OneMileHigh,
Lead Dioxide is alnternately referred to as Lead Peroxide.
***BUT***
The answer to your question is that it is "more" correct to identify Lead Dioxide as being used as the positive plate (just as you thought) because although it is used interchangeably with Lead Peroxide--that lead compound is not a true peroxide.
Hope this helps
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Patience is letting your motor idle when you feel like stripping your gears.