Interface modifications by anion receptors for high energy lithium ion batteries

Li-rich, Mn-rich (LMR) layered composite has attracted extensive interests because of its highest energy density among all cathode candidates for lithium ion batteries (LIB). However, capacity degradation and voltage fading remain the major challenges for LMR cathodes prior to their practical applications. Here, we demonstrate that anion receptor, tris(pentafluorophenyl)borane ((C6F5)(3)B, TPFPB), substantially enhances the stability of electrode/electrolyte interface and thus improves the cycling stability of LMR cathode Li/Li0.2Ni0.2Mn0.6]O-2. In the presence of 0.2 M TPFPB, Li[Li0.2Ni0.2Mn0.6]O-2 shows an improved capacity retention of 76.8% after 500 cycles. It is proposed that TPFPB effectively confines the highly active oxygen species released from structural lattice through its strong coordination ability and high oxygen solubility. The electrolyte decomposition caused by the oxygen species attack is therefore largely mitigated, forming reduced amount of byproducts on the cathode surface. Additionally, other salts such as insulating LiF derived from electrolyte decomposition are also soluble in the presence of TPFPB. The collective effects of TPFPB mitigate the accumulation of parasitic reaction products and stabilize the interfacial resistances between cathode and electrolyte during extended cycling, thus significantly improving the cycling performance of Li[Li0.2Ni0.2Mn0.6]O-2. (C) 2013 Elsevier B.V. All rights reserved.