An in situ method to prepare lithium microreference electrodes has been developed. The microreference electrodes are made by electrochemical deposition of metallic lithium from both the positive and negative electrodes onto a copper wire positioned in-between the two Li-based battery electrodes. The stability of these microreference electrodes was found to be dependent on the deposition current density and the thickness of the metallic lithium layer. A current density of 0.2 mA/cm 2 and a lithium layer thickness of 4 m were shown to be the most favorable deposition condition. When the potential of the electrodes eventually starts to degrade due to ''consumption'' of the deposit, the microreference electrodes can advantageously be recovered by lithium redeposition. The redeposited electrodes were verified to be as stable as the freshly prepared electrodes. The validity of the microreference electrode was confirmed by electrochemical impedance spectroscopy. The microreference electrodes were employed to monitor the electrode potentials during prolonged cycling. The as-obtained potential plots of both the positive and negative electrodes are present in this paper.

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An electrochemical method has been developed for the in situ determination of concentration gradients in the electrolyte of sealed Li-ion batteries by measuring the potential difference between microreference electrodes. Formulas relating the concentration gradient and the potential difference between the microreference electrodes were derived from the Nernst-Planck equation. The concentration gradients in Li-ion batteries are theoretically and experimentally proven to be linear at steady state under galvanostatic charging and discharging conditions. Based on this finding, both the diffusion coefficient of the lithium ions in the electrolyte and the diffusion overpotential related to the concentration gradient have been calculated. It was found that the concentration gradient is proportional to the applied current over a wide current range and that the obtained diffusion coefficient of lithium ions is almost constant. For the batteries studied in this work, the diffusion overpotential is already noticeable at 0.30 A and the limiting current is estimated to be 1.1 A, corresponding to a C-rate of 3.7.

A simple method based on alternating heating-quenching cycles is exploited to synthesize a three-dimensional (3D) macroporous graphene structure that is characterized by a hierarchically interconnected flexible network of high-quality graphene nanosheets with few oxygen-containing moieties. The structure can be employed as a suitable scaffold to load functional nanoparticles and as a fast transport channel for charge carriers. As a proof of concept, we fabricate novel graphene/P25 nanocomposites that are examined as stable high-performance anode materials for lithium ion batteries; the prepared nanocomposites feature excellent electrochemical performance with a capacity as high as 120 mA h g −1 after 100 cycles that is ∼ 4.8 times larger than that of bare P25.