14. Techno-economics Analysis on Sodium-Ion Batteries: Overview and Prospective

The total global battery demand is expected to reach nearly 1000 GWh per year by 2025 and exceed 2600 GWh by 2030 [1]. The expandability of lithium-ion batteries (LIBs) is one of the options; however, with the increasing shortage of lithium minerals and their uneven distribution around the world [2], the long-term development of LIBs could be constrained. In fact, the raw material demand driven by battery applications is estimated to experience unprecedented growth in the coming years. In detail, four battery metals are impacted the most by this growth towards 2030: lithium by a factor of 6, cobalt by a factor of 2, class 1 nickel by a factor of 24, and manganese by 1.2 [1].

In this context, sodium-ion battery (SIB) might become an important alternative considering its abundant resources, high cost-effectiveness, and high safety.

The early SIB development took place in parallel with the LIB development in the 1970s/1980s. Subsequently, their development slowed down considerably due to the higher energy density lithium-ion chemistry in the 1990s/2000s [3].

On the other hand, due to availability and price issues of Li-ion basic raw materials, related to the fast increase of demand from mobility, mobile electronics, and stationary applications confronted with limited availability of the supply side [4, 5], recently, the studies of sodium-ion batteries have rapidly become highly topical, as evidenced by the sharp increase in the number of research papers.

SIBs have the most similarities with LIBs in terms of working principle, typical electrode materials, and electrolyte formulations. Moreover, SIBs in principle can use the same technologies of LIB manufacturing lines, reducing development costs and timescales [6]. SIBs have the same working principle as LIBs, with the difference that the charge transfer relies on sodium ions instead of lithium ions and electrode RedOx reactions involve Na instead of Li. Both electrodes are deposited on metallic current collectors, immersed in a liquid electrolyte allowing for mobility of ions between electrodes, and separated by electrically non-conductive, porous (to allow ion mobility) layer preventing internal short circuit [3].

Moreover, sodium-ion chemistry allows to use aluminium, which is inactive in terms of reacting with sodium, for both anode and cathode current collectors, substituting in this way copper otherwise used as anode current collector in LIBs [2]. Therefore, changing the current collector from copper to aluminium cannot only greatly reduce the cost of the cell but also addresses the over-discharge issue, especially in organic solutions, and decreases the battery weight. According to [7], the cost shares of the current collector foils are 11.6% for copper and 2.7% for aluminium in terms of the total cost of a lithium-ion cell. Replacing the copper foil with an aluminium foil in a SIB would result in a cell material cost reduction of about 9%, with a corresponding battery cost reduction of about 3%. The exchange would consequently result in a 55% mass reduction but also a 50% volume increase relative to the exchanged foil.

On the other hand, since commercial graphite cannot be directly used as anode for SIBs, due to intercalation problems and a lack of stable Na–C compounds [8], SIBs might show a significant increase of the anode contribution to the total price. The commonly proposed alternative anode for SIBs is hard carbon, although it re-acts less with sodium than the lithium in graphite per unit mass and volume. In fact, hard carbon shows lower specific density than graphite, and thus thicker laminates are needed, and as the irreversible capacity is also larger, more active material is required, which could increase the costs [9].

Although different works investigated the use of hard carbon as anode for SIBs, in order to make it more practical [10‐12], commercial hard carbon prices kg⁻¹ are not available. But it has been reported that higher price comes from the high-cost precursors [10, 11]. However, in order to reduce SIB cost and increase its performances, there are different studies that focus on low-cost/high-yield synthesis of hard carbon using cheaper precursors (e.g. cellulose, corn stalks, phenolic resin) [10, 12]. Vaalma et al. used $15 kg⁻¹ as a price of hard carbon; however, it can be lowered up to $8 kg⁻¹, considering the efforts are being done to enhance the properties of the hard carbon [7, 10].

For the electrolyte, the differences are comparably small: the amount of lithium in the electrolyte is very low (0.5% for a 1 M LiPF6 solution in organic solvent), and correspondingly low is the potential for cost reductions by substituting it with an electrolyte using a less expensive sodium salt [13].

However, SIBs compared with LIBs show some drawbacks, which have slowed down its widespread diffusion, including a higher redox potential (−2.71 V for sodium compared with −3.04 V for lithium, both versus the standard hydrogen electrode), a higher atomic mass (23 g mol⁻¹ and 7 g mol⁻¹ for sodium and lithium, respectively), and a larger size (the Shannon ionic radii are 1.02 Å and 0.76 Å for sodium and lithium, respectively), which lead to a decrease in the theoretical energy density [5, 7]. At the cell level, these factors contribute to a decrease in performance.

While there are several works available in the literature on the costs of lithium-ion battery materials [14], cells, and packs, there is relatively little available analysis of these for sodium ion [15]. Moreover, most of the works focus on costs of material preparation and the electrodes/electrolytes taken in isolation, without considering the costs of the whole cell or battery system [16]. However, the cost percentage for active components (cathodes, anodes, and electrolytes) in cells is generally lower than 50% [7], while the costs of the inactive components (current collectors, binders, separators, etc.) are even higher than for those electrode materials. Therefore, the lack of a cost analysis makes it hard to evaluate the long-term feasibility of this storage technology.

For realistic cost predictions, calculations must be done for a certain battery cell with defined kWh. As sodium has a higher molecular weight and a larger size than that of lithium, the theoretical energy density may decrease, and the cost at the cell level can increase [5, 10].

A detailed cost analysis using the Argonne National Lab’s BatPaC model (a commonly applied battery cost model, with specifications for many common cathode chemistries, including SIB technology) has been undertaken by Faradion and suggests that material costs at a manufacturing scale will be less than $150 kWh⁻¹ [17]. This makes sodium technology cost competitive with the most inexpensive lithium technologies. The cost breakdown for the components for a Faradion 12 Ah pouch cell is as follows: anode active material = 26%, cathode active material = 28%, electrolyte = 12%, separator = 3%, current collectors = 13%, and miscellaneous components to a fabricate pouch cell-type battery = 18%.

Hirsh et al. [18] investigated the use of Na-ion batteries for grid energy storage, included a cost analysis of Na-ion cells for various sodium cathode chemistries, and included a comparison with the cost ($ per kWh) of LiCoO₂. The calculated values compare very favourably with those calculated by Faradion showing that cobalt-free Na ion to be between 40% and 60% lower cost in $ per kWh than LiCoO₂/graphite (which they calculate to be at 99 $ per kWh). The authors attribute this significant decrease in cost to the transition metal elements, particularly Co and Ni, which in Na-ion cathodes can be absent or minimised without the detrimental effect on performance observed in equivalent Li-ion cathodes of the same B-site composition.

Schneider et al. [19] compared cost and GHG emissions of LIBs and SIB reporting that current automotive LIB cell cost based on NMC111|C (186 $ (kWh)) is significantly below the evaluated sodium-ion alternatives. According to the authors, this finding is mainly due to the lower specific charges and voltage of the active materials of sodium-ion batteries, leading to higher material requirements and longer processing times per kWh of capacity. They further show current LIB superiority regarding greenhouse gas emissions and attribute this fact to the same mechanism. Consequently, the authors state that sodium-ion batteries can only become competitive if a performance similar to LIBs is achieved.

Vaalma et al. [7] compared SIB and LIB costs, considering 11.5 kWh, 7 kW battery, with a fixed number of cells as the model system. In detail, the authors compared the cell materials and battery costs of three LIB different chemistries (LMO–sG (LiMn₂O₄ with synthetic graphite), NCM(622)–nG (Li_1.05(Ni_0.6Co_0.2Mn_0.2)_0.95O₂ with natural graphite), and NCM(622)–SiC (Li_1.05(Ni_0.6Co_0.2Mn_0.2)_0.95O₂ with silicon/carbon composite)) with three different SIB chemistries (NMO–sHC (β-NaMnO₂ with standard hard carbon), ASC–PHC (advanced sodium-ion cathode material with phosphorus-hard carbon composite), and FSC–aPHC (future sodium-ion cathode (the working potential is increased by 0.2 V compared to ASC) with advanced PHC)). The LIB chemistries have been selected to illustrate the development of LIBs with increased energy density and lower cost, while the SIB chemistries are representative examples of a present (NMO–sHC), advanced (ASC–PHC), and future (FSC–aPHC) SIB.

The results of the study are shown in the following Table 14.1. Comparing the LIBs, large cost reductions in terms of the total cost of the cell materials result from changing the cathode material from LMO to NCM (622). Considering NMO–sHC, an example of a present SIB, a substantial increase in the cost of the cell materials relative to the three investigated LIBs is reported. More specifically, the anode cost increases with the use of sHC compared with natural or synthetic graphite owing to the lower density (1.50 g cm⁻³ for sHC versus 2.24 g cm⁻³ for graphite), which leads to increased electrolyte cost. Furthermore, the anode cost also increases because of the lower energy density of sHC (300 mAh g⁻¹ and 360 mAh g⁻¹ for sHC and graphite, respectively), and thus more active material is needed to achieve the target energy of the battery. Finally, the price of the active materials is higher with sHC ($15 kg⁻¹) than with natural graphite ($10 kg⁻¹). On the other hand, considering SIBs that are more advanced, a substantial cost decrease is calculated for ASC–PHC and FSC–aPHC owing to the use of anode materials that have a higher capacity (300 mAh g⁻¹ for sHC versus 700 mAh g⁻¹ for PHC and 900 mAh g⁻¹ for aPHC) and, in particular, exhibit a higher volumetric energy density despite the average working potential increasing by about 0.2 V with respect to hard carbon22. Again, the smaller amount of required electrolyte results in a large cost decrease. Therefore, the development of anode and cathode materials with higher volumetric energy densities is important because it simultaneously leads to a notable decrease in the cost of the conductive carbon and binder and, especially, the cost of the electrolyte.

With regard to the entire battery pack, the NMO–sHC battery shows different disadvantages with respect to the LIBs such as increased volume, mass, and cost. On the other hand, the FSC–aPHC cell chemistry would be competitive with NCM(622)–SiC in terms of cost, and although it has a higher mass and volume, these parameters may be less crucial for stationary applications.

However, as stated by the authors, the lifetime, energy efficiency, and safety influence on the cost of the final batteries were not considered in the analysis. These parameters strongly influence the costs of a storage system. In fact, for example, a NCM–graphite battery with a cost of about $3,000 and a cycle life of about 5,000 cycles would have a cost per kilowatt hour ($0.060 kWh⁻¹) that is more than twice that of a LFP–LTO battery with a cost of about $5,000 and a cycle life of 20,000 cycles ($0.025 kWh⁻¹).

Another similar study was conducted by [13] modifying BatPaC from a prismatic cell model to a cylindrical 18,650 cell model. In detail, the authors compared layered oxide SIB cells with two different LIB cell chemistries: lithium–nickel–manganese–cobalt–oxide cathodes and lithium–iron–phosphate cathodes. The study results show that the lithium–iron–phosphate battery shows the highest price per kWh of storage capacity (229 €/kWh), followed by the SIB at 223.4 €/kWh. On the other hand, the lithium–nickel–manganese–cobalt–oxide battery is the cheapest (168.5 €/kWh), due to its high energy density. When looking at the contribution of the battery materials to the final cell costs (per single 18,650 cell), the benefits of the SIB on a material level become clearer. Here, the SIB shows the lowest costs per single cell (0.50 €/cell), whereas the materials for the NMC-type cells are the most expensive (0.72 €/cell). However, these are costs per single cell and do not consider the storage capacity.

Moreover, since fluctuations in raw material prices are a major factor of concern for battery manufacturers [20], the authors perform a sensitivity analysis varying raw material prices. The results show a high sensitivity to fluctuations in the graphite/hard carbon prices. This is more severe for the SIB, where the share of anode active material is higher. Regarding the cathode materials, the highest fluctuations can be observed for cobalt and nickel. Lithium and copper, despite the variations in their price, which have a stronger impact on the final cell price, are comparably stable metals that did not fluctuate heavily over the past 10 years. However, recent increases in the price of lithium have been significant and might be triggered by an increasing demand for batteries, leading to potentially stronger impacts in LIB prices than previously noted. Thus, the high dependency of the actual NMC price on current nickel market prices, and cobalt market prices to a great degree, produces significant uncertainty for future price predictions. Since this situation also affects the SIB due to the high nickel content in the cathode, alternative nickel-free, SIB cathode chemistries could be an interesting option in this regard.

At this time, a direct comparison of the cost-effectiveness of LIBs and SIBs is not possible because SIBs have not been produced on a comparable scale to LIBs. In fact, although the commercialisation and production of these systems are still at a very infant stage as compared to LIBs, presently, there are few companies worldwide developing commercial Na-ion batteries for some niche applications: