Electrode processing based on the state-of-the-art materials represents a scientific opportunity toward a cost-effective measure for improving the lithium-ion battery performance. In this regard, perhaps the most important is the drying step in a typical non-aqueous based slurry processing which can profoundly impact the electrode microstructure and hence performance. Solvent evaporation during drying plays a critical role in the redistribution of the particulate phases consisting of active particle, conductive additive and binder. In this work, we attempt to provide a mechanistic understanding of the role of solvent evaporation on the electrode characteristics and performance via a combined experimental and theoretical analysis. This study elucidates that a non-uniform distribution of the constituent phases, especially the relatively mobile conductive additive and binder, can develop which depends on the solvent evaporation, particle diffusion and sedimentation attributes. Experimental results and theoretical analysis reveal the impact of evaporation rate on the conductive additive and binder distribution in the electrode microstructure and resulting electrochemical performance. Our analysis has shown that a slower two-stage drying, as opposed to a high-rate single-stage drying, allows for a favorable distribution of binder and conductive additive, thus reducing internal cell resistance and improving electrochemical performance. Increasing concerns about depleting fossil fuel reserves, energy security, and climate change have given rise to interest in the adoption of renewable energy in place of traditional, petroleum-based fuels. The implementation and usage of renewable energies have been limited due to lack of efficient storage and transportation infrastructure. Recent improvements in the energy density and durability of lithiumion batteries (LIBs) have made them an increasingly attractive means of energy storage. [1][2][3][4] Further improvements in lithium-ion technology would increase the viability of widespread adoption of electric vehicles and renewable energy integration into the electric grid. For example, improvements in the capacity of LIBs would not only improve the effective range of electric vehicles, 5,6 but also improve their cycle life by reducing the depth of discharge, which in turn increases the viability of LIBs for use in grid energy storage applications. 7The performance of Li-ion batteries depends on the electrode materials, the choice of electrolyte, and the cell architecture.4,8 A typical LIB positive electrode (cathode) is composed of a combination of Li-containing active material, conductive additive, polymeric binder, and pore space that is filled with an electrolyte. Typically, these are created by casting out and drying a thin film of slurry containing these multi-phase components. 19 but little attention is paid to the physical understanding of the electrode processing. The importance of this electrode preparation step cannot be overemphasized. In addition to determining the cel...

The lithium-ion battery (LIB) electrode represents a complex porous composite, consisting of multiple phases including active material (AM), conductive additive, and polymeric binder. This study proposes a mesoscale model to probe the effects of the cathode composition, e.g., the ratio of active material, conductive additive, and binder content, on the electrochemical properties and performance. The results reveal a complex nonmonotonic behavior in the effective electrical conductivity as the amount of conductive additive is increased. Insufficient electronic conductivity of the electrode limits the cell operation to lower currents. Once sufficient electron conduction (i.e., percolation) is achieved, the rate performance can be a strong function of ion-blockage effect and pore phase transport resistance. Even for the same porosity, different arrangements of the solid phases may lead to notable difference in the cell performance, which highlights the need for accurate microstructural characterization and composite electrode preparation strategies.

Particle size plays an important role in the electrochemical performance of cathodes for lithium-ion (Li-ion) batteries. High energy planetary ball milling of LiNi1/3Mn1/3Co1/3O2 (NMC) cathode materials was investigated as a route to reduce the particle size and improve the electrochemical performance. The effect of ball milling times, milling speeds, and composition on the structure and properties of NMC cathodes was determined. X-ray diffraction analysis showed that ball milling decreased primary particle (crystallite) size by up to 29%, and the crystallite size was correlated with the milling time and milling speed. Using relatively mild milling conditions that provided an intermediate crystallite size, cathodes with higher capacities, improved rate capabilities, and improved capacity retention were obtained within 14 μm-thick electrode configurations. High milling speeds and long milling times not only resulted in smaller crystallite sizes but also lowered electrochemical performance. Beyond reduction in crystallite size, ball milling was found to increase the interfacial charge transfer resistance, lower the electrical conductivity, and produce aggregates that influenced performance. Computations support that electrolyte diffusivity within the cathode and film thickness play a significant role in the electrode performance. This study shows that cathodes with improved performance are obtained through use of mild ball milling conditions and appropriately designed electrodes that optimize the multiple transport phenomena involved in electrochemical charge storage materials.

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational analysis. Testing of lithium-ion batteries in an academic setting has taken on several forms, but at the most basic level lies the coin cell construction. In traditional LIB electrode preparation, a multi-phase slurry composed of active material, binder, and conductive additive is cast out onto a substrate. An electrode disc can then be punched from the dried sheet and used in the construction of a coin cell for electrochemical evaluation. Utilization of the potential of the active material in a battery is critically dependent on the microstructure of the electrode, as an appropriate distribution of the primary components are crucial to ensuring optimal electrical conductivity, porosity, and tortuosity, such that electrochemical and transport interaction is optimized. Processing steps ranging from the combination of dry powder, wet mixing, and drying can all critically affect multi-phase interactions that influence the microstructure formation. Electrochemical probing necessitates the construction of electrodes and coin cells with the utmost care and precision. This paper aims at providing a step-by-step guide of non-aqueous electrode processing and coin cell construction for lithium-ion batteries within an academic setting and with emphasis on deciphering the influence of drying and calendaring. Video LinkThe video component of this article can be found at

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Despite the wide range of ideal applications for LIBs, there is still room for improvement in their performance. The effects of varying the composition and chemistry of LIBs are well documented [1-2], however a critical aspect that is often overlooked is the processing steps during fabrication. Typical processing parameters such as film thickness or evaporation have a large impact on critical parameters such as porosity of the electrodes, and thus can affect the electrochemical performance. During the solvent evaporation stage, a non-uniform distribution of electrode constituents can develop in cases where the solvent evaporation rate exceeds that of the diffusion rate of the mobile electrode constituents [3]. An even distribution of carbon black and binder throughout the electrode is crucial to ensuring the minimization of internal cell resistance, and therefore the maximum performance for a given electrode composition.  In this work, we evaluate the impact of evaporation rate on the distribution of binder and carbon black in the electrode microstructure and the subsequent electrochemical performance. Both single-stage and two-stage evaporation was considered, where the two-stage process consisted of a slow rate followed by  oven-drying, and the single-stage consisted solely of immediate oven drying, with two different rates. Figure 1 shows the evaporation rate as a function of overall electrode sheet weight percent. Here the first stage for the two-stage sheet occurs over approximately 16 hours, with a loss of roughly 20% by weight.  SEM images of the resulting microstructures indicate the vertical accumulation of carbon and binder on the surface of electrodes, with the increased carbon content in the case of the fast rate cases leading to the formation of a binder/carbon black composite that does not coat the active material particle surface, as shown in Figure 2. This through-plane (along the thickness) accumulation has been shown to decrease the rate performance, as shown in Figure 3. The experimental results combined with theoretical analysis is expected to shed insight into the optimal drying conditions that may yield an optimum distribution of electrode constituents.  References: 1.  M. Armand and J.M. Tarascon, Issues and Challenges  facing Rechargable Lithium Batteries. Nature, 414,      359 (2001). 2.  Handbook of Battery Materials, Second Edition. Edited by Claus Daniel and Jurgen O. Besenhard. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2011 by Wiley-VCH Verlag GmbH & Co. KGaA. 3.  A.F. Routh, Drying of Thin Colloidal Films. Rep. Prog.Phys., 76 (2013) Figure 1

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