Anionic Additive-Integrated Electrolyte Therapy: Enhancing High-Voltage Stability and Performance in Lithium-Ion Batteries

Abstract

Significant endeavours have been undertaken to advance the development of eco-friendly, abundant, cost-effective, and high-performance cathode materials for lithium-ion batteries. Among the various contenders for next-generation energy storage systems, spinel LiNi0.5Mn1.5O4 has emerged as a leading high-voltage cathode candidate, owing to its aforementioned benefits. Nonetheless, the widespread adoption of LNMO-based lithium-ion batteries is substantially impeded by the electrochemical instability of conventional carbonate electrolytes above 4.5 V. High-voltage cycling of such batteries results in rapid capacity degradation and metal-ion dissolution from the LNMO electrode into the electrolyte, particularly at elevated temperatures, further causing deposition of metal-ions on anode electrode. Therefore, stabilizing the electrode/electrolyte interface is crucial to achieve improved electrochemical performance of the Li-ion cell at high voltages. The utilization of sacrificial electrolyte additives is regarded as a straightforward and efficacious method to accomplish this objective. These additives form a protective layer on the cathode surface, mitigating electrolyte decomposition and transition metal-ion dissolution and deposition on anode’s surface. Various additives facilitating high-voltage cathode materials have been documented, encompassing fluorides and sulfonates. However, borate salt-containing additives are particularly promising within this context.In the present study, we endeavour to elucidate the surface modifications transpiring on the electrode’s surface when minute quantities of borate-based salt are employed as an additive in the conventional EC:EMC electrolyte for high-voltage operation. We explored the impact of the additive salt in a standard LiPF6-EC/EMC base electrolyte on the discharge capacity and rate performance of the LiNi0.5Mn1.5O4/Graphite based Li-ion cell. The electrochemical behaviour, morphological behaviour, and electrode-electrolyte interphase layer stability on the electrode were meticulously examined using high-resolution transmission electron microscopy (HR-TEM), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). These characterisations conformed the presence of an electrode-electrolyte interface forming a thin-layer via the sacrificial decomposition of the utilised additive. The introduction of this salt exhibits favourable effects on enhancing the electrochemical performance of the LiNi0.5Mn1.5O4/Graphite in high-voltage lithium-ion batteries. Notably, the utilised additive excels in mitigating irreversible capacity loss and reducing cycling fade, as it preferentially decomposes and forms a conductive, protective film that impedes subsequent electrolyte decomposition, thereby substantially enhancing cell performance.