Freestanding Macroporous Silicon and Pyrolyzed Polyacrylonitrile As a Composite Anode for Lithium Ion Batteries

Abstract

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.

Optimal Conditions for Fast Charging and Long Cycling Stability of Silicon Microwire Anodes for Lithium Ion Batteries, and Comparison with the Performance of Other Si Anode Concepts

“…From Table 1 it can be seen that the areal capacity of the present Si microwire anode is one of the highest among the different Si anode concepts, besides a couple of anodes made by slurry casting [13,14], where it is possible to add as much material as wanted, and a porous Si membrane [15]. In the case of the paste electrodes, when the amount of material is high, the fading is usually high due to stresses, as happens with the anode of [13].…”

“…One of the most important features of the Si microwire anode is that it does not contain anything else than the active material, avoiding additional weight. The porous Si membrane of [15] has high areal capacity due to the high amount of active material, but the charge density rate is low and the fading is large. This concept does not overcome the problems of fading due to material cracking for volume expansion when Li is incorporated and de-incorporated in Si.…”

Аноды для литий-ионных аккумуляторов на основе p-Si с самоорганизующимися макропорами

“…Электрохимическое трав- ление проводили в течение 45−90 мин при плотности тока 8 мА/см 2 . Для отделения мембраны от подложки ис-пользовался известный прием по увеличению плотности тока в финальной фазе анодирования [18][19][20], в нашем случае 10 мин при j = 21−25 мА/см 2 . При этом, как правило, достигается критическая плотность тока j PS , соответствующая переходу от режима порообразования к электрополировке.…”

Porous Silicon Formation by Anodization

“…Aside from the more common aqueous HF-based electrolytes, nonaqueous organic electrolytes in combination with a suitable fluoride source have been used, primarily for the production of macroporous layers both on silicon wafers (Propst and Kohl 1994;Rieger and Kohl 1995;Levy-Clement 1998, 2000;Flake et al 1999;Thakur et al 2012a) and in freestanding form (Thakur et al 2012b). Examples include acetonitrile, propylene carbonate, and dimethylformamide, with anhydrous HF (up to 2 M), tetrafluoroborate, and lithium fluoroborate being used as fluoride sources.…”