Electrolyte‐Dependent Sodium Ion Transport Behaviors in Hard Carbon Anode

Abstract

A comprehensive study is conducted on hard carbon (HC) series samples by tuning the graphitic local microstructures systematically as an anode for SIBs in both carbonate‐ (CBE) and glyme‐based electrolytes (GBE). The results reveal more detailed charge storage characters of HCs on the LVP section. 1) The LVP capacity is closely related to the prismatic surface area to the basal plane as well as the bulk density, regardless of electrolyte systems. 2) The glyme‐sodium ion complex can facilitate sodium ion delivery into the internal closed pores of the HCs along with not well‐ordered graphitic structures. 3) The glyme‐mediated sodium ion‐storage behavior causes significant decreases in both surface film resistance and charge transfer resistance, leading to enhanced rate capability. 4) The LVP originates from the formation of pseudo‐metallic sodium nanoclusters, which are the same in a CBE and GBE. These results provide insight into the sodium ion‐storage behaviors of HCs, particularly on the interrelationship between graphitic local microstructures and electrolyte systems. In addition, a high‐performance HC anode with a plateau capacity of ≈300 mA h g−1 is designed based on the information, and its workability is demonstrated in a full‐cell SIB device.

Enabling Fast Na+ Transfer Kinetics in the Whole‐Voltage‐Region of Hard‐Carbon Anodes for Ultrahigh‐Rate Sodium Storage

“…The full cell of HCM-1300-ZBE delivered a high energy density of 294.6 Wh kg -1 , and a high power density of 6.73 kW kg -1 (based on total mass of both electrodes, Figure 2h), surpassing the previously reported high-energy and high-power full cell (Table S14, Supporting Information). [2,17,33,[59][60][61][62][63][64][65]…”

Ether-based electrolytes for sodium ion batteries

“…Recently, it was exceptional that the solvent co-intercalation behavior in an ether-based electrolyte was demonstrated in a hard carbon electrode, facilitating fast sodium storage and a high-rate performance. 110,199,200 In a previous study on lithiumpenetrated hard carbon electrode, Li et al 199 conducted ab initio molecular dynamics (AIMD) simulations to understand the effect of an ether electrolyte (TEGDME) on sodium intercalation. The structural evolution of hard carbon was simulated in the system of NaClO 4 -TEGDME electrolyte.…”

“…However, the large amounts of defects and active surface in the hard carbon can induce electrolyte decomposition also. 200 The underlying mechanism of enhancing the rate and cycling capability of hard carbon in ether-based electrolytes was also investigated. 201 They found that the pillar ether solvent helped modulate the interfacial crystallographic structures of hard carbon, which functioned as a ''pseudo-SEI'' to facilitate fast sodium storage kinetics (Fig.…”

“…Recently, the electrolyte-dependent sodium storage behavior in hard carbon was detected. Yun et al 200 prepared a series of hard carbons at a heating temperature in the range of 1600 °C 2800 °C and tested their electrochemical behavior in EC/PC and DEGDME-based electrolytes. It was found that the galvanostatic discharge/charge profiles are similar in both ether and ester-based electrolytes.…”

A Reanalysis of the Diverse Sodium Species in Carbon Anodes for Sodium Ion Batteries: A Thermodynamic View

“…Furthermore, the type of electrolyte also affects the electrochemical behavior, that is, certain carbons behave differently in different solvents. [60,61] The typical voltage-capacity discharging profile of hard carbon is shown in Figure 2 and consists of at least one or two sloping regions (0.1-2.0 V, vs Na + /Na) and a plateau region (below 0.1 V, vs Na + /Na). The high capacity and high voltage of hard carbons as compared to soft carbons or graphite can be ascribed to a longer voltage plateau.…”