Dielectric Polarization in Inverse Spinel-Structured Mg2 TiO4 Coating to Suppress Oxygen Evolution of Li-Rich Cathode Materials

Surface LiMn1.4Ni0.5Mo0.1O4 Coating and Bulk Mo Doping of Li-Rich Mn-Based Li1.2Mn0.54Ni0.13Co0.13O2 Cathode with Enhanced Electrochemical Performance for Lithium-Ion Batteries

To improve the initial Coulombic efficiency, cycling stability, and rate performance of the Li-rich Mn-based Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode, the combination of LiMn_1.4Ni_0.5Mo_0.1O₄ coating with Mo doping has been successfully carried out by the sol-gel method and subsequent dip-dry process. This strategy buffers the electrodes from the corrosion of electrolyte and enhances the lattice parameter, which could inhibit the oxygen release and maintain the structural stability, thus improving the cycle stability and rate capability. After LiMn_1.4Ni_0.5Mo_0.1O₄ modification, the initial discharge capacity reaches 272.4 mAh g^-1 with a corresponding initial Coulombic efficiency (ICE) of 84.2% at 0.1C (1C = 250 mAh g^-1), far higher than those (221.5 mAh g^-1 and 68.9%) of the pristine sample. Besides, the capacity retention of the coated sample is enhanced by up to 66.8% after 200 cycles at 0.1C. Especially, the rate capability of the coated sample is 95.2 mAh g^-1 at 5C. XRD, SEM, TEM, XPS, and Raman spectroscopy are adopted to characterize the morphologies and structures of the samples. This coating strategy has been demonstrated to be an effective approach to construct high-performance energy storage devices.

Enhanced Activity and Reversibility of Anionic Redox by Tuning Lithium Vacancies in Li-Rich Cathode Materials

Li-rich Mn-based layered oxide cathodes (LLOs) are considered to be the most promising cathode candidates for lithium-ion batteries owing to their high-voltage platform and ultrahigh specific capacity originating from anionic redox. However, anionic redox results in many problems including irreversible oxygen release, voltage hysteresis, and so on. Although many efforts have been made to regulate anionic redox, a fundamental issue, the effect of lithium vacancies on anionic redox, is still unclear. Herein, we synthesized a series of LLO materials with different lithium vacancy contents by controlling the amount of lithium salt. Specifically, lithium-vacancy-type LLOs Li_1.11Ni_0.18Co_0.18Mn_0.53O₂ with a pompon morphology exhibit an ultrahigh specific capacity (293.9 mA h g^-1 at 0.1 C), an outstanding long-term cycling stability (173.5 mA h g^-1 after 300 cycles at 1 C), and an excellent rate performance (106 mA h g^-1 at 10 C). It reveals that lithium vacancy is a key factor to enhance anionic redox activity and reversibility. Lithium vacancies exhibit different inductive effects on the structure of the surface and bulk. Abundant surface oxygen vacancies and a surface spinel phase layer induced by lithium vacancies suppress irreversible oxygen release, while the bulk phase transformation and cation disorder combined with sufficient lithium vacancies in the bulk stabilize structure and improve anionic redox kinetic. The findings offer a significant theoretical guidance for the practical application of LLO materials.

Phase Compatible NiFe2O4 Coating Tunes Oxygen Redox in Li-Rich Layered Oxide

Li-rich layered oxides have attracted intense attention for lithium-ion batteries, as provide substantial capacity from transition metal cation redox simultaneous with reversible oxygen-anion redox. However, unregulated irreversible oxygen-anion redox leads to critical issues such as voltage fade and oxygen release. Here, we report a feasible NiFe₂O₄ (NFO) surface-coating strategy to turn the nonbonding coordination of surface oxygen into metal-oxygen decoordination. In particular, the surface simplex M-O (M = Ni, Co, Mn from MO₆ octahedra) and N-O (N = Ni, Fe from NO₆ octahedra) bonds are reconstructed in the form of M-O-N bonds. By applying both in operando and ex situ technologies, we found this heterostructural interface traps surface lattice oxygen, as well as restrains cation migration in Li-rich layered oxide during electrochemical cycling. Therefore, surface lattice oxygen behavior is significantly sustained. More interestingly, we directly observe the surface oxygen redox decouple with cation migration. In addition, the NFO-coating blocks HF produced from electrolyte decomposition, resulting in reducing the dissolution of Mn. With this strategy, higher cycle stability (91.8% at 1 C after 200 cycles) and higher rate capability (109.4 mA g^-1 at 1 C) were achieved in this work, compared with pristine Li-rich layered oxide. Our work offers potential for designing electrode materials utilizing oxygen redox chemistry.

Mechanochemical Synthesis and Structure of Lithium Tetrahaloaluminates, LiAlX4 (X = Cl, Br, I): A Family of Li-Ion Conducting Ternary Halides

State-of-the-art oxides and sulfides with high Li-ion conductivity and good electrochemical stability are among the most promising candidates for solid-state electrolytes in secondary batteries. Yet emerging halides offer promising alternatives because of their intrinsic low Li⁺ migration energy barriers, high electrochemical oxidative stability, and beneficial mechanical properties. Mechanochemical synthesis has enabled the characterization of LiAlX₄ compounds to be extended and the iodide, LiAlI₄, to be synthesized for the first time (monoclinic P2₁/c, Z = 4; a = 8.0846(1) Å; b = 7.4369(1) Å; c = 14.8890(2) Å; β = 93.0457(8)°). Of the tetrahaloaluminates, LiAlBr₄ exhibited the highest ionic conductivity at room temperature (0.033 mS cm^-1), while LiAlCl₄ showed a conductivity of 0.17 mS cm^-1 at 333 K, coupled with the highest thermal and oxidative stability. Modeling of the diffusion pathways suggests that the Li-ion transport mechanism in each tetrahaloaluminate is closely related and mediated by both halide polarizability and concerted complex anion motions.

A Novel Perovskite Electron-Ion Conductive Coating to Simultaneously Enhance Cycling Stability and Rate Capability of Li1.2 Ni0.13 Co0.13 Mn0.54 O2 Cathode Material for Lithium-Ion Batteries

Poor cycling stability and rate capability are two key issues needing to be solved for Li- and Mn-rich oxide cathode material for lithium-ion batteries (LIBs). Herein, a novel perovskite electron-ion mixed conductor Nd_0.6 Sr_0.4 CoO₃ (NSCO) is used as the coating layer on Li_1.2 Ni_0.13 Co_0.13 Mn_0.54 O₂ (LNCMO) to simultaneously enhance its cycling stability and rate capability. By coating 3 wt% NSCO, LNCMO-3NSCO exhibits an optimal cycling performance with a capacity retention of 99% at 0.1C (1C = 200 mA g^-1 ) after 60 cycles, 91% at 1C after 300 cycles, and 54% at 20C after 1000 cycles, much better than 78%, 63%, and 3% of LNCMO, respectively. Even at a high charge and discharge rate of 50C, LNCMO-3NSCO exhibits a discharge capacity of 53 mAh g^-1 and a mid-point discharge voltage of 2.88 V, much higher than those of LNCMO (24 mA h g^-1 and 2.40 V, respectively). Benefiting from the high electronic conductivity (1.46 S cm^-1 ) and ionic conductivity (1.48 × 10^-7  S cm^-1 ), NSCO coating not only suppresses transition metals dissolution and structure transformation, but also significantly enhances electronic conductivity and Li⁺ diffusion coefficient of LNCMO by an order of magnitude.

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%).

Deep Cycling for High-Capacity Li-Ion Batteries

As the practical capacity of conventional Li-ion batteries (LIBs) approaches the theoretical limit, which is determined by the rocking-chair cycling architecture, a new cycling architecture with higher capacity is highly demanded for future development and electronic applications. Here, a deep-cycling architecture intrinsically with a higher theoretical capacity limit than conventional rocking-chair cycling architecture is developed, by introducing a follow-up cycling process to contribute more capacity. The deep-cycling architecture makes full use of movable ions in both of the electrolyte and electrodes for energy storage, rather than in either the electrolyte or the electrodes. Taking LiMn₂ O₄ -mesocarbon microbeads (MCMB)/Li cells as a proof-of-concept, 57.7% more capacity is obtained. Moreover, the capacity retention is as high as 84.4% after 2000 charging/discharging cycles. The deep-cycling architecture offers opportunities to break the theoretical capacity limit of conventional LIBs and makes high demands for new-type of cathode materials, which will promote the development of next-generation energy storage devices.

Stabilizing Anionic Redox Chemistry in a Mn-Based Layered Oxide Cathode Constructed by Li-Deficient Pristine State

Li-rich cathode materials are of significant interest for coupling anionic redox with cationic redox chemistry to achieve high-energy-density batteries. However, lattice oxygen loss and derived structure distortion would induce serious capacity loss and voltage decay, further hindering its practical application. Herein, a novel Li-rich cathode material, O3-type Li_0.6 [Li_0.2 Mn_0.8 ]O₂ , is developed with the pristine state displaying both a Li excess in the transition metal layer and a deficiency in the alkali metal layer. Benefiting from stable structure evolution and Li migration processes, not only can high reversible capacity (≈329 mAh g^-1 ) be harvested but also irreversible/reversible anionic/cationic redox reactions are comprehensively assigned via the combination of in/ex situ spectroscopies. Furthermore, irreversible lattice oxygen loss and structure distortion are effectively restrained, resulting in long-term cycle stability (capacity drop of 0.045% per cycle, 500 cycles). Altogether, tuning the Li state in the alkali metal layer presents a promising way for modification of high-capacity Li-rich cathode candidates.

A review on the electrochemical reaction of Li-rich layered oxide materials

Lithium-rich layered oxide materials xLi2MnO3·(1 − x)LiMO2 (M = Mn, Co, Ni, Fe, Cr, etc.) as promising cathode candidates for high energy Li-ion batteries have been summarized in this review.

Large-Scale Synthesis of the Stable Co-Free Layered Oxide Cathode by the Synergetic Contribution of Multielement Chemical Substitution for Practical Sodium-Ion Battery

The O3-type layered oxide cathodes for sodium-ion batteries (SIBs) are considered as one of the most promising systems to fully meet the requirement for future practical application. However, fatal issues in several respects such as poor air stability, irreversible complex multiphase evolution, inferior cycling lifespan, and poor industrial feasibility are restricting their commercialization development. Here, a stable Co-free O3-type NaNi_0.4Cu_0.05Mg_0.05Mn_0.4Ti_0.1O₂ cathode material with large-scale production could solve these problems for practical SIBs. Owing to the synergetic contribution of the multielement chemical substitution strategy, this novel cathode not only shows excellent air stability and thermal stability as well as a simple phase-transition process but also delivers outstanding battery performance in half-cell and full-cell systems. Meanwhile, various advanced characterization techniques are utilized to accurately decipher the crystalline formation process, atomic arrangement, structural evolution, and inherent effect mechanisms. Surprisingly, apart from restraining the unfavorable multiphase transformation and enhancing air stability, the accurate multielement chemical substitution engineering also shows a pinning effect to alleviate the lattice strains for the high structural reversibility and enlarges the interlayer spacing reasonably to enhance Na⁺ diffusion, resulting in excellent comprehensive performance. Overall, this study explores the fundamental scientific understandings of multielement chemical substitution strategy and opens up a new field for increasing the practicality to commercialization.