Lithium-ion Battery Cathode Research Articles

Fulgide Derivatives as Photo-Switchable Coatings for Cathodes of Lithium Ion Batteries - A DFT Study.

Photo-switchable coatings for lithium ion batteries (LIB) can offer the possibility to control the diffusion processes from the electrode materials to the electrolyte and thus, for example, reducing the energy loss in the fully charged state. Fulgide derivatives, as known photo-switches, are investigated concerning their use as coating for vanadium pentoxide, a potential cathode material for LIB. With the help of Density Functional Theory calculations, two fulgide derivatives are characterized with respect to their photophysics, their aggregation behaviour on the cathode material and the ability to form self-assembled monolayers (SAM). Furthermore, the two states of the photo-switchable coating are tested with respect to lithium diffusion from the cathode material, passing the SAM and entering the electrolyte. We found a difference for the energy barriers depending on the state of the photo-switch, preferring its closed form. This behaviour can be used to prevent the loss of charge in batteries of portable devices.

The Development and Prospect of Stable Polyanion Compound Cathodes in LIBs and Promising Complementers.

Cathode materials are usually the key to determining battery capacity, suitable cathode materials are an important prerequisite to meet the needs of large-scale energy storage systems in the future. Polyanionic compounds have significant advantages in metal ion storage, such as high operating voltage, excellent structural stability, safety, low cost, and environmental friendliness, and can be excellent cathode options for rechargeable metal-ion batteries. Although some polyanionic compounds have been commercialized, there are still some shortcomings in electronic conductivity, reversible specific capacity, and rate performance, which obviously limits the development of polyanionic compound cathodes in large-scale energy storage systems. Up to now, many strategies including structural design, ion doping, surface coating, and electrolyte optimization have been explored to improve the above defects. Based on the above contents, this paper briefly reviews the research progress and optimization strategies of typical polyanionic compound cathodes in the fields of lithium-ion batteries (LIBs) and other promising metal ion batteries (sodium ion batteries (SIBs), potassium ion batteries (PIBs), magnesium ion batteries (MIBs), calcium ion batteries (CIBs), zinc ion batteries (ZIBs), aluminum ion batteries (AIBs), etc.), aiming to provide a valuable reference for accelerating the commercial application of polyanionic compound cathodes in rechargeable battery systems.

Improving the Cycle Stability of LiNiO2 through Al3+ Doping and LiAlO2 Coating.

In this study, we addressed the poor cycling and rate performance of LiNiO2, a material with ultrahigh nickel content considered a strong contender for high-energy-density lithium-ion battery cathodes. We introduced nano-Al2O3 during the lithiation process to achieve dual modified material through bulk phase element doping and in situ LiAlO2 coating. Comparison revealed notable improvements in the modified materials. In particular, LiNi0.99Al0.01O2 maintained a capacity retention rate of 73.1% after 300 cycles in a long-cycle test at 0.5C current density, outperforming the undoped material. In rate performance tests, the doped samples consistently exhibited higher discharge-specific capacities than that of the undoped counterpart. Notably, at a high current density of 5C, LiNi0.99Al0.01O2 exhibited a discharge-specific capacity of 101.75 mAh g-1. The results indicate that an appropriate amount of Al doping can effectively stabilize the layered structure of the cathode material and delay the irreversible phase transition from H2 to H3. Further, Al doping facilitates the formation of a LiAlO2 coating on the surface of the particles. This coating acts as a fast-ion conductor, enhancing the transport of lithium ions and reducing the erosion of the active material by the electrolyte.

Comprehensive study on lithium-ion battery cathode LiNixCoyMn1-x-yO2 as an air electrode for protonic ceramic fuel cells

The protonic ceramic fuel cells (PCFCs) exhibits a remarkable high-energy conversion efficiency and significant application potential at low temperatures. In this context, the layered ternary lithium-ion batteries (LIB) material, LiNixCoyMn1-x-yO2 (LNCM), is explored as a potential cathode for PCFCs. Utilizing density functional theory (DFT) calculations, we have conducted a comprehensive analysis of oxygen vacancies, hydration energy, density of states, and other pertinent properties to evaluate these ternary materials. Both theoretical and experimental findings suggest that LiNi0.5Co0.2Mn0.3O2 (LNCM523) may offer the optimal performance as a PCFCs cathode. Notably, after calcination in air at 700 °C for 100 h, LNCM523 displayed no phase transition or the emergence of new phases. The impedance of LNCM523, measured on a BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) electrolyte, is 0.225 Ω cm2 at 650 °C. At this temperature, the peak power density of the single cell reaches 355 mW cm−2. Moreover, during a 100-h stability test conducted at 550 °C, the output performance of the single cell remained unaltered. In electrolysis mode, at 650 °C and 1.3 V, the current density for electrolysis water attained 1.75 A cm−2. Based on these promising results, LNCM emerges as a viable cathode candidate for PCFCs.

Preparation of Single-Crystal Li-Rich Mn-Based Layered Oxides with Excellent Electrochemical Performance via Simple Stepwise High-Temperature Sintering.

Li-rich Mn-based layered oxides have attracted extensive attention in lithium-ion battery cathode materials due to their high specific capacity, wide operating voltage, and low cost. However, the large-scale production of single-crystal Li-rich Mn-based layered oxides remains a significant challenge. Herein, the morphology, structure, and electrochemical properties of a series of samples (Li1.2Ni0.13Co0.13Mn0.54O2) prepared by the solid-state method and the molten-salt flux method were assessed. Single-crystal particles exactly could be prepared by potassium chloride (KCl), but its electrochemical performance was inferior and the molten-salt flux method was too complicated for industry. Surprisingly, we found that water washing and annealing processes could enhance the cycling performance. Furthermore, single-crystal Li1.2Ni0.13Co0.13Mn0.54O2 with a particle size of 536 nm was successfully prepared by simple stepwise sintering (950 °C for 7 h, 1000 °C for 1 h, and 850 °C for 2 h), which delivered a specific capacity of 274.9 mAh·g-1 between 2.0 and 4.8 V at 0.1 C with 77.4% initial Coulombic efficiency and 82.1% capacity retention after 100 cycles at 0.1 C. This study may provide theoretical guidance for the industrial production of single-crystal Li-rich Mn-based layered oxides.

Highly Conductive Two-Dimensional FeTHBQ/Graphene Nanocomposite as the Cathode Material for Lithium-Ion Batteries.

Constructing high-performance coordination polymer (CP) cathodes for lithium-ion batteries based on the redox reactions of both high-potential transition metal ions and high-capacity organic ligands has attracted extensive attention. However, CP cathodes suffer from structural degradation, low electrical conductivity, and sluggish diffusion kinetics, resulting in poor cycling stability and inferior rate capability. Herein, the ultrafine FeTHBQ (THBQ = tetrahydroxy-1,4-benzoquinone) CP nanoparticles in situ grew on both sides of graphene nanosheets to form the uniform two-dimensional (2D) FeTHBQ/Graphene nanocomposite with a sandwich structure via a one-pot solvothermal method. The highly conductive graphene skeleton promotes the electronic conduction and structural stability for the 2D FeTHBQ/Graphene nanocomposite. Besides, compared with bulk FeTHBQ, the primary FeTHBQ nanoparticles in the FeTHBQ/Graphene nanocomposite have smaller particle sizes with larger specific surface areas. This not only shortens the Li+ diffusion distance in the FeTHBQ crystal but also benefits Li+ transfer between the electrolyte and the electrode. In the FeTHBQ/Graphene nanocomposite, the active material of FeTHBQ manifested multiple redox centers of transition metal ions (Fe3+/Fe2+) and carbonyls (C═O/C-O-) in THBQ ligands. Owing to the enhancements of structural stability, electronic conduction, and Li+ diffusion kinetics, the 2D FeTHBQ/Graphene nanocomposite presented a high lithium-ion storage capacity of 217.2 mA h g-1 at 50 mA g-1, a fast rate capability of 79.1 mA h g-1 at 5000 mA g-1, and a stable cycling performance of 87.2 mA h g-1 at 500 mA g-1 after 100 cycles. This work sheds light on the great opportunity for optimizing the electrochemical performances of CP-based functional electrode materials by combining with conductive substrates.

Digital Twin Reveals the Impact of Carbon Binder Domain Distribution on Performance of Lithium‐Ion Battery Cathodes

The rising demand for high‐performance lithium‐ion batteries (LIBs) emphasizes the need for precise electrode design. The carbon binder domain (CBD) within electrodes, crucial for electron transport and structural integrity, can impede lithium‐ion transport and reduce electrochemically active sites. This study leverages digital twin technology to investigate the impact of CBD distribution along the electrode thickness on LIB cathode performance. Virtual LIB cathodes with varying CBD configurations are generated, and their performance using 3D heterogeneous electrochemical modeling is evaluated. The results reveal that a steep CBD gradient significantly diminishes charge capacity compared to a mild gradient, particularly at higher current rates. This reduction is attributed to an increased tortuosity factor and an uneven distribution of electrochemical activity, which adversely affect mass transport and electrochemical reaction dynamics. These effects are more pronounced at lower porosities and higher loading levels. These findings highlight that optimizing CBD distribution is critical for advancing electrode design and enhancing LIB cathode performance.

Fully sp2 Carbon-Conjugated Covalent Organic Frameworks with Multiple Active Sites for Advanced Lithium-Ion Battery Cathodes.

Covalent organic frameworks (COFs) hold great promise for rechargeable batteries. However, the synthesis of COFs with abundant active sites, excellent stability, and increased conductivity remains a challenge. Here, chemically stable fully sp2 carbon-conjugated COFs (sp2c-COFs) with multiple active sites are designed by the polymerization of benzo[1,2-b:3,4-b':5,6-b'']trithiophene-2,5,8-tricarbaldehyde) (BTT) and s-indacene-1,3,5,7(2H,6H)-tetrone (ICTO) (denoted as BTT-ICTO). The morphology and structure of the COF are precisely regulated from "butterfly-shaped" to "cable-like" through an in situ controllable growth strategy, significantly promoting the exposure and utilization of active sites. When the unique "cable-like" BTT-ICTO@CNT is employed as lithium-ion batteries (LIBs) cathode, it exhibits exceptional capacity (396 mAh g-1 at 0.1 A g-1 with 97.9 % active sites utilization rate), superb rate capacity (227 mAh g-1 at 5.0 A g-1), and excellent cycling performance (184 mAh g-1 over 8000 cycles at 2.0 A g-1 with 0.00365 % decay rate per cycle). The lithium storage mechanism of BTT-ICTO is exhaustively revealed by in situ Fourier transform infrared, in situ Raman, and density functional theory calculations. This work provides in-depth insights into fully sp2c-COFs with multiple active sites for high-performance LIBs.

Accelerating Li-Ion Diffusion in LiFePO4 by Polyanion Lattice Engineering.

Despite the widespread commercialization of LiFePO4 as cathodes in lithium-ion batteries, the rigid 1D Li-ion diffusion channel along the [010] direction strongly limits its fast charge and discharge performance. Herein, lattice engineering is developed by the planar triangle BO3 3- substitution on tetrahedron PO4 3- to induce flexibility in the Li-ion diffusion channels, which are broadened simultaneously. The planar structure of BO3 3- may further provide additional paths between the channels. With these synergetic contributions, LiFe(PO4)0.98(BO3)0.02 shows the best performance, which delivers the high-rate capacity (66.8 mAhg-1 at 50 C) and long cycle stability (ultra-low capacity loss of 0.003% every cycle at 10 C) at 25°C. Furthermore, excellent rate performance (34.0 mAhg-1 at 40 C) and capacity retention (no capacity loss after 2500 cycles at 10 C) at -20°C are realized.

Enhanced cyclability and energy density of mid-nickel layered oxide cathode material LiNi0.55Mn0.25Co0.20O2 by niobium doping via solvothermal method

Ni-based layered oxide materials are among the most promising cathode materials for the next generation of lithium-ion batteries due to their higher energy capacity. However, capacity decay occurs due to degradation mechanisms that reduce the electrochemical performance of this type of material. This work aims to synthesize Nb-doped LiNi0.55Mn0.25Co0.20O2 (Nb-NCM) materials via the solvothermal method to enhance the cyclability and energy density of the layered oxide cathode. The effects of Nb doping on the microstructure and the electrochemical performance of the cathodes are investigated. The introduction of the contents of Nb expands the structural lattice parameters and decreases the Li+/Ni2+ cation mixing degree of the NCM cathode. Furthermore, the Nb doping enhances the electrochemical activity of LiNi0.55Mn0.25Co0.20O2, increasing its initial discharge capacity to 169.61 mAhg−1 when 1% of Nb was used as a dopant (1%Nb-NCM) in contrast to the capacity of 149.45 mAhg−1 presented by the pristine material. The modified 1.0%Nb-NCM material also exhibits remarkable cycling performance with a capacity retention of 92.7% after 100 cycles at the rate of 1 C (2.8–4.3 V). This work suggests a rational strategy for high-performance cathode for lithium-ion batteries, proposing the extension of Nb doping to enhance Ni-mid material's cyclability.

Tuning architectural synergy reactivity of nano-tin oxide on high storage reversible capacity retention of ammonium vanadate nanobelt array cathode for lithium-ion battery

Enabling ambient cycling stability of vanadium-based materials is of fundamental importance in the advancement of next generation electrodes for high-performance lithium-ion batteries. Although, extending these host layered nano-architectures illustrate the effective electrochemical activity by regulating the gallery space for fast Li+ storage, the reported structural integrity in terms of the cycling stability for vanadium-based cathodes is highly challenging. In present study, a series of NH4V4O10-SnO2 (NHV-SnO2) nanocomposite consisting of diverse contents of SnO2 (x: 5.0, 15.0 and 30.0 wt%) were synthesized through a three-step program based on sonochemical-calcination-hydrothermal treatment and employed as an advanced energetic material for lithium-ion battery cathodes. For the first time, understanding the impact of SnO2 loading on electrochemical reactions of NHV-based electrodes was regarded as an effective engineering strategy to optimize structural modulation and cell lifetime without distinct capacity fading. Notably, combination of NHV and SnO2 in optimum proportions not only enhances the specific surface area, but also expand buffer the volume change for lithium-ion intercalation/extraction. By this design, the assembled battery containing 15.0 wt% SnO2 illustrated stable capacities of 301.77 mAh g−1 (30 mA g−1) and 232.05 mAh g−1 (240 mA g−1) with capacity retention values as high as 97.94 % and 97.03 % for 50 cycles, respectively. Of note, the results described here could show a vital guidance toward designing better composite-based cathode material for energy storage devices.

Cobalt-free spinel–layered structurally integrated Li0.8Mn0.64Ni0.183Fe0.091O2 cathodes for lithium-ion batteries

Cobalt-free, Li-rich layered-spinel structurally integrated positive electrode (cathode) materials for lithium-ion batteries (LIBs), with nominal composition 0.6(Li1.2Mn0.56Fe0.08Ni0.16O2) 0.4(LiFe0.2Mn1.4Ni0.4O4) which can otherwise be written as Li0.8Mn0.64Ni0.183Fe0.091O2 (FeSL) are synthesized via simple citric acid-assisted sol-gel route. Four different final annealing temperatures (550 °C, 650 °C, 750 °C, and 850 °C) were chosen to investigate their influence on electrochemical performance. The obtained composite materials contain spinel (space group Fd3¯m) as well as Li-rich layered phases (space group C2/m) as revealed by X-ray diffraction (XRD), HRTEM and cyclic voltammetry investigations. The excellent electrochemical performance of the composite material could be attributed to the structural stability achieved by the integration of spinel and layered components. Selected synthesized composite materials exhibit high discharge capacities close to 200 mAh g−1. The FeSL750 shows better capacity retention (92(3)% at the 50th cycle and 82(5)% at the 70th cycle) and rate capability than the FeSL550 and FeSL650 samples. However, the FeSL850 sample shows different charge-discharge behaviour. The charge capacity corresponding to FeSL850 is found to increase up to the 20th cycle, then stabilizes and displays a capacity retention of almost 100 % at the 50th cycle and 91(1)% at the 70th cycle. The electrochemical mechanism of FeSL750 was elucidated via in operando XAS investigations, which reveal electrochemical activity from all transition metals.

In-depth approach and establishment from a structural perspective of LiFePO4 cathodes for lithium-ion batteries by a two-step sintering

Most synthesis of olivine LiFePO4 (LFP) studies have emphasized the importance of a two-step sintering process for the formation of a uniform carbon coating. However, in this study, it is found that, as an advantage of the two-step sintering process, stable carbonization not only improves lithium-ion conductivity by forming a coating layer but also increases the uniformity of the internal crystal structure. In addition to basic crystallinity and structure analysis using X-ray diffraction (XRD), in-depth calculations are performed to explain the formation mechanism of crystal structure according to the two-step sintering process and the temperature of the first sintering step. In particular, lattice defects and structural uniformity are closely investigated from the crystal structure perspective by comparing lattice micro-strain and dislocation density. Improvement in lithium-ion conductivity from structural uniformity is also demonstrated through cyclic voltammetry (CV) analysis. As a result, it is confirmed that LFP, which undergoes a high-temperature two-step sintering, has high capacity and excellent cycle retention at high rates. Furthermore, ex-situ XRD analysis demonstrates the performance difference according to lithium-ion mobility by comparing the LiFePO4/FePO4 two-phase transformation reaction of two-step sintered LFP and the plateau stability during charging.

Study on Cycle Performance and Rate Performance of Lithium Cobalt Oxide

Lithium cobalt oxide (LiCoO2 ) cathode material, with its high energy density and operating voltage, is currently a mainstream material for lithium-ion battery cathodes.   However,  the  crystal  structure  collapse  and  lattice  oxygen  evolution under high-voltage conditions lead to rapid capacity decay, severely limiting its practical applications.   This paper  analyzes the main factors affecting the cycle performance and rate performance of lithium cobalt oxide, considering the physic- ochemical properties of the particles, including elemental content and particle size, and provides a mathematical model linking these properties to electrochemical per- formance.  The study offers insights for the practical production of high-voltage lithium cobalt oxide materials. At the beginning, we embarked on investigating the correlation between the physicochemical attributes (encompassing elemental composition and particle size) of lithium cobalt oxide and its cycle performance. An Ordinary Least Squares (OLS) linear regression model was formulated, yielding a robust fit with an R-Squared value of 0.94. This model was subsequently optimized through the application of an XGBoost algorithm, achieving an R-Squared value nearing unity, signifying a remarkable enhancement in model accuracy. Visual analysis of the results pinpointed the primary determinants of cycle performance, arranged in descending order of significance: 'Cycle Index,' Mg content, particle size distribution (D10), Zn, and Al. Then, our attention shifted to examining the link between the aforementioned physicochemical characteristics and the rate performance of lithium cobalt oxide. The Jarque-Bera and Shapiro-Wilk tests confirmed the normality of the data, fulfilling the prerequisites for hypothesis testing. An OLS linear regression model was developed, demonstrating a strong goodness-of-fit with an R-Squared value exceeding 0.8. This model was further honed with an XGBoost model, which achieved an R-Squared score approaching 1, indicating a substantial refinement in model precision. The visualization of model outcomes illuminated the key factors influencing rate performance, ranked in descending order of importance: particle size distribution (D50), Al, Mn, Zn, Mg, Ni, and Fe. Lastly, we devised an optimal strategy that encompasses the incorporation of strategic doping elements, the utilization of high-temperature sol-gel methods to bolster cycle performance, and coating modifications aimed at enhancing rate performance. This holistic approach fosters the structural stability of lithium cobalt oxide crystals, fortifying their high-potential cycle capabilities, and concurrently elevating their rate performance.

The Effect of Mono-Halogenation on the Performance of Anthraquinone Cathode in Lithium-Ion Batteries

To investigate the effect of mono-halogenation on the performance of anthraquinone cathode in lithium-ion batteries, the structures and electrochemical properties of AQ derivatives functionalized with single chlorine and bromine were studied. The microstructure and morphology were characterized by XRD and SEM, and the electrochemical properties were conducted using galvanostatic charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy. 1-BrAQ, 2-BrAQ, and 2-ClAQ showed improved cyclic stability and higher platform voltage than the AQ cathode, and the capacity retention rates of 2-ClAQ and 2-BrAQ after 50 discharge cycles are 64.6% and 77.8%, respectively, which are twice the capacity retention rate of the AQ positive electrode under the same conditions.

Ambient-temperature aqueous electrochemical route for direct Re-functionalization of spent LFP cathodes of lithium-ion batteries

Relithiation is a critical step in the direct recycling process, which is the most promising method for spent LiFeIIPO4 (LFP) batteries recycling. It involves the reduction of FeIIIPO4 (FP) in a Li-ion-rich environment and is generally performed by high-temperature sintering or hydrothermal methods. This study proposes an ambient temperature electrochemical relithiation method in an aqueous solution. It follows a preliminary delithiation step described in our previous publications. The results confirmed that FP can be efficiently relithiated in either Li2SO4 or LiHCO3 electrolyte. The reaction follows mostly a Cottrellian behavior, determined from potentiostatic experiments, indicating that diffusion in solution is a critical mechanism. Application of this electrochemical relithiation process to FP originating from spent LFP resulted in a 96 % relithiation yield at a current efficiency of 91 %. The overall recycling process successfully re-functionalized deeply damaged spent LFP by recovering up to 99 % of the LFP's original discharge capacity, achieving up to 153 mAh g−1 at C/12. Meanwhile, the initial discharge capacity of the re-functionalized LFP at 1C attained 119 mAh g−1, which interestingly increased upon cycling, reaching 131 mAh g−1 after 225 cycles. This increase could be associated with electrochemical activation promoted by cycling-induced LFP crystal annealing and/or by electrochemical milling.

Synthesis and Electrochemical Performance Enhancement of Li2MnSiO4 Cathode Material for Lithium‐Ion Batteries via Mn‐Site Ni Doping

AbstractIn exploring the potential of Li2MnSiO4 as a cathode material for lithium‐ion batteries (LIBs), the key challenges often involve enhancing electronic conductivity and lithium‐ion diffusion rates. To address these issues, this paper proposes the combination of solid‐state doping and a two‐step calcination process to successfully prepare the Li2Mn1−xNixSiO4 series of cathode materials, where Ni substitutes Mn at different doping amounts (x = 0, 0.02, 0.04, 0.06, 0.08). The use of chemically equivalent Ni2+ ions to replace Mn2+ ions is an effective method. Since the ionic radius of Ni2+ is smaller than that of Mn2+, this substitution can create more voids in the lattice structure. These increased voids provide smoother channels for the transport of electrons and lithium ions, thereby improving the material's electrical conductivity. At a Ni doping amount of 0.06, the material exhibits optimal electrochemical performance, achieving a discharge capacity of 155 mAh g−1 at 0.1 C, significantly superior to undoped lithium manganese silicate. The doping of Mn sites with Ni significantly improves the conductivity and lithium‐ion diffusion capabilities of Li2MnSiO4, revealing the tremendous potential of doping strategies in optimizing the performance of LIBs cathode materials.

Nickel‐Manganese‐Based Layered Oxide for Sodium Ion Battery Cathode Materials

Sodium‐ion batteries (SIBs) have demonstrated significant potential as alternatives to conventional lithium‐ion batteries (LIBs) for modern grid and mobile energy storage applications, due to the abundant natural resources and low cost of sodium. Layered transition metal oxides (LTMOs) have attracted focused research attentions due to their high specific capacities, energy densities as well as the compatible preparation processes with those of LIBs cathode materials. Among these, Ni/Mn‐based LTMOs (NMLOs) are particularly noteworthy for their cost‐effectiveness and superior electrochemical performance, such as excellent capacity retention, voltage stability, high operating voltage and rate capability. In this review, we briefly introduce the synthesis methods of NMLOs, discuss the challenges, and summarize the solutions. The insights presented may contribute to the development of NMLOs based SIBs.

Naphthalene Diimide-Based Cyanovinylene-Containing Conjugated Organic Polymers for Efficient Lithium-Ion Battery Electrodes.

The pursuit of innovative organic materials and the examination of the "structure-function" correlation in lithium-ion batteries (LIBs) are crucial and highly desirable. Current research focuses on the creation of novel conjugated organic polymers with polycarbonyl groups and examining the impact of electrode structure on the function of lithium-ion batteries. In this paper, two novel cyanovinylene-based conjugated organic polymers, NBA-TFB and NBA-TFPB, are synthesized using a Knoevenagel condensation reaction with naphthalene diimide as the integral unit. The performance of NBA-TFB and NBA-TFPB as cathodes in lithium-ion batteries is investigated. Improved conductivity and increased active site density in NBA-TFPB resulted in superior electrochemistry compared to NBA-TFB. Specifically, NBA-TFPB exhibited a larger reversible capacity (87.58 mAh g-1 at 0.2C and 88.34% retention after 100 cycles), exceptional rate capability (66.13 mAh g-1 at 5C), and robust cycling stability (99.58% coulombic efficiency at 1C and 60.71% retention after 2000 cycles). This study expands the family of diimide-based naphthalene polymers and provides a strategy for enhancing the performance of organic electrode materials containing polycarbonyl structure.

Insulating behaviour in room temperature rhombohedral LiNiO2 cathodes is driven by dynamic correlation

Abstract Inspired by the experimental finding of a paramagnetic insulating state in rhombohedral LiNiO2, a lithium-ion battery cathode of great interest, we calculate the electronic, magnetic, and optical properties of LiNiO2 employing a range of single-particle and many-body methods. Within density-functional theory (DFT) using the generalized-gradient approximation (GGA), meta-GGA, and hybrid functionals, we obtain a ferromagnetic half-metallic ground state for rhombohedral LiNiO2, as has been seen previously. Self-consistent GW calculations including self-interaction corrections beyond DFT for various flavours show an electronic band gap albeit with a small quasiparticle peak at the Fermi energy. Moving beyond this, room temperature state-of-the-art dynamical mean-field theory (DMFT) calculations on rhombohedral LiNiO2 show for the first time a gap of combined Mott and charge-transfer character. The paramagnetic insulating state has a band gap of ~0.6 eV, in excellent agreement with experiments and is in sharp contrast to DFT calculations that require the presence of an extra structural symmetry breaking in the form of Jahn–Teller distortions to open a gap. We observe Ni to be in a +2 state in a d 8L configuration, with a charge-transfer ligand hole in O p, and identify the ligand hole state from the DMFT DOS. We further show that whereas DFT shows the presence of an unphysical metallic Drude peak in the optical absorption spectra, DMFT calculations capture the correct form of the optical absorption spectra, and have an excellent match with the calculated band gap as well. Our results clarify that at room temperature, it is the charge transfer gap with a Mott character that causes rhombohedral LiNiO2’s insulating nature; a structural distortion is not required.