Towards High Energy Density Batteries: Ultra Thick Electrodes and New Current Collector Architectures By Spark Plasma Sintering and Hard Templating Approach

Abstract

Spark Plasma Sintering (SPS) has proven to be an effective, rapid, and energy-efficient tool in the sintering of a variety of materials, such as ultrahigh temperature ceramics, composites, thermoelectric and magnetic compounds. Its main difference from the traditional sintering techniques (hot pressing, pressureless sintering, microwave sintering, etc) consists in the use of the direct pulsed current along with a uniaxial pressure to obtain well-compacted materials. Due to the fast heating/cooling rates and internally generated heat (resistive heating), the obtained compounds experience little to no particle growth while shortened sintering times ensure the absence of the unwanted side-reactions. Recently, SPS has been demonstrated to be used not only for the sintering of materials but also for their synthesis making it an attractive technique in the fabrication of thick high energy density electrodes for Li- or Na-ion battery application as well as in the synthesis of battery’s active material compounds or the fabrication of all-solid-state batteries [1-5].High energy density electrodes could be obtained by altering the electrode architectures. In pursuit of increasing the energy density, some methods suggest fabrication of (ultra)thick electrodes while others concentrate on the production of electrodes with a minimum amount of inactive materials (binder-free, conductive additive-free, integrated current collectors, etc). Owing to a rapid and highly efficient sintering process, SPS offers the luxury of obtaining simultaneously binder-free and (ultra)thick electrodes which suffer no structural degradation.Combined with novel integrated current collector architectures, SPS-fabricated (ultra)thick electrodes could provide high active material accessibility while working at elevated current rates thanks to controlled pore network morphology and improved electronic conductivity. In 2018 Elango et. al reported a successful Spark Plasma Sintering of the LiFePO4 and Li4Ti5O12 electrodes with controlled porosity by hard templating method (NaCl leaching) [1]. Obtained by SPS and templating approach ultrathick electrodes (1 mm thick) showed remarkable electrochemical performance at C/20 against lithium metal delivering areal capacities 4 times higher than those of the conventional tape-casted electrodes. This study coming from our group demonstrated the proof-of-concept in the fabrication of Li-ion battery electrodes with an ultrathick design by means of SPS. A follow-up study on the correlation between the electrode’s architecture (porosity level and pore size) and its electrochemical performance has been conducted [6] showing that a moderate increase of porosity and decrease in pore size improves the rate capability of the (ultra)thick electrodes (1 mm thick) by reducing the pore tortuosity and promoting more full electrolyte impregnation.Spark Plasma Sintering-based electrode fabrication technique is expected to be easily transferrable to other battery types like Na-ion batteries. However, commonly used Na-ion battery materials are not as widely produced as their Li counterparts and still require long and tedious synthesis procedures. In our work, we have recently demonstrated that SPS could be used to synthesize a common Na-ion battery cathode material – Na3V2(PO4)2F3 – in under only 40 min[2] which resembles a phase-pure compound with small particle size showing slightly enhanced electrochemical performance when compared to the solid-state synthesized NVPF. SPS-synthesized NVPF requires no further treatment and could be used directly as an active material component in the production of our thick binder-free electrodes.In this presentation, the detailed study on the correlation between the (ultra)thick electrode architecture (porosity, pore size/shape distribution, tortuosity, etc), synthesis/sintering parameters, nature of precursors, and the electrochemical performance will be discussed (both for Li- and Na-ion batteries). An insight into the fabrication of (ultra)thick electrodes with novel integrated current collector architectures and their impact on the structural integrity as well as the electrochemical performance of the electrode will be reported.[1] R. Elango et al., Advanced Energy Materials, Vol 8 Issue 15 (2018)[2] A. Nadeina et al., Energy Technol., 8: 1901304 (2020)[3] F. Lalère, et al, Journal of Power Sources, 247, 975-980 (2014)[4] G. Delaizir, et al., Adv. Funct. Mater., 22: 2140-2147 (2012)[5] A. Aboulaich, et al., Adv. Energy Mater., 1: 179-183 (2011)[6] R. Elango et al., submitted to Journal of Power Sources