# Intense pulsed light-induced Sn@SnO@C core-shell nanocomposite with controlled air oxidation from inkjet-printed Sn nanoparticles for advanced binder-free Li-ion batteries

Jawad Reslan, Omar Kassem, Vincent Barnier, Sergio Sao Joao, Aizhan Yendigoyeva, Thierry Djenizian, Mohamed Saadaoui

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Jawad Reslan, Omar Kassem, Vincent Barnier, Sergio Sao Joao, Aizhan Yendigoyeva, et al., Intense pulsed light-induced Sn@SnO@C core-shell nanocomposite with controlled air oxidation from inkjet-printed Sn nanoparticles for advanced binder-free Li-ion batteries. Journal of Energy Storage, 2025, 121, pp.116320. emse-05125657

HAL Id: emse-05125657

https://hal-emse.ccsd.cnrs.fr/emse-05125657v1

Submitted on 23 Jun 2025

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# Intense pulsed light-induced Sn@SnO@C core-shell nanocomposite with controlled air oxidation from inkjet-printed Sn nanoparticles for advanced binder-free Li-ion batteries

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Jawad Reslan<sup>a</sup>, Omar Kassem<sup>a</sup>, Vincent Barnier<sup>b</sup>, Sergio Sao-Joao<sup>b</sup>, Aizhan Yendigoyeva<sup>a</sup>, Thierry Djenizian<sup>a,c</sup>, Mohamed Saadaoui<sup>a,*</sup>

## ARTICLE INFO

Keywords:

Sn anodes

Lithium-ion battery

Inkjet printing

Sn nanoparticles

Intense pulse light

Light-matter interaction

## ABSTRACT

Tin (Sn) is a prominent anode material for improving the performances of Li-ion batteries (LIBs) thanks to its abundance and high theoretical capacity. However, Sn is hardly applied in industry because it suffers from large volume expansion during cycling, resulting in poor reliability. Although various synthesis methods have been applied to overcome these issues, most strategies focus on combining nano-sized Sn active material with nanoporous carbonaceous binders to buffer volume expansion and improve intrinsic electrical conductivity. However, this implies a reduction in the fraction of active Sn nanomaterial by the binders and contradicts the trend towards increasing the energy density of LIBs. In this paper, we propose a facile and ultrafast method to fabricate binder-free Sn electrodes at ambient conditions using the intense pulsed light (IPL) method. Sn nanoparticles (Sn NPs) inks (10 and 20 nm) were first prepared using chemical methods and inkjet-printed onto copper foil before IPL. We show that meticulous tuning of the IPL parameters to the optimal condition results in heating above the melting temperature of Sn NPs while maintaining the film morphology and nanoparticle size. This pre-melting condition leads to the local transformation of organic ligands into an amorphous carbon shell, reduces the thickness of the native Sn oxide shell and subsequently enhances electron transfer between Sn NPs. Finally, we demonstrate that these electrically conductive Sn anodes exhibit outstanding specific capacities of (over 700 mAh g⁻¹ after 200 cycles at 1C) with good cycling stability and rate capability.

## 1. Introduction

The rising global demand for efficient energy storage solutions reflects the shift towards renewable energy and electric vehicles. A key challenge is to create smaller batteries without sacrificing capacity. Thin film batteries offer compact designs with high energy storage, making them ideal for applications such as wearable electronics, smart cards, flexible displays, and energy harvesting systems [1]. Overcoming the manufacturing challenges is critical to unlocking their potential.

Tin (Sn) has been identified as a promising anode material due to its abundance and high theoretical capacity (994 mAh g⁻¹ compared to the 372 mAh g⁻¹ for commercialized graphite anodes) and low operating potential (<0.5 V vs. Li/Li⁺) [2,3]. However, the adoption of Sn as an anode material in LIBs requires specially designed nano-architectures to

buffer the significant mechanical strain that occurs during lithium insertion and extraction cycles [4], which leads to capacity fading and reduced cycling stability. Despite its potential, downsizing Sn to the nano-domain, such as nanoparticles, is challenging due to its high susceptibility to oxidation in air, tendency to self-aggregate, and interfacial issues, all of which negatively impact electrical conductivity. Organic binders such as polyvinylidene fluoride (PVDF) are commonly used with carbon materials to enhance the electronic and ionic conductivity of nano-Sn anodes, improve interfacial adhesion, and support capacity retention during cycling. However, the use of binders and additives reduces the percentage of active material, limits the energy density in LIBs, and raises toxicity concerns. In contrast, binder-free electrodes offer higher Li⁺ and electron conductivity, improved electrolyte wettability, and more room to accommodate volume expansion, leading to enhanced

<footnote><sup>a</sup> Mines Saint-Etienne, Centre CMP, Departement FEL, F - 13541 Gardanne, France</footnote>

<footnote><sup>b</sup> Mines Saint-Etienne, CNRS, UMR 5307 LGF, Centre SPIN, F - 42023 Saint-Etienne, France</footnote>

<footnote><sup>c</sup> Al-Farabi Kazakh National University, Center of Physical-Chemical Methods of Research and Analysis, Tole bi str., 96A, Almaty, Kazakhstan</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: Saadaoui@emse.fr (M. Saadaoui).</footnote>
capacity, cycling stability, and rate capability.

The growing interest in printing technologies within the LIB com-
munity has been driven by its potential for rapid prototyping, even of
complex 3D shapes, through computer-aided design. Printing allows
precise control of the thickness of electrode by adjusting the number of
printed layers, which has proven to be an effective solution for
increasing the energy density of batteries [5].

Printed anodes for batteries require the formulation of functional
inks in which the active material is dispersed in a solvent matrix. The
physicochemical properties of the ink, including particle size, must be
carefully tuned to ensure smooth flow through the nozzle head. After
printing, the ink must be sintered at elevated temperatures to evaporate
solvents and initiate nanoparticle bonding. In the case of an air-sensitive
active material such as Sn, sintering of these NPs will cause oxidation of
Sn to form SnOₓ and SnO₂, thus degrading the electronic conductivity of
the anode and causing mechanical adhesion problems at the current
collector interface. Capping the NPs with organic layers such as poly
(vinyl pyrrolidone) (PVP) [6], oleylamido [7], or thiol [8] can prevent
these issues while creating repulsive forces that also help to increase the
stability of the NPs within the ink. However, the stability of these par-
ticles requires ligands with a thickness above 2 nm, which tend to
degrade both electronic and ionic conductivities [9,10]. Therefore, it is
essential to decompose these ligands at elevated temperatures after
printing to allow electrons and lithium ions to flow into the active ma-
terials. However, this curing step is challenging as it involves the
oxidation of active materials that are prone to air oxidation and tend to
form aggregates rather than a continuous thin film.

Herein we show that rapid flash sintering using intense pulsed light (IPL) is capable of producing electrically conductive Sn anodes at ambient conditions. Sn NPs with diameters of 10 and 20 nm were synthesized via a chemical method, formulated into an ink with appropriate

rheological properties, and then printed using the inkjet technique. The
high optical absorptivity of the Sn NPs converts the absorbed light into
heat, which carbonizes the organic ligands sticking around the NPs. The
sintering mechanism is studied in detail and the electrochemical char-
acteristics show consistent cycling with increased discharge capacities.
This stability can be attributed to the retention of the initial diameter of
the NPs after IPL and their enhanced ionic and electrical conductivity of
the electrodes. This experimental design differs from our previously
published studies demonstrating the ability of IPL to form core-shell
Sn@graphene NPs exclusively on plastic substrates [19]. While limited
research has shown success in printing Sn films, achieving highly
conductive Sn electrodes has typically relied on conventional annealing
and low-vacuum techniques, without demonstrating their application in
LIBs. However, our study demonstrates the feasibility and potential of
using IPL technology to produce inkjet-printed Sn anodes for LIBs,
marking a significant advance in this field.

## 2. Results and discussion

2.1. Sn nanoparticles characterization

The first step is the preparation of Sn NPs with diameters below 20
nm, which have been shown to improve LIB performance [7]. Smaller
NPs also prevent nozzle clogging during inkjet printing due to their
significantly smaller average diameter compared to the nozzle [11].

Next, the PVP/(Sn(Oct)2) molar ratio is adjusted under the influence
of a strong chemical reducing agent (NaBH4) to control the growth of Sn
NPs [12,13]. Increasing the PVP/(Sn(Oct)2) molar ratio from 0.29 to
1.46 results in a decrease in particle size, yielding particles with mean
diameters of approximately 20 ± 5 nm (denoted 20-Sn) and 11 ± 3 nm
(denoted 10-Sn), respectively (Fig. 1a). The increase in PVP mass leads

<figure><img src="image_5.png" /><figcaption>Fig. 1. (a) TEM images and particle size histograms for two separate synthesis processes using 0.2 g and 1 g PVP, (b) HRTEM image of 10-Sn showing a core-shell structure, (c) XRD profiles of 10-Sn and 20-Sn.</figcaption></figure>
to more frequent capping of the growing Sn seeds, producing more uniform, near-spherical grains with regular shapes and smaller NPs due to reduced aggregation [14,15]. Conversely, decreasing the mass of PVP results in larger grain sizes due to less frequent capping. We verify that increasing the PVP/(Sn(Oct)2) molar ratio above 1.46 does not reduce the size of the NPs (below 10 nm), but instead leads to an excess of PVP in the solution, requiring an additional washing step after centrifugation, which may oxidize the NPs. On the other hand, decreasing the PVP/(Sn(Oct)2) molar ratio below 0.29 resulted in NPs of about 20 nm in size, but also causes aggregation, leading to a less stable Sn NPs solution.

High-resolution transmission electron microscopy (HRTEM) images for both 10-Sn and 20-Sn reveal a core-shell structure. The core with a lattice fringe with an interplanar spacing of 0.28 nm, corresponds to tetragonal β-phase Sn [16], while the amorphous shell consists of a PVP ligand and amorphous tin oxide (SnOx). X-ray diffraction (XRD) confirms that the nano-powders are well indexed to β-Sn. No other peaks corresponding to tin oxide or impurities were detected in the pattern (Fig. 1c).

## 2.2. Sn ink formulation

Two separate Sn inks were formulated, one with 10-Sn and the other with 20-Sn, each achieving a high solids content of 20 wt% in a mixed solvent system. The solvents are used to disperse the PVP@Sn NPs and adjust the viscosity to 10–12 mPa·s and the surface tension to 28–33 mN m⁻¹ to meet the requirements of the inkjet printhead. A small amount of glycerol, selected for its high vapor pressure [17], was added to limit rapid evaporation, thereby reducing the coffee-ring effect and improving print quality [18]. Glycerol also increases viscosity and

reduces surface tension, which improves flow control and substrate wetting. We found that a 45:45:10 volume ratio of Ethylene Glycol: Ethanol: Glycerol achieved the desired viscosity of 9 mPa·s and surface tension of 33 mN m⁻¹, resulting in highly stable inks that remain effective for several months when refrigerated (Fig. S3). Fig. 2a illustrates the inkjet printing process and droplet formation.

The ink was then inkjet-printed using an optimized waveform (Fig. 2b) at a voltage of 21 V and a frequency of 5 kHz (Fig. S2). The optimum drop spacing was set at 25 µm to ensure good surface coverage when printing a continuous film (Fig. 2c). Regarding the substrate, the surface energy of glass is found to be around 70 mN m⁻¹, which is higher than the surface tension of Sn ink, ensuring good drop formation on glass. However, an O₂ plasma treatment for 1 min was carried out on Cu foil prior to printing in order to optimize the printing conditions. The surface energy of Cu was increased to approximately match that of glass to meet the requirement of inkjet printing.

## 2.3. Intense pulsed light sintering of inkjet-printed Sn

The PVP capping layer improves ink stability and print performance but requires decomposition above 300 °C, which often alters particle size and morphology. For Sn NPs, conventional thermal annealing oxidizes them to SnO₂ [19], resulting in high electrical resistivity and low electrochemical affinity for lithium [20].

We then investigated the application of intense pulsed light (IPL) for the ultrafast sintering of inkjet-printed Sn films. A train of light micropulses was used, and the pulse profile was meticulously tuned to better match the thermal profile [21], resulting in a dry Sn thin film with thicknesses of approximately 2 µm and 2.4 µm for 10-Sn and 20-Sn films, respectively. The high optical absorptance of 10-Sn and 20-Sn printed

<figure><img src="image_6.png" /><figcaption>Fig. 2. (a) Schematic illustration of the working principle of inkjet printing, (b) Waveform generation for Dimatix inkjet printer, (c) Printed Sn NPs line on glass.</figcaption></figure>
films immediately after drying exceeds 70 % and 80 %, respectively, which falls within the wavelength range of the dominant irradiation spectrum of the xenon lamp (Fig. 3a).

The high optical absorptance of 20-Sn films and the limited heat capacity of the glass substrate result in significant heat generation via the photothermal effect. Overheating can promote oxidation and melting, so we optimized the heating profile to minimize the total time.

This control can be achieved by varying the cooling time between successive pulses (Toff) while keeping the irradiant energy density nearly constant by adjusting the voltage, pulse width and number of pulses (Table S1). Higher pulse frequency achieved by decreasing the Toff results in heat accumulation at the surface of the sample (Fig. 3b). Increasing the pulse frequency gradually reduces the electrical resistivity of the Sn thin film to a minimum of 123 ± 15 µΩ·cm, which is

<figure><img src="image_7.png" /><figcaption>Fig. 3. (a) Absorption coefficient vs. wavelength; The temperature pulse profiles for (b) 20-Sn (c) 10-Sn; Variation of electrical resistivity for 20-Sn and 10-Sn, respectively, with the change of (d) frequency and (e) temperature.</figcaption></figure>
ten times higher than the bulk Sn resistivity of 11 µΩ-cm. However, as the pulse frequency is increased beyond the optimum of 5.2 KHz, the electrical resistivity increases (Fig. 3d).

On the other hand, 10-Sn NPs films require a higher energy density to achieve sufficient heating due to their lower optical absorption (Table S1). The increase in irradiance was achieved by increasing the voltage applied to the lamps and the pulse width. However, since the 10-Sn films are more susceptible to oxidation in air during heating due to their significantly high surface-to-volume ratio, the total processing time was reduced by decreasing the number of pulses to three (Table S1).

For 10-Sn, decreasing the frequency by increasing the pulse width leads to an increase in the temperature at the surface of the film, which then reduces the electrical resistivity to a minimum value of 91 × 10³ µΩ-cm ± 20 × 10³ µΩ-cm (Fig. 3d). Similar to 20-Sn, an increase in pulse width above 250 µs leads to an increase in electrical resistivity.

Table 1 highlights various methods explored for Sn. Our approach is notable for effectively minimizing resistivity. While other methods can achieve low resistivity, many require impractical conditions for large-scale production, such as vacuum, N2 atmosphere, or plasma environments. These are unsuitable for the roll-to-roll methods favored by modern industry. Our process, however, achieves low resistivity and is compatible with roll-to-roll processing, making it ideal for scalable, cost-effective industrial applications.

## 2.4. Physical characterization of IPL sintered Sn NPs thin films

The variation of electrical resistivity with maximum temperature during IPL, plotted in Fig. 3e, shows that the electrical resistivity of Sn films decreases to a minimum value during stage I and then increases during stage II, regardless of the size of the Sn NPs.

In stage I, the decrease in electrical resistivity during IPL is attributed to the evaporation of residual solvents, such as ethylene glycol and glycerol, which remain in the film after drying at 135 °C. In addition, the decomposition of PVP ligands facilitates electron transfer between NPs [26]. Thermal characterization of 10-Sn and 20-Sn nano-powder indicates that PVP degradation occurs at 300 °C, above the melting point of Sn NPs but below the degradation temperature of pure PVP at 350 °C (see Fig. S1). This is consistent with Fig. 3e, which shows increased electrical conductivity of Sn films above 300 °C.

The Raman spectrum of printed Sn films annealed at different pulse frequencies is shown in Fig. 4a,b. The spectra are dominated by two broad overlapping D and G features which are the signature of the disordered carbon present in the film. This confirms that the PVP organic material has been transformed into amorphous carbon during annealing [27]. The D peak is attributed to the sp2 atoms in rings and the

<table><caption>**Table 1**

Overview of Sn synthesis methods and minimum electrical resistivity achieved.</caption><thead><tr><th>Material</th><th>Method</th><th>Conditions</th><th>Resistivity (µΩ-cm)</th><th>Ref</th></tr></thead><tbody><tr><td>Cu-Sn</td><td>Fabricate one-and two-dimensional structures by direct printing</td><td>Sintered under H2-N2 gas at 773 K for 2 h</td><td>120</td><td>[22]</td></tr><tr><td>Sn NPs</td><td>Printing and sintering under a N2 atmosphere</td><td>Vacuum at 160 °C</td><td>1100</td><td>[23]</td></tr><tr><td>Sn NPs</td><td>Inkjet printing and surface treatments of hydrogen reduction and plasma ashing</td><td>177.3 °C for 30 min</td><td>64.3</td><td>[24]</td></tr><tr><td>Sn metal salt</td><td>Inkjet printing and plasma sintering</td><td>plasma power of 150 W and an Ar background pressure of 650 mTorr</td><td>17.20</td><td>[25]</td></tr><tr><td>Sn NPs</td><td>Inkjet printing and IPL sintering</td><td>Ambient conditions</td><td>110</td><td>[This work]</td></tr></tbody></table>

G peak is due to the bond stretching in all sp2 atoms including rings and chains.

For the 20-Sn, increasing IPL pulse frequency and thus temperature leads to an increase in ID/IG peak intensity and a shift of the G peak position to a higher wavenumber. The same trend is observed for 10-Sn with a higher ID/IG ratio but with a negligible shift in the G peak position (Fig. 4c,d). The significant increase in D peak intensity upon IPL annealing indicates that the sp2 sites begin to form aromatic clusters. This is consistent with the clustering model, which states that increasing the temperature of amorphous carbon leads to the diffusion and condensation of sp2 into planar, π-bonded clusters of increasing size La [28,29], and ID/IG is proportional to La² (for La < 2 nm). The arrangement of sp2 into clusters leads to a decrease in electrical resistivity thus facilitating electron transfer between Sn NPs. The high electrical resistivity in 10-Sn with higher ID/IG is mainly attributed to the size effect [30].

SEM images (Fig. 5b,c) show that the reduction in electrical resistivity of the films upon IPL annealing occurs without evidence of Sn melting or morphological changes related to grain growth of the Sn NPs. Surface pre-melting, rather than volume melting, can shift the melting temperature of NPs at high heating rates, as seen in IPL annealing. We believe that surface pre-melting of Sn NPs during IPL annealing causes local conversion of PVP to amorphous carbon. This amorphous carbon layer is likely to inhibit the neck/grain growth of NPs [31], thereby maintaining the microstructure of the Sn thin film during stage I.

In stage II, the electrical resistivity starts to rise with temperature, which contradicts the typical behavior observed in metal NPs, where increasing temperature usually decreases the electrical resistivity due to increased sintering phenomena. This increase in resistivity is attributed to morphological changes in the film and grain growth observed by SEM (Fig. 5c). Under specific IPL conditions, the photothermal effect initiates the melting of Sn NPs, resulting in the coalescence of these initially nanosized particles into larger spherical islands throughout the volume of the film, not just at the surface, as shown in the SEM topography in Fig. S6. This process results in the creation of porosity within the film. These irregularities in film morphology are the primary cause of the increased electrical resistivity above a certain threshold. The melting of Sn NPs occurs at temperature different from its near-equilibrium melting point (Fig. S1). The high heating rate drives the nucleation of the liquid into the interior of the NPs, causing melting to occur at higher temperatures. Concurrently, the ultrafast cooling at the end of the IPL process leads to heterogeneous nucleation of Sn NPs and the growth of microscale particles [32].

In the spectral range of 50–500 cm⁻¹, for both nanoparticle sizes and stages, our investigations did not detect the presence of SnO₂ in the samples, which typically forms during the thermal annealing of Sn NPs [19]. Two peaks were observed at 115 cm⁻¹ and 211 cm⁻¹, corresponding to Sn (Fig. S4a,b). Although there was no shift in the Sn NPs peaks, the overall lack of significant oxidation in the films is due to the efficiency of the IPL process, characterized by its remarkably short heating time.

This observation is further supported by XPS surface analysis of printed films after different IPL treatments. Fig. 6a shows the Sn3d photoelectron peak observed on 20-Sn printed film subjected to an IPL sintering treatment based on 9 pulses of 3.9 J/cm² with Ton of 80 µs and cooling time Toff between each consecutive pulse of 110 µs. The Sn3d peak exhibits a component with a binding energy of 484.9 eV corresponding to the Sn NPs core and a second asymmetric component with a higher binding energy attributed to the oxide film surrounding the SnNPs core. The detection of photoelectrons coming from Sn3d core level of the atoms forming the metallic core indicates the nanometer size of the surrounding oxide film. The asymmetry of the oxide contribution is attributed to the presence of two oxidation states Sn²⁺ at 486.4 eV and Sn⁴⁺ at 487.4 eV which are consistent with previous experimental investigations of the oxidation of Sn NPs, suggesting the coexistence of SnO and SnO₂ in the temperature range between 400 and 900 °C [33].
<figure><img src="image_8.png" /><figcaption>Fig. 4. Raman spectra analysis over 1000–2000 cm⁻¹ for (a) 20-Sn and (b) 10-Sn printed films on glass. (c) ID/IG ratio and (d) G peak position.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Fig. 5. SEM images of 20-Sn films sintered by IPL under different frequencies (a) 2.5 KHz at 3.5 J/cm² (Stage I), (b) 5.2 KHz at 3.9 J/cm² (Optimal) and (c) 8.5 KHz at 4.2 J/cm² (Stage II).</figcaption></figure>

The same XPS analyses were carried out on 20-Sn sintered with IPL treatments, resulting in maximum temperatures that span the two stages of the resistance behavior observed in Fig. 3e. For each sample analyzed, the Sn3d photoelectron exhibits a component at 484.9 eV, confirming the limited oxidation due to the short heating time of the IPL treatment. The presence of both SnO and SnO₂ was also detected in IPL treatment conditions. In order to evaluate the effect of changing sintering conditions, in particular the maximum temperature reached, we used the core-shell-shell model developed by Shard [34], which allows to calculate the thicknesses of SnO and SnO₂ oxides surrounding the 20-Sn core using the ratios of intensities of Sn, Sn²⁺ and Sn⁴⁺, determined by adjusting the experimental spectra with synthetic lineshapes for each component. Details of the oxide thicknesses computation using the core-shell-shell model as well as the Sn3d spectra adjustments can be found in the supporting information. To determine thicknesses, an assumption was made for the duplex structure of the oxide. Considering that

oxidation of Sn NPs is an anionic process driven by the oxygen diffusion through the preformed oxide to form a new oxide at the metal/oxide interface as well as SnO formed at the initial stage of oxidation before being decomposed to SnO₂ [33], SnO and SnO₂ were considered as the inner and outer shells, respectively, as illustrated in Fig. 6b.

The evolution of SnO, SnO₂ and total oxide thicknesses, calculated as a function of the maximum temperature reached during the IPL treatment, are presented in Fig. 7. The XPS analyses reveal a change in Sn oxide thickness, comprising both SnO and a few atomic layers of SnO₂ (<1 nm), at varying temperatures. The thickness evolution shows a similar two-stage behavior as the resistance of the films with the maximum temperature reached during the IPL treatment. At lower temperatures (stage I), the presence of native oxide thickness is evident. However, when using the optimum sintering parameters, the oxide thickness decreases, probably due to the chemical reduction of Sn oxide by amorphous carbon formed from the PVP (SnO + C → Sn + CO₂), thus
<figure><img src="image_10.png" /><figcaption>Fig. 6. a) XPS spectrum of the Sn3d core level recorded on an inkjet printed Sn film sintered with IPL treatment with a maximum temperature of 526 °C resulting in a film resistivity of 123 µΩ·cm. The experimental spectrum is adjusted using synthetic components attributed to Sn²⁺, Sn⁴⁺ and Sn⁰. The intensities of these components are used to calculate oxide layers thicknesses of SnO and SnO₂ according to the repartition model described in b) and using the Shard [34], a formalism for peak intensities coming from NPs Core-Shell-Shell structure.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>Fig. 7. Oxides film thicknesses of SnO et SnO₂ calculated using the nano-particle Core-Shell-Shell XPS model of Shard [34], in function of the maximum temperature reached during the IPL sintering treatment of inkjet printed Sn film. A 2nd-degree polynomial fit of the total oxide film thickness on Sn NPs was added to highlight the two stages already observed on the resistance of printed films as illustrated in Fig. 3e.</figcaption></figure>

increasing the conductivity of the Sn film [35]. Conversely, at higher temperatures (stage II), the oxide thickness increases by 35 % compared to the native oxide layer, indicating that the increase in oxide thickness contributes to the rise in electrical resistivity observed at stage II.

## 2.5. Mechanism of sintering of Sn NPs

Fig. 8 shows a schematic illustration of the sintering mechanism of Sn NPs. In stage I, temperatures above 300 °C triggered the conversion of PVP to carbon. For 20-Sn, this process started due to air exposure and catalytic action but was not completed, resulting in high electrical resistivity. For 10-Sn, the larger surface-to-volume ratio allowed for a more extensive transformation into amorphous carbon, but the short duration at this temperature wasn't sufficient to reduce the resistivity significantly. As the temperature increased, the 20-Sn showed a reduction in resistivity due to the formation of more ordered carbon structures, while the 10-Sn benefited from the longer processing time to achieve optimum electrical resistivity.

In stage II, the resistivity increased with temperature, contrary to typical metallic behavior. This was due to significant morphological changes, where Sn NPs began to melt and coalesce into larger structures, creating porosity and irregularities within the film. These changes, driven by high heating rates during photonic sintering, resulted in increased resistivity as the initially nanosized particles formed larger, less conductive islands.

## 2.6. Electrochemical characterizations

The successful design and fabrication of Sn NPs binder and waste-free anode in flexible LIBs is demonstrated by their excellent electrochemical performance. These Sn NPs electrodes were constructed on Cu by irradiating the 20-Sn and 10-Sn films at a frequency of 5.2 kHz (63 µΩ·cm) and 3 kHz (6 × 10⁴ µΩ·cm), respectively. In the conventional sintering method of Sn on Cu, intermetallic formation occurs at different temperatures. However, our investigation revealed that the IPL treatment does not induce any intermetallic formation (see Fig. S7), even at elevated temperatures. This is likely due to the rapid nature of the IPL process. The comparison of different NP sizes allows a deeper understanding of size-dependent phenomena such as lithium-ion diffusion kinetics, volume expansion and surface effects, which are crucial for the design of high-performance LIB electrodes. All specific capacities have been derived from the weight of the active material.

Cyclic voltammetry (CV) tests are essential for a comprehensive
<figure><img src="image_12.png" /><figcaption>Fig. 8. Schematic illustration of the mechanism of sintering of Sn NPs.</figcaption></figure>

evaluation of the electrochemical characteristics of the system. These tests provide valuable insights into the redox behavior of the particles as anodes, their electron transfer kinetics during lithium insertion and extraction processes. Fig. 9a shows CV curves of the 20-Sn electrode between 0.05 and 3 V at a constant sweep rate of 0.05 mV s⁻¹. In the first cycle, three cathodic peaks were obtained at 0.05 V, 0.25 V and 0.53 V (vs. Li/Li⁺), corresponding to the reaction of Li⁺ with C, Sn and SnOₓ, respectively [36,37]. From the second cycle, we observed that the peak at 0.53 V became less defined, due to the reaction (Eq. 1). With each subsequent cycle, this peak became progressively less defined. Conversely, the peak at 0.25 V became sharper with each subsequent cycle, due to an increase in the activity of the reaction between Li⁺ and Sn within the volume of the anode or due to a change in the phases of the Li-Sn alloy (Eq. 2). Four distinct oxidation peaks at 0.4–0.8 V (vs. Li/Li⁺) originate from the delithiation reactions of the LiₓSn alloy [38]. The humps ranging from 1.03 to 1.52 V (vs. Li/Li⁺) can be seen in both cathodic and anodic directions, the humps are responsible for the catalytic decomposition of the electrolyte on Sn [39].

$$2x\text{Li}^+ + \text{SnO}_x + 2\text{xe}^- \rightarrow \text{Li}_2\text{O} + \text{Sn} \quad (1)$$

$$\text{Sn} + x\text{Li}^+ + \text{xe}^- \leftrightarrow \text{Li}_x\text{Sn} \quad (0 \le x \le 4.4) \quad (2)$$

During deep galvanostatic cycling between 0.05 and 3 V (Fig. 9b), the discharge specific capacity reached 1032 mAh g⁻¹ for the first cycle and stabilized at 700 mAh g⁻¹ for subsequent cycles at 1C. The charge/

discharge curves show almost perfect overlap, indicating exceptional cycling stability. Capacity retention from the 2nd to the 10th cycle increases progressively from 95.5 % to 97.1 %, demonstrating the robust and durable performance of the electrode over repeated charge and discharge cycles. The initial irreversible capacity fade was just under 30 %, representing a notable improvement, considering that it is typically in the range of 50–60 %. This fading is attributed to the formation of a Solid Electrolyte Interface (SEI) at the electrode surface, facilitated by the fluoroethylene carbonate (FEC) electrolyte additive [40]. The 20 nm Sn NPs electrode shows excellent cycling performance over a range of current densities. As the current rate is escalated from C/10 to C/5 and 1C, the Sn NPs electrode consistently exhibits high discharge capacities, which vary from 892 mAh g⁻¹ to 755 mAh g⁻¹ and 708 mAh g⁻¹, respectively. Remarkably, when the current rate is reduced C/10 in the 50th cycle, the capacity tends to recover, reaching almost 88 % of the initial specific capacity at 785 mAh g⁻¹ (Fig. 9c). This resilience highlights the adaptability and recovery potential of the Sn NPs electrode under different charging conditions.

To comprehensively investigate how NPs size affects battery performance such as capacity, cycling stability, and rate capability, we conducted electrochemical tests on 10 nm Sn NPs electrodes over a voltage range of 0.05–1.2 V. Beattie et al. [41] highlighted anomalous behavior at higher voltages for NPs sizes around 10 nm, it was observed that charging to 1.6 V resulted in an irreversible high voltage plateau near 1.5 V, leading to dramatically reduced capacity and poor cycling
<figure><img src="image_13.png" /><figcaption>**Fig. 9.** Performance of 20-Sn and 10-Sn as anodes for LIB; for 20-Sn (a) Cyclic voltammograms of the 1st to 5th cycles in a voltage range of 0.05–3.00 V at a sweep rate of 0.05 mV s⁻¹, (b) Charge/discharge profile of the Sn NPs electrode at 1C, (c) Electrochemical performance at multi-C-rates, for 10-Sn (d) Cyclic voltammograms of the 1st to 5th cycles in a voltage range of 0.05–1.2 V at a scanning rate of 0.05 mV s⁻¹, (e) Charge/discharge profile of the Sn NPs electrode at 1C, (f) Electrochemical performance at multi-C-rates, (g) Discharge capacity as a function of cycle number at 1C (h) CE during cycling.</figcaption></figure>

performance. This anomaly, attributed to the catalytic decomposition of the electrolyte on certain crystal faces of pure Sn particles, resulted in the formation of a thick layer of decomposed electrolyte on the electrode surface, hindering lithium ion diffusion. Therefore, by limiting the cycling voltage to 1.2 V for the 10 nm Sn NPs, we sought to mitigate this observed anomalous behavior and ensure a more stable cycling performance.

The CV curves of the 10 nm Sn NPs electrode, performed at a constant rate of 0.05 mV s⁻¹, showed distinct redox peaks in the 1st to 5th cycles, as shown in Fig. 9d. On the reduction side, peaks were observed at potentials of 0.3, 0.39, and 0.59 V (vs. Li/Li⁺), indicating the reactions between Li⁺ with C, Sn and SnOₓ during the electrochemical cycling. Conversely, oxidation peaks were observed at 0.2, 0.5, 0.66, and 0.76 V (vs. Li/Li⁺), corresponding to Li⁺ extraction from the LiₓSn alloys (0.4 < x < 0.7) [42,43]. The first cycle shows broader peaks between 0.05 and 0.8 V (vs. Li/Li⁺). This broader range suggests the formation of an SEI film on the carbonaceous surface, lithium alloying within the nanostructured Sn, and Li⁺ insertion into the C matrix [44].

Given that the open circuit voltage (OCP) of the cell is 3 V and the

cycling range is intended to be between 0.05 and 1.2 V, a rapid discharge (lithiation) was performed at a high C-rate prior to initiating deep galvanostatic cycling at 1C (Fig. 9e). This approach resulted in a discharge specific capacity of 1275 mAh g⁻¹ during the first cycle. However, in the 2nd cycle, the capacity decreased to 590 mAh g⁻¹ before gradually increasing with each subsequent cycle. Despite this initial decline, the capacity showed a notable recovery in subsequent cycles, stabilizing at 900 mAh g⁻¹ after 20 cycles. This initial decrease in capacity during the second cycle, followed by subsequent recovery, is attributed to the rapid discharge of the cell at a high C-rate, which induces rapid capacity fading and subsequent reactivation [45]. This alternative approach shows promising results in terms of cycling stability and high charging rate performance. As a result of this recovery phenomenon, the battery performance remained relatively stable even as the current rate was increased from C/10 to C/5 and 1C for the first 50 cycles (Fig. S10). Following these initial cycles, the half-cell functioned normally with varying kinetics. In particular, the battery showed a remarkably high discharge capacity, reaching 890 mAh g⁻¹ after 100 cycles at a C-rate of C/10, which is close to the theoretical capacity of Sn. This highlights the
adaptability and resilience of the Sn NPs electrode under different
charging conditions (Fig. 9f).

In addition, the long-term cycling performance of 20-Sn and 10-Sn
electrodes after pulse light and 20-Sn electrode without pulse light
under high charge/discharge rates of 1C was investigated (Fig. 9g). The
discharge capacity of a 20-Sn electrode without IPL annealing, cycled at
1C between 0.05 and 3 V, remains significantly low at around 20 mAh
g⁻¹, contributing minimal capacity after the first cycle. This underscores
the important role of IPL annealing in carbonizing the PVP encapsula-
tion around the Sn NPs, allowing enhanced lithium ion penetration and
interaction with the surface, thereby facilitating improved lithium ion
insertion. Moreover, the annealed 20-Sn electrode shows a slight initial
capacity decay, the electrode maintains an impressive reversible ca-
pacity of 700 mAh g⁻¹ over 200 cycles. In particular, the coulombic
efficiency (CE) approaches nearly 100 % at this high rate, underlining
the excellent lithium storage capability and sustained cycling perfor-
mance. In contrast, the annealed 10-Sn electrode shows a significant
initial capacity decay due to rapid initial discharge, which damages the
electrode. However, subsequent reactivation of the cell improves the
discharge capacity reaching 900 mAh g⁻¹ after 20 cycles and stabilizing
at around 850 mAh g⁻¹ after 40 cycles. The improved capacity of the 10-
Sn compared to the 20-Sn can be attributed to its smaller particle size.
Smaller NPs generally offer larger surface areas, which promote more
effective lithium ion diffusion and provide additional active sites for
lithium storage. Despite this, it is worth noting that the CE of 20-Sn
reached a higher value and stabilized faster than that of 10-Sn due to
the reactivation process of 10 nm NPs (Fig. 9h). The reason for this
disparity can be attributed to the reactivation process of the 10-Sn cell.
Nevertheless, it is worth noting that the CE of both cells approaches
nearly 100 % at this elevated rate, highlighting their remarkable lithium
storage capability and sustained cycling performance.

To further understand the outstanding electrochemical performance
of Sn electrodes, SEM analysis has been performed to observe the
morphological change of the 10-Sn and 20-Sn electrodes after 100
charge/discharge cycles at 1C. Fig. 10 show that Both electrodes
maintain their original appearance, although the surface of both elec-
trodes become rougher in comparison with the microstructure of
uncycled electrodes, supporting the benefits of carbon matrix embed-
ding Sn nanoparticles to prevent the pulverization and the particle ag-
gregation, thus ensuring long cycle stability.

To delve into the outstanding cycling performance of the Sn NPs
electrode, the electrochemical impedance spectra (EIS) were analyzed
after 1 cycle and 100 cycles for 10-Sn and 20-Sn electrodes. As shown in
Fig. S11a,b, the Nyquist plots exhibit a depressed semicircle in the mid-

frequency region, indicating internal resistances within the electrode.
The low-frequency straight line represents the characteristic signature of
lithium ion diffusion, modeled by Warburg-type diffusion impedance. A
modified Randles circuit was employed to characterize the impedance
spectra (Fig. S11c). For 20-Sn the charge transfer resistance (Rct) values
show a decrease from 470 Ω to 288 Ω after one and one hundred cycles,
respectively. In contrast, the Rct values for 10-Sn showed no significant
change (Table S2). The decrease in Rct after 100 cycles suggests that the
material is activated during cycling, indicating an enhancement in the
lithium-ion storage process. This analysis provides crucial insights into
the evolving electrochemical characteristics of the Sn NPs electrode over
extended cycling, underscoring its improved performance and stability.

To the best of our knowledge, no previously reported Sn NPs LIB
anodes without the use of a binder can withstand hundreds of charge/
discharge cycles at high rates. In fact, most of these Sn-based LIB anodes
show a cycle life of <200 cycles at a current density between 0.05 and 1
A g⁻¹, and their capacity retention remains unsatisfactory (Table S3).
This highlights the exceptionally innovative method employed which
spans chemical synthesis, ink formulation inkjet printing, and intense
pulse light annealing to produce high-quality Sn NPs anodes.

### 3. Conclusion

In conclusion, our research represents a significant advance in the
development of thin-film Sn NPs anodes using inkjet printing, an inno-
vative method supported by intense pulsed light technology. This
innovative approach marks the first use of intense pulsed light to
formulate Sn NPs electrodes free from complications such as oxidation
and aggregation. Using inkjet printing, we have achieved exquisite
uniformity and precise thickness control in our electrodes. By using
intense and fast IPL, we effectively extracted Sn NPs from PVP insu-
lation, creating conductive patterns that facilitate rapid electron transfer
and accommodate the large size fluctuations encountered during
charge-discharge cycles due to the nanoscale size of Sn NPs. These
electrodes demonstrated distinct capabilities across different NP sizes,
supported by comprehensive analyses including SEM, EDX, XPS, and
Raman spectroscopy. Overall, our results confirm that inkjet printing is a
promising fabrication technique for the generation of high-capacity Sn
NPs electrodes, with potential implications extending to the develop-
ment of fully inkjet-printed cells using a range of electrode materials.

### CRediT authorship contribution statement

Jawad Reslan: Writing – original draft, Software, Resources,

<figure><img src="image_14.png" /><figcaption>Fig. 10. SEM images of Sn electrodes after 100 cycles at 1C (a) 20-Sn, (b) 10-Sn.</figcaption></figure>
**Methodology, Investigation, Formal analysis, Data curation, Conceptualization.** **Omar Kassem:** Investigation, Formal analysis. **Vincent Barnier:** Investigation, Formal analysis. **Sergio Sao-Joao:** Investigation, Formal analysis. **Aizhan Yendigoyeva:** Software. **Thierry Djenizian:** Writing – review & editing, Project administration, Funding acquisition, Conceptualization. **Mohamed Saadaoui:** Writing – review & editing, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, 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.

Acknowledgements

This work has been supported by the Région Sud and partially funded by the research projects « HIPERSLIM » ANR21CE050009.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.est.2025.116320.

Data availability

The authors confirm that all data supporting this finding have been included in the main article and its ESI.

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