Cathodic reduction of graphite in organic solutions of alkali and NR4+ salts

Density functional theory (DFT) was used to investigate the effect of electrolyte additives such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl ethylene sulfite (VES), and ethylene sulfite (ES) in propylene carbonate (PC)-based Li-ion battery electrolytes on SEI formation at graphitic anodes. The higher desolvation energy of PC limits Li + intercalation into graphite compared to solvated Li + in EC. Li + (PC) 3 clusters are found to be unstable with graphite intercalation compounds and become structurally deformed, preventing decomposition mechanisms and associated SEI formation in favor of co-intercalation that leads to exfoliation. DFT calculations demonstrate that the reduction decomposition of PC and electrolyte additives is such that the first electron reduction energies scale as ES > VES > VEC >PC. The second electron reduction follows ES > VES > VEC > VC > PC. The reactivity of the additives under consideration follows ES > VES > VEC > VC. The data demonstrate the supportive role of certain additives, particularly sulfites, in PC-based electrolytes for SEI film formation and stable cycling at graphitic carbon-based Li-ion battery anodes without exfoliation or degradation of the anode structure. The lithium ion battery has been one of the primary power sources driving the digital age, and witnessed a resurgence in interest with the advent of nanoscale materials and advances in cell performance. [1][2][3][4][5][6] Much of the processes and mechanisms underpinning carbonate-based electrolytes in Li-ion batteries, particularly at the anode, still need to be resolved. 7,8 Some commonly used organic solvents are ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) etc. These organic electrolytes are decomposed during intercalation of lithium ions into graphite anode, resulting in the formation of the crucial solid electrolyte interphase (SEI) film. [9][10][11] This film plays an important role in determining capacity retention, cycle life and safety concerns in lithium ion batteries.12,13 SEI films typically comprise Li 2 O, Li 2 CO 3 and related carbonates, LiF (depending on salt used), and polymer phases together with olefins.14 Effective SEI films provide stable surface passivation without significant reduction in electron conduction (higher transfer resistance). On carbon (graphite) anodes, stable SEI films are crucial for stable cycling and are formed below ∼0.8 V vs. Li + /Li. In practical applications of lithium-ion batteries, the selection of the electrode material is critical, particularly when using high surface area nanomaterials. 15 Enhanced chemical stability against electrolyte oxidation and reduction, high ionic conductivity, high boiling points, and low melting points are required, as well as the ability to solvate a wide range of lithium salts such as LiPF 6 , LiBF 4 or LiClO 4 , 16-21 in aprotic and organic solvents such as ethylene carbonate (EC), propylene carbonate (PC), their mixtures, and ...

mentioning

confidence: 99%

The Role of Carbonate and Sulfite Additives in Propylene Carbonate-Based Electrolytes on the Formation of SEI Layers at Graphitic Li-Ion Battery Anodes

Bhatt¹,

O’Dwyer²

2014

“…carbon and later graphite. 20,21 The marketing term lithium ion batteries (LIB) was coined by Sony with the commercialization in 1991. 3 LIB have taken the battery market by storm.…”

Section: Lithium Cobalt Oxide; Licoomentioning

confidence: 99%

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes

Schipper

Erickson

Erk

et al. 2016

648

497

Lithium ion batteries have become an integral part of our daily lives. Among a number of different cathode materials nickel-rich LiNi x Co y Mn z O 2 is particularly interesting. The material can deliver high capacities of ∼195 mAh g −1 putting it on the map for electric vehicles. With an increasing nickel content, a number of issues arise in the material limiting its performance. The Li/Ni mixing, highly reactive surface and formation of micro cracks are the most pressing ones. An overview of recent literature exploring these phenomena is herein summarized and were applicable solutions will be highlighted. With the advent of lithium ion batteries (LIB) in 1991 came a rapidly increasing development of consumer electronics.1,2 Soon LIB were the power source of choice for manufacturer of laptop computers and cell phones. While smart phones are getting smaller and have to operate more energy demanding applications LIB have to keep up with the pace. Cell manufactures have developed more refined ways to assemble cells leading to high energy densities of modern LIB for consumer applications. 3,4 In the meantime, scientists have developed better active materials and are constantly improving over existing ones. 5 The early LIB used lithium cobalt oxide (LCO) as cathode and graphite as anode material. LCO has a high tap density making it an ideal choice for small devices. The battery market has grown tremendously over the last 35 years and is expected to increase even more rapidly within the next years. 6 With the new market segment of electrical vehicles (EV) becoming more important every year LIB have found an additional application with a huge potential. Even though fuel cells are a natural competitor for LIB the large commitment necessary to build a hydrogen infrastructure plays into the hands of eager battery suppliers.Electrical propulsion needs battery materials with high capacities to satisfy consumer demands of a ∼500 km driving range long cycle life.4,7 Several materials have been identified as viable candidates for EVs ranging from layered mixed transition metal oxides, layered lithium rich materials and lithium sulfur batteries. [8][9][10][11] The technologically most advanced material option is layered nickel rich LiNi x Co y Mn z O 2 (NCM, x > 0.6) cathodes. The current generation of some EVs is already employing NCM523. Unfortunately, the implementation of higher nickel contents still needs to overcome a number of challenges to be viable. The review at hand will outline the development of the NCM material family with the first emphasis being on the individual endmembers LiCoO 2 , LiNiO 2 and LiMnO 2 . Problems and recent advances of these materials will be outlined. The second emphasis will be on the layered material LiNi x Co y Mn z O 2 with a focus on nickel rich materials. Problems and attempted solutions to mitigate them will be presented.= These authors contributed equally to this work.* Electrochemical Society Fellow. z E-mail: schippf@biu.ac.il Lithium Cobalt Oxide; LiCoO 2The first lithium intercal...

“…Monomers, dimers, and trimers of phosphate esters were detected with a high homology rate. These products resulted from the decomposition of carbonate compounds and LiPF 6 . Several MS E data are shown in Figure 8.…”

Section: Analysis Of Mass Spectrometry By Lc-qtof/ms-mentioning

confidence: 99%

Liquid Chromatography-Quadruple Time of Flight Mass Spectrometry Analysis of Products in Degraded Lithium-Ion Batteries

Tochihara

Nara

Mukoyama

et al. 2015

The electrode surfaces of degraded lithium-ion batteries (LIB) were analyzed by liquid chromatography-quadrupole time of flight mass spectrometry (LC-QTOF/MS). The solid-electrolyte interphase (SEI) layer influences the performance of LIBs. Therefore, we conducted a study aimed at clarifying the deterioration mechanism of LIBs by examining the components in the SEI before and after degradation due to cycling. We believe that the change in the mass transfer characteristics at the electrode interface influenced by SEI deterioration can be clarified via LC-QTOF/MS, which would allow elucidation of the deterioration mechanism. The analysis results showed that the degradation products contain multiple components, including polymers of carbonate compounds and phosphate esters, which are formed via electrochemical and chemical reactions, resulting in remarkably reduced capacity. Since the invention of lithium-ion batteries (LIB), many research groups have actively conducted research on improving the battery performance.1-7 Excellent properties, including high capacity and high energy density, have been achieved owing to the work conducted so far. As a result, LIBs are not only used as power sources for mobile devices such as phones and personal computers, but are also used as power sources in electric vehicles, aviation, etc., as well as large-scale stationary power sources for smart grids. [8][9][10] Owing to the remarkable expansion in their applications, it is necessary that LIBs are highly durable and safe in various environments; as a result, durability tests for LIBs have been conducted under diverse settings. In addition, the battery deterioration mechanisms in various cases have been widely studied. 11-13To accurately understand the deterioration mechanism, it is necessary to utilize precise mass spectrometry techniques to determine the structure and composition of materials present at the electrode interface, including the electrode surface layer (i.e., solid electrolyte interface or SEI). By conducting a proper structural analysis, the deterioration mechanism can be discussed in terms of the exact reactions occurring at the interface. The chief analytical techniques that are used to structurally analyze the SEI layer include X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and nuclear magnetic resonance spectroscopy (NMR). 14-21All of these techniques enable the estimation of the skeletal structures of the compounds present in the SEI. However, since the structural formula obtained by these techniques is not supported by precise mass information, the exact reactions governing the deterioration mechanism cannot be deduced from these techniques. On the other hand, the use of precise mass spectrometry for analyzing the electrode interface, including the SEI layer, may allow accurate elucidation of the degradation behavior at the electrode interface by distinguishing between the degradation components and the components of the intrinsic SEI layer. Further, methods for suppr...