Formation of Surface Impurities on Lithium-Nickel-Manganese-Cobalt Oxides in the Presence of CO2 and H2O

Air Storage Impact on Surface Evolution of Stoichiometric and Li-Rich NMC811

In recent years, a type of layered oxide, LiNi x Mn y Co z O2 (NMC) where x+y+z = 1, has become the preferred cathode material for electric vehicle (EV) batteries. Despite some disorder in the crystal structure due to Li+/Ni2+ cation mixing, the composition offers a high specific capacity of up to 200 mAh g-1 at 4.3 V vs Li|Li+. The objective of this study is to comprehensively evaluate the structural and electrochemical changes in NMC811 after storage in ambient conditions. In this report, we study stoichiometric and Li-rich NMC811 in terms of their structural, morphological, and electrochemical differences. Following literature reports, a rigorous aqueous washing procedure was used alternatively to remove a possible lithium excess from the NMC surface. The findings of this study hold immense significance as they focus on the potential challenges that may arise due to the remaining lithium content or Li+ extraction from the near-surface NMC811 materials. There is no consensus in the literature on whether excess lithium can harm the material's structural and electrochemical properties, reduce performance and safety concerns, or be beneficial regarding its protective properties, for Ni-rich NMC. Proper treatment of as-synthesized Ni-rich NMCs helps to develop procedures to address the residual lithium compounds issues, leading to enhanced performance and safety. Here with this report, we show another aspect not being considered in the literature before, regarding morphological NMC811 reshaping and a mechanism of LRC transition and growth due to aging. In addition, we linked the selected structural parameters to the electrochemical performance of various NMC811 materials. We discuss the well-known structural factors and their limitations and introduce a doublet resolution criterion that can help in predicting electrochemical performance.

Revealing the impact of CO2 exposure during calcination on the physicochemical and electrochemical properties of LiNi0.8Co0.1Mn0.1O2

The synthesis atmosphere plays a fundamental role in determining the physicochemical properties and electrochemical performance of NMC811 cathode materials used in lithium-ion batteries. This study investigates the effect of carbonate impurities generated during synthesis by comparing three distinct samples: NMC811 calcined in ambient air, NMC811 calcined in synthetic air to mitigate carbonate formation, and NMC811 initially calcined in ambient air followed by annealing in synthetic air to eliminate carbonate species. Physicochemical characterization through XRD, SEM, FTIR, and TGA techniques revealed noticeable differences in the structural and chemical properties among the samples. Electrochemical assessments conducted via coin-cell testing demonstrate superior performance for materials synthesized in synthetic air, exhibiting an enhanced discharge capacity of 145.4 ± 4.8 mA h g-1 compared to materials synthesized in normal air (109.4 ± 4.3 mA h g-1) at C/10. More importantly, sample annealing in synthetic air after air calcination partially recovers the electrochemical performance of the cathode (142.1 ± 4.6 mA h g-1 at C/10) and this is related to the elimination of carbonate species from the ceramic powder. These findings highlight the importance of controlling synthesis conditions, particularly the atmosphere, to tailor the properties of NMC811 cathode materials for optimal lithium-ion battery performance.

Interface Stability and Reaction Mechanisms of Li3YCl5Br with High-Voltage Cathodes and Li Metal Anode: Insights from Ab Initio Simulations

Recent advancements in battery technology emphasize the critical role of solid electrolytes in enhancing the performance and safety of next-generation batteries. In this study, we investigate the interface stability and reaction mechanisms of Li3YCl5Br, a promising halide-based solid electrolyte, in contact with high-voltage Ni-Mn-Co (NMC) cathodes and a Li metal anode using ab initio molecular dynamics simulations. Our findings reveal that Li3YCl5Br reacts with charged NMC cathodes. This reaction involves changes in the oxidation states of Br- anions in Li3YCl5Br and d-element cations in NMC, as well as the diffusion of Li ions from the solid electrolyte to the cathode to maintain charge balance. The reaction is confined to the interface, suggesting bulk stability. Conversely, the Li/Li3YCl5Br interface exhibits significant instability, with a chemical reaction that results in substantial structural changes and the formation of LiCl and LiBr at the solid electrolyte surface and metallic Y at the Li anode surface. These insights provide valuable information for optimizing interfacial design, aiming at improving the performance and reliability of all-solid-state batteries using halide solid electrolytes.

Multifunctional Scavenger Boosts Cathode Interfacial Stability with Reduced Water Footprint for Direct Recycling of Spent Lithium-Ion Batteries

The burgeoning accumulation of spent lithium-ion batteries (LIBs), a byproduct from the widespread adoption of portable electronics and electric vehicles, necessitates efficient recycling strategies. Direct recycling represents a promising strategy to maximize the value of LIB waste and minimize harmful environmental outcomes. However, current efforts to large-scale direct recycling face challenges stemming from heterophase residues (e.g., Li2CO3, LiOH) in the recycled products and uncontrolled interfacial instability, often requiring repeated washing that generates significant wastewater. Here, a refined direct recycling process is proposed to improve cathode interface stability by leveraging in situ reaction between surface residual lithium species and a weak inorganic acid to form a conformal Li+ conductive coating that stabilizes the regenerated Ni-rich cathodes with significantly reduced water footprint. The findings reveal that the conductive coating also prevents direct contact between contaminants and the cathode surface, thus improving the ambient storage stability. By eliminating the need for extensive washing, this intensified recycling process offers a more sustainable approach with the potential to transition from laboratory to industrial-scale applications, improving both product quality and environmental sustainability.

Decoupling the air sensitivity of Na-layered oxides

Air sensitivity remains a substantial barrier to the commercialization of sodium (Na)-layered oxides (NLOs). This problem has puzzled the community for decades because of the complexity of interactions between air components and their impact on both bulk and surfaces of NLOs. We show here that water vapor plays a pivotal role in initiating destructive acid and oxidative degradations of NLOs only when coupled with carbon dioxide or oxygen, respectively. Quantification analysis revealed that reducing the defined cation competition coefficient (η), which integrates the effects of ionic potential and sodium content, and increasing the particle size can enhance the resistance to acid attack, whereas using high-potential redox couples can eliminate oxidative degradation. These findings elucidate the underlying air deterioration mechanisms and rationalize the design of air-stable NLOs.

Origins of High Air Sensitivity and Treatment Strategies in O3-Type NaMn1/3 Fe1/3Ni1/3O2

Sodium-ion layered oxides are one of the most highly regarded sodium-ion cathode materials and are expected to be used in electric vehicles and large-scale grid-level energy storage systems. However, highly air-sensitive issues limit sodium-ion layered oxide cathode materials to maximize cost advantages. Industrial and scientific researchers have been developing cost-effective air sensitivity treatment strategies with little success because the impurity formation mechanism is still unclear. Using density functional theory calculations and ab initio molecular dynamics simulations, this work shows that the poor air stability of O3-type NaMn1/3Fe1/3Ni1/3O2 (NMFNO) may be as follows: (1) low percentage of nonreactive (003) surface; (2) strong surface adsorption capacity and high surface reactivity; and (3) instability of the surface sodium ions. Our physical images point out that the high reactivity of the NMFNO surface originates from the increase in electron loss and unpaired electrons (magnetic moments) of the surface oxygen active site as well as the enhanced metal coactivation effect due to the large radius of the sodium ion. We also found that the hydrolysis reaction requires a higher reactivity of the surface oxygen active site, while the carbon hybridization mode transformation in carbonate formation depends mainly on metal activation and does not even require the involvement of surface oxygen active sites. Based on the calculation results and our proposed physical images, we discuss the feasibility of these treatment strategies (including surface morphology modulation, cation/anion substitution, and surface configuration design) for air-sensitive issues.

Microstructures of layered Ni-rich cathodes for lithium-ion batteries

Millions of electric vehicles (EVs) on the road are powered by lithium-ion batteries (LIBs) based on nickel-rich layered oxide (NRLO) cathodes, and they suffer from a limited driving range and safety concerns. Increasing the Ni content is a key way to boost the energy densities of LIBs and alleviate the EV range anxiety, which are, however, compromised by the rapid performance fading. One unique challenge lies in the worsening of the microstructural stability with a rising Ni-content in the cathode. In this review, we focus on the latest advances in the understanding of NLRO microstructures, particularly the microstructural degradation mechanisms, state-of-the-art stabilization strategies, and advanced characterization methods. We first elaborate on the fundamental mechanisms underlying the microstructural failures of NRLOs, including anisotropic lattice evolution, microcracking, and surface degradation, as a result of which other degradation processes, such as electrolyte decomposition and transition metal dissolution, can be severely aggravated. Afterwards, we discuss representative stabilization strategies, including the surface treatment and construction of radial concentration gradients in polycrystalline secondary particles, the fabrication of rod-shaped primary particles, and the development of single-crystal NRLO cathodes. We then introduce emerging microstructural characterization techniques, especially for identification of the particle orientation, dynamic changes, and elemental distributions in NRLO microstructures. Finally, we provide perspectives on the remaining challenges and opportunities for the development of stable NRLO cathodes for the zero-carbon future.

Quasi-dynamic study of electrochemical properties of O3-high-Ni ternary single-crystal cathode materials with mirror symmetry: a first-principles study

A total of 16 O3-type high-Ni ternary crystal structures with mirror symmetry were constructed based on the relative locations of Ni, Co, and Mn in order to design high operating voltage and high-capacity cathode materials for lithium-ion batteries. Transition states, powder X-ray diffraction (XRD) patterns, intercalation potentials, and (spin) electronic structures are computed and simulated based on first-principles calculations. The results show that the Li ion diffusion energy barrier, in the structure of the lowest energy counterpart a'aa', is only 0.9 eV. When charged to 75% state of charge (SOC), the Li layer spacing reaches a maximum under electrostatic attraction and Coulomb repulsion forces. The operating voltage and theoretical capacity are up to 4.79 V and 275 mA h g-1, respectively. High-spin Ni2+ participates in the reduction reaction as the main substance and is eventually oxidized to low-spin Ni4+. Intermediate-spin Co3+ also participates in the reduction reaction and is oxidized to low-spin Co4+, with charge compensation provided by O atoms. Mn does not participate in the redox reaction. This study is expected to enrich the library of high-nickel ternary cathode materials and provides a certain reference for the design of (ultra)high-nickel ternary cathode materials with excellent electrochemical properties.

Scalable Advanced Li(Ni0.8Co0.1Mn0.1)O2 Cathode Materials from a Slug Flow Continuous Process

Li[Ni_0.8Co_0.1Mn_0.1]O₂ (LNCMO811) is the most studied cathode material for next-generation lithium-ion batteries with high energy density. However, available synthesis methods are time-consuming and complex, restricting their mass production. A scalable manufacturing process for producing NCM811 hydroxide precursors is vital for commercialization of the material. In this work, a three-phase slug flow reactor, which has been demonstrated for its ease of scale-up, better synthetic control, and excellent uniform mixing, was developed to control the initial stage of the coprecipitation of NCM811 hydroxide. Furthermore, an equilibrium model was established to predict the yield and composition of the final product. The homogeneous slurry from the slug flow system was obtained and then transferred into a ripening vessel for the necessary ripening process. Finally, the lithium-nickel-cobalt-manganese oxide was obtained through the calcination of the slug flow-derived precursor with lithium hydroxide, having a tap density of 1.3 g cm^-3 with a well-layered structure. As-synthesized LNCMO811 shows a high specific capacity of 169.5 mAh g^-1 at a current rate of 0.1C and a long cycling stability of 1000 cycling with good capacity retention. This demonstration provides a pathway toward scaling up the cathode synthesis process for large-scale battery applications.