Well-Dispersed Garnet Crystallites for Applications in Solid-State Li-S Batteries

Improved Li-S Battery Performance with Dispersant/Plasticizer Co-Assisted Modification of a Poly(ethylene Oxide)/Li6.4La3Zr1.4Ta0.6O12 Solid Electrolyte

Lithium-sulfur batteries (LSBs) have garnered considerable attention over the past decade due to their high specific capacity and energy density. However, the poor safety and polysulfide shuttle phenomenon associated with liquid LSBs have been widely criticized. Solid-state electrolytes have the potential to overcome these issues, but their lower ionic conductivity and nonideal electrode/electrolyte interface contact as compared with liquid electrolytes remain a challenge in all-solid-state LSBs (ASSLSBs). This study applies the untested method of introducing a combination of dispersant and plasticizer as a "co-assisted" additive. We develop a polymer/ceramic composite electrolyte by combining poly(ethylene oxide)s, Li6.4La3Zr1.4Ta0.6O12 ceramic powder, the dispersant pluronic (C3H6O·C2H4O)x (F127), and the plasticizer succinonitrile (C2H4(CN)2) (SN). The dispersant F127 effectively prevents the aggregation of ceramic powders, whereas the plasticizer SN reduces the crystallinity of the composite polymer electrolytes and decreases the interface impedance, thereby enhancing the overall ion conductivity. The resulting composite electrolyte exhibits an ionic conductivity of 1.24 × 10-4 S cm-1 at room temperature, and when coupled with a commercial sulfur electrode, a high capacity of 1085 mA h g-1 is achieved. In addition, the batteries demonstrate a high capacity retention of 71% after 100 cycles at a current density of 0.2 C at room temperature, demonstrating considerable promise for ASSLSB applications.

Solid Electrolytes and Dendrite Dynamics in Solid-State Lithium-Sulfur Batteries

As the demand for safer lithium batteries grows, the quality of solid electrolytes, a critical component for solid-state lithium batteries (SSLBs) construction, has become increasingly important. SSLBs typically underperform compared to conventional batteries with liquid electrolytes. In this study, two ceramic-based composite solid electrolytes (CSEs) with differing dispersion qualities were prepared, consisting of dispersion-treated and as-received Li6.4La3Zr1.4Ta0.6O12 (LLZTO) particles within a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix. These two CSEs were assembled with a sulfur cathode into solid-state lithium-sulfur batteries (SSLSBs) and assessed using electrochemical impedance spectroscopy and distribution of relaxation times to investigate factors affecting battery performance. To clarify the individual contributions of the cathode and anode, a three-electrode configuration was employed, allowing a more detailed understanding of the internal processes of SSLSBs. Additional techniques, including critical current density testing, in situ optical microscopy for lithium dendrite observation, and finite element simulations, were utilized to evaluate the impact of LLZTO and PVDF-HFP dispersion uniformity on electrolyte and cell performances. Results reveal that low-quality CSEs led to uneven charge transport and increased lithium dendrite formation during cycling, significantly reducing battery lifespan. Importantly, while CSEs can mitigate the shuttle effect, uncontrolled lithium dendrite growth emerged as a primary cause of capacity decline and cell failure for solid-state batteries.

Comb-like poly(β-amino ester)-integrated PEO-based self-healing solid electrolytes for fast ion conduction in lithium-sulfur batteries

All-solid-state lithium-sulfur batteries (ASSLSBs) using poly(ethylene oxide) (PEO) electrolytes offer significant advantages in energy density and safety. However, their development is hampered by the slow Li+ conduction in solid polymer electrolytes and sluggish electrochemical conversion at the cathode-electrolyte interface. Herein, we fabricate a self-healing poly(β-amino ester) with a comb-like topological structure and multiple functional groups, synthesized through a Michael addition strategy. This material modifies the PEO-based solid-state electrolyte, creating fast Li+ transport channels and improving polysulfides conversion kinetics at the electrode surface. Consequently, both modified all-solid-state lithium symmetric cells and lithium-sulfur batteries exhibit improved electrochemical performance. This work demonstrates an expanded interpenetrating macromolecular engineering approach to develop highly ion-conductive solid polymer electrolytes for ASSLSBs.

Delocalized Lithium Ion Flux by Solid-State Electrolyte Composites Coupled with 3D Porous Nanostructures for Highly Stable Lithium Metal Batteries

This work investigates the root cause of failure with the ultimate anode, Li metal, when employing conventional/composite separators and/or porous anodes. Then a feasible route of utilizing Li metal is presented. Our operando and microscopy studies have unveiled that Li+ flux passing through the conventional separator is not uniform, resulting in preferential Li plating/stripping. Porous anodes alone are subject to clogging with moderate- or high-loading cathodes. Here we discovered it is necessary to seek synergy from our separator and anode pair to deliver delocalized Li+ to the anode and then uniformly plate Li metal over the large surface areas of the porous anode. Our polymer composite separator containing a solid-state electrolyte (SE) can provide numerous Li+ passages through the percolated SE and pore networks. Our finite element analysis and comparative tests disclosed the synergy between the homogeneous Li+ flux and current density reduction on the anode. Our composite separators have induced compact and uniform Li plating with robust inorganic-rich solid electrolyte interphase layers. The porous anode decreased the nucleation overpotential and interfacial contact impedance during Li plating. Full cell tests with LiFePO4 and Li[Ni0.8Mn0.1Co0.1]O2 (NMC811) exhibited remarkable cycling behaviors: ∼80% capacity retention at the 750th and 235th cycle, respectively. A high-loading NMC811 (4 mAh cm-2) full cell displayed maximum cell-level energy densities of 334 Wh kg-1 and 783 Wh L-1. This work proposes a solution for raising energy density by adopting Li metal, which could be a viable option considering only incremental advancement in conventional cathodes lately.

3D Asymmetric Bilayer Garnet-Hybridized High-Energy-Density Lithium-Sulfur Batteries

Lithium garnet Li₇La₃Zr₂O₁₂ (LLZO), with high ionic conductivity and chemical stability against a Li metal anode, is considered one of the most promising solid electrolytes for lithium-sulfur batteries. However, an infinite charge time resulting in low capacity has been observed in Li-S cells using Ta-doped LLZO (Ta-LLZO) as a solid electrolyte. It was observed that this cell failure is correlated with lanthanum segregation to the surface of Ta-LLZO that reacts with a sulfur cathode. We demonstrated this correlation by using lanthanum excess and lanthanum deficient Ta-LLZO as the solid electrolyte in Li-S cells. To resolve this challenge, we physically separated the sulfur cathode and LLZO using a poly(ethylene oxide) (PEO)-based buffer interlayer. With a thin bilayer of LLZO and the stabilized sulfur cathode/LLZO interface, the hybridized Li-S batteries achieved a high initial discharge capacity of 1307 mA h/g corresponding to an energy density of 639 W h/L and 134 W h/kg under a high current density of 0.2 mA/cm² at room temperature without any indication of a polysulfide shuttle. By simply reducing the LLZO dense layer thickness to 10 μm as we have demonstrated before, a significantly higher energy density of 1308 W h/L and 257 W h/kg is achievable. X-ray diffraction and X-ray photoelectron spectroscopy indicate that the PEO-based interlayer, which physically separates the sulfur cathode and LLZO, is both chemically and electrochemically stable with LLZO. In addition, the PEO-based interlayer can adapt to the stress/strain associated with sulfur volume expansion during lithiation.