
A sodium–sulfur (NaS) battery is a type of that uses liquid and liquid . This type of battery has a similar to , and is fabricated from inexpensive and low-toxicity materials. Due to the high operating temperature required (usually between 300 and 350 °C), as well as the highly reactive nature of sodium and The Na-S battery offers high theoretical capacity and energy density of ~ 1672 mAh g −1 and 1230 Wh kg −1 respectively based on the final discharge product Na 2 S. [pdf]
The solid-state Na-S batteries demonstrate a remarkable performance with high capacity and good stability. Room-temperature (RT) solid-state sodium-sulfur batteries (SSNSBs) are one of the most promising next-generation energy storage systems because of their high energy density, enhanced safety, cost-efficiency, and non-toxicity.
A sodium–sulfur (NaS) battery is a type of molten-salt battery that uses liquid sodium and liquid sulfur electrodes. This type of battery has a similar energy density to lithium-ion batteries, and is fabricated from inexpensive and low-toxicity materials.
It is clearly observed that our results demonstrate the highest rate performances (0.5 C and 1.0 C) with the highest capacities (over 750 mAh g −1 and 550 mAh g −1) for solid-state sodium-sulfur batteries at room temperature. The current density in our study is almost ten times higher than the regular conditions in the previous studies.
High-temperature sodium–sulfur (HT Na–S) batteries were first developed for electric vehicle (EV) applications due to their high theoretical volumetric energy density. In 1968, Kummer et al. from Ford Motor Company first released the details of the HT Na–S battery system using a β″-alumina solid electrolyte .
Sodium-sulfur batteries are practically used in stationary energy storage systems , , . However, they must operate at a high temperature of at least 300 °C to maintain the molten state of the Na and S electrodes , , .
However, state-of-the-art prototype Na-ion batteries can only deliver a specific energy density of approximately 150 Wh kg –1, which is a small fraction of their theoretical value . This made researchers shift their focus toward high-energy Na metal batteries, such as RT Na–S and Na–Se batteries.

A lithium-ion or Li-ion battery is a type of that uses the reversible of Li ions into solids to store energy. In comparison with other commercial , Li-ion batteries are characterized by higher , higher , higher , a longer , and a longer . Also note. According to the U.S. Department of Energy, lithium-ion batteries generally exhibit an energy density range of 150 to 250 Wh/kg for commercial applications. [pdf]
Energy density of batteries experienced significant boost thanks to the successful commercialization of lithium-ion batteries (LIB) in the 1990s. Energy densities of LIB increase at a rate less than 3% in the last 25 years . Practically, the energy densities of 240–250 Wh kg −1 and 550-600 Wh L −1 have been achieved for power batteries.
Strategies such as improving the active material of the cathode, improving the specific capacity of the cathode/anode material, developing lithium metal anode/anode-free lithium batteries, using solid-state electrolytes and developing new energy storage systems have been used in the research of improving the energy density of lithium batteries.
Recently, according to reports, Amprius announced that it has produced the first batch of ultra-high energy density lithium-ion batteries with silicon based negative electrode, which have achieved major breakthroughs in specific energy and energy density, and the energy density of the lithium battery reached 450 Wh kg −1 (1150 Wh L −1).
In order to achieve high energy density batteries, researchers have tried to develop electrode materials with higher energy density or modify existing electrode materials, improve the design of lithium batteries and develop new electrochemical energy systems, such as lithium air, lithium sulfur batteries, etc.
Theoretical energy density above 1000 Wh kg −1 /800 Wh L −1 and electromotive force over 1.5 V are taken as the screening criteria to reveal significant battery systems for the next-generation energy storage. Practical energy densities of the cells are estimated using a solid-state pouch cell with electrolyte of PEO/LiTFSI.
At present, the publicly reported highest energy density of lithium-ion batteries (lithium-ion batteries in the traditional sense) based on embedded reactive positive materials is the anode-free soft-pack battery developed by Professor Jeff Dahn's research team (575 Wh kg −1, 1414 Wh L −1) .

In general lithium ions move between the anode and the cathode across the electrolyte. Under discharge, electrons follow the external circuit to do electric work and the lithium ions migrate to the cathode. During charge the lithium metal plates onto the anode, freeing O 2 at the cathode. Both non-aqueous (with Li2O2 or LiO2 as the discharge products) and aqueous (LiOH as the dis. Lithium ions disperse from the anode during discharge and go to the porous cathode, where they react with ambient oxygen to generate lithium peroxide (Li2O2). [pdf]
Oxygen gas (O 2) introduced into the battery through the air cathode is essentially an unlimited cathode reactant source due to atmospheric air. Because of this the air cathode is the most important component of the system. The lithium metal reacts with oxygen gas to give electricity according to the following reactions: Discharge
The lithium–air battery (Li–air) is a metal–air electrochemical cell or battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow. [ 1 ] Pairing lithium and ambient oxygen can theoretically lead to electrochemical cells with the highest possible specific energy.
Lithium in the anode undergoes a redox reaction, and lithium ions (Li +) are constantly transported through the electrolyte to the cathode and react with oxygen molecules. Lithium oxide (Li 2 O) and lithium peroxide (Li 2 O 2) are generated in the air cathode. The general reaction are presented as:
The lithium-air battery works by combining lithium ion with oxygen from the air to form lithium oxide at the positive electrode during discharge. A recent novel flow cell concept involving lithium is proposed by Chiang et al. (2009). They proposed to use typical intercalation electrode materials as active anodes and cathode materials.
Lithium oxides form during discharging cycle as lithium ions are transferred to the cathode and react with incoming oxygen. The recharging process involves the reduction of lithium oxides (Li 2 O and Li 2 O 2). However, Li 2 O is not electrochemically active and subsequently not participating reversible reactions.
In typical Li-air batteries, oxygen gas is used as a cathode material along with a catalyst and porous carbon as a Li 2 O 2 reservoir in a cathode. Li metal is used as an anode which plays the basic role of Li source in Li-air batteries.
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