Elucidating the Role of Microstructure in Thiophosphate Electrolytes – a Combined Experimental and Theoretical Study of β‐Li₃PS₄

Abstract

Solid‐state batteries (SSBs) are promising candidates to significantly exceed the energy densities of today's state‐of‐the‐art technology, lithium‐ion batteries (LIBs). To enable this advancement, optimizing the solid electrolyte (SE) is the key. β‐Li3PS4 (β‐LPS) is the most studied member of the Li2S‐P2S5 family, offering promising properties for implementation in electric vehicles. In this work, the microstructure of this SE and how it influences the electrochemical performance are systematically investigated. To figure this out, four batches of β‐LPS electrolyte with different particle size, shape, and porosity are investigated in detail. It is found that differences in pellet porosities mostly originate from single‐particle intrinsic features and less from interparticle voids. Surprisingly, the β‐LPS electrolyte pellets with the highest porosity and larger particle size not only show the highest ionic conductivity (up to 0.049 mS cm–1 at RT), but also the most stable cycling performance in symmetrical Li cells. This behavior is traced back to the grain boundary resistance. Larger SE particles seem to be more attractive, as their grain boundary contribution is lower than that of denser pellets prepared using smaller β‐LPS particles.

Effect of Particle Size and Pressure on the Transport Properties of the Fast Ion Conductor t‐Li7SiPS8

“…[38] A recent study of Ates et al also points out that grain boundaries impact the ionic conductivity more than particle porosity and tortuosity. [39] As the pressure increases, this trend of lower ionic conductivity for the smaller PSD continues and is observed for all measured pressures.…”

Understanding Decomposition of Electrolytes in All-Solid-State Lithium–Sulfur Batteries

“…Additionally, Ates et al reported that β-LPS SE pellets with higher porosity and a larger particle size show higher ionic conductivity. This observation demonstrates the major effect of grain boundary resistance on the ionic conductivity of β-LPS . The pelletized pristine LPS, LPS-250, and LPS-510 have pellet densities of 1.82, 1.93, and 2.22 g cm –3 , which are calculated from the volume measured by the dimensions of the pellets, respectively.…”

“…This observation demonstrates the major effect of grain boundary resistance on the ionic conductivity of β-LPS. 40 The pelletized pristine LPS, LPS-250, and LPS-510 have pellet densities of 1.82, 1.93, and 2.22 g cm −3 , which are calculated from the volume measured by the dimensions of the pellets, respectively. The LPS with the lower pellet density and larger particle size shows higher ionic conductivity.…”

Oxide‐Based Solid‐State Batteries: A Perspective on Composite Cathode Architecture

“…[130] In contrast to this assumption, in a recent combined theoretical-experimental study of β-Li 3 PS 4 in which the microstructure (porosity, particle size and shape) was varied, a large contribution of the grain boundary resistance to the overall resistance was found. [131] The mechanical properties (quasi-malleability) of sulfides at ambient temperature likely eliminate the GB resistance between particles. Additionally, there appears to be little evidence that crystalline domains have a significant resistance contribution for charge transfer across GBs.…”

“…[ 130 ] In contrast to this assumption, in a recent combined theoretical‐experimental study of β‐Li 3 PS 4 in which the microstructure (porosity, particle size and shape) was varied, a large contribution of the grain boundary resistance to the overall resistance was found. [ 131 ]…”