New insights into a high potential spinel and alkylcarbonate-based electrolytes

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Pyridine sulfur trioxide (PyrSO 3 ), trimethyl amine sulfur trioxide (Me 3 NSO 3 ), and triethyl amine sulfur trioxide (Et 3 NSO 3 ) complexes have been investigated as electrolyte additives for lithium ion batteries. Incorporation of 0.5 to 2.0% of the SO 3 complexes into a PC/EMC (1:1 v/v) 1 M LiPF 6 baseline electrolyte affords reversible cycling of graphite anodes confirming generation of a stable Solid Electrolyte Interphase (SEI). Good cycling performance is observed for graphite/LiNi 0.5 Mn 1.5 O 4 cells cycled to high potential (4.8 V vs Li) containing PC based electrolyte with added SO 3 complexes. Ex-situ surface analysis via X-ray Photoelectron Spectroscopy (XPS) of the anodes reveals SO 3 complex reduction on the surface of the graphite anode generates a sulfur-based SEI containing sulfites, sulfide, and sulfate species. The presence of the sulfur containing species is likely critical for the stability of the SEI. Ex-situ XPS analyses of the LiNi 0.5 Mn 1.5 O 4 cathodes suggest that reaction of Me 3 NSO 3 or Et 3 NSO 3 complexes at high potential result in the generation of a stable passivation layer which affords good capacity retention and coulombic efficiency. The standard anode material in most commercial lithium ion batteries is graphite due to good specific capacity, low volumetric expansion upon Li + intercalation, relatively flat potential profile, excellent cyclability, and low cost. However, the reduction potential of lithiated graphite is below the stability window of most organic solvents and thus requires the formation of a Solid Electrolyte Interphase (SEI). 1,2Only a few electrolytes result in the formation of a stable SEI on graphite and most of these electrolytes include ethylene carbonate (EC) due to the critical role of EC in SEI formation.3 An alternative solvent, propylene carbonate (PC), has been already extensively studied for use in lithium-ion batteries due to its favorable physical properties: high relative permittivity (ε = 64.96) and wide operating temperature range (mp = -55• C, bp = 240 • C). 2 However, reduction of PC does not generate a stable SEI on graphite leading to continuous electrolyte reduction and graphite exfoliation. In addition, EC has recently been reported to have high reactivity with the surface of cathodes operating at high potential. 4,5 In order to use PC based electrolytes an electrolyte additive is required to assist with SEI formation. All of these sulfur compounds are soluble in the organic electrolytes, but anodic unstable at high potential. 6 Propane sultone is one of the most widely investigated sulfur based additives and has been reported to improve Li + conduction in the anode SEI. However, due to toxicity concerns there is an interest in finding an alternative to PS. Previously reported ex-situ surface analysis of graphite anodes cycled with PS suggests that the primary reduction product of PS is lithium propane sulfonate (RSO 3 Li). 19,20 In an effort to develop Additives for Designed Surface Modification (ADSM), 21 novel SO 3 based additiv...

Section: Resultsmentioning

confidence: 99%

Reversible Graphite Anode Cycling with PC-Based Electrolytes Enabled by Added Sulfur Trioxide Complexes

Demeaux

Dong

Lucht

2017

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“…Use of 5V class positive electrodes (cathodes) is a convenient way to increase LIBs energy density. It explains the development of promising "high voltage" materials like Li 3 3 spinel. Nevertheless, the use of new cathodes operating at high voltage leads to the degradation of the battery electrolyte, usually based on a mixture of cyclic and linear alkylcarbonates containing LiPF 6 as salt and functional additives.…”

mentioning

confidence: 99%

“…LNMO/LNMO symmetric cells were also used by Demeaux et al to study the degradation of the LNMO interface which was mainly attributed to manganese and nickel dissolution. 3 Hence, using symmetric cells is a convenient method for studying electrodes interfaces. In the current work, Li/Li and Gr/Gr cells have been built and cycled in a standard electrolyte containing or not SA as SEI additive.…”

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confidence: 99%

Reactivity of Succinic Anhydride at Lithium and Graphite Electrodes

Charton

Santos-Peña

Biller

et al. 2017

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Succinic anhydride (SA) is an useful electrolyte additive for high voltage cathodes but has also a negative impact on graphite (Gr) or Li anodes. For this reason, the Li/electrolyte and Gr/electrolyte interfaces were investigated at 20 • C and 45 • C using half or symmetrical cells. When SA is added at 1% by weight to the electrolyte (alkylcarbonate mixture + LiPF 6 ), an increase in the Li/Li cell impedance at 20 • C occurs owing to the formation of a resistive solid electrolyte interphase (SEI), composed of an inorganic inner layer and an organic outer layer, whereas at 45 • C or in absence of SA, the interphase is more inorganic in nature. The reversible capacity of graphite, cycled in Gr/Li half-cells in the presence of SA, is very low at 20 • C but almost ten times larger at 45 • C. Cycling symmetrical Gr/Gr cells at 45 • C indicates that Gr capacity is lower in the presence of SA in connection with the presence of an organic and polymer rich SEI. GC-MS analysis of the electrolyte after cycling shows that ethylene glycol bis-(alkylcarbonate) derivatives disappear when SA is present, owing to the ability of SA to react with lithium alkoxides to yield oligopolyester. Lithium ion batteries (LIBs) are a reliable way to store electric energy, with high gravimetric and volumetric energy density, which allows their application in nomad systems including electric and/or hybrid vehicles. However, electric vehicles range is unsuitable for most of the consumers and, therefore, energy density should be improved. In the past twenty years, many researches have been performed on electrode materials and electrolytes with the aim to enhance battery performance. Use of 5V class positive electrodes (cathodes) is a convenient way to increase LIBs energy density. It explains the development of promising "high voltage" materials like Li 3 V 2 (PO 4 ) 3 , 1 Li 2 CoPO 4 F 2 or the LiNi 0.5 Mn 1.5 O 4 (LNMO) 3 spinel. Nevertheless, the use of new cathodes operating at high voltage leads to the degradation of the battery electrolyte, usually based on a mixture of cyclic and linear alkylcarbonates containing LiPF 6 as salt and functional additives. Unfortunately, standard electrolytes are oxidized on 5 V cathodes and this significantly limits the battery cycling life. From the first cycles, electrolyte components degrade forming by-products, which in turn, can interact with electrodes surface. As an example, a passive layer is formed on graphite (Gr)/electrolyte interface at the first charge. This layer, known as the Solid Electrolyte Interphase (SEI), has a strong impact on the LIBs performances. Electrolyte formulation influences the chemical nature and structure of the SEI. With the aim to improve SEI quality and stability, SEI-forming additives like vinylene carbonate (VC) are generally added to the electrolyte in low amount (less than 5% by weight). These additives are designed to generate a protective passive layer on the active material surface preventing continuous electrolyte decomposition reactions.Whereas additives can be ...

“…8,33 Anodic stability of the STD electrolyte and the DMF-SO 3 electrolytes are presented in Figure 1. The STD formulation presents the best anodic stability with + which can be attributed to DMF-SO 3 oxidation.…”

Section: Resultsmentioning

confidence: 99%

“…5 Recent investigation of the failure mechanisms of LiNi 0.5 Mn 1.5 O 4 cells suggest that electrolyte decomposition, electrode/electrolyte interface degradation, gassing, and transition metal dissolution are leading factors. [6][7][8][9][10] Various methods have been proposed to inhibit the detrimental reactions on high voltage cathode materials. One of the most promising methods to improve the performance of LiNi 0.5 Mn 1.5 O 4 cathode films is via the incorporation of cathode film forming electrolyte additives that are sacrificially oxidized on the cathode surface to generate a cathode passivation layer.…”

mentioning

confidence: 99%

Improving the Performance of Graphite/LiNi_0.5Mn_1.5O₄Cells with Added N,N-dimethylformamide Sulfur Trioxide Complex

Dong

Demeaux

Zhang

et al. 2017

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N,N-dimethylformamide sulfur trioxide complex (DMF-SO 3 ) has been investigated as an electrolyte additive for LiNi 0.5 Mn 1.5 O 4 /graphite cells cycled to 4.8 V. Addition of 0.1% DMF-SO 3 to 1.2 M LiPF 6 in EC/EMC (3/7, v/v) standard electrolyte (STD) results in a significant improvement in the capacity retention and coulombic efficiency of LiNi 0.5 Mn 1.5 O 4 /graphite cells after 50 cycles at 45 • C. Ex-situ surface analysis of the electrodes after cycling has been conducted via scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy with attenuated total reflectance (IR-ATR). The surface analysis suggests that a uniform interfacial film is formed on the LiNi 0.5 Mn 1.5 O 4 surface composed of the decomposition products of DMF-SO 3 . The novel cathode surface films passivates the surface at high potential leading to the improved electrochemical performance.