Unlike normal Pikachu and Raichu, Lex was fused with Ion Energy when he was a Pichu which somehow made it possible for him to naturally produce Ion Energy.

Lex was caught in an Ion Generation test at the Eterna Forest, Ion Test and Research Facility as a young Pichu. He was discovered at the test sight and was taken in for examination to see if he was ok. The result was that he was somehow naturally producing Ion Energy. The Ion Energy generated during that test must of fused with Lex somehow. Later he was taught to control the power to a point so that he wouldn't accidentally reveal it. His carer discovered news that her colleuges were planning to experiement on Lex. Fearing the worst she take Lex away from the facility and told him to leave the area.

Like his normal Electricity, his Ion Energy builds up over time and would need to be discharged but it doesn't change how the pokemon behaves like with his electricity he would look and feel like he has a cold. Ion Energy builds up with him aware of how much he as in him and so the energy finds its own way out which is through, mostly, emotional periods. A common emotion that Ion Energy finds a way out is through anger. When Lex looses his focuse during an emotional episode Ion Energy is free to release itself. As like a warning to say like his opponent of an Ion Attack his cheeks turn blue and the Ion discharge would be coloured blue as well.