The divergent thinking technique of writing down everything that comes to mind about a topic without revising or proofreading until all of the information is recorded and then organizing it later is known as

This is "freewriting" - the practice of just writing, without worrying about how it sounds like, or the grammar and spelling. 

Freewriting is good when one wants to collect the ideas, but might be blocked while writing, always checking the spelling - and forgetting what one wanted to write. It is very good for collecting information or preparing a  first draft of the text.