Energy pseudocapacitive materials

Summarizing the above, it may be stated that activated carbons and pseudocapacitive materials in EC electrode structure are responsible for the energy storage parameters (specific energy), while non-active highly conductive carbon additives are responsible for the electrode internal resistance (EC specific power). 

Studies on the topic of capacitive storage are oriented toward the increase in energy density of supercapacitors by working on carbon, pseudocapacitive materials and electrolytes. 

AUG 13] Augustyn V., Come J., Low M.A., et al, Evidence of intercalation pseudocapacitance in high-rate lithium-ion energy storage materials . Nature Materials, vol. 6, pp. 518-522, 2013. 

The ESs mentioned above consist of two electrodes with the same type of capacitive materials made from either EDL capacitive materials or pseudocapacitive materials (symmetrical configuration). In order to further increase the operating potential window, energy, and power density, a new type of ES has been developed, which is known as hybrid capacitors. With extensive achievements in this area, various types of hybrid ESs have been developed. Generally, hybrid capacitors utilize both the EDL capacitance and faradaic reaction to store charges. The hybrid capacitors reviewed in this book include (1) ESs based on composite electrodes made from both EDL capacitive materials and pseudocapacitive materials (2) asymmetric ESs with one EDL electrode and another pseudocapacitive or battery-type electrode and (3) asymmetric ESs with one pseudocapacitive electrode and another rechargeable battery-type electrode. 

As noted previously, the high maximum capacitance induced by these types of redox processes is nof maintained over the available voltage range, which is normally limited to 0.6 V for most materials. Further the two-dimensional surface limitation, high costs of noble and rare metals, and low available surface area reduce usefulness for energy storage compared to other pseudocapacitive materials. 

Energy storage pseudocapacitive materials that have traditionally been investigated involve transition metal oxides and conductive polymers. Despite promising results realized from both approaches, several technical and cost challenges remain to be overcome. 

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