View source for ETF 9216 - Development and optimization of 3D-microbatteries (01.01.2012-31.21.2015)

== Short Description ==

Portable power supply in the form small-scale batteries, super-capacitors or fuel cells is a critical factor in many developing technologies today. A conventional lithium-ion battery, consisting of planar electrodes and fitting within dimensions of ~1 mm together with sensors, computation and communication circuits are typical components of Micro-Electromechanical devices (MEMS). However, for so small volumes, currently available batteries lack the ability to provide sufficient energy and power density. The 3D-Microbattery (3D-MB) achieves increased area-gain by use of the third dimension - the active material in the cell is deposited in the height as well. This design can theoretically increase the power density at least an order of magnitude. To simplify complicated experimental development of the
3D-MB, computer simulations are needed. Computer simulations based on Finite Element Method give a possibility to study the evolution and fluctuations of physical parameters relatively inexpensively, while giving detailed information about the performance of the battery and suggesting the best combination of material and geometrical parameters for the battery prototype. However, due to the large number of the parameters, the automated optimization of the battery architecture is needed. The development of the
optimization methodology to calculate the most suitable geometries is one of the aims of the current project. In cooperation of the participants of the EU FP-7 project Superlion the simulations result will be validated against recent experimental results on 3D-Microbatteries and the optimum geometries will be calculated for given combinations of material and geometrical parameters.

== Project outcomes ==

Portable power sources like small-scale batteries, super-capacitors or fuel cells has an critical impact on many developing technologies. In the microelectronics, the 2D micro-battery within the dimensions less than 1 mm has an inability to achieve sufficient energy density to power the device. The 3D micro-battery components are basically the same as for 2D, but has more complex spatial configuration and the electrodes are accessible for ions in the electrolyte from all three dimensions.
The main goals of the research are: (1) development of the methodology for optimization of the 3D micro-batteries and improvement of the models used in the simulations; (2) calculation of optimal geometrical and material parameters for the 3D trench, 3D interdigitated and 3D concentric models.
Simulations of the 3D trench model showed the basic tools usable to study the properties of ionic transport of the 3D micro-battery, also the main direction of the optimization - altering the material parameters and/or changing the shape of the electrodes. Smoothing the sharp edges and tips of the geometry leads to the more uniform electrochemical activity. The ratio of the conductivity of the materials for the positive and negative electrode should be at least 0.25, below that the distribution of current density and active materials becomes irregular.
3D interdigitated model has more complex geometry, but has increased surface-to-volume ratio. The objective function was developed for quantitative comparison of the geometries. The polymeric electrolyte has lower conductivity compared to liquid electrolyte, but smoother current density distribution inside the battery. The geometry optimised by the Level-set method show at least twice as high performance compared to the unoptimized geometry.
The concentric model has an optimum pillar height of 70 mkm and the distance between the pillars of 10 mkm. This configuration has increased capacity, homogeneous electrochemical activity all over the electrode surface and the most efficient utilization of the electrode and electrolyte material.