Nitrogen‐enriched nonporous carbon materials derived from melamine–mica composites are subjected to ammonia treatment to further increase the nitrogen content. For samples preoxidized prior to the ammonia treatment, the nitrogen content is doubled and is mainly incorporated in pyrrol‐like groups. The materials are tested as electrodes for supercapacitors, and in acidic or basic electrolytes, the gravimetric capacitance of treated samples is three times higher than that of untreated samples. This represents a tenfold increase of the capacitance per surface area (3300 µF cm−2) in basic electrolyte. Due to the small volume of the carbon materials, high volumetric capacitances are achieved in various electrolytic systems: 280 F cm−3 in KOH, 152 F cm−3 in H2SO4, and 92 F cm−3 in tetraethylammonium tetrafluoroborate/propylene carbonate.

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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.

X-ray photoelectron spectroscopy and scanning electron microscopy methods were used for analysis of the surface layers of lithium deposited at various current densities from propylene carbonate containing 1.0 ml dm3 LiC1O4 and various amounts of HF, to investigate the effect of HF in electrolytes on the surface reaction of lithium during electrochemical deposition. Our analyses indicate that the surface state of lithium and the morphology of lithium deposits are influenced by both the concentration of HF and the electrodeposition current. The first parameter for the electrodeposition of lithium is related to the chemical reaction rate of the lithium surface with HF and second to the electrodeposition rate of lithium. These results suggest that surface modification is effective in suppressing lithium dendrite formation when the chemical reaction rate with HF is greater than the electrochemical deposition rate of lithium. InfroductionThe reversibility of the lithium metal deposition-dissolution cycle is not very efficient for rechargeable lithium batteries. Therefore, understanding the electrochemical deposition of lithium is most important for development of high

The surface film on lithium immersed in various electrolytes was analyzed by x‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, and the potential sweep method. The surface film formed on lithium immersed in propylene carbonate or γ‐butyrolactone containing 1.0 mol dm−3 LiBF4 ( LiBF4/PC or LiBF4/γ‐BL ) for 3 days consists of normalLiF and a small amount of organic compounds. On the other hand, the surface film on lithium immersed in tetrahydrofuran (THF) containing 1.0 mol dm−3 LiBF4 false(LiBF4/THFfalse) consists of a large amount of organic compounds and normalLiF . normalLiF and organic compounds are formed by the chemical reaction of normalLiOH , Li2CO3 , and Li2O with HF involved in the electrolyte plus the direct reaction of the solvent with the lithium metal, respectively. The amount of organic compounds produced was influenced by the kind of solvent. For the formation of organic compounds, solvents have to permeate the normalLiF layer on the lithium. Probably, the permeability of the solvent is related to the formation of organic compounds. The permeability of the electrolyte is estimated quantitatively from the surface tension and viscosity. The surface tension and viscosity were obtained using the capillary rise method and Ostwald's viscometer, respectively. The surface tension and viscosity of LiBF4/THF were much smaller than those of LiBF4/PC or LiBF4/γ‐BL . This indicates that THF is more permeable than PC and γ‐BL. THF may easily reach the lithium metal surface to form a large amount of organic compounds. From these results, it can be concluded that the surface reaction of the lithium dose not only depends on the chemical properties of the lithium surface and electrolyte, but also on the physicochemical properties of the electrolyte.

Hard carbon is synthesized by heat-treating macroporous phenolic resin at different temperatures. We study influences of temperature on the structures and electrode properties of the hard carbon in Na and K cells. X-ray diffraction and scattering data of the samples confirm the decreased interlayer distance between sp2-carbon sheets and the expanded internal pores at the raised temperatures from 1100 to 1500 °C. Reversible capacities in Na cells increase with an increase in the heat-treatment temperature. Hard carbon carbonized at 1500 °C delivers the largest capacities of 386 and 336 mAh g–1 at 10 mA g–1 in Na and K cells, respectively.

The dissolution-deposition cycle behavior of Li metal electrodeposited in nonaqueous electrolyte containing a small amount of HF was investigated. In the first deposition process, Li particles with a smooth hemispherical shape were deposited on Ni in 1.0 M LiCF 3 SO 3 /propylene carbonate containing HF. The morphology of these fine Li particles is due to electrodeposition via migration of Li ϩ ions through a thin and compact surface film consisting of a LiF/Li 2 O bilayer, which was produced via surface modification by HF. After the first dissolution process, a residual film was observed on the entire surface of the Ni substrate. This residual film is derived from the surface film on the Li particles. Moreover, the residual film continuously accumulated on the electrode during the cycling. On the other hand, it was found that the coulombic efficiency of Li deposition-dissolution during cycling was much improved by the addition of HF. Unfortunately, the formation of dendritic Li was observed after the 45th cycle, suggesting that the accumulated thick residual film on the Li surface inhibits the supply of HF to the Li surface during the deposition process.

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