Exceptional Lithium Storage in a Co(OH)₂ Anode: Hydride Formation

Abstract

Current lithium ion battery technology is tied in with conventional reaction mechanisms such as insertion, conversion, and alloying reactions even though most future applications like EVs demand much higher energy densities than current ones. Exploring the exceptional reaction mechanism and related electrode materials can be critical for pushing current battery technology to a next level. Here, we introduce an exceptional reaction with a Co(OH) material which exhibits an initial charge capacity of 1112 mAh g, about twice its theoretical value based on known conventional conversion reaction, and retains its first cycle capacity after 30 cycles. The combined results of synchrotron X-ray diffraction and X-ray absorption spectroscopy indicate that nanosized Co metal particles and LiOH are generated by conversion reaction at high voltages, and Co H, LiO, and LiH are subsequently formed by hydride reaction between Co metal, LiOH, and other lithium species at low voltages, resulting in a anomalously high capacity beyond the theoretical capacity of Co(OH). This is further corroborated by AIMD simulations, localized STEM, and XPS. These findings will provide not only further understanding of exceptional lithium storage of recent nanostructured materials but also valuable guidance to develop advanced electrode materials with high energy density for next-generation batteries.

Reaction mechanism and additional lithium storage of mesoporous MnO2 anode in Li batteries

“…As the discharge proceeds, the XRD peaks belonging to MnO disappear, and a broad Mn metal peak centered at 2h = 42.5°is observed after achieving a discharge capacity of 2000 mAh/g, indicating that the MnO phase is converted into an amorphous Mn phase by the conversion reaction [26,51]. The amorphization process during the first discharge was generally observed in studies on nanostructured anode material [38,39,52].…”

Challenges and Design Strategies for Conversion-Based Anode Materials for Lithium- and Sodium-Ion Batteries

“…This results in a high capacity over the theoretical value, as in the mesoporous MnO 2 [34]. This extra capacity is attributed to abnormal charge storage reactions [11,46,47] such as electrolyte-derived surface layer [48], interfacial charge storage [49,50], reaction of lithium-containing species [43,51], and/or ion storage in defects/metallic lithium storage [52,53]. During subsequent charging, changes occur in the opposite manner.…”

“…In lithium-based system, various types of polyanionic metal compounds such as hydroxides, sulfates, carbonates, and oxalates undergo conversion reaction [51,90,93,123,124]. According to the conversion reaction mechanism, the theoretical capacity of these materials is lower than that of oxides with the same oxidation state of metal atoms because of their heavier molecular weight.…”

“…From the catalytic process of Co metal formed after the conversion reaction, the LiOH phase further reacts with lithium forming Li 2 O and LiH phases. With the contribution of LiOH, the theoretical capacity of Co(OH) 2 is expanded by three times with 6 mol of lithium per unit formula [51].…”

“…Therefore, the origins of additional capacity have attracted much attention [46,204,205], starting from the early 2000s [48,49]. The most widely accepted reasons for the additional capacity of conversion-based materials are electrolyte-derived surface layer [48], interfacial charge storage [49,50], and reactions of lithium-containing species [43,51,90].…”