What about,
Loon - https://loon.co/
Dandelion - https://dandelionenergy.com/
Wing - https://x.company/wing/
Chronicle - https://chronicle.security/
Malta - https://blog.x.company/introducing-malta-81bceb559061
Apple is almost 100% definitively not working on a molten salt energy storage solution I can promise you. And the reason is because it’s just not in it’s corporate structure or culture. Far too constrained / trapped in it’s niche to expand outwards into such a vastly different market.