An Overall Understanding of Sodium Storage Behaviors in Hard Carbons by an “Adsorption‐Intercalation/Filling” Hybrid Mechanism

Abstract

With the rapid development of renewable energy technologies, there is a growing demand for eco-efficient and low-cost electrochemical batteries for large-scale electric energy storage. Due to their similar redox chemistry but much lower material costs to lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) appear as a promising candidate for grid-scale electric storage applications. [1] However, the much larger radius of Na + (0.102 nm) than that of Li + (0.076 nm) leads to a kinetic restraint that seriously hinders the development of high-performance Na insertion materials, especially anode materials for SIBs. [2] For instance, graphite has acted successfully as a high capacity anode material in LIBs, but fails to serve as a Na storage anode for SIBs because of its thermodynamic limitation for the formation of stable Na-graphite intercalation compounds (GICs). [3] Fortunately, as a class of amorphous carbonaceous materials with larger interlayer spacing and rich chemically active defects, [4] hard carbon can reversibly accommodate Na ions and deliver a quite large capacity of 250-480 mA h g −1 , depending on different microstructures of the materials. [5] Usually, the microstructure of hard carbon can be briefly described as a hybrid of randomly oriented, rumpled, twisted pseudographitic nanodomains and amorphous nanodomains, in which there exist abundant defects and pores with various sizes. Typically, for sodium storage, hard carbon presents a sloping capacity at the high-potential region and a long plateau capacity at the low-potential region, the latter of which plays a decisive role in realizing the high-energy-density SIBs. However, due to the tremendous difference in the microstructure of hard carbon materials, the sodium storage mechanism on hard carbon remains elusive.In 2000, Stevens and Dahn first proposed an "insertionadsorption (filling)" mechanism based on the sodium storage behaviors in glucose-derived hard carbon. [6] The high potential sloping region and the low potential plateau region were attributed to the Na + insertion into carbon layers and Na + adsorption onto nanopores, respectively. Subsequently, this Hard carbon has the potential to serve as a high-capacity anode material for sodium-ion batteries (SIBs), however, its Na + storage mechanism, particularly on the low potential plateau, remains controversial. To overcome this issue, two types of hard carbons with different microstructures are employed and the relationship between the microstructures and Na + storage behaviors is evaluated. By the combination of operando X-ray diffraction, ex situ Raman spectroscopy, NMR, and theoretical calculation, it is found that the sodium storage capacities of the hard carbons in the low potential plateau region contain the concurrent contributions from both interlayer intercalation and micropores filling, and the ratio of the two contributors greatly depends on the microstructure of hard carbon materials. Moreover, an electrochemical pointer (potential inflection point at the end of the disc...

Organic–inorganic assembly engineering of core–double-shell VSe1.6/C@N–C⊂MoSe2 nanotubes for boosting Na+/K+ storage performance

“…The tail peak near 0.01 V is ascribed to the Na + insertion into the carbon matrix and the interface storage of Na + ions. 12,51 For the reversible oxidation process, the peaks at 1.56 and 1.69 V correspond to the conversion reaction from V/ Mo to and Na x VSe 1.6 and Na x MoSe 2 , respectively. And the following oxidation peaks at 1.86 and 2.07 V correspond to Na + removal to form VSe 1.6 and MoSe 2 , respectively.…”

Ion‐Migration Mechanism: An Overall Understanding of Anionic Redox Activity in Metal Oxide Cathodes of Li/Na‐Ion Batteries

“…applications. [1][2][3][4] However, they cannot yet fulfill the rapidly growing demand for even higher energy densities through applications like electric vehicles. For the current LIBs and SIBs, their energy densities are mainly restricted by the low capacities of cathode materials.…”

High-Voltage and Intrinsically Safe Sodium Metal Batteries Enabled by Nonflammable Fluorinated Phosphate Electrolytes

“…Rechargeable sodium batteries (RSBs) have attracted increasing attention for large-scale energy storage because of their similar mechanism to lithium rechargeable batteries, low cost, and natural abundance of Na. − To meet the demand of the practical application, it is necessary to explore advanced electrode materials to achieve high-energy-density RSBs. − Sodium metal has been considered a promising anode material, on account of its highest theoretical specific capacity (1166 mAh·g –1 ) and the lowest standard redox potential (−2.71 V vs SHE) in RSBs . However, compared with lithium metal, sodium metal is highly reactive, reacts with electrolytes more seriously during cycling, and may lead to higher potential safety hazards .…”