Energy stave

The Energy Stave is a Covenant ceremonial melee weapon. It is used exclusively by the Honor Guard Elites and Brutes and Light of Sanghelios. It is a long metal staff, and has a forked tip with a series of orange panels.

These weapons are long staves with a spear-like end that is similar in color to the "glowing armor panels" of their wielders. Not much is known about these exotic weapons, except that they have a length of 527 centimeters (17.3 feet). They do not seem to have much of a combat purpose but more a ceremonial one, as the Honor Guard Elites will use Plasma Rifle, Energy Sword, and Covenant Carbines in real combat. However, they were used by Brutes to subdue any Grunts and Jackals that came too close to the Council Chamber during one of the High Prophet of Truth's sermons regarding the discovery of the Sacred Icon. This weapon is never used in game-play by other characters.

Halo 2
They can be seen in the hands of the Brute Honor Guard during both the opening and closing cinematic of the Halo 2 level, Gravemind, but they are simply tossed aside, as the Brutes prefer other weaponry to protect the Hierarchs, and kill Master Chief.

Novels
It is also featured in the novelization Contact Harvest when the two San 'Shyuum go to the minister to recruit him as a Hierarch.

It can be seen in last sections of Halo: The Cole Protocol as well, when Zhar approached the Prophets with an Energy Sword at hand. Not much else was written, except that plasma was created at the tip of the spear.

Halo Wars
An early or different version of the weapon can be seen in a Halo Wars cinematic. It is not used in gameplay, only in cinematics.

This stave may have been completely remodeled into the one we see in Halo 2 as many aspects have changed, so this cannot be trusted to assess the Halo 2 era weapon. The changes from Halo Wars to Halo 2 include the added details and the orange-glowing symmetrical appearance as opposed to the blue asymmetrical appearance in Halo Wars.

Given that the Sangheili wielding the staves were Minors, it is likely that this version is reserved for more common use than those used by Honor Guards.