Combining Experimental and Theoretical Techniques to Gain an Atomic Level Understanding of the Defect Binding Mechanism in Hard Carbon Anodes for Sodium Ion Batteries

Abstract

Sodium ion batteries (NIBs) are an attractive alternative to lithium‐ion batteries in applications that require large‐scale energy storage due to sodium's high natural abundance and low cost. Hard carbon (HC) is the most promising anode material for NIBs; however, there is a knowledge gap in the understanding of the sodium binding mechanism that prevents a rational design of HC. This study tunes sucrose‐derived HC via synthesis temperature then evaluates the structural, physical, and electrochemical properties. Neutron total scattering is used to generate structural models by fitting pair distribution functions (PDF) with a combination of molecular dynamics and reverse Monte Carlo methods. From this model, the number and type of structural features are identified, quantified, and correlated to the galvanostatic charge/discharge. A method of PDF “fingerprinting” binding sites using Na probe atoms is developed and analyzing these PDFs reveals an atomistic view of ion binding sites responsible for “defect” storage mechanisms. Combining these techniques results in an atomic‐level study that provides a big picture of the Na‐binding mechanism in NIBs, which allows for more precise tuning of the structure–property relationships in the future. The methodologies developed will also enable new strategies for the analysis of amorphous functional materials.

Sodiation energetics in pore size controlled hard carbons determined via entropy profiling

“…DFT calculations on graphene surfaces with different point defects indeed suggest that sodium deposition near oxygenated defects is more favourable than on pristine graphene 14,53 . Morever, structural defects such as 5 or 7membered carbon rings may contribute to the curvature of the graphene layers 54 , and these defects may or may not be decorated with oxygen. Each of these defects would have a different local sodium binding energy.…”

Agricultural Wastes for Full-Cell Sodium-Ion Batteries: Engineering Biomass Components to Maximize the Performance and Economic Prospects

“…Instead of ordered carbon (graphite), disordered carbon, for example, hard carbon has shown promising electrochemical features such as low operating potential and considerable reversible capacity though the underlying storage mechanism remains elusive, including adsorption, intercalation, pore filling, or combination of them. More importantly, hard carbons are produced from diverse sources. − For example, reed straw, corncob and peanut shell, brewer spent grain, walnut shell, and grape pomace, corn straw, citrus peels, rape seed, and lotus stem have been carbonized into hard carbon with specific capacities ranging from 100 to 370 mAh/g. The diverse capacities from different biomass materials lead to the question of the role of each biomass component in determining the battery’s electrochemical performance.…”

Tracing Local Disorder in Near-Infrared-Upconverting Crystals of Li+-Doped Gd2O3 through the Gd(III)-O Bond Distance

“…In recent developments, the PDF analysis demonstrated a key role in understanding certain crucial mechanistic aspects in designing energy storage materials for enhanced performance. , Such a study had a profound significance in the context of Na + and Li + ion storage properties in a range of crystalline materials for battery-related applications. − The study of local disorder though paves a fundamental approach to optimize a number of physical properties in a wide range of functional crystalline materials; characterization of such short-range structural analysis remains largely unexplored in spite of offering an attractive field of study in the domain of crystal engineering.…”