Si-DRIVE

The Si-DRIVE H2020 project will tackle the major barriers to electric vehicle (EV) uptake, which relate to driving range, cost and recharge times, by completely re-imagining the lithium ion battery. Si-DRIVE will develop the next generation of rechargeable Li-ion batteries, allowing for cost competitive mass market EVs by transformative materials and cell chemistry innovations, delivering enhanced safety with superior energy density, cycle life and fast charging capability using sustainable and recyclable components.The technology encompasses amorphous Si coated onto a conductive copper silicide network as the anode with polymer/ionic liquid electrolytes and Li-rich high voltage (Co-free) cathodes via processes that are scalable and demonstrably manufacturable within Europe.The components have been demonstrated at TRL3 through preliminary lab-scale analysis, with a clear component improvement strategy to arrive at a TRL5 prototype demonstration by the end of Si-DRIVE. Comprehensive theoretical and experimental studies will probe and control interfacial processes that have heretofore limited Li-ion technologies to incremental gains, guiding materials design and eliminating capacity fade mechanisms.The Si-DRIVE technology will exceed the stringent demands of EV batteries where safety is paramount, by dramatically improving each component within the accepted Li-ion platform and achieving this in a market competitive process with whole of life considerations. The technology will also demonstrate suitability for 2nd life applications at reduced energy density beyond the primary EV lifetime, prior to cost effective materials recycling, consistent with a circular economy. The Si-DRIVE consortium boasts the required academic and industrial partner expertise to deliver this technology and spans material design and synthesis, electrochemical testing, prototype formation and production method validation, life cycle assessment and recycling process development.

Our role

Modelling: Gemmate Technologies is in charge of implementing models of the interface between the materials and cell components based on the Quantum Espresso DFT code, in particular the possible change of the Si copper-silicide interface and thus the change of the mechanical and adhesion properties.

Sustainability: Gemmate Technologies contributes to the enviromental impact and sustainability assessment of the full battery lifecycle by assessing and comparing the emissions and the mass/energy balance related to the cathode manufacturing.

Results acheived

Modelling

A multiscale investigation of an anode for lithium-ion batteries nanowires was developed, linking the nanoscale properties of the material components to their macroscopic mechanical and electrochemical behaviour. In this system, in which Cu₁₅Si₄ grown out of a copper substrate are coated with amorphous silicon, lithiation occurs in the silicon coating but not in the copper silicide core. A mathematical model was coupled to experiments performed for charging at different rates and used to predict lithium concentration and mechanical stresses during charging/discharging. In this workflow, Gemmate Technologies was able to obtain ab initio models for the amorphous Li_xSi phases and used them to calculate their elastic parameters and adhesion to the Cu₁₅Si₄ substrate. Results highlight how the progressive inclusion of Li into the amorphous Si coating causes a progressive softening of the material as well as a dramatic reduction in the adhesion to the copper silicide substrate. These processes complement the well-known volumetric expansion of the silicon anode in explaining the morphology evolution and progressive capacity fade of the anode that have been reported experimentally.

Figure 1: Optimised bulk structures of Cu₁₅Si₄ and Li_xSi phases: a)Cu₁₅Si₄; b) Si; c) Li_0,5Si; d) Li₁Si; e) Li₂Si; and f) Li_3,75Si. Cu atoms are depicted in dark brown, Si atoms in light brown, Li atoms in purple.

These model systems were then employed to compute the elastic properties of the Si-DRIVE anode at various degrees of lithiation, and to study the adhesion between the Si active material and the Cu₁₅Si₄ substrate. The results provided new information on the evolution of Li_xSi phases and Cu₁₅Si₄/Li_xSi interfaces during battery operation, which can complement experimental work in elucidating the behaviour of the material, as well as be implemented in larger scale mechanical models of the anode. Our work can be correlated with the experimentally reported morphological change of the material upon extensive cycling, suggesting that the substitution of Si-Si bonds with weaker Li-Si interactions contributes to the creation of a porous Si network from the Cu₁₅Si₄ nanowire coating by softening the lithiated material, and provides evidence supporting the choice of copper silicide nanowires as substrates for the Si active material by predicting no weakening in their adhesion upon lithiation.

The validity of this approach is confirmed by the insight provided by each individual modelling scale as well as from their combined use, which could not have been obtained had each model been designed separately. Several questions remain on the relationship between nanoscale morphology and performances of Si-based composite anodes, but we believe that the multiscale approach presented here provides a valuable tool for their solution, and might be applicable to a wider range of non-silicon materials with complex composite morphologies.

Sustainability

Gemmate Technologies assessed and compared, by means of tailored environmental indicators, the emissions and the mass/energy balance related to the production of novel materials for the cathode synthesis. As existing databases do not contain the data for the production of the innovative cathodic material studied in the project, this information will be collected on the basis of the lab synthesis experiments in combination with literature search. These analysis allow the consortium to formulate full LCA for the complete cell.

Research papers

A coupled electrochemomechanical model for the cycling of a Cu₁₅Si₄-hosted silicon nanowire