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.

Facile Synthesis of Platelike Hierarchical Li1.2Mn0.54Ni0.13Co0.13O2 with Exposed {010} Planes for High-Rate and Long Cycling-Stable Lithium Ion Batteries

Lithium-rich layered oxides are promising cathode candidates for the production of high-energy and high-power electronic devices with high specific capacity and high discharge voltage. However, unstable cycling performance, especially at high charge-recharge rate, is the most challenge issue which needs to be solved to foster the diffusion of these materials. In this paper, hierarchical platelike Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials were synthesized by a facile solvothermal method followed by calcination. Calcination time was found to be a key parameter to obtain pure layered oxide phase and tailor its hierarchical morphology. The Li-rich material consists of primary nanoparticles with exposed {010} planes assembled to form platelike layers which exhibit low resistance to Li⁺ diffusion. In detail, the product by calcination at 900 °C for 12 h exhibits specific capacity of 228, 218, and 204 mA h g^-1 at 200, 400, and 1000 mA g^-1, respectively, whereas after 100 cycles at 1000 mA g^-1 rate of charge and recharge the specific capacity was retained by about 91%.

The Origin of Capacity Fade in the Li2MnO3·LiMO2 (M = Li, Ni, Co, Mn) Microsphere Positive Electrode: An Operando Neutron Diffraction and Transmission X-ray Microscopy Study

The mechanism of capacity fade of the Li2MnO3·LiMO2 (M = Li, Ni, Co, Mn) composite positive electrode within a full cell was investigated using a combination of operando neutron powder diffraction and transmission X-ray microscopy methods, enabling the phase, crystallographic, and morphological evolution of the material during electrochemical cycling to be understood. The electrode was shown to initially consist of 73(1) wt % R3̅m LiMO2 with the remaining 27(1) wt % C2/m Li2MnO3 likely existing as an intergrowth. Cracking in the Li2MnO3·LiMO2 electrode particle under operando microscopy observation was revealed to be initiated by the solid-solution reaction of the LiMO2 phase on charge to 4.55 V vs Li(+)/Li and intensified during further charge to 4.7 V vs Li(+)/Li during the concurrent two-phase reaction of the LiMO2 phase, involving the largest lattice change of any phase, and oxygen evolution from the Li2MnO3 phase. Notably, significant healing of the generated cracks in the Li2MnO3·LiMO2 electrode particle occurred during subsequent lithiation on discharge, with this rehealing being principally associated with the solid-solution reaction of the LiMO2 phase. This work reveals that while it is the reduction of lattice size of electrode phases during charge that results in cracking of the Li2MnO3·LiMO2 electrode particle, with the extent of cracking correlated to the magnitude of the size change, crack healing is possible in the reverse solid-solution reaction occurring during discharge. Importantly, it is the phase separation during the two-phase reaction of the LiMO2 phase that prevents the complete healing of the electrode particle, leading to pulverization over extended cycling. This work points to the minimization of behavior leading to phase separation, such as two-phase and oxygen evolution, as a key strategy in preventing capacity fade of the electrode.

Fast-Rate Capable Electrode Material with Higher Energy Density than LiFePO4: 4.2V LiVPO4F Synthesized by Scalable Single-Step Solid-State Reaction

Use of compounds that contain fluorine (F) as electrode materials in lithium ion batteries has been considered, but synthesizing single-phase samples of these compounds is a difficult task. Here, it is demonstrated that a simple scalable single-step solid-state process with additional fluorine source can obtain highly pure LiVPO4F. The resulting material with submicron particles achieves very high rate capability ≈100 mAh g-1 at 60 C-rate (1-min discharge) and even at 200 C-rate (18 s discharge). It retains superior capacity, ≈120 mAh g-1 at 10 C charge/10 C discharge rate (6-min) for 500 cycles with >95% retention efficiency. Furthermore, LiVPO4F shows low polarization even at high rates leading to higher operating potential >3.45 V (≈3.6 V at 60 C-rate), so it achieves high energy density. It is demonstrated for the first time that highly pure LiVPO4F can achieve high power capability comparable to LiFePO4 and much higher energy density (≈521 Wh g-1 at 20 C-rate) than LiFePO4 even without nanostructured particles. LiVPO4F can be a real substitute of LiFePO4.

Improving the electrochemical performance of Li1.2Mn0.52Co0.13Ni0.13O2 by surface nitrogen doping via plasma treatment

A facile and effective route to introduce nitrogen on the surface of a material with improved electrochemical performance.

Glucose-assisted combustion synthesis of Li1.2Ni0.13Co0.13Mn0.54O2 cathode materials with superior electrochemical performance for lithium-ion batteries

Lithium-rich layered Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ cathode materials have been successfully fabricated by a glucose-assisted combustion method combined with a calcination treatment.

Effect of valence states of Ni and Mn on the structural and electrochemical properties of Li1.2NixMn0.8−xO2 cathode materials for lithium-ion batteries

Severe capacity fading and voltage decay of Li-rich layered oxides for lithium-ion batteries remain the major bottlenecks to commercialization.

Enhanced cycling stability and rate capability of Bi2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials for lithium-ion batteries

The LMNC-BO electrode presents an enhanced cycle performance, better rate capability and structural stability than bare LMNC.

Magnesium-Doped Li1.2[Co0.13Ni0.13Mn0.54]O2 for Lithium-Ion Battery Cathode with Enhanced Cycling Stability and Rate Capability

Mg-doped Li[Li0.2-2xMgxCo0.13Ni0.13Mn0.54]O2 is synthesized by introducing Mg ions into the transition-metal (TM) layer of this layered compound for substituting Li ions through a simple polymer-pyrolysis method. The structural and morphological characterization reveals that the doped Mg ions are uniformly distributed in the bulk lattice, showing an insignificant impact on the layered structure. Electrochemical experiments reveal that, at a Mg doping of 4%, the Li[Li0.16Mg0.04Co0.13Ni0.13Mn0.54]O2 electrode can deliver a larger initial reversible capacity of 272 mAh g(-1), an improved rate capability with 114 mAh g(-1) at 8 C, and an excellent cycling stability with 93.3% capacity retention after 300 cycles. The superior electrochemical performances of the Mg-doped material are possibly due to the enhancement of the structural stability by substitution of Li by Mg in the TM layer, which effectively suppresses the cation mixing arrangement, leading to the alleviation of the phase change during lithium-ion insertion and extraction.

Enhanced electrochemical performance and thermal stability of a CePO4-coated Li1.2Ni0.13Co0.13Mn0.54O2 cathode material for lithium-ion batteries

CePO₄ coating via a simple precipitation method enhances the thermal stability of the layered Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ cathode material.

Recent progress in Li-rich layered oxides as cathode materials for Li-ion batteries

This review systematically summarized Li-rich layered oxides and states the strategies to enhance such materials when used in Li-ion batteries.

Surfactant CTAB-assisted synthesis of Li1.13[Ni0.233Mn0.534Co0.233]0.87O2 with festoon-like hierarchical architectures as cathode materials for Li-ion batteries with outstanding performance

Surfactant CTAB-assisted Li_1.13[Ni_0.233Mn_0.534Co_0.233]_0.87O₂ composite presents high stable specific capacity (247.5 mA h g⁻¹) due to a stable mixed structure that can effectively alleviate the structure change during cycling.

Role of carbon coating in improving electrochemical performance of Li-rich Li(Li0.2Mn0.54Ni0.13Co0.13)O2 cathode

Li-rich Li(Li_0.2Mn_0.54Ni_0.13Co_0.13)O₂ cathode coated with carbon layer has been prepared by a hydrothermal approach. The enhanced performance is attributed to the carbon layer and surface spinels on particles.