Kinetic Limitations in Single‐Crystal High‐Nickel Cathodes

Ge, Mingyuan; Wi, Sungun; Liu, Xiang; Bai, Jianming; Ehrlich, Steven N.; Lu, Deyu; Lee, Ivan; Chen, Zonghai; Wang, Feng

doi:10.1002/anie.202012773

Cited by 98 publications

(86 citation statements)

References 33 publications

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“…Layered LiNi y Mn z Co 1−y−z O 2 cathodes with increasing nickel content, such as LiNi 0.8 Mn 0.1 Co 0.1 O 2 , are well-known to have higher capacity [1,2] but are intrinsically less stable than diffusion lengths, since achieving high rate capabilities requires facile transport of Li + ions through the cathode structure. [22,23] However, the increased surface area of nano-scale primary particles also enhances side reactions, leading to lower capacity retention. [19,[24][25][26] While the size of secondary particles does not change appreciably during calcination, [27] the same is not true for primary particles.…”

Section: Introductionmentioning

confidence: 99%

The Importance of Surface Oxygen for Lithiation and Morphology Evolution during Calcination of High‐Nickel NMC Cathodes

Wolfman

Wang

García

et al. 2022

Advanced Energy Materials

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both thermally and electrochemically. [2][3][4] Cathodes with high nickel content (y > 0.8) are also more difficult to synthesize, requiring oxygenrich calcination conditions, and are more prone to lithium/transition-metal siteexchange. [5][6][7][8][9] Thermal parameters play a critical role in the morphology of the final cathode, which strongly affects its rate performance and cyclability. Advanced understanding of the underlying chemistry during synthesis is necessary to enable Ni-rich cathodes to operate closer to their theoretical performance limits.Preparation of Ni-rich LiNi y Mn z Co 1−y−z O 2 cathode material is a two-stage process, first involving the co-precipitation of a Ni 0.8 Mn 0.1 Co 0.1 (OH) 2 species followed by calcination of the resultant precursor with a lithium salt, typically LiOH•H 2 O. Calcination, which requires prolonged times at temperatures up to 750-900 °C in pure oxygen condition for Ni-rich cathodes, is the most energy intensive step. [10] During this process, water is lost from Ni y Mn z Co 1−y−z (OH) 2 , and lithium and oxygen enter the structure forming the final LiNi y Mn z Co 1−y−z O 2 cathode. The details of this transformation are not fully understood. While both the hydroxide precursor and final LiNi y Mn z Co 1−y−z O 2 cathode share a layered structure, prior research has implicated an intermediate cubic structure resembling rock salt, [11] recently confirmed using in situ powder X-ray diffraction (XRD). [12,13] These phases share an oxygen sub-lattice, and so the mechanism has been ascribed to a topotactic transformation involving extensive cation ordering. [14,15] In addition, several competing processes occur at high temperatures, where cation mixing and particle growth have been shown to depend on calcination temperature and hold time. [16] The final cathode performance is closely tied to the morphology of the constituent particles. [17] LiNi 0.8 Mn 0.1 Co 0.1 O 2 often has a hierarchical structure consisting of large (≈10 μm) agglomerates of small (≈100 nm) single crystal primary particles. Secondary particle size is largely controlled by coprecipitation conditions, whereas primary particles are affected by thermal parameters during calcination.Smaller particles (<100 nm) result in higher rate capability, [18][19][20][21] attributed to increased surface area and shorter Nanoscale morphology has a direct impact on the performance of materials for electrochemical energy storage. Despite this importance, little is known about the evolution of primary particle morphology nor its effect on chemical pathways during synthesis. In this study, operando characterization is combined with atomic-scale and continuum simulations to clarify the relationship between morphology of cathode primary particles and their lithiation during calcination of LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC-811). This combined approach reveals a key role for surface oxygen adsorption in facilitating the lithiation reaction by promoting metal diffusion and oxidation, and simultaneously providing surface sites for ...

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Section: Introductionmentioning

confidence: 99%

The Importance of Surface Oxygen for Lithiation and Morphology Evolution during Calcination of High‐Nickel NMC Cathodes

Wolfman

Wang

García

et al. 2022

Advanced Energy Materials

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“…The fact that the core remains lithium deficient can be explained by the drastically reduced lithium diffusion coefficient and charge transfer kinetics (11,14) at near-full lithiation states (fig. S18).…”

Section: Lithium Heterogeneity At the End Of Dischargementioning

confidence: 99%

“…Significant world-wide effort is thus being devoted to understanding their underlying charging mechanisms to mitigate these shortcomings (3,8,9). Previous studies have attributed the first-cycle capacity losses to kinetic limitations due to slow lithium diffusion at near-full lithiation states, as a result of fewer lithium vacancies and decreased interlayer spacing (10,11). X-ray diffraction (XRD)-based methods have furthermore revealed several "phase segregation" phenomena during the delithiation of Ni-based layered cathodes (12)(13)(14)(15), despite the fact that the (de)lithiation of such materials intrinsically follows a solid-solution mechanism (12,16,17).…”

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confidence: 99%

Operando visualisation of kinetically-induced lithium heterogeneities in single-particle layered Ni-rich cathodes

Merryweather

Pandurangi

et al. 2022

Preprint

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Understanding how lithium-ion dynamics affect the (de)lithiation mechanisms of state-of-the-art nickel-rich layered oxide cathodes is crucial to improving electrochemical performance. Here, we directly observe two distinct kinetically-induced lithium heterogeneities within single-crystal LiNixMnyCo(1-x-y)O2 (NMC) particles using recently developed operando optical microscopy, challenging the notion that uniform (de)lithiation occurs within individual particles. Upon delithiation, a rapid increase in lithium diffusivity at the beginning of charge results in particles with lithium-poor peripheries and lithium-rich cores. The slow ion diffusion at near-full lithiation states – and slow charge transfer kinetics – also leads to heterogeneity at the end of discharge, with a lithium-rich surface preventing complete lithiation. Finite-element modelling confirms that concentration-dependent diffusivity is necessary to reproduce these phenomena. Our results show that diffusion limitations cause first-cycle capacity losses in Ni-rich cathodes.

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“…In addition, surface parasitic reaction may be suppressed in single‐crystals due to their smaller specific surface area, but recent studies indicate that the reduced surface‐related reaction in single crystals is outweighed by the kinetic limitation, i. e., sluggish Li (de)intercalation in the bulk particularly at the low state of charge (SOC) (Figure 16). [67] For the practical use of high‐Ni cathodes, the low Coulombic efficiency particularly during the first cycle is another big concern, but with the mechanistic origins still under debate [68–70] . Both surface reaction and sluggish Li re‐intercalation should be responsible, with the latter being found to be dominant in high‐Ni NMC cathodes.…”

Section: Perspectivesmentioning

confidence: 99%

Synthesis and Processing by Design of High‐Nickel Cathode Materials

Wang

Bai

2021

Batteries & Supercaps

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The high demand of lightweight, high energy density batteries for energy storage promotes new materials discovery and development. Despite the large number of battery materials being discovered, very few of them have been commercially deployed, mostly bottlenecked by synthesis and processing – namely, making certain phases with the desired structure and properties to meet the multifaceted performance requirements. Alternative to the traditional trial and error, we present here an in situ study aided synthesis‐ and processing‐by‐design approach. With specific examples, we illustrate how to use the approach to identify reaction pathways in synthesis and processing of high‐Nickel (Ni) cathode materials for next‐generation lithium‐ion batteries, thereby ensuring precise control of their structure, morphology, and surface properties. To the end, perspectives are provided on the wide applicability of the approach to solving critical issues inherent to high‐Ni cathodes and the new directions and opportunities in the area.

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Kinetic Limitations in Single‐Crystal High‐Nickel Cathodes

Cited by 98 publications

References 33 publications

The Importance of Surface Oxygen for Lithiation and Morphology Evolution during Calcination of High‐Nickel NMC Cathodes

The Importance of Surface Oxygen for Lithiation and Morphology Evolution during Calcination of High‐Nickel NMC Cathodes

Operando visualisation of kinetically-induced lithium heterogeneities in single-particle layered Ni-rich cathodes

Synthesis and Processing by Design of High‐Nickel Cathode Materials

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