Stepwise Dopant Selection Process for High‐Nickel Layered Oxide Cathodes

Surface Stabilization of O3-type Layered Oxide Cathode to Protect the Anode of Sodium Ion Batteries for Superior Lifespan.

LiNi0.8Co0.1Mn0.1O2 (NCM811), a high‐nickel layered oxide, has emerged as a frontrunner for next‐generation lithium‐ion batteries (LIBs) due to its high energy density, excellent rate performance, and cost‐effectiveness. However, NCM811 cathodes face multifaceted challenges, including cation mixing, microcracking, and residual lithium compounds, necessitating a comprehensive understanding for addressing these critical issues. In this review, we provide an in‐depth analysis of recent advancements, presenting actionable insights into effective strategies to address the key issues in the NCM811 cathode and proposing pathways for optimizing NCM811 cathodes in LIB applications. Additionally, the forward‐looking perspectives are explored in this review, highlighting the role of advanced material characterization techniques, theoretical modeling, and computational simulations in overcoming the inherent limitations of NCM811 cathodes. By synthesizing current knowledge and technological advancements, this review aims to serve as a foundational resource for researchers and industry professionals striving to enhance the performance and accelerate the commercialization of NCM811 cathode materials, contributing to the future of energy storage solutions.

Lithium-ion battery is considered to be one of the most promising energy storage systems that are able to satisfy the requirements of power battery, but the current energy density, power density and safety performance for lithium-ion batteries can't meet the needs of the development of electric vehicles. As the only lithium ions supplier, the cathode materials for lithium-ion batteries greatly limit the performance of lithium-ion battery.Therefore, the development of cathode materials with a higher energy density, higher power density and better safety performance is highly desired. Owing to high theoretical capacity, low cost, and low toxicity, ternary layered transition metal oxide cathode materials are considered to be the most promising cathode materials for the next-generation lithium-ion batteries. And in order to fully release the capacities of ternary layered transition metal oxide cathode materials high voltage is necessary, but the cycle stability is not good enough when ternary layered transition metal oxide cathode materials are set with a high voltage range. What’s more, the poor storage performance is another factor that restricts the wide application in electric vehicles. This review describes several common cathode materials, highlighting the advantages and disadvantages of ternary layered transition metal oxide cathode materials and modification progress.

Herein, a new P2‐type layered oxide is proposed as an outstanding intercalation cathode material for high energy density sodium‐ion batteries (SIBs). On the basis of the stoichiometry of sodium and transition metals, the P2‐type Na0.55[Ni0.1Fe0.1Mn0.8]O2 cathode is synthesized without impurities phase by partially substituting Ni and Fe into the Mn sites. The partial substitution results in a smoothing of the electrochemical charge/discharge profiles and thus greatly improves the battery performance. The P2‐type Na0.55[Ni0.1Fe0.1Mn0.8]O2 cathode delivers an extremely high discharge capacity of 221.5 mAh g−1 with a high average potential of ≈2.9 V (vs Na/Na+) for SIBs. In addition, the fast Na‐ion transport in the P2‐type Na0.55[Ni0.1Fe0.1Mn0.8]O2 cathode structure enables good power capability with an extremely high current density of 2400 mA g−1 (full charge/discharge in 12 min) and long‐term cycling stability with ≈80% capacity retention after 500 cycles at 600 mA g−1. A combination of electrochemical profiles, in operando synchrotron X‐ray diffraction analysis, and first‐principles calculations are used to understand the overall Na storage mechanism of P2‐type Na0.55[Ni0.1Fe0.1Mn0.8]O2.

Layered oxide materials are widely used in the field of energy storage and conversion due to their high specific energy, high efficiency, long cycle life, and high safety. Herein, We summarize the latest research progress in the field of layered metal oxide cathode materials from three aspects: challenges faced, failure mechanisms, and modification methods. We also compare the characteristics of lithium‐based layered oxides and sodium‐based layered oxides, and predict future development directions. The layered oxide cathode materials for sodium‐ion batteries and lithium‐ion batteries exhibit overall structural and operational similarities. There are also some differences, such as lattice parameters and application extent. Sodium‐ion battery cathode materials need to explore new materials and address structural instability issues, while lithium‐ion batteries require finding alternative materials and improving production efficiency. Future challenges for both types of materials include enhancing capacity and cycle performance, elucidating deep mechanisms, reducing costs, and improving resource sustainability. Future development should focus on balancing cycle stability and charge cut‐off voltage to meet the growing demand for battery applications.

Sodium-ion batteries (SIBs) are regarded as competitive candidates for the next generation of electrochemical energy storage (EES) systems due to their low cost and abundant sodium resources. Layered oxide cathodes have attracted much interest owing to their simple preparation process, high specific capacity and environmental friendliness. However, undesired cation migration during electrochemical reactions can lead to irreversible phase transitions and structural degradation of layered oxide cathode materials, resulting in a sharp decrease in specific capacity and energy density. Therefore, in order to find effective strategies to suppress cation migration, the fundamental failure mechanism of layered oxides and the practical approaches to solve this key scientific issue are thoroughly investigated, and herein the history and current status of developments in this field are also reviewed. Elemental doping and structural design can directionally modify the electronic structure, energy band structure and electronic density of states in layered oxides and enhance cation migration barriers, which benefits the improvement of electrochemical performance and structural stability during the whole sodiation/desodiation process. The summary and prospects of inhibiting cation migration in layered oxides provide insights into the development of advanced cathode materials with high energy density and excellent structural stability for the commercialization of SIBs.

Towards rational design of high performance Ni-rich layered oxide cathodes: The interplay of borate-doping and excess lithium

The limited theoretical capacity of traditional cathode materials solely based on transition metal (TM) redox has been a primary factor for the ceiling placed on the energy density of LIBs. In this regard, Li-rich layered oxides (LLOs) have received a great deal of attention, due to their high reversible capacity (> 250 mAh g-1) and high energy density (900 Wh kg-1), courtesy of the TM redox and the additional high-voltage O2- redox.1, 2 Although the electrochemical performance of Co-free LLOs is significantly less satisfactory, developing Co-free cathodes is inevitably a holy grail owing to cobalt’s economic, ethical, and political issues caused by high-cost toxicity. Therefore, studies on Co-free LLOs are necessary for creating long-term benefits for the cathode industry.Unfortunately, Co-free LLOs suffer from capacity and voltage decay on cycling, which for now obviously limits the materials use outside the academics laboratory. It is well accepted that that performance decay is primarily attributed to the irreversible anionic redox and structural degradation in LLOs. The doping strategy has been widely used to address the voltage decay of LLOs.3 While the dopant is typically introduced to the layered R m component, the lithium-rich component (C2/c) in the LLOs, which is the source of anionic redox, has always been ignored.Our team comprehensively investigates the structural involution of LLOs based on a Co-free Li-rich Mn-based Li1.2Ni0.2Mn0.6O2 (LNMO) cathode using in-operando and ex-situ synchrotron-based characterizations. We learned through mechanistic characterization that the transition from the monoclinic (C2/c) to the hexagonal (R-3m) behaviour is an intrinsic behaviour of LLOs for the first time. According to this structure-function relationship, we introduced a small quantity of one electrochemically active metal, ruthenium, into both R-3m and C2/c components in LNMO and found that the oxygen lattice and structural stability can be significantly improved by the site-specific doping against lithiation and delithiation processes.4 Additionally, reducing the irreversible TM migration is key to advancing the performance of layered oxide cathode materials. Contrary to many previous studies that emphasize suppressing cation migration, our team proposed that reversible tetrahedral-octahedral TM migration helps inhibit the formation of undesirable structural changes and phase transformation. The oxidation state of TM, such as Ni, Mn, and Co, are easily trapped into the octahedral sites in the Li layer due to their high octahedral-site splitting energy when a large amount of Li has extracted from the structure. By introducing Cr into LNMO, we found that Cr can migrate reversibly between the tetrahedral and octahedral sites, which makes Cr-doped LNMO possess significantly enhanced structural stability and thus achieve higher electrochemical performance than LNMO.In all, our research focuses on the site-specific doping of the Co-free LLOs and understanding the structure- and chemistry-function relationship of the LLOs. The findings in our work might provide possible pathways for the future design of high-performance cathode materials for lithium-ion batteries and may also apply to developing cathode materials for other energy storage systems.Reference S. Hu, A. S. Pillai, G. Liang, W. K. Pang, H. Wang, Q. Li and Z. Guo, Electrochem. Energy Rev., 2019, 2, 277-311.M. Han, J. Jiao, Z. Liu, X. Shen, Q. Zhang, H.-J. Lin, C.-T. Chen, Q. Kong, W. K. Pang, Z. Guo, R. Yu, L. Gu, Z. Hu, Z. Wang and L. Chen, Adv. Energy Mater., 2020, 10, 1903634.Y. Fan, W. Zhang, Y. Zhao, Z. Guo and Q. Cai, Energy Stor. Mater., 2021, 40, 51-71.Y. Fan, E. Olsson, G. Liang, Z. Wang, A. M. D'Angelo, B. Johannessen, L. Thomsen, B. Cowie, J. Li, F. Zhang, Y. Zhao, W. K. Pang, Q. Cai and Z. Guo, Angew. Chem. Int. Ed., 2022, DOI: 10.1002/anie.202213806.

The rapid capacity degradation and poor rate capability hinder the application of Rich-Ni layered LiNix Coy Mnz O2 (NCM) as cathode materials for high-energy lithium-ion batteries. In this study, density functional theory (DFT) calculations, combined with conventional electrochemical measurements, reveal from the atomic view that the dual improvements in electronic and ionic conductivities are the main facts for the property enhancement. The bandgap of the cathode material is reduced to 1.1623eV due to the increased number of electrons near the Fermi level after W intercalation. Such improved electronic conductivity subsequently leads to a suppressed polarization and reduced resistance, enabling an improved cycle life of up to 93.97% after 100 cycles at 0.5 C. Furthermore, the doping with W6+ also introduced a strong WO bond into the layered structure so that the thickness of the Li slab is expanded to 2.6476 Å, which reduces the energy barrier from 0.355 to 0.308eV for the migration of Li+ within the Li slab, as confirmed by the DFT calculation. Consequently, the rate performance is greatly improved due to the reduced diffusion energy, with a specific capacity of 159.11 mAg-1 even at 5 C rate, indicating high potential for future applications.

The electrochemical property and crystal structure of Li1+xNi0.45Co0.1Mn0.45O2 (0.05≤x≤0.4) cathode materials under 4.6V cut-off

Lithium-ion cells that employ nickel-rich NMC materials are prevalent because of their high capacity and ability to function at significantly elevated potentials vs Li+/Li. Nonetheless, these cells encounter issues such as a decline in capacity or thermal resistance, and various researchers are currently exploring the underlying causes of these phenomena. Zhang1 has compiled these findings, pointing out the most significant ones: cation mixing, present of residual lithium compounds, oxygen evolution and phase transition to rocksalt. Understanding the phenomena occurring during lithiation and delithiation of NMC can help in selecting the appropriate method to improve its properties. To understand this, scientists use various methods. Through a scanning electron microscopy (SEM), Cheng et al.2 observed grain cracking in the electrode material intensifying with successive cycles. They compared the NMC811 after 14 cycles for a cutoff potential of 4.1 vs. Li+/Li and 4.7 vs. Li+/Li. G anty et al.3 used in situ XRD studies to monitor changes in NMC811 during charge and discharge cycling, with particular emphasis on changes in the a and c unit cell parameters and the appearance of the H2 hexagonal phase during charging (significantly reduced lithium content in the structure). Also, Raman spectroscopy can be used to make comparisons of the changes occurring in the active material during its lithiation and delithiation. Flores et al.4 study layered active materials using Raman spectroscopy and was able to see significant changes in the structure, such as showing that the oxidation of Ni2+/Ni3+ ↔ Ni3+/Ni4+ is gradual.However, in situ techniques have limitations in combining various methods to test the same sample. To facilitate the use of several techniques, ex situ testing can be employed. In this research, nickel-rich NMC samples were analyzed using a combination of ex situ XRD, SEM, and Raman spectroscopy. This approach provides more information on the phenomena occurring during cell operation, allowing for better understanding of the problems that need to be addressed. SEM images can identify the presence of structural irregularities that can affect the material's electrochemical performance, including defects and cracks. XRD provides overall information on phases present in the bulk sample, their grain size, and crystallographic parameters, and allows for thorough Raman analysis. Ex situ Raman spectroscopy enables experiments to be carried out at a specific location, increases the reliability of tests, and provides detailed information on phase transitions and the causes of capacity drop during the cell operation. Together, these techniques provide valuable insights into the structural changes that occur in NMC622 material during lithiation and delithiation processes. By analyzing the crystal structure, and surface morphology of the cathode material before and after cycling, these techniques can help identify the mechanisms of degradation and suggest strategies for improving battery performance and lifespan. A detailed analysis will be presented during the conference. This work was funded by the National Center for Science in Poland through the Sonata BIS 11 programme (No. UMO-2021/42/E/ST5/00390).Reference: Zhang, S. S. Problems and their origins of Ni-rich layered oxide cathode materials. Energy Storage Mater 24, 247–254 (2020). Cheng, X. et al. Real-Time Observation of Chemomechanical Breakdown in a Layered Nickel-Rich Oxide Cathode Realized by in situ Scanning Electron Microscopy. ACS Energy Lett 6, (2021). Ghanty, C. et al. Li+-Ion Extraction/Insertion of Ni-Rich Li1+x(NiyCozMnz)wO2 (0.005<x<0.03; y: Z=8:1, w≈1) Electrodes: In situ XRD and Raman Spectroscopy Study. ChemElectroChem 2, (2015). Flores, E. et al. Cation Ordering and Redox Chemistry of Layered Ni-Rich Li xNi1-2 yCo yMn yO2: An Operando Raman Spectroscopy Study. Chemistry of Materials 32, (2020).

Despite its high energy density, high-voltage LiNi0.5Mn0.5O2 cathode which suffers from a poor cycle performance that originated from the cathode structural collapse is still far from commercialization. Doping heteroatom into the lattice of LiNi0.5Mn0.5O2 is believed to be a valid strategy in overcoming this bottleneck. Herein, Si was employed as a dopant to comprehensively improve the electrochemical performance of LiNi0.5Mn0.5O2. X-ray diffraction and Rietveld refinement revealed that doping Si into LiNi0.5Mn0.5O2 can optimize its structure, which reduced the degree of Li/Ni cation mixing. As a result, an enhanced interfacial reaction kinetics of Li-ion intercalation/de-intercalation could be achieved, rendering the doped LiNi0.5Mn0.5O2 a remarkably improved reversible capacity in comparison with its pristine. Moreover, it was found that Li0.99Si0.01Ni0.5Mn0.5O2 showed a significantly higher capacity than LiNi0.5Mn0.5O2 does at 25 °C. It is believed that this work affords an effective strategy for high-performance LiNi0.5Mn0.5O2 cathode.

Inhibiting phase conversion and improving cyclic stability of Ni-rich layered oxide by high-valence element concentration gradient doping

Direct ultraviolet-assisted conformal coating of nanometer-thick poly(tris(2-(acryloyloxy)ethyl) phosphate) gel polymer electrolytes on high-voltage LiNi1/3Co1/3Mn1/3O2 cathodes

High entropy induced lattice expansion in layered oxide cathode towards fast sodium storage