V. Focused Fundamental Research - EERE - U.S. Department of ...

V.B.2 Cell Analysis, High-energy Density Cathodes and Anodes (LBNL)
Thomas Richardson
Lawrence Berkeley National Laboratory
Environmental Energy Technologies Division
Berkeley, CA 94720
Phone: (510) 486-8619; Fax: (510) 486-8609
E-mail: TJRichardson@lbl.gov
Start Date: October 1, 2004
Projected End Date: September 30, 2012
Objectives
· Synthesize and evaluate new electrode materials with
improved energy density.
· Investigate the relationship of structure, morphology
and performance of cathode and anode materials.
· Explore kinetic barriers, and utilize the knowledge
gained to design and develop electrodes with
improved energy density, rate performance and
stability.
Technical Barriers
· Low energy density
· Poor cycle life
Technical Targets
· Available energy: 11.6 kWh
· Cycle life: 5,000 cycles
Accomplishments
· High voltage cathodes: Micron-sized, nanoporous,
carbon-coated spheres of lithium cobalt phosphate,
prepared by spray pyrolysis, were shown to have
superior utilization and rate capability.
· Cell analysis: Focused ion beam (FIB) tomography
was applied to composite electrodes to visualize the
sizes and shapes of voids, cracks, and agglomerated
particles, whose characteristics and distribution
directly impact cell performance.
Introduction
EV and PHEV batteries will have to have higher
energy densities with good power capability, long cycle
lives, and a high margin of safety. Advances in both anode
and cathode chemistries are needed to achieve these goals.
In addition, improving the design and construction of
electrodes and reducing irreversible capacity losses are key
routes to maximizing the utilization of theoretical
capacities.
Approach
High energy density cathodes. High voltage olivine
phosphates such as LiNiPO 4 and LiCoPO 4 have good
theoretical capacities, but have performed poorly in the
areas of utilization and rate. While the use of small
particles improves both parameters, it can lead to poor
packing densities and undesirable side reactions. Our
previous success with spray pyrolized LiFePO 4 suggested
that LiCoPO 4 might also benefit from the porous sphere
morphology.
Cell Analysis. The optimization of porous composite
electrodes is a subject of great interest. We have shown
using x-ray diffraction that the distribution of charge in
porous electrodes is affected by both electronic resistances
in the current collector and composite matrix and by
electrolyte polarization. 3D imaging techniques, however,
are needed to determine the internal structure of the
electrodes and the distribution of solids and pores.
Results
High energy density cathodes. In collaboration with
Marca Doeff, LiCoPO 4 /C nanoporous spheres were
prepared by ultrasonic spray pyrolysis from aqueous
precursor solutions. This material, with two discharge
plateaus of about equal capacity at 4.8 V and 4.7 V and a
theoretical capacity of 167 mAh/g, has previously suffered
from poor utilization, rate performance, and cycling
stability. The porous microspheres (Figure V - 8) consisting
of ~70 nm sized carbon coated LiCoPO 4 primary particles
had a residual carbon content of 2.4 wt.%. Electrodes
containing 10 wt % carbon black and 5 wt % PTFE
exhibited excellent rate capability in lithium half-cells,
delivering 123 mAh/g at C/10 and 80 mAh/g at 5C,. The
capacity retention at C/10 was 95% after 20 cycles, with
coulombic efficiencies of 97% after the first cycle. (Figure V
- 9).
The method is fast, simple, scalable, and energyefficient.
While the energy density of electrodes containing
these particles was not optimized, it exceeded those of
electrodes made from conventional nanoparticles.
FY 2011 Annual Progress Report 475 Energy Storage R&D