SEI growth on Lithium metal anodes in solid-state batteries quantified with coulometric titration time analysis

Abstract Lithium-metal batteries with a solid electrolyte separator are promising for advanced battery applications, however, most electrolytes show parasitic side reactions at the low potential of lithium metal. Therefore, it is essential to understand how much (and how fast) charge is consumed in these parasitic reactions. In this study, a new electrochemical method is presented for the characterization of electrolyte side reactions occurring on active metal electrode surfaces. The viability of this new method is demonstrated in a so-called anode-free stainless steel ∣ Li6PS5Cl ∣ Li cell. The method also holds promise for investigating dendritic lithium growth (and dead lithium formation), as well as for analyzing various electrolytes and current collectors. The experimental setup allows easy electrode removal for post-mortem analysis, and the SEI’s heterogeneous/layered microstructure is revealed through complementary analytical techniques. We expect this method to become a valuable tool in the future for solid-state lithium metal batteries and potentially other cell chemistries

Copper Thiophosphate (Cu3PS4) as an Electrode Material for Lithium Solid‐State Batteries with Lithium Thiophosphate (β–Li3PS4) Electrolyte

Lithium thiophosphate (β‐Li3PS4) is a promising solid electrolyte (SE) for solid‐state batteries (SSBs). A major limitation is its very narrow electrochemical stability window which is caused by redox reactions involving sulfur and phosphorous. As these redox processes can be reversible, thiophosphates can be also studied as electrode materials. Herein, the use of Cu3PS4 as an active electrode material for Li SSBs with β‐Li3PS4 as the SE is explored. Both compounds exhibit similarities in crystal structure and composition which may benefit their compatibility. An In/InLi alloy is used as the counter electrode. The influence of electrode composition and temperature (room temperature and 60 °C) on the cell behavior is investigated. For an electrode composition of Cu3PS4: β–Li3PS4: C65 = 40: 50: 10 wt%, the initial discharge capacity at 60 °C is 776 mAh g−1 which fades over 60 cycles to 508 mAh g−1 when cycled between 0.8 and 2.8 V (vs. Li+/Li) at 50 mA g−1 (254.8 μA cm−2). Analysis by X‐ray diffraction and X‐ray photoelectron spectroscopy shows that Cu3PS4 irreversibly decomposes during lithiation. During cycling, the redox activity is found to be due to Cu2S and S8 redox.Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347Peer Reviewe

Instability of the Li7SiPS8 Solid Electrolyte at the Lithium Metal Anode and Interphase Formation

Thiophosphate solid electrolytes containing metalloid ions such as silicon or germanium show a very high lithium-ion conductivity and the potential to enable solid-state batteries (SSBs). While the lithium metal anode (LMA) is necessary to achieve specific energies competitive with liquid lithium-ion batteries (LIBs), it is also well known that most of the metalloid ions used in promising thiophosphate solid electrolytes are reduced in contact with an LMA. This reduction reaction and its products formed at the solid electrolyte|LMA interface can compromise the performance of an SSB due to impedance growth. To study the reduction of these metalloid ions and their impact more closely, we used the recently synthesized Li7SiPS8 as a member of the tetragonal Li10GeP2S12 (LGPS) family. Stripping/plating experiments and the temporal evolution of the impedance of symmetric Li|Li7SiPS8|Li transference cells show a severe increase in cell resistance. We characterize the reduction of Li7SiPS8 after lithium deposition with in situ X-ray photoelectron spectroscopy, time-of-flight secondary-ion mass spectrometry, and solid-state nuclear magnetic resonance spectroscopy. The results indicate a continuous reaction without the formation of elemental silicon. For elucidating the reaction pathways, density functional theory calculations are conducted followed by ab initio molecular dynamics simulations to study the interface evolution at finite temperature. The resulting electronic density of states confirms that no elemental silicon is formed during the decomposition. Our study reveals that Li7SiPS8 cannot be used in direct contact with the LMA, even though it is a promising candidate as both a separator and a catholyte material in SSBs

Dissolution and Recrystallization Behavior of Li₃PS₄ in Different Organic Solvents with a Focus on N-Methylformamide

Solid-state batteries can be built based on thiophosphate electrolytes such as β-Li3PS4. For the preparation of these solid electrolytes, various solvent-based routes have been reported. For recycling of end-of-life solid-state batteries based on such thiophosphates, we consider the development of dissolution and recrystallization strategies for the recovery of the model compound β-Li3PS4. We show that recrystallization can only be performed in polar, slightly protic solvents such as N-methylformamide (NMF). The recrystallization is comprehensively studied, showing that it proceeds via an intermediate phase with composition Li3PS4·2NMF, which is structurally characterized. This phase has a high resistivity for the transport of lithium ions and must be removed in order to obtain a recrystallized product with a conductivity similar to the pristine material. Moreover, the recrystallization from solution results in an increase of the amorphous phase fraction next to crystalline β-Li3PS4Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.RST/Storage of Electrochemical Energ