Nonconductive Polymers Enable Higher Ionic Conductivities and Suppress Reactivity in Hybrid Sulfide–Polymer Solid State Electrolytes

Abstract

Hybrid ceramic−polymer solid state electrolytes are promising candidates to enable energy-dense lithium metal batteries by leveraging inorganic high ionic conductivity and flexible polymer mechanical properties. However, studies of hybrid electrolytes using sulfide-type inorganics such as Li 3 PS 4 (LPS) have largely focused on combining the inorganic with commercial poly(ethylene oxide) (PEO). PEO has proven to be insufficient for use in hybrid systems because it reacts with LPS and provides a competing pathway for ion transport, therefore producing a hybrid with low conductivity. Our work shows that using nonconductive, nonpolar polyethylene (PE) in hybrid electrolytes with LPS eliminates both polymer and inorganic degradation and remarkably, exhibits higher conductivities than those containing PEO at different polymer and salt concentrations. Using tracerexchange NMR, we observe that the nonconductive nature of PE allows for ion transport through the inorganic whereas PEO provides a separate, competing pathway for lithium transport. Furthermore, compared to pure LPS, these hybrids enable longer term lithium cycling at 60 °C. Our work shows that the path to enabling conductive and stable sulfide hybrids for solid state lithium-metal batteries may be through the use of nonconductive, nonreactive polymers.

In Situ Topological Interphases Boosting Stable Solid‐State Lithium Metal Batteries

“…b) Comparison of the cycle life of symmetric cells with CPDOL‐SPE and those of previously reported excellent SPEs at 60 °C. PEO with LAGP, [ 26 ] MIP‐SPE, [ 27 ] PEO/MnO, [ 28 ] PVA/UPy/PEG, [ 29 ] IMFPIL‐LiTFSI, [ 30 ] CHPEs‐Li, [ 31 ] PEO‐LPS, [ 32 ] CN‐PEO, [ 33 ] PEO‐MOF‐2. [ 34 ] c) Fitting results of interface impedances of Li/Li cells assembled with CPDOL‐SPE and PDOL‐SPE at different cycles.…”

“…As shown in Figure 5a, the resulting battery of long-term cycling at 0.25 C achieves a high initial discharge capacity of 158.6 mAh g −1 after activation, and exhibits a high capacity retention of 90.5% after 400 cycles at an operation time exceeding 3800 h. In sharp contrast, the battery using PDOL-SPE delivers a lower initial discharge capacity of 147.7 mAh g −1 and fluctuation of coulombic efficiencies owing to low ionic conductivity and the formation of an undesirable SEI. This undesirable SEI results in sluggish Li + transport kinetics, increased overpotential, and [26] MIP-SPE, [27] PEO/MnO, [28] PVA/UPy/PEG, [29] IMFPIL-LiTFSI, [30] CHPEs-Li, [31] PEO-LPS, [32] CN-PEO, [33] PEO-MOF-2. [34] eventually causes capacity fading with a lower capacity retention of 80.7% after 300 cycles (Figure 5b and Figure S27a, Supporting Information).…”

Impact of Processing Methodology on the Performance of Hybrid Sulfide-Polymer Solid State Electrolytes for Lithium Metal Batteries

“…[9][10][11] Recently, our group reported on the development of Li 3 PS 4 (LPS)-based hybrid electrolytes that leverage non-conductive, non-reactive polyethylene (PE) as the polymer component. 12 We observed that hybrids using PE had a higher conductivity than those made with PEO, primarily due to the degradation of both LPS and PEO that occurs upon synthesis of the LPS-PEO hybrid electrolyte. 12,13 Additionally, we discovered that PEO provides an alternative, competing pathway for ion-transport which ultimately lowers the conductivity of the overall hybrid.…”

“…12 We observed that hybrids using PE had a higher conductivity than those made with PEO, primarily due to the degradation of both LPS and PEO that occurs upon synthesis of the LPS-PEO hybrid electrolyte. 12,13 Additionally, we discovered that PEO provides an alternative, competing pathway for ion-transport which ultimately lowers the conductivity of the overall hybrid. We were able to overcome these challenges by substituting PEO with nonpolar, non-reactive PE.…”

Solid-State, Single-Ion Conducting, Polymer Blend Electrolytes with Enhanced Li+ Conduction, Electrochemical Stability, and Limiting Current Density

“…However, the high crystallinity of PEO below the melting temperature ( T m,PEO ≈ 62 °C for 10–20 kg/mol) leads to a significant reduction in conductivity near room temperature . There have been numerous studies focused on disrupting crystallinity in PEO using PEO-grafted polymethacrylates , and PEO-based copolymers. − For instance, poly­( oligo -oxyethylene methyl ether methacrylate) (POEM), with its ether-oxygen side chains, is promising in terms of significantly improved room-temperature conductivity vs analogous salt-doped PEO systems when the appropriate side-chain lengths are employed. , Other approaches also have been developed to decrease the crystallinity of PEO, including nanoparticle addition, − polymer blending, , and cross-linking. − Additionally, small-molecule plasticization − and low- T g segment introduction − have been shown to accelerate segmental relaxation, and polymer architecture modification can effectively alter the Li + -polymer coordination ,− and/or the Li + solvation-site connectivity. ,− Although improved overall conductivities have been achieved, the significant anion motion in these PEO-based electrolytes results in low t Li+ s (≈0.2) , and therefore relatively modest Li + conductivities (∼10 –4 S/cm at 60–100 °C).…”