Lithium-Ion Batteries: Challenges and Opportunities in an Evolving Lithium Economy presented by Michael M. Thackeray Almaden Institute 2009 Scalable Energy Storage: Beyond Lithium Ion San Jose, California August 26 - 27, 2009 Acknowledgments Chris Johnson (ANL), Sun-Ho Kang (ANL), Vilas Pol (ANL), Lynn Trahey (ANL/NU), Jack Vaughey (ANL), Khalil Amine (ANL), Mali Balasubramanian (APS-ANL), Swati Pol (APS-ANL), Harold Kung (NU), Dongwon Shin (NU), Chris Wolverton (NU) Department of Energy • Vehicle Technologies Program Office of Energy Efficiency and Renewable Energy • Energy Frontier Research Center Center for Electrical Energy Storage: Tailored Interfaces Office of Basic Energy Sciences This presentation has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC0206CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. 2 The First Oil Crisis (mid 1970’s) Non aqueous batteries - sodium or lithium? High temperature systems (300-450C) already established Na / -Al2O3 / S Chloride Silent Power, British Rail (UK) Brown Boveri (Germany) LiAl / LiCl, KCl / FeSx Argonne National Laboratory (USA) Oil crisis sparked the development of the sodium-metal chloride ‘Zebra’ battery (1978) Na / -Al2O3 , NaAlCl4/ MCl2 (M=Ni, Fe) CSIR (South Africa) Courtesy of www.copyright-free-pictures.org.uk 3 Theoretical and Practical Properties of Batteries (theoretical values based on the masses of active electrode and electrolyte components) System Negative electrode Positive electrode OCV (V) Th. Cap (Ah/kg) Th En. (Wh/kg) Pr. En. (Wh/kg) Lead – acid Pb PbO2 2.1 83 171 20-40 Ni-Cd Cd NiOOH 1.35 162 219 40-60 Ni-MH MH alloy NiOOH 1.35 ~178 ~240 60-80 Na-S (350C) Na S 2.1-1.78 (2.0) 377 754 120-150 Na-MCl2 (300C) Na NiCl2 2.58 305 787 80-100 Li-Ion LixC6 Li1-xMO2 4.2-3.0 (4.0) 95 (for x=0.6) 380 150-200 3.3-2.0 (2.6) ~340 ~884 ~150 (M=Co, Ni, Mn) Li-polymer Li VOx Lithium-ion systems offer the best near-term opportunities What lies ‘beyond lithium-ion’? 4 Ragone Plot of Various Electrochemical Energy-Storage Devices Specific Energy (Wh/kg) Range 1000 6 4 IC Engine Li-Air? Fuel Cells Li-Ion 100 h 2 100 6 4 2 Li-ion Na/NiCl2 Ni-MH Lead-Acid 10 10 hh Ni-MH Lead-Acid HEV goal 10 Capacitors 6 4 2 1 100 EV goal (EoL) PHEV-40 (EoL) PHEV-10 (EoL) Capacitors 1 1 hh 0.1h h 0.1 101 36 36 ss 10 2 3.6 s 10 3 10 4 Specific Power (W/kg) Acceleration Source: Amended from Product data sheets 5 The Sodium-Nickel Chloride Battery Cell Configuration: Operating Temperature: Cell Reaction: Na / -Al2O3, NaAlCl4 / NiCl2 300 C 2.58 V 2 Na + NiCl2 Ni + 2 NaCl Cells are assembled in the discharged state The close-packed Cl- lattice provides a stable framework for Na+ and M2+ ions The ‘insertion – displacement’ reaction is 100% efficient The volume expansion of the Cl- array during discharge = 45.6% Cells fail in short circuit mode – excellent for enhancing safety Excellent reversibility achieved through an electronically conducting M matrix, and through control of M grain growth at 300 C Implications for room temperature reactions? Intermetallic compounds? Photos: Courtesy of J. Coetzer and J. Sudworth, ‘Out of Africa’ 6 The Advent of Li-Ion Batteries (Sony Corporation - 1991) eLixC6 (Anode) Li+ LiCoO2 (Cathode) Lithium insertion/extraction reactions Highly energetic (4 V) systems Inherently unsafe; individual cells are protected from overcharge by costly electronic circuitry Flammable electrolytes scientific and technological motivation to discover and study alternative electrodes and electrolytes Cell voltage can be tailored by selection of anode and cathode materials 7 Impact of Li-Ion Batteries ~$8-10 billion market created over the past 18 years Applications: Consumer electronics and communications Transportation (‘Li economy’ driver) Hybrid-electric vehicles ‘and plug-in’ HEVs Pure electric vehicles – longer term viability Implantable medical devices Neuro-stimulators, pacemakers, defibrillators Aerospace, defense, power tools, toys Lithium batteries have become a strategic commodity in U.S. energy security 8 Li-Ion Batteries: 3.5 – 4 V Cathode Materials Ordered Rocksalt Layered LiMO2 (M=Co, Ni, Mn) Spinel LiM2O4 (M=Mn) Olivine LiMPO4 (M=Fe, Mn) • Capacity limited to ~ 0.5 Li per M atom (i.e., ~140 mAh/g) • Co4+ and Ni4+ unstable/highly oxidizing • Structure destabilized at low Li content • Layered LiMnO2 transforms to spinel • • • • • Capacity limited to <0.5 Li/Mn at 4 V Robust M2O4 spinel framework; 3-D channels High rate capability Jahn-Teller (Mn3+) distortion at 3 V Solubility problems at high potentials • • • • • Capacity limited to 1 Li/Fe; P inactive Excellent structural and thermal stability 1-D channels Poor electronic and Li-ion conductivity Poor packing density 9 Li-Ion Batteries: Anode Materials Carbon Graphite: <100 mV vs. Moderate capacity (372 mAh/g) Highly reactive, unsafe, SEI necessary Li0 LiC6 Metals, Semi-metals and intermetallic compounds Al, Si, CoSn, Cu6Sn5: <0.5 V vs. Li0 High gravimetric/volumetric capacities LiAl Large volume expansion on reaction with lithium Reactive, SEI necessary Greatest opportunity and challenge Metal Oxides Li4Ti5O12 (Li[Li1/3Ti5/3]O4) Spinel: 1.5 V vs. Li0 Low capacity (175 mAh/g) Very high rate capability Li7Ti5O12 Stable in nanoparticulate form 10 Hazards of Highly Energetic Batteries Despite the good statistical safety record of batteries in consumer electronics products, the occasional serious mishap does occur. A significant number of recalls of lithium ion batteries Millions of passengers fly every month Millions of batteries fly every day In air travel, it only takes one 2006 Philadelphia UPS flight So far, we’ve been lucky – lithium batteries to blame? During boarding, a laptop started burning in an overhead bin. The fire was extinguished on ramp. Dan Halberstein Lithium Battery Public Awareness Initiative U.S. Department of Transportation, 25th Annual Battery Seminar, Fort Lauderdale, March 17-19, 2008 11 USABC HEV Battery Goals Barriers Power Assist HEV Min. Max. Discharge Power, kW 25 (10s) 40 (10s) Regen Power, kW 20 (10s) 35 (10s) Available Energy, kWh 0.3 0.5 Available Energy, Wh/kg 7.5 12.5 Battery Mass, kg 60 Calendar Life, years 5 Operating Temperature, oC Cold Cranking Power*, kW Selling Price**, $ -30 to 52 5 7 500 800 *Three 2s pulses at -30oC with 10s rest between pulses **Price based on 100,000 batteries/year production level 12 Barriers Barriers PHEV Battery Goals Short-Term Long-Term SUV Car Discharge Power, kW 45 38 Regen Power, kW 30 25 Available Energy, kWh (Charge-Depleting) Available Energy, Wh/kg 3.4 ~80 11.6 ~140 Available Energy, kWh (Charge-Sustaining) 0.5 0.3 Range, miles 10 40 Battery Mass, kg 60 120 Calendar Life, years 15 15 Operating Temperature, oC -30 to 52 Cold Cranking Power*, kW 7 Selling Price**, $ 1,700 3,400 * Three 2s pulses at -30oC with 10s rest between pulses **Price based on 100,000 batteries/year production level 13 USABC EV Battery Goals Barriers Barr. Parameter of Fully Burdened System Minimum Goals for Long Term Commercialization Long-Term Goals Power Density, W/L 460 600 Specific Power (80% DOD), W/kg 300 400 Energy Density, (C/3) Wh/L 230 300 Specific Energy, (C/3) Wh/kg 150 200 Specific Power:Energy Ratio 2:1 2:1 Battery Mass, kg 267 200 Normal Recharge Time, hr 6 3-6 Operating Temperature, oC -40 to +50 -40 to +85 1000 1000 10 10 <150 <6000 100 <4000 Cycle Life – 80% DOD (Cycles) Life, years Selling Price – 25000 units, $/kWh @ 40 kWh, $ 14 Major Challenges Improve the energy and safety of Li-ion cells, without compromising power suppress oxygen release from high capacity metal oxide cathodes on charge at high potentials find alternative anodes to graphite that provide a high electrochemical capacity at 0.5 – 1.0 V vs. Li lithium alloys/intermetallic compounds, metal oxides? Exploit nano-particulate electrodes access intrinsic capacity (energy) of electrodes at high rates LiFePO4, Li4Ti5O12; high potential metal oxides? stabilize electrode surfaces (ANL-NU-UIUC EFRC) find alternative electrolytes and additives find effective redox shuttles to prevent overcharge 15 Designing High Capacity and Safe Electrode Structures for High Voltage Lithium-Ion Cells Argonne’s Approach: Use two-component ‘composite’ structures in which an electrochemically inactive Li2MnO3 component stabilizes an electrochemically active layered or spinel component layered-layered systems: xLi2MnO3(1-x)LiMO2 layered-spinel systems: xLi2MnO3(1-x)LiM2O4 M = Mn, Ni, Co focus on manganese-rich systems (cost advantage) 16 Structural Compatibility of Li2MnO3 and Layered LiMO2 Compounds Li2MnO3 (M4+) LiMO2 (M = Mn, Ni, Co) (M3+ or M4+/M2+) MO6 octahedra = Li Li2MnO3 (Li2OMnO2) is electrochemically inactive with respect to lithium insertion/extraction, whereas LiMO2 is active Strategy: Embed inactive Li2MnO3 component within layered LiMO2 structure to stabilize the electrode and to reduce the oxygen activity at the surface of charged (delithiated) electrode particles 17 Use Structural Units (instead of ion dopants) to Stabilize Electrochemically–Active Materials Electrodes r-MnO2 Al Na O -MnO2 Solid Electrolytes I N Ag Na+ conduction plane inactive -MnO2: Intergrowth of -MnO2 and ramsdellite-MnO2 -Al2O3 spinel block Na+ conduction plane inactive -Al2O3 Li2O spinel block Na+ conduction plane Li2O-stabilized -MnO2: 0.15Li2OMnO2 -alumina, Na2O11Al2O3 44AgI3(C11H22N3)I3 18 Compositional Phase Diagram: xLi2MnO3(1-x)LiMn0.5Ni0.5O2 Electrodes Mn0.5Ni0.5O2 (Mn4+; Ni4+) -0.33Li2O (Mn0.67Ni0.33O2; Mn4+; Ni4+) (0.33Li2MnO30.67Mn0.5Ni0.5O2) LixMn1-yNiyO2 tie-line (0x2) closepacked planes Li2MnO3 (Mn4+) X=0.67 X=0.33 X=0.50 Li2O is removed from the Li2MnO3 component at high potentials (>4.5 V) LiMn0.5Ni0.5O2 (Mn4+; Ni2+) (LiMn0.67Ni0.33O2; Mn3.5+; Ni2+) xLi2MnO3(1-x)LiMn0.5Ni0.5O2 tie-line Mn3+ concentration at the end of discharge is tailored by the Li2MnO3 content in the parent electrode (x) to suppress the Jahn-Teller distortion U.S. Pat. 6,677,082 (2004); U.S. Pat. 6,680,143 (2004) Li2Mn0.5Ni0.5O2 (Mn2+; Ni2+) (Li2Mn0.67Ni0.33O2; Mn2+; Ni2+) Johnson et al., Electrochem. Comm. (2004) 19 Li/0.3Li2MnO O2be used Irreversible capacity can 3●0.7LiMn 0.5Ni0.5 350 to offset SEI formation at anode 300 236 250 200 150 Cell Voltage V vs. Li Specific Capacity (mAhg) Electrochemistry of a Li/0.3Li2MnO30.7LiMn0.5Ni0.5O2 Cell (C/3) Charge Average Mn valence in Discharge discharged state = 3.54 100 4.8-2.75 V 0.25 mA/cm2 50 °C 50 0 0 5 10 90% of theoretical value 6 Cycle 40 5 262 mAh/g 4 3 2 1 0 0 25 50 75 100 125150175200 225250 Specific Capacity (mAh/g) 15 20 25 30 35 40 45 Cycle Number Johnson et al., Electrochem. Comm. (2004) 20 Safety Characteristics xLi2MnO3(1-x)LiMO2 Cathode (M=Mn, Ni, Co) Thermal Stability (DSC) Heat flow, W/g 40 30 20 Argonne cathode charged to 4.6 V H=650j/g Li[Ni0.8Co0.15Al0.05]O2 charged to 4.2 V H=1550j/g 10 0 150 200 250 300 Temperature (C) Courtesy of K. Amine, Argonne National Laboratory 21 The Challenge of Surface Stabilization Charging high-capacity xLi2MnO3(1-x)LiMO2 electrodes to a high potential (>4.4 V) damages the electrode surface and reduces the rate capability of the electrode: (1) LiMO2 MO2- + Li+ + /2 O2 + (1+2)e (2) Li2MnO3 MnO2 + 2 Li+ + O2 + 2e Oxygen loss, particularly through process (1), increases M cation concentration at the electrode surface that restricts Li diffusion and rate capability? LixNi1-xO rock salt structure at surface of Li1-xNi0.80Co0.15Al0.05O2 How does one prevent corrosion and cation disorder at the surface to allow high rate discharge and charge? (Thrust of EFRC) 22 Fluorination Fluorination of layered xLi2MnO3(1-x)LiMO2 electrodes (e.g., LiF, AlF3 Sun et al., Amine et al.) is known to improve capacity and cycling stability. F- ions within the bulk or at the surface? – gradient? Alternative Approach Use mildly acidic solutions containing fluorine to form robust oxy-fluoride (partially reduced) surface on electrode particles lowering oxygen activity. Use soluble salts with stabilizing cations and anions, e.g., (NH4)3AlF6; NH4PF6; NH4BF4 in water, methanol, etc Molarity of solutions ~2.5 x 10-3 M; pH 6.0 - 6.5 pH can be varied to tailor stability and first-cycle irreversibility loss 23 Relative Rate Capability: Li-ion cells C6/0.1Li2MnO30.9LiMn0.256Ni0.372Co0.372O2 200 Capacity / mAh g -1 0.1 mA/cm2 0.2 mA/cm2 150 100 4.5-3.0 V 0 0.5 mA/cm2 1 mA/cm2 Sample A Sample B Sample C Sample D 5 10 0.1 mA/cm2 1 mA/cm2 2 mA/cm2 Sample A untreated sample 5 mA/cm2 ~C/1 rate 15 20 25 Cycle Number Fluorinated electrodes provide higher capacity, lower impedance and improved rate: ~175 mAh/g at C/1 rate Insufficient energy/power for 40-mile PHEVs. Yardstick for PHEV: 200 mAh/g at a C/1 rate, average 3.5 V (or higher) Kang et al., J. Electrochem. Soc. (2008) 24 Integrated Olivine-Metal Oxide Structures/Surfaces? Olivine (LiFePO4) and Spinel (LiMn2O4) both have AB2O4 formulae with the A cations in tetrahedral sites and the B cations in octahedral sites In LiFePO4, the P cations are in tetrahedral sites In LiMn2O4, the Li cations are in tetrahedral sites Olivine has a hexagonally close packed structure Spinel has a cubic close packed structure Relatively small difference in the d-spacings of the close-packed layers in LiFePO4 and LiMn2O4 Can we synthesize ‘olivine-spinel’ composite structures, ‘olivine-layered’ structures or other close-packed phosphate structures to stabilize ccp spinel and layered metal oxide bulk structures and/or surfaces? 25 Hypothetical LiNiVO4 Spinel – LiNiPO4 Olivine Intergrowth Spinel LiNiVO4 ccp O layers tetrahedral V5+ octahedral Li+, Ni2+ Olivine LiNiPO4 tetrahedral P5+ hcp O layers octahedral Li+, Ni2+ In principle, a spinel-olivine intergrowth structure seems possible Experiment shows otherwise: CBED patterns and EDS signals (Ni/V or Ni/P) suggest that discrete olivine and spinel phases exist Can Li-M-PO4 films provide effective surface protection on metal oxides? Vaughey et al., Argonne National Laboratory 26 Li-M-PO4 surface treatment (e.g., M=Ni) (0.5Li2MnO30.5LiNi0.44Co0.25Mn0.31O2 electrodes in Li half cells) Cell voltage (V) Concept: Use Li-Ni-PO4 as a solid electrolyte below 5.0 V to protect surface of xLi2MnO3(1-x)LiMO2 electrode at high potentials Sol-gel treatment technique used Olivine LiNiPO4, Li3PO4 or defect Li3PO4, e.g., Li3-2xNixPO4? First-principles calculations indicate a small solid solution range in Li3-2xMxPO4 materials (Shin, Wolverton (NU – EFRC)) untreated 4.0 3.0 2.0 C/1 (1.0) C/3 (0.5) C/8 (0.2) C/16 (0.1) treated 4.0 3.0 C/1 (1.0) 2.0 0 50 C/2 (0.5) C/5 (0.2) C/11 (0.1) 100 150 200 250 300 Capacity (mAh/g) Treated electrodes meet the 200 mAh/g, C/1 rate, 3.5 V average, capacity/power yardstick for a 40-mile range PHEV at room temperature Kang et al., Electrochem. Comm. (2009) Figure 3 27 Playing it Safe Li4Ti5O12 (Spinel) / Li1+xMn2-xO4 (Spinel) Cells 55 C 13 12 11 10 6C 9 8 7 6 5 4 3 2 1 0 6C 2C - 50C rates 3.0 2.8 2.6 Voltage(V) Capacity, mAh 14 2.4 55 C 2.2 2.0 2C 5C 10C 20C 30C 40C 50C 1.8 LiMn2O4 vs. Graphite LiMn2O4 vs. Li4Ti5O12 1.6 1.4 0 10 20 30 40 50 60 70 80 90 100 110 % of 1C Capacity 0 100 200 300 Cycle number 400 500 Before ARC test After ARC test Relatively low energy cells (2.5 V) Outstanding power and cycling stability Safety is achieved by operating well above the potential of metallic lithium Being developed for HEV applications Courtesy of K. Amine and Enerdel 28 TiO2 Anodes? Li4Ti5O12 (2Li2O5TiO2) spinel accommodates 3 Li+ ions per formula unit during its transformation to rock-salt Li7Ti5O12 (Ti4+ to Ti3.4+): relatively low capacity – 175 mAh/g TiO2 structures, e.g., anatase, rutile, hollandite and TiO2-B would be more attractive anodes if, in nanoparticulate form, they could accommodate lithium reversibly and rapidly to the rock-salt stoichiometry LiTiO2 (Ti3+), for which the theoretical capacity is 335 mAh/g. 29 Carbon-Encapsulated TiO2-C Anodes EDS XRD A single-step, autogenic (solvent-less), and scalable process has been used to prepare single-phase TiO2 (anatase) nanoparticles encapsulated by an interconnected, electronically-conducting network of carbon nanoparticles that also protect the surface. V. Pol et al., Argonne National Laboratory 30 FESEM and HRTEM images of C-coated TiO2 The images demonstrate the likelihood that every TiO2 nanoparticle is completely encapsulated by a 2-4 nm layer of x-ray amorphous carbon, the thickness of which can be tailored by the temperature and length of the carbon combustion process. V. Pol, Thackeray et al., Argonne National Laboratory (EFRC) 31 TiO2-C/0.5Li2MnO30.5LiNi0.44Co0.25Mn0.31O2 Cells 200 mAh/g is delivered by both the TiO2 anode and metal oxide cathode Cells provide higher energy than Li-ion cells with Li4Ti5O12 anodes The autogenic process can be used to prepare a wide variety of C-protected nanoparticulate materials; the approach has implications for advancing the electrochemical properties of both anode and cathode nano-materials. V. Pol, Thackeray et al., Argonne National Laboratory (EFRC) 32 Alternative Anodes for Li Cells Lithium Alloys and Intermetallic Compounds Metals have dense structures and therefore expand significantly on reaction with Li, e.g. Al, Si, Sn, Sb LiAl Al + Li 300 mV 95% Volume Expansion (per Al atom) Fm-3m Fd-3m, 50% Al in interstitial sites Major structural rearrangement on lithium insertion Lithium alloys offer significantly higher gravimetric and volumetric capacities than graphite (372 mAh/g; 820 mAh/ml) 33 Cu6Sn5 Anodes Cu6Sn5 to Li2CuSn transition Electrochemistry: Cu6Sn5 vs. Sn Li 400-200 mV Cell Capacity (mAh/g) 400 Cu Sn Li Sn (1.2 V - 0.0 V) 350 Cu6Sn5 300 Sn (1.2 V - 0.2 V) Cu6Sn5 (1.2 V - 0.0 V) 250 Cu6Sn5 (1.2 V - 0.2 V) 200 150 100 Sn 50 0 0 5 10 15 20 25 Cycle Number 21.25 Li + Cu6Sn5 5 Li2+xCu1-xSn + (1+5x) Cu 6 Cu + 5 Li4.25Sn Strong structural relationship between Cu6Sn5, Li2CuSn and “Li3Sn” (x=1) exists. Li insertion/Cu displacement reaction: Max capacity 600 mAh/g. Mimics Na/NiCl2 reaction (100% efficient): 2 Na + NiCl2 2 NaCl + Ni. Cells assembled in discharged state; NaCl powder in porous Ni substrate. Volume expansion 50-60%. New approach to electrode design and current collection is required Kepler et al., Electrochem. and Solid-State Lett. (1999) 34 Electrodeposited Cu6Sn5/Sn on Cu Foam Electrodes 1. As-deposited Cu foam 2. Annealed Cu foam (500 C) 3. Cu6Sn5/Sn on Cu foam 1. As-deposited Cu-foam is brittle and powdery. 2. Annealing at 500 C strengthens Cu-foam to Cu foil contact, providing a sufficiently robust substrate for electrodeposition of Cu and Sn. Overall porosity maintained. 3. Morphology maintained after Cu6Sn5/Sn pulsed electrodeposition at -600mV vs. SCE. Sn concentration varies from ~20% within the porous electrode to ~90% at outermost surfaces. Trahey et al., J. Electrochem. Soc. (2009) 35 Electrochemistry: Cu6Sn5/Sn on Cu Foam Electrodes 2 1100 (a) 1.8 Charge Discharge 900 Capacity (mAh/g) 1.6 1.4 Potential (V) (b) 1000 1.2 1 0.8 0.6 800 700 600 500 400 300 0.4 200 0.2 100 0 0 18 19 20 21 22 23 24 Time (h) 25 26 27 28 0 5 10 15 20 25 30 35 40 45 50 55 60 Cycle Number Significant improvement in reversible capacity achieved (650 mAh/g vs. 200 mAh/g for ball-milled Cu6Sn5 samples). Results suggest excellent cycling of Sn within a copper-tin matrix electrode. Large irreversible capacity drop during early cycles attributed to electrolyte reactions with high surface area electrode to form passivation layer. Abrupt onset of capacity fade after 30 cycles - Li electrode or mechanical failure of Cu6Sn5/Sn electrode? Trahey et al., J. Electrochem. Soc. (2009) 36 Beyond Lithium-Ion: Li-Air – The Holy Grail? Li-ion conducting electrolyte O2 O2 Li-containing anode Porous C cathode with catalyst e.g., MnO2 O2 O2 O2 O2 O2 System Reaction OCV Th. Spec. Energy (V) (Wh/kg) Li/O2 2 Li + O2 2 Li2O2 4 Li + O2 2 Li2O 4 Li + O2 2 Li2O 3.1 2.9 2.9 3623 (incl. O) 5204 (incl. O) 11,202 (excl. O) Lithium-ion (M=Mn, Ni, Co) LixC6 + Li1-xMO2 C6 + LiMO2 3.6 ~900 Octane C8H18 + 12.5O2 8CO2 + H2O - ~13,000 (ex. O) 37 Exploitation of Li2O-Containing Electrodes: Electrochemical Activation of Li2MnO3 4.5-4.8 V Li2MnO3 (Li2OMnO2) MnO2 + 2 Li + ½ O2 (459 mAh/g) Net loss is Li2O at 4.5 to 4.8 V – irreversible reaction Two Li+ ions removed during electrochemical activation (charge) One Li+ ion reinserted into residual MnO2 component: Li + MnO2 LiMnO2 (229 mAh/g, mass of parent electrode) Use surplus Li to load anode: C6, metals or even bare substrate (Li metal) Use Li2MnO3 (or xLi2MnO3(1-x)LiMO2, M=Mn, Ni, Co) precursor in combination with high capacity charged cathodes, particularly where two electron transfer reactions are possible, e.g., Li1.2V3O8 (372 mAh/g) 38 C6/Li2MnO3Li1.2V3O8 Cells Li-O bonds in Li2MnO3 cathode precursor are broken at ~4.5 V vs. Li0 Li is inserted into C6 anode during charge During discharge, Li is inserted charged Li1.2V3O8 and residual MnO2 cathode components Implications for Li - O2 cells using MnO2 component as catalyst? Kang et al., Argonne National Laboratory 39 Alternative High-Li2O Content Precursors Antifluorite structures Li2O (Fm-3m) (a=4.614 Å) Li2O: Li - tetrahedral sites O - face-centered-cubic sites Li O Li5FeO4 (Pbca) Defect structures Li5FeO4: 5Li2OFe2O3 or Li1.25Fe0.25□0.5O 5 Li per Fe atom Li6MO4 (M=Mn, Co, Ni): 3Li2OMO or Li1.5M0.25□0.25O 6 Li per M atom (a=9.218 Å; b=9.213 Å; a=9.159 Å ) Li Fe O cf: Layered Li2MnO3 (Li2O:MnO2) 2 Li per Mn atom Abundant Li in defect structure provides good Li+ mobility 40 Electrochemical Extraction of Li from Li5FeO4 4 Li removed from Li5FeO4 (5Li2OFe2O3) in 2 steps at ~3.5 and ~4.0 V Slight evidence from XANES data of some Fe3+ Fe4+ oxidation predominantly Li2O extraction? Composition of delithiated product = “LiFeO2” (Li2OFe2O3) Exploit reversibility of the reaction when discharged against O2 electrode (Li2O content increases in the residual Fe2O3 electrode matrix) Johnson et al., Argonne National Laboratory 41 XANES Data: Chemical Delithiation of Li5FeO4 decreasing pre-edge features no change in edge position (iron oxidation state) Li5FeO4 samples chemically delithiated with NO2BF4/acetonitrile solution No apparent change in Fe3+ oxidation state Li2O extraction EXAFS shows evidence of formation of edge-shared Fe-octahedra as x. Gradual reduction in pre-edge peak height is consistent with conversion from tetrahedral Fe to octahedral coordination and ultimate ‘LiFeO2’ stoichiometry S. Pol, M. Balasubramanian et al., APS - Argonne National Laboratory 42 Summary Remarks Lithium-ion technology stands to broaden its impact on battery markets. Extremely versatile, strategic technology - battery chemistry can be tailored to suit needs. State-of-the-art lithium-ion batteries still compromised by safety, energy, power, life, operating temperature and cost constraints New, structurally-stable materials required: Exploitation of high potential metal oxide electrodes (>4.2 V) to increase energy and power Composite cathode structures with high-capacity (layered) / high-power (spinel) components? Nano-particulate metal, semi-metal or intermetallic anodes to replace graphite - increase both specific- and volumetric capacity? Electrode surface protection – use of additives Non-flammable electrolytes Li-air: the ultimate scientific and engineering challenge? 43