From what I understand, physics and chemistry are the biggest limiting factors to battery capacity. There’s only so much power you can fit into a given volume. If we’re going to see a major improvement in battery life, it’s likely going to come at the expense of performance or size and weight.
My guess is that at some point we’ll reach a tipping point where devices are about as fast as most users could ever want. That’s when manufacturers will start focusing on making chips that are comparible in power level to their predecessors but are far more energy efficient.