KR102425003B1 - Rechargeable lithium battery including same - Google Patents

Abstract

A lithium secondary battery comprising: a positive electrode having holes having an average particle diameter (D50) of 5 μm to 50 μm on a surface thereof, and including a positive electrode active material; a negative electrode comprising an anode active material; and electrolytes.

Description

Lithium secondary battery {RECHARGEABLE LITHIUM BATTERY INCLUDING SAME}

The present disclosure relates to a lithium secondary battery.

A lithium secondary battery, which has recently been spotlighted as a power source for portable and small electronic devices, uses an organic electrolyte, and thus exhibits a discharge voltage that is twice or more higher than that of a battery using an aqueous alkali solution, resulting in a high energy density.

As a cathode active material of a lithium secondary battery, LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1-x Co _x O ₂ (0 < x < 1) Lithium having a structure capable of intercalation of lithium ions and a transition metal, such as Oxides are mainly used.

Examples of the negative electrode active material include various types of carbon-based negative electrode active materials including artificial, natural graphite, and hard carbon capable of inserting/deintercalating lithium, or negative electrode active materials of oxides such as tin oxide and lithium vanadium-based oxide.

Recently, as a higher-capacity battery is required, a method of improving the energy density of an electrode has been tried as a method for further increasing the capacity of such a battery. As a method for improving the energy density of such an electrode, a method of increasing the electrode density (composite density) by rolling the positive electrode and the negative electrode more has been attempted, but this method has a limit in capacity increase.

In addition, when the electrode density of the electrode plate is too high, it is difficult to impregnate the electrolyte, and the electrolyte must penetrate well into the interior of the electrode plate, and lithium ions are deintercalated when the flow path is well formed from the top to the bottom of the electrode plate. This is easy, but when the electrode density is too high, there are no voids between the active materials and the flow path is blocked, so the capacity of the lithium ion battery may not be properly expressed or lithium may be deposited on the negative electrode to deteriorate the lifespan.

One embodiment of the present invention is to provide a lithium secondary battery having excellent electrolyte impregnation property in a high-composite electrode, and thus having excellent capacity and energy density.

According to one embodiment of the present invention, holes having an average particle diameter (D50) of 1200 nm to 50 μm are present on the surface, and the positive electrode includes a positive electrode active material; a negative electrode comprising an anode active material; And it provides a lithium secondary battery comprising an electrolyte.

An average particle diameter (D50) of the holes may be 5 μm to 50 μm.

The aspect ratio of the hole may be 0.5 to 2.

The ratio of the average particle diameter (D50) of the positive electrode active material to the average particle diameter (D50) of the holes may be less than 1, and the ratio of the average particle diameter (D50) of the positive active material to the average particle diameter (D50) of the holes is 0.2 to 0.6 can be

The composite material density of the positive electrode may be 2 g/cc to 4.3 g/cc.

A carbon coating layer may be formed on the surface of the hole.

In addition, the lithium secondary battery may be manufactured by performing a chemical conversion process on a battery prepared using a positive electrode, a negative electrode, and an electrolyte prepared using a positive electrode active material composition including a positive electrode active material and a pore former.

The specific details of other embodiments of the invention are included in the detailed description below.

The lithium secondary battery according to an embodiment of the present invention may exhibit excellent energy density and capacity due to excellent electrolyte impregnation property of the electrode.

1 is a view schematically showing the structure of a lithium secondary battery according to an embodiment of the present invention.
2 is a surface SEM photograph of a positive electrode obtained by disassembling a lithium secondary battery prepared according to Example 1 in a state before formation after rolling.
3 is a surface SEM photograph of a positive electrode obtained by disassembling a lithium secondary battery prepared according to Example 1 in a state after formation.
4 is a surface SEM photograph of a positive electrode obtained by disassembling a lithium secondary battery prepared according to Example 1 in a state after formation.
5 is a graph showing the weight of the lithium secondary batteries of Example 1 and Comparative Example 1 over time.
6 is a graph showing the capacity retention rate of the lithium secondary batteries of Example 1 and Comparative Example 1.

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.

A lithium secondary battery according to an embodiment of the present invention includes a positive electrode having holes having an average particle diameter (D50) of 1200 nm to 50 μm on the surface, and including a positive electrode active material; a negative electrode comprising an anode active material; and electrolytes.

Unless otherwise defined herein, the average particle diameter (D50) means the diameter of particles having a cumulative volume of 50% by volume in the particle size distribution.

In one embodiment of the present invention, the average particle diameter (D50) of the holes formed on the surface of the anode may be 1200 nm to 50 µm, and in another embodiment, 5 µm to 50 µm. When the average particle diameter (D50) of the hole is within the above range, the electrolyte impregnability is improved in the electrode, and the electrolyte can be well impregnated throughout the electrode because a flow path is formed in the electrode. It can also be increased.

When the hole is formed on the surface, it may have a hemispherical shape, but is not limited thereto, and any shape may be used. Further, even when the hole is formed inside the electrode, the shape does not need to be greatly limited.

An aspect ratio (aspect ratio, aspect ratio) of the hole may be 0.5 to 2. If the aspect ratio of the hole is out of the above range, the electrolyte may not be well impregnated.

A ratio of the average particle diameter (D50) of the positive electrode active material to the average particle diameter (D50) of the holes may be less than 1. In addition, a ratio of the average particle diameter (D50) of the positive electrode active material to the average particle diameter (D50) of the holes may be 0.2 to 0.6. When the ratio of the average particle diameter (D50) of the positive electrode active material to the average particle diameter (D50) of the holes is out of the above range, the capacity may be greatly reduced.

The composite material density of the positive electrode may be 2 g/cc to 4.3 g/cc. The higher the density of the composite material of the positive electrode is, the more dense the active material layer, so the electrolyte impregnation property may be reduced. The effect can be increased. That is, since the effect of improving the electrolyte impregnation according to the hole formation can be more effectively obtained as the density of the mixture is higher, better impregnation with the electrolyte can be obtained by forming holes in the anode having the density of the mixture within the above range.

The surface of the hole may further include a carbon coating layer. When the carbon coating layer is further present on the surface of the hole, the conductivity of the positive electrode active material layer (composite layer) is increased, so that the amount of the conductive material can be adjusted. The carbon of the carbon coating layer may be graphene, carbon black, carbon nanotubes, hydrocarbons such as methane, or a combination thereof. When the carbon coating layer is further formed, the thickness of the carbon coating layer may be 10 nm to 1 μm. When the carbon coating layer is further included, the content of the carbon coating layer may be 0.05 wt% to 0.5 wt% based on 100 wt% of the positive active material.

A lithium secondary battery having such a configuration may be manufactured by performing a chemical conversion process on a battery manufactured using a positive electrode, a negative electrode, and an electrolyte prepared using a positive electrode active material composition including a positive electrode active material and a wax-coated lithium metal. Hereinafter, a lithium secondary battery manufacturing process according to an embodiment of the present invention will be described in more detail below.

A positive electrode of a lithium secondary battery according to an embodiment of the present invention is manufactured using a positive electrode active material composition including a positive electrode active material and a wax-coated lithium metal. The content of the wax-coated lithium metal may be 0.1 wt% to 1 wt% based on 100 wt% of the positive active material. When the content of the wax-coated lithium metal is included in the above range, more appropriate battery cycle life characteristics may be exhibited.

In addition, a content ratio of the wax and lithium metal may be 0.5:1 to 3:1 by weight. When the content ratio of the wax and lithium metal is within the above range, battery characteristics can be more effectively improved, which is appropriate.

The average particle diameter (D50) of the lithium metal may be 1200nm to 50㎛. When the average particle diameter (D50) of the lithium metal is within the above range, a hole having an appropriate size may be formed.

The thickness of the wax coating, that is, the wax coating layer, may be 1 μm to 10 μm. When the thickness of the wax coating layer falls within this range, lithium metal can be easily handled in air.

In the wax-coated lithium metal, any process may be used for the wax coating process, so there is no need to limit it.

When lithium metal is used for the positive electrode, a short circuit may occur because the potential energy of the positive electrode and the potential energy of the lithium metal are different. A wax wraps around the lithium metal to prevent a short circuit.

In addition, the wax-coated lithium metal may be further coated with carbon. That is, a wax coating layer is present on the surface of the lithium metal, and a carbon coating layer may be present on the surface of the wax coating layer. The carbon of the carbon coating layer may be graphene, carbon black, carbon nanotubes, hydrocarbons such as methane, or a combination thereof. When the carbon coating layer is further formed, the thickness of the carbon coating layer may be 10 nm to 1 μm. In addition, the content of the carbon coating layer may be 0.05 wt% to 0.5 wt% based on 100 wt% of the lithium metal. When the content of the carbon coating layer is included in the above range, the use efficiency can be further improved, which is appropriate.

Examples of the wax include microcrystalline wax, olefin-based compound, and oil-type liquid wax. or a combination thereof. The microstalin wax is also called micro wax, and refers to a wax that has undergone a dewaxing and deoiling process by solvent extraction from high-viscosity lube distillate oil produced during crude oil refining, etc. , a wax containing branched-chain saturated hydrocarbons as a main component.

As the positive active material, A compound capable of reversible intercalation and deintercalation of lithium (a lithiated intercalation compound) may be used. Specifically, at least one of a complex oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used. As a more specific example, a compound represented by any one of the following formulas may be used. 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 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a E _2-b X _b O _4-c D _c (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); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _a FePO ₄ (0.90 ≤ a ≤ 1.8)

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 contain 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 the compound can be coated by a method that does not adversely affect the physical properties of the positive electrode active material (eg, spray coating, dipping method, etc.) by using these elements in the compound. Since the content can be well understood by those engaged in the field, a detailed description thereof will be omitted.

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

The binder is a material that serves to well adhere the positive active material particles to each other and also to adhere the positive active material to the current collector. Representative examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl blood Rollidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, etc. may be used, but the present invention is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, any electronically conductive material may be used without causing a chemical change. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based substances such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof.

The positive active material composition may further include a solvent, and the solvent may include, but is not limited to, N-methylpyrrolidone.

The content of the positive active material in the positive active material composition may be 85% to 97.6% by weight based on the total weight of the positive active material composition solid content. In addition, the content of the lithium metal coated with the wax may be 0.1 wt% to 1 wt% based on the total weight of the solid content of the cathode active material composition.

In addition, when the cathode active material composition further includes a binder, the content of the binder may be 1.0 wt% to 5 wt% based on the total solid weight of the cathode active material composition. In addition, when the positive electrode active material composition further includes a conductive material, the amount of the conductive material may be 1.3 wt% to 10 wt% based on the total solid weight of the positive electrode active material composition.

A positive electrode is manufactured by a conventional process of applying, drying, and rolling the positive electrode active material composition to a current collector. An Al foil may be used as the current collector, but is not limited thereto.

A lithium secondary battery is assembled in a conventional process using the positive electrode, the negative electrode including the negative electrode active material, and the electrolyte. The assembled lithium secondary battery is subjected to a chemical conversion process. According to the formation process, as lithium metal contained in the positive electrode is dissolved and eluted from the positive electrode, a hole is formed on the surface of the positive electrode. In addition, since the lithium metal as a whole is dissolved and eluted from the positive electrode, a hole may be formed throughout the interior of the positive electrode.

In addition, since the eluted lithium metal can compensate for the irreversible Li amount of the positive electrode active material that does not participate in the charge/discharge reaction as it participates in the reaction to form the SEI film during charging and discharging, the lithium secondary battery including the positive electrode has a capacity can be improved

In addition, in the chemical conversion process, lithium metal is dissolved and removed from the positive electrode. At this time, the wax coated on the lithium metal surface may also be removed, but some may remain in the positive electrode. When the wax remains on the positive electrode, since the wax is electrically inert and does not cause side reactions, even if the wax remains on the positive electrode, it does not adversely affect the battery. In addition, when lithium metal having a wax coating layer and a carbon coating layer formed on the surface is used, wax and carbon may remain in the positive electrode. In this case, a coating layer formed of carbon may be present on the surface of the hole.

The chemical conversion process may be carried out as a process of charging and discharging one to two times at 0.1C to 0.5C.

The negative electrode includes a current collector and an anode active material layer including a negative active material formed on the current collector.

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-shaped, flake-shaped, 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 lithium-doped and de-doped material include Si, Si-C composite, SiO _x (0 < x < 2), Si-Q alloy (wherein Q is an alkali metal, alkaline earth metal, a group 13 element, a group 14 element, An element selected from the group consisting of a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof, and not Si), Sn, SnO ₂ , a Sn-R alloy (wherein R is an alkali metal, an alkaline earth metal, an element selected from the group consisting of a group 13 element, a group 14 element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof (not Sn); You may mix and use SiO2 _. 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 may be 95 wt% to 99 wt% based on the total weight of the anode active material layer.

In one embodiment of the present invention, the negative active material layer includes a binder, and may optionally further include a conductive material. The content of the binder in the anode active material layer may be 1 wt% to 5 wt% based on the total weight of the anode active material layer. 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 well 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, and polyvinylidene fluoride. , polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

The water-soluble binder may include a rubber-based binder or a polymer resin binder. The rubber binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder is ethylene propylene copolymer, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, It may be one selected from acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

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.

The conductive material is used to impart conductivity to the electrode, and in the battery configured, any electronic conductive material can be used as long as it does not cause chemical change, for example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen carbon-based materials such as black and carbon fiber; 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.

The current collector may be 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.

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, methylpropionate, ethylpropionate, 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 bond aromatic rings or ether bonds), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. may be used. .

The organic solvents may be used alone or in mixture of one or more, and when one or more of the organic solvents are mixed and used, the mixing ratio may 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 1 may be used.

[Formula 1]

(In Formula 1, 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.

In order to improve battery life, the electrolyte may further include vinylene carbonate or an ethylene-based carbonate-based compound of Formula 2 as a lifespan improving additive.

[Formula 2]

(In Formula 2, 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 at least one of R ₇ and R 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 both not hydrogen.)

Representative examples of the ethylene-based carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. can be heard 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 the basic operation of a lithium secondary battery, and serves to promote 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 , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ), where x and y are natural numbers, for example It is an integer from 1 to 20), LiCl, LiI and LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate: LiBOB) one or more selected from the group consisting of supporting (supporting) It is included as an electrolyte salt.It is recommended that the concentration of the lithium salt be used within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is included in the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited; Lithium ions can move effectively.

A separator may exist between the positive electrode and the negative electrode depending on the type of the lithium secondary battery. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used. A polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, and polypropylene/polyethylene/poly It goes without saying that a mixed multilayer film such as a propylene three-layer separator or the like can be used.

1 is an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention. Although the lithium secondary battery according to an embodiment is described as an example of a prismatic shape, 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.

Referring to FIG. 1 , a lithium secondary battery 100 according to an embodiment includes an electrode assembly 40 wound with a separator 30 interposed between a positive electrode 10 and a negative electrode 20 , and the electrode assembly 40 . ) may include a built-in case 50. The positive electrode 10 , the negative electrode 20 , and the separator 30 may be impregnated with an electrolyte solution (not shown).

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

(Example 1)

LiCoO ₂ cathode active material (average particle diameter (D50): 20㎛) 97.4 wt%, microcrystalline wax (trade name: microcrystalline wax, manufacturer: Dongnam Petrochemical, city name: Seoul, country name: Korea) coated lithium metal (average Particle size (D50): 50 μm) 0.2 wt%, polyvinylidene fluoride 1.1 wt%, and Ketjen Black 1.3 wt% were mixed in an N-methyl pyrrolidone solvent to prepare a cathode active material slurry. The mixing ratio of the microcrystalline wax and the lithium metal was 0.7:0.3 by weight, and the thickness of the microcrystalline wax coating, that is, the coating layer, was 2 μm.

The positive electrode active material slurry was applied to an Al current collector, dried and rolled to prepare a positive electrode for a lithium secondary battery having a composite density of 4.0 g/cc.

98.5 wt% of the graphite anode active material and 1.5 wt% of a polyvinylidene fluoride binder were mixed in an N-methyl pyrrolidone solvent to prepare an anode active material slurry. The negative electrode active material slurry was coated on one surface of a Cu foil, dried and rolled to prepare a negative electrode having a composite density of 1.6 g/cc.

An electrolyte solution was prepared by using a mixed solvent of ethylene carbonate and dimethyl carbonate in which 1.0M LiPF ₆ was dissolved (1 : 1 volume ratio).

A polyethylene film was used as a separator.

A lithium secondary battery was manufactured in a conventional process using the positive electrode, the separator, the negative electrode, and the electrolyte solution. A formation process of charging and discharging the prepared lithium secondary battery once at 0.1C was performed.

(Example 2)

Instead of the lithium metal coated with microcrystalline wax, microcrystalline wax was coated on the lithium metal surface, and the microcrystalline wax coated with graphene was used in the same manner as in Example 1 above. .

(Comparative Example 1)

97.6 wt% of LiCoO ₂ cathode active material (average particle diameter (D50): 20 μm), 1.1 wt% of polyvinylidene fluoride, and 1.3 wt% of Ketjen black were mixed in an N-methyl pyrrolidone solvent to prepare a cathode active material slurry. The positive electrode active material slurry was applied to an Al current collector, dried and rolled to prepare a positive electrode for a lithium secondary battery having a composite density of 4.0 g/cc.

A lithium secondary battery was manufactured in a conventional process using the positive electrode and the negative electrode prepared in Example 1, the electrolyte, and the separator, and the chemical conversion process was performed in the same manner as in Example 1.

* SEM photo

In Example 1, the rolling process was performed, and the lithium secondary battery before the chemical conversion process was disassembled, and a 500 magnification SEM photograph of the positive electrode surface is shown in FIG. 2 . In addition, the lithium secondary battery subjected to the chemical conversion process in Example 1 was disassembled, and 50, 100, and 1000 magnification SEM images of the surface of the positive electrode are shown in (A), (B) and (C) in FIG. 3 , respectively. It was. In (A) and (B) of Fig. 3, the black dots indicate wax, and Fig. 3 (C) is an enlarged black dot indicated by the circle in Fig. 3 (A), as shown in (C). , it can be seen that holes having a particle size of about 38.7 μm are formed on the surface of the anode of Example 1.

That is, in the lithium secondary battery of Example 1, in which the lithium metal coated with microcrystalline wax was used for the positive electrode, after the chemical conversion process was performed, the lithium metal was eluted and removed from the positive electrode, so it can be seen that a hole is formed on the surface of the positive electrode. have.

In addition, by disassembling the lithium secondary battery subjected to the chemical conversion process in Example 1, 1000 magnification SEM images at various points on the surface of the positive electrode were taken in FIG. 4 (A), (B), (C), (D), (E). ) and (F) respectively. As shown in FIG. 4 , it can be seen that holes having a size of about 22 μm to about 41.2 μm are formed on the surface of the anode subjected to the chemical conversion process.

In addition, the aspect ratio of the hole formed on the surface of the anode may be about 0.8.

* Electrolyte impregnation experiment

While impregnating the positive electrode prepared in Example 1 and Comparative Example 1 in an electrolyte that is a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in which 1.0M LiPF ₆ was dissolved, the weight of the positive electrode according to the impregnation time was measured. Thus, the results are shown in FIG. 5 .

5, the weight of the positive electrode of Example 1 is greater than that of Comparative Example 1 at the same time, and it can be seen from this result that the electrolyte impregnation rate of Example 1 is faster than Comparative Example 1.

* Capacity retention rate evaluation

The lithium secondary battery subjected to the chemical conversion process according to Example 1 and Comparative Example 1 was subjected to 180 charge/discharge cycles at 0.5C. After every 50 charge/discharge cycles, the C-rate was changed to 0.2C, and charge/discharge was performed once.

The capacity retention rate results for charging and discharging are shown in FIG. 6 , and among the results of FIG. 6 , the results shown in the peak form are 0.2C charging and discharging results.

As shown in FIG. 6 , it can be seen that the lithium secondary battery according to Example 1 was able to perform a charge/discharge cycle 180 times, but in Comparative Example 1, a charge/discharge cycle could be performed up to about 130 times. In addition, it can be seen that the capacity retention rate of Example 1 was superior to that of Comparative Example 1. From this result, it can be seen that the charge/discharge cycle life characteristics of Example 1 are superior to those of Comparative Example 1.

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

Claims (8)

a positive electrode having holes having an average particle diameter (D50) of 1200 nm to 50 μm on the surface, and including a positive electrode active material and wax;
a negative electrode comprising an anode active material; and
electrolyte
As a lithium secondary battery comprising a,
The lithium secondary battery is a lithium secondary battery manufactured by performing a chemical conversion process on a battery prepared using the positive electrode, the negative electrode, and the electrolyte prepared using the positive electrode active material composition including the positive electrode active material and the lithium metal coated with the wax. battery. According to claim 1,
A lithium secondary battery having an average particle diameter (D50) of the holes of 5 μm to 50 μm. According to claim 1,
The aspect ratio of the hole is 0.5 to 2 lithium secondary battery. According to claim 1,
A ratio of the average particle diameter (D50) of the positive electrode active material to the average particle diameter (D50) of the holes is less than 1. 5. The method of claim 4,
A ratio of the average particle diameter (D50) of the positive electrode active material to the average particle diameter (D50) of the holes is 0.2 to 0.6. According to claim 1,
A lithium secondary battery having a composite density of the positive electrode of 2 g/cc to 4.3 g/cc. According to claim 1,
A lithium secondary battery in which a carbon coating layer is formed on the surface of the hole. delete

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