It's unknown if the Battle Club was made of Thundrainium when Grune was a ThunderCat of Thundera, but none the less he was using it in battles on Thundera. Ultimately, when he came back things to wolos releasing him, he seeked to develop his Battle Club with Thundrainium. He then used the club against Lion-O, then Jaga. Jaga's current sword was no match for the club, and Jaga wielding the Sword of Omens brought the battle to a stalemate, which finally was overcome with Lion-O gave his strength to Jaga.
Powers and Abilities
The mace is made of Thundrainium which he creates in The Ghost Warrior. The weapon has special properties that allows Grune to drain Jaga of his energy. It is able to defeat him even while using the Sword of Omens. Grune only lost due to the repercussions of his own treachery: after accepting Jaga's surrender he took the Sword of Omens, which destabilized his ghost form.