KR102341409B1 - Composite positive electrode active material for lithium ion battery, preparing method thereof, and lithium ion battery including positive electrode comprising the same - Google Patents

Abstract

a nickel-rich lithium-nickel-based compound having a nickel content of 50 to 100 mol% based on the total amount of transition metal; And a composite positive electrode active material for a lithium ion battery comprising a coating film containing a rare earth metal hydroxide formed on the surface of the nickel-rich lithium nickel-based compound, a method for manufacturing the same, and a lithium ion containing a positive electrode comprising the same The battery is presented.

Description

Composite positive electrode active material for lithium ion battery, preparing method thereof, and lithium ion battery including positive electrode comprising the same}

It relates to a composite positive electrode active material for a lithium ion battery, a manufacturing method thereof, and a lithium ion battery containing a positive electrode including the same.

Lithium ion batteries are used in various applications due to their high voltage and high energy density. For example, when a lithium ion battery is used in the field of electric vehicles (HEV, PHEV), etc., the lithium ion battery can operate at a high temperature, must charge or discharge a large amount of electricity, and must be used for a long time. It should have excellent lifespan characteristics.

Among the cathode active materials, LiCoO ₂ is the most used because of its excellent lifespan characteristics and charge/discharge efficiency, but it has a small capacity and is expensive due to the resource limitation of cobalt used as a raw material. There is a disadvantage in that there is a limit to price competitiveness. Lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ are rich in manganese resources used as raw materials, so they are inexpensive, environmentally friendly, and have the advantages of excellent thermal stability, but small capacity, high temperature characteristics and cycle characteristics, etc. I have this poor problem. In order to compensate for these shortcomings, the demand for nickel-rich positive electrode active material as a positive electrode active material has increased. Although the demand has started to increase as described above, the nickel-rich positive electrode active material has an excellent advantage of high capacity, but has problems such as swelling phenomenon caused by high unreacted lithium and gas generation due to reaction with electrolyte. In order to remove such unreacted Li, a water washing process is generally introduced, but in this case, the surface of the cathode active material is damaged during washing, thereby lowering capacity and high rate characteristics, and also causing another problem in that resistance increases when stored at a high temperature.

One aspect is to provide a composite positive electrode active material for a lithium ion battery having a reduced content of residual lithium and a method for manufacturing the same.

Another aspect is to provide a lithium ion battery with improved lifespan characteristics and high temperature storage characteristics by employing a positive electrode containing the above-described composite positive electrode active material.

According to one aspect,

a nickel-rich lithium-nickel-based compound having a nickel content of 50 to 100 mol% based on the total amount of transition metals; and

There is provided a composite positive electrode active material for a lithium ion battery including a coating film including a rare earth metal hydroxide formed on the surface of the nickel-rich lithium nickel-based compound.

The specific surface area of the composite positive electrode active material is 1.2 to 1.8 m ² /g.

According to another aspect, a nickel-rich lithium-nickel-based compound by heat-treating a transition metal hydroxide and a lithium precursor, which are precursors of a nickel-rich lithium-nickel-based compound having a nickel content of 50 to 100 mol% based on the total amount of transition metals, in an oxidizing atmosphere to obtain;

performing washing by adding and stirring a washing solution containing a salt containing a rare earth metal and water to the nickel-rich lithium nickel-based compound; and

There is provided a method for producing a composite positive electrode active material for a lithium ion battery to obtain the above-described composite positive electrode active material, including the step of drying the product that has undergone the washing step.

According to another aspect, there is provided a lithium ion battery including a positive electrode containing the above-described composite positive electrode active material.

The composite positive electrode active material according to an embodiment has a reduced content of residual lithium and an increase in specific surface area, so if a positive electrode using the same is employed, a lithium ion battery having improved capacity, lifespan and high temperature storage characteristics can be manufactured.

1 is a schematic diagram of a lithium secondary battery according to an exemplary embodiment.
2A to 2C show the results of scanning electron microscope analysis of the composite positive electrode active material prepared according to Example 1 and the positive electrode active material prepared according to Comparative Examples 1 and 2;
FIG. 3a is a transmission electron microscope (TEM) photograph of the composite positive electrode active material prepared according to Example 1. FIG.
FIG. 3B is an enlarged view of the square area of FIG. 3A .
4 shows the charging and discharging characteristics of lithium ion batteries prepared according to Preparation Examples 1-4 and Comparative Preparation Examples 1-2.

Hereinafter, a composite positive electrode active material for a lithium ion battery according to exemplary embodiments, a manufacturing method thereof, and a lithium ion battery having a positive electrode including the composite positive electrode active material will be described in more detail.

The composite cathode active material according to an embodiment may include a lithium nickel-based compound having a nickel content of 50 to 100 mol% based on the total amount of transition metals; and a coating film including a rare earth metal hydroxide formed on the surface of the lithium nickel-based compound.

The composite positive electrode active material according to an embodiment has a specific surface area of 1.2 to 1.8 m ² /g, and the specific surface area is increased compared to that of a general positive electrode active material.

A typical nickel-rich positive electrode active material has advantages of excellent capacity and high rate characteristics and low cost. However, cycle characteristics and stability are deteriorated due to residual lithium such as lithium hydroxide and lithium carbonate on the surface, and improvement is required. It is known to perform water washing by removing residual lithium present on the surface of the positive electrode active material.

However, in the case of water washing in this way, the surface of the positive electrode active material washed with water is exposed too much due to the removal of residual lithium, and the contact area with the electrolyte increases. The surface resistance of the positive electrode active material is increased and the high temperature storage characteristics are reduced.

Therefore, in order to solve the above problems, the present inventors use a cleaning solution containing a salt containing a rare earth metal and water for washing with water, and after washing using the same, go through a drying process to minimize the change of the positive electrode active material due to water washing while minimizing the change of the positive electrode active material To provide a composite cathode active material in which a rare earth metal hydroxide coating film is formed on the surface of The composite positive active material is a specific surface area of, for example 1.3 to 1.6m ² / g, particularly 1.357 to 1.563m ² / g. By using such a composite cathode active material, a lithium ion battery with improved electrochemical properties and high temperature storage properties can be manufactured.

The rare earth metal hydroxide includes, but is not limited to, yttrium hydroxide, cerium hydroxide, lanthanum hydroxide, eurobium hydroxide, gadolinium hydroxide, scandium hydroxide, and terbium hydroxide. and at least one selected from the group.

The content of the salt containing the rare earth metal in the washing solution is 0.1 to 1.0M, for example, 0.2 to 0.5M. When the content of the salt containing the rare earth metal is within the above range, the specific surface area of the composite cathode active material is controlled in an appropriate range, and using this, a lithium ion battery having excellent electrochemical properties and high temperature storage properties can be manufactured.

The content of the rare earth metal hydroxide is 0.14 to 1.4 parts by weight, for example 0.29 to 0.71 parts by weight, based on 100 parts by weight of the lithium nickel-based compound. When the content of the rare earth metal hydroxide is within the above range, a lithium ion battery having excellent electrochemical properties and high temperature storage properties can be manufactured.

The nickel-rich lithium nickel-based compound having the nickel content of 50 mol% to 100 mol% may include a compound represented by the following formula (1).

[Formula 1]

Li _x Ni _y M _1-y O ₂

In Formula 1, 0.9≤x≤1.2, 0.5≤y<1.0, M is at least one selected from cobalt (Co), manganese (Mn), and aluminum (Al).

The compound of Formula 1 includes, for example, a compound represented by Formula 2 or a compound represented by Formula 3 below.

[Formula 2]

Li _x Ni _y Co _z Mn _1-yz O ₂

In Formula 2, 0.9≤x≤1.2, 0.5≤y<1, 0≤z≤0.5, 0≤1-y-z≤0.5,

[Formula 3]

Li _x Ni _y Co _z Al _1-yz O ₂

In Formula 3, 0.9≤x≤1.2, 0.5≤y≤1.0, and 0≤z≤0.5.

The content of residual lithium in the composite cathode active material is as small as 0.15 wt% or less, for example, 0.11 to 0.13 wt%, based on the total amount of the composite cathode active material.

The nickel-rich lithium nickel-based compound is, for example, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.3 Mn _0.1 O ₂ , LiNi _0.7 Co _0.15 Mn _0.15 O _{2 ,} LiNi _0.8 Co _0.1 Mn _0.1 O, LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.88 Co _0.1 Al _0.02 O ₂ , LiNi _0.84 Co _0.15 Al _0.01 O _{2 ,} or mixtures thereof.

In the composite positive electrode active material according to an embodiment, the thickness of the coating film including the rare earth metal hydroxide is 500 nm or less, for example, 50 to 200 nm. When the thickness of the coating film is within the above range, it is possible to manufacture a lithium ion battery having good electrochemical properties and high temperature storage properties. The resistance change obtained from the resistance after high temperature storage measured at room temperature after storage at 60° C. for 7 days in the lithium ion battery is -3.1 to -5.2 Ω.

Hereinafter, a method for manufacturing a composite positive electrode active material according to an embodiment will be described.

First, nickel in which the content of nickel is 50 to 100 mol% based on the total amount of transition metals

A nickel-rich lithium nickel-based compound having a nickel content of 50 to 100 mol% based on the total amount of the transition metal is obtained by heat-treating the transition metal hydroxide and the lithium precursor, which are precursors of the rich lithium nickel-based compound, in an oxidizing atmosphere.

The transition metal hydroxide may be, for example, a compound represented by the following formula (4).

[Formula 4]

Ni _y M _1-y OH

In Formula 1, y is 0.5 to 1.0, and M is at least one selected from cobalt (Co), manganese (Mn), and aluminum (Al).

The compound of Formula 4 is, for example, a compound represented by Formula 5 or a compound represented by Formula 6 below.

[Formula 5]

Ni _y Co _z Mn _1-yz OH

In Formula 5, 0.5≤y<1, 0≤z≤0.5, 0≤1-y-z≤0.5,

[Formula 6]

Ni _y Co _z Al _1-yz OH

In Formula 6, y is 0.5 to 1.0, and z is 0 to 0.5.

The oxidizing atmosphere refers to oxygen or an atmospheric atmosphere, and the oxygen atmosphere refers to oxygen alone or a mixed gas of oxygen and an inert gas. As the inert gas, nitrogen, argon, helium, or the like may be used.

The heat treatment may be performed by heat treatment at 400 to 1200 °C, for example, 500 to 900 °C. When the heat treatment is in the above temperature range, it is possible to obtain a positive active material having a desired composition.

The heat treatment time is variable depending on the heat treatment temperature, but for example, it is carried out in the range of 5 minutes to 20 hours.

The transition metal hydroxide is, for example, Ni _0.5 Co _0.2 Mn _0.3 OH, Ni _0.6 Co _0.3 Mn _0.1 OH, Ni _0.7 Co _0.15 Mn _0.15 OH _, Ni _0.8 Co _0.1 Mn _0.1 OH, Ni _0.6 Co _0.2 Mn _0.2 OH, Ni _0.88 Co _0.1 Al _0.02 OH, Ni _0.84 Co _0.15 Al _0.01 O ₂ or a mixture thereof.

The transition metal hydroxide may be prepared by mixing a transition metal precursor, for example, one selected from a cobalt precursor, a manganese precursor, and an aluminum precursor, and a nickel precursor, and performing this by a co-precipitation method, a solid phase method, or the like. The production process of such a transition metal hydroxide follows a conventional method.

Nickel oxide, nickel acetate, nickel hydroxide, nickel nitrate, etc. may be used as the nickel precursor, and cobalt oxide, cobalt acetate, cobalt hydroxide, cobalt nitrate, etc. may be used as the cobalt precursor. And manganese oxide, manganese acetate, manganese hydroxide, manganese nitrate, etc. are used as the manganese precursor. Here, the contents of the nickel precursor and the cobalt precursor are stoichiometrically controlled to obtain the desired transition metal hydroxide.

As the lithium precursor, lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), lithium sulfate (Li ₂ SO ₄ ), lithium nitrate (LiNO ₃ ), etc. may be used, but any one commonly available in the art Available.

The content of the transition metal hydroxide and lithium precursor is stoichiometrically controlled to obtain a nickel-rich lithium nickel-based compound.

Subsequently, a washing process is performed by adding and stirring a washing solution containing a salt containing a rare earth metal and water to the nickel-rich lithium nickel-based compound prepared according to the above process. As a result of performing such a cleaning process, it is possible to remove residual lithium from the nickel-rich lithium nickel-based compound.

The salt containing the rare earth metal is, for example, at least one selected from the group consisting of rare earth metal acetate, rare earth metal sulfate, rare earth metal chloride, and rare earth metal nitrate. Salts containing rare earth metals are specifically yttrium acetate, yttrium sulfate, yttrium chloride, yttrium nitrate, cerium acetate, cerium sulfate, cerium chloride, cerium nitrate, lanthanum acetate, lanthanum sulfate, lanthanum chloride, lanthanum nitrate, eurobium. Acetate, eurobium sulfate, eurobium chloride, eurobium nitrate, gadolinium acetate, gadolinium sulfate, gadolinium chloride, gadolinium nitrate, scandium acetate, scandium sulfate, scandium chloride, scandium nitrate, terbium acetate and sulfate, terbium and at least one selected from the group consisting of terbium nitrate.

According to one embodiment, as a salt containing a rare earth metal, a composite cathode active material finally prepared by using a rare earth metal acetate such as yttrium acetate, cerium acetate, lanthanum acetate, eurobium acetate, gadolinium acetate, scandium acetate, or terbium acetate Lithium ion battery with improved electrochemical properties and high-temperature storage properties can be manufactured using the reduced residual lithium content and proper control of specific surface area properties.

A step of drying the product that has undergone the above-described washing step is carried out. Here, the drying is carried out, for example, at 200° C. or less, specifically in the range of 120 to 150° C. When drying is carried out in the above temperature range, it is possible to prepare a composite positive electrode active material having excellent electrochemical properties and high temperature storage properties.

A positive electrode having a positive electrode active material layer comprising a composite positive electrode active material according to an embodiment

It can be prepared according to the following procedure.

The positive electrode is prepared according to the following method.

A positive electrode active material composition in which a composite positive electrode active material, a binder, and a solvent are mixed is prepared.

A conductive agent may be further added to the cathode active material composition.

The positive electrode active material composition is directly coated and dried on a metal current collector to prepare a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to manufacture a positive electrode plate.

When manufacturing the positive electrode, in addition to the above-described composite positive electrode active material, a first positive electrode active material, which is a positive active material commonly used in a lithium ion battery, may be further included.

The first positive electrode active material may further include at least one selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide, but is not necessarily limited thereto. Any positive active material available in the art may be used.

For example, Li _a A _1-b B _b D ₂ (wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li _a E _1-b B _b O _2-c D _c (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _2-b B _b O _4-c D _c (wherein 0 ≤ b ≤ 0.5 and 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b B _c D _? (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-? F _? (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c D _? (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b B _c O _2-? F _? (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c O _2-? F ₂ (wherein 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 (in the above formula, 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 GeO ₂ (wherein, 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 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO 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); A compound represented by any one of the formulas of LiFePO _{4 may be used:}

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

In the cathode active material composition, the binder is polyamideimide, polyacrylic acid (PAA), polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetra fluoroethylene, polyethylene, polypropylene, lithium polyacrylate, lithium polymethacrylate, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, various copolymers, and the like.

The conductive agent may include, for example, at least one carbon-based conductive agent selected from the group consisting of carbon black, carbon fiber, and graphite. The carbon black may be, for example, selected from the group consisting of acetylene black, Ketjen black, Super P, channel black, furnace black, lamp black, and thermal black. The graphite may be natural graphite or artificial graphite.

As the solvent, butanol, acetonitrile, acetone, methanol, ethanol, N-methyl-2-pyrrolidone (NMP), etc. may be used, but any other commonly available solvent may be used.

Meanwhile, it is also possible to form pores in the electrode plate by further adding a plasticizer to the positive active material composition and/or the negative active material composition.

The content of the positive active material, the conductive agent, the binder, and the solvent is a level commonly used in a lithium ion battery. At least one of the conductive agent, the binder, and the solvent may be omitted depending on the use and configuration of the lithium ion battery.

The negative electrode can be obtained by carrying out almost the same method except for using the negative electrode active material instead of the positive electrode active material in the above-described positive electrode manufacturing process.

As the anode active material, a carbon-based material, silicon, silicon oxide, a silicon-based alloy, a silicon-carbon-based material composite, tin, a tin-based alloy, a tin-carbon composite, a metal oxide, or a combination thereof is used.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous, plate-like, flake-like, spherical or fibrous graphite, such as natural graphite or artificial graphite, and the amorphous carbon is soft carbon (low-temperature calcined carbon) or hard carbon (hard carbon). carbon), mesophase pitch carbide, calcined coke, graphene, carbon black, fullerene soot, carbon nanotube, and carbon fiber furnace, etc., but are not necessarily limited thereto, and in the art Anything that can be used is possible.

The negative active material may be selected from the group consisting of Si, SiOx (0<x<2, for example, 0.5 to 1.5), Sn, SnO ₂ , or silicon-containing metal alloys and mixtures thereof. As the metal capable of forming the silicon alloy, at least one selected from among Al, Sn, Ag, Fe, Bi, Mg, Zn, in, Ge, Pb and Ti may be used.

The negative active material may include a metal/metalloid capable of alloying with lithium, an alloy thereof, or an oxide thereof. For example, the metal/metalloid capable of alloying with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb, or a Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, a transition metal, a rare earth element, or a combination element thereof, but not Si), a Sn-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth element, or a combination element thereof , not Sn), MnOx (0<x≤2), and the like. The element Y includes 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, S, Se, Te, Po, or a combination thereof. For example, the oxide of the metal/metalloid alloyable with lithium may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, SnO ₂ , SiO _x (0<x<2), or the like.

For example, the negative active material may include one or more elements selected from the group consisting of a group 13 element, a group 14 element, and a group 15 element of the periodic table of elements.

For example, the negative active material may include one or more elements selected from the group consisting of Si, Ge, and Sn.

The conductive agent, binder, and solvent in the negative active material composition may be the same as those in the positive active material composition. And, the content of the negative active material, the conductive agent, the binder, and the solvent is a level commonly used in a lithium battery.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used.

The pore diameter of the separator is generally 0.01 to 10 μm, and the thickness is generally 5 to 20 μm. As such a separator, For example, olefin-type polymer|macromolecule, such as polypropylene; A sheet or non-woven fabric made of glass fiber or polyethylene is used. When a solid polymer electrolyte is used as the electrolyte, the solid polymer electrolyte may also serve as a separator.

Specific examples of the olefinic polymer among the separators include polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, A mixed multilayer film such as a polypropylene/polyethylene/polypropylene three-layer separator or the like can be used.

The lithium salt-containing non-aqueous electrolyte includes a non-aqueous electrolyte and a lithium salt.

As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, or an inorganic solid electrolyte is used.

The non-aqueous electrolyte includes an organic solvent. Any of these organic solvents may be used as long as they can be used as organic solvents in the art. For example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , fluoroethylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, etc. may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ and the like may be used.

The lithium salt is a material readily soluble in the non-aqueous electrolyte, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, Li (FSO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , 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), LiCl, LiI, or mixtures thereof. And for the purpose of improving charge/discharge characteristics, flame retardancy, etc. in the non-aqueous electrolyte, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoamide (hexamethyl phosphoramide), nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride etc. may be added. In some cases, in order to impart incombustibility, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included.

As shown in FIG. 1 , the lithium ion battery 11 includes a positive electrode 13 , a negative electrode 12 , and a separator 34 . The above-described positive electrode 13 , negative electrode 12 , and separator 14 are wound or folded and accommodated in the battery case 15 . Then, an organic electrolyte is injected into the battery case 15 and sealed with a cap assembly 16 to complete the lithium ion battery 11 . The battery case may have a cylindrical shape, a prismatic shape, or a thin film type.

A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is stacked in a bi-cell structure, it is impregnated with an organic electrolyte, and the obtained result is accommodated and sealed in a pouch, thereby completing a lithium ion polymer battery.

In addition, a plurality of the battery structures are stacked to form a battery pack, and the battery pack can be used in any device requiring high capacity and high output. For example, it may be used in a laptop computer, a smartphone, an electric vehicle, and the like.

The present invention will be described in more detail through the following examples and comparative examples. However, the examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1: Preparation of composite positive electrode active material

First, _{in order to prepare LiNi 0.84} Co _0.15 Al _0.01 O ₂ , a transition metal hydroxide precursor Ni _0.85 Co _0.15 (OH) ₂ was prepared according to the following procedure.

To _{100 g of Ni 0.85} Co _0.15 (OH) ₂ , 0.849 g of aluminum hydroxide (Al(OH) ₃ ) and 46.62 g of lithium hydroxide (LiOH ^. H ₂ 0) were added, and this was heat-treated at 760° C. in an oxygen atmosphere to LiNi _0.84 Co _0.15 Al. _0.01 O ₂ was prepared.

LiNi _0.84 Co _0.15 Al _0.01 O _{2 A} washing process was performed according to the following procedure.

LiNi _0.84 Co _0.15 Al _0.01 O ₂ 30 g 0.0043 g of yttrium acetate and 30 ml of water were added, and the mixture was stirred for about 30 minutes _{to perform a cleaning process of LiNi 0.84} Co _0.15 Al _0.01 O ₂ to prepare a composite cathode active material. ^{In the washing process, the content of yttrium acetate was about 0.1×10 −2} M with respect to the total amount of the washing solution used in the washing process (total weight of yttrium acetate and water). The positive active material had a structure including a core active material (LiNi _0.84 Co _0.15 Al _0.01 O ₂ ) and yttrium hydroxide on the surface of the core active material.

Example 2-4: Preparation of composite positive electrode active material

It was carried out according to the same method as in Example 1, except that the content of yttrium acetate was changed so that the content of yttrium acetate was about 0.2×10 ^-2 M, 0.5×10 ^-2 M, and 1.0×10 ^{-2 M, respectively.} A composite positive electrode active material was prepared.

Comparative Example 1: Preparation of positive active material

A cathode active material was prepared in the same manner as in Example 1, except that the cleaning process of _{LiNi 0.84} Co _0.15 Al _0.01 O _{2 was not performed.}

Comparative Example 2: Preparation of positive electrode active material

A cathode active material was prepared in the same manner as in Example 1, except that the cleaning process of _{LiNi 0.84} Co _0.15 Al _0.01 O _{2 was carried out in the following process.}

LiNi _0.88 Co _0.1 Al _0.02 O ₂ 30 g 30 ml of water was added thereto, and the mixture was stirred for about 30 minutes, followed by _{washing with LiNi 0.88} Co _0.1 Al _0.02 O ₂ water to prepare a cathode active material.

Production Example 1: Production of a lithium ion battery (coin half cell)

A slurry for forming a positive electrode active material layer was prepared by mixing a mixture of the composite positive electrode active material prepared according to Example 1, polyvinylidene fluoride, and carbon black as a conductive agent. N-methylpyrrolidone as a solvent was added to the slurry, and the mixing ratio of the positive electrode active material, polyvinylidene fluoride, and carbon black was 94:3:3 by weight.

The slurry prepared according to the above process was coated on an aluminum foil using a doctor blade to form a thin electrode plate, dried at 135° C. for more than 3 hours, and then rolled and vacuum dried to prepare a positive electrode.

A 2032-type coin half cell was manufactured using the positive electrode prepared according to Example 1 and the lithium metal counter electrode as the counter electrode. A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film was interposed between the positive electrode and the lithium metal counter electrode, and electrolyte was injected to prepare a lithium ion battery.

As the electrolyte, a solution containing _{1.3M LiPF 6} dissolved in a solvent in which ethylene carbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:4:3 was used.

Production Example 2-4: Preparation of lithium ion battery (coin half cell)

A lithium ion battery was manufactured in the same manner as in Preparation Example 1, except that the composite positive electrode active material prepared according to Examples 2-4 was used instead of the composite positive electrode active material prepared according to Example 1 when the positive electrode was manufactured.

Comparative Preparation Example 1-2: Preparation of lithium ion battery (coin half cell)

A lithium ion battery was manufactured in the same manner as in Preparation Example 1, except that the positive electrode active material prepared according to Comparative Example 1-2 was used instead of the composite positive electrode active material prepared according to Example 1 when the positive electrode was manufactured.

Evaluation Example 1: Scanning Electron Microscope

A scanning electron microscope analysis was performed on the composite positive active material prepared according to Example 1 and the positive electrode active material prepared according to Comparative Examples 1 and 2. Philips Sirion 200 was used for scanning electron microscope analysis.

The results of scanning electron microscope analysis of the composite positive electrode active material prepared according to Example 1 and the positive electrode active material prepared according to Comparative Examples 1 and 2 are shown in FIGS. 2A to 2C .

As shown in FIG. 2B , black stains were observed on the surface of the positive active material that was not cleaned according to Comparative Example 1. This black stain corresponds to lithium hydroxide and lithium carbonate as unreacted lithium. 2C is a scanning electron microscope photograph of the positive electrode active material that has been washed with water according to Comparative Example 2, and it can be seen that there is almost no stain on the surface of the positive electrode active material.

In contrast, it was confirmed that the composite positive electrode active material prepared according to Example 1 had no stain on the surface and a coating film was formed.

Evaluation Example 2: Specific Surface Area

The specific surface areas of the composite positive electrode active material prepared according to Example 1-3 and the positive electrode active material prepared according to Comparative Example 1-2 were measured using the BET method, and the results are shown in Table 1 below.

division of yttrium acetate
Concentration (M) Specific surface area of positive electrode active material (m ² /g) Example 1 0.1×10 ^-2 1.563 Example 2 0.2×10 ^-2 1.461 Example 3 0.5×10 ^-2 1.357 Example 4 1.0×10 ^-2 1.531 Comparative Example 1 - 0.191 Comparative Example 2 - 1.956

As shown in Table 1, the positive active material of Comparative Example 1 exhibited a low specific surface area due to the presence of unreacted lithium hydroxide and lithium carbonate on the surface of the particles and between the primary particles. In contrast, when the concentration of yttrium acetate exceeds about 0.5 M, the composite positive electrode active material prepared according to Examples 1-4 was coated in a larger amount on the surface, thereby exhibiting the effect of increasing the specific surface area again. As such, it was found that the specific surface area of the composite positive active material prepared according to Examples 1-4 was increased compared to the case of the positive electrode active material prepared according to Comparative Example 1.

In the positive electrode active material of Comparative Example 2, unreacted lithium was removed by washing with water, and unreacted lithium existing between the primary particles was removed together, so that the primary particles were fully exposed, and thus the composite positive electrode active material prepared according to Examples 1-4 It increased compared to the case of , showing high specific surface area characteristics. Although the specific surface area of the positive electrode active material of Comparative Example 2 was increased, as shown in other evaluation examples, the positive electrode active material was damaged. It was found that it was lowered compared to the battery. That is, from these results, it was found that the composite cathode active material of Examples 1-4 had specific surface area characteristics suitable for a lithium ion battery having excellent cell performance.

Evaluation Example 3: Measurement of content of unreacted lithium (residual lithium)

The content of unreacted lithium was measured in the composite positive electrode active material prepared according to Examples 1-4 to the positive electrode active material prepared according to Comparative Example 1-2.

The content of unreacted lithium was measured for each compound containing Li remaining (eg, LiOH or Li ₂ CO ₃ ) by a potentiometric neutralization titration method, and then the total amount of Li alone was separately calculated and obtained (TTL, Total Lithium). The calculation method is as in Equation 1 below.

[Equation 1]

TTL(Total Li) = LiOH analysis value (%)×Li/LiOH + Li ₂ CO ₃ analysis value (%)×2Li/Li ₂ CO ₃ = LiOH analysis value (%)×0.29 + Li ₂ CO ₃ analysis value ( %)×0.188

The measurement results for the content of unreacted lithium are shown in Table 2 below.

division of yttrium acetate
Concentration (10 ^-2 M) Content of unreacted lithium
(weight%) Example 1 0.1 0.11 Example 2 0.2 0.11 Example 3 0.5 0.12 Example 4 1.0 0.13 Comparative Example 1 - 0.47 Comparative Example 2 - 0.12

As shown in Table 2, it was found that, according to Comparative Example 1, a high amount of unreacted lithium was present. In addition, the positive active material prepared according to Comparative Example 2 showed a lower content of unreacted lithium compared to the case of Comparative Example 1 because unreacted lithium was removed through washing with water. On the other hand, it was found that the amount of residual lithium in the composite positive electrode active material prepared according to Example 1-4 was reduced compared to the positive electrode active material prepared according to Comparative Example 1-2. And it was found that even if the content of yttrium acetate was changed, the content of unreacted lithium was hardly changed.

Evaluation Example 4: Transmission electron microscopy / energy dispersive X-ray spectroscopy (transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDS), TEM / EDS)

TEM/EDS analysis was performed on the composite cathode active material prepared according to Example 1. Tecnai F30 of FEI company was used for TEM/EDS analysis.

The results of TEM analysis are shown in FIGS. 3A and 3B . 3A is a TEM photograph, and FIG. 3B is an enlarged view of the square area of FIG. 3A.

Referring to FIGS. 3A and 3B , since several particles overlapped on the surface of the composite positive active material, it was practically difficult to distinguish the phase of yttrium hydroxide. In addition, as a result of EDS mapping analysis for the square region of FIG. 3A , it was possible to confirm the presence of yttrium in the square region of FIG. 3A , that is, the surface region. From this, it can be seen that the composite positive active material prepared according to Example 1 has a coating film in which yttrium is present on the surface.

Evaluation Example 5: High-temperature storage characteristics

The lithium ion battery prepared according to Preparation Example 1-4 and Comparative Preparation Example 1-2 is charged with a constant current at room temperature (25° C.) at a current of 0.1 C rate until the voltage reaches 4.30 V (vs. Li), Then, while maintaining 4.30V in the constant voltage mode, it was cut-off at a current of 0.05C rate. Then, it was discharged at a constant current of 0.1C rate until the voltage reached 3.00V (vs. Li) during discharge (Hwaseong stage, 1 ^st cycle).

The lithium ion battery that has undergone the formation step is charged with a constant current at 25° C. at a rate of 0.5 C until the voltage reaches 4.30 V (vs. Li), and then at a current of 0.05 C while maintaining 4.30 V in the constant voltage mode. It was cut-off. Then, it was discharged at a constant current of 1.0C rate until the voltage reached 3.00V (vs. Li) during discharge. Residual capacity and recovery capacity were calculated based on the discharge value (mAh/g) at this time. Then, the lithium ion battery was charged with a constant current at 25° C. at a rate of 0.5 C until the voltage reached 4.30 V (vs. Li), and then cut off at a current of 0.05 C while maintaining 4.30 V in the constant voltage mode. -off). After the charging was completed, the resistance ( ) was measured before storage at a high temperature.

The battery charged to 4.3V was stored in an oven at 60°C for 7 days and then cooled to room temperature (25°C). Resistance of the cooled lithium-ion battery was measured after high-temperature storage.

The resistance change was calculated from the resistance before high-temperature storage and the resistance after high-temperature storage measured at room temperature (25°C) after storage in an oven at 60°C for 7 days. Some of the measured resistance changes are shown in Table 3 below. The resistance change in Table 3 below shows the difference between the resistance after high temperature resistance and the resistance before high temperature storage.

division Concentration of yttrium acetate (10 ^-2 M) high temperature storage
Resistance (Ω) Resistance after high temperature storage (Ω) Resistance change (Ω) Production Example 1 0.1 97.3 94.2 -3.1 Production example 2 0.2 92.8 87.6 -5.2 Production example 3 0.5 88.4 84.5 -3.9 Production example 4 1.0 86.8 82.8 -4 Comparative Production Example 1 - 14.5 23.7 +9.2 Comparative Production Example 2 - 213.1 237.1 +24

Referring to Table 3, the lithium ion battery prepared according to Comparative Preparation Example 1 had a significantly increased resistance after high-temperature storage compared to before high-temperature storage. And, the lithium ion battery of Comparative Preparation Example 2 had a lot of unreacted lithium removed through water washing, so the surface was exposed a lot, so the resistance was high, and the resistance after high temperature storage was increased compared to the case before high temperature storage. On the other hand, the lithium ion batteries manufactured according to Preparation Examples 1 to 4 exhibited reduced resistance after high-temperature storage compared to the case before high-temperature storage. From this, it was found that the lithium ion battery prepared according to Preparation Example 1-4 had improved high-temperature storage characteristics compared to the case of Comparative Preparation Example 1-2.

Evaluation Example 6: Charging/discharging characteristics (capacity retention rate)

In the lithium ion battery, the charging and discharging characteristics and the like were evaluated under the following conditions with a charger and discharger.

The lithium ion battery prepared according to Preparation Example 1-4 and Comparative Preparation Example 1-2 is charged with a constant current at room temperature (25° C.) at a current of 0.1 C rate until the voltage reaches 4.30 V (vs. Li), Then, while maintaining 4.30V in the constant voltage mode, it was cut-off at a current of 0.05C rate. Then, it was discharged at a constant current of 0.1C rate until the voltage reached 3.00V (vs. Li) during discharge (Hwaseong stage, 1 ^st cycle).

For the first charge/discharge, constant voltage charging was performed until reaching a current of 0.05C after constant current charging until it reached 4.3V with a current of 0.1C. After the charging was completed, the cells were subjected to a rest period of about 10 minutes, and then subjected to constant current discharge at a current of 0.1C until the voltage reached 3 V. In the second charge/discharge cycle, constant voltage charging was performed until it reached a current of 0.05C after constant current charging until it reached 4.3V with a current of 0.2C. After the charging was completed, the cells were subjected to a rest period of about 10 minutes, and then subjected to constant current discharge at a current of 0.2 C until the voltage reached 3 V.

For life evaluation, constant voltage charging was performed until reaching a current of 0.05C after constant current charging until it reached 4.3 V with a current of 1C. After the charging was completed, the cells were evaluated by repeatedly performing a cycle of performing constant current discharge 50 times until the voltage reached 3 V at a current of 1C after a rest period of about 10 minutes. The experimental results are shown in FIG. 4 and Table 4. The capacity retention rate was calculated from Equation 3 below.

[Equation 3]

Capacity retention rate [%] = [ ^{Discharge capacity of 50 th} cycle / Discharge capacity of 1 ^st cycle] × 100

division of yttrium acetate
Concentration (10 ^-2 M) 0.2C capacity (mAh/g) Capacity retention rate (%, @1C/1C) Production Example 1 0.1 200.6 Production example 2 0.2 201.6 87.6 Production example 3 0.5 200.8 84.5 Production example 4 1.0 199.9 82.8 Comparative Production Example 1 - 196.2 72.36 Comparative Production Example 2 - 199.3 77.13

As can be seen from FIGS. 4 and 4, the lithium ion battery prepared according to Comparative Preparation Example 1 has a high residual lithium, so there is no significant difference in 0.2C capacity, but in the case of 1C/1C lifespan, after 50 cycles, low capacity retention rate. In addition, the lithium ion battery prepared according to Comparative Preparation Example 2 had a small amount of residual lithium, but increased surface area and increased resistance. Due to this, the capacity retention rate was reduced compared to the case of Comparative Preparation Example 1. In contrast, it was found that the lithium ion battery manufactured according to Preparation Example 1-4 had improved 0.2C capacity and capacity retention rate compared to the lithium ion battery manufactured according to Comparative Preparation Example 1-2. When looking at the results in Table 4, when the concentration of yttrium acetate was about 0.2 to 0.5M, the capacity retention rate was more excellent, and specifically, when the concentration was 0.5M, the capacity retention rate showed the best results.

Although described above with reference to the manufacturing examples and examples, it will be understood by those skilled in the art that various modifications and changes can be made without departing from the spirit and scope set forth in the following claims. .

11: lithium ion battery 13: positive electrode
12: negative electrode 14: separator
15: battery case 16: cap assembly

Claims (14)

a nickel-rich lithium-nickel-based compound having a nickel content of 50 to 100 mol% based on the total amount of transition metal; and
It is a composite positive electrode active material for a lithium ion battery containing a coating film containing a rare earth metal hydroxide formed on the surface of the nickel-rich lithium nickel-based compound,
The specific surface area of the composite positive electrode active material is 1.357m ² /g to 1.563m ² /g,
The rare earth metal hydroxide is a product obtained by drying a product after adding and stirring a washing solution containing rare earth metal acetate and water at 200° C. or less,
The content of the rare earth metal acetate is 0.1 to 1.0M,
The nickel-rich lithium nickel-based compound is a compound represented by the following Chemical Formula 2 or 3,
The content of the rare earth metal hydroxide is 0.14 to 1.4 parts by weight based on 100 parts by weight of the nickel-rich lithium nickel-based compound,
The content of residual lithium in the composite positive electrode active material is 0.15 wt% or less based on the total amount of the composite positive electrode active material,
The rare earth metal hydroxide is yttrium hydroxide,
The rare earth metal acetate is yttrium acetate, a composite cathode active material for a lithium ion battery:
[Formula 2]
Li _x Ni _y Co _z Mn _1-yz O ₂
In Formula 2, 0.9≤x≤1.2, 0.5≤y<1, 0≤z≤0.5, 0≤1-yz≤0.5,
[Formula 3]
Li _x Ni _y Co _z Al _1-yz O ₂
In Formula 3, 0.9≤x≤1.2, 0.5≤y≤1.0, and 0≤z≤0.5. The composite cathode active material for a lithium ion battery according to claim 1, wherein the content of the rare earth metal hydroxide is 0.29 to 0.71 parts by weight based on 100 parts by weight of the nickel-rich lithium nickel-based compound. delete The composite positive electrode active material for a lithium ion battery according to claim 1, wherein the content of residual lithium in the composite positive active material is 0.11 to 0.13 wt% based on the total amount of the composite positive active material. According to claim 1, wherein the nickel-rich lithium nickel-based compound is LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.3 Mn _0.1 O ₂ , LiNi _0.7 Co _0.15 Mn _0.15 O _{2 ,} LiNi _0.8 Co _0.1 Mn _0.1 O, LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.88 Co _0.1 Al _0.02 O ₂ , LiNi _0.84 Co _0.15 Al _0.01 O _{2 ,} or a mixture thereof, a composite cathode active material for a lithium ion battery. The composite cathode active material for a lithium ion battery according to claim 1, wherein the coating film has a thickness of 500 nm or less. delete delete i) a transition metal hydroxide that is a precursor of a nickel-rich lithium nickel-based compound having a nickel content of 50 to 100 mol% based on the total amount of transition metal, and ii) a nickel-rich lithium nickel-based compound by heat-treating a lithium precursor in an oxidizing atmosphere to obtain;
performing washing by adding and stirring a washing solution containing rare earth metal acetate and water to the nickel-rich lithium nickel-based compound; and
Claims 1, 2, and 4 to 6 to obtain the composite positive electrode active material of any one of claims 1, 2, and 4 to 6, including drying the product after the washing step at 200 ° C.
The rare earth metal acetate is at least one selected from the group consisting of yttrium acetate, cerium acetate, lanthanum acetate, eurobium acetate, gadolinium acetate, scandium acetate and terbium acetate,
A method for producing a composite cathode active material for a lithium ion battery wherein the content of rare earth metal acetate in the washing solution is 0.1 to 1.0M. 10. The method of claim 9, wherein the transition metal hydroxide is Ni _0.5 Co _0.2 Mn _0.3 OH, Ni _0.6 Co _0.3 Mn _0.1 OH, Ni _0.7 Co _0.15 Mn _0.15 OH _, Ni _0.8 Co _0.1 Mn _0.1 OH, Ni _0.6 Co _0.2 Mn _0.2 OH, Ni _0.88 Co _0.1 Al _0.02 OH, Ni _0.84 Co _0.15 Al _0.01 O _{2 A} method of manufacturing a composite cathode active material for a lithium ion battery, or a mixture thereof. The method of claim 9, wherein the content of rare earth metal acetate in the cleaning solution is 0.2 to 0.5M. The method according to claim 9, wherein the drying is carried out at 120 to 150°C. A lithium ion battery containing a positive electrode comprising the composite positive electrode active material of any one of claims 1, 2, 4, 5 and 6. The lithium ion battery according to claim 13, wherein the resistance change obtained from the resistance after high temperature storage measured at room temperature after storage at 60° C. for 7 days in the lithium ion battery is -3.1 Ω to -5.2 Ω.

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