Highlights
Hard-carbon anode dominated with ultra-micropores (< 0.5 nm) was synthesized for sodium-ion batteries via a molten diffusion–carbonization method.
The ultra-micropores dominated carbon anode displays an enhanced capacity, which originates from the extra sodium-ion storage sites of the designed ultra-micropores.
The thick electrode (~ 19 mg cm−2) with a high areal capacity of 6.14 mAh cm−2 displays an ultrahigh cycling stability and an outstanding low-temperature performance.
Abstract
Pore structure of hard carbon has a fundamental influence on the electrochemical properties in sodium-ion batteries (SIBs). Ultra-micropores (< 0.5 nm) of hard carbon can function as ionic sieves to reduce the diffusion of slovated Na+ but allow the entrance of naked Na+ into the pores, which can reduce the interficial contact between the electrolyte and the inner pores without sacrificing the fast diffusion kinetics. Herein, a molten diffusion–carbonization method is proposed to transform the micropores (> 1 nm) inside carbon into ultra-micropores (< 0.5 nm). Consequently, the designed carbon anode displays an enhanced capacity of 346 mAh g−1 at 30 mA g−1 with a high ICE value of ~ 80.6% and most of the capacity (~ 90%) is below 1 V. Moreover, the high-loading electrode (~ 19 mg cm−2) exhibits a good temperature endurance with a high areal capacity of 6.14 mAh cm−2 at 25 °C and 5.32 mAh cm−2 at − 20 °C. Based on the in situ X-ray diffraction and ex situ solid-state nuclear magnetic resonance results, the designed ultra-micropores provide the extra Na+ storage sites, which mainly contributes to the enhanced capacity. This proposed strategy shows a good potential for the development of high-performance SIBs.
Sodium metal batteries (SMBs) are promising candidates for low‐cost but high‐energy energy storage applications. Both long‐term stability and safety of SMBs can be largely enhanced when liquid electrolytes (LEs) are replaced by gel polymer electrolytes (GPEs). However, the low room‐temperature (RT) ionic conductivity and inferior interfacial compatibility of GPEs severely restrain their practical use. Herein, a poly(butyl acrylate)‐based GPE with a high RT ionic conductivity of 1.6 mS cm−1 is developed by in‐situ polymerization. Symmetrical cells assembled with this GPE show ultralong cyclability over 900 h at 0.2 mA cm−2, and ultralow overpotential of 233 mV at 1 mA cm−2. Full cells based on Na3V2(PO4)3(NVP) cathodes (NVP||GPE||Na) display significantly improved rate capability than that of LEs, benefiting from the solvation structure of Na+ in the GPE with much lower desolvation energy. Furthermore, the NVP||GPE||Na pouch cells exhibit a stable capacity of ≈92 mA h g−1 for 50 cycles at 1 C and excellent flexibility. The work not only provides a reliable GPE to develop RT SMBs but also offers new insight into the role of polymer frameworks in the rate performance of SMBs.
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