Is it permissible to open a savings account with interest in a usurious bank with the intention of donating all the excess interest over the principal amount, and by doing so, does the money become permissible?

It is not permissible to deposit money in interest-based banks except out of necessity, such as to protect it from theft. If the questioner is in a Muslim country, she should search for an Islamic bank. If she does not find one and is compelled to deposit money in an interest-based bank, then she should place it in a current account that is free of interest. However, if she is compelled to place it in a savings account because a current account is unavailable, then she must dispose of the interest by spending it on charitable causes or giving it to the poor and needy, and it is not permissible for her to keep it for herself.