KR20210089097A - Rechargeable lithium battery - Google Patents

Abstract

Provided is a lithium secondary battery which comprises: a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; and a first function layer present between the positive electrode and the negative electrode. The first function layer comprises plate shaped poly olefin particles having the average diameter of 1 to 8 ㎛. The positive electrode comprises: a positive electrode active material layer comprising a positive electrode active material and a flame retardant; or has a stacked structure comprising the positive electrode active material layer and a second function layer comprising a flame retardant. According to the present invention, the lithium secondary battery implements high capacity and high energy density while exhibiting excellent thermal stability and physical stability.

Description

Lithium secondary battery {RECHARGEABLE LITHIUM BATTERY}

It relates to a lithium secondary battery.

As a driving power source for mobile information terminals such as mobile phones, notebook computers, and smart phones, lithium secondary batteries having high energy density and being easy to carry are mainly used. In addition, recently, research for using a lithium secondary battery as a driving power source for a hybrid vehicle or an electric vehicle or as a power storage power source by using a characteristic of high energy density is being actively conducted.

One of the main research tasks in the lithium secondary battery is to improve the safety of the secondary battery. For example, when a lithium secondary battery is heated due to an internal short circuit, overcharging, and overdischarging, an electrolyte decomposition reaction and thermal runaway phenomenon occur, the pressure inside the battery rapidly rises and explosion of the battery may be induced. Among them, when an internal short circuit of the lithium secondary battery occurs, the high electrical energy stored in each electrode is instantaneously conducted in the short-circuited positive and negative electrodes, so that the risk of explosion is very high.

Since such an explosion may inflict fatal damage to a user in addition to simply damaging the lithium secondary battery, it is urgent to develop a technology capable of improving the stability of the lithium secondary battery.

To provide a lithium secondary battery with improved stability.

One embodiment is a positive electrode comprising a positive electrode active material; a negative electrode including an anode active material; and a first functional layer present between the positive electrode and the negative electrode, wherein the first functional layer includes plate-shaped polyolefin particles having an average particle diameter of 1 μm to 8 μm, and the positive electrode includes a positive electrode active material and a flame retardant Provided is a lithium secondary battery having a stacked structure including a positive electrode active material layer or a positive electrode active material layer and a second functional layer including a flame retardant.

The lithium secondary battery according to the exemplary embodiment may exhibit excellent thermal and physical safety while implementing high capacity and high energy density.

1 is a diagram schematically illustrating a structure of an electrode assembly according to an exemplary embodiment.
2 is a diagram schematically showing the structure of a lithium secondary battery according to an embodiment.
3 is a scanning electron microscope photograph of polyethylene spherical particles in an aqueous dispersion state.
4 is a scanning electron microscope photograph of polyethylene plate-shaped particles according to an embodiment.
5 is a photograph of the thermal safety evaluation result of the battery prepared in Comparative Example 1. FIG.
6 is a photograph of the thermal safety evaluation result of the battery prepared in Comparative Example 2.
7 is a photograph of the thermal safety evaluation result of the battery prepared in Example 1. FIG.
8 is a photograph of the thermal safety evaluation result of the battery prepared in Example 2.
9 is a photograph of the thermal safety evaluation result of the battery prepared in Example 3. FIG.
10 is a photograph showing results of evaluation of penetration safety of the battery prepared in Comparative Example 1. FIG.
11 is a photograph showing results of evaluation of penetration safety of the battery prepared in Comparative Example 2. FIG.
12 is a photograph showing results of evaluation of penetration safety of the battery prepared in Example 1. FIG.
13 is a photograph showing results of evaluation of penetration safety of the battery prepared in Example 2. FIG.
14 is a photograph showing results of penetration safety evaluation of the battery prepared in Example 3. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

Unless otherwise defined herein, the average particle diameter means the diameter (D50) of particles having a cumulative volume of 50% by volume in the particle size distribution. The average particle diameter can be measured by a method well known to those skilled in the art, for example, it is measured with a particle size analyzer, or a transmission electron microscope (Transmission Electron Microscope) photograph or a scanning electron microscope (Scanning Electron Microscope) photograph. can also be measured as As another method, it is measured using a measuring device using a dynamic light-scattering method, data analysis is performed, the number of particles is counted for each particle size range, and the average particle size value calculated therefrom can get

A lithium secondary battery according to an embodiment includes a positive electrode including a positive electrode active material; a negative electrode including an anode active material; and a first functional layer present between the positive electrode and the negative electrode, wherein the first functional layer includes plate-shaped polyolefin particles having an average particle diameter of 1 μm to 8 μm, and the positive electrode includes a positive electrode active material and a flame retardant It may have a laminated structure including a positive electrode active material layer, or a positive electrode active material layer and a second functional layer including a flame retardant.

Hereinafter, the lithium secondary battery will be described with reference to FIGS. 1 and 2 .

1 is a cross-sectional view of an electrode assembly included in a lithium secondary battery according to an embodiment, and FIG. 2 is a diagram schematically illustrating a structure of a lithium secondary battery according to an embodiment of the present invention.

Referring to FIG. 1 , the electrode assembly 40 includes a positive electrode 10 including a positive electrode current collector 11 and a positive electrode active material layer 13 formed on the positive electrode current collector 11 ; A first functional layer 30 including a negative electrode current collector 21 and a negative electrode 20 including a negative electrode active material layer 23 formed on the negative electrode current collector 21 and present between the positive electrode 10 and the negative electrode 20 . ) is included.

Referring to FIG. 2 , a lithium secondary battery 100 according to an embodiment includes an electrode assembly 40 wound with a first functional layer 30 interposed between the positive electrode 10 and the negative electrode 20 , and the electrode It may include a case 50 in which the assembly 40 is incorporated. Although the lithium secondary battery according to an embodiment is described as having a prismatic shape as an example, the present invention is not limited thereto, and may be applied to various types of batteries such as a cylindrical shape and a pouch type.

Hereinafter, the positive electrode 10 including the positive electrode current collector 11 and the positive electrode active material layer 13 formed on the positive electrode current collector 11 will be described.

The positive electrode current collector 11 may be an aluminum foil, a nickel foil, or a combination thereof, but is not limited thereto.

According to one embodiment, the positive electrode 10 may include a positive electrode active material layer 13 including a positive electrode active material and a flame retardant. When a flame retardant is included in the positive electrode active material layer, when the temperature rises due to an internal short circuit due to an external impact such as penetration, the flame retardant vaporizes, suppresses the temperature increase inside the battery and prevents battery ignition, thereby improving battery safety. can On the other hand, since the performance of the conventional battery can be maintained during normal battery operation, battery safety can be remarkably improved when an event occurs, and normal charging and discharging characteristics can be secured under normal circumstances.

The flame retardant is a compound that delays flammability, and as long as it has an endothermic action within the range of about 80°C to 200°C, materials widely known in the art can be used without limitation. The flame retardant may be an organic flame retardant, and the organic flame retardant may be a phosphorus-based flame retardant, a halogen-based flame retardant, a nitrogen-based flame retardant, or a combination thereof.

The phosphorus-based flame retardant is, between ammonium phosphate, ammonium polyphosphate, trioctyl phosphate, dimethyl methylphosphate, trimethylolpropane methylphosphonic oligomer, pentaerythritol phosphate, cyclic neopentyl thio phosphoric anhydride, triphenyl phosphate, tricresyl phosphate, tert-butylphenyl diphenyl phosphate, tetra Phenyl mp-phenylene diphosphate (tetraphenyl mp-phenylenediphosphate), tris (2,4-dibromophenyl) phosphate (tris (2,4-dibromophenyl) phosphate), N,N'-bis (2-hydroxyethyl ) aminomethyl phosphonate (N,N'-bis(2-hydoxyethyl)aminomethyl phosphonate), phosphine oxide, phosphine oxide diols, phosphites, phosphonates ( phosphonates), triaryl phosphate, alkyldiaryl phosphate, trialkyl phosphate, resorcinaol bisdiphenyl phosphate (RDP), or a combination thereof. . Here, alkyl may be, for example, C1 to C10 alkyl, and aryl may be, for example, C3 to C30 aryl.

The halogen-based flame retardant is tribromophenoxyethane, tetrabromobisphenol-A (TBBA), octabromo diphenyl ether (OBDPE), brominated epoxy, brominated polycarbonate oligomer, brominated benzyl alkyl ether, brominated benzoic acid ester, It may be a phthalate acid ester, chlorinated paraffin, chlorinated polyethylene, an alicyclic chlorine-based flame retardant or a combination thereof.

In addition, the nitrogen-based flame retardant may be, for example, melamine or a melamine derivative, for example, the nitrogen-based flame retardant may be melamine, melamine phosphate, melamine cyanurate, or a combination thereof.

The content of the flame retardant is 0.001 wt% to 30 wt%, for example 0.01 wt% to 20 wt%, 0.1 wt% to 15 wt%, 0.1 wt% to 10 wt%, 0.1 wt% based on the total amount of the positive electrode active material layer 13 % to 5% by weight, or 0.1% to 4% by weight. While securing the safety of the battery within the above range, it is possible to suppress a decrease in battery performance due to a decrease in electrical conductivity.

The positive active material may include a compound including at least one of a complex oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof.

Specifically, the compound including at least one of a complex oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be a compound represented by any one of the following formulas. Li _a A _1-b X _b D ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5); Li _a A _1-b X _b O _2-c D _c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a E _1-b X _b O _2-c D _c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a E _2-b X _b O _4-c D _c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α ≤ 2); Li _a Ni _1-bc Co _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b X _c O _2-α T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b X _c O _2-α T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _b E _c G _d O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1) Li _a CoG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn _1-b G _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn _1-g G _g PO ₄ (0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiZO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2).

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may include at least one coating element compound selected from the group consisting of an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. can The compound constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. In the coating layer forming process, any coating method may be used as long as it can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements in the compound (eg, spray coating, immersion method, etc.). Since the content can be well understood by those engaged in the field, a detailed description thereof will be omitted.

The positive active material layer may further include a compound of Formula 1 below.

[Formula 1]

Li _a1 Fe _1-x1 M _x1 PO ₄

In Formula 1, 0.90 ≤ a1 ≤ 1.8, 0 ≤ x1 ≤ 0.7, and M is Mg, Co, Ni, or a combination thereof.

When the compound of Formula 1 is included in the cathode active material layer 13, the cathode active material comprising at least one of a complex oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof, and the The mixing ratio of the compound represented by Formula 1 may be 9:1 to 5:5 by weight. Since the compound represented by Formula 1 has low electronic conductivity, when it is included in excess outside the above range, resistance is increased and output characteristics are lowered, which is not preferable, and when it is included in too small amount, it is difficult to realize the desired thermal safety effect.

The positive active material layer 13 may further include a binder and a conductive material.

Examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride. , polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like can be used. In addition, in one embodiment, as the binder, an organic binder, which is polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, or a combination thereof, is used. It is more appropriate to use

The conductive material is used to impart conductivity to the positive electrode, and any electronically conductive material that does not cause chemical change in the configured battery can be used, for example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black , carbon-based materials such as carbon fibers; metal-based substances such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including a mixture thereof may be used.

According to another embodiment, the positive electrode may have a stacked structure including a positive electrode active material layer and a second functional layer including a flame retardant. The second functional layer may be present between the positive electrode active material layer and the positive electrode current collector, present on the positive electrode active material layer, or both.

The positive active material layer may include a positive active material, and optionally a binder and/or a conductive material, and the description thereof is as described above.

The positive active material layer and/or the second functional layer may further include the compound of Formula 1 above. When the compound of Formula 1 is included in the positive electrode active material layer and/or the second functional layer, it is appropriate to enhance safety.

The average particle diameter of the compound of Formula 1 may be 2 μm or less, and may be 0.2 μm to 1 μm. When the average particle diameter of the compound of Formula 1 is greater than 2 μm, it is not appropriate because electron conductivity is lowered, the utilization rate of the compound of Formula 1 is lowered, battery resistance is increased, and cycle life characteristics may be deteriorated. Unless otherwise defined herein, the average particle diameter means the diameter (D50) of particles having a cumulative volume of 50% by volume in the particle size distribution.

The compound of Formula 1 included in the positive active material layer and the second functional layer may be the same as or different from each other.

The second functional layer including the flame retardant may further include an aqueous binder. As the water-based binder, a binder strong against oxidation is suitable, for example, at an anode potential of 4.45V (vs. Li ⁺ ) or less, any water-based binder having oxidation resistance may be used. Examples of the aqueous binder include styrene-butadiene rubber, acrylate-based compounds, imide-based compounds, polyvinylidene fluoride-based compounds, polyvinylpyrrolidone-based compounds, nitrile-based compounds, acetate-based compounds, cellulose-based compounds, and cyano-based compounds. can be heard

Specific examples of the acrylate-based compound include polyacrylic acid (PAA), polymethylmethacrylate, polyisobutylmethacrylate, polyethylacrylate, and polybutylacrylate. acrylate), polyethylhexyl acrylate (poly(2-ethylhexyl acrylate)), or a combination thereof.

Specific examples of the imide-based compound include polyimide, polyamide imide, or a combination thereof. In addition, specific examples of the polyvinylidene fluoride-based compound include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride-co-tetrafluoro Ethylene, polyvinylidene fluoride-co-trifluoroethylene, polyvinylidene fluoride-co-trifluorochloroethylene and polyvinylidene fluoride-co-ethylenefluoride-hexafluoropropylene (polyvinylidene fluoride-co -hexafluoropropylene: PVdF), polyvinylidene fluoride-trichloroethylene, or a combination thereof, and a specific example of the polyvinylpyrrolidone-based compound is polyvinylpyrrolidone (polyvinylpyrrolidone) ), or a combination thereof.

In addition, specific examples of the nitrile-based compound include polyacrylonitrile, acrylonitrilestyrene-butadiene copolymer, or a combination thereof, and a specific example of the acetate-based compound is polyvinyl. Acetate (polyvinylacetate), ethylene-co-vinyl acetate (polyethylene-co-vinyl acetate), cellulose acetate (cellulose acetate), cellulose acetate butyrate (cellulose acetate butyrate), cellulose acetate propionate (cellulose acetate propionate), or a combination thereof may be mentioned, and specific examples of the cellulosic compound include cyanoethyl cellulose, carboxyl methyl cellulose, or a combination thereof, and specific examples of the cyano-based compound include cyanoethyl sucrose. (cyanoethyl sucrose).

The binder having excellent oxidation resistance not only binds well to the compound capable of reversibly intercalating and deintercalating lithium in the positive electrode active material layer, but also binds well to the compound of Formula 1, so that the second functional layer It is possible to maintain a strong bond between the and the positive electrode active material layer.

When an aqueous binder is used for the second functional layer, it is appropriate to use water that does not damage the electrode as a solvent when forming the second functional layer. If an organic binder rather than an aqueous binder is used for the second functional layer, the organic solvent used to form the first functional layer and the second functional layer damages the electrode, that is, a spring back problem occurs. And, this is not preferable because the electronic conductivity is lowered, the thickness of the battery may be excessively increased, and it is not suitable because it may have a structural adverse effect on the active material layer.

The thickness of the second functional layer may be 1㎛ to 13㎛, according to another embodiment, may be 2㎛ to 4㎛. When the thickness of the second functional layer is included in the above range, there may be an advantage of enhancing safety.

The thickness of the positive active material layer may be 30 μm to 70 μm, for example, 60 μm to 70 μm. When the thickness of the positive electrode active material layer is included in the above range, there may be an advantage in that the energy density increases as the thickness increases.

In addition, a ratio of the thickness of the second functional layer to the thickness of the positive active material layer may be 30:1 to 10:1. When the ratio of the thickness of the second functional layer to the thickness of the positive active material layer is included in the above range, there may be an advantage in obtaining a second functional layer that improves safety while minimizing a decrease in energy density. In particular, when the thickness of the second functional layer and the thickness of the active material layer are included in the above range, and the ratio of the thickness of the second functional layer to the thickness of the positive electrode active material layer is included in the above range, the thickness of the positive active material layer is Accordingly, there may be an advantage in that the second functional layer has an appropriate thickness to enhance safety.

The thickness of the positive electrode active material layer may be the thickness after performing a rolling process when manufacturing the positive electrode .

When the second functional layer includes the compound of Formula 1 and the aqueous binder, the mixing ratio may be 24:1 to 50:1 by weight, and 43:1 to 50:1 by weight. When the mixing ratio of the compound of Formula 1 and the aqueous binder is within the above range, there may be advantages in terms of energy density, adhesion, dispersibility, and the like.

When the second functional layer includes the compound of Formula 1 and the aqueous binder, a thickener may be further included. As the thickener, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K or Li may be used. When the second functional layer further includes a thickener, the content of the thickener may be 0.6 parts by weight to 2 parts by weight based on 100 parts by weight of the compound of Formula 1 above. When the content of the thickener is included in this range, there may be advantages in thickening and improving dispersibility while minimizing the increase in resistance.

The positive electrode can be prepared by coating a positive electrode active material slurry on a current collector, drying and rolling to form a positive electrode active material layer, and applying a positive electrode functional layer slurry containing a flame retardant and an aqueous binder to the positive electrode active material layer and drying. . After drying the positive electrode functional layer slurry, a rolling process may be further performed.

Accordingly, the cathode active material layer may have a dense structure, and the second functional layer may have a porous structure. The cathode active material slurry is a compound including at least one of a complex oxide of lithium and a metal selected from cobalt, manganese, nickel, and a combination thereof and/or a cathode active material, a binder, a conductive material, which is a compound represented by Formula 1 It includes ash and an organic solvent, and the second functional layer slurry may include a flame retardant, an aqueous binder, and a water solvent. As the organic solvent, N-methyl pyrrolidone may be used. In addition, in the cathode active material slurry, the content of the cathode active material, the binder, and the conductive material may be appropriately adjusted to obtain the cathode active material layer composition described above, and the content of the flame retardant and the water-based binder in the second functional layer is the second functional layer It can be suitably adjusted so that a composition may be obtained.

The negative electrode 20 facing the positive electrode 10 includes a negative electrode current collector 21 and a negative electrode active material layer 23 formed on the negative electrode current collector 21 .

As the negative electrode current collector 21, one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with conductive metal, and combinations thereof may be used. can

The anode active material layer 23 includes an anode active material. The negative active material includes a material capable of reversibly intercalating/deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

The material capable of reversibly intercalating/deintercalating lithium ions is a carbon material, and any carbon-based negative active material generally used in lithium ion secondary batteries may be used, and a representative example thereof is crystalline carbon. , amorphous carbon or these may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon ( hard carbon), mesophase pitch carbide, and calcined coke.

The lithium metal alloy includes lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn from the group consisting of Alloys of selected metals may be used.

Examples of the material capable of doping and dedoping lithium include Si, SiO _x (0 ≤ x ≤ 2), Si-Q alloy (wherein Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, group 15 element, 16 It is an element selected from the group consisting of group elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO ₂ , Sn-R alloy (wherein R is an alkali metal, alkaline earth metal, group 13 element, 14 group element, group 15 element, group 16 element, transition metal, rare earth element, and an element selected from the group consisting of combinations thereof, not Sn), and the like, and also at least one of them and SiO ₂ by mixing can also be used. The elements Q and R include 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, Tl, Ge, P, As, Sb, Bi, One selected from the group consisting of S, Se, Te, Po, and combinations thereof may be used.

Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide or lithium titanium oxide.

The content of the anode active material in the anode active material layer 23 may be 95 wt% to 99 wt% based on the total weight of the anode active material layer.

In one embodiment, the negative active material layer 23 includes a binder, and may optionally further include a conductive material. The content of the binder in the anode active material layer 23 may be 1 wt% to 5 wt% based on the total weight of the anode active material layer 23 . In addition, when the conductive material is further included, 90 wt% to 98 wt% of the negative active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material may be used.

The binder serves to well adhere the negative active material particles to each other and also to adhere the negative active material to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride. , polyethylene, polypropylene, polyamideimide, polyimide polytetrafluoroethylene, or a combination thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, ethylene propylene copolymer, polyethylene oxide, polyepichrome. Drin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof can be

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickener. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K or Li may be used. The amount of the thickener used may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative active material.

Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon-based materials such as carbon fiber, metal powders such as copper, nickel, aluminum, silver, or metal-based materials such as metal fibers, polyphenylene derivatives, etc. A conductive material including a conductive polymer or a mixture thereof may be used.

The first functional layer 30 present between the positive electrode 10 and the negative electrode 20 may include plate-shaped polyolefin particles having an average particle diameter of 1 μm to 8 μm.

For example, the first functional layer 30 may be formed on the anode active material layer 23 including the anode active material. In this case, since the functional layer 30 may serve as a separator preventing direct contact between the positive electrode 10 and the negative electrode 20 , a lithium secondary battery including the same may not include a separate separator.

According to another exemplary embodiment, the first functional layer 30 may be formed on one surface of the separator to be positioned in contact with the anode active material layer 23 .

The first functional layer 30 may be advantageous in improving thermal and physical safety of the battery by rapidly shutting down the battery in an abnormal operation or thermal runaway situation. The shape of the plate-shaped polyethylene particles will be described with reference to FIGS. 3 and 4 . 3 is a scanning electron microscope (SEM) photograph of polyethylene spherical particles in a dispersion state, and FIG. 4 is a SEM photograph of plate-shaped polyethylene particles. Referring to FIGS. 3 and 4 , a difference in shape can be confirmed between the plate-shaped polyethylene particles and the conventional spherical polyethylene particles. Therefore, when the plate-shaped polyolefin particles according to one embodiment are used, the first functional layer 30 can be made thinner and wider than when the conventional spherical polyolefin particles are used, and the plate-shaped polyolefin particles are rapidly melted to form a large area. There may be advantages to closing the ion channels.

In general, polyolefin, for example, polyethylene, depending on the density HDPE (High density polyethylene, density: 0.94 g / cc to 0.965 g / cc), MDPE (Medium density polyethylene, density: 0.925 g / cc to 0.94 g / cc), LDPE (Low density polyethylene, density: 0.91 g / cc to 0.925 g / cc), VLDPE (Very low density polyethylene, density: 0.85 g / cc to 0.91 g / cc) and the like can be classified.

The plate-shaped polyolefin particles may include polyethylene, polypropylene, polybutylene, a copolymer thereof, or a mixture thereof. The polyethylene particles may be used alone or in combination of two or more polyethylene polymers such as HDPE, MDPE, LDPE, and the like.

The melting point (Tm) of the plate-shaped polyolefin particles may be 80 °C to 150 °C, for example, 90 °C to 140 °C.

The density of the plate-shaped polyolefin particles may be 0.91 g/cc to 0.98 g/cc, and specifically, 0.93 g/cc to 0.97 g/cc.

The particle size of the plate-shaped polyolefin particles may be 1 μm to 8 μm, for example, 1.5 μm or more, 2.0 μm or more, or 2.5 μm or more, and 8 μm or less, 7.5 μm or less, 7 μm or less, 6.5 μm or less, 6.0 μm or less, 5.5 μm or less, 5 μm or less, 4.5 μm or less, 4 μm or less, 3.5 μm or less, or 3 μm or less.

The ratio of the major axis length to the minor axis length of the plate-shaped polyolefin particles may be 1 to 5, specifically 1.1 to 4.5, for example, 1.2 to 3.5.

In addition, the thickness of the plate-shaped polyolefin particles may be 0.2 μm to 4 μm, specifically, 0.3 μm to 2.5 μm, 0.3 μm to 1.5 μm, or 0.3 μm to 1 μm.

When the size of the plate-shaped polyolefin particles, the ratio of the major axis to the minor axis length, and the thickness are within the above ranges, the battery performance is secured by minimizing the movement resistance of lithium ions, and the shut-down function is further strengthened to reduce the heat generation of the battery can be suppressed early.

The first functional layer 30 may further include inorganic particles and/or a binder in addition to the plate-shaped polyolefin particles. Accordingly, it is possible not only to suppress the heat generation of the battery from the shut-down function of the plate-shaped polyethylene, but also to prevent a short circuit between the positive electrode and the negative electrode from the electrical insulation of the inorganic particles, and the binder binds the plate-shaped polyethylene and the inorganic particles, In addition, these may be bound to the anode active material layer. Accordingly, thermal/physical safety and lifespan characteristics of the battery may be improved.

The inorganic particles are, for example, Al ₂ O ₃ , SiO ₂ , TiO ₂ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, GaO, ZnO, ZrO ₂ , Y ₂ O ₃ , SrTiO ₃ , BaTiO ₃ , Mg (OH) ₂ , boehmite, or a combination thereof may be included, but is not limited thereto. In addition, the inorganic particles may further include organic particles including an acrylic compound, an imide compound, an amide compound, or a combination thereof, but is not limited thereto.

The inorganic particles may have a spherical shape, a plate shape, a cubic shape, or an amorphous shape. The average particle size of the inorganic particles may be 1 nm to 2500 nm, for example, 100 nm to 2000 nm, 200 nm to 1000 nm, or 300 nm to 800 nm.

The total amount of the plate-shaped polyolefin particles and the inorganic particles may be 80 wt% to 99 wt%, specifically 85 wt% to 97 wt%, 90 wt% to 97 wt% based on the total weight of the first functional layer 30 % by weight, 93% to 97% by weight or 95% to 97% by weight.

The plate-shaped polyolefin particles and the inorganic particles may be included in a weight ratio of 95:5 to 10:90, for example, 75:25 to 30:70, 70:30 to 35:65, 65:35 to 40:60, 60 :40 to 45:55 or 55:45 to 50:50 may be included. Accordingly, the thickness of the first functional layer 30 may be appropriately adjusted and the safety of the battery may be efficiently improved.

The binder may be the same as that used for the anode active material layer, and is not particularly limited as long as it is a binder generally used in a lithium secondary battery. Accordingly, the binder may be included in an amount of 1 wt% to 20 wt%, specifically 3 wt% to 15 wt%, 3 wt% to 10 wt%, 3 wt% based on the total weight of the first functional layer 30 % to 7% by weight or 3% to 5% by weight.

The thickness of the first functional layer 30 may be 1 μm to 10 μm, for example, 2 μm to 8 μm or 3 μm to 7 μm.

The negative electrode 20 is formed by coating a negative electrode active material slurry on a current collector, drying and rolling to form a negative electrode active material layer, and the negative electrode active material layer includes plate-shaped polyolefin particles having an average particle diameter of 1 μm to 8 μm. 1 It can be prepared by coating the functional layer slurry and drying it. After drying the 1st functional layer slurry, you may perform a rolling process further.

Accordingly, the anode active material layer 23 may have a dense structure, and the first functional layer 30 may have a porous structure. The negative electrode active material slurry is a material capable of reversibly intercalating/deintercalating lithium ions, lithium metal, lithium metal alloy, lithium doping and dedoping material, or transition metal oxide negative active material, binder, conductive material It includes ash and water, and the functional layer slurry may include plate-shaped polyolefin particles having an average particle diameter of 1 μm to 8 μm, inorganic particles, a binder, and an organic solvent. As the organic solvent, an alcohol-based solvent may be used. In addition, the content of the negative electrode active material, the binder and the conductive material in the negative electrode active material slurry can be appropriately adjusted to obtain the above negative electrode active material layer composition, and the average particle diameter of the functional layer is 1㎛ to 8㎛ plate-shaped polyolefin particles, inorganic The content of the particles and the binder may be appropriately adjusted so that the above-described composition of the first functional layer 30 is obtained.

When the lithium secondary battery according to an exemplary embodiment further includes a separator, the first functional layer may be formed on one surface of the separator, and in this case, the same slurry as described above may be used for the first functional layer. Polyethylene, polypropylene, polyvinylidene fluoride, or a polymer multilayer film having two or more layers thereof may be used as the separator, a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, polypropylene/polyethylene/ It goes without saying that a mixed polymer multilayer film such as a polypropylene three-layer separator may be used. Alternatively, the separator may be one in which a ceramic such as _{Al 2} O ₃ or SiO _{2 is coated on the polymer multilayer film.}

The anode 10 , the cathode 20 , and the first functional layer 30 may be impregnated with an electrolyte (not shown).

The electrolyte includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents may be used.

Examples of the carbonate-based solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), and the like may be used. Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, caprolactone. etc. may be used. As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used. In addition, cyclohexanone and the like may be used as the ketone-based solvent. In addition, as the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. may be used, and the aprotic solvent is R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms. , nitriles such as nitriles (which may contain double bonds, aromatic rings or ether bonds), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. may be used. .

The organic solvent may be used alone or in a mixture of one or more, and when one or more of the organic solvents are mixed and used, the mixing ratio can be appropriately adjusted according to the desired battery performance, which can be widely understood by those in the art. have.

In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9, the electrolyte may exhibit excellent performance.

The organic solvent may further include an aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon-based compound represented by the following Chemical Formula 3 may be used.

[Formula 3]

In Formula 3,

R ₁ to R ₆ are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 ,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1, 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Rottoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2, 3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3 ,5-triiodotoluene, xylene, and combinations thereof are selected from the group consisting of.

The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound of Formula 4 as a lifespan improving additive to improve battery life.

[Formula 4]

In Formula 4,

R ₇ and R ₈ are the same as or different from each other, and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms, wherein R ₇ and R _{At least one of 8} is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R ₇ and R ₈ are not both hydrogen.

Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. can When such a life-enhancing additive is further used, its amount can be appropriately adjusted.

The lithium salt is dissolved in an organic solvent, serves as a source of lithium ions in the battery, enables basic lithium secondary battery operation, and promotes movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , Li(FSO ₂ ) ₂ N(lithium bis(fluorosulfonyl)imide: LiFSI), LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiPO ₂ F ₂ , LiN (C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ), where x and y are natural numbers, for example, integers from 1 to 20, lithium difluorobisoxalato phosphate (lithium) difluoro(bisoxolato) phosphate), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate: LiBOB), and lithium difluoro(oxalato) borate ( LiDFOB) may be one or two or more selected from the group consisting of.

The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, the electrolyte may exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions may move effectively.

Hereinafter, Examples and Comparative Examples of the present invention will be described. The following examples are only examples of the present invention, but the present invention is not limited to the following examples.

Example 1

(1) Preparation of anode

A positive active material in which LiNi _0.6 Co _0.2 Mn _0.2 O ₂ and LiNi _0.6 Co _0.2 Al _0.2 O _{2 are mixed in a weight ratio of 80:20 and LiFePO 4} having an average particle diameter (D50) of 0.42 μm in a weight ratio of 98:2 96 wt%, polyvinylidene fluoride binder, 2 wt%, and Ketjen Black conductive material 2 wt% were mixed in N-methylpyrrolidone solvent to prepare a cathode active material slurry, and based on 100 parts by weight of the cathode active material slurry By adding 2 parts by weight of a melamine-based flame retardant, a cathode active material slurry containing a flame retardant is prepared. This is coated on an aluminum current collector, dried and rolled to prepare a positive electrode.

(2) Preparation of negative electrode

97 wt% of graphite, 1 wt% of carboxymethyl cellulose, and 2 wt% of styrene-butadiene rubber are mixed in an aqueous solvent to prepare a slurry of an anode active material. This is coated on a copper current collector, dried and rolled to prepare a negative electrode.

(3) Preparation of the first functional layer

It is plate-shaped and has a particle size of about 2 μm, the ratio of the length of the major axis to the length of the minor axis is about 2, and 48 wt% of polyethylene having a thickness of about 0.6 μm, 47 wt% of alumina having an average particle diameter (D50) of 0.7 μm, and 5 wt% of an acrylated styrene-based rubber binder mixed with an alcohol-based solvent to prepare a first functional layer slurry. A first functional layer capable of serving as a separator is prepared by coating and drying the first functional layer slurry on the prepared negative electrode active material layer.

(4) Preparation of battery

Using the negative electrode and the positive electrode having the first functional layer, 1.0 M LiPF ₆ dissolved in a solvent mixed with ethylene carbonate and dimethyl carbonate in a volume ratio of 50:50 is used as an electrolyte to prepare a lithium secondary battery by a conventional method do.

Example 2

In the preparation of the positive electrode of Example 1, a positive electrode and a battery were manufactured in the same manner as in Example 1, except that a flame retardant was not added to the positive electrode active material slurry, and a second functional layer containing a flame retardant was formed on the current collector. Specifically, a second functional layer slurry was prepared by mixing the same melamine-based flame retardant as used in Example 1, a carboxymethyl cellulose thickener, and an acrylate-based binder in a water solvent in a weight ratio of 2:1:1.5. This is applied to the current collector and dried to prepare a second functional layer. A positive electrode is manufactured by coating, drying, and rolling a positive electrode active material slurry to which a flame retardant is not added on the second functional layer.

Example 3

In the preparation of the positive electrode of Example 1, a positive electrode and a battery were prepared in the same manner as in Example 1, except that a flame retardant was not added to the positive electrode active material slurry, and a second functional layer containing a flame retardant was formed on the positive electrode active material layer. . Specifically, the positive electrode active material slurry to which the flame retardant is not added is applied to the current collector and dried, then the second functional layer slurry prepared in Example 2 is applied, dried and rolled to prepare a positive electrode.

Comparative Example 1

A positive electrode, a negative electrode, and a battery were prepared in the same manner as in Example 1, except that a flame retardant was not added to the positive electrode active material slurry in the preparation of the positive electrode of Example 1.

Comparative Example 2

A positive electrode, a negative electrode and a battery were manufactured in the same manner as in Example 1, except that the first functional layer was not introduced in Example 1 and a polyethylene/polypropylene two-layer membrane was used as a separator.

Evaluation Example 1: Thermal safety evaluation

The batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were charged at 4.3 V at 0.5 C rate, cut off at 0.05 C rate, and observed by keeping in a chamber at 134° C., Comparative Example 1, Comparative Example 2, The results of Example 1, Example 2, and Example 3 are sequentially shown in FIGS. 5 to 9 .

In Comparative Example 1, 5 out of 5 battery samples exploded, and in Comparative Example 2, 5 out of 6 battery samples exploded, whereas in Examples 1 to 3, none of the 3 battery samples exploded. It can be seen that the batteries according to the embodiments succeeded in early shutdown during thermal runaway, thereby ensuring thermal safety.

Evaluation Example 2: Penetration Safety Evaluation

The batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were charged at 4.3 V at 0.5 C rate and cut off at 0.05 C rate, and after 1 hour, 80 mm/sec using a pin having a diameter of 3 mm. The speed was observed to completely penetrate the center of the battery, and the results of Comparative Example 1, Comparative Example 2, Example 1, Example 2, and Example 3 are sequentially shown in FIGS. 10 to 14 .

In Comparative Examples 1 and 2, all 5 of the 5 battery samples exploded, whereas in Examples 1 to 3, none of the 5 battery samples exploded. It can be seen that the batteries of the embodiments succeeded in early shutdown before the battery exploded or ignited due to penetration, thereby securing penetration safety.

Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and this It goes without saying that it falls within the scope of the invention.

10: positive electrode
11: positive current collector
13: positive electrode active material layer
20: cathode
21: negative electrode current collector
23: anode active material layer
30: first functional layer
40: electrode assembly
50: case
100: lithium secondary battery

Claims (15)

a positive electrode including a positive active material;
a negative electrode including an anode active material; and
A lithium secondary battery comprising a first functional layer present between the positive electrode and the negative electrode,
The first functional layer includes plate-shaped polyolefin particles having an average particle diameter of 1 μm to 8 μm,
The anode is
or a cathode active material layer comprising a cathode active material and a flame retardant;
Having a laminated structure including a cathode active material layer and a second functional layer comprising a flame retardant,
lithium secondary battery. According to claim 1,
The lithium secondary battery includes the positive electrode active material layer and a positive electrode current collector supporting the same,
The second functional layer is present between the positive electrode active material layer and the positive electrode current collector, present on the positive electrode active material layer, or both of the lithium secondary battery. According to claim 1,
The second functional layer is a lithium secondary battery further comprising a compound of Formula 1:
[Formula 1]
Li _a1 Fe _1-x1 M _x1 PO ₄
In Formula 1,
0.90 ≤ a1 ≤ 1.8, 0 ≤ x1 ≤ 0.7, and M is Mg, Co, Ni, or a combination thereof. According to claim 1,
The cathode active material layer is a lithium secondary battery comprising a compound comprising at least one of a complex oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof. 5. The method of claim 4,
The cathode active material layer is a lithium secondary battery that further comprises a compound of Formula 1:
[Formula 1]
Li _a1 Fe _1-x1 M _x1 PO ₄
In Formula 1,
0.90 ≤ a1 ≤ 1.8, 0 ≤ x1 ≤ 0.7, and M is Mg, Co, Ni, or a combination thereof. According to claim 1,
The first functional layer is a lithium secondary battery that is located on the anode active material layer. According to claim 1,
The lithium secondary battery further includes a separator,
The first functional layer is a lithium secondary battery positioned on the separator. According to claim 1,
The flame retardant is an organic flame retardant lithium secondary battery. 9. The method of claim 8,
The organic flame retardant is a phosphorus-based flame retardant, a halogen-based flame retardant, a nitrogen-based flame retardant, or a combination thereof lithium secondary battery. 10. The method of claim 9,
The phosphorus-based flame retardant is, between ammonium phosphate, ammonium polyphosphate, trioctyl phosphate, dimethyl methylphosphate, trimethylolpropane methylphosphonic oligomer, pentaerythritol phosphate, cyclic neopentyl thio phosphoric anhydride, triphenyl phosphate, tricresyl phosphate, tert-butylphenyl diphenyl phosphate, tetra Phenyl mp-phenylene diphosphate (tetraphenyl mp-phenylenediphosphate), tris (2,4-dibromophenyl) phosphate (tris (2,4-dibromophenyl) phosphate), N,N'-bis (2-hydroxyethyl ) aminomethyl phosphonate (N,N'-bis(2-hydoxyethyl)aminomethyl phosphonate), phosphine oxide, phosphine oxide diols, phosphites, phosphonates ( lithium secondary which is phosphonates), triaryl phosphate, alkyldiaryl phosphate, trialkyl phosphate, resorcinaol bisdiphenyl phosphate (RDP), or a combination battery. 10. The method of claim 9,
The halogen-based flame retardant is tribromophenoxyethane, tetrabromobisphenol-A (TBBA), octabromo diphenyl ether (OBDPE), brominated epoxy, brominated polycarbonate oligomer, brominated benzyl alkyl ether, brominated benzoic acid ester, A lithium secondary battery comprising a phthalate acid ester, chlorinated paraffin, chlorinated polyethylene, an alicyclic chlorine-based flame retardant, or a combination thereof. 10. The method of claim 9,
The nitrogen-based flame retardant is, melamine, melamine phosphate, melamine cyanurate, or a combination thereof lithium secondary battery. According to claim 1,
The average particle size of the plate-shaped polyolefin particles is 2 ㎛ to 6㎛ lithium secondary battery. According to claim 1,
A lithium secondary battery wherein the ratio of the long axis length to the minor axis length of the plate-shaped polyolefin particles is 1 to 5. According to claim 1,
A thickness of the plate-shaped polyolefin particles is 0.2 μm to 4 μm.

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