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SEM images of the secondary particles of the two active materials for the cathodes NCM‐C (A, B) and NCM‐P (C, D). The NCM‐C secondary particles are granular and have a rough surface. In addition, they show a compact structure in which the primary particles (crystal grains) are hardly recognizable. The inner structure of NCM‐P particles is porous, and the particles have a rounded shape due to spray drying.
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Porous, nanostructured NCM achieves an improvement in the fast-charging capability and the durability of lithium-ion batteries. This improvement is attributed to an extended electrolyte—active material interface, where the electrochemical reactions take place and thus shorter diffusion paths inside the active material particles are necessary for ch...
Citations
... Nanostructured NCM particles have demonstrated notable benefits in energy storage applications, as evidenced by prior research. These advantages include the facilitation of rapid solid-state diffusion and charge transport, surpassing those of dense active materials [49,50]. Expanding on these findings, our study sought to analyze the pore size and surface area of NCM materials by varying the PVA molecular weight and content. ...
The growing need for lithium-ion batteries, fueled by the widespread use of electric vehicles (EVs) and portable electronic devices, requires high energy density and safety. The cathode material Li1-x(NiyCozMn1-y-z)O2 (NCM) shows promise, but attaining high efficiency necessitates optimization of both composition and manufacturing methods. Polycrystalline LiNiCoMnO2 powders were synthesized and assessed in this investigation using a polyvinyl alcohol (PVA) solution method. The study examined different synthesis conditions, such as the PVA to metal ions ratio and the molecular weight of PVA, to assess their influence on powder characteristics. Electrochemical analysis indicated that cathode materials synthesized with a relatively high quantity of PVA with a molecular weight of 98,000 exhibited the highest discharge capacity of 170.34 mAh/g and a high lithium-ion diffusion coefficient of 1.19 × 10−9 cm2/s. Moreover, decreasing the PVA content, irrespective of its molecular weight, led to the production of powders with reduced surface areas and increased pore sizes. The adjustments of PVA during synthesis resulted in pre-sintering observed during the synthesis process, which had an impact on the long-term stability of batteries. The electrodes produced from the synthesized powders had a positive impact on the insertion and extraction of Li+ ions, thereby improving the electrochemical performance of the batteries. This study reveals that cathode materials synthesized with a high quantity of PVA with a molecular weight of 98,000 exhibited the highest discharge capacity of 170.34 mAh/g and a high lithium-ion diffusion coefficient of 1.19 × 10−9 cm2/s. The findings underscore the significance of optimizing methods for synthesizing PVA-based materials to enhance the electrochemical properties of NCM cathode materials, contributing to the advancement of lithium-ion battery technology. The findings underscore the significance of optimizing methods for synthesizing PVA-based materials and their influence on the electrochemical properties of NCM cathode materials. This contributes to the continuous progress in lithium-ion battery technology.
... The drying behavior of the electrodes is influenced by the additional pore space of hierarchically structured materials, as described in detail by Klemens et al. [19]. At the beginning of the process, drying is similar to that of dense particles. ...
... In this case, an additional benefit could be derived from pore infiltration as the migrated binder accumulates on the electrode surface, where it blocks ion transport. By fixing the binder in and around the particles, this negative effect can be eliminated and an improved rate capability is observed for porous particles [19]. ...
... Schematic representation of the drying process of a particulate electrode with porous, nanostructured particles (Reprinted from Ref.[19] under CC BY license). ...
Nanoparticles have many advantages as active materials, such as a short diffusion length, low charge transfer resistance, or a reduced probability of cracking. However, their low packing density makes them unsuitable for commercial battery applications. Hierarchically structured microparticles are synthesized from nanoscale primary particles by targeted aggregation. Due to their open accessible porosity, they retain the advantages of nanomaterials but can be packed much more densely. However, the intrinsic porosity of the secondary particles leads to limitations in processing properties and increases the overall porosity of the electrode, which must be balanced against the improved rate stability and increased lifetime. This is demonstrated for an established cathode material for lithium-ion batteries (LiNi0.33Co0.33Mn0.33O2, NCM111). For active materials with low electrical or ionic conductivity, especially post-lithium systems, hierarchically structured particles are often the only way to produce competitive electrodes.
... However, a challenge for the large-scale deployment of laser drying is that the reduced space requirements are generally achieved through increased drying rates that can potentially cause detrimental degradation effects within the coating layer. Irrespective of the drying technology, high drying rates have repeatedly been shown to amplify the migration of binders and carbon black towards the electrode surface, causing the poor mechanical and electrochemical properties of dried electrodes [11][12][13]. This limits the applicability of laser drying on an industrial scale. ...
... Their findings suggest that higher drying rates are feasible in the initial stages of the drying process without compromising the mechanical and electrochemical properties of the electrode. This can be attributed to the fact that binder and carbon black migration is primarily caused by the capillary transport of the solvent towards the electrode surface, which predominantly occurs in later drying phases [11]. Therefore, a hybrid concept with an initial laser-based drying process at a high drying rate and subsequent convection-based drying at a low drying rate were investigated within this study. ...
... Initially, the wet film reaches the laser spot at ambient temperature, and is then heated to about 90 • C in the preheating zone. Subsequently, a state of quasi-equilibrium is established between the energy introduced by the laser and the energy transferred to evaporation, which results in a constant drying rate and coating temperature of approximately 90 to 100 • C. The quasi-equilibrium state persists as long as the coating surface remains sufficiently wetted by capillary transport and until film shrinkage is completed [11,16]. The equilibrium state accounts for the majority of the evaporation process [17,18], henceforth referred to as the evaporation zone in this study. ...
The drying of electrodes for lithium-ion batteries is one of the most energy- and cost-intensive process steps in battery production. Laser-based drying processes have emerged as promising candidates for electrode manufacturing due to their direct energy input, spatial homogeneity within the laser spot, and rapid controllability. However, it is unclear to what extent electrode and cell quality are affected by higher heating and drying rates. Hybrid systems as a combination of laser- and convection-based drying were investigated in an experimental study with water-processed LFP cathodes. The manufactured electrodes were compared with purely laser-dried and purely convection-dried samples in terms of drying times and quality characteristics. The electrodes were characterized with regard to physical properties like adhesion and electronic conductivity, as well as electrochemical performance using the rate capability. Regarding adhesion and electronic conductivity, the LFP-based cathodes dried in the hybrid-drying process by laser and convection showed similar quality characteristics compared to conventionally dried cathodes, while, at the same time, significantly reducing the overall drying time. In terms of electrochemical performance, measured by the rate capability, no significant differences were found between the drying technologies used. These findings demonstrate the great potential of laser- and convection-based hybrid drying of LFP cathodes to enhance the electrode-drying process in terms of energy efficiency and operational costs.
... However, as the mass loading of the active materials increased, the electrode thickness increased. During the drying process, as the temperature increases the light conductive materials and binders rise to the top of the electrode, which results in the delamination of the current collector and low adhesion between the electrode materials, resulting in microcracks Klemens et al., 2022). This makes the distribution of the electrode materials sporadic as the electrode thickness increases, which limits the laminated thickness. ...
To achieve a high energy density for Li-ion batteries (LIBs) in a limited space, thick electrodes play an important role by minimizing passive component at the unit cell level and allowing higher active material loading within the same volume. Currently, the capacity of active materials is close to the theoretical capacity; therefore, thick electrodes provide the clearest solution for the development of high-energy-density batteries. However, further research is needed to resolve the electrochemical and mechanical instabilities inside the electrode owing to its increased thickness. This review summarizes the various methods and recent research aimed at fabricating electrodes with low-torsion and uniform pore structure for fast ion transport, based on an in-depth consideration of the challenges encountered in thick electrodes. In addition, future developments and research directions necessary to apply these methods to the industry are presented. This review will be a valuable milestone for manufacturing robust thick electrodes with high performance and for realizing ultrahigh-capacity/density batteries in the future.
... The electrodes investigated originate from large-scale processing developed in cooperation with several institutes of KIT. [34][35][36] A detailed description focusing on NVP/C processing was recently provided by Klemens et al. 37 and here we briefly summarize the process. The slurry for NVP/C cathodes was mixed in a dissolver (Dispermat SN-10, VMA Getzmann), where carbon black (C65, C-Nergy) and graphite (KS6L, Timical-Imerys), a PVDF (Solef 5130, Solvay) binder-solvent solution with 7.5 wt.% and about 50 % of the required amount of NMP were dispersed. ...
... In a last mixing step, styrene-butadiene rubber (SBR, Zeon Europe) was added. The electrode coating and drying was carried out under quasi-isothermal drying conditions as a discontinuous process likewise described by Klemens et al. [34][35][36][37] The slurries were applied to an aluminum current collector by a doctor blade (ZUA 2000.60, Zehntner) and dried by an impingement dryer and temperature controlled heating plates, resulting in drying rates of 0.75 g m -2 s -1 in both cases. ...
Sodium-ion batteries are becoming an increasingly important complement to lithium-ion batteries. However, while extensive knowledge on the preparation of Li-ion batteries with excellent cycling behavior exists, studies on applicable long-lasting sodium-ion batteries are still limited. Therefore, this study focuses on the cycling stability of batteries composed of Na3V2(PO4)3/C based cathodes and hard carbon anodes. It is shown that full cells with a decent stability are obtained for ethylene carbonate / propylene carbonate electrolyte and the conducting salt NaPF6. With cathode loadings of 1.2 mAh/cm², after cell formation discharge capacities up to 92.6 mAh/g are obtained, and capacity retentions > 90 % over 1000 charge / discharge cycles at 0.5 C / 0.5 C are observed. It is shown that both, the additive fluoroethylene carbonate and traces of water in the cell, negatively affect the overall discharge capacity and cycling stability and should therefore be avoided. Remarkably, the internal resistances of well-balanced and wellbuilt cells did not increase over 1500 cycles and 5 months of testing, which is a very promising result regarding the possible lifespan of the cells. The initial loss of active sodium in hard carbon remains a major problem, which can only be partially reduced by proper balancing.
... 18 In particular, the pore network of the electrodes with porous particles and the influence of drying and calendering is investigated, since it is known from previous studies that porous particles can lead to improved electrode properties such as higher rate capability and less dependency on the drying rate for the investigated slurry configuration. 15,16,19,20 On the other hand, electrodes consisting of porous particles have higher porosity and, thus, lower energy density than those with compact particles. They therefore require high compaction and efficient drying conditions to reduce the porosity to levels known from compact particles. ...
... The electrodes were dried in a batch-wise working impingement dryer that allowed to set defined drying rates. 20 The isothermal drying temperatures for the drying rates 0.75, 1.5 and 3.5 g m 2 s −1 were 61, 73 and 85°C respectively (Eq. S4). ...
... 49,50 Previous publications have shown that this has a much stronger effect on the adhesion strength, volume resistance and rate capability of electrodes with NCM-C than those with NMC-P. 20 Müller et al. 15 and Klemens et al. 20 suggested that the lower binder concentration at the interface between electrode and current collector is the reason for a higher ohmic resistance of the electrodes, although the explicit contribution of the interface could not be measured directly. This statement becomes plausible when considering that the binder is normally associated with conductive carbon black in a CBD. ...
Previous investigations on porous NCM particles with shortened diffusion paths and an enlarged interface between active material and electrolyte showed improved rate capability and cycle stability compared to compact particles. Due to the additional intragranular porosity of the active material, the pore structure of the overall electrode, and, as consequence, the ionic transport in the pore phase, is altered. In addition, the particle morphology influences the ohmic contact resistance between the current collector and electrode film. These effects are investigated using impedance spectroscopy in symmetrical cells under blocking conditions. The ionic resistance and the tortuosity of the electrodes are determined and analyzed by a transmission line model. Tortuosity is higher for porous particles and increases more during calendering. This limits the options for densifying these electrodes to the same level as with compact particles. In a further approach, the method is used to explain the drying related performance differences of these electrodes. At higher drying rates, the contact and the ionic resistance of electrodes with compact particles increases more strongly as for electrodes with porous particles. These investigations provide new insights into the ion transport behavior and enable a better understanding of the impact of the electrode processing condition.
... Furthermore, unlike the tests proposed here, EIS could not be done prior to full cell assembly. 22 The mechanical peel test has historically been used as a proxy to evaluate electrode adhesion for evaluating characteristics of the interface between current collector and electrode [23][24][25][26][27][28] under the working hypothesis that greater adhesion of the electrode to the current collector reduces interfacial electronic contact resistance. [29][30][31] However, in the literature there is scant evidence that strong adhesive properties are equivalent to low electronic contact resistance. ...
Li-ion battery electrode electronic properties, including bulk conductivity and contact resistance, are critical parameters affecting cell performance and fast-charge capability. Contact resistance between the coating and current collector is often the largest electronic resistance in an electrode and is affected by chemical, microstructural, and interfacial variations. Direct measurements of contact resistance and bulk conductivity have proven to be challenging. In their absence, a mechanical electrode peel test is often used to compare adhesion and electrical contact resistance. However, using a micro-flexible-surface probe, contact resistance can be directly determined. This work compares contact resistance and mechanical peel strength of multiple commercial-grade HE5050 and NCM523 cathodes and graphite and silicon anodes. It was found that peel strength correlates well with contact resistance in a carefully curated data set (p < 0.05) and in some situations may be a good metric to estimate electrical properties. However, there were distinct outliers in the data set, indicating that peel strength may not accurately reflect electrical properties when there is significant variation in electrode composition. These results illustrate the value of the micro-flexible-surface probe in quantifying contact resistance and bulk conductivity to better understand how battery composition and processing steps affect microstructure and resulting cell performance.
As a popular energy storage equipment, lithium-ion batteries (LIBs) have many advantages , such as high energy density and long cycle life. At this stage, with the increasing demand for energy storage materials, the industrialization of batteries is facing new challenges such as enhancing efficiency, reducing energy consumption, and improving battery performance. In particular, the challenges mentioned above are particularly critical in advanced next-generation battery manufacturing. For batteries, the electrode processing process plays a crucial role in advancing lithium-ion battery technology and has a significant impact on battery energy density, manufacturing cost, and yield. Dry electrode technology is an emerging technology that has attracted extensive attention from both academia and the manufacturing industry due to its unique advantages and compatibility. This paper provides a detailed introduction to the development status and application examples of various dry electrode technologies. It discusses the latest advancements in commonly used binders for different dry processes and offers insights into future electrode manufacturing.
Two main goals for the industrial, slurry‐based electrode processing are a high process speed and the maximum possible material efficiency. This makes an increased drying rate and active material share favorable, but both are limited by adverse effects on the electrode quality. The adverse effects of fast drying are associated with the migration of binder. In this article, the slurry properties of water‐based graphite slurries are manipulated using a synthetic, layered silicate as additive. The influence of the polymer‐particle composite network on the viscosity, adhesion strength, and cell performance is investigated. By addition of a small amount of additive (0.5 wt% of the dry electrode), the binder migration is mitigated up to a drying rate of 6 g m⁻² s⁻¹ for graphite anodes with ≈4.2 mAh cm⁻² (corresponding with 30 s drying time) leading to a possible increase of eight times the process speed compared to drying with 0.75 g m⁻² s⁻¹ if adverse effects on the tortuosity of the electrodes can be solved. In this work, a combination of additive usage is pointed out with a multilayer approach and first insights are provided in how the binder migration may be mitigated to gain structurally optimized fast‐dried electrodes without losses in electrode quality.
The drying of solvent‐processed electrodes is a critical process step in the manufacturing of lithium‐ion batteries. The technology used to introduce the energy required for drying into the material, combined with the specified process parameters, significantly influences the resulting electrode properties. A major challenge is to counteract binder migration effects that may occur during drying of the porous electrode structure, causing a decrease in adhesion and electrochemical performance, especially for high drying rates. From this motivation, investigations on the influence of process design during near‐infrared drying of aqueous‐processed graphite anodes are carried out. A multistage drying design with varying parameters in specific drying sections with energy input by radiation is applied. The results show that the specific application of a three‐stage drying profile in combination with energy input by radiation enables a significant decrease in drying time by at least 60% while the electrode properties can be preserved. These findings indicate a beneficial development of binder distribution as a consequence of multistage NIR drying, evidenced by adhesion and electrochemical performance. Finally, the application of the multistage drying profile is theoretically transferred to an industrial‐scale roll‐to‐roll dryer, whereby the necessary dryer length can be reduced by 53%.
