Li2O-Based Cathode Additives Enabling Prelithiation of Si Anodes

Solid Electrolyte Interface Film-Forming and Surface-Stabilizing Bifunctional 1,2-Bis((trimethylsilyl)oxy) Benzene as Novel Electrolyte Additive for Silicon-Based Lithium-Ion Batteries

The application of Si-based anodes in lithium-ion batteries (LIBs) has garnered significant attention due to their high theoretical specific capacity yet is still challenged by the substantial volume expansion of silicon particles during the lithiation process, resulting in the instability of the electrode-electrolyte interphase and deteriorative battery performance. Herein, an ortho(trimethylsilyl)oxybenzene electrolyte additive, 1,2-bis((trimethylsilyl)oxy) benzene (referred to as BTMSB), has been investigated as a bifunctional electrolyte additive for Si-based LIBs. The BTMSB can form a uniform and robust LiF-rich solid electrolyte interphase (SEI) on the surface of Si-based material particles, adapting the huge volume expansion of the Si-based electrode and facilitating lithium-ion transport. Additionally, the BTMSB demonstrates the ability to scavenge hydrofluoric acid (HF) to stabilize the electrode-electrolyte interphase. The SiOx/C∥Li batteries with 2% BTMSB exhibit improved cycle performance and current-rate capabilities, of which the capacity retention retains 69% after 400 cycles. Furthermore, Si-based anode cells with higher theoretical specific capacities (1C = 550 mAh g-1) and NCM523∥SiOx/C pouch cells are constructed and evaluated, displaying superior cycle performance. This work provides valuable insights for the development of effective electrolyte additives and the commercialization of high energy density LIBs with Si-based anodes.

Sol/Antisolvent Coating for High Initial Coulombic Efficiency and Ultra-stable Mechanical Integrity of Ni-Rich Cathode Materials

The Ni-rich cathode holds great promise for high energy density lithium-ion batteries because of its high capacity and operating voltage. However, crucial problems such as cation disorder, structural degradation, side reactions, and microcracks become serious with increasing nickel content. Herein, a novel and facile sol/antisolvent coating modification of Ni-rich layered oxide LiNi_0.85Co_0.1Mn_0.05O₂ (NCM) is developed where we use ethanol to disperse the nanosized LiBO₂ to form the sol and adopt tetrahydrofuran (THF) as antisolvent to prepare the cluster of nanoparticles to be coated on the surface of NCM. The coating thickness can be tuned through the THF addition amount. The LiBO₂ nanorod deposition is formed as well over the crack of the NCM cathode, likely acting as a patch to repair the original defect of the intrinsic crack. The uniform LiBO₂ nanospherical particle coating together with LiBO₂ nanorod wrapping provides a double protection against electrolytes. Compared with the raw material, LiBO₂-coated LiNi_0.85Co_0.1Mn_0.05O₂ (LiBO₂-coated NCM) exhibits a high initial Coulombic efficiency of 90.3% at 0.2 C between 2.8 and 4.3 V vs Li⁺/Li, a superior rate capability, enhanced fast charge property at 3 C, and restricted microcrack formation. This simple in-site modification and repairing technology guarantees a good mechanical integrity of the polycrystalline Ni-rich cathode.

High-Energy-Density and Long-Lifetime Lithium-Ion Battery Enabled by a Stabilized Li2O2 Cathode Prelithiation Additive

Lithium-ion batteries (LIBs) typically suffer from large irreversible capacities caused by active lithium loss during formation of a solid electrolyte interface (SEI) at the anode side. Cathode prelithiation with preloaded additives has emerged as an effective strategy to solve the above issue. With ultrahigh theoretical capacity, Li₂O₂ serves as an excellent cathode prelithiation additive, whereas poor ambient stability limits its further development. In this study, we report a surface protection strategy to enable ambient processing of the Li₂O₂ additive. Li₂O₂ is well confined in poly(methyl methacrylate) (PMMA) nanofibers (P-Li₂O₂) via electrospinning, which exhibits greatly enhanced ambient stability compared with the unprotected one. Notably, when P-Li₂O₂ is preloaded in LiNi_0.5Co_0.2Mn_0.3O₂ cathodes (NCM-P-Li₂O₂), PMMA nanofibers remain stable during cathode slurry processing but readily dissolve in electrolytes and expose Li₂O₂ for effective electrochemical oxidation. Fabrication of P-Li₂O₂ allows systematic investigation of prelithiation behavior in full cells (NCM-P-Li₂O₂ cathodes paired with Si/Graphite anodes) and its impact on the electrochemical performance. Rational tuning of the prelithiation degree provides guidance for optimizing the amount of the cathode additive, which brings appealing cell lifetime and energy density.

Opportunities and Challenges of Li2 C4 O4 as Pre-Lithiation Additive for the Positive Electrode in NMC622||Silicon/Graphite Lithium Ion Cells

Silicon (Si)-based negative electrodes have attracted much attention to increase the energy density of lithium ion batteries (LIBs) but suffer from severe volume changes, leading to continuous re-formation of the solid electrolyte interphase and consumption of active lithium. The pre-lithiation approach with the help of positive electrode additives has emerged as a highly appealing strategy to decrease the loss of active lithium in Si-based LIB full-cells and enable their practical implementation. Here, the use of lithium squarate (Li2 C4 O4 ) as low-cost and air-stable pre-lithiation additive for a LiNi0.6 Mn0.2 Co0.2 O2 (NMC622)-based positive electrode is investigated. The effect of additive oxidation on the electrode morphology and cell electrochemical properties is systematically evaluated. An increase in cycle life of NMC622||Si/graphite full-cells is reported, which grows linearly with the initial amount of Li2 C4 O4 , due to the extra Li+ ions provided by the additive in the first charge. Post mortem investigations of the cathode electrolyte interphase also reveal significant compositional changes and an increased occurrence of carbonates and oxidized carbon species. This study not only demonstrates the advantages of this pre-lithiation approach but also features potential limitations for its practical application arising from the emerging porosity and gas development during decomposition of the pre-lithiation additive.