Fluorine‐Doped Antiperovskite Electrolyte for All‐Solid‐State Lithium‐Ion Batteries

Abstract

Af luorine-doped antiperovskite Li-ion conductor Li 2 (OH)X (X = Cl, Br) is shown to be ap romising candidate for as olid electrolyte in an all-solid-state Li-ion rechargeable battery.S ubstitution of F À for OH À transforms orthorhombic Li 2 OHCl to ar oom-temperature cubic phase,w hichs hows electrochemical stability to 9Vversus Li + /Li and two orders of magnitude higher Li-ion conductivity than that of orthorhombic Li 2 OHCl. An all-solid-state Li/LiFePO 4 with F-doped Li 2 OHCl as the solid electrolyte showed good cyclability and ahigh coulombic efficiency over 40 charge/discharge cycles.

Protons Enhance Conductivities in Lithium Halide Hydroxide/Lithium Oxyhalide Solid Electrolytes by Forming Rotating Hydroxy Groups

“…[25] Heating from RT to 40 °C leads to noticeable changes in the crystal lattice ( Figure 2C). Mistakenly previously treated as orthorhombic to cubic transition, [11,13,19] we have shown that at 40 °C contaminant-free Li 2 OHCl exists in the tetragonal phase with lattice parameters a = 3.91 Å, b = 3.91 Å, c = 3.92 Å ( Figure 2C). Mistakenly previously treated as orthorhombic to cubic transition, [11,13,19] we have shown that at 40 °C contaminant-free Li 2 OHCl exists in the tetragonal phase with lattice parameters a = 3.91 Å, b = 3.91 Å, c = 3.92 Å ( Figure 2C).…”

“…Conductivities of the uncontrollably doped Li 2 OHX can thus be significantly altered, since only 0.005 at% of dopants may be sufficient to drastically change the conductivity values. [11] Finally, uncontrolled moisture in the synthesis of these materials or leaks in the electrochemical cells were found (by our team and by another group [15,18] ) to significantly change the measured conductivities and may potentially be responsible for some of the previously reported conductivity values. Unfortunately, such a control is often ignored.…”

“…The understanding of the elemental composition is a necessity and is often neglected in other works, [6,11,16] therefore, making the evaluation of the influence of chemical composition on the ionic conductivities hard. Briefly, fast heating (>400 °C min −1 ) of dry LiOH mixed with dry LiX (X = Cl, Br) (1:1 molar ratio) from room temperature to 650 °C was performed to achieve a homogenous liquid melt followed by the melt-casting at 450 °C to obtain a solidified product.…”

“…Moreover, our technique, unlike many other reported ones, [6,11,16] allows synthesis of Li 2 OHCl and Li 2 OHBr with no impurities because we used graphite crucible and casted molten SSEs onto a graphite mold. Moreover, our technique, unlike many other reported ones, [6,11,16] allows synthesis of Li 2 OHCl and Li 2 OHBr with no impurities because we used graphite crucible and casted molten SSEs onto a graphite mold.…”

“…[17] In principle, such undesired doping of Li 2 OHX can be drastically minimized or fully avoided by decreasing reaction times, and using inert reaction vessels and careful control of the elemental composition. [11] Since the presence of thermodynamically unstable H 2 O induces undesirable side reactions and gas evolution in full cells during cycling [19] and since various solvated ions likely contribute to the total ion conduction of moist SSE, we believe it is extremely important to avoid moisture for careful comparative analysis. In addition, the similarity in the lattice parameters between Li 2 OHX and Li 3 OX may easily lead to a mix-up, unless X-ray diffraction (XRD) is conducted very accurately.…”