Elucidating the Effect of Iron Doping on the Electrochemical Performance of Cobalt‐Free Lithium‐Rich Layered Cathode Materials

Abstract

Lithium-rich materials provide the highest specific energies (up to 900 Wh kg −1) among all lithium-ion positive electrode materials. [1] Potentially meeting the high requirements for automotive applications, they receive much attention for use in "next-generation" Li-ion batteries (LIBs). Their large specific capacity originates from the structural peculiarity of lithium-rich layered materials, which can be seen as mixtures of two phases, LiMO 2 (M = Ni, Mn, and Co, rhombohedral R-3m structure) and Li 2 MnO 3 (monoclinic C2/m structure). This latter component provides additional lithium located inside the transition metal layer. [2] However, to access this additional capacity, the Li 2 MnO 3 component must be "activated" by charging to relatively high cutoff voltages (i.e., 4.6-4.8 V). [1a,3] During such activation, Li + ions are extracted from the structure while oxygen anion redox activity occurs possibly through a few different processes. However, transition metal migration into the formed Li vacancies correspondingly occurs, finally resulting in the phase transformation from layered to spinel-like and eventually, rock-salt structure. [4] This is widely regarded as the origin of the two main challenges of lithiumrich materials, that is, voltage and capacity degradation, leading to relatively poor cycle-life. To solve these issues, many strategies have been developed over the past years, which are, for example, modifications of the binder [5] or the electrolyte, [6] and surface treatments [4,7] and lattice doping [8] of the lithium-rich materials. Lattice doping is one of the most suitable methods to address the voltage fading as reported in a few earlier works. Nayak et al. [8b] could maintain higher specific capacity as well as discharge voltage upon cycling, by doping the structure with aluminum (on the account of manganese). This is due to the stabilized surface of the active material and suppressed transformation from layered to spinel-like phase. Chromium has also been adopted as a possible dopant and confirmed to be incorporated into the crystal lattice. It enabled higher average voltage, which was ascribed to a decreased amount of spinel domains generated upon cycling. [9] Moreover, other elements, such as Ti, [10] Mg, [11] and Cu [12] were investigated leading to similar improvements. Besides doping into the transitional metal layer, also lithium site The eco-friendly and low-cost Co-free Li 1.2 Mn 0.585 Ni 0.185 Fe 0.03 O 2 is investigated as a positive material for Li-ion batteries. The electrochemical performance of the 3 at% Fe-doped material exhibits an optimal performance with a capacity and voltage retention of 70 and 95%, respectively, after 200 cycles at 1C. The effect of iron doping on the electrochemical properties of lithium-rich layered materials is investigated by means of in situ X-ray diffraction spectroscopy and galvanostatic intermittent titration technique during the first charge-discharge cycle while high-resolution transmission electron microscopy is used to follow the structural ...

Inhibition of transition metals dissolution in cobalt-free cathode with ultrathin robust interphase in concentrated electrolyte

“…The result of Rietveld refinement is given in Supplementary Table 1 . The I 003 / I 104 intensity ratio is nearly 1.45 (>1.2), which indicates a low ratio of cation disordering 37 .

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Dual-anion ionic liquid electrolyte enables stable Ni-rich cathodes in lithium-metal batteries

“…Thereby, common strategies rely on lattice doping into the transition metal layer to enhance the structural stability of the cathodes. 9 Typically, dopant elements, such as Mg, 10 Ca, 11 Al, 12 and Ti, 13,14 are intended to prevent Ni 2+ migration into the lithium layer 15 and to strengthen the metal-oxygen bonding in order to restrain oxygen release and improve the thermal stability. 7 Another approach to mitigate the performance decay of such cathode materials is the application of a protective surface coating.…”

Reducing Capacity and Voltage Decay of Co‐Free Li1.2Ni0.2Mn0.6O2 as Positive Electrode Material for Lithium Batteries Employing an Ionic Liquid‐Based Electrolyte

“…LRNM was synthesized by a simple solid-state reaction method, as described previously. [35] The refined X-ray diffraction (XRD) pattern (χ 2 = 3.6, Rwp = 5.15) is shown in Figure 1a. The experimental and calculated patterns can well be indexed to the hexagonal layered α-NaFeO 2 structure with an R-3m space group.…”