【作者】 高珊；

【导师】 郭翠梨；

【作者基本信息】 天津大学 ， 化学工程与技术， 2021， 硕士

【摘要】 富镍层状正极材料LiNi_0.6Co_0.1Mn_0.3O₂（NCM613）具有能量密度高,成本低的优点,是一种非常有前景的正极材料,然而也存在着寿命短、倍率性能差等问题。针对以上问题,本研究制备了离子掺杂和表面包覆协同改性的NCM613正极材料,并研究了改性材料的结构性质以及在高截止电压的电化学性能,主要研究内容如下:采用固相法制备了B³⁺掺杂和LiBO₂包覆的NCM613正极材料,通过XRD、XPS、TEM等表征手段研究了改性对NCM613结构的影响。优选出的改性材料LBO-0.4在2.8-4.5 V,1C倍率下循环100次后容量保持率为94.8%,而未改性材料的保持率仅有79.7%;在高倍率5C下,经过1000次长周期循环后,LBO-0.4仍能放出100.5 mAh g^-1的容量,保持率为70.7%,远高于未改性样品不足1%的保持率。同时,B³⁺掺杂和LiBO₂包覆还提升了材料的锂离子扩散系数,降低了阻抗,提升了材料的倍率性能。次磷酸钠（NaH₂PO₂）在加热过程中分解产生还原性PH₃气体,本研究利用这个性质对富镍层状NCM613材料进行了改性,原位诱导NCM613表面的层状结构重构,转变成尖晶石和岩盐结构保护层,同时通过磷掺杂剂调节晶格参数。改性过程中原位形成的异质结构保护层与材料主体的层状结构兼容,在循环过程中不会脱落,有利于材料的长期循环稳定性。并且PO₄^3-掺杂和表面的尖晶石结构还有利于提升锂离子扩散速率。改性材料NCM613-0.3P和NCM613-0.6P在2.8-4.5 V的电压范围内,1C下经过700次循环后,分别有76.1%和77.3%的容量保持率,依然高于未改性材料200次循环后70.6%的容量保持率。NCM613-0.6P在5C下经过350次循环后,其容量保持率高达98.0%,而初始材料的容量保持率仅为25.7%。更多还原

【Abstract】 Nickel-rich layered cathodes LiNi_0.6Co_0.1Mn_0.3O₂（NCM613）are promising cathode materials because of their high energy density and low cost.However,they are facing problems such as short life and poor rate performance.In response to the above problems,this work prepared NCM613 cathode material modified by ion doping and surface coating,and studied the structural properties of the modified material and the electrochemical performance at high cut-off voltage.The main research content include:B³⁺doped and LiBO₂ coated NCM613 cathode material was prepared by solid state method.The effects of modification on the structure of NCM613 were studied by XRD,XPS,TEM and other characterization methods.The capacity retention of the optimized modified material LBO-0.4 is 94.8%after 100 cycles at 2.8-4.5 V and 1C,while the retention of the unmodified material is only 79.7%.At a high rate of 5C,LBO-0.4 can still discharge capacity of 100.5 mAh g^-1 after 1000 cycles and the retention is70.7%,which is much higher than that of the unmodified sample（less than 1%）.At the same time,B³⁺doping and LiBO₂ coating also improve the lithium ions diffusion coefficient,lower the impedance,and enhance the rate performance of the material.Sodium hypophosphite（NaH₂PO₂）is decomposed during heating to produce reducing PH₃ gas.In this work,the nickel-rich layered NCM613 material was modified by this property.The layered structure of NCM613 surface was reconstructed in situ and transformed into spinel and rock salt structure protective layer,and the lattice parameters are adjusted by phosphorus dopants.The heterogeneous structure protective layer formed in situ during the modification process is compatible with the layered structure of the material,and will not fall off during the cycle,which is beneficial to the long-term cycle stability of the material.The PO₄^3-doping and the spinel structure on the surface are beneficial to increase the lithium ions diffusion rate.Modified NCM613-0.3P and NCM613-0.6P exhibit the capacity retentions of 76.1%and 77.3%in the voltage range of 2.8-4.5 V,after 700 cycles at 1C,respectively,which are still higher than that of unmodified materials after 200 cycles,which is only 70.6%.And the NCM613-0.6P exhibits an impressive capacity retention of 98.0%after 350 cycles at5C,far superior to 25.7%of the pristine NCM613.更多还原