When you look for the electrode material, two main points are amount of energy that can be stored by the unit mass/volume and stability during cycling. Both parameters look not very good at first sight. Relatively big molar mass of FeCl3 will lead to the low energy density.

And problem with stability will appear because of the huge volume change. Already stage 6 compound has almost 30% expansion along c axis (Carbon, Vol. 36, No. 4, pp. 383-390) and for the stage 2 phase size along c will be almost twice larger. Due to resulting mechanical tension the graphite particles might break apart from the electrode during cycling.

This does not make such type of electrodes completely impossible (people work a lot on silicon anodes, where volume change is even larger), but the problem will not be easy to overcome.

Thank you very much as I had not considered the volume change. I see the main advantage as the Graphite Ferric Chloride is a good conductor better than graphite. Iike to see data on the PO4 compounds used as to conductivity. Do you know of any work that has examined Graphite FeCl3 Can you help? THANKS

FJS

Your concern about volume is valid. However, in regard to expansion the Graphite Ferric Chloride would be loaded in to the battery system in the fully expanded form along with the Graphite Lithium Anode and the battery would be in the fully charged condition when fabricated. 

You have to examine possibility of  oxidation of Cl- during charge-discharge operation.

Has any one examined the potential value Graphite Ferric Chloride as a Cathode to date.

Dear Francis,

I totally agree with Alexander and Indra, FeCl3-intercalated graphite would not be the wisest of choices. In my opinion you have to consider the following points:

-FeCl3 might be soluble in carbonate based electrolytes (I haven't checked the Carbon paper cited by Alexander at this time so I don't really know what did they use)

-the presence of FeCl3 might compromise stability of both electrolyte salt (generally LiPF6) and intercalated phase (Li+ might both attract Cl- or might compromise electrical stability due to the possibility of Fe reduction)

-consider solid electrolyte interphase (SEI) formation (are you familiar with this?): I suppose FeCl3 intercalated graphite has a bigger interplanar distance than Li+ intercalated graphite so what will happen to the electolyte when one reaches 1-0.7V?

-another issue: will an intercalated species intercalate something more? In other words: are crystalline sites still available for Li+ (take also into account electrostatic repulsion)?

- cathodic behavior might not be working at all since graphite intercalation takes place practically at 0-0.5 V vs Li+/Li so it acts almost as metallic Li. When you go, let's say to 3 to 4 V, graphite will not be active. You might not even have Fe oxidation because it starts already at +3 state (unless you discharge first and it is somehow reduced, hopefully not to metallic Fe, see comment n°2)

Hope this helps.

All the above opinions are of great value. I thank you for your responses.  If I change the subject a little  and ask the question, " will FePO4 work as a Battery Cathode in a Lithium Ion battery", what are your individual opinions?  Secondly, what happens if I add Li to the FePO4?  Again I welcome your responses.

Dear Francis,

Of course FePO4 works...but there's nothing new in it, the LiFePO4/FePO4 system is one of the most studied electrode materials EVER...not sure you can find something which has not been done yet.

If you want the technical answer, FePO4 is the charged state of LiFePO4 so it would not be possible to use it as such since you have to put some Li inside first (this way it automatically loses all interest). LiFePO4 on the other hand, is good and reliable provided it's nano and fully covered with carbon...but, as I said, almost everybody on the planet has been working with it so...

Hope this helps.

• Can you please comment on the Link, http://www.pubfacts.com/detail/24339264/Ferric-chloride-graphite-intercalation-compounds-as-anode-materials-for-Li-ion-batteries.
• and, https://www.deepdyve.com/lp/wiley/ferric-chloride-graphite-intercalation-compounds-as-anode-materials-RyTZZL0FTw
• Thank you

Dear Francis,

as soon as I'm able to get the paper...there's a problem with chemsuschem website...

I await you comments.

Can anyone give  me two consistent  values for the Gibbs Free energy of formation of  Ferrous Phosphate and Ferric Phosphate. I have searched with no luck.

Anxious to hear from you. I have read Dr Lillie Wang and associates paper titled "Ferric Chloride -Graphite Intercalation Compounds As Anode Materials for Lithium Ion Batteries" and found it very interesting and it perhaps opens the door to encourage further work on Graphite  Ferric Chloride material. very much like to hear your comments.  

Why is it not possible to find a value for the Gibbs's Free Energy of Formation for Ferric and Ferrous phosphate. These are  materials widely used in Lithium ion Batteries.