Nickel-rich Layered Oxide Cathodes Research Articles

Synthesis design of interfacial nanostructure for nickel-rich layered cathodes

High-energy nickel-rich layered oxide cathodes are one kind of the promising materials to electric vehicles powered by lithium-ion batteries. However, grain boundary structure and chemistry disintegration show the most serious challenges for these cathodes at long-term cycles, particularly under extreme temperatures and high voltages. Herein, we present a sustainable synthesis route to achieve a uniform surface/interface-coating of nickel-rich layered oxide secondary particles as well as grain boundaries. The obtained cathodes demonstrate dramatically enhanced rate capability and cycling stability in a wide temperature range from −40 ℃ to 60 ℃ even charged to the high cut-off voltage of 4.5 V. Moreover, the cathodes display a high humidity tolerance with scarcely any sign of impurity after exposure to an atmosphere with 98% relative humidity. The highly dense and resistive fluorine- and cobalt-rich interphase structures can effectively protect the particles from the simultaneous degradation of surface structure and side reactions with electrolytes at cycling. This facile interfacial nanostructure is further demonstrated with lower interface energy, facilitating the lithium-ions transport with lower interface impedance and improved stability. Thereby, this synthesis perspectives provide the new insights of nickel-rich lithium cathodes at grain boundary dimensions.

Mussel-inspired polydopamine-assisted uniform coating of Li+ conductive LiAlO2 on nickel-rich LiNi0.8Co0.1Mn0.1O2 for high-performance Li-ion batteries

A Li+ conductive LiAlO2 coating layer was uniformly covered on the surfaces of a nickel-rich LiNi0.8Co0.1Mn0.1O2 cathode material through a mussel-inspired, adhesive polydopamine-assisted approach. The adhesive and uniform PDA pre-coating on the Ni0.8Co0.1Mn0.1(OH)2 microspherical surfaces could act as a superior mediator to conformally concentrate the Al3+ precursor on the microsphere surfaces through chemical complexation, thus resulting in a uniform LiAlO2 coating on the LiNi0.8Co0.1Mn0.1O2 microspherical surfaces. The PDA-assisted uniform coating layer of Li+ conductive LiAlO2 could offer multifunctional effects, including effective prohibition of side-reactions between the LiNi0.8Co0.1Mn0.1O2 and electrolyte, significant suppression of the Li/Ni mixing in the LiNi0.8Co0.1Mn0.1O2 crystal lattices, and high Li-ion conductivity for fast electrochemical reactions. Therefore, the PDA-assisted LiAlO2 coated LiNi0.8Co0.1Mn0.1O2 cathode material ([email protected]) presents outstanding cycling stability and rate performance with high discharge capacity of 209 mAh/g at the 1st cycle at the current rate of 0.2 C, 178 mAh/g at the 100th cycle at the current rate of 0.2 C, 138 mAh/g at the 200th cycle at the current rate of 2 C, and 114 mAh/g at the 200th cycle at the current rate of 5 C. These encouraging results demonstrate that the mussel-inspired, adhesive PDA-assisted uniform coating of Li+ conductive LiAlO2 is a promising strategy to achieve high performance of nickel-rich layered oxide cathode material for advanced Li-ion secondary batteries.

Enhanced homogeneity of electrochemical reaction via low tortuosity enabling high-voltage nickel-rich layered oxide thick-electrode

Inhomogeneous electrochemical reactions during the charging-discharging process of high-voltage nickel-rich layered oxide cathodes play a major role in cracks formation and deteriorating cyclability. Especially in thick electrodes, the severe concentration polarization aggravates the inhomogeneity and further diminishes the cycle life. In this work, a low-tortuous thick electrode of LiNi0.7Co0.1Mn0.2O2 (NCM712) is constructed by the ice-templating strategy and the effect of low tortuosity on electrochemical performance is investigated. Low-tortuous NCM712 electrode exhibits reduced concentration polarization and fast lithium-ion transport kinetics, consequently enabling superior rate capability. Furthermore, benefiting from the effective electronic and ionic transport network in low-tortuous thick electrode, NCM712 particles present homogeneous electrochemical reaction and alleviated intragranular stress, which suppresses cation mixing and cracking formation at high voltage condition. The homogeneity of electrochemical reaction in the low-tortuous thick electrode is favorable to attain the structural integrity, the robust electrolyte interface and superior cyclability. This strategy provides a new concept to homogenize the electrochemical reaction of thick nickel-rich layered oxide electrodes by low tortuosity electrode architecture design, leading to superb electrochemical performance with high energy density.

Chemical and Structural Evolution During Solid-State Synthesis of Cobalt-Free Nickel-Rich Layered Oxide Cathode

Chemical and Structural Evolution During Solid-State Synthesis of Cobalt-Free Nickel-Rich Layered Oxide Cathode

Anchoring Interfacial Nickel Cations by Tunable Coordinative Structure for Highly Stabilized Nickel-Rich Layered Oxide Cathodes

Ni-rich LiNixCoyMn1−x-yO2 (NCM) cathode materials have received extensive attention on account of their high specific capacities and great application prospects in electric vehicles. While increasing Ni content in NCM can greatly increase initial discharge capacities, more highly reactive Ni4+ species in the delithiated state may facilitate irreversible phase transformation and undesirable interfacial reactions, leading to severe capacity degradation. Here we demonstrate an organic surface modification approach to modulate the surface coordinative structure of NCM cathode for enhanced cycling stability. We discover that the highly reactive Ni4+ cations can be anchored by strong electron-donating organic groups, especially under bidentate coordination, which mitigates excessive electrolyte decomposition and Ni dissolution into the electrolyte, inhibits the layered-to-rock salt phase transformation and suppresses the initiation and propagation of microcracks within the NCM cathodes. In consequence, the nickel-rich cathode coated with poly (acetoacetoxyethyl methacrylate) (PAAEM) with multiple ester groups exhibits a remarkable improvement in cycling stability, showing 91.3% retention of the initial capacity after 200 cycles. The present findings demonstrate that regulating surface coordinative structure is an efficient and practical strategy to modify the interfacial reactions for enhanced cyclability in Ni-rich layered oxide cathodes.

Nanoscale state-of-charge heterogeneities within polycrystalline nickel-rich layered oxide cathode materials

Nickel-rich cathodes (LiNi x Mn y Co 1-x-y O 2 , x > 0.6) permit higher energy in lithium-ion rechargeable batteries but suffer from accelerated degradation at potentials above 4.1 V versus Li/Li + . Here, we present a proof-of-concept in situ pouch cell and methodology for correlative 2D synchrotron transmission X-ray microscopy with 3D lab-based micro-CT. XANES analysis of the TXM data enables tracking of Ni edge energy within and between the polycrystalline NMC811 particles embedded in the operating electrode through its initial delithiation. By using edge energy as a proxy, state-of-charge heterogeneities can be tracked at the nanoscale, revealing the role of cracked particles as potential nucleation points for failure and highlighting the challenges in achieving uniform (de-)lithiation. We propose, in future work, to leverage the pouch cell design presented here for longitudinal TXM-XANES studies of nickel-rich cathodes across multiple cycles and operating variables and investigate the effect of dopants and microstructural optimization in mitigating degradation. In situ pouch cell design that is adaptable to various characterization methods Combined lab-based micro-CT and synchrotron XANES imaging approach Insights into spatio-temporal dependence of degradation in NMC811 There is significant interest in the energy storage community for in situ studies because of the codependence of spatial and temporal effects on the performance of an electrochemical cell. Tan et al. report a tab pouch cell design that maintains fidelity to commercially relevant cells while still allowing 3D measurements at the nanoscale.

Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

Optimizing the interface engineering and structural stability of nickel-rich layered oxide cathode by dual-function modification

Nickel-rich layered LiNi1-x-yCoxMnyO2 (1-x-y ≥ 0.6) cathode material has the advantage of high energy density, which is one of the hot topics in the field of new energy technology. Nonetheless, the nickel-rich layered oxide has serious interfacial and structural problems, resulting in unsatisfactory cycle performance and safety performance, which hinders large scale applications in the field of lithium-ion batteries. Here, a double modified LiNi0.82Co0.13Mn0.05O2 cathode material was prepared by a simple synthesis process with Zr4+ doping and LiBO2 coating, and has shown outstanding electrochemical performance. The initial discharge specific capacity is 200.8 mAh/g at 0.1C, and the capacity retention rate is also as high as 90.8% after 250 cycles at 1C. In-situ X-ray diffraction tests and density-functional theory calculations further reveal that the bulk Zr4+ doping is not only beneficial to maintain the stability of the crystal structure, but also to optimize the energy band structure of the material and increase the migration rate of lithium-ion. Moreover, the LiBO2 coating on the surface can effectively prevent the active material from directly contacting the electrolyte, and inhibit side reactions. The concept of “thick electrode” is introduced, and assembled into a pouch-type full cell with graphite as the anode, the high energy density is 302.8 Wh/kg and the retention rate after 1000 cycles is more than 80%. The safety performance test also shows that the nickel-rich layered oxide cathode has broad commercial potential application prospects.

Elevated stability of nickel-rich oxide cathode material with concentration gradient of transition metals via a novel size-controllable calcination method

Consumers are increasingly demanding the range and safety of the electric vehicles. Nickel-rich layered lithium transition-metal oxide cathode material with Ni content exceeding 80% has attracted extensive attention due to its high capacity. To suppress the decrease of cyclic and thermal stability due to the increase of nickel content, LiNi0.87Co0.06Mn0.07O2 particles with transition metal concentration gradient from the interior to the surface are realized. An efficient and low-cost method is proposed involves firstly forming the shell layer with low nickel content by a dry mechanofusion process and subsequently adopting a novel particle size-controllable calcination course. Through which a concentration gradient layer with a thickness of 1 µm is successfully formed, and the particle size of primary particles is effectively controlled at the range of 250–300 nm. The relationship between the calcination conditions, the morphology, particle size of primary particles and the electrochemical performance have been established. Capacity of 211.9 mAh/g and initial coulomb efficiency of 90.29% have been achieved by LiNi0.87Co0.06Mn0.07O2 with superficial transition metal concentration gradient, and the capacity retention rate at 1 C reached 86.1% after 400 cycles in a pouch cell. In addition, the thermal decomposition temperature is elevated from 220 °C to 242 °C, the safety of the Ni-rich material has been also effectively improved.

Tailoring electrolyte to enable high-rate and super-stable Ni-rich NCM cathode materials for Li-ion batteries

The detrimental effects on the electrochemical performances of high-capacity nickel-rich layered oxide cathode LiNi 0.8 Co 0.1 Mn 0.1 O 2 (Ni-rich NCM) are continuous irreversible phase transition, particle disintegration, and unstable cathode-electrolyte interface, which are usually induced by deleterious cathode-electrolyte reactions. Here, we report those side reactions are limited by a uniform inorganic/polymer cathode-electrolyte-interface (CEI) formed by in-situ electrochemical oxidation of a trace amount of dual additives in the traditional carbonate-based electrolytes. This CEI film not only eliminates the adverse cathode-electrolyte interface reaction and prevents the electrolyte penetration into the grain boundary but also hinders the formation of inactive rock-salt phase on the material surface. More significantly, it is demonstrated that this N, B, O-rich interface layer offers a fast Li + diffusion kinetic process to ensure a high-rate performance of the cathode, which is still a technical difficulty for the large application of Ni-rich NCM. Here, under the synergistic effect of dual additives containing lithium bis(oxalate)borate (LiBOB) and dopamine, the cell exhibits high-capacity retention over 92% after 200 cycles at 1 C, and also obtain a high specific capacity of 118 mA h g −1 at the high rate of 20 C. Building a stable and effect Li + -ion conductive interface film by optimizing the electrolyte formula is a facial and effective approach to develop aggressive high-capacity cathodes for high-energy storage applications. A performance optimization mechanism induced by a uniform inorganic/polymer cathode-electrolyte-interface (CEI) formed by in-situ electrochemical oxidation of a trace amount of dual additives in the traditional carbonate-based electrolytes. Here, under the synergistic effect of dual additives containing lithium bis(oxalate)borate (LiBOB) and dopamine, the cell exhibits high capacity retention over 90% after 200 cycles at 1 C, and also obtain a high specific capacity of 118 mA h g −1 at the high rate of 20 C. • Side reactions are limited by a uniform inorganic/polymer cathode-electrolyte-interface formed by electrochemical oxidation. • This N, B, O-rich interface layer hinders the formation of rock-salt phase on the cathode surface. • The CEI film formed by in-situ polymerization offers a fast Li + diffusion kinetic process to ensure a high-rate performance.

A review of nickel-rich layered oxide cathodes: synthetic strategies, structural characteristics, failure mechanism, improvement approaches and prospects

Nickel-rich layered oxide cathode materials have high specific capacity and are environmentally-benign, hence they are considered as the most relevant next-generation positive-electrode materials for lithium-ion batteries, particularly for powering plug-in hybrid electric vehicles and battery electric vehicles. The rich nickel content in layered oxides is highly beneficial in improving the energy density, but the cycle ability, rate capability and thermal stability inevitably decrease with the increase of nickel percentage, leading to the gradual failure of lithium-ion batteries. Therefore, it is an essential requisite to give a thorough review of previous research, thereby providing a clear understanding of the relationships between the material structure and their electrochemical activities, and improving the electrochemical performances of nickel-rich layered oxide cathode materials through reasonable modifications. In this article, the structural characteristics and synthetic methods are systematically reviewed. Particularly, the capacity failure mechanism and the corresponding improvement strategies of nickel-rich layered oxides are emphasized and discussed from atomic scale to macro-scale along with the latest literature review. A brief analysis of the perspectives is also presented with several possible research directions for technical and commercial success of nickel-rich layered oxide cathodes.

Formulating the Electrolyte Towards High-Energy and Safe Rechargeable Lithium-Metal Batteries.

Rechargeable lithium-metal batteries with a cell-level specific energy of >400 Wh kg-1 are highly desired for next-generation storage applications, yet the research has been retarded by poor electrolyte-electrode compatibility and rigorous safety concerns. We demonstrate that by simply formulating the composition of conventional electrolytes, a hybrid electrolyte was constructed to ensure high (electro)chemical and thermal stability with both the Li-metal anode and the nickel-rich layered oxide cathodes. By employing the new electrolyte, Li∥LiNi0.6 Co0.2 Mn0.2 O2 cells show favorable cycling and rate performance, and a 10 Ah Li∥LiNi0.8 Co0.1 Mn0.1 O2 pouch cell demonstrates a practical specific energy of >450 Wh kg-1 . Our findings shed light on reasonable design principles for electrolyte and electrode/electrolyte interfaces toward practical realization of high-energy rechargeable batteries.

Resolving atomic-scale phase transformation and oxygen loss mechanism in ultrahigh-nickel layered cathodes for cobalt-free lithium-ion batteries

Summary Doped LiNiO2 has recently become one of the most promising cathode materials for its high specific energy, long cycle life, and reduced cobalt content. Despite this, the degradation mechanism of LiNiO2 and its derivatives still remains elusive. Here, by combining in situ electron microscopy and first-principles calculations, we elucidate the atomic-level chemomechanical degradation pathway of LiNiO2-derived cathodes. We uncover that the O1 phase formed at high voltages acts as a preferential site for rock-salt transformation via a two-step pathway involving cation mixing and shear along (003) planes. Moreover, electron tomography reveals that planar cracks nucleated simultaneously from particle interior and surface propagate along the [100] direction on (003) planes, accompanied by concurrent structural degradation in a discrete manner. Our results provide an in-depth understanding of the degradation mechanism of LiNiO2-derived cathodes, pointing out the concept that suppressing the O1 phase and oxygen loss is key to stabilizing LiNiO2 for developing next-generation high-energy cathode materials.

What is the Role of Nb in Nickel-Rich Layered Oxide Cathodes for Lithium-Ion Batteries?

Nickel-rich layered metal oxide LiNi1–y–zMnyCozO2 (1 – y – z ≥ 0.8) materials are the most promising cathodes for next-generation lithium-ion batteries in electric vehicles. However, they lose more...

Morphological effect on high compaction density nickel-rich layered oxide cathodes during electrochemical lithiation and delithiation

The morphological effect of the blended single-crystalline Li[Ni0.8Co0.1Mn0.1]O2(NCM-C) and spherical secondary polycrystalline Li[Ni0.8Co0.1Mn0.1]O2(NCM-SP) cathodes (3:7 in weight) were systematically investigated. Calendering properties of the NCM-C, NCM-SP, and blended cathode were tested on a pilot-scale compactor. The values of maximal coating density and compaction resistance fitted by Heckel's equation indicate that the addition of moderate amounts of NCM-C into NCM-SP produced a significant improvement in the compaction degree and electrical conductivity of cathode laminate. The addition of NCM-C is also found to help reduce the generated electrode stress during electrochemical lithiation and delithiation which is confirmed by using the multi-beam optical sensor (MOS) technique. In the pouch-type full cell test utilizing artificial graphite as the negative electrode, the retained capacity is about 85.3% of its initial capacity by applying 1.0 C current at 25 °C after 700 cycles. The rate capability is also improved in the blended cathode even at a 2.0 C discharge rate, keeping 97.3% of its initial specific capacity (0.33C rate). It is suggested that the mixed electrode is considered to be a quite promising cathode electrode material to be applied for lithium-ion batteries.

Multifunctionality of cerium decoration in enhancing the cycling stability and rate capability of a nickel-rich layered oxide cathode.

The structural collapse and surface chemical degradation of nickel-rich layered oxide cathodes (NCM) of lithium-ion batteries during operation, which result in severe capacity attenuation, are the major challenges that hinder their commercial development. To improve the cycle and rate performances of LiNi0.8Co0.1Mn0.1O2 (NCM811), in this study, we have constructed a double-shell structure protective layer with a surface CeO2-x coating and interfacial spinel-like phase, which mitigate particle microcrack formation and isolate the NCM811 particles from electrolyte erosion. Additionally, during heat-treatment calcination, tetravalent cerium ions with strong oxidation ability can be partially doped into the material, which causes partial oxidation of Ni2+ to Ni3+, thereby reducing the Li+/Ni2+ mixing. The strong Ce-O bonds formed in the lattice help to improve the stability of the structure in the highly de-lithiated state. Thus, the synergy of multifunctional cerium modification effectively improves the structural stability and electrochemical kinetics of the material during cycling. Impressively, the obtained Ce-NCM811 exhibits capacity retention of 80.3% at a high discharge rate of 8 C after 500 cycles, which is much higher than that of the pristine cathode (only 44.3%). This work successfully designed a material with multi-functional Ce modification to provide a basis for Ni-rich cathode materials, which is crucial as it effectively improves the electrochemical performance.

Prelithiated Li-Enriched Gradient Interphase toward Practical High-Energy NMC–Silicon Full Cell

It is highly desirable to realize high-energy-density lithium-ion batteries consisting of nickel-rich layered oxide cathodes (Ni-rich NMC) and Si-based anodes. A critical challenge for Ni-rich NMC ...

In Situ Monitoring of Thermally Induced Effects in Nickel-Rich Layered Oxide Cathode Materials at the Atomic Level.

The thermal stability of cathode active materials (CAMs) is of major importance for the safety of lithium-ion batteries (LIBs). A thorough understanding of how commercially viable layered oxide CAMs behave at the atomic length scale upon heating is indispensable for the further development of LIBs. Here, structural changes of Li(Ni0.85Co0.15Mn0.05)O2 (NCM851005) at elevated temperatures are studied by in situ aberration-corrected scanning transmission electron microscopy (AC-STEM). Heating NCM851005 inside the microscope under vacuum conditions enables us to observe phase transitions and other structural changes at high spatial resolutions. This has been primarily possible by establishing low-dose electron beam conditions in STEM. Specific focus is put on the evolution of inherent nanopore defects found in the primary grains, which are believed to play an important role in LIB degradation. The onset temperature of structural changes is found to be ∼175 °C, resulting in phase transformation from a layered to a rock-salt-like structure, especially at the internal interfaces, and increasing intragrain inhomogeneity. The reducing environment and heat application lead to the formation and subsequent densification of {003}- and {014}-type facets. In the light of these results, postsynthesis electrode drying processes applied under reducing environment and heat, for example, in the preparation of solid-state batteries, should be re-examined carefully.

(Invited) Synthesis and Electrochemical Performance of Nb Coated/Substituted Nickel-Rich Layered Oxide Cathodes in Lithium Ion Batteries

Layered metal oxides have been considered the most important cathode materials in Li-ion batteries. Further, nickel rich LiNixCoyMn1-x-yO2 (x ≥ 0.8) cathodes are very attractive in automotive industry due to their high discharge capacities. However, the high nickel content creates a number of challenges, including high surface reactivity and structural instability. Through a wet chemistry method, Nb coated and substituted NMC 811 was prepared in a single step treatment. The coating layer and penetration of Nb can be controlled by sintering temperature. As a result, the 1st capacity loss, discharge capacity, rate performance and cycling stability were significantly improved. In addition, we found the Nb coating layer can increase the discharge capacity and Nb penetrated into NMC 811 can stabilize the structure. Acknowledgement: This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy, through the Advanced Battery Materials Research Program (Battery500 Consortium).

Origins of Capacity Fade and Material Degradation in Ni-Rich NMC Li-Ion Batteries

Nickel-rich layered oxide cathode materials are promising candidates for automotive lithium-ion batteries due to their low cost and high reversible capacity.1 However, paired with graphite anodes these materials exhibit faster voltage and capacity fading compared to isostructural LiNixMnyCozO2 (NMC) cathodes with lower nickel content.2 In this work we will explore the origins of capacity fade and material degradation in graphite/LiNi0.8Mn0.1Co0.1O2 (NMC811) full cells. With a focus on strategically designed electrochemical protocols (see Fig. 1), the role of several key cycling parameters (e.g. upper cut-off voltage, time at high voltage, phase transitions) on the degradation are decoupled. The aging processes are quantified in terms of the full cell capacity retention, impedance rise, electrode slippage, and NMC cathode deterioration. We find that most full cell capacity loss and impedance rise is caused by increasing the upper cut-off voltage to >4.2 V, with the impedance increase largely driven by concomitant full state-of-charge (SOC) cycling. Time spent at high voltage (voltage holds) has less impact on these parameters. These findings are supported by electron microscopy and spectroscopy experiments (SEM, high-resolution TEM, and STEM-EELS) on cycled electrodes, which show clear evidence for cycle history dependent degradation including particle cracking, shearing, and surface reconstruction. Figure 1