Fully Reversible Homogeneous and Heterogeneous Li Storage in RuO₂ with High Capacity

Abstract

In this paper, we report that Li can be stored in RuO2 with an unusually high coulombic efficiency. The process involves three electrochemical steps: i) formation of a Ru/Li2O nanocomposite, ii) formation of a Li‐containing surface film, and iii) interfacial deposition of Li within the Ru/Li2O matrix. Corresponding to the storage of 5.6 mole of Li ions per mole of RuO2, a high capacity of 1130 mAh g–1 is achieved. Furthermore, virtually all inserted Li ions can be extracted, corresponding to a nearly 100 % coulombic efficiency at the first cycle. Achieving a complete reversibility for such a Li storage system through complex heterogeneous solid‐state electrochemical reactions is possible because of the formation of nanoscale Ru/Li2O during Li insertion and nano‐RuO2 during Li extraction, in addition to the favorable transport properties of RuO2 itself.

Phase evolution for conversion reaction electrodes in lithium-ion batteries

“…3b). The higher capacity relative to the theoretical capacity (718 mAh g À 1 ) suggests that interfacial charge storage and/or reversible side reactions play roles in the extra capacity 22,36 . The reversible side reactions probably include but are not limited to lithium storage in carbon black 37 and CuO 38 at the surface of the Cu current collector, and reversible conversion of LiOH to Li 2 O and LiH 39 .…”

“…Specifically, phase conversion reactions have provided a rich playground for lithium-ion battery technologies with potential to improve specific/rate capacity and achieve high resistance to lithium metal plating [14][15][16][17][18][19] . Among the many potential candidates, transition metal oxides have received broad interests as lithium-ion battery anode materials [20][21][22][23][24][25][26][27] . Although electrochemistry and synthesis of transition metal oxides have been well studied 18,19 , the spatially resolved phase conversion pathways (for example, nucleation, charge distribution and anode-electrolyte interface (AEI) formation) remain elusive.…”

Tracking lithium transport and electrochemical reactions in nanoparticles

“…One of the promising classes of electrode materials that could meet these requirements is lithium conversion compounds, which have the advantage of accommodating more than one lithium per transition metal, boasting high theoretical capacities [2][3][4] , and in some cases, exhibit excellent capacity retention. A recent study of lithium conversion in the FeF 2 cathode offered the first experimental evidence of the formation of a conductive iron network, 5 which may provide the pathway for electron transport necessary for reversible lithium cycling 2,4,6,7 . However, these electrodes are typically plagued by poor cycling rate and a large cycling hysteresis 8,9 .…”

Atomic resolution observation of conversion-type anode RuO2during the first electrochemical lithiation

“…2b), the sharp diffraction spots were coarsened and extended into short curves. The red arrows referring to Ru (100), (101) and (110), while very weak diffuse diffraction rings appeared as Li2O (200) 20,34,35 As the lithiation process continued (Fig. 2c), RuO2 diffraction spots disappeared, leaving Ru and Li2O diffraction features.…”

“…[20][21][22] It also suffers from the volume expansion once upon lithiation and thus capacity dropping. 20,[23][24][25] The lithiation reaction follows as…”