skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Li + Defects in a Solid-State Li Ion Battery: Theoretical Insights with a Li 3 OCl Electrolyte

Abstract

In a solid-state Li ion battery, the solid-state electrolyte exits principally in regions of high externally applied potentials, and this varies rapidly at the interfaces with electrodes due to the formation of electrochemical double layers. Here, we investigate the implications of these for a model solid-state Li ion battery Li|Li 3OCl|C, where C is simply a metallic intercalation cathode. We use DFT to calculate the potential dependence of the formation energies of the Li + charge carriers in superionic Li 3OCl. We find that Li+ vacancies are the dominant species at the cathode while Li+ interstitials dominate at the anode. With typical Mg aliovalent doping of Li 3OCl, Li + vacancies dominate the bulk of the electrolyte as well, with freely mobile vacancies only ~ 10 -4 of the Mg doping density at room temperature. We study the repulsive interaction between Li+ vacancies and find that this is extremely short range, typically only one lattice constant due to local structural relaxation around the vacancy and this is significantly shorter than pure electrostatic screening. We model a Li 3OCl- cathode interface by treating the cathode as a nearly ideal metal using a polarizable continuum model with an ε r = 1000.more » There is a large interface segregation free energy of ~ - 1 eV per Li + vacancy. Combined with the short range for repulsive interactions of the vacancies, this means that very large vacancy concentrations will build up in a single layer of Li 3OCl at the cathode interface to form a compact double layer. The calculated potential drop across the interface is ~ 3 V for a nearly full concentration of vacancies at the surface. This suggests that nearly all the cathode potential drop in Li 3OCl occurs at the Helmholtz plane rather than in a diffuse space-charge region. We suggest that the conclusions found here will be general to other superionic conductors as well.« less

Authors:
 [1];  [2];  [3]; ORCiD logo [2]
  1. Stanford Univ., CA (United States). SUNCAT Center for Interface Science and Catalysis, Dept. of Chemical Engineering
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States). SUNCAT Center for Interface Science and Catalysis
  3. Technische Univ. Munchen, Garching (Germany). Chair for Theoretical Chemistry and Catalysis Research Center
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1369455
Grant/Contract Number:
AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 29; Journal Issue: 10; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; 36 MATERIALS SCIENCE

Citation Formats

Stegmaier, Saskia, Voss, Johannes, Reuter, Karsten, and Luntz, Alan C. Li+ Defects in a Solid-State Li Ion Battery: Theoretical Insights with a Li3 OCl Electrolyte. United States: N. p., 2017. Web. doi:10.1021/acs.chemmater.7b00659.
Stegmaier, Saskia, Voss, Johannes, Reuter, Karsten, & Luntz, Alan C. Li+ Defects in a Solid-State Li Ion Battery: Theoretical Insights with a Li3 OCl Electrolyte. United States. doi:10.1021/acs.chemmater.7b00659.
Stegmaier, Saskia, Voss, Johannes, Reuter, Karsten, and Luntz, Alan C. 2017. "Li+ Defects in a Solid-State Li Ion Battery: Theoretical Insights with a Li3 OCl Electrolyte". United States. doi:10.1021/acs.chemmater.7b00659.
@article{osti_1369455,
title = {Li+ Defects in a Solid-State Li Ion Battery: Theoretical Insights with a Li3 OCl Electrolyte},
author = {Stegmaier, Saskia and Voss, Johannes and Reuter, Karsten and Luntz, Alan C.},
abstractNote = {In a solid-state Li ion battery, the solid-state electrolyte exits principally in regions of high externally applied potentials, and this varies rapidly at the interfaces with electrodes due to the formation of electrochemical double layers. Here, we investigate the implications of these for a model solid-state Li ion battery Li|Li3OCl|C, where C is simply a metallic intercalation cathode. We use DFT to calculate the potential dependence of the formation energies of the Li+ charge carriers in superionic Li3OCl. We find that Li+ vacancies are the dominant species at the cathode while Li+ interstitials dominate at the anode. With typical Mg aliovalent doping of Li3OCl, Li+ vacancies dominate the bulk of the electrolyte as well, with freely mobile vacancies only ~ 10-4 of the Mg doping density at room temperature. We study the repulsive interaction between Li+ vacancies and find that this is extremely short range, typically only one lattice constant due to local structural relaxation around the vacancy and this is significantly shorter than pure electrostatic screening. We model a Li3OCl- cathode interface by treating the cathode as a nearly ideal metal using a polarizable continuum model with an εr = 1000. There is a large interface segregation free energy of ~ - 1 eV per Li+ vacancy. Combined with the short range for repulsive interactions of the vacancies, this means that very large vacancy concentrations will build up in a single layer of Li3OCl at the cathode interface to form a compact double layer. The calculated potential drop across the interface is ~ 3 V for a nearly full concentration of vacancies at the surface. This suggests that nearly all the cathode potential drop in Li3OCl occurs at the Helmholtz plane rather than in a diffuse space-charge region. We suggest that the conclusions found here will be general to other superionic conductors as well.},
doi = {10.1021/acs.chemmater.7b00659},
journal = {Chemistry of Materials},
number = 10,
volume = 29,
place = {United States},
year = 2017,
month = 4
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on April 26, 2018
Publisher's Version of Record

Save / Share:
  • Understanding the nature and formation of the solid–electrolyte interphase (SEI) formed in electrochemical storage devices, such as Li-ion batteries, is most important for improving functionality. Few experiments exist that adequately probe the SEI, particularly in situ. We perform predictive ab initio molecular dynamics simulations of the anode–electrolyte interface for several electrolytes and interface functionalizations. These show strongly differing effects on the reducibility of the electrolyte. Electrolyte reduction occurs rapidly, on a picosecond time scale. Orientational ordering of electrolyte near the interface precedes reduction. The reduced species depend strongly on surface functionalization and presence of LiPF6 salt. While LiPF6 salt inmore » ethylene carbonate is more stable at a hydrogen-terminated anode, oxygen/hydroxyl termination causes spontaneous dissociation to form LiF and other fluorophosphates. LiF migrates to the interface creating chainlike structures, consistent with experimental observations of LiF agglomeration. Inorganic products such as LiF and Li2CO3 migrate closer to the anode than purely organic components, consistent with their more ionic character. Significantly, we conclude that while the electrolyte reduction occurs at the molecular level near the interface, requiring specific alignments and proximity, the reducibility is governed by the average reduction potential barrier between the electrode (anode) and the electrolyte.« less
  • A solid-state reversible cell of the type Ag(Hg)/RbAg/sub 4/I/sub 5//I/sub 2/, TbAi, C, has been developed. The anodic and cathodic contact polarizations have been minimized by amalgamation of the silver electrode and the use of a suitable mixture made of tetrabutylammonium iodide (TbAi), iodine and graphite, respectively. The cell has an open-circuit voltage of 0.56v at 25/sup 0/C a total volume of 5 cm/sup 3/, an internal resistance of 30 ohms, short-circuit current of 1.5 A/Dm/sup 2/, and is rechargeable with high coulombic efficiency. 20 references.
  • An in-depth review is presented on the science of lithium-ion battery (LIB) solid electrolyte interphase (SEI) formation on the graphite anode, including structure, morphology, chemical composition, electrochemistry, formation mechanism, and LIB formation cycling. During initial operation of LIBs, the SEI layer forms on the graphite surfaces, the most commonly used anode material, due to side reactions with the electrolyte solvent/salt at low electro-reduction potentials. It is accepted that the SEI layer is essential to the long-term performance of LIBs, and it also has an impact on its initial capacity loss, self-discharge characteristics, cycle life, rate capability, and safety. While themore » presence of the anode SEI layer is vital, it is difficult to control its formation and growth, as the chemical composition, morphology, and stability depend on several factors. These factors include the type of graphite, electrolyte composition, electrochemical conditions, and cell temperature. Thus, SEI layer formation and electrochemical stability over long-term operation should be a primary topic of future investigation in the development of LIB technology. We review the progression of knowledge gained about the anode SEI, from its discovery in 1979 to the current state of understanding, and covers its formation process, differences in the chemical and structural makeup when cell materials and components are varied, methods of characterization, and associated reactions with the liquid electrolyte phase. It also discusses the relationship of the SEI layer to the LIB formation step, which involves both electrolyte wetting and subsequent slow charge-discharge cycles to grow the SEI.« less
    Cited by 24