Twin engine switching from pure to petrol mode

[K2mce]

Hi all, new here so sorry if this duplicates any questions. I’ve a late 2020 xc90 twin engine, I live 7 miles from work so should be able to commute there and back in full electric mode, however I put it in pure and most days, no matter how careful on the throttle I am, about half way there it turns on the petrol engine and keeps it on for about a third of the journey. The whole point of this car was I could commute fuel free and it’s deciding to override what I want it to do. Can anyone explain why? And how to stop it from doing this?