Design guidelines for a high-performance hard carbon anode in sodium ion batteries

Transition metal sulfides as anode materials for sodium‐ion batteries (SIBs) have the advantage of high capacity. However, their cycle‐life and rate performance at ultra‐high current density is still a thorny issue that limit the applicability of these materials. In this paper, the carbon‐embedded heterojunction with sulfur‐vacancies regulated by ultrafine bimetallic sulfides (vacancy‐CoS2/FeS2@C) with robust interfacial C‐S‐Co/Fe chemical bonds is successfully synthesized and explored as an anode material for sodium‐ion battery. By changing the ratio of two metal cations, the concentration of anion sulfur vacancies can be in‐situ adjusted without additional post‐treatment. The as‐prepared vacancy‐CoS2/FeS2@C anode material offers ultrahigh rate performance (285.1 mAh g−1 at 200 A g−1), and excellent long‐cycle stability (389.2 mAh g−1 at 40 A g−1 after 10000 cycles), outperforming all reported transition metal sulfides‐based anode materials for SIBs. Both in‐situ and ex‐situ characterizations provide strong evidence for the evolution mechanism of the phases and stable solid‐electrolyte interface (SEI) on the vacancy‐CoS2/FeS2@C surface. The density functional theory calculations show that constructing heterojunction with reasonable concentration of vacancies can significantly increase the anode electronic conductivity. Notably, the assembled vacancy‐CoS2/FeS2@C//Na3V2(PO4)3/C full‐cell shows a capacity of 226.2 mAh g−1 after 400 cycles at 2.0 A g−1, confirming this material's practicability.

Heterojunction Vacancies‐Promoted High Sodium Storage Capacity and Fast Reaction Kinetics of the Anodes for Ultra‐High Performance Sodium‐Ion Batteries

Zheng,

Ma,

Pei

et al. 2024

Construction of Low‐Softening‐Point Coal Pitch Derived Carbon Nanofiber Films as Self‐Standing Anodes Toward Sodium Dual‐Ion Batteries

Zhang,

Wang,

Yue

et al. 2024

To achieve high‐quality hard carbon nanofibers (HCNFs), and particularly flexible HCNFs films is the eternal pursuit from low‐cost coal pitch (CP). However, it is still trapped seriously by the inborn bottleneck of low‐softening‐point (LSP) characteristics of CP itself. Herein, an efficient Bi(NO3)3·5H2O‐assisted electrospinning‐carbonization methodology is creatively devised to obtain flexible HCNFs films directly from LSP CP. The essential roles of Bi(NO3)3·5H2O and pre‐oxidation in constructing flexible films are rationally proposed. With further regulation in Bi(NO3)3·5H2O dosage and calcination temperatures, specific micro‐structures/morphologies of flexible HCNFs films are finely optimized. The optimum HCNFs‐1.2 film is endowed with robust structural flexibility/stability, high‐content active oxygen/nitrogen groups, abundant graphic microcrystalline zones of large interlayer spacing, and convenient ion‐diffusion channels. Thanks to such remarkable merits, HCNFs‐1.2 retains a large reversible capacity of 125.3 mAh g‒1 over 1000 cycles at 1.0 A g‒1, when evaluated as a self‐supporting film anode for sodium dual‐ion batteries (SDIBs). Furthermore, the HCNFs‐1.2‐based SDIBs deliver a specific capacity of 90.9 mAh g‒1 at 0.1 A g‒1, along with a capacity retention of 78.4% after 1500 cycles at 1.0 A g‒1. The insightful understanding here will provide meaningful guidance for rational design of advanced flexible film electrodes toward next‐generation SDIBs and beyond.

Electrolyte Engineering of Hard Carbon for Sodium‐Ion Batteries: From Mechanism Analysis to Design Strategies

Cui,

Hou,

Zhou

et al. 2024

The hard carbon (HC) anodes with desirable electrochemical performances including high initial Coulombic efficiency, superior rate performance and long‐term cycling play an indispensable role in the practical application of sodium ion batteries (SIBs), which are closely related to the electrolytes them matched. Fully analyzing the mechanism of electrolyte engineering for HC anodes is crucial for promoting the commercialization of SIBs, but is still lacking. In this review, the correlation between physicochemical properties of the electrolyte and the electrochemical performance of HC is first summarized. And point out the crucial role of electrolyte properties, including ion conductivity, de‐solvation energy, and interface passivation ability for the Na+ storage in HC. Then, the formation process, composition, as well as structure of solid electrolyte interphase (SEI) on HC surface are mainly discussed, and the structure‐activity relationship of SEI is analyzed in depth. Moreover, based on the mechanism analysis, relevant electrolyte design strategies have been summarized. Finally, the challenges and future development directions of the electrolyte engineering of HC are proposed. This review is expected to provide professional theoretical guidance for the development of electrolyte and contribute to the rational design of high‐performance HC anodes, promoting the industrialization of SIBs.