Joule
ArticleRoll-to-roll solvent-free manufactured electrodes for fast-charging batteries
Context & scale
With the rapidly increasing demand for energy storage, the lithium-ion battery market keeps expanding. However, the conventional battery electrode manufacturing method involves toxic organic solvent and energy-consuming drying/recovering processes. The evaporation of the solvent leads to uneven materials distribution and the electrodes’ microstructure could impede the fast-charging ability. Here, we have developed a dry-printing method to avoid the toxic solvent in the conventional slurry cast method and skip the energy- and time-consuming drying process. The total manufacturing cost could be reduced by up to 15%, and the roll-to-roll system has huge potential to be scaled up. The properties and the mechanism of the dry electrodes have been deeply studied. The unique microstructure could also benefit the electrode with better fast-charging ability and longer cycle life. Thus, we believe this work paves a more efficient way for battery manufacturing with higher-quality electrode products.
Graphical abstract
Introduction
As the highly frequent extreme weather phenomena that happened in recent years alert us to the power of climate change, the control of greenhouse gases emission is urgent. In response to the United Nations Paris climate agreement (2015), the major emission countries and institutions such as the United States, the European Union, and China have claimed their net-zero pledge.1 These policies have accelerated the lithium ion batteries (LIBs) market surge, and the boost could last for decades. As a result, the LIBs market will expand from about 160 GWh in 2018 to 1,200 GWh by 2030 based on forecasts.2 In the LIBs market, electrical vehicles (EVs) make up the largest market share and have huge potential. Due to the limitation of charging time and the cost of organic solvent in the electrode manufacturing process, the development of EVs is retarded. Current electrode manufacturing technology uses a slurry of active materials (AMs), conductive carbon, binders, and organic solvent coated on a metallic substrate. However, the typical organic solvent is flammable, toxic, and expensive, necessitating the use of dry and recovery systems, which further increases the cost of electrode manufacturing. In addition, to meet the fast-charging demand from the EV market, the US Department of Energy (DOE) has published the targets for extremely fast-charging (XFC) batteries, which require charging 80% of the capacity within 15 min. However, the state-of-the-art battery technology has multiple difficulties for the fast-charging application. First, the graphite anode has a low operation potential plateau (<0.25 V vs. Li+/Li), which could cause Li plating on the surface by the overpotential.3,4 Second, the distribution of the conductive additive in the electrodes and the ion diffusivity in the electrolyte and solid phases (AMs) can limit the electron and Li+ transportation.5 Third, the high-tortuosity electrode microstructure could prolong the Li+ diffusion path and cause poor contact between the electrolyte and AMs interface.6,7
To overcome these challenges, numerous new materials have been discovered. Most of these novel materials are hard to be scaled up or applied in high-loading electrodes.8,9,10 Only a few studies are based on modifying the state-of-the-art battery system. The research that is based on the current commercial materials has the challenges of balancing the costs and performance. The studies on developing the manufacturing technologies such as solvent-free manufacturing and aqueous binder could reduce the production costs, improve throughput, and lower energy consumption.11 However, these innovations are always accompanied by disadvantages such as poor bonding strength, destruction of the AMs, and even a lower energy density.12,13,14,15 Other ways of modification, such as coating, doping, or developing special electrode structures, always bring extra costs.16,17,18,19 Most methods like freezing dry, atomic layer deposition (ALD), and chemical vapor deposition (CVD) are high-cost and hard to be scaled up.20,21,22 The paradox of cost and performance has been the largest dilemma for the battery industry.
Based on the XFC demand, we have developed a scalable dry-printing manufacturing technology to produce fast-charging electrodes (charge 78% capacity in less than 20 min). Besides the higher performance of the electrodes, this technology can avoid toxic and expensive organic solvents and save drying energy consumption.23 Here, we demonstrate the latest dry-printed (DP) cells with up-to-date commercial materials (LiNi0.6Mn0.2Co0.2O2 (NMC 622) and graphite), and the total manufacturing cost could be reduced by 15% based on the Argonne battery performance and cost (BatPaC) model.24 By skipping the drying and solvent recovery process, our solvent-free manufacturing method could also save 47% of total battery manufacturing energy consumption.25 The single-layer DP pouch cells built from the roll-to-roll continuous system exhibit better high-rate performance and higher cycling retention, compared with the commercial slurry cast (SL) cells. All the reference SL samples are prepared by Microvast, using industrially relevant electrode processing. The specific microstructures of DP electrodes are studied by different characterization methods and demonstrated with pseudo-2D modeling. The research results presented in this work show a potential new path for future low-cost fast-charging battery manufacturing and the implementation of advanced electrode design. The fundamental study of the electrodes’ properties and microstructure reveals the advantages of solvent-free manufactured electrodes and could benefit the related technology development.23,26,27,28
Section snippets
Electrodes fabrication and morphology
Targeting the fast-charging EV application, the scaled-up DP electrodes were prepared for single-layer pouch cell tests. Figure S2A shows the prepared DP cathode (DC) and anode electrodes, which have a flawlessly smooth surface and similar thickness and porosity as the reference SL electrodes. The fabrication of DP electrodes starts with powder mixing. Figures 1A and 1B show the scanning electron microscopy (SEM) images of the well-mixed cathode and anode powders. Part of the C65 and PVDF
Lead contact
Further information and requests for resources should be directed to and will be fulfilled by the lead contact, Yan Wang ([email protected]).
Materials availability
This study did not generate new unique reagents.
Electrode preparation
The AM powders (graphite [BTR] for anode and NMC622 [BASF] for cathode), PVDF binder powders (MTI), and Super C65 conductive agents (MSE Supplies) were loaded in a mass ratio of 90:5:5 in a mixing cup. Mixing was performed in a planetary mixer (FlackTek SpeedMixer). Figure S1A shows the setup of the roll-to
Acknowledgments
This work was supported by the Department of Energy, National Energy Technology Laboratory under award number DE-EE0006250 with the United States Advanced Battery Consortium LLC (USABC LLC) and Massachusetts Clean Energy Center. This research used resources from the FXI beamline (18-ID) of the National Synchrotron Light Source II. HPPC tests were carried out at Argonne National Laboratory, operated by the DOE Office of Science, by UChicago Argonne, LLC, under contract no. DE-AC02-06CH11357.
Author contributions
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