Miniaturization holds great promise in various fields including healthcare, environmental monitoring, building automation, and robotics. While many electronic components have been successfully miniaturized, small battery technologies continue to underperform larger batteries on volumetric and areanormalized bases. To date, researchers have explored a wide variety of methods for building improved small batteries. In this work a combination of dry etching, photopatterning, and slurry-based processing is shown to be a promising route for the fabrication of powerful and energy-dense small batteries.

Lithium batteries can operate with a safer “water-in-salt” electrolyte [Also see Research Article by Suo et al. ]

in which the battery materials for the anode, cathode, and solid electrolyte are formed and defined spatially through lithography. The synthesis of metal oxide thin-film structures using photosensitive metallorganics is well known in the fields of optical waveguides, electronics, and sensors among others. [8][9][10] Titanium dioxide, a negative electrode for lithiumion batteries, has been synthesized via photopatterning with resolution down to 10 nm. [8] Furthermore, ternary and quaternary oxides have been demonstrated, suggesting that cathode materials such as lithium cobalt oxide may be attainable. [9,10] Research related to photopatternable solid electrolytes has largely focused on polymers that can be cross-linked in the presence of UV radiation. [11][12][13][14] However, these studies have not demonstrated the ability to pattern solid electrolytes directly on electrodes.SU-8 is an epoxy-based negative photoresist that is used in the fields of semiconductors, microfluidics, and MEMS due to its spatial resolution at the sub-30 nm level and ability to pattern high aspect-ratio structures. [15,16] In this study, we demonstrate that SU-8 can be modified to become a gel electrolyte. Modification of SU-8 with a lithium salt improves ionic conductivity without sacrificing patternability. SU-8 as a gel electrolyte demon strates a high ionic conductivity at room temperature along with good electrochemical stability, mechanical rigidity, and the ability to photopattern with micrometer-scale resolution.Initial studies of SU-8 focused on the effect of adding a lithium perchlorate salt (LiClO 4 ) to the crosslinked structure of SU-8 photoresist. During UV exposure, the eight epoxide groups in the SU-8 monomer were opened by acid generated by the photoinitiator ( Figure S1, Supporting Information). These groups then form ether linkages with neighboring end groups and crosslinking continues at elevated temperatures during the postexposure and hard bake. The fabrication of SU-8 and mSU-8 samples is depicted in Scheme S1 (Supporting Information). Fourier-transform infrared (FTIR) spectroscopy was used to quantitatively evaluate this process and to elucidate the structure of SU-8 polymer after the incorporation of LiClO 4 . Figure 1a shows the FTIR spectrum of the SU-8 films with different degrees of crosslinking and that of the mSU-8 film. Spectra are normalized to the benzene ring peak at 1608 cm −1 , which does not go through any chemical changes during the crosslinking process. The three characteristic absorption peaks One of the important considerations for the development of on-chip batteries is the need to photopattern the solid electrolyte directly on electrodes. Herein, the photopatterning of a lithium-ion conducting solid electrolyte is demonstrated by modifying a well-known negative photoresist, SU-8, with LiClO 4 . The resulting material exhibits a room temperature ionic conductivity of 52 µS cm −1 with a wide electrochemical window (>5 V). Half-cell galvanostatic testing of 3 µm thin films spin-coated on amorphou...

Careful control of sol–gel chemistry allows for the encapsulation of water-reactive lithium polysulfides

No abstract