Classifications

• • 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
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
• • 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
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0567—Liquid materials characterised by the additives
• • 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
  • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
  • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
• • 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
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
• • 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 to an electrolyte for a rechargeable cell, particularly but not exclusively a lithium cell or a lithium ion cell.
• Rechargeable cells which incorporate an organic electrolyte with a lithium salt such as lithium hexafluorophosphate, a cathode of an insertion material such as titanium disulphide or lithium cobalt oxide into which lithium ions can be inserted, and an anode either of metallic lithium or a lithium alloy ('a lithium cell') or of a different insertion material ('a lithium ion cell') such as graphite. If such a cell is overcharged it may be degraded; this may result from oxidation of the organic solvent, or changes to the electrodes such as deposition of metallic lithium in a lithium ion cell. Overcharging may be prevented by monitoring the voltage of each cell in a battery and regulating it to remain below the voltage threshold at which degradation may occur.
• a lithium salt such as lithium hexafluorophosphate
• a cathode of an insertion material such as titanium disulphide or lithium cobalt oxide into which lithium ions can be inserted
• a complementary or alternative approach is to incorporate a redox chemical into the electrolyte which is oxidised at a voltage above the normal cell voltage but below the voltage at which degradation occurs.
• a redox chemical for example US patent application 744 344 (W.K. Behl) refers to the use of lithium iodide (which is oxidised at about 2.8 V), and describes the use of lithium bromide (which is oxidised at about 3.5 V relative to lithium) as organic electrolyte additives to provide overcharge protection;
• EP 0 319 182 B (EIC Labs/Abraham et al) describes the use of metallocenes for this purpose, which have redox potentials relative to lithium in the range about 1.7 to 3.7 volts, such as ferrocene for which the redox potential is 3.05 to 3.38 V.
• these redox chemicals are not suitable for use in cells where the normal charging cell voltage is above 3.8 volts.
• an electrolyte for use in a rechargeable cell whose voltage exceeds 3.8 volts during charging, the electrolyte including a redox chemical comprising substituted aromatic molecules in which protons are either absent, or are stabilised by molecular geometry against loss from the ionised form of the molecule.
• ⁇ protons refers to protons attached to carbon atoms next to an aromatic ring.
• aromatic molecules may be a substituted benzene of the
• R to R are selected from trihalomethyl groups
• R to R are as specified m (a) , and R s H or a halogen.
• R to R are all C 2 to C 5 alkyl groups, preferably ethyl groups.
• the voltage at which such redox chemicals undergo oxidation varies with the nature of the substituents, but can have values between 3.8 and 5.0 volts relative to Li/Li .
• the oxidised form, which is a cation, must be sufficiently stable that it can diffuse through the electrolyte to the other electrode where it is reduced back to its original, unionised, form before it undergoes any competing reactions.
• the electrolyte will comprise other ingredients, in particular a salt, and an organic liquid or a polymer.
• a salt for example it might comprise a solution of lithium hexafluorophosphate (1 molar) in a solvent comprising a mixture of organic carbonates such as ethylene carbonate, propylene carbonate, diethylcarbonate and/or dimethyl- carbonate.
• a polymer consisting principally of vinylidene fluoride, with a plasticizer such as propylene carbonate and a salt such as lithium perchlorate, which form a gel-like solid electrolyte.
• the redox chemical must be sufficiently soluble in the other organic ingredients, and it must be able to diffuse through the thickness of the electrolyte.
• the invention also provides a rechargeable cell including an electrolyte as specified above.
• the active cathode material is typically LiCo0 2 ,
• LiNi0 2 , LiMn0 2 , or LiMn 2 0 4 which operate at least partly in the range above .4.0 V, or mixtures of such oxides, or mixed oxides.
• the active anode material might be metallic lithium
• the use of graphitic carbon (which can insert lithium to form LiC 6 ) is preferred, as it avoids the potential hazards of metallic lithium.
• Figure 1 shows cyclic voltammograms for electrolyte with and without a redox chemical
• Figure 2 shows graphically the variation of cell voltage with charge during the first charge/discharge cycle, for test cells with and without a redox chemical
• Figure 3 shows graphically the variation of stored charge with cycle number for the said test cells, after repeated overcharging.
• the electrolyte was a mixture of organic carbonates such as propylene carbonate and diethyl carbonate (PC,
• the graph shows as broken lines the variations of current with voltage for the two tests, and as a solid line the difference between the two currents. It is evident from the difference that there is an oxidation peak at around 4.5 V, and that this is associated with a reduction peak at about the same voltage on the reverse sweep. This reverse peak shows that the oxidation of the hexaethylbenzene is reversible, and that the oxidised
• (cationic) form is stable for at least about 1 s in this electrolyte.
• Test cells were made using carbon coated onto copper foil as anode, and LiCo0 2 and carbon coated onto aluminium foil as cathode, the coatings including polyvinylidene fluoride (PVdF) as a binder and being on both sides of each of the foils. Electrical connection to the foils was obtained by removing the coating over a small area and spot welding an aluminium tag to the aluminium foil and a nickel tag to the copper foil. Rectangular strips of anode and cathode material were then wound into a spiral with sheets of separator material between them, and encased in a metal can with an insulator on the base. The cells each had a theoretical capacity of 1400 Ah.
• PVdF polyvinylidene fluoride
• Liquid electrolytes similar to those used in the voltammetry tests were then used to fill the cells, under a partial vacuum to preventing gas bubbles remaining.
• the organic carbonate/LiPF 6 electrolyte had no additive, and in the other cells hexaethylbenzene was also included at a concentration between 0.005 mol/litre and 0.1 mol/litre; in the cell A whose behaviour is shown in Figures 2 and 3 the hexaethylbenzene was 0.058 mol/litre.
• the cells A and B were then subjected to 11.5 charge and discharge cycles at 270 mA between 2.75 V and 4.2 V, so they ended up charged.
• Cell B's capacity after charging gradually decreased from 115% of its theoretical value to 106%, and its current efficiency gradually increased from about 94.5% to about 97%.
• Cell A behaved similarly, its capacity after charging decreasing from about 113% to 107%, and its current efficiency increasing from about 98.3% to a plateau at around 99.3%.
• the cells A and B were then overcharged, cycling at 270 mA between voltage limits of 4.0 V and 5.0 V for a period of 18 hours.
• Cell B experienced 250 cycles, and cell A experienced 150 cycles.
• the voltage limits of 2.75 V and 4.2 V were then reimposed. Referring to Figure 3 this shows graphically the cell capacity for these subsequent cycles for the cells A and B; for cell A the capacity on charging is slightly higher than that on discharging, whereas for cell B the capacity on discharging was slightly higher. Cycling of cell B was terminated after 12 cycles, whereas cell A experienced over 200 cycles.

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• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• General Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• Physics & Mathematics (AREA)
• Secondary Cells (AREA)
• Investigating Or Analysing Biological Materials (AREA)
• Battery Electrode And Active Subsutance (AREA)

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• 1997
  • 1997-08-15 GB GBGB9717220.9A patent/GB9717220D0/en active Pending
• 1998
  • 1998-08-11 DE DE69804470T patent/DE69804470T2/de not_active Expired - Fee Related
  • 1998-08-11 KR KR10-2000-7001509A patent/KR100529487B1/ko not_active Expired - Fee Related
  • 1998-08-11 JP JP2000510174A patent/JP2001516130A/ja active Pending
  • 1998-08-11 TW TW087113183A patent/TW419840B/zh not_active IP Right Cessation
  • 1998-08-11 WO PCT/GB1998/002416 patent/WO1999009606A1/en not_active Ceased
  • 1998-08-11 EP EP98938791A patent/EP1012897B1/en not_active Expired - Lifetime
  • 1998-08-11 AT AT98938791T patent/ATE215268T1/de not_active IP Right Cessation
  • 1998-08-11 US US09/485,346 patent/US6387571B1/en not_active Expired - Lifetime

Patent Citations (6)

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