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-
-alumina/sodium metal interfaces, making Na-
-alumina a promising solid electrolyte for high-energy all-solid-state batteries. However, integration of Na-
-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-
-alumina ceramic electrolyte with a slurry-casted porous NaCrO
2 cathode with infiltrated sodium hydroborates as secondary electrolyte. The hydroborate Na
4(B
12H
12)(B
10H
10) possesses similar sodium-ion conductivity of 1 mS cm
-1 at room temperature as Na-
-alumina and can be fully densified by cold pressing. Using the Na
4(B
12H
12)(B
10H
10) secondary electrolyte as interlayer between Na-
-alumina and NaCrO
2, we obtain a cathode-electrolyte interfacial resistance of only 25 cm
2 after cold pressing at 70 MPa. Proof-of-concept cells with a sodium metal anode and a NaCrO
2 cathode feature an initial discharge capacity of 103 mAh g
-1 at C/10 and 42 mAh g
-1 at 1 C with an excellent capacity retention of 88% after 100 cycles at 1 C 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.
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