Abstract
This computational research study analyzes the increase of the specific charge capacity that comes with the reduction of the anisotropic volume expansion during lithium ion insertion within silicon nanowires. This research paper is a continuation from previous work that studied the expansion rate and volume increase. It has been determined that when the lithium ion concentration is decreased by regulating the amount of Li ion flux, the lithium ions to silicon atoms ratio, represented by x, decreases within the amorphous lithiated silicon (a-LixSi) material. This results in a decrease in the volumetric strain of the lithiated silicon nanowire as well as a reduction in Maxwell stress that was calculated and Young’s elastic module that was measured experimentally using nanoindentation. The conclusion as will be seen is that as there is a decrease in lithium ion concentration there is a corresponding decrease in anisotropic volume and a resulting increase in specific charge capacity. In fact the amplification of the electromagnetic field due to the electron flux that created detrimental effects for a fully lithiated silicon nanowire at x = 3.75 which resulted in over a 300% volume expansion becomes beneficial with the decrease in lithium ion flux as x approaches 0.75, which leads to a marginal volume increase of ~25 percent. This could lead to the use of crystalline silicon, c-Si, as an anode material that has been demonstrated in many previous research works to be ten times greater charge capacity than carbon base anode material for lithium ion batteries.
Highlights
IntroductionThis volume expansion appears to occur during full lithiation described by the lithium-silicon material LixSi where x = 3.75 defines the state where the liathiated silicon nanowire is at full lithiation
The amplification of the electromagnetic field due to the electron flux that created detrimental effects for a fully lithiated silicon nanowire at x = 3.75 which resulted in over a 300% volume expansion becomes beneficial with the decrease in lithium ion flux as x approaches 0.75, which leads to a marginal volume increase of ~25 percent
This could lead to the use of crystalline silicon, c-Si, as an anode material that has been demonstrated in many previous research works to be ten times greater charge capacity than carbon base anode material for lithium ion batteries
Summary
This volume expansion appears to occur during full lithiation described by the lithium-silicon material LixSi where x = 3.75 defines the state where the liathiated silicon nanowire is at full lithiation When this occurs the volume expands at an uncontrollable anisotropic rate where the 110 crystallography direction could possibly increase 12 times greater than that of the 111 orthogonal direction within the silicon nanowire. The work drawn from Jung et al molecular dynamics/density functional theory (MD/DFT) simulation was created to study the atomistic behavior of the two-phase interfacial reaction front barrier that separates the c-Si and LixSi material [9] All of these works support the findings that the volume of silicon nanowires during lithium atom/ion insertion will increase non-isotopically by nature. The silicon lattice is fully lithiated with 30 lithium ions [13]
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