Sodium Storage Behavior in Natural Graphite using Ether‐based Electrolyte Systems

Abstract

This work reports that natural graphite is capable of Na insertion and extraction with a remarkable reversibility using ether-based electrolytes. Natural graphite (the most well-known anode material for Li-ion batteries) has been barely studied as a suitable anode for Na rechargeable batteries due to the lack of Na intercalation capability. Herein, graphite is not only capable of Na intercalation but also exhibits outstanding performance as an anode for Na ion batteries. The graphite anode delivers a reversible capacity of ≈150 mAh g −1 with a cycle stability for 2500 cycles, and more than 75 mAh g −1 at 10 A g −1 despite its micrometer-size (≈100 µm). An Na storage mechanism in graphite, where Na + -solvent co-intercalation occurs combined with partial pseudocapacitive behaviors, is revealed in detail. It is demonstrated that the electrolyte solvent species signifi cantly affect the electrochemical properties, not only rate capability but also redox potential. The feasibility of graphite in a Na full cell is also confi rmed in conjunction with the Na 1.5 VPO 4.8 F 0.7 cathode, delivering an energy of ≈120 Wh kg −1 while maintaining ≈70% of the initial capacity after 250 cycles. This exceptional behavior of natural graphite promises new avenues for the development of cost-effective and reliable Na ion batteries.

Flexible graphite film with laser drilling pores as novel integrated anode free of metal current collector for sodium ion battery

“…Obviously, the graphite film without drilling pores exhibits negligible electrochemical activity. Interestingly, when the drilling pores are formed on graphite films, which provide a large number of electrochemical active sites, reversible sodium ion intercalation/deintercalation peaks are observed, showing similar electrochemical behaviors with natural or artificial graphite electrode in the same electrolyte [14,15]. The charge/discharge profiles deliver a reversible capacity of 127.1 mAh g −1 (Fig.…”

“…Even at an increased current density of 500 mA g −1 , the discharge capacity remains 83.5 mAh g −1 , indicative of outstanding rate capability. The energy density of such NIBs system is 130.7 Wh kg − 1 based on the total electrode materials, which is superior to the NIB system with natural graphite anode and Na 1.5 VPO 4.8 F 0.7 cathode in the same electrolyte (120 Wh kg − 1 based on the electroactive materials) [15]. Moreover, even after 500 cycles, a desired capacity retention of 92.0% is retained at 100 mA g − 1 .…”

“…Fortunately, the situation changed when Adelhelm's group found that sodium can be reversibly intercalated into artificial graphite by taking advantage of co-intercalation mechanism in the form of ternary graphite intercalation compounds (t-GICs) in a diglyme-based electrolyte, which milestone graphite materials towards anode of NIBs [14]. More recently, Kang's group also investigated the Na + -solvent co-intercalation combined with partial pseudocapacitive behaviors in natural graphite [15]. However, the capacity retention and the energy density of the full cell should be further promoted.…”

Expanded graphitic materials prepared from micro- and nanometric precursors as anodes for sodium-ion batteries

“…Interestingly, this has been circumvented in part in recent studies by the use of ether-based electrolyte systems allowing the co-intercalation of Na + ions with solvent molecules between the graphene layers, thus moderately increasing the reversible capacity delivered by graphite-based electrodes (100-150 mA h g -1 ) [16,17].…”

Facile synthesis of T-Nb2O5 nanosheets/nitrogen and sulfur co-doped graphene for high performance lithium-ion hybrid supercapacitors

“…To quantitatively distinguish the contributions of diffusion-limited and capacitive elements, Equation (3) can be rewritten as [22,43]:…”