Name: elemental-sensitive detection of the chemistry in batteries through soft x-ray absorption spectroscopy and resonant inelastic x-ray scattering
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The Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory (LBNL) is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Q.L. thanks the China Scholarship Council (CSC) for financial support through the collaboration based on China 111 project No. B13029. R.Q. thanks the support from LBNL LDRD program. S.S. and Z.Z. thank the support from the ALS Doctoral fellowship.

1. Experimental Planning
Note: While sXES could be performed with lab-based equipment, sXAS and RIXS are synchrotron-based experiments, which requires access to the beamtime of a synchrotron facility. The procedure for applying for beamtime and running experiments could be different at different facilities, but they all follow a similar basic procedure.
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	<li>Check the facility website for the beamline directory (e.g., https://als.lbl.gov/beamlines/), or contact the scientists i...

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B. 25 (1), 17104 (2016).</li><li>Yang, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Key+electronic+states+in+lithium+battery+materials+probed+by+soft+X-ray+spectroscopy.">Key electronic states in lithium battery materials probed by soft X-ray spectroscopy.</a> Journal of Electron Spectroscopy and Related Phenomena. 190, 64-74 (2013).</li><li>Qiao, R., Yang, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interactions+at+the+electrode-electrolyte+interfaces+in+batteries+studied+by+quasi-in-situ+soft+x-ray+absorption+spectroscopy.">Interactions at the electrode-electrolyte interfaces in batteries studied by quasi-in-situ soft x-ray absorption spectroscopy.</a> Journal of Electron Spectroscopy and Related Phenomena. , (2017).</li><li>Lin, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synchrotron+X-ray+Analytical+Techniques+for+Studying+Materials+Electrochemistry+in+Rechargeable+Batteries.">Synchrotron X-ray Analytical Techniques for Studying Materials Electrochemistry in Rechargeable Batteries.</a> Chem Rev. , (2017).</li><li>Liu, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Why+LiFePO4+is+a+safe+battery+electrode:+Coulomb+repulsion+induced+electron-state+reshuffling+upon+lithiation.">Why LiFePO4 is a safe battery electrode: Coulomb repulsion induced electron-state reshuffling upon lithiation.</a> Phys Chem Chem Phys. 17 (39), 26369-26377 (2015).</li><li>Liu, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymers+with+tailored+electronic+structure+for+high+capacity+lithium+battery+electrodes.">Polymers with tailored electronic structure for high capacity lithium battery electrodes.</a> Adv Mater. 23 (40), 4679-4683 (2011).</li><li>Wu, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toward+an+Ideal+Polymer+Binder+Design+for+High-Capacity+Battery+Anodes.">Toward an Ideal Polymer Binder Design for High-Capacity Battery Anodes.</a> Journal of the American Chemical Society. 135 (32), 12048-12056 (2013).</li><li>Wang, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rhombohedral+prussian+white+as+cathode+for+rechargeable+sodium-ion+batteries.">Rhombohedral prussian white as cathode for rechargeable sodium-ion batteries.</a> J Am Chem Soc. 137 (7), 2548-2554 (2015).</li><li>Qiao, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distinct+Solid-Electrolyte-Interphases+on+Sn+(100)+and+(001)+Electrodes+Studied+by+Soft+X-Ray+Spectroscopy.">Distinct Solid-Electrolyte-Interphases on Sn (100) and (001) Electrodes Studied by Soft X-Ray Spectroscopy.</a> Advanced Materials Interfaces. 1 (100), (2014).</li><li>Shan, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bivalence+Mn5O8+with+hydroxylated+interphase+for+high-voltage+aqueous+sodium-ion+storage.">Bivalence Mn5O8 with hydroxylated interphase for high-voltage aqueous sodium-ion storage.</a> Nat Commun. 7, 13370 (2016).</li><li>Qiao, R., Chuang, Y. 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M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Na-Ion+Intercalation+and+Charge+Storage+Mechanism+in+2D+Vanadium+Carbide.">Na-Ion Intercalation and Charge Storage Mechanism in 2D Vanadium Carbide.</a> Advanced Energy Materials. , 1700959 (2017).</li><li>Zhuo, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+excess+lithium+in+LiMn2O4+and+Li1.15Mn1.85O4+electrodes+revealed+by+quantitative+analysis+of+soft+X-ray+absorption+spectroscopy.">Effect of excess lithium in LiMn2O4 and Li1.15Mn1.85O4 electrodes revealed by quantitative analysis of soft X-ray absorption spectroscopy.</a> Applied Physics Letters. 110, 093902 (2017).</li><li>Qiao, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transition-metal+redox+evolution+in+LiNi+0.5+Mn+0.3+Co+0.2+O+2+electrodes+at+high+potentials.">Transition-metal redox evolution in LiNi 0.5 Mn 0.3 Co 0.2 O 2 electrodes at high potentials.</a> Journal of Power Sources. 360, 294-300 (2017).</li><li>Qiao, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Revealing+and+suppressing+surface+Mn(II)+formation+of+Na0.44MnO2+electrodes+for+Na-ion+batteries.">Revealing and suppressing surface Mn(II) formation of Na0.44MnO2 electrodes for Na-ion batteries.</a> Nano Energy. 16, 186-195 (2015).</li><li>Qiao, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+evidence+of+gradient+Mn(II)+evolution+at+charged+states+in+LiNi0.5Mn1.5O4+electrodes+with+capacity+fading.">Direct evidence of gradient Mn(II) evolution at charged states in LiNi0.5Mn1.5O4 electrodes with capacity fading.</a> Journal of Power Sources. 273, 1120-1126 (2015).</li><li>Wu, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modification+of+Transition-Metal+Redox+by+Interstitial+Water+in+Hexacyanometallate+Electrodes+for+Sodium-Ion+Batteries.">Modification of Transition-Metal Redox by Interstitial Water in Hexacyanometallate Electrodes for Sodium-Ion Batteries.</a> Journal of the American Chemical Society. , (2017).</li><li>Liu, X., et al. <a target="_blank" 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The formidable challenge of improving the performance of energy storage materials requires advances of incisive tools to directly probe the chemical evolutions in battery compounds upon electrochemical operation. Soft X-ray core-level spectroscopy, such as sXAS, sXES, and RIXS, is a tool-of-choice for detecting the critical valence states of both the anions and cations involved in LIBs and SIBs.
Core-level spectroscopy techniques involve the strong excitation of core electrons to unoccupied st...

Developing high-performance batteries is one of the crucial requirements for realizing modern energy applications with environmentally benign resources and devices. Developing high-efficiency, low-cost, and sustainable energy storage devices has become critical for both electric vehicles (EVs) and the electric grid, with a projected energy storage market expansion of ten times in this decade. The ubiquitous Li-ion battery (LIB) technology remains a promising candidate for high energy-density and high power energy storage solutions1, while Na-ion batteries (SIBs) hold the promise of realizing low-cost and stable storage for green-grid applications2. However, the overall level of battery technology is well below what is required to meet the need of this new phase of mid-to-large scale energy storage1,3.
The pressing challenge of developing high-performance energy-storage system arises from the complex mechanical and electronic characteristics of the battery operations. Extensive efforts have focused on material synthesis and mechanical properties. However, the evolution of the chemical states of particular elements in battery electrodes is often under active debate for newly developed battery materials. In general, both LIBs and SIBs operate with evolving electronic states triggered by the transportation of the electrons and ions during the charge and discharge process, leading to the oxidation and reduction (redox) reactions of specific element(s). As the bottleneck for many performance parameters, battery cathodes have been paid much attention in research and developments4,5. A practical battery cathode material is often a 3d transition-metal (TM) oxide with particular structural channels for ion diffusion. Conventionally, the redox reaction is limited to the TM elements; however, recent results indicate that oxygen could possibly be utilized in reversible electrochemical cycling6. The redox mechanism is one of the most critical pieces of information for understanding an electrochemical operation, and a direct probe of the chemical states of battery electrodes with elemental sensitivity is thus highly desirable.
Synchrotron-based, soft X-ray spectroscopy is an advanced technique that detects the valence electron states in the vicinity of the Fermi level in battery materials7. Because of the high sensitivity of soft X-ray photons to the electrons of a specific element and orbital, soft X-ray spectroscopy could be utilized as a direct probe of the critical electron states in battery electrodes8, or at the interfaces in batteries9. Furthermore, compared with hard X-rays, soft X-rays are lower in energy and cover excitations of the low-Z elements, e.g., C, N, O, and of the 2p-to-3d excitation in the 3d TMs10.
The excitations of soft x-ray spectroscopy first involve electron transitions from a particular core state to an unoccupied state by absorbing energy from soft X-ray photons. The intensity of such soft X-ray absorption spectroscopy thus corresponds to the density of state (DOS) of the unoccupied (conduction-band) states with the existence of the excited core-holes. The X-ray absorption coefficient can be measured by detecting the total number of photons or electrons emitted during the decay process. The total electron yield (TEY) counts the total number of emitted electrons, and is thus a photon-in-electron-out (PIEO) detection mode. TEY has a shallow probe depth of several nanometers, and therefore is relatively surface sensitive, due to the shallow escape depth of electrons. However, as a photon-in-photon-out (PIPO) detection mode, the total fluorescence yield (TFY) measures the total number of emitted photons in the sXAS process. Its probe depth is about hundreds of nanometers, which is deeper than that of TEY. Due to the difference in probe depths, the contrast between TEY and TFY could provide important information for a comparison between the surface and bulk of the material.
sXES is a PIPO technique, corresponding to the decay of the exited state to fill the core hole, leading to the emission of X-ray photons at characteristic energies. If the core electron is excited to the continuum electron state far away from the sXAS threshold, it is a non-resonant X-ray fluorescence process corresponding to the decay of occupied (valence-band) electrons to the core holes, i.e., sXES reflects the DOS of the valence-band states. Otherwise, if the core electron is resonantly excited to exactly the absorption threshold, the resulting emission spectra feature strong excitation energy dependence. For this case, the spectroscopy experiments are denoted as resonant inelastic x-ray scattering (RIXS).
Because sXAS and sXES corresponds to the unoccupied (conduction-band) and occupied (valence-band) electron states, respectively, they provide complementary information on the electron states involved in the reduction and oxidation reactions in the battery electrodes upon electrochemical operation11. For low-Z elements, especially C12,13, N14, and O15,16,17, sXAS has been widely used for studying the critical electron states corresponding to both the electron transfer12,13 and chemical compositions15,16,17. For 3d TMs, sXAS of TM L-edges has been successfully demonstrated to be an effective probe of the TM redox reactions of V18, Mn19,20,21,22,23, Fe23,24,25,26, Co20,27, and Ni20,28. Because the TM-L sXAS features are dominated by the well-defined multiplet effect, which are sensitive to the different TM oxidation18,19,20,21,22,24,25,26,27,28 and spin states14,29, the TM sXAS data could enable even quantitative analysis of the TM redox couples in LIB and SIB electrodes27.
Compared with the popular employment of sXAS for battery material studies, RIXS is less often utilized due to the complexity of both the experiments and data interpretation for obtaining meaningful information related to battery performance10. However, due to the extremely high chemical-state selectivity of RIXS, RIXS is potentially a much more sensitive probe of the chemical state evolution in battery materials with inherent elemental sensitivity. Recent sXES and RIXS reports by Jeyachandran et al., have showcased the high sensitivity of RIXS to specific chemical configurations in the ion-solvation systems beyond sXAS30,31. With the recent rapid developments of high-efficiency RIXS systems32,33,34, RIXS has quickly shifted from a fundamental physics tool to a powerful technique for battery research, and occasionally becomes the tool-of-choice for specific studies of both the cation and anion evolution in battery compounds.
In this work, the detailed protocols for sXAS, sXES, and RIXS experiments are introduced. We cover the details of experimental planning, technical procedures for carrying out experiments, and more importantly, data processing for different spectroscopic techniques. Furthermore, three representative results in battery material studies are presented to demonstrate the applications of these three soft X-ray spectroscopy techniques. We note that the technical details of these experiments could be different at different end-stations and/or facilities. Additionally, ex-situ and in-situ experiments have very different setup procedures on sample handling due to the stringent requirements of ultra-high vacuum for soft X-ray spectroscopy35. But the protocol here represents the typical procedure and could serve as a common reference for soft X-ray spectroscopy experiments in various experimental systems at different facilities.

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			<td height="21" style="height:21px;width:216px;">Material</td>
			<td style="width:144px;"></td>
			<td style="width:119px;"></td>
			<td style="width:355px;"></td>
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			<td height="21" style="height:21px;">Electrode active materials</td>
			<td style="width:144px;">various</td>
			<td style="width:119px;"></td>
			<td>Synthesized in-house or obtained from various suppliers.</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;">Lithium foil</td>
			<td style="width:144px;">Sigma-Aldrich</td>
			<td>320080</td>
			<td style="width:355px;">Anode for half cells. Store and handle in an inert atmosphere glovebox under Ar. (www.sigmaaldrich.com)</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;">Sodium foil</td>
			<td style="width:144px;">Sigma-Aldrich</td>
			<td style="width:119px;">282065</td>
			<td style="width:355px;">Anode for half cells. Store and handle in an inert atmosphere glovebox under Ar. (www.sigmaaldrich.com)</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;">Electrolyte solutions</td>
			<td style="width:144px;">BASF</td>
			<td style="width:119px;">Contact vendor for desired formulations</td>
			<td style="width:355px;">http://www.catalysts.basf.com/p02/USWeb-Internet/catalysts/en/content/microsites/catalysts/prods-inds/batt-mats/electrolytes</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Synthetic flake graphite</td>
			<td style="width:144px;">Timcal</td>
			<td style="width:119px;">SFG-6</td>
			<td style="width:355px;">Conductive additive for electrodes. (www.timcal.com)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Indium foil</td>
			<td style="width:144px;">Sigma-Aldrich</td>
			<td style="width:119px;">357308</td>
			<td style="width:355px;">Used if collecting Carbon and Oxygen signals of power samples</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Argon gas</td>
			<td style="width:144px;">Air Products</td>
			<td style="width:119px;">Custom order, contact vendors</td>
			<td style="width:355px;">Argon used to fill glovebox where to assemble and store air-sensitive samples. (http://www.airproducts.com/products/gases.aspx)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Eqiupment</td>
			<td style="width:144px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">CCD</td>
			<td style="width:144px;">iKon-L</td>
			<td style="width:119px;">DO936N</td>
			<td style="width:355px;">Used to capture the emission photons when carrying out the sXES or RiXS experiment (http://www.andor.com/scientific-cameras/ikon-xl-and-ikon-large-ccd-series/ikon-l-936)</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Inert atmosphere glovebox</td>
			<td style="width:144px;">MBRAUN</td>
			<td style="width:119px;">MB200B</td>
			<td style="width:355px;">Used during air-sensitive samples assembly and storage. (http://www.mbraun.com/products/glovebox-workstations/mb200b-mod)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Battery Charge &#38; Discharge Tester</td>
			<td style="width:144px;">Bio-Logic</td>
			<td style="width:119px;">VMP3</td>
			<td style="width:355px;">Used to electrochemical cycling of battery materials. (https://www.bio-logic.net/en/)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Swagelok cell</td>
			<td style="width:144px;">MTI</td>
			<td style="width:119px;">EQ-HSTC</td>
			<td style="width:355px;">Used to contain the battery for electrochemical cycling</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sample holder</td>
			<td style="width:144px;">manufactured in lab</td>
			<td style="width:119px;"></td>
			<td>Used to hold the samples in the experiment</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Hardware tools</td>
			<td style="width:144px;">various</td>
			<td style="width:119px;"></td>
			<td style="width:355px;">Including tweezers, scissors (used to assemble samples), tongs (used to transfer sample holders), etc.&#160;</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Carbon and Copper tape</td>
			<td style="width:144px;">3M</td>
			<td style="width:119px;">Custom order, contact vendors</td>
			<td>Used to paste the samples onto sample holders</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Igor Pro</td>
			<td style="width:144px;">WaveMetrics</td>
			<td style="width:119px;">7.06</td>
			<td style="width:355px;">Used to process the experiment data. (https://www.wavemetrics.com/index.html)</td>
		</tr>
	</tbody>
</table>

elemental-sensitive detection of the chemistry in batteries through soft x-ray absorption spectroscopy and resonant inelastic x-ray scattering

Energy storage has become more and more a limiting factor of today's sustainable energy applications, including electric vehicles and green electric grid based on volatile solar and wind sources. The pressing demand of developing high-performance electrochemical energy storage solutions, i.e., batteries, relies on both fundamental understanding and practical developments from both the academy and industry. The formidable challenge of developing successful battery technology stems from the different requirements for different energy-storage applications. Energy density, power, stability, safety, and cost parameters all have to be balanced in batteries to meet the requirements of different applications. Therefore, multiple battery technologies based on different materials and mechanisms need to be developed and optimized. Incisive tools that could directly probe the chemical reactions in various battery materials are becoming critical to advance the field beyond its conventional trial-and-error approach. Here, we present detailed protocols for soft X-ray absorption spectroscopy (sXAS), soft X-ray emission spectroscopy (sXES), and resonant inelastic X-ray scattering (RIXS) experiments, which are inherently elemental-sensitive probes of the transition-metal 3d and anion 2p states in battery compounds. We provide the details on the experimental techniques and demonstrations revealing the key chemical states in battery materials through these soft X-ray spectroscopy techniques.

The sample holder and pasted samples are shown in Figure 1. Figure 7a is a typical RIXS image collected at a particular excitation energy with the spectrometer set to the interested edges. The image shown here was collected on a battery electrode material, LiNi0.33Co0.33Mn0.33O2, with an excitation energy of 858 eV and the detector set at about 500-900 eV range to cover...

Watch this Scientific Journal Video about Elemental-sensitive Detection of the Chemistry in Batteries through Soft X-ray Absorption Spectroscopy and Resonant Inelastic X-ray Scattering at JoVE.com

Elemental-sensitive Detection of the Chemistry in Batteries through Soft X-ray Absorption Spectroscopy and Resonant Inelastic X-ray Scattering

Here, we present a protocol for typical experiments of soft X-ray absorption spectroscopy (sXAS) and resonant inelastic X-ray scattering (RIXS) with applications in battery material studies.

Energy storage has become more and more a limiting factor of today's sustainable energy applications, including electric vehicles and green electric grid ...

Research

JoVE Journal

Chemistry

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Quantifying X-Ray Fluorescence Data Using MAPS

The quantification of X-ray fluorescence (XRF) microscopy maps by fitting the raw spectra to a known standard is crucial for evaluating chemical ...

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

This protocol describes fabricating microfluidic devices with low X-ray background optimized for goniometer based fixed target serial crystallography. The ...

Essential Metal Uptake in Gram-negative Bacteria: X-ray Fluorescence, Radioisotopes, and Cell Fractionation

We demonstrate a scalable method for the separation of the bacterial periplasm from the cytoplasm. This method is used to purify periplasmic protein for ...

Analysis of Minerals Produced by hFOB 1.19 and Saos-2 Cells Using Transmission Electron Microscopy with Energy Dispersive X-ray Microanalysis

This video presents the use of transmission electron microscopy with energy dispersive X-ray microanalysis (TEM-EDX) to compare the state of minerals in ...

Ligand-Mediated Nucleation and Growth of Palladium Metal Nanoparticles

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution ...

Improving High Viscosity Extrusion of Microcrystals for Time-resolved Serial Femtosecond Crystallography at X-ray Lasers

High-viscosity micro-extrusion injectors have dramatically reduced sample consumption in serial femtosecond crystallographic experiments (SFX) at X-ray ...

Biological Samples Preparation for Speciation at Cryogenic Temperature using High-Resolution  X-Ray Absorption Spectroscopy

The study of elements with X-ray absorption spectroscopy (XAS) is of particular interest when studying the role of metals in biological systems. Sample ...

In situ Grazing Incidence Small Angle X-ray Scattering on Roll-To-Roll Coating of Organic Solar Cells with Laboratory X-ray Instrumentation

We present an in-house, in situ Grazing Incidence Small Angle X-ray Scattering (GISAXS) experiment, developed to probe the drying kinetics of roll-to-roll ...