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Early Structure Change Diagnostics of Battery Materials for Design Optimization

J. Zhou, J. Wang, Y. Hu, L. Zuin, T. Regier, and T. BondCanadian Light Source Inc.Introduction:

Despite the many advances made in fundamental battery materials research, very few result in large-scale, commercially viable technologies. A significant bottleneck is the tedious and time-consuming performance testing of new battery systems. Element-specific X-ray absorption near-edge structures (XANES) spectroscopy and associated nanoscale chemical mapping tools can supply detailed information on the local chemistry of the individual elements, which can be used to investigate the chemical bonding and electronic structure of novel materials in bulk and at the surface. Synchrotron-based X-ray photoelectron spectroscopy (XPS) can be used to map the SEI depth profile non-destructively. Additionally, micro-XRD using a synchrotron source can be used to map charge/discharge processes in a time scale of milliseconds. Even more important, all of those techniques can be performed in-situ on an operating battery, which can be used to detect tiny structure changes in very short cycling period. This structural information can be combined with electrochemical data to improve prediction of battery performance on a much shorter timeframe than otherwise possible. This proposed approach may significantly reduce the time required to validate new battery technologies. This poster presents the application of XANES and STXM for correlating structure and performance in lithium ion batteries.

Techniques: XANES and STXM based on super bright light

Scanning transmission X-ray microscopy (STXM) is a soft X-ray spectromicroscopic technique based on XANES. It allows for quantitative chemical mapping of very small nanostructures. Above is an illustration of the STXM data reduction process.

1. Spectroscopic Insights to Cathode Surface/Interface Modification for Improved Performance and Storage Tolerance

LMFP is chemically anchored onto graphene via P-O-C bonding, which also changes the electronic and chemical properties to favor better electronic and ionic conductivity. These spectroscopic fingerprints could speed up screening of new cathode materials.

2. Nanoscale correlation studies using STXM

1) Regions with different rates of charging are found by imaging distribution of Fe3+ (fast) and Fe2+

(slow);

2) fast (Fe3+ ) region has stronger LMFP-graphene bonding

Chem. Commun., 2013, 49, 1765-1767

Phase transition during delithiation: size and surface bonding effects

Cascade (two phases separated in different particles) dictates the (de)lithiation process. Better C coating associates with fast (de)lithiation (fast nucleation)

P L-edge (a), Fe L-edge (c) and O K-edge (d) of LMFP/graphene and free standing LMFP

C K-edge XANES of LMFP/graphene and free standing graphene

STXM chemical maps of partially charged LMFP–C for visualizing the Fe valance distribution: (a) Fe2+ and (b) Fe3+, grey scale represents the thickness in nm; (c) the colour composite map of Fe2+ and Fe3+ The selected Fe2+ and Fe3+ regions are highlighted by the rectangular and circular box, respectively; (d) C K-edge XANES from the selected areas as displayed in 1(c).

Ultrafast LMFP/graphene composite

Phys. Chem. Chem. Phys., 2012, 14, 9578–9581 9579

Al2O3 coating on LiNi0.4Co0.2Mn0.4O2

NCM surface modification was carried out using a sol-gel process with aluminium isopropoxide as the Al source. The better thermal stability and electrolyte stability of modified NCM is visible, but the chemistry behind this improvement is not clear.

1555 1560 1565 1570 1575 1580

Abs

orpt

ion

(a.u

.)

Photon energy (eV)

TEY FY

520 525 530 535 540 545 550 555 560 565 570

Abs

orpt

ion

TEY

(a.u

.)

Photon energy (eV)

LiNiCoMnO2 Al2O3-LiNiCoMnO2

770 775 780 785 790 795 800

Ads

orpt

ion

TEY

(a.u

.)

Photon energy (eV)

LiNiCoMnO2 Al2O3-LiNiCoMnO2

XANES spectra reveal that Al is present in surface coating as Al(OH)3; The coating causes less Co 3d-O 2p hybridization and less surface reconstruction (less Li2CO3 after long term storage in air), all of which may relate to improved cathode safety.

Interfacial bonding and performance correlation study Binder distribution and side reaction distribution correlation

3 um550 600 650 700 750

0.01

0.02

0.03

0.04

0.05

OD

Photon energy (eV)

hot spot cold spot

680 685 690 695 700 705

norm

aliz

ed O

D

Photon energy (eV)

hot spot cold spot

PVDF

LiF+PVDF

774 776 778 780 782 784 786

norm

lized

OD

Photon energy (eV)

hot cold

Hot spot

Cold spot

XRF-based STXM indicates the existence of “hot spots” from a charged LiCoO2 electrode;

Those hot spots have higher relative concentrations of F;

F XANES shows that LiF is the dominated F species in both regions, but hot spots have more PVdF;

Co XANES shows that mixed Co2+, Co3+ and Co3.5+ are present in both regions, but hot spots have more Co3.5+

(a) O K-edge FY, (b) O K-edge TEY, and (c) C K-edge TEY/FY XANES spectra of discharged Li-O2 cathode electrodes to. (d) Schematic of discharge products formed at low and high capacity on CNTs onthe 1st discharge.

J. Phys. Chem. C 2012, 116, 20800−20805

X-ray absorption near edge structure (XANES) is a spectroscopic technique that is sensitive to the electronic, chemical and geometric structure of materials. This technique is sensitive to both surface (TEY) and bulk (FY).

Highlights:1) High-throughput screening of faster

discharge, safer and more stable electrode materials can be aided by XANES and STXM.

2) Electrode components and reactions (including side reactions) mapping by novel STXM shall aid electrode optimization (selection of binder and additives, components ratio, manufacturing process etl)

Al O Co

O F and Co O

FCo

F Co

Li2CO3

Co3+

Co3.5+

Co2+