NANOSTRUCTURED MATERIALS: APPLICATION IN ELECTROCHEMICAL … · Nanosized materials: application in electrochemical systems for energy conversion and storage A high energy Li-ion

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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


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

6


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)


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


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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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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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


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


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


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


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


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


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Calcined at 400 ºCLow crystallinity

Calcined at 800 ºCHigh crystallinity


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Low crystallinity

High crystallinity


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


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


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


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



[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


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


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


•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.

-----------

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


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


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).


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.

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NANOSTRUCTURED MATERIALS: APPLICATION IN ELECTROCHEMICAL … · Nanosized materials: application in electrochemical systems for energy conversion and storage A high energy Li-ion