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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - ULTIMATE (ULtra-ThIck Multi-mAterial baTtery Electrodes)

Teaser

Summary

Because of their high energy and power density, Li-ion batteries (LIB) are the most prominent energy storage technology for consumer electronic devices and electrical vehicles. Impressive achievements have been made in the discovery of new active materials to increase the battery energy density and in understanding interface effects to enhance both their performance and lifetime. Battery electrodes typically consist of Cu foils coated with the anode material and Al foils coated with the cathode material, which are spaced apart by a separator soaked in electrolyte. While the Cu, Al, and separator foils are essential for the operation of the battery, they are passive components that do not store energy and are essentially dead volume. The easiest way to decrease their relative fraction is to increase the thickness the active material coating. Unfortunately, thick electrodes are difficult to fabricate. Therefore, only very few groups have been able to substantially improve the areal loading of batteries, and are typically relying on specialized fabrication methods. Here we have prepare scalable ultra-thick battery electrodes with sophisticated structures for good electron and ion transport.

Work performed

We developed scalable process to construct bi-continuous Li-ion battery electrodes using thermally induced phase separation (TIPS) as described in the proposal. TIPS is a robust process as it only relies on changes of material solubility with temperature. It is therefore easy to scale-up, and suitable for manufacturing thick battery electrodes. The TIPS process creates a bi-continuous network of electrolyte providing good ion transport and electrode allowing for excellent electron transport. Importantly, we found an electrolyte that can be used as a solvent to drive the TIPS process. Specifically, all the electrode components such as active material, carbon additive and binder are simply mixed with the electrolyte while heating, and as they cool down, the TIPS process drives the bi-continuous network formation without the need for any additional solvent. This process is attractive because it incorporates the electrolyte as a continuous network, while compacting the electrode phase such as active material, carbon additive and binder without the need for drying, which represents important energy savings especially for thick electrodes and alleviates the need of solvent trapping. This new drying-free electrode fabrication approach also addresses the cracking and flaking problems which occur during the drying of classic thick battery electrodes. 500 Âµm thick electrodes made by this process outperform standard 60 to 150 Âµm thick electrodes both in areal and gravimetric capacity, even at high rates of 10C. Areal capacities of up to 24.3 mAh/cm2 are achieved using standard intercalation materials (LTO, LFP and NMC), resulting in excellent cycling stability. Capacity retentions of 87% are achieved over 500 cycles in full cells with 1 mm thick anodes and cathodes.

Final results

We verified the scalability of the TIPS process using a pilot scale roll-to-roll coating, which did not require any electrode drying. The areal capacities of TIPS electrodes are increasing linearly with the same slope up to thicknesses of 2mm, and then taper off for 3mm thick electrode. The latter allow increasing the areal capacity to 24.3 mAh/cm2 at C/20 and this thick battery electrode with high scalability is unprecedented. Importantly, the TIPS electrodes reduce the fabrication cost (less cutting and stacking steps, less use of expensive separators and current collectors, and no electrode drying). For example, to make a 3 Ah cell with an electrode area of 10cm 2, about 8 electrode stacks are needed with 2 mm TIPS electrodes whereas ~100 stacks are needed when using the thick conventional electrodes.