H. M. Dahn

Impact of Binder Choice on the Performance of α-Fe2O3 as a Negative Electrode

The electrochemical performance of negative electrodes based on commercially available micrometer-sized α-Fe 2 O 3 powder and four different binders was investigated. a-Fe 2 O 3 electrodes made using sodium carboxymethyl cellulose binder and two proprietary binders show better cycling performance than electrodes made from the conventional binder, polyvinylidene fluoride (PVDF). Heat-treating the PVDF electrodes to 300°C improves electrode performance dramatically. A specific capacity of over 800 mAh/g for over 100 cycles has been achieved for Li/α-Fe 2 O 3 cells with micrometer-sized a-Fe 2 O 3 , by contrast to many teachings in the literature where it is claimed nanometer sized particles are required to obtain such performance. As is the case for composite electrodes made from powders of metal alloys, we suggest that binder choice has a great impact on the performance of metal oxide electrodes demonstrating large volume expansion during lithiation, such as α-Fe 2 O 3 .

Impact of Rare Earth Additions on Transition Metal Oxides as Negative Electrodes for Lithium-Ion Batteries

Transition metal oxides have been proposed as negative electrode material candidates for lithium-ion batteries because they can reversibly react with lithium via a displacement reaction to deliver two to three times the specific capacity of graphite. However, the practical application of transition metal oxides has been frustrated by their inconvenient working potential. Here, the impact of the addition of rare earth (RE) elements to transition metal (TM) oxides as negative electrodes was studied. Thin films of pseudobinary misch-metal-Fe-O libraries (misch metal is a mixture of common RE elements) were prepared by combinatorial sputtering methods. Powdered perovskite-structured RE-TM-O 3 samples, including LaFeO 3 , CeFeO 3 , and LaCoO 3 , were synthesized by solid-state methods. The structural and electrochemical characterizations of these samples are presented here. It was found that the addition of RE elements decreases the working potential of TM oxides. However, the specific capacity is undesirably lowered.

Fe–C–N Oxygen-Reduction Catalysts Prepared by Mechanochemical Reaction

Fe-C-N oxygen-reduction catalysts were prepared by mechanochemical reaction of Fe x N (x = 2-4) and graphite under Ar using high-energy ballmilling. The activity of the catalyst toward the oxygen reduction reaction (ORR) depends on the ballmilling time and on the Fe x N precursor content. Heat-treatment up to 600°C does not significantly affect the activity, but the activity strongly decreases as the samples are heat-treated above 800°C in argon. The onset potential of a typical sample ballmilled for 12 h is 0.72 V versus reversible hydrogen electrode. About 20% of the product of oxygen reduction is H 2 O 2 and the other 80% is water. The X-ray diffraction pattern of the ballmilled material shows the formation of Fe 7 C 3 and disordered carbon, which presumably contains nitrogen, because the ball mills are sealed and the nitrogen cannot escape. This work demonstrates that mechanochemical synthesis is a useful technique for the preparation of Fe-C-N ORR catalysts.