WO2015149211A1 - A positive electrode active material and a li secondary battery - Google Patents

A positive electrode active material and a li secondary battery Download PDF

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Publication number
WO2015149211A1
WO2015149211A1 PCT/CN2014/074350 CN2014074350W WO2015149211A1 WO 2015149211 A1 WO2015149211 A1 WO 2015149211A1 CN 2014074350 W CN2014074350 W CN 2014074350W WO 2015149211 A1 WO2015149211 A1 WO 2015149211A1
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Prior art keywords
positive electrode
electrode active
active material
material according
metal
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PCT/CN2014/074350
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French (fr)
Inventor
Yuping Wu
Faxing WANG
Xiangwen GAO
Shiying XIAO
Akihiko Shirakawa
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Showa Denko K.K.
Fudan University
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Application filed by Showa Denko K.K., Fudan University filed Critical Showa Denko K.K.
Priority to PCT/CN2014/074350 priority Critical patent/WO2015149211A1/en
Publication of WO2015149211A1 publication Critical patent/WO2015149211A1/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
    • 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
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • 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

  • the present implementation relates to a positive electrode active material and a Li secondary battery.
  • Li secondary battery has been widely used in a portable mobile device such as a cell phone, a notebook computer and a digital electronic product and in an electric car. While mobile devices, electric cars and photovoltaic industry are developing, Li secondary battery presents more broad application prospect.
  • Electrochemical performance of a Li secondary battery largely depends on positive electrode active material.
  • the positive electrode active material generally is lithium cobalt oxide (LiCo0 2 ), spinel lithium manganate (LiMn 2 0 4 ), ternary material (Li(NiCoMn)0 2 ) and olivine-type lithium iron phosphate (LiFeP0 4 ).
  • Li 2 Mn0 3 is positive electrode active material of a new type of Li secondary battery, theoretical capacity is larger than 300 mAh g "1 , which is 100% higher than LiFeP0 4 , furthermore, Mn is abundant on earth.
  • a Li secondary battery with lithium metal oxide as positive electrode active material tend to release oxygen from lattice of lithium metal oxide during initial charge and it has very low initial coulombic efficiency, furthermore, discharge capacity of the Li secondary battery with lithium metal oxide after multiple charge-discharge cycles tends to be significantly reduced.
  • Li 2 Mn0 3 For example, some researchers focus on combining Li 2 Mn0 3 with other materials such as LiCo0 2 , LiCr0 2 , LiNio .5 Mn 1 .5O4, LiNii /3 Coi 3 Mni 3 0 2 or LiMn 2 0 4 . Although such solid solution has high discharge capacity, its initial coulombic efficiency is also very low, and oxygen is also released during initial charge.
  • the present invention features, in one aspect, overcoming defects of a Li secondary battery with Lithium metal oxide as positive electrode active material in oxygen release, low initial coulombic efficiency and significant decrease in discharge capacity after multiple charge-discharge cycles.
  • One aspect of the present invention is that a composite material of Lithium metal oxide and a material through which Li ions can be passed.
  • the material is selected from a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material, polymer or a combination thereof.
  • a positive electrode active material comprises a core portion and a coating layer on the core portion, wherein the core portion comprises a metal oxide compound and the coating layer comprises a material which can react with lithium and/or oxygen and prevent from releasing oxygen from the lattice of the metal oxide compound during charge-discharge cycles.
  • the present invention also provides the following preferable technical solutions.
  • the metal oxide compound has a general formula Li x M y O z and M is at least one selected from the group consisting of Co, Ni, Mn, Ti, V, Zr, Cr, Mg, Fe, Mo and Al.
  • the metal oxide compound has a general formula Li a M b O c (0 ⁇ a ⁇ l, 0 ⁇ b ⁇ l, 0 ⁇ c ⁇ l) and M is at least one selected from the group consisting of trivalent transition metal cation.
  • the metal oxide compound has a general formula Li 2-x M' x M"i -x 0 3-x (0 ⁇ x ⁇ l) and where M' is one or more ions having an average oxidation state of three, and where M" is one or more ions with an average oxidation state of four.
  • the metal oxide compound is Li 2 Mn0 3 .
  • the coating layer comprises at least one selected from the group consisting of a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material and a polymer.
  • the metal oxide is at least one selected from the group consisting of Co 3 0 4 , CoO, NiO, Ru0 2 , Mo0 3 , Mn0 2 V 2 0 3 and Pb0 2 .
  • the metal hydroxide is at least one selected from the group consisting of Ni(OH) 2 and Co(OH) 2 .
  • the metal oxyhydroxide is at least one selected from the group consisting of NiOOH and FeOOH.
  • the metal fluoride is at least one selected from the group consisting of FeF 3 , FeF 2 and CuF 2 .
  • the metal phosphate is at least one selected from the group consisting of FeP0 and A1P0 4 .
  • the lithium insertion material is at least one selected from the group consisting of LiCo0 2 , LiNi0 2 , Li 0 . 44 MnO 2 , LiMn 2 0 , LiNi 0 . 5 Mni. 5 O 4 , LiMnB0 3 , LiMnP0 4 and Li 2 MnSi0 4 .
  • the polymer is a conductive polymer.
  • the polymer is a ⁇ -electron conjugated polymer.
  • the ⁇ -electron conjugated polymer is at least one selected from the group consisting of polyacetylene, polypyrrole, polyaniline, polyparaphenylenevinylene and polythiophene.
  • the coating layer accounts for 0.5 mass % ⁇ 50 mass% of the total mass of the positive electrode active material. More preferably, the coating layer accounts for 1 mass% ⁇ 40 mass% of the total mass of the positive electrode active material.
  • Another aspect of the invention provides a Li secondary battery comprising the positive electrode active material.
  • the Li secondary battery of the present implementation by using the positive electrode active material, may prevent 0 2 from releasing during initial charge, and improve initial coulombic efficiency and discharge capacity after multiple charge-discharge cycles.
  • Fig 1(a) and Fig 1(b) are examples of ex-situ X-Ray Diffraction (ex-situ XRD) spectrum and X-Ray photoelectron Spectroscopy (XPS) energy spectrum of a Li secondary battery with FeP0 4 /Li 2 Mn0 3 as positive electrode active material, respectively.
  • Fig 2 is an example of a charge-discharge graph of a Li secondary battery with Li 2 Mn0 3 as positive electrode active material of comparative example 1.
  • Fig 3 is an example of a charge-discharge graph of a Li secondary battery with FeP0 4 /Li 2 Mn0 3 as positive electrode active material of embodiment 3.
  • Fig 4 is an example of a charge-discharge graph of a Li secondary battery with Co 3 0 4 /Li 2 Mn0 3 as positive electrode active material of embodiment 1 1.
  • the Li secondary battery referred to herein may be any Li secondary battery that is capable of utilizing the following positive electrode active material.
  • the positive electrode active material comprises a core portion comprised of Lithium metal oxide and a coating layer which coats the core portion, which can make Li ions pass through, and the coating layer comprises a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material, a polymer or a combination thereof.
  • the positive electrode active material comprises a core portion and a coating layer on the core portion, wherein the core portion comprises a metal oxide compound and the coating layer comprises a material which can react with lithium and/or oxygen and prevent from releasing oxygen from the lattice of the metal oxide compound during charge-discharge cycles.
  • the metal oxide compound can comprise at least one transition metal.
  • the transition metal can be oxidized and reduced during occluding and emitting lithium ions.
  • the metal oxide compound may be prepared by any method known to those skilled in the art without any limitation.
  • the metal oxide compound has a general formula Li x M y O z and M is at least one selected from the group consisting of Co, Ni, Mn, Ti, V, Zr, Cr, Mg, Fe, Mo and Al.
  • the metal oxide compound has a general formula Li a M b O c (0 ⁇ a ⁇ l, 0 ⁇ b ⁇ l, 0 ⁇ c ⁇ l) and M is at least one selected from the group consisting of trivalent transition metal cation.
  • the metal oxide compound has a general formula Li 2-x M' x M" 1-x 0 3-x (0 ⁇ x ⁇ l) and where M' is one or more ions having an average oxidation state of three, and where M" is one or more ions with an average oxidation state of four.
  • the metal oxide compound is Li 2 Mn0 3 .
  • the coating layer may be formed on the surface of the core portion by any method known to those skilled in the art without any limitation.
  • the coating layer can be formed by at least one method selected from the group consisting of precipitation method, solid phase method, impregnation method, hydro-thermal method, hydrolysis method and sol-gel method.
  • the coating layer can make Li ions pass through, that is, Li ions can go through the coating layer from the core portion and enter into electrolyte, or can go through the coating layer from electrolyte and arrive at the core portion, thereby realizing charge/discharge.
  • the coating layer is formed by piling up granular substances. In this case, Li-ions can go through the coating layer via gaps between the granular substances.
  • the coating layer comprises a material which can react with Li 2 0 and prevent from releasing oxygen in the lattice of the lithium metal oxide during charge-discharge cycles.
  • the coating layer comprises at least one selected from the group consisting of a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material and a polymer.
  • Metal of the metal oxide can be a transition metal or a typical element.
  • the metal oxide is at least one selected from the group consisting of Co 3 0 4 , CoO, NiO, Ru0 2 , Mo0 3 , Mn0 2 V 2 0 3 and Pb0 2 .
  • the metal hydroxide is at least one selected from the group consisting of Ni(OH) 2 and Co(OH) 2 .
  • the metal oxyhydroxide is at least one selected from the group consisting of NiOOH and FeOOH.
  • the metal fluoride is at least one selected from the group consisting of FeF 3 , FeF 2 and CuF 2 .
  • the metal phosphate is at least one selected from the group consisting ofFeP0 4 and A1P0 4 .
  • Lithium insertion material can be a material which can occlude and include lithium ion.
  • the lithium insertion material is at least one selected from the group consisting of LiCo0 2 , LiNi0 2 , Li 044 MnO 2 , LiMn 2 0 4 , LiNi 0 5 Mn 1 . 5 O 4 , LiMnB0 3 , LiMnP0 4 and Li 2 MnSi0 4 .
  • the polymer is a conductive polymer.
  • the polymer is a ⁇ -electron conjugated polymer.
  • the ⁇ -electron conjugated polymer is at least one selected from the group consisting of polyacetylene, polypyrrole, polyaniline, polyparaphenylenevinylene and polythiophene.
  • Content of the coating layer preferably accounts for 0.5 mass% ⁇ 50 mass% of total mass of the positive electrode active material. If content of the coating layer is higher than 0.5 mass%, it can have more influence on Lithium metal oxide, and effect of improvement is more significant. If content of the coating layer is less than 50 mass%, it will increase content of the core portion material (i.e., Li 2 Mn0 3 ), thereby more increasing discharge capacity of the battery.
  • the coating layer accounts for 1 mass% ⁇ -40 mass% of total mass of the positive electrode active material.
  • a coating layer of FeP0 4 most preferable content of which is 20 mass% ⁇ 30 mass%.
  • a coating layer of Co 3 0 4 most preferable content of which is 15 mass% ⁇ -30 mass%.
  • the positive electrode active material is Li 2 Mn0 3 coated by a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material, a polymer or a combination thereof.
  • the coating layer may prevent oxygen from releasing during initial charge, and can improve initial coulombic efficiency and discharge capacity after multiple charge-discharge cycles.
  • the positive electrode active material of the present implementation does not release 0 2 during initial charge. Meanwhile, as compared to the prior arts, Li 2 Mn0 3 without a coating layer, the positive electrode active material of the present implementation also has a charge/discharge process as shown in equation (5), thus, it can improve initial coulombic efficiency and discharge capacity after multiple charge-discharge cycles. This would be one example of the mechanisms in the present invention.
  • Charge/discharge reaction of positive electrode active material FeP0 4 /Li 2 Mn0 3 of the present implementation can be conducted as shown in the above equations (3)-(5). This mechanism can be proved by the ex-situ XRD and XPS spectra shown in Fig 1(a) and 1(b). Electrodes under test were taken out of the Li-ion batteries and rinsed with anhydrous DMC (Dimethyl carbonate), then washed by acetone and dried overnight.
  • DMC Dimethyl carbonate
  • the five spectra of Fig 1(a) from bottom to top represent ex-situ XRD spectra before charge cycle, 1 st charge to 4.8V, 1 st discharge to 2.0V, 2 nd discharge to 2.0V, 2 nd charge to 4.8V of positive electrode active material FeP0 4 /Li 2 Mn0 3 , respectively.
  • '*' represent peaks of FeP0 4
  • '#' represent peaks of Li y FeP0 4+x in Fig 1(a).
  • the five spectra of Fig 1(b) from bottom to top represent XRS spectra before charge cycle, 1 st charge to 4.8V, 1 st discharge to 2.0V, 2 nd charge to 4.8V, 2 nd discharge to 2.0V of positive electrode active material FeP0 4 /Li 2 Mn0 3 , respectively.
  • Potential difference may be 2.7-3.2 V, which may be equal to the potential difference when Li ions were extracted/inserted from/into Li y FePO x+4 and FeP0 4 t. Change in chemical valence of Fe caused by insertion/extraction of Li ions from/into Li y FePO x+ 4 was also confirmed by the XPS spectra shown in Fig 1(b).
  • the FeP0 4 in the positive electrode active material FeP0 4 /Li 2 Mn0 3 serves as a host to react with oxygen and "dead" Li ions, resulting to the existence of Li y FeP0 4+x being observed in the XRD spectra.
  • the Li ions were inserted/extracted into/from the Li y FeP0 4+x and active Mn0 2 .
  • discharge capacity of the positive electrode active material FeP0 4 /Li 2 Mn0 3 may be higher than its charge capacity.
  • equation (3) and equation (5) may be considered as the synergistic effect between Li 2 Mn0 3 and FeP0 4 .
  • Such synergistic effect successfully blocks the oxygen emission and improves capacity of the Li secondary battery.
  • Li 2 Mn0 3 prepared via solid phase method is used as a reference.
  • Li 2 Mn0 3 , acetylene black and polyvinylidene fluoride (PVDF) are accurately weighted in mass fraction of 80%: 10%: 10% and are uniformly mixed with l-Methyl-2-pyrrolidinone as solvent to form slurry.
  • the slurry is uniformly applied on an aluminum foil to form electrode plate.
  • the electrode plate is dried in vacuum below 120 ° C for more than 12 hours and is punched out by a puncher to prepare disk electrodes having diameter of 19 mm.
  • the metal lithium foil is taken as negative electrode.
  • the operating electrode is positive electrode.
  • Celgard (trademark) 2400 polypropylene micro-porous membrane, is used as membrane, lmol L "1 LiPF 6 /ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC) (in volume ratio 1 : 1 :1) is used as electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • Those are assembled into button cells in a glove box filled with high-purity argon. The button cells are used for testing electrochemical performance.
  • Initial charge/discharge curve and cycling performance are shown in Fig 2.
  • Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Embodiment 1 Embodiment 1
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example 1. 3 mass% of FeP0 4 to total mass of the positive electrode active material is coated on surface of Li 2 Mn0 3 via both precipitation method and solid phase method. Content of FeP0 4 is calculated by the concentration of ferric nitrate (Fe(N0 3 ) 3 -9H 2 0) and the concentration of diammonium hydrogen phosphate (( H 4 ) 2 HP0 4 ).
  • Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example 1. 8 mass% of FeP0 4 is coated on surface of Li 2 Mn0 3 via both precipitation method and solid phase method. Content of FeP0 4 is calculated by the concentration of ferric nitrate (Fe(N0 3 ) 3 -9H 2 0) and the concentration of diammonium hydrogen phosphate ((NH 4 ) 2 HP0 4 ).
  • Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example 1. 20 mass% of FeP0 4 is coated on surface of Li 2 Mn0 3 via both precipitation method and solid phase method. Content of FeP0 4 is calculated by the concentration of ferric nitrate (Fe(N0 3 ) 3 -9H 2 0) and the concentration of diammonium hydrogen phosphate ((NH 4 ) 2 HP0 4 ).
  • Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge curve and cycling performance are shown in Fig 3, and initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example. 5 mass% of Mn0 2 is coated on surface of Li 2 Mn0 3 via simple both impregnation method and solid phase method. Content of Mn0 2 is calculated by the concentration of manganese nitrate solution.
  • Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1. Embodiment 5
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example. 20 mass% of Mn0 2 is coated on surface of Li 2 Mn0 3 via both simple impregnation method and solid phase method. Content of Mn0 2 is calculated by the concentration of manganese nitrate solution.
  • Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example. 40 mass% of Mn0 2 is coated on surface of Li 2 Mn0 3 via both simple impregnation method and solid phase method. Content of Mn0 2 is calculated by the concentration of manganese nitrate solution.
  • Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Li 2 Mn0 3 Preparation of Li 2 Mn0 3 is the same as that of comparative example. 18 mass% of Mo0 3 is coated on surface of Li 2 Mn0 3 by conducting hydro-thermal treatment on peroxo molybdic acid sol (Mo0 2 (OH)(OOH)). Content of Mo0 3 is calculated by the concentration of peroxo molybdic acid sol prepared via simple substance metal molybdenum (Mo) having certain mass.
  • Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example. 20 mass% of Pb0 2 is coated on surface of Li 2 Mn0 3 via precipitation method. Content of Pb0 2 is realized by controlling a solution of lead nitrate (Pb(N0 3 ) 2 ) with certain concentration and a solution of sodium hydroxide (NaOH) with corresponding concentration under cetyltrimethyl ammonium bromide (CTAB) environment.
  • Pb(N0 3 ) 2 a solution of lead nitrate
  • NaOH sodium hydroxide
  • CTAB cetyltrimethyl ammonium bromide
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Embodiment 9 Preparation of Li 2 Mn0 3 is the same as that of comparative example. 8 mass% of Co 3 0 4 is coated on surface of Li 2 Mn0 3 via hydro-thermal method and solid phase method. Content of Co 3 0 4 is realized by controlling a solution of cobalt acetate (Co(CH 3 COO) 2 -4H 2 0) with certain concentration and aqueous ammonia ( ⁇ 3 ⁇ 2 0) with corresponding concentration.
  • Co(CH 3 COO) 2 -4H 2 0 cobalt acetate
  • ⁇ 3 ⁇ 2 0 aqueous ammonia
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example. 15 mass% of Co 3 0 4 is coated on surface of Li 2 Mn0 3 via hydro-thermal method and solid phase method. Content of Co 3 0 is realized by controlling a solution of cobalt acetate (Co(CH 3 COO) 2 -4H 2 0) with certain concentration and aqueous ammonia ( ⁇ 3 ⁇ 2 0) with corresponding concentration.
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example. Its initial charge/discharge curve and cycling performance are shown in Fig 4, and initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Embodiment 1 1 is a diagrammatic representation of Embodiment 1 1
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example. 20 mass% of Ru0 2 is coated on surface of Li 2 Mn0 3 via precipitation method and solid phase method. Content of Ru0 2 is realized by controlling a solution of ruthenium chloride (RuCl 3 ) with certain concentration and NaOH with corresponding concentration.
  • RuCl 3 ruthenium chloride
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example. 20 mass% of Ni(OH) 2 is coated on surface of Li 2 Mn0 3 via precipitation method. Content of Ni(OH) 2 is realized by controlling a solution of nickel dichloride (NiCl 2 -H 2 0) with certain concentration and aqueous ammonia ( ⁇ 3 ⁇ 2 0) with corresponding concentration.
  • NiCl 2 -H 2 0 nickel dichloride
  • ⁇ 3 ⁇ 2 0 aqueous ammonia
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1. Embodiment 13
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example. 18 mass% of FeF 3 is coated on surface of Li 2 Mn0 3 via precipitation method and drying method. Content of FeF 3 is realized by controlling a solution of ferric nitrate (Fe(N0 3 ) 3 -9H 2 0) with certain concentration and a solution of ammonium fluoride (NH 4 F) with corresponding concentration under cetyltrimethyl ammonium bromide (CTAB) environment.
  • a solution of ferric nitrate Fe(N0 3 ) 3 -9H 2 0
  • NH 4 F ammonium fluoride
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Li 2 Mn0 3 is the same as that of comparative example. 1 mass% of LiCo0 2 is coated on surface of Li 2 Mn0 3 via sol-gel method. Content of LiCo0 2 is realized by controlling a solution of lithium acetate (LiCH 3 C0O2H 2 0) with certain concentration, a solution of cobalt acetate (Co(CH 3 COO) 2 -4H 2 0) and a solution of citric acid (C H 8 0 7 ) under ethylene glycol environment.
  • LiCH 3 C0O2H 2 0 LiCH 3 C0O2H 2 0
  • Co(CH 3 COO) 2 -4H 2 0 a solution of cobalt acetate
  • citric acid C H 8 0 7
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Li 2 Mn0 3 is the same as that of comparative example. 5 mass% of LiCo0 2 is coated on surface of Li 2 Mn0 3 via sol-gel method. Content of LiCo0 2 is realized by controlling a solution of lithium acetate (LiCH 3 C0O2H 2 0) with certain concentration, a solution of cobalt acetate (Co(CH 3 COO) 2 -4H 2 0) and a solution of citric acid (C 6 H 8 0 7 ) under ethylene glycol environment.
  • LiCH 3 C0O2H 2 0 LiCH 3 C0O2H 2 0
  • Co(CH 3 COO) 2 -4H 2 0 a solution of cobalt acetate
  • citric acid C 6 H 8 0 7
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Li 2 Mn0 3 is the same as that of comparative example. 20 mass% of LiCo0 2 is coated on surface of Li 2 Mn0 3 via sol-gel method. Content of LiCo0 2 is realized by controlling a solution of lithium acetate (LiCH 3 C0O2H 2 0) with certain concentration, a solution of cobalt acetate (Co(CH 3 COO) 2 -4H 2 0) and a solution of citric acid (C 6 H 8 0 7 ) under ethylene glycol environment. Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Li 2 Mn0 3 is the same as that of comparative example. 20 mass% of LiMn 2 0 4 is coated on surface of Li 2 Mn0 3 via hydro-thermal method and solid phase method. Content of LiMn 2 0 4 is realized by controlling a solution of manganese nitrate (Mn(N0 3 ) 2 ) with certain concentration and lithium hydroxide (LiOH H 2 0) with different masses.
  • Mn(N0 3 ) 2 manganese nitrate
  • LiOH H 2 0 lithium hydroxide
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example. 30 mass% of PPy is coated on surface of Li 2 Mn0 3 via low temperature oxidation polymerization method. Content of PPy is realized by controlling pyrrole (Py) monomer with certain mass and a solution of ferric chloride (FeCl 3 -6H 2 0) with corresponding concentration under environment of excessive sodium dodecyl benzene sulfonate solution.
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
  • Preparation of Li 2 Mn0 3 is the same as that of comparative example. 30 mass% of FeOOH is coated on surface of Li 2 Mn0 3 via hydrolysis method. Content of FeOOH is realized by controlling a solution of ferric chloride (FeCl 3 -6H 2 0) with certain concentration.
  • Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1. Table 1
  • FeP0 4, Co 3 0 4 and Ni(OH) 2 are preferable coating materials because FeP0 4 /Li 2 Mn0 3j Co 3 0 4 /Li 2 Mn0 3 and Ni(OH) 2 /Li 2 Mn0 3 provide more than 90% of retention rate after 30% cycles.
  • FeF 3 and M0O3 are also preferable coating materials because FeF 3 /Li 2 Mn0 3 and Mo0 3 /Li 2 Mn0 3 provide relatively high discharge capacities.
  • Li secondary battery comprising the positive electrode active material of the above implementation.
  • Other components of the Li secondary battery involved in the present implementation may be any component required by a Li secondary battery that are known by those skilled in the art, and the description of which will be omitted here for brevity.
  • the Li secondary battery of the present implementation by using the above positive electrode active material, may prevent 0 2 from releasing during initial charge, and significantly improve initial coulombic efficiency and discharge capacity after multiple charge-discharge cycles.

Abstract

A positive electrode active material and a Li secondary battery are provided. The positive electrode active material according to an implementation comprises a core portion and a coating layer on the core portion, wherein the core portion comprises a metal oxide compound, and the coating layer comprises a material which can react with lithium and/or oxygen and prevent from releasing oxygen from the lattice of the metal oxide compound during charge-discharge cycles.

Description

A POSITIVE ELECTRODE ACTIVE MATERIAL AND A LI SECONDARY
BATTERY
TECHNICAL FIELD
The present implementation relates to a positive electrode active material and a Li secondary battery.
BACKGROUND
Li secondary battery has been widely used in a portable mobile device such as a cell phone, a notebook computer and a digital electronic product and in an electric car. While mobile devices, electric cars and photovoltaic industry are developing, Li secondary battery presents more broad application prospect.
Electrochemical performance of a Li secondary battery largely depends on positive electrode active material. In current commercially available Li secondary battery, the positive electrode active material generally is lithium cobalt oxide (LiCo02), spinel lithium manganate (LiMn204), ternary material (Li(NiCoMn)02) and olivine-type lithium iron phosphate (LiFeP04).
Li2Mn03 is positive electrode active material of a new type of Li secondary battery, theoretical capacity is larger than 300 mAh g"1, which is 100% higher than LiFeP04, furthermore, Mn is abundant on earth.
SUMMARY
A Li secondary battery with lithium metal oxide as positive electrode active material tend to release oxygen from lattice of lithium metal oxide during initial charge and it has very low initial coulombic efficiency, furthermore, discharge capacity of the Li secondary battery with lithium metal oxide after multiple charge-discharge cycles tends to be significantly reduced.
In order to solve those problems, some researches focus on solid solution.
For example, some researchers focus on combining Li2Mn03 with other materials such as LiCo02, LiCr02, LiNio.5Mn1.5O4, LiNii/3Coi 3Mni 302 or LiMn204. Although such solid solution has high discharge capacity, its initial coulombic efficiency is also very low, and oxygen is also released during initial charge.
The present invention features, in one aspect, overcoming defects of a Li secondary battery with Lithium metal oxide as positive electrode active material in oxygen release, low initial coulombic efficiency and significant decrease in discharge capacity after multiple charge-discharge cycles. One aspect of the present invention is that a composite material of Lithium metal oxide and a material through which Li ions can be passed. For example, the material is selected from a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material, polymer or a combination thereof.
Another aspect of the present invention is that a positive electrode active material comprises a core portion and a coating layer on the core portion, wherein the core portion comprises a metal oxide compound and the coating layer comprises a material which can react with lithium and/or oxygen and prevent from releasing oxygen from the lattice of the metal oxide compound during charge-discharge cycles.
The present invention also provides the following preferable technical solutions.
Preferably, the metal oxide compound has a general formula LixMyOz and M is at least one selected from the group consisting of Co, Ni, Mn, Ti, V, Zr, Cr, Mg, Fe, Mo and Al.
Preferably, the metal oxide compound has a general formula LiaMbOc (0<a<l, 0<b<l, 0<c<l) and M is at least one selected from the group consisting of trivalent transition metal cation.
Preferably, the metal oxide compound has a general formula Li2-xM'xM"i-x03-x (0<x<l) and where M' is one or more ions having an average oxidation state of three, and where M" is one or more ions with an average oxidation state of four.
Preferably, the metal oxide compound is Li2Mn03.
Preferably, the coating layer comprises at least one selected from the group consisting of a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material and a polymer.
Preferably, the metal oxide is at least one selected from the group consisting of Co304, CoO, NiO, Ru02, Mo03, Mn02 V203 and Pb02.
Preferably, the metal hydroxide is at least one selected from the group consisting of Ni(OH)2 and Co(OH)2.
Preferably, the metal oxyhydroxide is at least one selected from the group consisting of NiOOH and FeOOH.
Preferably, the metal fluoride is at least one selected from the group consisting of FeF3, FeF2 and CuF2.
Preferably, the metal phosphate is at least one selected from the group consisting of FeP0 and A1P04.
Preferably, the lithium insertion material is at least one selected from the group consisting of LiCo02, LiNi02, Li0.44MnO2, LiMn20 , LiNi0.5Mni.5O4, LiMnB03, LiMnP04 and Li2MnSi04.
Preferably, the polymer is a conductive polymer.
Preferably, the polymer is a π -electron conjugated polymer.
Preferably, the π-electron conjugated polymer is at least one selected from the group consisting of polyacetylene, polypyrrole, polyaniline, polyparaphenylenevinylene and polythiophene.
Preferably, the coating layer accounts for 0.5 mass %~50 mass% of the total mass of the positive electrode active material. More preferably, the coating layer accounts for 1 mass%~40 mass% of the total mass of the positive electrode active material. Another aspect of the invention provides a Li secondary battery comprising the positive electrode active material.
The Li secondary battery of the present implementation, by using the positive electrode active material, may prevent 02 from releasing during initial charge, and improve initial coulombic efficiency and discharge capacity after multiple charge-discharge cycles.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Fig 1(a) and Fig 1(b) are examples of ex-situ X-Ray Diffraction (ex-situ XRD) spectrum and X-Ray photoelectron Spectroscopy (XPS) energy spectrum of a Li secondary battery with FeP04/Li2Mn03 as positive electrode active material, respectively.
Fig 2 is an example of a charge-discharge graph of a Li secondary battery with Li2Mn03 as positive electrode active material of comparative example 1.
Fig 3 is an example of a charge-discharge graph of a Li secondary battery with FeP04/Li2Mn03 as positive electrode active material of embodiment 3.
Fig 4 is an example of a charge-discharge graph of a Li secondary battery with Co304/Li2Mn03 as positive electrode active material of embodiment 1 1.
DETAILED DESCRIPTION
Implementations of the present invention will be described below in detail in conjunction with accompany drawings.
One implementation of the present invention provides a positive electrode active material of Li secondary battery. The Li secondary battery referred to herein may be any Li secondary battery that is capable of utilizing the following positive electrode active material.
In one aspect of the present invention, the positive electrode active material comprises a core portion comprised of Lithium metal oxide and a coating layer which coats the core portion, which can make Li ions pass through, and the coating layer comprises a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material, a polymer or a combination thereof.
In another aspect of the present invention, the positive electrode active material comprises a core portion and a coating layer on the core portion, wherein the core portion comprises a metal oxide compound and the coating layer comprises a material which can react with lithium and/or oxygen and prevent from releasing oxygen from the lattice of the metal oxide compound during charge-discharge cycles.
The metal oxide compound can comprise at least one transition metal. The transition metal can be oxidized and reduced during occluding and emitting lithium ions.
The metal oxide compound may be prepared by any method known to those skilled in the art without any limitation. Preferably, the metal oxide compound has a general formula LixMyOz and M is at least one selected from the group consisting of Co, Ni, Mn, Ti, V, Zr, Cr, Mg, Fe, Mo and Al.
Preferably, the metal oxide compound has a general formula LiaMbOc (0<a<l, 0<b<l, 0<c<l) and M is at least one selected from the group consisting of trivalent transition metal cation.
Preferably, the metal oxide compound has a general formula Li2-xM'xM"1-x03-x (0<x<l) and where M' is one or more ions having an average oxidation state of three, and where M" is one or more ions with an average oxidation state of four.
Preferably, the metal oxide compound is Li2Mn03.
The coating layer may be formed on the surface of the core portion by any method known to those skilled in the art without any limitation. For example, the coating layer can be formed by at least one method selected from the group consisting of precipitation method, solid phase method, impregnation method, hydro-thermal method, hydrolysis method and sol-gel method.
The coating layer can make Li ions pass through, that is, Li ions can go through the coating layer from the core portion and enter into electrolyte, or can go through the coating layer from electrolyte and arrive at the core portion, thereby realizing charge/discharge. Preferably, the coating layer is formed by piling up granular substances. In this case, Li-ions can go through the coating layer via gaps between the granular substances.
The coating layer comprises a material which can react with Li20 and prevent from releasing oxygen in the lattice of the lithium metal oxide during charge-discharge cycles.
Preferably, the coating layer comprises at least one selected from the group consisting of a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material and a polymer.
Metal of the metal oxide can be a transition metal or a typical element. Preferably, the metal oxide is at least one selected from the group consisting of Co304, CoO, NiO, Ru02, Mo03, Mn02 V203 and Pb02.
Preferably, the metal hydroxide is at least one selected from the group consisting of Ni(OH)2 and Co(OH)2.
Preferably, the metal oxyhydroxide is at least one selected from the group consisting of NiOOH and FeOOH.
Preferably, the metal fluoride is at least one selected from the group consisting of FeF3, FeF2 and CuF2.
Preferably, the metal phosphate is at least one selected from the group consisting ofFeP04 and A1P04.
Lithium insertion material can be a material which can occlude and include lithium ion. Preferably, the lithium insertion material is at least one selected from the group consisting of LiCo02, LiNi02, Li044MnO2, LiMn204, LiNi0 5Mn1.5O4, LiMnB03, LiMnP04 and Li2MnSi04. Preferably, the polymer is a conductive polymer.
Preferably, the polymer is a π -electron conjugated polymer.
Preferably, the π-electron conjugated polymer is at least one selected from the group consisting of polyacetylene, polypyrrole, polyaniline, polyparaphenylenevinylene and polythiophene.
Content of the coating layer preferably accounts for 0.5 mass%~50 mass% of total mass of the positive electrode active material. If content of the coating layer is higher than 0.5 mass%, it can have more influence on Lithium metal oxide, and effect of improvement is more significant. If content of the coating layer is less than 50 mass%, it will increase content of the core portion material (i.e., Li2Mn03), thereby more increasing discharge capacity of the battery.
More preferably, the coating layer accounts for 1 mass%~-40 mass% of total mass of the positive electrode active material. For a coating layer of FeP04, most preferable content of which is 20 mass%~30 mass%. For a coating layer of Co304, most preferable content of which is 15 mass%~-30 mass%.
In one embodiment, the positive electrode active material is Li2Mn03 coated by a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material, a polymer or a combination thereof. The coating layer may prevent oxygen from releasing during initial charge, and can improve initial coulombic efficiency and discharge capacity after multiple charge-discharge cycles.
The example of the mechanism in the present invention is described as follows.
Charge/discharge reaction of Li2Mn03 without a coating layer is conducted as the following equations (1) and (2): oh ir 26
Li2Mn03 ► Li2Mn03-xMn02(active) + 2xLi++x/202+2xe~
Discharge
Mn02 (active)+wLi++we" ^ *~ LimMn02
Charge
(2)
As shown in equation (1), 02 is released during initial charge.
Charge/discharge reaction of Li2Mn03 with coating layer of FeP04 is conducted as the following equations (3) and (5):
Li2Mn03+FeP04
Figure imgf000007_0001
+ UyFeP04+x+(2x-y)U++(2x-y)e Discharge
Mn02 (activej+wL +zwe" ^ LimMn02
Charge
Discharge
LiyFeP04+x+«Li++we" ^ Liy+nFeP04+x
Charge
(5)
As shown in equation (3), the positive electrode active material of the present implementation does not release 02 during initial charge. Meanwhile, as compared to the prior arts, Li2Mn03 without a coating layer, the positive electrode active material of the present implementation also has a charge/discharge process as shown in equation (5), thus, it can improve initial coulombic efficiency and discharge capacity after multiple charge-discharge cycles. This would be one example of the mechanisms in the present invention.
Similarly, charge/discharge reaction of Li2Mn03 with coating layer of Co304 is conducted as the following equations (6).
Co304+xLi?0 < > LivCo3Ox÷4+(2x-y)Lr+(2x-y)e-
Charge " ( 6 )
Charge/discharge reaction of positive electrode active material FeP04/Li2Mn03 of the present implementation can be conducted as shown in the above equations (3)-(5). This mechanism can be proved by the ex-situ XRD and XPS spectra shown in Fig 1(a) and 1(b). Electrodes under test were taken out of the Li-ion batteries and rinsed with anhydrous DMC (Dimethyl carbonate), then washed by acetone and dried overnight.
The five spectra of Fig 1(a) from bottom to top represent ex-situ XRD spectra before charge cycle, 1st charge to 4.8V, 1st discharge to 2.0V, 2nd discharge to 2.0V, 2nd charge to 4.8V of positive electrode active material FeP04/Li2Mn03, respectively. '*' represent peaks of FeP04 and '#' represent peaks of LiyFeP04+x in Fig 1(a).
The five spectra of Fig 1(b) from bottom to top represent XRS spectra before charge cycle, 1st charge to 4.8V, 1st discharge to 2.0V, 2nd charge to 4.8V, 2nd discharge to 2.0V of positive electrode active material FeP04/Li2Mn03, respectively.
It can be seen from Fig 1 (a) that, after the first charge, the peak of XRD at 18.7° is shifted to a larger angle (right side), this shift may indicate a decrease in lattice spacing between the layers caused by Li extraction. During discharging, major peaks of XRD shift to smaller angles (left side), and this shift may indicate an increase in lattice constants caused by Li insertion. Some new peaks (represented by '#') are found after the first charge. These new peaks are similar to XRD peaks of LiyFeP04+x (y=0.45 and 0.75). Potential difference may be 2.7-3.2 V, which may be equal to the potential difference when Li ions were extracted/inserted from/into LiyFePOx+4 and FeP04 t. Change in chemical valence of Fe caused by insertion/extraction of Li ions from/into LiyFePOx+4 was also confirmed by the XPS spectra shown in Fig 1(b).
These data indicate that, the charge/discharge mechanism of the positive electrode active material FeP04/Li2Mn03 follows the above equations (3)-(5).
After the first charge, the FeP04 in the positive electrode active material FeP04/Li2Mn03 serves as a host to react with oxygen and "dead" Li ions, resulting to the existence of LiyFeP04+x being observed in the XRD spectra. During subsequent discharge-charge process, the Li ions were inserted/extracted into/from the LiyFeP04+x and active Mn02.
During the first discharge, because some "dead" Li ions and Li ions from the electrolyte were inserted into the LiyFeP04+x, discharge capacity of the positive electrode active material FeP04/Li2Mn03 may be higher than its charge capacity.
Thus, it can be seen that, equation (3) and equation (5) may be considered as the synergistic effect between Li2Mn03 and FeP04. Such synergistic effect successfully blocks the oxygen emission and improves capacity of the Li secondary battery.
To understand and explain the present implementation more clearly, some specific embodiments will be listed below and compared with comparative examples. It is appreciated that, however, invention of the present application is not limited to the specific embodiments listed below. We focus on Li2Mn03 as a core material, but the core material is not limited to Li2Mn03 . The present invention can prevent from releasing oxygen of lithium metal oxides in the same manner.
Comparative example 1
Li2Mn03 prepared via solid phase method is used as a reference.
(Electrochemical performance test of Li secondary battery)
Li2Mn03, acetylene black and polyvinylidene fluoride (PVDF) are accurately weighted in mass fraction of 80%: 10%: 10% and are uniformly mixed with l-Methyl-2-pyrrolidinone as solvent to form slurry. The slurry is uniformly applied on an aluminum foil to form electrode plate. The electrode plate is dried in vacuum below 120°C for more than 12 hours and is punched out by a puncher to prepare disk electrodes having diameter of 19 mm. The metal lithium foil is taken as negative electrode. The operating electrode is positive electrode. Celgard (trademark) 2400, polypropylene micro-porous membrane, is used as membrane, lmol L"1 LiPF6/ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC) (in volume ratio 1 : 1 :1) is used as electrolyte. Those are assembled into button cells in a glove box filled with high-purity argon. The button cells are used for testing electrochemical performance. Initial charge/discharge curve and cycling performance are shown in Fig 2. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1. Embodiment 1
Preparation of Li2Mn03 is the same as that of comparative example 1. 3 mass% of FeP04 to total mass of the positive electrode active material is coated on surface of Li2Mn03 via both precipitation method and solid phase method. Content of FeP04 is calculated by the concentration of ferric nitrate (Fe(N03)3-9H20) and the concentration of diammonium hydrogen phosphate (( H4)2HP04).
Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 2
Preparation of Li2Mn03 is the same as that of comparative example 1. 8 mass% of FeP04 is coated on surface of Li2Mn03 via both precipitation method and solid phase method. Content of FeP04 is calculated by the concentration of ferric nitrate (Fe(N03)3-9H20) and the concentration of diammonium hydrogen phosphate ((NH4)2HP04).
Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 3
Preparation of Li2Mn03 is the same as that of comparative example 1. 20 mass% of FeP04 is coated on surface of Li2Mn03 via both precipitation method and solid phase method. Content of FeP04 is calculated by the concentration of ferric nitrate (Fe(N03)3-9H20) and the concentration of diammonium hydrogen phosphate ((NH4)2HP04).
Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge curve and cycling performance are shown in Fig 3, and initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 4
Preparation of Li2Mn03 is the same as that of comparative example. 5 mass% of Mn02 is coated on surface of Li2Mn03 via simple both impregnation method and solid phase method. Content of Mn02 is calculated by the concentration of manganese nitrate solution.
Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1. Embodiment 5
Preparation of Li2Mn03 is the same as that of comparative example. 20 mass% of Mn02 is coated on surface of Li2Mn03 via both simple impregnation method and solid phase method. Content of Mn02 is calculated by the concentration of manganese nitrate solution.
Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 6
Preparation of Li2Mn03 is the same as that of comparative example. 40 mass% of Mn02 is coated on surface of Li2Mn03 via both simple impregnation method and solid phase method. Content of Mn02 is calculated by the concentration of manganese nitrate solution.
Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 7
Preparation of Li2Mn03 is the same as that of comparative example. 18 mass% of Mo03 is coated on surface of Li2Mn03 by conducting hydro-thermal treatment on peroxo molybdic acid sol (Mo02(OH)(OOH)). Content of Mo03 is calculated by the concentration of peroxo molybdic acid sol prepared via simple substance metal molybdenum (Mo) having certain mass.
Electrochemical performance test of Li secondary battery is the same as that of comparative example 1. Initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 8
Preparation of Li2Mn03 is the same as that of comparative example. 20 mass% of Pb02 is coated on surface of Li2Mn03 via precipitation method. Content of Pb02 is realized by controlling a solution of lead nitrate (Pb(N03)2) with certain concentration and a solution of sodium hydroxide (NaOH) with corresponding concentration under cetyltrimethyl ammonium bromide (CTAB) environment.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 9 Preparation of Li2Mn03 is the same as that of comparative example. 8 mass% of Co304 is coated on surface of Li2Mn03 via hydro-thermal method and solid phase method. Content of Co304 is realized by controlling a solution of cobalt acetate (Co(CH3COO)2-4H20) with certain concentration and aqueous ammonia (ΝΗ3Ή20) with corresponding concentration.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 10
Preparation of Li2Mn03 is the same as that of comparative example. 15 mass% of Co304 is coated on surface of Li2Mn03 via hydro-thermal method and solid phase method. Content of Co30 is realized by controlling a solution of cobalt acetate (Co(CH3COO)2-4H20) with certain concentration and aqueous ammonia ( Η3Ή20) with corresponding concentration.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example. Its initial charge/discharge curve and cycling performance are shown in Fig 4, and initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 1 1
Preparation of Li2Mn03 is the same as that of comparative example. 20 mass% of Ru02 is coated on surface of Li2Mn03 via precipitation method and solid phase method. Content of Ru02 is realized by controlling a solution of ruthenium chloride (RuCl3) with certain concentration and NaOH with corresponding concentration.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 12
Preparation of Li2Mn03 is the same as that of comparative example. 20 mass% of Ni(OH)2 is coated on surface of Li2Mn03 via precipitation method. Content of Ni(OH)2 is realized by controlling a solution of nickel dichloride (NiCl2-H20) with certain concentration and aqueous ammonia (ΝΗ3Ή20) with corresponding concentration.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1. Embodiment 13
Preparation of Li2Mn03 is the same as that of comparative example. 18 mass% of FeF3 is coated on surface of Li2Mn03 via precipitation method and drying method. Content of FeF3 is realized by controlling a solution of ferric nitrate (Fe(N03)3-9H20) with certain concentration and a solution of ammonium fluoride (NH4F) with corresponding concentration under cetyltrimethyl ammonium bromide (CTAB) environment.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 14
Preparation of Li2Mn03 is the same as that of comparative example. 1 mass% of LiCo02 is coated on surface of Li2Mn03 via sol-gel method. Content of LiCo02 is realized by controlling a solution of lithium acetate (LiCH3C0O2H20) with certain concentration, a solution of cobalt acetate (Co(CH3COO)2-4H20) and a solution of citric acid (C H807) under ethylene glycol environment.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 15
Preparation of Li2Mn03 is the same as that of comparative example. 5 mass% of LiCo02 is coated on surface of Li2Mn03 via sol-gel method. Content of LiCo02 is realized by controlling a solution of lithium acetate (LiCH3C0O2H20) with certain concentration, a solution of cobalt acetate (Co(CH3COO)2-4H20) and a solution of citric acid (C6H807) under ethylene glycol environment.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 16
Preparation of Li2Mn03 is the same as that of comparative example. 20 mass% of LiCo02 is coated on surface of Li2Mn03 via sol-gel method. Content of LiCo02 is realized by controlling a solution of lithium acetate (LiCH3C0O2H20) with certain concentration, a solution of cobalt acetate (Co(CH3COO)2-4H20) and a solution of citric acid (C6H807) under ethylene glycol environment. Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 17
Preparation of Li2Mn03 is the same as that of comparative example. 20 mass% of LiMn204 is coated on surface of Li2Mn03 via hydro-thermal method and solid phase method. Content of LiMn204 is realized by controlling a solution of manganese nitrate (Mn(N03)2) with certain concentration and lithium hydroxide (LiOH H20) with different masses.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 18
Preparation of Li2Mn03 is the same as that of comparative example. 30 mass% of PPy is coated on surface of Li2Mn03 via low temperature oxidation polymerization method. Content of PPy is realized by controlling pyrrole (Py) monomer with certain mass and a solution of ferric chloride (FeCl3-6H20) with corresponding concentration under environment of excessive sodium dodecyl benzene sulfonate solution.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1.
Embodiment 19
Preparation of Li2Mn03 is the same as that of comparative example. 30 mass% of FeOOH is coated on surface of Li2Mn03 via hydrolysis method. Content of FeOOH is realized by controlling a solution of ferric chloride (FeCl3-6H20) with certain concentration.
Electrochemical performance test of that material as positive electrode active material of Li secondary battery is the same as that of comparative example 1. Its initial charge/discharge capacity and discharge capacity after 30 cycles are summarized in Table 1. Table 1
Figure imgf000015_0001
It can be seen from Table 1 , Fig 2, Fig 3 and Fig 4 that, discharge capacity after 30 cycles of all the embodiments are larger than 100 mAh g"1, whereas that of comparative example 1 is only 87 mAh g"1. Initial discharge capacity of all the embodiments are larger than that of comparative example 1, and initial coulombic efficiency of all the embodiments are larger than that of comparative example 1. In particular, initial discharge capacity of all the embodiments 3, 6-8, 11-13, 18-19 are larger than initial charge capacity, that is, all the initial coulombic efficiency are larger than 100%. It can be seen from Table 1 that FeP04, Co304 and Ni(OH)2 are preferable coating materials because FeP04/Li2Mn03j Co304/Li2Mn03 and Ni(OH)2/Li2Mn03 provide more than 90% of retention rate after 30% cycles. FeF3 and M0O3 are also preferable coating materials because FeF3/Li2Mn03 and Mo03/Li2Mn03 provide relatively high discharge capacities.
Thus, it can be seen that, as compared to comparative example 1 without a coating layer, discharge capacity, coulombic efficiency and cycling performance of embodiments with a coating layer on surface of Li2Mn03 have been greatly improved. Another implementation of the invention provides a Li secondary battery comprising the positive electrode active material of the above implementation. Other components of the Li secondary battery involved in the present implementation may be any component required by a Li secondary battery that are known by those skilled in the art, and the description of which will be omitted here for brevity.
The Li secondary battery of the present implementation, by using the above positive electrode active material, may prevent 02 from releasing during initial charge, and significantly improve initial coulombic efficiency and discharge capacity after multiple charge-discharge cycles.
Although a positive electrode active material and a Li secondary battery of the present invention have been described hereinabove in conjunction with detailed implementations, the invention is not limited thereto. Various changes, replacements and modifications may be made to the invention by those skilled in the art within concept and scope of the present invention. All such changes, replacements and modifications are to be covered by scope of claims of the invention.

Claims

CLAIMS What is claimed is:
1. A positive electrode active material, comprising a core portion and a coating layer on the core portion, wherein the core portion comprises a metal oxide compound and the coating layer comprises a material which can react with lithium and/or oxygen and prevent from releasing oxygen from the lattice of the metal oxide compound during charge-discharge cycles.
2. The positive electrode active material according to claim 1, wherein the coating layer comprises at least one selected from the group consisting of a metal oxide, a metal hydroxide, a metal oxyhydroxide, a metal fluoride, a metal phosphate, a lithium insertion material and a polymer.
3. The positive electrode active material according to claim 1 or 2, wherein the metal oxide compound has a general formula LixMyOz and M is at least one selected from the group consisting of Co, Ni, Mn, Ti, V, Zr, Cr, Mg, Fe, Mo and Al.
4. The positive electrode active material according to claim 1 or 2, wherein the metal oxide compound has a general formula LiaMbOc (0<a<l, 0<b<l, 0<c<l) and M is at least one selected from the group consisting of trivalent transition metal cation.
5. The positive electrode active material according to claim 1 or 2, wherein the metal oxide compound has a general formula Li2-xM'xM"1-x03-x (0<x<l) and where M' is one or more ions having an average oxidation state of three, and where M" is one or more ions with an average oxidation state of four.
6. The positive electrode active material according to claim 1 or 2, wherein the metal oxide compound is Li2Mn03.
7. The positive electrode active material according to any one of claims 2 to 6, wherein, the metal oxide is at least one selected from the group consisting of Co304, CoO, NiO, Ru02, Mo03, Mn02 V203 and Pb02.
8. The positive electrode active material according to any one of claims 2 to 6, wherein, the metal hydroxide is at least one selected from the group consisting of Ni(OH)2 and Co(OH)2.
9. The positive electrode active material according to any one of claims 2 to 6, wherein, the metal oxyhydroxide is at least one selected from the group consisting of NiOOH and FeOOH.
10. The positive electrode active material according to any one of claims 2 to 6 wherein the metal fluoride is at least one selected from the group consisting of FeF3, FeF2 and CuF2.
11. The positive electrode active material according to any one of claims 2 to 6, wherein the metal phosphate is at least one selected from the group consisting of FeP04 and A1P04.
12. The positive electrode active material according to any one of claims 2 to 6, wherein the lithium insertion material is at least one selected from the group consisting of LiCo02, LiNi02, Li0. 4MnO2, LiMn20 , LiNi0.5Mni.5O4, LiMnB03, LiMnP04 and Li2MnSi04.
13. The positive electrode active material according to any one of claims 2 to 6, wherein the polymer is a conductive polymer.
14. The positive electrode active material according to any one of claims 2 to 6, wherein the polymer is a π -electron conjugated polymer.
15. The positive electrode active material according to claim 14, wherein the π-electron conjugated polymer is at least one selected from the group consisting of polyacetylene, polypyrrole, polyaniline, polyparaphenylenevinylene and polythiophene.
16. The positive electrode active material according to any one of claims 1 to 15, wherein the coating layer accounts for 0.5 mass%~50 mass% of total mass of the positive electrode active material.
17. The positive electrode active material according to any one of claims 1 to 16, wherein the coating layer accounts for 1 mass%~40 mass% of total mass of the positive electrode active material.
18. A Li secondary battery comprising the positive electrode active material according to any one of claims 1 to 17.
PCT/CN2014/074350 2014-03-31 2014-03-31 A positive electrode active material and a li secondary battery WO2015149211A1 (en)

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