These Pikachu were seen searching for Thunder Stones to evolve, with some of them found Thunder Stones and evolved into Raichu during the episode.
Team Rocket used a mecha to vacuum them up in an attempt to steal them, but Goh's newly caught Pikachu thwarts this attempt by destroying their mecha's pipe via evolving with a Thunder Stone she dug up. The group of Pikachu then blast off Team Rocket with a combined force of Thunderbolt.[1]