RustyNips

It was an oddly thin piece of gray material. Would any old thermal pad work?? (Granted it's thin enough)

I recently put a new battery into my pixel 3. It's from iFixit, so I assume it's good quality. However, when I was taking out the old battery, I had to cut what looked like a thermal pad off of the old battery, and didn't replace it on the new one. Now in Accubattery, I see my battery is overheating and slowing charge speed to accommodate. My question is: is there any way to properly cool the battery? Pastes, pads, other? Any help is appreciated, thanks.