The Future of Energy Storage: Detailed Description of Layered Structure and Porosity of Hard Carbons
Authors: Kalder Laura , Härmas Meelis , Aruväli Jaan , Lust Enn , Hark Eneli 
Published: September 2023

The effort of commissioning green and renewable energy with the growing list of critical raw materials demands innovations in energy storage and conversion [1]. The research on sodium-ion batteries (SIBs) has proved promising for large-scale stationary energy storage. Therefore, the crucial need for material research for SIB applications has motivated the studies on hard carbon anodes that have shown high reversible capacity and low working potential[2]. Nevertheless, the exact sodium storage mechanism in hard carbons remains uncertain, inspiring the detailed study of the structure of non-graphitized carbons. Yet, the structure of hard carbons has no long-range order, which complicates the exact characterization. Thus, we present a study focusing on the chemically activated hard carbons' porous and graphite-like structures with complementary wide- and small-angle scattering methods (Figure 1). The current presentation examines the exact impact of the ratio of activating agents on the structure of hard carbons and how the structure affects the ability to store sodium ions.

The studied materials were synthesized from D-glycose via hydrothermal carbonization and activated with zinc chloride with different ratios[3]. The evaluation of the layered structure of carbons from wide-angle x-ray scattering (WAXS) data was carried out with Ruland and Smarsly algorithm[4], which is more suitable for non-graphitic carbons than the typically used approaches. The porous structure was described with small-angle neutron scattering (SANS) data model-free analysis, combining Schiller, Mering, Perret, and Ruland approaches[5].
This presentation reveals exciting results from the detailed data analysis that opens new perspectives to the material development for SIB hard carbon anodes. During activation of the hard carbon materials activated with zinc chloride with ratios 1:1.5 and 1:2 significant differences in the interlayer arrangement, pore sizes, and the degree of disorder appeared. The presented results indicate the role of different structural parameters on the charge-discharge plateau and sloping regions, guiding to the better understanding of the sodium storage mechanism in hard carbon anode. The presentation demonstrates the interpretation of the results with a focus on improving energy storage capability. It is discussed: is the detailed structural analysis for the non-graphitic carbons a comprehensive and new sight into the future of energy storage?
[1] Critical Raw Materials for Strategic Technologies and Sectors in the EU A Foresight Study, (2020).
[2] A. Adamson, R. Väli, M. Paalo, J. Aruväli, M. Koppel, R. Palm, E. Hark, J. Nerut, T. Romann, E. Lust, A. Jänes, Peat-Derived Hard Carbons for High Capacity Sodium-Ion Batteries: Synthesis and Characterization, ECS Meet. Abstr., MA2020-02 (2020) 78.
[3] M. Härmas, T. Thomberg, A. Jänes, Effect of Zinc Chloride Activation on D-Glucose Derived Carbons Based Capacitors Performance in Ionic Liquid, J. Electrochem. Soc., 167 (2020) 080533.
[4] W. Ruland, B. Smarsly, X-ray scattering of non-graphitic carbon: an improved method of evaluation, J. Appl. Crystallogr., 35 (2002) 624–633.
[5] E. Härk, M. Ballauff, Carbonaceous Materials Investigated by Small-Angle X-ray and Neutron Scattering, C, 6 (2020) 82.

Figure 1