Your emergency fund should stay in savings or maybe some CDs.
If you decide to invest it you need be okay with it being down significantly when an emergency pops up. Also keep in mind many "emergency" situations come during times of a down market. Layoffs, furloughs, housing problems, etc. If you're okay with that risk, just invest it per your risk tolerance balancing stocks/bonds accordingly.
There is no magic short term investment that pays more than savings accounts without significant risk of being down when you need it.