High Performance Stretchable Li-ion Microbattery – HIPERSLIM

The fabrication of a micropillar array involves several key steps. It begins with the design of a silicon master. To maximize the surface area, it is crucial to control the shape and density of the structures, requiring very small spacings. Given the limitations of available fabrication techniques, alternative methods such as metal-assisted chemical etching (MACE) and deep reactive ion etching (DRIE) were considered to create pillars with a diameter of 10 µm and a height of 25 µm. Once the masters are created, flexible molds made of PDMS (polydimethylsiloxane) are fabricated to allow the pillars to be molded.

In addition to this approach, flexible, binder-free electrodes based on inks were printed onto various substrates. These inks, composed of tin nanoparticles or SiC-graphene, were first annealed using the innovative intense pulsed light (IPL) method. In parallel, self-healing monomers are synthesized, containing groups capable of forming hydrogen bonds for self-repair, particularly structures based on ureidopyrimidinone (UPy). These monomers are then copolymerized with an ionic conductor using a controlled radical polymerization technique, Nitroxide-Mediated Polymerization (NMP), to create block copolymers. These copolymers combine different desired properties in a single material. Initially, an attempt was made to work with a linear POE block, but this proved too fragile. Furthermore, high temperatures during the polymerization process led to monomer degradation. In response, branched copolymers were synthesized by Reversible Addition-Fragmentation Chain Transfer (RAFT), which allows for operation at lower temperatures.

To improve conductivity, other architectures are also being explored, such as oxanorbornene-based copolymers and double-crosslinked ionogels, which combine hydrogen bonds and reversible covalent bonds. This research aims to develop higher-performance materials for various applications, particularly in electronics and energy storage technologies. These advances could pave the way for more efficient and durable devices, incorporating self-repair systems to extend their lifespan and improve their reliability.

In the context of electrode material research, metal-assisted chemical etching (MACE) was deemed unsuitable, despite showing potential for creating metallic patterns. Suspensions were developed for cathode (LFP) and anode (LTO) materials, with a focus on conductive inks based on polyaniline-polyacrylic acid (PAA-PANI) and 3-hydroxy-4-nitrobenzoic acid (HNB), which offer excellent mechanical stability during demolding.

A proof of concept was performed with nanoprinted electrodes, where an LFP-PAA/PANI ink was structured into pillars on an aluminum foil. However, these fragile patterns showed signs of breakage during demolding. Alternatively, tin or silicon nanoparticle-based anodes, treated by an intense pulsed light (IPL) method, have demonstrated impressive specific capacities of over 700 mAh/g after 200 cycles, with good stability during charging and discharging.

Regarding electrolytes, several stretchable, self-healing polymers were synthesized. Three block copolymers were developed, the first exhibiting ionic conductivity but insufficient mechanical properties. A second block, based on polystyrene, offered improved mechanical properties and an optimal conductivity at 30°C of 1.5 × 10⁻⁵ S/cm. Polyoxanorbornenes were also explored. Their oxygen-rich structure could allow for improved conductivity. After polymerization, these copolymers demonstrated superior mechanical properties and were able to withstand deformation cycles of up to 100% without failure, although their ionic conductivity remained moderate at 4.2 × 10⁻⁶ S/cm. To optimize conductivity, ionogels incorporating dynamic covalent crosslinking networks were tested. These formulations have yielded good mechanical properties, with near-complete recovery after disconnection, and a high ionic conductivity of 1.4 × 10⁻⁴ S/cm at 30°C.

These advances in battery materials research aim to improve the performance and durability of energy storage systems, while exploring innovative solutions for electrolytes and electrodes, which could impact the fields of wearable technologies and electronic devices.

In general, advances in microbatteries are opening up future prospects in healthcare, wearable electronics, and the Internet of Things (IoT). The interdisciplinary nature of the subject has allowed research to expand beyond the challenges of electrochemical energy storage, exploring new methods for micro- and nanostructuring materials and polymer technology. Inventors Priyanka Jood and Victor Malgras are about to launch a startup, NIMPRINT, which aims to commercialize their nanostructuring technology for the transparent electrode market (CNRS pre-maturation grant obtained), the pixelated polarizer market (SATT maturation grant in negotiations), and the infrared sensor market (in collaboration with ONERA). Other academic collaborations have also been initiated, notably on thermo-plasmonic structures (AMUTech project with Fresnel obtained) or substrates for Raman biodetection (discussion with Paris Cité).

The ionogel electrolytes studied in this project also appear very promising, and this type of self-healing electrolyte deserves further development in the near future: an ANR (French National Research Agency) grant application is being considered (discussions are underway with the SOFTMAT Laboratory). The self-healing elastomeric materials obtained in this project also open up possibilities for use as high-density silicon-based anode binders, to address the issue of their large volume variation (300%) with lithium insertion/deinsertion. This research activity led to the grant of a MSCA-Doctoral Network project in March 2026 on self-healing materials for photovoltaic cells. In another area, the development of flexible electrodes has also paved the way for new projects, such as the development of flexible bioresorbable batteries, funded by the PEPR Batteries program (2023-2028). European projects have also been submitted on this topic: a MSCA-Doctoral Network in 2024 and 2025 and an EIC Pathfinder in 2025. The latter will be submitted again in May 2026.

Stretchable energy storage systems composed of micro-supercapacitors and microbatteries have attracted attention to meet the requirements of wearable technologies such as smart electronic textiles. However, performances of these flexible micropower sources remain well below the typical levels required due to the formation of multiple fractures and the subsequent loss of electrical contacts under chemical and mechanical strains. Thus, the challenge is to design safe and efficient energy storage devices showing high electrochemical performance with advanced mechanical properties to prevent crack issues during electrochemical and mechanical tests.
HIPERSLIM aims to fabricate a stretchable Li-ion microbattery delivering high areal capacity values (>1mAh.cm-2) while bearing strong deformation (up to 100%) for wearable technologies. The concept relies on the assembling of two stretchable substrates carrying arrays of serpentine micropillar electrodes and being separated by a self-healing polymer electrolyte. With respect to the state-of-the- arts, this new technological approach presents several advantages: i) a larger covering of the stretchable surface by the active materials, it can be over 70 %. ii) Unlike compact thin-films, micropillar electrodes present empty spaces that prevent the fracture of the materials and the formation of cracks at the electrode/current collector related to the volume variations of the electrodes during insertion/extraction of Li+. iii) 3D microstructured electrodes also increase the energy and power densities of the microbattery owing to the larger surface area established between the electrodes and the electrolyte. v) The use of an innovative self-healing polymer electrolyte, based on a block copolymer containing elastomeric and ionic conductor blocks with dynamic healing motifs (hydrogen bonds), also maintains a good quality of the electrode/electrolyte interface during the mechanical and electrochemical tests.
Compared to results reported in literature, the microbattery design proposed in this work will lead to high energy and power densities as well as long lifetime under multiple engineering strains. To circumvent scientific and technological locks and insure the success of the project within 42 months, it is required to join four main competences in: i) Flexible microelectronics, ii) Thin film deposition techniques and micropatterning processes, iii) Polymer Sciences, iv) Electrochemical energy storage.
In accordance with the complementary scientific and technical knowledges of the four partners, HIPERSLIM is naturally divided into 5 workpackages. 1) Project management and coordination. 2) Optimization of the electrode design by establishing a relationship between the maximal deformation of the substrate and the surface covered by the serpentine electrodes. 3) Fabrication of micropillar electrodes on stretchable substrate. 4) Synthesis and deposition of self-healing polymer electrolytes. 5) Electrochemical and mechanical characterizations of stretchable microbatteries as well as potential applications.
By completion of the tasks, HIPERSLIM will result in the fabrication of a stretchable Li-ion microbattery delivering high areal capacity values (>1mAh.cm-2) while accepting strong deformations (up to 100%) for wearable applications.
The exploitation of this new flexible/stretchable micropower source can be envisioned to provide sustainable energy for various low-power devices. As a final product, we propose to fabricate an extensible and body conformable electronic smart bracelet integrating one prototype.