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In article number 1900264, Jong Min Yuk and co‐workers visualize four types of semi‐coherent boundaries formed during sodiation in copper sulfide utilizing high‐resolution transmission electron microscopy. The semi‐coherent boundaries do not only act as mechanical pillars for pulverization‐tolerance, but also provide additional sodium transport paths for capacity recovery. The novel sodiation mechanism enables exceptionally stable sodium storage in copper sulfide.

Finding suitable electrode materials is one of the challenges for the commercialization of a sodium ion battery due to its pulverization accompanied by high volume expansion upon sodiation. Here, copper sulfide is suggested as a superior electrode material with high capacity, high rate, and long‐term cyclability owing to its unique conversion reaction mechanism that is pulverization‐tolerant and thus induces the capacity recovery. Such a desirable consequence comes from the combined effect among formation of stable grain boundaries, semi‐coherent boundaries, and solid‐electrolyte interphase layers. The characteristics enable high cyclic stability of a copper sulfide electrode without any need of size and morphological optimization. This work provides a key finding on high‐performance conversion reaction based electrode materials for sodium ion batteries.