Abstract
Improving the interfacial stability between the electrode and the electrolyte at high voltage is a key to successfully obtain high energy-density Li-ion batteries. Therefore, this study is dedicated to a novel multifunctional electrolyte additive, methoxytriethyleneoxypropyltrimethoxysilane (MTE-TMS), able to stabilize the interface of both Ni-rich layered LiNi0.85Co0.1Mn0.05O2 (NCM851005) cathode and graphite anode in a full-cell. Electrochemical tests reveal that the addition of 1 wt% MTE-TMS significantly improves the long-term cycling stability of the graphite‖NCM851005 full-cell, with an achieved maximum capacity of 198 mAh g−1 and its excellent capacity retention of 84% after 100 cycles at C/5 using upper voltage cut-off of 4.3 V vs Li+/Li. In contrast, the standard electrolyte in absence of MTE-TMS leads to a rapid performance fade. The significantly improved electrochemical performance is attributed to the formation of a stable surface protective film at both the cathode and the anode surfaces upon long-term cycling in elevated voltage window, and thus suppressing the electrolyte decomposition at and structural degradation of both cathode and anode, resulting as well in reduced transition metal transfer between the two electrodes.
Highlights
Lithium-ion batteries (LIBs) are widely used for portable devices, electrical vehicles, large-scale energy storage systems, and are subject to ongoing modifications to meet the growing demands for higher energy and power densities [1,2]
This study is dedicated to a novel multifunctional electrolyte additive, methoxytriethyleneoxypropyltrimethoxysilane (MTE-TMS), able to stabilize the interface of both Ni-rich layered LiNi0.85Co0.1Mn0.05O2 (NCM851005) cathode and graphite anode in a full-cell
Large-scale application of Ni-rich NCM cathodes is hindered by severe capacity fading during long-term cycling, which is mainly caused by the instability of the Ni-rich NCM cathode–electrolyte interface at high-voltage, utilization of which would lead to higher energy densities [6,7,8,9,10]
Summary
Lithium-ion batteries (LIBs) are widely used for portable devices, electrical vehicles, large-scale energy storage systems, and are subject to ongoing modifications to meet the growing demands for higher energy and power densities [1,2]. The highly oxidized state of Ni4+, formed upon Li+-deintercalation, is spontaneously reduced to Ni3+ and Ni2+ by accepting electrons from the electrolyte, causing severe oxidative decomposition of the electrolyte at the cathode−electrolyte interface [6,7,8,10] This leads to the formation of nucleophilic fluoride (F−) species, which in turn can corrode the transition metals from Ni-rich NCM, causing the structure deterioration of cathode materials [11], when the standard LiPF6 salt is used. The similar radius of Li+ (0.76 Å) to Ni2+ (0.69 Å) leads to the intermixing of Ni and Li layers, which results in the well-known phase transition from layered hexagonal structure (R3̄m) to spinel (Fd3̄m) and to cubic rock-salt (Fm3̄m), causing oxygen release and safety issues [8,12] This electrochemically inactive rock-salt phase hinders the Li+ diffusion at the cathode–electrolyte interface, resulting in capacity fading. Effective methods to overcome the instability of the interface for the Ni-rich
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