Ni-rich Layered Oxide Cathode Research Articles

Graphene collage on Ni-rich layered oxide cathodes for advanced lithium-ion batteries

The energy storage performance of lithium-ion batteries (LIBs) depends on the electrode capacity and electrode/cell design parameters, which have previously been addressed separately, leading to a failure in practical implementation. Here, we show how conformal graphene (Gr) coating on Ni-rich oxides enables the fabrication of highly packed cathodes containing a high content of active material (~99 wt%) without conventional conducting agents. With 99 wt% LiNi0.8Co0.15Al0.05O2 (NCA) and electrode density of ~4.3 g cm-3, the Gr-coated NCA cathode delivers a high areal capacity, ~5.4 mAh cm−2 (~38% increase) and high volumetric capacity, ~863 mAh cm-3 (~34% increase) at a current rate of 0.2 C (~1.1 mA cm-2); this surpasses the bare electrode approaching a commercial level of electrode setting (96 wt% NCA; ~3.3 g cm-3). Our findings offer a combinatorial avenue for materials engineering and electrode design toward advanced LIB cathodes.

Nanowelding to Improve the Chemomechanical Stability of the Ni-Rich Layered Cathode Materials

To satisfy the increasing energy density requirements for electric vehicles and grid-scale energy storage systems, Ni-rich layered oxide cathode materials are often fabricated as micron-sized secondary spherical particles consisting of nanosized single crystals. Unfortunately, the hierarchical structure inevitably induces intergranular cracks and parasitic reactions at the cathode-electrolyte interphase, aggravating chemomechanical instability and seriously hindering their practical application. Here, we propose a nanowelding strategy to build consolidation points at the grain boundary of the primary particles, which dramatically enhances the capacity retention and chemomechanical stability. Meanwhile, the oxygen vacancies in the ceria-based solid electrolyte possessing oxygen adsorbing and storage capability can restrain the active oxygenates in the surficial lattice to avoid oxygen evolution. Experimental characterization further confirms that this unique architecture can effectively prevent the liquid electrolyte from penetrating into the active material along the grain boundary and consequently eliminate the adverse effects, including intergranular cracks, cathode electrolyte interface formation and growth, and the layered structure-rock salt phase irreversible transition. This finding provides a promising approach to realize the rapid commercialization of highly stabilized nickel-rich cathode materials for high-performance lithium-ion batteries.

Fundamental and solutions of microcrack in Ni-rich layered oxide cathode materials of lithium-ion batteries

Ni-rich layered transition metal oxide is one of the most promising cathode materials for the next generation lithium-based automotive batteries due to its excellent electrochemical performances. Nevertheless, its further applications are capped by the structural/interfacial instability during the prolonged charging/discharging, leading to severe performance fading and serious safety concerns. Here, we provide a comprehensive review about challenges and solutions to modify Ni-rich layered cathodes specifically for microcrack failure. Firstly, the mechanism of microcrack formation and evolution are concluded thoroughly. Secondly, recent advances in stabilizing the structure/interface of Ni-rich cathodes are summarized such as surface coating, cation/anion doping, composition tailoring, morphology engineering and electrolytes optimization. Furthermore, strategies to mitigate the microcrack and then boost the electrochemical performance of Ni-rich cathodes at the chemical & mechanical engineering level are presented. More importantly, outlook and perspectives to facilitate the practical application of Ni-rich layered cathodes toward electrical vehicle application are provided as well. The information compiled herein can promote the understanding of the microcracks of Ni-rich cathode materials, including its fundamental science, characterization method, and strategies for designing crack-free Ni-rich cathode materials. Furthermore, we provide a new idea for material modification, which is perspective strategy from crystallographic, structural mechanics and chemistry under the guidance of “chemical-mechanical” effect. • The mechanism of microcrack formation and evolution are concluded. • Recent advances in stabilizing the structure/interface of Ni-rich cathodes are summarized. • Strategies to mitigate the microcrack and then boost the electrochemical performance of Ni-rich cathodes are presented. • Main challenges and the future horizons are outlooked.

Enabling stable and high-rate cycling of a Ni-rich layered oxide cathode for lithium-ion batteries by modification with an artificial Li+-conducting cathode-electrolyte interphase

An artificial Li+-conducting cathode-electrolyte interphase is successfully built on a NCM811 cathode surface through a nucleophilic reaction between polysulfides and vinylene carbonate.

Stabilization of a Highly Ni-Rich Layered Oxide Cathode through Flower-Petal Grain Arrays.

Nickel adds to the capacity of layered oxide cathodes of lithium-ion batteries but comprises their stability. We report a petal-grained Li[Ni0.89Co0.10Sb0.01]O2 cathode that is, nevertheless, stable. The stability originates from the ordering of the nanosized grains in a dense, flower-petal-like array, where the elongated and nearly parallel grains radiate from the center to the surface. The ordering of the grains prevents microcrack generation from abrupt lattice changes of the stressful H2-H3 phase transition. The tight packing of the nanograins is conserved upon cycling, preventing destructive seepage of the electrolytic solution into the particles. The half-cell, cycling between 2.7-4.3 V versus Li/Li+ at a 0.5 C rate retains 95.0% of its initial capacity of 220 mAh g-1 after 100 cycles. The full-cell, cycling with a graphite anode and between 3.0-4.2 V at a 1 C rate, retains 83.9% of its initial capacity after 1000 cycles.

Non-Equilibrium Lattice Heterogeneity As the Unified Kinetic Hurdle of Ni-Rich Layered Cathode for Ultrafast Lithium Ion Batteries

The significantly reduced capacity at a fast cycling rate is one of the most serious bottlenecks that prevent the large-scale application of Ni-rich layered oxide cathode for electrical vehicle batteries. Figuring out the capacity decline mechanism is crucial to addressing such hurdle and developing ultrafast lithium ion batteries. In this work, with operando synchrotron-based spectroscopy, we captured the formation of non-equilibrium separated phases during the extremely fast cycling of various Ni-rich layered oxides, in contrast to their solid-solution structural evolution pathway at slow cycling rate. Further, such non-equilibrium phase heterogeneity was demonstrated to be an effective capacity retention descriptor for Ni-rich layered oxide cathode: the capacity retention ratio is liner inversely proportional to the lattice heterogeneity at an extremely fast cycling rate (e.g., 10C), regardless of the composition and Ni content. Those detrimental non-equilibrium phase heterogeneity could be eliminated by raising the operation temperature, contributing to much higher lithium ion transport kinetics and better capacity retention during ultrafast cycling

High-Performance and Industrially Feasible Ni-Rich Layered Cathodematerials By Integrating Coherent Interphase

For developing the industrially feasible Ni-rich layered oxide cathode with extended cycle life, it is necessary to mitigate both the mechanical degradation due to intergranular cracking between primary particles and gasgeneration from the reaction between the electrolyte and residual Li in the cathode. To simultaneously resolve these two issues, we herein propose a simple but novel method to reinforce the primary particles in LiNi0.91Co0.06Mn0.03O2 by providing a Li-reactive material, whose spinel interphase is coherent with the surface of the cathode. The modified structure significantly outperforms analogous bare samples: they conserve more than90% of the initial capacity after 50 cycles and also exhibit a greater rate capability. By tracking the same particle location during cycling, we confirmed that the current method significantly reduces crack generation because theprovided coating material can penetrate inside the grain boundary of the secondary particle and help maintain the volume of the primary particle. Finally, first-principles calculations were implemented to determine the role of this spinel material, i.e., having intrinsically isotropic lattice parameters, superior mechanical properties, and only a small volume change during delithiation. We believe that the proposed method is straightforward and cost-effective; hence, it is directly applicable for the mass production of Ni-rich cathode material to enable its commercialization. Figure 1

Surface-Dependent Stress-Corrosion Cracking in Ni-Rich Layered Oxide Cathodes

Structural degradation is the principal driving force for rapid voltage decay and capacity fading of Ni-rich layered oxide (NLO) cathode materials upon cycling, but its working mechanism is not yet fully elucidated. Here we apply multi-scale electron microscopy/spectroscopy techniques and theoretical calculations on both polycrystalline and single-crystal NLOs, and describe their structural evolution upon cycling. We discover that both the intergranular and intragranular cracks initiate along polar (001) basal plane due to its large elastic anisotropy upon cycling and surface structure evolution and transition metal dissolution occur on nonpolar (104) fresh surface. With this surface-dependent stress-corrosion coupling effect, severe intergranular cracking that accumulates within the polycrystalline NLO aggregates accounts mostly for the fast voltage decay and capacity fading, whereas minor intragranular cracking and less surface damage lead to substantial improvements on cyclability and reversible capacity of single-crystal NLOs. A universal understanding of the surface-dependent degradation in both polycrystalline and single-crystal NLOs provides clues on designing new cathode materials with high energy density and long cycle life through grain-boundary engineering.

Correlating the phase evolution and anionic redox in Co-Free Ni-Rich layered oxide cathodes

Abstract Current trend of high-capacity Ni-rich layered cathode is to develop high-Ni and low-Co or Co-free oxides. The high Ni content layered oxides provide great advantages in capacity, cost and environmental benignity, similar to LiNiO2 parent compound. But they also inherit drawbacks in structural and chemical instability at high voltages upon cycling. Elemental substitution plays a profound role in addressing these challenges. This work elucidates the roles of Al doping in cationic redox and anionic oxygen activity in LiAlxNi1-xO2 using combined X-ray absorption spectroscopy (XAS), resonant inelastic X-ray scattering (RIXS) as well as operando differential electrochemical mass spectrometry (DEMS). Using synchrotron wide-angle X-ray scattering (WAXS), we extrapolate a general principle of phase transition and its coupling with lattice anionic oxygen redox. These findings shed light on the advancement of high-capacity, stable-cycling and safe-operating Ni-rich cathode materials for next generation Li-ion batteries.

Hydrothermal preparing agglomerate LiNi0.8Co0.1Mn0.1O2 cathode material with submicron primary particle for alleviating microcracks

Ni-rich layered oxides LiNixTM1-xO2 (TM = Co, Mn, Al, x > 0.6) cathode materials for lithium-ion batteries have an anisotropic volume change during lithium deintercalation process, which easily causes microcracks and rapid capacity decay. In the paper, carbonate precursor prepared by a urea-based hydrothermal method is lithiated at different temperatures of 750–850 °C to obtain agglomerate LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material with different primary sizes. The sample synthesized at 750 °C shows broadening diffraction peaks due to its near-nano grain size, which results in the merging of (006)/(012) and (018)/(110) peaks. The effect of anisotropic volume shrinkage is effectively weakened by fine grain range, which alleviates formation of intergranular crack that is commonly considered as an important reason for capacity decay of Ni-rich layered oxide cathode materials. In addition, two new types of intragranular microcracks are first identified in cyclic NCM811. One extends along the spinel phase and layered phase interface, and the other extends along the vertical (003) R crystal plane. The difference in atomic plane spacing during the electrochemical cycles plays a key role in the growth of intragranular microcracks.

Stabilizing effects of Al-doping on Ni-rich LiNi0.80Co0.15Mn0.05O2 cathode for Li rechargeable batteries

Ni-rich layered oxide cathodes with Ni content above 80% have considerable potential for Li rechargeable batteries due to their high capacity and low cost. However, what with stability issues, inferior cycle performance and thermal instability, studies are still underway to improve their performance. Herein, Al-doped Ni-rich (LiNi0.80Co0.15Mn0.05O2) cathode is investigated to stabilize structural, electrochemical, and thermal properties. Compared to undoped one, Al-doped Ni-rich cathode exhibits lower polarization potential, better rate capability, and cyclability. This can be attributed to the alleviation of anisotropic lattice changes and volume changes during cycling. More importantly, Al-doped Ni-rich cathode maintains a wider LiO6 interslab thickness without collapse at highly charged states, allowing Li-ions to be deintercalated/intercalated reversibly. This indicates that rigid structural integrity contributes to enhanced electrochemical performance. Furthermore, Al-doping improves thermal stability by delaying the onset temperatures of phase transformations during the heating process. These results demonstrate that Al-doping plays a major role in stabilizing the structure by suppressing abrupt lattice changes during cycling and the formation of a rock-salt phase during thermal decomposition reaction. Therefore, this study provides structural aspects of Al-doping effects on the stabilization of layered cathode materials for the high energy density of rechargeable batteries.

Improved high-voltage performance of LiNi0.87Co0.1Al0.03O2 by Li+-conductor coating

Ni-rich layered oxide cathode material is extensively studied as promising cathode material in high-energy lithium ion batteries. However, capacity decay, poor rate performance and thermal instability are critical challenges for commercialization. Herein, Ni-rich layered oxide cathode material (LiNi0.87Co0.1Al0.03O2) is synthesized via oxide precursor and further modified by amorphous Li+-ion conductor Li2O-BPO4 (LBP) coating. The LBP coating layer can facilitate the transfer of Li+ across the solid-electrolyte interface, reduce the side reaction between the cathode-and electrolyte as well as decrease cation mixing. Therefore, the NCA coated by LBP displays the improved cycling performance due to the increased interfacial stability, the decreased polarization and the intensified Li+ transport kinetics. Especially, 0.5 wt% LBP coated NCA (NCA@LBP-2) possesses the good capacity retention of 92.3% at 1C in 2.7–4.3 V and 76.2% at high-voltage in 2.7–4.7 V. Moreover, the sample shows an outstanding rate capability even after cycled at 10C. Hence, this effective coating strategy on Ni-rich cathode material improves the cycling stability and rate capability under high-voltage condition and shows a good application prospect in the practical production of NCA.

Enhanced cycling stability of nickel-rich layered oxide by tantalum doping

Ni-rich layered oxide cathode material is considered as a promising cathode material in Li-ion batteries owing to their high specific capacity. However, it suffers from poor cycling performance which hinder their commercial applications. The unstable oxygen retention is one of the main causes of structural deformation as well as lower cycling stability. Herein, a simple high-temperature solid state method is utilized to synthesize surface tantalum doped Ni-rich layered oxide cathode material (LiNi0.88Co0.09Al0.03O2) due to the stronger bond between Ta–O which intensifies the TM-O layer due to the positioning of Ta5+ in the TM layer. In the meantime, based on density functional theory (DFT) calculations it has been confirmed that the Ta-doped structure exhibits metallic behavior and lower Fermi level therefore it acquires better phase stability. The 1 wt% Ta-doped NCA (T2-NCA) reveals the best cycling performance of about 93% (4.3V at 1C). Even, it retains good cycling stability of 75% at high voltage (4.5 V) and 97.7% at high C-rate (5C). Therefore, a small amount of Ta surface doping on NCA plays an unneglectable role for enhancing the initial discharge capacity and cycling stability.

Probing Thermal Stability of Li-Ion Battery Ni-Rich Layered Oxide Cathodes by means of Operando Gas Analysis and Neutron Diffraction

Thermal stability is a crucial parameter that must be considered within the overall performance metrics of Ni-rich layered oxide cathodes. While the intrinsic structural stability of the cathode ma...

Uniform Coating of Se on Selenophilic Surfaces of Nickel-Rich Layered Oxide Cathode Materials for High Performance Li-Ion Batteries

A novel and uniform Se coating layer on the selenophilic surface of the Ni-rich layered metal oxide (LNCM) cathode material was constructed via a facile melt-diffusion approach. The high selenophilicity of the LNCM surfaces should attribute to the strong interactions of the exposed Ni, Co, and Mn atoms with Se coating through the formation of metal–Se bonds, resulting in the conformal and homogenous deposition of Se layers. The uniform Se coating layers could not only protect the Ni-rich LNCM cathode materials from the side reaction with the electrolytes but also reduce the degree of Li+/Ni2+ cation disorder. Therefore, owing to the multifunctional effects of Se coating, the Se-coated LNCM811 cathode materials exhibit excellent cyclic stability and rate performances with a high initial capacity of 205 mA h g–1 at 0.2 C and the high reversible capacities of 173 mA h g–1 at the 100th cycle at 0.2 C, 132 mA h g–1 at 200th cycle at 2 C, and 103 mA h g–1 at 300th cycle at 5 C. This present work indicates that the Se coating on the advanced Ni-rich layered metal oxide cathode material through the facile melt-diffusion approach should be promising for the high performance Li-ion battery.

Sulfonate-Based Artificial Cathode–Electrolyte Interface to Enhance Electrochemical Performance of Ni-Rich Layered Oxide Cathode Materials

Despite significant progress in the field of Li-ion battery development over the past 30 years, challenges associated with the gradual shift from small-scale to large-scale battery applications nec...

Gas Evolution in Lithium-Ion Batteries: Solid versus Liquid Electrolyte.

Gas evolution in conventional lithium-ion batteries using Ni-rich layered oxide cathode materials presents a serious issue that is responsible for performance decay and safety concerns, among others. Recent findings revealed that gas evolution also occurred in bulk-type solid-state batteries. To further clarify the effect that the electrolyte has on gassing, we report in this work-to the best of our knowledge-the first study comparing gas evolution in lithium-ion batteries with NCM622 cathode material and different electrolyte types, specifically solid (β-Li3PS4 and Li6PS5Cl) versus liquid (LP57). Using isotopic labeling, acid titration, and in situ gas analysis, we show the presence of O2 and CO2 evolution in both systems, albeit with different cumulative amounts, and possible SO2 evolution for the lithium thiophosphate-based cells. Our results demonstrate the importance of considering gas evolution in solid-state batteries, especially the formation and release of highly corrosive SO2, due to side reactions with the electrolyte.

Outstanding electrochemical performances of the all-solid-state lithium battery using Ni-rich layered oxide cathode and sulfide electrolyte

Although Ni-rich layered oxides with high specific capacity are considered to have potential application in all-solid-state lithium batteries (ASSLB) using sulfide electrolyte, the Ni-rich layered oxide/sulfide electrolyte interfacial instability is still a serious issue. To effectively improve the interfacial stability and electrochemical performances, LiNi0·8Co0·1Mn0·1O2 (NCM) precursor is for the first time coated with nano-thickness LiCoO2 (LCO) precursor to form core-shell NCM@LCO precursor, which is then calcined to form NCM@LCO material with Ni-poor surface. Subsequently a small amount of LiNbO3 (LNO) is further coated on the surface of NCM@LCO particles to form NCM@LCO@LNO material. As expected, NCM@LCO@LNO cathode displays the outstanding electrochemical performances especially cycle stability (capacity retention of 80% after 585 cycles at 0.612 mA cm−2), indicating that this strategy is very effective to construct high performance Ni-rich layered oxide cathodes for ASSLB using sulfide electrolyte. To our knowledge, the excellent results are firstly reported in the references related to ASSLB using sulfide electrolyte. Moreover, the performance improvement mechanism is also investigated by Raman spectra in combination with cyclic voltammetry. Our study reveals that this strategy can effectively suppress the irreversible phase transformation and interface side reaction for Ni-rich layered oxides.

In/ex-situ Raman spectra combined with EIS for observing interface reactions between Ni-rich layered oxide cathode and sulfide electrolyte

Abstract The interfacial instability between Ni-rich layered oxide cathodes and sulfide electrolytes is a serious problem, leading to poor electrochemical properties of all-solid-state lithium batteries (ASSLB). The chemical/electrochemical side reactions are considered to be the origin of the interfacial deterioration. However, the influence of chemical and electrochemical side reactions on the interfacial deterioration is rarely studied specifically. In this work, the deterioration mechanism of the interface between LiNi0.85-xCo0.15AlxO2 and Li10GeP2S12 is investigated in detail by combining in/ex-situ Raman spectra and Electrochemical Impedance Spectroscopy (EIS). It can be determined that chemical side reaction between LiNi0.8Co0.15Al0.05O2 and Li10GeP2S12 will occur immediately once contacted, and the interfacial deterioration becomes more serious after charge-discharge process under the dual effects of chemical and electrochemical side reactions. Moreover, our research reveals that the interfacial stability and the cycle performance of ASSLB can be greatly enhanced by increasing Al-substitution for Ni in LiNi0.85-xCo0.15AlxO2. In particular, the capacity retention of LiNi0.6Co0.15Al0.25O2 cathode after 200 cycles can reach 81.9%, much higher than that of LiNi0.8Co0.15Al0.05O2 cathode (12.5%@200 cycles). This work gives an insight to study the interfacial issues between Ni-rich layered oxide cathode and sulfide electrolyte for ASSLBs.

Dual-functional interfaces for highly stable Ni-rich layered cathodes in sulfide all-solid-state batteries

All-solid-state lithium-ion batteries (ASSLIBs) are expected as safe and high-performance alternatives to replace the conventional liquid-based lithium-ion batteries. However, the incompatible interface between the most cathode materials and sulfide-based solid electrolytes is still challenging the stable delivery of electrochemical performance for ASSLIBs. Herein, a dual-functional Li3PO4 (LPO) modification is designed for Ni-rich layered oxide cathodes in sulfide-based ASSLIBs to realize the high performance. The modified cathode demonstrates a significantly improved initial capacity of 170.6 ​mAh g-1 at 0.1C, better rate capability, and reduced polarization compared to the bare cathode. More importantly, a stable long-term cycling is achieved with a low capacity degradation rate of 0.22 ​mAh g-1 per cycle for 300 cycles at 0.2C. The detailed surface chemical and structural evolutions are studied via X-ray absorption near edge spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The results indicate that the LPO modification not only significantly suppresses the side-reactions with sulfide electrolyte but also helps to alleviate the deterioration of the microstructural cracks during the electrochemical reactions. This work provides an ideal and controllable interfacial design for realizing high performance sulfide-based ASSLIBs, which is readily applicable to other solid-state battery systems.