New Metal-Oxide Enhanced Iron Phosphate Material Offers Higher Energy Density

9 June 2009

Capacity of one of the LFP-NCO formulations. Source: Aleees. Click to enlarge.

Taiwan-based Advanced Lithium Electrochemistry (Aleees = Always Leading & Everlasting Energy for the Earth & uS) has developed a new iron phosphate (LFP) material for use in a lithium-ion battery cathode. The patent-pending LFP-NCO (Nano-Co-crystalline Olivine) LiFePO₄·zMO' (M'O = metal oxide) material is designed to address the low conductivity problem of traditional iron phosphate materials, reduce impurities in LiFePO₄, maintain the material consistency and offer an attractive price-performance ratio.

Dr. Pin-Jiun Wu, of Aleees and Taiwan’s National Synchrotron Radiation Research Center, presented the material during the Advanced Automotive Battery 2009 (AABC 2009) symposia and conference this week in Long Beach, California.

Iron phosphate as a cathode material offers a number of benefits, including greater environmental friendliness, low price, non-toxicity and exceptional stability, along with a theoretical specific capacity of 170 mAh g^-1. However, the material is challenged by poor rate performance because of a low electronic conductivity as well as material purity.

Other approaches to address the rate performance issue include minimizing the particle size to improve the kinetics and enhancing electronic conductivity through techniques such as doping or the addition of a conductive agent, such as using a carbon coating.

Aleees takes a different approach. The LFP NCO is a non-dividable single compound synthesized through a simultaneous crystallization process with compounds of lithium, iron, phosphate and metal as precursors to form at least two coexistent and interdependent crystalline structures. No doping or coating is involved in the production procedure, thereby making it simpler and less expensive, according to Aleees.

The prepared materials consist of an olivine phase base secondary crystallite particles with the surface area under 15 m²/g. The LFP-NCO composite has a fine and uniform particle size (mean particle size < 6µm, D95 in volume distribution < 10µm). High-resolution tunneling electron microscopy observation and energy dispersive spectroscopy, electron energy loss spectroscopy (EELS) mapping show the homogeneous distribution of metal oxide in the LFP-NCO crystal grain.

The carbon-coated LFP-NCO materials can improve the electro-conductivity significantly compared to that of pure LiFePO₄. Dr. Wu presented data showing electroconductivity of

compared to conductivity on the order of 10^-9 for pure LiFePO₄.

LFP-NCO exhibits a specific initial discharge capacity of about 155 mAh g^-1 at C/10 rate, 130 mAh g^-1 at 2C.