“Do me a solid"
There is a general consensus in the industry on the trend of developing towards solid-state batteries (SSB), in search of denser & safety batteries. SBB scale production should take place later this decade, reaching new market segments
TECHNOLOGY USUALLY ADVANCES at the rate of demand. Experts believe that we've reached the peak of what Li-ion batteries (LiB) are capable of, heating up the race to techs w/ higher energy densities [1]. As usual, manufacturers are struggling to increase energy capacity w/o increasing battery weight & cost [2].
Solid-state battery (SSB) has been described as the “next big thing” for electric vehicles (EVs) battery manufactures due to its potential to more than double (2 to 2.5x higher) the energy density of a standard LiB in a (much more) safe way, being the focus of innovation activities & patent deposits [3].
SSB tech involves replacing liquid-electrolyte w/ a solid one, where the ionic movement takes place. In fact, the complete removal of any liquid component aimed to a greatly enhanced safety of the overall device, as nothing in it can leak & ignite.
Li-ion batteries (LiB)
Currently, LiB is by far the global leader in electrochemical storage. Mainly comprised of the key components of cathode, anode, and electrolyte, LiB manufactures are actively seeking technological innovations and breakthroughs in various of these parts. Though revolutionary and ubiquitous, LiB has some drawbacks such as safe, recharge time, and materials supply chain issues, which leads to a high mfg. cost [4].
Sodium-ion batteries (SiB)
Although not yet commercial, a good option to avoid battery supply chain disruptions is Sodium-ion tech. Sodium-ion batteries (SiBs) are safer, cheaper, and cleaner than LiB, but have a lower energy density (about 2/3). Despite being similar in construction to LiB, SiB are potentially more eco-friendly as they mainly use sodium-chloride, abundant in ocean. Unlike LiB, they are not reliant on nickel, cobalt, and manganese, and instead use widely-available materials. Once in commercial production, they can complement LiB in many applications [5].
Solid-state batteries (SSB)
As time goes by, R&D could continuously reduce liquid content in battery electrolytes, but there remain critical technical challenges on the way to all-solid-state batteries (currently, industry is transiting from semi-solid - liquid: 5-10wt% - to all-solid-state). Developments in the late 20th and early 21st century have caused renewed interest in SSB tech, especially for EVs, from the 2010s onwards [6].
SSBs use solid electrodes (like LiBs) and a solid-electrolyte (SE), doing away w/ liquid or polymer gel electrolytes found in conventional Li-ion or Li-polymer batteries [7]. Commercial SSBs are already a reality, but in much smaller devices such as smartwatches, pacemakers, and RFID tags.
SSB can provide potential solutions for many problems of liquid LiBs, such as flammability, limited voltage, and poor cycling [8]. Cars equipped w/ SSB could be lighter, which increases range, and can take a third as long to recharge [9].
Materials proposed for use as SEs in SSBs include i) ceramics (e.g., oxides, sulfides, phosphates) and ii) solid polymers. Also, three major “technical routes” of SE are i) Polymer SE, ii) Oxide SE, and iii) Sulfide SE [5].
Like LiBs, SSBs typically contain nickel, manganese, and Lithium [10]. Cell chemistry of all-solid-state cells is in general the same as of liquid-electrolyte cells. Anode materials comprise carbon, Li-alloys, and metallic Lithium. Cathode materials are Li-based oxides (LCO, NCA), phosphates (LFP), and vanadium oxide [11]. The development of SSBs enriches the Lithium application scenarios in anode materials. Ideally, SSBs would use a pure lithium metal anode due to its high specific energy capacity.
SSB drawbacks
For EVs and storage applications (electrical grid, solar PV, and end use), SSBs are still in the prototype stage, mainly because they're expensive and difficult to produce in a larger size at scale. Two important obstacles remain in the development of SSB: durability & cost: SSBs might be 4+ times more expensive than a typical LiB [12].
The interfacial instability of the electrode-electrolyte has always been a problem in SSBs. After solid-state electrolyte contacts w/ electrode, chemical & electrochemical side reactions at the interface usually produce a passivated interface, which impedes the diffusion of Li+ across the electrode-solid-state-electrolyte interface.
Mechanical failure is also a critical issue in SSBs. It is caused by volume changes in anode and cathode during charge & discharge due to the addition & removal of Li-ions from host structures [13]. To end, SSBs have poor low-temperature performance and are subject to dendrite growth.
Industry perspective
After losing the race for LiB (CATL and LG have surpassed Panasonic [14]), Japan is at the forefront of SSBs and materials development.
Toyota leads the race for SSBs w/ over 1,300 patents related to SSBs. It announced the deepening of its decades-long partnership w/ Panasonic [9]. Following Toyota, Ford and BMW funded the startup Solid Power w/ USD 130 million, and as of 2022 the company has raised a total of USD 540 million. They will begin testing SSBs in late 2022 and hope to use them in EVs from 2025 [15].
Honda plans to launch an EV w/ SSB in 2028 or 2029. It has set their plan schedule to start operation of demonstration line for the production of all-solid-state batteries in Spring 2024. In Jan 2022, U.S. based company ProLogium Tech signed a technical cooperation agreement w/ Mercedes-Benz for SSB development & production arrangements [16]. Volkswagen invested USD 300 million in the U.S. startup QuantumScape and should go to market with SSBs by 2024 [17]. Nissan, Hyundai, and GM are conducting similar R&D in SSBs.
Key points
There is a general consensus in the industry on the trend of developing towards solid-state batteries [5]. In the future, trains, planes, and trucks may also use SSBs, setting the stage for much wider electrification of transportation than it can be visualized today. However, SSB are currently on a low-tech readiness level and basic research is still ongoing, w/ consequent uncertainties and concerns related to high production cost & scalability. Still, solid-liquid hybrid batteries w/ extremely low liquid-electrolyte content may be a more commercially practical solution [5].
04, January, 2023
* Professor at School of Electrical, Mechanical and Computer Engineering (EMC) of Federal University of Goiás (UFG)
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