edinburgh | may-16 | ions that can hop, skip and jump: lithium conduction in disordered,...
TRANSCRIPT
Ions that can Hop, Skip and Jump: Lithium Conduction in Disordered, Crystalline Solids
Eddie Cussen
Department of Pure and Applied Chemistry, The University of Strathclyde
Structure/Properties of Complex Oxides
T / K
Am
plitu
de o
f rel
axin
g
com
pone
nt o
f asy
mm
etry
Muon spin relaxation
Magnetic Frustration
2010
20 40 60T / K
Jahn Teller & Metal-Insulator
Instabilities
Ferromagnetism& magnetoresistance
Lithium ion conduction in Oxides
• LixLa2/3-xTiO3-δ best crystalline oxide phase, σRT ≈ 10-3
S cm -1
• Perovskite is close packed structure; central interstice is filled
• σ ≈ 10-6
S cm-1
for Pr and Nd analogues
West et al, J. Mater. Chem., 1995, 5(11), 1807
LixLa2/3-xTiO3-δ
Yashima et al, J. Am. Chem. Soc., 2005, 127, 3491
Li0.62La0.16TiO3 Structural Model (2005)
Lithium metal causes reductive intercalation of Li+
Li+ Electrolytes
• Fast Li+
conduction / no electronic conduction
• (Electro)Chemical Stability
• Ease of Preparation and Processing
Li salt in liquid/amorphous polymer
High Performance Solid State Batteries
• New solid electrolyte materials
• Improved stability will allow new electrodes for higher voltages
• Build these new materials into all solid state batteries
• In situ characterisation during battery operation
• Stabilise and characterise interface behaviour
Lithium Conduction in New Crystalline Materials
Organic polymer electrolytes used in Li-ion batteries – safety issues
Li-containing garnets combine high ionic conductivity (10-4 S cm-1) with desired electrochemical stability
In conventional garnet, eight cations in two octahedral, three cubic and three tetrahedral sites, latter filled with Li
Li-stuffed garnets as solid electrolytes
Amores, Cussen, Corr et al.; J. Mater. Chem. A, 2016
Have reduced synthesis times and temps for Al-doped LLZO garnets from 36 h at 1230 °C to 1 h at 1000 °C
Microwave synthesis of Li-stuffed garnets
Rietveld analysis in conjunction with ICP and EDX reveals stoichiometry of Li6.5Al0.25La2.92Zr2O12 is obtained
Amores, Cussen, Corr et al.; J. Mater. Chem. A, 2016
Li-stuffed garnets as solid electrolytes
Have reduced synthesis times and temps for Al-doped LLZO garnets from 36 h at 1230 °C to 1 h at 1000 °C
Microwave synthesis of Li-stuffed garnets
Rietveld analysis in conjunction with ICP and EDX reveals stoichiometry of Li6.5Al0.25La2.92Zr2O12 is obtained
Amores, Cussen, Corr et al.; J. Mater. Chem. A, 2016
Spin-polarized positive muons stop at interstitial sites with large electronegativity, expected to be near the oxygens in the garnet lattice
Li-diffusion in Li-stuffed garnets
Thermally activated region
Amores, Cussen, Corr et al.; J. Mater. Chem. A, 2016
Observe differences in Eact obtained from SR compared to EIS (0.55 eV)
Li-diffusion in Li-stuffed garnets
In EIS, resistance to Li-diffusion through grain-boundaries contributes to total resistance, increasing Eact for Li-conduction
SR acts as local probe sensing mostly intra-grain diffusion, without extrinsic interference
Z = R σ• Semicircles due to resistance to Li diffusion• Tail due to Pt blocking electrodes
Amores, Cussen, Corr et al.; J. Mater. Chem. A, 2016
Filled Td Empty Td
DisorderedStructures
Cussen, J. Mater. Chem, 2010
Lithium Mobility in Garnets
Lithium Mobility in Garnets
400 oCLi3Nd3Te2O12
Li4Nd3TeSbO12Li4.5Nd3Te0.5Sb1.5O12
Lithium Mobility in Garnets
• Li+ is the only mobile ion
• Multiple sites with 4 – 6 coordination
• Multiple hop distances 0.4 to 2.2 Å
• Inter-Cation repulsion from short Li...Li distances 2.4 Å
• A detailed, disordered & dynamic energy landscape
Ion Movement is a Complex,
Cooperative and Evolving Process
Lithium Mobility in Garnets
• Li salt dissolved in e.g. polyethylene oxide
• Structural studies of crystalline vs amorphous materials
• Li+ motion faster in amorphous phase
• Rotational motion of PEO portion facilitates Li+ migration
Ion Conduction in polymer electrolytes
Ion Conductivity in PEO : NH4SCN
1000 / T
ln (σ
T)
crystalline
amorphous
Solid State Electrochemistry, Bruce, West, Shriver et al, 1995
Lithium Sulfate
T < 575 oC
T > 575 oC
Tofield et al., J. Phys. C: Solid St. Phys., 13 (1980) 6441
T < 575 oC
T > 575 oC
Tofield et al., J. Phys. C: Solid St. Phys., 13 (1980) 6441
Lithium Sulfate
High T Li2SO4
Li+cation
Li+vacancy
High T Li2SO4
• Inorganic, non framework, crystalline conductors
• High degree of motion in majority of atoms
• LiBH4 shows fast ion conduction > 109oC
Target: RT conduction by chemical doping
Alkali Metal Borohydrides
LiBH4 structure at room temperature
Pnma distorted Wurtzite
LiBH4 structure at room temperature
Pnma distorted Wurtzite
• Phase transition at 109oC gives a hexagonal structure
• Li+ conduction increases from 10-5 up to 10-2 S cm-1
• Structure of the high temperature phase doubtful
• Halide substitution can reduce the Tc
Li+ conduction in LiBH4
M. Matsuo and S. Orimo. Adv. Energy Mater. 2011, 1, 161
LiBH4 – LiBr Phase Diagram
Li(BH4)1-xBrx Lithium Conductivity
Ea = 0.52(2) to 0.64(1) eV
Li(BD4)0.67Br0.33 Structure
• X-rays dominated by bromide scatter
• Single P63mc phase
• Isotopically enrich 7Li, 11B and D
• Neutron diffraction using GEM
• Multiple data banks
• Require detailed data at low d-space
Cascallana, Keen, Cussen & Gregory; Chem. Mater., 2015
Li(BD4)0.67Br0.33 Structure
Cascallana, Keen, Cussen & Gregory; Chem. Mater., 2015
Li(BD4)0.67Br0.33 Structure
Cascallana, Keen, Cussen & Gregory; Chem. Mater., 2015
Li(BD4)0.67Br0.33 Structure
Cascallana, Keen, Cussen & Gregory; Chem. Mater., 2015
Li(BD4)0.67Br0.33 Structure
Cascallana, Keen, Cussen & Gregory; Chem. Mater., 2015
Li(BD4)0.67Br0.33 Structure
Cascallana, Keen, Cussen & Gregory; Chem. Mater., 2015
Li(BD4)0.684(4)Br0.316(4)
• Disorder in: lithium position, BH4 orientation and BH4 vs Br position
• Raman suggests regular, flexible BH4 with Td symmetry
Variable temperature neutron scattering
300 400 500 T / K
Li(BH4)1-xBrx Lithium Conductivity
• Stabilise fast conducting phase to room temperature
• Li+ mobility and BH4- rotational disorder
• Strong coupling between anion orientation and Li+ conduction
Use ion mobility to access new, metastable Li+ conductors
Irene CascallanaMarco AmoresDr Hany El-Shinawi
Dr Mike O’CallaghanDr Thomas Yip
Acknowledgements
Prof. Duncan Gregory
Dr Serena Corr
Dr Jeremy Titman
Prof. George Chen
Dr David Keen ISIS
Dr Ron Smith ISIS
Dr Winfried Kockelmann ISIS
Dr Peter Baker ISIS muons
I15 beamline DiamondEPSRC
Preparation of Bromide doped LiBH4
• Ball milling :
(1-x) LiBH4 + x LiBr Li(BH4)1-xBrx
Followed by heating at 300OC for 5 hrs in N2
Preparation of Br-doped LiBH4 LiBH4
LiBr
Li(BH4)1/2Br1/2
Li(BH4)2/3Br1/3
2θ / o Cu Kα
Inte
nsity
/ ar
bitrr
ary
units
Li0.56(2)H0.45(2)LaTiO4HLaTiO4 + 1/2LiOH.H2O
RT Ion Exchange
Yip & Cussen, Chem. Commun., 2010: Inorg. Chem., 2013