Electricity: electrical systems and devices – Electrolytic systems or devices – Double layer electrolytic capacitor
Reexamination Certificate
2001-08-24
2003-10-07
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Double layer electrolytic capacitor
C361S503000, C361S504000, C361S512000, C361S526000
Reexamination Certificate
active
06631072
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a charge storage device and a method of manufacture thereof.
The invention has been developed primarily for use with the electrochemical charge storage devices such as supercapacitors and will be described hereinafter with reference to that application. It will be appreciated that supercapacitors are designated by terms such as ultra capacitors, electric double layer capacitors and electrochemical capacitors, amongst others, all of which are included within the term “supercapacitor” as used within this specification.
It is known to mass produce supercapacitors that have specific operational characteristics that fall within well defined ranges. Although mass production is advantageous from a cost point of view, there is an inherent lack of flexibility. That is, if the desired characteristics of a supercapacitor for a particular application fall outside the commonly available ranges a compromise solution is required. An alternative is to produce the desired supercapacitor as a one off or small run. The costs of this latter alternative are often prohibitive and, as such, rarely pursued.
Known supercapacitors generally find application in power supplies such as uninternuptible power supplies for computers or backup power supplies for volatile memory. Accordingly, it has been common to optimise these supercapacitors for high energy density, low self-discharge rates, and low cost.
More recently it has been thought that supercapacitors are theoretically applicable to high power pulsed applications. Indeed, some attempts have been made to adapt such supercapacitors as short term current sources or sinks. Examples of such applications include internal combustion engine starting, load power leveling for hybrid vehicles and a variety of pulsed communication systems. However, the success of these supercapacitors has been limited by factors such as a high equivalent series resistance, among others. For example, some prior art double layer capacitors make use of button cell or spiral wound technology. These, in turn, fall generally in one of two groups, the first group being concerned with high power applications and the second with low power applications. For the second group, but not the first, it has been possible to obtain high energy densities.
The first and second groups are broadly defined by the type of electrolyte used, those being aqueous and non-aqueous respectively. This is predominantly due to the lower resistance inherently offered by aqueous electrolytes which makes it better suited to high power, and hence high current, applications. That is, the low resistance results in lower I
2
R losses for aqueous electrolytes. The trade off, however, is that for these aqueous electrolytes the voltage that can be applied across a capacitive cell is extremely limited.
The second group of prior art double layer capacitors suffers the converse disadvantages. That is, while they provide a greater voltage window, which improves the available energy density, they also have had high internal resistances which make them unsuitable to the high power applications.
SUMMARY OF THE INVENTION
It is an object of the present invention, at least in the preferred embodiments, to overcome or substantially ameliorate one or more of the disadvantages of the prior art, or at least to provide a useful alternative.
According to a first aspect of the invention there is provided a charge storage device including:
a first electrode;
a second electrode being opposed to and spaced apart from the first electrode;
a porous separator disposed between the electrodes;
a sealed package for containing the electrodes, the separator and an electrolyte in which the electrodes are immersed; and
a first terminal and a second terminal being electrically connected to the first electrode and the second electrode respectively and both extending from the package to allow external electrical connection to the respective electrodes, wherein the gravimetric FOM of the device is greater than about 2.1 Watts/gram.
Preferably, the gravimetric FOM of the device is greater than about 2.5 Watts/gram. More preferably, the gravimetric FOM of the device is greater than about 3 Watts/gram. Even more preferably, the gravimetric FOM of the device is greater than about 3.5 Watts/gram. In some embodiments, the gravimetric FOM of the device is greater than about 5 Watts/gram.
More preferably, the first electrode and the second electrode form a capacitive cell and the device includes a plurality of the cells electrically connected in parallel and disposed within the package. In other embodiments, however, the cells are connected in series. In still further embodiments a combination of series and parallel connects are utilized. It will be appreciated that series connections allow the cells to be applied to higher voltage applications, while parallel connections allow the cells to provide a higher combined capacitance for the device. The ease at which these different connections are accommodated by the invention means that preferred embodiments are applicable to a wide variety of tasks ranging from high power systems to low power systems.
In a preferred form, the maximum operating voltage of the or each capacitive cell is less than about 4 Volts. More preferably, the maximum operating voltage of the or each capacitive cell is less than about 3.5 Volts. Even more preferably, the maximum operating voltage of the or each capacitive cell is less than about 3 Volts.
Preferably, the first electrode and the second electrode include a first carbon coating and a second carbon coating respectively wherein the surface area of carbon used in the coatings is greater than 20 m
2
/gram.
According to a second aspect of the invention there is provided a method of manufacturing a charge storage device, the method including the steps of:
providing a first electrode;
disposing a second electrode in opposition to and spaced apart from the first electrode;
disposing a porous separator between the electrodes;
containing within a sealed package the electrodes, the separator and an electrolyte, wherein the electrodes are immersed in the electrolyte; and
electrically connecting a first terminal and a second terminal to the first electrode and the second electrode respectively such that the terminals extending from the package to allow external electrical connection to the respective electrodes, wherein the gravimetric FOM of the device is greater than about 2.1 Watts/gram.
Preferably, the gravimetric FOM of the device is greater than about 2.5 Watts/gram. More preferably, the gravimetric FOM of the device is greater than about 3 Watts/gram. Even more preferably, the gravimetric FOM of the device is greater than about 3.5 Watts/gram. In some embodiments, the gravimetric FOM of the device is greater than about 5 Watts/gram.
More preferably, the first electrode and the second electrode form a capacitive cell and the device includes a plurality of the cells electrically connected in parallel and disposed within the package. In other embodiments, however, the cells are connected in series. In still further embodiments a combination of series and parallel connects are utilised.
In a preferred form, the maximum operating voltage of the or each capacitive cell is less than about 4 Volts. More preferably, the maximum operating voltage of the or each capacitive cell is less than about 3.5 Volts. Even more preferably, the maximum operating voltage of the or each capacitive cell is less than about 3 Volts.
Preferably, the first electrode and the second electrode include a first carbon coating and a second carbon coating respectively wherein the surface area of carbon used in the coatings is greater than 20 m
2
/gram.
According to a third aspect of the invention there is provided a charge storage device including:
a fist electrode;
a second electrode being opposed to and spaced apart from the first electrode;
a porous separator disposed between the electrodes;
a sealed package for containing the electrodes, the separator and an e
Jones Philip Andrew
Keshishian Sarkis
Mahon Peter John
Pandolfo Anthony Gaetano
Paul George Lange
Energy Storage Systems PTY LTD
Ha Nguyen
Kenyon & Kenyon
Reichard Dean A.
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