A series of previously unknown 2,4,5-tri-and 2,4,5,7-tetrasubstituted 1,8bis(dimethylamino)naphthalenes and their salts with HBF 4 containing bulky spherically shaped substituents (Me, Br, and SiMe 3 ) in the naphthalene ring has been synthesized. Using XRD analysis of 11 samples, the influence of the so-called "buttressing" and "clothespin" effects on their molecular structure and the NHN hydrogen bond geometry in the solid cations were investigated. The combined action of both effects has been shown to significantly increase the compression of the hydrogen bond. As a result, the previous record of the hydrogen bond shortness (N•••N = 2.524 Å) has been surpassed in favor of 2.502 Å found for the tetrafluoroborate of 2,4,5,7-tetramethyl-1,8-bis-(dimethylamino)naphthalene. The molecular structure of the latter differs by perfect symmetry and practically barrier-free proton transfer in the [NHN] + bond. On the basis of the results of quantum-chemical calculations, it is suggested that the value of 2.502 Å likely represents or lies very close to the theoretical limit for the short hydrogen bonds between the amine-type nitrogen atoms.

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Electrochemical cells using LiFePO4 cathode material are considered one of the safest and most resistant to overcharging among Li-ion batteries. However, if LiFePO4-based electrodes are exposed to high potentials, surface and structural changes may occur in the electrode material. In this study Li/LiFePO4 half-cells were overcharged under different modes with variable cut-off voltages and charge currents. The change in voltage profile, discharge capacity, surface layers composition, and crystalline structure were characterized after overcharge cycles. It was demonstrated that the cathode material is resistant to short-term overcharging up to 5 V, but undergoes irreversible changes with increasing overcharge time or potential. Thus, despite the well-known tolerance of LiFePO4-based batteries to overcharge, a long overcharge time or high cut-off voltage leads to destructive changes in the cathode and should be avoided.

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