of the lithium ions as a function of state of
charge. This change in environment is particularly problematic in layered structures where the slab
spacing decreases considerably when large amounts
of Li are removed, leading to a substantial reduction of Li mobility (25, 27, 28). However, in
cation-disordered structures, homogeneously
distributed cations should lead to a Li diffusivity
that is more independent of the Li concentration,
as is the case for electrode materials with the
spinel- and olivine-type structures. One issue that
requires more investigation is whether cation disordering will lead to a more sloped voltage profile than for well-ordered materials, as one
would expect from the wider distribution of Li-site energies in a disordered material. However,
this variance in the Li-site energy may be counteracted by a less effective Li-Li interaction, which
is responsible for the slope of the voltage curve
in layered materials (29). Hence, careful tailoring of the TM-Li to Li-Li ion interaction may
mitigate this effect. Given the insights presented
above, it may not be surprising that the highest-capacity layered materials are highly Li-excess
materials (18–20) that become more disordered
in the first few cycles because of a particular overcharge mechanism (30).
Our results may explain why disorder has not
been pursued as a strategy before: Most materials
synthesized are near stoichiometry (LiTMO2),
which is well below the percolation threshold for
0-TM diffusion. Therefore, these materials quick-
ly lose their capacity upon disorder as it renders
typical 1-TM channels inactive, while 0-TM chan-
nels are not percolating (7, 9, 21, 24). As a result,
disorder may have appeared to be a counter-
intuitive strategy. In contrast, our analysis points
to cation-disordered materials as a class of ma-
terials that can exhibit high capacity and high
energy density, thereby offering hope for sub-
stantial improvements in the performance of re-
chargeable Li batteries.
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Acknowledgments: Supported by the Robert Bosch Corporation,
by Umicore Specialty Oxides and Chemicals, and by a
Samsung Scholarship (J.L.). Computational resources from
the National Energy Research Scientific Computing Center
(NERSC) and from the Extreme Science and Engineering
Discovery Environment (XSEDE) are gratefully acknowledged.
The STEM work carried out at the Center for Functional
Nanomaterials, Brookhaven National Laboratory, was
supported by the U.S. Department of Energy, Office of
Basic Energy Sciences, under contract DE-AC02-98CH10886.
We thank N. Twu, S. Kim, and J. Kim for valuable discussions.
Materials and Methods
Figs. S1 to S8
25 September 2013; accepted 24 December 2013
Published online 9 January 2014;
Low Core-Mantle Boundary
Temperature Inferred from the
Solidus of Pyrolite
Ryuichi Nomura,1 Kei Hirose,1,2,3 Kentaro Uesugi,4 Yasuo Ohishi,4 Akira Tsuchiyama,5
Akira Miyake,5 Yuichiro Ueno1,2
The melting temperature of Earth’s mantle provides key constraints on the thermal structures of
both the mantle and the core. Through high-pressure experiments and three-dimensional x-ray
microtomographic imaging, we showed that the solidus temperature of a primitive (pyrolitic)
mantle is as low as 3570 T 200 kelvin at pressures expected near the boundary between the mantle
and the outer core. Because the lowermost mantle is not globally molten, this provides an
upper bound of the temperature at the core-mantle boundary (TCMB). Such remarkably low TCMB
implies that the post-perovskite phase is present in wide areas of the lowermost mantle. The low
TCMB also requires that the melting temperature of the outer core is depressed largely by impurities
such as hydrogen.
The core-mantle boundary (CMB), located at a depth of 2900 km inside Earth, is the interface between molten metal and rock.
The temperature jump across the thermal bound-
ary layer (TBL) above the CMB has been believed
to be about 1500 K (1), which has important con-
sequences for the dynamics and thermal evolution
in the mantle and the core. The temperature at
the top of the core should be lower than the
solidus temperature of a primitive mantle to
avoid global melting above the CMB. Conven-
tionally, the temperature at the CMB (TCMB) has
been estimated to be about 4000 K, primarily
based on the melting temperature of iron at the
inner core boundary (ICB), where solid and
liquid cores coexist (1–3). Such high TCMB im-
plies that MgSiO3-rich post-perovskite, a primary
mineral in the lowermost mantle, changes back
into perovskite with steeply increasing temper-
ature near the CMB (4), which allows detailed
modeling of the thermal structure in the CMB
region and the heat flux from the core into the
mantle (5). Previous experiments using laser-
heated diamond-anvil cell (DAC) techniques
showed that the solidus temperature of a primi-
tive mantle is about 4200 K at the CMB, sup-
porting the high TCMB around 4000 K (6–8). The
1Department of Earth and Planetary Sciences, Tokyo Institute
of Technology, Meguro, Tokyo 152-8551, Japan. 2Earth-Life
Science Institute, Tokyo Institute of Technology, Meguro,
Tokyo 152-8551, Japan. 3Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology,
Yokosuka, Kanagawa 237-0061, Japan. 4Japan Synchrotron
Radiation Research Institute, Sayo, Hyogo 679-5198, Japan.
5Division of Earth and Planetary Sciences, Kyoto University,
Kyoto, Kyoto 606-8502, Japan.
*Corresponding author. E-mail: firstname.lastname@example.org
(R.N.); email@example.com (K.H.)