Chemical Imaging of High Voltage Cathode Interface

Transcription

1 Chemical Imaging of High Voltage Cathode Interface Jigang Zhou Canadian Light Source (CLS) 34 th International Battery Seminar And Exhibit Fort Lauderdale, FL March 20-23,

2 Billion times brighter than lab X-ray 2

3 Solution provider Structure Performance Dynamic process inside cell Non-destructive depth profiling of SEI Versatile tools: 15+6 beamlines Dedicated industrial science group (IP protected) 3

4 About me Staff scientist at the Industrial Science group at CLS 20 years experiences on battery R&D and advanced characterizations Caring industrial needs Building up advanced characterization platform Studying interface in high voltage cathode and Solid battery ResearcherID:N

5 Outline Introduction: Challenges in interface study and solutions offered by large facility Examples Interface in RuO 2 coated LiNi 0.5 Mn 1.5 O 4 (LNMO) Interface imaging of large LNMO particle Interface imaging of cycled high voltage LCO composite electrode Conclusions 5

6 Interface and challenges in characterization Nanotechnology 26 (2015) Limited understanding of the buried interface being critical to charge transportation and electrolyte stability Surface analysis tool with deeper probe depth than popular XPS is needed (XAS) 6 Adv. Energy Mater. 2016, Coating PCCP, (33), Interface SEI J. Mater. Chem. A, 2015, 3, PCCP, (27), Chem Comm, (17), EES, (3), Rsc Adv, (39),

7 Chemical imaging of interface in composite electrode To gain Components distribution effects Interface variation within individual particle Chemistry on other components J. Power Sources Impacts to battery industry Crystalline face engineering for optimized cathode materials Optimization of electrode fabrication Optimization of battery operation 7

8 Interface depth profiling by XAS spectroscopy Element selective, chemical sensitive, probe depth variable and non-destructive Photon out (FY) electronic structure: DOS,spin state... Photon in Electron out (TEY) oxidation state X-ray absorption spectroscopy (XAS) concentration Photon energy (ev) SEI Coating nm 10 nm 8

9 Imaging (i) :Scanning Transmission X-ray Microscope (STXM) Features Isotropic phase transportation Element selective, chemical sensitive (XAS) 30 nm spatial resolution (can be sub 10 nm) Much less radiation damage Thin sample is needed Ni 2+ Ni 3+ Ni nm Anisotropic phase transportation EES, (3), Chem Comm, (17), JMCA, (38), JPCL, (11),

10 Novel STXM using FY or TEY yield Photon out (FY) Photon in Electron out (TEY) Monochromator and Refocusing Optics Zone Plate OSA Sample in Focus SEI Coating nm 10 nm Raster Scanned Sample Stage Detector PCCP, (33), Large electrode particle and composite electrode can be studied 10

11 Imaging (ii) :Photoemssion electron microscope (PEEM) Monochromatic X-rays Failure analysis correlation of components migration, agglomeration with degradation Fe 2+ CB um Features Element selective, chemical sensitive (XAS) Fast chemical mapping (field view mapping, nano XAS via TEY mode) Commercial composite electrode can be studied PVDF LFP Fe 3+

12 Case 1: Interface and Mn dissolution Mn 2+ Mn 4+ J. Mater. Chem. A, 2015, 3, Mn 2+ Mn 4+ MnO MnO FY (100 nm) Photon energy (ev) TEY (10 nm) RuO 2 coating cause Mn 2+ -like species in LNMO interface Related to phase change/cation or anion ordering Al 2 O 3 coating doesn t have such effect Much less Mn dissolution in RuO 2 coated LNMO 12

13 Case 2: Interface of large Fe-doped LNMO particle study by FY STXM Ni Fe Ni Fe (111) (100) (111) 4 um Fe aggregation in some regions 13 Identification of phase pure (111) and (100) face for chemistry comparison PCCP, (33), Adv Energy Mater, (3): 1662

14 Confirmation of chemistry difference Mn 3+ (100) (111) Mn 3+ Mn 4+ Mn 2 O 3 Mn 4+ MnO Photon energy (ev) More Mn 3+ in (100) face, might be relevant to its fast reaction rate Ni, Fe and O chemistry and Fe spin state are not face dependent Photon energy (ev) PCCP, (33),

15 Case 3 TEY STXM of large LNMO surface (most top 10 nm) Photon energy (ev) Mn with lower oxidation state on surface Chemistry difference between (111) and (100) can be confirmed Conductivity mapping 15

16 Case 4: Chemical imaging of cycled high voltage LCO LCO electrode (LCO:CB:PVDF 80:10:10) cycled in 1M LiPF6 in EC/DMC electrolyte with 0.1 M LBOB+5% dinitriles between 4.5 and 3 V at 1C for 3 times and then fully discharged (JES ) µm Co C LCO (001) face with less coverage CB clusters 16 ACS Appl. Mater. Interfaces 2016, 8,

17 Chemistry from various components 2 CoFO (b) Co PVDF LiF 1 Co 2+ CoF photon energy (ev) More Co 2+ in region 2 which is also CB aggregation region. CoF 2 formed (685 ev feature in F XAS) and rich in CB cluster region In contrast, less CoF 2 was formed and enriched on LCO surface wo B/N additives Photon energy (ev)

18 Additive effect on Co-O valence at interface O 2p-Co 3d cycled with B/N cycled wthout B/N Absorption (a.u.) O2p-Co 4sp Photon energy (ev) J. Am. Chem. Soc. 2013, 135, Lower Co-O covalence (might be via N-LCO interaction) in LCO cycled with B/N shall increase LCO stability during high voltage cycling. 18

19 Conclusions High voltage cathode interface under surface coating/sei is worthy to be studied for a better stabilization Various characterization tools are available at CLS to gain new insights on interface Elemental selective XAS can obtain interface information from top 10 nm and from top 100 nm Nano-XAS (STXM and PEEM) can get lateral mapping of interface in large particle or in composite electrode with 30 nm spatial resolution. 19

20 Acknowledgements Collaborators at CLS Dr. Jian Wang at SM beamline Dr. Tom Regier at SGM beamline Mr. Toby Bond and industrial science group Collaborators out of CLS Prof. Xiao-Qing Yang at BNL Prof. Haitao Fang at HIT Prof. Yong Yang at Xiamen University 20

21 backups 21

22 Detection modes for XAS Transmission µ µ t I t = Ioe or t = ln( I o / I t ) Yield (electron ~ 10 nm or Fluorescence nm) µt 22

23 Large facility for complex problems VA M1 PGM 23 Photon Energy Range: 130 ev ev Energy Resolution: E/ΔE Flux: 10 8 Photons/s (STXM), Photons/s (X-PEEM) X-PEEM M3PEEM M3STXM PEEM ES M4PEEM Ambient-STXM X-PEEM STXM ES Cryo-STXM (under commissioning) A-STXM C-STXM 23

24 Comparison with other techniques Chemical Information Content High NMR IR OM RM X-PEEM XPS EDS FM NSOM STEM-EELS SEM TEM STM AFM Low 100 mm 1 mm 10 nm 1 Å Technique Spatial Resolution Speciation Capability NMR > 1 µm excellent IR > 1 µm excellent Raman ~ 0.3 µm excellent Optical ~ 0.5 µm needs chromophores Scanning probe nm variable TOF-SIMS ~ 1 µm excellent (S)TEM - EELS < 10 nm good (but radiation damage!) Soft X-ray spectromicroscopy ~ 30 nm excellent Spatial Resolution Excellent combination of spatial resolution and chemical speciation Quantitative chemical analysis Multiple environments - wet, magnetic fields, cryo, surfaces etc. Much lower radiation damage than TEM-EELS 24 24

25 Data Acquisition and Analysis Fe 2p Normalization: ratio to I 0 Silicate (1) Graphite (2) 2 12 µm 1 Geophysical mineral from Athabasca basin Reference spectra from pure regions or external I TEY = Ω µρl I 0φ 4π sinθ Energy (ev) PEEM spectrum can be quantitative!! 25 U. Lanke, et al. unpublished data Unknown Systems: PCA-Cluster Analysis for all pixel spectra Known Systems: Pixel spectrum fit with linear reference spectra (SVD) 25

26 Interface and electrode stability (self discharge) Isotropic phase transportation Self discharge of fully charged LNMO via proton insertion Ni 4+ Ni 3+ Ni 2+ Ni 4+ Ni 3+ Interface (Ni 2+ )on large cube shaped LNMO stops the self discharge Ni 2+ Ni 3+ Ni nm Anisotropic phase transportation Fully discharged Ni Photon energy (ev) Intrinsic particle property causes different phase transportation 26

27 Additive effect on electronic structure of LCO interphase Electronic structure of electrodes with and without B/N can be compared such as the exposed LCO (001) facet Cycled with B/N Pristine Cycled without B/N Absorption (a.u.) Photon energy (ev) Much less Co2+ was formed without B/N. 27