氟化物和硼酸复合包覆对高镍正极性能的影响

Effect of fluoride and H3BO3 dual-coating on high-nickel cathode materials

高镍三元材料能量密度高和成本低,但使用中经常遭受性能衰退问题,这限制了其大规模应用。金属氟化物经常被用来包覆正极材料以改善其电化学性能,但其制备过程复杂、包覆层不均匀、可能生成强腐蚀性气体等。提供了一种简单通用的复合包覆策略,实现了高镍三元正极材料的均匀包覆并增强了其电化学性能。利用一步球磨法在高镍材料表面包覆了薄且均匀的氟化铈和硼酸锂涂层。该复合涂层没有影响材料的层状结构,反而促进了Li^(+)的脱出和嵌入过程。同时,均匀致密的涂层可以充当保护层以阻挡电解液腐蚀,减轻了电极与电解液之间的副反应带来的不利影响。因此,改性正极发挥了205.1 mAh/g的高比容量(裸样为198.0 mAh/g)和45℃循环300次后91.5%的容量保持率(市售样品为88.3%)。进一步使用其他常见的氟化物代替氟化铈,达到了类似的改善效果,特别是存储产气性能。这为设计商业化应用的高镍正极材料提供了一条通用的思路和有益的借鉴。

Recently,high-nickel ternary materials(Li[Ni_(1-x-y)Co_(x)Mn_(y)]O_(2),NCM)have the advantages of high energy density and low cost.However,they often suffer from degradation problems,limiting their large-scale applications.Metal fluorides are frequently used to coat the cathode materials to improve their electrochemical performances,but they have some flaws including complex processing process,uneven coating layer and strong corrosive gas produced during use.We proposed an effective dual-modification strategy to achieve uniform coating and thus enhance electrochemical performances of the cathode materials.The thin and uniform coating consisting of CeF_(3) and lithium boron oxide were formed on the surface of the NCM materials by a simple method.The composite coating did not affect the layered structure,but promote the intercalation and deintercalation process of Li^(+).Meanwhile,the coating served as a protective layer from electrolyte corrosion,thus alleviating the side reactions between electrodes and electrolytes.Therefore,the modified cathode delivers a higher specific capacity of 205.1 mAh/g(the bare NCM:198.0 mAh/g),and a better capacity retention of 91.5%in pouch cells after 300 cycles at 45℃(the commercial NCM:88.3%).Furthermore,similar improvements were achieved with the replacement of CeF_(3) with other fluorides,especially the storage performances.This work provides a general strategy and useful reference for the design of highnickel cathodes suitable for commercial applications.