Ni-rich Materials Research Articles

Novel Methodology of General Scaling-Approach Normalization of Impedance Parameters of Insertion Battery Electrodes – Case Study on Ni-Rich NMC Cathode: Part I. Experimental and Preliminary Analysis

Abstract Using a model system based on a Ni-rich NMC active material, we demonstrate the necessary experimental steps to perform reliable and accurate impedance measurements of active electrodes (cells) and the characterization techniques required for a meaningful analysis of the obtained impedance data. We demonstrate the practical application of a simple preliminary analysis in which mass normalization of impedance spectra together with the assumption of ideal capacitive behavior allows access to the total (chemical) insertion capacitance, C_total, of the studied active material in an electrode. We show that there is an exact quantitative relationship (equality) between C_total, and the differential capacitance, C_d, of porous insertion electrodes. The main objective is to provide experimenters with directly applicable tools and skills to develop a basic intuition for exploring and explaining the key phenomena observed in the impedance responses of porous Li-ion insertion cathodes. PART-2 will highlight the major advantages of analyzing impedance data using physics-based models. Any model that is based on elements with physical meaning and is correct should pass the “consistency test” included in the scaling relations.

Chemical Competing Diffusion for Practical All-Solid-State Batteries.

The thermal safety issues of currently available Ni-rich cathode-based power supplies brought in the development of all-solid-state batteries, yet the cascade reactions in Ni-rich materials and the chemo-mechanical degradation between the cathode and solid electrolyte diminished the cycle life. Here, by introducing a new heteroatom chemical competing diffusion strategy, we successfully stabilize the Ni-rich cathode and the contact face with an solid electrolyte. Combining extensive explorations in theoretical calculation and multiscale in/ex situ characterization, we elucidate the atomic-level chemical competing diffusion upon the topological lithiation of layered materials. The heteroatoms with higher binding energy to the coordinated oxygen served as the "oxygen anchor" in the bulk and alleviated the excessive oxygen oxidation through charge compensation, thus easing the chemical aggression of the solid electrolyte by evolved oxygen. Comparably, others were enriched in the surface and formed an ionic "diffusion regulator" with residual lithium, and the special ionic transfer regulation mechanism of the piezoelectric layer validly improved the interface compatibility with the solid electrolyte and weakened the space-charge layer in solid-state batteries. This helped the designed Ni-rich cathode-based sulfide solid-state battery exhibit excellent cyclability under 4.5 V (97.3% after 120 cycles). Our findings unlocked the structure-function relationship between the polarization field generated by the piezoelectric material and the electrode.

Synergistic doping chemistry enable the cycling properties of single-crystal Ni-rich cathode for lithium-ion batteries

Nickel-rich cobalt-low layered oxides have attracted much attention as positive electrode materials for high-energy lithium-ion batteries due to their high capacity and low cost, but their inherent stress accumulation and severe cationic mixed reactions will deteriorate the cycling performance. Herein, the nickel-rich single-crystalline LiNi0.90Co0.06Mn0.04O2 cathode material doped with W and Mg (NCM-WM) has been fabricated to overcome its structure degradation issues. It can be found that the Li/Ni cation mixture can be suppressed by the introduction of Mg2+ into Li+ situs and the replacement of transition metal ions by W6+. Meanwhile, the co-doing strategy synergistically depresses the irreversible H2-H3 phase transition to weaken the internal stress, and employs the heteroatoms as the pillar ions to prevent layer structure collapse. In addition, the reduced particle size induced by the W6+ and increased free electron resulted by Mg2+ can cooperatively improve the migration kinetics of ions and electrons in the process of cycling. As expected, the above advanced effects result in the prominent cycling properties (capacity retention of 86.7 %, 150 cycles, 2C) of the designed Ni-rich electrode materials. These results demonstrate that the co-doped design is a greatly effective strategy to reinforce the cycling performance of Ni-rich single-crystalline materials.

Surface Reconstruction Reduces Internal Stress of Ni-Rich Cathode Particles.

High-voltage Ni-rich layered cathode materials are undoubtedly a powerful driving force for high-energy density lithium batteries. However, residual lithium impurities on the surface of Ni-rich materials can cause more severe side reactions under high-voltage, leading to rapid decay. There is still no reliable mechanistic explanation for this phenomenon. It has been detected that residual alkali on the cathode surface under high voltage can cause obvious side reactions. This side reaction will affect the capacity retention of the material and increase the internal stress of the particles. In addition, the surface reconstruction of Ni-rich cathodes is achieved through simple chemical reactions, turning waste into treasure. The newly generated Ti-based layer not only repairs the structure of the nickel-rich material but also optimizes the material from a dynamic perspective. Removing residual lithium components on the cathode surface effectively reduces the hydrolysis and self-catalytic side reactions of PF6 - at the electrolyte cathode interface and suppresses gas generation during cycling, promoting the application of the next generation of high-energy density Ni-rich layered cathode-based lithium batteries with high-voltage.

Tuning Molten-Salt-Mediated Calcination in Promoting Single-Crystal Synthesis of Ni-Rich LiNixMnyCozO2 Cathode Materials

High Ni-content LiNixMnyCozO2 (NMC) cathodes (with x ≥ 0.8, x + y + z = 1) have gained attention recently for their high energy density in electric vehicle (EV) Li-ion batteries. However, Ni-rich cathodes pose challenges in capacity retention due to inherent structural and surface redox instabilities. One promising strategy is to make the Ni-rich NMC material in the form of single-crystal micron-sized particles, as they resist intergranular and surface degradation during cycling. Among various methods to synthesize single-crystal NMC (SC-NMC) particles, molten-salt-assisted calcination offers distinct processing advantages but at present, is not yet optimized or mechanistically clarified to yield the desired control over crystal growth and morphology. In this project, molten-salt-mediated transformation of Ni0.85Mn0.05Co0.15(OH)2 precursor (P-NMC) particles to LiNi0.85Mn0.05Co0.15O2 particles is investigated in terms of the crystal growth mechanism and its electrochemical response. Unlike previous studies that involved large volumes of molten salt, using a smaller volume of molten KCl is found to result in larger primary particles with improved cycling performance achieved via partial reactive dissolution and heterogeneous nucleation growth, suggesting that the ratio of molten salt volume to NMC mass is an important parameter in the synthesis of single-crystal Ni-rich NMC materials.

Synergistically regulating the structural tolerance of Co-free Ni-rich cathode materials at high-rate through multi-heteroatoms substitution

Cobalt-free, nickel-rich layered oxides are attracting extensive interest as cathodes to construct high-energy and sustainable lithium-ion batteries, but the intrinsic structure instability and weakened reaction kinetics deteriorate their application. Nowadays, doping engineering, especially multielement doping, has become an effective modification method for obtaining high-performance Ni-rich materials. Herein, the designed doping strategy with high oxidation states element (Zr4+, Mo6+) substituting transition metal element and Mg2+ replacing Li+ in LiNi0.9Mn0.1O2 (NM-ZMM) has been designed to enhance its electrochemical properties. The introduced doping elements with high oxidation states can generate the strong metal-O bond, which contributes to suppress the structural collapse induced by internal stress, and then maintain unblock ion channels for NM-ZMM. Meanwhile, the presence of Mg2+ can also be employed as the pillar ions to reinforce the structure stability, and occupy the Li-sites to inhibit lattice distortion during charging/discharging process. Thus, benefitting from the synergistic reinforcement of co-doping strategy, as-prepared NM-ZMM materials exhibit the prominent capacity retention (87.5 %, 210 cycles, 1C; 85.5 %, 2C, 150 cycles). Thereof, this creative strategy is crucial in strengthening the electrochemical performance of Ni-rich Co-free materials, which contributes to promote the development of high-performance and cost-effective Li-ion storage technology.

Suppressing high voltage chemo-mechanical degradation in single crystal nickel-rich cathodes for high-performance all-solid-state lithium batteries

Sulfide-based all-solid-state lithium batteries (SASSLBs) suffer from electrochemo.mechanical damage to Ni-rich oxide-based cathode active materials (CAMs), primarilycaused by severe volume changes, results in significant stress and strain cuase micro-cracks, and interfacial contact loss at potentials > 4.3 V(vs. Li/Li+). Quantifying micro-cracks and voids in cathode active materials (CAMs) can reveal the degradation mechanisms of Ni-rich oxide-based cathodes during electrochemical cycling. Nonetheless, the origin of electrochemical-mechanical damage remains unclear. Herein, We have developed a multifunctional PEG-based soft buffer layer (SBL) on the surface of carbon black (CB). This layer functions as a percolation network in the single crystal LiNi0.83Co0.07Mn0.1O2 and Li6PS5Cl composite cathode layer, ensuring superior ionic conductivity, reducing void formation and particle cracking, and promoting uniform utilization of the cathode active material in all-solid-state lithium batteries (ASSLBs). STEM-HAADF combined with nanoscale X-ray holo-tomography and plasma-focused ion beam scanning electron microscopy confirmed that the PEG-based SBL mitigated strain induced by reaction heterogeneity in the cathode. This strain produces lattice stretches, distortions, and the formation of curved transition metal oxide layers near the surface, contributing to structural degradation at elevated voltages. Consequently, ASSLBs with a LiNi0.83Co0.07Mn0.1O2 cathode containing LCCB-10 (CB/PEG mass ratio: 100/10) demonstrate a high areal capacity (2.53 mAh g–1/0.32 mA g–1) and remarkable rate capability (0.58 mAh g–1 at 1.4 mA g–1), with 88% capacity retention over 1000 cycles.

Pushing the Energy-Lifetime Frontier of Li-Ion Batteries: Study of Ni-Rich, Co-Free NMAW Cathode Material

Abstract Dopants and coatings have been widely used to improve the performance of Ni-rich positive electrode active materials. Previous studies have aimed to elucidate the mechanism by which Al and W improve lithium metal oxides, providing valuable insight on the design of enhanced electrode materials for Li-ion batteries. In this work, Al and W are compared as individual dopants as well as co-dopants in order to design an optimal Ni-rich, Co-free material. This involved studying the effect of synthesis temperature in the presence of Al and/or W as well as the effect that these metals have on the morphology of the resultant polycrystalline materials. In addition, structural analysis by X-ray diffraction, electrochemical analysis, and characterization of the mechanical strength of the materials were also conducted. The change in performance with the addition of Al and W depends greatly on particle size and chemical composition. Small sized Ni-rich polycrystalline particles (Ni content of 94%) with low contents of Al (3%) and W (1%) showed the greatest enhancement in energy density with good cycle life.

Improving the Performance of LiNi0.925Co0.065Mn0.01O2 via Ti4+& Nb5+ Co-Modifications.

Ni-rich layer-structured materials are some of the most promising cathodes owing to their attractive reversible capacity and cost-effectiveness. When the Ni content is increased to 90% and higher, mechanical deterioration becomes serious and leads to accelerated cyclic degradation, since removable Li+ is ∼0.85, accompanied by large lattice variation during operation. Here, we investigate the influences of Ti4+ bulky substitution, Nb5+ surface treatment, and their coutilization on the behavior of LiNi0.925Co0.065Mn0.01O2 (NCM92). In contrast to the limited positive effects of monousage, the coutilization of Ti4+ and Nb5+ obviously suppresses particles' pulverization, relying on their synergistic effects of the shape of lattice variation and the protection of a tough shell layer. As a result, Ti & Nb-LiNi0.925Co0.065Mn0.01O2 (TiNb-NCM92) presents the best capacity retention, as high as 90.2% after 300 cycles, much higher than NCM92 (49.0%), Ti-NCM92 (76.3%), and Nb-NCM92 (72.4%). Our approaches demonstrate that the serious mechanical challenges of ultrahigh nickel cathodes could be alleviated by various remedies coutilized together.

Coating Robust Layers on Ni-Rich Cathode Active Materials while Suppressing Cation Mixing for All-Solid-State Lithium-Ion Batteries.

This study focused on addressing the challenges associated with the incompatibility between sulfide solid electrolytes and Ni-rich cathode active materials (CAMs) in all-solid-state lithium-ion batteries. To resolve these issues, protective layers have been explored for Ni-rich materials. Lithium lanthanum titanate (LLTO), a perovskite-type material, is recognized for its excellent chemical stability and ionic conductivity, which render it a potential protective layer in CAMs. However, traditional methods of achieving the perovskite structure involve temperatures exceeding 700 °C, resulting in challenges such as LLTO agglomeration, secondary phase formation between LLTO and CAM, and cation mixing within the CAM. In this study, a rapid technique known as flash-light sintering (FLS) was employed to fabricate a uniform and pure perovskite protective layer without inducing cation mixing within the CAM. The LLTO-coated LiNi0.8Co0.1Mn0.1O2 (NCM811) with FLS treatment demonstrated minimal cation mixing and formed a fully covered dense layer. This resulted in a high initial capacity and effectively addressed the incompatibility issues between the sulfide electrolytes and CAM. The rapid FLS method not only streamlines the fabrication of LLTO-coated NCM811 but also provides opportunities for its broader application to materials that were previously deemed impractical because of high sintering temperatures.

Effect of Cobalt Substitution on the Activation of the LiNiO2 Discharge Reaction.

Cobalt (Co) has been introduced to most of the practical Ni-rich layered positive electrode materials owing to its ability to stabilize the layered structure and lessen cation-mixing. However, it has been unclear whether a highly ordered structure is essential or Co addition itself has some effects. In this study, we synthesized Co-substituted LiNiO2 (LNO) with and without the introduction of cation-mixing to investigate the detailed effects of Co on crystal/local structures and electrochemical properties. It was found that the charge-discharge reversibility of LNO was enhanced by Co substitution with an additional discharge capacity at around 3.5 V, showing that the reaction at the end of discharge was activated. This behavior was observed in Co-substituted LNO even if cation-mixing was largely introduced, implying the intrinsic effect of Co on reversibility. Solid-state NMR results showed that the local structure in LNO with cation-mixing significantly changed after charge-discharge, whereas that of Co-substituted LNO hardly changed even when cation-mixing was introduced, which seems to be responsible for better reversibility. Density functional theory calculation also supports the positive effect of Co on lithium transportation at the end of discharge.

On the Development of a Digital Data Management Platform for Battery Material and Processing Data

Research on battery materials and systems is broader than ever and a large amount of data is being generated. The data collected is often challenging to correlate or compare because they are not compiled in a structured way since no generally uniform data structure exists yet in the battery field. Besides, manufacturing steps and analysis parameters vary enormously from laboratory scale to industrial scale, from research institutions to consortia.Within the "DigiBatMat project" we have created a digital platform for battery material data and processing data that combines collected material data and knowledge within a defined structure based on taxonomies and ontologies. The structure of the digital platform was developed to cover the Battery LabFactory Braunschweig (BLB) pilot-scale production line for lithium-ion cells while being compatible with other battery production processes, for example at the laboratory bench scale. The platform’s underlying data structure is divided into an “electrode production” and “cell production” taxonomy, providing input modules for the most typical battery material and cell characterization methods. This approach offers a commercially available platform with a defined structure, which still allows flexibility for individual electrode and cell productions through option based input. Due to this structure, we aim to go beyond simple data storage by implementing functionalities that allow users to work with and analyze the data within the digital platform. Beside the functionalities we have implemented so far, which are shown here, we also aim to develop further functionalities that enable the identification of new correlations that are otherwise difficult or even impossible to obtain.A consistent data set is necessary to build up and validate such a digital platform. Hence, we specifically generated “reference” data and tested their management and analysis with the platform. We focus on three key use cases of collecting process data and characterizing electrodes and cells properties along the production process. In one of these key use cases we compare state-of-the-art cathodes with Ni-rich active materials, namely NMC811 and NCA. Data are collected from cells with such cathodes with varying loadings and electrode densities. Characterization of the electrodes includes, among other things, microscope data analysis of the microstructure and electrochemical characterization such as electrochemical impedance spectroscopy and rate capability. By showing how raw data can be imported into the database, processed and analyzed, we aim to demonstrate the possibilities and advantages of our digital platform.

Efficacy of atomic layer deposition of Al2O3 on composite LiNi0.8Mn0.1Co0.1O2 electrode for Li-ion batteries

LiNi0.8Mn0.1Co0.1O2 (NMC811) is a popular cathode material for Li-ion batteries, yet degradation and side reactions at the cathode-electrolyte interface pose significant challenges to their long-term cycling stability. Coating LiNixMnyCo1−x−yO2 (NMC) with refractory materials has been widely used to improve the stability of the cathode-electrolyte interface, but mixed results have been reported for Al2O3 coatings of the Ni-rich NMC811 materials. To elucidate the role and effect of the Al2O3 coating, we have coated commercial-grade NMC811 electrodes with Al2O3 by the atomic layer deposition (ALD) technique. Through a systematic investigation of the long-term cycling stability at different upper cutoff voltages, the stability against ambient storage, the rate capability, and the charger transfer kinetics, our results show no significant differences between the Al2O3-coated and the bare (uncoated) electrodes. This highlights the contentious role of Al2O3 coating on Ni-rich NMC cathodes and calls into question the benefits of coating on commercial-grade electrodes.

Na+ orientates Jahn-Teller effect to tune Li+ diffusion pathway and kinetics for Single-Crystal Ni-rich LiNixCoyMn1-x-yO2 cathode materials

Single-crystallization is an effective strategy for enhancing both capacity and stability of Ni-rich LiNi1-x-yCoxMnyO2 (NCM) cathode materials, especially at high cut-off voltages. However, the kinetics limitation of solid-phase Li+ diffusion is a major concern because of the long diffusion path in large single-crystal particles. To address this issue, we synthesize a Na-doped single-crystal LiNi0.82Co0.125Mn0.055O2 (NCM-Na) cathode material by a facile mixed-molten-salt sintering process. Na+ is revealed to be uniformly doped at the Li+ lattice sites within the entire single-crystal particles. This Na+ doping effectively enhances the dynamics of Li+ transport in the layered oxide phases. The NCM-Na material with 2 at.% Na doping shows a Li+ diffusion coefficient up to more than 8 times higher than pristine NCM. In-situ X-ray diffraction and finite element analysis demonstrate significantly facilitated H1-H2-H3 phase transition in NCM-Na materials, compared with the severe phase separation phenomenon in NCM counterpart, hoisting their rate capacity and structure stability. Thus, the NCM-Na material achieves a superior reversible capacity of 177.7 mAh/g at 5C, and a capacity retention of 94.4 % after 100 cycles at 0.5C at a high cut-off voltage of 4.5 V. By density function theory calculations, we reveal that Na+ doping can selectively stabilize the surrounding Li+ at the second farthest hexagonal vertexes by tuning the orientation of the Jahn-Teller effect of Ni3+. These Li+ ions frame a high-speed pathway for preferential Li+ diffusion, which promotes the Li+ diffusion kinetics even in highly delithiated states. Our findings provide insights into the Na+ doping mechanism and present a low-cost, highly efficient, and scalable method to enhance the performance of single-crystal Ni-rich NCM materials.

Zirconium effect on the lithiation mechanism of LiNi0.83Mn0.05Co0.12O2 positive electrode material

Ni-rich LiNi1-x-yMnxCoyO2 (x + y ≤ 0.2) materials are employed to enhance the energy density of lithium-ion batteries, while they are still facing the stability issue. Doping is considered as an efficient approach to improve the stability of the LiNi1-x-yMnxCoyO2 materials. A considerable number of studies have concluded that Zr-doping improves the stability when undoped and doped LiNi1-x-yMnxCoyO2 materials are lithiated under the same conditions. Unfortunately, a fundamental understanding of the Zr dopants role during lithiation conditions is still lacking. This work investigates the Zr effects on lithiation mechanism of LiNi0.83Mn0.05Co0.12O2 (NMC). The main findings are: First, the NMC and Zr-doped NMC have different lattice parameter growth speeds, and the (003) & (101) lattice planes form order structures at lower temperatures during lithiation process when the dopant is included. Second, Zr is prone to locate near the surface region of NMC secondary particles. Third, when lithiation time increases from 8 h to 12 h at 800 °C, the undoped NMC electrochemical performance deteriorates whereas the doped material improves. These findings highlight that understanding the mechanism behind lithiation conditions is essential for doped LiNi1-x-yMnxCoyO2. The insights revealed in this work can guide for design of other dopants for Ni-rich positive electrode materials.

Mitigating kinetic hindrance of single-crystal Ni-rich cathodes through morphology modulation, nickel reduction, and lithium vacancy generation achieved by terbium doping

Single crystallization has proven to be effective in enhancing the capacity and stability of Ni-rich LiNi1−x−yCoxMnyO2 (SNCM) cathode materials, particularly at high cut-off voltages. Nevertheless, the synthesis of high-quality single-crystal particles remains challenging because of severe particle agglomeration and irregular morphologies. Moreover, the limited kinetics of solid-phase Li+ diffusion pose a significant concern because of the extended diffusion path in large single-crystal particles. To address these challenges, we developed a Tb-doped single-crystal LiNi0.83Co0.11Mn0.06O2 (SNCM-Tb) cathode material using a straightforward mixed molten salt sintering process. The Tb-doped Ni-rich single crystals presented a quasi-spherical morphology, which is markedly different from those reported in previous studies. Tb4+ doping significantly enhanced the dynamic transport of Li+ ions in the layered oxide phase by reducing the Ni valence state and creating Li vacancies. A SNCM-Tb material with 1 at% Tb doping shows a Li+ diffusion coefficient up to more than 9 times higher than pristine SNCM in the non-diluted state. In situ X-ray diffraction analysis demonstrated a significantly facilitated H1-H2-H3 phase transition in the SNCM-Tb materials, thereby enhancing their rate capacity and structural stability. SNCM-Tb exhibited a reversible capacity of 186.9 mA h g−1 at 5 C, retaining 94.6% capacity after 100 cycles at 0.5 C under a 4.5 V cut-off. Our study elucidates the Tb4+ doping mechanisms and proposes a scalable method for enhancing the performance of single-crystal Ni-rich NCM materials.

Role of transition metal ratio on electrochemical and thermal properties of LiNixCoyMnzO2 layered materials for lithium-ion batteries

To reveal how the performance of LiNixCoyMnzO2 (NCM) changes as a function of transition metal (TM) composition, the effect of TM ratio on the structure, morphology, electrochemical performance and thermal behavior of different NCMs was systematically investigated. Increasing Ni content leads to higher reversible capacity but worse rate capability and cycling stability. Inhibited kinetics of Li+ and poor electronic conductivity cause major capacity loss in Ni-rich NCMs. Comparison of thermal behaviors was carried out via in-situ and ex-situ micro-calorimetry. With the decrease of Ni content, the thermal stability is significantly improved. The oxygen release related to phase transitions was evaluated based on Li residuals in delithiated NCMs, which verifies that Ni-rich materials exhibit severer structural deterioration, lower onset temperature and more heat release. Comprehensive characterization identifies that LiNi0.5Co0.3Mn0.2O2 strikes a well-balanced combination of electrochemical performance and safety features.

The dual modification of La and Zr of Ni-rich cathodes for improved cycling stability at elevated voltage and temperature

Nickel-rich layered oxides are regarded as a promising cathode material for next-generation lithium-ion batteries (LIBs) with advanced power capabilities. However, their poor cycling performance, especially under high voltage and temperature conditions, has seriously limited their large-scale application. In this work, a simple and effective strategy is proposed to enhance the structural and interface stability of Ni-rich materials by La4NiLiO8 coating and Zr doping. The interfacial side reactions and intergranular microcracks of the modified material are inhibited, which is helpful in improving the electrochemical performance. Therefore, the initial capacity of dual modification of La and Zr of Ni-rich cathode is 196.4 mA h g−1 at 4.5 V and exhibits excellent cycling performance with a capacity retention of 82.1 % after 200 cycles. Moreover, at 50 °C, the initial capacity of the modified material is 239.0 mA h g−1, and the capacity retention is 63.1 % after 100 cycles, representing a significant improvement of 94.8 % over the unmodified sample.

Organic coating strategy with oxidized oxygen anion capture to suppress lattice oxygen evolution of Ni-rich cathode materials at high voltage

Ni-rich layered oxide has attracted widespread attention due to its high capacity of over 200 mAh·g−1 at 4.5 V. However, how to solve its lattice oxygen evolution problem during high-voltage cycling remains the major challenge nowadays. It is still important to design stable and efficient Ni-rich layered oxides. Herein, an organic coating strategy was proposed for this challenge. Specifically, (C3H3N)n (PAN) was employed as a proof-of-concept organic coating with better electro-negativity on LiNi0.8Co0.1Mn0.1O2 to inhibit the lattice oxygen evolution. The CN functional groups in the PAN coating can adsorb Oα− (α < 2) and provide it with electrons for its reduction to stable O2−, thus inhibiting the continuous outward migration. As expected, in a voltage range of 2.7–4.5 V, the modified Ni-rich electrode displayed a high-capacity retention of 86.3 % after 200 cycles at 1C, 75.1 % after 350 cycles at 5C, and 83.1 % after 100 cycles at 1C and 55 °C. Furthermore, it also exhibited a high discharge specific capacity of 235.3 mAh·g−1 with a capacity retention of 75.5 % after 200 cycles under a cut-off voltage of 4.7 V. This innovative organic coating strategy presents new insights into suppressing the lattice oxygen evolution under high-voltage cycling by manipulating the surface chemistry of Ni-rich materials.

Nickel-rich ternary cathode material as a novel capping layer to improve lithium iron phosphate electrochemical performance

We use a facile high-temperature solid-phase method to coat a layer of Ni-rich ternary material (LiNi0.8Co0.1Mn0.1O2) on the surface of lithium iron phosphate. This active coating greatly improves the intrinsic conductivity of LiFePO4. Compared to the conventional carbon material cladding, since this cladding layer is electrochemically active, the problem of decreasing the proportion of active material due to the addition of a cladding layer can be avoided to a certain extent. Compared with the samples capped with conventional organic carbon source (151.2 mAh g−1) and inorganic carbon source (155.9 mAh g−1) at 0.2 C, the discharge specific capacity was as high as 165.7 mAh g−1. Capacity retention after 200 cycles is up to 98 %, which is much higher than that of glucose and graphene oxide (GO)-coated samples (95.9 %, 96.6 %). Even when charging and discharging cycles are performed at different multipliers (2C and 10C), the retention rate remains higher than the latter.