Recent developments in the synthesis of 2D materials from 3D layered precursors via deintercalation have made novel 2D materials more accessible and tunable. 2D MXenes (Mn+1Xn) are synthesized from 3D layered Mn+1AXn phases (M=early transition metal, A= group 13-14 elements, X=C or N). Analogous to graphene, MXenes have applications in various fields, such as electrocatalysis, sensors, energy storage, etc. Encouraged by this, numerous attempts have been made to synthesize boron analogs of MXenes: MBenes, even though bulk preparation of these phases remains in their infancy. A recent discovery of two layered polymorphs in the Li-Ni-B system: RT-LiNiB and HT-LiNiB (RT-room temperature, HT-high temperature) featuring alternating NiB and Li layers, motivated us to attempt the synthesis of 2D MBene. Similar to the 'A' atoms in MAX phases, deintercalation of loosely bonded Li atoms from the LiNiB compounds was achieved by exposing the precursors to various chemical environments (air, HCl, etc.) at room temperature. We demonstrated that by controlling reaction conditions and exposure time, Li layers could be controllably deintercalated from the precursors. Scanning transmission electron microscopy (STEM) data revealed the deintercalation process to advance layer by layer following a "zip-lock" mechanism: upon deintercalation of a Li layer, the "zip-lock" is closed, forcing adjacent [NiB] layers to condense. STEM and solid-state 7Li and 11B NMR spectroscopy data revealed that under the chemical methods employed, complete removal of Li atoms could not be achieved; instead, novel metastable borides (RT-Li0.6NiB, HT-Li0.4NiB) are formed. Partial topochemical deintercalation of Li made crystal structures of these borides extremely complex. Therefore, we solved the structures by utilizing a feedback loop of three state-of-the-art characterization techniques: STEM, X-ray Pair Distribution Function, and Density Functional Theory. Crystal structures of these compounds are composed of randomly distributed layered fragments Li[NiB], Li[NiB]2, and Li[NiB]3. Formation of the [NiB]2 and [NiB]3 condensed layers alters magnetic properties from temperature-independent paramagnet as in parent LiNiB to the spin-glassiness in RT-Li0.6NiB and HT-Li0.4NiB.

Topochemical deintercalation of Li from layered LiNiB

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.