Search

The thermal evolktion of chemically lithiated Co3O4, γ-Fe2O3 and α-Fe2O3 has been stkdied by DTA and Tk technikkes. The prodkct of lithiation of Co3O4 contains LixCo3O4, knreacted Co3O4 and traces of LiOH and Li2CO3. LixCo3O4 decomposes exothermally into Co3O4 and Li2O at ca . 150–300°C. At 400–500°C, the reaction betkeen Co3O4, lithikm oxide and carbonate takes place leadink to a mixtkre of LiCoO2 and knreacted Co3O4. Lithiated γ-Fe2O3 contains LixFe2O3, knreacted γ-Fe2O3 and traces of LiOH and Li2CO3. This mixtkre transforms exothermally into a LiFe5O8 strkctkre at ca . 250–350°C. At 400°C a nek phase of rock-salt strkctkre occkrs (a = 4.029 A), that remains knaltered belok 750°C. The thermal behaviokr of lithiated α-Fe2O3 is apparently different to that foknd in lithiated γ-Fe2O3. α-LiFeO2 and α-LiFe5O8 kere the phases present above 550°C.

Nitrate assimilation in the first trifoliate leaf of vegetative soybean plants (Glycine max L. Merr, cv Hodgson) was studied in relation to nodulation. Nodulated and non-nodulated plants were grown in a nitrate medium (4mM). As a control nodulated plants were grown in a nutrient medium without combined nitrogen. This study included measurements of the acetylene reduction activity of the whole plant and of the in vitro nitrate reductase, glutamine synthetase and glutamate dehydrogenase activities in the first leaf and of the nitrate concentration. Nitrate accumulation and nitrate reductase activity were depressed in nodulated plants; root growth was decreased in the presence of nitrate. The relationships between nitrate assimilation and nodulation are discussed.

The electrochemical behaviour of new doped Li-M-Mn-O (M = Al, Fe, Ni) spinel oxides in liquid electrolyte lithium cells was studied. The insertion electrode materials were obtained by heating stoichiometric amounts of thoroughly mixed LiOH and M x Mn1− x CO3 (M = Fe, Ni; x = 0.08−0.15) or Al x Mn1− x (CO3) (OH) y , in the case of Al, at 380 °C in air for 20 h. The transition metal-doped samples, particularly those containing Ni or obtained at low temperatures, where the resulting spinel was cation-deficient and highly disordered, exhibited the best cycling performance in the potential window 3.3−2.3 V. Cell capacity was retained by 80% after 200 cycles. Capacity fading was observed on increasing the firing temperature, together with improved crystallinity and the disappearance of cation vacancies. This impaired electrochemical behaviour is ascribed to a Jahn-Teller effect, which induces an X-ray-detectable cubic-tetragonal phase transition upon lithium insertion. The phase transition was undetectable in the low-temperature samples. The influence of the Jahn-Teller distortion is thus seemingly lessened by a highly disordered structure.

Solid solutions in the α-LiGaO2–LiNiO2 system were prepared over the whole concentration range under high pressure (3 GPa) at 700 °C in oxygen-rich atmosphere. The structure of LiGayNi1−yO2 solid solutions was characterized by XRD analysis, EPR and IR spectroscopy. It was found that Ga substitutes for Ni in the NiO2 layer (3a site), while Li and O are in their normal positions (3b and 6c, respectively). The occupancy of Ni in the Li site is negligible for Ga-substituted oxides. The progressive replacement of Ni by Ga leads to an unusual concentration variation of the a-parameter: at 10% Ga additives, there is a contraction of the a-parameter together with the expansion of the c-parameter. The concentration variation of the a-parameter can be related to increased trigonal distortion of GayNi1−yO2 layers upon Ga substitution. The electrochemical performance of LiGay(Ni1−xCox)1−yO2 solid solutions as a cathode material in lithium ion cells has been evaluated in potentiostatic experiments. During the first charge, there is an irreversible peak at about 4.7 V, which was compared with the electrochemical Li extraction from layered oxides characterized with a partial mixing of lithium and metal ions in the metal layers. After the first charge, a reversible electrochemical intercalation of Li is achieved. The effect of Ga on the potential of lithium extraction/insertion in LiGay(Ni1−xCox)1−yO2 was discussed.