Gel-type polymer electrolyte, lithium metal battery comprising same, and method for manufacturing same

Abstract

The present invention relates to a gel-type polymer electrolyte, a lithium metal battery comprising same, and a method for manufacturing same and, more specifically, comprises: an organic solvent; a lithium salt; an additive; and a crosslinked polymer, wherein a current collector includes an organic phosphate, the lithium salt includes at least one of a borate-based lithium salt and a fluorine-based lithium salt, and the organic phosphate is a low-molecular compound having a molecular weight (Mw) of 100-400 g / mol and is dispersed in the organic solvent.

Description

Gel-type polymer electrolyte, lithium metal battery including the same, and method for manufacturing the same

[0001] The present invention relates to a gel-type polymer electrolyte, a lithium metal battery comprising the same, and a method for manufacturing the same. More specifically, the invention relates to a gel-type polymer electrolyte comprising an organic phosphate dispersed within a cross-linked polymer, a lithium metal battery comprising the same, and a method for manufacturing the same.

[0002]

[0003] Currently available lithium batteries primarily use carbon-based negative electrode active materials, such as graphite. While carbon-based negative electrode active materials offer high stability due to their lack of volume change during charging and discharging, their low capacity necessitates the use of negative electrode active materials with higher capacities.

[0004] Lithium metal, which has a much larger theoretical capacity compared to carbon-based negative electrode active materials, can be used as a negative electrode active material. During charging and discharging, dendrites can form on the surface of lithium metal due to side reactions with the electrolyte, and as these dendrites grow, they can cause a short circuit between the positive and negative electrodes. Consequently, the lifespan characteristics of a lithium metal battery containing lithium metal may be degraded.

[0005]

[0006] The problem that the present invention aims to solve is to provide a gel-type polymer electrolyte with excellent thermal stability.

[0007] Another problem that the present invention aims to solve is to provide a lithium metal battery having excellent thermal stability and excellent lifespan characteristics.

[0008] Another problem that the present invention aims to solve is to provide a method for manufacturing the lithium metal battery.

[0009]

[0010] According to the concept of the present invention, a gel-type polymer electrolyte comprises an organic solvent; a lithium salt; an additive; and a crosslinking polymer, wherein the additive comprises an organic phosphate, and the lithium salt may comprise at least one of a borate-based lithium salt and a fluorine-based lithium salt. The organic phosphate may be a low-molecular compound having a molecular weight (Mw) of 100 g / mol to 400 g / mol and may be dispersed in the organic solvent.

[0011] A lithium metal battery according to the concept of the present invention may include a positive electrode comprising a positive current collector and a positive active material layer on the positive current collector, a negative electrode comprising a negative current collector, and an electrolyte layer disposed between the positive electrode and the negative electrode. The electrolyte layer may include the gel-type polymer electrolyte.

[0012] A method for manufacturing a lithium metal battery according to the concept of the present invention may comprise: forming an electrode assembly by stacking a negative electrode, a separator, and a positive electrode; injecting a composition for forming a gel-type polymer electrolyte into the electrode assembly; and curing the composition for forming a gel-type polymer electrolyte. The composition for forming a gel-type polymer electrolyte comprises an organic solvent; a lithium salt; an additive; and a crosslinkable monomer, wherein the additive comprises an organic phosphate, the organic phosphate is a low molecular weight compound having a molecular weight (Mw) of 100 g / mol to 400 g / mol, and the lithium salt may comprise at least one of a borate-based lithium salt and a fluorine-based lithium salt.

[0013]

[0014] According to one embodiment of the present invention, a low-molecular-weight organic phosphate included in a gel-type polymer electrolyte can function as a flame-retardant additive, and accordingly, a lithium metal battery containing the gel-type polymer electrolyte of the embodiment can have excellent thermal safety.

[0015]

[0016] FIG. 1 is a cross-sectional view showing a lithium secondary battery according to one embodiment of the present invention.

[0017] FIG. 2 is a cross-sectional view showing a lithium secondary battery according to one embodiment of the present invention.

[0018] Figure 3 is an enlarged cross-sectional view of the M region of Figure 2.

[0019] FIGS. 4 and 5 are cross-sectional views showing a lithium secondary battery according to other embodiments of the present invention.

[0020] FIG. 6 is an enlarged cross-sectional view of a portion of a gel-type polymer electrolyte according to embodiments of the present invention.

[0021] FIG. 7 is an enlarged view of a portion of a gel-type polymer electrolyte according to a comparative example of the present invention.

[0022] FIGS. 8 to 10 are schematic diagrams illustrating a lithium secondary battery according to one embodiment.

[0023] FIGS. 11a to 11c are cross-sectional views illustrating a method for manufacturing a lithium secondary battery according to embodiments of the present invention.

[0024]

[0025] In order to fully understand the structure and effects of the present invention, preferred embodiments of the present invention are described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various modifications can be made. The description of these embodiments is provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention.

[0026] In this specification, when a component is described as being on another component, it means that it may be formed directly on the other component or that a third component may be interposed between them. Additionally, in the drawings, the thicknesses of the components are exaggerated for the effective description of the technical content. Throughout the specification, parts indicated by the same reference numeral represent the same components.

[0027] The embodiments described herein will be described with reference to cross-sectional and / or plan views, which are exemplary illustrations of the invention. In the drawings, the thicknesses of films and regions are exaggerated for effective description of the technical content. Accordingly, the regions illustrated in the drawings are schematic in nature, and the shapes of the regions illustrated in the drawings are intended to illustrate specific forms of regions of the device and are not intended to limit the scope of the invention. Although terms such as first, second, third, etc., have been used to describe various components in the various embodiments of this specification, these components should not be limited by such terms. These terms are used merely to distinguish one component from another. The embodiments described and illustrated herein also include their complementary embodiments.

[0028] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, 'comprises' and / or 'comprising' do not exclude the presence or addition of one or more other components to the mentioned components.

[0029] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0030] Unless otherwise defined in this specification, the particle size may be the average particle size. Additionally, the particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. The average particle size (D50) may be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) value may be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Alternatively, it may be measured using a laser diffraction method. When measuring by laser diffraction, more specifically, after dispersing the particles to be measured in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasound of about 28 kHz at an output of 60 W, and then the average particle size (D50) at 50% of the particle size distribution in the measuring device can be calculated.

[0031] In this specification, "substitution" may mean that at least one hydrogen of a substituent or compound is substituted with a deuterium, a halogen group, a hydroxyl group, an amino group, a C1 to C30 amine group, a nitro group, a C1 to C40 silyl group, a C1 to C30 alkyl group, a C1 to C10 alkylsilyl group, a C6 to C30 arylsilyl group, a C3 to C30 cycloalkyl group, a C3 to C30 heterocycloalkyl group, a C6 to C30 aryl group, a C2 to C30 heteroaryl group, a C1 to C20 alkoxy group, a C1 to C10 fluoroalkyl group, a cyano group, or a combination thereof, unless otherwise defined.

[0032] For example, "substitution" may mean that at least one hydrogen in the substituent or compound is substituted with deuterium, a halogen group, a C1 to C30 alkyl group, a C1 to C10 alkylsilyl group, a C6 to C30 arylsilyl group, a C3 to C30 cycloalkyl group, a C3 to C30 heterocycloalkyl group, a C6 to C30 aryl group, a C2 to C30 heteroaryl group, a C1 to C10 fluoroalkyl group, or a cyano group. For example, "substitution" may mean that at least one hydrogen in the substituent or compound is substituted with deuterium, a halogen group, a C1 to C20 alkyl group, a C6 to C30 aryl group, a C1 to C10 fluoroalkyl group, or a cyano group. Alternatively, "substitution" may mean that at least one hydrogen in the substituent or compound is substituted with a deuterium, a halogen group, a C1 to C5 alkyl group, a C6 to C18 aryl group, a C1 to C5 fluoroalkyl group, or a cyano group. For example, "substitution" may mean that at least one hydrogen in the substituent or compound is substituted with a deuterium, a cyano group, a halogen group, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0033] In this specification, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state.

[0034] In this specification, “alloy” means a mixture of two or more metals.

[0035] In this specification, “electrode active material” refers to an electrode material capable of undergoing lithiation and delithiation.

[0036] In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0037] In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0038] In this specification, “lithiation” and “to lithiate” refer to the process of adding lithium to an electrode active material.

[0039] In this specification, “delithiation” and “to delithiate” refer to the process of removing lithium from an electrode active material.

[0040] In this specification, “charge” and “to charge” refer to the process of providing electrochemical energy to a battery.

[0041] In this specification, “discharge” and “discharge” refer to the process of removing electrochemical energy from a battery.

[0042] In this specification, “anode” and “cathode” refer to electrodes where electrochemical reduction and lithiation occur during the discharge process.

[0043] In this specification, “negative electrode” and “anode” refer to electrodes where electrochemical oxidation and delithiation occur during the discharge process. Although specific embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or cannot be anticipated may arise to the applicant or those skilled in the art. Accordingly, the appended claims, which may be filed and modified, are intended to include all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0044] A lithium metal battery according to exemplary embodiments is described in more detail below.

[0045] FIG. 1 shows a lithium secondary battery according to embodiments of the present invention.

[0046] Referring to FIG. 1, a lithium secondary battery may include a positive electrode (PEL), a negative electrode (NEL), and an electrolyte layer (GEL). The positive electrode (PEL) and the negative electrode (NEL) may be spaced apart from each other with a separator (SEP) in between. The electrolyte layer (GEL) may include a separator (SEP) and an electrolyte (GPE). The electrolyte (GPE) may be impregnated within the separator (SEP). The electrolyte (GPE) may be impregnated not only within the separator (SEP) but also within the positive electrode (PEL) and the negative electrode (NEL). However, the lithium secondary battery may further include additional functional layers disposed between each layer, such as an adhesion-enhancing layer.

[0047] FIG. 2 shows a lithium secondary battery according to one embodiment of the present invention.

[0048] Referring to FIG. 2, a lithium secondary battery may include a lithium metal layer (NAL) on a negative electrode current collector (COL1). More specifically, in a negative electrode structure in which a negative active material layer is omitted on the initial negative electrode current collector (COL1), a lithium metal layer (NAL) may be formed on the negative electrode current collector (COL1) according to the charging and discharging process. Accordingly, the lithium secondary battery may use lithium metal as the negative active material. During charging, lithium ions transferred from the positive electrode are deposited on the negative electrode current collector, and during discharging, the lithium deposited on the negative electrode current collector is leached out again and inserted into the positive electrode, thereby operating the battery. As described above, a lithium secondary battery using lithium metal as the negative active material may be defined as a lithium metal battery. In this specification, a lithium secondary battery may include a lithium metal battery.

[0049] The lithium metal layer (NAL) may include lithium or a lithium alloy. Since the lithium metal layer (NAL) is a metal layer containing lithium, it may function as, for example, a lithium reservoir. The lithium alloy may be, for example, Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, Li-Si alloy, etc., but is not limited to these; any alloy used as a lithium alloy in the relevant technical field may be possible. The lithium metal layer (NAL) may be composed of one of these alloys or lithium, or may be composed of various types of alloys. The lithium metal layer (NAL) may be, for example, a plated layer. The lithium metal layer (NAL) may be deposited on the negative electrode current collector (COL1) during the charging process of a secondary battery, for example.

[0050] Figure 3 is an enlarged view of the M region of Figure 2.

[0051] Referring to FIG. 3, a lithium metal layer (NAL) may be formed between a negative electrode current collector (COL1) and a separator (SEP). The lithium metal layer (NAL) may have a first thickness (TK). The first thickness (TK1) may be defined as the length from the negative electrode current collector to the most protruding peak with respect to the third direction (D3). The first thickness (TK1) is not particularly limited, but may be, for example, 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the first thickness (TK1) of the lithium metal layer (NAL) is excessively thin, it may be difficult for the lithium metal layer (NAL) to perform the role of a lithium reservoir. If the first thickness (TK1) of the lithium metal layer (NAL) is excessively thick, the mass and volume of the secondary battery increase, and there is a possibility that the cycle characteristics of the secondary battery may actually deteriorate.

[0052] FIG. 4 shows a lithium secondary battery according to another embodiment of the present invention.

[0053] Referring to FIG. 4, the negative electrode (NEL) may further include a protective layer (PTL) on the negative electrode current collector (COL1). The protective layer (PTL) may directly cover the surface of the negative electrode current collector (COL1). The protective layer (PTL) may be interposed between the negative electrode current collector (COL1) and the electrolyte layer (GEL). The protective layer (PTL) can reduce side reactions by reducing contact between lithium and the electrolyte layer (GEL). Additionally, it can induce uniform lithium electrodeposition by forming a uniform lithium ion flow at the negative electrode interface.

[0054] For example, the protective layer (PTL) may comprise at least one polymer selected from the group consisting of polyvinyl alcohol, polyimide, vinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, carboxymethylcellulose, and styrene-butyrene rubber. The protective layer (PTL) may further comprise an inorganic filler in addition to the polymer. For example, the inorganic filler may be selected from the group consisting of SiO2, Al2O3, Al(OH)3, AlO(OH), TiO2, BaTiO3, ZnO2, Mg(OH)2, Al (Aluminum Nitride), SiC (Silicon Carbide), and BoN (Boron Nitride). For example, the thickness of the protective layer (PTL) may be 1 μm to 20 μm.

[0055] Figure 5 shows a lithium secondary battery in another embodiment of the present invention.

[0056] Referring to FIG. 5, the negative electrode (NEL) may further include a host layer (HSL) on the negative electrode current collector (COL1). The host layer (HSL) may be interposed between the negative electrode current collector (COL1) and the electrolyte layer (GEL).

[0057] The host layer (HSL) can provide a space for lithium to be electrodeposited during the charging of a lithium secondary battery. For example, the host layer (HSL) may include a space for lithium to be electrodeposited, such as a porous structure. Lithium can be electrodeposited inside the host layer (HSL). The host layer (HSL) can suppress the formation of the aforementioned lithium electrodeposited layer (NAL). In this way, the host layer (HSL) can suppress lithium dendrites and suppress the increase in the volume of the battery caused by the formation of the lithium electrodeposited layer.

[0058] The host layer (HSL) may include a material having lithium affinity. For example, the host layer (HSL) may include carbon or a metal such as copper. The host layer (HSL) may have a 3D microstructure to maximize the specific surface area and to have porosity. For example, the host layer (HSL) may have a structure such as a sponge or a net.

[0059] The host layer (HSL) may further include a binder for mechanical stability. The binder within the host layer (HSL) can be any polymer used in lithium metal batteries without limitation.

[0060]

[0061] Anode (PEL)

[0062] The positive electrode (PEL) may include a positive electrode current collector (COL2) and a positive electrode active material layer (PAL) disposed on the positive electrode current collector (COL2). The positive electrode active material layer (PAL) may include a positive electrode active material, a conductive material, and a binder.

[0063] The positive current collector (COL2) can provide a reference surface on which the positive active material layer (PAL) is placed. The positive current collector (COL2) may include, for example, a plate or foil comprising indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.

[0064] Meanwhile, in one embodiment of the present invention, the positive current collector (COL2) may be omitted. Although not illustrated, a carbon layer with a thickness of 0.1 μm to 4 μm may be further disposed between the positive current collector (COL2) and the positive active material layer (PAL) to increase the bonding strength between the positive current collector (COL2) and the positive active material layer (PAL).

[0065] The positive electrode active material is a material capable of reversibly absorbing and desorbing lithium ions. The positive electrode active material may include, for example, lithium transition metal oxides such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganate, and lithium iron phosphate, as well as nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide, but is not necessarily limited to these. The positive electrode active material may be a single material or a mixture of two or more materials.

[0066] Lithium transition metal oxides are, for example, Li a A 1-b B b D2(0.90≤a≤1, 0≤b≤0.5), Li a E 1-b B b O 2-c D c (0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05), LiE 2-b B b O 4-c D c (0≤b≤0.5, 0≤c≤0.05), Li a Ni 1-b-c Co b B c D α (0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2), Li a Ni 1-b-c Co b B c O 2-α F α (0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2), Li a Ni 1-b-c Mn b B c D α(0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2), Li a Nor 1-b-c Mn b B c O 2-α F α (0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2), Li a Nor b E c G d O2(0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1), Li a Nor b Co c Mn d GeO2(0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1), Li a NiG b O2(0.9≤a≤1, 0.001≤b≤0.1), Li a CoG b O2(0.90≤a≤1, 0.001≤b≤0.1), Li a MnG b O2(0.90≤a≤1, 0.001≤b≤0.1), Li a Mn2GbO4(0.90≤a≤1, 0.001≤b≤0.1), QO2, QS2, LiQS2, V2O5, LiV2O5, LiIO2, LiNiVO4, Li 3-f J2(PO4)3(0≤f≤2), Li 3-fIt is a compound represented by any one of Fe2(PO4)3 (0≤f≤2) or LiFePO4. In such compounds, the uppercase “A” is Ni, Co, Mn, or a combination thereof; the uppercase “B” is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; the uppercase “D” is O, F, S, P, or a combination thereof; the uppercase “E” is Co, Mn, or a combination thereof; the uppercase “F” is F, S, P, or a combination thereof; the uppercase “G” is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; the uppercase “Q” is Ti, Mo, Mn, or a combination thereof; the uppercase “I” is Cr, V, Fe, Sc, Y, or a combination thereof; and the uppercase “J” is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0067] In one embodiment, the positive electrode active material may comprise a lithium transition metal oxide with a nickel (Ni) composition of 80% or more. By including a high content of nickel (Ni), the capacity of the battery can be improved. For example, the positive electrode active material is LiNi x Co y Mn z O2(0.8≤x≤1.0, 0≤y≤0.1, 0≤z≤0.1, x+y+z=1) may be included.

[0068] The positive electrode active material may include, for example, a lithium salt of a transition metal oxide having a layered rock salt type structure among the lithium transition metal oxides described above. The "layered rock salt type structure" is, for example, a cubic rock salt type structure. <111> It is a structure in which oxygen and metal atomic layers are alternately and regularly arranged in a specific direction, thereby forming a two-dimensional plane for each atomic layer. The "cubic rock salt type structure" represents a sodium chloride (NaCl) type structure, which is a type of crystal structure; specifically, it exhibits a structure in which face-centered cubic lattices (fcc) formed by cations and anions, respectively, are offset from each other by half the ridge of the unit lattice. Lithium transition metal oxides having such a layered rock salt type structure are, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn z O2(NCM) (0 <x<1,0<y<1, 0<z<1, x+y+z=1) 등의 삼원계 리튬전이금속산화물일 수 있다. 양극 활물질이 층상암염형 구조를 갖는 삼원계 리튬전이금속산화물을 포함하는 경우, 전지의 에너지 밀도가 커지고 열안정성이 향상될 수 있다.

[0069] The aforementioned compound contained in the positive electrode active material may be covered by a coating layer (not shown). The positive electrode active material may also be a mixture of the aforementioned compound and the compound to which the coating layer is added. Meanwhile, the coating layer added to the surface of the positive electrode active material may include, for example, oxides, hydroxides, oxyhydroxides, oxycarbonates, or hydroxycarbonates of the following coating elements. The compounds forming this coating layer are amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer may include, for example, Li2O-ZrO2 (LZO). The method for forming the coating layer is selected within a range that does not adversely affect the physical properties of the positive electrode active material. The method for forming the coating layer is, for example, spray coating or immersion.

[0070] When the cathode active material is a ternary lithium transition metal oxide, such as NCA or NCM, containing nickel (Ni), it is possible to increase the capacity density of the battery and reduce metal leaching from the cathode active material during the charged state. Consequently, the cycle characteristics of the battery during the charged state are improved. Meanwhile, "cycle characteristics" refers to the degree of degradation of a battery due to charging and discharging; batteries with high cycle characteristics degrade less due to charging and discharging, while batteries with low cycle characteristics degrade more due to charging and discharging.

[0071] The shape of the positive electrode active material may include particle shapes such as spheres or ellipsoids. The particle size and content of the positive electrode active material are not particularly limited.

[0072] The positive active material layer (PAL) may include a conductive material. The conductive material can increase the conductivity of the positive active material by providing conductivity without causing chemical changes in the battery. The conductive material may include carbon-based materials. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0073] The positive active material layer (PAL) may further include a binder. The binder may include a material for binding the positive active material, conductive material, etc. contained in the positive active material layer (PAL) and for improving the bonding strength with the positive current collector (COL2). The binder serves to effectively bond the positive active material particles to each other and also to effectively bond the positive active material to the positive current collector (COL2). Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0074]

[0075] Electrolyte layer (GEL)

[0076] The electrolyte layer (GEL) according to embodiments of the present invention may include a gel polymer electrolyte (GPE). The gel polymer electrolyte (GPE) can physically inhibit the growth of lithium dendrites. At the same time, it can provide a pathway for the movement of lithium ions due to its high ion conductivity. The stability of the lithium secondary battery according to embodiments of the present invention can be improved by introducing the gel polymer electrolyte (GPE). For example, the stability of a secondary battery using lithium metal as the negative electrode active material can be improved. As a result, a lithium secondary battery with improved energy density and lifespan characteristics can be provided.

[0077] FIG. 6 is an enlarged cross-sectional view of a portion of a gel-type polymer electrolyte (GPE) according to embodiments of the present invention.

[0078] Referring to FIG. 6, the gel polymer electrolyte (GPE) may include a liquid electrolyte (LIE) and a crosslinking polymer (CLP). More specifically, the gel polymer electrolyte (GPE) may have a structure in which the liquid electrolyte is contained within a polymer matrix. The polymer matrix can maintain a gel state by physically fixing the liquid electrolyte. As the crosslinking polymer (CLP) forms a crosslinking network and the liquid electrolyte (LIE) is introduced into the crosslinking network, the exposure of the electrolyte is minimized, and a uniform flow of lithium ions can be formed across the electrode. Consequently, the stability of the lithium battery can be improved as the liquid electrolyte (LIE) is incorporated into the crosslinking network of the crosslinking polymer (CLP).

[0079] The gel polymer electrolyte (GPE) may further include a crosslinking agent, a photoinitiator, a thermal initiator, etc. for crosslinking the crosslinked polymer (CLP). The crosslinking agent, the photoinitiator, etc. are not particularly limited as long as they are commonly used in the relevant technical field. Methods for forming the gel polymer electrolyte include curing using heat, UV, or high-energy radiation.

[0080] Liquid Electrolyte (LIE)

[0081] The liquid electrolyte (LIE) may include an organic solvent (ORS), a lithium salt (LIS), and an additive (ADT). The lithium salt (LIS) and the additive (ADT) may be dispersed in the organic solvent (ORS). The organic solvent (ORS), the lithium salt (LIS), and the additive (ADT) will be described in more detail below.

[0082] The additive (ADT) may include an organic phosphate that can act as a flame-retardant additive. The organic phosphate may be represented by the following chemical formula 1 or chemical formula 2.

[0083] [Chemical Formula 1]

[0084]

[0085] [Chemical Formula 2]

[0086]

[0087] In the above chemical formula 1, R1 to R3 may each independently be a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C3 to C10 cycloalkyl group, or a substituted or unsubstituted C6 to C10 aryl group.

[0088] In the above chemical formula 2, R4 to R7 may each independently be a substituted or unsubstituted C1 to C5 alkyl group, a substituted or unsubstituted C1 to C5 alkoxy group, a substituted or unsubstituted C2 to C5 alkenyl group, a substituted or unsubstituted C2 to C5 alkynyl group, or a substituted or unsubstituted C3 to C5 cycloalkyl group.

[0089] In the above chemical formulas 1 and 2, R1 to R7 may each be independently a substituted or unsubstituted C1 to C3 alkyl group, or a substituted or unsubstituted C1 to C3 alkoxy group. For example, the organic phosphate may include at least one of trimethyl phosphate (TMP), triethyl phosphate (TEP), tetraethyl pyrophosphate (TEPP), or a combination thereof.

[0090] The above organic phosphate can function as a flame-retardant additive. In the case of a lithium battery containing a gel-type polymer electrolyte, if heat is continuously accumulated inside the battery, the electrolyte may undergo thermal decomposition, generating a large amount of hydrogen radicals (H·) and hydroxyl radicals (OH·). Specifically, radicals may be formed as the polymer chains of the cross-linked polymer (CLP) contained in the gel electrolyte (GPE) undergo thermal decomposition at high temperatures, and hydrogen and hydroxyl radicals may be generated as organic solvents (ORS) or other additives (crosslinking agents, thermal initiators, etc.) decompose at high temperatures. Such hydrogen radicals and hydroxyl radicals may cause a chain reaction of combustion in the electrolyte, thereby reducing the safety of the battery.

[0091] The organic phosphate according to the embodiments of the present invention can generate phosphate radicals (PO·) or other phosphorus compounds upon combustion. Phosphate radicals or other phosphorus compounds can terminate a chain combustion reaction by reacting with H· and HO· to ​​neutralize them.

[0092] The organic phosphate according to the embodiments of the present invention may be a low-molecular compound having a molecular weight (Mw) of 400 g / mol or less. For example, the molecular weight of the organic phosphate may be 100 g / mol to 400 g / mol, or 100 g / mol to 200 g / mol. In the embodiments, the fact that the organic phosphate is a low-molecular compound may be a concept contrasted with the crosslinking polymer (CLP). In other words, the organic phosphate may exist independently as a compound distinct from the crosslinking polymer (CLP) as an additive.

[0093] In this specification, molecular weight may refer to a value representing the mass of a molecule in grams, and 1 mole (approx. 6.022 × 10⁻⁶) 23 It can represent the mass of a substance containing as many molecules as (number). Molecular weight can be measured using mass spectrometers, gas density measurements, cryoscopy, etc.

[0094] When the organic phosphate is a low-molecular-weight compound as described above, the flame-retardant performance of the organic phosphate can be exhibited more effectively. When the molecular weight of the organic phosphate is small, the additive (ADT) can easily penetrate into the polymer matrix and interact effectively with the cross-linked polymer (CLP), thereby rapidly removing hydrogen radicals (H·) and hydroxyl radicals (OH·). Furthermore, when the molecular weight of the organic phosphate is small, it can decompose more easily when exposed to heat, releasing phosphate radicals or other phosphorus compounds. Accordingly, the chain combustion reaction caused by hydrogen radicals (H·) and hydroxyl radicals (OH·) can be rapidly terminated.

[0095] FIG. 7 is an enlarged cross-sectional view of a portion of a gel-type polymer electrolyte (GPE) according to a comparative example of the present invention.

[0096] Referring to FIG. 7, in a gel-type polymer electrolyte (GPE) according to a comparative example of the present invention, an additive (ADT) containing an organic phosphate may be bonded to a cross-linked polymer (CLP). That is, the additive (ADT) may not be dispersed in the liquid electrolyte (LIE) but may exist in a form constituting part of the polymer chain (CLP). Here, the additive (ADT) may be part of the polymer, rather than in the form of a low-molecular-weight compound as described in FIG. 6.

[0097] Because the organic phosphate is bonded to the polymer chain (CLP), it may be difficult for phosphate radicals to be released from the organic phosphate when a combustion reaction occurs. Furthermore, since the organic phosphate is present inside the polymer chain (CLP), it may be difficult for rapid interaction to occur between the phosphate and the polymer chain (CLP). Consequently, when the additive (ADT) is bonded to the cross-linked polymer (CLP), the flame retardant effect of the phosphate may be reduced.

[0098] Referring again to FIG. 6, in a gel-type polymer electrolyte (GPE) according to an embodiment of the present invention, an additive (ADT) containing organic phosphate may be dispersed in an organic solvent (ORS) of a liquid electrolyte (LIE). In this case, when a combustion reaction occurs, the additive (ADT) can easily decompose to release phosphate radicals and effectively interact with the cross-linked polymer (CLP). Consequently, when the additive (ADT) is dispersed in an organic solvent (ORS), flame-retardant performance can be effectively exhibited.

[0099] The content of the additive (ADT) may be, for example, 1 to 30 weight%, 1 to 25 weight%, 1 to 20 weight%, 2 to 20 weight%, 3 to 20 weight%, or 3 to 15 weight% based on the total weight of the gel-type polymer electrolyte (GPE).

[0100] If the content of the additive (ADT) is less than 1% by weight relative to the total weight of the gel polymer electrolyte (GPE), it may not form enough PO· to ​​terminate the chain thermal decomposition process during the combustion of the electrolyte. In other words, thermal stability may be reduced.

[0101] If the content of the additive (ADT) exceeds 30% by weight relative to the total weight of the gel polymer electrolyte (GPE), the ionic conductivity may decrease. If the ionic conductivity decreases, the charge / discharge efficiency or lifespan characteristics of the lithium metal battery may be degraded.

[0102] Lithium salts (LIS) may be selected without restriction as long as they are used as lithium salts in the relevant technical field. For example, lithium salts (LIS) include LiSCN, LiN(CN)2, Li(CF3SO2)3C, Li(FSO2)2N(LiFSI), LiC4F9SO3, LiN(SO2CF2CF3)2, LiPF3(C2F5)3, LiCl, LiF, LiBr, LiI, LiB(C2O4)2, LiPF6, LiPF5(CF3), LiPF5(C2F5), LiPF5(C3F7), LiPF4(CF3)2, LiPF4(CF3)(C2F5), LiPF3(CF3)3, LiPF3(CF2CF3)3, LiPF4(C2O4)2, LiBF4, LiBF3(C2F5), lithium bis(oxalato) borate (LiBOB), lithium oxalyldifluoroborate (LIODFB), and lithium It may include lithium difluoro(oxalato)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2), LiN(SO2C2F5)2, LiCF3SO3, LiAsF6, LiSbF6, LiClO4, or any combination thereof.

[0103] For example, the lithium salt (LIS) may contain at least one of a borate-based lithium salt and a fluorine-based lithium salt, and may include at least one selected from the group consisting of lithium difluoro(oxalate)borate (LiDFOB), lithium bis(oxalate)borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0104] More specifically, the lithium salt (LIS) may include a borate-based lithium salt. For example, the lithium salt (LIS) may include at least one selected from the group consisting of lithium difluoro(oxalate)borate (LiDFOB), lithium bis(oxalate)borate (LiBOB), and lithium tetrafluoroborate (LiBF-4).

[0105] By including a borate-based compound in the lithium salt (LIS), the high-temperature stability of the liquid electrolyte (LIE) can be improved. Additionally, the generation of hydrofluoric acid (HF) due to side reactions within the liquid electrolyte (LIE) can be suppressed. Consequently, the chemical stability of the liquid electrolyte (LIE) can be improved.

[0106] The liquid electrolyte (LIE) may contain multiple different lithium salts (LIS). The concentration of each lithium salt (LIS) present in the liquid electrolyte (LIE) may be 0.1 M to 5.0 M.

[0107] Organic solvents (ORS) may be used without limitation as long as they are used as organic solvents in the relevant technical field. For example, organic solvents may be propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

[0108]

[0109] Crosslinked polymer (CLP)

[0110] Crosslinked polymers (CLPs) can be polymerization products of crosslinkable monomers.

[0111] The above-mentioned crosslinkable monomers are, for example, trimethylolpropane trimethacrylate (TMPTMA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, trimethylolpropane triacrylate, propoxylate (3) trimethylolpropane triacrylate (PO(3)TMPTA), propoxylated (6) trimethylolpropane triacrylate (PO(6)TMPTA), ethoxylated trimethylolpropane triacrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol triacrylate (PETA), propoxylated glyceryl triacrylate, tris(2-hydroxyethyl) It may include isocyanurate triacrylate (THEICTA), dipentaerythritol pentaacrylate (DPEPA), or a combination thereof.

[0112] The molecular weight of the crosslinked polymer (CLP) may be 1,000 g / mol or less. For example, the molecular weight of the crosslinked polymer (CLP) may be 1,000 g / mol to 10,000 g / mol or 1,000 g / mol to 5,000 g / mol. When the molecular weight of the crosslinked polymer is 10,000 g / mol or less, the impregnation to the anode may be increased. In addition, the ionic conductivity of the gel-type polymer electrolyte may be improved.

[0113] The content of the crosslinking polymer (CLP) may be, for example, less than 60 wt%, 1 wt% to 50 wt%, 1 wt% to 45 wt%, 1 wt% to 40 wt%, 1 wt% to 35 wt%, 1 wt% to 30 wt%, 1 wt% to 25 wt%, 1 wt% to 20 wt%, 1 wt% to 15 wt%, 1 wt% to 10 wt%, 1 wt% to 9 wt%, 1 wt% to 8 wt%, 1 wt% to 7 wt%, 1 wt% to 6 wt%, or 1 wt% to 5 wt% based on the total weight of the gel polymer electrolyte (GPE), but is not limited thereto as long as it is an appropriate concentration that can form the gel polymer electrolyte (GPE) by adding it to the liquid electrolyte (LIE).

[0114] A gel polymer electrolyte (GPE) can be formed by crosslinking a composition for forming a gel polymer electrolyte. The method of crosslinking the composition for forming a gel polymer electrolyte is not particularly limited and may be crosslinked by, for example, heat, ultraviolet light, etc. Thermal crosslinking may be used from the perspective of manufacturing efficiency. The composition for forming a gel polymer may include, for example, a thermal initiator. The thermal initiator may be, for example, t-amyl peroxide, azobis-based, etc., but is not limited to these; any material used as a thermal initiator in the relevant technical field is acceptable. The content of the thermal initiator may be 0.1% by weight or less or 0.05% by weight or less of the total weight of the composition for forming a gel polymer electrolyte. The crosslinking product of the composition for forming a gel polymer electrolyte may be, for example, the result of heat treatment at 40 to 120°C for 1 to 3 hours. The heat treatment conditions may be adjusted according to the type of thermal initiator used.

[0115]

[0116] Referring to FIGS. 8 to 10, a lithium secondary battery (LBT) according to embodiments of the present invention may include a positive electrode (PEL), a negative electrode (NEL), and a separator (SEP). A battery structure (BTS) may be formed by winding or folding the positive electrode (PEL), the negative electrode (NEL), and the separator (SEP). A plurality of positive electrodes (PEL), negative electrodes (NEL), and separators (SEP) may be stacked to form a battery structure (BTS). The battery structure (BTS) may be housed in a battery case (CAS). After injecting an electrolyte into the battery case (CAS), an electrolyte layer may be formed. The battery case (CAS) may be sealed with a cap assembly (CAB). The battery case (CAS) may be cylindrical, prismatic, thin-film, etc. A lithium secondary battery (LBT) may be manufactured by sealing the battery case (CAS). The lithium secondary battery (LBT) may be a cylindrical or prismatic secondary battery. Alternatively, the lithium secondary battery (LBT) may be a pouch-type lithium secondary battery in which a battery structure (BTS) is packaged in a pouch. The battery structure (BTS) may include an electrode tab (ELT). The electrode tab (ELT) may serve as an electrical pathway for inducing the formed current to the outside.

[0117]

[0118] FIGS. 11a to 11c are for illustrating a method for manufacturing a lithium secondary battery according to embodiments of the present invention. A method for manufacturing a lithium secondary battery according to embodiments of the present invention may include: forming an electrode assembly by stacking a negative electrode, a separator, and a positive electrode; injecting a composition for forming a gel-type polymer electrolyte into the electrode assembly; and curing the composition for forming a gel-type polymer electrolyte.

[0119] Referring to FIG. 11a, forming an electrode assembly may include preparing a positive electrode (PEL), preparing a negative electrode (NEL), and providing a separator (SEP) between the positive electrode (PEL) and the negative electrode (NEL).

[0120] Providing a positive electrode (PEL) may include preparing a positive electrode current collector (COL2), preparing a positive electrode active material slurry, and applying the positive electrode active material slurry onto the positive electrode current collector (COL2) to form a positive electrode active material layer (PAL).

[0121] Providing a negative electrode (NEL) may include preparing a negative electrode current collector (COL1). In some cases, it may further include forming a negative electrode active material layer on the negative electrode current collector (COL1), forming a protective layer on the negative electrode current collector, or forming a host layer on the negative electrode current collector.

[0122] Referring to FIG. 11b, a gel-type polymer electrolyte forming composition (GPC) can be injected into an electrode assembly. The gel-type polymer electrolyte forming composition (GPC) can be injected to fill the empty space of the electrode assembly. A separator (SEP) and / or a positive active material layer (PAL) can be impregnated with the gel-type polymer electrolyte forming composition (GPC).

[0123] A composition for forming a gel-type polymer electrolyte (GPC) comprises an organic solvent, a lithium salt, an additive, and a crosslinkable monomer, wherein the additive may include an organic phosphate. The composition for forming a polymer electrolyte (GPC) may further include a thermal initiator.

[0124] The above additive may be the same as described above with reference to FIG. 6. For example, the additive may include a low molecular weight organic phosphate having a molecular weight (Mw) of 100 g / mol to 400 g / mol, and the organic phosphate may be represented by the following chemical formula 1 or 2.

[0125] [Chemical Formula 1]

[0126]

[0127] [Chemical Formula 2]

[0128]

[0129] In the above chemical formulas 1 and 2, R1 to R7 may each be independently a substituted or unsubstituted C1 to C3 alkyl group, or a substituted or unsubstituted C1 to C3 alkoxy group. For example, the organic phosphate may include at least one of trimethyl phosphate (TMP) and triethyl phosphate (TEP).

[0130] The organic solvent, lithium salt, and crosslinking monomer may also be the same or similar as described above with reference to FIG. 6. For example, the organic solvent may include a carbonate-based solvent, and the lithium salt may include a borate-based lithium salt and / or a fluorine-based lithium salt. The crosslinking monomer may include at least one selected from the group consisting of trimethylolpropane trimethacrylate (TMPTMA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, trimethylolpropane triacrylate, and propoxylate (3) trimethylolpropane triacrylate (PO(3)TMPTA).

[0131] Referring to FIG. 11c, the gel-type polymer electrolyte forming composition (GPC) injected into the electrode assembly can be cured. More specifically, after the gel-type polymer electrolyte forming composition (GPC) is injected, a heat treatment process (HEP) can be performed on the electrode assembly. The heat treatment process (HEP) can be performed at a temperature of 40°C to 120°C for about 30 minutes to 120 minutes. An electrolyte layer can be formed through the heat treatment process (HEP). That is, through the heat treatment process (HEP), the crosslinking monomers within the gel-type polymer electrolyte forming composition (GPC) can be crosslinked to form a crosslinked polymer. The crosslinked polymer forms a crosslinked network, and a liquid electrolyte can be included on the crosslinked network. The crosslinked network can form a structure having mechanical properties. A liquid electrolyte is introduced into the cross-linking network to minimize the exposure of the liquid electrolyte and form a uniform lithium ion flow across the electrode. As a result, a lithium secondary battery with improved stability can be manufactured.

[0132]

[0133] The creative concept described herein will be explained in more detail below through embodiments and comparative examples of the present invention. However, the embodiments are merely illustrative and the scope of the creative concept described herein is not limited solely to these embodiments.

[0134] Example 1

[0135] (Preparation of composition for forming gel-type polymer electrolytes)

[0136] A liquid electrolyte was prepared by adding 1 M lithium hexafluorophosphate (LiPF6) and tetraethyl pyrophosphate (TEPP) to an organic solvent mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 volume ratio. At this time, TEPP was added in an amount of 6 wt% relative to the total weight of the gel-type polymer electrolyte.

[0137] A composition for forming a gel-type polymer electrolyte was prepared by adding the crosslinkable monomer TMPTMA (Trimethylolpropane trimethacrylate) to a liquid electrolyte. At this time, the content of TMPTMA is 5% by weight of the total weight of the gel-type polymer electrolyte.

[0138] (Lithium battery manufacturing)

[0139] A copper foil with a thickness of 10 μm was used as the cathode current collector.

[0140] LiNi, the positive active material 0.8 Co 0.15 Al 0.05 O2(NCA) powder and carbon conductive material (Super-P; Timcal Ltd.) were uniformly mixed in a weight ratio of 90:5, and then a PVDF (polyvinylidene fluoride) binder solution was added to prepare an anode active material slurry with a weight ratio of active material:carbon-based conductive material:binder = 90:5:5.

[0141] The prepared slurry was coated onto an aluminum substrate with a thickness of 20 μm using a doctor blade, dried under reduced pressure at 120 °C, and then rolled into a sheet shape using a roll press to manufacture an anode. The thickness of the anode active material layer was 80 μm.

[0142] A laminate was prepared by placing a polyethylene separator between the manufactured positive and negative current collectors. After injecting the gel-type polymer electrolyte forming composition prepared in Example 1 into the prepared laminate, a lithium battery containing a gel-type polymer electrolyte was manufactured by thermally crosslinking in a 70°C oven for 1 hour and 30 minutes.

[0143] The lithium battery had a positive electrode / gel-type polymer electrolyte (separator) / negative current collector structure.

[0144]

[0145] Example 2

[0146] (Preparation of composition for forming gel-type polymer electrolytes)

[0147] A composition for forming a gel-type polymer electrolyte was prepared in the same manner as in Example 1, except that trimethyl phosphate (TMP) was added instead of tetraethyl pyrophosphate (TEPP) in the preparation of the liquid electrolyte to an amount of 8% by weight relative to the total weight of the gel-type polymer electrolyte.

[0148] (Lithium battery manufacturing)

[0149] A lithium battery was manufactured using the same method as in Example 1.

[0150]

[0151] Example 3

[0152] (Preparation of composition for forming gel-type polymer electrolytes)

[0153] A liquid electrolyte was prepared by adding 0.6 M lithium tetrafluoroborate (LiBF4), 0.6 M lithium difluoro(oxalato)borate (LiDFOB), and trimethyl phosphate (TMP) to an organic solvent mixed with diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in a 2:1 volume ratio. At this time, TMP was added to be 8% by weight of the total weight of the gel-type polymer electrolyte.

[0154] A composition for forming a gel-type polymer electrolyte was prepared by adding the crosslinking monomer DPHA (dipentaerythritol hexacrylate) to a liquid electrolyte. At this time, the content of DPHA is 7% by weight relative to the total weight of the gel-type polymer electrolyte.

[0155] (Lithium battery manufacturing)

[0156] A lithium battery was manufactured using the same method as in Example 1.

[0157]

[0158] Example 4

[0159] (Preparation of composition for forming gel-type polymer electrolytes)

[0160] A liquid electrolyte was prepared by adding lithium bis(trifluoromethanesulfonyl)imide (LiTFSI 1 M) and trimethyl phosphate (TMP) to a dimethyl ether (DME) organic solvent. At this time, TMP was added at 14 wt% of the total weight of the gel-type polymer electrolyte.

[0161] A composition for forming a gel-type polymer electrolyte was prepared by adding the crosslinking monomer DPHA (dipentaerythritol hexacrylate) to a liquid electrolyte. At this time, the content of DPHA is 10 wt% with respect to the total weight of the gel-type polymer electrolyte.

[0162] (Lithium battery manufacturing)

[0163] A lithium battery was manufactured using the same method as in Example 1.

[0164]

[0165] Example 5

[0166] (Preparation of composition for forming gel-type polymer electrolytes)

[0167] A liquid electrolyte was prepared by adding 0.6 M lithium tetrafluoroborate (LiBF4), 0.6 M lithium difluoro(oxalato)borate (LiDFOB), and triethyl phosphate (TEP) to an organic solvent mixed with diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in a 2:1 volume ratio. At this time, TEP was added to be 10 wt% of the total weight of the gel-type polymer electrolyte.

[0168] A composition for forming a gel-type polymer electrolyte was prepared by adding the crosslinking monomer DPHA (dipentaerythritol hexacrylate) to a liquid electrolyte. At this time, the content of DPHA is 5% by weight relative to the total weight of the gel-type polymer electrolyte.

[0169] (Lithium battery manufacturing)

[0170] A lithium battery was manufactured using the same method as in Example 1.

[0171]

[0172] Comparative Example 1

[0173] A composition for forming a gel-type polymer electrolyte and a lithium metal battery were prepared in the same manner as in Example 3, except that triethyl phosphate (TEP) was not added during the preparation of the liquid electrolyte.

[0174]

[0175] Comparative Example 2

[0176] A composition for forming a gel-type polymer electrolyte and a lithium metal battery were prepared in the same manner as in Example 3, except that tris(2-ethylhexyl) phosphate (TEHP), having a molecular weight of about 434.65 g / mol, was added instead of triethyl phosphate (TEP) when preparing the liquid electrolyte, in an amount of 8% by weight relative to the total weight of the gel-type polymer electrolyte.

[0177]

[0178] Comparative Example 3

[0179] A composition for forming a gel-type polymer electrolyte and a lithium metal battery were prepared in the same manner as in Example 3, except that tris(biphenyl) phosphate (TBPP), having a molecular weight of about 554.57 g / mol, was added instead of triethyl phosphate (TEP) when preparing the liquid electrolyte, in an amount of 8% by weight relative to the total weight of the gel-type polymer electrolyte.

[0180]

[0181] Table 1 below shows the compositions of the above-described Examples 1 to 5 and Comparative Examples 1 to 3.

[0182]

[0183] Lithium Salt Organic Solvent Additive (Wt%*) Crosslinkable Monomer (Wt%*) Example 1 LiPF61 MEC, DECTEPP (6 wt%) TMPTMA (5 wt%) Example 2 LiPF61 MEC, DECTMP (8 wt%) TMPTMA (5 wt%) Example 3 LiBF40.6 M, LiDFOB0.6 MDEC, FECTMP (8 wt%) DPHA (7 wt%) Example 4 LiTFSI1 MDMETMP (14 wt%) DPHA (10 wt%) Example 5 LiBF40.6 M, LiDFOB0.6 MDEC, FECTEP (10 wt%) DPHA (5 wt%) Comparative Example 1 LiBF40.6 M, LiDFOB0.6 MDEC, FEC-DPHA (7 wt%) Comparative Example 2 LiBF40.6 M, LiDFOB0.6 MDEC, FECTEPHP (8 wt%) DPHA (7 wt%) wt%) Comparative Example 3LiBF40.6 M,LiDFOB 0.6 MDEC, FECTBPP(8 wt%)DPHA(7 wt%)

[0184] The above weight % is based on the total weight of the gel-type polymer electrolyte.

[0185]

[0186] Evaluation Example 1: Measurement of Ionic Conductivity

[0187] The ionic conductivity of the polymer gel-type polymer electrolytes prepared in Examples 1 to 5 and Comparative Examples 1 to 3 was measured and is shown in Table 2 below.

[0188] Ionic conductivity was measured using the AC impedance method. Specifically, ionic conductivity was measured by applying a voltage bias of 10 mV to the electrolyte in the frequency range of 0.1 Hz to 1 MHz, scanning the temperature, and measuring the resistance.

[0189]

[0190] Evaluation Example 2: Initial Charge / Discharge Efficiency and Lifetime Characteristics of Lithium Metal Batteries

[0191] The initial charge-discharge efficiency and lifespan characteristics of the lithium metal batteries of Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated under the following conditions, and the results are shown in Table 2 below.

[0192] Constant current charging was performed at 25°C with a current rate of 0.1 C until the voltage reached 4.2 V (vs. Li), and then cut-off was performed at a current rate of 0.05 C while maintaining 4.2 V in constant voltage mode. Subsequently, discharge was performed at a constant current rate of 0.1 C until the voltage reached 3.0 V (vs. Li) during discharge (formation cycle).

[0193] A lithium metal battery that has undergone a formation cycle was charged at a constant current rate of 0.2 C at 25°C until the voltage reached 4.2 V (vs. Li), and then cut off at a current rate of 0.05 C while maintaining 4.2 V in constant voltage mode. Subsequently, it was discharged at a constant current rate of 0.2 C until the voltage reached 3.0 V (vs. Li) during discharge (1st cycle). These cycles were repeated under the same conditions until the capacity retention rate reached 80%.

[0194] In all charge / discharge cycles, a 10-minute pause was taken after each charge / discharge cycle.

[0195] The initial charge / discharge efficiency (ICE) can be calculated according to the following mathematical formula 1.

[0196] <Mathematical Formula 1>

[0197] Initial charge / discharge efficiency [%] = [First cycle discharge capacity / First cycle charge capacity] × 100

[0198] Life characteristics are defined as the number of cycle repetitions until the capacity retention rate reaches 80%, and the capacity retention rate can be calculated according to the following mathematical formula 2.

[0199] <Mathematical Formula 2>

[0200] Capacity Retention Rate [%] = [Discharge Capacity after n cycles / Discharge Capacity at 1st cycle] × 100 (%)

[0201] (where n is a natural number greater than or equal to 2)

[0202]

[0203] Evaluation Example 3: Thermal Stability

[0204] The self-extinguish time of the gel-type polymer electrolyte used in the lithium metal batteries of Examples 1 to 5 and Comparative Examples 1 to 3 was measured to evaluate thermal stability, and the results are shown in Table 2 below.

[0205] Self-extinguishing time measurement refers to the time required for a sample to extinguish a fire on its own after being exposed to a flame under specific test conditions. To measure this, the gel-type polymer electrolytes used in Examples 1 to 5 and Comparative Examples 1 to 3 were coated to a uniform thickness on a non-combustible substrate. The electrolyte coated on the substrate was exposed to a flame using a torch, and the time it took for the flame on the burning electrolyte to be extinguished was measured and considered as the self-extinguishing time.

[0206] Ionic Conductivity (mS / cm) Initial Charge / Discharge Efficiency (%) Lifetime Characteristics (Number of Cycles) Self-Extinguishing Time (sec) Example 1 3.88 9.220 137 Example 2 3.68 9.419 832 Example 3 3.48 9.622 530 Example 4 3.18 8.222 227 Example 5 3.58 9.12 17 29 Comparative Example 1 3.28 9.212 100 Comparative Example 2 3.38 7.513 582 Comparative Example 3 3.08 6.714 875

[0207] Referring to Table 2, it can be seen that the lithium metal battery according to the embodiments has excellent lifespan characteristics and a short self-extinguishing time compared to the lithium secondary battery according to the comparative examples.

[0208] The above description describes specific embodiments for implementing the present invention. The present invention will include not only the embodiments described above, but also embodiments that can be simply modified or easily modified. Furthermore, the present invention will include technologies that can be easily modified and implemented using the embodiments. Accordingly, the scope of the present invention should not be limited to the embodiments described above, but should be defined by the claims set forth below as well as equivalents to the claims of this invention.

Claims

1. Comprising an organic solvent; a lithium salt; an additive; and a cross-linked polymer, The above additive includes organic phosphate, and The above lithium salt comprises at least one of a borate-based lithium salt and a fluorine-based lithium salt, and The above organic phosphate is a low-molecular compound having a molecular weight (Mw) of 100 g / mol to 400 g / mol and is dispersed in the above organic solvent, Gel-type polymer electrolyte.

2. In Paragraph 1, The above organic phosphate is represented by either of the following Chemical Formula 1 and Chemical Formula 2, Gel-type polymer electrolyte: [Chemical Formula 1] [Chemical Formula 2] In the above chemical formula 1, R1 to R3 are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C3 to C10 cycloalkyl group, or a substituted or unsubstituted C6 to C10 aryl group, and In the above chemical formula 2, R4 to R7 are each independently a substituted or unsubstituted C1 to C5 alkyl group, a substituted or unsubstituted C1 to C5 alkoxy group, a substituted or unsubstituted C2 to C5 alkenyl group, a substituted or unsubstituted C2 to C5 alkynyl group, or a substituted or unsubstituted C3 to C5 cycloalkyl group.

3. In Paragraph 2, The above R1 to R7 are each independently substituted or unsubstituted C1 to C3 alkyl groups or alkoxy groups, Gel-type polymer electrolyte.

4. In Paragraph 1, The above organic phosphate comprises at least one of trimethyl phosphate (TMP), triethyl phosphate (TEP), tetraethyl pyrophosphate (TEPP), or a combination thereof. Gel-type polymer electrolyte.

5. In Paragraph 1, The content of the above additive is 1% to 30% by weight based on 100% by weight of the total weight of the gel-type polymer electrolyte, Gel-type polymer electrolyte.

6. In Paragraph 1, The lithium salt comprises at least one selected from the group consisting of lithium difluoro(oxalate)borate (LiDFOB), lithium bis(oxalate)borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Gel-type polymer electrolyte.

7. In Paragraph 1, The above organic solvent includes a carbonate-based compound, and The above carbonate-based compound comprises dimethyl carbonate (DMC), diethyl carbonate (DEC), dimethyl ether (DME), methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, propylene carbonate, ethylene carbonate (EC), fluoroethylene carbonate (FEC), butylene carbonate, vinylene carbonate, or a combination thereof. Gel-type polymer electrolyte.

8. In Paragraph 1, The above-mentioned crosslinked polymer is a polymerization product of crosslinkable monomers, and The above crosslinkable monomers are trimethylolpropane trimethacrylate (TMPTMA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, trimethylolpropane triacrylate, propoxylate (3) trimethylolpropane triacrylate (PO(3)TMPTA), propoxylated (6) trimethylolpropane triacrylate (PO(6)TMPTA), ethoxylated trimethylolpropane triacrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol triacrylate (PETA), propoxylated glyceryl triacrylate, tris(2-hydroxyethyl) Comprising isocyanurate triacrylate (THEICTA), dipentaerythritol pentaacrylate (DPEPA), or a combination thereof, Gel-type polymer electrolyte.

9. In Paragraph 9, The above-mentioned crosslinkable monomer comprises at least one of trimethylolpropane trimethacrylate (TMPTMA) and dipentaerythritol hexaacrylate (DPHA). Gel-type polymer electrolyte.

10. In Paragraph 1, The molecular weight (Mw) of the above-mentioned crosslinked polymer is 1,000 g / mol to 10,000 g / mol, Gel-type polymer electrolyte.

11. In Paragraph 1, The content of the crosslinked polymer is 1% to 50% by weight based on 100% by weight of the total weight of the gel-type polymer electrolyte, Gel-type polymer electrolyte.

12. In Paragraph 1, further comprising a thermal initiator, Gel-type polymer electrolyte.

13. A positive electrode comprising a positive current collector and a positive active material layer on the positive current collector; A cathode comprising a cathode current collector; and It includes an electrolyte layer disposed between the anode and the cathode, The above electrolyte layer comprises the gel-type polymer electrolyte of claim 1, Lithium metal battery.

14. In Paragraph 13, The above-mentioned cathode current collector and the above-mentioned anode further include a separator between them, The above separator is impregnated into the above gel-type polymer electrolyte, and The gel-type polymer electrolyte is filled into the pores of the separator. Lithium metal battery.

15. In Paragraph 13, The above electrolyte layer and the above negative current collector further include a protective layer between them, The protective layer comprises at least one polymer selected from the group consisting of polyvinyl alcohol, polyimide, vinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, carboxymethylcellulose, and styrene-butyrene rubber. Lithium metal battery.

16. In Paragraph 13, The lithium metal layer between the electrolyte layer and the negative current collector is further included, The above lithium metal layer comprises lithium or a lithium alloy, Lithium metal battery.

17. In Paragraph 13, The above electrolyte layer and the above negative current collector further comprise a host layer between them, The above host layer provides a space for lithium to be electrodeposited, and The above host layer comprises at least one of carbon and metal, Lithium metal battery.

18. Forming an electrode assembly by stacking a cathode, a separator, and an anode; Injecting a composition for forming a gel-type polymer electrolyte into the electrode assembly; and Curing the above-mentioned gel-type polymer electrolyte forming composition; comprising, The above-mentioned gel-type polymer electrolyte forming composition is: It comprises an organic solvent; a lithium salt; an additive; and a crosslinkable monomer, The above additive includes organic phosphate, and The above organic phosphate is a low molecular weight compound with a molecular weight (Mw) of 100 g / mol to 400 g / mol, and The above lithium salt comprises at least one of a borate-based lithium salt and a fluorine-based lithium salt. Method for manufacturing a lithium metal battery.

19. In Paragraph 18, The above organic phosphate is represented by either of the following Chemical Formula 1 and Chemical Formula 2, Method for manufacturing a lithium metal battery: [Chemical Formula 1] [Chemical Formula 2] In the above Chemical Formulas 1 and 2, R1 to R7 are each independently substituted or unsubstituted C1 to C3 alkyl groups or alkoxy groups, Method for manufacturing a lithium metal battery.

20. In Paragraph 18, Curing the above-mentioned gel-type polymer electrolyte-forming composition includes a curing reaction using heat treatment, and The temperature of the above heat treatment is 40℃ to 120℃, Method for manufacturing a lithium metal battery.

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