S. Trussler

Precision Measurements of the Coulombic Efficiency of Lithium-Ion Batteries and of Electrode Materials for Lithium-Ion Batteries

Undesired reactions in Li-ion batteries, which lead to capacity loss, can consume or produce charge at either the positive or negative electrode. For example, the formation and repair of the solid electrolyte interphase consumes Li + and e - at the negative electrode. High purity electrolytes, elimination of water, various electrolyte additives, electrode coatings, and special electrode materials are known to improve cycle life and therefore must impact coulombic efficiency. Careful measurements of coulombic efficiency are needed to quantify the impact of trace impurities, additives, coatings, etc., in only a few charge-discharge cycles and in a relatively short time. The effects of cycle-induced and time-related capacity loss could be probed by using experiments carried out at different C-rates. In order to make an impact on Li-ion cells for automotive and energy storage applications, where thousands of charge-discharge cycles are required, coulombic efficiency must be measured on the order of 0.01 %. In this paper, we describe an instrument designed to make high precision coulombic efficiency measurements and give examples of its use on commercial Li-ion cells and Li half-cells. High precision coulombic efficiency measurements can detect problems occurring in half-cells that do not lead to capacity loss, but would in full cells, and can measure the impact of electrolyte additives and electrode coatings.

Design and Testing of a 64-Channel Combinatorial Electrochemical Cell

Design, testing, and performance of a 64-channel combinatorial electrochemical cell are described. This cell is used for high-throughput screening of materials for use as Li-ion rechargeable battery electrodes. Our sealedcell has 64 separate positive electrodes and Li foil for the reference and counter electrodes. This combinatorial electrochemical cell was designed to complement our existing combinatorial materials science infrastructure. Using the combinatorial electrochemical cell decreases the time and labor associated with test cell assembly, improves the repeatability of our assembly procedure, and increases the number of compositions we can test in a given amount of time. In this paper, we demonstrate that the results from the combinatorial electrochemical cell and from conventional 2325 coin-type test cells, containing electrodes of sputtered films prepared in the same sputtering run, are identical for electrodes of the same composition.

The amorphous range in sputtered Si–Al–Sn films

Abstract A magnetron sputtering system modified to produce ternary films has been used to map large portions of the ternary phase diagram for the Si–Al–Sn system. The system is unconventional because the stoichiometries of the elements sputtered on the substrates vary linearly with position and in an orthogonal manner. Variations in the composition and structure vs. position were obtained by electron microprobe analysis and X-ray diffraction, respectively. We found that the amorphous range spans all compositions with over 60 at.% silicon. Compositions containing less than 50 at.% silicon were mixtures of the amorphous phase and Sn and/or Al. No intermetallic phases were observed. A ternary non-equilibrium ‘phase diagram’ showing the phases produced in the sputtered films was constructed.