Polymer-Directed Crystal Growth Regulation: Template-Free Synthesis of Mesoporous Single-Crystalline Mn2OBO3.

Abstract

Transition metal borates are attractive anode candidates for lithium-ion batteries (LIBs) because of their high specific capacity and environmental benignity; however, their structural collapse induced by large volume changes during cycling leads to rapid capacity degradation. In this study, we report a polymer-directed crystal growth regulation strategy that enables the template-free synthesis of mesoporous single-crystalline Mn2OBO3 (MSC Mn2OBO3). Polyethyleneimine (PEI) acts as a bifunctional regulator, coordinating Mn2+ ions and hydrogen bonding with borate ions to modulate hydrolysis and condensation, thereby yielding a hybrid precursor. Subsequent hydrothermal treatment yields single-crystalline MnBO2OH nanobelts, which are converted by calcination into MSC Mn2OBO3. As an anode active material for lithium-ion batteries, MSC Mn2OBO3 delivers a reversible capacity of 1440 mAh g-1 at 0.2 A g-1, more than twice that of bulk Mn2OBO3. Notably, this polymer-directed strategy is readily extendable to doped MSC Mn2OBO3 (e.g., Fe, V, and Mg), providing a versatile platform for the design of porous single-crystalline materials for energy storage.

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