Design of LiAlO2 mosaic structure for preparing high nickel-based LiNi0.88Co0.07Al0.05O2 cathode material by simple hydrolysis method

Lithium-Ion Conductive Coatings for Nickel-Rich Cathodes for Lithium-Ion Batteries

Nickel (Ni)-rich cathodes are among the most promising cathode materials of lithium batteries, ascribed to their high-power density, cost-effectiveness, and eco-friendliness, having extensive applications from portable electronics to electric vehicles and national grids. They can boost the wide implementation of renewable energies and thereby contribute to carbon neutrality and achieving sustainable prosperity in the modern society. Nevertheless, these cathodes suffer from significant technical challenges, leading to poor cycling performance and safety risks. The underlying mechanisms are residual lithium compounds, uncontrolled lithium/nickel cation mixing, severe interface reactions, irreversible phase transition, anisotropic internal stress, and microcracking. Notably, they have become more serious with increasing Ni content and have been impeding the widespread commercial applications of Ni-rich cathodes. Various strategies have been developed to tackle these issues, such as elemental doping, adding electrolyte additives, and surface coating. Surface coating has been a facile and effective route and has been investigated widely among them. Of numerous surface coating materials, have recently emerged as highly attractive options due to their high lithium-ion conductivity. In this review, a thorough and comprehensive review of lithium-ion conductive coatings (LCCs) are made, aimed at probing their underlying mechanisms for improved cell performance and stimulating new research efforts.

Enhanced Cycling and Structure Stability of an Electron Transfer-Accelerating Polymer Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate)-Covered Mn-Based Layered Cathode with Ga3+ Doping for a Li-Ion Battery

Mn-based cathode material Li_1.20Mn_0.52Ni_0.20Co_0.08O₂ was proposed and ameliorated by surface-coating poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and doping Ga³⁺. X-ray diffraction and high-resolution transmission electron microscopy studies revealed that part of Ga³⁺ replacing the Ni site could reduce the Li⁺/Ni²⁺ mixing by forming a well-ordered layered structure and a homogeneous coating layer of PEDOT:PSS is covered on the surface of Li_1.20Mn_0.52Ni_0.19Co_0.08Ga_0.01O₂. The results of the electrochemical studies demonstrated the higher initial charging-discharging Coulombic efficiency, and outstanding rate capabilities and cyclic performance were obtained for the PEDOT:PSS-covered and Ga³⁺-doped samples. Especially, 2 wt % PEDOT:PSS-coated Li_1.20Mn_0.52Ni_0.19Co_0.08Ga_0.01O₂ delivered 38.3 mAh g^-1, which is larger than the pristine cathode at a 5C high rate. Meanwhile, it could retain 189.6 mAh g^-1 (90.3% of its initial discharge capacity at 45 °C) after 300 cycles with a 1C rate, while the pristine cathode only delivered 149.7 mAh g^-1 with 80.7% cycling retention left. The results strongly suggested that such PEDOT:PSS-coated and Ga³⁺-doped Mn-based layered structure materials demonstrated high potential as a cathode candidate especially for high-energy applications.

Conductive polymer polyaniline covering promotes the electrochemical properties of a nickel-rich quaternary cathode LiNi0.88Co0.06Mn0.03Al0.03O2

Conductive polymer PANI coated Ni-rich quaternary cathode LiNi0.88Co0.06Mn0.03Al0.03O2 demonstrates superior cycling performance owing to the stable surface protective layer.

Effective and Low-Cost In Situ Surface Engineering Strategy to Enhance the Interface Stability of an Ultrahigh Ni-Rich NCMA Cathode

Ultrahigh Ni-rich quaternary layered oxides LiNi_1-x-y-zCo_xMn_yAl_zO₂ (1 - x - y - z ≥ 0.9) are regarded as some of the most promising cathode candidates for lithium-ion batteries (LIBs) because of their high energy density and low cost. However, poor rate capacity and cycling performance severely limit their further commercial applications. Herein, an in situ coating strategy is developed to construct a uniform LiAlO₂ layer. The NH₄HCO₃ solution is added to a NaAlO₂ solution to form a weak alkaline condition, which can reduce the hydrolysis rate of NaAlO₂, thus enabling uniform deposition of Al(OH)₃ on the surface of a Ni_0.9Co_0.07Mn_0.01Al_0.02(OH)₂ (NCMA) precursor. The LiAlO₂-coated samples show enhanced cycling stability and rate capacity. The capacity retention of NCMA increases from 70.7% to 88.3% after 100 cycles at 1 C with an optimized LiAlO₂ coating amount of 3 wt %. Moreover, the 3 wt % LiAlO₂-coated sample also delivers a better rate capacity of 162 mAh g^-1 at 5 C, while that of an uncoated sample is only 144 mAh g^-1. Such a large improvement of the electrochemical performance should be attributed to the fact that a uniform LiAlO₂ coating relieves harmful interfacial parasitic reactions and stabilizes the interface structure. Therefore, this in situ coating approach is a viable idea for the design of higher-energy-density cathode materials.

Dual-Modified Compact Layer and Superficial Ti Doping for Reinforced Structural Integrity and Thermal Stability of Ni-Rich Cathodes

Nickel-rich layered oxides have been regarded as a potential cathode material for high-energy-density lithium-ion batteries because of the high specific capacity and low cost. However, the rapid capacity fading due to interfacial side reactions and bulk structural degradation seriously encumbers its commercialization. Herein, a highly stable hybrid surface architecture, which integrates an outer coating layer of TiO₂&Li₂TiO₃ and a surficial titanium doping by incorporated Ti₂O₃, is carefully designed to enhance the structural stability and eliminate lithium impurity. Meanwhile, the surficial titanium doping induces a nanoscale cation-mixing layer, which suppresses transition-metal-ion migration and ameliorates the reversibility of the H2 → H3 phase transition. Also, the Li₂TiO₃ coating layer with three-dimensional channels promotes ion transportation. Moreover, the electrochemically stable TiO₂ coating layer restrains side reactions and reinforces interfacial stability. With the collaboration of titanium doping and TiO₂&Li₂TiO₃ hybrid coating, the sample with 1 mol % modified achieves a capacity retention of 93.02% after 100 cycles with a voltage decay of only 0.03 V and up to 84.62% at a high voltage of 3.0-4.5 V. Furthermore, the ordered occupation of Ni ions in the Li layer boosts the thermal stability by procrastinating the layered-to-rock salt phase transition. This work provides a straightforward and economical modification strategy for boosting the structural and thermal stability of nickel-rich cathode materials.