Presenter : Sian E. Dutton

1. Smart Villages Battery Technology
and Recycling Workshop
S E Dutton

2. Dutton Group Research Activities
Stoichiometry
Crystal structure
Electronic structure
Physical properties
FUNCTIONAL ENERGY MATERIALS
(FEM)
Batteries
Magnetocalorics
Pyrochlores
Hybrid photovoltaics
Multiferroics

3. Sample preparation
• Solid state synthesis
• Controlled atmosphere to
tune O2 partial pressure
– Flowing gas (O2, Ar,
5%H2/Ar)
– In vacuo
– Dynamic vacuum

4. Measurement
• XRD – crystal structure analysis
• Neutron diffraction – crystal and magnetic
structure

5. Magnetic and Electronic measurements
• SQUID
• PPMS
• Battery testing

6. Uses of rechargeable batteries

7. Construction of a rechargeable battery

8. 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)

9. 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

10. 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

11. 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

12. Targets
High Voltage High Capacity
Reversible Rate capability

13. Targets
High Voltage High Capacity
Reversible Rate capability
Materials selection criteria
Oxide or polyanion groups
Mg-ions on a crystallographically distinct site
Redox active ions
Pathways for Mg-ion diffusion
Suitable ratio of Mg to redox active ions

14. Analogues of
electrodes in Li-ion
batteries
Make electrochemically
Mg-ion exchange
Make directly?
Targets
High Voltage High Capacity
Reversible Rate capability
Materials selection criteria
Oxide or polyanion groups
Mg-ions on a crystallographically distinct site
Redox active ions
Pathways for Mg-ion diffusion
Suitable ratio of Mg to redox active ions

15. Analogues of
electrodes in Li-ion
batteries
Make electrochemically
Mg-ion exchange
Make directly?
Explore Mg-
containing materials
with no Li-analogue
Identify suitable targets from reported
materials
Exploratory synthesis
Targets
High Voltage High Capacity
Reversible Rate capability
Materials selection criteria
Oxide or polyanion groups
Mg-ions on a crystallographically distinct site
Redox active ions
Pathways for Mg-ion diffusion
Suitable ratio of Mg to redox active ions

16. 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

17. 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/g
Mn2+

18. Performance in a Mg-ion battery
vs Mg with TFSI in ACN
3.5V cutoff

19. Performance in a Mg-ion battery
vs Mg with TFSI in ACN
2.5V cutoff

20. What is the maximum amount of Li
which can be removed?
• Test in a Li-ion cell

21. 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

22. MgMnB2O5 vs. Li – C/25
• Similar discharge
capacity to C/100
• Better efficiency
• 600 Wh/Kg is good
(LiCoO2 ~240Wh/Kg)

23. Le Bail refinements of cycled MgMnB2O5

24. • High capacity at
high rates (C/2)
• Batteries
operate over
multiple cycles

25. 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

26. Acknowledgements
• Hugh Glass
• Evan Keyser
• Zigeng Lui
• Jeongjae Lee
• Paul Bayley
• Clare Grey
• Dominic Wright