Classifications

• • 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
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
• • 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
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • 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
  • H01M4/04—Processes of manufacture in general
  • H01M4/0438—Processes of manufacture in general by electrochemical processing
  • H01M4/044—Activating, forming or electrochemical attack of the supporting material
  • H01M4/0445—Forming after manufacture of the electrode, e.g. first charge, cycling
• • 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
  • H01M4/364—Composites as mixtures
• • 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
  • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
• • 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
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0025—Organic electrolyte
  • H01M2300/0028—Organic electrolyte characterised by the solvent
  • H01M2300/0037—Mixture of solvents
  • H01M2300/004—Three solvents
• • 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 invention relates to a lithium secondary cell, the capacity of which is not significantly reduced after over-discharge and the capacity restorability of which after over-discharge is excellent, and more particularly, to a cathode active material comprising a lithium manganese oxide (LiM x Mn ⁇ - x ⁇ 2) having a layered structure as a cathode additive for improving over-discharge property, and a lithium secondary cell obtained by using the same.
• a cathode active material comprising a lithium manganese oxide (LiM x Mn ⁇ - x ⁇ 2) having a layered structure as a cathode additive for improving over-discharge property
• a light-weight lithium secondary cell having a high capacity is increasingly in demand.
• a lithium secondary cell may ignite and explode due to extreme heat emission, when it is over-charged or is in a short circuit state.
• a lithium secondary cell is over-discharged below a normal voltage range, its capacity is rapidly reduced so that it may not be used any more.
• an organic or an inorganic additive is used in a non-aqueous electrolyte solution, or the outer structure of a cell is changed for the purpose of ensuring the cell safety when a cell is over-charged or is in a short circuit state.
• the cell capacity is so rapidly reduced that charge/discharge of the cell may not be accomplished any more.
• a cell voltage is defined by a difference of a cathode voltage and an anode voltage. Additionally, when a cell is continuously discharged at .a low electric current, even after the cell voltage is decreased below a general-use voltage, the cathode voltage is not decreased any more due to the consumption of Li in the anode, and thus it is slowly decreased. On the other hand, the anode voltage is rapidly increased and eventually it is raised to 3.6 V, at which point a copper foil used as an anode collector is oxidized.
• the copper foil is dissolved in a copper ion state, contaminating electrolytes, is attached again to the surface of the anode during re-charge, and thus the anode active material becomes unusable. Therefore, when the oxidization of the copper foil occurs, the cell capacity is rapidly reduced after over-discharge, so that the cell becomes unusable.
• a spinel-structured lithium manganese oxide is generally used for the purpose of improving the thermal stability of a cathode.
• This provides an advantage of a low cost and a simple synthetic procedure.
• the cell using a spinel- structured lithium manganese oxide as a cathode active material has problems that the capacity is low, the cell life may be reduced by side reactions, the high- temperature property is poor and the conductivity is also low.
• many attempts to use a spinel-structured lithium manganese oxide partially substituted with other metals have been made.
• Korean ⁇ nexamined Patent Publication No. 2002-65191 discloses a spinel-structured lithium manganese oxide having excellent thermal stability, however, it provides a low capacity and cannot improve the over-discharge preventing capability.
• Korean Unexamined Patent Publication No. 2002-24520 discloses a cell, in which a lithium manganese oxide having a layered structure is used as a cathode active material having excellent thermal stability, and a phase transition is prevented during charge/discharge so that the cell life can be improved.
• the over-discharge preventing capability cannot be improved in this case.
• the present inventors tried to develop a cell, in which by using a lithium manganese oxide having a layered structure, the cell discharge is limited by a cathode, so that the cell capacity may not be significantly reduced after over-discharge.
• a cathode active material for a lithium secondary cell comprising a lithium manganese oxide having a layered structure as an additive for a cathode, and a lithium secondary cell obtained by using the same.
• a cathode active material for a lithium secondary cell comprising a lithium-transition metal oxide capable of lithium ion intercalation/ deintercalation, characterized by further comprising a lithium manganese oxide having a layered structure represented by the following formula 1 as an additive: [formula 1]
• LiM x Mni_ x 0 2 wherein, x is a number satisfying 0.05 ⁇ x ⁇ 0.5, and M is at least one metal selected from the group consisting of Cr, Al, Ni, Mn and Co.
• the lithium secondary cell according to the present invention comprises: (a) a cathode comprising the said cathode active material according to the present invention, (b) an anode, (c) a separator, and (d) a non- aqueous electrolyte solution containing a lithium salt and an electrolyte compound.
• the lithium manganese oxide used as an additive for a cathode active material according to the present invention is represented by the following formula 1 and has a layered structure: [formula 1]
• LiM x Mn ⁇ _ x 0 2 wherein, x is a number satisfying 0.05 ⁇ x ⁇ 0.5, and M is at least one metal selected from the group consisting of Cr, Al, Ni, Mn and Co.
• the lithium manganese oxide of formula 1 (LiM x Mna . - x 0 2 ) has a layered monoclinic, orthorhombic or hexagonal structure, and can be prepared by mixing lithium carbonate (Li 2 C0 3 ) , manganese oxide (Mn 2 0 3 ) and a metal oxide in solid phases and heat-treating the mixture at a high temperature under argon atmosphere.
• the lithium manganese oxide of formula 1 can act as a cathode active material, in which a structural change into a spinel structure represented by the following formula 2 occurs, when a cell is charged/discharged first : [formula 2] LiM 2x Mn 2 - 2x 0 4 wherein, x is a number satisfying 0.05 ⁇ x ⁇ 0.5, and M is at least one metal selected from the group consisting of Cr, Al, Ni, Mn and Co.
• the lithium manganese oxide of formula 1 having a layered structure is shown in FIG. 1, and the lithium manganese oxide of formula 2 having a spinel structure is shown in FIG. 2.
• the lithium manganese oxide of formula 1 having a layered structure deintercalates one mole of lithium per two oxygen atoms during the first charge, however, after the first charge/discharge cycle, due to the structural change into a spinel structure, it becomes a substance capable of lithium intercalation/ deintercalation in the ratio of 0.5 mole of lithium per two oxygen atoms. Accordingly, when the lithium manganese oxide of formula 1 having a layered structure is used in a cathode as an additive for a cathode active material, the cathode active material composition according to the present invention shows a large difference between initial charge capacity and initial discharge capacity.
• This irreversible capacity provides lithium ions in such an amount as to compensate for an irreversible lithium consumption reaction in an anode caused by the SEI film formation on the surface of the anode during the first charge, or more. Therefore, such amount of lithium ions may compensate for the high and irreversible capacity of the anode at the first charge/discharge cycle.
• the cathode active material composition according to the present invention which comprises a lithium-transition metal oxide capable of lithium ion intercalation/deintercalation and the lithium manganese oxide of formula 1 having a layered structure can inhibit the capacity reduction caused by over- discharge, due to the irreversibility of the lithium manganese oxide of formula 1 during the first charge/discharge cycle. This mechanism is shown in FIG. 7.
• a cell voltage is defined by the difference of electric potentials between a cathode and an anode. Over- discharge of a cell continuously proceeds until the cell voltage becomes 0 V, at which point the electric potentials of a cathode and an anode are the same.
• the voltage of an anode having a relatively high irreversible capacity increases rapidly, when an over-discharge occurs, and thus copper ions are dissolved from an anode collector, so that charge/discharge cycles may not progress successfully.
• the present invention adopted a method that an additive having a high irreversible capacity is added to a cathode.
• x is a number satisfying 0.05 ⁇ x ⁇ 0.5, preferably 0.05 ⁇ x ⁇ 0.2.
• x is less than 0.05., a side reaction such as manganese ion dissolution may be generated, while if x is 0.5 or more, a phase transition from a layered structure to a spinel structure does not occur in a charge/discharge cycle, and thus it is not possible to improve the over-discharge property.
• M is selected from the group consisting of Cr, Al, Ni, Mn and Co, and functions as a structure stabilizer.
• M is Cr or Al . If M is Cr or Al, the structure of formula 1 is more stabilized, and provides excellent high-temperature life and high-temperature shelf property.
• the lithium manganese oxide of formula 1 is LiCr 0 . ⁇ Mn 0 .9 ⁇ 2 .
• the lithium manganese oxide of formula 1 (LiM x Mn ⁇ - x 0 2 ) is preferably added in an amount of 1 to 50 parts by weight based on 100 parts by weight of a transition metal oxide.
• a transition metal oxide such as copper ion dissolution.
• the cathode potential preferably ranges from 2 V to 3.6 V and the anode potential preferably 3.6 V or less, when the full cell voltage becomes 0 V.
• the compound of formula 1 according to the present invention preferably LiCro.1Mno.9O 2
• a cathode of a cell comprising an anode active material having an irreversible capacity of 30% or less
• the irreversible capacity of the anode active material is more than 30%, the cell capacity is reduced, and thus the compound of formula 1 must be added to the cathode in an amount of 50 wt% or more of the cathode active material.
• Such an excessive addition of the compound of formula 1 may cause other problematic side reactions, the deterioration of life characteristics and cell capacity reduction.
• the compound of formula 1 is added to the cathode to the extent of compensating for the irreversible capacity of the anode, it is possible to obtain very excellent performance in an over-discharge test of a SCF (safety circuit free) cell, which does not need a protection circuit and is of interest to cell production companies recently.
• SCF safety circuit free
• the cathode active material used in the present invention is any one of general cathode active materials, however, it is preferable to use a lithium-transition metal oxide.
• n Ni n 0 4 LiMn 2 - n Co n 0 4 (0 ⁇ n ⁇ 2) , LiCoP0 4 , LiFeP0 4 , etc., may be used, and preferably, LiCo0 2 is used.
• anode active material graphite, carbon, lithium metal and alloy, etc., that are capable of lithium ion intercalation/deintercalation, may be used.
• artificial graphite is used.
• the anode may comprise a binder, in which the binder is preferably PVDF (Polyvinylidene fluoride) or SBR (Styrene Butadiene Rubber) .
• a porous separator is preferably used as a separator.
• a polypropylene-, a polyethylene- or a polyolefin-based porous " separator may be used, but it is not limited thereto.
• the electrolyte solution used in the present invention is a non-aqueous electrolyte solution and may comprise a cyclic carbonate and a linear carbonate.
• the cyclic carbonate includes, for example, ethylene carbonate (EC), propylene carbonate (PC) and gamma- butyrolactone (GBL) .
• the linear carbonate includes, for example, at least one carbonate selected from the group consisting of diethyl carbonate (DEC) , dimethyl carbonate (DMC) , ethylmethyl carbonate (EMC) and methylpropyl carbonate (MPC) .
• the electrolyte solution used in the present invention comprises a lithium salt in addition to the said carbonate compound.
• the lithium salt is preferably selected from the group consisting of LiC10 4 , LiCF 3 S0 3 , LiPF 6 , LiBF 4 , LiAsF 6 and LiN (CF 3 S0 2 ) 2 •
• the lithium secondary cell according to the present invention is manufactured by a conventional method, i.e., by inserting a porous separator between a cathode and an anode and introducing an electrolyte solution.
• the lithium secondary cell according to the present invention has the shape of a cylindrical can, an angular cell or a pouch.
• FIG. 1 is a structural model of a layered structure of the additive for a cathode active material represented by formula 1, before charge.
• FIG. 2 is a structural model of a spinel structure of the additive for a cathode active material represented by formula 2, after initial charge/discharge.
• FIG. 3 is a graph showing the result of a structural analysis of the additive for a cathode active material represented by formula 1, by X-ray diffraction.
• FIG. 4 is a graph showing the result of a structural analysis by X-ray diffraction, before and after a charge/discharge test of a coin type cell, when the lithium manganese oxide of formula 1 having a layered structure was used as an additive for a cathode active material .
• FIG. 5 is a curve showing the current and the cell voltage according to a charge/discharge test of the cell using the additive for a cathode active material according to the present invention.
• FIG. 6 is a graph showing the cell capacity test results of initial 50 charge/discharge cycles, when the lithium manganese oxide having a layered structure represented by formula 1 is used as an additive for a cathode active material in a coin-type cell.
• FIG. 7 is a graph showing the cathode potential and the anode potential, before and after using the additive for a cathode active material according to the present invention.
• FIG. 8 is a diagram showing the over-discharge test results of the following Example 1 and Comparative Example 1.
• FIG. 9 is a graph showing a full cell voltage during the over-discharge test of Comparative Example 1.
• FIG. 10 is a graph showing a full cell voltage during the over-discharge test of Example 1.
• Example 1 A pouch-type polymer cell of 383562 size was manufactured by a conventional method.
• LiCo0 2 was used as a cathode active material and LiCro. 1 Mno. 9 O 2 was added in the amount of 8 parts by weight based on 100 parts by weight of the cathode active material.
• LiCro. 1 Mno. 9 O 2 was prepared by mixing lithium carbonate, manganese oxide and chrome oxide in solid phases, heat-treating the mixture at a temperature of 1000°C under argon atmosphere for 12 hours, pulverizing the heat-treated mixture and further heat-treating the pulverized mixture at a temperature of 1100°C under argon atmosphere for 12 hours.
• Super-p and PVDF polymer used as a conductive agent and a binder, respectively, were added to NMP as a solvent to form cathode mixture slurry, and then the slurry was coated on an Al collector to obtain a cathode.
• artificial graphite and copper were used as an anode active material and an anode collector, respectively, and an EC/PC/DEC-based electrolyte solution containing 1M LiPF 6 was used to obtain a cell by a conventional method.
• Example 1 was repeated to obtain a cell, except that the additive for a cathode active material (LiCro.1Mno.9O2) was not used in the cathode.
• the additive for a cathode active material LiCro.1Mno.9O2
• FIG. 3 is a graph showing the result of a structural analysis of the lithium manganese oxide, LiCro. 1 Mno. 9 O 2 , used as an additive for a cathode active material in Example 1 by X-ray diffraction. According to FIG. 3, it is apparent that the lithium manganese oxide of formula 1 is a compound having a layered structure.
• the lithium manganese oxide having a layered structure LiCro. 1 Mno. 9 O 2 , was structurally changed into a spinel structure, after a coin-type cell obtained by using the same compound as an additive for a cathode active material experienced initial charge/discharge.
• the cell provided a very low first charge/discharge efficiency.
• the lithium manganese oxide provided a very low first charge/discharge efficiency.
• a charge/discharge efficiency of about 100% could be obtained in the following charge/discharge cycles, and thus reversible lithium intercalation/deintercalation could occur.
• Example 1 A charge capacity and a discharge capacity before and after an over-discharge test were determined using each of the pouch-type polymer cells of 383562 size obtained from Example 1 and Comparative Example 1, through a conventional method.
• the over-discharge test results are shown in FIG. 8.
• Each of the numbers means a discharge capacity restorability at 0.2C and 1C after over-discharge, based on a discharge capacity at 0.2 C and 1 C before over-discharge.
• Example 1 according to the present invention provided a discharge capacity restorability of 90% or more after an over-discharge test, and thus provided an excellent over- discharge preventing effect compared to Comparative Example 1.
• Example 1 In order to demonstrate the effect of the additive for a cathode active material on over-discharge, a three- electrode experiment was performed using the cells of Example 1 and Comparative Example 1.
• a base electrode (reference electrode) made of lithium metal was inserted to each of the pouch-type polymer cells of 383562 size obtained from Example 1 and Comparative Example 1. Then, the potential differences between the reference electrode and each of the cathode and the anode were measured in order to check how the cathode potential based on the base electrode and the anode potential based on the base electrode were changed in a practical cell during charge/discharge cycles.
• LiCro. 1 Mno. 9 O 2 providing a large irreversible capacity at the first charge/discharge cycle is added in order to control the irreversible capacities of the cathode and the anode adequately, and thus it is possible to prevent the increase of the anode voltage in an over-discharge test so that the cell capacity may not be significantly reduced after the over-discharge test.
• the compound of formula 1, preferably LiCro. 1 Mno. 9 O 2 is added to a cathode as an additive for a cathode active material to improve over-discharge properties, and the additive for a cathode active material can provide lithium ions in such an amount as to compensate for the irreversible capacity of an anode, or more. Accordingly, the anode voltage can be prevented from increasing during an over-discharge test so that a cell capacity restorability of 90% or more may be obtained after the over-discharge test.

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• 2003
  • 2003-04-09 KR KR10-2003-0022429A patent/KR100533095B1/ko not_active Expired - Lifetime
• 2004
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  • 2004-04-06 US US10/552,529 patent/US20070015055A1/en not_active Abandoned
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