Stream 4 (AFM): SPM Techniques on Energy Materials and Processes 10:00 - 12:00 Wednesday, 7th July, 2021 Sessions AFM/SPM Conference Session Session Organiser Ulrich Stimming

This session will bring together researchers from the Scanning Probe Microscopy community that are engaged in studying problems relating to energy. All researchers applying techniques, such as AFM, STM, scanning Kelvin probes, SECPM and more to energy related aspects are invited to submit their contributions. It is the goal of the session to demonstrate how the various SPM techniques are able to study materials as used in energy conversion and storage devices. SPM techniques can often be used under in-situ conditions, i.e. under control of the potential in electrochemical systems; this carries clear advantages compared to any vacuum- based characterisation techniques. It would be an important goal of the session to demonstrate the advantages of the in-situ approach.

10:00 - 10:30

10 Multi-functional and in-situ mapping techniques for optoelectronic devices

Dr Wing Chung Tsoi Swansea University, Swansea, United Kingdom

Abstract Text

Optoelectronic devices such as solar cells are very important to our society. There is active research on modified semiconducting materials and novel semiconducting materials to reduce the cost of production and enhance their functionalities. The performance of optoelectronic devices is strongly affected by the properties of the semiconductors and the device layers, including their chemical, structural, photo-physical/chemical properties. Therefore, it would be useful to obtain these properties and their optoelectronic properties in micron (even sub-micron) scale to understand how these properties affect the performance of the optoelectronic devices. Furthermore, the environment conditions around the optoelectronic devices could also affect its performance including stability. Therefore, it will also be useful to measure these properties in-situ with controlled environmental factors as well. Here, I will present our research on multi-functional and in-situ mapping techniques for optoelectronic devices. We have modified a Raman system to be able to perform Raman mapping, photoluminescence mapping, photocurrent mapping and electroluminescence mapping in the same local area in a device structure. Furthermore, by integrating with environmental chambers, we can also study these properties in-situ with different gas environment, temperature and humidity. Here, we demonstrated the beauty and usefulness of these techniques by applying them to study perovskite solar cells which is a promising type of solar cells with high power conversion efficiency, low-cost potential, and new functionalities. The techniques are able to probe the functionality of the perovskite solar cells in-depth. A perspective on the future development of these techniques will also be given.

Keywords

Raman, photoluminescence, photocurrent, electroluminescence, mapping, in-situ, optoelectronic devices, perovskite solar cells 10:30 - 10:42

54 Sequencing functional conjugated polymers by high resolution SPM imaging

Prof Giovanni Costantini , Coventry, United Kingdom

Abstract Text

In this talk I will demonstrate that high resolution scanning probe microscopy is capable of delivering crucial information — that cannot be achieved by any other current analytical method — about “real world” energy materials with a huge practical and technological relevance. In particular, I will show that by combining vacuum electrospray deposition (ESD) and high-resolution scanning tunnelling microscopy (STM) it is possible to image conjugated polymers used in organic electronics and photovoltaic devices with unprecedented detail. Based on this, it becomes possible to sequence the polymers by visual inspection and to determine their molecular mass distribution by simply counting the repeat units. Moreover, I will demonstrate that we can precisely determine the nature, locate the position, and ascertain the number of defects in the polymer backbone.1-3 The analysis of our high-resolution images univocally demonstrates that one of the main drivers for backbone conformation and polymer self-assembly is the maximization of alkyl side-chain interdigitation. On this basis, we investigate the 2D assembly of a series of conjugated polymers with the aim of gaining insight in the molecular microsctructure of the corresponding 3D functional thin films.4,5

High-resolution STM image of (a) poly(C14DPPF-F), (b) pBTTT, and (c) IDT-BT on Au(111).

References 1. D.A. Warr, L.M.A. Perdigão, H. Pinfold, J. Blohm, D. Stringer, A. Leventis, H. Bronstein, A. Troisi, G. Costantini, Sequencing conjugated polymers by eye, Sci. Adv. 4, eaas9543 (2018).

2. M. Xiao, B. Kang, S.B. Lee, L.M.A. Perdigão, A.M.T. Luci, S.P. Senanaya, M. Nikolka, M. Statz, Y. Wu, A. Sadhanala, S. Schott, R. Carey, Q. Wang, M. Lee, C. Kim, A. Onwubiko, C. Jellett, H. Liao, W. Yue, K. Cho, G. Costantini, I. McCulloch, and H. Sirringhaus, Anisotropy of charge transport in a uniaxially aligned fused electron deficient polymer by solution shear coating, Adv. Mater. 32, 2000063 (2020). 3. S.S. Lawton, D.A. Warr, L. M. A. Perdigão, Y. Changa, A. Pron, G. Costantini, and D.M. Haddleton, Determining the sequence and backbone structure of 'semi-statistical' copolymers as donor-acceptor polymers in organic solar cells, Sustain. Energy Fuels 4, 2026 (2020). 4. H. Chen, A. Wadsworth, C. Ma, A. Nanni, W. Zhang, M. Nikolka, A.M.T. Luci, L.M.A. Perdigão, K.J. Thorley, C. Cendra, B. Larson, G. Rumbles, T.D. Anthopoulos, A. Salleo, G. Costantini, H. Sirringhaus, and I. McCulloch, The Effect of Backbone Extension in Thienobenzo[b]indacenodithiophene Polymers for Organic Field-Effect Transistors, J. Am. Chem. Soc. 141, 18806 (2019). 5. D.A. Warr, et al., in preparation. Keywords

STM, conjugated polymers, microstructure, sequence, electrospray deposition

References 10:47 - 10:59

286 ReactorSTM study of Hydrodesulfurization over a Co-promoted MoS2 catalyst

Mahesh Krishna Prabhu, Dr. Irene M. N. Groot Leiden University, Leiden, Netherlands

Abstract Text

The abstract content is not included at the request of the author.

Keywords

STM, HDS, CoMoS 10:59 - 11:11

291 Investigation of SEI layer formation on HOPG using SPM

Dr Saisameera Mitta1,2, Prof. Dr. Ulrich Stimming1,2 1Newcastle University, Newcastle Upon Tyne, United Kingdom. 2The Faraday Institution, Didcot, United Kingdom

Abstract Text

The electrochemical processes that occur at the /electrolyte interfaces play a crucial role for the lithium- batteries (LIBs) performance [1,2]. The Solid-Electrolyte Interphase (SEI) formed on the negative electrode (Highly oriented pyrolytic graphite-HOPG) surface, which is described as a product of electrochemical reduction of electrolyte components, shifts the electrode potential into the electrolyte stability window [3] consequently preventing further electrolyte decomposition and stabilizing the electrode/electrolyte interface. The optimal SEI should act as a Li+ -ion conductor and an electronic insulator [4]. In modern lithium-ion batteries, the capacity fade is mainly ascribed to a growth of the SEI. A thorough understanding of the SEI formation mechanisms is crucial as batteries can benefit from a proper SEI, as it can increase their lifetime, cycle life and safety [5].

Within this work, we investigated the SEI nucleation and growth on HOPG substrates in 1 M LiPF6 in EC/DEC commercial electrolyte using in situ atomic force microscopy (AFM). We found that the SEI film prefers to nucleate and grow at defective sites like step edges rather than the basal planes. We were able correlate this with the local work functions (effective barrier height). We performed STM current-distance curves which yielded the effective tunnelling barrier. These experiments yielded a difference in barrier height at the step edge and the terrace of 0.5 eV as shown in fig 1.

Fig 1.: (a) Constant-current STM image of HOPG (b) Line trace correspond white line in (a) step height is about 0.38nm represents to monoatomic step of HOPG. Calculated local work functions on step edges and the terraces of freshly cleaved HOPG inside an Argon filled glove box are summarized in the below table.

This difference in barrier height expresses itself in a difference of the local electrochemical potential, with a value at the step edges being lower by 0.5 V as compared to the terrace, the basal plane. This can explain why the SEI layer formation starts at the step edges 0.5 V more negative than on the basal plane.

Keywords in situ atomic force microscopy, Li-ion battery, solid electrolyte interface

References

1. Peled, E. The Electrochemical Behavior of Alkali and Alkaline Earth Metals in Nonaqueous Battery Systems-The Solid Electrolyte Interphase Model. J. Electrochem. Soc. 1979, 126, 2047−2051. 2. Gauthier, M.; Carney, T. J.; Grimaud, A.; Giordano, L.; Pour, N.; Chang, H. H.; Fenning, D. P.; Lux, S. F.; Paschos, O.; Bauer, C.; Maglia, F.; Lupart, S.; Lamp, P.; Shao-Horn, Y. Electrode-Electrolyte Interface in Li- Ion Batteries: Current Understanding and New Insights. J. Phys. Chem. Lett. 2015, 6 (22), 4653−4672. 3. Goodenough, J. B., Manthiram, A. & Wnetrzewski, B. for lithium batteries. J. Power Sources 43, 269–275 (1993). 4. Seidl, L., Martens, S., Ma, J., Stimming, U. & Schneider, O. In situ scanning tunneling microscopy studies of the SEI formation on graphite electrodes for Li+-ion batteries. Nanoscale 2016, 8, 14004. 5. Balbuena, B. and Wang, Y., Lithium-Ion Batteries Solid-Electrolyte Interface, Imperial College Press, 2004. 11:11 - 11:23

335 Revealing the nanoscale fundamentals of batteries performance via x- sectional in-situ/operando Electrochemical SPM

Dr Yue Chen1,2, Dr Mangayarkarasi Nagarathinam3, Dr Sara Rodrigues Costa3,2, Dr Nuria Tapia-Ruiz3,2, Prof. Oleg Kolosov1,2 1Department of Physics, , Lancaster, United Kingdom. 2The Faraday Institution, Harwell Science and Innovation Campus, United Kingdom. 3Department of , Lancaster University, Lancaster, United Kingdom

Abstract Text

Fig. 1 BEXP + operando UFM measurements of nanomechanical properties of SEI formation on (a) the NCA commercial battery electrode and (b) HOPG model . Operando SFFM torsional vibration phase approaching spectra on deep-lithiated lithium titanite oxide (LTO) anode surface during the 1st cathodic scan.

Scanning Probe Microscopy (SPM) techniques have provided essential solutions for probing the nanophysical properties of battery materials, such as nano-electronic/ionic conductivity of battery materials [1] and Young's moduli of solid electrolyte interphase (SEI).[2] More significantly, in-situ/operando electrochemical (EC) SPM, operating simultaneously with the potentiometry/voltammetry in liquid electrochemical systems, has distinct advantages for observing the dynamic electrochemical processes (DEPs) happening on battery electrode/SEI- electrolyte (solid-liquid) interfaces,[3] especially the SEI formation and ion intercalation, which are critically important for lithium/sodium-ion batteries.

However, so far, the direct observations of the solid-liquid interfaces using in-situ/operando SPM are hindered by the rough topography and inhomogeneity on the battery solid electrode side. In this work we introduce the Beam Exit x-section nano-polishing (BEXP) to expand the studies of the commonly used model electrode, such as HOPG, with ultra-flat carbon atomic terraces and steps, to nano-sections of commercial composite electrodes (Fig.1a), and to artificial atomic scale steps in layered battery materials (Fig.1b). This enables the studies of ion-intercalations and SEI formations in the real-life materials for lithium/sodium ion batteries by a variety of in-situ/operando EC SPM modes. Furthermore, to overcome the limitation of traditional in- situ/operando EC SPM, that limit imaging to the immediate sample surface, we adapted the Ultrasonic force microscopy (UFM) [4] and Shear Force Modulation Microscopy (SFMM) modes to operation in the liquid electrolyte environment. With these ‘tip invasive’ SPM modes, the three-dimensional (3D) nano-rheology of the SEI layers was employed to provide detailed understanding of the in-depth distribution of the organic/inorganic species in SEI across the 2D area of the electrodes. The novel 3D nanorheology approach provides a 3D map of viscoelastic (complex phase and amplitude) response of the SIE to the local in-plane (shear) and out-of-plane modulation of the SPM tip.

By introducing the complementary sample preparation method and advanced SPM modes, several important DEPs, which are deeply ‘buried’ inside the operating lithium/sodium-ion battery, were observed in liquid electrolyte environment under battery operation conditions for the first time. To be specific, as shown in Fig. 1a, the dynamic CEI formations on the BEXP-polished commercial electrode surface was recorded by operando EC UFM mechanical mapping with high material sensitivity/contrast. The SEI formation on the graphite carbon atomic terraces and artificial steps were monitored and compared by operando SPM as shown in Fig. 1b, which confirmed that the SEIs formation are ‘defect-related’ at non-intercalation voltage range, while the SEIs formed on the edge sites are mainly ‘intercalation-related’ within the intercalation voltage range. Moreover, SSFM were used to study the 3D nanorheology of SEI layers formed on deep-lithiated/sodiated LTO/NTO anode surface. As shown in the torsional phase-Z approach-retract spectra in Figs. 1c, a significant phase shift can be found on the spectra C with clear transition from the viscoelastic response of the outer SEI layers to the solid- like response closer to the electrode surface. Furthermore, the 3D mechanical properties and exact geometry of the SEI layers can be reconstructed by the deconvolution of shear (torsional) amplitude and out-of-plane (vertical) deformation signals. An expansion to the lithium- intercalation induced cathode insulator-to- metal transition [5, 6] and the anode volume expansion/contraction [7] will also be discussed in this presentation.

In each characterization example, special attention will be paid to correlate the nanoscale SPM characterization results with the macroscopic battery performance, demonstrating the significant advantages of these in-situ/operando EC SPM approaches on the studies of energy materials and micro/nano-scale processes.

Keywords

X-section in-situ/operando electrochemical SPM; EC-SPM; Beam-Exit cross-sectional Polishing; BEXP; lithium-ion battery; sodium-ion battery; ion intercalation; solid-state-interphase; SEI.

References

1. Balke, N., et al., Nanoscale mapping of ion diffusion in a lithium-ion battery cathode. Nat Nanotechnol, 2010. 5(10): p. 749-54. 2. Weadock, N., et al., Determination of mechanical properties of the SEI in sodium ion batteries via colloidal probe microscopy. Nano Energy, 2013. 2(5): p. 713-719. 3. Pan, H., et al., Complementary sample preparation strategies (PVD/BEXP) combining with multifunctional SPM for the characterizations of battery interfacial properties. MethodsX, 2021. 8: p. 101250. 4. Robinson, B.J. and O.V. Kolosov, Probing nanoscale graphene-liquid interfacial interactions via Ultrasonic Force Spectroscopy. Nanoscale, 2014. 5. Chen, Y., et al., Insight into the intrinsic mechanism of improving electrochemical performance via constructing the preferred crystal orientation in lithium cobalt dioxide. Journal, 2020. 399. 6. Chen, Y., et al., In Situ Observation of the Insulator-To-Metal Transition and Nonequilibrium Phase Transition for Li1–xCoO2 Films with Preferred (003) Orientation Nanorods. ACS Applied Materials & Interfaces, 2019. 11(36): p. 33043-33053. 7. Chen, Y., et al., Suppressing volume change and in situ electrochemical atomic force microscopy observation during the lithiation/delithiation process for CuO nanorod array electrodes. Journal of Solid State Electrochemistry, 2018. 23(2): p. 367-377. 11:28 - 11:58

154 Characterization of active materials for lithium ion batteries using scanning probe techniques

Prof. Dr. Andreas Bund1, Dr. Svetlozar Ivanov1, Sebastian Mai1, Dr. Anna Dimitrova2, Mario Kurniawan1, Dr. Michael Stich1 1TU Ilmenau, Electrochemistry and Electroplating Group, Ilmenau, Germany. 2TU Ilmenau, Group Technical Physics I, Ilmenau, Germany

Abstract Text

This contribution will discuss recent results from the authors' labs on active materials for lithium ion batteries and their characterization. Special focus will be given to the formation of the solid electrolyte interphase (SEI). The SEI is a thin layer of decomposition products from the electrolyte at the negative electrode (usually graphite) and forms during the first charging cycles. The electrochemical and mechanical properties of the SEI are crucial for a safe and reliable function of the battery. Using in-situ electrochemical atomic force microscopy we studied the early stages of SEI formation at a carbon surface in a typical battery electrolyte. The results show that this is a very dynamic process with several intermediate stages. The discussion of the scanning probe microscopy will be complemented by results from other powerful methods, such as in-situ microgravimetry and photo electron spectroscopy.

Keywords

Batteries, Scanning probe technologies