B-/Si-containing electrolyte additive efficiently establish a stable interface for high-voltage LiCoO2 cathode and its synergistic effect on LiCoO2/graphite pouch cells.

An effective electrolyte additive, 3-(tert-Butyldimethylsilyoxy) phenylboronic acid (TBPB), is proposed to significantly improve the cycle stability of high voltage LiCoO2 (LCO) cathode. Experimental and computational results show that TBPB has a relatively higher oxidation activity than base electrolyte, and preferentially constructs a stable cathode electrolyte interphase (CEI) containing B-/Si- components on LCO surface. Theoretical calculation, XPS and NMR data show that TBPB-derived CEI layer contains B-F species and has the function of eliminating HF. The as-formed CEI effectively inhibits the detrimental side reactions from electrolyte decomposition and LCO surface structure reconstruction. The capacity retention of LCO/Li half-cell increases from 38.92% (base electrolyte) to 83.70% after 150 cycles at 1 C between 3.0 V and 4.5 V by adding 1% TBPB. Moreover, TBPB is also reduced prior to base electrolyte, forming an ionic conducting solid electrolyte interphase (SEI) on graphite surface. Benefiting from the synergistic effect between CEI layer on LCO cathode and SEI layer on graphite anode to effectively decrease the electrolyte decomposition, the capacity retention of commercial LCO/graphite pouch cell with 1% TBPB increases from 10.44% to 76.13% after 400 cycles at 1 C between 3.0 V and 4.5 V. This work demonstrates that TBPB can act as an effective film-forming additive for high energy density LCO cathode at high voltage, and provides novel insights for its commercial application from the aspect of synergistically interfacial stability.

Highly Enforced Rate Capability of a Graphite Anode via Interphase Chemistry Tailoring Based on an Electrolyte Additive.

The rate capability of lithium-ion batteries is highly dependent on the interphase chemistry of graphite anodes. Herein, we demonstrate an anode interphase tailoring based on a novel electrolyte additive, lithium dodecyl sulfate (LiDS), which greatly improves the rate capability and cyclic stability of graphite anodes. Upon application of 1% LiDS in a base electrolyte, the discharge capacity at 2 C is improved from 102 to 240 mAh g-1 and its capacity retention is enhanced from 51% to 94% after 200 cycles at 0.5 C. These excellent performances are attributed to the preferential absorption of LiDS and the as-constructed interphase chemistry that is mainly composed of organic long-chain polyether and inorganic lithium sulfite. The long-chain polyether possesses flexibility endowing the interphase with robustness, while its combination with inorganic lithium sulfite accelerates lithium intercalation/deintercalation kinetics via decreasing the resistance for charge transfer.