Roles of transition metals interchanging with lithium in electrode materials

Abstract

Roles of antisite transition metals interchanging with Li atoms in electrode materials of Li transition-metal complex oxides were clarified using a newly developed direct labeling method, termed powder diffraction anomalous fine structure (P-DAFS) near the Ni K-edge. We site-selectively investigated the valence states and local structures of Ni in Li0.89Ni1.11O2, where Ni atoms occupy mainly the NiO2 host-layer sites and partially the interlayer Li sites in-between the host layers, during electrochemical Li insertion/extraction in a lithium-ion battery (LIB). The site-selective X-ray near edge structure evaluated via the P-DAFS method revealed that the interlayer Ni atoms exhibited much lower electrochemical activity as compared to those at the host-layer site. Furthermore, the present analyses of site-selective extended X-ray absorption fine structure performed using the P-DAFS method indicates local structural changes around the residual Ni atoms at the interlayer space during the initial charge; it tends to gather to form rock-salt NiO-like domains around the interlayer Ni. The presence of the NiO-like domains in the interlayer space locally diminishes the interlayer distance and would yield strain energy because of the lattice mismatch, which retards the subsequent Li insertion both thermodynamically and kinetically. Such restrictions on the Li insertion inevitably make the NiO-like domains electrochemically inactive, resulting in an appreciable irreversible capacity after the initial charge but an achievement of robust linkage of neighboring NiO2 layers that tend to be dissociated without the Li occupation. The P-DAFS characterization of antisite transition metals interchanging with Li atoms complements the understanding of the detailed charge-compensation and degradation mechanisms in the electrode materials.

Learning from Electrochemical Data: Simple Evaluation and Classification of LiMO2‐type‐based Positive Electrodes for Li‐Ion Batteries

“…[9,14] Furthermore,i tw as reported that Ni 2 + ions in the Li + layer led to structural instability and therefore to increased irreversible specific capacity losses. [33] In accordance with the results obtained in this work, Co-free LiMO 2 active materials cannot competew ith LCO in terms of the electrochemical performanceo wing to the disadvantageously high amount of Ni 2 + ions and thus the increased degreeo fL i + /Ni 2 + cation mixing. In this regard, it was also reportedt hat detrimental Li + /Ni 2 + cation mixingc ould be diminished by adding Co 3 + ,w hich thus illustrates its still-indispensable role for stabilizing the structure of LiMO 2 cathodes.A sd isplayed in Figure 8, the implementation of addi-tionalC o 3 + to yield NMC442 and NMC111 results in increased structural stability relative to Co-free NMC550 with regardt ot he reversible extractable amount of Li + ions.T his leads to the conclusion that ad ecrease in undesired Ni 2 + ions is beneficial for the stability and specific energyo ft he resultingL iMO 2 material, even thought his is associated with ad ecrease in beneficial Mn 4 + ions and with an increase in chemically instable Co 3 + .…”

“…Mixing of the Li + /Ni 2+ cations decreases the interlayer distance of the Li + layer, which retards the transport kinetics of the Li + ions within the active material during operation and consequently deteriorates the electrochemical performance, especially at increased current rates . Furthermore, it was reported that Ni 2+ ions in the Li + layer led to structural instability and therefore to increased irreversible specific capacity losses . In accordance with the results obtained in this work, Co‐free LiMO 2 active materials cannot compete with LCO in terms of the electrochemical performance owing to the disadvantageously high amount of Ni 2+ ions and thus the increased degree of Li + /Ni 2+ cation mixing.…”

Electronic Structure of Anode Material Li2TiSiO5 and Its Structural Evolution during Lithiation

“…Atomic distances between Ti and apical (O 2 -1) and basal (O 1 ) oxygen atoms are observed to subtly elongated during the same process. This expansion of distorted TiO 6 octahedron is in accordance with bond length increase often observed during transition-metal reduction in MO 6 octahedra. − In general, a less distorted TiO 6 octahedron resulted as Ti atom shifts toward the basal plane of square pyramid (or “octahedron center”).…”

X-ray absorption near edge structure simulation of LiNi0.5Co0.2Mn0.3O2via first-principles calculation

“…6,35 In the Ni Li Kedge of the XANES spectrum in Li 0.89 N i1.11 O 2 with 11% Li/Ni cation mixing, a shi of the absorption edge does not occur and the Ni valence does not change when the Li amount decreases. 54 The formation energies of Li/Ni, Li/Co, Li/Mn where the amounts of Ni and Mn are the same. 16 In the case of NCM523, such as NCM, the 180 arrangement of the antiferromagnetic Ni 2+ -O-Ni 2+ is stabilized by a strong super exchange interaction.…”