Insertion‐type Nb 2 O 5 is a promising candidate for high‐power lithium‐ion anodes. Among the various polymorphs, monoclinic Nb 2 O 5 (H‐Nb 2 O 5 ) is considered as one of the most promising materials. Herein, the impact of decreasing the lower cutoff potential, i.e., increasing the amount of lithium that is inserted into the crystal structure, from the commonly used 1.0 V versus Li + /Li to 0.8 V and even 0.01 V is explored, yielding reversible specific capacities of 260, 280, and 400 mAh g −1 , respectively, at a specific current of 0.05 A g −1 . Remarkably, such increase in capacity does not come along with a deterioration of the cycling stability—at least initially. In fact, the comprehensive investigation of the reaction mechanism via operando / ex situ X‐ray diffraction, operando / ex situ X‐ray absorption spectroscopy, ex situ high‐resolution transmission electron microscopy, and operando isothermal microcalorimetry reveals that the extension of the voltage range does not affect the crystal structure during the first couple of cycles, but there is a continuous evolution upon long‐term cycling.

Invited for this month's cover is the group of Dr. Dominic Bresser at Helmholtz Institute Ulm (HIU). The cover picture shows the potential anode material Sn 0.9 Fe 0.1 O 2− δ ‐C for sodium‐ion batteries. Read the full text of the Research Article at 10.1002/batt.202300281 .

The Front Cover illustrates a sodium-ion battery cell using carbon-coated Sn0.9Fe0.1O2−δ as the anode active material and the electrochemical reaction with sodium towards NaxSn, Fe0 and NaxO. More information can be found in the Research Article by J. Asenbauer, D. Bresser and co-workers.

Tin oxide-based materials have been intensively investigated as alternative anodes for lithium-ion batteries due to their high specific capacity, environmental friendliness, non-toxicity, and ease of handling. However, the initial formation of Li 2 O upon lithiation is essentially irreversible, which has a severe effect on the first cycle Coulombic efficiency and the reversibly achievable capacity in general. [1] It has been shown that the incorporation of transition metal dopants can address this issue, as it enables the reversible formation and reformation of Li 2 O. [2] The choice of the dopant, however, plays a critical role for the long-term cycling stability, rate capability, and eventual energy density of the resulting lithium-ion cells. [3] While there have been intensive studies published already on the effect of different dopants for Li-ion battery applications, targeting an optimized combination for achieving enhanced cycling performance [3] and an in-depth understanding of the reaction mechanism, [4,5] the investigation as Na-ion battery active material has not been reported so far. In fact, our results show that the reaction mechanism is fundamentally different, while the incorporation of transition metal dopants is still favorable for the eventual charge storage via sodium cations. The resulting insights into the de-/sodiation mechanism are anticipated to enable the development of further enhanced electrode active materials for sodium-ion batteries and, thus, support the recent success of this alternative battery technology. Reference s [1] D. Bresser, S. Passerini, B. Scrosati, Energy Environ. Sci. 2016 , 9 , 3348. [2] Y. Ma, Y. Ma, G. Giuli, T. Diemant, R. J. Behm, D. Geiger, U. Kaiser, U. Ulissi, S. Passerini, D. Bresser, Sustain. Energy Fuels 2018 , 2 , 2601. [3] A. Birrozzi, J. Asenbauer, T. E. Ashton, A. R. Groves, D. Geiger, U. Kaiser, J. A. Darr, D. Bresser, Batter. Supercaps 2020 , 3 , 284. [4] J. Asenbauer, A. Wirsching, M. Lang, S. Indris, T. Eisenmann, A. Mullaliu, A. Birrozzi, A. Hoefling, D. Geiger, U. Kaiser, R. Schuster, D. Bresser, Adv. Sustain. Syst. 2022 , 6 , 2200102. [5] A. Birrozzi, A. Mullaliu, T. Eisenmann, J. Asenbauer, T. Diemant, D. Geiger, U. Kaiser, D. Oliveira de Souza, T. E. Ashton, A. R. Groves, J. A. Darr, S. Passerini, D. Bresser, Inorganics 2022 , 10 , 46.

The incorporation of transition metals (TMs) such as Co, Fe, and Mn into SnO2 substantially improves the reversibility of the conversion and the alloying reaction when used as a negative electrode active material in lithium-ion batteries. Moreover, it was shown that the specific benefits of different TM dopants can be combined when introducing more than one dopant into the SnO2 lattice. Herein, a careful characterization of Co and Mn co-doped SnO2 via transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction including Rietveld refinement is reported. Based on this in-depth investigation of the crystal structure and the distribution of the two TM dopants within the lattice, an ex situ X-ray photoelectron spectroscopy and ex situ X-ray absorption spectroscopy were performed to better understand the de-/lithiation mechanism and the synergistic impact of the Co and Mn co-doping. The results specifically suggest that the antithetical redox behaviour of the two dopants might play a decisive role for the enhanced reversibility of the de-/lithiation reaction.

Iron‐doped tin oxide (Sn0.9Fe0.1O2), and specifically carbon‐coated Sn0.9Fe0.1O2 (Sn0.9Fe0.1O2‐C) provides high reversible capacity and a reasonably low de‐/lithiation potential owing to the combined conversion and alloying mechanism. The initial (quasi‐)amorphization during the first lithiation, however, renders an in‐depth understanding of the reaction mechanism challenging. Herein, a comprehensive investigation via a set of highly complementary characterization techniques is reported, including operando X‐ray diffraction, ex situ 119Sn and 57Fe Mössbauer spectroscopy, ex situ 7Li NMR spectroscopy, operando isothermal microcalorimetry (IMC) of Li‖Sn0.9Fe0.1O2‐C coin cells, and electrochemical microcalorimetry of single Sn0.9Fe0.1O2‐C electrodes. The combination of these advanced techniques allows for detailed insights into the lithiation and delithiation mechanism and the potential determining processes, despite the (quasi‐) amorphous nature of the active material after the initial lithiation.

Academic research in the battery field frequently remains limited to small coin or pouch cells, especially for new materials that are still rather far from commercialization, which renders a meaningful evaluation at an early stage of development challenging. Here, the realization of large lab‐scale pouch cells comprising Sn 0.9 Mn 0.1 O 2 (SMO), prepared via an easily scalable hydrothermal synthesis method, as an alternative active material for the negative electrode and LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC 622 ) as a commercially available active material for the positive electrode is reported. Nine double‐layer pouch cells are connected in series and parallel, suitable for powering a remote‐controlled vehicle. Subsequently, these SMO‖NMC 622 cells are critically evaluated by means of an early‐stage life cycle assessment and compared to graphite‖NMC 622 cells, in order to get first insights into the potential advantages and challenges of such lithium‐ion chemistry.

For insertion-type lithium battery active materials, the crystal structure is of utmost importance, as it determines the possibility, reversibility, and kinetics of the Li+ de-/insertion. For alloying-type and conversion-type materials, however, the impact of the initial crystal structure has so far been considered less important, as it is commonly not recovered after the first lithiation. Herein, we had a closer look at the impact of the crystal structure by comparatively studying the electrochemical behavior of low-density hexagonal (a-quartz) and high-density tetragonal (rutile) GeO2 as model compounds. Based on the results obtained via a comprehensive set of complementary ex/in situ and operando techniques, it was found that the initial lithiation and the reversibility of the de-/lithiation reaction in general are greatly enhanced when starting from the low-density crystal structure. The introduction of iron stabilizes this low-density phase even at elevated calcination temperatures and, in addition, increases the contribution of the reconversion reaction to the reversible capacity as a result of the formation of ultrasmall metallic iron grains during the first lithiation.

The introduction of transition metal dopants such as Fe and Co in zinc oxide enables substantially enhanced reversible capacities and greater reversibility of the de-/lithiation reactions occurring. Herein, we report a comprehensive analysis of the electrochemical processes taking place in Mn-doped ZnO (Zn 0.9 Mn 0.1 O) and carbon-coated Zn 0.9 Mn 0.1 O upon de-/lithiation. The results shed light on the impact of the dopant chemistry and, especially, its coordination in the crystal structure. When manganese does not replace zinc in the wurtzite structure, only a moderate improvement in electrochemical performance is observed. However, when applying the carbonaceous coating, a partial reduction of manganese and its reallocation in the crystal structure occur, leading to a substantial improvement in the material’s specific capacity. These results provide important insights into the impact of the lattice position of transition metal dopants—a field that has received very little, essentially no attention, so far.

TiO 2 has been investigated as an alternative anode material candidate for lithium‐ion batteries for several years now due to its advantageous safety and rate capability in combination with its nontoxicity and abundance. Herein, the synthesis via laser pyrolysis is reported, which allows the single‐step, industrial‐scale realization of carbon‐coated TiO 2 nanoparticles. The modification of the synthesis parameters enables the variation of the rutile‐to‐anatase phase ratio. Following comprehensive physicochemical and electrochemical characterization, both the higher and lower rutile‐to‐anatase ratios show very stable cycling in lithium battery half cells, whereas the extended presence of the rutile phase limits the achievable specific capacity and lowers the apparent lithium‐ion diffusion coefficient, which leads to relatively lower capacities at elevated current densities.

High-capacity lithium-ion anodes such as alloying-, conversion-, and conversion/alloying-type materials are subjected to extensive volume variation upon lithiation/delithiation. However, a careful examination of these processes at the particle and electrode level as well as the impact of the kind of lithium-ion uptake mechanism is still missing. Herein, we investigated the volume variation upon lithiation/delithiation for a series of conversion/alloying materials with a varying relative contribution of the alloying and conversion reaction, i.e., carbon-coated ZnFe2O4, Zn0.9Fe0.1O, and Sn0.9Fe0.1O2 by operando dilatometry and ex situ scanning electron microscopy of the electrode cross section. While the theoretical estimation at the particle level indicates a rather large volume expansion of 113% (ZnFe2O4) and more, the true volume variation on the electrode level reveals very limited changes of only around 11% (ZnFe2O4). Combining the experimental findings with some theoretical considerations highlights the (to a certain extent unexpected) impact of the initial electrode porosity.

Owing to their unique combination of high energy and power density, lithium-ion batteries are now the state-of-the-art energy storage technology for powering small consumer electronics and increasingly also for large-scale applications like electric vehicles.[1] Yet, especially for the latter, there is a growing need for batteries that can provide not only high energy densities, but also the possibility to be rapidly recharged.[2] This is challenging for the currently used graphite anodes, since its low lithiation potential (~0.1 V vs. Li/Li+) in combination with the sluggish lithium transport across the solid electrolyte interphase (SEI) and within the graphite structure can lead to lithium plating and dendrite formation during fast charging, particularly at low temperatures.[3] To overcome this issue, various alternative anodes are being investigated, following, e.g., a conversion or an alloying mechanism.[4] While these alternatives frequently show higher capacities and rate capabilities, conversion materials still suffer from a significant voltage hysteresis, resulting in low energy efficiencies, and alloying materials suffer from extensive volume variations, leading to rapid capacity fading and low coulombic efficiencies. Conversion/alloying-materials (CAMs), as relatively new material class, combine the conversion and alloying mechanism in one single material.[5] In CAMs, such as Zn0.9Fe0.1O, nanograins of an alloying element and a percolating conductive network of transition metal nanoparticles are formed in situ by the initial (reversible) conversion reaction. This metallic nano-network enables fast de-/lithiation kinetics and renders them a promising candidate for high-power applications. Nevertheless, there is still a lack of knowledge about how to potentially tackle the remaining obstacles, i.e., the achievement of sufficiently high energy efficiencies and the volume variations occurring upon cycling. Herein, we report our findings towards an in-depth understanding of the de-/lithiation of (carbon-coated) Zn0.9Fe0.1O. Combining in situ microcalorimetry, in situ XRD, ex situ 7Li NMR, and ex situ 57Fe Mössbauer spectroscopy allowed us to propose a refined mechanism for the de-/lithiation reaction. Moreover, in situ dilatometry and ex situ cross-sectional SEM analysis reveal that the continuous volume variation at the electrode level is, in fact, in the range of 10%. This is much lower than theoretically predicted when considering bulk densities only – even if cycled within a 3-V potential window. Based on these results we highlight the beneficial effect of a limited operational voltage window, which we finally confirm for Zn0.9Fe0.1O/LiNi0.5Mn1.5O4 full-cells, providing an excellent energy efficiency of >93%, accompanied by an energy and power density of 284 Wh kg-1 and 1105 W kg-1, respectively. [1] N. Nitta, F. Wu, J. T. Lee, G. Yushin, Mater. Today 2015, 18, 252–264. [2] M. Li, J. Lu, Z. Chen, K. Amine, Adv. Mater. 2018, 30, 1800561. [3] J. Asenbauer, T. Eisenmann, M. Kuenzel, A. Kazzazi, Z. Chen, D. Bresser, Sustain. Energy Fuels 2020. [4] N. Loeffler, D. Bresser, S. Passerini, M. Copley, Johnson Matthey Technol. Rev. 2015, 59, 34–44. [5] D. Bresser, S. Passerini, B. Scrosati, Energy Environ. Sci. 2016, 9, 3348–3367.

Tin oxide-based materials have been intensively investigated as alternative anodes for lithium-ion batteries due to their high specific capacity, environmental friendliness, non-toxicity, and ease of handling.[1] However, the initial formation of Li2O upon lithiation is essentially irreversible, which has a severe effect on the first cycle coulombic efficiency and the reversibly achievable capacity in general.[2] It has been shown that the incorporation of transition metal dopants can address this issue, as it enables the reversible formation and reformation of Li2O.[3] The choice of the dopant, however, plays a critical role for the long-term cycling stability, rate capability, and eventual energy density of the resulting lithium-ion cells.[4] Herein, we show that the addition of specific combination of different dopants allows for further tailoring the electrochemical properties. We also demonstrate the production of such materials using a scalable continuous hydrothermal flow method. The performance of the best composition (Sn0.9Co0.05Mn0.05O2, SCMO) was further improved by applying a carbonaceous coating. The electrochemical investigation of the coated anode material was conducted in half-cells and in high-energy full-cells using high-voltage LiNi0.5Mn1.5O4 (LNMO) as active material for the cathode (Figure 1).[5] The performance of the full-cells was further enhanced by carefully optimizing the anode composition and fine-tuning the full-cell design, considering electrolytes and different pre-lithiation degrees. Reference s : [1] F. Zoller, D. Böhm, T. Bein, D. Fattakhova-Rohlfing, ChemSusChem., 1 2 , 4140 (2019) [2] I.A. Courtney and J.R. Dahn, J Electrochemical Soc., 144 , 2045 (1997) [3] D. Bresser, S. Passerini and B. Scrosati, Energy Environ. Sci. , 9 , 3348 (2016) [4] Y. Ma et al, Sustain. Energy Fuels, 2 , 2601 (2018) [5] A. Birrozzi et al., Batter. Supercaps, 3 , 284 (2020). Figure 1

It has been shown that the introduction of several transition metal (TM) dopants into SnO 2 lithium‐ion battery anodes can overcome the issues associated with the irreversible capacity loss from the conversion reaction of SnO 2 and the aggregation of the metallic Sn particles formed upon lithiation. As the choice of the single dopant, however, plays a decisive role for the achievable energy density – precisely its redox potential – we investigate herein TM co‐doped SnO 2 , prepared by using a readily scalable continuous hydrothermal flow synthesis (CHFS) process, to tailor the dis‐/charge profile and by this the energy density. It is shown that the judicious choice of different elemental doping combinations in samples made via CHFS simultaneously improves the cycling performance and the full‐cell energy density. To support these findings, we realized a lithium‐ion full‐cell incorporating the best performing co‐doped SnO 2 as negative electrode and high‐voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) as positive electrode–to the best of our knowledge, the first full‐cell based on such anode material in combination with LNMO as cathode active material.