The market for rechargeable batteries which is fundamentally driven by electric vehicles (EVs) and energy storage systems, has flourished. In India, electric two-wheelers are outrunning four-wheelers, with sales numbers surpassing 0.94 million vehicles in FY 2024.
World over, electric car sales rose to 18% in 2023, totalling 13.8 million vehicles, requiring over 600 GWh of lithium-ion batteries.
According to Benchmark Minerals Intelligence, at present, the capacity of lithium-ion batteries (LIBs) has surpassed 1 terawatt-hour (TWh), with production capacity projected to reach 6 TWh by the end of this decade. Advancements in Lithium-ion chemistries like LFP and NMC are still in progress to meet the demand for longer range and safety. While Western countries focus more on enhancing NMC’s energy density to over 350 – 400 Wh/kg to achieve a range of 1,000 km, China and India prioritize upgrading LFP to LMFP to achieve energy density over 220 Wh/Kg. These developments ensure the continued importance of lithium-ion technology.
Despite these developments, factors like fluctuating lithium prices and supply chain issues are prompting the need to search for alternatives. Sodium-ion batteries are emerging as a promising and favourable option, boasting a technology readiness level of 10, cost-effectiveness, fast-charging capability, good low temperature performance and transportable at 0V, making them a viable choice for future energy solutions.
Cathodes
The energy density of a cell depends on its capacity and voltage, both of which are influenced by the cathode active materials. Following lithium, sodium-based cathode materials present a commendable capacity, as sodium is both smaller and lighter than alternatives such as potassium and magnesium. Similar to lithium-ion battery (LIB) cathode materials, the cathode materials for sodium-ion batteries are categorized into three types: Transition Metal Oxides (NaxMO2), Polyanion Compounds (NaxMy[(XOm)n-]z), and Prussian Blue Analogues (NaxM[Fe(CN)6]·nH2O).
Among these, transition metal oxide-based SIBs offer the highest energy density but typically have a shorter cycle life compared to their counterparts. BYD claims that its transition metal oxide-based SIBs achieve an energy density of 140 Wh/kg with a cycle life of 3,600 cycles at 80% capacity retention and the HiNa Energy reports an energy density of 145 Wh/kg with over 4,500 cycles, while BYD’s polyanion system reaches 110 Wh/kg with a cycle life of 6,000 cycles.
On the Prussian blue front, CATL claims that it achieved an energy density of 160 Wh/kg, but it is little sceptical since it doesn’t disclose the cycle life. All sodium-ion cell manufacturers indicate that these performance results reflect their first-generation products.
Each company is developing second-generation cells targeting energy densities of 200 Wh/kg and cycle life of 6,000 to 10,000 cycles. If successful, this could capture a significant share of the market currently held by LFP lithium-ion cells.
Electrolytes
Generally, the electrolyte consists of three key components: salts, solvents, and additives. In lithium-ion batteries (LIBs), commonly used salts are lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI). In sodium-ion batteries (SIBs), these are replaced by sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imiden (NaFSI).
Despite sodium’s cost advantage, the price of NaPF6 is anticipated to decrease below LiPF6 once production hurdles are surmounted and economies of scale are achieved. The evolution towards sodium-based additives salts like NaFSI indicates a potential shift in battery technology.
As the demand for electric vehicles and energy storage is increasing, search for alternative battery materials is gaining momentum. While lithium-ion cells currently appear cost-effective due to a significant drop in lithium carbonate prices, the limited availability of lithium tends to have long term sustainability challenges. As a result, there is a significant shift towards sodium as a more abundant alternative, with sodium-ion battery (SIB) gigafactories planning over 100 GWh of capacity worldwide.
The launch of the world’s first electric vehicles equipped with SIBs by JAC in February 2023 is a significant milestone, showcasing a 25-kWh battery with a 250 km range. However, SIBs still have a long way to go to catch up with lithium-ion batteries (LIBs). Other alternative technologies, such as potassium-ion and magnesium-ion batteries, currently fall within Technology Readiness Levels (TRL) 4 and 5.
It may take another five years for these technologies to reach TRL 10 and achieve mass-scale production. In the meantime, aside from material scarcity, significant advancements in lithium-ion batteries (LIBs), particularly in NMC and LFP cells, raise an important question i.e. the next-generation non lithium batteries be able to match the performance of lithium-ion batteries despite their inherent material limitations.
Robin George is Vice President of Cell Technology Development at Log9 Materials. Views expressed are his own.