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.

Our main objective in this tutorial review is to provide insight into some of the questions surrounding single molecule detection (SMD) using surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS). Discovered thirty years ago, SERS is now a powerful analytical tool, strongly tied to plasmonics, a field that encompasses and profits from the optical enhancement found in nanostructures that support localized plasmon excitations. The spectrum of the single molecule carries the quantum fingerprints of the system modulated by the molecule-nanostructure interactions and the electronic resonances that may result under laser excitation. This information is embedded in vibrational band parameters. The dynamics and the molecular environment will affect the bandwidth of the observed Raman bands. In addition, the localized surface plasmon resonances (LSPR) empower the nanostructure with a number of optical properties that will also leave their mark on the observed inelastic scattering process. Therefore, controlling size, shape and the formation of the aggregation state (or fractality) of certain metallic nanostructures becomes a main task for experimental SERS/SERRS. This molecule-nanostructure coupling may, inevitably, lead to spectral fluctuations, increase photobleaching or photochemistry. An attempt is made here to guide the interpretation of this wealth of information when approaching the single molecule regime.

Lithium-ion (Li-ion) batteries have been developed for electric vehicle (EV) applications, owing to their high energy density. Recent research and development efforts have been devoted to finding the next generation of cathode materials for Li-ion batteries to extend the driving distance of EVs and lower their cost. LiNi(0.5)Mn(1.5)O(4) (LNMO) high-voltage spinel is a promising candidate for a next-generation cathode material based on its high operating voltage (4.75 V vs. Li), potentially low material cost, and excellent rate capability. Over the last decade, much research effort has focused on achieving a fundamental understanding of the structure-property relationship in LNMO materials. Recent studies, however, demonstrated that the most critical barrier for the commercialization of high-voltage spinel Li-ion batteries is electrolyte decomposition and concurrent degradative reactions at electrode/electrolyte interfaces, which results in poor cycle life for LNMO/graphite full cells. Despite scattered reports addressing these processes in high-voltage spinel full cells, they have not been consolidated into a systematic review article. With this perspective, emphasis is placed herein on describing the challenges and the various approaches to mitigate electrolyte decomposition and other degradative reactions in high-voltage spinel cathodes in full cells.

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