Aqueous Zn-ion batteries are plagued by a short lifespan caused by localized dendrites. High-concentration electrolytes are favorable for dense Zn deposition but have poor performance in batteries with glass-fiber separators. In contrast, low-concentration electrolytes can wet the separators well, ensuring the migration of zinc ions, but the dendrites grow rapidly. In this work, we propose an electrolyte gradient strategy wherein a zinc-ion concentration gradient is established from the anode to the separator, ensuring that the separator keeps a good wettability in low-concentration areas and the zinc anode achieves dendrite-free deposition in a high-concentration area. By using this strategy in a common electrolyte, zinc sulfate, a Zn||Zn symmetric cell achieves 14 000 ultralong cycles (exceeding 8 months) at 5 mA cm-2 and 1 mAh cm-2 . When the current is further increased to 20 mA cm-2 , the symmetric cell could still run for over 10 000 cycles. Assembled Zn||NVO full cells also demonstrate prominent performance. At a high current of 16 mA cm-2 , the NVO cathode with high loading (8 mg cm-2 ) still has a capacity of 58% after 1200 cycles. Overall, the gradient electrolyte strategy provides a promising approach for practical long-life Zn anodes with the advantages of simple operation and low cost.
Keywords: gradient electrolytes; long life; sodium carboxymethylcellulose; zinc anodes; zinc-ion batteries.
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