Concentration-Gradient Nb-Doping in a Single-Crystal LiNi_0.83Co_0.12Mn_0.05O₂ Cathode for High-Rate and Long-Cycle Lithium-Ion Batteries

Abstract

Single-crystalline nickel-rich layered oxides are promising cathode materials for building high-energy lithium-ion batteries because of alleviated particle cracking and irreversible phase transitions upon cycling, compared with their polycrystalline counterparts. Under a high state of charge, parasitic reactions tend to occur at the cathode− electrolyte interface, which could result in sluggish Li-ion diffusion kinetics and quickly faded electrochemical performance of cathodes. In this work, a concentration-gradient niobium-doping strategy was applied to modify the single-crystal LiNi 0.83 Co 0.12 Mn 0.05 O 2 cathode, with Nb concentration decreasing linearly from the surface to the core of the particle. As a result, the Nb-rich surface functions as an electrochemically active protective layer against electrolyte corrosion and transition metal dissolution, while the Nb-deficient core contributes to a higher capacity. The linear concentration gradient also minimizes structural transition from the surface to the core and helps to maintain structural integrity during repeated Li (de)intercalation. In addition, Nb-doping also assists to alleviate Li + /Ni 2+ mixing and increases the interlayer distance to enable faster Li-ion diffusion kinetics. By taking these advantages, the Nb-doped cathode materials (containing 1.0 atom% Nb) demonstrate a high reversible capacity, a high capacity retention, and improved rate capabilities. This work provides a general and facile approach to improve the storage performance of layered-oxide cathode materials by rationally tuning the bulk structure and interface with the electrolyte.

The role of niobium in layered oxide cathodes for conventional lithium-ion and solid-state batteries

“…Additional reports of other Ni-rich CAMs support the observed reduction in fraction of defects. 78,104,119,121,129–131 However, these claims contrast with the predicted trend, where high-valence dopants are expected to increase Ni 2+ content in LTMOs in order to maintain charge balance, facilitating the Li + /Ni 2+ cation mixing. 120,122,123,132,133 In this case, considering that Nb-doping is typically carried out concurrently with the lithiation of pCAM, it is likely that Ni 2+ is not completely oxidized during calcination to maintain charge balance.…”

Improvement of Thermodynamic Phase Stability and High-Rate Capability of Li Layered Oxides

“…The height of the phase transition barrier for LCTO is much lower than those for LCO, and the former results in the smooth charging/discharging curves upon cycling, but the stair-like voltage profile in the latter arises from the multiple-phase transition during (de)­lithiation . In addition, a multiple-phase transition plays an undesired role in deaccelerating Li-ion kinetics upon charging and discharging processes. , These considerations and the theoretical understanding led to examining the electrochemical performance of both cathode electrodes with various current density conditions, and we expect that the LCTO model exhibiting the smooth phase transition upon (de)­lithiation shows a greater electrochemical performance than LCO.…”

“…53 In addition, a multiple-phase transition plays an undesired role in deaccelerating Li-ion kinetics upon charging and discharging processes. 10,11 These considerations and the theoretical understanding led to examining the electrochemical performance of both cathode electrodes with various current density conditions, and we expect that the LCTO model exhibiting the smooth phase transition upon (de)lithiation shows a greater electrochemical performance than LCO.…”

“…6−9 However, multiple-phase transitions in LCO during the electrochemical process play an undesired role in decreasing the Li-ion kinetics. 10,11 In particular, the O3 to H1−3 (hybridized O1 and O3 phases) phase transition at the above cutoff voltage of 4.5 V, accompanied by c-axis contraction and lattice slab gliding, results in a fast deterioration of Li-ion diffusivity. 12,13 The drop in Li-ion diffusivity in the high-voltage region leads to a larger Li-ion gradient inside the LCO particles, resulting in greater internal strain followed by the degradation of mechanical performance.…”

In Situ Doping Polyanions Enables Concentration-Gradient Ni-Rich Cathodes for Long-Life Lithium-Ion Batteries

“…The onset potentials of gas evolution (O 2 and CO 2 ) of the three samples are all around 4.2 V. Compared with the massive evolution of the O 2 and CO 2 in NCM, the gas evolution in GNCM is suppressed to a certain extent, and after further modification by SiO 4 4– doping, there is only a trace amount of the CO 2 evolution in GNCM-Si. This phenomenon indicates that the strong Si–O bond and the reduced Ni 4+ content on the surface enhance the lattice oxygen stability, which is beneficial to improve the safety. − The safety of NCM, GNCM, and GNCM-Si was characterized by differential scanning calorimetry (DSC). The exothermic peak temperatures of NCM and GNCM are 218.9 and 224.5 °C, respectively.…”