Atomic Layer Deposition Technology for Li-ion Batteries by Beneq

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Overview

Beneq Oy, based in Finland, is a supplier of equipment and coating technology for global markets. Beneq turns innovations into success by developing applications and equipment for cleantech and renewable energy fields, especially in glass, solar and emerging thin film markets. Coating applications include optics, barriers and passivation layers, as well as energy generation and conservation. Beneq also offers complete coating services. Beneq's coating applications are based on two enabling nanotechnology platforms: Atomic Layer Deposition (ALD) and aerosol coating (nHALO® and nAERO®).

Introduction

Atomic layer deposition (ALD) is shifting from being a research tool in battery development to becoming a viable and industrial production tool for a number of specific products. Beneq ALD is pleased to be at the forefront of this development and capable of serving its customers in this growing hi-tech field.

Applications of Atomic Layer Deposition for Li-ion Batteries

ALD has recently been successfully applied to several materials needed in lithium-ion (Li-ion) batteries. Titanium nitride (TiN) diffusion barriers and platinum (Pt) cathode current collector materials have been developed by ALD for the non-active layers in 3D integrated batteries, see Fig. 1. ALD provides a significant performance improvement especially in applications where fully conformal coatings are needed on complex structures. In addition, Li-containing materials have, despite common doubt concerning feasibility, been deposited by ALD.

Figure 1. Schematic of a 3D battery integrated in a Sisubstrate. The cross-section shows the various functional layers in the battery stack as well as the candidate materials. (Source: Knoops, H.C.M. et al., ECS Trans., 25 (2009) pp. 333-344.)

ALD is a useful, and proven, coating method for several battery structures and material layers, including:

• fastening micro- and nano-sized particles to a substrate
• applying diffusion and corrosion barriers for metal surfaces
• controlling the diffusion properties of the surface of particles
• surface passivation in general
• tailoring the composition of porous materials

Due to their “bottom up” film growth mechanism, most ALD coatings are naturally pinhole-free. This feature is especially valuable in barrier and passivation applications. A major improvement in barrier properties is achieved already in a film thickness regime of 10 nm, see Fig. 2

Figure 2. Water vapor transmission rates versus thickness of Al₂O₃ ALD films grown at 120 °C on polyethylene naphthalate (PEN). (Source: Groner, M.D., et al., Appl. Phys. Lett., 88 (2006).)

Taking Atomic Layer Deposition into Powders and Particles

Combining conformal coating with particulate substrates creates completely new opportunities to modify the diffusion properties of battery materials and, most importantly, extend the lifetime and stability of the battery. To further strengthen its offering in ALD of powders and particles, Beneq has entered into a strategic partnership with ALD NanoSolutions, Inc., the pioneer and developer of Particle ALD™. Fig. 3 presents the beneficial effect ALD coatings on cathode particles have on the performance of Li-ion batteries.

Figure 3. Charge-discharge performance of Li-ion batteries with uncoated cathode particles (black) and LiCoO₂ cathode and graphite anode coated by ALD with 2 cycles (red) of alumina (Al₂O₃). Two ALD cycles of Al₂O₃ corresponds to a film approximately 2.5 Å (0.25 nm) in thickness. Charging occurred at 4.5 V, at 1C (Source: Jung, Y.S. et al. Adv. Mats. 22 (2010).)

Basics of Atomic Layer Deposition Technology

Atomic layer deposition (ALD) is a chemical gas-phase thin film deposition method. It is based on sequential, self-saturating surface reactions. Two or more precursor chemicals, each containing different elements of the materials being deposited, are introduced to the substrate surface sequentially, one at a time. Each precursor completely saturates the surface, thus forming a monolayer of material. ALD was initially developed for production of thin film electroluminescent (TFEL) flat panel displays, but today it is used for a variety of industrial applications, including semiconductor device manufacturing.

The advantages of ALD stem from the surface-controlled and self-saturating film growth principle, which can be utilized in many green energy concepts other than Li-ion batteries, including solar cells, proton exchange membrane fuel cells (PEMFC) and solid oxide fuel cells (SOFC).

ALD is an enabling coating technology for new and improved products. It provides coatings and material features which either cannot be achieved cost–efficiently with existing techniques, or then they cannot be achieved at all. In short, ALD offers:

• precise control of the film thickness, at true nanometer scale
• pinhole–free films for, e.g., superior barrier layers and surface passivation
• conformal coating of batches, large–area substrates and complex 3D objects, including porous bulk materials and powders
• engineered and new functional materials and structures, such as nanolaminates
• a highly repeatable and scalable process ready for industrial implementation

For powders and particles, ALD already has a proven track record of coating applications, including heterogeneous catalysts and nanofillers for polymer composites.

Atomic Layer Deposition Equipment Offered by Beneq

Beneq is a provider of coating equipment for research, development and production. We offer a diverse palette of ALD equipment, from pure research tools to industrial production workhorses. Some of our systems are application-specific and therefore focused on certain processes and properties. These application-specific systems are the result of in-depth work together with customers aiming for reliable production equipment and a solution for their opportunity. Below is a list of our ALD equipment offering.

• TFS 200, for ALD research, including Particle ALD™
• TFS 200R, for continuous ALD research
• TFS 500, for ALD R&D and batch production
• TFS 600, for OLED encapsulation
• TFS 1200, for CIGS solar cell buffer layer
• TFS NX300, for c-Si solar cell surface passivation
• P400A and P800, for ALD production (Fig. 4)

Figure 4. Beneq personnel tending to a P800 production unit. P400A units in fore- and background.

Source: Beneq

For more information on this source please visit Beneq