of two or more, the mixing ratio may be appropriately adjusted according to the desired performance of the battery, and may be, for example, a solvent for mixing 1,3-dioxolane and dimethoxyethane in a 1:1 volume ratio.

[0088] Preferred implementation scheme

[0089] Preferred embodiments will be described below to aid in understanding the invention. However, the following embodiments are provided to aid in understanding the invention, but the invention is not limited thereto.

[0090] Example 1

[0091] Preparation of capsules for lithium-sulfur secondary batteries

[0092] 5.0 g of LiNO3 (required for battery operation), 1.2 g of dipropylenetriamine (a crosslinking agent with two or more amino groups), 0.7 g of poly(ethylene glycol) diacrylate (Mn = 575) (a monomer containing ethylene glycol groups and having two or more acrylate groups), and 0.007 g of V-50 (Wako Chemical) (a water-soluble free radical initiator) were dissolved in 6.7 mL of water to prepare an aqueous phase. The prepared aqueous phase was mixed with an oil phase containing 150 g of paraffin oil (an oil phase component) and 7.5 g of SPAN80 (a surfactant), and stirred at 8000 rpm to prepare a water-in-oil emulsion. Then, after heating the emulsion to 50°C, 3.8 g of 1,4-butanediol diglycidyl ether (an epoxy compound with two or more epoxy groups) was added, and an amine-epoxy crosslinking reaction was carried out on the surface of the emulsion particles for 3 hours to form a shell. Then, after purging with nitrogen and raising the temperature to 65°C, free radical polymerization was used to form a hydrogel core. After the hydrogel core was formed, the upper layer of paraffin oil was removed from the emulsion, the precipitated particles were recovered, and then washed three times with hexane to remove surfactants and residual paraffin oil. Subsequently, the particles were dried in air at room temperature and then vacuum dried at 80°C for 12 hours to prepare capsules for lithium-sulfur secondary batteries.

[0093] Manufacturing of coin batteries

[0094] Example 2-1

[0095] A slurry of positive electrode active material, prepared by mixing 90 wt% sulfur, 5 wt% carbon black, and 5 wt% polyethylene oxide with acetonitrile, was coated onto an aluminum current collector and dried to prepare the positive electrode. A 50 μm thick layer of lithium metal was used as the negative electrode. The prepared positive and negative electrodes were placed facing each other, with a 20 μm thick polyethylene separator inserted between them. Then, an electrolyte containing DOL / DME (1:1), 1 M LiN(CF3SO2)2 (LiTFSI), 3.5 wt% LiNO3, and 1 wt% of the prepared lithium-sulfur secondary battery capsule was filled to prepare a coin cell type lithium-sulfur secondary battery.

[0096] Example 2-2

[0097] Except that the electrolyte contains 5.0% by weight of LiNO3, a coin cell type lithium-sulfur secondary battery was manufactured in the same manner as in Example 2-1.

[0098] Comparative Example 2-1

[0099] Except for the absence of a lithium-sulfur secondary battery capsule, a coin battery-type lithium-sulfur secondary battery is manufactured in the same manner as in Example 2-1.

[0100] Comparative Example 2-2

[0101] Except for the absence of a lithium-sulfur secondary battery capsule, a coin battery-type lithium-sulfur secondary battery is manufactured in the same manner as in Examples 2-2.

[0102] Comparative Examples 2-3

[0103] Except that the content of the lithium-sulfur secondary battery capsule is 3% by weight, the coin battery type lithium-sulfur secondary battery is manufactured in the same manner as in Example 2-1.

[0104] Comparative Examples 2-4

[0105] Except that the content of the lithium-sulfur secondary battery capsule is 3% by weight, the coin battery type lithium-sulfur secondary battery is manufactured in the same manner as in Examples 2-2.

[0106] Experimental Example 1: Measurement of the initial discharge capacity of a coin cell type lithium-sulfur secondary battery

[0107] To evaluate the performance of lithium-sulfur secondary batteries depending on the presence or absence and content of the lithium-sulfur secondary battery capsule of the present invention, the capacity of lithium-sulfur secondary batteries prepared in Examples 2-1 and 2-2 and Comparative Examples 2-1 and 2-2 was measured from 1.8V to 2.5V at 25°C using a charge / discharge measuring device.

[0108] Specifically, the first discharge capacity (initial discharge capacity) is measured by charging / discharging at 0.1C / 0.1C. In addition, the fourth discharge capacity is measured by charging / discharging three times at the initial 0.1C / 0.1C and then charging / discharging at 0.2C / 0.2C.

[0109] As a result, Figure 1 and Figure 2 As shown in the figure, it was confirmed that the lithium-sulfur secondary batteries of Examples 2-1 and 2-2 had higher discharge capacity and higher average voltage compared with Comparative Examples 2-1 and 2-2.

[0110] Experimental Example 2: Evaluation of the lifespan characteristics of a coin cell type lithium-sulfur secondary battery

[0111] To evaluate the lifespan characteristics of lithium-sulfur secondary batteries depending on the presence or absence of the lithium-sulfur secondary battery capsule, the lithium-sulfur secondary batteries manufactured in Examples 2-1 to 2-2 and Comparative Examples 2-1 to 2-4 were charged / discharged three times at a charge / discharge current rate of 0.1C / 0.1C and three times at a charge / discharge current rate of 0.2C / 0.2C, and then at a charge / discharge current rate of 0.3C / 0.5C.

[0112] The results are shown in Figure 3 and Figure 4 In other words, it was confirmed that, compared with Comparative Examples 2-1 and 2-2 which did not have lithium-sulfur secondary battery capsules and Comparative Examples 2-3 and 2-4 which had a lithium-sulfur secondary battery capsule content of 3% by weight, the lithium-sulfur secondary batteries of Examples 2-1 and 2-2 with a lithium-sulfur secondary battery capsule content of 1% by weight according to the present invention have excellent life characteristics.

[0113] Experimental Example 3: Analysis of LiNO3 Content in Capsules for Lithium-Sulfur Secondary Batteries

[0114] The content of additive (LiNO3) in the lithium-sulfur secondary battery capsule prepared in Example 1 was measured using thermogravimetric analysis (TGA, TA, TGA Q500) at a gas flow rate of 60 ml / min and a heating rate of 5 °C / min.

[0115] As a result, Figure 5 As shown, it was confirmed that in the capsule for lithium-sulfur secondary batteries according to Example 1, the polymer decomposes from 220°C and completes decomposition at 400°C, so the polymer content in the capsule is 58% by weight and the LiNO3 content is 42% by weight.

[0116] Experimental Example 4: Analysis of the shape and size of capsules for lithium-sulfur secondary batteries

[0117] The shape and particle size of the lithium-sulfur secondary battery capsules and pure LiNO3 (additive) prepared in Example 1 were observed using a SEM (Hitachi, S-4800).

[0118] As a result, Figure 6 As shown, it was confirmed that, unlike pure LiNO3, the lithium-sulfur secondary battery capsules in Example 1 are spherical particles with a particle size of 0.35 to 2.5 μm.

[0119] Experimental Example 5: Evaluation of the dissolution characteristics of capsules for lithium-sulfur secondary batteries

[0120] To confirm the dissolution characteristics of the capsule according to the invention in the electrolyte, 1.0 g of the lithium-sulfur secondary battery capsule prepared in Example 1 was added to 50 g of solvent (DME, DOL), and then 1 g of the upper solvent was collected each time at room temperature over time. The Li content in the electrolyte was analyzed by ICP-OES (PerkinElmer, Optima 8300W) to calculate the degree of dissolution of the additive (LiNO3).

[0121] As shown in Table 1, it was confirmed that, compared to the addition of pure additive (LiNO3), in the case of the lithium-sulfur secondary battery capsule according to the present invention, LiNO3 slowly dissolves into the electrolyte. Specifically, unlike the case of adding pure additive (LiNO3), in the case of the lithium-sulfur secondary battery capsule according to Example 1, even after 21 days, only 60.5% and 39.8% of the additive (LiNO3) contained in the original capsule were dissolved.

[0122] Table 1:

[0123]

[0124] All simple modifications and variations of this invention fall within its scope, and the specific scope of protection of this invention will be apparent from the appended claims.

Claims

1. A capsule for lithium-sulfur secondary batteries, the capsule comprising: A core containing materials and hydrogels necessary for forming and restoring the solid electrolyte interface (SEI layer); and A shell, the shell being made of a polymer surrounding the core. in, The material required for forming and restoring the solid electrolyte interface (SEI layer) is selected from at least one of the following: LiNO3, Be(NO3)2, NaNO3, Mg(NO3)2, Al(NO3)3, KNO3, Ca(NO3)2, Sc(NO3)3, Ti(NO3)4, VO(NO3)3, Cr(NO3)3, Mn(NO3)2, Fe(NO3)3, Fe(NO3)2, Co(NO3)2, Co(NO3)3, Ni(NO3)2, Cu(NO3)2, Zn(NO3)2, Ga(NO3)3, RbNO3, Sr(N O3)2, Y(NO3)3, Zr(NO3)4, Pd(NO3)2, AgNO3, Cd(NO3)2, Sb(NO3)3, Xe(NO3)2, CsNO3, Ba(NO3)2, Hg2(NO3)2, Hg(NO3)2, Tl(NO3)3, Tl NO3, Pb(NO3)2, Bi(NO3)3, BiO(NO3), FrNO3, Ra(NO3)2, La(NO3)3, Ce(NO3)3, Ce(NO3)4, Nd(NO3)3, Eu(NO3)3, Gd(NO3)3 and Tb(NO3)3.

2. The capsule for lithium-sulfur secondary batteries according to claim 1, wherein, The hydrogel is selected from acrylate polymers, polysaccharides, polyamino acids, and combinations of the above materials. The acrylate polymers include monomer-derived units containing two or more acrylate groups, including ethylene glycol groups.

3. The capsule for lithium-sulfur secondary batteries according to claim 1, wherein, The polymer is formed by crosslinking an epoxy compound having two or more epoxy groups with a crosslinking agent having two or more amino groups.

4. The capsule for lithium-sulfur secondary batteries according to claim 3, wherein, The epoxy compound having two or more epoxy groups is selected from at least one of the following: 1,4-butanediol diglycidyl ether (BDDE), ethylene glycol diglycidyl ether (EGDGE), 1,6-hexanediol diglycidyl ether, propylene glycol diglycidyl ether, poly(propylene glycol) diglycidyl ether, poly(butanediol) diglycidyl ether, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, polyglycerol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, or sorbitol polyglycidyl ether.

5. The capsule for lithium-sulfur secondary batteries according to claim 3, wherein, The crosslinking agent having two or more amino groups is selected from at least one of the following: ethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 1,8-diaminooctane, 1,10-diaminodecane, 1,12-diaminododecane, isophorone diamine, 1,2-cyclohexanediamine, piperazine, 2,5-diaminopyridine, 4,4'-diaminodicyclohexylmethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 1,3-bis(aminoethyl)cyclohexane, phenylenediamine, m-phenylenediamine, and diaminodiphenylmethane.

6. The capsule for lithium-sulfur secondary batteries according to claim 1, wherein, The capsules for lithium-sulfur secondary batteries have a particle size of 0.1 μm to 5.0 μm.

7. The capsule for lithium-sulfur secondary batteries according to claim 1, wherein, Based on the total weight of the capsule for lithium-sulfur secondary batteries, the content of the material required to form and restore the solid electrolyte interface is from 10% to 70% by weight.

8. A lithium-sulfur secondary battery, the lithium-sulfur secondary battery comprising... Capsule for lithium-sulfur secondary batteries according to any one of claims 1 to 7; positive electrode; negative electrode; Diaphragm; and Electrolyte in, The lithium-sulfur secondary battery also includes materials required for forming and restoring the solid electrolyte interface.

9. The lithium-sulfur secondary battery according to claim 8, wherein, Based on the total weight of the electrolyte, the content of the capsule for lithium-sulfur secondary batteries is from 0.1% to 6.0% by weight.

10. The lithium-sulfur secondary battery according to claim 8, wherein, Based on the total weight of the electrolyte, the total amount of materials required for forming and restoring the solid electrolyte interface contained in the lithium-sulfur secondary battery capsule, together with additional materials required for forming and restoring the solid electrolyte interface, is 0.1% to 10% by weight.

11. A method for preparing a capsule for lithium-sulfur secondary batteries, the method comprising the following steps: The aqueous phase portion is prepared by dissolving in water the materials required for forming and restoring the solid electrolyte interface (SEI layer), the monomers capable of forming hydrogels, and the crosslinking agents having two or more amino groups. A water-in-oil emulsion is prepared by mixing the aqueous phase with an oil phase containing oil components and surfactants. An epoxy compound having two or more epoxy groups is added to the emulsion to form a shell; Free radical polymerization is used to form the hydrogel core; as well as The oil phase component is removed from the emulsion and then dried. The material required for forming and restoring the solid electrolyte interface (SEI layer) is selected from at least one of the following: LiNO3, Be(NO3)2, NaNO3, Mg(NO3)2, Al(NO3)3, KNO3, Ca(NO3)2, Sc(NO3)3, Ti(NO3)4, VO(NO3)3, Cr(NO3)3, Mn(NO3)2, Fe(NO3)3, Fe(NO3)2, Co(NO3)2, Co(NO3)3, Ni(NO3)2, Cu(NO3)2, Zn(NO3)2, Ga(NO3)3, RbNO3, Sr ... Zn(NO3)2, Sr(NO3)2, Cu(NO3)2, Zn(NO3)2, Zn(NO3)2, Sr(NO3)2, Cu(NO3)2, Cu(NO3)2, Zn(NO3)2, Zn(NO3)2, Sr(NO3)2, Cu(NO3)2, Cu(NO3)2, Cu(NO3)2, Cu( NO3)2, Y(NO3)3, Zr(NO3)4, Pd(NO3)2, AgNO3, Cd(NO3)2, Sb(NO3)3, Xe(NO3)2, CsNO3, Ba(NO3)2, Hg2(NO3)2, Hg(NO3)2, Tl(NO3)3, T lNO3, Pb(NO3)2, Bi(NO3)3, BiO(NO3), FrNO3, Ra(NO3)2, La(NO3)3, Ce(NO3)3, Ce(NO3)4, Nd(NO3)3, Eu(NO3)3, Gd(NO3)3 and Tb(NO3)3.

12. The method for preparing a capsule for a lithium-sulfur secondary battery according to claim 11, wherein, The hydrogel is selected from acrylate polymers, polysaccharides, polyamino acids, and combinations of the above materials. The acrylate polymers include monomer-derived units containing two or more acrylate groups, including ethylene glycol groups.

13. The method for preparing a capsule for a lithium-sulfur secondary battery according to claim 12, wherein, The surfactant has a hydrophilic / lipophilic balance (HLB) value of 1 to 6.

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