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

V.B.10 Development of High Energy Cathode (PNNL)
Zhang, Liu – PNNL
increased the amount of the disordered phase. This finding
is consistent with the changes of lattice parameters
calculated from XRD data.
J
c d e
a
Figure V - 54: a) SEM image of LiNi0.5Mn1.5O4; b) and c) electron diffraction
patterns of LiNi0.5Mn1.5O4 in the [001] and [110] zone, respectively; d)SEM
b
image of LiNi0.45 Cr0.05Mn1.5O4; e) and f) electron diffraction patterns of
LiNi0.45 Cr0.05Mn1.5O4 in the [001] and [110] zones, respectively.
Figure V - 55a reveals that, after Cr-doping, the cycling
stability was significantly improved. This improvement
may be assigned to the increased content of disordered
phase and/or Mn 3+ ions that facilitate Li + ion diffusion
within the lattice. Meanwhile the surface modification
caused by Cr-doping may alleviate Mn dissolution in the
electrolyte. We note here that the intrinsic influencing
parameter on performance is the content of Mn 3+ instead of
doping. In other words, if the Mn 3+ concentration in pure
LiNi 0.5 Mn 1.5 O 4 can be modified to the same amount as in
LiNi 0.45 Cr 0.05 Mn 1.5 O 4 , the cycling stability also may be
improved for the undoped spinel, which is now under
investigation.
C/10
f
b
a
Figure V - 55: Comparison of a) cycling stability for LiNi0.5Mn1.5O4 and LiNi0.45Cr0.05Mn1.5O4 and b) voltage profiles of LiNi0.45 Cr0.05Mn1.5O4 tested with and
without LiBOB.
We also found that the low concentration of Li
bis(oxalato)borate (LiBOB) not only improves the first
cycle efficiency of LiNi 0.45 Cr 0.05 Mn 1.5 O 4 from 76% to 85%,
but the rate capability also increases with 0.25% LiBOB
(rate performances not shown here). LiBOB has an
oxidation potential at around 4.5 V vs. Li/Li + . When the
voltage reaches 4.5V, LiBOB will be decomposed first via
a ring-opening reaction to form a linear inorganic lithium
metaborate film that covers the cathode surface. This
protection film also is resistive to the trace amount of HF
and POF 3 generated by the hydrolysis and thermal
decomposition of LiPF 6 salt in the electrolyte. Therefore
further decomposition of the solvents and the dissolution
of Mn in the high-voltage spinel will be alleviated, thus
improving the Coulombic efficiency and cycling stability.
We also found that the coin-cells pans and separator
membranes significantly influence on the Coulombic
efficiency of the high-voltage cells, especially during the
first cycle.
Renewable Organic Cathodes. In FY 2010, we
investigated a novel organic cathode based on
poly(anthraquinonyl sulfide) (PAQS). This renewable
cathode was prepared using a simple poly-condensation
that has been applied commercially to synthesize poly(pphenylene
sulfide). PAQS is different from traditional
intercalation cathode materials because it allows 2e
transfer that leads to a high theoretical capacity of 225
mAh/g. The electrochemically active site is O instead of S
on the ring; therefore, the polysulfide dissolution issue
encountered in Li/S batteries can be avoided.
We synthesized a new organic cathode material,
poly(1,8-anthra-quinonyl sulfide) (P18AQS), and
compared it with the previously reported poly(1,5­
anthraquinonyl sulfide) (P15AQS) in terms of rate
capability (see Figure V - 56). We found that the substitution
position with less steric stress on the backbone is critical
for the electrochemical performances, thus providing clues
on the further design of new quinone-based cathodes.
Energy Storage R &D 516 FY 2011 Annual Progress Report