| CPC H01M 50/449 (2021.01) [H01M 10/0525 (2013.01); H01M 50/431 (2021.01); H01M 2220/20 (2013.01)] | 10 Claims |

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1. A composite separator, comprising:
a first base film and a second base film; and
an anode protection layer located between the first base film and the second base film in a thickness direction of the composite separator, for capturing transition metal ions, wherein
the anode protection layer comprises a complexing agent and a first oxide nanoparticle, the first oxide nanoparticle being capable of generating lithium oxide and a first elementary substance through a replacement reaction with metal lithium, and
a weight ratio of the complexing agent to the first oxide nanoparticle is from 0.06 to 0.13.
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