@vincentleo Are you only ever training biceps or you're doing a full workout with bicep training at the end? Just a bit confused reading the comments.
Here's some things you can try if it's an important goal for you.
Split your bicep training into heavy / light sessions.
On light sessions, do 5/7.5kg for 15-20 reps, ideally do 3-4 sets where possible, if you drop below 15 reps, lower the weight to complete your sets.
On heavy days - choose 10/12.25kg dumbbells and aim to do 3-6 clean reps, aim for 6, do 5 sets and stop if you drop below 3 reps.
After that, do some cable machine isometric (or with a barbell if you have access to sub 20kg bars) where you're holding the weight at the top, middle and bottom position while contracting your biceps hard.
Works up from 5kg to 7.5kg over 2-3 weeks while you progress your sets, ideally you'll be getting at least 3x20@5kg before you move up.
Likewise start at 10kg for 5x3@10kg and work up to 5x6(reps)@10kg before moving up to 12.25kg.
Eg:
Week 1: Monday - Light Sessions: 3x15@5kg
Week 2: Monday- Light Sessions: 4x15@5kg
Week 3: Monday - Light Sessions: 3x20@5kg
Week 4: Monday - Light sessions:
3x15@7.5kg
Volume goes 225kg / 300kg / 300kg / 337.5kg