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NANOSTRUCTURED MATERIALS: APPLICATION IN ELECTROCHEMICAL
SYSTEMS FOR ENERGY CONVERSION AND STORAGE
Julián Morales
Departamento de Química Inorganica e Ingeniería QuímicaUniversidad de Córdoba
Nanosized materials: application in electrochemical systems for energy conversion and storage
Great needs for electrical energy storage
-Mobile electronic devices (cell phones, computers, iPods…).-Transportation (electric and hybrid electric vehicles (PHEVs).-Load-leveling.-Effective commercialization of renewables sources (solar, wind power).
Needs satisfied by electrochemicaldevices: Supercapacitors, Batteries,Fuel Cells
● Inherent limits in performance reached by micrometer-sized bulk materials.
● A way to satisfy the increasing needs of consumer devices use of nanoestructuredmaterials that provide a better performance in some key properties.
Li-ionbatteries
Nanosized materials: application in electrochemical systems for energy conversion and storage
Advantages of the Li-ion Battery over other batteries
(i) The high potential of Li (Li+ / Li -3.04 V vs. SHE)(ii) Its low density: d = 0.53 g cm-3
High reaction rate ⇒ high specific power
⇒ High specific energy
nanosize-TiO2 / LiMn2O4
Li/air ~ 1500 Wh/kg
M. Gratzel 2005
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Nanosized materials: application in electrochemical systems for energy conversion and storage
Basic principles of LIB operation1990 Sony Energetics Inc. LiCoO2(+) / LiPF6 (EC: DMC) / C(graphite)(-). First
battery with commercial success
Battery potential: 3.6 VSpecific energy: 120-150 W h kg-1
(~half of theoretical energy)
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LiCoO2Expensive
Toxic
Li*charge
M- S. Whittingham MRS Bull.(2008)
Nanosized materials: application in electrochemical systems for energy conversion and storage
Criteria for selecting anode and cathode-High reversible reactivity towards Li ⇒ high capacity
-High difference in potential
Advantage of other anodic materials versus graphite ⇒ higher capacities.Disadvantage: (i) higher potential and/or
(ii) hystheresis between the charge and discharge curves
E = V C
Li4Ti5O12
Si
High specificenergy
Limited capacityLi plating A. S. Arico et al. Nat. Mater. 2005
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(most commercial batteries)
(choice)
(choice)
(Commercial batteries)
Nexelion
Nanosized materials: application in electrochemical systems for energy conversion and storage
Some beneficial properties of nanostructured materials
(i) Electrode/electrolyte interface increases: Example: MnO2 particle Increase in the Mn4+
fraction at the surface with decreasing particle size Increased reactivitySize Mn4+
1 nm …. 0.510 nm …. 0.05
(ii) Reaction rate increases: the reaction pathways for Li ion diffusion are shorterSize Time
τ = r2 / π D; D = 10−14 cm2 / s r = 10 nm τ = 1.5 mr = 1 πm τ = 270 h
(iii) Enhanced structural stability.
Vgr. LiMnO2 : nanocrystalline particles can accommodatedmore easily lattice strains caused by Jahn-Teller distortion
Two types of nanosize effects
Trivial size effects(increased surface-to-volume ratio)
True size effects(changes of local properties)
CoO + Li ⇔ Co + Li2O
High rate capability(higher power)
Enhanced capacity(higher energy)
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Nanosized materials: application in electrochemical systems for energy conversion and storage
Potential drawbacks of nanosize materials
(i) Tendency to form agglomerates difficulty to disperse the carbonblack and binder increase of the contact resistance of theelectrode capacity fading.
(ii) High surface area Increased secondary reactions (electrolytedecomposition)
High degree of irreversibility(low coulombic efficiency)
Poor cycle life
Anodes made fromnanosize particles
Formation of thick solid electrolyte interface (SEI)(extra current consumption, capacity lost, charge
polarization etc)
Cathodes at high voltage
The electrolyte can be oxidized; even the oxide framework can be
oxidized releasing oxygen
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Nanosized materials: application in electrochemical systems for energy conversion and storage
Anodes(i) Elements that reversibly alloy with Li: Sn; Sb(ii) Transition metal oxides: CuO and Cu2O (thin films); Fe2O3(iii) Spinel: Li4Ti5O12 (mainly as anode versus the following cathode materials
LiMn2O4; LiNi0.5Mn1.5O4 and LiFePO4)(iv) Graphitized carbons (commercial: meso carbon microbeads, nanotubes
nanofibers, nanoflakes). Cathodes
(i) Layered oxides: LiCoO2; LiNiCoO2; (ii) Spinels: ; LiMxMn2─xO4
(iii) Olivine: LiFePO4.Synthesis methods
(i) Mechanochemical procedures with polymers + calcination(ii) Precipitation with surfactants(iii) Hydrothermal(iv) Films: spray pyrolysis, spin coating, electrodeposition (low cost deposition
methods).
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Materials studied by our group
Si
LiFeO2
LiMn2O4LiNi0.5Mn1.5O4
Nanosized materials: application in electrochemical systems for energy conversion and storage
Elements that reversibly alloy with Li: Si (Sn)
M + x Li+ + x e− ⇔ LixM ( 0 ≤ x ≤ 4.4) (M = Si, Sn)
The theoretical capacity for Si is ~3600 mAh/g (Sn ~960 mAh/g) (theoretical capacity of graphite 372 mAh/g)
Main problem:Significant volume changes (~ 460%) ⇒ particle rupture
⇒ Conductivity loss⇒ Poor battery performance
¿How can be overcome this drawback?(1) Use of nanosize Si. Slight improvement (compared with micrometric´s)(2) Use of nanoparticles + an inactive matrix (coposite electrode)
(i) dispersing agent(ii) Buffering effect towards volume changes
J.L. Gomez Camer et al. Electrochem. Solid State Lett. (2008)
We have used cellulose fibers as dispersionagent (inactive towards Li)
Buffering effect of CF demonstratted
by In situ dilato-metric studies
J.L. Gomez Camer et al. Electrochim. Acta 2009
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Pure n-Si
n-Si:Cell. Fibers (50/50w)
n-Si
Nanosized materials: application in electrochemical systems for energy conversion and storage
Si nanowires: the material with the highest capacity
C. K. Chan et al.. Nature Nanotechnology December 2007
400% volume change
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Tendency to pulverize
Morphology maintenance
Nanosized materials: application in electrochemical systems for energy conversion and storage
Li-ión battery: (+) LiMn2O4/1M LiPF6 EC,DMC 1:1/Li4Ti5O12 (-)LiMn2O4 → Li1-xMn2O4 + Li4+xTi5O12 (charge process)
LiMn2O4 Li4Ti5O12
n-LMO/n-LTO
m-LMO/m-LTO
J. C. Arrebola et al. Nanotechnology (2007)
SEM
TEM
Best performance of nanosized materials in real Li-ion batteries
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Nano
Micro
Special attention to spinels: Illustrative example LiMn2O4
Electrodes made from spinelswith micro (m) and nano- (n)
size.
Cathode materials
1C
Nanosized materials: application in electrochemical systems for energy conversion and storage
Toshiba Super Charge Lithium Ion Battery –SCiB•Lithium Manganese oxide Spinel cathode –nanosizedLiMn2O4•Lithium Titanate Oxide anode –nanosized Li4Ti5O12•Recharge to 90% of full capacity in less than 5 minutes.•Excellent safety because of high level anode stability.•6000 cycles of full D.O.D to 90% of initial capacity.•Low temperature discharge from -30 C.
2.4 Voc 65 Wh/Kg 650 W/Kg
VW & Toshiba
Nanosized materials: application in electrochemical systems for energy conversion and storage
Electrochemical properties of Li-Mn-O spinel ⇒ improved by introducing
isomorphic substitutions: LiNi0.5Mn1.5O4
Route followed to optimize its electrochemical properties:
Modification of the crystallinity of nanometric spinel introducing a template agent in the protocol synthesis (e.g . PEG)⇒ Combination of nanometric size and high crystallinity.
Li[Ni2+0.5Mn4+
1.5]O4 Li0.5[Ni3+0.5Mn4+
1.5]O4 + 0.5 Li+ + 0.5 e–
□ [Ni4+0.5Mn4+
1.5]O4 + 0.5 Li+ + 0.5e–
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● Increase of the structure stability● Increase of the insertion/deinsertion voltage
(vs. Li ≈ 4.7 V (high voltage Li batteries)● Maintenance of capacity (148 mAh/g)
Cyclic voltammetry
Nanosized materials: application in electrochemical systems for energy conversion and storage
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Calcined at 400 ºCLow crystallinity
Calcined at 800 ºCHigh crystallinity
Nanosized materials: application in electrochemical systems for energy conversion and storage
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Low crystallinity
High crystallinity
Nanosized materials: application in electrochemical systems for energy conversion and storage
3,4 3,6 3,8 4,0 4,2 4,4 4,6 4,8 5,0
PEG sample at 400ºC
Potencial / V vs Li+/Li
PEG sample at 800ºC
10 20 30 40 50
20
40
60
80
100
120
10 20 30 40 50
Spec
ific
cap
acit
y /
Ah·
kg-1
C/4 2C 4C 8C 15C
Number of cycles
Poor reversibility(broad peaks)
Effect of Crystallinity
Effect of the synthesis method(improved rate capability)
High crystallinity
Low crystallinity
Synthesis with PEG Synthesis without PEG
LiNi0.5Mn1.5O4
Improved reversibility(narrow peaks)
J. C. Arrebola et al. Adv. Funct. Mater. 16, 1904 (2006)
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(4 min)
(4 h)
Capacity lossat high rates
Li extraction
Li insertion
Better maintenanceof capacity at high rates
Nanosized materials: application in electrochemical systems for energy conversion and storage
A high energy Li-ion battery based onnanosized LiNi0.5Mn1.5O4 cathode material
●Highly crystalline nanosized LiNi0.5Mn1.5O4 as positive electrode.●Meso carbon microbeads (MCMBs) as negative electrode.●Li bis-oxalate borate (LiBOB) instead of LiPF6 as electrolyte.●Best performance obtained by using a slight excess of spinel (a cathode/anode mole ratio of 1.3). ●Higher spinel contents caused the formation of metallic Li in the carbon andthe rapid degradation of battery performance
Calculated output energy 322Whkg-1
higher than thevalue reported forthe LiMn2O4/C cell(250Whkg-1).
Variation of the capacity of theLNMO/LiBOB/MCMB Li-ion cell as a function of the cycle number.Cycling rate: 1C. The inset showsthe dQ/dE plot for the first cycle.
J.C. Arrebola et al. / Journal ofPower Sources 183 (2008) 310–315
Nanosized materials: application in electrochemical systems for energy conversion and storage
LiNi0.5Mn1.5O4 //1 M Li (Bis Oxalate Borate) 1/1 EC/DMC// Si-Cellu.fibers-C. black
High capacity, good capacityretention (after first few cycle) and
Coulombic efficiency
J.C. Arrebola et al. Electrochem. Commun. 11 (2009) 1061
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A new Li-ion battery based on nanosized-Si as anode
Irreversible capacity
charge
discharge
Nanosized materials: application in electrochemical systems for energy conversion and storage
This work
C1013004.5Si/Cel/MCMBLiNi0.5Mn1.5O4
This work
C10C5
17001650
4.5Si/Cel/SuperPLiNi0.5Mn1.5O4
[8]C52253.0TiO2 (B)LiNi0.5Mn1.5O4
[8]C52202.0TiO2 (B)LiFePO4
[25]C51303.0Li4Ti5O12LiNi0.5Mn1.5O4
[24]C51202.5Li4Ti5O12LiMn2O4
[23]C51402.0Li4Ti5O12LiFePO4
[7]1C3254.2SnLiNi0.5Mn1.5O4
[6]C20350 4.0Cu-SnLiNi0.5Mn1.5O4
[12]10103.7Si thin filmLiMn2O4
[15]C511603.7Si thin filmLiCoO2
[14]C1025003.7Si thin filmLiCoO2
[13]C1020303.7Si thin filmLiCoO2
[5]C53254.5Carbon MCMBLiNi0.5Mn1.5O4
[22]-3003.7CarbonLiCoO2
Ref.RateSpecific capacity[1] (mA h
g-1)
Average voltage
(V)
AnodeCathode
Table 1. Voltage, specific capacity and charge/discharge rate for various Li-ion batteries.
Future work: To optimize the battery by (i)
decreasing the irreversible capacity; (ii)
increasing the delivered
capacity and rate capability
J.C. Arrebola et al. Electrochem.
Commun. 11 (2009) 1061
Nanosized materials: application in electrochemical systems for energy conversion and storage
Highly electroactive nanosized α-LiFeO2
LiFeIII O2 → x Li+ + xe− + Li 1−x Fe 1−xIII Fe x IV O2
Framework preservationon Li removaland insertion
J. Morales et al. Electrochem. Commun. 9 (2007) 2116, Electrochim. Acta 53 (2008) 6366
Charge/dischargecurves s-shaped
NaCl type structure
Size~ 50 nm
Capacities values ca. 150 mAh/g
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● Cheaper and less toxic than LiCoO2
Maintenanceof capacity on
cycling
Identification of Fe4+ by XPS
Nanosized materials: application in electrochemical systems for energy conversion and storage
Transparent electrode made from nanosized LiFeO2(with Ag nanopartices to improve conductivity)
Good electrochemical performance(tendency to maintain a capacity ca.
165 mAh/g after 30 cycles)
J. Morales et al. J. Mater. Chem. (in press)
Films prepared by spin coating from AgAcLiAc and Fe(acac)3 solutions calcined at400 ºC
Maintenance of thetransparency on cycling the cell
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Future application: photovoltaic-electrochemical lithium battery in a
transparent smart window
Nanosized materials: application in electrochemical systems for energy conversion and storage
•Potential store 5-10 times as muchenergy as today best systems.•Sensitive to humidity, very low rateof discharge.
What in the future? Lithium/Air battery2 Li + O2 Li2O2 3.10 V 4 Li + O2 2 Li2O 2.91 V
Schematic representation of a rechargeable Li/O2 battery.
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Future work● Solid electrolytes (Li+) to protect Li● Porous carbons● Efficient electrocatalysts for the cathode
P. G. Bruce et al.Angew. Chem. Int. Ed.
(2008)
α-MnO2 bulk
α-MnO2 NW
Nanosized materials: application in electrochemical systems for energy conversion and storage
Lead acid battery
J. Morales et al. Electrochem. Solid State Lett. 7, A75-A77 (2004).
Negative Positive electrode
Pb2+ + 2e- → Pb Pb2++ 2H2O + 2e- → PbO2 + 4H+ (charge)
CommercialPbO230 Ah/kg
n-PbO2 160 Ah/kg
(The in situ PbO 2prepared
in commercialbatteries only
delivers 120 Ah/kg)
Nanosized PbO2
TEM
Nano- PbO2
High charge/discharge rate
SEM
(ca. 1 h)
(6 min)
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Micro-PbO2
TEM SEM
Nanosized materials: application in electrochemical systems for energy conversion and storage
ConclusionsThe use of nanomaterials can improve the performance of LIB as a result of:
(i) The decrease in particle size-- increase in the area of the electrode/electrolyte interface ⇒ Increase the
electrode capacity and therefore the specific energy.
-- Decrease in the distance for Li displacement beneficial for Li ion diffusionImproved rate capability the battery provides higher power.
(ii) Effects related with special morphologies: nanotubes, nanorods, nanowire,porosity…
(iii) space/charge effects at the nanoparticle interface.
Development of new models or adaptation of those used for describingproperties of bulk materials.
Main drawbacks: synthesis methods are complex and expensive. Developmentof simple synthetic routes applicable on a large scale.
Strategies to avoid secondary reactions (increase the electrolyte stability, solidelectrolytes).
Nanosized materials: application in electrochemical systems for energy conversion and storage
ACKNOWLEDGEMENTS
Ph D
Lourdes Hernán Luis Sánchez Jesús Santos Alvaro Caballero Manuel Cruz José Carlos Arrebola
Postgraduate
Juán Luis Gómez Rafael TrocoliOscar VargasPaloma Ballesteros Mª Isabel Mármol.