Page 185 - Handbook of Battery Materials

154 5 Nickel Hydroxides

The Raman spectroscopic work of Jackovitz [31], Cornilsen et al. [32, 33], and
Audemer et al. [34] is the most direct spectroscopic evidence that the discharge
product in battery electrodes operating with the β/β cycle is different from
well-crystallized β-Ni(OH) 2 . The O–H stretching modes and the lattice modes in
the Raman spectra are different from those found for well-crystallized Ni(OH) 2
prepared by recrystallization from the ammonia complex, and are more similar to
those found for the initial material prepared by Barnard et al. [21] by precipitation
of the Ni(OH) 2 by adding 3 mol L −1 Ni(NO 3 ) 2 to hot 7 mol L −1 KOH. In discharged
electrodes, a Raman band at 3605 cm −1 is observed. This has been ascribed to
absorbed water molecules on the surface of the Ni(OH) 2 [34]. There have been
discrepant results in the Raman evidence for adsorbed water. However, some
water cannot be ruled out since the O–H modes are very poor Raman scatterers.
Infrared spectroscopy is much better at detecting water, and Jackovitz has seen
water-stretching modes in both the nondeuterated and deuterated material after
−1
discharge [31]. Audemer et al. have also seen this band at 1630 cm . Furthermore,
they have confirmed that both the Raman band at 3605 cm −1 and the IR band at
◦
◦
1630 cm −1 decrease at temperatures above 100 C and completely vanish at 150 C.
Neutron diffraction work on Ni(OH) 2 and Raman and IR spectroscopy clearly show
that discharge product in battery electrodes is closely related, but not identical, to
well-crystallized. β-Ni(OH) 2 . It probably has a defect structure, which facilitates
water adsorption and the electrochemical reactions.

5.3.1.2 α-Ni(OH) 2
α-Ni(OH) 2 , which has a highly hydrated structure, was first identified by Lotmar
and Fectknecht [35]. α-Ni(OH) 2 is a major component of the active material in
battery electrodes when nickel battery plaques are cathodically impregnated from
an aqueous Ni(NO 3 ) 2 solution at temperatures below 60 C [36]. α-Ni(OH) 2 can be
◦
prepared chemically by precipitation from dilute solutions at room temperature.
One method is simply to add an ammonia solution to a nickel nitrate solution
[20]. Another method is to add 0.5 or 1 mol L −1 KOH to 1 mol L −1 Ni(NO 3 ) 2 [21].
In both cases, the precipitate is filtered and washed. Methods for electrochemical
preparation of α-Ni(OH) 2 films on nickel substrates have been described [37, 38].
One method consists of cathodically polarizing a cleaned nickel sheet in a quiescent
−1
0.1 mol L −1 Ni(NO 3 ) 2 solution at 8 mA cm . There is reduction of nitrate and a
concomitant increase in pH at the electrode surface. This causes precipitation of
an adherent coating of α-Ni(OH) 2 on the nickel. A 100 s period of deposition will
produce 0.5 mg cm −2 of α-Ni(OH) 2 .
Determination of the structure of α-Ni(OH) 2 has been difficult, since sometimes
it exhibits no diffraction pattern [39]. After washing with water, a diffuse pattern
develops. Hydrothermal treatment eventually leads to well-crystallized β-Ni(OH) 2
[39, 40]. The evolution of the X-ray diffraction patterns is shown in Figure 5.3.
Bode proposed a layered structure for α-Ni(OH) 2 similar to that for β-Ni(OH) 2
[11]. His suggested structure was essentially identical to that shown for β-Ni(OH) 2
in Figure 5.2, except that between the (0 0 0 1) planes there are water molecules
that result in an expansion of the c-axis spacing to about 8 ˚ A. Bode proposed a