I would like to thank all authors who have posted their answers to my question. As a return to your contribution, I shall update you what has progressed on this discussion. As an invited speaker, I attended the 66th ISE Annual Meeting in Taipei (9-14 Oct 2015), and made a summary of all answers and comments provided here to the audience of Symposium 5 which was all about supercapacitors and the hybrids of supercapacitors and batteries. Particularly, I had included in my talk a screenshot of this forum showing the last comment from Dr. C. M. Friend. In addition, I had proposed new terms for the electrodes in rechargeable batteries and supercapacitors, namely, positrode (=positive electrode) and negatrode (negative electrode). More details are given in the attached file (positrode&negatrode.pdf). It is pleasing that the audience responded very positively and all agree that cathode and anode are the inappropriate terminology for rechargeable batteries and supercapacitors. There was however a question that if these new terms may be followed by others in the literature. I will wait and see, but would like know if you would use these new terms in your next publication, would you?   

It is true that terms anode/cathode and positive/negative electrode have been interchangeably used in literature in case of Li-ion batteries and indeed it is confusing. May be I am wrong but in my opinion, this tradition comes from the early work in battery field, e.g., Daniell Cell where owing to redox processes on each electrode, they were designated as anode and cathode and later the 'authors'  simply followed this tradition. However, many prominent authors have used the terms positive and negative electrode instead of anode/cathode as well (ref. Ch.7 of book "Carbons for electrochemical energy storage and conversion systems" by F. Beguin & E. Frackowiak). In my opinion too, the terms positive and negative electrodes should be used in Li-ion batteries case. Hence you have picked as interesting point and authors should not confuse the two terms.

Best regards

Qamar 

Dear Sir, I agree with the ideas proposed by Mr.Ali Hajian,

Cathode  is the electron source

I differ with Mr. Ali Hajian and Mr.Ghaleb AL-Dahash. in a galvanic cell, anode is the negative terminal because it is where the current flows into "the device" (i.e. the battery cell), whereas cathode is the positive terminal since that is where the current flows out of the device. 

However, in a electrolytic cell, anode is the positive terminal where oxidation occurs and cathode is where reduction occurs.

However, in rechargeable battery, the anode become cathode and vice versa during charging process. 

Therefore, I agree with Prof George Zheng Chen that term "negative" and "positive" electrode is more proper in electrochemistry point of view. However using anode and cathode term is also not entirely incorrect. this terminology is more widely used and technically correct also because discharge is the main process we want to achieve in a battery. Even Prof John B. Goodenough, who is pioneer in Li ion battery field, also uses the anode and cathode terminology.

http://link.springer.com/article/10.1007%2Fs10008-012-1751-2

Dear Prof. Chen,  I agree with Mr. Bhattacharjya's comment.  Historically, the term anode and cathode were defined based on the transfer of electron (electrochemical reaction) occurs at the electrode surface. In electrochemistry, the anode is where oxidation (removal of electron) occurs, and the cathode where reduction (addition of) occurs, which is a common definition. We have to keep in mind that most of the electrochemical process, we do supply DC potential in to the system.  For example, Electrolysis process - At the anode, Anions (negative ions) are forced by the electrical potential to react chemically and give off electrons (oxidation), which then flow up into driving circuit.

The same definition and Terminology was applied to the Galvanic cell and Primary batteries ( only Discharge is possible, there is no charging possibilities).  When we consider the Discharge process in a battery or galvanic cell, the anode is the negative electrode from which electrons flow out towards the external part of the circuit.  Internally, the positively charge cations are flowing away from the anode.  At the cathode (positive electrode), the electrons are consumed for the reduction reaction, hence, the terminal is electron deficient, there fore it is positive electrode.

From my understanding, the term Anode and Cathode in a Galvanic cell /Primary battery is based on the electrochemical reaction occurs at the electrode surface (transfer of electron).  As long as the battery is Primary type (there is no recharge option), there is no confusion with this term anode and cathode. But in case of secondary batteries (rechargeable batteries), the term Anode and cathode will be confusing, since charging involves reversible electrochemical process.

Therefore, many battery manufacturers use the term positive electrode (anode), and negative electrode (cathode).  This terminology helps to resolve the problem of  which electrode is the anode and cathode in a secondary battery.

In conclusion, the usage of the the term Anode and Cathode is only based on the discharge process (when the early researchers invented primary batteries). 

Thank you all for the above feedbacks/answers to my question. I am still concerned with the impact of the following description on, for example, our first year postgraduate students.

This new cell was composed of a silicon/carbon anode and a lithium iron phosphate cathode. For the cell to work properly,it needs to be activated i.e. charged/discharged for a few cycles under well controlled conditions. When the cell was initially charged, on the silicon/carbon anode, reduction of lithium ion occurs to produce a combination of lithium intercalation componds with carbon together with different lithium silicides. The cathode reaction will be the oxidation of the lithium iron phosphate ....

Of course, the above is my imagination based on the use anode and cathode terms in rechargeable batteries.

Dear Nihan, thanks for your feedback with an interesting observation. Would a student with proper electrochemical background write an expression like "in the course of charging the cell, the lithium ion is reduced on the silicon/carbon anode...."?

Dear Professor Chen,

The terms anode and cathode are based on the direction of flow of electrons. Free electron always travel through the external circuit from anode to cathode. In other terms, cell anode and cathode change accordingly to whether a cell is energized or being  de- energized. For a galvanic cell (de-energized) negative plate is anode and positive plate is cathode where as for electrolytic cell (energized cell) positive plate becomes anode and negative plate becomes cathode. Irrespective of the polarity electrons always travel from anode to cathode. Because of confusion over the use of words cathode and anode, positive and negative plate is preferably used.

As others said, the terminology or sign convention we use depend mainly on whether we usually work with galvanic cells or electrolytic cells.

https://en.wikipedia.org/wiki/Anode

With rechargeable batteries there is plenty of scope for confusion, take the case of the zinc bromine RFB; in discharge a galvanic cell, in charging electrolytic. On switching from discharge to charge the anode becomes cathode and vice versa.

https://en.wikipedia.org/wiki/Zinc%E2%80%93bromine_battery

A couple of quotes from the above ZnBr2 RFB wikipedia page

- "During charging zinc is electroplated onto conductive electrodes..."

- "On discharge the reverse process occurs, the metallic zinc plated on the negative electrodes dissolves in the electrolyte"

The first line is fine to my electrolytic ear, but the second ... that zinc dissolves from a negative electrode (which according to my tankhouse experience should be the cathode) just sounds odd - even though is it correct according to battery convention as others outlined.

So I'm sure that when I try to use battery technology there's bound to be occasions when I slip into my own terminology ... and get it wrong!

Dear sir,

I am I agree with the question. Anode and cathode can not be interchanged with positive and negative electrode unless we define the process i.e. charge or discharge , particular to battery. If we consider discharge, anode is where oxidation occurs hence it is negative but when we charge it is positive electrode (reduction).  

According to IUPAC def. anode is where oxidation occurs. This definition does not consider  any information of electrons after oxidation hence we can not talk about positive and negative conventions. 

Hence in my opinion we should define the process first and then give the designations. e.g. lithium is anode in Li S battery when it is discharging. 

I hope may someone enlighten this.

Dear Mike,

Thanks for sharing your thought with the rest of us. My understanding is that a negative electrode can be an anode or a cathode, and hence enable oxidation or reduction depending on the working condition, i.e. discharging or charging. Thus, it is correct to state the following (as in Wikipedia).

The metal deposits (via reduction of a metal ion) on the negative electrode during charging, and dissolves from the negative electrode during discharging (via oxidation of the metal to form the metal ion).

However, it is incorrect to simply replace "negative electrode" in the above statement by either anode or cathode. (I mean replace by only one of these two, but not both.)

Dear George,

I would recommend to use strictly the terms 'anode' and 'cathode' to locate oxidation and reduction, respectively, in any electrochemical cell. In many cases oxidation may occur at negative potentials (dependent on the potential reference) and using the term 'pozitively charged electrode' may be very confusing in this case.

Best regards,

Franti Hartl

Dear Prof Chen,

I completely agree with your point that the terms "Negative and Positive electrodes" are the correct terminology for the terminals of a rechargeable battery. As mentioned earlier in the responses "Anode and Cathode" can be only applied to the electrodes on which "Oxidation and Reduction" is taking place, respectively (according to the fundamentals of electrochemistry, one of the first defined terms in The Electrochemistry Bible, A. J. Bard's book). This cannot be for sure applied in rechargeable batteries in which the reactions are reversed during charge and discharge.

This issue is also well depicted and described in Chapter 1 of "Handbook of Batteries" By D. Linden and Th. Reddy.

Maybe this confusion is arising up by the introduction of "Anode and Cathode" as the "Negative and Positive" electrodes in very early parts of some electrochemical texts which are going to just describe the concept of galvanic cells as well as some papers focusing on primary cells.

Thank you for raising the question, sharing it, and clarifying the confusion,

Sincerely,

Afshin

That is really a big confusion for every beginner while facing the problem. It also confuses me sometimes, and I even need take a few seconds to distinguish them while I reading literature on battery.

I think the ambiguity between anode/cathode and positive/negative is from two different subjects. One is electrochemistry, and the other is electronic industry. The cathodic and anodic reactions come from electrochemistry. “Cathode” is a cathode and the reduction reaction occurs (cathodic reactions, gain of electrons). “Anode” is an anode, the oxidation reaction (anodic reactions, loss of electrons) occurs.

“Positive” and “Negative” are idioms in the electronic industry. There are no difference for the words “cathode” and “anode” in both two areas, and they still represent the reduction reaction and the oxidation reaction, respectively. However, in a rechargeable battery, the cathode is positive electrode, a negative electrode that is an anode in the discharge process. 

I think the authors must know the really answer is. But the gap is still there, it brings about confusion for readers.

Dear Prof.Chen

The question that you notice is undoubtedly important in terms of electrochemistry. I have always dealt with the so-called classical electrochemistry (instead of chemical current sources). So naturally my views are - the cathode – is a negatively charged electrode where reduction reaction occurs. The anode - is the opposite. In Soviet textbooks on electrochemistry (and I studied this science according to these books the most actively in the 70-80-ies of the last century) when considering the chemical current sources the name of electrodes – are the opposite. Yes, during the debates with scientists working in the field of chemical current sources some confusion takes place about the electrode charge. But if the physical meaning of the processes occurring at the electrodes are taken as a basis for the consideration then everything falls into place. So it is closer to my perception the arguments and explanations of  Jianxun Song when considering this issue. Sincerely Inessa

Dear Prof. Chen

I agree with Mr. Bhattacharjya and Mr. Balasingam's comment. I personally think that the ambiguity is the result of the development of the two disciplines—physics and electrochemistry. The concept of positive and negative are applied to the former, while the term cathode and anode are widely used in the latter.

1. In galvanic cell/primary batteries or non-rechargeable batteries, it is mainly because of discharge process, therefore, positive electrode is the cathode, because the reduction reactions is the only process, whereas negative is the anode, because the oxidation is the only process. In such a situation, I think we can assume that positive=cathode and negative=anode.

2. In secondary batteries (rechargeable batteries), both charge and discharge process are exist. For discharge process, as described above, we can assume that positive=cathode and negative=anode. However, for charge process, foreign electrons flow into the negative, therefore, in the negative electrode occurs reduction reaction, and in the positive electrode occurs oxidation reactions, in another words, positive is anode and negative is cathode in this case.

When I read some references about secondary battery, I also have the same confusion. Most of them used to use cathode materials refer to the positive material. Possibly just like the previous reviewers said, "discharge is the main process we want to achieve in a battery".

In batteries use the words positive terminal and negative terminals

in the case of electrolytic cells use the words anodes and cathodes

both oxidation and reduction can occur in the positive and negative plates

for example in Pb/ acid batteries

Pb to PbSO4  and PbSO4  to Pb

Pbo to Pb So4 and PbSO4 to Pb

so also in Ni/Cd cells

in the case of Li ion systems better use the words positive plates and negative plates

in the secondary systems , oxidation and reduction occurs in the positive plates

Dear Prof. Muralidharan,

Thank you for your answer. 

Still many Li-ion battery literature mentioned LiMn2O4 as a cathode material and Carbon as a anode material... So Prof. Chen's question is that...

(1) these authors do not know the difference between anode and negative electrode, (2) they do know, but just want to follow some early mistakes made by some well known "authors", and (3) the relevant science has been rewritten by some authority (but I am not aware of it)?

Why do some authors write anode (or cathode) in place of negative (or positive) electrode when reporting rechargeable battery research? - ResearchGate. Available from: https://www.researchgate.net/post/Why_do_some_authors_write_anode_or_cathode_in_place_of_negative_or_positive_electrode_when_reporting_rechargeable_battery_research#view=55c5da145dbbbdbc918b4568 [accessed Aug 9, 2015].

Sometimes we use the words positive electrodes and negative electrodes for Li ion batteries

I agree with Dr Mingsheng Tan on this. It could be due to the different disciplines between physics and electrochemistry.

What I know is that anode undergoes oxidation but it will be a negative terminal when it comes to a voltaic cell (electrons are being released) and a positive terminal when it comes to a electrolytic cell (simply because it's connected to a positive terminal of an electric source).

For rechargeable batteries it's confusing to me as well. So I'm assuming the author are referring to the discharging process only.

It's also confusing for me as well when it comes to supercapacitors.  In journals, it is more commonly to see the usage of anode/cathode rather than positive/negative terminals. I'm assuming the authors are referring anode=positive and I don't think there's any oxidation process going in supercapacitors that is based purely on EDLC.

For example: "These capacitors using carbon as the main electrode material for both anode and cathode with organic and aqueous electrolytes are commercialized and used in day to-day applications" Simple Capacitors to Supercapacitors - An Overview by M. Jayalakshmi

What's worse is for asymmetric supercapacitors metal oxides are usually employed as cathode materials and carbonaceous materials are usually the anode. Since we know that metal oxides undergo redox on its own, based on electrochemistry, it can be either anode or cathode. So to make my life easier, I would just assume that the author is just referring to cathode=negative. No need to consider whether it's charging or discharging.

dear John

please confine  to to what is accepted

Dear George

In my opinion it can make sense to use the terms anode or cathode in cases where the author have specified whether the system is charging or discharging. For example while discussing an irreversible reaction happening at the negative electrode while charging (in this case the cathode).

I do agree that using these terms can lead to confusion and I often see that happen.

Best Regards

Steffen

there are primary cells and secondary cells

the positive electrode is anode in primary cells and the negative one is cathode

in the case of secondary systems my earlier statements hold good

This is simply about conventions used in the battery industry.

When only primary (non-rechargeable) batteries were available, the negative electrode was the anode and since it is easier to write / say the single word "anode", presumably the convention to call the negative electrode "the anode" became fixed. Then secondary (rechargeable) batteries came along and yes, the negative electrode is acting as either an anode or cathode depending on whether it is in a discharge or charge operation but the convention to call the negative electrode by the shorter term continued. I think most people using the term in the field fully understand the meanings and that technically it is ambiguous to use the terminology in this way but if everyone understands that, the convention continues (though it will be confusing for new entrants to the field). If you are writing a scientific publication then naturally you need to make it very clear what your intended meaning is.

You could have a similar debate about the use of the term "microporous".

I would like to thank all authors who have posted their answers to my question. As a return to your contribution, I shall update you what has progressed on this discussion. As an invited speaker, I attended the 66th ISE Annual Meeting in Taipei (9-14 Oct 2015), and made a summary of all answers and comments provided here to the audience of Symposium 5 which was all about supercapacitors and the hybrids of supercapacitors and batteries. Particularly, I had included in my talk a screenshot of this forum showing the last comment from Dr. C. M. Friend. In addition, I had proposed new terms for the electrodes in rechargeable batteries and supercapacitors, namely, positrode (=positive electrode) and negatrode (negative electrode). More details are given in the attached file (positrode&negatrode.pdf). It is pleasing that the audience responded very positively and all agree that cathode and anode are the inappropriate terminology for rechargeable batteries and supercapacitors. There was however a question that if these new terms may be followed by others in the literature. I will wait and see, but would like know if you would use these new terms in your next publication, would you?   

To start with introduce in class rooms 

While. Making ppt use both terminologies

In redox flow batteries, for example, two different electrolytes are used. The same is also true for many electrolytic processes such as that used in the Chloralkali process.

To Annette Foelske-Schmitz: Thank you for sending me your comment via the RG MESSAGES. I copy it below so that your comment is shared with everyone here.

********

sorry for the late response, but I would go for positive and negative electrode. Makes sense for LIBS, EDLCs and FCs, anode and cathode are confusing if battary and fuel cell people talk to each other.

Kind regards,

Annette 

Dear Prof Chen, 

I agree with your suggestions of introducing positrode and negatrode wrt supercapacitors and rechargeable batteries. These new terms would reduce confusion.

But, rather than cathode and anode terms being inappropriate for use, it's that the terms are being used inappropriately, as mentioned by many here. If they are used correctly, at least with info on charging/discharging state, then they can be used in conjunction with negatrode and positrode. However, a similar situation arises in the presence of reverse charging...

Regards,

Oliver

Good to have the discussion here. It is inappropriate to use cathode and anode for rechargeable batteries, especially rechargeable Li-ion batteries. Let's do it now.

Thanks Dr. Chen for raising such questions.

This usage originates from the traditional batteries. When extended to rechargeable batteries, it can only stand for the discharge process. I agree to use

negative (or positive) electrode for rechargeable batteries and supercapacitors, more accurate and meaningful.