An Ultra‐Long‐Life Lithium‐Rich Li_1.2Mn_0.6Ni_0.2O₂ Cathode by Three‐in‐One Surface Modification for Lithium‐Ion Batteries

Abstract

Voltage decay and capacity fading are the main challenges for the commercialization of Li‐rich Mn‐based layered oxides (LLOs). Now, a three‐in‐one surface treatment is designed via the pyrolysis of urea to improve the voltage and capacity stability of Li1.2Mn0.6Ni0.2O2 (LMNO), by which oxygen vacancies, spinel phase integration, and N‐doped carbon nanolayers are synchronously built on the surface of LMNO microspheres. Oxygen vacancies and spinel phase integration suppress irreversible O2 release and help lithium ion diffusion, while N‐doped carbon nanolayer mitigates the corrosion of electrolyte with excellent conductivity. The electrochemical performance of LMNO after the treatment improves significantly; the capacity retention rate after 500 cycles at 1 C is still as high as 89.9 % with a very small voltage fading rate of 1.09 mV cycle−1. This three‐in‐one surface treatment strategy can suppress the voltage decay and capacity fading of LLOs.

Pseudo‐Bonding and Electric‐Field Harmony for Li‐Rich Mn‐Based Oxide Cathode

“…The oxidation peaks at about 4.0 V in cyclic voltammetry (CV) curves for all samples shown in Figure S6A–D, Supporting Information, are assigned to the slope region between 2.0 and 4.5 V in Figure 5A, resulted from the oxidation procedure of Ni 2+ /Co 3+ to Ni 4+ /Co 4+ along with the deintercalation of Li + from the lithium layer. [ 9b ] Moreover, the oxidation peaks at about 2.7 V, mainly originated from the Mn 3+ /Mn 4+ of the S ‐LMO, are obviously noticed for the modified samples but not observed for the pristine sample, demonstrating that the synchronous lithium oxidation strategy has successfully induced the formation of S ‐LMO (Figures S6B–D and S6F–H, Supporting Information). [ 31 ] Besides, the representative discharge plateau of the S ‐LMO shown in Figure 5A, further verifies the formation of the S ‐LMO and agrees well with the XRD results, which is beneficial for arousing the ISE.…”

“…These processes are accompanied with the evolution of lattice oxygen anions, corresponding to the most substantial oxidation peak at about 4.6 V in the CV curves. [ 13b,13c,32 ] It is apparent that the lowest voltage gap is detected in sample 3% LCO, indicating that the linkage‐functionalized modification accelerates the kinetics of the corresponding redox reaction, (Figure S7A, Supporting Information), [ 9b ] which is conducive to improve the rate performance. Note that the CV curves of the initial three cycles for 3% LCO are rarely changed, while those of the other samples are varied seriously, suggesting that a highly reversible structure transition process is presented for the 3% LCO electrode during the cycling process.…”

“…It is noticed that the peak around 3.0 V is gradually shifted to a lower potential, indicating that the LMO undergoes a phase transition from the superstructure to the spinel structure ascribed to the migration of Mn and the Jahn–Teller distortion of [MnO 6 ] octahedral, which was also observed in previous studies. [ 7a,9a ] In addition, a linear relationship of potential (V) versus scan rate (mV s −1 ) is presented, and the slope can be regarded as a parameter to assess the relative rate of phase transformation as displayed in Figure S7C, Supporting Information. The transformation rate (the slope) of 3% LCO is about ‐0.5933, much larger than that of the pristine sample (−1.1889), 1% LCO (−0.7154), and 5% LCO (−0.6056), demonstrating its optimized structure stability.…”

“…[ 1b,8 ] However, most spinel layer can only render one of the advantages in electronic and ion conductivity, whereas the application of linkage‐functionalized modification, which unites doping, phase induction, and coating, can manipulate both electronic and ion conductivity of the material. [ 6b,9 ]…”

Accurate Control of Initial Coulombic Efficiency for Lithium‐rich Manganese‐based Layered Oxides by Surface Multicomponent Integration

“…Raman spectroscopy was performed to identify surface structure (Figure 1 f–k; Supporting Information, Figure S5). For PL sample, two distinct and strong peaks around 485 cm −1 and 590 cm −1 represent the bending E g and stretching A 1g modes of the layered structure, [2a] and the peak at about 415 cm −1 is assigned to an A g mode of the monoclinic Li 2 MnO 3 phase [6] . The red shift of A 1g vibrations for NH 4 F treated samples indicates the formation of spinel phase, [6, 12] which is hard to detect by XRD due to low crystallinity.…”