Salgenx, an American clean tech startup founded in 2022, develops a high-energy and low-cost salt water flow battery. The battery stores electrical energy by electrolyzing sodium chloride aqueous electrolyte (NaCl/H₂O) and storing the sodium ions in the counter electrode and as-produced chlorine (Cl₂) in water-immiscible carbon tetrachloride (CCl₄) organic solvent. The fact that water and CCl₄ don’t mix and that Cl₂ dissolves easily in CCl₄ make it possible to make a high-energy flow battery without a membrane. This cuts the cost of materials and operation by a lot. This new salt water battery can be used to store electrical and thermal energy storage, desalinate seawater, and decarbonize other industrial processes.
Challenges: flow battery still costs too much
More and more solar cells and wind turbines are being used to generate clean electricity. The ability to store their electrical energy would significantly increase the efficiency and reliability of these intermittent renewable energy.
Flow batteries store and release electrical energy by using the movement of electrolytes. The electrolytes are stored outside the battery, and when the battery is charged or discharged, they are pumped through the battery. This is very different from lithium-ion batteries. The flow batteries are easy to scale up and can have a long lifespan of over 20 years. This makes them good candidates for energy storage applications.
However, the market adoption of flow batteries has been hampered by their high-cost materials and low energy density. Most flow battery systems use ion-permeable membranes, which are expensive and further increase capital and maintenance costs. Therefore, it is necessary to develop high-energy and low-cost flow batteries.
Salgenx has developed a low-cost, membrane-free salt water flow battery. It has a high energy density of 125.7 Wh/L and a round-trip energy efficiency of 91% at 10 mA/cm². The new flow battery charges through electrolyzing sodium chloride aqueous electrolyte (NaCl/H₂O) and storing the as-produced chlorine (Cl₂) in water-immiscible organic solvent such as carbon tetrachloride (CCl₄). The battery has a unique design of rotor discs inside the reactor chamber. These rotor discs create a vortex flow of both electrolytes for electrode cell dynamics. This further enhances battery efficiency while providing a more robust and simple reaction with less parts. Salgenx’s low-cost salt water battery is scalable and can last for more than 25 years.
Salgenx slat water battery
The diagram below depicts Salgenx salt water flow battery.
The salt water battery has a modular block electrode stack. NaCl aqueous electrolyte and water-immiscible organic solvent from their respective tanks enter the battery. They form a single vortex flow by the rotor discs in the reaction zone of the battery. After passing through and over respective electrodes, the single vortex flow is separated into organic and water phases, which then return to their respective tanks. Other necessary components of the battery include pumps, sensors, and a control system (not shown).
- Working electrode
The working electrode is loaded with catalysts, such as RuO₂-TiO₂ coated porous carbon (RuO₂-TiO₂@C), that accelerate the kinetics of chloride (Cl⁻) oxidation.
- Counter electrode
The counter electrode is loaded with NaTi₂(PO₄)₃, allowing for the rapid and reversible insertion and extraction of sodium ion (Na⁺) in NaCl/H₂O. NaTi₂(PO₄)₃ has a low sodium ion insertion and extraction potential and a long cycle life of 1,000 cycles.
- Flow liquids
The electrolyte of salt water is placed in a tank containing 6M NaCl.
In another tank, organic solvent, such as CCl₄, is stored. CCl₄ solvent provides a high Cl₂ solubility and is immiscible with salt water electrolyte.
How Salgenx salt water battery works
Salt water electrolyte and organic liquid enter the battery’s reaction zone. They form a single vortex flow by rotor discs in the battery. The vortex flow passes through and over their respective electrodes, then separates into aqueous and organic solvent phases. A device separates and returns the two flows to their respective tanks.
After a steady state operation is achieved, the power source applies a voltage to charge the battery.
On the working electrode, catalyst particles accelerate the chloride oxidation. The chloride in the NaCl aqueous solution is converted to chlorine gas (Cl₂):
2Cl⁻ → Cl₂ + 2e⁻
Because the solubility of Cl₂ in CCl₄ is three orders of magnitude higher than that in salt water solution of NaCl/H₂O, CCl₄ solvent strips chlorine ga from the aqueous solution. Therefore, Cl₂ generated during the charging process is stored in CCl₄. This significantly increases the coulombic efficiency (CE) to more than 90%.
On the counter electrode, sodium ions are inserted into NaTi₂(PO₄)₃ from the salt water solution:
NaTi₂(PO₄)₃ + 2e⁻ + 2Na⁺ → Na₃Ti₂(PO₄)₃
State of charge (SOC) is monitored by a chlorine concentration sensor in the organic phase. Once it reaches between 90-95% of its chlorine gas solubility limit, the battery is considered charged. The pumping operation could cease.
The energy storage comes from a large amount of trapped chlorine gas in the CCl₄ solvent and sodium ions in the water phase. Due to the separation of the tanks, discharge over time is incredibly limited.
The system is in a closed loop, so there is no chlorine gas leakage. There is a chlorine sensor that communicates instantly with the command and control processor. In the event of a power failure, NaCl is injected into the system to neutralize any chlorine.
During discharge, pumps are turned on. A steady state operation is achieved. A reverse voltage is applied to the battery. The dissolved chlorine gas returns to chloride ions and the discharge is started.
On the working electrode, dissolved chlorine gas reacts on the catalyst particles back into chloride:
Cl₂ + 2e⁻ → 2Cl⁻
Due to the low solubility of the chloride in the organic phase, it readily returns to the salt aqueous phase.
On the counter electrode, sodium ions are repelled by Na₃Ti₂(PO₄)₃ and return to the salt aqueous phase:
Na₃Ti₂(PO₄)₃ → NaTi₂(PO₄)₃ + 2e⁻ + 2Na⁺
State of Charge (SOC) is determined by the chlorine concentration in the organic phase. The battery is considered discharged once it reaches 0-5% of its charged value. The pumping operation ceases.
Cost of Salgenx salt water battery
The total material cost for this membrane-free salt water flow battery is estimated to be ~$5/kWh, making it the cheapest flow battery system currently available. Infrastructure costs are estimated to be $257kWh. The 3,000 kWh battery has a total cost of$500,000, or $166/kW.
- US7726331B1 Modular fluid handling device II
Salgenx Salt Water Battery Applications
Renewable energy storage
Salgenx salt water battery is cheap, has a high energy density, and lasts a long time. They are the best possible ways to store energy from renewable sources like wind and sun. The batteries can be used to power microgrids in remote and rural areas.
About 2% of the world’s carbon emissions come from data centers, which is about the same as what the global airline industry puts out. Data centers can reduce their carbon footprint by using renewable energy sources and more energy-efficient ways to cool. Salgenx salt water batteries can be used to store clean energy in data centers. Its flow of salt water can be used to cool things down and store heat.
Salgenx salt water batteries can be used to power telecommunications systems like base stations and cell towers in remote areas. They are reliable and last a long time.
In case the power goes out, a Salgenx salt water battery can be used to power critical infrastructure like hospitals and emergency services.
Charge Stations for EVs
Electric vehicle charging stations can use the Salgenx salt-water battery (EVs).
Desalination of brine and seawater
In a desalination system, the salt water battery can be used to take the salt out of brine or seawater. At the same time that the battery is being charged, the salt is removed from seawater. The system can use a renewable energy source, like solar power or wind turbine, to charge the battery and desalinate brine or seawater. This is good for the environment and saves money.
Marine Vessel Applications
Cruise ships and cargo ships can use the salt water flow battery to store energy and make seawater drinkable. Wind turbine generators on boats provide the power to charge the salt water battery and make desalinated water at the same time. When needed, the stored power can be sent back into the power grid.
Oil and Gas Industry
With the technology of the salt water flow battery, oil and gas wells will be able to use their well as a battery and also clean the water at the same time.
Flow batter market
The global flow battery market size is expected to grow from USD 289 million in 2023 to USD 805 million by 2028, at a CAGR of 22.8%.
Salgenx salt water battery products
Salgenx offers several battery systems:
- Salgenx SAMx 250 kWh Salt Water Array Battery System (Price: $99,000 or $378.00 per kW)
- Salgenx S3000 3 MWhr Completed Battery Pack System 48V (Price: $500,000 or $167.00 per kW)
- Salgenx S6000 6 MWhr Completed Battery Pack System 48V (Price: $900,000 or $150.00 per kW)
- Salgenx S12MW 12 MWhr Completed Battery Pack System 48V (Price: $1,600,000 or $133.00 per kW)
- Salgenx S18MW 18 MWhr Completed Battery Pack System 48V (Price: $2,250,000 or $125.00 per kW)
Gregory Giese is Founder.
Gregory Giese is CEO.