In this paper, we will describe in detail the setting up of a Design of Experiments (DoE) applied to the formulation of electrodes for Li-ion batteries. We will show that, with software guidance, Designs of Experiments are simple yet extremely useful statistical tools to set up and embrace. An Optimal Combined Design was used to identify influential factors and pinpoint the optimal formulation, according to the projected use. Our methodology follows an eight-step workflow adapted from the literature. Once the study objectives are clearly identified, it is necessary to consider the time, cost, and complexity of an experiment before choosing the responses that best describe the system, as well as the factors to vary. By strategically selecting the mixtures to be characterized, it is possible to minimize the number of experiments, and obtain a statistically relevant empirical equation which links responses and design factors.

Today, energy conversion devices typically rely on composite electrodes made of several materials interacting with one another. Understanding their individual and combined impacts on performance is essential in the pursuit of optimized systems. Unfortunately, this investigation is often disregarded in favor of quick publishable results. Here, designs of experiments are shown as capable of meeting both ends. Less than 100 different electrode formulations are defined with two active materials (LiFePO 4 and Li 4 Ti 5 O 12 ), two carbonaceous additives (carbon black and carbon nanofibers), and three binders (polyvinylidene fluoride, polyethylene-co-ethyl acrylate-co-maleic anhydride (Lotader 5500), and a hydrogenated nitrile butadiene rubber). Correlations with strong descriptive statistics are found between formulation and different limitations, indicating that maximum active material content should always be favored with a small fraction of both conductive additives and minimal binder content. With the help of designs of experiments, Lotader 5500-bound electrodes are optimized beyond typical formulations found in the literature.

Lotader 5500, a commercially-available polyethylene-co-ethyl acrylate-co-maleic anhydride thermoplastic elastomer, is investigated as a new binder for Li-ion battery composite electrodes with LiFePO 4 and Li 4 Ti 5 O 12 . This binder was chosen to enhance the cohesion and adhesion properties of the composite electrode it binds through its reactive functional groups; moreover, the absence of fluorine in its composition renders it more suitable than polyvinylidene fluoride (PVDF) in the battery recycling process, which often relies on pyrolysis. Lotader 5500's insolubility in a carbonate electrolyte is demonstrated, as well as its similar electrochemical behavior to PVDF in the 50 mV to 4.2 V range vs. Li + /Li. After demonstrating the high-rate performance of the half-cells, full cells were assembled, and cycled 1,000 times (charged at a constant voltage of 2.4 V and discharged at 10D), and all exhibit a final capacity of approximately 70 mAh.g −1 .

Studies pinpointed the limitation of power-related performance for Li-ion batteries to the microstructure of each electrode.1, 2 This random arrangement of the active material (AM) and carbon filling particles bound by a polymer is typically characterized through physical values such as tortuosity, porosity and Mac Mullin Number.3 There is nonetheless no consensus on what the best formulation is for a given set of electrode components. The relationship between microstructure and performance is investigated by planning and analyzing a Design of Experiments based on a Complex Mixture Design. Thirty different formulations were characterized where Li4Ti5O12 was the AM, and carbon black and carbon nanofibers were conductive fillers. As for the binder, two were studied: polyvinylidene fluoride and a fluorine-free thermoplastic elastomer.4 All other factors, e.g. rheology or experimenter bias, were closely monitored and finely controlled to remain identical for all samples. Electrochemical performance were studied at low, medium and high charging speeds to account for different limitations of full capacity retention. Statistical analysis showed clear correlations between the formulation and the electrodes’ capacity with very high descriptive statistics, e.g. R2. Lastly, strong correlations were found between capacity and microstructure, strengthening further the trust in the empirical equations. These robust models helped choosing optimal fluorine-free formulations that surpassed even the highest performing previous electrodes. 1. Vasileiadis, A.; Klerk, N. J. J. d.; Smith, R. B.; Ganapathy, S.; Harks, P. P. R. M. L.; Bazant, M. Z.; Wagemaker, M., Toward Optimal Performance and In‐Depth Understanding of Spinel Li4Ti5O12 Electrodes through Phase Field Modeling. Advanced Functional Materials 2018, 0 (0), 1705992. 2. Ngandjong, A. C.; Rucci, A.; Maiza, M.; Shukla, G.; Vazquez-Arenas, J.; Franco, A. A., Multiscale Simulation Platform Linking Lithium Ion Battery Electrode Fabrication Process with Performance at the Cell Level. The Journal of Physical Chemistry Letters 2017, 8 (23), 5966-5972. 3. Landesfeind, J.; Hattendorff, J.; Ehrl, A.; Wall, W. A.; Gasteiger, H. A., Tortuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy. Journal of The Electrochemical Society 2016, 163 (7), A1373-A1387. 4. Rynne, O.; Lepage, D.; Aymé-Perrot, D.; Rochefort, D.; Dollé, M., Application of a Commercially-Available Fluorine-Free Thermoplastic Elastomer as a Binder for High-Power Li-Ion Battery Electrodes. Journal of The Electrochemical Society 2019, 166 (6), A1140-A1146. With this presentation, we want to show the versatility and power of Designs of Experiments to the community, whether for electrode formulation or new material synthesis, as the input parameters can be easily interchangeable. Figure 1

Lithium-ion is currently the leading technology for electrochemical energy storage, especially in the transportation sector. The electrification of vehicles through the use of lithium-ion batteries (LiBs) is at the center of the world efforts to decrease atmospheric pollution by reducing CO2 emission. Due to the high efficiency of electrical motors, a net reduction in greenhouse gases is achieved upon electrification of vehicles even in areas where electricity is generated from fossil fuels. Yet, the rapidly growing production of LiB brings new concerns on the environmental cost of the technology. The analysis of a complete their life cycle, from mining precursors to recycling batteries at the end of their life, reveals that several steps of the cycle can be improved to further reduce the environmental footprint of lithium-ion batteries. It is in this context that our group got interested in developing alternative approached to electrode fabrication, a key aspect of LiB manufacturing. Currently, most of the electrode fabrication processes involves the use of organic solvents, typically N-methyl-2-pyrrolidone (or NMP), which is toxic and costly. As such, a considerable effort is spent during electrode fabrication to recuperate NMP vapors and prevent exposure to the workers and environment. Avoiding the use of any solvents during electrode fabrication would not only minimize the environmental impact but would also result into lower energy consumption. This contribution presents a study of a new solvent-free melt process technique to LiB electrode fabrication through the use of elastomeric binders. The impact of formulation on active material dispersion, microscopic morphology, electronic percolation and porosity will be discussed. With such parameters optimized, the electrochemical response of composite electrodes based on LiFePO4 and Li4Ti5O12 active materials were characterized both individually and as full cells. The battery performance will be compared with PVDF-based electrodes made with a conventional approach.