Sion Power ($70M for Licerion lithium metal battery for EVs)

Sion Power, an American battery company founded in 1994, develops high-energy lithium-metal rechargeable battery technology. The company recently announced plans to expand its battery manufacturing operations in Tucson by 2026.

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.

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.

Sion Power 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 structure of the lithium metal battery of Sion Power
The structure of the lithium metal battery of Sion Power.

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.

How Sion Power battery works

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.

The charging process of the lithium metal battery of Sion Power
The charging process of the lithium metal battery of Sion Power.

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.

The discharging process of the lithium metal battery of Sion Power
The discharging process of the lithium metal battery of Sion Power.

Sion Power innovations

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 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.

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.

The protective layer of lithium metal anode of Sion Power's battery
The protective layer of lithium metal anode of Sion Power’s battery.

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 crucial additives of the electrolyte in the lithium metal battery of Sion Power
The crucial additives of the electrolyte in the lithium metal battery of Sion Power.

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). 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. 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 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 Patent

  • US20210057753A1 Electrochemical cells and components comprising thiol group-containing species
  • US20220115704A1 Electrolytes for lithium batteries
  • US20220115705A1 Electrochemical cells comprising nitrogen-containing species, and methods of forming them
  • US20220115715A1 Electrolytes for reduced gassing
  • US20210135192A1 Protected electrode structures
  • US20210151841A1 Systems and methods for applying and maintaining compression pressure on electrochemical cells
  • US20220029191A1 Application of force in electrochemical cells
  • WO2021183858A1 Application of pressure to electrochemical devices including deformable solids, and related systems

Sion Power Battery Applications

Sion Power’s battery, particularly its Licerion® technology, have a wide range of applications, including aerospace and electric mobility, such as electric vehicles (EVs) and energy storage systems.

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 is funded by 2 investors. Cummins and BASF are the most recent investors.

Sion Power CEO

Tracy Kelley is CEO.

Sion Power Board Member and Advisor

Mark Heising is a Board member.

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