Synthesis of nanosized, electrochemically active lithium transition metal phosphates [Elektronische Ressource] / Michael Andreas Stark

Informations

• Publié par: universitat_ulm
• Publié le: 01 janvier 2011
• Nombre de lectures: 44
• Langue: Deutsch
• Poids de l'ouvrage: 8 Mo

Extrait

Synthesis of nanosized, electrochemically
active lithium transition metal phosphates





Dissertation zur Erlangung des akademischen Grades
Doktor der Naturwissenschaften
(Dr. rer. nat)

eingereicht an der
Fakultät für Naturwissenschaften
der Universität Ulm


vorgelegt von
Dipl. Chem. Michael Andreas Stark
aus Ulm,

2011























Amtierender Dekan: Prof. Dr. Axel Groß

Erstgutachterin: Prof. Dr. Nicola Hüsing
Zweitgutachter: Prof. Dr. Werner Tillmetz


Tag der Promotion: Ulm, den 12. Oktober 2011




















"So eine Arbeit wird eigentlich nie fertig,
man muss sie für fertig erklären,
wenn man nach der Zeit und den
Umständen das Möglichste getan hat."


Johann Wolfgang von Goethe
* 28. August 1749 Frankfurt/Main – † 22. März 1832 Weimar
































Ich widme diese Arbeit meiner Familie,
insbesondere meinen Eltern, die mich
während meines Studiums und der
anschließenden Doktorarbeit mit Geduld
begleitet und mir alle Möglichkeiten eröffnet
haben.






Abstract


Abstract

The increasing interest to develop new types of Li-ion batteries is motivated by the amplified
need of batteries with high charge and discharge rates. This will be necessary for applica-
tions in portable electronics, transportation, energy storage, and especially in hybrid electric
vehicles. To improve the charge/discharge rates, Li-ion diffusion through the active materials
of the batteries must be very fast. Strong research interests have been focused on
generating new active materials to replace the present LiCoO , because of the costs and the 2
toxicity of cobalt. An alternative are lithium transition metal phosphates, such as LiMnPO or 4
LiFePO due to their high thermal and electrochemical stability, low toxicity, costs and their 4
environmental acceptability.
Lithium iron phosphate has been broadly investigated for high power and large format
applications, and is now applicable in commercial cells. Based on this success, lithium
manganese phosphate also becomes more and more attractive, because its redox potential
+ is 4.1 V vs. Li/Li , being approximately 0.65 V higher than the potential of LiFePO .4
Before LiMnPO can be used as active material, research has to challenge two different 4
aspects. First of all, - demonstrated by Toyota and HPL some years ago -, for this material a
crystallite size reduction is very important to improve the rate performance. And second,
being the major drawback of olivine lithium transition metal phosphates, such as LiFePO 4
and LiMnPO , the electronic conductivity has to be improved. To overcome these problems 4
several aspects have been investigated in recent years, such as the development of various
novel synthesis routes towards LiMnPO (solid-state-, sol-gel-, hydrothermal reactions etc.), 4
cationic doping and coating with conducting agents, e.g. mainly with carbon.

In this doctoral thesis, nanocrystalline LiMnPO and LiFePO were successfully obtained by a 4 4
wet chemical hydrothermal synthesis under basic conditions at 150 °C. A phosphate-based
TMsurfactant, (Triton H-66), and glycine, an amino acid, were used as structure-directing
additives. The results demonstrate that the additives have intense effects on controlling the
nucleation and growth of LiMnPO , resulting in nanocrystalline LiMnPO with a high specific 4 4
surface area.
Furthermore, two methods to increase the ionic and electronic conductivity were developed,
at first by a wet chemical hydrothermal carbon coating synthesis with glucose at 160 °C and
second by a novel impregnation synthesis, in which carbon was used as a host material to
obtain a carbon/LiMnPO composite. 4
The results displayed that via the first method a carbon shell is formed around the particles,
while in addition the applied synthesis protocol also prevents a dramatic increase of the
Abstract


particle size during the coating process, which is an expected behaviour for commercial
methods, such as ball milling etc.. In addition, the second method showed promising results
with samples comprising a three dimensional carbon fibre network impregnated with lithium
manganese phosphate.
At last, amorphous LiMnPO was synthesized by a newly developed non-aqueous sol-gel 4
method at ambient conditions. This material consists of three-dimensionally connected
nanometer-sized particles that can be transformed into a crystalline substance by heat
treatment.
The different materials were characterized by X-ray diffraction (XRD), high-resolution
transmission electron microscopy (HR-TEM), high-resolution scanning electron microscopy
(HR-SEM), inductively coupled plasma-optical emission spectrometry (ICP-OES), Raman
spectroscopy and small angle X-ray scattering- (SAXS), nitrogen sorption- and thermogra-
vimetric-/differential thermal analysis (TGA-DTA).

The last chapter of this thesis deals with the application of thus prepared materials in Li-ion
rechargeable batteries. The cooperation partners, “Toyota Motors Corporation” and the
“Centre for Solar Energy and Hydrogen Research (ZSW, Baden-Württemberg)” performed
electrochemical measurements, illustrating that some samples showed very promising elec-
trochemical properties.

Kurzfassung der Dissertation


Kurzfassung der Dissertation

Das steigende Interesse neue Typen von Lithiumionenbatterien zu entwickeln, ist in der
verstärkten Nachfrage an Batterien mit schnellen Ladungs-/Entladungsraten begründet.
Diese sind insbesondere für die Anwendung in tragbaren Elektrogeräten, zum Transport, für
die Energiespeicherung und ganz speziell in Elektroautos zwingend notwendig. Um die
Ladungs-/Entladungsreaktionen zu verbessern, muss die Lithiumdiffusion durch das
Aktivmaterial der Batterie sehr schnell sein. Außerdem gibt es ein großes wissenschaftliches
Interesse daran ein neues Aktivmaterial zu entwickeln, welches das gegenwärtig verwendete
LiCoO , aufgrund der hohen Kosten und der Giftigkeit von Kobalt, ersetzt. Eine Alternative 2
hierfür sind auf Grund ihrer thermischen und elektrochemischen Stabilität, sowie geringen
Giftigkeit, Kosten und ihrer Umweltverträglichkeit, Lithiumübergangsmetallphosphate wie
LiMnPO oder LiFePO . 4 4
Lithiumeisenphosphat wurde im Bereich der Hochleistungs- und Großformatanwendung
umfassend untersucht und findet jetzt Anwendung in kommerziell erhältlichen Zellen.
Basierend auf diesem Erfolg, wird nun Lithiummanganphosphat mehr und mehr interessant.
+Dies liegt wiederu