Poly(Ethylene Oxide)-based Electrolyte for Solid-State-Lithium-Batteries with High Voltage Positive Electrodes: Evaluating the Role of Electrolyte Oxidation in Rapid Cell Failure

Abstract

polyethylene oxide (peo)-based solid polymer electrolytes (Spes) typically reveal a sudden failure in Li metal cells particularly with high energy density/voltage positive electrodes, e.g. Lini 0.6 Mn 0.2 co 0.2 o 2 (NMC622), which is visible in an arbitrary, time-and voltage independent, "voltage noise" during charge. A relation with SPE oxidation was evaluated, for validity reasons on different active materials in potentiodynamic and galvanostatic experiments. the results indicate an exponential current increase and a potential plateau at 4.6 V vs. Li|Li + , respectively, demonstrating that the main oxidation onset of the SPE is above the used working potential of NMC622 being < 4.3 V vs. Li|Li +. obviously, the Spe│NMC622 interface is unlikely to be the primary source of the observed sudden failure indicated by the "voltage noise". Instead, our experiments indicate that the Li | SPE interface, and in particular, Li dendrite formation and penetration through the Spe membrane is the main source. this could be simply proven by increasing the Spe membrane thickness or by exchanging the Li metal negative electrode by graphite, which both revealed "voltage noise"-free operation. The effect of membrane thickness is also valid with Lifepo 4 electrodes. in summary, it is the cell setup (peo thickness, negative electrode), which is crucial for the voltage-noise associated failure, and counterintuitively not a high potential of the positive electrode.

Effective Optimization of High Voltage Solid‐State Lithium Batteries by Using Poly(ethylene oxide)‐Based Polymer Electrolyte with Semi‐Interpenetrating Network

“…[16] This could be evidenced by proper experiments that could eliminate the volta-noise, for example, an exchange of Li with graphite-based negative electrode or by an increase of SPE thickness, both rendering Li dendrites and their respective penetration difficult. [16] In agreement to these findings, the ease of Li denrite penetration through the SPE could be detected and even visualized in proper Li|SPE|Li cells. [20] A solution for overcoming this failure is the integration of the linear, rather soft PEO-based SPE, into a more mechanically robust semi interpenetrating network (s-IPN) (Scheme 1).…”

“…[ 15 ] Indeed, a thorough investigation in our previous study confirmed a failure in an NMC622|SPE|Li cell, which is visible by an arbitrary appearance of “voltage noise,” typically emerging in initial cycles in random manner. [ 16 ] Micro‐shorts by Li dendrites, which is a morphology form of high surface area lithium, [ 17–19 ] were proven to be the origin of the this voltage noise failure; SPE oxidation as alternative reason for failure could be ruled out. [ 16 ] This could be evidenced by proper experiments that could eliminate the volta‐noise, for example, an exchange of Li with graphite‐based negative electrode or by an increase of SPE thickness, both rendering Li dendrites and their respective penetration difficult.…”

“…[ 16 ] Micro‐shorts by Li dendrites, which is a morphology form of high surface area lithium, [ 17–19 ] were proven to be the origin of the this voltage noise failure; SPE oxidation as alternative reason for failure could be ruled out. [ 16 ] This could be evidenced by proper experiments that could eliminate the volta‐noise, for example, an exchange of Li with graphite‐based negative electrode or by an increase of SPE thickness, both rendering Li dendrites and their respective penetration difficult. [ 16 ] In agreement to these findings, the ease of Li denrite penetration through the SPE could be detected and even visualized in proper Li|SPE|Li cells.…”

“…a) Charge/discharge cycle profiles for linear PEO‐ and s‐IPN PEO‐based SPEs (4.3–3.0 V; 30 mA g −1 ) in NMC622│SPE│Li cells at 60 °C. The use of a linear PEO‐based SPE results in a failure visible by the random appearance of voltage noise (exemplary profile), [ 16 ] while the cell with s‐IPN PEO‐based SPE operates failure‐free. b) As schematically shown, the failure can be attributed to (micro) short circuits originating from Li dendrite penetration through the linear PEO‐based SPE, [ 21 ] while the SPE based on PEO in an s‐IPN network can prevent this penetration and realize charge/discharge cycling without short circuits, thus without voltage noise‐failure.…”

Studies of composite films of polyethylene oxide doped with potassium hexachloroplatinate

“…1 The solid polyethylene oxide (PEO)-based PEs are among the essential materials for lithium-ion-polymer battery technology. 2 PEO is often being used as polymer matrix since it dissolves lithium salts based on the interaction between lithium ions and ether oxygens (EOs) in the polymer chains. 3 The technological relevance of PEO extends way beyond the energy storage area, and these polymers are also used for fuel cells and hybrid power sources supercapacitors.…”