Solid-state batteries, which are used in smartphones, power tools, and EVs, differ from Li-ion batteries in their use of electrolytes. While a Li-ion battery uses a liquid electrolyte, a solid-state battery uses a solid electrolyte.
In the case of Li-ion batteries, a separator is present to keep the cathode and anode apart. In solid-state batteries, the solid electrolyte plays the role of the separator as well.
While these are mere distinguishing features, the scientific and technological community developed solid-state batteries because they have improved stability with a solid structure and increased safety. They continue to work on them since these batteries maintain their form even if the electrolyte is damaged.
A solid-state battery comes with a higher energy density and hardly runs a risk of explosion or fire. Since it does not require the support of safety components, more space is available to insert active materials, increasing battery capacity. The improved energy density also ensures that the need for batteries remains low, resulting in an optimum EV battery system for the module and pack.
For these benefits, primarily, the market experts believe that solid-state batteries will emerge as a game changer in making EVs compete with ICEVs and, eventually, move ahead in the race. But that does not stop researchers from exploring how solid-state batteries could be made more useful. In one such research, scientists have posited the case of a high energy density ultra-thin Li metal solid-state battery enabled by a Li2CO3-proof garnet-type solid electrolyte.
While all these might sound too technical, in the coming segment, we delve deeper into understanding what the research intends to achieve!
Enabling An Ultra-Thin Lithium Metal Solid-State Battery Platform With High Stability And Energy Density
Professor Byoungwoo Kang and Dr Abin Kim from the Department of Materials Science and Engineering at POSTECH developed a solid electrolyte that enables an ultra-thin lithium metal solid-state battery platform with high stability and energy density.
The breakthrough achieved results by solving one of the most common causes of concern faced by solid-state batteries. What was that problem, and how could it be solved? Let”s have an in-depth look at it below!
The LLZO Concern
The gamet-type solid electrolyte used in solid-state batteries, which is also known as Li7La3Zr2O12 or LLZO, has high ionic conductivity. Simultaneously, it is also highly reactive and forms a contamination layer (Li2CO3) on its surface when exposed to air. This layer comes with several drawbacks or roadblocks, including the formation of a resistive barrier in cell construction, reduction in the contact and interfacial properties of the electrolytes and reactants, etc.
The innovation took up this roadblock and turned it around by focusing on the inherent essentials rather than working out an external remedy. The researchers developed an air-handleable LLZO (AH-LLZO) technology that could simultaneously enhance the surface and internal properties of LLZO and prevent the formation of contaminant layers.
They achieved their goal by developing a new hydrophobic compound (Li-Al-O) on both the surface and inside the material. This compound prevented the contamination from spreading internally by making the layer react only with air moisture.
The layer as a solution with improved contact and wettability properties also transpired into the development of ultra-thin lithium solid-state batteries, approximately one-tenth the thickness of a human hair.
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Why is the Research Considered a Breakthrough?
The results have led to a scenario where it is possible to prepare ultra-thin lithium metal layers, resulting in a meager capacity ratio of the anode to cathode, around 0.176 in solid-state batteries.
The experiment also allows for a significant reduction in the amount of lithium metal used, reducing the overall battery weight and volume and significantly improving energy density.
If implemented, the research and its findings would enable storage in the air without the need for special handling or facilities. Other than simplifying the entire process, the innovation leads to the production of garnet-type solid electrolytes packed with more practical usability.
While speaking about the future, Professor Byoungwoo Kang remarked:
“We will continue to work on ultra-thin lithium metal solid-state batteries that can achieve high safety and high energy density.”
The research shows that focusing on essentials can help us convert a product’s drawbacks into its strengths. Businesses and commercial entities are investing in research and resources to make solid-state batteries more conducive and beneficial for future automobiles. In the following segments, we look into such companies and their innovations.
#1. Solid Power
One company doing exceptional work in this field is Solid Power. Its all-solid-state batteries offer high energy, enhanced safety, longer life, and significant cost benefits.
It allows the use of higher-capacity electrodes like high-content silicon and lithium metal while enhancing safety standards by removing the reactive and volatile liquid and gel components.
The result is evident in batteries that can withstand and perform efficiently in extremely hot temperatures. The company claims that its products hold a 15-35% cost advantage over Li-ion packs.
Solid Power’s all-solid-state battery portfolio includes three major products: silicon EV Cells, Lithium Metal cells, and Conversion Reaction Cells.
Silicon EV Cell
It has a high-content silicon anode, which results in high charge rates and lower temperature capabilities. Solid Power’s proprietary sulfide-based solid electrolytes power the solution. It uses industry-standard, commercially mature NMC Cathodes.
Lithium Metal
The product derives its name from its high-energy Lithium metal anodes. It has incrementally better capacity than the Silicon EV cell, which has a specification of 390 Wh/kg, while the Lithium metal cell has 440 Wh/kg.
Conversion Reaction Cell
Among all the products in Solid Power’s portfolio, it has the maximum performance capacity of 560 wh/kg. Its uniqueness is in the ultra-low-cost and high-specific energy conversion-type cathode.
Based in Colorado, United States, Solid Power strongly believes in its batteries’ transformative capacity. It believes its all-solid-state battery cells would meet OEMs’ volume and cost requirements.
In its latest available investment deck, the company (Nasdaq: SLDP) claims to be the only publicly traded pure-play true solid-state battery developer to have raised US$700 million to date. The company thrives on its more-than-decade-long R&D investment history, which has resulted in nearly 50 global patent families and three industry-leading development partners (BMW, Ford, SK On).
#2. QuantumScape
QuantumScape, another major player in the field, declares to be on a mission to ‘transform energy storage with solid-state lithium-metal battery technology.’ It also claims to be enabling ‘greater energy density, faster charging, and enhanced safety’ – the three essential basic qualities the POSTECH research also focuses on.
One of QuantumScape’s most notable stand-out features is that it has developed the industry’s first anode-less cell design, resulting in high energy density with lowered material costs and simplified manufacturing.
The Quantumscape technology platform uses a variety of cathode chemistries to significantly improve the energy densities of today’s Nickel Manganese Cobalt (NMC) and Lithium Iron Phosphate (LFP)- based battery cells. Their efforts ensure optimization for diverse energy storage applications and keep the field ready to leverage future cathode chemistry advancements.
Another USP of the company is its separator material, which is made of ceramics that offer high conductivity, stability to lithium metal, resistance to dendrite formation, and low interfacial impedance. Another advantage of using ceramic is that it comes with enhanced safety as it is non-combustible and – therefore – safer than conventional polymer separators that comprise hydrocarbons and are more prone to burning.
QuantumScape works with a target of 800–1,000 Wh/L with its solid-state lithium-metal cells.
Financially, QuantumScape (NYSE: QS) is backed by more than US$2 billion worth of capital investments. It has more than 300 patents and patent applications in its kitty.
The Future of Solid-State Batteries
Solid-state batteries are no longer a technology of the future as the future has already arrived. Many cutting-edge research from best-in-class institutes are advancing its cause every day.
In January 2024, for instance, researchers from the Harvard School of Engineering and Applied Sciences (SEAS) presented a solid-state battery with a lithium metal capable of delivering 6,000 charge/discharge cycles—significantly more than any other pouch battery cell on the market.
The research is similar to the one we cited at the beginning of our article, as Harvard researchers also dealt with the familiar problem of dendrites forming on the anode’s surface.
Apart from the specialized businesses we’ve discussed, including Solid Power and QuantumScape, there are big guns involved in this field, too. For instance, in October 2023, Toyota and Idemitsu Kosan announced a partnership to develop solid-state batteries for EVs.
The vision that drove this collaboration was ambitious, to say the least. It said the following in the press release:
“Through this collaboration, the two companies, which lead the world in the fields including material development relating to all-solid-state batteries, seek to ensure the successful commercialization of all-solid-state batteries in 2027-28―as announced at the Toyota Technical Workshop in June 2023―followed by full-scale mass production.”
Another company that decided to take a big leap in this area was Honda. The company has been active in this space for quite some time now. In January 2024, the Honda authorities said that it was targeting a 50% reduction in weight—or, to put it another way, a 50% boost in energy density by weight.
The Honda CEO Toshihiro Mibe explained that if Honda wanted to create a car that costs $30,000, it could consider solid-state batteries because the battery costs would go down, the range would increase, and the cooling system could be simplified.
However, global efforts to make solid-state batteries more robust and safe are still facing some challenges. The objective is to optimize its basic properties, including safety, stability, energy performance, and electrochemical storage efficiency. The roadblocks, on the other hand, include long-term performance viability, economic viability, and the accurate delivery of specific power standards.
If we delve deeper, we will see that the challenges also include inadequate cycling performance in current solid-state batteries (SSBs) due to material degradation in anodes, cathodes, and electrolytes. The United States Council for Automotive Research has set a battery life target of a 10-year lifetime with 1000 cycles at 80% depth of discharge.
What stops solid-state batteries from often achieving this target is the formation of space-charge layers, which leads to slow interfacial kinetics and high impedance, and the growth of dendrites, which causes short circuits and safety hazards.
However, there are solutions to these challenges. Manufacturers would have to focus on producing high-energy-density SSBs and enhancements. After all, these products have high thermal stability, eliminating safety concerns even at temperatures exceeding 200 °C, whereas liquid electrolytes may pose threats at just above 70 °C. Solid-state electrolytes can offer leak-free operation and impart greater electrochemical stability than their liquid counterparts.
Solid-state electrolytes are also more desirable as they can reduce capacity fading and internal short circuits. Their high ionic conductivity and low electronic conductivity also ensure that vehicles are charged faster.
According to QuantumScape’s estimates, a vehicle that gets around 350 miles of range on a single charge using one of today’s premier traditional lithium-ion cells with an energy density of ~700 Wh/L could get between 400 and 500 miles of range using QuantumScape’s solid-state cells.
Overall, solid-state batteries are imperative for future mobility. They should be efficient, safe, cost-effective, and long-lasting.
Click here to learn why is it worth buying an EV now despite solid-state batteries on the horizon.
