Silicon continues to draw great interest as an anode
material for
lithium ion batteries due to its large specific capacity for lithium.
Macroporous silicon produced by electrochemical etching is one of
several anode materials of interest, but its energy density is oftentimes
limited due to its attachment to an unreactive silicon substrate.
Here, we present a novel “lift-off” method by which
a freestanding macroporous silicon film (MPSF) is electrochemically
detached from the underlying bulk silicon and combined with pyrolyzed
polyacrylonitrile (PAN), a conductive polymer that forms a conjugated-chain
chemical structure. We report the performance of these silicon thin
films with and without pyrolyzed PAN.
We present a novel method to tune the interaction potential from 5k B T to 40k B T in situ between micronsized superparamagnetic colloids. The potential is composed of a highly tunable long-range attraction induced via a rotating magnetic field and a short-range electrostatic repulsion. Various 2-D thermodynamic phases are observed in a colloidal suspension at different field strengths. Quantitative agreement is found between theory and experiments for dipolar interactions. A theory to account for the induced dipole due to neighboring particles is also presented. The effective three-body potential of a dilute trimer system is measured to account for many-body effects in the system. These results demonstrate an ideal model to study the phase behavior in 2-D systems.
One of the most exciting areas in lithium ion batteries is engineering structured silicon anodes. These new materials promise to lead the next generation of batteries with significantly higher reversible charge capacity than current technologies. One drawback of these materials is that their production involves costly processing steps, limiting their application in commercial lithium ion batteries. In this report we present an inexpensive method for synthesizing macroporous silicon particulates (MPSPs). After being mixed with polyacrylonitrile (PAN) and pyrolyzed, MPSPs can alloy with lithium, resulting in capacities of 1000 mAhg−1 for over 600+ cycles. These sponge-like MPSPs with pyrolyzed PAN (PPAN) can accommodate the large volume expansion associated with silicon lithiation. This performance combined with low cost processing yields a competitive anode material that will have an immediate and direct application in lithium ion batteries.
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