stability of the species Li, Li2(-) and Li2(+) increases in the order of:

Li2+ > Li > Li2- will be the order of stability as stability is directly proportion to bond order

Bond order of li2 is 1 while li2- and li2+ is o. 5So li2 is more stable among 3 ,Now in li2- and li2+ we have to check antibonding electron,, less antibonding more stability. Hence li2+ contain 2 antibonding, li2- contains 3 antibonding. Hence li2+>li2-So finally Li2>li2+ >li2-