In this study, nanosize NaCrO2 with enriched domain boundaries in individual particle was synthesized from nanosize cation-disordered rocksalt-type NaCrO2 prepared by mechanical milling. The sample delivers large reversible capacity without voltage plateaus associated with phase transitions as shown in Figure 1a. Ex-situ XRD data clearly indicates that the O3/P3 phase transition is effectively suppressed on charge/discharge processes. High-resolution TEM imaging shows that micrometer-size secondary particles consist of highly crystalline nanosize NaCrO2 particles. These nanosize domains are randomly aligned in the individual particle. We propose that randomly aligned particles with many grain boundaries cancel and suppress gliding of transition metal layers. Moreover, nanosize NaCrO2 shows better capacity retention in Na cells (Figure 1b) on the long-term cycle test.
From these results, we will further discuss the factors affecting phase transitions for O3-type layered structure as positive electrode materials of rechargeable Na batteries for more details.
This study was in part granted by MEXT program “Elements Strategy Initiative to Form Core Research Center”, MEXT; Ministry of Education Culture, Sports, Science and Technology, Japan. High-resolution TEM work was carried out with the support from Deakin Advanced Characterization Facility. A.M.G. acknowledges the funding support from Australian Research Council Discovery grant DP160101178.
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