High-capacity Cathode Materials Research Articles

Glassy Oxides as Positive Electrode Materials for Sustainable and High Energy Density Li-Ion and Na-Ion Batteries: First Attempts to Establish Relationships between Glass Compositions, Physicochemical Characterizations and Electrochemical Properties with Machine Learning and Design of Experiments Approaches

Today, rechargeable lithium-ion batteries (LIBs) represent one of the best alternatives to reduce our dependency on fossil fuels. LIBs are using cathode materials based on polycrystalline oxides or polyanionic compounds [1]. However, their performances can be limited by their crystalline structure when other compounds suffer from metallic dissolution and irreversible phase changes during cycling [2]. To overcome these key shortcomings, implementing glasses or glass-ceramics as cathode materials is an interesting approach [3]. Glasses have a structure composed of more free volume, and, in the literature that is mainly concerning glasses containing Vanadium transition metal, the glasses can so accept a large amount of lithium [4] and easily accommodate structural changes upon lithium ions extraction/insertion [5]. Furthermore, glass production is a scalable process and can be commercially easier to implement than most of synthesis processes of conventional cathode materials.The main objective targeted is to develop high capacity positive electrodes (up to 300mAh/g) for Li-ion batteries based on glassy oxides without critical transition metals such as Cobalt and Vanadium. The ambitious target is to exceed 1000Wh/kg at the active material level and so enable energy densities of 300-350 Wh/kg at the Li-Ion cell level. Additionally, the electrochemical behavior of some alkali-free glass compositions will be evaluated in sodium-ion configuration. The major scientific objective is to correlate the most relevant physicochemical properties of glass with the corresponding electrochemical performances using machine learning approaches or design of experiment methodology. For a better understanding of involved processes, three oxides glass families are studied as promising cathode materials for sustainable and high energy density lithium batteries. These oxides are composed of: i) a glass network-forming element (Si, B, P) leading to the 3 different families, ii) a transition metal (Mn, Fe, ...) and optionally iii) an alkali (Li, Na).The influence of the nature of the transition metal and the polyanionic group corresponding to the network-forming element (PO4, BO3, SiO4) on the electrical properties of the as-prepared glasses measured at different temperatures will be presented mainly for the lithiated compounds. For microstructural characterization, several techniques were coupled such as X-Ray Diffraction (XRD), SEM-EDX, DTA/TGA, Raman, IR and UV-Vis spectroscopies, Electrochemical Impedance Spectroscopy (EIS) and chronoamperometry.Finally, the electrochemical properties in terms of specific capacity, redox potentials, first cycle capacity loss, coulombic and energetic efficiencies of these materials were investigated in coin-cells vs lithium (or sodium) metal electrode. To understand the electrochemical processes involved in these materials at room temperature, SEM-EDX, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Mossbauër Spectroscopy for iron based compounds were coupled and performed on the as-prepared glasses and on ex-situ (after cycling) materials at different electrochemical states of charge.All the generated data and measurements were analyzed by machine learning approach and tools and in some cases compared with a more classical Design of Experiments (DOE) approach. For instance, figure 1 illustrates the contour diagram of first discharge capacities in the mixture diagram of phosphate glasses based on 3 different transition metal oxides. The final goal is to establish more precisely the relationships between the different glassy oxides structures and their electrochemical performances. First results of this important work of elaboration, characterization and data analysis will be presented here. This new study will bring significant elements to optimize both the glass composition and its elaboration conditions to obtain high performance cathode materials without critical materials.[1] Nitta, N. et al., Li-ion battery materials: present and future. Materials Today 18, 252–264 (2015).[2] Tesfamhret, Y. et al., On the Manganese Dissolution Process from LiMn2O4 Cathode Materials. ChemElectroChem 8, 1516–1523 (2021).[3] K. Kercher et al., « Mixed polyanion glass cathodes: Glass-state conversion reactions », J. Electrochem. Soc., vol. 163, no 2, p. A131-A137, 2016, doi: 10.1149/2.0381602jes [4] Afyon, S. et al., New High Capacity Cathode Materials for Rechargeable Li-ion Batteries. Scientific Reports 4, 7113 (2015).[5] Kindle, M. et al., Alternatives to Cobalt. ACS Sustainable Chemistry Engineering 9, 629–638 (2021). Figure 1

Study on Electrochemical Characteristics of Crystal Structure Changes Effects of Silicon Anode Materials for Lithium Ion Batteries

Graphite is widely used as a representative anode material in commercialized lithium-ion secondary batteries. However, with a theoretical capacity of 370 mAh/g, it is difficult to manufacture high-capacity/high-density lithium-ion secondary batteries. Therefore, research is actively underway to find high-capacity substances to replace graphite. Silicon anode materials are currently attracting attention as next-generation high-capacity cathode materials. Silicon forms Li4.4Si when fully charged through an alloying/dealloying process with lithium during the reaction. Graphite is intercalation/deintercalation in reaction with lithium and LiC6 is formed when fully charged. That's why silicon has a theoretical capacity of 3800 mAh/g, about 10 times that of graphite.However, silicon is a high-capacity electrode material that overcomes the theoretical capacity limit of graphite, and has the disadvantage of experiencing volume expansion of about 400% during repeated charge/discharge cycles. Problems such as material cracks due to volume expansion can affect the safety of the battery. Various studies are being conducted to solve silicon-related challenges to effectively utilize silicon materials. Previous studies have explored the use of binders or additives to mitigate volume expansion. In addition, various types of silicon materials such as Si alloy and SiOx are being developed to suppress volume expansion through matrix formation. Nevertheless, despite the development of silicon materials, structural changes in the charging and discharging process of silicon remain unclear.This study aims to analyze the structural changes that occur during the charging and discharging process of silicon. The experiment evaluates the electrochemical characteristics of crystalline silicon and amorphous silicon and compares the behavior and structural changes during charging/discharging. The volumetric expansion measurements are performed with electrochemical characterization, and ex-situ X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses are performed for comparison with crystal structural changes.

Gradient doping–induced triphasic intergrowth hexacyanoferrate cathode for high-performance sodium-ion batteries

As a high-capacity, high-voltage, and low-cost cathode material for sodium-ion batteries (SIBs), Na/Mn-based hexacyanoferrates (NaxMn[Fe(CN)6]1−y·□y·nH2O) typically exhibit poor structural reversibility and interfacial stability during cycling. In this study, we report the in-situ construction of a triphasic intergrowth Na/Mn/Zn-based hexacyanoferrate (mcr-Zn0.2Mn0.8) with concentration-gradient Zn distribution by an anion-controlled fractional precipitation route. Density functional theory calculations verify that the unique heterostructure arises from the different binding energies between cations and anions. A small amount of Zn2+ doping in the inner cubic/monoclinic phases enhances their structural reversibility during cycling by impeding lattice deformation induced by the Jahn–Teller effect of Mn3+. Meanwhile, the rhombohedral Zn-based hexacyanoferrate epitaxially grown on the surface diminishes the particle size of mcr-Zn0.2Mn0.8 resulting in short Na+ diffusion distance, and provides interface protection that suppresses detrimental electrolyte decomposition. Consequently, mcr-Zn0.2Mn0.8 exhibits a high discharge capacity of 121.1 mAh/g at 15 mA g−1, improved cycling stability at 750 mA g−1 with a capacity retention of 65.0 % after 2000 cycles, and enhanced rate capability with a discharge capacity of 71.4 mAh/g at 6000 mA g−1. The successful implementation of simultaneous surface and bulk modifications through a one-step reaction opens new possibilities for developing high-performance hexacyanoferrate cathode materials for SIBs.

Multi-metal substituted Fe-based Prussian blue as high-capacity cathode material for potassium ion batteries

Fe-based Prussian blue (FePB) has been widely studied as cathode materials of potassium ion batteries due to its three-dimensional open framework structure and large ion migration channels. In this study, the effect of the introduction of various metals (Co2+, Cu2+, Ni2+, Mn2+) on the rate and cycle properties of FePB was investigated. MnCoNiFePB cathode material shows better electrochemical performance, with the initial discharge capacity of 91.3 and 75.4 mAh g−1 (capacity retention is 56.7 % after 100 cycles) at 0.2C and 1C, respectively. These results inspire new ideas for the development and application of potassium ion battery electrode materials.

High-Entropy Prussian Blue Analogues as High-Capacity Cathode Material for Potassium Ion Batteries

Potassium ion batteries, due to their similar electrochemical principles to lithium-ion batteries and the abundance of metal sources, are considered one of the alternatives to lithium-ion batteries. The development of new cathode materials has always been a research focus in this field. Among them, Prussian blue materials, with their three-dimensional open and flexible metal framework structure, can efficiently and reversibly store potassium ions. However, Prussian blue cathode materials still face issues such as poor reversibility and low capacity, which limit their application scope. This study investigates the preparation of high-entropy Prussian blue analogues materials to enhance electrochemical performance. The doping of five different transition metals (Fe2⁺, Co2⁺, Cu2+, Ni2+, and Mn2+) sharing the same nitrogen coordination sites results in a configurational entropy greater than 1.5 R for the material. HEPB-1 cathode material (K1.75Mn0.26Fe0.01Ni0.01Cu0.08Co0.09 [Fe(CN)6]0.66·0.83H2O) shows better electrochemical performance, with the initial discharge capacity of 86.69 and 74.51 mAh g−1 (capacity retention is 75.2% after 100 cycles) at 20 and 100 mA g−1, respectively. The research results have provided new insights for the further development and application of potassium ion batteries.

Separating Cationic and Anionic Redox Activity in the Lithium-Rich Antiperovskite (Li2Fe)SO.

Lithium-rich antiperovskites promise to be a compelling class of high-capacity cathode materials due to the existence of both cationic and anionic redox activity. Little is however known about the effect of separating the electrochemical cationic process from the anionic process and the associated implications on the electrochemical performance. In this context, we report the electrochemical properties of the illustrative example of three different (Li2Fe)SO materials with a focus on separating cationic from anionic effects. With the high-voltage anionic process, an astonishing electrochemical capacity of around 400 mAh g-1 can initially be reached. Our results however identify the anionic process as the cause of poor cycling stability and demonstrate that the fading reported in previous literature is avoided by restricting to only the cationic processes. Following this path, our (Li2Fe)SO-BM500 shows strongly improved performance as indicated by constant electrochemical cycling over 100 cycles at a capacity of around 175 mAh g-1 at 1 C. Our approach also allows us to investigate the electrochemical performance of the bare antiperovskite phase excluding extrinsic activity from initial or cycling-induced impurity phases. Our results underscore that synthesis conditions are a critical determinant of electrochemical performance in lithium-rich antiperovskites, especially with regard to the amount of electrochemical secondary phases, while the particle size has not been found to be a crucial parameter. Overall, separating and understanding the effects of the cationic from the anionic redox activity in lithium-rich antiperovskites provides the route to further improve their performance in electrochemical energy storage.

Ab initio study on changing behaviors of lithium-rich layered composite cathode materials

The lithium-rich composite-layered oxide, xLi2MnO3•(1-x)LiM'O2, where M’ represents transition metals, is a promising cathode material with excellent capacity at high working voltage for lithium-ion batteries (LIBs). Nevertheless, an unusual charge-discharge feature is observed for this material with sloping and plateau regions during the initial charging. In this work, ab initio calculations based on density functional theory were employed to examine the stability of xLi2MnO3•(1-x)Li(Ni1/3Co1/3Mn1/3)O2 composite-layered cathode materials during the first charging. Optimized atomistic models for different compositions (x = 0.0, 0.3, 0.4, 0.5, 0.7, and 1) unveil a pseudo-rhombohedral or monoclinic-like structure within the solid solution phase, with simulated X-ray diffraction patterns closely matching experimental data. Using these atomistic models, the first charging process of the 0.4Li2MnO3•0.6Li(Ni1/3Co1/3Mn1/3)O2 cathode were investigated. There exists phase transition from a layered to a spinel structure. Additionally, Bader charge analysis reveals intriguing trends during the first delithiation process, where the valence states of Ni and Co gradual increase, while that of Mn almost remains unchanged. Simultaneously, significant oxidation of O is observed. This finding leads to further evaluations on oxygen vacancy formation in comparison to the energy required for delithiation. Defect formation energy calculations demonstrate that the plateau in charging curve is resulted from oxygen vacancy formation during the first charging. By empirical fitting oxygen chemical potential at μO = -1.200 eV, the calculated charging-discharging curves aligned well with experimental data during the first and second charging. Furthermore, the pathways of lithium and oxygen deintercalation are elucidated. This work contributes fundamental understandings on the xLi2MnO3•(1-x)LiM'O2 composite-layered oxides as cathode for LIBs, providing valuable guidance for further developments in high-capacity Co-lean cathode materials.

Advancing Lithium-Ion Batteries' Electrochemical Performance: Ultrathin Alumina Coating on Li(Ni0.8Co0.1Mn0.1)O2 Cathode Materials.

Ni-rich Li(NixCoyMnz)O2 (x ≥ 0.8)-layered oxide materials are highly promising as cathode materials for high-energy-density lithium-ion batteries in electric and hybrid vehicles. However, their tendency to undergo side reactions with electrolytes and their structural instability during cyclic lithiation/delithiation impairs their electrochemical cycling performance, posing challenges for large-scale applications. This paper explores the application of an Al2O3 coating using an atomic layer deposition (ALD) system on Ni-enriched Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cathode material. Characterization techniques, including X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, were used to assess the impact of alumina coating on the morphology and crystal structure of NCM811. The results confirmed that an ultrathin Al2O3 coating was achieved without altering the microstructure and lattice structure of NCM811. The alumina-coated NCM811 exhibited improved cycling stability and capacity retention in the voltage range of 2.8-4.5 V at a 1 C rate. Specifically, the capacity retention of the modified NCM811 was 5%, 9.11%, and 11.28% higher than the pristine material at operating voltages of 4.3, 4.4, and 4.5 V, respectively. This enhanced performance is attributed to reduced electrode-electrolyte interaction, leading to fewer side reactions and improved structural stability. Thus, NCM811@Al2O3 with this coating process emerges as a highly attractive candidate for high-capacity lithium-ion battery cathode materials.

First-Principles Study of High-Entropy Sulfides and their Alkali Metal-Doped Modification as Cathode Material for Sodium-Ion Batteries.

High-entropy materials (HEMs) have been explored as high-capacity cathode materials for sodium-ion batteries (SIBs) due to their excellent structural stability and abundant metal redox sites. Among them, high-entropy sulfides (HESs) have greater potential and more extensive research than high-entropy oxides, as they exhibit higher charging voltage and theoretical capacity as cathodes. Furthermore, alkali metal doping of HESs can further enhance their performance and broaden their application fields. Inspired by the cocktail effect of HEMs, we performed the first theoretical calculation of the properties of Na(MnFeCoNi)1/2S and its Li-doped derivative, Na7/8Li1/8(MnFeCoNi)1/2S, to understand their potential as SIB cathode materials. Using density functional theory based on first principles, we investigated the structure and electronic characteristics of Na(MnFeCoNi)1/2S and Na7/8Li1/8(MnFeCoNi)1/2S, and calculated their theoretical voltage and capacity, respectively. Compared with Na(MnFeCoNi)1/2S, Na7/8Li1/8(MnFeCoNi)1/2S showed better electronic performance in reducing the band gap and increasing the density of states, ultimately providing a specific capacity of 160.3 mAh ⋅ g-1 and a charging voltage of 4.85 V in sodium-ion storage. Moreover, Na7/8Li1/8(MnFeCoNi)1/2S exhibited remarkable structural stability throughout the sodium-ion deintercalation process, thus it can be reasonably concluded that Na7/8Li1/8(MnFeCoNi)1/2S can serve as an excellent cathode material for future SIB applications.

Oxygen vacancy H2V3O8 nanowires as high-capacity cathode materials for aqueous zinc-ion batteries

Oxygen vacancy H2V3O8 nanowires as high-capacity cathode materials for aqueous zinc-ion batteries

Insoluble Polyquinonyl Sulfide as High-Capacity Cathode Material for Magnesium Battery

Insoluble Polyquinonyl Sulfide as High-Capacity Cathode Material for Magnesium Battery

Polypyride intercalation boosting the kinetics and stability of V3O7·H2O cathodes for aqueous zinc-ion batteries

V3O7·H2O (VO) is a high capacity cathode material in the field of aqueous zinc ion batteries (AZIBs), but it is limited by slow ion migration and low electrical conductivity. In this paper, polypyridine (PPyd) intercalated VO with nanoribbon structure was prepared by a simple in-situ pre-intercalation, which is noted VO-PPyd. The total density of states (TDOS) shows that after the pre-intercalation of PPyd, an intermediate energy level appears between the valence band and conduction band, which provides a step that can effectively reduce the band gap and enhance the electron conductivity. Furthermore, the density functional theory (DFT) results found that Zn2+ is more easily de-intercalated from the V-O skeleton, which proves that the embeddedness of PPyd improves the diffusion kinetics of Zn2+. Electrochemical studies have shown that VO-PPyd cathode materials exhibit excellent rate performance (high specific capacity of 465 and 192 mA h g−1 at 0.2 and 10 A g−1, respectively) and long-term cycling performance (92.7% capacity retention rate after 5300 cycles), due to their advantages in structure and composition. More importantly, the energy density of VO-PPyd//Zn at 581 and 5806 W kg−1 is 375 and 247 W h kg−1, respectively. VO-PPyd exhibits excellent electrochemical properties compared to previously reported vanadium based cathodes, which makes it highly competitive in the field of high-performance cathode materials of AZIBs.

Temperature-dependent transformation of decavanadate-type {V10O28}6- clusters into {V3O7}- layer structures mediated by 3-quinuclidinol as a structural templating agent: Crystal architectures and mechanism

In this study, two novel vanadate with different dimensions were prepared by hydrothermal synthesis using 3-quinuclidinol as the structural templating agent, namely, zero-dimensional decavanadate [(C7H14NO)6(V10O28)]·2H2O (1) and two-dimensional vanadate [C7H14NO][V3O7]·H2O (2). At a low reaction temperature of 373 K, only crystal 1 is produced. As the reaction temperature is increased in the range of 393–473 K, {V10O28}6- clusters can transform into {V3O7}- layers and the ratio of the transformation gradually increases, resulting in the formation of crystal 2. To our knowledge, this is the first study to achieve a controllable transformation of the vanadium-oxygen anion structure with different dimensions solely through adjusting the reaction temperature, without changing the reactant type and feed ratio. The transformation mechanism also was investigated. The results show that the transformation is caused by the redox reaction between 3-quinuclidinol with {V10O28}6- polyoxoanion. Moreover, 2 possesses a large layer spacing due to the large 3-quinuclidinol cations acting as the “pillar”, resulting in exhibiting good capacity performance (262.4 mAh g−1 at 0.1 A g−1) as the cathode material for aqueous zinc ion batteries. This study not only provides a viable approach for the temperature-tuned transformation of different dimensional vanadium-oxygen anion structures, but also proves that layered vanadate containing large cations are potential high-capacity cathode materials for AZIBs.

Revisit of Polyaniline as a High-Capacity Organic Cathode Material for Li-Ion Batteries.

Polyaniline (PANI) has long been explored as a promising organic cathode for Li-ion batteries. However, its poor electrochemical utilization and cycling instability cast doubt on its potential for practical applications. In this work, we revisit the electrochemical performance of PANI in nonaqueous electrolytes, and reveal an unprecedented reversible capacity of 197.2 mAh g-1 (244.8 F g-1) when cycled in a wide potential range of 1.5 to 4.4 V vs. Li+/Li. This ultra-high capacity derives from 70% -NH- transformed to =NH+- during deep charging/discharging process. This material also demonstrates a high average coulombic efficiency of 98%, an excellent rate performance with 73.5 mAh g-1 at 1800 mA g-1, and retains 76% of initial value after 100 cycles, which are among the best reported values for PANI electrodes in battery applications.

Employing Graph Neural Networks for Predicting Electrode Average Voltages and Screening High-Voltage Sodium Cathode Materials.

For many years, humans have been relentlessly focused on enhancing battery longevity and boosting energy storage capacities. The performance and durability of a battery depend significantly on the material used for its electrodes. In this context, merging machine learning with density functional theory (DFT) calculations has emerged as a pivotal approach to advancing the exploration of battery crystal structures. We present a new method that combines a graph convolutional neural network (GNN) with a Transformer convolutional layer, which we call Transformer-GNN. To underscore its efficacy, we benchmarked Transformer-GNN against three established statistical machine learning models: Support Vector Machine, Random Forest, and XGBoost. We also developed a standard GNN, which we refer to as Basic-GNN. Additionally, we compared Basic-GNN with Transformer-GNN to highlight the improvements brought about by incorporating the Transformer convolutional layer. The Transformer-GNN model outperforms the other models, achieving the highest R2 value of 0.82 and the lowest mean squared error of 0.3161. Our findings demonstrate that the Transformer-GNN can profoundly understand battery crystal structures, thus forging the path toward more sophisticated and durable battery systems. Leveraging the GNN model's voltage predictions in tandem with the capacity data sourced from the database, we screened and pinpointed Na(NiO2)2 as a high-voltage (higher than 5 V), high-capacity sodium cathode material. We conducted DFT calculations on Na(NiO2)2 and revealed the migration mechanism of the Na ions.

Synergism of preintercalated manganese ions and lattice water in vanadium oxide cathodes for high-capacity and long-life Zn-ion batteries

Aqueous Zn-ion batteries (AZIBs) are recognized as a promising energy storage system with intrinsic safety and low cost, but its applications still rely on the design of high-capacity and stable-cycling cathode materials. In this work, we present an intercalation mechanism-based cathode materials for AZIB, i.e. the vanadium oxide with pre-intercalated manganese ions and lattice water (noted as MVOH). The synergistic effect between Mn2+ and lattice H2O not only expands the interlayer spacing, but also significantly enhances the structural stability. Systematic in-situ and ex-situ characterizations clarify the Zn2+/H+ co–(de)intercalation mechanism of MVOH in aqueous electrolyte. The demonstrated remarkable structure stability, excellent kinetic behaviors and ion-storage mechanism together enable the MVOH to demonstrate satisfactory specific capacity of 450 mA h g−1 at 0.2 A g−1, excellent rate performance of 288.8 mA h g−1 at 10 A g−1 and long cycle life over 20,000 cycles at 5 A g−1. This work provides a practical cathode material, and contributes to the understanding of the ion-intercalation mechanism and structural evolution of the vanadium-based cathode for AZIBs.

Medium-mediated high-crystalline Prussian blue toward exceptionally boosted sodium energy storage

Prussian blue and its analogues (PB/PBAs) represent a promising community of low cost and high capacity cathode materials for sodium ion batteries. Nevertheless, the synthesis-induced crystal deficiencies in the framework of PB/PBAs greatly degrade their sodium energy properties, which challenges the potential practicability. Herein, we demonstrate an effective strategy to regulate the PB crystallinity with advanced sodium energy by tuning the synthesis medium. A favorable agent of sodium polyacrylate is screened out as the reaction mediator, which creates a strong coordinating and highly viscous environment to produce high-crystalline PB (HC-PB). Remarkably, the HC-PB harvests an elevated capacity of 140 mAh g–1 at 0.2 C, superb rate capability (105 mAh g–1 at 30 C), and prominent capacity retention of 94.6 % over 1000 cycles at 10 C. The combination of in situ mechanistic and kinetic analyses reveals the rooting reasons for the performance enhancement. This study opens up a prospective and feasible medium-mediated pathway to accelerate the development of PB/PBAs toward sodium chemistry and beyond.

Al/Zr synergetic modification tailored low-cobalt single crystal LiNi0.72Co0.05Mn0.23O2 cathode for high-performance lithium-ion battery

Nickle (Ni)-rich layered oxides as promising candidate of high-capacity cathode materials have aroused extensive concern primarily regarding their higher specific capacity. However, the major hurdle of Ni-rich cathodes (Ni content ≥0.7) is their poor cycling stability, which often suffers from the release of oxygen, structural degradation and increased impedance during cycling, especially at high voltage or high temperature. Herein, we demonstrated a feasible solid phase method for easy industrialization based on the Al3+/Zr4+ co-doping in LiNi0.72Co0.05Mn0.23O2 (AXZY-NCM) single-crystal cathode. The optimized A0.5Z0.5-NCM single-crystal material exhibited greatly enhanced structural and thermal stability. XRD refinement results indicated that both Al3+ and Zr4+ were mainly located in transition metal (TM) sites, strengthening the layered structure through strong M-O bonds and inhibiting cation mixing. In-situ XRD revealed that the synergistic rivet effect of Al/Zr co-doping alleviates anisotropic lattice stress-strain during charge/discharge process. Accordingly, the A0.5Z0.5-NCM cathode can output a high initial capacity of 177.3 mAh g−1 at 1 C, and captured a more desirable capacity retention of 85.10 % than that of U-NCM (74.33 %) at 1 C over 200 cycles. Even at a high voltage of 4.5 V, its capacity retention can still reach 82.37 %, significantly surpassing the unmodified U-NCM (31.0 %). The above results demonstrated that well-designed dual doping is highly effective for strengthen structure stability and cycling performance of Ni-rich cathodes.

High-capacity dilithium hydroquinone cathode material for lithium-ion batteries.

Lithiated organic cathode materials show great promise for practical applications in lithium-ion batteries owing to their Li-reservoir characteristics. However, the reported lithiated organic cathode materials still suffer from strict synthesis conditions and low capacity. Here we report a thermal intermolecular rearrangement method without organic solvents to prepare dilithium hydroquinone (Li2Q), which delivers a high capacity of 323 mAh g-1 with an average discharge voltage of 2.8V. The reversible conversion between orthorhombic Li2Q and monoclinic benzoquinone during charge/discharge processes is revealed by in situ X-ray diffraction. Theoretical calculations show that the unique Li-O channels in Li2Q are beneficial for Li+ ion diffusion. In situ ultraviolet-visible spectra demonstrate that the dissolution issue of Li2Q electrodes during charge/discharge processes can be handled by separator modification, resulting in enhanced cycling stability. This work sheds light on the synthesis and battery application of high-capacity lithiated organic cathode materials.

Amorphous Cobalt Polyselenides with Hyperbranched Polymer Additive as High-Capacity Magnesium Storage Cathode Materials Through Cationic and Anionic Co-Redox Mechanism.

Rechargeable magnesium batteries (RMBs) are a promising energy-storage technology with low cost and high reliability, while the lack of high-performance cathodes is impeding the development. Herein, a series of amorphous cobalt polyselenides (CoSex, x>2) is synthesized with the assistance of organic amino-terminal hyperbranched polymer (AHP) additive and investigated as cathodes for RMBs. The coordination of cobalt cations with the amino groups of AHP leads to the formation of amorphous CoSex rather than crystalline CoSe2. The amorphous structure is favorable for magnesium-storage reaction kinetics, and the polyselenide anions provide extra capacities besides the redox of cobalt cations. Moreover, the organic AHP molecules retained in CoSex-AHP provide an elastic matrix to accommodate the volume change of conversion reaction. With a moderate x value (2.73) and appropriate AHP content (11.58%), CoSe2.7-AHP achieves a balance between capacity and cycling stability. Amorphous CoSe2.7-AHP provides high capacities of 246.6 and 94 mAh g‒1, respectively, at 50 and 2000 A g‒1, as well as a capacity retention rate of 68.5% after 300 cycles. The mechanism study demonstrates CoSex-AHP undergoes reversible redox of Co2+/3+↔Co0 and Sen 2‒↔Se2‒. The present study demonstrates amorphous polyselenides with cationic-anionic redox activities is as a feasible strategy to construct high-capacity cathode materials for RMBs.