Influence of VC and FEC Additives on Interphase Properties of Carbon in Li-Ion Cells Investigated by Combined EIS & EQCM-D

2020 ◽  
Author(s):  
Paul Kitz ◽  
Matthew Lacey ◽  
Petr Novák ◽  
Erik Berg
Keyword(s):  
Electrochemical Impedance ◽  
Solid Electrolyte Interphase ◽  
Electrochemical Quartz Crystal Microbalance ◽  
Gas Analysis ◽  
Side Reactions ◽  
Ion Diffusion ◽  
Battery Cell ◽  
Anode Passivation ◽  
Order Of Magnitude ◽  
Li Ion

<div>The electrolyte additives vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are well known for increasing the lifetime of a Li-ion battery cell by supporting the formation of an effective solid electrolyte interphase (SEI) at the anode. In this study combined simultaneous electrochemical impedance spectroscopy (EIS) and <i>operando</i> electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) are employed together with <i>in situ</i> gas analysis (OEMS) to study the influence of VC and FEC on the passivation process and the interphase properties at carbon-based anodes. In small quantities both additives reduce the initial interphase mass loading by 30 to 50 %, but only VC also effectively prevents continuous side reactions and improves anode passivation significantly. VC and FEC are both reduced at potentials above 1 V vs. Li<sup>+</sup>/Li in the first cycle and change the SEI composition which causes an increase of the SEI shear storage modulus by over one order of magnitude in both cases. As a consequence, the ion diffusion coefficient and conductivity in the interphase is also significantly affected. While small quantities of VC in the initial electrolyte increase the SEI conductivity, FEC decomposition products hinder charge transport through the SEI and thus increase overall anode impedance significantly. </div>

Influence of VC and FEC Additives on Interphase Properties of Carbon in Li-Ion Cells Investigated by Combined EIS & EQCM-D

2020 ◽  
Author(s):  
Paul Kitz ◽  
Matthew Lacey ◽  
Petr Novák ◽  
Erik Berg
Keyword(s):  
Electrochemical Impedance ◽  
Solid Electrolyte Interphase ◽  
Electrochemical Quartz Crystal Microbalance ◽  
Gas Analysis ◽  
Side Reactions ◽  
Ion Diffusion ◽  
Battery Cell ◽  
Anode Passivation ◽  
Order Of Magnitude ◽  
Li Ion

<div>The electrolyte additives vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are well known for increasing the lifetime of a Li-ion battery cell by supporting the formation of an effective solid electrolyte interphase (SEI) at the anode. In this study combined simultaneous electrochemical impedance spectroscopy (EIS) and <i>operando</i> electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) are employed together with <i>in situ</i> gas analysis (OEMS) to study the influence of VC and FEC on the passivation process and the interphase properties at carbon-based anodes. In small quantities both additives reduce the initial interphase mass loading by 30 to 50 %, but only VC also effectively prevents continuous side reactions and improves anode passivation significantly. VC and FEC are both reduced at potentials above 1 V vs. Li<sup>+</sup>/Li in the first cycle and change the SEI composition which causes an increase of the SEI shear storage modulus by over one order of magnitude in both cases. As a consequence, the ion diffusion coefficient and conductivity in the interphase is also significantly affected. While small quantities of VC in the initial electrolyte increase the SEI conductivity, FEC decomposition products hinder charge transport through the SEI and thus increase overall anode impedance significantly. </div>

Synthesis and Electrochemical Properties of Spherical LiFePO4/C Composite via Spray Drying

2015 ◽  
Vol 1120-1121 ◽  
pp. 554-558 ◽  
Author(s):  
Juan Mei Wang ◽  
Bing Ren ◽  
Ying Lin Yan ◽  
Qing Zhang ◽  
Yan Wang
Keyword(s):  
Diffusion Coefficient ◽  
Electrochemical Properties ◽  
Spray Drying ◽  
Electrochemical Impedance ◽  
Retention Rate ◽  
Lithium Ion ◽  
Constant Current ◽  
Ion Diffusion ◽  
Electrochemical Tests ◽  
Li Ion

In this work, spherical LiFePO4/C composite had been synthesized by co-precipitation and spray drying method. The structure, morphology and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron micrograph (SEM), transmission electron microscope (TEM), constant current charge-discharge tests and electrochemical impedance spectroscopy (EIS) tests. The spherical LiFePO4/C particles consisted of a number of smaller grains. The results showed that the morphology of LiFePO4/C particles seriously affected the Li-ion diffusion coefficient and electrochemical properties of lithium ion batteries. Electrochemical tests revealed the spherical LiFePO4/C composite had excellent Li-ion diffusion coefficient which was calculated to be 1.065×10-11 cm2/s and discharge capacity of 149 (0.1 C), 139 (0.2 C), 133 (0.5 C), 129 (1 C) and 124 mAhg-1(2 C). After 50 cycles, the capacity retention rate was still 93.5%.

scholarly journals The early-stage growth and reversibility of Li electrodeposition in Br-rich electrolytes

2020 ◽  
Vol 118 (2) ◽  
pp. e2012071118
Author(s):  
Prayag Biswal ◽  
Atsu Kludze ◽  
Joshua Rodrigues ◽  
Yue Deng ◽  
Taylor Moon ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Electrochemical Impedance ◽  
Early Stage ◽  
Solid Electrolyte Interphase ◽  
Growth Dynamics ◽  
Ion Diffusion ◽  
Reactive Metal ◽  
Metal Anode ◽  
Sem Image ◽  
Fine Control

The physiochemical nature of reactive metal electrodeposits during the early stages of electrodeposition is rarely studied but known to play an important role in determining the electrochemical stability and reversibility of electrochemical cells that utilize reactive metals as anodes. We investigated the early-stage growth dynamics and reversibility of electrodeposited lithium in liquid electrolytes infused with brominated additives. On the basis of equilibrium theories, we hypothesize that by regulating the surface energetics and surface ion/adatom transport characteristics of the interphases formed on Li, Br-rich electrolytes alter the morphology of early-stage Li electrodeposits; enabling late-stage control of growth and high electrode reversibility. A combination of scanning electron microscopy (SEM), image analysis, X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and contact angle goniometry are employed to evaluate this hypothesis by examining the physical–chemical features of the material phases formed on Li. We report that it is possible to achieve fine control of the early-stage Li electrodeposit morphology through tuning of surface energetic and ion diffusion properties of interphases formed on Li. This control is shown further to translate to better control of Li electrodeposit morphology and high electrochemical reversibility during deep cycling of the Li metal anode. Our results show that understanding and eliminating morphological and chemical instabilities in the initial stages of Li electroplating via deliberately modifying energetics of the solid electrolyte interphase (SEI) is a feasible approach in realization of deeply cyclable reactive metal batteries.

Influence of Water Contamination on the SEI Formation in Li-Ion Cells: An Operando EQCM-D Study

2019 ◽  
Author(s):  
Paul Kitz ◽  
Petr Novák ◽  
Erik Berg
Keyword(s):  
Viscoelastic Properties ◽  
Reaction Pathway ◽  
Solid Electrolyte Interphase ◽  
Electrochemical Quartz Crystal Microbalance ◽  
Co2 Gas ◽  
Decomposition Processes ◽  
Influence Of Water ◽  
Li Ion ◽  
Hydrolysis Of

The interphase formation on carbon (C) anodes in LiPF6/EC + DEC Li-ion battery electrolyte is analyzed by combining operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) with in situ online electrochemical mass spectrometry (OEMS). EQCM-D enables unique insights into the anode solid electrolyte interphase (SEI) mass/thickness, its viscoelastic properties, and changes of electrolyte viscosity during the initial formation cycles. The interphase in pure electrolyte is relatively soft (G’SEI ≈ 0.2 MPa, ηSEI ≈ 10 mPa s) and changes its viscoelastic properties dynamically as a function of electrode po-tential. With increasing electrolyte water content, the SEI becomes thicker and much more rigid. Doubly labeled D218O is added to the electrolyte in order to precisely track the reaction pathway of water at the anode by OEMS. In the first cycle between 2.6 – 1.7 V vs. Li+/Li water is reduced and hydroxide ions initiate an autocatalytic hydrolysis of EC. With large amounts of water initially present in the electrolyte, most of the formed CO2 gas is scavenged by reactions with hydroxide and alkoxide ions forming a thick, rigid, and Li2CO3 rich early interphase on the C anode. This layer alleviates the following electrolyte decomposition processes and slows the reduction of EC < 1 V vs. Li+/Li.

A Novel Technique for Estimation of the Solid Electrolyte Interphase Film Resistance for Li-Ion Batteries

2018 ◽  
Author(s):  
Shashank Arora
Keyword(s):  
Solid Electrolyte ◽  
Solid Electrolyte Interphase ◽  
Carbon Film ◽  
Open Circuit ◽  
Film Resistance ◽  
Battery Cell ◽  
Average Value ◽  
Sei Film ◽  
Li Ion ◽  
The Difference

Solid electrolyte interphase (SEI) film resistance is an important parameter in the study of charge transfer kinetics of a Li-ion battery. The passive film affects diffusion process of Li-ions. As such, it becomes essential to include film resistance in battery modelling. However, the traditional method of estimating the SEI film resistance is costly and time consuming. An indirect approach based on Ohm’s law is thus presented in this paper. It relies on determining the interfacial polarisation from the difference of open-circuit voltage measured immediately after switching off the applied current and the equilibrium voltage. The technique is simple, easy to implement and can be used for a quick estimation of SEI film resistance with reasonable accuracy. For instance, average value of SEI film resistance for commercial LFP battery cell is measured as 0.004 Ohm · m2 , which was found to be consistent with the values determined using the impedance spectroscopy techhnique in the published literature for lithium-carbon film electrodes.

Influence of Water Contamination on the SEI Formation in Li-Ion Cells: An Operando EQCM-D Study

2019 ◽  
Author(s):  
Paul Kitz ◽  
Petr Novák ◽  
Erik Berg
Keyword(s):  
Viscoelastic Properties ◽  
Reaction Pathway ◽  
Solid Electrolyte Interphase ◽  
Electrochemical Quartz Crystal Microbalance ◽  
Co2 Gas ◽  
Decomposition Processes ◽  
Influence Of Water ◽  
Li Ion ◽  
Hydrolysis Of

The interphase formation on carbon (C) anodes in LiPF6/EC + DEC Li-ion battery electrolyte is analyzed by combining operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) with in situ online electrochemical mass spectrometry (OEMS). EQCM-D enables unique insights into the anode solid electrolyte interphase (SEI) mass/thickness, its viscoelastic properties, and changes of electrolyte viscosity during the initial formation cycles. The interphase in pure electrolyte is relatively soft (G’SEI ≈ 0.2 MPa, ηSEI ≈ 10 mPa s) and changes its viscoelastic properties dynamically as a function of electrode po-tential. With increasing electrolyte water content, the SEI becomes thicker and much more rigid. Doubly labeled D218O is added to the electrolyte in order to precisely track the reaction pathway of water at the anode by OEMS. In the first cycle between 2.6 – 1.7 V vs. Li+/Li water is reduced and hydroxide ions initiate an autocatalytic hydrolysis of EC. With large amounts of water initially present in the electrolyte, most of the formed CO2 gas is scavenged by reactions with hydroxide and alkoxide ions forming a thick, rigid, and Li2CO3 rich early interphase on the C anode. This layer alleviates the following electrolyte decomposition processes and slows the reduction of EC < 1 V vs. Li+/Li.

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