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