Ultra-Thin AlPO4 Layer Coated LiNi0.7Co0.15Mn0.15O2 Cathodes With Enhanced High-Voltage and High-Temperature Performance for Lithium-Ion Half/Full Batteries.

Wei Li,Hao Pan,Jia Guo,Yunjiao Li,Lishan Yang,Xiaoming Xi,Jie Zhu,Yongxiang Chen

doi:10.3389/fchem.2020.00597

Abstract

Side-reactions in LiNi1−x-yCoxMnyO2 (0≤−x+y≤1) cathode materials are one kind of the problems that would deteriorate the surface structure and the electrochemical stabilities of the cathodes, especially when they are working at high cut-off voltages and high temperatures. In this study, an ultrathin (~10 nm) AlPO4 coating layer was fabricated through a two-step “feeding” process on LiNi0.7Co0.15Mn0.15O2 (NCM) cathode materials. The structure and chemical composition of the AlPO4 coating were studied by XRD, SEM, TEM, and XPS characterizations. Further electrochemical testing revealed that the AlPO4-coated LiNi0.7Co0.15Mn0.15O2 cathode exhibited enhanced electrochemical stabilities in the case of high cut-off voltage at both 25 and 55°C. In detail, the AlPO4-coated LiNi0.7Co0.15Mn0.15O2 could deliver 186.50 mAh g−1 with 81.5% capacity retention after 100 cycles at 1C over 3–4.5 V in coin cell, far higher than the 71.4% capacity retention of the pristine electrode. In prismatic full cell, the coated sample also kept 89.5% capacity retention at 25°C and 81.1% capacity retention at 55°C even after 300 cycles (2.75–4.35 V, 1C), showing better cycling stability than that of the pristine NCM. The ultrathin AlPO4 coating could not only keep the bulk structure stability from the surface degradation, but also diminishes the electrochemical resistance varies after cycles, thereby supporting the coated cathodes with enhanced electrochemical stability.

Highlights

To satisfy the urgently demand in continuously rising power density and energy for the Li-ion battery, high capacity cathode materials have been extensively studied by enterprises and research institutions (Konarov et al, 2017; Li et al, 2017; Hu et al, 2018; Bianchini et al, 2019; Zhao et al, 2020)
The discharge capacity increased from 163 mAh g−1 for LiNi1/3Co1/3Mn1/3O2 to 194 mAh g−1 for LiNi0.8Co0.1Mn0.1O2 in the potential range between 3.0 and 4.3 V (Noh et al, 2013)
Pristine LiNi0.7Co0.15Mn0.15O2 (NCM) materials were synthesized by mixing LiOH·H2O (Analytical grade, Tianqi Lithium Co., LTD, China) and commercial Ni0.7Co0.15Mn0.15(OH)2 (Hunan Brunep Recycling Corp., China) precursor with a molar ratio of 1.04:1 and calcining at 820◦C in O2 flow for 10 h

Summary

Introduction

To satisfy the urgently demand in continuously rising power density and energy for the Li-ion battery, high capacity cathode materials have been extensively studied by enterprises and research institutions (Konarov et al, 2017; Li et al, 2017; Hu et al, 2018; Bianchini et al, 2019; Zhao et al, 2020). Among the most promising cathode materials, LiNi1−x-yCoxMnyO2 (0≤−x+y≤1) are likely to achieve higher discharge capacities by improving both the nickel content and the cut-off. Electrochemical Stability of NCM Cathodes potentials (Noh et al, 2013; Du et al, 2015; Zeng et al, 2019). The discharge capacity increased from 163 mAh g−1 for LiNi1/3Co1/3Mn1/3O2 to 194 mAh g−1 for LiNi0.8Co0.1Mn0.1O2 in the potential range between 3.0 and 4.3 V (vs Li/Li+) (Noh et al, 2013). To up-regulate capacity, a higher potential is required, whereas the higher cut-off potential of LiNi1-x-yCoxMnyO2 is limited by significant capacity fading (Yang et al, 2013; Song et al, 2017; Chen et al, 2018; Lu et al, 2019). The conventional electrolyte can be oxidized at the cathode surface due to the presence of highly reactive Ni4+

Methods

Results

Conclusion