Feb 13, 2018: King Abdullah University of Science and Technology (KAUST) researchers have developed very thin silicon-backed lithium-ion battery, which is just 30µm. They have described the process in a paper titled “Flexible and biocompatible high-performance solid-state micro-battery for implantable orthodontic system” published in the npj Flexible Electronics journal.
The chip-scale flexible lithium-ion battery is 2.25×1.7mm and has an energy density of 200mWh/cm3 for a microcell that weighs 236µg. The cells are thin, but can be bent in a radius of just 1mm and can be put inside curvature of the dental arch when integrated into a dental brace.
The research aimed to boost the efficacy of dental braces as the researchers have combed orthodontics with phototherapy, which made the process of bone regeneration for tooth correction, cutting therapy faster.
New advances in panoramic X-ray imaging, intra-oral imaging scanners and biocompatible dental materials help to digitize the manufacture of dental braces. This enables slimmer fit which could be embedded near infrared LED arrays for non-invasive oral phototherapy.
The researchers started with an active battery stack built on bulk monocrystalline silicon as the host layer with silicon oxide (SiO2) as the insulation layer. Their experiment is based on Xenon difluoride (XeF2) dry etching process. They removed the Si substrate from the battery’s back until only SiO2 and aluminium (Al) remained as the bottom layers. Then they obtained a 30µm thin standalone and physically flexible active stack piling up a SiO2 insulation layer, a thick aluminium cathode current collector, a lithium cobalt oxide (LCO) cathode as the main source of lithium ions, a glass-like solid state lithium phosphorous oxynitride, titanium (Ti) as the anode current collector, all the stack being topped up with hermitically sealed protective layers. This “lithium-free” solid-state construction was tested for bio-compatibility and thermal endurance up to 90°C, before several cells were integrated into an optoelectronic system embedded in a three-dimensional printed smart dental brace.
They assembled the chip-scale batteries in a semi-transparent 3D printed dental brace, with on each individual tooth a battery connected in series with two die level NIR-LEDs operating from 1.8V (each battery delivering a voltage between 3 and 4.2V, with a discharging capacity up to 148μAh/cm2 depending on the current ratings). With such a custom fit, localized and personalized exposure could be designed for specific teeth or tooth region, stimulating biological cells for growth and accelerated bone remodelling.