New Insights into the Effects of Zr Substitution and Carbon Additive on Li_3–xEr_1–xZr_xCl₆ Halide Solid Electrolytes

Abstract

Halide solid electrolytes have been considered as the most promising candidates for practical high-voltage all-solidstate lithium-ion batteries (ASSLIBs) due to their moderate ionic conductivity and good interfacial compatibility with oxide cathode materials. Aliovalent ion doping is an effective strategy to increase the ionic conductivity of halide electrolytes. However, the effects of ion doping on the electrochemical stability window of halide electrolytes and carbon additive on electrochemical performance are still unclear by far. Herein, a series of Zr-doped Li 3−x Er 1−x Zr x Cl 6 halide solid electrolytes (SEs) are synthesized through a mechanochemical method and the effects of Zr substitution on the ionic conductivity and electrochemical stability window are systematically investigated. Zr doping can increase the ionic conductivity, whereas it narrows the electrochemical stability window of the Li 3 ErCl 6 electrolyte simultaneously. The optimized Li 2.6 Er 0.6 Zr 0.4 Cl 6 electrolyte exhibits both a high ionic conductivity of 1.13 mS cm −1 and a high oxidation voltage of 4.21 V. Furthermore, carbon additives are demonstrated to be beneficial for achieving high discharge capacity and better cycling stability and rate performance for halide-based ASSLIBs, which are completely different from the case of sulfide electrolytes. ASSLIBs with uncoated LiCoO 2 cathode and carbon additives exhibit a high discharge capacity of 147.5 mAh g −1 and superior cycling stability with a capacity retention of 77% after 500 cycles. This work provides an in-depth understanding of the influence of ion doping and carbon additives on halide solid electrolytes and feasible strategies to realize highenergy-density ASSLIBs.

Halide Solid‐State Electrolytes: Stability and Application for High Voltage All‐Solid‐State Li Batteries

“…For instance, Shao et al used a mechanochemical method to synthesize a series of Zr-doped Li 3−x Er 1−x Zr x Cl 6 HSSEs and systematically investigated the impact of Zr doping on the ECW. [151] A CV measurement performed on the LiIn/ LPSCl/HSSE/HSSE + VGCF cell to evaluate the Zr doping impact on the ECW of Li 3−x Er 1−x Zr x Cl 6 (Figure 11b-i). The Er 3+ ion begins to be reduced at 0.85 V and the oxidation potential of Li 3 ErCl 6 is 4.26 V (Figure 11b,c), showing a broad ECW of 0.85-4.26 V. After Zr doping of Li 3 ErCl 6 in the form of Li 2.6 Er 0.6 Zr 0.4 Cl 6 , the oxidation stability is reduced to 4.21 V while its reduction potential increased to 1.67 V (Figure 11d,e).…”

Re-investigating the structure-property relationship of the solid electrolyte Li 3-xIn1-xZrxCl6 and the impact of In-Zr(IV) substitution

“…The Zr(IV) replaces the M(III), and the excess charge is compensated by a lithium vacancy. In all cases, the ionic conductivity measured by impedance spectroscopy has been shown to increase up to a certain substituent concentration [18][19][20][21][22][23][24][25] .…”

“…For the chloride Li3M(III)Cl6, this was successfully achieved by Zr(IV) substitution for M(III) = Y (ref. 19 ), Er (ref 19,20 ), Yb (ref. [21][22][23] ), In (ref.…”

Electrochemically Stable Li3–xIn1–xHfxCl6 Halide Solid Electrolytes for All-Solid-State Batteries

“…In a rare example, Pan et al systematically investigated the effect of Zr doping on the electrochemical stability of Li 3 ErCl 6 . 23 It was found that although Zr doping improved the ionic conductivity, the higher reduction potential of Zr 4+ compared to In 3+ resulted in a reduced Li 3 ErCl 6 electrochemical stability window. However, no studies on the electrochemical stability of Li 3 InCl 6 , a very important member of the halide SE family, have been reported.…”

“…However, previous aliovalent substitution research has frequently overlooked electrochemical stability. In a rare example, Pan et al systematically investigated the effect of Zr doping on the electrochemical stability of Li 3 ErCl 6 . It was found that although Zr doping improved the ionic conductivity, the higher reduction potential of Zr 4+ compared to In 3+ resulted in a reduced Li 3 ErCl 6 electrochemical stability window.…”