I upgraded a 5th generation iPod to use an SDXC Memory Card. The links below are the items used. I also put Rockbox onto the machine ... it is big improvement!
https://www.amazon.com/gp/product/B000P9I6B6/ref=ox_sc_act_title_1?smid=A2YTOTK4U34HN6&psc=1
https://www.amazon.com/gp/product/B0143IISD0/ref=ox_sc_act_title_3?smid=ATVPDKIKX0DER&psc=1