The upside, in short, is density.

The silicon batteries can store alot more power in the same size and weight.

That means you can put alot more power into your existing size of hardware.

It’s also extremely beneficial for electric cars, which can either lower the weight on the car or put more juice in it. Both increasing the range.

For your point about replaceable batteries, it’s true. If we can replace batteries, the hardware will not be lost. But everything comes down to how often we need to replace them. How fast does these batteries really degrade in real world use? It can leave us with even worse ecological challenges and might be very expensive. We need a strong reuse culture for this to not be a new catastrophic environmental case.

The real deal is this though:

A third option is Solid State Batteries and is still the best solution for the future, but it’s not fully ready for commercial use yet. They do not seem to have any of the downsides from both lithium and silicon. But again, it’s not ready.