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| Fig. 1: Approximate gravimetric versus volumetric energy density for various battery chemistries. [7] (Image source: H. Prout, after Frith et al. [7]) |
The world's increasing shift towards electrification has driven up demand for energy storage, with batteries playing a pivotal role in applications such as transportation and consumer electronics. With the rise of electric vehicles and growing electronics markets, battery demand is set to skyrocket. In 2020, battery capacity was under 0.5 TWh. [1] By 2050, this number is expected to be 6 TWh, with the possibility of up to 12 TWh of battery capacity if sustainable development goals are met. [1] To date, lithium-ion batteries (LIBs) have been the favored battery technology due to their high energy density, wide ranging utility, and relatively low costs. However, LIBs are not without challenges, including resource scarcity and soaring raw material prices. In response to these concerns associated with lithium, sodium-ion batteries (SIBs) have emerged as a promising alternative. This report explores the potential of SIBs as a replacement for LIBs, examining their advantages and addressing the issues of resource availability and cost constraints associated with lithium-ion technology.
When comparing different battery chemistries, cost is one of the most important considerations. At the level of raw materials, sodium is orders of magnitude cheaper than lithium. In 2022, the cost of one metric ton of soda ash (sodium carbonate) was $140, compared to the steep price of $37,000 per metric ton for lithium carbonate. [2] Moreover, prices for lithium have surged in recent years - with a 23% compound annual growth rate (CAGR) from 2018 to 2022. [2] Most recently, in 2021 to 2022, lithium prices increased by an astonishing 194%. [2] With these staggering gaps in cost and the rising price of lithium, it may seem straightforward to conclude that SIBs are cheaper than LIBs. However, sodium and lithium are only one of dozens of raw material inputs to a battery cell. In fact, the raw material of lithium is only 1.5% of the total cost of a LIB today, and when analyzing the total cost of the battery, Vaalma et al. found that SIBs are not significantly cheaper than LIBs. [3] Thus, its important to consider the total cost of the battery, which does not show a significant advantage for SIBs. The cost per unit of stored energy must also be considered and will be discussed in the analysis on energy density.
Resource availability is a separate but related consideration for battery technology adoption. Lithium demand is expected to significantly outpace supply by 2030. [4] Given this supply-demand mismatch, it's possible that an extreme shortage of lithium could result in a dramatic price increase that makes SIBs significantly cheaper than LIBs. Sodium, which is vastly more prevalent than lithium, does not face this challenge. In fact, sodium can be found in Earth's crust at a concentration of 2.36%, vs. 0.00002% for lithium. [5] Thus, it's no surprise that the total supply of lithium reserves is drastically less than sodium. The global supply of lithium totals 98M tons. [2] Nearly ten-fold that amount of sodium can be found in the state of California alone (which has over 810 million tons of soda ash reserves). [2] In addition, the supply of lithium is highly concentrated in a few regions, whereas sodium is distributed more evenly across the globe, eliminating geopolitical concerns. [2] Thus, sodium presents a promising alternative to lithium with respect to resource availability and distribution.
However, even in a scenario where lithium shortages arise and prices dramatically increase, sodium falls short of lithium in terms of energy density. Energy density is the amount of energy that can be stored in a given amount of volume or mass. Both types of energy density, volumetric and gravimetric, are important and determine the applications a battery can be used in. Lithium's seat at the top left corner of the periodic table enables it to yield batteries with the highest possible energy density. Lithium is the lightest metal (6.94 amu) and has a small ionic radii (0.76 angstroms). [6] For the same valence (-1), sodium is heavier (23.00 amu) and larger (1.02 angstroms). [6] Thus, lithium-based batteries will always have an advantage in terms of energy density, due to the small, light nature of lithium.
Even with the inherent, advantageous properties of lithium, one might question if these advantages at the atomic level hold true at the macro level, given that lithium only makes up a small percentage of the battery. So, test data at the level of the cell can also be used to evaluate energy density. Even for one specific battery chemistry, the exact value of energy density is dependent on a multitude of factors including the test conditions, such as temperature, pressure, charge/discharge rates, and the form factor of the battery. For this reason, energy densities are typically presented as ranges. [7] Fig. 1 shows a map of multiple battery chemistries and the range of reported values of energy density from various publications. As expected, SIBs demonstrate lower energy density than LIBs both by volume and weight. [7] An analysis of theoretical energy density supports this, demonstrating that SIBs have lower theoretical energy densities than LIBs for all variations of component. [8] When analyzing energy density, it's important to note that simply adding more SIBs to compensate for the lower energy density is not usually feasible, as many applications have limits on the additional weight they can carry. Thus, sodium's lower energy density remains a significant obstacle to its adoption in high- energy-demand scenarios such as electric vehicles and aircraft.
Finally, it's important to combine both energy density and cost to consider the total cost per unit of stored energy to assess the scalability and market potential of different battery technologies. Multiple analyses have shown that SIBs are more expensive than LIBs when it comes to cost per capacity. One European study found SIBs cost per capacity to be 223.4 euros per kWh, versus 168.5 euros per kWh for the NMC-type LIB. [9] Another Canadian study found SIBs to be 125 CAD/kWh versus 110 CAD/kWh for NMC-type LIBs. [10] Its important to note that both studies found one variation of LIB (LFP-type) to be more expensive than SIB, so SIBs may be cost competitive against certain types of lower-energy density LIBs. However, writ large, LIBs outperform SIBs with respect to the amount of energy they can store for a given cost.
In summary, sodium-ion batteries cannot directly replace LIBs. However, in a world where lithium is in short supply, SIBs could provide an alternative in low-energy density applications such as grid storage. They offer potentially cost-effective options that can play a role in the energy storage landscape, though they will not suffice for high-energy-demand applications.
© Haley Prout. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] C. Xu, et al., "Future Material Demand For Automotive Lithium-Based Batteries." Commun. Mater. 1, 99 (2020).
[2] "Mineral Commodity Summaries 2023. U.S. Geological Survey, January 2023.
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