Deployment of micro-grids using renewable energy (solar and wind power) requires large-scale electrical energy storage (EES) systems. Currently, lithium-ion batteries (LIBs) are leading candidates for EES. High power density LIBs addressing intermittency of renewables use expensive lithium titanate as anode. Besides, lithium is a scarce resource. Sodium, on the other hand, is the sixth most abundant element on the Earth’s crust. Sodium-ion batteries (NIBs) operating at ambient temperature are expected to be durable, safe and inexpensive. Regardless of the relatively lower energy density of NIBs, they can effectively be employed in micro-grid applications, where the weight and footprint requirement are not severe.
We present here recently developed non-flammable sodium-ion conducting glyme based electrolyte displaying excellent storage performance of low voltage anodes as well as high voltage cathodes for sodium-ion cells. Employing this liquid electrolyte, non-flammable sodium-ion cells (18650-type) have been fabricated using rhombohedral Prussian Blue analogoue1 or sodium vanadium phosphate as cathode and hard carbon as anode with energy density in the range 40 – 60 Wh/kg (kg refers to the total 18650 full cell weight) and impressive 4C rate performance. This ultra-safe commercial type sodium-ion cells have relatively higher energy density than the reported aqueous (non-flammable) commercial NIBs. We further present thermal (DSC analyses) and safety parameters (heat losses and internal resistance evaluations) of the above 18650 cells which help in developing thermal management systems for NIB packs for possible micro-grids (100-500 kWh) to address the intermittency of renewable energy.
Size reduction in nanocrystals leads to a variety of unexpected exciting phenomena due to enhanced surface-to-volume
ratio and reduced length for the transport [1, 2]. Here, we consider the effects of nano-size on the kinetics and
thermodynamics and study its bearing on the lithium storage performance in insertion and conversion based Li storage
Firstly, we investigate the storage performance of nanocrystalline LiMnPO4 by insertion reaction. Ball milling
of LiMnPO4 synthesized by soft-template method with carbonaceous materials helps to reduce the grain size as well as
formation of a thin layer of carbon coating. Nanostructuring by ball milling process promotes high surface area of the
active electrode material for improved electrolyte wetting, short transport length for Li diffusion while the carbon
coatings facilitates electronic wiring all of which contribute to the enhanced storage performance. Additionally, we
show that combining nanostructuring with divalent cation doping further improves the storage performance of the
system which make them potential high voltage cathodes for real applications.
Secondly, we discuss the size effect on thermodynamics during the conversion reaction, considering Fe2O3 as
an example. The process of Li storage by conversion induces drastic size reduction, leading to stabilization of
metastable phase of γ-Fe2O3. We show here that apart from kinetics, thermodynamics at nanosize also limit the rate of
conversion reaction. Finally, we show that Fe2O3 can be a potential anode material for practical applications as they
demonstrate a high degree of reversibility ~ 90% and excellent high rate performance.
The Energy crisis happens to be one of the greatest challenges we are facing today. In this view, much effort has been
made in developing new, cost effective, environmentally friendly energy conversion and storage devices. The
performance of such devices is fundamentally related to material properties. Hence, innovative materials engineering is
important in solving the energy crisis problem. One such innovation in materials engineering is porous materials for
energy storage. Porous electrode materials for lithium-ion batteries (LIBs) offer a high degree of electrolyte-electrode
wettability, thus enhancing the electrochemical activity within the material. Among the porous materials, mesoporous
materials draw special attention, owing to shorter diffusion lengths for Li+ and electronic movement. Nanostructured
mesoporous materials also offer better packing density compared to their nanostructured counterparts such as
nanopowders, nanowires, nanotubes etc., thus opening a window for developing electrode materials with high
volumetric energy densities. This would directly translate into a scenario of building batteries which are much lighter
than today's commercial LIBs. In this article, the authors present a simple, soft template approach for preparing both
cathode and anode materials with high packing density for LIBs. The impact of porosity on the electrochemical storage
performance is highlighted.
Nanostructured materials have triggered a great excitement in recent times due to both fundamental interest as well as
technological impact relevant for lithium ion batteries (LIBs). Size reduction in nanocrystals leads to a variety of
unexpected exciting phenomena due to enhanced surface-to-volume ratio and reduced transport length. We will consider
a few examples of nanostructured electrode materials in the context of lithium batteries for achieving high storage and
high rate performances: 1) LiFePO4 nanoplates synthesized using solvothermal method could store Li-ions comparable to its theoretical capacity at C/10, while at 30C, they exhibit storage capacity up to 45 mAh/g. Size reduction (~30 nm) at the b-axis
favors the fast Li-ion diffusion. In addition to this, uniform ~5 nm carbon coating throughout the plates provides excellent electronically conducting path for electrons. This nano architecture enables fast insertion/extraction of both Li-ions as well as electrons; 2) Mesporous-TiO2 with high surface area (135m2/g) synthesized using soft-template method exhibits high
volumetric density compared to commercial nanopowder (P25), with excellent Li-storage behavior. C16 meso-TiO2 synthesized from CTAB exhibits reversible storage capacity of 288mAh/g at 0.2C and 109 mAh/g at 30C; 3) Zero strain Li4Ti5O12 anode material has been synthesized using several wet chemical routes. The best condition has been optimized to achieve storage capability close to theoretical limit of 175mAh/g at C/10. At 10C, we could retain lithium storage up to 88 mAh/g; 4) We report our recent results on α-Fe2O3 and γ-Fe2O3 using conversion reaction, providing insight for a better storage capability in γ-phase than the α-phase at 2C resulting solely from the nanocrystallinity.
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