This study demonstrates the possibility of manufacturing Li-ion batteries that cycle longer and use water in the processing, instead of hazardous organic solvents like NMP, thereby improving performance, reducing cost, and protecting the environment.
Anodes containing spherical natural graphite (SNG12) and cathodes containing LiFePO4, both from HydroQuebec, were prepared with aqueous-based polyacrylic acid (PAAH), its neutralized derivatives polyacrylic acid (PAAX) (X= Li, Na, and K), and with conventional poly(vinylidene difluoride) (PVDF) binders. A comparison of electrode performance was made between these three binder systems. The electrodes were optimized by adding elastic styrene butadiene rubber (SBR) and conductive vapor grown carbon fiber (VGCF) in the place of some of the PAAX. Initially, SNG12 and LiFePO4 electrodes were characterized in half cells with Li as the counter electrode. The electrochemistry results show that the use of
PAAX binders can significantly improve the initial coulombic efficiency, reversible capacity, and cyclability of SNG12 anodes and LiFePO4 cathodes as compared to that of electrodes based on a PVDF binder. By using an optimized composition for the anode and cathode, SNG12/LiFePO4 full cells with PAALi binder cycled 847 times with 70% capacity retention, which was a significant improvement over the electrodes with PVDF (223 cycles). This study demonstrates the possibility of manufacturing Li-ion batteries that cycle longer and use water in the processing, instead of hazardous organic solvents like NMP, thereby improving performance, reducing cost, and protecting the environment.
Polyacrylic acid powder with an average molecular weight of 450,000 was purchased from Sigma–Aldrich. PAALi, PAANa, and PAAK binders
were made from polyacrylic acid by stoichiometrically neutralizing it with lithium hydroxide, sodium hydroxide, and potassium hydroxide, respectively. The lithium hydroxide (99.9%), sodium hydroxide (98.5%), and potassium hydroxide (99.99%) were purchased from Sigma–Aldrich. PVDF (no. 1100) binder was supplied by Kureha, Japan. Anhydrous 1-methylpyrrolidinone (NMP) was purchased from Sigma–Aldrich. Vapor-grown carbon fiber (VGCF) and acetylene black (AB) were supplied by Showa Denko Carbon, Inc. Aqueous solutions of 40% SBR were obtained from Asahi Chemicals, Japan. An electrolyte of 1 M LiPF6 in EC: DEC, 1:2 by mass, waspurchased from Novolyte Technologies, Inc.
A comparative study of polyacrylic acid and poly(vinylidene difluoride) binders for spherical natural graphite/LiFePO4 electrodes and cells
Jin Chonga,b, Shidi Xuna,∗, Honghe Zhenga, Xiangyun Songa, Gao Liua, Paul Ridgwaya, Ji Qiang Wang b, Vincent S. Battagliaa a Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA b Tianjin Institute of Power Sources, Tianjin, 300381, China
Received 15 March 2011
Received in revised form 18 April 2011
Accepted 19 April 2011
Available online 23 April 2011
Spherical natural graphite
Aqueous based binder