Liquid-Feed Flame Spray Pyrolysis Synthesized Active Material Nanopowders: Toward Co-free, High-Energy Density, and Low-Cost Li-Ion Batteries

Abstract

High energy density batteries are enabling electrification on a global scale in almost every facet of life. Batteries that empower electric vehicles contain a wide array of materials with rigorous performance exigencies as defined by the consumer – inexpensive, fast charging, and long range. Active materials represent the largest cost fraction (cathode ~50%) and specify the upper performance limit. High energy density cathodes, which enable long range EV batteries, represent the greatest fraction of total materials cost due to the typical compositions containing mined transition metals such as Co, Ni, Mn, and Fe. There is a growing need for alternatives to commercialized high energy density cathode active materials (CAMs) for Li-ion batteries with chemistries less dependent on Co and Ni. In the past decade, particular attention has been placed on Mn- and/or Fe-based cathodes. Additionally, optimization of anode active materials (AAMs), typically composed of graphite and/or Si-based materials, is vital to high energy density cell realization. High entropy oxides (HEOs) are potential anode candidates for applications demanding high volumetric capacity; however, transition metals require careful consideration to minimize cost while maintaining performance. In this dissertation, we investigate the design, synthesis, characterization, and resulting performance of nano active materials synthesized via liquid feed-flame spray pyrolysis (LF-FSP). LF-FSP provides a high-throughput method (> kg/h) for nanoparticle (<100 nm APS) synthesis with a high level of compositional control facilitated by metalloorganic precursors. The synthesized materials demonstrate progress towards Co-free, low cost, and high energy density batteries. We studied the LF-FSP synthesis and characterization of two Co- and Cr-free, novel HEO compositions - replacing Co [(CoNiMnFeTi)3O4] with Zn [(ZnNiMnFeTi)3O4] and Cu [(CuNiMnFeTi)3O4] - for use as next generation AAMs. The goal of Cu/Zn as potential substitutes for Co is to lower cost while maintaining or improving electrochemical performance from either a material perspective or per cost basis. Compared to industry standard graphite, ZnNMFT showed gravimetric (480 mAh/gHEO vs. 372 mAh/gGraphite) and volumetric (2460 mAh/cm3HEO vs. 820 mAh/cm3Graphite) capacity gains. A decrease in performance was expected by replacing Co in favor of Zn/Cu; however, galvanostatic cycling results show improved performance for ZnNMFT (~2x) compared to both CoNMFT and CuNMFT on a lower cost basis. On the cathode side, we examined Li- and Mn-rich CAMs with spinel-based nanocomposite structures having stoichiometries LixMn1.5Ni0.5O4 (x=0.45-1.50) synthesized via liquid-feed flame spray pyrolysis. Initially amorphous and crystalline spinel phases transform to nanocomposites composed of spinel and monoclinic/layered phases post calcination (800ºC/6h/O2). With increasing Li content, monoclinic phase content increases at the expense of the base spinel phase. When cycled from 4.9 – 2.4 V, LixMn1.5Ni0.5O4 (x=1.26, 1.50) exhibited energy densities greater than 1000 Wh/kgCAM (~300 mAh/g) coupled with a green, aqueous binder. We studied the electrochemical performance of LFP and LFP-type materials synthesized using an alternative, scalable method – using metal carboxylate precursors via liquid feed-flame spray pyrolysis (LF-FSP). Four LiTMPO4 (TM = Fe, Mn, and/or Ni) nanoparticle systems with varying degrees of Fe substitution - LiFePO4, LiMn1/3Fe2/3PO4, LiMn2/3Fe1/3PO4, and LiNi1/3Mn1/3Fe1/3PO4 - were synthesized. As-produced materials exhibited spherical morphology (~100 nm APS) and amorphous phase but provided the target olivine phase after calcination. In electrochemical studies, practical energy density was maximized with 1:2 Mn:Fe ratio (LiMn1/3Fe2/3PO4) compared to LFP (491±9 vs 464±3 Wh/kg at 1.0C) while maintaining excellent capacity retention after 100 cycles (~96%).