The electrochemical behavior of chemically prepared α‐phase Al‐substituted normalNifalse(OH)2 was investigated in relation to its crystallinity. α‐Phase samples with 5–20% Al were prepared by precipitation, and the crystallinity was tailored by changing the metal/alkali ratio or the aging temperature. A highly crystallized sample was obtained without controlling the reaction pH. Both the utilization and half‐discharge potential increased as the sample crystallinity improved. A maximum capacity of 381 mAh/g and utilization of 190% were obtained. The crystallinity dependence of the cell performance was explained by the reduction of polarization because of a more ordered structure which led to a faster solid‐state reaction. © 1999 The Electrochemical Society. All rights reserved.

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We have systematically studied the behaviour of the absorption bands due to the O - H bond-stretching vibration and its polarization characteristics in with the use of well characterized crystals. It has been found that the O - H bond-stretching vibrational frequencies, , have a strong correlation with Nb concentration in the crystals as in the case of MgO-doped . The values of shift to the higher-frequency region when the Sc concentration in the crystal exceeds about 2.5 mol%. The magnitude of the frequency shift is smaller and the polarization dependence of the absorption bands due to is weaker in -doped than in MgO-doped . These features are attributed to the difference of the charge between and . We have also proposed an ideal defect structure model for -doped , which is based on the Li-site vacancy model as an intrinsic defect structure model. The observed behaviour of is consistently explained by the proposed defect structure model. This supports the justification of the extrinsic defect structure model based on the Li-site vacancy model for -doped as well as for MgO-doped .

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