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, Na2.7ZrCl5.3O0.7, 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 Na2S. In addition to the efficient ion transport, Na2.7ZrCl5.3O0.7 also shows an excellent deformability surpassing that of the widely studied Na3PS4, Na3SbS4, and Na2ZrCl6 solid electrolytes. The combination of these advantages allows the all-solid-state cell based on Na2.7ZrCl5.3O0.7 and NaCrO2 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 Na2.7ZrCl5.3O0.7-based cell can still deliver a discharge capacity of 80 mAh g−1 at 25 °C.