# 3D printing of NMC-based patterned electrodes by inkjet printing

Kinga Sztymela, Manuella Cerbelaud, Pierre-Marie Geffroy, Yolande Murat, Marguerite Bienia, Fabrice Rossignol

► To cite this version:

Kinga Sztymela, Manuella Cerbelaud, Pierre-Marie Geffroy, Yolande Murat, Marguerite Bienia, et al.. 3D printing of NMC-based patterned electrodes by inkjet printing. Open Ceramics, 2024, 20, pp.100699. 10.1016/j.oceram.2024.100699. hal-05004917

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# 3D printing of NMC-based patterned electrodes by inkjet printing

Kinga Sztymela<sup>a</sup>, Manuella Cerbelaud<sup>a,*</sup>, Pierre-Marie Geffroy<sup>a</sup>, Yolande Murat<sup>b</sup>,
Marguerite Bienia<sup>a</sup>, Fabrice Rossignol<sup>a,*</sup>

## ARTICLE INFO

**Keywords:**

NMC electrodes

Inkjet printing

3D structures

Formulation

Printability

## ABSTRACT

One interesting way of enhancing the properties of lithium-ion batteries is to produce electrodes with a 3D design. The aim of the 3D design is to allow the electrolyte to penetrate through the electrode volume, increasing the surface-to-volume ratio and reducing ion diffusion paths.

To achieve these designs, additive shaping processes are promising. In this article, we analyze the possibility of printing 3D structured electrodes using inkjet printing. The study focuses on Nickel Cobalt Manganese (NMC) based electrodes, commonly used as cathode materials. The importance of initial powder size and formulation will be discussed in terms of printability.

Finally, we show that it is possible to print 3D structures using NMC inks. Improvements need to be made to ensure greater printing stability.

## 1. Introduction

The fabrication of a three-dimensional (3D) electrode structure is a promising strategy to enhance battery performance [1]. 3D architectured battery offers advantages by facilitating the penetration of electrolyte among the active components. This leads to enhanced surface-to-volume ratios and shorter diffusion paths for Li-ions. Consequently, increasing the loading of active material (AM) without impeding ion diffusion becomes possible. As a result, 3D cells have the potential to achieve both high energy density and high power density [2].

In order to build this 3D architecture, additive manufacturing techniques are more and more envisaged such as fused filament fabrication [3], stereolithography [4], direct ink writing [5], aerosol jet printing [6], and inkjet printing [7]. Among them, inkjet printing, with its ability to deposit thin films, [8] or create 3D patterns [9] rapidly and with high precision, stands out as a promising method for fabricating Li-ion batteries (LIBs) [10]. The major challenge of this method is the formulation of printable ink [11]. In particular, inks must meet specific characteristics required by each printer, such as particle size, viscosity, surface tension and Z-number ($Z=1/\text{Oh}$ with Oh being the Ohnesorge number).

Recently, we reported on the possibility of printing anode electrodes based on silicon nanoparticles [12]. In this paper, we focus on the possibility of printing Ni-rich $LiNi_xCo_yMn_zO_2$ (NMC)-based electrodes as cathodes. NMC material is indeed interesting for portable applications

due to its high capacity and safety characteristics. This material is also an important candidate for automotive applications [13]. Moreover, numerous studies have shown that this material can be formulated in an aqueous solvent, which is also an advantage from an ecological point of view [14,15].

Electrode inks are complex suspensions made up of active materials, conductive additives and various polymer binders that enable to maintain the shaped electrode after drying. These inks, generally used in tape casting, do not meet the criteria for inkjet printing and must be adapted. The goal of this paper is to show how a NMC ink suitable for inkjet printing process can be prepared. In the following, we will focus on the formulation with two types of NMC particles: one with a micronic size that is currently used for electrodes shaped by tape-casting, and one with a nanometric size. All formulations are performed in water. First, we will discuss the particle size effect and particularly the problem of particle grinding. Then we will discuss ink formulation as well as their suitability for inkjet printing.

## 2. Experimental

### 2.1. Raw materials

$LiNi_{0.3}Mn_{0.3}Co_{0.3}O_2$ (NMC333) powders are purchased from Sigma Aldrich. Powder particles have irregular shapes in sizes below 50 nm (see Fig. 1a). Granulometry measurements give a $D_{50}$ of 402 nm for

<footnote><sup>a</sup> Univ. Limoges, CNRS, IRCER, UMR 7315, F-87000 Limoges, France</footnote>

<footnote><sup>b</sup> CEA, CEA Tech Nouvelle Aquitaine, F-33600 Pessac, France</footnote>

<footnote>* Corresponding authors.
E-mail addresses: manuella.cerbelaud@unilim.fr (M. Cerbelaud), fabrice.rossignol@unilim.fr (F. Rossignol).</footnote>
<figure><img src="image_4.png" /><figcaption>Fig. 1. (a) TEM pictures of the raw nanopowder; (b) SEM picture of raw micro powder and (c) TEM pictures of milled micro powder.</figcaption></figure>

powder put in suspension, which shows that this powder is aggre-
gated. According to the measurements, the maximum size of aggregates
is around 800 nm. In the following, this powder is called “NMC
nanopowder”.

LiNi₀.₆Co₀.₂Mn₀.₂O₂ (NMC622) powders are provided by Umicore. Powder particles are spherical with a mean diameter of around 10 µm (see Fig. 1b). In the following, this powder is called “NMC micro powder”. Super P Carbon Black from Alfa Aesar (BET surface = 62 m² g⁻¹) is used as conductive agent. The carboxymethylcellulose (CMC, Mw ≈ 90000, DS= 0.65–0.90) from Sigma Aldrich as well as Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) from Sigma Aldrich are used as binders. The dispersing additives used are BYK-9076 and BYK-22144 from the BYK society.

## 2.2. Experimental sections

Scanning electron microscope (SEM) LEO 1530PV from ZEISS and transmission electron microscope (TEM) JEOL 2010F are used to observe the morphology of powders.

Grinding is performed by high energy ball milling using E<sub>MAX</sub> from Retsch. E<sub>MAX</sub> is equipped with an external cooling system and circulator connected to the Emax system, which prevents any overheating of powders during the grinding. In order to minimize the reactivity between the powders and the solvent, grinding is not performed in water but in isopropanol, which is less polar. This solvent is chosen because it has already been used as cosolvent to shape NMC electrodes [16]. The dispersing agent BYK-9076 is used to avoid the aggregation of powder during the grinding. Zirconium oxide balls were used as grinding media. The ball sizes will be specified in the following. The objective is to achieve a particle size D90 below 1 µm.

The LA-950 Laser Particle Size Analyzer (Horiba) is used to measure the particle size distribution of powders before and after grinding. The analysis is performed in the wet mode, where the particles are dispersed in ethanol prior to measurement.

XRD analysis is performed using D8 ADVANCE diffractometer from Brucker. Diffractograms are collected over the angular range of 10-80° with a step size of 0.02°, and a dwell time of 0.9 s per increment. The X-ray wavelength (λ) is 1.5406 Å. Prior to the analysis, powders are dried and de-agglomerated.

Mass spectrometry is performed using Inductively Coupled Plasma (ICP) with an Optical Emission Spectrometer (OES) Optima 8300 from Perkin Elmer. The goal of this measure is to detect the elements leached by active materials when suspended in water. 1 w% of powder is stirred in water for 24 h. Suspension is then centrifuged and filtered using a 0.1 µm PTFE syringe filter from Whatman to keep the supernatent, that is analyzed as the sample for ICP analysis.

The viscosity as a function of the shear rate is evaluated using Discovery Hybrid Rheometer HR-2 from TA Instruments with double wall concentric cylinders steel geometry (inside cup diameter 40 mm, inner cylinder height 21 mm). To determine the optimal amount of dispersing agent, more precise viscosity measurements are also performed using the microfluidic rheometer Fluidicam RHEO from Formulaction.

The zeta potential versus pH is measured for each powder using Zetasizer Nano ZS from Malvern Panalytical.

The preparation process for inks involves two steps. First three individual suspensions are prepared: a suspension of binder in water by magnetic stirring and two suspensions composed respectively of NMC or carbon black in water with BYK 22144 by using a high-speed disperser at 1000 rpm for 10 min. Finally, the three individual suspensions are mixed together using a high-speed disperser at 1000 rpm for 10 min. Additionally, to prevent excessively large agglomerates, all the inks were filtered through 2 µm filters before inkjet printing.

Printing and printability tests are performed using piezoelectric drop-on-demand inkjet printer CeraPrinter X-Serie from Ceradrop with the printhead Dimatix SClass SL from Fujifilm, that has 128 nozzles of a nominal droplet volume of 80 pL and of diameter 50 µm. Recommendations for this printer are : a viscosity between 5 and 20 mPa s, a surface tension from 30 to 35 mN/m and a particle size lower than 1 µm. Fabrication is done onto an Aluminum current collector, with the possibility of heating the substrate holder up to 60 °C. The working distance (distance between the nozzle and the substrate) is fixed at 500 µm.

Images of cross-sections of printed structures were performed using Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) Crossbeam 550 from Zeiss.

The 3D view of printed patterns is obtained using the 4 K ultra-high accuracy digital microscope from Keyence. Sizes of splat are determined by measuring size with the software Image J. The size is obtained by averaging over 10 measurements.

## 3. Results and discussion

### 3.1. Grinding of NMC

One of the most important parameters when inkjet printing suspensions is the size of the powder particles. It is indeed recommended that the particle size should be at least 50 times smaller than the nozzle diameter to eliminate the risk of clogging [17,18]. Commercial printheads typically have nozzle orifices ranging from 22 to 50 µm, then it is crucial for the particle size to be within the sub-micron range [19].

The particles of the NMC micro powder are larger than this size and need thus to be milled for inkjet printing.

High energy ball milling is performed in two steps. The results are obtained using balls of 800 µm (10 min), then 100 µm (10 min). The total grinding time is 20 min. Particle size distributions of milled powders are shown in Fig. 2. After the first grinding phase with 800 µm beads, a reduction in particle size is observed. The *D*<sub>90</sub> is estimated at 1.3 µm, that means that 90% of particles are smaller than 1.3 µm. This particle size is still too large for inkjet printing, and a second grinding stage is required. Following this second stage with 100 µm beads, the *D*<sub>90</sub> is lowered to 800 nm, that is a size acceptable for inkjet printing.

The morphology of raw and high energy ball milled NMC micro powder powders is depicted in Fig. 1(c). The originally spherical particles are transformed into irregular shapes after grinding. To verify the effect of the grinding on the crystal structure of NMC, the crystal structure of milled NMC micro powder is compared to those of raw powder by XRD analysis (see Fig. 3). As a result of the milling, the doublets
<figure><img src="image_5.png" /><figcaption>Fig. 2. Particle size distribution of high energy ball-milled micro powder.</figcaption></figure>

(018)/(110) and (006)/(102) merge, indicating a loss of the layered structure. As already mentioned in the literature, the I(003)/I(104) ratio can vary following the grinding process [20]. This ratio serves as an indirect measure of the degree of cation mixing between Li⁺ and Ni²⁺ ions [20–22]. In this study, the I(003)/I(104) ratio does not change significantly after milling. Values of raw and milled particles are found around 0.5. Based on this observation, it seems that the grinding process has minimal impact on the degree of cation mixing within the structure. This finding contrasts with the results reported by Pan et al. [20] for ball milling, suggesting that ball milling reduces this ratio.

Another qualitative indication of the structural ordering is the R-factor, represented as $[I(006)+I(102)]/I(101)$, which estimates the system's hexagonal ordering. The hexagonal ordering increases as the R-factor decreases [23]. For raw powder, its value is 0.43, while after milling, it reaches 0.60. Therefore, it can be assumed that milled NMC micro powder experiences a crystal structure disorder due to grinding, but without a strong change in the degree of cation mixing. From an electrochemical point of view, in a well-ordered crystal structure, the pathways for Li-ion diffusion are clear and well-defined, allowing for efficient and rapid movement of ions during charge and discharge cycles. However, when there is a structural disorder, such as cation mixing, vacancies, or lattice distortions, the diffusion pathways become more convoluted and obstructed. The presence of disorder observed by XRD should then be detrimental for the electrochemical properties. Electrochemistry measurements have indeed confirmed that the ground NMC powders are not suitable for battery application (see Supporting Information) as it was already reported by Pan et al. for a softer grinding methodology based on ball milling [20]. In this paper, although grinding is faster and the temperature is controlled, powder degradation is not avoiding during the grinding.

The NMC micro powder being deteriorated by the grinding step appears thus not suitable for the printing of electrodes by inkjet printing. In the following, only the NMC nanopowder whose size is directly compatible with the inkjet printing requirement will be used.

## 3.2. Dissolution of NMC nanopowder in water

The formulations of ink are developed in water as already proposed in the literature [14,15]. In order to verify the effect of water on NMC nanopowders, different characterizations have been performed. First, the evolution of the pH of a dilute suspension of NMC (1 wt.%) has been monitored as a function of time (see Fig. 4). Upon adding NMC to water, the pH of the suspensions increases. The solution becomes basic

<figure><img src="image_6.png" /><figcaption>Fig. 3. XRD patterns of raw and high energy ball-milled NMC micro powder.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 4. Evolution of the pH as a function of time after introducing NMC nanopowders in water with a solid loading of 1 wt.%.</figcaption></figure>

after some minutes, indicating a reaction between NMC and water. Beyond 2 h, the pH remains quite constant around 12. In order to quantify eventual leaching of Li, Ni, Mn, and Co ions into the solution during the water exposure, ICP measurements are performed (after 24 h of immersion). No measurable quantities of Ni, Mn, and Co ions are detected, whereas an approximate amount of 0.4 wt% of Li is found to have leached into the water. As suggested in Ref. [14], Li could come from a combination of LiOH and $Li_2CO_3$. As already reported, change in pH and Li leaching can be explained by an ionic exchange between Li⁺ and H⁺ [14,24], that happens when NMC particles are put in water. However, the quantity of Li ions released in solution observed by ICP (0.4w%) is low.

Finally, in order to understand if the water exposure has an impact on the NMC structure, XRD analysis are performed. An aqueous suspension of 1 wt% of NMC nanopowder is thus prepared and left under agitation for 24 h. The powder is then dried and analyzed by XRD (see Fig. 5). No significant differences are observed between the spectra. The I(003)/I(104) ratios, that are as already mentioned, an indirect measure of the degree of cation mixing between Li⁺ and $Ni^{2+}$ ions in the lithium layer, are similar before and after water exposure (0.55 and 0.51 before and after water exposure, respectively). Additionally, the distinct separation between the (108) and (110) peaks in the spectrum indicates that the layered structure was not impacted by exposure to water. All these observations suggest that the NMC nanopowder is little affected in the presence of water and thus can be used in a water based ink formulation.
<figure><img src="image_8.png" /><figcaption>Fig. 5. XRD patterns of raw NMC nanopowder and NMC nanopowder after 24 h of water exposure.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Fig. 6. Zeta potential as a function of pH for the NMC nanopowder and CB powders.</figcaption></figure>

### 3.3. Formulation of the ink

Fig. 6 shows zeta potential as a function of pH for nano NMC and CB powders in water suspension.

Results show an isoelectric point of 3 and 4.5 for the carbon black and NMC nanopowder, respectively. Over a wide range of pH from 4.5 to 12, both carbon black and NMC are thus negatively charged, and therefore will not attract each other by electrostatic interactions. When NMC and carbon black are put in water, the pH raises above 8 and the zeta potential is higher than 20 mV in absolute value. However, suspensions are not stable, which can be explained by the hydrophobicity of carbon black particles.

To guarantee the stability of the suspension a dispersive agent is used.

One additive BYK-22144 is selected both for CB and NMC. This additive is chosen because it is efficient both for CB and NMC in water. The use of a single type of dispersant indeed helps prevent the possibility of undesirable interactions between the various components of the ink. The optimal amount of the dispersing agent is determined by viscosity measurements on dilute suspensions (see Fig. 7). The concentration at which the viscosity reaches a minimum represents the optimal amount of dispersing agent required to achieve stable dispersion. Both for nano NMC and carbon black powder, it is observed that adding the dispersant decreases the viscosity of the suspension, proving its beneficial effect on stability. The optimal amount of BYK-22144 for NMC is around 10 wt% (polymer mass/NMC powder mass). As for carbon black powder, the optimal quantity of the dispersing agent totaled to 50 wt%.

Suspensions are thus prepared with the amount of dispersing agent previously determined. In addition to carbon powders, NMC nanopowder and dispersant, a binder is added to the suspensions to assure

<table><caption>**Table 1**
Properties of NMC inks prepared with CMC or PEDOT:PSS binders.</caption><thead><tr><td>Binder</td><td>Surface tension (mN/m)</td><td>Viscosity (mPa s)</td><td>Density (g/ml)</td><td>Z</td></tr></thead><tbody><tr><td>CMC</td><td>41.3</td><td>4.4</td><td>0.87</td><td>~ 10</td></tr><tr><td>PEDOT:PSS</td><td>43.7</td><td>4.5</td><td>0.74</td><td>~ 9</td></tr></tbody></table>

cohesion of the printed electrodes. In the following, two formulations with two different binders will be tested. The first one is the carboxymethylcellulose CMC90000 that has already been used in literature for aqueous NMC formulation [25]. The second one is the PEDOT:PSS, that has given good results in the inkjet printing of silicon based electrodes [12].

To obtain a good stability, the final ink is prepared by mixing the different components that have already been suspended. For that, three different suspensions are prepared: a suspension of NMC with the dispersant, a suspension of CB with the dispersing agent and a solution of binder. The quantities of dispersants are the ones previously determined (10 w% for NMC and 50 w% for CB). Finally, all the suspensions are mixed together to obtain the ink using a high-speed disperser at 1000 rpm for 10 min. The relative quantity between CB/AM/Binder is fixed at 70/26/4 in mass. In this ratio, only the binder is taken into account. When all the organic additives (OA: binder + dispersing agent) are taken into account, the ratio AM/CB/OA is 58/22/20. At the end, in this formulation, the amount of AM is lower than the amount currently used in NMC composite electrode formulation. We have chosen to work in a first approximation with a smaller amount of AM because of the AM particle size. Indeed, for nanometric particles, it may be worthwhile to increase the CB/AM ratio to achieve better electronic conductivity [26]. The quantity of water is chosen in order to obtain a viscosity in the range of viscosity required for inkjet printing. First of all, the stability of the suspensions prepared with either CMC or PEDOT:PSS are confirmed by sedimentation tests. After one month, no sedimentation is clearly observed confirming the good stability of the inks whatever the binder.

The viscosity, surface tension, and density are measured for each formulation, and the resulting values, together with the Z number, are presented in Table 1. The values are in the ranges required for the printer used in this study.

### 3.4. Printability tests

Fig. 8 presents the results of the printability tests for the prepared cathode inks. These images display droplets ejected from the printer's nozzle at different stages of the drop generation process. High jetting frequency did not have a significant impact on the nozzle clogging, so 1000 Hz is used for the tests.

Both inks yielded stable individual droplets without any accompanying satellite droplets. However, in both cases, the droplets lacked axisymmetry from the straight vertical line trajectory, and this is more evident for inks prepared with PEDOT:PSS. Moreover, some nozzles clog after a few minutes of printing. Possible reasons for the instabilities include large agglomeration of powders, progressive deposition of thin multilayer of ink on the nozzle surface, air bubbles entrapment or viscoelasticity, as already reported in literature [11].

In the following, inkjet printing is carried out using only a single nozzle. This is due to the previously mentioned instabilities that cause nozzle clogging. Using a single nozzle allows to better control the ejection process by monitoring and addressing ejection issues if they occur. To demonstrate the possibilities of printing thin coatings, cathode layers are deposited on aluminum foil with the droplets overlapping by 25 µm and the temperature of the substrate holder set at 50 °C. The squares of 1 × 1 cm were printed, each made up of 10 layers deposited one upon the other, which takes approximately 5 min. FIB cross-section images of fabricated inkjet printed planar structures are presented in Fig. 9. Thin layers of around 4 µm are successfully deposited without
<figure><img src="image_10.png" /><figcaption>Fig. 7. (a) Viscosity as a function of BYK-22144 concentration for NMC nanopowder. (b) Viscosity as a function of BYK-22144 concentration for CB powder.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>Fig. 8. Drop generation process at different stages observed on one nozzle : (a) CMC- and (b) PEDOT:PSS-based NMC inks. The lines representing the projection axis have been added for clarity.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fig. 9. FIB cross-section images of printed layers: (a) CMC- and (b) PEDOT:PSS-based NMC inks.</figcaption></figure>

cracks. The surface rugosity seems more pronounced with the CMC binder.

To check the possibility of printing a 3D cathode structure, it is tested to build pillars by deposition of single splats one on top of each other. Fig. 10 first shows the deposition of a network of single splats. The splats deposited with inks prepared with CMC are evenly distributed on Al foil, creating a uniform square pattern. The diameter of a single droplet after drying is around 53 µm. Looking closely at the images of an isolated splat, it is visible that there is not much active material within it, which is due to the need for low viscous inks and thus containing few solid particles.

For inks prepared with PEDOT:PSS there is however a chaotic arrangement of splats, with no visible order. This can be explained by the

droplets axisymmetry deviation previously observed. The direction of this deviation is random and cannot be corrected by the printing. This deviation was not observed in our previous works with silicon [12] that let us think that it is not only the binder which is responsible for the deviation but rather the interactions between all the components within the droplets. To conclude, the formulation of ink with PEDOT:PSS and NMC is thus not suitable to print patterned electrodes by inkjet printing.

In order to show that 3D cathode architectures could be built with the ink containing the CMC binder, the pattern is repeated 20 times, depositing droplets of ink on top of the other. The goal is to see how successive droplets overlap. Initially, the substrate holder is heated up to 40 °C, so that the previously deposited layer dries before the following droplets are deposited. Fig. 11 shows images of the obtained
<figure><img src="image_13.png" /><figcaption>Fig. 10. SEM observations of single splats deposited with ink containing (a) CMC and (b) PEDOT:PSS.</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>Fig. 11. Observations of deposited pillars with ink containing CMC. (A) First line: pillars deposited with the substrate holder temperature of 40 °C: (a) and (b) SEM observations of pillars obtained by 20 passes and (c) 3D microscopy of pillars printed with 20 passes. The image is colorized according to the measured height (blue for the lowest and red for the highest, which is around 16 µm); (B) second line: pillars deposited with the substrate holder temperature of 60 °C: (d) and (e) SEM observations of pillars obtained by 20 passes and (f) 3D microscopy of pillars printed with 20 passes.</figcaption></figure>

structures. Pillars are successfully deposited. With these parameters, it is also observed that the pillars have a crater in the center. This shape is confirmed by 3D microscopy (see Fig. 11). According to this analyses, pillars have a height of around 2 µm in the center with edges of around 11 µm. This effect may be due to the migration of particles during the drying as it is often observed for sessile droplets [27,28]. One other explanation can be that the deposited droplets are not sufficiently dried before the deposit of the next droplet, thus the impact may cause material to be ejected to the sides. To modify the drying step, the temperature of the substrate is increased at 60 °C. In that case, drying is accelerated. Figs. 11(a-c) reveal effectively, that heating reduces this effect. The particles are more homogeneously spread within the pillar (see Fig. 11(d-f)). In all cases, the size of splats is found around 81 µm, that is larger than that of single splat (around 50 µm). All these results reveal the importance of the formulation for the ejection process. Changing the nature of polymer can have a strong effect on the droplet trajectory. We have succeeded in printing materials with the superposition of a few dozen drops. However, due to the process instabilities that causes nozzle clogging with time, printing thicker samples, particularly layers suitable for electrochemical characterization, was not feasible.

## 4. Conclusion

In this study, we formulated NMC-based aqueous inks for inkjet printing. Patterned electrodes with CMC90000 have been obtained by superimposing around 20 drops. The dots have a diameter of the order of 90 µm.

During this study, different challenges have been encountered during the formulation of the inks, which are complex because of its numerous components (active materials, carbonaceous additives, dispersant and organic binder). One of the critical parameters is the particle size, that has to be submicronic. We confirm that the grinding of these intercalation materials is detrimental to their subsequent electrochemical properties, and that initial materials already smaller than a micron are therefore required. This study also shows the importance of interactions between suspended components. Indeed, the droplets of inks prepared with PEDOT:PSS show a strong random deviation with NMC powders, whereas this binder is well suited to the ejection of silicon-based inks. In addition, as the suspensions are very dilute, it is necessary to heat the substrate to accelerate drying between ejections. Thin electrodes can be printed, however because of ejection instabilities over time, it was difficult to print thicker electrodes.
In conclusion, this work opens up prospects for NMC-based aqueous electrode ink printing. With the aim of increasing the height of pillars to few hundreds micrometers by superimposing a higher number of droplets, different improvements need to be done to make the process more stable. On the formulation side, trials with other types of CMC with different chain lengths or degrees of substitution could be envisaged to see what effect this has on stability during printing. It would be also interesting to increase the AM quantity for electrochemical purposes. On the other hand, technological improvements could also be envisaged, notably the implementation of a head washing unit during printing, which could enhance print stability over time.

CRediT authorship contribution statement

**Kinga Sztymela:** Writing – original draft, Visualization, Methodology, Investigation, Formal analysis, Data curation. **Manuella Cerbelaud:** Writing – original draft, Supervision, Methodology, Formal analysis. **Pierre-Marie Geffroy:** Writing – review & editing, Supervision. **Yolande Murat:** Writing – review & editing, Investigation, Formal analysis. **Marguerite Bienia:** Writing – review & editing, Investigation, Formal analysis. **Fabrice Rossignol:** Writing – review & editing, Supervision, Methodology, Formal analysis, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This project has received funding from the European Unions's Horizon 2020 research and innovation program under grant agreement N° 875029. This output reflects only the author's view and the European Union cannot be held responsible for any use that may be made of the information contained therein. The authors further acknowledge Umi core for providing the NMC622 powders, and the following colleagues Coralie Marcucci (CEA, Bordeaux), and David Peralta (CEA, Grenoble) for technical support.

Appendix A. Supplementary data

Supplementary material related to this article can be found online at https://doi.org/10.1016/j.oceram.2024.100699.

References

[1] J.W. Long, B. Dunn, D.R. Rolison, H.S. White, Three-dimensional battery architectures, Chem. Rev. 104 (10) (2004) 4463-4492, http://dx.doi.org/10.1021/cr020740l.

[2] Y. Zhu, J. Li, M.S. Saleh, H. Pham, T.P. Plateau, R. Panat, J. Park, Towards high-performance Li-ion batteries via optimized three-dimensional micro-lattice electrode architectures, J. Power Sources 476 (2020) 228593, http://dx.doi.org/10.1016/j.jpowsour.2020.228593.

[3] A. Maurel, S. Grugeon, B. Fleutot, M. Courty, K. Prashanthan, H. Tortajada, M. Armand, S. Panier, L. Dupont, Three-dimensional printing of a LiFePO₄/graphite battery cell via fused deposition modeling, Sci. Rep. 9 (1) (2019) 1-14, http://dx.doi.org/10.1038/s41598-019-54518-y.

[4] C. Li, J. Du, Y. Gao, F. Bu, Y.H. Tan, Y. Wang, G. Fu, C. Guan, X. Xu, W. Huang, Stereolithography of 3D sustainable metal electrodes towards high-performance nickel iron battery, Adv. Funct. Mater. 32 (40) (2022) 2205317, http://dx.doi.org/10.1002/adfm.202205317.

[5] L. Li, H. Tan, X. Yuan, H. Ma, Z. Ma, Y. Zhao, J. Zhao, X. Wang, D. Chen, Y. Dong, Direct ink writing preparation of LiFePO₄/MWCNTs electrodes with high-areal Li-ion capacity, Ceram. Int. 47 (15) (2021) 21161-21166, http://dx.doi.org/10.1016/j.ceramint.2021.04.119.

[6] R. Rodriguez, L.J. Deiner, B.H. Tsao, J.P. Fellner, Aerosol jet-printed LFP cathodes with bimodal pore distribution improve the rate capability of LIB cells, ACS Appl. Energy Mater. 4 (9) (2021) 9507-9512, http://dx.doi.org/10.1021/acsacm.1c01678.

[7] C.C. Ho, K. Murata, D.A. Steingart, J.W. Evans, P.K. Wright, A super ink jet printed zinc-silver 3D microbattery, J. Micromech. Microeng. 19 (9) (2009) 094013, http://dx.doi.org/10.1088/0960-1317/19/9/094013.

[8] Y. Zhao, Q. Zhou, L. Liu, J. Xu, M. Yan, Z. Jiang, A novel and facile route of ink-jet printing to thin film SnO₂ anode for rechargeable lithium ion batteries, Electrochim. Acta 51 (13) (2006) 2639-2645, http://dx.doi.org/10.1016/j.electacta.2005.07.050.

[9] M. Lejeune, T. Chartier, C. Dossou-Yovo, R. Noguera, Ink-jet printing of ceramic micro-pillar arrays, J. Eur. Ceram. Soc. 29 (5) (2009) 905-911, http://dx.doi.org/10.1016/j.jeurceramsoc.2008.07.040.

[10] S. Zhou, I. Usman, Y. Wang, A. Pan, 3D printing for rechargeable lithium metal batteries, Energy Storage Mater. 38 (2021) 141-156, http://dx.doi.org/10.1016/j.ensm.2021.02.041.

[11] K. Sztymela, M. Bienia, F. Rossignol, S. Mailley, S. Ziesche, J. Varghese, M. Cerbelaud, Fabrication of modern lithium ion batteries by 3D inkjet printing: opportunities and challenges, Heliyon 8 (12) (2022) e12623, http://dx.doi.org/10.1016/j.heliyon.2022.e12623.

[12] K. Sztymela, F. Rossignol, M. Bienia, N. Zapp, K. Nikolowski, M. Cerbelaud, Fabrication of 3D silicon anode by inkjet printing: Opportunities and challenges, J. Energy Storage 75 (2024) 109567, http://dx.doi.org/10.1016/j.est.2023.109567.

[13] S.-T. Myung, F. Maglia, K.-J. Park, C.S. Yoon, P. Lamp, S.-J. Kim, Y.-K. Sun, Nickel-rich layered cathode materials for automotive Lithium-ion batteries: Achievements and perspectives, ACS Energy Lett. 2 (1) (2017) 196-223, http://dx.doi.org/10.1021/acsenergylett.6b00594.

[14] M. Wood, J. Li, R.E. Ruther, Z. Du, E.C. Self, H.M. Meyer, C. Daniel, I. Belharouak, D.L. Wood, Chemical stability and long-term cell performance of low-cobalt, Ni-rich cathodes prepared by aqueous processing for high-energy Li-ion batteries, Energy Stor. Mater. 24 (2020) 188-197, http://dx.doi.org/10.1016/j.ensm.2019.08.020.

[15] F.A. Cetinel, W. Bauer, Processing of water-based LiNi₁/3Mn₁/3Co₁/3O₂ pastes for manufacturing lithium ion battery cathodes, Bull. Mater. Sci. 37 (2014) 1685-1690, http://dx.doi.org/10.1007/s12034-014-0733-7.

[16] Z. Du, K.M. Rollag, J. Li, S.J. An, M. Wood, Y. Sheng, P.P. Mukherjee, C. Daniel, D.L. Wood, Enabling aqueous processing for crack-free thick electrodes, J. Power Sources 354 (2017) 200-206, http://dx.doi.org/10.1016/j.jpowsour.2017.04.030.

[17] G. Vescio, J. López-Vidrier, R. Leghrib, A. Cornet, A. Cirera, Flexible inkjet printed high-k HfO₂-based MIM capacitors, J. Mater. Chem. C 4 (9) (2016) 1804-1812, http://dx.doi.org/10.1039/C5TC03307A.

[18] D. Kuscer, J.Z. Shen, Advanced direct forming processes for the future, in: Advanced Ceramics for Dentistry, Elsevier, 2014, pp. 375-390, http://dx.doi.org/10.1016/B978-0-12-394619-5.00023-7.

[19] J. Zikulnig, J. Kosel, Flexible printed sensors—Overview of fabrication technologies, in: Reference Module in Biomedical Sciences, 2021, http://dx.doi.org/10.1016/B978-0-12-822548-6.00010-8.

[20] T. Pan, J. Alvarado, J. Zhu, Y. Yue, H.L. Xin, D. Nordlund, F. Lin, M.M. Doeff, Structural degradation of layered cathode materials in lithium-ion batteries induced by ball milling, J. Electrochem. Soc. 166 (10) (2019) 1964, http://dx.doi.org/10.1149/2.0091910jes.

[21] S. Patoux, M.M. Doeff, Direct synthesis of LiNi₁/3Co₁/3Mn₁/3O₂ from nitrate precursors, Electrochem. Commun. 6 (8) (2004) 767-772, http://dx.doi.org/10.1016/j.elecom.2004.05.024.

[22] H.-J. Noh, S. Youn, C.S. Yoon, Y.-K. Sun, Comparison of the structural and electrochemical properties of layered Li [Ni₃Co₄Mn₄]O₂ (x=1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) cathode material for lithium-ion batteries, J. Power Sources 233 (2013) 121-130, http://dx.doi.org/10.1016/j.jpowsour.2013.01.063.

[23] J. Reimers, E. Rossen, C. Jones, J. Dahn, Structure and electrochemistry of Li,Fe₂Ni₁-δO₂, Solid State Ion. 61 (4) (1993) 335-344, http://dx.doi.org/10.1016/0167-2738(93)90401-N.

[24] S.-T. Myung, F. Maglia, K.-J. Park, C.S. Yoon, P. Lamp, S.-J. Kim, Y.-K. Sun, Nickel-rich layered cathode materials for automotive lithium-ion batteries: Achievements and perspectives, ACS Energy Lett. 2 (1) (2017) 196-223, http://dx.doi.org/10.1021/acsenergylett.6b00594.

[25] D.V. Carvalho, N. Loeffler, G.-T. Kim, M. Marinaro, M. Wohlfahrt-Mehrens, S. Passerini, Study of water-based lithium titanate electrode processing: The role of pH and binder molecular structure, Polymers 8 (8) (2016) http://dx.doi.org/10.3390/polym8080276.

[26] M. Cerbelaud, B. Lestriez, A. Videcoq, R. Ferrando, D. Guyomard, Understanding the structure of electrodes in Li-ion batteries: A numerical study, J. Electrochem. Soc. 162 (8) (2015) A1485, http://dx.doi.org/10.1149/2.0431508jes.

[27] D. Zang, S. Tarafdar, Y.Y. Tarasevich, M.D. Choudhury, T. Dutta, Evaporation of a droplet: From physics to applications, Phys. Rep. 804 (2019) 1-56, http://dx.doi.org/10.1016/j.physrep.2019.01.008, evaporation of a Droplet: From physics to applications.

[28] A. Shimoni, S. Azoubel, S. Magdassi, Inkjet printing of flexible high-performance carbon nanotube transparent conductive films by coffee ring effect, Nanoscale 6 (2014) 11084-11089, http://dx.doi.org/10.1039/C4NR02133A.