Tech Dive: Current Collectors
A dive into current collector innovators
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What are current collectors?
Current collectors aren’t the most attention-seeking component of a battery. 2D metal foils have been used for decades, with the main innovations being driving the thickness lower to increase energy density via deadweight reduction.
Over the last 5 years, it appears that lithium-ion batteries will reach a plateau in terms of performance, and will have various flaws as well as safety defects. Research has been focused on alternative materials, structures, pre-treatment methods, coatings, etc. When it comes to translating these to industry, we need an alternative as low-cost as current baseline current collectors to be considered.
In this technology dive issue, we explore 3 companies that are working on current collector innovations: Prieto Battery, Addionics, and Soteria Battery Innovation Group.
Review papers
The questions we’re looking at
Summary: What benefits will this novel current collector have?
Technology: How does this technology work?
Milestone: How much funding have they raised, and what kind of partnerships do they have?
Employees: How many people are on their team?
Prieto Battery
Prieto is designing and manufacturing a porous 3D current collector with an integrated anode and cathode for enhanced contact area and energy density. The company was founded by Prof Amy Prieto from Colorado State University and currently has 9 employees (LinkedIn).
Technology
The Prieto battery architecture is designed around a porous copper structure (copper foam), conformally coated by an ultra-thin polymer electrolyte and then surrounded by a cathode matrix. The result is a three-dimensionally structured lithium-ion battery composed of interpenetrating electrodes with extremely short Li+ diffusion distances and a power density that is orders of magnitude greater than comparable two-dimensional architectures in use today. The use of copper antimonide (Cu2Sb) electrodeposited onto copper foam adds a degree of stability to the anode and has already demonstrated excellent capacity over extensive cycling.
Using an electrodeposition method, Cu2Sb is directly deposited without the costly requirement of further annealing or other post-treatments. This technique ensures continuous electrical contact throughout the 3D anode. The fabrication of the electrolyte layer is accomplished through an electrochemical polymerization method specifically designed to uniformly encapsulate the entire conductive surface of the anode. The electrolyte is conformal and very thin to allow for the subsequent interpenetration into the structure by the cathode material. This layer is pin-hole free, which is critical for the overall performance of the battery (Source).
Antimony anode: Antimony is known for its theoretical specific capacity: it can deliver a high theoretical capacity of 660 mAh/g by forming Li3Sb compared to graphite (372 mAh/g) but lower than silicon (4200 mAh/g) (Source). Antimony has smaller volumetric expansion than silicon, limiting the 'pulverization' due to mechanical strain fracturing.
3D copper current collector: Prieto will use a copper foam substrate, approximately 98% air (or void space), increasing contact/surface area by 60x (Source). This improves contact between anode and current collector material, improving electron conductivity.
Solid-state electrolyte: Vinylic solid polymer electrolyte deposited onto surface of electrode material, allowing for multi-directional Li+ ion exchange with lower ionic resistance compared to traditional 'sandwich' structured batteries.
Relevant Patents
3-D interpenetrating electrodes: porous foam structure separated from interpenetrating cathode material (13) that fills the void space of the porous foam structure by a thin solid-state electrolyte (12) which has been reductively polymerized onto the anode material (14) in a uniform and pinhole-free manner, which will significantly reduce the distance which the Li-ions are required to traverse upon the charge/discharge of the battery cell over other types of Li-ion cell designs, and a procedure for fabricating the battery are described.
Method to electrodeposit solid-state coatings onto electrically conducting materials. Describes a method for electrochemically depositing an ionically conducting, electrically insulating coating onto the surface of electrode material.
Milestones
2021: $5.7m Series C
2018: Series B
2015: Undisclosed investment
2010: Company founded, undisclosed investment
Addionics
Addionics is working on 3D porous current collectors. The company was founded by Moshiel Biton, Vladimir Yufit, and Farid Tariq, and currently has 34 employees split between Israel and London (LinkedIn).
Technology
Addionics claims to have a low-cost manufacturing approach for porous 3D metal current collectors, and a model to optimize the porosity structure based on end applications. The 3D porous structures enable higher contact area with electrode active materials for improved energy density, less internal resistance, and better heat dissipation.
Relevant Patents
Electrochemically produced three-dimensional structures for battery electrodes. A continuous process for manufacturing by electrochemical deposition. Involves:
providing a first roller and a second roller for winding a continuous conductive substrate foil having two parallel sides, a first side bearing a substrate and acting like a working electrode where deposition and partial dissolution occur, and a second side acting as a counter electrode to close the circuit;
feeding said substrate to a space between an anode and a cathode;
depositing or dissolving said metal atoms on said first side in accordance with electrical signals sent to anode and cathode by a central managing unit, thereby creating a continuous 3D electrode structure comprising said metal atoms on said substrate
winding said 3D said second roll obtaining 3D current collectors wound on a roller and ready for use by unrolling and cutting to desired collector sizes.
Method and apparatus for continuous electrochemical production of three-dimensional structures. Involving electroplating steps, each step adding a cross-sectional layer of the 3D structure via an anode selected from a flat 2D anode grid array and forming a patterned template, thereby creating a deposition image on a cathode plate.
Liquid cold welding methods and apparatus. Involving multiple porous conductive substrate layers, immersing the substrate layers in an electrolyte solution; and applying electric current to the electrolyte solution to weld 2D porous layers together to form a 3D structure. (Disclaimer: Nicholas is a former employee at Addionics and inventor on this patent).
Milestones
2022: $27m Series A round
2021: Innovate UK grant funding
2020: $6m Seed round
2018: Company founded + Pre-Seed round
Soteria
Soteria is working on safer batteries to prevent thermal runway using (1) thermally stable separators made from advanced fibres and (2) metallized film current collectors that are engineered to stop the flow of current at hotspots. The company was founded in 2017 and employs 14 people (LinkedIn).
Shoutout to The Limiting Factor for doing an interview with Brian Morin (Soteria CEO) in 2020:
Technology
Soteria non-woven membranes are reinforced with aramid fibres (aromatic polyamide, used in things like ballistic body armour, aka Kevlar), resulting in a separator that won’t melt or shrink.
In addition, in a thermal event, the metallized-film current collectors burn out like a fuse by having the plastic membrane shrink at the localized hotspot, isolating the short circuit, while the rest of the cell continues to function. Plastic substrate of current collector thermally breaks down and isolates the electrochemically active materials from the defect within milliseconds
Patents
Method of manufacture of an energy storage device having an internal fuse. One metallized substrate is a current collector comprising a film with at least one metal coating, said current collector exhibiting a total thickness less than 20 microns, for Al and Cu films.
Current collector is unable to support a current through a point contact on the surface of the current collector, wherein said polymeric material substrate of said current collector exhibits heat shrinkage at 200° C.
Milestones
2021: Series A + Angel round
2020: Seed round
2017: Company founded
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