E-One Moli Energy (Canada)

Rechargeable lithium-ion batteries that use an aqueous electrolyte have been developed. Cells with LiMn(2)O(4) and VO(2)(B) as electrodes and 5 M LiNO(3) in water as the electrolyte provide a fundamentally safe and cost-effective technology that can compete with nickelcadmium and lead-acid batteries on the basis of stored energy per unit of weight.

Li/graphite and Li/petroleum coke cells using a in a 50:50 mixture of propylene carbonate (PC) and ethylene carbonate (EC) electrolyte exhibit irreversible reactions only on the first discharge. These irreversible reactions are associated with electrolyte decomposition and cause the formation of a passivating film or solid electrolyte interphase on the surface of the carbon. The amount of electrolyte decomposition is proportional to the specific surface area of the carbon electrode. When all the available surface area is coated with the film of decomposition products, further decomposition reactions stop. In subsequent cycles, these cells exhibit excellent reversibility and can be cycled without capacity loss.

The charge and discharge mechanisms of and cells near room temperature are studied by in situx‐ray diffraction and in situ 57Fe Mössbauer spectroscopy. The electrochemical behavior of these cells are compared, and their cell reactions are described. For , the cycling behavior of is reversible. However, for , structural decomposition of occurs, and disproportionation to nonstoichiometric and S is observed. Similarly, when cells are recharged to 2.8V, the cathode is a mixture of and S. Examination of the mixture by differential scanning calorimetry shows that and S react to form above 200°C. This explains why high temperature cells cycle reversibly while ambient temperature cells show poor reversibility.

${\mathrm{Li}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Cu}}_{\mathrm{x}}$${\mathrm{FeS}}_{2}$ forms a solid solution for 0\ensuremath{\le}x\ensuremath{\le}1. The crystal structures of ${\mathrm{LiCuFeS}}_{2}$ [a=3.807(2) A\r{} and c=6.352(1) A\r{}] and ${\mathrm{Li}}_{1\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$${\mathrm{CuFeS}}_{2}$, where \ensuremath{\delta}=0.35 [a=3.772(2) A\r{} and c=6.265(2) A\r{}] have been determined by single-crystal x-ray diffraction. Both structures, space group P3\ifmmode\bar\else\textasciimacron\fi{}m1, have hexagonal close-packed layers of sulfur with one formula unit per cell. In ${\mathrm{LiCuFeS}}_{2}$ the iron and copper atoms appear to equally and randomly fill all of the tetrahedral sites between two sulfur planes (layer II). The lithium atoms occupy the octahedral sites between the adjacent sulfur planes (layer I). When lithium atoms are removed from this compound (i.e., ${\mathrm{Li}}_{\mathrm{\ensuremath{\sim}}0.65}$${\mathrm{CuFeS}}_{2}$), some of the copper atoms in layer II move to tetrahedral sites of layer I. When all the lithium atoms are removed, a new hexagonal ${\mathrm{Cu}}_{\mathrm{x}}$${\mathrm{FeS}}_{2}$ phase (\ensuremath{\sim}0.25\ensuremath{\le}x\ensuremath{\le}1) forms. Differential scanning calorimetry shows that this phase is metastable. Upon heating, phase transitions to chalcopyrite and pyrite occur.