It has been shown that the introduction of several transition metal (TM) dopants into SnO2 lithium‐ion battery anodes can overcome the issues associated with the irreversible capacity loss from the conversion reaction of SnO2 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 SnO2, 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 SnO2 as negative electrode and high‐voltage LiNi0.5Mn1.5O4 (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.
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.
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.
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