A solid-state lithium battery material. The method includes the following steps: material purification; nano wet milling; homogeneous reaction; and ball milling, to obtain high-purity nano lithium sulfide. The high-purity nano lithium sulfide of the present invention and a preparation method thereof can achieve high purity, excellent performance, simple operation, and good social and economic benefits.

Disclosed herein is a method of: providing a polyaromatic hydrocarbon-M adduct solution and reacting the adduct with a sulfide compound having the formula Ni.sub.xFe.sub.1-xS.sub.2 to form a product having the formula M.sub.yNi.sub.xFe.sub.1-xS.sub.2. M is lithium or sodium. The value x is at least 0 and less than 1, and y is a positive number of at most 2. Also disclosed herein is a composition comprising M.sub.yNi.sub.xFe.sub.1-xS.sub.2. The M.sub.yNi.sub.xFe.sub.1-xS.sub.2 has a particle size of less than 1 m.

Disclosed herein is a method of: providing a polyaromatic hydrocarbon-M adduct solution and reacting the adduct with a sulfide compound having the formula Ni.sub.xFe.sub.1-xS.sub.2 to form a product having the formula M.sub.yNi.sub.xFe.sub.1-xS.sub.2. M is lithium or sodium. The value x is at least 0 and less than 1, and y is a positive number of at most 2. Also disclosed herein is a composition comprising M.sub.yNi.sub.xFe.sub.1-xS.sub.2. The M.sub.yNi.sub.xFe.sub.1-xS.sub.2 has a particle size of less than 1 m.