Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24061 , United States.
Department of Geosciences , Virginia Tech , Blacksburg , Virginia 24061 , United States.
ACS Appl Mater Interfaces. 2018 Jul 18;10(28):23842-23850. doi: 10.1021/acsami.8b06399. Epub 2018 Jul 9.
Nickel-rich layered cathode materials have the potential to enable cheaper and higher energy lithium ion batteries. However, these materials face major challenges (e.g., surface reconstruction, microcracking, potential oxygen evolution) that can hinder the safety and cycle life of lithium ion batteries. Many studies of nickel-rich materials have focused on ways to improve performance. Understanding the effects of temperature and cycling on the chemical and structural transformations is essential to assess the performance and suitability of these materials for practical battery applications. The present study is focused on the spectroscopic analysis of surface changes within a strong performing LiNiMnCoO (NMC811) cathode material. We found that surface chemical and structural transformations (e.g., gradient metal reduction, oxygen loss, reconstruction, dissolution) occurred quicker and deeper than expected at higher temperatures. Even at lower temperatures, the degradation occurred rapidly and eventually matched the degradation at high temperatures. Despite these transformations, our performance results showed that a better performing nickel-rich NMC is possible. Establishing relationships between the atomic, structural, chemical, and physical properties of cathode materials and their behavior during cycling, as we have done here for NMC811, opens the possibility of developing lithium ion batteries with higher performance and longer life. Finally, our study also suggests that a separate, systematic, and elaborate study of surface chemistry is necessary for each NMC composition and electrolyte environment.
富镍层状阴极材料有可能使锂离子电池更便宜、能量更高。然而，这些材料面临着重大挑战（例如表面重构、微裂纹、潜在的氧气析出），这可能会阻碍锂离子电池的安全性和循环寿命。许多对富镍材料的研究都集中在提高性能的方法上。了解温度和循环对化学和结构转变的影响，对于评估这些材料在实际电池应用中的性能和适用性至关重要。本研究集中于对表现强劲的 LiNiMnCoO（NMC811）阴极材料表面变化的光谱分析。我们发现，表面化学和结构的转变（例如梯度金属还原、氧损失、重构、溶解）在较高温度下比预期的更快、更深。即使在较低的温度下，降解也很快发生，最终与高温下的降解速度相匹配。尽管发生了这些转变，但我们的性能结果表明，更好性能的富镍 NMC 是可能的。如我们在这里对 NMC811 所做的那样，建立阴极材料原子、结构、化学和物理特性与其在循环过程中的行为之间的关系，为开发具有更高性能和更长寿命的锂离子电池开辟了可能性。最后，我们的研究还表明，对于每种 NMC 成分和电解质环境，都需要对表面化学进行单独、系统和精心的研究。
