Structural and Electrochemical Aspects of LiNi0.8Co

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Structural and Electrochemical Aspects of LiNi0.8Co0.1Mn0.1O2 Cathode Materials Doped by Various Cations Downloaded via ICAHN SCHOOL MEDICINE MOUNT SINAI on February 3, 2019 at 22:43:26 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Tina Weigel,†,‡ Florian Schipper,† Evan M. Erickson,† Francis Amalraj Susai,† Boris Markovsky,† and Doron Aurbach*,† †

Department of Chemistry, Faculty of Exact Sciences, Bar-Ilan University, Ramat-Gan 5290002, Israel Institute of Experimental Physics, Faculty of Chemistry and Physics, TU Bergakademie Freiberg, 09599 Freiberg, Germany

‡

S Supporting Information *

ABSTRACT: Ni-rich materials of layered structure LiNixCoyMnzO2, x > 0.5, are promising candidates as cathodes in high-energy-density Li-ion batteries for electric vehicles. The structural and cycling stability of Nirich cathodes can be remarkably improved by doping with a small amount of extrinsic multivalent cations. In this study, we examine development of a fast screening methodology for doping LiNi0.8Co0.1Mn0.1O2 with cations Mg2+, Al3+, Si4+, Ti4+, Zr4+, and Ta5+ by a “top-down” approach. The cathode material is coated by a precursor layer that contains the dopant, which then is introduced into the particles by diffusion during heat treatment at elevated temperatures. The methodology described herein can be applied to Ni-rich cathode materials and allows relatively easy and prompt identification of the most promising dopants. Then further optimization work can lead to development of high-capacity stable cathode materials. The present study marks Ta5+ cations as very promising dopants for Ni-rich NCM cathodes. potentials of 0.5).8 The nomenclature used for them is NCM523, NCM622, NCM811, etc., where the numbers reflect the atomic contents of Ni, Co, and Mn in the compounds. Nickel-rich layered cathode materials demonstrate higher capacity, higher rate capability, and lower cost than LiCoO2.9 As the content of nickel is higher, the specific capacity is higher and can be extracted at charging © XXXX American Chemical Society

Received: November 27, 2018 Accepted: January 14, 2019 Published: January 14, 2019 508

DOI: 10.1021/acsenergylett.8b02302 ACS Energy Lett. 2019, 4, 508−516

Letter

Cite This: ACS Energy Lett. 2019, 4, 508−516

Letter

ACS Energy Letters

described herein (beyond the scope of this Letter). The selection of dopants for this study was based on previous experience. In this work, Zr, Mg, Ti, Al, Si, and Ta are used for doping of the Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material. Data on the oxidation states of atoms and ion sizes of these dopants are provided in Table S1. On the basis of our previous experience in similar doping of NCM811 with dopant precursors, we set their concentration to be 1.5 mol %. The influence of dopants on the structural and electrochemical behavior of NCM811 cathodes was investigated with X-ray diffraction (XRD) on pristine materials, in situ XRD during the charging process (Li-deintercalation), and postmortem analysis of cycled electrodes by XRD as well. Electrochemical properties were characterized by long-term cycling experiments at 45 °C with different rates and impedance spectroscopy. The experimental work is described in detail in the Supporting Information. The doping procedures and the preparations of cells for in situ XRD measurements are described in Figures S1 and S2, respectively. The results of this work show how different cationic dopants can influence the electrochemical behavior of layered lithiated TM oxide cathode materials in lithium cells. In light of this study, several dopants can be marked as very promising, deserving further thorough studies and optimization. The XRD patterns of the undoped and doped NCM811 cathode materials before and after cycling are shown in Figures S3 and S4, respectively. The reflections in XRD pattern can be indexed on the basis of a hexagonal lattice with the α-NaFeO2 structure (space group R3̅ m).39 Oxygen ions occupy the 6c site, Li ions the 3a site, and TM ions (Ni, Co, Mn) the 3b site.40 Lithium sites are partially occupied by Ni ions due to their similar ionic radii (Ni2+ 0.69 Å and Li+ 0.76 Å).39 The splitting of the 006/102 and 108/110 reflections and a c/a value of about 4.9 are indicators for a well-ordered layered structure.39,40 The R003/104 ratio gives information about the degree of cation mixing and is a measure of the electrochemical reactivity of the cathode material as well.41 If the R003/104 ratio is significantly less than 1.2, then the 108 and 110 reflections are indistinguishable, which indicates contamination with rock salt domains. Such a contamination has an adverse effect on the specific capacity and stability.42 A low R003/104 ratio often indicates poor electrochemical properties.43 In our case, R003/104 is around 1.2, and the 108 and 110 reflections are clearly split. A comparison with the undoped material shows that the doped NCM811 materials have slight changes in the lattice parameters. A few changes of the c/a and R003/104 values are observed. This indicates that the doping processes used herein (a minor level of doping) have some influence on the crystal structure. The XRD patterns of all samples were assigned to layered NCM material of R3̅m space group. The resulting lattice parameters a and c, the unit cell volume VUC, the c/a ratio, the ratio of the integrated intensities of the 003 and 104 reflections R003/104, as well as χ2 andRBragg from the Rietveld refinement are listed in Table S2. The distribution of dopants in the particles is being studied further by HRTEM and element analyses (cross sectioning of particles cut by FIB), as we already described in previous publications. The doping processes used herein were found to be very effective for doping NCM cathodes with Zr4+ cations.33 Further parallel studies (beyond the scope of this Letter) examine the distribution of the other dopants. The electrochemical studies show a pronounced influence of all of the doping processes that can be assigned to both surface and bulk effects. All of our

chemical cycling by increasing oxygen and TM ion bond strength,19,20 and (4) increase in strength of the transition metal−oxide bond, which limits the contraction of the material at the end of charge when the NiIV−O bond becomes highly covalent, reducing O2− repulsion.21,22 It should be noted, however, that the dopant concentration needs fine optimization because too high dopant contents may lead to capacity and stability decrease.15,20 An alternative method to improve the performance of NCM electrodes is by coatings that mitigate the reactivity between the active mass and the electrolyte solution. Coating by oxides like TiO2, ZrO2, and Al2O 3 may form appropriate buffer zones that avoid detrimental surface reactions, as demonstrated by the following examples. Schipper et al. observed enhanced electrochemical performance of NCM811 cathodes by surface coating with ZrO2, which led to bulk doping during annealing at high temperature.23 Similarly, NCM811 cathodes showed improved stability due to coating with TiO2.24 Coating NCM622 electrodes with LiAlO2 demonstrated pronounced stabilization effects even when the cathodes were cycled with high cutoff voltages of 4.5−4.7 V in order to extract high specific capacity.25 Metal oxide coatings on NCMs at the nanoscale level can be carried out very successfully by atomic layer deposition (ALD) techniques that allow very rigorous thickness control.26 It should be noted that stabilizing cathodes comprising NCM materials from doping have already been explored. For instance, doping Ni-rich NCM with Zr, Al, and Ti multivalent ions has been shown to improve their structural stability and electrochemical properties, likely by preventing the migration of Ni2+ ions from the TM site to the Li sites.23,27−30 Another candidate for helpful doping is Mg ions, showing stabilization effects, but explanations for that are still under debate.31,32 Zr4+ ions probably occupy the Li sites and suppress the layered-tospinel transformation by inhibiting transport of Ni ions into the Li sites.33 Zr ions in the NCM structure are supposed to hinder Ni to Li site diffusion by increasing the energy barrier for it by a factor of 2.33,34 Other promising dopants are Fe,28,35 Cr,36 and Ga.37,38 Although a lot of work was devoted so far to stabilization of Ni-rich NCM cathodes, including intensive efforts related to doping, this work is novel, original, and important because it examines a new top-down methodology in which doping is reached by heat treatment of active mass particles covered by a surface layer that contains the dopants in their necessary oxidation state. Also, the work includes a direct comparison among different dopants and their effect on performance, which paves the way for combinatorial studies that enable fast optimization. It is important to note that this Letter intends to present only a first stage in full mapping of doping options for optimal Ni-rich NCM cathodes. In this preliminary stage, attractive and useful dopants can be identified by comparative electrochemical testing and elementary structural analysis. Then, thorough and deep studies related to each selected dopant, including the Li-ion diffusion mechanism, cation bulk and surface distribution, uniformity, concentration effects, and rigorous structural effects, are carried out, as we demonstrated recently with Zr-doped Ni-rich NCM cathodes.23 These previous studies showed clearly by cross sectioning of doped particles using STEM and HRTEM that this top-down approach indeed works and enables one to reach uniform doping by heat treatment of coated particles. Parallel thorough work is being carried out with the other doped materials 509

DOI: 10.1021/acsenergylett.8b02302 ACS Energy Lett. 2019, 4, 508−516

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ACS Energy Letters experience with doped Ni-rich NCM materials shows that there are segregation phenomena near the particles’ surfaces. The layer near the surface is always slightly richer in dopants compared to that of the bulk. Such segregation phenomena are supposed to be even more pronounced in the doped materials produced in this work via the top-down processes. The electrochemical performance of the doped and undoped materials is discussed in the following section. We focused on the electrochemical characterization at 45 °C similarly to that of NCM811−Zr doped electrodes studied at 30 °C.23 The discharge capacities vs cycle for the doped and undoped electrodes at 45 °C are presented in Figure 1. First, ratecapability tests up to 4C (C defined as 180 mAh g−1) and then cycling measurements at a C/3 rate were performed. In general, all doped materials show a decrease in the discharge capacity in the initial cycles at C/15−1C rates. However, at higher rates of 2C and 4C, aluminum- and tantalum-doped electrodes exhibit capacities close to those of undoped NCM811 cathodes. The results of cycling at elevated temperature (45 °C) may indicate that doping increases the electrodes’ impedance, probably due to the segregation phenomena that occur during the doping process forming intrinsic surface layers.44,45 In turn, all of the dopants used in this work improve the electrodes’ cycling stability during prolonged cycling at 45 °C, compared to the undoped NCM811 electrodes. Another important result is the relative stabilization of the hysteresis between average charge and discharge voltages upon cycling due to doping (Figure 1c). It is important to note that in order to exhibit differences among the reference and doped materials in relatively short experiments we show herein results of cycling tests carried out at 45 °C. Also, the cathodes that were tested during prolonged cycling (at 45 °C) underwent experiments at high rates. In such experiments, undoped NCM811 cathodes exhibit relatively fast capacity fading (Figure 1b, black star), which enables a clear differentiation in the behavior of the electrodes during relatively short experiments (20 cycles at the low rates). When the cycling experiments are conducted from the beginning at low rates, the capacity fading upon cycling is pronouncedly lower. The same trends are observed, but they become significant after much longer experiments. It was established that the Ta-doped electrodes show the highest initial discharge capacity at 45 °C as well as increased capacities and much more stable performance during 100 cycles at a C/3 rate (Figure 1b). The average capacity fading per cycle during prolonged cycling experiments is listed in Table S3. The improvement in capacity retention for all doped materials is clearly evident (e.g., Ta-doped NCM811 electrodes exhibited the lowest capacity fading of 0.10% per cycle compared to 0.47% per cycle for the undoped electrodes). In Figure 1c, we show the evolution of the voltage hysteresis during cycling, calculated from the difference between the mean charge and discharge voltages. As the specific energy of these systems is the product of the voltage and specific capacity, as the voltage hysteresis is lowered, the energy efficiency is higher. Except for Ti cations, the presence of dopants lowers the voltage hysteresis of these electrodes upon cycling. On the basis of many previous studies as described above, one of the major reasons for the capacity fading and voltage decay of these cathodes is that during the charging process Li ions are extracted from the lattice and TM ions with a similar radius (Ni2+) migrate to these positions. During the discharge process, the Li+ ions return to their original

Figure 1. (a) Discharge capacity obtained during the rate capability tests (C/15−4C, as indicated) followed by cycling at a C/3 rate, 45 °C. (b) Discharge capacities of NCM811 electrodes comprising undoped and doped active materials, in coin cells at 45 °C. (c) Voltage hysteresis (Uhys = Vcharge − Vdischarge) for electrodes comprising undoped and doped active cathode materials NCM811 at 45 °C. The results presented in this figure are averaged from several electrochemical cells running in parallel in the same instrument for statistical purposes. The accuracy of the capacity measurements was around 95% in these experiments. 510

DOI: 10.1021/acsenergylett.8b02302 ACS Energy Lett. 2019, 4, 508−516

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Figure 2. dQ/dV vs V plots for NCM811 electrodes comprising undoped (a) and doped active NCM811 materials with dopants Al (b), Ti (c), Mg (d), Si (e), Zr (f), and Ta (g), as indicated. Cycles 25, 50, 75, and 100 are shown.

structure to spinel and rock salt phases (lowering the average voltage).10,12,14 Therefore, the results of this work show that doping of the NCM811 material in the proposed way (relatively simple top-down approach) limits to some extent these capacity fading mechanisms, thus leading to improved cycling stability (through both surface and bulk effects). Voltage profiles for the various NCM811 cathodes (with and without dopants) are presented in Figure S5

positions, but the Li diffusion paths are hindered by TM ions remaining in the Li+ sites. Hence, the specific capacity decreases. Additionally, postmortem analyses of electrodes after cycling (not shown herein) indicate that cracks are formed in the particles due to stresses that develop during cycling that propagate during prolonged cycling. The surface area of the active mass thus increases, leading to detrimental side reactions and further loss of capacity. Finally, there are irreversible transformations of the original, desirable layered 511

DOI: 10.1021/acsenergylett.8b02302 ACS Energy Lett. 2019, 4, 508−516

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ACS Energy Letters Differential capacity (dQ/dV) plots for all electrodes are depicted in Figure 2. These plots are important indicators for tracking the retention of phases throughout cycling as electrochemistry is inherently more sensitive than structural characterization techniques such as XRD at detecting changes in electroactive phases. However, assignment of phase changes and redox centers to specific dQ/dV peaks can be difficult, often requiring in situ structural and electronic techniques such as XRD, neutron diffraction, or X-ray absorption spectroscopy. Considering the case of the undoped NCM811 electrode in Figure 2a, all four peaks in the differential capacity plots decrease throughout cycling. This indicates that the fading mechanisms for NCM811 involve general processes such as TM ion inactivation or various types of impedance growth. Aluminum doping of NCM (Figure 2b) seems to improve retention of all of these differential capacity peaks and therefore may limit one of these fading mechanisms. Because discharge processes (Li intercalation) for cathode materials are concomitant with reduction processes of TM ions involving Li+ reintercalation into the NCM lattice, these dopants impede to some extent lithium reinsertion, possibly due to their possible incorporation in the lithium sites and formation of surface layers (see further discussion). While this may cause a decrease in initial capacities, the cycling stability of the material can be improved despite these complications. This is the case for the Ta-doped NCM811, as shown in Figure 2g. It seems that for Si-doped and Ta-doped materials the cathodic peaks at around 3.5−3.75 V are not split probably due to the sluggish electrochemical kinetics of these electrodes (see the high charge-transfer resistance RCT in Figure 3b). The effect of doping as presented in Figure 2 proves that doping by the topdown approach described herein has a clear bulk effect (i.e., the dopants diffuse into the particles by heat treatment). Cells comprising NCM811 undoped and doped electrodes underwent impedance measurements. The cells’ impedance is obviously dominated by the response of the cathodes; thereby, we can discuss these results in terms of cathode behavior. As an example (single potential), Nyquist plots depicting the results of the impedance spectroscopy measurements at 4.2 V after 101 cycles are shown in Figure 3. Two semicircles are observed in impedance spectra, a small one related to the surface film resistance, Rsf (at high frequencies), and another one (bigger) ascribed to the overall charge-transfer resistance at the electrode−electrolyte interface, the so-called “chargetransfer resistance” Rct (at high-to-medium frequencies).46 Tails in Nyquist plots at very low frequencies (5−10 mHz) are referred to as the Warburg impedance or resistance of the solid-state Li-ion diffusion.33 We conclude that Ta-doped material shows the lowest impedance of charge-transfer resistance, followed by Al-, Zr-, and Mg-doped electrode samples. Similar results were observed for undoped NCM811 and for Ti- and Si-doped electrodes. Impedance spectra of cycled electrodes were measured at several equilibrium potentials. The potential-dependent overall charge-transfer resistance (from the medium-frequency features) and surface film resistance (from the high-frequency features), RCT and RSF, derived from impedance measurements are depicted in Figure 3b,c, respectively. Both RCT and RSF are calculated using ZView (from Scribner Associates) using an electrical circuit model with two RC time constants. From the results obtained, the charge-transfer resistances are much larger than the surface film resistances; indeed, the rate capability measurements in Figure 1a mainly correlate with the charge-

Figure 3. (a) Impedance spectra (Nyquist plots) measured at 4.2 V after 101 galvanostatic cycles of NCM811 undoped and doped electrodes, as indicated. Potential dependence of (b) chargetransfer resistance and (c) surface film resistance, derived from the high-to-medium-frequency and high-frequency semicircles, respectively, in Nyquist plots.

transfer resistances, e.g., RCT is the smallest for Ta < Al ≈ Zr < Mg < undoped ≈ Ti < Si. These results show that RCT can be significantly reduced by doping, with the exception of Si, which 512

DOI: 10.1021/acsenergylett.8b02302 ACS Energy Lett. 2019, 4, 508−516

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ACS Energy Letters shows RCT very similar to that of undoped electrodes. Doping may increase the surface film resistances of the materials to some degree, likely due to segregation and formation of surface layers that are resistive. Doping using the top-down approach may promote segregation and formation of a somewhat resistive surface layer that increases the high-frequency impedance of the electrodes (what is termed here as RSF). Hence, while the surface-related impedance (high frequencies) is higher for the doped electrodes (as can be expected), the overall charge-transfer impedance that dominates the overall cell impedance (by roughly an order of magnitude compared to the surface film-related impedance) is lower for the doped electrodes. Hence, these results obtained by EIS are in line with the other electrochemical data, showing how doping by the approach that we promote indeed improves the performance of commercial NCM811 cathode materials. We carried out comparative in situ XRD measurements of doped and undoped NCM811 cathodes in order to follow changes in their crystallographic parameters during delithiation processes. These studies substantiate the conclusion that the doping processes improve performance by bulk effects, as discussed above. The XRD patterns of the undoped and Tadoped NCM811 electrodes during the delithiation process are shown in Figure S6. The changes of the unit cell volume VUC and the lattice parameters a and c as a function of the Li content (x) are shown in Figure 4. The in situ XRD-derived data in Figure 4 show the decrease of VUC with lower Li content, ending in a strong volume contraction. This contraction is induced due to the removal of most of the Li+ from the lattice, leaving unshielded oxide slabs, between which Ni2+ cations migrate.47 Our results are in agreement with those obtained for electrode materials with an especially high Ni content that exhibit similar behavior.48 The a parameter decreases during charging from 3.6 to 4.3 V as the Li content decreases due to the smaller ionic radii of the Ni4+ vs Ni3+ or Ni2+ in the TM layer. Considering the c parameter, it initially increases because of the deintercalation of Li from the Li layer, which results in higher repulsive forces between the O2− layers. Furthermore, the deintercalation induces stronger covalent bonding between the TMs and O2−, leading to less localized electron density on the O2− ions and a decreased c parameter.49 The results show the pronounced effect of doping on the above parameters, thus strengthening the claims regarding the bulk effect of doping. Upon doping with Ta, Al, and Mg, the specific volume decreases pronouncedly at the end of charging. However, doping with these elements improves the electrochemical performance. Hence, the phenomenon of specific volume decrease is not correlated with detrimental capacity fading. As seen in Figure 1, the doped cathodes have lower initial discharge capacity. This lower initial specific capacity may limit irreversible structural changes caused by the change in the c parameter associated with formation of the hexagonal H3 phase near the end of charging. The relatively low initial specific discharge capacity observed with the tetravalent dopants Si, Zr, and Ti (compared to undoped cathodes, Figure 1a) can be correlated with relatively small changes in VUC (Figure 4a). Interestingly, Si-doped NCM811 electrodes show splitting of the structure in two hexagonal phases: one Lirich phase (H1) and one with lower Li content (H2).48−52 This two-phase splitting has been investigated previously mainly with synchrotron radiation experiments, showing that dopants with a significantly larger or lower ionic radius than Li

Figure 4. Unit cell volume VUC(a) and a (b) and c (c) lattice parameters as a function of the lithium content x in LixNi0.8Co0.1Mn0.1O2 calculated from in situ XRD measurements of NCM811 electrodes comprising undoped and doped active materials, as indicated.

facilitate the formation of two phases.48−51 It should be noted that the structural changes of NCM811 materials in the course 513

DOI: 10.1021/acsenergylett.8b02302 ACS Energy Lett. 2019, 4, 508−516

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ACS Energy Letters

observed at the end of charging, (2) increased Li+ intercalation kinetics, (3) decreased cation mixing, and (4) surface stabilization resulting in lowered impedance growth throughout cycling. Isolating the contributions of each of these issues is especially difficult considering their possible interrelation; for example, the electrode active surface area (and cell impedance) can be increased throughout cycling due to particle cracking, a phenomenon exacerbated by the large structural lattice contraction at the end of electrode charging. This Letter presents only a first screening stage. Obvious further studies should concentrate on the most effective dopants (as presented herein), exploring deeply electrochemical, surface, and structural behavior by surface- and bulk-sensitive techniques, like X-ray photoelectron and timeof-flight secondary ion spectroscopies, transmission electron microscopy, and nanobeam electron diffraction. Such studies will enable a judicious optimization, after which it will be possible to demonstrate improved performance in full cells.

of their lithiation/delithiation processes are not fully resolved. While the electrochemical data may indicate that the processes involve phase transitions (especially at around 4.25 V), there are reports that conclude that the processes involve mainly solid solution formation and changes in the oxidation state of Ni and Co ions.53 However, resolution of these points is not important for the main theme of this screening study. To investigate structural changes induced due to long-term cycling, the discharged electrodes (OCV around 3 V) after 101 cycles at 45 °C were investigated by powder XRD analysis, as shown in Figure S4. The XRD patterns show no additional reflections in the cycled materials, suggesting that no structural changes occur during cycling and indicating the materials’ high structural stability. Minor additional reflections originate from the aluminum foil current collector (on which the NCM811 was coated) and the carbon black and graphite additives used for the electrode fabrication. More information can be found in the Supporting Information, as well as the lattice parameters of cycled electrodes calculated by Rietveld refinement, which are listed inTable S4. In summary, this work included a comprehensive study of NCM811 cathode materials with a variety of cationic dopants using electrochemical and structural measurements. Some of the dopants studied in this work improve pronouncedly the electrochemical properties of NCM electrodes in lithium cells. We can highlight doping with Ta that increases the discharge capacity of the NCM811 cathodes at 45 °C and their long-term cycling stability, decreases their charge-transfer resistance, and lowers their voltage hysteresis compared to that of the undoped material. We can also conclude that the higher c parameter of the Ta-doped cycled electrodes (compared to undoped NCM811) indicates obvious dopant incorporation into the lattice. Higher resistance of the surface films measured for the doped materials, assigned to impeding surface layers, correlates well with the lower rate capability of the cathodes comprising doped materials. In turn, lower charge-transfer impedance of the doped cathodes also correlates with better stability and a decrease in the c parameter contraction at the end of the electrodes’ charging to 4.3 V. The Zr- and Mg-doped materials demonstrate enhanced cycling performance as well. These dopants worsen the rate capability of the material but improve cycling stability. The stability improvement can be correlated with a lower lattice contraction at the end of charging. Lower volumetric changes in the active mass upon lithiation/ delithiation processes mean lower stresses and thereby a lower level of cracking. The electrochemical cycling characteristics of the Al-, Si-, and Ti-doped NCM811 are enhanced compared to the undoped material, but the improvement is considerably lower in comparison to that with Ta, Zr, and Mg doping. In general, dopants with higher oxidation states and/or ionic radii similar to those of Li ions improve the structural and electrochemical properties of the NCM811 cathode material. Doping with ions of similar radius to the Li+ ion (0.76 Å) increases the interlayer distance (higher c parameters of the doped material) and reduces the cation mixing. This enables faster electrochemical processes and higher rate capabilities due to enhanced ionic conductivity.54,55 Dopants with high oxidation states inhibit Ni2+ migration and reduce the number of Jahn−Teller active Ni3+ ions.33 It is important to emphasize that the cause for improvement conferred by dopants is complex due to multiple structural and surface effects, including (1) limitation of the sharp c parameter contraction

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsenergylett.8b02302. Additional data and figures providing information on structural characterization and a detailed description of the experimental methods (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Francis Amalraj Susai: 0000-0003-3778-4200 Boris Markovsky: 0000-0001-7756-0071 Doron Aurbach: 0000-0001-8047-9020 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS T.W. thanks Freiberger Compound Materials GmbH and Federmann Enterprises Ltd. for financial support with the Federmann-Scholarship. Partial support for the work discussed herein was provided by BASF, the Israeli Prime Minister’s Office, and the Israeli Committee for Higher Education within the framework of the INREP project.

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REFERENCES

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DOI: 10.1021/acsenergylett.8b02302 ACS Energy Lett. 2019, 4, 508−516

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DOI: 10.1021/acsenergylett.8b02302 ACS Energy Lett. 2019, 4, 508−516