Reconstructions and Dynamics of β -Lithium Thiophosphate Surfaces

Lithium thiophosphate (LPS) is a promising solid electrolyte for next-generation lithium-ion batteries due to its superior energy storage, high ionic conductivity, and low-flammability properties. Despite its potential, the high reactivity of LPS with common contaminants such as atmospheric water, preparation solvents, and electrode materials poses significant challenges for commercialization. The lack of understanding regarding the structure, morphology, and chemical behavior of the surface of LPS slows down the search for solutions to these issues. Here, we utilize a machine-learning interatomic potential to achieve a fundamental atomistic understanding of the mechanical and chemical properties of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>β</a:mi></a:math>-<c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>Li</c:mi></c:math><e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msub><e:mi/><e:mn>3</e:mn></e:msub></e:math><g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>PS</g:mi></g:math><i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msub><i:mi/><i:mn>4</i:mn></i:msub></i:math> surfaces. Employing molecular-dynamics simulations, we identify relevant complexions formed by surface reconstructions, determine their surface energies, and compute the Wulff shape of <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mi>β</k:mi></k:math>-LPS. The most stable complexions exhibit properties distinctly different from the bulk, including amorphization, increased density, decreased conductivity, and large deformation of the structural building blocks. We demonstrate that these surfaces are not static but undergo significant dynamical activity at room temperature, which is clearly identified by an analysis featuring a time-averaged structural descriptor. Finally, we examine the changes of the electronic structure induced by the surface complexions as well as their effect on the reaction enthalpy with water, which provides us with details on changes in surface reactivity and active sites, underlining the importance of investigating surface complexions under realistic conditions.