Melt process for preparing alkali metal phosphate cathode materials from variable composition sources

A two-step melt process for preparing a sodium iron phosphate cathode material having a defined composition, the process comprising first and second melt steps and an intermediary analysis and correction step between the two melt steps, wherein:

• the first melt step comprises mixing reaction precursors to form a first melt pool having a first melt pool composition;
• the second melt step comprises adjusting the first melt pool composition based on results obtained in-situ from the intermediary analysis step such as to obtain a second melt pool having the defined composition;
• the reaction precursors comprise a material selected from the group consisting of Na-, Fe-, P-containing materials, spent cathode materials from used batteries, out of specification (off-spec) cathode materials, and combinations thereof;
• and
• the first and second melt steps are each independently conducted at a temperature between about 900 and about 1300° C., under an inert atmosphere or a controlled reducing pO2 atmosphere,
• optionally the second melt step and the intermediary analysis step are repeated a number of times,
• optionally post-synthesis steps are performed, which comprise at least one of:
• subjecting the second melt to solidification, subjecting a solidified material to a particles size reduction process, subjecting the material to a carbon-coating process.