$ Sn-P anodes for potassium-ion batteries
 insights from crystal structure prediction


Matthew Evans

6th September 2018


SMARTER6 Meeting, Ljubljana

croc croc cdt

Conversion anodes for beyond-Li batteries

Why batteries?

  • Electrification of transport
    • both personal and public
  • Computation
    • Mobile devices
    • Internet of Things etc.
  • Grid-level storage
    • load smoothing of intermittent renewables
    • lower costs, accelerate uptake of renewables
Conversion anodes:
n Li+ + AaBb ⟶ LixA + LiyB.

Conversion anodes for beyond-Li batteries

Why anodes? What's wrong with graphite?

anodes

The OQMD: Kirklin et al. npj Comp. Mat., 15010 (2015).

Conversion anodes for beyond-Li batteries

Why anodes? What's wrong with graphite? ...limited capacity, rate capability.

anodes

The OQMD: Kirklin et al. npj Comp. Mat., 15010 (2015).

Conversion anodes for beyond-Li batteries

Why beyond-Li? ...cheaper*, more sustainable, safer!

anodes

*Cost analysis of Na-ion batteries: Vaalma et al., Nature Reviews Materials 3, 18013 (2018).

Conversion anodes for beyond-Li batteries

Why beyond-Li? ...cheaper*, more sustainable, safer!

anodes

*Cost analysis of Na-ion batteries: Vaalma et al., Nature Reviews Materials 3, 18013 (2018).

Conversion anodes for beyond-Li batteries

Why beyond-Li? ...cheaper*, more sustainable, safer!

anodes

*Cost analysis of Na-ion batteries: Vaalma et al., Nature Reviews Materials 3, 18013 (2018).

Conversion anodes for beyond-Li batteries

Why K-Sn-P?

anodes

 

Transition metal phosphides: K-Sn-P

  • Earth-abundant, cheap materials.
  • Standard redox potential of K+/K (-2.93 V) comparable to Li+/Li (-3.04 V) (c.f. Na+/Na @ -2.71 V).
  • Highest capacity K-ion battery anode reported: Sn4P3.
    • W. Zhang et al, JACS 139(9), 2017
    • Phase chemistry of even the binaries is not well known: does K3P form? 13 K+ + Sn4P3 ⟶ 3 K3P + 4 KSn
  • Builds on previous work in our group on phosphides and stannides.

Previous work on stannides and phosphides

M. Mayo, K. Griffith et al., Chem. Mater. 28(7), (2016) 10.1021/acs.chemmater.5b04208

Previous work on stannides and phosphides

L. Marbella, M. Evans et al., JACS 140(25), (2018) 10.1021/jacs.8b04183

Where are the atoms?

Phase stability


Formation
Energy/atom
↓

Concentration, a   →

Crystal structure prediction


  1. Data mining
  2. Ab initio random structure searching (AIRSS)
  3. Genetic/evolutionary algorithms (GA)

K-Sn-P

  1. Data mining
    1. Experimental ksnp ksnp
    2. Theoretical ksnp ksnp
~ 50 structures
ksnp

K-Sn-P

  1. Data mining
    1. Experimental
      2. ksnp ksnp
    2. Theoretical ksnp ksnp
    3. Alchemical
~ 3,000 structures
ksnp
http://matador.science

K-Sn-P

  1. AIRSS
airss svg
~ 3,000 structures
ksnp
http://matador.science

K-Sn-P

  1. AIRSS
airss svg
~ 100,000 structures
ksnp

K-Sn-P

  1. GA

~ 100,000 structures
ksnp
http://ilustrado.rtfd.io

K-Sn-P

  1. GA

~ 150,000 structures
ksnp
http://ilustrado.rtfd.io

K-Sn-P

~ 3000 unique phases below 100 meV/atom from convex hull

ksnp

K-Sn-P

~ 2500 unique phases re-relaxed with high accuracy (~1 meV/atom)

ksnp

Binary K-Sn phase diagram

ksnp

Binary K-P phase diagram

ksnp

K3P

P 63/mmc vs P 63cm
ksnp ksnp

K-Sn-P

ksnp

K-Sn-P

ksnp

K-Sn-P

ksnp

K-Sn-P

ksnp

Novel ternary phases of K-Sn-P

KSn2P2 (left) and KSnP (right): layered van der Waals Zintl phase of SnP with intercalated K.
Isostructural to NaSn2As2 and KSnSb, found by AIRSS.

Novel ternary phases of K-Sn-P

K5SnP3 (left) and K8SnP4(right): Zintl phases with [SnP4]8- units.
ksnp ksnp
Isostructural to Na8TiAs4 and K5SnSb3.

K-Sn-P

ksnp

Summary

  • We are performing crystal structure prediction on metal phosphides, with the aim of finding the metal which maximises capacity with reasonable volume expansion.
  • Sampling a ternary composition space is tricky!
    • We have developed two main software packages, MATADOR and ilustrado to do so.
  • So far, this has been applied to the K-Sn-P system, with some success.
    • Binary phases: K3Sn17, KP7, K3P7, K5P4, and metastable KSn2, K3P.
    • 4 novel ternary phases have been found, K8SnP4, K5SnP3, KSnP and KSn2P2.
    • These phases extend predicted theoretical capacity by ~30% and ~20%.

What next?

  • Robustness of DFT results wrt. functional, dispersion corrections, pressure and temperature.
    • Improving our thermodynamic descriptors.
  • Experimental verification! All data will be open and explorable (soon™).
  • Can we use the wealth of metastable phases sampled to say something about kinetics?

Acknowledgements

ml-evs.github.io ▬ me388@cam.ac.uk ▬ www.andrewjmorris.org

K-Sn-P: Andrew Morris, Kent Griffith

AIRSS review: C. Pickard and R. Needs, JPCM 23(5), (2011) 10.1088/0953-8984/23/5/053201
LiP/NaP CSP: M. Mayo, K. Griffith et al., Chem. Mater. 28(7), (2016) 10.1021/acs.chemmater.5b04208
NaP CSP+NMR+XRD: L. Marbella, M. Evans et al., JACS 140(25), (2018) 10.1021/jacs.8b04183