Nanoporous-Carbon As Host Material for High-Performance Li-Ion Energy Storage
Authors: Wolak Matthaeus A. , Yelton W. Graham , Sava Gallis Dorina F. , Harrison Katharine Lee , Siegal Michael P. 
Published: February 2020

We study the feasibility of nanoporous-carbon (NPC) as an electrically conductive host material for reversible Li-ion energy storage. The efficiency of energy storage devices based on intercalation of Li-ions highly depends on the interstitial spacing of the host material, which can significantly limit the diffusion of ions. NPC offers with controlled mass density and surface area considerable advantages over other carbon allotropes. For example, the internal structure of NPC, which self-assembles during growth and consists of nano-fragments of aligned graphene sheet stacks, exhibits as much as a 55% larger interplanar spacing compared to crystalline graphite. Hence, NPC porosity is well controlled via its mass density as a result of defined process parameters, allowing for the NPC host material to accommodate efficient diffusion, as recently demonstrated for the reversible intercalation of Mg-ions.

To demonstrate viability as a host material for Li-ion intercalation, we grow NPC directly on 16 mm diameter stainless-steel disks for study as coin cell anodes. The NPC mass density is chosen to range from 0.8 – 1.7 g/cm3 for a series of coin cells which are electrochemically characterized. By varying the mass densities, a correlation between interplanar spacing and electrochemical response is established, revealing the most favorable NPC structure for rapid Li-ion intercalation. The correlating surface area of the most efficient NPC configurations is obtained through Brunauer–Emmett–Teller measurements as a function of nitrogen adsorption in the NPC framework. Moreover, the various NPC structures are investigated via transmission electron microscopy to verify successful diffusion of Li-ions into the NPC host material.

NPC represents a new approach for an efficient host material in Li-ion intercalation based energy storage devices with potentially faster diffusion rates. Using NPC as a host material may also enable implementing other atomic species with larger theoretical Li-storage capacity than graphitic carbons, such as Si. Si suffers from drastic volumetric expansion during cycling which leads to fast degradation as a result of embrittlement of the Si bulk, thus limiting its employment as a battery anode. The high porosity of NPC, however, may allow embedding Si atoms or clusters into an NPC host material. We will report on the ability to embed Si into NPC without collapsing the low mass density structure. The decoration of NPC structures with Si offers obvious advantages to crystalline graphite and Si composite architectures for battery anodes, as both the large Li-storage capacity of Si and rapid ionic intercalation into NPC can be made use of in one combined architecture.

This work is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.