In Situ Mitigation of First-Cycle Anode Irreversibility in a New Spinel/ FeSb Lithium-Ion Cell Enabled via a Microwave-Assisted Chemical Lithiation Process Zachary Moorhead-Rosenberg, Eric Allcorn, and Arumugam Manthiram* Materials Science and Engineering Program and Texas Materials Institute The University of Texas at Austin, Austin, Texas 78712, United States * S Supporting Information ABSTRACT: First-cycle irreversibility is a major problem that plagues many next-generation nanoscale anode materials which form solid- electrolyte interphase (SEI) layers. Without a method to compensate for this irreversible capacity loss, the full cells will face serious problems. The concept of a lithium reservoir in spinel cathodes was proposed in the early 90s to combat the irreversibility of graphite anodes, but chemical techniques to lithiate spinel have been complex or hazardous. We present in this study (i) a new facile microwave-assisted chemical lithiation technique for spinel oxide cathodes which is capable of inserting one extra lithium per formula unit using less expensive, readily available lithium hydroxide in polyol and (ii) two new advanced lithium-ion batteries combining a prelithiated 5 V spinel Li 1+ x Mn 1.5 Ni 0.5 O 4 or a 4 V spinel Li 1.05 + x Ni 0.05 Mn 1.9 O 4 cathode and a carbon-free FeSb-TiC alloy anode that has a high first-cycle irreversible capacity loss. We show that the extra chemically inserted lithium is necessary to achieve a complete utilization of the cathode capacity. The battery employing the 5 V spinel cathode exhibits good rate capability with an energy density of 260 Wh/kg based on total active mass. ■ INTRODUCTION Lithium-ion batteries have revolutionized the mobile elec- tronics industry and are now starting to have a noticeable impact on the personal transportation sector with the introduction of next-generation electric vehicles. 1-3 Most lithium-ion cells utilize the same graphitic-carbon anode which was first employed by Sony in 1990. 4 Graphite offers a gravimetric capacity of 372 mAh g -1 and a low potential vs the Li/Li + couple, maximizing the energy density of Li-ion full cells. On the other hand, sluggish insertion kinetics upon fast charging 5-7 is a significant drawback to the implementation of graphitic-carbon anodes in large-scale applications, which demand high power charging such as hybrid and electric vehicles. For these reasons, significant research over the past decade has been dedicated to the search for alternative anode materials with a higher average voltage vs Li/Li + to enhance the safety characteristics of the cell. Notable examples include metal-oxide conversion materials, 8 nano-TiO 2 , 9,10 Li 4 Ti 5 O 12 , 11-13 and Sn, 10,14,15 Sb, 16,17 and Si 18-20 alloy electrodes. In addition to the higher potential vs Li/Li + , many of these anode materials offer improved gravimetric and volumetric energy density compared to LiC 6 . In terms of stable high-power cycling capability, the spinel Li 4 Ti 5 O 12 stands out as a prominent next-generation anode. 13 However, the very high operating voltage vs Li/Li + (1.5 V) and limited gravimetric capacity (170 mAh g -1 ) reduce the overall energy density of full cells well below what is competitive with conventional graphite-based anodes. Recently, composite alloy anodes have emerged as alternative high-rate, high voltage anode materials due to average voltages around ∼0.5 V vs Li/Li + . Proper integration of the nanoalloy particles in a structural reinforcing matrix such as Al 2 O 3 or TiC prevents nanoparticle agglomeration and pulverization. 16,17,21,22 These composite anodes, containing active materials such as Sn, FeSb, and Cu 2 Sb, offer several advantages to Li 4 Ti 5 O 12 including lower voltage and higher capacity (between 200 and 400 mAh g -1 ), which results in a marked improvement in energy density if employed in a Li-ion full cell. Implementation of next-generation anode materials including TiO 2 , metal-oxides, and metal-alloys is largely inhibited by irreversible capacity loss stemming from first-cycle solid- electrolyte interphase (SEI) layer formation and other side reactions. 23 This irreversible capacity can reach as high as 40- 50% of the total gravimetric capacity depending on the anode material and prevents full utilization of the cathode active mass because a large fraction of the lithium ions in the as-prepared cathode are consumed in the irreversible reactions. The result is that the as-assembled full cell without anode pretreatment has a much reduced energy density. To combat this phenomenon in laboratory-scale testing, several complicated multistep process can be employed to prime the anodes before they are placed in full cells. Often this process involves mixing the anode with stabilized lithium metal powder (SLMP), 24 Li-metal strips, 19 or Received: July 4, 2014 Revised: August 25, 2014 Article pubs.acs.org/cm © XXXX American Chemical Society A dx.doi.org/10.1021/cm5024426 | Chem. Mater. XXXX, XXX, XXX-XXX