How will metallic lithium react with atomic oxygen?
As explained in Long-term ozone decline and its effect on night airglow
intensity of Li 6708 ˚A at Varanasi (25◦N, 83◦E)
and Halley Bay (76◦S, 27◦W) Journal of Earth System Science 120, No. 2, April 2011, pp. 291–300:

$\ce{Li + O -&gt; LiO}$

$\ce{Li + O2 -&gt; LiO2}$

$\ce{Li + O3 -&gt; LiO + O2}$

$\ce{LiO2 + O -&gt; LiO + O2}$

The article gives rate coefficients for each of these reactions.

The article also gives $\ce{Li}$, $\ce{O}$ and $\ce{O3}$ concentrations as a function of altitude for the range 80-99km (85km being considered the lower boundary of the thermosphere)