Semi-liquid anode for dendrite-free K-ion and Na-ion batteries

Herein a semi-liquid anode (SLA) with a main body of solid metal sodium (Na) or potassium (K) and a thin layer of liquid K-Na alloy anode (LAA) on its surface for sodium ion battery (SIB) or potassium ion battery (PIB) has been developed. It is found that only a thin layer of liquid alloy is enough to suppress dendrite growth. Solid metal of SLA provides continuous carrier source for electrochemical reactions and liquid alloy, keeping it abundant in Na/K content. The electrode would gain more stability and less resistance in this way. Also, this solid part supports fluid liquid alloy, saving much space and weight. SLA is also freed from the tedious and dangerous process of embedding liquid K-Na alloy into skeletal structures. With higher binding force between liquid and solid part, the SLA has better stability than LAA, enabling it to stay stable in all tested electrolyte solvents. The batteries with SLAs have long life spans of more than 1500 h, as well as good cycling and rate performance as full cells, which exhibited high specific capacities of 105 mAh/g (for PIB) and 120 mAh/g (for SIB) after harsh incremental current shock test of as large as 1000 mA/g. SLA has much better electrochemical performance than all-liquid anode and solid Na/K. It will inspire new thoughts to utilize liquid alloy in more practical ways and boost the commercialization of SIB and PIB.