The ultrafine-grained Ni-enriched Li[Ni0.95Co0.04Mo0.01]O2 (NCMo95) cathode achieved by inhibiting particle coarsening imparts the necessary mechanical toughness and significantly extends the battery life.

transportation emissions account for nearly one-quarter of all greenhouse gases. [1] However, the current fleet of EVs, mainly powered by lithium-ion batteries (LIBs), still falls short of performance standards, especially in driving range per charge, that are required for broad consumer appeal. A driving range comparable to that of an ICEV requires a substantial increase in the energy density of LIBs, whose capacity is largely limited by the cathode. [2][3][4] Archetypal cathodes for LIBs deployed in current EVs are layered Li[Ni x Co y (Al or Mn) 1−x−y ]O 2 (Al = NCA or Mn = NCM) oxide materials. [4][5][6][7] Both cathodes were derived from LiNiO 2 , which has a high theoretical capacity of 270 mAh g −1 . Multiple phase transitions during delithiation quickly deteriorate the reversible capacity of LiNiO 2 ; this inherent structural instability renders the cathode unsuitable for EV applications. NCA cathodes were developed by introducing Co 3+ and Al 3+ to LiNiO 2 to prevent multistep phase transitions and stabilize the structure, resulting in the Li[Ni 0.8 Co 0.15 Al 0.05 ]O 2 cathode, which currently powers the Tesla Model S. [8] In another example, Ni was partially replaced with Co and Mn to develop Li[Ni 1/3 Co 1/3 Mn 1/3 ]O 2 ; this cathode exhibited excellent capacity retention and thermal stability but its capacity was limited to 160 mAh g −1 . [9] To compensate for inferior capacity, Ni content was increased to x = 0.6; this cathode is also widely commercialized. Although both NCA and NCM cathodes are adequate, the energy density of 350 Wh kg −1 required to provide a drive range threshold of 300 miles per charge requires a new class of layered oxide cathodes. As Ni content exceeds x = 0.8, NCA and NCM cathodes are plagued by increasingly compromised battery life and thermal safety, due to rapid capacity fading and an abundance of unstable Ni 4+ species, as observed in LiNiO 2 . [4,[10][11][12][13] To overcome the inherent instability of Ni-rich NCM and NCA cathodes, we propose a new type of layered oxide cathode, Li[Ni x Co y W 1−x−y ]O 2 . Previous work indicates that W doping of LiNiO 2 substantially improved its cycling stability without sacrificing energy density. [14,15] In this study, we show that replacement of Al ions with W ions in a Ni-rich NCA layered oxide cathode markedly modifies the cathode microstructure through particle refinement and greatly improves the cycling stability of the cathode. We compare the electrochemical performance of the Li[Ni 0.9 Co 0.09 W 0.01 ]O 2 cathode (NCW90) to the well-characterized Li[Ni 0.885 Co 0.1 Al 0.015 ]O 2 (NCA89) to demonstrate its superior structural and thermal stability compared to the commercialized NCA cathode.Substituting W for Al in the Ni-rich cathode Li[Ni 0.885 Co 0.10 Al 0.015 ]O 2 (NCA89) produces Li[Ni 0.9 Co 0.09 W 0.01 ]O 2 (NCW90) with markedly reduced primary particle size. Particle size refinement considerably improves the cathode's cycling stability such that the NCW90 cathode retains 92% of its initial capacity after 1000 cycles (c...

A new class of layered cathodes, Li[NixCoyB1−x−y]O2 (NCB), is synthesized. The proposed NCB cathodes have a unique microstructure in which elongated primary particles are tightly packed into spherical secondary particles. The cathodes also exhibit a strong crystallographic texture in which the a–b layer planes are aligned along the radial direction, facilitating Li migration. The microstructure, which effectively suppresses the formation of microcracks, improves the cycling stability of the NCB cathodes. The NCB cathode with 1.5 mol% B delivers a discharge capacity of 234 mAh g−1 at 0.1 C and retains 91.2% of its initial capacity after 100 cycles (compared to values of 229 mAh g−1 at 0.1 C and 78.8% for pristine Li[Ni0.9Co0.1]O2). This study shows the importance of controlling the microstructure to obtain the required cycling stability, especially for Ni‐rich layered cathodes, where the main cause of capacity fading is related to mechanical strain in their charged state.

In article number 1902698, Chong S. Yoon, Yang‐Kook Sun and co‐workers develop a new type of Ni‐rich layered cathode, Li[Ni0.9Co0.09W0.01]O2 for next‐generation electric vehicles. Substituting W for Al in the NCA cathode reduces primary particle size. The particle size refinement improves the cycling stability of the cathode by suppressing microcrack propagation and preventing particle fractures. Thus, the cathode delivers a high energy density with a long battery life.

To achieve a longer driving range of electric vehicles (EVs) per charge, it is necessary that the development of advanced cathode materials, which largely determine the capacity of lithium-ion batteries. Currently, classical cathodes deployed in current EVs, layered Li[NixCoy(Al orMn)1−x−y]O2 (Al = NCA or Mn = NCM) oxide materials, has achieved the best performances for commercialization. However, these cathodes should be further improved to be competitive in the global market.1 Ni-rich NCA and NCM cathodes, delivering ever-closer to their theoretical specific capacity, are considered as promising candidates. However, increasing Ni content compromises battery lifetime and thermal stability due to rapid capacity fading and an abundance of unstable Ni4+ species, as observed in LiNiO2.2,3 Therefore, the development of new cathode materials that can overcome rapid capacity fading is necessary. In this presentation, we suggest a novel cathode material by introducing boron to the binary system Li[Ni0.9Co0.1]O2 (NC90) to create a new class of layered cathode materials, Li[Ni1−x−yCoxBy]O2 (NCB), to supplement NCM and NCA.4 The microstructure of NCB cathodes was tailored by adjusting the boron fraction, as the shape and dimensions of the primary particles depend on the boron fraction. The dramatic difference between the particle microstructure of an NCB cathode and those of NCA and NCM cathodes was confirmed. The NCB cathode exhibited a higher capacity with outstanding capacity retention, compared to the conventional NCA and NCM cathodes. A series of NCB cathodes with 0.5, 1.0, 1.5, and 2 mol% B systematically characterized to investigate the capacity fading mechanism and to determine the optimal microstructure for better cycling stability. References D. Andre, S.-J. Kim, P. Lamp, S. F. Lux, F. Maglia, O. Paschos, B. Stiaszny, J. Mater. Chem. A 2015, 3, 6709. H.-H. Ryu, K.-J. Park, C. S. Yoon, Y.-K. Sun, Chem. Mater. 2018, 30, 1155. D.-W. Jun, C. S. Yoon, U.-H. Kim, Y.-K. Sun, Chem. Mater. 2017, 29, 5048. H.-H. Ryu, N.-Y. Park, D. R. Yoon, U.-H. Kim, C. S. Yoon, Y.-K. Sun, Adv. Energy Mater. 2020, 10, 2000495.