High-Energy Cathodes via Precision Microstructure Tailoring for Next-Generation Electric Vehicles

Park, Nam-Yung; Ryu, Hoon‐Hee; Kuo, Liang-Yin; Kaghazchi, Payam; Yoon, Chong Seung; Sun, Yang Kook

doi:10.1021/acsenergylett.1c02281

Cited by 73 publications

(55 citation statements)

References 33 publications

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“…The segregated B may provide a protective coating layer on the cathode surface, similar to previous investigations on the segregation of specific elements. [ 21,29,41 ] Furthermore, even when the CSG‐NCAB87 cathode underwent 1000 more charge–discharge cycles than CSG‐NCA88, the impurity phase on the interior surfaces of the particles was much thinner than that in CSG‐NCA88 (Figure 5h). This demonstrates that the microstructural modification via B doping effectively suppresses the electrolyte exposure of the particle interior, that is, the Ni‐rich core region of the cathode, to the deleterious electrolyte.…”

Section: Resultsmentioning

confidence: 99%

High‐Energy Ni‐Rich Cathode Materials for Long‐Range and Long‐Life Electric Vehicles

Namkoong

Park

et al. 2022

Advanced Energy Materials

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of the global EV market, Li-ion battery (LIB) technology has progressed to meet the demand for longer driving ranges and extended service lives, while increasing the thermal stability and reducing the cost of the battery. As the performance of LIBs is largely determined by the cathode material, the development of high-performance LIBs for EVs has focused on increasing the capacity of the cathode by usingHowever, cathodes with a high Ni content suffer from inherent structural and chemical instabilities, which lead to rapid capacity fading and thermal instability. [3][4][5][6][7][8][9] In particular, the rapid capacity fading of Ni-rich layered cathodes is largely caused by microcracking and the resultant microstructural instability. [9][10][11][12][13][14][15][16][17][18][19] Microcracks create channels through which the electrolyte can infiltrate the cathode particles, which increases the surface area exposed to electrolyte and worsens parasitic electrolyte attack. The subsequent degradation of the internal surfaces accelerates the accumulation of NiO-like impurity layers at the cathode-electrolyte interface, which hinders electrochemical reactions. [9,[19][20][21][22][23][24][25] As microcracking is caused by abrupt contraction of the unit cells during the H2-H3 phase transition at a high state of charge (SoC), microstructural engineering to facilitate the dissipation of internal mechanical strain and mitigate microcracking in the cathode particles has been extensively investigated. [19,21,[24][25][26][27][28][29][30] One such engineered microstructure is a highly oriented microstructure in which elongated primary particles are aligned along the radial direction in the secondary particle periphery. This radial alignment of rod-shaped primary particles effectively dissipates localized strain by allowing the unit cell to contract and expand uniformly. Microstructural manipulation can be achieved by compositional gradient design of transition metal ions [19,24,25,31] or by doping with various atoms (e.g., B, Ta, Mo, W, and Sb) during lithiation. [18,[26][27][28][29][30]32,33] Furthermore, a reduction in volume deformation and internal stress inside the particle via Al doping can enhance the structural integrity and robustness of cathode. [30,34,35] In addition to microcracking, the time during which highly reactive Ni 4+ ions are exposed to the electrolyte when the cathode is in a highly charged state also affects the deterioration of the cathode. Although the exposure time is not Li-ion batteries (LIBs) in electric vehicles (EVs) are usually operated intermittently and maintained at high states of charge (SoCs) for long periods. Because the internal particles of Ni-rich cathodes are easily exposed to the electrolyte at high SoCs owing to mechanical instability, the electrolyte exposure time-during which highly reactive Ni 4+ ions react with the electrolyte-critically affects the degradation of the cathode. Here, 1 mol% B doping of a core-shell concentration gradient (CSG) Li[Ni 0.88 Co 0.10 Al 0.02 ]O 2 cathode (C...

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Section: Resultsmentioning

confidence: 99%

High‐Energy Ni‐Rich Cathode Materials for Long‐Range and Long‐Life Electric Vehicles

Namkoong

Park

et al. 2022

Advanced Energy Materials

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“…Therefore, an essential prerequisite for developing a Ni-rich cathode with a Ni fraction above 90% for EV applications is protecting the particle interior from electrolyte attack by suppressing microcracks. Although some effective approaches for suppressing microcracks have been developed, such as particle size refinement ,, and radial alignment of rod-shaped primary particles, ,,− innovative breakthroughs must be achieved for the practical use of high-energy Ni-rich cathodes with long-term stability.…”

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Degradation Mechanism of Ni-Rich Cathode Materials: Focusing on Particle Interior

et al. 2022

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In the development of Li-ion batteries for electric vehicles (EVs), Ni-rich layered oxides are anticipated to be promising cathode materials. However, the rapid capacity fading originating from microcracks has prevented practical applications of Ni-rich cathodes. Herein, we systematically perform post-mortem analyses of Li[Ni x Co y Mn 1-x-y ]O 2 (x = 0.8 and 0.9) cathodes after long-term cycling, focusing on the particle interior. The results demonstrate that microcracks and the resultant degradation of the secondary particle interior by exposure to the deleterious electrolyte are dominant factors in the deterioration of Ni-rich cathodes. Moreover, cathode degradation significantly decreases the ionic and electrical conductivities, leading to the partial electrochemical insulation inside the cathode particles. This insulation contributes to the kinetic loss of capacity at high C-rates and induces structural inhomogeneity in the cathode. A comprehensive understanding of the degradation mechanism of Ni-rich cathodes suggests guidelines for developing Ni-rich cathode materials that are appropriate for application in EVs.

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“…22−26 This behavior is not unique to W. Mo, Nb, and Sb are also observed to be enriched at grain boundaries. 27,28 The formation of secondary phases in the grain boundaries can potentially act as a barrier to prevent interdiffusion of transition metals during synthesis, therefore, making it possible to synthesize core−shell and other microstructures even with elements like Mg and Al which ordinarily diffuse rapidly. Stable thin shells may also be possible to produce without compromising the optimum synthesis temperature.…”

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“…Coatings of high-valence metal compounds have been explored in Ni-rich materials, including those with W, Ti, Ta, Sb, Nb, etc. − Tungsten addition has been reported previously to improve the performance and recently published work shows that W does not substitute into the TM layer but rather stays in the grain boundaries in the form of Li x W y O z secondary phases. − This behavior is not unique to W. Mo, Nb, and Sb are also observed to be enriched at grain boundaries. , The formation of secondary phases in the grain boundaries can potentially act as a barrier to prevent interdiffusion of transition metals during synthesis, therefore, making it possible to synthesize core–shell and other microstructures even with elements like Mg and Al which ordinarily diffuse rapidly. Stable thin shells may also be possible to produce without compromising the optimum synthesis temperature.…”

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Preventing Interdiffusion during Synthesis of Ni-Rich Core–Shell Cathode Materials

et al. 2022

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Surface reactions between Ni-rich cathode materials and electrolytes limit the achievable specific capacity and lifetime in the high energy density Li-ion batteries based on these cathode materials. A core−shell approach, which contains a less reactive shell-phase on top of a high-capacity core-phase, can be used to reduce these surface reactions. However, interdiffusion of the elements in the core and shell phases can occur during calcination, which limits the choice of elements to be used in the shell phase and the temperature window of synthesis, and often increases the minimum shell thickness. Tungsten oxide (WO 3 ) coating on the surface of precursors leads to the formation of Li x W y O z secondary phases during the heat treatment with LiOH• H 2 O. These Li x W y O z phases infuse into the grain boundaries and prevent interdiffusion between the core and shell phases. Tungsten-containing Ni-rich core−shell cathode materials with Mn-or Al-based shells show enhanced electrochemical performance because of reduced surface reactivity due to the core−shell microstructure and additional mechanical strength owing to the presence of Li x W y O z phases in the grain boundaries.

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High-Energy Cathodes via Precision Microstructure Tailoring for Next-Generation Electric Vehicles

Cited by 73 publications

References 33 publications

High‐Energy Ni‐Rich Cathode Materials for Long‐Range and Long‐Life Electric Vehicles

High‐Energy Ni‐Rich Cathode Materials for Long‐Range and Long‐Life Electric Vehicles

Degradation Mechanism of Ni-Rich Cathode Materials: Focusing on Particle Interior

Preventing Interdiffusion during Synthesis of Ni-Rich Core–Shell Cathode Materials

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