The worldwide demand for a clean and low-fuel-consuming transport promotes the
development of safe, high energy and power electrochemical storage and conversion
systems. Lithium-ion batteries (LIBs) are considered today the best technology for this
application as demonstrated by the recent interest of automotive industry in hybrid (HEV)
and electric vehicles (EV) based on LIBs. This thesis work, starting from the synthesis and
characterization of electrode materials and the use of non-conventional electrolytes,
demonstrates that LIBs with novel and safe electrolytes and electrode materials meet the
targets of specific energy and power established by U.S.A. Department of Energy (DOE)
for automotive application in HEV and EV.
In chapter 2 is reported the origin of all chemicals used, the description of the
instruments used for synthesis and chemical-physical characterizations, the electrodes
preparation, the batteries configuration and the electrochemical characterization procedure
of electrodes and batteries.
Since the electrolyte is the main critical point of a battery, in particular in large-
format modules, in chapter 3 we focused on the characterization of innovative and safe
electrolytes based on ionic liquids (characterized by high boiling/decomposition points,
thermal and electrochemical stability and appreciable conductivity) and mixtures of ionic
liquid with conventional electrolyte.
In chapter 4 is discussed the microwave accelerated sol–gel synthesis of the carbon-
coated lithium iron phosphate (LiFePO 4 -C), an excellent cathode material for LIBs thanks
to its intrinsic safety and tolerance to abusive conditions, which showed excellent
electrochemical performance in terms of specific capacity and stability.
In chapter 5 are presented the chemical-physical and electrochemical
characterizations of graphite and titanium-based anode materials in different electrolytes.
We also characterized a new anodic material, amorphous SnCo alloy, synthetized with a
nanowire morphology that showed to strongly enhance the electrochemical stability of the
material during galvanostatic full charge/discharge cycling.
Finally, in chapter 6, are reported different types of batteries, assembled using the
LiFePO 4 -C cathode material, different anode materials and electrolytes, characterized by
deep galvanostatic charge/discharge cycles at different C-rates and by test procedures of the DOE protocol for evaluating pulse power capability and available energy. First, we
tested a battery with the innovative cathode material LiFePO 4 -C and conventional graphite
anode and carbonate-based electrolyte (EC DMC LiPF 6 1M) that demonstrated to surpass
easily the target for power-assist HEV application. Given that the big concern of
conventional lithium-ion batteries is the flammability of highly volatile organic carbonate-
based electrolytes, we made safe batteries with electrolytes based on ionic liquid (IL). In
order to use graphite anode in IL electrolyte we added to the IL 10% w/w of vinylene
carbonate (VC) that produces a stable SEI (solid electrolyte interphase) and prevents the
graphite exfoliation phenomenon. Then we assembled batteries with LiFePO 4 -C cathode,
graphite anode and PYR 14 TFSI 0.4m LiTFSI with 10% w/w of VC that overcame the DOE
targets for HEV application and were stable for over 275 cycles. We also assembled and
characterized ―high safety‖ batteries with electrolytes based on pure IL, PYR 14 TFSI with
0.4m LiTFSI as lithium salt, and on mixture of this IL and standard electrolyte
(PYR 14 TFSI 50% w/w and EC DMC LiPF 6 50% w/w), using titanium-based anodes (TiO 2
and Li 4 Ti 5 O 12 ) that are commonly considered safer than graphite in abusive conditions.
The batteries bearing the pure ionic liquid did not satisfy the targets for HEV application,
but the batteries with Li 4 Ti 5 O 12 anode and 50-50 mixture electrolyte were able to surpass
the targets. We also assembled and characterized a lithium battery (with lithium metal
anode) with a polymeric electrolyte based on poly-ethilenoxide (PEO 20 –
LiCF 3 SO 3 +10%ZrO 2 ), which satisfied the targets for EV application and showed a very
impressive cycling stability.
In conclusion, we developed three lithium-ion batteries of different chemistries that
demonstrated to be suitable for application in power-assist hybrid vehicles: graphite/EC
DMC LiPF 6 /LiFePO 4 -C, graphite/PYR 14 TFSI 0.4m LiTFSI with 10% VC/LiFePO 4 -C and
Li 4 T i5 O 12 /PYR 14 TFSI 50%-EC DMC LiPF 6 50%/LiFePO 4 -C. We also demonstrated that
an all solid-state polymer lithium battery as Li/PEO 20 –LiCF 3 SO 3 +10%ZrO 2 /LiFePO 4 -C is
suitable for application on electric vehicles. Furthermore we developed a promising anodic
material alternative to the graphite, based on SnCo amorphous alloy.
| Identifer | oai:union.ndltd.org:unibo.it/oai:amsdottorato.cib.unibo.it:3427 |
| Date | 19 April 2011 |
| Creators | Damen, Libero <1980> |
| Contributors | Mastragostino, Marina |
| Publisher | Alma Mater Studiorum - Università di Bologna |
| Source Sets | Università di Bologna |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, PeerReviewed |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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