Citric acid and its analogues have been investigated as surface-modifying agents for Si nanoparticle anodes using electrochemical cycling, attenuated total reflectance infrared (ATR IR), and X-ray photoelectron spectroscopy (XPS). A Si nanoparticle anode prepared with citric acid (CA) has better capacity retention than one containing 1,2,3,4-butanetetracarboxylic acid (BA), but both electrodes outperform Si-PVDF. The Si-CA anode has an initial specific capacity of 3530 mA h/g and a first cycle efficiency of 82%. Surprisingly, the Si-CA electrode maintains a high specific capacity of ∼2200 mA h/g after 250 cycles, corresponding to 64% capacity retention, which is similar to the Si prepared with long-chain poly(acrylic acid) (PAA). On the contrary, the silicon electrode prepared with PVDF has a fast capacity fade and retains only 980 mA h/g after 50 cycles. The IR and XPS data show that the Si-CA electrode has an SEI composed primarily of lithium citrate during the first 50 cycles, resulting from the electrochemical reduction of citric acid. Only low concentrations of electrolyte reduction products are observed. The lithium citrate layer derived from CA stabilizes the silicon surface and suppresses electrolyte reduction, which likely contributes to the enhanced cycling performance of the Si nanoparticle anode.

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Silicon electrodes are of interest to the lithium ion battery industry due to high gravimetric capacity (∼3580 mAh/g), natural abundance, and low toxicity. However, the process of alloying and dealloying during cell cycling, causes the silicon particles to undergo a dramatic volume change of approximately 280% which leads to electrolyte consumption, pulverization of the electrode, and poor cycling. In this study, the formation of an ex-situ artificial SEI on the silicon nanoparticles with citric acid has been investigated. Citric acid (CA) which was previously used as a binder for silicon electrodes was used to modify the surface of the nanoparticles to generate an artificial SEI, which could inhibit electrolyte decomposition on the surface of the silicon nanoparticles. The results suggest improved capacity retention of ∼60% after 50 cycles for the surface modified silicon electrodes compared to 45% with the surface unmodified electrode. Similar improvements in capacity retention are observed upon citric acid surface modification for silicon graphite composite/ LiCoO 2 cells. Lithium ion batteries have been widely used in the portable electronic device market for over two decades due to high energy density, good rate capability, and long cycle life. [1][2][3] Graphite is the most frequently used commercial anode material. Although graphite has good performance, low cost and high capacity retention, the relatively modest storage capacity (∼370 mAh/g) has driven investigations of alternative anode materials.4 Different anode materials with greater storage capacity have been investigated including lithium metal, tin, silicon and other metal alloys. While lithium metal anodes are very appealing, dendrite formation after long term cycling results in significant safety concerns.5-7 Therefore, the use of lithium alloying compounds has been intensively investigated over the last decade. Silicon is the most attractive alloying anode material due to its high theoretical capacity. Lithiation of silicon results in the formation of alloys such as Li 15 Si 4 with a theoretical capacity of 3580 mAh/g. 8,9 In addition, silicon has a high volumetric capacity of 9786 mAh/ cm 3 . 10Silicon is abundant and has low toxicity which makes it a good candidate for an anode material for commercial batteries. Silicon also exhibits a discharge voltage of ∼0.4 V vs Li/Li + which allows it to maintain an open circuit potential which avoids lithium plating. 9,[11][12][13] While theoretically interesting, there are numerous factors that make silicon electrode use difficult. Some of the important factors include the volume variation during the lithiation and delithiation process of 280% which leads to pulverization of the electrode, instability of the SEI due to the volume variation, and damage to the electrode laminate.14,15 Numerous strategies have been undertaken to solve these stress induced problems that affect the electrochemical properties of the electrode including the use of nanoparticles, which limit the stress induced damage from larg...

High-energy nickel cobalt manganese oxides have been studied intensively as cathode materials for lithium-ion batteries. However, several hurdles need to be overcome to adopt these cathodes in commercial lithium-ion batteries. Herein, aluminum oxide (Al 2 O 3 ) coating was applied to high-energy nickel cobalt manganese oxides (HE-NCM, Li 1.33 Ni 0.27 Co 0.13 Mn 0.60 O 2+d ) by atomic layer deposition (ALD) and its effects on HE-NCM/graphite full cells were investigated. HE-NCM/graphite full cells have better cycling performance and efficiency when HE-NCM is coated with Al 2 O 3 . ICP-MS measurements show that the Al 2 O 3 coating can effectively prevent transition metal dissolution from HE-NCM. XPS and FT-IR analysis suggests that the surface film on HE-NCM cathodes does not change significantly with the Al 2 O 3 coating even after 50 cycles, however the surface film on graphite anodes shows a significant change. The resistance of graphite electrodes cycled with the uncoated HE-NCM is higher than that of graphite electrodes cycled with the Al 2 O 3 -coated HE-NCM due to the increased SEI thickness. The improved cycling performance of HE-NCM/graphite cells with Al 2 O 3 coating can be attributed to the minimized resistance increase on graphite as well as the suppression of cathode active material loss.

Silicon is a promising anode material for lithium ion batteries due to the high theoretical capacity (∼3600mAh/g). However, silicon-based electrodes face rapid degradation due to the extensive volume variation (∼300%) during the lithiation/delithiation process. Binders used in the electrode fabrication play a crucial role for silicon electrodes since it can reduce the mechanical fracture during the cycling process. Recent investigations suggest that in addition to the importance of the mechanical properties of the binder, the chemical reactions between the binder and the surface of the silicon particles also contribute to stabilization. Further investigations suggest that functionalized small molecules can also modify the surface of silicon particles and stabilize cycling. An inexpensive, environmentally friendly alternative has been investigated as a binder for silicon electrodes. Casein is a milk protein found in bovine milk rich in amine groups and carboxylic acid groups which can form bonds with the silanol groups in silicon. A comparative study conducted between PVDF and Casein as binders have shown that when casein was used as binder, it shows better performance compared to PVDF. Surface morphology and solid electrolyte interphase (SEI) was analyzed using electron microscopy techniques and spectroscopic methods and the results will be discussed.