From Micropores to Ultra-micropores inside Hard Carbon: Toward Enhanced Capacity in Room-/Low-Temperature Sodium-Ion Storage

Abstract

Highlights Hard-carbon anode dominated with ultra-micropores (< 0.5 nm) was synthesized for sodium-ion batteries via a molten diffusion–carbonization method. The ultra-micropores dominated carbon anode displays an enhanced capacity, which originates from the extra sodium-ion storage sites of the designed ultra-micropores. The thick electrode (~ 19 mg cm−2) with a high areal capacity of 6.14 mAh cm−2 displays an ultrahigh cycling stability and an outstanding low-temperature performance. Abstract Pore structure of hard carbon has a fundamental influence on the electrochemical properties in sodium-ion batteries (SIBs). Ultra-micropores (< 0.5 nm) of hard carbon can function as ionic sieves to reduce the diffusion of slovated Na+ but allow the entrance of naked Na+ into the pores, which can reduce the interficial contact between the electrolyte and the inner pores without sacrificing the fast diffusion kinetics. Herein, a molten diffusion–carbonization method is proposed to transform the micropores (> 1 nm) inside carbon into ultra-micropores (< 0.5 nm). Consequently, the designed carbon anode displays an enhanced capacity of 346 mAh g−1 at 30 mA g−1 with a high ICE value of ~ 80.6% and most of the capacity (~ 90%) is below 1 V. Moreover, the high-loading electrode (~ 19 mg cm−2) exhibits a good temperature endurance with a high areal capacity of 6.14 mAh cm−2 at 25 °C and 5.32 mAh cm−2 at − 20 °C. Based on the in situ X-ray diffraction and ex situ solid-state nuclear magnetic resonance results, the designed ultra-micropores provide the extra Na+ storage sites, which mainly contributes to the enhanced capacity. This proposed strategy shows a good potential for the development of high-performance SIBs.

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

“…This result is superior to the control samples, as well as the anode materials reported in literature (Figure 2f). [35,[56][57][58] Note that, we use ether (diglyme) electrolytes in this work, which are considered to show higher ionic conductivity at LT than ester type electrolytes, [35] for all the sample test. The significant differences among the LT performances indicate that the bulk structure of the electrode material also plays a critical role in enhancing the LT charge-storage ability.…”

Natural Stibnite for Lithium-/Sodium-Ion Batteries: Carbon Dots Evoked High Initial Coulombic Efficiency

“…Nevertheless, the practical application of Sb 2 S 3 suffers from poor conductivity, weak structural stability, lower initial Coulombic efficiency (ICE), and “shuttling effect” of polysulfide [ 2 , 3 ]. In order to tackle these key problems, multifarious ways have been proposed, such as combining with highly conductive carbonaceous materials [ 4 , 5 ], designing greatly stable structures [ 6 , 7 ], building interfacial bonds [ 8 ], and introducing doping heteroatoms [ 9 ]. Constructing Sb 2 S 3 /carbon composite is the most common and effective strategy [ 10 – 12 ].…”

Bacterial cellulose-derived micro/mesoporous carbon anode materials controlled by poly(methyl methacrylate) for fast sodium ion transport

“…† Besides, the capacity ratios of c-BC-1050 and c-BP 5 -1050 are calculated according to the analytical method proposed by Dunn. 37,41 The current can be divided into diffusion-controlled intercalation behavior (k 1 v 1/2 ) and surface induced capacitive behavior (k 2 v) at a fixed voltage, as follows: 15,29 iðvÞ…”

“…Fig. 6a and b show the GITT curves of the c-BC-1050 and c-BP 5 -1050 with a pulse current of 25 mA g −1 for 0.5 h between rest intervals for 2 h. According to Fick's second diffusion law, the Na + diffusion coefficient (D(Na + )) can be calculated based on the following equation: 15,42…”

“…Therefore, it is essential to develop hard carbon with the feature of fast sodium diffusion under mild carbonization temperatures, further realizing high low-potential capacity and satisfactory rate capability. 15 Cellulose-derived hard carbon anodes are a distinctive field of endeavor that stimulates intensive research of sodium storage behaviors because of their pure chemical components, abundant hydroxyl groups, and rich porous structure. 11 Several studies [16][17][18][19][20] used high-temperature carbonization, chemical surface modification, or a heteroatom-doped method to increase the performance of sodium ion storage.…”