Impact of Crystal Density on the Electrochemical Behavior of Lithium-Ion Anode Materials: Exemplary Investigation of (Fe-Doped) GeO₂

Abstract

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 (α-quartz) and high-density tetragonal (rutile) GeO 2 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.

GeO2 Nanoparticles Decorated in Amorphous Carbon Nanofiber Framework as Highly Reversible Lithium Storage Anode

“…In addition, some group 3 elements (Ga, In) [ 14 , 15 ], group 4 elements (Si, Ge, Sn) [ 16 , 17 , 18 ] and group 5 elements (Sb, Bi) [ 19 , 20 , 21 ] can form alloys with lithium at relatively low potentials (the corresponding alloying equation is N + Li ↔ NLi, where N presents transition group 3, 4 and 5 elements) [ 22 , 23 ]. However, the lithium storage mechanism of group 3–5 element-based oxides is rather complicated, and the related electrochemical reaction consists of alloying and conversion reaction processes [ 24 , 25 , 26 , 27 ]. It is worth noting that the latter suffers insufficient kinetics with lithium; thus, the corresponding conversion reaction displays a low degree of reversibility in many cases.…”

Toward the Potential Scale‐Up of Sn0.9Mn0.1O2‖LiNi0.6Mn0.2Co0.2O2 Li‐Ion Batteries – Powering a Remote‐Controlled Vehicle and Life Cycle Assessment

“…[19] These materials are commonly based on the oxide or sulfide of an alloying element such as zinc, germanium, or tin, which have been intensively studied in different compositions and morphologies due to their high capacities and low working voltage, [13,20,21] and contain additionally a small amount of one or more transition metals that confines the aggregation of the alloying element and ensures a sufficient electronic conductivity within the initial primary particles to enable the reversible formation of Li 2 O. [19,[22][23][24][25][26][27][28][29][30][31][32][33][34][35] As already shown in a previous study, the incorporation of the Mn dopant into the SnO 2 structure allows for stable cycling and high reversible capacities with good rate performance, precisely, 1276 mAh g −1 at 20 mA g −1 and 651 mAh g −1 at 2 A g −1 , for instance. [34] A first estimation of the achievable specific energy revealed a potential improvement, e.g., for LIBs comprising Sn 0.9 Mn 0.1 O 2 (SMO) as the active material for the negative electrode and LNMO for the positive electrode with about 480 Wh kg −1 compared to 454 Wh kg −1 for a LIB containing graphite and LNMO (based on the mass of the active materials only, experimental data for the anode and theoretical data for the cathode).…”

Tailoring Porous Transition Metal Oxide for High-Performance Lithium Storage

“…Numerous efforts have been investigated to improve the cyclic stability of TMOs; reducing the particle size to nanoscale has been revealed to be a feasible approach to tackle the existed problems in TMO anodes. − The active particles at nanoscale can not only buffer the stress accumulation from volume change but also shorten the diffusion pathway of lithium ions. − Besides, the large exposed area of TMO nanoparticles provides abundant active sites for surface/near-surface reactions compared with bulk state. − However, highly unstable thermodynamics of nanoparticles, such as huge surface energy, ineluctably induce the irreversible agglomeration of TMO nanoparticles and further result in an obvious loss of accessible active sites and subsequent degeneration in capacity retention. − Confining TMO nanoparticles into a 3D interconnected framework offers a feasible approach to overcome the mentioned challenge, where the fabricated 3D architecture can efficiently inhibit the intrinsic agglomeration of nanocrystallization to maintain the exposed active centers well. − Nevertheless, severe volume variation inevitably damages the formed SEI film under repeat dissolution and formation, which leads to a low Coulombic efficiency and poor cycle life. − The cracking of nanoparticles can be conceptually suppressed by the presence of interior space, which served as buffer for volume change and stabilization of SEI film. , However, constructing this type of gradient structure is rarely reported possibly due to the complex and rigorous reaction conditions.…”