A non-ideal contact at the electrode/solid electrolyte interface of a solid-state battery arising due to pores (voids) or inclusions results in a geometric constriction effect that severely ...deteriorates the electric transport properties of the battery cell. The lack of understanding of this phenomenon hinders the optimization process of novel components, such as reversible and high-rate metal anodes. Deeper insight into the constriction phenomenon is necessary to correctly monitor interface degradation and to accelerate the successful use of metal anodes in solid-state batteries. Here, we use a 3D electric network model to study the fundamentals of the constriction effect. Our findings suggest that dynamic constriction as a non-local effect cannot be captured by conventional 1D equivalent circuit models and that its electric behavior is not ad hoc predictable. It strongly depends on the interplay of the geometry of the interface causing the constriction and the microscopic transport processes in the adjacent phases. In the presence of constriction, the contribution from the non-ideal electrode/solid electrolyte interface to the impedance spectrum may exhibit two signals that cannot be explained when the porous interface is described by a physical-based (effective medium theory) 1D equivalent circuit model. In consequence, the widespread assumption of a single interface contribution to the experimental impedance spectrum may be entirely misleading and can cause serious misinterpretation.
Impedance spectroscopy is widely used in operando studies of solid‐state batteries for characterizing charge transport and correlating it with structural features. A typical impedance spectrum ...reveals, in addition to transport signals of the solid electrolyte, one or more contributions due to processes taking place at the electrode interfaces. The focus of this study is on reversible (parent) metal anodes and a 3D electric network model is used to analyze the variation of their impedance as a function of pressure, temperature, or aging during cycling. This provides a recipe for experimentalists on how to identify impedance contributions arising from different interface effects, such as, charge transfer, dynamic current constriction, and solid electrolyte interphase formation. Rules are derived for assigning the different interface signals or identifying the dominant contribution in case of similar frequency‐dependence and a standard procedure for analysis is proposed. The suggested procedure is applied to experimental data of half cells where lithium metal is in contact with garnet‐type Li6.25Al0.25La3Zr2O12. This case study yields unambiguously that geometric current constriction due to morphological instabilities at the metal anode interface during cycling is the rate‐limiting step for this type of metal anode, rather than the frequently assumed polarization resistance of the electric charge transfer migration process.
Various interfacial effects influence the impedance behavior of solid‐state batteries. In addition to electrical migration processes, geometric effects such as current constrictions due to pore or SEI formation have a major impact on the rate performance of batteries. This study proposes a guideline for the analysis of impedance data aiming to correlate the measurement signal with the unknown interfacial morphology.
Solid‐state batteries (SSBs) currently attract great attention as a potentially safe electrochemical high‐energy storage concept. However, several issues still prevent SSBs from outperforming today's ...lithium‐ion batteries based on liquid electrolytes. One major challenge is related to the design of cathode active materials (CAMs) that are compatible with the superionic solid electrolytes (SEs) of interest. This perspective, gives a brief overview of the required properties and possible challenges for inorganic CAMs employed in SSBs, and describes state‐of‐the art solutions. In particular, the issue of tailoring CAMs is structured into challenges arising on the cathode‐, particle‐, and interface‐level, related to microstructural, (chemo‐)mechanical, and (electro‐)chemical interplay of CAMs with SEs, and finally guidelines for future CAM development for SSBs are proposed.
In this perspective, the required properties and possible challenges for inorganic cathode active materials (CAMs) employed in solid‐state batteries (SSBs) are discussed and design principles are introduced. Solid‐state battery cathode challenges are structured on cathode‐, particle‐, and interface‐level, related to microstructural, (chemo‐)mechanical, and (electro‐)chemical interplay of CAMs with solid electrolytes and guidelines for future CAM development for SSBs are proposed.
In chronic inflammation regulatory immune cells, such as regulatory T cells and myeloid-derived suppressor cells (MDCS) can develop. Local signals in the inflamed tissue, such as cytokines and ...eicosanoids, but also contact dependent signals, can promote MDSC development. In the liver, hepatic stellate cells (HSC) may provide such signals via the expression of CD44. MDSC generated in the presence of HSC and anti-CD44 antibodies were functionally and phenotypically analyzed. We found that both monocytic (M-) and polymorphonuclear (PMN-) MDSC generated in the presence of αCD44 antibodies were less suppressive towards T cells as measured by T cell proliferation and cytokine production. Moreover, both M- and PMN- MDSC were phenotypically altered. M-MDSC mainly changed their expression of CD80 and CD39, PMN-MDSC showed altered expression of CD80/86, PD-L1 and CCR2. Moreover, both PMN- and M-MDSC lost expression of Nos2 mRNA, whereas M-MDSC showed reduced expression of TGFb mRNA and PMN-MDSC reduced expression of Il10 mRNA. In summary, the presence of CD44 on hepatic stellate cells promotes the induction of both M- and PMN-MDSC, although the mechanisms by which these MDSC may increase suppressive function due to interaction with CD44 is only partially overlapping.
Abstract
Enabling the lithium metal anode (LMA) in solid‐state batteries (SSBs) is the key to developing high energy density battery technologies. However, maintaining a stable electrode–electrolyte ...interface presents a critical challenge to high cycling rate and prolonged cycle life. One such issue is the interfacial pore formation in LMA during stripping. To overcome this, either higher stack pressure or binary lithium alloy anodes are used. Herein, it is shown that fine‐grained (
d
= 20 µm) polycrystalline LMA can avoid pore formation by exploiting the microstructural dependence of the creep rates. In a symmetric cell set‐up, i.e., LiǀLi
6.25
Al
0.25
La
3
Zr
2
O
12
(LLZO)ǀLi, fine‐grained LMA achieves > 11.0 mAh cm
−2
compared to ≈ 3.6 mAh cm
−2
for coarse‐grained LMA (
d
= 295 µm) at 0.1 mA cm
−2
and at moderate stress of 2.0 MPa. Smaller diffusion lengths (≈ 20 µm) and higher diffusivity pathway along dislocations (
D
d
≈ 10
−7
cm
2
s
−1
), generated during cell fabrication, result in enhanced viscoplastic deformation in fine‐grained polycrystalline LMA. The electrochemical performances corroborate well with estimated creep rates. Thus, microstructural control of LMA can significantly reduce the required stack pressure during stripping. These results are particularly relevant for “anode‐free” SSBs wherein both the microstructure and the mechanical state of the lithium are critical parameters.
Enabling the lithium metal anode (LMA) in solid‐state batteries (SSBs) is the key to developing high energy density battery technologies. However, maintaining a stable electrode–electrolyte interface ...presents a critical challenge to high cycling rate and prolonged cycle life. One such issue is the interfacial pore formation in LMA during stripping. To overcome this, either higher stack pressure or binary lithium alloy anodes are used. Herein, it is shown that fine‐grained (d = 20 µm) polycrystalline LMA can avoid pore formation by exploiting the microstructural dependence of the creep rates. In a symmetric cell set‐up, i.e., LiǀLi6.25Al0.25La3Zr2O12(LLZO)ǀLi, fine‐grained LMA achieves > 11.0 mAh cm−2 compared to ≈ 3.6 mAh cm−2 for coarse‐grained LMA (d = 295 µm) at 0.1 mA cm−2 and at moderate stress of 2.0 MPa. Smaller diffusion lengths (≈ 20 µm) and higher diffusivity pathway along dislocations (Dd ≈ 10−7 cm2 s−1), generated during cell fabrication, result in enhanced viscoplastic deformation in fine‐grained polycrystalline LMA. The electrochemical performances corroborate well with estimated creep rates. Thus, microstructural control of LMA can significantly reduce the required stack pressure during stripping. These results are particularly relevant for “anode‐free” SSBs wherein both the microstructure and the mechanical state of the lithium are critical parameters.
Microstructural dependence of creep rates in lithium metal anode (LMA) is exploited to significantly reduce the required stack pressure during stripping. A stable Liǀsolid–electrolyte interface for over 110 h is achieved at a moderate pressure of 2.0 MPa under an anodic load of 0.1 mA cm−2.
Solid‐state sodium batteries (SSNBs) have attracted extensive interest due to their high safety on the cell level, abundant material resources, and low cost. One of the major challenges in the ...development of SSNBs is the suppression of sodium dendrites during electrochemical cycling. The solid electrolyte Na3.4Zr2Si2.4P0.6O12 (NZSP) exhibits one of the best dendrite tolerances of all reported solid electrolytes (SEs), while it also shows interesting dendrite growth along the surface of NZSP rather than through the ceramic. Operando investigations and in situ scanning electron microscopy microelectrode experiments are conducted to reveal the Na plating mechanism. By blocking the surface from atmosphere access with a sodium‐salt coating, surface‐dendrite formation is prevented. The dendrite tolerance of Na | NZSP | Na symmetric cells is then increased to a critical current density (CCD) of 14 mA cm−2 and galvanostatic cycling of 1 mA cm−2 and 1 mAh cm−2 (half cycle) is demonstrated for more than 1000 h. Even if the current density is increased to 3 mA cm−2 or 5 mA cm−2, symmetric cells can still be operated for 180 h or 12 h, respectively.
Fast Na‐dendrite growth along the surface of Na3.4Zr2Si2.4P0.6O12 (NZSP) rather than through the ceramic is observed. Atmosphere and surface‐coating influence the surface‐dendrite growth on NZSP. After coating the NZSP surface with a protective layer, the critical current density of the Na | NZSP | Na symmetric cells increases up to 14 mA cm−2. The cell withstands galvanostatic cycling with 1 mA cm−2 and 1 mAh cm−2 for 1000 h.
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