Focus: Titanate Cathode Materials for Li-ion Batteries

Lithium metal titanate and zironate compounds phases are currently experiencing significant interest as potential new cathode active materials for next generation Li-ion batteries. Jerry Barker (and co-workers) is the named inventor on the issued US patents covering the use of LiMTiO4 and LiMZrO4 (where M= +3 oxidation state transition metal, US#6,103,419); and Li2MTiO4 and Li2MZrO4 (where M = +2 oxidation state transition metal, US#6,720,113) materials; in these energy storage applications.

Further information about these materials and their performance in Li-ion cells may be found in the issued US patents. Links to these patents may be found here:

J.Barker et al. US#6103419; LiMTiO4 and LiMZrO4 Cathode Materials (M = V, Cr, Fe, Mn etc.)

J.Barker et al. US#6720113; Li2MTiO4 and Li2MZrO4 Cathode Materials (M= Fe, Mn, Ni, Co etc.)

The US patent covering the novel synthesis method for some of these materials may be found here:

J.Barker et al. US#6706445; Titanate and Zirconate Synthesis Method

Jerry

Focus: Hybrid-ion Batteries

Hybrid-ion cells are a new and exciting concept in energy storage technology.

Background: During charge and discharge of conventional Li-ion cells, lithium ions are shuttled back-and-forth between the two insertion-based electrode materials. These processes are well understood and characterized.

In hybrid-ion cells, a non-lithium containing cathode material is coupled with a suitable lithium-based anode material such as graphite, hard carbon or lithium titanate, Li4/3Ti5/3O4. This simple but novel approach greatly increases the number of commercially useful cathode materials. By comparison with lithium, only a limited number of sodium insertion materials have been properly characterized for use in energy storage devices.

The electrochemical system is completed by the use of a conventional lithium-based non-aqueous electrolyte. During the initial charge process, Na ions are extracted from the cathode while concurrent lithium ion insertion occurs at the negative electrode. During subsequent cell discharge, lithium ions are extracted from the negative electrode while a mixed sodium/lithium insertion reaction occurs at the positive electrode. These reactions are fully reversible and in prototype cells very long lifetimes have been demonstrated. All the electroactive lithium ions in the electrochemical system originate from the electrolyte phase.

More details on this novel energy storage concept may be found below.

Hybrid-ion: A Lithium-ion Cell based on a Sodium Insertion Material.

J. Barker et al., ESL 9, A190, (2006)

Li4/3Ti5/3O4//Na3V2(PO4)2F3: An example of a Hydrid-ion Cell based on a non-graphitic anode

J.Barker et al., JES 154, A882, (2007)

Jerry

Focus: Sodium-ion Batteries

In my opinion, sodium-ion batteries represent an important energy storage alternative to conventional lithium-ion technology. Based on initial data these batteries should offer similar electrochemical characteristics to their lithium counterparts. In addition, they may provide some significant performance advantages such as: lower material costs and improved safety performance. These properties will be particularly important in future large format uses such as automotive (EV/PHEV) and stationary applications.

Based on these facts it is somewhat surprising that so little research effort has been dedicated to the commercial development of these energy storage systems. Part of the problem is the identification of suitable Na insertion anode materials. Unfortunately, graphite (the preferred negative electrode materials in Li-ion cells) does not allow significant Na ion uptake. Recent work, however has demonstrated significant amounts of sodium may be reversible cycled in disordered, hard carbon hosts. This has allowed the creation of some novel sodium-ion chemistries.

For instance, we recently reported the preliminary performance characteristics of the Hard Carbon//NaVPO4F cell. The abstract to the work may be found here:

Barker et al; A Sodium-ion Cell based on the Fluorophosphate Compound NaVPO4F

Further details on this, and other polyanion based sodium-ion cells may be found here:

Barker et al; US Patent #6872492

Jerry

LiMnPO4 News: HPL acquired by the Dow Chemical Company

Related to the discussions regarding the LiMnPO4 active material:

Green Car Congress (Nov. 12, 2009) reports that the Dow Chemical Company has announced the transfer to Dow of collective assets from High Power Lithium, HPL. HPL was spun out from Professor Graetzel’s laboratory at the EPFL (Ecole Polytechnique Federale de Lausanne, Switzerland) in 2003 and is focused on the development of nano-structured metal oxide energy storage materials and novel electrolytes for use in next generation lithium ion batteries.

HPL brings synthesis and development of novel nano-materials, the ability to process and optimize nano-materials for use in battery electrodes and cells, comprehensive physical and electrochemical characterization facilities and screening and development of novel electrolytes and systems.

More information may be found here:

Dow Chemical Company Press Release:

http://news.dow.com/dow_news/corporate/2009/20091112c.htm

High Power Lithium website:

http://www.highpowerlithium.com/

Jerry

LiMnPO4 - The Thermal Instability of the De-lithiated Phase

Further to the entry below - the paper by Guoying Chen and Thomas Richardson (Lawrence Berkeley Labs.) on the Thermal Instability of Olivine-type LiMnPO4 Cathodes has now been published in the J. Power Sources. The abstract may be found here:

http://dx.doi.org/10.1016/j.jpowsour.2009.08.046

In essence, the paper reports that de-lithiated LixMnPO4 is thermally unstable and reactive toward a lithium-ion electrolyte. Furthermore, the total evolved heat is 884 J g−1, comparable to that produced under similar conditions by charged LiCoO2 electrodes.

This is bad news for organizations developing next generation lithium-ion batteries based on this material and comes as somewhat of a surprise. Most commentators in this sector predicted that the thermal behaviour of the LiMnPO4 olivine phase would be similar to the iron analogue, LiFePO4.

Earth - The Story so Far

For some light relief from the joys of the Battery World, please check out the following video on YouTube:

http://www.youtube.com/watch?v=2gxHcNtzFrU

I am not sure which I like best - the video from the BBC's Planet Earth TV series or the wonderful music from Prefab Sprout.

IMO - Prefab Sprout are one of the most under-rated bands in pop history. Crazy name, great music. While you are on YouTube check out some more of their music. It's well worth it.

Have Fun!!

IBM and the Battery Project 500

IBM has entered the energy storage arena.

The Battery 500 Project is part of IBM's Big Green Innovations program and has stated aims to develop rechargeable batteries for an all-electric vehicle that will boost the EV range from less than 100 miles today to as much as 500 miles.

To achieve the stated aims, clearly a step change improvement over existing energy storage technology is required. Indeed it is suggested that a 10-fold increase in energy density is necessary. This has necessitated some radical thinking - and clearly the development of battery systems way beyond simple iterative improvements over existing Li-ion technology.

According to IBM researchers the solution may lie in the development of commercial Lithium-air (Li-air) batteries. The theoretical performance of these batteries looks extremely compelling and Li-air technology has been researched at several institutions for many years.

Li-air batteries differ from Li-ion technology in that the discharge reaction depends on access to atmospheric oxygen - essentially harnessing the oxygen in air at the cathode. Since there is no requirement for a heavy and expensive cathode active material - simply a catalysed bi-functional air electrode - this feature creates an impressive advantage over Li-ion in both cost and performance.

Check out this website for a video describing IBM's Battery Project 500:

http://asmarterplanet.com/blog/2009/09/the-battery-500-project.html

So what are the problems? There remain some very difficult technical challenges ahead. The use of metallic lithium at the anode will cause significant cycling and safety issues. Many of us can recall the problems experienced with the use of metallic Li electrodes during the development of rechargeable Li//V6O13 and Li//MoS2 cells in the 1980's and 1990's. Trying to make large format batteries for automotive applications will be particularly problematic. Quite rightly, the large autos companies are simply not interested in taking a risk with safety.

In addition, the properties of the bi-functional air electrode and the associated electrolyte will require significant innovation over the existing technology.

Still......the numbers do look impressive and us battery scientists do love a challenge!!

Not all lithium phosphate (olivine) cathodes materials are (thermally) the same.....

LiFePO4 (olivine) is now well established in the industry as a safe cathode material for large format Li-ion batteries. Due to its excellent rate properties it is also useful for some power applications. The inherent safety behavior of the de-lithiated (charged) Li1-xFePO4 phase results from the thermal stability of the Fe-O-P bond configuration.

The one major drawback with the use of LiFePO4 in Li-ion systems is the modest energy density and specific energy performance. These characteristics are driven primarily by the relatively low operating voltage of the lithium insertion/extraction reactions in LiFePO4 - typically around 3.4 V vs Li.

The Mn olivine analogue, LiMnPO4, presents some important advantages over LiFePO4. Most notably, the operating voltage of around 4.2 V vs Li, suggests that the energy density of Li-ion cells based on this material should be significantly improved. Until recently the poor electronic conductivity of the LiMnPO4 phase has meant that the material utilization has been disappointing, even at relatively low discharge rates. Recent optimization work, particuarly at the Swiss-based company, High Power Lithium (HPL), has led to some fairly impressive specific capacity figures (around 150 mAh/g) at moderate discharge drain rates. This type of material performance has promised improved Li-ion energy density. So far so good........

But here's the rub.....recent studies have suggested that the thermal stability of the de-lithiated Li1-xMnPO4 is actually quite poor. To compound the problem, the thermal decomposition reaction actually results in the release of oxygen:

2 MnPO4 --> Mn2P2O7 + 0.5 O2

This is exactly what we do not want!! In addition, the reaction may occur at temperatures as low as 210oC. This is a quite a surprise, since most workers in the field (including me!!) expected the Mn phase to behave (thermally) similarly to the LiFePO4.

This work has been reported by S-W. Kim and co-workers in a recent paper published in the Journal of the Electrochemical Society (156, A635, (2009)). Similar results have also been reported by T. Richardson from the Lawrence Berkeley National Labs in the US.

In summary, these safety data may have a profound negative impact on the safety performance of commercial Li-ion cells and batteries made using LiMnPO4.

So what next? If we really want next generation of Li-ion cells to offer the holy grail of both high energy density and excellent safety performance perhaps we should consider the lithium vanadium fluorophosphate, LiVPO4F (for details, see below). This material offers both.

ATVM Loan Programs: Decisions Imminent?

August 27, 2009: XP Vehicles, Inc., a California-based electric car maker was notified by the U.S. Department of Energy (US-DOE) that their Advanced Technology Vehicles Manufacturing (ATVM) loan program application had been rejected.

Based on this outcome it appears the rest of the decisions from the US-DOE on the successful recipients of the ATVM Loan Programs are now imminent. These decisions are bound to have a profound and lasting effect on the future success of the advanced Li-ion battery industry in the US. Several US battery companies (for example, A123 Systems, Valence Technology, AltairNano and others) have applied for ATVM Loans in order to fund the large scale manufacturing of large format Li-ion batteries in the US.

LiVPO4F: The Ideal Lithium-ion Cathode Material?

It is just possible that lithium vanadium fluorophosphate, LiVPO₄F, represents the perfect cathode material choice for the next generation of lithium-ion batteries. Look at some of its characteristics:

1. Excellent Energy Density. The combination of high operating voltage (around 4.2 V vs Li) and specific capacity (theoretical , 155 mAh/g) means that LiVPO₄F based Li-ion cells will have a similar energy density to conventional lithium cobalt oxide based chemistry.

2. Inherent Safety. Accelerating rate calorimetry (ARC) tests of the reactions between delithiated LiVPO₄F and 1 M LiPF₆ EC:DEC electrolyte showed that the thermal stability of LiVPO₄F is even better than LiFePO₄.

3. Cell Lifetimes. Lithium-ion testing of LiVPO₄F shows excellent cycle life behavior. It is predicted that these cells will cycle more than 1000 times while exhibiting less than 20 % capacity fade. This is superior performance to conventional Li-ion chemistry.

4. Material Costs. Both the vanadium raw materials and the preferred synthesis method (carbothermal reduction) are low cost.

5. Large Format. The electrochemical, safety and cost properties of the LiVPO₄F make it ideal for large format applications.

Check out the links below for more details:

doi:10.1016/j.ssi.2006.04.049

10.1016/j.elecom.2008.12.052

doi:10.1016/j.jpowsour.2005.03.126

doi:10.1016/j.jpowsour.2008.08.024