锐气 is the energetic, edge-of-the-blade kind of spirit - fresh, aggressive, ready to charge. Often paired with verbs of dulling: 挫锐气 ('blunt the fighting spirit'), 锐气大减 ('morale greatly diminished').
memory
锐 = sharp (the metal radical 钅 + 兑); 气 = spirit/energy. So literally 'sharp energy' - the keenness of a freshly honed blade applied to a person's drive.
