Spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode with high voltage plateau at around 4.7 V (vs. Li/Li + ) has attracted great attention. However, the lack of suitable electrolyte hinders its application. Although lithium difluoro(oxalate)borate (LiODFB)-based electrolyte has been proved to be suitable for high voltage electrolyte, traditional LiODFB-based electrolyte has poor low and high temperature performance. Therefore, we confirm that lithium difluorophosphate (LiPO 2 F 2 , LiDFP) as LiODFB-based electrolyte additive and dimethyl sulfite (DMS) as co-solvent significantly improve electrochemical performance of LNMO/Graphite full batteries at low and high temperature. Various physical and electrochemical techniques are used to investigate the effect of four electrolytes. The effect on cathode is mainly attributed to priority oxidation decomposition of LiDFP. The formed interface film can inhibit the dissolution of Mn 2+ , thereby improving the high temperature electrochemical performance. The effect on anode is that the interface film formed by LiODFB prevents continuous reduction of solvents and additive. The enhanced low temperature performance is due to the significantly increased ionic conductivity of DMS-containing electrolytes at low temperature. Besides, the formed of the cathode electrolyte interphase (CEI) membrane with low impedance by LiDFP can improve the kinetics of cathode/electrolyte interface, therefore enhancing the low and high temperature performance of LNMO/Graphite full cells.
Expanding the charge/discharge voltage range of the high‑nickel cathode material NCM811 is one of the most cost-effective ways to increase the specific energy density of lithium-ion batteries (LIBs). However, carbonate-based electrolytes fail to adapted to the high-voltage environment is susceptible to objectionable oxidative decomposition. Therefore, two widely used electrolyte additives, lithium difluorophosphate (LiDFP) and adiponitrile (ADN), were combined to enhance the performance of LIBs at 4.5 V through their synergistic effect. The results show that the specific discharge capacity and capacity retention rate (CRR) of the Li||NCM811 half-cell with 5ADN electrolyte at 150 cycles under 4.5 V are 161.9 mAh/g and 76.5 %, significantly higher than the 118 mAh/g and 60.1 % of the standard electrolyte cell (STD). Similarly, graphite||NCM811 full-cell also has high specific discharge capacity and excellent CRR compared with STD cell. Further confirmed by physical analysis methods, the LiF-rich interfacial film between the cathode and the electrolyte called cathode electrolyte interphase (CEI) film, is more robust and denser. Thereby, the integrity of the cathode material is well protected, effectively inhibiting the dissolution of transition metal (TM) from the cathode material, and, ultimately, resulting in excellent high-voltage electrochemical performance of the battery. In addition, theoretical calculations show that LiDFP and ADN have larger adsorption energies for Li + and Co 4+ , which can effectively reduce the deposition of Co 4+ to the anode and increase the dissociation of lithium salts. This work provides a novel insight into the effective application of high-voltage electrolytes.
Qiujun Wang,Wei Zhang,Ximing Liu,Huilan Sun,Di Zhang,Ranran Li,Fei Yuan,Qujiang Sun,Bo Wang
Poly(ethylene oxide) (PEO)-based solid electrolytes are considered one of the most promising solid electrolyte systems due to their favorable flexibility and lithium-salt dissolving capability. However, sluggish Li + transport kinetics caused by high crystallinity at room temperature and poor interfacial stability against high-voltage cathodes severely hinder their practical applications in high-energy-density solid-state lithium batteries. To address these challenges, a synergistic Li 3 OCl/LiDFP regulation strategy is proposed by incorporating lithium-rich antiperovskite Li 3 OCl and LiPO 2 F 2 (LiDFP) into a PEO-based composite electrolyte, enabling simultaneous enhancement of ionic conductivity and interfacial stability. The synergistic effect of Li 3 OCl and LiDFP effectively suppresses PEO crystallization, reducing the crystallinity from 31.13% to 7.79%, while facilitating Li + transport through reconstruction of the local solvation environment. The optimized PLLOC-6%LiDFP electrolyte delivers an ionic conductivity of 1.80 × 10 –5 S cm –1 . The corresponding Li∥Li symmetric cell exhibits stable cycling for over 850 h at 0.2 mA cm –2 and achieves a critical current density of 0.45 mA cm –2 . Furthermore, the Li∥NCM811 cell maintains a capacity retention of 78.68% after 200 cycles at 1 C and 25 °C. Interfacial characterization reveals the in situ formation of robust interphases enriched with LiF, Li 3 N, Li 3 PO 4 , and Li x POF y species during cycling, which effectively suppress parasitic interfacial reactions and promote Li + transport. This work provides an effective strategy for simultaneously improving ionic transport and high-voltage interfacial stability in PEO-based composite solid electrolytes. Download: Download high-res image (284KB) Download: Download full-size image
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