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Capacity fading during long-term cycling (>1500×) is still a critical challenge for Li-ion batteries that use Ni-rich layered oxides, e.g. LiNi0.8Co0.15Al0.05O2 (NCA), as the cathode. Microcracks have been previously recognized as one of the primary reasons for the observed capacity fade. Although there exists a generally developed mechanical understanding of microcracks, the role of the electrolyte has not been clearly understood, especially after extended cycling and at the atomic scale. Here, we unveil the microstructural evolution of spherical NCA secondary particles after long-term cycling using scanning transmission electron microscopy accompanied with electron energy loss spectroscopy. We found that the microcracks initiated and grew through grain boundaries, which then serve as the pathway for electrolyte penetration into secondary NCA particles. Additionally, the rock-salt phase reconstruction is prone to occur at the (003) surfaces of the primary particles or the crack surfaces, largely due to electrolyte (LiPF6 EC/EMC) corrosion. Crack propagation within the NCA grains is primarily a joint consequence from electrolyte corrosion and mechanical strain during lithiation/delithiation. During extended cycling, due to the distinctive surface facets, the primary grains located in the center of the secondary particles experience more intensive electrolyte corrosion, leading to a reduced contact with nearby particles, impairing the overall capacity. These results establish the initiation and growth mechanism of microcracks and voids in NCA-based cathodes during cycling and point out the role of the electrolyte in affecting the degradation of NCA-based cathodes.

High-nickel layered oxides, such as LiNi0.8Co0.1Mn0.1O2 (NCM-811), offer higher energy density than their low-nickel counterparts at a given voltage and are gaining major traction in automotive lit...

42CrMo steel belongs to low-alloy medium carbon steel and also belongs to ultra-high-strength steel. In this study, thermal compression tests (800°C - 1200°C, 0.01s-1 - 10s-1) and subsequent calculations proved that many material constants of 42CrMo alloy steel have a similar functional relationship with Z parameter: Material constants = a*Zb. The thermal processing maps under strains of 0.2, 0.4, 0.6 and 0.8 were established, and the practical application of the processing maps was verified in combination with metallographic diagram analysis. The optimum thermal processing parameters range of the material was obtained: the temperature range of 1000°C - 1125°C and the strain rate range of 3.16 s-1 - 10s-1.The dynamic recrystallization volume fraction model and grain size model of the material were established, and the typical sigmodal curve was obtained. The hot workability and recrystallization behavior of 42CrMo were further analyzed.

We present a comprehensive study of cycled high-Ni (LiNi1–xMxO2, M = metals), Li-rich (Li1+xMnyM1–x–yO2), and high-voltage spinel (LiMn1.5Ni0.5O4) electrodes with time-of-flight secondary ion mass ...

High-nickel layered oxide cathode materials will be at the forefront to enable longer driving-range electric vehicles at more affordable costs with lithium-based batteries. A continued push to higher energy content and less usage of costly raw materials, such as cobalt, while preserving acceptable power, lifetime and safety metrics, calls for a suite of strategic compositional, morphological and microstructural designs and efficient material production processes. In this Perspective, we discuss several important design considerations for high-nickel layered oxide cathodes that will be implemented in the automotive market for the coming decade. We outline various intrinsic restraints of maximizing their energy output and compare current/emerging development roadmaps approaching low-/zero-cobalt chemistry. Materials production is another focus, relevant to driving down costs and addressing the practical challenges of high-nickel layered oxides for demanding vehicle applications. We further assess a series of stabilization techniques on their prospects to fulfill the aggressive targets of vehicle electrification. The development of high-nickel layered oxide cathodes represents an opportunity to realize the full potential of lithium-ion batteries for electric vehicles. Manthiram and colleagues review the materials design strategies and discuss the challenges and solutions for low-cobalt, high-energy-density cathodes.

While it is accepted that paired NiLi and LiNi antisite defects are present in the important family of NMC cathode materials with the general formula Li(NixMnyCoz)O2, their formation mechanism and ...

Ultrahigh-Ni layered oxide cathodes (Ni content >90%) are at the forefront for potentially enabling higher-energy-density lithium-ion batteries. Unfortunately, they suffer from rapid capacity fade,...

High-nickel layered oxide cathodes with a Ni content of >90% show substantial potential for next-generation lithium-ion batteries (LIBs) due to their high capacity and lower cost. However, they are plagued by rapid capacity decay and poor thermal stability, which hamper their practical viability. We present here Li0.98Mg0.02Ni0.94Co0.06O2 (NC-Mg) with 2% Mg doping, aiming to provide a strategic guideline for solving the issues. The Mg2+ ions occupy the lithium layer and are proposed to act as pillar ions, which substantially enhance the structural reversibility and reduce the anisotropic lattice distortion upon cycling, thereby greatly improving the electrochemical and thermal stability of NC-Mg compared to the undoped LiNi0.94Co0.06O2 (NC). Specifically, NC-Mg delivers 214 mA h g–1 with a capacity retention of 80.1% after 500 cycles in pouch-type full cells, much higher than the retention of NC (56.3%). A discharge capacity of 158 mA h g–1 at 10C rate demonstrates its remarkable rate capability. Addition...

Summary By virtue of their prominent advantages in terms of capacity and voltage output and cost, O3-type layered transition-metal oxides are considered promising cathode materials for sodium-ion batteries (SIBs). However, their unstable electrochemistry at high voltages due to complex multiphase evolution in the bulk structure and continuous degradation of the electrolyte-cathode interphase hampers their practical viability. Here, we reveal a dual-stabilization effect of the cation dopants on the evolution of the bulk structure and electrode-electrolyte interphase of a Li-substituted O3-type cathode upon Na (de)intercalation. The incorporation of Li into the transition-metal layer could mitigate the Jahn-Teller distortion of the Ni3+ ion and prevent the loss of active transition-metal ions so that the unfavorable high-voltage phase transition and the degradation of the electrolyte-cathode interphase are suppressed. As a result, the Li-incorporated cathode material displays a high reversible capacity with good high-voltage durability to facilitate its service in high-energy-density SIBs.

Layered oxide cathodes with a high Ni content of >0.6 are promising for high-energy-density lithium-ion batteries. However, parasitic electrolyte oxidation of the charged cathode and mechanical degradation arising from phase transitions significantly deteriorate the cell performance and cycle life as the Ni content increases. We demonstrate here a significantly prolonged cycle life with superior cell performance by substituting a small-dose of Al (2 mol %) for Ni in LiNi0.92Co0.06Al0.02O2; the capacity retention after operating a full cell fabricated with graphite anode for 1000 cycles increases from 47% to 83% on going from the Al-free LiNi0.94Co0.06O2 to the Al-doped LiNi0.92Co0.06Al0.02O2 cathode. Through in situ X-ray diffraction, we provide the operando evidence that the Al-doping tunes the H2–H3 phase transition process from a two-phase reaction to a quasi-monophase reaction, minimizing the mechanical degradation. Furthermore, secondary-ion mass spectrometry reveals considerably suppressed transitio...

Benefiting from extremely high shear modulus and high ionic transference number, solid electrolytes are promising candidates to address both the dendrite-growth and electrolyte-consumption problems inherent to the widely adopted liquid-phase electrolyte batteries. However, solid electrolyte/electrode interfaces present high resistance and complicated morphology, hampering the development of solid-state battery systems, while requiring advanced analysis for rational improvement. Here, we employ an ultrasensitive three-dimensional (3D) chemical analysis to uncover the dynamic formation of interphases at the solid electrolyte/electrode interface. While the formation of interphases widens the electrochemical window, their electronic and ionic conductivities determine the electrochemical performance and have a large influence on dendrite growth. Our results suggest that, contrary to the general understanding, highly stable solid electrolytes with metal anodes in fact promote fast dendritic formation, as a result of less Li consumption and much larger curvature of dendrite tips that leads to an enhanced electric driving force. Detailed thermodynamic analysis shows an interphase with low electronic conductivity, high ionic conductivity, and chemical stability, yet having a dynamic thickness and uniform coverage is needed to prevent dendrite growth. This work provides a paradigm for interphase design to address the dendrite challenge, paving the way for the development of robust, fully operational solid-state batteries.

The formation of metallic lithium microstructures in the form of dendrites or mosses at the surface of anode electrodes (e.g., lithium metal, graphite, and silicon) leads to rapid capacity fade and poses grave safety risks in rechargeable lithium batteries. We present here a direct, relative quantitative analysis of lithium deposition on graphite anodes in pouch cells under normal operating conditions, paired with a model cathode material, the layered nickel-rich oxide LiNi0.61Co0.12Mn0.27O2, over the course of 3000 charge–discharge cycles. Secondary-ion mass spectrometry chemically dissects the solid–electrolyte interphase (SEI) on extensively cycled graphite with virtually atomic depth resolution and reveals substantial growth of Li-metal deposits. With the absence of apparent kinetic (e.g., fast charging) or stoichiometric restraints (e.g., overcharge) during cycling, we show lithium deposition on graphite is triggered by certain transition-metal ions (manganese in particular) dissolved from the cathod...

Undesired electrode–electrolyte interactions prevent the use of many high-energy-density cathode materials in practical lithium-ion batteries. Efforts to address their limited service life have predominantly focused on the active electrode materials and electrolytes. Here an advanced three-dimensional chemical and imaging analysis on a model material, the nickel-rich layered lithium transition-metal oxide, reveals the dynamic behaviour of cathode interphases driven by conductive carbon additives (carbon black) in a common nonaqueous electrolyte. Region-of-interest sensitive secondary-ion mass spectrometry shows that a cathode-electrolyte interphase, initially formed on carbon black with no electrochemical bias applied, readily passivates the cathode particles through mutual exchange of surface species. By tuning the interphase thickness, we demonstrate its robustness in suppressing the deterioration of the electrode/electrolyte interface during high-voltage cell operation. Our results provide insights on the formation and evolution of cathode interphases, facilitating development of in situ surface protection on high-energy-density cathode materials in lithium-based batteries., In lithium-ion batteries the interactions between the electrode and electrolyte represent a complex but critical process. Here the authors reveal the dynamic behaviour of interphases driven by conductive carbon through chemical and imaging analyses of a model transition-metal oxide cathode material.

As nickel-rich layered oxide cathodes start to attract worldwide interest for the next-generation lithium-ion batteries, their long-term cyclability in full cells remains a challenge for electric vehicles. Here we report a long-life Ni-rich layered oxide cathode (LiNi0.7Co0.15Mn0.15O2) with a uniform surface coating of the cathode particles with Li2ZrO3. A pouch-type full cell fabricated with the Li2ZrO3-coated cathode and a graphite anode displays 73.3% capacity retention after 1500 cycles at a C/3 rate. The Li2ZrO3 coating has been optimized by a systematic study with different synthesis approaches, annealing temperatures, and coating amounts. The complex relationship among the coating conditions, uniformity, and morphology of the coating layer and their impacts on the electrochemical properties are discussed in detail.

Nickel-rich layered oxides are one of the most promising cathode candidates for next-generation high-energy-density lithium-ion batteries. The advantages of these materials are high reversible capacity, high energy density, good rate capability, and low cost. However, they suffer from poor cyclability, particularly at elevated temperatures, and thermal instability which induces thermal runaway. In this review, we highlight the evolution of nickel-rich layered oxides from LiNiO2 to LiNi1−x−yCoxMnyO2 (1−x−y>0.5) in view of cationic substitutions, state-of-the-art understanding of the capacity fading mechanisms that is related to a complex surface chemistry of the particles, and various modification strategies to enhance the surface stability. Based on these considerations, the remaining challenges and the future research direction are also discussed.

Undesired reactions between layered sodium transition-metal oxide cathodes and air impede their utilization in practical sodium-ion batteries. Consequently, a fundamental understanding of how layered oxide cathodes degrade in air is of paramount importance, but it has not been fully understood yet. Here a comprehensive study on a model material NaNi0.7Mn0.15Co0.15O2 reveals its reaction chemistry with air and the dynamic evolution of the degradation species upon air exposure. We find that besides the extraction of Na+ ions from the crystal lattice to form NaOH, Na2CO3, and Na2CO3·H2O in contact with air, nickel ions gradually dissolve from the bulk to form NiO and accumulate on the particle surface as revealed by subnanometer surface-sensitive time-of-flight secondary ion mass spectroscopy. The degradation species on the surface are insulating, leading to an increase in interfacial resistance and declined electrochemical performance. We also demonstrate a feasible surface coating strategy for suppressing ...

The hot deformation behavior of 21-4N heat-resistant steel was studied by hot compression test in a deformation temperature range of 1000&ndash, 1180 &deg, C, a strain rate range of 0.01&ndash, 10 s&minus, 1 and a deformation degree of 60%, and the stress-strain curves were obtained. The functional relationship between flow stress and process parameters (deformation degree, deformation temperature, strain rate, etc.) of 21-4N heat-resistant steel during hot deformation was explored, the constitutive equation of peak stress was established, and its accuracy was verified. Based on the dynamic material model, the energy dissipation maps and destabilization maps of 21-4N heat-resistant steel were established at strains of 0.2, 0.4 and 0.6, and processing maps were obtained by their superposition. Within the deformation temperature range of 1060~1120&deg, C and a strain rate range of 0.01&ndash, 0.1 s&minus, 1, there is a stable domain with the peak efficiency of about 0.5. The best hot working parameters (strain rate and deformation temperature) of 21-4N heat-resistant steel are determined by the stable and instable domain in the processing maps, which are in the deformation temperature range of 1120&ndash, C and the strain rate range of 0.01&ndash, 1.

Although the determination of site occupancies is often a major goal in Rietveld refinement studies, the accurate refinement of site occupancies is exceptionally challenging due to many correlations and systematic errors that have a hidden impact on the final refined occupancy parameters. Through the comparison of results independently obtained from neutron and synchrotron powder diffraction, improved approaches capable of detecting occupancy defects with an exceptional sensitivity of 0.1% (absolute) in the class of layered NMC (Li[NixMnyCoz]O2) Li-ion battery cathode materials have been developed. A new method of visualizing the diffraction parameter space associated with crystallographic site scattering power through the use of f* diagrams is described, and this method is broadly applicable to ternary compounds. The f* diagrams allow the global minimum fit to be easily identified and also permit a robust determination of the number and types of occupancy defects within a structure. Through a comparison of neutron and X-ray diffraction results, a systematic error in the synchrotron results was identified using f* diagrams for a series of NMC compounds. Using neutron diffraction data as a reference, this error was shown to specifically result from problems associated with the neutral oxygen X-ray atomic form factor and could be eliminated by using the ionic O2- form factor for this anion while retaining the neutral form factors for cationic species. The f* diagram method offers a new opportunity to experimentally assess the quality of atomic form factors through powder diffraction studies on chemically related multi-component compounds.

Ni-rich layered oxide cathodes are facing a fundamental challenge of loss in performance as a result of air storage, hampering their practical application in lithium-ion batteries. We present here an investigation of extended air storage and a solution to overcome the chemical instability by coating the Ni-rich layered oxide with a Mn-based spinel oxide.

The ever-growing demand for advanced rechargeable lithium-ion batteries in portable electronics and electric vehicles has spurred intensive research efforts over the past decade. The key to sustaining the progress in Li-ion batteries lies in the quest for safe, low-cost positive electrode (cathode) materials with desirable energy and power capabilities. One approach to boost the energy and power densities of batteries is to increase the output voltage while maintaining a high capacity, fast charge–discharge rate, and long service life. This review gives an account of the various emerging high-voltage positive electrode materials that have the potential to satisfy these requirements either in the short or long term, including nickel-rich layered oxides, lithium-rich layered oxides, high-voltage spinel oxides, and high-voltage polyanionic compounds. The key barriers and the corresponding strategies for the practical viability of these cathode materials are discussed along with the optimization of electrolytes and other cell components, with a particular emphasis on recent advances in the literature. A concise perspective with respect to plausible strategies for future developments in the field is also provided.

The Ni-rich layered oxides with a Ni content of >0.5 are drawing much attention recently to increase the energy density of lithium-ion batteries. However, the Ni-rich layered oxides suffer from aggressive reaction of the cathode surface with the organic electrolyte at the higher operating voltages, resulting in consequent impedance rise and capacity fade. To overcome this difficulty, we present here a heterostructure composed of a Ni-rich LiNi0.7Co0.15Mn0.15O2 core and a Li-rich Li1.2-x Ni0.2Mn0.6O2 shell, incorporating the advantageous features of the structural stability of the core and chemical stability of the shell. With a unique chemical treatment for the activation of the Li2MnO3 phase of the shell, a high capacity is realized with the Li-rich shell material. Aberration-corrected scanning transmission electron microscopy (STEM) provides direct evidence for the formation of surface Li-rich shell layer. As a result, the heterostructure exhibits a high capacity retention of 98% and a discharge-voltage retention of 97% during 100 cycles with a discharge capacity of 190 mA h g-1 (at 2.0-4.5 V under C/3 rate, 1C = 200 mA g-1).