Sunday 26 September 2010

Lithium Vanadium Phosphate

I noticed recent press releases from GS Yuasa describing its efforts in developing lithium vanadium phosphate cathode materials for next generation Li-ion applications. A good link to this may be found at the Green Car Congress website:

GS Yuasa Prototypes Li-ion Batteries with Vanadium Phosphate Cathode Material

Nothing is disclosed by GS Yuasa about the precise chemical nature of this vanadium phosphate active material. The best known phase in this area is the monoclinic Nasison phase, Li3V2(PO4)3. This material promises to deliver safe, large format Li-ion batteries with improved energy density and rate performance over LiFePO4. Clearly the use of this material in Li-ion applications has been covered in numerous issued patents assigned to Valence Technology Inc., so it will be interesting to find out more about the GS Yuasa chemistry.

It will be intriguing to see how this progresses.

Jerry

Li2FeP2O7: A Potential New Active Material for Lithium-ion Batteries?

A article in JACS by Nishimura and co-workers recently caught my eye. The paper describes the promising electrochemical lithium insertion characteristics of the lithium iron diphosphate material, Li2FeP2O7. The link to the paper may be found here:

New Lithium Iron Pyrophosphate as 3.5 V Class Cathode for Lithium Ion Battery

The iron diphosphate demonstrates a reversible specific capacity of around 110 mAh/g at an operating voltage of about 3.5 V vs Li. These are encouraging characteristcs and when combined with the anticipated low cost and good thermal safety, this cathode material may represent an excellent choice for incorporation into large format Li-ion devices. I guess it could even challenge LiFePO4 in some limited applications.

The Li2FeP2O7 material actually represents just one example of a class of lithium metal diphosphates, Li2MP2O7 (where M = Fe, Co, Ni, Mn etc.). The use and preparation of these materials was first recognized in the following issued US patent (Inventors: Barker and Saidi, filed April 2003):

US#7008566: Oligo Phosphate-based Electrode Active Materials

I will wait with great interest to see the developments in this field. Clearly some of the analog materials such as Li2MnP2O7 may offer improved electrochemical behavior over the Fe phase. Will it be possible to extract both lithium ions from the structure?

Jerry