Bigger batteries mean fewer charging cycles, which is good. Faster charging means more heat, faster depletion of a limited resource, which is bad for the environment.
Silicon carbon anode batteries heat up significantly slower while charging than lithium-ion, which allows them to fast-charge to about 80% (compared to an iPhone at about 40%) before they get hot enough to trigger charge throttling. During the last charging phase, from 80% to 100%, they’re at maximum temperature, but for less time than a lithium-ion battery spends at that temperature. Because Si-C batteries charge so much faster, they spend only about 10–12 minutes in that final hot saturation phase, while a current iPhone's standard all-carbon anode battery might spend 30–40 minutes in its warm/throttled state trying to finish its last 20% of charge.
So if this all leads to less heat degradation, we might see iPhone batteries maintaining a better maximum charge over their lifespans, but for most current iPhones with their carbon-anode batteries, heat degradation is already pretty minor over the usual lifespan of an iPhone.
So once Apple starts installing silicon carbon batteries, we should see faster recharge and topping-up speeds, while generating less heat for most of a full charging cycle, and throttle-level heat for a much shorter time. And as with Android manufacturers that are already installing silicon carbon batteries, Apple is likely to increase the maximum wattage at which iPhones can be charged (mostly an increase in wired charging wattage compared to the anticipated Magsafe wattage increase), which will be another factor that allows them to charge faster than current iPhones. Hard to say whether that increase in charging wattage will create significantly more heat though, but from what I've been reading, because a silicon carbon battery is more efficient, a 60 watt charge on an Si-C battery can actually produce less internal heat than a 30 watt charge on a standard carbon-anode battery.
