Atomic Layer Deposition of Functional Layers for on Chip 3D Li‐Ion All Solid State Microbattery

Nowadays, millimeter scale power sources are key devices for providing autonomy to smart, connected, and miniaturized sensors. However, until now, planar solid state microbatteries do not yet exhibit a sufficient surface energy density. In that context, architectured 3D microbatteries appear therefore to be a good solution to improve the material mass loading while keeping small the footprint area. Beside the design itself of the 3D microbaterry, one important technological barrier to address is the conformal deposition of thin films (lithiated or not) on 3D structures. For that purpose, atomic layer deposition (ALD) technology is a powerful technique that enables conformal coatings of thin film on complex substrate. An original, robust, and highly efficient 3D scaffold is proposed to significantly improve the geometrical surface of miniaturized 3D microbattery. Four functional layers composing the 3D lithium ion microbattery stacking has been successfully deposited on simple and double microtubes 3D templates. In depth synchrotron X‐ray nanotomography and high angle annular dark field transmission electron microscope analyses are used to study the interface between each layer. For the first time, using ALD, anatase TiO₂ negative electrode is coated on 3D tubes with Li₃PO₄ lithium phosphate as electrolyte, opening the way to all solid‐state 3D microbatteries. The surface capacity is significantly increased by the proposed topology (high area enlargement factor – “thick” 3D layer), from 3.5 μA h cm^?2 for a planar layer up to 0.37 mA h cm^?2 for a 3D thin film (105 times higher).     

An Ultrahigh Energy Density Quasi‐Solid‐State Zinc Ion Microbattery with Excellent Flexibility and Thermostability

The rapid development of smart wearable and integrated electronic products has urgently increased the requirement for high‐performance microbatteries. Although few lithium ion microbatteries based on organic electrolytes have been reported so far, the problems, such as undesirable energy density, poor flexibility, inflammability, volatility toxicity, and high cost restrict their practical applications in the above‐mentioned electronic products. In order to overcome these problems, a low cost quasi‐solid‐state aqueous zinc ion microbattery (ZIMB) assembled by a vanadium dioxide (B)‐multiwalled carbon nanotubes (VO₂ (B)‐MWCNTs) cathode, a zinc nanoflakes anode, and a zinc trifluoromethanesulfonate‐polyvinyl alcohol (Zn(CF₃SO₃)₂‐PVA) hydrogel electrolyte is exploited. As expected, the ZIMB exhibits excellent electrochemical performance, e.g., a high capacity of 314.7 µAh cm^?2, an ultrahigh energy density of 188.8 µWh cm^?2, and a high power density of 0.61 mW cm^?2. Furthermore, the ZIMB also shows high flexibility and excellent high temperature stability: the capacity has no obvious decay when the bending angle is up to 150° and the temperature reaches 100 °C. The ZIMB provides a way to develop next‐generation miniature energy storage devices with high performance.     

In Operando Strain Measurement of Bicontinuous Silicon‐Coated Nickel Inverse Opal Anodes for Li‐Ion Batteries

Elastic strains are measured in operando in a nanostructured silicon‐coated nickel inverse opal scaffold anode, using X‐ray diffraction to study the Si (de)lithiation‐induced Ni strains. The volume expansion upon lithiation of the Si in the anode is constrained by the surrounding Ni scaffold, causing mismatch stresses and strains in the Si and Ni phases during cycling. The Ni strains are measured in operando during (dis)charge cycles, using diffraction peak position and peak broadness to describe the distribution of strain in the Ni. During lithiation, compressive strains in the Ni first increase linearly with charge, after which a gradually decreasing strain rate is observed as the maximum lithiation state is approached; upon delithiation a similar process occurs. In‐plane average compressive strains on the order of 990 ± 40 με are measured in the Ni scaffold during lithiation, corresponding to compressive stresses of 215 ± 9 MPa. The decreasing strain rates and decreasing maximum and recovered strains suggest that plasticity in Ni and/or Si, as well as delamination between Ni and Si, may occur during cycling. Rate sensitivity in capacity is correlated with strain and a maximum Ni compressive stress of 230 ± 40 MPa is measured at the maximum state of lithiation.     

Silicon‐Microtube Scaffold Decorated with Anatase TiO2 as a Negative Electrode for a 3D Litium‐Ion Microbattery

An optimized scaffold based on silicon microtubes is designed to increase the surface capacity of 3D lithium‐ion microbatteries. High‐depth, mechanically robust microstructures are fabricated using microelectronic facilities. Conformal deposition of anatase TiO₂ is achieved using atomic layer deposition, realizing the targeted improvement for microbatteries; a surface capacity of 0.2 mA h cm^–2 at a charge rate of C/10 is obtained in standard liquid electrolyte. This work paves the way for the fabrication of solid‐state 3D Li‐ion microbatteries with an efficient 3D scaffold.