Chemistry: electrical current producing apparatus – product – and – With control means responsive to battery condition sensing... – Temperature control
Reexamination Certificate
2000-07-24
2001-11-20
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With control means responsive to battery condition sensing...
Temperature control
C429S231950, C429S129000
Reexamination Certificate
active
06319627
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to electrochemcial devices. Electrochemical devices are typically made of thin electrode and separator layers.
An example of such an electrochemical device is described in Kejha et al U.S. Pat. No. 5,521,023. Kejha et al. describes using a sheet of perforated plastic material along with a liquid ion-conductive polymer. The ion-conductive polymer is cured to form a solid- or semi-solid-state electrolyte composite. The perforated plastic material helps maintain the separation between the electrode layers. The liquid ion-conductive polymer by itself may not sufficiently maintain the separation between the electrode layers.
Another manner of maintaining the separation between the electrode layers is to use a separator using a co-polymer/plasticizer separation layer. The co-polymer/plasticizer layer can be laminated to electrode layers. The co-polymers of the separator will mix with co-ploymers of the electrodes. Later, the plasticizer is removed and an electrolyte solution added. The electrolyte solution provides and ion-conductive path between the electrodes. The co-polymer of the separator provides a relatively constant separation distance for the separator. The co-polymer remains not significantly soluble in the electrolyte solution, so that separation of the electrodes is maintained.
It is desired to have an improved electrochemical device.
SUMMARY OF THE INVENTION
A problem with electrochemical devices is that, under some conditions, a battery runaway can occur. A runaway is a short between the electrode layers which causes the battery to heat up. The head of the thermal runaway can cause additional damage to the battery, further reducing the impedance of the battery. Avoiding such runaway problems is especially important for lithium batteries.
In the present invention, a polymer mesh material made of a material that will melt during battery runaway is used. This material can be placed in a separator layer, electrode layer, or between the battery layers. The mesh is sized so that a solid battery material can be positioned in the mesh holes.
When the mesh material melts, the internal impedance is increased and thermal energy is absorbed to cause the melting. In effect, the holes of the polymer mesh are fused shut. This is useful during thermal runaway, abuse or other elevated temperature conditions. In a preferred embodiment, the melting temperature of the mesh is less than 150° C. but more than 100° C. to allow the battery layers to be laminated under normal lamination pressures and temperatures. Possible plastic materials for the polymer mesh include polyethylene, polypropylene, polyethylene terephthalate, and various co-polymers.
In a preferred embodiment, the mesh is made of ppolypropylene, polyethylene or a polyethylene/polypropylene co-polymer.
When a co-polymer is used in the separator that is substantially non-soluble in an electrolyte material, the separation and uniformity of the electrode layers can be effectively maintained under normal conditions without a polymer mesh. Adding the polymer mesh with the desired melting point has the advantage that thermal runaway can be avoided.
Additionally, placing the polymer mesh in an electrode layer can also help prevent the thermal runaway of an electrochemical device.
REFERENCES:
patent: 4650730 (1987-03-01), Lunquist et al.
patent: 4741979 (1988-05-01), Faust
patent: 5521023 (1996-05-01), Kejha et al.
patent: 5756230 (1998-05-01), Gao et al.
patent: 6168880 (2001-01-01), Snyder et al.
Liu Wei
Snyder Kent
Yang Zhen
Brouillette Gabrielle
Harness & Dickey & Pierce P.L.C.
Valence Technology Inc.
Wills M.
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