Overlithiated oxide cathode materials show high capacity but poor cycle stability and voltage attenuation. In this work, a concentration difference driven molten salt ion exchange strategy is used to replace a small quantity of lithium ions by sodium ions. With the entry of sodium ions, the interplanar spacing is increased and the structure is stabilized. The electrochemical properties of materials have been improved obviously. The powder X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, and transmission electron microscopy are used to detect the entry of sodium ions and structural changes. The modified materials display high discharge specific capacity, excellent cycling performance, and reduced voltage attenuation.
An ultrathick lithium metal anode (LMA) is a prerequisite for developing practical lithium–sulfur (Li–S) batteries that simultaneously meet the requirements of high areal capacity, lean electrolyte, and limited excess Li. Inspired by the electrochemical process for an organosulfur cathode, herein, we reconfigure such a sulfur cathode by using an overlithiation strategy to enable the formation of a high performance LMA. Specifically, an applicable ultrathick LMA is successfully constructed by overlithiating a well-known organosulfur cathode material, sulfurized polyacrylonitrile (SPAN). SPAN contains a polymeric pyridine structure with an outstanding lithium-ion affinity, so that it can act as a lithiophilic matrix. More importantly, a Li2S-rich solid electrolyte interphase (SEI) can be generated on the surface of SPAN during the overlithiation process. The synergistic effect of the lithiophilic matrix and a robust SEI leads to a dense deposition of lithium, which enables one to form an ultrathick LMA (159 μm, 30 mAh cm–2) with high Coulombic efficiency (99.7%). Such an LMA paired with a sulfur cathode of high areal capacity (up to 16 mAh cm–2) shows stable cycling under practical conditions of a lean electrolyte (2.2 μL mgS–1) and a negative-to-positive capacity (N/P) ratio as low as 1.3. The applicability of the ultrathick LMA was further verified with Li–S pouch cells, indicating a highly prospective route toward realization of practical Li–S batteries.
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