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LITHIUM-IN-SILICON NANO-STRUCTURED ANODES FOR ON-CHIPBATTERY APPLICATIONS

Objective

The best anode for a lithium battery is LixSi, where x = 4 to 0. Small features of Si can more readily survive the associated volume change between x = 4 to 0. We will fabricate high-density arrays of Si pillars in the sub micron diameter range using the inexpensive method of Island Lithography. The electrochemical and mechanical properties of the pillar array-anodes will be studied by a verity of methods. The intention is that such anodes, as part of a lithium battery be integrated into Si chips principally for use in medical implants. A target of 1 µA/cm2 for 30 days down to half capacity is a goal. The best anode for a lithium battery is LixSi, where x = 4 to 0. Small features of Si can more readily survive the associated volume change between x = 4 to 0. We will fabricate high-density arrays of Si pillars in the sub micron diameter range using the inexpensive method of Island Lithography. The electrochemical and mechanical properties of the pillar array-anodes will be studied by a verity of methods. The intention is that such anodes, as part of a lithium battery be integrated into Si chips principally for use in medical implants. A target of 1 µA/cm2 for 30 days down to half capacity is a goal.

OBJECTIVES
The immediate objective is to find out if structuring the surface of Si (sub micron pillars made by Island Lithography) will give a multi-cycle Li/Si anode suitable for Si batteries. The long-term objective is to incorporate such structured anodes in an on-chip battery, suitable for, inter alia, medical implants. A programme of accelerated cycle testing will be carried out at the charging rate of 5 mA/cm2 for 15 min. 100 charge/discharge cycles would be considered complete success; 30 or more cycles would be considered as significant success.

DESCRIPTION OF WORK
The basic notion is that Si in the form of separated pillars (or truncated cones), will be able to undergo the stressful volume/structural changes in the Li insertion/extraction cycle more easily as micron or sub-micron diameter isolated structures than as a plane surface or compacted granules. The range of mean diameters and heights that can be fabricated using Island Lithography is well suited to finding the dimensions suitable for extended anode battery life. The charging current density for 5 micron high, 1 micron diameter pillars at 35% packing density is 5 mA/cm2 (for 15 minutes) to go to x = 4. This structure would give a continuous anode capacity of 1 µA/cm2 for 30 days for a half full capacity cycle. This activity would form a substantial part of the assessment. For the purposes of testing the anode-pillar it will not be necessary to construct a sealed battery unit. We will construct anodes in silicon (n-doped) in a range of mean diameters and packing density and heights. These anodes will be cycled in a liquid Li ion containing electrolyte and the cyclic-voltamagram measured as a function of cycle number, total lithium insertion and current density. Cycling will be continued to destruction. Also the anode potential, after insertion, will be followed as a function of time in order to follow the surface composition variation. The anodes will be inspected in the scanning electron microscope and by XRD. The more robust anodes will be further tested using a polymer electrolyte to more closely simulate the environment of a commercial battery. Optimisation and modelling of such Li/Si batteries will be carried out A Si structure of pillars 5 microns high, 1 micron in diameter and 35% packing density. This is sufficient in power and physical size for various medical applications.

Funding Scheme

ACM - Preparatory, accompanying and support measures

Coordinator

IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE
Address
South Kensington Campus
SW7 2AZ London
United Kingdom

Participants (1)

UNIVERSITA DEGLI STUDI DI ROMA "LA SAPIENZA"
Italy
Address
Piazzale Aldo Moro 5
00185 Roma