Hard carbon possesses the ability to store Li, Na, and K ions between stacked sp 2 carbon layers and voids (micropores). We have explored hard carbon as a candidate for negative electrode materials for Li-ion, Na-ion, and K-ion batteries. Hard carbon samples have been prepared by carbonizing sucrose at different heat treatment temperatures (HTTs) in the range of 700−2000 °C to make them structurally suitable for reversible Li, Na, and K insertion. Structures and particle morphology of the hard carbon samples synthesized at different HTTs were systematically characterized using X-ray diffraction, small-angle X-ray scattering, pair distribution function analysis, electron microscopy, Raman spectroscopy, and electron spin resonance spectroscopy. All these characterizations of hard carbon samples have revealed advanced ordering of carbons and reduction of carbon defects with increasing HTT. Thus, the average stacked carbon interlayer distance decreases, the number of the stacking layers increases, the layered domains grow in the in-plane direction, and interstitial voids enlarge. Electrochemical properties of the hard carbons were examined in nonaqueous Li, Na, and K cells. Potential profiles and reversible capacities upon galvanostatic charge/discharge processes in nonaqueous cells are significantly different depending on HTTs and different alkali metal ions. On the basis of these findings, strategies to design high-capacity hard carbon negative electrodes for high-energy-density Li-ion, Na-ion, and K-ion batteries are discussed.

For a nonaqueous sodium-ion battery (NIB), phosphorus materials have been studied as the highest-capacity negative electrodes. However, the large volume change of phosphorus upon cycling at low voltage causes the formation of new active surfaces and potentially results in electrolyte decomposition at the active surface, which remains one of the major limiting factors for the long cycling life of batteries. In this present study, powerful surface characterization techniques are combined for investigation on the electrode/electrolyte interface of the black phosphorus electrodes with polyacrylate binder to understand the formation of a solid electrolyte interphase (SEI) in alkyl carbonate ester and its evolution during cycling. The hard X-ray photoelectron spectroscopy (HAXPES) analysis suggests that SEI (passive film) consists of mainly inorganic species, which originate from decomposition of electrolyte solvents and additives. The thicker surface layer is formed during cycling in the additive-free electrolyte, compared to that in the electrolyte with fluoroethylene carbonate (FEC) or vinylene carbonate (VC) additive. The HAXPES and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) studies further reveal accumulation of organic carbonate species near the surface and inorganic salt decomposition species. These findings open paths for further improvement for the cyclability of phosphorus electrodes for high-energy NIBs.

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Hard Optimal carbonization of glucose, sucrose, maltose, cellulose, glycogen, and amylopectin is studied for Na-ion application.