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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SINTBAT (Silicon based materials and new processing technologies for improved lithium-ion batteries)

Teaser

Summary

Main objectives of the Sintbat project is the cost reduction as well as enhancement of energy storage capacity of VARTA battery storage systems while keeping at the same time the envisaged lifetime of 20-25 years.
Sintbatâ€™s approach is technology exploitation and combination of advanced functional electrode and electrolyte materials to develop a lithium-ion battery offering better performance in its use at lower costs and improved sustainability. A long lifetime of up to 20-25 years that requires approximately 10,000 cycles will be achieved by using analysis, simulation and modelling methods to investigate aging mechanisms. Moreover, critical analysis and modelling of aging and degradation mechanisms of key components and the verification within accelerated tests on operation level will help to overcome shortcomings regarding in-service time.

Work performed

Commercially available cells with silicon-based anodes were scouted by VMI and VS. To compare the cells, different cycling tests were performed. Based on the test results and cell performances, a product requirement document and general descriptions for the test procedures for the electrode and cell testing were created.
First generations of anodes with different silicon contents were developed and tested by CEA and VMI. The results of these measurements, done in pouch bag prototype cells, were compared to commercially available silicon containing cells. As it turned out, the cycle life and capacity retention of the developed electrodes are competitive compared to the industrial benchmark and exceed the benchmark anodes regarding silicon content and therefore energy density.
By cooperation of VMB and VMI, the developed first electrode generation was implemented into the CoinPowerÂ© cell system to increase the overall cell capacity by 10%. Since silicon-based electrodes are undergoing major thickness changes during cycling, XCT-measurements, performed by MCL, are used to investigate the influence of the volume changes during cycling on the mechanical integrity of the cell to extend cycle life and reduce failure frequency caused by mechanical issues.
MCL, in collaboration with VMI and CEA, develops a characterization toolbox suitable to analyse the 3D micro-structure of pristine Si-based anode material which is relevant for future Li-ion batteries used in industrial related storage solutions. This comprises (1) the measurement of the microstructure by using FIB-SEM and XCT to cover the length scales from mm to nm including 2D and 3D information, (2) the development of suitable image analysis algorithm to obtain accurate results regarding the microstructure of the electrode, and (3) the validation of the data by comparing FIB-SEM and XCT results. The performed 3D analysis shall provide design guidelines for an improved production. In addition, CEA and UU develop chemical and structural analysis of the aged Si-based electrodes using a combination of advanced spectroscopy, x-rays/neutron scattering, and imaging techniques, including the development of operando experiments to probe the real-time behaviour of electrodes while cycling.
At UW, the electrochemical parameters of first generation anodes have been determined. Various electrochemical methods such as CV, GITT and EIS have been adopted to evaluate Li-ion diffusion (both in solid-state anode material and liquid electrolyte), resistivity of SEI and parameters related to electron transfer kinetics. Determined values help in better understanding of processes ongoing during charging and discharging of electrodes present in the cells. Furthermore, parameters acquired from the experiments were transferred to UoW and will be used in electro-mechanical modelling of the cell behaviour.
Electrochemical and micro-chemomechanical models were developed to understand the Li-ion concentration profiles, predict stresses in a spherical Si particle due to volume expansion from Li-ion alloying with Si, and the effects of those stresses on the two-phase lithiation of spherical Si â€“particles. Initially spherical symmetry was assumed in the simulations and new numerical techniques were applied to solve the non-linear partial differential equations. The models form the foundation for the next phase of activity which includes a 3D microstructure reconstruction and a coupled chemo-mechanical Finite Element simulation of the anode behaviour during lithiation-delithiation, and a full electrochemical model of the Sintbat battery.
From VS different battery module designs and topologies as well as a thermal management concept were investigated. Here the deployment of a module containing several hundred round cells and featuring an energy content >3.5 kWh is envisaged.
Moreover, VS focused on the realization of the BMS which will be deployed within the battery module. Here, hardware as well as software as

Final results

Main ambition of the Sintbat project is the development of an advanced low-cost silicon-based Li-ion cell for energy storage applications using high energy and low-cost electrode materials and establishing of an aqueous cathode manufacturing process leading to a cost reduction of 31% in comparison to a conventional cell production process. This includes the development of a prelithiation process for the compensation of irreversible lithium loss due to continuous SEI formation of silicon based active materials for extended life time and cycle life. Multi scale modelling is used for lifetime enhancement and prediction supported by advanced in-situ, in operando and post mortem analysis. Further aspects are the establishment of standards for rapid aging helping the entire battery production in Europe to improve LIBs for another important sector, e.g. automotive, as well as the cell development and simulation of mechanical and electrochemical aging mechanism supported by non-destructive modern computed tomography. In the end, the project will realise full battery prototype cells with enhanced energy density (660 Wh/L) and cost effectiveness (<450 â‚¬/kWh CAPEX and <0.09 â‚¬/kWh OPEX). The optimised battery materials will be tested in different cell systems for feasible applications. A further highlight towards fast multiplication is the fact that not only the envisaged 26650 types will be achieved, but also CoinPowerÂ© cells as well as every conceivable cell format will be producible.