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Lithium Iron Phosphate (LiFePO4)

Battery as Energy Storage Material

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Current World Energy Status

Oil and Gas Production Coal Mining

Etc

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Current World Oil Reserve

Source : http://en.wikipedia.org/wiki/Oil_reserves

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Side effect of fossil fuel Air pollution

Acid rain Global warming

Etc

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Alternative Energy Provide

Solution Solar Energy Wind Energy

Nuclear Energy

Tidal Energy

Etc

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Battery Material Parameter

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Lithium Ion Battery

Why Lithium as battery material?

1. Low density (0.534 g/cm3)

2. Large specific capacity

(3860 Ah/kg)

3. lowest electrochemical

potential (-3.01 V vs NHE)4. lower self discharge

5. No memory effect

6. Prolonged service-life

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Why LiFePO4?

Compare to LiCoO2 battery, LiFePO4 :

Advantages :

1. Superior in thermal and

chemical stability

2. Less expensive3. Environmentally benign

4. Non-toxic

5. Longer cycle-life

Disadvantages

1. Lower energy density relative

to LiCoO2 (170 mAh/g vs 274

mAh/g)

2. Low conductivity (~10-9 S/cm)

LiFePO4 Battery

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LiFePO4 Battery

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Charging /Discharging of LiFePO4 Battery

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Attempts to Higher the Conductivity ofLiFePO

4Battery by modifiying Cathode

LiFePO4 has a limitation that is low conductivity, which leads to

high impedance and low rate capability for batteries using this

material. Approaches to solve that problem include but not limited

to:

1. Doping LiFePO4 with supervalent cations that enhance thematerial conductivity at the crystal level

2. Surface modification of LiFePO4 with Silver

3. Decreasing the particle size of LiFePO4 in order to make the

diffusion path of lithium shorter

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The resulting doped LiFePO4 materials

have lithium storage capacities that are

near the theoretical limit of 170 mAh/g at

low charge/discharge rates, and retain

significant discharge capacity at rates as

high as 6,000 mA/g of material.

But, doped olivine also show high defect

concentrations on the M1 site.

In one case, the unit cell volume contracts

(Fe3+ doped LiMgPO4), and in the othercase (Fe3+ doped LiNiPO4) it expands.

Doping LiFePO4 with Supervalent Cations(i.e Mg2+, Al3+, Ti4+, Zr4+, Nb 5+ and W6+)

Source : Chung, S. Y., Bloking, J. T. and Chiang, Y. M., (2002):

Electr onically conductive phospho-olivines as lithium storage electrodes,

Nature Materials, No.1, pp.123-128.

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The capacity of the silver coated LiFePO4 is larger than that of the pure

LiFePO4 and the ratio of increase in the capacity by coating is about 10% inall current densities, and the electronic conductivity is increase by factor of

108. The increased capacities by the coating are maintained even after

many charge/discharge reactions

Surface modification of LiFePO4 with Silver

Source : KS Park, JT Son, HT Chung, SJ Kim, CH Lee, KT Kang, HG Kim :

Surface modification by silver coating for improving electrochemical properties of LiFePO4,

Solid State Communications 129 (2004) 311314

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Decreasing the particle size of LiFePO4 in order tomake the diffusion path of lithium shorter

Source : KS Park, JT Son, HT Chung, SJ Kim, CH Lee, KT Kang, HG Kim :

Surface modification by silver coating for improving electrochemical properties of LiFePO4,

Solid State Communications 129 (2004) 311314

By decreasing the particle size of

LiFePO4 by soft chemistry method

and the addition of Ketjen carbon

black, specific capacity of 145 mAh/g

is achived. No significant capacity

fade was observed, even after morethan 400 charge/discharge cycles. At

low charge/discharge rates, an

increase of thecarbon amount from 5

to 16.7% leads to a constant increase

of the specific capacity of ~15 mAh/g,

whatever the C-rate used

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Attempts to Higher the Conductivity ofLiFePO

4Battery by modifiying Anode

in addition to modifying the cathode, someattempts are also done to improve the

electronic conductivity of LiFePO4 by

modifying the anode materials.

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TiO2 Nanowires as an Improved AnodeMaterial

By changing the anode from

LixC6 to TiO2 nanowire, the

capacity of LiFePO4 battery

increase to 225 mAh/g.

But the overall cell potential

range is reduce to 1.5 V

Source : Graham Armstrong, A. Robert Armstrong, Peter G. Bruce,Priscilla Reale, and Bruno Scrosati :

TiO2 Nanowires as an Improved Anode Material for Lithium-Ion Batteries Containing LiFePO4 or

LiNi0.5Mn1.5O4 Cathodes and a Polymer Electrolyte

Advanced Materials, Vol.18 Issue 19

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Temperature Effect on LiFePO4 Battery

It is being reported that the capacity of a

LiFePO4/graphite cell with LiPF6

electrolyte fades rapidly at high

temperature 55C due to Fe dissolution

from cathode and subsequent

deposition of the Fe ions on the graphite

anode to form an unfavorable superficial

layer. Increasing the temperature

to 37 and 55 C, the cells show

significant capacity loss after 100 cycles

especially at 55 C. Similar capacity fade

was also reported when storing the cells

at 3.8 V for four weeks at 55 C.

Source : K. Amine, J. Liu, I. Belharouak :

High-temperature storage and cycling of C-LiFePO4/graphite Li-ion cells

Electrochemistry Communications 7 (2005) 669673

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Enhanced High Temperature ofLiFePO4 Battery

Addition of vinylene carbonate (VC) in

electrolyte solution has been found to

greatly improve the high-temperature

55C cycling performance of LiFePO4

based Li-ion batteries. It has been

established that the VC additive

remarkably suppresses Fe dissolution

from LiFePO4 cathode and hence,

subsequent Fe deposition on the anode

side.

Source : Hung-Chun Wu, Ching-Yi Su, Deng-Tswen Shieh, Mo-Hua Yang and Nae-Lih Wu :

Enhanced High-Temperature Cycle Life of LiFePO4-Based Li-Ion Batteries by Vinylene Carbonate as

Electrolyte Additive

Electrochemical and Solid-State Letters,9 (12 ) A537-A541

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Summary

1. LiFePO4 offer a safer battery technology especially for electric vehicle

application due to its thermal and chemical stability

2. LiFePO4 offer a more environment benign battery technology

3. A further attempt to increase the electronic conductivity of LiFePO4is needed

4. The development of anode material, cathode material, electrolyte

material and binder material is needed to improve the performance of

LiFePO4 battery for future application