Stabilizing Effects on Structural and Thermal Properties of Al-Doped Ni-Rich Layered Oxides for Li Rechargeable Batteries
Authors: Jeong Mihee , Lee Wontae , Lee Eunkang , Yoon Won-Sub 
Published: December 2020

One of the key strategies to achieve high energy density for Li rechargeable batteries is through improved layered oxides cathode materials. Ni-rich layered oxides with Ni content above 80% have been under extensive attention as promising cathodes for next-generation Li-ion batteries due to the merits of high capacity, low cost, and low toxicity [1–3]. However, these materials still require further improvement to overcome inferior capacity retention and poor thermal stability originated from Ni-rich environments [1,4].

We investigated Al-doped LiNi0.80Co0.15Mn0.05O2 and undoped LiNi0.80Co0.15Mn0.05O2 layered cathodes in view of the structural, electrochemical, and thermal properties. Synchrotron-based X-ray techniques were used to analyze their structural behavior systematically during electrochemical reactions and thermal decomposition. High resolution powder diffraction (HRPD) results show that Al-doping in Ni-rich NCM cathode alleviates anisotropic lattice distortion and structural collapse as well as preserves a wider LiO6 interslab thickness, even at highly deintercalated states comparing to the undoped cathode. Al-doped Ni-rich cathode exhibits lower polarization potential, better rate capability, and cyclability compared to undoped one. This can be attributed to the alleviation of anisotropic lattice changes and volume changes during cycling. More importantly, Al-doped Ni-rich cathode maintains a wider LiO6 interslab thickness without collapse at highly charged states, allowing Li-ions to be deintercalated/intercalated reversibly. This indicates that rigid structural integrity contributes to enhanced electrochemical performance. Moreover, in situ X-ray diffraction (XRD) during the heating process and differential scanning calorimetry (DSC) analysis demonstrate that Al-doped NCM cathode outperforms bare NCM cathode significantly in terms of thermal aspects. Specially, Al-doping improves thermal stability by delaying the onset temperatures of phase transformations during the heating process. These results demonstrate that Al-doping plays a major role in stabilizing the structure by suppressing abrupt lattice changes during cycling and the formation of a rock-salt phase during thermal decomposition reaction.

Based on these experimental results, we will provide the structural evidence for the Al-doping effects on Ni-rich layered materials, thereby guiding for the strategical design factor in the development of layered cathodes with high performance. More detailed results and discussion will be presented in the PRiME 2020.

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