Li-ion Step up to 5V 8A
(Expanding my comment as an answer)

For currents higher than say 3 or 4 Amps, you generally will have to search for Boost "Controller IC" instead of Boost Converter. The difference is that the controller IC has all the logic and smarts but require external MOSFETs.

Currents higher than a few Amps are difficult to handle in the same IC package. By using external MOSFETs, the high currents are handled outside.

Take a look at TI and Linear for higher power stuff and make use of their free design tools (e.g. TI WEBENCH Power Designer, Linear LTPowerCAD and LTSpice).

Keep in mind that there's a big tradeoff: it's now on you to design a good board layout that handles the high currents, minimizes noise coupling, provides good grounding to your IC, keeps the switching noise away from the analog sense lines using separate digital and analog grounds, etc.

If you go this route, make sure you very carefully review the recommended layouts and read the advice in the application notes several times. SMPS layouts that use external MOSFETs are tricky. If you just "wire stuff up" your SMPS will most likely be unstable, run hot, and possibly damage itself and your load.

Also, component selection is very critical. If you're new, then just find an app note that shows an example circuit and use those exact components. If you chose your own components, you will have to learn about inductor saturation, self-resonance, ESR, capacitor ESR and dielectric types, transistor switching speed, gate capacitance, Miller effect, threshold voltage, and then simulate the design taking all that into account! So if you're new and want something quick, scour the datasheets and app notes for a recommended example circuit and use what's already been tested.