Electrochemistry and structure of the cobalt-free Li_1+xMO₂(M = Li, Ni, Mn, Fe) composite cathode

Abstract

The development of cathode materials with high capacity and cycle stability is essential to emerging electricvehicle technologies, however, of serious environmental concern is that materials with these properties developed so far contain the toxic and expensive Co. We report here the Li-rich, Co-free Li1+xMO2 (M = Li, Ni, Mn, Fe) composite cathode material, prepared via a template-free, one-step wet-chemical method followed by conventional annealing in an oxygen atmosphere. The cathode has an unprecedented level of cation mixing, where the electrochemically-active component contains four elements at the transition-metal (3a) site and 20% Ni at the active Li site (3b). We find Ni2+/Ni3+/Ni4+ to be the active redox-center of the cathode with lithiation/delithiation occurring via a solid-solution reaction where the lattice responds approximately linearly with cycling, differing to that observed for iso-structural commercial cathodes with a lower level of cation mixing. The composite cathode has ∼75% active material and delivers an initial dischargecapacity of ∼103 mA h g-1 with a reasonable capacity retention of ∼84.4% after 100 cycles. Notably, the electrochemically-active component possesses a capacity of ∼139 mA h g-1, approaching that of the commercialized LiCoO2 and Li(Ni1/3Mn1/3Co1/3)O2 materials. Importantly, our operando neutron powder-diffraction results suggest excellent structural stability of this active component, which exhibits ∼80% less change in its stacking-axis than for LiCoO2 with approximately the same capacity, a characteristic that may be exploited to enhance significantly the capacity retention of this and similar materials. The development of cathode materials with high capacity and cycle stability is essential to emerging electric-vehicle technologies, however, of serious environmental concern is that materials with these properties developed so far contain the toxic and expensive Co. We report here the Li-rich, Co-free Li 1+x MO 2 (M = Li, Ni, Mn, Fe) composite cathode material, prepared via a template-free, one-step wetchemical method followed by conventional annealing in an oxygen atmosphere. The cathode has an unprecedented level of cation mixing, where the electrochemically-active component contains four elements at the transition-metal (3a) site and 20% Ni at the active Li site (3b Importantly, our operando neutron powder-diffraction results suggest excellent structural stability of this active component, which exhibits ~ 80% less change in its stacking-axis than for LiCoO 2 with approximately the same capacity, a characteristic that may be exploited to enhance significantly the capacity retention of this and similar materials.

Structural Studies of Capacity Activation and Reduced Voltage Fading in Li-Rich, Mn-Ni-Fe Composite Oxide Cathode

“…8,28 The Rietveld refinement ( Figure S3a, Supplementary Material) with only rhombohedral phase cannot fit the small shoulder-like monoclinic peaks however it is consistent with the fit of similar cathode materials reported elsewhere. 42 The sizes of the crystallites along and perpendicular to the <001> direction by this fitting are estimated to be 41 nm and 11 nm respectively. Similarly, the refinement that only considers monoclinic phase ( Figure S3b) features small peaks between 20 to 25 degrees which are not resolved/present in the XRD pattern of MNF521.…”

One-dimensional nanostructured design of Li1+x(Mn1/3Ni1/3Fe1/3)O2 as a dual cathode for lithium-ion and sodium-ion batteries

“…The uniform charge-discharge curves appear the same, as reported elsewhere, 26,27 presenting the characteristic feature of layered structures with a single phase reaction. 47 As shown, there is also an obvious improvement in cycling performance of LMNFO NFs, compared to NPs, which could be ascribed to the impact of the high surface area, 1D nanober morphology in terms of their well-interconnected network with the electrolyte, due to their signicant wettable properties and better charge transfer characteristics during the cycling process. 47 In charge-discharge behaviour, it is assumed that Mn oxidation couldn't take place or be involved in the electrochemistry, however, further observations on Mn redox couples are explained in the cyclic voltammetry section.…”

“…The assembled coincells in the half-cell conguration were electrochemically tested in a voltage window of 2-4.5 V in order to avoid unnecessary degradation reactions associated with carbonate based electrolytes at high voltage. 47 In charge-discharge behaviour, it is assumed that Mn oxidation couldn't take place or be involved in the electrochemistry, however, further observations on Mn redox couples are explained in the cyclic voltammetry section. Fig.…”

Micropatterning of poly(p‐phenylene vinylene) by femtosecond laser induced forward transfer

“…The heating is a consequence of a nonlinear absorption process along with the cumulative effect of high repetition rate lasers. 20,27 Although the donor film is transparent to the wavelength, nonlinear absorption takes place only in the focal volume where the intensity is high enough to cause a nonlinear optical process, thus confining the laser material interaction to micrometer scales. Since the time interval between two consecutive pulses (200 ns) is shorter than the thermal diffusion time (ca μs), there is an increase in temperature because the lattice does not cool before the next pulse achieves the same spot.…”