Electrolyte for a rechargeable cell

• US 6,387,571 B1
• Filed: 02/08/2000
• Issued: 05/14/2002
• Est. Priority Date: 08/15/1997
• Status: Expired due to Term

• Current Assignee: Nexeon Limited
• Original Assignee: Accenture PLC
• Inventors: Lain, Michael Jonathan, Neat, Robin John
• Primary Examiner(s): KALAFUT, STEPHEN J
• Application Number:
  US09/485,346
• Time in Patent Office: 826 Days
• Field of Search: 429/324, 429/326, 429/347, 429/303
• US Class Current: 429/303
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 10/0565 Polymeric materials, e.g. gel-type or solid-type
• CPC Class Codes: H01M 10/0567 characterised by the additives
• CPC Class Codes: H01M 10/4235 Safety or regulating additives or arrangements in electrodes, separators or electrolyte H01M10/4242 takes precedence
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

An electrolyte for use in a rechargeable cell whose charging voltage exceeds 3.8 volts includes a redox chemical comprising a substituted aromatic molecule in which α hydrogens are either absent, or are sterically against loss from the ionized form of the molecule. Such as chemical can act as a redox shuttle during overcharge, suppressing damage to the cell and preventing the deposition of metallic lithium during the overcharge of a lithium ion cell, but does not affect normal operation of the cell during either charge or discharge. One such molecule is hexaethyl benzene.

Claims

1. An electrolyte for use in a rechargeable lithium or lithium ion cell whose voltage exceeds 3.8 volts during charging, the electrolyte comprising a lithium salt in solution in an organic solvent, the electrolyte also comprising an organic polymer, so it is a polymeric gel electrolyte, wherein the electrolyte includes a redox chemical comprising substituted aromatic molecules in which there are a protons, and the a protons are stabilized by molecular geometry against loss from the ionized form of the molecule.

2. An electrolyte as claimed in claim 1 wherein the redox chemical is at a concentration between 0.005 mole/liter and 0.1 mole/liter.

3. An electrolyte as claimed in claim 1 wherein the solvent comprises at least one organic carbonate.

4. A rechargeable cell including an electrolyte as claimed in claim 1.

5. A rechargeable cell as claimed in claim 4 including an anode comprising carbon, a cathode comprising an oxide of a transition metal, such that lithium ions can be reversibly intercalated into both the carbon of the anode and the oxide of the cathode, the anode and the cathode being separated by the electrolyte.

9. An electrolyte as claimed in claim 1 wherein the redox chemical is at a concentration between 0.005 mole/liter and 0.1 mole/liter.

6. An electrolyte for use in a rechargeable lithium or lithium ion cell whose voltage exceeds 3.8 volts during charging, the electrolyte comprising a lithium salt in solution in an organic solvent, wherein the electrolyte includes a redox chemical comprising a substituted benzene of the general formula C₆R¹R²R³R⁴R⁵R⁶ in which:

a) R¹ to R⁶ are selected from trihalomethyl groups, C₂ to C₁₀ alkyl groups, or halogen-substituted C₂ to C₁₀ alkyl groups;

or

b) R¹ to R⁵ are as specified in (a), and R⁶ is H or a halogen,

so that α

protons are either absent, or are stabilized by molecular geometry against loss from the ionized form of the molecule.

7. An electrolyte as claimed in claim 6 wherein R¹ to R⁶ are all C₂ to C₅, alkyl groups.

8. An electrolyte as claimed in claim 7 wherein R¹ to R⁶ are all ethyl groups.

10. An electrolyte as claimed in claim 6 wherein the solvent comprises at least one organic carbonate.

11. An electrolyte as claimed in claim 6 also comprising an organic polymer, so it is a polymeric gel electrolyte.

12. A rechargeable cell including an electrolyte as claimed in claim 6.

13. A rechargeable cell as claimed in claim 12 including an anode comprising carbon, cathode comprising an oxide of a transition metal, such that lithium ions can be reversibly intercalated into both the carbon of the anode and the oxide of the cathode, the anode and the cathode being separated by the electrolyte.