论文部分内容阅读
锂金属具有超高的理论容量(3860 mAh·g-1)、低氧化还原电位(-3.04 V)被认为是最具前途的负极材料之一.然而,锂枝晶生长、以及“死锂”等问题阻碍了其实际应用.发展亲锂载体来调控锂成核行为是抑制锂枝的有效方法.本工作中我们采用石墨烯负载的氧配位钴单原子(Co-O-G SA)作为锂沉积载体,调节锂的成核和生长行为.Co-O-G SA具有均匀的亲锂位点、高电导率、以及高表面积(519m2·g-1),可显著降低锂沉积过程中局部电流密度,提高锂在循环过程中的可逆性.因此,基于Co-O-GSA锂负极在电流密度为1 mA·cm-2,沉积容量1 mAh·cm-2时具有99.9％的库伦效率和优异的倍率性能,在8 mA·cm-2高电流密度下寿命达到1300 h.在对称电池中,Co-O-G SA锂负极(Co-O-G SA/Li)在1 mA·cm-2的电流密度下,电压稳定在18mV,寿命达到780h.当匹配硫正极,获得全电池在0.5C(1C=1675mA·g-1)的条件下,具有1002mAh·g-1的比容量,1000次循环过程中仅有0.036％的容量衰减率.本工作为通过调控单原子的配位环境来实现无枝晶锂负极提供了重要的见解.“,”Lithium(Li)-based batteries are the dominant energy source for consumer electronics,grid storage,and electrified transportation.However,the development of batteries based on graphite anodes is hindered by their limited energy density.With its ultrahigh theoretical capacity(3860 mAh·g-1),low redox potential(-3.04 V),and satisfactorily low density(0.54 g·cm-3),Li metal is the most promising anode for next-generation high-energy-density batteries.Unfortunately,the limited cycling life and safety issues raised by dendrite growth,unstable solid electrolyte interphase,and“dead Li”have inhibited their practical use.An effective strategy is to develop a suitable lithiophilic matrix for regulating initial Li nucleation behavior and controlling subsequent Li growth.Herein,single-atom cobalt coordinated to oxygen sites on graphene(Co-O-G SA)is demonstrated as a Li plating substrate to efficiently regulate Li metal nucleation and growth.Owing to its dense and more uniform lithiophilic sites than single-atom cobalt coordinated to nitrogen sites on graphene(Co-N-G SA),high electronic conductivity,and high specific surface area(519 m2.g-1),Co-O-G SA could significantly reduce the local current density and promote the reversibility of Li plating and stripping.As a result,the Co-O-G SA based Li anodes exhibited a high Coulombic efficiency of 99.9％at a current density of 1 mA·cm-2 with a capacity of 1 mAh·cm-2,and excellent rate capability(high current density of 8 mA·cm-2).Even at a high plating capacity of 6 mAh·cm-2,the Co-O-G SA electrode could stably cycle for an ultralong lifespan of 1300 h.In the symmetric battery,the Co-O-G SA based Li anode(Co-O-G SA/Li)possessed a stable voltage profile of 18 mV for 780 h at 1 mA·cm-2,and even at a high current density of 3 mA·cm-2,its overpotential maintained a small hysteresis of approximately 24 mV for＞550 h.Density functional theory calculations showed that the surface of Co-O-G SA had a stronger interaction with Li atoms with a larger binding energy,-3.1 eV,than that of Co-N-G SA(-2.5 eV),leading to a uniform distribution of metallic Li on the Co-O-G SA surface.More importantly,when matched with a sulfur cathode,the resulting Co-O-G SA/lithium sulfur full batteries exhibited a high capacity of 1002 mAh·g-1,improved kinetics with a small polarization of 191 mV,and an ultralow capacity decay rate of 0.036％ per cycle for 1000 cycles at 0.5C(1C=1675 Ma·g-1)with a steady Coulombic efficiency of nearly 100％.Therefore,this work provides novel insights into the coordination environment of single atoms for the chemistry of Li metal anodes for high-energy-density batteries.