WO2001029916A1 - A method for preparing a carbon anode for lithium ion batteries - Google Patents

A method for preparing a carbon anode for lithium ion batteries Download PDF

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WO2001029916A1
WO2001029916A1 PCT/SI2000/000020 SI0000020W WO0129916A1 WO 2001029916 A1 WO2001029916 A1 WO 2001029916A1 SI 0000020 W SI0000020 W SI 0000020W WO 0129916 A1 WO0129916 A1 WO 0129916A1
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lithium ion
polyelectrolyte
ion batteries
anode
carbon
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PCT/SI2000/000020
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French (fr)
Slovenian (sl)
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Miran GABERŠČEK
Marjan Bele
Stane Pejovnik
Jernej Drofenik
Robert Dominko
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Kemijski inštitut
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Priority to AU75692/00A priority Critical patent/AU7569200A/en
Publication of WO2001029916A1 publication Critical patent/WO2001029916A1/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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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
    • 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
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • 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
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0416—Methods of deposition of the material involving impregnation with a solution, dispersion, paste or dry powder
    • 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
    • H01M4/043—Processes of manufacture in general involving compressing or compaction
    • 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
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • H01M2004/027—Negative 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

  • This invention relates the field of chemical technology, specifically to chemical sources of electrical energy. It refers to a novel method for the preparation of a carbon anode and to the resulting carbon anode to be used in lithium ion (storage) batteries or accumulators respectively, of the type: carbon (anode) / anhydrous liquid electrolyte / transition element oxide (cathode).
  • the subgroup of lithium ion batteries yielding a current density of 1 ⁇ Acm "2 to 1
  • mAcm comprises an anode, which is conventionally made of carbon powder,
  • the carbon powder is of various origin, and may be chosen from coke, carbon black, native or synthetic graphites and the like. ((1). J.R.Dahn, A.K. Sleigh, H. Shi, J.N.Reimers,
  • the conventional mode for the manufacture of anodes comprises in principle: mixing a suspension of carbon powder with a binder suspension on the base of Teflon® (PTFE) or polyvinylidene difluoride (PVDF), and finally coating a current collector (copper, aluminum, graphite plates and the like) with said mixture. Prior to the use the coating is dried for several hours in an inert atmosphere at a temperature of about 100-140 °C. ((1) T.D. Tran, J. H. Feikert, X. Song, K. Kinoshita, J. Electrochem. Soc, 142 (1995) 3297-3302; (2) N. Imanishi, Y. Takeda, O.
  • Yamamoto in: Lithium Ion Batteries, Fundametals and Performance, Ed. M. Wakihara, O. Yamamoto, Kodansha, Tokyo and Wiley- VCH, Weinheim, 1998, p. 98-126; (3) I. Tamura, M. Nagasima, Y. Ikezawa, and T. Takamura, Denki Kagaku, 60 (1992) 926).
  • a conventional method for the manufacture of an anode for lithium ion batteries is the following:
  • the electrochemically active anode material is usually carbon powder on the base of coke, carbon black, graphite, pyrolysed polymers, carbon fibres or mixtures of these materials ((1) (2) N. Takami, A. Satoh, M. Hara, T. Ohsaki, J. Electrochem. Soc, 142 (1995) 371-378, (3) T.D. Tran, J. H. Feikert, X. Song, K. Kinoshita, J. Electrochem. Soc, 142 (1995) 3297-3302; (4) N. Imanishi, Y. Takeda, O. Yamamoto, in. Lithium Ion Batteries, Fundamentals and Performance, Ed. M. Wakihara, O. Yamamoto, Kodansha, Tokyo and Wiley- VCH, Weinheim, 1998, p. 98-126).
  • the above-referenced materials are obtained by thermal treatment of the starting substances at a temperature from 1000 °C to 3000 °C (J.R. Dahn, A.K. Sleigh, H. Shi, J.N. Reimers, Electrochimica Acta, 38 (1993) 1179 -1191 ).
  • the dimensions of the carbon particles are typically 1-50 ⁇ m, and their surface
  • polyelectrolytes for example gelatin
  • polyelectrolytes for example gelatin
  • food manufacture A.G. Ward, A. Courts, in "The Science and Technology of Gelatin", Academic Press, London, 1977
  • photography C.E. Mees, C.E. Kenneth, in "The Theory of Photographic Process", Macmillan, New York, 1966
  • electrochemistry G.M. Brown, G.A. Hope, J. Electroanal. Chem., 397 (1995) 293
  • Polyelectrolytes are used as stabilisers in suspensions ((1) TJ. Maternaghan,
  • the stabilisation is achieved by means of a steric hindrance, represented by polyelectrolyte molecules ("hair-like structure") after the adsorption by the substrate, and the emulsions become stabilised as a result of the modification of the properties of the intercalated layer.
  • Typical problems of the above-described, hitherto known processes and the anodes resulting therefrom are: a) during the first intercalation (first charging of the batteries) a substantial portion, notably 20-40 % of the lithium ions reacts chemically with the electrolyte, and the products form a passivating film on the surface of the carbon particles ((1). M. Jean, A. Tranchant, R. Messina, J. Electrochem. Soc, 143 (1996) 391-394, Reactivity of lithium intercalated into petroleum coke in carbonate electrolytes; (2) K. Kanamura, S. Toriyama, S. Shiraishi, and Z. Takehara, J. Elecrochem. Soc, 142 (1995) 1383-1389; (3) D. Aurbach, A.
  • the novel method minimizes the technical problems discussed above in a) - d), and yields carbon anodes, characterised by superior properties for the use in lithium ion batteries.
  • Carbon particles intended for the use as an electrochemically active anode material are subjected to the action of the polyelectolyte solution.
  • the polyelectrolyte is adsorbed on the surface of each carbon particle modifying its physico-chemical characteristics.
  • the modification of the surface of the carbon particles is the very essence of this invention, and it results in the following unexpected, advantageous characteristics of the method and product:
  • the irreversible lithium loss due to the passivation is reduced to max. 15 %.
  • the adsorbed polyelectrolyte acts simultaneously as a binder for the carbon particles.
  • the addition of PVDF or PFTE is not required.
  • the mass percentage of the polyelectrolyte in the anode material does not exceed 1 %.
  • the energy density of the anode material is accordingly higher than in the case when conventional binders are used.
  • the solution was prepared by dissolving the water-soluble polyelectrolyte in deionised water.
  • Polyelectrolytea were used, which formed a "hair-like" structure on the boundary between the particle and the electrolyte (for example proteins, cellulose derivatives, gums and the like)
  • the "hair-like” structure means, that after the adsorption the tails or meshes of the polyelectrolyte project from the particle surface into the interior of the solution
  • the polyelectrolyte modified according to point 4 1 was applied in the surface treatment of carbon particles, which were later used as an electrochemically active anode material Under stirring, a known amount of carbon particles was added to a corresponding amount of the solution of the modified polyelectrolyte After 2-30 minutes the treated particles were separated (filtered off) by a Nutsch (suction) filter The obtained filter cake was used in the manufacture of the anode b Manufacture of the anode from surface-treated carbon particles
  • Particles with the adsorbed polyelectrolyte are removed from the solution by filtration, and the obtained material is coated on a copper sheet
  • the coating is compressed under a pressure of 100-5000 kPa, and dried several hours in vacuo or in an inert atmosphere The final thickness of the coating is within the range 50-200 ⁇ m
  • the dried electrode is transferred into a dry chamber for the performance of electrochemical tests
  • the method for preparing a carbon anode for lithium ion batteries in accordance with this invention is performed by a) preparing a polyelectrolyte solution appropriate for the formation of the "hair- like" structure on the surface of the carbon particles, by dissolving 0 1 to 10 g of the polyelectrolyte chosen from proteins, cellulose derivatives, gums, or mixtures thereof, in 1 L of deionised water under moderate stirring at a temperature of 30 to 100 °C, b) mixing 1 to 10 g carbon particles comprising graphenic layers, said particles having dimensions of 1 to 50 ⁇ m, and a specific surface of 2 to 50 m " g " , by stirring into 1 L of the above-obtained solution preheated to about room temperature, kept for 2 to 30 minutes, and modified to a pH value of 7 to 9, followed by the filtration through a Nutsch filter; and c) coating the black cake from the Nutsch filter on a copper sheet and further processing in a conventional manner into an anode for lithium
  • the polyelectrolytes used are gelatin or arabic gum.
  • the stirring is performed at about 200 rpm.
  • the carbon particles used are graphite.
  • the pH value is modified by the addition of an acid or a base in order to achieve a minimal charge on the macromolecule.
  • a further object of this invention is a carbon anode for lithium ion batteries, obtainable in accordance with one of the claims 1 to 5.
  • the preformed gelatin solution was modified with a corresponding amount of 0.1 M NaOH, in order to adjust the pH value within the range 7-9.
  • Working example B Preparation of the arabic gum solution
  • a 0.01-1 % solution of arabic gum spraygum irx No. 28830 produced by Coloides Naturels International, France was used.
  • the solution was prepared by dissolving 0.1-10 g of arabic gum in 1 L of deionised water at 30-100 °C, under moderate stirring (approximately 200 rpm) with a magnetic stirrer. Prior to the use, the temperature of the solution was always adjusted to room temperature.
  • Working example C Treatment of carbon particles in a polyelectrolyte solution The gelatin and the arabic gum respectively, modified according to point 4.1 , were applied to the surface of the carbon particles that were subsequently used as an electrochemically active anodic material.
  • Particles having adsorbed the polyelectrolyte were filtered from the solution, and the obtained material was deposited on a copper sheet.
  • the coating was compressed under a pressure of 1000 kPa, and dried during 10 hours in vacuo at 100 °C. The final thickness of the coating was about 50 ⁇ m.
  • the dried electrode was transferred into a dry chamber, where the electrochemical tests were performed.
  • Figure 1 represents the first charging/discharging of the anode made of graphite Timrex SFG44 and treated with gelatin Fluka No. 48722.
  • Figure 2 represents the first charging/discharging of the anode made of graphite Timrex SFG44, with the addition of the binder 5 wt.% Teflon® /Aldrich 44, 509-6).
  • Figure 3 represents the dependence of the reversible capacitance on the number of cycles, for the anode made of graphite SFP44 treated with gelatin.
  • Figure 4 represents the dependence of the reversible capacitance on the number of cycles, for the anode made of graphite SFP44 and 5 % Teflon®.

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Abstract

According to this method a polyelectrolyte solution appropriate for the formation of the 'hair-like' structure on the surface of the carbon particles, is prepared by dissolving 0.1 to 10 g of the polyelectrolyte chosen from proteins, cellulose derivatives, gums, or mixtures thereof, in 1L of deionised water under moderate stirring at a temperature of 30 to 100 °C; and then 1 to 10 g carbon particles comprising graphenic layers, said particles of having dimensions of 1 to 50 νm, and a specific surface of 2 to 50 m-2g-1, are mixed under stirring into 1L of the above-obtained solution preheated to about room temperature, kept for 2 to 30 minutes, and modified to a pH value of 7 to 9, followed by the filtration through a Nutsch filter; and coating the black cake from the Nutsch filter on a copper sheet and further processing in a conventional manner into an anode for lithium ion batteries. the novel method avoids the use of conventional binders, and yields carbon anodes possessing superior properties for the use in lithium ion batteries.

Description

A method for preparing a carbon anode for lithium ion batteries
1. Technical Field of Invention
This invention relates the field of chemical technology, specifically to chemical sources of electrical energy. It refers to a novel method for the preparation of a carbon anode and to the resulting carbon anode to be used in lithium ion (storage) batteries or accumulators respectively, of the type: carbon (anode) / anhydrous liquid electrolyte / transition element oxide (cathode).
2. State of the Art
The subgroup of lithium ion batteries yielding a current density of 1 μAcm"2 to 1
mAcm" comprises an anode, which is conventionally made of carbon powder,
having a typical particle size of 1-50 μm. The carbon powder is of various origin, and may be chosen from coke, carbon black, native or synthetic graphites and the like. ((1). J.R.Dahn, A.K. Sleigh, H. Shi, J.N.Reimers,
Electrochimica Acta, 38 (1993) 1179-1191 ; (2) N. Takami, A. Satoh, M. Hara, T. Ohsaki, J. Electrochem. Soc. 142 (1995) 371-378; (3) T.D. Tran, J.H. Feikert, X. Song, K. Kinoshita, J. Electrochem. Soc, 142 (1995) 3297-3302). The sole requirement is the presence (contents) of graphenic layers, intercalated by
lithium ions (N. Imanishi, Y. Takeda, O. Yamamoto, in: Lithium Ion Batteries, Fundamentals and Performance, Ed. M. Wakihara, O. Yamamoto, Kodansha, Tokyo and Wiley-VCH, Weinheim, 1998, p. 98-126).
The conventional mode for the manufacture of anodes comprises in principle: mixing a suspension of carbon powder with a binder suspension on the base of Teflon® (PTFE) or polyvinylidene difluoride (PVDF), and finally coating a current collector (copper, aluminum, graphite plates and the like) with said mixture. Prior to the use the coating is dried for several hours in an inert atmosphere at a temperature of about 100-140 °C. ((1) T.D. Tran, J. H. Feikert, X. Song, K. Kinoshita, J. Electrochem. Soc, 142 (1995) 3297-3302; (2) N. Imanishi, Y. Takeda, O. Yamamoto, in: Lithium Ion Batteries, Fundametals and Performance, Ed. M. Wakihara, O. Yamamoto, Kodansha, Tokyo and Wiley- VCH, Weinheim, 1998, p. 98-126; (3) I. Tamura, M. Nagasima, Y. Ikezawa, and T. Takamura, Denki Kagaku, 60 (1992) 926).
A conventional method for the manufacture of an anode for lithium ion batteries is the following:
The electrochemically active anode material is usually carbon powder on the base of coke, carbon black, graphite, pyrolysed polymers, carbon fibres or mixtures of these materials ((1) (2) N. Takami, A. Satoh, M. Hara, T. Ohsaki, J. Electrochem. Soc, 142 (1995) 371-378, (3) T.D. Tran, J. H. Feikert, X. Song, K. Kinoshita, J. Electrochem. Soc, 142 (1995) 3297-3302; (4) N. Imanishi, Y. Takeda, O. Yamamoto, in. Lithium Ion Batteries, Fundamentals and Performance, Ed. M. Wakihara, O. Yamamoto, Kodansha, Tokyo and Wiley- VCH, Weinheim, 1998, p. 98-126).
The above-referenced materials are obtained by thermal treatment of the starting substances at a temperature from 1000 °C to 3000 °C (J.R. Dahn, A.K. Sleigh, H. Shi, J.N. Reimers, Electrochimica Acta, 38 (1993) 1179 -1191 ). The dimensions of the carbon particles are typically 1-50 μm, and their surface
2 -1 areas are within the range 2-50 m g . The powder is dispersed either in
ethanol or in methanol, acetone etc. To the dispersion are added 5-10% by weight of PTFE or PVDF ((1). T.D. Tran, J.H. Feikert, X. Song, K. Kinoshita, J. Electrochem. Soc, 142 (1995) 3297-3302; (2) N. Imanishi, Y. Takeda, O. Yamamoto, in: Lithium Ion Batteries, Fundamentals and Performance, Ed. M. Wakihara, O. Yamamoto, Kodansha, Tokyo and Wiley-VCH, Weinheim, 1998, p. 98-126, (3) I. Tamura, M. Nagasima, Y. Ikezawa, and T. Takamura, Denki Kagaku, 60 (1992) 926), in dispersed or powdered form. The obtained dispersion is thoroughly mixed and used for the coating of a copper foil or a graphite plate. The resulting electrode is compressed under 500-2000 kPa in a press. The final thickness of the coating is 50-200 μm. The electrode is dried in vacuo for 10-14 hours at a temperature of 100-140 °C. The adsorption of the polyelectrolytes by the particles:
The adsorption of the polyelectrolytes (for example gelatin) has been studied and used for example in food manufacture (A.G. Ward, A. Courts, in "The Science and Technology of Gelatin", Academic Press, London, 1977), photography (C.E. Mees, C.E. Kenneth, in "The Theory of Photographic Process", Macmillan, New York, 1966), electrochemistry (G.M. Brown, G.A. Hope, J. Electroanal. Chem., 397 (1995) 293), biology, medicine etc. Polyelectrolytes are used as stabilisers in suspensions ((1) TJ. Maternaghan,
O.B. Banghan, R.H. Ottewill, J. Photogr. Sci. 28 (1980); (2) V.V. Rodin, V.
Izmailova, Polym. Sci. 272 (1994) 433), as well as in emulsions (H.J. Muller, H. Hermel, Colloid Polym. Sci, 272 (1994) 433). In the first case, the stabilisation is achieved by means of a steric hindrance, represented by polyelectrolyte molecules ("hair-like structure") after the adsorption by the substrate, and the emulsions become stabilised as a result of the modification of the properties of the intercalated layer.
3. Technical Problem
Typical problems of the above-described, hitherto known processes and the anodes resulting therefrom are: a) during the first intercalation (first charging of the batteries) a substantial portion, notably 20-40 % of the lithium ions reacts chemically with the electrolyte, and the products form a passivating film on the surface of the carbon particles ((1). M. Jean, A. Tranchant, R. Messina, J. Electrochem. Soc, 143 (1996) 391-394, Reactivity of lithium intercalated into petroleum coke in carbonate electrolytes; (2) K. Kanamura, S. Toriyama, S. Shiraishi, and Z. Takehara, J. Elecrochem. Soc, 142 (1995) 1383-1389; (3) D. Aurbach, A. Zaban, Y. Ein-Eli, I. Weissman, O. Chusid, B. Markovsky, M. Levi, E. Levi, A. Schechter, and E. Granot, 8th Int. Meet. Lithium Batteries, Nagoya, Japan, 1996, Extended Abstracts, p. 77-80; (4) W. Xing, J.R. Dahn, J. Elecrochemical Soc, 144 (1997) 1195-1201). The formation of a passivating film is an irreversible process, and for this reason the lithium spent during this process is not reusable in the subsequent discharging and charging of the battery. b) Since the contents of the binder are only about 5-10% by weight, it is very difficult to achieve an optimal bonding of the carbon particles during the manufacture of the anode. The extensive volumetric changes (30-200 %) (J.O. Besenhard, M. Winter, J. Power Sources, 54 (1995) 228), during the intercalation and deintercalation result in a gradual loss of the physical and accordingly electrical contact of the discrete particles with other particles in the anode. This is one of the main causes for the degradation of lithium batteries during the cycling. c) Since PTFE and PVDF are electrical insulators, the local conductivity is severely impaired by their presence in the anode. d) PTFE and PVDF are electrochemically inactive materials. Their presence directly diminishes the energy density of lithium batteries.
4. Description of the solution of the problem with working embodiments. Proposed is a novel method for the manufacture of a carbon anode, which avoids the use of conventional (classical) binders, and applies instead a treatment of the carbon particles surface with a polyelectrolyte before the manufacturing of the anode. The use of polyelectrolytes in the manufacture of anodes for lithium ion batteries has not been described in the literature as yet.
The novel method minimizes the technical problems discussed above in a) - d), and yields carbon anodes, characterised by superior properties for the use in lithium ion batteries.
Carbon particles intended for the use as an electrochemically active anode material, are subjected to the action of the polyelectolyte solution. The polyelectrolyte is adsorbed on the surface of each carbon particle modifying its physico-chemical characteristics. The modification of the surface of the carbon particles is the very essence of this invention, and it results in the following unexpected, advantageous characteristics of the method and product: The irreversible lithium loss due to the passivation is reduced to max. 15 %. a) The adsorbed polyelectrolyte acts simultaneously as a binder for the carbon particles. The addition of PVDF or PFTE is not required. b) The mass percentage of the polyelectrolyte in the anode material does not exceed 1 %. The energy density of the anode material is accordingly higher than in the case when conventional binders are used.
4.1 Preparation of the polyelectrolyte solution
The solution was prepared by dissolving the water-soluble polyelectrolyte in deionised water. Polyelectrolytea were used, which formed a "hair-like" structure on the boundary between the particle and the electrolyte (for example proteins, cellulose derivatives, gums and the like) The "hair-like" structure means, that after the adsorption the tails or meshes of the polyelectrolyte project from the particle surface into the interior of the solution
The preformed polyelectrolyte solution was modified before the adsorption by changing the pH value or by the addition of a suitable ionic surfactant respectively The effected change of the charge density on the polyelectrolyte yielded a maximal adsorption a Treatment of carbon particles in polyelectrolyte solution
The polyelectrolyte modified according to point 4 1 , was applied in the surface treatment of carbon particles, which were later used as an electrochemically active anode material Under stirring, a known amount of carbon particles was added to a corresponding amount of the solution of the modified polyelectrolyte After 2-30 minutes the treated particles were separated (filtered off) by a Nutsch (suction) filter The obtained filter cake was used in the manufacture of the anode b Manufacture of the anode from surface-treated carbon particles
Particles with the adsorbed polyelectrolyte are removed from the solution by filtration, and the obtained material is coated on a copper sheet The coating is compressed under a pressure of 100-5000 kPa, and dried several hours in vacuo or in an inert atmosphere The final thickness of the coating is within the range 50-200 μm The dried electrode is transferred into a dry chamber for the performance of electrochemical tests
The method for preparing a carbon anode for lithium ion batteries in accordance with this invention is performed by a) preparing a polyelectrolyte solution appropriate for the formation of the "hair- like" structure on the surface of the carbon particles, by dissolving 0 1 to 10 g of the polyelectrolyte chosen from proteins, cellulose derivatives, gums, or mixtures thereof, in 1 L of deionised water under moderate stirring at a temperature of 30 to 100 °C, b) mixing 1 to 10 g carbon particles comprising graphenic layers, said particles having dimensions of 1 to 50 μm, and a specific surface of 2 to 50 m" g" , by stirring into 1 L of the above-obtained solution preheated to about room temperature, kept for 2 to 30 minutes, and modified to a pH value of 7 to 9, followed by the filtration through a Nutsch filter; and c) coating the black cake from the Nutsch filter on a copper sheet and further processing in a conventional manner into an anode for lithium ion batteries.
Preferably, the polyelectrolytes used are gelatin or arabic gum.
Preferably, the stirring is performed at about 200 rpm.
Preferably, the carbon particles used are graphite.
Preferably, the pH value is modified by the addition of an acid or a base in order to achieve a minimal charge on the macromolecule.
A further object of this invention is a carbon anode for lithium ion batteries, obtainable in accordance with one of the claims 1 to 5.
Working example A: Preparation of the gelatin solution
In experimental work a 0.01-1 % solution of gelatin No. 48722 produced by Fluka was used. The solution was prepared by dissolving 0.1-10 g of gelatin in 1 L of deionised water at 30-100 °C, under moderate stirring (approximately 200 rpm) with a magnetic stirrer. Prior to the use, the temperature of the solution was always adjusted to room temperature.
Before the adsorption, the preformed gelatin solution was modified with a corresponding amount of 0.1 M NaOH, in order to adjust the pH value within the range 7-9.
Working example B: Preparation of the arabic gum solution In experimental work a 0.01-1 % solution of arabic gum spraygum irx No. 28830 produced by Coloides Naturels International, France, was used. The solution was prepared by dissolving 0.1-10 g of arabic gum in 1 L of deionised water at 30-100 °C, under moderate stirring (approximately 200 rpm) with a magnetic stirrer. Prior to the use, the temperature of the solution was always adjusted to room temperature. Working example C: Treatment of carbon particles in a polyelectrolyte solution The gelatin and the arabic gum respectively, modified according to point 4.1 , were applied to the surface of the carbon particles that were subsequently used as an electrochemically active anodic material. To 100 mL of modified polyelectrolyte were added 1-10 g of Timrex SFG44 under stirring. After 2-30 minutes the treated particles SFG44 were separated by means of a Nutsch filter. The obtained filter cake was used in the preparation of the anode.
Working example D: Preparation of the anode from the surface-treated carbon particles
Particles having adsorbed the polyelectrolyte were filtered from the solution, and the obtained material was deposited on a copper sheet. The coating was compressed under a pressure of 1000 kPa, and dried during 10 hours in vacuo at 100 °C. The final thickness of the coating was about 50 μm. The dried electrode was transferred into a dry chamber, where the electrochemical tests were performed.
The invention is illustrated by the enclosed Figures 1-4.
Figure 1 represents the first charging/discharging of the anode made of graphite Timrex SFG44 and treated with gelatin Fluka No. 48722. Figure 2 represents the first charging/discharging of the anode made of graphite Timrex SFG44, with the addition of the binder 5 wt.% Teflon® /Aldrich 44, 509-6).
Figure 3 represents the dependence of the reversible capacitance on the number of cycles, for the anode made of graphite SFP44 treated with gelatin. Figure 4 represents the dependence of the reversible capacitance on the number of cycles, for the anode made of graphite SFP44 and 5 % Teflon®.

Claims

PATENT CLAIMS
1. A method for for preparing a carbon anode for lithium ion batteries, characterised by a) preparing a polyelectrolyte solution appropriate for the formation of a "hairlike" structure on the surface of the carbon particles, by dissolving 0.1 to 10 g of the polyelectrolyte chosen from proteins, cellulose derivatives, gums, or mixtures thereof, in 1 L of deionised water under moderate stirring at a temperature of 30 to 100 °C; b) mixing 1 to 10 g carbon particles comprising graphenic layers, said particles having dimensions of 1 to 50 μm, and a specific surface of 2 to 50 m" g" , by stirring into 1 L of the above-obtained solution, preheated to about room temperature, kept for 2 to 30 minutes, and modified to a pH value of 7 to 9, followed by the filtration through a Nutsch filter; and c) coating the black cake from the Nutsch filter on a copper sheet and further processing in a conventional manner into an anode for lithium ion batteries.
2. A process as claimed in claim 1a, characterised in, that the polyelectrolyte used is gelatin.
3. A process as claimed in claim 1a, characterised in, that the polyelectrolyte used is arabic gum.
4. A process as claimed in claim 1a, characterised in, that it is performed at about 200 rpm.
5. A process as claimed in claim 1b, characterised in, that the carbon particles used are graphite.
6. A process as claimed in claim 1b, characterised in, that the pH value is modified by the addition of an acid or a base, in order to achieve a minimal charge on the macromolecule.
7. A carbon anode for lithium ion batteries, characterized in, that it is obtainable in accordance with one of the claims 1 to 5.
PCT/SI2000/000020 1999-10-19 2000-10-06 A method for preparing a carbon anode for lithium ion batteries WO2001029916A1 (en)

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WO2002047188A1 (en) * 2000-11-28 2002-06-13 Kemijski, Institut Method for the preparation of a cathode for lithium ion batteries
EP1662592A1 (en) * 2003-07-15 2006-05-31 Itochu Corporation Current collecting structure and electrode structure
US20120219852A1 (en) * 2011-02-27 2012-08-30 Gm Global Technology Operations Llc. Negative electrode for a lithium ion battery
US11430979B2 (en) 2013-03-15 2022-08-30 Ppg Industries Ohio, Inc. Lithium ion battery anodes including graphenic carbon particles

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002047188A1 (en) * 2000-11-28 2002-06-13 Kemijski, Institut Method for the preparation of a cathode for lithium ion batteries
EP1662592A1 (en) * 2003-07-15 2006-05-31 Itochu Corporation Current collecting structure and electrode structure
EP1662592A4 (en) * 2003-07-15 2008-09-24 Itochu Corp Current collecting structure and electrode structure
US20120219852A1 (en) * 2011-02-27 2012-08-30 Gm Global Technology Operations Llc. Negative electrode for a lithium ion battery
US9153819B2 (en) * 2011-02-27 2015-10-06 GM Global Technology Operations LLC Negative electrode for a lithium ion battery
US11430979B2 (en) 2013-03-15 2022-08-30 Ppg Industries Ohio, Inc. Lithium ion battery anodes including graphenic carbon particles

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