Low Na-β′′-alumina electrolyte/cathode interfacial resistance enabled by a hydroborate electrolyte opening up new cell architecture designs for all-solid-state sodium batteries

Abstract

Development of low-resistance electrode/electrolyte interfaces is key for enabling all-solid-state batteries with fast-charging capabilities. Low interfacial resistance and high current density were demonstrated for Na-β''-alumina/sodium metal interfaces, making Na-β''-alumina a promising solid electrolyte for high-energy all-solid-state batteries. However, integration of Na-β''-alumina with a high-energy sodium-ion intercalation cathode remains challenging. Here, we report a proof-of-concept study that targets the implementation of a Na-β''-alumina ceramic electrolyte with a slurry-casted porous NaCrO2 cathode with infiltrated sodium hydroborates as secondary electrolyte. The hydroborate Na4(B12H12)(B10H10) possesses similar sodium-ion conductivity of 1 mS cm-1 at room temperature as Na-β''-alumina and can be fully densified by cold pressing. Using the Na4(B12H12)(B10H10) secondary electrolyte as interlayer between Na-β''-alumina and NaCrO2, we obtain a cathode-electrolyte interfacial resistance of only 25 Ω cm2 after cold pressing at 70 MPa. Proof-of-concept cells with a sodium metal anode and a NaCrO2 cathode feature an initial discharge capacity of 103 mAh g-1 at C/10 and 42 mAh g-1 at 1C with an excellent capacity retention of 88% after 100 cycles at 1C at room temperature. Ion-milled cross-sections of the cathode/electrolyte interface demonstrate that intimate contact is maintained during cycling, proving that the use of hydroborates as secondary electrolyte and as an interlayer is a promising approach for the development of all-solid-state batteries with ceramic electrolytes.

Li7La3Zr2O12 Protonation as a Means to Generate Porous/Dense/Porous-Structured Electrolytes for All-Solid-State Lithium-Metal Batteries

“…On the cathode side, the porous layer is infiltrated with molten polymer catholyte to ensure a good LLZO/cathode contact. This allows us to avoid/decrease the applied stack pressure upon cycling, necessary to establish a good cathode/LLZO physical contact for planar ceramics. , We further show that the generated porous/dense/porous LLZO improves the electrochemical performance in terms of rate capability and long-term stability in symmetric Li/LLZO/Li cells and in Li/LLZO/LFP full cells using PEO–LiTFSI as a catholyte. The proposed method is expected to be readily transferable to thin LLZO tapes with thicknesses below 200 μm avoiding the complications associated with sintering of bilayer and trilayer LLZO structures paving to way to the integration of porous LLZO anodes into a competitive all-solid-state lithium-metal battery.…”

“…This allows us to avoid/decrease the applied stack pressure upon cycling, necessary to establish a good cathode/LLZO physical contact for planar ceramics. 37,38 We further show that the generated porous/dense/porous LLZO improves the electrochemical performance in terms of…”

Modulating the cathode interface in sodium-beta alumina-based semi-solid-state sodium cells using liquid-organic electrolytes

“…9,[11][12][13] It especially applies to the interface between the polycrystalline Na + conductor sodium-beta alumina solid electrolyte (BASE) and the negative electrode (NE, hereaer called the anode) 14,15 as well as to the positive electrode (PE, hereaer called cathode). 16 Several methods exist for modulating the BASEjPE interface, e.g., adding ionic liquids, [17][18][19] polymers, 20,21 or additional electrolytes. 16 Small amounts of liquid-organic electrolytes (LOE) can also modify the interfaces.…”

A Medium-Temperature All-Solid-State Sodium Battery Utilizing Sodium-Beta Alumina and a Polymeric Composite Positive Electrode

“…Recently, a hydroborate interlayer with NaCrO 2 active material was used, resulting in a cell with a cycle life of 100 cycles but a limited voltage range due to hydroborate's oxidative stability. 32 In the other two cases, ionic liquids provided favorable BASE|PE interface kinetics. 33,45 Both cells exhibited remarkable cycle life with more than 500 cycles and rate capabilities (>6 C) thanks to the ionic liquid.…”

“…Several sodium-based cell concepts using BASE at intermediate temperatures were published recently. [26][27][28][29][30][31][32][33] However, combining BASE with sodium and transition metal oxide active materials, all rigid in nature, poses challenges in establishing an intimate interface contact in solid-state batteries operating at intermediate temperatures. The intimate interface contact is crucial for fast charge transfer and long cycle life.…”