Binder free (BF) graphite electrodes were utilized to investigate the effect of electrolyte additives fluoroethylene carbonate (FEC) and vinylene carbonate (VC) on the structure of the solid electrolyte interface (SEI). The structure of the SEI has been investigated via ex-situ surface analysis including X-ray Photoelectron spectroscopy (XPS), Hard XPS (HAXPES), Infrared spectroscopy (IR) and transmission electron microscopy (TEM). The components of the SEI have been further investigated via nuclear magnetic resonance (NMR) spectroscopy of D 2 O extractions. The SEI generated on the BF-graphite anode with a standard electrolyte (1.2 M LiPF 6 in ethylene carbonate (EC) / ethyl methyl carbonate (EMC), 3/7 (v/v)) is composed primarily of lithium alkyl carbonates (LAC) and LiF. Incorporation of VC (3% wt) results in the generation of a thinner SEI composed of Li 2 CO 3 , poly(VC), LAC, and LiF. Incorporation of VC inhibits the generation of LAC and LiF. Incorporation of FEC (3% wt) also results in the generation of a thinner SEI composed of Li 2 CO 3 , poly(FEC), LAC, and LiF. The concentration of poly(FEC) is lower than the concentration of poly(VC) and the generation of LAC is inhibited in the presence of FEC. The SEI appears to be a homogeneous film for all electrolytes investigated. Lithium ion batteries have been used to power portable electronic devices for decades. Interest in lithium ion batteries has expanded to include electric vehicles (EV) due to their high energy density. [1][2][3] However, the calendar life of many lithium ion batteries is insufficient for the >10 year life expectancy of an EV.1 Thus there have been many recent investigations on methods to improve the calendar life of lithium ion batteries. Graphite is the most widely used anode material in lithium ion batteries. 4,5 During the initial charging cycles of the lithium ion battery a Solid Electrolyte Interphase (SEI) is generated on the graphite surface.6,7 The SEI acts as a passivation layer to inhibit further electrolyte reduction. 8 The SEI generated from standard ethylene carbonate based electrolytes has moderate thermal stability which leads to moderate calendar life. 9 In an effort to improve the stability of the SEI many film forming additives have been investigated. 10,11 Vinylene Carbonate (VC) and Fluoroethylene Carbonate (FEC) are among the most widely investigated electrolyte additives.12 VC has been used in many lithium ion batteries to increase first cycle efficiency, improve the high temperature stability, and improve the calendar life.13-16 FEC has largely been used in silicon-based anode materials to improve capacity retention, but has also been investigated with graphite anodes.15,17 However, there have been limited direct comparisons of the effects from FEC and VC on graphite electrodes especially related to differences in the structure of the anode SEI.The investigations of the components and morphology changes on graphite anode surfaces upon incorporation of small quantities of additives in a standard electrolyte 1....

A novel series of lithium alkyl trimethyl borates and lithium aryl trimethyl borates have been prepared and investigated as cathode film forming additives.

Additives such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are commonly added to lithium-ion battery electrolytes in order to form a solid electrolyte interphase (SEI) on the anode, suppressing continuous solvent reduction. In this work, we directly compare VC and FEC by analyzing the SEI with FTIR and XPS, and the evolved gases with on-line electrochemical mass spectrometry (OEMS) in different model systems. Since both additives evolve mainly CO 2 during formation, the effect of CO 2 as an additive is compared to the addition of VC and FEC. While Li 2 CO 3 is as expected the main SEI compound found due to the added CO 2 , surprisingly no CO was detected in the gas phase of such cells. Based on FTIR, NMR and OEMS analyses of cells filled with 13 C labeled CO 2 , we suggest a mechanism explaining the beneficial effects of CO 2 and hence also of CO 2 evolving additives in lithium-ion battery cells. While the generation of polycarbonate from FEC or VC reduction is observed, the generation of Li 2 CO 3 may be as important as the generation of polycarbonate.

The fundamental understanding of the electrode/electrolyte interfacial processes in lithium–sodium ion batteries (LIBs) and of their dynamics upon cycling is of prime importance for the development of new-generation electrode materials. Operando analyses using the utmost sensitive techniques are required to produce an accurate depiction of the underlying processes at the origin of the battery performance decay. Although enhanced Raman spectroscopy through the use of signal nanoamplifiers shows the required sensitivity, its implementation in operando conditions and particularly on functional materials in contact with organic electrolytes remains challenging. This work using extensive optimization of shell-isolated nanoparticle-enhanced Raman spectroscopy conditions for operando diagnosis of LIB materials, including the design of near-infrared active amplifiers and the control of the photon dose, demonstrates the possibility to track the dynamics of composition of the electrode/electrolyte interface upon cycling of LIB coin-cells and uncovers the origin of the irreversible capacity of tin electrodes proposed as an alternative to graphite anodes.