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New NMR Approaches For Studying Battery Materials and Fast Ionic Conductors

New NMR Approaches For Studying Battery Materials and Fast Ionic Conductors Julien Breger, Meng Jiang, Young Joo Lee, Wonsub Yoon, Namjum Kim, Francis Wang, John Palumbo and Clare P. Grey SUNY Stony Brook. Introduction. Part I: Batteries How do rechargeable batteries work?

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New NMR Approaches For Studying Battery Materials and Fast Ionic Conductors

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  1. New NMR Approaches For Studying Battery Materials and Fast Ionic Conductors Julien Breger, Meng Jiang, Young Joo Lee, Wonsub Yoon, Namjum Kim, Francis Wang, John Palumbo and Clare P. Grey SUNY Stony Brook

  2. Introduction • Part I: Batteries How do rechargeable batteries work? What are some of the technological requirements for 21st century devices? Where are some of the fundamental scientific breakthroughs required to achieve these goals? What “New” approaches can be used to investigate Li-ion battery materials? Introduction to NMR Application to spinels and layered materials • Part II: Ionic Conductors Mechanisms for ionic conduction in solids Devices that require rapid ionic conductivity Studying motion by NMR Applications to Aurivillius phases

  3. Part I. Rechargeable Batteries: Applications and Demands • Portable (electronic) technologies have created an increasingly high demand for batteries that • last considerably longer and deliver power faster • are non-toxic and may be readily recycled • are cheaper and much lighter.. • Applications include: • Electric and Hybrid Electric Vehicles (EVs and HEVs) • Golf carts, wheel chairs and industrial vehicles • Laptops • Cell-phones • digital cameras • Camcorders, portable tools • Artificial hearts (current battery lasts 4 hours!) • memory backup, energy storage, • generators, power for remote locations...

  4. Low Power (high energy) High Power Different Applications Have Very Different Power Requirements • Portable Electronics (Cell phones, laptops, PDA, digital cameras) • Medical Devices • Portable tools • Back-up power (UPS) • EVs and HEVs • Electric bikes/scooters • “Industrial” EV, forklifts, golf carts • Power Storage for Renewable Energy

  5. -MnO2 (cathode) Li (anode) Charge Li+ Separator (electrolyte) Li+ Discharge Li/MnO2 bobbin cell Chemistry is not reversible Batteries come in two types: • Primary: discharged once and discarded - lower energy/capacity applications • Secondary: rechargeable and can be used over again (e.g., Ni/Cad), rocking chair batteries Cathode: LiCoO2 Anode: Graphite LixC 3 V

  6. What is in a battery? The Ni/Cd or NiCad Rechargeable Cell Negative electrode Electrolyte Positive electrode (anode) (aqueous) (cathode) Cd0 + 2OH- Ni3+OOH + H2O + e- --> Cd2+(OH)2 + 2e---> OH- + Ni2+(OH)2 • OH- ions released at the cathode travel to the anode where they react with the 1.35V Cell Cd metal. I.e., electrolyte must allow ionic but not electric conduction • Difference in the couples (reduction potentials) of the two 1/2 cells determines the cell voltage Cd NiOOH OH- e-

  7. What is required to build a rechargeable battery? • Design a cell in which the chemistry is reversible over many cycles e.g., the lead acid (car) battery: (Pb0 + Pb4+O2 + H2SO4 -> 2Pb2+SO4 + 2H2O) 2V Requirements: • large differences in the potentials of the half cells (i.e., Pb4+/Pb2+ and Pb2+/Pb0 => High voltages • Light materials => High energy densities • An electrolyte that does not react with the anode or the cathode (under as wide as possible temperature range) • An electrolyte with high ionic conductivity Allows rapid discharge • Conducting anodes and cathodes => (and charge) (Allows current to be removed) I.e., high power densities • Non-toxic materials • Stable in charged and uncharged states H2 evolution; unstable in discharged state

  8. Much higher voltages may be achieved with Li-ion batteries • In theory, a more than 2V gain in voltage can be achieved with a Li+/Li anode • Li is also v. light ---> higher energy densities • Some electrochemistry: E0 (V) Li+(aq) + e- -> Li (s) -3.04 PbSO4(s) + 2e- -> Pb(s) + SO42-(aq) -0.36 Cd(OH)2 + 2e- -> Cd(s) -0.824 [Cd2+(aq) + 2e- -> Cd(s) -0.402] 2H+(aq) + 2e- -> H20 J. -M. Tarascon Nature ‘01 E.g., LiTiS2 ----> TiS2 + Li Whittingham et al. ‘72 but….

  9. The big advance in this field came with the development of the SONY “Rocking-Chair” battery in 1990 • LiCoO2, J. Goodenough (1980) • 2ndary host material, Murphy et al., and Scrosati et al. (‘78 and ‘80) • Lithium shuttles backwards between two layered compounds • Very high voltage (4 V; cf Ni/Cd @ 1.35 V)

  10. Solid state chemistry at the cathode end... Positive Electrode Polymer Binder Co3+ is oxidized to Co4+ on Li removal (deintercalation) I.e., during charging Carbon black voltage vs. Li/Li+ Intercalation Oxide Co Li O Ohzuku et al. J. Electrochem Soc. 140, 1862, ‘93

  11. Charging And at the anode end.. • Graphite anode forms an intercalation compound LixC Tarascon Nature, ‘01 Energy density Cycle Life Voltage SONY Cell 90 Wh/kg 500-1000 4V Pb acid 30 250-500 2V Ni/Cd 30-35 300-700 1.3V Ni metal hydride 50 300-600 1.2V Energy density (Whkg-1)

  12. Why is more research needed?Some disadvantages of the LiCoO2 cell • Co is toxic and expensive • Not sufficient Co globally to meet perceived demands for rechargeables • Only 0.5 of the Li can be removed. I.e., low capacity • V. slow to charge and discharge (low power) - not suitable for E.V.s, H.E.V.s or other high power applications - Li

  13. What is motivating all this work?New markets for Li Power tools Bosch, Makita, Cooper, Milwaukee, Metabo all have high end powertools with Li-ion batteries spinels Already happening Currently all NiMH Clearly effort to go to Li-ion (e.g., Toyota, Johnson Controls, Samsung) Hybrid Vehicles Conservative estimate of 3.5% HEV market penetration in 2010 requires 1 Million KWh of battery capacity.$1-3 Billion dollar market Soon to come? Power back-up (small and large) Future market?

  14. A Large Growth is Predicted for the Li-ion Battery Technology - which will be driven by improvements in performance Ni-Cd Ni-MH Li-ion expensive, high power, average energy density, no further improvement expected Still expensive, lower power, high energy, safety inexpensive, high power, low energy Market $1 Billion $0.6 Billion $4 Billion World-wide battery market From The Cobalt report (2005)

  15. Alternative LiB Materials Under Consideration: Voltage vs. Capacity Cathodes • “Issues and challenges facing rechargeable lithium batteries”, J.-M. Tarascon and M. Armand, Nature 414, 359-367 (2001) LiCoO2 Anodes C Li metal

  16. Some Advances in the Anode Field: Nanoparticles and Composites • Metals and alloys show v. high capacities (e.g, Si = 4200 mAhg-1 approx. 10x that of graphite), but suffer from extremely large volume expansions • => use a composite (of nanoparticles/domains) to absorb stresses during cycling (less problem with reactions with electrolytes at low voltage - fewer safety issues) • Field sparked off by the discovery of Tin-Based Amorphous Oxides (TCO): Sn1.0B0.56P0.4Al0.4O3.6(Kubota, Matsufuji, Maekawa, Miyasaka, Science, 276, 1997) TCO : SnO + SnO2 --> Li2O + Sn ----> LixSn Li2O CoO + 2Li ---> Li2O + Co (740 mAhg-1) S. Grugeon… J.-M. Tarascon, 2003

  17. Other approaches - extrusion/displacement reactions • InSb + Li ---> Li3Sb + In --> LixIn • Cu2Sb + Li ---> Li3Sb + In M. M. Thackeray, J. Vaughey (1999) J. Dahn • Cu2.33V4O11 + x Li ----> LixCu2.33-y V4O11 + yCu M. Morcrette, J. -M. Tarascon (2001) Reversibility?

  18. What other cathode materials are being investigated? • Both Fe and Mn oxides have been studied extensively as alternative cathode materials (cheap and non-toxic) E.g.: • 3 dimensional structures such as: -Manganese Spinels LiMn2O4 --> MnO2+ Li -Good electronic conductivity - high power low capacity LiFePO4and related phosphates - low capacity -Poor electronic conductivity - good rate performance (with C coating) • New layered Materials such as Li(NiMn)0.5O2, Li(Co1/3Mn1/3Ni1/3)O2 (Mn4+) • High capacity ---poorer rate performance? • Layered lithium vanadates (for static power supplies) C LiFePO4

  19. Improving the materials performance requires a fundamental understanding of how materials function and what structural/electronic properties limit battery performance • Structures of the materials as they are cycled • Where are the Li+ intercalated into the structure? • Electronic properties - • How do they change as Li+ is removed? • Ionic conductivities • How do the Li+ ions move through the lattice? • Effect of structure and electronic properties on voltage (e.g., Co3+ -> Co4+; Fe2+->Fe3+) • Li+ in oct vs. tet. sites • A whole variety of experimental and theoretical methods have been used to study these systems including: • Electrochemistry (voltages … infer structural changes) • Diffraction methods (long range structure) • XANES (local structure and oxidation state) • Solid state NMR (local structure)

  20. WHY NMR? Solid State NMR can be used to obtain: Local atomic structure + Local electronic structure In theory, we can use NMR to study these systems and determine: where the Li+ ions are, their local coordination environments, and the Mn electronic structure ...…..at each stage of charge/dischargeto obtain fundamentalinformation about how the battery works …and how the battery fails Mn(IV) (III) Mn Oxidn states? LiMn2O4 We perform lithium NMR, since the lithium is directly involved in the electrochemical process...

  21. But what is nuclear magnetic resonance (or NMR)? • Require nuclei (e.g., 1H, 13C, 6Li, 7Li, 31P) that have non-zero nuclear spins • Spin-1/2 vs. quadrupolar (I>1/2) • Nuclei behave like tiny bar magnets in a magnet field DE Each nucleus has a characteristic energy splitting DE, which depends on the magnetic field strength B0 => element specific Detect signal at frequency corresponding to DE, with intensity proportional to no. of spins => quantitative Bo

  22. S Basement @ Stony Brook NMR of Solids • NMR spectra of solids are broadened by the anisotropic interactions (interactions whose magnitude depends on the orientation wrt field), e.g.,: • Chemical shift anisotropy • Dipolar coupling (Nuclei interact with each other, in the same way that two bar magnets interact) • Quadrupolar interaction • 6Li (I = 1); 7Li (I = 3/2) • Much of the chemical information can be lost • Cf liquids NMR where the tumbling of the molecules removes these interactions B0 q rIS I HD = -D(3cosq - 1)IzSz D = g I g Sh/2pr3 Liquid NMR, e.g., CH3CH2OH 1H Solid State 1H NMR

  23. Bo = 54o 44’ rt Most of the anisotropic interactions may be removed by Magic Angle Spinning: The bigger the interaction, the faster we need to spin Axial CSA Powder pattern nr Slow MAS (3cos2q - 1) = 0 nr time Frequency, w Faster MAS nr Rotor period = 1/nr

  24. NMR is also very sensitive to motion • E.g., Two Site Exchange • kr(A-B) • A <----------------> B f (Hz) Slow exchange k << f Timescale Hz kHz MHz Intermediate regime k same order as f Lineshape changes T1r T1 Loss of satellite transitions T2 • NMR can be used to: • extract correlation times and activation energies for motion • determine which sublattices are mobile Fast exchange k >> f

  25. Many of the battery materials are paramagnetic, which introduces additional complications d electrons Mn4+ Co3+ Co4+ Li2MnO3 (LiMn2O4) LiCoO2 Li1-xCoO2 B0 NMR ESR meff T1e Magnetic moment- depends on the no. of unpaired e-  Time averaged value of magnetic moment ac no field NMR timescale In order to extract structural information, we need to understand the effect of the unpaired electrons on the NMR spectra

  26. 520 1 0 0 0 8 0 0 6 0 0 4 0 0 2 0 0 0 m p p The Fermi-contact shift results in large shifts - these shifts contain both structural and electronic information • The Fermi Contact Shift: measure of the unpaired electron spin density transferred from the paramagnet to the NMR nucleus Hc = IzAs<Sz> <Sz>  c E.g., LiMn2O4 6Li MAS NMR Fermi Contact Shift Mn t2g Typical chemical shift for diamagnetic compound Li C.f. J-coupling and magnetic coupling H N C H

  27. Li Mn Mn q rIS I <SZ> Mn Li Zn The sidebands are largely caused by the dipolar coupling, which contains geometric information • The dipolar interaction: through space coupling to nearby nuclear or e- spins Li2MnO3 B0 Oh (2b) Li0.5Zn0.5[Mn1.5Li0.5]O4 • Very different sideband patterns are observed, depending on the arrangement of Mn around the central Li. Oh (4a)

  28. 520 1 0 0 8 0 0 6 0 0 0 0 2 0 0 0 4 0 m p p NMR spectra are also sensitive to electronic conductivity mechanism • LiMn2O4 is a hopping semiconductor • Li “sees” an average oxidation state => only one local environment Li (8a Td) Mn (16d Oh) C.f. metals - Knight shifts seen

  29. 520 512 ? 650 C 551 588 512 590 600 C 554 635 498 575 546 550 C 630 1000 800 600 400 200 0 ppm But… how do we explain the different local environments seen in LiMn2O4 as a function of synthesis temperature? Synthesis Temperature 850 ºC .. and obtain chemical information from these systems • Materials synthesized at lower temperatures show: • better cathode performance • higher average Mn (IV) oxidation states

  30. Understanding the 6Li NMR Shifts: Use of Model Mn III/IV compounds

  31. Litet[Li1/3Mn5/3]octO4 Lithium “Hyperfine Shift Scale” • use shift as a “fingerprint” of different Li local environments Li2Mn4O9 Mn3+, Mn4+ K2NiF4 cmpds Mn3+ rock salts Li in Lilayers Li in Mn4+ layers Mn4+ layered materials Mn3.5+ spinel Tet Li Oct Li Tet Li Mn4+ spinel 2500 2000 1500 1000 500 0 -500 ppm

  32. The Fermi contact shift depends on the coordination environment & nature of the orbital overlap 16c O Mn Li4Mn5O12 Li2Mn2O9 Li2MnO3 Li

  33. We can rationalize the shifts by using the same approach used to analyze magnetic couplings between spins: “Goodenough- Kanamori Rules” 90º Bo t 2g Li Spinel: +ve shift:~ 300 ppm -ve shift: ~ -100 ppm t 2g 122º Li d 2 z 180º Transfer to an empty dz2: spins align with e- in t2g orbitals to maximize exchange interaction 12 x 122º 12 x ~ 64 ppm

  34. DFT calculations can be used to help understand the causes of these hyperfine shifts, by calculating the unpaired e- spin density on Li Layered LiCr0.1Co1.9O2 Cr3+, d3; isoelectronic with Mn4+ +ve Co LiCoO2 Co 90° interaction 0 Li 180° interaction Li Co -ve spin density = -ve shift Li 90° interaction CrO Plot spin densities of: Dany Carlier Gerd Ceder Michel Menetrier I.e., unpaired e- density t2g

  35. We can now use this hyperfine shift scale to investigate Li local structure in cathode materials EXAMPLE 1: The effect of cation doping on the Spinel Structure • E.g. I, Spinels: MnO2 (Mn4+) - + Li -> LiMn2O4 - + Li --> Li2Mn2O4 (Mn3+) One source of capacity fade comes from the Jahn Teller Distortion that occurs in the discharged state (for Mn oxidation states of 3.5 and less). • Expansion and contraction of the unit cell can cause grains to lose contact with each other and the carbon in cathode =>suggested to be responsible for severe drop in capacity • Potential solution: Cation doping is used to raise the average manganese oxidation state of Mn at the end of discharge to above 3.5 Local Macroscopic Mn3+

  36. 550 583 639 2300 674 * * * * 2500 2000 1500 1000 500 0 -500 -1000 ppm Li - Excess Spinels E.g., Li[Li0.05Mn1.95]O4 = Li[Li0.05Mn4+0.25Mn3.51.70]O4 5 “Mn3.5+” ions oxidized per Li+ dopant : Average oxidation state = Mn3.56+ Tet Li Mn3.5+ LiMn2O4 Oct Li (spinel) Increasing oxidation state

  37. Eg energy levels perturbed near the defect sites  localization of e- holes 550 583 eg 639 2300 674 * * * * t2g 2500 2000 1500 1000 500 0 -500 -1000 Mn3+ Mn4+ Mn3+ Mn4+ ppm Defect The Additional Resonances are due to Mn4+ sites near tet Li Oct Li Mn (IV) Li Oct Site • Mn4+-rich regions are created near Oct Li Li(OMn3.5+)12-x(OMn4+)x

  38. 520 551 588 512 590 554 635 498 575 546 630 1000 800 600 400 200 0 ppm Lithium-excess materials are also formed at low temperatures, even for “stoichiometric” compounds 7Li MAS NMR 45 kHz MAS LiMn2O4 850 C Tet. Li 650 C Mn oxidn state increases 513 Oct. Li 2300 600 C * * Li1+xMn2-xO4 + Mn2O3 * 550 C * * x40 6Li MAS NMR 9 kHz MAS 4000 3000 2000 1000 0 PPM

  39. Li NMR can be used to determine whether Li+ substitutes on the oct. or tet. site of the spinel cathode materials LiM’xMn2-xO4 Td Oh 283C • Helps explain why Zn2+ systems don’t work so well - Zn2+ in tet site blocks Li+ diffusion (J. -S. Kim.. M. M. Thackeray, JES, ‘03) • Concentration of “extra” peaks related to oxidation state of dopant metal Td LiCr0.1Mn1.9O4 LiNi0.1Mn1.9O4 LiZn0.1Mn1.9O4 Oh Li1.05Mn1.95O4 Oh

  40. End Bolt Copper Plunger Battery Cycler Swagelock Li Anode Filter Paper Polypropylene Separator LiMn2O4 Cathode Following the Electrochemical Process Li1.05Mn1.95O4 at 4V Swagelock-type Cell Capacity (mAhg-1) End Bolt

  41. Oct Li Li1.05Mn1.95O4:1st Charge • Li+ ions are removed from local environments containing progressively more Mn4+ ions as the charging proceeds • Li remains in the oct. site throughout • Li+- ion mobility increases - particularly in 1st 1/2 of charge Increasing Mn oxidation state

  42. 25 % 485 557 10 % 1000 500 0 -500 -1000 Loss of structure => Mobility Li+ (+ e- ?) jump rates > 2 kHz f (Hz) Slow exchange k << f 25% 10% Intermediate regime k same order as f Fast exchange k >> f ppm

  43. Local Structure in Doped Spinels Random cation (Li+) doping on the octahedral site will: 1. Create Mn4+ ions nearby the dopant cations 2. Prevent Li+ removal from sites near octahedral Li+ 3. Create a 3D framework with a distribution of charges from 1 to 4+ All these factors help prevent the formation of a series of phases with long range lithium-ion ordering during cycling => Helps improve the capacity retention? Lix [Li0.05Mn1.95]OhO4 Oct. Li Tet. Li Panasonic

  44. Example II: Ni2+/Mn4+ Layered Cathodes, Li[NixMn(2-x)/3Li(1-2x)/3]O2: A Combined XAS, Diffraction, DFT and NMR Study LiNiO2 • These compounds may be viewed as solid solutions between Li2Mn4+O3 (Li(Li0.33Mn0.67)O2) and Li(NiMn4+)0.5O2 Li[Li1/3Mn2/3]O2 Li(Ni1/2Mn1/2)O2 0 1/3 1/10 x = 1/2 V Capacity: mAhg-1 LiCoO2 LiMnO2 Ni, Mn DATA From: Z. Lu, D. D. MacNeil, J. R. Dahn, ESSL4, (2001) A191-A194. Li(NiMn)0.5O2(T. Ohzuku, J. Dahn) Isostructural with LiCoO2 Oxidation/reduction process involves multiple electrons (Ni2+ -> Ni4+ ???) Li

  45. Approx. 200 mAhg-1 reversible capacity can be obtained • Similar capacities obtained by other groups for: • x = 1/2 (T. Ohzuka) • Li excess materials (C. Johnson and M. M. Thackeray; Z. Lu and J. Dahn) • Is the redox active metal Ni2+? • How do these systems function? • How does local structure effect electrochemical performance? 20 cycles C/20 LiMn0.5Ni0.5O2

  46. c c c a. Local Structure: Li[Li1/3Mn2/3]O2 • Li sites in Li and Mn layers readily resolved Mn Li in lithium layers Mn * * * * * 3000 2000 1000 0 -1000 PPM MAS speed: 36 kHz

  47. Ni doped compounds show similar spectra Ni2+ (d8) no unpaired t2g e- Li[Li1/9Mn5/9Ni3/9]O2 Li2MnO3 shifts Mn/Ni Mn/Ni Li in the Li layers Mn: 6 5 Li in the Ni/Mn layers near Mn4+ • Li2MnO3-type local environments still observed

  48. “Li[Ni0.5Mn0.5]O2” • 6Li NMR shows that there are still Li ions in the Ni/Mn layers, near Mn4+ even tho’ these are not predicted based on the stoichiometry Ni/Mn Li Li2MnO3 shifts • Li+[Ni2+0.5Mn4+0.5]O2 --> • Li1-xNix[Mn0.5Ni0.5-xLix]O2 Mn/Ni Li in the Ni/Mn layers near Mn4+ ppm • This is consistent with Ni2+ substitution in the Li layers (c.f. Dahn 2002)

  49. 006 104 10-2 110 10-8 009 101 Neutron Diffraction (ISIS, GEM) are consistent with Ni2+/Li+ exchange model Bank 4 • Extra peaks: superstructure peaks as seen for honey-comb ordering of Li2MnO3 (J. Solid-State Chem. August2005) • Exchange of Ni and Li ions between the TM and Li layers: 8 ± 2 % of site exchange: consistent with NMR 7Li(Ni0.5Mn0.5)O2 Rwp = 6.32% Li Li/Mn layer in Li2MnO3 Mn

  50. Local structure as a function of Ni content? Li2MnO3 shifts Li in the Li layers Mn/Ni Li[Ni1/10Mn19/30Li8/30]O2 Li[Ni1/3Mn5/9Li1/9]O2 • Li in Ni/Mn layers is predominantly near Mn4+ and not Ni2+for all compositions • What does this tell us about the cation ordering in the Ni/Mn layers? LiNi0.5Mn0.5O2 Li in the Ni/Mn layers near Mn4+

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