In order to employ Li-ion batteries (LIBs) in next-generation hybrid electric and/or plug-in hybrid electric vehicles (HEVs and PHEVs), LIBs must satisfy many requirements: electrodes with long lifetimes (fabricated from inexpensive environmentally benign materials), stability over a wide temperature range, high energy density, and high rate capability. Establishing long-term durability while operating at realistic temperatures (5000 charge-depleting cycles, 15 year calendar life, and a range from À46 8C to þ66 8C) for a battery that does not fail catastrophically remains a significant challenge. [1] Recently, surface modifications of electrode materials have been explored as viable paths to improve the performance of LIBs for vehicular applications.[2] The cycle life and safety issues have been largely satisfied for Li x MO 2 (M ¼ Co, Ni, Mn, etc.) cathodes by coating the active material particles with a metal oxide and/or metal phosphate. [2a,2b,3] For anode, state-of-the-art materials such as Si suffer from significant volume expansion/contraction during charge-discharge leading to rapid capacity fade.[4] Natural graphite (NG) is a realistic candidate anode, for vehicular applications, due to its high reversible capacity, low and flat potential relative to Li/Li þ , moderate volume change, and low cost.[5] In previous reports, the performance of NG was improved by surface modifications with mild oxidation, [6] coating with amorphous carbon,[5c] metal oxides (Al 2 O 3 , ZrO 2 ), [5a,7] and metal phosphate (AlPO 4 ).[5b] These efforts were performed in order to mitigate the solid electrolyte interphase (SEI) [8] that is formed on the NG surface by reductive decomposition of the electrolyte during initial charge-discharge especially at elevated temperatures. The decomposition of the SEI at elevated temperature ($80 8C) is exothermic and initiates thermal runaway. [9] In most previous reports films of metal oxides and metal phosphates have been deposited on powder electrode materials with 'sol-gel' wet-chemical methods.

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An alumina surface coating is demonstrated to improve electrochemical performance of MoO(3) nanoparticles as high capacity/high-volume expansion anodes for Li-ion batteries. Thin, conformal surface coatings were grown using atomic layer deposition (ALD) that relies on self-limiting surface reactions. ALD coatings were tested on both individual nanoparticles and prefabricated electrodes containing conductive additive and binder. The coated and non-coated materials were characterized using transmission electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and galvanostatic charge/discharge cycling. Importantly, increased stability and capacity retention was only observed when the fully fabricated electrode was coated. The alumina layer both improves the adhesion of the entire electrode, during volume expansion/contraction and protects the nanoparticle surfaces. Coating the entire electrode also allows for an important carbothermal reduction process that occurs during electrode pre-heat treatment. ALD is thus demonstrated as a novel and necessary method that may be employed to coat the tortuous network of a battery electrode.