Lithium secondary battery having improved safety

Abstract

According to an embodiment of the present invention, provided is a lithium secondary battery comprising: a positive electrode in which a positive electrode mixture layer including a positive electrode active material and an inorganic solid electrolyte is formed on one surface or both surfaces of a positive electrode current collector; a negative electrode in which a negative electrode mixture layer including a Si-based active material as a negative electrode active material is formed on one surface or both surfaces of a negative electrode current collector; a separator interposed between the positive electrode and the negative electrode; and a lithium non-aqueous electrolyte including a lithium salt and a non-aqueous organic solvent, wherein the inorganic solid electrolyte is included in an amount of 1.5 wt% to 5 wt% based on the total weight of the positive electrode mixture layer, and is uniformly distributed in the positive electrode mixture layer.

Description

Lithium secondary batteries with improved safety

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0187352, filed December 20, 2023, and Korean Patent Application No. 10-2024-0184497, filed December 12, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a lithium secondary battery with improved safety, and more particularly, to a lithium secondary battery including an inorganic solid electrolyte in the positive electrode and a lithium non-aqueous electrolyte.

[0004] Recently, as the application areas of lithium secondary batteries have rapidly expanded to include not only power supply for electronic devices such as electric, electronic, communication, and computer devices, but also power storage for large-area devices such as automobiles and power storage devices, the demand for high-capacity, high-output, and high-stability secondary batteries is increasing.

[0005] Typically, lithium secondary batteries include a cathode, an anode, a separator interposed between the anode and cathode, an electrolyte, an organic solvent, and other components. The cathode, due to its unstable structure when charged, can generate oxygen. This generation of oxygen poses a significant risk of ignition, and research and development are being conducted to improve the safety of lithium secondary batteries.

[0006] Separators are used to ensure electrical insulation between the positive and negative electrodes, and thin films made of polyolefin are commonly used. However, polyolefin-based separators can easily shrink in high-temperature environments, failing to provide insulation between the positive and negative electrodes. If electrical insulation between the positive and negative electrodes is lost, a short circuit can occur, and this can react with oxygen generated by the unstable positive electrode, potentially leading to ignition. In other words, if a short circuit occurs in a charged lithium secondary battery in a high-temperature environment, the battery may catch fire.

[0007] Accordingly, all-solid-state batteries using solid electrolytes are being widely studied to ensure the safety of lithium secondary batteries, the field of which is expanding. However, it is known that they are far from commercialization level as they do not exhibit the same output, capacity, and lifespan performance as lithium-ion batteries using liquid electrolytes.

[0008] Therefore, the biggest issue in the industry is to ultimately implement a battery with improved safety that does not ignite even at very high temperatures. However, in lithium-ion batteries that use liquid electrolytes, it is very difficult to prevent ignition due to volatilization of the liquid electrolyte and oxygen generation at the positive electrode at high temperatures. Therefore, active research is being conducted to reduce the explosive power of the battery to secure time for users to evacuate.

[0009] The present invention aims to improve the safety of a lithium secondary battery by delaying ignition and reducing explosive power of the lithium secondary battery including a Si-based active material as a negative electrode active material.

[0010] According to one embodiment of the present invention,

[0011] A positive electrode having a positive electrode active material and a positive electrode composite layer including an inorganic solid electrolyte formed on one or both sides of a positive electrode current collector,

[0012] A negative electrode having a negative electrode composite layer containing a Si-based active material as a negative electrode active material formed on one or both sides of a negative electrode current collector.

[0013] A separator interposed between the positive electrode and the negative electrode, and

[0014] A lithium non-aqueous electrolyte comprising a lithium salt and a non-aqueous organic solvent,

[0015] A lithium secondary battery is provided in which the above-mentioned inorganic solid electrolyte is included in an amount of 1.5 wt% to 5 wt% based on the total weight of the positive electrode mixture layer and is uniformly distributed within the positive electrode mixture layer.

[0016] Here, when the positive electrode mixture layer is divided in half in the thickness direction, the inorganic solid electrolyte may be included in the upper layer at 40 to 60 wt% and the lower layer at 40 to 60 wt% based on the total weight of the inorganic solid electrolyte, and more specifically, when the upper layer and the lower layer are each divided in half, the inorganic solid electrolyte may be included in each layer at 20 to 30 wt% based on the total weight of the inorganic solid electrolyte.

[0017] In addition, as the inorganic solid electrolyte is uniformly distributed throughout, 50% to 90% of the total surface area of ​​the positive electrode active material may be covered by the inorganic solid electrolyte.

[0018] The above inorganic solid electrolyte may be an oxide-based solid electrolyte having a NASICON structure.

[0019] The above inorganic solid electrolyte may be an oxide-based solid electrolyte represented by the following chemical formula 1.

[0020] [Chemical Formula 1]

[0021] Li 1+x M' 2-x M x (PO4)3

[0022] In the above chemical formula 1,

[0023] 0 <x<2 이고,

[0024] M' is at least one selected from the group consisting of Ti, Zr, Ge, Sn, and Hf, and M is at least one selected from the group consisting of Cr, Al, Mg, Ga, Sc, Y, In, and La.

[0025] The above oxide-based solid electrolyte may be a lithium aluminum titanium phosphate (LATP)-based compound in which M' is Ti and M is Al.

[0026] The loading amount of the positive electrode mixture layer of the positive electrode is 400 mg / 25 cm 2 600mg / 25cm 2 It could be.

[0027] The above Si-based active material may be represented by the following chemical formula 2.

[0028] [Chemical Formula 2]

[0029] SiOx

[0030] Here, 0 <x≤2이다.

[0031] The above Si-based active material may be included in an amount of 1 to 20 wt%, specifically 1 to 10 wt%, based on the total weight of the negative electrode active material.

[0032] The above lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10, LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl) imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2), LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2).

[0033] A lithium secondary battery wherein the non-aqueous organic solvent is a single solvent or a mixed solvent of two or more solvents selected from the group consisting of carbonate-based organic solvents, ether-based organic solvents, and ester-based organic solvents.

[0034] The above separator may be an SRS separator in which a coating layer including inorganic particles and a binder is formed on one or both sides of a polyolefin-based substrate.

[0035] Figure 1 is a SEM-EDS photograph of Experimental Example 1 according to Example 1.

[0036] Figure 2 is a SEM-EDS photograph of Experimental Example 1 according to Comparative Example 1.

[0037] Figure 3 is a SEM-EDS photograph of Experimental Example 1 according to Comparative Example 2.

[0038] Figure 4 is a graph showing the results of Experimental Example 2 according to Example 1.

[0039] Figure 5 is a graph showing the results of Experimental Example 2 according to Comparative Example 1.

[0040] Figure 6 is a graph showing the results of Experimental Example 2 according to Comparative Example 2.

[0041] Hereinafter, the terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0042] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in their common sense to those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0043] The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms, unless specifically stated otherwise. As used herein, the terms "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0044] In this specification, when it is said that a part includes a certain component, this does not mean that other components are excluded, but rather that other components may be included, unless specifically stated otherwise.

[0045]

[0046] A lithium secondary battery according to one embodiment of the present invention,

[0047] A positive electrode having a positive electrode active material and a positive electrode composite layer including an inorganic solid electrolyte formed on one or both sides of a positive electrode current collector,

[0048] A negative electrode having a negative electrode composite layer containing a Si-based active material as a negative electrode active material formed on one or both sides of a negative electrode current collector.

[0049] A separator interposed between the positive electrode and the negative electrode, and

[0050] A lithium non-aqueous electrolyte comprising a lithium salt and a non-aqueous organic solvent,

[0051] The above-mentioned inorganic solid electrolyte is included in an amount of 1.5 wt% to 5 wt% based on the total weight of the positive electrode mixture layer, and is characterized in that it is uniformly distributed within the positive electrode mixture layer.

[0052]

[0053] anode

[0054] The positive electrode has a structure in which a positive electrode composite layer including a positive electrode active material and an inorganic solid electrolyte is formed on one or both sides of a positive electrode current collector.

[0055] Here, the positive electrode mixture layer can be formed by applying, 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 can further include electrode materials such as a conductive agent and a binder in addition to the above materials.

[0056] The positive electrode current collector may be any conductive material that does not induce chemical changes in the battery, and is not particularly limited. For example, the current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like.

[0057] The positive electrode current collector (121) may have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to increase adhesion to the positive electrode active material layer. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0058] The above-mentioned positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. More specifically, the lithium metal oxide may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(wherein, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (wherein, 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 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are atomic fractions of 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 (Here, M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, -0.5≤a≤0.5, 0≤x≤0.5, 0≤b≤0.1), and any one or two or more compounds thereof may be included.

[0059] Among these, the lithium metal oxides are LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 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 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 0.8 Co 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)O2), lithium iron phosphate (e.g., LiFePO4), etc., and any one of these or a mixture of two or more thereof may be used.

[0060] The above positive electrode active material may be included in an amount of 60 to 98 wt%, preferably 80 to 98 wt%, and more preferably 90 to 98 wt%, based on the total weight of the positive electrode composite layer.

[0061] The above-mentioned inorganic solid electrolyte may include at least one lithium metal oxide or lithium metal phosphate selected from a Nasicon-type solid electrolyte, a Lisicon-type solid electrolyte, a Garnet-type solid electrolyte, a Perovskite-type solid electrolyte, and a LiPON-type solid electrolyte, and more specific examples thereof include at least one selected from the group consisting of a LAGP (lithium aluminum germanium phosphate) compound, an LLZO (lithium lanthanum zirconium oxide) compound, a LATP (lithium aluminum titanium phosphate) compound, an LLZTO (lithium lanthanum zirconium tantalum oxide) compound, an LLTO (lithium lanthanum titanium oxide) compound, a LSTP (lithium silicon titanium phosphate) compound, and a LGPO (lithium germanium phosphate) compound.

[0062] More specifically, the inorganic solid electrolyte may be a NASICON-type solid electrolyte among the above examples, which may be an oxide-based solid electrolyte having a NASICON structure, and more specifically, may be represented by the following chemical formula 1.

[0063] [Chemical Formula 1]

[0064] Li 1+x M' 2-x M x (PO4)3

[0065] In the above chemical formula 1,

[0066] 0 <x<2 이고,

[0067] M' is at least one selected from the group consisting of Ti, Zr, Ge, Sn, and Hf, and M is at least one selected from the group consisting of Cr, Al, Mg, Ga, Sc, Y, In, and La.

[0068] Most specifically, these may be lithium aluminum titanium phosphate (LATP) compounds where M' is Ti and M is Al.

[0069] Such inorganic solid electrolyte may be included in an amount of 1.5 wt% to 5 wt%, and specifically, 2 wt% to 3 wt%, based on the total weight of the positive electrode composite layer.

[0070] If the content is too low outside the above range, it is difficult to obtain the explosive power reduction effect intended by the present invention, and if the content is too high, there is a problem that the resistance of the lithium secondary battery increases, which is not desirable.

[0071] Additionally, the inorganic solid electrolyte can be uniformly distributed within the positive electrode mixture layer.

[0072] 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 included in the two or more layers does not exceed 20 wt% when the total weight of the inorganic solid electrolyte is 100 wt%.

[0073] In other words, when the above-mentioned positive electrode composite layer is divided into two based on the thickness direction, the content of the inorganic solid electrolyte included in each of the upper and lower layers does not exceed a ratio of 40:60 to 60:40 when the entire inorganic solid electrolyte is 100 wt%.

[0074] Therefore, when the positive electrode mixture layer is divided in half based on the thickness direction, the inorganic solid electrolyte may be included in the upper layer at 40 to 60 wt% and the lower layer at 40 to 60 wt% based on the total weight of the inorganic solid electrolyte.

[0075] More specifically, when the upper layer and the lower layer are each divided into halves based on the thickness direction, the inorganic solid electrolyte may be included in each layer at 20 to 30 wt% based on the total weight of the inorganic solid electrolyte.

[0076] Here, dividing the positive electrode mixture layer in half based on the thickness direction does not mean that the positive electrode mixture layer is formed in two or more layers, but means that the positive electrode mixture layer formed for the analysis is divided into upper and lower layers based on the thickness direction.

[0077] In addition, since the inorganic solid electrolyte is evenly distributed within the positive electrode mixture layer, it can cover the positive electrode active material surface by 50% or more, specifically 50% to 90% of the total positive electrode active material surface area, more specifically 50% to 80%, and most specifically 60% to 80%.

[0078] If the surface of the positive electrode active material is covered by less than 50% outside the above range, it is not preferable because the safety intended by the present application cannot be sufficiently secured.

[0079] Moreover, the average diameter (D50) of the inorganic solid electrolyte particles may be 50 nanometers to 10 micrometers, specifically 50 nanometers to 5 micrometers, and more specifically 50 nanometers to 1 micrometer.

[0080] If the particle size is too small outside the above range, agglomeration between particles may occur due to reduced dispersibility. Conversely, if the particle size is too large, large pores are formed by the inorganic solid electrolyte, which is rather unfavorable in terms of resistance. In other words, if the particle size is within the above range, the lithium ion conductivity of the positive electrode can be increased, thereby reducing resistance and exhibiting improved secondary battery performance.

[0081] The average diameter (D50) described above refers to the particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve. The D50 can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution.

[0082] The conductive agent is a component for further improving the conductivity of the positive electrode active material, and the conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, 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 crystal structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0083] The above-mentioned conductive material may be included in an amount of 0.1 to 20 wt%, specifically 0.5 to 10 wt%, and more specifically 0.5 to 5 wt%, based on the total weight of the positive electrode composite layer.

[0084] The above 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0085] Typically, the binder may be included in an amount of 0.5 to 20 wt%, specifically 0.5 to 10 wt%, and more specifically 0.5 to 5 wt%, based on the total weight of the positive electrode composite layer.

[0086] In addition, the above-mentioned other additives may further include, for example, fillers as components that suppress expansion. The fillers are not particularly limited as long as they can suppress expansion of the electrode without causing chemical changes in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; and the like.

[0087] Meanwhile, the loading amount of the above-mentioned anode composite layer of these two electrodes is 400 mg / 25 cm 2 600mg / 25cm 2 It can be, in detail, 450mg / 25cm 2 600mg / 25cm 2 It can be, more specifically, 450mg / 25cm 2 550mg / 25cm 2 It could be.

[0088] That is, in the case of the present invention, even if a high-loading positive electrode is used, high secondary battery safety can be secured by the uniform distribution of the inorganic solid electrolyte.

[0089]

[0090] cathode

[0091] The above negative electrode has a structure in which a negative electrode composite layer is formed on one or both sides of a negative electrode current collector.

[0092] Here, the negative electrode composite layer can be formed by applying, drying, and rolling a negative electrode slurry containing a negative electrode active material to a negative electrode current collector, and at this time, in addition to the negative electrode active materials, the negative electrode slurry can further include electrode materials such as a conductive material and a binder as described above.

[0093] The negative electrode current collector (111) is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0094] The above-mentioned negative electrode collector (111) can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode collector, it can also form fine irregularities on the surface of the negative electrode collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0095] Meanwhile, the present invention is characterized in that safety is secured by controlling the content of an inorganic solid electrolyte, and thus sufficient safety can be secured even when using a Si-based active material having a large heat generation amount. Therefore, the negative electrode according to the present invention can include a Si-based active material as the negative electrode active material.

[0096] Specifically, the Si-based active material may be represented by the following chemical formula 2.

[0097] [Chemical Formula 2]

[0098] SiOx

[0099] Here, 0 <x≤2이다.

[0100] The above Si-based active material may be included specifically in an amount of 1 to 20 wt% based on the total weight of the negative electrode active material, and more specifically in an amount of 1 to 10 wt%.

[0101] In addition, the present invention may further include, as a negative electrode active material, at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0102] As the carbon material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries can be used without particular limitation, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0103] As the above 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 may be used.

[0104] The above metal composite oxides include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, LixFe2O3(0≤x≤1), Li x WO2(0≤x≤1) and Snx Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 로 이루어진 군에서 선택되는 것이 사용될 수 있다.

[0105] In addition to the SiOx, the materials capable of doping and dedoping the lithium include Si-based active materials such as Si, Si-Y alloys (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn-based active materials such as SnO2, Sn-Y (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and at least one of these may be mixed with SiO2 for use. The above element Y may 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.

[0106] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0107] Meanwhile, the negative electrode active material may be included in a total of 60 to 99 wt%, preferably 80 to 99 wt%, and more preferably 90 to 98 wt%, based on the total weight of the negative electrode active material layer.

[0108]

[0109] membrane

[0110] The separator can be used without any special restrictions as long as it is a separator commonly used in lithium secondary batteries, and it is particularly desirable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity.

[0111] For example, as a separator, a porous polymer film including a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., can also be used as a separator.

[0112] Or, it may be an SRS (Safety Reinforced Separator) membrane in which a coating layer including a binder and inorganic particles is formed on one or both sides of a polymer, specifically a polyolefin-based substrate, as described above.

[0113] The SRS separator is as described above. Specifically, the polyolefin substrate of the SRS separator is as described above, and the coating layer includes inorganic particles and a binder.

[0114] Here, the inorganic particles play a dual role: they form micropores by allowing the formation of empty spaces between the inorganic particles, and they also serve as a type of spacer that maintains their physical form. Furthermore, since the inorganic particles generally have a property of not changing their physical properties even at temperatures exceeding 200°C, the formed organic-inorganic mixed layer possesses excellent heat resistance.

[0115] The inorganic particles described above are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present 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 capabilities, it is preferable to use particles with as high an ion conductivity as possible, as this can enhance performance by increasing the ionic conductivity within the electrochemical device. In addition, when the inorganic particles have a high density, it is difficult to disperse them during manufacturing, and there is also the problem of weight increase during the manufacturing of the secondary battery, so it is preferable to use particles with as low a density as possible. In addition, when using inorganic particles with a high dielectric constant, they can contribute to an increase in the dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte. Finally, inorganic particles with thermal conductivity are even more preferable, as they have excellent heat absorption capabilities, which prevents heat from being concentrated locally, forming a heating point and leading to thermal runaway.

[0116] For the reasons mentioned above, the inorganic particles are preferably at least one 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) inorganic particles having piezoelectricity, (c) thermally conductive inorganic particles, and (d) inorganic particles having lithium ion transfer capability.

[0117] The above piezoelectric inorganic particles are non-conductive at normal pressure, but when a certain pressure is applied, they are materials that have the property of conducting electricity due to a change in their internal structure. In addition, when a certain pressure is applied and they are stretched or compressed, they generate electric charges, so that one side is charged positively and the other side is charged negatively, and they are materials that have the function of generating a potential difference between the two sides.

[0118] Examples of the above piezoelectric inorganic particles include BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT) hafnia (H f O2) or mixtures thereof, but are not limited thereto.

[0119] The above inorganic particles having lithium ion transfer capability refer to inorganic particles that contain lithium elements but do not store lithium and have the function of transferring lithium ions. Since the inorganic particles having lithium ion transfer capability can transfer and move lithium ions due to a type of defect existing within the particle structure, they can prevent a decrease in lithium mobility and thus a decrease in battery capacity.

[0120] Examples of inorganic particles having the above lithium ion transfer capability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), 리튬알루미늄티타늄포스페이트(Li x Al y Ti z (PO4)3, 0 <x<2, 0<y<1, 0<z<3), 14Li2O-9Al2O3-38TiO2-39P2O5등과 같은 (LiAlTiP) x O y Series glass (0 <x<4, 0<y<13), 리튬란탄티타네이트(Li x La y TiO3, 0 <x<2, 0<y<3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4 x Ge y P z S w, 0 <x<4, 0<y<1, 0<z<1, 0<w<5), Li3N 등과 같은 리튬나이트라이드(Li x N y , 0 <x<4, 0<y<2), Li3PO4-Li2S-SiS2등과 같은 SiS2계열 glass (Li x Si y S z , 0 <x<3, 0<y<2, 0<z<4), LiI-Li2S-P2S5등과 같은 P2S5계열 glass (Li x P y S z , 0 <x<3, 0<y<3, 0<z<7), 또는 이들의 혼합물 등이 있으나, 이에 한정되는 것은 아니다.

[0121] Additionally, examples of inorganic particles having a dielectric constant of 1 or greater include, but are not limited to, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC, or mixtures thereof.

[0122] The above thermally conductive inorganic particles are materials having insulating properties by providing low thermal resistance but no electrical conductivity, and may be, for example, at least one selected from the group consisting of aluminum nitride (AlN), boron nitride (BN), alumina (Al2O3), silicon carbide (SiC), and beryllium oxide (BeO), but are not limited thereto.

[0123] When the aforementioned high-k inorganic particles, piezoelectric inorganic particles, thermally conductive inorganic particles, and inorganic particles having lithium ion transfer capability are mixed, their synergistic effect can be doubled.

[0124] The size of the above-mentioned inorganic particles is not limited, but it is preferably in the range of 0.001 to 10 ㎛ to ensure an appropriate porosity between the inorganic particles. If it is less than 0.001 ㎛, dispersibility is reduced, making it difficult to control physical properties. If it exceeds 10 ㎛, the thickness increases, resulting in a deterioration in mechanical properties. In addition, due to the excessively large pore size, the coating layer cannot sufficiently function, increasing the probability of an internal short circuit occurring during battery charging and discharging.

[0125] The content of the above-mentioned inorganic particles is not particularly limited, but is preferably in the range of 1 to 99 wt%, and particularly 10 to 95 wt%, per 100 wt% of the mixture of inorganic particles and binder. When it is less than 1 wt%, the content of the binder becomes too high, which may reduce the pore size and porosity due to a decrease in the empty space formed between the inorganic particles, thereby reducing the mobility of lithium ions. Conversely, when it exceeds 99 wt%, the content of the binder becomes too low, which may result in a decrease in the adhesive strength between the inorganic particles, thereby reducing the mechanical properties of the coating layer.

[0126] Meanwhile, the binder is not limited as long as it does not cause a side reaction with the electrolyte, but in particular, one having a glass transition temperature (Tg) as low as possible can be used, preferably in the range of -200 to 200°C. This is because the mechanical properties of the final insulating film can be improved.

[0127] In addition, the above-mentioned binder does not necessarily need to have ion conducting ability, but it is more preferable to use a polymer having ion conducting ability.

[0128] Therefore, it is preferable that the binder have a permittivity constant as high as possible, and since the degree of salt dissociation in the electrolyte actually depends on the permittivity constant of the electrolyte solvent, the higher the permittivity constant of the polymer, the better the degree of salt dissociation in the electrolyte. The permittivity constant of the polymer is preferably 1 or more, specifically, in the range of 1.0 to 100 (measurement frequency = 1 kHz), and is particularly preferably 10 or more.

[0129] In addition to the aforementioned functions, the binder may have the characteristic of being gelled when impregnated with a liquid lithium non-aqueous electrolyte, thereby exhibiting a high degree of swelling. In fact, if the binder is a polymer having an excellent electrolyte impregnation rate, the electrolyte injected after battery assembly permeates the polymer, and the polymer retaining the absorbed electrolyte has electrolyte ion conducting ability. Therefore, if possible, the solubility index should be set to be 15 to 45 MPa. 1 / 2 Polymers are preferred, with a viscosity of 15 to 25 MPa. 1 / 2 and 30 to 45 MPa 1 / 2 The range is more desirable. The solubility index is 15 MPa. 1 / 2 Less than and 45 MPa 1 / 2 If it exceeds , it becomes difficult to be impregnated (swelled) by a conventional liquid lithium non-aqueous electrolyte for batteries.

[0130] Examples of such binders include polyvinylidene fluorideco-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, It may be at least one selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and polyvinylalcohol.

[0131] The total thickness of the separator may be 5 micrometers to 20 micrometers, specifically 5 micrometers to 15 micrometers, and more specifically 6 micrometers to 13 micrometers. When the thickness of the separator satisfies the above range, the resistance value of the lithium secondary battery can be minimized while effectively preventing a short circuit between the positive and negative electrodes. As a result, the reduction in energy density of the lithium secondary battery can be prevented and the life characteristics can be improved.

[0132]

[0133] lithium non-aqueous electrolyte

[0134] The above lithium salt is used as a medium for transferring ions in a lithium secondary battery. Lithium salt is, for example, Li as a cation. + , and the anion is 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 selected from the group consisting of

[0135] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (lithium bis(fluorosulfonyl) imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2) and LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2), but it is preferable to include Li(N(SO2CF3)2) in terms of excellent stability.

[0136] In addition to these, lithium salts commonly used in the electrolyte of lithium secondary batteries can be used without limitation.

[0137] The above lithium salt can be appropriately changed within a commonly usable range, but in order to obtain an optimal effect of forming a film for preventing corrosion on the electrode surface, it can be included in the lithium non-aqueous electrolyte at a concentration of 0.5 M to 3 M, specifically, a concentration of 1 M to 2.5 M, and more specifically, a concentration of 1 M to 2 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during high-temperature storage of a lithium secondary battery is sufficient, and the viscosity of the electrolyte is appropriate, so that the electrolyte impregnation property can be improved.

[0138] The above non-aqueous organic solvent is not limited as long as it minimizes decomposition due to oxidation reactions, etc., within the voltage range of the charge / discharge process of a lithium secondary battery and can exhibit its properties together with additives. For example, carbonate-based organic solvents, ether-based organic solvents, or ester-based organic solvents can be used alone or in combination of two or more, and specifically, carbonate-based organic solvents can be used.

[0139] Among the organic solvents, the carbonate-based organic solvent may include at least one of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. 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), and specifically, may include a mixed solvent of ethylene carbonate having a high dielectric constant and propylene carbonate having a relatively low melting point compared to ethylene carbonate.

[0140] In addition, the linear carbonate-based organic solvent is a solvent having low viscosity and low dielectric constant, and may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, and more specifically, may include dimethyl carbonate.

[0141] The above ether organic solvent may be any 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 thereof, but is not limited thereto.

[0142] The above ester organic solvent may include at least one selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents.

[0143] Specific examples of the linear ester organic solvent include, but are not limited to, 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 thereof.

[0144] The above cyclic ester organic solvent may be, as a specific example, 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 thereof, but is not limited thereto.

[0145] Among the above ester solvents, cyclic carbonate compounds are preferably used because they are high-viscosity organic solvents with high dielectric constants and thus easily dissociate lithium salts in lithium non-aqueous electrolytes. When these cyclic carbonate compounds are mixed with low-viscosity, low-dielectric constant linear carbonate compounds such as dimethyl carbonate and diethyl carbonate and linear ester compounds in an appropriate ratio, a lithium non-aqueous electrolyte with high electrical conductivity can be produced, and thus they can be used more preferably.

[0146] Furthermore, the lithium non-aqueous electrolyte may further include a functional additive, and the functional additive may be included to prevent cathode collapse from occurring in a high-power environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and swelling improvement effects during high-temperature storage.

[0147] Specifically, the functional additive may include at least one functional additive selected from the group consisting of, as representative examples, 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.

[0148] The above sultone-based compound may include at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone, and may be included in an amount of 0.3 wt% to 5 wt%, specifically 1 wt% to 5 wt%, based on the total weight of the lithium non-aqueous electrolyte. When the content of the sultone-based compound in the lithium non-aqueous electrolyte exceeds 5 wt%, an excessively thick film may be formed on the electrode surface, which may cause an increase in resistance and a deterioration in output, and the resistance may also increase due to an excessive amount of additive, which may deteriorate the output characteristics.

[0149] The above sulfite compound may include at least one compound 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-dimethyl propylene sulfite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, and 1,3-butylene glycol sulfite, and may be included in an amount of 3 wt% or less based on the total weight of the lithium non-aqueous electrolyte.

[0150] The above sulfone compound may include at least one compound selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methylethyl sulfone, and methylvinyl sulfone, and may be included in an amount of 3 wt% or less based on the total weight of the lithium non-aqueous electrolyte.

[0151] The above sulfate-based compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and may be included in an amount of 3 wt% or less based on the total weight of the lithium non-aqueous electrolyte.

[0152] In addition, the halogen-substituted carbonate-based compound may include fluoroethylene carbonate (FEC) and may be included in an amount of 5 wt% or less based on the total weight of the lithium non-aqueous electrolyte. If the content of the halogen-substituted carbonate-based compound in the lithium non-aqueous electrolyte exceeds 5 wt%, cell swelling performance may deteriorate.

[0153] In addition, the nitrile compound may include at least one compound selected from the group consisting of succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0154] The cyclic carbonate compound may be vinylene carbonate (VC) or vinylethylene carbonate, and may be included in an amount of 3 wt% or less based on the total weight of the lithium non-aqueous electrolyte. If the content of the cyclic carbonate compound in the lithium non-aqueous electrolyte exceeds 3 wt%, the cell swelling suppression performance may deteriorate.

[0155] The above phosphate compound may include at least one compound selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethyl silyl phosphate, trimethyl silyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphite, and may be included in an amount of 3 wt% or less based on the total weight of the lithium non-aqueous electrolyte.

[0156] The above borate compound may include lithium oxalyldifluoroborate, and may be included in an amount of 3 wt% or less based on the total weight of the lithium non-aqueous electrolyte.

[0157] The lithium salt-based compound is a compound different from the lithium salt included in the lithium non-aqueous electrolyte, and may include at least one compound selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2) and LiBF4), and may be included in an amount of 3 wt% or less based on the total weight of the lithium non-aqueous electrolyte.

[0158] The functional additives may be mixed in two or more types and included in an amount of 20 wt% or less, specifically 0.1 wt% to 10 wt%, based on the total weight of the lithium non-aqueous electrolyte. If the content of the functional additive exceeds 20 wt%, there is a possibility that excessive side reactions may occur within the lithium non-aqueous electrolyte during charging and discharging of the battery. In particular, since they are not sufficiently decomposed at high temperatures, they may exist as unreacted substances or precipitated substances within the lithium non-aqueous electrolyte at room temperature. Accordingly, side reactions that reduce the lifespan or resistance characteristics of the lithium secondary battery may occur.

[0159]

[0160] Hereinafter, examples will be described to demonstrate that a lithium secondary battery according to one embodiment of the present invention exhibits improved effects.

[0161]

[0162] <Example 1>

[0163] Manufacturing of anodes

[0164] An aluminum (Al) metal thin film with a thickness of 15 micrometers is prepared as a cathode current collector, and Li(Ni) is applied as a cathode 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): A cathode slurry was prepared by dispersing carbon nanotubes as a conductive material and PVDF as a binder in a weight ratio of 93:3:1:3 in NMP solvent, and coating, drying, and rolling to a thickness of 60 micrometers to produce a cathode (loading amount 450 mg / 25 cm 2 ) was manufactured.

[0165] Manufacturing of cathode

[0166] Next, a 20 micrometer thick copper (Cu) metal film was prepared as a negative electrode current collector, and a negative electrode slurry was prepared by dispersing a mixture of graphite and SiO2 (9:1 by weight) as a negative electrode active material, carbon black as a conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene-butadiene rubber (SBR) as a binder in a weight ratio of 95:1:1.5:2.5 in water on one surface of the copper metal film, coating, drying, and rolling to prepare a negative electrode to a thickness of 75 micrometers.

[0167] Manufacturing of electrode assemblies

[0168] An electrode assembly was manufactured by interposing a polyolefin material separator (thickness: 15 micrometers) between the positive electrode and the negative electrode.

[0169] Manufacturing of lithium secondary batteries

[0170] A lithium non-aqueous electrolyte was used in which LiPF6 was dissolved 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).

[0171] The electrode assembly manufactured above was inserted into a battery case, and the lithium non-aqueous electrolyte was injected to manufacture a secondary battery.

[0172]

[0173] <Comparative Example 1>

[0174] In the positive electrode of the above Example 1, Li(Ni) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 )O2: A lithium secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of carbon nanotubes as a conductive material and PVDF as a binder was 96:1:3.

[0175]

[0176] Comparative Example 2

[0177] An aluminum (Al) metal thin film with a thickness of 15 micrometers is prepared as a cathode current collector, and Li(Ni) is applied as a cathode 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): A lithium secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of carbon nanotubes as a conductive material and PVDF as a binder was 95:1:1:3.

[0178]

[0179] Experimental Example 1

[0180] SEM photographs of cross-sections were taken in the thickness direction through the center of the anodes manufactured in Example 1, Comparative Examples 1, and 2, and EDS analysis was performed.

[0181] At this time, the analysis was conducted by dividing the upper and lower layers in the thickness direction, and the results are shown in Figures 1 to 3 and Table 1 below.

[0182] Example 1 Comparative Example 1 Comparative Example 2Upper layer (wt%)Lower layer (wt%)BareUpper layer (wt%)Lower layer (wt%)C7.598.358.056.937.28O32.1231.8931.7828.2129.27F2.512.622.272.112.2Al0.70.680.610.640.67P1.221.310.070.480.45Ti0.991.0300.40.35Mn4.464.334.454.824.72Co2.962.863.063.213.13Ni47.4346.9449.7252.5951.92Total100100100100100

[0183] Referring to the following Figures 1 to 3 and Table 1, it can be confirmed that when an inorganic solid electrolyte is included, the inorganic solid electrolyte is distributed in a similar content in both the upper and lower layers of the positive electrode mixture layer.

[0184]

[0185] Experimental Example 2

[0186] The lithium secondary batteries of Example 1 and Comparative Examples 1 to 2 were fully charged at 25°C with a constant current of 0.33C until the voltage reached 4.2 V, and a heating pad made of mica was attached to these lithium secondary batteries to increase the temperature at 300 W / min for 1 minute, and then 300 W was maintained to create an external ignition environment, and while maintaining these conditions, the voltage, pressure, and temperature of the lithium secondary batteries were measured over time, and the results are shown in Figures 4 to 6 below.

[0187] The difference between the maximum pressure measured at the time of explosion of the above lithium secondary batteries and the initially set atmospheric pressure was defined as the explosion pressure, and the time from the point at which the pressure began to change to the maximum pressure was defined as the reaction time.

[0188] A relatively lower explosion pressure and longer reaction time indicate a lower explosive power of the lithium secondary battery. The results are shown in Table 2 below.

[0189] Example 1 Comparative Example 1 Comparative Example 2 Explosion pressure (bar) 2.14 2.45 2.37 Reaction time (sec) 5.8 3 5.13 5.35 Explosion pressure / Reaction time 0.36 9 0.48 4 0.445

[0190] Referring to Table 2 above, it can be confirmed that when the content of the inorganic solid electrolyte exceeds 1 wt% according to the present invention, the safety is significantly improved. This demonstrates that in the case of a lithium secondary battery containing SiO2 and generating a high amount of heat, the content of the inorganic solid electrolyte must be above a certain level to ensure the level of safety intended by the present invention.

[0191] Even when the content of the inorganic solid electrolyte is 1 wt%, as shown in Table 1 above, it can be seen that the inorganic solid electrolyte is uniformly distributed, but does not exhibit the effect intended by the present invention.

[0192]

[0193] Anyone with ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

[0194] 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 amount or more to cover 50% or more of the surface of the positive electrode active material, delay ignition of the lithium secondary battery, lower the explosion pressure, increase the reaction time, and reduce the explosive power, so that the safety of the lithium secondary battery can be improved.

[0195] Moreover, since the lithium secondary battery according to the present invention includes a Si-based active material as the negative active material, the amount of heat generated is large, which poses a significant safety issue. However, high safety can be secured by controlling the content of the inorganic solid electrolyte.

Claims

1. A positive electrode having a positive electrode active material and a positive electrode composite layer including an inorganic solid electrolyte formed on one or both sides of a positive electrode current collector; A negative electrode having a negative electrode composite layer including a Si-based active material as a negative electrode active material formed on one or both sides of a negative electrode current collector. A separator interposed between the positive electrode and the negative electrode, and A lithium non-aqueous electrolyte comprising a lithium salt and a non-aqueous organic solvent, A lithium secondary battery, wherein the above-mentioned inorganic solid electrolyte is included in an amount of 1.5 wt% to 5 wt% based on the total weight of the positive electrode mixture layer and is uniformly distributed within the positive electrode mixture layer.

2. In paragraph 1, A lithium secondary battery, wherein when the positive electrode composite layer is divided in half based on the thickness direction, the inorganic solid electrolyte is included in the upper layer at 40 to 60 wt% and the lower layer at 40 to 60 wt% based on the total weight of the inorganic solid electrolyte.

3. In paragraph 2, A lithium secondary battery, wherein when the upper layer and the lower layer are each divided in half based on the thickness direction, the inorganic solid electrolyte is included in each layer at 20 to 30 wt% based on the total weight of the inorganic solid electrolyte.

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

5. In paragraph 1, The above inorganic solid electrolyte is a lithium secondary battery having an oxide-based solid electrolyte having a NASICON structure.

6. In paragraph 1, The above inorganic solid electrolyte is a lithium secondary battery which is an oxide-based solid electrolyte represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x M' 2-x M x (PO4)3 In the above chemical formula 1, 0 <x<2 이고, M' is at least one selected from the group consisting of Ti, Zr, Ge, Sn, and Hf, and M is at least one selected from the group consisting of Cr, Al, Mg, Ga, Sc, Y, In, and La.

7. In paragraph 6, The above oxide-based solid electrolyte is a lithium secondary battery, which is a lithium aluminum titanium phosphate (LATP) compound where M' is Ti and M is Al.

8. In paragraph 1, The loading amount of the above bipolar composite layer is 400 mg / 25 cm 2 600mg / 25cm 2 Lithium secondary battery.

9. In paragraph 1, The above Si-based active material is a lithium secondary battery represented by the following chemical formula 2. [Chemical formula 2] SiOx Here, 0 <x≤2이다.

10. In paragraph 1, A lithium secondary battery, wherein the above-mentioned Si-based active material is included in an amount of 1 to 20 wt% based on the total weight of the negative electrode active material.

11. In paragraph 10, A lithium secondary battery, wherein the above-mentioned Si-based active material is included in an amount of 1 to 10 wt% based on the total weight of the negative electrode active material.

12. In paragraph 1, The above lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 A lithium secondary battery, which is a single material or a mixture of two or more materials selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (lithium bis(fluorosulfonyl) imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2, LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2).

13. In paragraph 1, A lithium secondary battery wherein the above non-aqueous organic solvent is a single solvent or a mixed solvent of two or more solvents selected from the group consisting of a carbonate-based organic solvent, an ether-based organic solvent, or an ester-based organic solvent.

14. In paragraph 1, The above separator is a lithium secondary battery, which is an SRS separator in which a coating layer containing inorganic particles and a binder is formed on one or both sides of a polyolefin-based substrate.

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