The difference between pseudocapacitive and battery-like behaviour is simply that the former is still capacitive and hence featured by rectangular CVs and linear GCDs, whilst the latter always presents peak-shaped CVs and non-linear GCDs.

It is unfortunate that some authors had incorrectly linked peak-shaped CVs to pseudocapacitance, which caused confusion in the literature.

I shall mention that both mechanisms are faradaic in nature, but one is capacitive (resulting from electron transfer in and from the conduction band like that in a semiconductor) and the other is Nernstian (resulting from electron transfer to and from isolated energy levels like that in a molecule dissolved in solution, or in a redox active but poorly conducting or insulating material.)

Dear Mr Sahoo,

Some authors are suggesting that pseudocapacitors based on materials which exhibits battery-like behavior involve both capacitive faradaic storage with non-capacitive faradaic storage should be called supecapattery (as a hybrid material combining both pseudocapacitor and battery) The subject is fairly new so I suggest to look at these papers for more insight.

I hope that it will help you.

L. Guan et al. Capacitive and non-capacitove faradaic charge storage Electrochim. Acta

http://www.sciencedirect.com/science/article/pii/S0013468616302389

B. Akinwolemiwa et al. Redox Electrolytes in Supercapacitors J. Electrochem. Soc.

http://jes.ecsdl.org/content/162/5/A5054.full

http://www.sciencedirect.com/science/article/pii/S0013468616302389

http://jes.ecsdl.org/content/162/5/A5054.full

Dear Adam Moyseowicz,

Thank you for your recommendation of our publications.

In addition, I shall mention that  the late Prof. Conway had long ago criticised the use of electrode materials with battery-like performance, e.g. peak-shaped CVs and non-linear GCDs, for capacitance analysis. The citation of Conway's original paper is given below.

B.E. Conway, Transition from supercapacitor to battery behavior in electrochemical energy-storage, Journal of the Electrochemical Society 138 (1991) 1539–1548.

George Chen 

Thanks Dr. Adam Moyseowicz for your answer. My question is there any fundamental diffrence between a pseudocapacitor and a battery mterial?

I think that each material should be considered separately, like pseudocapacitive materials based on conductive polymers differs from the metal oxides or hydroxides. In my opinion I would stay with the nomenclature of pseudocapacitors for materials that gives response for non-faradaic and faradaic capacitive behavior in contrary to materials with sharp and strong CV response in a narrow potential range like it is observed for batteries. Although I found this division very subjective, so maybe more experienced researchers could state their opinion and help you with this matter.

Adam Moyseowicz

Thank you Dr. Morseowich.

Thank you Dr. Chen for your answer.

The difference between pseudocapacitive and battery-like behaviour is simply that the former is still capacitive and hence featured by rectangular CVs and linear GCDs, whilst the latter always presents peak-shaped CVs and non-linear GCDs.

It is unfortunate that some authors had incorrectly linked peak-shaped CVs to pseudocapacitance, which caused confusion in the literature.

I shall mention that both mechanisms are faradaic in nature, but one is capacitive (resulting from electron transfer in and from the conduction band like that in a semiconductor) and the other is Nernstian (resulting from electron transfer to and from isolated energy levels like that in a molecule dissolved in solution, or in a redox active but poorly conducting or insulating material.)

Thank you Dr. Chen. Then, MnO2 and RuO2 are the only TMOs which exhibit pseudocapacitive property. Co, Ni oxides are  not pseudocapacitor?

Dear Reamkrishna Sahoo,

Almost all redox active transition metal oxides can exhibit some degree of pseudocapacitance.

It is in most cases the potential window that makes the difference. For example, for NiO in an alkaline electrolyte, it can present the capacitive behaviour if the potential window is limited to be narrower than 0.5 V. In a wider potential window, NiO offers a greater charge capacity, but also becomes non-capacitive.

I believe the same is true for Co-based oxides.

George Chen

Thank you very much sir for this infor mation. It will help me a lot. Will provide me some refferences about this.

pseudocapacitor term is derived due to presence of additional faradaic contribution together with mainly no faradaic charge storage in RuO2 materials. However with the progress in this field now many pseudocapacitive materials have mainly faradaic charge storage along with minor non-faradaic. however, these type of system should be called aqueous rechargeable battery. In battery field also use of nanostructured carbon and many other metal compound show minor non-faradaic contibution also along with faradaic charge storage.

Thank you Mr. Bhattacharjya, for your answer. Will you please explain it with an example. because i am little bit confused. Whether, Ni or Co based oxides/ hydroxides in aq. KOH solution are pseudocapacitors or not? if yes, then what is the diffrence from its battery behaviour in LiPF6 electrolyte.

Dear Dhrubajyoti Bhattacharjya,

I can see that you are following those authors who are unable to understand the difference between the capacitive and non-capacitive faradaic charge storage mechanisms. In other words, faradaic storage alone can be capacitive, and a proper pseudcapacitor that utilises the capacitive faradaic storage mechanism is NOT the same as a battery.

Dear Ramkrishna Sahoo,

In most reported studies of Ni or Co based oxides/ hydroxides in aq. KOH solutions, the CVs are peak-shaped and hence the materials are not pseudocapacitive in the explored potential range. However, if the potential range is reduced, NiO can behave very close to a capacitor. (cf. Srinivsan V, Weidner JW, J Electrochem Soc 147 (2000) 880.) My expectation is that Co based oxides can also show capacitive behaviour in a proper potential range. However, in the wide potential range explored in the literature, it is clear that these materials are  not capacitive but behave more like a battery electrode. Consequently, it is inappropriate to associate these materials with capacitance, and the claimed very high specific capacitance values are mostly misleading.

I agree with George Zheng Chen,

In addition to his answer, I like to add one more point that will help to understand what type of material it is. The boundary between pseudocapacitor and battery is very thin. In order to distinguish the type of materials, you must observe the Ragone plot of your result. The Ragone plots can distinguish the materials in a precise manner.

Thank you Mr. Patil. Will you plesase elaborate your anwer regardig ragone plot?

Thank you Dr. Chen for your valuable answer.

Dear Ramkrishna Sahoo, 

Please look at the Ragone plots in the following articles. 

http://pubs.rsc.org/en/Content/ArticleLanding/2014/EE/c4ee00960f#!divAbstract

http://www.nature.com/nmat/journal/v7/n11/full/nmat2297.html

http://pubs.rsc.org/en/Content/ArticleLanding/2011/NR/c0nr00594k#!divAbstract

The Ragone plot itself shows the relationship between power density (kW/L) and energy density (Wh/L) or specific power (kW/kg) and specific energy (Wh/kg) of a device, either battery or supercapacitor, and hence cannot differentiate between the capacitive and non-capacitive charge storage mechanisms.