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Design of highly conductive solid thin film electrolyte for stack integration within optical and energy storage applications

Final Report Summary - HI-CONDELEC (Design of Highly Conductive Solid Thin Film Electrolyte for Stack Integration within Optical and Energy Storage Applications)

The project was dedicated to the development of thin films of a high conductive solid ionic conductor for Lithium. Promising applications areas for thin film manufactured materials are micro batteries (electrochemical energy storage), micro-supercapacitors (energy impulsion) and electrochromic devices (i.e. smart windows or displays). The challenge lied in the development of solid electrolytes (glasses and crystallized materials) and thin film technology that would provide new physical properties (very high ionic and electronic conductivity) and increased chemical and mechanical stability. Thin film solid electrolytes require rather specific properties that sometimes are difficult to obtain at the same time, therefore the main objective of the HICONDELEC project was to develop fundamental knowledge in order to enable an optimum design of the solid lithium conducting glass electrolytes with predefined physical and chemical characteristics. A multidisciplinary approach combining simulation, theory, experiment, validation and use was chosen, in order to maximise the fundamental understanding of ionic and electronic conductivity phenomena and thermo-electro-mechanical behaviour.

HICONDELEC developed powerful computational tools for materials modelling related to:
- Materials behaviour: for the investigation of the fundamental mechanisms of ionic and electronic conductivity and their interaction with thin film properties, integrating multi-scale simulations from the atomic scale to the glass structure scale (from 0.1 to 10 nm).
- Materials processing and use: for the investigation of the mechanical behaviour and stability of the thin film electrolyte prepared by sputtering, of the stack integration process and of its use.
In addition, modelling was based on and supported by properties measurements thanks to appropriate characterisation techniques of electrical, mechanical, thermal, environmental and optical properties of the thin film electrolytes.

The HI-CONDELEC work programme was split down into five work packages:
- one work package (WP0) dedicated to the R&D approach strategy and management of knowledge, including review of the requirements for characterisations and modelling, integration of the results by all partners to give further orientations on electrolyte to consider and knowledge management (intellectual property right, transfer of skills and expertise within the consortium, and exploitation plan).
- two work packages dedicated to the set up and running of simulations (ionic and mechanical) that will be performed in parallel all along the project to model the solid state thin film electrolyte (WP1 and WP2).
- one work package (WP3) that will deal with materials engineering of thin film, i.e. including the preparation of thin films to be characterised and modelled, the development of appropriate targets for chosen electrolytes and preliminary industrial tests for a first assess of the integration of the new electrolyte into industrial environment by test on large targets.
- one work package (WP4) dedicated to the integration of the selected electrolytes into complete systems: micro-batteries, microsupercapacitors and electrochromic cells for further evaluation.

The objectives of main technical WPs are summarized below:

WP0 - R&D approach and knowledge management:
- Define requirements for characterisation samples.
- Ensure integration of the results from the modelling teams (WP1 and WP2) and materials engineering teams (WP3) and update the HI-CONDELEC R&D orientations.
- Prepare the industrial exploitation of the HI-CONDELEC results.
- Communicate the results of the projects outside the consortium to ensure their dissemination within the scientific community.

WP1 - Ionic and electronic modelling:
- Suggest favourable anions for glassy electrolytes from ab-initio calculations.
- Model the fundamental physics of ionic conductivity.
- Relate the glass structure to transport properties.
- Conclude on rate limiting factors for high ionic conductivity of thin film solid electrolyte and understand how to obtain high ionic conductivities.

WP2 - Mechanical modelling:
- Develop a complete modelling approach for thin film assemblies under combined thermal, mechanical and electrical evaluation.
- Carry out optimisation of the thin-film assemblies for the project applications.
- Validate the model by experimental feedback and recommend the best design of the component.
- Identify the critical factor(s) controlling fracture point and durability of the system.

WP3 - Materials engineering on solid-state thin film electrolyte:
- Experimental studies on electrolyte elaboration: determination of the sputtering parameters for the preparation of electrolyte thin films.
- Experimental research on materials (gradients of composition): preparation of series of materials in order to investigate the ionic conduction mechanisms.
- Preparation of the integration of the thin films into application systems by preliminary studies on large scale targets and deposition parameters.

WP4 - Integration into application devices:
- Integrate the developed electrolyte into the final object. WP1 to WP3 will define optimised composition and structure of electrolyte.
- The electrolyte will be integrated into the stack representative of its application (Microbattery, Microsupercapacity, Electrochrome).
For each of its application it will be necessary to adjust the optimisation according to its specific stack.

The achieved results of the project included the following:
- Several factors determined concerning both basic structural property relationships as well as relations to process parameters and conditions. New optimum compositions suggested based on the acquired knowledge.
- Algorithm of the mechanical optimisation of mechanical parameters was developed, critical factors were identified and the procedure established.
- New families of materials were developed.
- A target fabrication procedure and a target bonding procedure was developed.
- One exploitable electrolyte for microbatteries, but none for microsupercapacitors and maybe one for smart windows but after huge development at reducing film defects.