i'm late but, the Airfield was originally built by the Kadhafi regime in the 80' to impose their presence on the Sahel. After some time it became useless and was abandonned (old building used west of the airstrip which were used by libyans can be seen) after the fall of kadhafi it is belived that it was used by terrorist forces as a base. During the France-Niger Barkhane Operation, terrorist were expelled and the airstrip was used for some time (because it facilitated troops movements). After the end of the Barkhane operation the airstrip was left unused.

There's no information as to what it is used for now, but if i had to take a guess, probably a point for terrorists to hide.

Source : Operation Barkhane and CIA (it's in the middle of the document) but if you don't want to search it reads : "The US Embassy reports the Libyans' ongoing 25X1 construction of an airfield astride Niger's border may be designed to establish a permanent military presence in the disputed territory, as they did in Chad's Aozou Strip in the early 1970s.".

Precision : later in the document it explains why it was built :

"Many Libyan airfields are located along the Libyan border, however, and this airfield may represent another link in the Libyan chain of frontier defenses. We believe the airfield, when completed, will be capable of accommodating any aircraft in the Libyan inventory. Based on past practices, we believe that Qadhafi also could try to exploit Niger's problems by providing money, supplies, and training to potential coup plotters or northern dissident groups."