Na Sungmin, Oh Rena, Song Jungyeon, Lee Myoung-Jae, Park Kwangjin, Park Gyeong-Su
Department of Mechanical Engineering, Gachon University, Seongnam 13120, Republic of Korea.
Soft Foundry Institute, Seoul National University, Seoul 08826, Republic of Korea.
ACS Nano. 2025 Jan 21;19(2):2136-2147. doi: 10.1021/acsnano.4c10476. Epub 2025 Jan 9.
Nickel-rich NCM cathode materials promise lithium-ion batteries with a high energy density. However, an increased Ni fraction in the cathode leads to complex phase transformations with electrode-electrolyte side reactions, which cause rapid capacity fading. Here, we show that an initial formation cycle at 0.1 C with a higher cutoff voltage (≥4.35 V) increases the stability of Ni-rich NCM (LiNiCoMnO) particles during cycling at 1 C. We unveil that the formation of intragranular nanovoids is directly associated with the initial formation cycle at a lower charging cutoff voltage when oxygen vacancies are introduced at the Ni-rich NCM particle surface, due to irreversible electrolyte decomposition at the cathode-electrolyte interface. Nanovoid evolution of the Ni-rich NCM particles after 50 cycles increases the NiO-like rock salt phase; it results in intragranular cracks, which cause structural instability via heterogeneous phase distribution. This work demonstrates the importance of controlling Ni-rich NCM surface chemistry from the initial formation cycle to achieve better cycling stability.
富镍的NCM正极材料有望实现具有高能量密度的锂离子电池。然而，正极中镍含量的增加会导致复杂的相变以及电极与电解质的副反应，从而导致容量迅速衰减。在此，我们表明，在0.1 C下以较高截止电压（≥4.35 V）进行的初始形成循环可提高富镍NCM（LiNiCoMnO）颗粒在1 C循环过程中的稳定性。我们揭示，当由于阴极-电解质界面处不可逆的电解质分解而在富镍NCM颗粒表面引入氧空位时，颗粒内纳米空隙的形成与较低充电截止电压下的初始形成循环直接相关。50次循环后富镍NCM颗粒的纳米空隙演化增加了类NiO岩盐相；这会导致颗粒内裂纹，通过不均匀的相分布导致结构不稳定。这项工作证明了从初始形成循环开始控制富镍NCM表面化学以实现更好的循环稳定性的重要性。
