Widespread adoption of electric vehicles (EVs) and renewable energy technology requires lithium-ion batteries of high energy-density and low cost. Today, a typical lithium-ion battery comprises many layers of composite electrode films (typically 50−100 μm in thickness) coated on both sides of aluminum and copper foils and stacked alternatively with separators. The high content of inactive materials (e.g., separators, metal foil current collectors, conductive additives, binder and packaging) of the existing design leads to high material and manufacturing cost and reduced energy-density (both gravimetric and volumetric). A great deal of research effort has so far been focused on new electrode materials or new battery chemistries that offer promise for high energy-density. Another simple and straightforward approach to increasing energy density and reducing cost is adoption of thicker and/or denser electrodes. This approach has been relatively much less explored, possibly due to apparent transport limitations and manufacturing challenges. In the limit of large electrode thickness and high current-density, lithium salt depletion within the electrolyte-filled porosity becomes rate-limiting and reduces the accessible capacity of the electrode material.¹ Previous work show that transport kinetics of thick electrodes can be significantly improved through rational design and tailoring of the topology of electrode pore structure to lower tortuosity.^2-6 Despite the favorable electrochemical properties of previously demonstrated low-tortuosity electrodes, their sintering-based preparation is incompatible with conventional slurry-based electrode processing.^{2, 3, 6} Such processing also precludes the use of conductive carbon, binder, or any other electrode additive that cannot survive the sintering.

Here we report a non-sintering, emulsion-based, magnetic-alignment method that is simple, scalable, and naturally produces aligned porosity favorably oriented normal to the electrode plane. Unlike previous magnetic-alignment methods, which may only work with anisotropic particles such as natural graphite flakes (as anode),^{4, 5} our method is not limited to certain particle shapes or electrode materials and can be generally applied to both cathodes and anodes without sintering. We prepare thick LiCoO₂ cathodes (>400 µm) with ultrahigh areal capacity (up to ~14 mAh cm⁻² versus 2-4 mAh cm^-2 of conventional electrodes) through magnetic alignment of emulsion-based slurries. The LiCoO₂ cathodes are confirmed to have low tortuosity via DC-depolarization experiments and deliver high areal capacity (>10 mAh cm^-2) in galvanostatic discharge tests at practical C-rates and model electric vehicle drive-cycle tests. This simple fabrication method can also be applied to meso-carbon microbead (MCMB) graphite anodes and potentially many other materials to enable high energy-density full batteries based on thick electrodes.

References:

1. Doyle , M., Newman , J., Analysis of capacity–rate data for lithium batteries using simplified models of the discharge process. J. Appl. Electrochem. 27, 846-856 (1997).

2. Sander, J. S., et al., High-performance battery electrodes via magnetic templating. Nature Energy 1, 16099 (2016).

3. Bae, C.-J., Erdonmez, C. K., Halloran, J. W., Chiang, Y.-M., Design of Battery Electrodes with Dual-Scale Porosity to Minimize Tortuosity and Maximize Performance. Adv. Mater. 25, 1254-1258 (2013).

4. Billaud, J., et al., Magnetically aligned graphite electrodes for high-rate performance Li-ion batteries. Nature Energy 1, 16097 (2016).

5. Wood, V., Ebner, M. O. J. Method for the production of electrodes and electrodes made using such a method, EP2793300 A1. 2014.

6. Sebastian Behr, Ruhul Amin, Yet-Ming Chiang, Tomsia, A. P., Highly-Structured, Additive-Free Lithium-Ion Cathodes by Freeze-Casting Technology. Ceramic Forum International 92, 39-43 (2015).

Acknowledgement:

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, Subcontract No. 7056592 under the Advanced Battery Materials Research (ABMR) Program.