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

Zhang, Liu – PNNL
V.B.10 Development of High Energy Cathode (PNNL)
LiMnPO 4 can be tuned simply by adjusting the Li content
in the synthesis step, which provides important clues on
the activation and stabilization of phosphate-based cathode
materials.
Figure V - 52: Rietveld refinement of XRD data of the LixMnPO4 series. Refinements for x = 0.8 and 1.1 compositions are done using two phases, LiMnPO4
and Mn2P2O7. Mn2P2O7 peaks are marked with blue arrows. Green arrows indicate small impurity peaks of Li3PO4. Red arrows indicate unidentified impurities
in Li0.5MnPO4.
C/20
Figure V - 53: Cycling stability of LixMnPO4 (0.5≤ x ≤1.2) between 2.0 and
4.5 V at C/20 rate. (1C=150 mA/g).
Synthesis of High-Voltage Spinel LiNi 0.5 Mn 1.5 O 4 .
We have developed a novel synthesis approach for
preparing high-voltage spinel LiNi 0.5 Mn 1.5 O 4 and its Crsubstituted
phase that involves only milling and heating.
Both LiNi 0.5 Mn 1.5 O 4 and LiNi 0.45 Cr 0.05 Mn 1.5 O 4 have cubic
structures that can be indexed into the Fd-3m space group.
For the undoped spinel, a trace amount of Li x Ni 1-y O was
identified. After 5% substitution of Ni by Cr in
LiNi 0.5 Mn 1.5 O 4 , no Li x Ni 1-y O impurity was observed in the
XRD pattern, which indicated a pure spinel phase.
Rietveld refinements showed an increase of the lattice
parameter from a = 8.17396(8) Å in LiNi 0.5 Mn 1.5 O 4 to
8.1860(1) Å after Cr-doping, which suggests an increased
amount of the disordered phase.
Figure V - 54 compares the morphologies of the pure and
Cr-substituted spinels. LiNi 0.5 Mn 1.5 O 4 exhibits a uniform
particle size distribution as shown in Figure V - 54a. The
octahedral particle diameters were around 2 μm and further
aggregated into secondary particles. After Cr-doping, the
morphology of the spinel did not change much. However,
the octahedral shape of the spinel particles became more
distinct as shown in Figure V - 54d. LiNi 0.5 Mn 1.5 O 4 consists
of both ordered and disordered phases as revealed by Figure
V - 54b and Figure V - 54c. The highlighted reflections are
forbidden by the Fd-3m space group. The occurrence of
the super lattice pattern was caused by the ordering
between Ni 2+ and Mn 4+ , which indicates the coexistence of
an ordered phase in the undoped spinel that cannot be
directly observed from XRD pattern. However, after Crdoping,
the extra diffraction spots were no longer
observable in Figure V - 54e and Figure V - 54f, both of which
showed typical spinel patterns. In other words, Cr-doping
FY 2011 Annual Progress Report 515 Energy Storage R&D