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Process for improving lithium ion cell
| Details |
Inventors: Chi, Ignacio; Ramaswami, Karthik; Kuo, Han C.; Todino, Christa;
Assignee: Duracell inc. (Bethel, CT)
Primary Examiner: Skapars; Anthony
Assistant Examiner:
Attorney, Agent or Firm: Douglas; Paul I., Josephs; Barry D.
The efficacy of a passivating layer in a rechargeable lithium ion cell is increased by heating the charged cell and storing the charged cell for a pre-determined period of time. |
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DETAILED DESCRIPTION In practicing the process of this invention, a passivating layer, which is the solid-electrolyte interface, is formed at the surface of one or both electrodes by the side reactions which take place when the lithium cell is charged.
The charged lithium cell is aged at a temperature of between about 20.
degree.
C.
and about 75.
degree.
C.
for a period of time sufficient to increase the efficacy of the passivating layer.
The temperature at which the charged lithium cell is maintained will vary depending upon the non-aqueous solvent used, the electrolyte used, and the composition of the anode and the cathode.
These compositional factors contribute to a determination of the optimum temperature and time at which the secondary lithium cell is stored.
Generally speaking, in order to increase the efficacy of the passivating layer of a charged lithium cell, the charged cell may be maintained at a temperature of from about 20.
degree.
C.
to about 65.
degree.
C.
for a period of time of from about one hour to about two months.
For example, when the anode is a synthetic or natural graphitic carbon, the cathode is a lithiated metal oxide, the electrolyte salt is lithium hexaflourophosphate and the solvent is ethylene carbonate, the cell, after charging, may then be stored at a temperature of from about 45.
degree.
C.
to about 60.
degree.
C.
for a period of time of from about one hour to about seventy two hours in order to increase the efficacy of the passivating layer for increasing the heat stability of the rechargeable lithium cell.
Any rechargeable lithium cell, whether previously used or first being charged, may have the efficacy of its passivating layer increased to increase the heat stability of the cell by practicing the process of this invention.
In order to effectively practice the process of this invention, the cell, before being subjected to the process of this invention, must have been charged to between 10% of its maximum acceptable charge to about 100% of the cell's maximum acceptable charge
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