Particle Size Effects in Lithium ion batteries

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Particle Size Effects in Lithium ion batteries Marnix Wagemaker1, Swapna Ganapathy1, Deepak P. Singh1, Wouter J.H. Borghols1,2, Ugo Lafont1, Lucas Haverkate1, Vanessa Peterson3, Gordon J.

1 Particle Size Effects in Lithium ion batteries Marnix Wagemaker1, Swapna Ganapathy1, Deepak P. Singh1, Wouter J.H. Borghols1,2, Ugo Lafont1, Lucas Haverkate1, Vanessa Peterson3, Gordon J. Kearley3, Fokko M. Mulder1 1Faculty of Applied Sciences, Delft University of Technology, The Netherlands 2Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, Jülich Centre for Neutron Science at FRM II, Garching, Germany 3Australian Nuclear Science & Technology Organization, Bragg Institute, Menai, NSW 2234 Australia 1 Vermelding onderdeel organisatie

2 Fundamental aspects of Materials and Energy (FAME) Radiation, Radionuclides and Reactors (R 3 ) Faculty of Applied Sciences Delft University of Technology, The Netherlands TUD, TNW, R3, FAME prof. Ekkes H. Brück: prof. Fokko M. Mulder: Niels H. van Dijk Stephan W.H. Eijt: Marnix Wagemaker Magnetocaloric materials H-Storage, Fuel-cell, Li-ion and Solar Cell materials Structural and Magnetic materials H-Storage, Solar cell materials Li-ion, H-storage materials 19 April

- e - Li + Li + Li + Electrode Density Functional Theory Phase Diagram DFT

3 Techniques Neutron Scattering Structure Nuclear Magnetic Resonance Ion environment and dynamics Li + Li + Electrolyte Phase Diagram e - Li + Li + e - e - e - Li + Li + Li + Electrode Density Functional Theory Phase Diagram DFT Calculations Cluster Expansion Electronic Structure E Fermi Ionic Mobility Li + 19 April

$Diffraction, SANS, NDP Li-ion/H-storage 10-1$

4 Techniques Neutrons NMR DFT MD QENS, ID Li-ion/H-storage T1, T2, Exchange correlation time [s] Neutrons NMR DFT Diffraction, SANS, NDP Li-ion/H-storage correlation length [nm] 19 April

5 Neutronen versus X-rays X-ray Neutron H Li 19 April

6 Outline Introduction Energy Storage Li-ion batteries Why Nano electrode materials Why not only Nano (impact porosity in electrodes) Impact Interfaces in LiFePO 4 Impact Surfaces in Li 4 Ti 5 O 12 Conclusions 19 April

7 19 April

8 200 Need for Efficient Electricity Storage Enabling renewables Wind energy integrated over US. Efficient mobility Range ~ 150 km 100% Charge ~ 8 hour Li-ion battery weight ~ 250 kg v 3 [m 3 /s 3 ] hours Cheap efficient electricity storage 3 x less installed power! Required: 10 x energy density (comparable to gasoline) 19 April

Energy storage for mobility Energy density = Capacity density x Potential Power density = Current density x Potential Effective Energy Density Gasoline Full

9 Energy storage for mobility Energy density = Capacity density x Potential Power density = Current density x Potential Effective Energy Density Gasoline Full of CO 2 Energy Density (Wh/kg) Electrical storage: 2x every 30 years Ni-Cd Lead-Acid Ni-MH Year Li-ion 19 April

10 Li-ion batteries Electrode Materials Li 4 Ti 5 O V LiFePO V 19 April

11 Why Nano? Li + d 2d Diffusion time: t 2 d π D d = 1 μm D = cm 2 /s d = 43 nm D = cm 2 /s t = 53 min t = 6 s Charge battery in Seconds! Local Depletion Electrolyte 19 April

12 Vary electrode film thickness ~25 μm 19 April

13 Impact of porosity Compact Specific Capacity mah/g hour 30 min 12 min 6 min 200 μm compact 200 μm porous 2 min 1 min Add ~ 5% (volume) Porosity Charge Cycles 1 μm 19 April

14 Impact of porosity Porosity Improve (dis)charge rate (power density) Improve energy density (factor 2 possible) ~10 μm ~25 μm Al Foil Positive electrode ~300 μm ~20-25 μm ~25 μm ~10 μm Separator Neg. Electrode Cu Foil ~100 μm 19 April

15 Impact Particle size on Li-ion electrode properties Phase 1 Phase 2 LiFePO 4 : Impact Interface Li 4 Ti 5 O 12 : Impact Surface 19 April

16 Nano effects LiFePO 4 LiFePO 4 19 April

17 Impact nano size on material properties LiFePO 4 Shrinking miscibility gap with decreasing particle size α α β β x α Source: Kobayashi et al, Adv. Funct. Mat. 2009, 19, 395 Source: Meethong et al, Electrochem Sol. State L. 2007, 10, A134 α β FePO4 LiFePO4 Shrinking miscibility gap? 19 April

18 Impact nano size on material properties LiFePO 4 Diffuse Interface 1 Gmix = ghom () c + ( c) ik( c) ρdv 2 V Cahn & Hilliard 1958 Overall composition x=0.5 Source: Burch et al, Nano Let. 2009, 9, 3975 Calculations predict shrinking miscibility gap 19 April

19 Question and Goal Shrinking miscibility gap with decreasing particle size Diffuse interface model predicts also shrinking miscibility gap due to the interface α α β β Source: Kobayashi et al, Adv. Funct. Mat. 2009, 19, 395 Source: Burch et al, Nano Let. 2009, 9, 3975 Question Can we directly observe the shrinking miscibility gap? Goal (1) Impact size and overall composition on the solubility limits (2) Compare results with prediction diffuse interface model 19 April

$diffraction nano$ LiFePO 4 200 nm

20 Accurate Li-occupancies: Neutron diffraction nano LiFePO nm Li xa FePO 4 Li xb FePO 4 22 nm ANSTO 50 nm ISIS 140 ± 20 nm 70 ± 18 nm Intensity [a.u.] 35 nm ILL PSI 70 nm 35 ± 10 nm 22 ± 8 nm D-space [Å] 19 April

21 Anisotropic strain Anisotropic strain parameters Li xa FePO 4 a Li xb FePO 4 Source: Chen et al, ESSL 2008, 9, A295 Coexisting Li xa FePO 4 with Li xb FePO 4 a b 19 April

22 Fourier Density Difference Maps Li-poor Li xa FePO 4 Li-rich Li xb FePO nm 19 April

23 Results Fixed Overall Composition 1.0 Overall Composition Li 0.5 FePO Solubility limits x α and x β x α x β a α a β Cell Volume [Å 3 ] Size [nm] 19 April

24 Calculation Diffuse Interface Local composition x a-direction in LiFePO 4 a Position [nm] b Energy Penalty Diffuse Interface: 1 Gmix = ghom() c + ( c) ik( c) ρdv 2 V Cahn & Hilliard 1958 Decrease miscibility gap with decreasing particle size Source: Burch et al, Nano Let. 2009, 9, 3975 This work: (1) Repeat calculations Burch et al. Direct comparison ND results (2) Expand calculations Impact overall composition Li x FePO 4 and compare with ND results 19 April

25 Vary particle size Overall Composition Li 0.5 FePO 4 Local composition x x a Solubility limits x α and x β a nm b Position [nm] x b x a nm Size [nm] b a Position [nm] 1.0 x b nm x b 0.2 x a a Position [nm] b 19 April

26 1.0 Vary overall composition Solubility x α and x β nm 35 nm 22 nm 22 nm 35 nm 22 nm 25 nm 35 nm 140 nm nm x in Li x FePO x a x=0.3 a b Position [nm] x b x a x=0.5 a b Position [nm] x b x a 0.2 x=0.7 a b Position [nm] x b 19 April

27 Calculated Phase-Size Diagram Solubility limits x α and x β Decreasing particle size Conclusions 30 Decreasing miscibility gap with decreasing particle size Particle Size [nm] Li Li FePO 44 Solubility limits depend on overall composition Diffuse 120 interface appears to explain both phenomena Compositions are continuously changing while charging! Overall Solubility Composition limits x in α and Li x FePO x β 4 Overall composition x in Li x FePO 4 19 April

28 Nano effects Li 4 Ti 5 O 12 Li-16c Li-8a [Li 1/6 Ti 5/6 ]O 6 Li 4 Ti 5 O 12 : Li 8a Li 7 Ti 5 O 12 : Li 16c 19 April

Introduction Li 4+x Ti 5 O 12 Spinel Micro Spinel Li 4+x Ti 5 O 12 Li-8a < 9 nm Li 4 Ti 5 O 12 Li on 8a Li 7 Ti 5 O 12 Li on 16c Li-16c M. Wagemaker et al, J. Phys. Chem. B, 113 (2009) 224 and M.

29 Introduction Li 4+x Ti 5 O 12 Spinel Micro Spinel Li 4+x Ti 5 O 12 Li-8a < 9 nm Li 4 Ti 5 O 12 Li on 8a Li 7 Ti 5 O 12 Li on 16c Li-16c M. Wagemaker et al, J. Phys. Chem. B, 113 (2009) 224 and M. Wagemaker et al, Advanced Materials 18 (2006) 3169 Phase transition from Li 4 Ti 5 O 12 (Li-8a) to Li 7 Ti 5 O 12 (Li-16c) Zero strain In equilibrium nano-domains -> Very low interface energy 19 April

Impact nano-size Li-ion: spinel Li 4+x Ti 5 O 12 Voltage (V) 2.5 0 1 2 3 4 2.

0 x in Li 4+x Ti 5 O 12 12 nm 31 nm 0 50 100 150 200 Capacity (mah/g) C/10

(1) Extra What capacity is the origin suggests of the 16c extra and capacity

30 Impact nano-size Li-ion: spinel Li 4+x Ti 5 O 12 Voltage (V) x in Li 4+x Ti 5 O nm 31 nm Capacity (mah/g) C/10 galvanostatic (dis)charge V Borghols et al, J. Am. Chem. Soc. 131 (2009) Å 1.81 Å Short Li + -Li + distances high repulsive energy Li 8a Li 16c Questions (1) Extra What capacity is the origin suggests of the 16c extra and capacity 8a occupation in smaller particles? (2) How Energetically can we understand unlikely because the apparent of short reduced Li 16c -Li 8a miscibility distance gap Goal Use Neutrons to see where the Li goes 19 April

$Intensity (a.u.) Neutron Diffraction ISIS (POLARIS) 12 nm 31 nm micro 0.5 1.0 1.5 2.0 2.$ $2 0.0 Bulk 31 nm 12 nm 0 1 2 3 4 Li fraction (x in Li 4+x Ti 5 O 12 ) 8a 16c 8a O c Ti Ox Li 8a Li 16c$

31 Intensity (a.u.) Neutron Diffraction ISIS (POLARIS) 12 nm 31 nm micro d-space (Å) In addition to maximum capacity Li 7 Ti 5 O 12 (all 16c) 8a occupancy in small particles Fourier 0.8 density difference (datamodel) showing the Li-ion e positions Site occupation Bulk 31 nm 12 nm Li fraction (x in Li 4+x Ti 5 O 12 ) 8a 16c 8a O c Ti Ox Li 8a Li 16c 19 April

Surface storage spinel Li 4+x Ti 5 O 12 Equilibrium Crystal (Wulff) shape Dominated by (100) surface Surface Surface Surface Li 4+x Ti 5 O 12 Surface Surface Surface

32 Surface storage spinel Li 4+x Ti 5 O 12 Equilibrium Crystal (Wulff) shape Dominated by (100) surface Surface Surface Surface Li 4+x Ti 5 O 12 Surface Surface Surface Calculate voltage from formation energies (DFT) at the near surface environment Li 7+x Ti 5 O 12 (100) Slabs 6.4 nm thick Empty Occupied 8a Empty Occupied 16c 19 April

33 Surface storage spinel Li 4+x Ti 5 O 12 Calculated Voltage Slab 6.4 nm Measured size dependence nm slab Surface 1.5 Voltage x in Li 4+x Ti 5 O 12 Empty Occupied 8a Empty Occupied 16c Surface storage leads to intrinsic change voltage curve (Gibbs Free Energy) Explains curved shape and large capacity 19 April

34 Origin: Surface relaxation Bulk Li 8a -Li 16c 1.81 Å Larger Li 8a -Li 16c distances near the surface -> lower energy/higher voltage 19 April

35 Conclusions LTO Voltage (V) x in Li 4+x Ti 5 O nm Measured 31 nm Measured 6.4 nm slab Calc nm slab Calc nm slab Calc Capacity (mah/g) Surface storage explains higher capacity smaller particles Surface storage explains curved voltage shape (apparent decrease miscibility gap) Surfaces may be used to tailor the electrode properties 19 April

36 General Conclusions Size effects in Electrode Materials: (1) Solubility limits are not only changed, also not constant, will impact the Li-ion diffusion and phase behavior (2) Surface storage shows potential to tune electrode properties 19 April

37 Acknowledgments DISE Delft Institute for Sustainable Energy VIDI, and beamtime ISIS ISIS/PSI/ILL/ANSTO Support at beamlines 19 April

38 Anisotropic temperature factors Curved Li-ion diffusion path b-direction Nishimura et al, Nat. Mat. 2008, 7, April

39 Cell volume [Å 3 ] nm 35 nm 25 nm 22 nm a Li-Poor b Li-Rich x in Li x FePO 4 22 nm 25 nm 35 nm 140 nm V Cell [Å 3 ] Vegard s Law In the Miscibility gap: No x in Li x FePO4 Increasing overall composition Outside the Miscibility gap: Yes (Kobayashi et al. Adv. Func. Mat ) 19 April

Supplementary Figure 1: Sketch of XRD-EIS pouch cell design with Titanium current collectors serving as XRD windows, parafilm, kapton tape made from

Supplementary Figure 1: Sketch of XRD-EIS pouch cell design with Titanium current collectors serving as XRD windows, parafilm, kapton tape made from polyimide used to seal Titanium (Ti) current collectors