Process and Product Development

Micro Battery

© Fraunhofer IZM
Structures for coplanar micro battery

1. Customized secondary micro battery
Where ever ultra-miniaturization is required like wireless sensor nodes or medical applications, the silicon embedded secondary lithium ion battery developed at Fraunhofer IZM can be used as electrical buffer storage. Shape and size as well as voltage, capacity and power performance can be adapted to the application requirements. 

Typical appliactions are active RFID, miniaturized sensors and medical implants like intra ocular pressure sensor, micro hearing aid, blood pressure sensors.

For energy autarkic systems which harvest ambient energy the electrochemical storage has to be as small as possible for a given storage requirement to reduce self-discharge since self-discharge current scales with capacity and has to be compensated by the harvester.

The most important parameters are summarized in the following table:

Size [mm] 2x2 ... 2x12 ... 12x12
Thickness [mm] 0.5
Capacity [mAh/cm²] 0.5 ... 1.2
Energy [mWh/cm²] 2.5 ... 5
Mean discharge voltage [V] 2.5; 3.7
Max. discharge current [mA/cm²] 2 - 6

2. Materials development and testing for lithium batteries
The wafer based micro battery technology can be further elaborated to integrate reference electrodes and arrange the battery cells in an area array. Thus several hundreds of electrochemical test cells are fabricated and encapsulated on the same substrate. Programmable precision volume dispensers will be used to realize combinatorial material variations.

The test cells will allow the cost-efficient routine laboratory measurement of electrochemical cells. The setup is composed of a “backplane box” with detachable contacts for working and reference electrodes, supplying independent potentials and currents to each device. These are designed to accommodate an array of cells for a variety of purposes. With help of that device all the interactions between electrolyte and electrodes, the reactions which play an important role towards long term stability and cycle life can be investigated with the help of high-throughput screening methods on cell level. Contaminations are precluded due to clean room processing and single-use of the test cells. Tests can be performed with both: novel materials from latest research and industrially proven materials. Degradation mechanisms during long-term and cycle life testing can be evaluated more detailed since a sufficiently high number of test cells can be used. Simultaneous tests of identical samples operated at varying temperature and current density can be performed with a high statistical confidence. Laminates of battery electrodes and separators are tested in standard Swagelok or EL-Cells.

3. Battery test service
The battery test laboratory acts as an independent test facility were any kind of battery can be tested. 400 programmable test channels and climate chambers are available in the ranges 5V, 20V, 45V,  150 µA … 5A. Tests can be performed according to battery standards like IEC 509, IEC 21A 227, 228,230. 239,256, IEC35 1025, IEC 86-4, DIN, EN 60285, 60622, 60623, 61434, 60086, DIN IEC 61960

The most suited battery can be identified according to benchmarking tests.