Rapidly growing demand for the development of batteries with high capacity, lower costs, and a longer cycle life has led researchers to not only improve today's Li-ion batteries but also look toward future alternatives to today's Li-ion chemistries. As the manufacturing scale of Li-ion batteries increased dramatically over the past decade, costs fell, and today, the cost of Li-ion batteries is more closely tied to the cost of the raw materials, placing increased value on finding lower-cost materials.
Furthermore, in the next decade, the supply chain of lithium and other critical materials like cobalt and nickel will be significantly stressed due to dramatic increases in battery manufacturing capacity. Alternative chemistries – including novel lithium chemistries and lithium alternatives – may be a solution for use in electric vehicles. Startups, university research teams, battery manufacturers, and automakers are rushing to develop these chemistries and are planning to reduce their reliance on expensive raw materials like lithium, cobalt, and nickel – all-important but costly ingredients. In this insight, we analyze the patent activity, discussing alternative electrode chemistries and which ones are the most promising candidates to succeed today's Li-ion batteries in electric vehicles.
Lithium chemistries play a crucial role in vehicle electrification, as their high energy density and falling costs essentially enabled the electric vehicle. While today, many chemistries use nickel and cobalt, the nonmetal cathode alternatives explored below have the potential to lower costs wither fewer, cheaper materials.
- Lithium-sulfur batteries: Lithium-sulfur (Li-S) batteries are promising because of the high theoretical specific energy the chemistry offers and potential low costs due to the availability of sulfur in nature. The battery uses sulfur as the cathode active material and metallic lithium as the anode material. Unlike conventional batteries, in which lithium-ion (Li-ion) is reversibly integrated into lattice sites of the crystal structure, Li-S is a conversion-type cathode. During discharging, Li-ions react with sulfur to form polysulfide compounds. A large amount of academic research has been done on Li-S chemistry over the past decade, and an equal number of patents have been published, thus making Li-S a major area of interest not only for academic researchers but also for industries. Though a lot of effort and investment has been put into the chemistry, it has seen limited commercial success. The chemistry suffers from poor cycle life, and the polysulfide ions cause severe redox shuttle; thus, lithium corrosion can also be observed. Although electric vehicles are the primary target for the implementation of the chemistry, they are more suited for electric aviation, as the industry values specific energy more than the automotive industry. Generally, developers of Li-S battery technology need to make a significant trade-off between achieving high specific energy and high cycle life. One good example of this is Oxis Energy, which recently entered bankruptcy after being a leader in developing this technology. In our 2018 conversation with the company, it claimed it could achieve 400 Wh/kg in cells that provided 60 cycles or 1,400 cycles in cells that provided 220 Wh/kg (the company dropped development of the longer-cycle-life chemistry in 2020). The struggles Oxis has faced will likely impact the future implementation of the technology. Li-S technology has had a tumultuous path toward commercialization, and it will be at least a decade before we see this chemistry compete with incumbent Li-ion technology in electric vehicles.
- Lithium-air batteries: Lithium-air (Li-air) batteries have the highest theoretical density among all the Li-ion chemistries. The metal-air batteries use metallic lithium as the anode and air as the cathode (oxygen is the cathode and is enclosed in a chamber to pump it into the battery). The patent activity has been consistent, and academic institutions have increasingly been working on developing lab-scale Li-air batteries over the past five years. Though efforts are underway to make the Li-air battery into reality, there are major challenges that the chemistry has to overcome. The Li-metal electrolyte interface has been a barrier, and most of the academic institutions working on this chemistry have reported decomposition reactions that occur at the interface. However, the biggest drawback is the utilization of ambient air as the cathode. The atmospheric air contains other gases, such as nitrogen and carbon dioxide, and the presence of these gases affects the performance of the battery, while the supply of pure oxygen is a major hurdle. The poor cycle life and lower power output are also among the technical limitations the technology faces. Li-air technology is still in its early stage, and fundamental research holds the key to the chemistry being commercialized for use in vehicles and other applications.
Multivalent batteries use chemistries with alternative charge carriers to lithium ions, which can shuttle multiple electrons per reaction. Unlike lithium, which produces one electron per oxidation reaction, multivalent chemistries release two or three electrons per reaction.
- Aluminum-ion batteries: Aluminum-ion batteries (Al-ion) are considered because of the high specific volumetric capacity of aluminum and its lower cost due to its availability in the Earth's crust. Aluminum is the metal anode, and aluminum batteries can be tested in an aqueous and nonaqueous condition. Aluminum has three valence electrons, which gives it the advantage of a higher energy density potential. Analyzing the patent graph, we can see that though not much investment has gone into the implementation of Al-ion batteries, the chemistry is slowly picking up pace on the road to development and ultimately commercialization. Despite their low cost and likely low environmental impact, aluminum batteries exhibit some drawbacks. More studies need to be done on the electrolyte for use in the aqueous system, as the system has a limited electrochemical stability window, and researchers have also reported quick capacity fading in the chemistry, while the presence of trivalent Al ions has been known to limit the cathode choices. Despite the drawbacks, Al-air batteries have been looked upon as a potential chemistry for use in micromobility. The nonrechargeable chemistry's most promising use case has been the joint venture between Indian Oil Corporation and Israeli company Phinergy to develop Al-air batteries for three-wheelers and scooters across India – a country that has supported Al-ion battery projects due to a lack of domestic lithium resources.
- Magnesium-ion batteries: Magnesium-ion (Mg-ion) batteries are divalent and studied as potential electric vehicle batteries due to the vast availability of magnesium in the Earth's crust and the high theoretical volumetric capacity that the chemistry exhibits. Studies have indicated that Mg has better recyclability, without any degradation of its physical properties. However, magnesium is heavy, which means that the battery is naturally heavy, and this may play a role in the deployment of this chemistry in EVs. There is extensive research underway to identify the ideal cathode, anode, and electrolytes for the chemistry. Although the work is in the preliminary stage, which is indicative of the patent filings, there are many challenges that need to be overcome. The initial research has indicated that Mg is highly sensitive to surface reactions, and this may be a barrier when choosing the electrolyte. The sluggish kinetics caused by the larger magnesium ions are also seen as a major problem resulting in low power output. Despite these issues, the chemistry may be better-suited for large-scale energy storage rather than EV applications due to the high volumetric capacity.
- Calcium-ion batteries: Calcium batteries, or Ca-ion batteries, have been researched for a long time. Calcium is abundant in the Earth's crust, and this is the reason why scientists are looking to tap Ca-ion batteries as potential EV batteries. Despite having complex electrochemistry, the calcium metal can be tested with conventional electrolytes, and the divalent nature of the Ca ions also provides an advantage in terms of high volumetric capacity. A recent research study also indicated a high specific energy of 300 Wh/kg in Ca-thionyl chloride cells. However, the chemistry faces many barriers and challenges. Researchers are reporting large volume changes due to the insertion of Ca ions, and similar to Mg-ion batteries, Ca-ion batteries have been found to have sluggish kinetics resulting from slow diffusion. Still in their infancy, Ca-ion batteries are a chemistry that will not see commercialization within the next two decades.
The multivalent battery configurations are still in early-stage research, and fundamental research is needed before these chemistries can be considered for commercial uses. Al-ion is the one exception, with pilot trials underway, but it has remained in the small pilot stage for the better part of the past decade. Though the bulk of patent activity indicates Li-S chemistry as the major research area, the failure of Oxis Energy – a leader in Li-S development – has hampered the commercialization and the future outlook of the chemistry. While sluggish kinetics affect multivalent batteries, practical implementation is a major hurdle for Li-air batteries. Though there have been efforts to dedicate investments toward the implementation of next-generation batteries, commercialization of these chemistries beyond lab-scale research and small-scale testing is nonexistent. Although some alternative chemistries sound attractive, with promises of lower materials costs and wider mineral availability, clients should realize that these technologies are trying to beat a moving target, as Li-ion batteries continue to fall in costs with significant planned manufacturing capacity expansions. Disruption in the next 15 years is highly unlikely. Clients in the automotive space are encouraged to monitor academic publications for breakthroughs in these chemistries over the next 10 years but avoid placing direct bets on internal development of these chemistries.