You don't. Emergency funds are for emergencies. Higher yields are possible with various different investments but they all come with additional risk. You do not want to have an emergency fund they may drop in value during a period which you may need to draw on your emergency fund, such as a market downturn that leaves you unemployed. Similarly, you want to be able to access emergencies funds quickly. Emergencies are…
Honest question: unless you're American, what kind of emergency could require a large volume of cash in less than a week? In the US it makes sense for medical bills or a broken car or something but in a country with sane healthcare and public transit, I'm having trouble thinking of anything.
There's also natural disasters or unexpected maintenance, appliances dying, roof/plumbing leaking, etc.
In general though, i think for most EU countries a few thousand euros is enough of an emergency fund, depending on circumstances of course.