Synthesis and Characterization of the Lithium-Rich Core–Shell Cathodes with Low Irreversible Capacity and Mitigated Voltage Fade

Abstract

Lithium-rich layered Ni–Mn–Co oxide materials have been intensely studied in the past decade. Mn-rich materials have serious voltage fade issues, and the Ni-rich materials have poor thermal stability and readily oxidize the organic carbonate electrolyte. Core–shell (CS) strategies that use Ni-rich material as the core and Mn-rich materials as the shell can balance the pros and cons of these materials in a hybrid system. The lithium-rich CS materials introduced here show much improved overall electrochemical performance compared to the core-only and shell-only samples. Energy dispersive spectroscopy results show that there was diffusion of transition metals between the core and shell phases after sintering at 900 °C compared to the prepared hydroxide precursors. A Mn-rich shell was still maintained whereas the Co which was only in the shell in the precursor was approximately homogeneous throughout the particles. The CS samples with optimal lithium content showed low irreversible capacity (IRC), as well as high capacity and excellent capacity retention. Sample CS2-3 (the third sample in the 0.67Li1+x (Ni0.67Mn0.33)1–x O2·0.33Li1+y (Ni0.4Mn0.5Co0.1)1–y O2 CS2 series) had a reversible capacity of ∼218 mAh/g with 12.3% (∼30 mAh/g) irreversible capacity (IRC) and 98% capacity retention after 40 cycles to 4.6 V at 30 °C at a rate of ∼C/20. Differential capacity versus potential (dQ/dV versus V) analysis confirmed that cells of the CS samples had stable impedance as well as a very stable average voltage. Apparently, the Mn-rich shell can effectively protect the Ni-rich core from reactions with the electrolyte while the Ni-rich core renders a high and stable average voltage.

Comparison of Single Crystal and Polycrystalline LiNi0.5Mn0.3Co0.2O2Positive Electrode Materials for High Voltage Li-Ion Cells

“…Galvanostatic charge/discharge cycling using standard 2325 coin cells with lithium metal as the negative electrode was done using an E-One Moli Energy Canada battery testing system. All the cells were tested with a current density of 10 The details of the synthesis of similar precursors has been described by J. Li et al 37,38 The dried precursors were mixed with a stoichiometric equivalent of Li 2 CO 3 (from Umicore, >99%) by hand grinding using a mortar and pestle until a homogenous consistency was achieved (about 10-15 minutes). Samples with Li/transition metal (TM) ratios of 1.15, 1.20 and 1.25 were prepared.…”

Synthesis of Single Crystal LiNi0.5Mn0.3Co0.2O2for Lithium Ion Batteries

“…The details of the synthesis of similar precursors has been described by J. Li et al 10,11 Precursors with three different sizes, labelled as large (L), medium (M) and small (S), were prepared individually by adjusting the pH and stirring rate. Unless specified, precursor L was * Electrochemical Society Fellow.…”

The Effect of Interdiffusion on the Properties of Lithium-Rich Core-Shell Cathodes

“…21,22,36 Conversely, Figures 5b1, 5b2 and 5b3 show this plateau is barely noticeable in the CS20 series prepared at 900…”

“…[18][19][20] These have a high Ni content in the core and increasing Mn content from the core to the surface, with a maximum Mn content on the surface of ∼50%. In our previous report, 17,21 Li-rich and Mn-rich materials 22,23 were used as the protecting shell for voltages above 4.5 V. It was shown that the Li-rich and Mn-rich shell protected the Ni-rich core from reactions with the electrolyte while the Ni-rich core rendered a high and stable average voltage. 21 Diffusion of the cations between the core and shell phases occurs during sintering to prepare the NMC core-shell oxide.…”