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Electrochemical Supercapacitors for Energy Storage and Delivery
This process causes a slow decline of cell voltage, like a self-discharging
process.
Leaking current through short circuit pathway — Self discharging in a
series stack can occur through a short circuit pathway induced by improper
isolation of electrodes. In addition, if the cells in the stack do not have equal
capacitances, overcharging can occur on some cells resulting in self discharging. This problem requires optimized manufacturing procedures to
ensure quality control [23].
5.8 Patent Review
This section will review the patents filed in the past decade (Table 5.2) for
electrochemical ES issues such as electrode materials, electrolytes, and procedures. A wide range of electrolytes and derivative electrode materials
including electric double-layer capacitive carbons, pseudocapacitive metals
(metal oxides), and electrically conducing polymers (ECPs) will be discussed.
5.8.1 Patents on Electrode Materials
Carbon materials are widely used across electrochemical systems such as
batteries, fuel cells, and ESs and are of research interest in both academic
and industrial settings. A tremendous number of patents claim their preparation and production procedures, including the variables of carbon precursors, carbonization, and possible activation methods at various incremental
temperature rates, exposure times, and repeatable steps.
One noted patent presented by the U.S. Department of Energy (US 6,299,850
B1) describes an activation method for the carbonization of a polyimide or
other polymeric material in which an aqueous HNO 3 oxidizing agent followed
by multiple thermal treatments is used. The resulting activated carbon material
possesses a high volumetric capacitance of 300 F/cm 3 . Several commercial firms
developed similar proprietary methods in the synthesis of activated carbon.
Since the early 1990s, activation processes have expanded to include fibrous
materials to enhance accessible surface area, for example, carbon precursor polyacrylonitrile and poly(vinylidene fluoride) (PVDF) used to develop
fibers for use in electrodes. Carbon aerogels were also demonstrated by the
U.S. military to enhance capacitance through electropolymerization of various electroactive polymers [polyaniline, polyarylamine, polypyrrolepoly(omethoxyaniline)]. The production of thin polymer films (< 10 nm), particularly
with poly(-methoxyaniline), produces a negligibly changed porosity considered responsible for improved performance.
Advancements in nanomaterials have yielded recent patents that focus
on single walled and multi-walled carbon nanotubes (CNTs) and graphene