Techie stuff about how it works here:
https://www.computerworld.com/article/3235176/mobile-wireless/wireless-charging-explained-what-is-it-and-how-does-it-work.html
There would seem to be no reason why using wireless charging should be better or worse for a phone's battery than conventional charging. The concerns raised by some people seem to relate to the differences that the availability of such charging might make to people's habits regarding when they charge their phones:
To get the most out of a phone's battery you should charge it to a bit above half full and then give it the next charge (back to the same level) when it's got to to a bit below half full. Letting the battery go totally flat, before charging it up fully again, will tend to shorten the life of a modern battery. (Confusingly, that's exactly what we were all advised to do with older-style batteries).
Similarly (but probably with a less damaging effect) constantly topping up a battery to full charge at every available opportunity will leave it with a somewhat shortened lifespan (or with a reduced capacity for holding a charge). If people have got charging signals available from mats and other devices in their homes and offices, there's the potential for that 'constant top-up' effect to come into play. (Some wireless charging devices can now charge a phone from several metres away so, even if your own charging device is turned off, it could still be taking a charge from a neighbour's device).
https://www.computerworld.com/article/3229750/mobile-wireless/is-wireless-charging-bad-for-your-smartphone.html