Discharge lithium nickel oxides

Lithium-nickel oxides form various lithium compounds, lithium hydroxides (LiOH), Li2C03, nickel hydroxide (Ni(OH)2), nickel carbonate (NiC03) and nickel oxide (NiO). Figure 51 shows the discharge characteristics of lithium-nickel oxides synthesized from these compounds. They were heat-treated at 850 °C for 20 h in air. Although the lithium nickel oxides showed a smaller discharge capacity than that of LiCo02, LiOH and Ni(OH)2 were considered to be appropi-ate raw materials. 

Figure 52. Discharge characteristics of some lithium-nickel oxides and LiCoO, (current density 0.25 mA cm2).

Figure 2.52 shows the discharge characteristics of LiCo02 and Uthium-nickel oxides prepared from LiOH and Ni(OH)2 at 650, 750, and 850 °C. lithium-nickel oxide heat-treated at 750 °C showed nearly the same discharge capacity as IiCo02 while the discharge potential was lower than that of LiCo02. Composition of these... 

Substituted nickel oxides, such as LiNii j /3ojAl/l2, are prime candidates for the cathode of advanced lithium batteries for use in large-scale systems as required for hybrid electric vehicles. On charging these mixed oxides the nickel is oxidized first to Ni + then the cobalt to Co +. SAFT has constructed cells with these substituted nickel oxides that have been cycled 1000 times at 80% depth of discharge with an energy density of 120—130 Wh/kg. ... 

In spite of their low solubility ( 5 x 10 M litre), HFeOJ ions diffuse to the positive electrode and are oxidized to solid FeOOH causing further dissolution of iron and its continous transfer to the positive electrode. The process is irreversible, the potential of the nickel electrode being too positive, even during discharge, for the reduction of trivalent iron. Further decrease of capacity is caused by the lowering of oxygen overpotential on the nickel oxide in the presence of FeOOH. The self-discharge and iron transfer processes are somewhat inhibited by additives to the electrode (sulfur) or electrolyte (e.g., lithium and sulfide ions, or hydrazine sulfate). 

Lithium ion batteries are generally manufactured (assembled) in the discharged state, that is, the negative electrode is a pure carbon material and the positive electrode is made of lithiated cobalt or nickel oxides or of lithium-manganese spinel. This is because of the fact that lithiated cobalt and nickel oxides, same as lithium-manganese spinels, are much more stable toward exposure to the atmosphere than lithiated carbon materials that interact with oxygen and water from the air vigorously. 

Figure 2.5 shows the evolution of the SOH of a lithium-ion device comprising two insertion materials (graphite for the negative electrode and mixed cobalt/nickel oxide for the positive electrode). Cycling was performed to a DOD of 75% for a C/5 charge/discharge current amplitude. 

Fig. 17.2 The first chaige-dischaige curves of lithium-manganese-cobeilt-nickel mixed oxide with U/(Mn + Co + Ni) ratio = 1.00, 1.05, 1.10, 1.15, and 1.20. Only a constant current was apphed for discharge...

According to the data sheets, lithium-ion battery systems based on nickel-cobalt-aluminum oxide (NCA) cathodes, as they are offered by the company Saft [16], offer a calendar life of 20 years and 6000 cycles at a depth of discharge of 60%, which is more than enough but still 40% of the installed capacity will not be used to achieve this target. 

---