Date of Award
2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Mechanical Engineering
Committee Chair
George Nelson
Committee Member
Guangsheng Zhang
Committee Member
Judith Schneider
Committee Member
Nicholas Ginga
Committee Member
Yu Lei
Research Advisor
George Nelson
Subject(s)
Sodium ion batteries, Anodes--Materials, Metallic composites
Abstract
Sodium-ion batteries represent a promising alternative to lithium-ion technology for large-scale energy storage due to sodium's abundance, global availability, and cost advantages. However, developing high-capacity anodes that simultaneously deliver substantial energy density and stable cycling performance remains a critical challenge for its commercial viability. This dissertation investigates tin/hard carbon composite anodes as a solution to the fundamental trade-off between specific capacity and cycling stability in sodium-ion battery systems. While tin offers exceptional theoretical capacity through alloying reactions, it suffers from massive volume expansion during sodiation/desodiation, leading to particle pulverization and rapid capacity degradation. On the other hand, hard carbon has good chemical, thermal and structural stability, but with lower specific capacity. The composite approach aims to leverage tin's high capacity while mitigating its mechanical instability through carbon's buffering properties. Systematic evaluation of tin/hard carbon composites with varying weight ratios revealed distinct performance trends. Anodes with tin as the sole active material achieved the highest initial capacities but experienced severe degradation due to rapid structural failure. Progressive incorporation of hard carbon systematically improved cycling stability of the tin-based anodes, although with reduced capacities. The higher carbon content compositions demonstrated better stability over fifty cycles, with retained capacities eventually surpassing those of high-tin formulations due to improved cycling durability. Comprehensive characterization through electrochemical, microstructural, and crystallographic analysis provided insights into composite behavior. Cyclic voltammetry demonstrated that hard carbon incorporation preserved tin's multi-phase electrochemical signature during extended cycling, maintaining phase reversibility that was lost in pure tin systems. The carbon framework prevented particle agglomeration and maintained electrical connectivity, enabling consistent access to tin's capacity. Microstructural analysis provided visual evidence of the underlying degradation mechanisms and behavior. For the pure tin anode, increased structural failure with particle pulverization and electrode delamination was observed, while carbon-rich composites maintained coherent electrode architecture. This difference is attributed to the carbon matrix providing both mechanical support and electrical connectivity through percolated conductive networks. The research establishes that modest carbon additions can achieve significant improvements in cycling stability while maintaining energy densities substantially higher than conventional hard carbon anodes. This scalable synthesis approach using direct mixing of commercially available materials provides a practical approach to increasing capacity while ensuring compatibility with existing battery manufacturing infrastructure.
Recommended Citation
Amai, Joseah, "The effect of micro-sized tin/hard carbon composition on sodium-ion battery performance" (2025). Dissertations. 459.
https://louis.uah.edu/uah-dissertations/459