This project concerned the development of high performance, safe and durable Lithium (Li) batteries.
The objective was the development of fluorinated electrolyte/separator and binders in combination with active electrodes (anode LiC6 and cathode LiNixMn2-xO4 - 4,7V) for high performance, safe and durable Li batteries.
The main deliverables of the project were the development of cell prototypes capacity 10Ah on which performance assessment would be conducted. The AMELIE prototype performances would be assessed towards the following objectives for EV and PHEV applications:
- High specific energy: cells 200 Wh/kg;
- Improved life time: 1000 cycles, 80% DOD for EV applications;
- High calendar life: 10 years;
- High recyclability/recovery/reuse: battery components 85% recycled;
- Improved competitiveness.
The utilisation of higher performing "inactive" organic materials (polymers and ionomers) will enable the reduction of the amount of the same materials, while increasing the energy and power densities of the battery and consequently decreasing the cost per kWh of the final battery. In addition, the reuse of the components will contribute to the cost reduction of the battery. To this end, a complete Life Cycle Analysis of the new battery components has been performed.
To take up these challenges, academic and private organisations partnered up in the AMELIE consortium. As the developments in this field are extremely interconnected, improved Lithium ion batteries for the automotive sector could only be manufactured by the synergistic optimisation of all their components: active materials and binders for electrodes, gel polymers, lithium salts and solvents for the ionic conductors. Although innovative materials are a key lever of such improvements, the cell design will be essential for both improved performance and safety.
Starting from the current specifications or data described in other European projects, such as HELIOS or LIBERAL, the specifications of the AMELIE cell have been adapted towards EVs and PHEVs. The final AMELIE cell is prismatic with soft packaging (12.5 Ah capacity at 1C rate) and with the agreed specifications on energy/power, cyclability, calendar life and 5 specifications on safety.
One of the first objectives was the set up the synthesis and up-scaling of the high voltage cathode materials. LiNi0.4Mn1.6O4 was selected as the most promising cathode material to meet the AMELIE specifications.
Six new vinylidene fluoride (VDF) copolymers binders, were successfully polymerised and studied as advanced binder materials for graphite based negative electrodes and high voltage cathode materials contributing to the optimisation of the electrodes formulations. These newly developed copolymers offer an enhanced cohesion of the electrode particles and improve adhesion to the metallic current collector, leading thereby, to an improved electrical contact and electrochemical performance.
Furthermore, a suitable additive has been detected, forming an improved surface film on these active particles, resulting in a reduced self-discharge and lowered interfacial resistance to work beyond the commonly used electrochemical stability window.
In the meantime, 9 polymers, PVDF based, were polymerised and three were selected to target an improved stability and interaction with the electrolyte. The Diffusion Induced phase Separation (DISP) Process was considered to be more adaptable than the thermally induced phase separation process to prepare macroporous membranes. Dense membranes were produced, at lab level, by solvent casting.
The NCC route successfully demonstrated an improvement of rigidity of a factor 3 at ambient temperature and a factor 10 at 90C. This achievement was superior to the crosslinking approach.
Five fluorinated solvents and four different sulfonamide based Lithium Salts were synthesised and their electrochemical stability was tested. The respective solubility of the salts in the solvents was tested and the most promising salts were combined with the new solvents, sometimes in binary mixtures to tune the ionic conductivity through the intrinsic ions mobility and the final viscosity of the electrolyte.
In order to anticipate the final target of long-term cyclability on the final cell prototype, a shorter duration protocol of cell testing w
In order to access thinner membranes, promising resins were mechanically reinforced using Nanocrystalline cellulose (NCC) as a first approach. A new method to crosslink some specifically modified polymers was developed, as well as to evaluate if this second approach was achievable.
Innovating for the future: technology and behaviour:
- Promoting more sustainable development
Further research is necessary:
Future work will mostly focus on the identification of further suitable additives, the tuning of new electrolyte/separator systems, the continuing improvement of the electrode formulation and processing, as well as the investigation of active-inactive material interfaces to enable further optimisation of the targeted lithium-ion full cell and its subsequent up-scaling.
The study on the separators has indicated that some very specific polymers with high content of comonomer, could be advantageously used in combination with fluorinated solvent to form gel polymer membranes. Reinforcing these membranes with NCC will enable the reduction of the thickness of these membranes and consequently reduce the final impedance of the cell, improve the power performances and reduce the cost of the membrane.