Cobalt free nanomaterials as positive electrodes for Lithium ion battery

Erstveröffentlichung
2019-03-04Authors
Balasubramanian, Prasanth
Referee
Tilmetz, WernerKaiser, Ute
Dissertation
Faculties
Fakultät für NaturwissenschaftenInstitutions
ZE ElektronenmikroskopieExternal cooperations
Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW)Abstract
Cathode materials with improved specific energy, energy density, safety and
reduced cost are essential for developing next generation Li-ion battery technology.
This can be made possible by exploring new chemistries of cathode materials, which
exhibit either higher operating voltages or higher specific capacity compared to the
materials currently available in the market. As a result, new materials’ utilizing multielectron step redox reaction has gained attention. Such materials can exchange more
than one Li-ion per formula unit and therefore, specific energy is improved. In my
thesis, I focus on fundamental understanding of such cathode materials and establish
a strong relationship between the physical properties of the active cathode materials
and their electrochemical behaviour. This study leads to a proposition that nano-sizing
is the key to further improve the specific energy of cathode materials for Li-ion
batteries. My thesis provides a scope to further analyse and optimize materials as well
as electrode preparation methods for nano-crystalline materials, and thus realizing a
high-energy Li-ion cell with materials using different redox steps.
Among the polyanion-based cathode materials, layered Li9V3(P2O7)3(PO4)2
(LVPP) is investigated as a high voltage cathode. In comparison to the commercially
available LiFePO4, where 1 Li-ion per formula unit is exchanged, LVPP is theoretically
predicted to exchange 6 Li-ions from the structure utilizing V3+ to V5+ redox reactions
at an average potential of 4.2 V, thus delivering specific capacity of 173 mA h g -1. The
feasibility of multi-electron step reactions in phosphate-based LVPP cathode and the
factors influencing the overall electrochemical behaviour has been explored. In
addition, the mechanism of Li extraction/insertion during charge and discharge is
investigated and the structural transformations are studied by means of in situand ex
situ X-ray diffraction. The results obtained suggest that by optimizing the material
synthesis for crystallite size and using specific cycling conditions facilitates multielectron step redox reactions in LVPP.
Among the oxide based cathode materials, LiNi0.5Mn1.5O4 (LMNO) is one of the
most promising cathode materials because of its high operating potential at 4.7 V, and
a theoretical specific capacity of 146 mA h g -1 . Furthermore, LMNO is completely
cobalt-free, which makes it cost-effective compared to the commercially available
cathode materials. Even though LMNO consists of two active redox centres such as Ni
and Mn, only the Ni (II) Ni (IV) redox reaction has received considerable attention.
v
However, when additionally utilizing the Mn redox reactions much improvement in the
capacity can be obtained. The feasibility of multi-electron step reactions involving both
Mn and Ni redox centres and the factors influencing the reversibility, overall capacity
and kinetics have been studied. The electrochemical investigations on the Mn (IV) to
Mn (III) redox reactions in LMNO clearly suggest that optimizing two important factors
such as crystallite size and potential window are very important to improve both the
specific capacity and kinetics. In the potential window of 2.4 – 4.9 V specific capacities
from both Mn and Ni redox plateaus are exploited and a very high reversible capacity
of 250 mA h g-1 has been demonstrated. This is put forth as the state of art for the
cobalt free LMNO based cathodes.
Date created
2018
Subject headings
[GND]: Lithium-Ionen-Akkumulator | Elektrochemie[LCSH]: Electric batteries | Lithium-ion batteries | Electrochemistry | Electrodes
[DDC subject group]: DDC 540 / Chemistry & allied sciences
Metadata
Show full item recordDOI & citation
Please use this identifier to cite or link to this item: http://dx.doi.org/10.18725/OPARU-12030
Balasubramanian, Prasanth (2019): Cobalt free nanomaterials as positive electrodes for Lithium ion battery. Open Access Repositorium der Universität Ulm und Technischen Hochschule Ulm. Dissertation. http://dx.doi.org/10.18725/OPARU-12030
Citation formatter >