Unveiling the Roles of Trace Fe and F Co-doped into High-Ni Li-Rich Layered Oxides in Performance Improvement

High-Ni Li-rich layered oxides (HNLOs) derived from Li-rich Mn-based layered oxides (LRMLOs) can effectively mitigate the voltage decay of LRMLOs but normally suffered from decreased capacity and cycling stability. Herein, an effective, simple, and up-scalable co-doping strategy of trace Fe and F ions via a facile expanded graphite template-sacrificed approach was proposed for improving the performance of HNLOs. The trace Fe and F co-doping can far more effectively improve both its rate capability and cycling stability in a synergistic manner compared to the introduction of individual Fe cations and F anions. The co-doping of Fe and F increased the Li-O bonds by a magnitude far larger than the summation of the increments by their individual doping, quite favorable for the performance. The trace Fe doping can escalate the capacity and enhance the rate capability significantly by increasing the components of lower valence transition metals to activate their redox reactions more effectively and improving both the electronic and ionic conduction. In contrast, trace F can improve the cycling stability remarkably by lowering the O 2p band top to suppress the lattice oxygen escape effectively which were revealed by density functional theory calculations. The co-doped cathode exhibited excellent cycling stability with a superior capacity retention of 90% after 200 cycles at 1 C, much higher than 64% for the pristine sample. This study offers an idea for synergistically improving the performance of Li-rich layered oxides by co-doping trace Fe cations and F anions simultaneously, which play a complementary role in performance improvement.

Lithium Antievaporation-Loss Engineering via Sodium/Potassium Doping Enables Superior Electrochemical Performance of High-Nickel Li-Rich Layered Oxide Cathodes

Low-cost Mn- and Li-rich layered oxides suffer from rapid voltage decay, which can be improved by increasing the nickel content to derive high nickel Li-rich layered oxides (HNLO) but is normally accompanied by reduced capacity and inferior cycling stability. Herein, Na or K ions are successfully doped into the lattice of high nickel Li-rich Li_1.2-xM_xNi_0.32Mn_0.48O₂ (M = Na, K) layered oxides via a facile expanded graphite template-sacrificed approach. Both Na- and K-doped samples exhibit excellent rate capability and cycling stability compared with the un-doped one. The Na-doped sample shows a capacity retention of 93% after 200 cycles at 1C, which is quite outstanding for HNLO. The greatly improved electrochemical performances are attributed to the increased effective Li content in the lattice via Li antievaporation-loss engineering, the expanded Li slab, the pillaring effect, the increased C2/m component, and the improved electronic conductivity. Different performances by the introduction of sodium and potassium ions may be ascribed to their different ionic radii, which give rise to their different doping behaviors and threshold doping amounts. This work provides a new idea of enhancing electrochemical performance of HNLO by doping proper alien elements to increase the lattice lithium content effectively.

A Synergistic Effect of Na+ and Al3+ Dual Doping on Electrochemical Performance and Structural Stability of LiNi0.88Co0.08Mn0.04O2 Cathodes for Li-Ion Batteries

The synergistic effect of Na⁺/Al³⁺ dual doping is investigated to improve the structural stability and electrochemical performance of LiNi_0.88Co_0.08Mn_0.04O₂ cathodes for Li-ion batteries. Rietveld refinement and density functional theory calculations confirm that Na⁺/Al³⁺ dual doping changes the lattice parameters of LiNi_0.88Co_0.08Mn_0.04O₂. The changes in the lattice parameters and degree of cation mixing can be alleviated by maintaining the thickness of the LiO₆ slab because the energy of Al-O bonds is higher than that of transition metal (TM)-O bonds. Moreover, Na is an abundant and inexpensive metal, and unlike Al³⁺, Na⁺ can be doped into the Li slab. The ionic radius of Na⁺ (1.02 Å) is larger than that of Li⁺ (0.76 Å); therefore, when Na⁺ is inserted into Li sites, the Li slab expands, indicating that Na⁺ serves as a pillar ion for the Li diffusion pathway. Upon dual doping of the Li and TM sites of Ni-rich Ni_0.88Co_0.08Mn_0.04O₂ (NCM) with Na⁺ and Al³⁺, respectively, the lattice structure of the obtained NNCMA is more ideal than those of bare NCM and Li⁺- and Na⁺-doped NCM (NNCM and NCMA, respectively). This suggests that NNCMA with an ideal lattice structure presents several advantages, namely, excellent structural stability, a low degree of cation mixing, and favorable Li-ion diffusion. Consequently, the rate capability of NNCMA (83.67%, 3 C/0.2 C), which presents favorable Li-ion diffusion because of the expanded Li sites, is higher than those of bare NCM (78.68%), NNCM (81.15%), and NCMA (83.18%). The Rietveld refinement, differential capacity analysis, and galvanostatic intermittent titration technique results indicate that NNCMA exhibits low polarization, favorable Li-ion diffusion, and a low degree of cation mixing; moreover, its phase transition is hindered. Consequently, NNCMA demonstrates a higher capacity retention (84%) than bare NCM (79%), NNCM (82%), and NCMA (82%) after 50 cycles at 1 C. This study provides insight into the fabrication of Ni-rich NCMs with excellent electrochemical performance.

Improved adsorption performance and magnetic recovery capability of Al–Fe co-doped lithium ion sieves

Al–Fe co-doped H1.6(Al0.3Mn0.7)1.6Fe0.1O4 lithium-ion sieves exhibit magnetic recovery properties and excellent recycling performance.

Highly reversible Li-ion full batteries using a Mg-doped Li-rich Li1.2Ni0.28Mn0.468Mg0.052O2 cathode and carbon-decorated Mn3O4 anode with hierarchical microsphere structures

Microsphere structured Mg-doped Li-rich Li1.2Ni0.28Mn0.468Mg0.052O2 cathode and carbon-decorated Mn3O4 anode materials were prepared for application to lithium-ion full batteries. As-assembled lithium-ion full batteries exhibited enhanced electrochemical performances like high charge/discharge capacity, and long-term capacity retention.

Preparation and Electrochemical Characterization of La and Al Co-doped NCM811 Cathode Materials

LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) became a research hot point because of its low cost, environmental friendliness, and excellent electrochemical performance. However, Li⁺/Ni²⁺ intermixing is an essential factor affecting its applicability. Doping could be an important method to improve the electrochemical performance of NCM811-based cathode materials. In this work, La and Al co-doped NCM811 was prepared by a solid-state method. Results from X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) and electrochemical performance were discussed in depth. These showed that when La and Al doping concentrations were 1 and 0.5%, the samples showed the best performance. The as-improved performances were mainly attributed to the reduced Li⁺/Ni²⁺ intermixing, suppressed phase transition, and decreased potential polarization and impedance.

Dual Substitution Strategy in Co-Free Layered Cathode Materials for Superior Lithium Ion Batteries

A dual substitution strategy is introduced to Co-free layered material LiNi_0.5Mn_0.5O₂ by partially replacing Li and Ni with Na and Al, respectively, to achieve a superior cathode material for lithium ion batteries. Na⁺ ion functions as a "pillar" and a " cationic barrier" in the lithium layer while Al³⁺ ion plays an auxiliary role in stabilizing structure and lattice oxygen to improve the electrochemical performance and safety. The stability of lattice oxygen comes from the binding energy between the Ni and O, which is larger due to higher valences of Ni ions, along with a stronger Al-O bond in the crystal structure and the "cationic barrier" effect of Na⁺ ion at the high-charge. The more stable lattice oxygen reduces the cation disorder in cycling, and Na⁺ in the Li layer squeezes the pathway of the transition metal from the LiM₂ (M = metal) layer to the Li layer, stabilizing the layered crystal structure by inhibiting the electrochemical-driven cation disorder. Moreover, the cathode with Na-Al dual-substitution displays a smaller volume change, yielding a more stable structure. This study unravels the influence of Na-Al dual-substitution on the discharge capacity, midpoint potential, and cyclic stability of Co-free layered cathode materials, which is crucial for the development of lithium ion batteries.

Dual-Site Doping Strategy for Enhancing the Structural Stability of Lithium-Rich Layered Oxides

Lithium-rich layered oxide (LLO) cathode materials are considered to be one of the most promising next-generation candidates of cathode materials for lithium-ion batteries due to their high specific capacity. However, some inherent defects of LLOs hinder their practical application due to the oxygen loss and structure collapse resulting from intrinsic anion and cation redox reactions, such as poor cycle stability, sluggish Li⁺ kinetics, and voltage decay. Herein, we put forward a facile synergistic strategy to respond to these shortcomings of LLOs via dual-site doping with cerium (Ce) and boron (B) ions. The doped Ce ions occupy the octahedral sites, which not only enlarge the cell volume but also stabilize the layered framework and introduce abundant oxygen vacancies for LLOs, while B ions occupy the tetrahedral sites in the lattice, which block the migration path of transition metal (TM) ions and reduce the oxygen loss using the strong B-O bond. Based on this dual-site doping effect, after 100 cycles at 1 C, the dual-site doped materials exhibit excellent structural stability with a capacity retention of 91.15% (vs 75.12%) and also greatly suppress the voltage decay in LLOs with a voltage retention of 93.60% (vs 87.83%).

Microstructures and electrochemical performances of TiO2-coated Mg–Zr co-doped NCM as a cathode material for lithium-ion batteries with high power and long circular life

Mg–Zr-Ti co-modified NCM with excellent electrochemical performance is obtained by a solid-state method.

Synergistic effect of uniform lattice cation/anion doping to improve structural and electrochemical performance stability for Li-rich cathode materials

There has been extensive research into lithium-rich layered oxide materials as candidates for the nextgeneration of cathode materials in lithium-ion batteries, due to their high energy density and low cost; however, their poor cycle life and fast voltage fade hinder their large-scale commercial application. Here, we propose a novel cation/anion (Na⁺/PO₄ ^3-) co-doping approach to mitigate the discharge capacity and voltage fade of a Co-free Li_1.2Ni_0.2Mn_0.6O₂ cathode. Our results show that the synergistic effect of cation/anion doping can promote long cycle stability and rate performance by inhibiting the phase transformation of the layered structure to a spinel or rock-salt structure and stabilizing the well-ordered crystal structure during long cycles. The co-doped sample exhibits an outstanding cycle stability (capacity retention of 86.7% after 150 cycles at 1 C) and excellent rate performance (153 mAh g^-1 at 5 C). The large ionic radius of Na⁺ can expand the Li slab to accelerate Li diffusion and the large tetrahedral PO₄ ^3- polyanions with high electronegativity stabilize the local structure to improve the electrochemical performance.

Improved electrochemical properties and kinetics of an LiMn2O4-based cathode co-modified via Cu doping with truncated octahedron morphology

Spinel LiMn₂O₄ has been widely investigated as a cathode material for lithium-ion batteries, but it suffers from a limited cycle life due to the dissolution of Mn and structural distortion.

Hierarchical Li-rich oxide microspheres assembled from {010} exposed primary grains for high-rate lithium-ion batteries

The wide particle size distribution of LLO microspheres assembled from {010} exposed primary grains is proposed to improve their Li⁺ kinetics and tap-density.

Synthesis of polythiophene/graphite composites and their enhanced electrochemical performance for aluminum ion batteries

The illustration of the electrochemical process for high capacity aluminum ion batteries based on polythiophene/graphite composite cathode materials.