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.

To remain as relevant as possible, academic researchers need to be able to produce electrodes for lithium ion batteries that are comparable to those used in industry. This requires both a high percentage of active material and a high electrode density. Furthermore, the electrodes also need to adhere well enough to the current collecting foil to prevent particle detachment during cycling. While much of the knowledge needed to produce such electrodes is widely known in the industrial sphere, it is not readily available in the academic literature. Now that Li-ion battery technology has matured, reports of materials and cells tested using impractical electrodes are of limited value. This report outlines an effective method for producing high density, high capacity electrodes that have low amounts of binder and carbon black while still possessing excellent adhesion and electrochemical performance.

An apparatus was built to make accurate and precise in situ measurements of the volumes of gas evolved in Li-ion pouch cells during operation. With a thin film load cell accurately measuring the weight of a cell submerged in a fluid, the volume of a pouch cell can be precisely monitored using Archimedes' Principle. Examples showing the utility and sensitivity of the device have been selected from measurements made during the formation cycle (very first charge and discharge) of Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 /graphite (NMC) Li-ion pouch cells. Gas production occurs at the very beginning of the formation cycle but quickly stops for cells containing a variety of electrolytes. The volume of the pouch cell then decreases with time. The testing of cells with various electrolyte additives indicated that the common additive, vinylene carbonate, is very effective at reducing the amount of gas formed during formation, but the best results among the additives reported here were obtained by using a combination of 2% vinylene carbonate and 2% prop-1-ene 1,3-sultone. The additives vinyl ethylene carbonate and ethylene sulfite were found to delay the onset of gas production during formation.

A multitarget sputtering machine with a water-cooled rotating substrate table has been modified to produce films on 75 mm × 75 mm wafers which map large portions of ternary phase diagrams. The system is unconventional because the stoichiometries of the elements sputtered on the wafer vary linearly with position and in an orthogonal manner. Subsequent screening of film properties is therefore quite intuitive, since the compositional variations are simple. Depositions are made under continuous rotation, so either intimate mixing of the elements (fast rotation) or artificial layered structures (slow rotation) can be produced. Rotating subtables mounted on the main rotating table hold the 75 mm × 75 mm substrates. Stationary mask openings over the targets and mechanical actuators that rotate the subtables in a precise manner accomplish the linear and orthogonal stoichiometry variations. Deposition of a film spanning the range SiSn x Al y (0 < x, y < 1), with Sn content increasing parallel to one edge on the wafer and Al content increasing in a perpendicular direction, is given to illustrate the effectiveness of the method. Since the system was easily and inexpensively built, it has enabled our research program in combinatorial materials synthesis to begin without large scale funding.

Wound LiCoO 2 /graphite cells with 1 M LiPF 6 EC:EMC electrolyte containing 1 wt%, 2 wt% vinylene carbonate (VC), 0.3 wt% trimethoxyboroxine (TMOBX) and 2 wt% VC + 0.3 wt% TMOBX were subjected to extended storage studies. After storage, the electrodes were studied using the symmetric cell and electrochemical impedance spectroscopy (EIS) approach described by previous workers. This approach allows the impact of an additive on the impedance of the negative and the positive electrode to be distinguished. Compared to the control cells, adding 1 wt% VC reduced the positive electrode impedance and only slightly affected the negative electrode impedance. Adding 2 wt% VC reduced the positive electrode impedance and greatly increased the negative electrode impedance. An addition of 0.3 wt% TMOBX greatly decreased the positive electrode impedance and slightly increased the negative electrode impedance. Compared to the cells with 2% VC only, adding 2% VC + 0.3% TMOBX decreased the positive electrode impedance without affecting the negative electrode impedance leading to a significant reduction in full cell impedance. These results help explain why the combination of VC and TMOBX additives can be effective in LiCoO 2 /graphite cells designed for long life time.Lithium-ion batteries have high gravimetric and volumetric energy densities which make them suitable for portable electronics and electric vehicle applications. However, parasitic reactions between the electrolyte and the electrochemically active material limit their lifetime, especially at elevated temperatures. Electrolyte additives are generally used in commercial batteries to improve capacity retention and calendar life. [1][2][3] Although it is very apparent that electrolyte additives play an important role, the details of how they work are poorly understood. The most-studied additive, vinylene carbonate (VC) has been shown to change the chemistry of the passivation film on the graphite electrode. 4-7 It is not clear whether this changed film is actually a better film, because recent experiment by Xiong 8 show that only at 60 • C are the parasitic reactions with electrolyte reduced in rate in the presence of VC: at lower temperatures, the reactions are accelerated. Burns et al. and Sinha et al.,9,10 have shown that VC strongly reduces the rate of reactions between the electrolyte and the charged positive electrode, and it seems that the major impact of VC may be at the positive electrode.Burns et al. studied electrolyte additives in wound prismatic cells using high precision coulometry and electrochemical impedance spectroscopy (EIS). 11 These methods show how additives affect the cycling performance, coulombic efficiency, charge and discharge end-point capacity slippage rates and potential drop during storage. As a motivation for the work in this paper, Figure 1 reviews some of the earlier work by Burns et al., 11 where cells were first tested for 600 hours at 40 • C on the high precision charger, then impedance spectra were collected and then cells were cycled f...