I wrote recently about this here: Electroneutrality in molecular dynamics simulation - #5 by srtee (although it’s hard to find this particular post by search, so I don’t blame you for not finding it).
I still stand by my conclusion that such simulations are often useless. In this particular case, the material Li2PO3 doesn’t exist as a stable bulk material (since it’s non-neutral!), and calculating the diffusivity of lithium in a non-existent material may not be the best use of computer time.
You would be better served either calculating for an actually stable material (so that experimental verification is possible at least in principle), or working out a more physically valid way to calculate whatever else you may be wanting to calculate.