Ion Storage Systems is a company that creates solid-state lithium-ion batteries that are safer, lighter, and enable form factors with tighter packing density that enhance system performance. The company’s battery technology is based on its versatile core structure and is cobalt-free, non-swelling, durable, and has a wide temperature range. Ion Storage Systems has raised $52 million in total funding to continue developing its battery technology and is productizing its Gen1 EXTREME All-Purpose Hybrid battery platform technology.
Challenges: lithium battery
Lithium (Li) metal batteries are widely regarded as promising candidates for next-generation energy storage due to their significantly higher theoretical energy densities and capacities than lithium ion battery technology. However, the utilization of Li metal anodes has been hindered for a long time by the safety hazard posed by the risk of Li dendrite growth and the resulting potential for short circuits.
Diverse strategies for enhancing Li metal anodes include confining Li metal in porous host materials, developing protective layers for the Li-electrolyte interface, and modifying the organic electrolytes. Due to the inherent high reactivity of Li metal and the potential for dendrite formation by Li in liquid electrolytes, as well as the flammability and leakage potential of the vast majority of organic electrolytes, it is desirable to further enhance the performance and safety of Li metal anodes.
It is anticipated that solid-state batteries will significantly enhance the safety profile of Li metal anodes. Solid-state electrolytes, particularly ceramic Li-ion conductors, have an exceptional ability to prevent the formation of Li dendrites, eliminate the risk of short circuits, and are non-flammable and non-leaching. However, the lithiophobicity of ceramic Li-ion conductors has led to a poor interface contact between the solid electrolyte and the Li metal, as well as a substantial interface resistance.
Adding polymeric interlayers, coating lithiophilic layers, and controlling the surface chemistry at the interface are methods for enhancing the Li-solid electrolyte interface. Due to the presence of grain boundaries in the solid-state electrolyte, Li may form dendrites and penetrate the electrolyte, causing a short circuit. In addition, during Li plating and stripping, a significant volume change can occur, which can degrade the interface contact between the solid electrolyte and Li anode, thereby increasing the impedance of the solid anode during cycling. The poor solid interface contact and volume change of Li anodes during cycling can limit the battery’s useful capacity.
Ion Storage Systems Technology
Ion Storage Systems develops porous-dense bilayer structured garnet solid-state electrolytes for Li metal batteries with a high energy density, a simple fabrication process, and stable cycling performance. As depicted in the figure below, the li-ion conducting garnet framework consists of a porous layer that hosts Li metal and a dense layer that acts as a separator to prevent Li metal dendrite penetration and potential short-circuits.
Based on the bilayer garnet framework and high mass-loading Li(Ni0.5Mn0.3Co0.2)O2 (NMC) cathodes, the Li metal battery has a energy density of 330 Wh/kg (972 Wh/L), significantly higher than all current garnet-based Li metal batteries.
The structure of the lithium metal battery
The figure below depicts the structure of the solid-state Li metal battery based on the 3D Li-ion conducting bilayer garnet framework.
The anode consists of lithium metal hosted in a 3D Li-ion conducting porous-dense bilayer garnet framework. Dense layer and porous layer thicknesses are approximately 20 and 50 μm, respectively. Li metal resides within the porous layer. On top of the porous layer, a copper layer is deposited to serve as a negative current collector.
The cathode consists of active materials of NMC particles loaded within a conductive matrix (carbon and PVDF), as well as an aluminum foil that acts as a positive current collector. To ensure ionic conductivity, the cathode film is filled with liquid electrolyte (1 M LiPF6 in ethylene carbonate: diethyl carbonate, 1:1 volume ratio).
To enhance the ionic conductivity between the dense layer of the garnet framework and the cathode, a PVDF-HFP-based gel electrolyte (10 μm thickness) serves as an interlayer.
The working mechanism of the lithium metal battery
Before cycling, the porous garnet is fully coated with Li metal by infiltrating the melted lithium metal foil, as shown in the figure below. Void space within the framework can host additional Li from the cathode side.
When the battery is charged, as depicted in the figure below, Li metal is plated into the framework and fills the void space in the framework. After a full cycle, the deposited Li is striped away, returns to the cathode, and generates void space again in the porous layer. The framework is still coated with Li metal after discharging, resulting in a constant garnet/Li interface with stable resistance.
As depicted in the figure below, this porous-dense bilayer garnet framework only permits Li deposition from the current collector where Li-ions from the garnet skeleton have access to electrons from the Cu or Li deposited on Cu. Li metal nucleates on the garnet skeleton and can grow smoothly without forming Li dendrites in the pores of the garnet host. The Li metal rises and remains separated from the separator layer during deposition. The subsequent Li stripping causes the Li metal to fall from the dense garnet layer separator to the current collector.
As the plating/stripping of Li results in the rise/fall of the anode in the host structure and away from the separator layer, internal short-circuits caused by Li penetration are further prevented, indicating promising cycling stability and enhanced protection against thermal runaway.
Key innovations
Ion Storage Systems’s key innovation is the porous-dense bilayer structured garnet solid-state electrolyte, which enables solid-state Li metal batteries with a high energy density, a simple fabrication process, stable cycling performance, and a high level of safety.
The chemical composition of the garnet solid-state electrolyte is Li6.75La2.75Zr1.75Ca0.25Nb0.25O12, which was synthesized by mixing and calcining powders of LiOH, La2O3, CaCO3, ZrO2, and Nb2O5 at 900 ºC. By using garnet powders, the dense and porous garnet tapes were first fabricated separately. Then, both tapes were laminated, followed by sintering at a high temperature to produce porous-dense bilayer structured garnet solid-state electrolyte with good ionic conductivity.
The dense tape was fabricated by mixing Li6.75La2.75Zr1.75Ca0.25Nb0.25O12 powders with fish oil, polyvinyl butyral (PVB) and butyl benzyl phthalate (BBP) in toluene and isopropanol (IPA) to prepare the slurry, which was then cast using doctor blade onto a Mylar sheet. To make the porous tape, poly(methyl methacrylate) (PMMA) spheres were added to the slurry. The pore size of the porous layer can be controlled by the size and the content of polymer based pore formers. Both dense and porous tapes were laminated and hot-pressed to form a bilayer structure, which was sintered for 6 h at 1100 ºC to ensure good ionic conductivity.
To conduct electrons, a thin layer of Cu (about 200 nm) was deposited on the top of the porous layer of the 3D garnet by e-beam evaporation. Due to the directional deposition by e-beam evaporation technique, Cu was not found inside the porous layer; it serves only as a current collector. The Cu current collector deposited on the garnet framework significantly reduces the interfacial resistance.
The porous garnet layer was filled with Li metal by a melt-infiltration method. The garnet host was first coated with ZnO (20 nm thickness) by atomic layer deposition (ALD) to improve the wetting property of the garnet with molten Li foil. A thin Li foil (30 μm) was melted on top of the garnet pellet and infused into the pores of the upper layer by capillarity.
Cathodes with high-loading NMC particles were fabricated by casting cathode slurry on aluminum foil. There is an interlayer between cathode and garnet. The interlayer is a PVDF-HFP based gel electrolyte with 10 μm thickness, which was soaked in electrolyte (1M LiPF6 in ethylene carbonate: diethyl carbonate, 1:1 volume ratio) before assembly. To make a battery, the gel electrolyte interlayer and NMC cathode were laminated on the dense side of the bilayer garnet with Li metal inside. After assembly, liquid electrolyte (1 M LiPF6 in ethylene carbonate: diethyl carbonate, 1:1 volume ratio) was injected inside the cathode to ensure ionic conductivity.
Besides, the bilayer garnet framework can be used in other types of solid-state lithium batteries, such as solid-state lithium sulfur batteries with sulfur cathodes (e.g. S, LixS) and Li metal/Li compound anodes, as well as solid-state lithium air batteries with Li-Air cathodes and Li metal/Li compound anodes.
Ion Storage Systems Patent
- WO2018183771A1 Solid-state hybrid electrolytes, methods of making same, and uses thereof
Ion Storage Systems Products
Ion Storage Systems aims to scale up the solid-state Li metal batteries based on the porous-dense bilayer structure garnet electrolyte and produce 10 MWh annually by the end of 2023.
Ion Storage Systems Funding
Ion Storage Systems has raised a total of $52.5M in funding over 5 rounds, including three Grant rounds, a Seed round, and a Series A round. Their latest funding was raised on Jan 9, 2022 from a Series A round.
Ion Storage Systems Investors
Ion Storage Systems is funded by 8 investors, including VoLo Earth Ventures, Alsop Louie Partners, C3, Tenaska, Toyota Ventures, Bangchak, Alumni Ventures, and Clear Creek Investments. Tenaska and Toyota Ventures are the most recent investors.
Ion Storage Systems Founder
Eric Wachsman and Greg Hitz are Founders.
Ion Storage Systems CEO
Ricky Hanna is CEO.
Ion Storage Systems Board Member and Advisor
Joseph Goodman and Todd Crescenzo are board members.
