Modified LiFePO4 cathode material for lithium ion

batteries

Reporter: Guohui Qin April 29 2013

1.Introduction

Advantage: Disadvantage:

high theoretical specific capacity

a flat voltage profile

high safety

high thermal stability

environmental benignity

low cost

poor electronic conductivity

low ionic diffusivity

2.Improved method

Doping MWCNTs and PANI conducting materials

Effects:1.Improving the conduct of LiFePO4

2. The effective dispersion of three-dimentional network and uniform carbon layer developed not only allow better penetration of electrolyte to promote lithium ion diffusion3. As low as a 5.9% carbon content promotes a high tap density

3.Modified LiFePO4

Polyaniline/LiFePO4/multi-walled carbon nanotubes composite was prepared by an in-situ multi-walled carbon nanotubes embedding approach that involves a hydrothermal process and a facile electro-polymerization polyaniline process.

4.Fig.1 Morphology

a. Pure LiFePO4

b.LiFePO4/MWCNTs

c and dPANI/LiFePO4/MWCNTsat various magnifications

material at various magnifications

The exist problem was the dispersion of MWCNTs

Question 1

To our knowledge, the addition of carbon can suppress the growth of LiFePO4,however,the modified LiFePO4 particles grew bigger compared with the pure LiFePO4 material (Fig.1(a)vs.(b)).What are the possible reasons causing the presented result? Is the addition of citric acid as the chelating agent the key factor on this point ? Thank you for your guidance.

5.Fig.2XRD spectrogram

The elements of C and N are not distinctively detected in the PANI/LiFePO4/MWCNTs sample possibly due to their low content.

(i) pristine LiFePO4

(ii)LiFePO4/MWCNTs

(iii)PANI/LiFePO4/MWCNT

(iv)MWCNTs

6.Fig.3the initial charge–discharge curves of all the samples at C/10

Question2

A maximum capacity of 169.8mAhg−1(nearly to its theoretical capacity 170mAhg-1) are found in PANI/LiFePO4/MWCNTs at a low rate C/10,As for the reason caused its high capacitygood electronic contact by retaining the ability to coat individual nanoparticles with the tridimensional networks and overall carbon coating.Can the pseudocapacitance of PANI contribute to it?I did not find related references.Thank for your guidance.