Zr-containing phosphate coating to enhance the electrochemical performances of Li-rich layer-structured Li[Li0.2Ni0.17Co0.07Mn0.56]O2

Unveiling the Stability Mechanism of Oriented Ni-Rich Layered Oxides

Single-crystal and polycrystalline structures are the two main structural forms of the Ni-rich layered cathode for lithium-ion batteries. The structural difference is closely related to the electrochemical performance and thermal stability, but its internal mechanism is unclear and is worthy of further exploration. In this study, both polycrystalline and single-crystal LiNi0.83Co0.12Mn0.05O2 cathodes were prepared by adjusting the calcination temperature and mechanical post-treatment, respectively. Systematic comparisons were made to assess the effects of different grain structures on the electrochemical performance and thermal stability. The study revealed the superior thermal stability of monocrystalline cathodes, attributing it to oxygen vacancies and phase transitions. From the perspective of grain boundaries, it was demonstrated that the diffusion of oxygen vacancies and the reduction of Ni in polycrystalline cathodes exhibit anisotropy. This research elucidates the origins of the superior thermal stability of monocrystalline cathodes in lithium-ion batteries, providing valuable insights into battery material design.

Integrating a Ferroelectric Interface with a Well-Tuned Electronic Structure in Lithium-Rich Layered Oxide Cathodes for Enhanced Lithium Storage

Li-rich layered oxides (LLOs) are considered promising candidates for new high-energy-density cathode materials for next-generation power batteries. However, their large-scale applications are largely hindered by irreversible Li/O loss, structural degradation, and interfacial side reactions during cycling. Herein, we demonstrate an integration strategy that tunes the electronic structure by La/Al codoping and constructs a ferroelectric interface on the LLOs surface through Bi_0.5Na_0.5TiO₃ (BNT) coating. Experimental characterization reveals that the synergistic effect of the ferroelectric interface and the well-tuned electronic structure can not only promote the diffusion of Li⁺ and hinder the migration of O^n- but also suppress the lattice volume changes and reduce interfacial side reactions at high voltages up to 4.9 V vs Li⁺/Li. As a result, the modified material shows enhanced initial capacities and retention rates of 224.4 mAh g^-1 and 78.57% after 500 cycles at 2.0-4.65 V and 231.7 mAh g^-1 and 85.76% after 200 cycles at 2.0-4.9 V at 1C, respectively.

Surface Reduction Stabilizes the Single-Crystalline Ni-Rich Layered Cathode for Li-Ion Batteries

The surface of the layered transition metal oxide cathode plays an important role in its function and degradation. Modification of the surface structure and chemistry is often necessary to overcome the debilitating effect of the native surface. Here, we employ a chemical reduction method using CaI₂ to modify the native surface of single-crystalline layered transition metal oxide cathode particles. High-resolution transmission electron microscopy shows the formation of a conformal cubic phase at the particle surface, where the outmost layer is enriched with Ca. The modified surface significantly improves the long-term capacity retention at low rates of cycling, yet the rate capability is compromised by the impeded interfacial kinetics at high voltages. The lack of oxygen vacancy generation in the chemically induced surface phase transformation likely results in a dense surface layer that accounts for the improved electrochemical stability and impeded Li-ion diffusion. This work highlights the strong dependence of the electrode's (electro)chemical stability and intercalation kinetics on the surface structure and chemistry, which can be further tailored by the chemical reduction method.

High-Ni cathode material improved with Zr for stable cycling of Li-ion rechargeable batteries

The Zr solvent solution method, which allows primary and secondary particles of LiNi0.90Co0.05Mn0.05O2 (NCM) to be uniformly doped with Zr and simultaneously to be coated with an Li2ZrO3 layer, is introduced in this paper. For Zr doped NCM, which is formed using the Zr solvent solution method (L-NCM), most of the pinholes inside the precursor disappear owing to the diffusion of the Zr dopant solution compared with Zr-doped NCM, which is formed using the dry solid mixing method from the (Ni0.90Co0.05Mn0.05)(OH)2 precursor and the Zr source (S-NCM), and Li2ZrO3 is formed at the pinhole sites. The mechanical strength of the powder is enhanced by the removal of the pinholes by the formation of Li2ZrO3 resulting from diffusion of the solvent during the mixing process, which provides protection from cracking. The coating layer functions as a protective layer during the washing process for removing the residual Li. The electrochemical performance is improved by the synergetic effects of suitable coatings and the enhanced structural stability. The capacity-retentions for 2032 coin cells are 86.08%, 92.12%, and 96.85% at the 50th cycle for pristine NCM, S-NCM, and L-NCM, respectively. The superiority of the liquid mixing method is demonstrated for 18 650 full cells. In the 300th cycle in the voltage range of 2.8-4.35 V, the capacity-retentions for S-NCM and L-NCM are 77.72% and 81.95%, respectively.

Li3PO4 modification on a primary particle surface for high performance Li-rich layered oxide Li1.18Mn0.52Co0.15Ni0.15O2via a synchronous route

A Li-rich layered oxide, Li_1.18Mn_0.52Co_0.15Ni_0.15O₂, with Li₃PO₄ modification on the surface of a primary particle, was synthesized by a facile synchronous method.

Integrated Surface Functionalization of Li-Rich Cathode Materials for Li-Ion Batteries

As candidates for high-energy density cathodes, lithium-rich (Li-rich) layered materials have attracted wide interest for next-generation Li-ion batteries. In this work, surface functionalization of a typical Li-rich material Li_1.2Mn_0.56Ni_0.17Co_0.07O₂ is optimized by fluorine (F)-doped Li₂SnO₃ coating layer and electrochemical performances are also enhanced accordingly. The results demonstrate that F-doped Li₂SnO₃-modified material exhibits the highest capacity retention (73% after 200 cycles), with approximately 1.2, 1.4, and 1.5 times of discharge capacity for Li₂SnO₃ surface-modified, F-doped, and pristine electrodes, respectively. To reveal the fundamental enhancement mechanism, intensive surface Li⁺ diffusion kinetics, postmortem structural characteristics, and aging tests are performed for four sample systems. The results show that the integrated coating layer plays an important role in addressing interface compatibility, not only limited in stabilizing the bulk structure and suppressing side reactions, synergistically contributing to the performance enhancement for the active electrodes. These findings not only pave the way to commercial application of the Li-rich material but also shed new light on surface modification in batteries and other energy storage fields.

Enhanced electrochemical property of FePO4-coated LiNi0.5Mn1.5O4 as cathode materials for Li-ion battery

Pristine LiNi_0.5Mn_1.5O₄ and FePO₄-coated one with Fd-3m space groups were prepared by a sol-gel method. The structure and performance were studied by X-ray diffraction (XRD) rietveld refinement, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectrometer (EDS) mapping, electrochemical impedance spectroscopy (EIS) and charge-discharge tests, respectively. The lattice parameters of all samples almost remain the same from the Rietveld refinement, revealing that the crystallographic structure has no obvious difference between pristine LiNi_0.5Mn_1.5O₄ and FePO₄-coated one. All materials show similar morphologies with uniform particle distribution with small particle size, and FePO₄ coating does not affect the morphology of LiNi_0.5Mn_1.5O₄ material. EDS mapping and HRTEM show that FePO₄ may be successfully wrapped around the surfaces of LiNi_0.5Mn_1.5O₄ particles, and provides an effective coating layer between the electrolyte and the surface of LiNi_0.5Mn_1.5O₄ particles. FePO₄ (1wt%)-coated LiNi_0.5Mn_1.5O₄ cathode shows the highest discharge capacity at high rate (2C) among all samples. After 80 cycles, the reversible discharge capacity of FePO₄ (1wt%) coated LiNi_0.5Mn_1.5O₄ is 117mAhg^-1, but the pristine one only has 50mAhg^-1. FePO₄ coating is an effective and controllable way to stabilize the LiNi_0.5Mn_1.5O₄/electrolyte interface, and avoids the direct contact between LiNi_0.5Mn_1.5O₄ powders and electrolyte, then suppresses the side reactions and enhances the electrochemical performance of the LiNi_0.5Mn_1.5O₄.

Improved Cycling Stability and Fast Charge-Discharge Performance of Cobalt-Free Lithium-Rich Oxides by Magnesium-Doping

Layered Li-rich, Co-free, and Mn-based cathode material, Li_1.17Ni_0.25-xMn_0.58Mg_xO₂ (0 ≤ x ≤ 0.05), was successfully synthesized by a coprecipitation method. All prepared samples have typical Li-rich layered structure, and Mg has been doped in the Li_1.17Ni_0.25Mn_0.58O₂ material successfully and homogeneously. The morphology and the grain size of all material are not changed by Mg doping. All materials have a estimated size of about 200 nm with a narrow particle size distribution. The electrochemical property results show that Li_1.17Ni_0.25-xMn_0.58Mg_xO₂ (x = 0.01 and 0.02) electrodes exhibit higher rate capability than that of the pristine one. Li_1.17Ni_0.25-xMn_0.58Mg_xO₂ (x = 0.02) indicates the largest reversible capacity of 148.3 mAh g^-1 and best cycling stability (capacity retention of 95.1%) after 100 cycles at 2C charge-discharge rate. Li_1.17Ni_0.25-xMn_0.58Mg_xO₂ (x = 0.02) also shows the largest discharge capacity of 149.2 mAh g^-1 discharged at 1C rate at elevated temperature (55 °C) after 50 cycles. The improved electrochemical performances may be attributed to the decreased polarization, reduced charge transfer resistance, enhanced the reversibility of Li⁺ ion insertion/extraction, and increased lithium ion diffusion coefficient. This promising result gives a new understanding for designing the structure and improving the electrochemical performance of Li-rich cathode materials for the next-generation lithium-ion battery with high rate cycling performance.

Surface Modification of Li-Rich Cathode Materials for Lithium-Ion Batteries with a PEDOT:PSS Conducting Polymer

Composites of lithium-rich Li1.2Ni0.2Mn0.6O2 and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (

PEDOT

PSS) are synthesized through coprecipitation followed by a wet coating method. In the resulting samples, the amorphous conductive polymer films on the surface of the Li1.2Ni0.2Mn0.6O2 particles are 5-20 nm thick. The electrochemical properties of Li1.2Ni0.2Mn0.6O2 are obviously enhanced after

PEDOT

PSS coating. The composite sample with an optimal 3 wt % coating exhibits rate capability and cycling properties that are better than those of Li1.2Ni0.2Mn0.6O2, with an excellent initial discharge capacity of 286.5 mA h g(-1) at a current density of 0.1 C and a discharge capacity that remained at 146.9 mA h g(-1) at 1 C after 100 cycles. The improved performances are ascribed to the high conductivity of the

PEDOT

PSS coating layer, which can improve the conductivity of the composite material. The

PEDOT

PSS layer also suppresses the formation and growth of a solid electrolyte interface. Surface modification with

PEDOT

PSS is a feasible approach for improving the comprehensive properties of cathode materials.

Enhancement in the electrochemical performance of zirconium/phosphate bi-functional coatings on LiNi0.8Co0.15Mn0.05O2 by the removal of Li residuals

The effect of bi-functional coatings consisting of Zr and phosphate (P) on the electrochemical performance of Li_1.0Ni_0.8Co_0.15Mn_0.05O₂ (NCM) has been investigated.