Over the course of the anime, pikachu has absorbed bolts of electricity and transferred that into it's thunderbolt several times, causing a super-powered thunderbolt, we already know pikachu has the ability static, stated by brock a few times (including ash vs paul) but pikachu's hidden ability is lightening rod, which absorbs electric attack and boosts special attack, this seems like pikachu has both static and lightening rod, despite the fact pokemon can only have 1 ability, it's never been stated that pikachu has lightening rod, plus this ability was only introduced in gen 5. Although i think pokemon planned it from the start since no other electric pokemon has had this power that pikachu does, plus in the the most recent anime ep, rival destinies ep 49, pikachu does the same thing, only with electro ball and team rocket again says pikachu is special. So i think pikachu somehow has the second ability lightening rod as well as static, and somehow pikachu's lighening rod is more powerfull than normal. Other than this, pikachu is on par with ash's other pokemon most of the time.