Sepion Technologies ($16M to develop lithium metal battery using innovative membrane)

Sepion Technologies, an American battery company founded in 2015, develops lithium metal batteries using its innovative separator of a hybrid polymer-ceramic composite membrane. The separator prevents the growth of lithium dendrites on the lithium metal anode of batteries and is only permeable to lithium ions and impermeable to electrolyte solvents.

Challenges: lithium battery

The majority of today’s Li-ion batteries use graphite anodes to store charge. Unfortunately, graphite anodes fundamentally limit the energy density of the battery, as six space-Wasting carbon atoms are required for each electron and lithium ion stored in graphite after a battery charge. Without more energy-dense electrodes, the amount of energy that can be stored in each Li-ion battery will plateau below the level required to electrify transportation in a sustainable manner.

Using pure lithium metal as the anode can increase abode capacity by a factor of ten. However, the risk of catastrophic battery failure resulting from the growth of lithium dendrites at the lithium anode has proven to be an insurmountable obstacle. At the anode, Li metal electroplates during charging as undesirable needle-like dendrites rather than desirable smooth sheets. These dendrites propagate until the anode and cathode are connected by conductive lithium, causing short circuit and fires.

Sepion Technologies Technology

Sepion Technologies developed a separator with a hybrid polymer-ceramic composite membrane coating layer that prevents the growth of lithium dendrites on the lithium metal anode. This is made possible by the membrane’s permeability to lithium ions and impermeability to electrolyte solvents. The lithium metal batteries based on the membranes have twice the the gravimetric energy density of today’s Li-ion batteries and can be produced by leveraging the current Li-ion manufacturing infrastructure.

Sepion Technologies battery

As depicted in the figure below, Sepion technologies’s lithium metal battery consists of a lithium metal anode, a NMC based cathode, a membrane coated separator, and a liquid electrolyte.

The structure of a lithium metal battery of Sepion Technologies
The structure of a lithium metal battery of Sepion Technologies (ref. US11394082).

The liquid electrolyte contains lithium ions and electrolyte solvent. The separator isolates the anode and cathode, allowing only lithium ions to pass between them. The separator consists of at least a membrane layer which faces to the lithium metal anode. The membrane layer is typically laminated on a membrane support.

The membrane support is an electrolyte permeable porous polymer (polypropylene and polyethylene). It has pore diameters between 10 and 500 nm, a porosity between 30% and 60%, and thickness between 15 and 30 um, which is 5 to 25 times thicker than the membrane layer. The membrane layer facing the lithium metal anode is a hybrid polymer-ceramic composite membrane that is only permeable to lithium ions in the liquid electrolyte.

How Sepion Technologies battery works

When charging, as depicted in the figure below, lithium ions transport through the separator and are reduced to lithium metal at the anode. Because the membrane layer facing the lithium metal anode is only permeable to lithium ions and substantially impermeable to electrolyte solvents, the lithium metal grows in a direction where the lithium ions in the membrane reach the lithium metal, which is very different from the lithium metal growth in a solvent electrolyte. Thus, the growth of lithium dendrites is suppressed.

The charging of the lithium metal battery of Sepion Technologies
The charging of the lithium metal battery of Sepion Technologies.

When discharging, as shown 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 of the Li metal battery.

Sepion Technologies innovations

Sepion Technologies’s key innovation is a separator with at least one membrane layer that faces to the lithium metal anode and is only permeable to lithium ions but substantially impermeable to electrolyte solvent. This separator prevents the growth of lithium dendrites in lithium metal batteries and enables the use of liquid electrolytes. Therefore, lithium metal batteries production can leverage the existing Li-ion manufacturing infrastructure.

As depicted in the figure below, the membrane is a hybrid polymer-ceramic composite. The polymer is porous (10-40% porosity, 0.5-2 nm pores) and functions as a framework that hosts easily-processed precursors of Li-ion conducting ceramic materials within the nanopores. After standard polymer processing of the membrane at near ambient temperature, ceramic precursors are trapped in the nanopores of the polymer matrix and transform into a robust, percolating Li-conducting phase.

The membrane structure of the lithium metal battery of Sepion Technologies
The membrane structure of the lithium metal battery of Sepion Technologies

Traditional inorganic Li-ion conductors must be processed at high temperature (>300 ºC) and pressure, resulting in membranes that are brittle, expensive, small area, and unsuitable for mass production or deployment in electric vehicles (EVs). In contrast, the Sepion Technologies’s invention is amenable to large-scale polymer processing, such as roll-to-roll coating, while retaining the dendrite-blocking rigidity of ceramic Li-ion conductors, which is essential for the commercialization of Li-metal batteries.

As shown in the figure below, the membrane’s porous polymer is a ladder polymer with angular spiro centers (red color) and absence of rotatable bonds in the polymer backbone or bonds with restricted bond rotation in the backbone. These characteristics provide inefficient solid-state packing with porosity of between about 10% and 40%. The polymers can also be cross linked polymers with good solubility in solvents, as shown in the figure below.

A porous polymer of the membrane developed by Sepion Technologies
A porous polymer of the membrane developed by Sepion Technologies (ref. US11394082).
A cross linked porous polymer of the membrane developed by Sepion Technologies
A cross linked porous polymer of the membrane developed by Sepion Technologies.

The pores of the polymer are filled with an inorganic component, leaving a non-porous or partially porous membrane layer. The inorganic phase is microstructured, having domains between 0.5 and 2 nm. The inorganic component may include lithium halides, lithium oxy-nitride, Li7P3S11, Li10GeP2S12, Li10SiP2S12, etc. The inorganic component is introduced into the nanopores of the porous polymer via solution casting with the polymer, in-polymer-pore transformation of inorganic precursors, vapor deposition, or chemical transformation with the polymer.

Sepion Technologies Patent

  • US11394082 Electrochemical cells with ionic sequestration provided by porous separators
  • US20190326578A1 Microstructured ion-conducting composites and uses thereof
  • WO2020264386A1 Membranes for aqueous redox flow batteries

Sepion Technologies Battery Applications

Sepion Technologies is focused on advancing lithium-metal batteries (LMBs) for electric vehicles (EVs) and e-mobility applications. The company’s technology aims to enable safe, energy-dense, and cost-effective lithium-metal batteries, with a focus on long-range and low-cost electric transportation.

Sepion Technologies Products

Sepion is testing its technology with customers, including battery manufacturers and automotive manufacturers. The company is also constructing a pilot manufacturing line that will help deliver more samples to customers and refine their materials to meet customer needs.

Sepion Technologies Funding

Sepion Technologies has raised a total of $16M in funding over 2 rounds:

Their latest funding was raised on Nov 18, 2021 from a Series A round.

The funding types of Sepion Technologies.
The funding types of Sepion Technologies.

Sepion Technologies Investors

Sepion Technologies is funded by 6 investors:

Alumni Ventures and Fine Structure Venture are the most recent investors.

The funding rounds by investors of Sepion Technologies.
The funding rounds by investors of Sepion Technologies.

Sepion Technologies Founder

Brett Helms and Peter Frischmann are Co-Founders.

Sepion Technologies CEO

Peter Frischmann is CEO.

Sepion Technologies Board Member and Advisor

Alex Luce is a board observer.

Brett Helms, Peter Frischmann, and Randolph Chan are board members.

Randolph Chan is an advisor.

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