According to Tina Casey in her July 29, 2015 article on cleantechnica.com, “lithium-ion (Li-Ion) is the gold standard for chemical energy storage.” However, Casey points out that there are a number of emerging technologies on the horizon, like those being developed by UK-based companies Oxis Energy and Faradion: both are working on alternatives that could test Li-ion’s leadership position and reduce the cost of electric vehicles. The American Chemical Society recently profiled the two companies and their technologies in its Chemical & Engineering News publication.
What I found most interesting is the significant range and differences in battery material chemistries (e.g. lead acid, Nickel Metal Hydride, LiFePO4 , NaNiVPO4 and NaNi0.33Fe0.33Mn0.33O2… to list only a few… whew!) as we seek to optimize energy storage potential, recharge-ability, safety and cost. The two charts shown here illustrate some of the chemical compositions against just two dimensions.
Sourced from AccessibleCleanEnergy.com
Sourced from Faradion.co.uk
Earlier this summer, Oxis announced that it will be ready to bring its lithium-sulphur (Li-S) battery to market next year. According to Chemical & Engineering News, Oxis plans to “double what any Li-Ion battery can deliver” within about four years, bringing the energy density of its battery cells to 500 Wh per kilogram. The near-term goal, according to the company’s website, is 400 Wh per kilogram. If Oxis can succeed in using half the material to provide the same performance as Li-ion, that would bring down the cost of an electric vehicle significantly. The company is aiming for a cost of $125 per kWh in the near term. Tesla’s recent announcements anticipate that the cost of Li-ion batteries would drop to around $200 per kWh “in the near future,” while estimates have it at around $250–300 per kWh today.
Oxis’s Li-S cells also claim high lifecycle performance, seeing cycles of more than 1,000 before capacity reduces to 80%. The most recent information on the company’s website describes the expectation of approximately 2,000 cycles to 80%.
According to Oxis, its cells have a 100% available depth-of-discharge, compared to 80% for Li-Ion. Unlike Li-Ion, the Oxis cell can’t be damaged by over-discharging and have an indefinite shelf life. Oxis also points out the Li-S cell has a smaller environmental footprint than Li-ion energy storage chemistry. The company also gets Brownie points for sourcing its sulfur by reclaiming oil refinery waste.
[Note: Per Casey, “sulfur represents a natural cathode partner for metallic Li and, in contrast with conventional Li-Ion cells, the chemicals processes include dissolution from the anode surface during discharge and reverse lithium plating to the anode while charging. As a consequence, Li-S allows for a theoretical specific energy in excess of 2700Wh/kg, which is nearly 5 times higher than that of Li-Ion”.]
Faradion
Faradion also sailed across CleanTechnica’s radar this year, when it demonstrated a sodium-ion battery on an electric bicycle. That’s a big deal because, while sodium-ion energy storage is proven technology, until now it has been considered too bulky for use in electric vehicles.
Faradion has made a sodium-ion battery with an energy density (a measure of how much power can be packed into a battery cell) of 140 to 150 Wh per kg. This compares with about 170 Wh per kg for lithium-ion cells based on cathodes made of lithium cobalt oxide. Faradion claims to be on track to hike the density to more than 200 Wh per kg by 2017. At that level of energy density, sodium-ion would compare very favourably to Li-ion, providing the same performance at a cost of about 30% less.
Faradion notes that in sodium-ion technology, the base material is abundant compared to lithium, and that the battery can be drained completely for safe storage and shipping.
Faradion has a ways to go before it can scale up, but there may be advantages in supporting further R&D:
- Na-ion materials have lower material costs than Li-Ion materials (e.g. sodium carbonate is apparently < 10 % of the cost of the equivalent lithium salt). Furthermore, cathode and electrolyte costs can be ~ 50 % of cell costs.
- Current collectors in sodium-ion cells can be fabricated from aluminum rather than the more expensive copper necessary in lithium cells
- Na-ion materials can be processed in the same way as Li-Ion materials at every step, from the synthesis of the active materials to the electrode processing…Existing Li-Ion manufacturing lines can be used to make Na-ion batteries
All in all… chemistry, materials (and rare metals) matter.
Until soon… Ian
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