Dual-Salts Localized High-Concentration Electrolyte for Li- and Mn-Rich High-Voltage Cathodes in Lithium Metal Batteries.

Limited electrochemical stability windows of conventional carbonate-based electrolytes pose a challenge to support the Lithium (Li)- and manganese (Mn)-rich (LMR) high-voltage cathodes in rechargeable Li-metal batteries (LMBs). To address this issue, a novel localized high-concentration electrolyte (LHCE) composition incorporating LiPF6 and LiTFSI as dual-salts (D-LHCE), tailored for high-voltage (>4.6 Vvs.Li) operation of LMR cathodes in LMBs is introduced. 7Li nuclear magnetic resonance and Raman spectroscopy revealed the characteristics of the solvation structure of D-LHCE. The addition of LiPF6 provides stable Al-current-collector passivation while the addition of LiTFSI improves the stability of D-LHCE by producing a more robust cathode-electrolyte interphase (CEI) on LMR cathode and solid-electrolyte interphase (SEI) on Li-metal anode. As a result, LMR/Li cell, using the D-LHCE, achieved 72.5% capacity retention after 300 cycles, a significant improvement compared to the conventional electrolyte (21.9% after 100 cycles). The stabilities of LMR CEI and Li-metal SEI are systematically analyzed through combined applications of electrochemical impedance spectroscopy and distribution of relaxation times techniques. The results present that D-LHCE concept represents an effective strategy for designing next-generation electrolytes for high-energy and high-voltage LMB cells.

Li0.5La0.5TiO3 as an Ionic Conducting Additive Enhancing the High-Voltage Performance of LiNi0.8Mn0.1Co0.1O2 Cathodes in Lithium-Ion Batteries.

Although high-voltage (e.g., >4.3 VvsLi) operation can increase specific capacity and energy of Ni-rich NMC cathodes, it accelerates the oxidative decomposition of electrolytes and surface degradation of NMC cathodes, leading to rapid capacity fading. This work presents a novel approach that employs Li0.5La0.5TiO3 (LLTO) solid-electrolyte as a Li-ion conductor and surface passivation agent to stabilize the cathode/electrolyte interphase (CEI) layer of the LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode and enhance its high-voltage performances. The LLTO particles improve Li-ion transportation across the CEI layer, as evidenced by its reduced impedance in Nyquist plots. Furthermore, passivation of CEI by LLTO mitigates parasitic reactions (e.g., transition metal dissolution) that occur on the graphite solid electrolyte interphase layer during extended cycles of pouch-cells. As a result, pouch-cells with the 1 or 5 wt % LLTO-blended NMC811 cathodes can deliver 19-23% increase in specific capacity and improved cycle life (1000 cycles) at high voltages (up to 4.4 V), comparing to bare NMC811 cathodes. Post-mortem characterization of pouch-cells quantitatively identified the degradation sources of NMC811 cathode at high-voltages, which highlighted the improvement mechanisms of LLTO blended-cathodes.