Precipitation Revisited: Shape Control of LiFePO4 Nanoparticles by Combinatorial Precipitation

Abstract

Tunable precipitation strategy to control the shape of nanoparticles of a three-component system is presented. The strategy is devised from understanding the effects of precursor addition sequences on the morphology of resultant precipitates. LiFePO4, one of the most potential candidate as a cathode material of lithium ion batteries for electric vehicles, was used as a representative model of the three (Li, Fe, and PO4)-component system. According to the precursor addition sequence, three different precipitation methods were adopted: coprecipitation (Copr) and two different types of sequential precipitations (Seq1 and Seq2). Solubility product (K-sp) of intermediate precipitates (Li3PO4 and Fe-3(PO4)(2)) is the key parameter to help the precipitation processes understood. In Copr, the intermediate precipitates are formed simultaneously under K-sp-governed competition. In Seql and Seq2, Li3PO4 precipitates prior to Fe-3(PO4)(2). When Fe2+ is introduced into the suspension of Li3PO4, the preformed precipitate is sacrificed to supply PO43- for Fe-3(PO4)(2) precipitation due to the stronger tendency (smaller value of K-sp) of precipitation of Fe-3(PO4)(2). Also, the interaction between a cationic surfactant and PO43- makes the difference between Seq1 and Seq2. As a conclusion of the effects of precursor sequence, the shape of particles spans from spherical nanoparticles through a hollow sphere secondary structure of the same nanoparticles to nanoplates. Each own morphology developed by different precipitation methods leads to different intercalation/deintercalation behavior of lithium ions in conventional rechargeable battery cells.