Understanding Transition-Metal Dissolution Behavior in LiNi_0.5Mn_1.5O₄ High-Voltage Spinel for Lithium Ion Batteries

Abstract

The high-voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) spinel is a promising candidate for a positive electrode in lithium ion batteries, but LNMO/graphite full-cells display severe capacity fading issues due to Mn dissolution. In this study, the dissolution behaviors of Mn and Ni were examined systematically under various conditions such as state of charge (SOC), temperature, storage time, and crystal structure of LNMO. In addition, surfaces of calendar-or cycle-aged LNMO and graphite electrodes were analyzed by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), or time-of-flight secondary ion mass spectrometry (TOF-SIMS). The chemical composition of aged electrolyte was determined by gas chromatography (GC) analysis after storage of LNMO electrodes under different conditions. It was found that the amounts of dissolved Mn and Ni and diethyl ether, a decomposition product of diethyl carbonate (DEC) in electrolyte, increased with SOC, temperature, and storage time. The decomposition of electrolyte can be explained, in part, by the self-discharge behavior of LNMO, which promotes electrolyte oxidation. Additional HF is believed to be generated during the formation of diethyl ether (via dehydration reaction from EtOH, another decomposition product of DEC), which accelerates Mn and Ni dissolution from LNMO. In addition, various reaction products that form as a result of Mn and Ni dissolution, such as LiF, MnF 2 , NiF 2 , and polymerized organic species, were found on the surface of LNMO electrodes, which will increase battery-cell impedance.

Probing the Electrode-Electrolyte Interface in Cycled LiNi0.5Mn1.5O4by XPS Using Mg and Synchrotron X-rays

“…Raman, EIS and FT-IR measurements are not specifically sensitive to the surface chemistry of parasitic species formed during electrochemical conditioning, and conventional, lab-based XPS probes only ∼ 2 nm of product, whereas EEI thicknesses are typically larger. Such information is critical for understanding the relative contributions of electrolyte decomposition 10,13,14 and transition metal dissolution 15,16 to the EEI and capacity fade, about which there is considerable debate. In this study, we used X-ray photoelectron spectroscopy (XPS) spectra collected with conventional and synchrotron X-rays at different excitation energies to study the depth distribution of various chemical species of the EEI in Li/LNMO cells after 5 and 10 cycles.…”

Developing New Functionalities of Superconcentrated Electrolytes for Lithium-ion Batteries

“…42 Based on this idea, we next applied the salt-concentrating strategy to a nextgeneration 5 V-class positive electrode, spinel LiNi 0.5 Mn 1.5 O 4 , 23 which has suffered from transition-metal dissolution in the presence of HF. 47 Here we adopted a low-dielectric solvent, DMC, which is only weakly coordinated with cations, with the aim of minimizing the oxidative dissolution of Al cations at such high potentials as 5 V vs. Li + /Li. Figure 7 shows the charge-discharge performances of LiNi 0.5 Mn 1.5 O 4 /graphite full cells at 40°C.…”

Surface stability of spinel MgNi0.5Mn1.5O4 and MgMn2O4 as cathode materials for magnesium ion batteries

“…In order to determine whether the Ni dopant prefers to segregate at the surface or not, we calculated the formation energy of a Ni atom replacement of a Mn atom in the MMO slabs with stable surface. The formation energy was calculated using [49], Mn dissolution is believed to be the main cause of capacity degradation of the LiMn 2 O 4 [50][51][52], which is also responsible for the charge capacity fading of MnO 2 used as cathode of MIBs [8]. In order to solve this problem, surface modification of the cathode electrode is an effective way to reduce the side reactions.…”