Pitch Derived Carbon As Light Weight and High-Power Sodium-Ion Battery Anode
Authors: Ghosh Sourav , Kiran Kumar V , Biswas Sanjay , Martha Surendra Kumar 
Published: May 2020

Li-ion batteries (LIBs) are fulfilling the current need of humankind, the high abundance, and accessibility of sodium, making Na-ion batteries (NIBs) a promising LIBs supplement in the large-scale energy storage application.1, 2 However, the commercial success of NIBs demands an appropriate cathode and anode material. From the cathode material viewpoint, the literature reports suggest that O3/P2 type layered oxide can deliver a reasonable capacity with good cycling stability2. Graphite, the state-of-art anode material in LIBs is electrochemically inactive to intercalate Na-ions. Na-ion intercalation into graphite lattice is a thermodynamic driven process, where most Na-rich graphite intercalation compounds (GIC) prepared to date is NaC64 with a1 capacity of only 35 mAh g-1.3 However, Li-ion and K-ion form the stage one Li-GIC and K-GIC having the formula LiC6 and KC8, which makes them electronically active in Li- and K-ion battery, respectively. 4,5

To realize the large scale application of sodium-ion batteries, a stable, cost-effective anode is desired. Carbon-based anode materials are always attractive because of ease of fabrication, cost, and feasibility towards practical application. The pioneering work of Dahn and Stevens on hard carbon anode, reports the sodiation capacity of 300 mAh g-1 at room temperature.6 Later on, the hard carbon derived from different precursors such as a polymer, biomass, resin, etc., and applied as anode for Na-ion battery.7 However, hard carbon materials mostly suffer from poor carbon synthesis yield and high cost.8 Therefore, exploring cost-effective precursors and process is very crucial to realize the large scale application of NIB.
Pitch is a potential low-cost precursor to synthesize soft carbon anode for NIBs. However, it does not exhibit decent Na-ion storage. Herein, we report the facile synthesis of pitch derived-binder less-metal free-freestanding anode for storing Na-ions by one-step pyrolysis process between the temperature range 700-1000 oC under nitrogen atmosphere. We replace conventional Cu-current collectors with carbon fiber (CFs). The electrode architecture not only eliminates the metallic current collector, conductive diluents and inactive organic binder but also provides an ideal porous network for sodium-ion and electrolyte diffusion into the bulk of the electrode. The freestanding electrode delivers a reversible capacity of 310 mAh g-1 in compare to 180 mAh g-1 for conventional electrode at the current density of 50 mA g-1. The cycling stability over 500 cycles (at 1 A g-1) and C-rate performance of freestanding anode dictate it as a promising anode for NIBs. The overall charge storage properties of conventional and freestanding-film are quantified into pseudocapacitive and diffusion-control Na+ intercalation. Further, the freestanding film is implemented as anode in order to realize its practical application in sodium-ion full cell. It is believed that the study may open up a new approach to modify the pitch based soft-carbon precursors as anode for low-cost, high-energy NIBs.

Acknowledgments

SG acknowledges MHRD, VKK acknowledges UGC-NET, Govt. of India, and SKM acknowledges Research Center Imarat (DRDO), Hyderabad under grant no. RCI/CAAT/8151/CARS-358 for financial support.

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