Final Report: Combustion Synthesis of Nanoparticle Metal Phosphate Cathode Materials for Improved Lithium Ion BatteriesEPA Contract Number: EPD04033
Title: Combustion Synthesis of Nanoparticle Metal Phosphate Cathode Materials for Improved Lithium Ion Batteries
Investigators: Evenson, Carl R.
Small Business: Eltron Research & Development Inc.
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2004 through August 31, 2004
Project Amount: $69,999
RFA: Small Business Innovation Research (SBIR) - Phase I (2004) RFA Text | Recipients Lists
Research Category: Nanotechnology , SBIR - Nanotechnology , Small Business Innovation Research (SBIR)
This research project focused on the production of nanoparticle metal phosphates for improved lithium ion battery cathodes. Nickel-cadmium batteries have a significant worldwide environmental impact because of improper disposal. As a consequence, toxic heavy metals such as nickel and cadmium are released into the environment and have severe adverse affects on humans. Lithium ion batteries are slowly replacing nickel-cadmium batteries in many applications; however, new cathode materials are needed to further increase the efficiency and lower the cost of lithium ion batteries to completely replace nickel-cadmium batteries. Doped and undoped metal phosphates offer an alternative battery cathode material in both lithium ion batteries and potentially multivalent cation batteries. Nanoparticle phosphates offer the possibility of increased lithium ion intercalation for improved efficiency, low cost, and minimal environmental impact. A modified combustion synthesis method was used to synthesize metal phosphate ceramic particles in the range of 10-50 nm. Particles were characterized with x-ray diffraction, surface area measurements, and scanning electron microscope analysis. Finally, the ability of the nanoparticle phosphates to intercalate lithium cations was tested and compared to larger particle analogs synthesized by traditional ceramic processing methods.
Eltron Research, Inc., produced two different phosphate battery cathode materials using a modified combustion synthesis method. By varying the synthesis conditions, surface areas of the product ranged from 61 to 168 m2/g. Scanning electron microscopy showed an agglomerated powder product with particle sizes ranging from 12 nm to 33 nm. Equivalent powders also were prepared by traditional solid-state processing. The powders produced by solid-state methods had lower surface areas, ranging from 3.8 to 11.8 m2/g, and particle sizes between 0.17 and 0.53 μm.
Powders prepared by combustion and solid-state methods were characterized by two different methods to demonstrate the advantages of nanoparticles over micron-sized particles. First, lithium was intercalated into the prepared materials by reduction with n-butyllithium. Results showed that high surface area nanoparticle powders intercalated 34.5 percent more lithium than the equivalent micron-sized powder. Secondly, lithium ion battery cathodes were prepared using tape casting techniques. Coin cells were assembled and tested to determine the specific capacity of the prepared phosphate cathode materials. Results showed that nanoparticle phosphates had a specific capacity 42 percent higher than the equivalent micron-sized powder prepared by solid-state synthesis. The benefit of doping was demonstrated by showing that nanoparticle powder doped with a small amount of a different metal had a specific capacity 31 percent higher than the undoped nanoparticle powder.
This research project clearly demonstrated that a modified combustion synthesis can be used to prepare single-phase nanoparticle phosphates for lithium ion battery applications. Intercalation and battery testing results showed the benefit of nanoparticle cathode materials compared to micron-sized powders. Combustion synthesis is a low-cost synthetic method that is easily scalable for commercial production. High surface area phosphate battery materials have significant market potential in lithium ion secondary battery cathode applications, including cell phones, PDAs, laptop computers, and digital cameras. The small particle sizes achievable with combustion synthesis will allow maximizing lithium ion battery capacity and lifetime, while minimizing production costs. In addition, phosphate materials are environmentally friendly, and this synthesis method can easily be modified to produce other phosphate-based battery materials for applications such as multivalent cation batteries.