Why till now Smartphone batteries haven’t improved?

The main reason behind this cause is Weight and Performance. If Mobile Phone companies want to improve battery life then they have 2 options.

1. They can compromise the performance of the processor which will use less battery which I don't think any mobile manufacturer company will do.

2. Or they can use big batteries which will make the phone very bulky just like old models such as Nokia 2233.

Well, a few reasons for the not-so-satisfactory performance of smartphone batteries could be as follows -

1. Lesser innovation in battery technology
Smartphone components like processors, cameras displays have been witnessing enormous development. But, the battery technology is not keeping its pace with these components. The development is happening at a slower pace. All other components are becoming smaller, while the batteries still occupy more space.

2. Smartphones are becoming thinner and slimmer
With the smartphones tending to be thinner and slimmer, as a result of which even the batteries are getting thinner. This causes compromises on the part of battery performance.

Yes, there is an ongoing experiment to make more powerful battery. I present you the current problem and the experiment which is ongoing to solve

Most of our mobile devices are powered with Li-Ion battery. It has the following problems.
1. Ageing
2. Expensive when compared to Nickel Cadmium battery. So we cannot mass produce this.
3. High internal resistance which diminishes efficiency.


Experiment
Eesha Khare, an Indian origin American student who gets frustrated when her battery goes down. So asked herself why can't the battery backup last longer? This question leads her to an invention which will make a battery backup to last longer.

Eesha Khare's findings
She founded a super capacitor which stores energy way higher than current capacitor stores.

The idea is battery charges and discharges slowly, whereas capacitor charges and discharges faster. A capacitor can store energy and is used for charging, while the battery is used for discharging. So combining both technologies (super capacitor and battery), a battery can charge faster and discharge slower.

It means with 20 seconds of charging the backup lasts for a day long.

This is just prototype which she presented in Intel's science fair. This prototype is proven to work in real time. Using this technology one can even charge a car in seconds.