Hanyang/BMW team develops high-energy density Li-ion battery with carbon-nanotube-Si composite anode and NCM concentration gradient cathode
Researchers from Hanyang University in Korea and the BMW Group have developed a new fully operational, practical Li-ion rechargeable battery combining high energy density with excellent cycle life. A report on their work is published in the RSC journal Energy & Environmental Science.
A carbon nanotube (CNT)-Si composite anode with extremely stable long-term cycling provides a discharge capacity of 2364 mAh g-1 at a tap density of 1.1 g cm-3; a two-sloped full concentration gradient (TSFCG) Li[Ni0.85Co0.05Mn0.10]O2 cathode, with a Ni-enriched core and Mn-enriched layer, yields a discharge capacity of 221 mAh g-1. The full cell generates an energy density of 350 Wh kg-1 with excellent capacity retention for 500 cycles at 1 C rate—satisfying the energy density limit imposed by the drive range requirement for EVs.
|Energy density of different LIBs. Comparison of the CNT-Si/TSFCG against the currently developed LIBs. LCO: LiCoO2, NCM333: Li[Ni⅓Co⅓Mn⅓]O2, NCM523: Li[Ni0.5Co0.2Mn0.3]O2, Li[Ni0.85Co0.05Mn0.15]O2. Lee et al. Click to enlarge.|
Li[Ni0.8Co0.1Mn0.1]O2 (NCM) and Li[Ni0.8Co0.15Al0.05]O2 (NCA) in particular are the most promising candidates for EVs among the next-generation of high energy density cells owing to their high capacity, outstanding rate capability, and low cost. Despite the advantages, increasing the Ni fraction in the NCM cathodes negatively impacts the lifetime and safety of the battery, particularly when higher cut-off voltages and high electrode packing densities are pursued. A number of strategies have been explored to increase the stability of the Ni-enriched NCM cathode material by suppressing the parasitic side reactions with the electrolyte.
Among them, a compositionally graded cathode material in which concentrations of the transition metals continuously varied from the particle center to the surface appears to be the most promising since the graded cathodes have demonstrated remarkable improvements over cathodes with single uniform composition, not only in lifetime and safety, but also in battery power due to the superior Li+ diffusion kinetics. However, like conventional NCM cathodes, it is challenging to increase the Ni concentration above 80% even in the compositionally graded NCM cathodes; hence, a NCM cathode that is compositionally graded with multi-level gradients was introduced in this work to maximize the Ni content near the particle core.
Among anode materials for LIB, Si exhibits the highest gravimetric capacity (3579 mAh g-1, when charged to Li15Si4); however, a large volume change during cycling often results in pulverization, electrical contact loss, and constant evolution of the solid-electrolyte interphase (SEI), leading to rapid capacity fading. … The anode strategy proposed in this work is to develop a composite anode consisting of structurally defective Si micro-particles encapsulated by carbon nanotubes, fabricated via the simple ball-milling of nanoporous Si and carbon nanotubes (CNTs).—Lee et al.
For the full cell configuration, the researchers added vinylene carbonate (VC) to the electrolyte to aid the formation of a stable SEI layer on the CNT-Si anode for long term cycling.
Joo Hyeong Lee, Chong Seung Yoon, Hwang Jang-Yeon, Sung-Jin Kim, Filippo Maglia, Peter Lamp, Seung-Taek Myung and Yang-Kook Sun (2016) “High-energy-density lithium-ion battery using carbon-nanotube-Si composite anode and compositionally graded Li[Ni0.85Co0.05Mn0.10]O2 cathode” Energy Environ. Sci. doi: 10.1039/C6EE01134A