Realization of a sodium-ion capacitor by pre-metalation of a hard carbon anode using sodium azide as sacrificial cathodic material
[ 1 ] Wydział Technologii Chemicznej, Politechnika Poznańska | [ 2 ] Instytut Chemii i Elektrochemii Technicznej, Wydział Technologii Chemicznej, Politechnika Poznańska | [ SzD ] doctoral school student | [ P ] employee
2023
abstract
english
EN Metal-ion capacitors (MICs) are hybrid electrochemical energy storage systems capable of delivering up to ca. 4 times higher specific energy than electrical double-layer capacitors (EDLCs). This is achieved by combining a battery-type negative electrode (e.g., metalated hard carbon (HC)) with an EDL positive electrode (typically from activated carbon (AC)) in which the electrolyte anions are reversibly electrosorbed. One crucial aspect in the conceptualization, design, and optimization of MICs is the premetalation of the negative electrode, i.e., the formation of a solid electrolyte interphase (SEI) and doping of this electrode. Among the few pre-metalation methods available, the incorporation of a sacrificial material containing a metal ion (M) in the positive electrode is the most attractive one, owing to its cost-effectiveness. The M element is extracted by electrochemical oxidation and transferred to the negative electrode. An optimal sacrificial material for MICs should meet several criteria, including: (i) a relatively low oxidation potential to avoid electrolyte decomposition, (ii) a high irreversible capacity to reduce its amount in the positive electrode, (iii) stability in the ambient atmosphere for easy electrodes fabrication, and (iv) generation of non-detrimental by-products for optimal device performance. NaN3 is a rare material that fulfills all these requirements and has already been successfully implemented in sodium-ion batteries. In this context, an (+)AC-NaN3//HC(-) cell equipped with reference electrode was realized, and electrochemical oxidation was conducted to transfer sodium from NaN3 to HC. The evolving gas during the oxidation process was analyzed with internal pressure measurement. The result indicates that only a few galvanostatic cycles are needed to completely oxidize the sacrificial material. Subsequently, the electrochemical performance of a (+)AC//NaxHC(-) laminate Sodium-ion capacitor (NIC) equipped with reference electrode was investigated by galvanostatic charge/discharge cycling. The NIC laminate cell demonstrated a very stable performance during 4000 cycles at 200 mA g-1. Furthermore, the discharge tests conducted at constant power revealed that the device maintained an almost constant output energy density of 42.3 Wh kg-1 up to a specific power of 2 kW kg-1 (based on the total active mass of both electrodes). During the presentation, detailed information and results on the fabrication and performance of the laminate cell, including a new design of negative electrodes incorporating novel materials, will be provided.
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