Christian Kuss

Polypyrrole:carboxymethyl cellulose, a sustainable and conducting battery electrode binder, maintains its chemical identity, even in lithium intercalation negative electrodes.

In lithium-ion batteries (LIBs), polymeric binders are crucial for maintaining the mechanical integrity of electrodes and ensuring continuous conductive pathways for both ions and electrons. The choice of binder material and its functional groups can significantly impact the battery's performance 1. Water-processable binders, in particular, offer both ecological and economic advantages. Among these, aqueous sodium carboxymethyl cellulose (CMC-Na) has shown promise in enhancing electrochemical performance compared to conventional binders, such as polyvinylidene fluoride (PVDF), especially when used in anodes 2. Unlike PVDF, CMC is biodegradable, water-soluble, and contains functional groups (–COOH and –OH) that form hydrogen bonds, improving its adhesion properties 3. Furthermore, CMC is cost-effective. However, CMC's intrinsic insulating nature limits its electron conductivity, which can hinder performance during cycling. This limitation can be addressed by using CMC as a dopant in polypyrrole (PPy), creating a conductive PPy:CMC composite with enhanced electrical conductivity, as well as thermal and environmental stability 4,5,6. In this study, we investigate the use of PPy:CMC composites as conducting binders in graphite anodes and evaluate the associated degradation mechanisms. Two types of graphite electrodes were fabricated: Graphite:PVDF:C and Graphite:PPy:CMC. To assess electrode stability and binder interactions with active materials and electrolytes, a range of characterization techniques were employed. Electrochemical stability and behavior were analyzed via galvanostatic cycling, cyclic voltammetry (CV), and impedance spectroscopy (EIS). Kinetic properties, lithium-ion transport, and interfacial resistance were also examined. Degradation products and mechanisms were investigated using X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and energy dispersive X-ray spectroscopy (EDX). Electrode morphology and homogeneity were examined with scanning electron microscopy (SEM). The results provide valuable insights into the potential of PPy:CMC as a conducting binder in graphite anodes, laying the foundation for future research into high-energy-density anodes for LIBs and other energy storage applications. References 1. Shi, Y., Zhou, X. & Yu, G. Material and Structural Design of Novel Binder Systems for High-Energy, High-Power Lithium-Ion Batteries. Acc Chem Res 50, 2642-2652, doi:10.1021/acs.accounts.7b00402 (2017). 2. Song, J. et al. Interpenetrated Gel Polymer Binder for High-Performance Silicon Anodes in Lithium-ion Batteries. Advanced Functional Materials 24, 5904-5910, doi:10.1002/adfm.201401269 (2014). 3. Lingappan, N., Kong, L., Pecht, M. J. R. & Reviews, S. E. The significance of aqueous binders in lithium-ion batteries. 147, 111227 (2021). 4. Demirci, S., Sutekin, S. D. & Sahiner, N. Polymeric Composites Based on Carboxymethyl Cellulose Cryogel and Conductive Polymers: Synthesis and Characterization. Journal of Composites Science 4, doi:10.3390/jcs4020033 (2020). 5. Chou, S. L. et al. Tin/polypyrrole composite anode using sodium carboxymethyl cellulose binder for lithium-ion batteries. Dalton Trans 40, 12801-12807, doi:10.1039/c1dt10396b (2011). 6. Sasso, C. et al. Polypyrrole and polypyrrole/wood-derived materials conducting composites: a review. BioResources 6 (2011).

Polypyrrole is a popular conjugated polymer that becomes highly conductive in its p-doped state. The intrinsically non-polar nature of the conjugated bond network limits the processing options of such polymers. Surfactants and polyanions help increase dispersity of conductive polymer in suitable solvents for processing. However, while such dispersions can be highly stable, they are formed by complex nanostructures that significantly impact the conducting polymer composite’s bulk properties. Similarly, complex nanostructures can be formed when surfactants or polyelectrolytes serve as templates during the polymerization of the conducting polymer precursor. Following the report of polypyrrole:carboxymethyl cellulose composites in battery electrodes as conductive binders, we are here investigating the role that nanostructure control can have in optimizing their performance. Using methyl orange as a structural template, we can control the composite’s nanoscopic shape between nanospheres and nanofibers. In the bulk material, the latter gives rise to significantly increased electronic conductivity and capacitance in battery use conditions, underlining the opportunities for improved performance of conducting polymer composites by controlling synthesis conditions.

Intercalation is the fundamental process underlying lithium‐ion batteries and related technologies. While intercalation is electrochemically induced in batteries, it can also be performed with chemical redox agents. In principle, the two processes are equivalent, although there can be differences, such as rate control, side reactions, and charge transfer mechanisms. Chemically induced intercalation can be used where electrochemical methods are impractical or impossible and continues to inspire innovative applications. This chemistry is important in synthesis and pretreatment of intercalation materials, with novel impactful applications emerging that range from lithium recycling to intercalation material‐based redox flow batteries. This review summarizes the use of chemical intercalation and serves as a resource for selecting and optimizing methods specific to material and application. Covering the whole life cycle of intercalation materials: development, synthesis, use, and finally recycling, it can be expected that these reactions will continue to have great impact on the path toward efficient and cheap energy storage.

The unique properties of conducting polymers make them ideally suited for applications in organic electronics, photovoltaics, and energy storage systems. Depending on the specific application, they can outperform metal-based electronics by cost, mechanical flexibility, molecular design opportunities, and environmental impact. Many composites of conducting polymers with polyanions can be processed in water. However, the facile processing of such composites comes at a cost of reduced conductivity. In this manuscript, electronic conductivity dependence on composition for a composite of polypyrrole (PPy) with carboxymethyl cellulose (CMC) has been studied. Secondary ion mass spectrometry and electron energy loss spectroscopy mapping indicate the formation of a nanostructure forming PPy-rich nanospheres with a CMC-rich surface coverage. This structure requires inter-particle electron conduction to occur via quantum tunneling. Variations in the tunneling distance are dependent on the applied pressure, giving rise to a pressure-dependent electronic conductivity and thus piezoresistance. This behavior opens new applications of conducting polymer composites in pressure-sensitive electronic devices, providing metal-free alternatives to quantum tunneling composites.

Currently, rechargeable batteries are used in everyday life applications, such as in mobiles, cameras, laptops, and cars. Accordingly, the demand for rechargeable batteries, in particular Lithium-ion batteries, is increasing. Their electrodes consist of at least four different materials: active material, a conductive additive, polymer binder, and current collector. The battery performance in terms of cycling performance, energy density, mechanical integrity, and ionic and electronic mobility depends on these materials.¹ The casting procedure, the multiscale packing during the evaporation process after casting, the accumulation of the conductive additive, the adhesive failure during the charging and discharging process, and the natural irregular shape of the electrode materials produce an inhomogeneous electrode microstructure. ² This inhomogeneity causes current density variation and a non-uniform Lithium ion concentration leading to damage to the battery structure, reducing the capacity, and degrading the battery. ² The electrode microstructure and its effect on the battery performance have great importance. As such, several techniques have been developed to investigate electrode microstructure. Each technique gives specific information. Here, we will combine scanning electron microscopy (SEM), scanning electrochemical microscopy (SECM), and battery cycling to study the effect of microstructure on the battery performance. SECM is a high resolution probe technique that scans the electrode surface using an ultra-microelectrode. Thus it can measure the electrode`s local conductivity.^{3 , 4} Therefore, we can quantify the inhomogeneous microstructure distribution. Thus, by combining these results with SEM and cycling test results we will be able to find the correlation between the battery performance and the distribution of the microstructure. References: Stein M, Chen CF, Robles DJ, Rhodes C, Mukherjee PP. Non-aqueous electrode processing and construction of lithium-ion coin cells. J Vis Exp. 2016;2016(108):1-10. doi:10.3791/53490 Xiong R, Zhang T, Huang T, Li M, Zhang Y, Zhou H. Improvement of electrochemical homogeneity for lithium-ion batteries enabled by a conjoined-electrode structure. Appl Energy. 2020;270(May):115109. doi:10.1016/j.apenergy.2020.115109 Ventosa E, Schuhmann W. Scanning electrochemical microscopy of Li-ion batteries. Phys Chem Chem Phys. 2015;17(43):28441-28450. doi:10.1039/c5cp02268a Polcari D, Dauphin-Ducharme P, Mauzeroll J. Scanning Electrochemical Microscopy: A Comprehensive Review of Experimental Parameters from 1989 to 2015. Chem Rev. 2016;116(22):13234-13278. doi:10.1021/acs.chemrev.6b00067

In an effort to minimize green house gas emissions, the development of renewable energy storage has become important, especially for the transportation industry.(I) Currently, the most effective energy storage solution is Li-ion batteries due to their long cycle life and high energy density.(I) However, this current technology uses highly reactive and flammable liquid electrolytes which are both limited by their limited charging speed through a liquid medium and their unsafe nature.(II) For this reason, many large companies such as Hyundai and Samsung have heavily invested in the development of all-solid-state batteries (ASSB), seen as the next step in safe fast-charging energy storage.(III) However, problems remain that need to be solved before ASSBs can become commercially viable. One of these problems is cycling stability, where battery performance significantly drops after a few charge/discharge cycles, notably through mechanical degradation and interfacial contact issues caused by volume changes of the active material against a rigid solid electrolyte.(I) For this reason, there is growing interest in increasing the system’s mechanical flexibility thus preventing degradation by the use of ionically conductive polymers as soft binders and volume buffers.(IV) One potential choice for such materials are environmentally friendly natural biopolymers such as cellulose derivatives like carboxymethyl cellulose (CMC), whose functional groups coordinate cations during transport. CMC has already been shown to act as a binder that increases mechanical stability for electrodes of current Li-ion technology and exhibits proton conductivity in fuel cell applications. It is also being investigated for its potential in ASSBs, Na-ion, and Zn batteries where it has been shown to have high durability and that it combines well with a variety of other polymers when used as binders or as a solid electrolyte in these batteries.(IV-VII) To further our understanding of incorporating this biopolymer in batteries, we are studying the effects of various aspects of CMC film preparation on their ionic conductivity such as salt concentration and film homogeneity. In addition, to the preparation parameters, we investigated the activation energy of ion transport for CMC films of differing concentrations through temperature dependence measurements. Furthermore, we investigated the structure of these materials with infrared spectroscopy and differential scanning calorimetry to see the effects of salt concentration on the microstructure. This data is of importance in assessing the impact of CMC binders and will lay a foundation for optimizing binder choice for cheap and biodegradable components in both current and next-generation battery technology. References (I) Li, L.; Deng, Y.; Chen, G. Status And Prospect Of Garnet/Polymer Solid Composite Electrolytes For All-Solid-State Lithium Batteries. Journal of Energy Chemistry 2020, 50, 154-177. (II) Zheng, Y.; Li, X.; Li, C. A Novel De-Coupling Solid Polymer Electrolyte Via Semi-Interpenetrating Network For Lithium Metal Battery. Energy Storage Materials 2020, 29, 42-51. (III) Eckhouse, B. Samsung Venture, Hyundai Investing in Battery Producer. https://www.bloomberg.com/news/articles/2018-09-10/samsung-and-hyundai-investing-in-solid-state-battery-producer. (IV) Shetty, S.; Ismayil; Shetty, G. Enhancement Of Electrical And Optical Properties Of Sodium Bromide Doped Carboxymethyl Cellulose Biopolymer Electrolyte Films. Journal of Macromolecular Science, Part B 2020, 59 (4), 235-247. (V) Darjazi, H.; Staffolani, A.; Sbrascini, L.; Bottoni, L.; Tossici, R.; Nobili, F. Sustainable Anodes For Lithium- And Sodium-Ion Batteries Based On Coffee Ground-Derived Hard Carbon And Green Binders. Energies 2020, 13 (23), 6216. (VI) Dueramae, I.; Okhawilai, M.; Kasemsiri, P.; Uyama, H.; Kita, R. Properties Enhancement Of Carboxymethyl Cellulose With Thermo-Responsive Polymer As Solid Polymer Electrolyte For Zinc Ion Battery. Scientific Reports 2020, 10 (1). (VII) Sasso, C.; Beneventi, D.; Zeno, E.; Petit-Conil, M.; Chaussy, D.; Belgacem, M. Carboxymethylcellulose: A Conductivity Enhancer And Film-Forming Agent For Processable Polypyrrole From Aqueous Medium. Synthetic Metals 2011, 161 (5-6), 397-403.

Aqueous electrode processing has been considered an important movement to make the overall battery fabrication process less toxic and more environmental-friendly¹. The traditional approach focuses on mixing common aqueous binders such as carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and styrene-butadiene rubber (SBR) with carbon additives to form conductive, water-processable electrode matrices². This design, however, is unlikely to improve electrode interconnection, where carbon additives still loosely adhere to active materials³. Utilizing a better electrode matrix is believed to enhance both mechanical and electrical connections of electrode architecture, thus improving battery capacity and stability. Our recent work has demonstrated the design concept of conducting polymer composites as self-conductive and water-processable electrode matrices for Li-ion batteries⁴. By using in situ chemical polymerization method, polypyrrole:carboxymethyl-cellulose (PPy:CMC) composites, as a representative, were synthesized facilely and at low cost. The molecular structure of PPy:CMC composites composes of carboxyl groups from CMC as main anionic dopants for the positively charged PPy polymer chain. Their unique adhesion enables PPy:CMC composites to sufficiently connect active materials electrically and mechanically despite their low intrinsic electrical conductivity. As a result, cathodes with PPy:CMC composites and LiCoO₂ or LiNi_1/3Mn_1/3Co_1/3O₂ showed promising cycling performance even at a 1-C rate, which is rarely reported for carbon-additive-free electrodes. Also, aqueous electrode casting is feasible for PPy:CMC-based electrodes, thus addressing toxicity and intensive-energy consumption associated with the current NMP-based electrode processing. Furthermore, their compatibility in Li-ion battery chemistry has also been tested employing SEM, EIS and XPS. This work shows initial efforts in designing a new kind of electrode matrix that enables a greener fabrication of Li-ion batteries. References J. Zhao, X. Yang, Y. Yao, Y. Gao, Y. Sui, B. Zou, H. Ehrenberg, G. Chen, and F. Du, Adv. Sci., 5, 1700768 (2018). D. Bresser, D. Buchholz, A. Moretti, A. Varzi, and S. Passerini, Energy Environ. Sci., 11, 3096–3127 (2018). V. A. Nguyen and C. Kuss, J. Electrochem. Soc., 167, 065501 (2020). V. A. Nguyen, J. Wang, and C. Kuss, J. Power Sources Adv., 6, 100033 (2020).