Semiconductor Materials for Water Splitting

Lithium Ion Battery

A lithium ion battery is a type of rechargeable battery in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging.

The negative electrode is made up of carbon mostly graphite. Recently, graphene based electrodes (based on 2D and 3D structures of graphene) have also been used as electrodes for lithium batteries.

The positive electrode is metal oxide (generally one of three materials):

1. a layered oxide (lithium cobalt oxide),
2. a polyanion (lithium iron phosphate)
3. a spinel (lithium manganese oxide).

The electrolyte is a lithium salt in an organic solvent. The electrolyte is typically a mixture of organic carbonates such as ethylene carbonate or diethyl carbonate containing complexes of lithium ions. These non-aqueous electrolytes generally use non-coordinating anion salts such as lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate monohydrate (LiAsF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4) and lithium triflate (LiCF3SO3).

Properties:

1. The most popular types of rechargeable batteries for portable electronics
2. high energy density
3. tiny memory effect
4. low self-discharge

Applications:

home electronics, military, battery electric vehicle and aerospace

Uses:

Li-ion batteries provide lightweight, high energy density power sources for a variety of devices. To power larger devices, such as electric cars, connecting many small batteries in a parallel circuit is more effective and more efficient than connecting a single large battery. Li-ion batteries are used in telecommunications applications.

Difference between Flow Batterie and Lithium Ion Batteries        :

1. Li-ion batteries offer good charging performance at cooler temperatures and may even allow 'fast-charging' within a temperature range of 5 to 45 °C. Charging should be performed within this temperature range. At temperatures from 0 to 5 °C charging is possible, but the charge current should be reduced while the voltage efficiency of the Vanadium Redox Flow Battery is found to increase from 86.5% to 90.5% at 40 mA/cm2 when the operating temperature is increased from   15 °C to 55°C. The peak discharge power density is also observed to increase from 259.5 mW/cm2 to 349.8 mW/cm2 at the same temperature increment.
2. Lithium-ion battery provides an average potential difference at its terminals of 3.7 V for LiCoO2 and 3.3 V for LiFePO4 while in case of flow batteries the cell voltage (in practical applications)  from 1.0 to 2.2 volts.
3. The applied voltage to recharge the solar flow battery is reduced to 2.9 Volts compared to over 3.6 Volts for conventional lithium-iodine batteries, resulting in an energy savings of up to 20%.
4. One of the biggest advantages of flow batteries is that they can be almost instantly recharged by replacing the electrolyte liquid, while simultaneously recovering the spent material for re-energization.
5. Redox flow batteries offer an economical, low vulnerability means to store electrical energy at grid scale. Redox flow batteries also offer greater flexibility to independently tailor power rating and energy rating for a given application than other electrochemical means for storing electrical energy. Redox flow batteries are suitable for energy storage applications with power ratings from 10’s of kW to 10’s of MW and storage durations of 2 to 10 hours.
6. Different classes of flow cells (batteries) have been developed, including redox, hybrid and membraneless. The fundamental difference between conventional batteries and flow cells is that energy is stored as the electrode material in conventional batteries but as the electrolyte in flow cells.
7. Li+ rechargeable batteries have a self-discharge rate typically stated by manufacturers to be 1.5-2% per month while Flow batteries can release energy continuously at a high rate of discharge for up to 10 h. They also have no self-discharge as there is no reaction outside of the reaction chamber while Flow batteries differ in both form and function to the more common lithium-ion batteries. They store their active chemicals – liquid electrolytes – in two external tanks. To generate power, these liquids are pumped into a central stack with two electrodes that are separated by a membrane. They exchange ions across this membrane, and this generates electricity. To store electricity, the process is reversed.

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1. Flow batteries are safer and more scalable than lithium-ion batteries, and they can withstand greater temperatures or periods of idleness, which makes them well suited to storing and releasing the energy produced by renewable energy such as solar panels and wind turbines – particularly in the home.
2. The caveat is that the standard electrolyte materials are vanadium and bromide, which are expensive, dangerous, and toxic commodity metals. Nearly 79 percent of existing flow batteries adhere to this standard.
3. Since Li-ion batteries contain less toxic metals than other types of batteries which may contain lead or cadmium. They are generally categorized as non-hazardous waste. Li-ion battery elements including iron, copper, nickel and cobalt are considered safe for incinerators and landfills. These metals can be recycled, but mining generally remains cheaper than recycling. At present, not much is invested into recycling Li-ion batteries due to costs, complexities and low yield. The most expensive metal involved in the construction of the cell is cobalt. Lithium iron phosphate is cheaper but has other drawbacks. Lithium is less expensive than other metals used, but recycling could prevent a future shortage. The manufacturing processes of nickel and cobalt for the positive electrode and the solvent, present potential environmental and health hazards. Manufacturing a kg of Li-ion battery takes energy equivalent to 1.6 kg of oil. While Flow batteries are environment friendly.