ncm¦lto cells in (lp30 vs. il) electrolytes click to edit ... · pdf fileclick to edit...

Click to edit Master title stylePaul Scherrer Institut, Electrochemistry Laboratory, CH-5232 Villigen PSI, Switzerland

email@psi.ch

ELECTROCHEMISTRY LABORATORY

BA

TT

ER

IES

0

75150225300375

020406080100

0 50 100 150 200 250 3000

75150225300375

020406080100

/ Charge/Discharge RT Efficiency RT

Spe

cific

cha

rge

[mA

h/g]

Cycle

Cou

lom

bic

effic

ienc

y [%

]

Mario El Kazzi, Erik J. Berg, Claire Villevieille, Pe tr NovákPaul Scherrer Institut, Electrochemical Storage Energy Section, CH-5232 Villigen PSI, Switzerland

Mario.el-kazzi@psi.ch

ELECTROCHEMISTRY LABORATORY

BA

TT

ER

IES

Electrochemical performance and XPS surface analyses of HE-NCM¦LTO cells in (LP30 vs. IL) electrolytes

Scan me!

Objective Post mortem XPS – Process flow

Cycled with LP30* Cycled with BMIMBF 4**

Standard PSI CellGlove box assembling/disassembling

(I) (II)

Washed with DMC

Unwashed

Electrode

LP30

1M LiBF 4/BMIMBF 4

1 11

22

4

3 3

BF4

BMIM

LiPF6DMC EC

Sample holder

PSI XPS spectrometer

Transfer chamber

Under Aratmosphere

Al K α monochromatic source (500µm, 150W)

Flood Gun for charge compensation

Al K α and Mg K α non-monochromatic sources

Ar sputtering gun for depth profile analysis

UV lamp for band structure

HE-NCM LTO HE-NCM LTOWashed Unwashed Washed Unwashed Washed Unwashed Washed Unwashed

Conclusions

IntroductionThe instability of (electrode/electrolyte interface) at h igh temperatures (> 50 °C) and potentials (> 4.5 V) of the most common carbonate-base d electrolytes is limiting thedevelopment of the next generation of high specific energy L i-ion batteries.[1] However, these problems can mainly be o vercome by the use of ionic liquids (ILs) as alternativeelectrolyte solution. Their physical properties such as th ermal (> 120°C)/electrochemical (> 5.5 V) stability and low vapor pressu re make them a promising electrolytes.[2]

References

Negative Li4Ti5O12 (LTO)

Spinel structure

PositiveLi(Ni, Co, Mn)O 2 (HE-NCM)

Electrodes

�HE-NCM cycled versus the LTO plateau within thecutoff limits [2.4 V – 5.1 V vs. Li/Li+ ].

�LP30* and IL-based (1M LiBF4 in BMIMBF4)**used as electrolytes.

* 1M LiPF 6 with ethylene carbonate and dimethyl carbonate(EC:DMC 1:1)

** C8H15BF4N2, Cation: 1-Butyl-3-methylimidazolium, Anion: Tetrafluoroborate

80% Active material10% Super P

(Carbon)10% PVDF

[CF2-CH2]n

~20nm

Post mortem XPS and SEM

Electrochemical performance

�SEI & SPI surface composition and morphologyafter cycling.

�The origin and mechanism of the surface layerformation and its impact on the cell performance.

469 462 455

198 195 192

Binding Energy (eV)405 402 399

294 288 282

C=O

Super P

CF3

Ti4+

Ti3+

Ti2+

Unwashed

WashedDMC

� Formation of thick surface layer on LTO however is lesspronounced on HE-NCM.

� Detection of TiFx species on both electrodes related to the Ticorrosion of the cell.

� Detection of Mn and Co on LTO due to the transition metaldissolution in the electrolyte.

� After washing agglomeration of the IL on the active particles.

� Detection of IL decomposition product on both electrodes

� No detection of Ti on positive or Mn on negative electrodes

C1s Ti2p

Inte

nsity

(ar

b. u

nits

)

294 288 282

469 462 455

656 648 640

Mn2p

Pristine

C1s Ti2p Mn2p

294 288 282

469 462 455

656 648 640

Binding Energy (eV) Binding Energy (eV)

296 292 288 284

Binding Energy (eV)

Inte

nsity

(ar

b. u

nits

)

405 402 399

695 690 685

198 195 192

C1s N1s F1s B1s

Unwashed

WashedDMC

469 462 455

198 195 192

Binding Energy (eV)405 402 399

Inte

nsity

(ar

b. u

nits

)

294 288 282

C1s N1sTi2p Ti2p N1sC1s B1sB1s

Neat dropletBMIMBF 4

Financial support from BASF SE is gratefully acknowledged

� Good electrochemical cycling was demonstrated with LP30, however with the IL 36% less specificcharge was obtained with continuous fading up to 30 mAh/g after 130 cycles

� Important impact of the washing was observed on the surface composition mainly on LTO surface

With LP30 With BMIMBF 4

Super P

1

4

3

2CF3

BF4BF4

CF3

BMIM

C=OO-C=O

CO3

TiF4 TiF4

TiF4 Ti4+

Ti4+

Ti3+

C-OC=O

O-C=O

CFx

X≥2

CFx

X≥2

Super P

HydrocarbonCF2 CH2

PVdF

Super PC-C

Li2CO3

O-C=OC=O

C-O

Hydrocarbon

CF3

[1] John B. Goodenough , Rechargeable batteries: challenges old and new,J. Solid State Electrochem, 2012 16 2019-2029.

[2] M. Armand, F. Endres, D. R. MacFarlane, H. Ohno, B.Scrosati , Ionic-liquid materials for the electrochemicalchallenges of the future, Nature Materials, 2009 8 621-629.

2µm 2µm 2µm 2µm 2µm 2µm 2µm 2µm

Mn4+