Let's start with the 'Chi' in Tai Chi and the 'Qi' in Qigong.
'Chi' in Tai Chi and 'Qi' in Qigong
'Chi' and 'Qi both mean the same. It is just a different way of writing 'life energy'.
'Chi' or 'Qi' is the energy that moves through all things and all life.
Tai Chi is a Chinese Martial Arts form helping you to get that life energy flowing. Tai Chi is a way of exercising: gentle physical exercises combined with mindful stretches and releases of stuck energy. There are many different forms of Tai Chi.
Qigong (meaning 'life energy work') is another way of flowing your life energy. 'Qi' in Qigong means life energy and 'Gong' means practise.
Difference Tai Chi and Qigong
Tai Chi, as a Martial Arts form, focuses on building physical strength.
In my experience, Qigong movements can be less complicated than some of the Tai Chi movements.
Qigong exercises and meditation exercises focus more on awareness, energy, self-healing, and encourages practitioners to develop themselves spiritually.
'Shibashi 18' - the form you learn at Qigong London - combines the strengths of both Tai Chi and Qigong.