Boosting the electrochemical performance of LiNiO2 by extra low content of Mn-doping and its mechanism
Boosting the electrochemical performance of LiNiO2 by extra low content of Mn-doping and its mechanism
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DOI：
10.1016/j.electacta.2022.140345
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发表时间：
2022-04
影响因子：
6.6
通讯作者：
Tao Xu;Fanghui Du;Ling Wu;Zhongxu Fan;Lina Shen;Jun-chao Zheng
中科院分区：
文献类型：
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作者：
Tao Xu;Fanghui Du;Ling Wu;Zhongxu Fan;Lina Shen;Jun-chao Zheng
为新一代电动汽车开发高能量密度的无钴锂离子电池材料的迫切需求，促使人们对掺杂常量元素稳定的LiNiO2的研究产生了关注。在这些元素中，锰通常被用来稳定正极材料的晶体结构，以获得更好的电化学性能。然而，由于Mn掺杂引起的Li+/Ni2+阳离子无序对电化学行为的影响被忽略不计。为了阐明掺锰的确切效果，本文采用固相元素热互扩散的方法合成了超低锰含量的掺锰LiNiO2。在高温焙烧条件下，以包覆含锰凝胶的球形物种为前驱体，可以将锰均匀地掺杂到LiNiO2材料的骨架中。结果表明，少量的Mn掺杂可以很好地稳定LiNiO2的晶体结构和电化学循环过程中二次粒子的完整性，使材料具有良好的电化学循环性能和热稳定性。然而，由于在合成过程中形成了Li+/Ni2+阳离子混合，并在电化学循环中引入了Li+/Ni2+阳离子混合，因此材料的倍率性能强烈依赖于掺杂Mn的量。在微量掺杂的情况下，晶格的增大有利于Li+离子在晶体中的扩散。然而，掺锰量高的材料中Li+/Ni2+离子混合严重，使材料的倍率性能变差。因此，在这种情况下，最佳的Mn含量为4mol%，使材料在0.1C下的初始容量为202mAHg−1，在0.5C下200次循环后的容量保持率为85.41%。
The urgent demands of developing Co-free materials for lithium ion batteries with high energy density for next generation electric vehicles have driven the attention of researches to LiNiO2stabilized by doping of common elements. Among those elements, manganese is usually used to stabilize cathode material crystal structures to achieve better electrochemical performances. However, the Li+/Ni2+cation disorder causing by Mn doping is greatly neglected of the effect on electrochemical behaviors. In order to elucidate the exact effect of Mn-doping, herein, we synthesize Mn-doped LiNiO2with extra low Mn content by using the solid-state element thermal interdiffusion strategy. Under calcination at high temperature, with the spherical species coated with Mn-containing gel as the precursor, Mn can be evenly doped into the framework of LiNiO2material. It is demonstrated that the small amount of Mn-doping can greatly stabilize both the crystal structure of LiNiO2and integrity of the secondary particles during the electrochemical cycling to provide the excellent electrochemical cycling performance and thermal stability of the materials. Nevertheless, the rate capability of the materials is strongly dependent on the amount of the doped Mn, due to the Li+/Ni2+cation mixing formed in the synthesis process and introduced in the electrochemical cycling. In the presence of a tiny quantity of the doped Mn, the enlarged crystal lattice would be favorable to the diffusion of the Li+ions in the crystal. However, serious Li+/Ni2+cation mixing of the materials with high content of the Mn-doping deteriorates the rate performance of the materials. Thus, in this case, the Mn content is optimized to be 4 mol%, endowing the material with an initial capacity of 202 mAh g−1at 0.1 C, and a capacity retention of 85.41% after 200 cycles at 0.5 C. For the Mn-doped LiNiO2materials, it is suggested that to control the Li+/Ni2+cation mixing would be crucial for gaining the materials with superior electrochemical performance.