Multifunctional Umbrella: In Situ Interface Film Forming on the High-Voltage LiCoO2 Cathode by a Tiny Amount of Nanoporous Polymer Additives for High-Energy-Density Li-Ion Batteries.

The LiCoO2 (LCO) cathode is foreseen for extensive commercial applications owing to its high specific capacity and stability. Therefore, there is considerable interest in further enhancing its specific capacity by increasing the charging voltage. However, single-crystal LCO suffers from a significant capacity degradation when charged to 4.5 V due to the irreversible phase transition and unstable structure. Herein, an ultra-small amount (0.5% wt. in the electrode) of multi-functional PIM-1 (a polymer with intrinsic microporosity) additive is utilized to prepare a kind of binder-free electrode. PIM-1 modulates the solvation structure of LiPF6 due to its unique structure, which helps to form a stable, robust, and inorganic-rich cathod-eelectrolyte interphase (CEI) film on the surface of LCO at a high voltage of 4.5 V. This reduces the irreversible phase transition of LCO, thereby enhancing the cyclic stability and improving the rate performance, providing new perspectives for the electrodes fabrication and improving LCO-based high-energy-density cathodes.

One Stone for Multiple Birds: A Versatile Cross-Linked Poly(dimethyl siloxane) Binder Boosts Cycling Life and Rate Capability of an NCM 523 Cathode at 4.6 V.

Increasing working voltage is a promising way to increase the energy density of lithium-ion batteries. Cycling and rate performance deteriorated due to excessive electrolyte decomposition and uncontrolled formation of a cathode-electrolyte interface (CEI) layer at a high voltage. A new concept is proposed to construct a high-voltage-stable electrode-electrolyte interface. An elastomeric poly(dimethyl siloxane) (PDMS) binder is incorporated into the electrode to modify the LiNi0.5Co0.2Mn0.3O2 (NCM 523) particle surface via an in situ cross-linking reaction between hydroxy-terminated PDMS and methyl trimethoxy silane promoted by moisture at ambient conditions (MPDMS). Improved electrochemical performance is achieved with the MPDMS binder in terms of reversible capacity (201 vs 185 mAh·g-1 at 0.2C), capacity retention (80 vs 68%, after 300 cycles at 1C), and rate performance (55.6% increase at 5C), as demonstrated by the NCM 523||Li half-cell. The NCM 523||graphite full-cell also shows improved performance at 4.6 V (147 vs 128 mAh·g-1, 82 vs 76%, after 200 cycles at 1C). The mechanism studies indicate that MPDMS exerts multiple effects, including cathode surface passivation, solvation structure tuning, electrolyte uptake enhancement, and mechanical stress relief. This work provides an inspiring route to realize high-voltage application of lithium-ion battery technology.