WO2020124361A1 - Positive active material for rechargeable lithium battery, positive electrode and rechargeable lithium battery including the same - Google Patents

Positive active material for rechargeable lithium battery, positive electrode and rechargeable lithium battery including the same Download PDF

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Publication number
WO2020124361A1
WO2020124361A1 PCT/CN2018/121740 CN2018121740W WO2020124361A1 WO 2020124361 A1 WO2020124361 A1 WO 2020124361A1 CN 2018121740 W CN2018121740 W CN 2018121740W WO 2020124361 A1 WO2020124361 A1 WO 2020124361A1
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WIPO (PCT)
Prior art keywords
active material
positive active
aerogel
lithium battery
rechargeable lithium
Prior art date
Application number
PCT/CN2018/121740
Other languages
French (fr)
Inventor
Mingzi Hong
Zhanliang TAO
Huanju MENG
Zhen Zhang
Fangyi CHENG
Pengfei Zhou
Jun Chen
Original Assignee
Samsung Sdi Co., Ltd.
Nankai University
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Application filed by Samsung Sdi Co., Ltd., Nankai University filed Critical Samsung Sdi Co., Ltd.
Priority to KR1020207008703A priority Critical patent/KR20210100526A/en
Priority to PCT/CN2018/121740 priority patent/WO2020124361A1/en
Priority to CN201880009979.5A priority patent/CN111587501B/en
Publication of WO2020124361A1 publication Critical patent/WO2020124361A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • a positive active material for a rechargeable lithium battery and a positive electrode and a rechargeable lithium battery including the same are disclosed.
  • a positive active material of a rechargeable lithium battery may be lithium cobalt oxide, lithium nickel cobalt aluminum composite oxide, lithium nickel manganese cobalt composite oxide, and the like.
  • a positive active material for a rechargeable lithium battery having improved cycle-life characteristics and cell resistance characteristics and a positive electrode including the same are provided.
  • a rechargeable lithium battery having improved cycle-life characteristics and cell resistance characteristics by including the positive electrode including the positive active material is provided.
  • a positive active material for a rechargeable lithium battery includes a lithium composite metal oxide represented by Chemical Formula 1 and a surface layer on the surface of the lithium composite metal oxide and including aerogel.
  • M' is at least one element selected from Co, Mn, Ni, Al, Mg, and Ti
  • a method of preparing a positive active material for a rechargeable lithium battery includes drying an aerogel particle and forming a surface layer including the dried aerogel particle on the surface of a lithium composite metal oxide.
  • a positive electrode including the positive active material for a rechargeable lithium battery and a rechargeable lithium battery including the same are provided.
  • a positive active material for a rechargeable lithium battery having cycle-life characteristics and cell resistance characteristics and a positive electrode including the same are provided.
  • a rechargeable lithium battery having improved cycle-life characteristics and cell resistance characteristics by including the positive electrode including the positive active material is provided.
  • FIG. 1 is a schematic view of a positive active material for a rechargeable lithium battery according to an embodiment.
  • FIG. 2 is a schematic view showing a structure of a rechargeable lithium battery including a positive electrode including a positive active material according to an embodiment.
  • FIG. 3 shows a transmission election microscopic (TEM) image of a positive active material for a rechargeable lithium battery according to an embodiment.
  • TEM transmission election microscopic
  • FIG. 4 shows an X-ray diffraction analysis result of the positive active materials for a rechargeable lithium battery according to Example 1 and Comparative Example.
  • FIG. 5 is a graph showing cycle-life characteristics of the coin half-cells including the positive active materials for a rechargeable lithium battery according to Example 1 (solid line) and Comparative Example (dotted line) .
  • FIG. 6 is a graph showing cell resistance characteristics of the coin half-cells including the positive active materials for a rechargeable lithium battery according to Example 1 and Comparative Example.
  • the generally used method includes a mode diameter showing the maximum value of the distribution, a median diameter corresponding to the center value of integral distribution curve, a variety of average diameters (numeral average, length average, area average, mass average, volume average, etc. ) , and the like.
  • average sizes or average particle diameters means to numeral average sizes or numeral average diameters in the present disclosure, and it is obtained by measuring D50 (particle diameters at a position of distribution rate of 50 %) .
  • FIG. 1 is a schematic view of a positive active material for a rechargeable lithium battery according to an embodiment.
  • a positive active material for a rechargeable lithium battery 11 according to an embodiment includes a lithium composite metal oxide 12 and a surface layer 13 disposed on the lithium composite metal oxide 12.
  • the lithium composite metal oxide 12 may include a lithium nickel-based oxide. Specifically, the lithium composite metal oxide 12 may be represented by Chemical Formula 1.
  • M' is at least one element selected from Co, Mn, Ni, Al, Mg, and Ti
  • lithium composite metal oxide 12 represented by Chemical Formula 1 specifically, a lithium nickel-based oxide having a nickel content of greater than or equal to 60 mol%is used as a positive active material 11, a rechargeable lithium battery having electrochemical characteristics such as rate capability and the like as well as high capacity may be realized.
  • the lithium composite metal oxide 12 may be a lithium nickel-based oxide represented by Chemical Formula 2.
  • the ternary lithium nickel cobalt aluminum-based oxide or lithium nickel cobalt manganese-based oxide represented by Chemical Formula 2 may exhibit excellent battery characteristics by combining high capacity of lithium nickel oxide, thermal stability and economic feasibility of lithium aluminum (manganese) oxide, and stable electrochemical characteristics of lithium cobalt oxide.
  • the surface layer 13 may include aerogel. Since the positive active material 11 according to the present embodiment forms the surface layer 13 with aerogel, the damage to the active material when forming the surface layer 13 may be small and the side reaction with the electrolyte may be suppressed, and the cell resistance may be enhanced to improve cycle-life characteristics of a battery.
  • the aerogel of the surface layer 13 may be hydrophobic aerogel.
  • the aerogel may include hydrophobic aerogel.
  • the surface layer 13 may be for example in an amount of 0.05 wt%to 3 wt%, for example 0.1 wt%to 3 wt%based on 100 wt%of the lithium composite metal oxide 12.
  • the lithium composite metal oxide 12 may be protected from external materials such as an electrolyte solution, moisture, or carbon dioxide effectively while not inhibiting charge and discharge reactions of the lithium composite metal oxide 12.
  • the aerogel may be for example included in a ratio of greater than or equal to 50 wt%, greater than or equal to 60 wt%, greater than or equal to 70 wt%, greater than or equal to 80 wt%, greater than or equal to 90 wt%, or even 100 wt%.
  • the ratio of the aerogel of the surface layer 13 is within the ranges, the lithium composite metal oxide may be protected from external materials such as an electrolyte solution, moisture, or carbon dioxide effectively while not inhibiting charge and discharge reactions of the lithium composite metal oxide.
  • the surface layer 13 may have hydrophobicity.
  • the hydrophobicity of the surface layer 13 may be caused by the hydrophobic aerogel.
  • the hydrophobicity of the surface layer 13 may be caused by the hydrophobic aerogel.
  • the hydrophobic surface may suppress structure collapse of the positive active material due to moisture.
  • the surface layer 13 may cover at least one part or a whole part of the surface of the lithium composite metal oxide 12.
  • the lithium composite metal oxide 12 may be effectively protected from external materials such as an electrolyte solution, moisture, or carbon dioxide.
  • the surface layer 13 may be formed in a shape of a film or an island covering the whole or a part of the lithium composite metal oxide 12.
  • the thickness of the surface layer 13 may vary depending on a size of the lithium composite metal oxide 12, the material of the aerogel, the hydrophobization degree of the aerogel, and the like, but may be for example 20 nm to 100 nm, for example 20 nm to 90 nm, for example 20 nm to 80 nm, for example 20 nm to 70 nm, for example 30 nm to 70 nm, or for example about 50 nm.
  • the lithium composite metal oxide 12 may be protected from external materials such as an electrolyte solution, moisture, or carbon dioxide effectively while not inhibiting charge and discharge reactions of the lithium composite metal oxide 12.
  • a specific surface area of the aerogel may vary depending on a material of the aerogel, a particle size of the used aerogel, and the like, but may be for example 80 m 2 /g to 300 m 2 /g, for example 100 m 2 /g to 300 m 2 /g, for example 150 m 2 /g to 250 m 2 /g, or for example about 200 m 2 /g.
  • the specific surface area of the aerogel may be measured by a known BET (Brunauer-Emmett-Teller) specific surface area measuring device.
  • an average particle diameter of the aerogel particle may vary depending on a thickness of the surface layer 13, a material of the aerogel, a hydrophobization degree of aerogel, and the like, but may be for example 5 nm to 50 nm, for example 10 nm to 50 nm, for example 20 nm to 50 nm, for example 20 nm to 40 nm, for example about 30 nm.
  • the aerogel may include silica (SiO 2 ) aerogel.
  • the aerogel may be silica aerogel.
  • the silica aerogel may be prepared by a method of washing/drying a silica wet gel, and the like.
  • the silica aerogel may be subjected to a hydrophobization treatment to prepare a silica aerogel having a high hydrophobization degree.
  • the silica aerogel may be relatively easily available materials, and the surface layer 13 having high hydrophobicity may be formed at relatively low cost by using the silica aerogel treated to have hydrophobicity.
  • the hydrophobic aerogel according to an embodiment may include an aerogel made of various materials processed to have hydrophobicity, for example, carbon aerogels that is subjected to a hydrophobization treatment.
  • the positive active material 11 is prepared by forming the surface layer 13 having hydrophobicity on the surface of the lithium composite metal oxide 12, and thereby the lithium composite metal oxide 12 may be protected from external materials such as an electrolytic solution, moisture, carbon dioxide, and the like. As a result, a side reaction of the lithium composite metal oxide 12 may be minimized to prepare the positive active material 11 having improved cycle-life characteristics and cell resistance characteristics.
  • the method of preparing the positive active material according to the present embodiment includes drying aerogel particles and forming the surface layer 13 including the dried aerogel particles on the surface of the lithium composite metal oxide 12.
  • the aerogel particles may be produced by the method as described above or may be commercially available.
  • Examples of usable aerogel particles may include silica aerogel particles but are not limited to.
  • the aerogel particles may be subjected to a separate hydrophobization treatment or hydrophobized aerogel particles.
  • the hydrophobization treatment may be performed by a conventional method known in the art and may be carried out before the drying.
  • a drying temperature may vary depending on a material and a size of the aerogel particle, residual moisture amount, and the like, but may be for example greater than or equal to 50 °C, greater than or equal to 60 °C, greater than or equal to 70 °C, for example less than or equal to 120 °C, less than or equal to 110 °C, less than or equal to 100 °C, or less than or equal to 90 °C, for example 50 °C to 120 °C, for example 60 °C to 120 °C, for example 80 °C.
  • a drying time may vary depending on a material and a size of the aerogel particle, residual moisture amount, a drying temperature, and the like, but may be for example greater than or equal to 1 hour, greater than or equal to 2 hours, or greater than or equal to 3 hours, and for example less than or equal to 8 hours, or less than or equal to 7 hours, for example 1 hour to 8 hours, for example 3 hours to 7 hours, for example 5 hours.
  • the surface layer 13 including dried aerogel particles is formed on the lithium composite metal oxide 12.
  • the dried aerogel particles are mixed with the lithium composite metal oxide 12 in a predetermined ratio, so that the dried aerogel particles may be disposed on the whole surface or at least one part of the lithium composite metal oxide 12.
  • the lithium composite metal oxide 12 may be the lithium nickel-based oxide and specifically, a compound represented by Chemical Formula 1, for example, a compound represented by Chemical Formula 2.
  • the lithium nickel-based oxide 12 may be synthesized in a method known in the related art, and accordingly, this synthesis method will not be described.
  • the aerogel particles and the lithium composite metal oxide 12 may be mixed in a weight ratio of 0.001: 1 to 0.02: 1. Accordingly, the aerogel particles are formed into the surface layer 13 covering at least one part of the surface of the lithium composite metal oxide 12.
  • the mixing process may be for example performed at a speed of 1000 rpm to 5000 rpm, for example, about 3000 rpm.
  • the aerogel particles When the mixing speed is less than 1000 rpm, the aerogel particles may be not uniformly adhered on the surface of the lithium composite metal oxide 12 and fail in forming a uniform surface layer, but when the mixing speed is greater than 5000 rpm, the lithium composite metal oxide 12 may be broken during the mixing.
  • the mixing process of the aerogel particles and the lithium composite metal oxide 12 is performed under a dry atmosphere. Accordingly, the lithium composite metal oxide 12 may be prevented from a direct contact with moisture during the mixing process, and since the mixing is performed under a non-aqueous condition, a post-heat-treatment process may be omitted.
  • the mixing process of the aerogel particle with the lithium composite metal oxide 12 may be performed at room temperature. Accordingly, the overall mixing process may be easily controlled.
  • the aerogel particles and the lithium composite metal oxide 12 may be formed into the surface layer 13 without other additives during the mixing process. Accordingly, the overall mixing process may be maintained under the non-aqueous condition, and after the mixing process, a non-reaction material, a side-reaction material, and the like do not need to be removed. Accordingly, a washing process may be omitted.
  • the method of preparing the positive active material 11 provides the positive active material 11 through a process of mixing aerogel particles and the lithium metal oxide 12 without a separate additive at room temperature and thus may relatively simply control the entire process and have excellent process reproducibility.
  • the method of preparing the positive active material maintains a room temperature non-aqueous process over the entire process and thus may prevent performance deterioration of the lithium composite metal oxide 12 due to moisture.
  • the method needs no post-heat treatment process and thus may prevent a side reaction which may occur on the surface of the positive active material 11.
  • the positive active material 11 prepared using the method of the positive active material according to an embodiment may exhibit cycle-life characteristics and cell resistance characteristics as described above.
  • FIG. 2 is a schematic view showing a structure of a rechargeable lithium battery including a positive electrode including a positive active material according to an embodiment.
  • the rechargeable lithium battery 21 of FIG. 2 includes a positive electrode 23 including the positive active material according to an embodiment, a negative electrode 22, and a separator 24.
  • the positive electrode 23 and the negative electrode 22 may be manufactured by coating a composition for forming a positive active material layer and a composition for forming a negative active material layer on each current collector, respectively, and drying the same.
  • composition for the positive active material layer may be prepared by mixing a positive active material, a conductive agent, a binder, and a solvent wherein the positive active material is the positive active material 11 according to the above embodiment.
  • the binder may help binding of active materials, conductive agent, and the like and binding them on a current collector, and may be added in an amount of 1 to 50 parts by weight based on a total weight, 100 parts by weight of the positive active material.
  • Non-limiting examples of such a binder may be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC) , starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene terpolymer (EPDM) , sulfonated EPDM, a styrene butadiene rubber, a fluorine rubber, various copolymers, and the like.
  • the amount thereof may be 2 to 5 parts by weight based on a total weight, 100 parts by weight of the positive active material. When the amount of the binder is within the range, the binding force of the active material layer to
  • the conductive agent is not particularly limited as long as it does not cause a chemical change of a battery and has conductivity and may be for example, graphite such as natural graphite or artificial graphite; a carbon-based material such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and the like; a conductive fiber such as a carbon fiber or a metal fiber, and the like; carbon fluoride; a metal powder such as an aluminum or nickel powder; zinc oxide, a conductive whisker such as potassium titanate, and the like; a conductive metal oxide such as a titanium oxide; a conductive material such as a polyphenylene derivative, and the like.
  • graphite such as natural graphite or artificial graphite
  • a carbon-based material such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and the like
  • a conductive fiber such as a carbon fiber or a metal fiber, and the like
  • the amount of the conductive agent may be 2 to 5 parts by weight based on a total weight, 100 parts by weight of the positive active material. When the amount of the conductive agent is within the range, conductivity characteristics of the resultant electrode are improved.
  • Non-limiting examples of the solvent may be N-methyl pyrrolidone, and the like.
  • the positive current collector may have a thickness of 3 ⁇ m to 500 ⁇ m, is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity, and may be for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel of which the surface is treated with carbon, nickel, titanium, or silver.
  • the current collector may have fine irregularities formed on a surface thereof to increase adhesive force of the positive active material, and various forms such as a film, a sheet, a foil, a net, a porous body, foam, or a non-woven fabric body.
  • a negative active material a binder, a conductive agent, and a solvent are mixed to prepare a composition for a negative active material layer.
  • the negative active material may use a material capable of intercalating and deintercalating lithium ions.
  • Non-limiting examples of the negative active material may be a carbon-based material such as graphite or carbon, a lithium metal, an alloy thereof, a silicon oxide-based material, and the like. According to an embodiment of the present invention, silicon oxide may be used.
  • the binder may be added in an amount of 1 part by weight to 50 parts by weight based on a total weight, 100 parts by weight of the negative active material.
  • Non-limiting examples of the binder may be the same as the positive electrode.
  • the conductive agent may be omitted depending on the kind of the negative active material contained in the composition for forming a negative active material layer, and may be used in an amount of 0 to 1 part by weight based on a total weight, 100 parts by weight of the negative active material. When the amount of the conductive agent is within the range, conductivity characteristics of the resultant electrode are improved.
  • the conductive agent and the solvent may use the same materials as those used in manufacturing the positive electrode.
  • the negative current collector may have a thickness of 3 ⁇ m to 500 ⁇ m.
  • a negative current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity and may be for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper, or stainless steel of which the surface is treated with carbon, nickel, titanium, or silver, an aluminum-cadmium alloy, and the like.
  • it may have fine irregularities formed on a surface thereof to increase adhesive force of the negative active materials, and various forms such as a film, a sheet, a foil, a net, a porous body, foam, or a non-woven fabric body, like the positive current collector.
  • a separator is disposed between the positive electrode and the negative electrode manufactured according to the above processes.
  • the separator may generally have a pore diameter of 0.01 ⁇ m to 10 ⁇ m and a thickness of 5 ⁇ m to 300 ⁇ m.
  • Specific examples may be an olefin-based polymer such as polypropylene, polyethylene, and the like; or a sheet or a nonwoven fabric formed of a glass fiber.
  • the solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator.
  • a lithium salt-containing non-aqueous electrolyte may be composed of a non-aqueous electrolyte and a lithium salt.
  • the non-aqueous electrolyte may be a non-aqueous electrolyte, an organic solid electrolyte, or inorganic solid electrolyte.
  • the non-aqueous electrolyte may be for example aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyro lactone, 1, 2-dimethoxyethane, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1, 3-dioxolane, formamide, N, N-dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, ether, methyl propionate, ethyl prop
  • the organic solid electrolyte may be for example a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphoric acid ester polymer, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and the like.
  • the inorganic solid electrolyte may be for example Li 3 N, LiI, Li 5 NI 2 , Li 3 N-LiI-LiOH, LiSiO 4 , LiSiO 4 -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.
  • the lithium salt is a material which is readily soluble in the non-aqueous electrolyte, and for example, LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2 ) 2 NLi, lithium chloroborate, lower aliphatic lithium carbonates, tetraphenyl lithium borate, imides, and the like.
  • the positive electrode 23, the negative electrode 22, and the separator 24 are wound or folded and accommodated in the battery case 25. Then, an organic electrolytic solution is injected into the battery case 25 and the cap assembly 26 is sealed to complete the rechargeable lithium battery 21 as shown in FIG. 2.
  • the battery case 25 may be cylindrical, prismatic, thin film, and the like.
  • the rechargeable lithium battery 20 may be a large-scale thin film-type battery.
  • the rechargeable lithium battery may be a lithium ion battery.
  • a cell structure including a separator between the positive electrode and the negative electrode may be formed.
  • the cell structure is stacked in a bi-cell structure and then impregnated with an organic electrolyte solution, and the resulting product is received in a pouch and sealed to complete a lithium ion polymer battery.
  • a plurality of cell structures may be stacked to form a battery pack, and such a battery pack may be used for all devices requiring a high capacity and a high power. For example, it may be used for a laptop, a smart phone, an electric vehicle, and the like.
  • the rechargeable lithium battery has improved storage stability, cycle-life characteristics, and high-rate characteristics at a high temperature and may be used in an electric vehicle (EV) .
  • EV electric vehicle
  • PHEV plug-in hybrid electric vehicle
  • the rechargeable lithium battery according to an embodiment uses the positive active material for a rechargeable lithium battery as a positive active material, and thus may exhibit excellent cycle-life characteristics and cell resistance characteristics.
  • a rechargeable lithium battery according to an embodiment may use for example a lithium nickel cobalt aluminum oxide as the lithium composite metal oxide, generation of NiO and oxygen by a reaction with moisture or carbon dioxide in in air or production of inert materials such as LiOH, LiCO 3 , and the like may be minimized. Therefore, with respect to positive active materials having various compositions, a positive electrode having excellent electrochemical characteristics and stability and a rechargeable lithium battery including the same may be provided.
  • Hydrophobic silica aerogel particles having an average particle diameter of 30 nm (aspecific surface area of 150 m 2 /g to 200 m 2 /g, Aladin) were prepared.
  • the hydrophobic silica aerogel particles were put in an oven at 80 °C under -0.1 MPa and dried for about 5 hours under vacuum.
  • the mixed material was put in a crucible and then, fired under an oxygen (O 2 ) atmosphere at 680 °C to 730 °C, for example, at 710 °C for 10 hours to 20 hours to obtain a fired product of a NCA material.
  • the NCA material had a composition of LiNi 0.915 Co 0.075 Al 0.01 O 2 .
  • the vacuum-dried hydrophobic silica aerogel particles and the NCA material were put in a glove box and weighed to obtain a mixture of the vacuum-dried hydrophobic silica aerogel particles and the NCA material in a weight ratio of 0.002: 1.
  • the mixture was put in a ball mill at room temperature (25 °C) under a dry atmosphere and then, mixed at a speed of 3000 rpm for about 2 hours to prepare a positive active material.
  • a positive active material was prepared according to the same method as Example 1 except for using a mixture prepared by mixing the vacuum-dried hydrophobic silica aerogel particles and the NCA material in a weight ratio of 0.001: 1.
  • a positive active material was prepared according to the same method as Example 1 except for using a mixture prepared by mixing the vacuum-dried hydrophobic silica aerogel particles and the NCA material in a weight ratio of 0.005: 1.
  • a positive active material was prepared according to the same method as Example 1 except for using a mixture prepared by mixing the vacuum-dried hydrophobic silica aerogel particles and the NCA material in a weight ratio of 0.01: 1.
  • Each positive active material according to Examples 1 to 4 and Comparative Example was mixed , polyvinylidene fluoride (PVDF) and denka black dissolved in N-methyl-2-pyrrolidone in a mass ratio of 92: 4: 4 and then, put in a centrifugal mixer (Thinky tm Corp. ) and dispersed at a speed of 2000 r/min for 15 minutes to respectively obtain slurry.
  • the slurry was uniformly coated on an Al thin film and dried in a vacuum-dry chamber at 110 °C for 10 hours to obtain a positive electrode plate substrate having a loading weight of 8 mg/cm 2 to 10 mg/cm 2 .
  • the positive electrode plate substrate was perforated with a punching machine to prepare a disk-shaped positive electrode plate substrate having a diameter of 10 mm, and the disk-shaped positive electrode plate substrate was compressed under a pressure of 4 MPa, dried at 110 °C for 10 hours, and rapidly moved into a glove box to obtain a positive electrode plate.
  • the positive electrode plate was used as a positive electrode, and metal lithium was used as a counter electrode of the positive electrode to manufacture a coin-type half-cell (CR2032 type) .
  • FIG. 3 shows a transmission election microscope (TEM) image of Example 1.
  • TEM transmission election microscope
  • the positive active materials according to Examples 1 to 4 were all not shown in FIG. 1 but respectively included a surface layer including a hydrophobic silica aerogel covering the surface of the NCA material, as shown in FIG. 1.
  • FIG. 4 shows X-ray diffraction analysis results of the positive active materials according to Example 1 and Comparative Example.
  • Example 1 further included a surface layer formed of a hydrophobic silica aerogel unlike Comparative Example but showed the same peak position and intensity as those of Comparative Example. Accordingly, the NCA material was coated with the hydrophobic silica aerogel according to Example but showed no structural change.
  • Example 1 showed that a surface layer formed of a hydrophobic silica aerogel was formed on the surface of the NCA material without changing the structure of the NCA material.
  • the rechargeable lithium battery cells according to Example 1 and Comparative Example were constant current-charged at a 1 C rate up to a voltage of 4.3 V and then, constant voltage-charged up to a current of 0.005 C (1/200 C) , while 4.3 V was maintained, at 60 °C. Subsequently, the rechargeable lithium battery cells were discharged at a constant current of 1 C down to a voltage of 3.0 V as one cycle, which was 50 times repeated. Cycle-life characteristics of the rechargeable lithium battery cells were evaluated under the following condition, and the results are shown in FIG. 5. In FIG. 5, the cycle-life characteristics of the rechargeable lithium battery cell according to Example 1 were marked as a solid line, and the cycle-life characteristics of the rechargeable lithium battery cell according to Comparative Example was marked as a dotted line.
  • Example 1 using the NCA material having a surface layer formed of a hydrophobic silica aerogel as a positive active material showed excellent cycle-life characteristics compared with Comparative Example.
  • Example 1 using the NCA material having a surface layer formed of a hydrophobic silica aerogel as a positive active material showed improved cell resistance characteristics compared with Comparative Example. Accordingly, the surface layer suppressed a side reaction of the NCA material and thus reduced interface resistance.

Abstract

Provided are a positive active material for a rechargeable lithium battery including a lithium composite metal oxide represented by Chemical Formula 1 and a surface layer on the surface of the lithium composite metal oxide and including aerogel, and a positive electrode and a rechargeable lithium battery including the same. Chemical Formula 1 is described in the detailed description.

Description

POSITIVE ACTIVE MATERIAL FOR RECHARGEABLE LITHIUM BATTERY, POSITIVE ELECTRODE AND RECHARGEABLE LITHIUM BATTERY INCLUDING THE SAME Technical Field
A positive active material for a rechargeable lithium battery and a positive electrode and a rechargeable lithium battery including the same are disclosed.
Background Art
As portable electronic devices, communication devices, and the like are developed, there are needs for development of a rechargeable lithium battery having a high energy density.
A positive active material of a rechargeable lithium battery may be lithium cobalt oxide, lithium nickel cobalt aluminum composite oxide, lithium nickel manganese cobalt composite oxide, and the like.
However, as a positive active material contacts external materials such as an electrolytic solution, moisture, and carbon dioxide at high temperature, there are risks of generating side-reaction materials such as lithium hydroxide and lithium salts, which are gases such as oxygen or electrochemically inactive materials. Since the side-reaction materials deteriorates cycle-life characteristics and thermal stability of the positive active material, it is necessary to prevent a direct contact of the electrolytic solution or external materials with the positive active material during charging and discharging.
SUMMARY
Technical Problem
A positive active material for a rechargeable lithium battery having improved  cycle-life characteristics and cell resistance characteristics and a positive electrode including the same are provided.
A rechargeable lithium battery having improved cycle-life characteristics and cell resistance characteristics by including the positive electrode including the positive active material is provided.
Technical Solution
According to an embodiment, a positive active material for a rechargeable lithium battery includes a lithium composite metal oxide represented by Chemical Formula 1 and a surface layer on the surface of the lithium composite metal oxide and including aerogel.
[Chemical Formula 1]
Li a (Ni xM' yM" z) O 2
In Chemical Formula 1, M' is at least one element selected from Co, Mn, Ni, Al, Mg, and Ti, M” is at least one element selected from Ca, Mg, Al, Ti, Sr, Fe, Co, Mn, Ni, Cu, Zn, Y, Zr, Nb, and B, 0.8 < a ≤ 1.3, 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, and x+y+z = 1.
According to another embodiment, a method of preparing a positive active material for a rechargeable lithium battery includes drying an aerogel particle and forming a surface layer including the dried aerogel particle on the surface of a lithium composite metal oxide.
Another according to an embodiment, a positive electrode including the positive active material for a rechargeable lithium battery and a rechargeable lithium battery including the same are provided.
Advantageous Effects
A positive active material for a rechargeable lithium battery having cycle-life characteristics and cell resistance characteristics and a positive electrode including the same are provided.
In addition, a rechargeable lithium battery having improved cycle-life  characteristics and cell resistance characteristics by including the positive electrode including the positive active material is provided.
Brief Description of Drawings
FIG. 1 is a schematic view of a positive active material for a rechargeable lithium battery according to an embodiment.
FIG. 2 is a schematic view showing a structure of a rechargeable lithium battery including a positive electrode including a positive active material according to an embodiment.
FIG. 3 shows a transmission election microscopic (TEM) image of a positive active material for a rechargeable lithium battery according to an embodiment.
FIG. 4 shows an X-ray diffraction analysis result of the positive active materials for a rechargeable lithium battery according to Example 1 and Comparative Example.
FIG. 5 is a graph showing cycle-life characteristics of the coin half-cells including the positive active materials for a rechargeable lithium battery according to Example 1 (solid line) and Comparative Example (dotted line) .
FIG. 6 is a graph showing cell resistance characteristics of the coin half-cells including the positive active materials for a rechargeable lithium battery according to Example 1 and Comparative Example.
Description of Embodiments
The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. The drawings and description are to be regarded as illustrative in nature and  not restrictive. Like reference numerals designate like elements throughout the specification.
In many embodiments, elements having the same structure are represented by the same reference numerals and are described in the represented embodiment, and only the different structures will be described in the other embodiments.
In an embodiment, for sizes or particle diameters of various particles, although they may be numerized by a measurement to show an average size of a group, the generally used method includes a mode diameter showing the maximum value of the distribution, a median diameter corresponding to the center value of integral distribution curve, a variety of average diameters (numeral average, length average, area average, mass average, volume average, etc. ) , and the like. Unless particularly mentioning otherwise, average sizes or average particle diameters means to numeral average sizes or numeral average diameters in the present disclosure, and it is obtained by measuring D50 (particle diameters at a position of distribution rate of 50 %) .
Hereinafter, a positive active material for a rechargeable lithium battery according to an embodiment is described.
FIG. 1 is a schematic view of a positive active material for a rechargeable lithium battery according to an embodiment. Referring to FIG. 1, a positive active material for a rechargeable lithium battery 11 according to an embodiment includes a lithium composite metal oxide 12 and a surface layer 13 disposed on the lithium composite metal oxide 12.
The lithium composite metal oxide 12 may include a lithium nickel-based oxide. Specifically, the lithium composite metal oxide 12 may be represented by Chemical Formula 1.
[Chemical Formula 1]
Li a (Ni xM' yM" z) O 2
In Chemical Formula 1, M' is at least one element selected from Co, Mn, Ni, Al,  Mg, and Ti, M” is at least one element selected from Ca, Mg, Ba, Al, Ti, Sr, Fe, Co, Mn, Ni, Cu, Zn, Y, Zr, Nb, and B, 0.8 < a ≤ 1.3, 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, and x+y+z = 1. When the lithium composite metal oxide 12 represented by Chemical Formula 1, specifically, a lithium nickel-based oxide having a nickel content of greater than or equal to 60 mol%is used as a positive active material 11, a rechargeable lithium battery having electrochemical characteristics such as rate capability and the like as well as high capacity may be realized.
For example, the lithium composite metal oxide 12 may be a lithium nickel-based oxide represented by Chemical Formula 2.
[Chemical Formula 2]
Li a (Ni xCo yM" z) O 2
In Chemical Formula 2, M” is at least one element selected from Al, Mg, Ba, Ti, Zr, Y, and Mn, 0.8 < a ≤ 1.3, 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, and x+y+z = 1. On the other hand, in Chemical Formula 2, M” may be Al, 0.8 < a ≤ 1.3, 0 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2, and x+y+z = 1.
The ternary lithium nickel cobalt aluminum-based oxide or lithium nickel cobalt manganese-based oxide represented by Chemical Formula 2 may exhibit excellent battery characteristics by combining high capacity of lithium nickel oxide, thermal stability and economic feasibility of lithium aluminum (manganese) oxide, and stable electrochemical characteristics of lithium cobalt oxide.
The surface layer 13 may include aerogel. Since the positive active material 11 according to the present embodiment forms the surface layer 13 with aerogel, the damage to the active material when forming the surface layer 13 may be small and the side reaction with the electrolyte may be suppressed, and the cell resistance may be enhanced to improve cycle-life characteristics of a battery.
In an embodiment, the aerogel of the surface layer 13 may be hydrophobic aerogel.  For example, in an embodiment, the aerogel may include hydrophobic aerogel. The surface layer 13 may be for example in an amount of 0.05 wt%to 3 wt%, for example 0.1 wt%to 3 wt%based on 100 wt%of the lithium composite metal oxide 12. When the surface layer 13 is included in the positive active material 11 within the ranges, the lithium composite metal oxide 12 may be protected from external materials such as an electrolyte solution, moisture, or carbon dioxide effectively while not inhibiting charge and discharge reactions of the lithium composite metal oxide 12.
In the surface layer 13, the aerogel may be for example included in a ratio of greater than or equal to 50 wt%, greater than or equal to 60 wt%, greater than or equal to 70 wt%, greater than or equal to 80 wt%, greater than or equal to 90 wt%, or even 100 wt%. When the ratio of the aerogel of the surface layer 13 is within the ranges, the lithium composite metal oxide may be protected from external materials such as an electrolyte solution, moisture, or carbon dioxide effectively while not inhibiting charge and discharge reactions of the lithium composite metal oxide.
In an embodiment, the surface layer 13 may have hydrophobicity. The hydrophobicity of the surface layer 13 may be caused by the hydrophobic aerogel. In an embodiment, the hydrophobicity of the surface layer 13 may be caused by the hydrophobic aerogel. The hydrophobic surface may suppress structure collapse of the positive active material due to moisture.
In an embodiment, the surface layer 13 may cover at least one part or a whole part of the surface of the lithium composite metal oxide 12. When the surface layer 13 covers the whole part of the surface of the lithium composite metal oxide 12, the lithium composite metal oxide 12 may be effectively protected from external materials such as an electrolyte solution, moisture, or carbon dioxide. In addition, the surface layer 13 may be formed in a shape of a film or an island covering the whole or a part of the lithium composite metal oxide 12.
In an embodiment, the thickness of the surface layer 13 may vary depending on a size of the lithium composite metal oxide 12, the material of the aerogel, the hydrophobization degree of the aerogel, and the like, but may be for example 20 nm to 100 nm, for example 20 nm to 90 nm, for example 20 nm to 80 nm, for example 20 nm to 70 nm, for example 30 nm to 70 nm, or for example about 50 nm. When the thickness of the surface layer 13 is within the ranges, the lithium composite metal oxide 12 may be protected from external materials such as an electrolyte solution, moisture, or carbon dioxide effectively while not inhibiting charge and discharge reactions of the lithium composite metal oxide 12.
In an embodiment, a specific surface area of the aerogel may vary depending on a material of the aerogel, a particle size of the used aerogel, and the like, but may be for example 80 m 2/g to 300 m 2/g, for example 100 m 2/g to 300 m 2/g, for example 150 m 2/g to 250 m 2/g, or for example about 200 m 2/g. When the specific surface area of the aerogel satisfies the ranges, the positive active material for a rechargeable lithium battery 11 according to an embodiment may exhibit excellent lithium ion conductivity. The specific surface area of the aerogel may be measured by a known BET (Brunauer-Emmett-Teller) specific surface area measuring device.
In an embodiment, an average particle diameter of the aerogel particle may vary depending on a thickness of the surface layer 13, a material of the aerogel, a hydrophobization degree of aerogel, and the like, but may be for example 5 nm to 50 nm, for example 10 nm to 50 nm, for example 20 nm to 50 nm, for example 20 nm to 40 nm, for example about 30 nm.
In an embodiment, the aerogel may include silica (SiO 2) aerogel. For example, the aerogel may be silica aerogel. When the surface layer 13 is formed using silica aerogel, cycle-life characteristic and cell resistance of a battery may be improved. The silica aerogel may be prepared by a method of washing/drying a silica wet gel, and the like.  The silica aerogel may be subjected to a hydrophobization treatment to prepare a silica aerogel having a high hydrophobization degree. The silica aerogel may be relatively easily available materials, and the surface layer 13 having high hydrophobicity may be formed at relatively low cost by using the silica aerogel treated to have hydrophobicity. However, the scope of the present invention is not limited thereto, and the hydrophobic aerogel according to an embodiment may include an aerogel made of various materials processed to have hydrophobicity, for example, carbon aerogels that is subjected to a hydrophobization treatment.
As described above, the positive active material 11 according to an embodiment is prepared by forming the surface layer 13 having hydrophobicity on the surface of the lithium composite metal oxide 12, and thereby the lithium composite metal oxide 12 may be protected from external materials such as an electrolytic solution, moisture, carbon dioxide, and the like. As a result, a side reaction of the lithium composite metal oxide 12 may be minimized to prepare the positive active material 11 having improved cycle-life characteristics and cell resistance characteristics.
Hereinafter, a method of preparing a positive active material according to an embodiment is described.
The method of preparing the positive active material according to the present embodiment includes drying aerogel particles and forming the surface layer 13 including the dried aerogel particles on the surface of the lithium composite metal oxide 12.
First, the aerogel particles may be produced by the method as described above or may be commercially available. Examples of usable aerogel particles may include silica aerogel particles but are not limited to. The aerogel particles may be subjected to a separate hydrophobization treatment or hydrophobized aerogel particles. The hydrophobization treatment may be performed by a conventional method known in the art and may be carried out before the drying.
First, drying of the prepared aerogel particles is performed. Residual moisture inside the aerogel particles may be removed through drying and the moisture remaining in the aerogel particles may be prevented from being in a direct contact with the lithium composite metal oxide 12 in the subsequent coating process.
In an embodiment, a drying temperature may vary depending on a material and a size of the aerogel particle, residual moisture amount, and the like, but may be for example greater than or equal to 50 ℃, greater than or equal to 60 ℃, greater than or equal to 70 ℃, for example less than or equal to 120 ℃, less than or equal to 110 ℃, less than or equal to 100 ℃, or less than or equal to 90 ℃, for example 50 ℃ to 120 ℃, for example 60 ℃ to 120 ℃, for example 80 ℃.
In an embodiment, a drying time may vary depending on a material and a size of the aerogel particle, residual moisture amount, a drying temperature, and the like, but may be for example greater than or equal to 1 hour, greater than or equal to 2 hours, or greater than or equal to 3 hours, and for example less than or equal to 8 hours, or less than or equal to 7 hours, for example 1 hour to 8 hours, for example 3 hours to 7 hours, for example 5 hours.
Then, the surface layer 13 including dried aerogel particles is formed on the lithium composite metal oxide 12. Specifically, the dried aerogel particles are mixed with the lithium composite metal oxide 12 in a predetermined ratio, so that the dried aerogel particles may be disposed on the whole surface or at least one part of the lithium composite metal oxide 12. The lithium composite metal oxide 12 may be the lithium nickel-based oxide and specifically, a compound represented by Chemical Formula 1, for example, a compound represented by Chemical Formula 2. The lithium nickel-based oxide 12 may be synthesized in a method known in the related art, and accordingly, this synthesis method will not be described. On the other hand, the aerogel particles and the lithium composite metal oxide 12 may be mixed in a weight ratio of 0.001: 1 to 0.02: 1. Accordingly, the  aerogel particles are formed into the surface layer 13 covering at least one part of the surface of the lithium composite metal oxide 12. The mixing process may be for example performed at a speed of 1000 rpm to 5000 rpm, for example, about 3000 rpm.
When the mixing speed is less than 1000 rpm, the aerogel particles may be not uniformly adhered on the surface of the lithium composite metal oxide 12 and fail in forming a uniform surface layer, but when the mixing speed is greater than 5000 rpm, the lithium composite metal oxide 12 may be broken during the mixing.
In an embodiment, the mixing process of the aerogel particles and the lithium composite metal oxide 12 is performed under a dry atmosphere. Accordingly, the lithium composite metal oxide 12 may be prevented from a direct contact with moisture during the mixing process, and since the mixing is performed under a non-aqueous condition, a post-heat-treatment process may be omitted. In an embodiment, the mixing process of the aerogel particle with the lithium composite metal oxide 12 may be performed at room temperature. Accordingly, the overall mixing process may be easily controlled.
On the other hand, the aerogel particles and the lithium composite metal oxide 12 may be formed into the surface layer 13 without other additives during the mixing process. Accordingly, the overall mixing process may be maintained under the non-aqueous condition, and after the mixing process, a non-reaction material, a side-reaction material, and the like do not need to be removed. Accordingly, a washing process may be omitted.
As described above, the method of preparing the positive active material 11 according to an embodiment provides the positive active material 11 through a process of mixing aerogel particles and the lithium metal oxide 12 without a separate additive at room temperature and thus may relatively simply control the entire process and have excellent process reproducibility.
On the other hand, the method of preparing the positive active material according to an embodiment maintains a room temperature non-aqueous process over the entire  process and thus may prevent performance deterioration of the lithium composite metal oxide 12 due to moisture. In addition, the method needs no post-heat treatment process and thus may prevent a side reaction which may occur on the surface of the positive active material 11.
In addition, the positive active material 11 prepared using the method of the positive active material according to an embodiment may exhibit cycle-life characteristics and cell resistance characteristics as described above.
Hereinafter, a structure of a rechargeable lithium battery including a positive electrode including the positive active material according to an embodiment and a method of manufacturing the same are described.
FIG. 2 is a schematic view showing a structure of a rechargeable lithium battery including a positive electrode including a positive active material according to an embodiment.
The rechargeable lithium battery 21 of FIG. 2 includes a positive electrode 23 including the positive active material according to an embodiment, a negative electrode 22, and a separator 24.
The positive electrode 23 and the negative electrode 22 may be manufactured by coating a composition for forming a positive active material layer and a composition for forming a negative active material layer on each current collector, respectively, and drying the same.
The composition for the positive active material layer may be prepared by mixing a positive active material, a conductive agent, a binder, and a solvent wherein the positive active material is the positive active material 11 according to the above embodiment.
The binder may help binding of active materials, conductive agent, and the like and binding them on a current collector, and may be added in an amount of 1 to 50 parts by weight based on a total weight, 100 parts by weight of the positive active material.  Non-limiting examples of such a binder may be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC) , starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene terpolymer (EPDM) , sulfonated EPDM, a styrene butadiene rubber, a fluorine rubber, various copolymers, and the like. The amount thereof may be 2 to 5 parts by weight based on a total weight, 100 parts by weight of the positive active material. When the amount of the binder is within the range, the binding force of the active material layer to the current collector is good.
The conductive agent is not particularly limited as long as it does not cause a chemical change of a battery and has conductivity and may be for example, graphite such as natural graphite or artificial graphite; a carbon-based material such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and the like; a conductive fiber such as a carbon fiber or a metal fiber, and the like; carbon fluoride; a metal powder such as an aluminum or nickel powder; zinc oxide, a conductive whisker such as potassium titanate, and the like; a conductive metal oxide such as a titanium oxide; a conductive material such as a polyphenylene derivative, and the like.
The amount of the conductive agent may be 2 to 5 parts by weight based on a total weight, 100 parts by weight of the positive active material. When the amount of the conductive agent is within the range, conductivity characteristics of the resultant electrode are improved.
Non-limiting examples of the solvent may be N-methyl pyrrolidone, and the like.
The positive current collector may have a thickness of 3 μm to 500 μm, is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity, and may be for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel of which the surface is treated with carbon, nickel, titanium, or silver. The current collector may have fine irregularities  formed on a surface thereof to increase adhesive force of the positive active material, and various forms such as a film, a sheet, a foil, a net, a porous body, foam, or a non-woven fabric body.
Separately, a negative active material, a binder, a conductive agent, and a solvent are mixed to prepare a composition for a negative active material layer.
The negative active material may use a material capable of intercalating and deintercalating lithium ions. Non-limiting examples of the negative active material may be a carbon-based material such as graphite or carbon, a lithium metal, an alloy thereof, a silicon oxide-based material, and the like. According to an embodiment of the present invention, silicon oxide may be used.
The binder may be added in an amount of 1 part by weight to 50 parts by weight based on a total weight, 100 parts by weight of the negative active material. Non-limiting examples of the binder may be the same as the positive electrode.
The conductive agent may be omitted depending on the kind of the negative active material contained in the composition for forming a negative active material layer, and may be used in an amount of 0 to 1 part by weight based on a total weight, 100 parts by weight of the negative active material. When the amount of the conductive agent is within the range, conductivity characteristics of the resultant electrode are improved.
The conductive agent and the solvent may use the same materials as those used in manufacturing the positive electrode.
The negative current collector may have a thickness of 3 μm to 500 μm. Such a negative current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity and may be for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper, or stainless steel of which the surface is treated with carbon, nickel, titanium, or silver, an aluminum-cadmium alloy, and the like. In addition, it may have fine irregularities formed on a surface thereof to  increase adhesive force of the negative active materials, and various forms such as a film, a sheet, a foil, a net, a porous body, foam, or a non-woven fabric body, like the positive current collector.
A separator is disposed between the positive electrode and the negative electrode manufactured according to the above processes.
The separator may generally have a pore diameter of 0.01 μm to 10 μm and a thickness of 5 μm to 300 μm. Specific examples may be an olefin-based polymer such as polypropylene, polyethylene, and the like; or a sheet or a nonwoven fabric formed of a glass fiber. In the case that a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator.
A lithium salt-containing non-aqueous electrolyte may be composed of a non-aqueous electrolyte and a lithium salt. The non-aqueous electrolyte may be a non-aqueous electrolyte, an organic solid electrolyte, or inorganic solid electrolyte.
The non-aqueous electrolyte may be for example aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyro lactone, 1, 2-dimethoxyethane, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1, 3-dioxolane, formamide, N, N-dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, or combinations thereof.
The organic solid electrolyte may be for example a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphoric acid ester polymer, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and the like.
The inorganic solid electrolyte may be for example Li 3N, LiI, Li 5NI 2,  Li 3N-LiI-LiOH, LiSiO 4, LiSiO 4-LiI-LiOH, Li 2SiS 3, Li 4SiO 4, Li 4SiO 4-LiI-LiOH, Li 3PO 4-Li 2S-SiS 2, and the like.
The lithium salt is a material which is readily soluble in the non-aqueous electrolyte, and for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10Cl 10, LiPF 6, LiCF 3SO 3, LiCF 3CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, CH 3SO 3Li, CF 3SO 3Li, (CF 3SO 2)  2NLi, lithium chloroborate, lower aliphatic lithium carbonates, tetraphenyl lithium borate, imides, and the like.
The positive electrode 23, the negative electrode 22, and the separator 24 are wound or folded and accommodated in the battery case 25. Then, an organic electrolytic solution is injected into the battery case 25 and the cap assembly 26 is sealed to complete the rechargeable lithium battery 21 as shown in FIG. 2.
The battery case 25 may be cylindrical, prismatic, thin film, and the like. For example, the rechargeable lithium battery 20 may be a large-scale thin film-type battery. The rechargeable lithium battery may be a lithium ion battery. A cell structure including a separator between the positive electrode and the negative electrode may be formed. The cell structure is stacked in a bi-cell structure and then impregnated with an organic electrolyte solution, and the resulting product is received in a pouch and sealed to complete a lithium ion polymer battery. In addition, a plurality of cell structures may be stacked to form a battery pack, and such a battery pack may be used for all devices requiring a high capacity and a high power. For example, it may be used for a laptop, a smart phone, an electric vehicle, and the like.
In addition, the rechargeable lithium battery has improved storage stability, cycle-life characteristics, and high-rate characteristics at a high temperature and may be used in an electric vehicle (EV) . For example, it may be used in a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV) .
The rechargeable lithium battery according to an embodiment uses the positive  active material for a rechargeable lithium battery as a positive active material, and thus may exhibit excellent cycle-life characteristics and cell resistance characteristics.
In addition, a rechargeable lithium battery according to an embodiment may use for example a lithium nickel cobalt aluminum oxide as the lithium composite metal oxide, generation of NiO and oxygen by a reaction with moisture or carbon dioxide in in air or production of inert materials such as LiOH, LiCO 3, and the like may be minimized. Therefore, with respect to positive active materials having various compositions, a positive electrode having excellent electrochemical characteristics and stability and a rechargeable lithium battery including the same may be provided.
Hereinafter, the embodiments are illustrated in more detail with reference to examples. These examples, however, are not in any sense to be interpreted as limiting the scope of the invention. Furthermore, what is not described in this disclosure may be sufficiently understood by those who have knowledge in this field and will not be illustrated here.
(Preparation of Positive Active Material)
Example 1
Hydrophobic silica aerogel particles having an average particle diameter of 30 nm (aspecific surface area of 150 m 2/g to 200 m 2/g, Aladin) were prepared. The hydrophobic silica aerogel particles were put in an oven at 80 ℃ under -0.1 MPa and dried for about 5 hours under vacuum.
On the other hand, nickel cobalt aluminum metal composite hydroxide having Ni, Co, and Al in a mole ratio of 0.915: 0.075: 0.01 was mixed with lithium hydroxide (LiOH) to have a mole ratio of Li/ (Ni+Co+Al) = 1.03 to 1.05. The mixed material was put in a crucible and then, fired under an oxygen (O 2) atmosphere at 680 ℃ to 730 ℃, for example, at 710 ℃ for 10 hours to 20 hours to obtain a fired product of a NCA material. The NCA material had a composition of LiNi 0.915Co 0.075Al 0.01O 2.
Subsequently, the vacuum-dried hydrophobic silica aerogel particles and the NCA material were put in a glove box and weighed to obtain a mixture of the vacuum-dried hydrophobic silica aerogel particles and the NCA material in a weight ratio of 0.002: 1. The mixture was put in a ball mill at room temperature (25 ℃) under a dry atmosphere and then, mixed at a speed of 3000 rpm for about 2 hours to prepare a positive active material.
Example 2
A positive active material was prepared according to the same method as Example 1 except for using a mixture prepared by mixing the vacuum-dried hydrophobic silica aerogel particles and the NCA material in a weight ratio of 0.001: 1.
Example 3
A positive active material was prepared according to the same method as Example 1 except for using a mixture prepared by mixing the vacuum-dried hydrophobic silica aerogel particles and the NCA material in a weight ratio of 0.005: 1.
Example 4
A positive active material was prepared according to the same method as Example 1 except for using a mixture prepared by mixing the vacuum-dried hydrophobic silica aerogel particles and the NCA material in a weight ratio of 0.01: 1.
Comparative Example
LiNi 0.915Co 0.075Al 0.01O 2, the NCA material synthesized in Example 1, was used as a positive active material.
(Manufacture of Rechargeable Lithium Battery Cell)
Each positive active material according to Examples 1 to 4 and Comparative Example was mixed , polyvinylidene fluoride (PVDF) and denka black dissolved in N-methyl-2-pyrrolidone in a mass ratio of 92: 4: 4 and then, put in a centrifugal mixer (Thinky tm Corp. ) and dispersed at a speed of 2000 r/min for 15 minutes to respectively obtain slurry. The slurry was uniformly coated on an Al thin film and dried in a  vacuum-dry chamber at 110 ℃ for 10 hours to obtain a positive electrode plate substrate having a loading weight of 8 mg/cm 2 to 10 mg/cm 2. The positive electrode plate substrate was perforated with a punching machine to prepare a disk-shaped positive electrode plate substrate having a diameter of 10 mm, and the disk-shaped positive electrode plate substrate was compressed under a pressure of 4 MPa, dried at 110 ℃ for 10 hours, and rapidly moved into a glove box to obtain a positive electrode plate.
The positive electrode plate was used as a positive electrode, and metal lithium was used as a counter electrode of the positive electrode to manufacture a coin-type half-cell (CR2032 type) . Herein, an electrolyte solution was prepared by dissolving 1.15 M LiPF 6 in a mixed solvent of ethylene carbonate (EC) , ethylmethyl carbonate (EMC) , and dimethyl carbonate (DMC) (EC: EMC: DMC=a volume ratio of 1: 2: 2) , and polyethylene (PE) was used as a separator.
Evaluation 1: TEM Analysis of Positive Active Material
FIG. 3 shows a transmission election microscope (TEM) image of Example 1. Referring to FIG. 3, a surface layer was formed of an silica aerogel on the NCA material.
The positive active materials according to Examples 1 to 4 were all not shown in FIG. 1 but respectively included a surface layer including a hydrophobic silica aerogel covering the surface of the NCA material, as shown in FIG. 1.
Evaluation 2: X-ray Diffraction Analysis of Positive Active Material
FIG. 4 shows X-ray diffraction analysis results of the positive active materials according to Example 1 and Comparative Example.
Referring to FIG. 4, Example 1 further included a surface layer formed of a hydrophobic silica aerogel unlike Comparative Example but showed the same peak position and intensity as those of Comparative Example. Accordingly, the NCA material was coated with the hydrophobic silica aerogel according to Example but showed no structural change.
In addition, referring to FIGS. 3 and 4 together, Example 1 showed that a surface layer formed of a hydrophobic silica aerogel was formed on the surface of the NCA material without changing the structure of the NCA material.
Evaluation 3: Cycle-life Characteristics of Rechargeable Lithium Battery Cell
The rechargeable lithium battery cells according to Example 1 and Comparative Example were constant current-charged at a 1 C rate up to a voltage of 4.3 V and then, constant voltage-charged up to a current of 0.005 C (1/200 C) , while 4.3 V was maintained, at 60 ℃. Subsequently, the rechargeable lithium battery cells were discharged at a constant current of 1 C down to a voltage of 3.0 V as one cycle, which was 50 times repeated. Cycle-life characteristics of the rechargeable lithium battery cells were evaluated under the following condition, and the results are shown in FIG. 5. In FIG. 5, the cycle-life characteristics of the rechargeable lithium battery cell according to Example 1 were marked as a solid line, and the cycle-life characteristics of the rechargeable lithium battery cell according to Comparative Example was marked as a dotted line.
Referring to FIG. 5, Example 1 using the NCA material having a surface layer formed of a hydrophobic silica aerogel as a positive active material showed excellent cycle-life characteristics compared with Comparative Example.
Evaluation 4: Cell Resistance Characteristics of Rechargeable Lithium Battery Cell
Complex impedance of the rechargeable lithium battery cells according to Example 1 and Comparative Example was evaluated under a frequency of 0.1 Hz to 100 kHz at 60 ℃ by using electrical impedance spectroscopy (EIS) , and the results are shown in FIG. 6. In FIG. 6, an x axis denotes “a real number part (Z) , ” and a y axis denotes “an imaginary number part treated with a negative number (-Z') ” of the complex impedance.
Referring to FIG. 6, Example 1 using the NCA material having a surface layer formed of a hydrophobic silica aerogel as a positive active material showed improved cell resistance characteristics compared with Comparative Example. Accordingly, the surface  layer suppressed a side reaction of the NCA material and thus reduced interface resistance.
While this invention has been described in connection with what is presently considered to be practical example embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Description of Symbols
11: positive active material             12: lithium composite metal oxide
13: surface layer                        21: rechargeable lithium battery
22: negative electrode                   23: positive electrode
24: separator                            25: battery case
26: cap assembly

Claims (10)

  1. A positive active material for a rechargeable lithium battery, comprising
    a lithium composite metal oxide represented by Chemical Formula 1, and
    a surface layer on the surface of the lithium composite metal oxide and including aerogel:
    [Chemical Formula 1]
    Li a (Ni xM' yM" z) O 2
    wherein, in Chemical Formula 1, M'is at least one element selected from Co, Mn, Ni, Al, Mg, and Ti, M” is at least one element selected from Ca, Mg, Ba, Al, Ti, Sr, Fe, Co, Mn, Ni, Cu, Zn, Y, Zr, Nb, and B, 0.8 < a ≤ 1.3, 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, and x+y+z = 1.
  2. The positive active material of claim 1, wherein the surface layer has a thickness of 20 nm to 100 nm.
  3. The positive active material of claim 1, wherein the aerogel has a specific surface area of 100 m 2/g to 300 m 2/g.
  4. The positive active material of claim 1, wherein the aerogel is a hydrophobic aerogel.
  5. The positive active material of claim 1, wherein the aerogel comprises a hydrophobic aerogel particle, and
    the hydrophobic aerogel particle has an average particle diameter of 5 nm to 50 nm.
  6. The positive active material of claim 1, wherein the aerogel comprises a silica aerogel.
  7. A method of preparing a positive active material for a rechargeable lithium battery, comprising
    drying an aerogel particle,
    forming a surface layer including the dried aerogel particle on the surface of a lithium composite metal oxide.
  8. The method of claim 7, wherein the aerogel particle comprises a hydrophobic aerogel particle.
  9. A positive electrode comprising the positive active material for rechargeable lithium battery of any one of claim 1 to claim 6.
  10. A rechargeable lithium battery, comprising
    the positive electrode of claim 9;
    a negative electrode; and
    a separator between the positive electrode and the negative electrode.
PCT/CN2018/121740 2018-12-18 2018-12-18 Positive active material for rechargeable lithium battery, positive electrode and rechargeable lithium battery including the same WO2020124361A1 (en)

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US20220411558A1 (en) 2020-10-08 2022-12-29 Lg Chem, Ltd. Method of preparing vinyl cyanide compound-conjugated diene rubber-aromatic vinyl compound graft copolymer, method of preparing thermoplastic resin composition including the same, and thermoplastic resin composition including the same
CN112421037A (en) * 2020-11-04 2021-02-26 成都新柯力化工科技有限公司 Hydrophobic NCA positive electrode material of lithium battery and preparation method

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