Overcoming the Na-ion conductivity bottleneck for the cost-competitive chloride solid electrolytes

Chloride solid electrolytes possess multiple advantages for the construction of safe, energy-dense all-solid-state sodium batteries, but presently the chlorides with sufficiently high cost-competitiveness for commercialization almost all exhibit low Na-ion conductivities of around 10 −5  S cm −1 or lower. Here, we report a chloride solid electrolyte, Na 2.7 ZrCl 5.3 O 0.7 , which reaches a Na-ion conductivity of 2.29 × 10 −4  S cm −1 at 25 °C without involving overly expensive raw materials such as rare-earth chlorides or Na 2 S. In addition to the efficient ion transport, Na 2.7 ZrCl 5.3 O 0.7 also shows an excellent deformability surpassing that of the widely studied Na 3 PS 4 , Na 3 SbS 4 , and Na 2 ZrCl 6 solid electrolytes. The combination of these advantages allows the all-solid-state cell based on Na 2.7 ZrCl 5.3 O 0.7 and NaCrO 2 to realize stable room-temperature cycling at a much higher specific current than those based on other non-viscoelastic chloride solid electrolytes in literature (120 mA g −1 vs. 12–55 mA g −1 ); after 100 cycles at such a high rate, the Na 2.7 ZrCl 5.3 O 0.7 -based cell can still deliver a discharge capacity of 80 mAh g −1 at 25 °C.