Manufacturing Low Cost Nano-Coatings for High Performance Battery Materials

It is now widely accepted that both high-end (Gen 3 materials) and low-end (e.g. Gen 1-2 LiCoO₂, NCA, NMC, etc.) electrode powders alike can benefit from surface coatings as a means to provide an optimized interfacial transition between the electrode and the electrolyte, independent of type of battery or system.  In spite of the significant public and private investment in new battery materials, efforts on those that are under development today still tend to focus on features and attributes of the bulk materials.  Significant cost savings can be realized without sacrificing performance by encapsulating today’s materials with coatings tailored to improve the electrode-electrolyte interface.  The two primary surface coating technologies that have been studied are Co-Precipitation (CP) and Atomic Layer Deposition (ALD), with results showing significant favor to ALD as shown in Figure 1. ALD coatings, which can be optimized for each system for composition, thickness, and uniformity, have been proven to reduce capacity fade with cycling, improve thermal stability, allow for safe charging to higher voltages, and reduce degradation under high temperature storage. These coatings can also reduce costs by eliminating the need for overbuilding, and be done without affecting capacity or internal resistivity.

ALD has found enormous application in the semiconductor industry owing to its conformal sub-nanometer thickness deposition capability, but until recently has been regarded as non-scalable technology for powder materials due to excessive capital cost of processing. Early research on ALD applications for batteries focused on coatings for electrodes with a drive toward roll-to-roll processing. However, through significant effort it has been determined that roll-to-roll processing of battery electrodes via ALD is prohibitively expensive. Particle ALD has been extensively studied as well and shown improved performance of battery materials comparable to electrode-ALD improvements, and in many cases shown even greater performance enhancement. Similar to electrode-ALD coating however, particle-ALD has remained a small scale laboratory-only research tool due to of the inability to scale-up the primary processing technique, which is a vacuum fluidized bed reactor. Even though ALD as a process has been proven to impart significant benefit to batteries materials, the capital cost of commercial scale production has to-date prevented its widespread adoption.

To remove the cost barrier of ALD-enabled batteries, PneumatiCoat Technologies (PCT) has developed a semi-continuous high throughput particle-ALD (HTP-ALD) pilot plant which has demonstrated the capability to meet the needs of commercial demand for battery materials with little increase in at-scale cost per kg of battery materials.  PCT has refined and validated a pilot-scale high throughput ALD coating system capable of 200kg/day scale, for Li-ion cathode powders that can meet the automotive industry mandate of low add-on cost (at scale).  The price point attainable with PCT’s high throughput gas-phase processing is significantly cheaper than even the most generous projections for manufacturing liquid-phase co-precipitation techniques ($3-5/kg) or batch-based ALD systems ($7-10/kg). Equally as important as meeting cost and performance criteria, PCT has demonstrated the semi-continuous technology to be capable of producing materials with a high degree of repeatability, a factor not often found with fluidized bed treatments and lab scale systems. Figure 2 shows a radar plot for 35 sub-batches of material coated using an early prototype of PCT’s original semi-continuous HTP-ALD system. The HTP-ALD pilot plant is also designed for plug-and-play scale-up capability in which simply making components larger or setting up automatic feeding systems will allow for nearly any desired level of production using existing powder processing techniques.

With the PCT pilot plant meeting projected cost targets and capability for producing high quality materials at pilot scale, the barriers to commercial scale ALD-enabled batteries have been greatly reduced. Ultimately this technology will allow battery manufacturers to eliminate the embedded costs of overbuilding, and these higher performance materials can be adopted at lower net cost and thereby reduce the cell and pack level $/kWh.