Silicon anode solid-state batteries
Research on solid-state batteries has focused on lithium metal anodes. Alloy-based anodes have received less attention in part due to their lower specific capacity even though they should be safer. Tan
et al
. developed a slurry-based approach to create films from micrometer-scale silicon particles that can be used in anodes with carbon binders. When incorporated into solid-state batteries, they showed good performance across a range of temperatures and excellent cycle life in full cells. —MSL
All-solid-state batteries are expected to enable batteries with high energy density with the use of lithium metal anodes. Although solid electrolytes are believed to be mechanically strong enough to prevent lithium dendrites from propagating, various reports today still show cell failure due to lithium dendritic growth at room temperature. While cell parameters such as current density, electrolyte porosity and interfacial properties have been investigated, mechanical properties of lithium metal and the role of applied stack pressure on the shorting behavior is still poorly understood. Here, we investigated failure mechanisms of lithium metal in all-solid-state batteries as a function of stack pressure, and conducted in situ characterization of the interfacial and morphological properties of the buried lithium in solid electrolytes. We found that a low stack pressure of 5 MPa allows reliable plating and stripping in a lithium symmetric cell for more than 1000 hours, and a Li | Li6PS5Cl | LiNi0.80Co0.15Al0.05O2 full cell, plating more than 4 µm of lithium per charge, is able to cycle over 200 cycles at room temperature. These results suggest the possibility of enabling the lithium metal anode in all-solid-state batteries at reasonable stack pressures.
Sulfide-based
solid electrolytes are promising candidates for all
solid-state batteries (ASSBs) due to their high ionic conductivity
and ease of processability. However, their narrow electrochemical
stability window causes undesirable electrolyte decomposition. Existing
literature on Li-ion ASSBs report an irreversible nature of such decompositions,
while Li–S ASSBs show evidence of some reversibility. Here,
we explain these observations by investigating the redox mechanism
of argyrodite Li6PS5Cl at various chemical potentials.
We found that Li–In | Li6PS5Cl | Li6PS5Cl–C half-cells can be cycled reversibly,
delivering capacities of 965 mAh g–1 for the electrolyte
itself. During charging, Li6PS5Cl forms oxidized
products of sulfur (S) and phosphorus pentasulfide (P2S5), while during discharge, these products are first reduced
to a Li3PS4 intermediate before forming lithium
sulfide (Li2S) and lithium phosphide (Li3P).
Finally, we quantified the relative contributions of the products
toward cell impedance and proposed a strategy to reduce electrolyte
decomposition and increase cell Coulombic efficiency.
Rechargeable solid-state sodium-ion batteries (SSSBs) hold great promise for safer and more energy-dense energy storage. However, the poor electrochemical stability between current sulfide-based solid electrolytes and high-voltage oxide cathodes has limited their long-term cycling performance and practicality. Here, we report the discovery of the ion conductor Na3-xY1-xZrxCl6 (NYZC) that is both electrochemically stable (up to 3.8 V vs. Na/Na+) and chemically compatible with oxide cathodes. Its high ionic conductivity of 6.6 × 10−5 S cm−1 at ambient temperature, several orders of magnitude higher than oxide coatings, is attributed to abundant Na vacancies and cooperative MCl6 rotation, resulting in an extremely low interfacial impedance. A SSSB comprising a NaCrO2 + NYZC composite cathode, Na3PS4 electrolyte, and Na-Sn anode exhibits an exceptional first-cycle Coulombic efficiency of 97.1% at room temperature and can cycle over 1000 cycles with 89.3% capacity retention at 40 °C. These findings highlight the immense potential of halides for SSSB applications.
Enabling
long cyclability of high-voltage oxide cathodes is a persistent
challenge for all-solid-state batteries, largely because of their
poor interfacial stabilities against sulfide solid electrolytes. While
protective oxide coating layers such as LiNbO3 (LNO) have
been proposed, its precise working mechanisms are still not fully
understood. Existing literature attributes reductions in interfacial
impedance growth to the coating’s ability to prevent interfacial
reactions. However, its true nature is more complex, with cathode
interfacial reactions and electrolyte electrochemical decomposition
occurring simultaneously, making it difficult to decouple each effect.
Herein, we utilized various advanced characterization tools and first-principles
calculations to probe the interfacial phenomenon between solid electrolyte
Li6PS5Cl (LPSCl) and high-voltage cathode LiNi0.85Co0.1Al0.05O2 (NCA). We
segregated the effects of spontaneous reaction between LPSCl and NCA
at the interface and quantified the intrinsic electrochemical decomposition
of LPSCl during cell cycling. Both experimental and computational
results demonstrated improved thermodynamic stability between NCA
and LPSCl after incorporation of the LNO coating. Additionally, we
revealed the in situ passivation effect of LPSCl electrochemical decomposition.
When combined, both these phenomena occurring at the first charge
cycle result in a stabilized interface, enabling long cyclability
of all-solid-state batteries.
All solid-state batteries (ASSBs) have the potential to deliver higher energy densities, wider operating temperature range, and improved safety compared with today's liquid-electrolyte-based batteries. However, of the various solid-state electrolyte (SSE) classespolymers, sulfides, or oxidesnone alone can deliver the combined properties of ionic conductivity, mechanical, and chemical stability needed to address scalability and commercialization challenges. While promising strategies to overcome these include the use of polymer/oxide or sulfide composites, there is still a lack of fundamental understanding between different SSE−polymer−solvent systems and its selection criteria. Here, we isolate various SSE−polymer−solvent systems and study their molecular level interactions by combining various characterization tools. With these findings, we introduce a suitable Li 7 P 3 S 11 SSE−SEBS polymer−xylene solvent combination that significantly reduces SSE thickness (∼50 μm). The SSE−polymer composite displays high room temperature conductivity (0.7 mS cm −1) and good stability with lithium metal by plating and stripping over 2000 h at 1.1 mAh cm −2. This study suggests the importance of understanding fundamental SSE−polymer−solvent interactions and provides a design strategy for scalable production of ASSBs.
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