Severe safety concerns are impeding the large-scale employment of lithium/sodium batteries. Conventional electrolytes are highly flammable and volatile, which may cause catastrophic fires or explosions. Efforts to introduce flame-retardant solvents into the electrolytes have generally resulted in compromised battery performance because those solvents do not suitably passivate carbonaceous anodes. Here we report a salt-concentrated electrolyte design to resolve this dilemma via the spontaneous formation of a robust inorganic passivation film on the anode. We demonstrate that a concentrated electrolyte using a salt and a popular flame-retardant solvent (trimethyl phosphate), without any additives or soft binders, allows stable charge–discharge cycling of both hard-carbon and graphite anodes for more than 1,000 cycles (over one year) with negligible degradation; this performance is comparable or superior to that of conventional flammable carbonate electrolytes. The unusual passivation character of the concentrated electrolyte coupled with its fire-extinguishing property contributes to developing safe and long-lasting batteries, unlocking the limit toward development of much higher energy-density batteries.

严重的安全隐患阻碍了锂/钠电池的大规模使用。常规电解质高度易燃且易挥发，可能会导致灾难性的火灾或爆炸。将阻燃性溶剂引入电解质中的努力通常导致电池性能下降，因为这些溶剂不能适当地钝化碳质阳极。在这里，我们报告了一种盐浓缩电解质设计，可通过在阳极上自发形成坚固的无机钝化膜来解决这一难题。我们证明，使用盐和流行的阻燃溶剂（磷酸三甲酯）的浓缩电解质，不添加任何添加剂或软性粘合剂，可以使硬碳和石墨阳极的稳定充放电循环超过1次，000个周期（一年以上），退化程度可忽略不计；该性能可与常规可燃碳酸盐电解质相比或更高。浓电解质具有非同寻常的钝化特性以及其灭火特性，有助于开发安全耐用的电池，从而为开发更高能量密度的电池打开了无限的极限。