The electrolyte filling process of battery cells is one of the time-critical bottlenecks in cell production. Wetting is of particular importance here, since only completely wetted electrode sections are working. In order to accelerate and facilitate this process, the authors of this study developed a method to significantly increase the wettability of graphite-based anodes by a laser surface modification using low energy nanosecond laser pulses. The anode surface microstructure was evaluated by means of white-light interferometry and scanning electron microscopy. The assessment of wettability was done by drop test and capillary rise test of the liquid electrolyte. The results show that there is a predominantly selective ablation process for laser energy inputs below 2 J/m by which the graphite active material remains unaffected and the binder material is decomposed. The observed increase in surface roughness correlates with the increasing wettability. Investigations using Raman spectroscopy showed that laser treatment leads to a damage on the crystalline structure of the graphite particle surface. However, treating an entire anode including 6 wt% binder and conductive carbon black has shown that the overall amorphous content of the anodes surface can be reduced by 32% through treating the surface with a laser energy of 1.29 J/m. Up to that point, which is the resulting parameter range for the selective process, it is possible to ablate the amorphous binder and carbon black phase coevally exposing graphite particles while keeping their crystalline structure. Exceeding that range, ablation of the whole anode composite dominates and amorphization of the graphite surface occurs. The electrode’s capacity was tested on half-cells in coin cell format. For the whole laser parameter range investigated, the anodes capacity matches the mass loss caused by laser ablation. No additional capacity loss was observed due to amorphization of the exterior graphite particle’s surface.

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Perforation of lithium-ion battery electrodes has recently become an increasing interest in science and industry. Perforated electrodes have shown improved electrochemical properties compared to conventional, nonperforated electrodes. It has been demonstrated that through perforation, the fast-charging capability and the lifetime of these batteries can be significantly improved. The electrodes for lithium-ion batteries consist of a copper foil onto which the electrode material is applied as a porous layer. This layer is mainly composed of active material particles, which are bound together by a binder phase. Here, synthetic graphite was used as an active material. Up to now, it has been shown that an advantageous and precise perforation geometry can be produced by ultrashort laser pulse ablation. Since the ablation volumes during perforation of the porous electrode material with ultrashort laser pulses are unusually high compared to solids, this work investigates the parameter dependency on the ablation mechanisms in detail. For this purpose, in particular, single-pulse ablation was investigated with respect to the ablation thresholds at different pulse durations. The pulse durations were varied over a large range from 400 fs to 20 ps. By varying the number of pulses per perforation up to 50 and the single-pulse energy up to 45  μJ, it could be shown that a homogeneous ablation down to the conductor foil through the 63  μm thick active material layer can be achieved.

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In addition to costs, safety and durability, energy density and fast-charging capability are the key requirements for Li-ion batteries for automotive applications. To meet these requirements, new cell chemistries are being developed, such as silicon-containing anodes. Likewise, electrode designs with high mass loading, respectively high layer thickness and a high density are being researched. However, such high-energy electrodes exhibit significant transport resistances due to their design, which has a negative effect on the electrode kinetics and thus the fast-charging capability. In our presentation, we will use the example of NMC-based cathodes and graphite anodes to show how the electrode kinetics can be improved by systematically influencing the electrode microstructure and the electrode surface. Short and ultra-short pulsed near infrared laser processes as well as mechanical embossing methods using needle type tools are used. In doing so, near-surface “quasi 2D” modification and three-dimensional structuring of the electrodes active mass were investigated. We will demonstrate how a specific adjustment of the laser parameters e.g. energy per unit length allows a roughening of the electrode surface and a selective removal of the binder-conductive additive compound without damaging or significantly ablating the active material. This “quasi 2D” modification offers the advantage that the capacity is largely retained. Electrochemical analyses such as rate tests show an improvement of up to 25% in the fast-charging capability. Electrochemical impedance analyses using symmetrical cells underline these findings by revealing a reduced transport resistance. In tendency, the higher the laser energy input and surface roughness, the more pronounced the observed effects – with a loss of active material also being observed at high laser input. Comparatively, perforated (i.e. three-dimensionally microstructured) electrodes, are investigated. The results obtained are comparable to the surface-near modification. However, in the case of perforation by laser, about 10% of active material is removed, which is reflected in a corresponding loss of capacitance. Electrodes perforated by microembossing also show significantly improved electrode kinetics, but without material removal and capacity loss. This makes microembossing appear to be an interesting and alternative microstructuring process. Finally, the combination of both processes – “quasi 2D” plus 3D – is investigated to combine the beneficial effects of both. The differently processed electrodes were also subjected to various rapid aging tests such as 100 charge/discharge cycles with a current mode of C/3 as well as interspersed fast charging cycles. The modified graphite anodes exhibit a lower tendency to Li plating than unprocessed reference anodes, and the degradation is lower than for the reference electrodes. For instance, the perforated anodes exhibited a capacity retention of 96%. In addition to a significant improvement of the electrochemical performance, a clear enhancement of the electrolyte wetting is demonstrated. Droplet tests and rising height tests showed an improved wettability by a factor of 4 to 5, depending on the type of microstructuring. The process development and the electrochemical analyses were closely accompanied by microscopic and material analyses e.g. by means of white light interferometry, nano-CT, SEM and TEM as well as Raman spectroscopy to reveal the most important process-microstructure-property relationships. To sum it up, we believe that the presented microstructural modifications are very attractive – both, in terms of electrochemical performance as well as from a manufacturing point of view. Figure 1

Lithium‐ion batteries (LIBs) play a crucial role in using renewable sources. Vanadates have been applied as anode material due to the combined diffusion mechanisms and higher and stable capacities. Despite the interest in vanadates as anode materials, only a few studies have considered Ca2V2O7 (CVO) as an active material for LIBs. This work focuses on the use of CVO as a potential alternative anode‐active material for LIBs. Additionally, we investigate the effect of the conductive additive (C65) on the electrochemical properties of the electrodes, utilizing densified electrodes with a porosity of about 40 %. In doing so, this study provides important insights into new materials for LIBs, where the electrodes were manufactured using the commercial slurry methodology, replacing graphite by CVO – which was synthesized via the Pechini route (D50: 8 μm after milling). In summary, the results reveal that the amount of C65 positively affects the electrode‘s capacity. An increase in specific capacity was observed by up to 30 % using 10 wt.% C65. Such electrodes showed 235 mAh/gAM at C/10 and, when cycled at 1 C, completed 300 cycles with a retained capacity of 39 %. The results demonstrate that CVO might be a promising anode material for LIB energy storage systems.

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