Environmental Engineering Reference
In-Depth Information
glasses (mostly for high temperature applications). For automotive applications
where ESS performance and durability are paramount, the Li(Ni, Co, M)O
2
(M
¼
Al
or Mn) based positive electrode is being actively investigated; however, durability of
this electrode at high temperatures is not known [10]. It was found that electrode
structural changes occurred in the LiNiCoAlO
2
positive particles, leading to increase
in resistance. Kim and Cho [11] argue that replacement of cobalt in the popular
LiCoO
2
cell with nickel, to take advantage of its lower cost and high capacity,
introduces a number of significant problems. First is the moisture intake into the
cathode slurry, leading to gelation of the positive electrode mix and non-uniformity
of the final electrode film. Second is the issue of structural instability above 60
C.
This is confirmed by storage at 90
C, where it is found that nickel and other active
metal ions dissolve into the electrolyte, resulting in cathode particle coating with
Li
2
CO
3
and the attendant process of gas evolution. Third is the problem of strong O
2
gas evolution above 200
C, leading to thermal run-away. The authors demonstrated
that use of lithium-reactive Co
3
(PO
4
)
2
nanoparticle coating completely blocked the
metal ion dissolution during storage at 90
C.
Metal doping and coatings are also reported for the LiNi
1/3
Co
1/3
Mn
1/3
O
2
chemistry because of its cost and performance, but its low electrode density and low
specific capacity compared to higher nickel content electrodes remains an issue. In
Reference 12 EnerDel reported on the safety of lithium ion for automotive applica-
tions and noted that LiNi
1/3
Co
1/3
Mn
1/3
O
2
is slated for production in 2010 as cell to
module to systems for EVs and HEVs. To improve capacity, layered oxides (Co,
NMA, NMC), spinel (LiMn
2
O
4
) and olivine (LFP) structures are being pursued,
leading to 100% SOC capacity of 278 mAh/g. Henriksen [13] describes the devel-
opment of high capacity positive electrodes for application to PHEV that have a
capacity of
>
150 mAh/g, typical of conventional lithium ion, which is realized from
(1) increased particle density (1.3 to
>
2 g/cc), (2) increased rate capability (
C
/24
!
C
/3) and (3) optimized processing conditions for higher capacity density and stabi-
lity. Henriksen's work points out that the major contributor to impedance rise is the
interfacial impedance of the positive (
þ
) electrode. The most probable mechanisms
are reduced interfacial diffusion due to changes in surface films or oxide surface
layers and the preferential isolation of small active material particles.
The problems encountered with present lithium ion processing amount to
challenges facing those pushing a now two decades old slurry process to meet the
demands of vehicle application in plug-in and BEVs. The performance of the battery is
simply inadequate to meet vehicle demands for power and energy. Until this dilemma
is solved, the prospects of a commercially viable PHEV or EV remain unknown.
To conclude these sections on battery systems, a compilation of advanced
battery system technologies is listed in Table 10.3 that gives specific attributes of
each technology, representative cycling capability and a metric listed as energy-life
to quantify the throughput energy of each battery system until it enters wear-out
mode. Wear-out mode of a battery system is taken as the point at which its capacity
has diminished by 20% of rated.
Table 10.3 contains some interesting comparative data. The table itself is
composed of ESS technologies that have been optimized either for energy storage
