Capacity Degradation of Zero-Excess All-Solid-State Li Metal Batteries Using a Poly(ethylene oxide) Based Solid...

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Solid-state polymer electrolytes (SPEs) like poly(ethylene oxide) (PEO) offer flexibility advantages over ceramic electrolytes for solid-state lithium metal batteries (SSLBs).
• Zero-excess all-solid-state lithium metal batteries (ZESSLBs), also known as anode-free SSLBs, require excellent interfacial contact for efficient operation.
• Concerns exist regarding PEO's potential to consume limited lithium in ZESSLBs, leading to low Coulombic efficiencies and system failure.

Purpose of the Study:

• To investigate the reactivity between PEO SPEs and freshly deposited lithium under realistic battery operating conditions within ZESSLBs.
• To quantify the impact of PEO-SPE/lithium interaction on the electrochemical performance and capacity retention of ZESSLBs.
• To elucidate the degradation mechanisms in PEO-based ZESSLBs, focusing on the role of residual solvents and water.

Main Methods:

• Design of ZESSLBs incorporating an all-ceramic half-cell and a PEO electrolyte interlayer.
• Development of a method to shuttle lithium to the cathode, enabling PEO SPE separation for analysis without cathode interference or Li foil contamination.
• Electrochemical cycling of ZESSLBs with solvent-free and solvent-casted PEO SPEs to evaluate capacity degradation.

Main Results:

• ZESSLBs utilizing PEO SPEs exhibited significant capacity degradation compared to those with a Li metal anode.
• The degradation was directly linked to the reaction of lithium with PEO, residual solvents, and water present in the PEO electrolyte.
• Formation of inactive 'dead lithium' was observed, further contributing to capacity fade, influenced by the presence or absence of residual solvent.

Conclusions:

• Direct contact between PEO electrolytes and deposited lithium must be avoided in ZESSLBs with limited lithium reserves.
• The reactivity of PEO with lithium and associated degradation pathways are critical challenges for PEO-based ZESSLB development.
• Strategies to mitigate PEO-lithium interfacial reactions are essential for realizing stable and efficient anode-free solid-state lithium metal batteries.