About two-thirds of your smartphone's guts are taken up by its lithium-ion battery. That means the processor, camera, touchscreen, and all of its other components need to be squeezed into a tiny space.
One solution to generally terrible battery life has been to make bigger smartphones that can pack bigger batteries. But several researchers are testing batteries with different chemicals, including lithium imide or silicon, which can last longer than today's lithium-ion batteries.
The problem is that lithium-ion batteries are the most practical solution in terms of both packing power and not blowing up (usually). Though lithium imide batteries are closer to becoming a reality, they only offer about a 10% improvement in battery life. In other words, don't expect a battery life revolution anytime soon.