Hanyang University & BMW Develop Lithium-Ion Battery With High Energy Density Using Carbon Nanotube Silicon Composite Anode

Originally published on CleanTechnica.

A new, fully functional lithium-ion battery design featuring high energy density and a good cycle life has been created by researchers at Hanyang University and BMW Group, according to recent news from the company and university.

The new work has been detailed in a paper published in the RSC journal Energy & Environmental Science. Here’s the abstract from that:

A fully operational practical Li-rechargeable battery system delivering unprecedented high energy density with excellent cycle life was proposed using the state-of-the-art cathode and anode technologies. Based on the simple ball-milling process, a carbon nanotube (CNT)-Si composite anode with extremely stable long-term cycling, while providing a discharge capacity of 2364 mAh g-1 at a tap density of 1.1 g cm-3, was developed. For cathode, a two-sloped full concentration gradient (TSFCG) Li[Ni0.85Co0.05Mn0.10]O2 cathode, designed to obtain maximum possible discharge capacity by having Ni-enrich core and to simultaneously ensure high chemical and thermal stability by having outer Mn-enriched layer, yielded a discharge capacity of 221 mAh g-1. Integrating the CNT-Si composite and the TSFCG cathode in a full cell configuration, the full cell generated 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. The proposed battery system satisfied the demands for energy storage for vehicle applications in terms of energy density, power and cycle life.

Here’s an excerpt from the paper, explaining the background of the work:

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).

Interesting work. Considering that BMW seems to be in no hurry as far as electric vehicles go, though, who knows how relevant the company’s involvement is.