International audienc

The electrochemical behavior of Li-graphite intercalation anodes .in ethylene and diethyl carbonates (EC-DEC) solutions was studied using surface sensitive Fourier transform infrared spectroscopy (FTIR) and impedance spectroscopy in conjunction with standard electrochemical techniques. Three different solvent combinations, four different salts: LiBF4, LiPF6, LiC104, and LiAsF6, and the influence of the presence of CO2 were investigated. Graphite electrodes could be cycled hundreds of times obtaining a reasonable reversible capacity. The best electrolyte was found to be LiAsF6 and the presence of CO2 in solutions considerably increased the reversible capacity upon cycling. This improved performance is due to precipitation of the ethylene carbonate reduction product, (CH2OCO2Li)2, which is an excellent passivating agent, on the electrode surface. Aging processes of these surface films and their influence on the electrode properties are discussed.

No abstract

We demonstrate herein that Mn and not Mn, as commonly accepted, is the dominant dissolved manganese cation in LiPF-based electrolyte solutions of Li-ion batteries with lithium manganate spinel positive and graphite negative electrodes chemistry. The Mn fractions in solution, derived from a combined analysis of electron paramagnetic resonance and inductively coupled plasma spectroscopy data, are ∼80% for either fully discharged (3.0 V hold) or fully charged (4.2 V hold) cells, and ∼60% for galvanostatically cycled cells. These findings agree with the average oxidation state of dissolved Mn ions determined from X-ray absorption near-edge spectroscopy data, as verified through a speciation diagram analysis. We also show that the fractions of Mn in the aprotic nonaqueous electrolyte solution are constant over the duration of our experiments and that disproportionation of Mn occurs at a very slow rate.

Li-ion batteries (LIBs) today face the challenge of application in electrified vehicles (xEVs) which require increased energy density, improved abuse tolerance, prolonged life, and low cost. LIB technology can significantly advance through more realistic approaches such as: i) stable high-specific-energy cathodes based on Li Ni Co Mn O (NCM) compounds with either Ni-rich (x = 0, y → 1), or Li- and Mn-rich (0.1 < x < 0.2, w > 0.5) compositions, and ii) chemically active separators and binders that mitigate battery performance degradation. While the stability of such cathode materials during cell operation tends to decrease with increasing specific capacity, active material doping and coatings, together with carefully designed cell-formation protocols, can enable both high specific capacities and good long-term stability. It has also been shown that major LIB capacity fading mechanisms can be reduced by multifunctional separators and binders that trap transition metal ions and/or scavenge acid species. Here, recent progress on improving Ni-rich and Mn-rich NCM cathode materials is reviewed, as well as in the search for inexpensive, multifunctional, chemically active separators. A realistic overview regarding some of the most promising approaches to improving the performance of rechargeable batteries for xEV applications is also presented.