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Materials for Ageing Resistant Li-ion High Energy Storage for the Electric Vehicle

Final Report Summary - MARS-EV (Materials for Ageing Resistant Li-ion High Energy Storage for the Electric Vehicle)

Executive Summary:
Li-ion batteries today exceed by a factor of 2.5 any competing technology thanks to their energy density. Although already in the market place, progress is still required to meet the stringent requirements of the electric transportation market: e.g. increase of energy density and significant enhancement of service life on both cell level (standardization of cell design, cell chemistry, material costs) and battery level (module design, battery management system with active cell balancing, packaging, thermal management system) thanks to innovative materials and technologies and optimization of process characteristic.
Research and development activities within MARS-EV project aim to overcome the ageing phenomenon in Li-ion cells by focusing on the development of new electrochemistries: high-energy electrode materials (250 Wh/kg at cell level) via sustainable scaled-up synthesis and safe electrolyte systems with improved cycle life (> 3000 cycles at 100%DOD). Through industrial prototype cell assembly and testing coupled with modelling, the understanding of the ageing behaviour at the electrode and system levels will be improved. Finally, it will address a full life cycle assessment of the developed technology.
The MARS-EV project has six main objectives:
1. synthesis of novel nano-structured, high voltage cathodes (Mn, Co and Ni phosphates and low-cobalt, Li-rich NMC) and high capacity anodes (Silicon alloys and interconversion oxides);
2. development of green and safe, electrolyte chemistries, including ionic liquids, with high performance even at ambient and sub-ambient temperature, as well as electrolyte additives for safe high voltage cathode operation;
3. investigation of the peculiar electrolyte properties and their interactions with anode and cathode materials;
4. understanding the ageing and degradation processes with the support of modelling, in order to improve the electrode and electrolyte properties and, thus, their reciprocal interactions and their effects on battery lifetime;
5. realization of up to B5 format pre-industrial pouch cells with optimized electrode and electrolyte components and eco-designed durable packaging; and
6. boost EU cell and battery manufacturers via the development of economic viable and technologically feasible advanced materials and processes, realization of high-energy, ageing-resistant, easily recyclable cells.
The project concept is thus translated to the following activities and targets:
Electrode materials will be synthesized at lab-scale: nanosized LiFexMn(1-x)PO4, LiNiPO4, LiCoPO4 and Li-rich NMC systems with low cobalt content will be synthesized choosing the most suitable synthesis route to obtain nanostructured composite particles targeting 900Wh/kg and 3000 cycles at 100%DoD. On the other side, besides the use of graphite as anodic material, new Si/C based, spinel ferrites and Li metal anodes will be considered to achieve 1000 mAh/g stable capacity over 1000 cycles. Best performing materials will be scaled-up in two generations.
The interface electrode/electrolyte is one of the most critical points to achieve high density, good cyclability and power rate. Moreover the use of polymer electrolytes is mandatory for Li-ion cell safety. Membranes with high mechanical properties, ecofriendly and reinforced, UV and/or thermally cured and based on epoxy resins will be considered.
Li-ion cells from the lab-scale (<1000 cm2) to the preindustrial scale (up to 20000 cm2, B5 format) will be realized as proof of concept and tested on electrochemical performance, lifetime and safety.
The choice of materials, synthesis methods and the cell assembly processes will be driven by the Life Cycle Assessment that will be realized taking into account the recyclability of the complete cells (>50% recycling rate). Modelling at the materials level (electrode/electrolyte interface) as well as the system level (cell ageing, SOH at different regimes) will also guide the materials and cell development and testing.


Project Context and Objectives:
Activities within the first stage of the project focused on the development at lab-scale of high energy electrode materials through easily scalable, potentially low cost and environmentally friendly synthesis methods, as well as safer electrolytes. Within the second stage, scaling-up of selected high energy electrode materials was accomplished, as well as the modelling and analysis of the cell ageing behaviour on baseline cells. Finally, the scaled-up manufacturing of electrodes (high-voltage cathode and optimized graphite anode) and prototype cells [10Ah GEN1 (C/LFP) and small 1Ah GEN2 cells with LNMO and LCP] has been carried out. Cellulose-based packaging can be used as packaging for cells. Electrical and thermal models have been completed. The LCA on Gen2 has been achieved, as well as hydrometallurgical recycling and closed-loop materials recovery.

Main achievements:
• Definition of MARS-EV battery pack architecture for small BEV City Car (~Daimler Smart) and translation to cell and materials specification and selection criteria.
• Synthesis of novel nano-structured high energy active materials at lab-scale:
o Low temperature synthesis of LiMPO4 (M=Fe, Mn) using Ionic Liquids has been studied. A method to recover and purify the ionic liquid utilised as reaction medium was developed using NaOH, in order to make possible the recycling for further syntheses.
o Li2Mn3Si4O12/C nanocomposite preparation providing more than 200 mAh/g at C/20 but low cycle-life.
o High voltage cathodes: C-coated LiCoPO4 (LCP/C) by Flame Spray Pyrolisis (FSP) and VOx-coated Li-rich NMC with increased capacity and cycle life (~850 Wh/kg-active)
▪ C-LiCoPO4 by FSP has been produced at 1kg-scale (GEN2 upscaling) and delivered for electrode manufacturing.
o High capacity anodes: Ni-doped Silicon MWCNT with compatible electrolyte, achieving 600 mAh/g for more than 400 cycles; new approach for ART-SEI formation by Si ball milling with LiF providing 2500-2000 mAh/g-Si for >110 cycles. Improvement of the formulation and procedure of anode preparation by replacement of 10%MWCNTs by 0.5%SWCNTs and knife milling instead of high-energy ball milling method.
▪ Si:Ni [1:0.075] with 0.5%SWCNTs and knife milling exhibit over 1000mAh/granode, for 250 of cycles.
o MEG-2 optimised graphite has been developed providing 350mAh/g at >1C in technical electrodes, to be used in GEN2 cells and also benchmarked in another EU H2020 project.
• Electrode preparation using aqueous binders: Li-rich NMC with CMC and Na-alginate has been proven, as well as for high-voltage LNMO commercial spinel (in absence of available LCP); Silicon anode can be prepared with aqueous binders (Li-PAA). Manufacturing in coating line for pouch cell assembly:
o GEN1 anode with surface modified graphite MEG-1.
o High-voltage LNMO commercial spinel for small GEN2 cells.
o LCP cathode formulation with waterborne binders was developed but could not be upscaled. Electrode with PVdF/NMP formulation was produced instead.
o GEN2 anode with surface modified graphite MEG-2 has been manufactured.
• Development of green and safe, electrolyte chemistries with high performance even at ambient and sub-ambient temperature for MARS-EV electrode chemistries:
o Additives for high-V cathodes (Li-rich NMC): VC+SB combination delivered capacity of 440 Wh·kg-1 (cathode+anode) or 815 Wh kg-1 (cathode): 1M LiPF6 in EC:DMC (1:1 w/w) + (2%VC+4%SB) upscaled to 1L (GEN1).
o Additive screening for LCP cathode operation (up to 4.95V): TTSPi and TFEC provide enhanced cycling stabilities and coulombic efficiencies in LCP/graphite full cells. 1M LiPF6 in EC:DMC (1:1 w/w) + 2%TTSPi upscaled to 200mL (GEN2).
o High purity (through lower cost purification route) pyrrolidinium-based ILs (TFSI and FSI): LiTFSI-PYR13TFSI-EC/DMC has shown the highest conduction values whereas the additive-free LiTFSI-PYR13FSI-EMIFSI sample behaves as well as the mixed IL/organic electrolytes. At room temperature, conductivity values of 10-2 S cm-1 are approached. Not compatible with LCP.
o Non-flammable Solid Polymer Electrolytes (UV-cured) showing conductivities of 0.5 mS·cm-1 (RT), wide ESW and mechanical integrity. Long-term performance in both Li-metal and Li-ion cells and cycling at high-V (LNMO).
• Development of eco-designed cellulose-based durable cell packaging: water vapour and oxygen transference barrier properties achieved. New generation of paper based barrier product suitable for housing Li cells. [PVdC/M2/MFCPVdC], thickness ~96μm; ~125g/m2. Weight reduction of -69% vs. standard ALF pouch material.
• Manufacturing of GEN1 10Ah cells with 1st selected materials: MEG-1 96% aqueous anode and conventional LFP-PVdF cathode.
• Manufacturing and testing of GEN1 10Ah cells with water-based electrodes: MEG-2 94% aqueous anode and LFP cathode.
• Manufacturing and testing of GEN2 1Ah cells with waterborne LNMO/MEG2 and NMP-based LCP/MEG2: LNMO cells (4.7V) with stable cycling for >250 cycles.
• Development of a cell model including electrical, thermal and ageing characteristics:
o Design of Experiment for ageing tests of baseline C/NMC and C/LFP commercial cells. Test protocols and test matrix were developed. Baseline 2.15Ah 18650 C/NMC completed and 15Ah pouch C/LFP cells still ongoing (>4000cycles).
o Cycling and calendar models are developed in accordance to the ageing test: Model checked with aged batteries (SoH down to 90%) with 0.6% average absolute error under NEDC profile for both cells chemistries. SoH estimation completed.
o Modelling of the thermal behaviour on cell and pack level has been carried out employing a multi-physics (electrochemical, thermal, fluid-dynamic) and multi-scale approach (Unit-cell, Pouch cell, Module and Pack).
o Electro-thermal model completed and used for life-time optimization and battery pack control: 1st and 2nd order equivalent circuit model was parameterized and validated for NMC cells, with good accuracy for the prediction of the temperature. Life-time model provided enhancement of more than 100% when operating the cells at 45°C.
o 3D Imaging (tomography) supported modeling: IN-OPERANDO has been realized for Silicon anodes. 3D reconstructing commercial battery electrodes (LFP cathode, Gen0 & Gen1 cells) utilizing newly developed contrast enhancing epoxies A new approach for mechanical testing to measure the mechanical properties of electrochemically deposited dendrites in Zn-air, applicable to Li anode.
• Environmental assessment of the product through LCA and development of optimized cells recycling process (target of a minimum of 50% recycling rate).
o Regulatory assessment on REACH and CLP (GHS) aspects completed for MARS-EV materials: no restrictions were found
o Baseline LCA (commercial NMC and LFP cells) completed, showing lower impact for LFP cells produced by aqueous electrode processing. Continually updated and refined as more primary data is obtained (mass production vs. pilot-scale)
o LCA of new “Gen2” cell, LCP/Graphite chemistry and cellulose based packaging: environmental impact consistent, and in some cases lower, than commercial cells.
o Recycling assessment: use of a hydrometallurgical route improves the efficiency of cell recycling to 76% and allows a closed loop system to obtain precursor material for electrodes. Recycled graphite from the cells has shown 300mAh/g.

Project Results:
Activities within the last year of the project have focused on the scaled-up manufacturing of electrodes (high-voltage cathode and optimized graphite anode) and prototype cells [10Ah GEN1 (C/LFP) and small 1Ah GEN2 cells with LNMO and LCP]. Cellulose-based packaging can be used as packaging for cells. Electrical and thermal models have been completed. The LCA on Gen2 has been achieved, as well as hydrometallurgical recycling and closed-loop materials recovery.
Main results within this period are:
• Synthesis of novel nano-structured high energy active materials:
o High voltage cathodes: C-LiCoPO4 by FSP has been produced at 1kg-scale (GEN2 upscaling) and delivered for electrode manufacturing.
o High capacity anodes: Si:Ni [1:0.075] with 0.5%SWCNTs and knife milling exhibit over 1000mAh/granode, for 250 of cycles.
o Additional MEG-2 type and MEG-3 graphites evaluated, observing variations in rheology of slurries.
• Electrode preparation using aqueous binders: Manufacturing in coating line for pouch cell assembly
o High-voltage LNMO commercial spinel for small GEN2 cells.
o LCP cathode formulation with waterborne binders was developed but could not be upscaled. Electrode with PVdF/NMP formulation was produced instead.
o GEN2 anode with surface modified graphite MEG-2 has been manufactured.
• Development of green and safe, electrolyte chemistries with high performance even at ambient and sub-ambient temperature for MARS-EV electrode chemistries:
o Additive screening for LCP cathode operation (up to 4.95V): TTSPi and TFEC provide enhanced cycling stabilities and coulombic efficiencies in LCP/graphite full cells. 1M LiPF6 in EC:DMC (1:1 w/w) + 2%TTSPi upscaled to 200mL (GEN2).
o High purity pyrrolidinium-based ILs (TFSI and FSI): LiTFSI-PYR13FSI-EMIFSI shows conductivity values of 10-2 S cm-1 at RT but not compatible with LCP.
o Non-flammable Solid Polymer Electrolytes (UV-cured) with 0.5 mS·cm-1 (RT): Long-term performance in both Li-metal and Li-ion cells and cycling at high-V (LNMO).
• New generation of paper based barrier product suitable for housing Li cells. [PVdC/M2/MFCPVdC], thickness ~96μm; ~125g/m2. Weight reduction of -69% vs. standard ALF pouch material.
• Manufacturing and testing of GEN1 10Ah cells with water-based electrodes: MEG-2 94% aqueous anode and LFP cathode.
• Manufacturing and testing of GEN2 1Ah cells with waterborne LNMO/MEG2 and NMP-based LCP/MEG2: LNMO cells (4.7V) with stable cycling for >250 cycles.
• Development of a cell model including electrical, thermal and ageing characteristics:
o Cycling and calendar model checked with aged batteries (SoH down to 90%) with 0.6% average absolute error under NEDC profile for both cells chemistries. SoH estimation completed.
o Electro-thermal model completed and used for life-time optimization and battery pack control: 1st and 2nd order equivalent circuit model was parameterized and validated for NMC cells, with good accuracy for the prediction of the temperature. Life-time model provided enhancement of more than 100% when operating the cells at 45°C.
o 3D Imaging (tomography) supported modeling: 3D reconstructing commercial battery electrodes (LFP cathode, Gen0 & Gen1 cells) utilizing newly developed contrast enhancing epoxies A new approach for mechanical testing to measure the mechanical properties of electrochemically deposited dendrites in Zn-air, applicable to Li anode.
• Environmental assessment of the product through LCA and development of optimized cell recycling process (min. of 50% recycling rate).
o LCA of new “Gen2” cell, LCP/Graphite chemistry and cellulose based packaging: environmental impact consistent, and in some cases lower, than commercial cells.
o Recycling assessment: use of a hydrometallurgical route improves the efficiency of cell recycling to 76% and allows a closed loop system to obtain precursor material for electrodes. Recycled graphite from the cells has shown 300mAh/g.

Potential Impact:
The successful resolution of scientific and engineering challenges for battery materials and cell manufacturing within MARS-EV will lead to breakthroughs in Li-ion batteries not only for electric vehicles (EV) but also for large-scale energy storage, and thus for a sustainable mobility and quality of life. Various economic studies repeatedly show that the transition to EVs is heavily dependent on the progress of battery technology (mainly cost reduction and increase in energy density). MARS-EV addresses this issue by increasing the energy density of sustainable materials while maintaining a minimum cycle life above the existing technologies.
MARS-EV addresses reduction costs driven not only by active material energy density, but also from the components processing conditions. The use of water based binders, an order of magnitude cheaper than conventional fluorinated ones will drive down the cell manufacturing costs, besides being more environmentally friendly and eco-sustainable at the end of life of the cells. The initial inversion and running costs of the solvent recovery system would be avoided and distilled water is also cheaper than 50% of pure NMP (0.20 €/L vs. 0.90 €/L).
The proposed active materials themselves are safe, non-toxic and environmentally benign and as a consequence derived processes, such as electrode preparation and cell assembly are very "working-condition-friendly". There are also high expected economic impact and possibilities of market introduction of the most promising materials to be studied and developed in MARS-EV.
Cathode active materials account for around 40% of the cell cost as the major constituent in weight. Driven by the increase in EVs, the cathode materials production will grow to 190kMT in 2020 (EV Battery Tech Conference, 2012). By then, LFP and NMC will dominate the automotive market (65kMT), increasing significantly their market share. Proposed development of phosphates with increased voltage, for instance, will directly enter the market in competition with LFP. Proposed processes give important advantage in terms of industrialization of products as they are based on green synthesis.
The anode market (2012) amounts to 7400t (Natural Graphite: 67%, Artificial graphite: 14%, Hard Carbon/Soft Carbon: 17%). Europe currently has a very small market share and all top competitors are in Japan. However, this market is predicted to grow very rapidly to 12 times this size by 2018. New modified ageing resistant negative active materials developed within MARS-EV could tap into this growing market, in an immediate scenario with graphite anode developments and beyond 2016 with the high capacity anodes.
In the case of electrolytes, a significant increasing number of companies working on batteries and supercaps are ordering ionic liquids to develop new electrolytes. This indicates that ionic liquids are being considered by the industry key players as potential materials for the development of new and safer electrolytes. Concerning EV and PHEV, an increase of sales up to 7Mio of units, expected in 2020, means that huge volumes of electrolytes will be needed. Such potential volumes as well as switching from batch production to continuous flow production processes will help lowering costs of ionic liquids down to 5 times the cost of regular flammable electrolytes (estimated 100€/kg). This may lead to an increase of only 14% of the Li-ion cell total cost (from 190$/kWh up to 215$/kWh) without taking into account the improved performances and the enhancement of safety issues.
Therefore, MARS-EV project will have a strategic impact for the participating institutions, in particular the industrial partners since it will provide possibilities to diversify their technologies and product portfolios and to be on the forefront of important emerging markets. The project results will stimulate economic growth in European key markets (chemical, materials, process engineering, sustainable mobility and energy).

List of Websites:
Project public website address: www.mars-ev.eu
Contact e-mail: imeatza@cidetec.es; iurdampilleta@cidetec.es