Extended Solid Solutions and Coherent Transformations in Nanoscale Olivine Cathodes

Abstract

Nanoparticle LiFePO4, the basis for an entire class of high power Li-ion batteries, has recently been shown to exist in binary lithiated/delithiated states at intermediate states of charge. The Mn-bearing version, LiMn(y)Fe(1-y)PO4, exhibits even higher rate capability as a lithium battery cathode than LiFePO4 of comparable particle size. To gain insight into the cause(s) of this desirable performance, the electrochemically driven phase transformation during battery charge and discharge of nanoscale LiMn0.4Fe0.6PO4 of three different average particle sizes, 52, 106, and 152 nm, is investigated by operando synchrotron radiation powder X-ray diffraction. In stark contrast to the binary lithiation states of pure LiFePO4 revealed in recent investigations, the formations of metastable solid solutions covering a remarkable wide compositional range, including while in two-phase coexistence, are observed. Detailed analysis correlates this behavior with small elastic misfits between phases compared to either pure LiFePO4 or LiMnPO4. On the basis of time- and state-of-charge dependence of the olivine structure parameters, we propose a coherent transformation mechanism. These findings illustrate a second, completely different phase transformation mode for pure well-ordered nanoscale olivines compared to the well-studied case of LiFePO4.

Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery electrodes

“…Thus, at a given cycling rate, a lower barrier reduces the local current density, increases the active particles fraction, and improves the current homogeneity (Fig. S11) 48 . Yet another somewhat counter-intuitive route is to lower the reaction rate and exchange current density, which would increase the active particle population.…”

“…Additionally, Nb doping 46 and V substitution 47 in LFP reduce the lattice mismatch and increase the solubility limits, both strong indicators of decreased transformation barrier. Mn substitution in LiFePO 4 , on the other hand, has been shown to eliminate the nucleation barrier and result in extensive solid solubility upon lithiation 48 . Yet another somewhat counter-intuitive route is to lower the reaction rate and exchange current density, which would increase the active particle population.…”

Characterization of Gas‐Solid Reactions using In Situ Powder X‐ray Diffraction

“…molten hydrides, and allows higher working pressures and more abrupt changes of pressure. [3] This is desirable for investigation of fast solid-gas reactions, e.g. for reversible solid state hydrogen storage.…”

“…new information on lithium insertion reactions in lithium ion batteries [3] and on reaction mechanisms in conversion type cathodes. [4] Solid-gas reactions were initially investigated in order to explore reaction mechanisms within heterogeneous catalysis.…”

Li 3 V 2 (PO 4 ) 3 /LiFePO 4 composite hollow microspheres for wide voltage lithium ion batteries

“…For example, LiMnyFe1−yPO4 (LMFP) solid solutions are of particular interest due to the low cost of Mn and the ∼4 V intercalation potential for Mn 2+ /Mn 3+ , which provides higher working voltage (energy density) without exceeding the stability window of common electrolytes. LMFP of y < 0.6 composition exhibits even higher rate capability as a lithium battery cathode than LiFePO4 because of the formations of metastable solid solutions [11].…”