edinburgh | may-16 | the winton programme for the physics of sustainability
TRANSCRIPT
Smart Villages Battery Technology and Recycling Workshop
S E Dutton
Dutton Group Research Activities
StoichiometryCrystal structure Electronic structure
Physical properties
FUNCTIONAL ENERGY MATERIALS (FEM)
BatteriesMagnetocalorics
PyrochloresHybrid photovoltaics
Multiferroics
Sample preparation• Solid state synthesis
• Controlled atmosphere to tune O2 partial pressure– Flowing gas (O2, Ar, 5%H2/Ar)– In vacuo– Dynamic vacuum
Measurement• XRD – crystal structure analysis
• Neutron diffraction – crystal and magnetic structure
Magnetic and Electronic measurements
• SQUID• PPMS• Battery testing
Uses of rechargeable batteries
Construction of a rechargeable battery
Solid state electrolytes and all solid state batteries
New electrodes for Li-ion and Na-
ion batteries
Mg-ion batteries
F. Lalère, et al., J Power Sources 247, 975 (2014)
Mg-ion batteries - motivation• Divalent ions
– generate more charge per intercalated ion • Possibility of using Mg anodes
– allows for higher energy densities• Cost and abundance
– Scaleable technology
Mg-ion batteries
• Reversible Mg-ion battery with MgxMo6S8 as the cathode
• Capacity = 70 mAh/g
• Voltage = 1-1.3 V
Aurbach, Nature 407 (2000) 724
Mg-ion batteries - practicalities
• Chemistry of Mg2+ is very different to Li+
– Mg2+ is often used as a dopant in electrodes for Li-ion batteries• assumed to be immobile• Often form materials with mixed Mg and transition metal
sites – Inherently lower voltage (by 0.73 V vs. Li)– Higher charge to radius ratio gives slower diffusion
• Whole battery systems not optimised– Current electrolytes are not stable at higher voltages– SEI formed on charge which limits capacity
TargetsHigh Voltage High Capacity
Reversible Rate capability
TargetsHigh Voltage High Capacity
Reversible Rate capability
Materials selection criteriaOxide or polyanion groups
Mg-ions on a crystallographically distinct siteRedox active ions
Pathways for Mg-ion diffusionSuitable ratio of Mg to redox active ions
Analogues of electrodes in Li-ion
batteriesMake electrochemically
Mg-ion exchangeMake directly?
TargetsHigh Voltage High Capacity
Reversible Rate capability
Materials selection criteriaOxide or polyanion groups
Mg-ions on a crystallographically distinct siteRedox active ions
Pathways for Mg-ion diffusionSuitable ratio of Mg to redox active ions
Analogues of electrodes in Li-ion
batteriesMake electrochemically
Mg-ion exchangeMake directly?
Explore Mg-containing materials with no Li-analogue
Identify suitable targets from reported materials
Exploratory synthesis
TargetsHigh Voltage High Capacity
Reversible Rate capability
Materials selection criteriaOxide or polyanion groups
Mg-ions on a crystallographically distinct siteRedox active ions
Pathways for Mg-ion diffusionSuitable ratio of Mg to redox active ions
Analogues of Li-ion batteries
• Preparation can be difficult– Often made electrochemically by removing Li and
then cycling vs. Mg• Intrinsically lower capacity – One Li-ion is replaced by ½ Mg-ion
• Not optimised for Mg-ion transport
Explore Mg-containing Materials
• High operating voltage• Higher capacities• Versatile structures– Can vary the TM ion• Mn, Fe, Co, V, Ni
– Can vary the oxidation state of the TM• Alter voltage of materials
MgMnB2O5
Theoretical capacity = 296 mAh/gMn2+
Performance in a Mg-ion battery
vs Mg with TFSI in ACN3.5V cutoff
Performance in a Mg-ion battery
vs Mg with TFSI in ACN2.5V cutoff
What is the maximum amount of Li which can be removed?
• Test in a Li-ion cell
What about putting Li into the structure?
• Reaches full theoretical capacity• There may be some side reactions as not completely reversible
• Though could be Li just occupy different sites
Intercalation of 1.25 Li
MgMnB2O5 vs. Li – C/25
• Similar discharge capacity to C/100
• Better efficiency• 600 Wh/Kg is good
(LiCoO2 ~240Wh/Kg)
Le Bail refinements of cycled MgMnB2O5
• High capacity at high rates (C/2)
• Batteries operate over multiple cycles
Conclusions
• It is possible to remove Mg ions from MgMnB2O5
• Overpotential is reduced when cycling vs. Li– Need to optimise construction of Mg-ion batteries
• Can reversibly cycle ~1.25 Li in demagnesiated MgMnB2O5
– Reversible over multiple cycles– Can be carried out at high rates
Acknowledgements
• Hugh Glass• Evan Keyser• Zigeng Lui• Jeongjae Lee• Paul Bayley• Clare Grey• Dominic Wright