Reaction of Li with Alloy Thin Films Studied by In Situ AFM

Abstract

Many intermetallic materials deliver poor capacity retention when cycled vs. Li. Many authors have attributed this poor capacity retention to large volume expansions of the active material. Here we report the volume changes of continuous and patterned films of crystalline Al, crystalline Sn, amorphous Si ͑a-Si͒, and a-Si 0.64 Sn 0.36 as they reversibly react with Li measured by in situ atomic force microscopy ͑AFM͒. Although these materials all undergo large volume expansions, the amorphous phases undergo reversible shape and volume changes. The crystalline materials do not. We attribute this difference to the homogeneous expansion and contraction that occurs in the amorphous materials. Inhomogeneous expansion occurs in the crystalline materials due to the presence of coexisting phases with different Li concentrations. Thin films of a-Si and a-Si 0.64 Sn 0.36 show good capacity retention with cycle number.

Variation of stress with charging rate due to strain-rate sensitivity of silicon electrodes of Li-ion batteries

“…Following our previous work [5] and validated by experiments [5,[36][37][38], we take the volume of the film, f V , to be linear in the state of charge…”

“…where 0 f V is the initial volume of the film, β is related to the atomic volumes ( ) Ω by ( ) [37,38]. Both groups found that the volume increased linearly with lithium concentration [37,38].…”

Stable silicon-ionic liquid interface for next-generation lithium-ion batteries

“…Silicon's low working voltage and high-theoretical specific capacity of 3,579 mAh g À 1 , nearly ten times higher than that of state-ofthe-art graphite anodes, have encouraged widespread research efforts aimed at developing a viable Si-based electrode [9][10][11][12] . The substantial gains in specific and volumetric capacity simply through the implementation of an active material such as Si offer a glimpse into the future of lighter and smaller batteries.…”

Lithium Permeation through Thin Lithium–Silicon Films for Battery Applications Investigated by Neutron Reflectometry

“…After as teady decreasefor approximately 3hof annealing, the 6 Li fraction reaches ap lateau at 68 %. In parallel, the 7 Li fraction in the 6 LiNbO 3 startso ut at 8%,i ncreases at the same rate,a nd reaches its plateau at 32 %a lso after 3h.E xcept for the slightly different starting values, both lithium isotope fractions in the nat LiNbO 3 exactly mirror this behavior. It is further obviousf rom the plot that the lithium isotopes do not show ac omplete equilibration at about 50 %.…”

“…This is mainly due to ar eversibility of shape and volume changes during electrodec ycling because of am ore homogeneous expansion and contraction of amorphous silicon. [7] In this context, an important question is also whether electrode lithiation is al ithium-diffusion-or interface-reaction-controlled process. [8,9] Consequently,areliable determination of atomic/ionic transport properties is highly desirable.…”