Sion Power is a company that develops high-energy lithium-metal rechargeable battery technology. The company recently announced plans to expand its battery manufacturing operations in Tucson by 2026. Sion Power’s mission is to produce the highest energy batteries for travel below and above the clouds with total peace of mind. The company is developing advanced batteries for various applications, including electric vehicles and aerospace.
Challenges: high capacity lithium battery
It is desirable to use lithium metal electrodes in lithium batteries due to their high energy density. However, lithium metal electrodes are prone to undesirable reactions during the fabrication and cycling of the electrochemical cells. Using innovative techniques, several companies have developed stable lithium metal batteries to overcome this obstacle.
Adden Energy developed battery-level mechanical constriction and multilayer electrolytes. Cuberg developed a lithium metal alloy anode and compatible ionic liquid electrolytes. SES developed a functional coating for lithium metal anode and high-salt-concentration electrolyte. Ion Storage Systems developed porous-dense bilayer Li-ion conducting garnet framework to host lithium metal anode. Sepion Technologies developed a separator with a hybrid polymer-ceramic composite membrane coating layer that is only permeable to lithium ions but substantially impermeable to electrolyte solvents.
Sion Power Technology
Sion Power developed high energy lithium metal batteries based on utilizing stable lithium metal anode fabricated with its own innovative vacuum deposition systems, coating lithium metal anode with polymer/ceramic hybrid layer, optimizing electrolyte additives, and applying mechanical force to the batteries.
The structure of the battery
The figure below depicts the structure of Sion Power’s lithium metal battery, which consists of a lithium metal anode protected by a polymer/ceramic hybrid layer, a separator, a high energy density LiNixMnyCozO2 (NMC) based cathode, and a liquid electrolyte. The batteries are subject to an anisotropic force.
The lithium metal layer is typically 15 microns thick. It has a passivation layer formed upon exposure to a gas (such as CO₂) that can react with lithium in the system. The passivated lithium metal anode has a protection layer made of polymer surfactants and lithium-ion conducting ceramic particles. The majority of ceramic particles are fused together to facilitate good ionic conductivity.
The separator and cathode are available commercially. Since the lithium metal anode has a protective layer to prevent the formation of lithium dendrites during the cycling processes, the battery can use a thin porous separator (such as 9 microns-thick polyolefin, Tonen) that separates both electrodes and permits ionic communication between them over a short distance. The high energy battery uses NMC active material (such as BASF NCM622) based cathode, which typically consists of NMC particles mixed with carbon and polymer binder.
The electrolyte contains lithium salt, a mixture of solvents, and critical additives that allow the battery to operate more stably and at a lower temperature.
There is an anisotropic force applied normally to the battery that can improve performance during charging and/or discharging by reducing problems such as dendrite formation and surface roughening of the electrode while improving current density.
The working mechanism of the battery
The figure below depicts the charging process of the battery. Lithium ions transport through the separator and are reduced to lithium metal at the anode. The lithium metal protective layer conducts lithium ions and reduces the exposure of lithium metal to electrolyte solvents significantly, thereby preventing the growth of lithium dendrites. Also thanks to the anisotropic force applied to the battery, a smooth lithium metal film grows at the interface of lithium metal anode and ceramic particles.
When discharging, as depicted in the figure below, the lithium metal is oxidized to lithium ions which diffuse through the separator towards the cathode, as depicted in the figure below.
Sion Power has developed the key technology for fabricating lithium metal anode using a roll-to-roll vacuum deposition system that is capable of mass-producing anodes. The battery uses liquid electrolyte and commercially available separators and high energy density anode materials. Therefore, the scale production of the batteries can use the existing lithium-ion battery production lines without the need to develop new production lines.
1. The fabrication of Li metal anode
The Sion Power’s roll-to-roll vacuum deposition system can deposit a thin layer of lithium metal (thickness between 1 and 50 microns) on a flexible substrate. The deposited lithium metal has a passivation layer (thickness between 10 nm and 5 microns) formed by exposing the lithium metal to a gas that is reactive to lithium metal, such as CO₂. The passivated lithium metal anode can be handled in a typical dry room instead of a glove box filled with inert gas.
The system uses a polymer web to deposit an ultrathin layer of copper (between 100 and 500 nm) that serves as the current collector via thermal evaporation or sputtering. Between the polymer substrate and copper layer, it is advantageous to have a release layer to facilitate the packing and assembly of the lithium metal anode. The system then deposits a suitable thickness of lithium metal on the copper substrate. The lithium metal film deposited has a plurality of columnar structures. A passivation layer is formed by exposing the lithium metal layer to a gas that is reactive with lithium metal, such as a mixture of carbon dioxide and nitrogen. The images below show scanning electron micrographs of the layer comprising lithium metal before (left) and after (right) the formation of a passivating layer disposed thereon.
The roll-to-roll vacuum deposition system consists of the main components of drums, sources of lithium metal (referred to as “deposition sources” and “lithium ‘trim’ sources”), sources of gas (referred to as “gas manifolds”), and thickness sensors. The figure below shows an example of an arrangement of the main components of the system.
Sensors monitor the thickness of deposited layers. Other sensors may be included to monitor deposition rates and the morphology of the deposited films.
Each drum in a modular lithium deposition system translates the substrate through the plurality of modules. Each drum also communicates with a cooling/heating system in order to independently maintain the desired temperature of the substrate between −35 and 60 ºC. This is advantageous, as the deposition process may heat the vacuum chamber to a high temperature, causing the polymer substrate to melt and degrade. The drums can reduce and maintain the substrate’s temperature at the desired level. The lower substrate temperature than the deposition environment facilitates the condensation of the lithium metal gas to form a layer with a desired morphology onto the cooled substrate.
The shield is close to the substrate. It is positioned between the substrate and a container that contains a source of lithium metal. The shield restricts the mobility of gas positioned between the shield and the substrate and tends to maintain a relatively constant atmosphere in this region to facilitate uniform film deposition. Accordingly, the introduction of a cooled inert gas into the space between the shield and the substrate serves to cool the substrate for an appreciable period of time and prevent the introduction of warmer species therein.
- Deposition sources
Two sources configured to each drum can improve the uniformity of the film (e.g., reduces variations in thickness, chemical composition, and/or porosity along the cross-web direction).
- Gas source
Gas manifolds introduce cooled gas into the space between the shield and the substrate in order to cool the substrate.
The figure below depicts a cross-section of an example of a modular lithium deposition system comprising three modules, from left to right: a chamber in which a substrate can be unwound from a roll, two vacuum chambers in which one or more layers may be deposited, and a chamber in which the substrate can be wound around a roll.
2. Approaches to enable stable Li metal battery
(1) Protection layer of Li metal anode
The figure below shows the images of a hybrid protective layer deposited on the lithium metal to prevent the formation of lithium dendrites. The protection layer consists of lithium ion conducting ceramic particles and polymer surfactants. The protection layer is deposited via aerosol deposition method and has a thickness between 2 and 15 microns. Most ceramic particles in the protection layer are fused together during the deposition process to facilitate ionic conductivity. The protection layer is chemically stable in the electrolyte, thereby acting as a protective layer to reduce the lithium metal’s exposure to the electrolyte solvents and improves the battery cycle life.
To make the protection layer, a mixture of ceramic particles, polymer surfactant, and hard beads that favors size formation is milled. The mixture is then dried, and the beads are separated through sieving. The mixture of milled ceramic particles and polymeric surfactants is then combined with suitable solvents to form slurry for aerosol deposition on the lithium metal anode. During aerosol deposition, the pressure and temperature of the carrier gas are adjusted so that the majority of ceramic particles have sufficient energy to fuse together.
The milled ceramic particles preferably have a narrow size distribution with a median diameter between 600 nm and 6 microns, as ceramic particles that are either too large or too small or have too wide size distribution are unsuitable for forming the ceramic layer via aerosol deposition method. The ceramic particle materials can be selected from Li22SiP2S18, Li24MP2S19, LiMP2S12 (M=Sn, Ge, Si), etc.
Polymeric surfactants can reduce the surface energy of ceramic particles and cause steric stabilization during milling, allowing ceramic particles to be closer to one another. This may result in smaller sized particles after milling, a narrower distribution in particle sizes after milling, and improved fusion of ceramic particles in the ceramic layer. However, polymeric surfactant may result in an undesirable decrease in lithium ion conductivity of the ceramic film. Therefore, the optimal content of polymeric surfactant is beneficial to minimize the drop in ionic conductivity of the ceramic layer when the polymeric surfactant is added.
The polymer surfactants can be selected from polyacrylic acid, polyethylene glycol (e.g., PEG400, polyethylene glycol tert-octylphenyl ether – Triton X-100), polyvinylpyrrolidone (e.g., PVP40, PVP8), CMC, silicon polymeric surfactant, polysaccharide, polysulfonate, sulfonated styrene/maleic anhydride copolymer, polyacrylamide, polyvinylidene fluoride, and/or polyvinylidene chloride.
(2) Additives of electrolytes
The liquid electrolyte contains lithium salts, such as lithium bis(fluorosulfonyl)imide (LiFSI), LiPF6, and lithium bis(oxalato)borate (LiBOB), as well as an organic solvent mixture of fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC) and additives. The additives, as shown in the figure below, are crucial because they may improve the battery’s performance.
The addition of conjugated, negatively-charged nitrogen-containing ring species to the electrolyte, such as lithium 1H-1,2,4-triazolate (US20220115705A1), forms a protective solid electrolyte layer (SEI) on the surface of electrodes. The conjugated, negatively-charged nitrogen-containing ring species react with a lithium metal or transition metal to produce a protective SEI capable of reducing the area of the electrode exposed directly to the electrolyte and protecting electrodes from deleterious reactions with certain species present in the electrolyte. The SEI formed in this manner is particularly stable and has a relatively low resistance, which is advantageous in comparison to SEI formed in other ways.
The addition of silylated sulfonic acid esters to the electrolyte, such as bis-trimethylsilylsulfate, methylenedisulfonic acid bis(Trimethylsilyl) ester, and p-toluenesulfonic acid trimethylsilyl ester (US20220115715A1), may reduce the formation of gaseous by-products in the battery by forming a coating on the surface of the electrode. The coating forms as a result of silylated sulfonic acid esters reacting with transition metal at the surface of the electrode. The coating can prevent an electrode from reacting with the electrolyte solvents, thereby minimizing the formation of gaseous decomposition products (e.g., decomposed solvent).
The addition of a critical amount of aromatic hydrocarbon solvent to the electrolyte, such as α, α, α-trifluorotoluene (TFT), is capable of separating electrolyte phase from a single liquid phase into at least two or more liquid phases, due to the limited solubility of aromatic hydrocarbon solvent in the organic solvent and its limited solubility for lithium salt. The electrolyte system with immiscibility decreases the rate of solvent decomposition during cell cycling and enhances the cycle life.
Additionally, the battery with α, α, α-trifluorotoluene based electrolyte shows outstanding performance at low temperatures (−25 ºC), as shown in the figure below. The battery also shows rapid charge conditions. For example, a battery with such electrolyte was charged at 4C rate charge from zero state of charge (SOC) to 100% SOC (15 min charge duration, 480 mA) and discharged at 300 mA. The battery achieved a charge efficiency of 99.7% at fast charge and retained this efficiency for over 80 cycles.
(3) Application of pressure
The application of an anisotropic force to the battery can reduce the problems of dendrite formation and surface roughening of the electrode, thereby improving performance during charging and/or discharging and increasing current density. Important is the application of a relatively uniform force so that each cell experiences a relatively similar pressure distribution, and pressure on multiple cells must be managed simultaneously.
Sion Power’s battery stack contains components arranged in an advantageous manner. As depicted in the figures below, the battery consists of multiple cells arranged in stacks, carbon fiber endplates connected by compression rods, and a power bus and battery management system on the top of the battery. The stack is subjected to an anisotropic force of at least 10 kgf/cm2 through fastening the compression rods that are coupled to the carbon fiber endplates.
The multicomponent stack, as shown in the figure below, comprises electrochemical cells, thermally conductive solid article portions (illustrated as aluminum cooling fins with locating holes and locating slots for alignment), and thermally insulating solid article portions that are compressible. The arrangement promotes unexpectedly efficient heat transfer away from the electrochemical cells, while also facilitating compensation for applied forces and cell breathing and facilitating relatively uniform pressure distributions.
Sion Power Products
Sion Power is developing products of Licerion Electric Vehicle (Licerion-EV) and Licerion High Energy (Licerion-HE) rechargeable lithium metal batteries for the applications in electric mobility, aerospace, and uncrewed aerial vehicles.
Verified through third-party testing, Licerion-EV batteries meet or exceed automotive requirements. Key attributes are fast charge capability, long cycle life, and broad temperature range capability in a 400 Wh/kg and 780 Wh/L, 17.4 Ah pouch cell.
Licerion-HE batteries are designed to meet the requirements of multiple aerospace applications and uncrewed aerial vehicles. This high energy, lightweight pouch cell boasts 490 Wh/kg and 900 Wh/L with an impressive 5C pulse discharge rate capability.
Sion Power Funding
Sion Power has raised a total of $70M in funding over 2 Corporate rounds. Their latest funding was raised on Nov 30, 2021.
Sion Power Investors
Sion Power CEO
Tracy Kelley is CEO.
Sion Power Board Member and Advisor
Mark Heising is a Board member.