ALD Improves Battery Materials

ALD coatings stabilize materials. ALD coatings on anode and cathode powders improve battery performance. The stabilizing nature of ALD coatings reduce metal dissolution, reduce SEI formation, and reduce lithium inventory loss. These effects can lead to the following benefits, depending on the application:

• Higher V operation (and associated higher capacity)
• Longer calendar lifetime
• Longer cycle life
• Less gas generation
• Lower impedance growth over cycling, leading to higher capacity after cycling
• Enhanced safety (higher thermal runaway onset T, ARC measurement, etc.)
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Such benefits have been observed on the following materials:

Cathode powders: NCM (>80%Ni, 811, 721, 622, 532), LCO (at 4.5V, 4.6V), NCA (>80%Ni, >90%Ni), LMO (spinel and non-spinel types), LMNO

Anode powders: natural graphite, synthetic graphite, Si/C composites, silicon

For coatings on cathode powders, the higher the Ni concentration, the less stable the cathode materials and the more important the surface coating. For high Ni materials, ALD coatings provide the most benefit versus other coating methods.For coatings on anode powders, even just a very thin ALD coating can provide significantly enhanced cell cycle lifetimes and higher voltage performance.When combining a coated cathode with a coated anode, even more benefits can be observed for certain systems such as LCO/graphite systems. These benefits include higher initial specific discharge capacities and higher capacity retention over cycle life.

Various ALD chemistries are possible

ALD coatings of various materials have shown to enhance battery performance in different applications and in different ways. Aluminum oxide is the main chemistry of choice for most processes and can improve battery performance metrics discussed in this article. However, many companies are now exploring advanced coatings such as those designed to have higher Li-ion mobilities and transport numbers. These advanced ALD coatings are often applicable to lithium ion batteries, hybrid batteries containing solid state components, and fully solid-state battery systems. Advanced ALD coatings under current exploration for battery materials include metal oxides (other than aluminum oxide), lithium metal oxides, metal phosphates, metal fluorides. Advanced ALD coatings that may also be considered for battery materials include polymer coatings, hybrid oxide/carbon coatings, sulfur-coating coatings and others.

Example Data of ALD-Coated Battery Materials

Although ALD coated materials show benefits on a variety of battery materials, recent coatings have shown particular benefit for fast charging of NMC 811 and high voltage operation of LCO. This recent work shown below is of importance for automotive batteries (NMC811) and consumer electronics (LCO).