Realizing Improved Sodium-Ion Storage by Introducing Carbonyl Groups and Closed Micropores into a Biomass-Derived Hard Carbon Anode

Enhancing the Low-Temperature Performance of Sodium-Ion Battery by Introducing Nanodiamonds in Anode Prepared from Cattail Grass

Sodium-ion batteries (SIBs) have received much attention as ideal candidates for next-generation large-scale energy storage systems, but their performance significantly deteriorates at low temperatures, limiting their application in cold or high-altitude environments. This work presents an easier approach to improving low-temperature performance by incorporating nanodiamonds (NDs) into hard carbon anodes derived from cattail grass. The modified anode shows a larger specific surface area, offering more active sites for Na+. After 90 cycles at 0.1 A g-1, the reversible capacity of the modified anode reaches 365.1 mA h g-1 at room temperature and remains 245.1 mA h g-1 at -40 °C. Even under a high current density of 1.0 A g-1, it delivered 108.2 mA h g-1 after 500 cycles with a capacity retention rate of 90%. The improved low-temperature performance is attributed to the introduced NDs in SIBs, which in crease the number of the reversible active sites, reduce charge transfer resistance, lower activation energy, and effectively inhibit the formation of Na dendrites. This work presents a potential pathway into designing efficient and stable anode materials for SIBs at low temperatures.

Deconstruction Engineering of Lignocellulose Toward High-Plateau-Capacity Hard Carbon Anodes for Sodium-Ion Batteries

Biomass-derived hard carbon is a promising anode material for commercial sodium-ion batteries due to its low cost, high capacity, and stable cycling performance. However, the intrinsic tight lignocellulosic structure in biomass hinders the formation of sufficient closed pores, limiting the specific capacity of obtained hard carbons. In this contribution, a mild, industrially mature pretreatment method is utilized to selectively regulate biomass components. The hard carbon with a rich closed pore structure is prepared by optimizing the appropriate ratio of biomass composition. Optimized etching conditions enhanced the closed pore volume of hard carbon from 0.15 to 0.26 cm3 g-1. Consequently, the engineered hard carbon exhibited excellent electrochemical performance, including a high reversible capacity of 346 mAh g-1 with a high plateau capacity of 254 mAh g⁻¹ at 50 mA g⁻¹, robust rate capability, and cycling stability. The optimized hard carbon shows an 88 mAh g⁻¹ increase in plateau capacity compared to hard carbon from directly carbonizing bamboo fibers. This mature approach provides an easy-to-operate industrial pathway for designing high-capacity biomass-based hard carbons for sodium-ion batteries.

Multieffect Preoxidation Strategy to Convert Bituminous Coal into Hard Carbon for Enhancing Sodium Storage Performance

Preoxidation is an effective strategy to inhibit the graphitization of coals during carbonization. However, the single effect of the traditional preoxidation strategy could barely increase surface-active sites, hindering further enhancement of sodium storage. Herein, a multieffect preoxidation strategy was proposed to suppress structural rearrangement and create abundant surface-active sites. Mg(NO3)2·6H2O helps to introduce oxygen-containing functional groups into bituminous coal at 450 °C, which acted as a cross-linking agent to inhibit the rearrangement of carbon layers and promote structural cross-linking during the subsequent thermal carbonization process. Besides, the residue solid decomposition product MgO would react with carbon to create surface-active sites. The obtained coal-based hard carbon contained more pseudographitic domains and sodium storage active sites. The optimized sample could deliver an excellent capacity of 287.1 mAh g-1 at 20 mA g-1, as well as remarkable cycling stability of capacity retention of 96.1% after 200 cycles at 50 mA g-1, and notable capacity retention of 88.9% after 1000 cycles at 300 mA g-1. This work provides an effective and practical strategy to convert low-cost bituminous coal into advanced hard carbon anodes for sodium-ion batteries (SIBs).

Exploring Carbonization Temperature to Create Closed Pores for Hard Carbon as High-Performance Sodium-Ion Battery Anodes

Biomass-derived porous carbon materials are meaningful to employ as a hard carbon precursor for anode materials of sodium-ion batteries (SIBs) from a sustainability perspective. Here, a straightforward approach is proposed to develop rich closed pores in pinenut-derived carbon, with the aim of improving Na+ plateau storage by adjusting the pyrolysis temperature. The optimized sample, namely the pinenut-derived carbon at 1300 °C, demonstrates remarkable reversible specific capacity of 278 mAh g-1, along with a high initial Coulomb efficiency of 85% and robust cycling stability (with a capacity retention of 89% after 800 cycles at 0.2 A g-1). In situ and ex situ analyses unveil that the developed closed pores play a significant role in enhancing the plateau capacity, providing compelling evidence for the "adsorption-filling" mechanism. Moreover, the corresponding full-cell achieves a high energy density of 245.7 Wh kg-1 (based on the total weight of both electrode active materials) and exhibits outstanding rate capability (191.4 mAh g-1 at 3 A g-1).

Releasing Free Radicals in Precursor Triggers the Formation of Closed Pores in Hard Carbon for Sodium-Ion Batteries

Increasing closed pore volume in hard carbon is considered to be the most effective way to enhance the electrochemical performance in sodium-ion batteries. However, there is a lack of systematic insights into the formation mechanisms of closed pores at molecular level. In this study, a regulation strategy of closed pores via adjustment of the content of free radicals is reported. Sufficient free radicals are exposed by part delignification of bamboo, which is related to the formation of well-developed carbon layers and rich closed pores. In addition, excessive free radicals from nearly total delignification lead to more reactive sites during pyrolysis, which competes for limited precursor debris to form smaller microcrystals and therefore compact the material. The optimal sample delivers a large closed pore volume of 0.203 cm3 g-1, which leads to a high reversible capacity of 350 mAh g-1 at 20 mA g-1 and enhanced Na+ transfer kinetics. This work provides insights into the formation mechanisms of closed pores at molecular level, enabling rational design of hard carbon pore structures.

Molecular Engineering Enabling High Initial Coulombic Efficiency and Rubost Solid Electrolyte Interphase for Hard Carbon in Sodium-Ion Batteries

Hard carbon (HC) as a potential candidate anode for sodium-ion batteries (SIBs) suffers from unstable solid electrolyte interphase (SEI) and low initial Coulombic efficiency (ICE), which limits its commercial applications and urgently requires the emergence of a new strategy. Herein, an organic molecule with two sodium ions, disodium phthalate (DP), was successfully engineered on the HC surface (DP-HC) to replenish the sodium loss from solid electrolyte interphase (SEI) formation. A stabilized and ultrathin (≈7.4 nm) SEI was constructed on the DP-HC surface, which proved to be simultaneously suitable in both ester and ether electrolytes. Compared to pure HC (60.8 %), the as-designed DP-HC exhibited a high ICE of >96.3 % in NaPF6 in diglyme (G2) electrolyte, and is capable of servicing consistently for >1600 cycles at 0.5 A g-1 . The Na3 V2 (PO4 )3 (NVP)|DP-HC full-cell with a 98.3 % exceptional ICE can be cycled stably for 450 cycles, demonstrating the tremendous practical application potential of DP-HC. This work provides a molecular design strategy to improve the ICE of HC, which will inspire more researchers to concentrate on the commercialization progress of HC.

Recent Advances of Pore Structure in Disordered Carbons for Sodium Storage: a Mini Review

Disordered carbons as the most promising anode materials for sodium ion batteries (SIBs) have attracted much attention, due to the widely-distributed sources and potentially high output voltage when applied in full cells owing to the almost lowest voltage plateau. The complex microstructure makes the sodium storage mechanism of disordered carbons controversial. Recently, many studies show that the plateau region of disordered carbons are closely related to the embedment of sodium ion/semimetal in nanopores. In this regard, the classification, characterization and construction of nanopores are exhaustively discussed in this review. In addition, perspectives about the controllable construction of nanopores are presented in the last section, aiming to catch out more valuable studies include not only the construction of closed pores to enhance capacity but also the design of carbon materials to understand Na storage mechanism.