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@ARTICLE{Woolley:1025073,
      author       = {Woolley, Henry Michael and Vargas-Barbosa, Nella},
      title        = {{E}lectrochemical {C}haracterization of {T}hiophosphate-
                      {I}onic {L}iquid {H}ybrid {L}ithium {E}lectrolytes {A}gainst
                      {L}i {M}etal},
      journal      = {Meeting abstracts},
      volume       = {MA2023-01},
      number       = {6},
      issn         = {1091-8213},
      address      = {Pennington, NJ},
      publisher    = {Soc.},
      reportid     = {FZJ-2024-02661},
      pages        = {986 - 986},
      year         = {2023},
      abstract     = {(Almost) solid-state batteries that utilize thiophosphate
                      solid electrolytes (SE) are an exciting technology emerging
                      as a potential alternative to lithium-ion batteries. When
                      used alongside a lithium metal anode they can offer the high
                      energy densities [1] required to meet the increasing demand
                      for energy storage. However, they suffer from numerous
                      issues which predominately occur at the cathode- or anode-SE
                      interface. Issues include dendrite propagation through gaps,
                      pores and grain boundaries of the solid electrolyte which
                      can eventually puncture electrolyte crystallites and lead to
                      cell failure. [2] Thiophosphate electrolytes are also
                      unstable both chemically and electrochemically. As a result
                      of the SEs having a low electrochemical stability window
                      reduction or oxidation can occur at the anode or cathode
                      interface, forming a resistive solid electrolyte interphase
                      (SEI). [3] Finally, the ionic contact between Li metal anode
                      and electrolyte is poor and thus high interfacial impedances
                      can arise. These impedances can be dynamic which increase
                      during stripping of the lithium and decrease during plating.
                      [4] To solve some of the interfacial issues there is the
                      option to add a small of amount of liquid electrolyte at the
                      lithium metal-electrolyte interface. The liquid electrolyte
                      can fill in the gaps and pores at the interface thus
                      improving the ionic contact whilst allowing a more stable
                      interface. Whilst the ionic contact can be improved the
                      inherent instability of thiophosphate electrolytes against
                      the liquid electrolyte means that a new interphase known as
                      the solid-liquid electrolyte interphase (SLEI) can form. The
                      presence of this interphase can therefore lower the energy
                      density and round-trip efficiencies of cells which utilize
                      hybrid electrolytes meaning that minimizing the SLEI
                      resistance and maximizing total ionic conductivities is
                      important in hybrid cells. [5]In this work a hybrid of the
                      thiophosphate argyrodite Li6PS5Cl and the ionic liquid
                      x-LiTFSI-1-butyl 1-methylpiperidinium TFSI (BMPipTFSI) with
                      LiTFSI concentrations of 0.25 M and 0.5 M was studied. The
                      choice of SE and liquid electrolyte boils down to the high
                      ionic conductivity of the SE and the electrochemical and
                      thermal stability of the ionic liquid. Temperature-dependent
                      ionic conductivity measurements showed that hybrid systems
                      exhibit lower in room temperature ionic conductivities and
                      higher total activation energies. This hints at the presence
                      of a SLEI forming between the LE and SE. To study how the
                      SLEI resistances changes over time, ion blocking potential
                      impedance spectroscopy measurements were performed. These
                      measurements were performed at 10 °C to allow for the
                      resistance contributions to be better resolved and showed a
                      SLEI resistance of around 45-50 Ω cm2 for both hybrids.
                      Over the period of 130 hours this resistance changed
                      minimally (around 5 Ω cm2 on average) indicating good
                      stability of the SLEI. To further test the suitability of
                      this hybrid alongside lithium metal anodes impedance
                      measurements in symmetrical lithium cells
                      (Li0|LE|LPCL|LE|Li0) were undertaken. In this case
                      galvanostatic impedance spectroscopy (GEIS) with an applied
                      current density of ±0.4 mA cm-2 was used to probe the
                      changes in resistance contributions in the system over the
                      period of stripping (positive current) and plating (negative
                      current). For cells with just SE a large change in the
                      resistance owing to the electrochemical reaction (ECR) (Li0
                      ↔ Li+ + e-) occurred during stripping and plating
                      indicating the dynamic nature of the ionic contact at the
                      interface. For the hybrid electrolyte cells, this ECR
                      resistance is decreased and becomes more stable however a
                      larger interphase resistance is present. This resistance is
                      a combination of the resistances of both the SLEI (the
                      interphase between the LE and SE) and the SEI (the
                      interphase between LE and Li anode) and it changes over
                      stripping and plating showing that the S(L)EIs which are
                      present are dynamic. Finally, post-mortem SEM/EDX of the
                      surface of samples show a change in morphology and the
                      presence of decomposition products from both the liquid and
                      solid electrolytes. These studies show that the
                      LPCL-BMPipTFSI hybrid is stable and improve ionic contact at
                      the lithium metal anode interface. Further testing in half
                      Li-S cells will determine the suitability of the use of the
                      ionic liquid at the cathode side of the cell.References[1]
                      J. Janek and W. G. Zeier, Nat Energy, 2016, 1, 16141. [2] M.
                      B. Dixit et al. Matter, 2020, 3, 2138-2159 [3] G. Dewald et
                      al. Chem Mater, 2019, 31, 8328-8337. [4] T. Krauskopf et al.
                      Chem. Rev, 2020, 7745-7794. [5] H. M. Woolley and N. M.
                      Vargas-Barbosa, under review.},
      cin          = {IEK-12},
      ddc          = {540},
      cid          = {I:(DE-Juel1)IEK-12-20141217},
      pnm          = {1221 - Fundamentals and Materials (POF4-122)},
      pid          = {G:(DE-HGF)POF4-1221},
      typ          = {PUB:(DE-HGF)16},
      doi          = {10.1149/MA2023-016986mtgabs},
      url          = {https://juser.fz-juelich.de/record/1025073},
}