Boosting the Development of Hard Carbon for Sodium‐Ion Batteries: Strategies to Optimize the Initial Coulombic Efficiency

Abstract

Given the merits of affordable cost, superior low‐temperature performance, and advanced safe properties, sodium‐ion batteries (SIBs) have exhibited great development potential in large scale energy storage applications. Among various emerging carbonaceous anode materials applied for SIBs, hard carbon (HC) has recently gained significant attention regarding their relatively low cost, wide availability, and optimal overall performance. However, the insufficient initial Coulombic efficiency (ICE) of HC is the main bottlenecks, which is inevitably hindering their further commercial applications. Herein, an in‐depth holistic exposition about the reasons causing the unsatisfied ICE and the recent advances on effective improvement strategies are comprehensively summarized in this review, which have been divided into two aspects including the intrinsic property (degree of graphitization, pore structure, defect, et al.) and the extrinsic factor (electrolyte, electrode materials, et al.). In addition, future prospects and perspectives on HC to enable practical application in SIBs are also briefly outlined.

Achieving All‐Plateau and High‐Capacity Sodium Insertion in Topological Graphitized Carbon

“…L-CDC also exhibits a certain slope and plateau in its electrochemical behavior since it is treated at 1200 °C, which is similar to the treatment temperature of commercial hard carbon in general. The diffusion coefficients obtained by specific GITT calculations are similar to the findings of previous work, [35,41,42] with the first half of the plateau region decreasing and the last part of the second half showing an abrupt increase in the sodium-ion diffusion coefficient. In contrast, for the H-TPGC, the diffusion coefficient shows a decrease followed by a continuous flattening throughout the long low potential full plateau region (Figure S29, Supporting Information).…”

Sustainable Fabrication of a Practical Hard Carbon Anode for a Sodium-Ion Battery with Unprecedented Long Cycle Life

“…52 The results of X-ray photoelectron spectroscopy (XPS) of HCs (Figure 2d) illustrate the ratio of carbon to oxygen (C/ O) of GCHC-1200 (18.26), GCHC-1400 (14.59), and GCHC-1600 (20.22) after enzymatic hydrolysis is lower than that of CHC-1400 (33.75). This is due to the increase of sp 3 hybridized carbon at C−O bond defect sites. 53 The XPS fine spectra reveal the bond configuration of C 1s and O 1s.…”

“…53 The XPS fine spectra reveal the bond configuration of C 1s and O 1s. C 1s (Figure S4) presents five separation peaks at 284.8, 285.3, 286.7, 288.4, and 290.7 eV, belonging to sp 2 -C, sp 3 -C, C−O, C�O, and π−π*, respectively. 54 The detailed composition of C 1s of different samples (Table S2) shows that the relative content of sp 2 -C increases and sp 3 -C decreases with the increase of the pyrolysis temperature.…”

“…C 1s (Figure S4) presents five separation peaks at 284.8, 285.3, 286.7, 288.4, and 290.7 eV, belonging to sp 2 -C, sp 3 -C, C−O, C�O, and π−π*, respectively. 54 The detailed composition of C 1s of different samples (Table S2) shows that the relative content of sp 2 -C increases and sp 3 -C decreases with the increase of the pyrolysis temperature. This result reflects the reduction of defects and oxygen concentration, which promote the formation of the sp 2 -C structure.…”

“…1 However, the larger ionic radius and accommodating void of a sodium ion unavoidably lead to higher requirements for electrode materials compared to a lithium ion. 2,3 In recent years, numerous research studies have been carried out on lots of anode materials, such as graphite, 4,5 nongraphitic carbon, 6−8 titanium materials, 9−11 alloys, 12,13 and organic compounds. 14−16 To be sure, low cost and ultralong cycling performance are at the core of boosting the commercialization process of SIBs.…”