Spontaneous Li-Ion Transfer from Spinel Li₄Ti₅O₁₂Surfaces: Deterioration at Li₄Ti₅O₁₂/Electrolyte Interfaces Stored at Room Temperature

Abstract

Spinel lithium titanium oxide (LTO; Li 4 Ti 5 O 12 ) is one of attractive negative electrode materials for high-performance lithium-ion batteries. We studied the changes of LTO-electrode surfaces in contact with liquid electrolytes without electrochemical operation, as the basic state of a stored cell. The electrochemical properties of the LTO-crystal electrode were greatly deteriorated after soaking in a liquid electrolyte (1 M LiPF 6 in PC) for 2 weeks at room temperature. Spinel LTO structure was changed into rock-salt like structure at the surface region. Spinel lithium titanate (LTO; Li 4 Ti 5 O 12 ) is one of the attractive negative electrode materials for high-performance lithium-ion batteries (LIBs), due to its superior cycle stability with high-rate chargedischarge performance.1 These excellent properties of LTO are concerned with the negligible lattice-parameter change and the simple phase conversion mechanism between the spinel LTO phase and the Li-inserted LTO phase (Li 7 Ti 5 O 12 ) with ordered rock-salt structure. 2,3The chemical stability or electrochemical durability of LTO-based electrodes is crucial to design high-performance LIBs for power sources of electrical vehicles or for large-scale energy storage, which requires high safety, long-life performance, and robustness. For this purpose, we have to understand not only the bulk-electrode phenomena, but also the phenomena at solid-electrode/liquid-electrolyte interfaces, such as solvation-desolvation, Li-ion absorption-desorption, and transfer as well as so-called solid electrolyte interface (SEI) formation. For LTO/liquid-electrolyte interfaces, several studies were performed under some electrochemical conditions. The reactions at LTO surfaces in contact with liquid electrolytes were also investigated in our previously study. 4 We revealed irreversible surface morphology changes during the 1st charge-discharge cycle. After the 1 st cycle, we observed the generation of the surface layer of a Li-rich phase (Li 2 TiO 3 ) with cubic rock-salt structure. 4 This surface layer on a LTO crystal would be some kind of SEI and contribute to the stability or efficiency of charge-discharge cycles. While the electrochemical reactions or associated structural changes at electrode surfaces have been studied under the electrochemical operation, the reactions or associated changes in the static condition are also important to fully understand the performance of electrodes. Especially, the basic interactions between electrode surfaces and liquid electrolytes before or after the charge-discharge operation should greatly affect a lot of battery phenomena, such as self-discharging, 5 alternation of electrode materials and electrolyte, 6-9 decomposition of electrolyte molecules and gas-generation, 5,10-12 which often lead to the deterioration of electrochemical performance and safety of battery cells. 13,14 As for the LTO-electrode/liquid-electrolyte interfaces in the static condition, the decomposition reaction of solvate molecules and the structural changes at ele...

Challenges of Spinel Li4Ti5O12 for Lithium‐Ion Battery Industrial Applications

“…Gao et al [149] calculated the surface work function using density functional theory (DFT). From electron energyloss spectroscopy with scanning-TEM mode (STEM-EELS) observations, Kitta et al [151] clarified that the Li-rich phase is a rock-salt-like disordered spinel phase (Figure 11b). The Li-rich surface causes the chemical potential to approach or even reach the LUMO of the electrolyte, especially with the assistance of temperature excitation.…”

“…Li et al [157] selected phenolic resin as the carbon source and prepared an in situ carbon-coated Adv. [151] Copyright 2015, The Electrochemical Society. 2017, 7, 1601625 www.advenergymat.de www.advancedsciencenews.com (right) Expected structure of the disordered-spinel phase.…”

Scaling up “Nano” Li4Ti5O12for High-Power Lithium-Ion Anodes Using Large Scale Flame Spray Pyrolysis

“…As apparent from the corresponding potential profiles (Figure 7b), this low efficiency is basically related to the occurrence of irreversible reactions during the constant voltage (CV) step applied after discharge to 1.0 V, presumably related to side reactions at the electrode/electrolyte interface, i.e., electrolyte decomposition. 34,[45][46][47] Indeed, the irreversible capacity recorded during the CV step accounts for about 10%, 18%, and 20% for PAA-, CMC-, and PVdF-based electrodes, respectively. The large differences (stressed by the application of a CV step at 1.0 V) highlight the substantial impact of the utilized binder on the electrode/electrolyte interface stability and suggest that it is decreasing in the order PAA > CMC > PVdF.…”

Effect of Pre-Cycling Rate on the Passivating Ability of Surface Films on Li4Ti5O12 Electrodes

“…Many previous works have reported that the voltage corresponding to the reaction of LTO with lithium (1.55 V vs. Li/Li + ) is too high to reductively decompose electrolytes. However, recent studies have demonstrated that electrolyte decomposition does occur and generates surface films on the LTO surface, even when the cell is operated within the stability window of the common salts and solvents used in LIBs [23][24][25][26][27][28]. Song et al [27] reported the formation of a surface film on an LTO surface, which is significantly enhanced by the presence of conductive carbon in the composite LTO electrodes.…”

“…Song et al [27] reported the formation of a surface film on an LTO surface, which is significantly enhanced by the presence of conductive carbon in the composite LTO electrodes. Kitta et al [25,28] found that the SEI layer generated during the first cycle prevents irreversible structural changes on the LTO surface. He et al [24,26] reported gas evolution accompanied by electrolyte decomposition on the LTO surface and concomitant film formation.…”