Lithium-ion batteries with improved safety

Abstract

According to one embodiment of the present invention, a lithium secondary battery is provided comprising a positive electrode having a positive electrode mixture layer containing a positive electrode active material and an inorganic solid electrolyte formed on one or both sides of a positive electrode current collector, a negative electrode having a negative electrode mixture layer containing a negative electrode active material formed on one or both sides of a negative electrode current collector, a separation membrane interposed between the positive electrode and the negative electrode, and a gel-type electrolyte, wherein the inorganic solid electrolyte is contained in an amount of 0.5% to 2% by weight based on the total weight of the positive electrode mixture layer and is uniformly distributed within the positive electrode mixture layer.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority rights based on Korean Patent Application No. 10-2023-0187350 dated December 20, 2023, and Korean Patent Application No. 10-2024-0184498 dated December 12, 2024, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery with improved safety, and more specifically, to a lithium secondary battery that includes an inorganic solid electrolyte in the positive electrode and a gel-type electrolyte. [Background technology]

[0003] Recently, the application areas of lithium-ion batteries have been rapidly expanding, not only to power supply for electronic devices such as electrical, electronic, telecommunications, and computers, but also to power storage and supply for large-area devices such as automobiles and energy storage devices. As a result, there is a growing demand for rechargeable batteries that are high capacity, high output, and highly stable.

[0004] Generally, lithium secondary batteries include a positive electrode, a negative electrode, a separation membrane between the positive and negative electrodes, an electrolyte, an organic solvent, etc. The positive electrode may generate oxygen due to its unstable structure when charged, and if oxygen is generated, there is a high risk of ignition. Therefore, research and development efforts are being made to improve the stability of lithium secondary batteries.

[0005] Separation membranes are used to ensure electrical insulation between the positive and negative electrodes, and thin membranes made of polyolefin are commonly used. However, polyolefin-based separation membranes can easily shrink in high-temperature environments, making it impossible to insulate between the positive and negative electrodes. If electrical insulation between the positive and negative electrodes becomes impossible, a short circuit can occur, potentially leading to ignition when it interacts with oxygen generated by the unstable positive electrode. In other words, if a short circuit occurs in a charged lithium-ion battery in a high-temperature environment, the lithium-ion battery may catch fire.

[0006] Therefore, in order to ensure the safety of lithium secondary batteries, a field that is expanding, all-solid-state batteries that use solid electrolytes are being widely researched. However, to date, they have not been able to achieve the same output, capacity, and lifespan performance as lithium-ion batteries that use liquid electrolytes, and it is known that they are far from being at a commercial level.

[0007] Therefore, the biggest topic of discussion in this industry is ultimately the realization of a battery with improved safety that will not ignite even at extremely high temperatures. However, in lithium-ion batteries that use liquid electrolytes, it is extremely difficult to prevent ignition caused by the volatilization of the liquid electrolyte and the generation of oxygen at the positive electrode at high temperatures. As a result, research is actively underway to reduce the explosive force of the battery and ensure that users have time to evacuate. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to improve the safety of lithium secondary batteries by delaying ignition and reducing explosive force. [Means for solving the problem]

[0009] According to one embodiment of the present invention, A positive electrode comprising a positive electrode mixture layer containing a positive electrode active material and an inorganic solid electrolyte formed on one or both sides of a positive electrode current collector, A negative electrode in which a negative electrode mixture layer containing a negative electrode active material is formed on one or both sides of a negative electrode current collector, A separation membrane is interposed between the positive electrode and the negative electrode, It contains a gel-type electrolyte, The inorganic solid electrolyte is included in an amount of 0.5% to 2% by weight based on the total weight of the positive electrode mixture layer, and is uniformly distributed within the positive electrode mixture layer, providing a lithium secondary battery.

[0010] Here, when the positive electrode mixture layer is divided in half based on its thickness, the inorganic solid electrolyte can be contained in the upper layer at a rate of 40% to 60% by weight and in the lower layer at a rate of 40% to 60% by weight, based on the total weight of the inorganic solid electrolyte. More specifically, when the upper layer and the lower layer are each divided in half based on their thickness, the inorganic solid electrolyte can be contained in each layer at a rate of 20% to 30% by weight, based on the total weight of the inorganic solid electrolyte.

[0011] Furthermore, because the inorganic solid electrolyte is distributed uniformly throughout, 50% to 90% of the total surface area of ​​the positive electrode active material can be covered by the inorganic solid electrolyte.

[0012] In this case, the inorganic solid electrolyte can be an oxide-based solid electrolyte having a NASICON structure, and more specifically, it can be an oxide-based solid electrolyte represented by the following chemical formula 1.

[0013] [Chemical formula 1] Li 1+x M' 2-x M x (PO4)3 In the aforementioned chemical formula 1, 0 <x<2であり、 M' is one or more elements selected from the group consisting of Ti, Zr, Ge, Sn, and Hf, and M is one or more elements selected from the group consisting of Cr, Al, Mg, Ga, Sc, Y, In, and La.

[0014] More specifically, the oxide-based solid electrolyte can be a lithium aluminum titanium phosphate (LATP) compound in which M' is Ti and M is Al.

[0015] The loading amount of the positive electrode mixture layer of the positive electrode is 400 mg / 25 cm 2 Above ~600mg / 25cm 2 It can be the following:

[0016] On the other hand, the lithium secondary battery may include a gel-type electrolyte, which comprises at least one polymerizable compound selected from the group consisting of i) a lithium salt, ii) a non-aqueous organic solvent, and iii) polymerizable monomers, oligomers, and copolymers having polymerizable unsaturated functional groups. At least a portion of the polymerizable unsaturated functional groups can be cured.

[0017] In this case, the polymerizable unsaturated functional group can be one or more selected from the group consisting of vinyl groups, epoxy groups, allyl groups, and (meth)acrylic groups.

[0018] The aforementioned non-aqueous organic solvent can be a carbonate-based organic solvent.

[0019] Furthermore, the gel-type electrolyte may further contain a polymerization initiator, which may be a photoinitiator or a thermal initiator, and may be included in an amount of 0.01 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the polymerizable compound.

[0020] Furthermore, the gel-type electrolyte may further contain a functional additive, which may be one or more selected from the group consisting of sultone compounds, sulfite compounds, sulfone compounds, sulfate compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and lithium salt compounds. [Brief explanation of the drawing]

[0021] [Figure 1] This is an SEM-EDS image of Experimental Example 1 according to Example 1. [Figure 2] This is an SEM-EDS image of Experimental Example 1 using Comparative Example 3. [Figure 3] This graph shows the results of Experimental Example 2 based on Example 1. [Figure 4] This graph shows the results of Experimental Example 2 based on Example 2. [Figure 5] This graph shows the results of Experimental Example 2 using Example 3. [Figure 6] This graph shows the results of Experimental Example 2 using Comparative Example 1. [Figure 7] This graph shows the results of Experimental Example 2 using Comparative Example 2. [Figure 8] This graph shows the results of Experimental Example 2 using Comparative Example 3. [Figure 9] This is a graph of the volume retention rate based on Experimental Example 3. [Modes for carrying out the invention]

[0022] Hereafter, terms and words used in this specification and in the claims shall not be construed to be limited to their ordinary or dictionary meanings, but rather to be construed in a sense and concept consistent with the technical idea of ​​the present invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0023] Unless otherwise defined, all terms used herein (including technical and scientific terms) should be used in a sense that is commonly understood by a person of ordinary skill in the art to which this invention pertains. Furthermore, terms defined in commonly used dictionaries should not be interpreted ideally or excessively unless explicitly defined otherwise.

[0024] The terms used herein are for illustrative purposes only and are not intended to limit the invention. In this specification, singular nouns include plural nouns unless otherwise specified. The terms “comprises” and / or “comprising” as used herein do not preclude the presence or addition of one or more other components beyond those mentioned.

[0025] In this specification, when a part includes a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0026] A lithium secondary battery according to one embodiment of the present invention is A positive electrode comprising a positive electrode mixture layer containing a positive electrode active material and an inorganic solid electrolyte formed on one or both sides of a positive electrode current collector, A negative electrode in which a negative electrode mixture layer containing a negative electrode active material is formed on one or both sides of a negative electrode current collector, A separation membrane is interposed between the positive electrode and the negative electrode, It contains a gel-type electrolyte, The inorganic solid electrolyte is contained in an amount of 0.5% to 2% by weight based on the total weight of the positive electrode mixture layer, and is characterized by being uniformly distributed within the positive electrode mixture layer.

[0027] positive electrode The positive electrode has a structure in which a positive electrode mixture layer containing a positive electrode active material and an inorganic solid electrolyte is formed on one or both sides of the positive electrode current collector.

[0028] Here, the positive electrode mixture layer can be formed by coating, drying, and rolling a positive electrode slurry containing a positive electrode active material and an inorganic solid electrolyte onto a positive electrode current collector. At this time, the positive electrode slurry may further contain electrode materials such as a conductive material and a binder, in addition to the aforementioned materials.

[0029] The positive electrode current collector only needs to have conductivity without inducing chemical changes in the battery, and is not particularly limited. For example, as the current collector, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.

[0030] The positive electrode current collector can have a thickness of 3 μm to 500 μm, and fine irregularities can also be formed on the surface of the positive electrode current collector to enhance the adhesive force to the positive electrode active material layer. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0031] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it can include lithium metal oxides containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni p Co q Mn r)O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of the independent elements respectively, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is one or more selected from Al, Mg, and Ti, X is one or more selected from F, S, and N, -0.5 ≤ a ≤ 0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1)), etc., and one or two or more of these compounds can be included.

[0032] Among these, in terms of enhancing the capacity characteristics and stability of the battery, the lithium metal oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co[[ID=I5]] 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 ] )O2 and Li(Ni 0.8 Mn 0.1 \ Co 0.1 )O2, etc.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8Co 0.15 Al 0.05 )O2 etc.), or lithium nickel manganese cobalt aluminum oxide (e.g., Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 ) can be O2, lithium iron phosphate (e.g., LiFePO4), etc., and one or more of these can be used as a mixture of two or more.

[0033] The positive electrode active material can be included in an amount of 60% to 98% by weight, preferably 80% to 98% by weight, and more preferably 90% to 98% by weight, based on the total weight of the positive electrode mixture layer.

[0034] The inorganic solid electrolyte mentioned above includes one or more lithium metal oxides or lithium metal phosphates selected from NASICON-type solid electrolytes, LISICON-type solid electrolytes, Garnet-type solid electrolytes, Perovskite-type solid electrolytes, and lithium phosphate nitride (LiPON)-type solid electrolytes. More specifically, examples include one or more selected from the group consisting of LAGP (lithium aluminum germanium phosphate) compounds, LLZO (lithium lanthanum zirconium oxide) compounds, LATP (lithium aluminum titanium phosphate) compounds, LLZTO (lithium lanthanum zirconium tantalum oxide) compounds, LLTO (lithium lanthanum titanium oxide) compounds, LSTP (lithium silicon titanium phosphate) compounds, and LGPO (lithium germanium phosphate) compounds.

[0035] More specifically, the inorganic solid electrolyte can be an oxide-based solid electrolyte having a NASICON structure, as a NASICON-type solid electrolyte among the above examples, and can be represented in more detail by the following chemical formula 1.

[0036] [Chemical formula 1] Li 1+xM' 2-x M x (PO4)3 In the aforementioned chemical formula 1, 0 <x<2であり、 M' is one or more elements selected from the group consisting of Ti, Zr, Ge, Sn, and Hf, and M is one or more elements selected from the group consisting of Cr, Al, Mg, Ga, Sc, Y, In, and La.

[0037] More specifically, these can be lithium aluminum titanium phosphate (LATP) compounds in which M' is Ti and M is Al.

[0038] Such inorganic solid electrolytes can be included in an amount of 0.5% to 2% by weight, more specifically, 0.5% to 1% by weight, based on the total weight of the positive electrode mixture layer.

[0039] If the content falls outside the above range and is too low, it is difficult to obtain the intended effect of reducing explosive force, and if the content is too high, it is undesirable as it increases the resistance of the lithium secondary battery.

[0040] Furthermore, the inorganic solid electrolyte can be uniformly distributed within the positive electrode mixture layer.

[0041] Here, "uniformly distributed" means that when the positive electrode mixture layer is divided into two or more layers based on the thickness direction, the difference in the content of the inorganic solid electrolyte contained in the two or more layers does not differ by more than 20% by weight when the total weight of the inorganic solid electrolyte is taken as 100% by weight.

[0042] In other words, when the positive electrode mixture layer is divided into two parts based on its thickness, the inorganic solid electrolyte content in the upper and lower layers does not deviate from a ratio of 40:60 to 60:40, when the total inorganic solid electrolyte content is considered to be 100% by weight.

[0043] Therefore, when the positive electrode mixture layer is divided in half along its thickness, the inorganic solid electrolyte can be contained in the upper layer at a rate of 40% to 60% by weight and the lower layer at a rate of 40% to 60% by weight, based on the total weight of the inorganic solid electrolyte.

[0044] More specifically, when the upper layer and the lower layer are each divided in half along the thickness direction, the inorganic solid electrolyte can be contained in each layer at a concentration of 20% to 30% by weight, based on the total weight of the inorganic solid electrolyte.

[0045] Here, dividing the positive electrode mixture layer in half based on its thickness does not mean that the positive electrode mixture layer is formed of two or more layers, but rather that the positive electrode mixture layer formed for the analysis is divided into an upper layer and a lower layer based on its thickness.

[0046] Furthermore, since the inorganic solid electrolyte is evenly distributed within the positive electrode mixture layer, it can cover 50% or more of the surface area of ​​the positive electrode active material, more specifically 50% to 90%, more specifically 50% to 80%, and most specifically 60% to 80%.

[0047] If the positive electrode active material surface is covered by less than 50% outside the aforementioned range, the safety intended by this application is not sufficiently ensured, which is undesirable.

[0048] Furthermore, the average diameter (D50) of the inorganic solid electrolyte particles can be 50 nanometers to 10 micrometers, more specifically 50 nanometers to 5 micrometers, and even more specifically 50 nanometers to 1 micrometer.

[0049] If the size is too small and falls outside the aforementioned range, interparticle aggregation may occur due to decreased dispersibility. Conversely, if it is too large, the inorganic solid electrolyte will form large pores, which is detrimental in terms of resistance. In other words, when the size is within the above range, the lithium-ion conductivity of the positive electrode is increased, resistance is reduced, and improved secondary battery performance can be achieved.

[0050] The average diameter (D50) described above refers to the particle size that corresponds to 50% of the cumulative volume in the particle size distribution curve. D50 can be measured, for example, using the laser diffraction method. This laser diffraction method can generally measure particle sizes ranging from submicron to several millimeters, and can yield highly reproducible and high-resolution results.

[0051] The conductive material is a component for further improving the conductivity of the positive electrode active material, and such a conductive material is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. Examples of such conductive materials that can be used include carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystalline structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive 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.

[0052] The conductive material may be included in an amount of 0.1% to 20% by weight, more specifically 0.5% to 10% by weight, or more specifically 0.5% to 5% by weight, based on the total weight of the positive electrode mixture layer.

[0053] The binder is a component that assists in bonding between the conductive material, the positive electrode active material, and the positive electrode current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0054] Typically, the binder can be included in an amount of 0.5% to 20% by weight, more specifically 0.5% to 10% by weight, or more specifically 0.5% to 5% by weight, based on the total weight of the positive electrode mixture layer.

[0055] Furthermore, the aforementioned other additives may include, for example, fillers as components that suppress expansion. The fillers are not particularly limited as long as they can suppress the expansion of the electrodes without inducing chemical changes in the battery, and for example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers; etc. can be used.

[0056] On the other hand, the loading amount of the positive electrode mixture layer in such a positive electrode is 400 mg / 25 cm 2 ~600mg / 25cm 2 It can be, for details, 450mg / 25cm 2 ~600mg / 25cm 2 It can be, and for more details, 450mg / 25cm 2 ~550mg / 25cm 2 It can be.

[0057] In other words, in the case of this invention, even when a high-loading positive electrode is used, high secondary battery safety can be ensured by the uniform distribution of the inorganic solid electrolyte.

[0058] negative electrode The negative electrode has a structure in which a negative electrode mixture layer is formed on one or both sides of the negative electrode current collector.

[0059] Here, the negative electrode mixture layer can be formed by coating, drying, and rolling a negative electrode slurry containing a negative electrode active material onto a negative electrode current collector. In this case, the negative electrode slurry may further contain electrode materials such as conductive materials and binders as described above, in addition to the negative electrode active material.

[0060] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treatments with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used.

[0061] The negative electrode current collector can typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the negative electrode current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0062] The negative electrode active material may include at least one selected from the group consisting of lithium metal, carbon materials capable of reversibly intercalating / deintercalating lithium ions, metals or alloys of these metals with lithium, metal composite oxides, materials capable of doping and dedoping lithium, and transition metal oxides.

[0063] As the carbon material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material generally used in lithium ion secondary batteries can be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or both of these can be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0064] As the metal or an alloy of these metals with lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn or an alloy of these metals with lithium can be used.

[0065] Examples of the metal composite oxide include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0≦x≦1), Li x WO2(0≦x≦1) and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) can be used.

[0066] As the substance capable of doping and undoping lithium, Si, SiO x(0 < x ≤ 2), an Si-Y alloy (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), Sn, SnO₂, Sn-Y (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), etc. can be mentioned, and also, at least one of these can be mixed with SiO₂ and used. As the element Y, it can be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0067] Examples of the transition metal oxide include a lithium-containing titanium composite oxide (LTO), a vanadium oxide, a lithium vanadium oxide, etc.

[0068] The negative electrode active material can be contained at 60% to 99% by weight, preferably 80% to 99% by weight, more preferably 90% to 98% by weight based on the total weight of the negative electrode active material layer.

[0069] When using the metal itself without forming a negative electrode binder layer on the negative electrode, it can be manufactured by a method such as physically bonding, rolling, or depositing the metal on the metal thin film itself or the negative electrode current collector. For the deposition method, an electric vapor deposition method or a chemical vapor deposition method (chemical vapor deposition) can be used for the metal.

[0070] For example, the metal bonded / rolled / deposited on the metal thin film itself or the negative electrode current collector can include one kind of metal selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu), and indium (In), or an alloy of two kinds of metals, etc.

[0071] Separation membrane The separation membrane can be any type commonly used as a separation membrane in lithium secondary batteries, and it is particularly preferable that it has low resistance to ion movement of the electrolyte and excellent moisture absorption capacity for the electrolyte.

[0072] For example, as a separation membrane, a porous polymer film containing polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used as a separation membrane.

[0073] Alternatively, it can be an SRS (Safety Reinforced Separator) separation membrane in which a coating layer containing a binder and inorganic particles is formed on one or both sides of a polymer substrate as described above.

[0074] The SRS separation membrane is as described above. Specifically, the polyolefin substrate of the SRS separation membrane is as described above, and the coating layer contains inorganic particles and a binder.

[0075] Here, the inorganic particles serve both to form micropores by enabling the creation of empty spaces between them and to act as a kind of spacer that can maintain its physical form. Furthermore, since the inorganic particles generally have the property of not changing their physical properties even at high temperatures of 200°C or higher, the formed organic / inorganic mixed layer will have excellent heat resistance.

[0076] The inorganic particles are not particularly limited as long as they are electrochemically stable. In other words, the inorganic particles usable in this invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the battery to which they are applied. In particular, when using inorganic particles with ion transfer capability, it is preferable that they have as high an ionic conductivity as possible, as this can improve performance by increasing the ionic conductivity within the electrochemical element. Furthermore, if the inorganic particles have a high density, it is not only difficult to disperse them during manufacturing, but there is also the problem of increased weight during the manufacturing of secondary batteries, so it is preferable that they have as low a density as possible. In addition, in the case of inorganic materials with a high dielectric constant, it is possible to improve the ionic conductivity of the electrolyte by increasing the degree of dissociation of electrolyte salts in the liquid electrolyte, such as lithium salts. Finally, inorganic particles with thermal conductivity are even more preferable because they have excellent heat absorption capacity, which suppresses the phenomenon of heat becoming locally concentrated and forming heat-generating points that lead to thermal runaway.

[0077] For the reasons stated above, the inorganic particles are preferably one or more selected from the group consisting of (a) high dielectric constant inorganic particles having a dielectric constant of 1 or more, 5 or more, preferably 10 or more, (b) piezoelectric inorganic particles, (c) thermally conductive inorganic particles, and (d) inorganic particles having lithium ion transport capability.

[0078] The aforementioned piezoelectric inorganic particles are insulators at normal pressure, but when a certain pressure is applied, they become electrically conductive due to a change in their internal structure. They not only exhibit high dielectric constant characteristics with a dielectric constant of 100 or more, but when stretched or compressed under a certain pressure, they generate electric charge, causing one side to become positively charged and the opposite side negatively charged, thus creating a potential difference between the two sides.

[0079] Examples of piezoelectric inorganic particles include BaTiO3, Pb(Zr,Ti)O3(PZT), and Pb 1-x La x Zr 1-y Ti yO3(PLZT), Pb(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), hafnia (H f O2), or mixtures thereof, among others, but not limited thereto.

[0080] The inorganic particles having lithium ion transfer ability refer to inorganic particles that contain lithium element but do not store lithium and have the function of moving lithium ions. The inorganic particles having lithium ion transfer ability can transfer and move lithium ions due to a kind of defect existing inside the particle structure, so it can prevent the decrease of lithium mobility and prevent the reduction of battery capacity.

[0081] Examples of the inorganic particles having lithium ion transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glass (glass) (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 S4, such as lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as Li3N (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass (glass) such as Li3PO4-Li2S-SiS2 (Lix Si y S z (where 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glasses such as LiI-Li2S-P2S5 x P y S z (where 0 < x < 3, 0 < y < 3, 0 < z < 7), or mixtures thereof, etc., but not limited thereto.

[0082] Further, examples of inorganic particles having a dielectric constant of 1 or more include SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC, or mixtures thereof, etc., but not limited thereto.

[0083] The heat-conductive inorganic particles are substances that provide low thermal resistance but do not provide electrical conductivity and have insulating properties. For example, they can be one or more selected from the group consisting of aluminum nitride (AlN), boron nitride (BN), alumina (Al2O3), silicon carbide (SiC), and beryllium oxide (BeO), but not limited thereto.

[0084] When the above-described high-dielectric-constant inorganic particles, piezoelectric inorganic particles, heat-conductive inorganic particles, and inorganic particles having lithium ion transfer ability are mixed, these enhancing effects can be doubled.

[0085] The size of the inorganic particles is not limited, but is preferably in the range of 0.001 μm to 10 μm for an appropriate porosity between the inorganic particles. If it is less than 0.001 μm, the dispersibility decreases and it is difficult to adjust the physical properties. If it exceeds 1 μm, the thickness increases and the mechanical physical properties decrease, and due to the overly large pore size, the sufficient role of the coating layer cannot be fulfilled, and the probability of internal short circuit during battery charge and discharge increases.

[0086] The content of the inorganic particles is not particularly limited, but is preferably in the range of 1% to 99% by weight per 100% by weight of the mixture of inorganic particles and binder, and more preferably 10% to 95% by weight. If it is less than 1% by weight, the binder content will be excessively high, which may reduce the pore size and porosity due to the decrease in the empty spaces formed between the inorganic particles, potentially reducing the mobility of lithium ions. Conversely, if it exceeds 99% by weight, the binder content will be too low, which will weaken the adhesive strength between the inorganic materials and reduce the mechanical properties of the coating layer.

[0087] On the other hand, the binder is not limited as long as it does not undergo a side reaction with the electrolyte, but it is preferable to use one with a glass transition temperature (Tg) as low as possible, preferably in the range of -200°C to 200°C. This is because it can improve the mechanical properties of the final insulating film.

[0088] Furthermore, while the binder does not necessarily need to have ion-conducting ability, it is even more preferable to use a polymer that does have ion-conducting ability.

[0089] Therefore, the binder is preferably one with a high dielectric constant, as the degree of salt dissociation in the electrolyte actually depends on the dielectric constant of the electrolyte solvent. The higher the dielectric constant of the polymer, the better the degree of salt dissociation in the electrolyte can be. The dielectric constant of the polymer can be 1 or higher, more specifically in the range of 1.0 to 100 (measurement frequency = 1 kHz), and is particularly preferably 10 or higher.

[0090] In addition to the functions described above, the binder may have the characteristic of gelling upon impregnation with liquid electrolyte, thereby exhibiting a high electrolyte impregnation rate (degree of swelling). In fact, if the binder is a polymer with excellent electrolyte impregnation rate, the electrolyte injected after battery assembly will penetrate the polymer, and the polymer holding the absorbed electrolyte will acquire electrolyte ion conductivity. Therefore, if possible, the solubility index should be 15 MPa. 1 / 2 ~45 MPa1 / 2 A polymer is preferred, and 15MPa 1 / 2 ~25MPa 1 / 2 and 30MPa 1 / 2 ~45 MPa 1 / 2 A range is even more preferable. Solubility index of 15 MPa 1 / 2 Less than and 45 MPa 1 / 2 If the value exceeds a certain level, it becomes difficult for the material to be impregnated (swelled) by a typical liquid electrolyte used in batteries.

[0091] Examples of such binders include poly(vinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. It can be one or more selected from the group consisting of propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, and polyvinyl alcohol.

[0092] The total thickness of the separation membrane can be 5 to 20 micrometers, more specifically 5 to 15 micrometers, and more specifically 6 to 13 micrometers. When the thickness of the separation membrane is within the above range, it is possible to effectively prevent short circuits between the positive and negative electrodes while minimizing the resistance of the lithium secondary battery. As a result, it is possible to prevent a decrease in the energy density of the lithium secondary battery and improve its lifespan characteristics.

[0093] Gel-type electrolytes The gel-type electrolyte comprises i) a lithium salt, ii) a non-aqueous organic solvent, and iii) comprising at least one polymerizable compound selected from the group consisting of polymerizable monomers, oligomers, and copolymers having polymerizable unsaturated functional groups, At least a portion of the polymerizable unsaturated functional groups can be cured.

[0094] Here, the lithium salt is used as a medium for transferring ions within a lithium secondary battery. The lithium salt is, for example, Li as a cation. + It contains, and as an anion, F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AlO2 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N -, (FSO2)2N - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - , C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2) 2CH - CF3(CF2)7SO3 - and SCN - At least one of the following groups is selected.

[0095] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 It may include a single substance or a mixture of two or more substances selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, lithium bis(fluorosulfonyl)imide (LiFSI (Lithium bis(fluorosulfonyl) imide, LiN(SO2F)2)), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI (lithium bis(pentafluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2)), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2)), but it is preferable to include Li(N(SO2CF3)2) in terms of superior stability.

[0096] In addition to these, lithium salts commonly used as electrolytes in lithium secondary batteries can be used without restriction.

[0097] The lithium salt can be appropriately modified within a range of normal use, but in order to obtain the effect of forming an optimal corrosion-preventive coating on the electrode surface, it can be included in the electrolyte at a concentration of 0.5 M to 3 M, more specifically, 1 M to 2.5 M, and more specifically, 1 M to 2 M. When the concentration of the lithium salt meets the above range, the effect of improving the cycle characteristics during high-temperature storage of the lithium secondary battery is sufficient, the viscosity of the electrolyte is appropriate, and the electrolyte impregnation is improved.

[0098] The aforementioned non-aqueous organic solvent is not limited as long as it minimizes decomposition by oxidation reactions within the voltage range of the lithium secondary battery's charge-discharge process and can exhibit its properties together with the additive. For example, carbonate-based organic solvents, ether-based organic solvents, or ester-based organic solvents can be used individually or in combination of two or more types, and in particular, carbonate-based organic solvents can be used.

[0099] Of the aforementioned organic solvents, the carbonate-based organic solvent may include at least one of cyclic carbonate-based organic solvents and linear carbonate-based organic solvents. Specifically, the cyclic carbonate-based organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate (FEC). Specifically, it may include a mixed solvent of ethylene carbonate having a high dielectric constant and propylene carbonate having a relatively lower melting point compared to ethylene carbonate.

[0100] Furthermore, the linear carbonate-based organic solvent is a solvent having low viscosity and low dielectric constant, and may contain at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and more specifically, it may contain dimethyl carbonate.

[0101] The ether-based organic solvent may be one selected from the group consisting of ethylene glycol dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more of these, but is not limited thereto.

[0102] The ester-based organic solvent mentioned above is at least one selected from the group consisting of linear ester-based organic solvents and cyclic ester-based organic solvents.

[0103] The linear ester-based organic solvent can typically be any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, or a mixture of two or more of these, but is not limited to these examples.

[0104] The cyclic ester organic solvent may, but is not limited to, one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more of these.

[0105] Among the ester-based solvents, cyclic carbonate compounds are preferred because they are high-viscosity organic solvents with high dielectric constants and effectively dissociate lithium salts in the electrolyte. Furthermore, by mixing such cyclic carbonate compounds with low-viscosity, low-dielectric-constant linear carbonate compounds and linear ester compounds such as dimethyl carbonate and diethyl carbonate in appropriate ratios, a gel-type electrolyte with high electrical conductivity can be produced, and this method is even more preferred.

[0106] On the other hand, the polymerizable monomer, oligomer, or copolymer polymer is a substance having a polymerizable unsaturated functional group, for example, a polymerizable unsaturated functional group selected from the group consisting of vinyl groups, epoxy groups, allyl groups, and (meth)acrylic groups, and is a compound that can be transformed into a gel type by polymerization or crosslinking, and is not particularly limited as long as it is used as a polymerizable monomer, oligomer, or polymer in the production of ordinary gel-type electrolytes.

[0107] More specifically, the polymerizable monomer or oligomer is, as non-limiting examples, tetraethylene glycol diacrylate, polyethylene glycol diacrylate (molecular weight 50-20,000), 1,4-butanediol diacrylate, 1,6-hexandiol diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, and pentaerythritol ethoxylate tetraacrylate. (ethoxylate tetraacrylate), dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, polyethylene glycol diglycidyl ether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane (1,2,7,Examples include, but are not limited to, 8-diepoxyoctane, 4-vinylcyclohexenedioxide, butyl glycidyl ether, diglycidyl 1,2-cyclohexanedicarboxylate, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and glycidyl methacrylate. These compounds can be used individually or in combination of two or more.

[0108] Furthermore, typical examples of the copolymer include at least one copolymer selected from the group consisting of allyl 1,1,2,2-tetrafluoroethyl ether (TFE)-(2,2,2-trifluoroethyl acrylate) polymer, TFE-vinyl acetate, TFE-(2-vinyl-1,3-dioxolane) polymer, TFE-vinyl methacrylate polymer, TFE-acrylonitrile polymer, TFE-vinyl acrylate polymer, TFE-co-methyl acrylate polymer, TFE-methyl methacrylate (MMA) polymer, and TFE-2,2,2-trifluoroethyl acrylate (FA) polymer.

[0109] The polymer formed through the curing of the aforementioned substance may be included in an amount of 0.01% to 10% by weight based on the total weight of the gel-type electrolyte. If the polymer content exceeds 10% by weight, the amount of polymerizable substance increases during the production of the gel-type electrolyte, resulting in the disadvantage of obtaining a gel with high resistance because gelation occurs excessively quickly or is formed excessively densely. Conversely, if the content is less than 0.01% by weight, the effect of gelation is not obtained, which is undesirable.

[0110] On the other hand, the gel-type electrolyte of the present invention may further contain a polymerization initiator for polymerization of the polymerizable unsaturated functional group, and conventional thermal or photoinitiators known in the art may be used. For example, the initiator may be decomposed by heat to form radicals, which can then react with polymerizable monomers, oligomers, or polymers by free radical polymerization to form a gel-type electrolyte.

[0111] More specifically, examples of polymerization initiators include benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide. Examples include, but are not limited to, organic peroxides such as peroxides, hydroperoxides, and one or more azo compounds selected from the group consisting of 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN; 2,2'-Azobis(iso-butyronitrile)), and 2,2'-azobisdimethyl-valeronitrile (AMVN; 2,2'-Azobisdimethyl-Valeronitrile).

[0112] The polymerization initiator can be decomposed in a lithium secondary battery by heat, for example, heat between 30°C and 100°C, or by decomposition at room temperature (5°C to 30°C) to form radicals, and the polymerizable monomer, oligomer, or polymerizable unsaturated functional groups of the polymer can react by free radical polymerization to form a gel-type electrolyte.

[0113] The polymerization initiator may be included in an amount of 0.01 to 20 parts by weight, more specifically 0.01 to 1 part by weight, based on 100 parts by weight of the polymerizable compound.

[0114] When the polymerization initiator is in the range of 0.01 to 20 parts by weight, the gel conversion rate can be increased to ensure gel-type electrolyte properties, pre-gelling reactions can be prevented, and the electrolyte wetting properties to the electrode can also be improved.

[0115] Furthermore, the gel-type electrolyte may further contain a functional additive, which may be included to prevent the induction of negative electrode collapse in high-power environments, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and swelling improvement effects during high-temperature storage.

[0116] Specifically, the functional additive may include, as a representative example, one or more functional additives selected from the group consisting of sultone compounds, sulfite compounds, sulfone compounds, sulfate compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and lithium salt compounds.

[0117] The sultone compound mentioned above includes at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone, and can be included in an amount of 0.3% to 5% by weight, specifically 1% to 5% by weight, based on the total weight of the gel-type electrolyte. If the content of the sultone compound in the gel-type electrolyte exceeds 5% by weight, an excessively thick film may be formed on the electrode surface, potentially causing increased resistance and output degradation. Furthermore, the resistance due to an excessive amount of additive may also increase, potentially degrading the output characteristics.

[0118] The aforementioned sulfite-based compounds include one or more compounds selected from the group consisting of ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethylpropylene sulfite, 4,5-diethylpropylene sulfite, 4,6-dimethylpropylene sulfite, 4,6-diethylpropylene sulfite, and 1,3-butylene glycol sulfite, and can be included in an amount of 3% by weight or less based on the total weight of the gel-type electrolyte.

[0119] The sulfone compound mentioned above includes one or more compounds selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone, and can be included in an amount of 3% by weight or less based on the total weight of the gel-type electrolyte.

[0120] The aforementioned sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and can be included in an amount of 3% by weight or less based on the total weight of the gel-type electrolyte.

[0121] Furthermore, the halogen-substituted carbonate compound may be fluoroethylene carbonate (FEC), and may be included in an amount of 5% by weight or less based on the total weight of the gel-type electrolyte. If the content of the halogen-substituted carbonate compound in the gel-type electrolyte exceeds 5% by weight, the cell swelling performance may deteriorate.

[0122] Furthermore, the nitrile compounds include at least one compound selected from the group consisting of succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0123] The cyclic carbonate compound may be vinylene carbonate (VC) or vinylethylene carbonate, and may be included in an amount of 3% by weight or less based on the total weight of the gel-type electrolyte. If the content of the cyclic carbonate compound in the gel-type electrolyte exceeds 3% by weight, the cell swelling suppression performance may deteriorate.

[0124] The phosphate compound mentioned above includes one or more compounds selected from the group consisting of lithium difluoro(bisoxalato) phosphate, lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphate, and can be included in an amount of 3% by weight or less based on the total weight of the gel-type electrolyte.

[0125] The borate compound mentioned above is lithium oxalyl difluoroborate, and can be included in an amount of 3% by weight or less based on the total weight of the gel-type electrolyte.

[0126] The lithium salt compound is a compound different from the lithium salt contained in the gel-type electrolyte, and includes one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2) and LiBF4), and can be included in an amount of 3% by weight or less based on the total weight of the gel-type electrolyte.

[0127] The functional additives may be a mixture of two or more types, and may be included in an amount of 20% by weight or less, specifically 0.1% to 10% by weight, based on the total weight of the gel-type electrolyte. If the content of the functional additives exceeds 20% by weight, excessive side reactions may occur in the gel-type electrolyte during battery charging and discharging. In particular, they may not decompose sufficiently at high temperatures and may remain unreacted or precipitated in the gel-type electrolyte at room temperature. This may result in side reactions that reduce the lifespan or resistance characteristics of the lithium secondary battery.

[0128] In the following, an example will be described to demonstrate that the lithium secondary battery of one embodiment of the present invention exhibits improved effects.

[0129] <Example 1> Manufacturing of positive electrodes A 15-micrometer thick aluminum (Al) metal thin film is prepared as the positive electrode current collector, and Li(Ni) is used as the positive electrode active material on one surface of the aluminum metal thin film. 0.8 Mn 0.1 Co 0.1 )O2: As an inorganic solid electrolyte, Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP): Carbon nanotubes as conductive material; PVDF as binder; are dispersed in NMP solvent in a weight ratio of 95:1:1:3 to produce a cathode slurry, which is then coated to a thickness of 60 micrometers, dried, and rolled to form a cathode (loading amount 450 mg / 25 cm²). 2 They manufactured ).

[0130] Manufacturing of negative electrodes Next, a 20-micrometer thick copper (Cu) metal thin film was prepared as the negative electrode current collector. A negative electrode slurry was produced by dispersing graphite as the negative electrode active material, carbon black as the conductive material, carboxymethylcellulose (CMC) as the thickening agent, and styrene-butadiene rubber (SBR) as the binder in water in a weight ratio of 95:1:1.5:2.5 on one side of the copper metal thin film. This slurry was then coated to a thickness of 75 micrometers, dried, and rolled to produce the negative electrode.

[0131] Manufacturing of electrode assemblies An electrode assembly was manufactured by placing a separation membrane (thickness: 15 micrometers) made of polyolefin material between the positive electrode and the negative electrode.

[0132] Manufacturing of lithium-ion batteries LiPF6 was dissolved in a non-aqueous organic solvent having a composition of ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 (volume ratio) to a concentration of 1.0 M. Trimethylolpropane triacrylate was added as a polymerizable compound at a concentration of 4% by weight relative to the total weight, and azobisisobutyronitrile (AIBN, V59) was added as a polymerization initiator at a concentration of 0.02 parts by weight relative to 100 parts by weight of the polymerizable compound to prepare a gel polymer electrolyte composition.

[0133] The manufactured electrode assembly was inserted into a battery case, and the manufactured gel polymer electrolyte composition was poured in to produce a secondary battery. Subsequently, after the battery case underwent electrolyte wetting at room temperature for two days, the gel polymer electrolyte composition was left in a 60°C chamber for five hours to polymerize, thereby producing a lithium secondary battery.

[0134] <Example 2> A lithium secondary battery was manufactured in the same manner as in Example 1, except that the polymerizable compound in the gel polymer electrolyte composition of Example 1 was added in an amount of 10% by weight relative to the total weight.

[0135] <Example 3> In the positive electrode of Example 1 described above, Li(Ni) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 )O2: As an inorganic solid electrolyte, Li 1.4 Al 0.4 Ti 1.6 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of carbon nanotubes as the conductive material and PVDF as the binder was 94:2:1:3.

[0136] <Comparative Example 1> In the positive electrode of Example 1 described above, Li(Ni) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of O2, carbon nanotubes as conductive material, and PVDF as binder was 96:1:3, and instead of a gel polymer electrolyte composition, a liquid electrolyte was injected by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent having a composition of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) = 30:70 (volume ratio) and only the impregnation process was carried out.

[0137] <Comparative Example 2> A lithium secondary battery was manufactured in the same manner as in Example 1, except that a positive electrode similar to that in Example 1 was used, and instead of the gel polymer electrolyte composition of Example 1, a liquid electrolyte was injected by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent having a composition of ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 (volume ratio), and only the impregnation process was carried out.

[0138] <Comparative Example 3> In the positive electrode of Example 1 described above, Li(Ni) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1A lithium secondary battery was manufactured in the same manner as in Example 1 above, except that the weight ratio of O2 (carbon nanotubes as conductive material) and PVDF (PVDF as binder) was set to 96:1:3.

[0139] <Comparative Example 4> In the positive electrode of Example 1 described above, Li(Ni) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 )O2: As an inorganic solid electrolyte, Li 1.4 Al 0.4 Ti 1.6 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of carbon nanotubes as the conductive material and PVDF as the binder was set to 93:3:1:3.

[0140] <Experimental Example 1> The positive electrodes manufactured in Example 1 and Comparative Example 3 were cut in the thickness direction, penetrating the center, and SEM images of the cross-sections were taken, followed by EDS analysis.

[0141] At this time, the analysis was carried out by dividing the material into upper and lower layers in the thickness direction, and the results are shown in Figures 1 and 2 and Table 1 below.

[0142] [Table 1]

[0143] Referring to Figures 1 and 2 below, and Table 1 above, it can be confirmed that the inorganic solid electrolyte is distributed in very similar amounts in both the upper and lower layers of the positive electrode mixture layer according to the present invention.

[0144] <Experimental Example 2> The lithium secondary batteries of Examples 1-3 and Comparative Examples 1-3 were fully charged at 25°C with a constant current of 0.33C until the voltage reached 4.2V. A heating pad made of mica was attached to these lithium secondary batteries, and the temperature was raised at 300W / min for 1 minute. Then, an external ignition environment was created by maintaining 300W, and the voltage, pressure, and temperature of the lithium secondary batteries were measured over time while maintaining these conditions, as shown in Figures 3-8 below.

[0145] The difference between the maximum pressure measured at the time of the lithium secondary battery explosion and the initially set atmospheric pressure was defined as the explosion pressure, and the time from the point when the pressure began to change until the maximum pressure was defined as the reaction time.

[0146] A relatively low explosion pressure and a long reaction time indicate a weaker explosive force in the lithium-ion battery. The resulting values ​​are shown in Table 2 below.

[0147] [Table 2]

[0148] Referring to Figures 3 to 8 below and Table 2 above, the lithium secondary battery in the example using LATP as the positive electrode and a gel-type electrolyte according to the present invention showed the most advantageous values ​​in terms of explosion pressure and reaction time, with an explosion pressure of 1.29 bar and a reaction time of 10.1 s. In the case of Comparative Example 1, the explosion pressure was 1.46 bar and the reaction time was 8.3 s. It can be seen that Example 1 showed an 11.6% decrease in explosion pressure and a 21.7% increase in reaction time compared to Comparative Example 1. When converted to explosion pressure per reaction time, it can be confirmed that there is a difference of 27.4%, with Example 1 at 0.128 bar / sec and Comparative Example 1 at 0.176 bar / sec.

[0149] Similarly, it can be confirmed that Comparative Example 2, which does not use a gel-type electrolyte, and Comparative Example 3, which does not use LATP as the positive electrode, also show results similar to those of Comparative Example 1.

[0150] <Experimental Example 3> For the lithium secondary batteries of Example 1 and Comparative Examples 1-3 described above, CC-CV charging was performed at 25°C, 0.33C, and 4.2V, followed by CC discharge at 0.33C. This process was repeated 300 times, and the discharge capacity retention rate over 300 cycles was determined by setting the discharge capacity per cycle to 100%. The results are shown in Table 3 and Figure 9 below.

[0151] Furthermore, the DC resistance of the lithium secondary batteries of Examples 1-3 and Comparative Examples 1-4 was measured using the Hybrid Pulse Power Characterization (HPPC) method, and the results are shown in Table 3 below.

[0152] The DC resistance measurement was performed by first confirming the capacity of the lithium secondary battery by CC / CV charging under 0.33C, 4.2V, and 0.05C cut-off conditions, and then CC discharging under 0.33C and 2.5V cut-off conditions. After that, the lithium secondary battery, which had been fully charged under the same charging conditions, was discharged to about 50% of its capacity to set the State of Charge (SOC) to 50, and then the DC resistance was measured at that SOC through subsequent discharge at 2.5C for 10 seconds.

[0153] [Table 3]

[0154] Referring to Table 3 above, it can be seen that the resistance of Example 1 and Comparative Example 2, in which LATP was added, is relatively low. In this case, it can be seen that the resistance of the lithium secondary battery decreases by about 2% to 3% compared to when LATP is not added. However, from Example 1 and Comparative Example 4, it can be seen that when the LATP content is 3% by weight, the resistance actually increases.

[0155] On the other hand, since the capacity retention rates are similar, it can be seen that there is no performance degradation of other lithium secondary batteries due to this invention.

[0156] Anyone with ordinary skill in the art to which this invention belongs can make various applications and modifications within the scope of this invention based on the above. [Industrial applicability]

[0157] In the lithium secondary battery according to the present invention, the inorganic solid electrolyte is not only uniformly distributed within the positive electrode, but is also included in a predetermined content or higher, covering 50% or more of the surface of the positive electrode active material, and together with the electrolyte gels, thereby delaying the ignition of the lithium secondary battery, lowering the explosion pressure, increasing the reaction time, and reducing the explosive force, thus exhibiting the effect of improving the safety of the lithium secondary battery.

[0158] Furthermore, the lithium secondary battery of the present invention allows the inorganic solid electrolyte to be uniformly distributed in the thickness direction even under high loading, which is effective in ensuring the safety of the lithium secondary battery even under high loading.

Claims

1. A positive electrode comprising a positive electrode mixture layer containing a positive electrode active material and an inorganic solid electrolyte formed on one or both sides of a positive electrode current collector, A negative electrode in which a negative electrode mixture layer containing a negative electrode active material is formed on one or both sides of a negative electrode current collector, A separation membrane is interposed between the positive electrode and the negative electrode, It contains a gel-type electrolyte, A lithium secondary battery wherein the inorganic solid electrolyte is contained in an amount of 0.5% to 2% by weight based on the total weight of the positive electrode mixture layer and is uniformly distributed within the positive electrode mixture layer.

2. The lithium secondary battery according to claim 1, wherein when the positive electrode mixture layer is divided in half with respect to its thickness, the inorganic solid electrolyte is contained in the upper layer at a rate of 40% to 60% by weight and in the lower layer at a rate of 40% to 60% by weight, based on the total weight of the inorganic solid electrolyte.

3. The lithium secondary battery according to claim 2, wherein when the upper layer and the lower layer are each divided in half with respect to the thickness direction, the inorganic solid electrolyte is contained in each layer in an amount of 20% by weight or more and 30% by weight or less, based on the total weight of the inorganic solid electrolyte.

4. The lithium secondary battery according to claim 1, wherein 50% to 90% of the total surface area of ​​the positive electrode active material is covered by the inorganic solid electrolyte.

5. The lithium secondary battery according to claim 1, wherein the inorganic solid electrolyte is an oxide-based solid electrolyte having a NASICON structure.

6. The lithium secondary battery according to claim 1, wherein the inorganic solid electrolyte is an oxide-based solid electrolyte represented by the following chemical formula 1: [Chemical formula 1] Li １＋ｘ M' ２－ｘ M ｘ (PO ４ ) ３ In the aforementioned chemical formula 1, 0 < x < 2, M' is one or more elements selected from the group consisting of Ti, Zr, Ge, Sn, and Hf, and M is one or more elements selected from the group consisting of Cr, Al, Mg, Ga, Sc, Y, In, and La.

7. The lithium secondary battery according to claim 6, wherein the oxide-based solid electrolyte is a lithium aluminum titanium phosphate (LATP) compound in which M' is Ti and M is Al.

8. The loading amount of the positive electrode mixture layer is 400 mg / 25 cm ２ Above 600 mg / 25 cm ２ The lithium secondary battery according to claim 1, which is as follows:

9. The aforementioned gel-type electrolyte is i) Lithium salts, ii) Non-aqueous organic solvents, and iii) comprising at least one polymerizable compound selected from the group consisting of polymerizable monomers, oligomers, and copolymers having polymerizable unsaturated functional groups, A lithium secondary battery according to any one of claims 1 to 8, wherein at least a portion of the polymerizable unsaturated functional groups are cured.

10. The lithium secondary battery according to claim 9, wherein the polymerizable unsaturated functional group is one or more selected from the group consisting of vinyl groups, epoxy groups, allyl groups, and (meth)acrylic groups.

11. The lithium secondary battery according to claim 9, wherein the non-aqueous organic solvent is a carbonate-based organic solvent.

12. The lithium secondary battery according to claim 9, wherein the gel-type electrolyte further comprises a polymerization initiator, the polymerization initiator being a photoinitiator or a thermal initiator.

13. The lithium secondary battery according to claim 12, wherein the polymerization initiator is contained in an amount of 0.01 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the polymerizable compound.

14. The lithium secondary battery according to claim 9, wherein the gel-type electrolyte further comprises a functional additive, the functional additive being one or more selected from the group consisting of sultone compounds, sulfite compounds, sulfone compounds, sulfate compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and lithium salt compounds.

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