Boosting the cycling stability of Ni-rich layered oxide cathode by dry coating of ultrastable Li3V2(PO4)3 nanoparticles

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.

Atomic-Scale Characterization of Microscale Battery Particles Enabled by a High-Throughput Focused Ion Beam Milling Technique

The cathode materials in lithium-ion batteries (LIBs) require improvements to address issues such as surface degradation, short-circuiting, and the formation of dendrites. One such method for addressing these issues is using surface coatings. Coatings can be sought to improve the durability of cathode materials, but the characterization of the uniformity and stability of the coating is important to assess the performance and lifetime of these materials. For microscale particles, there are, however, challenges associated with characterizing their surface modifications by transmission electron microscopy (TEM) techniques due to the size of these particles. Often, techniques such as focused ion beam (FIB)-assisted lift-out can be used to prepare thin cross sections to enable TEM analysis, but these techniques are very time-consuming and have a relatively low throughput. The work outlined herein demonstrates a FIB technique with direct support of microscale cathode materials on a TEM grid that increases sample throughput and reduces the processing time by 60-80% (i.e., from >5 to ∼1.5 h). The demonstrated workflow incorporates an air-liquid particle assembly followed by direct particle transfer to a TEM grid, FIB milling, and subsequent TEM analysis, which was illustrated with lithium nickel cobalt aluminum oxide particles and lithium manganese nickel oxide particles. These TEM analyses included mapping the elemental composition of cross sections of the microscale particles using energy-dispersive X-ray spectroscopy. The methods developed in this study can be extended to high-throughput characterization of additional LIB cathode materials (e.g., new compositions, coating, end-of-life studies), as well as to other microparticles and their coatings as prepared for a variety of applications.

LiNbO3 Coating and F- Doping Stabilize the Crystal Structure and Ameliorate the Interface of LiNi0.88Co0.06Mn0.03Al0.03O2 to Improve the Electrochemical Properties and Safety Capability

Ni-rich layered materials Li[NixCoyMnzAl1-x-y-z]O2 (x > 0.8) are regarded as the competitive cathode for practical applications in lithium-ion batteries owing to the large discharging capacity. Nevertheless, the strong oxidation activity, the poor structure, and the thermal stability at the electrode-electrolyte interface would lead to much trouble, for example, inferior electrochemical properties and acute safety issues. To ameliorate the above problems, this work reports a strategy for the double modification of F- doping and LiNbO3 covering in LiNi0.88Co0.06Mn0.03Al0.03O2 cathode via using high-temperature calcining and ball-milling technology. As a result, the cathodes after F- doping and LiNbO3 covering not only demonstrate a more stabilized crystal structure and particle interface but also reduce the release of high-activity oxygen species to ameliorate the thermal runaway. The electrochemical tests show that the LiNbO3-F--modified cathode displays a superior rate capability of 159.3 mAh g-1 at 10.0 C and has the predominant capability retention of 92.1% in the 200th cycle at 25 °C, much superior than those (125.4 mAh g-1 and 84.0%) of bare cathode. Thus, the F- doped and LiNbO3-coated Ni-rich oxides could be a promising cathode to realize the high capacity and a stabilized interface.

Advancements and Challenges in High-Capacity Ni-Rich Cathode Materials for Lithium-Ion Batteries

Nowadays, lithium-ion batteries are undoubtedly known as the most promising rechargeable batteries. However, these batteries face some big challenges, like not having enough energy and not lasting long enough, that should be addressed. Ternary Ni-rich Li[NixCoyMnz]O2 and Li[NixCoyAlz]O2 cathode materials stand as the ideal candidate for a cathode active material to achieve high capacity and energy density, low manufacturing cost, and high operating voltage. However, capacity gain from Ni enrichment is nullified by the concurrent fast capacity fading because of issues such as gas evolution, microcracks propagation and pulverization, phase transition, electrolyte decomposition, cation mixing, and dissolution of transition metals at high operating voltage, which hinders their commercialization. In order to tackle these problems, researchers conducted many strategies, including elemental doping, surface coating, and particle engineering. This review paper mainly talks about origins of problems and their mechanisms leading to electrochemical performance deterioration for Ni-rich cathode materials and modification approaches to address the problems.

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.

Mitigation of Oxygen Evolution and Phase Transition of Li-Rich Mn-Based Layered Oxide Cathodes by Coating with Oxygen-Deficient Perovskite Compounds

Li-rich Mn-based layered oxide cathodes with a high discharge capacity hold great promise for high energy density lithium-ion batteries. However, application is hampered by voltage and capacity decay and gas evolution during cycling due to interfacial side reactions. Here, we report coating by oxygen-deficient perovskite La0.9Sr0.1CoO3 using the Pechini process. X-ray photoelectron spectroscopy and scanning transmission electron microscopy both exhibit a uniform coating layer with a high oxygen vacancy concentration. The coating effectively mitigates the first cycle irreversible capacity loss and voltage decay while increasing cyclability. Optimized coating improves capacity retention from 55.6% to 84.8% after 400 cycles at 2 C. Operando differential electrochemical mass spectroscopy shows that such a coating can significantly mitigate the release of oxygen and carbon dioxide. Electrochemical impedance spectroscopy and post-mortem analysis indicate that the coating layer forms a stable interface and restricts structure evolution and cation mixing during cycling, conferring these cathode materials with better cycling and voltage stability. The perovskite can be applied to other cathodes with high voltage and capacity to suppress interfacial side reactions toward developing stable high energy density batteries.

Interfacial processes in electrochemical energy systems

Electrochemical energy systems such as batteries, water electrolyzers, and fuel cells are considered as promising and sustainable energy storage and conversion devices due to their high energy densities and zero or negative carbon dioxide emission. However, their widespread applications are hindered by many technical challenges, such as the low efficiency and poor long-term cyclability, which are mostly affected by the changes at the reactant/electrode/electrolyte interfaces. These interfacial processes involve ion/electron transfer, molecular/ion adsorption/desorption, and complex interface restructuring, which lead to irreversible modifications to the electrodes and the electrolyte. The understanding of these interfacial processes is thus crucial to provide strategies for solving those problems. In this review, we will discuss different interfacial processes at three representative interfaces, namely, solid-gas, solid-liquid, and solid-solid, in various electrochemical energy systems, and how they could influence the performance of electrochemical systems.