Rational Route for Increasing Intercalation Capacity of Hard Carbons as Sodium‐Ion Battery Anodes

Abstract

Hard carbon (HC) is the most promising candidate for sodium‐ion battery anode materials. Several material properties such as intensity ratio of the Raman spectrum, lateral size of HC crystallite (La), and interlayer distance (d002) have been discussed as factors affecting anode performance. However, these factors do not reflect the bulk property of the Na+ intercalation reaction directly, since Raman analysis has high surface sensitivity and La and d002 provide only one‐dimensional crystalline information. Herein, it was proposed that the crystallite interlayer area (Ai) defined using La, d002, and stacking height (Lc) governs Na+ intercalation behavior of various HCs. It was revealed that various wood‐derived HCs exhibited the similar total capacity of approximately 250 mAh g−1, whereas the Na+ intercalation capacity (Ci) was proportional to Ai with the correlation coefficient of R2=0.94. The evaluation factor of Ai was also adaptable to previous reports and strongly correlated with their Ci, indicating that Ai is more widely adaptable than the conventional evaluation methods.

Revisit Electrolyte Chemistry of Hard Carbon in Ether for Na Storage

“…On the other hand, HC in DGM also shows an electrode polarization (∼0.08 V) smaller than that in EC/DEC (∼0.15 V) for the redox reaction at 0.1 V. It indicates the fast electrochemical reaction kinetics. 46 − 48 This conclusion is also supported by rate performances ( Figure 1 f). The capacity difference between DGM and EC/DEC increases as the current density increases.…”

A 3D‐Printed, Freestanding Carbon Lattice for Sodium Ion Batteries

“…Given the small specific BET surface area mentioned above, a slope capacity lower than 100 mAh g −1 was expected from our previous study that showed proportionality between the two values. [ 10 ] The 3D‐printed HC electrodes showed a Coulombic efficiency (CE) of 80% in the 1st cycle, which is superior to the typical value of 73% for HC electrodes. [ 50 ] The low Coulombic efficiency for the 1st cycle is attributed to the formation of an SEI layer, which has been widely studied for a series of electrodes and electrolytes including hard carbon and 1.0 m LiPF 6 PC as used in this work.…”

“…In order to use the stored energy when needed and as fast as desired, batteries must exhibit high capacity and high power at an affordable cost. Researchers have made tremendous efforts to develop such technologies including silicon anodes for lithium-ion batteries (LIBs) with a gravimetric capacity an order of magnitude higher than graphite, [1][2][3] solid state electrolytes to improve the safety of batteries, [4] replacement of inorganic compounds by organic materials which requires less energy for mass production, [5][6][7][8][9] and substitution of lithium by other more abundant metals such as sodium, [10][11][12][13][14] potassium, [11] calcium, [15] magnesium, [16] aluminum, [17] and zinc. [17] Nevertheless, it still remains a challenging goal to simultaneously achieve high performance and low cost as they generally conflict with each other.One possible way to achieve this goal is to increase the mass loading of active materials in a single cell (Figure 1).…”

Understanding of Sodium Storage Mechanism in Hard Carbons: Ongoing Development under Debate

“…Li et al [57] highlighted the importance of graphene layer orientation and edge sites' structural heterogeneity to increase the nucleation density of the Na x C intercalation compounds. More recently, Katsuyama et al [58] proposed that the Na + intercalation capacity in wood-derived hard carbons was proportional to the crystallite interlayer area with a correlation coefficient of 0.94. To some extent, the domain size could be represented with crystallite size La, which is usually determined by the Raman technique (Figure 3a) according to the equation La = 2.4 × 10 −10 λ 4 nm (I G /I D ).…”