Elucidating the Effect of the Dopant Ionic Radius on the Structure and Electrochemical Performance of Ni-Rich Layered Oxides for Lithium-Ion Batteries

Comparative impact of surface and bulk fluoride anion doping on the electrochemical performance of co-free Li-rich Mn-based layered cathodes

Li-rich Mn-based (LMR) layered oxides are considered promising cathode materials for high energy-density Li-ion batteries. Nevertheless, challenges such as irreversible oxygen loss at the surface during the initial charge, alteration of the bulk structure, and poor rate performance impede their path to commercialisation. Most modification methods focus on specific layers, making the overall impact of modifications at various depths on the properties of materials unclear. This research presents an approach by using doping to adjust both surface and bulk properties; the materials with surface and bulk fluoride anion doping are synthesised to explore the connection between doping depth, structural and electrochemical stability. The surface-doped material significantly improves the initial Coulombic efficiency (ICE) from 77.85% to 85.12% and limits phase transitions, yet it does not enhance rate performance. Conversely, doping in bulk stands out by improving both rate performance and cyclic stability: it increases the specific discharge capacity by around 60 mAh g-1 and enhances capacity retention from 57.69% to 82.26% after 300 cycles at 5C. These results highlight a notable dependence of material properties on depth, providing essential insights into the mechanisms of surface and bulk modifications.

Dual-Responsive and Aggregation-Induced-Emission Probe for Selective Imaging of Infectious Urolithiasis

Identifying infected stones is crucial due to their rapid growth and high recurrence rate. Here, the calcium-magnesium dual-responsive aggregation-induced emission (AIE)-active probe TCM-5COOH (Tricyano-methlene-pyridine-5COOH), distinctively engineered to distinguish high-threat infection calculi from metabolic stones, is presented. Upon incorporation of flexible alkyl carboxyl group, TCM-5COOH featuring five carboxyl moieties demonstrates excellent water solubility and enhanced penetration into porous infectious stones. The robust chelation of TCM-5COOH with stone surface-abundant Ca2+ and Mg2+ inhibits vibrational relaxation, thus triggering intense AIE signals. Remarkably, the resulting complex exhibits high insolubility, effectively anchoring within the porous structure of the infection calculi and offering prolonged illumination. Jobs' plot method reveals similar response characteristics for Ca2+ and Mg2+, with a 1:2 coordination number for both ions. Isothermal titration calorimetry (ITC) results demonstrate higher enthalpy change (ΔH) and lower entropy change (ΔS) for the reaction, indicating enhanced selectivity compared to TCM-4COOH lacking the alkyl carboxyl group. Synchrotron X-ray absorption fine spectroscopy (XAFS) validates TCM-5COOH's interaction with Ca2+ and Mg2+ at the microlevel. This dual-responsive probe excels in identifying infectious and metabolic calculi, compatible with endoscopic modalities and laser excitation, thereby prompting clinical visualization and diagnostic assessment.

Interpretable Machine Learning To Accelerate the Analysis of Doping Effect on Li/Ni Exchange in Ni-Rich Layered Oxide Cathodes

In Ni-rich layered oxide cathodes, one effective way to adjust the performance is by introducing dopants to change the degree of Li/Ni exchange. We calculated the formation energy of Li/Ni exchange defects in LiNi0.8Mn0.1X0.1O2 with different doping elements X, using first-principles calculations. We then proposed an interpretable machine learning method combining the Random Forest (RF) model and the Shapley Additive Explanation (SHAP) analysis to accelerate identification of the key factors influencing the formation energy among the complex variables introduced by doping. The valence state of the doping element effectively regulates Li/Ni exchange defects through changing the valence state of Ni and the strength of the superexchange interaction, and COOPSU-SD and MagO were proposed as two indicators to assess superexchange interaction. The volume change also affects the Li/Ni exchange defects, with a larger volume reduction corresponding to fewer Li/Ni exchange defects.

High Voltage Cycling Stability of LiF-Coated NMC811 Electrode

The development of LiNi0.8Mn0.1Co0.1O2 (NMC811) as a cathode material for high-energy-density lithium-ion batteries (LIBs) intends to address the driving limitations of electric vehicles. However, the commercialization of this technology has been hindered by poor cycling stability at high cutoff voltages. The potential instability and drastic capacity fade stem from irreversible parasitic side reactions at the electrode-electrolyte interface. To address these issues, a stable nanoscale lithium fluoride (LiF) coating is deposited on the NMC811 electrode via atomic layer deposition. The nanoscale LiF coating diminishes the direct contact between NMC811 and the electrolyte, suppressing the detrimental parasitic reactions. LiF-NMC811 delivers cycling stability superior to uncoated NMC811 with high cutoff voltage for half-cell (3.0-4.6 V vs Li/Li+) and full-cell (2.8-4.5 V vs graphite) configurations. The structural, morphological, and chemical analyses of the electrodes after cycling show that capacity decline fundamentally arises from the electrode-electrolyte interface growth, irreversible phase transformation, transition metal dissolution and crossover, and particle cracking. Overall, this work demonstrates that LiF is an effective electrode coating for high-voltage cycling without compromising rate performance, even at high discharge rates. The findings of this work highlight the need to stabilize the electrode-electrolyte interface to fully utilize the high-capacity performance of NMC811.

La-Doped Ultrahigh-Nickel Layered Oxide Cathode with Enhanced Cycle Stability for Li-Ion Batteries

Currently, ultrahigh-nickel layered oxide is one of the most promising cathodes for lithium-ion batteries, with the advantages of high theoretical capacity and low cost. However, some problems in ultrahigh-nickel layered oxides are more serious, such as irreversible structural transformation, particle cracking, and side reactions at the electrode/electrolyte interface, resulting in the fast decay of the discharge capacity and midpoint potential. In this work, La doping is introduced into ultrahigh-nickel layered LiNi_0.9Co_0.1O₂ oxide to improve the cycle stability on both discharge capacity and midpoint potential. As demonstrated, La can be doped successfully into the subsurface of LiNi_0.9Co_0.1O₂ oxide, and the morphology of the oxide microspheres is not changed obviously by La doping. Compared with the pristine sample, the La-doped sample presents improved electrochemical performance, especially good cycle stabilization on both discharge capacity and midpoint potential. In addition, after a long-term cycle, the La-doped sample still maintains a relatively complete spherical morphology. It means that the pillaring effect of La with a large radius is helpful in accommodating the volume change caused by the insertion/extraction of Li ions, thus easing the anisotropic stress accumulation and microcrack growth inside the microspheres of the La-doped sample.

Organo-Soluble Decanoic Acid-Modified Ni-Rich Cathode Material LiNi0.90Co0.07Mn0.03O2 for Lithium-Ion Batteries

Ni-rich layered oxides as cathode materials deliver a higher capacity than those used currently, in hopes of improving the energy density of Li-ion batteries. However, the surface residual alkali and the interfacial parasitic reactions caused by the rich nickel bring a series of problems such as surface slurrying, structure deterioration, mechanical fracture, and capacity decay. Herein, different from the common surface coating strategies with inorganics, an organo-soluble acid modification approach is proposed to meet the challenges. For LiNi_0.90Co_0.07Mn_0.03O₂ (NCM90), decanoic acid can react with the residual lithium salts on the surface to form an organic lithium salt-dominant modification layer. During cycling, an organic lithium-involved cathode/electrolyte interface (CEI) layer is rapidly formed. Specially, the solubility of decanoic acid in the organic electrolyte makes the CEI layer keep strong interaction with NCM90, thin but effective. Consequently, the modified NCM90 exhibits notable performances in terms of structural stability, mechanical integrity, and capacity retention.