Disclaimer: I've not personally tested this in detail...
To apply specific formatting to an image token (thus applying an image style to the URL) I think you'll have to define a "token" view mode for relevant node content type. Once this view mode is setup you should be able to configure display settings on your field_image field (within this view mode) which should used when the token is rendered.
Some instructions on that are available here.
To get full field token support, and therefore this feature, I think you have enable the actual token module. It looks like core's token support does not fully cover field tokens in this way.
It may also be worth looking into the imagecache_token module. If I'm not mistaken it would allow you to declare an image style on your token directly via chaining, something like [node:field_image:style_name]. However, that module is not available as a stable release yet, and it's compatibility with field tokens is not totally clear.