钠离子电池Na_(0.62)K_(0.05)Mn_(0.7)Ni_(0.2)Co_(0.1)O_(2)正极材料:钾离子掺杂且{001}面稳定的中空多面体

Hollow Na_(0.62)K_(0.05)Mn_(0.7)Ni_(0.2)Co_(0.1)O_(2)polyhedra with exposed stable{001}facets and K riveting for sodium-ion batteries

钠离子电池中,正极材料至关重要,在很大程度上决定了整个电池的能量密度等性能.层状氧化物是钠离子电池中最有潜力的正极材料之一.然而,层状氧化物仍面临着不可逆相变、容量低、空气稳定性差和循环寿命短等缺点,限制了其实际应用.为了解决相关问题,本研究成功制备了中空结构的Na_(0.62)K_(0.05)Mn_(0.7)Ni_(0.2)Co_(0.1)O_(2)多面体正极材料.其中,少量的大尺寸钾离子实现了对材料中相应钠离子的取代;镍离子的较高氧化还原电位使得氧化物正极材料能够在空气中稳定保存.在100 mA g^(-1)电流密度下放电100次后,仍可保持115.0 mA h g^(-1)的放电比容量.在500 mA g^(-1)的较大电流密度下,材料仍然可实现104.1 mA h g^(-1)的较高放电比容量.研究结果表明,充放电过程中,氧化物正极材料的P2到O2的相变得到了有效地抑制.同时钾离子在层间的嵌入掺杂,使得氧化物正极的钠离子层间距增大,提升了钠离子的迁移速率.因此,Na_(0.62)K_(0.05)Mn_(0.7)Ni_(0.2)Co_(0.1)O_(2)应用于钠离子电池正极时展现出较大的吸引力和应用前景.

Recently,there has been an increased interest in sodium-ion batteries(SIBs),in which cathodes that directly determine the performance of batteries play a critical role.Among the cathode materials,layered oxide cathodes are the most fascinating electrode materials for SIBs.However,irreversible phase transition,low capacity,poor air stability,and inferior cycling stability limit the application of layered oxides.In this study,hollow P2-Na_(0.62)K_(0.05)Mn_(0.7)Ni_(0.2)Co_(0.1)O_(2)polyhedra consisting of nanosheets with exposed stable{001}facets and a small amount of large-size K+ions partly replacing Na+ions were successfully obtained.By virtue of the high redox potential of Ni2+/4+,it can be stored in air for several days.It also exhibits a high discharge capacity of115.0 mA h g^(-1)after 100 cycles at 100 mA g^(-1).A preeminent discharge capacity of 104.1 mA h g^(-1)can be achieved even at500 mA g^(-1).Results showed that such performances are related to the block of phase transition from P2 to O2 and to the riveting of K+ions,which expands the interlayer space(d(O-Na-O))and accelerates the transfer of sodium.Thus,the P2-Na_(0.62)K_(0.05)Mn_(0.7)Ni_(0.2)Co_(0.1)O_(2)cathode is one of the promising cathode materials for SIBs.