Stabilizing High-Voltage Cathodes via Ball-Mill Coating with Flame-Made Nanopowder Electrolytes.

LiMn1.5Ni0.5O4 (LMNO) spinel has recently been the subject of intense research as a cathode material because it is cheap, cobalt-free, and has a high discharge voltage (4.7 V). However, the decomposition of conventional liquid electrolytes on the cathode surface at this high oxidation state and the dissolution of Mn2+ have hindered its practical utility. We report here that simply ball-mill coating LMNO using flame-made nanopowder (NPs, 5-20 wt %, e.g., LiAlO2, LATSP, LLZO) electrolytes generates coated composites that mitigate these well-recognized issues. As-synthesized composite cathodes maintain a single P4332 cubic spinel phase. Transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS) show island-type NP coatings on LMNO surfaces. Different NPs show various effects on LMNO composite cathode performance compared to pristine LMNO (120 mAh g-1, 93% capacity retention after 50 cycles at C/3, ∼67 mAh g-1 at 8C, and ∼540 Wh kg-1 energy density). For example, the LMNO + 20 wt % LiAlO2 composite cathodes exhibit Li+ diffusivities improved by two orders of magnitude over pristine LMNO and discharge capacities up to ∼136 mAh g-1 after 100 cycles at C/3 (98% retention), while 10 wt % LiAlO2 shows ∼110 mAh g-1 at 10C and an average discharge energy density of ∼640 Wh kg-1. Detailed postmortem analyses on cycled composite electrodes demonstrate that NP coatings form protective layers. In addition, preliminary studies suggest potential utility in all-solid-state batteries (ASSBs).

LiAlO2/LiAl5O8 Membranes Derived from Flame-Synthesized Nanopowders as a Potential Electrolyte and Coating Material for All-Solid-State Batteries.

Recently, γ-LiAlO2 has attracted considerable attention as a coating in Li-ion battery electrodes. However, its potential as a Li+ ceramic electrolyte is limited due to its poor ionic conductivity (<10-10 S cm-1). Here, we demonstrate an effective method of processing LiAlO2 membranes (<50 µm) using nanopowders (NPs) produced via liquid-feed flame spray pyrolysis (LF-FSP). Membranes consisting of selected mixtures of lithium aluminate polymorphs and Li contents were processed by conventional tape casting of NPs followed by thermocompression of the green films (100 °C/10 kpsi/10 min). The sintered green films (1100 °C/2 h/air) present a mixture of LiAlO2 (∼72 wt %) and LiAl5O8 (∼27 wt %) phases, offering ionic conductivities (>10-6 S cm-1) at ambient with an activation energy of 0.5 eV. This greatly increases their potential utility as ceramic electrolytes for all-solid-state batteries, which could simplify battery designs, significantly reduce costs, and increase their safety. Furthermore, a solid-state Li/Li3.1AlO2/Li symmetric cell was assembled and galvanostatically cycled at 0.375 mA cm-2 current density, exhibiting a transference number ≈ 1.

Solid Electrolytes for Li-S Batteries: Solid Solutions of Poly(ethylene oxide) with LixPON- and LixSiPON-Based Polymers.

We report here efforts to synthesize free-standing, dry polymer electrolytes that exhibit superior ionic conductivities at ambient for Li-S batteries. Co-dissolution of poly(ethylene oxide) (PEO) (Mn 900k) with LixPON and LixSiPON polymer systems at a ratio of approximately 3:2 followed by casting provides transparent, solid-solution films 25-50 µm thick, lowering PEO crystallinity, and providing measured impedance values of 0.1-2.8 × 10-3 S/cm at ambient. These values are much higher than simple PEO/Li+ salt systems. These solid-solution polymer electrolytes (PEs) are (1) thermally stable to 100 °C; (2) offer activation energies of 0.2-0.5 eV; (3) suppress dendrite formation; and (4) enable the use of lithium anodes at current densities as high as 3.5 mAh/cm2. Galvanostatic cycling of SPAN/PEs/Li cell (SPAN = sulfurized, carbonized polyacrylonitrile) shows discharge capacities of 1000 mAh/gsulfur at 0.25C and 800 mAh/gsulfur at 1C with high coulumbic efficiency over 100 cycles.

Polymer Precursor Derived LixPON Electrolytes: Toward Li-S Batteries.

Efforts to develop polymer precursor electrolytes that offer properties anticipated to be similar or superior to (lithium phosphorus oxynitride, LiPON) glasses are reported. Such precursors offer the potential to be used to process LiPON-like thin glass/ceramic coatings for use in all solid state batteries, ASBs. Here, LiPON glasses provide a design basis for the synthesis of sets of oligomers/polymers by lithiation of OP(NH2)3-x(NH)x [from OP(NH)3],OP(NH2)3-x(NHSiMe3)x and [P═N]3(NHSiMe3)6-x(NH)x. The resulting systems have degrees of polymerization of 5-20. Treatment with selected amounts of LiNH2 provides varying degrees of lithiation and Li+ conducting properties commensurate with Li+ content. Polymer electrolytes impregnated in/on Celgard exhibit Li+ conductivities up to ∼1 × 10-5S cm-1 at room temperature and are thermally stable to ∼150 °C. A Li-S battery assembled using a Li6SiPON composition polymer electrolyte exhibits an initial reversible capacity of 1500 mAh gsulfur-1 and excellent cycle performance at 0.25 and 0.5 C rate over 120 cycles at room temperature.