Well, not only water obviously:<p>> To address these limitations, Professor Kim’s team proposed a hollow nanofiber protective layer capable of controlling lithium-ion growth through both physical and chemical means. This protective layer was manufactured through an environmentally friendly electrospinning process* using guar gum* extracted from plants as the primary material and utilizing water as the sole solvent.<p>It doesn't seem like a very expensive process, but I have no idea how much the price will increase