Insight into the effect of Nb5+ on the crystal structure and electrochemical performance of the Li-rich cathode materials

Simple and Ingenious Manner To Build Li-Rich Layered Materials with Surface Layered/Spinel Heterostructures and Li Deficiencies

“…At the same time, minor peaks at around 20−25°are exhibited in the XRD profiles, which consisted of the α-NaFeO 2 structure containing the C2/m space group. 19,29 Besides, the characteristic peaks of the spinel structure are presented in the LR-S sample (panels a and b of Figure 2), indicating that the addition of the precursor may reduce the ratio of Li/TM and generate the spinel structure in a local crystallographic structure in the LR-S material after the high-temperature post-treatment process. The lattice parameters of the LR-0 and LR-S samples are given in Table 1, and the result showed that the LR-S sample has larger cell parameters and lattice volumes.…”

“…To ameliorate the above shortcomings, many strategies, such as ion doping, surface modification, and spinel/layered structure construction, were proposed in the past decades. ,− The introduction of the spinel-like phase into the surface or host of the LR sample is considered to be an effective path, owing to the three-dimensional (3D) lithium ion diffusion paths, stable lattice oxygen, and structural compatibility, which may mitigate the transformation from the layered to spinel structure and acquire outstanding cycling performances of the modified LR materials in the removal/uptake processes. − The preparation methods of introducing the spinel phase into the LR materials includes wet chemical oxidation and secondary calcination, ion exchange and annealing procedure, and carbothermal reduction. − Although modified LR materials displayed good cycling performances and rate capability, these preparation methods are complex and time-consuming.…”

Improving the Electrochemical Performance of Co-Free Li-Rich Layered Oxides via a Dual Modification of Nb5+ Doping and Oxygen Vacancy Regulation

“…The crystal structure of the materials was analyzed by XRD. As shown in Figure , the main diffraction peaks of all samples are matched with the LiTMO 2 phase ( R 3̅ m ), and a weak peak at around 20–25° corresponds to the Li 2 MnO 3 phase ( C 2/ m ). , In addition, it can be seen from the local magnifications of (003) and (104) peaks in Figure b,c that the peak position shifts to a lower 2θ degree with the increase of Nb doping, which is mainly due to the doping of larger radius Nb 5+ into the lattice . As revealed in Figure d,e and Table , more abundant information about the crystal structure can be obtained by XRD Rietveld refinement.…”

“…21,22 In addition, it can be seen from the local magnifications of (003) and (104) peaks in Figure 3b,c that the peak position shifts to a lower 2θ degree with the increase of Nb doping, which is mainly due to the doping of larger radius Nb 5+ into the lattice. 23 As revealed in Figure 3d,e and Table 1, more abundant information about the crystal structure can be obtained by XRD Rietveld refinement. The low values of R P and R WP ensure the reliability of the fitting results.…”

Role of Substitution Elements in Enhancing the Structural Stability of Li-Rich Layered Cathodes

“…In most cases, introducing a certain amount of inert element (e.g., Sn 4+ and Ti 4+ ) , to replace TM element in lithium-rich cathodes has been proven to be an effective way to access better electrochemical performance in restraining voltage decay and capacity loss, and the profaned principles of element substitution are either a similar ionic radius or same valency; the regularly used substituting elements are marked in the periodic table of elements (Scheme ). What is regretted is the degree of matching between pristine TM elements and substituents, such as electronegativity, redox activity, and TM–O binding energy, which are commonly ill-considered carefully − (Scheme ). Also, the affecting influence of inert elements is completely attributed to the increase of the TM­(3d/4d/5d)–O­(2p) band overlap (the covalent character of TM–O bonds is enhanced) and therefore enhances the covalent character of TM–O bonds, which anchors the oxidized lattice oxygen (e.g., O 2 n – , O n – , TM–O n – ), slows down the cation mixing, and restrains the TM migration .…”