High-Capacity Oxide Cathode beyond 300 mAh/g

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

As the electric vehicles (EVs) market is growing rapidly, lithium ion batteries (LIBs) have received great attention as a suitable power source owing to its high-energy density and excellent power characteristic. To extend a driving mileage of the EVs, it is crucial to further improve the energy density of LIBs. Since the specific capacity and operating voltage of cathode materials are important factors for determining the energy density of LIBs, many researches focus on the development of advanced cathode materials with high specific capacity and high operating voltage. Among various cathode materials, layered cathode materials (e.g., LiMO2, M = transition metal) have been one of the most popular cathode materials in LIBs. The electrochemical properties of these cathode materials are tunable by the choice of transition metals in the host structure; i) Mn secures structural stability, ii) Co increases power characteristic, and iii) Ni contributes to a specific capacity of the materials. In order to increase the achievable specific capacity, researchers have designed the layered cathode materials with a high Ni content (>80%) and they offer a high reversible capacity more than 190 mA h g-1. Unfortunately, Ni-rich layered cathode materials suffer from poor thermal and structural stabilities arising from the high Ni content in the structure. To overcome these limitations, therefore, structural modifications on the Ni-rich cathode materials is highly required to suppress undesirable side reactions and formations of impurities (e.g., NiO). Herein, we prepare Mn surface-doped NCM811 (Mn-NCM811) with a core-shell structure via a simple wet-coating process using lithium ethoxide and Mn acetate precursors. Various structural and electrochemical investigations support that Mn-rich shell can effectively improve the structural and thermal stabilities of Ni-rich core, leading to the significant improvement in electrochemical performance of Ni-rich layered cathode materials even at a high operating temperature of 60 °C. From the results, we emphasize the importance of material design and this study will provide practical guidelines for development of Ni-rich layered cathode materials for LIBs.

Nickel-rich layered oxide cathodes are promising for next-generation lithium-ion batteries due to their high energy density and lower cost compared to the lithium cobalt oxide (LCO) cathode. However, their practical application is often limited by their thermal instability at high nickel content, which is associated with oxygen evolution and the risk of thermal runaway. In this study, discrete cerium oxide (CeO2) nanoparticles were coated on Li[Ni0.91Co0.05Mn0.03Al0.01]O2 (NCMA) cathodes via the coprecipitation method in water. CeO2 with the low redox potential of Ce3+/Ce4+ couple serves as an oxygen storage material on the surface of the NCMA cathode. The CeO2-coated NCMA (C-NCMA) shows 30% less total heat release and a higher onset temperature of cathode decomposition than uncoated NCMA (P-NCMA) due to 3.6% less oxygen release and robust barriers between the NCMA cathode surface and the electrolyte. Furthermore, long-term cycling stability at 25 °C and enhanced cycling performance at 45 °C with a low cutoff voltage (4.2 V) were observed for C-NCMA due to the suppression and delay of the H2–H3 phase transition peak, despite the kinetic hindrance from the relatively thick CeO2 nanoparticles. At a higher cutoff voltage (4.5 V) under severe cycling conditions, C-NCMA shows a capacity retention of 96.4% after 60 cycles compared to 84.4% for P-NCMA. To obtain both enhanced thermal stability and improved cycling performance, the cutoff voltage should be pushed to a higher value for these discrete CeO2 nanoparticle coating morphologies. This study presents an outlook on the rationale for applying discrete nanoparticle coatings to nickel-rich cathode materials for future battery development.

Current research in the field of lithium-ion batteries (LIBs) is geared towards stabilizing the electrode-electrolyte interfaces to improve the LIB cycling stability and storage capacity. In particular, irreversible reactions between non-aqueous electrolytes and metal oxide cathode surfaces can corrode the active material and reduce LIB performance. Protective coatings on the cathode surface can mitigate these issues, and atomic layer deposition (ALD) is well-suited to prepare ultrathin, conformal, corrosion-resistant barrier layers on the surface of the electrodes. While there are reports that some metal oxide and metal fluoride barrier coatings on select cathodes can improve LIB performance, there is no general understanding of why certain ALD coating/cathode combinations are beneficial while others are not. This problem is complicated by the move towards complex LIB cathodes such as lithium nickel manganese cobalt oxide (NMC) materials that may have multiple phases present on the surface including hydroxides and carbonates. Understanding how the ALD precursors react on these materials to create protective coatings is challenging and requires a systematic study to elucidate the surface chemistry of the ALD precursors with each component of the complex oxide surface. Therefore, this work aims at understanding the effects of ALD precursor exposures and ALD coatings on the surface electronic structure of LIB cathode materials.Al2O3 and AlF3 were selected as prototypical metal oxide and metal fluoride surface coatings as they are widely reported in literature due to their ability to act as barrier coatings on cathodes. Additionally, the ALD precursor vapors used for these coatings, i.e., trimethyl aluminium (TMA) and hydrogen fluoride pyridine (HFpy), were adsorbed on the surfaces of these cathode materials under typical ALD conditions to observe their effect on the surface composition and electronic state. The cathode materials chosen for this study included all of the component oxides for NMC cathodes (i.e. Li, Ni, Mn, and Co) in all common oxidation states (e.g., MnO, MnO2, and Mn2O3) as well as selected ternary, quaternary, and quinary forms. In each case, the substrate surface was characterized using X-ray photoelectron spectroscopy (XPS) before and after surface treatment to elucidate changes in the surface composition and charge state induced by the individual ALD precursors and the ultrathin coating. Overall, this fundamental study will assist in the design and synthesis of novel ALD barrier coatings that demonstrate the highest sensitivity on multi-element cathode materials, ultimately leading to robust electrode-electrolyte interfaces for high-performance LIBs.

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.

Synergetic ternary metal oxide nanodots-graphene cathode for high performance zinc energy storage

The development of advanced cathode materials is crucial for improving the energy density, stability, and rate performance of Na-ion batteries (NIBs). Two promising strategies—lithium doping stabilization and high-entropy engineering—have been explored to address key challenges such as phase instability, sluggish sodium diffusion, and capacity degradation. In this study, we compare and highlight the design principles and performance enhancements achieved through these approaches.In the first strategy, lithium doping was employed to stabilize the P2-structured layered oxide cathode, Na0.66(Li0.18Fe0.12Mn0.7)O2 [1]. A major limitation in P2-type cathodes is the irreversible and detrimental P2–O2 phase transition at high voltage, which leads to structural degradation and poor cyclability. By partially substituting manganese with lithium in the transition metal layer, the P2-O2 phase transition was effectively eliminated. This structural stabilization enabled high capacity retention of ~87% after 80 cycles with an initial capacity of 190 mAh g⁻¹ within a wide voltage range of 1.5–4.5 V. Operando synchrotron X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectroscopy confirmed the reversibility of lithium migration and the structural integrity of the cathode material over prolonged cycling.The second strategy involves high-entropy engineering in the Na0.6(Ti0.2Mn0.2Co0.2Ni0.2Ru0.2)O2 cathode, where equiatomic mixing of multiple transition metals (TMs) was leveraged to enhance entropy stabilization and Na-ion diffusion kinetics[2]. The uniform distribution of TMs disrupted Na/vacancy ordering, reducing phase transitions and promoting a solid solution-type sodium extraction mechanism. This multi-principal component (MPC) cathode exhibited remarkable rate capability, delivering a high discharge capacity of 164 mAh g⁻¹ at 0.1 C and retaining 68 mAh g⁻¹ at an ultra-high rate of 86 C. Computational modeling using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations demonstrated the existence of a percolating network of low-barrier diffusion pathways, facilitating rapid sodium transport.The two works underscore the importance of tailored cation substitution strategies in optimizing layered oxide cathodes for next-generation NIBs. By fine-tuning compositional design and leveraging advanced computational and in situ characterization techniques, it is possible to engineer materials that overcome current performance limitations. Most recent research focusing on integrating these approaches to develop cathodes that simultaneously offer high capacity, robust cyclability, and superior rate performance will also be discussed.[1] L.F. Yang, X. Li, J. Liu, S. Xiong, X.T. Ma, P. Liu, J.M. Bai, W.Q. Xu, Y.Z. Tang, Y.Y. Hu, M.L. Liu, H. Chen, Lithium-Doping Stabilized High-Performance P2-Na0.66Li0.18Fe0.12Mn0.7O2 Cathode for Sodium Ion Batteries, Journal of the American Chemical Society, 141 (2019) 6680-6689.[2] L.F. Yang, C. Chen, S. Xiong, C. Zheng, P. Liu, Y.F. Ma, W.Q. Xu, Y.Z. Tang, S.P. Ong, H.L. Chen, Multiprincipal Component P2-Na-0.6(Ti0.2Mn0.2Co0.2Ni0.2Ru0.2)O-2 as a High-Rate Cathode for Sodium-Ion Batteries, JACS Au, 1 (2021) 98-107.

Lithium ion batteries are widely used for portable electronics and are currently being incorporated into electric vehicles due to the high gravimetric and volumetric energy density. However, cost, safety, cycle and calendar life, energy, and power density are some of the major obstacles to the widespread use of lithium-ion batteries for vehicle applications. Among these problems, energy and power density are some of the most significant. To achieve higher energy and power density, many efforts have been addressed to improve the specific capacity and discharge voltage of the cathode materials. For example, cathode materials which could transport two Li ions such as Li2FeSiO4 and Li2FePO4F have been proposed and investigated as a high capacity cathode material, in which two electrons-exchange are involved upon charge-discharge process thus offering higher capacity, 323 and 292 mAh g-1, respectively. Another effective way to improve the energy density of lithium ion batteries is to expand the operating potential of the cathode material. Most commercial lithium ion batteries contain layered lithium transition metal oxide such as LiCoO2 or LiNi1/3Mn1/3Co1/3O2 which typically operates at approximately 4.1 V vs. Li/Li+. Cathode materials with an operating potential over 4.5 V (vs Li/Li+) have been developed, including LiMnPO4, LiNiPO4 and LiCoPO4, and LiNi0.5Mn1.5O4. Among these promising new cathodes, LiNi0.5Mn1.5O4 has attracted much attention in recent years because of the high intercalation/deintercalaition potential of 4.8 (vs. Li/Li+) and excellent rate performance. However, a major difficulty in using these high-voltage materials is the instability of the standard electrolyte, LiPF6, in organic carbonate solvents, in contact with the cathode surface at operating potentials over 4.5 V. Various methods have been proposed to inhibit the detrimental reactions on high voltage cathode materials. One of them is adopting inert surface coatings, such as Al2O3, ZnO, and Bi2O3 to prevent the oxidation of the electrolyte. Surface coated cathodes have cyclability superior to that of uncoated material; however, the surface coating method has a negative effect on the discharge capacity of the material and may be difficult to scale for commercial applications. Since the oxidative stability of current LiPF6/carbonate electrolyte is considered to be limited by the oxidative stability of the organic solvents, there has been significant interest in development of novel organic solvents with high anodic stability. Sulfone, lactone, organic nitriles, and fluorinated carbonates were reported to be stable over 5 V (vs. Li/Li+), but most of them have high viscosity or do not favor the formation of a protective solid electrolyte interface (SEI) on graphite anode. Alternatively, there have been several investigations of the incorporation of cathode film forming additives which are sacrificially oxidized on the cathode surface to generate a cathode passivation layer similar in nature to the anode SEI. Some additives have been investigated which improve the performance of Li/LiNi0.5Mn1.5O4 cells, including dimethyl methyl phosphonate and Lithium bis(oxalato)borate (LiBOB). Most recently, the extension research work of LiBOB on Graphite/LiNi0.5Mn1.5O4 full cells was also reported. The incorporation of LiBOB significantly improves the cycling performance of graphite/LiNi0.5Mn1.5O4 cells when cycled at elevated temperature (55 oC) and high voltage (4.8 V vs Li/Li+). However, huge gas generation was observed upon cycling at high voltage and elevated temperature, which is not acceptable in practical applications. Therefore, novel electrolyte system is still highly need to drive the applications of high voltage cathode materials in lithium ion batteries. Several types of novel additives are developing in our laboratory to meet the requirements of high voltage cathode materials upon cycling at over 4.5 V, vs. Li/Li+. Reference: [1] M. Xu, L. Zhou, Y. Dong, Y. Chen, A. Garsuch, B. L. Lucht. J. Electrochem. Soc ., 2013, 160: A2005. [2] S. Dalavi, M. Xu, B. Knight, B. L. Lucht, J. Power Sources, 2011, 196, 2251. [3] M. Xu, D. Lu, A. Garsuch, B. L. Lucht, J. Electrochem. Soc. , 2012, 159, A2130. [4] M. Xu, Y. Liu, W. Li, X. Li, S. Hu, Electrochem. Commun. , 2012, 18, 123. Acknowledgment This research work is supported by the National Natural Science Foundation of China (21373092, 21273084), the Joint Project of National Natural Science Foundation of China and Natural Science Foundation of Guangdong (No. U1134002).

Lithium-ion batteries (LIBs) using organic liquid electrolytes have been applied in portable devices such as laptops and cellular phones owing to its wide electrochemical stability, high voltages, and excellent energy density. LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode have attracted significant interest as the cathode materials for LIBs owing to their high capacity, excellent rate capability and low cost. NCM523 cathode materials have a disadvantage of structural instability, which caused by the reduction of Ni ions releases oxygen from the crystal structure at the high temeprature or high charged state, which can lead thermal runaway by reacting with the flammable electrolyte. The use of organic liquid electrolytes in LIBs raises safety issues due to its flammable character and the impact on the explosion is greater in particular for relatively large systems such as electrical vehicles and grid storage. To overcome the safety issues, solid state batteries (SSBs) using a non-combustible solid state Li-ion conductor are regarded as the realistic alternative to prohibit the leakage of liquid electrolytes and the resultant fire hazards. However, due to the large resistance in the electrode-electrolyte interface, the capacity retention and cycle effieciency of the SSBs become worse. Previous studies on SSBs have been mainly focused on developing solid state electrolytes with high ion conductivity. Despite growing interest in stability, the systematic studies of safety of SSBs depending on the type of electrolyte has never been evaluated so far. It is necessary for understanding structural deformations on the cathode material in the effects of the reactions beween the electrode and various types of electrolytes, which is essential for ensuring the safety of the batteries. In this study, we investigate the structural degradation and thermal stability on NCM523 cathode materials by taking an advantage of in situ transmission electron microscopy (TEM) in various electrolyte conditions, including conventional liquid electrolyte, poly(ethylene oxide) (PEO) complexes with LiClO4 (PEO-based solid electrolyte), and PEO/LiClO4/Li1.3Al0.3Ti1.7(PO4)3 (LATP) composite electrolyte (PEO-inorganic composite electrolyte). Since the LATP oxide electrolyte has brittleness and the PEO has flexibility, it adopts a composite electrolyte having inorganic and organic phases with good interface contact with the cell electrode. A cell composed of each electrolyte was prepared and charged with cut-off voltages of 3.9 V and 4.3 V at a rate of 0.05 C after the second formation process for stabilzing the cell. The capacity at the same cut-off voltage decreases in the order of conventional liquid electrolyte, PEO-based solid electrolyte, and PEO-inorganic composite electrolytes. To understand the thermal stability and the degradation mechanism, modifications in selected-area electron diffraction (SAED) and electron energy-loss (EEL) spectra of oxygen K-edge and transition metal (Ni, Co, Mn) L-edges of each of charged NCM523 cathode materials are monitored in real time at the range from room temperature to 300°C. Our work demonstrated that contact resistance at the interface between the electrode and electrolyte is important factor. This work provides important information on the relationship with structural deformation and thermal stability of the cathode materials, which is an essential part of the rational design to develope for high engergy densities and safe SSBs. All the details will be available at the meeting. Acknowledgement This work was supported by the Korea Institute of Science and Technology (KIST) Institutional Program (Project 2E28142). This work was also supported by the National Research Foundation of Korea (NRF) grant (No. 2018R1A2B2005205).

A novel low-cobalt single-crystal lithium-rich manganese-based layered oxide cathodes with enhanced electrochemical performances

Development of new cathode materials with even better performance and lower cost is needed to meet the ever-increasing global demand on lithium-ion batteries. As such, extensive efforts have been devoted to developing next-generation cathodes for high-energy Li-ion batteries, e.g., Li-rich transition metal oxides. As a counterpart to the conventional cation-ordered layered oxides, cation-disordered rocksalts (DRXs) have emerged as a new class of high-capacity cathode materials. One unique advantage of the DRX chemistry is the structural flexibility that substantially lessens the elemental constraints and enables the incorporation of a wide variety of TMs and fluorine anion at a decent amount in the crystal lattice. As a result, the dominant TMs have been extended from redox-active Ni and Co in layered cathodes to cost-effective and earth-abundant Mn and Fe as well as redox-inactive TM (e.g., Nb, Ti, Zr, Mo) to facilitate the DRX phase formation. This exceptional chemical diversity largely opens up the opportunity to tune the material compositions for optimal performance through the control of redox reactions.In this talk, I will present our recent work on several high-capacity cathodes based on Mn and Ni redox centers. We specifically focused on understanding the redox chemistry, including cationic and anionic redox, using combined electrochemical, soft X-ray absorption (XAS), and resonant inelastic X-ray spectroscopy (RIXS) techniques. This presentation summarizes the different TM and O redox behaviors and their roles in the electrochemical processes of these high-capacity cathodes. I will then show some examples on how this understanding leads to improved cathodes with enhanced performance by tailoring the redox reactions.

Recently, lithium ion batteries (LIBs) have received great attention as a suitable power source for electric vehicles (EVs) because of its highest energy and power densities among currently available energy storage systems. For successful implementation the achievable energy density of current LIBs should be further improved to meet the industrial requirements. In this respect, the development of advanced materials is crucial for improving the energy density of LIBs. During the last decade, layered lithium transition metal oxides (e.g., LiMO2, M = transition metal) have been used as the most popular cathode materials in commercial LIBs [1]. From a structural point of view, Li+ can be reversibly inserted and extracted in the given structure based on the redox reactions of transition metals. Therefore, the choice of transition metals is crucial for determining the electrochemical properties of these cathode materials. By increasing the Ni concentration, the reversible capacity of the cathode materials can be effectively increased due to the double redox reaction of Ni2+/Ni4+. In practice, high-Ni layered cathode materials (Ni > 80%) can offer a high reversible capacity over 200 mAh g-1 [2]. As a result of increasing the Ni concentration, however, the cathode materials suffer from poor cycle performance and thermal stability mainly induced by side reactions with electrolyte and residual Li at the surface. To overcome these limitations, effective surface coatings are required to make the surface more stable and suppress undesirable side reactions [3]. Herein, we propose a surface coating with LiNbO3 onto NCM811 cathode material to minimize undesirable side reactions as well as improve the thermal stability [4]. Thanks to the high ionic conductivity and thermal resistance of LiNbO3, LiNbO3 coated NCM811 exhibit much improved cycle performance and rate capabilities even at high operating temperature of 60 oC. Moreover, we also investigate the effect of LiNbO3 crystallinity on the electrochemical properties of LiNbO3 coated NCM811. It would provide a practical guideline for the development of a highly reliable high-capacity cathode material for EV applications.

Lithium (Li)-rich manganese (Mn)-rich oxides (LMR) have been considered as feasible cathode materials for high-energy lithium ion batteries because they possess high theoretical specific energy over 900 Wh kg−1. However, the undesirable cathode/electrolyte interfacial reaction due to the high working voltages, which results in electrolyte decomposition, transition-metal ion dissolution and surface corrosion, is considered one of the obstacles that significantly prevent their applications in electric vehicles for years.[1, 2] Although numerous efforts have been devoted to address the surface stability issues on LMR, most of them were limited to room temperature. The continuous upsurge in demand for electric vehicles requires lithium ion batteries to be operated under elevated temperatures. While, the state-of-the-art LiPF6-organocarbonate electrolytes are not compatible with LMR cathode due to the high operating voltage, which also get worse at elevated temperatures.[3] Here, an optimized localized high-concentration electrolyte (LHCEs) is studied in graphite (Gr)-based LMR full cells at 25, 45 and 60 °C. The cycling stabilities and the interfacial properties on the surfaces of both cathode and anode under different temperatures are systemically investigated. It is revealed that the LHCE enables the formation of more protective electrode/electrolyte interphases on both anode and cathode, which, in turn, lead to significantly improved cycling stability and enhanced rate capability under the selected temperatures. The electrode/electrolyte interphases formed in LHCE are found to be less susceptible towards elevated temperatures than those in conventional LiPF6-based electrolyte. The mechanistic understanding on the function of the LHCE in Gr||LMR cells under high temperatures provides valuable perspectives of electrolyte development for practical application of LMR cathodes in high energy density batteries over a wide temperature range. References C. Wang, et al., Overlooked electrolyte destabilization by manganese (II) in lithium-ion batteries. Nature Communications, 2019, 10(1), 3423.H. Pan, et al., Li- and Mn-rich layered oxide cathode materials for lithium-ion batteries: a review from fundamentals to research progress and applications, Molecular Systems Design & Engineering, 2018, 3(5), 748.M.-T.F., Rodrigues, et al., A materials perspective on Li-ion batteries at extreme temperatures, Nature Energy, 2017, 2(8), 17108.

<p indent="0mm">The pursuit of next-generation energy storage systems has intensified research on lithium-sulfur (Li-S) batteries, which offer high energy density and low cost. However, the practical application of Li-S batteries is hindered by issues such as the shuttle effect, low electrical conductivity of sulfur, and large volume changes during cycling. Organic electrode materials possess advantages such as safety, environmental friendliness, sustainability, design flexibility, and low cost, making them promising cathode materials for high-capacity lithium batteries. Among them, organosulfur has received increasing attention with the development of lithium-sulfur batteries. Similar to sulfur cathodes, organosulfur electrodes can provide a relatively high theoretical capacity based on the reversible breaking and formation of S–S bonds. However, inherent problems such as poor conductivity, sluggish redox kinetics, unsatisfactory cycling stability, and the solubility of cycling products seriously hinder the development of organosulfur cathode materials. Doping heteroatoms into organosulfur molecules to design and synthesize new organosulfur molecules is an effective strategy to improve the performance of organic sulfur cathodes. Heteroatom doping offers a versatile method to modify the electronic structure and chemical reactivity of organosulfur cathodes. By introducing elements such as oxygen (O), nitrogen (N), selenium (Se), tellurium (Te) and phosphorus (P), researchers aim to tailor the material’s properties to improve conductivity, accelerate redox reactions, stabilize electrode interfaces, and mitigate dissolution issues of reaction intermediates. Hybridized organosulfur cathode materials have received more and more attention due to their unique design strategy and flexible electrochemical modulation. Therefore, the research progress in heteroatom-containing organosulfur cathode materials is reviewed comprehensively in this paper, summarizing their applications in lithium battery systems. It primarily discusses heteroatom-containing small molecule organic sulfur and polymer organic sulfur materials, and concludes with the challenges and prospects for organic sulfur cathode materials. It covers synthetic strategies to incorporate heteroatoms, characterization techniques to elucidate their structural and electrochemical properties, and their performance as cathode materials in various battery configurations. The discussion encompasses mechanistic insights into how heteroatoms influence charge storage mechanisms, ion diffusion kinetics, and overall battery performance metrics. Despite the promising advances, challenges remain, including the precise control of heteroatom doping levels, maintaining structural integrity during cycling, and optimizing synthesis methods for scalability and cost-effectiveness. Furthermore, the environmental impact and recyclability of these materials are critical considerations for their sustainable application in energy storage technologies. Looking forward, the development of heteroatom-containing organic sulfur cathode materials holds significant potential to address current limitations and unlock new opportunities for next-generation rechargeable batteries. Future research directions focus on refining synthetic techniques, enhancing material stability and cycling performance, exploring novel heteroatom combinations, and integrating these materials into practical battery systems that meet the increasing demands for high-energy-density and sustainable energy storage solutions. In conclusion, heteroatom-doped organic sulfur cathode materials represent a significant advancement in the field of Li-S batteries. The synergistic effect of organic-inorganic hybridization, combined with the tunability of heteroatom doping, offers a promising avenue for the development of high-performance energy storage systems. Further research is needed to fully exploit the potential of these materials and to address the remaining challenges for their practical application.

The Li- and Mn-rich layered oxide cathode material class is a promising cathode material type for high energy density lithium-ion batteries. However, this cathode material type suffers from layer to spinel structural transition during electrochemical cycling, resulting in energy density losses during repeated cycling. Thus, improving structural stability is an essential key for developing this cathode material family. Elemental doping is a useful strategy to improve the structural properties of cathode materials. This work examines the influences of Mg doping on the structural characteristics and degradation mechanisms of a Li1.2Mn0.4Co0.4O2 cathode material. The results reveal that the prepared cathode materials are a composite, exhibiting phase separation of the Li2MnO3 and LiCoO2 components. Li2MnO3 and LiCoO2 domain sizes decreased as Mg content increased, altering the electrochemical mechanisms of the cathode materials. Moreover, Mg doping can retard phase transition, resulting in reduced structural degradation. Li1.2Mn0.36Mg0.04Co0.4O2 with optimal Mg doping demonstrated improved electrochemical performance. The current work provides deeper understanding about the roles of Mg doping on the structural characteristics and degradation mechanisms of Li-and Mn-rich layered oxide cathode materials, which is an insightful guideline for the future development of high energy density cathode materials for lithium-ion batteries.