I'm in Sweden, but further south. I can't comment on northvolt specifically (though I've heard mixed stories about how they treat their workers, so your DH might want to get a bit more of a sense of the work culture before committing).
Northvolt is in Skellefteå, right? I'm not a huge fan of the town. I think both Umeå is much nicer, potentially due to being a university town, it has more going on. I have heard that skellefteå is struggling a bit to absorb the recent influx of workers, and house prices are going up quite a bit, albeit starting from a (very) low base. The upside is that I think that because there is such an influx of new people there is more effort to try and reach out and integrate people, think for example monthly drinks, socials, and other activities to help people settle.
Where are you moving from? If you're currently in Inverness then it might not be too different. If you're in a big city, or just generally most places in England, it'll be a big change. Skellefteå is a long way from any other town. 9+ hours to get to Stockholm, unless you fly. Getting to the UK would require flying to Stockholm first (I think).
Imho, it can work if you're up for a complete lifestyle change. If you're not too fussed about city life, but can imagine enjoying cross country skiing, ice skating, snowmobiling then it could be a great adventure. I'm currently visiting a town not far from Skellefteå and the snow has already arrived. Even in November temperatures can drop to -10 or colder. I think you have to be willing to accept (or even better, be enthusiastic) about the prospect of 6 months of winter, because otherwise it's very, very hard.
If your DH applies, I'd 100% recommend you both come over for a visit before committing.