A Strategy to Make High Voltage LiCoO₂Compatible with Polyethylene Oxide Electrolyte in All-Solid-State Lithium Ion Batteries

Abstract

Interface stability between cathode and electrolyte is closely related to the interface resistance and electrochemical performance of all-solid-state lithium ion batteries (LIBs). However, the significant interface issues between cathode and all-solid-state polymer electrolyte have been researched rarely. Here, we demonstrate that severe interface decomposition reactions occur continually and deteriorate the cycling life of high voltage LiCoO 2 /cellulose-supported poly(ethylene oxide) (PEO)-lithium difluoro(oxalato)borate (LiDFOB)/Li battery between 2.5 and 4.45 V vs. Li/Li + . To improve the interface stability between LiCoO 2 and PEO-LiDFOB electrolyte, we modify the LiCoO 2 surface by a thin layer of high ionic conducting and electrochemical oxidation resistant poly(ethyl cyanoacrylate) (PECA) through in-situ polymerization method. The PECA coating layer significantly suppresses the continuous decomposition of lithium difluoro(oxalato)borate (LiDFOB) salt in PEO electrolyte. As a result, the PECA-coated LiCoO 2 /PEOLiDFOB/Li battery shows decreased interface resistance and enhanced cycling stability. This work will enlighten the understanding of interface stability and enrich the modification strategy between cathode and polymer electrolyte as well as boost the further development of all-solid-state LIBs. Polymer electrolyte-based all-solid-state lithium ion batteries (LIBs) with the merits of flexibility, high energy density and high safety have been researched for a long time.1-5 Nevertheless, their applications are still challenged by the interface issues between electrode and solid-state electrolyte. The thorny interface issues mainly refer to the inherent space charge layer and detrimental chemical reactions at the electrode and electrolyte interface, which lead to large interface impedance and then deteriorate the fast charging/discharging ability and cycling stability of all-solid-state LIBs. [6][7][8][9] Polyethylene oxide (PEO) electrolyte with high ion conductivity and good interface stability with Li metal has been successfully used in commercial polymer LIBs, in which the cathode material is LiFePO 4 instead of LiCoO 2 . The failure application of PEO electrolyte in LiCoO 2 -based high energy density LIBs is mainly due to the interface decomposition reactions of PEO at high voltage. Shiro Seki et al. have proposed that the oxidation decomposition of PEO electrolyte takes place from 4.0 V vs. Li/Li + , which leads to continuous increasing of LiCoO 2 /PEO interfacial resistance and results in poor cycle performance at 4.4 V vs. Li/Li + . 10 Moreover, during high voltage charging of LiCoO 2 , the highly oxidized Co 4+ ions will accelerate the oxidation decomposition of PEO electrolyte.11 It can be concluded that the cathode/polymer electrolyte interface characteristic is quite essential to the electrochemical performance of all-solid-state LIBs, especially for the high voltage cathode LiCoO 2 and PEO electrolyte. However, the interface oxidation decomposition products and reaction mechanism between ...

Organoboron‐Containing Polymer Electrolytes for High‐Performance Lithium Batteries

“…It has been widely accepted that the electrode-electrolyte interface layer plays an imperative role in enhancing the high voltage performance of electrolytes. Substantial efforts have been explored to increase the high voltage stability of PEs, including salt additives, [95,96] artificial passivation layers, [97,98] and multilayer strategies. [99,100] Among these strategies, in situ formation of an amorphous protective layer by introducing functional lithium salts seem attractive.…”

Interfaces Between Cathode and Electrolyte in Solid State Lithium Batteries: Challenges and Perspectives

“…solid state lithium batteries assembled with PEO-based SPE and LATP modified LiCoO 2 shows high capacity retention (93.2% after 50 cycles) at 4.2 V, which suggests that surface coating can effectively suppress PEO oxidation at high voltage (Yang et al, 2018). By cathode coating, PVCA-coated LiCoO 2 also showed much enhanced cycling stability of PEO based SPE at 4.45V (Ma et al, 2017).…”

Energy-Density Improvement in Li-Ion Rechargeable Batteries Based on LiCoO2 + LiV3O8 and Graphite + Li-Metal Hybrid Electrodes

“…The voltage window of the cell in this experiment is lower than the current trend. However, the industrial feasibility of this electrode system is acceptable in utilization considering a multi-cell pack system application or the next generation LiBs system, such as lithium-sulfur or lithium-air [28,29,30,31]. Electrochemical impedance spectroscopy (Solartron SI1280B, Anyang, Gyeonggi-do, Korea) was performed from 10 −1 to 10 5 Hz at 5 mV s −1 .…”

“…In this study, we report a novel battery system consisting of an LCO + LVO hybrid cathode and a graphite + LP hybrid anode. Because the electrochemical performance of the cathode active materials (LCO and LVO) with respect to their cycle performance and rate capability has been previously characterized [14,15,16,17,18,28,29,30], the main objective of this study was to increase the discharge capacity and energy density during the first 20 cycles. The discharge capacity and energy density of the optimized hybrid cathode were 182.88 mA h g −1 and 629.24 W h kg −1 , respectively, representing enhancements of 28.76% and 15.25%, respectively, as compared with the corresponding values for bare LCO.…”