A.D.W. Todd

Tin–Transition Metal–Carbon Systems for Lithium-Ion Battery Negative Electrodes

Magnetron cosputter deposited ternary libraries of Sn 1-x-y M x C y (M = Ti, V and Co) (0 < x < 0.5 and 0 < y < 0.5) have been studied structurally and electrochemically using combinatorial and high-throughput methods. Each of the sputtered Sn 1-x M x binary systems shows an amorphous composition range where the specific capacity for lithium decreases with M content. Adding carbon to the amorphous binaries, to make ternaries, causes the precipitation of crystalline Sn in the cases when M = Ti or V, but not when M = Co. We believe this is because stable carbides of Ti and V exist but stable Co carbides do not. The sputtered Sn-Co-C system was found to have a large amorphous range and the initial amorphous atomic arrangement in certain compositions are stable over at least 27 charge-discharge cycles of 600 mAh/g. Crystalline Sn was found to precipitate in composition ranges having competitive specific capacity in the Sn-Ti-C and Sn-V-C libraries causing rearrangement of the atoms during cycling leading to poor capacity retention.

Combinatorial Study of Tin-Transition Metal Alloys as Negative Electrodes for Lithium-Ion Batteries

A survey of the structural and electrochemical properties of combinatorially sputter deposited Sn-transition metal alloys [Sn 1-x M x (0 0.48 to at least x = 0.65 for M = Ti, x > 0.39 to at least x = 0.60 for M = V, 0.47 < x < 0.73 for M = Cr, and 0.28 < x < 0.43 for M = Co. Electrochemical tests using a 64 channel Li/Sn 1-x M x combinatorial electrochemical cell show that the specific capacity of the alloys drops with transition metal content, as expected. The Sn 1-x Co x system shows an amorphous phase with the largest specific capacity, primarily because the amorphous phase is reached at the lowest transition metal content for Sn 1-x Co x . Capacity retention vs cycle number is generally best for those compositions that are amorphous or highly nanostructured. Arguments are presented to suggest that amorphous Sn 1-x V x alloys are the best choice among Sn 1-x M x alloys. Comparison with literature results for samples prepared by mechanical alloying, electrodeposition, vacuum deposition, etc. is made.

Comparison of Mechanically Milled and Sputter Deposited Tin–Cobalt–Carbon Alloys Using Small Angle Neutron Scattering

Small angle neutron scattering (SANS) is used to compare nanostructured Sn-Co-C alloys produced by vertical axis mechanical attriting to those produced by magnetron sputter deposition. The attrited materials have grain sizes that vary with composition and are on the order of 60 A in size. The sputter deposited materials are either amorphous or have a grain size of approximately 10 A, depending on the composition. The SANS results are used to further understand the electrochemistry of these materials when used as negative electrodes for lithium-ion batteries and to understand why mechanically alloyed Sn-Co-C alloys are far from reaching their expected theoretical specific capacity while sputtered alloys achieve capacities much closer to the expected value.

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.