US 7,227,737 B2Granted

Electrode design

AssigneeMaxwell Technologies, Inc.

InventorsPorter Mitchell, Xiaomei Xi, Linda Zhong, Bin Zou

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Abstract

Electrodes of a double-layer capacitor are designed so that sub-capacitors formed at each electrode are stressed substantially equally at the rated voltage of the double-layer capacitor. In an exemplary embodiment, each electrode includes a current collector and an active electrode layer, such as a layer of activated carbon. The electrodes are held apart by a porous separator, and the assembly is immersed in an electrolyte. The thicknesses of the active electrode layers differ, resulting in asymmetrical construction of the capacitor. Different thicknesses cause the sub-capacitors to have different capacitances. When voltage is applied to the double-layer capacitor, the voltage is divided unequally between the unequal sub-capacitors. Properly selected thicknesses allow the voltages at the sub-capacitors to stress equally each sub-capacitor. The rated voltage of the double-layer capacitor can then be increased without overstressing the sub-capacitors.

Claims14

Dependent claims

A double-layer capacitor, comprising:

an electrolyte;
a positive electrode layer of a first thickness, the positive electrode layer being immersed in the electrolyte;
and
a negative electrode layer of a second thickness, the negative electrode layer being immersed in the electrolyte;
wherein:
a first sub-capacitor is formed at an interface between the positive electrode layer and the electrolyte;
a second sub-capacitor is formed at an interface between the negative electrode layer and the electrolyte;
and
the first and second thicknesses are selected by:
determining a positive voltage limit for the first sub-capacitor and a negative voltage limit for the second sub-capacitor;
dividing the positive voltage limit by the negative voltage limit to obtain a first ratio of the second sub-capacitor to the first sub-capacitor;
and
setting relative thicknesses of the positive electrode layer and the negative electrode layer so that capacitance of the second sub-capacitor is substantially equal to a product of the first ratio and the capacitance of the first sub-capacitor.

10 more elements

Dependencies are inferred from the claim text.

Facts

Application: 10/974,091Filed 27 Oct 2004 · continuation in part
Priority: 2 Apr 2004
Published: US 2006/0148112 A16 Jul 2006
Granted: 5 Jun 2007
Term ends: Not estimatedThe source records don’t support an estimate.

Classification27 codes

H01G 11/26
Electrodes: characterised by their structure, e.g. multi-layered, porosity or surface features
H01G 11/32
Characterised by their material: carbon-based
H01M 4/02
Electrodes: electrodes composed of, or comprising, active material
H01M 4/0404
Methods of deposition of the material: by coating on electrode collectors