Lithium batteries are great for cell phones, laptops, UPSs and other similar applications that require small size and light weight. I have a 12VDC Li battery powered drill that is terrific.
As for engine start batteries, I don't believe they are ready yet.
Also, a major LiFePo battery manufacturer just went out of business recently.
I was thinking about using Li batteries for starting my diesel motor home engine. In order to get similar capacity to the lead acid batteries used currently, I would need to spend over $700.00 on lithium batteries.
For engine starting and high capacity, lead-acid is still the best.
But, they sure are heavy and an environmental hazard.