Aspen Aerogels (United States)

In lithium ion batteries, Si-based anodes possess the highest specific capacity from four to 10 times greater than graphite [1, 2]. However, up to 400% volume expansion of Si during lithiation results in anode pulverization due to mechanical stresses. To avoid mechanical degradation of silicon, the critical value of the silicon particle size/wall thickness should be below the required threshold of <50nm [3,4]. Thus, it is crucial to maintain the silicon particle size in this range. The second major requirement for silicon anode in lithium ion batteries is to have the second conductive phase, e.g. graphite or graphene, in the form of a flexible coating that can withstand lithiation-delithiation without deterioration of the carbon phase. The goal is to develop a silicon-based anode that can withstand lithiation-delithiation cycles without mechanical degradation.Through using structured silica precursors, the goal is to reduce the silica to silicon while maintaining its structure and porosity and thus mitigate the degradation during cycling. Two types of silicon oxide precursor materials that meet these requirements have been evaluated, among them hollow silica microspheres from 3M and silica aerogel from Aspen Aerogels. The major steps including silica synthesis and magnesium vapor reduction will be discussed.Preparation of Si precursor materials has been performed by magnesium reduction followed by the removal of unnecessary impurities such as magnesium oxide and silica by washing the material in 1M HCl followed by 1% HF. Preliminary data from XRD confirms Si formation from the magnesiothermic reduction. SEM, TEM, EDS, BET, XRD, and Raman spectroscopy will be presented to analyze the structure and morphology of the materials. Structure dependent electrochemical properties such as cyclic voltammetry, cycleability, galvanostatic discharge, and cycle stability will be discussed.Fig. 1: (A) TGA for 3M silica microspheres (iM30K) and (B) TGA for Aspen Aerogels’ SiO2 aerogel with Mg with the corresponding SEM images (C) 3M microspheres and (D) Silica aerogel precursors. (E) XRD for reduced SiO2 aerogel: top profile is fully washed reduced Si, middle profile is after reduction but before washing, and bottom profile is for a Si nanopowder reference to vindicate successful Si reduction from SiO2.

not Available.

ABSTRACTHigh performance polyimides have been widely investigated as materials with excellent thermal, mechanical, and electronic properties due to their highly rigid structures. Aspen has developed an approach to prepare polyimide aerogels which have applications as low dielectric constant materials, separation membranes, catalyst supports and insulation materials. In this paper, we will discuss the preparation of polyimide-silica hybrid aerogel materials with good mechanical strengths and low thermal conductivities. The polyimide-silica hybrid aerogels were made by a two-step process and the materials were characterized to determine thermal conductivity and compressive strength. Results show that compressive moduli of the polyimide-silica hybrid aerogels increase dramatically with density (power law relationship). Thermal conductivity of the aerogels is dependent on the aging conditions and density, with the lowest value achieved so far being ~12 mW/m-K at ambient conditions. The relationship between aerogel density and surface area, thermal stability, porosity and morphology of the nanostructure of the polyimide-silica hybrid aerogels are also described in this paper.