They are improving Li-Ion cells as we speak.
Minute holes could dramatically improve battery performance
They estimate they can increase Li-Ion cell capacity by tenfold (10 times current storage capacity). When this comes out, we'll stop measuring cells by mAh and have to use Ah. A 2000 mAh cell would then be able to hold 20000 mAh, equal to 20 Ah. That would power today's smartphone for about a week. A simply flip phone would probably last a month. A tablet would probably last 4-5 days of moderate use.
The downside is that it's only good for 150 charge cycles. But 150 weeks is just shy of 3 years. So heavy users would have to replace it once every 1.5 years, at the most. Light users would probably not have to replace it until 3 years. Or we'll just have to wait for them to improve the technology to maintain more charging cycles.
It's coming