Blitz this dump - knocking all walls out as part of battery? (7)

I believe the answer is:

lithium

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'blitz this dump knocking all walls out as part of battery?' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

This is the entire clue.

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(Other definitions for lithium that I've seen before include "Lightest alkali metal" , "Chemical element (Li), used in batteries" , "Soft silvery element" , "Lightest-known metal" , "Light metallic element" .)

I've seen this clue in The Independent.

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